Abstract
The reaction between (Dipp)2PH and one equivalent of n-BuLi, PhCH2Na or PhCH2K in THF gives the complexes [(Dipp)2P]Li(THF)3 (2a), {[(Dipp)2P]Na(THF)2}2 (3a) and [(Dipp)2P]K(THF)4 (4a), respectively [Dipp = 2,6-iPr2C6H3]. Exposure of these compounds to vacuum yields the alternative solvates [(Dipp)2P]Li(THF)2 (2b), [(Dipp)2P]Na(THF)1.5 (3b), and [(Dipp)2P]K (4b), respectively; the alternative adduct [(Dipp)2P]Na(PMDETA) (3c) was prepared by treatment of 3a with PMDETA. Treatment of (Dipp)(Mes)PH or (Mes)2PH with one equivalent of n-BuLi in THF gives the complexes [(Dipp)(Mes)P]Li(THF)3 (7a) and [(Mes)2P]2Li2(THF)2(OEt2) (8a) after crystallisation from diethyl ether [Mes = 2,4,6-Me3C6H2]; crystallisation of 8a from hexane gives the alternative adduct [(Mes)2P]Li(THF)3 (8b). Exposure of 7a, 8a and 8b to vacuum leads to loss of coordinated solvent, yielding the solvates [(Dipp)(Mes)P]Li(THF)2 (7b) and [(Mes)2P]Li(THF) (8c). The solid-state structures of complexes 2a, 3a, 3c, 4a, 7a, 8a, and 8b have been determined by X-ray crystallography. Variable-temperature 31P{1H} and 7Li NMR spectroscopy indicates that 2b, 3b and 7b are subject to a monomer-dimer equilibrium in solution, where the monomeric forms are favoured at low temperature. In contrast, variable-temperature 31P{1H} and 7Li NMR spectroscopy suggests that 8c is subject to a dynamic equilibrium between a dimer and a cyclic trimer in solution, where the trimer is favoured at low temperatures.
Highlights
Alkali metal phosphides are key intermediates in the synthesis of secondary and tertiary phosphine ligands and are ubiquitous metathesis reagents for the synthesis of main group, transition metal and f-element phosphide complexes
Variable-temperature 31P{1H} and 7Li NMR spectroscopy suggests that 8c is subject to a dynamic equilibrium between a dimer and a cyclic trimer in solution, where the trimer is favoured at low temperatures
Single crystals of 3a and 4a were obtained by crystallisation of the crude materials from a mixture of light petroleum and the form (THF) or diethyl ether and THF, respectively, while single crystals of the adduct [(Dipp)2P]Na(PMDETA) (3c) were obtained by crystallisation of 3a from n-hexane in the presence of one equivalent of PMDETA
Summary
Alkali metal phosphides are key intermediates in the synthesis of secondary and tertiary phosphine ligands and are ubiquitous metathesis reagents for the synthesis of main group, transition metal and f-element phosphide complexes. The alkali metal species are of interest in their own right and have been shown to adopt a wide variety of structural motifs in the solid state, ranging from monomers to dimers, trimers, tetramers, higher oligomers (often with ladder-like catenated P2Li2 rings), polymers, and 3-dimensional networks.[1,2,3,4,5,6,7,8,9,10,11] The degree of oligomerisation is determined by the interplay between the size of the metal cation, the steric demands of the ligand substituents. We present the crystal structures of these compounds, comment on the frequently observed coordinated solvent loss, and describe their solution behaviour
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