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(SiMe ₂ Ph) ₃ }] ₂ (1) was prepared by reacting CoCl ₂ with [Li{C(SiMe ₂ Ph) ₃ }(THF)] in a 1:2 ratio. Attempts to synthesize the corresponding iron(I) species led to the iron(II) salt [Li(THF) ₄ ][Fe ₂ (-Cl) ₃ {C(SiMe ₂ Ph) 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 ?-bonded to the central carbon of the alkyl group -C(SiMe ₂ Ph) ₃ and ?-bonded to one of the phenyl rings of the -C(SiMe ₂ Ph) 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 ?-bonded to the central carbon of a terminal -C(SiMe ₂ Ph) 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).