Phosphines structure

Table II. Effect of Phosphine Structure on the Hydrogenation of Acetophenone"...

The materials obtained are extremely stable,43 because the electron pair of the phosphine structure has been donated to an oxygen atom. A final series of chains of this type are the poly(phosphorylamides). An example, the poly(phosphoryldimethylamide) chain, is shown in 6.48. These polymers have interesting elastomeric properties, but presumably are hydrolytically sensitive.42... 

By way of contrast, fewer gas-phase structures of transition metal complexes are known a few d°-d4 hexafluorides (all octahedral), d°-d tetrachlorides (tetrahedral), and some 18-electron carbonyl and phosphine structures typified by tetrahedral Ni(C0)4, octahedral... 

Alkene Hydroarylation. The enantioselective addition of aryl iodides to norbomene has been reported using a palladium(II) complex of (5, iS )-CHIRAPHOS. The reaction of norbomadiene with 4-methoxyiodobenzene proceeded with 30% ee (eq 5). Enantioselectivities were dependent upon phosphine structure (see (+)-trans-(2S,3S)-Bis(diphenylphosphino)bicyclo[2.2.1 ]hept-5-ene). 

About 250 papers and patent applications appear annually in the area of hydroformylation, most of them dealing with new phosphine structures and catalytic results obtained therewith. Discussion of this huge number of ligands would go far beyond the limitations of this contribution. A few selected examples will be described later, in Section 2.1.1.5. 

Thirupathi, N., Liu, X., Verkade John, G. Reactions of tris(amino)phosphines with arylsulfonyl azides product dependency on tris(amino)phosphine structure. Inorg. Chem. 2003, 42, 389-397. 

The phosphorus product was not definitively identified. From a bromination experiment it was concluded that some double bond character remained in the hydrocarbon part. The product from 1-decene indicated about one acidic hydrogen for each two phosphorus atoms. Furthermore, the product appears to contain the tertiary phosphine structure, since treatment with CS2 produced the red color characteristic of tertiary phosphines. Oxidation by nitric acid has been... 

As recounted, these studies demonstrate that two of the three expected intermediates in asymmetric hydrogenation may be directly observed, but the expected dihydride is too fleeting. There are two further experiments which are pertinent to this issue. A related diphosphine-iridium alkene complex reacts with dihydrogen at low temperatures and a series of alkene dihydrides are observed prior to the formation of the expected alkyl hydride. Based on the H-NMR chemical shifts of the respective Ir-H species, the initial addition (or to be more correct the initially observed species) possesses H trans to alkene and H trans to phosphine only at higher temperatures does this rearrange to the expected H trans to amide and H trans to phosphine structure (Fig. 9a) [36]. A more directly relevant experiment involves para-enriched hydrogen, and in the illustrated case a transient dihydride is observed. A problem is that the spectral characteristics are not entirely in accord with expectations for the proposed structure (the supposed trans-P-Rh-H coupHng is 4 Hz rather than ca. 120 Hz), but the presence of some transient Rh dihydride is definitive based on the evi-... 

The top reaction (where R = phenyl, R = R" = methyl) has been run with a different diphosphine using a polymeric surfactant as the anion for rhodium to give 90-92% ee.85 Optimization of the phosphine structure would probably raise this to the levels shown in 10.38. The polymeric surfactant was derived from a copolymer of acrylamide with maleic anhydride (10.39). 

The importance of water as a solvent has led to the development of water-soluble phosphines. This has been achieved by the incorporation of hydrophilic substituents into the phosphine structure. The choice of substituents, whether anionic, cationic, or neutral, depends on the exigencies of the end use. The anionic species [Ph2P(3-C6H4S03)] Na+ has been used to afford a water-soluble palladium catalyst (37) by Du Pont workers. 

A complexity, yet at the same time a source of fascinating chemistry, of systems based on phosphorus is that the phosphorus may appear in functional groups where this atom is attached to anywhere from one to six other atoms. This has led to a description of the group by its coordination number (C.N.), which refers to this number of attached atoms. Thus simple phospholes are designated as having C.N.-3, but the coordination number may range from two to six. However, some of these coordination numbers are rather rare, and most of phosphole chemistry is based on C.N.-3 and C.N.-4, which includes especially the oxides, sulfides, and salts of the phosphines. Structures for the various coordination numbers are given below. 

Many of the chiral bidentate phosphines synthesized in the last years have also been tested for enantioselective ketone reduction. Some of the results achieved are compiled in Table 2. The influence of phosphine structure on optical selectivity and catalytic activity is considerable, but a reliable correlation could not yet be found. It seems that chiral bidentate 6w(diphenyl)phosphines, like prophos forming 5-membered chelate rings with the rhodium atom and used with great success for the hydrogenation of dehydroaminoacids, are not suitable for ketone reduction because of very low reaction rates. 

Scheme 24 Synthesis of conformationally constrained phosphinic structures at position Pj by (a) Nasopoulou et al. [108] and (h) Matziari et al. [75] (TIS triisopropylsilane, DMF dimethylformamide)...

This dicarboxylic ester is then copolycondensed with the other reactants in PET manufacture to produce a flame-retardant polyester [63745-01-7]. The advantage of this rather unusual phosphinate structure is its high thermal and hydrolytic stability. The fabric is probably used mainly for furnishings in public buildings in Japan. 

PhOSphinatGS. Phosphinate structures confer flame retardancy to polyester fibers (discussed separately below). 

An X-ray structure study on [139] established the existence of the doubly bridged phosphinate linkage 32). Another structure study on a monomeric compound is available that also established the existence of a doubly bridged diphenyl phosphinate structure (139). These examples are to be weighed against the recent structural evidence discussed above for metal phosphinate polymers. 

As shown in Tables 4.10 and 4.11, mostof IIIA and IIIB were almost inactive in pre-emergence and post-emergence applications at 2.25 kg ai/ha. As shown in Tables 4.10 and 4.11 the introduction of 2-NO2 or 2-Cl,4-N02 as Y on the phenoxy-benzene ring in the phosphinate structure was not beneficial to herbicidal activity. 

Poly(metal phosphinates) were prepared from phosphinic acid and metal ion such as Zn(II) or Cr(IlI) [41,42], These polymers contained tetrahedral Zn(II) centers and symmetric bridging 0,0 -phosphinate groups in polymeric structure. The zinc phosphinate structure (32) with alkyl chains on the phosphorus melted. 

---