Tetranuclear Complexes Containing Bimetallic Tetracarboxylates and Ferrocene − Models for Subunits of One‐Dimensional Organometallic Polymers

The tetranuclear compounds M2(O2C-R)4L2 [M = Rh, R = nC7H15, L = ferrocenyl-4-pyridylacetylene (FPA) (1a); M = Rh, R = CH3, L = FPA (1b); M = Mo, R = CF3, L = FPA (2b); M = Rh, R = nC7H15, L = 4-ferrocenylpyridine (FP) (3a); M = Rh, R = CH3, L = FP (3b); M = Mo, R = nC7H15, L = FP (4a); M = Mo, R = CF3, L = FP (4b)] have been synthesized by the reaction of bimetallic tetracarboxylates with L in a 1:2 ratio, in a noncoordinating solvent. The reaction of Mo2(O2C-nC7H15)4 with FPA in a 1:2 molar ratio leads to a trinuclear compound Mo2(O2C-nC7H15)4(FPA) (2a). A soluble oligomer [Rh2(O2C-nC7H15)4(BPEF)]n [5, BPEF = 1,1′-bis(4-pyridylethynyl)ferrocene] is obtained by the reaction of Rh2(O2CnC7H15)4 with BPEF in a 1:1 ratio in CH2Cl2 or CHCl3, whereas the reaction of Mo2(O2C-nC7H15)4 with BPEF leads to a pentanuclear compound [Mo2(O2C-nC7H15)4]2(BPEF) (6), even when BPEF is in excess. 1H NMR, Raman, UV/Vis absorption spectroscopy and cyclic voltammetry indicate that the metal-metal bonds are weakened by the metal-axial ligand interaction and the donor-acceptor interactions occurring between the building blocks of the multinuclear compounds and oligomers. The interaction between the bimetallic centers and the ferrocene moiety is enhanced by shortening the distances between them. This shortening is achieved by modification of the axial ligand from FPA to FP. A significant electronic communication between the ferrocene units is not observed.

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