Dialkylphosphine oxides

Dialkylphosphine oxides are another class of highly efficient ligands for coupling reactions using Pd or Ni (equation 85). Electron-poor fluoroazines and -diazines react already in the presence of NiClafdppp) , while hindered and electron-rich P(Bu-t)3 and (t-Bu)2P(S)H can be used for the coupling of unactivated aryl chlorides in the presence of Ni. 

Dialkyl-ligated tropocoronand complexes, with Hf(IV), 4, 811 Dialkylphosphine oxides, and Grignard reagent reactivity,... 

Biphasic conditions also circumvent the salt solubility problem but classic phase transfer conditions using aqueous sodium hydroxide suffer from competing hydrolysis of the phosphorus(III) esters. However, Kem and co-workers found that butyl esters (their substrate was dibutyl phosphonate) are sufficiently stable to provide Michaelis-Becker products in high yields dialkylphosphine oxides were also suitable substrates.67 Salvatore and co-workers have recently developed an efficient biphasic solid-liquid procedure utilising the cesium cation effect Protocol 7. 

If further evidence of the difficulty of reducing the P=0 bond were needed, the recent findings of Yamashita et al ° provide interesting confirmation. Many a-hydroxyalkyldiphenylphosphine oxides (13) were converted into the corresponding alkyldiphenylphosphine oxides (14) in 33-73% yield, with PCb-KI (equation 21). No competing reduction of the P==0 bond was apparently observed. Majew-ski has reported the disproportionation of dialkylphosphine oxides into dialkyIphosphines and phos-phinic acids (equation 22). The reaction proceeds in yields of over 90% and the phosphines are easily isolated by distillation. 

Hydrolysis of chloridites yields phosphonates (6.321). Phosphorochloridites can be converted into phosphonic acids - with dialkylphosphine oxides the equilibrium (6.322) lies mainly to the right-hand side. 

The first isomer can be prepared from sodium dialkyl phosphinite and a dialkylphosphorochlori-dite at -78°C. Isomers of this type are usually very unstable and will easily oxidise or hydrolyse. The second type of isomer can be obtained from a dialkylphosphine oxide and a phosphorochloridite... 

The amount of tertiary phosphine oxides formed from phosphines increases with the polarity of the solvent [158]. Aromatic solvents display a particular effect. Especially in toluene, which is a favored solvent of several hydroformylation reactions, oxidation is slow up to a temperature of 60 "C. Beyond this temperature, a rapid increase in oxidation was observed. When tributylphosphine was treated with air in dry ethanol, the corresponding esters and 1-butanol were formed (Scheme 2.46). When water was present, the corresponding dialkylphosphine oxide was additionally detected. 

PCy3, jp-substituted phenyl(PR2) ligands (R = Cy or /-Bu), sulfonated fluorenyl dialkylphosphines, and diaryl- or dialkylphosphine oxides have also shown good reactivity in Suzuki reactions of heteroaryl halides/boronic acids. 

Dialkylphosphine oxides are also highly efficient ligands for or Ni-... 

Oxidative Phosphinylation A New Route to Dialkylphosphinic Acid Derivatives... 

Unsymmetrical trialkyIphosphine oxides are accessible by treatment of dialkylphosphinic halides with Grignard reagents (121). Di-n-butyl-methylphosphine oxide was obtained by the following reaction. 

There are various specific colour tests for special classes of organophosphorus compounds. Tertiary phosphines, R3P, for example, produce a rose red colour in a carbon tetrachloride solution of m-dinitrobenzene. Trialkylphosphine oxides, R3PO, and dialkylphosphinic acids, RjPfOlOH produce a blue colour in a toluene solution of nickel bromide. A chloroform solution of PhjPO reacts with a chloroform solution of iodine to form an insoluble yellow compound and so forth. 

Trofimov et al. carried out the addition of dialkylphosphines and dialkylphosphine chalcogenides to tris(4-vinylbenzyl)phosphine oxide under radical conditions. The trisphosphines were converted to the... 

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