Numerous heteroleptic 2,6-di-tert-butyl-4-methylphenolate (BHT) magnesium complexes have been synthesized by treatment of (BHT)MgBu(THF)₂ with various alcohols. Molecular structures of the complexes have been determined by X-ray diffraction. The magnesium coordination number in [(BHT)Mg(μ-OBn)(THF)]₂ (3) and [(BHT)Mg(μ-O-tert-BuC₆H₄)(THF)]₂ (4) is equal to 4. Complexes formed from esters of glycolic and lactic acids, [(BHT)Mg(μ-OCH₂COOEt)(THF)]₂ (5) and [(BHT)Mg(μ-OCH(CH₃)COOCH₂COO^tBu)(THF)]₂ (6) contain chelate fragments with pentacoordinated magnesium. Compounds 3–6 contain THF molecules coordinated to magnesium atoms. Complex {(BHT)Mg[μ-O(CH₂)₃CON(CH₃)₂]}₂ (7) does not demonstrate any tendency to form an adduct with THF. It has been experimentally determined that complexes 3 and 5 are highly active catalysts of lactide polymerization. The activity of 4 is rather low, and complex 7 demonstrates moderate productivity. According to DOSY NMR experiments, compounds 3 and 5 retain their dimeric structures even in THF. The free energies of model dimeric [(DBP)Mg(μ-OMe)(Sub)]₂ and monomeric (DBP)Mg(OMe)(Sub)₂ products on treatment of [(DBP)Mg(μ-OMe)(THF)]₂ with a series of σ-electron donors (Sub) have been estimated by DFT calculations. These results demonstrate that the substitution of THF by Sub in a dimeric molecule is an energetically allowed process, whereas the dissociation of dimers is energetically unfavorable. DFT modeling of ε-CL and (DL)-lactide ROP catalyzed by dimeric and monomeric complexes showed that a cooperative effect of two magnesium atoms occurs within the ROP for binuclear catalytic species. A comparison of the reaction profiles for ROP catalyzed by binuclear and mononuclear species allowed us to conclude that the binuclear mechanism is favorable in early stages of ROP initiated by dimers 3 and 5.

We report here that the heteroleptic BHT-Mg(OR) complex, i.e. [(BHT)Mg(OBn)(THF)]₂ (Mg3), represents an effective and versatile ring-opening polymerisation (ROP) catalyst for several cyclic ethylene phosphate monomers (CEPMs), such as ethylene phosphates with methoxy- (MeOEP, 1), isopropoxy- (ⁱPrOEP, 2), and tert-butoxy- (^tBuOEP, 3) substituents, N,N-diethyl ethylene phosphoramidate (Me₂NEP, 4) as well as ethyl (EtPPn, 5) and tert-butyl (^tBuPPn, 6) ethylene phosphonates. Mg3 retains its catalytic activity over a broad temperature range from −50 to 100 °C and efficiently carries out the fast and controlled polymerisation of CEPMs with sterically unhindered alkoxy groups with less than 1% chain branching even at near-complete conversion. Compared with ROP catalysed by 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), Mg3 performs much better in the polymerisation of CEPMs with bulky groups and of monomers sensitive to strong nucleophiles, such as ^tBuOEP.

The mechanism of the C–N cross-coupling reaction, catalyzed by Pd/NHC, was evaluated at the molecular and nanoscale levels. The first evidence for the involvement of a “cocktail”-type system in the Buchwald–Hartwig reaction is provided.