The coordination and activation of azobenzene by Ru5(μ5-C) cluster complexes

Abstract

The reaction of Ru5(μ5-C)(CO)15, 1 with azobenzene, PhN = NPh, yielded the pentaruthenium carbido cluster compound Ru5C(CO)13(C6H4N=NC6H5)[μ-H], 4 containing a chelating ortho-metalated azobenzene ligand on one of the ruthenium atoms in a opened square-pyramidal Ru5C cluster. Compound 4 is electronically unsaturated and it readily adds one CO ligand at 25 °C to yield the electronically saturated complex Ru5C(CO)14(C6H4N=NC6H5)[μ-H], 5. Ru5C(CO)13(μ-η2-Ph)[μ-Au(NHC)], 3 reacts with azobenzene to yield the azobenzene complex Ru5C(CO)13(μ−η2−PhN = NPh)(η1−Ph)[μ−Au(NHC)], 6, NHC = 1,3-bis(2,6-diisopropylphenyl-imidazole-2ylidene), which contains a novel bridging di-σ-η2-N,N-coordinated azobenzene ligand across an open edge of an Ru5C cluster. Compound 6 eliminated benzene and was transformed to the new compound Ru5C(CO)13(C6H4N=NC6H5)[μ−Au(NHC)], 7 when heated to 105 °C for 3 h. Compound 7 is similar to 4 except that it has an Au(NHC) group in the place of the bridging hydrido ligand in 4. Compound 7 is also formally electronically unsaturated like 4. All of the new compounds were characterized by single-crystal X-ray diffraction analyses. The structures, bonding and reactivity of the complexes are discussed.