Organophosphine ligands

Catalyst reactivation without the need for concentration of the catalyst solution and/or separation of the organophosphine ligand has been disclosed [40] using a variety of compounds including alkynes having the formulae shown in Figure 2.13. 

The sonochemistry group in Shanghai have also reported that the fragmentation of aryl /ert-phosphines in the presence of lithium can be promoted effectively using ultrasonic irradiation [45]. Triphenylphosphines could almost quantitatively be changed into lithium diphenylphosphides and phenyl lithiums in the presence of lithium metal under ultrasonic irradiation [Eq. (5)]. Sonochemical reaction was accomplished in 25 min at ambient temperature with no induction period. The reaction rate was increased by a factor of 6, compared with silent conditions. The method has been used for the preparation of some organophosphine ligands. 

Head-to-tail dimerization of isoprene. Heck et al. have found that dimerization of isoprene to head-to-tail dimers can be controlled by use of palladium catalysts in combination with organophosphine ligands. Thirty-six experiments are reported in which the various important variables were explored. The most satisfactory results were obtained with ( i/ -CoHoPdOAc), 2 P(o-CaH4CH3)s, N(CaHs)3, and formic acid, with THF as solvent. In this way the two head-to-tail dimers can be obtained in 79% yield (equation I). These dimers were separated... 

Organophosphine ligands are particularly successful in helping the metal provide a favorable coordination site that is sufficiently electron-rich to provide strong back-donation into the vacant dinitrogen tt -orbitals and help stabilize the metal-dinitrogen bond. 

Shmidt, F. K., Mironova, L. V, Kalabina, G. A., Proidakov, A. G., and Kalabina, A. V, Propylene dimerization in the presence of catalytic system based on nickel complexes with organophosphinic ligands, Neftekhimia, 16, 547, 1976. 

The synthesis of a series of chiral organophosphine oxide/sulfide-substituted binaphtholate ligands has recently been reported by Marks and Yu and their corresponding lanthanide complexes characterized. These complexes, generated in situ from Ln[N(TMS)2]3, cleanly catalysed enantioselective intramolecular hydroamination/cyclisation of 1-amino-2,2-dimethyl-4-pentene albeit with a low enantioselectivity of 7% ee (Scheme 10.82). 

Copper(I) nitrate complexes with organophosphines, arsines, and stibines can be readily prepared in good yield in alcohol solution by such ligand reduction reactions.9 In the cases of the arsines and stibines, addition of copper powder... 

Since 1948-50, by using as reactants isonitriles, phosphorus trihalides, and tertiary phosphines, we have gained important insight into the dependence of reactions of metal carbonyls with bases upon the nature of the ligand. Organophosphines were introduced into carbonyl chemistry even prior to 1948 by Reppe and Schweckendiek (7). In general, these ligands react only by substitution of CO, and do not cause disproportionation. Thus nickel carbonyl frequently reacts with complete displacement of carbon monoxide, as we were first able to demonstrate in the reaction with phenyl isonitrile (8). 

A variety of organophosphine transition-metal complexes have been used for the detection of SO2 [149]. Cook et al. used triphenyl- and tribenzyl phosphine compounds as ligands bound to Cu and Mn. Varying the ligand affects the Lewis acid strength of the metal complex, and hence, its ability to bind SO2. One complex (bis(tribenzylphosphine)copper(II) thiophenolate — [Cu(PBz3)2)SPh]) exhibited a reversible response to SO2 that was linear in the range of lO-KKK) mg/L. 

Silylphosphines, (R3Si)3P, are well known. On the basis of electronegativity (Table 1) they are weaker n acids than organophosphines. With the isolation of R2Si=PR compounds, an increased variety of structmes is available. Six-membered silicon-phosphorus heterocycles (1) have been proposed as ligands for catalyst candidates, owing to the steric accessibility of the transition metal. 

Once again, the drive for improved performance in transition metal ion-catalysed processes has continued to stimulate the synthesis of new types of organophosphine and tervalent phosphorus-ester and -amide ligands. Activity in the chemistry of heteroaromatic phosphorus ring systems and low-coordination number p -bonded systems has also remained at a high level. New mechanistic insights into the Mitsunobu reaction have been reported, and interest in synthetic applications of Staudinger/Mitsunobu procedures has continued to develop. 

The sol-gel method was applied for the preparation of heterogenized complexes such as Structure 3 based on the polycondensation of suitable trialkoxy-silyl-substituted organosulphides, organophosphines, and organoamines bound as ligands to a given complex (Pt, Rh, Ir, Ru). They were employed in the hydrosilylation of allyl chloride and other olefins [88]. 

Miscellaneous Methods of Preparing Phosphines. Approaches to the synthesis of specific types of organophosphine have been reviewed, covering phosphinoaryloxazolines, /ra j-2,5-disubstituted phospholanes, " new chiral phosphines which have been reported since 1990, chiral hydroxyphos-phines, and phosphorus-sulfur donor ligands.The uses of phosphine (PH3) in the synthesis of organophosphines has also been reviewed. A direct route for the synthesis of arylphosphines is offered by the reaction of... 

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