Reaction of 2,3-bis(methylthio)pyrrolo[1,2-a]benzimidazol-1-one with BrRe(CO)3(THF)2: X-ray diffraction structure, redox chemistry, and luminescence behavior of fac-BrRe(CO)3{N,S-2,3-bis(methylthio)pyrrolo[1,2-a]benzimidazol-1-one}

The reaction of the heterocyclic ligand 2,3-bis(methylthio)pyrrolo[1,2-a]benzimidazol-1-one with the rhenium(I) compound BrRe(CO)3(THF)2 has been explored and found to give the new complex fac-BrRe(CO)3(N,S-heterocycle) (1) upon stirring at room temperature. The same product has also been isolated in lower yield by heating BrRe(CO)5 and the starting heterocycle. Compound 1 has been isolated and characterized in solution by IR and NMR spectroscopies, and the N,S-chelation mode exhibited by the ancillary heterocyclic ligand has been confirmed by X-ray diffraction analysis. The redox properties of 1 have been investigated by cyclic voltammetry, where an irreversible reduction is observed at Epc=-0.63V. The nature of the LUMO in 1 has been evaluated through the means of extended Hückel MO calculations, and the electrochemical and MO data are discussed relative to the parent heterocyclic ligand that possesses a low-lying, ligand-based π* LUMO. The photophysical behavior of the starting heterocycle and compound 1 has been analyzed in CH2Cl2 and MeCN solvents; emission quantum yields at room temperature are on the order of 10−5 in CH2Cl2 and one order of magnitude higher in MeCN. The lowest excited state arises from an intraligand (IL) transition resulting from a π → π* excitation that is confined to the heterocycle.

Graphical abstractThe ligand substitution chemistry of the heterocyclic ligand 2,3-bis(methylthio)pyrrolo[1,2-a]benzimidazol-1-one with fac-BrRe(CO)3(THF)2 has been examined and found to give fac-BrRe(CO)3(N,S-heterocycle). The new rhenium(I) compound has been isolated and characterized in solution by IR and NMR spectroscopies, and the chelation of the heterocycle to the rhenium center through the nitrogen and 3-methylthio groups was established by X-ray crystallography. The redox properties, MO data, and photophysical behavior of fac-BrRe(CO)3(N,S-heterocycle) are reported.Figure optionsDownload full-size imageDownload as PowerPoint slide