International audienceOver the past five years, Ga(III) and most notably In(III) precursors have attracted a growing interest for application in ROP catalysis of cyclic esters, primarily lactide, and may now be considered as potentially efficient ROP initiators of cyclic esters/carbonates. Despite their higher cost (vs. Al), Ga and In derivatives exhibit key attractive features including: (i) Ga(III) and In(III) are biocompatible metal centers and (ii) their precursors are typically more stable than organoaluminum species in polar media. The present contribution reviews discrete Ga(III) and In(III) compounds thus far developed as ROP initiators of cyclic esters/carbonates. The very few reports on Ga(III)-mediated ROPs of cyclic ethers are also included. In addition to the ROP performances of such species, the synthesis and structural characterization of these initiators are also provided and thoroughly discussed with, whenever appropriate, the establishment of structure/reactivity relationships and mechanistic pathways

International audienceA series of dialkylaluminum and -indium {ONR}MR′2 complexes (M = Al, R′ = Me; M = In, R′ = Me, CH2SiMe3) stabilized by a phenoxy-imine {ONR}− ligand platform, with variable R-imino substituents and functionalized by a bulky o-SiPh3 in the phenoxy moiety, has been prepared and structurally characterized in solution and in the solid state. {ONR}AlMe2 complexes reacted with alcohols, in particular with alkyl (S)-H-lactate, to generate the corresponding {ONR}Al(OR)2 compounds. On the other hand, the indium complexes {ONR}InR′2 proved largely inert toward alcohols. When they were combined with an alcohol (iPrOH, BnOH), the {ONR}AlMe2 complexes promoted the living (immortal) ring-opening polymerization ((i)ROP) of racemic lactide (rac-LA) with a good control over the molecular weights and various microstructures, dependent on the R-imino substituent. Complexes having benzyl-type imino substituents enabled the achievement of significant isotacticity (Pm up to 0.80), following grossly the bulkiness of the aryl moiety. The analogous {ONR}InR′2 proved similarly active for the (i)ROP of rac-LA in presence of an external alcohol, but the polymerizations were less controlled and none of the complexes induced stereoselectivity, except one (3a,Pm = 0.70). Kinetic studies revealed different rate laws, with an apparent zero-order dependence on monomer for the aluminum system 1m/iPrOH and a first-order dependence on monomer for the analogous indium system 3m/iPrOH. On the basis of the stoichiometric reactivity of model compounds, two different operative ROP mechanisms are suggested, depending on the nature of the metal center: Al-based complexes proceed through coordination-insertion, while In-based complexes are proposed to operate through an activated monomer mechanism