Synthesis, characterization and reactivity of tribenzylphosphine rhodium and iridium complexes

New rhodium and iridium complexes, with the formula [MCl(PBz3)(cod)] [M = Rh (1), Ir (2)] and [M(PBz3)2(cod)]PF6 [M = Rh (3), Ir (4)] (cod = 1,5-cyclooctadiene), stabilized by the tribenzylphosphine ligand (PBz3) were synthesized and characterized by elemental analysis and spectroscopic methods. The molecular structures of 1 and 2 were determined by single-crystal X-ray diffraction. The addition of pyridine to a methanol solution of 1or 2, followed by metathetical reaction with NH4PF6, gave the corresponding derivatives [M(py)(PBz3)(cod)]PF6 [M = Rh (5), Ir (6)]. At room temperature in CHCl3 solution, 4 converted spontaneously to the ortho-metallated complex [IrH(PBz3)(cod){η2-P,C-(C6H4CH2)PBz2}]PF6 (7) as a mixture of cis/trans isomers via intramolecular C–H activation of a benzylic phenyl ring. The reaction of 3 or 4 with hydrogen in coordinating solvents gave the dihydrido bis(solvento) derivative [M(H)2(S)2(PBz3)2]PF6 (M = Rh, Ir; S = acetone, acetonitrile, THF), that transformed into the corresponding dicarbonyls [M(H)2(CO)2(PBz3)2]PF6 by treatment with CO. Analogous cis-dihydrido complexes [M(H)2(THF)2(py)(PBz3)2]PF6 (M = Rh, Ir) were observed by reaction of the py derivatives 5 and 6 with H2.

Graphical abstractNew neutral and cationic rhodium and iridium complexes containing one or two molecules of tribenzylphosphine have been synthesized and fully characterized. The bis(tribenzylphosphine)iridium derivative 4 converts in solution to ortho-metallated cis-[IrH(PBz3)(cod){η2-P,C-(C6H4CH2)PBz2}]PF6 that transforms into the thermodynamic trans-isomer already at room temperature.Figure optionsDownload full-size imageDownload as PowerPoint slide