Synthesis, characterization, crystal structures and reactivity of a series of ruthenium nitrene and nitrido carbonyl clusters containing bridging alkyne ligands

The reactions of [Ru3(CO)9(µ3-CO)(µ3-NOMe)] 1 with alkynes, PhC2R, in n-hexane afforded the new cluster [Ru3(CO)9(µ3-NOMe)(µ3-η2-RC2Ph)] (2a, R = H; 2b, R = Ph) in high yields. The molecules consist of an open triangular core of three metal atoms with triply bridging alkyne and µ3-NOMe ligands on opposite sides of the cluster. Upon thermolysis in n-octane, [Ru4(CO)9(µ-CO)2(µ4-NOMe)(µ4-η2-HC2Ph)] 3a, [Ru4(CO)9(µ-CO)2{µ4-NC(O)OMe}(µ4-η2-HC2Ph)] 4a and [Ru5(CO)13(µ-CO)(µ4-NH)(µ4-η2-HC2Ph)] 5a were isolated from 2a, while [Ru4(CO)9(µ-CO)2(µ4-NOMe)(µ4-η2-PhC2Ph)] 3b, [Ru4(CO)9(µ-CO)2{µ4-NC(O)OMe}(µ4-η2-PhC2Ph)] 4b, [Ru4(CO)9(µ-CO)2(µ4-NH)(µ4-η2-PhC2Ph)] 6b and [Ru6(CO)13(µ-H)(µ5-N)(µ3-η2-PhC2Ph)2] 7b were obtained from 2b. The structures of 3a, 3b, 4a and 4b consist of a slightly twisted square base of four metal atoms with quadruply bridging alkyne and µ4-NOMe or µ4-NC(O)OMe ligands on opposite sides of the clusters. Cluster 5a has a structure analogous to that of 3a with quadruply bridging phenylacetylene and µ4-nitrene (NH) ligands but differs from 3a due to the presence of a Ru(CO)4 group on one edge of the tetraruthenium cluster, whilst cluster 7b contains six ruthenium atoms and a µ5-N nitrido atom. Five ruthenium atoms out of the six arrange in a novel wingtip-bridged metal skeleton. The binuclear metallapyrrolidone complex [Ru2(CO)6{µ-η3-HC2(Ph)C(O)N(OMe)}] 8a was isolated from the direct reaction of 1 and phenylacetylene in refluxing n-octane, in which interaction of phenylacetylene with CO and the NOMe nitrene moiety was observed. Complex 3a converts into 4a in refluxing n-octane with or without bubbling CO. Substitution of MeCN with 3a led to the activated [Ru4(CO)8(µ-CO)2(NCMe)(µ4-NOMe)(µ4-η2-HC2Ph)] 9a in moderate yields. Monosubstituted [Ru4(CO)8(µ-CO)2(PPh3)(µ4-NOMe)(µ4-η2-HC2Ph)] 10a was isolated stoichiometrically when 9a was stirred with PPh3. However, direct substitution on 3a with PPh3 in the presence of Me3NO gives disubstituted [Ru4(CO)7(µ-CO)2(PPh3)2(µ4-NOMe)(µ4-η2-HC2Ph)] 11a in addition to 10a. Nucleophilic attack of H– takes place on 3a and 4a and of I– on 3a, a terminal carbonyl ligand is replaced by these anionic ligands and the products were characterized by negative ionization fast atom bombardment mass spectrometry.