Sustainable Catalysis : Rational Pd Loading on MIL-101Cr-NH2 for More Efficient and Recyclable Suzuki-Miyaura Reactions

Palladium nanoparticles have been immobilized into an amino-functionalized metal-organic framework (MOF), MIL-101Cr-NH2, to form Pd@MIL-101Cr-NH2. Four materials with different loadings of palladium have been prepared (denoted as 4-, 8-, 12-, and 16wt%Pd@MIL-101Cr-NH2). The effects of catalyst loading and the size and distribution of the Pd nanoparticles on the catalytic performance have been studied. The catalysts were characterized by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared (FTIR) spectroscopy, powder X-ray diffraction (PXRD), N-2-sorption isotherms, elemental analysis, and thermogravimetric analysis (TGA). To better characterize the palladium nanoparticles and their distribution in MIL-101Cr-NH2, electron tomography was employed to reconstruct the 3D volume of 8wt%Pd@MIL-101Cr-NH2 particles. The pair distribution functions (PDFs) of the samples were extracted from total scattering experiments using high-energy X-rays (60keV). The catalytic activity of the four MOF materials with different loadings of palladium nanoparticles was studied in the Suzuki-Miyaura cross-coupling reaction. The best catalytic performance was obtained with the MOF that contained 8wt% palladium nanoparticles. The metallic palladium nanoparticles were homogeneously distributed, with an average size of 2.6nm. Excellent yields were obtained for a wide scope of substrates under remarkably mild conditions (water, aerobic conditions, room temperature, catalyst loading as low as 0.15mol%). The material can be recycled at least 10times without alteration of its catalytic properties.

Studies on Transformations of H-Phosphonates into DNA Analogues Containing P-S or P-C Bonds

In this thesis, mechanistic and synthetic studies on transformations of H-phosphonates into DNA analogues containing P-S or P-C bonds are described. Configurational stability of dinucleoside H-phosphonates and the stereochemical course of their sulfurisation in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) were investigated. In light of these studies, the reported stereoselective sulfurisation of dinucleoside H-phosphonates and benzoylphosphonates in the presence of DBU was proved to be incorrect. Efficient protocols for the synthesis of new nucleotide analogues with non-ionic C-phosphonate internucleotide linkages were developed. The synthesis of dinucleoside 2-pyridylphosphonates was successfully performed by a DBU-promoted reaction of H-phosphonate diesters with N-methoxypyridinium salts. The thio analogues, 2-pyridyl- and 4-pyridyl phosphonothioate diesters, could be obtained by modifying the reactions developed for their oxo counterparts. Dinucleoside 3-pyridylphosphonates were prepared via a palladium(0)-catalysed cross coupling strategy that could be extended also to the synthesis of nucleotide analogues with metal-complexing properties, i.e. terpyridyl- and bipyridylphosphonate derivatives. Oligonucleotides modified with pyridylphosphonate internucleotide linkages have been prepared and preliminary studies on their hybridisation properties and resistance towards enzymatic degradation were performed. Finally, nucleotidic units for the incorporation of pyridylphosphonate groups at the 5’-terminus of oligonucleotides were designed. Condensations of such units with a suitably protected nucleoside afforded after oxidation the expected dinucleoside (3’-5’)-phosphates with pyridylphosphonate monoester functions at the 5’-ends.

Catalytic reactions with palladium supported on mesocellular foam : Applications in hydrogenation, isomerization, and C-C bond forming reactions

The major part of this thesis concerns the development of catalytic methodologies based on palladium nanoparticles immobilized on aminopropyl-functionalized siliceous mesocellular foam (Pd0-AmP-MCF). The catalytic activity of the precursor to the nanocatalyst, PdII-AmP-MCF is also covered by this work. In the first part the application of Pd0-AmP-MCF in Suzuki-Miyaura cross-coupling reactions and transfer hydrogenation of alkenes under microwave irradiation is described. Excellent reactivity was observed and a broad range of substrates were tolerated for both transformations. The Pd0-AmP-MCF exhibited high recyclability as well as low metal leaching in both cases. The aim of the second part was to evaluate the catalytic efficiency of the closely related PdII-AmP-MCF for cycloisomerization of various acetylenic acids. The catalyst was able to promote formation of lactones under mild conditions using catalyst loadings of 0.3 - 0.5 mol% at temperatures of up to 50 oC in the presence of Et3N. By adding 1,4-benzoquinone to the reaction, the catalyst could be recycled four times without any observable decrease in the activity. The selective arylation of indoles at the C-2 position using Pd-AmP-MCF and symmetric diaryliodonium salts is presented in the third part. These studies revealed that Pd0-AmP-MCF was more effective than PdII-AmP-MCF for this transformation. Variously substituted indoles as well as diaryliodonium salts were tolerated, giving arylated indoles in high yields within 15 h at 20 - 50 oC in H2O. Only very small amounts of Pd leaching were observed and in this case the catalyst exhibited moderate recyclability. The final part of the thesis describes the selective hydrogenation of the C=C in different α,β-unsaturated systems. The double bond was efficiently hydrogenated in high yields both under batch and continuous-flow conditions. High recyclability and low metal leaching were observed in both cases.