New open tetraaza nickel(II) and palladium(II) complexes. Different reactivity of the electrogenerated M(0) species toward difunctional substrates

A series of neutral and cationic Ni(II) and Pd(II) complexes with the open tetraaza ligand bisoxazoline bisamine N-4, were prepared and characterized. Neutral complexes presented dimeric structures of stoichiometry [M-2(mu-N-4)X-4] (M = Ni (1), Pd (2)) and underwent slow decomplexation in coordinating solvents. Cationic monomeric [M(N-4)]Y-2 (M = Ni (3), Pd (4)) compounds were stable in solution and were efficient catalysts in electrochemical reactions involving difunctional substrates, unsaturated o-haloaryl and o-halobenzyl ethers. [Ni(N-4)](2+)-catalyzed reactions led to intramolecular cyclization products via initial oxidative addition on the C-X bond, whereas [Pd(N-4)](2+)-catalyzed processes involved the cleavage of the C-O bond. Furthermore, organometallic sigma-Ni(II) (7a,b) and pi-allylpalladium(II) (8a,b) complexes were prepared in order to study the intermediate species proposed in the catalytic cycles.