Synthesis, structure and reactivity of terphenyl-substituted germylium-ylidene cations

The first examples of isolable two-coordinate terphenyl-substituted germylium-ylidenes are reported. These systems, of composition [(NHC)(Ar)Ge](+), exploit a range of aryl and NHC substituents (Ar-Mes, Ar-Trip; IMe4, IPrMe) and are isolated by employing weakly coordinating borate or aluminate counter-ions. The use of the smallest combination of substituents used in this study (IMe4 and Ar-Mes) results in the formation of a dicationic dimer, [(IMe4)(Ar-Mes)Ge=Ge(Ar-Mes)(IMe4)](2+), which can also be viewed as an imidazolium-functionalized digermene. Increasing the steric loading (at either the NHC or terphenyl ligand) leads to the formation of the monomeric germylium-ylidene cations [(IMe4)(Ar-Trip)Ge](+), [(IPrMe)(Ar-Mes)Ge](+), and [(IPrMe)(Ar-Trip)Ge](+), stabilized in the solid state to varying degrees by secondary interactions with the peripheral arene TC systems or C-H bonds. These three systems are characterized by widening C-Ge-C angles (101.7(1), 105.0(2) and 107.2(1)degrees, respectively) as the steric profiles of the germanium-bound substituents increase. In the case of dication [(IMe4)(Ar-Mes)Ge=Ge(Ar-Mes)(IMe4)](2+), its ability to act as a functional source of the corresponding monomeric germylium-ylidene, [(IMe4)(Ar-Mes)Ge](+), is demonstrated through its reaction with PhSiH3 in bromobenzene solution, which generates the monomeric Ge-IV species [(IMe4)(Ar-Mes)Ge(H)(SiH2Ph)](+) via Si-H oxidative addition at germanium. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

This study reported isolable two-coordinate terphenyl-substituted germylium-ylidenes, which are stabilized in the solid state by exploiting the field effects of different ligands and secondary interactions. The research expands our understanding of these systems by demonstrating the ability to stabilize monomeric germylium-ylidene cations through these methods.