The [M ₆ (S ₂ C ₂ Ph ₂ ) ₆ ] (M = Ni, Pd, Pt) Series: Multielectron Reservoirs That Sustain Ligand-Based Oxidations and Metal-Based Reductions

A complete [M₆(S₂C₂R₂)₆] series (M = Ni (1), Pd (2), Pt (3); R = Ph), the rarest variety among homoleptic dithiolene transition-metal compounds, has been prepared by reaction between [M(S₂C₂Ph₂)₂] and a M⁰ source. The platinum member of this set is the first of its type. Diffraction-quality crystals, grown with high reproducibility by evaporation from PhNO₂ solutions, reveal fully reduced [Ph₂C₂S₂]²⁻ dianions and an octahedral M₆ core that is reduced to C₂ symmetry by the fusion of a mononuclear D2h [M(S₂C₂Ph₂)₂] fragment upon a C₄-symmetric base. The [Ni₆(S₂C₂Ph₂)₂]¹⁻ monoanion, prepared by Cp*₂Co reduction, shows only modest structural differences from its neutral counterpart. In CH₂Cl₂, 1 and 2 can undergo two reductions and an oxidation, while 3 sustains two reductions and two oxidations. In benzonitrile, 1 sustains three reversible oxidations at potentials that are shifted appreciably to less positive values. The cathodic processes are shown by density functional theory (DFT) calculations to involve an MO largely of metal-sulfur composition that has contributions throughout the C₄-symmetric pentametallic base of the assembly, while the oxidations are largely ligand-based and confined to the monometallic [M(S₂C₂Ph₂)₂] cap. The absorption spectra are marked by multiple overlapping bands that produce a continuous, tapering absorption profile of unresolved shoulders and swells.