Toggle Main Menu Toggle Search

Open Access padlockePrints

Mechanisms and rates of proton transfer to coordinated carboxydithioates: studies on [Ni(S2CR){PhP(CH2CH2PPh2)2}]+ (R = Me, Et, Bun or Ph)

Lookup NU author(s): Dr Ahmed Alwaaly, Emeritus Professor Bill CleggORCiD, Professor Richard Henderson, Professor Mike ProbertORCiD, Dr Paul Waddell

Downloads

Full text for this publication is not currently held within this repository. Alternative links are provided below where available.


Abstract

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 hydrogenbonded precursor, {[Ni(S2CR)(triphos)](+)center dot center dot center dot HCl} (K-1(R)) and this is followed by the intramolecular proton transfer (kR(2)) 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.


Publication metadata

Author(s): Henderson RA; Clegg W; Probert MR; Waddell PG; Alwaaly A

Publication type: Article

Publication status: Published

Journal: Dalton Transactions

Year: 2015

Volume: 44

Issue: 7

Pages: 3307-3317

Print publication date: 21/02/2015

Online publication date: 06/01/2015

Acceptance date: 23/12/2014

ISSN (print): 1477-9226

ISSN (electronic): 1477-9234

Publisher: Royal Society of Chemistry

URL: http://dx.doi.org/10.1039/c4dt03543G

DOI: 10.1039/c4dt03543G


Altmetrics

Altmetrics provided by Altmetric


Share