Synthesis of carbazole by Ru3(CO)12-catalyzed reductive carbonylation of 2-nitrobiphenyl : the crystal and molecular structure of Ru3( 3-NC6H4-o-C6H5)2(CO)9

The Ru3(CO)12-catalyzed reductive carbonylation of 2-nitrobiphenyl 1 in acetonitrile gives carbazole 2 and 2-aminobiphenyl 3. Compound 3 is the major reaction product in tetrahydrofuran, toluene, toluene-methanol, thiophene and cis-cyclooctene. Some products deriving from intermolecular insertion into the solvent are also found with acetonitrile, thiophene and cis-cyclooctene. By reaction of 2-nitrosobiphenyl 7 with Ru3(CO)12, the nitrene complex Ru3(μ3-NC6H4-o-C6H5)2(CO)9 11 has been isolated and its crystal structure has been determined. Compound 11 is orthorhombic, space group P212121 with a = 11.160(4), b = 11.472(2), c = 25.478(6) Å, Z = 4, R = 0.019, Rw = 0.028, for 3161 independent reflections with I>3σ(I). The ortho-substituent phenyl ring of the nitrene ligands in compound 11 is free to rotate around the CC bond and thus can assume the proper arrangement to allow insertion of nitrogen into the aromatic CH bond to give carbazole 2. This possibility has been confirmed by treating 11 with CO (50 bar) at 220°C to obtain 2 and Ru3(CO)12