Pd-catalysed reactions of alkynes with model distannanes and poly[di-(n-butyl)]stannane

Abstract

A reinvestigation of Pd-catalysed alkyne (R′–CCH; R′ = H, Ph) insertion chemistry involving R₃SnSnR₃ (3a: R = Me; 3b: R = n-Bu) was undertaken. Model distannyl ethylenes 4a–b (Me₃SnCHCR′SnMe₃) and 5a–b ((n-Bu)₃SnCHCR′Sn(n-Bu)₃) were reproduced and further characterized by NMR (¹¹⁹Sn, ¹³C, ¹H) and UV-Vis spectroscopy. In the presence of an excess of phenylacetylene, dimerization–carbostannylation of compound 4b yielded the new conjugated butadiene, (Z,Z)-1,4-bis(trimethylstannyl)-1,4-diphenyl-buta-1,3-diene (9). An X-ray structure determination of 9 reveals a symmetrical double-bond Z confirmation. Compound 9 was further characterized by NMR, UV-Vis spectroscopy, and MS. A DFT analysis of model compounds (4a–b, 5a–b, 9) and the experimental and theoretical λ_max values from the UV-Vis spectra were also compared. Acetylene and phenylacetylene Pd-catalysed insertion into the backbone of poly[di-(n-butyl)]stannane 12 resulted in new, modest molecular weight, partially inserted alkene tin polymers (13a–b) that were also characterized by GPC, NMR, UV-Vis spectroscopy and elemental analysis.