Activation of Ene-Diamido Samarium Methoxide with Hydrosilane for Selectively Catalytic Hydrosilylation of Alkenes and Polymerization of Styrene: an Experimental and Theoretical Mechanistic Study

Samarium methoxide
incorporating the ene-diamido ligand L­(DME)­Sm­(μ-OMe)2Sm­(DME)­L (1; L = [DipNC­(Me)­C­(Me)­NDip]2–, Dip = 2,6-iPr2C6H3, and DME = 1,2-dimethoxyethane) has been prepared and structurally
characterized. Complex 1 catalyzed the syndiospecific
polymerization of styrene upon activation with phenylsilane and regioselective
hydrosilylation of styrenes and nonactivated terminal alkenes. Unprecedented
regioselectivity (>99.0%) for both types of alkenes has been achieved
with the formation of Markovnikov and anti-Markovnikov products in
high yields, respectively, whereas the polymerization of styrene resulted
in the formation of syndiotactic silyl-capped oligostyrenes. The kinetic
experiments and density functional theory calculations strongly support
a samarium hydride intermediate generated by σ-bond metathesis
of the Sm–OMe bond in 1 with PhSiH3. In addition, the observed regioselectvity for hydrosilylation and
polymerization is consistent with the calculated energy profiles,
which suggests that the bulky ene-diamido ligand and samarium hydride
intermediate have important roles for regio- and stereoselectivity.