Aluminium complexes containing N,N 0 -chelating amino-amide hybrid ligands applicable for preparation of biodegradable polymers Hana Kampov  a a , Emílie Riemlov  a a , Jitka Klikarov  a a , Vladimír Pejchal b , Jan Merna c , Petr Vlas  ak d , Petr  Svec a , Zde  nka R  u  zi  ckov  a a , Ale  sR  u  zi  cka a, * a Department of General and Inorganic Chemistry, Faculty of Chemical Technology, University of Pardubice, Studentsk a 573, CZ-532 10 Pardubice, Czech Republic b Institute of Organic Chemistry and Technology, Faculty of Chemical Technology, University of Pardubice, Studentsk a 573, CZ-532 10 Pardubice, Czech Republic c Department of Polymers, Faculty of Chemical Technology, Institute of Chemical Technology, Technick a 5, CZ-166 28 Prague 6, Czech Republic d SYNPO a.s., S.K. Neumanna 1316, CZ-532 07 Pardubice, Czech Republic article info Article history: Received 26 October 2014 Received in revised form 8 December 2014 Accepted 9 December 2014 Available online 18 December 2014 Keywords: Poly(trimethylene carbonate) Polycaprolactone Lactide esterification Aluminium Amino-amide ligand abstract Five aluminium complexes containing N,N'-chelating ligands ([2-(Me 2 NCH 2 )C 6 H 4 N(R)]  ;R ¼ H, SiMe 3 or benzyl (Bn)) were prepared and structurally characterized by NMR and crystallographic techniques. Aluminium atoms in all compounds are pseudotetrahedrally coordinated with extremely short intra- molecular interaction of the pendant amino group (d(AleN) ¼ 1.96e2.00 Å). The catalytic performance of selected complexes (~0.1e0.2 mol. %), either with or without an external co-initiator, in ring opening (co) polymerization of ε-caprolactone, L-lactide and trimethylene carbonate was tested yielding satisfactory to excellent amount of polymeric material with M n ~ 15e70 kg/mol for ε-caprolactone, and ~30 kg/mol for trimethylene carbonate with good degree of control over the molar mass distribution, initiation ef- ficiency. An excellent conversion of L-lactide to methyl (S,S)-O-lactyllactate is observed upon catalysis by one of the complexes at room temperature. © 2014 Elsevier B.V. All rights reserved. Introduction Magnesium, zinc, aluminium and tin(II) compounds are frequently studied as initiators for ring opening polymerization (ROP) of various cyclic precursors to biodegradable polymers [1]. One of the promising metals from this series is aluminium, where the respective complexes could be obtained by the small molecule (HCl, CH 4 ,H 2 , etc.) or salt (LiCl) elimination reactions. Moreover, aluminium is highly abundant and cheap metal and therefore its applications as initiators of ROP mainly of lactides [2] and ε-cap- rolactone [1c,d] have been accelerated in the past few years. Aluminium amides which reveal a plethora of structural motifs, synthetic and new materials uses, as well as numerous applications in catalysis are the most prominent species [3]. Although the aluminium amides containing bulky amido ligands have trigonal planar geometry [4], there are two other structurally impressive groups of aluminium amides. A plethora of such compounds tend to be monomeric with the coordination number of four and the pseudotetrahedral arrangement with accommodation of one solvent donor to the metal centre [3]. The largest class of aluminium amides can be described either as homo- or heteroleptic dimers with four-membered planar or non-planar Al 2 N 2 or Al 2 X 2 (N means nitrogen ligand, X heteroatom) core [5]. Next to that, some compounds with higher coordination numbers [6], higher aggre- gation degrees [7], aluminium imides [8], heterometallic species [9] and aluminium(I) amides [10] were also reported. Excluding a large class of aluminium b-diketiminates and compounds with similar conjugated ligands, chelated aluminium amides where the five- membered diazametalla ring is formed [8aec,11] are much more populated than those with a six-membered C 3 N 2 Al cycle [12] which is probably caused by the metal size. To the best of our knowledge, the direct use of aluminium am- ides and in particular anilides as catalysts for preparation of biodegradable polymers is only rarely reported up to now [13]. In this paper we report on the synthesis and structure of N,N 0 -chelated aluminium amino-amides and its use in catalytically driven ROP of ε-caprolactone, L-lactide and trimethylene carbonate. * Corresponding author. Fax: þ420 466037068. E-mail address: ales.ruzicka@upce.cz (A. R u zi cka). Contents lists available at ScienceDirect Journal of Organometallic Chemistry journal homepage: www.elsevier.com/locate/jorganchem http://dx.doi.org/10.1016/j.jorganchem.2014.12.010 0022-328X/© 2014 Elsevier B.V. All rights reserved. Journal of Organometallic Chemistry 778 (2015) 35e41