The effect of anions in the synthesis and structure of pyrazolylamidino copper(II) complexes.

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(HNC(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)(HNC(Me)pz)] (3) and [CuCl(HNC(Et)pz)] (4). Four more new complexes, [Cu(μ-Cl)(HNC(Me)pz)(pzH)][X] (X = ClO, 5 and BF, 9) and [Cu(μ-Cl)(HNC(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. HNC(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(HNC(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.