| Abstrakt: |
With a view to applications in bifunctional catalysis, a modular cross-coupling strategy has been used to prepare amine bis(imidazolium) salts (3aand 3b) and an amine mono(imidazolium) salt (6) as precursors to chelating amido-NHC ligands. Treating the pro-ligands 3with 3 equivalents of the bulky base KHMDS and Pd(OAc)2or PtCl2(COD) gave the four amido bis(N-heterocyclic carbene) pincer complexes [CNC-R]M-I [M = Pd (7) or Pt (8); R = i-Pr (a) or n-Bu (b)], including the first examples of platinum complexes of a CNC ligand. The reaction of 7awith AgOTf in pyridine gave the cationic complex {[CNC-i-Pr]Pd-py}OTf (9a). Heating a mixture of amine mono(imidazolium) salt 6with PdCl2or K2PtCl4, K2CO3and KI in pyridine at 100 °C gave the complexes [C,NH]MI2py [M = Pd (10) or Pt (11)], in which the amine arm of the NHC ligand is not deprotonated and does not coordinate to the metal. For a solution of 10in 1,4-dioxane, deprotonation of the amine occurred in a biphasic reaction with aqueous KOH at 40 °C, giving the dimeric amido complex {[C,N]Pd(μ-OH)}2(12). The more inert Pt analogue 11was unreactive under the same conditions. Solid-state structures of the complexes 7a, 7b, 9a, 10, 11and 12have been determined by single crystal X-ray diffraction. [ABSTRACT FROM AUTHOR] |
