Reactions of cobalt(III) complexes with free radicals derived from thymine

The nature of interaction of Co(III) complexes such as Co(III)EDTA and Co(III)NTA with transient adducts of thymine such as TOH^˙, T^˙?, and TH^˙ formed in the gamma radiolysis of thymine were studied. The study shows that TOH radicals do not undergo electron transfer reaction with Co(III) complexes whence no radiosensitization of thymine by Co(III) complexes was observed. Electron transfer however, takes place from T^˙? and TH^˙ to Co(III) complexes. A plausible mechanism of radiolysis of thymine in presence of Co(III) complexes is discussed. © 1994 John Wiley & Sons, Inc.     

Reactions of tris(oxalato)cobaltate(III) with two-electron reductants

The tris(oxalato)cobaltate(III) complex [Co(C(2)O(4))(3)](3-), E(o)(Co)(III/II)=+0.57 V) is readily reduced by the 2e(-) reagents, Sn(II) and Ge(II), in contrast to (NH(3))(5)CoCl(2+) and (NH(3))(5)CoBr(2+), which are unreactive toward these donors. Rates for the oxalato oxidant are only 10(-3)-10(-2) as great as those for vitamin B(12a)(aquacob(III)alamin, E(o)+0.35 V at pH 1), in accord with the suggestion that reductions of corrin-bound cobalt(III) by Sn(II) and Ge(II) occur predominantly through an additional path involving Co(i). Reductions of the oxalato complex by 2e(-) donors are taken to proceed by initial formation of odd-electron intermediates (e.g., Sn(III) and Ge(III)) which react rapidly with Co(III). Such a two-step sequence is in keeping with the observed behavior of the rare reductant, Ti(II), which is found to be oxidized by [Co(C(2)O(4))(3)](3-) more slowly than (independently prepared) Ti(III) under comparable conditions.     

Reactions of free radicals with η-allylpalladium(II) complexes: cyclohexyl radicals

Allyl palladium complexes of the types [(η³-allyl)PdCl]₂, (η³-allyl)PdCl(PPh₃) and [(η³-allyl)Pd(PPh₃)₂]Cl (allyl=C₃H₅, 1-MeC₃H₄, 2-MeC₃H₄, 1-PhC₃H₄, 2-PhC₃H₄) react with cyclohexyl radicals derived from the visible light photolysis of (c-hex)Co(DMG)₂(py). The reactions proceed via initial attack of the free radical at the metal center, followed by β-hydrogen elimination and subsequent reductive elimination of propene, 1-butene, isobutene, 3-phenylpropene and 2-phenylpropene, respectively. The 3-phenylpropene can be catalytically isomerized to the thermodynamically more stable 1-phenylpropene by either palladium metal or palladium(0) products, but the formation of 1-butene and 3-phenylpropene as primary products is unusual. A mechanism, differing in many ways from that proposed previously for analogous reactions of phenyl and trityl radicals, is proposed for the overall reaction and supported by use of the labeled cobaloxime, (2,2,6,6-D₄-c-hex)Co(DMG)₂(py).     

Reactions of tris(trimethylsilylmethyl)-stannyllithium with peroxides

Conclusions The reactions of tris(trimethylsilylmethyl)stannyllithium with tert-butyl peroxide, trimethyl(tertbutylperoxy)silane, triphenyl(tert-butylperoxy)germane, benzoyl peroxide and dicyclohexyl peroxydicarbonate proceed with a heterolytic cleavage of the peroxide group. In the unsymmetrical peroxides the less shielded oxygen atom is subjected to attack.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2776–2778, December, 1973.     

Reactions of polyfluoroalkanethioamides with tris(diethylamino)phosphine

Structure of reaction products obtained from tris(diethylamino)phosphine with N,Ndialkylpolyfluoroalkanethioamides depends on the length of the polyfluoroalkyl substituent in the latter. In the case of morpholides of perfluorothiopropionic and perfluorothiobutyric acids the main reaction products are fluoro-containing aminoacetylenes: 4-(perfluoroalkan-1-yn-1-yl)morpholines, and also tris(diethylamino)phosphine sulfide and tris(diethylamino)difluorophosphorane. From morpholides or piperidides of ω-H-perfluorothiovaleric acid with a longer perfluoroalkyl substituents amides of cis- and trans-perfluoropent-2-enethiocarboxylic acids were obtained.     

Reactions of radicals with hydrolyzed Bi(III) ions: a pulse radiolysis study

Radiolytic reduction of BiOClO4 in aqueous solutions leads to the formation of bismuth clusters and larger nanoparticles. The mechanisms of redox reactions of the polycationic Bi(III) species that exist in the solution were investigated with pulse radiolysis. The kinetic and spectral properties of the transients formed by the reaction of these species with the primary radicals from water radiolysis are reported. The single-electron reduction product, Bi9(OH)224+, absorbs at lambdamax = 273 nm, while the OH adduct, Bi9(OH)235+, has a broad absorption spectrum with a maximum at 280 nm and a shoulder at 420 nm. Several rate constants were measured: k (e-aq + Bi9(OH)225+) = 1.2 x 1010 M-1 s-1 and k (OH + Bi9(OH)225+) = 1.5 x 109 M-1 s-1. The reduced species, Bi9(OH)224+ further reacts with (CH3)2COH radicals, but not with CH2C(CH3)2OH radicals from t-butanol, to produce a doubly reduced polynuclear species. A few reactions of the reduction of the Bi salt in the presence of poly(acrylic acid) are also described. In the presence of the polymer, a metal-polymer complex is formed prior to the irradiation, and the reduction reactions are significantly slowed down.     

Reactions of free radicals with polymers—II: Abstraction reactions of methyl and acetyl radicals with poly(vinyl acetophenone)

The kinetics of H abstraction by methyl and acetyl radicals from poly(vinyl acetophenone) (PVAP) films (4 × 10³ mm thick) have been investigated, both radicals being derived from the polymer by photolysis (λ ≥ 300 nm) under high vacuum conditions (pressure < 10^?4 Pa). Differential equations have been obtained to describe the simultaneous diffusion and reaction of each of the radicals, and the solutions (both steady and non-steady state conditions) have been used in conjunction with experimental data (including yields of methane and acetaldehyde) to obtain values of rate constants for abstraction. which it is argued is likely to occur predominantly at the α-carbon atoms in the polymer. Both steady and non-steady state calculations yield the same values of rate constants. Values of these constants have been compared with each other and that for methyl radical abstraction is compared with data obtained for abstraction from other styrene polymers. PVAP is less reactive than polystyrene towards methyl radicals. Factors accounting for these differences, including diffusant volume, polymer free volume and the energetics of formation of the transition state for abstraction in the various polymers, are considered. Theoretical rates of product formation, based on the solutions of the equations, are compared with the experimental yields of methane and acetaldehyde; a good correspondence is observed for approx. 3 hr reaction time. Subsequent discrepancies between the two sets of data are attributed to the radiation modified diffusion and optical characteristics of the polymer.     

Reactions of tris(2-pyridyl)phosphines and tris(2-pyridyl)phosphine oxides with some electrophiles

Treatment of tris(2-pyridyl)phosphine or tris(2-pyridyl)phosphine oxide with electrophiles such as chlorine, bromine, deuterium chloride, or benzenediazonium chloride gave unusual coupling products, i.e., 5-chloro-, 5-bromo-, 5-deuterio-, or 5-phenylazo-2,2′-bipyridyls, respectively, as a major coupling product in each case. This is considered to be the result of electrophilic substitution on a pyridyl ring in a pentacovalent phosphorane intermediate formed in each reaction. © 1997 John Wiley & Sons, Inc. Heteroatom Chem 8: 439–449, 1997     

Reactions of tris(amino)phosphines with arylsulfonyl azides: product dependency on tris(amino)phosphine structure

The Staudinger reaction of N(CH2CH2NR)3P [R = Me (1), Pr (2)] with 1 equiv of N3SO2C6H4Me-4 gave the ionic phosphazides [N(CH2CH2NR)3PN][SO2C6H4Me-4] [R = Me (3), R = Pr (5a)], and the same reaction of 2 with N3SO2C6H2Me3-2,4,6 gave the corresponding aryl sulfinite 5b. On the other hand, the reaction of 1 with 0.5 equiv of N3SO2Ar (Ar = C6H4Me-4) furnished the novel ionic phosphazide [[N(CH2CH2NMe)3P]2(mu-N3)][SO2Ar] (6). Data that shed light on the mechanistic pathway leading to 3 were obtained by low temperature 31P NMR spectroscopy. A crystal and molecular structure analysis of the phosphazide sulfonate [N(CH2CH2NMe)3PN3][SO3C6H4Me-4] (4), obtained by atmospheric oxidation of 3, indicated an ionic structure, the cationic part of which is stabilized by a transannular P-N bond. A crystal and molecular structure analysis of 6 also indicated an ionic structure in which the cation features two untransannulated N(CH2CH2NMe)3P cages bridged by an azido group in an eta 1: mu: eta 1 fashion. The reaction of P(NMe2)3 with N3SO2Ar (Ar = C6H4Me-4) in a 1:0.5 molar ratio furnished [[(Me2N)3P]2(mu-N3)][SO2-Ar] (11) in quantitative yield. On the other hand, the same reaction involving a 1:1 molar ratio of P(NMe2)3 and N3SO2Ar produced a mixture of 11, [(Me2N)3PN3][SO2Ar] (12), and the iminophosphorane (Me2N)3P=NSO2Ar (10). In contrast, the bicyclic tris(amino)phosphines MeC(CH2NMe)3P (7) and O=P(CH2NMe)3P (8) reacted with N3SO2-Ar (Ar = C6H4Me-4) to give the iminophosphorane MeC(CH2NMe)3P=NSO2Ar (14) (structured by X-ray means) and O=P(CH2NMe)3P=NSO2Ar (16) via the intermediate phosphazides MeC(CH2NMe)3PN3SO2Ar (13) and O=P(CH2NMe)3PN3SO2Ar (15), respectively. The variety of products obtained from the reactions of arylsulfonyl azides with proazaphosphatranes (1 and 2), acyclic P(NMe2)3, bicyclic tris(amino)phosphines 7 and 8 are rationalized in terms of steric and basicity variations among the phosphorus reagents.     

Reactivity of tris(trimethylsilyl)silane toward diarylaminyl radicals

Absolute rate constants for the reaction of tri-tert-butylphenoxyl radical (ArO*) with (TMS)(3)SiH were measured spectrophotometrically in the temperature range 321-383 K. Rate constants for the hydrogen abstraction from (TMS)(3)SiH by diarylaminyl radicals of type (4-X-C(6)H(4))(2)N* were determined by using a method in which the corresponding amines catalyze the reaction of ArO* with (TMS)(3)SiH. At 364.2 K, rate constants are in the range of 2-50 M(-)(1) s(-)(1) for X = H, CH(3), CH(3)O, and Br, whereas the corresponding value for ArO* is 3 orders of magnitude lower. A common feature of these reactions is the low preexponential factor [log(A/M(-1)s(-1)) of 4.4 and 5.2 for ArO* and Ph(2)N*, respectively], which reflects high steric demand in the transition state. A semiempirical approach based on intersecting parabolas suggests that the observed reactivity is mainly related to the enthalpy of the reaction and allowed to estimate activation energies for the reaction of (4-X-C(6)H(4))(2)N* and ArO* radicals with a variety of silicon hydrides.     

Reactions of hydropolysilanes with alcohols catalysed by tris(triphenylphosphine)chlororhodium

[RhCl(PPh₃)₃] is a very effective catalyst for the cleavage of Si-Si bonds by alcohols.