Abstract :
The edge-bridged open ruthenocenes bis(η5-6,6-dimethylcyclohexadienyl)ruthenium (1), bis(η5-2,6,6-trimethylcyclohexadienyl) ruthenium (2), bis(η5-3,6,6-trimethylcyclohexadienyl)ruthenium (3), bis(η5-2,4,6,6-tetramethylcyclohexadienyl)ruthenium (4) are prepared by reactions between di-μ-chlorodichlorobis[(1-3η:6-8η)-2,7-dimethyloctadienyl] diruthenium and the corresponding dienes. Compound 4 can also be prepared in lower yield by reduction of RuCl3 · nH2O with zinc in the presence of 2,4,6,6-tetramethylcyclohexadiene. Variable temperature 1H NMR studies of 1–4 reveal rapid rotation about the Ru–C bonds. The barrier to rotation in 4 is 7.7 kcal/mol with a gauche–eclipsed ground state conformation. Even lower barriers to rotation in 1–3 contribute to the inability to accurately measure their activation energies in toluene.
