Aspects of Divalent Rare-Earth-Metal Alkyl and Amide Chemistry

Abstract

Defined metalmethyl compounds were first reported in the middle of the 19th century and the interest in metal alkyls is still growing. So far 26 out of 60 non-radioactive metals have been found to form homoleptic isolable methyl componds [M(CH3)x] (x = 1–6). The report on the successful synthesis of dimethylcalcium [CaMe2]n triggered further research on the often discussed parallels of alkaline-earth metals and the divalent rare-earth-metals Sm2+, Eu2+ and Yb2+. Dimethylytterbium [YbMe2]n could be accessed via the reaction of the donor-free precursor [Yb{N(SiMe3)2}2]2 with methyllithium. [YbMe2]n was fully characterized and follow–up chemistry was investigated. Noteworthily, the protonolysis reaction of [YbMe2]n with protic hydrotris(3–tBu–5–Me–pyrazolyl)borate HTptBu,Me gave the first terminal Yb2+ methyl complex [TptBu,MeYb(CH3)(thf)] providing direct evidence of the existence of the methyl precursor. Further, the synthesis of the divalent dimethyl compounds of samarium and europium was attempted. The focus of the second part of this work was the synthesis of new rare-earth-metal imide complexes. Through a one-pot salt-metathesis reaction (LnI2(thf)2 + KTptBu,Me + KNHR with Ln = Sm, Eu, Yb and R = 2,6-iPr-C6H3, 2,6-Me-C6H3, 3,5-CF3-C6H3, SiPh3) or a protonolysis approach (TptBu,MeYb(N(SiMe3)2) + H2NR, R = R = 2,6-iPr-C6H3, 3,5-CF3-C6H3, SiPh3) efficient access to amide complexes [TptBu,MeYbNH(R)(thf)x] (R = 2,6-iPr-C6H3, 2,6-Me-C6H3, 3,5-CF3-C6H3, SiPh3) could be gained. All synthesized complexes were fully characterized and their reactivity toward Lewis acids and bases as well as their redox chemistry was further investigated. The obtained compounds are potential precursor complexes for the synthesis of rare-earth-metal imide complexes