Hiltrud Grondey

Oriented Periodic Mesoporous Organosilica (PMO) Film with Organic Functionality Inside the Channel Walls

The first examples of an oriented periodic mesoporous organosilica (PMO) film, containing a variety of organic groups (ethane, ethene, benzene, thiophene) inside the channel walls, are reported. The mesostructure of the PMO film appears oriented with respect to the surface of the underlying glass substrate. Liquid-crystal topological defects in the precursor gels are replicated in the resulting PMO film and are evident in polarized optical microscopy images, recorded between crossed-polarizers, which show fan-type optical birefringence texture characteristic of the mesostructure.

Sequential Hydroboration–Alcoholysis and Epoxidation–Ring Opening Reactions of Vinyl Groups in Mesoporous Vinylsilica

We report the sequential transformation of vinyl groups into hydroborate and alcohol as well as vinyl into epoxide and diol functional groups in hexagonal mesoporous vinylsilica materials, denoted meso-vinyl-SiO2. The first transformation proceeds quantitatively through the hydroborylated derivative. After appropriate quenching, the hydroborylated materials are stable at ambient conditions and can undergo transformation into alcohols and various other functional groups. The pore volume and pore size uniformity were found not to be greatly affected by quenching of the hydroboranes with methanol, but they were reduced by quenching with water due to the deposition of boron-containing species in the channels. Complete conversion of hydroborylated materials to alcohol-functionalized materials required basic conditions and treatment time of several hours. Although this led to a significant structural shrinkage, decrease in pore volume, and decrease in ordering, there was no evidence of a partial collapse or removal of substantial parts of the pore walls under optimized synthesis conditions. This is the first successful conversion of organic groups of a functionalized ordered mesoporous silica host in alkaline solution, conditions known to be detrimental for silica frameworks. Epoxidation of the vinyl groups and subsequent conversion of the resulting epoxides into diols are also briefly described. The chemical transformation through epoxidation affords ordered mesoporous silica materials functionalized with potentially chiral organic groups, which could find applications in asymmetric catalysis and chiral separations. It was found that the epoxidation was slower than hydroboration and resulted in a lower degree of conversion. These two examples of hydroboration–alcoholysis and epoxidation–ring opening reactions of terminally bonded vinyl groups in meso-vinyl-SiO2 demonstrate the novel concept of sequential organic chemical transformations harbored inside the ordered channels of mesoporous organosilica materials.

Synthesis, structure and polymerization behaviour of borane adducts of a phosphorus-bridged [1]ferrocenophane, [(η-C5H4)2FePPh]

Phosphorus(III)-bridged [1]ferrocenophanes cannot be polymerized via transition-metal catalyzed ring-opening polymerization, presumably due to the phosphorus lone pair ligating the catalyst. We have investigated a potential solution to this problem, which involves protection of the phosphorus lone pair through the formation of borane adducts. The adducts [(η-C5H4)2FeP(Ph)BX3] (2, X=H; 3, X=Cl) were synthesized in high yield from the reactions of appropriate boranes with P-phenylphospha[1]ferrocenophane, 1, and fully characterized by NMR, UV–Vis, MS, elemental analysis, and X-ray crystallography. Ring-opening polymerizations of 2 and 3 have been attempted both thermally and using transition-metal catalysts, resulting in insoluble polymeric products, [(η-C5H4)2FeP(Ph)BX3]n (5, X=H; 6, X=Cl), which have been characterized by solid-state NMR and by pyrolysis-MS. Well-defined borane adducts of poly(ferrocenylphenylphosphine), [(η-C5H4)2FeP(Ph)BX3]n (5b, X=H; 6b, X=Cl) were synthesized and characterized to provide comparative data for the insoluble products 5a, 6a and 6c. The data support the conclusion that both 2 and 3 may be ring-opened thermally to provide polymeric products consistent with the corresponding adducts of poly(ferrocenylphenylphosphine) 4. In contrast, transition-metal catalyzed ROP proceeds inefficiently, leading predominantly to products of unknown structure.

Bio-Inspired Nanocomposites: From Synthesis Toward Potential Applications

In recent years, the extraordinary properties of bio-inspired nanocomposites have stimulated great interest in the development of bottom-up synthetic approaches to organic-inorganic hybrid materials in which molecular scale control is exerted over the interface between the organic and inorganic moieties. These developments have led to advanced materials with novel properties and potential use in catalysis, sensing, separations and environmental remediation. Periodic mesoporous organosilica (PMO) materials are an entirely new class of nanocomposites with molecularly integrated organic/inorganic networks, high surface areas and pore volumes, and well ordered and uniform size pores and channels. We recently have extended the approach to include novel PMO materials incorporating chiral and heteroatom-containing organic functional groups inside the inorganic framework that may be useful in asymmetric catalysis, enantiomeric separations and heavy metal remediation.