Phosphine-Scavenging Role of Gold(I) Complexes ... - ACS Publications

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Phosphine-Scavenging Role of Gold(I) Complexes from Pd(PtBu3)2 in the Bimetallic Catalysis of Carbostannylation of Alkynes Yousef Khaledifard,† Bahare Nasiri,†,‡ Saeid A. Javidy,† Atena Vaziri Sereshk,† Brian F. Yates,*,§ and Alireza Ariafard*,†,§ †

Department of Chemistry, Faculty of Science, Central Tehran Branch, Islamic Azad University, ShahrakGharb, Tehran, Iran Young Researchers and Elite Club, Central Tehran Branch, Islamic Azad University, Tehran, Iran § School of Physical Science (Chemistry), University of Tasmania, Private Bag 75, Hobart, Tasmania 7001, Australia ‡

S Supporting Information *

ABSTRACT: Density functional theory (DFT) at the M06 level was utilized to compare the reactivity of Pd(PtBu3)2 with that of Pd2(dba)3 in catalyzing carbostannylation of alkynes in the presence of [AuL]+, where L is a phosphine ligand. In both cases, a common active catalyst is found to be responsible for conducting the reaction. The underlying reason for this is that [AuL]+ is capable of acting as a phosphine scavenger and removing both phosphines from Pd(PtBu3)2. The phosphine scavenger property of the cationic gold complexes may find applications in other catalytic coupling reactions. We also found that other Lewis acids such as AuCl, CuCl, and ZnCl2 might have potential for use as phosphine scavengers from palladium(0) bis(phosphine) complexes.

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INTRODUCTION Bimetallic catalysis which involves two identical or dissimilar metals has recently been the subject of many studies.1 The importance of bimetallic catalysis was highlighted by Blum and co-workers in detailed studies on the carbostannylation of alkynes (eq 1).1,2 They demonstrated that the simultaneous use of Au(I) and Pd(0) effectively catalyzed the reaction where excess AuI was applied (eq 1).

Scheme 1. Catalytic Cycle Proposed for Carbostannylation of Alkynes Catalyzed by Pd(0)/Au(I)

It should be noted that, among the different Pd catalysts tested for this reaction, the use of Pd2(dba)3 resulted in the formation of product in 73% yield. Our recent computational results showed that Pd2(dba)3 in the presence of alkyne and vinylstannane is converted to intermediate 2 and then the coordination of 2 to [AuL]+ forms the key intermediate 3, which is an active catalyst in the catalytic cycle (Scheme 1).3 The catalytic cycle depicted in Scheme 1 summarizes our computational findings as follows: the catalytic reaction is commenced by the rearrangement of intermediate 3 to palladium gold vinyl intermediate 4, by which Pd is formally oxidized by two units, transmetalation of Sn to Pd gives intermediate 5, Au to Pd transmetalation produces complex 6, and finally alkenyl−vinyl reductive elimination leads to formation of the final product and regeneration of active © XXXX American Chemical Society

catalyst 3. Although Pd2(dba)3 can drive such a catalytic reaction in good yield (73%), Pd(PtBu3)2 was also reported to be capable of catalyzing the corresponding reaction and affords product 1 in an acceptable yield (39%).2 In this study, we intend to investigate computationally the mechanism of the carbostannylation using Pd(PtBu3)2 and show how an active catalyst (3 or 7, Scheme 1) is generated from this precatalyst. The key finding of our study is that [AuL]+ by coordination to Received: March 30, 2017

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DOI: 10.1021/acs.organomet.7b00237 Organometallics XXXX, XXX, XXX−XXX

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Organometallics Pd(PtBu3)2 serves as a phosphine scavenger and easily opens a coordination site for binding of other substrates such as alkyne and vinylstannane.

increases, the antibonding property between the phosphine lone-pair orbitals and the s + dz2 orbital of the palladium increases as well, thereby leading to an increase in the HOMO energy and thus in basicity of the linear complex. For instance, our calculations show that the replacement of PtBu3 with PCl3 (a weaker σ donor ligand) decreases the binding energy by 14.6 kcal/mol. For different Pd(0) complexes, an excellent linear correlation with R2 = 0.98 between the Pd−Au binding energy and the HOMO energies confirms the above statement (Figure 1a). In order for the carbostannylation reaction to proceed, one PtBu3 ligand should be extruded from binuclear complex 13. As shown in eq 2 (Figure 2a), the direct dissociation of the PtBu3

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RESULTS AND DISCUSSION To address the above objectives, we need to know which possible adducts are initially formed. We were intrigued by the result that the binding of Pd(PtBu3)2 to [AuL]+ yields a strongly bound adduct;4 13 was calculated to be the most stable among related adducts shown in Scheme 2 with a binding Scheme 2. Relative Stabilities of Different Gold Adductsa

a

The relative Gibbs and electronic energies (in parentheses) calculated at the M06-CPCM/BS2//B3LYP/BS1 level in dichloromethane are given in kcal/mol.

energy of 40.7 kcal/mol. It follows that Pd(PtBu3)2 is a stronger Lewis base than other substrates, as is evident from the fact that Pd(PtBu3)2 possesses a higher-lying HOMO with an energy level of −4.00 eV; the HOMO energy levels for the vinylstannane and the alkyne are calculated to be lower in energy (−6.92 and −7.85 eV, respectively). The antibonding character of the HOMO of the linear transition-metal complexes with d10 configuration causes these complexes to be basic (Figure 1b).5 However, this basicity is affected by the nature of the L ligands. As the donicity of the L ligand

Figure 2. (a) Gibbs free energy changes (kcal/mol) for phosphine dissociation from 13, 15, and 13 assisted by a gold complex. (b) Optimized structures with selected structural parameters (bond lengths in angstroms) for 13, TS13‑17, and 17 (H atoms omitted for clarity).

from 13 with ΔG = 27.1 kcal/mol is extremely energy consuming. Consistent with the previous studies, the same is true when the loss of PtBu3 occurs from Pd(PtBu3)2;6 a Gibbs free energy of 24.7 kcal/mol is calculated for the corresponding dissociation (eq 3 in Figure 2a). Since the carbostannylation reaction proceeds under mild conditions (eq 1), an alternative mechanism for phosphine dissociation is envisioned. Interestingly, we found that the gold metal center in 13 can serve as a phosphine scavenger7 and abstract a phosphine from the Pd center via transition structure TS13‑17, affording the adduct 17 (eq 4 in Figure 2a).8 This adduct subsequently undergoes a facile fragmentation to give intermediates 16 and 18. The overall reaction 13 → 16 + 18 is endergonic by 13.1 kcal/mol and occurs with an activation free energy of 15.8 kcal/mol, indicating that formation of the monoligated intermediate 16 in the presence of the gold complex is accelerated and becomes thermodynamically more feasible. This monoligated intermedi-

Figure 1. (a) Plot of the Pd−Au binding energy (kcal/mol) versus the HOMO energy (eV) of different Pd(0) phosphine complexes. (b) Schematic view of the HOMO of PdL2 where Pd has an oxidation state of 0. B


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Organometallics

newly formed intermediate (22), the [Au(PMe3)(PtBu3)]+ cation is weakly bound to the Pd center and thus undergoes a barrierless substitution reaction to afford 23. The linear complex 23 can be in equilibrium with 2 by coordination of an alkyne substrate. The associative substitution of the alkene group in π complex 9 by the alkyne ligand of intermediate 2 by surmounting an energy barrier of 11.2 kcal/mol produces active catalyst 3, from which the carbostannylation occurs. A more detailed description as to how the carbostannylation is complete from this intermediate can be found elsewhere.3 However, for the sake of convenience, the energy profile of the carbostannylation from 3 has been provided in Figure S1 in the Supporting Information. It is inferred from Figure 3 that the phosphine migration (transformation 21 → TS21‑22 → 22) with an activation energy as modest as 13.3 kcal/mol is the ratedetermining step for formation of the active catalyst 3. It can be concluded from the above results that both ligands of a palladium bis(phosphine) complex can be easily scavenged by two cationic gold complexes in the presence of a coordinating substrate such as the vinylstannane. Now we turn our attention to determine whether there is any possibility for carbostannylation to take place from complex 7 (Scheme 1). This species can be formed by coordination of the alkyne to 19 followed by an associative exchange reaction between 24 and 9 (Figure 4). According to the catalytic cycle

ate can gain slightly higher stability (about 2.8 kcal in terms of Gibbs free energy) via coordination to solvent (CH2Cl2). The structures of 13, TS13‑17, and 17 are shown in Figure 2b. It should be noted at this juncture that the Pd−Au bond in 17 is about 21.7 kcal/mol weaker than that in 13. The weakening of the Pd−Au bond is reflected in elongation of the Pd−Au bond distance; the Pd−Au bond in 17 (2.929 Å) is about 0.323 Å longer than that in 13 (2.606 Å) (Figure 2b). The Au−Pd bond in 17 is principally formed by the interaction of the HOMO of [Au(PMe3)(PtBu3)]+ with the LUMO of Pd(PtBu3), while that in 13 is formed by the interaction of the LUMO of [AuPMe3]+ with the HOMO of Pd(PtBu3)2. The HOMO of [Au(PMe3)(PtBu3)]+ (−10.67 eV) is lower in energy than that of Pd(PtBu3)2 (−4.00 eV), and the LUMO of Pd(PtBu3) (−1.08 eV) is higher in energy than that of [AuPMe3]+ (−7.46 eV). The large energy gap between the HOMO and the LUMO results in the Pd−Au bond in 17 being relatively weak. In other words, [Au(PMe3)(PtBu3)]+ is a weaker Lewis base than Pd(PtBu3)2 and Pd(PtBu3) is a weaker Lewis acid than [AuPMe3]+, rendering the interaction between [Au(PMe3)(PtBu3)]+ and Pd(PtBu3) relatively weak. The coordination of vinylstannane to 16 leads to a greater stabilization and formation of intermediate 19 (eq 4 in Figure 2a). This intermediate can be a branching point for two different pathways: (a) abstraction of the phosphine ligand by another gold(I) complex followed by carbostannylation from 3 or (b) simultaneous coordination of the alkyne and the gold(I) complex to 19 and then carbostannylation from 7 (Scheme 1). In order for the active complex 3 to be formed, [AuL]+ is surmised to be initially bonded to 19. Since the π complex 9 is the most stable adduct in the absence of Pd(PtBu3)2 (Scheme 2), it is expected that the gold(I) species is in the form of this π complex. As shown in Figure 3, the key intermediate 21 is formed via dissociation of vinylstannane from adduct 20, in which both gold and palladium have a three-coordinate environment. By analogy with 13, intermediate 21 is reactive toward the migration of phosphine from palladium to gold via transition structure TS21‑22 to give intermediate 22. In this

Figure 4. Calculated energy profile for cthe arbostannylation reaction starting from 7 on the basis of the mechanism given in Scheme 1. The relative Gibbs and electronic energies (in parentheses) calculated at the M06-CPCM/BS2//B3LYP/BS1 level in dichloromethane are given in kcal/mol.

discussed in Scheme 1, it is assumed that the rearrangement of intermediate 7 to palladium gold vinyl complex 25 is the first step of the process. As reported previously, the Sn to Pd transmetalation (vinyl/vinyl exchange) occurs via an oxidative addition/reductive elimination process.3,9 The vinylstannane is oxidatively added to the Pd(II) center with an overall activation energy of 18.5 kcal/mol. The IRC calculation from TS25‑26 indicates that the oxidative addition product is not a local minimum and, once it is formed, it is involved in the Sn−C reductive elimination (without any barrier) to afford 26. The catalytic reaction is complete from this intermediate (26) by the Au to Pd transmetalation and the C−C reductive elimination via transition structures TS26‑27 and TS27‑7,

Figure 3. Calculated energy profile for abstraction of phosphine ligand from 19 by gold complex 9 and formation of active catalyst 3. The relative Gibbs and electronic energies (in parentheses) calculated at the M06-CPCM/BS2//B3LYP/BS1 level in dichloromethane are given in kcal/mol. C


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Organometallics respectively. The highest energy point on the energy profile is found to be TS25‑26. This transition structure is about 10.9 kcal/ mol higher in energy than the highest energy point on the energy profile illustrated in Figure 3 (TS21‑22). From this comparison, it can be deduced that the carbostannylation reaction using Pd(PtBu3)2 is most likely to proceed via active catalyst 3 by extrusion of both phosphine ligands from Pd(PtBu3)2 scavenged by 2 equiv of the gold complex. This conclusion is supported by additional single-point calculations at different levels of theory. All of the calculations predict that TS21‑22 lies below TS25‑26; for example, the relative Gibbs energies of TS21‑22 using M06-SMD/BS2, M06-CPCM/BS3, M06-D3-CPM/BS2, and M06-D3-CPCM/BS3 are 3.2, 4.9, 5.7, and 6.1 kcal/mol, respectively, whereas the relative Gibbs energies of TS25‑26 are 15.9, 17.9, 12.4, and 15.0 kcal/mol, respectively. We should emphasize at this point that the carbostannylation process from 7 with ΔG⧧ = 18.5 kcal/mol (Figure 4) is more energy demanding than that from 3 with ΔG⧧ = 10.5 kcal/mol (Figure S1 in the Supporting Information). This difference can be mostly related to the steric bulk of PtBu3. For example, the steric hindrance of PtBu3 effectively turns off the Au−Pd interaction in 25 and does not allow the Au center to interact with the empty site on the Pd(II) center, resulting in a significant instability at the vital stationary points such as the transition structure related to the transmetalation process (TS25‑26). This statement finds support in the view that the Pd−Au bond distance in 25 (3.126 Å) is considerably longer than that in 4 (2.852 Å) (Figure 5).

Table 1. Calculated Gibbs Free Energies (kcal/mol) for Formation of the Mono(phosphine) Complex Pd(PtBu3) Starting from [(PtBu3)2Pd-AuL]+ and Pd(PtBu3)2 Using Single-Point Calculations at Various Levels of Theory in CH2Cl2a

functional

basis set

solvation model

ΔG1 (kcal/mol)

ΔG2 (kcal/mol)

M06 M06 M06 M06-D3 M06-D3 B3LYP-D3 B3LYP-D3 B3LYP-D3 B97D B97D

BS2 BS2 BS3 BS2 BS3 BS2 BS3 BS3 BS3 BS2

CPCM SMD CPCM CPCM CPCM CPCM CPCM SMD CPCM CPCM

13.1 14.3 11.9 18.8 17.6 15.4 14.6 15.6 18.6 19.4

24.7 24.5 24.6 28.5 28.3 24.2 24.5 24.5 26.6 26.2

a

As discussed in the text, Pd(PtBu3) is slightly stabilized by coordination to CH2Cl2 solvent.

binuclear complex with that produced by Pd(PtBu3)2 at different levels of theory (for details see Table S2 in the Supporting Information). All of the calculations confirm that, regardless of the level of theory, the monoligated Pd complex produced by [(PtBu3)2Pd-AuL]+ has a much lower energy. As can be anticipated, the lower the energy of the monoligated Pd complex, the more efficient the catalysis. On the basis of these results, [(PR3)2Pd-AuL]+ is predicted to be a more active catalyst than Pd(PR3)2 in many catalytic reactions. Effect of Ligand and Metal Modifications. To assess how modifications of the ligand and the metal center affect the phosphine scavenger activity, the Lewis acidic metal complexes [AuPPh3]+, AuCl, CuCl, and ZnCl2 were employed for removing a phosphine ligand from Pd(PtBu3)2. The details of these investigations are summarized in Table 2. A similar trend in energetics was found by replacing [AuPMe3]+ with

Figure 5. Calculated Au−Pd bond distances (Å) of 4 and 25 (H atoms omitted for clarity).

Table 2. Calculated Gibbs Free Energies (kcal/mol) for All Species Involved in Formation of the Mono(phosphine) Complex Pd(PtBu3) Starting from (PtBu3)2Pd-[M], Where [M] is a Lewis Acidic Metal Complex, Using M06-CPCM/ BS2//B3LYP/BS1 Calculations in CH2Cl2

The capability of cationic gold complexes to scavenge a phosphine ligand from Pd(PR3)2 to generate a mono(phosphine) complex might find broad applicability in many catalytic reactions. For instance, this feature might facilitate the cross-coupling reactions of aryl chlorides with aryl stannanes.10 The oxidative addition of aryl chlorides to Pd(0) is considered as the first step of the catalytic cycle. Since mono(phosphine) Pd complexes are much more reactive than bis(phosphine) complexes, the inert aryl chlorides prefer to be added to Pd(PR3).11 Bulky phosphine ligands such as PtBu3 are used to support the formation of such low-coordinated complexes.6,12 However, the inherent instability of the mono(phosphine) complexes causes the whole catalysis process to be very energy consuming. The presence of 1 equiv of [AuL]+ as a phosphine scavenger enables it to produce a low-energy monoligated Pd complex from which the catalytic reaction is expected to occur more smoothly. To further confirm that [(PtBu3)2Pd-AuL]+ produces a lower energy monoligated Pd complex, more test calculations were carried out. Table 1 compares the relative energy of monoligated Pd complex 16 produced by the D

[M]

15 + [M]

TS13‑17

17

18 + 16

[AuPMe3]+ [AuPPh3]+ AuCl CuCl ZnCl2

27.3 29.1 31.6 28.2 6.7

15.8 15.2 12.3 10.6 12.1

7.5 5.1 −3.4 2.3 9.9

13.1 12.1 6.7 13.5 18.5


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Organometallics [AuPPh3]+, implying that the steric influence of the larger PPh3 ligands on removing the phosphine ligand is insignificant. In contrast, the replacement of [AuPMe3]+ with AuCl considerably increases the stability of the monoligated complex 16 and reduces the energy of transition structure TS13‑17. This difference mainly arises from the fact that PtBu3 interacts with AuCl more strongly than with [AuPMe3]+; the Au−PtBu3 bond in [PtBu3AuCl] (BDFE = 49.7 kcal/mol) is about 10.8 kcal/ mol stronger than that in [Au(PMe3)(PtBu3)]+ (BDFE = 38.9 kcal/mol) (BDFE = bond dissociation free energy). In Table 2, the phosphine-scavenging activity of [AuPMe3]+ with CuCl was also compared; this copper complex is usually used as a phosphine scavenger from Grubbs and Hoveyda catalysts.13 The calculations indicate that the stability of mono(phosphine) complex produced by CuCl is comparable to that produced by [AuPMe3]+, suggesting that the copper complex might be a good replacement for [AuPMe3]+ in generating a low-energy monoligated Pd complex. Finally, the reactivity of ZnCl2 for removing a PtBu3 from Pd(PtBu3)2 was explored. In contrast to the Cu and Au complexes, ZnCl2 is weakly bonded to Pd(PtBu3)2 and gives a monoligated Pd complex that is 18.5 kcal/mol higher in energy than the reference point 13. It is evident from these comparisons that gold complexes, particularly AuCl, are efficient Lewis acids for generating a monoligated Pd complex with low energy.

energetics, other methods for single-point calculations such as M06D3,24 B3LYP-D3, and B97D25 using basis sets BS1−BS3 were also used; BS3 utilizes def2-TZVP for all atoms along with the effective core potentials including scalar relativistic effects for Au, Pd, and Sn. To assess how sensitive the results are to the solvation model, we also employed the SMD solvation model for selected species.26 A very similar energy trend was obtained when the optimizations were conducted in a continuum dichloromethane solvent rather than in the gas phase. For example, using the M06-CPCM/BS2//B3LYP/ BS1 calculations, the relative energies of 13, TS13‑17, and 17 are 0.0, 15.8, and 7.5 kcal/mol, respectively, while with the M06-CPCM/ BS2//B3LYP-CPCM/BS1 calculations the relative energies are 0.0, 15.7, and 7.7 kcal/mol, respectively. The replacement of [AuPMe3]+ by [AuPPh3]+ does not have a significant effect on the relative energies of the vital transition structures and intermediates of energy profiles given in Figures 3 and 4 (Table S4 in the Supporting Information).

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* Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.7b00237.

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CONCLUSION The cationic gold complex [AuL]+ was found to have the ability to strongly bind to Pd(PtBu3)2 to form [(PtBu3)2Pd-AuL]+.14,15 The gold center in this binuclear complex can serve as a phosphine scavenger and form a mono(phosphine) Pd complex with low energy. As such, a more efficient catalytic process is predicted when [(PR3)2Pd-AuL]+, instead of Pd(PR3)2, is used as the precatalyst for coupling reactions. Under the right conditions, the gold complexes are able to remove even both phosphines from Pd(PR3)2 with moderate activation energies. The phosphine scavenger activity of the cationic gold complexes can be extended to other Lewis acids such as AuCl, CuCl, and ZnCl2, among which AuCl is calculated to be the most efficient.

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ASSOCIATED CONTENT

S

Computational details and additional data (PDF) Cartesian coordinates of all calculated species (XYZ)

AUTHOR INFORMATION

Corresponding Authors

*E-mail for B.F.Y.: [email protected]. *E-mail for A.A.: [email protected]. ORCID

Alireza Ariafard: 0000-0003-2383-6380 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors gratefully acknowledge the generous allocation of computing time from the Australian National Computational Infrastructure and the University of Tasmania.

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COMPUTATIONAL DETAILS

REFERENCES

(1) (a) Hirner, J. J.; Shi, Y.; Blum, S. A. Acc. Chem. Res. 2011, 44, 603−613. (b) Pérez-Temprano, M. H.; Casares, J. A.; Espinet, P. Chem. - Eur. J. 2012, 18, 1864−1884. (c) Powers, D. C.; Ritter, T. Acc. Chem. Res. 2012, 45, 840−850. (d) Hashmi, A. S. K. Acc. Chem. Res. 2014, 47, 864−876. (2) Shi, Y.; Petrson, S. M.; Haberaecker, W. W., III; Blum, S. A. J. Am. Chem. Soc. 2008, 130, 2168−2169. (3) Ariafard, A.; Rajabi, N. A.; Atashgah, M. J.; Canti, A. J.; Yates, B. F. ACS Catal. 2014, 4, 860−869. (4) For direct interaction of gold(I) with palladium(II) see: (a) Casado, A. L.; Espinet, P. Organometallics 1998, 17, 3677−3683. (b) Pérez-Temprano, M. H.; Casares, J. A.; de Lera, Á . R.; Á lvarez, R.; Espinet, P. Angew. Chem., Int. Ed. 2012, 51, 4917−4920. (c) Hansmann, M. M.; Pernpointner, M.; Döpp, R.; Hashmi, A. S. K. Chem. - Eur. J. 2013, 19, 15290−15303. (d) Carrasco, D.; PérezTemprano, M. H.; Casares, J. A.; Espinet, P. Organometallics 2014, 33, 3540−3545. (e) delPozo, J.; Gioria, E.; Casares, J. A.; Á lvarez, R.; Espinet, P. Organometallics 2015, 34, 3120−3128. (5) Younesi, Y.; Nasiri, B.; BabaAhmadi, R.; Willans, C. E.; Fairlamb, I. J. S.; Ariafard, A. Chem. Commun. 2016, 52, 5057−5060. (6) (a) McMullin, C. L.; Jover, J.; Harvey, J. N.; Fey, N. Dalton Trans. 2010, 39, 10833−10836. (b) McMullin, C. L.; Fey, N.; Harvey, J. N. Dalton Trans. 2014, 43, 13545−13556.

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Gaussian 09 was used to fully optimize all the structures reported in this paper at the B3LYP level17 of density functional theory (DFT). The effective core potential of Hay and Wadt with a double-ξ valence basis set (LANL2DZ)18 was chosen to describe Sn, Pd, and Au. The 631G(d) basis set was used for other atoms. Polarization functions were also added for Sn (ξf = 0.180), Pd (ξf = 1.472), and Au (ξd = 1.050).19 This basis set combination will be referred to as BS1. Frequency calculations were carried out at the same level of theory as those for the structural optimization. Transition structures were located using the Berny algorithm. Intrinsic reaction coordinate (IRC) calculations20 were used to confirm the connectivity between transition structures and minima. To further refine the energies obtained from the B3LYP/ BS1 calculations, we carried out single-point energy calculations for all of the structures with a larger basis set (BS2) in dichloromethane using the CPCM solvation model21 at the M0622 level. BS2 utilizes the def2TZVP basis set on Sn, Pd, and Au and the 6-311+G(2d,p) basis set on other atoms. An effective core potential including scalar relativistic effects was used for Sn, Pd, and Au atoms.23 All thermodynamic data were calculated at the standard state (298.15 K and 1 atm). To estimate the corresponding Gibbs free energies in dichloromethane, entropy corrections were calculated at the B3LYP/BS1 level and added to the single-point potential energies. To test whether the results obtained from M06-CPCM/BS2//B3LYP/BS1 provide reasonable E


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Organometallics

(23) Weigend, F.; Furche, F.; Ahlrichs, R. J. Chem. Phys. 2003, 119, 12753−12762. (24) Grimme, S.; Ehrlich, S.; Goerigk, L. J. Comput. Chem. 2011, 32, 1456−1465. (25) Grimme, S. J. Comput. Chem. 2006, 27, 1787−1799. (26) Marenich, A. V.; Cramer, C. J.; Truhlar, D. G. J. Phys. Chem. B 2009, 113, 6378−6396.

(7) For an example relating to phosphine scavengers see: Wang, C.; Friedrich, S.; Younkin, T. R.; Li, R. T.; Grubbs, R. H.; Bansleben, D. A.; Day, M. W. Organometallics 1998, 17, 3149−3151. (8) For transition structures similar to TS13‑17 see: (a) Kovács, G.; Lledós, A.; Ujaque, G. Angew. Chem., Int. Ed. 2011, 50, 11147−11151; (a1) Angew. Chem. 2011, 123, 11343−11347. (b) Couce-Ríos, A.; Kovács, G.; Ujaque, G.; Lledós, A. ACS Catal. 2015, 5, 815−829. The above studies report the migration of a cationic gold moiety from a carbon to a nitrogen center via a triangular transition structure. (9) Carrasco, D.; García-Melchor, M.; Casares, J. A.; Espinet, P. Chem. Commun. 2016, 52, 4305−4308. (10) (a) Espinet, P.; Echavarren, A. M. Angew. Chem., Int. Ed. 2004, 43, 4704−4734. (b) Cordovilla, C.; Bartolome, C.; Martinez-Ilarduya, J. M.; Espinet, P. ACS Catal. 2015, 5, 3040−3053. (11) (a) Barrios-Landeros, F.; Carrow, B. P.; Hartwig, J. F. J. Am. Chem. Soc. 2009, 131, 8141−8154. (b) Xue, L.; Lin, Z. Chem. Soc. Rev. 2010, 39, 1692−1705. (12) (a) Ariafard, A.; Yates, B. F. J. Am. Chem. Soc. 2009, 131, 13981−13991. (b) Fu, G. C. Acc. Chem. Res. 2008, 41, 1555−1564. (13) (a) Dias, E. L.; Nguyen, S. T.; Grubbs, R. H. J. Am. Chem. Soc. 1997, 119, 3887−3897. (b) Dias, E. L.; Grubbs, R. H. Organometallics 1998, 17, 2758−2767. (c) Ulman, M.; Grubbs, R. H. J. Org. Chem. 1999, 64, 7202−7207. (d) Kingsbury, J. S.; Harrity, J. P. A.; Bonitatebus, P. J., Jr.; Hoveyda, A. H. J. Am. Chem. Soc. 1999, 121, 791−799. (e) Garber, S. B.; Kingsbury, J. S.; Gray, B. L.; Hoveyda, A. H. J. Am. Chem. Soc. 2000, 122, 8168−8179. (14) Various levels of theory (B3LYP-D3, M06, M06-D3, and B97D) all predict that [AuL]+ binds to Pd(PtBu3)2 much more strongly than the other substrates (Table S1 in the Supporting Information). (15) The nature of the anionic X ligand of [LAuX] affects the thermodynamic stability of [(PtBu3)2Pd-AuL]+. For example, when X− is Cl− (a strongly coordinating ligand), the reaction LAuX + Pd(PtBu3)2 → [(PtBu3)2Pd-AuL]+ + Cl− (L = PMe3) is calculated to be endergonic by 11.8 kcal/mol, whereas when X− is PF6− (a weakly coordinating ligand), the corresponding reaction becomes exergonic by −23.9 kcal/mol. (16) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.; 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.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09, Revision D.01; Gaussian, Inc., Wallingford, CT, 2009. (17) (a) Lee, C. T.; Yang, W. T.; Parr, R. G. Phys. Rev. B: Condens. Matter Mater. Phys. 1988, 37, 785−789. (b) Miehlich, B.; Savin, A.; Stoll, H.; Preuss, H. Chem. Phys. Lett. 1989, 157, 200−206. (c) Becke, A. D. J. Chem. Phys. 1993, 98, 5648−5652. (18) (a) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 270−283. (b) Wadt, W. R.; Hay, P. J. J. Chem. Phys. 1985, 82, 284−298. (19) (a) Ehlers, A. W.; Dapprich, M. S.; Gobbi, A.; Höllwarth, A.; Jonas, V.; Köhler, K. F.; Stegmann, R.; Veldkamp, A.; Frenking, G. Chem. Phys. Lett. 1993, 208, 111−114. (b) Höllwarth, A.; Böhme, M.; Dapprich, S.; Ehlers, A. W.; Gobbi, A.; Jonas, V.; Köhler, K. F.; Stegmenn, R.; Veldkamp, A.; Frenking, G. Chem. Phys. Lett. 1993, 208, 237−240. (20) (a) Fukui, K. J. Phys. Chem. 1970, 74, 4161−4163. (b) Fukui, K. Acc. Chem. Res. 1981, 14, 363−368. (21) Barone, V.; Cossi, M. J. Phys. Chem. A 1998, 102, 1995−2001. (22) Zhao, Y.; Truhlar, D. G. Acc. Chem. Res. 2008, 41, 157−167. F


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