Influence of Phenyl Substituents on Diamagnetic Cobalt(III) Dithiocarbamate Complexes

Abstract

Single-crystal X-ray structural determinations have been recorded at c.295 K for the tris ( dithiocarbamato )cobalt(III) compounds [Co(S₂CNMePh)₃] and [Co(S₂CNPh₂)₃]. [Co(S₂CNMePh)₃] crystallizes in space group P2₁/a with a 25.207(6), b 12.778(2), c 9.497(2)Ǻ, β 116.40(2)°. [Co(S₂CNPh₂)₃] crystallizes in space group Pī with a 14.979(6), b 13.169(4), c 10.683(3)Ǻ, α 71.53(3),β 88.15(3),γ 82.35(3)°. The structures were refined to residuals of 0.039 and 0.062 for 2184 and 4068 'observed' reflections respectively. The cobalt-59 n.m.r. chemical shift of the sparingly soluble diphenyl compound is found to be 6450 ppm downfield from K₃Co(CN)₆, compared with 6660 ppm for the methyl phenyl compound and 6830 ppm for the non-phenyl-substituted dimethyl compound, a result reflecting increase in the ligand -field strengths of the ligands in this series of compounds in the order Me₂ < Me Ph < Ph₂. Average geometric parameters (Ǻ) are: methyl phenyl, Co-S 2.270(6), C-S 1.699(6), C-N 1.341(9), S…S 2.803(2), N-C_phenyl 1.446(5), N-C_methyl 1.45(1); diphenyl, Co-S 2.267(8), C-S 1.699(4), C-N 1.335(4), S…S 2.805(2), N-C_phenyl 1.449(6). Solid-state carbon-13 chemical shifts for thecarbon atom of the NCS₂ fragment are 204, 207 and 210 ppm for [Co(S₂CNMe₂)₃], [Co(S₂CNMePh)₃] and [Co(S₂CNPh₂)₃] respectively. By comparison, the carbon-13 chemical shifts for cobalt complexes with saturated hydrocarbon substituents which span the range of ligand -field strengths do not show the same systematic trends: [Co(S₂CN(CH₂)₄)₃], 201 ppm ; [Co(S₂CNEt₂)₃], 204 ppm ; and [Co(S₂CNPrⁱ₂)₃], 204 ppm , [Co(S₂CN(CH₂Ph)₂)₃], 207 ppm . For the unsaturated hydrocarbon system, [Co(S₂CN(CH)₄)₃], this value is 211 ppm . These results correspond closely to solution carbon-13 data and constitute good evidence that the ligand substituent effects in the compounds are similar in the two states. The increase in ligand -field strength with phenyl substituent is rationalized in terms of a combination of steric and electronic effects.