Bridge functionalized bis-N-heterocyclic carbene rhodium(I) complexes and their application in catalytic hydrosilylation

Symmetrically bridged bis-N-heterocyclic carbene rhodium (I) complexes and their catalytic application for transfer hydrogenation reaction

“…[M(bis-carbene)I 2 (OAc)], with a t Bu group [32]. However, following our previous method [38] we synthesized the rhodium(I) complexes with t Bu wingtip groups, which also show activity in the transfer hydrogenation. Likewise Reaction conditions: S/C/B ¼ 100: 1: 10 with 1 mmol of acetophenone and 0.01 mmol of KOH in 10 mL of i-PrOH at 80 ; yields determined by GC.…”

“…Likewise Reaction conditions: S/C/B ¼ 100: 1: 10 with 1 mmol of acetophenone and 0.01 mmol of KOH in 10 mL of i-PrOH at 80 ; yields determined by GC. Reaction conditions of 3c: S/C/B ¼ 100: 0.5: 10. the previously published complexes 1c, 3c and 5c [38] the new rhodium complexes 2c and 4c are synthesized by the same method shown in Scheme 3 [38]. The rhodium precursor [Rh(COD)OEt] 2 was prepared in situ from [Rh(COD)Cl] 2 by reaction with sodium hydride at room temperature under an argon atmosphere.…”

“…The bromine salts 1ae5a were dissolved in a minimum amount of water and added to a saturated solution of KPF 6 in water [38]. The precipitated imidazolium hexafluorophosphate salts were filtered off, washed with water and diethyl ether and dried under vacuum yielding the imidazolium salts 1be5b.…”

“…Peris and co-workers demonstrated that rhodium(III) and iridium(III) complexes of achiral chelating bis(carbene) ligands are promising catalysts for the transfer hydrogenation of ketones using 2-propanol as hydrogen source and various amounts of KOH as co-catalyst [18]. Our group has recently reported a series of palladium [37] and rhodium [38] complexes, ligated with bridged bisimidazolium based ligands with a functional OH-group attached to the bridging moiety. These air-stable complexes are easy to synthesize and have been successfully employed as catalysts for Suzuki coupling and hydrosilylation [38].…”

“…Our group has recently reported a series of palladium [37] and rhodium [38] complexes, ligated with bridged bisimidazolium based ligands with a functional OH-group attached to the bridging moiety. These air-stable complexes are easy to synthesize and have been successfully employed as catalysts for Suzuki coupling and hydrosilylation [38]. In this work it is shown that such compounds can also be applied as catalysts for transfer hydrogenation.…”