Role of Ligand to Control the Mechanism of Nitric Oxide Reduction of Copper(II) Complexes and Ligand Nitrosation

详细信息    查看全文

• 作者：Apurba Kalita ; Pankaj Kumar ; Ramesh C. Deka ; Biplab Mondal
• 刊名：Inorganic Chemistry
• 出版年：2011
• 出版时间：December 5, 2011
• 年：2011
• 卷：50
• 期：23
• 页码：11868-11876
• 全文大小：416K
• 年卷期：v.50,no.23(December 5, 2011)
• ISSN：1520-510X

文摘

The nitric oxide reactivity of two copper(II) complexes, 1 and 2 with ligands L₁ and L₂, respectively, [L₁ = 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane, L₂ = 5,5,7-trimethyl-[1,4]-diazepane] have been studied. The copper(II) center in complex 1 was found to be unreactive toward nitric oxide in pure acetonitrile; however, it displayed reduction in methanol solvent in presence of base. The copper(II) center in 2, in acetonitrile solvent, on exposure to nitric oxide has been found to be reduced to copper(I). The same reduction was observed in methanol, also, in case of complex 2. In case of complex 1, presumably, the attack of nitric oxide on the deprotonated amine is the first step, followed by electron transfer to the copper(II) center to afford the reduction. Alternatively, first NO coordination to the Cu(II) followed by NO⁺ migration to the secondary amine is the most probable in case of complex 2. The observation of the transient intermediate in UV鈥搗isible and FT-IR spectroscopy prior to reduction in case of complex 2 also supports this possibility. In both cases, the reduction resulted into N-nitrosation; in 1, only mononitrosation was observed whereas complex 2 afforded dinitrosation as major product along with a minor amount of mononitrosation. Thus, it is evident from the present study that the macrocyclic ligands prefer the deprotonation pathway leading to mononitrosation; whereas nonmacrocyclic ones prefer the [Cu^II鈥揘O] intermediate pathway resulting into nitrosation at all the available sites of the ligand as major product.