Metal-containing polymers bearing pendant nickel(ii) complexes of Goedken's macrocycle

Abstract

The design, synthesis, and polymerization of a norbornene-based monomer bearing a nickel(II) complex of Goedken's macrocycle (endo-13) and the characterization of the resulting polymer (14) are described. Detailed studies of the ring-opening metathesis polymerization of endo-13 using the 3-bromopyridine adduct of Grubbs’ 3^rd generation catalyst revealed that the polymerization shares many characteristics associated with a living polymer, but deviated from ideal behavior when high degrees of polymerization were targeted. The installation of a 3-hexylphenyl substituent at the macrocyclic backbone allowed for the realization of soluble polymers and shut down an oxidative dimerization pathway commonly associated with metal complexes of Goedken's macrocycle. The cyclic voltammogram of the polymer 14 was comprised of two one-electron oxidation waves (0.21 V and 0.70 V relative to ferrocene/ferrocenium) associated with the stepwise oxidation of the macrocyclic ligand backbone and a one electron reduction wave associated with the reduction of nickel(II) to nickel(I) (−2.07 V). Solution and solid-state UV-vis absorption spectra recorded for polymer 14 revealed a strong π → π* absorption (λ_max = 390 nm) and a ligand-to-metal charge transfer band (λ_max = 590 nm) typical of nickel(II) complexes of Goedken's macrocycle, and confirmed the absence of macrocycle–macrocycle interactions. This work has ultimately led to the development of a controlled polymerization route to a rare example of a side-chain nickel-containing polymer with potentially useful properties.