Cooperative Effects of Aniline with DMSO in RuII Complexes: Tuning the Reactivity for Ring-Opening Metathesis Polymerization

Abstract

The complex cis,fac-[RuCl2(DMSO–O)(DMSO–S)3] [1] reacted with aniline (NH2Ph) under reflux to produce the complex trans,cis,cis-[RuCl2(DMSO–S)2(NH2Ph)2] [2], whereas at room temperature the resulting complex was cis,fac-[RuCl2(DMSO–S)3(NH2Ph)] [3]. The complexes were characterized by FTIR, EPR, 1H and 13C NMR, electronic spectra, and the crystal structure of 2 was determined by single X-ray crystallography. The influence of NH2Ph and DMSO as ancillary ligands in the new complexes was then evaluated for ring-opening metathesis polymerization (ROMP) of norbornene (NBE), norbornadiene (NBD), and dicyclopentadiene (DCPD) in presence of ethyl diazoacetate (EDA) with different [monomer]/[Ru] molar ratios. Homopolymers of NBE with molecular weights in the order of magnitude of 105 g.mol–1 and insoluble polymers in CHCl3 from NBD and DCPD were obtained in different yields depending of the starting complex, reaction time (5 and 30 min), and temperature (25 and 50 °C). Valorous results were obtained for polyNBD, polyDCPD, and copolymerizations from NBE with NBD or DCPD using the new complexes, affording higher yields than with 1. In conclusion, beneficial effects are observed when DMSO and the weak σ-donor NH2Ph ligands are arranged in the same coordination sphere of Ru(II) pre-catalysts for ROMP.