Synthesis of Dinuclear Zinc Alkynyls and Their Use in Catalytic Silicon−Carbon Bond Formation

Abstract

Zincation of bis(2-pyridylmethyl)amine (dipicolylamine) and phenylacetylene with dimethylzinc yields dimeric [(PhC≡CZn){μ-N(CH2Py)2}]2 (1). The use of bulky bis[bis(trimethylsilyl)methyl]zinc gives the amine adduct [{(Me3Si)2CHZn}(C≡CPh){HN(CH2Py)2}] (2). Treatment of 2 with another equivalent of bis[bis(trimethylsilyl)methyl]zinc yields dinuclear [{(Me3Si)2CHZn}2(μ-C≡CPh){μ-N(CH2Py)2}] (3), which possesses a central four-membered Zn2NC ring. Alternatively, 3 is accessible by conversion of the hydride [{(Me3Si)2CHZn}2(μ-H){μ-N(CH2Py)2}] (4) with phenylacetylene. The addition reaction of 3 with benzaldehyde gives the corresponding alkoxide [{(Me3Si)2CHZn}2{μ-OCH(C≡CPh)Ph}{μ-N(CH2Py)2}] (5). The complexes 1−3 and 5 were characterized in solution by NMR spectroscopy (C6D6) and in the solid state by single-crystal X-ray analysis. The electronic structure of complex 3 was examined by DFT methods. The phenylacetylide 3 and the hydride 4 were found to be the key intermediates in the two-step catalytic process of cross-dehydrocoupling of aryl silanes with phenylacetylene, also supported by NMR spectroscopic studies. Phenylsilane reacts with phenylacetylene to afford mono-, di-, and trialkynylphenylsilane. The reaction of diphenylsilane and phenylacetylene mainly leads to diphenyl(phenylethynyl)silane (7), which was isolated in good yields.