Iron‐based catalysts bearing bis(imido)–pyridine ligands for the polymerization of tert‐butyl acrylate

Iron(II) dichloride complexes bearing a tridentate nitrogen donor ligand were investigated for the homopolymerization of tert‐butyl acrylate after activation with methylaluminoxane. Two new complexes were synthesized, 2,6‐bis[1‐(cyclohexylimido)ethyl]pyridine iron chloride (FeCl₂) and 2,6‐bis[1‐(isopropylimido)ethyl]pyridine FeCl₂, and the single‐crystal X‐ray structure of the latter one was determined. Turnover frequencies of the catalysts during polymerization ranged from 36 to 241 cycles/mol/h. The obtained polymers exhibited weight‐average molecular weights ranging from 24,000 to 438,500 g/mol, and the molar mass distribution varied between 1.8 and 4.3. Activity of the catalytic system and the molar mass of the polymer are influenced by the ligand structure of the complexes as well as other polymerization conditions such as monomer concentration and temperature. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1380–1389, 2003     

Nitro‐substituted iron(II) tridentate bis(imino)pyridine complexes as high‐temperature catalysts for the production of α‐olefins

A new series of nitro‐substituted bis(imino)pyridine ligands {2,6‐bis[1‐(2‐methyl‐4‐nitrophenylimino)ethyl]pyridine, 2,6‐bis[1‐(4‐nitrophenylimino)ethyl]pyridine, (1‐{6‐[1‐(4‐nitro‐phenylimino)‐ethyl]‐pyridin‐2‐yl}‐ethylidene)‐(2,4,6‐trimethyl‐phenyl)‐amine, and 2,6‐bis[1‐(2‐methyl‐3‐nitrophenylimino)ethyl]pyridine} and their corresponding Fe(II) complexes [{p‐NO₂? o‐Me? Ph? N?C(Me)? Py? C(Me)?N? Ph? o‐ Me? p‐NO₂}FeCl₂ ( 10 ), L₂FeCl₂ ( 11 ), {m‐NO₂? o‐Me? Ph? N?C(Me)? Py? C(Me)?N? Ph? o‐Me? m‐NO₂}FeCl₂ ( 12 ), and {p‐NO₂? Ph? N?C(Me)? Py? C(Me)?N? Mes}FeCl₂ ( 14 )] were synthesized. According to X‐ray analysis, there were shortenings of the axial Fe? N bond lengths (up to 0.014 Å) in para‐nitro‐substituted complex 10 and (up to 0.015 Å) in meta‐nitro‐substituted complex 12 versus the Fe(II) complex without nitro groups [{o‐Me? Ph? N?C(Me)? Py? C(Me)?N? Ph? o‐Me}FeCl₂ ( 1 )]. Complexes 10 , 12 , and 14 afforded very active catalysts for the production of α‐olefins and were more temperature‐stable and had longer lifetimes than parent non‐nitro‐substituted Fe(II) complex 1 . The reaction between FeCl₂ and a sterically less hindered ligand [p‐NO₂? Ph? N?C(Me)? Py? C(Me)?N? Ph? p‐NO₂] resulted in the formation of octahedral complex 11 . A para‐dialkylamino‐substituted bis(imino)pyridine ligand [p‐NEt₂? o‐Me? Ph? N?C(Me)? Py? C(Me)?N? Ph? o‐Me? p‐NEt₂] and the corresponding Fe(II) complex [{p‐NEt₂? o‐Me? Ph? N?C(Me)? Py? C(Me)?N? Ph? o‐Me? p‐NEt₂}FeCl₂ ( 16 )] were synthesized to evaluate the effect of enhanced electron donation of the ligand on the catalytic performance. According to X‐ray analysis, there was a shortening (up to 0.043 Å) of the axial Fe? N bond lengths in para‐diethylamino‐substituted complex 16 in comparison with parent Fe(II) complex 1 . © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2615–2635, 2006     

High‐temperature catalysts for the production of α‐olefins based on iron(II) and iron(III) tridentate bis(imino)pyridine complexes modified by nitrilo group

Series of Fe(II) and Fe(III) tridentate bis(imino)pyridine complexes without nitrilo groups 2–6 and with nitrilo groups 7–13 were synthesized. According to X‐ray analysis, the introduction of nitrilo groups in para‐ and ortho‐positions tends to result in shorter axial Fe? N bonds. Both types of complexes, 2–6 and 9–13 , afforded very productive catalysts for the production of α‐olefins with higher K values and better linearity of Schultz–Flory distribution α‐olefins than the parent methyl substituted Fe(II) complex 1 . Noticeably, the complexes functionalized with a para‐nitrilo group 9–13 tend to make α‐olefins with higher K values of the Schultz–Flory distribution, more ideal distributions, and less of the heavier insoluble fractions of α‐olefins than corresponding nonsymmetrically substituted complexes without para‐nitrilo groups 2–6 . Statistically significant correlations were obtained between % solids of total α‐olefins and the blocked solid angle fraction in the +z hemisphere ( = 51.3%, p = 0.012) and between catalyst productivity and total blocked solid angle fraction ( = 43.5%, p = 0.023). The modest values of show that, while steric effects are significant, they are not the sole factor determining catalyst performance. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 585–611, 2008     

Mechanochemical Synthesis of 3d Transition‐Metal–1,2,4‐Triazole Complexes as Precursors for Microwave‐Assisted and Thermal Conversion to Coordination Polymers with a High Influence on the Dielectric Properties

The complexes [MCl₂(TzH)₄] (M=Mn ( 1 ), Fe ( 2 ); TzH=1,2,4‐1H‐triazole) and [ZnCl₂(TzH)₂] ( 3 ) have been obtained by mechanochemical reactions of the corresponding divalent metal chloride and 1,2,4‐1H‐triazole. They were successfully used as precursors for the formation of coordination polymers either by a microwave‐assisted reaction or by thermal conversion. For manganese, the conversion directly yielded [MnCl₂TzH] ( 4 ), whereas for the iron‐containing precursor, [FeCl₂TzH] ( 6 ), was formed via the intermediate coordination polymer [FeCl(TzH)₂]Cl ( 5 ). For cobalt, the isotypic polymer [CoCl(TzH)₂]Cl ( 7 ) was obtained, but exclusively by a microwave‐induced reaction directly from CoCl₂. The crystal structures were resolved from single crystals and powders. The dielectric properties were determined and revealed large differences in permittivity between the precursor complexes and the rigid chain‐like coordination polymers. Whereas the monomeric complexes exhibit very different dielectric behaviour, depending on the transition metal, from “low‐k” to “high‐k” with the permittivity ranging from 4.3 to >100 for frequencies of up to 1000 Hz, the coordination polymers and complexes with strong intermolecular interactions are all close to “low‐k” materials with very low dielectric constants up to 50 °C. Therefore, the conversion procedures can be used to deliberately influence the dielectric properties from complex to polymer and for different 3d transition‐metal ions.