Coupling Postsynthetic High-Temperature Oxidative Thermolysis and Thermal Rearrangements in Isoreticular Zinc MOFs

Herein, we report coupling in situ high temperature
postsynthetic modifications (PSMs) in metal–organic frameworks
(MOFs). Thermo-reactive propargyloxy-functionalized zinc IRMOFs (isoreticular
metal–organic frameworks) prepared from 2-(prop-2-yn-1-yloxy)-[1,1′-biphenyl]-4,4′-dicarboxylic
acid (H2bpdcOCH2CCH) were investigated for their
high-temperature postsynthetic rearrangement (PSR) chemistry to heterocyclic
chromenes and benzofurans and then coupled to solid–gas reactions
with molecular oxygen. The selectivity for the initial molecular rearrangements
was found to be inverted in the porous MOF environment compared to
conventional melt reactions of the ester compound Me2bpdcOCH2CCH and proceeded far more easily than the solid-state transformation
from H2bpdcOCH2CCH, showing the potential of
MOFs to give rise to different chemistry. The major oxidative process
was thermolysis of the chromene ring with a minor pathway of allylic-type
oxidation to give heterocyclic chromenone functionality. The sequence
was also successful on a series of two-component multivariate IRMOF
frameworks prepared from thermo-reactive H2bpdcOCH2CCH and thermo-resistant H2bpdcOMe linkers, demonstrating
that these reactions can be used with known crystal engineering strategies.
All transformations were fully compatible with the requirements to
maintain MOF crystallinity and porosity as evidenced by surface area
analysis and X-ray powder diffraction measurements. This work contributes
to establishing the feasibility of high-temperature solid–gas
manifolds for MOF PSM.