Reactions of μ₃‐Alkenyl Triruthenium Carbonyl Clusters with Alkynes: Synthesis of Trinuclear μ‐//‐Alkyne, μ‐Vinylidene, and μ‐Dienoyl Derivatives

Abstract

The reactions of doubly face-capped triruthenium cluster complexes of the type [Ru(3)(mu(3)-kappa(2)-HNNMe(2))(mu(3)-kappa(2)-R(2)CCHR(1))(mu-CO)(2)(CO)(6)] (HNNMe(2) = 1,1-dimethylhydrazide; R(2)CCHR(1) = alkenyl ligand) with terminal and internal alkynes have been studied in refluxing toluene. The following derivatives have been isolated from these reactions: [Ru(3)(mu(3)-kappa(2)-HNNMe(2))(mu(3)-kappa(2)-R(2)CCHR(1))(mu-kappa(2)-//-HCCH)(CO)(7)] (R(1) = R(2) = H, 5; R(1) = Ph, R(2) = H, 6; R(1) = CH(2)OMe, R(2) = H, 7 a; R(1) = H, R(2) = CH(2)OMe, 7 b) from acetylene, [Ru(3)(mu(3)-kappa(2)-HNNMe(2))(mu(3)-kappa(2)-HCCH(2))(mu-kappa(2)-//-PhCCPh)(CO)(7)] (11) from diphenylacetylene, and three isomers of [Ru(3)(mu(3)-kappa(2)-HNNMe(2))(mu(3)-kappa(2)-HCCH(2))(mu-kappa(2)-//-PhCCH)(CO)(7)] (14, 15 a, and 15 b) from phenylacetylene. These products result from substitution of a CO ligand by the alkyne and contain an Ru--Ru edge bridged by the alkyne ligand in a parallel manner. DFT calculations on selected isomeric products have helped to establish that the type of Ru--Ru edge bridged by the alkyne depends more on kinetic factors related to the size of the alkyne substituents than on the thermodynamic stability of the final products. The preparation of triruthenium cluster complexes with mu-//-alkyne ligands is unprecedented and seems to relate to the fact that the starting trinuclear complexes have their two triangular faces protected by capping ligands. The clusters bearing mu-//-acetylene (5-7) are thermodynamically unstable with respect to their transformation into edge-bridging vinylidene derivatives, [Ru(3)(mu(3)-kappa(2)-HNNMe(2))(mu(3)-kappa(2)-HCCHR)(mu-kappa(1)-CCH(2))(CO)(7)] (R = H, 8; Ph, 9; CH(2)OMe, 10). DFT calculations have shown that complex 8 is 11.2 kcal mol(-1) more stable than its precursor 5. The thermolysis of compound 11 leads to [Ru(3)(mu(3)-kappa(2)-HNNMe(2))(mu-kappa(4)-H(2)CCHCPhCPhCO)(mu-CO)(2)(CO)(5)] (12), which contains a novel edge-bridging dienoyl ligand that arises from an unusual coupling of diphenylacetylene, carbon monoxide, and the ethenyl ligand of complex 11. A chloro-bridged dimer of trinuclear clusters, [Ru(6)(mu-Cl)(2)(mu(3)-kappa(2)-HNNMe(2))(2)(mu(3)-kappa(2)-HCCH(2))(2)(mu-kappa(2)-PhCCHPh)(2)(mu-CO)(2)(CO)(10)] (13), has been prepared by treating compound 11 with hydrogen chloride. Therefore, edge-bridging parallel alkynes are susceptible to protonation to give edge-bridging alkenyl ligands. Compound 13 is the first complex to contain two alkenyl ligands on a trinuclear cluster, one face-capping and the other edge-bridging.

Reversible Transformation of a μ3-η3-C3 Ring into μ3-η2-Ethyne and μ-Vinylidene Ligands at a Triruthenium Site upon Deprotonation and Protonation

“…Because 4 contains a μ 3 -methylidyne ligand instead of the hydride in 5 , the μ 3 -η 2 coordination of the vinylidene ligand is suppressed to satisfy the coordinatively saturated 48-electron configuration. Notably, 4 contains three different hydrocarbyl moieties, μ 3 -ethyne, μ 3 -methylidyne, and μ-vinylidene, in its structure and represents the first structurally determined trinuclear complex with a μ-alkenylidene ligand. − …”

“…The lack of π coordination also causes a remarkable downfield shift of the 13 C signal of the C β atom in 4 (δ 101.7) in comparison to those of the μ 3 -η 2 -CCH 2 ligands in 5 (δ 70.1), [(Cp*Ru) 3 (μ 3 -η 2 - n PrCCH)­(μ 3 -η 2 -CCH 2 )­(μ-H)] ( 6 ; δ 68.9), and 7 (δ 56.9) (Table ). Although the C α signal in 4 (δ 261.6) was located considerably more upfield than those of the μ 3 -η 2 -vinylidene complexes 5 – 7 (δ 306.4–296.6), its chemical shift is similar to those of the reported triruthenium μ-vinylidene complex [Ru 3 (μ-CCH 2 )­(μ 3 -κ 2 -HNNMe 2 )­(μ 3 -η 2 -HCCH)­(CO) 7 ] (δ 248.4) and diruthenium μ-vinylidene complex [{CpRu­(CO)} 2 (μ-CCH 2 )­(μ-CO)] (δ 240.1) …”

The Bridging Acetylene to Bridging Vinylidene Rearrangement in a Triruthenium Carbonyl Cluster: A DFT Mechanistic Study

“…Rearrangements of edge-bridging κ 2 -alkynes to edge-bridging κ 1 -vinylidene ligands , (Figure , central scheme) are well represented in the alkyne chemistry of binuclear and higher-nuclearity complexes. Face-capping κ 2 -alkyne to face-capping κ 2 -vinylidene rearrangements (Figure , bottom scheme), although rarer, have also been observed in some transition metal carbonyl cluster complexes .…”

Reactivity of a triruthenium alkenyl cluster complex with conjugated diynes: Coupling of two diyne molecules via a face-capping diyne intermediate

“…doi:10.1016/j.jorganchem.2007. 10.024 clusters with edge-bridging parallel alkyne or edge-bridging vinylidene ligands, in which the original alkenyl ligand remains intact [7]. Edge-bridging dienoyl derivatives that arise from a three-component coupling of alkyne, alkenyl and carbonyl ligands have also been isolated from these reactions [7].…”

“…However, to date, the number of reports dealing with triruthenium carbonyl cluster complexes containing alkenyl ligands is relatively small [1][2][3][4][5][6][7][8][9], despite the fact that some of these clusters have been recognized as intermediates or as catalyst precursors for alkyne-alkene codimerization [8] and alkyne hydrogenation [9], dimerization [2b], polymerization [2b] and hydroformylation [2c] processes.…”