质子向镍硫醇盐配合物的转移。2. [Ni(SC(6)H(4)R - 4)(PhP[CH(2)CH(2)PPh(2)](2))](+)（R = NO(2)、Cl、H、Me或MeO）反应中限速的分子内质子转移

Proton transfer to nickel-thiolate complexes. 2. Rate-limiting intramolecular proton transfer in the reactions of [Ni(SC(6)H(4)R-4)(PhP[CH(2)CH(2)PPh(2)](2))](+) (R = NO(2), Cl, H, Me, or MeO).

作者信息

Autissier Valerie, Zarza Pedro Martin, Petrou Athinoula, Henderson Richard A, Harrington Ross W, Clegg William C

机构信息

Department of Chemistry, School of Natural Sciences, University of Newcastle, Newcastle upon Tyne, NE1 7RU UK.

出版信息

Inorg Chem. 2004 May 17;43(10):3106-15. doi: 10.1021/ic0303237.

DOI:10.1021/ic0303237

PMID:15132616

Abstract

The protonation of Ni(SC(6)H(4)R-4)(triphos) (triphos = PhPCH(2)CH(2)PPh(2); R = NO(2), Cl, H, Me, or MeO) by lutH (lut = 2,6-dimethylpyridine) to form Ni(S(H)C(6)H(4)R-4)(triphos) is an equilibrium reaction in MeCN. Kinetic studies, using stopped-flow spectrophotometry, reveal that the reactions occur by a two-step mechanism. Initially, lutH rapidly binds to the complex (K(2)(R)) in an interaction which probably involves hydrogen-bonding of the acid to the sulfur. Subsequent intramolecular proton transfer from lutH to sulfur (k(3)(R)) is slow because of both electronic and steric factors. The X-ray crystal structures of Ni(SC(6)H(4)R-4)(triphos) (R = NO(2), H, Me, or MeO) show that all are best described as square-planar complexes, with the phenyl substituents of the triphos ligand presenting an appreciable barrier to the approach of the sterically demanding lutH to the sulfur. The kinetic characteristics of the intramolecular proton transfer from lutH to sulfur have been investigated. The rate of intramolecular proton transfer exhibits a nonlinear dependence on Hammett sigma(+), with both electron-releasing and electron-withdrawing 4-R-substituents on the coordinated thiolate facilitating the rate of proton transfer (NO(2) > Cl > H > Me < MeO). The rate constants for intramolecular proton transfer correlate well with the calculated electron density of the sulfur. The temperature dependence of the rate of the intramolecular proton transfer reactions shows that deltaH() is small but increases as the 4-R-substituent becomes more electron-withdrawing [deltaH = 4.1 (MeO), 6.9 (Me), 11.4 kcal mol(-)(1) (NO(2))], while DeltaS() becomes progressively less negative [deltaS = -50.1 (MeO), -41.2 (Me), -16.4 (NO(2)) cal K(-)(1) mol(-)(1)]. Studies with lutD show that the rate of intramolecular proton transfer varies with the 4-R-substituent [(k(3)(NO)2)(H)/(k(3)(NO)2)(D) = 0.39; (k(3)(Cl))(H)/(k(3)(Cl))(D) = 0.88; (k(3)(Me))(H)/(k(3)(Me))(D) = 1.3; (k(3)(MeO))(H)/(k(3)(MeO))(D) = 1.2].

摘要

Ni(SC(6)H(4)R - 4)(triphos)（triphos = PhPCH(2)CH(2)PPh(2)；R = NO(2)、Cl、H、Me或MeO）与lutH（lut = 2,6 - 二甲基吡啶）在乙腈中发生质子化反应形成Ni(S(H)C(6)H(4)R - 4)(triphos)是一个平衡反应。采用停流分光光度法进行的动力学研究表明，该反应通过两步机理进行。首先，lutH迅速与配合物结合（K(2)(R)），这种相互作用可能涉及酸与硫之间的氢键作用。随后，由于电子和空间因素，lutH向硫的分子内质子转移（k(3)(R)）较慢。Ni(SC(6)H(4)R - 4)(triphos)（R = NO(2)、H、Me或MeO）的X射线晶体结构表明，所有这些配合物最好描述为平面正方形配合物，triphos配体的苯基取代基对空间位阻较大的lutH接近硫形成了明显的阻碍。研究了lutH向硫的分子内质子转移的动力学特征。分子内质子转移速率对哈米特σ(+)呈现非线性依赖关系，配位硫醇盐上的给电子和吸电子4 - R取代基均促进质子转移速率（NO(2) > Cl > H > Me < MeO）。分子内质子转移的速率常数与计算得到的硫的电子密度有很好的相关性。分子内质子转移反应速率的温度依赖性表明，ΔH()较小，但随着4 - R取代基吸电子能力增强而增大[ΔH = 4.1（MeO），6.9（Me），11.4 kcal mol(-)(1)（NO(2)）]，而ΔS()逐渐变得不那么负[ΔS = -50.1（MeO），-41.2（Me），-16.4（NO(2)）cal K(-)(1) mol(-)(1)]。用lutD进行的研究表明，分子内质子转移速率随4 - R取代基而变化[((k(3)(NO)2)(H))/((k(3)(NO)2)(D)) = 0.39；((k(3)(Cl))(H))/((k(3)(Cl))(D)) = 0.88；((k(3)(Me))(H))/((k(3)(Me))(D)) = 1.3；((k(3)(MeO))(H))/((k(3)(MeO))(D)) = 1.2]。