The reactions of dialkylgallium hydrides with tert-butylethynylbenzenes—a systematic investigation into the course of hydrogallation reactions

Abstract

The reactions of bis- and tris(tert-butylethynyl)benzenes with dialkylgallium hydrides afforded two different types of products. 1,4-Di(tert-butylethynyl)benzene and dialkylgallium hydrides R₂GaH bearing relatively small substituents (R = Et, nPr) gave the expected addition products with each CC triple bond inserted into a Ga–H bond. The intact GaR₂ groups are attached to those carbon atoms which are in α-position to the benzene rings, and intermolecular Ga–C interactions led to the formation of one-dimensional coordination polymers. In contrast secondary reactions with the release of the corresponding trialkylgallium derivatives GaR₃ (R = Et, nPr, iPr, CH₂tBu, tBu) were observed for all hydrogallation reactions involving the trisalkyne 1,3,5-tris(tert-butylethynyl)benzene. A similar reaction was observed upon treatment of the 1,4-bisalkyne with a dialkylgallium hydride bearing a relatively bulky substituent (R = neopentyl). Cyclophane type molecules are formed in all these cases with two or three gallium atoms in the bridging positions between both benzene rings.