Synthesis and X-ray structures of cyclorhodated indole-tert-thiocarboxamides

Indole-1(and 3)-N,N-dimethylthiocarboxamide, 3-(1-pyrrolidinothiocarbonyl) indole and -1-methylindole (HL) react with hexachlorotetrakis(tri-n-butylphosphine) dirhodium(III) to give cyclorhodated complexes, [Rh(L) Cl-2(PBu3)(2)] with L acting as a C-S chelate ligand (PBu3 = tri-n-butylphosphine) and indole-2-N,N-dimethylthiocarboxamide forms [Rh(L) Cl-2(PBu3)(2)] with L acting as an N-S chelate. 1-Methylindole-2-N,N-dimethylthiocarboxamide and 2-(1-pyrrolidinothiocarbonyl)-1-methylindole did, however, not react under similar conditions. The complexes were characterized by spectroscopic methods and the structures of the four complexes with HL = indole-1- and 3-N, N-dimethylthiocarboxamide, and 3-(1-pyrrolidinothiocarbonyl) indole and -1-methylindole were confirmed by X-ray analysis. The octahedral complex [Rh(L) Cl-2(PBu3)(2)] had trans-(PBu3)(2) and cis-(Cl)(2) arrangements and L was coordinated through the S and indole ring C2 atoms to form a five-membered chelate ring. The unreactivity of 1-methylindole-2-N, N-dimethylthiocarboxamide and 2-(1-pyrrolidino) thiocarbonyl-1-methylindole may be due to steric hindrance caused by the additional 1-methyl substituent.