Influence of Ligand Electronic Effects on the Structure of Monovalent Cobalt Complexes

The syntheses, spectroscopic properties, and structures of the monovalent cobalt complexes, [PhTt^tBu]Co(L), 1-L {PhTt^tBu = phenyltris[(tert-butylthio)methyl]borate; L = PPh₃, PMe₃, PEt₃, PMe₂Ph, PMePh₂, P(OPh)₃, CNBu^t}, are described. Complexes 1-L are prepared via the sodium amalgam reduction of [PhTt^tBu]CoCl in the presence of L. The complexes display magnetic moments and paramagnetically shifted ¹H NMR spectra consistent with triplet, S = 1, ground states. The molecular geometries, determined by X-ray diffraction methods, reveal that some of the complexes display structures in which the L donor is moved off of the inherent 3-fold axis. In the most extreme cases (e.g., 1-P(OPh)₃ or 1-CNBu^t), the geometries can be described as cis-divacant octahedra. The origin of the geometric distortions is a consequence of the electronic characteristics of L as first deduced by Detrich et al. for [Tp^Np]Co(L) (J. Am. Chem. Soc. 1996, 118, 1703). The results establish a linear correlation between the magnitude of the structural distortion and the electronic parameter of the phosphine donor.