Structurally Defined Zincated and Aluminated Complexes of Ferrocene Made by Alkali-Metal Synergistic Syntheses

Reaction
of ferrocene with 1 or 2 molar equiv of the synergistic-operative
bimetallic sodium zincate base TMEDA·Na­(μ-TMP)­(μ-tBu)­Zn­(tBu) yields mainly mono- or dizincated
complexes TMEDA·Na­(μ-TMP)­[μ-(C5H4)­Fe­(C5H5)]­ZntBu (1) and [TMEDA·Na­(μ-TMP)­Zn­(tBu)]2(C5H4)2Fe (2). Likewise,
the separated pairing of Li­(TMP) and (TMP)­AliBu2 in the presence of THF can mono- or dimetalate ferrocene
in a synergistic two-step lithiation/trans-metal-trapping protocol
to give THF·Li­(μ-TMP)­[μ-(C5H4)­Fe­(C5H5)]­Al­(iBu)2 (4) or [THF·Li­(μ-TMP)­Al­(iBu)2]2(C5H4)2Fe (5). In the absence of Lewis donating cosolvents,
a 4-fold excess of the sodium zincate appears to produce an unprecedented
4-fold zincated ferrocene of formula Na4(TMP)4Zn4(tBu)4[(C5H3)2Fe] (3), whereas when donor solvent
is withheld from the lithium/aluminum pairing, only dimetalation of
ferrocene is possible. Tetrametalation seems to be inhibited by the in situ generation of TMP­(H) via amido basicity, which then
acts as a Lewis donor toward lithium, preventing inverse-crown formation
and preferentially forming the Lewis acid–Lewis base adduct
[TMP­(H)·Li­(μ-TMP)­Al­(iBu)2]2(C5H4)2Fe (6). With the exception of 3, all aforementioned complexes
have been characterized by X-ray crystallography, while 1–6 have also been studied by solution NMR spectroscopic
studies.