The discovery that reduction of Cp'3Ln (Cp' = C5H4SiMe3) by potassium graphite in the presence of 2.2.2-cryptand (crypt) could generate the complexes [K(crypt)][Cp'3Ln] provided the first crystallographically-characterizable molecules containing yttrium, holmium, erbium, praseodymium, gadolinium, terbium, and lutetium in the formal +2 oxidation state. This Cp'3Ln/K reaction originated from earlier studies of dinitrogen reduction using a combination of a Ln3+ complex and an alkali metal in reactions designated as LnA3/M (A = anion; M = alkali metal) since the mechanism was unknown. The LnA3/M dinitrogen reduction studies, primarily with A = N(SiMe3)2, generally formed (N=N)2− and (N2)3− complexes and not isolable Ln2+ complexes of formula MLnA3 as found for A = Cp' with the [K(crypt)][Cp'3Ln] complexes. The isolation of [K(crypt)][Cp'3Ln] allows an evaluation of bona fide Ln2+ complexes, MLnA3, as intermediates in the dinitrogen reductions. The synthesis and reactivity of MLnA3 complexes with A = amides and cyclopentadienyls will be compared with the results of analogous LnA3/M reactions in efforts to connect these two areas of reductive rare-earth metal chemistry.

Recent advances in the chemistry of the rare-earth metals in the formal +2 oxidation state

253rd National Meeting (2017)

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