Iron(II) and Zinc(II) Complexes with Tetradentate Bis(pyrazolyl)methane Ligands as Catalysts for the Ring‐Opening Polymerisation of rac‐Lactide

Abstract

A new subgroup of bis(pyrazolyl)methane ligands has been developed through the synthesis of the first N,N,N,Ntetradentate bis(pyrazolyl)methane compounds, namely, bis-(pyrazolyl)bipyridinylmethane [HC(Pz) 2 Bipy, L1] and bis(3,5methylpyrazolyl)bipyridinylmethane [HC(3,5-MePz) 2 Bipy, L2].From these ligands, a large variety of new mononuclear Fe II and Zn II complexes with counterions ranging from halides to carboxylates and sulfate were synthesised and characterised by [a]

New Kids in Lactide Polymerization: Highly Active and Robust Iron Guanidine Complexes as Superior Catalysts

“…The three hybrid guanidines werer eactedw ith iron(II) chloride, and the molecular structures of the complexes [FeCl 2 (TMGqu)] (1), [FeCl 2 (TMGasme)] (2), and [FeCl 2 (TMG5NMe 2 asme)] 2 (3)w ere determined by single-crystal XRD (Figure 1a nd Ta ble 1). 4 and 5 have been reported to be the fastestk nown robust catalysts with ab iocompatible metal for the polymerization of LA [20] but they werea lso surpassed by 2 and 3.A lthough iron catalyst have often been slower than the equivalent zinc catalysts, [16] our study shows for the first time that by simply changing the metal center in the complex from zinc to iron the polymerization activity is enhanced by af actor of five. [18] All complexes have at etra-coordinated iron center with coordination by the two donors of the hybrid guanidinel igand and two chloride ions.…”

“…[6] The industrially used catalyst for the polymerization of LA is tin(II)octanoate [Sn(Oct) 2 ]w ith alcohol as co-initiator;h owever,w hile the polymer degrades, tin residues accumulate in the environment (e.g.,t hrough industrial composters). [16] Here, we presentt he first robust complexes with a biocompatible metal that are more active in the polymerization of LA than Sn(Oct) 2 . [6a, 8] Ah uge variety of catalysts are already known for the ROP of LA.…”

“…TMG5NMe 2 asme is an enhancement of TMGasme with an electron-donating group in para-position to the guanidine unit. [16] However,w ith ap olymerization rate more than three magnitudesh igher,t his title belongs now to 3.T his high activity takes iron catalysts into the league of the most active catalysts knownf or bulk polymerizations. From the CÀN-bondl engths of the guanidine unit, the degree of delocalization (1)w as calculated ands howedt hat the guanidine units of the three complexesa re completely delocalized.…”

“…1.26 AE 0.07 6 [16] [Fe(TFA) 2 (HC(pz) 2 bpy)]0.13 ChemSusChem 2019ChemSusChem , 12,2161ChemSusChem -2165 www.chemsuschem.org 2019 Wiley-VCH Verlag GmbH &Co. KGaA, Weinheim 5000:1 were applied, and linear data were obtained for all experiments, which shows the high activity of 2 and 3 even at very low catalystc oncentrations. The data obtainedf or Sn(Oct) 2 are in line with literature if the different polymerization temperatures are taken into account.…”

Cyclic Polyester Formation with an [OSSO]‐Type Iron(III) Catalyst

“…[3] The metal-mediated ring-opening polymerization (ROP) of lactides and lactonesi s, nowadays, the most efficient catalytic process for APEs production. Fe complexes activei nt he ROP of cyclic esters are limited, [11][12][13][14][15][16][17][18][19][20][21][22][23] and no examples have been reported that produce cAPEs. [5] Amongo thers, polymers with ac yclic topologya re an intriguing synthetic target because the lack of chain-ends and the high conformational constraintl ead to materialp roperties that are different from their linear analogues.…”