On the usability of salt metathesis reactions for the synthesis of sterically crowded tris-formamidinate Ln(iii) complexes: success and limits. Spontaneous reduction of Eu(iii) to Eu(ii)

Homoleptic [Ln(FormDipp)(3)] (FormDipp(-) = CH(NDipp)(2)(-) (Dipp = 2,6-diisopropylphenyl), Ln = Nd, Eu) complexes bearing three bulky formamidinate ligands were successfully obtained using the salt metathesis approach, viz. the reaction of [Ln(FormDipp)(2)Cl(thf)(n)] (Ln = Nd (n = 2), Ln = Eu (n = 1)) with K(FormDipp) in toluene at 100 degrees C. This method is not useful for the Ln smaller than Eu: all attempts to realize it for Gd and Tb were unsuccessful. In the case of Eu, the tris-formamidinate complex was obtained in toluene, but in a thf/toluene mixture, a spontaneous reduction of Eu(iii) to Eu(ii) leading to the formation of [Eu(FormDipp)(2)(thf)(2)] was observed. The Eu(iii) to Eu(ii) conversion is rather sterically induced. UV-Vis spectroscopy monitoring of the reaction indicates it to be a zero-order process. Possible routes of the reaction are proposed.

Automated summary

In this study, homoleptic complexes containing three bulky formamidinate ligands were successfully synthesized using the salt metathesis approach. The method was found to be unsuitable for metals smaller than Eu, and a spontaneous reduction of Eu(iii) to Eu(ii) was observed. UV-Vis spectroscopy monitoring indicated that the reaction is a zero-order process.