Addition of phosphines

Commercial phosphine derivatives are produced either by the acid-cataly2ed addition of phosphine to an aldehyde or by free-radical addition to olefins, particulady a-olefins. The reactions usually take place in an autoclave under moderate pressures (<4 MPa (580 psi)) and at temperatures between 60 and 100°C. 

Textile Flame Retardants. The first known commercial appHcation for phosphine derivatives was as a durable textile flame retardant for cotton and cotton—polyester blends. The compounds are tetrakis(hydroxymethyl)phosphonium salts (10) which are prepared by the acid-cataly2ed addition of phosphine to formaldehyde. The reaction proceeds ia two stages. Initially, the iatermediate tris(hydroxymethyl)phosphine [2767-80-8] is formed. 

The addition of phosphines to fiuoroolefins is of free radical nature [6, 7, (equations 2-5)... 

The use of ionic liquids as reaction media for the palladium-catalyzed Heck reaction was first described by Kaufmann et ak, in 1996 [85]. Treatment of bromoben-zene with butyl acrylate to provide butyl trans-cinnamate succeeded in high yield in molten tetraallcylammonium and tetraallcylphosphonium bromide salts, without addition of phosphine ligands (Scheme 5.2-16). 

The overall sequence of three steps may be called the Wittig reaction, or only the final step. Phosphonium salts are also prepared by addition of phosphines to Michael alkenes (hke 15-8) and in other ways. The phosphonium salts are most often converted to the ylids by treatment with a strong base such as butyllithium, sodium amide, sodium hydride, or a sodium alkoxide, though weaker bases can be used if... 

Although a wide variety of metals were claimed as active catalysts for formaldehyde hydrophosphination, platinum salts were preferred. Similarly, Group 10 metal salts were used to catalyze acrylonitrile hydrophosphination. Russian workers showed that Ni(II) or Co(II) salts in the presence of ammonia or amines would also catalyze the addition of phosphine to formaldehyde [6]. More recently, academic and industrial interest in these reactions was sparked by a series of papers by Pringle, who investigated late metal phosphine complexes as hydrophosphination catalysts. These and related studies are arranged below by substrate. 

The discussion of the activation of bonds containing a group 15 element is continued in chapter five. D.K. Wicht and D.S. Glueck discuss the addition of phosphines, R2P-H, phosphites, (R0)2P(=0)H, and phosphine oxides R2P(=0)H to unsaturated substrates. Although the addition of P-H bonds can be sometimes achieved directly, the transition metal-catalyzed reaction is usually faster and may proceed with a different stereochemistry. As in hydrosilylations, palladium and platinum complexes are frequently employed as catalyst precursors for P-H additions to unsaturated hydrocarbons, but (chiral) lanthanide complexes were used with great success for the (enantioselective) addition to heteropolar double bond systems, such as aldehydes and imines whereby pharmaceutically valuable a-hydroxy or a-amino phosphonates were obtained efficiently. 

The Michael addition of phosphine nucleophiles to nitroalkenes provides novel P-nitro phosphonates, as in Eq. 4.32.38 Yamashita and coworkers have shown that the nucleophilic addition of Ph2POH to chiral nitroalkenes derived from sugars proceeds stereoselectively to the S- -isomer (Eq. 4.32) in high diastereoselectivity (ds 11 1). 

Successive addition of phosphine to an aldehyde and then reaction with an azomethine gives 1,3,5-azoxaphosphorinanes (8) (74MI1) possessing both P—C—O and P—C—N fragments [Eq. (6)]. 

Thus, the rule of Keulemans (49), that a-quaternary carbon formyl compounds are not formed, was followed. The olefin isomerized to allow formyl attachment to a primary carbon atom. Addition of phosphine, which decreases isomerization, resulted in no reaction. 

Dilworth, J.R., Griffiths, D.V., Hughes, J.M., and Morton, S., Synthesis of 2-S-(2-tetrahydropyranyl)thioethylphosphines and 2-mercaptoethylphosphines by free radical addition of phosphines to 2-(vinylthio)tetrahydropyran, Phos-ph Sulf, Silic. Relat. Elem., 71, 249, 1992. 

Harrison, K.N., Hoye, P.A.T., Orpen, A.G., Pringle, P.G., and Smith, M.B., Water-soluble, zero-valent, platinum-, palladium,- and nickel-P(CH2OH)3 complexes catlaysts for the addition of phosphine to formaldehyde, J. Chem. Soc., Chem. Commun., 1096, 1989. 

Before examining the reaction of deactivated alkenes, the phosphonium salt synthesis was applied to 1,3-dienes.21 When ( )-6-phenyl-l,3-hexadiene was treated with equimolar amounts of PPh3 and CF3S03H in the presence of RhH(PPh3)4 (2.5 mol%) in THF at 0 °C for 3 h, ( )-(6-phenyl-3-hexenyl)triphenylphosphonium salt was obtained in 89% yield after anion exchange with LiPF6 and recrystallization (Scheme 16). The addition of phosphine and hydrogen occurred at the 1- and 2-carbon atoms of the 1,3-diene, respectively. The reaction of (7)-1,3-dienes was then performed for comparison. 

Phosphines, as nucleophiles, add to many unsaturated substrates giving metal-lated ylides. Scheme 17 collects some representative examples of the addition of phosphines to carbyne complexes, giving (57) [132], to allenylidenes (58) [133], a-alkenyls (59) [134], or a-alkynyls (60) [135]. Moreover, reaction of phosphines with 7i-alkenes [136] and 71-aIkynes (61)-(64) [137-140] have also been reported. It is not possible to explain in depth each reaction, but the variety of resulting products provides an adequate perspective about the synthetic possibihties of this type of reactions. 

Several reports have appeared on the effect of additives on the Pauson-Khand reaction employing an alkyne-Co2(CO)6 complex. For example, addition of phosphine oxide improves the yields of cyclopentenones 119], while addition of dimethyl sulfoxide accelerates the reaction considerably [20]. Furthermore, it has been reported that the Pauson-Khand reaction proceeds even at room temperature when a tertiary amine M-oxide, such as trimethylamine M-oxide or N-methylmorpholine M-oxide, is added to the alkyne-Co2(CO)6 complex in the presence of alkenes [21]. These results suggest that in the Pauson-Khand reaction generation of coordinatively unsaturated cobalt species by the attack of oxides on the carbonyl ligand of the alkyne-Co2(CO)6 complex [22] is the key step. With this knowledge in mind, we examined further the effect of various other additives on the reaction to obtain information on the mechanism of this rearrangement. 

Maddaford reported the diastereoselective synthesis of C-glycosides 29 using conjugate addition catalyzed by cationic rhodium catalysts such as [Rh(COD)2]BF4 (Eq. 1) [24]. Addition of phosphine hgands to the reaction system inhibited the conjugate addition. It is likely that the enone 28 derived from the pyranose is less reactive toward the conjugate addition. 

Recently, arylation of methyl acrylate was intensively studied [15-21], Phenylation with Ph3BiX2 was largely affected by X, as shown in Scheme 6. PdCl2 as well as Pd2(dba)3 (dba = dibenzylideneacetone) are efficient catalysts, whereas the addition of phosphine ligands retards the phenylation e.g., PdCl PPh3 afforded no... 

The addition of phosphine to olefins provides today a generally applicable method for the syntheses of organophosphines. Stiles, Rust and Vaughan were the first to study the reaction systematically. It is catalysed by organic peroxides such as, for example, di-t-butyl peroxide, by a, a -azobis-isobutyro-nitrile by other free radical sources or by exposing the reaction mixture to UV- or X-radiation. The PHj radicals, produced according to Eq. (77), react further with olefins thus producing PH2 radicals continually. 

The addition of phosphine to olefins is accelerated by acidic and basic catalysts. Under the influence of non-oxidising acids or Lewis acid such as, for example, methanesulphonic acid, benzenesulphonic acid, trifluoro-acetic acid or boron trifluoride phosphine is quickly added to olefins at pressures of 20-40 at, and temperatures of 30-60 °C. It is assumed that the reaction proceeds via a carbonium ion which is first formed thus ... 

The addition of phosphine to 5,6-dideoxy-l,2-0-isopropylidene-D-xylo-hex-5-enfuranose 14) takes place when the reaction mixture is irradiated with UV-light. A mixture of 5,6-dideoxy-l, 2-0-isopropylidene-o -D-xylo-hexa-furanose-phosphine 15) and bis-6-(5,6-dideoxy-l, 2-0-isopropylidene-a-D-xylo hexanose)phosphine (f 6) is probably formed but the components could not be separated. In the presence of atmospheric oxygen these are converted to the corresponding phosphonous acid 17) and the secondary phosphine oxide (25), respectively... 

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