C3‐Symmetric Lanthanide Tris(alkoxide) Complexes Formed by Preferential Complexation and Their Stereoselective Polymerization of rac‐Lactide

Arnold, Polly L.; Buffet, Jean-Charles; Blaudeck, Robert P.; Sujecki, S.; Blake, Alexander J.; Wilson, Claire

doi:10.1002/anie.200801279

Cited by 154 publications

(68 citation statements)

References 36 publications

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“…Although the latter could indicate the presence of stronger Ga-C 6-Mes bond in solution [25], it rather reflects the stronger donor properties of 6-Mes vs SIMes/IMes in the light of both the structure of 1, as well as the weaker Ga-C 6-Mes evidenced by the X-ray analysis of Me 2 Ga(OCPh 2 Me)(6-Mes) (3) (see below). While the carbene carbon signal in 13 C NMR could not be observed for Me 2 GaOMe(6-Mes), which was synthesized analogously to 1, the 1 H NMR was in line with the presence of the equilibrium presented in Scheme 1 (see the Supplementary Materials), and therefore, similarly to 1, indicated weaker Ga-C 6-Mes bond in comparison with Ga-C NHC of Me 2 GaOMe(NHC) (NHC = SIMes, IMes).…”

Section: Reactivity Of [Me2m(μ-or)]n (M= Ga In ; or = Och2ch2ome Ommentioning

confidence: 99%

“…The analysis of the strength of In-C6-Mes bond of 2 in solution, in comparison with In-CNHC bonds of already characterized Me3In(NHC) adducts [3,21,23], was in sharp contrast with the solid state result. In solution, the shift between free and coordinated NHCs in 13 Although the reaction of 6-Mes with [Me 2 In(µ-OMe)] 3 led to the formation of Me 2 InOMe(6-Mes) complex (see the Supplementary Materials), which was more stable in comparison with Me 2 In(OCH 2 CH 2 OMe)(6-Mes), it seemed to disproportionate more readily in comparison with Me 2 InOMe(NHC) (NHC = SIMes, IMes), and as result could not be isolated in contrast to the latter [3]. While we could not estimate the strength of In-C 6-Mes in the case of Me 2 InOR(6-Mes), due to the tendency of the latter to disproportionate , it could be analyzed for the Me 3 In(6-Mes) (2).…”

Section: Reactivity Of [Me2m(μ-or)]n (M= Ga In ; or = Och2ch2ome Ommentioning

confidence: 99%

“…The analysis of the strength of In-C 6-Mes bond of 2 in solution, in comparison with In-C NHC bonds of already characterized Me 3 In(NHC) adducts [3,21,23], was in sharp contrast with the solid state result. In solution, the shift between free and coordinated NHCs in 13 [30], the analysis of the strength of a M-C NHC bond using the 13 C NMR spectroscopy could be influenced by other factors affecting the distribution of electron density at carbene carbon. However, it must be noticed that the shift between free and coordinated NHCs in solution, using 13 C NMR spectroscopy, reflected stronger donor properties of 6-Mes in comparison with SIMes and IMes.…”

Section: Reactivity Of [Me2m(μ-or)]n (M= Ga In ; or = Och2ch2ome Ommentioning

confidence: 99%

“…interpretations of molecular structures [30], the analysis of the strength of a M-CNHC bond using the 13 C NMR spectroscopy could be influenced by other factors affecting the distribution of electron density at carbene carbon. However, it must be noticed that the shift between free and coordinated NHCs in solution, using 13 C NMR spectroscopy, reflected stronger donor properties of 6-Mes in comparison with SIMes and IMes.…”

Section: Reactivity Of [Me2m(μ-or)]n (M= Ga In ; or = Och2ch2ome Ommentioning

confidence: 99%

“…Moreover, they represent isoselective catalysts for the ring-opening polymerization (ROP) of rac-lactide (rac-LA), which are additionally highly active at low temperatures. Therefore, they still constitute rare examples of isoselective catalysts operating at mild conditions, both among group 13 metal complexes [5][6][7][8][9], and beyond [10][11][12][13]. Importantly, both the structure and reactivity of Me 2 MOR(NHC) (M = Ga, In; NHC = SIMes, IMes) were found to be strongly dependent on the M-C NHC bond.…”

Section: Introductionmentioning

confidence: 99%

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Probing the Effect of Six-Membered N-Heterocyclic Carbene—6-Mes—on the Synthesis, Structure and Reactivity of Me2MOR(NHC) (M = Ga, In) Complexes

et al. 2018

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Abstract:The investigation of the reactivity of six membered N-heterocyclic carbene 1,3-bis(2,4,6-trimethylphenyl)-3,4,5,6-tetrahydropyrimidin-1-ylidene (6-Mes) towards dialkylgallium and dialkylindium alkoxides/aryloxides has shown that both steric hindrances and donor properties of 6-Mes significantly influence the strength of M-C 6-Mes bond, as well as the formation, structure and reactivity of Me 2 MOR(6-Mes) (M = Ga, In) complexes. While the reactions of simple dimethylgallium alkoxides with 6-Mes lead to the formation of stable monomeric Me 2 Ga(OCH 2 CH 2 OMe)(6-Mes) (1) and Me 2 GaOMe(6-Mes) complexes, the analogous Me 2 InOR(6-Mes) are unstable and disproportionate to methylindium alkoxides and Me 3 In(6-Mes) (2). The use of bulky alkoxide ligand-OCPh 2 Me or aryloxide ligand-OC 6 H 4 OMe allowed for the synthesis of stable Me 2 M(OCPh 2 Me)(6-Mes) (M = Ga (3) and In (4)) as well as Me 2 M(OC 6 H 4 OMe)(6-Mes) (M = Ga (5) and In (6)). The structures of 1-6 have been determined using both spectroscopic methods in solution and X-ray diffraction studies, which confirmed the effect of both steric hindrances and donor properties of 6-Mes on their structure and catalytic properties in the ring-opening polymerization (ROP) of rac-lactide.

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Section: Reactivity Of [Me2m(μ-or)]n (M= Ga In ; or = Och2ch2ome Ommentioning

confidence: 99%

Section: Reactivity Of [Me2m(μ-or)]n (M= Ga In ; or = Och2ch2ome Ommentioning

confidence: 99%

“…The analysis of the strength of In-C 6-Mes bond of 2 in solution, in comparison with In-C NHC bonds of already characterized Me 3 In(NHC) adducts [3,21,23], was in sharp contrast with the solid state result. In solution, the shift between free and coordinated NHCs in 13 [30], the analysis of the strength of a M-C NHC bond using the 13 C NMR spectroscopy could be influenced by other factors affecting the distribution of electron density at carbene carbon. However, it must be noticed that the shift between free and coordinated NHCs in solution, using 13 C NMR spectroscopy, reflected stronger donor properties of 6-Mes in comparison with SIMes and IMes.…”

Section: Reactivity Of [Me2m(μ-or)]n (M= Ga In ; or = Och2ch2ome Ommentioning

confidence: 99%

Section: Reactivity Of [Me2m(μ-or)]n (M= Ga In ; or = Och2ch2ome Ommentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Probing the Effect of Six-Membered N-Heterocyclic Carbene—6-Mes—on the Synthesis, Structure and Reactivity of Me2MOR(NHC) (M = Ga, In) Complexes

et al. 2018

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Stereoselective Ring‐Opening Polymerization of Heterocyclic Monomers

Takeuchi

2014

Encyclopedia of Polymer Science and Technology

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Recent progress in stereoselective ring‐opening polymerization of heterocyclic monomers, especially polymerization and copolymerization of epoxides and lactones, is summarized. Zn, Al, Co, and Cr complexes promote stereospecific ring‐opening polymerization of epoxides as well as copolymerization of epoxides with carbon dioxide. Enantioselective polymerization of epoxide is also achieved to afford optically active polyethers. Cr and lanthanide complexes promote stereoselective polymerization of β‐butyrolactone. Stereospecific polymerization of lactide has been achieved by using varieties of metal catalysts, including Al, Ga, In, Mg, Ca, Sn, Zn, Ti, Zr, Hf, Ge, and rare earth metals. Organic catalysts such as carbenes and phosphazene bases are also utilized for the synthesis of stereoregular polylactide. By utilizing those stereoselective polymerizations, more stereogradient and stereoblock copolymers have been synthesized. Polylactides with high degree of stereoregularity show high melting points. One‐to‐one mixtures of isotactic poly( l ‐lactide) and poly( d ‐lactide) or stereoblock copolymer of l ‐lactide and d ‐lactide show higher melting points compared with the polymer of homochiral monomer, due to the formation of stereocomplex.

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Metal‐Size Influence in Iso‐Selective Lactide Polymerization

et al. 2014

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Iso-selective initiators for the ring-opening polymerization (ROP) of rac-lactide are rare outside of Group 13. We describe the first examples of highly iso-selective lutetium initiators. The phosphasalen lutetium ethoxide complex shows excellent iso-selectivity, with a P i value of 0.81-0.84 at 298 K, excellent rates, and high degrees of polymerization control. Conversely, the corresponding La derivative exhibits moderate heteroselectivity (P s = 0.74, 298 K). Thus, the choice of metal center is shown to be crucial in determining the level and mode of stereocontrol. The relative order of rates for the series of complexes is inversely related to metallic covalent radius: that is, La > Y > Lu.Polylactide (PLA), a degradable polymer obtained from renewable resources, is one of the leading commercial alternatives to petrochemical plastics. [1] PLA is produced by the metal-catalyzed ring-opening polymerization (ROP) of lactide (LA). [2] The central challenge in this field of catalysis is to combine high rates with excellent stereocontrol, ideally without the need for expensive chiral auxiliaries or ligands. [3] Iso-selectivity using rac-LA is especially important and useful because the product, stereoblock/complex PLA, has superior properties. [4] For example, it is a crystalline polymer with a higher melting temperature (T m ) and better mechanical properties than isotactic poly-L-lactide (PLLA). In some cases, T m is elevated by as much as 50 8C, greatly improving thermal stability and enabling PLA to compete as an engineering polymer. [5] However, rac-LA iso-selective catalysts remain scarce, with the majority being chiral aluminum salen complexes or derivatives. [3b, 4a, 6] Although these compounds show impressive degrees of stereocontrol, they are often extremely slow and require unacceptably high catalyst loadings, typically taking hours or days to reach completion even at 1 mol % catalyst loading. There are only a handful of other, non-aluminum based, iso-selective catalysts, [7] the structures of three of the most selective of these are shown in Figure 1. [8] In 2008, Arnold and co-workers reported a homochiral yttrium complex that showed good iso-selectivity (C, P i = 0.75, 298 K). [8a,b] Subsequently, we reported yttrium phosphasalen complexes (Figure 1, structures A and B), which combined very high rates with promising isoselectivity (P i = 0.74, 298 K). [8c] Herein, we report the performance of lutetium and lanthanum phosphasalen complexes. For such Group 3 lanthanide complexes, the coordination geometries are predominantly influenced by steric factors. In this regard, it is relevant that lutetium has a slightly smaller covalent radius than yttrium (1.87 versus 1.90 ), whilst lanthanum is significantly larger (2.07 ). [9] The use of different lanthanide centers enables an investigation of the influence of atomic size and coordination environment on polymer tacticity. Both metals have precedence in lactide ROP catalysis, [10] although lutetium is rarely investigated. [10b,e,f,h] Okuda a...

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C₃‐Symmetric Lanthanide Tris(alkoxide) Complexes Formed by Preferential Complexation and Their Stereoselective Polymerization of rac‐Lactide

Cited by 154 publications

References 36 publications

Probing the Effect of Six-Membered N-Heterocyclic Carbene—6-Mes—on the Synthesis, Structure and Reactivity of Me2MOR(NHC) (M = Ga, In) Complexes

Probing the Effect of Six-Membered N-Heterocyclic Carbene—6-Mes—on the Synthesis, Structure and Reactivity of Me2MOR(NHC) (M = Ga, In) Complexes

Stereoselective Ring‐Opening Polymerization of Heterocyclic Monomers

Metal‐Size Influence in Iso‐Selective Lactide Polymerization

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