Open-Ended Metallodithiolene Complexes with the 1,2,4,5-Tetrakis(diphenylphosphino)benzene Ligand: Modular Building Elements for the Synthesis of Multimetal Complexes.

Open-ended, singly metalated dithiolene complexes with 1,2,4,5-tetrakis(diphenylphosphino)benzene (tpbz) are prepared either by ligand transfer to [ClM(tpbz)] from (RCS)SnR' (R = CN, R' = Me; R = Me, R' = Bu) or by a direct reaction between tpbz and [M(SCR)] (M = Ni, Pd, Pt; R = Ph, -anisyl) in a 1:1 ratio. The formation of dimetallic [(RCS)M(tpbz)M(SCR)] attends these syntheses in modest amounts, but the open-ended compounds are readily separated by silica chromatography. As affirmed by X-ray crystallographic characterization of numerous members of the set, the [(RCS)M(tpbz)] compounds show dithiolene ligands in their fully reduced ene-1,2-dithiolate form conjoined with divalent Group 10 ions. Minor amounts of octahedral [(PhCS)Pt(tpbz)], a presumed intermediate, are isolated from the preparation of [(PhCS)Pt(tpbz)]. Heterodimetallic [(PhCS)Pt(tpbz)Ni(SCMe)] is prepared from [(PhCS)Pt(tpbz)]; its cyclic voltammogram, upon anodic scanning, shows two pairs of closely spaced, but resolved, 1e oxidations corresponding first to [RCS] - 1e → [RCSS] and then to [RCSS] - 1e → [R(C═S)]. The open diphosphine of [(RCS)M(tpbz)] can be oxidized to afford open-ended [(RCS)M(tpbzE)] (E = O, S). Synthesis of the octahedral [(dppbO)Ni][I] [dppbO = 1,2-bis(diphenylphosphoryl)benzene] suggests that the steric profile of [(RCS)M(tpbzE)] is moderated enough that three could be accommodated as ligands around a metal ion.