INTRAMOLECULAR REDOX CHEMISTRY OF MOLECULES WITH ALKYNE AND CCO3 CLUSTER FUNCTIONALITIES - ELECTRONIC INTERACTION AND STRUCTURAL ISOMERISM IN REDUCED CLUSTERS WITH MULTIPLE REDOX CENTERS

The redox chemistry by of the tricobaltcarbon clusters [CCo3(CO)9]2, OC[CCo3(CO)9]2, and Cn[CCo3(CO)9]2 (n = 2,4), linked by formal single and/or triple carbon-carbon bonds, is contrasted with that of molecules with only a single cluster redox center, RCnCCo3(CO)9. The latter clusters undergo a reversible reduction process, whereas molecules with linked clusters display electrochemical responses indicative of interacting redox centers. After the formation of a radical anion, in which the electron is delocalized via the Co3C-Cn-CCo3 link, a CE mechanism gives a new species with a reversible redox couple. Spectroscopic evidence suggests that this new species is a bridged-carbonyl isomer of the initial radical anion. Formation of the isomers is attributed to electron delocalization through the carbyne link and steric influence of the equatorial CO groups. An improved synthesis of [CCo3(CO)9]2 and the X-ray structure analysis of the compound (MeO)3P(CO)8Co3CC=CCCo3(CO)7[P(OMe)3]2, (Pbca; a = 18.074 (4) angstrom, b = 37.534 (7) angstrom, c = 12.918 (4) angstrom, Z = 8) are also reported.