Hydrostannylation of Olefins by a Hydridostannylene Tungsten Complex

Abstract

Reaction of the aryltin(II) hydride {Ar iPr6Sn(μ-H)}2 (Ar iPr6 = −C6H3-2,6-(C6H2-2,4,6- i Pr3)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(Ar iPr6)H}, (1). Complex 1 reacted rapidly with ethylene, or propylene under ambient conditions to yield the corresponding hydrostannylated organometallic species, W(CO)5{Sn(Ar iPr6)(Et)} (2), or W(CO)5{Sn(Ar iPr6)( n Pr)} (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(Ar iPr6)(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(Ar iPr6)}]+[H(dbu)]−, is 18.2 kcal/mol less stable than the observed coordination product 4.

Small molecule activation by well-defined compounds of heavy p-block elements

“…The ratedetermining step of this transformation is the Sn-C/Si-H bond metathesis (as suggested by DFT calculations) with an energy barrier of 71.3 kcal mol À1 explaining the low conversion. 48 The tin cluster 20, which has already been discussed in Section 2, also reacts with five equivalents of ethylene to form compound 38 (Scheme 14). Similar to the reaction with H 2 , this transformation is also accompanied by the elimination of the four tin atoms of compound 20, which do not bear an organic ligand.…”

“…The rate-determining step of this transformation is the Sn–C/Si–H bond metathesis (as suggested by DFT calculations) with an energy barrier of 71.3 kcal mol −1 explaining the low conversion. 48…”