Group 10 Metal Dithiolene Bis(isonitrile) Complexes: Synthesis, Structures, Properties, and Reactivity

The reaction of [(Ph₂C₂S₂)₂M] (M = Ni²⁺, Pd²⁺, Pt²⁺) with 2 equiv of RNC (R = Me (a), Bn (b), Cy (c), ^tBu (d), 1-Ad (e), Ph (f)) yields [(Ph₂C₂S₂)­M­(CNR)₂] (M = Ni²⁺, 4a–f; M = Pd²⁺, 5a–f; M = Pt²⁺, 6a–f), which are air-stable and amenable to chromatographic purification. All members have been characterized crystallographically. Structurally, progressively greater planarity tends to be manifested as M varies from Ni to Pt, and a modest decrease in the CN bond length of coordinated CNR appears in moving from Ni toward Pt. Vibrational spectroscopy (CH₂Cl₂ solution) reveals ν_CN frequencies for [(Ph₂C₂S₂)­M­(CNR)₂] that are substantially higher than those for free CNR and increase as M ranges from Ni to Pt. This trend is interpreted as arising from an increasingly positive charge at M that stabilizes the linear, charge-separated resonance form of the ligand over the bent form with lowered C–N bond order. UV–vis spectra reveal lowest energy transitions that are assigned as HOMO (dithiolene π) → LUMO (M–L σ*) excitations. One-electron oxidations of [(Ph₂C₂S₂)­M­(CNR)₂] are observed at ∼+0.5 V due to Ph₂C₂S₂^2– → Ph₂C₂S^–S^• + e^–. Chemical oxidation of [(Ph₂C₂S₂)­Pt­(CN^tBu)₂] with [(Br-p-C₆H₄)₃N]­[SbCl₆] yields [(Ph₂C₂S^–S^•)­Pt­(CN^tBu)₂]⁺, identified spectroscopically, but in the crystalline state [[(Ph₂C₂S^–S^•)­Pt­(CN^tBu)₂]₂]²⁺ prevails, which forms via axial Pt···S interactions and pyramidalization at the metal. Complete substitution of MeNC from [(Ph₂C₂S₂)­Ni­(CNMe)₂] by 2,6-Me₂py under forcing conditions yields [(2,6-Me₂py)­Ni­(μ₂-η¹,η¹-S′,η¹-S″-S₂C₂Ph₂)]₂ (8), which features a folded Ni₂S₂ core. In most cases, isocyanide substitution from [(Ph₂C₂S₂)­M­(CNMe)₂] with monodentate ligands (L = phosphine, CN^–, carbene) leads to [(Ph₂C₂S₂)­M­(L)­(CNMe)]ⁿ (n = 0, 1−), wherein ν_CN varies according to the relative σ-donating power of L (9–21). The use of 1,3-bis­(2,6-diisopropylphenyl)­imidazol-2-ylidene (IPr) provides [(Ph₂C₂S₂)­M­(IPr)­(CNMe)] for M = Ni (18), Pd (19), but for Pt, attack by IPr at the isocyanide carbon occurs to yield the unusual η¹,κC-ketenimine complex [(Ph₂C₂S₂)­Pt­(C­(NMe)­(IPr))­(CNMe)] (20).