Deprotonation of N-heterocyclic carbenes to afford heterobimetallic organolanthanide complexes
Deprotonation of N-heterocyclic carbenes to afford heterobimetallic organolanthanide complexes
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DOI：
10.1021/om050895u
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发表时间：
2006-03-13
期刊：
影响因子：
2.8
通讯作者：
Liddle, ST
中科院分区：
文献类型：
--
作者：
Arnold, PL;Liddle, ST
胺系N-杂环卡宾(NHC)稀土配合物[Ln(L)N“(2)][L=t-BuNCH2-CH2{C(NCHCHNt-Bu)}；N”=N(SiMe3)(2)；Ln=Y(1)，Sm(4)]，当用萘化钾处理时，在NHC主链上发生区域特定的去质子化反应生成Ln(III)-K(I)杂双金属配合物[N“(2)Ln(L-)K(DME)](2)[Ln=Y(2)，Sm(5)；L-=二阴离子t-BuNCH2-CH2{C(NCCHNt-Bu)}]，这是第一个C，C‘-桥联两种金属的NHC配体的例子。对于具有高还原潜力的Y(III)来说，还原似乎将一个电子注入到杂环环中，从而为选择性地提取H原子而启动了NHC。然而，当还原电位低得多且容易获得的配合物4用萘化钾处理时，观察到较高比例的金属中心还原化学；只有一小部分4在NHC被还原，相应地得到低得多的5。试图分离在还原4中观察到的Sm(II)物种导致分离KN“和4；假定的Sm(II)配合物在歧化和配体重新分配方面明显不稳定。化合物1与KC8反应无反应，化合物4与KC8反应生成[Sm(L)N“(Mu-OCH3)](2)(6)，这是金属介导的自由基C-O活化和裂解二甲醚溶剂的产物，化合物2与Me3SiCl定量反应消除KCl生成配合物[Ln(L‘)N”(2)](3)[L’=t-BuNCH2CH2{C(NCSiMe(3)CHNt-Bu)}]。钾还原的NHC络合物[K](+)[t-BuNHCH2{CH2C(NCHCHNt-Bu)}](中心点-)(7)是第一个化学生成的稳定的NHC阴离子。化合物2、5和6的结构经X-射线单晶衍射、H-1和C-13核磁共振波谱和CHN显微分析确证。化合物3经H-1和C-13核磁共振确证，化合物7经EPR和H-1核磁共振确证。
Amido-tethered N-heterocyclic carbene (NHC) lanthanide complexes, [Ln(L)N"(2)] [L = t-BuNCH2-CH2{C(NCHCHNt-Bu)}; N" = N(SiMe3)(2); Ln = Y (1), Sm (4)], when treated with potassium naphthalenide, undergo regiospecific deprotonation at the NHC backbone to generate the Ln(III)-K(I) heterobimetallic complexes [N"(2)Ln(L-)K(DME)](2) [Ln = Y (2), Sm (5); L- = the dianion t-BuNCH2-CH2{C(NCCHNt-Bu)}], which are the first examples of NHC ligands that C,C'-bridge two metals. For yttrium(III), which has a high reduction potential, it appears that reduction injects an electron into the heterocycle ring, thus priming the NHC for selective H atom abstraction. However, when complex 4, which has a much lower and accessible reduction potential, is treated with potassium naphthalenide, a higher proportion of metal-centered reduction chemistry is observed; only a small percentage of 4 is reduced at the NHC, giving correspondingly much lower yields of 5. Attempts to isolate the Sm(II) species observed in the reduction of 4 resulted in isolation of KN" and 4; the putative Sm(II) complex is apparently unstable with respect to disproportionation and ligand redistribution. Treatment of 1 with KC8 affords no reaction; treatment of 4 with KC8 affords [Sm(L)N"(mu-OCH3)](2) (6), a product of metal-mediated radical C-O activation and cleavage of the DME solvent. Compound 2 reacts quantitatively with Me3SiCl to eliminate KCl and generate the complex [Ln(L')N"(2)] (3) [L' = t-BuNCH2CH2{C(NCSiMe(3)CHNt-Bu)}]. The potassium-reduced NHC complex [K](+)[t-BuNHCH2{CH2C(NCHCHNt-Bu)}](center dot-) (7) is also reported; 7 is the first chemically generated stable NHC radical anion. Compounds 2, 5, and 6 have been characterized by X-ray crystallography, H-1 and C-13 NMR spectroscopy, and CHN rnicroanalyses. Compound 3 has been characterized by H-1 and C-13 NMR spectroscopy, and compound 7 by EPR and H-1 NMR spectroscopy.