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In the reaction between 3-picoline, 2-bromo-5-methylpyridine, 2-methylquinoline, 3-methylisoquinoline, and [M(R-(+)-BINAP)][OTf]2 (M = Pd, Pt; BINAP = 2,2‘-bis(diphenylphosphino)-1,1‘-binaphthyl), the nature and the distribution of the products were investigated by various physical and spectroscopic methods. The α-substituents on the heteroaryl ring, such as the bromine atom in 2-bromo-5-methylpyridine or the methyl group in 2-methylquinoline, tend to promote the simultaneous formation of mono(heteroaryl)- and bis(heteroaryl)-containing products. The reaction of the most sterically demanding 2-methylquinoline favors the formation of mono(heteroaryl) complexes exclusively within the limits of NMR detection. Reaction of 3-picoline with the chiral Pd(II) and Pt(II) bis(triflates) results in the formation of diastereomeric, square-planar, cationic complexes, due to the hindered rotation about the metal−nitrogen heteroaryl bond. 1H NMR variable-temperature studies of [M(R-(+)-BINAP)(3-picoline)2][OTf]2 were performed. The activation barriers for the rotation of the β-picoline ligands around the M−N linkage axis were determined for [Pd(R-(+)-BINAP)(3-picoline)2][OTf]2 and [Pt(R-(+)-BINAP)(3-picoline)2][OTf]2 by a kinetic line shape analysis of the methyl signals. The Gibbs free energy of activation was found to be 12(±0.5) kcal/mol for the Pd complex 15 and 14(±0.5) kcal/mol for the Pt complex 16. Ab initio calculations (HF/lanl2dz) of model complexes [dpe]Pd(HNCH2)2 2+ and [dpe]Pt(HNCH2)2 2+ (dpe = diphosphinoethylene) provided insights into the observed results. The nitrogen−metal π−σ-interaction is found to be stronger for the Pt complex, resulting in a higher energy barrier for the rotation around the Pt−N bond compared to the rotation around the Pd−N bond. A comparison is made between the covalent and coordinated Pt(II) complexes, and the similarities and differences of their dynamic behavior are discussed.

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