Homogeneous catalytic coupling reactions of alkynes and alkenes mediated by organoruthenium complexes
Abstract
The ruthenium trihydride complexes $\rm C\sb5Me\sb5Ru(PR\sb3)H\sb3$ (R = Cy, Ph, Me) were found to catalyze the dimerization reaction of terminal alkynes HC$\equiv$CR (R = Ph, CH$\sb2$Ph, t-Bu, SiMe$\sb3$, n-Bu) to produce cis- and trans-1,4-disubstituted enynes RCH=CHC$\equiv$CR and 1,3-disubstituted enynes CH$\sb2$=C(R)C$\equiv$CR. The selective product formation was effected by modulating both the catalyst environment and the alkyne substrates. A rare form of dimer, cumulene PhCH$\sb2$CH=C=C=CHCH$\sb2$Ph, was cleanly obtained from the dimerization of HC$\equiv$CCH$\sb2$Ph with PCy$\sb3$-substituted catalyst. The key intermediate, coordinatively unsaturated acetylide species $\rm C\sb5Me\sb5Ru(PPh\sb3)C\equiv$CPh was generated in situ from the reaction of ruthenium-vinylidene complex $\rm C\sb5Me\sb5Ru(PPh\sb3)$(Cl)=C=CHPh with a base. This in situ generated ruthenium-acetylide species was also found to catalyze the cross coupling reaction of terminal (HC$\equiv$CR; R = t-Bu, s-Bu, i-Bu, SiMe$\sb3$) and internal $\rm (R\sp\prime C\equiv CR\sp{\prime\prime};\ R\sp\prime = Me,\ Et,\ CO\sb2Me;\ R\sp{\prime\prime}$ = COMe, CO$\sb2$Me, CO$\sb2$Et) alkynes. High regio- and stereoselective formation of enynes R$\sp{\prime\prime}$CH=C(R$\sp\prime$)(C$\equiv$CR) have been observed for internal alkynes with an electron withdrawing group, in which the acetylide from a terminal alkyne was added $\beta$ to the electron withdrawing group. A key intermediate $\beta$-agostic species $\rm C\sb5Me\sb5(PPh\sb3)RuC(CH\sb3){=}C(CH\sb3)C{\equiv}CBu\sp{t}$ was isolated from the reaction of $\rm C\sb5Me\sb5Ru(PPh\sb3)(Cl){=}C{=}CHBu\sp{t}$ with 2-butyne in the presence of NaOMe. These results are consistent with a mechanism involving a migratory insertion of a metal acetylide to a coordinated alkyne. The in situ generated coordinatively unsaturated acetylide species $\rm C\sb5Me\sb5Ru(PPh\sb3)C{\equiv}CPh$ was also shown to react readily with a variety of small molecules such as CO, H$\sb2,$ CO$\sb2,$ O$\sb2,$ CH$\sb2$=CH$\sb2$ and CH$\sb3$CHO. The ruthenium trihydride complex $\rm C\sb5Me\sb5Ru(PPh\sb3)H\sb3$ was found to be an efficient catalyst for the cross coupling reaction between silyl-substituted alkynes $\rm HC{\equiv}CSiR\sb3\ (SiR\sb3=SiMe\sb3,\ SiEt\sb3,\ SiMe\sb2Bu\sp{t})$ and functionalized alkenes CH$\sb2$=CHE (E = COMe, OAc, CN). High regio- and stereoselective formation of (Me$\sb3$SiC$\equiv$C)(Me$\sb3$Si)C=$\rm CHCH\sb2CH\sb2COCH\sb3$ has been obtained that the acetylide group was trans to the vinylic hydrogen. Isolated complex $\rm C\sb5Me\sb5(PPh\sb3)Ru(\eta\sp2$-CH$\sb2$=CHCOMe)C$\equiv $CSiR$\sb3$ has been shown to be an active catalyst for the cross coupling reaction.
This paper has been withdrawn.