Reductions trialkylphosphines

The reduction of a solution of a trialkylphosphine copper(I) iodide complex (CuIPR ) with preformed lithium naphthalide (LiNp) in THF or DME under argon was found to give a more reactive copper species, which will undergo oxidative addition with a variety of organic substrates at room... 

The substitution of trialkylphosphine for carbon monoxide also makes the metal-hydrogen bond more hydridic in character and results in increased reduction of the initially formed aldehyde to alcohol. Slaugh and Mullineaux (52) compared Co2(CO)g and [Co2(CO)8 + 2PBu3], each at reaction conditions of 150°C, 500 psi, H2/CO I.0, for the hydroformylation of 1-pentene. The products consisted of hexyl aldehydes and hexyl alcohols in the ratios of 95 5 and 30 70, respectively. In a negative aspect of the reaction, they observed 23% hydrogenation of alkene to alkane at a reaction temperature of 195°C with the phosphine-modified catalyst. Tucci (54) reported less alkane formation (4-5%) under more favorable reaction conditions (I60°C, H2/CO 1.2, 1 hour reaction time). 

The reduction of disulfide bonds with trivalent phosphines has been known for some time (Ruegg and Rudingder, 1977 Kirley, 1989 Levison etal., 1969). Unfortunately, trialkylphosphines generally are water-insoluble, undergo autoxidation, and are extremely odious. 

Solution phase chemical synthesis is a convenient way for making surfactant coated magnetic nanoparticles, as described in various reviews [12-18]. Monodisperse Co nanoparticles with standard deviation less than 10% are synthesized by decomposition of Co2(CO)8 [19-22] or Co(rj3-C8Hi3X n4-C8Hi2) [23] and reduction of cobalt salt [24,25] in the presence of oleic acid and trialkylphosphine, or trialkylphosphine oxide, or alkylamine. Monodisperse iron nanoparticles are normally prepared from decomposition of Fe(CO)5 [26-28]. However, metallic iron-based particles from this decomposition procedure are difficult to characterize due to the chemical instability. A recent synthesis using decomposition of Fe[NSiMe3)2]2 offers a promising approach to monodisperse Fe nanocrystals [29]. 

New nickel-benzyne complexes (143-147) have been prepared by reaction of o-dihaloarenes with Ni(COD)2 in the presence of a trialkylphosphine followed by reduction of the oxidative addition product with either Li or 1% Na/Hg in ether [e.g., Eq. (23)]. The oxidative addition reaction depends on the nature of substituents on the arene and fails to occur when strong electron-donating groups are present. Based on NMR and mass spectrometry (MS) data, the new complexes were formulated as monomeric. It had been... 

Complexes with trialkylphosphines which are more basic and sterically less demanding than triarylphosphines are generally less active due to a lower tendency to dissociation. Ligands, as well as the polarity of the reaction medium, may also influence the nature of the active species. For example, whereas in the case of triphenylphosphine the hydrogenation cycle is initiated by a Rhra dihydride species, hydrogenations with the water-soluble analogue RhCl(tppms)3 (tppms = Ph2PC6H4S03Na) involve instead a Rh1 hydride formed by water-assisted reductive HC1 elimination (c/. monohydride complexes discussed below) ... 

Dimethylphosphine has been prepared by alkylation of phospho-nium iodide with methjd iodide and by reductive cleavage of phosphorus sulfides with methyImagnesium bromide. Diethyl-, dibutyl-, and dicyclohexylphosphines have been prepared by reduction of the corresponding tetraalkyldiphosphine disulfides with lithium hydroaluminate in ether. This latter method gives dialkylphosphines uncontaminated by mono- and trialkylphosphines. 

Scheme 1 shows the desired Heck reaction of alkoxy-DSB 1 with 2. The formation of 3 is accompanied by two destructive pathways the reductive debromination of 1 to 4 as a side reaction and the protodesilylation to 5 as a subsequent reaction. Particularly the latter limits the reaction conditions in terms of time and temperature. The phosphine is a decisive factor in this system consisting of three reactions a fine-tuning of the reaction conditions is possible via electronic and steric effects of the substituents in the phosphine electron-rich trialkylphosphines 6 and 7 strongly favor the reduction. Fast coupling reactions were observed with tris-o-tolylphosphine 8, the chelating diphosphine dppe 9 being even more efficient in terms of turnover, yield, and suppression of side reactions. Compared with Heck reactions of polycyclic or electron-deficient arenes with 2 [21, 22], the yield of 3 is only moderate. The reactivity of bromo-distyrylbenzenes 1 and 12 -14 in the coupling reaction is controlled by the substituents on the opposite side of the n-system (Fig. 1, Table 2) a compensation for the electron-donating alkoxy groups by a cyanide (13) or exchange of donors with electronically neutral alkyl side chains strongly improves the yields.

If an alkyl halide is added to the reaction mixture after reduction but without isolating the trialkylphosphine, tetraalkylphosphonium halides are formed in 65 to 76% yield ... 

Numerous reducing agents have been applied for the cleavage of disulfides in peptides. Reduction with sodium in liquid ammonia, with cysteine, 2-mer-captoethanol, 2-mercaptoacetic acid, 2-mercaptoethylamine (cysteamine), borohydrides and trialkylphosphines were used both for preparative and for... 

The Cadogan reaction refers to the deoxygenation of o-nitrostyrenes 1 or o-nitrostilbenes with trialkyl phosphite or trialkylphosphine and subsequent cyclization of the resulting intermediate nitrene 2 to form indoles 3. The reductive cyclization protocol has also been exploited to prepare a variety of A -containing heterocyclic compounds including carbazoles, indazoles, benzimidazole, benzotriazoles, anthranils, phenazines, phenothiazines, quinolines, and related compounds. 

Treatment of alkylsulfenyl methyl thiocarbonates derived from alkyl thiols and Scm-Cl with triphenylphosphine at 0 °C in benzene generates 5 alkyl methyl thiocarbonates in good yield (78% for alkyl = benzyl) (eq 13). Arylsulfenyl methyl thiocarbonates do not parallel this behavior vs. triphenylphosphine but they react cleanly with tributylphosphine (e.g., in dioxane-water) to generate the free arylthiol (see below).The reductive cleavage of alkylsulfenyl methyl thiocarbonates with trialkylphosphines (McsP, EtsP, BU3P) can be achieved with practically quantitative yields in protic solvents (THF-water) in the presence of acids... 

The reduction of allylic halides or acetates, as well as benzyl halides, can be achieved by the Pd-catalyzed reaction with formate ions in the biphasic system of toluene-water or heptane-water in the presence of hydrophilic phosphine ligands TPPMS, sodium 3-(diphenylphosphino)benzoate, and PEG-modilied trialkylphosphine. The process is accelerated by the addition of PEGJ ... 

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