Phosphines diphosphines

A variety of enantiopure or enantiomerically enriched phosphines, diphosphines, phosphites, diphosphites, phosphinephosphites, thiols, dithiols, P,N-ligands, and P,S-ligands have been developed as chiral modifiers of rhodium and platinum catalysts [1-7], Representative chiral ligands discussed in this chapter are shown in Figure 7.1. 

Bedford and colleagues found that phosphines, diphosphines, arsines, and bulky triaryl phosphites are convenient ligands [51]. Best results were obtained with... 

Scheme 26. Reactions of M6(CO),6 (M = Rh, Ir) with phosphines, diphosphines, and norbornadiene. ETPO, 4-ethyl-2,6,7-trioxa-l-phosphabi-cyclo[2.2.2]octane.

Manufacture of calcium hypophosphile by the treatment of white phosphorus with a boiling slurry of lime (desorption of phosphine, diphosphine. and hydrogen) 62... 

There are four comprehensive reference texts on phosphine coordination chem-istry. Two are somewhat out-of-date, but the article by Levason is more recent. However, all four give much useful information on synthetic procedures for the preparation of primary, secondary and tertiary phosphines diphosphines multidentate and macrocyclic phosphines mixed Group 15 donor and mixed Group 15/16 donor systems and phosphorus-containing heterocycles. The coordination chemistry of phosphorus has expanded to include P4 fragments, Pg rings, and even naked phosphorus atoms, for example, nine-coordinate P and -Pg systems. ... 

Many compounds of the types in Table 9.6 can be made by adding sulphur to the appropriate phosphine. Diphosphine disulphides are thus derived from biphosphines, bis(phosphinodthioic) acids from di-secondary biphosphines (9.584), alkylene bis(alkylphosphine sulphides) and aUcylene bis(phosphinodithioic)acids (Table 9.6) from secondary alkylene biphosphines (9.585, 9.586), and alkylene bis(dialkylphosphine sulphides) from alkylene diphosphines. Reaction (9.583) can also be noted. 

Many complexes have been studied by this combination of techniques, especially 77 -allyl derivatives with chiral auxiliary ligands, such as phosphines,diphosphines, " A jP-donors, and N,N-These ligands are characterized by their large size that sufficiently intrudes in the allylic coordina-... 

Some phosphoms—hydrogen compounds are pyrophoric, eg, diphosphine [13445-50-6] 2 4 common impurity in phosphine. Such contaminated phosphine usually ignites spontaneously on contact with air. 

All phosphoms oxides are obtained by direct oxidation of phosphoms, but only phosphoms(V) oxide is produced commercially. This is in part because of the stabiUty of phosphoms pentoxide and the tendency for the intermediate oxidation states to undergo disproportionation to mixtures. Besides the oxides mentioned above, other lower oxides of phosphoms can be formed but which are poorly understood. These are commonly termed lower oxides of phosphoms (LOOPs) and are mixtures of usually water-insoluble, yeUow-to-orange, and poorly characteri2ed polymers (58). LOOPs are often formed as a disproportionation by-product in a number of reactions, eg, in combustion of phosphoms with an inadequate air supply, in hydrolysis of a phosphoms trihahde with less than a stoichiometric amount of water, and in various reactions of phosphoms haUdes or phosphonic acid. LOOPs appear to have a backbone of phosphoms atoms having —OH, =0, and —H pendent groups and is often represented by an approximate formula, (P OH). LOOPs may either hydroly2e slowly, be pyrophoric, or pyroly2e rapidly and yield diphosphine-contaminated phosphine. LOOP can also decompose explosively in the presence of moisture and air near 150° C. 

Commercially, phosphinic acid and its salts are manufactured by treatment of white phosphoms with a boiling slurry of lime. The desired product, calcium phosphinite [7789-79-9], remains ia solution andiasoluble calcium phosphite [21056-98-4] is precipitated. Hydrogen and phosphine are also formed, the latter containing sufficient diphosphine to make it spontaneously flammable. The details of this compHcated reaction, however, are imperfectly understood. Under some conditions, equal amounts of phosphoms appear as phosphine and phosphite, and the volume of the hydrogen Hberated is nearly proportional to the hypophosphite that forms. 

Phosphine generated by the above procedures is usually contaminated to varying degrees with diphosphine, which renders it spontaneously flammable. Pure phosphine can be produced by hydrolysis of phosphonium iodide [12125-09-6] PH I, which can be made by the action of water on a mixture of phosphoms and diphosphoms tetraiodide [13455-00-0] (71). 

With bulky diphosphines Bu2P(CH2) PBu2 (n = 8-12), similar reactions of the diphosphines with MCl2(PhCN)2 give separable mixtures of monomer, dimer and trimer. With small phosphines (n = 5-7) dimers predominate (Figure 3.48). 

P-Chirogenic diphosphine 19, which rhodium-chelate complex forms a seven-membered ring (rare case for P-stereogenic ligand), was also prepared in reasonable yield (68%) using the wide chemistry of secondary phosphine borane [37]. Deprotonation of the enantiomerically enriched ferf-butylmethylphos-phine-borane 88 (Scheme 15) followed by quenching with a,a -dichloro-o-xylene and recrystallization afforded optically active diphosphine-borane 89 (precursor of free phosphine 19). 

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]. 

A P NMR study of stoichiometric reactions using the di-primary phosphine H2PCH2CH2CH2PH2 provided more information on the reaction mechanism (Scheme 5-12, Eq. 2). Norbornene was displaced from Pt(diphosphine)(norbornene) by ethyl acrylate. Reaction with the diphosphinopropane was very fast this gave the hydrophosphination product, which, remarkably, did not bind Pt to give Pt(diphos-phine), instead, Pt(diphosphine)(norbornene) was observed [12]. 

Similar catalytic reactions allowed stereocontrol at either of the olefin carbons (Scheme 5-13, Eqs. 2 and 3). As in related catalysis with achiral diphosphine ligands (Scheme 5-7), these reactions proceeded more quickly for smaller phosphine substrates. These processes are not yet synthetically useful, since the enantiomeric excesses (ee s) were low (0-27%) and selectivity for the illustrated phosphine products ranged from 60 to 100%. However, this work demonstrated that asymmetric hydrophosphination can produce non-racemic chiral phosphines [13]. 

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