Stoichiometric and Catalytic Reactions Involving Si−H Bond Activations by Rh and Ir Complexes Containing a Pyridylindolide Ligand

Abstract

New rhodium and iridium complexes containing the bidentate, monoanionic 2-(2‘-pyridyl)indolide (PyInd) ligand were prepared. The bis(ethylene) complex (PyInd)Rh(C2H4)2 (3) reacted with triethylsilane at 60 °C to produce the 16-electron Rh(V) bis(silyl)dihydride complex (PyInd)RhH2(SiEt3)2 (4). Both 3 and 4 catalyzed the chloride transfer reaction of chlorobenzene and Et3SiH to give Et3SiCl and benzene in the absence of base. In the presence of LiNiPr2, catalytic C−Si coupling was observed, to produce Et3SiPh. Analogous Ir complexes of the type (PyInd)IrH2(SiR3)2, where R3 = Et3 (6a), Me2Ph (6b), Ph2Me (6c), or Ph3 (6d), were not catalytically active in this chloride transfer chemistry. The molecular structure of 6c, determined by X-ray crystallography, may be described as having a highly unusual bicapped tetrahedral geometry. DFT calculations indicate that this distortion is associated with the d4 electron count and the presence of highly trans-influencing silyl ligands. The reaction of 6a with PMe3 (5 equiv) produced (PyInd)IrH(SiEt3)(PMe3)2 (7), while the reaction with PPh3 (1 equiv) generated a mixture of isomers that was converted to (PyInd)IrH(SiEt3)(PPh3) (8) upon heating in benzene at 80 °C. Complexes 7 and 8 exhibit regular octahedral and distorted square pyramidal geometries, respectively.