Browsing by Author "Komath Mallissery, Samith"

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Open Access
Synthesis and immobilisation of unsaturated, functional phosphorus ligands and their metal complexes
(2009) Komath Mallissery, Samith; Gudat, Dietrich (Prof. Dr.)
The present study aimed (i) to immobilise palladium catechol phosphines on TiO2 and study the immobilised and remobilised species in various solvents by HR MAS NMR, (ii) to synthesise novel functionalized phosphinines and their complexes capable to anchor on a solid carrier, and to immobilise them on inorganic supports, (iii) to develop some novel gold(I) phosphinine complexes and phosphinine stabilized gold nanoparticles, and study the mode of ligand coordination on the gold surface by 31P CP MAS NMR spectroscopy, (iv) to develop and anchor suitable functional derivatives of monophosphaferrocenes onto inorganic surface by covalent tethering method and study the anchoring process by CP MAS NMR spectroscopy. For the first topic, two isomeric forms of palladium catechol phosphines were initially tested for immobilisation on different specimens of TiO2, neutral TiO2 and slightly acidic TiO2 nanoparticles. Successful deposition of the complexes on both materials was monitored by 31P CP MAS NMR. The study of both dry specimens and suspensions by 31P HR MAS NMR experiments with and without cross polarization and magic angle spinning in combination cleared that the complexes immobilised on neutral TiO2 redissolved in polar solvents, and that the mobility of those species was greatly effected by the ligand structure. The studies showed that immobilised complexes on slightly acidic TiO2 nanoparticles are definitely more tightly bound and gave no evidence for either the occurrence of leaching or of any base induced reaction. However, eventhough the deposition of complexes on neutral titania is feasible they can be easily eluted by polar solvents. The use of the immobilised complex as catalyst in a carbon - carbon cross coupling reaction was also demonstrated in this context. The successful deposition of phosphine complexes on TiO2 motivated to develop complexes of phosphinines having similar functionality on the aromatic moiety that could serve as a suitable candidate for the immobilisation on TiO2. In this regard, two isomeric forms of novel phosphinines bearing OH- functionalities in the vicinal positions of the aromatic moiety were developed from the corresponding pyrylium salt. These species then served as ligands for the development of gold(I) complexes. The behavior of so formed gold(I) phosphinine upon attempts towards their immobilisation on TiO2 surface was monitored by 31P CP MAS NMR. Spectral studies revealed that the ligands were successfully deposited on TiO2 surfaces, but modified structurally during the immobilisation process. The choice of silica as a solid carrier was also investigated; a functionalized phosphinine was synthesised and anchored onto a silica surface. The characterization of the supported material by 31P MAS NMR revealed that nearly 25% of the ligand has retained its identity on the carrier, but that the immobilisation was also accompanied by the formation of decomposition products on the surface. Au NPs of phosphinines with different gold - phosphorus ratios were prepared according to a previously reported procedure and charaterized by 31P CP MAS NMR spectroscopy. The comparison of the spectral data with those of authentic Au-phosphinine complexes and also with XPS measurements suggested that gold nanoparticles appeared to be in the form of cationic clusters with the Cl- as the counter ion and contained terminal P coordinated phosphinine ligands bound to Au(I) centres, together with decomposition products. A monophosphaferrocene was prepared and attempted to immobilise via covalent tethering onto amino functionalized HMS materials by Schiff condensation. However, spectral analysis of the immobilised material has not given an adequate information to eluicdate the structure of the immobilised species. Thus the immobilisation of monophosphaferrocene by reductive amination was carried out and, the anchored material so obtained was studied and compared with the relative soluble compounds by NMR methods. The solid state NMR studies revealed that monophosphaferrocene which was immobilised onto the silica surface exists in two diastereomeric forms. Further the anchoring process of monophosphaferrocene onto capped amino functionalized HMS was also investigated by solid state NMR methods and showed that here also anchored monophosphaferrocene exists in two diastereomeric forms but the capping was not persistant in the immobilised material.