Late transition metal complexes of bulky mono- and bi-nucleaeting ligands : synthesis and catalytic applications

In Chapter One, a background to the application of binucleating ligands in biomimetic chemistry sets the scene for a comprehensive discussion of homogeneous catalysis in the field. Chapter Two describes the strategies employed for the preparation of sterically encumbered multidentate oligopyridylimine ligands. In Chapters Three and Four, the new oligopyidylimine ligands prepared in Chapter Two are treated with divalent metal halides (iron, cobalt, nickel, zinc) and the resultant complexes fully characterised. Specifically, Chapter Three focuses on the reactivity of the potentially pentadentate ligands [bis(imino)terpyridine and imino-quaterpyridine] while Chapter Four concentrates on the resulting coordination chemistry of the potential tetra-, hexa- and hepta-dentate ligands [imino-terpyridine, bis(imino)quaterpyridine and bis(imino)quinquepyridine]. In both chapters, theoretical calculations (DFT) on pre-identified complexes are used in order to investigate the effect of the R substituent (H vs. Me) and metal centre on the coordination chemistry of the ligand. To conclude the synthetic work, the screening for polymerisation or oligomerisation of ethylene is systematically investigated with a selection of the new complexes. In Chapter Five, the synthesis of multidentate ligands featuring sterically encumbered imino-pyridine end-groups linked by phenyl-, thiophene- and phenolate-spacers is studied. The new (pro)ligands are fully characterised and their coordination chemistry with the same series of divalent metal halides is investigated. Furthermore, derivatisation of pre-identified bimetallic complexes is performed. Finally, a selection of the bimetallic compounds is screened as precatalysts for the oligomerisation and/or polymerisation of ethylene

Dimethyl-aluminium complexes bearing naphthyl-substituted pyridine-alkylamides as pro-initiators for the efficient ROP of ε-caprolactone

Three sterically-enhanced 2-imino-6-(1-naphthyl)pyridines, 2-{CMe=N(Ar)}-6-(1-C10H7)C5H3N [Ar = 2,6-i-Pr2C6H3 (L1dipp), 2,4,6-i-Pr3C6H2 (L1tripp), 4-Br-2,6-i-Pr2C6H2 (L1Brdipp)], differing only in the electronic properties of the N-aryl group, have been prepared in high yield by the condensation reaction of 2-{CMe=O}-6-(1-C10H7)C5H3N with the corresponding aniline. Treatment of L1dipp, L1tripp and L1Brdipp with two equivalents of AlMe3 at elevated temperature affords the distorted tetrahedral 2-(amido-prop-2-yl)-6-(1-naphthyl)pyridine aluminum dimethyl complexes, [2-{CMe2N(Ar)}-6-(1-C10H7)C5H3N]AlMe2 [Ar = 2,6-i-Pr2C6H3 (1a), 2,4,6-i-Pr3C6H2 (1b), 4-Br-2,6-i-Pr2C6H2 (1c)], in good yield. The X-ray structures of 1a–1c reveal that complexation has resulted in concomitant C–C bond formation via methyl migration from aluminum to the corresponding imino carbon in L1aryl; in solution, the restricted rotation of the pendant naphthyl group in 1 confers inequivalent methyl ligand environments. The ring opening polymerization of ε-caprolactone employing 1, in the presence of benzyl alcohol, proceeded efficiently at 30 °C producing polymers of narrow molecular weight distribution with the catalytic activities dependent on the nature of the substituent located at the 4-position of the N-aryl group with the most electron donating i-Pr derivative exhibiting the highest activity (1b > 1a > 1c); at 50 °C 1b mediates 100% conversion of the monomer to polycaprolactone (poly(CL)) in one hour. In addition to 1a, 1b and 1c, the single crystal X-ray structures are reported for L1dipp and L1tripp

Dimethyl-Aluminium Complexes Bearing Naphthyl-Substituted Pyridine-Alkylamides as Pro-Initiators for the Efficient ROP of epsilon-Caprolactone

Three sterically-enhanced 2-imino-6-(1-naphthyl)pyridines, 2-{CMe=N(Ar)}-6-(1-C10H7)C5H3N [Ar = 2,6-i-Pr2C6H3 (L1dipp), 2,4,6-i-Pr3C6H2 (L1tripp), 4-Br-2,6-i-Pr2C6H2 (L1Brdipp)], differing only in the electronic properties of the N-aryl group, have been prepared in high yield by the condensation reaction of 2-{CMe=O}-6-(1-C10H7)C5H3N with the corresponding aniline. Treatment of L1dipp, L1tripp and L1Brdipp with two equivalents of AlMe3 at elevated temperature affords the distorted tetrahedral 2-(amido-prop-2-yl)-6-(1-naphthyl)pyridine aluminum dimethyl complexes, [2-{CMe2N(Ar)}-6-(1-C10H7)C5H3N]AlMe2 [Ar = 2,6-i-Pr2C6H3 (1a), 2,4,6-i-Pr3C6H2 (1b), 4-Br-2,6-i-Pr2C6H2 (1c)], in good yield. The X-ray structures of 1a–1c reveal that complexation has resulted in concomitant C–C bond formation via methyl migration from aluminum to the corresponding imino carbon in L1aryl; in solution, the restricted rotation of the pendant naphthyl group in 1 confers inequivalent methyl ligand environments. The ring opening polymerization of ε-caprolactone employing 1, in the presence of benzyl alcohol, proceeded efficiently at 30 °C producing polymers of narrow molecular weight distribution with the catalytic activities dependent on the nature of the substituent located at the 4-position of the N-aryl group with the most electron donating i-Pr derivative exhibiting the highest activity (1b > 1a > 1c); at 50 °C 1b mediates 100% conversion of the monomer to polycaprolactone (poly(CL)) in one hour. In addition to 1a, 1b and 1c, the single crystal X-ray structures are reported for L1dipp and L1tripp