Phosphine 140 Reaction centre

The different products obtained from the analogous reaction of diphenyl-phosphine oxide are explained in terms of the hardness of nucleophilic centres involved. Similar reactions with 2-methyl-3,4,5-triphenylcyclo-pentadienone gave the phosphonate (39). Gallagher and Jenkins have... 

The Heck reaction has proven to be an extremely useful method for the formation of C-C bond at a vinyl carbon centre. There are numerous reported examples of enantioselctive Pd catalyzed C-C bond forming reactions.10"13 Surprisingly, reports of Heck transformations using amino acid based phosphine, phosphinite ligands are rare. Recently Gilbertson reported a proline derived phosphine-oxozoline ligand in a catalytic asymmetric Heck reaction.5 In this paper we present some novel amino acids derived ligands as part of a catalytic system for use in asymmetric Heck reactions. 

Other related compounds are the diphosphine disulfides R2P(S)P(S)R2 14, which contain a direct phosphorus-phosphorus bond, and polysulfur fe(dior-ganophosphine sulfides) R2P(S)-S -P(S)R2 in which the two phosphorus centres are connected by a chain of one of more sulfur atoms. R2P(S)P(S)R2 compounds are accessible from heating secondary phosphine sulfides with thiophosphinic chlorides (Equation 10) or by reaction of fephosphines with... 

Attaching a pyridine group on the phosphine (e.g. PPh2Py) is also believed to enhance the catalytic activity in methyl methacrylate synthesis by picking up protons in solution and transferring them to the metal centre, which then uses them in the reaction [26], Such a process has been termed a proton messenger. 

A study of the kinetics and products of the thermolysis of a series of diaryl-phosphinic azides has been reported.119 Diethyl 1-diazomethylphosphonates undergo an aldol-type reaction with aldehydes to give l-diazo-2-hydroxyalkylphosphonates (152).120 Acidification of the diazophosphonates (153) possessing a chiral phosphorus centre yields mixtures of diastereoisomers (154) and epimers at C. For given R1 and R2, the reaction becomes increasingly stereoselective for X= OAc < Cl < OTs. It may be argued that protonation of (153) will yield a mixture of diastereoisomeric di-... 

Phosphoramidites are probably the most versatile ligands in this series as in amidites the substituents at the nitrogen atom are in close proximity to the metal centre and also the substituents could carry chiral centres. In Figure 4.22 we have depicted the simplest derivative, named Monophos , which is highly efficient for asymmetric hydrogenation but for a variety of other reactions as well. The ligand is much easier to make than most, if not all, chiral bidentate phosphine ligands and surely commercial applications will appear. 

The starting diol was transformed into the dibromide by elemental bromine with triphenyl phosphine adduct which undergoes the Arbuzov-Michaelis reaction under somewhat drastic conditions at 150 °C (step a). Catalytic removal of the benzyl group was performed by a Pd/C catalyst (step b) and the alcohol formed was allowed to react with dichloropurine in the presence of triphenylphosphine and diethylazodicarboxylate (Mit-sunobu reaction) (step c). Finally the desired product was obtained by reaction with methylamine (step d) and the removal of ethyl groups at the phosphorus centre was performed by transilylation using trimethyliodosilane (step e). 

In all the above reactions the hydrido phosphorus centre acts as a pen-tavalent phosphorus. Interesting reactions are known in which the tautomer of the hydridophosphazene containing a P(III) centre acts as a trivalent phosphine towards transition metals. Thus N3P3Ph4(Me)H on treatment with MCI2 (M = Pd, Pt) [246] or AUCI3 [247] results in complexes [N3P3Ph4(Me)H]2 MC1 (M = Pd or Pt n = 2, M = Au n = 3). These complexes have been shown to possess phosphorus-metal coordinate bonds (Eq. 49). 

The aminolysis of Y-phenyl X-benzoates by piperidine in 20 mol% DMS0-H20 at 25 °C proceeded, on the basis of a curved Brpnsted-type plot, via a zwitterionic tetrahedral intermediate with a change in the RDS the curvature centre of the plots was at p Ka = 6.4 regardless of the electronic nature of the substituent X in thebenzoyl moiety 27 The rates of aminolysis of a series of Y-phenyl benzoates by acylic secondary amines were compared with new results for similar reactions with Y-phenyl diphenylphosphi-nates (discussed further in the section Phosphates and Phosphinates). The results showed that the C=0 compounds were more reactive than the P=0 compounds 28... 

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