Cu(II) Catalytic Cycle in

Article Cite This: Organometallics 2019, 38, 2502−2511

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Theoretical and Experimental Studies: Cu(I)/Cu(II) Catalytic Cycle in CuI/Oxalamide-Promoted C−N Bond Formation Devita V. Morarji and Kamlesh K. Gurjar* Chemical Department, VGEC, Ahmedabad, Gujarat, India 382424

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S Supporting Information *

ABSTRACT: In modern Ullmann−Goldberg reactions, cheaper aryl chlorides are poor substrates. Recently, attention has been paid to facile CuI/oxalamide-promoted arylation of heteroatoms (N, O, and S) using cheaper aryl chlorides. However, the mechanism of the reaction and the role of oxalamides have not yet been investigated. In the present investigation, theoretical (density functional theory) and supporting in situ 1H NMR spectroscopy, UV−vis spectroscopy, Fourier transform infrared spectroscopy, and cyclic voltammetry studies have been performed to provide insight into the various aspects of the mechanism. Five different possible pathways have been investigated. [LCu(NHNu)] is the active copper catalytic species, in which L (oxalamide) coordinates Cu(I) through both −CO groups. Our studies show that the reaction follows an outer-sphere single-electron transfer pathway. Moreover, these studies also address the reason for the deactivation of a copper catalyst.

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INTRODUCTION Copper(I) and N,N/N,O/O,O-type ligand-promoted C−heteroatom bond formation methods have been developed as a low-cost alternative to Pd-mediated coupling reactions.1−3 C−heteroatom bond formation reactions have extensive applications in the synthesis of bioactive molecules, agrochemicals, and polymers.4−7 Ligand-controlled selectivity and orthogonality of C−O/C−N bond formation is an additional advantage of copper-mediated reactions.8,9 More reactive aryl halides (iodides and bromides) are very good substrates in these C−N/O/S coupling reactions; comparatively, aryl chlorides require harsh reaction conditions.10,11 The performance and suitability of the ligand depend on the nature of the nucleophiles.12−21 It indicates that a change in the electronic nature of ligands has a great impact on the direction and the reaction conditions. Recently, a large number of ligands have been developed to facilitate these reactions. Unfortunately, they were only found to be efficient for more active aryl halides (ArI and ArBr).22,23 Sincere efforts have been made to develop milder reaction conditions and broadening the substrate scope.11,24−29 However, activation of aryl chlorides has continued to remain a big challenge, until the introduction of oxalic diamides.24,25,30−33 Recently, Ma and co-workers discovered efficient oxalamide ligands (Figure 1) that allow aryl chlorides to be used as the substrate in milder conditions. N,N′-Bis(2,4,6-trimethoxyphenyl)oxalamide (BTMPO) analogues were reported to be very efficient ligands in C−N coupling reactions.24,32 Additionally, Lee’s group reported the first copper-catalyzed coupling of thiols with inactivated aryl chlorides by using oxalic diamides as the ligands.33 As previously mentioned, the suitability of a ligand depends on © 2019 American Chemical Society

the nature of its coupling partners; therefore, screening of a ligand is a very tedious task in these reactions. Understanding the coordination between the ligand and copper(I) and structure−activity relationship between the ligand and an active copper catalytic species will be a great advantage to predict the performance of the ligands. Several reports on the importance of the CuI/oxalamide system in coupling reactions have been published.24,25,30−35 There is an extensive scope for the investigation of the mechanism of CuI/oxalamide-promoted reactions. On the basis of density functional theory (DFT) studies, Ahmad and co-workers reported that the coupling reaction of PhCl and benzylamine follows oxidative addition−reductive elimination (OA−RE).36 It was proposed that before being coordinated with Cu(I), the ligand undergoes double deprotonation and forms dianion (complex 1, Figure 1). However, experimental evidence is not available in favor of the proposed intermediate. If ligands form dianionic species (L2−), it should be a natural competitor of the nucleophile (NuH), and the arylation of ligands should take place. Several computational studies are also available on Cumediated coupling reactions considering aryl iodide/aryl bromide, and the OA−RE path has been suggested (Scheme 1).37−45 Buchwald and co-workers proposed the free radical pathway for these reactions to explain the ligand-driven C−O/C−N selectivity.13,46 Notably, σ-bond metathesis and π-complexation were discarded because of lack of appropriate evidence.10 Aryl chlorides are more reducible and more likely to follow Received: April 3, 2019 Published: June 13, 2019 2502

DOI: 10.1021/acs.organomet.9b00224 Organometallics 2019, 38, 2502−2511

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Figure 1. Cross-coupling reaction of aryl chlorides with nucleophiles,24,36 proposed intermediates, and DFT-predicted equilibrium.

Scheme 1. Possible Reaction Pathways of Cu-Mediated Coupling Reactions

are considered to be a catalytic system, base, and solvent, respectively (Scheme 2).

a free radical pathway. Therefore, previously proposed mechanisms for aryl iodides could not be extended for aryl chlorides. Computational and supporting experimental studies were performed to investigate the mechanism of arylation of aniline with chlorobenzene. CuI/BTMPO(L2), K2CO3, and DMSO

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RESULTS AND DISCUSSION In Situ Fourier Transform Infrared (FTIR) Spectroscopic Studies. In situ 1H NMR and FTIR studies were performed to 2503


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Organometallics Scheme 2. Model Set of Reactions for DFT Studies

used to find the degree of deprotonation of the −NH group. The ratio of peak areas (NH/phenyl-H, 1.0/4.72) for solutions of L1/CuI and L1/CuI/base remains unchanged. Previous studies reported a Δδ = 2−3 ppm significant upfield chemical shift in the NMR peak of −NH, where −NH−M (M = metal) coordination takes place.47−50 However, there is a small upfield chemical shift (Δδ = −0.01 ppm) in the NMR peaks of CuI/L1 and CuI/L1/ base (δ = 10.80 ppm) solutions. Very small upfield chemical shifts also appear in phenyl-H peaks. It clearly indicates the presence of CO−Cu coordination and the absence of NH− Cu coordination. Further, the absence of change in the ratio of integrated peak areas (NH/phenyl-H) indicates that the deprotonation of N−H does not occur in the presence of a base (Figure 3), and previously suggested intermediate 1 does not appear in the solution. An electrostatic potential map of L2 also validates this hypothesis as the electron density around CO is much higher than that around N−H (see Figure S15). On the basis of the above discussion in which the ligand coordinates through CO, we assumed three possible active catalytic species: CCS1, CCS2, and CCS3 (Figure 1). DFT-predicted equilibrium between species CCS3 and CCS4 indicates that CO−Cu coordination favors NH−Cu coordination by 10 kcal/mol free energy. Further, CCS3 is a more favorable (ΔG = −9.6 kcal/mol) species than CCS1 in equilibrium (Figure 4). CCS3 is neutral, and it ensures a higher concentration in equilibrium and better solubility. It is also in agreement with the previous proposed active [LCuNu] species in Ullmann coupling reactions of aryl iodides and nucleophile (NuH).11,38 CCS1 is a positively charged species, and its formation is highly unfavorable (ΔG = 25 kcal/mol). Considering CCS3 as the most probable species, OA-RE, hydrogen atom transfer (HAT), single-electron transfer (SET), σ-bond metathesis, and π-complexation mechanisms were investigated to find the catalytic pathway. Computational Studies. Oxidative Addition−Reductive Elimination Mechanism. A Cu(I)/Cu(III) catalytic cycle based on two-electron redox processes has often been proposed for Ullmann-type coupling reactions in which aryl halide undergoes oxidative addition at copper(I) to form an aryl−copper(III) intermediate. Coupling of the nucleophile and aryl moieties gives the coupled product through a reductive elimination step, and consequently, an active Cu(I) complex is regenerated.10 In the present case, the OA step is highly unfavorable due to a very high free energy (ΔG) barrier (85.3 kcal/mol). However, the reductive elimination step is slightly more favorable (ΔG = 70.9 kcal/mol) (Figure 5). In the reported set of reaction conditions24 (80−120 °C), it seems difficult to overcome these energy barriers. Attempts were also made to optimize the η2 complex, which is, in general, intermediate in the OA of aryl iodides.37 In contrast, the η2 complex does not stabilize in the case of aryl chlorides. In view of the above information, it can be concluded that reactions of aryl chlorides do not follow OA−RE pathways, which is the favorable path for the reactions of aryl iodides.10,11 Halogen Atom Transfer Mechanism. In this mechanism, the aryl radical is formed by transfer of a halogen atom from the aryl

probe the deprotonation of ligand L1. In the IR spectrum of L1, stretching bands of N−H and CO appear at 3302 cm−1 and 1680 (sym) cm−1, respectively (Figure 2). Further, L1 (0.6 g)

Figure 2. In situ recorded FTIR spectra of L1 and L1/CuI.

and CuI (0.475 g) (1:1 molar ratio) were added to THF (10 mL) and properly stirred (25−30 min). The solution was dried by evaporating THF, and the FTIR spectrum of the resulting mixture was recorded in ATR mode. A significant shift toward lower wavenumbers was noticed in the C−Ostr band (1664 cm−1) of L1. However, a significant shift was not observed in the N−Hstr band (3299 cm−1). A shift in the CO band toward the lower wavenumber indicates the interaction of the ligand with Cu(I) and provides direct evidence of CO−Cu(I) ligation. The absence of shifting in the position of the N−H band indicates that neither of −NH− groups directly participate in bonding with Cu(I). Assignment of bands in the IR spectrum was also verified by the DFT-calculated vibrational spectrum of L1, and the calculated spectrum ensures the origin of the 1680 cm−1 band from CO stretching. In the calculated vibrational spectrum, it appears at 1683 cm−1 (Figure S4). K2CO3 has poor solubility in THF; therefore, the FTIR spectrum of a mixture of L1, CuI, and base (K2CO3) could not be recorded. DMSO is not found to be suitable in the current setup because it does not readily evaporate. In Situ 1H NMR Spectroscopic Studies. To investigate the ligation (L1−Cu) in the presence of a base, in situ 1H NMR spectra of L1 were recorded under N2 with different additives (CuI and base). The solution of L1 (0.625 mmol, 0.015 g) was prepared in DMSO-d6, and the spectrum was recorded. CuI (2 equiv) and base (K2CO3, 4 equiv) were added sequentially in the solution of L1 (1 equiv). The entire process was performed under N2. During the recording of the spectra, the solution was kept in a sealed NMR tube. At every step, the spectrum was recorded 25−30 min (35 °C) after the desired additives were mixed. In the 1H NMR spectrum of L1, −NH hydrogens have a chemical shift at δ = 8.1 ppm and phenyl hydrogens have a chemical shift at δ = 7.0−7.9 ppm. Interestingly, with the addition of CuI as well as CuI/base, a significant chemical shift (δ) was not observed in the signal of −NH. The ratio of integrated peak areas of N−H (2 H) and phenyl-H (10 H) was 2504


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Figure 3. Chemical shift (δ) in −NH and phenyl-H, in situ 1H NMR of L1, L1/CuI, and L1/CuI/base (K2CO3) in DMSO-d6.

Figure 4. Possible active copper(I) catalytic species (CCS) and DFT-predicted equilibrium.

Figure 5. Calculated free energy profile for the OA−RE pathway. In optimized geometries, hydrogen atoms are omitted for more clarity. 2505


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Figure 6. Calculated free energy profile for HAT mechanism. In optimized geometries, hydrogen atoms are omitted for more clarity.

Figure 7. Calculated free energy profile for the SET mechanism. In optimized geometries, hydrogen atoms are omitted for more clarity.

directly coordinate to the aryl halide and only a single electron is transferred. For DFT studies of the SET path, the previously reported model has been adopted.13 Separately, energies were calculated for Cu(II) species and [PhCl]− anion free radical, and the sum of these two values is considered for calculation of overall energy barrier (ΔG = 39.7 kcal/mol). It is lower than the previously reported barrier (53.1 kcal/mol)46 for aryl iodide in SET, and it is also in agreement that aryl chlorides are more reducible than aryl iodides11 (Figure 7). Other species CCS1 and CCS2 were also investigated, and the ΔG barriers were 98.2 and 99.4 kcal/mol, respectively. These energy barriers are unreasonably high, and CCS1 and CCS2 cannot be the initial active species. The dissociative electron transfer in the SET mechanism has two types, outer-sphere SET and inner-sphere SET, and two different models are used to calculate the activation energy of these paths. In the outer-sphere SET, electron transfer takes place from CCS3 to PhCl and C−Cl bond dissociation occurs in two sequentially different steps to deliver the [PhCl]− radical (eq 1). In such type of cases, Marcus−Hush theory52−54 is applicable.

halide to the active Cu(I) complex. It is an oxidative addition of halogen atom (X) to Cu(I) by single electron transfer, forming Cu(II)X complex and a phenyl radical.10,44 In previous studies, though several groups13,46,51 made sincere efforts to optimize the transition state (TS) for HAT, unfortunately, their attempts were unsuccessful and therefore authors estimated activation energy of AT mechanism by the sum of separately calculated energies for Cu(II)X complex and a phenyl radical. However, this estimation is inappropriate and significantly underestimates the energy barrier. We have successfully optimized the TS for AT pathway and it has an overall free energy barrier of 78.8 kcal/mol (Figure 6), while the earlier proposed13,51 estimation method gives 4.9 kcal/mol free energy barrier. It is important to mention that the appropriate energy barrier can only be calculated by TS optimization. A comparison of the free energy values indicates that this path is more favorable than OA-RE path. Single-Electron Transfer Mechanism. In the SET mechanism, the Cu(I) complex oxidizes by one-electron transfer to the aryl halide. This delivers an aryl halide radical anion and Cu(II) species.10 The aryl halide radical anion dissociates into an aryl free radical and halide. The aryl free radical couples with the nucleophile to deliver the product and transfers an electron back to the Cu(II) species. This type of electron transfer is called “outer-sphere” SET, where the Cu(I) species does not

outer-sphere ET, Marcus−Hush theory −Cu(II)

Cu(I) + PhCl ⎯⎯⎯⎯⎯⎯⎯→ [PhCl]−• → [Ph]• + Cl− 2506

(1)


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Figure 8. σ-Bond metathesis and π-complexation, optimized geometries of TS. Hydrogen atoms are omitted for more clarity.

Figure 9. In situ UV−vis spectra of intermediate copper species in the C−N coupling reaction of PhNH2 and PhCl in the presence of CuI/L1 (a) and in C−N coupling reaction of PhNH2 and PhI in the presence of CuI/N,N′-dimethylethane-1,2-diamine (b).

The barriers for σ-bond metathesis (98 kcal/mol) and π-complexation (103.7 kcal/mol) are unreasonably large, even higher than the energy barrier for oxidative addition (Figure 8). In Situ UV−vis Spectroscopic Studies. Free radical and AT mechanisms operate via Cu(II), and OA operates via a Cu(III) intermediate species. Cu(II) and Cu(III) species have different patterns in electronic spectra. Cu(II) species have a unique d−d transition absorption band59,60 around 400−700 nm, and Cu(III) species have a spectrum pattern similar to that of the Ni(II) species.41,61 Considering the same, in situ UV−vis spectroscopic studies were performed to investigate the presence of intermediate Cu(II) and Cu(III) species in the reaction. In the in situ recorded spectrum of the reaction of chlorobenzene and aniline in the presence of oxamide (L1)/CuI/Cs2CO3/DMSO (Figure 9a), an absorption band is observed at λmax = 547 nm. The spectrum pattern indicates the presence of a Cu(II) species and the absence of a Cu(III) species in solution. Sometimes the Cu(I) species might turn into a blue colored Cu(II) species due to air oxidation. Therefore, it is difficult to establish the actual origin of Cu(II). However, it is reported that on the addition of the nucleophile, the Cu(II) species that originate from air oxidation disappear (reduction of Cu(II) into Cu(I) by the nucleophile).59 Solution color became pale yellow during the reaction. The crude product of the reaction was analyzed in GC-MS (see the Supporting Information for mass spectra of the product diphenylamine and the ligand). To validate the difference in mechanistic pathways followed by aryl chlorides and aryl iodides, in situ UV−vis spectroscopic studies of the coupling reaction of iodobenzene and aniline was also conducted in the

inner-sphere ET, Savéant’s model −Cu(II)

Cu(I) + PhCl ⎯⎯⎯⎯⎯⎯⎯→ [Ph]• + Cl−

(2)

In the inner-sphere SET, electron transfer and C−Cl bond cleavage occur simultaneously (eq 2). In such types of cases, Savéant’s model55−58 is applicable. Free energies of activation for SET pathways can also be predicted by these two models. We have extended both models (the detailed method is given in the Supporting Information) to estimate the activation free energy barriers for the outer-sphere (Marcus−Hush theory) and innersphere (Savéant’s model) SET mechanisms. Applying these models, activation free energy for the inner-sphere and outersphere SET are 52.3 and 41.0 kcal/mol, respectively, with the outer-sphere SET having a lower ΔG value. The energy calculated for outer-sphere SET by Marcus−Hush model is slightly higher (1.3 kcal/mol) than the directly calculated activation energy of 39.7 kcal/mol. Notably, the outer-sphere SET mechanism is more favorable than the inner-sphere SET, OA−RE, and HAT (Figure 7). Despite being discarded in earlier reports,10,13 we have calculated the free energy barrier for the σ-bond metathesis and π-complexation pathways. In the σ-bond metathesis pathway, Cu(I) coordinates with a nucleophile as well as a halogen, and a four-centered transition state forms. That facilitates the attack of the nucleophile at the ring. In the π-complexation pathway, Cu(I) coordinates to the ring and makes it electron-deficient. Electron deficiency at the ring invites the nucleophile to displace the halide.10,11 2507


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Figure 10. Cyclic voltammetry was performed in a three-electrode cell under a N2 atmosphere at 30 °C at a scan rate of 0.04 V s−1. The working electrode was a glassy carbon disk (area = 0.071 cm2). Ten scans were taken for a 10 mL solution containing degassed and dried DMSO (see the Supporting Information for more detail).

additives (aniline and chlorobenzene). Also, the peaks corresponding to Cu(III) species were not observed.64 As mentioned previously for in situ spectroscopic and CV studies, there is no evidence of the appearance of Cu(III). Considering the calculated energy barriers of different possible pathways for the proposed active species CCS3 and the results of in situ studies, it can be proposed that the reaction follows the outer-sphere SET pathway involving a Cu(I)/Cu(II) redox couple.

presence of a CuI/N,N′-dimethylethane-1,2-diamine/Cs2CO3/ toluene system. The recorded spectrum (Figure 9b) clearly indicates the presence of intermediate Cu(III) species in the system (762, 1028, and 1090 nm). The spectrum of the visible species shows good agreement with the previously reported spectra of Cu(III) and Ni(II) species.41,62 In Situ Cyclic Voltammetry Studies. Cyclic voltammetry (CV) studies were also reported to be a tool in the mechanistic studies of the Ullmann reaction, as it is helpful to find the oxidation state of an active species.63 The CV studies of ligand L1 and L1/K3PO4 (40 mM/40 mM) in DMSO do not show any oxidation peak with respect to deprotonated ligand, hence deprotonation of the ligand does not occur. In studies of CuI (10 mM), an irreversible reduction peak of Cu(I) appears at −0.705 V, and with addition of L1, the peak shifts to −0.862 V. Possibly, the peak (−0.862 V) belongs to the L1-ligated Cu(I) species (Figure 10). The oxidation peak of Cu(I)/Cu(II) appears at +0.202 V, and with sequential addition of a ligand and a base (K3PO4), it shifts to +0.268 and +0.5 V, respectively. Notably, with addition of the base, the oxidation peak of Cu(I) disappears, indicating that the base promotes the disproportionation of Cu(I) into Cu(0) and Cu(II).19 Disproportionation is a general cause for deactivation of a copper catalyst.19 These results are consistent with the previous studies on base-promoted deactivation of a catalyst.18,14,20,41 A significant effect was not observed with the addition of other

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CONCLUSION As evident from the experimental studies, the ligand does not undergo deprotonation during the reaction and coordinates with Cu(I) through CO. On the basis of experimental and theoretical results, it can be concluded that the CCS3 intermediate is the most favorable active catalytic species, and the reaction proceeds through the outer-sphere SET pathway. Further, CV studies indicate that mainly the base is responsible for the disproportionation of the active Cu(I) species and, consequently, for the deactivation of the catalyst. The present study will contribute to a further understanding of the mechanism of the reaction and the role of the ligand and base.

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EXPERIMENTAL AND COMPUTATIONAL SECTION

The Gaussian 09 package65 was used for calculations. Hybrid DFT (20% HF exchange) calculations were performed at the B3LYP level66 2508


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Organometallics using the 6-31+g (d,p) basis set51 for C, H, N, O, and Cl atoms and effective core potential (ECP)/LANL2DZ basis set13 for Cu, K, and I (at 298 K, in DMSO). The solvation model C-PCM with a universal force field was employed for solvent DMSO. We optimized geometries without any constraint, and single-point energy calculations were performed. Zero point and thermal corrections to Gibb’s free energy were adjusted from harmonic vibrational frequency calculations at 298 K. We used the Berny algorithm for the optimization of transition states. Transition states were confirmed by a single imaginary frequency corresponding to the atoms involved. Backward and forward direction intrinsic reaction coordinates were performed on transition states. Additionally, we have also performed the calculations for the crucial reaction paths with dispersion correction (DFT-D3) (Table S1).67 See the Supporting Information for experimental details of in situ CV and the synthesis of L1.

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(8) Rovira, M.; Soler, M.; Güell, I.; Wang, M.-Z.; Gómez, L.; Ribas, X. Orthogonal Discrimination among Functional Groups in UllmannType C−O and C−N Couplings. J. Org. Chem. 2016, 81 (17), 7315− 7325. (9) Shafir, A.; Lichtor, P. A.; Buchwald, S. L. N- versus O-Arylation of Aminoalcohols: Orthogonal Selectivity in Copper-Based Catalysts. J. Am. Chem. Soc. 2007, 129 (12), 3490−3491. (10) Sperotto, E.; van Klink, G. P. M.; van Koten, G.; de Vries, J. G. The Mechanism of the Modified Ullmann Reaction. Dalton Trans. 2010, 39 (43), 10338−10351. (11) Sambiagio, C.; Marsden, S. P.; Blacker, A. J.; McGowan, P. C. Copper Catalysed Ullmann Type Chemistry: From Mechanistic Aspects to Modern Development. Chem. Soc. Rev. 2014, 43 (10), 3525−3550. (12) Maiti, D.; Buchwald, S. L. Orthogonal Cu- and Pd-Based Catalyst Systems for the O- and N-Arylation of Aminophenols. J. Am. Chem. Soc. 2009, 131 (47), 17423−17429. (13) Jones, G. O.; Liu, P.; Houk, K. N.; Buchwald, S. L. Computational Explorations of Mechanisms and Ligand-Directed Selectivities of Copper-Catalyzed Ullmann-Type Reactions. J. Am. Chem. Soc. 2010, 132 (17), 6205−6213. (14) Lo, Q. A.; Sale, D.; Braddock, D. C.; Davies, R. P. Mechanistic and Performance Studies on the Ligand-Promoted Ullmann Amination Reaction. ACS Catal. 2018, 8 (1), 101−109. (15) Giri, R.; Brusoe, A.; Troshin, K.; Wang, J. Y.; Font, M.; Hartwig, J. F. Mechanism of the Ullmann Biaryl Ether Synthesis Catalyzed by Complexes of Anionic Ligands: Evidence for the Reaction of Iodoarenes with Ligated Anionic CuI Intermediates. J. Am. Chem. Soc. 2018, 140 (2), 793−806. (16) Amal Joseph, P. J.; Priyadarshini, S. Copper-Mediated C−X Functionalization of Aryl Halides. Org. Process Res. Dev. 2017, 21 (12), 1889−1924. (17) Deldaele, C.; Evano, G. Room-Temperature Practical CopperCatalyzed Amination of Aryl Iodides. ChemCatChem 2016, 8 (7), 1319−1328. (18) Sherborne, G. J.; Adomeit, S.; Menzel, R.; Rabeah, J.; Bruckner, A.; Fielding, M. R.; Willans, C. E.; Nguyen, B. N. Origins of High Catalyst Loading in Copper(i)-Catalysed Ullmann-Goldberg C-N Coupling Reactions. Chem. Sci. 2017, 8 (10), 7203−7210. (19) Sung, S.; Sale, D.; Braddock, D. C.; Armstrong, A.; Brennan, C.; Davies, R. P. Mechanistic Studies on the Copper-Catalyzed NArylation of Alkylamines Promoted by Organic Soluble Ionic Bases. ACS Catal. 2016, 6 (6), 3965−3974. (20) Ajitha, M. J.; Pary, F.; Nelson, T. L.; Musaev, D. G. Unveiling the Role of Base and Additive in the Ullmann-Type of Arene-Aryl C−C Coupling Reaction. ACS Catal. 2018, 8 (6), 4829−4837. (21) Zhou, G.; Chen, W.; Zhang, S.; Liu, X.; Yang, Z.; Ge, X.; Fan, H.J. A Newly Designed Carbohydrate-Derived Alkylamine Promotes Ullmann Type C−N Coupling Catalyzed by Copper in Water. Synlett 2019, 30, 193. (22) Strieter, E. R.; Blackmond, D. G.; Buchwald, S. L. The Role of Chelating Diamine Ligands in the Goldberg Reaction: A Kinetic Study on the Copper-Catalyzed Amidation of Aryl Iodides. J. Am. Chem. Soc. 2005, 127 (12), 4120−4121. (23) Liu, X.; Chang, S.; Chen, X.; Ge, X.; Qian, C. Efficient Ullmann C−X Coupling Reaction Catalyzed by a Recoverable FunctionalizedChitosan Supported Copper Complex. New J. Chem. 2018, 42 (19), 16013−16020. (24) Zhou, W.; Fan, M.; Yin, J.; Jiang, Y.; Ma, D. CuI/Oxalic Diamide Catalyzed Coupling Reaction of (Hetero)Aryl Chlorides and Amines. J. Am. Chem. Soc. 2015, 137 (37), 11942−11945. (25) Fan, M.; Zhou, W.; Jiang, Y.; Ma, D. Assembly of Primary (Hetero)Arylamines via CuI/Oxalic Diamide-Catalyzed Coupling of Aryl Chlorides and Ammonia. Org. Lett. 2015, 17 (23), 5934−5937. (26) Zhao, Y.; Wang, X.; Kodama, K.; Hirose, T. Copper-Catalyzed Coupling Reactions of Aryl Halides and Phenols by 4,4’-Dimethoxy2,2’-Bipyridine and 4,7-Dimethoxy-1,10-Phenanthroline. ChemistrySelect 2018, 3 (44), 12620−12624.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.9b00224. General procedure for preparation of L1, in situ studies (UV−vis, CV, FTIR), and NMR spectra (PDF) Cartesian coordinates for the optimized geometries (XYZ)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Devita V. Morarji: 0000-0003-3979-6336 Kamlesh K. Gurjar: 0000-0002-1924-3809 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We are thankful to MRC-MNIT, Jaipur, India, for use of the analytical facilities (NMR). We are grateful to Prof. N. M. Misra, PDPU, Gandhinagar, India, for use of the computational facility. We thank Dr. Sudhanshu Sharma, IIT Gandhinagar, India, for the CV study. We are thankful to VGEC, Ahmedabad, for providing the necessary facilities.

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REFERENCES

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