Diphosphine oxides

As mentioned in Sect. 2.2, phosphine oxides are air-stable compounds, making their use in the field of asymmetric catalysis convenient. Moreover, they present electronic properties very different from the corresponding free phosphines and thus may be employed in different types of enantioselective reactions, m-Chloroperbenzoic acid (m-CPBA) has been showed to be a powerful reagent for the stereospecific oxidation of enantiomerically pure P-chirogenic phos-phine-boranes [98], affording R,R)-97 from Ad-BisP 6 (Scheme 18) [99]. The synthesis of R,R)-98 and (S,S)-99, which possess a f-Bu substituent, differs from the precedent in that deboranation precedes oxidation with hydrogen peroxide to yield the corresponding enantiomerically pure diphosphine oxides (Scheme 18) [99]. 

BINAP [2,2 -bis(diphenylphosphino)-1,1 -binaphthyl] is commercially available or can be prepared according to a literature procedure.3 The diphosphine is slowly oxidized in air to give the corresponding mono and diphosphine oxides that can be removed by column chromatography (silica gel, benzene) under an inert atmosphere. 

The wide-rim CMPO calix[4]arenes are the most efficient compounds for the extraction of trivalent actinides and lanthanides. They are also the compounds that display the highest selectivity along the lanthanide series, provided that phosphorus atoms are linked to phenyl groups. They also display a higher selectivity than the calixarene-bearing diphosphine oxide, where the phosphorus atom is linked to phenyl units CPo21.176- ... 

Synthesis of chiral atropisomeric diphosphine type ligands is a current challenge in chemical research because their late transition metal complexes usually provide high enantioselectivity in homogenous catalytic reactions. [28] In practical point of view, preparation and optical resolution of racemic diphosphine oxides followed by the reduction of the separated enantiomers are usually more advantageous than an expensive enantioselective synthesis of one diphosphine enantiomer. [29]... 

A series of dialkylsilylene diphosphites (138) has been prepared for use as chelating ligands.Chlorophosphines react sluggishly with trialkyl phosphites, but the reaction has now been shown to be catalysed by Lewis acids and then to give high yields of diphosphine oxides, e.g. 

Several chiral columns and elution conditions were screened to find the best column to determine the optical purity of nine of the undeiivatized diphenylphosphine and diphosphine oxide ligands describe above. Supelcosil LC-(R)-phenyl and (R)-naphthyl urea based columns and cellulose tris(4-methyl-phenylcarbamate) coated on silica (Chiralcel OG) were very efficient in these separations. All the atropisomers could be analyzed using these three columns (98JC(A795)289,02CHR25). 

Sym. diphosphine oxides from 2 phosphinous acid chloride molecules >P(0)P(0)<... 

Simple diphosphines are readily oxidised by air. Tetraphenyl diphosphine, if spread on a filter paper it will get quite hot during the formation of tetraphenyl diphosphine oxide (6.669). 

The structural formulae of the symmetrical derivatives (6.731a) can be compared with those of diphosphines (6.731b), diphosphine oxides (6.731c) and hypophosphoric esters (6.731d). 

Resolution of phosphine oxides involves protonation of the weakly basic phosphoryl group by the chiral auxiliary. This method showed limited success for simple monophosphine oxides (entries 1, 2 and 10) but is better suited to resolve compounds bearing carboxylic acid groups (entries 11 and 12) or diphosphine oxides (entries 16-20). It is still sporadically used nowadays, as for the compounds of entries 19 and 20. 

The secondary phosphine oxide shown in entries 7 and 8 is the most important representative of the family of F-stereogenic secondary phosphine oxides (SPOs), which can be used directly as P-donor ligands to transition metals. Furthermore, this particular compound has been also used to prepare many mono- and diphosphine oxides by stereoselective alkylation and other reactions. ... 

It was demonstrated that the reaction proceeds without racemisation of the stereogenic phosphorus atom and with total selectivity towards the ( )-alke-nylphosphine oxide. Unexpectedly, it was also possible to dimerise phosphine oxide 109 (with R = Me) with 5% of 112b to obtain the corresponding optically pure ( )-diphosphine oxide in 85% yield. The crystal structure of this compound has been determined by X-ray diffraction and has been used as dipolarophile in 1,3-dipolar cycloadditions with nitrones, yielding several optically pure diphosphine oxides. Similar homometathesis reactions have been investigated in more detail by Grela, Pietrusiewicz, Butenschon and co-workers with other (racemic) substrates such as 109 and different catalysts. Gouverneur and co-workers studied a similar dimerisation of... 

Tin(IV)-chloride-mediated double aldol reaction of acyclic ketones is rendered stereoselective by a chiral phosphine oxide, (5)-BE JAPO it is proposed that the catalyst controls the first aldol and the substrate controls the second. Another chiral diphosphine oxide, this one based on thiophene, catalyses direct aldols in high delee Chiral a-silyloxy ketones derived from lactate (61) undergo titanium(IV)-mediated aldols giving diastereomerically pure syn-syn adducts (62) in high yield, irrespective of the alkyl groups fianking the silyl or carbonyl. 

On the other hand, the asymmetric allylation of aldehydes was also successfully performed in the presence of chiral easily available biheteroaromatic diphosphine oxides, such as tetraMe-BITIOPO, which is the precursor of the industrially produced tetraMe-BITIOP. Using this organocatalyst, the reaction afforded homoallyllic alcohols in fair-to-good yields and with enantio-selectivities of up to 95% ee, as shown in Scheme 2.50. 

New chiral spiro[4,4]-diphosphine oxides catalyse double-aldols of ketones with two molecules of aldehyde in good yield, de and ee ... 

For example, access to axial chirality can be realized under cobalt catalysis using a chiral cobalt(I) complex [4], However, the use of chiral iridium and rhodium species dramatically improved the scope and enantioselectivities obtained for this cycloaddition. Tanaka and coworkers synthesized an atropoisomeric diphosphine oxide in 97% ee, by treatment of the suitable hexayne with [Rh(cod)2]BF4 in the presence of (7 )-TolBINAP as source of chirality (double [2-1-2-1-2] cycloaddition). Subsequent reduction afforded an axially chiral bidentate ligand as a single enantiomer (Scheme 7.1) [5]. 

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