Thermal Isomerization Studies of Small Metallocarboranes. Cage Rearrangement Equilibria and Reversible Cobalt Atom Migrations.

摘要

The vapor phase thermal behavior of six-,seven-and eight-vertex mono,seven-,eight-,and nine-vertex dicobaltacarboranes,and a ten-vertex tricobaltacarborane was examined. In addition to phenomena of types previously observed in metallocarborane studies, e.g.,intramolecular migration of metal and carbon atoms,and intermolecular transfer of cobalt and boron,several processes novel to metallocarborane chemistry were found,including the conversion of a cobaltacarborane to a carborane via ejection of cobalt,the migration of cobalt from a 5-to a 4-coordinate polyhedral vertex,and two examples of cage rearrangement equilibria involving reversible metal-metal cleavage. The isomerization of 1,7,2,3-(eta-C5H5)2Co2C2B3H5was examined, a mechanism proposed,and the equilibrium constant determined as a function of temperature. (Modified author abstract)