Bis-triarylphosphines

R)- and (S)-(6,6 -Dimethylbiphenyl-2,2 -diyl)bis(diphenylphosphine), BIPHEMP (1). This is the first example of an optically active bis(triarylphosphine) containing the axially disymmetric biphenyl group. The 6,6 -dimethyl groups are used to... 

The nickel-catalyzed transformation of aromatic halides into the corresponding nitriles by reaction with cyanide ions is reported. Both tris(triarylphosphine)nickel(0) complexes and tY2ins-chloro( aryl )bis( triarylphosphine )nickel(II) complexes catalyze the reaction. The influence of solvents, organophos-phines, and substituents on the aromatic nucleus on catalytic cyanation is studied. A mechanism of the catalytic process is suggested based on the study of stoichiometric cyanation of ti3ins-chloro(aryl)bis(triphenylphosphine)nickel-(II) complexes with NaCN and the oxidative addition reaction of Ni[P(C6H5)3]s with substituted aryl halides. 

We have measured the PMR spectra of some bis(triarylphosphine) complexes of the Co(II) and Ni(II) halides in CDCl solution. These compounds are paramagnetic with approximately tetrahedral coordination about the metal atom (6-8), Isotropic shifts for the various protons in these complexes in solution at 25, referred to the diamagnetic ligand resonances, are given in Table I, and are shown schematically in Fig. 1. 

The base-promoted condensation of tris[(2-chloromethyl)phenyl]phos-phine and tris(2-mercaptophenyl)phosphine under high dilution conditions gave (10%) the congested w,in-bis(triarylphosphine) 51 the trisulfone and its central P-protonation are also reported (130L2179). tructurally related cyclophanes in which only one P-center in 51 was replaced with either N or iR (R = H or Me) has also appeared (13T10316). 

Other species tested in situ are chelating bis-imidazolium structures with phe-nylene spacers [48], and bidentate C-P ligands [49] that achieved, in the case of triarylphosphine-imidazolium salts, very good yields for a wide variety of substituted aryl bromides (Scheme 6.11) [50]. 

From the results of the 1,3-diene addition reaction, the metal-catalyzed reaction of unactivated alkenes was examined, and it was found that the palladium complex effectively catalyzed the a rt-Markovnikov addition of triarylphosphines and bis(trifluoromethanesulfonyl)imide (Tf2NH).24... 

Methods (i) and (ii) require palladium(II) salts as reactants. Either palladium acetate, palladium chloride or lithium tetrachloropalladate(II) usually are used. These salts may also be used as catalysts in method (iii) but need to be reduced in situ to become active. The reduction usually occurs spontaneously in reactions carried out at 100 °C but may be slow or inefficient at lower temperatures. In these cases, zero valent complexes such as bis(dibenzylideneacetone)palladium(0) or tetrakis(triphenylphos-phine)palladium(O) may be used, or a reducing agent such as sodium borohydride, formic acid or hydrazine may be added to reaction mixtures containing palladium(II) salts to initiate the reactions. Triarylphosphines are usually added to the palladium catalysts in method (iii), but not in methods (i) or (ii). Normally, 2 equiv. of triphenylphosphine, or better, tri-o-tolylphosphine, are added per mol of the palladium compound. Larger amounts may be necessary in reactions where palladium metal tends to precipitate prematurely from the reaction mixtures. Large concentrations of phosphines are to be avoided, however, since they usually inhibit the reactions. 

---