C−H activation: Rh-phosphine complexes can activate C−H bonds in otherwise unreactive alkanes. Quantum chemical calculations provide mechanistic insights into the generation of the active species which is formed via the light-induced CO dissociation at Rh(I) complexes featuring trimethylphosphine and 1,2-bis(dimethylphosphino)ethane. The calculations align well with experimental photochemical studies on the Rh(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 in combination with multireference wavefunction-based methods. We have identified that the photocleavage of CO proceeds via the metal-centered excited state (³MC, ), which is populated through intersystem crossing 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.