Novel Di- and Trinuclear Palladium Complexes Supported by N,N′-Diphosphanyl NHC Ligands and N,N′-Diphosphanylimidazolium Palladium, Gold, and Mixed-Metal Copper-Gold Complexes

The reaction of the trinuclear complex [Ag-3(mu(3)-PCNHCP,kappa P,kappa C-NHC,C-kappa P)(2)] (OTf)(3) (Ag3; PCNHCP = N,N'-bis(di-tert- butylphosphanyl)imidazol-2-ylidene) with [Pd(dba)(2)] afforded the trinuclear palladium complex [Pd-3(mu(3)-PCNHCP,kappa P,kappa C-NHC,kappa P)(2)](OTf)(2) (Pd3) and the dinuclear palladium(I) complex [Pd-2(mu(2)-PCNHCP,kappa P,kappa C-NHC,kappa P)(2)](OTf)(2) (Pd2). The assignment of the oxidation state of the metals in the mixed-valence Pd3 chain as Pd-0-Pd-II-Pd-0 was based on the reactivity of the complex with 2,6-dimethylphenyl isocyanide and density functional theory calculations. Reaction of PCNHCP with [PdMe2(tmeda)] afforded the palladium(II) complex [PdMe2(PCNHCP,kappa P,kappa C-NHC)] (Pd-Me2), with PCNHCP acting as a bidentate ligand. The reaction of PCNHCP with [Pd(dba)(2)] led to a dinuclear palladium(0) complex [Pd-2(mu(2)-PCNHCP,kappa P,kappa C-NHC,kappa P)](dba) (Pd2-dba); attempted replacement of the remaining dba by PCNHCP failed. The imidazolium triflate PCHP, precursor to PCNHCP, was reacted with [Pd-2(dba)(3)]center dot CHCl3 to give the (2 + 2) metalla-mesocyclic cationic palladium(0) complex [Pd-2(mu(2)-PCHP,kappa P,kappa P)(2)] (PCHP-Pd2), which resisted further deprotonation of the imidazolium cation. In contrast, PCHP reacted with [AuCl(tht)] to give [Au2Cl2(mu(2)-PCHP,kappa P,kappa P)] (PCHP-Au2), in which one Au-Cl moiety is bound to each P donor. Further reaction of PCHP-Au2 with [Au{N(SiMe3)(2)}(PPh3)] afforded a mixture of the trinuclear [Au-3(mu(3)-PCNHCP,kappa P,kappa C-NHC,kappa P)(2)](OTf)(3) (Au3) and [AuCl(PPh3)], while reaction with [CuMes](5), where Mes = 2,4,6-trimethylphenyl, resulted in a novel, centrosymmetric, heterometallic complex [Au(2)Mes(2)(Cu4Cl4)(PCHP,kappa P,kappa P)(2)] (PCHP-AuCu) featuring a new PCHP-AuMes metalloligand bridging a Cu center dot center dot center dot Cu diagonal of a Cu4Cl4 cubane via the P and AuMes functionalities.