OCTOBER 1966
gem-DIPHOSPHINOALKANES
3391
gem-Diphosphinoalkanes. Preparation and Characterization H. R. HAYSAND T. J. LOGAN The Procter and Gamble Cmpany, Miami Val& Laborahries, Cincinnati, Ohio 46,939 Received Apm‘ll8, 1966 The preparation of several members of a new class of organophosphorus compounds, gem-diphosphinoalkanes, by the lithium aluminum hydride reduction of the corresponding alkylidenediphosphonyl tetrachlorides, is described. Although the parent compound, diphosphinomethane, was obtained in low yields (1-6%), 1,l-diphosphinopentane and two higher homologs were obtained in moderately good yields (28-52%). Mono primary phosphines were obtained as by-products in 6-13% yields. In general the structures of the gem-diphosphinoalkanes were confirmed by proton and phosphorus nmr spectral analysis. However, because the proton nmr spectra of the 1,l-diphosphinoalkanes were more complex than was originally anticipated, a rigorous structure proof of 1,l-diphosphinopentane was made. This was accomplished by mass spectral analysis, the phosphorus nmr spectrum, and oxidation to the known 1,l-pentylidenediphosphonic acid. I n general, the gem-diphosphinoalkanes were found to be quite thermally stable. The reduction of two gem-diphosphonates was briefly investigated as an alternate route to the gem-diphosphinea.
I n general, compounds such as simple gem-diols, gem-hydroxyamines12 and gem-diamines possessing a hydrogen on nitrogen2 are relatively unstable. These compounds are characterized by their ease of elimination of water, ammonia, or amines to form aldehydes, ketones, or imines, respectively. I n contrast, hydroxymethyldialkylphosphines are relatively stable and readily isolated in the pure state.a Furthermore, certain gem-dithiols have been prepared and characterizeda4 These facts and the recently reported preparation of bis(ethylphosphino)methane5 led us to investigate the preparation of compounds containing two PH2 groups attached to the same carbon atom.6 The route to gem-diphosphinoalkanes that we chose to investigate was the reduction of alkylidenediphosphonyl tetrachlo0 RR’C(&Cl&
+ LiAlHd +RR’C(PH&
rides with lithuim aluminum hydride. The gem-diphosphonyl tetrachlorides were selected over the gemdiphosphonates because carboxylic acid chlorides are more readily reduced with metal hydrides in general than are esters’ and becausegem-diphosphonates possessing an a-hydrogen atom are rapidly metalated with sodium hydride (see Experimental Section). We hoped to avoid the possibility of this complicating side reaction with lithium aluminum hydride. Subsequently, the reduction of two gem-diphosphonates was briefly investigated and the results are summarized in Table I along with the properties of the gem-diphosphinoalkanes. The parent compound diphosphinomethane (I)6 was obtained in low yields from the reduction of solid methylenediphosphonyl tetrachloride with lithium alu(1) D. J. Cram and G. 9. Hammond, “Organic Chemistry,” McGraw-Hill Book Co., Inc., New, York, N. Y., 1959, pp 271-272. (2) C. R. Noller, “Chemistry of Organic Compounds,” W. B. Saunders Co. Inc., Philadelphia, Pa., 1965,pp 233 and 826. (3) (a) L. Maier, Progr. Inorg. Chem., 6, 185 (1963); (b) H.R. Hays, unpublished results from these laboratories. (4) R. Mayer, J. Morgenatern. and J. Fabian, Angew. Chem. Intern. Ed. Engl., 8, 277 (1964). (5) K.Issleib and G. Doll, 2. Anorg. Allgem. Chem., 894,259 (1963). (6) L. Maier, Angew. Chem. Intern. Ed. En&, 4, 984 (1965). Subsequent to our work Maier has reported the preparation of several u,o-diphosphinoalkanes [(CHz),(PHz)z, n = 1-41 by reduction of the tetraalkyl alkylenediphoaphonates a t the German Chemical Society Meeting in Bonn, Germany, Sept. 13-18, 1965. The reference cited is a brief abstract of this talk and the full details of the preparation of diphosphinomethane (n 1) have not been published a t this time. (7) M. N. Rerick, “Selective Reductions of Organic Compounds with Complex Metal Hydrides,” Metal Hydrides, Inc., Beverly, Mass., 1959, Table VI.
-
minum hydride in dibutyl ether at 0-5°.8 The structure of I was confirmed by phosphorus (Table I) and proton nmr spectral analyses. I n the latter the PH region of the spectrum consisted of two triplets centered a t 7 7.13 (JPH = 202 CPS, JPHCH = 7.2 CPS).~The gas phase infrared spectrum of a sample of I collected from the gas chromatograph is given in Table I. Possible reasons for the low yields of I are discussed in a later portion of this paper. Better results were obtained when 1,l-alkylidenediphosphonyl tetrachlorides were reduced under the conditions used to prepare I. For example, 1,l-diphosphinopentane (11) was isolated in moderately good yields along with low yields of n-amylphosphine from the corresponding gem-diphosphonyl tetrachloride. The properties and identification of these products are described below. The PH region of the proton nmr spectrum of I1 was more complex than was orginally anticipated.1° For this reason the identity and purity of I1 were rigorously established in the following manner. Gas chromatographic analyses of I1 on three different columns and under a wide variety of conditions showed only one symmetrical peak.” The mass spectrum of I1 showed m/e peaks a t 136 and 103 corresponding to the parent peak (M) of I1 and the C5H12Pfragment resulting from M - PH2,respectively. No evidence of either higher or (8) Dodecylphosphine was obtained in 71% yield from dodecylphosphony1 dichloride using similar conditions (Le., 0-5a, 30-min reduction time, diethyl ether solvent). Both reductions were quite exothermic. (9) In all b u t one case the yield of I was estimated b y gas chromatographic analyses of the dibutyl ether solution. Distillation in one case gave a mixture of I and dibutyl ether in which the proton nmr spectrum was recorded. Consequently, the methylene protons were obscured. Subsequent distillation a t atmospheric pressure gave a much purer sample of I ; however, the sample of I ignited and was lost when it was inadvertently exposed to a trace of air. (10) (a) From a firstorder consideration of the proton nmr spectra of 8ecbutylphosphine and a number of other primary phosphines we had originally anticipated a pair of doublets (JPH = ca, 200 cps, JCHPH = ea 7 cps) for the P H portion of the spectrum of 11. Subsequently, higher resolution and closer inspection of several of the spectra under consideration showed more complex patterns than could be explained b y a simple first-order analysis. A detailed analysis will be presented in a later communication. (b) Proton nmr spectra obtained early in this study suggested an alternate structure, 12-diphosphinopentane. In addition to being highly unlikely from a chemical standpoint, this struoture was excluded on the basis of the following facts. The phosphorus chemical shifts of the four isomeric butylphosphines are widely different ( i . e . , iso- 151 ppm, n- 140 ppm, see- 116 ppm, and t- 82 ppm). The initial phosphorus nmr spectrum of 11, however, was not resolved beyond a broadened triplet, suggesting two identical or nearly identical phosphorus atoms (within 10 cps) attached to the same carbon atom. (11) One of these columns, a 30% silicone rubber on Chromosorb W, was capable of excellent resolution of mixtures of either t-. sec-, and n-butylphosphosphines or t-, iso-, and n-butylphosphines. The sec- and isobutylphosphines were not resolved on this column.
HAYSAND LOGAN
3392
VOL. 31
TABLE I g~-DIPHOSPHINOALKANES 0
t
RR'C(PXz)1
R
X
R'
RR'C(PH2)z
yield
BP, 'C (mm)
Pal nmr," ppm
JPH,~ CPS
% yield of RR'CHPHs
H H c1 I 1-6 83-85 126b,c 199 d C4H9 H c1 I1 44-5 1 53-55 (9) 109 194 8-11e C4H9 CaHs c1 I11 2f 94-95 (9) 91 194 9 88-90 (0.1) 108 192 h H c1 IV 40 CioHzt V 28-52 103-105 (0.1) 107 193 6-13' CllH23 H c1 CH3 CHa c1 VI 2 j 74 192 k CJL9 €I OEt VI1 18l 103-105 (4-5) 105 191 1g
