Title full: Mixed-ligand systems containing quadruple bonds. Capture and structural characterization of an intermediate in the ligand exchange process leading to new carboxylates of the dimolybdenum(4+ unit. Synthesis and X-ray crystallographic and electrochemical studies of Mo2[(η5-C5H4CO2)Fe(η5-C5H5)]2 (O2CCH3)2(C5H5N) 2 and [Mo2](η5-C5H4CO2)Fe(η5-C5H5)]4 (ax-CH3CN)(ax-DMSO)](DMSO)2. The compounds Mo2[(η5-C5H4CO2)Fe(η5-C5H5)]2 (O2CCH3)2(C5H5N)2 and [Mo2[(η5-C5H4CO2)Fe(η5-C5H5)]4(ax-CH3CN)(ax-DMSO)](DMSO)2 have been prepared by ligand exchange on Mo2(O2CCH3)4 by ferrocenemonocarboxylic acid. The first compound, an intermediate in the complete carboxylate exchange process used in the synthesis of more exotic carboxylates of the quadruply-bonded dimolybdenum(4+) unit crystallizes in the orthorhombic system space group Pbca (no. 61), with a 8.063(1), b 20.653(2), c 21.095(1) Å, V 3513(3) Å3 and Z = 4. The structure was refined to discrepancy indices R1 = 0.057 and R2 = 0.068. The compound is (a) the first reported tetracarboxylate of dimolybdenum(4+) possessing two different carboxylate ligands; (b) an example of the relatively rare trans geometry seen only infrequently in dimers containing a mixture of bridging ligands. The second compound is the final product for the ligand exchange process. It crystallizes in the triclinic system, space group P1 (no. 2), with a 11.877(7), b 13.491(11), c 9.922(12) Å. α 105.57(2), β 105.62(2), γ 101.86(2)°, V 1407(6) Å3 and Z = 1. The compound possesses both eclipsed and staggered ferrocene moieties. The structure was refined to discrepancy indices R1 = 0.0632 and R2 = 0.107. Both compounds exhibit one-electron oxidations with potentials very close to that of the ferrocene-ferrocenium couple itself. Attempts to further oxidize either of the compounds led to their destruction. © 1987.
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