Difunctional Pyrazole Derivatives − Key Compounds en Route to Multidentate Pyrazolate Ligands

Straightforward syntheses for some basic functional pyrazole derivatives are reported. These compounds serve as starting materials for the preparation of a series of new 3,5‐donor‐substituted multifunctional pyrazole compounds, which may act as compartmental dinucleating ligand scaffolds for the controlled assembly of bimetallic complexes. The thp‐protected 3,5‐bis(chloromethyl)pyrazole ( 1 ), and in particular the more reactive 3,5‐bis(bromomethyl) analogue 3 , permit efficient attachment of various N‐donor side arms through nucleophilic substitution reactions. The preparation of the enantiomerically pure (methoxymethyl)pyrrolidine derivative 2e by this route makes use of the intrinsic C 2 symmetry of the pyrazole‐based framework, and a dizinc complex 2e· (ZnCl 2 ) 2 has been characterized crystallographically. The thp‐protected pyrazoledicarbaldehyde 6 affords access to pyrazole derivatives bearing aldimine donor side arms, which may be viewed as coupled dinucleating versions of α‐diimine ligands. DIBAH reduction of thp‐protected dimethyl 1 H ‐pyrazole‐3,5‐dicarboxylate 4 yields the unsymmetrically functionalized methyl 3‐hydroxymethyl‐1 H ‐pyrazole‐5‐carboxylate 8 , which has been analyzed by X‐ray crystallography. Compound 8 is shown to provide a route to unsymmetrical pyrazole ligands with different chelating side arms in the heterocycle 3‐ and 5‐positions, such as the thioether/amine system 11 .