X-RAY CRYSTAL-STRUCTURES OF CP-ASTERISK-NI(PET3)X [X=BR, O(P-C6H4ME),NH(P-C6H4ME), S(P-C6H4ME), OCH3, CH2C6H5, ME, H, PET3- UNDERSTANDING DISTORTIONS AND TRANSINFLUENCES IN CYCLOPENTADIENYL COMPLEXES(] )

The syntheses of CpNi(PEt3)Me and Cp*Ni(PEt3)Br have been accomplishe d, starting from the useful starting material CpNi(PEt3)(acac). The X -ray crystal structures of CpNi(PEt3)X (X = Br, O(p-C6H4Me), NH(p-C6H 4Me), S(p-C6H4Me), OCH3, Me, CH2Ph, H, PEt3+) have been determined, pr oviding a large sample of similar structures for the analysis of ring distortions as well as a systematic variation of X in order to evaluat e the trans influence felt by opposite sides of the cyclopentadienyl r ing. Major advances include demonstration that Cp can reduce its elect ron donation to a metal without ''slipping'', the rational analysis of cyclopentadienyl distortions, and a well-supported trans-influence se ries for cyclopentadienylmetal complexes. In sum, d(8) CpNiL2 complex es are similar to d(8) NiL4 square-planar complexes in terms of bond l engths, binding geometry, and trans influences.