BICAAC-Derived Covalent and Cationic Ir(I) Complexes: Application of Ir(BICAAC)Cl(COD) Complexes as Catalysts for Transfer Hydrogenation and Hydrosilylation Reactions

The ambiphilic bicyclic (alkyl)-(amino)-carbenes ((Me/iPr)BICAAC) upon reaction with [IrCl-(COD)]2 smoothly afford mononuclear Ir-(I) complexes that have been spectroscopically and structurally characterized. These complexes exhibit good catalytic activity for transfer hydrogenation (TH) of 4-chlorobenzaldehyde using isopropyl alcohol (iPrOH), with turnover frequency values ranging between 6269 and 8093 h(-1). Choosing the covalent complex Ir-((Me)BICAAC)-Cl-(COD) as a catalyst, a wide array of carbonyls and imines functionalized with electron-withdrawing and electron-donating substituents have been surveyed and afforded their reduced products in moderate-to-good yields. No detachment of the BICAAC unit from the Ir center was observed upon prolonged heating of Ir-((Me)BICAAC)-Cl-(COD) in toluene-d( 8 )or isopropyl alcohol-d( 8), which evidenced good thermal stability of the catalyst. Complex Ir-((Me)BICAAC)-Cl-(COD) was also found to be catalytically active for the hydrosilylation of a variety of aldehydes using triethylsilane (Et3SiH).