Synthesis, Characterisation, Crystal Structures, Reactivity, and Electrochemistry of Ruthenium-Nitrido, Ruthenium-Cobalt-Imido and Ruthenapyrrolidone Carbonyl Clusters Containing Alkyne Ligands

Abstract

Thermolysis of [Ru3(CO)9(μ3-NOMe)(μ3-η2-PhC2Ph)] (1) with two equivalents of [Cp*Co(CO)2] in THF afforded four new clusters, brown [Ru5(CO)8(μ-CO)3(η5-C5Me5)(μ5-N)(μ4-η2-PhC2Ph)] (2), green [Ru3Co2(CO)7(μ3-CO)(η5-C5Me5)2(μ3-NH){μ4-η8-C6H4C(H)C(Ph)}] (3), orange [Ru3(CO)7(μ-η6-C5Me4CH2){μ-η3-PhC2(Ph)C(O)N(OMe)}] (4) and pale yellow [Ru2(CO)6{μ-η3-PhC2(Ph)C(O)N(OMe)}] (5). Cluster 2 is a pentaruthenium μ5-nitrido complex, in which the five metal atoms are arranged in a novel “spiked” square-planar metal skeleton with a quadruply bridging alkyne ligand. The μ5-nitrido N atom exhibits an unusually low frequency chemical shift in its 15N NMR spectrum. Cluster 3 contains a triangular Ru2Co–imido moiety linked to a ruthenium–cobaltocene through the μ4-η8-C6H4C(H)C(Ph) ligand. Clusters 4 and 5 are both metallapyrrolidone complexes, in which interaction of diphenylacetylene with CO and the NOMe nitrene moiety were observed. In 4, one methyl group of the Cp* ring is activated and interacts with a ruthenium atom. The “distorted” Ru3Co butterfly nitrido complex [Ru3Co(CO)5(η5-C5Me5)(μ4-N)(μ3-η2-PhC2Ph)(μ-I)2I] (6) was isolated from the reaction of 1 with [Cp*Co(CO)I2] heated under reflux in THF, in which a Ru−Ru wing edge is missing. Two bridging and one terminal iodides were found to be placed along the two Ru−Ru wing edges and at a hinge Ru atom, respectively. The redox properties of the selected compounds in this study were investigated by using cyclic voltammetry and controlled potential coulometry. 15N magnetic resonance spectroscopy studies were also performed on these clusters.