Group IV Complexes of Tridentate Salicylaldiminato Ligands and

Group IV Complexes of Tridentate Salicylaldiminato Ligands and Their Catalytic Activity in ROP of ε-CL, rac-LA and Epoxides International Conference and Exhibition on Biopolymers and Bioplastics 12 th August, 2015 San Francisco, USA Dipa Mandal Dept. of Chemistry IIT Madras, India

Introduction Ø Polylactide (PLA) and Polycaprolactone (PCL) are eco-friendly green polymers Ø Renewable resources in their monomers Ø Biodegradable by enzymes or micro organisms Applications Ø Used as absorbable suture materials in surgery Ø In the fields of controlled drug delivery system Ø Used as packaging materials 2

Ring-Opening Polymerization (ROP) for the synthesis of biodegradable polymers 3

Uses of group IV complexes in catalysis Ø Olefin polymerization (non-biodegradable polymers) Ø ROP of cyclic esters and lactides (biodegradable polymers) Coordination behaviour of Ti(IV), Zr(IV) and Hf(IV) complexes 4

Objectives Ø Synthesis of group IV complexes using [NNO]-type donor ligands Ø Characterization of those complexes by single crystal X-ray diffraction, NMR and Mass techniques Ø Utilization of those complexes as catalyst for ROP Ø Mechanistic study by NMR and MALDI techniques Ø Kinetic studies 5

Synthesis of Ti(IV), Zr(IV) and Hf(IV) complexes of [NNO]-type tridentate salicylaldiminato ligands Chakraborty, D. , Mandal, D. , Ramkumar, V. , Subramanian, V. , Sundar, J. V. Polymer, 2015, 56, 157. 6

Single crystal X-ray structures of 1 b and 2 b Monoclinic Space group: P 2(1)/c C−N 4 bond distance =1. 468(4) Å Triclinic Space group: P-1 C−N 3 (imine) bond distance =1. 294(2) Å 7

Single crystal X-ray structures of 1 c and 1 d Monoclinic Space group: P 2(1)/c C−N 2 (imine) bond distance = 1. 298(3) Å Monoclinic Space group: C 2/c C−N 1 bond distance = 1. 467(4) Å 8

Plausible mechanism for the Meerwein-Ponndorf-Verley [MPV]-type reduction product Scheme 2. Plausible route for the hydride transfer. [Carpentier, J. F. et al. Organometallics, 2012, 31, 5511. ] 9

Energy profile using DFT calculations: 6 k. J mol-1 12 k. J mol-1 10. 16 k. J mol-1 [1 b 1, TS[1 b 1], 1 b 2, 1 b 3 when, R= t. Bu and 2 b 1, TS[2 b 1], 2 b 2, 2 b 3 when, R= Cl] 10

ROP of ε-CL and rac-LA under solvent-free conditions Table 1. Results for ROP of ε-CL and rac-LA Entry Catalyst Monomer Yield [%] Time [min] Mna (obs) [kg mol-1] Mnb (theo) [kg mol-1] Mw/Mn (PDI) 1 1 a ε-CL 96 5 25. 22 22. 90 1. 16 2 1 b ε-CL 98 6 26. 62 23. 19 1. 14 3 1 c ε-CL 97 5 30. 55 22. 90 1. 15 4 2 a ε-CL 97 2 31. 17 22. 90 1. 18 5 2 b ε-CL 98 2 30. 27 22. 90 1. 08 6 2 c ε-CL 96 3 33. 86 22. 90 1. 13 7 1 a rac-LA 96 72 29. 02 28. 90 1. 15 0. 83 8 1 b rac-LA 98 74 30. 55 29. 24 1. 12 0. 80 9 1 c rac-LA 97 81 29. 79 28. 90 1. 13 0. 82 10 2 a rac-LA 98 58 30. 85 28. 90 1. 18 0. 83 11 2 b rac-LA 98 62 31. 17 28. 90 1. 09 0. 84 12 2 c rac-LA 96 64 29. 22 28. 90 1. 11 0. 81 Conditions: [M]/[Cat. ] = 200: 1, at 100 o. C for ε-CL and 140 o. C for rac-LA. a. Measured by GPC at 27 °C in THF relative to polystyrene standards. b. M (theo) = [M] /[C] × mol wt (monomer) + mol wt (end group). n o o c. P is the probability for heterotactic enrichment calculated from homonuclear decoupled r 1 H NMR spectrum. Pr c 11

Microstructure Analysis of the PLA obtained from rac-LA using 2 b: Heterotactic-rich PLA [ Pr = 0. 84] 1 H NMR spectrum (500 MHz, in CDCl of the methine region of PLA 3) Homonuclear decoupled 1 H NMR Spectrum of the methine region of PLA [s and i stand for syndiotactic and isotactic dyads] 12

Polymerizations in different [M]/[Cat. ] ratio using 2 b with rac-LA Plots of Mn and Mw/Mn vs. [M]o/[C]o Mn(obs) values with monomer conversion using catalyst 2 b for [M]o/[C]o= 200 Plots of Mn & Mw/Mn vs. rac-LA conversion 13

End-group analysis of the PLA obtained from rac-LA using 2 b at [M]o/[C]o= 20: 1 Fig. a) 1 H NMR spectrum in CDCl 3 Fig. b) MALDI-TOF spectrum 14

Coordination-insertion Mechanism for ROP: 15

ROP of epoxides [rac-CHO, rac-PO and rac-SO] under solvent-free conditions Table 2. Results for ROP of CHO, SO and PO No. Monomer Catalyst Temp. [o. C] Time [h] Yield [%] TOFa Mnb (obs) [kg mol-1] Mw/Mn (PDI) 1 CHO 1 b 90 12 73 60. 8 37. 26 1. 58 2 CHO 2 b 90 12 78 65. 0 44. 19 1. 56 3 PO 1 b 30 14 55 39. 3 37. 05 1. 64 4 PO 2 b 30 14 59 42. 1 39. 90 1. 48 5 SO 1 b 120 18 65 36. 1 49. 55 1. 52 6 SO 2 b 120 18 71 39. 4 50. 12 1. 49 Conditions: [M]/[Cat. ] = 1000: 1. a Turnover frequency = mol of monomer × (mol of cat)-1 h-1. b. Measured by GPC at 27 °C in THF relative to polystyrene standards. 16

Conclusions Ø New group 4 complexes containing [NNO]-type salicylaldiminato ligands have been synthesized and characterized. Ø These complexes acted as active initiators towards the bulk ROP of ε-CL and rac-LA. Ø They are also stereoselective initiators to produce heterotactic-rich PLA for the ROP of rac-LA. Ø All complexes are moderate active catalysts for epoxide polymerizations. 17

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