Reactivity of [Ru3(μ3-NPh)(μ3-CO)(CO)9] towards Activated Alkynes and Diynes − Isolation of a Trinuclear Intermediate During the Formation of Bi- and Tetranuclear Products

Abstract

Treatment of the trinuclear imido-bridged cluster compound [Ru3(μ3-NPh)(μ3-CO)(CO)9] (1) with activated alkynes (methyl propynoate and methyl phenylpropynoate) and diynes (diphenylbutadiyne, 2,4-hexadiyne, 1,6-diphenyloxy-2,4-hexadiyne, and 1-trimethylsilyl-1,4-pentadiyne) in hexanes at reflux temperature leads to separable mixtures of the tetranuclear and binuclear derivatives [Ru4(μ4-NPh)(μ4,η2-RC≡CR′)(μ-CO)2(CO)9] and [Ru2{μ,η3-RC=CR′C(O)NPh}(CO)6], respectively. While the former complexes feature a phenylimido ligand in a rather rare μ4-coordination mode, the binuclear compounds contain acrylamido ligands that result from the coupling of a CO ligand and the original phenylimido ligand of 1 with the incoming alkyne or diyne. Surprisingly, all the products derived from diynes contain a pendant (non-coordinated) alkyne functionality. The isolation of the trinuclear derivative [Ru3(μ3-NPh)(μ3,η2-PhC≡CC≡CPh)(CO)9] (9) in the reaction of 1 with diphenylbutadiyne and the fact that its thermolysis leads to a mixture of [Ru4(μ4-NPh)(μ4,η2-PhC≡CC≡CPh)(μ-CO)2(CO)9] and [Ru2{μ,η3-C(C≡CPh)=C(Ph)C(O)NPh}(CO)6] support the proposal that trinuclear species containing coordinated alkyne or diyne ligands, similar to 9, are intermediates in the synthesis of all the bi- and tetranuclear products. Only one of the two possible regioisomers of each product (that might have arisen from the asymmetry of the alkyne or diyne reagents used) is formed. The origin of this regioselectivity is also discussed.