New pyridyl modified phosphines: Synthesis and late transition-metal coordination studies

Using a phosphorus based Mannich condensation reaction the new pyridylphosphines {5-Ph2PCH2N(H)}C5H3(2-Cl)N (1-Cl) and {2-Ph2PCH2N(H)}C5H3(5-Br)N (1-Br) have been synthesised in good yields (60% and 88%, respectively) from Ph2PCH2OH and the appropriate aminopyridine. The ligands 1-Cl and 1-Br display variable coordination modes depending on the choice of late transition-metal complex used. Hence P-monodentate coordination has been observed for the mononuclear complexes AuCl(1-Cl) (2), AuCl(1-Br) (3), RuCl2(p-cymene)(1-Cl) (4), RuCl2(p-cymene)(1-Br) (5), RhCl2(Cp∗)(1-Cl) (6), RhCl2(Cp∗)(1-Br) (7), IrCl2(Cp∗)(1-Cl) (8), IrCl2(Cp∗)(1′-Cl) (8′), IrCl2(Cp∗)(1-Br) (9), cis-/trans-PdCl2(1-Cl)2 (10), cis-/trans-PdCl2(1-Br)2 (11), cis-PtCl2(1-Cl)2 (12) and cis-PtCl2(1-Br)2 (13). Reaction of Pd(Me)Cl(cod) (cod = cycloocta-1,5-diene) with either 1 equiv. of 1-Br or the known pyridylphosphines 1′-Cl, 1-OH or 1-H gave the P/N-chelate complexes Pd(Me)Cl(1-Br–1-H) (14)–(17). All new compounds have been fully characterised by spectroscopic and analytical methods. Furthermore the structures of 4, 5, 10 and 16 · (CH3)2SO have been elucidated by single crystal X-ray crystallography. A crystal structure of the dinuclear metallocycle trans,trans-[PdCl2{μ-P/N-{Ph2PCH2N(H)}C5H4N}]2 · CHCl3, 18 · CHCl3, has also been determined. Here 1-H bridges, using both P and pyridyl N donors, two dichloropalladium centres affording a 12-membered ring with the PdCl2 units adopting a head-to-tail arrangement.