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Magnetic Nonequivalence of the C Atoms of Prochiral Diphenylmethyl Groups in 13C-NMR Spectroscopy.

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It therefore seems likely that the ( 1 ) + ( 2 ) and ( 1 ) + ( 3 ) AAF* of
4.3 kcal/mol (1 66°C) reflects the true chair-boat transition state free
energy difference for this system.
[lo] This pathway is analogous to the ionic mechanism suggested by Weiss
er a / . [I b, 1 c] for the silver-catalyzed conversion of bicyclopropenyls
to Dewar benzenes, except that due to the extreme difficulty of generating
charge-separated species in the gas phase, neutral diradicals rather
than ionic intermediates are probably involved here; see, for example,
a) L . Salem and C . Rowland, Angew. Chem. 84, 86 (1972); Angew.
Chem. Int. Ed. Engl. 1 1 , 92 (1972); b) E . F. Hayes and A. K . Q .
Siu, J. Am. Chem. Soc. 93, 2090 (1971); c) L. Salem and W-D. Stohrer,
to be published; d) W A . Coddard and J. H.Davis, unpublished results.
[ l l ] Interestingly, we have been unable to find a study in the literature
ofcyclopropenylcarbinyl radicals to use as a model for the ring expansion
of ( 4 a ) and ( 4 h ) . It seems likely, however, that the strain relief and
incipient allylic delocalization generated in the transition state for such
an expansion would render it an extremely facile process.
[I21 R. Breslow, .I.
Napirrski, and A. H . Schmidr, J. Am. Chem. Soc. 94,
5906 ( 1 972).
“Arsenobenzene”,C&-h=AS-C6H5,
as a Bridging p3 Ligand in a Transition Metal Complex[**]
By Gottfried Huttner, Hans-Georg Schmid, Albin Frank, and
O K Orarna[*l
In an attempt to synthesize the arsinidene complex ( I ) [ ’ ] ,
according to:
OC,
1<co
P,
‘0
0
‘
A s - C r : 2 5 3 pm
As-Cr’: 2 6 4 pm
0
Fig. 1. Molecular structure of the arsenobenzene complex (2).
In the only example of a R2As2 complex yet known,
(OC)4Fe(C6F5As)2141,
the ligand is merely stabilized by x addition to a carbonylmetal fragment.
Evidence supporting formulation of the complex (2) with
an As=As double bond is provided by the arsenic-arsenic
interatomic distance (Fig. 1). which is 9pm shorter than
the As-As single bond in C5H5(C0)2Mn[PhHAsj 2Mn(CO),C,H5 ( 2 4 6 ~ r n ) [ ~inl , spite of the elongation due to
coordination.
Received: December 30, 1975 [Z 38R IE]
German version: Angew. Chem 88.255 11976)
CAS Registry numbers:
Na,[Cr,1CO),,].
15616-67-8: C,H,AsCI,. 696-28-6:
(OC),CrAs(C,H,)Li,. 55590-59-5; CI,(C,H,)AsCr(CO),.
[Cr(CO),],Aa,(C,H,),.
58448-95-6
58448-94-5;
[ I ] C . Hurmer and H.-G. Schmid, Angew. Chem. 87, 454 (1975); Angew.
Chem. Int. Ed. Engl. 14, 433 (1975).
[2] G. Hurtner and H . C . Schmid, to be published.
[3] 1157 diffractometer data (“Syntex P21”); solution with “Syntex XTL”
(Rl=O.O6).
[4] P. S. Elmes, P. Levereft, and B. 0.Wesr, Chem. Commun. 1971, 747.
[5] G . Huttner, H . 4 . Schmid and H . Lorenz, unpublished.
Magnetic Nonequivalence of the C Atoms of Prochiral
Diphenylmethyl Groups in 3C-NMR Spectroscopy
we surprisingly isolated not ( I ) but instead the red complex
( 2 ) ,m.p. 142°C (dec.), among other hitherto unidentified products. The new compound (2) can also be prepared[’’ according to :
-
( C O ) , C r A s ( C s H 5 ) L i 2 + C12(C6H5)AsCr(CO)5
- LiCl
(2) +
*.*
The molecular ion of (2) does not appear in its mass
spectrum; however, intense peaks are observed for the fragment ions Ph2As2Cr(CO), (m/e=496) and Ph2As2 (rn/e= 304).
The IR spectrum exhibits absorptions which are characteristic
of phenyl groups; the band pattern in the vco region indicates
the presence of several differently coordinated Cr(CO), units.
The ‘H-NMR spectrum (solution in CD2C12) only shows
signals due to phenyl protons.
X-Ray structure analysis[31shows that arsenobenzene, PhAs=As-Ph, which is homologous to azobenzene, is stabilized
as a ligand in the complex (2). The two arsenic atoms both
form coordinative bonds to Cr(CO), groups. In addition.
the As=As double bond participates in x-interaction with
a third Cr(CO), group (cf. Fig. 1).
p]
Doz. Dr. G . Huttner, H.-G. Schmidt, DipLChem. A. Frank, and 0.
Orama
Anorganisch-chemisches Institut der Technischen Universitat
Arcisstrasse 21. 800 Miinchen 2 (Germany)
[**I
This work was supported by the Deutsche Forschungsgemeinschaft
and the Fonds der Chemischen Industrie.
234
By Hans Otto Kalinowski, Bernd Renger, and Dieter Seehachl*l
The magnetic nonequivalence of diastereotopic groups
manifested in ‘H-NMR spectra has proved to be of value
in the elucidation of stereochemical problems[’]. Only very
few comparable studies have so far been performed in I3CNMR spectros~opy[~-~!
We here report the magnetic nonequivalence of the C atoms of diastereotopic phenyl groups
in tertiary alcohols of type ( I )[,I.
(la-h)
Table 1 shows thechemical shift differences of the 13C-NMR
signals of the phenyl carbon atoms of these compounds. The
relatively large difference of the signals for the ring C’ atoms
is not surprising since these atoms are located closest to
thecenterofchirality(except in thecaseof(1i)); themagnitude
of the difference remains practically constant within the classes
of compounds ( l a - c ) and (Id-h). The largest splittings are
observed for the carbonyl-containing compounds (I a-c), in
which effective hydrogen bonding could be responsible for
[‘I
Dr. H. 0. Kalinowski, Dipl.-Chem. B. Renger, and Prof. Dr. D. Seebach
Institut fur Organische Chemie des Fachbereichs 14 der Universitiit
Heinrich-Buff-Ring 58, 6300 Giessen (Germany)
Anye%,. Chem. Iiir. Ed. Engl.
/ Vol. 15 ( 1 9 7 6 ) No. 4
Table I . Chemical shift difference A6 of the "C-NMR signals of the ring carbon atoms in ( I ) ( r a . 1 M solution in CDCI,; 30°C) [a]
Compound ( 1 )
Rl
R'
Signals of C '
[wml
C'
c
4
~
H
H
H
CHn
H
-NH-(CHz)4-
H
-NH-CH(CH~)~CHZ)~-
H
-NH+CH2)2-CH(CH3)-CH2-
H
-NH+CH2)'-CH(CH3)-
H
-NH+CHz)3-
H
-&+CH~)~-
COOCzHS
Cle
H
[a]
[b]
[c]
[d]
SCHJ
ChHS
147.6
144.5
148.6
145.2
148.9 [b]
145.5
147.8
144.7
146.6
144.4
146.6
144.5
146.0
143.8
147.4
145.0
148.3
145.5
145.0 [c]
144.6
145.9
144.7
~-
3.1
-
3.4
0.4
3.4 [h]
0.3 [b]
3.1
0.1
-
0.2
2.2
0.6
0.5
0.8
2.1
0.5
0.5
0.3
2.2
0.5
0.3
0.5
2.4
0.7
2.8
0.3
0.3
0.4
0.7
0.3
1.2
>0.1 [d]
-.
0.3
0. I
~
-
0.3
20.1 [d]
0.3
0.1
The spectra were recorded with a C F T 20 Varian instrument (8K store. accuracy: 0.05 ppm).
I n dimethyl sulfoxide as sollent (to rupture the H bonds. cf. ref [6]): dilution of the solution has no effect on the splitting and chemical shift ofthe slgnals
In dimethyl sulfoxide as solvent.
In the phenyl region there are 12 signals of which only those for C ' and C4 can be unequivocally assigned. The splitting of the signals for C', Ch
and C', C 5 is in any case greater than 0.1 ppm since the lines are separated from each other by more than 0.1 ppm.
preference of a particular conformer (see Table 1, b). Comparison of the chemical shift differences observed for the signals
of atoms C2 and C6, C3 and C5 and C4, shows that, although
significantly smaller than for C' except in the case of (li),
they d o not decrease with increasing distance from the center
of chirality, as is claimed in the literature['.2! Instead, the
magnitude of the difference alternates or (in one case) is observable only for the atom C4. No explanation of this finding
can yet be given. While there does seem to be a relationship
between the magnitude of the chemical shift difference (compound (Zb,cf;g))and the inductive and mesomeric substituent
effect-the C atoms in positions 3 and 5 seem to be the
least affected -this explanation appears unsatisfactory in view
of the similarity of the compounds.
Received: December 23, 1975;
revised: January 9, 1976 [Z 390 I€]
German version : Angew. Chem 88. 246 (1 976)
CAS Registry numbers:
[ I n ) . 58473-61-3: [ l h ) . 20428-72-2: [ l r ) . 58473-62-4:
( I d ) . 467-60-7: ( 1 0 ) . 58473-63-5: (If). 58473-64-6:
[ l g ) . S847.1-65-71 [ I j ) . 52791-94-3
[ l ] W B. Jrtininys. Chem. Rev. 75, 307 (1975).
[2] J . I . Kroschwirz, M . Winokur, H . J . Reich,'and J . D. Roberts, J. Am.
Chem. Soc. 91. 5927 (1969).
[3] J . Dabrowski er a/., Org. Magn. Reson. 4, 131, 137, 443 (1973); 5 , 483
(1973); D. Dodrell and N. V Riggs, Aust. J. Chem. 25, 2715 (1972).
141 P . E. Rakira and R . Wright, Inorg. Nucl. Chem. Lett. 1 1 , 47 (1975),
first reported the magnetic nonequivalence of diastereotopic phenyl
groups in a diphenylsilyl compound.
[S] Compounds ( I u - c ) were prepared at this institute in connection with
the projected doctoral thesis of W L a n g e r . ~ - ( f d - g ) ; B. Renger, projected
thesis; D. Seebach and D. Enders, Angew. Chem. 87, 1 (1975); Angew.
Chem. Int. Ed. Engl. 14, 15 (1975).-[Ih,i); D. Enders, B. Renger, and
D. Seebuch, t o be published.--(Ij): D. Seebach and K . H . Geiss, Angew.
Chem. 86,202 (1974); Angew. Chem. Int. Ed. Engl. f3.202 (1974).- Satisfactory elemental analyses and spectroscopic data are available for all
compounds. -- Other a-substituted diphenylmethanols which contain no
center of chirality in the molcule d o not display any signal splitting
for the geminal phenyl groups in the "C-NMR spectrum.
[6] H. Kessler,and M . Branik, Tetrahedron 30, 781 (1974).
Anyew. Chetn. Inr. Ed. Eiigl.
Voi. 15 ( 1 9 7 6 ) No. 4
Tris(3-methylborolan-l-yl)amine, an Electron-Deficient
Triborylamine
By Wolfgang Storch and Heinrich Noth"]
Dedicated to Professor J . Goubeau on the occasion of his 75th
birthday
Alkyl-substituted borylamines (1) are stable. whereas diborylamines ( 2 ) readily decompose with elimination of BR,"]
and tris(diorganylboryl)amines (3) were hitherto unknown[".
Existence of the predicted N(BF2)3with D3hsymmetry[3a1
has so far not been demonstrated e ~ p e r i m e n t a l l y 'The
~ ~ ~B3N
.
skeletal unit of a triborylamine can be synthesized, however,
if the boron atoms have substituents capable of n back-bonding
and if 1,3 nucleophilic rearrangement is impeded by incorporation in a ring
the electron-rich compound ( 4 ) may
be cited as example[4a1.Above 150°C the latter mentioned
stabilization effect raises the decomposition threshold in bis(borolan-I-y1)amines compared to [(CH3)2B]2NCH3 to over
lSO"C[51.This has now made it possible to synthesize also
the electron-deficient triborylamine ( 9 ) of type ( 3 ) in accordance with Equation (a), where exact control of stoichiometry
and temperature permits stepwise replacement of the (CH3)3Sn
groups of (5) by the 3-methylborolanyl group.
The higher temperature and longer reaction time required
on progressive removal of (CH3)3Sn groups reflects the
expected decrease in basicity of the nitrogen in the series
f5)-(9).
r]Prof. Dr. H. Noth and Dr. W. Storch
Institut fur Anorganische Chemie der Universitat
Meiserstrasse 1 , 8000 Miinchen 2 (Germany)
235
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spectroscopy, diphenylmethane, nmr, 13c, group, prochiral, atom, magnetic, nonequivalence
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