Ring-Opening Polymerization of L-Lactide Catalyzed by Potassium-Based Complexes: Mechanistic Studies

Two non-toxic potassium compounds, 1 and 2, with a commercial oximate ligand have been prepared and fully spectroscopically characterized. Their activity as catalysts for the ring-opening polymerization (ROP) process of LLA has been studied, showing that they are extremely active and able to polymerize the monomer in a few minutes. For derivative 2, the presence of a crown ether in the potassium coordination sphere affects the nuclearity of the compound and consequently its solubility, with both aspects having an influence in the polymerization process. Detailed studies of the polymerization mechanism have been performed, and an unusual anionic mechanism was observed in absence of a co-initiator. Indeed, the monomer deprotonation generates a lactide enolate, which initiates the polymerization propagation. On the contrary, when a 1:1 ratio of cat:BnOH is used, a mixture of mechanisms is observed, the anionic mechanism and the activated monomer one, while from a cat:BnOH ratio of 1:2 and over, only the activated monomer mechanism is observed.

Photoactivated silicon–oxygen and silicon–nitrogen heterodehydrocoupling with a commercially available iron compound

A commercially available iron readily engages in catalytic Si–O and Si–N bond formation under visible light irradiation.

Half-sandwich ruthenium(ii) complexes with tethered arene-phosphinite ligands: synthesis, structure and application in catalytic cross dehydrogenative coupling reactions of silanes and alcohols

The preparation of the tethered arene-ruthenium(ii) complexes [RuCl₂{η⁶:κ¹(P)-C₆H₅(CH₂)_nOPR₂}] (R = Ph, n = 1 (9a), 2 (9b), 3 (9c); R = ⁱPr, n = 1 (10a), 2 (10b), 3 (10c)) from the corresponding phosphinite ligands R₂PO(CH₂)_nPh (R = Ph, n = 1 (1a), 2 (1b), 3 (1c); R = ⁱPr, n = 1 (2a), 2 (2b), 3 (2c)) is presented. Thus, in a first step, the treatment at room temperature of tetrahydrofuran solutions of dimers [{RuCl(μ-Cl)(η⁶-arene)}₂] (arene = p-cymene (3), benzene (4)) with 1-2a-c led to the clean formation of the corresponding mononuclear derivatives [RuCl₂(η⁶-p-cymene){R₂PO(CH₂)_nPh}] (5-6a-c) and [RuCl₂(η⁶-benzene){R₂PO(CH₂)_nPh}] (7-8a-c), which were isolated in 66-99% yield. The subsequent heating of 1,2-dichloroethane solutions of these compounds at 120 °C allowed the exchange of the coordinated arene. The substitution process proceeded faster with the benzene derivatives 7-8a-c, from which complexes 9-10a-c were generated in 61-82% yield after 0.5-10 h of heating. The molecular structures of [RuCl₂(η⁶-p-cymene){ⁱPr₂PO(CH₂)₃Ph}] (6c) and [RuCl₂{η⁶:κ¹(P)-C₆H₅(CH₂)_nOPⁱPr₂}] (n = 1 (10a), 2 (10b), 3 (10c)) were unequivocally confirmed by X-ray diffraction methods. In addition, complexes [RuCl₂{η⁶:κ¹(P)-C₆H₅(CH₂)_nOPR₂}] (9-10a-c) proved to be active catalysts for the dehydrogenative coupling of hydrosilanes and alcohols under mild conditions (r.t.). The best results were obtained with [RuCl₂{η⁶:κ¹(P)-C₆H₅(CH₂)₃OPⁱPr₂}] (10c), which reached TOF and TON values up to 117 600 h^-1 and 57 000, respectively.