Home > Our People > Academic Staff

Research Interests

Organometallic Chemistry and Catalysis

Our current research is centered on the synthesis of N-heterocyclic Carbenes (NHC) transition metal complexes and their application in catalysis. We are especially interested in the following sub-areas:

1) Carbene-carboxylate complexes of Pd(II)

Mixed dicarboxylato-bis(carbene) complexes of palladium(II) belong to an interesting novel class of complexes, which are scarcely investigated so far. We have shown that mono- and dicarbenes can stabilize the Pd-carboxylato moiety efficiently and therefore prevent reductive decomposition and auto-ionization processes - two important side-reactions that lead to catalysts deactivation of phosphine-carboxylato complexes. The preferably cis-configured complexes are highly active in the Mizoroki-Heck reaction.

2) Benzimidazolin-2-ylidene complexes of Nickel(II)

Nickel carbene complexes are potential cost-saving alternatives to Pd-catalysts. However, only few nickel carbene complexes have been reported so far due to the lack of synthetic procedures for their preparation. We have developed a one-pot approach for the synthesis of the first benzimidazolin-2-ylidene complexes of nickel(II) using ammonium salts as ionic liquids. With this methodology, a library of nickel(II) NHC complexes of different steric demands have been synthesized and structurally characterized. The dependence of sterically demanding substituents on the catalytic activities of these complexes is currently under investigation. Some of the complexes exhibit rare preagostic C-H xxx Ni interactions.

3) Carbene complexes incorporating hemilabile sulfur donor functions

Complexes with hemilabile functionalities are known to have increased catalytic activities and NHC ligands incorporating N-, O- and P-donor functions have been reported recently. Carbene ligands with S-donor functions on the other hand are very rare. We have developed a modular approach to S-functionalized NHCs and studied their unique hemilabile behavior.

4) Cleavage of dinuclear Pd(II) carbene complexes

We have reported a novel dimeric benzimidazolin-2-ylidene complex of palladium(II), which is active in the Suzuki-Miyaura coupling of aryl bromides and chlorides in pure water as environmentally benign solvent. Rare C-H xxx Pd preagostic interactions are also observed in this dimer. Cleavage of the dimeric complex with various ligands (CH₃CN, PPh₃, Halide salts, Isocyanides, Pyridines, etc) results in mononuclear or bridged dinuclear complexes with interesting properties.

5) N,S-heterocyclic carbene and their complexes

We are investigating N,S- and N,O-heterocyclic carbenes and their complexes as alternatives to the commonly known N,N-heterocyclic analogues. Since sulfur is less and oxygen more electronegative than nitrogen, we expect a different donor-ability of N,S-and N,O-heterocyclic carbenes, which may lead to interesting complex properties. In collaboration with the group of Prof. Hahn in Munster, Germany, we have prepared benzothiazolin-2-ylidene complexes of Ir(I) and studied the donor strength of N,S-heterocyclic carbenes.

Representative Publications

1. H. V. Huynh*, D. LeVan, F. E. Hahn*, T.S.A. Hor "Synthesis and Structural Characterization of mixed Carbene-Carboxylate Complexes of Palladium(II)" J. Organomet. Chem. 2004, 689, 1766-1770.
2. H. V. Huynh*, J. H. H. Ho, T. C. Neo, L. L. Koh "Solvent-controlled selective Synthesis of a trans-configured Benzimidazoline-2-ylidene Palladium(II) Complex and Investigations of its Heck-type catalytic activity" J. Organomet. Chem. 2005, 690, 3854-3860.
3. H. V. Huynh*, C. Holtgrewe, T. Pape, L. L. Koh, E. Hahn* "Synthesis and Structural Characterization of the First Bis(benzimidazolin-2-ylidene) Complexes of Nickel(II)" Organometallics 2006, 25, 245-249.
4. H. V. Huynh*, T. C. Neo, G. K. Tan "Mixed Dicarboxylato-Bis(carbene) Complexes of Palladium(II): Synthesis, Structures, trans-cis Isomerism and Catalytic Activity" Organometallics 2006, 25, 1298-1302.
5. S. K. Quek, I. Lyapkalo*, H. V. Huynh "Synthesis and Properties of N,N'-dialkyl-imidazolium bis(nonafluorobutane-1-sulfonyl)imides: a new subfamily of ionic liquids" Tetrahedron 2006, 62, 3137-3145.
6. S. K. Quek, I. Lyapkalo*, H. V. Huynh "A New Highly Efficient Method for the Synthesis of tert-Alkyl Nitroso Compounds" Synthesis 2006, 1423-1426.
7. H. V. Huynh*, N. Meier, T. Pape, F. E. Hahn* "Benzothiazolin-2-ylidene Complexes of Iridium(I)" Organometallics 2006, 25, 3012-3018.
8. H. V. Huynh*, Y. Han, J. H. H. Ho, G. K. Tan "Palladium(II) Complexes of a sterically bulky, benzannulated N-Heterocyclic Carbene with unusual C H^...Pd and C_carbene^...Br interactions" Organometallics 2006, 25, 3267-3274.
9. H. V. Huynh*, C. H. Yeo, G. K. Tan "Hemilabile Behavior of a Thioether-functionalized N-Heterocyclic Carbene ligand" Chem. Commun. 2006, 3833-3835.
10. S. K. Yen, L. L. Koh, F. E. Hahn, H. V. Huynh*, T. S. A. Hor* "Convenient Entry to Mono- and Dinuclear Palladium(II) Benzothiazolin-2-ylidene Complexes and their Activities towards Heck-Coupling" Organometallics 2006, 25, 5105-5112.
11. K. E. Neo, Y. Y. Ong, H. V. Huynh, T. S. A. Hor "A single-molecular pathway from heterometallic MM' (M = BaII, MnII; M' = CrIII) oxalato complexes to intermetallic composite oxides" J. Mater. Chem. 2007, 17, 1002-1006.
12. Y. Han, H. V. Huynh* "Preparation and characterization of the first pyrazole-based remote N-heterocyclic carbene complexes of palladium(II)" Chem. Commun. 2007, 1089-1091.
13. Y. Han, H. V. Huynh*, L. L. Koh "Pd(II) Complexes of a Sterically Bulky, Benzannulated N-Heterocyclic Carbene and Their Catalytic Activities in the Mizoroki-Heck Reaction" J. Organomet. Chem. 2007, 692, 3606-3613.
14. S. K. Yen, L. L. Koh, H. V. Huynh*, T. S. A. Hor* "Pd(II) complexes of N,S-heterocyclic carbenes with pendant and coordinated allyl function and their Suzuki coupling activities" Dalton Trans. 2007, 3952-3958.
15. Y. Han, H. V. Huynh*, G. K. Tan "Mono- vs Bis(carbene) Complexes: A Detailed Study on Platinum(II)-Benzimidazolin-2-ylidenes" Organometallics 2007, 26, 4612-4617.
16. K. E. Neo, H. V. Huynh, L. L. Koh, W. Henderson, T. S. A. Hor* "Dinuclear PCP pincer complexes from Lewis acidic [Pd(OTf)(PCP)] and basic [Pd(4-Spy)(PCP)] (OTf = triflate; 4-Spy = 4-pyridinethiolate; PCP = -CH(CH₂CH₂PPh₂)₂ Dalton Trans. 2007, 5701-5709.
17. Y. Han, H. V. Huynh*, G. K. Tan "Syntheses and Characterizations of Pd(II) Complexes incorporating a N-Heterocyclic Carbene and Aromatic N-Heterocycles" Organometallics 2007, 26, 6447-6452.
18. Y. Han, H. V. Huynh*, G. K. Tan "Palladium(II) Pyrazolin-4-ylidenes: Remote N-Heterocyclic Carbene Complexes and Their Catalytic Application in Aqueous Suzuki-Miyaura Coupling" Organometallics 2007, 26, 6581-6585.
19. H. V. Huynh*, R. Jothibasu, L. L. Koh "Dipalladium bis(m-isopropylthiolato) complexes with a [Pd₂S₂] core supported by N-heterocyclic carbenes" Organometallics 2007, 26, 6852-6856.
20. R. Jothibasu, H. V. Huynh*, L. L. Koh "Au(I) and Au(III) complexes of a sterically bulky benzimidazole-derived N-heterocyclic carbene" J. Organomet. Chem. 2008, 693, 374-380.
    S. K. Yen, L. L. Koh, H. V. Huynh*, T. S. A. Hor* "Pd(II) complexes with mixed benzothiazolin-2-ylidene and phosphine ligands and their catalytic activites toward C-C coupling reactions" Dalton Trans. 2008, 699-706.
21. K. E. Neo, H. V. Huynh, L. L. Koh, W. Henderson, T.S. A. Hor* "Isolation and Crystallographic Characterization of Solvate- and Anion-Stabilized PCP Pincer Complexes of Palladium(II)" J. Organomet. Chem. 2008, 693, 1628-1635.
22. H. V. Huynh*, L. R. Wong, P. S. Ng "Anagostic Interactions and Catalytic Activities of Sterically Bulky Benzannulated N-Heterocyclic Carbene Complexes of Nickel(II)" Organometallics 2008, 27, 2231-2237.
23. A. T. Normand, S. K. Yen, H. V. Huynh, T. S. A. Hor, K. J. Cavell* "Catalytic Annulation of Heterocycles via a Novel Redox Process Involving the Imidazolium Salt N-Heterocyclic Carbene Couple" Organometallics 2008, 27, 3153-3160.
24. S. K. Yen, L. L. Koh, H. V. Huynh, T. S. A. Hor* "Mono- and dinuclear palladium(II) N,S-Heterocyclic carbene complexes" Chemistry - An Asian Journal 2008, 3, 1649-1656.
25. Y. Han, Y.-T. Hong, H. V. Huynh* "Ag(I) and Pd(II) Complexes of a 1,3-Dibenzhydryl Substituted Benzannulated N-Heterocyclic Carbene: Unexpected Rearrangement, Structures and Catalytic Studies" J. Organomet. Chem. 2008, 693, in press, doi:10.1016/j.jorganchem.2008.06.037
26. Rotamers of Palladium Complexes bearing IR active N-Heterocyclic Carbene ligands: Synthesis, Structural Characterization and Catalytic Activities. H. V. Huynh and J. Wu; J Organomet Chem, 2009, 694, 323-331.
27. Mixed carbene-isocyanide Pd(II) complexes: synthesis, structures and reactivity towards nucleophiles. Y. Han and H. V. Huynh; Dalton Trans, 2009, 2201-2209.
28. Formation of homoleptic tetracarbene versus cis chelating dicarbene complexes of Nickel(II) and applications in Kumada-Corriu couplings. H. V. Huynh and R. Jothibasu; Eur J Inorg Chem, 2009, 1926-1931.
29. Synthesis, structural characterization and catalytic activity of a palladium(II) complex bearing a new ditopic thiophene-N-heterocyclic carbene ligand. H. V. Huynh and Y. X. Chew; Inorg Chim Acta, 2009, DOI: 10.1016/j.ica.2009.02.035
30. Mixed Azido-N-Heterocyclic Carbene Complexes of Ni(II) as Template for New Organometallics bearing Carbodiimido, Tetrazolato and Abnormal Tetrazolin-5-ylidene Ligands. R. Jothibasu and H. V. Huynh; Organometallics, 2009, 28, 2505-2511.
    
31. Pd(II) Pyrazolin-4-ylidenes: Substituent-Effects on the Formation and Catalytic Activity of Pyrazole-based Remote NHC Complexes. Y. Han and H. V. Huynh; Organometallics, 2009, 28, 2778-2786.
32. Syntheses and catalytic activities of pseudo-pincer and CSC pincer-type Pd(II) complexes derived from benzannulated N-heterocyclic carbenes. H. V. Huynh, D. Yuan and Y. Han; Dalton Trans, 2009, 7262-7268.
33. ¹³C NMR Spectroscopic Determination of Ligand Donor Strengths using N-Heterocyclic Carbene Complexes of Palladium(II). H. V. Huynh, Y. Han, R. Jothibasu and J. A. Yang; Organometallics, 2009, DOI: 10.1021/om900667d.