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

摘要

The reaction of [(2,2'-bpy)(CO)_3Re(4,4'-bpy)](CFJSOJ) with M_2(O_2CR)_4 (M = Mo, R = CFJ; M = Rh, R = CHJ) leads to the tetranuclear complexes [(2,2'-bpy)(CO)JRe(4,4'-bpy)h[M_2(O_2CR)_4](CFJSOJ)_2 (I, 2). They are characterized by elemental analysis, 'H, IJC and 19F NMR, IR spectroscopy, and examined by UV-spectroscopy, cyclic voltammetry and thermogravimetry (TGA). The molecular structure of the rhodium-complex 2 is additionally determined by X-ray single crystal analysis, revealing comparatively strong axial Rh-N interactions. The Rh-Rh bond distance (approximately 239.5 pm) is within the expected range. No evidence for intramolecular electronic communication between the Re(I)-ligands via the central metal-metal unit has been found in these tetra nuclear systems in CH_3CN solution, probably due to the tilt of the 4,4'-bipyridine ligand which prevents proper orbital overlap. Oligomers 3 and 4 with backbones consisting of M~(O_2CR)_4 (M = Mo, R = CFJ; M = Rh. R = CH3) and Re(CO)3Br(4,~'-bpyh have also been prepared. The elemental analyses are consistent with the stoichiometry M2(O2CR)4- Re(CO)3Br(4,4'-bpy)2 = 1:1. Complexes 3 and 4 are not square with the rhenium(I)-centers at the corners but oligomers with zig-zag chain structures, according to IR-spectroscopy. The rhodium-complex 4 is insoluble in all common solvents, whereas the molybdenum derivative 3 dissolves in the strongly coordinating donor solvent DMF most likely due to the replacement of Re(CO)_3Br(4,4'-bpy)_2 by DMF in the axial positions of Mo_2(O_2CCFJ)_4. TGA studies indicate the strength of the metal-axial li,gand interactions both in the tetranuclear complexes and in the oligomers in the solid state.