Synthesis, interionic structure, and reactivity toward CO and p-methylstyrene of palladacyclic compounds bearing alpha-diimine ligands

Palladacyclic compounds [Pd(C6H4(C6H5C=O)C=N-R)(N-N)] [X] (R = Et, Pr-i, 2,6-(Pr2C6H3)-Pr-i; N-N=bpy=2,2'-bipyridine, or 1,4-(o,o'-dialkylaryl)-1,4-diazabuta-1,3-dienes; [X](-)=[BF4](-) or [PF6](-)) were synthesized from the dimers [(Pd(C6H4(C6H5C=O)C=N-R)(mu-Cl)}2] and N-N ligands. Their interionic structure in CD2Cl2 was determined by means of F-19,H-1-HOESY experiments and compared with that in the solid state derived from X-ray single-crystal studies. [Pd(C6H4(C6H5C=O)C=N-R)(N-N)[X] complexes were found to copolymerize CO and p-methylstyrene affording syndiotactic or isotactic copolymers when bpy or 1,4-(o,o'-dimethylaryl)-1,4-diazabuta-1,3-dienes were used, respectively. The reactions with CO and p-methylstyrene of the bpy derivatives were investigated. Two intermediates derived from a single and a double insertion of CO into the Pd-C bonds were isolated and completely characterized in solution.