Formal Diels–Alder dimerisation of cyclo-octatetraene induced by carbonylruthenium complexes
Abstract
Heating cyclo-octatetraene (cot) in heptane with [Ru4H4(CO)12] yields a previously unknown dimer of cot formally due to Diels–Alder self-addition, and derivatives [Ru(CO)3(C16H16)] and [Ru2(CO)5(C16H16)]. These complexes are also formed on reaction of [Ru3(CO)12] with cot, but no free dimer is produced. Evidence for the intermediacy of [Ru(CO)3(η4-C8H8)] in these reactions is provided by its yielding both cot dimer complexes on treatment with cot. A complex [Fe(CO)3(C16H16)] of a known cot dimer is obtained when [Fe(CO)3(η4-C8H8)] is heated with cot. Reaction of the new dimer with [Fe2(CO)9] provides its tricarbonyliron complex, while [Ru3(CO)12] yields [Ru(CO)3(C16H16)] and also [Ru3H2(CO)9(C16H14)]. The complex [Ru2(CO)5(C16H16)], which undergoes a unique fluxional process, is readily carbonylated to give [Ru2(CO)6(C16H16)], a fluxional cyclo-octatriene-based species. Mechanisms of the cot dimerisations are discussed and a stepwise metal template path is favoured.