Phosphines displacement reactions

In the case of platinum, the Pt(0) complex Pt(85)3(PPh3) was isolated from the reaction of Pt(PPh3)4 and silylene 85 <2001JOM209, 2003JOM321>. The only characterized complex of coin metals with l,3,2(A2)diazasiloles is the tetrahedral Cu(l) complex 111, which was obtained by phosphine displacement reaction from CuI(PPh3)3. 

Complexes with other phosphines can be prepared by the general route of refluxing IrCl3 or IrClg- in an alcohol that acts as the source of CO, then adding the phosphine. In certain cases, a displacement reaction can be used... 

The nucleophilic displacement reactions with azide, primary amines, thiols and carboxylatc salts arc reported to be highly efficient giving high (>95%) yields of the displacement product (Table 9.25). The latter two reactions are carried out in the presence of a base (DBU, DABCO). Radical-induced reduction with tin hydrides is quantitative. The displacement reaction with phenolates,61j phosphines,6M and potassium phthalimide608 gives elimination of HBr as a side reaction. 

We discovered a complementary procedure for conversion of OMen to other functional groups. The ester P-OMen bond was shown to be cleaved in a stereoselective manner reductively [85,86]. The cleavage takes place with almost complete preservation of stereochemical integrity at phosphorus. The reducing agents are usually sodium or Hthium naphthalenide, lithium biphenyUde, and Hthium 4,4 -di-fert-butylbiphenyl (LDBB). The species produced is then quenched with an alkyl hahde or methanol to afford tertiary or secondary phosphines, respectively (Scheme 5b). Overall, the displacement reaction proceeds with retention of configuration. 

A. Preparation.—Halogen displacement reactions have been used to prepare a number of new aminofluorophosphines. Aminodifluorophos-phine (1) has been prepared for the first time, from either bromodifluoro-phosphine or chlorodifluorophosphine, and ammonia. Studies of its n.m.r. spectrum have been made (see Chapter 11). The related NN-difluoroaminodifluorophosphine (2) has been prepared, from difluoroiodo-phosphine, and found to be explosive. Two syntheses of A-alkyl-amino-difluorophosphines have been reported, one of which was complicated by the subsequent formation of the phosphorane (3) and the bis-(A-alkylamino)fluorophosphine (4). 

These compounds have been prepared via oxidative addition reactions between the appropriate phosphate or phosphine and either a quinone or via displacement reactions with a suitable diol. Compounds 81 and 83 were prepared by such a displacement reaction between monocyclic pentaoxyphosphorane 317 and 3-fluorocatechol or catechol in toluene, respectively. This reaction takes advantage of the chelation effect of forming a bicyclic system from a monocyclic one <1997IC5730>. Compound 82 and compound 84 were synthesized via oxidation addition between tetrachloroquinone and the respective sulfur-containing cyclic phosphate or phosphine <1997IC5730>. Compound 93 was prepared from the phosphine 318 and the diol 319 in the presence of iV-chlorodiisopropylamine in an ether solution <1998IC93>. 

The reaction of ethylene at -20°C and 1 atm with the phosphine-free catalyst prepared from 77-allylnickel chloride and ethylaluminum dichloride in chlorobenzene results in the rapid formation of a mixture of ethylene dimers with lesser amounts of higher oligomers. The dimer fraction consists mainly of 2-butenes and the trimer fraction of 3-methylpentenes and 2-ethyl-1-butene as well as a minor amount of hexene (97). From the composition of the products it can be concluded that the displacement reaction predominates over the insertion reaction when using the phosphine-free catalyst and that the direction of addition of both the H—Ni and C2H5—Ni species is mainly of the Ni — C2 type. 

There is certain similarity in the order of reactivities between SnAt displacement reactions and oxidative additions in palladium chemistry. Therefore, the ease with which the oxidative addition occurs for these heteroaryl chlorides has a comparable trend. Even a- and y-chloroheterocycles are sufficiently activated for Pd-catalyzed reactions, whereas chlorobenzene requires sterically hindered, electron-rich phosphine ligands. 

BioH14 is a mdo-polyborane, therefore, it is expected that it forms adducts with Lewis bases. This is indeed the case but with concomitant loss of hydrogen as shown in Eq. (51). These adducts of the type BioHi2-2L (L = amines, pyridine, phosphines, nitriles, dialkylsulfides inter alia) proved to be versatile reagents. For instance, when triethylamine is used to replace acetonitrile from the adduct not only does the expected replacement occur but in preference also a proton shift (most likely prior to the base displacement reaction) with cluster closure to the decahydro-doso-decaborate(2—) (Eq. 52) ... 

In several cases the >j -coordinated diyne ligand can be displaced by other ligands. The pentane-soluble, thermally stable compounds Ni(L2) (HC2C2H) (n= 1, 2 L2 = dippe, dippp) react with P(OPh)3 to give Ni P(OPh)3 4 with liberation of diyne and the bis-phosphine. The reaction of Ni(dippp) 2(/z-/ M- -HC2C2H) with four equivalents of CO resulted in polymerization of the butadiyne released from the metal center and the formation of Ni(CO)2(dippp). ... 

Aresta (54) and Deutscher (56) have also prepared chelate complexes by reacting the Giignard reagent formed from platinum bromide. The structure shown in Fig. 42 a has been attributed to the product of this reaction on the basis of its i.r. spectrum. Triphenyl phosphine displaces the coordinated double bonds to peld the complex... 

Another simple oligomerization is the dimerization of propylene. Because of the formation of a relatively less stable branched alkylaluminum intermediate, displacement reaction is more efficient than in the case of ethylene, resulting in almost exclusive formation of dimers. All possible C6 alkene isomers are formed with 2-methyl-1-pentene as the main product and only minor amounts of hexenes. Dimerization at lower temperature can be achieved with a number of transition-metal complexes, although selectivity to 2-methyl-1-pentene is lower. Nickel complexes, for example, when applied with aluminum alkyls and a Lewis acid (usually EtAlCl2), form catalysts that are active at slightly above room temperature. Selectivity can be affected by catalyst composition addition of phosphine ligands brings about an increase in the yield of 2,3-dimethylbutenes (mainly 2,3-dimethyl-1-butene). 

A less common approach to the synthesis of phosphinates is the reaction of electrophilic phosphonates with carbon nucleophiles such as Grignard reagents or lithium enolates. For example, the phosphinic acid analogue 71 of the amino acid statine was synthesized by displacement of tert-butyl lithioacetate on a 5-phenyl phosphonothioate 70 (Scheme 23)d104l The racemic diastereomers of the 5-phenyl phosphonothioate were obtained in pure form, and the displacement of the phenylsulfanyl moiety was found to be stereospecific, although the stereocenter at phosphorus would later be lost on hydrolysis of the ester. A similar displacement reaction has been described using the p h osp h on och I ori d ate.1711... 

Displacement reactions have been carried out in liquid ammonia (—33 °C) with R3P, R3As, R3Sb, ditertiary phosphines, bipy and phen22 leading to complete substitution of CN groups (equations 4-6). 

Displacement reactions of phosphines by some non-activated alkenes and alkynes have also been reported.67... 

One problem with this method is that the workup must be done carefully as die amine products tend to complex tenaciously with the aluminum salts formed from the LAH upon workup and thus are not recovered easily. There are standard workups which avoid these issues, but these should be followed carefully. Reduction of azides by catalytic reduction, phosphine or phosphite reagents, or Sn(II) chloride are all effective methods. The azides are also available from displacement reactions and give primary amines upon reduction. 

Additions to functionalized three-carbon olefins have been studied extensively. We have used methyl acrylate as a standard olefin since it always reacts only at the terminal carbon and the a,/3-double bond in the product is always trans. The stereospecificity of its reactions with vinylic halides varies with structure. The simple 1-halo-l-alkenes with methyl acrylate under normal conditions give mixtures of E,Z- and E,E-dienoates. The reaction is more selective with the bromides than with the iodides and the stereoselectivity increases with increasing triphenylphosphine concentration. This occurs because the excess phosphine displaces the hydridopalladium halide group from the diene 7r-complex before readdition to form the ir-allylic species occurs (see Equation 6). The disubstituted vinylic bromides react stereospecifically with methyl acrylate (4). 

A series of ligand displacement reactions has been investigated in which a phosphine replaces a carbonyl group, the ease of reaction depending on both M and the silyl residue. Triphenyl or trialkyl phosphine can remove only one CO molecule in Mn, Re, Co, and Fe complexes, even under forced conditions,... 

Other ligands have been synthesized more recently utilizing the same synthetic and theoretical philosophy.52,53 A chiral ditosylate or dimesylate is generally reacted with a metal phosphide to produce the diphosphine ligand. There have been problems with these displacement reactions with secondary ditosylates as has been discussed earlier. More recent procedures report success with phosphine oxide or borane anions. 

The cyclic phosphinate (96) has been isolated from the reaction of dichloro(methyl)phosphine with the ethoxycarbonylimine derived from hexafluoroacetone. Treatment of trichloro(organo)phosphonium-hexafluorophosphate salts with dichloro(diethylamino)phosphine results in the halophosphonium salts (97). Some reactions of dichloro(-)menthylphosphine have been reported.As usual, nucleophilic displacement reactions of halogenophosphines have received attention as routes to new systems of interest as ligands.Of particular interest in this connection is a report of the synthesis of the phosphorus-functionalised calixarenes (98). Only one chlorine atom of dichloro(phenyl)-phosphine is replaced on treatment with an excess of dicyclohexylamine, enabling the stepwise synthesis of the chiral aminophosphines (99), described as air-stable solids. 

Aryl ethers. Pd-mediated C-O bond formation ameliorates the undesirable feature of the Ullmann method employing stoichiometric quantities of copper salts. Electron-deficient ArBr and electron-rich ArONa are suitable reaction partners. Electron-poor phosphine ligands improve the yields of the displacement reaction between aryl bromides and sodium phenoxides. 

Potassium organophosphide reagents also continue to find applications in synthesis. Direct displacement of fluoride from fluoroaromatic substrates by potassium diphenylphosphide is the key step in the synthesis of the phosphi-noarylsulfoxides (88), water-soluble phosphino-amino acid systems, e.g. (89), ° and the chiral benzoxazine system (90). Related displacement of fluoride by potassium monophenylphosphide has been used to prepare a series of hydrophilic triarylphosphines, e.g. (91). Among new phosphines prepared by conventional displacement reactions by potassium diphenylphosphide on... 

---