Well-Defined ENENES Re and Mn Complexes and Their Application in Catalysis: The Role of Potassium tert-Butoxide

Abstract

A new family of air-stable Re and Mn complexes bearing bidentate NNS (ENENES) ligands with the general formula E(CH 2 ) 2 NH(CH) 2 SR (E = −NC 4 H 8 O or −NC 5 H 10 , R = Ph or thiophenyl) is introduced. All Re and Mn complexes were catalysts for the hydrogenation of aldehydes. The Mn catalysts were active at milder conditions. A rhenium−hydride complex, featuring cis Re−H and N− H moieties, was isolated to provide an insight into the mechanism for this reaction. DFT (B3PW91-D3) and experimental data suggest that there are two pathways for this system, with and without the presence of the base (t-BuOK). The pathway that included t-BuOK was lower in energy, providing a greater driving force for the overall reaction.

Synthesis of Polyethyleneimines from the Manganese‐Catalysed Coupling of Ethylene Glycol and Ethylenediamine

“…These data suggest the significance of base in a hydrogen borrowing process for the synthesis of PEI‐1 via formation and hydrogenation of imines; a phenomenon that has been commented upon before [15, 42, 43] . The role of potassium tert butoxide in lowering the barrier for aldehyde hydrogenation through aiding alcohol release from the metal center has also been recently reported [44] . Indeed, performing the reaction at 150 °C with KO t Bu (10 mol %) now almost exclusively forms PEI‐1 (Table 2; Entry 7), albeit with very poor conversion (isolated yield 18 %).…”

“…[15,42,43] The role of potassium tertbutoxide in lowering the barrier for aldehyde hydrogenation through aiding alcohol release from the metal center has also been recently reported. [44] Indeed, performing the reaction at 150 °C with KO t Bu (10 mol %) now almost exclusively forms PEI-1 (Table 2; Entry 7), albeit with very poor conversion (isolated yield 18 %).…”

Synthesis of Polyethyleneimines from the Manganese Catalyzed Coupling of Ethylene Glycol and Ethylenediamine

“…[12,28,29] The role of potassium tertbutoxide in lowering the barrier for aldehyde hydrogenation through aiding alcohol release from the metal center has also been recently reported. [30] Indeed, performing the reaction at 150 °C with KO t Bu (10 mol%) now almost exclusively forms PEI-1 (Table 2; Entry 7), albeit with very poor conversion (isolated yield 18%). Increasing the vessel size from 100 mL to 250 mL or changing the ratio of ethylene glycol : ethylene diamine from 1:1 to 1:4 made little difference to the yield obtained and did not change the observed selectivity significantly (Table 2; Entries 8 and 9, respectively).…”

Manganese Catalysed Synthesis of Polyketones Using Hydrogen Borrowing Approach

“…The role of the base in lowering the barriers for the (de)hydrogenation reactions catalysed by analogous pincer complexes has been reported in the past. 65,66 In pursuit of methods to make (semi)renewable plastics, we envisioned if a polyketone can be made from a diol sourced from the depolymerisation of waste plastic such as PET (polyethylene terephthalate). To achieve this, we carried out a two-step process where PET waste (sourced from a plastic bottle) was hydrogenatively depolymerised in a pressure reactor using the Milstein's ruthenium PNN catalyst (5, 2 mol%, and KO t Bu, 10 mol%) in tAmOH solvent to form 1,4-benzenedimethanol and ethylene glycol in approximately quantitative yields as confirmed by the 1 H NMR spectroscopy.…”