Browsing by Subject "Metal-organic framework"

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Phosphine- and arsine-containing metal-organic frameworks as solid-state ligands
(2020-05-07) Sikma, Ronald Eric; Humphrey, Simon M.; Krische, Michael J.; Que, Emily; Freeman, Benny D.
Metal-Organic Frameworks (MOFs) are an exciting new class of porous materials that display exceptional structural diversity and broad functional tunability. These materials are of particular interest for gas storage, separations, and catalysis. This work centers on the creation of new MOF materials incorporating P(III) and As(III) Lewis basic sites, known as Phosphine/Arsine Coordination Materials (PCMs/ACMs). These permit the incorporation of secondary 4d/5d metals bound to the soft P(III)/As(III) lone pairs before, during, or after MOF formation. In this sense, PCMs/ACMs can act as solid-state ligands, binding reactive metals in well-defined coordination environments while orienting them periodically throughout a porous crystalline structure. The presence of these secondary metals can drastically enhance the performance of the materials for targeted applications. The first reported triarylarsine-containing MOF, ACM-1, was obtained using a unique arsine linker with phenylpyridyl linkages. ACM-1 was metallated with Au(I) post-synthetically to yield Au-ACM-1, which was characterized by single-crystal X-ray diffraction. The material incorporated Au₂Cl₂ dimers in a sterically constrained cis-As2 pocket, which resulted in an exceptionally short Au···Au aurophilic contact of 2.76 Å. Incorporation of Au(I) allowed the material to function as a heterogeneous catalyst for the hydroalkoxylation of 4-pentyn-1-ol, and also enhanced the solid-state luminescent properties of the material. A broad library of triaryl arsine ligands and new ACMs was achieved, most of which were structurally characterized and evaluated as solid-state ligands. Other materials were obtained with trans-oriented Lewis basic sites. PCM-102 was structurally characterized and found to be a versatile solid-state ligand. Upon addition of low-valent metals, the framework undergoes a distortion to form trans-P₂M complexes (M = Cu(I), Ag(I), Au(I), Rh(I)). Metallation of PCM-102 was found to drastically enhance the gas uptake properties of the resulting materials, and the Ag(I) material was evaluated for the separation of propane and propylene. Additionally, one of the first examples of Lewis acid pillaring was achieved in Ag-PCM-201, in which Ag(I) connects adjacent two-dimensional sheets to form a three-dimensional structure. This was also accomplished using an Os(I) dimer in Os₂-PCM-201, which displayed interesting reactivity and selectivity for adsorption of H₂.
The development of metal-organic frameworks using palladium metal complexes for catalysis and the utilization of a dihaloimidazolidinedione for easy acid chloride generation
(2016-08) Nguyen, An Ngoc-Michael; Humphrey, Simon M.; Jones, Richard A
Part 1. Metal-Organic Frameworks (MOFs) have been extensively studied due to their functional versatility and well-defined, porous structures. It is, however, exceptionally rare to find MOFs that use late transition metal complexes as a building block. Incorporation of these complexes would have immediate applications in catalysis and enhanced gas adsorption/storage. Furthermore, because of the MOF’s well-defined structures, heterogeneous catalysis properties can be more readily studied and improved. Herein, 1,2-bis(bi(para-carboxyl)phenylphosphino)benzene palladium dichlo-ride’s (PdCl2(BBCB)) catalytic ability is studied using the Mizoroki-Heck reaction, and 1,2-bis(bi(4-carboxy-biphenyl-4’-phosphino))ethane palladium dichloride (PdCl2(BBCE-1L)) is used to make a MOF with an enlarged pore size and greater catalytic ability. BBCB, a tetra-para-carboxylic acid derivative of dppb, is used to form a palladium dichloride bis(phosphine) complex. This complex was found to perform a Mizoroki-Heck reaction in decent yields despite formation of palladium black. BBCE-1L, a tetra-4-carboxylic acid biphenyl derivative of dppe, was then developed to deter palladium black formation and enlarge the pore size of the MOF. A MOF was made using a Zn(II) paddlewheel as the metal node and PdCl2(BBCE-1L) as the organic linker. This MOF was found to have moderate thermal stability and potentially high pore volume. Part 2. Acid chloride generation is a widely researched field for the synthesis of amides and esters, motifs found throughout nature and pharmaceuticals. Recently, we found that dihaloimidazolidinediones could substitute a variety of alcohols with halogens through an amide-stabilized carbocation. As an extension of this chemistry, we were able to activate most carboxylic acids into the corresponding acid chloride with near quantitative yields. Mechanistic studies of electronic and steric effects suggest that the rate-determining step is the nucleophilic attack of a free chloride ion on the carbonyl center to produce the corresponding acid chloride. Electronic effects of ring size on electrophilicity was also observed and explained through analysis of a simplified Walsh diagram.