A simple one-pot route to stable formamidinatoiodidolanthanoid(iii) complexes from lanthanoid metals

A number of formamidinatoiodidolanthanoid(III) complexes, [Ln(DFForm)2I(thf)2] and [Ln(DFForm)I2(thf)3] (DFFormH = N,N′-bis(2,6-difluorophenyl)formamidine) and [Ln(DippForm)I2(thf)3] (DippFormH = N,N′-bis(2,6-diisopropylphenyl)formamidine) have been synthesized in good yields by one-pot direct reactions of the corresponding free metals with iodine and DFFormH or DippFormH in suitable ratios and are stable to rearrangement. Heteroleptic metal–organic lanthanoid(iii) halides, LnXX′2 or LnX2X′ (X = anionic ligand; X′ = Cl, Br, I), are vital reagents for the synthesis of functionalised heteroleptic compounds, LnXX′′2 or LnX2X′′, including X′′ = hydride, amide, alkoxide, aryloxides, and cyclopentadienyl,1 which have various applications in magnetization,2a cancer diagnosis and therapy,2b electrochemical potentials,2c and catalysts.2d,e These reagents have been mainly prepared by metathesis reactions between LnX′3 and MX in appropriate stoichiometric ratios [eqn (1)].1 However, such syntheses can be problematic owing to alkali metal halide retention/‘ate’ complex formation1g,h,3 or the occurrence of rearrangement reactions, especially for dihalides4e.g. [eqn (2)]. For X′ = Cl, this unwanted outcome is aided by the low solubility of LnCl3(solv). However, we have now devised a simple, efficient, one pot route to stable Ln(Form)nI3−n (Form = N,N′-diarylformamidinate; n = 1 or 2) compounds of potential general significance. Following the failure of many lanthanoid metals to react with AgC6F5 and N,N′-bis(2,6-difluorophenyl)formamidine (DFFormH) in redox transmetallation/protolysis to give Ln(DFForm)3 complexes,5 we examined the effect of activation of the metals with a small amount of iodine6 on the outcome. From several reactions, either a low yield of [Ln(DFForm)2I(solv)] (solv = py or thf) complexes or an inseparable mixture of these compounds and [Ln(DFForm)3(solv)n] was obtained.5 To see if this setback could be turned into a synthetic positive, we have examined the reactions of Ln metals with iodine and DFFormH, and we now report that this method provides a simple one-pot synthesis of [Ln(DFForm)nI3−n(thf)m] (n = 1 or 2) complexes in good yield. In addition, with the much bulkier N,N′-bis(2,6-diisopropylphenyl)formamidine (DippFormH), [Ln(DippForm)I2(thf)3] were prepared. The products are stable to rearrangement. The method has wide potential application to a range of weak acid proligands