Structural and Reactivity Consequences of Reducing Steric Bulk of N,N′‐Diarylformamidinates Coordinated to Lanthanoid Ions

Abstract

AbstractRedox 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.