Redox-Active Metallodithiolene Groups Separated by Insulating Tetraphosphinobenzene Spacers.

Compounds of the type [(S2 C2 R2 )M(μ-tpbz)M(S2 C2 R2 )] (R = CN, Me, Ph, p-anisyl; M = Ni, Pd, Pt; tpbz = 1,2,4,5-tetrakis(diphenylphosphino)benzene) have been prepared by transmetalation with [(S2 C2 R2 )SnR'2 ] reagents, by direct displacement of dithiolene ligand from [M(S2 C2 R2 )2 ] with 0.5 equiv of tpbz, or by salt metathesis using Na2 [S2 C2 (CN)2 ] in conjunction with X2 M(μ-tpbz)MX2 (X = halide). X-ray crystallography reveals a range of topologies (undulating, chair, bowed) for the (S2 C2 )M(P2 C6 P2 )M(S2 C2 ) core. The [(S2 C2 R2 )M(μ-tpbz)M(S2 C2 R2 )] (R = Me, Ph, p-anisyl) compounds support reversible or quasireversible oxidations corresponding to concurrent oxidation of the dithiolene terminal ligands from ene-1,2-dithiolates to radical monoanions, forming [(- S• SC2 R2 )M(μ-tpbz)M(- S• SC2 R2 )]2+ . The R = Ph and p-anisyl compounds support a second, reversible oxidation of the dithiolene ligands to their α-dithione form. In contrast, [(S2 C2 (CN)2 )Ni(tpbz)Ni(S2 C2 (CN)2 )] sustains only reversible, metal-centered reductions. Spectroscopic examination of [(- S• SC2 ( p-anisyl)2 )Ni(μ-tpbz)Ni(- S• SC2 ( p-anisyl)2 )]2+ by EPR reveals a near degenerate singlet-triplet ground state, with spectral simulation revealing a remarkably small dipolar coupling constant of 18 × 10-4 cm-1 that is representative of an interspin distance of 11.3 Å. This weak interaction is mediated by the rigid tpbz ligand, whose capacity to electronically insulate is an essential quality in the development of molecular-based spintronic devices.