Metal vapor synthesis as a straightforward route to group 10 homoleptic carbene complexes

The co-condensation of nickel, palladium, or platinum vapor with the N,N'-di-tert-butyl heterocyclic carbene 1,3-di-N-tert-butylimidazol-2-ylidene [C{N(Bu-t)CH}(2)] (L) provides a novel and straightforward synthesis of the stable, two-coordinate homoleptic metal carbene complexes NiL2 (1), PdL2 (2), and PtL2 (3). A single-crystal X-ray structural determination of 2 and 3 shows the two complexes to be isomorphous; in the solid state the metal center is linear and two-coordinate and the molecules approach D-2d symmetry with a dihedral angle of 90 degrees between the planar rings of the two ligand heterocycles. The metal center in 2 appears to be an essential mediator in the quantitative conversion of the ligated carbene into dihydroimidazoline, which is cleanly eliminated from a solution of the complex under an atmosphere of dihydrogen; 2 also reversibly coordinates ethene.