Mechanistic Insights into the Formation of N2O by a Nickel Nitrosyl Complex

Reaction of [Ni­(NO)­(bipy)­(Me2phen)]­[PF6] with 1 equiv of nitric oxide (NO) in CH2Cl2 results in the formation of N2O and [{(Me2phen)­Ni­(NO)}2(μ–η1-N:η1-O)-NO2)]­[PF6] (3), along with the known complex, [Ni­(bipy)3]­[PF6]2 (4). The isolation of complex 3, which contains a nitrite ligand, demonstrates that the reaction of [Ni­(NO)­(bipy)­(Me2phen)]­[PF6] with exogenous NO results in NO disproportionation and not NO reduction. Complex 3 could also be accessed by reaction of [Ni­(NO)­(Me2phen)]­[PF6] (5) with (Me2phen)­Ni­(NO)­(NO2) (7) in good yield. Complexes 3, 5, and 7 were fully characterized, including analysis by X-ray crystallography in the case of 3 and 7. Furthermore, addition of 0.5 equiv of bipy to [Ni­(NO)­(bipy)]­[PF6] results in formation of the hyponitrite complex, [{(bipy)­Ni­(κ2-O2N2)}­η1:η1-N,N-{Ni­(NO)­(bipy)}2]­[PF6]2 (9), in modest yield. Importantly, the hyponitrite ligand in 9 is thought to form via coupling of two NO– ligands and not by coupling of a nucleophilic nitrosyl ligand (NO–) with an electrophilic nitrosyl ligand (NO+). X-ray crystallography reveals that complex 9 features a new binding mode of the cis-hyponitrite ligand.

将配合物[Ni(NO)(2,2'-联吡啶(bipy))(二甲基-1,10-邻菲啰啉(Me2phen))]六氟磷酸盐与1当量的一氧化氮(NO)在二氯甲烷(CH2Cl2)中反应，生成一氧化二氮(N2O)和[{(Me2phen)Ni(NO)}₂(μ–η¹-N:η¹-O)-NO₂)]六氟磷酸盐(3)，同时得到已知配合物[Ni(bipy)₃][PF₆]₂(4)。分离得到的配合物3含有亚硝酸盐配体(nitrite ligand)，这证实[Ni(NO)(bipy)(Me2phen)][PF₆]与外源性NO的反应发生的是NO的歧化反应，而非NO还原反应。配合物3亦可通过配合物[Ni(NO)(Me2phen)][PF₆](5)与(Me2phen)Ni(NO)(NO₂)(7)反应，以良好产率制备得到。对配合物3、5和7开展了全面表征，其中配合物3和7通过X射线晶体衍射(X-ray crystallography)完成了结构解析。此外，向[Ni(NO)(bipy)][PF₆]中加入0.5当量的联吡啶，可得到中等产率的连二次硝酸根配体(hyponitrite ligand)配合物[{(bipy)Ni(κ²-O₂N₂)}η¹:η¹-N,N-{Ni(NO)(bipy)}₂][PF₆]₂(9)。值得注意的是，配合物9中的连二次硝酸根配体被认为是通过两个NO⁻配体的偶联形成，而非亲核型亚硝酰配体(NO⁻)与亲电型亚硝酰配体(NO⁺)的偶联。X射线晶体衍射分析表明，配合物9展现出顺式连二次硝酸根配体的一种新型配位模式。