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

A new tripod bridging ligand 2-{bis(diisopropylphosphino)methyl}-1-methylim idazole, MeImCH(Pi-Pr-2)(2) (PPN) was synthesized conveniently by reacting 2-{bis(trimethylsilyl)methyl}-1-methylimidazole and chlorodiisopropylphosph ine. The dicationic dinuclear complex [Cu-2(PPN)(2)][ClO4](2) (1) was prepa red by the reaction of the ligand with [Cu(MeCN)(4)]ClO4 in acetonitrile. T he reaction of the ligand with AgNO3 in propane-2-ol followed by addition o f NH4PF6 led to the formation of a similar type complex [Ag-2(PPN)(2)][PF6] (2) (2). The X-ray diffraction studies of 1 and 2 revealed a mu (2) - eta ( 1): eta (2) tripod-like bonding of the PPN ligand, with one P and one N ato m 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 M2P4C2 and a 10-membered M2P2N2C4 ring are thus formed with this new functional d iphosphine ligand. In both complexes the two metal ions are held in very cl ose proximity [2.6707 Angstrom for 1 and 2.859(3) Angstrom for 2]. Complex 1 underwent a rapid ligand exchange process in solution. Besides these dinu clear complexes the ligand also afforded a mononuclear palladium complex. [ PdCl2(PPN)] (3). when it was treated with an equimolar amount of [PdCl2(PhC N)(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 ha nd, a P,P-bridged dinuclear Pd(I) complex [Pd2Cl2(PPN)(2)] (4) was achieved by reacting two moles of the ligand with one mole of [PdCl3(PhCN)(2)], fol lowed by the addition of one mole of Pd(dba)(2) [dba = dibenzylideneacetone ]. (C) 2001 Elsevier Science Ltd. All rights reserved.