Neutral and Cationic Heteroscorpionate Aluminum Complexes:  Synthesis, Structure, and Ring-Opening Polymerization of ε-Caprolactone

“…The NMR tube was vigorously shaken and a 1 H NMR spectrum was immediately recorded, showing the conversion of 3 + into the Al-hexyl cation 5 + along with the formation of poly(isobutene). After NMR analysis, the orange solution of [5] Tables 1 and 3. The cell parameters were determined from reflections taken from one set of ten frames (1.08 steps in f angle), each at 20 s exposure.…”

Section: Data For Chd 2 CLmentioning

confidence: 99%

“…[2] In this regard, some of these cations have already been used as alkene oxide, [3] (d,l)-lactide, [4] e-caprolactone, [5] and olefin [6] polymerization catalysts. Among this class of compounds, four-coordinate Alalkyl cations of the type [{LX}Al(R)(L)] + (LX À = bidentate monoanionic ligand, L = labile ligand) are the most studied as they combine a low-coordination with a cationic metal center, resulting in highly Lewis acidic species.…”

Section: Introductionmentioning

confidence: 99%

“…The reactivity of low-coordinate Al-alkyl cations toward cyclic esters such as e-caprolactone and lactides is also of interest and remains largely unexplored. [5] Here, we report the synthesis and structures of well-defined, low-coordinate Al-alkyl and -alkoxide cationic complexes incorporating a bulky aminophenolate ligand. The reactivity of these cations toward e-caprolactone and lactides, as well as the characterizations of a few structurally unusual Al complexes, are also presented.…”

Section: Introductionmentioning

confidence: 99%

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Well‐Defined Cationic Alkyl– and Alkoxide–Aluminum Complexes and Their Reactivity with ε‐Caprolactone and Lactides

Dagorne¹,

Bideau²,

Welter³

et al. 2007

Chemistry A European J

104

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We describe the synthesis, structure, and reactivity of low-coordinate Al-alkyl and -alkoxide cationic complexes incorporating the sterically bulky aminophenolate bidentate ligand 6-(CH(2)NMe(2))-2-CPh(3)-4-Me-C(6)H(2)O- (N,O). These complexes are derived from the ionization of neutral dialkyl Al complexes (N,O)Al2) (1 a, R=Me; 1 b, R=iBu), readily obtained by alkane elimination between AlR3 and the corresponding aminophenol ligand, with the alkyl abstracting reagents B(C(6)F(5))3 and [Ph(3)C][B(C(6)F(5))4]. The reactions of 1 a,b with B(C(6)F(5))3 yield complicated mixtures or decomposition products, however the ionization of the Al-diisobutyl derivative 1 b with [Ph(3)C][B(C(6)F(5))4] affords a stable four-coordinate Al-PhBr cationic adduct [(N,O)Al(iBu)(PhBr)]+ (3+), as deduced from elemental analysis data. Complex 3+ readily coordinates Lewis bases such as THF to form the corresponding adduct [(N,O)Al(iBu)(thf)]+ (4+), and also rapidly chain-transfers with 1-hexene to yield the three-coordinate Al-hexyl cation [(N,O)Al-hexyl]+ (5+). Both cations 3+ and 5+ slowly dimerize to form unprecedented organoaluminum dications [(N,O)AlR+]2 (3'++, R=iBu; 5'++, R=hexyl) as deduced from X-ray crystallographic analysis. Cation 3+ reacts quickly with iPrOH to form a stable Lewis acid/base adduct [(N,O)Al(iBu)(HOiPr)]+ (6+), which constitutes the first X-ray characterized adduct between an Al-alkyl complex and a simple ROH. The Al-ROH proton in 6+ is readily abstracted by NMe(2)Ph to form the neutral isopropoxide Al complex [(N,O)Al(iBu)(OiPr)] (7). Upon reaction with THF, cation 6+ undergoes an intramolecular proton transfer to yield the ammonium Al-THF complex [(eta1-HN,O)Al(iBu)(OiPr)(thf)] (8 b+), in which the aminophenolate is eta1-coordinated to the Al center. Cation 8 b+ can then be converted to the desired Al-alkoxide derivative [(N,O)Al(OiPr)(thf)](+) (10+), by an intramolecular protonolysis reaction, as confirmed by X-ray crystallography. The synthesized Al-alkyl cations form robust four-coordinate adducts in the presence of cyclic esters such as epsilon-caprolactone and (D,L)-lactide, but no insertion chemistry occurs, illustrating the poor ability of the Al-R+ moiety to ring-open. In contrast, the Al-alkoxide cation 10+ polymerizes epsilon-caprolactone in a controlled manner with excellent activity, but is inactive in the polymerization of (D,L)-lactide and L-lactide. Control experiments with L-lactide show that cation 10+ ring-opens L-lactide to yield a robust five-coordinated Al--lactate cation [(N,O)Al(eta2-L-lactate-OiPr)(thf)]+ (13+), derived from a monoinsertion of L-lactide into the Al--OiPr bond of 10+, that does not further react. Cation 13+ may be regarded as a structurally characterized close mimic of the initial intermediate in the ring opening polymerization (ROP), of lactides by [{LX}M(OR)(L)] (where LX-=bidentate monoanionic ligand and L=labile ligand) metal complex initiators.

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“…[98][99][100][101][102][103][104][105][106][107] Nomura [98] studied the aluminum complexes containing phenoxyimine ligand for initiating polymerization of ɛ-caprolactone and found that the aluminum complexes 71 exhibited living polymerization characteristics when low monomer conversion, increasing conversion resulted in widening the PDI of PCL. Redshaw [99] also investigated the aluminum complexes 72 and 73 for ROP of ɛ-caprolactone, these catalyst system showed produced polymers with 44640 g/mol molecular weight, but, 46% monomer conversion.…”

Section: No Ligandmentioning

confidence: 99%

Review – recent development of ring-opening polymerization of cyclic esters using aluminum complexes

Ruan

Xiao

et al. 2013

Designed Monomers and Polymers

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With the development of the technology of ring-opening polymerization (ROP) rapidly, many novel aluminum complexes have been designed, synthesized, and applied in initiating ROP of cyclic esters and new stereoregular polymerization mechanism of lactide polymerization have been reported. In this review, the mechanism for ROP of cyclic ester, synthesis of aluminum complexes containing tetradendete ligand, tridentate ligand, bidentate ligand, and bimetallic complexes containing aluminum were reviewed. We hope to give some helpful information for designing aluminum complexes, improving activity, and stereoregularity of aluminum complexes.Keywords: ring-opening polymerization; cyclic ester; aluminum complexes; stereoregularity IntroductionAliphatic polyester is biodegradable and biocompatible materials, which prepared using ring-opening polymerization (ROP) of cyclic ester such as lactide, caprolactone. trimethylene carbonate, and other cyclic ester. [1,2] Due to effective influences of microstructure, molecular weight, and polydispersity indexes (PDIs) on polyester physicochemical properties, the controlled/living ROP for synthesis of polyester which enables the ready to control these parameters attracted an extraordinary amount of research recently.[3-6] During the last two decades, the improvement in catalyst makes it possible to design and synthesis of polyester. [7][8][9][10]

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Neutral and Cationic Heteroscorpionate Aluminum Complexes: Synthesis, Structure, and Ring-Opening Polymerization of ε-Caprolactone

Cited by 99 publications

References 42 publications

The modification of bis(pyrazol-1-yl)methanes by chalcogen (S and Se) and their related reactions with organotin chloride and M(CO)5THF (M = Mo and W)

The modification of bis(pyrazol-1-yl)methanes by chalcogen (S and Se) and their related reactions with organotin chloride and M(CO)5THF (M = Mo and W)

Well‐Defined Cationic Alkyl– and Alkoxide–Aluminum Complexes and Their Reactivity with ε‐Caprolactone and Lactides

Review – recent development of ring-opening polymerization of cyclic esters using aluminum complexes

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