Tricarbonyl ReI Complexes from Functionalised Pyridine–Triazole Derivatives: From Mononuclear to Unexpected Dimeric Complexes

As a variation of the commonly used bipy ligand in Re(CO)3 chemistry, a series of structurally related complexes in which bipy is replaced by pyridine–triazole ligands (or pyta) bearing a pendant acetyl group on the triazole ring were prepared efficiently by the click chemistry approach. Depending on the nature of the pendant arm, different ReI complexes were obtained. Surprisingly, starting from the ligand with unprotected acetyl group yielded two structural isomers of Re(CO)3 dimeric species. One isomer (compound 5a) was isolated and characterised by X‐ray crystallography. The rhenium atoms are octahedrally coordinated to three carbonyl groups in fac arrangement and to two nitrogen atoms of one pyta and an oxygen atom of the other. DFT calculations confirmed that the isolated isomer represents the thermodynamically favoured form. As expected, these complexes exhibited luminescence. To conclude, the unexpected formation of 5 represents an original strategy toward the synthesis of new luminescent rhenium(I) dimeric (multimeric) species.