Disentangling Norrish-type and Rh Catalysed Decomposition of Aldehydes for the Use as CO Donors

Abstract

This study presents a detailed mechanistic investigation of the photocatalytic decomposition of different aldehydes via various Norrish reaction pathways and their subsequent role in the carbonylation of hydrocarbons, particularly toluene, using [Rh(PMe3)2 (Cl)(CO)] as a catalyst. Utilizing 1H NMR spectroscopy, we quantitatively analysed the kinetics of the reaction network, focusing on the formation of key products such as alkanes and alkenes. The results reveal multiple well-explainable structure-property relationships for different aldehyde structures. In addition, the presence of [Rh(PMe3)2(Cl)(CO)] significantly dampens the decomposition rates, suggesting an intersystem crossing between photoactivated aldehydes and the Rh complex, potentially lowering the aldehyde's excited state lifetime. Furthermore, we explored the structural characterization of Rh-phosphine complexes formed during the reaction, though the exact structures remain elusive.