Alkali metal complexes of sterically demanding amino-functionalised secondary phosphanide ligands

Abstract

The reaction between {(Me₃Si)₂CH}PCl₂ (4) and one equivalent of either [C₆H₄-2-NMe₂]Li or [2-C₅H₄N]ZnCl, followed by in situ reduction with LiAlH₄ gives the secondary phosphanes {(Me₃Si)₂CH}(C₆H₄-2-NMe₂)PH (5) and {(Me₃Si)₂CH}(2-C₅H₄N)PH (6) in good yields as colourless oils. Metalation of 5 with BuⁿLi in THF gives the lithium phosphanide [[{(Me₃Si)₂CH}(C₆H₄-2-NMe₂)P]Li(THF)₂] (7), which undergoes metathesis with either NaOBu^t or KOBu^t to give the heavier alkali metal derivatives [[{(Me₃Si)₂CH}(C₆H₄-2-NMe₂)P]Na(tmeda)] (8) and [[{(Me₃Si)₂CH}(C₆H₄-2-NMe₂)P]K(pmdeta)] (9) after recrystallisation in the presence of the corresponding amine co-ligand [tmeda = N,N,N′,N′-tetramethylethylenediamine, pmdeta = N,N,N′,N″,N″-pentamethyldiethylenetriamine]. The pyridyl-functionalised phosphane 6 undergoes deprotonation on treatment with BuⁿLi to give a red oil corresponding to the lithium compound [{(Me₃Si)₂CH}(2-C₅H₄N)P]Li (10) which could not be crystallised. Treatment of this oil with NaOBu^t gives the sodium derivative [{[{(Me₃Si)₂CH}(2-C₅H₄N)P]Na}₂·(Et₂O)]₂ (11), whilst treatment of 10 with KOBu^t, followed by recrystallisation in the presence of pmdeta gives the complex [[{(Me₃Si)₂CH}(2-C₅H₄N)P]K(pmdeta)]₂ (12). Compounds 5–12 have been characterised by ¹H, ¹³C{¹H} and ³¹P{¹H} NMR spectroscopy and elemental analyses; compounds 7–9, 11 and 12 have additionally been characterised by X-ray crystallography. Compounds 7–9 crystallise as discrete monomers, whereas 11 crystallises as an unusual dimer of dimers and 12 crystallises as a dimer with bridging pyridyl-phosphanide ligands.