Kaur Mandeep, U Din Reshi Noor, Patra Kamaless, Bhattacherya Arindom, Kunnikuruvan Sooraj, Bera Jitendra K
Department of Chemistry and Center for Environmental Sciences and Engineering, Indian Institute of Technology Kanpur, Kanpur, 208016, India.
School of Chemistry, Indian Institute of Science Education and Research Thiruvananthapuram, Vithura, Thiruvananthapuram, 695551, India.
Chemistry. 2021 Jul 21;27(41):10737-10748. doi: 10.1002/chem.202101360. Epub 2021 Jun 8.
A CpIr(III) complex (1) of a newly designed ligand L featuring a proton-responsive pyridyl(benzamide) appended on N-heterocyclic carbene (NHC) has been synthesized. The molecular structure of 1 reveals a dearomatized form of the ligand. The protonation of 1 with HBF in tetrahydrofuran gives the corresponding aromatized complex [CpIr(L H)Cl]BF (2). Both compounds are characterized spectroscopically and by X-ray crystallography. The protonation of 1 with acid is examined by H NMR and UV-vis spectra. The proton-responsive character of 1 is exploited for catalyzing α-alkylation of ketones and β-alkylation of secondary alcohols using primary alcohols as alkylating agents through hydrogen-borrowing methodology. Compound 1 is an effective catalyst for these reactions and exhibits a superior activity in comparison to a structurally similar iridium complex [Cp*Ir(L )Cl]PF (3) lacking a proton-responsive pendant amide moiety. The catalytic alkylation is characterized by a wide substrate scope, low catalyst and base loadings, and a short reaction time. The catalytic efficacy of 1 is also demonstrated for the syntheses of quinoline and lactone derivatives via acceptorless dehydrogenation, and selective alkylation of two steroids, pregnenolone and testosterone. Detailed mechanistic investigations and DFT calculations substantiate the role of the proton-responsive ligand in the hydrogen-borrowing process.
合成了一种新设计配体L的CpIr(III)配合物(1)，该配体在N-杂环卡宾(NHC)上连接了质子响应性吡啶基(苯甲酰胺)。1的分子结构显示配体为去芳构化形式。1在四氢呋喃中与HBF质子化得到相应的芳构化配合物[CpIr(L H)Cl]BF(2)。两种化合物均通过光谱和X射线晶体学进行了表征。通过1H NMR和紫外可见光谱研究了1用酸的质子化情况。利用1的质子响应特性，通过借氢方法以伯醇为烷基化剂催化酮的α-烷基化和仲醇的β-烷基化。化合物1是这些反应的有效催化剂，与缺乏质子响应性酰胺侧基的结构相似的铱配合物[Cp*Ir(L )Cl]PF(3)相比，表现出更高的活性。催化烷基化的特点是底物范围广、催化剂和碱负载量低、反应时间短。1的催化效果还体现在通过无受体脱氢合成喹啉和内酯衍生物，以及对两种甾体化合物孕烯醇酮和睾酮的选择性烷基化反应中。详细的机理研究和密度泛函理论计算证实了质子响应性配体在借氢过程中的作用。
