The Impact of ortho‐substituents on Bonding in Silver(I) and Halogen(I) Complexes of 2‐Mono‐ and 2,6‐Disubstituted Pyridines: An In‐Depth Experimental and Theoretical Study

Abstract

AbstractThe coordination nature of 2‐mono‐ and 2,6‐disubstituted pyridines with electron‐withdrawing halogen and electron‐donating methyl groups for [N−X−N]+ (X=I, Br) complexations have been studied using 15N NMR, X‐ray crystallography, and Density Functional Theory (DFT) calculations. The 15N NMR chemical shifts reveal iodine(I) and bromine(I) prefer to form complexes with 2‐substituted pyridines and only 2,6‐dimethylpyridine. The crystalline halogen(I) complexes of 2‐substituted pyridines were characterized by using X‐ray diffraction analysis, but 2,6‐dihalopyridines were unable to form stable crystalline halogen(I) complexes due to the lower nucleophilicity of the pyridinic nitrogen. In contrast, the halogen(I) complexes of 2,6‐dimethylpyridine, which has a more basic nitrogen, are characterized by X‐crystallography, which complements the 15N NMR studies. DFT calculations reveal that the bond energies for iodine(I) complexes vary between −291 and −351 kJ mol−1 and for bromine between −370 and −427 kJ mol−1. The bond energies of halogen(I) complexes of 2‐halopyridines with more nucleophilic nitrogen are 66‐76 kJ mol−1 larger than those of analogous 2,6‐dihalopyridines with less nucleophilic nitrogen. The experimental and DFT results show that the electronic influence of ortho‐halogen substituents on pyridinic nitrogen leads to a completely different preference for the coordination bonding of halogen(I) ions, providing new insights into bonding in halogen(I) chemistry.