Browsing by Author "Hutton, Alan T"

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    Olefin oligomerization reactions theoretical studies using cyclometallated palladium(II) catalysts and experimental studies on platinum(II) analogues
    (2012) Zheng, Feng; Moss, John R; Hutton, Alan T; Mapolie, Selwyn F; Van Sittert, Cornie GCE
    Ethylene oligomerization reactions catalysed by cyclometallated palladium(II) N-benzylidenebenzylamine complexes were studied theoretically. Density functional theory (DFT) calculations are reported on the interaction of various MAO models with the methylated pre-catalyst. The neutral MAO dissociation process is shown to remain the major interaction that takes place in the Pd/MAO interactions. On the other hand, the formal methyl abstraction process could be also feasible if more energy is provided. Therefore, the relative energies were calculated for intermediates and transition states for both Cossee-type and metallacycle mechanisms.
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    Oxidation of waxes using microwave-generated singlet molecular oxygen
    (1999) Beigley, John Robertson; Hutton, Alan T
    Waxes are a widely used chemical commodity throughout the world due to certain intrinsic properties. Applications vary widely, including such obvious ones as candles and polishes, less obviously coatings, ink, and cosmetics, and more obscurely, hot melt adhesives, textile processing and chewing gum. The waxes used are obtained from a variety of sources, natural, mineral, and synthetic. The properties of the wax determine its suitability for a particular application. For certain of the latter, a wax containing Oxygen groups is often the most appropriate type. While there are a number of such waxes that occur naturally, there are also many more in which the raw wax has undergone oxidation by chemical processes. Generally, this is done utilising elevated temperatures, and passing air or oxygen through the wax. Oxidation then takes place via a free radical process. Singlet molecular oxygen is a higher-energy state species of oxygen, in which the two electrons in the π* 2p antibonding molecular orbitals, while remaining unpaired, are excited to antiparallel spin. Reactions of singlet oxygen are very site-specific, resulting in more specific products compared to the free radical process. It was considered that oxidation of waxes by reaction with singlet oxygen might produce different products compared to the thermal oxidation, and also compared to oxidation using ozone. An apparatus was set up to test this theory. The singlet oxygen was generated by passing a stream of oxygen through a microwave beam to form a plasma, the resulting singlet oxygen-containing gas being reacted with molten wax. Optimisation of the setup was performed before performing reactions, using several different waxes. The experiments were duplicated by ones with the microwave switched off, so that any results could be ascribed to the presence of singlet oxygen, and not normal oxygen. A similar apparatus was set up to react the same waxes with ozone, the latter being generated by passing oxygen through an electrical discharge-type generator. Blank runs with the electric discharge apparatus switched off, were also carried out to be able to distinguish any reaction due to the unozonised oxygen. The results showed that the singlet oxygen only reacted with a particular type of wax, namely oxidised polyethylene wax (AC6-29), although other effects were caused by the heat of the plasma. The ozone, on the other hand, reacted readily with all types of waxes tested. Other experiments were also conducted to investigate the use of microwave technology for chemical purposes, including development of an analytical method for saponification value determination in which microwaves replaced conventional heating.
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    Structural and spectroscopic studies with dithizone and its derivatives
    (1980) Hutton, Alan T; Irving, H M N H
    An X-ray crystal structure detennination of 3-nitro-l,5-di(2,6-dimethylphenyl) fonnazan, ArN:N•C(N02):N•NHAr (Ar= 2,6-dimethylphenyl), has shown that the N-N-C-N-N chain is stabilized by an unusual hydrogen bond in the closed-ring syn,s-cis configuration relative to the formal double C=N and single C-N bonds. The bond lengths reveal complete n-electron delocalization along the chain which results in a mesomeric structure; the possibility of such a mesomeric structure existing in solution rather than a rapid tautomeric equilibrium between two limiting forms of the resonance hybrid has been considered in the light of i.r. and n.m.r. spectroscopic measurements. The temporal changes in the visible absorption spectrum of S-methyldithizone, PhN:N•C(SCH3):N•NHPh, have been shown to arise from syn-anti isomerization about the fonnal C=N double bond and rotation about the C-N single bond by considering the evidence provided by i. r. and n.m.r. spectroscopic studies combined with the X-ray crystal structure of the di(o-tolyl) homologue. The parent compound dithizone, PhN:N•C(SH):N•NHPh, previously thought to exist as an equilibritim of thiol and thione forms in solution has now been shown to consist of a single species in solution mainly by consideration of its n.m.r. spectroscopic properties. Organomercury(II) complexes of dithizone have been shown to be photochromic in solution; X-ray crystal structure detenninations of phenyland methylmercury(II) dithizonate, besides revealing rare three-coordination of mercury, have been combined with spectroscopic measurements on the normal and activated fonns to reveal the structure of the labile photo-isomers.
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    Studies on photochromic and potentially mesogenic mercury(II) dithizonates
    (1994) Cromhout, Natalie Lyn; Hutton, Alan T
    The 4-( 4 '-n-alkoxybenzylideneanilino )mercury(II) dithizonates, CₙH₂ₙ₊₁ OC₆H₄CH=C₆H₄-Hg(HDz) (n = l, 4, 12, 14 or 18), were prepared by complexation of dithizone (1,5-diphenyl- thiocarbazone, H 2 Dz) with the corresponding 4-(4'-n-alkoxybenzylideneanilino)mercury(II) acetates. The 4-( 4 '-n-alkoxybiphenyl)mercury(II) dithizonates, CₙH₂ₙ₊₁ OC6H4 C6H4- Hg(HDz) (n = 4, 5, 10, 14 or 18), were similarly prepared by reaction of dithizone with the appropriate 4-(4'-n-alkoxybiphenyl)mercury(II) bromides, although the latter compounds, derived from the 4-n-alkoxy-4'-bromobiphenyls, were not isolated. The preparation of the 4- ( 4'-n-octyloxyazobenzene)mercury(II) dithizonate, C₈H₁₇OC₆H₄N=NC₆H₄Hg(HDz),from 4-n-octyloxy-4'-bromoazobenzene was attempted but the chosen synthetic method was not successful. The thermal behaviour of those series of compounds isolated was investigated by polarized optical microscopy and differential scanning calorimetry. The organomercury(II) acetates displayed a limited, poorly-defined mesomorphism and the type of any mesophase formed remains unidentified. The 4-n-alkoxy-4'-bromobiphenyls (alkoxy = CₙH 2 n+ 1 0, n = 3-5, 10-12, 14-16 or 18) exhibited liquid crystalline behaviour within a broad temperature range for the compounds with n ~ 10 and the nature of the mesophases was tentatatively assigned as smectic D and C. The 4-n-alkoxy-4'-bromoazobenzenes (alkoxy = CₙH 2 n+I0, n = 5, 10, 12 or 14) showed monotropic (n = 5, 10 or 12) or enantiotropic (n = 14) nematic and smectic A mesophases. However, none of the dithizonate derivatives was mesomorphic and this was attributed to the geometry of the dithizonate ligand. The organomercury(II) dithizonates were photochromic in organic solvents, displaying reversible colour changes from yellow to blue on irradiation with visible light. The visible absorption spectra of these solutions were recorded and appeared to be independent of the nature of the long-chain organic ligand. This photochromism was not observed in the solid state.
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    Synthesis and biological evaluation of salicylaldimine complexes based on an alkylated PTA scaffold
    (2017) Cassells, Irwin; Hutton, Alan T; Prince, Sharon; Stringer, Tameryn
    Cancer remains one of the largest pandemics in the world, with millions affected by this disease every year. Since the discovery of the anticancer properties of cisplatin and other platinum-based drugs, metal-based chemotherapies have been extensively researched. Due to the elevated levels of toxicity of many platinum-based drugs, a rise in research using other metal-based drugs for the treatment of cancer has been observed. Of these, platinum group metals such as ruthenium, rhodium and iridium have shown great promise over the last several decades. RAPTA-type (ruthenium arene 1,3,5-triaza-7-phosphaadamantane) complexes have shown great promise in vivo for the treatment of certain cancers. Combining RAPTA with other biologically active groups has often resulted in increased potency and selectivity against various cancer cells in vitro. In this study, we investigated the synthesis, characterisation and biological evaluation of salicylaldimine complexes with an alkylated PTA scaffold. All of the metal complexes were screened for their activity against MCF7 breast cancer cells in vitro, in addition, the most active complexes were screened against Chinese Hamster Ovarian (CHO) non-cancerous cells to evaluate their selectivity. A series of salicylaldimine ligands, as well as a benzyl alkylated PTA scaffold were prepared. Complexes of these ligands were synthesised by a reaction with [RuCl(µ-Cl)(p-cymene)]₂, [RhCl(µ-Cl)(Cp*)]₂ or [IrCl(µ-Cl)(Cp*)]₂. In addition to this, new PTA containing analogues of these neutral complexes were also prepared by reacting the afore mentioned salicylaldimine complexes with the alkylated PTA scaffold. All the compounds were characterised using an array of techniques including NMR spectroscopy, IR spectroscopy and mass spectrometry. Single crystal X-ray diffraction (XRD) was used to confirm the bidentate coordination mode of the salicylaldimine ligand to the metal centre, as well as the presence of the metal-phosphorus bond for the alkylated PTA complexes. All of the metal complexes were evaluated against the MCF7 breast cancer cell line. The ruthenium and iridium salicylaldimine complexes showed comparable or greater cytotoxicity than cisplatin at 20 µM against the MCF7 cancer cells, as well as greater cytotoxicity than their rhodium counterparts. Three of the salicylaldimine complexes exhibited potent activity (18 < IC₅₀ < 21 M). Selectivity studies showed that two of these complexes had a greater affinity for cancerous cells than for the CHO non- cancerous cells. All the alkylated PTA complexes were less cytotoxic than cisplatin against the MCF7 cancer cells. Preliminary mechanistic studies of the most active complexes suggest ruthenium undergoes solvation prior to 5'-GMP binding, whereas iridium was inert to the solvation process.
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    Synthesis, characterization and liquid crystalline properties of organometallic complexes of chromium, cobalt and platinum
    (1997) Starr, Earl Jeffrey; Moss, John R; Hutton, Alan T
    Chapter 1 provides a concise review of concepts and previous studies in liquid crystal chemistry as they relate to metallomesogens, highlighting their advantages over purely organic liquid crystal systems. Chapter 2 reports on a mild synthetic route starting from [Co(DH)₂(py){(CH₂)ₘOH}] (DH = the monoanion of dimethylglyoxime; py = pyridine; m = 3 or 8) to give the ester-functionalized cobaloximes [Co(DH)₂(py){(CH₂)ₘOC(O)(CH₂)ₙC₆H₄R}] (n = 0, 2 or 5; R = H, o-, m-, p-OCH₃, p-OC₇H₁₅ or p-OC₉H₁₉), 1- 9. The esterification occurred chemoselectively to extend the hydroxy alkyl group, without affecting the oxime entities on the DH ligands. None of these complexes displayed mesogenic properties. This chapter also details the synthesis and characterization of the new complexes [Co(DH)₂(C₆H₄₀CₘH₂ₘ₊₁)(n-OST)] (m = 8, 10 or 12; n-OST = trans-4-n-alkoxy-4'stilbazole; n = 8, 10 or 12), 11 - 17, which possess greater structural anisotropy and consequently displayed an enantiotropic smectic C mesophase. The extended rod-like core and the central position of the bulky metal system proved useful in promoting the formation of the mesophase. Variation of the above cobaloxime-stilbazole system afforded the complexes [Co(DH)iC₆H₄₀C₁₂H₂₅)(R-OST)] 18, [Co(DH)₂(C₁₄H₂₉)(12- OST)] 19, and [Co(DH)₂(C₁₄H₂₉)(R-OST)] 20 (where R = C(O)C₆H₄₀C₉H₁₉). These complexes were non-mesomorphic, despite possessing favourable rod-like structures. The synthesis and characterization of the novel octahedral stilbazole complexes [PtMe₂X₂(n-OST)₂] (X= I or Br; n = 3 - 10 or 12), 21- 30, is described in Chapter 3. The shorter-chain homologues melted cleanly to the isotropic state while the complexes with n = 8 - 10 or 12 developed an unusual pseudo-isotropic phase around 80 °C and on further heating, the samples displayed a smectic C phase around 150 °C. The alignment of the molecules to give the mesophase occurred despite the fact that the complexes possessed an angular structure resulting from the cis geometry of the n-OST ligands. The complexes [PtMe₂RX(n-Diim)], [PtMe₂X₂(8-Diim)] and [ {PtMe₂Br(9- Diim)}₂(μ-p-(CH₂)₂C₆H₄)] (R =Me, Et, n-Pr; X= I or Br; n-Diim = N,N'-bis-4'-(4-nalkoxybenzoyloxyphenyl)- 1,4-diaza-1,3-butadiene), 31- 42, were synthesized in a one- pot procedure from the dimeric complex [Pt₂Me₄(μ-SMe₂)₂] and the respective n-Diim ligand to give the square-planar intermediate [PtMe₂(n-Diim)], which underwent subsequent oxidative addition in the presence of an alkyl halide RX (R = Me, Et, n-Pr) or a dihalide X₂ (X = Br or I). An aromatic-like metallocyclic ring was proposed to explain the anomaly in the NMR resonances of the protons close to the coordination sphere in the square-planar complexes. The longer-chain complexes (i.e. n = 6 - 10) exhibited wide temperature-range enantiotropic nematic phases. Further, modification of the axial ligands to increase the bulkiness of the central metal core (R = Me to n-Pr, X = Br or I) generally led to lower-melting materials. However, many of the complexes were thermally unstable, decomposing at their clearing temperatures. Chapter 4 describes the synthesis and characterization of the novel ionic complexes Y[PtC₁₃(olefin)] (where Y = K, H₂₁C₁₀NH₃, NMe₄, NEt₄ and olefin = CH₂=CHC₆H₄- C(O)OC₆H₄₀R, R = C₇H₁₅ , C(O)C₆H₄₀CH₃ or C(O)C₆H₄₀C₈H₁₇), 43 - 50. By careful choice of the reaction conditions and work-up solvents, most of the individual reaction steps produced high yields of the desired products. The meso genic behaviour was found to be dependent on the length of the rod-like core, the length of the flanking alkoxy chain, and more importantly, the nature of the cation used. Only the long-chain alkylammonium complexes displayed stable nematic phases. Variation of the now established mesogemc platinum(II)-olefin system afforded the complexes [PtC₁₂(olefin)(N-donor)] (N-donor = 4,4'-bipy, H₂NC₄H₉, H₂NC₁₀H₂₁ or 4-0ST), 51- 54. Except for the 4,4'-bipy complex 51 which was non-mesomorphic, the remaining complexes displayed well-formed nematic phases. The greater structural anisotropy of the stilbazole complex 54 produced a mesophase with a wider temperature range than that observed for the alkylamine complexes. Finally, Chapter 5 reports on a simple one-pot synthesis leading to the new complexes [ {η⁶-C₆H₄R₂-1,4}Cr(CO)₃] (where R = OC(O)C₆H₄₀CnH₂n+l (n = 1, 6 - 10) or OC(O)C₆H₄C₅H₁₁ ) and [ {η⁶-C₆H₄(R')(C₆H₄R')-1,4 }Cr(CO)₃] (R' = OC(O)C₆H₄₀C₁₀H₂₁), 55 - 62. The procedure involved thermal reaction of Cr(CO)₆ with hydroquinone and subsequent esterification of the para hydroxyl functionalities with various mesogenic carboxylic acid compounds. Infrared monitoring of the reaction mixture provided useful data in identifying the reaction intermediates. Despite the bulky nature of the central chromium system, the rigid unit comprising three aromatic rings proved sufficient to stabilize enantioptropic nematic phases similar to those observed for the metal-free analogues. Modification of the organic backbone in these complexes to incorporate cyclohexylene rings and the biphenylene unit had pronounced effects on the temperature range of the observed mesophase.
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    The synthesis, characterization and reactivity of metallacycloalkanes and their precursors
    (2010) Madzivire, Cecilia Rutendo; Moss, John R; Hutton, Alan T
    A series of bis(alkenyl)platinum(II) complexes of the type [PtL2{(CH2)nCH=CH2h](L2 = 1 ,3-bis( diphenylphosphino )propane and n = 3-6) have been successfully synthesized and characterized by IH, I3C and 31p NMR spectroscopy, elemental analysis and mass spectrometry. I3C NMR data for these complexes is herein presented for the first time. A new route for the synthesis of dicarbonyldibromide rhenium complexCp*Re(CO)2Br2 affording the product in very high yields is also herein reported.
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    Synthetic and structural studies on early transition metal siloxides
    (1993) Jones, Robert Edward; Hutton, Alan T
    [Super- and subscripts in abstract] n-Bu3SiOH was prepared from both n-Bu3SiH and n-Bu3SiCI. Reactions of n-Bu3SiOH with NaH, LiBun, MC15 (M = Ta or Mo) and Cp2MCl2 (Cp = 115-C5H5, M = Ti or Zr) were investigated, in some cases using the base Et3N as a hydrogen chloride acceptor. Na+(QSiPh3r was prepared from the reaction of Ph3SiOH with NaH, but in poor yield. Ph3SiOH was reacted with TaCI5, but the product, if formed at all, was intractable. When Ph3SiOH was reacted with Cp2MC12 (M = Ti or Zr) products were isolated and characterised, viz. [Cp2 TiCl(OSiPh3)]n (n = 1 or 2) and Cp2Zr(OSiPh3)2. Single crystals Cp2Zr(OSiPh3h were studied using X-ray photographic techniques. They crystallise in the monoclinic system with a = 35. 7, b = 10.4, c = 21.1 A, f3 = 97.7 °, V= 7763 A3. A full crystal structure analysis was not possible due to failure of the diffractometer software to locate the monoclinic unit cell determined by photographic methods. Ph3 SiOH was also reacted with Cp 2ZrC12 (Cp = 115-C5Me5) and the product was tentatively assigned to be Cp 2Zr(OSiPh3h as a pure sample could not be obtained. An interesting spirocompound, Ti[OSiPh2(0SiPh2)30h, was prepared from Ph2Si(0Hh and Ti(n-Bu0)4 and the crystal structure determined by X-ray crystallography. It crystallises in the monoclinic system, space group P21/n, a = 13.805(5), b = 27.545(5), c = 23.476(9) A, f3 = 94.41(3) 0 , V= 8901(5) A3, Z = 4, R = 0.0831 for 5528 reflections with Ire/> 2a(Iref).
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    Transition metal complexes of bis(diphenylphosphino)methane, dithizone and dithiolenes: structural, spectroscopic, electrochemical and computational studies
    (2012) Wewers, Francois; Hutton, Alan T
    A series of heterobi- and tri-metallic complexes were prepared by the metallation of the carbanion derived from [M(CO)₄(dppm)] (M = Cr, Mo or W), [ML(dppm)] (L= dithiolene; M = Pd or Pt), or the cationic precursor, [Ru(Cp)(PPh3)(dppm)]PF₆. The complexes were characterized by ¹H and ³¹P NMR, IR and UV/Vis spectroscopies and X-ray crystallography. The presence of electrochemical communication in these complexes was investigated by means of cyclic voltammetry. Correlation studies of electrochemical potentials and 31P NMR data or carbonyl stretching frequencies of the Group 6 mercurated complexes show that the mercury atom does facilitate the flow of electrons through the four-membered chelate ring. However, this effect has been established to be weak. Similar weak electronic effects were found to exist in the case of the Ru, Pd and Pt complexes. Evidence of "through-space" communication was established to be present in the ferrocenyl derivatives. X-ray crystallographic studies show that mercuration of the carbanion neutralizes the residual electron density in the chelate ring for the chromium bi- and tri-metallic complexes. This was also demonstrated for the cationic ruthenium complex. X-ray crystallographic studies were performed on dithizone and its corresponding salt in an attempt to resolve or explain the often debated tautomerism of this molecule in the solid state and in solution. The structure of the parent molecule showed the co-existence of the two tautomeric forms in a single structure, with a 2:1 preference for the symmetrical keto form, compared to the enol form. DFT calculations have been performed and have been shown to be mutually consistent with structural data, showing a negligible energy difference of 3.1 kcal mol⁻¹ between the two forms. Computational calculations were also performed to investigate the solution characteristics of the dithizonate salt. An analysis of the HOMO and Fukui functions show the sulfur atom to be the most nucleophilic and therefore the preferred site for deprotonation with an energy barrier of 17 kJ mol⁻¹ compared to the nitrogen atom. While the 1H NMR spectrum shows evidence of the existence of proton exchange in solution, we were unable to model this. However, DFT solution studies show that the keto form is most stabilized. A series of palladium and platinum dithizonate complexes, with the general formula, [M(PP)(Hdptc)]X or [M(PP)(dptc)] (PP = mono- or bidentate phosphine ligand; M = Pd or Pt; X = PF₆ or BPh₄), was prepared and investigated for their photochromic behaviour. None of these complexes exhibited any photochromism. X-ray crystal structures of [Pt(COD)(dptc)] and [Pt(dppf)(dptc)] were determined. Both complexes contain the dithizone ligand in a doubly deprotonated, or secondary, form. Synthetic routes to the preparation of mixed dithiolene-dithizone complexes of mercury and platinum were developed. The complexes were characterized by ¹H and ¹³C NMR, IR and UV/Vis spectroscopies and X-ray crystallography. Spectroscopic studies show that the mercury complexes are all photochromic, while the platinum complex showed no photochromism in solution. Electrochemical studies show the absence of rich electrochemical activity for the Hg complexes. The [Pt(mnt)(Hdptc)]⁺ complexes, in contrast, showed greater redox activity. X-ray studies on the analogous complexes, Ph₄As[Hg(mnt)(Hdptc)] and Bu₄N[Pt(mnt)(Hdptc)] revealed an absence of any S···S or Metal···S interactions, often associated with planar sulfur rich ligands.