Ray W. Matthews

Carbon-13 and proton NMR parameters of mono- and di-organothallium(III) derivatives

Carbon-13 and proton coupling constants and chemical shifts are reported for di- and mono-organothallium(III) compounds of the types TlR2X and TlRX2 respectively (X = anionic species). The nature of R was varied over thirty acyclic alkyl, alicyclic alkyl and alkenyl groups. Series of related derivatives were studied to identify the major factors upon which the NMR parameters depend. Several new organothallium(III) derivatives have been synthesised. The effects of solvent and anion (X) changes on the NMR parameters are generally minor. The major factor influencing J(Tl-C) and J(Tl-H) is the number of R groups attached to thallium and the ratios of analogous couplings in TlR2X and TlRX2 are generally close to the value of 12.2 predicted on the assumption that the Fermi contact contribution dominates these coupling constants. Couplings to thallium for acyclic alkyl R groups depend on the degree of substitution in R and follow the patterns |1J| > |3J| > |2J| > |4J|, ±1J, ∓2J, ±3J for J(Tl-C) and, with few exceptions, |3J| > |2J| > |4J|, ∓2J, ±3J, ±4J for J(Tl-H). Values of 3J(Tl-H) for cyclopropyl derivatives are included with existing data to quantify Karplus-type stereochemical dependence. The values of 3J(Tl-C) and 3J(Tl-H) for TlR2X (R = cyclohexyl) suggest a preference for equatorial substitution by thallium, and a similar conclusion seems reasonable for R = cyclopentyl. |nJ(Tl-C)| in alkenyl derivatives follows the same pattern as for R = acyclic alkyl, but in contrast to alkyl derivatives, 1J and 2J have the same sign. Thallium-proton couplings 2J and 3J also have the same sign for R = alkenyl. Compounds with α,β-unsaturated R groups have very large values of 1J(Tl-C) compared to those with saturated R groups. These increases can be partly attributed to changes in hybridization at the α-carbon atom. The effects of the Cl substituent on 1J(Tl-C), 2J(Tl-H) and 1J(C-H) for Tl(ClCH2)X2 are discussed in terms of the Fermi contact contribution to these coupling constants. Substituent effects on carbon-13 chemical shifts are reported.

The influence of anion, solvent and concentration on the thallium-205, carbon-13 and proton NMR parameters of the dimethylthallium(III) ion

Abstract Thallium-205, carbon-13 and proton NMR spectra have been determined for the dimethylthallium(III) derivatives (CH3)2TIX (X  NO3, I, OC6H5) as a function of solvent and concentration. The NMR parameters most sensitive to changes in the environment of the thallium nucleus are the 205TI chemical shift and 1J(205Tl13C). The thallium-205 chemical shift varies within a 300 ppm range as anion, solvent and concentration are changed, demonstrating the potential of this parameter as a probe for the environment of thallium. The nature of the solvent is the strongest influence on 1J(205Tl13C), the greatest change being observed for (CH3)2TINO3 between water and pyridine. The solvent dependence of 1J(205Tl-13C) and2 J(205Tl1H) is discussed in terms of the approximate expression for the Fermi contact mechanism for spin—pin coupling.

Carbon-13 and proton NMR parameters of neopentyl-and trimethylsilylmethyl-thallium(III) derivatives and the x-ray crystal structure of bis(trimethylsilylmethyl)chlorothallium(III)

Abstract Carbon-13 and proton NMR spectra have been determined for organothallium (III) derivatives of the types RTlX 2 and R 2 TlX (R  (CH 3 ) 3 CCH 2 or (CH 3 ) 3 SiCH 2 ; X  Cl, Br or O 2 CCH(CH 3 ) 2 ). The dependence of coupling of 13 C and 1 H to thallium on the number and nature of R groups is discussed in terms of the Fermi contact mechanism for spinspin coupling. The crystal structure of [(CH 3 ) 3 SiCH 2 ] 2 TlCl has been determined. The compound crystallises in the monoclinic space group P 2 1 / n , with a 10.618, b 24.492, c 6.017 A, β 99.76°. The molecule is dimeric with each four-coordinate thallium atom bonded unequally to two bridging chlorine atoms. The CTlC angle is 168°.

X-ray structures of the dimeric dimethylthallium(III) Derivatives, [(CH3)2TlX]2 (X = OC6H5, OC6H4Cl-o, SC6H5; relevance of 1J(205Tl- 13C) and 2J(205Tl1H) as structural probes

Abstract X-ray structures of dimethylthallium(III) derivatives, [(CH3)2TlX]2 (x = OC6H5, OC6H4Cl-o, SC6H5 confirm their formulation as discrete dimers. There is no apparent correlation between the CTlC angle (

The Preparation of Dimethyl α -Hydroxyphosphonates and the Chemical Shift Non-Equivalence of Their Diastereotopic Methyl Ester Groups

Dimethyl α -hydroxyalkyl-, α -hydroxybenzyl-, α -hydroxyfurfuryl-, and α -hydroxy-α -thienylmethyl-phosphonates have been prepared in good yield by the alumina-catalyzed reaction of dimethyl phosphite with the corresponding alkanals, aryl aldehydes (or aryl methyl ketones), furfuraldehyde, and 2- or 3-thiophenecarboxaldehyde, respectively, thus confirming the general utility of this synthetic procedure. The 1H and 13C nmr spectra of the products exhibit characteristic chemical shift non-equivalence of the diastereotopic methyl ester groups, for which a tentative order of non-equivalence is reported and discussed.

1-AMINO-1-ARYL- AND 1-AMINO-1-HETEROARYL-METHANEPHOSPHONIC ACIDS AND THEIR N-BENZHYDRYL–PROTECTED DIETHYL ESTERS: PREPARATION AND CHARACTERIZATION

n-Benzhydryl-protected diethyl[3.3pc] esters of 1-amino-1-aryl- (phenyl, cumyl, p-dimethylaminophenyl, piperonyl, 1′-naphthyl, 9′-anthryl, 1′-pyrenyl) and 1-amino-1-heteroaryl- (furyl, 2′-thienyl, 3′-thienyl, 2′-pyrrolyl)-methanephosphonic acids, prepared by the addition of diethyl phosphite to the corresponding benzhydryl imines, have been isolated, purified, and characterized. The presence of chiral α -carbon and prochiral phosphorus in these esters gives rise to complicated features in their NMR spectra, which are discussed. Hydrolysis of the crude 1-aryl compounds in situ gave modest yields of the corresponding aminophosphonic acids (except for 1′-pyrenyl). Of the 1-heteroaryl derivatives, only the 2′-thienyl compound gave the expected aminophosphonic acid; in other cases, alternative[-18pc] modes of decomposition may occur under hydrolytic conditions. NMR and mass spectral data are given for all products.

Carbon-13 NMR parameters and molecular structure of {2-exo-bicyclo [2.2.1] hept-exo-3-acetato-5-enyl}-5,10,15,20-tetraphenylporphinatothallium(III)

Abstract The compound {2- exo -bicyclo [2.2.1] hept- exo -3-acetato-5-enyl}-5,10,15,20-tetraphenylporphinatothallium (III) has been synthesized and its molecular structure determined. The compound crystallizes in the monoclinic space group P 2 1 , with a 13.112, b 29.193, c 11.249 A, β 102.17°, Z = 4. The organothallium(III) group is situated above the plane of the porphyrin ring with the thallium atom displaced 0.9 A from the N 4 plane. The thallium atom and the acetato group are attached cis-exo to the bicyclo [2.2.1] unit. Carbon-13 spectra show shielding effects arising from the porphyrin ring current.

Macrocyclic helicates: complexes of a 34-membered Schiff-base ligand

A unique double helical macrocyclic configuration of a new 34-membered Schiff-base macrocycle results from convergence of its two pyridine-2,6-diyldiimine units for meridional coordination of divalent metal ions; X-ray structure analysis establishes the cobalt(II), nickel(II) and zinc(II) complexes as the first structurally characterised macrocyclic helicates.

Molecular motion of the dimethylthallium(III) cation in aqueous solution

Thallium-205 spin-lattice relaxation times in the dimethylthallium cation have been measured over a range of temperature at frequencies of 21·96, 34·73 and 231·6 MHz. Although the relaxation is typically dominated by the chemical shift anisotropy (CSA) mechanism a contribution from the spin rotation (SR) mechanism has also been quantified. A value of the chemical shift anisotropy for this linear ion from other work (5550 ppm) enabled calculation of the reorientational correlation time τ⊥. An Arrhenius temperature dependence was found with a τ⊥ value of 39·1 ± 0·5 ps at 298 K and an activation energy of 19·7 ± 0·7 kJ mol-1. The axial symmetry, the linear thallium environment, a knowledge of Δσ, and of the isotropic shift have allowed an absolute shift scale to be determined which is in close agreement with previous estimates by other workers. Assignment of the shift zero allowed calculation of the spin rotation constant C ⊥, as 73·4 kHz. Hence values for the angular momentum correlation time τ J⊥ could be ...

Enhanced Replication of R5 HIV‐1 Isolates in vitro by a Small‐Molecule Reagent Targeting HIV‐1 Protease

CHEMICAL ENHANCEMENT: Designed to target HIV-1 protease, a novel γ-hydroxyphosphonate has been found to significantly enhance viral replication in a panel of clinically relevant R5 HIV-1 isolates. This unexpected result constitutes the first instance of a small molecule capable of doing this, and it has implications for the preparation and use of R5 isolates in vaccine and drug development.