Facial vs. Meridional Coordination Modes in ReI Tricarbonyl Complexes with a Carbodiphosphorane-based Tridentate Ligand

The reactivity of the novel cationic ligand precursor [(dppm)(2)CH](PF6) (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, PF6). The facial coordination mode is retained in fac-[({dppm}(2)C)Re(CO)(3)](PF6) (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)](PF6) (mer-3) is observed under irradiation with UV-light.

Automated summary

The reactivity of a novel cationic ligand precursor with a weak anion and [ReBr(CO)(5)] was studied, resulting in the formation of dicationic complexes with different coordination modes. Quantum chemical investigations showed that the meridional coordination mode is thermodynamically favored. Isomerization from facial coordination to meridional coordination was observed under UV-light irradiation.