Oligomerisation of alkynes at a pentamethylcyclopentadienylruthenium centre

Abstract

Reactions between the neutral vinylidene RuCl(=C=CHPh)(PPh₃)Cp* 2 and AgC≡CCO₂Me gave Ru{ŋ₁-C(C≡ CPh)= CHC(O)OMe-O}(PPh₃)Cp* 3, while either LiC≡CPh or HC≡CPh/NaOMe afforded the known Ru{ŋ³-PhCHCHC= CPh(C≡CPh)}(PPh₃)Cp* 1. Similarly, RuCl{=C=CH(CO₂Me)}(PPh₃)Cp* 4 reacted with HC≡CPh/NaOMe to give Ru{η³-CH(CO₂Me)CHC=CPh(C≡CCO₂Me)}(PPh₃)Cp* 5. Complex 3 reacted with HC≡CCO₂R (R = Me or Et) to give the 1,3,4,5-tetraen-1-yls Ru{η¹,η²-C(CO₂R)=CHCPh=C=C=CH(CO₂Me)}(PPh₃)Cp* (R = Me 6 or Et 7)] and with HC≡CSiMe₃ to give a mixture of Ru{η³-CH(CO₂Me)C(CH=CHSiMe₃)C=CPhC≡CSiMe₃}(PPh₃)Cp* 8 and Ru{η³-CH(CO₂Me)CHC=CPh(C≡CSiMe₃)}(PPh₃)Cp* 9. Crystal structures of 1, 3 and 5–8 were determined. These reactions provide routes to the stepwise formation of novel non-cyclic oligomers of 1-alkynes, with 8 containing the first example derived from four alkynes.