Monodentate cyclic phosphine

The use of copper catalysts based on chiral phosphorus ligands to assist 1,4-additions of dialkylzinc reagents has in recent years produced major breakthroughs, with excellent enantioselectivities. A number of monodentate and bidentate phos-phoramidites, phosphites, phosphonites, and phosphines are now available as chiral ligands for alkyl transfer to a variety of cyclic and acyclic enones. So far. 

Several catalytic systems have been investigated for hydroamination of unsaturated bonds [16]. Takahashi et al. reported the telomerization of 1,3-dienes in the presence of an amine leading to octadienylamine or allylic amines when palladium catalysts are used in association with monodentate or bidentate phosphine ligands, respectively [17]. Dieck et al. demonstrated the beneficial effect of addition of an amine hydroiodic salt in the hydroamination reaction of 1,3-dienes in which the allylic amines are produced via an intermediate Jt-allyl palladium complex [18]. Coulson reported the Pd-catalyzed addition of amines to allenes where dimerization is incorporated [4]. This reaction presumably proceeds via a cyclic palladium intermediate in which the Pd activates the olefinic bond for nucleophilic attack the reactions are therefore different from pronucleophilic additions. 

Finally, the reaction of succinic anhydride 111 with a 1 2 mixture of (cod)2Ni and a monodentate phosphine generated a reactive monomeric nickelalactone, which underwent rapid aggregation to form cyclic oligomer 112 (Equation 39) <20050M272>. 

When carbon chain poly(phosphines) act as multidentate ligands they form chelate rings containing carbon, phosphorus and a metal atom. They can be made by reactions analogous to those employed for monodentate derivatives above. In reaction (8.137) a linear complex is first formed, but on raising the temperature a cyclic derivative is obtained. 

One consequence of the practical reversibility of the decarboxylation step is that loss of CO2 is not instantaneous. Stereochemically homogeneous cyclic carbonates sometimes equilibrate under paUadium(0) catalysis when Pd(PPh3)4 is used as the catalyst source, or in other words, when monodentate phosphines are used to stabilize Pd(0), but not in the presence of bidentate phosphinest (Scheme 8). 

The use of MejSiSnBuj in these nickel-catalyzed coupling reactions of dienes with aldehydes results in the formation of stannylated cyclic product homoallylic alcohols. The reaction may proceed via the oxidative addition of Ni(0) into the Si-Sn bond [227]. Moderate chiral induction is observed in this reaction when a monodentate phosphine ligand is employed [228]. 

---