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Interplay between Two-Electron and Four-Electron Donor Carbonyl Groups in Oxophilic Metal Systems:  Highly Unsaturated Divanadocene Carbonyls

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journal contribution
posted on 21.03.2007, 00:00 by Qian-shu Li, Xiuhui Zhang, Yaoming Xie, R. Bruce King, Henry F. Schaefer
The divanadocene carbonyls Cp2V2(CO)n (n = 5, 4, 3, 2, 1; Cp = η5-C5H5) have been studied by density functional theory using the B3LYP and BP86 functionals. The global minimum for Cp2V2(CO)5 with a V⋮V distance of 2.452 Å (BP86) is essentially the same as the structure of the known Cp2V2(CO)5 determined by X-ray diffraction. The global minimum of Cp2V2(CO)4 is a triplet electronic state with a V⋮V distance of 2.444 Å (BP86). However, slightly higher energy singlet Cp2V2(CO)4 structures are found either with a V⋮V distance of 2.547 Å (BP86) and one four-electron donor bridging CO group or with a VV distance of 2.313 Å (BP86) and all two-electron donor bridging CO groups. Comparison is made between Cp2V2(CO)3 and the recently synthesized quintuply bonded RCrCrR (R = bulky aryl group) complexes of Power and co-workers. Four-electron donor bridging carbonyl groups become more prevalent upon further decarbonylation, leading ultimately to three singlet Cp2V22-μ-CO)2 isomers as well as triplet, quintet, and septet structures of Cp2V2(CO) with extremely low ν(CO) frequencies around 1400 cm-1. Our most remarkable structural finding is the extremely short vanadium−vanadium distance (1.80 Å, BP86) predicted for the singlet structure of Cp2V2(CO).