Diaryliodonium as a double σ-hole donor: the dichotomy of thiocyanate halogen bonding provides divergent solid state arylation by diaryliodonium cations

Abstract

X-ray crystallography data revealed the dichotomy of thiocyanate-involving noncovalent interactions in [Ar¹Ar²I](SCN), as reflected in the generation of two types of supramolecular aggregates: (i) previously unreported 4-membered heterotetramers (Ar¹/Ar² = 4-ClC₆H₄/2,4,6-(MeO)₃C₆H₂, 4-BrC₆H₄/2,4,6-(MeO)₃C₆H₂; 2 examples) featuring exclusively halogen bond (XB) N-XB-bound SCN⁻ anions, and (ii) the 8-membered cyclic heterotetramers (Ar¹/Ar² = Ph/Ph, Ph/2,4,6-(MeO)₃C₆H₂, 4-FC₆H₄/2,4,6-(MeO)₃C₆H₂, 3,5-Me₂C₆H₃/4-MeOC₆H₄, 3,5-Me₂C₆H₃/2,4,6-(MeO)₃C₆H₂; 5 examples) with two N,S-XB-bound thiocyanates featuring both S⋯I and N⋯I noncovalent contacts. In all cases, the I^III centers function as a double σ-hole donor to provide two directional XBs. The XB preorganization affects the chemoselectivity of the thiocyanate arylation in the solid-state: the heating of [Ar¹Ar²I](SCN) exhibiting either N-, or N,S preorganized XBs leads to extremely rare N-arylation or the conventional S-arylation, respectively. The charge-assisted XBs in [Ar¹Ar²I](SCN) were studied using density functional theory (DFT) calculations combined with a molecular electrostatic potential surface analysis and the quantum theory of atoms in molecules (QTAIM). Competition between the N- and N,S-XB interactions was studied, including the recognition of energy differences between the I⋯N and I⋯S contacts. The computational data were useful to rationalize the divergent solid-state N- or S-arylation of thiocyanates.