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

Abstract

3‐Aryl‐5‐(2‐pyridyl)pyrazoles and related compounds are easily accessible via the reaction of the appropriate 1,3‐diketone with hydrazine hydrate. The central pyrazole rings show a far‐reaching equalization of the bond lengths. In the crystalline state dimeric and strand‐like structures are observed due to the formation of intermolecular N–H···N hydrogen bridges between the pyrazole N–H functionality and a pyrazole or pyridyl base. The structures mainly depend on the steric demand of the aryl groups. Planar 3‐aryl‐5‐(2‐pyridyl)pyrazoles also show π stacking reducing the solubility in common organic solvents.

Stabilization of a Snub Bisphenoidal Environment of Strontium in Bis[3‐(1‐naphthyl)‐5‐(2‐pyridyl)‐2H‐pyrazole]strontium Bis[3‐(1‐naphthyl)‐5‐(2‐pyridyl)pyrazolate] by Strong Hydrogen Bridges

“…Selected bond lengths of complex 2 are summarized in Table 1 and compared with the values of the starting material 3‐(1‐naphthyl)‐5‐(2‐pyridyl)‐2 H ‐pyrazole ( 1 ). This pyrazole crystallizes as a one‐dimensional polymer with intermolecular hydrogen bridges between pyrazole and 2‐pyridyl bases 37. In the strontium complex 2 the bridging hydrogen atoms between the ligands A and C as well as ligands B and D were refined isotropically.…”

“…Decomposition points were measured with a Reichert‐Jung Apparatus Type 302102. [(thf) 2 Sr{N(SiMe 3 ) 2 } 2 ]47,48 and pyrazole 1 37 were prepared according to literature procedures.…”

Manganese(I)-Based CORMs with 5-Substituted 3-(2-Pyridyl)Pyrazole Ligands

“…In this study, we present a flexible modular system that allows to attach diverse functional groups at the periphery of 3-(2-pyridyl)pyrazole ligands which are known to act as strong bidentate Lewis bases [31] whereas the central manganese carbonyl unit remains nearly unaffected. Based on our extensive experience with 5-substituted 3-(2-pyridyl)pyrazoles (2-PyPz R H, 1; see Scheme 1 [32,33]), we screened manganese(I)-based photoCORMs with these bidentate ligands at a 14-electron (OC)3MnBr moiety to demonstrate the variability of this substance class. Scheme 1.…”