Molecular Zinc Hydride Cations [ZnH]<sup>+</sup>: Synthesis, Structure, and CO<sub>2</sub> Hydrosilylation Catalysis
Florian Ritter, Thomas P. Spaniol, Iskander Douair, Laurent Maron, Jun Okuda
Abstract
Abstract Protonolysis of [ZnH 2 ] n with the conjugated Brønsted acid of the bidentate diamine TMEDA ( N , N , N′,N′ ‐tetramethylethane‐1,2‐diamine) and TEEDA ( N , N , N′ , N′ ‐tetraethylethane‐1,2‐diamine) gave the zinc hydride cation [(L 2 )ZnH] + , isolable either as the mononuclear THF adduct [(L 2 )ZnH(thf)] + [BAr F 4 ] − (L 2 =TMEDA; BAr F 4 − =[B(3,5‐(CF 3 ) 2 ‐C 6 H 3 ) 4 ] − ) or as the dimer [{(L 2 )Zn)} 2 (μ‐H) 2 ] 2+ [BAr F 4 ] − 2 (L 2 =TEEDA). In contrast to [ZnH 2 ] n , the cationic zinc hydrides are thermally stable and soluble in THF. [(L 2 )ZnH] + was also shown to form di‐ and trinuclear adducts of the elusive neutral [(L 2 )ZnH 2 ]. All hydride‐containing cations readily inserted CO 2 to give the corresponding formate complexes. [(TMEDA)ZnH] + [BAr F 4 ] − catalyzed the hydrosilylation of CO 2 with tertiary hydrosilanes to give stepwise formoxy silane, methyl formate, and methoxy silane. The unexpected formation of methyl formate was shown to result from the zinc‐catalyzed transesterification of methoxy silane with formoxy silane, which was eventually converted into methoxy silane as well.