Effect of peripheral donor substituents on the binding modes of phosphinomethanide ligands. Synthesis and crystal structures of alkali metal derivatives of an O-functionalised phosphinomethanide ligand

Abstract

The O-functionalised tertiary phosphine {(Me₃Si)₂CH}P(C₆H₄-2-CH₂OMe)₂ (9) is accessible via the reaction of {(Me₃Si)₂CH}PCl₂ with two equivalents of in situ generated 2-LiC₆H₄CH₂OMe. Phosphine 9 is readily deprotonated by BuⁿLi to give the lithium phosphinomethanide [[{(Me₃Si)₂C}P(C₆H₄-2-CH₂OMe)₂]Li] (13), which undergoes metathesis reactions with the alkoxides MOR [M = Na, K, R = Bu^t; M = Rb, R = 2-ethylhexyl] to give the heavier alkali metal phosphinomethanides [[{(Me₃Si)₂C}P(C₆H₄-2-CH₂OMe)₂]M]_n in good yields [M = Na (14), n = 2; M = K (15), Rb (16), n = ∞]. Compounds 9, [{(Me₃Si)₂CH}P(C₆H₄-2-CH₂OMe)₂LiBr]₂ (10), and 14–16 have been studied by X-ray crystallography; in the solid state 14 adopts a dimeric structure, whereas 15 and 16 crystallise as one-dimensional polymers.