Hsieh Chang-Chih, Liao Po-Kuang, Chen Chia-Wei, Chiang Ming-Hsi, Horng Yih-Chern
Institute of Chemistry, Academia Sinica, Taipei 11528, Taiwan.
Department of Chemistry, National Changhua University of Education, Changhua 50058, Taiwan.
Dalton Trans. 2023 Apr 4;52(14):4429-4441. doi: 10.1039/d3dt00103b.
Six new pyrazolylamidino Cu(II) complexes are synthesized directly from the reactions of Cu(X) salts (X = ClO, BF, or Cl) and pyrazole (pzH) in nitrile solution (RCN, R = Me or Et) at 298 K the metal-mediated coupling of RCN with pzH: [Cu(HNC(R)pz)(X)] (X = ClO or BF, R = Me, 1 or 7 and Et, 2 or 8, respectively) and dichloro Cu(II) complexes [CuCl(μ-Cl)(HNC(Me)pz)] (3) and [CuCl(HNC(Et)pz)] (4). Four more new complexes, [Cu(μ-Cl)(HNC(Me)pz)(pzH)][X] (X = ClO, 5 and BF, 9) and [Cu(μ-Cl)(HNC(Et)pz)(pzH)(X)] (X = ClO, 6 and BF, 10), are obtained indirectly from the anion substitution reaction with Cl ions in 1 and 7, and 2 and 8, respectively. All complexes are characterized by EA, FTIR, UV-vis and EPR spectroscopy and X-ray crystallographic analyses. HNC(Et)pz or pzH is unobserved in both the nitrile-exchange reaction of 2 to -1 and the anion-substitution reaction of 2 to -5 in the CDCN solution. The H NMR results reveal that the pzH-RCN coupling is intramolecular and reversible on a Cu(II) center. The crystal structures of these complexes show diverse supramolecular assemblies through imino NH⋯anion hydrogen bonds and pyrazolylamidino pz-pz (π⋯π) and pz-Cu(II) (π⋯metal) interactions. EPR results suggest weak magnetic couplings between Cu(II) centers in the polynuclear Cu(II) complexes. The yield and rate of the formation of 1 are higher in the reaction of Cu(ClO) with a 4-fold molar excess of pzH compared with a 2-fold excess, indicating that [Cu(pzH)] is the more active species for pzH-RCN coupling. The highest rate for the formation of 1 is achieved when [Cu(pzH)(ClO)] is used in MeCN solution. Thus, a plausible synthetic path for synthesizing pyrazolylamidino Cu(II) complexes is established. An intermediate species, [Cu(HNC(Me)pz)(pzH)][ClO] (1a), is proposed for the synthetic process based on spectroscopic studies and DFT calculations. The reaction of [Cu(pzH)X] (X = ClO, Cl, NO, or BF) in MeCN solution suggests that the lability of coordinated anions upon nitrile substitution affects the rate of the formation of bis-pyrazolylamidino Cu(II) complexes.
通过铜（X）盐（X = ClO、BF或Cl）与吡唑（pzH）在腈溶液（RCN，R = Me或Et）中于298 K下直接反应合成了六种新型吡唑基脒铜（II）配合物：RCN与pzH的金属介导偶联反应：[Cu(HNC(R)pz)(X)]（X = ClO或BF，R = Me时为1或7，R = Et时为2或8）以及二氯铜（II）配合物[CuCl(μ-Cl)(HNC(Me)pz)]（3）和[CuCl(HNC(Et)pz)]（4）。另外四种新型配合物，[Cu(μ-Cl)(HNC(Me)pz)(pzH)][X]（X = ClO时为5，BF时为9）和[Cu(μ-Cl)(HNC(Et)pz)(pzH)(X)]（X = ClO时为6，BF时为10），分别通过在1和7以及2和8中与Cl离子的阴离子取代反应间接获得。所有配合物均通过元素分析（EA）、傅里叶变换红外光谱（FTIR）、紫外可见光谱（UV-vis）、电子顺磁共振光谱（EPR）以及X射线晶体学分析进行表征。在CDCN溶液中，2到 -1的腈交换反应和2到 -5的阴离子取代反应中均未观察到HNC(Et)pz或pzH。氢核磁共振（H NMR）结果表明，pzH-RCN偶联在铜（II）中心上是分子内的且可逆。这些配合物的晶体结构通过亚氨基NH⋯阴离子氢键以及吡唑基脒pz-pz（π⋯π）和pz-铜（II）（π⋯金属）相互作用展示出多样的超分子组装。电子顺磁共振结果表明多核铜（II）配合物中铜（II）中心之间存在弱磁耦合。与2倍过量相比，在Cu(ClO)与4倍摩尔过量的pzH反应中，1的产率和形成速率更高，表明[Cu(pzH)]是pzH-RCN偶联中更具活性的物种。当在乙腈溶液中使用[Cu(pzH)(ClO)]时，1的形成速率最高。因此，建立了一种合理的合成吡唑基脒铜（II）配合物的合成路径。基于光谱研究和密度泛函理论（DFT）计算，为合成过程提出了一种中间物种[Cu(HNC(Me)pz)(pzH)][ClO]（1a）。[Cu(pzH)X]（X = ClO、Cl、NO或BF）在乙腈溶液中的反应表明，腈取代时配位阴离子的不稳定性会影响双吡唑基脒铜（II）配合物的形成速率。
