Catalytic activity of iridium siloxide complexes in cross-linking of silicones by hydrosilylation Original Research Article

A series of catalytic examinations have shown that monomeric iridium siloxides ([Ir(cod)(PCy3)(OSiMe3)] (II), [Ir(CO)(PPh3)2(OSiMe3)] (III) and [Ir(CO)(PCy3)2(OSiMe3)] (IV)) are effective catalysts for model homogeneous hydrosilylation of vinyltris(trimethylsiloxy)silane as well as cross-linking of commercial polysiloxane system. The results of stoichiometric reactions of iridium siloxide with heptamethyltrisiloxane and observed catalytic properties are consistent with the mechanism of catalysis involving a generation of the key-intermediate (16e tetracoordinate Ir–H complex) responsible for the catalytic cycle. Experiments allowed explaining the effect of oxygen on the catalytic activity of phosphine-containing iridium siloxide complexes. The curing process of polysiloxanes catalyzed by iridium siloxide II and IV complexes occurs at a higher temperature (about 200 °C) than the same system catalyzed by Karstedt—diallylmaleate system (130 °C). The enthalpies of the reaction are comparable (−30 to −38 kJ/mol) for both catalysts but the inhibitor is not required for the iridium-catalyzed process.