Pentamethylcyclopentadienyl cobalt carbonyl dimers containing multiple metal–metal bond character: preparation, structural analysis (including X-ray crystallographic determinations), and bonding implications of [Co2(η5-C5Me5)2(µ2-CO)2]n(n=–1 or 0)

Abstract

Syntheses and structural characterizations (including X-ray crystallographic determinations) of[Na(2,2,2-crypt)]⁺[Co₂(η⁵-C₅Me₅)₂(µ₂-CO)₂]^–·[where (2,2,2-crypt)= N(C₂H₄OC₂H₄OC₂H₄)₃N] and Co₂(η⁵-C₅Me₅)₂(µ₂-CO)₂ have resulted in (at least) a partical resolution of the contradiction between previously available structural data and theory in correlating metal–metal bond-length defferences and bond order (B.O.) for structurally analogous nitrosyl- and carbonyl-bridged cyclopentadienyl metal dimers; a distinct contraction of 0·034 Å in the Co–Co bond length is observed upon going from the paramagnetic [Co₂(η⁵-C₅Me₅)₂(µ₂-CO)₂]^–· monoanion [2·372(1)Å; B.O. = 1·5] to its oxidized neutral dimer [2·338(2)Å; B.O. = 2·0], which is consistent with the presumed removal of the unpaired electron from an M.O. primarily composed of out-of-plane antibonding dπ* dimetal character.