Reactivity of a 1-azavinylidene-bridged triruthenium carbonyl cluster with alkynes. Synthesis of binuclear derivatives containing new C-H or C-N and C-C bonds formed by alkyne insertion into M-H or M-N and M-C bonds

Treatment of the 1-azavinylidene cluster complex [Ru-3(mu-H)(mu-N=CPh2)(CO)(10)] (1) with an excess of diphenylacetylene or 1-phenyl-1-propyne, in 1,2-dichloroethane at reflux temperature, gives the metallacyclic derivatives [Ru-2{mu-PhC=CR-CPh=CR-N=CPh(C6H4)}(mu-CO)(CO)(4)] (2, R = Ph; 3, R = Me). These reactions represent the first examples of insertion of weakly electrophilic alkynes into metal-nitrogen bonds, since compounds 2 and 3 contain novel ligands that result from the orthometalation of a phenyl group of the original 1-azavinylidene ligand, the insertion of the corresponding alkyne molecule into a ruthenium-nitrogen bond, and the insertion of a second alkyne molecule into a ruthenium-carbon bond. At lower temperature (THF under reflux), the reactions of compound 1 with the same alkynes or with 3-hexyne, acetylene, phenylacetylene, p-tolylacetylene, or tertbutylacetylene proceed via cluster. fragmentation and insertion of the corresponding alkyne into a ruthenium-hydrogen bond, resulting in the binuclear alkenyl derivatives [Ru-2(mu-(RC)-C-1=CHR2)(mu-N=CPh2)(CO)(6)] (4, R-1 = R-2 = Ph; 5, R-1 = Ph, R-2 = Me; 6, R-1 = R-2 = Et; 7, R-1 = R-2 = H; 8, R-1 = ph, R-2 = H; 9, R-1 = p-MeC6He4 R-2 = H; 10a, R-1 = Bu-t, R-2 = H; 10b, R-1 = H, R-2 = (BU)-B-t). Compounds 10a and 10b were obtained as an unseparable mixture. Unlike 4 and 5, which react further with the corresponding alkyne at higher temperature (1,2-dichloroethane under reflux) to give the corresponding metallacyclic derivatives 2 and 3, compounds 6-10 do not give any metallacyclic derivative when treated with more alkyne at higher temperatures. The higher reactivity of 4 and 5, as compared with that of 6-10, seems to be associated with the nature of their alkenyl ligands, which are derived from internal alkynes containing at least one phenyl group. The molecular structures of compounds 2, 3, and 9 have been determined by X-ray diffraction methods.