Article pubs.acs.org/Organometallics
Metal−Ligand Bonding Situation in Ruthenophanes Containing Multibridged Cyclophanes Sérgio E. Galembeck,*,† Giovanni F. Caramori,*,‡ Alechania Misturini,‡ Leone C. Garcia,§ and Renato P. Orenha† †
Departamento de Química, FFCLRP, Universidade de São Paulo, Ribeirão Preto, 14040-901 São Paulo, Brazil Departamento de Química, Universidade Federal de Santa Catarina, Campus Universitário Trindade, CP 476, Florianópolis, 88040-900 Santa Catarina, Brazil § Instituto Federal de Educaçaõ , Ciência e Tecnologia de Santa Catarina IFSC Campus, São José, 88103-310 Santa Catarina, Brazil ‡
S Supporting Information *
ABSTRACT: Cation−π interactions in a set of ruthenophanes [Ru(η6-CnHn)(NH3)3]2+ (n = 16, 18, 20, 22, and 24) (1−9), containing multibridged cyclophanes as ligands, including [2.2]paracyclophane and its multibridged analogs, [2n]cyclophanes, are analyzed in terms of SAPT0/TZP and Su−Li EDA analyses. The calculations reveal that the coordination with cation [Ru(NH3)3]2+ affects the structures of [2n]ciclophane ligands, mainly the planarity of the coordinating ring. The EDA results show that the gradual addition of ethano bridges in [2n]cyclophanes tends to strengthen the cation−π interaction between [Ru(NH3)3]2+ and [2n]cyclophane. Both Su−Li EDA and SAPT0 are in line, suggesting that the cation−π interactions present a predominant covalent character in complexes 1−9.
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toward Ru2+ ion, therefore minimizing the repulsion between the π clouds in aromatic moieties of [2.2]paracyclophane. We have also observed that electron-donating substituents stabilize the cation−π interaction, while electron-withdrawing substituents weaken it. In addition, by means of two complementary energy decomposition schemes, we verified that the cation−π interactions in ruthenophanes are constituted mainly by orbital contribution (covalent character) than by electrostatic character.5 Recently, we have reported the electronic transport properties of ruthenophanes14 and how substituents affects such properties. The analysis of the total transmission functions showed that the substitution constrains the energies in which the probability of electronic transmission is significant, suggesting that the conductance at zero bias is dependent on the nature of the substituent. The negative differential resistance (NDR) effect was also observed, and it is dependent on both the nature of the substituent and the employed bias. The ruthenophanes studied showed nonohmic behavior, suggesting their potential use as electronic molecular devices such as switches, oscillators, or frequency multipliers. Continuing our interest in ruthenium chemistry,15,16 in this work we investigate whether the gradual increase in the number of bridges, going from [22](1,4)cyclophane to [26](1,2,3,4,5,6)-
INTRODUCTION Cyclophanes are versatile molecules, specially due to their intrinsic molecular structure, which comprises two or more aromatic moieties held by saturated or unsaturated bridges.1 An important property of cyclophanes is their strong π-donor ability, which comes from the π−π interactions between the aromatic rings.2−4 Such a feature makes cyclophanes good πligands, able to coordinate with transition metals, and producing complexes held by cation−π interactions.5,6 Among complexes containing cyclophane ligands, those with [2n]-cyclophanes are intriguing since they can interact with one or more transition metals simultaneously, leading to the formation of multinuclear transition-metal complexes and also building up metallic clusters.7 The combination of ruthenium ions and [2n]-cyclophane ligands forms complexes called ruthenophanes, which have been synthesized and characterized by Boekelheide and coworkers,8−13 who claimed that ruthenophanes are suitable as conducting polymers. We have a particular interest to comprehend the metal−ligand bonding situation in such complexes, including the entailed electronic properties. We have already determined the role of long-distance substitution and protonation at [2.2]-paracyclophane ligand in the nature of ruthenium−arene interactions.5 Our results revealed that the coordination with ruthenium(II) increases the nonplanarity of the ring bound to the ruthenium atom in [2.2]-paracyclophane, indicating the presence of an outflow of the electron density © XXXX American Chemical Society
Received: May 26, 2017
A
DOI: 10.1021/acs.organomet.7b00393 Organometallics XXXX, XXX, XXX−XXX
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Organometallics
Figure 1. Optimized structures of ruthenophanes [Ru(η6-CnHn)(NH3)3]2+ (n = 16) (1), (n = 18) (2−4), (n = 20) (5−7), (n = 22) (8), and (n = 24) (9), containing multibridged [2n]cyclophane ligands, [22](1,4)cyclophane (a), and its multibridged analogues with 3−6 ethano bridges [23](1,2,3)cyclophane (b), [23](1,2,4)cyclophane (c), [23](1,3,5)cyclophane (d), [24](1,2,3,4)cyclophane (e), [24](1,2,3,5)cyclophane (f), [24](1,2,4,5)cyclophane (g), [25](1,2,3,4,5)cyclophane (h), and [26](1,2,3,4,5,6)cyclophane “superphane” (i) at BP86-D3/def2-TZVP. DF-SAPT calculations by use of Douglas−Kroll−Hess relativistic correction at second-order (DKH2).35,36 The all-electron TZP-DKH basis set bult by Jorge et al.37,38 was used. DF-SAPT-DKH2 calculations were made by PSI4 1.1.39 Su−Li EDA was performed by using MP2/def2-TZVP26 model as implemented in GAMESS-US version r3-2013.40 The relativistic effects on the Su−Li EDA were included by means of all-electron Sapporo’s basis set41,42 in conjunction LUT-IOTC scheme.43−45 One of the most rigorously formulated energy component analysis is SAPT. The perturbation expansion of the interaction energy leads to a sum of terms that can be recognized as electrostatic, Eelst, induction, Eind, dispersion, Edisp, and exchange repulsion, Eexch, energies. Different choices of truncation of the expansion are possible for the SAPT-based wave function. One of them is the SAPT0 approach, in which the intermolecular interactions are described in terms of second-order perturbation theory, and the intramolecular correlation is neglected.18,19,46 In Su−Li EDA, the interaction energy is decomposed into a number of physically meaningful components such as electrostatic, exchange, repulsion, and polarization:
cyclophane, superphane, has in fact any direct effect on the nature and magnitude of the cation-π interactions between ruthenium(II) and [2n]-cyclophane ligands. For that reason, the set of complexes [Ru(η6-CnHn)(NH3)3]2+ (n = 16, 18, 20, 22, and 24) (1−9) was studied (Figure 1). The nature of cation−π interactions was characterized by using two different energy decomposition schemes, including Su−Li EDA 17 and SAPT0,18−20 in which [2n]-cyclophane ligands and [Ru(NH3)3]2+ cation were considered as interacting fragments (Figure 1).
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COMPUTATIONAL METHODS
Geometries of complexes [Ru(η6-Cn Hn)(NH3)3]2+ (n = 16, 18, 20, 22, and 24) (1−9) were optimized by using the model BP86-D321−25/ def2-TZVP.26 All-electron relativistically recontracted basis sets derived from Ahlrichs def2-TZVP were employed,27 as implemented in ORCA v3.0.1 package.28 Scalar-relativistic effects were included by means of zero-order regular approximation (ZORA).27,29 The interaction energy for (1) was calculated by RI-SCS-MP230 /def2TZVPP,26 by Turbomole 6.3 software.31 DF-SAPT020 was calculated with all-electron TZP basis sets,32 built by Jorge et al. DF computations use def2-TZVP auxiliary basis.33 All core orbitals were kept frozen. SAPT calculations were made by PSI4 program.34 The interaction energy between [Ru(NH3)3]2+ and [22](1,4)cyclophane in (1) calculated by SAPT0/TZP is very close to the value obtained by RI-SCS-MP2/def2-TZVPP. Relativistic effects were also included in
ΔE int(HF) = ΔEele + ΔEex + ΔErep + ΔEpol
(1)
ΔE int(MP2) = ΔEele + ΔEex + ΔErep + ΔEpol + ΔEdisp
(2)
Physically, the electrostatic term, ΔEele, corresponds to the interaction energy for the process of bringing the fragments into the final configuration of the molecule, but keeping constant their wave B
DOI: 10.1021/acs.organomet.7b00393 Organometallics XXXX, XXX, XXX−XXX
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Organometallics Table 1. Selected Geometric Parameters of Ruthenophanes 1−9a dihedrals (°)
distances (Å)
comp.
bridge position
DX1
DX2
Db
(X1−X2)
(X1−Ru)
(Cbh−Cbh ′)
(Cb−Cb′ )
1 2 3 4 5 6 7 8 9
1,4 1,2,3 1,2,4 1,3,5 1,2,3,4 1,2,3,5 1,2,4,5 1,2,3,4,5 1,2,3,4,5,6
13.47 17.95 18.50 5.98 21.30 12.13 19.55 19.75 1.46
12.72 12.09 14.42 5.26 11.63 9.83 11.93 9.69 0.35
13.18 16.58 1.08 0.28 9.95 0.83 0.89 0.55 0.38
2.838/3.093b 3.321 2.839 2.711/2.800 2.882 2.689 2.720/2.688 2.653/2.650 2.582/2.628
1.590 1.666 1.695 1.697 1.700 1.699 1.733 1.713 1.777
2.669 2.738/2.518 2.631 2.672 2.680/2.541 2.700/2.636/2.494 2.612 2.634/2.552/2.568 2.576/2.588
1.607 1.602/1.564 1.612 1.627 1.612/1.588 1.632/1.616/1.597 1.611 1.629/1.595/1.613 1.611
Including the largest out-of plane dihedral angles of cyclophane rings, DX1 and DX2, and bridges Db distances between ring centroids, (X1−X2), ′ ) and bridge distance between Ru2+ and cyclophane ring centroid, (X1−Ru), and average distance between equivalent bridgehead carbons, (Cbh−Cbh carbons (Cb−C′b). bValues in italics depict geometric parameters of the isolated [2n]cyclophanes.47−51 a
Table 2. Su−Li-EDA Analysis (kcal·mol−1) for Complexes 1−9 Using MP2/def2-TZVP Modela comp. 1 2 3 4 5 6 7 8 9 a
ΔEele −138.45 −139.48 −137.47 −134.53 −137.87 −135.36 −135.60 −130.85 −115.95
(20%) (19%) (20%) (20%) (20%) (20%) (20%) (20%) (20%)
ΔEex −260.39 −270.85 −256.90 −249.71 −258.32 −250.37 −251.25 −243.38 −202.11
(37%) (38%) (37%) (37%) (37%) (37%) (37%) (37%) (37%)
ΔErep
ΔEpol −214.76 −222.26 −212.64 −204.60 −215.08 −206.06 −210.14 −205.88 −178.10
534.57 556.03 526.51 509.86 529.13 510.75 514.55 495.21 405.24
(31%) (31%) (31%) (30%) (31%) (30%) (31%) (31%) (31%)
ΔEdisp −84.04 −89.42 −84.36 −84.44 −85.45 −84.90 −83.39 −82.11 −73.63
(12%) (12%) (12%) (13%) (12%) (13%) (12%) (12%) (13%)
ΔEint(HF)
ΔEint(MP2)
−79.03 −76.56 −80.51 −78.97 −82.13 −81.04 −82.43 −84.90 −90.92
−163.07 −165.98 −164.87 −163.41 −167.58 −165.94 −166.33 −167.01 −164.55
The percentage of stabilizing contributions is shown in parentheses. ΔEy =
(ΔEy) × 100 (ΔEele + ΔEex + ΔEpol + ΔEdisp)
(%)
functions as in isolated fragments. In Su−Li EDA, the exchange repulsion energies consist of both exchange, ΔEex, and repulsion, ΔErep contributions. In HF level, the former is given in terms of exchange integrals involving r1ij, while the latter involves integrals over the kinetic energy and electron−nuclear Coulombic operators. The term ΔErep is a mixture of electron−electron repulsion and electron−nuclear and electron kinetic energy effects. The sum of exchange and repulsion terms in Su−Li EDA corresponds for RHF cases to the exchange− repulsion term in Kitaura−Morokuma EDA. The polarization term, ΔEpol, involves interactions between occupied and unoccupied orbitals within the same fragment and also interactions between occupied orbitals from one fragment with the unoccupied orbitals of the other fragments and vice versa. The polarization contribution in Su−Li EDA includes both polarization, charge transfer and mixing terms of Kitaura−Morokuma scheme. In general, in other decomposition methods, exchange and repulsion are grouped into the so-called Pauli repulsion component. Dispersion energy, ΔEdisp (eq 2), is derived through correlation methods such as MP2 or CCSD(T). The dispersion term in Su−Li EDA is in fact the MP2 correction to Hartree−Fock interaction energy, including higher-order corrections to the electrostatic, exchange−repulsion, and polarization energies.
the coordinating ring in [2n]cyclophane ligands (Table 1). The largest dihedral values describing the out-of-plane distortions of both benzene rings (DX1, coordinated to [Ru(NH3)3]2+, and DX2, noncoordinated ring, see Figure 1) reveals that not only the number of bridges but also their relative location affect the planarity of rings. Obviously, the main characteristic of multibridged [2n]cyclophane is retained with the coordination. For instance, complexes 1−4, which contain only 2 or 3 ethano bridges, relieve strain by distorting their aromatic rings from planarity, while in multibridged [2n]cyclophane such as 5−9 such effect is much less significant, since the aromatic portions are more tethered by the large number of ethano bridges. According to Table 1, complexes 4 and 9 exhibit the smallest DX1 and DX2 dihedral values when contrasted with those of 1, therefore diminishing the boat-shaped geometry of cyclophane decks. However, systems as 3 and 5−8 retain the boat-shaped geometry, with DX1 and DX2 values larger than those of 1 (Table 1). Another important characteristic of multibridged [2n]cyclophane is the decrease in the distance between the aromatic moieties as additional ethano bridges are added. For instance, the inter-ring distances (X1−X2) in the most symmetric complexes (1, 4, and 7−9) decreases with the gradual addition of ethano bridges, keeping the same feature as in [2n]cyclophane ligands. A tinny deviation is observed for 7, in which the (X1−X2) distance is slightly larger than that in 4. Naturally, it is not a general rule for all multibridged [2n]cyclophanes, since depending on the bridge position the aromatic portions have more degrees of freedom to relieve the
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RESULTS AND DISCUSSION Geometries. The structures of [2n]cyclophane ligands are considerably strained, but thermally stable, as previously reported by Boekelheide.47−51 Generally, the strain in [2n]cyclophane is relieved by distorting benzene rings from planarity as well as the ethano bridges from eclipsed arrangement. The calculated structures of complexes 1−9 reveals that the coordination with cation [Ru(NH3)3]2+ affects the structures of [2n]ciclophane ligands, mainly the planarity of C
DOI: 10.1021/acs.organomet.7b00393 Organometallics XXXX, XXX, XXX−XXX
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Table 3. SAPT0/TZP Analysis (kcal·mol−1) for Compounds Containing Cyclophanes with Different Number/Position of the Bridges 1−9a comp. 1 2 3 4 5 6 7 8 9
Eelst −202.59 −204.47 −200.29 −193.79 −201.62 −194.79 −199.75 −189.22 −162.35
(43%) (43%) (43%) (43%) (43%) (43%) (44%) (42%) (42%)
Eexch b
315.01 325.51 309.56 297.98 311.18 298.22 304.52 289.15 233.71
(2.09) (2.14) (2.02) (1.97) (1.99) (1.93) (1.97) (1.84) (1.49)
Eind c
−204.88 −210.99 −202.87 −196.38 −204.67 −197.46 −199.81 −196.65 −172.42
Edisp
(44%) (44%) (44%) (44%) (44%) (44%) (44%) (44%) (44%)
b
−58.52 −61.94 −59.33 −59.14 −61.12 −60.36 −59.58 −60.34 −56.01
(13%) (13%) (13%) (13%) (13%) (13%) (13%) (14%) (14%)
ESAPT0 b
ECT
−150.99 −151.90 −152.94 −151.33 −156.23 −154.39 −154.62 −157.06 −157.07
−25.81 −26.01 −23.98 −20.78 −24.17 −20.79 −25.05 −19.86 −12.26
(13%)d (12%) (12%) (11%) (12%) (11%) (13%) (10%) (7%)
Relative contribution of the componentes, in parentheses. bContribution (%) to the total attractive energy. c|Eexch/ESAPT0| dRelation between ECT and Eind (%) a
37% of attractive interactions, except for compound 9 (about 35.5%). The polarization is around 31% in all cases. The electrostatic and dispersion components, respectively, correspond to about 20 and 12%. These data show that the cation−π interaction in the studied compounds is mainly of a covalent nature, since the polarization and exchange components are higher than the electrostatic one. As the nature of the interaction is mostly covalent, it is dependent on the contributions of the terms of polarization and exchange. The presence of more bridges amplifies this effect. However, it is important to notice that the polarization occurs in both directions of ligand → metal and ligand ← metal, and consequently, the increase in the number of bridges promotes a redistribution of the electron density of the system through the bridges, which justifies the absence of toothpaste-tube effect. The inclusion of scalar-relativistic effects on the Su−Li EDA analysis was performed for complexes 1, 4, and 7, by using the all-electron Sapporo’s basis set41,42 in conjunction LUT-IOTC scheme.43−45 The results presented in Table S2 reveal a similar behavior, indicating that by increasing the number of bridges a more significant cation−π interactions are obtained. Therefore, the inclusion of such effects does not modify the observed qualitative tendency. In line with Su−Li EDA, SAPT0 shows that the increase of number of bridges promotes a larger interaction between cation [Ru(NH3)3]2+ and the cyclophane ligand (Table 3). As exception, from 8 to 9, ESAPT0 is practically the same. However, in contrast with Su−Li EDA, SAPT0 does not show a correlation between the distortion of the ring that is interacting with the cation and the interaction energy, ESAPT0, for compounds with the same number of bridges. But, the electrostatic, Eelst, induction, Eind ,and exchange, Eexch, components present a correlation with the distortion of the ring (Table 3). Also, the absolute value of the ratio between Eexch and ESAPT0 presents the same relation, indicating an increase of Pauli repulsion with the distortion of the ring under analysis (Table 3). Results for SAPT0-DKH2 calculations for complexes 1, 4, and 7 indicate that the inclusion of these corrections are not significant and do not affect the qualitative interpretation of results (Tables 3 and S1). These observations are in line with a study that compares RECP and DKH2 relativistic approximations, which conclude that the effect of these treatments are similar.16 The interaction energy calculated by Su−Li EDA and SAPT0 present a correlation only for isomers or compounds with the same number of bridges. Compounds 8 and 9 present a lower
inter-ring strain, as observed for complexes 2 and 5. The calculations also reveal that in complexes 1, 2, and 5 the ethano bridges are staggered while in 3, 4, and 6−9 they are less distorted and more eclipsed which is an direct consequence of the interplay between the through-space and through-bond interactions and their symmetry restrictions which decouple the hyperconjunction as already observed by Heilbronner.52,53 It should be expected that the systematic increase in the number of ethano bridges which brings both aromatic moieties closer together with inter-ring distances (X1−X2) smaller than the sum of van der Waals radii would destabilize the π electrons distribution pumping them to the external side of aromatic moieties in a sort of toothpaste-tube effect52,53 as coined by Heilbronner. If that were the case, then we should expect a shortening of metal−ligand distances (Ru−X1) between cation [Ru(NH3)3]2+ and [2n]cyclophane surface. Nonetheless, a systematic increase of the (Ru−X1) values is observed with the gradual addition of ethano bridges, especially for the most symmetrical species (1, 4, 7, and 9), which is entirely in line with the Su−Li EDA analysis and revealed that 9 exhibits the smallest electronic repulsion term as well as the less stabilizing electrostatic and exchange contributions (Table 2) as discussed in the next section. Bonding Analysis. The Su−Li EDA results (Table 2) unveil that in comparison with 1 (ΔEint(MP2) = −163.07 kcal· mol−1), the addition of ethano bridges in [2n]cyclophanes tends to strengthen the cation−π interaction between [Ru(NH3)3]2+ and [2n]cyclophane. For instance, by considering the most symmetric complexes (1, 4, 7, and 9), the total interaction energy, ΔEint(MP2), values are −163.07, −163.41, −166.33, and −164.55 kcal·mol−1, respectively, revealing that the addition of more ethano bridges provides only a small amount of stabilization to the metal−ligand bonds, contrary to what should be expected. Curiously, the distances (X1−Ru) and (X1−X2) (Table 1) tend to increase and to decrease, respectively, along the series (1, 4, 7, and 9), unveiling that in this case the through-bond and through-space interactions should prevail over the cation−π as previously observed by Heilbronner.52,53 It is also important to emphasize that all Su− Li EDA components follow the same trend in this series of complexes. For complexes containing [2n]cyclophane ligands with the same number of bridges, the ethano bridge position affects the magnitude of the cation−π interactions, so the more the coordinating ring distorts from planarity, the more stabilizing the interaction becomes (Table 2). The percentage contribution indicates that the exchange component accounts for about D
DOI: 10.1021/acs.organomet.7b00393 Organometallics XXXX, XXX, XXX−XXX
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SAPT0 interaction energy, indicating that the closeness of the rings decreases the interaction energy between both fragments, probably by decreasing the electron density in the ring that interacts with Ru. The main factor of this change is the reduction in the exchange−repulsion energy. Also, the charge transfer energy increases significantly. Both facts reinforce the hypothesis that there are significant changes in the electron density in the region of the cyclophane that interacts with [Ru(NH3)3]2+. The same behavior for 8 and 9 is observed for Su−Li EDA, but it is not so pronounced as for SAPT0. Moreover, from SAPT0 complexes 1−9 show a cation−π interaction which is predominantly covalent due the large weight of induction energy in attractive total energy. The large weight of electrostatic component in these cases also reflects the overlap between the charge clouds of electron distribution of soft metal ruthenium and π cloud from ring DX1 in the [2n]cyclophane. According to the classification proposed by Hobza et al.,54 these complexes are electrostatic dominated, or the electrostatic energy is at least twice as large as the dispersion component.
Article
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.7b00393. Relativistic results for SAPT0-DKH2 and MP2-LUTIOTC/Sapporo-DK-DZP-2012 calculations (PDF) Cartesian coordinates of complexes 1−9 (ZIP)
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AUTHOR INFORMATION
Corresponding Authors
*E-mail:
[email protected]. Phone: +55 (16)3315-3765. Fax: +55 (16)3315-4838. *E-mail:
[email protected]. Phone: +55 48 3721-3644. ORCID
Sérgio E. Galembeck: 0000-0001-5018-4643 Giovanni F. Caramori: 0000-0002-6455-7831
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Notes
The authors declare no competing financial interest.
CONCLUDING REMARKS The calculations reveal that in complexes 1−9 the coordination with cation [Ru(NH3)3]2+ affects the structures of [2n]ciclophane ligands, mainly the planarity of the coordinating ring. In multibridged [2n]cyclophanes, a decrease of the distance between the aromatic moieties is observed as more ethano bridges are added. A systematic increase of the metal− ligand distance (Ru−X1) is observed with the gradual addition of ethano bridges, particularly for the most symmetrical species (1, 4, 7, and 9), which is entirely in line with EDA analyses, pulling down the hypothesis of the toothpaste-tube effect. The Su−Li EDA results show that the addition of ethano bridges in [2n]cyclophanes tends to strengthen the cation−π interaction between [Ru(NH3)3]2+ and [2n]cyclophane. The results also reveal that cation−π interactions in the studied compounds are mainly of covalent nature, since the polarization and exchange components are higher than the electrostatic one. In line with Su−Li EDA, SAPT0 calculations show that by increasing the number of bridges the cation−π interaction becomes stronger, as revealed by more negative ΔEint(MP2) in Su−Li EDA and ESAPT0 values. The interaction energy calculated by Su−Li EDA and SAPT0 are in significant agreement, particularly for compounds with the same number of bridges. The obtained results reinforce the hypothesis that there are significant changes in the electron density in the region of the cyclophane that interacts with [Ru(NH3)3]2+. SAPT0/TZP indicates that the most important attractive terms are electrostatic and induction. Similar to the observation of Caramori et al.,5 SAPT0 indicates that ruthenium-[2n]cyclophanes interaction is electrostatically dominated by the large electrostatic component, compared to dispersion energy. Both Su−Li EDA and SAPT0 are in line, suggesting that the cation−π interactions are predominantly covalent in compounds 1−9. The first explains it due the larger weight of Epol and Eex components compared to that of Eele for ΔEint(MP2). The second is because of larger weight of Eind compared to that of ESAPT0, with emphasis for the also significantly weight of Eelst due the overlap between the charge clouds: electron density of Ru and π electrons of cyclophane ring. Relativistic corrections for Su−Li EDA and SAPT0 are not expressive, and for the studied compounds, it is not necessary to consider these treatments.
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ACKNOWLEDGMENTS We thank the Brazilian agencies Coordenaçaõ de Aperfeiçoá Superior (CAPES), Programa de mento de Pessoal de Nivel Apoio à Pós-Graduaçaõ (PROAP), Conselho Nacional de ́ Desenvolvimento Cientifico e Tecnológico (CNPq) (Grant 304447/2010-2), and São Paulo Research Foundation (FAPESP, Fundaçaõ de Amparo à Pesquisa do Estado de São Paulo) (Grants 2008/02677-0 and 2014/50265-3) for financial support. S.E.G. thanks CNPq for research fellowships (Grants 304393/2013-4 and 308254/2016-3). R.P.O. thanks FAPESP for graduate fellowships (Grants 2011/20351-7 and 2015/ 15176-2). G.F.C. thanks CNPq (Grant 302408/2014-2) for the research fellowship and the Centro Nacional de Supercomputaçaõ CESUP-UFRGS for the excellent computational service provided. We also acknowledge Ali Faez Taha for technical assistance.
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REFERENCES
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DOI: 10.1021/acs.organomet.7b00393 Organometallics XXXX, XXX, XXX−XXX
