Binuclear Cyclopentadienylcobalt Carbonyls: Comparison with Binuclear Iron Carbonyls

TLDR: The binuclear cyclopentadienylcobalt carbonyls Cp2Co2(CO)n (n = 3, 2, 1; Cp = eta5-C5H5) are studied by density functional theory using the B3LYP and BP86 functionals to find the experimentally known monobridged and tribridged isomers to be similar in energy.

Abstract: The binuclear cyclopentadienylcobalt carbonyls Cp2Co2(CO)n (n = 3, 2, 1; Cp = η5-C5H5) are studied by density functional theory using the B3LYP and BP86 functionals. The experimentally known monobridged isomer Cp2Co2(CO)2(μ-CO) and the tribridged isomer Cp2Co2(μ-CO)3 of Cp2Co2(CO)3 with formal Co−Co single bonds are found to be similar in energy, with the precise relative energies of the two isomers depending on the functional chosen. For Cp2Co2(CO)2, the experimentally known coaxial isomer Cp2Co2(μ-CO)2 with two bridging CO groups and a formal CoCo double bond (2.360 A by B3LYP or 2.346 A by BP86) is found to lie 38.2 (B3LYP) or 34.9 kcal/mol (BP86) below a perpendicular isomer ⊥-Cp2Co2(CO)2. Similarly, for Cp2Co2(CO), the coaxial isomer Cp2Co2(μ-CO) with one bridging CO group and a formal Co⋮Co triple bond (2.021 A by B3LYP or 2.050 A by BP86) is found to lie 9.36 (B3LYP) or 9.62 kcal/mol (BP86) below the corresponding perpendicular isomer ⊥-Cp2Co2(CO). This coaxial isomer Cp2Co2(μ-CO) is a possible int...