Water-Soluble Triisopropylphosphine Complexes ... - ACS Publications

Organometallics 2009, 28, 561–566

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Water-Soluble Triisopropylphosphine Complexes of Ruthenium(II): Synthesis, Equilibria, and Acetonitrile Hydration ´ gnes Katho´,‡ and Ferenc Joo´*,‡ Marta Martı´n,† Henrietta Horva´th,† Eduardo Sola,*,† A Departamento de Quı´mica de Coordinacio´n y Cata´lisis Homoge´nea, Instituto de Ciencia de Materiales de Arago´n, UniVersidad de Zaragoza-CSIC, E-50009 Zaragoza, Spain, Research Group of Homogeneous Catalysis, Hungarian Academy of Sciences, Debrecen, Hungary, and Institute of Physical Chemistry, UniVersity of Debrecen, H-4010 Debrecen, Hungary ReceiVed September 3, 2008

The complex [RuCl(NCMe)4(PiPr3)]BF4 (1) and its water-soluble dicationic products of chloride replacement by PiPr3 (2), P(OMe)3 (3), Hpz (4), MeOH (5), and H2O (6) have been prepared and characterized. The chloride dissociation constant of 1 in water (Kd ) 2.0 M) and the pKa (10.5) for the deprotonation of the water ligand of 6 have been determined by NMR methods. The conjugate base of 6, [Ru(OH)(NCMe)4(PiPr3)]+ (7), has been observed to isomerize into an amidate complex in route to acetonitrile hydration. Consistently, 6 has been found to catalyze the selective hydration of acetonitrile to acetamide in aqueous solution at pH 10.5 and 353 K, with initial TOF about 50 h-1. Introduction Water-soluble and aquo organometallics attract attention in the context of catalysis mainly because of the technological advantages that could result from their operation in aqueousorganic biphasic media,1,2 but also due to remaining challenges concerning the selectivity of certain catalytic hydrations.3,4 Most compounds investigated within this context are versions of catalysts that have already been successful in organic solvents, turned water-soluble through the use of ligands with solubilizing groups, such as water-soluble phosphines.5 However, less attention is paid to the catalytic properties of other complexes that are water-soluble as a consequence of their ionic nature or due to the ions generated in aqueous media after dissociation of charged ligands, generally halides.6 Nevertheless, such charged metal complexes are ubiquitous, and the aquation processes that could dissolve them in water can become very favorable due to the strong solvent coordination and the high

* Corresponding author. E-mail: [email protected]. † Instituto de Ciencia de Materiales de Arago´n. ‡ Hungarian Academy of Sciences and Institute of Physical Chemistry. (1) (a) Cornils; B.; Herrmann, W. A.; Horva´th; I. T.; Leitner, W.; Mecking, S.; Olivier-Bourbigou, H.; Vogt, D., Eds. Multiphase Homogeneous Catalysis; Wiley-VCH: Weinheim, 2005. (b) Adams, D. J.; Dyson, P. J.; Tavener, S. T. Chemistry in AlternatiVe Reaction Media; Wiley: Chichester, 2004. (d) Behr, A. Angewandte homogene Katalyse; WileyVCH: Weinheim, 2008. (2) (a) Joo´, F. Aqueous Organometallic Catalysis; Kluwer: Dordrecht, 2001. (b) Cornils, B., Herrmann, W. A., Eds. Aqueous-Phase Organometallic Catalysis, 2nd ed.; Wiley-VCH: Weinheim, 2004. (3) (a) Borman, S. Chem. Eng. News 2004, 82, 42–43. (b) Grotjahn, D. B. Chem.-Eur. J. 2005, 11, 7146–7153. (c) Richard, C. J.; Parkins, A. W. New J. Chem. 2008, 32, 151–158. (4) Kukushkin, V. Y.; Pombeiro, A. J. L. Inorg. Chim. Acta 2005, 358, 1–21. (5) (a) Phillips, A. D.; Gonsalvi, L.; Romerosa, A.; Vizza, F.; Peruzzini, M. Coord. Chem. ReV. 2004, 248, 955–993. (b) Horva´th, I. T.; Lantos, D. In ComprehensiVe Organometallic Chemistry, 3rd ed.; Mingos, D. M. P., Crabtree, R. H., Eds.; Elsevier, 2007; Vol. 1, pp 823-845. (6) Representative examples and leading references: (a) Wu, X.; Li, X.; Zanotti-Gerosa, A.; Pettman, A.; Liu, J.; Mills, A. J.; Xiao, J. Chem.-Eur. J. 2008, 14, 2209–2222. (b) Li, C.-J. Chem. ReV. 2005, 105, 3095–3165. (c) Breno, K. L.; Pluth, M. D.; Landorf, C. W.; Tyler, D. R. Organometallics 2004, 23, 1738–1746. (d) Russell, M. J. H.; Murrer, B. A. US Patent 4,517,390, 1985.

solvation energies of the resulting ions.7 Furthermore, such phenomena may generate in aqueous solution compounds with reactivities and catalytic properties very different from those of the precursor complexes in organic solvents8 and possibly also more suitable for green catalytic technologies.9 This type of chemistry is described in the following for the new cationic complex [RuCl(NCMe)4(PiPr3)]BF4 (1), a precursor of a variety of water-soluble complexes that do not contain any solubilizing phosphine but contain the hydrophobic PiPr3.

Results and Discussion The complex [RuCl(NCMe)4(PiPr3)]BF4 (1) has been prepared in a one-pot process starting from the conventional ruthenium precursor [RuCl2(cod)]n (cod ) 1,5-cyclooctadiene), by reaction with 1 equiv of the phosphonium salt [HPiPr3]BF4 in refluxing acetonitrile under a dihydrogen atmosphere (eq 1).10 The compound has been isolated as a pale yellow solid in 65% yield. A compound with a related cation, [RuCl(NCMe)4(PPh3)][Ru2Cl2(O2CC6H4-p-OMe)4], has been reported to result from the reaction of the polymeric compound [Ru2Cl(O2CC6H4-pOMe)4]n with PPh3 and acetonitrile, although it is formed in very poor yield.11 Figure 1 displays the structure of the cation of 1 determined by X-ray diffraction. The symmetry of the structure is compatible with the simple 13C{1H} and 1H NMR spectra obtained from the solutions of 1 in CDCl3. The Ru-N distances corresponding to the four equatorial acetonitriles are similar to those in other Ru(II) complexes with mutually trans acetoni(7) Helm, L.; Merbach, A. E. Chem. ReV. 2005, 105, 1923–1959. (8) For examples, see: (a) Ohnishi, Y.; Nakao, Y.; Sato, H.; Sakaki, S. Organometallics 2006, 25, 3352–3363. (b) Kova´cs, G.; Ujaque, G.; Lledo´s, A.; Joo´, F. Eur. J. Inorg. Chem. 2007, 287, 9–2889. (c) Joubert, J.; Delbecq, F. Organometallics 2006, 25, 854–861. (d) Papp, G.; Horva´th, H.; Katho´, ´ .; Joo´, F. HelV. Chim. Acta 2005, 88, 566–573. A (9) Sheldon, R. A.; Arends, I.; Hanefeld, U. Green Chemistry and Catalysis; Wiley-VCH: Weinheim, 2007. (10) The same synthetic procedure has allowed us to prepare closely related iridium complexes: Sola, E.; Navarro, J.; Lo´pez, J. A.; Lahoz, F. J.; Oro, L. A.; Werner, H. Organometallics 1999, 18, 3534–3546. (11) Das, B. K.; Chakravarty, A. R. Inorg. Chem. 1992, 31, 1395–1400.

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Figure 1. Molecular structure of the cation of 1. Selected bond distances (Å) and angles (deg): Ru-Cl 2.4713(8), Ru-P 2.3253(8), Ru-N(1) 2.011(2), Ru-N(2) 2.019(2), Ru-N(3) 2.025(2), Ru-N(4) 2.026(2);P-Ru-Cl179.67(3),N(1)-Ru-N(3)173.11(9),P-Ru-N(1) 94.84(7).

triles12 and clearly shorter than those typical in ruthenium compounds with labile acetonitrile ligands (2.1 Å or longer).13 In agreement with this, the substitution of these acetonitriles has not been observed even in the presence of an excess of good ligands such as phosphines. On the contrary, substitution of the chloride ligand of 1 to form dicationic complexes has been found to be an easy process (eq 1). The quantitative chloride replacement by triisopropylphosphine (2), trimethylphosphite (3), or pyrazol (4) requires just 1 equiv of these reactants, whereas weaker ligands such as methanol (5) or water (6) must be present in large excess. In fact, in the case of methanol, quantitative formation of the substitution product requires the removal of chloride with a silver salt since, even in methanol-d4 solution, the equilibrium still contains 50% of compound 1. Due to this, the methanol complex 5 has been isolated only as the bis-tretrafluoroborate salt, [Ru(MeOH)(NCMe)4(PiPr3)](BF4)2, denoted as 5-BF4. In the case of water as solvent, the aquation of the chloride ligand to form [Ru(H2O)(NCMe)4(PiPr3)]2+ (6) is essentially (12) For example: (a) Ryabov, A. D.; Le Lagadec, R.; Estevez, H.; Toscano, R. A.; Hernandez, S.; Alexandrova, L.; Kurova, V. S.; Fischer, A.; Sirlin, C.; Pfeffer, M. Inorg. Chem. 2005, 44, 1626–1634. (b) Widegren, J. A.; Weiner, H.; Miller, S. M.; Finke, R. G. J. Organomet. Chem. 2000, 610, 112–117. (c) Appelbaum, L.; Heinrichs, C.; Demtschuk, J.; Michman, M.; Oron, M.; Scha¨fer, H. J.; Schumann, H. J. Organomet. Chem. 1999, 592, 240–250. (d) Katayama, H.; Ozawa, F. Organometallics 1998, 17, 5190–5196. (13) Allen, F. H. The Cambridge Structural Database: a quarter of a million crystal structures and rising. Acta Crystallogr. 2002, B58, 380– 388.

Figure 2. Molecular structures of the cations of 2-BF4 (above) and 6-BF4 (below). Selected bond distances (Å) and angles (deg): 2-BF4: “A-labeled” atoms are generated by the -x + 1, -y, -z + 1 symmetry transformation; Ru-P 2.4440(9), Ru-N(1) 2.019(3), Ru-N(2) 2.013(3); P-Ru-P(A) 180.00(3), P-Ru-N(1) 90.79(8), N(1)-Ru-N(2) 87.74(11). 6-BF4: Ru-O 2.217(3), Ru-P 2.3028(11), Ru-N(1) 2.003(3), Ru-N(2) 2.012(4), Ru-N(3) 2.017(3), Ru-N(4) 2.013(3); P-Ru-O 178.76(11), N(1)-Ru-N(3) 167.96(13), O-Ru-N(1) 83.64(13).

complete (by NMR). The equilibrium constant for chloride ligand dissociation (Kd ) [6][Cl-]/[1]) has been evaluated in aqueous solutions with excess chloride (ca. 25 equiv). Around room temperature, the exchange between 1 and 6 is slow on the NMR time scale, so that the 31P NMR resonance corresponding to each complex can be integrated separately. The value obtained for Kd at 298 K, 2.0 M, is 20 times higher than that found for the related cationic complex [RuHCl(CO)(mtppms)3]BF4 under the same conditions (9.8 × 10-2 M at 298 K, mtppms ) m-diphenylphosphinobenzenesulfonic acid, Na salt).8d Figure 2 shows the structures of the PiPr3 derivative 2 and the aquo-complex 6. In both cases, the diffraction experiment has been carried out on bis-tetrafluoroborate salts, which seem to crystallize easier and better. The equatorial plane of both octahedra is very similar and almost equal to that of the precursor complex (Figure 1). The only noticeable difference among the three structures is in the Ru-P distance, which, as expected, increases by increasing the σ-donor capability of the

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[Ru(CO)3(H2O)3]2+ (pKa ) -0.14 at 262 K),17 [Ru(tpa)(H2O)2]2+ (pKa ) 2.1, tpa ) tris(2-pyridylmethyl)amine),18 and [Ru(η6-benzene)(en)(H2O)]2+ (pKa ) 7.7).16 Since the acidity of coordinated water depends on the metal ion and the other ligands in the coordination sphere, the unusually high pKa value of species 6 should be attributed to the high basicity of the alkylic phosphine, an unusual ligand in aqueous chemistry.

Figure 3. 31P NMR spectroscopic titration of the equilibrium between 6 and 7: [6-BF4]0 ) 0.03 M, T ) 298 K. pH* is the pH meter reading in D2O.

trans ligand,14 irrespective of the cation charge. A complex closely related to 6, with the NHC ligand IMes instead of PiPr3, has been reported to result from degradation of a secondgeneration Grubbs catalyst, in acetonitrile/water as solvent.15 In this latter compound, the Ru-OH2 distance is slightly shorter than in 6: 2.199(4) vs 2.217(3) Å. In aqueous solution, the aquo complex 6 behaves as an acid, in equilibrium with the conjugate base [Ru(OH)(NCMe)4(PiPr3)]+ (7) (eq 2). This new species has been isolated as a tetrafluoroborate salt after treatment of 6 with 1 equiv of aqueous KOH in dichloromethane. The IR spectrum of 7 in KBr displays a characteristic ν(O-H) stretching mode at 3365 cm-1, while the 1H NMR resonance attributable to the OH proton appears in CD2Cl2 at δ -1.11, as a doublet with a JHP coupling constant of 1.5 Hz. As in all previous compounds, the NMR spectra also indicate four equivalent acetonitrile ligands, confirming that 7 retains the structure of its dicationic precursor 6.

Consistently with the latter conclusion, the equilibrium between 6 and 7 is fast on the NMR time scale at room temperature, giving rise to exchange-averaged NMR resonances that shift as the equilibrium position changes. The chemical shift of the 31P NMR resonance in D2O, which changes about 11 ppm on going from 6 to 7, has been used to evaluate the equilibrium position at different pH and determine the acid dissociation constant of 6. As can be seen in Figure 3, the cation [Ru(H2O)(NCMe)4(PiPr3)]2+ (6) is a weak acid showing appreciable deprotonation only above pH 9. Analysis of the δ versus pH data results in a value for the pKaH2O of 10.5 at 298 K. The value is significantly higher than those common for related aquo Ru(II) dications, including those investigated as anticancer agents, for which a high pKa constitutes an advantage.16 Some orientative examples are the cations (14) Coe, B. J.; Glenwright, S. J. Coord. Chem. ReV. 2000, 203, 5–80. (15) Kim, M.; Eum, M.-S.; Jin, M. Y.; Jun, K.-W.; Lee, C. W.; Kuen, K. A.; Kim, C. H.; Chin, C. S. J. Organomet. Chem. 2004, 689, 3535– 3540. (16) Wang, F.; Chen, H.; Parsons, S.; Oswald, I. D. H.; Davidson, J. E.; Sadler, P. J. Chem.-Eur. J. 2003, 9, 5810–5820.

The hydroxo complex 7 is stable in basic aqueous solution at room temperature, but it has been observed to slowly evolve in dichloromethane as solvent. The initial product of this evolution, an isomeric amidate complex [Ru{NH(CO)Me}(NCMe)3(PiPr3)]BF4 (8), could be characterized by NMR spectroscopy in CD2Cl2. The 1H spectrum of the compound shows the signals expected for an acetamido ligandsa NH broad signal at δ 4.24 and singlet at δ 1.97 for the methyl groupswhile the 13C{1H} spectrum shows a singlet at a chemical shift characteristic of a carbonyl function, δ 182.93. The spectra, however, are less explicit for the rest of the structure of 8, which should be considered with caution. At room temperature, the NMR signals suggest a Cs structure in which the symmetry plane contains the phosphorus atom and relates two acetonitrile ligands. The remaining acetonitrile produces broad signals in both the 13C{1H} and 1H NMR spectra. Upon cooling of the sample to 233 K, these latter signals progressively narrow to eventually allow for the observation of a 13C{1H} doublet at δ 119.39 with a JCP coupling constant of 15.1 Hz, attributable to an acetonitrile quaternary carbon trans to phosphorus. In turn, the signals corresponding to the other acetonitriles progressively broaden, suggesting that they could decoalesce at lower temperature. Nevertheless, a general broadening of the spectra below 230 K, probably related to the slow motion of the phosphine substituents, hid this proposed decoalescence. In light of the spectroscopic information available, the most likely structure for 8 is that of eq 3, in which dissociation of the acetonitrile trans to phosphine seems to trigger the facile fluxional rearrangement of the resulting five-coordinate moiety at room temperature.

Amidate complexes such as 8 have been often postulated as intermediates in nitrile hydrations,4,19 although only in a few instances have such intermediates been detected and character-

(17) Meier, U. C.; Scopelliti, R.; Solari, E.; Merbach, A. E. Inorg. Chem. 2000, 39, 3816–3822. (18) Hirai, Y.; Kojima, T.; Mizutani, Y.; Shiota, Y.; Yoshizawa, K.; Fukuzumi, S. Angew. Chem., Int. Ed. 2008, 47, 5772–5776. (19) (a) Ahmad, T. J.; Zakharov, L. N.; Tyler, D. R. Organometallics 2007, 26, 5179–5187. (b) Crestani, M. G.; Are´valo, A.; Garcı´a, J. J. AdV. Synth. Catal. 2006, 348, 732–742. (c) Breno, K. L.; Pluth, M. D.; Tyler, D. R. Organometallics 2003, 22, 1203–1211.

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ized.20 Among the various different mechanistic proposals to explain their formation, the intramolecular nucleophilic attack of hydroxide onto a cis nitrile ligand seems the alternative that better fits the characteristics of the reaction leading to 8. Also, it is conceivable that such nucleophilic attack could be relatively disfavored in aqueous solution due to the stabilization of the coordinated OH- by hydrogen bonding to surrounding water.21 Although 8 could not be isolated due to its limited stability, it could be reacted in the NMR tube with ca. 1 equiv of a mixture acetonitrile/water, to regenerate 7 and produce acetamide (NMR and GC-MS). In agreement with the cycle of stoichiometric reactions of eq 3, the aquo complex 6-BF4 has been found to catalyze the selective hydration of acetonitrile to acetamide in aqueous solutions at basic pH. Working at pH 10.5 and 353 K, and using a NCMe/H2O/Ru ratio 10 000/10 000/1, the initial turnover frequencies (TOF) reach values of about 50 h-1, an activity that compares well to that reported for other transition metal catalysts.4,19c,22 No direct (uncatalyzed) hydration of acetonitrile has been observed under these working conditions, and hydrolysis products other than acetamide have not been detected by GC. The only species detectable by 31P{1H} NMR in concentrated samples mimicking the catalytic solutions (acetonitrile-d3:D2O 1:1 at 353 K) are those of the equilibrium in eq 2, either in the active reactions at basic pH, where 7 is the major species, or in inactive acid samples, where the equilibrium is totally shifted to 6. In summary, we have prepared and characterized the complex [RuCl(NCMe)4(PiPr3)]BF4, which due to its labile chloride ligand constitutes a convenient precursor for the synthesis of water-soluble complexes containing the PiPr3 ligand. The high basicity of this phosphine, very unusual in aqueous chemistry, seems to favor chloride ligand dissociation (Kd ) 2.0 M) and diminish the acidity of the aquation product [Ru(H2O)(NCMe)4(PiPr3)]2+ (pKa ) 10.5), thus conferring relatively unusual properties to these compounds. The conjugate base of this aquation product, [Ru(OH)(NCMe)4(PiPr3)]+, can extensively form only at basic pH, but seems to play a key role in the catalytic hydration of acetonitrile to acetamide, through its isomerization into an amidate complex.

Experimental Section Equipment. C, H, N analyses were carried out in a Perkin-Elmer 2400 CHNS/O analyzer. MS data were recorded on a VG Autospec double-focusing mass spectrometer operating in the positive mode; ions were produced with the Cs+ gun at ca. 30 kV, and 3-nitrobenzyl alcohol (NBA) was used as the matrix. Infrared spectra were recorded in KBr using a FT-IR Perkin-Elmer Spectrum One spectrometer. NMR spectra were recorded on Bruker Avance 400 or 300 MHz spectrometers. 1H (400.13 or 300.13 MHz) and 13C (100.6 or 75.5 MHz) NMR chemical shifts were measured relative to partially deuterated solvent peaks, but are reported in ppm relative (20) (a) Leung, Ch. W.; Zheng, W.; Wang, D.; Ng, S. M.; Yeung, Ch. H.; Zhou, Z.; Lin, Z.; Lau, Ch. P. Organometallics 2007, 26, 1924–1933. (b) Hetterscheid, D. G. H.; Kaiser, J.; Reijerse, E.; Peters, T. P. J.; Thewissen, S.; Block, A. N. J.; Smits, J. M. M.; de Gelder, R.; Bruin, B. J. Am. Chem. Soc. 2005, 127, 1895–1905. (c) Yi, Ch. S.; He, Z.; Guzei, I. A. Organometallics 2001, 20, 3641–3643. (d) Tellers, D. M.; Ritter, J. C. M.; Bergman, R. G. Inorg. Chem. 1999, 38, 4810–4818. (e) Kim, J. H.; Britten, J.; Chin, J. J. Am. Chem. Soc. 1993, 115, 3618–3622. (21) (a) Roesky, H. W.; Singh, S.; Yussuf, K. K. M.; Maguire, J. A.; Hosmane, R. S. Chem. ReV. 2006, 106, 3813–3843. (b) Burn, M. J.; Fickes, M. G.; Hartwig, J. F.; Hollander, F. J.; Bergman, R. G. J. Am. Chem. Soc. 1993, 115, 5875–5876. (c) Zinn, P. J.; Sorell, T. N.; Powell, D. R.; Day, V. W.; Borovik, A. S. Inorg. Chem. 2007, 46, 10120–10132. (22) Cadierno, V.; Francos, J.; Gimeno, J. Chem.-Eur. J. 2008, 14, 6601–6605.

Martı´n et al. to tetramethylsilane. 31P (162.0 or 121.5 MHz) chemical shifts were measured relative to H3PO4 (85%). Coupling constants, J, are given in hertz. Generally, spectral assignments were achieved by 1H COSY, 13C DEPT, and 1H/13C-HSQC experiments. X-ray data were collected at 100.0(2) K on a Bruker SMART APEX CCD diffractometer with graphite-monochromated Mo KR radiation (λ ) 0.71073 Å) using ω scans (0.3°). Data were collected over the complete sphere by a combination of four sets and corrected for absorption using a multiscan method applied with the SADABS program.23 The structures were solved by the Patterson method. Refinement by full-matrix least-squares on F2 using SHELXL9724 was similar for all complexes including isotropic and subsequently anisotropic displacement paramenters for all non-hydrogen nondisordered atoms. Synthesis. All manipulations were carried out under argon by standard Schlenk techniques. Solvents were purified by known methods and distilled under argon before use. Complex [RuCl2(cod)]n was prepared as previously reported.25 Synthesis of [RuCl(NCMe)4(PiPr3)](BF4) (1). [HPiPr3](BF4) (884.6 mg, 3.57 mmol) was added to a suspension of [RuCl2(cod)]n (1.00 g, 3.57 mmol for n ) 1) in 40 mL of acetonitrile, and the mixture was refluxed under dihydrogen (P ) 1 bar) for 40 h. The resulting yellow solution was filtered through Celite, concentrated under vacuum to ca. 0.5 mL, cooled in ice, and treated with diethyl ether to give a pale yellow solid. The solid was separated by decantation, washed with diethyl ether, and dried in vacuo: yield 1.27 g (65%). Anal. Calcd for C17H33BClF4N4PRu: C, 37.28; H, 6.07; N, 10.23. Found: C, 36.79; H, 6.29; N, 10.01. MS (FAB+, m/z (%)): 461 (50) [M+], 420 (38) [M+ - NCMe] 379 (100) [M+ - 2NCMe]. IR (KBr, cm-1): 2285 ν(NtC), 1060 ν(BF4). 1H NMR (CDCl3, 293 K): δ 1.22 (dd, JHP ) 13.2, JHH ) 6.9, 18H, PCHCH3), 2.41 (m, 3H, PCHCH3), 2.43 (s, 12H, NCCH3). 31P{1H} NMR (CDCl3, 293 K): δ 59.77 (s). 13C{1H} NMR (CDCl3, 293 K): δ 4.57 (s, NCCH3), 19.19 (s, PCHCH3), 25.33 (d, JCP ) 22.4, PCHCH3), 125.20 (s, NCCH3). Crystals suitable for the X-ray diffraction study were obtained by slow diffusion of diethyl ether into a dichloromethane solution of the complex at 253 K. Synthesis of [Ru(NCMe)4(PiPr3)2](BF4)(Cl) (2). A solution of 1 (90.5 mg, 0.17 mmol) in dichloromethane (5 mL) was treated with trisisopropylphosphine (52 µL, 0.28 mmol) and allowed to react at room temperature for 4 h. The resulting solution was evaporated to dryness, and the residue was cooled to 213 K and washed with diethyl ether to afford a pale yellow solid, which was separated by decantation and dried in vacuo: yield 69.7 mg (60%). Anal. Calcd for C26H54BClF4N4P2Ru: C, 44.11; H, 7.69; N, 7.91. Found: C, 44.31; H, 7.52; N, 7.70. MS (FAB+, m/z (%)): 586 (35) [M+], 545 (50) [M+ - NCMe] 504 (100) [M+ - 2NCMe]. IR (KBr, cm-1): 2286 ν(NtC), 1036 ν(BF4). 1H NMR (CD2Cl2, 293 K): δ 1.39 (dvt, N ) 13.5, JHH ) 6.6, 18H, PCHCH3), 2.54 (s, 12H, NCCH3), 2.56 (m, 3H, PCHCH3). 31P{1H} NMR (CD2Cl2, 293 K): δ 27.09 (s). 13C{1H} NMR (CD2Cl2, 293 K): δ 4.87 (s, NCCH3), 19.42 (s, PCHCH3), 24.13 (vt, N ) 18.9, PCHCH3), 130.99 (s, NCCH3). Synthesis of [Ru(NCMe)4(PiPr3)2](BF4)2 (2-BF4). A solution of 6-BF4 (vide infra, 95.0 mg, 0.15 mmol) in 20 mL of dichloromethane was treated with trisisopropylphosphine (47 µL, 0.25 mmol), and the resulting mixture was stirred under argon for 30 min. The mixture was evaporated to dryness, and the product was washed with 5 × 3 mL of diethyl ether to afford a white solid: yield 85.4 mg (75%). Anal. Calcd for C26H54B2F8N4P2Ru: C, 41.12; H, 7.17; N, 7.38. Found: C, 41.32; H, 7.00; N, 7.17. Crystals for (23) Blessing, R. H. Acta Crystallogr. 1995, A51, 33–38. SADABS: Area-detector absorption correction; Bruker-AXS, Madison, WI, 1996. (24) SHELXTL Package v. 6.10; Bruker-AXS: Madison, WI, 2000. Sheldrick, G. M. SHELXS-86 and SHELXL-97; University of Go¨ttingen: Go¨ttingen, Germany, 1997. (25) Albers, M. O.; Ashworts, T.; Oosthuizen, H. E.; Singleton, E. Inorg. Synth. 1989, 26, 69.

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Table 1. Summary of Crystallographic Data for 1, 2-BF4, and 6-BF4 1 formula description, color M cryst size [mm3] cryst syst space group a [Å] b [Å] c [Å] β [deg] V [Å3] Z Fcalcd [g cm-3] µ [mm-1] 2θ range [deg] index ranges reflns collected indep reflns obsd data [I g 2σ(I)] refinement method absorption corr data/restraints/params final R indices [R] goodness of fit on F2 largest diff peak [e Å3]

C17H33BClF4N4PRu irregular block, colorless 547.77 0.24 × 0.16 × 0.12 monoclinic P2(1)/c (No. 14) 14.1734 (11) 11.8002 (9) 16.4097 (13) 113.9240 (10) 2508.7 (3) 4 1.450 0.835 3.1 e 2θ e 57.8 -19 e h e 18 -15 e k e 15 -21 e l e 22 28 249 6185 [Rint ) 0.0661] 3858 6185/0/272 R1 ) 0.035, wR2 ) 0.056 0.726 0.725

the X-ray diffraction experiment were obtained by slow evaporation of chloroform solutions at room temperature. Synthesis of [Ru(NCMe)4{P(OMe)3}(PiPr3)](BF4)(Cl) (3). The compound was prepared as described for 2, using 1 (90.5 mg, 0.17 mmol) and trimethylphosphite (32 µL, 0.28 mmol): yield 57.1 mg (50%). Anal. Calcd for C20H42BClF4N4O3P2Ru: C, 35.76; H, 6.30; N, 8.34. Found: C, 36.16; H, 6.29; N, 8.45. MS (FAB+, m/z (%)): 550 (10) [M+]. IR (KBr, cm-1): 2291 ν(NtC), 1034 ν(BF4). 1H NMR (acetone-d6, 293 K): δ 1.42 (dd, JHP ) 13.0, JHH ) 7.2, 18H, PCHCH3), 2.66 (s, 12H, NCCH3), 2.71 (m, 3H, PCHCH3), 3.99 (d, JHP ) 10.7, 9H, POCH3). 31P{1H} NMR (acetone-d6, 293 K): δ 28.55 (d, JPP ) 455.0, PiPr3), 120.53 (d, JPP ) 455.0, P(OMe)3). 13 C{1H} NMR (acetone-d6, 293 K): δ 2.99 (s, NCCH3), 18.69 (s, PCHCH3), 23.53 (dd, JCP ) 19.9, JCP′ ) 3.5, PCHCH3), 53.04 (d, JCP ) 6.9, POCH3), 129.57 (s, NCCH3). Synthesis of [Ru(NCMe)4{P(OMe)3}(PiPr3)](BF4)2 (3-BF4). Trimethylphosphite (15 µL, 0.18 mmol) was slowly added at 273 K to a solution of 6-BF4 (vide infra, 90.0 mg, 0.14 mmol) in 10 mL of dichloromethane, and the resulting mixture was stirred under argon for 30 min. The solution was evaporated to dryness under vacuum, and the residue was washed with diethyl ether to afford a white solid: yield 68.8 mg (68%). Anal. Calcd for C20H42B2F8N4O3P2Ru: C, 33.22; H, 5.85; N, 7.75. Found. C, 33.26; H, 5.41; N, 7.92. Synthesis of [Ru(Hpz)(NCMe)4(PiPr3)](BF4)(Cl) (4). The compound was prepared as detailed for 2, using 1 (90.5 mg, 0.17 mmol) and pyrazole (18.1 mg, 0.27 mmol): yield 73.3 mg (70%). IR (KBr, cm-1): 3418 ν(NH), 2289 ν(NtC), 1050 ν(BF4). Anal. Calcd for C20H37BClF4N6PRu: C, 39.00; H, 6.06; N, 13.65. Found: C, 38.92; H, 6.30; N, 13.55. MS (FAB+, m/z (%)): 493 (36) [M+ - H], 452 (58) [M+ - H - NCMe] 411 (100) [M+ - H 2NCMe]. 1H NMR (CDCl3, 293 K): δ 1.29 (dd, JHP ) 13.2, JHH ) 7.0, 18H, PCHCH3), 2.39 (m, 3H, PCHCH3), 2.55 (s, 12H, NCCH3), 6.49, 7.90, 8.10 (all br, 1H each, CH), 14.18 (br, 1H, NH). 31P{1H} NMR (CDCl3, 293 K): δ 53.78. 13C{1H} NMR (CDCl3, 293 K): δ 4.95 (s, NCCH3), 19.21 (d, JCP ) 6.0, PCHCH3), 24.87 (d, JCP ) 22.0, PCHCH3), 106.70 (d, JCP ) 2.3, CH), 127.23 (s, NCCH3), 132.1 (d, JCP ) 1.9, CH), 141.87 (s, CH). Synthesis of [Ru(Hpz)(NCMe)4(PiPr3)](BF4)2 (4-BF4). The compound was prepared as detailed for 2-BF4, using 6-BF4 (vide infra, 50.0 mg, 0.08 mmol) and pyrazole (5.4 mg, 0.08 mmol):

2-BF4 C26H54B2F8N4P2Ru · 2CHCl3 irregular block, colorless 997.74 0.16 × 0.08 × 0.06 monoclinic P2(1)/n (No. 14) 10.9787 (9) 17.9817 (14) 11.5691 (9) 106.9210 (10) 2185.0 (3) 2 1.517 0.859 4.3 e 2θ e 57.5 -14 e h e 14 -23 e k e 23 -15 e l e 15 20 201 5285 [Rint ) 0.0730] 3521 full matrix least-squares on F2 multiscan (SADABS) 5285/0/240 R1 ) 0.0474, wR2 ) 0.0718 0.866 0.936

6-BF4 C17H35B2F8N4OPRu prism, colorless 617.15 0.14 × 0.10 × 0.08 monoclinic P2(1)/n (No. 14) 9.7534 (5) 15.2583 (8) 18.3284 (10) 95.9070 (10) 2713.2 (2) 4 1.511 0.708 3.5 e 2θ e 57.8 -13 e h e 13 -20 e k e 20 -23 e l e 24 31 427 6699 [Rint ) 0.0739] 4076 6699/152/453 R1 ) 0.0497, wR2 ) 0.0934 0.888 0.980

yield 43.8 mg (82%). Anal. Calcd for C20H37B2F8N6PRu: C, 36.00; H, 5.99; N, 12.60. Found: C, 35.91; H, 5.31; N, 12.90. [Ru(CD3OD)(NCMe)4(PiPr3)](BF4)(Cl) (5). The NMR spectra of compound 1 (10.0 mg, 0.02 mmol) in methanol-d4 (0.5 mL) obtained at 293 K indicated the presence of a ca. 1:1 mixture of compounds 1 and 5. The signals corresponding to 5 were assigned by comparison with those of 5-BF4. Data for 5: 1H NMR (methanold4, 293 K): δ 1.27 (dd, JHP ) 13.7, JHH ) 7.1, 18H, PCHCH3), 2.35 (m, 3H, PCHCH3), 2.54 (s, 12H, NCCH3). 31P{1H} NMR (methanol-d4, 293 K): δ 69.80 (s). Synthesis of [Ru(MeOH)(NCMe)4(PiPr3)](BF4)2 (5-BF4). A solution of 1 (250.0 mg, 0.45 mmol) in 20 mL of methanol was treated with AgBF4 (89.0 mg, 0.45 mmol) and stirred in the dark at room temperature for 1.5 h. The resulting suspension was filtered through Celite and concentrated in vacuo. The residue was cooled in liquid nitrogen, and diethyl ether was added to precipitate a solid. The solvent was removed by decantation, and the residue was washed with 4 × 5 mL of diethyl ether to afford a pale yellow solid: yield 232.6 mg (81%). IR (KBr, cm-1): 3420 ν(OH), 2287 ν(NtC), 1049 ν(BF4). Anal. Calcd for C18H37B2F8N4OPRu: C, 34.25; H, 5.91; N, 8.88. Found: C, 33.89; H, 5.75; N, 9.04. 1H NMR (CD2Cl2, 293 K): δ 1.28 (dd, JHP ) 13.8, JHH ) 7.2, 18H, PCHCH3), 2.36 (m, 3H, PCHCH3), 2.55 (s, 12H, NCCH3), 3.70 (d, JHH ) 4.2, 3H, CH3OH), 4.93 (q, JHH ) 4.2, 1H, CH3OH). 31 P{1H} NMR (CD2Cl2, 293 K): δ 70.25 (s). 13C{1H} NMR (CD2Cl2, 293 K): δ 4.03 (s, NCCH3), 18.92 (s, PCHCH3), 25.63 (d, JCP ) 25.3, PCHCH3), 52.72 (s, CH3OH), 127.32 (s, NCCH3). [Ru(D2O)(NCMe)4(PiPr3)](BF4)(Cl) (6). The spectra of compound 1 in D2O obtained at 293 K indicated the quantitative formation of a new compound, the data of which agree with those obtained from a sample of solid 6-BF4 (vide infra). Data for 6: 1H NMR (D2O, 293 K): δ 1.20 (dd, JHP ) 13.4, JHH ) 7.1, 18H, PCHCH3), 2.28 (m, 3H, PCHCH3), 2.48 (s, 12H, NCCH3). 31P{1H} NMR (D2O, 293 K): δ 69.70 (s). Synthesis of [Ru(H2O)(NCMe)4(PiPr3)](BF4)2 (6-BF4). The complex was prepared as described for 5-BF4 in a mixture of acetone (20 mL) and water (0.5 mL). Pale yellow solid: yield 233.1 mg (83%). IR (KBr, cm-1): 3434 ν(OH), 2284 ν(NtC), 1059 ν(BF4). Anal. Calcd for C17H35B2F8N4OPRu: C, 33.09; H, 5.72; N, 9.08. Found: C, 32.84; H, 5.67; N, 9.09. 1H NMR (CDCl3, 293 K): δ 1.21 (dd, JHP ) 13.8, JHH ) 7.5, 18H, PCHCH3), 2.29 (m, 3H,

566 Organometallics, Vol. 28, No. 2, 2009 PCHCH3), 2.49 (s, 12H, NCCH3), 5.11 (br, 2H, H2O). 31P{1H} NMR (CDCl3, 293 K): δ 72.20 (s). 13C{1H} NMR (CDCl3, 293 K): δ 3.67 (s, NCCH3), 18.81 (s, PCHCH3), 25.34 (d, JCP ) 24.8, PCHCH3), 127.05 (s, NCCH3). The crystals for theX-ray diffraction experiment were obtained from dichloromethane solutions layered with diethyl ether. Synthesis of [Ru(OH)(NCMe)4(PiPr3)](BF4) (7). A solution of 6-BF4 (101.4 mg, 0.16 mmol) in 10 mL of dichloromethane at 258 K was treated with KOH (31 µL, 0.18 mmol; 5.9 N in H2O) and stirred for 20 min. The resulting suspension was filtered through Celite and evaporated to dryness. The residue was dissolved in 5 mL of dichloromethane at 258 K, filtered again through Celite, and concentrated to ca. 0.5 mL. Addition of diethyl ether at 233 K caused the precipitation of a white solid, which was washed with diethyl ether and dried in vacuo: yield 33.8 mg (63%). IR (KBr, cm-1): 3365 ν(OH), 2284 ν(NtC), 1059 ν(BF4). Anal. Calcd for C17H34BF4N4OPRu: C, 38.57; H, 6.47; N, 10.59. Found: C, 38.13; H, 6.14; N, 10.48. 1H NMR (CD2Cl2, 233 K): δ -1.11 (d, JHP ) 1.5, 1H, OH), 1.27 (dd, JHP ) 12.7, JHH ) 7.1, 18H, PCHCH3), 2.37 (br m, 3H, PCHCH3), 2.56 (s, 12H, NCCH3). 31P{1H} NMR (CD2Cl2, 233 K): δ 55.30 (s). 13C{1H} NMR (CD2Cl2, 233 K): δ 4.16 (s, NCCH3), 18.99 (s, PCHCH3), 25.67 (br, PCHCH3), 125.68 (s, NCCH3). [Ru{HN(CO)Me}(NCMe)3(PiPr3)](BF4) (8). A solution of 7 in CD2Cl2 was monitored by 1H and 31P{1H} NMR at 273 K. After 40 min the spectra indicated the quantitative formation of 8. 1H NMR (CD2Cl2, 233 K): δ 1.21 (br dd, JHP ) 12.4, JHH ) 7.2, 18H, PCHCH3), 1.97 (s, 3H, CH3), 2.28 (br m, 3H, PCHCH3), 2.46 (br, 6H, NCCH3), 2.49 (s, 3H, NCCH3), 4.24 (br, 1H, NH). 31P{1H} NMR (CD2Cl2, 233 K): δ 64.98 (s). 13C{1H} NMR (CD2Cl2, 233 K): δ 4.62 (br, NCCH3), 4.78 (s, NCCH3), 18.96 (br, PCHCH3), 24.90 (br, PCHCH3), 27.20 (s, CH3), 119.39 (d, JCP ) 15.1, NCCH3), 125.68 (br, NCCH3), 182.93 (s, C). pKa Determination. The NMR samples were prepared dissolving 13.0 mg of 6-BF4 in 0.5 mL of D2O. The pH’s were adjusted to the desired value using NaOH and directly measured in the NMR tube with a pH meter. The values read by the pH meter in D2O

Martı´n et al. (pH*) were transformed into pH using the relation pH ) 0.929pH* + 0.41.26 The pKaH2O, which characterizes the acid dissociation of 6 in H2O solution, was calculated using the 31P{1H} chemical shift and pH data by means of the general computational program for determining stability constants, PSEQUAD.27 Catalytic Acetonitrile Hydration. The complex 6-BF4 (6.17 mg, 0.01 mmol) was dissolved under argon in a mixture of acetonitrile (4.1 g, 5.22 mL, 100 mmol) and water (1.8 g, 100 mmol), previously deoxygenated. The pH of the resulting solution was adjusted to 10.5 by addition of aqueous KOH (22.0 µL of a 0.10 N solution). The resulting solution was transferred into a 25 mL flask provided with a magnetic stirrer and a PTFE stopcock. The flask was closed and immersed into a thermostated bath, where the reaction was stirred at 353 K. The reaction was periodically stopped and opened to take samples of ca. 1 µL, which were analyzed by GC-MS on an Agilent 6890 Series GC System provided with a 5973 Network mass selective detector. The column used was a HP-5MS (cross-linked methyl silicone gum, 30 m × 0.25 mm × 0.25 µm film thickness). Data: time (h)/(%) conversion: 2/1.1; 4/2.0; 6/3.0; 10/4.8; 20/8.0; 48/11.0; 120/15.2.

Acknowledgment. This work was supported by the Spanish MEC/FEDER (grant CTQ2006-01629/BQU and Consolider Ingenio 2010, grant INTECAT CSD2006-0003) and the Hungarian National Research and Technology Office, National Research Fund (NKTH-OTKA K 68482). The work has been carried out within a bilateral collaboration of CSIC and the Hungarian Academy of Sciences. Supporting Information Available: X-ray crystallographic file for the complexes 1, 2-BF4, and 6-BF4 in CIF format. This material is available free of charge via the Internet at http://pubs.acs.org. OM8008553 (26) Krezel, A.; Bal, W. J. Inorg. Biochem. 2004, 98, 161–166. (27) Ze´ka´ny, L.; Nagypa´l, I. In Computational Methods for the Determination of Stability Constants; Leggett, D., Ed.; Plenum: New York, 1985.