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Abstract:The reaction of [(OC) 5 MnBr] with substituted 3-(2-pyridyl)pyrazoles) 2-PyPz R H (1a-l) in methanol or diethyl ether yields the yellow to orange manganese(I) complexes, and 1-adamantyl (l). The carbonyl ligands are arranged facially, leading to three chemically different CO ligands due to different trans-positioned Lewis donors. The diversity of the substituent R demonstrates that this photoCORM backbone can easily be varied with a negligible influence on the central (OC) 3 MnBr fragment, because the structural parameters and the spectroscopic data of this unit are very similar for all these derivatives. Even the ferrocenyl complex 2k shows a redox potential for the ferrocenyl subunit which is identical to the value of the free 5-ferrocenyl-3-(2-pyridyl)pyrazole (1k). The ease of variation of the starting 5-substituted 3-(2-pyridyl)pyrazoles) offers a modular system to attach diverse substituents at the periphery of the photoCORM complex.

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3‐(2‐Furanyl)‐5‐(2‐pyridyl)pyrazole (1) and 3‐(1‐adamantyl)‐5‐(2‐pyridyl)pyrazole (2) crystallize as hydrogen‐bridged tetrameric molecules, whereas 3‐ferrocenyl‐5‐(2‐pyridyl)pyrazole (3) forms hydrogen‐bridged dimers in the solid state. Deprotonation of the appropriate pyrazole with n‐butyllithium in ethereal solvents or with diethylzinc yields the dimers of (η1‐1, 2‐dimethoxyethane)lithium 3‐(2‐furanyl)‐5‐(2‐pyridyl)pyrazolate (4), (η1‐1, 4‐dioxane)lithium 3‐(1‐adamantyl)‐5‐(2‐pyridyl)pyrazole (5), and ethylzinc 3‐(2‐furanyl)‐5‐(2‐pyridyl)pyrazolate (6). Exposure of a solution of 6 to ambient conditions leads to hydrolytic decomposition and the formation of bis{(ethylzinc hydroxide) zinc bis[3‐(2‐furanyl)‐5‐(2‐pyridyl)pyrazolate]} (7). This tetranuclear zinc complex contains two tetra‐ and two hexa‐coordinate metal atoms.

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.