Homogeneous catalytic coupling reactions of alkynes and alkenes mediated by organoruthenium complexes

Nianhong Liu, Marquette University

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.

Recommended Citation

Nianhong Liu, "Homogeneous catalytic coupling reactions of alkynes and alkenes mediated by organoruthenium complexes" (January 1, 1998). Dissertations (1962 - 2010) Access via Proquest Digital Dissertations. Paper AAI9842435.
http://epublications.marquette.edu/dissertations/AAI9842435

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