Influence of Ion Pairing in Inter-Ring Haptotropic Rearrangements in

Article pubs.acs.org/Organometallics

Influence of Ion Pairing in Inter-Ring Haptotropic Rearrangements in Cationic Cyclopentadienyl Complexes of Ruthenium with Naphthalene: A DFT Investigation E. O. Fetisov,† I. P. Gloriozov,† Yu. F. Oprunenko,*,† J.-Y. Saillard,*,‡ and S. Kahlal‡ †

Chemistry Department, M. V. Lomonosov Moscow State University, Vorob’evy Gory, 119899 Moscow, Russia Institut des Sciences Chimiques de Rennes, UMR 6226 CNRS-Université de Rennes 1, F-35042 Rennes cedex, France

‡

S Supporting Information *

ABSTRACT: DFT calculations have been performed on the naphthalene cationic complex η6-C10H8RuCp+ in the presence of different anions. In a first step, geometry optimization of the PF6− salt carried out in the presence of 15 solvent molecules for 3 different solvents (methylene chloride, acetone, and water) indicated that ion pairing occurs in the less polar methylene chloride solvent, whereas the ions are separated in the more polar acetone and water. In a subsequent step, the inter-ring haptotropic rearrangement (IRHR) of η6-C10H8RuCp+ has been modeled both as an isolated cation (separated ion pairs (SIP)) and in the presence of a counterion (contact ion pair (CIP)). The IRHR activation barrier is found to be much lower in the CIP case due to the cation−anion interaction, which tends to reduce the metal unsaturation during the process. The size of the anion is also important. Small anions such as BF4− favor lower barriers. These results should also hold for photochemically induced IRHR processes, since the SIP mechanism involves structurally similar intermediates and transition states.

1. INTRODUCTION Currently transition-metal π complexes are widely used in organic and organometallic chemistry to solve different catalytic and synthetic tasks. For example, such compounds with substituted aromatic rings provide reliable and effective control of regio- and stereoselectivity of metalation processes (e.g., lithiation) and subsequent reaction of salts obtained with electrophiles. Such approaches are used in particular in the synthesis of various pharmaceuticals and other biologically active substances.1 This important and extensive class of compounds has been thoroughly investigated, mainly for monoarene ligands and, to a somewhat lesser extent, for polyaromatic ligands (PAL). When only one part of a PAL is bonded to a transition-metal moiety, it is generally quite labile and various dynamic processes can occur, such as inter-ring haptotropic rearrangements (IRHRs). These intramolecular reactions correspond to the shifting of the transition-metal moiety from one ring to another one. In particular, IRHRs have been observed in a series of naphthalene organometallic complexes with different metal hapticities (Scheme 1).2 Thermally induced intramolecular η6:η6-IRHR processes have been investigated experimentally (for labeled complexes) and theoretically. Since the pioneering semiempirical work of Albright et al.,3 DFT investigations have been performed mostly for chromium tricarbonyl complexes of PAL4−8 and only to some extent for molybdenum and tungsten.5 On the other hand, it is quite strange and intriguing that η6:η6-IRHR in synthetically available and very stable PAL complexes of the © XXXX American Chemical Society

Scheme 1

iron triad (Fe, Ru, Os), which are important from a synthetic practical point of view, have been virtually not investigated.9−11 The influence of photochemical activation on such rearrangements has been poorly and not thoroughly investigated, although many thermally induced reactions have photochemical analogues12−14 which might be quite complex and possibly involve not only the lowest triplet state.15 This is why we have decided to investigate the aforementioned problems theoretically in order to stimulate searches for experimental support of the existence of such IRHRs in various PAL complexes of transition metals and to analyze them correctly. In this paper we investigate intramolecular η6:η6-IRHR in the cationic cyclopentadienyl naphthalene complex of ruthenium (Scheme 2). So far, only two thermoinduced rearrangements of RuCp+ with PAL have been described16,17 (Scheme 3) (for Fe10 and Received: April 17, 2013

A

dx.doi.org/10.1021/om4003335 | Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

namic functions (Gibbs activation energies, G) at 298.15 K were calculated using an approximation of restricted rotator and harmonic oscillator. Reaction paths were found by the intrinsic reaction coordinate (IRC) method. All calculations were performed using the MBC100k cluster at the Joint Supercomputer Center (JSCC) (Moscow, Russia) with the use of the PRIRODA04 program written by Laikov.27 The representations of the molecular orbitals were made using the MOLEKEL4.3 program28 using results obtained from singlepoint calculations calculated with the Gaussian 09 package29 on the PRIRODA04-optimized structures, employing the PBE functional, and using the standard LANL2DZ-pol basis set.

Scheme 2

Scheme 3

3. RESULTS AND DISCUSSION 3.1. Solvent Dependence of Ion Pairing. A comprehensive study of the structure of ion pairs for cationic arene ruthenium complexes and their solvent dependence has been carried out by Pregosin and collaborators.19 It was shown by means of diffusion NMR with pulse gradient of the field (1H PGSE) and 2D NMR of heteronuclear Overhauser (1H,19F HOESY) for the (arene)RuCp+PF6− salts that in dichloromethane such ion pairs are in contact (contact ion pairs, CIP) and they are separated in acetone (separated ion pairs, SIP). 1 19 H, F HOESY also accurately describes relative cation−anion arrangements, and 1H PGSE NMR does the same concerning their extent of association based on diffusion coefficients D, which are similar for anions and cations in the case of the existence of 100% CIP. Theoretical support of experimental data concerning the nature of ion pairs was found by DFT calculations on I. In the first stage, the mutual cation−anion arrangement was optimized for a CIP, starting from the X-ray structure of the PF6− salt of I.30 Then, in order to estimate the influence of solvent explicitly, 15 solvent molecules (methylene chloride, acetone, or water) were added in arbitrary positions all around the ion pair and the geometries of the whole systems were further optimized. The cation−anion distance was found to increase with solvent polarity, as exemplified by the d(Ru−P) distance, which is equal to 5.215, 5.686, and 6.129 Å in methylene chloride, acetone, and water, respectively. Although such a static computational approach with a lmited number of solvent molecules is only indicative and not exhaustive as a molecular dynamics investigation would be, one should acknowledge that it fits quite well with the experimental data concerning ion pairing for such salts in methylene chloride and acetone. Water was chosen as one of our considered solvents in our calculations, because many organometallic reactions of salts of arene complexes of the iron triad take place in water, in particular the intercalation of Ru complexes in a DNA duplex.31 In the following, we explore in detail the influence of ion pairing on the IRHR mechanism with consideration of both CIP and SIP situations. It should be mentioned that, owing to the lack of corresponding experimental material in the literature, the computational results presented in this article have heuristic importance and provide the possibility to develop in the future research in the field of the reactivity and dynamic behavior of such complexes. 3.2. Haptotropic Rearrangement in the Case of Separated Ion Pairs. In the first step we investigated IRHR in SIP. Metal shifting proceeds from I-Pr (atom numbering used in this work is presented in Figure 1) in the classical way:3 i.e., along the edge of the ligand with RuCp+ exit on the periphery of naphthalene ligand through enantiomorphic transition states (I-TS and I-TS′, ωim = 79.2i cm−1) and the symmetric intermediate I-IM in accordance with the scheme I-

Os11 such IRHRs were discussed but not firmly proved). Though these reactions are difficult to compare owing to the important structural differences of the ligands, it is evident that the η6:η6-IRHR activation barrier in such complexes depends to a great extent on the nature of the solvent. Namely, η6:η6-IRHR is sufficiently rapid in the nonpolar CH2Cl2 solvent (hours)16 and extremely slow (weeks) in the much more polar acetone solvent.17 This means that IRHR activation barriers in these cationic complexes depend on cation−anion interactions. This agrees well with the fact that for more than two decades it has been well-known that reaction rates of the majority of processes in organometallic salts depend on the structure of ion pairs.18,19 The aim of this work was to investigate the structure and dynamic behavior of the cationic naphthalene complex η6C10H8RuCp+ (I), an important species from the point of view of catalysis,20 C−C21 and C−H22 bond activation, and anticancer drugs,23 in the presence of different coordinating anions.

2. COMPUTATIONAL DETAILS The geometries of molecules, transition states, and intermediates were fully optimized by means of density functional theory (DFT) calculations. The PBE functional24 and scalar-relativistic theory were used, the latter employing the four-component spin-free Hamiltonian derived by Dyall25 and applied variationally.26 The full electron basis sets L1 were used, where L1 stands for double set size. The numbers of contracted and primitive functions used in L1 are respectively {2,1}/{6,2} for H, {6,4,3,1}/{10,9,7,4} for B, C, and F, {9,7,5,2}/ {14,13,11,6} for P, {15,14,13,8,4}/{23,22,20,17,13} for Sb, and {15,14,13,9,6,2}/{23,22,20,17,14,7} for Ru.26 Such functionals and basis sets were chosen as the result of a systematic investigation of the geometry of various metal complexes and the rates of organometallic reactions which was accomplished in our laboratory during the past decade as well as a result of comparative calculations in the course of this work. Corrections for zero-point energies were calculated in the harmonic approximation. Stationary points on the potential energy surface (PES) were identified by analyzing Hessians. The thermodyB


Organometallics

Article

Figure 1. Carbon atom numbering for I.

Pr → I-TS1 → I-IM1 → I-TS1′ → I−Pr (maximum on PES ΔG = 39.4 kcal/mol). Stationary structures on the PES and their relative energies are presented in Figure 2. The energetic profile of the IRHR process is shown in Figure 3. One can see that the activation energy of such a rearrangement is sufficiently high to considerably complicate the experimental observation of this process. To our knowledge, there has been a single theoretical investigation of the RuCp+ migration along a PAL plane in the literature, namely with PAL = coronene.32 The IRHR was calculated in the gas phase without considering interaction with the counterion (RISM-SCF DFT). These conditions are practically similar to the situation realized in the case of the IRHR for SIP of a salt of I in acetone or water. The reaction mechanism found in this study is qualitatively similar to that found by us for I: enanthiomorphic transition states arranged on the periphery of the ligand and an intermediate of slightly lower energy. The activation barrier was found to be lower by ∼6 kcal/mol than that calculated by us for IRHR in SIP in I. The reason for this relatively high barrier is the rather high energy of the I-IM intermediate, which is an unsaturated 14electron species considering that the coordinated C(4)− C(4a)−C(5) unit is a 2-electron donor as would be, for instance, an η3-allyl cation. Consistently, the MO diagram of IIM (Figure 4) exhibits two low-lying accepting orbital LUMOs of large 4d(Ru) character, one of σ type and the other one intermediate between δ and π type. 3.3. Haptotropic Rearrangement in the Case of Contact Ion Pairs. In a subsequent step, the IRHR mechanism was investigated for CIP (existing in dichloromethane) considering different anions. The hexafluorophosphate salt II was first investigated. We first looked for the ion pair structures of lowest energy. Since many local minima were expected due to the isotropic nature of the dominant Coulomb interaction, the search was limited to the minima in which the PF6− anion is in contact with Ru. Only a minimum of this type is expected to be involved as the reacting structure of II in an IRHR process involving anion participation. Several starting

Figure 3. Reaction path for the η6:η6-IRHR in I (isolated molecule approximation and difference in zero-point energy ignored).

Figure 4. Frontier MO diagram of I-IM.

geometries, in which the anion is approaching the metal from each of the four possible “sides” of the cationic complex, were tested. Interestingly, only two slightly different minima were found. Considering the orientation of I shown in Figure 1, one of the minima (noted II-Pr) has PF6− located on the right side and the other one (noted II-Pr′) on the front side. These two minima are shown in Figure 5.

Figure 2. Top views of the IRHR stationary structures in the SIP case and their relative energies (kcal/mol) and hapticities. C


Organometallics

Article

The geometries of the two structures from Table 1 have some minor differences, which are related to (1) the rotational conformations for the cyclopentadienyl rings relative to the naphthalene ligand and (2) the anion−cation orientations. Such differences could be explained by the crystal forces which exist in the solid state but which are absent in the gas phase. The metal is situated above the center of one of the sixmembered rings of naphthalene, but a strict analysis of the bond distances of II-Pr shows some tendency of the metal for η4 coordination. The naphthalene and cyclopentadienyl ligands are planar. Such similarities between the structure of a CIP in solution and the corresponding solid-state structure are not uncommon in organometallic chemistry.33 The IRHR mechanism in the CIP case was investigated assuming both II-Pr and II-Pr′ as the starting structures. In the case of II-Pr, the mechanism is considerably changed in comparison to the SIP process and becomes much more complicated. It occurs according to the scheme II-Pr → II-TS1 → II-IM1 → II-TS2 → II-IM2 → II-TS3 → II-IM3 → II-TS4 → II-IM3′ → II-TS3′ → II-IM2′ → II-TS2′ → II-IM1′ → IITS1′ → II-Pr (maximum on PES ΔG = 28.5 kcal/mol). The four transition states and three intermediates of the first half of the whole IRHC process are presented in Figure 7 with their relative energies (kcal/mol) and hapticities. The calculated model of cation−anion interactions is wellknown34 and takes place in the process of IRHR via the metal and bridge fluorine atom. This interaction is supposed to help to reduce coordinative unsaturation of the various intermediates and transition states. The existence of such an interaction is supported by Ru−F as well as P−F distances. Looking at the starting structure of II-Pr, the Ru−F distances are long and no significant associated covalent interaction occurs, as confirmed by the computed Mulliken charge of the PF6 unit, which is close to −1 (−0.95). Thus, only a Coulomb anion−cation stabilizing interaction and possibly weak H···F bonding are present in II-Pr. The II-IM1 intermediate exhibits a η4coordinated naphthalene, as well as one short Ru−F contact (2.237 Å). Assuming that the PF6− anion is a 2-electron donor, II-IM1 is an 18-electron species. Consistently, the computed Mulliken charge of the PF6 unit in II-IM1 (−0.62) is significantly different from −1. Both II-IM2 and II-IM3 intermediates exhibit the same η2-coordinated naphthalene (through C(1) and C(2)) and differ mainly in the rotational orientation of the Cp ligand. In both intermediates two short Ru−F contacts are present (2.5−2.7 Å), indicating that PF6− is a formal 4-electron donor. The II-IM2 and II-IM3 computed Mulliken negative charge of the PF6 unit (−0.56) is lower than in II-IM1. Therefore, II-IM2 and II-IM3 are formally 18electron species; II-IM2 and II-IM3 lie at lower energy than IIIM1 because the presence of two Ru−F contacts in the former intermediates allows a closer anion−cation proximity and consequently stronger stabilization by ionic interaction. Looking now at II-TS4, its η3-coordinated structure is strongly related to that of I-IM (or I-TS). However, II-TS4 exhibits in addition two Ru−F short contacts, which make it a formally 18electron species (Mulliken charge of the PF6 unit −0.57). This is exemplified by the Ru−F antibonding character of the two LUMO’s of II-TS4, which are shown on the left side of Figure 8. One should note also that in II-TS4 the cyclopentadienyl and naphthalene ligands are bending away in a different direction as in I-IM, with the noncoordinated part of naphthalene getting closer to the cyclopentadienyl ring.

Figure 5. Selected views of II-Pr and II-Pr′ and their relative energies (kcal/mol). Distances are given in Å.

They can be considered as isoenergetic at our level of calculations. It should be noted that no minimum could be found with PF6− located on the left side: i.e., above the uncomplexed ring of naphthalene. Any starting geometry with the anion approaching on that side ended up at the II-Pr′ minimum. The reason is likely to be steric in origin. It is also interesting to note that the II-Pr minimum could also be obtained from a starting geometry taken from a cut of an ion pair out of the solid-state X-ray structure of II30 and that it is in good agreement with this crystal structure. This can be seen in Figure 6, which displays both calculated and X-ray structures of II-Pr, and in Table 1, where selected bond distances for these structures are presented.

Figure 6. Top and side views of II-Pr.

Table 1. Comparison of Experimental and Calculated Structural Parameters (Å) for II-Pr bond

DFT

X-ray

Ru−C1 Ru−C2 Ru−C3 Ru−C4 Ru−C4a Ru−C8a Ru−C9 Ru−C10 Ru−C11 Ru−C12 Ru−C13 C4a-C8a C2−C3 C6−C7 av deviation

2.216 2.224 2.225 2.218 2.310 2.309 2.214 2.207 2.184 2.182 2.203 1.453 1.424 1.425 0.015

2.218 2.221 2.218 2.200 2.284 2.262 2.179 2.190 2.182 2.172 2.180 1.441 1.422 1.428

D


Organometallics

Article

Figure 7. Side views of transition states and intermediates and their relative energies (kcal/mol) and hapticities. Distances are given in Å.

involving CIP is considerably lower than in the case of SIP. Owing to the complexity of this CIP IRHR mechanism in comparison to the SIP one, one may wonder why II-Pr does not connect directly with II-TS4 or perhaps with II-IM2 via an η3 coordination mode. It turns out that a search for such a direct transit remained unsuccessful. The reason for the a priori counterintuitive pathway of Figure 7 lies in the fact that the PF6− anion attracts the RuCp moiety toward the outer periphery of the naphthalene ligand all along the IRHR pathway. This behavior is in line with the significance of ionpairing interactions in CIP. Considering now II-Pr′ as the starting structure, the mechanism (not shown here) is much more simple and resembles that of the SIP case, with a similar transition state and reaction intermediate. There are no Ru−F contacts during this IRHR process, and consistently the computed energy barrier (38.3 kcal/mol) is close to that of the SIP process. The reason lies in the fact that the Cp ligand bends in the same way as for the SIP case (Figure 2), i.e., toward the anion, and consequently it closes the open space and shields the Ru atom from the PF 6− anion and thus reduces cation−anion interactions, as exemplified by the shortest Ru−F distance in the transition state (3.772 Å), which is much longer than the corresponding distances in any of the transition states of Figure 7. Similar calculations were also performed with the hexafluoroantimonate anion (SbF6−) as the counterion in CIP. The reaction mechanism is absolutely the same as that corresponding to the case of PF6− for II-Pr, with a slightly increased

Figure 8. LUMO and LUMO+1 of II-TS4 and III-IM3.

Thus, although the Ru−F covalent interactions which are present along the whole IRHR mechanism in the case of CIP are not very strong, they help to reduce coordinative unsaturation along the whole process and therefore tend to stabilize the various transition states and intermediates. In addition, these interactions provide favorable conditions for stronger anion−cation Coulomb stabilizing interactions. The limiting step is associated with II-TS1, which has a reduced Ru−naphthalene coordination and a single and rather long Ru−F contact. Nevertheless, the IRHR activation energy E


Organometallics

Article

activation barrier (maximum on PES ΔG = 29.8 kcal/mol) and is thus not presented below in detail. The increase in activation barrier can be explained by the fact that SbF6− has lower coordinating ability than PF6−. The IRHR mechanism was also investigated in the case of the tetrafluoroborate (BF4−) salt of I (compound III). To our knowledge, there is no reported crystal structure for this compound. The two CIP structures of lowest energy that we found, namely III-Pr and III-Pr′, are shown in Figure 9. In III-

In Figure 10 three transition states and three intermediates are presented as well as their relative energies (kcal/mol) and hapticities. Since the anion coordinates to the metal on top of the naphthalene plane, the cyclopentadienyl and naphthalene ligands are bending away in such a manner that the noncoordinated ring of naphthalene is moved away from the cyclopentadienyl ring. This bending is similar to that found in the SIP process (see Figure 2) and opposite to that found in the case of the CIP process involving PF6− (see Figure 7). The III-IM1 intermediate is η4 coordinated to naphthalene and exhibits one short Ru−F contact (2.202 Å). It can therefore be considered as formally an 18-electron species. Consistently the Mulliken charge of its BF4 fragment (−0.65) is significantly different from −1. In contrast to the case of the PF6− salt II, two intermediates, namely III-IM2 and III-IM3, are formally unsaturated 16-electron species, with only one short Ru−F contact (2.136 and 2.107 Å, respectively). The reason comes from the fact that the BF4− ligand is now located on the sterically hindered side of the metal. Nevertheless, this unique Ru−F contact is shorter than those found in the various intermediates and transition states of the IRHR process of II. Consistently, the associated anion−cation electron transfer in III-IM2 and III-IM3 is significant (BF4 Mulliken charge ∼−0.59). Moreover, the bending of the ligands in the C10H8RuCp+ fragment during the IRHR CIP process is energetically more favored in III than in II, especially at the beginning of the process. For example the η4-C10H8RuCp+ fragment is more stable by 0.67 eV in III-IM1 than in II-IM1. This can be explained by the fact that the bending in III resembles that in I (SIP process), whereas in II it is forced to occur the other way because of the larger size of the PF6− anion. Consistently, the MO diagram of III-IM3 is strongly related to that of I-IM, except it has only one low-lying accepting orbital (the δ/π-type LUMO), whereas the σ-type

Figure 9. Selected views of III-Pr and III-Pr′ and their relative energies (kcal/mol). Distances are given in Å.

Pr the anion coordinates to the metal on the opposite side of the naphthalene ligand in comparison with II-Pr. III-Pr resembles II-Pr′. The IRHR mechanism was investigated assuming only the absolute minimum III-Pr as the starting structure. The reaction occurs according to the scheme III-Pr → III-TS1 → III-IM1 → III-TS2 → III-IM2 → III-TS3 → III-IM3 → III-TS3′ → III-IM2′ → III-TS2′ → III-IM1′ → III-TS1′ → III-Pr (maximum on PES ΔG = 19.7 kcal/mol).

Figure 10. Side views of transition states and intermediates and their relative energies (kcal/mol) and hapticities. Distances are given in Å. F


Organometallics

Article

with sufficient lifetimes could lead to an effective coordination of ruthenium with guanine. This makes such complexes quite attractive as prospective anticancer agents. In particular, the pentamethylcyclopentadienyl relative of I has very high selective antiproliferative action to some lines of malignant cells such as human carcinoma and two phenotypes of breast cancer.38 We have optimized the geometries of possible intermediates in the course of thermally induced IRHR with guanine. The structures of these stable complexes are presented in Figure 12. Probably such coordination could be realized also for intermediates appearing in the course of photoinduced IRHR, especially in the presence of photosensitizers. The computed Ru−N distance indicates that strong bonding interaction. They are similar to experimentally found Ru−N distances in intercalated DNA ruthenium arene complexes. This makes it possible to consider I and VI as prospective anticancer agents.

LUMO+1 lies 1.1 eV above, because of its Ru−F antibonding nature (see right side of Figure 8). The different computed activation barriers of the IRHR afforded by η6-C10H8RuCp+ in the various SIP and CIP cases are summarized in Table 2. Table 2. Counterion Influence on the IRHR Activation Barrier (kcal/mol) in the Salts of the Cationic Complex η6C10H8RuCp+ anion ΔG⧧act,

kcal/mol

SIP

SbF6−

PF6−

BF4−

39.4

29.8

28.5

19.7

3.4. Miscellaneous Considerations. It has been shown previously that IRHR in substituted naphthalene ruthenium complexes proceeds much faster under much milder conditions in water with UV irradiation (Scheme 4) than in the case of thermally induced IRHR.14

4. CONCLUDING REMARKS In this paper, we have shown by DFT calculations that, in the case of salts of the naphthalene cationic complex η6C10H8RuCp+, the existence of contact ion pairs in solution may considerably reduce the activation energy of the IRHR process (by ∼10 to 20 kcal/mol depending on the anion nature). Of course, our modelization approach has two major limitations, which render our results perhaps less quantitative as one would predict, considering simply the level of theory used. (1) Although we used many trial structures in conjunction with our chemical intuition to explore the potential energy surfaces, such a static investigation does not allow the full investigation of all possible spatial configurations. Only molecular dynamics simulations would allow such a complete exploration. However, quantum molecular dynamics would have been much more demanding in terms of computational effort. Moreover, assuming that quantum molecular dynamics results would be different from ours, they would necessarily correspond to activation energies lower than our predicted barriers and thus not contradicting but rather reinforcing our conclusions, our predicted barriers corresponding to upper limits. (2) Because of computational limitations, we have calculated IRHR pathways without considering solvent molecules. It is likely that the first sphere of solvent molecules is, to some extent, involved in the process. With weakly coordinating solvents such as dichloromethane, this effect can be safely neglected. With strongly coordinating solvents, the IRHR process can be significantly modified. In the case of very polar and coordinating solvents, although the ion pairs are separated,

Scheme 4

We have calculated the activation barrier for this UV-induced process for ruthenium complex of naphthalene as SIP I. The IRHR reaction takes place in the exited low-lying triplet state IPr-triplet via intermediate I-IM-triplet and transition states ITS-triplet (ωim = 76.9i cm−1) and symmetrical I-TS′-triplet. It should be noted that the fact that photoinduced reactions occur in the triplet state is very characteristic for such complexes.35 In I-Pr-triplet Ru is η4-coordinated. Such a η6→η4 decrease in hapticity for PAL complexes is quite usual. This phenomenon takes place, for example, in the course of the two-electron reduction of the naphthalene complex C10H8Cr(CO)336 or in the reaction of dihydrogen addition to the anthracene complex C12H10Mo(PMe3)3.37 Generally, the rearrangement mechanism is similar to the thermally induced mechanism, but the activation barrier is much lower (ΔG⧧ = 13.4 kcal/mol; Figure 11). It is well-known that many arene complexes of ruthenium (including PAL complexes) have been tested clinically as anticancer agents. Probably the anticancer action starts from coordination of the metal with guanidine N7 in DNA duplex. The appearance of coordinatively unsaturated low-lying intermediates in the IRHR course (especially UV-induced)

Figure 11. Side views of stationary structures and their relative energies (kcal/mol) and hapticities. G


Organometallics

Article

Figure 12. Structures of possible intermediates exhibiting Ru−N coordination to guanine, susceptible to appear in the course of thermally induced IRHR. (4) (a) Oprunenko, Yu. F.; Gloriozov, I. P. J. Organomet. Chem. 2009, 694, 1195−1211. (b) Oprunenko, Yu. F.; Gloriozov, I. P. Russ. Chem. Bull., Int. Ed. 2010, 59, 2061−2067. (c) Oprunenko, Yu. F.; Gloriozov, I. P. Russ. Chem. Bull., Int. Ed. 2011, 60, 213−222. (d) Oprunenko, Yu. F.; Gloriozov, I. P. Russ. J. Phys. Chem. A 2012, 86, 979−986. (5) Pfletschinger, A.; Dolg, M. J. Organomet. Chem. 2009, 694, 3338− 3342. (6) (a) Dötz, K. H.; Stendel, J., Jr.; Müller, S.; Nieger, M.; Ketrat, S.; Dolg, M. Organometallics 2005, 24, 3219−3228. (b) Ketrat, S.; Müller, S.; Dolg, M. J. Phys. Chem. A 2007, 111, 6094−6102. (c) Hegele, P.; Santhamma, D.; Schnakenburg, G.; Fröhlich, R.; Kataeva, O.; Nieger, M.; Kotsis, K.; Neese, F.; Dötz, K. H. Organometallics 2010, 29, 6172− 6185. (7) (a) Jiménez-Halla, J. O. C.; Robles, J.; Sola, M. J. Phys. Chem. A 2008, 112, 1202−1213. (b) Jiménez-Halla, J. O. C.; Robles, J.; Sola, M. Organometallics 2008, 27, 5230−5240. (8) Nikitin, K.; Bothe, C.; Müller-Bunz, H.; Ortin, Y.; McGlinchey, M. J. Organometallics 2012, 31, 6183−6198. (9) (a) Deramchi, K.; Maouche, B.; Kahlal, S.; Saillard, J.-Y. Inorg. Chim. Acta 2011, 370, 499−504. (b) Deramchi, K.; Maouche, B.; Fadel, L.; Kahlal, S.; Saillard, J.-Y. Inorg. Chim. Acta 2012, 391, 98− 104. (10) Kündig, E. P.; Jeger, P.; Bernardinelli, G. Inorg. Chim. Acta 2004, 357, 1909−1919. (11) Freedman, D. A.; Gill, T. P.; Blough, A. M.; Koefod, R. S.; Mann, K. R. Inorg. Chem. 1997, 36, 95−102. (12) (a) Jahr, H. C.; Nieger, M.; Dötz, K. H. Chem. Eur. J. 2005, 689, 2662−2673. (b) Woolf, A.; Chaplin, A. B.; McGrady, J. E.; Alibadi, M. A. M.; Rees, N.; Draper, S.; Murphy, F.; Weller, A. S. Eur. J. Inorg. Chem. 2011, 1614−1625. (13) (a) Zhu, G.; Tanski, J. M.; Churchill, D. G.; Janak, K. E.; Parkin, G. J. Am. Chem. Soc. 2002, 124, 13658−13659. (b) Zhu, G.; Pang, K.; Parkin, G. J. Am. Chem. Soc. 2008, 130, 1564−1565. (14) Perekalin, D. S.; Karlsyan, E. E.; Petrovskii, P. V.; Borisova, A. O.; Lyssenko, K. A.; Kudinov, A. R. Eur. J. Inorg. Chem. 2012, 1485− 1492. (15) Hülsen, M.; Norman, P.; Dolg, M. J. Organomet. Chem. 2011, 696, 3861−3866. (16) Koeford, R. S.; Mann, K. R. J. Am. Chem. Soc. 1990, 112, 7287− 7293. (17) Seiders, T. J.; Baldridge, K. K.; O’Connor, J. M.; Siegel, J. S. Chem. Commun. 2004, 950−951. (18) Lehmann, R. E.; Bockman, T. M.; Kochi, J. K. J. Am. Chem. Soc. 1990, 112, 458−459. (19) Moreno, A.; Pregosin, P. S.; Veiros, L. F.; Albinati, A.; Rizzato, S. Chem. Eur. J. 2008, 14, 5617−5629. (20) Bartholomew, C. H.; Farrauto, R. J. Fundamentals of Industrial Catalytic Processes, 2nd ed.; Wiley-Interscience: New York, 2006. (21) Weissermel, K.; Arpe, H.-J. Industrial Organic Chemistry, 4th ed.; Wiley-VCH: New York, 2003. (22) Crabtree, R. H.; Parnell, C. P. Organometallics 1984, 3, 1727− 1731. (23) Loughrey, B. T.; Cunning, B. V.; Healy, P. C.; Brown, C. L.; Parsons, P. G.; Williams, M. L. Chem. Asian J. 2012, 7, 112−121.

the solvent can play a similar role as the anion in the CIP case and the activation barrier can also be reduced by the occurrence of solvent coordination. Thus, with these cautions in mind, one can conclude safely that, assuming weakly coordinating solvents, the IRHR activation barrier depends on the strength of ion pairing (CIP and SIP) and on the anion nature. In the case of SIP, the activation barrier of the intramolecular IRHR process is higher than in the case of CIP, due to the participation in the latter case of the counterion in the interaction with the coordinatively unsaturated organometallic fragment. This interaction reduces the metal unsaturation and reinforces the cation−anion Coulombic interaction by getting them closer to each other. Thus, in the case of CIP (low-polarity solvents), the more coordinating the anion, the lower the expected activation barrier. However, the size of the anion is also important. Small anions such as BF4− favor lower barriers. These results should also hold for photochemically induced IRHR processes, since the SIP mechanism involves structurally similar intermediates and transition states.

■

ASSOCIATED CONTENT

S Supporting Information *

Tables giving total energies and Cartesian coordinates of all the stationary structures discussed in this paper and a figures giving the optimized geometry of the (η6-C10H8RuCp+)(PF6−) ion pair in the presence of 15 solvent molecules. This material is available free of charge via the Internet at http://pubs.acs.org.

■

AUTHOR INFORMATION

Corresponding Author

*Y.F.O.: fax, + 7 (495) 932 8846; e-mail, oprunenko@nmr. chem.msu.su. J.-Y.S.: e-mail, [email protected]. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS We thank the Alexander von Humboldt Foundation (Bonn, Germany) for providing a workstation and auxiliary computer facilities for density functional theory calculations. J.-Y.S. thanks the Institut universitaire de France for support.

■

REFERENCES

(1) Berger, A.; Djukic, J.-P.; Michon, C. Coord. Chem. Rev. 2002, 225, 215−238. (2) (a) Oprunenko, Yu. F. Russ. Chem. Rev. 2000, 69, 683−704. (b) Gridnev, I. D. Coord. Chem. Rev. 2008, 252, 1798−1818. (3) Albright, T. A.; Hofmann, P.; Hoffmann, R.; Lillya, C. P.; Dobosh, P. A. J. Am. Chem. Soc. 1983, 105, 3396−3411. H


Organometallics

Article

(24) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. Rev. Lett. 1996, 77, 3865−3868. (25) Dyall, K. G. J. Chem. Phys. 1994, 100, 2118−2127. (26) Laikov, D. N. Chem. Phys. Lett. 2005, 416, 116−120. (27) (a) Laikov, D. N. Chem. Phys. Lett. 1997, 281, 151−156. (b) Laikov, D. N.; Ustynyuk, Yu. A. Russ. Chem. Bull., Int. Ed. 2005, 54, 820−826. (28) Flükiger, P.; Lüthi, H. P.; Portmann, S.; Weber, J. Molekel 4.3; Swiss Center for Scientific Computing, Manno, Switzerland, 2000− 2002; http://www.cscs.ch/molekel. (29) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, revision E.01; Gaussian, Inc., Wallingford, CT, 2004; http://www.gaussian.com. (30) Karlsyan, E. E.; Perekalin, D. S.; Petrovskii, P. V.; Lyssenko, K. A.; Kudinov, A. R. Russ. Chem. Bull., Int. Ed. 2008, 57, 2201−2203. (31) Yan, Y. K.; Melchart, M.; Habtermariam, A.; Sadler, P. Chem. Commun. 2005, 4764−4776. (32) Sato, H.; Kikumori, C.; Sakaki, S. Phys. Chem. Chem. Phys. 2011, 13, 309−313. (33) See for example: (a) Fulton, R. J.; Sklenak, S.; Bouwkamp, M. W.; Bergman, R. G. J. Am. Chem. Soc. 2002, 124, 4722−4737. (b) Macchione, A. Chem. Rev. 2005, 105, 2039−2073. (34) Honeychuck, R. V.; Hersh, W. H. J. Am. Chem. Soc. 1989, 111, 6056−6070. (35) Alamiry, M. A. H.; Brennan, P.; Coleman, A.; Long, C.; Pryce, M. T. Organometallics 2009, 28, 94−99. (36) Rieke, R. D.; Henry, W. P.; Arney, J. S. Inorg. Chem. 1987, 26, 420−427. (37) Zhu, G.; Janak, K. E.; Figueroa, J. S.; Parkin, G. J. Am. Chem. Soc. 2006, 128, 5452−5461. (38) Loughrey, B. T.; Cunning, B. V.; Healy, P. C.; Brown, C. L.; Parsons, P. G.; Williams, M. L. Chem. Asian J. 2012, 7, 112−121.

I


Influence of Ion Pairing in Inter-Ring Haptotropic Rearrangements in

Recommend Documents