Article pubs.acs.org/Organometallics
How Does an Earth-Abundant Copper-Based Catalyst Achieve AntiMarkovnikov Hydrobromination of Alkynes? A DFT Mechanistic Study Xi Deng,† Yanfeng Dang,† Zhi-Xiang Wang,*,†,‡ and Xiaotai Wang*,§ †
School of Chemistry and Chemical Engineering, University of the Chinese Academy of Sciences, Beijing 100049, People’s Republic of China § Department of Chemistry, University of Colorado Denver, Campus Box 194, P.O. Box 173364, Denver, Colorado 80217-3364, United States ‡ Collaborative Innovation Center of Chemical Science and Engineering, Tianjin 300072, People’s Republic of China S Supporting Information *
ABSTRACT: The first catalytic hydrohalogenation of alkynes was recently achieved using a copper(I) N-heterocyclic carbene (NHC) complex, and the reaction was found to be syn and antiMarkovnikov selective. The present work is a density functional theory (DFT) computational study (B3LYP and M06) on the detailed mechanism of this remarkable catalytic reaction. The reaction begins with a phenoxide additive turning over the precatalyst (NHC)CuCl into (NHC)Cu(OAr), which subsequently transmetalates with the hydride source Ph2SiH2 to deliver the copper(I) hydride complex (NHC)CuH. (NHC)CuH undertakes hydrocupration of the substrate RCCH via alkyne coordination and subsequent migratory insertion into the Cu−H bond, forming (E)-(NHC)Cu(CHCHR). The migratory insertion step determines the syn selectivity because it occurs by a concerted pathway, and it also determines the anti-Markovnikov regioselectivity that arises from the charge distributions across the Cu−H and CC bonds. The brominating agent (BrCl2C)2 uses the bromonium end to attack the Cu-bound vinylic carbon atom of (E)-(NHC)Cu(CHCHR), leading to the final (E)-alkenyl bromide product (E)-RHCCHBr, as well as the copper(I) alkyl complex (NHC)Cu(CCl2CBrCl2), which undergoes β-bromide elimination to give the catalyst precursor (NHC)CuBr for the next cycle. (NHC)CuBr reacts with the phenoxide to regenerate the active catalyst (NHC)Cu(OAr). The computational results rationalize the experimental observations, reveal new insights into the mechanism of the Cu(I)-catalyzed hydrobromination of alkynes, and have implications for other catalytic functionalization reactions of alkynes involving active [Cu]−H intermediates. achieved the first catalytic hydrohalogenation of alkynes and observed syn and anti-Markovnikov selectivities, using a copper(I) N-heterocyclic carbene (NHC) complex (Scheme 1).14 The accomplishment of the reaction with a catalyst based on the earth-abundant metal copper made it even more interesting. Copper(I) hydride species generated from transmetalation of copper(I) complexes with hydrosilanes were previously exploited to catalyze the hydrocarboxylation15,16 and semihydrogenation17,18 of alkynes. This prior knowledge and some preliminary mechanistic studies led Lalic and co-workers to propose that the hydrobromination reaction proceeds by transmetalation of a copper(I) phenoxide complex with the hydrosilane to form a copper(I) hydride complex, which undertakes hydrocupration of the alkyne substrate, followed by
1. INTRODUCTION There has been much ongoing interest in the development of catalysts based on earth-abundant 3d transition metals.1 The application of such base metals to homogeneous catalysis has obvious economic benefits, because they are considerably less expensive than precious metals. Furthermore, the study of 3d transition-metal catalysis could lead to the discovery of new organometallic reactivity at a fundamental level. Alkenyl (vinyl) halides are useful intermediates in organic synthesis, acting as coupling partners in cross-coupling reactions2,3 and as precursors to various organometallic reagents.4 The traditional hydrometalation of alkynes, followed by electrophilic halogenation of the metal alkenyl intermediate, has remained a common method for synthesizing alkenyl halides.5−13 This approach, however, involves using stoichiometric amounts of highly reactive metal reagents, thereby limiting functional group compatibility and generating environmentally unfriendly byproducts. Recently, the Lalic group has © XXXX American Chemical Society
Received: March 27, 2016
A
DOI: 10.1021/acs.organomet.6b00246 Organometallics XXXX, XXX, XXX−XXX
Article
Organometallics
corrected enthalpies and free energies at 298.15 K and 1 atm, using the B3LYP/BS1 harmonic frequencies. This combined use of M06 and B3LYP has been successfully applied to investigate various transitionmetal-catalyzed reactions,23−34 including organocopper systems.31−34 The free energies (kcal/mol) obtained with M06/BS2//B3LYP/BS1 were generally used in the following discussions. For comparison purposes, the key transition states optimized with B3LYP/BS1 were subject to reoptimization with M06/BS1 and single-point energy calculations with M06/BS2//M06/BS1, and the M06/BS2//M06/ BS1 outcomes were consistent with the M06/BS2//B3LYP/BS1 results (Figures S2 and S3 in the Supporting Information). Natural bond orbital (NBO) charges were calculated for selected structures at the M06/BS2 level in toluene solution using the SMD solvation model. All calculations were performed with Gaussian 09.35
Scheme 1. Copper-Catalyzed Hydrobromination of Alkynes
bromination of the resulting alkenylcopper(I) intermediate by (BrCl2C)2.14 However, a detailed mechanism of this remarkable catalytic reaction has not been explored, with intriguing questions such as why and how (BrCl2C)2 acts as a uniquely effective brominating agent. In this detailed mechanistic study, we investigate all the important phases of the catalytic reaction, including catalyst initiation and transmetalation, alkyne hydrocupration, copper(I) alkenyl bromination, and catalyst regeneration, in order to propose the complete and most favorable pathway, elucidate the origins of the syn and anti-Markovnikov selectivities, and elaborate the novel reactivity of alkenylcopper(I) complexes with (BrCl2C)2. We also demonstrate that the main reaction (i.e., alkyne hydrobromination) overrides the competing reaction of hydrosilylation of alkynes. An important goal of these studies is to gain new insights into the mechanism of this Cu(I)-catalyzed hydrobromination of alkynes, which can be useful for the further development of this and other related reactions.
3. RESULTS AND DISCUSSION 3.1. Initiation of Catalyst and Formation of Organocopper(I) Hydrides. Lalic and co-workers discovered phenoxide additives to be the proper turnover reagents for their specific reaction system, with 2-tert-butylphenoxide (the phenoxide/OAr hereafter) giving the best yield.14,36 Our calculations indicate that, by a ligand substitution reaction, the phenoxide can turn the precatalyst IPrCuCl (1) into IPrCu(OAr) (2), namely the active catalyst (Figure 1). This initiation reaction is endergonic by 4.1 kcal/mol, as estimated by approximating phenoxide and chloride ions as the attacking and leaving groups, respectively. In actuality, the lesser solubility of potassium chloride in the reaction solvent, in comparison to that of the potassium phenoxide, could provide the driving force. Note that Lalic et al. showed that a controlled reaction of 1 with the phenoxide in the absence of any other reactant produced 2 in high yield.14 For the transmetalation of IPrCu(OAr) (2) with the hydrosilane Ph2SiH2, we located a concerted pathway of σ-bond metathesis via the four-centered transition state TS1. TS1 has an attainable free energy of activation of 18.9 kcal/mol and proceeds to the threecoordinate copper(I) complex 3 with a weak Cu−O dative bond at 2.57 Å. The dissociation of the aryl silyl ether from 3 via TS2 is facile with a small free energy of activation of 1.6 kcal/mol and leads to the copper(I) hydride complex IPrCuH (4). We also considered the possible transmetalation reaction of IPrCuCl (1) and Ph2SiH2, which proved to be much disfavored kinetically and thermodynamically (Figure S1 in the Supporting Information).
2. COMPUTATIONAL METHODS We computed the reaction as shown in Scheme 1 using the actual catalyst and reagents, except for replacing the alkyne substrate with a somewhat shortened model, RCCH, where R = 4MeOC6H4(CH2)2. Geometries were optimized and characterized by frequency calculations to be minima or transition states (TSs) at the B3LYP19/BS1 level in the gas phase, BS1 designating a mixed basis set of SDD20 for copper and 6-31G(d,p) for other atoms. The energies were then refined by M0621/BS2//B3LYP//BS1 single-point energy calculations with solvation effects modeled by SMD22 in toluene solution in accordance with the experimental conditions, BS2 denoting a mixed basis set of SDD for copper and 6-311++G(d,p) for other atoms. The refined energies were converted to zero-point energy-
Figure 1. Free energy profile for the initiation of the catalyst 2 and formation of the copper(I) hydride complexes. The relative free energies are given in kcal/mol and are mass balanced (similarly hereinafter). Selected bond distances are given in Å. B
DOI: 10.1021/acs.organomet.6b00246 Organometallics XXXX, XXX, XXX−XXX
Article
Organometallics
Figure 2. Free energy profiles for the pathways of hydrocupration of the alkyne substrate via alkyne insertion into the monomer 4 (A) and the dimer 4′ (B). Electronic energies (zero point energy corrected) are given in kcal/mol in parentheses. The numbers shown in purple on 4, 4′, 5, 7, TS4, and TS6 denote NBO charges on selected atoms.
(IPrCuH)2 (4′) as a more stable stationary point than 4 (by 3.8 kcal/mol), which serves as the resting state for 4 (Figure 1). 3.2. Hydrocupration of Alkynes. It has been reported that an (NHC)copper(I) hydride undertakes hydrocupration of 3-hexyne to produce the isolable complex (E)-(NHC)Cu(3hexenyl).41 In addition, computational studies on (NHC)CuHcatalyzed hydrocarboxylation of alkynes have characterized the pathway of syn-constrained migratory insertion of PhCCPh into the Cu−H bond.42 Furthermore, there has been experimentally confirmed hydrocupration of terminal alkynes involved in the (NHC)CuH-catalyzed semihydrogenation of alkynes.17 In computing the hydrocupration of the alkyne substrate RCCH (R = 4-MeOC6H4(CH2)2), we considered the potential reaction pathways involving the migratory insertion of alkyne into both the monomer IPrCuH (4) and the dimer (IPrCuH)2 (4′), as shown in Figure 2.
We attribute the feasibility of the transmetalation of IPrCu(OAr) (2) with Ph2SiH2 to the resultant Si−O bond (110 kcal/mol) in the transition state and silicon-containing product that is relatively strong due to the small size of the O atom. By contract, owing to the larger size of the Cl atom in IPrCuCl (1), the Si−Cl bond (90 kcal/mol) would not be strong enough to facilitate the transmetalation of 1 with Ph2SiH2. This insight also corroborates with the experimental works (i.e., hydrocarboxylation,15,16 semihydrogenation,17,18,37 hydroamination,38 and hydroalkylation39,40) reported before and after the reaction under discussion, in which the CuI−X complexes (X = alkoxide, carboxylate, fluoride) that transmetalate with hydrosilanes all have a Cu−O or Cu−F dative bond containing the small O or F donor atom. (NHC)copper(I) hydride complexes such as IPrCuH (4) have been known experimentally to aggregate into dimers.41 Indeed, we have located the dinuclear copper complex C
DOI: 10.1021/acs.organomet.6b00246 Organometallics XXXX, XXX, XXX−XXX
Article
Organometallics
bound Hδ− in 7 and TS6. Thus, 5 and TS4 are correspondingly more stable than 7 and TS6. On the basis of these analyses, we conclude that the electronic factors cause the hydrocupration reaction to favor the anti-Markovnikov alkenylcopper(I) product 6. Analyses of the interactions of the frontier molecular orbitals of IPrCuH (4) and the alkyne substrate also illustrate the electronic effects on the anti-Markovnikov regioselectivity of the hydrocupration reaction. Alkyne migratory insertion into the Cu−H bond of 4 involves formation of new C−H and Cu− C bonds and cleavage of the Cu−H σ bond and one CC π bond. Thus, the participating frontier molecular orbitals are the Cu−H σ and σ* orbitals of 4 and the CC π and π* orbitals of the alkyne, as shown in Figure 3. The two sets of frontier
Figure 2A presents the two parallel pathways via alkyne insertion into the monomeric complex 4. The regioselectivity stems from the different orientations of the unsymmetrical RCCH toward the Cu−H bond in the substrate-uptaking transition states TS3 and TS5, which proceed respectively to 5 and 7, the η2-alkyne π complexes. Intermediates 5 and 7 undergo subsequent intramolecular migratory insertion via the concerted and therefore syn-constrained TS4 and TS6 to form the anti-Markovnikov and Markovnikov copper(I) alkenyl complexes 6 and 8, respectively. The anti-Markovnikov pathway (red) leading to the (E)-alkenylcopper(I) complex 6 is thermodynamically and kinetically more favorable than the Markovnikov pathway (blue) in both the alkyne coordination and insertion steps, and the free energy difference (1.8 kcal/ mol) between TS4 and TS6 (the rate-determining barriers) gives a calculated regioselectivity of 95%. This agrees qualitatively with the experimental result that the (E)-alkenyl bromide (E)-RHCCHBr was the only final product observed. Furthermore, the alkyne insertion step from 5 to 6 via TS4 is highly irreversible (ΔG = −34.6 kcal/mol). Figure 2B shows the anti-Markovnikov (red) and Markovnikov (blue) pathways of hydrocupration by alkyne insertion into the dinuclear complex (IPrCuH)2 (4′) via TS7 and TS8, which have higher kinetic barriers than the analogous insertion-intomonomer pathways shown in Figure 2A with rate-limiting states TS4 and TS6. The smaller of TS7 and TS8 (i.e., TS7) is higher than the smaller of TS4 and TS6 (i.e., TS4) by 3.9 kcal/ mol, and such a gap essentially rules out the pathways of hydrocupration via alkyne insertion into the dimer (IPrCuH)2 (4′). A comparison of 4 and 4′ shows that the NBO charges for the Cu−H bond change from Cu+0.311−H−0.529 in 4 to Cu+0.251−H−0.449 in 4′. The smaller Cu−H bond polarity in 4′ would contribute to the higher energy of TS7 in comparison to TS4. In addition, TS7 would require a trimolecular orientation that is worse for entropy than the bimolecular TS4, as reflected by the significant difference between ΔΔG⧧(TS7−TS4) and ΔΔE⧧(TS7−TS4) (Figure 2). Such are the plausible factors that make TS7 less favorable than TS4. Although anti-Markovnikov selectivity is commonly observed for the hydrometalation of alkynes, Markovnikov selectivity has been reported for transition-metal-catalyzed hydrometalation reactions.5,43 To unravel the origins of the anti-Markovnikov regioselectivity for the particular hydrocupration reaction shown in Figure 2A, we considered both electronic and steric factors in the selectivity-determining barriers TS4 and TS6 and their immediate precursors 5 and 7. Analyses of their optimized geometries did not reveal any significant steric bias, which led us to focus on the electronic effects.44 We analyzed the NBO charges on the atoms of the CC and Cu−H bonds because they participate directly in the alkyne migratory insertion (Figure 2A). In each of 5, 7, TS4, and TS6, the Cu−H bond is polarized with a partial positive and negative charge on Cu (ranging from 0.258 to 0.286) and H (ranging from −0.102 to −0.350), respectively; the CC bond has partial negative charges on both C(sp) atoms, but the charge on the terminal carbon atom is significantly more negative than that on the internal carbon atom. These NBO charge distributions suggest that the Cuδ+−Cδ−(sp,terminal) attractive interactions in 5 and TS4 of the anti-Markovnikov pathway are stronger than the Cuδ+−Cδ−(sp,internal) attractive interactions in 7 and TS6 of the Markovnikov pathway. Furthermore, the repulsive interactions between Cδ−(sp,internal) and Cu-bound Hδ− in 5 and TS4 are less than those between Cδ−(sp,terminal) and Cu-
Figure 3. M06/BS1-calculated frontier molecular orbitals of IPrCuH (4) and the alkyne substrate RCCH (R = 4-MeOC6H4(CH2)2) with spatial plots, atomic contributions/coefficients, and energies given in eV.
molecular orbital interactions, which occur between the filled Cu−H σ and the CC π* orbitals and between the filled C C π and the Cu−H σ* orbitals, are both energetically viable. Such interactions, as demonstrated by the atomic contributions/coefficients of the molecular orbitals, clearly favor the Cu−C(sp,terminal) and H−C(sp,internal) bond formations; that is, the anti-Markovnikov pathway. 3.3. Bromination vs Silylation. (BrCl2C)2 (1,2-dibromotetrachloroethane), a commercially available compound, had previously been employed as a brominating agent in several organic reaction systems.45−47 Lalic and co-workers found that (BrCl2C)2 reacted with (E)-alkenylcopper(I) complexes (e.g., 6) to give an (E)-alkenyl bromide product and the complex IPrCuBr, as well as the byproduct tetrachloroethylene.14 In addition, the reaction was not affected by adding the free radical trapping agent TEMPO, indicating that the bromination of 6 with (BrCl2C)2 does not involve free radical intermediates.14 D
DOI: 10.1021/acs.organomet.6b00246 Organometallics XXXX, XXX, XXX−XXX
Article
Organometallics
Figure 4. Free energy profiles for the bromination of 6 by (BrCl2C)2. The numbers shown in purple on 6, (BrCl2C)2, TS9, and TS10 are NBO charges on selected atoms.
To elucidate the novel reactivity of (BrCl2C)2 with the alkenylcopper(I) complex 6, we analyzed the NBO charges on selected atoms in (BrCl2C)2 and 6 (Figure 4). The Cu− C(vinylic) bond in 6 is polarized with a partial positive and negative charge on Cu (0.397) and C (−0.696), respectively. In (BrCl2C)2, the C−Br bond has a partial positive charge on Br (0.160). Such NBO charge distributions demonstrate that (BrCl2C)2 can act as a bromonium-like electrophile to attack the copper-bound vinylic carbon atom in 6, for which we located both the two-centered TS9 and three-centered TS10 (Figure 4). There exist the Cδ−(vinylic)−Brδ+ attractive interactions in both TS9 and TS10, but TS10 is higher in energy than TS9 by 4.3 kcal/mol because it is destabilized by the Cuδ+−Brδ+ repulsive interaction. TS9 proceeds to the completion of bromonium transfer and formation of the ion pair 11, in which the Cu(I) center binds to the CC bond, forming a π-complex cation that is associated with the carbanion BrCl2CCCl2−. The combination of the IPrCuI cation and the carbanion results in the IPrCu(I) alkyl complex 12, with the release of the (E)-alkenyl bromide product. In the higher-energy pathway, TS10 proceeds to the three-coordinate zwitterionic Cu(I) complex 13 containing weak Cu−Cl and Cu−Br dative bonds, which undergoes facile cation−anion combination via TS11 to produce 12 and the (E)-alkenyl bromide. In addition to the electrophilic bromination pathways, we considered the oxidative C(sp3)−Br addition and reductive C(sp2)−Br elimination/coupling mechanism consisting of TS12, the Cu(III) complex 14, and TS13 (Figure 4). This proved to be the least favored pathway with the highest energy barriers. This outcome is understandable because it would be difficult for coppera 3d transition metalto achieve the high +3 oxidation state under the mild reaction conditions (25 °C in toluene solution) because of the high activation free energy.48
Therefore, the bromination reaction of 6 with (BrCl2C)2 occurs by the lowest-energy pathway via TS9 to deliver the alkenyl bromide (E)-RHCCHBr and complex 12. It is kinetically viable with a free energy of activation of 8.7 kcal/mol (TS9−6), and thermodynamically irreversible due to the large driving force of 36.9 kcal/mol (12−6). For comparison, we have considered the bromination of 6 by (BrH2C)2. This reaction is disfavored because (BrH2C)2 is a poor electrophilic brominating agent with its bromine atom possessing a partial negative rather than positive charge (Figure S4 in the Supporting Information). We have also considered the possible chlorination of complex 6 by (BrCl2C)2, which proves to be much disfavored (Figure S5 in the Supporting Information). Alternatively, complex 6 could undertake a σ-bond metathesis/silylation reaction with Ph2SiH2 to give (E)-Ph2HSiC CHR, a product of hydrosilylation of the alkyne substrate, and regenerate IPrCuH (4), the pathway of which is computed and shown in Figure 5. However, this silylation reaction via TS14 would be much less favorable than the bromination of 6 via TS9 to deliver the hydrobromination product (E)-RHC CHBr. Kinetically, TS14 is higher than TS9 by 20.4 kcal/mol, and thermodynamically, the silylation reaction is less exergonic
Figure 5. Free energy profile for the silylation of 6 with Ph2SiH2. E
DOI: 10.1021/acs.organomet.6b00246 Organometallics XXXX, XXX, XXX−XXX
Article
Organometallics
−73.3 kcal/mol; the rate-limiting step is the alkyne migratory insertion into IPrCuH (4), with the overall kinetic barrier TS4 that is 25.8 kcal/mol relative to the catalyst resting state 4′.50 The alkyne migratory insertion/hydrocupration step determines both the syn and anti-Markovnikov selectivities, leading to the final product (E)-RHCCHBr. The computed reaction pathway matches and explains the experimental observations.
than the bromination reaction by 35.8 kcal/mol. These computational results give a good explanation for the experimental fact that no product of hydrosilylation was observed.14 To explain the high energy of TS14, we examined its optimized structure and identified three significant steric repulsions involving nonbonding atoms: C···Ha at 2.42 Å, Si···Hb at 3.18 Å, and Si···Hc at 2.87 Å (Figure 6). These steric
4. CONCLUSIONS We have presented a detailed and plausible mechanism for the newly developed Cu(I)-catalyzed anti-Markovnikov hydrobromination of alkynes on the basis of DFT computations. The phenoxide additive turns over the precatalyst IPrCuCl (1) into the active catalyst IPrCu(OAr) (2), which undertakes transmetalation with the hydride source Ph2SiH2 to form the copper(I) hydride complex IPrCuH (4) that dimerizes to the resting state (IPrCuH)2 (4′). The small size of oxygen and strong Si−O bond thereof facilitate the transmetalation. For the subsequent hydrocupration of the substrate RCCH, the reaction kinetics favor the pathway of RCCH inserting into the monomer IPrCuH (4). Having the overall kinetic barrier and being thermodynamically irreversible, this migratory insertion step determines both the syn and anti-Markovnikov selectivities, with the former arising from the concerted nature of the elementary reaction and the latter originating from the electronic factors: namely, the specific magnitudes and directions of the Cu−H and CC bond polarities. The (E)alkenylcopper(I) complex 6 from the hydrocupration contains the polarized Cuδ+−Cδ−(vinylic) bond, and the brominating agent (BrCl2C)2 has the polarized Brδ+−Cδ− bond. Consequently, (BrCl2C)2 uses the bromonium end to attack the vinylic carbon atom of 6, thereby delivering the final (E)alkenyl bromide product (E)-RHCCHBr and the copper(I) alkyl complex IPrCu(CCl2CBrCl2) (12). The competing silylation reaction of 6 with Ph2SiH2 would be disfavored. Complex 12 isomerizes to the rotamer 15 that undergoes βbromide elimination to give the catalyst precursor IPrCuBr (17) for the next cycle, and 17 reacts with the phenoxide to regenerate the active catalyst IPrCu(OAr) (2). The computational results constitute a complete reaction pathway that fully rationalizes the observed phenomena, thereby demonstrating rich experimental−theoretical synergy. The discovery of the phenoxide as a proper turnover reagent and the use of the brominating agent (BrCl2C)2 by the experimentalists were crucial to the success of the first catalytic and Cu(I)-promoted anti-Markovnikov hydrobromination of alkynes. The present computational study has revealed new
Figure 6. Optimized structure of TS14 with selected interatomic distances given in Å. Hydrogen atoms are omitted for clarity except for those under discussion.
hindrances each occur within a distance that is less than the sum of the van der Waals radii of the participating atoms (H 1.20 Å, C 1.70 Å, and Si 2.10 Å),49 which would add up to a significantly destabilizing effect on TS14. 3.4. Catalyst Regeneration. The next phase of the reaction is catalyst regeneration. As shown in Figure 7, complex 12 isomerizes through the rotation of the C−C bond to 15, a conformation that facilitates the subsequent β-bromide elimination via the four-centered TS15 to give the Cu(I) η2tetrachloroethylene π complex 16. The dissociation of tetrachloroethylene from 16 is thermodynamically favorable and delivers the catalyst precursor IPrCuBr (17), which undergoes substitution of phenoxide for bromide to regenerate IPrCu(OAr) (2). In a similar vein to that for IPrCuCl (1), the transmetalation of IPrCuBr (17) with Ph2SiH2 was ruled out due to unfavorable kinetic and thermodynamic parameters (Figure S6 in the Supporting Information). In summary, for the complete reaction pathway beginning with the formation of IPrCu(OAr) (2) from the precatalyst 1 and cycling though the regeneration of 2 from 17 (Figures 1−3 and 6), the thermodynamics are highly favorable, with ΔG =
Figure 7. Free energy profile for catalyst regeneration. F
DOI: 10.1021/acs.organomet.6b00246 Organometallics XXXX, XXX, XXX−XXX
Article
Organometallics
(18) Semba, K.; Fujihara, T.; Xu, T.; Terao, J.; Tsuji, Y. Adv. Synth. Catal. 2012, 354, 1542−1550. (19) (a) Lee, C. T.; Yang, W. T.; Parr, R. G. Phys. Rev. B: Condens. Matter Mater. Phys. 1988, 37, 785−789. (b) Becke, A. D. J. Chem. Phys. 1993, 98, 5648−5652. (20) (a) Andrae, D.; Häussermann, U.; Dolg, M.; Stoll, H.; Preuss, H. Theor. Chim. Acta 1990, 77, 123−141. (b) Roy, L. E.; Hay, P. J.; Martin, R. L. J. Chem. Theory Comput. 2008, 4, 1029−1031. (21) Zhao, Y.; Truhlar, D. G. Theor. Chem. Acc. 2008, 120, 215−241. (22) Marenich, A. V.; Cramer, C. J.; Truhlar, D. G. J. Phys. Chem. B 2009, 113, 6378−6396. (23) Lu, G.; Fang, C.; Xu, T.; Dong, G.; Liu, P. J. Am. Chem. Soc. 2015, 137, 8274−8283. (24) Dang, Y.; Qu, S.; Tao, Y.; Deng, X.; Wang, Z.-X. J. Am. Chem. Soc. 2015, 137, 6279−6291. (25) Bartoszewicz, A.; Gonzalez Miera, G.; Marcos, R.; Norrby, P.O.; Martın -Matute, B. ACS Catal. 2015, 5, 3704−3716. (26) Herbert, M. B.; Suslick, B. A.; Liu, P.; Zou, L.; Dornan, P. K.; Houk, K. N.; Grubbs, R. H. Organometallics 2015, 34, 2858−2869. (27) Haynes, M. T.; Liu, P.; Baxter, R. D.; Nett, A. J.; Houk, K. N.; Montgomery, J. J. Am. Chem. Soc. 2014, 136, 17495−17504. (28) Cannon, J. S.; Zou, L.; Liu, P.; Lan, Y.; O’Leary, D. J.; Houk, K. N.; Grubbs, R. H. J. Am. Chem. Soc. 2014, 136, 6733−6743. (29) Hong, X.; Liang, Y.; Houk, K. N. J. Am. Chem. Soc. 2014, 136, 2017−2025. (30) Dang, Y.; Qu, S.; Wang, Z.-X.; Wang, X. J. Am. Chem. Soc. 2014, 136, 986−998. (31) Yang, Y.; Liu, P. ACS Catal. 2015, 5, 2944−2951. (32) Williams, T. J.; Bray, J. T. W.; Lake, B. R. M.; Willans, C. E.; Rajabi, N. A.; Ariafard, A.; Manzini, C.; Bellina, F.; Whitwood, A. C.; Fairlamb, I. J. S. Organometallics 2015, 34, 3497−3507. (33) Zhao, G.; Liu, H.; Zhang, D.; Huang, X.; Yang, X. ACS Catal. 2014, 4, 2231−2240. (34) Ariafard, A.; Zarkoob, F.; Batebi, H.; Stranger, R.; Yates, B. Organometallics 2011, 30, 6218−6224. (35) Frisch, M. J., et al. Gaussian 09, revision A.01; Gaussian, Inc., Wallingford, CT, 2009. (36) Alkoxide additives, such as tert-butoxide, did not work properly for this particular reaction system, as they were found to cause the formation of the alkynyl bromide (R′CCBr) rather than the hydrobromination product, apparently because of their overly strong basicity.14 (37) Pape, F.; Thiel, N. O.; Teichert, J. F. Chem. - Eur. J. 2015, 21, 15934−15938. (38) Shi, S.-L.; Buchwald, S. Nat. Chem. 2014, 7, 38−44. (39) Uehling, M.; Suess, A.; Lalic, G. J. Am. Chem. Soc. 2015, 137, 1424−1427. (40) Suess, A.; Uehling, M.; Kaminsky, W.; Lalic, G. J. Am. Chem. Soc. 2015, 137, 7747−7753. (41) Mankad, N. P.; Laitar, D. S.; Sadighi, J. P. Organometallics 2004, 23, 3369−3371. (42) (a) Fan, T.; Sheong, F. K.; Lin, Z. Organometallics 2013, 32, 5224−5230. (b) Zhao, Y.; Liu, Y.; Bi, S.; Liu, Y. J. Organomet. Chem. 2013, 745-746, 166−172. (43) Hibino, J.; Matsubara, S.; Morizawa, Y.; Oshima, K.; Nozaki, H. Tetrahedron Lett. 1984, 25, 2151−2154. (44) Dang, L.; Zhao, H.; Lin, Z.; Marder, T. B. Organometallics 2007, 26, 2824−2832. (45) Hupe, E.; Knochel, P. Org. Lett. 2001, 3, 127−130. (46) Perron, J.; Joseph, B.; Mérour, J.-Y. Tetrahedron 2003, 59, 6659−6666. (47) Jung, S. H.; Hwang, G.-S.; Lee, S. I.; Ryu, D. H. J. Org. Chem. 2012, 77, 2513−2518. (48) It has been proposed that copper-catalyzed Ullmann-type reactions involve oxidative addition of Cu(I) to form Cu(III) intermediates. These reactions occur at considerably higher temperatures than 25 °C. For a recent review see: Sambiagio, C.; Marsden, S. P.; Blacker, A. J.; McGowan, P. C. Chem. Soc. Rev. 2014, 43, 3525− 3550.
insights into the mechanism of this reaction, especially the functions of the phenoxide and (BrCl2C)2, as well as the regeneration of the catalyst. These insights are expected to have implications for better understanding and further developing catalytic hydrohalogenation and other functionalization reactions of alkynes involving active [Cu]−H intermediates.
■
ASSOCIATED CONTENT
* Supporting Information S
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.6b00246. Additional computational results and energies of the optimized structures (PDF) Cartesian coordinates of the optimized structures (XYZ)
■
AUTHOR INFORMATION
Corresponding Authors
*E-mail for Z.-X.W.:
[email protected]. *E-mail for X.W.:
[email protected]. Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS We acknowledge support for this work by the National Science Foundation of China (Grant Nos. 21173263, 21373216, and 21573233) and the University of Colorado Denver. We thank Professor Yan-Bo Wu for assistance in analyzing NBO charges.
■
REFERENCES
(1) (a) Pirnot, M.; Wang, Y.; Buchwald, S. Angew. Chem., Int. Ed. 2016, 55, 48−57. (b) Bullock, R.; Helm, M. Acc. Chem. Res. 2015, 48, 2017−2026. (c) Su, B.; Cao, Z.-C.; Shi, Z.-J. Acc. Chem. Res. 2015, 48, 886−896. (d) Li, Y.-Y.; Yu, S.-L.; Shen, W.-Y.; Gao, J.-X. Acc. Chem. Res. 2015, 48, 2587−2598. (e) Rodriguez-Ruiz, V.; Carlino, R.; Bezzenine-Lafollée, S.; Gil, R.; Prim, D.; Schulz, E.; Hannedouche, J. Dalton Trans. 2015, 44, 12029−12059. (2) Nicolaou, K. C.; Bulger, P. G.; Sarlah, D. Angew. Chem., Int. Ed. 2005, 44, 4442−4489. (3) Metal-catalyzed cross-coupling reactions; De Meijer, A., Diederich, F., Eds.; Wiley-VCH: Weinheim, Germany, 2004; Vols. 1 and 2. (4) Organometallics in Synthesis, Third Manual; Schlosser, M., Ed.; Wiley: Hoboken, NJ, 2013. (5) Gao, F.; Hoveyda, A. H. J. Am. Chem. Soc. 2010, 132, 10961− 10963. (6) Zhang, H. X.; Guibe, F.; Balavoine, G. J. Org. Chem. 1990, 55, 1857−1867. (7) Brown, H.; Hamaoka, T.; Ravindran, N.; Subrahmanyam, C.; Somayaji, V.; Bhat, N. G. J. Org. Chem. 1989, 54, 6075−6079. (8) Chen, S.-M. L.; Schaub, R. E.; Grudzinskas, C. V. J. Org. Chem. 1978, 43, 3450−3454. (9) Hart, D. W.; Blackburn, T. F.; Schwartz, J. J. Am. Chem. Soc. 1975, 97, 679−680. (10) Zhao, Y.; Snieckus, V. Org. Lett. 2014, 16, 390−393. (11) Wipf, P.; Jahn, H. Tetrahedron 1996, 52, 12853−12910. (12) Masuda, Y.; Hoshi, M.; Arase, A. J. Chem. Soc., Perkin Trans. 1 1992, 2725−2726. (13) Huang, Z.; Negishi, E.-i. Org. Lett. 2006, 8, 3675−3678. (14) Uehling, M.; Rucker, R.; Lalic, G. J. Am. Chem. Soc. 2014, 136, 8799−8803. (15) Fujihara, T.; Xu, T.; Semba, K.; Terao, J.; Tsuji, Y. Angew. Chem., Int. Ed. 2011, 50, 523−527. (16) Zhang, Y.; Riduan, S. Angew. Chem., Int. Ed. 2011, 50, 6210− 6212. (17) Whittaker, A.; Lalic, G. Org. Lett. 2013, 15, 1112−1115. G
DOI: 10.1021/acs.organomet.6b00246 Organometallics XXXX, XXX, XXX−XXX
Article
Organometallics (49) Bondi, A. J. Phys. Chem. 1964, 68, 441−451. (50) (a) Kozuch, S.; Shaik, S. Acc. Chem. Res. 2011, 44, 101−110. (b) Kozuch, S. WIREs Comput. Mol. Sci. 2012, 2, 795−815.
H
DOI: 10.1021/acs.organomet.6b00246 Organometallics XXXX, XXX, XXX−XXX
