Coordination of a Schiff base as an iminium-phenone zwitterion in a double ligand-bridged fac-[Re(CO)3]+ dimer

•Double ligand-bridged dimer•Tridentate O2N-donor ligand•Iminium-phenone zwitterion•Crystal structures

The ligand-bridged dimers [Re(CO)3(μ-H2salet)]2 (1) and [{Re(CO)3}2(μ-salpd)] (2) are formed by the reactions of [Re(CO)5Cl] with the potentially heptadentate Schiff base 2,2′,2″-tris(salicylideneimino)triethylamine (H3salet) and the hexadentate N1-(3-(2-hydroxybenzylidene-amino)propylamino)ethyl)-benzylidenepropane-1,3-diamine (H2salpd) respectively. In 1, the two H2salet ligands bridge two fac-[Re(CO)3]+ moieties. Mono-dentate coordination is by a neutral phenone oxygen atom, generated by the conversion of one salicylideneimine entity to an iminium zwitter-ion. In 2 each fac-[Re(CO)3]+ core resides in a ‘3 + 0’ environment. In both complexes π–π interaction between the phenolate rings contribute to the stability. The crystal structures of 1 and 2 were determined by X-ray single crystal diffraction. Spectroscopic results are also reported.

Graphical abstractThe ligand-bridged dimers (μ-H2salet)2[Re(CO)3]2 (1) and (μ-salpd)[Re(CO)3]2 (2) are formed by the reactions of [Re(CO)5Cl] with the potentially heptadentate Schiff base 2,2′,2″-tris(salicylideneimino)triethylamine (H3salet) and the hexadentate N1-(3-(2-hydroxybenzylidene-amino)propylamino)ethyl)-benzylidenepropane-1,3-diamine (H2salpd) respectively. In 1, the two H2salet ligands bridge two fac-[Re(CO)3]+ moieties in a ‘2 + 1’-type donor atom set. Mono-dentate coordination is by a neutral phenone oxygen atom, generated by the conversion of one salicylideneimine entity to an iminium zwitter-ion. In 2 each fac-[Re(CO)3]+ core resides in a ‘3 + 0’ environment. In both complexes π–π interaction between the phenolate rings contribute to the stability.Figure optionsDownload full-size imageDownload as PowerPoint slide