Diphosphine monoxides

Ligands like diphosphine monoxides Ph2P(CH2)raP(0)Ph2, ((235a) n = 1-3) and / Tol2P-(CH2)-P(0)/ Tol2 consist of a soft phosphino group and hard phosphoryl group. With nickel they form... 

An A-phosphinoylhemiaminal (3) has been used as a precursor to trifluoromethyl-ketimines (4) in situ alkylation with a dialkylzinc in the presence of a diphosphine monoxide auxiliary gives chiral , ,o -trifluoromc(.hyl amines (5) in high yield and ee up to 99%.16... 

Reactions with Phosphorns(iii) Compounds.— The reaction of monochlorophosphines with secondary phosphine oxides generally gives diphosphine monoxides (49), except when R=CF8- Another exception is the case with R=t-butyl, when the phos-phinous anhydride (50 R=Bu ) is the stable product. The isomeric mono-oxide (49 R=Bu ) is formed when di-t-butylphosphine oxide reacts as its anion, but the product is readily isomerized. By contrast, the monoxide (49 R=Pr ) is stable. ... 

Reactions of Phosphonium Salts.— Asymmetric induction is observed on alkaline hydrolysis of the prochiral phosphonium salts (132) under phase-transfer conditions in the presence of an optically active quaternary ammonium salt, forming the chiral oxides (133) with a 0—8 % enantiomeric excess. Alkaline hydrolysis of monobenzyl quaternary salts of a,co-bis(diphenylphosphino)alkanes gives a route to diphosphine monoxides, e.g., (134). Aqueous hydrolysis of (dibromo-fluoromethyl)triphenylphosphonium bromide gives a high yield of dibromo-fluoromethane and triphenylphosphine oxide. When the reaction is carried out in the presence of radiolabelled Br, the evidence points to the involvement of the dibromofluoromethyl carbanion, and not to a carbene intermediate as was observed in the reaction of the related (bromodifluoromethyl)phos-phonium salt. ... 

Phosphine-containing ally lie alcohols 301 undergo facile [2,3]-sigmatropic rearrangements with chlorophosphines, furnishing highly enantioenriched (dr 25 1) or enantiopure, crystalline diphosphine monoxides boranes 302, which were deprotected by treatment with DABCO with formation of 303. The configuration at the newly-formed stereocenter is opposite to that expected based on prior studies, and an ab initio computational evaluation of the possible transition states was performed to explain the stereochemical course of the reaction (Scheme 101) [199]. 

R=Et, Ph, o-Tol, Cy, 1-Nphth, 1-Furanyl Scheme 101 Synthesis of diphosphine monoxides 303... 

Diphosphine monoxides Phosphinous anhydrides Diphosphoxanes 20 Phosphonium anhydrides... 

Hydrophosphination of secondary propargylic alcohols generates phosphine-containing 0 allylic alcohols that undergo facile [2,3]-sigmatropic rearrangements with chlorophos-phines to give enantioenriched diphosphine monoxides (Scheme 54). 

Figure 15.8 a simple example is presented of a subsequent insertion of CO and methanolysis of the palladium acyl intermediate [14], This is not a very common reaction, because both the ligand requirements and the redox conditions for Wacker and carbonylation chemistry are not compatible. For insertion reactions one would use cis coordinating diphosphines or diimines, which makes the palladium centre more electron-rich and thus the nucleophilic attack in the Wacker part of the scheme will be slowed down. In addition, the oxidants present may lead to catalytic oxidation of carbon monoxide. 

Alternating copolymerization of carbon monoxide with ethene was discovered in the early 1950s [112] and has been attracting much interest lately. Among the several metals such as, Ni(II), Pd(II), and Rh(I) that can promote this reaction [113], Pd(II) complexes with a cis-chelating diphosphine ligand and a non-coordinating counter anion were selected as the catalysts of choice and have been studied extensively [114,115]. 

Asymmetric [4+1] cycloaddition of vinylallenes and carbon monoxide is promoted by a cationic Rh complex formed in situ from [Rh(cod)2]PF6 and chiral diphosphine ligand, (R.R)-Me-DuPHOS to afford 2-alkylidene-3-cyclopentenones with high asymmetric induction [72] (Eq. 8A.48). 

The influence of the type of alcohol and of the carbon monoxide partial pressure on the asymmetric induction has been investigated in the asymmetric hydrocarbalkoxylation of 2-phenyl-1-propene using (-)DIOP as the chiral ligand (18). For the same substrate different chiral phosphines and diphosphines were used also (17, 24). 

Direct Synthesis from the Metals. The first zerovalent compound prepared, namely Ni(CO)4, was first obtained by this method—i.e., from active nickel and carbon monoxide at ordinary temperature and pressure mi)- Though not largely applicable, this method can be used in some other cases. K4[Ni(CN)4] could be prepared from metallic nickel and potassium cyanide (205), while some chloro- (156), bromo- 125) and fluorophosphine (118) and some tertiary diphosphine (44) could react with metallic nickel to give the tetracoordinated nickel(O) derivatives. 

We have already discussed this method for Ni(CO)4. It completely replaces carbon monoxide only with some diphosphines 43) and with un-... 

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