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Hydrozirconation of Nitriles Proof of a Linear Heteroallene Structure in (Benzylideneamido)zirconocene Chloride.

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~ t r a t e s ~ ' ~ .It~ -therefore
~].
seemed an attractive reagent for
the transformations 1 +2.
Hydrolysis of la-f catalyzed by porcine liver esterase
proceeded in 0.1 M phosphate buffer suspensions. The initial saponification was indicated by the decrease of pH,
which was maintained at pH 7 or 8 by addition of 1 N
NaOH. Only one ester group is saponified. After acidification, 2a-f are recovered by extraction (EtzO). Diastereomeric purities (to check for possible isomerizations) were
determined by GC after reacidification (MeOH/
HC(OMe)3). Enantiomeric ratios were determined on the
crude products by 250 MHz 'H-NMR spectroscopy with
( )-(R)-a-methylbenzylamine, independent of, usually unreliable, rotational data of derivatives (Table 1).
The absolute configuration of 2aI7] was known, that of
2b was determined by selective base (NaH/dimethyl sulfoxide) isomerization to the known trans-enantiomer 4b,
and that of 2c by conversion to the known['b1lactones 3c/
ent-k. The absolute configurations of le, f were known
from X-ray structure determinations['].
The observed enantiomer ratios are quite high in most
cases (somewhat higher at pH 7 than at pH 8, possibly due
to some non-enzymatic hydrolysis) and can be further increased by recrystallization. The highest values were found
for 2b and 2f, which were formed as enantiomerically
pure compounds. The only exception was (+)-2d, which
was formed in very low enantiomeric purity.
The absolute and relative reaction rates (Table 1) were
determined under standardized conditions, although the
amount of enzyme can be reduced from 100 (or 1000) to 10
unitdmmol of substrate.
Whereas lb-f are transformed at synthetically useful
rates (usually faster at pH 8 by a factor of 2 to 5), l a does
not function as a substrate under these conditions[41.Even
at high enzyme concentrations the reaction l a +2a is very
slow, making this process unsuitable synthetically despite
the relatively high enantiomer ratio.
Because of the favorable enantiomer ratios and reaction
rates, the formation of 2b, c, e, f is of particular synthetic
interest. The reactions were therefore scaled-up from the
usual 10-50 mmol to 700-1000 mmol. For example,
100 g of optically pure (-)-2b can be obtained by this
method in a single experiment.
Preliminary studies using esterase on CNBr-activated
Sepharose (1.3 mg protein/mL gel; specific activity: 50%
of the soluble enzyme) reveal that the enantiomeric purities obtained are identical for both enzyme preparations.
+
lH), 1.72 (m, lH), 2.14 (m, 2H), 3.74 (s, 3H), 11.36 (bs,
1 H).
Received: June 30, 1983;
revised: October 12, 1983 [Z 437 IE]
German version: Angew. Chem. 96 (1984) 55
CAS Registry numbers:
la, 20315-30-4; l b , 826-34-6; lc, 2607-03-6; Id, 4841-91-2; le, 1687-29-2; If,
4841-84-3; (-)-2a, 81873-51-0; ( i)-Za, 81873-49-6; (-)-2b, 88335-86-8; (+)2b, 88335-87-9; (+)-2c, 88335-88-0; (-)-2c, 88335-89-1; Zd (isomer I), 8831564-4; Zd (isomer 2), 88335-90-4; (+)-Ze, 88335-91-5; (-)-2e, 88335-92-6;
(+)-Zf, 88335-93-7; (-)-2f, 88335-94-8; 3c, 88335-95-9; ent-3c, 75658-85-4;
4b, 88335-97-1 ; ent-4b, 88335-96-0; esterase, 9013-79-0.
[I] a) F.-C. Huang, L. F. Hsu Lee, R. S. D. Mittal, P. R. Ravikumar, J. A.
Chan, C. J. Sih, E. Caspi, C. R. Eck, J. Am. Chem. Soc. 97 (1975) 4144; b)
I. J. Jakovac, H. B. Goodbrand, K. P. Lok, J. B. Jones, ibid. 104 (1982)
4659.
[2] M. Schneider, N. Engel, P. Honicke, unpublished.
[3] For earlier work in this area see also: H. Kosmol, K. Kieslich, H. Gibian,
Justus Liebigs Ann. Chem. 711 (1968) 38.
[4] M. Schneider, N. Engel, H. Boensmann, Angew. Chem. 96 (1984) 54; Angew. Chem. Int. Ed. Engl. 23 (1984) 66.
[5] M. Arita, K. Adachi, Y. Ito, H. Sawai, M. Ohno, J. Am. Chem. Soc. 105
(1983) 4049.
[6] C. C. Shroff, W. S. Stewart, S. J. Uhm, J. W. Wheeler, J . Org. Chem. 36
(1971) 3356.
[7] M.-J. De Vos, A. Krief, J . Am Chem. SOC.104 (1982) 4282.
[8] The assignments for Zb, c are, in our opinion, not unambiguous, and we
are presently preparing derivatives of 2a-c for X-ray structure analysis.
191 We are grateful to Dr. H.-J. Guis. Darmstadt, for communicating his previous results with l e , f . H.-J. Gais, Habilitationsschrift, Technische
Hochschule Darmstadt 1980, determined the absolute configurations of
l e , f by X-ray structure analysis of the corresponding ephedrine salts.
For applications in natural products synthesis: H.-J. Gais, K. L. Lukas,
Angew. Chem., in press.
Hydrozirconation of Nitriles:
Proof of a Linear Heteroallene Structure in
(Benzy1ideneamido)zirconoceneChloride**
By Gerhard Erker*, Wolfgang Fromberg, Jerry L. Atwood,
and William E. Hunter
In general, dialkylideneammonium ions adopt a linear
heteroallene structure (1, sp-hybridized nitrogen). Only exceptionally in cases of extreme stabilization of the carbenium ion center is a bent heteroallyl structure (2, e.g.,
R- NR;) more favored"]. Substitution of the carbenium
carbon center by an isolobal, electron deficient metal fragment['"], i. e. formal exchange of CRF in 1 by the Cp,ZrCl
moiety[2b1,leads to systems for which the structures 1' and
2', analogous to 1 and 2, respectively, are possible. How-
Experimental Procedure
(-)-2b: Porcine liver esterase (1000 units) is added to a
vigorously stirred mixture of l b (15.8 g, 0.1 mol) and 100
mL phosphate buffer (0.1 M, pH 8). The start of the hydrolysis is indicated by a rapid decrease of the pH 8 value. pH
8 is maintained throughout the reaction (tl,z = 25 h) by addition of 1 N NaOH. After addition of 100 mL (0.1 mol)
NaOH the reaction stops. The cooled, stirred reaction mixture is acidified with 5 N HCl to pH 2 and extracted continously with EtzO. The organic phase is dried, all solvents
are removed, and the residue is treated with Et20 (15 mL)
and crystallized first at 0°C and subsequently for 2 d at
-30°C. The colorless crystals of (-)-2b, 13.5 g (93%),
m.p.=82"C, [a]:: - 13.2 (c 1.7, CHC13), are collected by
filtration. Recrystallization from benzene (20 mL) yields 12
g of enantiomerically pure (-)-2b, [a]:: -15.3 (c 1,
CHC13); 250MHz 'H-NMR (solvent CDC13): 6= 1.36 (m,
68
0 Verlag Chemie GmbH, 0-6940 Weinheim, 1984
[*I
[**I
1
2
1'
2'
Priv.-Doz. Dr. G. Erker, W. Fromberg
Abteilung fur Chemie der Universitat
Postfach 1021 48, D-4630 Bochum 1 (FRG)
Prof. Dr. J. L. Atwood, Dr. W. E. Hunter
Department of Chemistry, University of Alabama (USA)
This work was supported by the Fonds der Chemischen Industrie (G. E.)
and by a NATO Research Grant (No. 0425183; J. L. A. and G. E.).
0570-0833/84/0101-0068 $02.50/0
Angew. Chem. I n f . Ed. Engl. 23 (1984) No. 1
ever, the preferred ground-state structure of uncharged
metal complexes can be determined experimentally much
more easily than for the carbenium ion systems.
We obtained the C-substituted (methy1eneamido)zirconocene chlorides 5a and 5b as moisture-sensitive, yellow
solids in high yields by hydrozirconation of benzonitrile
and acetonitrile, re~pectively[~].
In addition to the typical
absorptions of the bent metallocene, an intense -C=N
stretching frequency is observed in the IR spectra of 5a
and 5b (in toluene; v=1678 and 1700 cm-I, resp.). In
Schiff s bases with +C-N=CHR
groups this band appears at slightly lower wave numbers[41.The 'H- and I3CNMR spectral data of the -N=CHR moiety in the complex are very similar to those of many comparable organic
systems[41: 'H, [I3c] ([Ddbenzene), 5a: 6=9.0 [167.3 (d,
J = 168 Hz)]; 5b: 6=8.3 [167.5 (d, J=168 Hz)]. It is noteworthy that a chemical differentiation of the cyclopentadienyl ligands on the zirconocene moiety, which would be
expected for a metalla-ally1 structure 2', cannot be detected by NMR spectroscopy in 5a, even at low temperatures [Cp, 'H [I3c] ([D6]benzene): 6=5.9 [111.1]) or 5b
(6=5.8 [110.7]).
X-ray structure analysis of 5a (Fig. 1; crystals from toluene) confirms the chemical equivalence of the Cp ligands. The Cp(centr.),Zr,Cp'(centr.) plane is orientated
orthogonally to the C(arom.),Cl,Hl plane. The most
striking feature of the molecular structure of 5a is the almost linear Zr-Nl-Cl- moiety (170.5(5)"). The C=N
bond distance (1.259(7) A) is somewhat shorter than that
of normal C=N (sp') double-bond systems. In contrast,
the metal-nitrogen linkage is extremely short: at 2.013(5) A
in 5a it is, to the best of our knowledge, the shortest Zr-N
bond in a molecular zirconium compound known to
dater5]. Despite this pronounced Zr-N1 interaction, the
Nl-Zr-Cl angle (101.1(2)') and the Zr-C1 bond length
(2.497(2) A) are clearly within the normal order of magnitude16].
I
the linear Zr-N1 -C1 moiety ; hydrozirconation usually
proceeds with cis-stereochemistry['].
r
7
3
a , R = Ph; b, R
5
= Me
The similarity between the structural chemistry of the
positively charged organic system 1 and that of the electrically neutral organometallic compound 5 allows us to
hope that other examples of "cation chemistry without
charges" will be found in the future. Presently, we are investigating whether the resonance interaction between
electronically unsaturated, bent, metallocene moieties and
organic 71 systems gives rise to compounds which show
reactions similar to resonance stabilized carbocations.
Received: August 23, 1983 [Z 528 IE]
German version: Angew. Chem. 96 (1984) 72
CAS Registry numbers:
3, 37342-97-5; 4a, 100-47-0; 4b, 75-05-8; 5a, 61993-60-0; Sb, 62053-83-2.
[I] E.-U. Wiirthwein, Angew. Chem. 93 (1981) 110; Angew. Chem. Int. Ed.
Engl. 20 (1981) 99; ibid. 95 (1983) 247; 22 (1983) 252; Angew. Chern.
Suppl. 1983, 264; see also A. Schmidpeter, S. Lochschmidt, A. Willhalm,
Angew. Chem. 95 (1983) 561; Angew. Chem. Int. Ed. Engl. 22 (1983) 545;
Angew. Chem. Suppl. 1983, 710.
121 a) R. Hoffmann, Angew. Chem. 94 (1982) 725; Angew. Chem. Int. Ed.
Engl. 21 (1982) 711; b) J. W. Lauher, R. Hoffmann, J. Am. Chem. SOC.98
(1976) 1729; P. Hofmann, P. Stauffert, N. E. Schore, Chem. Ber. 115
(1982) 2153.
[3] 5a: 92% yield, m.p. 124°C (decomp.); 5b: 81% yield, m.p.=106"C (decamp.); see also P. Etievant, G. Tainturier, B. Gautheron, C. R. Acad.
Sci.. S b . C 283 (1976) 233; Bull. SOC.Chim. Fr. 1978, 292.
[4] J.-C. Guillemin, J.-M. Denis, Angew. Chem. 94 (1982) 715; Angew. Chem.
Int. Ed. Engl. 21 (1982) 690; Angew. Chem. Suppl. 1982, 155, and literature cited therein; cf. also M. R. Collier, M. F. Lappert, J. McMeeking,
Inorg. Nuel. Chem. Lett. 7 (1971) 689.
[5] a) R V. Bynum, W. E. Hunter, R. D. Rogers, J. L. Atwood, Inorg. Chem.
19 (1980) 2368; b) R. D. Sanner, J. M. Manriquez, R. E. Marsh, J. E. Bercaw, J. Am. Chem. SOC.98 (1976) 8351.
[61 G. Erker, K. Kropp, J. L. Atwood, W. E. Hunter, Organornetallies 2
(1983), in press.
[7] P. C. Wailes, H. Weigold, A. P. Bell, J. Organomet. Chem. 27 (1971) 373;
D . W.Hart, T. F. Blackburn, J. Schwartz, J. Am. Chem. Soc. 97 (1975)
679; J. A. Labinger, D. W. Hart, W. E. Seibert, J. Schwartz, &id. 97(1975)
3851.
W
Fig. 1. Molecular structure of 5s in the crystal. Space group P2Jc;
a =7.456(6), b = 12.655(7), c = 16.305(8) j3=94.09(6)", V = 1534.6 A
', Z=4,
1695 observed reflextions, R =0.034, R,=0.041. Details of the crystal structure investigation may be obtained from the Fachinformationszentrum Energie Physik Mathematik, D-7514 Eggenstein-Leopoldshafen by quoting the
depository number CSD 50559, the names of the authors, and the journal citation.
A,
5a can therefore be considered as an organometallic
compound with heteroallene structure of type 1' with sphybridized nitrogen. In contrast to the trivalent carbenium
ion center in 1,the incorporation of the isolobal Cp'ZrC1
moiety with tetravalent zirconium could principally lead to
stereoisomeric heteroallene systems. However, in the reaction of the nitriles 4 with 3 apparently only one isomer is
formed in each case. In 5a, C1 and H1 are arranged cis to
Angew. Chem. Int. Ed. Engl. 23 (1984) No. I
The Scope of Radical CC-Coupling by the
"Tin Method"**
By Bernd Giese*, Juan Antonio Gonzalez-Gomez, and
Tom Witzel
Alkyl halides undergo CC-coupling on reaction with tributyltin hydride in the presence of electron-deficient alkenes"]. We have now found that when alkyl iodides are
employed in the reaction, the tin salts are necessary only as
catalysts ; moreover, we have also succeeded in carrying
out the reaction with alcohols instead of with halides.
[*I Prof. Dr. B. Giese, DipLIng. J. A. Gonzalez-Gomez,
[**I
Dip1.-Ing. T.Witzel
Institut fiir Organische Chemie und Biochemie
der Technischen Hochschule
Petersenstrasse 22, D-6100 Darrnstadt (FRG)
This work was supported by the Fonds der Chemischen Industrie
0 Verlag Chemie GmbH, 0-6940 Weinheim, 1984
0570-0833/84/0101-0069 $02.50/0
69
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nitrile, structure, proof, zirconocene, hydrozirconation, chloride, heteroallene, linear, benzylideneamido
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