Expanded-Ring N-Heterocyclic Carbenes for the Stabilization of Highly Electrophilic Gold(I) Cations
Expanded-Ring N-Heterocyclic Carbenes for the Stabilization of Highly Electrophilic Gold(I) Cations
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DOI：
10.1002/chem.201404939
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发表时间：
2014-12-08
影响因子：
4.3
通讯作者：
Aldridge, Simon
中科院分区：
文献类型：
--
作者：
Phillips, Nicholas;Dodson, Tristan;Aldridge, Simon
本文研究了用空间位阻的Dipp取代的扩环NHC（Dipp = 2，6-iPr（2）C（6）H（3））从含氯或含氯前体合成高度亲电Au-I配合物的策略。因此，已经合成了（NHC）AuH类型的络合物（对于NHC = 6-Dipp或7-Dipp），并且显示出比基于辅助咪唑亚基供体的络合物具有显著更多的富电子电子的特征。这一发现与这些NHC的较强的S-供体特征一致，并且允许氢化物配体的质子化。这种化学反应导致二氢的损失和[（NHC）Au]（+）片段被捕获在含有桥连氢化物的双核金阳离子内。相反，在（NHC）AuH中的氢化物配体被B（C6 F5）（3）活化，产生一种（在低温下）具有类似于“游离”硼酸根阴离子的光谱特征的[HB（C6 F5）（3）]（-）片段的物质。随后的重排涉及B-C键断裂和芳基转移到亲碳金属中心。在使用Na[BArf（4）]（Arf = C6 H3（CF 3）2- 3，5）的卤化物提取条件下，[（NHC）AuCl]（NHC = 6-Dipp或7-Dipp）类型的体系生成双核配合物[{（NHC）Au}（2）-（μ-Cl）]（+），其在金处仍然是足够亲电的，以诱导芳基从[BAr 4f]（-）抗衡离子中提取。
Strategies for the synthesis of highly electrophilic Au-I complexes from either hydride-or chloride-containing precursors have been investigated by employing sterically encumbered Dipp-substituted expanded-ring NHCs (Dipp = 2,6-iPr(2)C(6)H(3)). Thus, complexes of the type (NHC) AuH have been synthesised (for NHC = 6-Dipp or 7-Dipp) and shown to feature significantly more electron-rich hydrides than those based on ancillary imidazolylidene donors. This finding is consistent with the stronger s-donor character of these NHCs, and allows for protonation of the hydride ligand. Such chemistry leads to the loss of dihydrogen and to the trapping of the [(NHC)Au](+) fragment within a dinuclear gold cation containing a bridging hydride. Activation of the hydride ligand in (NHC) AuH by B(C6F5)(3), by contrast, generates a species (at low temperatures) featuring a [HB(C6F5)(3)](-) fragment with spectroscopic signatures similar to the "free" borate anion. Subsequent rearrangement involves B-C bond cleavage and aryl transfer to the carbophilic metal centre. Under halide abstraction conditions utilizing Na[BArf(4)] (Arf = C6H3(CF3)2-3,5), systems of the type [(NHC) AuCl] (NHC = 6-Dipp or 7-Dipp) generate dinuclear complexes [{(NHC) Au}(2)-(mu-Cl)](+) that are still electrophilic enough at gold to induce aryl abstraction from the [BAr4f](-) counterion.