Charge‐Neutral and Cationic Complexes of Large Alkaline Earths for Ring‐Opening Polymerization and Fine Chemicals Catalysis

Carpentier, Jean‐François; Liao, Bo; Sarazin, Yann

doi:10.1002/9781118742952.ch28

Cited by 8 publications

(1 citation statement)

References 73 publications

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“…Catalyst systems explored for lactide polymerization have been based almost exclusively on d 0 metals (groups 1–4 and lanthanides, in particular Mg, Y, and Zr) and d 10 metals (group 12 and main group, in particular Zn, Al, and Sn). ,− , In contrast to α-olefins, d n transition metals have not been used extensively in lactide polymerization. Of these, iron-based catalysts have received the most attention, including some highly active catalysts and, more recently, switchable catalysts .…”

Section: Introductionmentioning

confidence: 99%

Mechanism and Stereocontrol in Isotactic rac-Lactide Polymerization with Copper(II) Complexes

2017

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Reaction of N-R,N′-R′-2,5-diiminopyrroles (R = R′ = S-CH(Me)Ph; R = R′ = CH 2 Ph; R = S-CH(Me)Ph, R′ = H) with Cu(OMe) 2 in the presence of chelating alcohols, ROH (R1 = C 2 H 4 NMe 2 , R2 = C 2 H 4 Py, R3 = CH 2 Py, R4 = CMe 2 Py) yielded the dinuclear, alkoxide-bridged complexes L 2 Cu 2 (OR) 2 . The complexes catalyze the polymerization of rac-lactide at room temperature with catalyst concentrations of 1−3 mM in 4−24 h (v = k[cat][monomer] with k = [2.3(5)] × 10 2 − [6.5( 6)] × 10 2 M −1 h −1 ). EPR and mechanistic studies indicate that the complexes remain dinuclear during the polymerization reaction. In complexes with OR1, both alkoxides of the dimer initiate polymerization, with OR2 or OR3 only one alkoxide initiates polymerization, and OR4 is inactive in polymerization. The nature of the bridging ligand in the dinuclear complex determines stereocontrol. Independent of the spectator ligand L, complexes which retain an OR3 or OR4 bridging ligand in the active species show preference for isotactic polymerizations (P m = 0.60−0.75), while those with only polymeryloxo bridges or OR2 as the bridging ligand provide atactic polymer. Stereocontrol follows a chain-end control mechanism, with the catalytic site likely adapting to the configuration of the chain end.

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Section: Introductionmentioning

confidence: 99%

Mechanism and Stereocontrol in Isotactic rac-Lactide Polymerization with Copper(II) Complexes

2017

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Isotactic rac‐Lactide Polymerization with Copper Complexes: The Influence of Complex Nuclearity

2015

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Diiminopyrrolide copper alkoxide complexes, LCuOR (OR 1 = N,N-dimethylamino ethoxide,O R 2 = 2-pyridyl methoxide), are active for the polymerization of rac-lactide at ambient temperature in benzene to yield polymers with M w / M n = 1.0-1.2. X-ray diffraction studies showed bridged dinuclear complexes in the solid state for both complexes.W hile LCuOR 1 provided only atactic polylactide,LCuOR 2 produced partially isotactic polylactide (P m = 0.7). The difference in stereocontrol is attributed to ad inuclear active species for LCuOR 2 in contrast to am ononuclear species for LCuORThe biocompatibility of polyesters and their potential biodegradability in the human body or the environment has generated interest in the controlled polymerization of lactone monomers.I np articular,t he polymerization of lactide to polylactic acid (PLA) has been widely studied (Scheme 1) because PLA is marketed as ab iodegradable packaging material and lactide/glycolide copolymers find medical applications as biodegradable sutures,bone grafts,ordrug delivery carriers. [1][2][3][4][5] Although alarge variety of metal complexes have been investigated for rac-lactide polymerization, [6][7][8][9][10][11][12][13][14][15][16][17] the factors determining stereochemistry in the coordinationinsertion polymerization of rac-lactide often remain unclear.It is well established that chain-end control by the growing polymer chain typically leads to ap reference for alternating RR,SS-insertion, which can lead to highly stereoregular heterotactic PLA given sufficient bulk of the spectator ligands.[18]Isoselective polymerization is rare outside group 13 metal catalysts and mechanisms of stereocontrol are often poorly understood. In salan aluminum complexes, for example,Gibson et al. reported in 2004 adrastic change in stereocontrol from highly isotactic (P m = 0.70) to highly heterotactic (P m = 0.04) upon simple exchange of phenyl for 2,4-dichlorophenyl substituents.[19] Only recently,K ol et al. showed that the polymerization is autoinhibiting for dichlorophenyl substituents and requires chain transfer to ac atalyst centre of opposite chirality to continue. [20] In another example,W illiams et al. reported al ikewise dramatic change of stereocontrol from highly isotactic (P m = 0.75) in lutetium phosphasalen complexes to heterotactic (P m = 0.28) in the analogous lanthanum complex and attributed this to increased ligand flexibility. [21] We have recently reported the first highly active copperbased catalysts for the polymerization of rac-lactide, [22][23][24] which was shortly followed by similar work from others. [25][26][27][28][29] Thec atalytic performance of 1 (Scheme 1) in particular was outstanding:very high activity,noevidence for side reactions or chain termination even in the absence of monomer,a nd narrow polydispersities even under immortal polymerization conditions.The main drawbacks of 1 were the unfavourable Schlenk equilibrium (Scheme 1), which limited catalyst optimization, and the lack of stereocontrol. [23] In an attempt to...

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Isotactic rac‐Lactide Polymerization with Copper Complexes: The Influence of Complex Nuclearity

2015

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Diiminopyrrolide copper alkoxide complexes, LCuOR (OR(1)=N,N-dimethylamino ethoxide, OR(2)=2-pyridyl methoxide), are active for the polymerization of rac-lactide at ambient temperature in benzene to yield polymers with M(w)/M(n)=1.0-1.2. X-ray diffraction studies showed bridged dinuclear complexes in the solid state for both complexes. While LCuOR(1) provided only atactic polylactide, LCuOR(2) produced partially isotactic polylactide (P(m)=0.7). The difference in stereocontrol is attributed to a dinuclear active species for LCuOR(2) in contrast to a mononuclear species for LCuOR(1).

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Charge‐Neutral and Cationic Complexes of Large Alkaline Earths for Ring‐Opening Polymerization and Fine Chemicals Catalysis

Cited by 8 publications

References 73 publications

Mechanism and Stereocontrol in Isotactic rac-Lactide Polymerization with Copper(II) Complexes

Mechanism and Stereocontrol in Isotactic rac-Lactide Polymerization with Copper(II) Complexes

Isotactic rac‐Lactide Polymerization with Copper Complexes: The Influence of Complex Nuclearity

Isotactic rac‐Lactide Polymerization with Copper Complexes: The Influence of Complex Nuclearity

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