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

Redox transmetallation/protolysis reactions between rare‐earth metals, Hg(C 6 F 5 ) 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 (La 1 ), Ce (Ce 2 ), Nd (Nd 3a ), Sm (Sm 4a )], 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)] (Lu 5 ) remains solvated with a seven coordinate monomeric structure. The dimeric species Sm 4a is cleaved by treatment with Ph 3 PO, N , N′ ‐bis(2,6‐difluorophenyl)formamidine (DFFormH), or [K( p ‐TolForm)(18‐Crown‐6)] producing [Sm( p ‐TolForm) 3 (Ph 3 PO) 2 ] (Sm 4b ), [Sm(DFForm) 2 ( p ‐TolForm)(thf) 2 ] (Sm 4c ), and the charge separated [K(18‐Crown‐6)][Sm( p ‐TolForm) 4 ] (Sm 4e ) respectively, the last being the first complex with a discrete [Ln(ArForm) 4 ] – ion.