Higher Phosphines

Together with phosphine, noticeable amounts of diphosphine and higher phosphines are formed by the hydrolysis of calcium phosphide thus, this reaction can be used for the preparation of such compounds. Quesnel reported that the formation of diphosphine can be avoided when aqueous hydrochloric acid is added drop-wise to a mixture of calcium phosphide and copper chloride (proportions by weight, CaaPj CuClj = 10 1) in boiling alcohol, for example, methanol, or in dioxane. 

Baudler and her co-workers have described in detail the preparation of larger quantities of phosphine by the hydrolysis of calcium phosphide. Higher phosphines (see page 51) formed simultaneously, are thermally decomposed to phosphorus, phosphine and hydrogen. It is noteworthy that, on storage in steel cylinders the diphosphine concentration in phosphine, originally less than 1%, increases. It is, even after several months, so small that the gas is not spontaneously inflammable in contact with air, whereas, after about one year, it is spontaneously inflammable. 

Our experience has shown that the hydrolysis of aluminium phosphide with cold water is the most suitable method for the laboratory preparation of phosphine. Here it is important that the aluminium phosphide be as pure as possible in order to avoid the formation of spontaneously inflammable phosphine. The presence of small quantities of diphosphine and also higher phosphines are responsible for this spontaneous inflammability 96.276-278) jj. gp, pears, however, that these are only formed when P—P bonds are already present in the phosphide. Accordingly the hydrolysis of aluminium phosphide, prepared from the elements with phosphorus in slight excess, always leads to spontaneously inflammable phosphine. The formation of diphosphine and higher phosphines from aluminium or alkaline earth metal phosphides, which contain excess phosphorus, can be easily understood when the lattices of these compounds are considered. 

In the course of mass spectroscopic investigations of the hydrolysis products of calcium phosphide, Baudler and her co-workers could find no evidence for the existence of OPH3 as an oxidation product of PH3 In contrast, oxides of higher phosphines were observed, even when the hydrolysis of calcium phosphide was carried out with the strictest exclusion of oxygen. The... 

Triphosphine, P3H5, has been identified as a product from the hydrolysis of CaaPj or Mg3P2 in acidic media by mass spectroscopy In addition, using mass spectroscopic analysis Baudler and her co-workers 436.437) able to identify the following higher phosphines formed during the hydrolysis or the disproportionation of diphosphine ... 

The spontaneously inflammable nature of the higher phosphines decreases with increasing phosphorus content. At room temperature or on exposure to light, phosphorus-rich, yellow, solid phosphines are rapidly formed these can also be obtained directly by thermal decomposition of diphosphine. The literature on these types of higher phosphorus hydrides which are, in general, solid and are thus refered to as solid phosphorus hydrides is abundant and... 

Generally, octatriene formation is favored by higher temperatures, higher phosphine and/or butadiene concentrations and, importantly, by an increase in steric bulk of either the ligand or the nucleophile. Indeed, Harkal et al. showed a selectivity switch from telomerization products to 1,3,7-octatriene formation by altering the steric demand of the /V-heterocyclic carbene ligand in the reaction of butadiene with isopropanol under further identical reaction conditions [48]. For the more basic nucleophiles, such as the alcohols, the telomer products are stable under experimental conditions, i.e. product formation is irreversible, but for more acidic substrates such as phenol, product formation is reversible and more 1,3,7-octatriene will be formed after the substrate has been depleted. 

The addition of R-Pd to the double bond and the elimination of Pd-H from it are both syn. Thus, the relative stereochemistry of the double bond is inverted (equation 22). Mixtures of stereoisomers are in fact produced, since the /3-elimination reaction is reversible. Lower reaction temperatures and higher phosphine concentrations increase the stereoselectivity of the reaction. 

Protonic acid cleavage of group IVB element (Si, Ge)-P bonds is most valuable synthetically to prepare P—H bond-containing higher phosphines or metal complexes ... 

In the biphase hydroformylation of 1-hexene the conversion rate strongly depends on the phosphorus to rhodium ratio (P/Rh ratio). An increase of the P/Rh ratio from 50 1 to 100 1 and to 150 1 results in a decrease of the conversion from 33% to 18% and to 9% respectively (Table 3). This may be due to the shift of the 1, 2 and 3 (Scheme 1). At higher phosphine concentrations the formation of the catalytically active species is suppressed. Furthermore the salt effect is much more pronounced in the aqueous catalyst solution than in homogeneous organic systems. 

Details for synthesizing PH3 from duminium phosphide have been given, and the chemistry and physical properties of phosphine have been reviewed. Short sections on the higher phosphines are also included. 

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