膦基（硅基）卡宾碱度的理论与实验研究。

Theoretical and experimental investigation of the basicity of phosphino(silyl)carbenes.

作者信息

Martin David, Illa Ona, Baceiredo Antoine, Bertrand Guy, Ortuño Rosa M, Branchadell Vicenç

机构信息

Laboratoire d'Hétérochimie Fondamentale et Appliquée, UMR CNRS 5069, Université Paul Sabatier, 118, route de Narbonne, F-31062 Toulouse Cedex 04, France.

出版信息

J Org Chem. 2005 Jul 8;70(14):5671-7. doi: 10.1021/jo0508447.

DOI:10.1021/jo0508447

PMID:15989352

Abstract

[reaction: see text] The reactivity of phosphino(trimethylsilyl)carbenes 1 with several organic acids has been examined in order to evaluate the pKa values of the conjugate acids. Carbenes 1 react efficiently with C-organic acids such as 1,3-dimesitylimidazolium chloride, phenylacetylene, acetonitrile, and acetyltrimethylsilane, which have pKa's in DMSO in the range 18-31. However, the reaction of the conjugate acids 1H+ with the anion perturbs the determination of the genuine basicity of 1. Theoretical calculations have been performed in order to quantify the basicity of phosphino(trimethylsilyl)carbenes 1 and to compare them with that of N-heterocyclic carbenes 2. The pKa of 1H+ in DMSO has been computed to be in the 23.0-23.4 range, so that 1 is not strong enough as a base to spontaneously deprotonate organic acids such as phenylacetylene, acetonitrile, or acetyltrimethylsilane. However, its conjugate acid 1H+ is a strong electrophile and easily reacts with the nucleophilic conjugate bases of these acids leading to the formation of the corresponding phosphorus ylides.

摘要

[反应：见正文] 为了评估共轭酸的pKa值，已研究了膦基（三甲基硅基）卡宾1与几种有机酸的反应活性。卡宾1能与C-有机酸如1,3-二甲基咪唑鎓氯化物、苯乙炔、乙腈和乙酰基三甲基硅烷有效反应，这些酸在二甲亚砜中的pKa范围为18 - 31。然而，共轭酸1H⁺与阴离子的反应干扰了对1真实碱度的测定。已进行理论计算以量化膦基（三甲基硅基）卡宾1的碱度，并将它们与N-杂环卡宾2的碱度进行比较。已计算出1H⁺在二甲亚砜中的pKa在23.0 - 23.4范围内，因此1作为碱的强度不足以使苯乙炔、乙腈或乙酰基三甲基硅烷等有机酸自发去质子化。然而，其共轭酸1H⁺是一种强亲电试剂，很容易与这些酸的亲核共轭碱反应，导致形成相应的磷叶立德。