Lithium phosphides isolation

Aiming at preparing a phosphino-borane ILjPBR with PB doublebond character,43 Karsch reacted the lithium phosphide LiPMes2 with tribromoborane (Scheme 19).44 Instead of the desired compound 25, they isolated the PB 26a that results formally from the 1,2-addition of a C-H bond of a mesityl group across the PB double bond of 25. The 31P and... 

After slow warming to 20°C, a clear colorless solution finally results, whose P-NMR spectrum indicates nearly complete formation of 90. In the following work-up, compound 90 can be isolated as colorless needle-shaped crystals. As its melting point is reached (about 49°C), it degrades slowly, manifested by a turning of the color to yellow. At this point, formation of MeP(SiMe3)2 can be demonstrated. Formation of 90 according to Eq. (15) indirectly proves that the reaction of the cyclotetraphosphane 85 with LiMe yields an open-chain n-tetraphosphide the position occupied by lithium is nevertheless not yet determined. In order to reach a definite conclusion about this, the phosphide 89, obtained in a further reaction of 85 with Li(n-Bu) (THF/ —50°C), was transformed into the methyl derivative 91 by MeCl, as indicated in Eq. (16). 

Reaction of triarylphosphanes with lithium metal affords the lithium diarylphosphide. Similarly, tris(2-pyridyl)phosphane reacts with lithium metal in THF with cleavage of a P-pyridyl bond and ligand coupling to 2,2 -bipyridine and lithium bis(2-pyridyl)phosphide. After hydrolysis, the bis(2-pyridyl)phosphane was isolated in 66% yield, but no yield was reported for the bipyridine.39... 

The synthesis and uses of alkali metal phosphides have been reviewed. Alkali metal diphenyl-phosphides are readily obtained by cleavage of a phenyl group from PPh, by lithium in tetra-hydrofuran (THF), sodium or lithium in liquid ammonia or potassium in dioxane (equation 3). The metal-phenyl product can be destroyed by addition of a calculated amount of Bu Cl or NH4X. Usually MPPhj compounds are prepared in situ, but they can be isolated, usually as solvates. These compounds can also be obtained from Ph2PCl and the alkali metal, or from Ph2PH and alkyl-lithium. ... 

Investigations by Bielang and R.D. Fischer (1978) demonstrate that the reactions of dicyclopentadienyl ytterbium chloride with lithium di(cyclohexyI)phosphide, lithium cyclohexylphosphide and lithium phenylphosphide are rather complicated. The decomposition behavior of these very sensitive substances is complex. It was possible to isolate Cp2YbP(QHji)2, but Cp2YbPHPh and Cp2YbPHQH decompose with formation of polymeric species [CpYbPPh] and [CpYbPQH,] . 

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