Singh Vivek Kumar, Donthireddy S N R, Illam Praseetha Mathoor, Rit Arnab
Department of Chemistry, Indian Institute of Technology, Madras, Chennai 600036, India.
Dalton Trans. 2020 Sep 1;49(34):11958-11970. doi: 10.1039/d0dt02142c.
Dialkylation of the 1,3-bis(1,2,4-triazol-1-yl)benzene with ethyl bromide results in the formation of [L-H2]Br2 which, upon salt metathesis with NH4PF6, readily yields the bis(triazolium) salt L-H22 with non-coordinating counterions. L-H22 and Ag2O react in a 1 : 1 ratio to yield a binuclear AgI-tetracarbene complex of the composition (L)2Ag22 which undergoes a facile transmetalation reaction with [Cu(SMe2)Br] to deliver the corresponding CuI-NHC complex (L)2Cu22. In contrast, the [L-H2]Br2 reacts with [Ir(Cp*)Cl2]2 to generate a doubly C-H activated IrIII-NHC complex 5. Similarly, the triazolinylidene donor supported diorthometalated RuII-complex 6 is also obtained. Complexes 5 and 6 represent the first examples of a stable diorthometalated binuclear IrIII/RuII-complex supported by 1,2,4-triazolin-5-ylidene donors. The synthesized IrIII-NHC complex 5 is found to be more effective than its RuII-analogue (6) for the reduction of a range of alkenes/alkynes via the transfer hydrogenation strategy. Conversely, RuII-complex 6 is identified as an efficient catalyst (0.01 mol% loading) for the β-alkylation of a wide range of secondary alcohols using primary alcohols as alkylating partners via a borrowing hydrogen strategy.
1,3 - 双（1,2,4 - 三唑 - 1 - 基）苯与溴乙烷进行二烷基化反应生成[L - H₂]Br₂，[L - H₂]Br₂与NH₄PF₆进行盐复分解反应后，容易生成具有非配位抗衡离子的双（三唑鎓）盐L - H₂₂。L - H₂₂与Ag₂O以1∶1的比例反应，生成组成为(L)₂Ag₂₂的双核AgI - 四卡宾配合物，该配合物与[Cu(SMe₂)Br]发生容易的金属转移反应，生成相应的CuI - NHC配合物(L)₂Cu₂₂。相比之下，[L - H₂]Br₂与[Ir(Cp*)Cl₂]₂反应生成双C - H活化的IrIII - NHC配合物5。类似地，还得到了三唑啉亚基供体支持的邻位金属化RuII - 配合物6。配合物5和6代表了由1,2,4 - 三唑啉 - 5 - 亚基供体支持的稳定的邻位金属化双核IrIII/RuII - 配合物的首例。发现合成的IrIII - NHC配合物5通过转移氢化策略还原一系列烯烃/炔烃时比其RuII类似物（6）更有效。相反，RuII - 配合物6被确定为一种高效催化剂（负载量0.01 mol%），用于通过借氢策略使用伯醇作为烷基化试剂对多种仲醇进行β - 烷基化反应。
