Department of Chemistry, University of Leicester, University Road, Leicester, UK LE1 7RH.
Dalton Trans. 2011 Jan 14;40(2):495-505. doi: 10.1039/c0dt01149e. Epub 2010 Nov 18.
With a view to applications in bifunctional catalysis, a modular cross-coupling strategy has been used to prepare amine bis(imidazolium) salts (3a and 3b) and an amine mono(imidazolium) salt (6) as precursors to chelating amido-NHC ligands. Treating the pro-ligands 3 with 3 equivalents of the bulky base KHMDS and Pd(OAc)(2) or PtCl(2)(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 7a with AgOTf in pyridine gave the cationic complex {[CNC-i-Pr]Pd-py}OTf (9a). Heating a mixture of amine mono(imidazolium) salt 6 with PdCl(2) or K(2)PtCl(4), K(2)CO(3) and KI in pyridine at 100 °C gave the complexes [C,NH]MI(2)py [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 10 in 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 11 was unreactive under the same conditions. Solid-state structures of the complexes 7a, 7b, 9a, 10, 11 and 12 have been determined by single crystal X-ray diffraction.
为了应用于双功能催化，采用模块化交叉偶联策略制备了胺双（咪唑啉）盐（3a 和 3b）和胺单（咪唑啉）盐（6），作为螯合酰胺-NHC 配体的前体。用 3 当量的大位阻碱 KHMDS 和 Pd(OAc)(2)或 PtCl(2)(COD)处理前体配体 3，得到了四个酰胺双（N-杂环卡宾）钳形配合物[CNC-R]M-I[M=Pd（7）或 Pt（8）；R=i-Pr（a）或 n-Bu（b）]，包括 CNC 配体的第一个铂配合物实例。7a 与 AgOTf 在吡啶中的反应得到了阳离子配合物{[CNC-i-Pr]Pd-py}OTf（9a）。在吡啶中加热胺单（咪唑啉）盐 6 与 PdCl(2)或 K(2)PtCl(4)、K(2)CO(3)和 KI 的混合物，在 100°C 下得到配合物[C,NH]MI(2)py[M=Pd（10）或 Pt（11）]，其中 NHC 配体的胺臂未被去质子化并且不与金属配位。对于 10 在 1,4-二恶烷中的溶液，在 40°C 的水 KOH 的两相反应中发生了胺的去质子化，得到了二聚酰胺配合物{[C,N]Pd(μ-OH)}(2)（12）。在相同条件下，更惰性的 Pt 类似物 11 没有反应。配合物 7a、7b、9a、10、11 和 12 的固态结构通过单晶 X 射线衍射确定。
