Syntheses and Molecular Structures of [(thf)₄Li] [{(thf)Li}M(C₄H₈)₃] (M = Zr, Hf) and Their Solution Behavior

Abstract

The reaction of MCl4(thf)2 (M = Zr, Hf) with 1,4‐dilitiobutane in diethyl ether at –25 °C or at 0 °C with a molar ratio of 1 : 3 yields the homoleptic “ate” complexes [(thf)4Li] [{(thf)Li}M(C4H8)3] 1‐Zr (M = Zr) and 1‐Hf (M = Hf). The crystalline compounds form ion lattices with solvent‐separated [(thf)4Li]+ cations and [{(thf)Li}M(C4H8)3]– anions. The NMR spectra at –20 °C show magnetic equivalence of the M–CH2 and of the β‐CH2 groups of the butane‐1,4‐diide ligands on the NMR time scale. Analogous reactions of MCl4(thf)2 with 1,4‐dilithiobutane with a molar ratio of 1 : 2 proceed unclear. However, single crystals of [Li(thf)4] [HfCl5(thf)] (2) can be isolated with the hafnium atom in a distorted octahedral coordination sphere of five chloro and one thf ligand. NMR spectra allow to elucidate the time‐dependent degradation of 1‐Hf and 1‐Zr in THF and toluene at 25 °C via THF cleavage. Addition of tmeda to a solution of 1‐Zr allows the isolation of intermediately formed [{(tmeda)Li}2Zr(nBu)2(C4H8)2] (3).

The Mechanism of Lithium Zincate‐Mediated I/Zn Exchange Revisited: A Computational Microsolvation Approach in THF**

“…[40] It should be mentioned that Li + is known to adopt the tetrasolvated solid-state structure [Li(THF) 4 ]. + [41] However, a dissociation process that straightforwardly generates a tetrasolvated Li + is inconceivable because the alkali metal of Et 3 ZnLi can be coordinated by three THF molecules at most and not four (See Scheme SI.9), for steric congestion reasons. Therefore, [Li(THF) 4 ] + should be produced by subsequent exergonic solvation of [Li(THF) 2 ] + resulting from the dissociation of C, that is in a secondary process which cannot be honestly viewed as a part of the dissociation step (Schemes 10 and SI.9).…”