Rhodium derivatives structural parameters

Y. Kawabata and coworkers Chemistry Letters (1976), 1213—1214) have reported on the asymmetric hydrogenation brought about by a Rhodium catalyst complexed with a phosphonite derivative of cellulose. Pittman and coworkers (Preprints D/v. Petroleum Chem. 22 (1977), 1196) have attached a (-) DIOP—Rh—catalyst to cross linked styrene-divinylbenzene resins. This polymer displayed activity for the asymmetric hydroformila-tion of styrene, and a study of the dependence of the optical yield from various structural parameters of the polymer has been carried out. J. K. Stille and coworkers ( 7. Am. Chem. Soc. 100 (1978), 264) have prepared a chiral polymer-immobilized (-)DIOP-Rh(I) catalyst which is active in the asymmetric hydrogenation of a-acetamido acrylic acid derivatives with optical yields as high as 86%. Since optical yields were higher in ethanol than in other solvents (e.g. tetrahydrofurane), also a copolymer was prepared, which contained a chiral alcoholic function in addition to the Rh-catalytic function (T. Masuda and J. K. Stille,... 

The SHAPES force field" has been implemented in CHARMM and used to examine the structures of several square planar rhodium complexes. This force field is based on angular overlap considerations and treats angular distortions for a variety of geometries. Spherical internal coordinates and Fourier potential functions form the basis for the description of these molecular shapes. The parameters for this force field were derived from normal coordinate analysis, ab initio calculations, and structure-based optimizations. The average rms deviation for bond lengths was 0.026 A, and the average rms deviation for bond angles was 3.2°. 

Enantioselection can be controlled much more effectively with the appropriate chiral copper, rhodium, and cobalt catalyst.The first major breakthrough in this area was achieved by copper complexes with chiral salicylaldimine ligands that were obtained from salicylaldehyde and amino alcohols derived from a-amino acids (Aratani catalysts ). With bulky diazo esters, both the diastereoselectivity (transicis ratio) and the enantioselectivity can be increased. These facts have been used, inter alia, for the diastereo- and enantioselective synthesis of chrysan-themic and permethrinic acids which are components of pyrethroid insecticides (Table 10). 0-Trimethylsilyl enols can also be cyclopropanated enantioselectively with alkyl diazoacetates in the presence of Aratani catalysts. In detailed studies,the influence of various parameters, such as metal ligands in the catalyst, catalyst concentration, solvent, and alkene structure, on the enantioselectivity has been recorded. Enantiomeric excesses of up to 88% were obtained with catalyst 7 (R = Bz = 2-MeOCgH4). 

---