A study of ligand exchange processes at early transition metal centres: synthesis, mechanism and applications to polymer synthesis

This thesis describes studies into the exchange reactivity of early transition metal species containing mono- and dianionic ligands, examining both the intermetal exchange of such ligands and the exchange to and from external substrates. Studies on the metathesis polymerisation of functionalised monomers using well-defined Schock initiators are described. Chapter 1 highlights the electronic and structural aspects of the ligands employed in this thesis (including oxo, imido, alkylidene, alkoxide and amide moieties) and briefly reviews intermetal ligand exchange reactions. In addition, applications of the olefin metathesis reaction, namely R.O.M.P and ADMET, are reviewed employing the well-defined Schrock type initiators. Chapter 2 describes the preparation of Mo(NBu(^t))(_2)(OBu(^t))(_2), and examines the reactivity of its imido ligands towards a series of organic substrates including aryl amines, benzaldehyde, dioxygen and isocyanates. Intermetal imido-imido exchange reactivity is inspected for Mo(NR)(_2)X(_2) and CpMo(NBu(^t))(_2)Cl systems. The intermetal oxo-imido exchange reaction between Mo(NBu(^1))(_2)(OR)(_2) and Mo(O)(_2)(OR)(_2) is investigated, in which the role of acid catalysis is examined. The effects of increasing the elecu-on withdrawing properties of the ancillary alkoxide ligands by progressive fluorination are probed. The favourable position of the oxo-imido exchange reaction is exploited in the synthesis of the oxo-imido complexes Mo(O)(NBu(^t))(OBu(^t))2, Mo(O)(NBu(^t))(OR(^6))(_2) and Mo(O)(NBu(^t))Cl(_2).dme. The intermetal exchange reactivity of mono-anionic X-type ligands is then explored in systems of the type MoQ(_2)X(_2) (Q = O, NBu(^t); Q(_2) = (NAr)(CHCMe(_2)Ph); X = CI, OR, NHR).Chapter 3 presents the attempted synthesis of a half-sandwich niobium bis (imido) complex of general formula CpNb(NR(^1))(NR(^2)), starting with the synthesis of imido-amide complexes CpNb(NR)(NR(^1)R(^2))Cl (R = Bu(^t), R(^1) = R(^2) = Et; R = Ar, R(^1) = Bu(^t) R(^2) = H) via the reaction of CpNb(NR)Cl(_2) with lithium amides. Further reaction of these imido-amide species with lithium amides result in the formation of CpNb(NBu(^t))(NHBu(^t))(_2) and CpNb(NBu(^t))(NHBu(^t)(NE(_t2)). The reactivity of the imido ligand in CpNb(NBu(^t))X(_2) is investigated towards aryl amines, butanol, dioxygen and H(_2)O. Complexes of the type CpNb(NBu(^t))X(_2) (X = Br, OPr(^3), OR(_f)(^3), OR(_f_(^6) and NC(_4)H(_4)) are isolated and employed in mono-anionic intermetal exchange reactions, the results from which are compared with those from analogous reactions in chapter 2.Chapter 4 outlines metathesis polymerisation studies on hetero-cyclopentenes using the well-defined molybdenum Schrock initiators. The R.O.M.P of 2,3- and 2,5- dihydrofurans are reported. A metallacycle adduct is isolated in the reaction of Mo(NAr)(CHCMe(_2)Ph)(OBu(^t))(_2) with vinylene carbonate. The reaction of l-(amino)-3- borolenes with the Schrock initiators is described and a product characterised as a 1- (amino)-2-borolene by X-ray crystallography. The factors that may effect the polymerisability of hetero-cyclopentenes are briefly considered. In addition, the reactivity of functionalised acyclic diallyl species of the type Q(CH(_2)CHCH(_2))(_2) (Q = O, NH, PPh, O(_2)CO) are explored with the Schrock initiators in acyclic diene metathesis reactions (ADMET). Diallyl ether is found to undergo catalytic ring closure to 2,5 dihydrofuran, while diallyl phenyl-phosphine gives l-phenyl-2,5 dihydrophosphole

Regulating Cable Television Rates: A Phantom First Amendment Problem

Public concern over cable television\u27s status as a monopoly has generated a movement to allow local franchising authorities to regulate cable service rates. Because the courts have yet to hear a First Amendment challenge to imposing rate regulation on a member of the media, the constitutionality of cable rate regulation is not settled. This Comment argues that the restriction on speech resulting from rate regulation is outweighed by the substantial government interest in preventing unfair monopoly pricing practices

Design and development of a hybrid flexible manufacturing system : a thesis presented in fulfilment of the requirements for the degree of Master of Technology at Massey University

Volumes 1 and 2 merged.The ability of a manufacturing environment to be able to modify itself and to incorporate a wide variety of heterogeneous multi-vendor devices is becoming a matter of increasing importance in the modern manufacturing enterprise. Many companies in the past have been forced to procure devices which are compatible with existing systems but are not as suitable as other less compatible devices. The inability to be able to integrate new devices into an existing company has made such enterprises dependent on one vendor and has decreased their ability to be able to respond to changes in the market. It is said that typically 60% of orders received in a company are new orders. Therefore the ability of a company to be able to reconfigure itself and respond to such demands and reintegrate itself with new equipment requirements is of paramount importance. In the past much effort has been made towards the integration of shop floor devices in industry whereby such devices can communicate with each other so that certain tasks are able to be achieved in a single environment. Up until recently however much of this was carried out in a very much improvised fashion with no real structure existing within the factory. This meant that once the factory was set up it became a hard-wired entity and extensibility and modiflability were difficult indeed. When formalised Computer Integrated Manufacturing (CIM) system architectures were developed it was found that although they solved many existing shortcomings there were inherent problems associated with these as well. What became apparent was that a fresh approach was required that took the advantages of existing architectures and combined them into an new architecture that not only capitalised on these advantages but also nullified the weaknesses of the existing systems. This thesis outlines the design of a new FMS architecture and its implementation in a factory environment on a PC based system

Reduction of blade-vortex interaction noise using higher harmonic pitch control

An acoustics test using an aeroelastically scaled rotor was conducted to examine the effectiveness of higher harmonic blade pitch control for the reduction of impulsive blade-vortex interaction (BVI) noise. A four-bladed, 110 in. diameter, articulated rotor model was tested in a heavy gas (Freon-12) medium in Langley's Transonic Dynamics Tunnel. Noise and vibration measurements were made for a range of matched flight conditions, where prescribed (open-loop) higher harmonic pitch was superimposed on the normal (baseline) collective and cyclic trim pitch. For the inflow-microphone noise measurements, advantage was taken of the reverberance in the hard walled tunnel by using a sound power determination approach. Initial findings from on-line data processing for three of the test microphones are reported for a 4/rev (4P) collective pitch control for a range of input amplitudes and phases. By comparing these results to corresponding baseline (no control) conditions, significant noise reductions (4 to 5 dB) were found for low-speed descent conditions, where helicopter BVI noise is most intense. For other rotor flight conditions, the overall noise was found to increase. All cases show increased vibration levels