Unexpected CO Dependencies, Catalyst Speciation, and Single Turnover Hydrogenolysis Studies of Hydroformylation via High Pressure NMR Spectroscopy.

Rhodium bis(diazaphospholane) (BDP) catalyzed hydroformylation of styrene is sensitive to CO concentration, and drastically different kinetic regimes are affected by modest changes in gas pressure. The Wisconsin High Pressure NMR Reactor (WiHP-NMRR) has enabled the observation of changes in catalyst speciation in these different regimes. The apparent discrepancy between catalyst speciation and product distribution led us to report the first direct, noncatalytic quantitative observation of hydrogenolysis of acyl dicarbonyls. Analysis and modeling of these experiments show that not all catalyst is shunted through the off-cycle intermediates and this contributes to the drastic mismatch in selectivities. The data herein highlight the complex kinetics of Rh(BDP) catalyzed hydroformylation. In this case, the complexity arises from competing kinetic and thermodynamic preferences involving formation and isomerization of the acyl mono- and dicarbonyl intermediates and their hydrogenolysis to give aldehydes.