The chemistry of N-benzylidene-1,4-phenylenediamine palladacycles: The crystal and molecular structure of the first tetranuclear palladacycle with bridging Ph2PCH2PPh2 ligands
摘要:
The reaction of the tetranuclear halide-bridged complexes 1-2(a-d) with Ph2PCH2PPh2 (dppm) or Ph2PC(=CH2)PPh2 (vdpp) in 1:2 molar ratio and NH4PF6 afforded the novel tetarnuclear palladacycles 3-6 (a, c, d) as 1:2 electrolytes with bridging diphosphine and halogen ligands. The structure of 4a has been determined by X-ray diffraction analysis, and represents the first example of a tetranuclear palladacycle with bridging dppm and halogen ligands. Reaction of 1-2(a-d) with (Ph2PCH2CH2)(2)PPh (triphos) in 1:2 molar ratio gave 7(a-d) bearing two pentacoordinated palladium atoms. The structure of 7a, as determined by X-ray diffraction analysis, shows the distorted square pyramidal geometry around the metal centers. Treatment of 1-2(a-d) with dppm, vdpp or Ph2PN(Me)PPh2 (dppma) in 1:4 molar ratio gave the dinuclear palladacycles 8-10(a-d) with a chelating diphosphine ligand at each metal center; further treatment of 9(a-c) with the nucleophiles pyrrolidine, piperidine, morpholine or 4-methylpiperidine gave the Michael addition derivatives 11-12(a-c), 13b, 13c and 14c, promoted by the withdrawing effect of the palladacycle which activates the C=CH2 double bond. (C) 2009 Elsevier B.V. All rights reserved.