Zhang Guoqi, Zeng Haisu, Zadori Nora, Marino Camila, Zheng Shengping, Neary Michelle C
Department of Sciences, John Jay College and PhD Program in Chemistry, The Graduate Center of the City University of New York New York 10019 NY USA
Department of Chemistry, Hunter College, The City University of New York New York 10065 NY USA.
RSC Adv. 2023 Sep 22;13(40):28089-28096. doi: 10.1039/d3ra06113b. eCollection 2023 Sep 18.
Homoleptic complexes adopting octahedral coordination modes are usually less active in catalysis due to the saturated coordination around metal centers that prevents substrate activation in a catalytic event. In this work, we demonstrated that a homoleptic octahedral cobalt complex (1) of 4'-pyridyl-2,2';6',2''-terpyridine that experienced monoprotonation at the non-coordinating pyridyl moiety upon crystallization could serve as a highly efficient precatalyst for the hydroboration of styrene derivatives with Markovnikov selectivity. The solid-state structure of this precatalyst along with relevant homoleptic Co and Fe complexes has been characterized by X-ray crystallography. In the solid state, 1 features one-dimensional hydrogen-bonded chains that are further stacked by interchain π⋯π interactions. The newly synthesized complexes (1-3) along with several known analogues (4-6) were examined as precatalysts for the hydroboration of alkenes. The best-performing system, 1/KOBu was found to promote Markovnikov hydroboration of substituted styrenes with high turnover frequencies (TOFs) up to ∼47 000 h, comparable to the most efficient polymeric catalyst [Co(pytpy)Cl] reported to date. Although some limitations in substrate scope as well as functional group tolerance exist, the catalyst shows good promise for several relevant hydrofunctionaliation reactions.
由于金属中心周围的饱和配位阻止了催化过程中底物的活化，采用八面体配位模式的均配配合物在催化中通常活性较低。在这项工作中，我们证明了一种4'-吡啶基-2,2';6',2''-三联吡啶的均配八面体钴配合物（1），在结晶时非配位吡啶部分发生单质子化，可作为苯乙烯衍生物进行马氏选择性硼氢化反应的高效前催化剂。通过X射线晶体学对该前催化剂以及相关的均配钴和铁配合物的固态结构进行了表征。在固态中，1具有一维氢键链，通过链间π⋯π相互作用进一步堆积。将新合成的配合物（1-3）以及几种已知类似物（4-6）作为烯烃硼氢化反应的前催化剂进行了研究。发现性能最佳的体系1/KOBu能以高达约47000 h的高周转频率（TOF）促进取代苯乙烯的马氏硼氢化反应，与迄今为止报道的最有效的聚合物催化剂[Co(pytpy)Cl]相当。尽管底物范围和官能团耐受性存在一些限制，但该催化剂在几个相关的加氢官能化反应中显示出良好的前景。
