Rare Earth Starting Materials and Methodologies for Synthetic Chemistry

The number of rare earth (RE) starting materials used in synthesis is staggering, ranging from simple binary metal-halide salts to borohydrides and "designer reagents" such as alkyl and organoaluminate complexes. This review collates the most important starting materials used in RE synthetic chemistry, including essential information on their preparations and uses in modern synthetic methodologies. The review is divided by starting material category and supporting ligands (i.e., metals as synthetic precursors, halides, borohydrides, nitrogen donors, oxygen donors, triflates, and organometallic reagents), and in each section relevant synthetic methodologies and applications are discussed.

Synthesis and Reactivity of Bis(silylene)-Coordinated Calcium and Divalent Lanthanide Complexes

Divalent lanthanide complexes of Eu (1) and Yb (2) coordinated by a chelating pyridine-based bis(silylene) ligand were isolated and fully characterized. Compared to the EuII complex 1, the YbII complex 2 presents a lower thermal stability, resulting in the activation of one SiII -N bond and formation of an YbIII complex (3), which features a unique silylene-pyridyl-amido ligand. The different thermal stability of 1 and 2 points towards reduction-induced cleavage of one SiII -N bond of the bis(silylene) ligand. Successful isolation of the corresponding redox-inert bis(silylene) CaII complex (5) was achieved at low temperature and thermal decomposition into a CaII complex (4) bearing the same silylene-pyridyl-amido ligand was identified. In this case, the thermolysis reaction proceeds through another, non-redox induced, mechanism. An alternative higher yielding route to 4 was developed through an in situ generated silylene-pyridyl-amine proligand.

Inserted products of lithium silylquinolylamide dimers [{8-(2-R-C9H5N)N(Me3Si)}Li·OEt2]2 (R = H or Me) with dimethylcyanamide and their reactive derivatives with metal halides

Li, Ti, Fe and Co complexes bearing 8-quinolyl-linked guanidinate ligands have been synthesized and characterized. The structures of all complexes show various coordinative modes with the same multi-dentate ligands.

Divalent europium and ytterbium complexes supported by a bulky 2-pyridyl amido ligand: synthesis, structure and reactivity studies

Metallation of the N-arylated 2-pyridyl amine [HN(C6H3Pr(i)2-2,6)(2-C5H3N-6-Me)] (1) with potassium hydride in Et2O and THF yielded potassium amides [{KL(OEt2)}2] [L = N(C6H3Pr(i)2-2,6)(2-C5H3N-6-Me)] (2) and KL(THF)2 (3), respectively. Treatment of LnI2(THF)2 (Ln = Eu, Yb) with 2 afforded the corresponding Ln(II) amido complexes [EuL(μ-L)2K(THF)] (4) and [YbL2(THF)2] (5). In contrast, an analogous reaction of SmI2(THF)2 with 2 only led to the isolation of homoleptic Sm(III) triamide [SmL3] (6). The reaction chemistry of divalent complexes 4 and 5 was examined. Oxidation of the Eu(II) amido complex 4 by iodine yielded the trivalent [EuL3] (7), whereas addition of Yb(II) diamide 5 to iodine led to the isolation of the bis(amido) Yb(III) iodide complex [YbL2(I)(THF)] (8). Complex 8 could also be prepared by the reaction of 5 with copper(I) iodide. A subsequent reaction of 8 with KOBut gave, unexpectedly, the Yb(III) triamide [YbL3] (9). Reactions of complex 5 with diphenyl dichalcogenides PhEEPh (E = S, Se, Te) also gave [YbL3] (9) as the only isolable product. The solid-state structures of complexes 2 and 4–9 were elucidated by X-ray diffraction analysis.