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)]${}_n$.