A series of tridentate NˆNˆN iron(II) and cobalt(II) dichloride complexes bearing 2-(1H-2-benzimidazolyl)-6-(1-(arylimino)ethyl)pyridines were synthesized and characterized by elemental and spectroscopic analyses. Single-crystal X-ray diffraction studies of representative examples of the cobalt and iron complexes confirm distorted bipyramidal geometry around the metal center. Upon coordination of a methanol solvent molecule, a geometry change to distorted octahedral was observed. The steric and electronic effects on catalytic activity are evaluated for different substituents in the arylimino part of the ligand: Me, Et, i Pr, Cl, and Br in ortho-and Me and H in para-position. On treatment with methylaluminoxane (MAO) or modified MAO (MMAO), the iron(II) complexes exhibited good activities of up to 10 6 g • mol -1 (Fe) • h -1 for ethylene oligomerization and moderate activities for polymerization, while cobalt(II) complexes showed moderate activities for ethylene dimerization. The best activities were observed with iron complexes with bulky i Pr groups in the aryl moiety. In comparison to the analogues containing the 2-(1-alkyl-2-benzimidazolyl)-6-(1-(arylimino)ethyl)pyridines, the iron complexes bearing 2-(1H-2-benzimidazolyl)-6-(1-(arylimino)ethyl)pyridines showed the best activity toward ethylene reactivity.

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2-(2-Benzoxazolyl)-6-(1-(arylimino)-ethyl)pyridines (L) were designed as ligands, and their nickel complexes LNiX2 (X = Cl, 1a−7a; X = Br, 1b−7b) were formed. All ligands were fully characterized by NMR, FT-IR spectra, and elemental analyses, while the nickel complexes were examined by FT-IR spectra and elemental analyses. The molecular structures of nickel complexes were established by single-crystal X-ray diffraction. Complex 6a possesses coordination number 6 by coordination of one ligand, two moles of methanol, and one chloride anion, whereas complexes 1b and 5b possess coordination number 5 with distinct distortions, for 1b toward trigonal-bipyramidal geometry and for 5b toward square-pyramidal geometry. The nickel complex 1a was evaluated in the catalytic oligomerization of ethylene with different alkylaluminums as cocatalysts, and diethylaluminum chloride (Et2AlCl) proved to be the most effective. Upon activation with Et2AlCl, all nickel complexes showed outstanding thermal stability and good catalytic activity toward ethylene dimerization with high selectivity for α-C4.

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A series of iron(II) dichloride complexes (Fe 1 –Fe 7 ) ligated by 2-(2-benzoxazolyl)-6-[1-(arylimino)ethyl]pyridines was synthesized and characterized [aryl = 2,6-R12C6H3; R1 = Me ( 1 ), Et ( 2 ), iPr ( 3 ), Cl ( 4 ), Br ( 5 ); 2,6-Me2C6H2-4-R2, R2 = Me ( 6 ), Br ( 7 )]. The molecular structures of Fe 1 , Fe 3 , and Fe 5 were determined by the single-crystal X-ray diffraction. Complexes Fe 1 and Fe 3 both display distorted trigonal-bipyramidal geometries, whereas complex Fe 5 is a distorted square pyramid. Upon activation with modified methylaluminoxane, all iron complexes showed moderate to good activities [up to ca. 106 g(product)?×?(mol Fe)–1 h–1?bar–1] for the oligomerization and polymerization of ethylene, with high selectivity for vinyl-terminated oligomers or polyethylene waxes

A series of 2-(imidazole-2-yl)phenol ligands L1-L6 with the general composition 4-R(4)-5-R(3)-6-R(2)-2-(4,5-R(1),R(1)-1H-imidazole-2-yl)phenol (L1: R(1) = C(2)H(5), R(2) = R(3) = R(4) = H; L2: R(1) = C(6)H(5), R(2) = R(3) = R(4) = H; L3: R(1) = C(6)H(5), R(3) = OCH(3), R(2) = R(4) = H; L4: R(1) = C(6)H(5), R(4) = OCH(3), R(2) = R(3) = H; L5: R(1) = C(6)H(5), R(3) = H, R(2) = R(4) = CH(3); L6: R(1) = C(6)H(5), R(3) = H, R(2) = R(4) = t-Bu) and L7 (2,4-di-tert-butyl-6-(1H-phenanthro[9,10-d]imidazol-2-yl)phenol) and their neutral Zn(II) complexes (Z1-Z7) were synthesized and characterized by spectroscopic and elemental analyses. Molecular structures of L1, L5, Z1, and Z2 were confirmed by single-crystal X-ray diffraction. L1 crystallized in the monoclinic Cc space group, while L5, Z1, and Z2 all crystallized in the triclinic P1 space group. One-dimensional arrays based on continuous pi-pi stacking interactions and hydrogen bonding were observed for L1 and Z1, while L5 existed as discrete dimeric stack units. Z2 formed hydrogen-bonded 1D network structures but was completely devoid of pi-pi stacking interactions. Emission processes were found to be more dependent on the substituents on phenol as well as condensed media. In contrast to general conclusions on closely related systems in the literature, significant photorelaxation from the excited enol state was observed in the cases of L1 in methanol and L4 in both THF and methanol. Therefore, there exists a certain unusual hindering factor to keto-enol phototautomerism in the ligand-solvent systems. The sensing property of zinc(II) complexes was explored regarding the effects of substituents in their ligands. It was observed that coordination to the zinc(II) ion led to emission quenching for L1 and L2 while causing an enhancement of fluorescent intensity for L3, L4, L5, and L6. A linear relationship was observed between the emission intensity and the concentration of the zinc ion at the 10(-8) M level. Compared to other zinc compounds in this work, fluorescence enhancement in Z3 and Z4 showed that the methoxyl substituent is favorable for fluorescent enhancement.

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