Palladium Complexes with the Tridentate Dianionic Ligand Pyridine-2,6-dicarboxylate, dipic. Crystal Structure of [Pd(dipic)(PBu3)]2

Abstract
The reactions of [Pd(acac)2] or [Pd(OAc)2]3 with pyridine-2,6-dicarboxylic acid (H2dipic) in acetonitrile afford [Pd(dipic)(NCMe)] in high yield. This complex has been used as starting material in the preparation of a variety of neutral an anionic complexes. The dipicolinate anion behaves as a tridentate ligand in all cases, but two modes of 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-ray determination of the structure of a dimer, [Pd(dipic)(PBu3)]2 (monoclinic, space group P21/n, a = 18.144(4) Å, b = 13.191(2) Å, c = 19.571(3) Å, β = 113.45(2)°, Z = 4, R = 0.050, Rw = 0.054) shows that the ligand is coordinated to one palladium in a η2-N,O chelate fashion and one oxygen atom of the other carboxylate group makes a bridge to the other palladium atom, in a novel bonding mode for the dipic ligand.

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