Deacon, Glen B., Junk, Peter C., Macreadie, Lauren K., and Werner, Daniel (2014) Structural and reactivity consequences of reducing steric bulk of N,N'-diarylformamidinates coordinated to lanthanoid ions. European Journal of Inorganic Chemistry, 2014 (30). pp. 5240-5250.

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Abstract

Redox transmetallation/protolysis reactions between rare-earth metals, Hg(C6F5)2, and N,N'-bis(4-methylphenyl)formamidine (p-TolFormH) in THF initially produce a THF solvated species [Ln(p-TolForm)3(thf)2] (Ln = La, Ce, Nd, Sm). Upon addition of non-coordinating solvents, coordinated THF is rapidly liberated, producing unsolvated, dimeric complexes of the general formula [Ln(p-TolForm)3]2 [Ln = La (La1), Ce (Ce2), Nd (Nd3a), Sm (Sm4a)], containing rare μ-1κ(N,N'):2κ(N,N') formamidinate ligands bridging between the two metal centres. Such binding is unprecedented in rare-earth N,N'-diarylformamidinate chemistry, and is generally uncommon in formamidinate or amidinate coordination chemistry. This tendency for THF liberation is metal size dependent since the smaller lutetium analogue [Lu(p-TolForm)3(thf)] (Lu5) remains solvated with a seven coordinate monomeric structure. The dimeric species Sm4a is cleaved by treatment with Ph3PO, N,N'-bis(2,6-difluorophenyl)formamidine (DFFormH), or [K(p-TolForm)(18-Crown-6)] producing [Sm(p-TolForm)3(Ph3PO)2] (Sm4b), [Sm(DFForm)2(p-TolForm)(thf)2] (Sm4c), and the charge separated [K(18-Crown-6)][Sm(p-TolForm)4] (Sm4e) respectively, the last being the first complex with a discrete [Ln(ArForm)4]– ion.

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