Selenide, triphenylphosphine

Submitted by PHILIP NICPON and DEVON W. MEEK Checked by BRUCE M. FOXMANt and F. A. COTTONf 

Tertiary phosphine selenides have been prepared either by direct fusion of the tertiary phosphine with elemental selenium or by refluxing the phosphine with selenium in an inert solvent. In the case of a solid phosphine, such preparations often require numerous and time-consuming extractions to obtain the pure phosphine selenide. 

The reaction of triphenylphosphine with potassium selenocy-anate rapidly produces quite pure material in almost quantitative yield. The procedure outlined below is simple and appears to be particularly advantageous for preparation of selenide derivatives of solid phosphines, f Actual working time required for the synthesis is 1 to 2 hours, and the total elapsed time is less than 1 day. 

Triphenylphosphine selenide crystallizes from absolute ethanol as small white needles which melt at 187 to 188°. The compound is very soluble in dichloromethane moderately soluble in hot methanol, hot ethanol, hot acetonitrile, hot benzene, and hot 1-butanol and insoluble in ether and water. The PSe infrared stretching frequency occurs at 562 cm. i (Nujol mull). 

95% yields by the above procedure tri-p-tolylphosphine selenide, m.p. 198 to 198.5° tri-m-tolylphosphine selenide, m.p. 139 to 140° diphenyl[3-(dimethylamino)propyl]phos-phine selenide, (C6Hs)2P(Se)CH2CH2CH2N(CH3)2, m.p. 90 to 91° and ethylenebis(diphenylphosphine selenide), (C6H5)2-P(Se)CH2CH2P(Se)(C6H5)2, m.p. 194 to 195°. 

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Diselenetane derivative 39 reacts with elemental selenium in the presence of a catalytic amount of triphenyl-phosphine or triphenylphosphine selenide to give 1,2,4-triselenolane 65 in 37% yield (Scheme 9) <2001TL3881>. The reaction with propiolic acid under reflux conditions in toluene affords selenodioxenone 66 (25%) and trace amounts of compound 67 <2004BCJ1933>. 

The reactions of /< //-butylarylmethylenetriphenylphosphoranes with elemental selenium yield the corresponding 1,3-diselenetanes 39 (24%) and 85 (26%) along with the 1,2,4-triselenolane derivatives 86 and triphenylphosphine selenide (Scheme 25) <2001TL3881>. 

Several of the procedures discussed in the sulfoxide section describe the successful extension of the method to the reduction of selenoxides, - - and there is little doubt that many of the other procedures cited earlier could be used likewise. Sakaki and Oae used triphenylphosphine selenide and similar se-lenides to reduce selenoxides to selenides in 79-93% yield (equation 19). Using a chiral phosphine selenide, these workers showed that the phosphine oxide formed had suffered predominant inversion, with a stereospecificity of over 80%. Detty has reported the application of the silane PhSeSiMes (12) to the reduction of selenoxides and telluroxides. The reactions are rapid and proceed essentially quantitatively, even in the presence of a hydroxy or carbonyl group. 

Triphenylphosphine selenide, potassium selenocyanate, 3-methyl-2-selenoxobenzothiazole sodium 0,0-diethyl phosphorotelluronate," 0,0-dialkyIphosphoroselenoic acid salts" and benzenese-lenocarboxamide, have all been reported as reagents capable of one-step deoxygenation of epoxides. 

Under the same conditions triphenylphosphine selenide was ineffective. ... 

Bis-3,4-(trifluoromethyl)-l,2-diselenete 651 is prepared by refluxing selenium with hexafluoro-2-butyne. It reacts with triphenylphosphine and triphenyl-arsine. Triphenylphosphine selenide was isolated, but no other compounds were identified.Ring-opened complexes with nickel, copper, vanadium, molybdenum (652), tungsten, iron, and cobalt are analogous to complexes of the 1,2-dithiete (527) (Section XXXV.2.C.). 

A new one-pot method has been developed by Kraszewski for the synthesis of aryl nucleoside phosphate (3a-p) and phosphorothioate (4a-p) diesters. This method, based on H-phosphonate chemistry, employed diphenyl phosphoroch-loridate and a series of phenols. Depending on the substituents present on the phenols, oxidation conditions were optimized to avoid competing hydrolysis. A versatile procedure that permits easy access to H-phosphonoselenoate monoesters (5) has been developed by Stawinski. These monoesters, obtained by selenisation of a phosphinate using triphenylphosphine selenide in combination with trimethylsilyl chloride, reacted with a suitable nucleoside in pyridine/acetonitrile in the presence of diphenyl phosphorochloridate to yield... 

Most of the examples of seleniranes and telluriranes shown as the unstable intermediates in the organic synthesis are derived from oxiranes. As discussed previously in Section 1.07.6.2, seleno-cyanate anions react with epoxides at room temperature to deposit selenium via the selenirane intermediate and form the corresponding alkenes. On the other hand, triphenylphosphine selenide and trifluoroacetic acid constitute an effective and mild combination of reagents for carrying out the deoxygenation of epoxides (67) to alkenes via cyclic intermediate (68) (Scheme 12) <73CC253>. 

Epoxide deoxygenation by or via phosphine oxides or selenides continues to attract attention. Further study of deoxygenation by triphenylphosphine selenide (30) has implicated episelenide intermediates, and n.m.r., chemical,... 

The chemical and electrochemical oxidations of triphenylphosphine sulphide and phosphorothioates in acetonitrile have been investigated.In both reactions, triphenylphosphine sulphide initially gives a product formulated as a dimeric di-cation (39), but this rapidly decomposes on removal of the solvent or exposure to air. Triphenylphosphine oxide and sulphide form radical anions on treatment with potassium in ether at low temperature or by one-electron reduction at a Hg cathode in DMF. The photo-oxidation (sensitized by polymer-supported Rose Bengal) of triphenylphosphine selenide to the oxide has been shown to be highly solvent-dependent. 

C1BH12M0S6, Tris(benzene-1,2-dithiolato)molybdenum(VI), 42B, 942 ClbHi2N2PdS2, Bis(8"mercaptoquinolinato)palladium, 39B, 824 ClbHi2N2PtS2 f Bis(8-mercaptoquinolinato)platinum, 39B, 824 ClbHj 3O9OS3PS2 f (M"Hydrido)-(M"dithioformato)-bis(tricarbonyl-osmium)-tricarbonyl(dimethylphenylphosphine)osmium, 46B, 1212 ClbHi5Cl2HgPSe, Triphenylphosphine selenide mercury(II) chloride, 40B, 1128... 

Triphenylphosphine oxide, triphenylphosphine sulfide and triphenylphosphine selenide recrystallized from light petroleum, benzene and ethanol, respectively. 

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