Metal-hydrocarbon complexes bond distances

Evidence for donation from metal orbitals into the antibonding molecular orbitals of the alkynyl group has b en obtained from studies of the infrared spectra of such complexes. Foi the platinum compounds (Et3P)2Pt(C=CR)2 the C=C stretching frequencies occur ca. 2100 cm" which is about ISO cm lower than those found in disubstituted acetylenic hydrocarbons (2260 — 2190 cm ), suggesting a lowering of the C=C bond order. The C=C distance in the compound (Et3P)2Ni(C=CPh)2 however, is very close (1-18 0 02 A) to that found in the free acetylene PhC=CPh (1-19 0-03 A). 

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