Synthesis of an Electron-Deficient Triruthenium Hydrido Complex Having a Bridging Carbonyl Ligand: Influence of a CO Ligand on the Properties and Reactivities of a Hydrido Cluster

Abstract

A novel triruthenium hydrido cluster, (Cp*Ru)3(μ3-H)­(μ-H)2(μ-CO) (4; Cp* = η5-C5Me5), having a bridging CO ligand was synthesized by the reaction of {Cp*Ru­(μ-H)}3(μ3-O) (3) with methanol. Upon introduction of a CO ligand, the cyclic voltammogram of 4 demonstrated a significant shift of the redox potential in the positive direction in comparison to a pentahydrido complex, {Cp*Ru­(μ-H)}3(μ3-H)2 (1), which adopts the same 44-electron configuration. Owing to its coordinatively unsaturated nature, 4 readily reacted with butadiene, terminal alkynes, and alkenes similarly to the parent pentahydrido complex 1. However, the reactivity was slightly different from that of 1, and the influence of the CO ligand at the triruthenium site was evaluated by the reaction of various unsaturated hydrocarbons. The reaction of 4 with 1,3-dienes yielded a diene adduct, {Cp*Ru­(μ-H)}3(μ-η2:η2-s-cis-H2CCRCHCH2)­(CO) (5a, R = H; 5b, R = Me) without elimination of dihydrogen. In the same manner as for 1, 4 reacted with phenylacetylene to yield a μ3-η2:η2(⊥)-alkyne complex, (Cp*Ru)3(μ-H)­{μ3-η2:η2(⊥)-PhCCH}­(μ3-CO) (7a); in contrast, an isomeric μ3-pentenylidene complex, (Cp*Ru)3(μ-H)­{μ3-η2-CC­(nPr)­H}­(μ-CO) (9b), was obtained by reaction with 1-pentyne. A series of products was obtained by the reaction of 4 with ethylene molecules. A μ3-ethylidyne complex, (Cp*Ru)3(μ-H)2(μ3-CMe)­(μ-CO) (11), was initially formed, accompanied by the formation of ethane at ambient temperature. The treatment of 11 with ethylene resulted in the removal of hydrido ligands, affording a μ3-vinylidene complex, (Cp*Ru)3(μ-H)­(μ3-η2-CCH2)­(μ-CO) (9a). At higher temperatures, a second ethylene molecule was incorporated in the triruthenium plane and an equilibrated mixture of a μ3-ethylidyne−μ-ethylidyne complex, (Cp*Ru)3(μ-H)­(μ-CMe)­(μ3-CMe)­(μ-CO) (13), and μ3-ethylidyne−μ-vinyl complex, (Cp*Ru)3(μ-H)­(μ3-CMe)­(μ-η2-CHCH2)­(μ-CO) (12), was obtained. The formation of a μ3-η3-C3 ring on the Ru3 plane was observed upon the thermolysis of the equilibrated mixture at 180 °C, which clearly demonstrates the coupling of the two C2 moieties placed on each face of the triruthenium plane.

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

“…Although the formal oxidation state of the Ru 3 centers in 3a is lower than that in 6, the E 1/2 0/+ value shifted in the positive direction relative to that of 6 (E 1/2 0/+ = −731 mV, E p,a 0/+ = −673 mV). 46 This result suggests that the HOMO of 3a was substantially stabilized upon the introduction of a p-cymene group, despite its lower formal oxidation state.…”

“…Treatment of 3a with 1 atm of D 2 at 25 °C resulted in 50% deuteration at the Ru−H site after 3 h. Although the H/D exchange rate was considerably lower than that of 6 (100% deuteration in 3 h at 25 °C), it was comparable to that of [(Cp*Ru) 3 (μ-H) 2 (μ 3 -H)(μ-CO)]. 46 Thermolysis of 3a in C 6 D 6 also led to the deuteration of hydrides, although the reaction proceeded sluggishly. The Ru− H site was only 10% deuterated after 48 h at 80 °C, while the hydrides in 6 were converted by 73% after 40 h at 80 °C.…”

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 C(2)–C(3) distance of 1.42 Å in the optimized DFT structure is typical for μ 3 -η 2 -alkyne ligands parallel to one of the M–M edges of a M 3 triangle. , The optimized C(4)–C(5) distance (1.331 Å) is considerably shorter than the C–C bond length of the μ 3 -η 2 -CCH 2 ligand in [(Cp*Ru) 3 (μ 3 -η 2 -CCH 2 )­(μ-H)­(μ-CO)] ( 7 ; 1.389(8) Å), probably due to the absence of π coordination.…”

“…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), 20 [(Cp*Ru) 3 (μ 3 -η 2 -n PrCCH)(μ 3 -η 2 -CCH 2 )(μ-H)] (6; δ 68.9), 26 and 7 (δ 56.9) (Table 2). 16 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) 21 and diruthenium μ-vinylidene complex [{CpRu(CO)} 2 (μ-CCH 2 )(μ-CO)] (δ 240.1). 27 Takemoto et al demonstrated that the reaction of [(Cp*Ru) 2 (μ-CH)(μ-NPh)] + with KN(SiMe 3 ) 2 resulted in the formation of a μ-carbido complex via the exclusive deprotonation of the μ-methylidyne ligand.…”

“…Recently, we reported another route to the μ 3 -η 3 -C 3 skeleton, which involves the coupling of two hydrocarbyl moieties at a neutral Ru 3 site; thermolysis of a μ 3 -ethylidyne-μ-ethylidyne complex, [(Cp*Ru) 3 (μ 3 -CMe)­(μ-CMe)­(μ-H)­(μ-CO)], resulted in the formation of a triruthenium complex containing a face-capping μ 3 -η 3 -C 3 ring, [(Cp*Ru) 3 (μ 3 -η 3 -C 3 MeH 2 −)­(μ 3 -CO)] (Scheme a) . Notably, the same complex was also synthesized by Ernst et al through the reaction of [Cp*RuCl] 4 with trans -3-methyl-3-butanal in the presence of K 2 CO 3 (Scheme b) .…”