Organometallic mediated radical polymerization of vinyl acetate using bis(imino)pyridine vanadium trichloride complexes

Abstract

The synthesis and characterization of one novel proligand and six novel vanadium(III) trichloride complexes is described. The controlled radical polymerization activity towards vinyl acetate of these, and eight other bis(imino)pyridine vanadium trichloride complexes previously reported, is investigated. Those complexes possessing variation at the N-aryl para-position with no steric protection offered by ortho-substituents (4 examples) result in poor control over poly(vinyl acetate) polymerization. Control is improved with increasing steric bulk at the ortho-position of the N-aryl substituent (4 examples) although attempts to increase steric bulk past isopropyl were unsuccessful. Synthesizing bis(imino)pyridine vanadium trichloride complexes with substituted imine backbones restores polymerization control when aliphatic substituents are used (4 examples) but ceases to make any drastic improvements on catalyst lifetime. Modification of the polymerization conditions is also investigated, in an attempt to improve the catalyst lifetime. Expansion of the monomer scope to include other vinyl esters, particularly those derived from renewable resources, shows promising results.

Ddpd as Expanded Terpyridine: Dramatic Effects of Symmetry and Electronic Properties in First Row Transition Metal Complexes

“…The magnetic susceptibility of VCl 3 (tpy) (χT = 0.744 cm −1 K mol −1 at 290 K) and mer-VCl 3 (ddpd) (χT = 0.879 cm −1 K mol −1 at 290 K; Figure S4) is less than expected for a (t 2g ) 2 electron configuration ( 3 T 1 ground state) and has been ascribed to the splitting of the 3 T 1 ground state by the ligand field [148]. and these complexes have been employed in radical polymerization catalysis [152]. VCl3(ddpd) crystallised in the monoclinic space group P21/n as a monomeric complex with meridional ddpd coordination (Figure 11a), isostructural to mer-CrCl3(ddpd) [126].…”

“…Yet, structural data of VCl 3 (tpy) and VCl 3 (L) are lacking. A few solid-state structures of VCl 3 (bimpy) (bimpy = 2,6-bis(imino)pyridine) ligands forming five-membered chelate rings) have been reported and these complexes have been employed in radical polymerization catalysis [152]. VCl 3 (ddpd) crystallised in the monoclinic space group P2 1 /n as a monomeric complex with meridional ddpd coordination (Figure 11a), isostructural to mer-CrCl 3 (ddpd) [126].…”

New Phenomena in Organometallic‐Mediated Radical Polymerization (OMRP) and Perspectives for Control of Less Active Monomers

“…The polymerization of other vinyl esters has been reported for 11 (pivalate, benzoate,50 and chloroacetate51) and 19 (propionate, pivalate, benzoate, laureate, and stearate) 11d. 47 While esters of aliphatic acids are well‐controlled like the acetate, the benzoate yields broader distributions with both 11 and 19 .…”

“…Vanadium complexes of type 19 11c,d, 47 have also yielded controlled polymerization of VAc in combination with a radical source (AIBN, reverse ATRP conditions), but only upon warming to 120°, which requires work in sealed ampules and leads to catalyst death after about 6 h, attributed to irreversible radical addition to the non‐innocent diiminopyridine ligand. The best results were obtained with a sterically protected aryl group (Dipp) as the N substituent and alkyl chains as the imine carbon substituents.…”

Understanding the mechanisms of transition metal catalysed redox reactions

“…This reaction has been exploited as an alternative equilibrium for reversibly deactivating propagating radicals under the banner of 'organometallic mediated radical polymerisation' (OMRP -Scheme 4-1). OMRP has been successfully conducted using a variety of transition metals including vanadium, [189][190] chromium, 191 molybdenum 5 and iron. 69,[192][193] The pioneering work of Wayland et al 64 utilised a tetramesitylporphyrinato complex of cobalt as the capping agent and cobalt remains the most popular transition metal for effecting these transformations.…”