Electronic structure of neutral and monoanionic tris(benzene-1,2-dithiolato) metal complexes of molybdenum and tungsten

The reaction of 3 equiv of the ligand 2-mercapto-3,5-di-tert-butylaniline, H-2[L-N,L-S], or 3,5-di-tert-butyl-1,2-benzenedithiol, H-2[L-S,L-S], with 1 equiv of [MoO2(acac)(2)] or WCl6 (acac = acetonylacetate(1-)) in methanol or CCl4 afforded the diamagnetic neutral complexes [Mo-V(L-N,L-S)(2)(L-N,S(center dot))](0) [Mo-V(L-S,L-S)(2)(L-S,S(center dot))], and [W-V(L-S,L-S)(2)(L-S,S(center dot))], where (L-N,S(center dot))(-) and (L-S,S(center dot))(-) represent monoanionic pi-radical ligands (S-rad = (1)/(2)), which are the one-electron oxidized forms of the corresponding closed-shell dianions (L-N,L-S)(2-) and (L-S,L-S)(2-). Complexes are trigonal-prismatic members of the electron-transfer series [ML3](z) (z = 0, 1-, 2-). Reaction of and with [N(n-Bu)(4)](SH) in CH2Cl2 under anaerobic conditions afforded paramagnetic crystalline [N(n-Bu)(4)][Mo-V(L-S,L-S)(3)] and [N(n-Bu)(4)][W-V(L-S,L-S)(3)] . Complexes have been characterized by X-ray crystallography. S K-edge X-ray absorption and infrared spectroscopy prove that a pi-radical ligand (L-S,S(center dot))(-) is present in neutral whereas the monoanions [M-V(L-S,L-S)(3)](-) contain only closed-shell dianionic ligands. These neutral species have previously been incorrectly described as [M-VI(L)(3)](0) complexes with a Mo-VI or W-VI (d(0)) central metal ion; they are, in fact M-V (d(1)) (M = Mo, W) species: [Mo-V(L-S,L-S)(2)(L-S,S(center dot))] and [W-V(L-S,L-S)(2)(L-S,S(center dot))] with a diamagnetic ground state S-t = 0, which is generated by intramolecular, antiferromagnetic coupling between the M-V (d(1)) central ion (S-M = (1)/(2)) and a ligand pi radical (L-S,S(center dot))(-) (S-rad = (1)/(2)).