Phosphines Triphenylphosphine

You have already met phosphonium salts in Chapter 5 where you saw the reaction of a phosphine (triphenylphosphine) with an alkyl halide (methyl iodide). 

The literature contains descriptions of acrylonitrile polymerization initiated by three different phosphorus bases, triethyl phosphine, triphenylphosphine, and triethyl phosphite. 

This method can be used to prepare commercially the best of all known tertiary phosphines, triphenylphosphine (PPh3). Its combination of favorable physical properties (air-stable solid, easy to handle) and solubility in organic media has resulted in extensive uses as a ligand in coordination or organometallic chemistry or as a reagent in organic synthesis. 

Mukaiyama aldol reactions. Silyl keteneacetals undergo condensation with aldehydes under the influence of tris(2,4,6-trimethoxyphenyl)phosphine. Triphenylphosphine is slightly less efficient and aliphatic phosphines such as t-BujP are much infenior. 

DEHYDRATION Alumina. Phosphorus pentoxide. Rhodium(Ill) chloride-Triphenyl-phosphine. Triphenylphosphine-Carbon tetrachloride. 

The in situ formation of Pd(0) complexes takes place when Pd(OAc)2 is associated with various phosphines (i) aromatic phosphines (p-Z—C6H4)3P (Z = EDG or EWG). The formation of the Pd(0) complex follows a Hammett correlation with a positive slope [20]. The more electron-deficient the phosphine, the faster the reduction process this is in agreement with the intramolecular nucleophilic attack of the acetate onto the ligated phosphine as proposed in Scheme 1.13 (ii) aliphatic phosphines [20] (iii) water-soluble phosphines, triphenylphosphine trisulfonate (trisodium salt) [25] and triphenylphosphinetricarboxylate (trilithium salt) [26]. One major exception is the tri-o-tolylphosphine P(o-Tol)3, which cannot reduce Pd(OAc)2 to a Pd(0) complex in DMF or THE. Instead, an activation of one C-H bond of the tolyl moieties by Pd(OAc)2 takes place, leading to a dimeric P,C-palladacycle (see Section 1.5), as reported by Herrmann et al. in 1995 [27]. Such a Pd(ll) P,C-palladacycle catalyses Mizoroki-Heck reactions [27]. It is, however, a reservoir of a Pd(0) complex, as recently established by d Orly6 and Jutand [28] in 2005 (see Section 1.5). 

Hydroboration of Pyridines. P)ridines could be hydroborated under Rh catalysis to furnish A-borylated 1,2-dihydropyridines. Maximal yields and the least amount of A-borylated 1,4-dihydropyridine could be obtained with PCy3 compared with other phosphines. Triphenylphosphine and PCys produced diminished yields and favored the 1,4-dihydropyridine product (eq 41). 

Diphenyldisulfide reacted slowly while di-(i T,A/ -dimethylaminophenyl) disulfide reacted more readily. When R is ethyl, benzyl, o-nitrophenyl, p-nitrophenyl, dibenzhydryl, benzthiozoyl, 9-fluorenyl, or antipyryl, the disulfide is stable to treatment with triphenylphosphine for 10 hours at 80° C, and no monosulfide is produced. Electron-donoring groups in the phosphine also increase the rate of reaction. Disulfides of the type R(S=)C—S—S—C(==S)—R react very quickly with phosphines. Triphenylphosphine will remove the sulfur from an ethylene sulfide... 

Related Reagents. Diphosphorus Tetraiodide Tri-n-butyl-phosphine Triphenylphosphine Raney Nickel. 

Phosphine Oxides. Development of cyanoethylphosphine oxide flame retardants has been discontinued. Triphenylphosphine oxide [791 -28-6] C gH OP, is disclosed in many patents as a flame retardant, and may find some limited usage as such, in the role of a vapor-phase flame inhibitor. 

Some compounds are named as derivatives of the simple phosphoms hydrides (phosphines). For example, dimethylphosphine [676-59-5], (CH2)3PH triphenylphosphine oxide [791-28-6], (CgH3)3P=0 1,2-dimethyldiphosphine [53684-00-7], CH PHPHCH diethyliodophosphine [20472-47-3], (C2H3)2PI phosphonium iodide [12125-09-6], PH" P tetramethylphosphonium chloride [1941 -19-1], (CH3) P" C1 and phenylphosphonium bromide [55671-96-0], CgH PHjBr-. 

Halophosphines can be reduced to phosphines. Various methods have been employed to recover the product, but yields are only fair. Triphenylphosphine [603-35-0] is prepared from ben2ene and phosphoms trichloride ... 

A useful apphcation of phosphines for replacing a carbonyl function with a carbon—carbon double bond is the Wittig reaction (91). A tertiary phosphine, usually triphenylphosphine, treated with the appropriate alkyl halide which must include at least one a-hydrogen, yields the quaternary salt [1779A9-3] which is then dehydrohalogenated to form the Wittig reagent, methylenetriphenylphosphorane [19943-09-5] an yhde. 

The processiag costs associated with separation and corrosion are stiU significant ia the low pressure process for the process to be economical, the efficiency of recovery and recycle of the rhodium must be very high. Consequently, researchers have continued to seek new ways to faciUtate the separation and confine the corrosion. Extensive research was done with rhodium phosphine complexes bonded to soHd supports, but the resulting catalysts were not sufficiently stable, as rhodium was leached iato the product solution (27,28). A mote successful solution to the engineering problem resulted from the apphcation of a two-phase Hquid-Hquid process (29). The catalyst is synthesized with polar -SO Na groups on the phenyl rings of the triphenylphosphine. 

More recent examples have employed a milder reagent system, triphenyl-phosphine and dibromotetrachloroethane to generate a bromo-oxazoline, which is subsequently dehydrohalogenated. Wipf and Lim utilized their method to transform intermediate 11 into the 2,4-disubstituted system of (+)-Hennoxazole k Subsequently, Morwick and coworkers reported a generalized approach to 2,4-disubstituted oxazoles from amino acids using a similar reagent combination, triphenylphosphine and hexachloroethane. ... 

The initial step of olefin formation is a nucleophilic addition of the negatively polarized ylide carbon center (see the resonance structure 1 above) to the carbonyl carbon center of an aldehyde or ketone. A betain 8 is thus formed, which can cyclize to give the oxaphosphetane 9 as an intermediate. The latter decomposes to yield a trisubstituted phosphine oxide 4—e.g. triphenylphosphine oxide (with R = Ph) and an alkene 3. The driving force for that reaction is the formation of the strong double bond between phosphorus and oxygen ... 

A halogenating system related to the preceding case is formed by the reaction of triphenylphosphine with molecular bromine or chlorine. The system is not as sensitive to moisture as the phosphine-carbon tetrahalide system (see preceding section), but it suffers from the disadvantage that hydrohalic acids are produced as the reaction proceeds. Nevertheless, sensitive compounds can be successfully halogenated by the system, as exemplified by the preparation of cinnamyl bromide from the alcohol. 

Soderberg and coworkers have developed a palladium-phosphine-catalyzed reductive iV-het-eroannuladon of 2-nitrostyrenes forming indoles in good yields For example, reaction of 6-bromo-2-nitrostyrene with carbon monoxide in the presence of a catalytic amount of palladium diacetate (6 mol% and triphenylphosphine 124 mol% in acetonitrile at 30 gives 4-bromoindole in 86% yield fEq 10 62 Several functional groups, such as esters, ethers, bromides, tnflates, and additional nitro groups, have been shown to be compatible with the reaction conditions... 

It was recently found that the modification of neutral phosphine ligands with cationic phenylguanidinium groups represents a very powerful tool with which to immobilize Rh-complexes in ionic liquids such as [BMIM][PFg] [76]. The guani-dinium-modified triphenylphosphine ligand was prepared from the corresponding iodide salt by anion-exchange with [NH4][PFg] in aqueous solution, as shown in Scheme 5.2-15. The iodide can be prepared as previously described by Stelzer et al. [73]. 

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