Synthesis and molecular structures of metal complexes (M = Al, Mn, Fe or Co) supported by sterically encumbered salicylaldiminate ligands

Copolymerization of β‐Butyrolactones into Functionalized Polyhydroxyalkanoates Using Aluminum Catalysts: Influence of the Initiator in the Ring‐Opening Polymerization Mechanism

“…The increase of the rate of the reaction in the presence of the metal complex has been previously observed for other nucleophilic organic bases acting as organocatalysts, and has been attributed to the coordination of the metal center to the lactone which increases the reactivity of the carbonyl group and facilitate the ROP reaction. [ 59 ]…”

“…In contrast, the AMM proceeds through the nucleophilic attack of the initiator, DMAP, on the carbonyl group of the monomer BBL, which is activated via its interaction with the aluminum centre. [ 59 ] The growth of the polymer chain occurs through the nucleophilic attack of the anionic growing chain on successive activated monomer molecules prompting the ring opening (Scheme 3).…”

“…[ 72,74 ] Besides, in our catalyst system, this deprotonation will be favored by the interaction of the monomer with the aluminum since it enhances the acidity of the carbonyl group. [ 59 ] Once the crotonate is formed, it will initiate the propagation of the chain via the O‐alkyl cleavage following an AROP mechanism.…”

“…The Al─Cl bond distance in the non-disordered molecule (2.1640(9) Å), is within the range of values reported for half-salen chloro-derivatives (2.104-2.219 Å). [59][60][61][62] Al─O and Al─N bond lengths are also in the classical range while, as observed for compound 1, the Al─O bonds (1.7599 (17) and 1.7636(16) Å) fall within the shortest ones (1.75 to 1.85 Å), and Al─N ones, although shorter than in 1 (1: 2.107(6) to 2.123(6) Å; 2: 2.0457(18) and 2.052(18) Å)), are still among the longest ones reported (1.95 to 2.15 Å range). [63] As pointed out in the molecular structure of 1, this structural peculiarity could result in the lability of the Al─N bonds.…”

“…The increase of the rate of the reaction in the presence of the metal complex has been previously observed for other nucleophilic organic bases acting as organocatalysts, and has been attributed to the coordination of the metal center to the lactone which increases the reactivity of the carbonyl group and facilitate the ROP reaction. [59] The ROP of BBL mediated by catalyst 2 in the presence of BnOH revealed more sluggish, requiring a longer reaction time at 100 °C to reach high monomer consumption and leading to poor conversion at a higher temperature (Table 1, entries 6, 10). Replacing BnOH by DMAP enabled to reach higher conversions (entries 7-9).…”