Solid-State Structure and Solution Reactivity of [(Ph3P)4Ru(H)2] and

Article pubs.acs.org/Organometallics

Solid-State Structure and Solution Reactivity of [(Ph3P)4Ru(H)2] and Related Ru(II) Complexes Used in Catalysis: A Reinvestigation Hamidreza Samouei, Fedor M. Miloserdov, Eduardo C. Escudero-Adán, and Vladimir V. Grushin* Institute of Chemical Research of Catalonia (ICIQ), Tarragona 43007, Spain S Supporting Information *

ABSTRACT: X-ray analysis of [(Ph3P)4Ru(H)2] (1) prepared by a literature procedure [Young, R.; Wilkinson, G. Inorg. Synth. 1990, 28, 337] shows that 1 is cocrystallized with PPh3, explaining the previously reported observations of free phosphine in solutions of 1. Lattice PPh3-free forms of 1 have also been obtained, structurally characterized, and found to generate small quantities of uncoordinated PPh3 and another species (A) in solution. Against previous beliefs, however, A is not [(Ph3P)3Ru(H)2] (2), but [(Ph3P)3Ru(H2)(H)2] (3) that forms in the reaction of 1 with adventitious water. This reaction apparently occurs via PPh3 loss from 1 to give 2, followed by H2O coordination, Ru(H)(OH2)/Ru(H2)(OH) rearrangement, H2 loss, and dimerization to give [(Ph3P)4Ru2(H)2(μ-OH)2] (4). The H2 thus produced is trapped with 2 to give 3. Complexes 3·0.5C6H6, 3·2THF, 4·2H2O, [(Ph3P)3Ru(N2)(H)2] (5), and [(Ph3P)2(H)Ru(μ-H)3Ru(PPh3)3]·0.5THF (6·0.5THF) have been structurally characterized for the first time. Also for the first time, a single-crystal X-ray diffraction study of the long-known “[(Ph3P)4RuCl2]” (7) has been performed to finally demonstrate that 7 is, in fact, [(Ph3P)3RuCl2]·PPh3, precisely as proposed by Hoffman and Caulton as early as 1975 [Hoffman, P.R.; Caulton, K.G. J. Am. Chem. Soc. 1975, 97, 4221].

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room-temperature 31P NMR spectrum of the isolated crystalline product displayed, in addition to the two 1:1 resonances from 1, a singlet at −5.5 ppm due to PPh3. Interestingly, the 1 to free PPh3 molar ratio of ca. 2:1 determined by integration of the 31 P NMR signals remained constant regardless of the batch of 1 and solvent used (THF, toluene, benzene) in a broad range of temperatures (25 to −90 °C in THF or toluene). This observation prompted us to perform a crystallographic study of 1. X-ray quality crystals were obtained from a saturated benzene solution of 1 produced in the reaction of [(Ph3P)3RuCl2] with NaBH4 in the presence of PPh3 in the recommended ca. 25-fold excess.13 X-ray diffraction showed that 1 was cocrystallized with PPh3 and C6H6 in a 4:2:5 ratio, 1·0.5PPh3·1.25C6H6, in full accord with the solution 31P NMR data. This composition was also consistent with the integral intensities of the signals in the 1H NMR spectrum (THF-d8) of 1 precipitated in the synthesis,13 without additional recrystallization. Addition of hexanes to dilute solutions of 1·0.5PPh3·1.25C6H6 in benzene produced crystals of 114 and 1·1.5C6H6 (Figure 1) that did not contain extra PPh3, as established by X-ray diffraction. Full details of all three X-ray studies (1·0.5PPh3·1.25C6H6, 1, and 1·1.5C6H6) are presented in the Supporting Information. The structure of 1 is maintained in solution, as follows from the 1H and 31P NMR data.4 Intriguingly, ca. 0.5 h after recrystallized, phosphine-f ree 1 was dissolved in THF, benzene, or toluene under argon, a small peak from uncoordinated PPh3 (ca. 5−7% of the total integral intensity) could be clearly seen in the 31P{1H} NMR spectrum. The formation of free

INTRODUCTION Since the original reports1,2 on the preparation of the title complex 45 years ago, [(Ph3P)4Ru(H)2] (1) has been recognized and widely used as an excellent catalyst for a variety of organic transformations.3 The activity of coordinatively saturated 1 as added catalyst is attributed to the loss of one PPh3 ligand, leading to the formation of reactive [(Ph3P)3Ru(H)2] (2), as shown in eq 1.

The presence of free phosphine has been observed4,5 in solutions of 1 by 31P NMR. Linn5 has reported an actual 31P NMR spectrum of 1 in benzene-d6 at 27 °C, displaying, in addition to the main signals from 1, two low intensity singlet resonances. While the upfield weak signal (−5.5 ppm) was clearly from free PPh3, the other extra peak (57 ppm) was assigned to 2.5 In some papers,6−9 isolation of 2 has been claimed, and in some others,10,11 this species might have been detected in situ. Although 2 has been convincingly proposed as a highly reactive intermediate,1b,4,10,11 there have been no reports of unambiguous characterization of 2 in the solid state or in solution. Puzzled by the lack of certainty about the existence of elusive 2, and in continuation of our work with Ru complexes,12 we attempted detection and characterization of 2 in solutions of well-defined 1.

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RESULTS AND DISCUSSION Complex 1 was prepared by the widely used literature procedure.13 In accord with the previous reports,4,5 the © XXXX American Chemical Society

Received: October 21, 2014

A

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Figure 2. ORTEP drawing of [(Ph3P)3Ru(H2)(H)2]·2THF (3·2THF) with THF molecules and all H atoms except Ru-H omitted and thermal ellipsoids drawn to the 50% probability level.

Figure 1. ORTEP drawing of [(Ph3P)4RuH2]·1.5C6H6 (1·1.5C6H6) with benzene molecules and all H atoms, except Ru-H, omitted and thermal ellipsoids drawn to the 50% probability level.

and 2.20 Å for 3·2THF, in line with the formulation of 3 as a classical−nonclassical hydride.15 The presence of the strongly trans-influencing hydride in both 3·0.5C6H6 and 3·2THF is also manifested by the Ru−P bond distances for the mutually trans phosphines being ca. 0.06−0.08 Å shorter than for the third PPh3 ligand. The formation of PPh3 and 3 from 1 and H2O in THF-d8 was accompanied by the appearance of yet another species (B). The 1H and 31P NMR signals from B were weak and could be clearly seen only at higher conversion and after long acquisition times. In the 1H NMR spectrum, B displayed a triplet at −24.15 ppm (JH‑P = 36 Hz) and a broad singlet of roughly equal intensity at −0.80 ppm. A singlet at 74.8 ppm from B was observed in the 31P NMR spectrum. These NMR parameters coincided with those previously reported16 for a hydrido hydroxo complex formulated as [(Ph3P)2Ru(H)(OH)(L)] (L = H2O or THF). Integration of the 1H and 31P NMR signals indicated that this hydroxo hydride B and 3 were produced in a ca. 1:1 molar ratio. After heating at 65 °C for 30 min, the reaction solution deposited dark red crystals of X-ray quality. Single-crystal X-ray diffraction performed on one of those crystals established its structure (Figure 3) as [(Ph3P)4Ru2(H)2(μ-OH)2]·2H2O (4·2H2O).

PPh3 (ca. −5.5 ppm) was accompanied by the appearance of a weak singlet resonance of roughly the same intensity from another species (A) at 57.6 ppm in the 31P NMR spectrum. In parallel, a low intensity broadened singlet at −7.1 ppm appeared in the hydrido region of the 1H spectrum. No further significant growth in intensity of the new resonances was detected for an additional 12 h. The 31P NMR spectral pattern observed by us was virtually identical with the one previously reported by Linn.5 As mentioned above, Linn identified A as [(Ph3P)3Ru(H)2] (2), the product of PPh3 dissociation from 1. In accord with this assignment, we found that dissolving 1 in the presence of free PPh3 (11 equiv) strongly inhibited the formation of A. On the other hand, we also noticed that considerably smaller quantities of A (ca. 3%) were produced when samples of 1 were prepared in silylated NMR tubes. Furthermore, NMR spectra of samples of 1 prepared and measured in fluoropolymer PTFE-FEP tube liners displayed barely detectable resonances from A and free PPh3. These observations were inconsistent with A being 2 but rather suggested that the formation of A might instead deal with trace adventitious water. Given the water assay of 5−10 ppm in the solvents used with [1] = ca. 7 × 10−3 M, the main moisture source must have been the glass surface of the NMR tubes rather than the solvent. The aforementioned experiments in silylated NMR tubes and PTFE-FEP liners provided strong support to this conclusion. Moreover, deliberate addition of water to solutions of 1 in THF gave rise to higher yields of A. Full conversion of 1 to A could not be reached, however, even after thorough optimization. Therefore, we attempted identification of A in situ. All 1H and 31P NMR parameters measured for A in the temperature range of +25 to −85 °C (THF-d8 or toluene-d8), including the T1 value of 34 ms (benzene-d6; 25 °C; 500 MHz) appeared virtually indistinguishable from those of the wellknown tetrahydride [(Ph3P)3Ru(H2)(H)2] (3).15 The identity of A as [(Ph3P)3Ru(H2)(H)2] was further confirmed by spiking 1 H and 31P NMR experiments with an authentic sample of 3. Although the tetrahydride 3 has been broadly used and studied in considerable detail, there have been no reports of its crystal structure. The difficulty in obtaining an X-ray structure of 3 is due to its crystallization in the form of thin, fiber-like needles. In the current work, we have succeeded in obtaining singlecrystal X-ray structures of 3·2THF (Figure 2) and 3·0.5C6H6. Modeling the hydride positions produced the H−H bond distances of 0.99, 1.84, and 2.41 Å for 3·0.5C6H6 and 1.00, 1.96,

Figure 3. ORTEP drawing of [(Ph3P)4Ru2(H)2(μ-OH)2]·2H2O (4·2H2O) with water molecules and all H atoms except Ru-H and OH omitted and thermal ellipsoids drawn to the 50% probability level.

The results described above indicate that solutions of 1 do not produce 2 in NMR-observable quantities, at least under conditions employed in the current work. There is little doubt, however, that 1 does lose PPh3 to generate 2,17 which determines the reactivity of 1 toward adventitious water, as proposed in Scheme 1. B

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Scheme 1. Reaction of [(Ph3P)4RuH2] (1) with Water

Figure 4. ORTEP drawing of [(Ph3P)3Ru(H)2(N2)] (5) with all H atoms except Ru-H omitted and thermal ellipsoids drawn to the 50% probability level.

Steric crowding around Ru in 1 forces one of the phosphine ligands to come off the metal, likely via a dissociative mechanism. This reversible process leading to 2 can be suppressed by the addition of extra PPh3 that shifts the equilibrium between 1 and 2 toward the former. Coordination of a water molecule to the vacant site of 2 gives rise to [(Ph3P)3Ru(H)2(OH2)] with one hydride cis and one trans to the aqua ligand. Intramolecular proton transfer from the aqua ligand to the proximal hydride is expected to be facile, leading to an isomeric hydroxo η2-H2 complex.18 Dihydrogen dissociation from this complex, followed by dimerization through the terminal OH ligands, produces 4, and the trapping of the H2 released with 2 gives 3. The proposed mechanism presented in Scheme 1 accounts for all of the observations made in the current study of solution behavior of 1. As follows from the experiments performed in regular and silylated NMR tubes and in PTFE-FEP liners (see above), 2 produced from 1 can undergo similar transformations with Si-OH and water adsorbed on the surface of the glass. The above experiments with air-sensitive Ru complexes were conducted in an argon rather than nitrogen atmosphere. Under N2, solutions of both 1 and 3 gave rise to [(Ph3P)3Ru(N2)(H)2] (5) in various quantities, as was detected by 1H and 31P NMR and confirmed using an authentic sample of 5.19 The independent synthesis of 5 gave us an opportunity to perform a single-crystal diffraction study of this long-known,20 yet hitherto structurally uncharacterized, complex (Figure 4). Even under argon containing adventitious N2, solutions of 1 and 3 produced small, yet NMR-detectable, quantities of 5 after a few hours, although N2 in 5 is known19a to bind to Ru more weakly than H2 in 3. Contamination with N2 of the argon atmosphere in a circulation glovebox can represent a serious problem when working with 1 and 3. Not sequestered by the purifier, N2 gradually accumulates in the glovebox atmosphere after entering with adventitious air and/or with chemicals/solvents sealed under nitrogen. Attempts to detect [(Ph3P)3Ru(H)2(OH2)] by 1H and 31P NMR in the reaction of 5 with water were unsuccessful, and only the formation of 1, 3, and 4 was observed (Scheme 1). Some of the NMR samples deposited small quantities of wellshaped red crystals on standing at room temperature for days. X-ray analysis of one of those crystals revealed its structure, [(Ph3P)2(H)Ru(μ-H)3Ru(PPh3)3]·0.5THF (6·0.5THF), as shown in Figure 5. This dinuclear tetrahydride has been previously isolated and characterized in solution,21 but not in the crystal state.

Figure 5. ORTEP drawing of [(Ph3P)2(H)Ru(μ-H)3Ru(PPh3)3]· 0.5THF (6·0.5THF) with THF and all H atoms except Ru-H omitted and thermal ellipsoids drawn to the 50% probability level.

It has been demonstrated21 that 6 can form from 3 via H2 dissociation, followed by dimerization of the resultant 2 and loss of a phosphine. This reaction pathway lends additional support to the formation of 2 from 1. The structure of 1 with cocrystallized PPh3 (see above) prompted us to address the long-standing22 question of whether or not [(Ph3P)4RuCl2] (7) can exist. Both [(Ph3P)3RuCl2] and [(Ph3P)4RuCl2] were first reported by Stephenson and Wilkinson23 almost 50 years ago. Back then, the two complexes were formulated on the basis of elemental analysis data, and already in 1975, Hoffman and Caulton wrote: “The reactions of PPh3 with commercial “ruthenium trichloride hydrate” are puzzling. Reaction in methanol with a 6:1 PPh3:Ru ratio produces dif ferent products at ref lux temperature (RuC12(PPh3)3) and room temperature (RuC12(PPh3)4). The reaction chemistry of both tris and tetrakis complexes appears to be the same, but the structure of the latter is unknown. Both are dark solids which form solutions with similar colors.”22 The observation of two resonances with relative intensities 3:1 in the 31P NMR spectrum of 7, one from [(Ph3P)3RuCl2] and one from PPh3, suggested full dissociation of one phosphine from 7 in solution. Furthermore, analysis of the literature data along with considerations of ligand crowding around Ru and d-d transitions (color) prompted Hoffman and Caulton to “tentatively propose C

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(6·0.5THF) have been structurally characterized for the first time. Also for the first time, single-crystal X-ray diffraction has been performed on the puzzling “[(Ph3P)4RuCl2]” (7). The X-ray study has finally demonstrated that complex 7 is, in fact, [(Ph3P)3RuCl2]·PPh3, exactly as proposed by Hoffman and Caulton 40 years ago.

that RuC12(PPh3)4 does not have four-coordinated phosphines in the solid, but instead contains RuC12(PPh3)3 molecules and “lattice PPh3”” and consequently express that “A crystal structure determination should prove interesting.”22 We are now pleased to report such a structure determination confirming exactly what was proposed 40 years ago. An X-ray study performed on 7 prepared by the original procedure23b showed clearly (Figure 6) that the tetraphosphine

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EXPERIMENTAL SECTION

All manipulations were performed under argon in a glovebox or using Schlenk techniques, unless noted otherwise. RuCl3·xH2O, PPh3, and NaBH4 were used as received. Anhydrous, oxygen-free hexane, benzene, benzene-d6, toluene-d8, THF, and THF-d8 were obtained by distillation from Na/OCPh2 under argon and stored over freshly activated 4 Å molecular sieves in an argon-filled glovebox. [(Ph3P)3RuCl2] was prepared by the literature procedure.23b NMR spectra were recorded on Bruker Avance Ultrashield 400 and 500 MHz spectrometers. Singlecrystal X-ray diffraction studies were performed on Bruker FR591 and Apex DUO Kappa 4-axis diffractometers equipped with APEX II 4K CCD area detectors. As demonstrated (see above), complexes 1 and 3 easily form solvates and 1 can also contain lattice PPh3. The composition of these materials may vary significantly depending on minor changes in crystallization conditions. It is, therefore, recommended that each batch of the complexes obtained be carefully analyzed by 1H and 31P NMR to determine the amount of cocrystallized solvents and/or PPh3. [(Ph3P)4Ru(H)2] (1). A slightly modified literature procedure13 was used. A 250 mL three-neck round-bottom flask equipped with a rubber septum, a gas inlet, and a PTFE-coated magnetic stir-bar was charged with PPh3 (6.00 g, 22.88 mmol), C6H6 (60 mL), and MeOH (100 mL). After agitation under argon for 10 min, [(Ph3P)3RuCl2] (1.00 g, 1.04 mmol) was added and the reaction mixture was stirred for an additional 10 min. As stirring continued, NaBH4 (1.50 g, 39.65 mmol) was added in 5 portions over a period of 20 min. During the addition, the originally brown reaction mixture turned yellow. After stirring for an additional hour, the mixture was diluted with deaerated MeOH (100 mL), the yellow solid was filtered under argon, washed with deaerated MeOH (3 × 20 mL), deaerated and deionized water (4 × 20 mL), and again with deaerated MeOH (3 × 20 mL), and dried under vacuum. The product containing cocrystallized phosphine (see above) is air-sensitive in solution and in the solid state. The yield was 1.30 g (90%; calculated for [(Ph3P)4Ru(H)2]·0.5PPh3· 1.25C6H6). 1H NMR (C6D6, 25 °C), δ: 7.44−6.73 (m), −10.13 (m). 31 1 P{ H} NMR (C6D6, 25 °C), δ: 49.1 (t, J = 13.8 Hz, 2P), 40.9 (t, J = 13.8 Hz, 2P), −5.5 (s, 0.5P). [(Ph3P)3Ru(H2)(H)2] (3). A slightly modified literature procedure19 was used. A 1 L round-bottom flask equipped with a rubber septum, a gas inlet, and a PTFE-coated magnetic stir-bar was charged under argon with [(Ph3P)3RuCl2]·PPh323b (3.69 g, 3.02 mmol) and a deaerated 4:3 v/v mixture of ethanol and benzene (460 mL). To this mixture, at stirring, NaBH4 (420 mg, 11.1 mmol) was added in small portions over a period of 10 min. The originally brown reaction mixture turned lighter in color, and a white precipitate appeared within 20 min of agitation. After stirring for an additional 2 h, the pinkish slurry was filtered under argon and the off-white product was thoroughly washed on the filter with deaerated EtOH (1 × 40 mL), deaerated water (2 × 30 mL), deaerated EtOH (2 × 40 mL), and deaerated hexane (2 × 40 mL). Drying the washed solid first with a flow of argon and then under vacuum (∼1 mbar) for 10 min gave crude 3 (2.30 g) containing cocrystallized benzene (1 molecule) and residual water (1H NMR). For further purification, the crude product (1.03 g) was dissolved under argon in warm (ca. 50 °C) THF (50 mL) and allowed to cool to room temperature. After 6 h at −32 °C, the precipitated fiber-like white needle crystals were separated by filtration, washed with THF (3 × 3 mL), and dried first with a flow of argon and then under vacuum (∼1 mbar) for 10 min. The yield of the thus recrystallized slightly off-white, air-sensitive 3 (1.3 THF solvate) was 0.61 g (46%). 1H NMR (C6D6, 25 °C), δ: 7.41 (br s, 18H), 6.96, (t, J = 7.3 Hz, 9H), 6.88 (t, J = 7.5 Hz, 18H), −7.07 (br s, 4H). 31P{1H} NMR (C6D6, 25 °C), δ: 57.6 (s).

Figure 6. ORTEP drawing of [(Ph3P)3RuCl2]·PPh3 (7·PPh3) with all H atoms omitted and thermal ellipsoids drawn to the 50% probability level.

complex is indeed [(Ph3P)3RuCl2] with one PPh3 cocrystallized in the lattice. Therefore, we suggest that the formula [(Ph3P)4RuCl2] that is still used in modern reports24 and even in the current catalogs of some chemical companies should be modified to [(Ph3P)3RuCl2]·PPh3.

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CONCLUSIONS Our reinvestigation of the well-known Ru catalyst [(Ph3P)4Ru(H)2] (1) has shown that the widely used literature procedure13 employing PPh3 in large excess can produce 1 cocrystallized with PPh3. The established (X-ray) composition 1·0.5PPh3·1.25C6H6 explains the previously reported observations of free PPh3 in solutions of 1.25 Lattice phosphine-free forms of 1 have also been obtained and structurally characterized. Interestingly, solutions of pure 1, free of PPh3, also exhibit weak 31P NMR signals from uncoordinated PPh3 as well as from another species. The latter, however, is not [(Ph3P)3Ru(H)2] (2) as previously believed, but rather [(Ph3P)3Ru(H2)(H)2] (3), a mixed classical−nonclassical hydride that is produced in the reaction of 1 with adventitious water. This reaction also gives rise to an equimolar quantity of a hydrido hydroxo complex that has been structurally characterized as [(PPh3)4Ru2(H)2(μ-OH)2] (4) in the crystal state. A plausible proposed mechanism for this reaction involves PPh3 dissociation from 1 to give 2, followed by H2O coordination, Ru(H)(OH2)/ Ru(H2)(OH) rearrangement, and loss of H2. The latter is trapped with 2 to give 3, whereas the 5-coordinate product of the intramolecular proton transfer, [(Ph3P)3Ru(H)(OH)], dimerizes upon phosphine loss to give 4. While our study certainly confirms PPh3 dissociation from 1, elusive 2 could not be isolated, nor even detected by NMR spectroscopy under conditions used in the current work. We are unaware of reports of unambiguous characterization of [(Ph3P)3Ru(H)2] (2) in the solid state or in solution. Complexes 3·0.5C6H6, 3·2THF, 4·2H2O, [(Ph3P)3Ru(N2)(H)2] (5), and [(Ph3P)2(H)Ru(μ-H)3Ru(PPh3)3]·0.5THF D

dx.doi.org/10.1021/om5010572 | Organometallics XXXX, XXX, XXX−XXX

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[(Ph3P)4Ru2(H)2(μ-OH)2]·2H2O (4·2H2O). In a glovebox, a 5 mm NMR tube was charged with [(Ph3P)4Ru(H)2] (10 mg, 0.01 mmol) and THF (0.6 mL), sealed with a rubber septum, and brought out. Deaerated water (0.1 mL) was added via a microsyringe, and the tube was kept at 70 °C (oil bath) for 1 h. During that period, the color of the reaction mixture changed from yellow to deep red. On standing at room temperature, red X-ray quality crystals of 4·2H2O were formed. [(Ph3P)3Ru(N2)(H)2] (5). Inside an argon-filled glovebox, a 20 mL vial was charged with [(Ph3P)3Ru(H2)(H)2] (3; 200 mg, 0.224 mmol) and benzene (10 mL), sealed with a rubber septum, and brought out. Pure N2 was bubbled through this mixture via a syringe needle for 1 h. During that time, the volume of the reaction solution had reduced to ca. 5 mL (1 h). The vial was brought back to the glovebox. The reaction mixture was treated with hexane (15 mL) and kept at −30 °C for 1 h. The precipitated 5 was separated by decantation, washed with hexane (2 × 5 mL), and dried under vacuum. The yield of off-white microcrystalline 5 was 180 mg (87%). [(Ph3P)3Ru(N2)(H)2] is airsensitive in solution and in the solid state. 1H NMR (C6D6, 25 °C), δ: 7.57−6.81 (m), −8.53 (br dt, J = 77 Hz, 30 Hz, 1H), −12.71 (br s, 1H); 31P{1H} NMR (C6D6, 25 °C), δ: 56.2 (d, J = 16 Hz, 2P), 43.7 (t, J = 16 Hz, 1P). [(Ph3P)3RuCl2]·PPh3 (7).23b A solution of RuCl3·xH2O (0.60 g, 2.4 mmol) in MeOH (150 mL) in a 250 mL flask was stirred under reflux in an argon atmosphere for 15 min. After cooling to room temperature, PPh3 (3.60 g, 13.7 mmol) was added and the reaction mixture was agitated at room temperature for 3 h. The solid was separated by filtration. Keeping the mother liquor at room temperature under argon overnight produced 0.36 g of well-shaped, X-ray quality brown crystals of [(Ph3P)3RuCl2]·PPh3.

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O.; Hota, N. K.; Sadavoy, L.; Yuen, J. M. C. J. Organomet. Chem. 1973, 54, 259. (8) (a) Nolan, S. P.; Belderrain, T. R.; Grubbs, R. H. Organometallics 1997, 16, 5569. (b) McKinty, A. M.; Stephan, D. W. Dalton Trans. 2014, 43, 2710. (9) Aranyos, A.; Csjernyik, G.; Szabó, K. J.; Bäckvall, J.-E. Chem. Commun. 1999, 351. (10) Linn, D. E., Jr.; Halpern, J. J. Am. Chem. Soc. 1987, 109, 2969. (11) Gómez-Bengoa, E.; Cuerva, J. M.; Mateo, C.; Echavarren, A. M. J. Am. Chem. Soc. 1996, 118, 8553. (12) Samouei, H.; Grushin, V. V. Organometallics 2013, 32, 4440. (13) Young, R.; Wilkinson, G. Inorg. Synth. 1990, 28, 337. (14) For an early crystallographic study of 1, see: Immirzi, A.; Luccarelli, A. Cryst. Struct. Commun. 1972, 1, 317. (15) (a) Crabtree, R. H.; Hamilton, D. G. J. Am. Chem. Soc. 1986, 108, 3124. (b) Gusev, D. G.; Vymenits, A. B.; Bakhmutov, V. I. Inorg. Chim. Acta 1991, 179, 195. (16) (a) Cole-Hamilton, D. J.; Wilkinson, G. Nouv. J. Chim. 1977, 1, 141. (b) Chaudret, B. N.; Cole-Hamilton, D. J.; Nohr, R. S.; Wilkinson, G. J. Chem. Soc., Dalton Trans. 1977, 1546. (17) Kirss, R. U.; Eisenschmid, T. C.; Eisenberg, R. J. Am. Chem. Soc. 1988, 110, 8564. (18) (a) This proposed mechanism lends strong support from the previously reported18b−e H/D exchange in complexes of the type [LnM(H)(D2O)] and the formation of [(IMes)2Ru(CO)2(OH)(H)] from [(IMes)2Ru(CO)(H2O)(H)2] (under CO).18e These reactions involve proton transfer between the M-OH2 and M-H sites, apparently via a hydroxo η2-H2 intermediate. Protonation of terminal transitionmetal hydrides often produces dihydrogen complexes.18f−i (b) Crabtree, R. H.; Lavin, M.; Bonneviot, L. J. Am. Chem. Soc. 1986, 108, 4032. (c) Leoni, P.; Sommovigo, M.; Pasquali, M.; Midollini, S.; Braga, D.; Sabatino, P. Organometallics 1991, 10, 1038. (d) Milet, A.; Dedieu, A.; Kapteijn, G.; van Koten, G. Inorg. Chem. 1997, 36, 3223. (e) Jazzar, R. F. R.; Bhatia, P. H.; Mahon, M. F.; Whittlesey, M. K. Organometallics 2003, 22, 670. (f) Kubas, G. J. Metal Dihydrogen and σ-Bond Complexes; Kluwer Academic/Plenum: New York, 2001. (g) Jessop, P. G.; Morris, R. H. Coord. Chem. Rev. 1992, 121, 155. (h) Crabtree, R. H.; Hamilton, D. G. Adv. Organomet. Chem. 1988, 28, 299. (i) Heinekey, D. M.; Oldham, W. J., Jr. Chem. Rev. 1993, 93, 913. (19) (a) Knoth, W. H. J. Am. Chem. Soc. 1972, 94, 104. (b) Knoth, W. H. Inorg. Synth. 1974, 15, 31. (20) Knoth, W. H., Jr. J. Am. Chem. Soc. 1968, 90, 7172. (21) Van Der Sluys, L. S.; Kubas, G. J.; Caulton, K. G. Organometallics 1991, 10, 1033. (22) Hoffman, P. R.; Caulton, K. G. J. Am. Chem. Soc. 1975, 97, 4221. (23) (a) Stephenson, T. A.; Wilkinson, G. J. Inorg. Nucl. Chem. 1966, 28, 945. (b) Hallman, P. S.; Stephenson, T. A.; Wilkinson, G. Inorg. Synth. 1970, 12, 237. (24) (a) Nomura, K.; Kuromatsu, Y. J. Mol. Catal. A 2006, 245, 152. (b) Schley, N. D.; Dobereiner, G. E.; Crabtree, R. H. Organometallics 2011, 30, 4174. (c) Pingen, D.; Lutz, M.; Vogt, D. Organometallics 2014, 33, 1623. (25) Given the propensity of 1 to cocrystallize with PPh3, one might wonder why 1 from the reaction of [(Ph3P)3RuCl2] with NaBH4 in the presence of excess PPh3 analyzes well for [(Ph3P)4Ru(H)2] (Calcd.: C, 75.0; H, 5.4; P, 10.7. Found: C, 75.1; H, 5.7; P, 10.4),13 rather than for [(Ph3P)4Ru(H)2]·0.5PPh3·1.25C6H6 (Calcd.: C, 77.0; H, 5.6; P, 10.1), the composition found in the current work. In the formation of 1, however, NaCl is byproduced, which is poorly soluble in the benzene− MeOH reaction medium and, therefore, most likely coprecipitates with 1. In this way, contamination with NMR-silent NaCl is highly probable, unless the product is washed with water (ref 11 and this work). Some compositions of 1 containing not only cocrystallized PPh3 and C6H6 but also coprecipitated NaCl are indistinguishable from 1 by microanalytical data, e.g., [(Ph3P)4Ru(H)2]·0.5PPh3· 0.25NaCl (Calcd.: C, 75.0; H, 5.4; P, 10.7) or [(Ph3P)4Ru(H)2]· 0.5PPh3·1.25C6H6·0.5NaCl (Calcd.: C, 75.4; H, 5.5; P, 9.9).

ASSOCIATED CONTENT

S Supporting Information *

Full details of crystallographic studies (CIF). This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (V.V.G.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank Prof. Antonio M. Echavarren and Prof. Vladimir I. ́ Bakhmutov for fruitful discussions and Dr. Marta Martinez Belmonte and Dr. Eddy Martin for crystallographic studies. This work was supported by the ICIQ Foundation and the Spanish Government (Grant CTQ2011-25418). F.M.M. is grateful to the Government of Spain (MICINN) for the FPI Ph.D. Scholarship (BES-2012-054922).

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REFERENCES

(1) (a) Yamamoto, A.; Kitazume, S.; Ikeda, S. J. Am. Chem. Soc. 1968, 90, 1089. (b) Ito, T.; Kitazume, S.; Yamamoto, A.; Ikeda, S. J. Am. Chem. Soc. 1970, 92, 3011. (2) Levison, J. J.; Robinson, S. D. Chem. Ind. 1969, 1514. (3) See, for example: (a) Arockiam, P. B.; Bruneau, C.; Dixneuf, P. H. Chem. Rev. 2012, 112, 5879. (b) Murahashi, S.-I., Ed. Ruthenium in Organic Synthesis; Wiley-VCH: Weinheim, Germany, 2004. (c) Bruneau, C., Dixneuf, P. H., Eds. Ruthenium Catalysts and Fine Chemistry; Topics in Organometallic Chemistry; Springer: Berlin, Germany, 2004; Vol. 11. (4) Komiya, S.; Yamamoto, A. J. Mol. Catal. 1979, 5, 279. (5) Linn, D. E., Jr. J. Chem. Educ. 1999, 76, 70. (6) Levison, J. J.; Robinson, S. D. J. Chem. Soc. A 1970, 2947. (7) (a) Eliades, T. I.; Harris, R. O.; Zia, M. C. J. Chem. Soc. D 1970, 1709. (b) The complex originally formulated as [(Ph3P)3RuH2]7a was later shown7c by the same group to be [(Ph3P)3RuH4]. (c) Harris, R. E

dx.doi.org/10.1021/om5010572 | Organometallics XXXX, XXX, XXX−XXX