Lewis tertiary phosphines

However, these trends, which cannot provide an absolute scale for Lewis acidity and basicity, do not necessarily allow predictions of what kind of adducts will be formed.18 Gallane GaH3 for instance forms more stable adducts with phosphines than with amines. Consequently, reactions between H3Ga-<— NMe3 and tertiary phosphines PR3 yield the corresponding phosphine adducts. In sharp contrast, A1H3 forms significantly more stable adducts with amines than phosphines.19... 

The two-coordinate phosphorus atom of a phosphonio-phospholide moiety is generally a weaker Lewis-base than a tertiary phosphine as a consequence, the complexes are thermally less stable (this holds in particular for metal fragments with low back donation capability, e.g. Mn(CO)4Cl) [35, 43], benzophospholide ligands are easily displaced by tertiary phosphines such as PhsP [27, 44], and bidentate ligands comprising a phosphonio-ben-zophospholide and a phosphine site react with transition metal fragments preferentially at the phosphine site coordination of both phosphorus atoms is only observed if the substrate offers two vacant coordination sites [27, 47]. 

Contrary to early reports,16 pentacarbonylhydridorhenium is air stable.6 The neat liquid, however, is moderately sensitive to light, turning yellow with formation of Re3H(CO)14.9 Pentacarbonylhydridorhenium is stable up to 100 °C, whereupon it decomposes to form Re2(CO)10 and H2.1 Substitution of carbonyl groups in ReH(CO)5 by tertiary phosphines and other Lewis bases is well known and apparently occurs by a radical chain pathway.6 More detailed surveys of the reactivity of ReH(CO)5 have been summarized elsewhere.10,11... 

Selenium-containing six-membered ring heterocycles have proved to be useful catalysts in a variety of transformations. The Baylis-Hillman reaction involves the reaction of alkenes containing electron-withdrawing groups such as a,/3-unsaturated carbonyl compounds with aldehydes leading to carbon-carbon bond formation (Equation 79). The reaction is promoted by tertiary amines such as l,4-diazabicyclo[2.2.2]octane (DABCO), or tertiary phosphines and Lewis acids. Unfortunately, the Baylis-Hillman reaction is severely limited because it proceeds only very slowly <1998CC197>. Much research has been carried out in attempts to increase the rate of this reaction. 

The bis(silylamide) complexes Ln N(SiMe3)2 2 and their adducts with Lewis bases such as thf and tertiary phosphines... 

The complex [Co(dmgh)(NO)] would be expected to react in the same fashion as the compounds just discussed, but under comparable conditions (e.g., in the presence of Lewis bases) it gives a mixture of nitrato and nitro products (192). The factors that infiuence the proportion of nitro and nitrato products have not been established by mechanistic studies, but a possible pathway involves the isomerization of the peroxy intermediate (35) to the nitrato species (37), as indicated in Fig. 20, or by further oxidation of the nitro product. Recent studies (193) have shown that the nitro complex is a reactive intermediate in the formation of [RuCl(N03)(bpy)2]. Tertiary phosphine complexes of the platinum metals also tend to give nitrato products (194)-. 

Although the starting methyl compound exists as a mixture of the geometrical isomers, the acetyl derivative occurs only with the acyl group cis to the nitrogen atom of the pyridine ligand. Kinetic studies have shown that the rate of CO insertion decreases as the Lewis base character of the tertiary phosphine increases. 

Reaction in equation (d) occurs normally with tertiary phosphines " , reaction in equation (e) occurs with isocyanides , whereas reactions in equation (f) take place with Lewis bases that contain nitrogen and oxygen donor atoms " . Reactions with tertiary phosphines exhibit disproportionation [equation (g)], followed by the neutral substitution product ... 

Many homoleptic organogold compounds are Lewis acidic. For example, trimethylgold, prepared from gold(III) bromide and methyllithium, is stabilized by complexation with amines or tertiary phosphines, in Me3Au L. The dimeric compounds, (R2AuX)2, are prepared from [Au(py)Cl3] and me thy lmagnesium iodide76. 

Nucleophilic catalytic reactions are usually addition and substitution reactions. A diverse array of Lewis bases (e.g., tertiary phosphines, tertiary amines, pyridines, and imidazoles) have been shown to serve as nucleophilic catalysts. Nucleophilic reactions typically occur at C=X and activated C=C multiple bonds. In a general form for a reaction... 

Miscellaneous Reactions of Phosphines.- The basicities of a series of bidentate phosphines have been determined by a study of their enthalpies of protonation with trifluoromethanesulphonic acid in 1,2-dichloroethane. Ring-opening of sultones via nucleophilic attack by nitrogen occurs on treatment with tri-(2-pyridyl)phosphine, with the formation of the water-soluble phosphine systems (91). A novel aldehyde-olefination procedure is afforded by the reactions of aldehydes, diazomethanes, and tertiary phosphines in the presence of a catalytic amount of the powerful Lewis acid methyltrioxorhenium. Attempts to prepare carboxyphenylphosphines by the ring metallation of triphenylphosphine followed by... 

In the preceding examples, the asymmetric catalyst is a Lewis acid and hence the catalytic processes reported so far involve electrophilic activation by a metal-centred chiral Lewis acid. There is another strategy, although less explored, which consists of designing chiral Lewis bases for nucleophilic catalysis. It is well known that Lewis bases such as nitrogen heterocycles and tertiary phosphines and amines catalyse a variety of important chemical processes. For instance 4-(dimethylamino)pyridine (DMAP) catalyses the acylation of alcohols by anhydrides the mechanism by which DMAP accelerates this process provides an instmctive illustration of how nucleophiles can... 

The asymmetric arylation or alkylation of racemic secondary phosphines catalyzed by chiral Lewis acids in many cases led to the formation of enantiomerically enriched tertiary phosphines [120-129]. Chiral complexes of ruthenium, platinum, and palladium were used. For example, chiral complex Pt(Me-Duphos)(Ph)Br catalyzed asymmetric alkylation of secondary phosphines by various RCH2X (X=C1, Br, I) compounds with formation of tertiary phosphines (or their boranes) 200 in good yields and with 50-93% ee [121]. The enantioselective alkylation of secondary phosphines 201 with benzyl halogenides catalyzed by complexes [RuH (/-Pr-PHOX 203)2] led to the formation of tertiary phosphines 202 with 57-95% ee [123, 125]. Catalyst [(R)-Difluorophos 204)(dmpe]Ru(H)][BPh4] was effective at asymmetric alkylation of secmidaiy phosphines with benzyl bromides, whereas (R)-MeOBiPHEP 205/dmpe was more effective in the case of benzyl chlorides (Schemes 65, 66, and 67) [125—127]. 

Another class of compounds whose cations may not be precipitated by the addition of hydroxide ions are the most stable complexes of metal cations with Lewis bases, such as ammonia, amines, and tertiary phosphines. Because of the large number of these compounds and their wide range of properties, it is not possible to give a general procedure for separating the cations. In many cases, metal sulfides can be precipitated directly from aqueous solutions of the complexes by the addition of aqueous sodium sulfide. If a test-tube experiment shows that other measures are needed, the addition of hydrochloric acid to produce a slightly acidic solution will often decompose the complex by protonation of the basic ligand. Metal ions that form insoluble sulfides under acid conditions can then be precipitated by drop wise addition of aqueous sodium sulfide. 

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