PALLADIUM COMPLEXES WITH THE TRIDENTATE DIANIONIC LIGAND PYRIDINE-2,6-DICARBOXYLATE, DIPIC - CRYSTAL-STRUCTURE OF [PD(DIPIC)(PBU(3))](2)

The reactions of [Pd(acac)(2)] or [Pd(OAc)(2)](3) with pyridine-2,6-di carboxylic acid (H(2)dipic) in acetonitrile afford [Pd(dipic)(NCMe)] i n high yield. This complex has been used as starting material in the p reparation of a variety of neutral an anionic complexes. The dipicolin ate anion behaves as a tridentate ligand in all cases, but two modes o f coordination are found, depending on the ligand: as a pincer ligand O,N,O-bonded to the same palladium, giving mononuclear complexes, and as an O,N-chelate N,O'-bridging ligand in dinuclear complexes. An X-ra y determination of the structure of a dimer, [Pd(dipic)(PBu(3))](2) (m onoclinic, space group P2(1)/n, a = 18.144(4) Angstrom, b = 13.191(2) Angstrom, c = 19.571(3) Angstrom, beta = 113.45(2)degrees, Z = 4, R = 0.050, R(w) = 0.054) shows that the ligand is coordinated to one palla dium in a eta(2)-N,O chelate fashion and one oxygen atom of the other carboxylate group makes a bridge to the other palladium atom, in a nov el bonding mode for the dipic ligand.