Department of Chemistry, University of Utah, 315 South 1400 East, Salt Lake City, Utah 84112-0850, USA.
J Am Chem Soc. 2012 Sep 12;134(36):15154-62. doi: 10.1021/ja3075924. Epub 2012 Sep 4.
The reaction of Ni(COD)(2), IPr, and nitrile affords dimeric Ni(IPr)RCN in high yields. X-ray analysis revealed these species display simultaneous η(1)- and η(2)-nitrile binding modes. These dimers are catalytically competent in the formation of pyridines from the cycloaddition of diynes and nitriles. Kinetic analysis showed the reaction to be first order in Ni(IPr)RCN, zeroth order in added IPr, zeroth order in nitrile, and zeroth order in diyne. Extensive stoichiometric competition studies were performed, and selective incorporation of the exogenous, not dimer bound, nitrile was observed. Post cycloaddition, the dimeric state was found to be largely preserved. Nitrile and ligand exchange experiments were performed and found to be inoperative in the catalytic cycle. These observations suggest a mechanism whereby the catalyst is activated by partial dimer-opening followed by binding of exogenous nitrile and subsequent oxidative heterocoupling.
Ni(COD)(2)、IPr 和腈反应以高产率得到二聚体Ni(IPr)RCN。X 射线分析表明这些物种显示出同时的 η(1)-和 η(2)-腈结合模式。这些二聚体在炔烃和腈的环加成反应中形成吡啶时具有催化活性。动力学分析表明反应对Ni(IPr)RCN呈一级反应，对加入的 IPr 呈零级反应，对腈呈零级反应，对炔烃呈零级反应。进行了广泛的化学计量竞争研究，观察到了外源性、非二聚体结合腈的选择性掺入。加成后，发现二聚体状态基本保持。进行了腈和配体交换实验，发现它们在催化循环中不起作用。这些观察结果表明，该催化剂的活化机制是部分二聚体打开，然后结合外源性腈，随后进行氧化杂偶联。
