Department of Chemistry, Wayne State University, 5101 Cass Ave, Detroit, MI 48202, USA.
Dalton Trans. 2018 Nov 21;47(43):15353-15363. doi: 10.1039/c8dt03405b. Epub 2018 Oct 3.
This work focuses on the application of dicobalt octacarbonyl (Co(CO)) as a metal precursor in the chemistry of formally low-valent cobalt with redox-active bis(imino)pyridine [NNN] ligands. The reactions of both mononucleating mesityl-substituted bis(aldimino)pyridine (L) and dinucleating macrocyclic xanthene-bridged di(bis(aldimino)pyridine) (L) with Co(CO) were investigated. Independent of the metal-to-ligand ratio (1 : 1 or 1 : 2 ligand to Co(CO)), the reaction of the dinucleating ligand L with Co(CO) produces a tetranuclear complex [Co(L)(CO)] featuring two discrete [CoNNN] units. In contrast, a related mononucleating bis(aldimino)pyridine ligand, L, produces different species at different ligand to Co(CO) ratios, including dinuclear [Co(CO)(L)] and zwitterionic [Co(L)][Co(CO)]. Interestingly, [Co(L)(CO)] features metal-metal bonds, and no bridging carbonyls, whereas [Co(CO)(L)] contains cobalt centers bridged by one or two carbonyl ligands. In either case, treatment with excess acetonitrile leads to disproportionation to the zwitterionic [CoNNN][Co(CO)] units. The electronic structures of the complexes described above were studied with density functional theory. All the obtained bis(imino)pyridine complexes serve as catalysts for cyclotrimerization of methyl propiolate, albeit their reactivity is inferior compared with Co(CO).
这项工作专注于二羰基合钴（Co(CO)）作为具有氧化还原活性双（亚胺基）吡啶[NNN]配体的形式低价钴化学中的金属前体的应用。研究了单核取代的均三甲苯基双（亚胺基）吡啶（L）和双核大环香豆素桥联二（双（亚胺基）吡啶）（L）与 Co(CO)的反应。独立于金属与配体的比例（1：1 或 1：2 配体与 Co(CO)），双核配体 L 与 Co(CO)的反应产生了一种具有两个离散[CoNNN]单元的四核配合物[Co(L)(CO)]。相比之下，相关的单核双（亚胺基）吡啶配体 L 在不同的配体与 Co(CO)的比例下产生不同的物种，包括双核[Co(CO)(L)]和两性离子[Co(L)][Co(CO)]。有趣的是，[Co(L)(CO)]具有金属-金属键，没有桥接羰基，而[Co(CO)(L)]含有由一个或两个羰基配体桥接的钴中心。在任何情况下，用过量的乙腈处理都会导致歧化反应生成两性离子[CoNNN][Co(CO)]单元。上述配合物的电子结构用密度泛函理论进行了研究。所有获得的双（亚胺基）吡啶配合物都可用作甲基丙炔酸酯的环三聚反应的催化剂，尽管它们的反应性不如 Co(CO)。
