Synthesis and Structure of Cyclotrigermenium Salts of Tetrakis{3,5‐bis(trifluoromethyl)phenyl}borate, Tetrakis(pentafluorophenyl)borate and Tetrakis{4‐[tert‐butyl(dimethyl)silyl]‐2,3,5,6‐tetrafluorophenyl}borate: A Stable Free Germyl Cation in the Condensed Phase

Abstract

The reaction of tetrakis(tri-tert-butylsilyl)cyclotrigermene (1a) with Ph3C+[3,5-(CF3)2C6H3]4B− (TFPB−), Ph3C+(C6F5)4B− (TPFPB−), and Ph3C+[4-(tBuMe2Si)C6F4]4B− (TSFPB−) in benzene produced the stable free tris(tri-tert-butylsilyl)cyclotrigermenium ion (2a+) with the corresponding tetraarylborate as the counterion. The crystal structures of 2a+TFPB− and 2a+TSFPB− reveal a free germyl cation with a two π-electron system. The three-membered ring of germanium atoms constitutes an almost equilateral triangle. The cyclotrigermenium tetraarylborates, 2a+TFPB−, 2a+TPFPB−, and 2a+TSFPB−, are stable in solution. The spectroscopic data show that 2a+ is a free germyl cation, does not coordinate to either the solvent molecules (dichloromethane, chloroform, toluene, or diethyl ether) or the counter anions (TFPB−, TPFPB−, or TSFPB−). The tris(tri-tert-butylgermyl)cyclotrigermenium ion (2b+) was also characterized.