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, H2[LN,S], or 3,5-di-tert-butyl-1,2-benzenedithiol,
H2[LS,S], with 1 equiv of [MoO2(acac)2] or WCl6 (acac = acetonylacetate(1-)) in methanol or CCl4 afforded the
diamagnetic neutral complexes [MoV(LN,S)2(L•N,S)]0 (1), [MoV(LS,S)2(L•S,S)] (2), and [WV(LS,S)2(L•S,S)] (3), where (L•N,S)-
and (L•S,S)- represent monoanionic π-radical ligands (Srad = 1/2), which are the one-electron oxidized forms of the
corresponding closed-shell dianions (LN,S)2- and (LS,S)2-. Complexes 1−3 are trigonal-prismatic members of the
electron-transfer series [ML3]z (z = 0, 1−, 2−). Reaction of 2 and 3 with [N(n-Bu)4](SH) in CH2Cl2 under anaerobic
conditions afforded paramagnetic crystalline [N(n-Bu)4][MoV(LS,S)3] (4) and [N(n-Bu)4][WV(LS,S)3] (5). Complexes 1−5
have been characterized by X-ray crystallography. S K-edge X-ray absorption and infrared spectroscopy prove that
a π-radical ligand (L•S,S)- is present in neutral 2 and 3, whereas the monoanions [MV(LS,S)3]- contain only closed-shell dianionic ligands. These neutral species have previously been incorrectly described as [MVI(L)3]0 complexes
with a MoVI or WVI (d0) central metal ion; they are, in fact MV (d1) (M = Mo, W) species:  [MoV(LS,S)2(L•S,S)] and
[WV(LS,S)2(L•S,S)] with a diamagnetic ground state St = 0, which is generated by intramolecular, antiferromagnetic
coupling between the MV (d1) central ion (SM = 1/2) and a ligand π radical (L•S,S)- (Srad = 1/2).