SYNTHESIS AND STRUCTURE OF PALLADIUM(II) COMPLEXES WITH N(21),N(22)-BRIDGED PORPHYRIN LIGANDS

Palladium complexes of N(21),N(22)-(etheno)-bridged porphyrins were sy nthesized by the reaction of palladium(II) chloride and N(21),N(22)-(e theno)-tetraphenylporphyrins or N(21),N(22) -(etheno)-octaethyl-5,22-d ihydroporphyrins. The metallation proceeded via an initially produced monoprotonated porphyrin with a palladate anion. Dinuclear complexes i ncluding two PdCl2 units were preferentially produced and were convert ed into mononuclear complexes by a treatment with a saturated aqueous NaCl solution. Single-crystal X-ray diffraction shows the di-mu-chloro dipalladium(II) structure of the dinuclear complex, N(21),N(22)-(EtC=C Et)(TPP)(PdCl2)(2). CH2Cl2. H2O (TPP = 5,10, 15,20-tetraphenylporphyri n dianion). Pd(1) is coordinated by two adjacent imine nitrogens of th e porphyrin as the terminal ligands and placed out of the porphyrin 4N mean plane by 1.32 Angstrom. The distal Pd(2) is placed at a distance of 3.78 Angstrom from the porphyrin 4N mean plane and comes close to the porphyrin ring with a dihedral angle of 139.8 degrees between the two square planes of the Pd coordination. The NMR spectrum in solution indicated the influence of the distal Pd(2) on the porphyrin ring. Th e etheno bridge keeps the geometry of the 4N core of the porphyrin rel atively undeformed in comparison with the previously reported methano bridge, which accounts for the enhanced stability of Pd(II) complexes.