Polymers with a backbone consisting of bimetallic tetracarboxylates and organometallic rhenium(1) complexes: Synthesis, characterization, and structural examination

Anorganisch-Chemisches Institut der Technischen Universität München, Lichtenbergstraβe, 4, D-85747 Garching bei Munich, Germany The reaction of [(2,2′-bpy)(CO)₃Re(4,4′-bpy)] (CF₃SO₃) with M₂(O₂CR)₄ (M = Mo, R = CF₃; M = Rh, R = CH₃₎ leads to the tetranuclear complexes [(2,2′- bpy)(CO)₃Re(4,4′-bpy)]₂[M₂ (O₂CR)₄](CF₃SO₃)₂ (1, 2). They are characterized by elemental analysis, ¹H, ¹³C 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 tetranuclear systems in CH₃CN 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 M₂(O₂CR)₄ (M = Mo, R = CF₃; M = Rh, R = CH₃₎ and Re(CO)₃Br(4,4′-bpy)₂ 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 Mo₂(O₂CCF₃)₄. TGA studies indicate the strength of the metal-axial ligand interactions both in the tetranuclear complexes and in the oligomers in the solid state.