3-(2-Pyridyl)-5-(2-thienyl)pyrazole and Complexes of Its Anion with Lithium, Magnesium, Calcium, and Zinc Ions



5-(2-Furanyl)-3-(2-pyridyl)pyrazole (1) and 3-(2-pyridyl)-5-(2-thienyl)pyrazole (2) oligomerize through hydrogen bridges in the solid state to yield tetramers and dimers, respectively. The pyrazole units are very acidic and, therefore, deprotonation of 2 with the organometallic reagents LiN(SiMe3)2, PhLi, ZnMe2, and ZnEt2 allows the synthesis of (tetrahydrofuran)lithium 3-(2-pyridyl)-5-(2-thienyl)pyrazolate (3a), bis[methylzinc 3-(2-pyridyl)-5-(2-thienyl)pyrazolate] (4a), and bis[ethylzinc 3-(2-pyridyl)-5-(2-thienyl)pyrazolate] (4b). Recrystallization of 3a in the presence of 1,4-dioxane yields catena-[(1,4-dioxane)lithium 3-(2-pyridyl)-5-(2-thienyl)pyrazolate] (3b). Magnesiation of 2 yields different products depending on the organometallic magnesium reagent applied. The use of butylmagnesium chloride gives tris(tetrahydrofuran)magnesium chloride 3-(2-pyridyl)-5-(2-thienyl)pyrazolate (5). Employment of the diphenylmagnesium–1,4-dioxane complex leads to the formation of bis(tetrahydrofuran)magnesium bis[3-(2-pyridyl)-5-(2-thienyl)pyrazolate] (6), whereas the more aggressive diethylmagnesium–1,4-dioxane complex also metalated the thienyl substituent to yield bis[bis(tetrahydrofuran)magnesium 3-(2-pyridyl)-5-(2-thienyl-5-ide)pyrazolate] (7). A trinuclear calcium complex, tris(tetrahydrofuran)tricalcium μ3-hydroxide iodide tetrakis[3-(2-pyridyl)-5-(2-thienyl)pyrazolate] (8), is isolated after calciation of 2 and inadvertent hydrolysis during recrystallization.