| The synthesis of thermally stable ligands and their metal complexes can be expected to broaden the scope of homogeneous catalysis to include endothermic processes, which may normally require high temperatures to occur efficiently. Polyheterocyclic aromatic hydrocarbons with donor atoms represent a new approach to expand this area of homogeneous catalysis.; A new family of tridentate nitrogen pincer ligands with thermal stability have been introduced by the new compound benzo[1,2-h:5,4-h′]diquinoline 6a and its derivatives 6b–c. The structure is based on the anthracene skeleton with two angularly annulated pyridine rings and is highly conjugated with trans directing donor atoms to promote metal complexation. This polyaromatic dinitrogen heterocycle readily undergoes cyclometalation to form rigid, thermally stable complexes with Pt group metals (Pd ( 7a–c, 8a,c), Pt (9a–c), Ir ( 11a–c, 12a–c), Rh (10a–c). These complexes have been characterized by NMR, mass spectrometry, and x-ray crystallography. Preliminary results show that the palladium complex 7a is an active catalyst for Heck coupling reaction of bromobenzene with acrylates to give di and tri-substituted olefins. The platinum complex 9a shows some activity for the activation of methane, and is luminescent.; Other nitrogen based polyaromatic heterocyclic pincer ligands with the NNC ((5,6,8,9-tetrahydronaphtho[1,2-b][1,10]phenanthroline (H2thnp) (17) and naphtha [1,2-b][1,10] phenanthroline (np) (19 )) and CNC ((5,6,8,9-tetrahydrodibenzo [c,h]acridine (18)) motifs have been studied. NNC ligands 17 and 19 readily undergo cyclometalation with Pt group metals (Pd, Pt, Ir) to form rigid, thermally stable complexes. The PdNNC complex (27) also undergoes the Heck coupling reaction of bromobenzene with acrylates to give di and tri-substituted olefins. The CNC ligand 18 was found to undergo double C-H activation with platinum. These complexes have been characterized by NMR, mass spectrometry, and x-ray crystallography. |
