The Role of Alkoxide Initiator, Spin State, and Oxidation State in Ring-Opening Polymerization of ε-Caprolactone Catalyzed by Iron Bis(imino)pyridine Complexes

Abstract

Density functional theory (DFT) is employed to characterize in detail the mechanism for the ring-opening polymerization (ROP) of ε-caprolactone catalyzed by iron alkoxide complexes bearing redox-active bis(imino)pyridine ligands. The combination of iron with the non-innocent bis(imino)pyridine ligand permits comparison of catalytic activity as a function of oxidation state (and overall spin state). The reactivities of aryl oxide versus alkoxide initiators for the ROP of ε-caprolactone are also examined. An experimental test of a computational prediction reveals an Fe(III) bis(imino)pyridine bis-neopentoxide complex to be competent for ROP of ε-caprolactone.

A new family of complexes derived from bis(imino)pyridine‐type ligands: Crystal structures and bio‐molecular interaction studies

“…[ 11,12 ] In this concern, steric and electronic effects again influence the catalytic performance of bis(imino)pyridine [NNN] ligands supported transition metal complexes. [ 13,14 ] However, in literature, bis(imino)pyridine [NNN]‐type ligands are scarce, [ 9,10 ] and in this report, we have successfully synthesized bis(imino)pyridine‐type 2,6‐bis(( E )‐1‐phenyl‐2‐(( E )‐3‐phenylallylidene)hydrazinyl)pyridine ligand. This ligand exhibited a strong π‐acidic character due to the presence of extended conjugation in the ligand frame.…”

“…[ 7,8 ] Bis(imino)pyridine [NNN] ligands are among the most widely used ancillary ligands in the transition metal chemistry and catalysis. [ 9,10 ] The effectiveness of these ligands is due to their redox non‐innocence (acceptability of 1–3 electrons) facilitating redox transformations in main‐group metal centers. [ 11,12 ] In this concern, steric and electronic effects again influence the catalytic performance of bis(imino)pyridine [NNN] ligands supported transition metal complexes.…”

Coordination Ring-Opening Polymerization of Cyclic Esters: A Critical Overview of DFT Modeling and Visualization of the Reaction Mechanisms

“…However, zero toxicity of iron-based catalysts has been a significant cause for the search of Fe-based polymerization catalysts. Recently, Cramer et al studied εCL ROP catalyzed by bis(imino)pyridine Fe complexes 27 [72] with the use of DFT modeling at the M06-L level [84] Def2-TZVP and Def2-SVP basis sets (for Fe and residue atoms, respectively) [100]. It was found that high-spin species are more Lewis acidic than low-spin intermediates.…”

“…Metal complexes studied in DFT modeling of εCL ROP [55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77]. …”

Reversible redox controlled acids for cationic ring-opening polymerization

“…[1][2][3] While living polymerization methodologies in conjunction with carefully chosen and timed monomer additions produce well-defined materials (e.g., block copolymers 2 ), the ability to control chain growth with an external stimulus could lead to many advanced structures and architectures with potentially interesting physical properties. These externally controlled polymerization methodologies rely on changes in chemical reactivity upon application of an external stimulus (chemical, [4][5][6][7][8][9][10][11][12][13][14][15][16][17] electrochemical, [18][19][20] photochemical, [21][22][23][24][25][26][27][28][29][30] thermal, [31][32][33] mechanochemical [34][35][36][37] ), which precisely regulates the incorporation of monomers at a growing polymer chain end. In addition to promoting the synthesis of advanced structures and architectures, 30,45 the spatiotemporal control afforded by these externally controlled polymerizations has enabled the development of new lithographic [38][39][40][41]<...>…”