N-heterocyclic-carbene complexes

During the last decade N-heterocyclic carbene complexes of transition metals have been developed for catalytic applications for many different or-... 

Independently, Caddick et al. reported microwave-assisted amination of aryl chlorides using a palladium-N-heterocyclic carbene complex as the catalyst (Scheme 99) [lOlj. Initial experiments in a domestic microwave oven (reflux conditions) revealed that the solvent is crucial for the reaction. The Pd source also proved very important, since Pd(OAc)2 at high power in DMF gave extensive catalyst decomposition and using it at medium and low power gave no reaction at all. Pd(dba)2/imidazohum salt (1 mol% catalyst loading) in DME with the addition of some DMF was found to be suitable. Oil bath experiments indicated that only thermal effects are governing the amination reactions. 

Synthesis and structural characterization of linear Au(l) N-heterocyclic carbene complexes New analogues of the Au(l) phosphine drug auranofin. Journal of OrganometaUic Chemistry, 690, 5625-5635. 

Aqueous two-phase hydrogenations are dominated by platinum group metal catalysts containing water-soluble tertiary phosphine ligands. The extremely stable and versatile N-heterocyclic carbene complexes attracted only limited interest, despite the fact that such complexes were described in the literature [62-65]. Recently, it was reported that the water-soluble [RuXY(l-butyl-3-methylimi-dazol-2-ylidene) ( 76-p-cymene)]n+ (X=Ch, H20 Y = C1-, H20, pta) complexes preferentially hydrogenated cinnamaldehyde and benzylideneacetone at the C = C double bond (Scheme 38.5) with TOF values of 30 to 60 h 1 in water substrate biphasic mixtures (80 °C, lObar H2) [66]. 

Iridium N-Heterocyclic Carbene Complexes and Their Application as Homogeneous Catalysts... 

We reported the use of M-heterocyclic carbene complexes (NHC) for the catalytic activation of methane [55,56]. We found that solutions of N-heterocyclic carbene complexes of palladium(II) in carboxylic acids catalyze the conversion of methane to the corresponding methylesters. The high thermal stability of palladium(II) carbene complexes could be shown for complex 18 (Scheme 22), which we also structurally characterized [120]. An extraordinary feature is the unprecedented resistance of the palladium-NHC-complexes 18-22 under the acidic oxidizing conditions which are necessary for the CH-activation and functionalization. 

Peris E (2006) Routes to N-Heterocyclic Carbene Complexes. 21 83-116 Popp BV, Stahl SS (2007) Palladium-Catalyzed Oxidation Reactions Comparison of Benzo-quinone and Molecular Oxygen as Stoichiometric Oxidants. 22 149-189 Prashad M (2004) Palladium-Catalyzed Heck Arylations in the Synthesis of Active Pharmaceutical Ingredients. 6 181-204... 

Flickey JL, Ruhayel RA, Barnard PJ, Baker MV, Bemers-Price SJ, Filipovska A (2008) Mitochondria-targeted chemotherapeutics the rational design of gold(I) N-heterocyclic carbene complexes that are selectively toxic to cancer cells and target protein selenols in preference to thiols. J Am Chem Soc 130 12570-12571... 

---