Facial vs. Meridional Coordination Modes in Re I Tricarbonyl Complexes with a Carbodiphosphorane‐based Tridentate Ligand

The reactivity of the novel cationic ligand precursor [(dppm) 2 CH](PF 6 ) ( 1 ) with a weakly coordinating anion and [ReBr(CO) 5 ] is reported. The initial coordination results in the formation of the facially coordinated dicationic complex fac‐ [({dppm} 2 CH)Re(CO) 3 ]X 2 ( fac‐ 2 , X=Br, PF 6 ). The facial coordination mode is retained in fac‐ [({dppm} 2 C)Re(CO) 3 ](PF 6 ) ( fac‐ 3 ) upon deprotonation of the central cationic donor group. Quantum chemical investigations indicate that for both complexes, 2 and 3 , the meridional coordination mode is thermodynamically favored. In line with these findings, the isomerization of the facially coordinated complex fac‐ 3 to the meridionally coordinated complex mer‐ [({dppm} 2 C)Re(CO) 3 ](PF 6 ) ( mer‐ 3 ) is observed under irradiation with UV‐light.