<strong>Chapter One</stong> provides an introduction to the chemistry of pentalene and its derivatives encompassing ligand synthesis, organometallic chemistry, and in particular ethylene polymerisation. In the second half, cationic polymerisation is introduced encompassing both main-group and transition-metal initiated polymerisations. The limitations of cationic ethylene polymerisation are highlighted. <strong>Chapter Two</stong> describes the synthesis of a series of related complexes based on the Pn*MCp^R(X) motif for application as ethylene polymerisation catalysts. The products are characterised by NMR spectroscopy, single crystal X-ray diffraction, elemental analysis and, where relevant, EPR spectroscopy. <strong>Chapter Three</stong> details the application of aforementioned Pn*MCp^R(X) complexes as ethylene polymerisation catalysts, tested in solution co-catalysed by methylaluminoxane, and in the slurry phase, immobilised on a variety of inorganic supports. Very high activities are observed for the zirconium congeners of this non-classic polymerisation motif, with the Cp ligand observed to affect activity more dramatically than the "X" ligand. <strong>Chapter Four</stong> gives an account of mechanistic investigations examining the activity of the Pn*MCp^R(X) catalysts. Pre-catalyst activation studies implicate the formation of cationic derivatives, which are rationally synthesised. The unexpected activity of [Pn*ZrCp]⁺ towards ethylene polymerisation is investigated by in-situ gas uptake measurements and small molecule activation studies, which do not readily accommodate a coordination-insertion mechanism. An alternative cationic initiation mechanism is proposed and explored. <strong>Chapter Five</stong> describes the synthesis of titanium and zirconium hydride and deuteride complexes. Using either LiAlH₄/D₄ or H₂/D₂ as the hydrogen source, trimetallic hydride clusters are synthesised. Preliminary investigations into their reactivity with small molecules is presented. <strong>Chapter Six</stong> details the synthesis of reduced permethylpentalene titanium complexes. Chlorine atom abstraction, scrambling of the Pn* ligand, and dinitrogen activation was observed depending on the nature of the reducing agent and the stoichiometry employed. <strong>Chapter Seven</stong> provides experimental details and characterising data for the complexes presented in the preceding five chapters.

The focus of this thesis is the synthesis of organometallic complexes incorporating the η8-permethylpentalene titanium moiety (η⁸-Pn*Ti), their characterisation, and their reactivity with small molecules. <b>Chapter One</b> summarises the chemistry of the pentalene molecule, from its instability in the free state to the incorporation of the hydrocarbon into organometallic complexes. The chapter continues with a review of the coordination modes available to Pn and concludes with a brief discussion on the effects of permethylation of hydrocarbon ligands and the advent of permethylpentalene (Pn*). <b>Chapter Two</b> documents the improved synthesis of [Pn*TiCl(μ-Cl)]₂ utilising isomeric control imparted on the Pn* synthon, Pn*(SnMe₃)₂. This protocol permits access to a variety of methylated compounds through metathesis chemistry, of which five have been crystallographically elucidated, revealing the fold angle to be reliant on an interplay between steric and electronic factors. Mono-, bi- and trimetallic {Pn*TiMe₂, [Pn*TiMe(μ-Cl)]₂ and [Pn*Ti(μ-Me)]₂(μ-CH₂), and [Pn*TiMe(μ-Me)₂]₂Mg respectively} species were synthesised dependent on the methylating agent employed and they displayed varying thermal stabilities, with the dimeric nature of [Pn*TiMe(μ-Cl)]₂ proving crucial in the formation of [Pn*Ti(μ-Cl)]₂(μ-CH₂). <b>Chapter Three</b> describes the incorporation of classical organometallic ligands into the Pn*Ti moiety, including the first examples of benzyl, alkyl, aryl, allyl and η¹-Cp bound to a PnTi fragment. Seven complexes have been structurally characterised including the first ever crystal structure of a π-hydrocarbon bound Ti species bearing two CH₂^tBu groups, Pn*Ti(CH₂^tBu)₂, and the fluxional mixed hapticity complex Pn*Ti(η⁵-Cp)(η¹-Cp), whose η¹-Cp rearranges via a 1,2-sigmatropic shift. <b>Chapter Four</b> investigates the reactivity of the monomeric dialkyls, Pn*TiR₂ (R = Me, CH₂Ph, CH₂SiMe₃ and CH₂^tBu) with CO₂, CO and H₂. All four compounds demonstrate “normal” insertion of the CO₂ moiety into both Ti-R bonds, revealing a symmetrical bidentate coordination of the RCO₂ units. Computational studies have highlighted two competing pathways for their reaction with CO, dependent on the concentration of CO and size of R, which results either in formation of an enediolate or a titanoxirane. The reaction with H₂ yields the fascinating trimeric mixed valence, [Pn*Ti(μ₂-H)]₃(μ₃-H), the first structurally characterised example of a trimeric Ti-H species and the first to include a Ti-(μ₃-H) moiety. (Pn*TiCl)₂(μ-O) is formed by the action of adventitious H₂O and possesses a linear Ti-O-Ti bridge with a degree of Ti-O double bond character, supported by crystallographic data and DFT calculations. <b>Chapter Five</b> discusses ethylene polymerisation studies on the monomeric dialkyl complexes Pn*TiR₂ (R = Me, CH₂Ph, CH₂SiMe₃ and CH₂^tBu) using the activators [Ph₃C][B(C₆F₅)₄], [PhNMe₂H][B(C₆F₅)₄], AlⁱBu₃ and H₂. <b>Chapter Six</b> presents full experimental procedures for all of the syntheses and reactions outlined in Chapters Two to Five. <b>Chapter Seven</b> details characterising data for all novel compounds, and crystallographic data in the form of CIF files may be found in the electronic version.

The purpose of this project has been to expand the η8 binding mode of the permethylpentalene ligand into uranium, zirconium and hafnium chemistry. All three of these elements have shown intriguing, high-hapticity carbocyclic chemistry and, because of their relatively large size, are excellent candidates for the development of organometallic permethylpentalene chemistry. Chapter one of this thesis will review previous work on η n carbocyclic ring chemistry of these elements, where n = 6 - 8. This introduction will include the unsaturated rings systems where all the ,carbons are bonded to the metal centre, specifically η6 arene systems, η 7 cyclohept.atriene systems, and η 8 cyclooctatetraene and pentalene systems. Species of lower hapticity (e .g. the η 6 binding mode of cycloheptatriene) will not be covered but reviews, where available, will be referenced. Chapter two documents the successful synthesis and characterisation of η 8 permethylpentalene uranium (IV) species. Initially, the uranocene equivalent, UPn*2 was synthesised and characterised structurally, magnetically and electrochemically. From here, a half-sandwich synthon [U Pn*CI4][Li(TMEDA)h was synthesised which was used for further salt metathesis chemistry in order to make a number of mixed sandwich complexes. Chapter three is an account of the synthesis and characterisation of zirconium and hafnium η 8 permethylpentalene species. Initial work focused on the synthesis of a suitable synthon analogous to that used for the previously synthesised titanium species. However, this route was unsuccessful and an alternative species was formed, [MPn*(μ-Cl)3/2]2(μCl)2[Li(THF)x(Et2O)y]. This species could be made on a multi-gram scale and proved to be a sui table synthon for further synthesis. Salt metathesis reactions were undertaken and a number of new species were synthesised and characterised including mixed-sandwich, alkyl, aryl and allyl species. Chapter four reports the results of polymerisation testing that was undertaken for selected synthesised compounds. All compounds catalysed the formation of poly(ethylene), with the group 4 mixed sandwich species being particularly active catalysts. Two of the zirconium species, ZrPn*CpCI and ZrPn*Cp2 were therefore used for further optimisation experiments which were somewhat limited due to the high activity of the compounds. These were useful in gaining insight into conditions that should be investigated on a larger reaction scale. Chapter five gives the full experimental details for all the syntheses described in chapters two and three as well as details of instrumentation used for characterisation, and also gives the respective loadings of catalyst and co-catalyst employed in the polymerisation testing reported in chapter four. Chapter six presents the full characterisation data obtained for the compounds synthesised and the electronic appendix attached as a CD at the back of the thesis contains the crystal data .cif files and the DFT output files (.out). ,

Although the chemistry of benzenoid and nonbenzenoid quinones have been the subject of extensive theoretical and experimental studies, the extent of our present understanding regarding the geometries and stabilities of quinones of pentalene is meager. After studying the existence of cyclopentadienone and its reactivity as a diene and dienophile in the literature, the study of some related species, particularly the ones with fully unsaturated pentalenic structures were started. In this thesis, the elusive compound bicyclo[3.3.0]octa-3,5,8-triene-2,7-dione was tried to synthesize by using the synthetic strategy which was developed by us. We used cycloheptatriene as the starting material. The bicyclic endoperoxiedes mixture obtained by the photooxygenation of cycloheptatriene was v treated with triethylamine to give tropone in high yield. Selective reduction of tropone afforded cyclohepta-3,5-dione which was converted by the way of photochemistry to the bicyclo[3.2.0]hept-6-en-3-one. After protection of the carbonyl group, dibromocarbene was added to the double bond to give desired bicyclic compound with pentalene skeleton. Substitution of the allylic bromide with hydroxyl group followed by PCC oxidation resulted in the formation of a diketone. All efforts to convert this diketone into fully conjugated system failed.

ABSTRACT FUNCTIONALIZATION OF SATURATED HYDROCARBONS: HIGH TEMPERATURE BROMINATION G&uuml / nbaS, Duygu Deniz M.S., Department of Chemistry Supervisor: Prof. Dr. Metin Balci June 2006, 174 pages Although saturated hydrocarbons are readily available and extremely cheap starting materials, they can not be used in synthetic chemistry without prior activation. Efficient functionalization of alkanes leading to the production of useful organic chemicals in an industrial scale is of considerable interest for the chemical and pharmaceutical industries and remains a long-term challenge for chemists. In this respect, halogenations of hydrocarbons which leads to a variety of useful synthetic intermediates is an open avenue which deserves special attention. It is also noteworthy to mention that efficient methods for selective functionalization of saturated bicyclic hydrocarbons still remains elusive, albeit a number of methods employing various reagents have been developed for the C&amp / #8211 / H bond activation of open chain and monocyclic alkanes. Herein, we will investigate the high temperature bromination reactions as a method for functionalization of saturated bicyclic hydrocarbons such as octahydropentalene (1), octahydro-1H-indene (2) and 1a,2,7,7a-tetrahydro-1H-cyclopropa[b]naphthalene (3). The scope and the limitations of the reaction will reveal the regio-and stereoselectivity. Furthermore, formation mechanism of the products will be discussed and the chemistry of these compounds will be extended for further functionalization

This thesis expands the scope for using the permethylpentalene ligand and its precursors in the synthesis of organometallic complexes. <strong>Chapter one</strong> begins with a brief review of linked metallocenes, with which multimetallic compounds bridged by pentalene ligands have often been compared, followed by a comprehensive review of the routes used to make pentalenes and substituted pentalenes. Organometallic compounds of pentalenes are introduced, with a focus on bimetallic systems. <strong>Chapter two</strong> explores the diversification of substituents added to the permethylpentalene (Pn*) precursor WeissH₄, to include ethyl and isopropyl groups. Low-symmetry mono-, di-, tri- and tetraalkylated products are formed, eight such organic molecules have been identified by NMR spectroscopy, and two characterised crystallographically. It has been demonstrated that subsequent hydrolysis and decarboxylation of two of these products produces low-symmetry alkylpentalene precursors. The chapter concludes with discussions on the selectivity exhibited in these reactions, and the assignment of stereochemistry. <strong>Chapter three</strong> describes the synthesis of the first homoleptic double metallocene complex of iron. Fe₂Pn*₂ has been characterised by X ray diffraction, and cyclic voltammetry studies demonstrate four accessible oxidation states (-1, 0, +1, +2). Magnetic measurements in the solid and solution state reveal an unusual triplet configuration, and DFT calculations indicate the origin of a high magnetic moment likely resides in unquenched orbital angular momentum contributions from SOMOs which have metal d character. Fe₂Pn*₂ is EPR silent at 5, 40, and 300 K both in solution and the solid state, suggesting a large zero-field splitting parameter. The reaction of the di-iron complex with carbon monoxide, ethylene and H2 is reported; the bimetallic CO adduct, Fe₂(&mu; &eta;⁵,&eta;³ Pn*)(&mu; &eta;⁵,&eta;¹ Pn*)(CO)₂, has been crystallographically characterised, and contains a highly distorted allylic bonding motif, which to the author’s knowledge is believed to be unique among iron complexes. <strong>Chapter four</strong> discusses the interaction of the bidentate Pn* ligand in anti bimetallic fused metallocenes. A new ligand exchange route has been developed to access the complexes (MCp)₂Pn* (M = Co, Ni), and the isostructural complexes (MCp*)₂Pn* have been made for M = Fe, Co, Ni by salt metathesis reactions. All five complexes have been characterised by single crystal X-ray crystallography, and have diamagnetic ground states in solution in common with their Pn bridged analogues. Variable temperature NMR studies reveal a spin-equilibrium between S = 0 and S = 1 in the dinickel complexes. DFT calculations reproduce the spin states found, and suggest the distortion towards &eta;³ coordination observed on crossing from Fe, to Co, to Ni, results from population of orbitals with M―bridgehead antibonding character. The electronic structures show it is important to draw comparisons between isoelectronic linked metallocenes. Electrochemical studies on the diiron, dicobalt, and (NiCp)₂Pn* complexes reveal at least three redox events for each. <strong>Chapter five</strong> documents the successful synthesis and characterisation of monometallic complexes of iron and manganese with Pn*H ligands. The isostructural complexes Fe(Pn*H)₂ and Mn(Pn*H)₂ can have been characterised crystallographically, and are potential precursors for accessing heterometallic, and multimetallic complexes. Mn(Pn*H)₂ is a rare example of a manganese sandwich compound and magnetic studies on a single isomer in the solution and solid states suggest it adopts intermediate spin states of S = 2 in solution, and S = 3/2 in the solid state. <strong>Chapter six</strong> gives experimental details for all syntheses and studies described in the preceding chapters. <strong>Chapter seven</strong> provides characterising data for all new compounds. Fitting data for VT NMR and SQUID studies are provided in the <strong>appendix</strong> at the end of this thesis. Crystallographic data in the form of .cif files, DFT output files, and raw SQUID data, can be found in the <strong>electronic appendix</strong>.