OCTOBER1967 THECHEMISTRY OF DIPHOSPHINEDISULFIDES. I11 2999 The Chemistry of Diphosphine Disulfides. 111. Influence of Structure on the Course of Phosphinothioic Halide-Grignard Reactions’ N. K. PATELAND H. JAMESHARWOOD Department of Chemistry, The University of Akron, Akron, Ohio 44304 Received January 4, 1967 Reactions of dimethyl-, diethyl-, or di(n-propy1)phosphinothioic halides with Grignard reagents give trisub- stituted phosphine sulfides in high yield. In conflict with results reported by Bogolyubov, it was not possible to obtain diphosphine disulfides from these reactions. Methylphenylphosphinothioic chloride reacts with ali- phatic or aromatic Crignsrd reagents to yield both trisubstituted phosphine sulfides and meso-1,2-dirnethyl-ll2- diphenyldiphosphine disulfide. Diphenylphosphinothioic chloride reacts with aliphatic Grignard reagents to yield tetraphenyldiphosphine disulfide, but it reacts with aromatic Grignard reagents to yield trisubstituted phosphine sulfides. These results indicate that metal-halogen exchange processes precede the P-P coupling step involved in diphosphine disulfide formation. The high stereoselectivity of the coupling step can be ex- plained by the mechanism S S II /I RR’PCl + R”MgX RR‘PMgX + R”C1 The reactions of Grignard reagents with thiophos- these latter reactions. Interestingly, alkynyl Grignard phorus halides can take several courses, depending on reagentsl1,l2yield only phosphine sulfides in these re- the structures of the thiophosphorus halide and the actions. Grignard reagent.2-e Thiophosphoryl chloride reacts Harwood and Pollart13 observed that disubstituted with simple aliphatic Grignard reagents to yield di- phosphinothioic halides, in contrast to thiophosphoryl phosphine disulfides in high yield, but this reagent re- halides or substituted phosphonothioic halides, yield acts with acetylenic,’ vinyl,5 aromatic, lo benzyl, lo or only phosphine sulfides when treated with Grignard hindereds alkyl Grignard reagents to yield trisubsti- reagents. On the basis of this observation, these tuted phosphine sulfides primarily. workers concluded that either reduction or metal-halo- gen exchange processes precede the P-P coupling step ss involved in diphosphine disulfide formation. Recently, II II R~P-PRz however, Bogoly~bov~~obtained results which are in- f consistent with such an interpretation; he reported RMgX PSCl, + isolating tetraethyldiphosphine disulfide in 50% yield RaP=S and tetra-n-propyldiphosphine disulfide in 24% yield It is interesting to note that those Grignard reagents from reactions of the corresponding phosphinothioic which yield phosphine sulfides when treated with PSCll chlorides with Grignard reagents. are also the Grignard reagents which are initiators for In order to resolve the conflicting results obtained by the stereospecific polymerization of methyl meth- Bogolyubov and by Harwood and Pollart, to define bet- acrylate.* The parallelism noted for the behavior of ter the scope of the stepwise phosphine sulfide synthe- various Grignard reagents in these two widely different sis outlined by the latter workers, and to obtain ad- reactions is extremely good. ditional information related to the mechanism of the The behavior of Grignard reagents toward alkyl- or reaction yielding diphosphine disulfide derivatives, the arylphosphonothioic dihalides parallels, in general, reactions of a series of substituted phosphinothioic their behavior toward PSCl,, except that diphosphine halides with Grignard reagents were investigated in disulfides (instead of trisubstituted phosphine sulfides) the present study. have been obtained from the reactions of alkylphos- phonothioic dihalides with aromatic and benzyl Gri- Results gnard reagent^.^^'^ Racemic and meso forms of dial- Aliphatic Grignard-Dialkylphosphinothioic Halide Re- kyldiaryldiphosphine disulfides have been obtained by actions.-Because of its significance to previous in- (1) Presented before the Division of Organic Chemistry at the 152nd terpretations of the mechanism and scope of Grignard- National Meeting of the American Chemical Society, New York, N. Y., Sept thiophosphoryl halide reactions, it seemed important to 1966. check Bogolyubov’s claim that some dialkylphosphino- (2) A. H. Cowley, Chem. Reo., 66, 617 (1965). (3) K. D. Berlin, T. H. Austin, M. Peterson. and M. Nagabhushnam, thioic chlorides react with alkyl Grignard reagents to Topics Phosphorus Chem., 1, 15 (1964). yield diphosphine disulfides. When reactions of di- (4) L. Maier, Proer. Inore. C‘hem., 6, 27 (1963). (5) H. Niebergall and B. Langenfeld, Chem. Ber., 96, 64 (1962). (11) G. M. Rogolyubov and A. A. Petrov, Zh. Obshch. Khim., 86, 988 (6) L. Maier, Topics Phosphorus Chem., I, 43 (1965). (1965); Chem. Abstr.. 63, 998lh (1965);J. Gen. Chem. USSR,86, 994 (1965). (7) G. M. Bogolyubov and A. A. Petrov, Zh. Ohshch. Khim., 86, 704 (12) G. M. Bogolyubov, K. 9. Mingafeva, and A. A. Petrov, Zh. Obshch. (1965); Chem. Abstr., 68, 4430 (1965);J. Gen. Chem. USSR,86, 705 (1965). Khim.. 36, 1566 (1965); Chem. Abslr.. 68, 17860~(1965); J. Gen. Chem. (8) A. Niahioka, H. Watanake, K. Abe, and Y. Sono, J. Polumer Sci., 18, USSR,86, 1570 (1965). 241 (1960). (13) H. J. Harwood and K. A. Pollart, J. Ore. Chem., 28, 3430 (1963). (9) L. Maier, Chem. Ber., 94, 3043 (1961). (14) G. %I. Bogolyubov, Zh. Obshch. Khim., 86, 754 (1965); Chem. Abslr., (10) P. C. Crofts and K. Goeling. J. Chem. Soc., 2486 (1964). 68, 4327 (1965); J. Gen. Chem. USSR,$6, 755 (1965). 3000 PATELAND HARWOOD VOL. 32 ethylphosphinothioic chlroide with ethylmagnesium obtained in these studies cast considerable light on the bromide (or chloride) were conducted in the present mechanism of the reaction yielding diphosphine di- study, triethylphosphine sulfide was obtained in yields sulfide derivatives, as will be discussed next. ranging from 70 to 90%, and there was no indication that any diphosphine disulfide derivatives were present Discussion among the reaction products. Since Bogolyubov’s paper did not provide specific reaction conditions, we In an earlier paper,13 we concluded that the P-P varied our conditions extensively in an effort to obtain coupling step in reactions yielding diphosphine di- results similar to his. Reaction temperature, reagent sulfides is preceded either by a reduction step yielding concentrations, and order of addition were changed, an RP=S-type intermediate or else by a metal-halogen but in no instance was any tetraethyldiphosphine di- exchange reaction. Either process was consistent with sulfide obtained. Excess magnesium, in various forms, the observation that thiophosphorus compounds con- was added to some of the reaction systems, but the re- taining two or more phosphorus-halogen bonds tend to action course was not changed. yield diphosphine disulfide when treated with Grignard Similarly, we obtained tri(n-propy1)phosphine sulfide reagents, whereas other thiophosphorus compounds in 73% yield from the reaction of dipropylphosphin- usually yield phosphine sulfides in such reactions. othioic chloride with propylmagnesium chloride, and Since several phosphinothioic halides were noted in the found no evidence for the presence of tetrapropyldiphos- present study to yield diphosphine disulfides when phine disulfide in the reaction mixture. In addition, treated with Grignard reagents, it is no longer necessary the reactions of dimethylphosphinothioic bromide, di- to require the participation of a reduced intermediate, ethylphosphinothioic bromide, or di(n-propy1)phos- such as RP=S, in the P-P coupling process. Instead, phinothioic bromide with methyl-, ethyl-, or n-propyl- it seems much more likely that a metal-halogen ex- magnesium bromide produced trisubstituted phosphine change process precedes the coupling step. sulfides in yields ranging from 44 to 77% (cf. Table I). KOdiphosphine disulfide derivatives mere obtained from S S these reactions, although their properties are such that they should be easily isolated. S S ss We are unable to explain the results of Bogolyubov It /I tl I1 at this point and believe that the general course of RzPCl + RzPMgC1 +RzP-PRZ + MgC1, dialkylphosphinothioic halide-Grignard reactions leads to trisubstituted phosphine suljides13 and not to diphos- Evidence that metal-halogen processes occur during phine disuljide deravatives.14 these reactions was obtained by submitting the reaction Grignard Reactions Involving Alkylaryl- or Diaryl- mixtures to gas-liquid partition chromatographic phosphinothioic Halides.-In contrast to the results analysis. We observed that ethyl chloride is formed in described above, we obtained both diphosphine di- the initial stages of ethylmagnesium bromide-diphenyl- sulfide derivatives and trisubstituted phosphine sulfides phosphinothioic chloride reactions. Once formed, ethyl from the reactions of Grignard reagents with aryl- chloride rapidly disappears, presumably owing to subse- substituted phosphinothioic halides. The relative quent reaction with ethylmagnesium bromide. yields of these products seem to depend on the struc- If one assumes that’metal-halogen exchange must be tures of the reactants. For example, diphenylphos- favorable, both kinetically and thermodynamically, for phiriothioic chloride reacted with phenylmagnesiuin diphosphine disulfide formation to take place, then the results obtained in previously reported thiophos- bromide to yield only ‘6 triphenylphosphine sulfide, whereas the corresponding reaction with ethylmagne- phorus halide-Grignard reactions can be explained. siuni bromide yielded only’j the diphosphine