Computational Modelling and Mechanistic Insight into Light‐Driven CO Dissociation of Square‐Planar Rhodium(I) Complexes

Abstract

The activation step of Vaska‐type Rh(I) complexes, such as the photocleavage of the Rh‑CO bond, plays an important role in the subsequent C‐H activation. To elucidate the details of the photochemistry of Vaska‐type Rh(I) complexes, such as trans‐Rh(PMe3)2(CO)(Cl), we here present a computationally derived picture as obtained at the density functional level of theory (DFT) in combination with multireference wavefunction‐based methods. We have identified that the photocleavage of CO proceeds via the metal‐centered excited state, which is populated through intersystem crossing (ISC) from the dipole‐allowed excited state S1. Moreover, the present study unraveled the reasons for the low C‐H activation efficiency when using Rh featuring the bidentate ligand 1,2‐bis(dimethylphosphino)ethane (dmpe), namely due to its unfavorable photochemical properties, i.e., the small driving force for light‐induced CO loss and the fast deactivation of 3MC state back to the singlet ground state. In this study, we provide theoretical insight into mechanistic details underlying the light‐induced CO dissociation process, for Rh complexes featuring PMe3 and dmpe ligands.