Synthesis of C1-symmetric tripod ligands containing a P,P,N donor set -η2-coordination in d8-metal complexes

Article abstract of DOI:10.1002/ejic.200200448

Tripod ligands RC(CH₂X)(CH₂Y)(CH₂Z) (X, Y, Z = NR2, PR2) are accessible from α,β-unsaturated esters R(=CH2)COOR′. The key steps in this synthetic approach are Michael additions of amines and phosphanes to produce RCH(COOR′)(CH2X) (X = NR2, PR2) (2 and 3), followed by hydroxymethylation with paraformaldehyde to result in RC(COOR′)(CH₂OH)(CH₂X) (X = NR₂) (4). Standard transformations of this C₁-symmetric precursor allow for the synthesis of tripod ligands such as PhC(CH₂pz)(CH₂PPh₂)(CH₂PMes) (11). Coordination of these ligands with d⁸-metal ions [nickel(II), palladium(II), rhodium(I)] results in square-planar complexes with the chelate cycles in half-chair, twist-boat or boat conformations, depending on the specific substitution pattern. Coordination through two phosphane donors with the nitrogen donor acting as a dangling arm is generally preferred throughout. Detail preparative procedures and complete characterisation by analytical methods, including X-ray analysis of the coordination compounds, are given. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.