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Kinetic and Theoretical Studies on the Protonation of [Ni(2-SC₆H₄N){PhP(CH₂CH₂PPh₂)₂}]⁺: Nitrogen versus Sulfur as the Protonation Site

Lookup NU author(s): Professor Athinoula Petrou, Professor William Clegg, Dr Ross Harrington, Professor Richard Henderson

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Abstract

The complexes [Ni(4-Spy)(triphos)]BPh4 and [Ni(2-Spy)(triphos)]BPh4 {triphos = PhP(CH2CH2PPh2)(2), 4-Spy = 4-pyridinethiolate, 2-Spy = 2-pyridinethiolate} have been prepared and characterized both spectroscopically and using X-ray crystallography. In both complexes the triphos is a tridentate ligand. However, [Ni(4-Spy)(triphos)](+) comprises a 4-coordinate, square-planar nickel with the 4-Spy ligand bound to the nickel through the sulfur while [Ni(2-Spy)(triphos)](+) contains a 5-coordinate, trigonal-bipyramidal nickel with a bidentate 2-Spy ligand bound to the nickel through both sulfur and nitrogen. The kinetics of the reactions of [Ni(4-Spy)(triphos)](+) and [Ni(2-Spy)(triphos)](+) with lutH(+) (lut = 2,6-dimethylpyridine) in MeCN have been studied using stopped-flow spectrophotometry, and the two complexes show very different reactivities. The reaction of [Ni(4-Spy)(triphos)](+) with lutH(+) is complete within the deadtime of the stopped-flow apparatus (2 ms) and corresponds to protonation of the nitrogen. However, upon mixing [Ni(2-Spy)(triphos)](+) and lutH(+) a reaction is observed (on the seconds time scale) to produce an equilibrium mixture. The mechanistic interpretation of the rate law has been aided by the application of MSINDO semiempirical and ADF calculations. The kinetics and calculations are consistent with the reaction between [Ni(2-Spy)(triphos)](+) and lutH(+) involving initial protonation of the sulfur followed by dissociation of the nitrogen and subsequent transfer of the proton from sulfur to nitrogen. The factors affecting the position of protonation and the coupling of the coordination state of the 2-pyridinethiolate ligand to the site of protonation are discussed.

Publication metadata

Author(s): Petrou AL, Koutselos AD, Wahab HS, Clegg W, Harrington RW, Henderson RA

Publication type: Article

Publication status: Published

Journal: Inorganic Chemistry

Year: 2011

Volume: 50

Issue: 3

Pages: 847-857

Print publication date: 07/02/2011

Online publication date: 10/01/2011

ISSN (print): 0020-1669

ISSN (electronic): 1520-510X

Publisher: American Chemical Society

URL: http://dx.doi.org/10.1021/ic101444d

DOI: 10.1021/ic101444d

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