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Detection of Rigid Rotamers in Disubstituted Cyclopentadienylcobalt Complexes.

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The proton can then react either with this compound or
with ( I ) in an oxidative addition, the latter reaction applying
only if the initially formulated equilibria are not shifted completely to the side of the cationic species because of the selected
molar ratio ( I :RX. That steric and not electronic effects
are actually decisive for the rearrangement of ( A ) to ( B ) is
evidenced by the observation that the cation [C5H5(PMe3)2CoSnMe3]+ formed from (1) and Me3SnC1 is kinetically
completely inertC4', although the stability of Me3Sn+ (which
would be a likely migrating particle) is distinctly greater than
that of Me3C+.
Two alternative mechanisms-namely
a direct attack of
RX at the ring as well as formation of HX by p-elimination
from RX-are ruled out on the following grounds:
1. Addition o f R +to the ring would lead to initial formation
of a cationic cyclopentadiene complex in which the group
R assumes an exo position at the sp3 hybridized C atom.
Owing to the favorable steric conditions for interaction
of the metal with the endo-H atom in such an intermediate
the cation [CsH4R(PMe3)2CoH]' should be formed--even
at a molar ratio of ( I ) : RX = 1 : 1. But this is not the case.
2. On formation of HX from RX (possibly catalyzed by
( 1 )) the product ratio [C5H4R(PMe3)2CoH]+: [C5H5(PMe3)2CoH]+ should not be dependent upon the concentration of RX in the manner observed. The cation
[C5HS(PMe3)2CoH]+ would then have to be formed even
with an excess of RX, but this is also not the case.
Reaction of ( I ) with Me3SiCl leads to a paramagnetic
product. Use of Me3SiOS02CF3 as silylating reagent leads
to formation of the cation [CSH4SiMe3(PMe3)2CoH]+,which
can be precipitated as the PF6 salt (6). The NMR data
o f f 6 ) are listed-together with those of (3)-(5)-in
Table 1.
necessary for the electrophilic substitution of Fe(CsHs)2 or
C5H5Mn(C0)3.We attribute this to the consitierubly higher
basicity of the metal atom of ( 1 ), which at the same time
also explains why a stable secondary product with a
C5H4RM-H bond can be isolated in the reaction of this
complex but not in the reactions of ferrocene and cyclopentadienyltricarbonylmanganese with RX.
Procedure
( 3 ) - ( 5 ) ; A threefold excess of alkyl bromide is added
dropwise at -78°C to a solution of ( I ) (1 mmol) in ether
(5 ml). O n slowly thawing out, a light-brown precipitate forms
which is extremely air-sensitive and is therefore dried directly
in the reaction flask. Addition of NH4PF6 (2mmol) to the
solid residue followed by methanol (5 ml) leads to formation
of light-yellow crystals, which are filtered off and washed
with cold ethanol and ether. Recrystallization from acetone/ether affords the analytically pure PF6 salt; yield 85--95 %.
( 6 ) ; Preparation analogous to that above except that the
ester Me3SiOS02CF3is used instead of RBr; yield >95 %.
(7)-(10): To the corresponding salt (3)--(6) ( 1 mmol)
in a little T H F (3-5 ml) is added NaH (ca. 3 mmol). After
spontaneous evolution of gas has subsided the solvent is
removed in uucuo and the residue extracted with pentane.
Filtration and removal of the pentane affords a dark brown
oil which is extremely air-sensitive. The yield is quantitative.
Received: August 8, 1977 [Z 82621 IE]
German version: Angew. Chem. 89, 835 (1977)
CAS Registry numbers:
( 1 1, 63413-01-4: ( 2 ) , 64508-16-3; (3),.64508-14-1:
( 4 ) . 64508-12-9; ( 5 ) .
Table I. 'H-NMR data of [CsH1R(PMe3)rCoH]PF6 in CDJNOl (6 values, T M S int.; J in Hzt.
Complex
Cyclopentadienyl
H3.4
H2.S
PMe,
(.o
4.68 m
4.63 m
4.61 m
5.12 m
5.11 m
5.17 m
1.50 vt
1.53 vt
1.55 vt
- 15.67 t
- 15.54 t
-15.40 t
80
82
(6)
4.72111
5.40m
1.51vt
-16.23t
83
(31
(41
Co-H
R
Jpii
81
C H J - 1.15 d ; C H : 2.47 sept [JHH=6.6]
C H 3 : 1.15 s
C-CHJ: 1.21 s: C H I : [a]; CH2-CH3:
0.77 t [JHH=7.5]
CHJ:0.17s
[a] Masked by signal of the PMe, protons
Table 2. 'H-NMR data of C5H,RCo(PMe,), in ChDn
(6 values, T M S int.; J in Hz).
Complex
Cyclopentadienyl
H2.5
H 1.1
PMe,
(7)
3.62 m
4.60 m
1.00 v t
(8)
3.58 rn
3.49 m
4.65 m
4.61 m
1.05 vt
0.98 vt
(9)
(10)
3.61 m
64508-39-0: (6). 64508-37-8; (7). 64508-26-5, ( 8 ) . 64508-25-4; I Y ), 6450833-4; ( l o ) , 64521-04-6
R
[I]
4.88 m
0.99 vt
.
~~~~
C H , : 1.25 d ; C H :
= 7.01
2.62 sept [JHH
CH,: 1.33 s
C-CH,: 1.21 S; C H Z :
I .57 q [JHH
= 7.01:
C H I - C H , : [a]
C H 3 : 0.30 s
[2]
[3]
[4]
151
Basic Metals. Part 6. This work was supported by the Deutsche Forschungsgemeinschaft. the Fonds der Chemischen Industrie, and Bayer
AG. Leverkusen.-Part 5 : K . Leoiihurd, H. W~riier.Angew. Chem RY.
656 (1977); Angew. Chem. Int. Ed. Engl. 16, 649 (1977).
C . E . Coatrs, M . L . H . Green, K . Wudr. Organometallic Compounds,
3. Ed., Vol. 11. Methuen. London 1968, Chap. 4.
H . Werrier.. W Ho/mrmri, Chem. Ber., iu press.
K . De!,, H. Weriier, J . Organomet. Chem. 137. C 2 8 (1977).
For NMR data of ( 2 ) see ref. 131.
~~
[a] Masked by signal of the PMe3 protons.
A quantitative transformation of the cationic hydrido complexes ( 3 )- ( 6 ) into the corresponding neutral compounds
( 7 ) - ( 1 0 ) (Table 2) is possible with NaH in tetrahydrofuran.
Detection of Rigid Rotamers in Disubstituted Cyclopentadienylcobalt Complexes" J
[ C S H ~ R ( P M ~ ~ ) ~ C+OH
H-] ++ CSH4RCo(PMe3)Z
+ H2
(7), R=i-C3H7
(81, R = t-C4H9
(Y), R = C ( C H ~ ) Z C ~ H S
(101, R=Si(CH3)3
By Werner Hofmann, Wolfgang Buchner, and Helmut Werner"]
In general, the barrier to rotation about the metal-to-ring
bond in bis(q 5-cyclopentadienyl)metalcomplexes is very small;
The extraordinarily mild reaction conditions for the ring
substitution of ( 1 ) differ markedly from those which are
A n g e w Chem. lilt. Ed. Etigl. 16 ( 1 9 7 7 ) NU.i i
[*] Prof. Dr. H. Werner, Dr. W. Buchner, Dip1.-Chem. W. Hofmann
Institut fur Anorganische Chemie der Universitiit
Am Hubland, D-8700 Wurzburg (Germany)
795
for ferrocenes it is 2-5 kcal/mol[21.Estimated values for other
metallocenes and for cyclopentadienylmetal carbonyls are of
the same order of magnitude. In the case of substituted monocyclopentadienyl complexes C5H5.,R,ML, it should be possible by choice of sufficiently bulky substituents R and voluminous (especially not rod-shaped) ligands L to hinder rotation
about the metal-to-ring bond to such an extent that certain
conformers can be frozen. We have now succeeded in demonstrating the first such frozen conformation for half-sandwich
complexes of cobalt.
Monosubstituted derivatives of cyclopentadienylbis(trimethy1phosphane)cobalt such as ( I ) and (2) are accessible
via the intermediate [C5H4R(PMe3)2CoH]X[31.The disubstituted cationic complexes (3)-(5) and the neutral compounds
(6)-(8)
can be obtained in an analogous way.
I
NaH
I
p,
Me,P 1 "H
In the case of (3) and (6) no fixed rotamers are detectable.
In the temperature range from -60 to +25"C the 'H- and
I 3C-NMR spectra each show the very characteristic virtual
triplet of spectral type X,AA'XA for protons[41and AA'X for
I3C of the PMe3 groups ( X = ' H or I3C; A=31P), which
is also observed for the complexes C5H4RC~(PMe3)2
and
[C5H4R(PMe3)2CoH]PFs(R=H, i-C3H7,t-CdH, e t ~ . ) [and
~'
whose appearance requires chemical equivalence of the two A
nuclei. The triplet splitting of the signals of the cyclopentadienyl ring in (3) and in (6) by the two phosphorus atoms
likewise affords proof of the equivalence of the phosphane
ligands and thus of unhindered rotation about the metal-toring bond.
By way of contrast, the NMR data of ( 5 ) and (8) prove
the presence of rigid rocarner.s-even at 100°C. Thus a typical
AB pattern is observed for the two phosphorus ligands in
the 31P-NMRspectrum at - 60°C which at higher temperature
is no longer resolved owing to the quadrupole moment of
cobalt. At 25 to 100"C, however, the non-equivalence of the
PMe3 ligands is very clearly revealed in the 'H- and I3C-NMR
spectra: in no case is a virtual triplet observed, since the
condition for a spectrum of the type X,AA'XA or AA'X is no
longer fulfilled owing to the dissimilarity of the phosphorus
atoms. On the contrary, the 'H-NMR spectra show two doublets (4Jpc,pcHis very small) for PMe3 protons, while the 13CNMR spectra show two doublets of doublets for the corresponding C atoms, each due to simple PH and PC coupling.
The rigid structure of ( 5 ) and ( 8 ) (Table 1 and 2) is most
evident from the different, no longer time averaged, phosphorus coupling constants of the 13C- and 'H-NMR signals of
the corresponding ring atoms. From these data and the fact
that two chemically non-equivalent tert-butyl groups are
detectable for ( 5 ) it follows without doubt that (4)and ( B )
are the rotamers of ( 5 ) and ( 8 ) obtained in the synthesis,
and are probably the most stable ones.
I
/C"\
Me3P
PMe,
PMe,
161 - 18)
13)- ( 5 )
(31, 1 6 ) : R = K' = i - C 3 H 7
141, (7): R = i-C,H,, R = I-C,H,
(j),i8J:
R
= R = t-C,Hg
Table 1. 'H-NMR data of (3). (S), ( 6 ) and ( 8 ) (6 values, T M S int.; J in Hz; 25°C. 100MHz).
Solvent
(5)
CD 3N 02
(6)
ChDb
(8)
ChDh
Ring-H
5.03,
4.81,
4.30,
3.40,
1 H. m
1 H, m
1 H. m
'JHH
= 2.0.
HJ.' :
R
CO-H
1.55. 18H. v t
~ ' J P+*JPHI
H
= 10.2
2.64, 2 H, sept. J H H = 7.0
I .26, 6 H, d. JHH
= 7.0
1.24. 6 H. d. JHH= 7.0
1.23,YH.s
1.20, 9 H , s
-I5
1.56, 9 H , d. J p ~ = 9 . 5
I .53, 9 H. d, JPH
= 10.2
I H, txt,
,JPH= 3.0
H4.': 3.79, 2 H. dxt.
4 J ~ ~ = 2 ., 0J p, ~ = 2 . 0
H2:
3.37, 1 H, txd,
H2:
PMe3
'JHH=2.0, 'Jp~=6.0
3.69, 2 H. dxd,
4 J ~ H = 2 . 0 1' J ~ =4.5
H
I .04. 1 X H. vt
I2JPHf4JpHI
=7.2
2.57. 2 H. sept, JHH= 6.6
1.27, 6 H . d, J m = 6 . 6
1.23, 6 H . d, JHH
= 6.6
1.11.9H,d, JpH=6.5
1.00, 9 H . d. J p ~ = 6 . 5
1.28. 18H, s
39. 1 H. t.
JpH
= 77
-1556. l H , t , J p , ( = 8 0
Table 2. "C-NMR data of (51, (6) and ( 8 ) ('H-decoupled, 6 values, T M S int.: J in Hz: 25°C. 22.636 M H r ) .
(5)
Solvent
Ring-C
[Dd
Acetone
C,,3
~2.4.5
(61
CbDb
Cl.3:
C':
C4.S:
(8)
ChDsCD3
C' '.
C2.
C4.5:
t
121.44, bs [a]
1 17.24, bs [a]
86.18, t. Jpc=2.2
83.08, d. J p c ~ 5 . 1
71.58, dd. Jplc=4.4
Jp&=2.I
107.34, bs [a]
7485, t. J p c = 2 2
71.28, t, J p c = 1.5
110.86, d, J p c ~ 2 . 2
69.18, d, Jpc=3.7
69.83, d, Jpc = 3.7
PMe,
R
22.69. dd.
'Jpc=28.7. ,Jpc=1,5
21.27, dd,
1J
~ 28~ 7, =3 ~ p c <1.5
CMe,.
CCH,
[b]
31.64, s
31.51, s
24.15, vt.
l'Jp~+~'JpcI=22
CHMe2:
CCH,
24.37, dd.
l
~ 17.7,
~ 3 ~~~ , . ==3 . 0
23.41. dd.
'Jpc=17.7. 'Jpc=3.0
CMe3:
CCH3:
28.00, s
26.05. s
24.53. s
29.21, s
32.00, s
[a] PC coupling not resolved: [b] masked by signal of the solvent.
796
Atiyew. Cliem. I i i i . E d . Enql. 16 ( 1 9 7 7 ) No. 11
Synthesis of Bridged 1,3,2h3,4h3-Diazadiphosphetidines
The complexes (4) and ( 7 ) with mixed substituents fit
into the series between (3)/(6) (freely rotating) and ( 5 ) / ( 8 )
(rigid). Two different types of phosphorus atoms are recognizable in the "P-NMR spectrum of ( 7 ) at - 60°C, thus indicating a frozen conformation (analogous to ( B ) ) . Above - 10°C
a "thawing" of this arrangement and a slow rotation about
the cobalt-to-ring axis is observed (change in the splitting
of the NMR signals of the phosphane H and C atoms). Below
- IO'C, for example, a doublet of doublets is observed in the
"C-NMR spectrum at 6=24.62 with lJPc=17.3 and
3Jpc,,pc= 5.5 Hz, which at higher temperature converts into a
virtual triplet (6=25.14 with IIJpc+
'JpcOpcI=22.8 Hz, 50"C,
in [D,]acetone). In the case of ( 4 ) no definite conclusions
can be drawn from NMR data regarding hindered or restricted rotation about the cobalt-to-ring axis, since the two
phosphorus atoms are bonded, as a result of unsymmetrical
ring substitution, to a prochiral cobalt atom and are therefore
non-equivalent in any case.
The question why two tert-butyl substituents (in ( 5 )
and ( 8 ) )hinder rotation of the cyclopentadienyl ring, whereas
two isopropyl substituents (in (3) and ( 6 ) ) d o not, might
be explained in terms of a "gear mechanism". When a 1,3-(tC4H9)2C5H3ring is present it is obviously impossible on
rotation about the metal-ring axis for the rwt-butyl groups
By Roclney Keat and David G. Tliompson[*I
1 ,3,2h3,4h3-Diazadiphosphetidines
of type ( I ) have recently
attracted considerable attention[']. Geometrical isomers of
these heterocycles are characterized by exceptionally large
'P chemical shift differences""
and by differences in
chemical reactivity''].
We have now succeeded in "bridging" the 1,3-di-tert-butyl2,4-dichloro-l ,3,2h3,4h3-diazadiphosphetidine
( I ) to give the
new crystalline bicyclic compounds ( 4 ) , ( 5 0 ) and ( 5 b ) . The
compounds were characterized by elemental analyses, mass
spectra, and the spectral data shown in Table 1. Variable
amounts of polymeric materials are also formed, but generally
the proportion is much less than in the condensation of aromatic diols with 1,3,2h5,4h5-diazadiphosphetidines,
where they
No bicyclic compound of type
are the exclusive
( 4 ) was isolated on reaction of N,N'-dimethyltrimethylenediamine with (1 ).
-'s4]
( 5 a / , n = 2 ; 15b), n = 3
Table I . Selected physical properties of the bicyclic compounds ( 4 ) .
and ( 5 h )
(4)
A A
Fig. 1. Steric requirements for rotation according to the "gear mechanism"
in compound ( 6 ) (schematic).
to get past the trimethylphosphane ligands-despite rotation
about the C-CMe3 bond. However, if one of the three methyl
groups is replaced by an H atom ( i e . i-C3H7 instead of
t-C4H9)then it appears possible that the two ring substituents
are so oriented during the rotation that at the moment of
sliding past a trimethylphosphane the H atom of the isopropyl
group is directed inwards (cf. Fig. 1).
Received: August 8, 1977 [ Z 826b IE]
German version: Angew. Chem. X9. 836 (1977)
CAS Registry numbers:
I I ), 64508-26-5; ( 2 ) , 64508-25-4; ( 3 ) , 64508-24-3; ( 4 ) . 64508-22-1; ( 5 1 ,
64508-20-9; (6). 64508-18-5:( 7). 64508-17-4; (8),64521-07-9; " C , 14762-74-4
Stereochemical Studies on Coordination Compounds, Part I . This work
was supported by the Deutsche Forschungsgemeinschaft. the Fonds
der Chemischen Industrie, and Bayer AG, Leverkusen.
[ 2 ] M. Rosetihlirm: Chemistry of the Iron Group Metallocens, Part 1. WileyInterscience. New York 1965, p. 45.
[3] H . M m e r . W Hofiiiumr, Angew. Chem. 89, 835 (1977); Angew. Chem.
Int. Ed. Engl. 16. 794 (1977).
[4] R. K . Harris, Can. J . Chem. 4 2 , 2275 (1964).
[I]
A n g n r . Chum. l n t . E d . Eiigl. 16 ( 1 9 7 7 ) N o . 1 1
M.p. r C ]
B. p. ["C.'torr]
Yield ["<,I
6p (in CDC13)
S L C H (in
~ CDC13) [a]
IJPZCH~
J P N P Z C H ~ [Hz]
~
[a]
v(P-N-P)
asymm. [cm-'1
(in Nujol)
+
(50)
65 -67
(j(t)
(5h)
36-~38
73:O.l
20
155.0
3.12
5 6 [b]
23
177.5
4.17
9.1
20
135.4
3.97
6.6
846
86 1
x99
182
[a] Z = O o r N.
[b] I J P W H ~+ J P U P N C H ~=~ 13.8 Hz
It is not clear what causes the large 31P shift differences
between geometrical isomers of diazadiphosphetidines of type
( I )I4], but conformational changes within the diphosphetidine
ring and the exocyclic (or bridging) groups are clearly implicated, especially when the difference in shift between ( 5 a )
and ( 5 b ) is considered.
Experimental
7,8-Di-tert-Butyl-2,5-dinzetl~yl-2,5,7,8-t~tra~za-l
i 3 , h i'-ciiphosphabiryclo[4.1.l]octane (4): A solution of (2) (2.75 g,
31.2mmol) in ether (30ml) is slowly added with stirring at
ambient temperature to a solution of ( I ) (4.30g. 15.6mmol)
[*] Dr. R Kcat, D G Thompson
Department of Chemistry. University of Glasgow
Glasgow G12 XQQ (U.K.)
191
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rigid, detection, disubstituted, complexes, rotamer, cyclopentadienylcobalt
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