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. 2018 Sep 18;8(56):32269-32282.
doi: 10.1039/c8ra06057f. eCollection 2018 Sep 12.

Role of C, S, Se and P donor ligands in copper(i) mediated C-N and C-Si bond formation reactions

Katam Srinivas  1 , Ganesan Prabusankar  1
Affiliations

Role of C, S, Se and P donor ligands in copper(i) mediated C-N and C-Si bond formation reactions

Katam Srinivas et al. RSC Adv. .

Abstract

The first comparative study of C, S, Se and P donor ligands-supported copper(i) complexes for C-N and C-Si bond formation reactions are described. The syntheses and characterization of eight mononuclear copper(i) chalcogenone complexes, two polynuclear copper(i) chalcogenone complexes and one tetranuclear copper(i) phosphine complex are reported. All these new complexes were characterized by CHN analysis, FT-IR, UV-vis, multinuclear NMR and single crystal X-ray diffraction techniques. The single crystal X-ray structures of these complexes depict the existence of a wide range of coordination environments for the copper(i) center. This is the first comparative study of metal-phosphine, metal-NHC and metal-imidazolin-2-chalcogenones in C-N and C-Si bond formation reactions. Among all the catalysts, mononuclear copper(i) thione, mononuclear copper(i) N-heterocyclic carbene and tetranuclear copper(i) phosphine are exceedingly active towards the synthesis of 1,2,3-triazoles as well as for the cross-dehydrogenative coupling of alkynes with silanes. The cross-dehydrogenative coupling of terminal alkynes with silanes represents the first report of a catalytic process mediated by metal-imidazolin-2-chalcogenones.

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Conflict of interest statement

There are no conflicts to declare.

Figures

Chart 1
Chart 1. σ-donor and π-accepting nature of PPh3, NHC and NHCE ligands.
Chart 2
Chart 2. Known catalytic comparisons between NHCE–metal and NHC–metal-supported Cu(i) complexes.
Chart 3
Chart 3. Types of ligands studied for copper(i)-mediated 1,3-dipolar cycloaddition of alkynes with azides.
Scheme 1
Scheme 1. Synthesis of 1–5.
Fig. 1
Fig. 1. Selected bond lengths (Å) and angles (°) for 1 (E = S, X = Cl): C(1)–S(1), 1.699(3), S(1)–Cu(1), 2.129(11), Cu(1)–Cl, 2.098(13), C(1)–S(1)–Cu(1), 109.13(11), N(1)–C(1)–N(2), 109.2(3), N(1)–C(1)–S(1), 129.6(3), N(2)–C(1)–S(1), 123.7(2), S(1)–Cu(1)–Cl, 165.94(6); for 2 (E = S, X = Br): C(1)–S(1), 1.699(3), S(1)–Cu(1), 2.135(9), Cu(1)–Br, 2.222(6), C(1)–S(1)–Cu(1), 108.61(10), N(1)–C(1)–N(2), 106.4(2), N(1)–C(1)–S(1), 129.6(2), N(2)–C(1)–S(1), 124.1(2), S(1)–Cu(1)–Br, 163.97(4); for 3 (E = S, X = I): C(1)–S(1), 1.699(8), S(1)–Cu(1), 2.142(3), Cu(1)–I, 2.385(16), C(1)–S(1)–Cu(1), 108.0(3), N(1)–C(1)–N(2), 105.4(7), N(1)–C(1)–S(1), 129.3(6), N(2)–C(1)–S(1), 125.3(6), S(1)–Cu(1)–I, 160.72(10); for 4 (E = Se, X = Br): C(1)–Se(1), 1.855(5), Se(1)–Cu(1), 2.241(11), Cu(1)–Br, 2.222(12), C(1)–Se(1)–Cu(1), 105.84(15), N(1)–C(1)–N(2), 106.6(5), N(1)–C(1)–Se(1), 129.3(4), N(2)–C(1)–Se(1), 124.1(4), Se(1)–Cu(1)–Br, 163.34(6); for 5 (E = Se, X = I): C(1)–Se(1), 1.842(4), Se(1)–Cu(1), 2.252(9), Cu(1)–I, 2.389(8), C(1)–Se(1)–Cu(1), 104.86(13), N(1)–C(1)–N(2), 105.9(4), N(1)–C(1)–Se(1), 129.5(3), N(2)–C(1)–Se(1), 124.6(3), Se(1)–Cu(1)–I, 159.60(4).
Chart 4
Chart 4. The representation of H(3)⋯Cl(1) bond distances in 1 and H(2)⋯E(1) bond distances and C(2)–H(2)–E(1) bond angles in molecules 2–5.
Scheme 2
Scheme 2. Synthesis of 7 and 9.
Scheme 3
Scheme 3. Synthesis of 11.
Fig. 2
Fig. 2. (a) Molecular structure of 7. Hydrogen atoms and dichlorocuprate counter ions have been omitted for clarity. Selected bond lengths (Å) and angles (°): C(1)–Se(1), 1.856(3), Se(1)–Cu(1), 2.253(3), Cu(2)–Cl(1), 2.090(2), C(1)–Se(1)–Cu(1), 105.24(9), N(1)–C(1)–N(2), 106.1(3), N(1)–C(1)–Se(1), 131.1(2), N(2)–C(1)–Se(1), 122.7(2), Se(1)–Cu(1)–Se(1′), 180.0. (b) The molecular structure of 9. Hydrogen atoms and hexafluoro phosphate counter anions have been omitted for clarity. Selected bond lengths (Å) and angles (°): C(1)–Se(1), 1.853(3), Se(1)–Cu(1), 2.252(3), C(1)–Se(1)–Cu(1), 104.61(10), N(1)–C(1)–N(2), 106.0(3), N(1)–C(1)–Se(1), 123.0(2), N(2)–C(1)–Se(1), 130.9(2), Se(1)–Cu(1)–Se(2), 180.0. (c) The molecular structure of 11. Hydrogen atoms and hexafluoro phosphate counter anions have been omitted for clarity. Selected bond lengths (Å) and angles (°): C(1)–Se(1), 1.849(3), Se(1)–Cu(1), 2.267(3), C(1)–Se(1)–Cu(1), 105.89(9), N(1)–C(1)–N(2), 105.7(2), N(1)–C(1)–Se(1), 122.7(2), N(2)–C(1)–Se(1), 131.6(2), Se(1)–Cu(1)–Se(2), 180.0.
Scheme 4
Scheme 4. Expected solution-state structure of 7 as suggested by NMR studies.
Scheme 5
Scheme 5. Synthesis of 12 and 13.
Scheme 6
Scheme 6. Synthesis of 14.
Fig. 3
Fig. 3. Solid state structure of 12. Selected bond lengths (Å) and angles (°): Cu(1)–P(1), 2.248(2), Cu(2)–P(2), 2.227(2), Cu(1)–Cu(2), 2.843(19), Cu(1)–I(1), 2.713(14), Cu(1)–I(2), 2.645(14), Cu(2′)–I(1), 2.590(14), Cu(2)–I(2), 2.533(14), Cu(1)–I(1)–Cu(2′), 105.86(4), Cu(1)–I(2)–Cu(2), 66.57(4), Cu(1′)–I(2)–Cu(2′), 64.72(2).
Fig. 4
Fig. 4. (a) Solid-state structure of 13. Selected bond lengths (Å) and angles (°): C(1)–Se(1), 1.867(7), Se(1)–Cu(1), 2.553(14), Cu(1)–I, 2.650(12), Cu(1′)–I, 2.660(13), C(1)–Se(1)–Cu(1), 95.3(2), C(1)–Se(1)–Cu(1′), 103.4(2), N(1)–C(1)–N(2), 106.8(6), N(1)–C(1)–Se(1), 127.3(5), N(2)–C(1)–Se(1), 125.9(5), Cu(1)–Se(1)–Cu(1′), 160.72(10). (b) Solid state structure of 14. Selected bond lengths (Å) and angles (°): C(1)–Se(1), 1.859(5), Se(1)–Cu(1), 2.336(9), C(8)–Se(2), 1.874(5), Se(2)–Cu(1), 2.323(10), C(15)–Se(3), 1.842(10), Se(3)–Cu(1), 2.352(10), C(1)–Se(1)–Cu(1), 102.35(15), C(8)–Se(2)–Cu(1), 99.85(16), C(15)–Se(3)–Cu(1), 98.6(3), Se(1)–Cu(1)–Se(2), 126.86(4), Se(1)–Cu(1)–Se(3), 114.60(4), Se(2)–Cu(1)–Se(3), 118.49(4), N(1)–C(1)–N(2), 106.0(5), N(1)–C(1)–Se(1), 125.6(4), N(2)–C(1)–Se(1), 128.3(4), N(3)–C(8)–N(4), 106.0(5), N(3)–C(8)–Se(2), 127.1(4), N(4)–C(8)–Se(2), 126.9(4), N(5)–C(15)–N(6), 108.7(12), N(5)–C(15)–Se(3), 125.1(10), N(6)–C(15)–Se(3), 126.2(11).
Fig. 5
Fig. 5. (a) Solution UV-vis spectra of complexes 1–5 in acetonitrile at 298 K with 1.2 × 10−5 M solutions. (b) Solid-state UV-vis spectra of complexes 1–5 at 298 K. (c) Solution UV-vis spectra of complexes 6–11 in acetonitrile at 298 K with 1.2 × 10−5 M solutions. (d) Solid state UV-vis spectra of complexes 6–11 at 298 K. (e) Solution UV-vis spectra of complexes 12–14 in acetonitrile at 298 K with 1.2 × 10−5 M solutions. (f) Solid state UV-vis spectra of complexes 12–14 at 298 K.
Scheme 7
Scheme 7. [3+2] cycloaddition of benzylazide with phenyl acetylene.
Fig. 6
Fig. 6. The screening of catalysts 1–14 in click catalysis. Reaction conditions: phenyl acetylene (1.2 mmol), benzyl azide (1.0 mmol), catalyst (1 mol%) and neat conditions at RT. Entries: 15, CuCl only; 16, only CuI; 17, IMesS and CuCl; 18, IMes.HCl and CuCl; 19, PPh3 and CuI; 20, 0.5 mol% 12 for 4 h; %Y, %isolated yield by column chromatography.
Chart 5
Chart 5. Catalysts used for the substrate scope in click catalysis.
Fig. 7
Fig. 7. Solvent screening in various solvents using catalysts 3 (black), 6 (red) and 12 (green); reaction conditions: phenylacetylene (1.2 mmol), benzylazide (1.0 mmol), catalyst (1 mol%) and solvent at RT. Entries: 1, in water; 2, in DMSO : water; 3, in THF : water; 4, in tBuOH : water; 5, in tBuOH; 6, in DMSO; and 7 in THF. % Y, % isolated yield by column chromatography.
Scheme 8
Scheme 8. [3+2] cycloaddition of arylazides with terminal alkynes.
Chart 6
Chart 6. 1,2,3-Triazoles isolated by click catalysis by 3, 6 and 12 in water (see ESI-2, Table S2-1†).
Chart 7
Chart 7. Plausible mechanisms for the Huisgen coupling reaction by catalyst 3.
Chart 8
Chart 8. Expected steric hindrance at the metal centre in 3 and 14.
Chart 9
Chart 9. Catalysts used for the cross-dehydrogenative coupling of alkynes with hydrosilanes.
Scheme 9
Scheme 9. Cross-dehydrogenative coupling of terminal alkynes with hydrosilanes.
Chart 10
Chart 10. Possible mechanisms for the dehydrogenative coupling of silanes by catalyst 3.
Chart 11
Chart 11. Alkynylsilanes isolated by 3, 6 and 12. Reaction conditions for X and XI: phenylacetylene (0.80 mmol), diphenylsilane (0.40 mmol), catalyst (1 mol%), base (20 mol%), solvent (1.0 mL). (See ESI-2, Table S2-2†).
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