Insertion of Substituted Alkynes into the Pd-C Bond of Methyl and Vinyl Palladium(II) Complexes Bearing Pyridylthioethers as Ancillary Ligands. The Influence of Ligand Substituents at Pyridine and Sulphur on the Rate of Insertion

The palladium(II) chloro methyl complexes bearing the bidentate 6-R-C5H3N-2-CH2SR' (RN-SR'; R = H, Me, Cl; R' = Me, t-Bu, Ph) and the potentially terdentate 2,6-(CH2SR')(2)-C5H3N (S-N-S(R'); R'= Me, t-Bu, Ph) pyridylthioethers as ancillary ligands were synthesized, characterized, and reacted with substituted alkynes ZC equivalent to CZ (Z = COOMe, Z' = COOt-Bu, Z" = COOEt). The reactions were followed under second-order conditions by H-1 NMR technique, and the reaction rates were determined. The corresponding vinyl derivatives were synthesized, and in the case of the complexes [PdCl(ZC=CZMe)(MeN-SPh)] and [PdCl(ZC= CZMe)(C1N-St-Bu)] (Z = COOMe) reaction rates for alkyne insertion yielding the corresponding butadienyl complexes were also determined. The rate of insertion of the second alkyne on the vinyl complex is more than 3 orders of magnitude lower than the first insertion rate in both the studied complexes, thereby allowing easy separation between vinyl and butadienyl derivatives and an easy preparation of mixed butadienyl esters. Furthermore, the reaction rates are strongly dependent on the steric and electronic features of the ancillary ligands. In particular, the distortion of the complex main coordination plane, induced by the substituent in position 6 of the pyridine ring, was found to significantly influence the substrate reactivity. The structures of the mono-inserted vinyl [PdCl(ZC CZMe)(MeN-St-Bu)] (1) and the bis-inserted butadienyl [PdCl((ZC=CZ)(2)Me)(MeN-St-Bu)] (2) complexes were determined by X-ray diffraction, and the persistence of a structural distortion of the complex skeleton was observed. Moreover, the distortion may be related to facile ancillary ligand displacement, a feature that can be exploited for the synthesis of substrates that would not be easily obtained otherwise

Kinetic Studies of the Oxidative Addition and Transmetallation Steps Involved in the Cross-Coupling of Alkynyl Stannanes with Aryl Iodides Catalysed by teta2-(Dimethyl fumarate)(iminophosphane)palladium(0) Complexes

The complexes [Pd(eta(2)-dmfu)(P-N)] {dmfu = dimethyl fumarate; P-N = 2-(PPh2)C6H4-1-CH=NR, R = C6H4OMe-4 (1a), CHMe2 (2a), C6H3Me2-2,6 (3a), C6H3(CHMe2)(2)-2,6 (4a)} undergo dynamic processes in solution which consist of a P-N ligand site exchange through initial rupture of the Pd-N bond at lower energy and an olefin dissociation-association at higher energy. According to equilibrium constant values for olefin replacement, the complex [Pd(eta(2)-fn)(P-N)] (fn = fumaronitrile, 1b) has a greater thermodynamic stability than its dmfu analogue 1a. The kinetics of the oxidative addition of ArI (Ar = C6H4CF3-4) to 1a and 2a lead to the products [PdI(Ar)(P-N)] (1c, 2c) and obey the rate law, k(obs) = k(1A) + k(2A)[ArI]. The k(1A) step involves oxidative addition to a reactive species [Pd(solvent)(P-N)] formed from dmfu dissociation. The k2A step is better interpreted in terms of oxidative addition to a species [Pd(eta(2) -dmfu) (solvent) (kappa(1)-P-N)] formed in a pre-equilibrium step from Pd-N bond breaking. The complexes 1c and 2c react with PhCequivalent toCSnBu(3) in the presence of an activated olefin (ol = dmfu, fn) to yield the palladium(0) derivatives [Pd(eta(2)-ol)(P-N)] along with lSnBu(3) and PhCequivalent toCAr. The kinetics of the transmetallation step, which is rate-determining for the overall reaction, obey the rate law: k(obs) = k(2T)[PhCequivalent toCSnBu(3)]. The k(2T) values are markedly enhanced in more polar solvents such as CH3CN and DMF. The solvent effect and the activation parameters suggest an associative S(E)2 mechanism with substantial charge separation in the transition state. The kinetic data of the above reactions in various solvents indicate that, for the cross-coupling of PhCequivalent toCSnBu(3) with ArI catalysed by 1a or 2a, the rate-determining step is represented by the oxidative addition and that CH3CN is the solvent in which the highest rates are observed. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004

Mechanism of nucleophilic attack by secondary anilines on the nitrile group in platinum(II) ortho-cyanobenzyl complexes

Mechanism of nucleophilic attack by secondary anilines on the nitrile group in platinum(II) ortho-cyanobenzyl complexes

Mechanisms of nucleophilic and electrophilic attack on carbon bonded palladium(II) and platinum(II) complexes

none4A systematic mechanistic study is reported for the formation of palladium(II) carbene complexes by nucleophilic attack of aromatic amines on isocyanide derivatives. The most prominent step of the reaction involves direct attack of the amine nitroge on the isocyanide carbon to give an intermediate which then is converted to the final carbene species by the agency of the entering amine itself which behaves as a bifunctional catalyst. The rate of the primary step is affected by the donor ability of the entering amine, by the electrophilic character of the isocyanide carbon, and by steric crowdiness around the reacting centers, with the solvent also playing an important role. The reaction system displays a high versatility through a proper choice of the substituents on the amine and isocyanide aromatic rings and of the ancillary ligands in the metal complex. A mechanistic study is also described of the cleavage of the platinum-carbon σ-bond by electrophilic attack by the proton on organoplatinum(II) complexes. The particular mechanism which is operative, viz. direct electrophilic attack at the metal-carbon bond or oxidative addition/reductive elimination, appears to be the result of many factors. These include electronic and steric properties of the cleaved group and of ancillary ligands, steric configuration of the substrate, nature of the electrophile and solvating ability of the medium.noneU. Belluco;R.A. Michelin;P. Uguagliati;B. CrocianiBelluco, Umberto; Michelin, Rino; P., Uguagliati; B., Crocian

Characterising colloidal quantum dots for biomedical applications

This thesis is comprised of seven sections which I will summarize here. 1. Introduces the study and sets out aims and objectives. 2. Introduces colloidal quantum dots and relevant mechanical concepts. Also serves to present the position of this work being undertaken in the field. 3. The experimental methods used throughout the thesis are introduced and described. 4. Results of preliminary studies performed on 610nm colloidal quantum dots in a PMMA matrix are presented and studied in order to develop an analytic technique to describe the dot behaviour. 5. Using the results of section 4 we show that it is possible to calculate the concentration of the dot solution using data supplied from the manufacturer and as a result we are able to calculate the photo-activation probability per dot per photon at a given photon energy. 6. Results of an extensive study of 655nm colloidal quantum dots in various pH environments in order to simulate cellular conditions. Results are analyzed at length and we propose mechanisms for the observed behaviour and the consequences of our results to the use of colloidal quantum dots in biomedical, especially cellular imaging, applications.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Reactions of coordinated nitriles. I. Mechanism of formation of amidino complexes of attack of Primary anilines of Pt(II) ortho-cyanobenzyl complexes

The reaction of the dimeric o-cyanabenzly complex cis-[Pt(o-CH2C6H4CN)(PPh3)2]2(BF4)2 with primary anilines to form monomeric amidino complexes cis-[Pt(o-CH2C6H4C=NH)(p-YC6H4NH)(PPH3)2]BF4 in DCE is a biphasic process. The first, rapid stage involves displacement of the nitrile group by the entering amine leading to al labile mononuclear amino complex bearing a dangling -CN group. This intermediate reacts with the amine in the second slower stage via attack of the amine nitrogen on the nitrile carbon to yield the final Pt(II)-amidino species