P,N chelating ligands

Figures 8E.3-8E.6 show a selection of some ligands that have been successfully used in the palladium-catalyzed AAA reaction. They are classified into four categories 1) chiral phosphines, 2) dinitrogen ligands, 3) P,N-chelate ligands, and 4) mixed chelate ligands. Although this...

Figure 3.10 Examples of a CO insertion and b CH3 migration, in a square-planar Pd complex with a P—N chelating ligand. Note that the migration mechanism retains the cis configuration between the CO group and the chelate nitrogen atom.

Asymmetric palladium-catalyzed alkylation of various allylic acetates occurred in water or in an aqueous/organic biphasic medium, using as ligands phosphines derived from carbohydrates [29], amphiphilic resin-supported MOP and P,N-chelating ligands [30, 31], or BINAP in the presence of surfactants [32] enantio-selectivities up to 85%, 98%, and 92% have been obtained in the alkylation of 1,3-diphenyl-2-propenyl acetate, respectively. 

Nickel complexes with P,N-chelating ligands in catalytic ethylene dimerization and oligomerization 05ACR784. 

N. W. Alcock, J. M. Brown, D. I. Hulmes, Tetrahedron Asymmetry 1993,4, 743-756. Synthesis and resolution of 1-(2-diphenylphosphino-l-naphthyl)isoquinoline a P-N chelating ligand for asymmetric catalysis. 

PdCUI (L2 = 2 PPha or several N-N or P-N chelating ligands) reacts with alcohols or amines in the presence of CO and a base to yield bis-alcoxycarbonyl or carbamoyl complexes respectively (eqs. 15, 16) ... 

In this chapter, we focus on P,N-chelating ligands and some of their transition metal complexes because their intrinsic properties, immense structural diversity, and broad range of applications attract increasing attention [3]. Such heterofunctional ligands associate hard nitrogen donor(s) with soft phosphoms donor(s) and offer considerable chemical and structural diversity. They may also generate hemilabile systems endowed with enhanced reactivity. 

P,N-CHELATING LIGANDS BASED ON OXAZOLINE/THIAZOLINE SYSTEM... 

Among the diverse N-functional moieties associated with P,N-chelating ligands, the heterocycles oxazoline and thiazoline as well as their substituted derivatives have enjoyed special attention. The P-donor group can be connected through a spacer to the 2-position of the oxazoline ring or to the 4-position, as in the basic subunits shown in Scheme 14.3. 

Numerous complexes possess P,N-chelating ligands that form six-membered ring systems. Depending on the relative position of the phosphorus (including phosphines, phosphinites, and aminophosphines) and oxazoline/thiazoUne donor groups, four types of subunits can be considered (Scheme 14.14). 

Phosphaferrocenes find increasing use as ligands both chiral and achiral for example, a number of new P,N-chelate ligands based on pyridyl-substituted phosphaferrocenes have been prepared—the synthesis uses 2-formyl-3,4-dimethylphosphaferrocene as a precursor. A typical complex is shown as 57. A range of 2-(2 -pyridyl)phosphafer-rocenes have also been prepared and used as ligands an example of which is shown as 58. A number of chiral ligands such as phosphaferrocene-oxazoline ligands have also been prepared and are used in asymmetric catalysis, for example, 59. ... 

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