Cyclopentadienylruthenium phosphine complexes. Part 3. Some complexes derived from 1-alkynes: molecular and crystal structure of the cumulene derivative [Ru{C(CF3):C(H)C(CF3):C:C:CH(CF3)}(PPh3)(η-C5H5)]

Abstract

Reactions between [RuX(PPh₃)₂(η-C₅H₅)](X = H, Me, or CH₂Ph) and the alk-1-ynes RC₂H (R = CO₂Me, COMe, CF₃, or C₆F₅) have given products resulting from interaction of one, two, or three alkyne molecules per molecule of ruthenium complex. Methyl propiolate and the hydrido-compound afford the η¹-alkynyl complex [Ru(C⋮CCO₂Me)(PPh₃)₂(η-C₅H₅)], the 1,3,4-η³-buta-1,3-dienyl complex [[graphic omitted]CH(CO₂Me)}-(PPh₃)(η-C₅H₅)], and the 1,4,5-η³-penta-1,3,4-trienyl complex [[graphic omitted]CMe-(CO₂Me)}(PPh₃)(η-C₅H₅)]. The methyl- and benzyl-ruthenium complexes give only the corresponding η³-but-adienyl complexes. Ethynyl methyl ketone and the methylruthenium complex afforded [[graphic omitted]-Me]:CHMe}(PPh₂)(η-C₅H₅)]. The structure of the 1,3,4,5-tetraenyl complex [[graphic omitted]C:CHCF₃}(PPh₃)(η-C₅H₅)], obtained from HC₂CF₃ and [RuMe(PPh₃)₂(η-C₅H₅)], was determined by a single crystal X-ray study. This shows that the acetylenic fragments have joined head-tail, head-tail, tail-head, and that whereas the first carbon atom of the chain (head, carrying a CF₃ group) is directly bonded to the ruthenium atom, the other attachment is an η-interaction at the tail-tail juxtaposition. The whole unsaturated system, including the metal atom, is essentially planar.

The product [[graphic omitted]Ph₂}(η-C₅H₅)] from HC₂C₆F₅ and the hydride contains a 10-membered RuPC₈ heterocycle. Possible mechanisms for the formation of these complexes are discussed.