Reactivity of [RU2 (mu-eta(1):eta(1)-N=CPh2)(mu-eta(1):eta(2)- PhC=CHPh)(CO)(6)] with alkynes. Insertion reactions of nonactivated alkynes into Ru-C and Ru-N bonds

The mu -1-azavinylidene-mu -alkenyl diruthenium complex [Ru-2(mu-eta (1):et a (1)-N=CPh2)(,mu-eta (1):eta (2)-Ph-C=CHPh)(CO)(6)] (1) reacts with excess 1-phenyl-1-propyne or 3-hexyne in 1,2-dichloroothane at reflux temperature to give cis-stilbene and the metallacyclic derivatives [Ru-2{mu-eta (3):et a (4)-(RC)-C-1=(CRCR1)-C-2=(CRN)-N-2=CPh(C6H4)}(mu -CO)(CO)(4)](2, R-1 = Ph , R-2 = Me; 3,R-1 = R-2 = Et). These compounds contain ligands that result from the ortho metalation of a phenyl group of the original 1-azavinylidene ligand, the release of cis-stilbene, the insertion of the corresponding al kyne molecule into a Ru-N bond, and the insertion of a second alkyne molecu le into a Ru-C bond. The reaction of compound 1 with phenylacetylene in 1,2 -dichloroethane at reflux temperature gives cis-stilbene, [Ru-2{mu-eta (1): eta (2)-N=CPh(C6H4)}(mu-eta (2):eta (4)-PhC=CHCH=CPh)(CO)(5)] (4), and [Ru{ n(5)-PhC=CHCPh=CHCPh=CHN=CPh(C6H4)}(CO)(2)] (5). The hydrocarbyl ligand of 4, which can be described as a 1,4-diphenylbuta-1,3-diene-1,4-diyl ligand, arises from a head-to-head dimerization of phenylacetylene, whereas the org anic ligand of 5 results from an unprecedented insertion of phenylacetylene into a Ru-N bond in addition to a head-to-tail trimerization of phenylacet ylene. Thermolysis of compound 1 in refluxing 1,2-dichloroethane gives the tetranuclear derivative [C48H30N2O8Ru4] (6) and the binuclear product [Ru-2 (mu-eta (1):eta (1)-N=CPh2)(mu-eta (3):eta (4)-PhCH=CPhCPh=CPh)(CO)(4)] (7) . The molecular structure of complex 6 remains unknown. Compound 7 contains a bridging dienyl ligand (with a phenyl substituent n(2)-coordinated to a Ru atom) that arises from the coupling of diphenylacetylene with the diphen ylalkenyl ligand of 1. Mechanistic proposals that account for the formation of complexes 2-7 from compound I are given. The new C-N bonds of compounds 2, 3, and 5 are remarkable because they have been formed by migratory inse rtion of weakly electrophilic alkynes into Ru-N bonds, a process that has h itherto been very seldom observed only with internal alkynes and never with terminal alkynes.