Unconventional Facile Way to Metallanaphthalenes from Metal

Article pubs.acs.org/Organometallics

Unconventional Facile Way to Metallanaphthalenes from Metal Indenyl Complexes Predicted by DFT Calculations: Origin of Their Different Thermodynamics and Tuning Their Kinetics by Substituents Jinglan Fan, Xuerui Wang, and Jun Zhu* State Key Laboratory of Physical Chemistry of Solid Surfaces, Fujian Provincial Key Laboratory of Theoretical and Computational Chemistry, Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, People’s Republic of China S Supporting Information *

ABSTRACT: Metallaaromatics have attracted considerable interest from both experimentalists and theoreticians over the past three decades. However, most studies in this field have focused on metallabenzene, in which a CH group is replaced by a transition metal fragment. In comparison with monocyclic metallabenzenes, bicyclic metallanaphthalenes are rather limited. Thus, it is urgent to explore more synthetic approaches to this less developed system. One of the difficulties in the synthesis of metallanaphthalenes could be due to its low thermodynamic stability relative to the metal indenyl complexes. Here we present a thorough theoretical investigation by quantum chemical calculations to explore the possibility of realizing traditionally “unstable” metallanaphthalenes by an isomerization of traditionally “stable” metal indenyl complexes. We systematically investigated how different substituent(s) at different position(s) on the metallacycle affect such a rearrangement. Our results indicate that although indenyl complexes are known to be thermally robust, it should be possible to shift the thermodynamic and kinetic balance toward the metallanaphthalene complexes by choosing proper ancillary substituents on the metallabicycle, which is in sharp contrast to the traditional facile isomerization of metallabenzenes to cyclopentadienyl (Cp) complexes. Therefore, our findings suggest a novel avenue to metallanaphthalenes.

■

INTRODUCTION

can undergo migratory insertion reactions to give cyclopentadienyl complexes, 7 and electron-donating groups (EDGs) on the metallacycle can stabilizing metallabenzene with respect to the formation of the corresponding Cp complexes.8 Lin, Jia, and their co-workers successfully synthesized and isolated three rhenabenzenes by introducing alkoxy groups to the rhenabenzene ring in 2010.9 One may wonder whether metal indenyl complexes can be used as starting material for the formation of metallanaphthalenes considering the similarity of metallabenzene and metallanaphthalene. Our ongoing interest in aromaticity has led us to investigate these metallabicycles.10 Here we report a density functional theory (DFT) study on an unconventional facile way to metallanaphthalenes by an isomerization of metal indenyl complexes (Figure 2).

Metallaaromatics have long intrigued synthetic and theoretical chemists on account of their aromaticities and unusual reactivities as the chemical properties of both organometallic complexes and aromatic organic compounds can be displayed. Metallabenzene,1−3 one of the most typical examples, has been extensively studied both experimentally and theoretically since it was first predicted by Hoffman in 1979 and synthesized in 1982 by Roper.4 However, metallanaphthalenes, organometallic compounds formed by substitution of a CH group in naphthalene by an isolobal transition metal fragment, are less developed, and only very limited species5,6 are isolated (Figure 1) until now due to their low thermodynamic stability, which leads to thermodynamically more stable metal indenyl complexes.22 Previous studies indicate that metallabenzenes

■

COMPUTATIONAL METHODS

Molecular structures of all the complexes were fully optimized at the B3LYP11 level of density functional theory without any constraints. The PCM model12 with benzene as the solvent and the UAKS cavity were used to optimize all of the structures. Frequency calculations were performed at the same level of theory to confirm that all stationary points were minima (no imaginary frequency) or transition Figure 1. Reported examples of isolated metallanaphthalenes (I and II). TpMe2 = hydrotris(3,5-dimethylpyrazolyl)borate). © 2014 American Chemical Society

Received: March 9, 2014 Published: April 23, 2014 2336

dx.doi.org/10.1021/om500245q | Organometallics 2014, 33, 2336−2340

Organometallics

Article

Figure 2. Proposed isomerization of the osmium indenyl complex to osmanaphthalene. states (one imaginary frequency). Specifically, the imaginary frequencies of three TS1 with zero, one, and two methoxy groups in Figure 5a are 373.9i, 347.0i, and 333.4i, respectively. Similarly, they are

Figure 5. (a) Energy profiles calculated for the conversion of metal indenyl complexes to osmanaphthalenes. The Gibbs free energies are given in kcal mol−1. (b) Selected bond distances (Å) and Wiberg bond indices (in italics) of the metal−carbon bonds and carbon−carbon bonds in the transition states. order to examine the effect of basis sets, we employed a larger 6-311+ +G(d,p) basis set17 to perform single-point calculations on the complexes 5 and 6 (Figure 3) and TS1 (R1 = R2 = H, Figure 5a). The additional calculations show that the basis set dependence is small. For example, using the 6-31+G(d) basis set for C, O, and H atoms and the LanL2DZ basis set for the other atoms with benzene as the solvent, the relative energies of TS1 and 6 to 5 are 32.5 and −11.5 kcal mol−1, respectively. Using the larger 6-311+G(d,p) basis set in the benzene solvent, the relative energies are 32.8 and −10.7 kcal mol−1, respectively. All the calculations were performed with the Gaussian 0318 software package. The natural bond orbital analysis,19 as implemented in Gaussian 03, was also used to obtain Wiberg bond indices (bond orders).20 Structures were visualized by the CYLview program.21

Figure 3. Reaction energies for the formation of complexes 2, 4, 6, and 8 from metal Cp and indenyl complexes 1, 3, 5, and 7. The Gibbs free energies are given in kcal mol−1. The selected MC and M−C bond lengths (Å) and Wiberg bond indices (in italics) are listed on the right.

■

RESULTS AND DISCUSSION Effect of Thermodynamic Factors on the Conversion of Indenyl Complexes to Corresponding Metallanaphthalenes. At first sight, one could consider that metallanaphthalenes might be similar to metallabenzenes, which are readily converted into metal Cp complexes. Thus, they should transform into thermodynamically more stable metal indenyl complexes. However, DFT calculations indicate that osmanaphthalene 6 is more thermodynamically stable than corresponding metal indenyl complex 5 by −11.5 kcal mol−1 (Figure 3), which is in sharp contrast to the previous calculations.22 To probe the origin of the different thermodynamic stabilities of osmanaphthalenes, we investigate the effect of the ligand and metal center. As shown in Figure 3, our results suggest that the ligands attached to the metal center have a significant effect on the relative stability of osmanaphthalenes in

Figure 4. (a) Shortest H···H distance (Å) in the optimized nonplanar structure of osmanaphthalene complex with an OMe substituent at the C7 position. (b) Structure of the optimized osmanaphthalene complex with a PMe3+ substituent at the C6 position. 364.0i, 351.3i, and 329.2i for three corresponding TS2, respectively. Calculations of intrinsic reaction coordinates13 were also performed on transition states to confirm that such structures are indeed connecting two minima. The effective core potentials of Hay and Wadt with double-ζ valence basis sets (LanL2DZ) were used to describe Os, Ru, Cl, and P,14 while the standard 6-31+G(d)15 basis set was used for C, O, and H atoms. Polarization functions were also added for Cl(ζ(d) = 0.514), P(ζ(d) = 0.340), Ru(ζ(f) = 1.235), and Os(ζ(f) = 0.886).16 In 2337

dx.doi.org/10.1021/om500245q | Organometallics 2014, 33, 2336−2340

Organometallics

Article

a stabilizing effect at the C6 position, and almost no effect at the C4 and C5 positions were observed. The stabilization of the PMe3+ substituent at the C6 position could be due to the weaker steric repulsion between the PMe3+ substituent and the H atom attached to the metallabicycle (Table S1 and Figure 4b). It is well known that the staggered conformer of ethane with the shortest H···H distance of 2.54 Å is more stable than the eclipsed conformer with that of 2.36 Å by 12 kJ mol−1 because of the steric effect.25 As shown in Figure 4, the shortest H···H distances between the PMe3+ substituent and the H atom attached to C6 is 2.347 Å, indicating that the repulsion is smaller than that at other osmanaphthalenes (for example, 2.074 Å at the C3 position, 2.150 Å at the C4 position, and 2.045 Å at the C7 position). Therefore, the corresponding indenyl complex is destabilized, leading to a stabilizing effect for the PMe3+ substituent at the C6 position. Effect of Kinetic Factors on the Conversion of Indenyl Complexes to Corresponding Metallanaphthalenes. As mentioned above, an osmanaphthalene with a methoxy substituent at the C1 or C3 position shows amazing stability. In this section we investigated the kinetic factors of the conversion. It is well known that thermodynamically stable species might not be isolated at room temperature if the reaction barrier is high. Therefore, it is necessary to investigate the kinetics of the conversion of indenyl complexes to corresponding metallanaphthalenes. As shown in Figure 5, two pathways were examined. In path 1, the PMe3 ligand first coordinates to the metal center of an η5-indenyl complex, leading to η1-indenyl complex IN1, followed by the isomerization to an osmanaphthalene through TS1. In path 2, the coordination of the PMe3 ligand to the metal center occurs after the isomerization of η5-indenyl complex RE to η1-indenyl complex IN2. For the unsubstituted η5-indenyl complex, the reaction barriers in both pathways are computed to be 32.5 kcal mol−1. When one methoxy group is introduced at the C1 position, the reaction barrier (26.8 kcal mol−1) is still slightly high, although the product is stabilized significantly. As shown in Table 1, the C3 position is the second choice to stabilize an osmanaphthalene. So when two methoxy groups are introduced at the C1 and C3 positions, the stabilization should be enhanced. Indeed, the product is further stabilized slightly. More importantly, the reaction barrier becomes as low as 23.5 kcal mol−1. Thus, the isomerization becomes favorable both thermodynamically and kinetically, leading to a facile way to an osmanaphthalene. A plausible explanation is given for the observations. In a textbook on organometallic chemistry,24 two types of metal carbenes can be classified: the Fischer and the Schrock type (Figure 6). The electron-deficient Fischer carbene carbon can be stabilized by the lone pair of a π-donor substituent. Therefore, an electron-donating substituent at the carbene carbon of a given metal carbene complex plays a stabilizing role, as illustrated in Figure 6. In the transition states (Figure 7), Os−C8 bonds are significantly lengthened. Thus, the C8 carbon could be regarded as a vinyl carbon. As the Os−C1 bond retains some double-bond character, the C1 carbon could be considered as a carbene carbon. An o-methoxy substituent should stabilize the carbene carbon of the transition states. A psubstituent is normally expected to give a similar effect to that of an o-substituent. Therefore, the transition states with methoxy substituents at the C1 and C3 positions have been stabilized, leading to a significant decrease of the reaction barriers. Indeed, the Os−C bond lengths of the transition states

comparison with osmium indenyl complexes. When the PMe3 ligand was added to replace one chloride ligand, osmanaphthalene becomes less stable than the osmium indenyl complex by 5.8 kcal mol−1. The relative stability of ruthenanaphthalene relative to the ruthenium indenyl complex was also examined. Interestingly, the ruthenium indenyl complex becomes more stable than ruthenanaphthalene by 9.2 kcal mol−1. When the indenyl ligand is changed to the Cp ligand, the instability of osmabenzene relative to the Cp complex is enhanced by 7.4 kcal mol−1 in comparison with that of osmanaphthalene relative to the indenyl complex, which could be attributed to the indenyl effect.23 In addition, all these data could be rationalized by the strength of the MC bond. Specifically, osmanaphthalene 6 has a stronger OsC bond than osmanaphthalene 2 due to the more electron rich metal center caused by the negative charge. In comparison with osmanaphthalene 6, ruthenanaphthalene 8 has less diffuse d orbitals, leading to weaker metal−carbon double bonds. Therefore, we choose complexes 5 and 6 as the reaction models for the following study on osmanaphthalenes. The effect of substituents on such an isomerization is also investigated. The EDG and the electron-withdrawing group (EWG) were both examined. We first systematically studied how the methoxy substituent influences the stability of osmanaphthalenes relative to the metal indenyl complexes. As shown in Table 1, the methoxy substituent at the C1, C3, and Table 1. Substituent Effect of OMe and PMe3+ on the Isomerization of Indenyl Complexes to the Corresponding Osmanaphthalenesa

R

H

C1 C2 C3 C4 C5 C6 C7

−11.5 (−26.5)

OMe −20.2 −13.8 −16.6 −9.5 −10.9 −15.1 −4.5

(−36.0) (−28.4) (−31.0) (−24.6) (−25.2) (−30.9) (−19.4)

PMe3+ −1.6 (−16.9) −7.1 (−21.1) 1.7 (−12.1) −11.5(−25.5) −11.9 (−25.5) −15.2 (−28.7) 6.1 (−10.1)

a

Relative Gibbs free energies and electronic energies (in parentheses) at 298 K are given in kcal mol−1.

C6 positions has a significant stabilizing effect, a destabilizing effect at the C7 position, and almost no effect at other positions on metallanaphthalene. It is understandable that the EDG at the ortho or para position can stabilize a metal carbene complex;24 the destabilizing effect of the methoxy group at the C7 position can be attributed to the nonplanar structure (Figure 4a, dihedral angle ∠C9−C8−Os−C1 = 30.1°, ∠C9− C8−C7−C6 = 13.2°) and the H···H repulsion in osmanaphthalene, reducing the aromaticity of the two rings. The effect of an electron-withdrawing substituent, PMe3+, was also examined. As shown in Table 1, the position of PMe3+ on the metallabicycle influences the thermodynamic stability of osmanaphthalenes relative to the indenyl complexes. Specifically, a destabilizing effect at the C1, C2, C3, and C7 positions, 2338

dx.doi.org/10.1021/om500245q | Organometallics 2014, 33, 2336−2340

Organometallics

■

Article

ACKNOWLEDGMENTS We acknowledge financial support from the Chinese National Natural Science Foundation (21172184), the National Basic Research Program of China (2011CB808504), the Program for New Century Excellent Talents in University (NCET-130511), the Program for Changjiang Scholars and Innovative Research Team in University, and the Fundamental Research Funds for the Central Universities (2012121021).

■

Figure 6. Singlet and triplet forms of a carbene can be considered as the parents of the Fischer and Schrock carbene complexes.

Figure 7. The carbene carbon and vinyl carbon of transition state.

confirm this explanation. Specifically, the OsC1 bond lengths (1.951 and 1.918 Å) of the transition states TS1 and TS2 with one methoxy substituent become longer than those (1.948 and 1.906 Å) without a methoxy substituent, whereas the transition states TS1 and TS2 with two methoxy substituents have the longest OsC1 bonds (1.956 and 1.934 Å).

■

CONCLUSION The thermodynamic and kinetic factors on the isomerizations of a series of indenyl complexes to osmanaphthalenes have been investigated by DFT computations. By changing one ligand from PMe3 to the chloride, such an isomerization could become thermodynamically favorable. In addition, both the EDG and EWG have a significant effect on such an isomerization. Our calculations demonstrate that the rearrangement from indenyl complexes to metallanaphthalenes can be both thermodynamically and kinetically favorable by choosing proper substituents on the metallacycle, suggesting a facile, unconventional way to prepare osmanaphthalenes from metal indenyl complexs.

■

ASSOCIATED CONTENT

■

AUTHOR INFORMATION

REFERENCES

(1) Recent studies of osmabenzenes: (a) Gong, L.; Chen, Z.; Lin, Y.; He, X.; Wen, T. B.; Xu, X.; Xia, H. Chem.−Eur. J. 2009, 15, 6258− 6266. (b) Wang, T.; Zhang, H.; Han, F.; Long, L.; Lin, Z.; Xia, H. Chem.−Eur. J. 2013, 19, 10982−10991. (c) Gong, L.; Lin, Y.; Wen, T. B.; Zhang, H.; Zeng, B.; Xia, H. Organometallics 2008, 27, 2584−2589. (d) Clark, G. R.; Johns, P. M.; Roper, W. R.; Wright, L. J. Organometallics 2006, 25, 1771−1777. (e) Xia, H.; He, G.; Zhang, H.; Wen, T. B.; Sung, H. H. Y.; Williams, I. D.; Jia, G. J. Am. Chem. Soc. 2004, 126, 6862−6863. (f) Zhao, Q.; Cao, X. Y.; Wen, T. B.; Xia, H. Chem.−Asian J. 2013, 8, 269−275. (g) Frogley, B. J.; Wright, L. J. Coord. Chem. Rev. 2014, DOI: 10.1016/j.ccr.2014.01.019. (h) ElHamdi, M.; El Bakouri El Farri, O.; Salvador, P.; Abdelouahid, B. A.; El Begrani, M. S.; Poater, J.; Solá, M. Organometallics 2013, 32, 4892− 4903. (i) Iron, M. A.; Martin, J. M.; van der Boom, M. E. J. Am. Chem. Soc. 2003, 125, 11702−11709. (j) Iron, M. A.; Lucassen, A. C.; Cohen, H.; van der Boom, M. E.; Martin, J. M. J. Am. Chem. Soc. 2004, 126, 11699−11710. (2) Recent studies of iridabenzenes: (a) Dalebrook, A. F.; Wright, L. J. Organometallics 2009, 28, 5536−5540. (b) Paneque, M.; Poveda, M. L.; Rendón, N.; Á lvarez, E.; Carmona, E. Eur. J. Inorg. Chem. 2007, 2711−2720. (c) Wu, H. P.; Ess, D. H.; Lanza, S.; Weakley, T. J. R.; Houk, K. N.; Baldridge, K. K.; Haley, M. M. Organometallics 2007, 26, 3957−3968. (d) Clark, G. R.; Lu, G. L.; Roper, W. R.; Wright, L. J. Organometallics 2007, 26, 2167−2177. (e) Á lvarez, E.; Paneque, M.; Poveda, M. L.; Rendón, N. Angew. Chem., Int. Ed. 2006, 45, 474−477. (f) Ilg, K.; Paneque, M.; Poveda, M. L.; Rendón, N.; Santos, L. L.; Camona, E.; Mereiter, K. Organometallics 2006, 25, 2230−2236. (g) Wu, H. P.; Weakley, T. J. R.; Haley, M. M. Chem.−Eur. J. 2005, 11, 1191−1200. (h) Chin, C. S.; Lee, H.; Eum, M. S. Organometallics 2005, 24, 4849−4852. (i) Chin, C. S.; Lee, H. Chem.Eur. J. 2004, 10, 4518−4522. (j) Bleeke, J. R.; Behm, R. J. Am. Chem. Soc. 1997, 119, 8503−8511. (k) Bleeke, J. R.; Behm, R.; Xie, Y. F.; Chiang, M. Y.; Robinson, K. D.; Beatty, A. M. Organometallics 1997, 16, 606−623. (l) Bleeke, J. R. Acc. Chem. Res. 2007, 40, 1035−1047. (3) Recent studies of other metallabenzenes. Rhenabenzene: (a) Poon, K. C.; Liu, L.; Guo, T.; Li, J.; Sung, H. H. Y.; Williams, I. D.; Lin, Z.; Jia, G. Angew. Chem., Int. Ed. 2010, 49, 2759−2762. Platinabenzenes: (b) Jacob, V.; Landorf, C. W.; Zakharov, L. N.; Weakley, T. J. R.; Haley, M. M. Organometallics 2009, 28, 5183−5190. (c) Landorf, C. W.; Jacob, V.; Weakley, T. J. R.; Haley, M. M. Organometallics 2004, 23, 1174−1176. (d) Jacob, V.; Weakley, T. J. R.; Haley, M. M. Angew. Chem., Int. Ed. 2002, 41, 3470−3473. Ruthenabenzene: (e) Zhang, H.; Xia, H.; He, G.; Wen, T. B.; Gong, L.; Jia, G. Angew. Chem., Int. Ed. 2006, 45, 2920−2923. (f) Yang, J.; Jones, W. M.; Dixon, J. K.; Allison, N. T. J. Am. Chem. Soc. 1995, 117, 9776−9777. (4) (a) Thorn, D. L.; Hoffmann, R. Nouv. J. Chim. 1979, 3, 39−45. (b) Elliott, G. P.; Roper, W. R.; Waters, J. M. J. Chem. Soc., Chem. Commun. 1982, 811−813. (5) Paneque, M.; Posadas, C. M.; Poveda, M. L.; Rendón, N.; Salazar, V.; Onate, E.; Mereiter, K. J. Am. Chem. Soc. 2003, 125, 9898−9899. (6) Liu, B.; Xie, H.; Wang, H.; Wu, L.; Zhao, Q.; Chen, J.; Wen, T. B.; Cao, Z.; Xia, H. Angew. Chem., Int. Ed. 2009, 48, 5461−5464. (7) (a) Yang, J.; Jones, W. M.; Dixon, J. K.; Allison, N. T. J. Am. Chem. Soc. 1995, 117, 9776−9777. (b) Wu, H. P.; Lanza, S.; Weakley, T. J. R.; Haley, M. M. Organometallics 2002, 21, 2824−2826. (c) Gilbertson, R. D.; Lau, T. L. S.; Lanza, S.; Wu, H. P.; Weakley, T. J. R.; Haley, M. M. Organometallics 2003, 22, 3279−3289. (d) Wu,

S Supporting Information *

The supplemental file SI.xyz containing the computed Cartesian coordinates of all of the species reported in this study is available free of charge via the Internet at http://pubs. acs.org. The file may be opened as a text file to read the coordinates or opened directly by a molecular modeling program such as Mercury (version 3.3 or later, http://www. ccdc.cam.ac.uk/pages/Home.aspx) for visualization and analysis. Corresponding Author

*E-mail: [email protected]. Homepage: http://junzhu. chem8.org. Notes

The authors declare no competing financial interest. 2339

dx.doi.org/10.1021/om500245q | Organometallics 2014, 33, 2336−2340

Organometallics

Article

H. P.; Weakley, T. J. R.; Haley, M. M. Chem.−Eur. J. 2005, 11, 1191− 1200. (e) Johns, P. M.; Roper, W. R.; Woodgate, S. D.; Wright, L. J. Organometallics 2010, 29, 5358−5365. (f) Zhang, H.; Feng, L.; Gong, L.; Wu, L.; He, G.; Wen, T. B.; Yang, F.; Xia, H. Organometallics 2007, 26, 2705−2713. (8) (a) Bleeke, J. R. Chem. Rev. 2001, 101, 1205−1228. (b) He, G.; Xia, H.; Jia, G. Chin. Sci. Bull. 2004, 49, 1543−1553. (c) Wright, L. J. Dalton Trans. 2006, 15, 1821−1827. (d) Landorf, C. W.; Haley, M. M. Angew. Chem., Int. Ed. 2006, 45, 3914−3936. (e) Cao, X. Y.; Zhao, Q.; Lin, Z.; Xia, H. Acc. Chem. Res. 2014, 47, 341−354. (9) Poon, K. C.; Liu, L.; Guo, T.; Li, J.; Sung, H. H. Y.; Williams, I. D.; Lin, Z.; Jia, G. Angew. Chem., Int. Ed. 2010, 49, 2759−2762. (10) (a) Zhu, J.; Dahlstrand, C.; Smith, J. R.; Villaume, S.; Ottosson, H. Symmetry 2010, 2, 1653−1682. (b) Zhu, J.; Bhandary, S.; Sanyal, B.; Ottosson, H. J. Phys. Chem. C 2011, 115, 10264−10271. (c) Zhao, Q.; Gong, L.; Xu, C.; Zhu, J.; He, X.; Xia, H. Angew. Chem., Int. Ed. 2011, 50, 1354−1358. (d) Zhao, Q.; Zhu, J.; Huang, Z.-A.; Cao, X. Y.; Xia, H. Chem.−Eur. J. 2012, 18, 11597−11630. (e) Yang, Y.-F.; Cheng, G.-J.; Zhu, J.; Zhang, X.; Inoue, S.; Wu, Y.-D. Chem.−Eur. J. 2012, 18, 7516−7524. (f) Zhu, J.; An, K.; Schleyer, P. v. R. Org. Lett. 2013, 15, 2442−2445. (g) Fan, J.; An, K.; Wang, X.; Zhu, J. Organometallics 2013, 32, 6271−6276. (h) Zhu, J.; Fogarty, H. A.; Möllerstedt, H.; Brink, M.; Ottosson, H. Chem.−Eur. J. 2013, 19, 10698−10707. (i) Zhu, C.; Li, S.; Luo, M.; Zhou, X.; Niu, Y.; Lin, M.; Zhu, J.; Cao, Z.; Lu, X.; Wen, T. B.; Xie, Z.; Schleyer, P. v. R.; Xia, H. Nat. Chem. 2013, 5, 698−703. (j) Huang, C.; Hao, Y.; Zhao, Y.; Zhu, J. Organometallics 2014, 33, 817−822. (k) Zhu, C.; Luo, M.; Zhu, Q.; Zhu, J.; Schleyer, P. v. R.; Wu, J.; Lu, X.; Xia, H. Nat. Commun. 2014, 5, 3265. (l) An, K.; Zhu, J. Eur. J. Org. Chem. 2014, DOI: 10.1002/ejoc.201301810. (m) Huang, Y.; Wang, X.; An, K.; Fan, J.; Zhu, J. Dalton Trans. 2014, DOI: 10.1039/C3DT53528B. (n) Wang, X.; Zhu, C.; Xia, H.; Zhu, J. Organometallics 2014, DOI: 10.1021/om500170w. (11) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648−5652. (b) Miehlich, B.; Savin, A.; Stoll, H.; Preuss, H. Chem. Phys. Lett. 1989, 157, 200−206. (c) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37, 785−789. (d) Stephens, P. J.; Devlin, F. J.; Chabalowski, C. F.; Frisch, M. J. J. Phys. Chem. 1994, 98, 11623−11627. (12) Scalmani, G.; Frisch, M. J. J. Chem. Phys. 2010, 132, 114110. (13) (a) Fukui, K. J. Phys. Chem. 1970, 74, 4161−4163. (b) Fukui, K. Acc. Chem. Res. 1981, 14, 363−368. (14) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 299−310. (15) Clark, T.; Chandrashakar, J.; Spitznagel, G. W.; Schleyer, P. V. R. J. Comput. Chem. 1983, 4, 294−301. (16) Huzinaga, S. Gaussian Basis Sets for Molecular Calculations; Elsevier Science Publishing Co.: Amsterdam, The Netherlands, 1984. (17) Krishnan, R.; Binkley, J. S.; Seeger, R.; Pople, J. A. J. Chem. Phys. 1980, 72, 650−654. (18) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, V. G.; 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.; 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. (19) Glendening, E. D.; Reed, A. E.; Carpenter J. E.; Weinhold, F. NBO, Version 3.1., Theoretical Chemistry Institute, University of Wisconsin, Madison, 1996.

(20) (a) Wiberg, K. B. Tetrahedron 1968, 24, 1083−1096. (b) Fradera, X.; Poater, J.; Simon, S.; Duran, M.; Sola, M. Theor. Chem. Acc. 2002, 108, 214−224. (21) Legault, C. Y. CYLview, 1.0b; Université de Sherbrooke, 2009 (http://www.cylview.org). (22) He, G.; Zhu, J.; Hung, W. Y.; Wen, T. B.; Sung, H. H. Y.; Williams, I. D.; Lin, Z.; Jia, G. Angew. Chem., Int. Ed. 2007, 46, 9065− 9068. (23) (a) Crabtree, R. H. The Organometallic Chemistry of the Transition Metals, 4th ed.; Wiley: New York, 2005; pp 110−112. (b) Hart-Davis, A. J.; Mawby, R. J. J. Chem. Soc. A 1969, 2403−2407. (c) Calhorda, M. J.; Romão, C. C.; Veiros, L. F. Chem.−Eur. J. 2002, 8, 868−875. (d) Calhorda, M. J. Dalton Trans. 2011, 40, 11138−11146. (24) Crabtree, R. H. The Organometallic Chemistry of the Transition Metals, 4th ed.; Wiley: New York, 2005; pp 310−311. (25) Mo, Y.; Wu, W.; Song, L.; Lin, M.; Zhang, Q.; Gao, J. Angew. Chem., Int. Ed. 2004, 43, 1986−1990.

2340

dx.doi.org/10.1021/om500245q | Organometallics 2014, 33, 2336−2340