Polymers with a backbone consisting of bimetallic tetracarboxylates and organometallic rhenium(I) complexes: synthesis, characterization, and structural examination

The reaction of [(2,2 ' -bpy)(CO)(3)Re(4,4 ' -bpy)](CF3SO3) with M-2(O2CR)( 4) (M = Mo. R = CF3: M = Rh, R = CH3) leads to the tetranuclear complexes [ (2,2 ' -bpy)(CO)(3)Re(4,4 ' -bpy)](2)[M-2(O2CR)(4)](CF3SO3)(2) (1, 2). They are characterized by elemental analysis, H-1 C-13 and F-19 NMR, IR spectro scopy, and examined by UV-spectroscopy, cyclic voltammetry and thermogravim etry (TGA). The molecular structure of the rhodium-complex 2 is additionall y determined by X-ray single crystal analysis, revealing comparatively stro ng axial Rh-N interactions. The Rh-Rh bond distance (approximately 239.5 pm ) is within the expected range. No evidence for intramolecular electronic c ommunication between the Re(I)-ligands via the central metal-metal unit has been found in these tetranuclear systems in CH3CN solution, probably due t o the tilt of the 4,4 ' -bipyridine ligand which prevents proper orbital ov erlap. Oligomers 3 and 4 with backbones consisting of M-2(O2CR)(4) (M = Mo, R = CF3: M = Rh, R = CH3) and Re(CO)(3)Br(4,4 ' -bpy)(2) have also been pr epared. The elemental analyses are consistent with the stoichiometry M-2(O2 CR)(4)-Re(CO)(3)Br(4,4 ' -bpy)(2) = 1:1. Complexes 3 and 4 are not square w ith the rhenium(I)-centers at the corners but oligomers with zig-zag chain structures, according to IR-spectroscopy, The rhodium-complex 4 is insolubl e in all common solvents, whereas the molybdenum derivative 3 dissolves in the strongly coordinating donor solvent DMF most likely due to the replacem ent of Re(CO)(3)Br(4,4 ' -bpy)(2) by DMF in the axial positions of Mo-2(O2C CF3)(4). TGA studies indicate the strength of the metal-axial ligand intera ctions both in the tetranuclear complexes and in the oligomers in the solid state. (C) 2001 Elsevier Science Ltd. All rights reserved.