Phosphines carbonates

A halogenating system related to the preceding case is formed by the reaction of triphenylphosphine with molecular bromine or chlorine. The system is not as sensitive to moisture as the phosphine-carbon tetrahalide system (see preceding section), but it suffers from the disadvantage that hydrohalic acids are produced as the reaction proceeds. Nevertheless, sensitive compounds can be successfully halogenated by the system, as exemplified by the preparation of cinnamyl bromide from the alcohol. 

The behavior of 3 toward ether or amines on the one hand and toward phosphines, carbon monoxide, and COD on the other (Scheme 2), can be qualitatively explained on the basis of the HSAB concept4 (58). The decomposition of 3 by ethers or amines is then seen as the displacement of the halide anion as a weak hard base from its acid-base complex (3). On the other hand, CO, PR3, and olefins are soft bases and do not decompose (3) instead, complexation to the nickel atom occurs. The behavior of complexes 3 and 4 toward different kinds of electron donors explains in part why they are highly active as catalysts for the oligomerization of olefins in contrast to the dimeric ir-allylnickel halides (1) which show low catalytic activity. One of the functions of the Lewis acid is to remove charge from the nickel, thereby increasing the affinity of the nickel atom for soft donors such as CO, PR3, etc., and for substrate olefin molecules. A second possibility, an increase in reactivity of the nickel-carbon and nickel-hydrogen bonds toward complexed olefins, has as yet found no direct experimental support. 

Dimethyl 2-methylenepentanedioate. Methyl acrylate (30.0 g, 349 mmol) (distilled immediately before use) and dry pyridine (30 ml, CAUTION) containing tris(cyclohexyl)phosphine-carbon disulphide complex (2.0 g, 6 mmol) (1) are refluxed under nitrogen for 16 hours. The deep red solution is cooled and the pyridine removed under reduced pressure. The residue is taken up in ether (400 ml) and the solution washed with aqueous 1 m hydrochloric acid (3 x 40 ml). The combined aqueous layers are extracted with ether (2 x 50 ml) and the combined organic layers washed with 1 m hydrochloric acid (30 ml), saturated brine (40 ml) and saturated aqueous sodium hydrogen carbonate (2 x 30 ml), dried over sodium sulphate and evaporated. Distillation of the oil gives dimethyl 2-methylenepentanedioate (23.8 g, 79%) as a liquid, b.p. 66-68 °C/1 mmHg i.r. (thin film) 1738, 1715, 1635cm-1. 

Notes. (1) Pyridine was stored over potassium hydroxide and distilled immediately before use. The tris(cyclohexyl)phosphine-carbon disulphide complex is prepared by the method of K. Issleib and A. Brack.9 This involves the addition of carbon disulphide to an ethereal solution of tricyclohexylphosphine, the precipitate is washed with light petroleum (b.p. 50-60 °C), and recrystallised under a nitrogen atmosphere from either methanol, ethanol or dioxane the complex has m.p. 118 °C. 

Tri-0-acetylxanthosine (78) reacts with triphenyl phosphine-carbon tetrachloride (2 equiv.) in dichloromethane at reflux to give the 6-chloro derivative in good yield. This product yields the pyridinium salt (79) with aqueous pyridine which is a versatile reagent for the synthesis of other substituted purines (Scheme 28) [95JCS(P1)15]. 

The unique phosphine-carbon dioxide complex Cp2Ti (C02)PMe3 is prepared by treatment of Cp2Ti(PMc3)2 with dry CO2 at -180°C (equation 50). Slow thermal decomposition of Cp2Ti(C02)PMc3 at room temperature leads principally to Cp2Ti(CO)2. ... 

AMIDES Catecholborane. o-Nitrophenyl thiocyanate. Nitiosonium hexafluoro-phosphate. Sodium superoxide. Tri-ethoxydiiodophosphorane. Triphenyl-phosphine-Carbon tetrachloride. 

In this catalyst system, addition of phosphine or decrease in partial pressure of CO (or of total pressure at constant synthesis-gas ratio) shifts the phosphine-carbon monoxide ligand-exchange equilibrium toward the phosphine-substituted species (right to left in scheme 8.13). A decrease in phosphine concentration or an increase in CO pressure shifts it in the opposite direction (left to right). Addition of base shifts equilibrium downward, from the acids to the anions. In the presence of phosphine in an at least moderate excess, thermodynamics strongly favors HCo(CO)3Ph over HCo(CO)4, but Co(CO)4" remains very strongly favored over Co(CO)3Ph under all conditions of practical interest. 

Dichloro(l, 3-propanediyl)platinum and its bis(pyridine) derivative have been studied by a number of authors. Dichloro(l,3-propanediyl)platinum, and the corresponding substituted 1,3-propanediyl platinum compounds release the parent cyclopropane on treatment with potassium cyanide, potassium iodide, a tertiary phosphine, carbon monoxide, and other ligands.2,6 Reduction by means of hydrogen or lithium aluminum hydride yields chiefly isomeric substituted propanes. Dichlorobis(pyridine)(l,3-propanediyl)platinum in refluxing benzene yields a pyridinium ylid complex, - (CH3CH2CHNC5Hs)-PtpyCla. 

Palladiiim(II) acetate-tertiary phosphine-carbon monoxide... 

Peptide synthesis. Wieland and Seeliger7 have used the combination of triphenyl phosphine-carbon tetrachloride and triethylamine for coupling of Bocamino acids with amino acid esters to form peptides. However, extensive racemization is observed. 

French workers prefer the use of tris(dimethylamino)phosphine-carbon tetrachloride for reactions of this type. These reagents are used to substitute one hydroxy-group in 1,3-diols. Heating the salt (44) gives the chloride directly, or the phosphine oxide may be displaced by added nucleophiles. Addition of sodium methoxide gives the oxetans (45). The same reagents can be used to activate selectively the primary hydroxy-group of hexoses and hence allow it to be displaced by added nucleophiles. ... 

Dehydration reactions using the tertiary phosphine-carbon tetrachloride adduct have appeared quite regularly in the literature again this year. Among those reported have been the dehydrations of oximes to nitriles, carboxylic acids to anhydrides, and the amides (37) to the cumulenes (38). Further reaction of the dehydration product from treatment of the... 

CS2 can bind in monodentate end-on, bidentate chelate, bridging, or rj forms (Scheme 26). Most complexes of CS2 are low-valent electron-rich species, for example [Mo(Cp)(CO)2(/]2-CS2)] (51), [Ru(CO)2(PPh3)2( ] -CS2)] (52), and [Pt(PPh3)2 ( -CS2)] (53). Conversion of coordinated CS2 to CS and CS3 fragments can occur on coordination. The coordination chemistry of phosphine-carbon disulfide adducts (S2CPR3) has been reviewed these versatile ligands can act as 2 to 8 electron donors to metal centres. ... 

In principle, the three main approaches to the synthesis of phosphonic and phosphinic acid derivatives consist in (i) the generation of phosphorus-carbon bonds in the presence of other functional groups at phosphorus which, themselves, very often act to block the formation of a second (or third) phosphorus-carbon bond (ii) modifications in the phosphonic or phosphinic carbon moieties or (iii) modifications, at phosphorus in tetra-coordinate compounds which already possess phosphorus-carbon bonds reactions of this last type are considered in Chapter 6. 

Triphenyl(trichloromethyl)phosphonium chloride and (dichloromethylene)tri-phenylphosphorane are important intermediates in the reaction system triphenyl-phosphine/carbon tetrachloride. Solutions of (dichloromethylene)triphenyl-phosphorane, which is a convenient Wittig reagent, were first prepared by the addition of dichlorocarbene to triphenylphosphine in chloroform. However, the ylide could not be separated without degradation caused by the reaction medium. 

ALLYLIC CHLORIDES Triphenyl-phosphine-Carbon tetrachloride. 

The phosphine-carbon tetrachloride combination has proven to be a versatile dehydrating agent. Primary amides (110, 111) and aldoximes (112) are... 

Transformation to the tosylate and reaction with lithium chloride in a polar aprotic solvent such as hexamethylphosphoramide or dimethylformamide appears to be a general procedure/" Triphenyl phosphine-carbon tetrabromide has been used successfully in the transformation of a primary allylic alcohol to the bromide without... 

Carbon tetrabromide (s.a. Triphenyl-phosphine/carbon tetrabromide) Carbon tetrachloride... 

Earlier, cationic Ir catalysts suffered from the hydrogenolysis of the phosphine-carbon bond occurring at reaction temperatures above 130 C [108,109]. In contrast, the iridium bis(phosphine) PCP-pincer complexes showed higher thermal stabilities [110, 111]. For example, iridium ( PCP)Ir(H2), Ir-2(H2), quantitatively catalyzed the transfer hydrogenation of cyclohexane into cyclohexene in the presence of tbe at 200 °C. Moreover, Ir-pincer complex Ir-2(H2) displayed TONs up to 1000 at 200 °C. 

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