The complexes [MCl(2)(kappa2-N approximately N')] (N approximately N' = 2-C(5)H(4)N-CH2-NHAr; Ar = 4-MeC(6)H(4), a; 2,6-Me(2)C(6)H(3), b; 4-MeOC(6)H(4), c; 4-CF(3)C(6)H(4), d; M = Pd, 1a-d; Pt, 2a-d) have been prepared and fully stereochemically characterized both in the solid state and in solution. Their behavior in DMSO-d6 solution is dependent on the substituents of the aryl group and on the metal. Complexes of palladium with substituents at the para position (1a, 1c, 1d) display a dynamic 1H NMR pattern when the solutions are heated. An enantiomeric exchange Slambda/Rdelta is suggested to explain such behavior. On the basis of the calculated negative DeltaS values, an associative mechanism involving the solvent is proposed. Under the same conditions, analogous complexes of platinum (2a, 2c, 2d) proved to be unstable, and release of the N approximately N' ligand was observed. Complexes 1b and 2b show temperature-variable 1H NMR spectra without any evidence accounting for enantiomeric exchange or decoordination. DFT calculations on models of 1a and 1b show that diastereomeric exchange Sdelta/Slambda is a process where the complex with the higher sterical hindrance, 1b, has a lower energy barrier.

The reaction of the complex [Pd(κ3‐NN′O)CH3] [NN′O = 2‐Py‐CH=N‐(o‐C6H4)O–] (1a) with nitromethane affords a mixture of 2a and 2b. In this reaction methylation of the ligand takes place. These complexes display exchange equilibrium in solution. The methylation reaction is proposed to occur through nucleophilic attack of the nitronate anion on the iminic carbon atom. DFT calculations are presented in order to support a part of the mechanism and these calculations show that the participation of water in the migration of a proton is important. The crystal structure of the derivative productafter spontaneous release of methane (3) is presented as well. Attempts to extend the reaction to other nitroalkanes resulted in a mixture of complexes that was not easy to characterize. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

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