Nanoscale microreactor-encapsulation of 16-membered hexaaza macrocycle nickel(II) complexes: In situ one-pot template synthesis (IOPTS), characterization and catalytic activity

Abstract

Nanoscale microreactor containing “1,3,7,9,11,15-hexaazacyclohexadecane “[Ni([16]aneN 6)] 2+” 2, 1,9-dimethyl- “[Ni((Me) 2[16]aneN 6)] 2+” 3; 1,9-diethyl- “[Ni((Et) 2[16]aneN 6)] 2+” 4; 1,9-dibuthyl- “[Ni((Bu) 2[16]aneN 6)] 2+” 5; and 1,9-dibenzyl-1,3,7,9,11,15-hexaazacyclohexadecane “[Ni((Benzyl) 2[16]aneN 6)] 2+” 6”, were successfully prepared by the in situ one-pot template synthesis (IOPTS) of formaldehyde and 1,3-propylenediamine (pn) with alkyl and benzyl amine within the nanodimensional pores of zeolite-Y. These complexes were entrapped in the supercage of Y-zeolite by a two-step process in the liquid phase: (i) inclusion of a Ni(II) precursor complex, [Ni(pn) 2] 2+-NaY 1-NaY, and (ii) IOPTS of the nickel(II) precursor complex with the formaldehyde and amine. The new materials “[Ni([16]aneN 6)] 2+-NaY 2-NaY, [Ni((Me) 2[16]aneN 6)] 2+-NaY 3-NaY, [Ni((Et) 2[16]aneN 6)] 2+-NaY 4-NaY , [Ni((Bu) 2[16]aneN 6)] 2+-NaY 5-NaY, [Ni((Benzyl) 2[16]aneN 6)] 2+-NaY 6-NaY” were characterized by several techniques: chemical analysis and spectroscopic methods (FT-IR, UV/VIS, XRD, BET, DRS). Analysis of the data indicates that the Ni(II) complexes are encapsulated in the nanodimensional pores of zeolite-Y and exhibit different from those of the free complexes, which can arise from distortions caused by steric effects due to the presence of sodium cations, or from interactions with the zeolite matrix. The host–guest nanoscale hexaaza macrocycle catalyzes the oxidation of cyclohexene with molecular oxygen. Oxidation of cyclohexene with homogeneous catalyst gave 2-cyclohexene-1-one, 2-cyclohexene-2-ol and epoxy cyclohexane whereas, oxidation with heterogeneous catalyst resulted in the formation of 2-cyclohexene-1-one and 2-cyclohexene-1-ol. “[Ni((Benzyl) 2[16]aneN 6)] 2+-NaY shows significantly higher catalytic activity than other catalysts. The effect of temperature, and the amount of 6-NaY used on the catalytic activity and product selectivity were discussed.