Experimental Study of Reductive Elimination of H2 ... - ACS Publications

Mar 21, 2012 - Organometallics , 2012, 31 (8), pp 2996–3001. DOI: 10.1021/om2009759 .... K.M.-C. Wong , V.K.-M. Au , V.W.-W. Yam. 2013,59-130 ...
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Experimental Study of Reductive Elimination of H2 from Rhodium Hydride Species Daisuke Inoki,†,‡ Takahiro Matsumoto,†,§ Hidetaka Nakai,†,§ and Seiji Ogo*,†,‡,§ †

Department of Chemistry and Biochemistry, Graduate School of Engineering, Kyushu University, 744 Moto-oka, Nishi-ku, Fukuoka 819-0395, Japan ‡ Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency (JST), Kawaguchi Center Building, 4-1-8 Honcho, Kawaguchi-shi, Saitama 332-0012, Japan § International Institute for Carbon-Neutral Energy Research (WPI-I2CNER), Kyushu University, 744 Moto-oka, Nishi-ku, Fukuoka 819-0395, Japan S Supporting Information *

ABSTRACT: A RhIII monohydride terpyridine complex undergoes reductive elimination of H2 in CH3CN to form a dinuclear RhII complex with a metal−metal bond. Kinetic studies have revealed that the conversion from the monohydride species to the dinuclear species with evolution of H2 obeys first-order kinetics and have determined the kinetic deuterium isotope effect value to be 2.0. We discuss the mechanism for the reductive elimination of H2 from rhodium hydride species.

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electrons into metal centers (Figure 1b).3 This is an important new direction, and we look forward to hearing of future successes with this design principle. No examples of reductive elimination of H2 from dinuclear dihydride species with a full metal−metal bond have been reported (Figure 1c).5,6 A related approach is to make use of a bimolecular species that brings the hydrido ligands together in a transient assembly (Figure 1d).6,8−10,13b Though such intermediates have been previously proposed in the reductive elimination of H2, experimental evidence has been insufficient. Here, we describe the synthesis and characterization of the low-valent RhI complex [RhI(terpy)(CH3 CN)](CF3SO3) ([1](CF 3SO3), terpy = 2,2′:6′,2″-terpyridine), the RhIII monohydride complex [RhIII(terpy)(CH3CN)2(H)](CF3SO3)2 ([2](CF3SO3)2), and the dinuclear Rh II complex [Rh II 2 (terpy) 2 (CH 3 CN) 4 ](CF3SO3)4 ([3](CF3SO3)4), which results from reductive elimination of H2 from 2 in CH3CN.

INTRODUCTION Reductive elimination of H2 from hydride species has long been an attractive subject in organometallic and inorganic chemistry.1−14 This is because H2 reductive elimination is a useful method for extracting electrons from hydrido ligands and storing them in the metal center. Typical hydride species that reductively eliminate H2 via intra- and intermolecular pathways have been reported or proposed, as shown in Figure 1. Many reports of the reductive

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Materials and Methods. All experiments were carried out under an N2 atmosphere by using standard Schlenk techniques and a glovebox. CH3CN and CD3CN were distilled over CaH2, and diethyl ether was distilled from sodium/benzophenone prior to use. H2 gas was purchased from Taiyo Toyo Sanso Co., Ltd., D2O (99.9% D) was purchased from Cambridge Isotope Laboratories, Inc., H2O was purchased from Wako Pure Chemical Industries, Ltd., and CF3SO3H was purchased from Tokyo Chemical Industry Co., Ltd.; these were used without further purification. [Rh III (terpy)(Cl) 3 ] 15 and CF3SO3D16 were prepared by the literature procedures.

Figure 1. Some of the previously reported candidates of precursors for reductive elimination of H2.

elimination from mononuclear dihydride species have been described (Figure 1a).1 It is well-known that cis coordination of hydrido ligands to the metal center facilitates reductive elimination, and most contemporary work focuses on achieving this confirmation. Recently, bis(μ-hydrido) dimetal complexes have been reported to reductively eliminate H2 and extract © 2012 American Chemical Society

EXPERIMENTAL SECTION

Received: October 13, 2011 Published: March 21, 2012 2996

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23.1, and 29.9 μmol, respectively) were 92−99% based on [2](CF3SO3)2. Kinetic Measurement of Reductive Elimination of Dihydrogen from 2 and D-labeled 2 by UV−vis Spectroscopy. Addition of CH3CN solutions of CF3SO3H (50.0 mM, 200 μL) and CF3SO3D (50.0 mM, 200 μL) into an CH3CN solution of [1](CF3SO3) (5.0 mM, 200 μL) at 25 °C under an N2 atmosphere rapidly generated 2 (2.5 mM) and D-labeled 2 (2.5 mM), respectively. The rates of the conversion from 2 and D-labeled 2 to 3 with evolution of H2 and D2, respectively, were measured by monitoring the UV−vis spectral changes (319 nm). The first-order rate constants were determined by least-squares curve fits (kH = 4.4 × 10−4 s−1 and kD = 2.2 × 10−4 s−1). The first-order rate constant under the dilute conditions (2, 0.25 mM) was determined by the same manner as described above, except dilute CH3CN solutions of CF3SO3H (5.0 mM, 200 μL) and 1 (0.50 mM, 200 μL) were used (kH = 4.2 × 10−4 s−1). X-ray Crystallographic Analysis. X-ray-quality crystals of [1]4(CF3SO3)4 and [3](CF3SO3)4 were obtained from an CH3CN solution diffused by diethyl ether. Crystallographic data for [1]4(CF3SO3)4 and [3](CF3SO3)4 have been deposited with the Cambridge Crystallographic Data Center as CCDC reference numbers 848096 and 838746, respectively. Copies of the data can be obtained free of charge on application to the CCDC, 12 Union Road, Cambridge CB2 1EZ, U.K. Measurements were made on a Rigaku/ MSC Saturn CCD diffractometer with confocal monochromated Mo Kα radiation (λ = 0.7107 Å). Data were collected and processed using the CrystalClear program (Rigaku). All calculations were performed using the teXsan crystallographic software package of Molecular Structure Corp.

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H NMR spectra were recorded on a JEOL JNM-AL300 spectrometer. The chemical shifts were referenced to tetramethylsilane (TMS, 0.00 ppm) in CD3CN. IR spectra of solid compounds in KBr disks were recorded on a Thermo Nicolet NEXUS 6700 FT-IR instrument from 400 to 4000 cm−1 using 2 cm−1 standard resolution at 25 °C. Gas chromatography (GC) analyses of H2 and D2 were conducted by Shimadzu GC-14B and GC-8A (He carrier) instruments with a MnCl2−alumina column (model: Shinwa OGO-SP) at −196 °C (liquid N2) and with a thermal conductivity detector. UV−vis spectra were recorded on a JASCO V-670 UV−visible−near-IR spectrophotometer at 25 °C (cell length 0.10 cm). Elemental analysis data were obtained by a PerkinElmer 2400II series CHNS/O analyzer. [RhI(terpy)(CH3CN)](CF3SO3) ([1](CF3SO3)). A suspension of [RhIII(terpy)(Cl)3] (22.2 mg, 50.2 μmol) and AgNO3 (27.2 mg, 160 μmol) in H2O (50 mL) was stirred at 25 °C for 12 h, and the precipitating AgCl was removed by filtration. The resulting solution was stirred under an H2 atmosphere (0.1 MPa) at 25 °C for 6 h and then evaporated to dryness. The residual deep blue solid was dissolved into an CH3CN solution (5.0 mL) of CF3SO3Na (40.0 mg, 233 μmol) to yield a deep purple solution. The resulting solution was filtered, to which was slowly added diethyl ether (20 mL) to afford deep purple crystals. The crystals were collected by filtration, washed with diethyl ether, and dried in vacuo (isolated yield: 54% based on [RhIII(terpy)(Cl)3]). 1H NMR (300 MHz, in CD3CN, referenced to TMS, 25 °C): δ 7.36−8.26 (m, 11H, terpyH). FT-IR (cm−1, KBr disk): 3074 (C− H), 2928 (C−H), 2291 (CN), 2268 (CN), 2251 (CN), 1598 (aromatic CC or CN), 1549 (aromatic CC or CN), 1456 (aromatic CC or CN), 1378, 1324, 1262 (CF3SO3), 1152, 1029 (CF3SO3), 757, 707. Anal. Calcd for [1](CF3SO3) (C18H14N4F3O3RhS): C, 41.08; H, 2.68; N, 10.65; S, 6.09. Found: C, 40.83; H, 2.38; N, 10.39; S, 6.04. [RhIII(terpy)(CH3CN)2(H)](CF3SO3)2 ([2](CF3SO3)2). Addition of CF3SO3H (50 μL, 56 μmol) to a solution of [1](CF3SO3) (6.0 mg, 12.5 μmol) in CH3CN (500 μL) resulted in formation of the hydride complex 2. The solution changed from deep purple to pale yellow (yield: 99% based on [1](CF3SO3) by 1H NMR spectroscopy). 1H NMR (300 MHz, in CD3CN, referenced to TMS, 25 °C): δ −16.97 (d, 1JRh,H = 15.8 Hz, 1H, Rh−H), 7.83 (t, 2H, 5- and 5″-H of terpyH), 8.35 (t, 2H, 4- and 4″-H of terpyH), 8.40−8.45 (m, 5H, 3-, 3′-, 4′-, 5′-, and 3″-H of terpyH), 8.78 (d, 2H, 6- and 6″-H of terpyH). [RhIII(terpy)(CH3CN)2(D)](CF3SO3)2 ([D-labeled 2](CF3SO3)2). The D-labeled complex [D-labeled 2](CF3SO3)2 was obtained in the same manner as described for the preparation of [2](CF3SO3)2, except CF3SO3D was used. [RhII2(terpy)2(CH3CN)4](CF3SO3)4 ([3](CF3SO3)4). A pale yellow solution of [2](CF3SO3)2 (12.5 μmol) in CH3CN (500 μL) was stirred for 4 h to afford a red solution, to which was slowly added diethyl ether (2 mL). The resulting solution was allowed to stand for a few days to yield red crystals of [3](CF3SO3)4, which were collected by filtration and dried in vacuo (isolated yield: 90% based on [2](CF3SO3)2). 1H NMR (300 MHz, in CD3CN, referenced to TMS, 25 °C): δ 7.75 (t, 4H, 5- and 5″-H of terpyH), 8.02−8.08 (m, 8H, 3-, 3′-, 5′-, and 3″-H of terpyH), 8.22−8.30 (m, 6H, 4-, 4′-, and 4″-H of terpyH), 8.38 (d, 4H, 6- and 6″-H of terpyH). FT-IR (cm−1, KBr disk): 3085 (C−H), 2934 (C−H), 2332 (CN), 2304 (CN), 2254 (C N), 1604 (aromatic CC), 1573 (aromatic CC or CN), 1471 (aromatic CC or CN), 1452 (aromatic CC or CN), 1259 (CF3SO3), 1163, 1031 (CF3SO3), 772. Anal. Calcd for [3](CF3SO3)4·CH3CN (C44H37N11F12O12Rh2S4): C, 35.86; H, 2.53; N, 10.45; S, 8.70. Found: C, 35.94; H, 2.54; N, 10.36; S, 8.83. Quantitative Analysis of H 2 Produced by Reductive Elimination from 2 by GC. A 3 mL vial was charged with an CH3CN solution (1.0 mL) of [2](CF3SO3)2 (10.0, 20.0, 30.0, 40.0, 50.0, and 60.0 μmol) and a stir bar under an N2 atmosphere and was capped with a septum. The resulting solution was stirred for 2 h to gradually form the dinuclear RhII complex [3](CF3SO3)4 with evolution of H2. A color change occurred from pale yellow to red. The gas present in the vial was sampled using a gastight syringe and analyzed for H2 gas by GC. The yields of H2 (4.78, 9.62, 14.7, 18.9,

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RESULTS AND DISCUSSION The low-valent RhI complex [1](CF3SO3) was prepared from the treatment of [RhIII(terpy)(Cl)3] with AgNO3, H2, and CF3SO3Na. Addition of diethyl ether to the CH3CN solution of 1 resulted in growth of the deep purple crystals suitable for Xray analysis (Figure 2). Complex 1 adopts a discrete tetramerized structure that consists of a zigzag chain of [RhI(terpy)(CH3CN)]+ units stacked in a twisted conformation. The Rh2−Rh1−Rh1* angle is 172.16(2)°. There are two different Rh···Rh distances in the chain: 3.1520(6) Å for Rh1···Rh2 and 3.0693(7) Å for Rh1···Rh1*. Both of these distances are consistent with the previously reported RhI···RhI distances for the dimer stacking (3.040(3)−3.287(2) Å).17 The terpy···terpy stacking interaction is suggested by the stacking distances, which are within favorable π−π interaction distances seen in organic molecules (3.3−3.6 Å).18 The torsion angles of N4−Rh1−Rh2−N8 and N4−Rh1−Rh1*−N4* found in [1]4(CF3SO3)4 are 51.0(1) and 180.0°, respectively. Complex 1 adopts the associated structure in solution as well as in the solid, which is confirmed by concentration-dependent UV−vis spectra of 1 (Figure 3). The associated structure of 1 reminds us to study bimolecular reductive elimination of H2 because the close intermolecular distance is favorable for a bimolecular reaction.

Oxidative addition of H+ from CF3SO3H to the low-valent RhI complex 1 in CH3CN afforded the RhIII hydride complex 2 2997

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Figure 2. ORTEP drawing of [1]4(CF3SO3)4 with ellipsoids at the 50% probability level. The counteranions (CF3SO3), solvated molecules (CH3CN), and hydrogen atoms are omitted for clarity. Selected interatomic distances (l/Å) and angles (ϕ/deg): Rh1···Rh2 = 3.1520(6), Rh1···Rh1* = 3.0693(7), Rh1−N1 = 2.019(3), Rh1−N2 = 1.911(3), Rh1−N3 = 2.024(3), Rh1−N4 = 2.025(3), Rh2−N5 = 2.025(3), Rh2−N6 = 1.908(3), Rh2−N7 = 2.036(3), Rh2−N8 = 2.008(4); Rh2−Rh1−Rh1* = 172.16(2), N1−Rh1−N2 = 80.9(1), N1−Rh1−N3 = 161.0(1), N1−Rh1−N4 = 98.9(1), N2−Rh1−N3 = 80.5(1), N2−Rh1−N4 = 176.5(1), N3−Rh1−N4 = 99.5(1), N5− Rh2−N6 = 80.1(1), N5−Rh2−N7 = 159.4(1), N5−Rh2−N8 = 97.8(1), N6−Rh2−N7 = 80.1(1), N6−Rh2−N8 = 173.6(1), N7− Rh2−N8 = 101.3(1), N4−Rh1−Rh2−N8 = 51.0(1), N4−Rh1− Rh1*−N4* = 180.0.

Figure 4. (a) 1H NMR spectrum of [2](CF3SO3)2 from the reaction of [1](CF3SO3) (12.5 μmol) with CF3SO3H (56 μmol) in CD3CN (500 μL) under an N2 atmosphere (the † symbol denotes the resonance of acetonitrile). (b) 1H NMR spectrum enlarged in the region between −16.3 and −17.6 ppm.

spectrum shows only one hydride species derived from 2 and no signal based on interaction of 2 with D-labeled 2. Second, UV−vis spectra of 2 were measured in CH3CN under an N2 atmosphere when the concentration of 2 was changed. Concentration-independent UV−vis spectra were observed. In contrast to the case for 1, no evidence of equilibrium between a discrete and associated species was obtained. Finally, a 1H NMR study was conducted under a high pressure of H2 (4 MPa) in CD3CN to prevent generation of H2 via reductive elimination (vide infra). The 1H NMR spectrum of 2 under 4 MPa of H2 is identical with that under an N2 atmosphere. According to these results, there is no direct evidence for an intermolecular interaction under these conditions. We could not isolate the hydride complex 2 because unstable 2 gradually transforms into the dinuclear RhII complex 3 with generation of H2 via reductive elimination (eq 2). In the 1H

Figure 3. Concentration-dependent UV−vis spectra of [1](CF3SO3) (0.25, 1.0, and 2.5 mM) in CH3CN under an N2 atmosphere.

(eq 1). This hydride complex was characterized by 1H NMR spectroscopy, although the position of the hydrido ligand was not determined (Figure 4). The 1H NMR spectrum of the RhIII hydride complex 2 in CD3CN exhibits a doublet peak in the metal hydride region at −16.97 ppm, which is expected from the spin−spin interaction of the hydride with the RhIII center possessing a nuclear spin of 1/2. The Rh−H coupling constant for 2 (1JRh,H = 15.8 Hz) is comparable to those for [RhIII(CN)5(H)]3− (1JRh,H = 13.1 Hz),19a [RhIII(Tp)(PPh3)(H)2] (Tp = hydrotris(1-pyrazolyl)borate, 1JRh,H = 18.9 Hz),19b and [RhIII(PP3)(H)2]+ (PP3 = P(CH2CH2PPh2)3, 1JRh,H = 14.7 Hz).19c Intermolecular interactions such as π−π stacking between the hydride complexes were investigated by three experiments on 2. First, the hydride complex 2 was mixed with the deuteride complex [RhIII(terpy)(CH3CN)2(D)]2+ (D-labeled 2) (ratio 1:1) in CD3CN under an N2 atmosphere. The 1H NMR

NMR spectrum of 3 in CD3CN, the signals were observed in the diamagnetic region. This suggests that the spins of d electrons from the two RhII centers are coupled antiferromagnetically through the metal−metal bond in solution. The structure of the dinuclear RhII complex 3 was characterized by X-ray analysis (Figure 5). X-ray-quality red 2998

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instead of CF3SO3H. The quantitative analysis showed that one molecule of H2 was generated from two molecules of the hydride complex 2 (Figure 6). These results suggest that the

Figure 6. H2 production from [2](CF3SO3)2 (10.0, 20.0, 30.0, 40.0, 50.0, and 60.0 μmol) in CH3CN (1.0 mL) determined by GC analysis.

Figure 5. ORTEP drawing of [3](CF3SO3)4 with ellipsoids at the 50% probability level. The counteranions (CF3SO3) and hydrogen atoms are omitted for clarity. Selected interatomic distances (l/Å) and angles (ϕ/deg): Rh1−Rh2 = 2.6898(3), Rh1−N1 = 2.052(2), Rh1−N2 = 1.943(2), Rh1−N3 = 2.051(2), Rh1−N4 = 2.025(2), Rh1−N5 = 2.170(2), Rh2−N6 = 2.057(2), Rh2−N7 = 1.935(2), Rh2−N8 = 2.048(2), Rh2−N9 = 2.046(2), Rh2−N10 = 2.203(2); N1−Rh1−N2 = 80.69(9), N1−Rh1−N3 = 160.73(8), N1−Rh1−N4 = 100.35(9), N1−Rh1−N5 = 90.28(8), N2−Rh1−N3 = 80.50(8), N2−Rh1−N4 = 177.43(8), N2−Rh1−N5 = 91.70(8), N3−Rh1−N4 = 98.27(8), N3− Rh1−N5 = 86.14(8), N4−Rh1−N5 = 85.96(8), N6−Rh2−N7 = 80.31(9), N6−Rh2−N8 = 160.35(8), N6−Rh2−N9 = 99.13(8), N6− Rh2−N10 = 89.39(8), N7−Rh2−N8 = 80.50(8), N7−Rh2−N9 = 179.17(8), N7−Rh2−N10 = 92.95(9), N8−Rh2−N9 = 100.01(8), N8−Rh2−N10 = 87.43(8), N9−Rh2−N10 = 86.42(8), Rh2−Rh1− N5 = 172.37(6), Rh1−Rh2−N10 = 173.85(6), N4−Rh1−Rh2−N9 = 48.47(9).

production of H2 is due to the bimolecular reductive elimination of H2. It is confirmed that the photochemistry is not involved in the production of H2 from 2; the quantitative generation of H2 from 2 was observed in the dark.22 The reaction mechanism for the reductive elimination was investigated by the following kinetic analysis. The conversion from 2 to 3 with evolution of H2 was monitored by UV−vis spectroscopy (Figure 7a,b). The absorption band at 319 nm,

crystals of [3](CF3SO3)4 were obtained from slow diffusion of diethyl ether into an CH3CN solution of [3](CF3SO3)4. The two Rh centers, each having an octahedral geometry, are linked by a metal−metal bond to form a dinuclear structure. The RhII−RhII distance found in 3 (2.6898(3) Å) is shorter than the RhI···RhI distances found in the tetramerized structure of [1]4(CF3SO3)4 (3.1520(6) and 3.0693(7) Å) and is comparable to the RhII−RhII single-bond distances found in [RhII2(CH3CN)10]4+ (2.624(1) Å)20a and [RhII2(CH3CN)8(H2O)2]4+ (2.625(1) Å).20b Thus, the dinuclear RhII complex 3 has a RhII−RhII single bond, as expected by 1H NMR spectroscopy (vide supra). The terpy···terpy stacking interaction is suggested by X-ray analysis. The stacking distance is within favorable π−π interaction distances seen in organic molecules (3.3−3.6 Å).18 The torsion angle of N4− Rh1−Rh2−N9 found in 3 (48.47(9)°) is larger than those found in [RhII2(terpy)2(CH3CN)2(PhCO2)]3+ (21.6° (average))21a and [RhII2(CH3CN)10]4+ (44.8(2)°).20a The terpy ligand in 3 is bound asymmetrically to the Rh atom. The Rh−N bond distances to the central pyridyl N atoms (Rh1−N2 and Rh2−N7) are approximately 0.1 Å shorter than those to the outer pyridyl N atoms (Rh1−N1, Rh1−N3, Rh2−N6, and Rh2−N8). This tendency is seen in 1 and the related complexes [RhII2(terpy)2(CH3CN)2(PhCO2)]3+ and [RhII2(terpy)2(Cl)2(CH3CO2)]+.21 The H2 production via reductive elimination from the hydride complex 2 was confirmed by GC analysis. The D2 production from D-labeled 2 was observed using CF3SO3D

Figure 7. (a) UV−vis spectral changes of [2](CF3SO3)2 (2.5 mM) to [3](CF3SO3)4 with evolution of H2 in CH3CN at 25 °C under an N2 atmosphere. (b) Time profile of the absorbance at 319 nm and the least-squares curve fit as first-order kinetics. (c) First-order kinetic plots for the absorbance changes at 319 nm of [2](CF3SO3)2 (2.5 mM) and [D-labeled 2](CF3SO3)2 (2.5 mM).

derived from 2, decreased as the absorption bands at 341 and 357 nm, derived from 3, increased. The reaction obeys firstorder kinetics over 5 half-lives, where the first-order rate constant kH is obtained as a slope of the linear first-order plot as shown in Figure 7c (kH = 4.4 × 10−4 s−1). The first-order dependence of the reaction is confirmed by the fact that the 2999

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first-order rate constants are nearly the same when the concentration of the starting hydride complex 2 is changed from 0.25 to 2.5 mM. The kinetic deuterium isotope effect value (kH/kD) is determined as 2.0 using CF3SO3D instead of CF3SO3H (kD = 2.2 × 10−4 s−1), which is consistent with those of the reductive elimination of dihydrogen from the other hydride species.1g,3a,d The kinetic experiments suggest that the bimolecular reductive elimination of H2 involves the ratelimiting cleavage of the Rh−H bond, followed by formation of Rh−Rh and H−H bonds to generate the dinuclear complex 3 and H2, respectively. There is a possibility that the bimolecular association is facilitated through π−π stacking interaction. With regard to the reductive elimination, Halpern has proposed three mechanisms: two-center concerted, one-center concerted, and stepwise mechanisms.13b The first step of the stepwise mechanism, that is, metal−hydride bond cleavage, is consistent with that of the proposed mechanism in this study. Unlike the case for our Rh(terpy) system, Rh(porphyrin) systems have shown reversible oxidative addition/reductive elimination of H2, where RhIII hydride species are more thermodynamically stable than RhII species.7a,9b Figure 8 summarizes a proposed mechanism of the evolution of H2 from the low-valent RhI complex 1 in CH3CN. Oxidative

ASSOCIATED CONTENT

S Supporting Information *

CIF files giving crystallographic data for 1 and 3. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*Tel: +81-92-802-2818. Fax: +81-92-802-2823. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank Professor Kiyoshi Isobe for valuable discussions. This work was supported by the World Premier International Research Center Initiative (WPI), the Global COE Program “Science for Future Molecular Systems”, and grants-in-aid 18065017 (Chemistry of Concerto Catalysis), 19205009, and 23655053 from the Ministry of Education, Culture, Sports, Science, and Technology (MEXT) of Japan and the Basic Research Programs CREST Type “Development of the Foundation for Nano-Interface Technology” from the JST of Japan.

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REFERENCES

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Figure 8. Proposed mechanism for the oxidative addition of H+ and the reductive elimination of H2 with the Rh(terpy) complexes in CH3CN.

addition of H+ from CF3SO3H to 1 yields the RhIII hydride complex 2. The monohydride complex 2 undergoes the reductive elimination of H2, which obeys first-order kinetics, to form the dinuclear RhII complex 3.

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Article

CONCLUSIONS

We have described a unique bimolecular assembly for the reductive elimination of H2. The concept of the bimolecular assembly provides organometallic and inorganic chemists with an important new paradigm for the design of catalysts that can extract electrons from H2. By opening up a new direction in catalyst design, we can look forward to enhanced possibilities in the generation of hydrogen power. 3000

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Organometallics

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