No description available.

Activated cyclopropanes have been extensively used in synthetic chemistry as precursors for cycloaddition reactions. The rationale behind this is their ability to undergo ring-opening when activated by a Lewis acid, this can be enhanced further by the presence of a carbocation stabilising group like electron-rich aromatics. The stabilised dipole formed after ring opening can be trapped with suitable electrophiles such as imines and aldehydes via a [3+2] cycloaddition reaction. This results in the synthesis of pyrrolidines and tetrahydrofurans in excellent yields but moderate diastereoselectivity. Similarly, 6-membered heterocycles can be formed via a [3+3] cycloaddition reaction of activated cyclopropanes with nitrones. Now to extend the scope of the methodology, a [3+3] dipolar cycloaddition has been developed using activated 2,3 disubstituted cyclopropane diesters to access a range of highly functionalised oxazines in moderate to good yields (50-75%) and with reasonable diastereoselectivity. The use of activated symmetrical disubstituted cyclopropanes afforded the desired oxazines in a regio- and diastereocontrolled manner, while the use of unsymmetrical cyclopropanes significantly reduced the diastereoselectivity of the reaction. The stereochemistry outcome of the reaction developed was determined by nOe analyses and X-ray diffraction structures could be recorded in some examples. A new methodology has also been developed to gain access to novel N-heterocyclic- and phenol- substituted cyclopropanes in one step from the corresponding cyclopropene via a conjugated addition.

This Thesis describes the synthesis and characterisation of new Group 2 tetrahydroborate, alkoxide and organohydroborate complexes and their uses as catalysts for the living ROP and immortal ring-opening polymerisation (iROP) of &epsilon;- caprolactone and rac-lactide. <strong>Chapter One</strong> introduces cyclic esters and possible mechanistic pathways leading to polyesters by ROP. Living and immortal ROP, including their kinetic characteristics are discussed. An overview of ROP from an industrial perspective is also given. <strong>Chapter Two</strong> describes the synthesis and characterisation of a new series of Group 2 tetrahydroborate complexes supported by a 3-methyl, 5-tert-butyl tris(pyrazolyl)hydroborate ligand. Their activities towards the ROP of &epsilon;-caprolactone are presented. Detailed mechanistic studies using spectroscopic techniques are discussed and a new mechanism is proposed. <strong>Chapter Three</strong> describes the ROP of rac-lactide using the Group 2 tetrahydroborate complexes introduced in Chapter Two, including their mechanistic studies. <strong>Chapter Four</strong> introduces the new immortal ROP using trialkyl borate and organoborane derivatives as chain-transfer agents (CTAs). The immortal ROP of &epsilon;- caprolactone and rac-lactide using Group 2 initiators with trialkyl borates/organoboranes as CTAs from either in situ generation or external addition is discussed. Possible immortal ROP pathways using this new class of CTAs are illustrated. <strong>Chapter Five</strong> details the synthesis and characterisation of a new series of Group 2 organohydroborate complexes. The &epsilon;-caprolactone and rac-lactide ROP activity shown by the complexes presented is discussed and compared with those obtained from the corresponding tetrahydroborate analogues. <strong>Chapter Six</strong> contains experimental details and characterising data for the new complexes reported in this Thesis. <strong>CD Appendix</strong> contains .CIF files for all the new crystallographically-characterised complexes.

Aluminium salen and aluminium salan complexes are excellent catalysts for the ring-opening polymerisation of lactide. This thesis studied their efficacy in the polymerisation of novel monomers and their ability to build new macrostructures. Aluminium salen and aluminium salan complexes were tested as catalysts for ring-opening polymerisation of common aliphatic monomers where controlled polymer synthesis has not yet been achieved with similar systems. Excellent control over molecular weight and dispersity was achieved for β-caprolactone polymerisation, with high molecular weights accessible. Immortal polymerisation could also be performed with an extremely high level of chain transfer agent (up to 100 equivalents) and the highest monomer turnover (10000 monomer equivalents) with aluminium salen catalysts to date. Addition of functional groups to the monomer was also studied; the effect of steric bulk in polymerisation of methylsubstituted derivatives was significant. Protected alcohol functionalities can also be introduced into easily synthesised homopolymers and copolymers. The first example of synthesising a polyester with aromatic functionality within the polymer backbone via polymerisation of cyclic ester monomers was studied with an aluminium salen catalyst. 2,3-Dihydro-5H-1,4-benzodioxepin-5-one polymerisation was facile and proceeded under mild conditions. The resulting polymer could be depolymerised back to starting monomer with the same aluminium salen catalyst under dilute conditions. Random, AB diblock and ABA triblock copolymers were readily synthesised with L-lactide and β-butyrolactone as comonomers. Block copolymers with β-butyrolactone could also be selectively depolymerised, to give poly(3-hydroxybutyrate) homopolymers. Attempted polymerisation of a range of other aromatic monomers was unsuccessful due to addition of steric bulk, changing orientation of the monomer ester bond or decreasing the ring size. Synthesis of homopolymer and ABA triblock copolymers with L-lactide and alkyl-substituted β-lactones was investigated. Homopolymerisation of all alkyl-substituted β-lactones resulted in well controlled polymer, with rate decreasing as alkyl-substituent length increased. A sequential addition of monomers method with β-butyrolactone, β-valerolactone and β-heptanolactone was employed for copolymer synthesis. Copolymers synthesised from β-butyrolactone and β-valerolactone resulted in tunable glass transition and melting temperatures. Copolymers synthesised from β-heptanolactone resulted in thermoplastic elastomers exhibiting microphase separation, supported by differential scanning calorimetry and small-angle X-ray scattering. Finally, optimisation of in situ generated carbonylation catalysts was studied. Optimisation of literature complexes allowed for synthesis of β-valerolactone, β- heptanolactone, β-tridecalactone, 4-chloro-β-butyrolactone and β-6-heptenolactone on relatively large scales under much easier experimental protocols. Additionally, tuning of ortho-phenylene bridged salen ligand framework gave to structure-activity relationships. Using this optimised catalyst system, 4-chloro-β-butyrolactone and β- 6-heptenolactone were prepared and used in ring opening polymerisation. Well controlled and efficient polymerisation of 4-chloro-β-butyrolactone was easily achieved with aluminium salen and salan catalysts. Homopolymers and block copolymers with poly(ethylene glycol) and β-6-heptenolactone were readily synthesised.

There is an emerging interest in the development of sustainable materials with high performance. Cellulose is promising in this regard as it is a renewablere source with high specific properties, which can be utilized as strong reinforcements in novel biocomposites. However, to fully exploit the potential ofcellulose, its inherent hydrophilic character has to be modified in order toimprove the compatibility and interfacial adhesion with the more hydrophobicpolymer matrices commonly used in composites.In this study, the grafting of poly(ε-caprolactone) (PCL) and poly(L-lactide)(PLLA) from cellulose surfaces, via ring-opening polymerization (ROP) of ε-caprolactone and L-lactide, was investigated. Both macroscopic and nano-sizedcellulose were explored, such as filter paper, microfibrillated cellulose (MFC),MFC-films, and regenerated cellulose spheres. It was found that thehydrophobicity of the cellulose surfaces increased with longer graft lengths, andthat polymer grafting rendered a smoother surface morphology.To improve the grafting efficiency in the ROP from filter paper, both covalent(bis(methylol)propionic acid, bis-MPA) and physical pretreatment (xyloglucanbisMPA)were explored. The highest grafting efficiency was obtained with ROPfrom the bis-MPA modified filter papers, which significantly increased amountof polymer on the surface, i.e. the thickness of the grafted polymer layer.MFC was grafted with PCL to different molecular weights. The dispersability innon-polar solvent was obviously improved for the PCL grafted MFC, incomparison to neat MFC, and the stability of the MFC suspensions was better maintained with longer grafts. PCL based biocomposites were prepared from neat MFC and PCL grafted MFCwith different graft lengths. The polymer grafting improved the mechanical properties of the composites, and the best reinforcing effect was obtained when PCL grafted MFC with the longest grafts were used as reinforcement.A bilayer laminate consisting of PCL and MFC-films grafted with different PCL graft lengths displayed a gradual increase in the interfacial adhesion with increasing graft length.The effect of grafting on the adhesion was also investigated via colloidal probeatomic force microscopy at different temperatures and time in contact. A significant improvement in the adhesion was observed after polymer grafting. / QC 20100730

We report the application of our rhodium-catalyzed nucleophilic ring-opening methodology to the enantioselective synthesis of nitrogen-substituted polycyclic heterocycles. By using a cationic Rh(I) triflate catalyst in the presence of the chiral Josiphos ligand PPF-PtBu2, the ring opening reactions on dihydrooxaquinoline and dihydrooxaisoquinoline using different nucleophiles afford access to multiple dihydroquinolines and dihydroisoquinolones in high yield and high enantioselectivity (up to 99% total yield and >99%ee). A variety of nucleophiles were shown to be compatible with the catalytic system. The electronic effects in the new ring opening reactions were investigated using a variety of nucleophiles. It was found that reactivity and enantioselectivity of the ring opening products depends on the electronic effects as well as the position of the substituents on the substrates. Good yields and high ee of regioisomeric products are obtained using electron donating substituents, whereas electron withdrawing substituents decelerate the reactions.

We report the application of our rhodium-catalyzed nucleophilic ring-opening methodology to the enantioselective synthesis of nitrogen-substituted polycyclic heterocycles. By using a cationic Rh(I) triflate catalyst in the presence of the chiral Josiphos ligand PPF-PtBu2, the ring opening reactions on dihydrooxaquinoline and dihydrooxaisoquinoline using different nucleophiles afford access to multiple dihydroquinolines and dihydroisoquinolones in high yield and high enantioselectivity (up to 99% total yield and >99%ee). A variety of nucleophiles were shown to be compatible with the catalytic system. The electronic effects in the new ring opening reactions were investigated using a variety of nucleophiles. It was found that reactivity and enantioselectivity of the ring opening products depends on the electronic effects as well as the position of the substituents on the substrates. Good yields and high ee of regioisomeric products are obtained using electron donating substituents, whereas electron withdrawing substituents decelerate the reactions.

A series of tetravalent zirconium and hafnium complexes were supported by diarylamido-phosphino [PNP]- (bis(o-diisopropylphosphinophenyl)amide) ligand. The reaction of MCl4(THF)2 (M = Zr, Hf) with [PNP]Li in toluene at room temperature generates [PNP]MCl3 as solid in 60 % yield. Polyalkyl complexes which are lack of £]-hydrogen have been achieved in synthesis of [PNP]MR3 (R = Me, CH2SiMe3) or [PNP]M(CH2SiMe3)2(E) (E = Cl, Me) since we could control the desired product from steric effect. An X-ray diffraction study of [PNP]ZrCl3 showed it to be a chloride-bridged binuclear species {[PNP]MCl2(£g-Cl)}2 in which both metal atoms are 7-coordinate whereas that of [PNP]MCl3(THF) revealed a mononuclear, 7-coordinate core structure. The phosphine fluxional exchange were found in those complexes, monitoring variable temperature 31P NMR, their fluxionality were calculated by line shape analysis. By heating [PNP]M(CH2SiMe3)2(Cl) in solution, we can afford new alkylidene complexes [PNP]M(Cl)(=CHSiMe3) via intramolecular £\-abstraction. Through Eyring plot analysis, the activation energy of [PNP]Zr(CH2SiMe3)2(Cl) £\-abstraction is ∆H‡ = 16.49(19) kcal/mol and ∆S‡ = −25.64(19) cal/mol•K; [PNP]Hf(CH2SiMe3)2(Cl) £\-abstraction is ∆H‡ = 18.70(36) kcal/mol and ∆S‡ = −23.12(36) cal/mol•K. The mixture [PNP]Hf(=CHSiMe3)(Cl) could not isolate with any purification, but [PNP]Hf(=CHSiMe3)(CH2SiMe3) obtained through directly alkylation. Here we also identified multiple alkylidene derivatives of [PNP]M(=CHSiMe3)(X) (X = Cl, CH2SiMe3). The X-ray structured and solution NMR data of those alkylidene complexes can be ascribed to evidence of £\-agostic interaction with metal center. A novel zwitterionic complex [PNP]Zr(£g2-CHSiMe3)2(AlMe2) was characterized by X-ray and been received a bisalkylidene complex which was synthesized through addition Lewies acid (AlMe3) into [PNP]Zr(=CHSiMe3)(CH2SiMe3). Group 4 alkylidene was acting as catalyst to metathesize ethylene or norbornene. The complexes [PNP]M(=CHSiMe3)(Cl) have highly streotic selectivity catalyst for ring-opening metathesis polymerization (ROMP) of norbornene. It is important to emphasize the great significance of the catalyst discoveries and improvements for both academic research and industry.

Biodegradable aliphatic polycarbonates are important components of non-toxic thermoplastic elastomers, which have a variety of medical applications. Industrially, aliphatic polycarbonates derived from six-membered cyclic carbonates such as trimethylene carbonate (TMC or 1,3-dioxan-2-one) are produced via ring-opening polymerization (ROP) processes in the presence of a tin catalyst. It is worth mentioning that TMC is readily obtained by transesterification of 1,3-propanediol with various reagents including phosgene and its derivatives. Therefore, it has been of great interest to investigate greener routes for the production of this important class of polymers. Toward this goal, the synthesis of aliphatic polycarbonates via the metal catalyzed alternative coupling of oxetanes and carbon dioxide represents an attractive alternative. The use of an abundant, inexpensive, non-toxic, and biorenewable resource, carbon dioxide, makes this method very valuable. Furthermore, in this reaction, the sixmembered cyclic carbonate byproduct, TMC, can also be ring-opened and transformed into the same polycarbonate. For over a decade, the Darensbourg research group has successfully utilized metal salen complexes as catalysts for the epoxide/CO2 copolymerization process. Hence, this dissertation focuses on the examination of these complexes as catalysts for the oxetane/CO2 copolymerization reaction and the further elucidation of its mechanism. Chromium(III) salen derivatives in the presence of an azide ion initiator were determined to be very effective catalysts for the coupling of oxetanes and carbon dioxide providing polycarbonates with minimal amounts of ether linkages. Kinetic and mechanistic investigations performed on this process suggested that copolymer formation proceeded by two routes. These are the direct enchainment of oxetane and CO2, and the intermediacy of trimethylene carbonate, which was observed as a minor product of the coupling reaction. Anion initiators which are good leaving groups, e.g. bromide and iodide, are effective at affording TMC, and hence, more polycarbonate can be formed by the ROP of preformed trimethylene carbonate. Research efforts at tuning the selectivity of the oxetane/CO2 coupling process for TMC and/or polycarbonate produced from the homopolymerization of preformed TMC have been performed using cobalt(II) salen derivatives along with anion initiators. Lastly, investigations of this process involving 3-methoxy-methyl-3-methyloxetane will be presented.

The work reported herein describes efforts to create ring-opening metathesis block copolymers and homopolymers. The block copolymers were studied to gain insight into the local nanoscale environment of a block copolymer thin film. Additionally, perylene containing homopolymers were characterized in light of their possible use as an n-type material. In the first section of the thesis, the synthesis of diblock copolymers consisting of two blocks with very different dynamics is described. The covalent attachment of a molecular rotor which is sensitive to its local environment allowed the study of the dynamics of the polymers in thin films. The emissive intensity as a function of temperature allowed us to see discontinuity in the rates of change, indicating a change in the local environment corresponding to the transition of the polymer from a glassy to rubbery state. The corresponding temperature, to this event, is known as the glass transition temperature, Tg. Additionally, a polymer featuring a covalently bound n-type molecule, perylene diimide, was synthesized. The photophysical properties, including aggregation in dilute solution, are described. The material is expected to demonstrate the ability to efficiently transport negative charge, acting as n-type material in organic electronics. / text