Syntheses, Structural Characterization and

1. Syntheses, Structural Characterization and Catalytic Applications of N-Heterocyclic Carbene Nickel(II) Complexes 學 生 : 李光凡 指導老師 : 于淑君 博士 2009 / 01 / 20 Department of Chemistry & Biochemistry Chung Cheng University

2. N-Heterocyclic Carbenes [M] • NHCs are most frequently prepared via deprotonation of the corresponding azolium salts • NHCs are stronger σ-donors than the most electron rich phosphine - less likely to dissociate from the metal during the reaction • NHCs have come to replace phosphines in many organometallic and organic reactions • NHCs can be useful spectator ligands, tunable electronically and sterically

3. N-Heterocyclic Carbenes as Ligands - In the early 90's NHC were found to have bonding properties similar to trialklyphosphanes( -PR3 ) and alkylphosphinates( -OP(OR)R2 ). - compatible with both high and low oxidation state metals - examples: - reaction employing NHC's as ligands: Herrmann, W. Angew. Chem. Int. Ed.2002, 41, 1290-1309.

4. The Catalytic Applications of Ni(II) • Heck Coupling Reaction ( ) • Ullmann Reaction ( ) • Reduction of Aryl Halides ( ) • Aryl Amination ( ) • Grignard Cross-Coupling Reaction ( ) • Suzuki Coupling Reaction ( ) • Cycloaddition ( )

5. Motivation • The replacement of palladium(II) with a nickel(II) center is challenging and offers access to • cost-saving catalysts • -PdCl2 10g $508 (Aldrich) => 1g $50.8 • -NiCl2 50g $26.8 (Aldrich) => 1g $0.53 • Using NHCs ligand to replace phosphine ligand in organomatallic catalysis • -Immobilization of NHC-Ni(II) complexs onto Au Nanoparticles • Developing a practical and effective process for the reduction of highly toxic chloroarenes into arenes • -due to chloroarenes’ deleterious environmental and health impact

6. (paramagnetic) NiCl42- (diamagnetic) Ni(CN)42- Crystal Filed Splitting of d8-M2+ Square Planar and Tetrahedral Complexes • Most first row transition metals prefer tetrahedral while the second and third- • row transition metals prefer square planar (Δo increses down to the group). • For first-row metal ions such as Ni2+ (a d8 species), tetrahedral arrangement is • preferred if the supporting ligands are large and weak-field. If the ligands are • small and are strong-field, the planar arrangement will be preferred. Greenwood, Chemistry of the elements; p. 1347

7. Square Planar-to-Tetrahedral Isomerization of Ni(PPh2R)2X2 • The tetrahedral structure is increasingly favored in the orders • P(C2H5)3 < P(C2H5)2C6H5 < PC2H5(C6H5)2 < P(C6H5)3 • -Steric effect • SCN < Cl < Br < I • -Due to the decrease ofcrystal field strength of the ligand R. G. Hayter, F. S. Humiec. Inorg. Chem. 1965, 4, 1701-1706.

8. Isomerism of Square Planar and Tetrahedral Structures of Ni[P(CH2Ph)Ph2]2Br2in the Same Unite Cell Square-Planar Tetrahedral Kilbourn. B. T.; Powell. H. M.J. Chem. Soc. (A), 1970, 1688-1693

9. The First Nickel(II)-Carbene Complexes Lappert, M. F.; Pye, P. L . J. Chem. Soc., Dalton Trans.1977, 2172-2180

10. Two Examples of Ni(II)-Carbene Complexes Matsubara, K.; Ueno, K.; Shibata, Y. Organometallics 2006, 25, 3422-3427 D. S. McGuinness et.al. Organometallics 2002, 21, 175-181

11. Silver(I)-Carbene Complexes as Carbene Transfer Agents Wang, H. M. J.; Lin, I. J. B. Organometallics1998, 17, 972-975

12. Synthesis of Ni(II)-Carbene Complex through the Ag(I)-Carbene Transfer Reagent Xi, Z.; Zhang, X.; Chen, W.; Fu, S.; Wang, D. Organometallics 2007, 26, 6636–6642

13. Experimental Preparation of Nickel(II) Complex Catalyst syn-form anti-form

14. 1H NMR Spectra of [Hmim]HBr, AgBr[hmim], and NiBr2[hmim]2 *CDCl3 H 2H CH3

15. *CDCl3 C C 13C NMR Spectra of [Hmim]HBr, AgBr[hmim], and NiBr2[hmim]2

16. FAB-MS Spectrum of NiBr2[hmim]2 Calculated MS Data [M – Br]+ Experimental MS Data [M – Br]+ Experimental MS Data [M – 2Br]+ Calculated MS Data [M – 2Br]+

17. 1567 NiBr2[hmim]2 3152, 3119 1220 1467 2951, 2929, 2858 703 744, 723 AgBr[hmim] 1560 1218 3141, 3086 2952, 2924, 2857 748 1464 [hmim]HBr 826 620 1569 imidazole ν (ring stretching) 1463 3136, 3059 763 2955, 2930, 2858 1169 imidazole ring ν (C–H) aliphatic ν (C–H) imidazole H–C–C & H–C–N bending IR Spectra of [Hmim]HBr, AgBr[hmim], and NiBr2[hmim]2

18. Single-Crystal X-ray Structure of NiBr2[hmim]2 Range of Ni(II)-C 1.88 ~ 1.95 Å Range of Ni(II)=C 1.80 ~ 1.85 Å dihedral angle 3.68o

19. Reduction of Aryl Halides by NaOMe Catalyzed by Pd(PPh3)4 Zask, A.; Helquist, P. J. Org. Chem. 1978, 43, 1619-1620

20. Catalytic Dehalogenation of Aryl Halides by a Palladium/Imidazolium Salt SIMes.HCl M. S. Viciu et. al. Organometallics 2001, 20, 3607-3612

21. IMes.HCl Ni(II) Catalyzed Reduction of Aryl Halides CpNi(IMes)Cl Kelly, R. A., III; Scott, N. M.; Diez-Gonzalez, S.; Stevens, E. D.; Nolan, S. P. Organometallics 2005, 24, 3442-3447 Desmarets, C.; Kuhl, S.; Schneider, R.; Fort, Y. Organometallics 2002, 21, 1554-1559

22. entry solvent, temperature (oC) time conversion (%)a 1 1,4-dioxane, 105 5 min 91 2 THF, 65 7 hr 71 a Yields were determined by NMR. entry pretreatment time conversion (%)a 1 5 min 1 hr 40 2 hr 67 2 1 hr 1 hr 44 2 hr 58 a Yields were determined by NMR. Ni(II)-Catalyzed Reduction of Aryl Halides

23. Ni(II)-Catalyzed Reduction of Aryl Halides

24. Ni(II)-Catalyzed Reduction of Aryl Bromides

25. Ni(II)-Catalyzed Reduction of Aryl Chlorides

26. Ni(II)-Catalyzed Reduction of Aryl Bromides

27. Proposed Mechanism for the Reduction of Aryl Halides Desmarets, C.; Kuhl, S.; Schneider, R.; Fort, Y. Organometallics2002, 21, 1554-1559

28. Zero-, First-, and Second-order Kinetic Equations Zero-order kinetics First-order kinetics Second-order kinetics

29. Plots of [A], ln[A], and 1/[A] vs. Time for the entry 1 and entry 2

30. Plots of [A], ln[A], and 1/[A] vs. Time for the entry 3 and entry 4

31. Plots of [A], ln[A], and 1/[A] vs. Time for the entry 5 and entry 6

32. Plots of [A], ln[A], and 1/[A] vs. Time for the entry 7 and entry 8

33. Ni(II)-Catalyzed Reduction of Aryl Halides

34. Conclusions • The carbene transfer reaction of AgBr[hmim]with Ni(CH3CN)2Br2 afforded our target nickel(II) catalyst NiBr2[hmim]2 as a red powder in high yield. • The air-stable catalyst NiBr2[hmim]2 was characterized by 1H- and 13C NMR, ESI-MS, IR, EA as well as X-ray crystallography. • We have successfully demonstrated the catalytic activity of the Ni(II) complex for the reduction of aryl halides in short reaction times. • We also have found that dehalogenation follows the first-order kinetics when the catalyst concentration falls into the range of 0.00218-0.00436 M.

35. Immobilization of AgBr(NHC) onto Surfaces of Au-NPs

36. Immobilization of NiBr2(NHC)2 onto Surfaces of Au-NPs