Chiral Palladium(II)-Bis(trichlorosilyl) Complexes. Synthesis, Structure, and Combined QM/MM Computational Studies

(1, Dichloro{1-{(R)-1-[(S)-2-(diphenylphosphino-kP)ferrocenyl]ethyl}-3,5-dimethyl-1H-pyrazole-kN}palladium 2, dichloro{1-{(R)-1-[(S)-2-(diphenylphosphino-kP)ferrocenyl]ethyl}-3-phenyl-5-methyl-1H-pyrazole-kN}palladium 3 dichloro{1-{(R)-1-[(S)-2-(diphenylphosphino-kP)ferrocenyl]ethyl}-3-(2,4,6-trimethylphenyl)-1H-pyrazole-kN}palladium) previously used as catalyst precursors in the asym. hydrosilylation of olefins, react with an excess of HSiCl3 in CH2Cl2 to afford the corresponding bis(trichlorosilyl) derivs. (4-6). (5-6) Were characterized by x-ray crystallog. and show unusual structural properties. A severe deviation from the ideal square-planar geometry was obsd., as well as extremely elongated Pd-P bonds (Pd-P = 2.4559(16) .ANG. for 5 and 2.504(2) .ANG. for 6). The nature of the uncommon structural features obsd. in the bis(trichlorosilyl) derivs. was explored with d. functional theory calcns. and the combined quantum mechanics/mol. mechanics (QM/MM) method. Using the combined QM/MM approach a systematic series of model systems were constructed in which the steric and electronic influences of the substituent groups were selectively removed or altered. The technique has allowed the exact nature of the geometric distortions to be pinpointed. [on SciFinder (R)]