Stability imparted by encumbering m-terphenyl isocyanide ligands has enabled isolation and structural characterization of several species relevant to the mechanism of alkyne hydrostannation, including an exceedingly rare example of MoI-alkyne thought to be intermediate in pre-catalyst activation. Activity of MoI2(CO)2(CNArDipp2)2 (Dipp = 2,6-diisopropylphenyl) in hydrostannation is unprecedented. At low loadings (0.1 – 2 mol%), complete conversion of most alkynes to the corresponding vinylstannane can be achieved in in less than fifteen minutes with excellent regioselectivity. Most notably, this system extends regioselectivity beyond previous examples which have shown high α-selectivity for alkynes featuring propargyl-substituted electron withdrawing groups. MoI2(CO)2(CNArDipp2)2 maintains α-selectivity for propargyl-substrates (80 – 93% α-), but gives the reverse β-substituted product with aryl-substituted alkynes(88 – 91% β-). Factors governing regioselectivity have been investigated. NMR and computational evidence suggest the catalyst’s well-defined coordination sphere modulates regiocontrol by exploiting minor electronic variations of the two alkynyl C-atoms.

Well-defined molybdenum isocyanide catalysts for regioselective hydrostannation

251st National Meeting (2016)

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