Carbene complexes. Part VIII. Chromium(0), iron(0), rhodium(I), iridium(I), nickel(II), palladium(II), platinum(II), and gold(I) mono- and oligo-carbene species from electron-rich olefins

The reaction of the electron-rich olefin 1,1′,3,3′-tetramethyl-2,2′-bi-imidazolidinylidene (I)(L2) or, in one case, of bis(N-methylbenzothiazolinylidene)(II)(L′2) with various transition metal d6 or d8 complexes yields mono- di-, or tri-carbene metal complexes of Cr0, Fe0, RhI, IrI, NiII, PdII, PtII, or AuI, such as cis-Cr(CO)4(L)2, [Ir(CO)(L)3]+, or cis-[PtMe(PPh3)(L)2]+. The reactions involve (i) displacement from the metal of a negative (Cl–, I–) or neutral [CO, tertiary phosphine, or π-allyl (transformed into σ-allyl)] ligand or ligands by one or more nucleophilic carbene moieties L or L′, (ii), for [Rh(CO)2Cl]2, bridge-splitting by L, or (iii) displacement of a halide anion by BF4–. The twenty-four new carbene complexes are stable and their ready formation in high yield serves as a further demonstration of the scope of electron-rich olefins as reagents in transition metal chemistry. They clearly behave as nucleophilic carbene (L or L′) transfer reagents.