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Three new Pd(II) complexes, i.e. [PdCl{sub 2}L]{sub 2} (A), PdCl{sub 2}L{sub 2} (B) and [Pd({mu}-Cl)(L-H)]{sub 2} (C), each with two diethyl [{alpha}-(4-benzenazoanilino)-2-hydroxybenzyl]phosphonates (L) bound to either one or two palladium atoms, are synthesized and characterized by elemental analysis, by IR, UV-vis and solid-state {sup 13}C-NMR spectra. Complexes B and C are additionally characterized by {sup 1}H-, {sup 13}C- and {sup 31}P-NMR and electrospray mass spectrometry (ESMS) studies using dimethylformamide (DMF) as a solvent. In DMF solution adducts A and B undergo spontaneous rearrangement into the cyclopalladated complex C. Dynamic {sup 1}H-NMR study of this rearrangement as well as of the reactions of L with PdCl{sub 2} and Na{sub 2}PdCl{sub 4} revealed a complex equilibrium in DMF solutions and enabled the formation mechanism of all involved species to be resolved. The complex A is immediately solvolyzed producing two molecules of intermediate M [PdCl{sub 2}(L)(DMF)]. Complex M was also the first intermediate in the reaction of L with PdCl{sub 2}. Once present in concentration above 10{sup -5} mol{sup -3} M dimerizes very fast into chloro-bridged dimer [PdCl({mu}-Cl)(L)]{sub 2} (D) which undergoes cyclopalladation and converts into the complex C. The formation of C from the intermediate D is clearly demonstrated by the concentrationmore » dependence of the cyclopalladation reaction which has order greater than one. Chloride ions, released by cyclopalladation, react with D by splitting chloro-bridge and binding to metal atoms to produce byproduct [PdCl{sub 3}(L)]{sup -} (T). The same species T are formed in the reaction of L with Na{sub 2}PdCl{sub 4} whereby a chloride ion is replaced by the ligand L. The complex B undergoes similar, but slower, solvolytic reaction producing M and L while further reaction steps are identical as in the solvolysis of A.« less |
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