Yttrium Phosphasalen Initiators for <i>rac</i>-Lactide Polymerization: Excellent Rates and High Iso-Selectivities

Bakewell, Clare; Cao, Thi-Phuong-Anh; Long, Nicholas J.; Goff, Xavier F. Le; Auffrant, Audrey; Williams, Charlotte K.

doi:10.1021/ja310003v

Cited by 215 publications

(149 citation statements)

References 48 publications

Supporting

Mentioning

143

Contrasting

Order By: Relevance

“…17,[33][34][35][36] Schiff base metal complexes have found numerous uses in coordination chemistry and catalysis, [37][38][39][40][41][42] alkoxide yttrium complexes supported by such ligands being intensely researched as initiators for the ring-opening polymerization of cyclic esters. 17,[35][36][43][44][45][46][47][48][49][50] On the other hand, reports of structurally characterized alkyl or aryl rare earth complexes bearing an imine functionality in the backbone are rare, [51][52] the majority being represented by phosphinimine ligands. [53][54][55][56][57][58][59][60] In our lab, the synthesis of an electrophilic metal alkyl complex supported by a Schiff base ferrocene ligand would continually fail.…”

Section: Introductionmentioning

confidence: 99%

Yttrium-Alkyl Complexes Supported by a Ferrocene-Based Phosphinimine Ligand

Brosmer

Diaconescu

2015

Organometallics

View full text Add to dashboard Cite

The synthesis and characterization of two yttrium alkyl complexes supported by a bisphosphinimine ferrocene ligand, NP by NMR spectroscopy, electrochemical measurements, and elemental analysis. Reactivity studies were also carried out, however, the lack of prolonged thermal stability at ambient temperature of these molecules led to decomposition before the clean formation of reaction products could be observed.1

show abstract

Section: Introductionmentioning

confidence: 99%

Yttrium-Alkyl Complexes Supported by a Ferrocene-Based Phosphinimine Ligand

Brosmer

Diaconescu

2015

Organometallics

View full text Add to dashboard Cite

show abstract

“…We have recently demonstrated that these ligands are more flexible and electron-donating than their carbon analogues [12] and that they provide efficient and selective initiators for rac-lactide polymerization. [13] In the present work, we wish to report the synthesis and characterization of a Ni II phosphasalen complex and its one-electron oxidation which leads to a temperaturepersistent high-valent tetracoordinated Ni III complex. With the objective of studying the oxidation of a [Ni-(Psalen)] complex, we chose a ligand featuring substituents on the ortho and para positions of the phenoxide rings to increase its stability, and preferred tert-butyl groups for solubility reasons.…”

mentioning

confidence: 99%

A Tetracoordinated Phosphasalen Nickel(III) Complex

et al. 2013

Self Cite

View full text Add to dashboard Cite

The oxidation of a Ni II complex bearing a tetradentate phosphasalen ligand, which differs from salen by the presence of an iminophosphorane (P = N) in place of an imine unit, was easily achieved by addition of a silver salt. The site of this oxidation was investigated with a combination of techniques (NMR, EPR, UV/Vis spectroscopy, X-ray diffraction, magnetic measurements) as well as DFT calculations. All data are in agreement with a high-valent Ni III center concentrating the spin density. This markedly differs from precedents in the salen series for which oxidation on the metal was only observed at low temperature or in the presence of additional ligands or anions. Therefore, thanks to the good electron-donating properties of the phosphasalen ligand, [Ni(Psalen)]+ represents a rare example of a tetracoordinated high-valent nickel complex in presence of a phenoxide ligand.N,N' -ethylenebis(salicylimine) (salen) derivatives constitute a very successful class of ligands that have found numerous applications in inorganic chemistry and catalysis. [1] Their extraordinary popularity comes from their easy synthesis, allowing a variety of skeleton variations, and their ability to coordinate to a great number of different metal ions. Moreover the presence of two phenoxide and imine functions is reminiscent of the coordination environment generated by two histidine and two tyrosine residues, encountered in several enzymes. Thus, in 1998, the one-electron oxidation of a (salen)copper(II) complex was described, and the resulting persistent phenoxy radical was established as a biomimetic functional model of galactose oxidase.[2] Since then, one-electron-oxidized metal salen complexes of firstrow transition metals have received considerable attention. [3] Depending on the nature of the redox-active orbitals, oxidation of salen complexes leads either to high-valent metal centers (metal-centered oxidation) or to species where the ligand is oxidized to a radical (ligand-centered oxidation). Therefore, various factors may affect the oxidation site, as it was nicely illustrated in the case of nickel salen complexes. In noncoordinating solvents, one-electron oxidation occurs on the ligand, and the unpaired electron is highly delocalized over the salen moiety with a small contribution of the nickel orbitals.[3b, 4] However, in coordinating solvents, or in the presence of exogenous ligands such as pyridine or coordinating anions, the geometry of the complex is modified and so is the site of the oxidation, allowing the formation of Ni III complexes.[4a,b, 5] Temperature-dependent behavior, that is, valence tautomerism, was also described in a few examples.[5b, 6] Moreover, the overall electronic distribution may be finely tuned by the substituents of the phenoxide rings. They influence not only the site of the oxidation (which takes place at the most electron-rich phenoxide ring) as evidenced with complexes featuring unsymmetrical salen, [3c, 7] but also the extent of radical delocalization. [3b, 8] The hybridization o...

show abstract

“…Very recently, Auffrant and Williams reported that yttrium phosphasalen complex (33) shows high isoselectivity as well as high activity for the polymerization of rac-lactide. The combination of such very high rates, excellent polymerization control, tolerance to low loadings, and high isoselectivity is very rare and noteworthy (106). Mg complexes with diamide ligand such as 34 promote isotactic polymerization of rac-lactide to afford stereoblock copolymer, although P m is not clear (107).…”

Section: Polymerization Of Lactidesmentioning

confidence: 99%

Stereoselective Ring‐Opening Polymerization of Heterocyclic Monomers

Takeuchi

2014

Encyclopedia of Polymer Science and Technology

View full text Add to dashboard Cite

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.

show abstract

Yttrium Phosphasalen Initiators for rac-Lactide Polymerization: Excellent Rates and High Iso-Selectivities

Cited by 215 publications

References 48 publications

Yttrium-Alkyl Complexes Supported by a Ferrocene-Based Phosphinimine Ligand

Yttrium-Alkyl Complexes Supported by a Ferrocene-Based Phosphinimine Ligand

A Tetracoordinated Phosphasalen Nickel(III) Complex

Stereoselective Ring‐Opening Polymerization of Heterocyclic Monomers

Contact Info

Product

Resources

About