Diphosphine disulphides

The crystal structures of a number of diphosphine disulphides (121) and (122) show a remarkable constancy in the bond lengths. Two types of molecule are observed in the crystal of the tetramethyl compound (121, X = Y = Me). The crystal structure of triphenylphosphine oxide (P—C 176 pm, P—O 164 pm) varies little from that observed in the uranium oxide complexes, and does not confirm P—O bond lengthening in complexes, as indicated by vp=.o (see Section 3C). 

A further illustration has appeared28 of the reactivity of simple a-keto-alkyldi-phenylphosphine oxides (31) towards addition reactions, as outlined in Scheme 5. In the same paper, alkylation of chloro(di-t-butyl)phosphine (32) by alkyl benzoates is described 28 see Chapter 3 for details. A similar acylation reaction of tetramethyl-diphosphine disulphide (33) has been described, although the acetylphosphine sulphide (34) was not isolated.29... 

The desulphurization of diphosphine disulphides with tributylphosphine has been used to prepare tetramethyldiphosphine (19). ... 

The problem of the formation of diphosphine disulphides from phosphonothioic dichlorides and Grignard reagents has received further... 

The main drawback to the use of Grignard reagents in conjunction with thiophospho-ryl chloride or bromide in the synthesis of phosphono- and phosphino-thioic halides is the ready formation (subject to the nature of the group R in the reagent) of diphosphine disulphides, 40 and, indeed, this reaction forms the most widely used process for the synthesis of the latter this ready accessibility is in contrast to the relative sparcity of data on the corresponding dioxides, by no means so easily obtainable. 

The action of alkyl halide on diphosphine disulphides (40)(Scheme 9)(X = Cl, Br, or I) provides mixtures of phosphine sulphides and thiophosphinic halides, which may be separable "l... 

Trimeric phosphinoborane derivatives can be obtained by reacting lithium or sodium borohy-dride with phosphinyl (9.35) or phosphine halides (9.36) or diphosphine disulphides (9.37). 

Secondary phosphine sulphides can be obtained in a variety of reactions including the action of caustic soda on aliphatic diphosphine disulphides, or hydrogen sulphide on phosphinous amides. Secondary phosphine sulphides readily add more sulphur to give phosphino dithioic acids (6.79) -an excess produces diphosphine derivatives (below). 

Phosphinothionic (thiophosphinic) chlorides can be obtained by reacting phosphorus pentachlo-ride with phosphinothioic acids (9.429), by the action of sulphuryl chloride on diphosphine disulphides (9.430) or by the action of thiophosphoryl chloride on phosphinyl chlorides (9.431). 

Phosphinodithioic acids, R2P(S)SH, (9.433a) can be made in up to 90% yields by the action of secondary phosphines on sulphur in dilnte ammonia. The ammonium salts so obtained can then be converted into the corresponding acids with HCl (9.434). Phosphinodithioic adds can in some instances be obtained from phosphinothioic halides and sodium hydrosulphide (9.435). They may also be made by a Friedel-Crafts-type reaction with benzene (9.436). Metal salts may be produced directly by the action of sulphur and alkali sulphide, or sulphur and metal, on diphosphine disulphides (Figure 9.23). 

Phosphinothioic acids, R2POSH, are obtainable by direct addition of sulphur to a secondary phosphine oxide or phosphinous ester, or by treatment of a diphosphine disulphide with NaOH or thiophosphinic chloride with NaOH followed by mineral acid (Eigure 9.24). 

Many compounds of the types in Table 9.6 can be made by adding sulphur to the appropriate phosphine. Diphosphine disulphides are thus derived from biphosphines, bis(phosphinodthioic) acids from di-secondary biphosphines (9.584), alkylene bis(alkylphosphine sulphides) and aUcylene bis(phosphinodithioic)acids (Table 9.6) from secondary alkylene biphosphines (9.585, 9.586), and alkylene bis(dialkylphosphine sulphides) from alkylene diphosphines. Reaction (9.583) can also be noted. 

Diphosphine disulphides can also be made by heating secondary phosphine sulphides with phos-phinothionic chloride (9.595), and if diphosphine disulphides are heated with diphosphines, R 2P-PR 2, under appropriate conditions unsymmetrical monosulphides R 2P-P(S)R2 result. Symmetrical disulphides are obtainable by the SO2 oxidation of secondary phosphines (6.268). 

Symmetrical diphosphine disulphides are thermally quite stable and oxidation with nitric add or hydrogen peroxide gives phosphonic adds. With halogens, either thiophosphinyl halides, R2PSCI or halogeno phosphoranes, R2PCI3 can be obtained. Diphosphine disulphides are very reactive and if heated with 10% NaOH solution, they are split into a sodium phosphinothionate and a secondary phosphine sulphide. 

Desulphurisation can be effected with tributylphosphine (9.596). If heated with ethylene and iodine as catalyst, some diphosphine disulphides are transformed into alkylene bis(organophosphine) sulphides (9.597). These same compounds may also be obtained in low yield from alkylene bis(phosphonothioic dichlorides) (9.598). 

Compelling spectroscopic evidence in support of the mixed valence formulation (all other known diphosphine disulphides contain P— P bonds) has been presented, together with supporting chemical evidence. Thus, both compounds react with hydrogen chloride to form the quinquevalent thioacid and tervalent... 

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