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Elemento-Organic Amines and Imines.

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Elemento-Organic Amines and Imines
By 0. J. Scherer[*l
Amines with mixed substituents containing two or three El- N bonds [**I are relatively
stable if one or two of these bonds are (CH3)3 Si-N bonds. I R and IH-NMR studies
indicate that the ( p
d ) x bond components of the element-nitrogen bonds steadily
decrease from silicon, phosphorus, and surfur to ward their higher homologs. Because
of the di#erences in the polarities of the element-nitrogen bonds, these substances can be
used for selective insertion and cleavage reactions. The reaction of metalated N-silylaminoarsines with methyl chloride as well as the reaction of metalated N-trimethyl(I Va)element-substituted amino-tert-brttylphosphines with halogenotriniethyl(I Valelement compounds open new, simple routes for the conversion of elemento-organic amine systems
into irnine systems. The problem of reversible and irreversible (CH3)sEl Iigand migration
(1,3 shift) is discussed for trimethyl( I Va)element-substituted benzamidines, diaminophosphines, aminoiminophosphoranes, suljinamides, and aminosulfimines.
--f
1. Introduction
Whereas compounds of nitrogen with its five neighboring elements have mostly been known for a long
time and have been extensively studied, compounds
of nitrogen with the other nine elements in the portion
of the periodic system shown were very much an
unexplored field until about ten years ago.
c
p[
Si
Ge
Sn
Pb
P
As
Sb
Bi
2. Bis(organoe1ement)-Substituted Amines with
Two Different Hetero Atoms
2.1. IVa/IVa Elements
If two hydrogen atoms in ammonia or a primary
amine are imagined to be replaced by the organoelement ligands X and Y,we formally obtain the
following class of compounds:
0
S
Se
Te
R
R
x/
\y
=
X,Y
H, alkyl, aryI
=
organoelement ligand
Po
The often extreme sensitivity of element-nitrogen
compounds of this type to moisture and oxygen,
their not infrequent extreme thermal instability, and
their toxicity (particularly that of the heavier homologs) may have been major causes of the striking
neglect of this field of study.
Compounds of this type [e.g. (2), (4), (9), and (IO)]
with different group IVa elements are best synthesized
by double decomposition of lithium N-methyl-N-trimethyl(1Va)elementamides [e.g. ( I ) , ( 3 ) , and ( 5 ) ]
with halogenotrimethyl(1Va)element compounds. The
“lithium methylamide” derivatives can be prepared
Table I . Physical properties of the compounds ( 2 ) , ( 4 ) , (9) and (10).
To permit the investigation and discussion of the
thermal stabilities, reactivities, bonding, and Iigand
migration reactions of elemento-organic nitrogen
compounds containing different hetero atoms, it was
first necessary to synthesize many model substances 111.
B.p. (“Cjtorr)
147j760
42/12
59-61/11
42-43/0.5
172/735
28/2
4912
46-48/0.1
SO-S2jO.I
63-6610.1
66-68/0.1
61 -63/0.5
83-85/0.5 [b]
129- 132/0.5 [c]
It was found very useful in many cases to attach one
or two trimethylsilyl groups to the nitrogen atom,
possibly because the bulky trimethylsilyl ligand
provides favorable steric conditions, and may also
strengthen the G bond by (p + d)x bonding[zl with
the ‘‘lone’’ pair of electrons on the nitrogen.
[*I Doz. Dr. 0. J . Scherer
Institut fur Anorganische Chemie der Universitat
87 Wiirzburg, Rontgenring I 1 (Germany)
[**I El = a higher IVa, Va, or VIa element; by IVa, Va, and
VIa elements are meant elements of the IV, V, and VI main
groups of the periodic system.
111 0.J . Scherer, abstracts from Habilitationsschrift, Universitat Wiirzburg 1967.
Angew. Chem. internat. Edit. / Vol. 8 (1969)/ No. 1I
[a] R
7
(CH~)JSI-NCHJ. [b] M.p.
=
22-23 ’C. [c] M.p. = 90-92 “C.
-~
121 a) E . g . D. P . Craig, A. MaccoN, R . S. N y h o h , L . E. Orgel, and
L . E . Sufton, J. chem. SOC.(London) 1954, 332; b) E . A. V . Ebsworth: Volatile Silicon Compounds. Pergamon Press, Oxford
1963, p. 101; c) U.Wannagat, Advances inorg. Chem. Radiochem. 6, 225 (1964).
861
both by metalation [eq. (a)] and by cleavage of
element-nitrogen bonds [eq. (b) and (c)] (for examples
see Table 1).
+ RLi
(CH3)3Si-N(CH3)-H
+ (CH3)3Si-N(CH3)-Li
R
(a) [3]
[(CH3)2Ge-N(CH3)13
+ LiCl
(CH3)$%N(CH3)-EI(CH3)3
Sn (Zc), Pb (2d)
=
4 RH
(1)
+ (CH~)IEICI +
(I)
El
CH3, n-CdH9
=
Organo(1Va)element derivatives of ammonia, e . g . (7),
R = H,are difficult to prepare,since the compounds R3EI-NH2
required as starting materials are thermally stable only if R
is a bulky ligand. With R = CH3, El = Si [101 o r Gefill, the
monoorgano(1Va)element derivative (CH3)3EI-NH2 immediately condenses to give [ ( C H ~ ) J E I ] ~ Nand
H NH3, whereas
the tin analog gives only the tertiary aminerl21.
c o [31
(2)
+ 3 CH3Li
+
3 (CH&Ge-N(CH+Li
(b) [4]
The simplest member of the silicon series[l3J is triethylsilylamine. The metalation of this compound with n-butyllithium and substitution of the product with chlorotrimethylgermane 1141 presents n o difficulties.
(3)
+ (CH3)3ElCI
(3)
+ (CH3)3Ge-N(CH3)-EI(CH3)3
(4)
El = Si (4a), Ge (46), Sn (4c), Pb (4d)
+
+ LiCl
141
(CH~)3Sn-N(CH3)-Sn(CH3)3
CH3Li
+ (CH3)3Sn-N(CH3)-Li
(CH&Sn
+
(c) [51
As is shown in Section 4, (12) is the key substance for the
synthesis of elemento-organic amines containing three
different hetero atoms.
151
Nearly all elemento-organic amines with two different
hetero atoms are water-clear, moisture-sensitive liquids
that can be purified by vacuum distillation. The lead
compounds (2d), (4d), and (9d), which exhibit
remarkable thermal stability, also deserve special
mention, since comparable plumbylamines with an
alkyl group in place of the ligand (CH3)3El are
extremely unstable, even when the lead atom carries
bulky groups 1151. The sensitivity to water, as expected,
increases rapidly from the silicon compound to the
lead compound. Among the N-silylated stannylamines
( l o ) the water sensitivity is least for (IOd), which can
even be handled in air for short periods. This special
behavior is probably due to steric effects, the tin atom
being shielded from nucleophilic attack by the four
N-methyl-N-trimethylsilylaminogroups.
Comparison of the 1H-NMR spectra of the compounds (2), (4), and (9) reveals the following relations
(see Table 2):
(5)
+
(5)
(CH3)3EICI + (Zc), (4c)
El = Si. Ge
+ LiCl
(CH&Si-NC(CH3)3-Li
has also been allowed to
react with (CH3)3ElCI compounds (El = Ge, Sn, Pb)
in accordance with eq. (a') [61.
Owing to the ease with which N-methyl-N-trimethylsilylamine can be obtained from chlorotrimethylsilane
and methylamine, (1) has been the most widely used
compound for syntheses of this type.
+ (CH3)zSiCIz
(I)
+ (CH3)3Si-N(CH3)-Si(CH3)2-CI
(6)
(6)
+ LiCl
+ 2 RNH2
+ (CH3)3Si-N(CH3)-Si(CH3)2-N(R)-H
R
(7)
R
H, CH3
=
(8)
+ RNH2 HCI
( 7)
15~71
+ n-CdH9Li
=
[S, 71
+ n-C4Hlo
+ (CH,),Si-N(CH,)-Si(CH&-N(R)-Li
H [gal, CH3 [5, 71
(8)
8(CH3)3Si [(2)1, 8(CH3)3Ge [(4)1, and B(CH3)zSi [(9)1
+ (CH3)sEICI
+ (CH3)3Si-N(CH3)-Si(CH3)2-N(R)-EI(CH3)3+ LiCl
(9)
R = CH3, El = Ge (96) [51, Sn (9c) [7], Pb (9d) [5];
R = H, El = Ge [gal
n (1)
n=1
+ (CHd4-nSnXn
+
+ (CH3)4-nSn[N(CH3)-Si(CH3)31n n LiX
4; X = CI, Br
(10)
[91
--f
[3] 0. J . Scherer and M . Schmidt, J. organometallic Chem. 3,156
(1965).
[4] a) I. Ruidisch and M. Schmidt, Angew. Chem. 76, 686 (1964);
Angew. Chem. internat Edit. 3, 367 (1964); b) I. SchumannRuidisch and B. Jutri-Mebert, J. organometallic Chem. 11, 77
(1968).
I51 D . Biller, Diplomarbeit, Universitat Wiirzburg 1966.
[6] I . Schumann-Ruidisch, W. Kalk, and R . Briining, Z . Naturforsch. 236, 307 (1968).
[71 0. J . Scherer, D . Biller, and M . Schmidt, Inorg. nuclear
Chem. Letters 2, 103 (1966).
181 a) 0. J . Scherer and D . Biller, Angew. Chem. 79, 410 (1967);
Angew. Chem. internat. Edit. 6,446 (1967); b) unpublished.
191 0. J . Scherer and P . Hornig, J. organometallic Chem. 8, 465
(1967).
862
unlike 8CH3(N'), are displaced to higher fields on
transition from El = Si to its higher homologs.
Whereas the hetero atom has no appreciable influence on Jl3CH(Si) and J13CH(Ge), h3CH(N1) decreases
slightly from El = Si to El = Pb. These results indicate
that the (p + d)x strengthening of the El-N bond
decreases from silicon to its higher homologs. If the
(CH&Si-N(CH3) group is attached instead of CH3
to the silicon atom in class (2), the hetero atom El in
[lo] R . 0 . Sauer, J. Amer. chem. SOC.66,1707 (1944).
[ l l ] I. Ruidisch and M . Schmidt, Angew. Chem. 76, 229 (1964);
Angew. Chem. internat. Edit. 3, 231 (1964).
[12] a) K. Jones and M . F. Lappert, Proc. chem. SOC.(London)
1962, 358; J. chem. SOC.(London) 1965, 1944; b) K . Sisido and
S . Kozima, J. org. Chemistry 29, 907 (1964); c) W. L. Lehn, 3.
Amer. chem. SOC.86,305 (1964); d) 0.J . Scherer, J . F. Schmidt,
and M . Schmidt, Z. Naturforsch. 196, 447 (1964).
[13] R. Fessenden and J . S . Fessenden, Chem. Reviews 61, 361
(1961).
[14] 0.J . Scherer and D . Biller, 2. Naturforsch. 226, 1079 (1967).
1151 W. P. Neumann and K . Kiihlein, Tetrahedron Letters 1966,
3419.
Angew. Chem. internat. Edit. J Vol. 8 (1969) J No. I 1
Table 2. 1H-NMR data (in Hz) lor the bis[organo(IVa)elementl-substituted amines (2). (41, ( 9 ) , and (10) (in CCh, TMS as internal standard).
All the coupling constants given in the tables are absolute values obtained from the band splitting. The signs 1771 of the coupling constants are neglected.
F CHdN1)
S(CH3)zSi
S CHdN3
-t0.6
~
8 CHAEI)
’13CH(Si)
.~
J13CH(NI:
’13CH(E1)
-16.3
-13.0
120.0
119.2
118.0
137.5
136.0
133.0
127.0
129.5
-168.5
-56.0
120.0
133.0
136.5
-157.5
-166.0
-10.8
127.0 If]
126.8 [f]
135.5
134.5
-181.0
-145.5
-149.5
-156.0
-55.0
- 4.0
-16.0
-13.0
126.0 [fl
133.5
I
-148.5
-153.0
-156.0
-5.8
-3.6
-1.0
I
-145.5
-145.5
-145.5
-170.5
- 156.0
-145.0
-158.0
J
~
i ’EINCH
~
53.4
55.8
65.5 [c]
43.6 1
45.5 [bl
78.0 [dl
53.5 {
56.0
64.8 Icl
46.8
49.0 [bl
95.0 id]
53.0
56.0) la]
66 0 [cl
420 \
45.0 rbl
76.0 [dl
47.0 {
49.5 I [bl
}
I
}
I
-57.0
-20.0
117.5
133.0
129.5
:}
-28.5
117.5
133.5
131.0
70.1 1
73.5
[a]
I
-158.0
118.0
~ Ref.
134.5
50.4
52.8
63.8
66.8
} [bl
1
Ibl
(9) now has a pronounced influence only on 8(CH3)2Si
Whereas insertion o f the isocyanate into the Si--N
and 8CH3(N1), while G(CH3)3Si and 8CH3(N2), the
bond cannot be absolutely ruled out in the case of
signals of the ligands situated farther away from El,
R=CH3, the absence of J117,1l9Sn-N-C-~
coupling
show practically no measurable change.
for (13), R=C6H5, indicates addition to the more polar
Sn-N bond for this substance at least. A moderate
In the N-silylated stannylamines ( l o ) , GCH3(Si) and
excess of isocyanate leads to mixtures of products a s a
8CH3(Sn) show an almost linear displacement to lower
result of further “insertion reactions” while a larger
fields as the number IZ of methyltrimethylsilylamino
excess leads to trimerization of the isocyanate [181.
groups is increased, whereas 8CH3(N) is practically
Benzonitrile, which does not react with the Si-N bond
unaffected by n. The increases in the coupling constants
of (CH3)3Si-N(CH3)-H [191, forms a benzamidine
5117, 119Sn-C-H
and J 1 1 7 , 119Sn-N-C-H
are greatest
derivative
with (CH&Sn-N(CH& [201. (2c) gives no
for the transitions n = 2 + 3 and n = 3
4 respecindication
[I91
of reaction in accordance with eq. (d),
tively. It should be mentioned that J117, I19Sn-N-C-H
even
under
more
forcing conditions (several hours at
for (IOd) n = 4, is greater than JII~,II~s~-c--H
for
higher
temperatures).
(2c) and (lob), n = 2. The values of 63.8 and 66.8 Hz
are considerably higher than those of the class of
H3
(CH,),Si-N-Sn(CH,), + C&-CEN
unsilylated compounds [(C2H5)2N]nSn(CH3)4-n [161.
--f
7
The elemento-organic amines containing different
hetero atoms differ in the polarities of the elementnitrogen bonds; a selective “insertion reaction” of a
1,2-dipole should therefore be favored. It is known
from examples in the literature 1171 that even the Si-N
bond, which is the least polar in this group, reacts
smoothly with most 1,2-dipoles. N-Methyl-N-trimethylsilyl-N-trimethylstannylamine(2c) and methyl or
phenyl isocyanate react under mild conditions (low
temperature, high dilution, and a slight excess of (2c))
to form 1:l adducts (13) 1181.
(d)
Sn(C H3 )3
-X,
CsHs-C,
r-Si(CH3)3
(14)
..
CH3
The difference in the reactions of ( C H ~ ) ~ S I - - N ( C H ~ ) ~
and (2c) is due either to steric effects or to decreased
basicity in the latter compound as a result of the
(p
d)x bond to the silicon atom.
--f
2.1.1. E l e m e n t o - O r g a n i c B e n z a m i d i n e s
7H3
( CH3)3Si-N-Sn( CH3)3
+ R-N=C=O
(2cJ
R
y-33
4
(2r)
=
CH3, C&
7
( CH3)3Si-N-C - N-Sn( CH3)3
(13)
[16] M . R . Kulo, C. G. Krei/er, and J . Lorberrh, Chem. Ber. 97,
1294 (1964).
[171 Cf.e.g. H . Ulrich: Cycloaddition Reactionsof Heterocumulenes. Academic Press, London 1967, Vol. 9, p. 187ff.
1181 0. J . Scherer, D . Biller, and G . Bonse, unpublished.
Angew. Chem. internat. Edit. 1 Vol. 8 (1969) No. I1
Elemento-organic benzamidines (16)L19-233 containing different group 1Va elements are obtained by
addition of lithium N-alkyl-N-trimethylsilylamidesto
1191 0. 1. Scherer and P. Hornig, Chem. Ber. 101, 2533 (1968).
[20] T. A . George, K . Jones, and M . F. Lappert, J. chem. SOC.
(London) 1965, 2157.
1211 C. Kriiger, E. G. Rochow, and U.Wannagat, Chem. Ber. 96,
2138 (1963).
[22] W. P. Neumann and E. Heymann, Liebigs Ann. Chem. 683,
24 (1965).
1231 W. P . Neumann and K . Kiihlein, Tetrahedron Letters 1966,
3423.
863
oN-E1(CH3),
(15) + (CH3)3ElCl
-+
CsHs-C,
+
LiCl
(16) can be discussed only if one assumes the occurrence of either metal-proton coupling across five
bonds or shortening of the coupling path by additional
coordinate bonding of Sn and Pb to the singly-bonded
amidine nitrogen atom. This coupling can be explained
much more simply if ( I d d ) and (16e) are formulated
as the isomers (17).
(e)
N- Si(CH3)3
A
(16)
An answer to the question of the predominant isomer
is provided by the N'-trimethyl(1Va)element-substituted N, N-dimethylbenzamidines (19), which can
be obtained from lithium dimethylarnide, benzonitrile,
and (CH3)3EIC1 (El = Si, Ge, Sn)[191.
E l = Si; R = CH3(16a), C2H5 (16h), E l = G e f16c),
Sn(l6d), Pb (16% R = CH3
benzoniti ile followed by reaction with chlorotrimethyl(1Va)element compounds [eq. (e)] 1191.
The compounds (16) are moisture-sensitive liquids
that can be distilled in a n oil-pump vacuum. They are
rapidly split at the element-nitrogen bond by water
and alcohol to form the free base (which was identified
as the hydrochloride). Owing to the proximity of the
two nitrogen atoms to each other, these compounds
are ideal models for the investigation of ligand
migration reactions. The isomers (17) and (18) of
( 1 6 ) must also be considered.
N-Li
(CH3)2NLi + CsH5-CSN
4
C6H5-C:
N(CH3)z
E l = Si (19a). Ge(19h), Sn(l9c)
The fact that no coupling with the CH3N group
(Jl17, l19Sn-N-C-HL0)
is observed in the IH-NMR
spectrum of (19c) may be taken as strong evidence
that the benzamidines (16c)-(16e) are in the isomeric
form (17). This is supported by the fact that for all
(CH3)3EI groups bound to the imine nitrogen atom,
Table 3. 1H-NMR data (in Hz) for the benzamidine derivativcs (16) and (19) (in CCL, TMS as internal standard) [19!. SC6Hdm) is omitted.
4CHAN)
S CH,-CHz(N)
S CH3(EI)
S CHdSi)
I
I
-153.0
-53.0 (t)
-174.5(q)
-154.0
-154.0
-161.0
-171.5
-169.0
-169.5
1
-12.0
1--3O'C)
0.0 (35 "C)
+ 16.5
+ 15.5
+ 17.5
+17.0
1
-25.5
-17.5
-64.5
+
55.0/57.0
32.0
6.0
+ 9.5
52.5/55.0
The *H-NMR spectra of (16a) and (16b) (Table 3)
exhibit in addition to the expected phenyl and Nmethyl resonances, a broad signal in the trimethylsilyl
region at 35 "C (even at high dilution), which splits
into two singlets of equal area at about -30 "C. This
observation points to a reversible intramolecular
migration (1,3 shift) of the two trimethylsilyl ligands.
Despite frequent modification of the preparation conditions,
silicon derivatives always contain small quantities of a "byproduct"; o n the basis of its I R and 1H-NMR spectra and
its element analysis, it is concluded that this product has the
structure of the isomer (18) 1191. The two isomers are not in
equilibrium with each other, at least after the reaction at
room temperature, as is shown by the fluctuation of the
quantity of (18).
the resonance is distinctly displaced toward higher
fields. The difference between the chemical shifts of
trimethylelement ligands attached to the amine and
to the imine nitrogen atoms of the benzamidine is
about 30 Hz (Table 3).
The ligand arrangement required in (17) does not
conflict with the reaction path proposed in eq. (el if
one considers the reaction scheme 1 for the formation
of (Ida)-(lde).
a) Adduct (IS) does not react, as required by eq. (e), in the
form (IS), but in the form (15'), to give (17). This explanation is not convincing, since (IS) and (CH&SiCl on the one
hand and lithium methylamide, benzonitrile, and chlorotrimethylsilane (but not chlorotrimethylstannane) o n the
other give mixtures of isomers[191. The formation of (15')
by insertion of benzonitrile into the Si-N
bond of
(CH3)$-N(CH3)-Li
was ruled out by the reaction of
(CH3)3Si--N(CH3)--H with benzonitrile.
Unlike the bis-silylated compounds (16a) and (166),
the compounds (16c), (16d), and (16e) are entirely in
the form of one isomer. Since the 1H-NMR spectra
of (16d) and (16e) also exhibit J I I ~ , I ~ ~ s ~ - Nand
- c - H b) Though reaction (e) takes place as indicated, (16c)-(I6e)
JZO7pb-N-C-H
coupling respectively, the structure
unlike ( 1 6 ~ )and (16b), undergo an irreversible ligand ex-
864
Angew. Chem. internat. Edit. 1 Vol. 8 (1969) J No. I 1
Licl
membered ringsr241). This is a very clear illustration
of the stabilizing influence of the trimethylsilyl Iigand.
The N-silylated stannabenzimidazolidine (20) is
obtained by this method from A',"-bis(trimethylsily1)o-phenylenediamine and bis(diethy1amino)dimethylstannane [24a].
/
Si(CHd3
(17)
-
(18)
/
Scheme 1. El = Si-Pb;
R
=
CH,, CzH5.
change (step A in Scheme 1). The tendency of the elements
Ge, Sn, and Pb (unlike Si) to increase their coordination
number above four may be the driving force for the rearrangement of (16) into (17). Unlike in (16'), a gain in energy due
to further limiting resonance structures is possible in the
modified form (17') of (17)
(20)
Si(CH&
2.2. IVa/Va Elements
The tendency of silicon to achieve the greatest possible
(g + d)x bond strengthening would also oppose the substitution on the imine nitrogen.
Nothing definite can be said at present about the mechanism
of this ligand exchange reaction. The ability of the organo(1Va)element substituents to migrate is probably strongly
influenced by the mutual proximity of the two nitrogen
atoms and the ease of displacement of the x electrons inside
the amidine skeleton. Since (16a) and (166) give isomer
mixtures, it must be assumed that here at least the rearrangement from (16) to (17) does not proceed via (18), but that a
synchronous mechanism must be considered for the ligand
migration (cf. Section 2.2.1).
2.1.2. H e t e r o c y c l e s
Bis[organo(IVa)element] combinations in which one
hetero atom forms part of a ring while the other is
exocyclic can be obtained by synthetic variants of
transamination with cyclization [24aI.
Phosphorus-nitrogen compounds with a (CH&Si
group on the nitrogen are obtained almost exclusively
by cleavage of bis-silylated amines with phosphorus
halides 1251. Attempts to prepare these compounds in
the same way as their analogs with IVa elements, i.e.
from lithium N-methyl-N-trimethylsilylamide(I) and
methylphosphorus halides, have been unsuccessful 1261.
Reactions of ( I ) with methylhalogeno and trihalogeno
compounds of arsenic, antimony, and bismuth, on the
other hand, have been successful [27aJ.
+
n (CH3)3Si-NCH3-Li
(CH3)3-nElXn
(1)
+ [(CH3)3Si-NCH31n EL(CHJ)~-~ nLiX
+
121)
El = As, n = 1-3, X = CI, Br; El = Sb, n
El = Bi, n = 1-3, X = Br
=
1 -3, X
=
CI, Br;
As-(N-Methyltrimethylsilylamino)dimethylarsine(2la)
is also formed by cleavage of an As-N bond of
N,N-bis(dimethy1arsino)methylamine with methyllithium and reaction of the lithium N-methyl-Ndimethylarsinoamide (22), formed in accordance with
eq. (f) with chlorotrimethylsilane [27bl. Methyllithium
cleaves the As-N bond of (21a) only under more
forcing conditions (approx. 70 "C)[31.
+
( C H ~ ) ~ A S - N ( C H ~ ) - A S ( C H ~ )CH3Li
~
+ (CH&As-N(CH3)-Li
+ As(CH&
(f)
122)
122)
+ (CH&SiCI
+
+ (CH~)~AS-N(CH~)-S~(CH& LiCl
(2la)
&(CH3)3
n
= 0, 1,
2
It is interesting to note that with CH3 instead of the
(CH3)3Si group, only the six-membered analogs can
be prepared [24a1 (polymerization occurs with the five1241 a) 0. J . Scherer, J . Schmidt, J . Wokulat, and M . Schmidt,
Z . Naturforsch. 206,183 (1964); b) C. H. Yoder and J . J. Zuckerman, J. Amer. chem. SOC.88, 4831 (1966).
Angew. Chem. internat. Edit. / Yol. 8 (1969)J No. I I
A new, simple route to the relatively little-investigated
class of iminoarsoranes is provided by the reaction of
an N-metalated aminoarsine with methyl chloride [40al.
[25] Cf. e.g. 0. J . Scherer, Organometallic Chem. Reviews, Part
A 3, 281 (1968).
[26] 0. J . Scherer and P . Hornig, unpublished.
I271 a) 0.J . Scherer, P. Hornig, and M . Schmidt, J. organometallic
Chem. 6, 259 (1966); b) 0.J . Scherer and M . Schmidt, Angew.
Chem. 76,787 (1964); Angew. Chem. internat. Edit. 3, 702 (1964).
865
[(CH~)~C]~AS-NLI-S~(CH~)~
CH3Cl
-+
-LiCI
(p
d)x-strengthening of the El-N
->
bond from
[ ( C H ~ ) ~ C ] ~ A S ( C H ~ ) = N - - S I ( C H ~ ) ~= As to Bi.
Nearly all compounds (21) are colorless liquids, whose
sensitivity to oxygen and moisture decreases with
increasing n and increases from the arsenic to the
bismuth compounds. Like the tin derivative ( I o c ) , the
with
around room temperature.
On comparison of the chemical shifts of
the homologous series (CH3)3Si-N(CH3)El(CH3)2,
Synthesis of compounds of the type (21) with aminophosphines instead of amines of group IVa elements
leads surprisingly readily to compounds having this
desired
of
and Va elements, in which
the thermal stability of the primary and secondary
aminophosphines, compounds which have not been
extensively studied, is increased by suitable ligands on
the phosphorus atom, e.g. the (CH3)3C group 128-31aJ.
1/2 I(CH3)3Cl2P-N[Sn(CH3)312
rl’+
1/2 [ ( C H ~ ) ~ C ] ~ P - N H Z
[(CH3)3C]*P-NH-Sn(CH3)3
(26~)
[(CH~)~S~-N(CH~)]ZEICH~,
and [(CH3)3Si-N(CH3)]3EI,
El = As to Bi, it is found that 8CH3(Si) and 8CH3(N)
vary in the same direction as for corresponding
compounds with El = IVa elements (Section 2.1).
[(CH3)3Si-N(CH3)],El(CH3)3-n compounds with El =
As to Bi, n = 1-3, like the comparable tin compounds
-1
I;-.
+
(1)
[(CH,)~CIZP(H)=N-S~(CH~)~
(27)
--/b
[(CH3)3C]2P[Sn(CH3)3]=NH
(28) (j)
It should be mentioned that the tin derivative (26c)
unlike most stannylamines with N H bonds [12al, does
not undergo dismutation at high temperatures
[eq. (91.
A type of “Michaefis-Arbuzov rearrangement” into
one of the two possible iminophosphoranes (27) or
Table 4. Physical properties and 1H-NMR data (in Hz) of the compounds (21) (in CC14, TMS as internal
standard).
Compound
1
I
I
-50
11-13
I
-3.5
-153.0
-5.5
67-70/0.1
-6.5
-159.5
-153.5
44-4611
59-61/0.1
78-79/0.1
31-32/0.1
70-71/0.1
90-92/0.1
9-11
27-29
I
44-46/11
55-59/0.1
-3.0
-5.0
-6.5
0.0
-3.0
-4.5
(I#), show a shift of GCH3(Si) toward lower field
strengths with increasing n; 8CH3(N), on the other
hand, is differently influenced (Table 4).
The spectra, like those of the IVa element compounds,
can be interpreted by assuming a decrease in the
c H3
-162.0
-168.0
-161.5
-200.0
-213.0
-213.0
I
-59.5
-66.5
-48.5
-52.5
-70.0
-70.0
(28) [eq. ($1 is not observed even when (26c) is heated
at 150 “C for 20 hours.
The first known low molecular weight diaminophosphine is (29) [)la, 321, which can be silylated with
chlorotrimethylsilane in the presence of an auxiliary
base [eq. (k)].
cH3
(CH&C-P(NH2)2
+ 2 (CH3)3SiCI
(d[2s’
&H3 (23)
R
=
CH,, n-CPHg
The new compounds of the type (24) exhibit interesting
relations in their 1H-NMR spectra, and can be used
for a wide variety of chemical reactions [28,303.
cH3
(23)
+
(CH3)3E1C1 + [‘P-XHi1(CH3),
+
LiCl
(g‘)[281
?fI
CH3
(24)
E l = Si (24a). G e (24b). Sn (24c)
[(CH&C]2P-NR-H
--f
+ n-C4HgLi
[(CH3)3ClzP-NR-Li
+ n-C4Hlo
(h)
(25)
(25)
+ (CH3)3ElCI
+
[(CH3)3C]2P-NR-EI(CH&
(26)
R
R
=
=
866
+ LiCl
(h’)
H; El = Si (26a), Ge (26b), Sn (26c), Pb (26d) [29,30]
CH3; El = Si (26e) [ 3 0 ]
[28] 0. J . Scherer and J . Wokulut, Z. anorg. allg. Chem. 361, 296
(1968).
1291 0. J . Scherer and G . Schieder, Angew. Chem. 80, 83 (1968);
Angew. Chem. internat. Edit. 7, 75 (1968).
[30] 0. J . Scherer and G . Schieder, Chem. Ber. 101,4184 (1968).
[31] a) 0.J . Scherer and P. Klusmann, Angew. Chem. 80, 560
(1968); Angew. Chem. internat. Edit. 7, 541 (1968); b) Cf.
(C6H&P[NSi(CH3)3] [NLiSi(CH&I: H. Schmidbaur, K . Schwirten, and H. H . Pickel, Chem. Ber. 102,564 (1969); c) Cf. H. Schmidbaur, W. Wolfsberger,K . Schwirten, and H . H . Pickel, Progress in
Coordination Chemistry XI. ICCC, Haifa 1968, Elsevier, New
York 1968, p. 378.
[32] 0. J . Scherer and P . Klusmann, Z. anorg. allg. Chem., in
press.
Angew. Chem. internat. Edit. 1 Vol. 8 (1969) / N o . I 1
a clear indication of the pseudohalogen character of
trimethylsilyl azide 1301.
CI H3
cP(S)-N$
- SH3
i(CH3)3
+ (CHMIN,
1Y
(266), (26~)
I
CH3
(32)
+ [(CH~)~C]ZP-NH
-Si(CH3)3
+ (CH,),EIN,
7H3
I@ 4
cn I (24a)
,po--p;J-S~(cH~)~
7
c,fN-si(cH3)3
(CH,),SiN,
y-Si( C H3)3
On reaction of (CH3)3Si-N(CH3)Li (1) with tertbutyldichlorophosphine instead of with methylphosphorus halides 1261, it is even possible to displace
the chlorine atoms successively1321.
The aminoiminodiazaphospholidine derivative (33) is
formed not only from (24a), but also on reaction of
(24‘) with two moles of trimethylsilyl azide 1281.
CH3
CH3
FH3k
C,P-N-P:
k
2 (CH,),SiN,
-2
N,
-
(33)
+
c1
(CH3)3C-P(
c1
-+
Polymers
(m)
+
FH3
(CH3)3Si-N-Li
(1)
+
(CH3)3C-P:
LiCl
y-Si(C H3)3
N
I
CH3
(p)
El = Ge, Sn
(36)
CH3
CH3
(24’1
(36) is an important starting material for the synthesis
of diaminophosphines with different ligands on the
On the other hand, if the two phosphorus atoms in
amino groups 1321.
(24’) are separated by the -N(CH~)-(CH~)X-N(CH~)N(R)-H
group, the P-N bond is not broken 1281.
(36) + 2 R-NHz
(CH3)3C-P:
--.)
N-Organo(1Va)element-substituted aminophosphines
(26) are almost quantitatively oxidized to P-chloroiminophosphoranes (34) by carbon tetrachloride f29,301
N(CH3) -Si( CH3)3
(37)
+
(P‘)
RNHz’HC1
R
f26’
3
[(CH~)~C]ZP(CL)=N-E~(CH~)~
(n)
HCCI3
-
(34)
El
=
Si (34a), Ge (34bj, Sn (34c)
Whereas oxidation with trimethylsilyl azide leads, in the
case of the silicon compound (26a) [eq. (o)][301, to the
desired compound,
(35)
=
e.g. H (37a), CH3 (376)
(37a) does not exist in the isomeric form expected
from eq. (p’). The “more symmetrical” isomer
(CH3)3CP[NHSi(CH,)3](NHCH3) has been formed
by an irreversible (CH&Si/H ligand exchange [321.
At this point we shall discuss the 1H-NMR spectra of
compounds that illustrate the influence of the hetero
atom and of the oxidation state of the phosphorus on
the P-N(CH3) coupling constant. The models ( 2 4 ) ,
(31) -(33), and (38) satisfy these requirements(Tab1e5).
7 H3
c
H
FH3
X-N-Y
the reactions with (266) and (26c) lead merely to
cleavage [eq. (p)] of the Ge-N or Sn-N bond; this is
6%
X = P, P-CH3, P=S, P=N-Si(CH&
Y = (CH3)3El, E l = Si + Sn
(38)
Table 5. IH-NMR data (in Hz) for the compounds (24). (26).and (31)--/34) (in benzene, TMS as external standard).
~
6 CHdEI)
(24u)
(246)
124~)
(31) [a]
132)
(331 [bl
-142.0
-146.3
-152.5
-165.6
-120.5
-139.0
(d)
(d)
(d)
(d)
(d)
(d)
-128.0
-136.7
-148.7
-180.0
-121.5
-129.0
=
+
}
+
+
+
-=
-28.5
-33.9
-36.2
-41.2
-47.2
-49.0
-58.4
(d)
(d)
(d)
(d)
(d)
(d)
(d)
J31PNCH,(R)
Icl
J31PNCH3
12.5
12.3
12.2
10.7
12.2
9.8
3.3
4.5
7.3
15.1
14.5
14.3
Ref.
2.0
1.1
0.55
0
0.6
0.3
0
0
0.5
0
0
11.0
10.9
10.7
10.8
17.3
17.0
16.7
14.5 Hz (in CDCI3);
-N(CH3)-tCH~)2-N(CH3)-~
structure.
[cl R
+
l.O(d)
-14.7 (d)
-17.0 (d)
-31.06)
- 2.5 (s)
- 5l.O
. 0(d)
(~)
+21.2 (d)
12.0 (d)
16.3 (s)
-29.3 (s)
+11.5 (d)
0.0 (s)
5.5 (s)
(260)
12661
(26~)
(264
(344
(346)
134cl
[a1 6 C H D - 1 4 4 . 5 (d), J31pcH
(d)
(d)
(d)
(d)
(d)
(d)
6 (CH,)K(P)
- 0.35 Hz; J , , , , l19Sn-c-H
and JzorPb-C-H
were not given;
Ibl J3,p,NsicH
6 CHz(R) possesses, with the exception of (31) IS CH2(R)-224.0 (d), J3rpNcH,(R) = 8.8 Hzl a multiplet
Angew. Chem. internal. Edit. / Vof. 8 (1969) No. II
867
In (38), the oxidation state of the phosphorus has little
influence, and the ligand Y has practically none, on
the coupling h1pNCH3(R) of the phosphorus with
the protons of the ring CH3N group. The coupling
of the phosphorus with the
constant J~IPNCH,
protons of the CH3N bridge, on the other hand, shows
a distinct dependence both on X and on Y . The
to X = P V [e.g.
constant increases from X =
(24a) + (32); 3.3 + 14.5 Hz]; J~IPNCH,(R) remains
practically unchanged (12.5 + 12.2 Hz). The influence
of the hetero atom Y on the coupling constant
J~IPNCH,
can be observed in the compounds (24a) +
[24c), since it increases from 3.3 to 7.3 Hz. In (33),
long-range coupling of the phosphorus is found only
with the protons of the trimethylsilyl group bound to
the imine nitrogen atom (J3lP=NSiCH, = 0.35 Hz) [281.
Whereas J3IPCCH for [(CH3)3C]2P-NH-El(CH3)3
(26a)-(26c) is practically unaffected by the ligand El
on the nitrogen atom, the long-range coupling
J~IPNEICH,
decreases from 0.6 to 0 Hz [(26u) (26c)l. As expected, JHPCCH
of the compounds
(26a) -(26c) containing trivalent phosphorus increases on oxidation to the pentavalent phosphorus
compounds (34a)-(34c). The only sign of the
influence of the hetero atom is a small linear decrease.
J3IpNEICH is observed only for the silicon derivative
(34a).
Though the chemical shift varies with concentration
when benzene is used as the solvent, 8CH3(N) and
~ C H ~ ( N Rshow
)
the same tendency toward lower
fields for El = Si -+ Sn as in corresponding IVa/IVa
combinations.
the reaction of N,N’-organoelement-substituted diaminophosphines with tetrahalogenomethanes [31a,32J
[eq. (r), cf. eq. (n)], and the oxidation of stannylphosphines with phenyl azide 136).
(30) +
cx,
-
(CIi3I3C\ ,N-Si(CH,j3
/P\
+ HCX3
X N-Si(CH3)3
(I)
(41)
X = C1(41a), B r (4Ih)
(41a) contains a reactive P-CI bond, as is shown by
the reaction with dimethylamine [31a93*1,
A number of other aminoiminophosphoranes (43)
and (46) containing only one trimethyl(1Va)element
group can be synthesized both in analogy with eq. (r)
from (37b) and carbon tetrachloride 1321
and by alcoholysis of NJV”’bis(trimethylsily1)aminoiminophosphoranes, metalation with n-butyllithium,
and reaction with e.g. chlorotrimethylsilane [eq.
(s)] D O , 351.
2.2.1. N,N’-B i s ( o r g a n o e 1e m e n t ) - S u b s t i t u t e d
Aminoiminophosphoranes
B
(44)
Like the benzamidines (16), the structurally related
aminoiminophosphoranes (39) are suitable for the
study of ligand migration processes.
R = H (&a), CH3 (44b)
The first compound was obtained from triphenylsilyl
azide and diphenylphosphine L331. Other possible
routes to these compounds are the oxidation of aminophosphines with silyl azides f28,30731a1 [eq. (q), cf.
eq. (I), (m), (011,
(44) + n-C4H&i
(26e) + (CH3)3SiN3
-
N-S1( CH3)3
[(CH3)3C]zP:
+ N2 (4)
N- Li
//
[(CH3)3C]2P,
(45)
(45)
+
(CH3)3SiC1
-
R
the cleavage of a P-N bond in diphosphinoarnined28,
341 [eq. (q’), cf. eq. (m)] with silyl azides,
(40)
&H3
+ Polymers
(q’)
(331 K . L. Paciorek and R. H. Kratzer, J. org. Chemistry 31, 2426
(1 966).
[341 J. Wokulat, Dissertation, Universitat Marburg 1967.
+ n-C4H10
(s)
R
N-Si(CH3),
[(CH3),CIZ<
=
+
LiCl
N-H
(46)
dH3
8-H
R = H (45a), C H3 (4Sb)
N-Si(CH3),
(39)
868
-
B
A
(S‘)
H (46a), CH3 (46b)
The tautomeric form with the trimethylsilyl group on
the amine nitrogen atom can be definitely ruled out
for (46) on the basis of IR and 1H-NMR studies [351.
The trimethylstannyl ligand can be introduced instead
of trimethylsilyl in compounds of the type (43) by
means of the multistep synthesis shown in scheme 2 C321.
_____
[35] 0.J . Scherer and G . Schieder, J. organometallic Chem. 19,
315 (1969).
1361 H . Schumann and A . Roth, J. organometallic Chem. 11, 125
(1968).
Angew. Chem. internat. Edit.
1 Vol. 8 (1969) 1 No. I I
(47)
(CH3)3C\
0N-CH3
K
H3C N-CH3
x CH,OH
(CH,),S~CI
- LiCl
(48)
&(CH3)3
(CH3)3C,
.p\
H3C N-CH3
n-C,H9Li
t
-“-C4H10
&(CH&
1
-(CH,),SiOCH,
(CH3)3C, ,N-CH3
,p\
H3C N-CH3
Scheme 2.
Attempted reactions of the metalation products of
(35) and (42) with chlorotrimethylsilane have been
unsuccessful evidently on steric grounds r31a3321. The
amide (52) is dimeric in benzene, as is shown by
cryoscopic molecular weight determinations. Its
1H-NMR spectrum contains only one sharp signal
for the “differently bound” trimethylsilyl ligands (in
various solvents and at high dilutions). These facts are
best explained by the structure (52a) for the molecule
in solution [31a, 31b, 321.
(CH3)3C, ,)N-S1(CH3)3
IP
\
(CH3)2N N-Si(CH,),
I
Li
(CH3)3?
Si(CH3)3
(CHdzN, ,N-Li--?$ /C(CH&
,P<\.
,:,p\
(CH3)3C N--Li-N
N(CH3)2
( CH3),Si
Si( CH,),
(52)
(52ai
R1 = R2 = C6H518b1. In compounds containing
different hetero atoms, the two isomeric forms [(54a)
and (54b) in this case] are stable even at 15O0C[35I.
If the CH3 group in the bis-silylated compounds /33),
(39), and (40) is replaced by a proton, (35) is obtained
with R1 = R2 = (CH3)3C[30], and (42) with R1 =
(CH3)3C, R2 = (CH3)2N [31a, 321. A reversible intermolecular proton exchange can be detected in both
compounds
R: ,jN-Si(CH3)3
However, reaction of impure bis(trimethylsily1)aminodimethylphosphine[371lprepared from [(CH3)3Si]2NNa
and (CH3)zPCl; see also section 3.21 with trimethylsilyl azide gives the first triply silylated aminoiminophosphorane (53) 131a. 321.
(53) &A(CH3)3
On the basis of the general formula (54), we find a
number of important questions in connection with
reversible and irreversible migration processes:
1. How do the ligands R1, R2, and R3 influence the
ability of the R:El and R:El groups to migrate?
2. What part is played here by the ligands R4 and R5,
and what part by the hetero atom El?
3. What happens if the R:El group and R3 are replaced
by CH3?
Compounds of the type (33), (39), and (40), unlike
benzamidine (16a), do not exhibit migration of the
trimethylsilyl groups (even at high temperatures) in
any of the four examples studied R1 = R2 =
(33) C2*1; R* = R 2 =
-N(CH3)-(CH,)2-N(CH3)(CH&C (39) [3OJ; R1 = R2 = CH3 (40) [341, and
[37] 0. J . Scherer, unpublished.
Angew. Chem. internat. Edit. J Vol. 8 (1969) J No. I 1
-
L
,p\
R 2 N-Si(CH&
&
( CRH
Si
Si(CH3)3
:- h,N-H--N,
- 1
/R2
/R. ,F\R’
R 2 N--H-N
(CH3),Si
S~(CHS)~
( 3 . 5 ~(42)
The NMR spectra in both cases contain one signal for
the “differently bound” trimethylsilyl groups at high
concentrations in benzene, and two trimethylsilyl
signals at lower concentrations [3O,31a3321. Coalescence
of the two signals can be observed by the addition of
catalytic quantities of methanol [but not traces of
amine, e.g. (CH3)zNHI.
If tetrahydrofuran is used as the solvent for (35) [301,
and acetone for (42) [321 (tetrahydrofuran gives no
splitting in this case) instead of benzene, the spectrum
both in concentrated and in dilute solution contains
two (CH3)3Si signals, which do not merge even on
heating or an addition of small quantities of methanol.
This supports the assumption that the formation of
hydrogen bonds (detectable by IR spectroscopy [301)
with the solvent [381 takes precedence over the intermolecular proton exchange in this case.
The proton exchange also stops when the (CH3)zN
group in (42) is replaced by the halogen atoms CI
(4Ia) and Br (41b). Since the IR spectrum contains
no evidence of hydrogen bonding to the halogen 1321,
[38] Cf. e . g . H . Suhr: Anwendung der kernmagnetischen Resonanz in der organischen Chemie. Springer, Berlin 1965, p. 111 ff.
869
this difference in the behavior of (4Ia) and (416) on
the one hand and (35) and (42) on the other can
perhaps be attributed to inductive effects.
A reversible intramolecular 1,3-trimethylsilyl migration
occurs when the proton is replaced by the (CH3)3Si
ligand [3% 3 h 321. This migration, which has a low
activation energy, can be “frozen in” at about -20 “C.
would be expected for a pentacoordinated Sn atom
with a trigonal bipyramidal arrangement, even with
fast pseudorotation) indicates that even at this temperature the system is “stereochemically nonrigid”.
All the results support the hypothesis that reversible
intramolecular (CH3)3M ligand migration in organo(1Va)element - substituted aminoiminophosphoranes
appears to be favored whenever, instead of a new
isomeric form [e.g. (53b) or RIR2P(=NCH3)
(N[Si(CH3)3]2) for the compounds (33), (39), and
(40)], a n identical molecule [as a transition state, a
molecule with identical N ligands (e.g. A)] can be
postulated as an intermediate.
2.3. Va/Va Elements
The replacement of a (CH3)3Si group on the amine
nitrogen atom by the (C2H&Si group in (53) leads to
a compound (53a) 18bI that shows no splitting of the
(CH3)3Si signal in the N M R spectrum even at -55 “C
and a t high dilution. This observation is open to
several interpretations:
Compounds containing the atomic grouping
RzP-NRI-EIR; (El = As --f Bi) are at present known
only in the form of aminophosphinoarsines
( C F ~ ) ~ P - N R - A S ( C F ~R=H,
) ~ , CH3 [391.
Novel compounds of this type can be prepared by
reaction of the lithium N-phosphinoamides (23) and
(25) mentioned in equations (8) and (hj with dimethyl(Va)element halides or 2-chloro-l,3-dimethyl-l,3,2diazaarsenolane [27bl eq. (t’) (cf. Table 6).
1. The reversible intramolecular migration proceeds
too rapidly even at -55 “C.
2. The substance is in the form of an “inner” symmetrical complex with pentacoordinated silicon (corresponds to transition state A).
C H?
(23)
+
+
(CH3)2E1C1 -D
L i C l (t)[281
3. Both trimethylsilyl groups are bound to the amino
nitrogen atom (this assumption is supported by the
P=N band in the I R spectrum), and give no 1,3
migration in this isomeric form (53b).
The driving force for the formation of (536) may be the
preference for the formation of sterically “balanced”
molecules [cf. compound (37u)I. If the model compounds mentioned are modified in such a way that
only one trimethyl(1Va)element ligand is now bound
to the amine nitrogen atomr321, (48) exhibits a
reversible intramolecular 1,3 migration of the (CH&EI
ligand, which stops at - 5 5 ° C and can be readily
detected by the splitting of the CH3N doublet (NMR)
into two doublets[321. 8CH3(N) for (51) consists of
only one doublet down to -55 “C, even at high dilution.
The absence of J i i 7 , i i 9 s n - ~ - ~ - ~ coupling (which
[(CH3)&]2P-NR-Li
+
(CH3)dsCl
+ [ ( CH3)sC IzP- NR -A s( C H3)2
+
LiC1[40b’
(5 7)
R = H, CH3
The parent compound from which these alkylsubstituted products are derived, i. e. &As-dimethyl(N-dimethylphosphino-N-methy1amino)arsine (58),
can also be prepared in this way [341.
+
(CH~)ZP-N(CH~)-L~ (CH3)zAsCl
+ ( C H ~ ) ~ P - N ( C H ~ ) - A S ( C H ~LiCl
)~
+
(-58)
[39] J. Singh and A . B. Burg, J. Amer. chem. SOC.88, 718 (1966).
[40]a) 0.J. Scherer and W.M . Junssen,J. organometallic Chem.
16, P 69 (1969); b) ibid., in press.
870
Angew. Chem. internat. Edit.
Vol. 8 (1969) J No. 11
Table 6. 1H-NMR data (in Hz) for the compounds (SS) and (58) (in benzene, TMS as external standard].
Compound
8 CHANR)
155ai
(5561
(55~)
--146.0 (d)
-148.5 (d)
-154.0 (d)
I
S CHdEI)
--138.0(t)
-148.3 (d)
-163.0 (d)
-154.0 (d)
(581
6 CH3(P)
-58.3 (d)
-61.5 (d)
-53.0(d)
-60.5 (d)
I
;;;PNCH,(R)
12.7
12.3
12.5
-60.3 (d)
Like the compounds (24a)-(24c), the compounds
(55) exhibit a n increase in J ~ I P N C
from
~ I ~El = P to
El = Sb (3.4-8.9 Hz), while J31pNCH2(R) remains
practically unchanged. Unlike (24a), the first member
( 5 5 ~ )shows n o long-range coupling JXPNEICH
(this
is a l s o true of the reference substance (55') 1411). The
long-range coupling is however observed for the
arsenic and antimony compounds (556) and ( 5 . 5 ~ )
respectively. Comparison of the compounds (55b) and
(58) reveals that the ligand on the phosphorus does
not appreciably influence the coupling constants and
chemical shifts of the -N(CH3)-As(CH& residue.
3.4
6.0
8.9
6.3
0
0.45
0.35
0.70
6.6
6.25
obtained when (59) is allowed to react with chlorotrimethylstannane or aluminum chloride instead of
with chlorotrimethylsilane. Since the decomposition
of (61) into (62) is accompanied by almost exclusive
formation of trimethylsiloxytrimethylstannane, this
must be taken as evidence of an intramolecular decomposition. N,N'-Dimethyl-N,N'-bis(trimethylsily1)sulfinyldiamide (63a), which can be synthesized in
accordance with eq. (u),
2.4. IVa/VIa Elements
Bis(organoe1ement)-substituted amines with this combination of elements are confined to the elements
silicon and sulfur. Until recently these compounds
were nearly always synthesized by heterolysis of Nsilylated nitrogen compounds with sulfur halides L251.
We found that lithium N-alkyltrimethylsilylamides
add smoothly to N-phenylthionylimide (N-sulfinylaniline) to give (59)l42J.
P
(CH3)3Si-N-Li
+
I+
yi(CH3)3
C6H5-N=S=0 + C6H5-N-S-N-R
8
c~H~-N-S-N-R
6
(61)
(59)
forms colorless crystals immediately after distillation;
on storage in a stoppered flask at room temperature,
these crystals slowly decompose into hexamethyldisiloxane and sulfur N,N'-dimethyldiimide [42bI.
1H-NMR spectroscopic measurements show that (630) has
decomposed to an extent of about 40 % after three days, and
about SO% after three weeks. Further enrichment of the
thermally very unstable C H 3 N = S = N C H 3 [431 is impossible
at room temperature. Attempts to prepare the ethyl and
phenyl derivatives (63b) and (63c) in accordance with eq. (u)
showed that both suffer partial decomposition (detectable by
NMR spectroscopy) during the reaction. Sulfur N,N'-diphenyldiimide is obtained by this method in a yield of 40 %.
Organo(IVa/VIa)element-substituted amines can also
be obtained by nucleophilic cleavage of sulfur-sulfur
bonds (for detailed discussion cf. Section 3.3), as is
shown by the reaction of dimethyldisulfane with
metalated N,N'-bis(trimethylsilyl)alkyIenediamines[44J.
* C,H5-N=S=N-R
- (CH1)~SnOSi(CH3),
(62)
R = Alkyl
Substitution of the 1:l adducts (59) with chlorotrimethylsilane gives N,N'-disilylated sulfinyldiamides
(60), which split off hexamethyldisiloxane at temperatures above 100 "C. The resulting sulfur N-alkylN'-aryldiimides (62) can be isolated in this way in a
fairly pure state. The pure compounds are however
Selective hydrolysis o r alcoholysis of the Si-N bond to form
the silicon-free aminosulfanes CH~S-NH-(CHZ),-NH-SCH~
cannot be achieved with (64) (the compounds are recovered
unchanged). More vigorous reaction conditions (e.g. acid o r
alkaline hydrolysis) lead at higher acid or base concentrations
to simultaneous cleavage of the S-N bond. This may be
regarded as evidence of the unusual stability of this class of
substances toward hydrolysis.
[41] 0 .J . Scherer and J . Wokulat, 2. Naturforsch. 22b, 414 (1967).
[42] a) 0.J.Scherer and P. Hornig, Angew. Chem. 78,176(1966);
Angew. Chem. internat. Edit. 5 , 7 2 9 (1966); b) P . Hornig, Dissertation, Universitat Wurzburg 1968.
1431 B. Cohen and A. G . MacDiarmid, J. chem. SOC. (London) A
1966, 1780.
[44] 0.J . Scherer and J . Wokulat, Z. anorg. allg. Chem. 357, 92
Angew. Chem. internat. Edit. / Vot. 8 (1969) 1 No. I I
(1968).
871
3. Tris(organoe1ement)-Substituted Amines with
Two Different Hetero Atoms
3.1. IVa/IVa Elements
Tris(organoe1ement)-substituted amines can be derived
from the ammonia molecule in the same way as
bis(organoe1ement)-substituted amines.
X
The compounds (65) differ very markedly in their
behavior toward protonic solvents. (65b), like (65u),
El = Si, is surprisingly resistant to moisture. This
behavior, which is unusual for alkylgermaniumnitrogen compounds, is probably due to steric factors.
(65c) and (65d) react immediately with water at the
Sn-N and Pb -N bonds respectively.
The tris(organoe1ement)-substituted amines are suitable
for the study of the relative inductive effects of the
IVa elements (cf. also[511). This effect can either
Y
N
''
X
X,Y
= organoelement
ligand
I
t
I
I
*I
An excellent starting material for the synthesis of
bis(trimethylsilyl)trimethyl(IVa)element-substituted
amines (65) 1451 is sodium bis(trimethylsilyl)amide,
which was synthesized by Wannugat 1461 (Table 7).
$1
-SiI
=
Ge
+
El-
il
-Si-
-Si-
B
C
I
A
El
I
I
Si- -Si
-El
I
Pb
weaken (-I effect, A) or strengthen (+I effect, C) the
Si-N bonds, which are strengthened in the symmetrically substituted derivative (B) by equal sharing of
Table 7. Physical properties and spectra of the compounds (65) (in CCI4, TMS as internal standard).
(65~)[a]
(656)
( 6 5 ~ [bl
)
78-80/13
(6%) [c]
85-87/3
54-56/1
58-59/1
67-69
29-32
20-22
-
10.7
118.0
118.0
7.2
5.0
118.0
0
118.0
(6.5~)is also formed from bis(trimethylsily1)amine and
N,N-diethyltrimethylstannylamine1471. Alkoxy derivatives are also known in the germanium series [481. Lithium N-triethylsilyl-N- trimethylgermylamide(66) 1141
has proved valuable as a starting material for the
synthesis of the compounds (67) with a new IVa/IVa
element combination [8bl.
the formally "lone" pair of electrons on the nitrogen
atom. IR (increase in the frequency of the antisymmetric SiN(Si) stretching vibration for El = Si +
Pb) and 1H-NMR spectra (shift of 8CH3(Si) to
higher field strengths for El = Si + Pb; J13CH(Si)
remains constant), as can be seen from Table 7,
indicate strengthening of the Si-N bond by the
incorporation of the hetero atom El, i.e. a + I effect
(C):
(CH&Pb
[(CH3)3Sn]zNSi(CH3)3 can be obtained both from
lithium bis(trimethylstanny1)amide [12dI and chlorotrirnethylsilane [though the product always also
contains (65c)l and by substitution of impure sodium
trimethylsilylamide with chlorotrimethylstannane [491.
1451 a) 0. J. Scherer and M . Schmidt, Angew. Chem. 75, 642
(1963); Angew. Chem. internat. Edit. 2,161 (1963); b) J. organometallic Chem. I, 490 (1964).
[46] U.Wannagat and H. Niederprum, Chem. Ber. 94,1540 (1961).
[47] J . Lorberth and M. R . Kula, Chem. Ber. 98, 520 (1965).
[48] A . Koster-Pflugmacher and E . Termin, Naturwissenschaften
51, 554 (1964).
[49] 0. J . Scherer and M . Schmidt, Sci. Commun. Internat. Sympos. on Organosilicon Chemistry, Prague 7965, p. 315.
8 72
(CH3)3Sn > (CH3)3Ge > (CH3)3Si
As in the case of the bis(organoe1enient)-substituted
amines with different hetero atoms, these observations
can be taken as evidence that (p 3 d)x strengthening
of the El-N bond is of minor importance for the
higher homologs of silicon [521. Two other classes of
compounds, i. e. the heterosiloxanes, which were
studied by Schmidbaur 1531 and the trimethyI(1Va)element azides, which were investigated by Thuyer and
West [54J,exhibit the same relations.
[SO] Cf. e . g . J. Goubeau and J . Jimdnez-Barbed, Z. anorg. allg.
Chem. 303, 217 (1960).
[Sl] a) Cf. e.g. T. N . Srivastava and M . Onyschuk, Canad. J .
Chem. 41, 1244 (1963); b) R . W. Bort, C. Eaborn, K . C. Pande,
and T. W. Swaddle, J. chem. SOC. (London) 1962,1217.
[52] Cf. e . g . E . W . Randall and J . J . Zuckerman, J. Amer. chern.
SOC.90, 3167 (1968).
[53] H . Schmidbaur, Angew. Chem. 77, 206 (1965); Angew.
Chem. internat. Edit. 4, 201 (1965).
[54] J . S.Thayer and R . West, Inorg. Chem. 3, 889 (1964).
Angew. Chem. internat. Edit.
1 Vol. 8 (1969) 1 No. 11
3.1 .l. H e t e r o c y c l e s
Cyclic amines of this type with two different hetero
atoms were described by Fink [551 in the form of the
four-membered heterocycles (68).
Si(CH3)3
E l = B (68a), P (686)
(68)
+
Si(CH3)3
2 LiCI
Starting with metalated bis(N-triethylsi1ylamino)dimethylgermane (69) [14J,it is possible to synthesize not
only the derivatives (70) [e.g.(v)] but also spiranes (71)
[eq. (v’)] [8bl.
silyl azide [eq. (s”)]. Unlike bis(trimethylsily1)amineL581, (726) does not react with excess chlorodimethylarsine to give tris(dimethy1arsino)amine
[(CH~)~ASI~N.
3.2.1. N,P-B i s ( o r g a n o e 1erne n t ) - S u b s ti t u t e d
Iminophosphoranes
Attempts to prepare compounds of the type (72) by
the reverse route, i. e . by substitution of N-silylated
lithium N-phosphinoamides (73) in accordance with
eq. (w) led us to the first N,P-bis(organo(1Va)element)substituted iminophosphoranes (7.5) 129,301, but gave
no amines (74).
[ ( CH3)3CIzP- N L i - E l ( CH3)3
I 73)
(CH3)3E1’Cl
,El’(C H3)3
N,
0
[(CH3),ClZP-NLi-E1(CH3)3
i I t ( C H 3 ) 3 c10
E1(CH3)3
(74)
(w)
k
fLiC1
[ ( C H S ) ~ Id’C
+
\
-
LiY
[(CH&C lzy=N-EUCH3)3
(75)
El“rH3)3
El = El‘ = Si (75a); El = Si, El’ = G e (756);
El = S i , El‘ = Sn (732); El = Ge, El‘ = Si (75d);
El = El’ = Ge (752); El = Ge, El’ = Sn (‘75f).
3.2. IVa/va EIements
Attempts to obtain definite N-silylated phosphorusnitrogen compounds by reaction of PC13 I561 or
variously substituted phosphorus chlorides with
sodium bis(trimethylsily1)amide have been successful
only in the case of chlorodiphenylphosphine [571.
Whereas bis(trimethylsily1)aminodimethylphosphine
(72a) [3%321 cannot be obtained in the pure state
(detectable by N M R spectroscopy) in accordance with,
[(CH3)3Si]2NNa
+ (CH3)zEICI
=
As was found by Schrnitz-DLi Mont and Jansen 1591, on
the other hand, substitution occurs on reaction of
( C ~ H S ) ~ P - N K - S ~ ( C Hwith
~ ) ~ chlorotrimethylsilane.
(75d) rearranges irreversibly into the isomer (756)
when heated at 120-130 “C for several hours; so far
as we know, this is the first exampIe of isomerism of
an iminophosphorane.
?(CH3)3
A
[(CH3)3C] z P = N - G ~ ( C H ~-=-+
)~
i72)
El
The fact
that
(75b)
is
obtained
from
[(CH3)3C]2P-NLi-Si(CH3)3 and chlorotrimethylgermane, and (75d) from [(CH&C]2P-NLi-Ge(CH3)3
and chlorotrimethylsilane shows that the reaction is
actually an addition (path C ) and not a substitution
(path A). If (74) were the intermediate, the end
product should be the same in both cases, i.e. (7.5).
P (72a), As (72b), Sb (72c)
1754
the analogous reactions with chlorodimethylarsine [581
and chlorodimethylstibine 111 present n o difficulties.
In view of the incompleteness of the class of substances
(72), we shall not discuss their IH-NMR spectra in
detail [8CH3(Si) is slightly displaced toward higher
field strengths from (726) to ( 7 2 ~ )-10.0
;
-8.5 Hz].
--f
(72a), unlike (72b), gives the triply silylated aminoiminophosphorane (53) on oxidation with trimethyl[55] W . Fink, Angew. Chem. 78, 803 (1966); Angew. Chem.
internat. Edit. 5, 760 (1966).
[561 U . Wannagat, Angew. Chem. 75,173 (1963); Angew. Chem.
internat. Edit. 2, 161 (1963).
1571 H . Noth and L. Meinel, Z . anorg. allg. Chem. 349,225 (1967).
Angew. Chem. internat. Edit. 1 Vol. 8 (1969) 1 No. I 1
p(CH3h
[(CH3)3C]2P=N-Si(CH3)3
(756)
It is not yet known whether this rearrangement proceeds intermolecularly or intramolecularly [(74)would
presumably occur as an intermediate in the latter
case]. The stronger tendency of silicon, as compared
with its heavier homologs, to form (p + d)n bond
components may be the driving force of this ligand
exchange. Another decisive factor may be the more
favorable energy balance resulting from the conversion
I581 0.J . Scherer and M . Schmidt, Angew. Chem. 76,144 (1964);
Angew. Chem. internat. Edit. 3, 137 (1964).
[59] 0. Schmitz-Du Mont and W. Jansen, Angew. Chem. 80, 399
(1968); Angew. Chem. internat. Edit. 7, 382 (1968).
8 73
of Ge-N and Si-P bonds into Si-N and Ge-P
bonds.
All the iminophosphoranes (75) are sublimable solids,
and their sensitivity to moisture decreases in the
following order:
(75f) 3 (752) > (75d) > (752)
> (75b)
> (75a)
The increased reactivity of the El’-P as compared
with the El-N bond is clearly shown in the alcoholysis
[eq. (x)] and in the reaction with carbon tetrachloride
[eq. (x’)], which leads in quantitative yield to the Pchloroiminophosphorane (34a) prepared earlier in
accordance with eq. (n).
bonds increases as the substituent R becomes more
strongly electron-attracting L441. If the cleavage of dialkyldisulfanes (very few anions A cleave dimethylor diethyldisulfane) is taken as a measure of the
N[Si(CH3)3]2@, it can
nucleophilic strength of A 0
be seen that sodium bis(trimethylsily1)amide is one of
the strongest nucleophilic agents. If the disulfane
derivative in eq. (y) is replaced by dimethyldiselenane,
the reaction yields bis(trimethylsily1)aminomethylselenane (78) 1441.
Q
[(CH3)3Si]zN-Se-CH3
( 78)
The alcoholysis of (75a) suggests that iminophosphoranes of the type (76), or at least these model
substances, are unstable and rearrange into the thermodynamically more stable isomeric aminophosphine
(NH + PH tautomerism has so far been observed
only in cyclotriphosphazenes 1601).
3.3. IVa/VIa Elements
Sulfur-sulfur bonds can be broken both electrophilically
and nucleophilically 161,621.
Sodium bis(trimethylsily1)amide not only reacts with
chlorosulfanes 1631, s 8 1641, and dithiocyanogen 1651 to
form N-silylated aminosulfanes having the composition
but also readily cleaves a wide range of disulfane
derivatives [eq. (y)] 144,661.
Comparison of the 1H-NMR and I R spectra of (78)
with those of the analogous sulfur compound (77a)
shows that the replacement of sulfur by selenium leads
to slight changes in $CH3(Si) and v,,SiN(Si), the
chemical shift being displaced to higher field strengths
[(77a) -10.7, (78) -9.2 Hz], and the antisymmetric
SiN(Si) stretching vibration to higher wave numbers
[(77a) 935, (78) 940 cm-11. These observations are in
good agreement with the results obtained for tris(organo(IVa/IVa)element)-substituted amines. However, the differences are more pronounced than for the
latter (cf. Section 3.1).
A distinct weakening of the “thiophilic character” in
alkali metal silylamides can be achieved by introduction of electron-attracting substitutents on the
silicon atom. [(i-C3H70)3Si]zNNa cleaves only the
sulfur-sulfur bond of the particularly reactive diethyl
dithiodiformate 1441.
+
[CZH~OC(O)S]Z [(i-C3H70)3Si]2NNa
+ [(i-C3H,O)3Si]2N-S-C(O)-O-C~H5
+ CzHsOC(0)SNa
(791
Many of the N-silylated aminosulfanes are surprisingly
insensitive to water. Their chemical behavior toward
thionyl chloride is interesting. In most cases cleavage
of the Si-N and not of the S-N bond occurs, even
under very mild conditions “571.
This cleavage of disulfanes confirms the observation
that the ease of nucleophilic cleavage of sulfur-sulfur
(601 A. Schmidpeter and J . Ebeling, Angew. Chem. 80,,197 (1968);
Angew. Chem. internat. Edit. 7, 209 (1968).
(611 E.g. A. J. Parker and N . Kharasch, Chem. Reviews 59, 583
(1959).
[62] E.g. M . Schmidt, osterr. Chemiker-Ztg. 64, 236 (1963).
[63] U.Wannagat and H. Kuckerfz,Angew. Chem. 74,117 (1962);
Angew. Chem. internat. Edit. 1 , 113 (1962).
[64] 0. J . Scherer and M . Schmidt, Naturwissenschaften 50, 302
(1963).
(651 0.J.Scherer and M.Schmidt, Z. Naturforsch. I8b, 415 (1963).
(661 O . J . Scherer and M . Schmidt, Angew. Chem. 75,139 (1963);
Angew. Chem. internat. Edit. 2, 98 (1963).
874
This provided the first preparative route to the Nalkylsulfenylthionylimides,as well as to many other
derivatives of this class of compounds (67,681.
[67] a) 0.J.Scherer and R.Schmitt, Chem. Ber. I O I , 3302 (1968);
b) Ire Symposium international sur la Chimie des Composes
organiques du Silicium, Bordeaux 1968, p. 165.
[68] 0. J . Scherer and R . Schrnift, unpublished.
Angew. Chem. internal. Edit. 1 Vol. 8 (I9691 No. 11
3.4. Ligand Migration Processes in N-silylated
Sulfinamides and Aminosulfimines
Fluxional organometallic molecules (particularly
transition element compounds) have recently been
intensively studied 1691. Whereas amides I [701, thioamides [711, ureas [721, and amidines (skeleton IV) are
used to study the 1,3 migration of (CH3)3EI Iigands
attached to nitrogen for elements of group IVa, aminophosphine oxides I1 [731 and aminoiminophosphoranes
V for elements of group Va, N-silylated sulfinamides
111 and aminosulfimines VI should be suitable for this
purpose in the case of group VJa (Scheme 3).
I
I1
111
IV
V
VI
If the CH3 group on the sulfur atom is replaced by
c6H5, no amine-imine tautomerization is observed
between about -50 and 100 "C.
The difference in the behavior of (81) and (82) is
probably due to an increase in the electron density on
the oxygen atom as a result of the inductive effect of
the methyl group.
1,2-Addition of methyllithium is also possible in the
case of sulfur bis(trimethylsily1)diimide 1751.
Scheme 3. The free valences on the N represent (CH&EI ligands.
Methyllithium adds to the double bond system of Nsulfinyltrimethylsilylamine. The 1:1 adduct reacts
further with chlorotrimethylsilane to give the bissilylated sulfinamide (81) [741.
(CH3)3Si-N=S=O + CH3Li
(83), like the analogous aminoiminophosphoranes,
exhibits dynamic properties.
,;?
-+
Li
(CH3)3Si-NLS-CH3
+ (CH,),SiCI
1-
LiCl
The 1H-NMR spectrum of (81) (in CCl4 solution and
undiluted at 35°C contains three (CH3)3Si and two
CH3S signals. Whereas coalescence of the silyl and
sulfenyl signals occurs at about 100 OC, the spectrum
resumes its original form when the specimen is cooled
to 35 "C again. This shows that (81) is in equilibrium
with its imine tautomer (81a) at 35 "C [about 60 % of
(81) and 40 % of (Sla)], this equilibrium being displaced even more in favor of the amine form (81) on
further cooling t o -50 "C.
[691 For example, F. A. Cotton,Accounts chem. Res. 1,257 (1968).
[701 a) J. Pump and E. G. Rochow, Chem. Ber. 97, 627 (1964);
b) L . Birkofer and A . Ritter, Angew. Chem. 77,414 (1965); Angew.
Chem. internat. Edit.4,417 (1965); c ) J . F . KIebe and J . B. Bushjr.,
Sci. Commun. internat. Sympos. on Organosilicon Chemistry.
Prague 1965, p. 328.
[711 K . Itoh, K . Matsuzaki, and Y. Ishii, J. chem. SOC.(London)
C 1968, 2709.
I721 a) J . F. Klebe, J . B. Bush jr., and J . E. Lyons, J. Amer. chem.
SOC.86,4400 (1964); b) I . Matsuda, K . Itoh, and Y. Ishii, J. chem.
SOC.(London) C 1969, 701.
[731 M . Meyer zur Heyde, Tetrahedron Letters 1969, 1425.
I741 0.J . Scherer and R.Schmitt,Tetrahedron Letters 1968,6235.
Angew. Chem. internat. Edit.
N,N',N"-Tris(trimethylsily1)-S-methylaminosulfimine
1 Vol. 8 (1969) 1 No. I I
The IH-NMR spectrum contains one (CH&Si signal
at 35 OC, even at high dilution, two at about -50 OC,
and three a t about -80 "C.
It may be concluded from these observations that the
reversible intramolecular (CH3)3Si ligand migration
indicated in the formulas stops at about -5OoC[7s1.
The additional splitting of the signal due to the aminebound (CH3)3Si groups a t about -80 "C can be interpreted as resulting from hindered rotation about the
S-N bond.
4. Tris(organoe1ement)-SubstitutedAmines with
Three Different Hetero Atoms
The number of possible combinations for the formula
X
Y
N
' '
X, Y, 2 = organoelement ligand
z
I751 0. J . Scherer and R . Schmitt, J. organometallic Chem. 16,
P 11 (1969).
875
which would appear to be large “on paper”, is limited
in practice, since only one synthetic route has so far
led to the desired result. The starting material is a
primary elemento-organic amine that has no great
tendency toward condensation and whose elementnitrogen bond is not unstable toward organolithium
compounds.
These conditions are satisfied by N-triethylsilylamine
and aminodi-tert-butylphosphine derivatives with
elements of the second short period. The choice of the
second ligand is also limited, since the elementnitrogen bond in this compound also must resist
cleavage during the metalation. I n tris(organoe1ement)substituted amines with three different homologs from
one group of the periodic system, only an element
from the first long period is possible.
It should be noted that in the case of @8), the desired
result cannot be obtained by double decomposition (761,
but only by transamination.
The variety of possibilities offered by this interesting
field of elemento-organic nitrogen compounds with
different hetero atoms is finally illustrated by the
syntheses of two heterocycles [W
(69)
(84a) and (84b) are the first stable ammonia derivatives
with three different homologs of carbon [8a, 8b, 141.
The introduction of the third ligand is practically free
from any restrictions, as is shown by the following
reactions [eq. (z), (2’). and (z”)]:
(66) + CH3El-ElCH3
E l = S (S~Q), Se (85bj
+
(c~H5)3Si\
N-El-CH,
(CH3)3Ge/
(85)
+
+
X2E1(CH3),
-
Si(C2H5)3
,
+ 2 LiCl
p:
Si(C2H5)3 (89)
(CH3)2Ge\N\
/El(CH3),
El = Sn(89a), n = 2, X = Cl“*]
E l = B (89b), n = 1, X = Br‘8b1
CH3E1Li
lz)
Like sodium bis(trimethylsilyl)amide, (66) also cleaves
chalcogen-chalcogen bonds [*bl [eq. (z)]. The reaction
of this compound with dimethyl(Va)element-halogen
compounds presents difficulties only in the case of
chlorodimethylphosphine
Special thanks are due to Dip1.-Chem. D . Biller, Dr.
P. Hornig, W. M. Janssen, P. Klusmann, Dipl.-Chem.
G. Schieder, Dr. J. Schmidt, Dipl.-Chem. R. Schmitt,
and Dr. J. Wokulat for their valuabIe Cooperation, to
Professor Max Schmidt for his kind encouragement,
and to the Deutsche Forschungsgemeinschaft and the
Verband der Chemischen Industrie for their financial
support.
Received: October 15, 1968
[A 724 IEJ
German version: Angew. Chem. 81, 871 (1969)
Translated by Express Translation Servive (London)
In addition to tris(organoe1ement)-substituted amines
with IVa/VIa and IVa/Va combinations, IVa/IIIa
combinations are also possible [@J].
876
1761 Cf. H. Noth and H . Vahrenkamp, J. organometallic Chem.
16, 357 (1969).
1771 For example W . McFurlune, Quart. Reviews 23, 187 (1969).
Angew. Chem. internat. Edit. VoI. 8 (1969) No. II
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