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Reactivity Study of Unsymmetrical β‑Diketiminato Copper(I) Complexes: Effect of the Chelating Ring Wan-Jung Chuang,†,‡ Sung-Po Hsu,§,∥ Kuldeep Chand,†,‡ Fu-Lun Yu,†,‡ Cheng-Long Tsai,†,‡ Yu-Hsuan Tseng,†,‡ Yuh-Hsiu Lu,†,‡ Jen-Yu Kuo,†,‡ James R. Carey,†,‡,⊥ Hsuan-Ying Chen,†,‡ Hsing-Yin Chen,†,‡ Michael Y. Chiang,†,‡,# and Sodio C. N. Hsu*,†,‡ †

Department of Medicinal and Applied Chemistry, Kaohsiung Medical University, Kaohsiung 807, Taiwan Department of Medical Research, Kaohsiung Medical University Hospital, Kaohsiung 807, Taiwan § Department of Physiology, School of Medicine, College of Medicine, Taipei Medical University, Taipei 110, Taiwan ∥ Graduate Institute of Medical Sciences, College of Medicine, Taipei Medical University, Taipei 110, Taiwan ⊥ Department of Applied Chemistry, National University of Kaohsiung, Kaohsiung 804, Taiwan # Department of Chemistry, National Sun Yat-Sen University, Kaohsiung 804, Taiwan ‡

S Supporting Information *

ABSTRACT: β-Diketiminato copper(I) complexes play important roles in bioinspired catalytic chemistry and in applications to the materials industry. However, it has been observed that these complexes are very susceptible to disproportionation. Coordinating solvents or Lewis bases are typically used to prevent disproportionation and to block the coordination sites of the copper(I) center from further decomposition. Here, we incorporate this coordination protection directly into the molecule in order to increase the stability and reactivity of these complexes and to discover new copper(I) binding motifs. Here we describe the synthesis, structural characterization, and reactivity of a series of unsymmetrical N-aryl-N′-alkylpyridyl β-diketiminato copper(I) complexes and discuss the structures and reactivity of these complexes with respect to the length of the pyridyl arm. All of the aforementioned unsymmetrical ß-diketiminato copper(I) complexes bind CO reversibly and are stable to disproportionation. The binding ability of CO and the rate of pyridyl ligand decoordination of these copper(I) complexes are directly related to the competition between the degree of puckering of the chelate system and the steric demands of the Naryl substituent.

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INTRODUCTION During the past several decades, β-diketiminato chelating ligands have been used throughout coordination chemistry as sterically crowded spectator ligands that stabilize coordinatively unsaturated metal centers.1−3 An outline of β-diketiminato copper(I) complexes and their applications is shown on Scheme 1. In particular, copper(I) complexes containing N,N′-aryl-substituted β-diketiminato ligands have been widely studied.4−9 For example, Tolman and co-workers have prepared and studied N,N′-aryl β-diketiminato copper complexes that mimic the dioxygen activation of copper-containing metalloproteins.10−20 Likewise, Warren and co-workers reported a series of N,N′-aryl β-diketiminato copper nitrene and carbene complexes used for amination reactions and for catalytic cyclopropanation, respectively.21−30 Recently, re© XXXX American Chemical Society

searchers have reported the synthesis and analyses of N,N′alkyl β-diketiminato copper(I) complexes containing Lewis bases or olefin ligands. These compounds have been reported to have applications in atomic layer deposition or chemical vapor deposition.31−37 Indeed, many authors have observed that these complexes were very susceptible to disproportionation, probably due to the open coordination site.5,35,38 For the disproportionation of a β-diketiminato copper(I) complex (see Scheme 2), the corresponding copper(II) complex and a black material of copper(0) were reported separately by Ito and Schaper et al.5,35 It has been found that a coordinating solvent or Lewis base is required to prevent disproportionation and to Received: November 30, 2016

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DOI: 10.1021/acs.inorgchem.6b02876 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry Scheme 1. Structural Illustrations of β-Diketiminato Copper(I) Complexes and Their Applications

ascertained. Third, an increase in stability of β-diketiminato copper(I) complexes may be realized due to pyridyl arm chelation. To address these issues, four unsymmetrical N-arylN′-alkyl β-diketiminato ligands bearing pendant pyridyl groups (Chart 1) and their corresponding copper(I) complexes were prepared and characterized. The results suggest that pendant pyridyl arms on the N-aryl-N′-alkyl β-diketiminato ligands may act as hemilabile Lewis bases protecting the copper(I) center.46−49 According to IR and NMR studies, the length of the pyridyl arm influences the binding mode interconversion and binding ability of carbon monoxide in solution of these copper(I) complexes. The steric demands of the N-aryl substituent group play only a minor role in the CO binding (on/off rate) and solution binding behavior.

Scheme 2. Illustration of the Disproportionation during Formation of a β-Diketiminato Copper(I) Complex by Itoh’s Report

block the coordination site of the copper(I) center from further decomposition. However, what is lacking in the literature is a thorough study of a systematic ligand set that prevents copper(I) disproportionation. On the basis of previous studies of symmetric N,N′-alkyl- or N,N′-aryl-substituted β-diketiminato copper complexes and our previous work on biomimetic copper complexes,39−44 we decided to vary the ligand framework to probe new binding motifs and reactivity in copper chemistry. β-Diketiminato copper(I) complexes were synthesized by replacing the symmetric N,N′-alkyl- or N,N′-aryl-substituted ligands with unsymmetrical N-aryl-N′-alkyl-substituted ligands.45 The copper(I) complexes containing unsymmetrical N-aryl-N′alkyl β-diketiminato ligands may display different binding modes in comparison to the N,N′-alkyl or N,N′-aryl analogues. The preparation of these compounds will allow us to probe three important issues. First, we can determine how the length of the pendant pyridyl arm is able to effect the coordination behavior of these copper(I) complexes. Second, which of the sterically encumbered substituents that allows binding can be

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RESULTS AND DISCUSSION Synthesis and Characterization of Copper(I) Complexes. Several synthetic procedures have been described for the preparation of copper(I) β-diketiminato complexes having varying ancillary substituents close to the metal center.4,5,21−24,34,35,50,51 It is worth mentioning that the βdiketiminato copper(I) complexes are very susceptible to disproportionation. Thus, a coordinating solvent or Lewis base may be required for synthesis of these complexes.5,35,51 We chose CuOtBu as a copper(I) source to synthesize the N-arylN′-alkyl β-diketiminato copper(I) complexes. Indeed, CuOtBu as a copper(I) source was previously reported by Warren et al. as an economical and soluble starting material for the preparation of copper(I) complexes.52 Direct reactions of

Chart 1. Representation of the N-Aryl-N′-alkyl β-Diketiminato Ligand Sets

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DOI: 10.1021/acs.inorgchem.6b02876 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry Scheme 3. Synthesis of the N-Aryl-N′-alkyl β-Diketiminato Copper(I) Complexes

CuOtBu with L1H−L4H in hexane at room temperature for 1 h afforded the corresponding CuL1−CuL4 complexes (Scheme 3). All four copper(I) complexes were characterized by 1H NMR, 13C NMR, and elemental analysis. The 1H NMR spectra of CuL1−CuL4 complexes show an upfield shift (e.g. for Py-Hα 7.86 ppm for CuL1) in comparison to the ligand precursor (8.38 ppm for L1H), indicating that coordination between the copper(I) ion and pendant pyridyl group is retained in solution. In order to understand the influence of the pyridyl group as a chelating arm to prevent disproportionation, we prepared the two ligands L1PhH and L3PhH (Chart 2), containing a phenyl

The geometries and bond parameters of the two independent molecules of CuL1 in the unit cell are very similar; thus, only one of the structures is represented in Figure 1a. The anionic ligand L1− of monomer CuL1 serves as a tridentate ligand for Cu and has a slightly distorted T-shaped coordination geometry, with a nearly planar five-membered ring produced by a chelating pyridylmethyl arm. The monomer CuL2 compound exhibits a nearly planar distorted Y-shaped coordination geometry. The pyridylethyl arm of CuL2 forms a six-membered chelate ring with a twist-boat form connecting the planar six-membered diazapentadienyl (NCCCN) bidentate chelate ring with a bridging copper. The anionic ligand of L3− serves as a tridentate ligand in the solid state of monomer CuL3 and displays a slightly distorted T-shaped coordination geometry that is similar to the coordination of L1− in CuL1. The CuL4 monomer also shows a nearly planar distorted Yshaped coordination geometry about the copper center. Similar to the case for CuL2, the CuL4 complex forms a twist-boat-like pyridylethyl arm chelate ring with an NCCCN bidentate chelate six-membered ring with a bridging copper. Interestingly, the two pyridyl ligand bridged dinuclear cyclometalated Cu(I) complexes Cu2(μ-L1)2 and Cu2(μ-L4)2 are found after recrystallization in a coordinating solvent. Each of the molecular structures of Cu2(μ-L1)2 and Cu2(μ-L4)2 consists of two β-diketiminato copper subunits (in a threecoordination environment) bridged by two pyridylalkylamide linkers. These arrangements result in the formation of 10- and 12-membered metallamacrocycles in Cu2(μ-L1)2 and Cu2(μL4)2 (Figure 1e,f), respectively. Cu2(μ-L1)2 and Cu2(μ-L4)2 exhibit a slightly distorted Y-shaped coordination geometry, which may be due to the chelated ring strain release to form the bridging complex. The copper complexes CuL1, CuL2, CuL3, CuL4, Cu2(μ-L1)2, and Cu2(μ-L4)2 all display three-coordinate geometries. The differences in the molecular structures clearly suggest disparities due to the effective steric effect imposed by their respective Naryl substituents and length of the pyridyl arm supporting the β-diketiminato ligands. The N-aryl ring is also twisted from perpendicular with respect to the NCCCN plane in CuL1, CuL2, CuL3, and CuL4. The N-aryl ring twist angles of 18.17 and 18.46° for CuL1 and 13.65° for CuL2 are much larger than the 2.21° for CuL3 and 9.21° for CuL4, indicating the steric influence of the ortho position on the N-aryl substituents. The Cu−N(py) bond lengths (1.932−1.958 Å) of CuL1, CuL2,

Chart 2. Representation of the Two N-Aryl-N′-alkyl βDiketiminato Ligands L1PhH and L3PhH

group, to compare with L1H and L3H, containing a pyridyl group. Replacing the pyridyl arm with a phenyl arm may cause disproportionation during copper(I) complex formation. Indeed, direct reactions of CuOtBu with L1PhH or L3PhH in hexane at room temperature afford disproportionation products, as indicated by a black material of copper(0) and an intractable strongly colored product. These observations suggest that the pyridyl arm of N-aryl-N′-alkyl β-diketiminato ligands (L1H−L4H) could prevent their corresponding copper(I) complexes from disproportionation. Molecular Structures of N-Aryl-N′-alkyl β-Diketiminato Copper(I) Complexes. X-ray-quality crystals of CuL1− CuL4 complexes were obtained in hexane at −20 °C. Crystallographic analyses revealed that CuL1, CuL2, CuL3, and CuL4 complexes are mononuclear. On the other hand, recrystallization of CuL1 and CuL4 in a coordinating solvent (CH3CN for CuL1, THF for CuL4; Scheme 3) gives the ligandbridged dinuclear cyclometalated copper(I) complexes Cu2(μL1)2 and Cu2(μ-L4)2, respectively. Representations of the molecular structures of CuL1, CuL2, CuL3, CuL4, Cu2(μ-L1)2, and Cu2(μ-L4)2 are shown in Figure 1, with selected bond distances and angles given in Table 1. C

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Figure 1. ORTEP drawings of complexes CuL1 (a), CuL2 (b), CuL3 (c), CuL4 (d), Cu2(μ-L1)2 (e), and Cu2(μ-L4)2 (f) (50% ellipsoids; hydrogen atoms not shown for clarity).

Table 1. Selected Bond Lengths (Å) and Angles (deg) for Complexes CuL1, CuL2, CuL3, CuL4, Cu2(μ-L1)2, and Cu2(μ-L4)2 CuL1 Cu−N(amide(aryl)) Cu−N(amide(alkyl)) Cu−N(py) C−C(NCCCN backbone) C−N(NCCCN backbone) N(amide)−Cu−N(amide) N(amide(aryl))−Cu−N(py) N(amide(alkyl))−Cu−N(py) ∠NCCCN(aryl)a a

molecule A

molecule B

CuL2

CuL3

CuL4

Cu2(μ-L1)2

Cu2(μ-L4)2

1.876(4) 1.987(4) 1.952(4) 1.401(7) 1.421(7) 1.342(6) 1.311(6) 99.92(16) 173.72(16) 84.27(16) 71.83

1.877(4) 1.992(4) 1.949(4) 1.381(6) 1.418(6) 1.353(6) 1.317(6) 100.00(16) 174.14(16) 84.08(16) 71.54

1.8915(19) 2.005(2) 1.932(2) 1.401(3) 1.420(4) 1.332(3) 1.306(3) 98.80(9) 160.82(9) 100.06(9) 76.35

1.876(5) 1.995(6) 1.938(5) 1.406(9) 1.418(9) 1.295(8) 1.335(8) 99.3(2) 175.9(3) 84.5(2) 87.79

1.885(2) 1.997(2) 1.934(2) 1.392(4) 1.422(4) 1.319(3) 1.343(4) 100.85(9) 153.30(10) 101.61(9) 80.42

1.947(11), 1.933(11) 1.994(11), 1.980(11) 1.971(12), 1.956(11) 1.39(2), 1.42(2) 1.44(2), 1.42(2) 1.35(2), 1.34(2) 1.31(2), 1.31(2) 98.8(5), 99.8(5) 140.7(5), 137.2(5) 120.5(5), 123.0(5) 79.23, 86.06,

1.975(3) 1.951(2) 1.958(2) 1.405(5) 1.417(5) 1.327(4) 1.326(4) 98.90(10) 120.18(11) 137.33(10) 89.36

Angle between the NCCCN backbone plane and N-aryl ring.

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Figure 2. Variable-temperature 1H NMR spectra of the CuL1 complex (3.4−5.6 ppm).

CuL3, and CuL4 are similar to reported data for N,N′-arylsubstituted β-diketiminato copper(I) complexes containing pyridine or lutidine ligation.23,53 Therefore, the pyridyl arms of our ligand sets (L1−, L2−, L3−, and L4−) may act as neutral donors to the copper ion while the NCCCN backbone serves as an anionic donor. The bond distances of the NCCCN backbone for the copper complexes CuL1, CuL2, CuL3, CuL4, Cu2(μ-L1)2, and Cu2(μ-L4)2 are similar to those of the relatively well-known deprotonated anionic β-diketiminato ligand.5,11,15,17,20,21,23,28,34−37,53 In general, the pyridylmethyl arms form five-membered chelate rings with the anionic β-diketiminato moieties. The chelating L1− and L3− ligands give tridentate three-coordinated mononuclear compounds CuL1 and CuL3. In addition, the pyridylethyl arms of L2− and L4− give stable twist-boat confirmations for the six-membered chelate ring in monomers CuL2 and CuL4. Coordinating solvents may force the chelating pyridylalkyl arm to unchelate, forming the ligand-bridged dinuclear cyclometalated copper(I) complexes Cu2(μ-L1)2 and Cu2(μ-L4)2. NMR Study of Copper(I) Complexes. Due to the crystallographically observed various binding modes of copper(I) complexes, it is important to understand the structure of copper complexes CuL1, CuL2, CuL3, CuL4, Cu2(μ-L1)2, and Cu2(μ-L4)2 in solution. Solution NMR studies in acetonitrile-d3 and toluene-d8 at room temperature of complexes Cu2(μ-L1)2 and Cu2(μ-L4)2 show NMR signals and chemical shifts similar to those for complexes CuL1 and CuL4. On the basis of these NMR observations and crystallization results described above, the dinuclear structures are obtained from modestly coordinating solvents such as MeCN and THF, whereas mononuclear structures are obtained from alkane solvents. Therefore, we

suggest that pyridylalkyl arm bridged dimerization may result from the coordinating solvent-induced crystallization process. In order to understand the solution behaviors and to gain insight into the dynamic processes of CuL1−CuL4, variabletemperature 1H NMR experiments (VT-1H NMR) were performed. The VT-1H NMR spectra for CuL1 and CuL3 recorded between 20 and −90 °C in toluene-d8 are similar (Figures S9 and S11 in the Supporting Information). Particularly revealing portions of the spectra with assignments for CuL1 are shown in Figure 2. At 20 °C, a singlet (b1) at 4.96 ppm for the central −CH proton on the NCCCN backbone and another singlet (d1) at 4.12 ppm for methylene −CH2 protons of the pyridylmethyl arm are observed, suggesting the presence of a CuL1 species. Upon cooling, the intensity of the central −CH peak at 4.96 ppm decreases while a new −CH singlet appears at 4.91 ppm (b1′). Concurrently, the peak due to the methylene −CH2 protons at 4.12 ppm also decreases in intensity, while two new doublets appear at vastly different chemical shifts (5.39 ppm, d1a′; 4.52 ppm, d1b′; J = 12 Hz), indicating a pattern of diastereotopic methylene −CH2 protons. The multiplets at 3.57 ppm (j1) attributed to the isopropyl substituent methine −CH protons also change upon cooling. We interpret these changes in the 1H NMR spectrum upon cooling to indicate that the monomer CuL1 species is the major species present at higher temperature and the dimer Cu2(μ-L1)2 is the major species present at lower temperature (Scheme 4). The Cu2 (μ-L1) 2 dimer is structurally different from monomer CuL1 and shows a major change in the chemical shift difference of the methylene protons (Figure 2). We estimate the equilibrium constants (Keq = [Cu2(μ-L1)2]/ [CuL1]2) at each temperature by integrating the singlets for the ligand backbone −CH protons and obtained thermodynamic parameters from an Arrhenius plot of ln Keq versus 1/T E

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the pyridylethyl arm. Lowering of the temperature provokes a progressive splitting of the two sets of signals (d2 and e2) which become three sets (d2b, d2a + e2b, and e2a) at −90 °C. This overlapping behavior suggests that, during cooling, a chelating pyridylethyl ring flipping fluxional process is taking place in solution (depicted in Scheme 5). As deduced from the

Scheme 4. Interconversion of CuL1/Cu2(μ-L1)2

Scheme 5. Possible Conformational Changes of the SixMembered Metallacycle CuL2 (Figure S13 in the Supporting Information): ΔH° = −14.8 ± 0.5 kJ mol−1 and ΔS° = −57.9 ± 2.3 J mol−1 K−1. The large chemical shift differences between the methylene signals in Cu2(μ-L1)2 and the negative entropy value for the equilibrium with CuL1 are consistent with a dimeric complex bearing a bridged intermolecular pyridylmethyl arm. For the CuL3/ Cu2(μ-L3)2 system, the interconversion behavior also obtained from the VT-1H NMR investigation of CuL3 (Figure S11 in the Supporting Information) is consistent with the thermodynamic parameters (Figure S14 in the Supporting Information): ΔH° = −27.9 ± 0.4 kJ mol−1 and ΔS° = −97.7 ± 1.8 J mol−1 K−1. A similar monomer/tetramer interconversion was reported by Tolman et al. for copper(I) β-diketiminato compounds with thioether substituents. However, in this case only the tetramer was identified in the crystalline state.15 The VT-1H NMR spectra recorded between 20 and −90 °C in toluene-d8 for CuL2 and CuL4 are also similar (Figures S10 and S12 in the Supporting Information). Particularly revealing portions of the spectra for CuL2 with assignments are shown in Figure 3. The 1H NMR spectrum of CuL2 at room temperature shows a singlet (b2) at 4.82 ppm for the central −CH on the NCCCN backbone and two sets of signals (d2 and e2) at 2.62 and 3.27 ppm for the diastereotopic ethylene −CH2 protons of

coalescence behavior of the ethylene resonance, both CuL2 and CuL4 have the same ΔG⧧ values (9.8 kcal mol−1) during the ring flipping fluxional process.54 Similar behaviors have been described in the literature and have been attributed to the ring flipping of six-membered rings.55,56 The diffusion-ordered spectroscopy (DOSY) technique is a powerful tool to obtain molecular parameters such as molecular weight (MW) and hydrodynamic radii in solution.57−60 An NMR tube with toluene-d8 solvent was loaded with a given copper(I) complex and three internal references to examine their DOSY at room temperature. Diffusion (D) and MW values of complexes CuL1−CuL4 are given in Table S1 in the Supporting Information. The diffusion coefficient data of 8.340 × 10−10 m2/s for CuL2 (MW value 426) and 9.980 × 10−10 m2/ s for CuL4 (MW value 403) are consistent with the monomeric structure ( N-aryl-N′-alkyl-substituted > N,N′-arylsubstituted ligand. Synthesis of Copper(I)−PPh3 Complexes. In addition to understand the reactivity of CuL1−CuL4 discussed above, we prepared four N-aryl-N′-alkylpyridyl β-diketiminato copper(I) triphenylphosphine complexes by treatment of their parent copper(I) complexes CuL1−CuL4 with 1 equiv of PPh3. All copper(I)−PPh3 adducts were characterized by 1H NMR, 13 C{1H} NMR, 31P{1H} NMR, and elemental analysis. X-rayquality crystals of the four N-aryl-N′-alkylpyridyl β-diketiminato copper(I)−PPh3 complexes were grown by layering hexane onto a toluene solution. Due to the similarity of the four copper(I) PPh3 adduct structures about the copper center, only L1Cu(PPh3) is represented in Figure 5; the other structures are shown in Figures S5−S7 in the Supporting Information for L2Cu(PPh3), L3Cu(PPh3), and L4Cu(PPh3), respectively. The copper centers are also trigonally coordinated by one phosphorus atom and two nitrogen donors of the βdiketiminato ligand. The uncoordinated pyridyl arm is pendant and far away from the copper center, which is consistent with the 1H NMR spectral results. The C−N and C−C bond distances of the β-diketiminato ligand are in agreement with delocalization of the NCCCN backbone (Table 5).

Figure 5. ORTEP drawing of L1Cu(PPh3) (50% ellipsoids; hydrogen atoms not shown for clarity).

geometry of these copper(I) complexes is explained on the basis of chelation for CuL1−CuL4 or bridged dimerization binding modes for Cu2(μ-L1)2 and Cu2(μ-L4)2, which is dependent on their crystallization conditions. Room-temperature NMR investigations indicate that the dicopper complexes Cu2(μ-L1)2 and Cu2(μ-L4)2 have NMR chemical shifts similar to those of the monocopper isomer counterparts CuL1 and CuL4, respectively. The VT-1H NMR and DOSY experiments indicate that the length of the pyridyl arm governs the solution behavior of CuL1−CuL4. During temperature changes, CuL1 and CuL3 display monomer/dimer interconversion, presumably due to the ring strain of the five-membered pyridylmethyl arm. For longer pyridylethyl arms, CuL2 and CuL4 are fluxional on the NMR time scale because of the twist-boat puckering chelate ring system. It has been observed that β-diketiminato copper(I) complexes are very susceptible to disproportionation.5,35,38 By introduction of a hemilabile pyridyl group, disproportionation was not observed in CuL1−CuL4 complexes, but this did not prevent oxidization. A reactivity study of the CuL1−CuL4 complexes revealed that the pyridyl arm is decoordinated by addition of CO, 2,6-CNC6H3Me2, or PPh3. On the basis of our studies, the electron-donating ability for the three types of βdiketiminato ligand sets is N,N′-alkyl-substituted > N-aryl-N′alkyl-substituted > N,N′-aryl-substituted ligand. The equilibrium constants for CO adduct formation depend on the degree of competition provided by the length of the pyridyl arm (major) and the steric demand of the N-aryl substituent

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CONCLUSIONS A series of unsymmetrical N-aryl-N′-alkylpyridyl β-diketiminato copper(I) complexes were synthesized, and their structures were characterized using single-crystal X-ray diffraction. The I

DOI: 10.1021/acs.inorgchem.6b02876 Inorg. Chem. XXXX, XXX, XXX−XXX

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Table 5. Selected Bond Lengths (Å) and Angles (deg) for L1Cu(PPh3), L2Cu(PPh3), L3Cu(PPh3), and L4Cu(PPh3) Complexes Cu−N(amide(aryl)) Cu−N(amide(alkyl)) Cu−P C−C(NCCCN backbone) C−N(NCCCN backbone) N(amide)−Cu−N(amide) N(amide(aryl))−Cu−P N(amide(alkyl))−Cu−P ∠NCCCN(aryl)a a

L1Cu(PPh3)

L2Cu(PPh3)

L3Cu(PPh3)

L4Cu(PPh3)

1.943(2) 1.961(2) 2.1706(6) 1.407(3) 1.395(3) 1.331(3) 1.322(3) 93.37(7) 141.31(5) 121.31(5) 85.43

1.949(3) 1.956(3) 2.169(1) 1.409(4) 1.397(5) 1.328(5) 1.318(5) 98.6(1) 133.47(8) 127.80(8) 89.89

1.937(2) 1.952(2) 2.1587(6) 1.399(4) 1.397(4) 1.333(3) 1.329(3) 98.24(8) 136.74(6) 124.98(6) 87.33

1.933(3) 1.948(3) 2.156(1) 1.413(5) 1.382(5) 1.335(5) 1.325(5) 98.6(1) 134.99(9) 126.21(9) 77.77

Angle between the NCCCN backbone plane and N-aryl ring. 5.11 (s, 1H, backbone-CH), 4.22 (s, 2H, CH2Py), 3.70 (septet, 2H, J = 7.1 Hz, ArCH(CH3)2), 1.97 (s, 3H, backbone-CH3), 1.90 (s, 3H, backbone-CH3), 1.47 (d, 6H, J = 7.1 Hz, ArCH(CH3)2), 1.31 (d, 6H, J = 7.1 Hz, ArCH(CH3)2). 13C{1H} NMR (C6D6, 125 MHz, 298 K, δ): 165.14, 161.97, 161.82, 150.81, 150.02, 141.06, 135.78, 124.05, 123.81, 123.27, 122.06, 95.06, 53.15, 28.56, 24.73, 24.62, 23.44, 21.34. Anal. Calcd for C23H30CuN3: C, 67.04; H, 7.34; N, 10.24. Found: C, 66.99; H, 7.38; N, 10.28. CuL2. Under an inert atmosphere a solution of L2H (1.03 g, 2.96 mmol) in 10 mL of hexane was added to a slurry of CuOtBu (0.40 g, 2.96 mmol) in 15 mL of hexane and stirred for 60 min. This complex was isolated from hexane to give red crystals of CuL2 (0.98 g, 77%). 1 H NMR (toluene-d8, 400 MHz, 293 K, δ): 7.95 (ddd, 1H, J = 5.6, 2.2, 1.2 Hz, Py1), 7.20−7.12 (m, 3H, Ar-H), 6.81 (ddd, 1H, J = 2.2, 7.6, 7.6 Hz, Py3), 6.45 (ddd, 1H, J = 7.6, 1.2, 1.2 Hz, Py4), 6.22 (ddd, 1H, J = 5.6, 7.6, 1.2 Hz, Py2), 4.83 (s, 1H, backbone-CH), 3.65 (septet, 2H, J = 6.8 Hz, ArCH(CH3)2), 3.28 (dd, J = 4.4, 4.0 Hz, 2H, CH2CH2Py), 2.62 (dd, J = 4.6, 4.0 Hz, 2H, CH2CH2Py), 1.84 (s, 3H, backboneCH3), 1.82 (s, 3H, backbone-CH3), 1.37 (d, 6H, J = 6.8 Hz, ArCH(CH3)2), 1.28 (d, 6H, J = 6.8 Hz, ArCH(CH3)2. 1H NMR (C6D6, 500 MHz, 298 K, δ): 7.96 (d, 1H, J = 5.5 Hz, Py1), 7.27−7.19 (m, 3H, Ar-H), 6.78 (dd, 1H, J = 7.5, 7.6 Hz, Py3), 6.43 (d, 1H, J = 7.6 Hz, Py4), 6.20 (dd, 1H, J = 5.5, 7.5 Hz, Py2), 4.93 (s, 1H, backboneCH), 3.74 (septet, 2H, J = 6.7 Hz, ArCH(CH3)2), 3.30 (dd, J = 4.3, 3.8 Hz, 2H, CH2CH2Py), 2.63 (dd, J = 4.3, 3.8 Hz, 2H, CH2CH2Py), 1.89 (s, 3H, backbone-CH3), 1.88 (s, 3H, backbone-CH3), 1.42 (d, 6H, J = 6.7 Hz, ArCH(CH3)2), 1.31 (d, 6H, J = 6.7 Hz, ArCH(CH3)2). 13 C{1H} NMR (C6D6, 125 MHz, 298 K, δ): 163.30, 161.80, 161.59, 150.53, 149.99, 141.19, 137.01, 125.42, 123.86, 123.74, 122.27, 94.26, 47.45, 41.69, 28.47, 24.85, 24.15, 23.58, 21.70. Anal. Calcd for C24H32CuN3: C, 67.65; H, 7.57; N, 9.86. Found: C, 67.71; H, 7.59; N, 9.78. CuL3. Under an inert atmosphere a solution of L3H (1.00 g, 3.26 mmol) in 3 mL of hexane was added to a slurry of CuOtBu (0.44 g, 3.26 mmol) in 5 mL of hexane and stirred for 60 min. This complex was isolated from hexane to give orange crystals of CuL3 (1.07 g, 88%). 1H NMR (toluene-d8, 400 MHz, 293 K, δ): 7.81 (br s, 1H, Py1), 6.89 (s, 2H, Ar-H1,2), 6.76 (d, 1H, J = 7.6 Hz, Py3), 6.45 (d, 1H, J = 7.6 Hz, Py2), 6.24 (br s, 1H, Py4), 4.98 (s, 1H, backbone-CH), 4.19 (s, 2H, CH2Py), 2.37 (s, 6H, ortho ArCH3), 2.24 (s, 3H, para ArCH3), 1.90 (s, 3H, backbone-CH3), 1.84 (s, 3H, backbone-CH3). 1H NMR (C6D6, 400 MHz, 298 K, δ): 7.82 (br s, 1H, Py1), 6.95 (s, 2H, Ar-H1,2), 6.69 (d, 1H, J = 7.8 Hz, Py3), 6.44 (d, 1H, J = 7.8 Hz, Py2), 6.17 (br s, 1H, Py4), 5.08 (s, 1H, backbone-CH), 4.25 (s, 2H, CH2Py), 2.45 (s, 6H, ortho ArCH3), 2.26 (s, 3H, para ArCH3), 1.96 (s, 3H, backbone-CH3), 1.92 (s, 3H, backbone-CH3). 13C{1H} NMR (C6D6, 100.06 MHz, 298 K, δ): 161.76, 150.92, 135.86, 131.65, 130.98, 129.81, 122.21, 122.09, 95.28, 53.64, 23.86, 21.70, 20.09. Anal. Calcd for C20H24CuN3: C, 64.93; H, 6.54; N, 11.36. Found: C, 64.14; H, 6.55; N, 11.32. CuL4. Under an inert atmosphere a solution of L4H (1.05 g, 3.26 mmol) in 2 mL of hexane was added to a slurry of CuOtBu (0.44 g,

(minor). Taken together, these results imply that the pyridyl arm prevents disproportionation and the length of the arm can influence the reactivity of β-diketiminato copper(I) complexes. On the basis of these conclusions, future work will consist of studying this donor arm ligand set for new copper(I) catalysts and for the generation of new binding motifs for bioinspired complexes.

■

EXPERIMENTAL SECTION

All manipulations involving N-aryl-N′-alkyl β-diketiminato ligands and copper(I) complexes were carried out under an atmosphere of purified dinitrogen in a drybox or using standard Schlenk techniques. Chemical reagents were purchased from Aldrich Chemical Co. Ltd., Lancaster Chemicals Ltd., or Fluka Ltd. All reagents were used without further purification, apart from all solvents, which were dried over Na (Et2O, THF) or CaH2 (CH2Cl2, CH3CN) and then thoroughly degassed before use. Pure CuOtBu and N-aryl-N′-alkyl β-diketiminato ligands L1H−L4H were synthesized following published procedures.45,64−66 Ligands L1PhH and L3PhH were prepared by procedures similar to those for L1H, which are described in the Supporting Information. IR spectra were recorded using a Varian FT-IR 640 spectrometer. In situ FTIR measurements were performed using a Mettler Toledo ReactIR iC10 system equipped with a HgCdTe (MCT) detector and a 0.625 in. SiComp probe. 1H NMR and 13C NMR spectra were acquired using a Varian Gemini-200 proton/carbon FT NMR, a 400 MHz NMR, or a Varian Gemini-500 proton/carbon FT NMR spectrometer. Elemental analyses were performed using a Heraeus CHN-OS Rapid Elemental Analyzer. Cyclic voltammetry measurements were taken in 10−4 M MeCN solutions using 0.1 M (Bu4N)(PF6) as supporting electrolyte and referenced to Fc+/0. A platinum-wire counter electrode, glassy-carbon working electrode, and Ag/AgCl (MeCN) reference electrode were used. Preparation of Cu(I) Complexes. The syntheses of CuL1−CuL4 were carried out using similar procedures. A representative example for the synthesis of CuL1 is given below. CuL1. Under an inert atmosphere a solution of L1H (1.00 g, 2.86 mmol) in 15 mL of hexane was added to a slurry of CuOtBu (0.39 g, 2.86 mmol) in 30 mL of hexane, and the mixture was stirred for 60 min. The solvent was removed under vacuum and the residue extracted with 75 mL of hexane and filtered through a plug of Celite. The volume was reduced and the solution was placed at −20 °C overnight, yielding the orange crystalline solid CuL1 (0.95 g, 81%). 1H NMR (toluene-d8, 400 MHz, 298 K, δ): 7.92 (d, 1H, J = 5.4 Hz, Py1), 7.20−7.12 (m, 3H, Ar-H), 6.76 (dd, 1H, J = 6.3, 7.6 Hz, Py3), 6.43 (d, 1H, J = 7.6 Hz, Py4), 6.29 (dd, 1H, J = 5.4, 6.3 Hz, Py2), 5.01 (s, 1H, backbone-CH), 4.16 (s, 2H, CH2Py), 3.61 (septet, 2H, J = 6.8 Hz, ArCH(CH3)2), 1.90 (s, 3H, backbone-CH3), 1.87 (s, 3H, backboneCH3), 1.40 (d, 6H, J = 6.8 Hz, ArCH(CH3)2), 1.29 (d, 6H, J = 6.8 Hz, ArCH(CH3)2). 1H NMR (C6D6, 500 MHz, 298 K, δ): 7.86 (d, 1H, J = 5.5 Hz, Py1), 7.26−7.18 (m, 3H, Ar-H), 6.71 (dd, 1H, J = 7.2, 7.7 Hz, Py3), 6.41 (d, 1H, J = 7.7 Hz, Py4), 6.26 (dd, J = 5.5, 7.2 Hz 1H, Py2), J

DOI: 10.1021/acs.inorgchem.6b02876 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

H1,2), 6.69 (d, 1H, J = 8.6 Hz, Py4), 6.55 (dd, 1H, J = 6.2, 8.2 Hz, Py2), 4.76 (s, 1H, backbone-CH), 3.89 (dd, 2H, J = 5.0, 4.6 Hz, CH2CH2Py), 2.96 (dd, 2H, J = 5.0, 4.6 Hz, CH2CH2Py), 2.21 (s, 6H, ortho ArCH3), 2.20 (s, 3H, para ArCH3), 1.88 (s, 3H, backbone-CH3), 1.66 (s, 3H, backbone-CH3). 13C{1H} NMR (C6D6, 100 MHz, 298 K, d):179.78, 165.79, 162.89, 161.46, 150.83, 150.48, 136.44, 132.7, 130.69, 129.89, 124.44, 121.83, 96.13, 54.92, 42.93, 22.86, 22.47, 21.64, 19.63. General Procedure for the Preparation of Copper(I) 2,6Xylyl Isocyanide Complexes. To the appropriate Cu(I) complex (typically 0.1 g) in toluene (3 mL) was added an equimolar amount of 2,6-xylyl isocyanide (2,6-CNC6H3Me2) solution in toluene (2 mL). The resulting yellow-brown solution was stirred for 3 h under an inert atmosphere. The solution was filtered and concentrated to half of its original volume, layered with hexane (5 mL), and kept at −20 °C overnight. Yellow crystals formed after 1 day. L1Cu(2,6-CNC6H3Me2). Yield: 86%. 1H NMR (C6D6, 400 Hz, 298 K, δ): 8.49 (d, 1H, J = 5.7 Hz, Py1), 7.55 (dd, 1H, J = 7.4, 7.9 Hz, Py3), 6.5−7.22 (m, 6H, Ar (CN) + Ar-H), 6.28 (dd, 1H, J = 5.7, 7.4 Hz, Py2), 6.46 (d, 1H, J = 7.9 Hz, Py4), 5.38 (s, 2H, CH2Py), 4.94 (s, 1H, backbone-CH), 3.57 (septet, 2H, J = 7.8 Hz, ArCH(CH3)2), 2.00 (s, 3H, backbone-CH3), 1.85 (s, 3H, backbone-CH3), 1.69 (s, 6H, ortho Ar(CH3)2(CN)), 1.35 (d, 6H, J = 7.8 Hz, ArCH(CH3)2), 1.30 (d, 6H, J = 7.8 Hz, ArCH(CH3)2). 13C NMR (C6D6, 100 Hz, 298 K, δ): 166.45, 165.15, 163.28, 153.24, 150.88, 149.86, 141.14, 136.46, 135.46, 128.99, 128.31, 124.42, 123.94, 122.19, 121.77, 96.08, 62.56, 28.79, 25.46, 24.05, 23.89, 21.34, 18.91. Anal. Calcd for C32 H39 N4: C,70.76; H, 7.23; N, 10.31. Found: C, 70.76; H,7.26 ; N, 10.34. L2Cu(2,6-CNC6H3Me2). Yield: 82%. 1H NMR (C6D6, 400 Hz, 298 K, δ): 8.48(d, 1H, J = 5.7 Hz, Py1), 6.96−7.19 (m, 6H, Ar(CN) + ArH), 6.68 (dd, 1H, J = 7.6, 7.8 Hz, Py3), 6.60 (d, 1H, J = 7.8 Hz, Py4), 6.53 (dd, 1H, J = 5.7, 7.6 Hz, Py2), 4.89 (s, 1H, backbone-CH), 4.2 (s, 2H, J = 4.5, 3.9 Hz, CH2CH2Py), 3.56 (septet, 2H, J = 6.8 Hz, ArCH(CH3)2), 3.52 (dd, 2H, J = 4.5, 3.9 Hz, CH2CH2Py), 2.00 (s, 3H, backbone-CH3), 1.87 (s, 6H, ortho Ar(CH3)2(CN)), 1.84 (s, 3H, backbone-CH3), 1.33 (d, 6H, J = 6.8 Hz, ArCH(CH3)2), 1.28 (d, 6H, J = 6.8 Hz, ArCH(CH3)2). 13C NMR (C6D6, 100 Hz, 298 K, δ): 165.59, 162.51, 162.04, 154.06, 151.15, 150.40, 141.29, 136.15, 135.81, 129.12, 124.26, 123.99, 123.90, 121.52, 95.77, 55.70, 44.66, 28.72, 25.58, 24.14, 23.83, 22.92, 19.08. Anal. Calcd for C33H41N4: C, 71.13; H, 7.42; N, 10.05. Found: C, 71.11; H, 7.50; N, 10.06. L3Cu(2,6-CNC6H3Me2). Yield: 79%. 1H NMR (C6D6, 400 MHz, 298 K, δ): 8.50 (d, 1H, J = 5.9 Hz, Py1), 7.54 (dd, 1H, J = 7.9, 8.1 Hz, Py3), 7.15 (d, 1H, J = 8.1 Hz, Py4), 6.88 (s, 2H, Ar-H1,2), 6.43−6.65 (m, 4H, Ar(CN) + Py2), 5.42 (s, 2H, CH2Py), 4.95 (s, 1H, backbone-CH), 2.39 (s, 6H, ortho ArCH3), 2.21 (s, 3H, para ArCH3), 2.03 (s, 3H, backbone- CH3), 1.82 (s, 3H, backbone- CH3), 1.67 (s, 6H, ortho Ar(CH3)2(CN)). 13C NMR (C6D6,100 MHz, 298 K, δ): 166.50, 165.13, 162.92, 153.66, 151.48, 149.88, 136.54, 135.41, 131.80, 130.60, 129.65, 128.22, 122.20, 121.74, 96.07, 62.78, 23.03, 22.73, 21.63, 20.01, 18.87. Anal. Calcd for C29H33CuN4: C, 69.50; H, 6.64; N, 11.18. Found: C, 69.53; H, 6.67; N, 11.16. L4Cu(2,6-CNC6H3Me2). Yield: 86%. 1H NMR (C6D6, 400 MHz, 298 K, δ): 8.47 (d, 1H, J = 6.0 Hz, Py1), 7.09 (dd, 1H, J = 8.0, 8.2 Hz, Py3), 6.98 (d, 1H, J = 8.2 Hz, Py4), 6.9 (s, 2H, Ar-H1,2), 6.50−6.70 (m, 4H, Ar(CN) + Py2), 4.88 (s, 1H, backbone-CH), 4.22 (dd, 2H, J = 5.6, 4.6 Hz, CH2CH2Py), 3.49 (dd, 2H, J = 5.6, 4.6 Hz, CH2CH2Py), 2.37 (s, 6H, ortho ArCH3), 2.23 (s, 3H, para ArCH3), 2.03 (s, 3H, backbone-CH3), 1.84 (s, 3H, backbone-CH3), 1.81 (s, 6H, ortho Ar(CH3)2(CN)). 13C NMR(C6D6,100 MHz, 298 K, δ): 165.44, 162.16, 162.01, 154.14, 151.68, 150.40, 136.11, 135.63, 131.59, 130.72, 129.56, 128.98, 128.31, 124.08, 121.49, 95.74, 55.83, 44.55, 23.00, 22.89, 21.65, 20.04, 18.99. Anal. Calcd for C30H35CuN4: C, 69.94; H, 6.85; N, 10.88. Found: C, 69.86; H, 6.78; N, 10.90. General Procedure for the Preparation of Copper(I) PPh3 Complexes. To an appropriate Cu(I) complex (typically 0.1 g) in toluene (3 mL) was added an equal molar amount PPh3 solution in toluene (2 mL). The resulting yellow solution was stirred for 1 h under an inert atmosphere. The solvent was evaporated under vacuum

3.26 mmol) in 4 mL of hexane and stirred for 60 min. This complex was isolated from hexane to give red crystals of CuL4 (0.99 g, 79%). 1 H NMR (toluene-d8, 400 MHz, 293 K, d): 7.91 (d, 1H, J = 5.6 Hz, Py1), 6.93 (s, 2H, Ar-H1,2), 6.81 (dd, 1H, J = 8.2, 7.6 Hz, Py3), 6.45 (d, 1H, J = 7.6 Hz, Py4), 6.24 (dd, 1H, J = 5.6, 8.2 Hz, Py2), 4.82 (s, 1H, backbone-CH), 3.29 (dd, 2H, J = 5.0, 4.4 Hz, CH2CH2Py), 2.62 (dd, 2H, J = 5.0, 4.4 Hz, CH2CH2Py), 2.39 (s, 6H, ortho ArCH3), 2.28 (s, 3H, para ArCH3), 1.86 (s, 3H, backbone-CH3), 1.78 (s, 3H, backbone-CH3). 1H NMR (C6D6, 400 MHz, 298 K, δ): 7.95 (d, 1H, J = 5.2 Hz, Py1), 7.00 (s, 2H, Ar-H1,2), 6.78 (dd, 1H, J = 8.0, 7.4, Hz, Py3), 6.42 (d, 1H, J = 7.4 Hz, Py4), 6.19 (dd, 1H, J = 5.2, 8.0 Hz Py2), 4.93 (s, 1H, backbone-CH), 3.30 (dd, 2H, J = 4.8, 4.2 Hz, CH2CH2Py), 2.62 (dd, 2H, J = 4.8, 4.2 Hz, CH2CH2Py), 2.48 (s, 6H, ortho ArCH3), 2.30 (s, 3H, para ArCH3), 1.90 (s, 3H, backboneCH3), 1.87 (s, 3H, backbone-CH3). 13C{1H} NMR (C6D6, 100.06 MHz, 298 K, δ): 163.63, 161.83, 161.36, 151.39, 150.15, 137.21, 131.47, 130.91, 129.81, 125.60, 122.54, 94.46, 47.77, 41.85, 23.49, 21.99, 21.73, 20.13. Anal. Calcd for C20H26CuN3: C, 64.93; H, 6.54; N, 11.36. Found: C, 64.14; H, 6.55; N, 11.32. Calcd for C42H52Cu2N6: C, 65.69; H, 6.82; N, 10.94. Found: C, 65.11; H, 6.89; N, 11.01. L2Cu(μ-OH)2CuL2. A solution of L2Cu in MeCN (50 mg in 10 mL) was oxygenated by bubbling of O2 at ambient temperature for 60 s. The resulting green-brown solution was layered with 10 mL of toluene and allowed to stand at −20 °C. Brown single crystals formed after 3 days and were either mounted for analysis by X-ray crystallography or collected by decanting the mother liquor, washed with cold toluene, and dried in vacuo (23 mg). Anal. Calcd for C48H66Cu2N6O2: C, 65.06; H, 7.51; N, 9.48. Found: C, 65.09; H, 7.49; N, 9.51. Reaction of Cu(I) Complexes with CO. General Procedure. A 10 mL Schlenk flask under an inert atmosphere was charged with a 40 mM solution of the desired Cu(I) complex in toluene (5 mL) and sealed using a septum. Carbon monoxide was bubbled through the solution at room temperature, at which point the IR spectrum was recorded. For NMR examination, the desired Cu(I) complex was dissolved in C6D6 (1.0 mL) in a screw-capped NMR tube. Carbon monoxide was gently bubbled into the solution for 20 min at ambient temperature, during which time the color changed from red-orange to yellow. The CO adducts were immediately characterized by 1H and 13 C{1H} NMR spectroscopy. L1Cu−CO. 1H NMR (C6D6, 400 MHz, 298 K, δ): 8.46 (d, 1H, J = 5.6 Hz, Py1), 7.11−7.10 (m, 3H, Ar-H), 7.07 (dd, 1H, J = 7.6, 8.0 Hz, Py3), 7.01 (d, 1H, J = 8.0 Hz, Py4), 6.6 (dd, 1H, J = 5.6, 7.6 Hz, Py2), 4.88 (s, 2H, CH2Py), 4.85 (s, 1H, backbone-CH), 3.3 (septet, 2H, J = 7.3 Hz, ArCH(CH3)2), 1.91 (s, 3H, backbone-CH3), 1.71 (s, 3H, backbone-CH3), 1.19 (d, 6H, J = 7.3 Hz, ArCH(CH3)2), 1.18 (d, 6H, J = 7.3 Hz, ArCH(CH3)2). 13C{1H} NMR (C6D6, 100 MHz, 298 K, δ): 179.18 (CO), 166.63, 164.09, 163.82, 150.33, 150, 141.16, 136.69, 125.44, 124.21, 122.97, 122.52, 96.43, 61.48, 28.64, 25.25, 23.97, 23.59, 23.05. L2Cu−CO. 1H NMR (C6D6, 400 MHz, 298 K, δ): 8.46 (d, 1H, J = 5.8 Hz, Py1), 7.13−7.11 (m, 3H, Ar-H) 7.05 (dd, 1H, J = 7.7, 7.8 Hz, Py3), 6.72 (d, 1H, J = 7.8 Hz, Py4), 6.59 (dd, 1H, J = 5.8, 7.7 Hz, Py2), 4.78 (s, 1H, backbone-CH), 3.98 (dd, 2H, J = 4.7, 4.1 Hz, CH2CH2Py), 3.29 (septet, 2H, J = 6.7 Hz, ArCH(CH3)2), 3.04(dd, 2H, J = 4.7, 4.1 Hz, CH2CH2Py), 1.88 (s, 3H, backbone-CH3), 1.69 (s, 3H, backbone-CH3), 1.2 (d, 6H, J = 6.7 Hz, ArCH(CH3)2), 1.18 (d, 6H, J = 6.7 Hz, ArCH(CH3)2). 13C{1H} NMR (C6D6, 100 MHz, 298 K, δ): 179.98, 166.14, 163.54, 161.21, 150.58, 150.16, 141.24, 136.33, 125.34, 124.26, 124.19, 121.8, 96.41, 55.32, 43.61, 28.62, 25.36, 24.06, 23.61, 22.58. L3Cu−CO. 1H NMR (C6D6, 400 MHz, 298 K, δ): 8.43 (d, 1H, J = 4.2 Hz, Py1), 7.04 (dd, 1H, J = 7.0, 7.8, Py3), 6.99 (d, 1H, J = 7.8 Hz, Py4), 6.85 (s, 1H, Ar-H1,2), 6.58 (dd, 1H, J = 4.2, 7.0 Hz, Py2), 4.89 (s, 2H, CH2Py), 4.85 (s, 1H, backbone-CH), 2.19 (s, 6H, ortho ArCH3), 2.17 (s, 3H, para ArCH3), 1.93 (s, 3H, backbone-CH3), 1.67 (s, 3H, backbone-CH3). 13C{1H} NMR (C6D6, 100 MHz, 298 K, δ): 179.87, 166.49, 163.79, 163.65, 150.74, 150.29, 136.72, 132.91, 130.49, 129.89, 122.87, 122.44, 96.37, 61.5, 22.98, 22.77, 21.59, 19.64. L4Cu−CO. 1H NMR (C6D6, 400 MHz, 298 K, d): 8.40 (d, 1H, J = 6.2 Hz, Py1), 7.02 (dd, 1H, J = 8.2, 8.6 Hz, Py3), 6.89 (s, 2H, ArK

DOI: 10.1021/acs.inorgchem.6b02876 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

The in situ IR spectra were obtained in the 2050−2100 cm−1 range. A buildup of copper(I)−CO adducts was observed at 2065 cm−1. The decarbonylation of copper(I)−CO adducts was carried out by bubbling dry N2 gas through the solution at room temperature. Using the in situ IR monitoring results and calculated absorbance to molar concentration, plots of time (seconds) versus [LCuI−CO] were found to be linear, and the slope afforded the representative kCO and k−CO values; KCO values could be determined using eqs 1 and 2. On the basis of previous literature, the concentration of CO was assumed to be constant under saturation conditions.68 X-ray Crystal Structure Determinations. Single-crystal X-ray diffraction data were measured on a Bruker Nonius Kappa CCD diffractometer using Mo Kα radiation (λ = 0.71073 Å). The SMART program was used for data collection.69 Cell refinement and data reduction were performed using the SAINT program.70 The structures were determined using the SHELXTL/PC program71 and refined using full-matrix least squares. All non-hydrogen atoms were refined anisotropically, whereas the hydrogen atoms were placed at calculated positions and included in the final stage of refinements with fixed parameters. A summary of the relevant crystallographic data for all copper(I) complexes is provided in Tables S1−S3 in the Supporting Information.

and the residue extracted with hexane. The solution was evaporated again to give yellow product. L1Cu(PPh3). Yield: 96%. 1H NMR (C6D6, 400 MHz, 298 K, δ): 8.42 (ddd, 1H, J = 5.7, 2.3, 1.3 Py1), 7.32 (d, 1H, J = 5.8, 5.6 Hz, Ar-H2), 7.19 (ddd, 2H, J = 2.3, 7.7, 7.7 Hz, Py3), 7.14 (ddd, 1H, J = 7.7, 1.3, 1.3 Hz, Py4), 7.10- 6.86 (m, 16H, J = 6.8 Hz, PPh3 + Ar-H1,3) 6.65 (ddd, 1H, J = 7.7, 5.7, 1.3 Hz, Py2), 5.16 (s, 2H, CH2Py), 5.09 (s, 1H, backbone-CH), 3.63 (septet, 2H, J = 6.9 Hz, ArCH(CH3)2), 1.95 (d, 6H, J = 5.5 Hz, backbone-CH3), 1.30 (d, 6H, J = 6.9 Hz, ArCH(CH3)2), 0.96 (d, 6H, J = 6.9 Hz, ArCH(CH3)2). 13C{1H} NMR (C6D6, 100 MHz, 298 K, δ): 167.59, 164.53, 163.39, 151.48, 149.94, 141.3, 136.38, 134.44, 130.21, 129.45, 124.49, 124.28, 121.26, 96.72, 62.17, 30.72, 28.93, 24.46, 24.32, 22.71. 31P{1H} NMR (C6D6, 162 MHz, 298 K, δ): 3.24. Anal. Calcd for C41H47CuN3P: C, 73.03; H, 6.73; N, 6.23. Found: C, 72.99; H, 6.76; N, 6.21. L2Cu(PPh3). Yield: 97%. 1H NMR (C6D6, 400 MHz, 298 K, δ): 8.37 (d, 1H, J = 5.6 Hz, Py1), 7.29 (m, 6H, PPh3 + Ar-H2), 7.29 (dd, 1H, J = 7.9, 7.8 Hz, Py3), 7.13 (d, 1H, J = 4.9, 4.4 Hz, Ar-H2), 6.99 (m, 11H, PPh3 + Ar-H1), 6.57 (dd, 1H, J= 5.6, 7.9 Hz, Py2), 6.31 (d, 1H, J = 7.8 Hz, Py4), 4.96 (s, 1H, backbone-CH), 4.03 (dd, 2H, J = 4.4, 3.7, 5.9 Hz, CH2CH2Py), 3.59 (septet, 2H, J = 6.8 Hz, ArCH(CH3)2), 2.96 (dd, 2H, J = 4.4, 3.7 Hz, CH2CH2Py), 2.1 (s, 3H, backbone-CH3), 1.87 (s, 3H, backbone-CH3), 1.22 (d, 6H, J = 6.8 Hz, ArCH(CH3)2), 0.9 (d, 6H, J = 6.8 Hz, ArCH(CH3)2). 13C{1H} NMR (C6D6, 100 MHz, 298 K, δ): 166.12, 162.59, 161.47, 151.72, 150.14, 141.62, 135.9, 134.65, 130.34, 129.61, 124.45, 124.24, 123.44, 121.35, 96.48, 56.48, 43.20, 28.75, 24.62, 24.43, 22.21. 31P{1H} NMR (C6D6, 162 MHz, 298 K, δ): 2.74. Anal. Calcd for C42H47CuN3P: C, 73.28; H, 6.88; N, 6.10. Found: C, 73.23; H, 6.90; N, 6.11. L3Cu(PPh3). Yield: 98%. 1H NMR (C6D6, 400 MHz, 298 K, δ): 8.39 (ddd, 1H, J = 5.8, 2.4, 1.4 Hz, Py1), 7.36 (ddd, 1H, J = 2.4, 7.8, 7.8 Hz, Py3), 7.08 (ddd, 1H, J = 7.6, 1.4, 1.4 Hz, Py4), 6.98- 6.80 (m, 16H, PPh3 + Ar-H1,3), 6.60 (ddd, 1H, J = 5.8, 7.8, 1.4 Hz, Py2), 5.17 (s, 2H, CH2Py), 5.04 (s, 1H, backbone-CH), 2.25 (s, 3H, para ArCH3), 2.2 (s, 6H, ortho ArCH3), 1.95 (s, 3H, backbone-CH3), 1.83 (s, 3H, backbone-CH3). 13C{1H} NMR (C6D6, 100 MHz, 298 K, δ): 167.3, 164.67, 162.89, 151.54, 149.9, 136.48, 134.51, 131.79, 131.02, 130.14, 129.88, 129.35, 121.29, 96.68, 62.3, 23.48, 22.69, 21.71, 19.79. 31P{1H} NMR (C6D6, 162 MHz, 298 K, δ): 2.92. Anal. Calcd for C38H39CuN3P: C, 72.19; H, 6.22; N, 6.65. Found: C, 72.17; H, 6.23; N, 6.66. L4Cu(PPh3). Yield: 98%. 1H NMR (C6D6, 400 MHz, 298 K, δ): 8.40 (d, 1H, J = 5.3 Hz, Py1), 7.30 (m, 7H, J = 8.1, 7.5 Hz, PPh3 + Py3), 6.98 (m, 9H, PPh3), 6.76 (s, 2H, Ar-H1,3), 6.58 (dd, 1H, J = 7.5 Hz, Py4), 6.35 (d, 1H, J = 5.3, 8.1 Hz, Py2), 4.95 (s, 1H, backbone-CH), 4.08 (dd, 2H, J = 4.9, 4.1 Hz, CH2CH2Py), 3.03 (dd, 2H, J = 4.9, 4.1 Hz, CH2CH2Py), 2.24 (s, 3H, para ArCH3), 2.19 (s, 6H, ortho ArCH3), 2.12 (s, 3H, backbone-CH3), 1.81 (s, 3H, backbone-CH3). 13 C{1H} NMR (C6D6, 100 MHz, 298 K, δ): 165.77, 162.05, 161.55, 151.8, 150.17, 135.96, 134.56, 131.61, 131.27, 130.22, 129.83, 129.47, 123.53, 121.37, 96.185, 56.53, 43.74, 23.59, 22.33, 21.73, 19.87. 31 1 P{ H} NMR (C6D6, 162 MHz, 298 K, δ): 2.35. Anal. Calcd for C39H41CuN3P: C, 72.48; H, 6.39; N, 6.50. Found: C, 72.58; H, 6.43; N, 6.45. Diffusion Ordered Spectroscopy (1H-DOSY) Experiments. The internal reference method was employed for DOSY experiments at room temperature according to previous literature procedures.58,67 Three different molecular weight compounds were chosen: tetramethylsilane (TMS, MW = 88.23), hexamethyldisiloxane (HMDSO, MW = 162.38), and 1,2-bis(trimethoxysilyl)ethane (BTMSE, MW = 270.43). These three internal references and CuLn were placed in an NMR tube, and 0.7 mL of toluene-d8 was added. After the DOSY experiment was recorded, log D vs log MW values of the three internal references were plotted (see the Supporting Information). The molecular weight could then be obtained by a calibration curve of the D value of the desired complex. Carbon Monoxide Binding Constant Measurements. Kinetic measurements were taken using a ReactIR spectrophotometer (Mettler Toledo). The spectrophotometer was continuously purged with carbon monoxide at room temperature during the measurements.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b02876. Additional figures and tables as described in the text (PDF) Crystallographic data (CIF) Crystallographic data (CIF) Crystallographic data (CIF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail for S.C.N.H.: [email protected]. ORCID

Sodio C. N. Hsu: 0000-0002-2576-7289 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We gratefully acknowledge financial support from the Ministry of Science and Technology of Taiwan (MOST 102-2113-M037-008-MY3; MOST 104-2632-M-037-001), NSYSU-KMU Joint Research Project (NSYSUKMU 105-P006), and Kaohsiung Medical University “Aim for the Top University Grant, Grant No. KMU-TP105PR12”. We thank Mr. TingShen Kuo, National Taiwan Normal University, for X-ray structural determinations and Mr. Min-Yuan Hung, Center for Research Resources and Development of KMU, for use of their facilities.

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REFERENCES

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DOI: 10.1021/acs.inorgchem.6b02876 Inorg. Chem. XXXX, XXX, XXX−XXX