Three new Pd(II) complexes, i.e. [PdCl
2L]
2 (
A), PdCl
2L
2 (
B) and [Pd(μ-Cl)(L-H)]
2 (
C), each with two diethyl [α-(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
13C-NMR spectra. Complexes
B and
C are additionally characterized by
1H-,
13C- and
31P-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
1H-NMR study of this rearrangement as well as of the reactions of
L with PdCl
2 and Na
2PdCl
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
2(L)(DMF)]. Complex
M was also the first intermediate in the reaction of
L with PdCl
2. Once present in concentration above 10
−5 mol dm
−3M dimerizes very fast into chloro-bridged dimer [PdCl(μ-Cl)(L)]
2 (
D) which undergoes cyclopalladation and converts into the complex
C. The formation of
C from the intermediate
D is clearly demonstrated by the concentration 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
3(L)]
− (
T). The same species
T are formed in the reaction of
L with Na
2PdCl
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.
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