Nickel(ii)dibenzotetramethyltetraaza[14]annulene complex immobilized on amino-functionalized TUD-1: an efficient catalyst for immediate and quantitative epoxidation of cyclohexene under ambient conditions

Abstract

A nickel(II)dibenzotetramethyltetraaza[14]annulene complex (Nitmtaa) is prepared and immobilized on amino-functionalized TUD-1 (N-TUD-1) via a Ni–N (NH₂) bond to obtain a stable and reusable new nanocatalyst named as Nitmtaa@N-TUD-1. The catalytic activity performance of this new nanocatalyst was evaluated in the epoxidation of cyclohexene under ambient conditions (25 °C, 1 atm) using meta-chloroperoxybenzoic acid (m-CPBA) as the oxidant, and CH₂Cl₂/CH₃CN (1 : 1 v/v) as the solvent. (3-Aminopropyl)triethoxysilane (APTES) was first grafted on the TUD-1 surface, then Nitmtaa was added and coordinated with amine groups on the TUD-1 surface to produce the nanocatalyst Nitmtaa@N-TUD-1. The structure and morphology of the obtained nanocatalyst were studied using SEM, HR-TEM, BET analysis, FTIR spectroscopy, and powder XRD analysis. The thermal stability was investigated using TGA and DTA. HR-TEM and XRD results revealed a high dispersion of Nitmtaa on the TUD-1 surface. The obtained nanocatalyst exhibited an immediate and quantitative epoxidation reaction of cyclohexene to cyclohexene oxide under ambient conditions with a high turnover frequency (TOF) of ∼42.11 s⁻¹. Moreover, the catalyst Nitmtaa@N-TUD-1 maintained the high catalytic activity performance and exhibited high stability in four successive cycles. The atomic absorption spectroscopy (AAS) experiments performed on the filtrate after each cycle showed a negligible leaching of Nitmtaa from the support N-TUD-1. A plausible reaction mechanism pathway is also proposed.