NMR investigation of substituent effects on strength of π-π stacking and hydrogen bonding interactions to supports the formation of [2+2] photodimerization in (para-X-ba):::(bpe)∥(bpe):::(para-X-ba) complexes

We have investigated the ability of para-X-phenylboronic acid (para-X-ba) to enable reactivity of trans-1,2-bis(4-pyridyl)ethylene (bpe) to direct intermolecular [2 + 2] photodimerization via computational chemistry. Para-X-ba would support the formation of discrete four component hydrogen bonded molecular assemblies wherein pi-pi stacking of a pyridyl-functionalized alkene would conform to undergo [2 + 2] photodimerization. We have demonstrated by computational H-1 NMR data the effect of electron-withdrawing and donating substituents in (para-X-ba):::(bpe)parallel to(bpe):::(para-X-ba) complexes to assemble bpe into pi-pi stacking via -(B)O - H center dot center dot center dot N-hydrogen bonds to react to afford (para-X-ba):::tpcb:::(para-X-ba) complexes (X= NO2, CN, F, Cl, Br, C(O)CH3, OCH3, OH, NH2 and H where parallel to and center dot center dot center dot denote pi-pi stacking and hydrogen bonds). Also, these interactions have been investigated at M05-2X/6-311++G** level of theory in detail in terms of the energetic, geometrical parameters and electron density properties to characterize and to examine the strengthening of the interactions. There are good relationships between the NMR, AIM, energy data and Hammett constants. (C) 2020 The Author(s). Published by Elsevier B.V. on behalf of King Saud University.