Synthesis of an Electron-Deficient Triruthenium Hydrido Complex

Article pubs.acs.org/Organometallics

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 Yuta Takahashi,† Yumiko Nakajima,† Hiroharu Suzuki,† and Toshiro Takao*,†,‡ †

Department of Applied Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro-ku, Tokyo 152-8552, Japan ‡ JST, ACT-C, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan S Supporting Information *

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(μH)}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:η2s-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(μH)(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.

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INTRODUCTION

unprecedented face-capping coordination to the trinuclear site, unlike the usual κ(N) coordination.3 This ability also arises from the enhanced back-donation to the π* orbitals from the triruthenium core. Bond breaking at the electron-rich multinuclear center results in the formation of multiple M−C bonds. However, excessively strong M−C bonds are an obstacle to the elimination of the substrates from the multinuclear center. In fact, the hydrogenation of the closo-ruthenacyclopentadiene complex, leading to the regeneration of 1, requires harsh conditions and proceeds sluggishly.4 Thus, to apply the remarkable reactivity of polyhydrido clusters to catalysis, the electronic properties of the multinuclear site must be modified to reduce the M−C

We have explored the chemistry of polyhydrido clusters aiming at the development of novel reactions unique to multinuclear compounds.1 At multinuclear sites, it is expected that inert bonds, such as C−H and C−C bonds, are readily activated by the cooperative interaction of neighboring metal centers. We have shown that the triruthenium pentahydrido complex {Cp*Ru(μ-H)}3(μ3-H)2 (1; Cp* = η5-C5Me5) reacts with linear alkanes to yield a closo-ruthenacyclopentadiene complex following several C−H bond cleavages.2 Complex 1 is composed of electron-donating Cp* groups and hydrido ligands. Because hydrido ligands do not reduce the electron density at the metal center, the metal centers of 1 should be electron-rich, which contributes to the facile oxidative addition of C−H bonds. The electron-rich metal centers of 1 also allow the coordination of pyridine and nitrile ligands, forming an © XXXX American Chemical Society

Received: June 17, 2017

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DOI: 10.1021/acs.organomet.7b00465 Organometallics XXXX, XXX, XXX−XXX

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Organometallics bond strength. With the aim of controlling the electronic environment, triruthenium polyhydrido clusters capped by a triply bridging ligand, {Cp*Ru(μ-H)}3(μ3-E) (E = BR,5 AlEt, GaMe,6 NR,7 O,1b S8), have been synthesized. Among these triply bridging ligands, those composed of group 13 elements formally act as two-electron ligands, unlike the μ3-imido and μ3oxo ligands, which act as four-electron donors. Thus, the number of valence electrons of triruthenium clusters containing a triply bridging group 13 element is the same as that of the parent pentahydrido complex 1: that is, a 44-electron configuration. Such a highly unsaturated nature is promising for the incorporation of multiple substrates into the trimetallic site and, hence, their coupling reactions.9 Carbonyl is one of the most readily available and common ligands and is a two-electron ligand that can adopt a facecapping coordination mode. Since the early days of organometallic chemistry, carbonyl ligands have been used to stabilize low-valent metal centers.10 For trinuclear complexes, three principal coordination modes of a carbonyl ligand are known: terminal, bridging, and triply bridging. The formal electron count of these CO ligands is the same regardless of the coordination mode, and the CO ligand can readily alter its coordination mode at a multimetallic site, resulting in the rapid site exchange of the CO ligand between the terminal and bridging positions.11 The flexibility of the CO ligand on a multimetallic site is distinct from those of other triply bridging ligands. Furthermore, whereas the replacement of two hydrides by a CO ligand at a multinuclear site does not change the number of valence electrons, the formal oxidation state of metal centers is reduced by 2. In addition, this reduces the coordination numbers at the metal centers, resulting in a considerable difference in the reactivity of a polyhydrido cluster. However, the introduction of a carbonyl ligand into the triruthenium site of 1 is hampered by the high reactivity of CO. Treatment of 1 with 1 atm of CO results in the immediate formation of a paramagnetic tetracarbonyl complex, {Cp*Ru(μCO)}3(μ3-CO) (2).1b Because the four CO ligands of 2 are tightly bound to the metal centers, 2 does not show any reactivity. Therefore, the number of CO ligands should be limited to one to obtain a reactive 44-electron cluster. Wellknown methods to generate a carbonyl ligand include the decarbonylation of an organic carbonyl compound, such as an aldehyde or primary alcohol.12 Decarbonylation is superior to the addition of CO gas in terms of the controllability of the reaction. We report herein the synthesis of a novel triruthenium trihydrido complex having a μ-CO ligand, (Cp*Ru)3(μ3-H)(μH)2(μ-CO) (4), by the reaction of {Cp*Ru(μ-H)}3(μ3-O) (3) with methanol. The reactivity of 4 with unsaturated hydrocarbons is discussed to evaluate the influence of a CO ligand introduced to a triruthenium site.

immediately converted to a mixture of 4 and the bis(μ3-oxo) complex upon the addition of methanol. Complex 4 was isolated using column chromatography on alumina in 61% yield. The molecular structure of 4 was determined by X-ray diffraction (XRD), as shown in Figure 1. Because two

Figure 1. Molecular structure and labeling scheme of 4 with thermal ellipsoids at 30% probability. Selected bond lengths (Å) and angles (deg): Ru(1)−Ru(2) = 2.6623(2), Ru(1)−Ru(3) = 2.6992(2), Ru(2)−Ru(3) = 2.6916(2), Ru(1)−C(1) = 1.998(2), Ru(2)−C(1) = 2.010(2), C(1)−O(1) = 1.186(3); Ru(2)−Ru(1)−Ru(3) = 60.263(6), Ru(2)−Ru(1)−C(1) = 48.57(6), Ru(1)−Ru(2)−Ru(3) = 60.549(6), Ru(1)−Ru(2)−C(1) = 48.17(6), Ru(1)−Ru(3)−Ru(2) = 59.188(6), Ru(1)−C(1)−Ru(2) = 83.26(8), Ru(1)−C(1)−O(1) = 138.42(17), Ru(2)−C(1)−O(1) = 138.19(17).

independent molecules with similar geometrical features are present in the unit cell, only one molecule is shown. The triruthenium framework forms an isosceles triangle with sides of 2.6623(2), 2.6916(2), and 2.6992(2) Å, where the Ru(1)− Ru(2) bond bridged by a CO group is the shortest. These values are slightly shorter than the Ru−Ru bond lengths of 1 (average 2.75 Å).1b This slight shrinkage of the Ru3 skeleton is likely due to the reduction in electron density at the Ru3 center upon the incorporation of a π-acidic CO group in place of two hydrides. The shortening of the Ru−Ru bond of {Ru(PCy3)(CO)(μ-CO)}3(μ3-H)2 (Cy = cyclohexyl), which has a 44electron configuration, in comparison to that of a saturated triruthenium complex was also noted by Süss-Fink et al., and the Ru−Ru bond lengths (2.6702(6), 2.6931(7), and 2.7180(7) Å) are comparable to those of 4.13 The reduction of the electron density at the metal centers of 4 is clearly seen in the cyclic voltammetry (CV) analysis, showing a significant shift of the redox potential in the positive direction in comparison to that of 1 (4, E1/2 = −578 mV; 1, E1/2 = −731 mV vs Fc/Fc+). In the X-ray analysis, the positions of the hydrido ligands were successfully determined during Fourier synthesis; the H(3) atom is coordinated to the Ru3 site as a triply bridging hydride, while the other two hydrides, H(1) and H(2), are located at the Ru(2)−Ru(3) and Ru(1)−Ru(3) edges as

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RESULTS AND DISCUSSION Synthesis of (Cp*Ru)3(μ3-H)(μ-H)2(μ-CO) (4). The μ3-oxo complex 3 reacted with methanol at ambient temperature to yield a mono(μ-carbonyl) complex, 4, via dehydration (eq 1). A similar dehydration reaction was also observed in the reaction of 3 with ammonia, leading to a μ3-imido complex.7c Because 3 was highly air sensitive, we did not isolate it from the reaction mixture after the reaction of 1 with 1.13 equiv of O2. This reaction yielded a mixture of 3 and bis(μ3-oxo) complexes in a ratio of 88/12.1b While 3 readily reacts with methanol, the bis(μ3-oxo) complex did not react. Thus, the mixture was B

DOI: 10.1021/acs.organomet.7b00465 Organometallics XXXX, XXX, XXX−XXX

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Organometallics bridging hydrides on the face opposite to the μ3-hydride. The μ-CO group is located on the same side as the H(1) and H(2) atoms, and the dihedral angle between the Ru(1)−C(1)− Ru(2) plane and the Ru3 plane is 143°. Owing to the steric repulsion with the μ-CO and μ-H ligands, the three Cp* groups are bent toward the μ3-hydride by 11° (average) with respect to the Ru3 plane. In spite of the unsaturated nature of 4, the Ru− C and C−O distances at the μ-CO group (average 2.00 and 1.19 Å, respectively) were not significantly different from those found in the μ-CO ligands in the coordinatively saturated triruthenium complexes containing three Cp* groups (Ru−C, 1.97−2.16 Å; C−O, 1.18−1.21 Å).14−16 In the IR spectrum, a strong absorption arising from ν(μ-CO) was observed at 1739 cm−1. Although the structure of 4 contains a noncrystallographic mirror plane bisecting the triruthenium plane through the μCO ligand, the 1H NMR spectrum of 4 recorded at 20 °C displays only one broad signal for the hydrides at δ −12.17 and one sharp Cp* signal at δ 1.87 ppm. This indicates that the μCO ligand migrates among the three Ru−Ru edges, generating a time-averaged C3 structure. As the temperature was decreased, the broad hydride signal split into two signals resonating at δ −21.48 and −9.30 ppm with an intensity ratio of 1/2 at −100 °C (Figure 2). The sharp Cp* signal observed at 20 °C also

optimized using density functional theory (DFT) calculations, and A is estimated to be less stable than 4 by ca. 1 kcal mol−1 at 298 K (see Figure S11 in the Supporting Information). In addition, small signals derived from another species, B, began to appear below −70 °C. Two small hydrido signals were observed at δ −3.59 and −9.31 ppm, in which the latter was superimposed on one of the hydride signals of 4. The ratio between 4 and B at −100 °C is roughly estimated to be 12/1. Irradiation at δ −3.59 ppm at −70 °C resulted in a decrease in the signal intensities of the hydrides of 4 by ca. 50%. This strongly implies that 4 equilibrates with B on the NMR time scale. Because two hydrido signals with an intensity ratio of 1/2 were observed, B must adopt a Cs structure like that of 4. However, we could not optimize a Cs structure for a possible isomer of 4 by DFT calculations. Thus, we tentatively assigned B as a THF adduct of 4. While numerous examples of trinuclear complexes having both μ-CO and hydrides are known, those with a 44-electron configuration are still quite limited.13,18 Owing to its electron deficiency, 4 is expected to show high reactivity like that of the parent pentahydrido complex 1. At first, the reaction of 4 with 1 atm of D2 was examined, which resulted in deuteration at the Ru−H site by 50% after 3 h at 25 °C (eq 2). Although the

formation of a hydrogen adduct was not observed, the liberation of HD was clearly confirmed by a triplet signal at δ 4.43 (t, JH−D = 42.7 Hz). This implied that H/D exchange proceeds via an associative manner as pentahydrido complex 1 did,1b while the rate of H/D exchange of 4 was considerably slower than that of 1 (100% deuteration within 3 h). Reaction of 4 with Butadiene. The reactivity of 4 toward unsaturated hydrocarbons was then investigated. Complex 4 smoothly reacted with butadiene at 25 °C to afford a coordinatively saturated complex, 5a, that contains a μ-η2:η2s-cis-butadiene ligand (eq 3). The reaction of Ru3(CO)12 with

Figure 2. Variable-temperature 1H NMR spectra of 4 showing (a) Cp* and (b) hydrido regions (400 MHz, THF-d8).

split into two peaks at δ 1.86 and 1.85 ppm. The lowtemperature spectrum agreed with the X-ray structure of 4, having a Cs-symmetrical structure. Casey et al. showed that site exchange between μ-CO and μ3CO ligands in (Cp*Co)3(μ-H)2(μ-CO)(μ3-CO) occurs on the NMR time scale.17 Thus, the migration of the μ-CO ligand via a face-capping CO seems to be reasonable (Scheme 1). The structure of intermediate A, which contains a μ3-CO ligand, was

acyclic 1,3-dienes results in the formation of μ3-dimetalloallyl complexes, {Ru(CO)3}3(μ-H)(μ3-η3-CRCHCR′), and this reaction has been widely investigated.19 Because the reaction is usually performed at elevated temperature (ca. 90 °C), the formation of an intermediary diene adduct has not been observed. Shapley and co-workers isolated a triosmium complex ligated by an s-trans-butadiene ligand by the reaction of Os3(μH)2(CO)10 with 1,3-butadiene at ambient temperature.20 The s-cis form in 5 is favored because of the steric repulsion arising from the surrounding Cp* groups. We have previously reported that 1 reacts with isoprene to afford the μ3-η2:η2-s-cis-isoprene

Scheme 1. Plausible Mechanism of the Dynamic Behavior of 4

C

DOI: 10.1021/acs.organomet.7b00465 Organometallics XXXX, XXX, XXX−XXX

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Organometallics

fashion at the Ru(1) atom, which was not ligated by the butadiene ligand. Accordingly, ν(CO) is considerably blue shifted, appearing at 1880 cm−1 in the IR spectrum. In the 13C NMR spectrum, the 13C signal derived from the terminal CO group resonated at δ 207.5 ppm. In the 1H NMR spectrum of 5a, two sharp signals for the Cp* groups were observed at δ 1.77 and 1.73 ppm in a 2/1 ratio. The signals for the hydrides appeared at δ −13.66 (t) and −22.60 (d) also with an intensity ratio of 1/2. The signals stemming from the s-cis-butadiene moiety resonated at δ 0.53, 1.82, and 2.44 ppm as complicated multiplets arising from their magnetic inequivalence.24 The 13C signals stemming from the butadiene ligand (δ 26.8 (Cout, t, JC−H = 153 Hz) and 41.2 (Cin, d, JC−H = 154 Hz)) were observed in a significantly higher magnetic field region upon μ-η2:η2 coordination in comparison to those of uncomplexed 1,3-butadiene (δ 116.6 (Cout) and 137.2 (Cin)),25 and these chemical shifts are comparable to those of s-cis-butadiene complex 6 (δ 31.0 and 49.3).21 Reaction of 4 with Alkynes. The reaction of 4 with another four-electron ligand, alkyne, was also investigated. Complex 4 readily reacted with phenylacetylene to yield the (⊥)-alkyne complex 7a, where the alkyne ligand was coordinated to one of the Ru−Ru edges in a perpendicular fashion (eq 4). The ⊥ coordination mode of alkynes to a

complex 6, which has an agostic Ru−H−C interaction at one terminal carbon atom (Chart 1).21 Complex 6 was gradually converted into a μ3-η3-dimetalloallyl complex by subsequent C−H bond scission followed by the insertion of the olefinic moiety into a Ru−H bond. Chart 1. Molecular Structure of 6

The 1,3-diene ligand in 5 adopted an s-cis structure like that of 6, but the agostic Ru−H−C interaction is not present owing to the coordinatively saturated nature of 5. While 1 reacts with butadiene, eliminating dihydrogen, the hydrido ligands in 4 were not eliminated along with the formation of 5. Hence, 5 adopts a coordinatively saturated 48-electron configuration. Although the thermolysis of 5a in toluene afforded a complex mixture of unidentified complexes, the starting trihydrido complex 4 was cleanly regenerated upon the thermolysis of 5b at 50 °C, liberating isoprene in the process. The steric repulsion between the methyl group of the diene moiety and the surrounding Cp* groups promotes the clean decoordination of isoprene from the triruthenium core, while dehydrogenation leading to decomposition may occur during the thermolysis of 5a. The μ-η2:η2 coordination of the s-cis-butadiene ligand on one Ru−Ru edge, as well as the presence of a terminal CO ligand in 5a, was confirmed by XRD, as shown in Figure 3. The πbonded C(2)C(3) distance of 1.420(11) Å is comparable to the inner C(3)−C(3#) distance (1.469(14) Å). This implies that there is a localization of the π electrons at C(2)C(3) bonds, as seen in previous μ-η2:η2-diene complexes.22,23 Alongside the incorporation of butadiene, the coordination mode of the CO ligand was altered from a μ to a terminal

trinuclear site is characteristic of trinuclear complexes adopting a 46-electron configuration.26 In contrast to the reaction with butadiene, two hydrido ligands in 4 were eliminated as dihydrogen, which was confirmed by the singlet appearing at δ 4.47 ppm in the 1H NMR spectrum. The X-ray crystal structure of 7a clearly shows the perpendicular coordination of the μ3-alkyne ligand to the Ru(2)−Ru(2#) edge, as well as the face-capping coordination of the CO ligand (Figure 4). There is a crystallographic mirror plane bisecting the Ru3 triangle, and the alkyne and the μ3-CO ligands are located on the mirror plane. Because three sharp signals assignable to the Cp* groups were observed at δ 1.68, 1.72, and 1.85 ppm in the 1H NMR spectrum recorded at 25 °C, the hydride must be located at the Ru(1)−Ru(2) or Ru(1)−Ru(2#) edge. However, the position of the μ-hydrido ligand was not determined because of the presence of the mirror plane. Such an unsymmetrical structure has also been observed in a similar phenylacetylene complex capped by a μ3borylene ligand, (Cp*Ru)3{μ3-η2:η2(⊥)-PhCCH}(μ3-BH)(μH) (8b).27 The formal oxidation state of the metal centers of 7a was lower than those of the related (⊥)-PhCCH complexes {Cp*Ru(μ-H)}3{μ3-η2:η2(⊥)-PhCCH} (8a),28 (Cp*Ru)3{μ3η2:η2(⊥)-PhCCH}(μ3-BH)(μ-H) (8b),27 and (Cp*Ru)3{μ3η2:η2(⊥)-PhCCH}(μ3-BO)(μ-H)2 (8c),29 synthesized previously. The reduced metal center in 7a would cause enhanced back-donation to the alkyne moiety and, hence, considerable elongation in the C−C bond. However, the geometric parameters of 7a are not significantly different from those of

Figure 3. Molecular structure and labeling scheme of 5a with thermal ellipsoids at 30% probability. Selected bond lengths (Å) and angles (deg): Ru(1)−Ru(2) = 3.0670(8), Ru(2)−Ru(2#) = 3.0635(10), Ru(1)−C(1) = 1.835(10), Ru(2)−C(2) = 2.159(8), Ru(2)−C(3) = 2.204(7), C(1)−O(1) = 1.159(12), C(2)−C(3) = 1.420(11), C(3)− C(3#) = 1.469(14); Ru(2)−Ru(1)−Ru(2#) = 59.92(2), Ru(2)− Ru(1)−C(1) = 82.9(3), Ru(1)−Ru(2)−Ru(2#) = 60.04(1), C(2)− Ru(2)−C(3) = 38.0(3), Ru(1)−C(1)−O(1) = 174.2(8), C(2)− C(3)−C(3#) = 123.5(5). D

DOI: 10.1021/acs.organomet.7b00465 Organometallics XXXX, XXX, XXX−XXX

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are estimated to be ΔH⧧ = 11.5 ± 0.4 kcal mol−1 and ΔS⧧ = −20.6 ± 1.3 cal mol−1 K−1 and ΔH⧧ = 40.2 ± 1.6 kcal mol−1 and ΔS⧧ = +62.9 ± 5.1 cal mol−1 K−1, respectively. Notably, the motion of the alkyne ligand in 7a was significantly reduced in comparison to that in 8a. We have previously observed the dynamic behavior of a μ3-(⊥)-alkyne ligand at a trinuclear site, termed a switchback motion, in which the alkyne ligand moves around the trinuclear site by altering the positions of the inner and outer acetylenic carbons.30 For 8a, the activation parameters for the switchback motion were estimated to be ΔH⧧ = 14.0 ± 0.3 kcal mol−1 and ΔS⧧ = 0.2 ± 1.0 cal mol−1 K−1. The extremely large ΔH⧧ and ΔS⧧ values for the dynamic motion of the alkyne ligand in 7a implies that the rotation proceeds in a manner different from that occurring in 8a. In particular, the large positive ΔS⧧ value suggests that the switchback motion of the alkyne ligand requires a change in the coordination mode of the μ3-CO ligand at the Ru3 site. In contrast to the reaction of 4 with phenylacetylene, the μ3η2-pentenylidene complex 9b was obtained by the reaction of 4 with 1-pentyne (eq 5). The μ3-1-hexyne complex {Cp*Ru(μ-

Figure 4. Molecular structure and labeling scheme of 7a with thermal ellipsoids at 30% probability. Selected bond lengths (Å) and angles (deg): Ru(1)−Ru(2) = 2.7074(3), Ru(2)−Ru(2#) = 2.8048(3), Ru(1)−C(1) = 2.046(3), Ru(1)−C(3) = 2.130(2), Ru(2)−C(1) = 2.224(2), Ru(2)−C(2) = 1.9993(18), Ru(2)−C(3) = 2.2372(19), C(1)−O(1) = 1.195(3), C(2)−C(3) = 1.415(4); Ru(2)−Ru(1)− Ru(2#) = 62.395(8), Ru(1)−Ru(2)−Ru(2#) = 58.801(4), Ru(1)− C(1)−O(1) = 137.1(2), Ru(2)−C(1)−O(1) = 131.00(13), C(2)− C(3)−C(4) = 119.5(2).

8a−c. This was likely due to an offset by the electronwithdrawing CO group. Although the Cp* signals were observed to be inequivalent at 0 °C, two signals began to broaden as the temperature increased (Figure 5). Above 50 °C, the other Cp* signal also

H)}3{μ3-η2:η2(⊥)-nBuCCH} (8d), which has three hydrido ligands, has been shown to equilibrate with a μ3-η2hexenylidene complex, {Cp*Ru(μ-H)}3{μ3-η2-CC(nBu)H} (10d), above 70 °C;15 thus, it is rational to assume that 9b was formed via the (⊥)-alkyne complex 7b.31 Unlike the equilibrium between 8d and 10d, where the 8d/10d ratio was estimated to be 53/47 at 80 °C, the equilibrium between 7b and 9b largely shifts toward 9b. This fact implies that the μ3alkenylidene form is effectively stabilized by the μ-CO group, likely owing to its electron-withdrawing nature. The μ-CO and μ3-pentenylidene ligands are placed almost coplanar, as shown in Figure 6, which implies that there are some electronic interactions. The formation of a μ3-pentenylidene ligand was confirmed by the presence of a doublet of doublets resonating at δ 6.71 ppm (dd, JH−H = 9.9, 2.8 Hz) in the 1H NMR spectrum and the 13 C signals observed at δ 297.6 (Cα) and 77.2 ppm (Cβ, d, JC−H = 152 Hz). While these 13C NMR data are typical values for μ3alkenylidene ligands,1a,4,15,32,33 the introduction of a μ-CO group in place of two hydrides causes a considerable upfield shift of the α carbon in comparison to that of 10d (δ 326.3).15 The singlet appearing at δ 264.6 ppm in the 13C NMR spectrum indicates that the CO ligand adopts a bridging coordination mode, which was consistent with the strong absorption at 1728 cm−1 in the IR spectrum. The molecular structure of the μ3-pentenylidene complex 9b was determined and confirmed by XRD (Figure 6). The μ3-pentenylidene ligand is σ-bonded to the Ru(1) and Ru(2) atoms and π-bonded to Ru(3) through the C(2)C(3) bond. The C(2)C(3) distance (1.394(4) Å) lies in the typical range for the CαCβ distances in a μ3-alkenylidene ligand placed on a triruthenium plane (1.35−1.44 Å).1a,4,32a,b,34 The Ru(1)−Ru(2) edge is also bridged by a CO ligand. Consequently, the Ru(1)−Ru(2) bond is significantly shorter than the other Ru−Ru bonds (Ru(1)−Ru(3) = 2.8635(3) Å,

Figure 5. (a) Variable-temperature 1H NMR spectra of 7a showing the Cp* region and (b) simulated spectra obtained using exchange rates k1 and k2 (400 MHz, C6D6).

started to broaden. However, the coalescence of these signals did not occur up to 70 °C. These spectral changes can be rationalized by the combination of the hydrido migration between the Ru(1)−Ru(2) and Ru(1)−Ru(2#) edges and the rotation of the alkyne ligand on the Ru3 plane. The spectral changes were successfully simulated, and the activation parameters for the hydride migration and the alkyne rotation E

DOI: 10.1021/acs.organomet.7b00465 Organometallics XXXX, XXX, XXX−XXX

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accompanied by the formation of ethane (Scheme 2). The formation of 11 was confirmed by the characteristic downfield shift of the μ3-ethylidyne carbon (δ 390.4). Scheme 2. Series of Products Obtained by the Reaction of 4 with Ethylene

Figure 6. Molecular structure and labeling scheme of 9b with thermal ellipsoids at 30% probability. Selected bond lengths (Å) and angles (deg): Ru(1)−Ru(2) = 2.6014(3), Ru(1)−Ru(3) = 2.8635(3), Ru(2)−Ru(3) = 2.9948(3), Ru(1)−C(1) = 2.035(2), Ru(1)−C(2) = 2.025(3), Ru(2)−C(1) = 1.980(2), Ru(2)−C(2) = 1.984(3), Ru(3)−C(2) = 2.014(2), Ru(3)−C(3) = 2.231(3), C(1)−O(1) = 1.187(3), C(2)−C(3) = 1.394(4); Ru(2)−Ru(1)−Ru(3) = 66.260(8), Ru(1)−Ru(2)−Ru(3) = 61.073(8), Ru(1)−Ru(3)−Ru(2) = 52.667(7), Ru(1)−C(1)−Ru(2) = 80.76(9), Ru(1)−C(1)−O(1) = 138.1(2), Ru(2)−C(1)−O(1) = 140.6(2), Ru(1)−C(2)−Ru(2) = 80.89(9), Ru(1)−C(2)−C(3) = 143.7(2), Ru(2)−C(2)−C(3) = 134.6(2).

Ru(2)−Ru(3) = 2.9948(3) Å). The Ru(1)−Ru(2) distance (2.6014(3) Å) corresponds to the reported RuRu distances containing a μ-CO group (2.505−2.712 Å),35 and a double bond between the Ru(1) and Ru(2) atoms makes 9b coordinatively saturated. Notably, the μ-CO and μ3-alkenylidene ligands are almost coplanar (the sum of the interior angles of the square defined by Ru(1), Ru(2), C(1), and C(2) is 359.95°). The local diruthenium structure is very similar to that of (Cp*Ru)2(μ-NPh)(μ-CO) reported by Takemoto et al., where the multiple interaction between the Ru atoms through the orbitals of the bridging ligand is postulated on the basis of DFT calculations.35c The hydrido ligand bridges the Ru(1) and Ru(3) atoms and is beneath the propyl group on the μ3-pentenylidene ligand. While the Ru(1)−Ru(3) bond bridged by the hydride is shorter than the unbridged Ru(2)−Ru(3) bond, the opposite situations were seen in {Os(CO)3}3{μ3-η2-CC(OEt)H}(μ-H)236 and {Ru(CO)3}3(μ3-η2-CCPhH)(μ-H)2,34d where the hydridebridged M−M bond is longer than the unbridged bond. The location of the hydrido ligand can vary, producing positional isomers, although only 9b was isolated by recrystallization. As mentioned later, the hydride in 9 can move between the two Ru−Ru edges (Ru(1)−Ru(3) and Ru(2)−Ru(3)), producing the positional isomer 9b′. However, no distinct signals arising from the isomer were observed in the 1 H NMR spectrum recorded at −80 °C. This fact suggests that 9b is much stable than 9b′ or the motion of the hydride is fast enough to average the spectrum even at −80 °C. The fluxional behavior of 9 will be discussed further later. Reaction of 4 with Ethylene. We have previously reported that the μ3-alkenylidene complex 10 can be synthesized by the reaction of 1 with 1-alkenes.32b The reaction of 4 with ethylene also afforded the μ3-vinylidene complex 9a, but this was not the initial product. The initial product of the reaction was the μ3ethylidyne complex 11, which was quantitatively obtained,

The difference in the products can be rationalized by considering the reactivity of the vinyl intermediate C shown in Scheme 2. Whereas the positional relationship between the μvinyl ligand and the μ-CO ligand in C, as well as the position of the μ-ethylidene ligand in D, is not clear at present, we tentatively propose a plausible mechanism, as shown in Scheme 2. In the reaction of the pentahydrido complex 1 with alkene, αC−H bond scission would occur in the coordinatively unsaturated μ-vinyl intermediate, (Cp*Ru)3(H)2(μ-η2-CH CRR′), formed by the extrusion of hydrides from (Cp*Ru)3(H)4(μ-η2-CHCRR′) via hydrogenation of alkene.32b In contrast, the insertion of the μ-vinyl group into a Ru− H bond took place in C, leading to the formation of μethylidene intermediate D. Although limited examples are known for the formation of a μ-alkylidene ligand via the insertion of a μ-alkenyl group into an M−H bond,37 Lewis et al. demonstrated the transformation of a μ-alkenyl group into a μalkylidene by the uptake of CO in Os4(μ-H)3(μ-η2-CH CPhH)(CO)11.37a We also observed the transformation of the bis(μ-vinyl) complex {Cp*Ru(μ-H)} 3 (μ-η 2 -CHCH 2 ) 2 , which was obtained by the reaction of 1 with acetylene, to a μ-ethylidene−μ3-η2-ethyne complex.32c Owing to the replacement of two hydrides with μ-CO, hydrogenation of alkene would be suppressed in C. Instead, insertion of the vinyl group into a Ru−H bond took place, and subsequently the oxidative addition of the C−H bond at the μ-ethylidene ligand of D afforded 11. The molecular structures of 11 was determined by XRD, as shown in Figure 7, which clearly shows that the Ru3 triangle of 11 is capped by a μ3-ethylidyne ligand. The positions of hydrido ligands were successfully determined and found to be bridging hydrides at the Ru(1)−Ru(2) and Ru(1#)−Ru(2) edges. The μ-carbonyl ligand is located on the crystallographic F

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Figure 8. Molecular structure and labeling scheme of 9a with thermal ellipsoids at 30% probability. Selected bond lengths (Å) and angles (deg): Ru(1)−Ru(2) = 2.5919(6), Ru(1)−Ru(3) = 2.8553(6), Ru(2)−Ru(3) = 2.9879(6), Ru(1)−C(1) = 2.022(5), Ru(1)−C(2) = 2.006(5), Ru(2)−C(1) = 1.990(5), Ru(2)−C(2) = 1.996(5), Ru(3)−C(2) = 2.005(5), Ru(3)−C(3) = 2.234(6), C(1)−O(1) = 1.199(6), C(2)−C(3) = 1.389(8); Ru(2)−Ru(1)−Ru(3) = 66.328(16), Ru(1)−Ru(2)−Ru(3) = 61.068(15), Ru(1)−Ru(3)− Ru(2) = 52.60(1), Ru(1)−C(1)−Ru(2) = 80.5(2), Ru(1)−C(1)− O(1) = 138.5(4), Ru(2)−C(1)−O(1) = 140.5(4), Ru(1)−C(2)− Ru(2) = 80.74(19), Ru(1)−C(2)−Ru(3) = 90.8(2), Ru(2)−C(2)− Ru(3) = 96.6(2), Ru(1)−C(2)−C(3) = 139.2(4), Ru(2)−C(2)−C(3) = 139.5(4), Ru(3)−C(2)−C(3) = 80.1(3).

Figure 7. Molecular structure and labeling scheme of 11 with thermal ellipsoids at 30% probability. Selected bond lengths (Å) and angles (deg): Ru(1)−Ru(1#) = 2.7002(5), Ru(1)−Ru(2) = 2.7189(4), Ru(1)−C(1) = 2.009(4), Ru(1)−C(2) = 1.972(3), Ru(2)−C(2) = 2.148(4), C(1)−O(1) = 1.187(6), C(2)−C(3) = 1.490(7); Ru(2)− Ru(1)−Ru(1#) = 60.228(7), Ru(1)−Ru(2)−Ru(1#) = 59.545(13), Ru(1)−C(1)−Ru(1#) = 84.45(19), Ru(1)−C(1)−O(1) = 137.53(11), Ru(1)−C(2)−Ru(1#) = 86.39(19), Ru(1)−C(2)− Ru(2) = 82.46(15), Ru(1)−C(2)−C(3) = 130.58(17), Ru(2)− C(2)−C(3) = 127.2(3).

mirror plane, bisecting the Ru3 triangle: that is, at the Ru(1)− Ru(1#) edge. There could be an isomer, which contains a μ3-CO ligand; however, no isomer was detected in solution. The reason the CO ligand adopts a doubly bridging position in 11 is uncertain at present, but subtle differences in the environment of the trinuclear site, as well as the nature of the substituent at the alkylidyne carbon, could affect the coordination mode of CO. While a μ coordination of CO was determined in [{Fe(CO)3}3(μ3-CR)(μ-CO)]− (R = H, OCH2OMe),38 a μ3 coordination was observed in [{Fe(CO)3}3(μ3-CCH2CH CH2)(μ3-CO)]−, which contains a μ3-allylmethylidyne ligand.39 The thermolysis of 11 was then examined to obtain the μ3vinylidene complex 9a. Complex 9a was formed upon thermolysis at 70 °C, but the reaction proceeded sluggishly, taking 26 days to yield 9a in 61% yield. In contrast, the formation of 9a was effectively accelerated in the presence of ethylene. Complex 11 was transformed into 9a at 25 °C with the concomitant formation of ethane. This result indicates that reductive elimination of dihydrogen was suppressed, as seen in the reaction of 4 with butadiene, while the hydrido ligands in 11 were extruded more efficiently by the hydrogenation of the incoming ethylene molecule. The 13C signals derived from the α and β carbons of the μ3vinylidene ligand were observed at δ 296.6 and 56.9 (t, JC−H = 157 Hz), respectively. These chemical shifts are comparable to those of 9b obtained from 1-pentyne (Cα, δ 297.6; Cβ, δ 77.2). The molecular structure of 9a was determined by XRD using a green single crystal obtained from a cold hexane solution, and the structure is shown in Figure 8. Although the position of the hydrido ligand in 9a was not determined, the structural parameters of 9a were almost the same as those of 9b. The μ3vinylidene group was σ-bonded to the Ru(1) and the Ru(2) atoms, to which the μ-CO was coordinated. The Ru(2)−Ru(3) bond (2.9879(6) Å) is substantially longer than the Ru(1)− Ru(3) bond (2.8553(6) Å). Such inequivalence was also seen in 9b, in which the unbridged bond was longer than the hydridobridged bond by 0.13 Å. Thus, we can reasonably assume that

the hydrido ligand is also located at the shorter Ru(1)−Ru(3) edge in 9a. Although the environments of each Ru center were inequivalent, the 1H NMR spectrum showed two Cp* signals at δ 1.70 and 1.67 ppm with an intensity ratio of 2/1. The vinylidene protons were also observed to be equivalent at δ 4.85 at 25 °C. The shapes of these signals were maintained even at −80 °C and showed no broadening. Concerning the dynamic motion of μ3-alkenylidene complexes, Deeming and co-workers have established that the μ3vinylidene ligand in {Os(CO)3}3{μ3-CC(OEt)H}(μ-H)2 rotates via a vertical orientation with respect to the triosmium plane, resulting in both enantiomerization and interconversion between the two positional isomers (path B in Scheme 3).36 A similar dynamic motion has also been reported for [{Co(CO)3}3{μ-CC(i-Pr)H}9]+ by Norton and co-workers.40 In contrast to the preceding cases, the rotation of the μ3vinylidene ligand does not induce the time-averaged Cs spectrum. Therefore, these spectral features can be rationalized by the rapid migration of hydride between the Ru(1)−Ru(3) and Ru(2)−Ru(3) edges (path A in Scheme 3). A mechanism involving the formation of a μ3-alkylidyne ligand is also possible (path C in Scheme 3), but this is unlikely because it requires a highly unsaturated 44-electron configuration, and also because of the fact that the enantiomerization was not observed in 9b on increasing the temperature at least up to 80 °C. In addition, spin saturation transfer (SST) was not observed between the hydride and vinylidene protons, which suggests that the equilibrium between 9a and the unsaturated μ3-ethylidyne isomer would be negligible for the site exchange. The migration of a hydride leading to the site exchange of vinylidene protons has also been reported in {Os(CO)3}3(μH)2(μ3-η2-CCH2).41 We previously demonstrated a dynamic motion of a μ3-vinylidene ligand, which showed a pivoting motion between the two Ru−Ru edges (path D in Scheme 3).32c In the case of 9, path D is also unlikely, as such pivoting motion would not produce the time-averaged spectrum. G

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in Os3(μ-H)(μ-CCH2CMe2H)(CO)10 to a μ-vinyl group via a 1,2-shift of the β-hydrogen was elucidated by Green et al.43 The molecular structure of 13 was determined by XRD as shown in Figure 9. Because 13 has a disordered structure with

Scheme 3. Possible Dynamic Motions of the μ3-Alkenylidene Complex 9

Figure 9. Molecular structure and labeling scheme of 13 with thermal ellipsoids at 30% probability. Selected bond lengths (Å) and angles (deg): Ru(1)−Ru(2) = 2.7099(4), Ru(1)−Ru(3) = 2.7492(4), Ru(2)−Ru(3) = 2.7461(4), Ru(1)−C(4) = 2.026(3), Ru(2)−C(4) = 2.024(3), Ru(3)−C(4) = 2.013(3), C(4)−C(5) = 1.457(5); Ru(2)− Ru(1)−Ru(3) = 60.40(1), Ru(1)−Ru(2)−Ru(3) = 60.51(1), Ru(1)− Ru(3)−Ru(2) = 59.09(1), Ru(1)−C(4)−Ru(2) = 83.99(12), Ru(1)− C(4)−Ru(3) = 85.79(12), Ru(1)−C(4)−C(5) = 128.0(3), Ru(2)− C(4)−Ru(3) = 85.71(13), Ru(2)−C(4)−C(5) = 128.2(2), Ru(3)− C(4)−C(5) = 129.7(2).

respect to the positions of the μ-CO and μ-CMe ligands, the positions of these ligands could not be determined. Nevertheless, the presence of the μ-ethylidyne ligand in addition to the μ3-ethylidyne ligand was inferred by 13C NMR spectroscopy. In the 13C NMR spectrum of 13, two distinctive signals were observed at δ 388.3 and 318.5 ppm, which were assigned to signals originating from the μ-CMe and μ3-CMe groups, respectively. It is well-known that μ-alkylidyne carbons resonate downfield of those of a μ3-alkylidyne ligand.43−45 Notably, complex 13 possesses two kinds of ethylidyne ligands, μ- and μ3-ethylidynes. While several bis(μ3-alkylidyne) complexes are known, there are few adopting different coordination modes.45,46 Such a bis(alkylidyne) complex is very important in relation to reversible C−C bond scission of an alkyne ligand on a multinuclear site; Shapley and Chi synthesized the bis(alkylidyne) complex {CpW(CO)}2{Os(CO)3}(μ-CTol)(μ3-CTol), which contains alkylidyne ligands with different coordination modes, upon decarbonylation of {CpW(CO)2}2{Os(CO)3}(μ-η2(∥)-TolCCTol).45b Although the position of the hydride in 13 was not determined owing to the disordered structure, the presence was strongly inferred by the 1H signal appearing at δ −20.84. The hydride would be placed at the Ru−Ru edge which was not bridged by the μ-CO and μ-CMe ligands. We have previously shown consecutive carbyne migrations across the Ru3 plane of a μ3-alkyne−μ3-alkylidyne complex, resulting in the metathesis of the two hydrocarbyl moieties.47 This metathesis reaction proceeds via the partial breaking of the trinuclear skeleton, leading to the formation of a μ3-metallacyclobutenyl intermediate. In contrast, the Ru3 skeleton of 13 was reinforced by the μ-CO group. Therefore, the reactivity of the bis(alkylidyne) complex 13 is expected to differ from that of the μ3-alkyne−μ3-alkylidyne complex. Thus, the thermolysis of the equilibrated mixture of 12 and 13 was examined to

Formation of Bis(ethylidyne) Complex. The unsaturated nature of 9a allowed further uptake of ethylene into the trinuclear core. When the reaction of 4 with 1 atm of ethylene was carried out at 110 °C, a mixture of the μ3-ethylidyne−μvinyl complex 12 and μ3-ethylidyne−μ-ethylidyne complex 13 was obtained in a ratio of 1/15. Although 12 was not isolated, the formation of 12 was deduced on the basis of the characteristic signals of the μ-vinyl group at δ 2.58 (d, JH−H = 7.2 Hz), 3.56 (d, JH−H = 10.4 Hz), and 7.80 ppm (dd, JH−H = 10.4, 7.2 Hz). The μ-vinyl structure was also suggested by the structure of the analogous μ-isocyanido complex (Cp*Ru)3(μ3CH)(μ-η2-CHCPhH)(μ-H)(μ-CNtBu), which has been previously reported.42 A mixture of crystals of 12 and 13 was obtained by recrystallization, and the initial ratio between 12 and 13 was estimated to be 1/5 by the 1H NMR spectrum recorded in 20 min at 23 °C. The population of 12 gradually decreased, and the 12/13 ratio became steady after 30 h, where it was estimated to be 1/15. Although SST was not observed between 12 and 13, this result implied equilibrium between these species in solution. A similar transformation of the μ-alkylidyne ligand H

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Organometallics investigate the skeletal rearrangement of the hydrocarbyl moieties, aiming, in particular, at the coupling reaction. The thermolysis of the mixture at 180 °C resulted in the formation of a mixture of 14 and 15 with a ratio of ca. 1/3 with small amounts of unidentified complexes (eq 6). Among these

Figure 10. Molecular structure and labeling scheme of 15 with thermal ellipsoids at 30% probability. Selected bond lengths (Å) and angles (deg): Ru(1)−Ru(2) = 2.6822(9), Ru(1)−Ru(3) = 2.6978(10), Ru(2)−Ru(3) = 2.6863(9), Ru(1)−C(1) = 2.044(13), Ru(1)−C(3) = 2.072(8), Ru(1)−C(4) = 1.998(8), Ru(2)−C(1) = 2.039(16), Ru(2)−C(2) = 2.000(14), Ru(2)−C(4) = 2.020(8), Ru(3)−C(2) = 2.080(13), Ru(3)−C(3) = 2.065(8), Ru(3)−C(4) = 2.002(8), C(1)− O(1) = 1.206(18), C(2)−C(3) = 1.422(16); Ru(2)−Ru(1)−Ru(3) = 59.91(2), Ru(1)−Ru(2)−Ru(3) = 60.33(2), Ru(1)−Ru(3)−Ru(2) = 59.76(2), Ru(1)−C(1)−Ru(2) = 82.1(5), Ru(1)−C(1)−O(1) = 138.9(13), Ru(2)−C(1)−O(1) = 138.7(12), Ru(1)−C(4)−Ru(2) = 83.8(3), Ru(1)−C(4)−Ru(3) = 84.8(3), Ru(2)−C(4)−Ru(3) = 83.8(3).

species, 14 has been reported by Ernst and co-workers, and the structure containing a three-membered carbon ring on the Ru3 plane has been unambiguously determined by XRD.48 Formation of 14 indicates that the two C2 moieties placed on each face of the Ru3 plane are combined, as seen in the previous bis(alkylidyne) complexes.45b,49 For the formation of a μ3-η3-C3 ring, we have reported that the two-electron oxidation of a μ3dimetalloallyl complex results in the exclusive formation of a μ3η3-C3 ring on a triruthenium cluster.14,50 This implies that the C3 ring was constructed via an allylic structure and the electrondeficient Ru3 core owing to the presence of a CO group would promote the formation of the C3 ring, as seen in the oxidation reaction. While dihydrogen was removed from the Ru3 core to form 14, methane elimination was required to form 15. Although the mechanism for methane elimination is unclear at present, the liberation of methane was confirmed by the 1H NMR spectrum, which contains a singlet at δ 0.86 ppm. Similar C−C bond scission has also been seen in the thermolysis of a triruthenium complex containing a μ-alkyl ligand, affording a μ3-methylidyne complex as a consequence of C−C bond cleavage.15 Thus, the formation of a μ-ethylidene ligand via the migration of a hydride to the μ-ethylidyne carbon would be the initial step for the formation of 15. Complex 15 was characterized as a μ3-methylidyne−μ3η2(∥)-ethyne complex containing a μ-CO ligand. The 1H NMR spectrum displayed two Cp* signals at δ 1.78 and 1.81 ppm with an intensity ratio of 2/1. The ethyne protons resonated at δ 8.49 as a doublet coupled with a μ3-methylidyne proton appearing at δ 14.97 ppm (JH−H = 1.0 Hz). The Cs-symmetrical structure of 15 was also corroborated by XRD, as shown in Figure 10.

eliminated from the cluster core, alongside the reaction with butadiene. The suppression of hydrogen elimination was also seen in the thermolysis of μ3-ethylidyne complex 11, leading to the formation of the μ3-vinylidene complex 9a. Accepting and eliminating dihydrogen from the metal centers is a crucial point in considering the reactivity of a polyhydrido cluster. The fact that the replacement of two hydrides by CO suppresses the hydrogen elimination would be important information in the design of a novel cluster catalysis. The introduction of a CO ligand in place of two hydrido ligands does not alter the electron configuration of the cluster, but the formal oxidation state of the metal centers was reduced by 2. In addition, the replacement of two hydrides with a CO ligand also causes a reduction of the coordination number at the metal centers. Whereas the reason has not been clearly understood yet, these factors are likely responsible for the suppression of the reductive elimination of hydrides in comparison to the hydrido analogue. The π-acidic nature of CO makes the triruthenium center electron deficient, as shown in the CV analysis. More importantly, this induced a different skeletal rearrangement of hydrocarbyl ligands, as seen in the formation of 14, which contains a μ3-η3-C3 ring. It is also noteworthy that the insertion of CO into a Ru−C bond was not observed in this study, in contrast to the ruthenium clusters supported by Cp (Cp = η5-C5H5) or CO ligands, in which the insertion of CO into a Ru−C bond at a multinuclear site often took place.51 The electron-donating Cp* groups would cause enhanced back-donation to the π*(CO) orbital, strengthening the Ru−CO bond. Instead, the coordination mode of the CO ligand has been shown to change between the terminal, μ, and μ3 modes, accompanied by a reaction with unsaturated hydrocarbons, as seen in the fluxional process of 4. Such flexibility, arising from the motion of a CO

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CONCLUSION We succeeded in introducing one CO group to the triruthenium plane by the reaction of mono(μ3-oxo) complex 3 with methanol and obtained the novel triruthenium hydrido cluster 4 containing a μ-CO ligand. The coordinatively unsaturated nature of 4 allowed the uptake of dienes, alkynes, and alkenes into the triruthenium core, similar to the case for the parent pentahydrido complex 1. However, in contrast to the reaction of 1 with a diene, hydrido ligands in 4 were not I

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An enhanced rigid-bond restraint (SHELX keyword RIGU) was applied to the Cp*Ru fragments containing the disordered Cp* group in 4, 5a, 7a, 9a, 11, 13, and 15.54 For the structures of 5a and 9a checkCIF reported some A alerts due to the large peaks. However, the peaks are close to the Ru atoms and can be ascribed to the summation terminated error (typical for heavy-atom structures). The metal-bound hydrogen atoms in 4, 9b, and 11 were found by the difference Fourier synthesis and refined isotropically, while the positions of metal-bound hydrogen atoms in 5a, 7a, 9a, and 13 were not determined. In addition, the hydrogen atoms of the μ-CMe ligand in 13 and the μ3-η2(∥)-HCCH ligand in 15 could not be refined. Crystal data and results of the analyses are given in Table S1 in the Supporting Information. Variable-Temperature NMR Spectra and NMR Simulations. Variable-temperature NMR studies were performed in NMR tubes equipped with a J. Young valve using a Varian INOVA-400 Fourier transform spectrometer. The NMR simulation for the 1H NMR spectrum of 5a recorded at 25 °C was performed using gNMR v5.0.6.0 (2006 Ivory Soft). Final simulated line shapes were obtained via an iterative parameter search on the coupling constants, and the details of the fitting procedure are shown in the Supporting Information. The NMR simulations for the temperature-dependent Cp* signals of 7a were also performed via an iterative parameter search on the exchange constants k1 and k2, which were the rates for the site exchange of the hydride and the rotation of the phenylacetylene ligand, respectively. Details of the fitting procedure are also shown in the Supporting Information. The rate constants k1 and k2 that accurately modeled the experimental spectra at each temperature are also given in the Supporting Information. The activation parameters ΔH⧧ and ΔS⧧ were determined from the plot of ln(k/T) versus 1/T. Estimated standard deviations (σ) in the slope and y intercept of the Eyring plot determined the error in ΔH⧧ and ΔS⧧, respectively. The standard deviation in ΔG⧧ was determined from the formula σ(ΔG⧧)2 = σ(ΔH⧧)2 + [Tσ(ΔS⧧)]2 − 2Tσ(ΔH⧧)·σ(ΔS⧧). Computational Details. DFT calculations for 4 and A, which is the possible isomer of 4, were carried out at the B3LYP level in conjunction with the Stuttgart/Dresden ECP55 and associated with triple-ζ SDD basis sets for Ru. For C, H, and O, 6-31(d) basis sets were employed. No simplified model compounds were used for the calculations. Initial geometries for the optimization were based on the crystallographically determined structure for 4. All calculations were performed using the Gaussian 09 software suite.56 The molecular structures were drawn using the GaussView version 5.0 program.57 Frequency calculations at the same level of theory as geometry optimizations were performed on the optimized structure to ensure that minima exhibit only positive frequency. Information on the atom coordinates (xyz files) for all optimized structures are collected in Tables S12 and S14, and selected bond distances and angles are given in Tables S11 and S13 in the Supporting Information. Preparation of (Cp*Ru)3(μ3-H)(μ-H)2(μ-CO) (4). Complex 1 (2.03 g, 2.84 mmol), THF (325 mL), and methanol (65 mL) were charged in a 500 mL Schlenk tube. After the solution was cooled in a dry ice/methanol bath, the reaction flask was degassed by a vacuum line. Then, 1.1 equiv (ca. 77 mL, 18.0 °C, 3.2 mmol) of O2 was introduced into the reaction flask by the use of a gas sphere (12.84 mL) six times at −78 °C. The solution was stirred under reduced pressure for 2 h at −60 °C and 10 min at 0 °C. The solution turned from brown to dark green. After the solvent was removed under reduced pressure, 300 mL of methanol was added under an argon atmosphere. The mixture was stirred until the dark green solid was dissolved. The solution was dark brown. After the solvent was removed under reduced pressure, the residual solid was dissolved in hexane (ca. 300 mL) and purified by column chromatography on alumina (Merck, Art. No. 1097) using toluene as an eluent. The second black band including 4 was collected. Dryness under reduced pressure gave 4 (1.29 g, 1.74 mmol, 61% yield) as a black solid. A single crystal used for the diffraction study was obtained by recrystallization from a hexane solution of 4 stored at −30 °C. 1H NMR (400 MHz, THF-d8, −100 °C): δ 1.86 (s, 30H, C5Me5), 1.85 (s, 15H, C5Me5), −9.30 (d, 2H, JH−H = 2.8 Hz, Ru-H), −21.48 ppm (t, 1H, JH−H = 2.8 Hz, Ru-H). 13C NMR (100 MHz, benzene-d6, 23 °C):

ligand, results in reactivity different from that of the parent pentahydrido complex 1. We will continue to explore the reactivity of 4 to develop the novel catalytic reaction characteristics for multimetallic compounds.

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EXPERIMENTAL SECTION

General Procedures. All experiments were carried out under an argon atmosphere. All compounds were treated with Schlenk techniques. Dehydrated toluene, tetrahydrofuran (THF), diethyl ether, hexane, and methanol used in this study were purchased from Kanto Chemicals and stored under an argon atmosphere. p-Xylene was dried over MS-3A and stored under an argon atmosphere. Benzene-d6, THF-d6, and toluene-d8 were dried over sodium-benzophenone ketyl and stored under an argon atmosphere. Other materials used in this research were used as purchased. Complex 1 was prepared according to the previously published method.1b 1H and 13C NMR spectra were recorded on Varian INOVA 400 and Varian 400-MR Fourier transform spectrometers. 1H NMR spectra were referenced to tetramethylsilane as an internal standard. 13C NMR spectra were referenced to the natural-abundance carbon signal of the solvent employed. IR spectra were recorded on a JASCO FT/IR-4200 spectrophotometer. Elemental analysis was performed on a PerkinElmer 2400II series CHN analyzer. Cyclic voltammograms were performed using a BAS CV-50W voltammetric analyzer interfaced to a personal computer. The working electrode was platinum, and the counter electrode was a platinum wire. The reference electrode was a silver wire housed in a glass tube sealed with a porous Vycor tip and filled with a 0.1 M solution of AgNO3 in acetonitrile. The data obtained relative to a reference electrode (Ag/ Ag+) were converted to the potential relative to the redox potential of ferrocene, which was measured under the same conditions at the same time. Tetrabutylammonium hexafluorophosphate (TBAPF6; Wako) was recrystallized from THF, dried under vacuum, and stored under an argon atmosphere. A concentration of ∼1 mM of complexes 1 and 4 in 0.1 M TBAPF6 in THF was used. X-ray Diffraction Studies. Single crystals of 4, 5a, 7a, 9a,b, 11, 13, and 15 for the X-ray analyses were obtained directly from the preparations described below and mounted on nylon Cryoloops with Paratone-N (Hampton Research Corp.). Diffraction experiments were performed on a Rigaku R-AXIS RAPID imaging plate diffractometer with graphite-monochromated Mo Kα radiation (λ = 0.71069 Å). Cell refinement and data reduction were performed using the PROCESSAUTO program.52 Intensity data were corrected for Lorentz− polarization effects and absorption. The structures were solved by direct methods using SHELXT-2014/5 and further refined with SHELXL-2014/7.53 All non-hydrogen atoms were found by the difference Fourier synthesis and were refined anisotropically. The refinements were carried out by least-squares methods based on F2 with all measured reflections. In the case of 4, the carbon atoms in the Cp* group attached to Ru(5) was disordered and refined with 55%/ 45% occupancy. The μ-CO ligand in molecule 2 was disordered over two sites, the Ru(4)−Ru(5) and Ru(5)−Ru(6) edges, and refined with 54%/46% occupancy. In the case of 5a, the Cp* groups attached to Ru(1) and Ru(2) were disordered and refined with 50%/50% and 52%/48% occupancies, respectively. In the case of 7a, the Cp* group attached to the Ru(1) was disordered with 50%/50% occupancy. In the case of 9a, the Cp* group attached to Ru(3) was disordered and refined with 56%/44% occupancy. In the case of 11, the Cp* group attached to Ru(2) was disordered with 50%/50% occupancy. In the case of 13, the Cp* groups attached to Ru(1), Ru(2), and Ru(3) were disordered with 65%/35%, 60%/40%, and 63%/37% occupancies, respectively. The μ-CO and μ-CMe ligands were disordered over the three sites, whose occupancies were estimated to be at 31%/43%/28% and 45%/21%/34%, respectively. In the case of 15, the Cp* group attached to Ru(2) was disordered with 54%/46% occupancy. The C(2) atom of the μ3-η2-(∥)-HCCH ligand was disordered over two sites, at the Ru(3)−Ru(2) and Ru(2)−Ru(3) edges, with 53%/47% occupancy. The EADP restraint and the EXYZ restraint were applied to all atoms of the μ-CO and μ-CMe ligands in 15 due to the disorder. J

DOI: 10.1021/acs.organomet.7b00465 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics δ 262.9 (s, CO), 89.5 (s, C5Me5), 12.1 ppm (q, JC−H = 127 Hz, C5Me5). IR (KBr, cm−1): νCO 1739. Anal. Calcd for C31H48ORu3: C, 50.32; H, 6.54. Found: C, 49.94; H, 6.89. In the hydrido region of the 1 H NMR spectrum, signals derived from B, which was considered to be a THF adduct of 4, were observed at δ −3.59 and −9.31 below −70 °C, where the ratio between 4 and B was estimated to be 12/1. H/D Exchange Reaction of 4 with 1 atm of D2. Complex 4 (9.6 mg, 0.013 mmol) and C6D6 (0.5 mL) were charged in an NMR tube equipped with a J. Young valve. After the solution was frozen in a dry ice/methanol bath, the NMR tube was degassed by the vacuum line. Then, 1 atm of D2 was introduced into the tube. The tube was stored at 25 °C, and the reaction was monitored periodically by means of 1H NMR spectroscopy. The signal intensity of hydrides of 4 decreased to 50% after 3 h, while it decreased to 19% after 53 h. Preparation of {Cp*Ru(μ-H)}3(μ-η2:η2-C4H6)(CO) (5a). Complex 4 (102.4 mg, 0.138 mmol) and toluene (25 mL) were charged in a 50 mL Schlenk tube. After the solution was cooled in a dry ice/methanol bath, the reaction flask was degassed by a vacuum line. Then, 1 atm of butadiene was introduced into the reaction flask. The solution was stirred for 30 min at 25 °C. The solution immediately turned from dark brown to purple. After the solvent was removed under reduced pressure, the residual solid was dissolved in toluene (ca. 10 mL) and purified by column chromatography on alumina (Merck, Art. No. 1097) using toluene as an eluent. The first purple band including 5a was collected. Drying under reduced pressure afforded 5a (100.3 mg, 0.126 mmol, 91% yield) as a purple solid. A single crystal used for the diffraction study was obtained by recrystallization from the toluene solution of 5a stored at −30 °C. 1H NMR (400 MHz, benzene-d6, 23 °C): δ 2.44 (m, 2H, −CHCHH′), 1.82 (m, 2H, −CHCHH′; exo), 1.77 (s, 30H, C5Me5), 1.73 (s, 15H, C5Me5), 0.53 (m, 2H, −CHCHH′; endo), −13.66 (t, 1H, JH−H = 2.6 Hz, Ru-H), −22.60 ppm (d, 2H, JH−H = 2.6 Hz, Ru-H). 13C NMR (100 MHz, benzene-d6, 23 °C): δ 207.5 (s, CO), 92.9 (s, C5Me5), 90.0 (s, C5Me5), 41.2 (d, JC−H = 154 Hz, −CH = CH2), 26.8 (t, JC−H = 153 Hz, −CHCH2), 11.5 (q, JC−H = 127 Hz, C5Me5), 10.5 ppm (q, JC−H = 126 Hz, C5Me5). IR (KBr, cm−1): νCO 1880. Anal. Calcd for C35H54ORu3: C, 52.94; H, 6.86. Found: C, 52.72; H, 6.70. Preparation of {Cp*Ru(μ-H)}3(μ-η2:η2-CH2CMeCHCH2)(CO) (5b). Complex 4 (78.6 mg, 0.106 mmol), diethyl ether (40 mL), and isoprene (0.53 mL, 50 equiv) were charged in a 50 mL Schlenk tube. The solution truned from dark brown to purple. The solution was stirred for 1 h at 25 °C and passed through a glass frit. After concentration, purple precipitates were obtained from the solution stored at −30 °C. Analytically pure 5b was obtained by washing the precipitates three times with 2 mL of hexane (54.6 mg, 67.6 μmol, 64% yield) as a purple crystalline solid. 1H NMR (400 MHz, toluene-d8, 0 °C): δ 2.25 (dd, 1H, JH−H = 10.2, 7.6 Hz, CHH′ CMeCHCHH′), 2.20 (s, 1H, CHH′CMeCHCHH′; exo), 1.80 (s, 15H, C5Me5), 1.75 (s, 15H, C5Me5), 1.70 (s, 15H, C5Me5), 1.56 (s, 3H, Me), 1.50 (d, 1H, JH−H = 7.6 Hz, CHH′CMeCHCHH′; exo), 0.98 (d, 1H, JH−H = 1.0 Hz, CHH′CMeCHCHH′; endo), 0.23 (dd, 1H, JH−H = 10.2, 1.0 Hz, CHH′CMeCHCHH′; endo), −14.31 (s, 1H, Ru-H), −21.37 (s, 1H, Ru-H), −24.57 ppm (s, 1H, RuH). 13C{1H} NMR (100 MHz, toluene-d8, 0 °C): δ 208.0 (CO), 92.9 (C5Me5), 90.31 (C5Me5), 90.29 (C5Me5), 50.9 (CCMeCHC or CCMeCHC), 48.1 (CCMeCHC or CCMeCHC), 30.3(CH2 or −CMe), 28.3 (CH2 or −CMe), 27.6 (CH2 or −CMe), 11.7 (C5Me5), 11.4 (C5Me5), 10.5 ppm (C5Me5). IR (KBr, cm−1): νCO 1879. Anal. Calcd for C36H56ORu3: C, 53.51; H, 6.99. Found: C, 53.52; H, 6.73. Preparation of (Cp*Ru)3(μ-H)(μ3-η2:η2(⊥)-PhCCH)(μ3-CO) (7a). Complex 4 (86.8 mg, 0.117 mmol), toluene (20 mL), and phenylacetylene (15.0 μL, 1.16 equiv) were charged in a 50 mL Schlenk tube. The solution was stirred for 1 h at 25 °C. The solution turned from dark brown to reddish brown. After the solvent was removed under reduced pressure, the residual solid was dissolved in hexane (ca. 10 mL) and purified by column chromatography on alumina (Merck, Art. No. 1097) using a mixed solvent of toluene and hexane (1/5 in a volume ratio) as an eluent. The first brown band including 7a was collected. Drying under reduced pressure afforded 7a

(76.1 mg, 90.6 μmol, 77% yield) as a brown solid. A single crystal used for the diffraction study was obtained by recrystallization from a toluene solution of 7a stored at −30 °C. 1H NMR (400 MHz, benzene-d6, 25 °C): δ 11.14 (s, 1H, PhCCH), 7.01 (dd, 2H, JH−H = 7.4, 7.4 Hz, m-Ph), 6.76 (t, 1H, JH−H = 7.4 Hz, p-Ph), 5.91 (brd, 2H, oPh), 1.85 (s, 15H, C5Me5), 1.72 (s, 15H, C5Me5), 1.68 (s, 15H, C5Me5), −6.79 ppm (s, 1H, Ru-H). 13C NMR (100 MHz, benzene-d6, 23 °C): δ 263.7 (s, CO), 204.2 (d, JC−H = 181 Hz, outer-PhCCH), 147.4 (s, ipso-Ph), 126.8 (dd, JC−H = 155, 9 Hz, Ph), 125.0 (dt, JC−H = 156, 7 Hz, Ph), 121.9 (dt, JC−H = 157, 5 Hz, Ph), 95.0 (s, innerPhCCH), 93.42 (s, C5Me5), 93.37 (s, C5Me5), 88.6 (s, C5Me5), 11.32 (q, JC−H = 127 Hz, C5Me5), 11.26 (q, JC−H = 127 Hz, C5Me5), 10.6 ppm (q, JC−H = 127 Hz, C5Me5). IR (KBr, cm−1): νCO 1683. Anal. Calcd for C39H52ORu3: C, 55.76; H, 6.24. Found: C, 55.87; H, 6.30. Preparation of (Cp*Ru)3(μ-H){μ3-η2-CC(nPr)H}(μ-CO) (9b). Complex 4 (80.3 mg, 0.109 mmol), toluene (20 mL), and 1-pentyne (0.100 mL, 9.47 equiv) were charged in a 50 mL Schlenk tube. The solution was stirred for 2 h at 25 °C. The solution turned from dark brown to green. After the solvent and remaining 1-pentyne were removed under reduced pressure, the residual solid was dissolved in hexane and filtered through a Celite pad. After concentration, green precipitates were obtained from the solution stored at −30 °C. A 49.5 mg amount of 9b was obtained by decantation (61.4 μmol, 57% yield). A single crystal used for the diffraction study was obtained by recrystallization from a hexane solution of 9b stored at −30 °C. 1H NMR (400 MHz, benzene-d6, 23 °C): δ 6.71 (dd, 1H, JH−H = 9.9, 2.8 Hz, μ 3 -CC(nPr)H), 2.46 (m, 1H, −CH 2 CH 2 CH 3 or −CH2CH2CH3), 1.82 (s, 15H, C5Me5), 1.70 (s, 15H, C5Me5), 1.64 (s, 15H, C5Me5), 1.34 (m, 1H, −CH2CH2CH3 or −CH2CH2CH3), 1.21 (t, 3H, JH−H = 7.4 Hz,−CH2CH2CH3), −10.17 ppm (s, 1H, RuH). Two methylene proton signals derived from the μ3-pentenylidene group were obscured by the Cp* signals. 13C NMR (100 MHz, benzene-d6, 23 °C): δ 297.6 (s, μ3-CC(nPr)H), 264.6 (s, CO), 94.3 (s, C5Me5), 90.6 (s, C5Me5), 83.9 (s, C5Me5), 77.2 (d, JC−H = 152 Hz, μ3-CC(nPr)H), 41.3 (t, JC−H = 127 Hz, −CH2−), 29.0 (t, JC−H = 125 Hz, −CH2−), 14.6 (q, JC−H = 124 Hz, −CH3), 12.0 (q, JC−H = 126 Hz, C5Me5), 11.3 (q, JC−H = 127 Hz, C5Me5), 10.3 ppm (q, JC−H = 127 Hz, C5Me5). IR (KBr, cm−1): νCO 1719. Anal. Calcd for C36H54ORu3: C, 53.64; H, 6.75. Found: C, 53.35; H, 6.94. Preparation of (Cp*Ru)3(μ-H)2(μ3-CMe)(μ-CO) (11). Complex 4 (2.3 mg, 3.1 μmol) and C6D6 (0.4 mL) were charged in an NMR tube equipped with a J. Young valve. After the solution was frozen in a dry ice/methanol bath, the NMR tube was degassed by a vacuum line. Then, 1 atm of ethylene was introduced into the reaction flask and the NMR tube kept at 25 °C. Exclusive formation of 11 was confirmed by the 1H NMR spectrum recorded 1 h later. A single crystal used for the diffraction study was obtained by recrystallization from a THF solution of 11 stored at −30 °C. 1H NMR (400 MHz, benzene-d6, 23 °C): δ 3.25 (s, 3H, μ3-CMe), 1.92 (s, 30H, C5Me5), 1.48 (s, 15H, C5Me5), −9.75 ppm (s, 2H, Ru-H). 13C NMR (100 MHz, benzene-d6, 23 °C): δ 390.4 (s, μ3-CMe), 239.4 (s, CO), 96.9 (s, C5Me5), 85.2 (s, C5Me5), 46.7 (q, JC−H = 126 Hz, μ3-CMe), 11.9 (q, JC−H = 127 Hz, C5Me5), 10.8 ppm (q, JC−H = 127 Hz, C5Me5). IR (KBr, cm−1): νCO 1715. Because 11 was contaminated with a small amount of 9a owing to the rapid reaction of 11 with ethylene, a sufficient amount of 11 for the carbon analysis (ca. 2 mg) was not obtained. Preparation of (Cp*Ru)3(μ-H)(μ3-η2-CCH2)(μ-CO) (9a). Complex 4 (124.1 mg, 0.168 mmol) and toluene (25 mL) were charged in a 50 mL Schlenk tube. After the solution was cooled in a dry ice/ methanol bath, the reaction flask was degassed by a vacuum line. Then, 1 atm of ethylene was introduced into the reaction flask. The solution was stirred for 4 days at 25 °C. The solution turned from dark brown to green. After the solvent was removed under reduced pressure, the residual solid was dissolved in hexane (ca. 10 mL) and purified by column chromatography on alumina (Merck, Art. No. 1097) using a mixed solvent of THF and hexane (1/40 in volume ratio) as an eluent. The first green band including 9a was collected. Drying under reduced pressure afforded 9a (75.5 mg, 99.8 μmol, 59% yield) as a green solid. A single crystal used for the diffraction study was obtained by recrystallization from a hexane solution of 9a stored at −30 °C. 1H K

DOI: 10.1021/acs.organomet.7b00465 Organometallics XXXX, XXX, XXX−XXX

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Organometallics NMR (400 MHz, benzene-d6, 23 °C): δ 4.85 (s, 2H, μ3-CCH2), 1.70 (s, 30H, C5Me5), 1.67 (s, 15H, C5Me5), −10.90 ppm (s, 1H, RuH). 13C NMR (100 MHz, benzene-d6, 23 °C): δ 296.6 (s, μ3-C CH2), 265.8 (s, CO), 92.0 (s, C5Me5), 83.6 (s, C5Me5), 56.9 (t, JC−H = 157 Hz, μ3-CCH2), 12.3 (q, JC−H = 126 Hz, C5Me5), 10.2 ppm (q, JC−H = 127 Hz, C5Me5). IR (KBr, cm−1): νCO 1733. Anal. Calcd for C33H48ORu3: C, 51.88; H, 6.33. Found: C, 51.75; H, 6.05. Preparation of an Equilibrated Mixture of (Cp*Ru)3(μ-H)(μ3CMe)(μ-η2-CHCH2)(μ-CO) (12) and (Cp*Ru)3(μ-H)(μ3-CMe)(μCMe)(μ-CO) (13). Complex 4 (103.4 mg, 0.1397 mmol) and toluene (20 mL) were charged in a 50 mL Schlenk tube. After the solution was cooled in a dry ice/methanol bath, the reaction flask was degassed by a vacuum line. Then, 1 atm of ethylene was introduced into the reaction flask. The solution was stirred for 3 days at 110 °C. The solution turned from dark brown to brown. After the solvent was removed under reduced pressure, the residual solid was dissolved in toluene and purified by column chromatography on alumina (Merck, Art. No. 1097) using toluene as an eluent. The second black band including 12 and 13 was collected. Drying under reduced pressure afforded a mixture of 12 and 13 (87.0 mg, 0.110 mmol, 79% yield) as a black solid. The ratio of 12 to 13 at 23 °C was estimated to be 5/95 on the basis of signal intensities of the 1H NMR spectrum of the mixture. A single crystal used for the diffraction study of 13 was obtained by recrystallization from a THF solution of the mixture stored at −30 °C. Data for 12 are as follows. 1H NMR (400 MHz, benzene-d6, 23 °C): δ 7.80 (dd, 1H, JH−H = 10.4, 7.2 Hz, μ-CHCHH′), 4.09 (s, 3H, μ3CMe), 3.56 (d, 1H, JH−H = 10.4 Hz, μ-CHCHH′), 2.58 (d, 1H, JH−H = 7.2 Hz, μ-CHCHH′), 1.89 (s, 15H, C5Me5), 1.73 (s, 15H, C5Me5), 1.49 (s, 15H, C5Me5), −21.45 ppm (s, 1H, Ru-H). Due to the low population of 12, 13C NMR data for 12 was not obtained. Data for 13 are as follows. 1H NMR (400 MHz, benzene-d6, 23 °C): δ 4.51 (s, 3H, μ3-CMe), 2.29 (s, 3H, μ-CMe), 1.86 (s, 15H, C5Me5), 1.74 (s, 15H, C5Me5), 1.65 (s, 15H, C5Me5), −20.84 ppm (s, 1H, Ru-H). 13C NMR (100 MHz, benzene-d6, 23 °C): δ 388.3 (s, μ-CMe), 318.5 (s, μ3-CMe), 244.3 (s, CO), 98.7 (s, C5Me5), 97.4 (s, C5Me5), 95.7 (s, C5Me5), 43.6 (q, JC−H = 125 Hz, μ3-CMe), 43.4 (q, JC−H = 127 Hz, μCMe), 11.01 (q, JC−H = 126 Hz, C5Me5), 10.99 (q, JC−H = 126 Hz, C5Me5), 9.5 ppm (q, JC−H = 127 Hz, C5Me5). IR (KBr, cm−1): νCO 1732. Anal. Calcd for C35H52ORu3: C, 53.08; H, 6.62. Found: C, 53.30; H, 6.69. Thermolysis of an Equilibrated Mixture of 12 and 13. Preparation of (Cp*Ru)3(μ3-CH)(μ3-η2(∥)-HCCH)(μ-CO) (15). A mixture of 12 and 13 (36.7 mg, 0.0463 mmol) and p-xylene (10 mL) were charged in a 20 mL Schlenk tube equipped with a J. Young valve. After the solution was frozen in a dry ice/methanol bath, the reaction flask was degassed by a vacuum line. Then, 1 atm of argon was introduced into the reaction flask. The solution was stirred for 3.5 days at 180 °C. The solution turned from brown to orange. After the solvent was removed under reduced pressure, the residual solid was dissolved in toluene (ca. 4 mL) and purified by column chromatography on alumina (Merck, Art. No. 1097) using toluene as an eluent. The first orange band was collected. Drying under reduced pressure afforded a 32.9 mg amount of a mixture of 14 (21%), 15 (74%), and unidentified complexes (ca. 5%) as an orange solid. The formation of 14 was confirmed by the 1H NMR spectrum displaying characteristic signals at δ 5.97 (s, 2H, μ3-η3-C3MeH2), 2.15 (s, 3H, μ3-η3-C3MeH2), 1.76 (s, 15H, Cp*), and 1.75 ppm (s, 30H, Cp*). The mixture and toluene (10 mL) were charged in a 100 mL Schlenk tube. After the solution was cooled in a dry ice/methanol bath, the reaction flask was degassed by a vacuum line. Then, 1 atm of O2 was introduced into the reaction flask to transform 14 into an insoluble material for the separation of 15. The solution was stirred for 5 days at 80 °C. The solution turned from orange to greenish orange, and green precipitates were formed. After the solvent was removed under reduced pressure, the residual solid was dissolved in hexane (ca. 30 mL) and purified by column chromatography on alumina (Merck, Art. No. 1097) using toluene as an eluent. The first orange band including 15 was collected. Drying under reduced pressure afforded 15 (6.8 mg, 8.4 μmol, 18% yield) as an orange solid. A single crystal used for the diffraction study was obtained by recrystallization from a

toluene solution of 15 stored at −30 °C. 1H NMR (400 MHz, benzene-d6, 23 °C): δ 14.97 (t, 1H, JH−H = 1.0 Hz, μ3-CH), 8.49 (d, 2H, JH−H = 1.0 Hz, μ3-η2(∥)-HCCH), 1.81 (s, 15H, C5Me5), 1.78 ppm (s, 30H, C5Me5). 13C NMR (100 MHz, benzene-d6, 23 °C): δ 318.8 (d, JC−H = 157 Hz, μ3-CH), 235.7 (s, CO), 164.0 (d, JC−H = 158 Hz, μ3-η2(∥)-HCCH), 97.5 (s, C5Me5), 92.8 (s, C5Me5), 11.8 (q, JC−H = 126 Hz, C5Me5), 10.4 ppm (q, JC−H = 127 Hz, C5Me5). IR (KBr, cm−1): νCO 1753. Anal. Calcd for C34H48ORu3: C, 52.63; H, 6.24. Found: C, 52.60; H, 5.99.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.7b00465. Crystal data and results of XRD studies of 4, 5a, 7a, 9a,b, 11, and 13−15, results of DFT calculations for 4 and its isomer A, NMR spectra of 4, 5a,b, 7a, 9a,b, and 11−15, results of a VT 1H NMR study for 7a using spectral simulation and simulation for the 1H NMR spectrum of the butadiene moiety in 5a, and IR spectra of 4, 5a,b, 7a, 9a,b, 11, a mixture of 12 and 13, and 15 (PDF) Atom coordinates of the optimized structures of 4, A (a possible isomer of 4), 5a, 9a, and 11 (XYZ) Accession Codes

CCDC 1555071−1555078 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

* E-mail for T.T.: [email protected]. ORCID

Hiroharu Suzuki: 0000-0002-9718-1375 Toshiro Takao: 0000-0002-5393-112X Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by JST ACT-C Grant Number JPMJCR12YA, Japan. REFERENCES

(1) (a) Takao, T.; Suzuki, H. Bull. Chem. Soc. Jpn. 2014, 87, 443− 458. (b) Suzuki, H.; Kakigano, T.; Tada, K.; Igarashi, M.; Matsubara, K.; Inagaki, A.; Oshima, M.; Takao, T. Bull. Chem. Soc. Jpn. 2005, 78, 67−87. (c) Suzuki, H. Eur. J. Inorg. Chem. 2002, 2002, 1009−1023. (2) (a) Inagaki, A.; Takemori, T.; Tanaka, M.; Suzuki, H. Angew. Chem., Int. Ed. 2000, 39, 404−406. (b) Suzuki, H.; Inagaki, A.; Matsubara, K.; Takemori, T. Pure Appl. Chem. 2001, 73, 315−318. (3) (a) Takao, T.; Kawashima, T.; Matsubara, K.; Suzuki, H. Organometallics 2005, 24, 3371−3374. (b) Kawashima, T.; Takao, T.; Suzuki, H. Angew. Chem., Int. Ed. 2006, 45, 7615−7618. (c) Takao, T.; Kawashima, T.; Kanda, H.; Okamura, R.; Suzuki, H. Organometallics 2012, 31, 4817−4831. (4) Moriya, M.; Tahara, A.; Takao, T.; Suzuki, H. Eur. J. Inorg. Chem. 2009, 2009, 3393−3397. (5) Okamura, R.; Tada, K.; Matsubara, K.; Oshima, M.; Suzuki, H. Organometallics 2001, 20, 4772−4774. (6) Ohashi, M.; Matsubara, K.; Iizuka, T.; Suzuki, H. Angew. Chem., Int. Ed. 2003, 42, 937−940. L

DOI: 10.1021/acs.organomet.7b00465 Organometallics XXXX, XXX, XXX−XXX

Article

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DOI: 10.1021/acs.organomet.7b00465 Organometallics XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.organomet.7b00465 Organometallics XXXX, XXX, XXX−XXX