Theoretical investigation on possible mechanisms on regioselective formation of (η-siloxyallyl)tungsten complexes |
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Authors: | Siwei Bi Yuxia Liu Guang Chen Lisheng Zhang Min Sun Ping Li |
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Institution: | aSchool of Chemistry and Chemical Engineering, Qufu Normal University, 57 Jingxuan West Road, Qufu, Shandong 273165, PR China |
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Abstract: | Selective formation of (η3-siloxyallyl)tungsten complexes by reaction of hydrido(hydrosilylene)tungsten complexes with α,β-unsaturated carbonyl compounds was reported experimentally. The mechanisms have been investigated by employing the model reaction of Cp(CO)2(H)W Si(H)–{C(SiH3)3}] (R), derived from the original experimental complex Cp′(CO)2(H)W Si(H)–C(SiMe3)3] (1a, Cp′ = Cp*; 1b, Cp′ = η5-C5Me4Et), with methyl vinyl ketone, under the aid of the density functional calculations at the b3lyp level of theory. It is theoretically predicted that the route involving migration of the hydride to silicon to afford a 16e intermediate Cp(CO)2W–SiH2–{C(SiH3)3}] is inaccessible (route 2), supporting the proposition by experiments. Another route, via 2 + 4] cycloaddition followed by directly Si–H reductive elimination, is theoretically predicted to be accessible (route 1). In route 1, two possible paths with different attacking directions of the oxygen of methyl vinyl ketone at Si (W Si) are put forward. The attack at the Si atom from the hydride (H1) side of the plane W–Si–H1 in R is found to be preferred kinetically. The regioselectivity for formation of (η3-siloxyallyl)tungsten complexes, where only the exo-anti isomer was obtained, is discussed based on the consideration of thermodynamics and kinetics. |
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Keywords: | Transition-metal silylene complexes [2  +  4] cycloaddition η 3-Siloxyallyl complexes Regioselectivity |
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