Mono-cyclononatetraenyl lanthanide complexes

The synthesis of the first half-sandwich complexes based on the cyclononatetraenyl (Cnt = C$_9$H$_9^−$) ligand ([Ln$^{III}$(η$^9$-Cnt)(η$^3$-BH$_4$)$_2$(thf)] (Ln = La, Ce)) is reported. The title compounds were obtained from the reaction of [Ln(BH$_4$)$_3$(thf)$_3$] and [K(Cnt)]. Further solvation of [LnIII(η$^9$-Cnt)(η$^3$-BH$_4$)$_2$(thf)] with tetrahydrofuran (THF) resulted in a reversible decoordination of the Cnt ring and the formation of the ionic species [Ln$^{III}$(η$^3$-BH$_4$)$_2$(thf)$_5$][Cnt]. Removal of THF from [La$^{III}$(η$^9$-Cnt)(η$^3$-BH$_4$)$_2$(thf)] gave the polymeric compound [La$^{III}$(μ-η$^2$:η$^2$-BH$_4$)$_2$(η$^3$-BH$_4$)(η$^9$-Cnt)]$_n$.