McIver, R. T.; Pople, J. A.; Schleyer, P. v. R. J . Am. Chem. Soc. 1974.96, 7162. McKelvey, J. M.; Alexandratos, S.; Streitwieser, A,; Abboud, J. L. M.; Hehre, W. J. Ibid. 1976, 98, 244. Radom, L.; P o p pinger, D.; Haddon, R. C. Carbonium Ions 1976, 5, 2303. (4) Williams, J. E.; Streitwieser, A. J. Am. Chem. SOC. 1975, 97, 2634 and references cited therein. (5) (a) Hopkinson, A. C.; Lien, M. H.; Yates, K.; Mezey, P. G.; Csizmadia, I. G. J. Chem. Phys. 1977, 67, 517. (b) McKay, G. I.; Lien, M. H.; Hopkinson, A. C.; Bohme, D. K. Can.

Eine einfache Synthese von (R.R)-3,4-Bis(diphenylphosphino)pyrrolidin (6a)und Rhodium Complexes for the Asymmetric Hydrogenation of a-(Acy1arnino)acrylic Acid DerivativesA simple synthesis of (R,R)-3,4-bis(diphenylphosphino)pyrrolidine (6a) and some N-substituted derivatives 6b-m is described. 61 and 6m are optically active tetraphosphanes, composed of two (R,R)-3,4-bis(diphenylphosphino)pyrrolidine units and a dicarboxylic residue. The structure of the parent compound 6a was determined by X-ray diffraction. From the phosphanes 6a -m the cationic 1,5-cyclooctadiene-bisphosphane-rhodium complexes 7a-rn were prepared. The complexes 71 and 7m are ligand bridged bis(rhodium) dications. The complexes 7a-m were used for the asymmetric catalytic hydrogenation of the a-(acy1amino)acrylic acid derivatives 9a -I. Enantiomeric excesses up to 100% were achieved. Between 1 and 70 at the optical yields do not depend on the hydrogen pressure. The substrateJcatalyst ratio can be as high as 5ooOoJ1. *) Zusammenarbeit bei der Verkiirzung der urspriinglich langeren Synthese von 6b.

The energetic and structural relationships among various C2H2NM isomers (M = Li, Na, MgH, and the anion) are explored by theoretical calculations. The cyanomethyl anion, CH2CN-, is predicted to have a pyramidal structure but with a very low inversion barrier of 0.3 kcal/mol (MP2/6-3l+G*//6-3l+G*). At the same level of ab initio theory, a significantly higher barrier of 2.8 kcal/mol is found for the isocyanomethyl anion, CH2NC-. r-Delocalization in CH2CN-results in a large stabilization relative to CH3-(calculated 45.3, experimental 44.4 kcal/mol). In contrast, the CH2NC-anion is stabilized (by 36.3 kcal/mol relative to CH3-) largely inductively by the sp-hybridized nitrogen. Extensive ab initio examination of the lithium, sodium, and magnesyl (MgH) derivatives of these anions (as well as those of isomeric structures) found lithium-bridged and, to a somewhat lesser extent, sodium-bridged geometries 7 and 12 to be favored. The magnesyl derivatives, 1 and 12, have more covalent character and nearly classical structures. The metallated ketenimine forms, M-N=C=CH2( 2 , M = Li, Na, MgH), are next lowest in energy. The metallated nitrile ylides, M-C=N=CH2, are substantially higher in energy than the bridged forms but also show the geometrical variations associated with increasing ionic character. Other C2H2NM isomers, including metallated aminoacetylenes and carbene complexes, are energetically unfavorable. The energy orderings of the acyclic C2HlNM isomers also reflect the relative stabilities of the parent systems (in kcal/mol), e.g., CH3CN (O.O), CH3NC (+20.8), H2C=C=NH (+35.3), HCC-NH2 (+51.4), HC=N==CH2 (+69.0), at the 6-31G*//6-31G* level. More revealing are the stabilization energies relative to CH3M or to NH2M, depending on the principal site of metal attachment of the metal derivatives based on the parent C2H3N structures. Thus, the amino (vs. NH2M) stabilization energies, 40.9 kcal/mol for Na-N=C=CH2 and 32.4 kcal/mol for Li-N=C=CH2 (3-21G//3-21G), are 70% and 56% those of the free anion; the value for M=MgH (23.3 kcal/mol) is decreased even further. Likewise, the methyl stabilization energies (vs. CH3M) of the CH,(M)CN forms (Li, 21.5; Na, 23.2; and MgH, 8.7 kcal/mol) are all substantially less than that of the free anion, 45.3 kcal/mol (CHICN-vs. CH3-). Similar attenuation is found for the CH2(M)NC species vs. the CHINC-anion. Aggregation and solvation effects were probed by MNDO calculations. The most stable unsolvated dimers of both LiCH2CN and LiCH2NC are indicated to prefer eight-membered-ring structures, but solvation favors the alternative four-membered-ring N-lithiated ketenimine dimer form of the former, which may be the structure in the solid state.The importance of cyano-stabilized carbanions as synthetic intermediates is underscored by Volume 31 of "Organic Reactions", the latest in a series of reviews devoted to this topic1 The sodium salt of propionitrile was first described almost a 100 years ago.2 Lithium derivatives of aliphatic nitriles were reported by Ziegler in 19323 and the corresponding...

No abstract

No abstract