O₂-Dependent Aliphatic Carbon−Carbon Bond Cleavage Reactivity in a Ni(II) Enolate Complex Having a Hydrogen Bond Donor Microenvironment; Comparison with a Hydrophobic Analogue

A mononuclear Ni(II) complex having an acireductone type ligand, and supported by the bnpapa (N,N-bis((6-neopentylamino-2-pyridyl)methyl)-N-((2-pyridyl)methyl)amine) ligand, [(bnpapa)Ni(PhC(O)C(OH)C(O)Ph)]ClO4 (14), has been prepared and characterized by elemental analysis, 1H NMR, FTIR, and UV−vis. To gain insight into the 1H NMR features of 14, the air stable analogue complexes [(bnpapa)Ni(CH3C(O)CHC(O)CH3)]ClO4 (16) and [(bnpapa)Ni(ONHC(O)CH3)]ClO4 (17) were prepared and characterized by X-ray crystallography, 1H NMR, FTIR, UV−vis, mass spectrometry, and solution conductivity measurements. Compounds 16 and 17 are 1:1 electrolyte species in CH3CN. 1H and 2H NMR studies of 14, 16, and 17 and deuterated analogues revealed that the complexes having six-membered chelate rings for the exogenous ligand (14 and 16) do not have a plane of symmetry within the solvated cation and thus exhibit more complicated 1H NMR spectra. Compound 17, as well as other simple Ni(II) complexes of the bnpapa ligand (e.g., [(bnpapa)Ni(ClO4)(CH3CN)]ClO4 (18) and [(bnpapaNi)2(μ-Cl)2](ClO4)2 (19)), exhibit 1H NMR spectra consistent with the presence of a plane of symmetry within the cation. Treatment of [(bnpapa)Ni(PhC(O)C(OH)C(O)Ph)]ClO4 (14) with O2 results in aliphatic carbon−carbon bond cleavage within the acireductone-type ligand and the formation of [(bnpapa)Ni(O2CPh)]ClO4 (9), benzoic acid, benzil, and CO. Use of 18O2 in the reaction gives high levels of incorporation (>80%) of one labeled oxygen atom into 9 and benzoic acid. The product mixture and level of 18O incorporation in this reaction is different than that exhibited by the analogue supported the hydrophobic 6-Ph2TPA ligand, [(6-Ph2TPA)Ni(PhC(O)C(OH)C(O)Ph)]ClO4 (2). We propose that this difference is due to variations in the reactivity of bnpapa- and 6-Ph2TPA-ligated Ni(II) complexes with triketone and/or peroxide species produced in the reaction pathway.以bnpapa（N,N-双((6-新戊基氨基-2-吡啶基)甲基)-N-((2-吡啶基)甲基)胺）为配体、负载有酰还原酮型配体的单核镍(II)配合物[(bnpapa)Ni(PhC(O)C(OH)C(O)Ph)]ClO4（编号14）已被合成，并通过元素分析、氢核磁共振（1H NMR）、傅里叶变换红外光谱（FTIR）以及紫外-可见吸收光谱（UV−vis）进行了表征。为深入探究配合物14的氢核磁共振谱特征，我们合成了两种空气稳定的类似物配合物[(bnpapa)Ni(CH3C(O)CHC(O)CH3)]ClO4（编号16）与[(bnpapa)Ni(ONHC(O)CH3)]ClO4（编号17），并通过X射线晶体衍射、氢核磁共振、傅里叶变换红外光谱、紫外-可见吸收光谱、质谱以及溶液电导率测试对其进行了表征。配合物16与17在乙腈（CH3CN）中属于1:1型电解质物种。对配合物14、16、17及其氘代类似物开展的氢核磁共振与氘核磁共振（2H NMR）研究表明，带有外源性配体六元螯合环的配合物（14与16）在溶剂化阳离子内部不存在对称面，因此其氢核磁共振谱图更为复杂。配合物17，以及其他以bnpapa为配体的简单镍(II)配合物（例如[(bnpapa)Ni(ClO4)(CH3CN)]ClO4（编号18）与[(bnpapaNi)2(μ-Cl)2](ClO4)2（编号19））的氢核磁共振谱图均与阳离子内部存在对称面的情况相符。将配合物[(bnpapa)Ni(PhC(O)C(OH)C(O)Ph)]ClO4（编号14）与氧气（O2）反应，会导致酰还原酮型配体发生脂肪族碳-碳键断裂，同时生成[(bnpapa)Ni(O2CPh)]ClO4（编号9）、苯甲酸、联苯甲酰与一氧化碳（CO）。在反应中使用氧-18（18O2）时，有超过80%的标记氧原子会被掺入到配合物9与苯甲酸中。该反应的产物组成与氧-18掺入率，与以疏水性6-Ph2TPA为配体的类似物配合物[(6-Ph2TPA)Ni(PhC(O)C(OH)C(O)Ph)]ClO4（编号2）的反应结果存在差异。我们认为，该差异源于以bnpapa与6-Ph2TPA为配体的镍(II)配合物，与反应路径中生成的三酮和/或过氧化物物种的反应活性存在差异。