Complexes of a dianionic bis(diphosphinomethanide) with lithium, sodium, potassium and zirconium. Effect of substitution on the Schlenk dimerisation of vinylidene phosphines

Abstract

The vinylidene phosphine (Prⁿ₂P)₂CCH₂ (1) undergoes Schlenk dimerisation on treatment with an excess of any of the alkali metals Li, Na or K to give the butane-1,4-diide complexes [(L)M{(Prⁿ₂P)₂CCH₂}]₂ [(L)M = (THF)₂Li (6), (THF)₃Na (7b), (DME)₂K (8b)], after recrystallisation. Whereas the reaction between the analogous phenyl derivative (Ph₂P)₂CCH₂ and K results in cleavage of a P–C bond, 1 reacts smoothly with K to give 8, with no evidence for P–C cleavage. Compound 6 is an excellent ligand transfer reagent: metathesis reactions between either 6 or its phenyl analogue [(THF)₂Li{(Ph₂P)₂CCH₂}]₂ (2) and two equivalents of Cp₂ZrCl₂ in THF give the corresponding dinuclear zirconocene derivatives [Cp₂Zr(Cl){(R₂P)₂CCH₂}]₂ in good yields [R = Ph (11), Prⁿ (12)]. Compounds 6, 7b, 8b, 11 and 12 have been characterised by multi-element NMR spectroscopy and, where possible, by elemental analysis; compounds 6, 7b, 11 and 12 have additionally been characterised by X-ray crystallography.