Reactions of a Triruthenium Pentahydrido Complex with Imines

Article pubs.acs.org/Organometallics

Reactions of a Triruthenium Pentahydrido Complex with Imines Leading to the Formation of a Perpendicularly Coordinated Iminoacyl Ligand and the Scission of a CN Bond on a Triruthenium Plane Hideyuki Kanda, Takashi Kawashima, Toshiro Takao, and Hiroharu Suzuki* Department of Applied Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology, O-okayama, Meguro-ku, Tokyo 152-8552, Japan S Supporting Information *

ABSTRACT: The reaction of a triruthenium pentahydrido complex, {Cp*Ru(μ-H)}3(μ3-H)2 (1; Cp* = η5-C5Me5), with N-benzylidenemethylamine resulted in the exclusive formation of a perpendicularly coordinated iminoacyl complex, (Cp*Ru)3(μ-η2:η2(⊥)-PhCNMe)(μ-H)2 (3b), as a result of C−H bond scission of imine. However, the treatment of 1 with N-benzylideneaniline at 100 °C caused C−N bond cleavage to yield the μ3-benzylidyne−μ3-phenylimido complex (Cp*Ru)3(μ3-CPh)(μ3-NPh)(μ-H)2 (7c) and the μ3-methylidyne−μ3-phenylimido complex (Cp*Ru)3(μ3-CH)(μ3-NPh)(μ-H)2 (8). The formation of 7c is in strong contrast to the C−N bond scission occurred in (Cp*Ru)3(μ-η2:η2(⊥)-PhCNH)(μ-H)2 (3a), which required heating at 180 °C. The structural and spectral properties of μ3-η2:η2(⊥)-nitrile complex 2, cationic μ3-η2:η2(⊥)-iminoacyl complex 6, and neutral μ3-η2:η2(⊥)-iminoacyl complex 3 revealed a clear trend of the activation of the C−N bond on a Ru3 plane. The thermolysis of 3b proceeded in a different manner to yield a μ3-methylidyne−μ3-η2(∥)-iminoacyl complex, (Cp*Ru)3(μ3-CH)(μ3-HNCH)(μ-H) (9), as a consequence of both C−N and C−C bond scission.

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INTRODUCTION For several decades, the reactivity of a cluster compound toward alkynes has been intensively studied in order to reveal the properties of hydrocarbon molecules on a metal surface.1 Considerable numbers of alkyne-substituted clusters have been prepared thus far, and their reactivities leading to various derivatives, such as acetylide, vinylidene, and alkylidyne complexes, have also been well documented.2 In contrast to the extensive research in alkyne-cluster chemistry, few efforts have been made toward the elucidation of the reactivity of a nitrile molecule bound to a multimetallic center. Further, because the transformation of nitriles into amines and amides using a heterogeneous catalyst is one of the fundamental processes in the chemical industry,3 it is important to understand the reactivities and the properties of a nitrile ligand on a multimetallic center. In their pioneering studies in 1979, Kaesz and co-workers elucidated the transformation of a μ3-nitrile ligand into a μ3-imido ligand on a triiron complex;4 however, thus far, limited studies have been conducted using trimetallic complexes.5 A few years ago, we synthesized a triruthenium cluster containing a perpendicularly coordinated benzonitrile ligand, {Cp*Ru(μ-H)}3(μ3-η2:η2(⊥)-PhCN) (2), by the reaction of 1 with benzonitrile (Scheme 1).6 In contrast to the well-known reactivity of a hydrido cluster with a nitrile that leads to the formation of a μ-alkylideneamido complex,7 a nitrile molecule was shown to be π-bonded to the Ru3 core without hydrogenation. Unlike Kaesz’s μ3-nitrile complex, the nitrile © 2012 American Chemical Society

Scheme 1. Transformation of Benzonitrile into a Nitrido Ligand via the Formation of a Perpendicularly Coordinated Nitrile and Iminoacyl Complex

ligand in 2 was coordinated to the Ru3 core by directing the nitrogen atom outside the Ru3 core.6,8 Therefore, the lone-pair Received: December 12, 2011 Published: February 9, 2012 1917

dx.doi.org/10.1021/om201230u | Organometallics 2012, 31, 1917−1926

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the introduction of a methyl group on the nitrogen atom in place of hydrogen causes a considerable decrease in the mobility of the μ3-iminoacyl ligand. It was not clear whether the reduced mobility of the μ3-iminoacyl group in 3b was a result of steric or electronic effects, but a similar trend was also observed in the case of μ3-η2:η2(⊥)-alkyne complexes. The ΔG⧧298 K value of the switchback motion of a μ3-alkyne ligand in {Cp*Ru(μ-H)}3(μ-η2:η2(⊥)-PhCCH) has been estimated to be 14.0 ± 0.3 kcal mol−1, and that of {Cp*Ru(μ-H)}3(μ-η2:η2(⊥)-PhCCMe) has been found to be 17.0 ± 0.4 kcal mol−1.12 In the 13C NMR spectrum, a singlet assignable to the inner carbon of the μ3-η2:η2(⊥)-iminoacyl ligand appeared at δ 160.6, which was comparable to that of 3a (δ 161.4).9,13 The signal underwent a considerable downfield shift as compared to that of the μ3-η2:η2(⊥)-nitrile complex 2 (δ 97.8).6 The upfield shift of the signal for the inner carbon of the nitrile ligand in 2 was attributed to the hypervalency of the inner carbon atom, which was connected to the three metal centers, the phenyl ring, and the nitrogen atom. Although the connectivity in the vicinity of the imino carbon in 3 seemingly resembled that of 2, the marked difference in the chemical shifts between 2 and 3 strongly indicates that the bonding interaction between the triruthenium core and the C−N moiety in the μ3-iminoacyl complexes was different from that in the nitrile complex. This was probably due to a reduction in the bond order of the C−N bond. The reaction of 1 with benzonitrile was complete within 6 h at ambient temperature, whereas the reaction of 1 with N-benzylidenemethylamine required a longer duration (5 days) even at 100 °C. The deceleration of the reaction could be attributed to the steric repulsion between the imine and the surrounding Cp* groups. Therefore, an excess amount of imine (5 equiv) was required to accelerate the reaction. During the formation of 3b, four hydrido ligands were removed from the cluster, probably as dihydrogen. Although no intermediate was observed, the removal of dihydrogen proceeded in a stepwise manner via the formation of 5b containing a μ3-η2(∥)-iminoacyl ligand. In fact, the treatment of 3b with 1 atm of dihydrogen resulted in the rapid formation of 5b, and facile regeneration of 3b was observed upon evacuation at ambient temperature. In the 1H NMR spectrum of 5b measured at −40 °C, four hydrido signals were observed at δ −18.76, −16.77, −14.77, and −14.10, and three signals for the Cp* groups were observed at δ 1.53, 1.83, and 1.89. Although the molecular structure of 5b was not confirmed by conducting an X-ray diffraction study, these structural features strongly imply the parallel coordination of the iminoacyl group to the Ru3 core. Upon parallel coordination, the phenyl group of the μ3-η2(∥)iminoacyl group did not experience strong ring-current shielding from the Cp* groups, which was observed in complex 3b. Thus, the signals of the phenyl group resonated between δ 6.7 and 7.6. The interconversion of the μ3-iminoacyl complexes between the parallel and the perpendicular forms depends on the formal electron count resembling that observed in the μ3-alkyne complexes;14 an alkyne ligand in an unsaturated, trimetallic, 46electron cluster is shown to be coordinated on a trimetallic plane perpendicular to one M−M edge, whereas that in a saturated, 48electron cluster is coordinated parallel to one M−M edge. Complex 3b was alternatively synthesized by the reaction of 2 with methyl triflate followed by the treatment with NaOMe (eq 2). Similar to the protonation of 2 leading to the formation of the cationic μ3-η2:η2(⊥)-iminoacyl complex [(Cp*Ru)3(μ3-η2:η2(⊥)-PhCNH)(μ3-H)(μ-H)2]+ (6a),6 the methylation

electrons at the nitrogen atom did not engage in coordination to the ruthenium atoms; this caused the migration of a hydrido ligand to the nitrogen atom to form a perpendicularly coordinated μ3 -η 2 :η 2 (⊥)-iminoacyl complex, (Cp*Ru) 3 (μ3-η2:η2(⊥)-PhCNH)(μ-H)2 (3a).9 The subsequent thermolysis of 3a at 180 °C resulted in C−N bond cleavage leading to the formation of a μ3-nitrido complex 4. Thus, complex 3a is envisaged as an intermediate for breaking a C−N bond. In fact, the C−N distance in 3 (1.391(6) Å) was observed to be longer than that in 2 (1.358(6) Å). Similar to the case for nitrile, an imine also contains an unsaturated C−N bond, and it has been sometimes observed that μ3-iminoacyl complexes are directly obtained by the reaction of a cluster with imine; the reaction of M3(CO)12 (M = Ru, Os) with imine results in the formation of μ3-η2(∥)and μ-iminoacyl complexes as a consequence of C−H bond scission of the imine.10 Therefore, the μ3-η2:η2(⊥)-iminoacyl complex 3 is expected to be obtained by the reaction of 1 with imine, thus enabling the modification of the electronic properties of the μ3-iminoacyl group, in particular at the nitrogen atom. In this article, we report the reactions of the triruthenium pentahydrido complex 1 with N-benzylideneamine, RNC(H)Ph (R = Me, Ph), to yield a μ3-η2:η2(⊥)iminoacyl complex as well as C−N bond scission on a Ru3 plane.

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RESULTS AND DISCUSSION The treatment of 1 with N-benzylidenemethylamine at 100 °C resulted in the exclusive formation of 3b, which possesses an iminoacyl ligand bridged at one Ru−Ru edge in a perpendicular fashion (eq 1). Owing to the reduction in steric repulsion

between the μ3-iminoacyl ligand and the Cp* groups surrounding the Ru3 core, the large phenyl group was located inside the Ru3 core. This caused a significant upfield shift of the signal derived from the ortho protons at the phenyl group by the ring current shielding effect of the Cp* groups, and the signal resonated at δ 6.11.11 In the 1H NMR spectrum of 3b recorded at ambient temperature, two sharp signals assignable to the Cp* groups were observed at δ 1.76 and δ 1.86 with an intensity ratio of 2:1. The signals were sharp up to 45 °C. In contrast, the Cp* signals of 3a were observed to broaden at 25 °C and reached a low-temperature limit at −10 °C.9 It is assumed that the μ3-iminoacyl ligand in 3b is intrinsically fluxional and shows switchback motion on the Ru3 plane.12 Thus, this implies that 1918


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of the nitrile ligand occurred at the nitrogen atom to yield 6b. Unlike the deprotonation of 6a resulting in the regeneration of the μ3-nitrile complex 2, the treatment of the N-methylated 6b with a base resulted in the removal of one hydrido ligand from the metal center and afforded the μ3-iminoacyl complex 3b. In the 13C NMR spectrum of 6b, the signal for the inner carbon atom of the μ3-iminoacyl ligand was observed at δ 142.0. This value was comparable to that of 6a (δ 139.3). Despite the reduction in the electron density owing to the cationic charge, the signal for the imino carbon of these cationic complexes underwent an upfield shift of ca. 20 ppm compared to those of the neutral complexes 3a,b. A similar trend was also observed between the face-capping pyridine complex and its protonated pyridinium complex;15 the 13C signals for the μ3-η2:η2:η2-pyridine ligand were observed at δ 34.5, 35.2, 35.7, 58.5, and 60.3, which underwent an upfield shift of 10−20 ppm upon protonation at the nitrogen atom. These upfield shifts were probably due to the localization of a cationic charge at the nitrogen atom in the cationic complexes. As a result, backdonation from a metal center to the iminoacyl group was effectively enhanced, thus producing a large shielding effect. The molecular structures of 3b and 6b (Figures 1 and 2, respectively) were determined by X-ray diffraction studies. In both structures, it can be observed that the μ3-iminoacyl ligands bisect the Ru3 core with the nitrogen atoms directed outside the Ru3 core. In the case of 3b, the complex has a crystallographic mirror plane bisecting the triruthenium plane and the iminoacyl group was just located on this mirror plane. The structural parameters in the vicinity of the center of 3b resembled those of 3a containing a μ3-η2:η2(⊥)-PhCNH ligand, but they are significantly different from those of the parent μ3nitrile complex 2. The N(1)−C(1) distance in 3b (1.392(7) Å) is slightly larger than that in 2 (1.358(6) Å), and the Ru(1)− C(1) distance (2.023(6) Å) is significantly smaller than that in 2 (2.124(5) Å). These features signify the strong back-donation from the Ru3 core to the π*(CN) orbital of 3b, and these observations are consistent with the marked difference in the chemical shift of the inner carbon as mentioned above. While the Ru(1)−Ru(2) distance of 2.7814(5) Å in 3b is similar to that in 2 (2.7670(4) Å), the Ru−Ru distance at which the iminoacyl ligand was perpendicularly coordinated (Ru(2)− Ru(2A) = 3.0530(7) Å) was notably larger than that at which the nitrile ligand was perpendicularly coordinated in 2 (2.9363(7) Å). In the case of 3a, further thermolysis causes C−N bond scission to yield the μ3-nitrido complex 4.9 This C−N bond scission appears to proceed via the reversible Ru−Ru bond

Figure 1. Molecular structure and labeling scheme of 3b with thermal ellipsoids at the 30% probability level. Selected bond lengths (Å) and angles (deg): Ru(1)−Ru(2), 2.7814(5); Ru(2)−Ru(2A), 3.0530(7); Ru(1)−C(1), 2.023(6); Ru(2)−C(1), 2.375(4); Ru(2)−N(1), 2.025(3); N(1)−C(1), 1.392(7); N(1)−C(2), 1.471(8); C(1)−C(3), 1.492(8); Ru(2)−Ru(1)−Ru(2A), 66.571(10); Ru(1)−Ru(2)−Ru(2A), 56.714(9); Ru(2)−C(1)−Ru(2A), 79.96(16); Ru(1)−C(1)− C(3), 122.2(4); Ru(1)−C(1)−N(1), 120.9(4); N(1)−C(1)−C(3), 116.7(5); Ru(2)−N(1)−Ru(2A), 97.8(2); C(1)−N(1)−C(2), 121.9(5).

Figure 2. Molecular structure and labeling scheme of 6b with thermal ellipsoids at the 40% probability level. The anionic part (BPh4−) was omitted for clarity. Selected bond lengths (Å) and angles (deg): Ru(1)− Ru(2), 2.74599(12); Ru(1)−Ru(3), 2.75501(12); Ru(2)−Ru(3), 2.98980(13); Ru(1)−C(1), 2.0914(11); Ru(2)−C(1), 2.3647(12); Ru(3)−C(1), 2.3222(11); Ru(2)−N(1), 2.0371(10); Ru(3)−N(1), 2.0464(10); N(1)−C(1), 1.3712(15); C(1)−C(3), 1.4847(16); N(1)− C(2), 1.4661(15); Ru(2)−Ru(1)−Ru(3), 65.844(3); Ru(1)−Ru(2)− Ru(3), 57.223(3); Ru(1)−Ru(3)−Ru(2), 56.933(3); Ru(2)−C(1)− Ru(3), 79.27(4); Ru(1)−C(1)−C(3), 119.94(8); Ru(1)−C(1)−N(1), 121.89(8); N(1)−C(1)−C(3), 118.16(10); Ru(2)−N(1)−Ru(3); 94.13(4), C(1)−N(1)−C(2), 122.36(10).

cleavage observed during the carbyne fragment migration in (Cp*Ru)3(μ3-η2(∥)-HCCC3H7)(μ3-CC4H9)(μ-H)2.16 The key intermediate in the carbyne migration was a μ3-ruthenacyclobutenyl complex, which was formed via the coupling between the two hydrocarbyl moieties placed on both the faces of the trimetallic plane concomitant by the Ru−Ru bond cleavage. Thus, 1919


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the elongation of the Ru−Ru bond in 3 is consistent with the aforementioned mechanism of C−N bond scission involving Ru− Ru bond cleavage. The structural parameters of the cationic μ3-iminoacyl complex 6b were similar to those of the previously reported 6a. The N(1)−C(1) (1.3712(15) Å), Ru(1)−C(1) (2.0914(11) Å), and Ru(2)−Ru(3) (2.98980(13) Å) distances in 6b correspond to the intermediate values observed for 2 and 3b as well as to the chemical shift of the imino carbon atom. In Table 1, selected structural parameters along with the 13C NMR data of the inner carbon atom of 2, 3a,b, and 6a,b are Table 1. Selected Structural and Spectral Data for the μ3-η2:η2(⊥)-Nitrile and Iminoacyl Complexes d(C−N) (Å) (Cp*Ru)3(μ-η2:η2(⊥)PhCN)(H)3 (2) [(Cp*Ru)3(μ-η2:η2(⊥)PhCNH)(H)3]+ (6a) [(Cp*Ru)3(μ-η2:η2(⊥)PhCNMe)(H)3]+ (6b) (Cp*Ru)3(μ-η2:η2(⊥)PhCNH)(H)2 (3a) (Cp*Ru)3(μ-η2:η2(⊥)PhCNMe)(H)2 (3b)

d(Ru−C) (Å)

d(Ru−Ru) (Å)

δC (ppm)

1.358(6)

2.124(5)

2.9363(7)

97.8a

1.351(5)

2.098(4)

2.9830(5)

139.3b

1.3712(15)

2.0914(11)

2.98980(13)

142.0c

1.391(6)

2.010(5)

3.0826(11)

161.4d

1.392(7)

2.023(6)

3.0530(7)

160.6d

Conditions: toluene-d8, −40 °C. bConditions: acetone-d6, −40 °C. Conditions: acetone-d6, 25 °C. dConditions: benzene-d6, 25 °C.

a c

given. The 13C signals of the inner carbon showed a significant downfield shift from δ 98 in 2 to δ 161 in 3. Although the differences in the C−N bond distances were rather small, other structural features were found to show a clear trend along with the vertical line. The Ru−Ru bond distance at which the C−N moiety was π-bonded, d(Ru−Ru), increased in the order 2 < 6 < 3. Further, the distance between the inner carbon atom and the ruthenium atom to which the C−N moiety was not π-bonded, d(Ru−C), decreased in the same order. The interaction of the C−N moiety with the Ru3 core was expected to become stronger in the order 2 < 6 < 3. Although C−N bond scission did not occur in 6, spectral data suggest that the iminoacyl moiety in 6 was also activated to some extent. The migration of a hydrido ligand to the μ3-nitrile ligand in 2 as a proton possibly reduced the bond order of the C−N bond and caused an increase in the electron density at the metal centers. The C−N bond scission on the hydrido cluster is attributed to such an ambivalent function of the hydrido ligand. In contrast to the reaction of 1 with N-benzylidenemethylamine, the reaction of 1 with N-benzylideneaniline at 100 °C afforded a mixture of μ3-imido complexes 7c and 8 as a consequence of C−N bond cleavage (eq 3). However, although no intermediate was detected during the reaction, the reaction appeared to proceed via the formation of a μ3-η2(∥)-iminoacyl complex 5c and the μ3-η2:η2(⊥)-iminoacyl complex 3c as observed in the case of 3b. Because of the presence of a bulky phenyl group on the nitrogen atom, the conversion of 1 proceeded more slowly than the reaction with N-benzylidenemethylamine (10 days). However, owing to the electron-withdrawing nature of the phenyl group on the nitrogen atom, the imine group was susceptible to a strong back-donation from the metal centers, and it caused facile C−N bond cleavage even at 100 °C. This is in strong contrast to the C−N bond cleavage of 3a occurring at 180 °C.9

For the formation of the μ3-methylidyne complex 8, C−C bond cleavage at the imino carbon atom along with the uptake of dihydrogen was necessary. The mechanistic details for the formation of 8 are unclear at present, but the oxidative addition of a C−C bond of benzonitrile is well-known.17 A considerable amount of 8 (ca. 20%) was produced in a closed vessel; however, its yield decreased to 10% upon the removal of dihydrogen by periodic evacuation. This result implies that there exists a reaction path that leads to C−C bond cleavage upon the incorporation of dihydrogen. Owing to the difficulty in distinguishing between a nitrogen and a carbon atom by means of an X-ray diffraction study, p-methoxy-substituted imine, MeO(C6H4)CHNPh, was employed for the diffraction study. Because there were two independent molecules possessing similar structural features in the unit cell, only one molecule of 7d is shown in Figure 3. Both the Ru3 faces of 7d are capped by the μ3-phenylimido and the μ3-benzylidyne ligands, and this clearly indicates the scission of the C−N bond of N-benzylideneaniline on the Ru3 plane. In contrast to the thermolysis of 3a that leads to the formation of the μ3-nitrido−μ3-diruthenaallyl complex 4, both substituents on the imine moiety remained in contact with the carbon and nitrogen atoms. This implies that the C−N bond cleavage of an imine on the trimetallic plane proceeds in a manner similar to the C−C bond scission of an alkyne ligand on a trimetallic plane.18 The imido group is coordinated in the Ru3 core in a μ3 fashion, but the lengths of the Ru−N bonds are slightly different; among the three Ru−N bonds, the Ru(1)−N(1) distance (2.095(4) Å) is slightly larger than the other distances (Ru(2)−N(1), 2.003(4) Å; Ru(3)−N(1), 2.020(4) Å). As a result, the N(1)−C(9) bond slightly tilts toward the Ru(1) atom, as observed in other μ3-phenylimido complexes reported previously.19 A similar tendency is also observed in the case of 1920


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shown to be nonfluxional.19 The mechanism for this dynamic process will be discussed later. An X-ray diffraction study of 8 was also performed using a red crystal obtained from a cold pentane solution; the molecular structure of 8 is shown in Figure 4. The complex has a

Figure 3. Molecular structure and labeling scheme of 7d with thermal ellipsoids at the 40% probability level. Selected bond lengths (Å) and angles (deg): Ru(1)−Ru(2), 2.6861(5); Ru(1)−Ru(3), 2.6942(5); Ru(2)−Ru(3), 2.7358(4); Ru(1)−N(1), 2.095(4); Ru(1)−C(1), 2.040(3); Ru(2)−N(1), 2.003(4); Ru(2)−C(1), 2.010(3); Ru(3)− N(1), 2.020(4); Ru(3)−C(1), 2.006(3); N(1)−C(9), 1.465(6); C(1)−C(2), 1.401(5); Ru(2)−Ru(1)−Ru(3), 61.125(12); Ru(1)− Ru(2)−Ru(3), 59.584(11); Ru(1)−Ru(3)−Ru(2), 59.291(12); Ru(1)−N(1)−Ru(2), 81.86(15); Ru(1)−N(1)−Ru(3), 81.77(14); Ru(2)−N(1)−Ru(3), 85.69(16); Ru(1)−C(1)−Ru(2), 83.10(12); Ru(1)−C(1)−Ru(3); 83.52(12), Ru(2)−C(1)−Ru(3), 85.89(12).

Figure 4. Molecular structure and labeling scheme of 8 with thermal ellipsoids at the 40% probability level. Selected bond lengths (Å) and angles (deg): Ru(1)−Ru(2), 2.6843(3); Ru(2)−Ru(2A), 2.7195(4); Ru(1)−N(1), 2.063(3); Ru(1)−C(1), 2.038(3); Ru(2)−N(1), 2.0305(19); Ru(2)−C(1), 1.991(2); N(1)−C(2), 1.400(4); Ru(2)− Ru(1)−Ru(2A), 60.874(5); Ru(1)−Ru(2)−Ru(2A), 59.565(5); Ru(1)−N(1)−Ru(2), 81.94(9); Ru(2)−N(1)−Ru(2A), 84.08(10); Ru(1)−C(1)−Ru(2), 83.55(11); Ru(2)−C(1)−Ru(2A), 86.15(13).

crystallographic mirror plane with Ru(1), C(1), and N(1). The Cp* rings of 8 are tilted toward the less bulky μ3-methylidyne moiety, whereas those of 7d are nearly perpendicular to the Ru3 plane. This tilt was attributed to the steric repulsion between the Cp* groups and the phenyl group on the nitrogen atom. The distances of the Ru(1)−N(1) and Ru(1)−C(1) bonds are slightly greater than those of other Ru−N and Ru−C bonds as observed in 7d. The hydrido ligands are placed on the Ru(1)−Ru(2) and Ru(1)−Ru(2A) edges. The distances of these Ru−Ru bonds are greater than that of the unbridged Ru(2)−Ru(2A) bond by 0.04 Å. The 1H NMR spectrum of 8 measured at −80 °C also indicated an approximate Cs structure of the cluster skeleton. The signals for the Cp* groups appeared at δ 1.84 and 1.58 with an intensity ratio of 2:1, which coalesced above −40 °C owing to the site exchange of the hydrido ligands (Figure 5). In addition to the broadening of the Cp* signals, changes in the shapes of the hydrido and the methylidyne signals were also observed, as shown in Figure 5. The hydrido ligands resonated at δ −19.04 as a sharp singlet at −80 °C and broadened with an increase in temperature. Simultaneously, the signal for the methylidyne proton resonating at δ 15.20 also broadened with an increase in temperature. Irradiation at the hydrido signal at −40 °C resulted in a significant decrease in the signal intensity of the methylidyne signal. This clearly indicated the site exchange between the hydride and the methylidyne proton, as shown in Scheme 2. This dynamic process can be rationalized by assuming the formation of the μ-methylidene intermediate B via the migration of a hydrido ligand onto the methylidyne carbon. The site exchange was realized by the subsequent pivot motion of the generated μ-methylidene ligand on the Ru3 core followed by the oxidative addition of a C−Ha bond.

the μ3-benzylidyne ligand; the Ru(1)−C(1) bond distance (2.040(3) Å) is greater than that of other the Ru−C bonds (Ru(2)−C(1), 2.010(3) Å; Ru(3)−C(1), 2.006(3) Å). Although the positions of the two hydrido ligands could not be determined by Fourier synthesis, the differences in the Ru− Ru bond lengths imply that the hydrido ligands are present on the Ru(1)−Ru(2) and Ru(1)−Ru(3) edges; the Ru(1)−Ru(2) distance (2.6861(5) Å) and the Ru(1)−Ru(3) distance (2.6942(5) Å) are notably smaller than the Ru(2)−Ru(3) distance (2.7358(4) Å). The 1H NMR spectrum of 7c measured at −80 °C was in accord with a crystal structure showing a pseudo-Cs structure of the cluster core; two sharp singlets assignable to the Cp* signals resonated at δ 1.84 and 1.08 with an intensity ratio of 2:1. The Cp* group bonded to Ru(1) resonated at a considerably high magnetic field region reported for the methyl signal of a Cp* group bonded to a trimetallic core. In contrast to the case for 7c, the Cp* signals of 8 were observed in the normal region: i.e., at δ 1.84 and 1.58 with an intensity ratio of 2:1 (vide infra). Therefore, the marked upfield shift of the Cp* signal on the Ru(1) atom in 7c in contrast to 8 can be attributed to the presence of a phenyl group on the alkylidyne carbon. This upfield shift was probably due to the ring current shielding effect of the two phenyl groups on each bridging ligand tilted toward the Cp* group on the Ru(1) atom. These Cp* signals broadened with an increase in the temperature, and they coalesced into one peak at δ 1.65 at ambient temperature. A time-averaged spectrum was obtained from the motion of the hydrido ligands. However, an isoelectronic bis(μ3-phenylimido) complex, (Cp*Ru)3(μ3-NPh)2(μ-H), was 1921


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formation of a μ-methylidene ligand is regarded as a key step in the Fischer−Tropsch reaction, and several hydrido clusters having a μ3-alkylidyne ligand have been thus far investigated. Fehlner and co-workers established that a triiron complex having both hydrides and a μ 3 -methylidyne ligand, Fe3(CO)9(μ3-CH)(μ-H)3, equilibrates with μ3-methylene and μ-methyl complexes, Fe 3 (CO) 9 (μ 3 -η 2 -HCH)(μ-H) 2 and Fe3(CO)9(μ3-η2:η2-H2CH)(μ-H), respectively, via agostic C−H interactions; moreover, the free energy of activation for the site exchange between the methylidyne proton and hydride has been estimated to be ΔG⧧318 K = 13 kcal mol−1.20 Similar behaviors have been observed for the Ru and Os congeners, M3(CO)9(μ3-CH)(μ-H)3 (M = Ru, Os),21 and (Cp*Ir)(CpCo)2(μ3-CH)(μ3-CO)(μ-H), respectively.22 The thermolysis of μ3-η2:η2(⊥)-iminoacyl complex 3a resulted in C−N bond cleavage, as mentioned in the Introduction. Thus, complex 3b was also subjected to heating at 180 °C, but neither a μ3-methylimido nor a μ3-nitrido ligand was formed. However, complex 9, which contains μ3-methylidyne and μ3-η2(∥)-HN CN ligands on each face of the Ru3 core, was exclusively obtained and isolated in 85% yield (eq 4). Although the mechanistic details

Figure 5. 1H NMR spectra of 8 measured at various temperatures showing (A) methylidyne, (B) Cp*, and (C) hydrido regions (400 MHz, tetrahydrofuran-d8).

This motion of the μ-methylidene ligand also provided the time-averaged C3 structure, as observed in the NMR spectrum measured at ambient temperature. The formation of an intermediary μ-alkylidene group within the NMR time scale is crucial for the fluxionality, and this appeared to be the reason for the isoelectronic bis(μ 3 -phenylimido) complex, (Cp*Ru)3(μ3-NPh)2(μ-H), to be nonfluxional. Although the formal electron counts of these complexes were identical (48e), the formal oxidation state of the μ3-imido−μ3-alkylidyne complexes was higher than that of the bis(μ3-imido) complex. Therefore, reductive bond formation occurred more readily in 7 and 8 than in the bis(μ3-imido) complex. The migration of a hydrido ligand onto a μ3-methylidyne carbon leading to the

are not clear, it was established that the scission of the C−N and C−C(ipso-Ph) bonds was necessary in this transformation. The phenyl group was probably eliminated as benzene.

Scheme 2. Plausible Mechanism for the Site Exchange between the Methylidyne Proton and Hydrido Ligand in 8

1922


Organometallics

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In the 1H NMR spectrum of 9, three singlets for the Cp* groups were observed at δ 1.78, 1.83, and 1.93. A signal for the hydrido ligand appeared at δ −23.22. A sharp singlet resonated at δ 17.09 indicating the presence of a μ3-methylidyne ligand. A broad signal at δ 6.70 was assignable to the NH group, whereas a well-resolved doublet resonating at δ 8.35 (JHH = 4.8 Hz) was assigned to the CH group on the μ3-η2(∥)-HNCH moiety. The molecular structure of 9 was confirmed by an X-ray diffraction study shown in Figure 6, which clearly indicates the

reactivities observed in the thermolysis of 3b are most probably attributable to the steric effect of the substituent group on the nitrogen atom.

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SUMMARY AND CONCLUSION The reactions of the triruthenium pentahydrido complex 1 with imines were examined to investigate the influence of the substituent group on the nitrogen atom on the reactivity of a CN bond. The electronic effect was clearly observed in the reaction of 1 with N-benzylideneaniline that resulted in the facile CN bond cleavage of imine. Whereas the thermolysis of 3a, which has a μ3-η2:η2(⊥)-PhCNH ligand, required heating at 180 °C to break a CN bond, the reaction of 1 with N-benzylideneaniline proceeded even at 100 °C to yield a mixture of μ3-imido−μ3-alkylidyne complexes 7 and 8, as a result of CN bond cleavage. It was anticipated that CN bond cleavage was effectively facilitated by the enhanced electron-withdrawing nature of a transient PhCNPh group in 3c as compared to that of the PhCNH group in 3a, but the intermediary μ3-η2:η2(⊥)iminoacyl complex was not observed during the reaction. The formation of a μ3-η2:η2(⊥)-iminoacyl complex was confirmed by the reaction of 1 with N-benzylidenemethylamine, which exclusively afforded 3b, having a μ3-η2:η2(⊥)PhCNMe ligand. In contrast to the reaction of 1 with Nbenzylideneaniline yielding μ3-imido−μ3-alkylidyne complexes, the thermolysis of 3b at 180 °C resulted in the formation of the μ3-methylidyne−μ3-η2(∥)-iminoacyl complex 9. In this reaction, both the C−Ph bond and the C−N bond were broken to form a μ-η2(∥)-HCNH group. Although mechanistic details of the formation of 9 are unclear, the different reactivities are most probably attributable to the presence of a β-hydrogen atom in the N−Me group. The steric and spectral data of the μ3-η2:η2(⊥)-nitrile complex 2, cationic μ3-η2:η2(⊥)-iminoacyl complex 6, and neutral μ3-η2:η2(⊥)-iminoacyl complex 3 showed interesting trends in the bonding interaction of a C−N moiety with the trimetallic core. These results indicated that back-donation into a nitrile ligand from the Ru3 center was enhanced by both the introduction of an electrophile onto the nitrogen atom and the deprotonation from the metal center. Currently, we are investigating the reactivities of μ3-η2:η2(⊥)-nitrile and μ3-η2:η2(⊥)-iminoacyl complexes with small molecules.

Figure 6. Molecular structure and labeling scheme of 9 with thermal ellipsoids at 30% probability level. Selected bond lengths (Å) and angles (deg): Ru(1)−Ru(2), 2.7218(8); Ru(1)−Ru(3), 2.7120(9); Ru(2)−Ru(3), 2.7477(8); Ru(1)−C(1), 2.128(10); Ru(1)−C(2), 2.027(7); Ru(1)−N(1), 2.103(9); Ru(2)−C(1), 2.021(10); Ru(2)− C(2), 2.021(6); Ru(3)−C(2), 2.024(7); Ru(3)−N(1), 2.019(10); N(1)−C(1), 1.370(13); Ru(2)−Ru(1)−Ru(3), 60.75(2); Ru(1)− Ru(2)−Ru(3), 59.45(2); Ru(1)−Ru(3)−Ru(2), 59.79(2); C(1)− Ru(1)−N(1), 37.8(4); Ru(1)−C(1)−Ru(2), 82.0(4); Ru(2)−C(1)− N(1), 109.6(7); Ru(1)−C(2)−Ru(2), 82.0(4); Ru(1)−C(2)−Ru(3), 84.0(3); Ru(2)−C(2)−Ru(3), 85.6(3); Ru(1)−N(1)−Ru(3), 82.3(3); Ru(3)−N(1)−C(1), 110.2(7).

elimination of the phenyl group from the imine moiety. Owing to the difficulty in distinguishing between carbon and nitrogen atoms, their positions in the HNCH group could not be determined. Therefore, they were considered as disordered structures with a 50:50 occupation ratio. The iminoacyl group is bridged between Ru(2) and Ru(3) in a parallel fashion, and the Ru(2)−Ru(3) bond is more elongated (2.7477(8) Å) than the other Ru−Ru bonds. Because there is no significant difference in the lengths of Ru(1)−Ru(2) (2.7218(8) Å) and Ru(1)−Ru(3) (2.7120(9) Å) bonds, the hydrido ligand is most probably coordinated to the Ru(2)−Ru(3) edge. The C(1)−N(1) bond distance of 1.370(13) Å lies in the reported range for the μ3-η2(∥)iminoacyl group (1.280−1.431 Å).23 As discussed previously, the uptake of dihydrogen liberated during the thermolysis of 3c appeared to play an important role in the formation of 8. Thus, the participation of liberated dihydrogen was also anticipated in this case. Dihydrogen was possibly formed by β-hydrogen elimination from the N−Me group. The scission of two C−H bonds, which are adjacent to the nitrogen atom of an aliphatic amine on a multimetallic site, yielding a μ3-iminoacyl group, has been well documented in the literature.10a,24 Although the mechanistic details are not clear at present, it was considered that the C−H bond cleavage at the N−Me group occurred prior to the C−N bond cleavage of the iminoacyl group in the thermolysis of 3b. Thus, the different

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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, pentane, tetrahydrofuran, and methanol used in this study were purchased from Kanto Chemicals and stored under an argon atmosphere. Diethyl ether, decane, benzene-d6, and tetrahydrofuran-d8 were dried over sodium-benzophenone ketyl and stored under an argon atmosphere. Other materials used in this research were used as purchased. Triruthenium pentahydrido complex {Cp*Ru(μ-H)}3(μ3−H)2 (1)25 and the perpendicularly coordinated benzonitrile complex (Cp*Ru)3(μ-H)2(μ3−H)(μ3-η2:η2(⊥)-PhCN) (2)6 were prepared according to a previously published method. 1H and 13C NMR spectra were recorded on a Varian INOVA-400 spectrometer. 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. Elemental analysis was performed on a Perkin-Elmer 2400II series CHN analyzer. X-ray Diffraction Studies. Single crystals of 3b, 6b, 7d, 8, and 9 for the X-ray analyses were obtained directly from the preparations described below and mounted on glass fibers. Diffraction experiments were performed on a Rigaku R-AXIS RAPID imaging plate diffractometer with graphite-monochromated Mo Kα radiation 1923


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Preparation of {Cp*Ru(μ-H)}3(μ3-H)(μ3-η2(∥)-PhCNMe) (5b). Tetrahydrofuran-d8 (0.5 mL), 3b (1.4 mg, 1.7 μmol), and ferrocene as an internal standard were charged in an NMR tube equipped with a J. Young valve. After the NMR tube was evacuated with cooling in a liquid nitrogen bath, 1 atm of dihydrogen was introduced into the tube. The solution was then warmed up to room temperature, and the solution was stayed for 1 h. Quantitative formation of 5b was confirmed by the 1H NMR spectrum. After the solvent was removed under reduced pressure, the residual solid was dissolved into 0.5 mL of tetrahydrofuran-d8 . The 1H NMR spectrum of the solution demonstrated that 3b was regenerated in a 61% yield. 1H NMR (400 MHz, −40 °C, THF-d8): δ −18.76 (m, 1H, RuH), −16.77 (m, 1H, RuH), −14.77 (m, 1H, RuH), −14.10 (d, JHH = 7.6 Hz, 1H, RuH), 1.53 (s, 15H, C5Me5), 1.83 (s, 15H, C5Me5), 1.89 (s, 15H, C5Me5), 2.77 (s, 3H, NCH3), 6.70 (d, JHH = 8.0 Hz, 1H, o-Ph), 6.96 (t, JHH = 7.2 Hz, 1H, p-Ph), 7.17 (dd, JHH = 8.0, 7.2 Hz, 1H, m-Ph), 7.23 (dd, JHH = 8.0, 7.2 Hz, 1H, m-Ph), 7.55 ppm (d, JHH = 8.0 Hz, 1H, o-Ph). 13 C{1H} NMR (400 MHz, −40 °C, THF-d8): δ 11.7 (C5Me5), 12.4 (C5Me5), 12.8 (C5Me5), 52.0 (PhCNMe), 86.6 (C5Me5), 91.3 (C5Me5), 91.3 (C5Me5), 123.8 (Ph), 126.7 (Ph), 127.4 (Ph), 127.5 (Ph), 130.6 (Ph), 148.4 (ipso-Ph), 177.2 ppm (PhCNMe). Owing to the instability of 5b, we could not prepare 5b as an analytically pure form. Complex 5b was therefore characterized on the basis of 1H and 13 C NMR data, which are represented in the Supporting Information. Preparation of the Triflate Salt of [{Cp*Ru(μ-H)}3(μ3-η2:η2(⊥)PhCNMe)]+ (6b). Diethyl ether (10 mL) and complex 2 (45.4 mg, 55.7 μmol) were charged in a 50 mL Schlenk tube. The solution was cooled to −78 °C with a dry ice/methanol bath. After methyl triflate (6.3 μL, 55.7 μmol) was added to the solution with vigorous stirring, the solution was gradually warmed to room temperature and stirred for 30 min. During the reaction, immediate formation of a black precipitate was observed. The black precipitate was separated by removing the supernatant and washed three times with 5 mL of diethyl ether. The residual solid was then dried under vacuum, and a 48.0 mg amount of 6b as a triflate salt was obtained (49.0 μmol, 88%). A single crystal used for the diffraction study was prepared from a tetrahydrofuran/diethyl ether solution of a BPh4 salt of 6b, which was obtained by anion exchange using NaBPh4. 1H NMR (400 MHz, 25 °C, acetone-d6): δ −22.69 (s, 1H, RuH), −3.09 (s, 2H, RuH), 1.74 (s, 15H, C5Me5), 1.98 (s, 30H, C5Me5), 4.26 (s, 3H, NCH3), 5.66 q(d, JH−H = 7.6 Hz, 2H, o-Ph), 7.01 (t, JH−H = 7.6 Hz, 1H, p-Ph), 7.18 ppm (dd, JH−H = 7.6, 7.6 Hz, 2H, m-Ph). 13C NMR (100 MHz, 25 °C, acetone-d6): δ 11.3 (q, JC−H = 128 Hz, C5Me5), 11.9 (q, JC−H = 128 Hz, C5Me5), 49.7 (q, JC−H = 139 Hz, NCH3), 91.8 (s, C5Me5), 95.5 (s, C5Me5), 124.3 (d, JC−H = 158 Hz, p-Ph), 126.4 (d, JC−H = 162 Hz, m-Ph), 128.7 (d, JC−H = 162 Hz, o-Ph), 141.7 (s, ipso-Ph), 142.0 ppm (s, CN). Anal. Calcd for C39H56F3NO3Ru3S: C, 47.84; H, 5.76; N, 1.43. Found: C, 47.71; H, 5.64; N, 1.48. Treatment of 6b with Sodium Methoxide. Methanol (5 mL) and a triflate salt of 6b (81.0 mg, 82.7 μmol) was charged in a 50 mL Schlenk tube. A methanol solution of sodium methoxide (55.0 mg, 1.02 mmol/5 mL) was added with vigorous stirring at room temperature, and the solution was stirred for 4 h. After the solvent was removed under reduced pressure, the residue was extracted with 5 mL of pentane four times. The combined extract was filtered through a Celite pad. Dryness of the filtrate under reduced pressure afforded 3b as a brown solid (68.1 mg, 82.1 μmol, 99%). Reaction of {Cp*Ru(μ-H)}3(μ3-H)2 (1) with PhCHNPh. Toluene (10 mL), complex 1 (117.5 mg, 0.165 mmol), and N-benzylideneaniline (299.4 mg, 1.652 mmol) were charged in a 20 mL glass tube equipped with a J. Young valve. The reaction mixture was heated at 100 °C for 10 days with vigorous stirring. The solution turned from reddish brown to reddish purple. The solvent was then removed under reduced pressure. The 1H NMR spectrum of the resulting residue showed that 1 was completely converted into 7c and 8, at which point the ratio between 7c and 8 was estimated at 7:2. After the residue was dissolved in 5 mL of pentane, the residue was purified by column chromatography on alumina (Merck, Art. No. 1097) with pentane. The first purple band including 7c was collected, and dryness under reduced pressure afforded 7c as a purple solid (77.7 mg, 87.2 μmol, 53%).

(λ = 0.710 69 Å). In all samples, cell refinement and data reduction were performed using the PROCESS-AUTO program.26 Intensity data were corrected for Lorentz−polarization effects and empirical absorption. The structures were solved by the Patterson method using the SHELXS-97 program and refined by the SHELXL-97 program package.27 All non-hydrogen atoms were found by the difference Fourier synthesis and were refined anisotropically except for the disordered atoms described below. For 3b and 8, the carbon atoms in the Cp* group bonded to Ru(1) were located in the ratio of 50:50 and refined isotropically. For 9, the disordered atoms at C(1) and N(1) were located in the ratio of 50:50 and refined isotropically, and the carbon atoms in the Cp* group bonded to Ru(3) were located in the ratio of 50:50 and refined isotropically. Owing to the disordered structure in 9, the positions of the hydrogen atoms in to the μ3-HC NH moiety were not determined. The refinement was carried out by least-squares methods based on F2 with all measured reflections. The metal-bound hydrogen atoms of 3b, 6b, and 8 were located in the difference Fourier map and refined isotropically. Crystal data and results of the analyses are listed in the Supporting Information (Table S-1). Variable-Temperature NMR Spectra and Dynamic NMR Simulations. Variable-temperature NMR studies were performed in flame-sealed NMR tubes in THF-d8 for 8 using a Varian INOVA-400 Fourier transform spectrometer with tetramethylsilane as an internal standard. NMR simulations for the Cp*, hydride, and methylidyne signals were performed using gNMR v4.1.0 (1995−1999 Ivory Soft). The 1H−1H coupling constants between the hydride and the methylidyne proton were estimated at JH−H = 1.10 Hz. The final simulated line shapes were obtained via an iterative parameter search upon the exchange constant k. Full details of the fitting procedure may be found in the Supporting Information. The rate constants k 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. Preparation of (Cp*Ru)3(μ-H)2(μ3-η2:η2(⊥)-PhCNMe) (3b). Toluene (10 mL), {Cp*Ru(μ-H)}3(μ3-H)2 (1; 71.9 mg, 0.101 mmol), and N-benzylidenemethylamine (62.0 μL, 0.499 mmol) were charged in a 20 mL glass tube equipped with J. Young valve. The reaction mixture was heated at 100 °C for 10 days with vigorous stirring. The color of the solution turned from reddish brown to brown. After the solvent was removed under reduced pressure, the residual solid was dissolved in 5 mL of pentane. The remaining N-benzylidenemethylamine was removed by column chromatography on alumina (Merck, Art. No. 1097) with pentane. Then, the eluent was changed to methanol, and the third purple band including 3b was collected. After the solvent was removed under reduced pressure, the residual solid was then dissolved in 5 mL of toluene and purified by column chromatography on alumina (Merck, Art. No. 1097) with toluene. The first brown band was collected, and dryness under reduced pressure afforded 3b as a brown solid (10.8 mg, 0.013 mmol, 13% yield). A red single crystal used for the diffraction study was prepared from a diethyl ether solution of 3b stored at 2 °C. 1H NMR (400 MHz, 25 °C, benzene-d6): δ −8.10 (s, 2H, RuH), 1.76 (s, 30H, C5Me5), 1.86 (s, 15H, C5Me5), 4.74 (s, 3H, NCH3), 6.12 (dd, JH−H = 7.0, 1.2 Hz, 2H, o-Ph), 6.90 (t, JH−H = 7.4 Hz, 1H, p-Ph), 7.09 ppm (dd, JH−H = 7.4, 7.0 Hz, 2H, m-Ph). 13C NMR (100 MHz, 25 °C, benzene-d6): δ 12.1 (q, JC−H = 126 Hz, C5Me5), 12.5 (q, JC−H = 126 Hz, C5Me5), 52.7 (q, JC−H = 136 Hz, NCH3), 80.7 (s, C5Me5), 90.6 (s, C5Me5), 123.8 (d, JC−H = 161 Hz, p-Ph), 125.5 (d, JC−H = 158 Hz, m-Ph), 126.7 (d, JC−H = 160 Hz, o-Ph), 149.1 (s, ipso-Ph), 160.6 ppm (s, CN). Owing to the air and moisture sensitivity of 3b, we could not prepare 3b as an analytically pure form. Complex 3b was therefore characterized on the basis of 1H and 13C NMR data, which are represented in the Supporting Information. Reaction of 1 with PhCHNMe in an NMR Tube. Benzene-d6 (0.5 mL), {Cp*Ru(μ-H)} 3 (μ 3 -H) 2 (1; 4.1 mg, 5.7 μmol), N-benzylidenemethylamine (3.6 μL, 0.029 mmol), and ferrocene as an internal standard were charged in an NMR tube equipped with a J. Young valve. The NMR tube was heated at 100 °C for 136 h. The reaction was monitored by 1H NMR, and quantitative formation of 3b was observed. 1924


Organometallics

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(s, 15H, C5Me5), 1.83 (s, 15H, C5Me5), 1.93 (s, 15H, C5Me5), 6.70 (br, W1/2 = 14.7 Hz, 1H, HCNH), 8.35 (d, JH−H = 4.8 Hz, 1H, HCNH), 17.09 ppm (s, 1H, μ3-CH). 13C NMR (100 MHz, 25 °C, benzene-d6): δ 11.8 (q, JC−H = 126 Hz, C5Me5), 11.9 (q, JC−H = 126 Hz, C5Me5), 90.0 (s, C5Me5), 91.0 (s, C5Me5), 93.7 (s, C5Me5), 166.8 (d, JC−H = 153 Hz, HCNH), 339.2 ppm (d, JC−H = 156 Hz, μ3-CH). Anal. Calcd for C32H49NRu3: C, 51.18; H, 6.58; N, 1.87. Found: C, 51.22; H, 6.44; N, 1.51.

Complex 8 was included in the second band, but 8 was not completely separated from 7c. Data for (Cp*Ru)3(μ-H)2(μ3-CPh)(μ3-NPh) (7c) are as follows. 1H NMR (400 MHz, −80 °C, tetrahydrofuran-d8): δ −19.46 (s, 2H, RuH), 1.08 (s, 15H, C5Me5), 1.84 (s, 30H, C5Me5), 6.77 (m, 3H, Ph), 6.89 (m, 1H, Ph), 7.04 (m, 2H, Ph), 7.10 ppm (m, 4H, Ph). 13C NMR (100 MHz, 25 °C, tetrahydrofuran-d8): δ 11.7 (br q, JC−H = 126 Hz, C5Me5), 95.1 (brs, C5Me5), 120.8 (d, JC−H = 157 Hz, Ph), 122.9 (d, JC−H = 153 Hz, Ph), 124.4 (d, JC−H = 158 Hz, Ph), 126.3 (d, JC−H = 156 Hz, Ph), 126.7 (d, JC−H = 158 Hz, Ph), 127.9 (d, JC−H = 153 Hz, Ph), 161.8 (s, ipso-Ph), 168.1 ppm (s, ipso-Ph). Anal. Calcd for C43H57NRu3: C, 57.96; H, 6.45; N, 1.57. Found: C, 57.56; H, 6.41; N, 1.29. Reaction of {Cp*Ru(μ-H)}3(μ3-H)2 (1) with PhCHNPh under Vacuum. Benzene-d6 (1.0 mL), complex 1 (16.9 mg, 0.024 mmol), and N-benzylideneaniline (21.3 mg, 0.118 mmol) were charged in a 50 mL Schlenk tube with ferrocene (7.0 mg, 0.038 mmol) as an internal standard. The solution was divided into the two portions, and each solution was charged into an NMR tube equipped with a J. Young valve. Both NMR tubes were heated at 100 °C for 10 days in an oil bath. During this period, one of the NMR tube was degassed in each 24 h. The yields of 7c and 8 were measured by means of 1H NMR. While complexes 7c and 8 were formed in 70 and 20% yields, respectively, in the NMR tube without evacuation, complexes 7c and 8 were formed in 80 and 10% yields in the NMR tube on undergoing periodic evacuation. Reaction of {Cp*Ru(μ-H)}3(μ3-H)2 (1) with p-MeO-C6H4-CH NPh. Toluene (10 mL), complex 1 (254.4 mg, 0.356 mmol), and (4-methoxybenzylidene)aniline (376.0 mg, 1.780 mmol) were charged in a 20 mL glass tube equipped with a J. Young valve. The reaction mixture was heated at 100 °C for 16 days with vigorous stirring. The color of the solution turned from reddish brown to reddish purple. The solvent was then removed under reduced pressure. After the residue was dissolved in 5 mL of pentane, the residue was purified by column chromatography on alumina (Merck, Art. No. 1097). The first purple band including 8 was collected by using pentane as eluent, and the second purple band including 7d was collected by using toluene as eluent. Dryness under reduced pressure afforded 8 (91.8 mg, 0.113 mmol, 32%) and 7d (71.3 mg, 0.079 mmol, 22%) as purple solids. Red single crystals used for the diffraction studies of 7d and 8 were prepared from the pentane solutions of them stored at −30 °C. Data for (Cp*Ru)3(μ-H)2{μ3-CC6H4(OMe)}(μ3-NPh) (7d) are as follows. 1 H NMR (400 MHz, 25 °C, tetrahydrofuran-d8): δ −19.31 (s, 2H, RuH), 1.61 (br s, 45H, C5Me5), 3.74 (s, 3H, OCH3), 6.68 (d, JH−H = 8.8 Hz, 2H, −C6H4-OMe), 6.76 (t, JH−H = 7.2 Hz, 1H, p-Ph), 6.81 (d, JH−H = 7.6 Hz, 2H, o-Ph), 6.99 (dd, JH−H = 7.6, 7.2 Hz, 2H, m-Ph), 7.08 ppm (d, JH−H = 8.8 Hz, 2H, −C6H4-OMe). Anal. Calcd for C44H59NORu3: C, 57.37; H, 6.46; N, 1.52. Found: C, 57.57; H, 6.50; N, 1.63. Data for (Cp*Ru)3(μ-H)2(μ3-CH)(μ3-NPh) (8) are as follows. 1H NMR (400 MHz, −80 °C, tetrahydrofuran-d8): δ −19.04 (s, 2H, RuH), 1.58 (s, 15H, C5Me5), 1.84 (s, 30H, C5Me5), 6.48 (d, JH−H = 7.2 Hz, 2H, o-Ph), 6.66 (d, JH−H = 7.2 Hz, 1H, p-Ph), 6.93 (dd, JH−H = 7.2, 7.2 Hz, 2H, m-Ph), 15.20 ppm (s, 1H, μ3-CH). 13C NMR (100 MHz, −80 °C, tetrahydrofuran-d8): δ 11.3 (q, JC−H = 127 Hz, C5Me5), 12.5 (q, JC−H = 126 Hz, C5Me5), 93.4 (s, C5Me5), 94.0 (s, C5Me5), 119.6 (d, JC−H = 156 Hz, p-Ph), 123.3 (d, JC−H = 156 Hz, o-Ph), 128.4 (d, JC−H = 154 Hz, m-Ph), 170.2 (s, ipso-Ph), 323.2 ppm (d, JC−H = 157 Hz, μ3-CH). Anal. Calcd for C37H53NRu3: C, 54.53; H, 6.55; N, 1.72. Found: C, 54.19; H, 6.38; N, 1.42. Preparation of (Cp*Ru)3(μ3-CH)(μ-H)(μ3-η2(∥)-HCNH) (9). Decane (3 mL) and complex 3b (10.9 mg, 0.013 mmol) were charged in a 20 mL glass tube equipped with a J. Young valve. The reaction mixture was heated at 180 °C for 8 days with vigorous stirring. The color of the solution turned from brown to reddish brown. The solvent was then removed under reduced pressure. After the residue was dissolved in 1 mL of toluene, the residue was purified by column chromatography on alumina (Merck, Art. No. 1097) with 1/1 toluene/pentane. The first orange band including 9 was collected. Dryness under reduced pressure afforded 9 as an orange solid (8.6 mg, 0.012 mmol, 88%). Red single crystals used for the diffraction studies were prepared from a pentane solution of 9 stored at −30 °C. 1H NMR (400 MHz, 25 °C, benzene-d6): δ −23.22 (s, 1H, RuH), 1.78

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ASSOCIATED CONTENT

* Supporting Information S

Figures, tables, and CIF files giving 1H and 13C NMR charts of 3b and 5b, details of the simulation for the VT-NMR studies of 8, and selected crystallographic data for 3b, 6b, 7d, 8, and 9. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by a Grant-in-Aid for Scientific Research in Innovative Areas “Molecular Activation Directed toward Straightforward Synthesis” from NEXT, Japan. H.K. thanks the global-COE program of the Japan Society for the Promotion of Science for financial support.

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REFERENCES

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