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

Daniel Werner,Glen Deacon,Peter Junk

doi:10.3390/inorganics5020026

Daniel Werner, Glen Deacon + Show 1 more

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https://doi.org/10.3390/inorganics5020026

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Abstract

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′):η4(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.

Highlights

With the ability to adopt numerous coordination modes, flexible N,N 0 -bis(aryl)formamidinates have earned a special place in coordination chemistry [1,2,3,4,5]
The potential to form metal–arene interactions, such as η6 coordination, has been largely observed in group one chemistry [8,9,10,11,12,13], though some examples are known in f -block chemistry [14]
In almost all examples of this aromatic coordination, the phenyl rings contained alkyl-substituents in either the 2,6 positions, or in the 2,4,6 positions (e.g., Me). This is likely due to a combination of steric pressure, which starves the metal centre from coordination of additional donors, and increased electron donation from the aromatic ring caused by the alkyl substituents. Another means to engage the aromatic component in coordination is through the addition of donor functionalities (e.g., OMe, F), especially in the ortho-positions, thereby transforming the formamidinate ligand into a tri- [15,16,17], or tetra-dentate (e.g., N,N 0,X or N,N 0,X,X0 ) [17], chelate, with examples across a variety of different metal classes [18]

Summary

Introduction

With the ability to adopt numerous coordination modes, flexible N,N 0 -bis(aryl)formamidinates (and by extension aryl-functionalised amidinates) have earned a special place in coordination chemistry [1,2,3,4,5]. In almost all examples of this aromatic coordination, the phenyl rings contained alkyl-substituents in either the 2,6 positions (e.g., iPr, Et, Me), or in the 2,4,6 positions (e.g., Me) This is likely due to a combination of steric pressure, which starves the metal centre from coordination of additional donors, and increased electron donation from the aromatic ring caused by the alkyl substituents. Another means to engage the aromatic component in coordination is through the addition of donor functionalities (e.g., OMe, F), especially in the ortho-positions, thereby transforming the formamidinate ligand into a tri- [15,16,17], or tetra-dentate (e.g., N,N 0 ,X or N,N 0 ,X,X0 ) [17], chelate, with examples across a variety of different metal classes [18]

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