The Synthesis of Dimeric Re I –Phenylenediimine Conjugates: Spectroscopic and Electrochemical Studies

A series of dimeric Re I (CO) 3 compounds have been prepared by means of a one‐pot reaction of [Re(CO) 5 X] (X = Cl, Br), pyridine‐2‐carboxyaldehyde, and o ‐, m ‐, or p ‐phenylenediamine. For the m ‐ and p ‐substituted phenylenediamine reactions, phenyl‐bridged bis(pyridine‐2‐carbaldimine) compounds of the formula [Re(CO) 3 X] 2 (μ‐PPC) [ 3 – 7 ; X = Cl, Br; μ‐PPC = m ‐ or p ‐phenylene bis(pyridine‐2‐carbaldimine)] were produced, with m ‐phenylenediamine forming a mixture of isomers. For reactions with o ‐phenylenediamine, multiple products formed (compounds 8 – 11 ), which ranged from the desired o ‐phenylene bis(pyridine‐2‐carbaldimine) adduct to 2‐pyridylbenzimidazole and bridging dipyridinylquinoxaline complexes. An example of each complex was structurally elucidated by single‐crystal X‐ray methods. The dimeric m ‐ and p ‐phenylene‐bridged Re(CO) 3 X compounds, including a sulfonate derivative designed to improve solubility, were investigated for possible photophysical applications through the use of UV/Vis spectroscopy and cyclic voltammetry; the study revealed coupling between the rhenium centers.