Synthesis and structures of crystalline bis(trimethylsilyl)methanido complexes of potassium, calcium and ytterbium

Abstract

Crystalline [K(μ-R)(thf)] ∞ ( 1) was obtained from equivalent portions of n-butyllithium in hexane, bis(trimethylsilyl)methane (RH) and potassium t-butoxide in thf, removal of volatiles and extraction with hexane. Desolvation of 1 in a vacuum led to KR. The first three-coordinate metallate(II) alkyls [K(MR 3)] ∞ [M=Ca ( 2), M=Yb ( 3)] of calcium and ytterbium(II) were prepared from the appropriate metal(II) iodide and three equivalents of KR in benzene. Mixing LiR, YbI 2 and two equivalents of KR in a mixture of diethyl ether and small amount of thf yielded the red (like 3) [Li(thf) 4][YbR 3] ( 4). Each of 1– 4 was obtained in good yield and was characterised by multinuclear NMR spectra in C 6D 6 and single crystal X-ray diffraction. The central metal is in a trigonal planar 1 or pyramidal 2– 4 environment and the average MC bond lengths are 2.98 ( 1), 2.50 ( 2), 2.52 ( 3 and 4) Å. Crystalline 2 and 3 are isomorphous and consist of double chains of [MR 3] − anions linked by K + cations along the a axis, whereas complex 4 has an ionic structure with isolated [Li(thf) 4] + cation and [YbR 3] − anion.