Structural and mechanistic look at the orthoplatination of aryl oximes by dichlorobis(sulfoxide or sulfide)platinum(II) complexes

Structural and mechanistic aspects of orthoplatination of acetophenone and benzaldehyde oximes by the platinum(II) sulfoxide and sulfide complexes [PtCl(2)L(2)] (2, L = SOMe(2) (a), rac-SOMePh (b), R-SOMe(C(6)H(4)Me-4) (c), and SMe(2) (d)) to afford the corresponding platinacycles cis-(C,S)-[Pt(II)(C(6)H(3)-2-CR'=NOH-5-R)Cl(L)] (3, R, R' = H, Me) have been investigated. The reaction of acetophenone oxime with sulfoxide complex 2a in methanol solvent occurs noticeably faster than with sulfide complex 2d due to the fact that the sulfoxide is a much better platinum(II) leaving ligand than the sulfide. Evidence is presented that the orthoplatination is a multistep process. The formation of unreactive dichlorobis(N-oxime)platinum(II) cations accounts for the rate retardation by excess acetophenone oxime and suggests the importance of pseudocoordinatively unsaturated species for the C-H bond activation by Pt(II). A comparative X-ray structural study of dimethyl sulfoxide platinacycle 3b (R = R' = Me) and its sulfide analogue 3e (R = H, R' = Me), as well as of SOMePh complex 3c (R = H, R' = Me), indicated that they are structurally similar and a sulfur ligand is coordinated in the cis position with respect to the sigma-bound phenyl carbon. The differences concern the Pt-S bond distance, which is notably longer in the sulfide complex 3e (2.2677(11) A) as compared to that in sulfoxide complexes 3b (2.201(2)-2.215(2) A) and 3c (2.2196(12) A). Whereas the metal plane is practically a plane of symmetry in 3b due to the H-bonding between the sulfoxide oxygen and the proton at carbon ortho to the Pt-C bond, an S-bonded methyl of SOMePh and SMe(2) is basically in the platinum(II) plane in complexes 3c and 3e, respectively. There are intra- and intermolecular hydrogen bond networks in complex 3b. An interesting structural feature of complex 3c is that the two independent molecules in the asymmetric unit of the crystal reveal an extremely short Pt-Pt contact of 3.337 A.     

Decontamination of radionuclides on construction materials

A wide variety of materials can become contaminated by radionuclides, either from a terrorist attack or an industrial or nuclear accident. The final disposition of these materials depends, in large part, on the effectiveness of decontamination measures. This study reports on investigations into the decontamination of a selection of building materials. The aim has been to find an effective, easy-to-use and inexpensive decontamination system for radionuclides of cesium and cobalt, considering both the chemical and physical nature of these potential contaminants. The basic method investigated was surface washing, due to its ease and simplicity. In the present study, a basic decontamination formulation was modified by adding isotope-specific sequestering agents, to enhance the removal of cesium(I) and cobalt(II) from such construction materials as concrete, marble, aluminum and painted steel. Spiking solutions contained ¹³⁴Cs or ⁶⁰Co, which were prepared by neutron activation in the SLOWPOKE-2 nuclear reactor facility at the Royal Military College of Canada. Gamma spectroscopy was used to determine the decontamination efficiency. The results showed that the addition of sequestering agents generally improved the radiological decontamination. Although the washing of both cesium and cobalt from non-porous materials, such as aluminum and painted steel, achieved a 90–95 % removal, the decontamination of concrete and marble was more challenging, due to the porous nature of the materials. Nevertheless, the removal efficiency from 6-year-old concrete increased from 10 % to approximately 50 % for cobalt(II), and from 18 to 55 % for cesium(I), with the use of isotope binding agents, as opposed to a simple water wash.     

Physical characterization of uranium oxide pellets and powder applied in the Nuclear Forensics International Technical Working Group Collaborative Materials Exercise 4

Journal of Radioanalytical and Nuclear Chemistry - Physical characterization is one of the most broad and important categories of techniques to apply in a nuclear forensic examination. Physical...     

The application of radiochronometry during the 4th collaborative materials exercise of the nuclear forensics international technical working group (ITWG)

Journal of Radioanalytical and Nuclear Chemistry - In a recent international exercise, 10 international nuclear forensics laboratories successfully performed radiochronometry on three low enriched...     

An investigation into the use of ionizing radiation for the destruction of sulphur mustard

Chemical warfare agents have been stockpiled for almost a decade and their destruction has become an environmental issue that will continue to require attention for many years. There are hundreds of thousands of tonnes yet to be destroyed, and the current chemical or incineration techniques are not without problems. While many researchers are seeking better chemical techniques, we decided to try ionizing radiation to destroy sulphur mustard with the goal of producing non-toxic products. We irradiated a variety of sulphur mustard samples by both a mixed field source (β, γ and neutrons) and a pure gamma source. The mixed field irradiation of wet sulphur mustard for long irradiation times was the most successful at destroying the chemical agent.     

Pseudo-rotation mechanism for fast olefin exchange and substitution processes at orthometalated C,N-complexes of platinum(II)

Bridge splitting in chloroform of the orthometalated chloro-bridged complex [Pt(micro-Cl)(2-Me(2)NCH(2)C(6)H(4))](2)(1), with ethene, cyclooctene, allyl alcohol and phosphine according to 1+ 2L --> 2[PtCl(2-Me(2)NCH(2)C(6)H(4))(L)], where L = C(2)H(4)(3a), C(8)H(14), (3b), CH(2)CHCH(2)OH (3c), and PPh(3)(4a and 4b) gives monomeric species with L coordinated trans or cis to aryl. With olefins the thermodynamically stable isomer with L coordinated cis to aryl is formed directly without an observable intermediate. With phosphine and pyridine, the kinetically controlled trans-product isomerizes slowly to the more stable cis-isomer. Bridge splitting by olefins is slow and first-order in 1 and L, with largely negative DeltaS(++). Substitution of ethene cis to aryl by cyclooctene and allyl alcohol to form 3b and 3c, and substitution of cot from 3b by allyl alcohol to form 3c are first order in olefin and complex, ca. six orders of magnitude faster than bridge cleavage due to a large decrease in DeltaH(++), and with largely negative DeltaS(++). Cyclooctene exchange at 3b is first-order with respect to free cyclooctene and platinum complex. All experimental data for olefin substitution and exchange are compatible with a concerted substitution/isomerization process via a turnstile twist pseudo-rotation in a short-lived labile five-coordinated intermediate, involving initial attack on the labile coordination position trans to the sigma-bonded aryl. Bridge-cleavage reactions of the analogous bridged complexes occur similarly, but are much slower because of their ground-state stabilization and steric hindrance.     

Kinetic resolution of esters via metal catalyzed methanolysis reactions

Some chiral lanthanide complexes of the Schiff base adducts of: a) bis(2-pyridylcarboxaldehyde) and (1R),(2R)-trans-1,2-diaminocyclohexane (Pyr-R,R'-chxn: 3); b) 6-methyl-2-pyridylcarboxaldehyde and (1R),(2R)-trans 1,2-diaminocyclohexane (MePyr-chxn, 4); and c) 2,6-pyridyldicarboxaldehyde and (1R),(2R)-trans-1,2-diaminocyclohexane ((Pyr-R,R'-chxn)(2), 5) have been screened for their utility to promote kinetic resolution via metal catalyzed alcoholyses of the p-nitrophenyl esters of chiral D- and L-Boc-protected glutamine and phenylalanine. Solvents were varied to optimize the kinetic selectivity values, defined as k(2)(L)/k(2)(D) or k(2)(D)/k(2)(L), for the methanolysis and in some cases, ethanolysis of these substrates. At ambient temperature the greatest selectivity was found for the ethanolysis of Boc-Gln-OPNP, catalyzed by 3:Yb(3+):((-)OEt) (k(2)(L)/k(2)(D) = 7.2). The greatest selectivity for Boc-Phe-OPNP is k(2)(D)/k(2)(L) = 3.9 for its methanolysis promoted by 5:La(3+):((-)OMe). A kinetic method is introduced for the determination of both d and l rate constants for catalyzed alcoholysis from a single kinetic experiment. The activation parameters DeltaH(double dagger) and DeltaS(double dagger) were determined for the metal catalyzed methanolysis and ethanolysis of the Boc-Gln-OPNP substrates, and selectivity factors were found to increase at lower temperatures. A low temperature time course for the ethanolysis of racemic Boc-Gln-OPNP catalyzed by 3:Yb(3+):((-)OEt) at -15 degrees C indicated that after 3 hours 60% residual d-enantiomer was observed having an enantiomeric excess of >95% ee. The activation parameters for the ethanolysis of the same substrate catalyzed by (Pyr-R,R'-chxn)(2):La(3+):((-)OEt) predict a k(2)(D)/k(2)(L) = 40.4 at -40 degrees C with a large ee of >99% with approximately 80% of l isomer remaining at that temperature which has been experimentally confirmed.