{Phenoxy-imine}aluminum versus -indium Complexes for the Immortal ROP of Lactide: Different Stereocontrol, Different Mechanisms

• DOI: 10.1021/om301155m
• Publication Date: 2013-03-11T19:21:37Z
• Authors: Mickael Normand; Vincent Dorcet; Evgeny Kirillov; Jean-François Car...
• Keywords: Moiety; Lactide; Imine; Reactivity

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