PCP pincer ligand

Palladium complexes of inexpensive, easily synthesized bis(phosphinite) PCP -pincer ligands show good activity in the Suzuki coupling of deactivated and sterically hindered aryl bromides.256... 

Scheme 3 Syntheses of metal complexes of fluorous PCP pincer ligands 10-Rf ...

Johansson et al. [48] were interested in improving this bimetallic system, and proposed the existence of PCP-pincer ligands (2,6-bis[(di-t-butylphosphino)methyl]... 

Schwartsburd, E. Poverenov, L. J. W. Shimon, and D. Milstein, Organometallics, 2007, 26, 2931. The steric bulk of the PCP pincer ligand helps to stabilize the Pt-CO complex, and the electronic properties of the naphthyl group enhance the susceptibility of the CO group... 

Ruthenium complexes also catalyze the anti-Markovnikov hydroamination of vinylarenes. In this case, the combination of l,5-bis(diphenylphosphino)pentane (DPPPent), triflic acid, and a ruthenium(II) precursor generates a catalyst for the additions of secondary amines to vinylarenes (Equation 16.72). This mixture of catalyst components has been shown to generate a cationic Ti -arene complex of a PCP pincer ligand generated from the DPPPent ligand. The mechanism of this reaction involves nucleophilic attack of the amine on an Ti -vinylarene complex, as described in more detail in the section on the mechanisms of hydroamination. 

Reitsamer et al. [83] recently reported a palladium complex of a PCP pincer ligand that engages in a d -d ° with the AuCl fragment. The ligand, while involving a two-coordinate carbon atom, is not accurately described as a carbene but rather as a carbodiphosphorane. In this description, the central carbon(O) atom is coordinated... 

Steinke et al. synthesized a new type of PCP pincer ligand where the central carbon donor is a saturated NHC (Figure 4.11) [45]. These structures showed a considerable twisting of the ligand framework above and below with respect to the square plane of the metal complex and the PCP donors. In solution, this twisting is not fixed, as the two possible chiral conformations exchange first on the NMR time scale. 

A Pd(II)-Pd(0) interaction was reported in compound 157 with a Pd(II)-Pd(0) distance at 3.0389(11)A (Entry 1, Table 10.10) (Figure 10.14) [117]. It represents a very rare example of a nonplanar diamagnetic Pd(II) moiety, and the Pd(0) center slightly deviates from linearity and points toward the Pd(II) center. Complex 157 was made from the reduction of [LPdX] (L = PCP pincer ligand, X = Cl or CFjCOj) using sodium metal as reductant. 

A chiral PCP pincer ligand has been used in the palladium-catalyzed addition of secondary phosphines to nitroalkenes (Scheme 4.27) [20]. The reactions were carried out at -40 °C in dichloromethane with a slight excess of the secondary phosphine and afforded excellent yields of the addition products. The process was highly regioselective for addition to the carbon beta to the nitro group. The enantioselectivity was less consistent and the authors noted some substrate dependence with the highest selectivity observed with para-substituted nitrostyrenes and the lowest with meta- and ortho-substituted substrates. The products were isolated as phosphine oxides in order to facilitate purification. 

SCHEME 4.27 Use of a P-stereogenic PCP pincer ligand in asymmetric hydrophosphination reactions [20]. 

Metallic complexes with pincer ligands are known for their high stability. In order to recover the pincer palladium complex, a perfluoroaUcylated P-C-P (PCP) pincer ligand was prepared in two steps, which can form a stable complex with Ni(II),... 

Scheme 7.9 Perfluoroalkylated PCP pincer ligand and related reactions.

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