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

Abstract

Keywords: Zinc / Lithium / Calcium / Magnesium / N ligands 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(SiMe 3 ) 2 , PhLi, ZnMe 2 , and ZnEt 2 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 rea-

Gold(I)‐Catalysed Alkene Cycloaddition Reactions of Propargyl Acetals

“…Small aggregates, being soluble in common organic solvents, can be achieved if large substituents were kept at the central metal atoms as, for example, in dimeric bis[bis(trimethylsilyl)methylzinc 3, 5‐bis(2‐pyridyl)pyrazolate] 8. In order to ensure solubility in organic solvents, we investigated 5‐(2‐pyridyl)pyrazolates with phenyl9 and thienyl groups10 in 3‐position, which represent weak and soft Lewis‐bases. Herein we extend our investigations on 3‐(2‐furanyl)‐ ( 1 ),10 3‐(1‐adamantyl)‐ ( 2 ), and 3‐ferrocenyl‐5‐(2‐pyridyl)pyrazole ( 3 )11 with 3‐positioned substituents with significantly different steric and electronic properties.…”

“…In order to ensure solubility in organic solvents, we investigated 5‐(2‐pyridyl)pyrazolates with phenyl9 and thienyl groups10 in 3‐position, which represent weak and soft Lewis‐bases. Herein we extend our investigations on 3‐(2‐furanyl)‐ ( 1 ),10 3‐(1‐adamantyl)‐ ( 2 ), and 3‐ferrocenyl‐5‐(2‐pyridyl)pyrazole ( 3 )11 with 3‐positioned substituents with significantly different steric and electronic properties. Quantum chemical calculations on monomeric 3‐phenyl‐5‐(2‐pyridyl)pyrazole showed that a hydrogen bridge between the pyridyl and the pyrazole units stabilizes a cis conformation.…”

“…The dimethylformamide complex of lithium 5‐(2‐pyridyl)pyrazolate crystallized as a one‐dimensional polymer with tetra‐coordinate alkali metal ions 17. Substituents in 3‐position of the 5‐(2‐pyridyl)pyrazolate anion lead to the formation of discrete dimers in the crystalline state (R/L = Ph/thf,9 R/L = thienyl/thf10). The use of 1, 4‐dioxane (diox) allows to connect these dimers by bridging ether molecules 10.…”

“…Substituents in 3‐position of the 5‐(2‐pyridyl)pyrazolate anion lead to the formation of discrete dimers in the crystalline state (R/L = Ph/thf,9 R/L = thienyl/thf10). The use of 1, 4‐dioxane (diox) allows to connect these dimers by bridging ether molecules 10. In all cases, the cations are bound between the pyridyl and the pyrazolato bases of a cis‐5‐(2‐pyridyl)pyrazolate anion.…”

“…Unsubstituted zinc bis(pyrazolate) forms coordination polymers,18 whereas 5‐(2‐pyridyl)pyrazolates crystallize as dimeric molecules with the zinc atoms in the 5‐(2‐pyridyl)pyrazolate pockets 8–10. The pyrazoles itself act as monodentate Lewis‐bases and are able to stabilize small zinc complexes 19…”