Potassium C–F Interactions and the Structural Consequences in N,N'-Bis(2,6- difluorophenyl)formamidinate Complexes

Treatment of K[N(SiMe3)2] with N,N′-bis(2,6-difluorophenyl)formamidine (DFFormH) in toluene, resulted in the formation of [K(DFForm)]∞ (1) as a poorly soluble material. Upon dissolution in thf and layering with n-hexane, 1 was crystallised and identified as a two-dimensional polymer, in which all fluorine and nitrogen atoms, and also part of one aryl group, bridge between four symmetry equivalent potassium ions, giving rise to a completely unique μ4-(N,N,F,F):(N,N):η(Ar-C(2,3,4,5,6)):(F”,F ′ ′) DFForm coordination. The two-dimensional nature of the polymer could be deconstructed to one dimension by crystallisation from neat thf at −35 ◦C, giving [K2(DFForm)2(thf)2]∞ (2), where the thf molecules bridge the monomeric units. Complete polymer dissociation was observed when 1 was crystallised from toluene/n-hexane mixtures in the presence of 18-crown-6, giving [K(DFForm)(18-crown-6)] (3), which showed unprecedented κ(N,Cispo,F) DFForm coordination, rather than the expected κ(N,N′) coordination.