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(CH 2 Py) 2 }] 2 ( 1 ). The use of bulky bis[bis(trimethylsilyl)methyl]zinc gives the amine adduct [{(Me 3 Si) 2 CHZn}(C≡CPh){HN(CH 2 Py) 2 }] ( 2 ). Treatment of 2 with another equivalent of bis[bis(trimethylsilyl)methyl]zinc yields dinuclear [{(Me 3 Si) 2 CHZn} 2 (μ-C≡CPh){μ-N(CH 2 Py) 2 }] ( 3 ), which possesses a central four-membered Zn 2 NC ring. Alternatively, 3 is accessible by conversion of the hydride [{(Me 3 Si) 2 CHZn} 2 (μ-H){μ-N(CH 2 Py) 2 }] ( 4 ) with phenylacetylene. The addition reaction of 3 with benzaldehyde gives the corresponding alkoxide [{(Me 3 Si) 2 CHZn} 2 {μ-OCH(C≡CPh)Ph}{μ-N(CH 2 Py) 2 }] ( 5 ). The complexes 1 − 3 and 5 were characterized in solution by NMR spectroscopy (C 6 D 6 ) 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.