Phenylimidorhenium(V) complexes with 1,3-diethyl-4,5-dimethylimidazole-2-ylidene ligands

The phenylimidorhenium(V) complexes [Re(NPh)X-3(PPh3)(2)] (X = Cl, Br) react with the N-heterocyclic carbene (NHC) 1,3-diethyl-4,5-dimethylimidazole-2-ylidene (L-Et) under formation of the stable rhenium(V) complex cations [Re(NPh)X(L-Et)(4)](2+)(X = Cl, Br), which call be isolated as their chloride or [PF6](-) salts. The compounds are remarkably stable against air, moisture and ligand exchange. The hydroxo species [Re(NPh)(OH)(L-Et)(4)](2+) is formed when moist solvents are used during the synthesis. The rhenium atoms in all three complexes are coordinated in a distorted octahedral fashion with the four NHC ligands in equatorial planes of the molecules. The Re-C(carbene) bond lengths between 2.171(8) and 2.221(3) angstrom indicate mainly sigma-bonding between the NHC ligand and the electron deficient d(2) metal atoms. Attempts to prepare analogous phenylimido complexes from [Re(NPh)Cl-3(PPh3)(2)] and 1,3-diisopropyl-4,5-dimethylimidazole-2-ylidene (Li-Pr) led to a cleavage of the rhenium-nitrogen multiple bond and the formation of the dioxo complex [ReO2(Li-Pr)(4)](+).