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 sp ²-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 five-and 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 γ-methylene-γ-butyrolactone. A dinuclear Rh(I) complex was the most active catalyst, demonstrating a significant degree of bimetallic cooperativity.