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Mechanism of proton transfer to coordinated thiolates: encapsulation of acid stabilizes precursor intermediate

Lookup NU author(s): Ahmed Alwaaly, Emeritus Professor Bill Clegg, Dr Ross Harrington, Professor Athinoula Petrou, Professor Richard Henderson

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Abstract

Earlier kinetic studies on the protonation of the coordinated thiolate in the square-planar [Ni(SC6H4R'-4)(triphos)](+) (R' = NO2, Cl, H, Me or MeO) by lutH(+) (lut = 2,6-dimethylpyridine) indicate a two-step mechanism involving initial formation of a (kinetically detectable) precursor intermediate, {[Ni(SC6H4R'-4)(triphos)]center dot center dot center dot Hlut}(2+) (K-1(R)), followed by an intramolecular proton transfer step (k(2)(R)). The analogous [Ni(SR)(triphos)]BPh4 {R = Et, Bu-t or Cy; triphos = PhP(CH2CH2PPh2)(2)} have been prepared and characterized by spectroscopy and X-ray crystallography. Similar to the aryl thiolate complexes, [Ni(SR)(triphos)](+) are protonated by lutH(+) in an equilibrium reaction but the observed rate law is simpler. Analysis of the kinetic data for both [Ni(SR)(triphos)](+) and [Ni(SC6H4R'-4)(triphos)](+) shows that both react by the same mechanism, but that K-1(R) is largest when the thiolate is poorly basic, or the 4-R' substituent in the aryl thiolates is electron-withdrawing. These results indicate that it is both NH center dot center dot center dot S hydrogen bonding and encapsulation of the bound lutH(+) (by the phenyl groups on triphos) which stabilize the precursor intermediate.


Publication metadata

Author(s): Alwaaly A, Clegg W, Harrington RW, Petrou AL, Henderson RA

Publication type: Article

Publication status: Published

Journal: Dalton Transactions

Year: 2015

Volume: 44

Issue: 26

Pages: 11977-11983

Print publication date: 14/07/2015

Online publication date: 08/06/2015

Acceptance date: 08/06/2015

ISSN (print): 1477-9226

ISSN (electronic): 1477-9234

Publisher: Royal Society of Chemistry

URL: http://dx.doi.org/10.1039/c5dt01716e

DOI: 10.1039/c5dt01716e


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