Abstract

The reaction of [Re(CO)(3)(THF)Br](2) and 2,2'-bipyrimidine (bpm) in dichloromethane at room temperature employing a stoichiometric 2:1 ratio leads to a mixture of [(bpm)Re(CO)(3)Br] (21%) and anti- [Br(CO)(3)Re(mu-bpm)Re(CO)(3)Br] (79%). When a 1:1 ratio is used, only anti-[Br(CO)(3)Re(mu-bpm)Re(CO)(3)Br] is obtained in a 89% yield. The reaction of [Re(CO)(5)Br] and (bpm) leads to [(bpm)Re(CO)(3)Br] as a single product. [(bpm)Re(CO)(3)Br] and anti- [Br(CO)(3)Re(mu-bpm)Re(CO)(3)Br] display one and two rhenium(I) centers of distorted octahedral coordination geometry respectively, each with a facial ligand correlation. The intramolecular metal to metal distance is 5.8508(16) angstrom in anti- [Br(CO)(3)Re(mu-bpm)Re(CO)(3)Br] . The HOMO-LUMO gap for [(bpm)Re(CO)(3)Br] results 0.74 eV larger (3.03 vs 2.29 eV) than the computed for anti- [Br(CO)(3)Re(mu-bpm)Re(CO)(3)Br]. In the same sense, the anti-isomer is computed to be 0.14 eV (13.4 kJ mol(-1 ) more stable compared to the hypothetical syn-[Br(CO)(3)Re(mu-bpm)Re(CO)(3)Br]. Cyclic voltammetry shows that the difference between the Re-I/Re-II reduction and its Re-I/Re-II oxidation in terms of potential is about 3.46 V for [(bpm)Re(CO)(3)Br], while this value diminishes to 2.62 V for anti- [Br(CO)(3)Re(mu-bpm)Re(CO)(3)Br] . Following this tendency, the MLCT band for [(bpm)Re(CO)(3)Br] is centered at 385 nm (DMF), while it is red-shifted almost 100 nm for anti- [Br(CO)(3)Re(mu-bpm)Re(CO)(3)Br] . While [(bpm)Re(CO)(3)Br] emits at 680 nm (excited at 380 nm), anti- [Br(CO)(3)Re (mu-bpm)Re(CO)(3)Br] remains non-emissive, which is attributed to a favored vibrational deactivation path.