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

Abstract

Using a phosphorus based Mannich condensation reaction the new pyridylphosphines {5-Ph 2PCH 2N(H)}C 5H 3(2-Cl)N ( 1- Cl) and {2-Ph 2PCH 2N(H)}C 5H 3(5-Br)N ( 1- Br) have been synthesised in good yields (60% and 88%, respectively) from Ph 2PCH 2OH 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), RuCl 2( p-cymene)( 1-Cl) ( 4), RuCl 2( p-cymene)( 1- Br) ( 5), RhCl 2(Cp ∗)( 1- Cl) ( 6), RhCl 2(Cp ∗)( 1- Br) ( 7), IrCl 2(Cp ∗)( 1- Cl) ( 8), IrCl 2(Cp ∗)( 1′- Cl) ( 8′), IrCl 2(Cp ∗)( 1- Br) ( 9), cis-/ trans-PdCl 2( 1- Cl) 2 ( 10), cis-/ trans-PdCl 2( 1- Br) 2 ( 11), cis-PtCl 2( 1- Cl) 2 ( 12) and cis-PtCl 2( 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 · (CH 3) 2SO have been elucidated by single crystal X-ray crystallography. A crystal structure of the dinuclear metallocycle trans, trans-[PdCl 2{μ-P/N-{Ph 2PCH 2N(H)}C 5H 4N}] 2 · CHCl 3, 18 · CHCl 3, 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 PdCl 2 units adopting a head-to-tail arrangement.