Electronic structure of transition metal ions and clusters

This thesis uses density functional theory (DFT) to explore the electronic structure and reaction mechanisms of open-shell transition metal ions and clusters. The early part of the thesis (Chapters 2 and 3) is devoted to high-valent metal-oxo species, both mono- and bimetallic, while Chapter 4 describes some aspects of copper-catalysed carbon-carbon bond formation. Finally, Chapter 5 highlights the role of DFT in computing magnetic and spectroscopic properties of exchange-coupled iron clusters. Whilst the chemistry contained in the thesis is rather diverse, the underlying theme of open-shell transition metal ions is common to all chapters. Moreover, we are primarily concerned with the ways in which interactions between two or more adjacent open-shells (either two metals or a metal and a ligand radical) control structure and reactivity. After a brief introduction to relevant theoretical aspects in Chapter 1, we use Chapter 2 to establish a link between the electronic structure of the high-valent Mn(V)=O porphyrin monomer species and their ability to perform oxidation reactions. The reaction profiles for oxidation of a range of substrates depend critically on the electronic structure of the isolated oxidant. Where the electronic ground state is genuinely best described as Mn(V)=O, the interaction between oxidant and substrate is repulsive at large separations, only becoming attractive when the incoming nucleophile approaches close enough to drive an electron out of oxide p manifold. In contrast, where the ground state is better described as an oxyl radical form, Mn(IV)-O.+, the oxidation occurs in sequential one-electron steps, the first of which is barrierless. In Chapter 3, we extend these ideas to bimetallic systems, where the presence of two high-valent manganese centres allows the system to oxidise water. Specifically, we focus on two model systems which have been shown to oxidise water, a Mn-porphyrin-based system synthesised by Naruta and a Mn-based system reported by McKenzie where the ligands contain a mixture of pyridine and carboxylate donors. In both cases, we again find that the emergence of oxyl radical character is the key to the reaction chemistry. However, the radical character is ‘masked’ in the electronic ground states, either by transfer of an electron from the porphyrin ring (Naruta) or by formation of a di-μ-oxo bridge (McKenzie system). In Chapter 4 we turn our attention to copper chemistry, and the role of copper complexes in catalysing atom transfer radical additions (Kharasch additions). In this reaction, the copper cycles between Cu(I) and Cu(II) oxidation states, and the result is the formation of a new C-C bonds. This Chapter makes extensive use of hybrid QM/MM techniques to model the environment of the copper centre in the target polypyrazolylborate-copper complexes (TpxCu). Finally, in Chapter 5 we consider the electronic structure, magnetic and spectroscopic properties of a pair of exchange-coupled Fe3 clusters, [Fe3(μ3-O)(μ-4-O2N-pz)6X3]2- (where pz = pyrazolato, X = Cl, Br). Our primary goal was to establish how well broken-symmetry DFT is able to reproduce the observed Mössbauer spectroscopic parameters, which are extensively used to identify the chemical environments of iron species and, in the case of mixed-valence clusters, to establish the degree of delocalisation of the additional electrons. In recent years DFT has proved able to compute these parameters with encouraging accuracy, but it is not clear to what extent the known deficiencies in broken-symmetry wavefunctions will compromise this ability. Our work suggests that neither the isomer shift nor the quadrupole splitting are strongly influenced by the nature of the coupling between the metal ions, suggesting that broken-symmetry solutions can be used as a basis for computing these parameters in more complex clusters

Calculation on the mechanism of proton reduction catalyzed by cubic [Mo₃S₄Pd] clusters

令和5年度 京都大学化学研究所 スーパーコンピュータシステム 利用報告

Determining optimal flight paths for cellular network connectivity for the transmission of real-time physiological data in support of big data analytics during airborne critical care transport

This thesis presents a methodology for determining the optimal flight paths between two geographical points based on distance and cellular reception over the path. This methodology consists of two main concepts: coverage map generation, and path planning. Coverage map generation creates a grid map of the total planning space that contains coverage information for each grid point. Coverage is calculated based on geographical and technical information regarding each cell tower in the planning area. The planning step utilises the coverage map to plan a route based on minimum distance and maximum coverage, which is then smoothed into a feasible route for an aircraft to follow. This methodology is demonstrated in an airborne critical care transport within the Province of Ontario in Canada context. Leveraging available cellular information, this methodology is used to determine optimal paths between various care centres or their closest airport. Evaluation reveals that optimal routes can be found through this methodology

N₂-Reduction catalyzed by Biomimetic [Mo₃S₄Fe] Clusters: A Computational Study

令和3年度 京都大学化学研究所 スーパーコンピュータシステム 利用報告

Mechanistic and computational studies of the atom transfer radical addition of CCI(4) to styrene catalyzed by copper homoscorpionate complexes

Experimental as well as theoretical studies have been carried out with the aim of elucidating the mechanism of the atom transfer radical addition (ATRA) of styrene and carbon tetrachloride with a TpxCu(NCMe) complex as the catalyst precursor (Tpx = hydrotrispyrazolyl−borate ligand). The studies shown herein demonstrate the effect of different variables in the kinetic behavior. A mechanistic proposal consistent with theoretical and experimental data is presented.We thank the MICINN (Grants CTQ2008-00042BQU, CTQ2008-06866-CO2-02/BQU, and Consolider Ingenio 2010 CSD2006-0003) and the Junta de Andalucía (Proyecto P07-FQM-02794) for financial support.Peer Reviewe

Chemo-, Regio-, and Stereoselective Silver-Catalyzed Aziridination of Dienes: Scope, Mechanistic Studies, and Ring-Opening Reactions

Silver complexes bearing trispyrazolylborate ligands (Tpx) catalyze the aziridination of 2,4-diene-1-ols in a chemo-, regio-, and stereoselective manner to give vinylaziridines in high yields by means of the metal-mediated transfer of NTs (Ts = p-toluensulfonyl) units from PhI=NTs. The preferential aziridination occurs at the double bond neighboring to the hydroxyl end in ca. 9:1 ratios that assessed a very high degree of regioselectivity. The reaction with the silver-based catalysts proceeds in a stereospecific manner, i.e., the initial configuration of the C=C bond is maintained in the aziridine product (cis or trans). The degree of regioselectivity was explained with the aid of DFT studies, where the directing effect of the OH group of 2,4-diene-1-ols plays a key role. Effective strategies for ring-opening of the new aziridines, deprotection of the Ts group, and subsequent formation of ¿-amino alcohols have also been developed