This journal is c The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2013 New J. Chem. Cite this: DOI: 10.1039/c3nj40916c Imino phenoxide complexes of group 4 metals: synthesis, structural characterization and polymerization studies† Tanmoy Kumar Saha, Mrinmay Mandal, Debashis Chakraborty* and Venkatachalam Ramkumar A complete library of new alkoxides containing group 4 metals and the imino phenol ligand were synthesized in high yields and purity. These compounds showed catalytic activity towards the polymerization of L-lactide (L-LA), rac-lactide (rac-LA), e-caprolactone (CL), d-valerolactone (VL), rac-b- butyrolactone (rac-BL), ethylene and propylene. The zirconium catalysts were found to yield better polymerization results in comparison to the titanium and hafnium analogues. The number average molecular weight (M n ) values of the polymers are very high for LA and CL with controlled molecular weight distributions (MWDs). Analyses of MALDI-TOF and 1 H NMR spectra of low M n oligomers reveal that the ligand initiates the ring-opening polymerization (ROP). For ethylene and propylene polymerization, we have achieved moderate to good activity using MAO as a co-catalyst. 1 Introduction In the modern era, there has been a continuous decrease in research based on commodity polymers owing to the rapid consumption of non-renewable petroleum resources. Non-biodegradability of these polymers is also an important issue that has posed a key threat to the ultimate fate of such polymers. 1,2 Currently, scientists are more focused on studying biodegradable polymers due to growing environmental awareness of the harmful effects of non-biodegradable materials. 1,3–6 This has initiated an active impetus for extensive research on polymers that can be derived from completely renewable natural resources like corn and sugar beet. 7–10 These polymers are not only biodegradable, but also bioassimilable as their hydrolysis in physiological media furnishes non-toxic side products. 10 At the same time, they are completely environmentally benign. Besides, they have tremendous impact on the biomedical and pharmaceutical industry in vital applications like drug delivery, fabrication of biodegradable sutures, medical implants, ligating clips, bone pins and scaffolds for tissue engineering. 3,11–15 Synthesis of these biodegradable polymers by ROP of cyclic esters and LA is a hot area of current interest 16–19 since it is a very convenient and easy method to synthesize these polymers. Out of the numerous methods available, the coordination-insertion mechanism 20–28 is a popular choice for ROP as it has the ability to produce high molecular weight polymers (M n ) with narrow MWDs. In recent times, we have reported several group 4 metal catalysts containing a bis(imino)phenoxide ligand backbone for the ROP of cyclic esters and lactides (LA) 29,30 as group 4 metal catalysts 31,32 are very efficient and popular for performing such polymerization. We observed excellent activity of these complexes towards the ROP of cyclic esters and LA, but the major drawback was that the observed M n was far higher than the theoretical value. Inspired by these results, we wanted to explore the effect of the imino phenoxide ligand complexes of group 4 metals upon the polymerization of cyclic esters and LA. In 2008, Davidson’s group reported group 4 metal catalysts comprising of a chiral imino phenoxide type ligand that has a benzyl spacer arm. 32c Our goal was to see the electronic effect of the imino phenoxide ligand without any spacer. The invention of high density polyethylene and methyl- aluminoxane (MAO) as a potent activator of sandwich type metallocene complexes showed a new path in the area of olefin polymerization. 33 An important reason for the synthesis of molecular catalysts stems from the provision of opportunities related to the issues concerning polymerization mechanism and stereospecificity. Although single site homogeneous catalysts have gained appreciable attention for olefin polymerization, Department of Chemistry, Indian Institute of Technology Madras, Chennai 600036, Tamilnadu, India. E-mail: dchakraborty@iitm.ac.in; Fax: +91 44 2257 4202; Tel: +91 44 2257 4223 † Electronic supplementary information (ESI) available: Includes NMR spectra and experimental details. CCDC 891894–891896. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c3nj40916c Received (in Victoria, Australia) 11th October 2012, Accepted 8th January 2013 DOI: 10.1039/c3nj40916c www.rsc.org/njc NJC PAPER Downloaded by University of Miami on 03 March 2013 Published on 09 January 2013 on http://pubs.rsc.org | doi:10.1039/C3NJ40916C View Article Online View Journal