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No description available.

Selective hydrogenation of acetylene in excess ethylene, which will selectively remove acetylene from ethylene, is of paramount significance in the petrochemical and polymer industries. The key issues in this process are activity, selectivity and green oil formation. In this thesis, first-principles calcu lations within the density functional theory (OFT) framework together with experimental methods are introduced to study this important process. The selective hydrogenation of acetylene to ethylene on several Pd surfaces and Pd surfaces with subsurface species as well as a number of Pd based alloys are investigated using OFT calculations to understand the acetylene hydrogenation activity, the selectivity of ethylene formation and the formation of butadiene, considered to be the precursor of green oil formation . The general trend of the activity, selectivity and butadiene formation over these catalysts are obtained and discussed . In order to understand the recently reported experimental results showing the promotion effects of Au on Ni and B on Pd, these systems are studied, and the activity and selectivity of acetylene hydrogenation and the 1,3 -butadiene formation over these surfaces are obtained and compared. Experimentally, the selective hydrogenation of acetylene is tested with Pd/Ah03, PdAglAl20 3 and Li2COr Pd/Ab03 catalysts under tail-end (TE) conditions, The performance of these catalysts are introduced and compared. Using several characterization techniques, the origin of the performance of these catalysts is understood. The development of the two-step model to determine the general adsorption energy window based on an understanding of the rate determining steps of reactant adsorption and desorption only, i.e. the Sabatier principle will also be presented in this thesis. Our work shows that the combination of OFT calculations and experimental methods is powerful to investigate chemical reactions occurring on surfaces, which are important in the area of heterogeneous catalysis

This thesis describes the synthesis and properties of systems of the general type ML(_x)-bridge- ML(_x), and related 'mixed-valence' derivatives. The efficacy of the l.l'-ferrocenediyl unit (Fc') as a bridge between two redox-active metal centres, is investigated by examination of the properties of a series of complexes, 1,1'-{Cp'(PP)RuC=C}(_2)Fc’, and the related binuclear model systems Ru(C=CFc)(PP)Cp'. Whilst interactions through an ethyndiyl bridge occur between one Ru(PP)Cp' moiety and a ferrocenyl centre, in the l,l'-{Cp'(PP)RuC=C}(_2)Fc' systems no interaction between the terminal Ru(PP)Cp' groups is observed. A comparative study of the redox and spectroscopic properties of the family of complexes [{Ru}(_2)(u-C≡CXC≡C)](^n+) [{Ru} = Ru(PPh(_3))(_2) Cp, Ru(dppe)Cp*; X = 1,4- C(_6)H(_4), l,4-C(_10)H(_6), 9,10-C(_14)H(_8); n = 0, 1, 2] is presented, together with those of the related mononuclear compounds. Comparison of the results with DFT calculations of the electronic structure allows the properties of the diethynylaryl-bridged, bimetallic complexes to be rationalised in terms of a significant contribution of the diethynylaryl bridging ligand to the SOMO. The electronic properties of the 1,12-diethynyl carborane-bridged species 1,12- {Ru(dppe)Cp*}(_2)(u-C≡C-CB(_10)H(_10)C-C≡C), and the related mononuclear complex Ru(C≡C-CB(_10)H(_10)H)(dppe)Cp*, are assessed by a combination of electrochemical and spectroscopic techniques. The results allow a comparison of the 'three-dimensional' aromatic spacer l,12-C(_2)BH(_10) with the phenylene analogue. Explorations of the acetylide chemistry of the Fe(dppe)’_n’ fragment are described. The resulting air stable complexes provide a convenient entry point to the acetylide chemistry of the octahedral iron fragment. The details of additional crystal structures obtained by single crystal X-ray diffraction methods, together with a brief description of the chemistry associated with them, are presented in the appendix.

This thesis describes the use of heterobimetallic alkyne complexes in asymmetric organic synthetic pathways. Unlike previous protocols in the literature, the source of chiral control is due to the inherent chirality of the heterobimetallic core and not from an external source. A new method for the preparation of Co(CO)3MoCp(CO)2-alkyne complexes has been addressed with a view to a more rapid and cleaner preparation of these complexes, adapting previously known literature methodology. Preparation of diastereomerically-enriched alcohol complexes has also been attempted.

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Αντικείμενο της παρούσης διδακτορικής διατριβής αποτελεί ο υπολογισμός των ηλεκτρικών πολυπολικών ροπών (διπολική έως και δεκαεξαπολική) ακετυλενικών αλυσίδων οι οποίες υπάγονται στους γενικούς τύπους H-(C≡C)n-H, Χ-(C≡C)n-H και Χ-(C≡C)n-X, n=1–7, X=F, Cl, Br, I, CN, NC, η συστηματική μελέτη των (υπερ)πολωσιμοτήτων των μη υποκατεστημένων ακετυλενικών αλυσίδων Η-(C≡C)n- H, n=3–7 και τέλος ο υπολογισμός των ηλεκτρικών ιδιοτήτων αλληλεπίδρασης συστημάτων του τύπου Η-(C≡C)n-H…Ηe, n=1–7. Σε όλες τις περιπτώσεις χρησιμοποιήθηκαν οι ab initio μέθοδοι SCF και MP2 καθώς και οι ευρέως χρησιμοποιούμενες DFT μέθοδοι B3LYP, B3PW91 και mPW1PW91. Στους υπολογισμούς των ηλεκτρικών πολυπολικών ροπών χρησιμοποιήθηκε η βάση ccpVDZ σε όλες τις περιπτώσεις και ιδιαίτερη έμφαση δόθηκε στον τρόπο μεταβολής των υπό μελέτη ιδιοτήτων με την μεταβολή του υποκαταστάτη στα άκρα της αλυσίδας. Στους υπολογισμούς των ηλεκτρικών (υπερ)πολωσιμοτήτων των μη υποκατεστημένων ακετυλενικών αλυσίδων Η-(C≡C)n-H χρησιμοποιήθηκαν ελάχιστα πολωμένα σύνολα βάσης και πραγματοποιήθηκε σύγκριση με τα αποτελέσματα που προέκυψαν από την χρήση μεγαλύτερων συνόλων βάσης. Για τον υπολογισμό των εν λόγω ιδιοτήτων χρησιμοποιήθηκε η μέθοδος του πεπερασμένου πεδίου. Τέλος πραγματοποιήθηκαν υπολογισμοί των ηλεκτρικών ιδιοτήτων αλληλεπίδρασης συστημάτων Η-(C≡C)n-H…Ηe για δυο συγκεκριμένες διαμορφώσεις ενώ για την αποφυγή του σφάλματος υπέρθεσης συνόλου βάσης χρησιμοποιήθηκε η υπερμοριακή προσέγγιση των Boys-Bernardi. / The purpose of the present doctoral dissertation is the calculation of the electric multipole moments (dipole up to hexadecapole) of acetylenic chains under the general formulas H-(C≡C)n-H, Χ-(C≡C)n-H and Χ-(C≡C)n-X, n=1–7, X=F, Cl, Br, I, CN, NC, the systematic study of the (hyper)polarizabilities of the non substituted acetylenic chains Η-(C≡C)n-H, n=3–7 and finally the calculation of interaction induced electric properties of systems of the general formula Η-(C≡C)n-H…Ηe, n=1– 7. In all cases considered the ab initio SCF and MP2 methods have been used along with the very popular DFT methods B3LYP, B3PW91 and mPW1PW91. For the electric multipole moment calculations the cc-pVDZ basis set has been used in all cases and special attention has been paid in the way the properties of interest change by changing the substituent at the ends of the acetylenic chains. For the electric (hyper)polarizability calculations on the non substituted acetylenic chains H-(C≡C)n- H minimally polarized basis sets have been used and comparison was made with the results obtained by using larger basis sets. In order to calculate the above mentioned properties the finite field method was applied. Finally, calculations were performed in order to calculate the interaction induced electric properties of the systems Η-(C≡C)n- H…Ηe for two particular configurations while in order to avoid the basis set superposition error the Boys-Bernardi counterpoise method has been applied.