Synthesis of tetra- and pentacoordinate palladium complexes of functionalized N-heterocyclic carbenes and a comparative study of their catalytic activities
作者:Xiaoming Zhang、Qinqin Xia、Wanzhi Chen
DOI:10.1039/b903285a
日期:——
Palladium complexes, [Pd(1-butyl-3-((7-methyl-1,8-naphthyridin-2-yl)methyl)imidazolylidene)2](PF6)2 (1), [Pd(3-methyl-1-(pyrimidin-2-yl)imidazolylidene)2(CH3CN)](PF6)2 (4), [Pd(3-benzyl-1-(pyrimidin-2-yl)imidazolylidene)2(CH3CN)](PF6)2 (5), [Pd(3-ethyl-1-(pyrimidin-2-yl)imidazolylidene)2Cl](PF6) (6), and [Pd(3-benzyl-1-(pyrimidin-2-yl)imidazolylidene)Cl2] (7), have been prepared viatransmetallation of corresponding in situ generated silver-carbene complexes. These palladium complexes have been characterized by NMR spectroscopy and elemental analyses, and their structures were determined by X-ray single-crystal diffraction. Complexes 1 and 7 are tetracoordinate displaying square-planar geometry. Complexes 4–6 are pentacoordinate showing uncommon square-pyramidal geometry with acetonitrile or chloride at the equatorial position. The Suzuki and Hiyama coupling reactions of a wide range of aryl bromides and chlorides have been comparatively investigated by using tetracoordinate moncarbene, tetracoordinate dicarbene, and pentacoordinate dicarbene palladium complexes as catalysts. The tetracoordinate moncarbene palladium complex showed the highest catalytic activity for both coupling reactions.
通过相应的原位生成的银卡宾配合物的转移金属化反应,制备了钯配合物,即[Pd(1-丁基-3-((7-甲基-1,8-萘啶-2-基)甲基)咪唑啉基)2](PF6)2 (1),[Pd(3-甲基-1-(嘧啶-2-基)咪唑啉基)2(CH3CN)](PF6)2 (4),[Pd(3-苄基-1-(嘧啶-2-基)咪唑啉基)2(CH3CN)](PF6)2 (5),[Pd(3-乙基-1-(嘧啶-2-基)咪唑啉基)2Cl](PF6) (6),以及[Pd(3-苄基-1-(嘧啶-2-基)咪唑啉基)Cl2] (7)。这些钯配合物通过核磁共振光谱和元素分析进行了表征,其结构由X射线单晶衍射确定。配合物1和7是四配位的,呈现平面四方形几何构型。配合物4-6是五配位的,展示了罕见的四方锥几何构型,其中乙腈或氯位于赤道位置。通过使用四配位单卡宾、四配位双卡宾和五配位双卡宾钯配合物作为催化剂,比较研究了广泛的芳基溴化物和氯化物的铃木和Hiyama偶联反应。四配位单卡宾钯配合物在这两种反应中显示出最高的催化活性。