名称:
                                Novel Ag(I), Pd(II), Ni(II) complexes of N,N′-bis-(2,2-diethoxyethyl)imidazole-2-ylidene: Synthesis, structures, and their catalytic activity towards Heck reaction
                             
                            
                                摘要:
                                Tetra-ether substituted imidazolium salts, LHX ( where LH = N,N'-bis(2,2-diethoxyethyl) imidazolium cation and X = Br, BF4, PF6, BPh4, NO3 and NTf2 anions) were derived from imidazole. Attempts to produce aldehyde functionalized imidazolium salt through acid hydrolysis of LHBr resulted an unexpected tetra-hydroxy compound LAHBr and the dialdehyde compound LBHBr. Reaction of LHBr with Ag2O afforded [L2Ag][AgBr2] (1). Mononuclear Pd-complex trans-[L2PdCl2] (2) and dinuclear Pd- complex [(LPdCl2)(2)] ( 3) were obtained by 1: 1 and 1: 2 reaction of in situ generated Ag-carbene with Pd(CH3CN)(2)Cl-2. cis-[LPdPPh3Cl2] (4) was synthesized from reaction of PPh3 with dinuclear complex 3. Hydrolysis of 3 under acidic conditions also generates a hydroxy derivative 3A and the aldehyde derivative 3B. Direct heating of LHBr with Ni(OAc)(2)center dot 4H(2)O at 120 degrees C under vacuum generated trans-[L2NiBr2] (5). These complexes were characterized by NMR, mass, elemental analysis, and X-ray single crystal diffraction analysis. Pd- Pd interaction was observed in 3. All the Pd complexes exhibited excellent catalytic activity in Heck reaction. (C) 2008 Elsevier B. V. All rights reserved.