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

Abstract

A DFT computational study on the reaction that transforms the triruthenium cluster [Ru3(μ3-κ2-HNNMe2)(μ3-κ2-HCCH2)(μ-κ2-HCCH)(CO)7] (1), which contains an edge-bridging acetylene ligand, into the derivative [Ru3(μ3-κ2-HNNMe2)(μ3-κ2-HCCH2)(μ-κ1-CCH2)(CO)7] (2), which contains an edge-bridging vinylidene ligand, is reported. The reaction pathway with the lowest energy barrier (pathway 1, 37.4 kcal mol−1) is a four-step process that releases 10.7 kcal mol−1. It involves the participation of a hydrido-alkynyl intermediate (arising from the oxidative addition of an acetylene C−H bond). It has been shown that the polymetallic (at least bimetallic) nature of the system and the hemilabile character of the face-capping vinyl ligand play important roles in the operating mechanism. Seven alternative reaction pathways, one of them also involving an acetylene C−H oxidative addition mechanism and the remaining six involving a 1,2-hydrogen-shift of an H atom of the edge-bridging acetylene, were also found to connect compounds 1 and 2 on the potential energy surface of the system, but they all are kinetically disfavored with respect to pathway 1.

Mechanism and Origins of Z Selectivity of the Catalytic Hydroalkoxylation of Alkynes via Rhodium Vinylidene Complexes To Produce Enol Ethers

“…The mechanism for the terminal alkyne to vinylidene isomerization within metal complexes has been studied extensively by computational and experimental means. − For d 6 metal systems such as Ru(II) and Mn(I) complexes, the reaction generally proceeds via either a direct 1,2-hydrogen shift or an indirect 1,2-hydrogen shift. − However, electron-rich d 8 metal complexes such as Rh(I), according to early studies, tend to undergo a formal oxidative addition of the C–H bond to give an alkynyl hydride intermediate, followed by a 1,3-hydrogen shift to afford the vinylidene complex. − Although both uni- and bimolecular pathways were proposed for the 1,3-hydrogen shift, a combination of crossover experiments and DFT calculations has essentially ruled out the bimolecular mechanism. , We considered all three possible pathways starting from 3 and computed the transition states and intermediates, as shown in Figure .…”

DFT Study of Internal Alkyne-to-Disubstituted Vinylidene Isomerization in [CpRu(PhC≡CAr)(dppe)]+

“…The acetylene-to-vinylidene rearrangement in the coordination sphere of a transition metal is a thermodynamically favorable process in most cases. This type of transformation reaction has been experimentally observed in mononuclear complexes or in bi- and trinuclear derivatives . The vinylidene complexes play important roles as intermediates in the synthesis of various organic compounds from alkyne complexes.…”

Synthesis and Chemistry of Ammonioethenyl and Phosphonioethenyl Ligands in Zwitterionic Dirhenium Carbonyl Complexes

“…It was somewhat unexpected to find the formation of zwitterions 10a , 11a , 11b , and 12 which contain a CCH 2 grouping in these reactions using the reagent HCCH. However, there are a number of previous reports that demonstrate the formation of vinylidene CCH 2 ligands from ethyne, HCCH, by hydrogen shifts in the presence of metal atoms. , Evidence has been presented for two mechanisms for these hydrogen atom shifts: (1) a 1,2-carbon-to-carbon “concerted” hydrogen shift and (2) a 1,2-hydrogen shift involving a metal-containing intermediate with a hydride and acetylide ligand formed by the oxidative addition of a CH bond to a metal atom …”