A hemilabile binucleating pincer ligand for self-assembly of coordination oligomers and polymers

Abstract

The bis(PNP)-donor pincer ligand 1,4-C₆H₄{N(CH₂CH₂PPh₂)₂}₂, 1, contains weakly basic nitrogen donor atoms because the lone pairs of electrons are conjugated to the bridging phenylene group, and this feature is used in the synthesis of oligomers and polymers. The complexes [Pd₂X₂(µ-1)](OTf)₂, X = Cl, Br or OTf, contain the ligand 1 in bis(pincer) binding mode (µ-κ⁶-P₄N₂), but [Pd₄Cl₆(µ_3–1)₂]Cl₂ contains the ligand in an unusual unsymmetrical µ₃-κ⁵-P₄N binding mode. The bromide complex is suggested to exist as a polymer [{Pd₂Br₄(µ₄-1)}_n] with the ligands 1 in µ₄-κ⁴-P₄ binding mode. The methylplatinum(II) complexes [Pt₂Me₄(µ-1)] and [Pt₂Me₂(µ-1)](O₂CCF₃)₂ contain the ligand 1 in µ-κ⁴-P₄ and µ-κ⁶-P₄N₂ bonding modes, while the silver(I) complex [Ag₂(O₂CCF₃)₂ (µ-1)] contains the ligand 1 in an intermediate bonding mode in which the nitrogen donors are very weakly coordinated. The complexes [Pd₂(OTf)₂(µ-1)](OTf)₂ and [Ag₂(O₂CCF₃)₂(µ-1)] react with 4,4′-bipyridine to give polymers [Pd₂(µ-bipy)(µ-1)](OTf)₄ and [Ag₂(µ-bipy)(µ-1)](O₂CCF₃)₂.