- Mechanisms and rates of proton transfer to coordinated carboxydithioates: Studies on [Ni(S2CR){PhP(CH2CH2PPh2)2}]+ (R = Me, Et, Bun or Ph)
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The complexes [Ni(S2CR)(triphos)]BPh4 (R = Me, Et, Bun or Ph; triphos = PhP{CH2CH2PPh2}2) have been prepared and characterised. X-ray crystallography (for R = Et, Ph, C6H4Me-4, C6H4OMe-4 and C6H4Cl-4) shows that the geometry of the five-coordinate nickel in the cation is best described as distorted trigonal bipyramidal, containing a bidentate carboxydithioate ligand with the two sulfur atoms spanning axial and equatorial sites, the other axial site being occupied by the central phosphorus of triphos. The reactions of [Ni(S2CR)(triphos)]+ with mixtures of HCl and Cl- in MeCN to form equilibrium solutions containing [Ni(SH(S)CR)(triphos)]2+ have been studied using stopped-flow spectrophotometry. The kinetics show that proton transfer is slower than the diffusion-controlled limit and involves at least two coupled equilibria. The first step involves the rapid association between [Ni(S2CR)(triphos)]+ and HCl to form the hydrogen-bonded precursor, {[Ni(S2CR)(triphos)]+...HCl} (KR1) and this is followed by the intramolecular proton transfer (kR2) to produce [Ni(SH(S)CR)(triphos)]2+. In the reaction of [Ni(S2CMe)(triphos)]+ the rate law is consistent with the carboxydithioate ligand undergoing chelate ring-opening after protonation. It seems likely that chelate ring-opening occurs for all [Ni(S2CR)(triphos)]+, but only with [Ni(S2CMe)(triphos)]+ is the protonation step sufficiently fast that chelate ring-opening is rate-limiting. With all other systems, proton transfer is rate-limiting. DFT calculations indicate that protonation can occur at either sulfur atom, but only protonation at the equatorial sulfur results in chelate ring-opening. The ways in which protonation of either sulfur atom complicates the analyses and interpretation of the kinetics are discussed. This journal is
- Alwaaly, Ahmed,Clegg, William,Henderson, Richard A.,Probert, Michael R.,Waddell, Paul G.
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p. 3307 - 3317
(2015/03/05)
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- Dithio and Thiono Esters, 59. - Reactions of Aliphatic Dithio Acid Dianions with Carbon Disulfide
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Dianions 2 of dithioacids 1 and carbon disulfide yield in a kinetically controlled reaction at -78 deg C S-adducts (e.g. 3, 13) or in a thermodynamically controlled reaction at room temperatur C-adducts .Acidification of 10 and subsequent reactions give rise to the tetrathiomalonic acids 18 and its derivatives 19 with 2,6,9,10-tetrathiaadamantane structure.Deprotonation of 10a leads to the tetrathiomalonic acid tetraanion (20) which may be alkylated to yield the tetrakis(alkylthio)allenes 21.By condensation of the dithioacid dianions 2, the tetrathiomalonic acid trianion 10 and the tetrathiomalonic a cid tetraanion (20) with 2,3-dichloro-1,4-naphthoquinone (32) a number of naphtho-1,3-dithiole-4,9-diones (e.g. 33, 35, 37) are obtained. - Key Words: Dithio acid dianions / Tetrathiomalonic acid / Anions / Tetrathiomalonic acid tetraanion / Dithioacrylic esters / Thio acids / Allenes, alkylthio- / Naphtho-1,3-dithiole-4,9-diones / Malonic acid, tetrathio- / Acrylic acid, dithio
- Hartke, Klaus,Rettberg, Norbert,Dutta, Dinah,Gerber, Hans-Dieter
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p. 1081 - 1090
(2007/10/02)
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