Heteroleptic Square Planar Cobalt(I/II) Complexes

Reduction of the cobalt(II) chloride complex, Ph2B((t)BuIm)(2)Co(THF)Cl (1) in the presence of (BuN)-Bu-t equivalent to C affords the diamagnetic, square planar cobalt(I) complex Ph2B((t)BuIm)(2)Co(C equivalent to(NBu)-Bu-t)(2) (2). This is a rare example of a 16-electron cobalt(I) complex that is structurally related to square planar noble metal complexes. Accordingly, the electronic structure of 2, as calculated by DFT, reveals that the HOMO is largely d(z)(2) in character. Complex 2 is readily oxidized to its cobalt(II) congener [Ph2B((t)BuIm)(2)Co(C=(NBu)-Bu-t)(2)]BPh4 (3-BPh4), whose EPR spectral parameters are characteristic of low-spin d(7) with an unpaired electron in an orbital of d(z)(2) parentage. This is also consistent with the results of DFT calculations. Despite its 16-electron configuration and the d(z)(2) parentage of the HOMO, the only tractable reactions of 2 involve one electron oxidation to afford 3.