Iodine Molecules within Triethylenediamine-Based Metal–Organic Frameworks for Hydrolysis/Alkylation Tandem Reactions

The
integration of radionuclide iodine molecules in metal–organic
frameworks (MOFs) for organic synthesis is attracting considerable
research attention due to their specific catalytic performance. However,
understanding the comprehensive catalytic behaviors of different types
of molecular iodine encapsulated in MOFs for a sequential organic
transformation is a great challenge. To address this issue, we have
designed two triethylenediamine-functionalized MOFs assembled from
1,3,5-tricarboxyphenyl-2-(triethylenediaminemethyl)benzene-linker
and {Cd(COO)3N} or {Cu4(u3-OH)2(COO)6N} clusters. Both MOFs show
good stability and adsorption of I2 in the solution and
vapor phases. Catalysts obtained after treatment with ethyl acetate
present efficient catalytic activity in hydrolysis/alkylation tandem
reactions in water. The mechanistic investigations disclose a sequential
catalytic process comprising a “hidden” Brønsted
acid catalytic hydrolysis of acetals to aldehydes followed by the
I2-bonding Lewis acid catalytic alkylation of aldehydes
to 3,3′-disubstituted 1H-indoles.