3-Phenyl-5-(2-pyridyl)pyrazolato Complexes of Lithium, Magnesium, Calcium, and Zinc

Abstract

Metalation of 3-phenyl-5-(2-pyridyl)pyrazole (HPz, 1) with alkyllithium and -zinc compounds in tetrahydrofuran (thf) yields dinuclear products [(thf)Li(Pz)] 2 (2) and [MeZn(Pz)] 2 (3), respectively. Magnesiation of 1 with diethylmagnesium in tetrahydrofuran in the presence of 1,4-dioxane leads to cocrystallization of mononuclear [(thf) 2 Mg(Pz) 2 ] (4a) and [(diox) 2 Mg(Pz) 2 ] (4b). Metalation of 1 with KH followed by a metathesis reaction with CaI 2 in tetrahydrofuran leads to the formation of dinuclear [{(thf) 2 Ca}(µ-Pz) 3 Ca(Pz)] (5) with the calcium atoms in different coordination environments. The ligand precursor 1 crystallizes as a dimer with N-H· · ·N bridges between the pyrazole fragments. The pyrazolate anions of the metal complexes 2 to 5 exhibit similar structural parameters regardless of a bridging or terminal coordination mode and the electronegativity of the coordinated metal.

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

“…Due to this aggregation behavior, the ferrocenyl moieties are able to freely rotate and to not interfere with neighboring groups. This structural principle was also found for 3‐thienyl‐5‐(2‐pyridyl)pyrazole10 and 3, 5‐bis(2‐pyridyl)pyrazole,10,20 whereas 3‐phenyl‐5‐(2‐pyridyl)pyrazole dimerizes by intermolecular hydrogen bridges only between pyrazole nitrogen atoms 9…”

“…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.…”

“…A tautomeric form with an N–H bond at the pyridyl moiety is much higher in energy because this bonding situation involves a break‐up of aromaticity of the pyridyl group 12. In the solid state this pyrazole dimerizes by intermolecular hydrogen bridges between the pyrazole nitrogen atoms 9. Quantum chemical calculations at the free 3‐phenyl‐5‐(2‐pyridyl)pyrazolate anion reveal that the trans isomer associated to rotation around the C–C bond between the pyridyl and pyrazolate rings is favored, whereas in monomeric sodium 3‐phenyl‐5‐(2‐pyridyl)pyrazolate a cis arrangement is preferred with the cation between the pyrazolate and the pyridyl bases and a η 2 ‐coordination mode to both of the pyrazolate nitrogen atoms seems to be disadvantageous 13…”

“…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.…”

Synthesis, Structures, and Spectroscopic Properties of 3‐Aryl‐5‐(2‐pyridyl)pyrazoles and Related Pyrazoles

“…On the one hand, aryl groups in 3‐position with different steric influence can be chosen; on the other hand, the aromatic aza ligand in 5‐position can be altered. Examples include pyrazoles with phenyl,8,9 2‐pyridyl,5,9 2‐(6‐methyl)pyridyl,10 thienyl,5 furanyl,5 and ferrocenyl groups11,12 in 3‐position and aromatic aza bases such as 2‐pyridyl,5,9 2‐(6‐methyl)pyridyl10 and pyrazinyl substituents13 in 5‐position. These derivatives represent precursor compounds for diverse metal complexes.…”