Iridium Oxidation States in Catalytic Hydrogenation Intermediates (original) (raw)

2014, Journal of the Brazilian Chemical Society

Os conhecidos hidretos de irídio(III) [IrH 2 (NCMe) 3 (PiPr 3)]BF 4 , [IrH(h 3-C 3 H 5)(NCMe) 2 (PiPr 3)] BF 4 , [IrH(E-CH=CHPh)(NCMe) 3 (PiPr 3)]BF 4 e [IrH{C(Ph)=CH 2 }(NCMe) 3 (PiPr 3)]BF 4 , derivados do precursor catalítico tipo Crabtree [Ir(cod)(NCMe)(PiPr 3)]BF 4 , foram investigados em reações com substratos tipicamente envolvidos na catálise homogênea de hidrogenação. Novos complexos como as espécies tris-etileno irídio(I) [Ir(NCMe)(h 2-C 2 H 4) 3 (PiPr 3)]BF 4 , os produtos de inserção de difenilacetileno [IrH{Z-C(Ph)=CHPh}(NCMe) 3 (PiPr 3)]BF 4 e [Ir(h 3-C 3 H 5){Z-C(Ph)=CHPh} (NCMe) 2 (PiPr 3)]BF 4 , e os derivados de [Ir(k 2 O-acac)(h 3-C 3 H 5){Z-C(Ph)=CHPh}(PiPr 3)] e [Ir{k 2 CC 6 H 4-2-E-(CH=CPh)}(NCMe) 3 (PiPr 3)]BF 4 , foram caracterizados. O conjunto de observações experimentais sugere que espécies irídio(I), embora acessíveis, são improváveis como intermediários de hidrogenação. Baseados em experimentos de deuteração, uma nova tautomerização do hidreto de alquenil a carbeno foi proposta. The known iridium(III) hydrides [IrH 2 (NCMe) 3 (PiPr 3)]BF 4 , [IrH(h 3-C 3 H 5)(NCMe) 2 (PiPr 3)] BF 4 , [IrH(E-CH=CHPh)(NCMe) 3 (PiPr 3)]BF 4 and [IrH{C(Ph)=CH 2 }(NCMe) 3 (PiPr 3)]BF 4 , derived from the Crabtree-type catalyst precursor [Ir(cod)(NCMe)(PiPr 3)]BF 4 , 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)(h 2-C 2 H 4) 3 (PiPr 3)]BF 4 , the products of diphenylacetylene insertion [IrH{Z-C(Ph)=CHPh}(NCMe) 3 (PiPr 3)]BF 4 and [Ir(h 3-C 3 H 5){Z-C(Ph)=CHPh}(NCMe) 2 (PiPr 3)]BF 4 , and the derivatives of the latter [Ir(k 2 O-acac) (h 3-C 3 H 5){Z-C(Ph)=CHPh}(PiPr 3)] and [Ir{k 2 CC 6 H 4-2-E-(CH=CPh)}(NCMe) 3 (PiPr 3)]BF 4 , 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.