SYNTHESIS OF CARBAZOLE BY RU3(CO)12-CATALYZED REDUCTIVE CARBONYLATION OF 2-NITROBIPHENYL - THE CRYSTAL AND MOLECULAR-STRUCTURE OF RU3(MU-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(mu-3-NC6H4-o-C6H5)2(CO)9 11 has been isolated and its crystal structure has been determined. Compound 11 is orthorhombic, space group P2(1)2(1)2(1) with a = 11.160(4), b = 11.472(2), c = 25.478(6) angstrom, Z = 4, R = 0.019, R(w) = 0.028, for 3161 independent reflections with I > 3-sigma(I). The ortho-substituent phenyl ring of the nitrene ligands in compound 11 is free to rotate around the C-C bond and thus can assume the proper arrangement to allow insertion of nitrogen into the aromatic C-H bond to give carbazole 2. This possibility has been confirmed by treating 11 with CO (50 bar) at 220-degrees-C to obtain 2 and Ru3(CO)12.