1,2,3-Triazole based ligands with phosphine and pyridine functionalities: synthesis, Pd^II and Pt^II chemistry and catalytic studies

This manuscript describes the syntheses of pyridine appended triazole-based mono- and bisphosphines, [o-Ph₂P(C₆H₄){1,2,3-N₃C(Py)C(H)}] (2), [o-Br(C₆H₄){1,2,3-N₃C(Py)C(PPh₂)}] (3), [C₆H₅{1,2,3-N₃C(Py)C(PPh₂)}] (4), [Ph₂P(C₆H₄){1,2,3-N₃C(Py)C(PPh₂)}] (5) and [3-Ph₂P-2-{1,2,3-N₃C(Ph)C(PPh₂)}C₅H₃N] (6), their palladium and platinum chemistry and catalytic applications. These ligands upon treatment with [M(COD)Cl₂] (M = Pd or Pt) yielded complexes with different coordination modes, depending on the reaction conditions. Both κ²-P,N and κ²-P,P coordination modes were observed in many of the complexes indicating the ambidentate nature of these ligands. Monophosphine 2 in the presence of a base afforded rare fused-5,6-membered PCN pincer complexes [MCl{o-Ph₂P(C₆H₄){1,2,3-N₃C(Py)C(H)}}-κ³-P,C,N] (7, M = Pd; 8, M = Pt), whereas the reactions of 4 with [M(COD)Cl₂] (M = Pd, Pt) produced κ²-P,N chelate complexes [MCl₂{C₆H₅{1,2,3-N₃C(Py)C(PPh₂)}-κ²-P,N}] (9, M = Pd; 10, M = Pt). Similar reactions of 5 and 6 resulted in κ²-P,P chelate complexes [MCl₂{{3-Ph₂P-2-{1,2,3-N₃C(Ph)C(PPh₂)}C₅H₃N}-κ²-P,P}] (11, M = Pd; 12, M = Pt) and [MCl₂{3-Ph₂P-2-{1,2,3-N₃C(Ph)C(PPh₂)}C₅H₃N}-κ²-P,P}] (13, M = Pd; 14, M = Pt), respectively. The palladium(II) complexes have shown excellent catalytic activity in the α-alkylation reaction of acetophenone derivatives.