Metal complexes of sterically hindered pyrazolylpyridines. The single crystal X-ray structure of [Cu(L1)2]BF4 (L1=1-{pyrid-2-yl}-3-{2′,5′-dimethoxyphenyl} pyrazole)

Article abstract of DOI:10.1016/S0277-5387(97)00228-3

Reaction of potassium 3{5}-(3′,4′-dimethoxyphenyl)pyrazolide with 2-bromopyridine in diglyme at 130°C for 3 days followed by an aqueous quench, affords 1-{pyrid-2-yl}-3-{3′,4′-dimethoxyphenyl}pyrazole (L²) in 69% yield after recrystallisation from hot hexanes. Complexation of [Cu(NCMe)₄]BF₄ by 2 molar equivalents of 1-{pyrid-2-yl}-3-{2′,5′-dimethoxyphenyl}pyrazole (L¹) or L² in MeCN at room temperature, followed by concentration and crystallisation with Et₂O, gives [Cu(L)₂]BF₄ (L=L¹, L²) in good yields. Treatment of AgBF₄ with L¹ or L² in MeNO₂ similarly gives [Ag(L)₂]BF₄ (L=L¹, L²); reaction of AgBF₄ with L² in MeCN gives a product of stoichiometry [Ag(L²)(NCMe)]BF₄. The ¹H NMR spectra of the [M(L)₂]BF₄ complexes show peaks arising from a single coordinated ligand environment. The single crystal X-ray structure of [Cu(L¹)₂]BF₄ shows a tetrahedral complex cation with Cu-N=2.011(8), 2.036(8), 2.039(8), 2.110(8) A. The Cu¹ centre is close to tetrahedral, the dihedral angle between the least-squares planes formed by the Cu atom and the N donor atoms of the two ligands being 88.3(3)°. Complexation of hydrated Cu(BF₄)₂ by L² in MeCN at room temperature yields [Cu(L²)₂](BF₄)₂. The cyclic voltammograms of the three Ag¹ complexes in MeCN/0.1 M Buⁿ₄ NPF₆ are suggestive of extensive ligand dissociation in this solvent.