Monomeric alkali metal complexes of a sterically demanding, donor-functionalised secondary phosphide ligand

Abstract

The novel sterically demanding, amino-functionalised secondary phosphine (2-Me₂NCH₂C₆H₄)RPH [R = CH(SiMe₃)₂] was synthesized by the reaction of RPCl₂ with [Li{C₆H₄CH₂NMe₂-2}], followed by reduction with LiAlH₄. The compound is readily metallated with BuⁿLi to yield the lithium phosphide [Li{PR(C₆H₄CH₂NMe₂-2)}(THF)₂] 1·2THF, in which the ligand binds to Li through both its N and P. Metathesis between 1 and NaOBu^t or KOBu^t yielded the sodium and potassium phosphides [M{PR(C₆H₄CH₂NMe₂-2)}] (M = Na 2 or K 3), respectively. Compound 2 crystallises as the monomeric adduct [Na{PR(C₆H₄CH₂NMe₂-2)}(tmen)], in which the formally four-co-ordinate Na exhibits a short contact with one of the ipso-carbons of the phosphide ligand. Compound 3 crystallises in the presence of pmdien as the mononuclear adduct [K{PR(C₆H₄CH₂NMe₂-2)}(pmdien)] in which the potassium centre is only five-co-ordinate, although again showing a short K· · ·C_ipso contact. The compounds have been characterised by multinuclear NMR spectroscopy, and 1–3 by X-ray crystallography.