Hydrosilylation of Terminal Alkynes Catalyzed by a ONO-Pincer Iridium(III) Hydride Compound: Mechanistic Insights into the Hydrosilylation and Dehydrogenative Silylation Catalysis

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• 作者：Jesús J. Pérez-Torrente ; Duc Hanh Nguyen ; M. Victoria Jiménez ; F. Javier Modrego ; Raquel Puerta-Oteo ; Daniel Gómez-Bautista ; Manuel Iglesias ; Luis A. Oro
• 刊名：Organometallics
• 出版年：2016
• 出版时间：July 25, 2016
• 年：2016
• 卷：35
• 期：14
• 页码：2410-2422
• 全文大小：637K
• 年卷期：0
• ISSN：1520-6041

文摘

The catalytic activity in the hydrosilylation of terminal alkynes by the unsaturated hydrido iridium(III) compound [IrH(κ³-hqca)(coe)] (1), which contains the rigid asymmetrical dianionic ONO pincer ligand 8-oxidoquinoline-2-carboxylate, has been studied. A range of aliphatic and aromatic 1-alkynes has been efficiently reduced using various hydrosilanes. Hydrosilylation of the linear 1-alkynes hex-1-yne and oct-1-yne gives a good selectivity toward the β-(Z)-vinylsilane product, while for the bulkier t-Bu-C≡CH a reverse selectivity toward the β-(E)-vinylsilane and significant amounts of alkene, from a competitive dehydrogenative silylation, has been observed. Compound 1, unreactive toward silanes, reacts with a range of terminal alkynes RC≡CH, affording the unsaturated η¹-alkenyl complexes [Ir(κ³-hqca)(E-CH═CHR)(coe)] in good yield. These species are able to coordinate monodentate neutral ligands such as PPh₃ and pyridine, or CO in a reversible way, to yield octahedral derivatives. Further mechanistic aspects of the hydrosilylation process have been studied by DFT calculations. The catalytic cycle passes through Ir(III) species with an iridacyclopropene (η²-vinylsilane) complex as the key intermediate. It has been found that this species may lead both to the dehydrogenative silylation products, via a β-elimination process, and to a hydrosilylation cycle. The β-elimination path has a higher activation energy than hydrosilylation. On the other hand, the selectivity to the vinylsilane hydrosilylation products can be accounted for by the different activation energies involved in the attack of a silane molecule at two different faces of the iridacyclopropene ring to give η¹-vinylsilane complexes with either an E or Z configuration. Finally, proton transfer from a η²-silane to a η¹-vinylsilane ligand results in the formation of the corresponding β-(Z)- and β-(E)-vinylsilane isomers, respectively.