title: Selective sp3 C-H activation of ketones at the beta position by Ir(I). Origin of regioselectivity and water effect.
abstract: The reaction of the cationic (PNP)Ir(I)(cyclooctene) complex (1) (PNP = 2,6-bis-(di-tert-butylphosphinomethyl)pyridine) with 2-butanone or 3-pentanone results in the selective, quantitative activation of a beta C-H bond, yielding O,C-chelated complexes. Calculations show that the selectivity is both kinetically (because of steric reasons in the rate determingin step (RDS)) and thermodynamically controlled, the latter as a result of carbonyl oxygen coordination in the product. The RDS is formation of the eta2-C,H intermediates from the complexed ketone intermediates. Water has a strong influence on the regioselectivity, and in its presence, reaction of 1 with 2-butanone gives also the alpha terminal C-H activation product. Computational studies suggest that water can stabilize the terminal alpha C-H activation product by hydrogen bonding, forming a six-membered ring with the ketone, as experimentally observed in the X-ray structure of the acetonyl hydride aqua complex.
authors.affiliation: Departments of Organic Chemistry and Chemical Services, The Weizmann Institute of Science, Rehovot, 76100, Israel.
authors.forename: Moran
authors.initials: M
authors.lastname: Feller
authors.forename: Amir
authors.initials: A
authors.lastname: Karton
authors.forename: Gregory
authors.initials: G
authors.lastname: Leitus
authors.forename: Jan M L
authors.initials: JM
authors.lastname: Martin
authors.forename: David
authors.initials: D
authors.lastname: Milstein