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

The reaction of [(Ph2C2S2)(2)M] (M = Ni2+, Pd2+, Pt2+) with 2 equiv of RN C (R = Me (a), Bn (b), Cy (c), Bu-t (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 nu(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 pi) -> LUMO (M-L sigma*) excitations. One-electron oxidations of [(Ph2C2S2) M(C NR)(2)] are observed at similar to+0.5 V due to Ph2C2S22- -> (Ph2C2S-S center dot) + e(-). Chemical oxidation of [(Ph2C2S2)Pt(C (NBu)-Bu-t)(2)] with [(Br-p-C6H4)(3)N][SbCl6] yields [((Ph2C2S-S center dot)) Pt(C (NBu)-Bu-t)(2)](+), identified spectroscopically, but in the crystalline state [[((Ph2C2S-S center dot))Pt(C (NBu)-Bu-t)(2)](2)](2+) prevails, which forms via axial Pt center dot center dot center dot S interactions and pyramidalization at the metal. Complete substitution of MeNC from [(Ph2C2S2)Ni(C NMe)(2)] by 2,6-Me(2)py under forcing conditions yields [(2,6-Me(2)py)Ni(mu(2)-eta(1),eta(1)-S',eta(1)-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 nu(C N) varies according to the relative s-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 eta(1),kappa C-ketenimine complex [(Ph2C2S2)Pt(C(NMe)(IPr))(C NMe)] (20).