Reactive Indolyl Complexes of Group 9 Metals

A series of novel indolyl-imine ligand precursors have been synthesized. In particular, bidentate, tridentate, and potentially tetradentate ligands were prepared, each containing both indolyl sp2-N and imine sp2-N donors. A series of neutral rhodium(I) and iridium(I) complexes of these ligands were synthesized, including monometallic and bimetallic complexes. The X-ray structures of three of the monometallic complexes with bidentate indolyl-imine ligands were determined. In each complex, the metal center was in a square planar conformation, as expected for Rh(I) and Ir(I) complexes. The fiveand six-membered metallocycles formed on complexation of the metal with the ligands were all planar, and the aromaticity of the ligands was maintained. The Rh(I) complex with the tridentate indolyl ligand (L) reacted at room temperature with CH2Cl2 to form the Rh(III) chloromethyl complex [Rh(L)(CO)-(CH2Cl)(Cl)] via oxidative addition of the C-Cl bond of CH2Cl2. The Rh/Ir(I) indolyl-imine complexes are efficient catalysts for the intramolecular cyclization of 4-pentynoic acid to form c-methylene-c-butyrolactone. A dinuclear Rh(I) complex was the most active catalyst, demonstrating a significant degree of bimetallic cooperativity.