The coordination chemistry of the C1-symmetric bis(silyl)methyl ligand [CH(SiMe3){SiMe(OMe)2}]− revisited: Li/M- (M = Zn, Tl, Ce), Li4- or Ce2-methoxy-bridged alkyls

Abstract

The following crystalline oligonuclear metal alkyls have been synthesised under mild conditions and structurally characterised: [(THF)Li(μ-A)(μ-Cl)(μ₃-OMe)Zn]₂ (3), [Li(μ-A)₂Tl]₂ (4 and 4′), [Li₄(μ-A)₃(μ₃-OMe)] (5), [(μ-A)Li₂(μ-A)₂(μ₃-OMe)Ce(A)] (6) and [Ce(A)(μ₂-OMe){μ₂-OS(O)(CF₃)O}]₂ (11) [A = CH(SiMe₃){SiMe(OMe)₂}]. Compounds 2–6 were obtained from [Li(μ-A)]_∞ (1) and ZnCl₂ (3), TlCl (4 and 4′ and 5) and CeCl₃ (6), and 11 was isolated from K(A) (prepared from 1 + KOBu^t) and cerium(III) triflate Ce(OTf)₃. The principal novel features are (i) and (ii) as follows. As for (i), the diversity of ligand-to-metal bonding is noteworthy, the ligand being (a) C,O-bridging in 3 {as in the known compounds 1 and in [Li₂Mg₅(μ₃-OMe)₆(μ₂-OMe)₂(μ₂-A)₄] (2)}; (b) C,O,O′-bridging and O,O′-chelating in 4 and 4′; (c) C,O,O′-bridging in 5; (d) C,O,O′-bridging and C,O-chelating in 6; and (e) C,O-chelating in 11. Regarding (ii), it is interesting that the ligand [A]⁻ is surprisingly ready to undergo fragmentation by Si–OMe cleavage and thereby present bridging methoxy ligands (μ₂-OMe)₂ to a pair of Ce³⁺ ions in 11, or μ₃-OMe acting as a cap for triangular arrays of three hard metal ions (Mg₃ in 2, LiZn₂ in 3, Li₃ in 5, and Li₂Ce in 6).