Phenoxybis(imine) complexes of vanadium: structure, ethylene polymerization, and ring opening polymerization of ε-caprolactone

A number of phenoxybis(imine) compounds (<i>p</i>-RL^<i>n</i>H) (R = Me, <i>t</i>-Bu) derived from 2,6-diformyl-4-methylphenol or 2,6-diformyl-4-<i>t</i>-butylphenol and substituted anilines bearing 2,6-dimethyl (<i>p</i>-RL1H), 2,6-diisopropyl (<i>p</i>-RL2H), 2-<i>tert</i>-butyl (<i>p</i>-RL3H), 2-iodo (<i>p</i>-RL4H), 2,3,4,5,6-pentafluoro (<i>p</i>-RL5H), 2-trifluoromethyl (<i>p</i>-RL6H) and 2-iodo,4-fluoro (<i>p</i>-RL7H) substituents were prepared and subsequently reacted with [VO(OR')₃] (R' = Et, i-Pr) in the presence of Me₃Al. The molecular structures of the bis(chelate) vanadyl products [VO(L^<i>n</i>)₂] 1 (<i>n</i> = 1, R = Me), 3 (<i>n</i> = 2, R = Me), 11 (<i>n</i> = 6, R = Me), two solvatomorphs of 12 (<i>n</i> = 6, R = <i>t</i>-Bu) and 14 (<i>n</i> = 7, R = <i>t</i>-Bu) in which the metal adopts a square pyramidal geometry, have been determined. Molecular structures are also reported for the bis(imino)phenol compounds <i>p</i>-MeL3H and <i>p</i>-MeL5H. The complexes 1-14 (<i>n</i> = 1 to 7) have been screened for their ability to act as catalysts for the ring opening polymerization (ROP) of ε-caprolactone. ROP results revealed that the systems could achieve high conversions, particularly under air, at 130 °C in toluene or as melts. Kinetics studies indicate complexes 6 and 12 are the most efficient catalysts, whilst the products formed are cyclic (minor) and linear polymers (major) as identified by MALDI-ToF mass spectra. Complexes 1 and 2 have been screened as pre-catalysts for the polymerization of ethylene in the presence of EADC (ethylaluminium dichloride) and ETA (ethyl trichloroacetate) at various temperatures and for the co-polymerization of ethylene with propylene. In the case of ethylene polymerization, the thermal stability was improved compared with tetra-dentate quinolin-8-ylimino vanadyl complexes previously evaluated. In ethylene/propylene copolymerization, complexes 1 and 2 produced 'ethylene/propylene copolymer' with a higher propylene content than the tetra-dentate quinolin-8-ylimino vanadyl complexes.