Cationic organoiron mixed-sandwich hydrazine complexes: Reactivity toward aldehydes, ketones, β-diketones and dioxomolybdenum complexes

This review covers comprehensively the authors work during the present decade based on the chemistry of ionic organometallic hydrazines formulated as [(η⁵-Cp′)Fe(η⁶-Ar-NHNH₂)]⁺PF₆^- (Cp′ = C₅H₅, C₅Me₅; Ar = aryl), that could be considered as a new generation of hydrazines owing to the changes provoked by the coordination of the 12-electron Cp′Fe⁺ fragment both in the electronic properties of the aromatic ring and in the hydrazine group. The reactivity of this new class of hydrazine is obviously centered, as in the classic Fischer's organohydrazines, Ar-NHNH₂, on the -NHNH₂ functional unit which is able to react with aldehydes, RCH({double bond, long}O) (R = alkyl, aryl, ferrocenyl (Fc)) and ketones, RR′C{double bond, long}O (R = alkyl, aryl; R′ = alkyl, aryl, Fc), to afford ionic organometallic hydrazones. Likewise, the mixed-sandwich hydrazine precursors react with β-diketones Me-C({double bond, long}O)-CH₂-C({double bond, long}O)-Me to afford ionic organometallic pyrazoles, and with cis-dioxo-molybdenum complexes, e.g. [MoO₂(S₂CNEt₂)₂], to afford ionic organometallic mono-organodiazenido complexes in which the two metal centers are connected by a μ,η⁶:η¹-aryldiazenido bridge. While some ionic hydrazones exhibit NLO properties, the ionic organodiazenido hybrid complexes exhibit charge-transfer features.