Synthesis and Structural Characterization of a Dimeric Cobalt(I) Homoleptic Alkyl and an Iron(II) Alkyl Halide Complex

The homoleptic cobalt­(I) alkyl [Co­{C­(SiMe2Ph)3}]2 (1) was prepared by reacting CoCl2 with [Li­{C­(SiMe2Ph)3}­(THF)] in a 1:2 ratio. Attempts to synthesize the corresponding iron­(I) species led to the iron­(II) salt [Li­(THF)4]­[Fe2(μ-Cl)3{C­(SiMe2Ph)3}2] (2). Both 1 and 2 were characterized by X-ray crystallography, UV–vis spectroscopy, and magnetic measurements. The structure of 1 consists of dimeric units in which each cobalt­(I) ion is σ-bonded to the central carbon of the alkyl group −C­(SiMe2Ph)3 and π-bonded to one of the phenyl rings of the −C­(SiMe2Ph)3 ligand attached to the other cobalt­(I) ion in the dimer. The structure of 2 features three chlorides bridging two iron­(II) ions. Each iron­(II) ion is also σ-bonded to the central carbon of a terminal −C­(SiMe2Ph)3 anionic ligand. The magnetic properties of 1 reveal the presence of two independent cobalt­(I) ions with S = 1 and a significant zero-field splitting of D = 38.0(2) cm–1. The magnetic properties of 2 reveal extensive antiferromagnetic exchange coupling with J = −149(4) cm–1 and a large second-order Zeeman contribution to its molar magnetic susceptibility. Formation of the alkyl 1 and the halide complex 2 under similar conditions is probably due in part to the fact that Co­(II) is more readily reduced than Fe­(II).