Synthesis and crystal structures of bis(diphenylphosphanyl)methanides of lithium and calcium as well as of their borane adducts

Abstract

The reaction of Li{HC(PPh₂)₂}, which forms [(tmeda)(thf)Li{HC(PPh₂)₂}] (1) in the presence of appropriate Lewis bases, with KOtBu and CaI₂ in THF yields [(thf)₃Ca{CH(PPh₂)₂}₂] (2). In complexes 1 and 2 the bis(diphenylphosphanyl)methanide anions act as bidentate ligands via the phosphorus atoms. Lithiation of H₂C(PPh₂-BH₃)₂ in diethyl ether leads to the formation of [(Et₂O)₂Li{CH(PPh₂-BH₃)₂}] (3) which can be recrystallized from 1,2-dimethoxyethane (DME) leading to the formation of solvent-separated [(dme)₃Li]⁺ [HC(PPh₂-BH₃)₂]⁻ (3′). The reaction of 3 with KOtBu and then with anhydrous CaI₂ yields [(thf)Ca{CH(PPh₂-BH₃)₂}₂] (4). In compound 4 a Ca–C bond of 2.754(3) Å is observed in the solid state to only one of the anions whereas the other anion only binds via the borane units.