Cd(II), Zn(II), and Pd(II) Complexes of an Isoindoline Pincer Ligand: Consequences of Steric Crowding

The sterically crowded isoindoline pincer ligand, 6‘-MeLH, prepared by condensation of 4-methyl-2-aminopyridine
and phthalonitrile, exhibits very different reaction chemistry with Cd2+, Zn2+, and Pd2+. Three different ligand
coordination modes are reported, each dependent upon choice of metal ion. This isoindoline binds to Cd2+ as a
charge-neutral, zwitterionic, bidentate ligand using imine and pyridine nitrogen atoms to form the eight-coordinate
fluxional complex, Cd(6‘-MeLH)2(NO3)2. In the presence of Zn2+, however, loss of a pyridine arm occurs through
solvolysis and tetrahedrally coordinated complexes are formed with coordination of pyrrole and pyridine nitrogen
atoms. Reaction with Pd2+ produces the highly distorted, square planar complex Pd(6‘-MeL)Cl in which a deprotonated
isoindoline anion coordinates as a tridentate pyridinium NNC pincer ligand.