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{sub 2}[L{sub N,S}], or 3,5-di-tert-butyl-1,2-benzenedithiol, H{sub 2}[L{sub S,S}], with 1 equiv of [MoO{sub 2}(acac){sub 2}] or WCl{sub 6} (acac = acetonylacetate(1-)) in methanol or CCl{sub 4} afforded the diamagnetic neutral complexes [MoV(L{sub N,S}){sub 2}(L{sup {center_dot}}{sub N,S})]{sup 0} (1), [MoV(L{sub S,S}){sub 2}(L{sup {center_dot}}{sub S,S})] (2), and [W{sup V}(L{sub S,S}){sub 2}(L{sup {center_dot}}{sub S,S})] (3), where (L{sup {center_dot}}{sub N,S}){sup -} and (L{sup {center_dot}}{sub S,S}){sup -} represent monoanionic {pi}-radical ligands (S{sub rad} = 1/2), which are the one-electron oxidized forms of the corresponding closed-shell dianions (L{sub N,S}){sup 2-} and (L{sub S,S}){sup 2-}. Complexes 1-3 are trigonal-prismatic members of the electron-transfer series [ML{sub 3}]{sup z} (z = 0, 1-, 2-). Reaction of 2 and 3 with [N(n-Bu){sub 4}](SH) in CH{sub 2}Cl{sub 2} under anaerobic conditions afforded paramagnetic crystalline [N(n-Bu){sub 4}][Mo{sup V}(L{sub S,S}){sub 3}] (4) and [N(n-Bu){sub 4}][W{sup V}(L{sub S,S}){sub 3}] (5). Complexes 1-5 have been characterized by X-ray crystallography. S K-edge X-ray absorption and infrared spectroscopy prove that a {pi}-radical ligand (L{sup {center_dot}}{sub S,S}){sup -} is present in neutral 2 and 3, whereas the monoanions [M{sup V}(L{sub S,S}){sub 3}]{sup -} contain only closed-shell dianionic ligands. These neutral species have previously been incorrectly described as [M{sup VI}(L){sub 3}]{sup 0} complexes with a Mo{sup VI} or W{sup VI} (d{sup 0}) central metal ion; they are, in fact M{sup V} (d{sup 1}) (M = Mo, W) species: [Mo{sup V}(L{sub S,S}){sub 2}(L{sup {center_dot}}{sub S,S})] and [W{sup V}(L{sub S,S}){sub 2}(L{sup {center_dot}}{sub S,S})] with a diamagnetic ground state S{sub t} = 0, which is generated by intramolecular, antiferromagnetic coupling between the M{sup V} (d{sup 1}) central ion (S{sub M} = 1/2) and a ligand radical (L{sup {center_dot}}{sub S,S}){sup -} (S{sub rad} = 1/2).