MOF‐Stabilized Perfluorinated Palladium Cages Catalyze the Additive‐Free Aerobic Oxidation of Aliphatic Alcohols to Acids

Abstract

Extremely high electrophilic metal complexes, composed by a metal cation and very electron poor σ‐donor ancillary ligands, are expected to be privileged catalysts for oxidation reactions in organic chemistry. However, their low lifetime prevents any use in catalysis. Here we show the synthesis of fluorinated pyridine‐Pd2+ coordinate cages within the channels of an anionic tridimensional metal‐organic framework (MOF), and their use as efficient metal catalysts for the aerobic oxidation of aliphatic alcohols to carboxylic acids without any additive. Mechanistic studies strongly support that the MOF‐stabilized coordination cage with perfluorinated ligands unleashes the full electrophilic potential of Pd2+ to dehydrogenate primary alcohols, without any base, and also to activate O2 for the radical oxidation to the aldehyde intermediate. This study opens the door to design catalytic perfluorinated complexes for challenging organic transformations, where an extremely high electrophilic metal site is required.

Metal–organic frameworks as chemical nanoreactors for the preparation of catalytically active metal compounds

“…In particular, the fully fluorinated ligand, bis(2,3,5,6-tetrafluoro-pyridin-4-yl)acetylene (L 3 ), allows us to synthesise and precisely characterise by SCXRD a Pd II 6 square metal–organic polygon, which shows efficient catalytic behaviour in the aerobic oxidation of aliphatic alcohols to carboxylic acids without any additive. 114 This work nicely illustrated the dual role of MOFs as chemical nanoreactors, enabling the formation of SCCs, that in the homogenous phase could not be assembled due to the poor Sigma-donor ability of L 3 , and transferring the stability from the MOF to the assembled SCC, through weak supramolecular interactions, which make possible to fully take advantage of the electrophilic potential of palladium cations constituting the SCC.…”

Combinatorial Coordination Self‐Assembly for Organopalladium Cages with Fine‐Tuned Structure and Function

“…Due to the divergent feature of L 22 , reaction of it with Pd II gave polymeric products, as suggested by the extremely broadened NMR spectra. In their early report, combination of banana-shaped bidentate L 14 , L 21 with Pd II ions formed a heteropletic cis-[Pd 2 (L 14 ) 2 (L 21 ) 2 ] cage. [82] Given that L 22 and L 23 composed of a pair of L 14 covalently linked by flexible or rigid units, respectively, and the assembly of L 22 with L 21 or L 23 with L 21 was tested.…”

“…[82] Given that L 22 and L 23 composed of a pair of L 14 covalently linked by flexible or rigid units, respectively, and the assembly of L 22 with L 21 or L 23 with L 21 was tested. The results indicated that mixed-ligand assembly of L 22 and L 21 in CD 3 CN led to a heteroleptic twocavities [Pd 4 (L 21 ) 4 (L 22 ) 2 ] cage. In DMSO-d 6 , the same components afforded a [Pd 3 (L 21 ) 4 L 22 ] pseudo-tetrahedron.…”

“…In DMSO-d 6 , the same components afforded a [Pd 3 (L 21 ) 4 L 22 ] pseudo-tetrahedron. Interestingly, treating L 21 , L 23 with Pd II ions in 2 : 1 : 2 ratio yielded a heteroleptic tetranuclear [Pd 4 (L 21 ) 4 (L 23 ) 2 ] cage, which can convert into a heteroleptic barrel-shaped [Pd 6 (L 21 ) 6 (L 23 ) 3 ] cage by 2,7-napthalene disulfonate guest. Unfortunately, the authors have not discussed the scenario for the last remaining binary ligand combination self-assembly with L 22 and L 23 .…”

“…Impressively, the dissymmetry factor j g lum j of the host-guest complex was four times larger than that of the empty Pd 2 (L 11 ) 2 (L 12M/P ) 2 hosts. The authors inferred that guest encapsulation induced enhancement of structural rigidity may be respon- 21 , L 22 and L 23 with Pd II ions. [86] sible for the larger j g lum j value of host-guest complex.…”