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

Abstract A new tripod bridging ligand 2-{bis(diisopropylphosphino)methyl}-1-methylimidazole, MeImCH(P i -Pr 2 ) 2 (PPN) was synthesized conveniently by reacting 2-{bis(trimethylsilyl)methyl}-1-methylimidazole and chlorodiisopropylphosphine. The dicationic dinuclear complex [Cu 2 (PPN) 2 ][ClO 4 ] 2 ( 1 ) was prepared by the reaction of the ligand with [Cu(MeCN) 4 ]ClO 4 in acetonitrile. The reaction of the ligand with AgNO 3 in propane-2-ol followed by addition of NH 4 PF 6 led to the formation of a similar type complex [Ag 2 (PPN) 2 ][PF 6 ] 2 ( 2 ). The X-ray diffraction studies of 1 and 2 revealed a μ 2 -η 1 :η 2 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 2 P 4 C 2 and a 10-membered M 2 P 2 N 2 C 4 ring are thus formed with this new functional diphosphine ligand. In both complexes the two metal ions are held in very close proximity [2.6707 A for 1 and 2.859(3) A for 2 ]. Complex 1 underwent a rapid ligand exchange process in solution. Besides these dinuclear complexes the ligand also afforded a mononuclear palladium complex, [PdCl 2 (PPN)] ( 3 ), when it was treated with an equimolar amount of [PdCl 2 (PhCN) 2 ] in benzene. In 3 the ligand acts as a bidentate chelate through its two phosphorus atoms, leaving the imidazole donor dangling. On the other hand, a P,P-bridged dinuclear Pd(I) complex [Pd 2 Cl 2 (PPN) 2 ] ( 4 ) was achieved by reacting two moles of the ligand with one mole of [PdCl 2 (PhCN) 2 ], followed by the addition of one mole of Pd(dba) 2 [dba=dibenzylideneacetone].