Alkali metal complexes of a naphthylamine-substituted phosphanide

Abstract

The reaction between {(Me₃Si)₂CH}PCl₂ and one equivalent of [C₁₀H₆-8-NMe₂]Li, followed by in situreduction with LiAlH₄, gives the secondary phosphane {(Me₃Si)₂CH}(C₁₀H₆-8-NMe₂)PH (1) in good yield as a colourless crystalline solid. Metalation of 1 with BuⁿLi in diethyl ether gives the lithium phosphanide [{[{(Me₃Si)₂CH}(C₁₀H₆-8-NMe₂)P]Li}₂(OEt₂)] (2), which undergoes metathesis with either NaOBu^t or KOBu^t to give the heavier alkali metal derivatives [[{(Me₃Si)₂CH}(C₁₀H₆-8-NMe₂)P]Na(tmeda)] (3) and [[{(Me₃Si)₂CH}(C₁₀H₆-8-NMe₂)P]K(pmdeta)] (4), after recrystallisation in the presence of the corresponding amine co-ligand [tmeda = N,N,N′,N′-tetramethylethylenediamine, pmdeta = N,N,N′,N″,N″-pentamethyldiethylenetriamine]. Compounds 2–4 have been characterised by ¹H, ¹³C{¹H} and ³¹P{¹H} NMR spectroscopy, elemental analyses and X-ray crystallography. Dinuclear 2 crystallises with the phosphanide ligands arranged in a head-to-head fashion and is subject to dynamic exchange in toluene solution; in contrast, compounds 3 and 4 crystallise as discrete monomers which exhibit no dynamic behaviour in solution. DFT calculations on the model compound [{[(Me)(C₁₀H₆-8-NMe₂)P]Li}₂(OMe₂)] (2a) indicate that the most stable head-to-head form is favoured by 15.0 kcal mol^–1 over the corresponding head-to-tail form.