Synthesis and reaction chemistry of boryliridium hydride complexes formed by oxidative addition of catecholborane to iridium(I): Lessons for metal-catalyzed hydroboration

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• 作者：Joseph S. Merola ; Joseph R. Knorr
• 关键词：Iridium ; Hydroboration ; Alkyne insertion ; Catecholborane ; Catalysis ; Vinyl borane
• 刊名：Journal of Organometallic Chemistry
• 出版年：15 January, 2014
• 年：2014
• 卷：750
• 期：Complete
• 页码：86-97
• 全文大小：1227 K

文摘

The mechanism of catalytic hydroboration was studied through the use of an iridium model complex. Oxidative addition of the B-H bond in (1,2-phenylenedioxy)borane (catecholborane) to (Me₃P)₃Ir(COE)(Cl) (COE聽=聽cyclooctene) produces mer-(Me₃P)₃Ir(Cl)(H)(BO₂C₆H₄) (1). Compound 1 reacted with alkynes to form vinyliridium complexes and will catalyze the hydroboration of alkynes with (1,2-phenylenedioxy)borane. The mechanism of catalytic hydroboration of acetylenes with catecholborane involves: oxidative addition of the B-H bond to the iridium center, followed by chloride dissociation and acetylene coordination, migratory-insertion into the Ir-H bond to form the metallo-vinyl complex, and finally reductive elimination to produce trans-alkylvinylboronate esters.

A stable metallo-vinyl complex was produced in the reaction of 1 with dimethylacetylene dicarboxylate and displayed two isomers in solution, one of which showed fluxional behavior. Single crystal X-ray diffraction elucidated a single solid-state structure, but the structures of the isomers in solution and the fluxional properties were studied with NMR spectroscopy and DFT calculations.