Morozov Oleg S, Lunchev Andrey V, Bush Alexander A, Tukov Aleksandr A, Asachenko Andrey F, Khrustalev Victor N, Zalesskiy Sergey S, Ananikov Valentine P, Nechaev Mikhail S
A. V. Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, Leninsky Prosp., 29, Moscow, 119991 (Russian Federation).
Chemistry. 2014 May 12;20(20):6162-70. doi: 10.1002/chem.201303760. Epub 2014 Mar 28.
A series of six- and seven-membered expanded-ring N-heterocyclic carbene (er-NHC) gold(I) complexes has been synthesized using different synthetic approaches. Complexes with weakly coordinating anions [(er-NHC)AuX] (X(-) = BF4(-), NTf2(-), OTf(-)) were generated in solution. According to their (13)C NMR spectra, the ionic character of the complexes increases in the order X(-) = Cl(-) < NTf2(-) < OTf(-) < BF4(-). Additional factors for stabilization of the cationic complexes are expansion of the NHC ring and the attachment of bulky substituents at the nitrogen atoms. These er-NHCs are bulkier ligands and stronger electron donors than conventional NHCs as well as phosphines and sulfides and provide more stabilization of [(L)Au(+)] cations. A comparative study has been carried out of the catalytic activities of five-, six-, and seven-membered carbene complexes [(NHC)AuX], [(Ph3 P)AuX], [(Me2S)AuX], and inorganic compounds of gold in model reactions of indole and benzofuran synthesis. It was found that increased ionic character of the complexes was correlated with increased catalytic activity in the cyclization reactions. As a result, we developed an unprecedentedly active monoligand cationic [(THD-Dipp)Au]BF4 (1,3-bis(2,6-diisopropylphenyl)-3,4,5,6-tetrahydrodiazepin-2-ylidene gold(I) tetrafluoroborate) catalyst bearing seven-membered-ring carbene and bulky Dipp substituents. Quantitative yields of cyclized products were attained in several minutes at room temperature at 1 mol % catalyst loadings. The experimental observations were rationalized and fully supported by DFT calculations.
通过不同的合成方法合成了一系列六元环和七元环的扩环N-杂环卡宾（er-NHC）金（I）配合物。在溶液中生成了带有弱配位阴离子的配合物[(er-NHC)AuX]（X(-)=BF4(-)、NTf2(-)、OTf(-)）。根据它们的(13)C NMR光谱，配合物的离子特性按X(-)=Cl(-)<NTf2(-)<OTf(-)<BF4(-)的顺序增加。阳离子配合物稳定化的其他因素是NHC环的扩环以及在氮原子上连接庞大的取代基。这些er-NHC是比传统NHC以及膦和硫化物更大的配体和更强的电子供体，并且能为[(L)Au(+)]阳离子提供更多的稳定性。对五元、六元和七元卡宾配合物[(NHC)AuX]、[(Ph3P)AuX]、[(Me2S)AuX]以及金的无机化合物在吲哚和苯并呋喃合成的模型反应中的催化活性进行了比较研究。发现配合物离子特性的增加与环化反应中催化活性的增加相关。结果，我们开发了一种前所未有的活性单配体阳离子[(THD-Dipp)Au]BF4（1,3-双(2,6-二异丙基苯基)-3,4,5,6-四氢二氮杂环庚三烯-2-亚基金（I）四氟硼酸盐）催化剂，其带有七元环卡宾和庞大的Dipp取代基。在室温下，以1 mol %的催化剂负载量，几分钟内即可获得环化产物的定量产率。密度泛函理论（DFT）计算对实验观察结果进行了合理解释并提供了充分支持。
