Rate-Limiting Spin Crossover and Cp Ligand Involvement During Ir(III) Retro-Hydroformylation Catalysis

While catalytic hydroformylation is a well-establishedreaction,there are only a few reports of homogeneous catalyzed retro-hydroformylationwhere carbon monoxide and dihydrogen are eliminated from an aldehydeto generate an olefin. Our in-depth assessment of reaction pathwaysusing density functional theory and metadynamics calculations foraldehyde retro-hydroformylation by cyclopentadienyl phosphine-typeIr(III) catalysts has revealed two surprising and uniqueaspects of catalysis: (1) Catalytic cycle turnover is determined bythe rate of singlet-triplet spin state crossover; and (2) during catalysis,after C-H bond activation, a transient Ir-III-Hintermediate undergoes intramolecular proton transfer to give a dearomatized & eta;(4)-Cp-H diene ligand. This Ir-I intermediateprovides the key coordination unsaturation to enable decarbonylationand & beta;-hydride elimination reaction steps. Overall, these mechanisticinsights set the stage for the design of novel retro-hydroformylationmolecular catalysts.

Automated summary

Through density functional theory and metadynamics calculations, our study on the aldehyde retro-hydroformylation pathway using cyclopentadienyl phosphine-type Ir(III) catalysts has revealed two surprising and unique aspects of catalysis: (1) The turnover of the catalytic cycle is determined by the rate of singlet-triplet spin state crossover; and (2) During catalysis, after C-H bond activation, a transient Ir-III-H intermediate undergoes intramolecular proton transfer to give a dearomatized η(4)-Cp-H diene ligand. These mechanistic insights provide a foundation for the design of novel retro-hydroformylation molecular catalysts.