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

摘要

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 hydrositylation of vinyltris(trimethylsiloxy) si lane 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 degrees C) than the same system catalyzed by Karstedt-diallylmateate system (130 degrees 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. (c) 2006 Elsevier B.V. All rights reserved.