Experimental and Theoretical Investigation of Z−E Alkene Isomerization in [(Cy3P)2Cl2Ru]2(μ-CHCHCHCH) and Related Vinylalkylidenes

摘要: The conjugated diruthenium bisalkylidene complex [(Cy3P)2Cl2Ru]2(μ-CHCHCHCH) (1, an inseparable 10:1 mixture of E and Z alkene isomers 1E 1Z) the separate monoruthenium alkylidene complexes (Cy3P)2Cl2RuCHCHCHCHCH2 (2E 2Z) (Cy3P)2Cl2RuCHCHCHCH3 (3E 3Z) have each been synthesized through stoichiometric reaction olefin metathesis catalysts. Each pair undergo Z−E isomerization, though isomerization rates their dependencies on excess PCy3 are very different. Isomerization in 1 is fastest, with ΔH⧧ = 100 ± 5 kJ/mol ΔS⧧ 67 3 J/(mol K) (1Z to 1E) or 49 (1E as determined by dynamic NMR, giving t1/2 11 s for approach equilibrium at 25 °C. rate this shows no phosphine dependence. Isomerizations 2Z 3Z slower (t1/2 5−20 h), but former promoted PCy3, while latter inhibited. In presence (Z)-1,3,5-hexatriene, much slo...