Activation of Linear Alkanes by a Hydrido Triruthenium Cluster and Associated Skeletal Rearrangements

Abstract

We explored polyhydrido cluster reaction chemistry for over two decades, developing rational syntheses of di-, tri-, tetra-, and pentanuclear clusters of ruthenium. In our study of cluster chemistry, we found that triruthenium pentahydrido complex [{Cp*Ru(¯-H)} 3 (¯3-H) 2 ] (1) (Cp*: η 5 -C 5 Me 5 ) reacts with linear alkanes to exclusively afford a closoruthenacyclopentadiene complex 2. The reaction mechanism has been elucidated by the isolation and alternative preparation of several important intermediates by the reaction of 1 with other hydrocarbons, such as alkynes, dienes, and alkenes. The mechanism is shown to consist of two reversible and four irreversible steps involving dihydrogen elimination, where the cooperative interaction of neighboring metal centers with hydrocarbons on the cluster is clearly seen. Facile migration of a hydride from a metal center to the carbon atom is also observed during the reaction, which emphasizes the crucial role of hydrido ligands in the skeletal rearrangement of hydrocarbyl ligands on a polyhydrido cluster. In addition, coupling reaction between two hydrocarbyl ligands placed on each face of the triruthenium core with concomitant partial cleavage of the cluster skeleton has also been observed. Such a flexible cluster skeleton enables unusual transformation of hydrocarbons on the cluster.

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

“…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) …”

Syntheses and Properties of Triruthenium Polyhydrido Complexes Composed of 1,2,4-tri-tert-butylcyclopentadienyl and p-Cymene Ruthenium Units

“…In particular, hydrides can tightly bind multiple transition-metal centers without decreasing the electron density at these metal centers. − Removal of hydrides via dihydrogen elimination or hydrogenation of unsaturated molecules leads to the generation of vacant sites at the neighboring metal centers. , Thus, polyhydrido clusters are considered to be suitable and versatile precursors of the multimetallic active species. − In fact, several unprecedented bond activations, such as NN bond cleavage − and C–C bond activation of benzene and ethylene, have been achieved on the electron-rich multimetallic site of non-carbonyl polyhydrido clusters. We have also demonstrated the unique reactivities of non-carbonyl polyhydrido clusters composed of [Cp*Ru] (Cp* = η 5 -C 5 Me 5 ) units toward hydrocarbons. ,, …”

“…We have also demonstrated the unique reactivities of non-carbonyl polyhydrido clusters composed of [Cp*Ru] (Cp* = η 5 -C 5 Me 5 ) units toward hydrocarbons. 12,21,22 Condensation reactions using polyhydrido complexes are some of the most reliable methods for preparing polyhydride clusters. However, this method is restricted to the cases where the individual starting polyhydrido complexes are readily available and are stable enough to be handled under normal conditions.…”

μ3‐η2:η2:η2‐Coordination of Primary Silane on a Triruthenium Plane

“…We previously reported the reaction of 1 with linear alkanes leading to the formation of the closo ‐ruthenacyclopentadiene complex, and demonstrated the mechanism of the skeletal rearrangement performed on the Ru 3 plane 18. However, the initial stage of the reaction, namely the incorporation of an alkane into the Ru 3 plane, is still unknown.…”