Theoretical Study of Dihydrogen Activation by a Trinuclear Ruthenium

Article pubs.acs.org/Organometallics

Theoretical Study of Dihydrogen Activation by a Trinuclear Ruthenium μ3-Imido Complex Yumiko Nakajima,*,† Shigeyoshi Sakaki,*,‡ Yoshihide Nakao,‡ and Hiroharu Suzuki§ †

Institute for Chemical Research, Kyoto University and JST-PRESTO, Uji, Kyoto 611-0011, Japan Fukui Institute for Fundamental Chemistry, Kyoto University, Nishihiraki-cho, Takano, Sakyo-ku, Kyoto 606-8103, Japan § 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: Dihydrogen activation by a triruthenium μ3imido complex, (CpRu)3(μ3-NH)(μ-H)3 (1; Cp = η5-C5H5), was theoretically investigated with the DFT method. Each of the three Ru centers can react with dihydrogen via a transition state, (CpRu)3(μ3-NH)(η2-H2)(μ-H)3 (TS1), with a moderate energy barrier. This TS1 corresponds to a transition state for the approach of a dihydrogen molecule to one of the Ru centers. After TS1, the hydrogen−hydrogen bond cleavage occurs without any other energy barrier to produce the pentahydrido intermediate, (CpRu)3(μ3-NH)(μ-H)3(H)2 (INT1), without formation of a dihydrogen complex as an intermediate. In the hydrogen−hydrogen cleavage, the dπ orbitals of three ruthenium centers overlap with the hydrogen−hydrogen σ* orbital to form the charge transfer from the ruthenium to the hydrogen−hydrogen moiety. Natural population analysis indicates that all three ruthenium centers cooperatively participate in the changes in electronic structure during this process. INT1 further undergoes a nitrogen−hydrogen bond formation, which occurs through drastic changes in the binding mode of the amide group and hydrides, to afford a μ-amido complex, (CpRu)3(μ-NH2)(μ-H)4 (2). This process proceeds with a moderate activation barrier. Natural population analysis of this step reveals that one bridging hydride approaches the imido N atom, concomitantly changing from a hydride to a proton-like hydrogen atom with a simultaneous increase in the N atomic population. Fluxional positional changes of hydrides are crucial for the facile N−H bond formation, in which the Ru3 core plays important roles.

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INTRODUCTION Dihydrogen activation on a transition-metal site is one of the key steps in catalytic reactions.1 Its mechanism has been intensively studied for the last decades based on both experimental and theoretical methods,2,3 and we nowadays have a good understanding of dihydrogen activation by mononuclear transition-metal complexes. However, mechanistic studies of dihydrogen activation by multimetallic systems, which is known to exhibit striking reactivity as a result of cooperative functions of multinuclear centers, still remain rather unexplored.4 To elucidate the mechanism, several theoretical studies have been carried out,5 in which heterolytic hydrogen−hydrogen cleavage was mainly discussed. So far, our group is investigating ruthenium polyhydrido clusters supported by ancillary Cp* (=η5-C5Me5) ligands to reveal their intrinsic reactivity toward various organic substrates.6,7 In these attempts, we found that dihydrogen activation by a μ3-(imido) complex, (Cp*Ru)3(μ3-NH)(μ-H)3 (1R), easily occurs to form a μ-amido complex, (Cp*Ru)3(μNH2)(μ-H)4 (2R) (Scheme 1).8 In the reaction, both hydrogen−hydrogen bond cleavage and nitrogen−hydrogen bond formation successively proceeded. These results suggest that heterolytic hydrogen−hydrogen bond cleavage occurs, where one hydrogen atom of the dihydrogen molecule is bound with the NH group and the other is bound with the Ru atom. © 2012 American Chemical Society

Scheme 1. Reaction of 1 with Dihydrogen

However, careful kinetic studies revealed that hydrogen− hydrogen bond cleavage proceeds via oxidative addition on the Ru3 core of 1R.8a These experimental results suggest that the hydrogen−hydrogen bond cleavage by 1R is not a simple reaction where the Ru3 core plays crucial roles. In this report, we theoretically investigated dihydrogen activation by 1R with the DFT method to shed clear light on the detailed reaction mechanism, and the electronic process of this activation, and a synergy effect of the triruthenium− polyhydride system that facilitates the bond cleavage of a dihydrogen molecule. Received: May 3, 2012 Published: July 18, 2012 5342

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Figure 1. Geometry changes in the H−H bond activation of dihydrogen by 1 and possible orientation for dihydrogen access (inset). Orange-colored hydrogen atoms, H1 and H2, originated from the dihydrogen molecule.

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RESULTS AND DISCUSSION Geometry and Energy Changes of the H−H σ-Bond Cleavage. Because the real triruthenium polyhydride system with Cp* ligands is too large, we explored here a model complex (CpRu)3(μ3-NH)(μ-H)3 (1) in which Cp* ligands are replaced by Cp (=η5-C5H5), to reduce the computational cost; the difference in energetics between the real and the model systems is not large, as mentioned in the Supporting Information, page S2. Because the diamagnetic nature was indicated in 1 and 2 by spectroscopic data, only the closed-shell singlet state was calculated here. The optimized geometry of 1 takes Cs symmetry (Figure 1), in which two Ru−Ru bonds are short (2.720 Å) and a remaining Ru−Ru bond is long (2.891 Å). These Ru−Ru bond distances are in the range of a Ru−Ru single bond found in similar triruthenium complexes with a μ3imido ligand.9

Previous experimental studies suggested that hydrogenation of 1R starts with incorporation of a dihydrogen molecule on the empty space that exists at the position opposite to the imido ligand.8c Considering this experimental result and symmetry of 1, we investigated two possible approaching paths, a and b, in the dihydrogen activation reaction; see Scheme 2. In path a, a dihydrogen molecule approaches the Ru1 atom through transition state TS1a to afford a pentahydrido intermediate INT1a without formation of a dihydrogen complex as an intermediate, as shown in Figure 1. In the structure of TS1a, the H1−H2 bond distance is 0.767 Å and the Ru1−H1 and Ru1−H2 distances are 2.215 and 2.184 Å, respectively, suggesting that a strong bonding interaction is not formed between the Ru1 and the dihydrogen molecule. When going to TS1a from 1, one bridging hydrido ligand μ-H3 changes to a terminal hydride to offer a coordinating site on the 5343

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Scheme 2. Possible Orientations for Dihydrogen Access, Paths a and b

Ru1 for the molecular dihydrogen. Hydrogen−hydrogen bond cleavage occurs on the Ru1 upon going to INT1a from TS1a, in which H1 is bound with the Ru1 as a terminal hydrido ligand, but H2 moves to the bridging position between Ru1 and Ru2. The energy barrier (Ea, including zero-point energy correction) of this process is 16.2 kcal/mol, and the reaction energy (ΔE) is −3.4 kcal/mol. In path b, a dihydrogen molecule approaches the Ru2 atom to form a pentahydrido intermediate INT1b through a transition state TS1b, which is structurally similar to TS1a; see the H1−H2 bond of 0.764 Å and the Ru2−H1 and Ru2−H2 bonds of 2.207 and 2.249 Å, respectively. As is the case in path a, one bridging hydride H5 changes to a terminal hydride when going to TS1b. Upon going to INT1b, hydrogen−hydrogen bond cleavage occurs on the Ru2 center with a moderate activation barrier Ea of 16.0 kcal/ mol and reaction energy of −3.5 kcal/mol. These results indicate that both paths a and b lead to the similar pentahydrido intermediates, INT1a and INT1b, with almost the same energy barrier and reaction energy. It is, therefore, concluded that the dihydrogen activation by 1 occurs through both paths a and b. Electronic Process of H−H σ-Bond Cleavage. The H1− H2 bond distance (0.767 and 0.764 Å) in TS1a and TS1b is not different very much from that of a free dihydrogen molecule (0.742 Å).10 Consistent with the H1−H2 bond distance, the ruthenium−hydrogen bonds (ca. 2.2 Å) are much longer than the normal ruthenium−hydrogen bond distances of molecular dihydrogen ruthenium complexes (1.5−1.8 Å).11 These geometrical features suggest that the interaction between dihydrogen and ruthenium is not strong at this stage. The H1− H2 bond is completely broken; see the H1−H2 bond distances of 1.915 and 1.870 Å in INT1a and INT1b, respectively. IRC calculation revealed that the energy monotonously decreases upon going to INT1a/b from TS1a/b (Figure 2a). On the basis of these results, it is concluded that TS1a/b corresponds to the transition state for the approach of a dihydrogen molecule to the Ru center, and a hydrogen−hydrogen bond cleavage smoothly occurs after TS1a/b without a further activation barrier. In Figure 2b, changes in bond distances are summarized along path b. Interestingly, the H1−H2 bond is a little elongated in the early stage of the reaction, though the Ru2− H1, Ru2−H2, and Ru3−H2 distances monotonously become shorter. After the Ru2−H1 and Ru2−H2 distances stop changing, the H1−H2 starts to become longer. Thus, the H1−H2 bond cleavage occurs in a considerably late stage of the reaction, when the Ru3−H2 reaches almost 2 Å; in other words, the H1−H2 bond cleavage cannot be performed only by one Ru center but can be by two Ru centers. These observations strongly indicate that the cooperative action of at least two ruthenium centers is crucial for the H−H σ-bond

Figure 2. (a) Energy changes of the reaction from 1 + H2 to INT1a/ INT1b. (b) Changes in bond distances of the Ru3(H2) core along path b.

cleavage. The similar structural changes are also observed in path a; see the Supporting Information, Figure S6. To shed clear light on the role of the Ru3 core, orbital interactions were examined along path b. Figure 3 exhibits the HOMO-6 at TS1b and a reaction stage A between TS1b and INT1b, in which the H1−H2 bond distance is elongated to

Figure 3. (a) HOMO-6 of TS1b and (b) HOMO-6 at the reaction stage A*. Insets show schematic pictures of major orbital contributions. *See Figure 2 for the reaction stage A. 5344

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1.05 Å and the Ru3−H2 distance is 2.21 Å (see Figure 2 for the reaction stage A).12 No bonding overlap between the H1−H2 σ* antibonding and Ru2 dπ orbitals is observed in the HOMO6 of TS1b, which is consistent with the little elongated H1−H2 bond in TS1b. However, such a bonding overlap is clearly observed at stage A. Interestingly, Ru1 and Ru3 dπ orbitals participate in the HOMO-6 in a bonding way. This orbital interaction shows that three ruthenium centers cooperatively participate in the dihydrogen activation, facilitating the charge transfer (CT) from the Ru3 core to the H1−H2 σ* orbital. In particular, it is noted that the dπ orbital of adjacent Ru3 extends toward the H2 atom in the same phase to participate in the bond cleavage. Through this orbital interaction, the H2 atom easily changes to a bridging hydride between Ru2 and Ru3, leading to the formation of INT1b. To obtain further information on the facile hydrogen− hydrogen bond cleavage, electron population changes are plotted against the IRC in path b (Figure 4). When going to

Through the whole reaction, both Ru2 and Ru3 atomic populations increase, because these rutheniums accept a hydrogen terminus after the hydrogen−hydrogen bond cleavage. In addition, the Ru1 atomic population slightly increases. All of these results lead to a clear conclusion that the hydrogen−hydrogen bond cleavage occurs via oxidative addition to one Ru center through cooperative participation of at least two Ru centers. The similar features, including the cooperative actions of three ruthenium centers, are also observed in orbital interactions and natural populations in path a; see the Supporting Information, Figures S9−S11. Formation of Imido Species. The next issue to be elucidated is how easily the final imido product 2 is formed from INT1a and INT1b. Here, we pursued the formation reaction of the final imido product 2 from INT1b, because INT1a is almost the same as INT1b, in which bond formation occurs between the imido N atom and either H2 or H3 atom. However, all the attempts to find a concerted one−step reaction were unsuccessful. We finally found the following stepwise process from INT1b to 2, as seen in Figure 1. In the first step, one bridging hydride H4 ligand moves further outside of the Ru3 core and finally takes a position coplanar on the Ru3 plane. Concomitantly, the H5 atom moves to the bridging position between Ru1 and Ru3 from the terminal position through transition state TS2 to afford INT2. Through this process, the dihedral angle H4−Ru3−Ru1−Ru2 considerably increases to 177.8° by 51.5°. The first step needs a moderate energy barrier of 6.8 kcal/mol. The geometry of INT2 resembles well that of TS2. Consistent with the product-like TS2, this process is endothermic. In the second step, the H4 atom approaches the NH group through transition state TS3 to afford a final product 2 including the N−H4 bond. Simultaneously, the H1 and H3 atoms move to the bridging positions between Ru2−Ru3 and Ru1−Ru3, respectively. The reaction barrier of this step is 15.5 kcal/mol. In TS3, the N−H4 bond distance is 1.352 Å and the Ru1−H4 and Ru3−H4 bond distances are slightly elongated to 1.829 Å. This N−H4 bond distance is considerably longer than the normal nitrogen−hydrogen bond (ca. 1.1 Å), suggesting that weak bonding interactions still remain between the N−H bond and two Ru centers like the agostic interaction of the C− H bond. After TS3, significantly large geometrical changes must occur to reach the final product 2. Because it is not obvious that TS3 connects INT2 and 2, we performed an IRC calculation to investigate this process carefully.15 The IRC calculation clearly shows that 2 is formed from INT2 through TS3, as shown in Figure 5a, where energy changes are presented with some important structures, B1, B2, and B3. Figure 5b summarizes changes in bond distances of the Ru3(NH2) core along the IRC from INT2 to 2. Upon going to 2 from TS3, the Ru3−N bond distance monotonously becomes longer. This is because the N atom considerably moves outside of the Ru3 core and finally becomes a bridging amido ligand between Ru1 and Ru2 atoms in 2. For instance, the N atom, which exists at the position above the center of the Ru3 core in TS3, starts to move outside of the Ru3 core, as shown in B1, B2, and B3, and finally reaches the bridging position in 2. The N−H4 bond distance becomes shorter and reaches 1.062 Å at the reaction stage B1. Upon going from INT2 to B1 through TS3, the N−H4 bond distance monotonously becomes shorter but changes little after B1,

Figure 4. Population changes in H−H bond activation of dihydrogen by 1 (path b).

TS1b from 1 + H2, the H1 and H2 atomic populations moderately decrease, indicating that the CT occurs from the σbonding orbital of the dihydrogen molecule to the Ru2. However, the Ru2 atomic population somewhat decreases. In accordance with this, the H5 atomic population slightly increases. These population changes arise from the conversion of the bridging hydride H5 to the terminal hydride on the Ru3 center. Concomitant with these changes, the Ru1 and Ru3 atomic populations slightly increase. Upon going to stage A from TS1b, the Ru2 atomic population considerably increases, whereas both H1 and H2 atomic populations further decrease. These results strongly indicate that the CT still occurs from the σ-bonding orbital of the dihydrogen molecule to the Ru2 center in this reaction stage. Such population changes are also observed in previously reported theoretical studies on the formation of σ complexes.13 It is noted that the H1 and H2 atomic populations start to moderately increase and the Ru2 atomic population moderately decreases after stage A, in which the H1−H2 bond elongation starts to occur. These results indicate that the CT from the Ru2 atom to the dihydrogen molecule is indispensable for the H1−H2 bond cleavage. This is consistent with the good overlap between the H1−H2 σ*antibonding orbital and the Ru2 dπ orbital found in stage A; see Figure 3. Upon going to INT1b from A, the CT from Ru2 dπ to both H1 and H2 becomes stronger, leading to further increases in both H1 and H2 atomic populations. The similar electron population changes are observed in the typical oxidative addition reaction.14 5345

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Figure 6. HOMO-10 of TS3. Inset shows major orbital contributions.

Figure 5. (a) Energy change of the reaction from INT3 to 2 via TS3. (b) Changes in bond distances of the Ru3(NH) core.

showing that the N−H bond formation is almost completed around the reaction stage B1. Through this process, the terminal H1 becomes a bridging hydride between Ru2 and Ru3. Interestingly, the H3 atom once becomes a terminal hydride on the Ru1 but then moves to a bridging position between the Ru1 and the Ru3, as shown by geometries B2, B3, and 2. All of these complicated geometry changes, including drastic site exchanges of hydrides, occur in one step with the monotonous energy decrease, as shown in Figure 5a. Such fluxional behavior of hydrides in the triruthenium polyhydride system is consistent with our experiments; for example, variable-temperature 1H NMR study reveals that the site exchange between two sets of hydrides in 2 smoothly occurs at RT with ΔH‡ and ΔS‡ of 12.6 kcal/mol and 3.6 kcal/mol/K, respectively. It is known that the nitrogen−hydrogen reductive elimination is often triggered by addition of a dative ligand;16 actually, nitrogen−hydrogen bond formation is rarely observed in the absence of an added ligand.17 Thus, it should be noted that the nitrogen−hydrogen bond is smoothly formed with a rather low energy barrier in the present system despite the absence of a dative ligand. This facile nitrogen−hydrogen bond formation is understood based on orbital interactions. In TS3, the HOMO-10 includes a bonding interaction between the N and the H4 atoms (Figure 6). The π orbital of the N atom directly extends toward the H4 atom in a bonding fashion, facilitating the N−H4 bond formation. In the step of the N−H4 bond formation, the electron distribution considerably changes as follows: Upon going to TS3 from INT2, the H4 atomic population significantly decreases, as shown in Figure 7, whereas the N atomic population significantly increases. These population changes demonstrate that the H4 approaches the N atom with changing to a proton-like H atom. The H4 atomic population further decreases and the N atomic population further increases until the N−H4 bond is formed at B1. The Ru3 atomic population moderately decreases on going to B2 from INT2, and then increases on going to 2. However, the Ru1 and Ru2 atomic

Figure 7. Population changes from INT2 to 2.

populations somewhat decrease through the step. This is because two hydrides, H1 and H3, approach the Ru3 atom to afford the final product 2. The key point of this process is the complicated positional changes of the H5 ligand. In INT1b, no hydride ligand exists near the NH ligand; note that the NH ligand exists below the Ru3 core but that all of the hydrido ligands are above the Ru3 core. The H5 ligand takes a terminal position on the Ru3 in INT1b, but it moves to the bridging position between Ru1 and Ru3, when going to TS2 from INT1b. As a result, the bridging H4 can move to the position below the Ru3 core, which is necessary for the bonding interaction between the NH ligand and the H4 atom, as shown by the HOMO-10 at TS3. These geometrical changes indicate that the H5 ligand plays crucial roles in the formation of the N−H4 bond as a dative ligand. In other words, the triruthenium polyhydride complex is reactive for the activation of the dihydrogen molecule and the N−H bond formation because of the fluxional interexchange between bridging and terminal hydride ligands.

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CONCLUSION We presented the detailed understanding of the dihydrogen activation by a triruthenium μ3-imido complex 1. Though this reaction seems to be a heterolytic cleavage of a hydrogen− hydrogen σ-bond, affording the hydride on the Ru center and the proton-like H on the N atom, the hydrogen−hydrogen bond cleavage occurs in a similar manner to the oxidative addition to afford the terminal and bridging hydrides. In this reaction, one of the three ruthenium centers can accept a dihydrogen molecule. After TS1, which corresponds to the transition state for the approach of the dihydrogen to the Ru, the hydrogen−hydrogen bond cleavage smoothly occurs without a further energy barrier; note that the dihydrogen adduct is not formed as an intermediate in this process. This extremely facile hydrogen−hydrogen bond cleavage is quite 5346

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rare and seems to be characteristic for the triruthenium system of 1; note that the hydrogen−hydrogen bond cleavage by a mononuclear Ru(II) complex mostly occurs in a heterolytic fashion, which is assisted by either a surrounding base or basic ligand, and the highest energy barrier normally lies in the stage of the hydrogen−hydrogen bond cleavage.2d,e,3b,h Orbital analysis indicates well the cooperative participation of ruthenium centers, which facilitates the charge transfer from the ruthenium dπ orbitals to the hydrogen−hydrogen σ* orbital. Also, natural population analysis reveals too that all ruthenium centers participate in changes in the electronic structure during the hydrogen−hydrogen bond cleavage. The next is the facile nitrogen−hydrogen bond formation, leading to the formation of the amido species 2 without addition of any dative ligand. This process occurs with considerably large positional changes of the amido group, concomitantly with drastic changes in the binding mode of hydrides; some of them change to bridging hydrides from terminal hydrides but some of them once change to terminal ones from bridging ones. Electron population analysis on this N−H bond formation step revealed that the hydride approaches the N atom with changing to a proton-like hydrogen atom. The electron populations of all the three rutheniums and hydrides also change in accordance with the geometrical changes of the Ru3(NH2)(H)4 core, indicating that the synergy effects of three Ru centers are important in this reaction. The observed both electronically and geometrically flexible behavior of hydrides is another important key property of the triruthenium polyhydride system. From these computations, we wish to emphasize that 1R easily performs hydrogen−hydrogen cleavage and nitrogen−hydrogen formation because of the cooperative action of three ruthenium centers and the flexible behavior of the hydride.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (Y.N.), sakaki.shigeyoshi. [email protected] (S.S.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially supported, in part, by Grant-in-Aids on specially promoted science and engineering for ‘‘Theoretical Study of Complex Electronic Systems Including d Electron’’ (No. 22000009) and for Young Scientists (B) from MEXT. The authors would like to thank Prof. Fumiyuki Ozawa for his generous support.

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REFERENCES

(1) (a) Kubas, G. J. Chem. Rev. 2007, 107, 4152. (b) Ito, M.; Ikariya, T. Chem. Commun. 2007, 5134. (c) Marie, P.; Büttner, T.; Breher, F.; Floch, P. L.; Grützmacher, H. Angew. Chem., Int. Ed. 2005, 44, 6318. (d) Clapham, S. E.; Hadzovic, A.; Morris, R. H. Coord. Chem. Rev. 2004, 248, 2201. (e) Noyori, R.; Ohkuma, T. Angew. Chem., Int. Ed. 2001, 40, 40. (f) Crabtree, R. T. The Organometallic Chemistry of the Transition Metals, 5th ed.; Wiley: New York, 2009. (2) For experimental studies, see: (a) Gunanathan, C.; Gnanaprakasam, B.; Iron, M. A.; Shimon, L. J. W.; Milstein, D. J. Am. Chem. Soc. 2010, 132, 14763. (b) Friedrich, A.; Drees, M.; Schmedt auf der Günne, J.; Schneider, S. J. Am. Chem. Soc. 2009, 131, 17552. (c) Heiden, Z. M.; Rauchfuss, T. B. J. Am. Chem. Soc. 2009, 131, 3593. (d) Iuliis, M. Z.-D.; Morris, R. H. J. Am. Chem. Soc. 2009, 131, 11263. (e) Clapham, S. E.; Guo, R.; Iuliis, M. Z.-D.; Rasool, N.; Lough, A. J.; Morris, R. H. Organometallics 2006, 25, 5477. (f) Webster, C. E.; Gross, C. L.; Young, D. M.; Girolami, G. S.; Scultz, A. J.; Hall, M. B.; Eckert, J. J. Am. Chem. Soc. 2005, 127, 15091. (g) Curtis, C. J.; Miedaner, A.; Ciancanelli, R.; Ellis, W. W.; Noll, B. C.; DuBois, M. R.; DuBois, D. L. Inorg. Chem. 2003, 42, 216. (3) For theoretical studies, see: (a) Tao, J.; Li, S. Dalton Trans. 2010, 39, 857. (b) Kovács, G.; Rossin, A.; Gonsalvi, L.; Lledós, A.; Peruzzini, M. Organometallics 2010, 29, 5121. (c) Zeng, G.; Guo, Y.; Li, S. Inorg. Chem. 2009, 48, 10257. (d) Yang, X.; Hall, M. B. J. Am. Chem. Soc. 2009, 131, 10901. (e) Nagaraja, C. M.; Parameswaran, P.; Jemmis, E. D.; Jagirdar, B. R. J. Am. Chem. Soc. 2007, 129, 5587. (f) Hedberg, C.; Källström, K.; Arvidsson, P. I.; Brandt, P.; Andersson, P. G. J. Am. Chem. Soc. 2005, 127, 15083. (g) Bruschi, M.; Fantacci, P.; Gioia, L. D. Inorg. Chem. 2003, 42, 4773. (h) Belkova, N. V.; Besora, M.; Epstein, L. M.; Lledós, A.; Maseras, F.; Shubina, E. J. Am. Chem. Soc. 2003, 125, 7715. (4) For experimental studies, see: (a) Tard, C.; Pickett, C. J. Chem. Rev. 2009, 109, 2245. (b) Capon, J.-F.; Gloaguen, F.; Pétillon, F. Y.; Schollhammer, P.; Talarmin, J. Coord. Chem. Rev. 2009, 253, 1476. (c) Matsumoto, T.; Itakura, N.; Nakaya, Y.; Tatsumi, K. Chem. Commun. 2011, 47, 1030. (d) Matsumoto, T.; Nakaya, Y.; Itakura, N.; Tatsumi, K. J. Am. Chem. Soc. 2008, 130, 2458. (e) Morvan, D.; Capon, J.-F.; Gloaguen, F.; Pétillon, F. Y.; Schollhammer, P.; Talarmin, J.; Yaouanc, J.-J.; Michaud, F.; Kervarec, N. J. Organomet. Chem. 2009, 694, 2801. (f) Capon, J.-F.; Gloaguen, F.; Pétillon, F. Y.; Schollhammer, P.; Talarmin, J.; Eur., J. Inorg. Chem. 2008, 4671. (g) Adams, R. D.; Boswell, E. M.; Hall, M. B.; Yang, X. Organometallics 2008, 27, 4938. (h) Cheah, M. H.; Borg, S. J.; Best, S. P. Inorg. Chem. 2007, 46, 1741. (i) Brown, S. D.; Mehn, M. P.; Peters, J. C. J. Am. Chem. Soc. 2005, 127, 13146. (j) Zhou, T.; Mo, Y.; Zhou, Z.; Tsai, K. Inorg. Chem. 2005, 44, 4941. (k) Justice, A. K.; Linck, R. C.; Rauchfuss, T. B.; Wilson, S. R. J. Am. Chem. Soc. 2004, 126, 13214. (l) Rauchfuss, T. B. Inorg. Chem. 2004, 43, 14. (m) Georgakaki, I. P.; Miller, M. L.; Darensburg, M. Y. Inorg. Chem. 2003, 42, 2489. (n) Startsev, A. N.; Zakharov, I. I.; Parmon, V. N. J. Mol. Catal. A: Chem. 2003, 192, 113. (o) Aubart, M. A.; Chandler, B. D.; Gould, R. A. T.; Krogstad, D. A.; Schoondergang, M. F. J.; Pignolet, L. H. Inorg. Chem. 1994, 33, 3724.

Geometries were optimized with the DFT method, where the B3LYP functional was used for exchange-correlation terms.18 We ascertained that each equilibrium geometry exhibited no imaginary frequency and transition states exhibited one imaginary frequency, except for TS1a; in TS1a, a very small imaginary frequency derived from Cp rotation around the Ru−Cp centroid did not disappear even when we employed tight convergence. We carried out IRC calculations, to check that the transition states TS1a, TS1b, TS2, and TS3 connected the reactant and product. Energy and population changes were evaluated with the DFT(B3LYP) using the DFT-optimized geometries. For all calculations, core electrons of Ru were replaced (up to 3d) with effective core potentials (ECPs), where a (341/321/31) basis set was used for valence electrons of Ru.19 For Cp, 6-31G(d) basis sets were used. For N and H atoms of the hydrides, imido ligand, and dihydrogen, 6-311G(d,p) basis sets were used. The Gaussian 03 program package20 was used for all calculations. Population analysis was carried out with the method of Weinhold et al.21 Molecular orbitals were drawn with the Molstudio program package.

S Supporting Information *

Energy changes of the reaction; changes in bond distances and electron populations along path a; structure and important orbitals of A; geometry changes from INT3 to 2; important orbitals of TS3; geometry comparison of the Ru3(NH)(H)5 core of all species; imaginary frequencies of TS1a, TS1b, TS2, and TS3; important NBO charges of all species; and Cartesian coordinates of all species. This material is available free of charge via the Internet at http://pubs.acs.org. 5347

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(17) (a) Basch, H.; Musaev, D. G.; Morokuma, K. Organometallics 2000, 19, 3393. (b) Driver, M. S.; Hartwig, J. F. Organometallics 1998, 17, 1134. (18) (a) Becke, A. D. Phys. Rev. 1988, A38, 3098. (b) Becke, A. D. J. Chem. Phys. 1983, 98, 5648. (c) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. 1988, B37, 785. (19) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 299. (20) Pople, J. A.; et al. Gaussian 03, revision C. 02; Gaussian, Inc.: Wallingford, CT, 2004. See the Supporting Information for the full citation. (21) Reed, A. E.; Curtiss, L. A.; Weinhold, F. Chem. Rev. 1988, 88, 899.

(p) Gastel, F. V.; Corrigan, J. F.; Doherty, S.; Taylor, N. J.; Carty, A. J. Inorg. Chem. 1992, 31, 4492. (5) For theoretical studies, see: (a) Siegbahn, P. E. M.; Tye, J. W.; Hall, M. B. Chem. Rev. 2007, 107, 4414. (b) Siegbahn, P. E. M.; Bloomberg, M. R. A.; Pavlov, M. W. n.; Crabtree, R. H. JBIC, J. Biol. Inorg. Chem. 2001, 6, 460. (c) Greco, C.; Fantucci, P.; De Gioia, L.; Suarez-Bertoa, R.; Bruschi, M.; Talarmin, J.; Schollhammer, P. Dalton Trans. 2010, 39, 7320. (d) Moc, J.; Musaev, D. G.; Morokuma, K. J. Phys. Chem. A 2003, 107, 4929. (e) Miyachi, H.; Shigeta, Y.; Hirao, K. J. Phys. Chem. A 2005, 109, 8800. (e) Basch, H.; Musaev, D. G.; Morokuma, K. Organometallics 2000, 19, 3393. (6) For experimental studies, see: (a) Kameo, H.; Nakajima, Y.; Namura, K.; Suzuki, H. Organometallics 2011, 30, 6703. (b) Takao, T.; Moriya, M.; Kajigaya, M.; Suzuki, H. Organometallics 2010, 29, 4770. (c) Takao, T.; Moriya, M.; Suzuki, H. Organometallics 2008, 27, 4248. (d) Kawashima, T.; Takao, T.; Suzuki, H. J. Am. Chem. Soc. 2007, 129, 11006. (e) Nakajima, Y.; Kameo, H.; Suzuki, H. Angew. Chem., Int. Ed. 2006, 45, 950. (f) Kawashima, T.; Takao, T.; Suzuki, H. Angew. Chem., Int. Ed. 2006, 45, 7615. (g) Takao, T.; Inagaki, A.; Murotani, E.; Imamura, T.; Suzuki, H. Organometallics 2003, 22, 1361. (h) Takemori, T.; Inagaki, A.; Suzuki, H. J. Am. Chem. Soc. 2001, 123, 1762. (i) Inagaki, A.; Takemori, T.; Tanaka, M.; Suzuki, H. Angew. Chem., Int. Ed. 2000, 39, 404. (j) Matsubara, K.; Inagaki, A.; Tanaka, M.; Suzuki, H. J. Am. Chem. Soc. 1999, 121, 7421. (7) For theoretical studies, see: (a) Khoroshun, D. V.; Inagaki, A.; Suzuki, H.; Vyboishchikov, S. F.; Musaev, D. G.; Morokuma, K. J. Am. Chem. Soc. 2003, 125, 9910. (b) Inagaki, A.; Musaev, D. G.; Toshifumi, T.; Suzuki, H.; Morokuma, K. Organometallics 2003, 12, 1718. (8) (a) Kameo, H.; Nakajima, Y.; Suzuki, H. Eur. J. Inorg. Chem. 2007, 1793. (b) Nakajima, Y.; Suzuki, H. Organometallics 2005, 24, 1860. (c) Nakajima, Y.; Inagaki, A.; Suzuki, H. Organometallics 2004, 23, 4040. (9) (a) Nakajima, Y.; Suzuki, H. Organometallics 2003, 22, 959. (b) Lausarot, P. M.; Operti, L.; Vaglio, G. A.; Valle, M.; Tiripicchio, A.; Camellini, M. T.; Graiboldi, P. Inorg. Chim. Acta 1986, 103, 122. (c) Bhaduri, H.; Gopalkrishnan, K. S.; Sheldrick, G. M.; Clegg, W.; Stalke, D. J. Chem. Soc., Dalton Trans. 1983, 2339. (10) Emsley, J., Ed. The Elements, 3rd ed.; Oxford University Press: New York, 1998. (11) (a) Grellier, M.; Vendier, L.; Chaudret, B.; Albinati, A.; Rizzato, S.; Mason, S.; Sabo-Etienne, S. J. Am. Chem. Soc. 2005, 127, 17592. (b) Borowski, A. F.; Donnadieu, B.; Daran, J.-C.; Sabo-Etienne, S.; Chaudret, B. Chem. Commun. 2000, 543. (c) Albinati, A.; Klooster, W. T.; Koetzle, T. F.; Fortin, J. B.; Ricci, J. S.; Eckert, J.; Fong, T. P.; Morris, R. H.; Golombeck, A. P. Inorg. Chim. Acta 1997, 259, 351. (12) For the structure and important orbitals of A, please see the Supporting Information, Figures S7 and S8. (13) (a) Ochi, N.; Nakao, Y.; Sato, H.; Sakaki, S. J. Am. Chem. Soc. 2007, 129, 8615. (b) Biswas, B.; Sugimoto, S.; Sakaki, S. Organometallics 2000, 19, 3895. (c) Koga, N.; Obara, S.; Morokuma, K. J. Am. Chem. Soc. 1984, 106, 4625. (d) Obara, S.; Koga, N.; Morokuma, K. J. Organomet. Chem. 1984, 270, C33. (e) Goddard, R. J.; Hoffmann, R.; Jemmis, E. D. J. Am. Chem. Soc. 1980, 102, 7667. (14) (a) Sakaki, S.; Mizoe, M.; Musashi, Y.; Biswas, B.; Sugimoto, M. J. Phys. Chem. A 1998, 102, 8027. (b) Sakaki, S.; Ieki, M. J. Am. Chem. Soc. 1993, 115, 2373. (c) Low, J. J.; Goddard, W. A., III J. Am. Chem. Soc. 1986, 108, 6115. (d) Low, J. J.; Goddard, W. A., III Organometallics 1986, 5, 609. (e) Tatsumi, K.; Hoffmann, R.; Yamamoto, A.; Stille, J. K. Bull. Chem. Soc. Jpn. 1981, 54, 1857. (15) Energy changes of the reaction from INT2 to 2 via TS3 and structural changes from TS3 to 2 are summarized in the Supporting Information, Figures S5 and S12. (16) (a) Glueck, D. S.; Newman, L. J.; Bergman, R. G. Organometallics 1991, 10, 1462. (b) Cowan, R. L.; Trogler, W. C. J. Am. Chem. Soc. 1989, 111, 4750. (c) Cowan, R. L.; Trogler, W. C. Organometallics 1987, 6, 2451. (d) Yamamoto, T.; Sano, K.; Yamamoto, A. Chem. Lett. 1982, 907. 5348

dx.doi.org/10.1021/om300372k | Organometallics 2012, 31, 5342−5348