A new tripod PPN bridging ligand and its copper, silver and palladium complexes: syntheses, characterizations and X-ray structures

摘要

A new tripod bridging ligand 2-{bis(diisoprQPYlphosphino)methyl}-I-methylimidazole, MeImCH(Pi-Pr_2)_2 (PPN) was synthe- sized conveniently by reacting 2-{bis(trimethylsilyl)methyl}-I-methylimidazole and chlorodiisopropylphosphine. The dicationic dinuclear complex [Cu_2(PPN)_2][ClO_4]_2 (I) was prepared by the reaction of the ligandwith[Cu(MeCN)_4]CIO_4 in acetonitrile. The reaction of the ligand with AgNO_3 in propane-2-o1 followed by addition of NH_4PF_6 led to the formation of a similar type complex [Ag_2(PPN)d[PF_6b (2). The X-ray diffraction studies ofl and 2 revealed a J.12-1l1:1l2 tripod like bonding of the PPN ligand, with one P and one N atom chelating to one metal ion and the remaining one p atom binds to another metal ion, affording a face-to-face type molecule. An eight-membered M~P4C~ and a 10-membered M~P_2N_2C_4 ring are thus formed with this new f}lnctional diphosphine ligand. In both cbmplexes the tWo metal ions are held in very close proximity [2.6707 A for I and 2.859(3) A for 2]. Complex 1 underwent a rapid ligand exchange process in solution. Besides these dinucleitr complexes the ligand also afforded a mononuclear palladium complex, (PdCI_2(PPN)] (3), when it was treated with an equimolar amount of [PdCl_2(PhCN)~] in benzene. In 3 the ligand acts as a bidentate c1)elate through its two phosphorus atoms, leaving the imidazole donor dangling. On the other hand, 1 P ,P-bridged dinuclear Pd.(I) complex [Pd_2CI~(PPN)d (4) was achieved by reacting two moles of the ligand with .one ~ole of (PdCl_2(PhCN)d, foll ed by ~he addition of one mole of Pd(dba)2 [dba = dibenzylideneacetone].