Alkali-metal-mediated zincation (AMMZn) meets N-heterocyclic carbene (NHC) chemistry: Zn-H exchange reactions and structural authentication of a dinuclear Au(I) complex with a NHC anion
Alkali-metal-mediated zincation (AMMZn) meets N-heterocyclic carbene (NHC) chemistry: Zn-H exchange reactions and structural authentication of a dinuclear Au(I) complex with a NHC anion
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DOI：
10.1039/c3sc52101j
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发表时间：
2013-01-01
期刊：
影响因子：
8.4
通讯作者：
Hevia, Eva
中科院分区：
文献类型：
--
作者：
Armstrong, David R.;Baillie, Sharon E.;Hevia, Eva
结合合成中两个不断发展的领域，即协同双金属和N-杂环卡宾（NHC），本研究报告了使用锌酸钠[（TMEDA）NaZn（TMP）（tBu）（2）]（1）作为金属化试剂分离游离NHC和Zn-NHC络合物的碱金属介导锌化（AMMZn）的第一中间体。（THF）（3）Na[：C{[N（2，6-iPr（2）C（6）H（3））]（tBu（2））}]（2）和[Na（THF）（6）]（+）[tBu（2）Zn：C{[N（2，6-iPr（2）C（6）H（3））]（tBu（2））}]（-）（4），由1与不饱和游离NHC IPr反应产生（IPr = 1，3-双（2，6-二异丙基苯基咪唑-2-亚基）和NHC络合物ZntBu（2）IPr（3）分别证明在这两种情况下，这种混合金属方法可以容易地促进NHC配体的不饱和主链的选择性C4锌化。此外，阴离子NHC片段的产生使得能够通过其正常（C2）和异常（C4）位置与NHC系统进行双配位，稳定通常未被检测到的动力学AMMZn中间体，并提供了关于这些混合金属试剂如何操作的新的机理见解。与此相反，当NHC-络合物3与更常规的单金属碱如tBuLi反应时，配位卡宾的去质子化被抑制，反而有利于共络合以得到NHC-稳定的[IPr中心点LiZntBu（3）]（5）。显示2作为其阴离子NHC单元到过渡金属络合物的转移剂的潜力，该中间体与两摩尔当量的[ClAu（PPh 3）]反应以提供新的双金物种[ClAu：C{[N（2，6-iPr（2）C（6）H（3））]（2）CHCAu（PPh 3）}]（6），这是由前所未有的双转移反应产生的，该双转移反应涉及NHC骨架上的阳离子（Na+）和中性（ZntBu（2））实体的同时交换。
Merging two evolving areas in synthesis, namely cooperative bimetallics and N-heterocyclic carbenes (NHCs), this study reports the isolation of the first intermediates of alkali-metal-mediated zincation (AMMZn) of a free NHC and a Zn-NHC complex using sodium zincate [(TMEDA)NaZn(TMP)(tBu)(2)] (1) as a metallating reagent. The structural authentication of (THF)(3)Na[:C{[N(2,6-iPr(2)C(6)H(3))](2)CHCZn(tBu(2))}] (2) and [Na(THF)(6)](+)[tBu(2)Zn:C{[N(2,6-iPr(2)C(6)H(3))](2)CHCZn(tBu(2))}](-) (4), resulting from the reactions of 1 with unsaturated free NHC IPr (IPr = 1,3-bis(2,6-di-isopropylphenylimidazole-2-ylidene) and NHC complex ZntBu(2)IPr (3) respectively demonstrates that in both cases, this mixed-metal approach can easily facilitate the selective C4 zincation of the unsaturated backbone of the NHC ligand. Furthermore, the generation of anionic NHC fragments enables dual coordination through their normal (C2) and abnormal (C4) positions to the bimetallic system, stabilising the kinetic AMMZn intermediates which normally go undetected and provides new mechanistic insights in to how these mixed-metal reagents operate. In stark contrast to this bimetallic approach when NHC-complex 3 is reacted with a more conventional single-metal base such as tBuLi, the deprotonation of the coordinated carbene is inhibited, favouring instead, co-complexation to give NHC-stabilised [IPr center dot LiZntBu(3)] (5). Showing the potential of 2 to act as a transfer agent of its anionic NHC unit to transition metal complexes, this intermediate reacts with two molar equivalents of [ClAu(PPh3)] to afford the novel digold species [ClAu:C{[N(2,6-iPr(2)C(6)H(3))](2)CHCAu(PPh3)}] (6) resulting from an unprecedented double transmetallation reaction which involves the simultaneous exchange of both cationic (Na+) and neutral (ZntBu(2)) entities on the NHC framework.