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 Mo 2[(η 5-C 5H 4CO 2)Fe(η 5-C 5H 5)] 2(O 2CCH 3) 2(C 5H 5N) 2 and [Mo 2](η 5-C 5H 4CO 2)Fe(η 5-C 5H 5)]

Abstract

The compounds Mo 2[(η 5-C 5H 4CO 2)Fe(η 5-C 5H 5)] 2(O 2CCH 3) 2(C 5H 5N) 2 and [Mo 2[(η 5-C 5H 4CO 2)Fe(η 5-C 5H 5)] 4( ax-CH 3CN)( ax-DMSO)](DMSO) 2 have been prepared by ligand exchange on Mo 2(O 2CCH 3) 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) Å 3 and Z = 4. The structure was refined to discrepancy indices R 1 = 0.057 and R 2 = 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 P 1 (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) Å 3 and Z = 1. The compound possesses both eclipsed and staggered ferrocene moieties. The structure was refined to discrepancy indices R 1 = 0.0632 and R 2 = 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.