Synthesis and characterization of cobalt(II) and cobalt(III) complexes of substituted dibenzotetraaza[14]annulenes

Instant and quantitative epoxidation of styrene under ambient conditions over a nickel(ii)dibenzotetramethyltetraaza[14]annulene complex immobilized on amino-functionalized SBA-15

Nickel(ii)dibenzotetramethyltetraaza[14]annulene complex (Nitmtaa) was synthetized and immobilized on post amino-functionalized SBA-15 (N-SBA-15) to obtain a stable and reusable nanocatalyst named as Nitmtaa@N-SBA-15. Here (3-aminopropyl)triethoxysilane (APTES) was first grafted on the surface SBA-15, then Nitmtaa was added and coordinated on the silica surface via APTES amine groups. The structure and morphology, and thermal stability of the prepared nanocatalyst was investigated using SEM, HR-TEM, BET, FT-IR, powder XRD, and TGA. HR-TEM and XRD results revealed a high dispersion of Nitmtaa on the SBA-15 surface. The catalytic activity of this nanocatalyst was evaluated in the epoxidation of styrene, under ambient conditions, using meta-chloroperoxybenzoic acid (m-CPBA) as the oxygen donor. This nanocatalyst showed an immediate and quantitative epoxidation of styrene with high turn-over-frequency ∼31.58 s⁻¹. Moreover, the superior catalytic activity and high stability of Nitmtaa@N-SBA-15 could be maintained after four successive cycles. A possible reaction mechanism is also proposed.

Immediate and quantitative epoxidation of styrene under ambient conditions catalyzed by new nanocatalyst obtained by immobilizing nickel(ii)dibenzotetramethyltetraaza[14]annulene in amino-functionalized SBA-15.

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

Nickel(ii)dibenzotetramethyltetraaza[14]annulene complex immobilized on amino-functionalized TUD-1 as a new nanocatalyst for spontaneous and quantitative epoxidation of cyclohexene under ambient conditions.

Diastereoselective Radical-Type Cyclopropanation of Electron-Deficient Alkenes Mediated by the Highly Active Cobalt(II) Tetramethyltetraaza[14]annulene Catalyst

A new protocol for the catalytic synthesis of cyclopropanes using electron‐deficient alkenes is presented, which is catalysed by a series of affordable, easy to synthesise and highly active substituted cobalt(II) tetraaza[14]annulenes. These catalysts are compatible with the use of sodium tosylhydrazone salts as precursors to diazo compounds in one‐pot catalytic transformations to afford the desired cyclopropanes in almost quantitative yields. The reaction takes advantage of the metalloradical character of the Co complexes to activate the diazo compounds. The reaction is practical and fast, and proceeds from readily available starting materials. It does not require the slow addition of diazo reagents or tosylhydrazone salts or heating and tolerates many solvents, which include protic ones such as MeOH. The Co^II complexes derived from the tetramethyltetraaza[14]annulene ligand are easier to prepare than cobalt(II) porphyrins and present a similar catalytic carbene radical reactivity but are more active. The reaction proceeds at 20 °C in a matter of minutes and even at −78 °C in a few hours. The catalytic system is robust and can operate with either the alkene or the diazo reagent as the limiting reagent, which inhibits the dimerisation of diazo compounds totally. The protocol has been applied to synthesise a variety of substituted cyclopropanes. High yields and selectivities were achieved for various substrates with an intrinsic preference for trans cyclopropanes.