Comparison of Isoelectronic Heterometallic and Homometallic Binuclear Cyclopentadienylmetal Carbonyls: The Iron–Nickel vs. the Dicobalt Systems

Abstract

The heterometallic binuclear cyclopentadienylironnickel carbonyl compounds Cp2FeNi(CO)n (n = 3, 2, 1; Cp = η5‐C5H5) have been studied by density functional theory (BP86) for comparison with the isoelectronic homometallic dicobalt derivatives Cp2Co2(CO)n. The FeNi tricarbonyl is shown to be the doubly bridged isomer Cp2Fe(CO)Ni(μ‐CO)2 with an Fe–Ni distance of 2.455 Å (BP86), in accord with experiment and in contrast to Cp2Co2(CO)3 where singly and triply bridged but not doubly bridged isomers are found. The dicarbonyl compounds Cp2FeNi(μ‐CO)2 and Cp2Co2(μ‐CO)2 both have analogous doubly bridged structures with M=M distances around 2.35 Å, suggesting formal M=M double bonds. The monocarbonyl compounds have analogous singly bridged axial structures Cp2FeNi(μ‐CO) and Cp2Co2(μ‐CO) with metal–metal distances in the range 2.05 Å (M2 = Co2) to 2.12 Å (M2 = FeNi) consistent with the formal M≡M triple bonds required for the favored 18‐electron configuration. Open‐shell states of Cp2FeNi(μ‐CO) are found to have even lower energies than the closed‐shell structure, which indicates that the ground state of Cp2FeNi(μ‐CO) might be a high spin structure. However, the global minimum for the monocarbonyl is found to be a singlet “hot dog” perpendicular Cp2NiFe(CO) structure with a terminal CO group bonded to the iron atom. Other higher energy perpendicular structures are also found for Cp2FeNi(CO)n (n = 3, 2, 1) with terminal CO groups and bridging Cp rings. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Unsaturation in binuclear heterometallic carbonyls: the cyclopentadienyliron manganese carbonyl CpFeMn(CO)nsystem as a hybrid of the Cp2Fe2(CO)nand Mn2(CO)nsystems

“…10 Subsequently Cp 2 FeNi(CO) 3 and the related unsaturated Cp 2 FeNi(CO) n (n = 2, 1) systems were studied by density functional theory. 11,12 The mixed cyclopentadienyl molybdenum-ruthenium carbonyl Cp(CO) 3 Mo-Ru(CO) 2 Cp (Fig. 2) was synthesized by Pakkanen et al and used to generate a bimetallic heterogeneous catalyst for hydrodesulfurization reactions.…”