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

• Published in: Polyhedron Vol. 196; p. 115006
• Main Authors: Mangan, Robert J., Davies, Alexander R., Hicks, Jamie, Sindlinger, Christian P., Thompson, Amber L., Aldridge, Simon
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.03.2021
• Subjects: Bond activation; Cation; Germanium; Low valent; N-Heterocyclic carbene; Germanium; Cation; Low valent; Bond activation; N-Heterocyclic carbene
• ISSN: 0277-5387
• DOI: 10.1016/j.poly.2020.115006

The first examples of isolable terphenyl-substituted germylium-ylidenes, [(NHC)(Ar)Ge]+, are reported. These are shown to be either mono- or dimeric in the solid state depending on the bulk of the aryl and NHC substituents. In the case of dinuclear systems, the ability to act as a functional source of the monomer can demonstrated through the activation of PhSiH3 via Si–H oxidative addition. [Display omitted] •The first examples of isolable structurally characterized terphenyl-substituted germylium-ylidenes are reported.•Degree of aggregation of [(NHC)(Ar)Ge]+ unit in the solid state is shown to be dependent on combined steric bulk of NHC and Ar substituents.•Monomeric germylium-ylidene cations [(IMe4)(ArTrip)Ge]+, [(IPrMe)(ArMes)Ge]+, and [(IPrMe)(ArTrip)Ge]+ are shown to be stabilized in the solid state to varying degrees by secondary interactions with the peripheral arene πi systems or CH bonds.•Dication [(IMe4)(ArMes)Ge=Ge(ArMes)(IMe4)]2+, is shown to act as an functional source of the corresponding monomeric germylium-ylidene, [(IMe4)(ArMes)Ge]+, in its reaction with PhSiH3 which generates the monomeric GeIV species [(IMe4)(ArMes)Ge(H)(SiH2Ph)]+ via Si–H oxidative addition at germanium. 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 (ArMes, ArTrip; 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 ArMes) results in the formation of a dicationic dimer, [(IMe4)(ArMes)Ge=Ge(ArMes)(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)(ArTrip)Ge]+, [(IPrMe)(ArMes)Ge]+, and [(IPrMe)(ArTrip)Ge]+, stabilized in the solid state to varying degrees by secondary interactions with the peripheral arene π 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)°, respectively) as the steric profiles of the germanium-bound substituents increase. In the case of dication [(IMe4)(ArMes)Ge=Ge(ArMes)(IMe4)]2+, its ability to act as a functional source of the corresponding monomeric germylium-ylidene, [(IMe4)(ArMes)Ge]+, is demonstrated through its reaction with PhSiH3 in bromobenzene solution, which generates the monomeric GeIV species [(IMe4)(ArMes)Ge(H)(SiH2Ph)]+ via Si–H oxidative addition at germanium.