Organometallic single-chain polymer nanoparticles via intra-chain cross-linking with dinuclear μ-halo(diene)Rh(I) complexes

An approach towards the expansion of Rh(I)-containing single-chain polymer nanoparticles (SCNPs) using linear polymers and μ-halo(diene)Rh(I) dimers as cross-linkers in high dilution was explored. Initially, the effects of utilizing different anionic ligands, i.e., halides, together with various labile alkene ligands, such as ethylene, 1,5-cyclooctadiene and 1,5-hexadiene, on the stability and activity of the resulting Rh(I) cross-linking complexes were examined. While the ethylene complexes for bromide and iodide bridges resulted too unstable and the 1,5-cyclooctadiene ligand produced inert complexes, the 1,5-hexadiene ligands provided the proper equilibrium of stability and lability to achieve efficient polymer folding. Thus, a range of new organometallic nanoparticles could be obtained via a direct exchange between the 1,5-hexadiene labile ligands of the Rh(I) complexes, and the corresponding 1,5-hexadiene elements present in ROMP derived 1,5-polycyclooctadiene (PCOD) and 1,4-polybutadiene (PBD). Notably, SEC analysis of the single-chain nanoparticles both for PCOD and PBD revealed the expected decrease in the hydrodynamic radius (R_h) of the parent polymer, indicating that other anions can also be used as elements in the cross-linking moieties to form these organometallic nanoparticles. Moreover, all of the Rh-SCNPs displayed intrinsic semi-conductivities in the range of similar undoped organic conjugated polymers, expanding the possible uses of this methodology for many applications.