Aryl phosphines

Other notable examples are the orthometallation (orthophenylatioti) reactions of many complexes of aryl phosphines (PAr3) and aryl phosphites P(OAr)3 with platinum metals in pailiculai, e,g, ... 

The osmium(VI) complexes 0s02X2(PR3)2 are not generally obtainable with the smaller alkyl and alkyl(aryl)phosphines, which tend to be good... 

In a related strategy, ethynylphosphines (81) have been prepared with a view to synthesising polyphosphacyclopolyyne materials such as (82) (Scheme 24) [70]. Interaction between the phosphorus lone pairs and the organic 71-systems is supported by the fact that the phosphorus atoms of mono- and di-silyl-capped analogues of bis(arylphosphine) derivative (81) exhibit an unusually low inversion barrier (65 kj mol versus 130-140 kj mol for classical alkyl-or aryl-phosphines). Indeed, the rings (82) exhibit values of at ca. 300 nm, consistent with this assumption. 

As with aldol and Mukaiyama addition reactions, the Mannich reaction is subject to enantioselective catalysis.192 A catalyst consisting of Ag+ and the chiral imino aryl phosphine 22 achieves high levels of enantioselectivity with a range of N-(2-methoxyphenyljimines.193 The 2-methoxyphenyl group is evidently involved in an interaction with the catalyst and enhances enantioselectivity relative to other A-aryl substituents. The isopropanol serves as a proton source and as the ultimate acceptor of the trimethyl silyl group. 

Iodination reagents combined with aryl phosphines and imidazole can also effect reductive conversion of diols to alkenes. One such combination is 2,4,5-triiodoimidazole, imidazole, and ttiphenylphosphine.297 These reagent combinations... 

Second generation BINAPHOS-type ligands have been developed recently. Placing 3-methoxy substituents on the aryl phosphine unit furnishes a catalyst which allows for an enantioselective hydroformylation of vinylfurans (Scheme 19) [68]. 

Palladium-catalyzed aromatic C—O bond formation is less developed than palladium-catalyzed aryl amination. Except when the aryl halide is strongly electron deficient,107-110 catalysts ligated by the conventional aryl phosphines such as DPPF and BINAP are ineffective for coupling of... 

There now are available a number of alkyl azide compounds that may be used in click chemistry reactions and the Staudinger ligation processes. It is not recommended, however, to use aryl azide compounds, as these are light sensitive and photoreactive as well as highly susceptible to reduction in the presence of thiols. Unfortunately, at the time of this writing there are fewer choices in aryl phosphine compounds to participate in this reaction, as commercial sources of labeling reagents are limited. 

In an early investigation (28, 59, 60), critical combinations of several reaction parameters were discovered to produce unusually high yields of the linear isomer. The parameters included low partial pressure of carbon monoxide, high concentration of phosphite or aryl phosphine ligands, and low total gas pressure. The catalyst was a soluble complex of rhodium, formed in situ from rhodium metal in many cases. Isomer ratios of 10 1 to 30 1 were obtained by appropriate selection of these reaction parameters. Losses to alkane were minimal, even with Pm as low as 10 psi. Tables XI-XIV illustrate the effects of these various reaction parameters on the product composition. 

In 1993 Burk, Brown, and coworkers confirmed that DuPHOS complexes exhibit the same anti-lock-and-key mechanistic motif as seen for aryl phosphine ligated catalysts [41], In 1998 by Burk and coworkers reported an unexpected and interesting result [34], With substrates having R<, = aryl, selectivity of 99% e.e. for the S product resulted from (S,S)-Me-DuPHOS-Rh hydrogenations, but the R product was obtained with similarly high enantioselectivity when Ra = t-Bu or adamantyl. In other words, the simple change of an aryl substituent to a bulky alkyl completely reverses the sense of enantioselection. 

Tertiary aryl phosphines react with 2,4-dinitrochlorobenzene to form the salts... 

Many simple oxidation reactions of tertiary alkyl or aryl phosphines are less straightforward in phosphines with silylamino substituents 1 °... 

Iodination reagents combined with aryl phosphines and imidazole can also effect reductive conversion of diols to alkenes. One such combination is 2,4,5-triiodoimidazole, imidazole, and triphenylphosphine.215 These reagent combinations are believed to give oxyphosphonium intermediates which then serve as leaving groups, forming triphenylphosphine oxide as in the Mitsunobu reaction (see Section 3.2.4). The iodide serves as both a... 

Aryl phosphines, for example, PPh3 and PMePh2, display a net electron-acceptor character comparable to those of linear organoisocyanides, and the latter phosphine has the same Pi value as phos-I--------------------1... 

It has been found in the meantime that reaction (1) is generalizable (752), and that oxidative additions of this type occur for such widely differing substrates H2Y as ethylene, benzene 130), cyclic olefins, alkyl and aryl phosphines, aniline 337, 406), and H2S 130), ail of which give the same product structure with a triply-bridging Y ligand. The stability of these third-row transition metal clusters has stiU prevented catalytic reactions of these species, but it is likely that similar ones are involved in olefin and acetylene reactions catalyzed by other metal complexes. 

PR = trialkyl, triaryl, mixed alkyl and aryl phosphines... 

Compared with the analogous hydrogenation of aldehydes, the reaction requires somewhat more drastic conditions (about 200°C and 6 hrs), but the temperature is still within the stability range of the cobalt carbonyl phosphine complexes containing tertiary alkyl phosphines as ligands. If aryl phosphines are used, a more or less pronounced decomposition of the carbonyl complexes can be observed (as indicated by the IR... 

Numerous alkyl and aryl phosphine, arsine and stibine compounds are described as being silver solvents. Examples are tris(p-hydroxyphenyl)phosphine and bis(2-carboxyethyl)methyl-phosphine.72... 

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