Hydrostannylation of Olefins by a Hydridostannylene Tungsten Complex

Abstract

Reaction of the aryltin(II) hydride {AriPr6Sn(μ-H)}2 (AriPr6 = −C6H3-2,6-(C6H2-2,4,6-iPr3)2) with two equivalents of the tungsten carbonyl THF complex, [W(CO)5(THF)], afforded the divalent tin hydride transition metal complex, W(CO)5{Sn(AriPr6)H}, (1). Complex 1 reacted rapidly with ethylene, or propylene under ambient conditions to yield the corresponding hydrostannylated organometallic species, W(CO)5{Sn(AriPr6)(Et)} (2), or W(CO)5{Sn(AriPr6)(nPr)} (3), via olefin insertion into the Sn–H bond. Treatment of 1 with the Lewis base dbu (dbu = 1,8-diazabicycloundec-7-ene) afforded the Lewis acid–base complex, W(CO)5{Sn(AriPr6)(dbu)H} (4), indicating that the Lewis acidity of the tin atom is preserved in 4. The complexes were characterized by X-ray crystallography, and by UV–visible, FT-IR, and multinuclear NMR spectroscopies. DFT calculations suggest hydrostannylation of ethylene with 1 proceeds via coordination of ethylene to the tin atom, then insertion into the Sn–H bond. Further computational study on the reactivity of 1 toward Ph3SiH indicated that the rate-determining step involves the metathesis reaction of a Sn–C/Si–H bond with a very high energy barrier of 71.3 kcal/mol. The calculated proton abstraction product of 1 with dbu, [W(CO)5{Sn(AriPr6)}]+[H(dbu)]−, is 18.2 kcal/mol less stable than the observed coordination product 4.