Phosphane/phosphine production

A radical diphosphanylation of alkynes using tetraorganodiphosphanes as precursors for phosphanyl radicals has been applied to the synthesis of a doubly phosphinated diene 200 (Scheme 2.37)7 Tetraphenyldiphosphane was generated in situ from diphenylphosphane with an excess of chlorodiphenylphosphane in the presence of triethylamine. Addition of the phosphanyl radical to one C = C triple bond in the dialkyne 199 leads to vinyl radical 201, which undergoes a 5-exo cyclization (out of a Z-configured vinyl radical to minimize sterical hindrance in the cyclization) to give vinyl radical intermediate 202. The latter is trapped by a second phosphine moiety in a radical substitution step. The radical cyclization product is ultimately isolated as bis-phosphane sulfide 200 after treatment of the intermediate phosphane 203 with sulfur. 

Reaction of tris(2-pyridyl)phosphane (8) with chlorine in methylene dichloride or acetonitrile gave chlorotris(2-pyridyl)phosphonium chloride or its covalent isomer tris(2-pyridyl)phosphonium dichloride (20). Treatment of the dichloride derivative with dilute HCl afforded the coupling product, 2,2 -bipyridine (16), whereas tris(2-pyridyl)phosphine oxide (9) was isolated from the reaction with sodium hydroxide. 

Treatment of tris(2-pyridyl)phosphane or phosphine oxide with chlorine in acetonitrile in the presence of a small amount of water or an alcohol gave the 5-chloro-2,2 -bipyiidine (21) as the major ligand coupling product. 

Sterically more demanding phosphanes such as tris(< -toluene)phosphine introduce steric congestion to the transition state of the alkylation which resembles the initial product of this reaction, the complex of palladium(O) with the product alkene. Since the less sterically encumbered exocyclic complex A is energetically favored over the endocyclic complex B, a preferential attack of the nucleophile at the higher substituted endocyclic site results27,34. 

The selectivity to linear product is improved by using a cobalt trialkyl phosphine complex, but the major product is the corresponding alcohol. The use of rhodium triphenylphosphine hydrocarbonyl gives a still higher selectivity to linear aldehyde under milder conditions. These advantages are retained by using a water-soluble rhodium complex with sulphonated phosphane ligands, which provides a novel two-phase mode of operation (recently commercialized). ... 

The co-production of isobutyraldehyde has always proved embarrassing, but the introduction of rhodium liganded with a phosphine (Union Carbide) or phosphane (Ruhrchemie/Rhone-Poulenc) as catalyst permits milder reaction conditions and gives -/iso-ratios of 8 1 or more (see section 11.7.8.2). 

Alkylation at Phosphorus. Phosphines and phosphites undergo easy quaternization. Thus methylation of tris(2,6-dimethyl-phenoxy)phosphine with MeOTf, followed by treatment of the product with sodium 2,6-dimethylphenoxide, gave methyltetrakis (2,6-dimethylphenoxy)phosphane. Methoxyphosphonium tri-flates are relatively stable intermediates in Arbuzov reactions Phosphine oxides and sulfides are alkylated. S-Methylation of chiral phosphine sulfides, followed by treatment with hexam-ethylphosphorous triamide, has been advocated as a general synthesis of optically active phosphines. ... 

Use as a Reducing Agent. Tris(TMS)phosphine can be used as a reducing agent for the selective removal of the two axial fluorine atoms in difluorotris(perfluoroalkyl)phosphoranes, to give the corresponding tris(perfluoroalkyl)phosphanes. Trimethylsilyl fluoride is produced as an easily removable by-product (eq 23). ... 

Although a few technical processes - for example, a fiiran synthesis - were already in use in the late 1940s, hydroformylation was not accepted for use in fine chemicals synthesis or in natural products chemistry for a long time owing to regioselectivity deficits. This changed very much with the advent of tailored Rhodium catalysts and with the observation that phosphanes and phosphine oxides are directing the formylation [50] even in a fairly complex molecule such as 107 [51]. 

The same research group also described the first example of the phospha-Stork reaction. The carbon-carbon coupling of aryl aldehydes with bullgr vinyl phosphanes i.e. mesityldivinylphosphine) was possible with the help of B(C6F5)3. In addition the reaction of dimesityl(vinyl)-phosphine with bullq enones yielded the corresponding substituted cyclobutane products (Scheme 2). 

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