Beyond the metal–metal triple bond in binuclear cyclopentadienylchromium carbonyl chemistry†
Abstract
The cyclopentadienylchromium carbonyls Cp2Cr2(CO)n and Cp*2Cr2(CO)n (Cp = η5-C5H5 and Cp* = η5-Me5C5; n = 3, 2) have been studied by density functional theory using the B3LYP and BP86 functionals. Triplet and singlet structures are found for Cp2Cr2(CO)3, with the triplet isomer having an apparent CrCr triple bond (2.295 Å by BP86) and predicted to have a lower energy than the singlet isomer having an apparent CrCr quadruple bond (2.191 Å by BP86). Quintet, septet, and singlet structures, as well as a highly spin contaminated triplet structure, were found for the dicarbonyl Cp2Cr2(CO)2. In all of the Cp2Cr2(CO)n (n = 3, 2) structures the carbonyls are asymmetric semi-bridging groups, typically with differences of 0.3–0.5 Å between the shortest and longest M–C distances. Very little difference was found between the structures and energetics of the corresponding Cp and Cp* derivatives. These DFT studies suggest that the reported unstable photolytic