Iridium Oxidation States in Catalytic Hydrogenation Intermediates

• Autor(a) principal: Navarro,Janeth
• Data de Publicação: 2014
• Outros Autores: Martín,Marta, Sola,Eduardo
• Tipo de documento: Artigo
• Idioma: eng
• Título da fonte: Journal of the Brazilian Chemical Society (Online)
• Texto Completo: http://old.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532014001202314
• topic: homogeneous catalysis; hydrogenation; iridium catalysts; mechanism

The known iridium(III) hydrides [IrH2(NCMe)3(PiPr3)]BF4, [IrH(h3-C3H5)(NCMe)2(PiPr3)]BF4, [IrH(E-CH=CHPh)(NCMe)3(PiPr3)]BF4 and [IrH{C(Ph)=CH2}(NCMe)3(PiPr3)]BF4, derived from the Crabtree-type catalyst precursor [Ir(cod)(NCMe)(PiPr3)]BF4, have been investigated in reactions with substrates typically involved in homogeneous catalytic hydrogenations. New complexes such as the iridium(I) tris-ethylene species [Ir(NCMe)(h2-C2H4)3(PiPr3)]BF4, the products of diphenylacetylene insertion [IrH{Z-C(Ph)=CHPh}(NCMe)3(PiPr3)]BF4 and [Ir(η3-C3H5){Z-C(Ph)=CHPh}(NCMe)2(PiPr3)]BF4, and the derivatives of the latter [Ir(k2O-acac)(η3-C3H5){Z-C(Ph)=CHPh}(PiPr3)] and [Ir{k2C-C6H4-2-E-(CH=CPh)}(NCMe)3(PiPr3)]BF4, have been characterized. The set of experimental observations suggests that iridium(I) species, though accessible, are unlikely hydrogenation intermediates. On the basis of deuteration experiments, a new hydride-alkenyl to carbene tautomerization is proposed.