Bis(pyrazol-1-yl)acetic Acid Bearing Ferrocenyl Substituents

The
new compound 4-ferrocenyl-3,5-dimethylpyrazole (4; fcdmpzH)
has been synthesized from 4-iodo-3,5-dimethyl-1-tritylpyrazole
(2) via a Negishi type cross-coupling reaction and subsequent
deprotection of the intermediate 4-ferrocenyl-3,5-dimethyl-1-tritylpyrazole
(3; fcdmpzTrt). Reaction of the pyrazole 4 with dichloromethane, base, and phase transfer catalyst results
in the chelating N,N ligand bis­(4-ferrocenyl-3,5-dimethylpyrazol-1-yl)­methane
(5; bfcdmpzm). Bis­(4-ferrocenyl-3,5-dimethylpyrazol-1-yl)­ketone
(6; bfcdmpzk) is obtained by reacting 4 with
NEt3 and triphosgene. The N,N,O heteroscorpionate ligand
bis­(4-ferrocenyl-3,5-dimethylpyrazol-1-yl)­acetic acid (7; H­[bfcdmpza]) can be accessed by reacting pyrazole 4 with dibromoacetic acid, KOtBu, and phase transfer
catalyst and subsequent acidic workup. The heteroscorpionate ligand
H­[bfcdmpza] (7) is suitable to bind metal ions in a κ3 coordination mode, as could be proven by the formation of
a the bis-ligand complex [Fe­(bfcdmpza)2] (8). The molecular structures of 3, 5, 6, and 8 have been obtained by single-crystal
X-ray structure determination. The electrochemical properties of the
four ferrocenyl-substituted compounds 3–6 have been studied by cyclic voltammetric measurements and
discussed as well.