Efficient ring-opening polymerization of ɛ-caprolactone using anilido-imine–aluminum complexes in the presence of benzyl alcohol

Amidophosphine Boranes as Hydroboration Reagents for Nitriles, Alkynes, and Carboxylic Acids

We report here the hydroboration of nitriles, alkynes, and carboxylic acids using amidophosphine boranes {(BH3)(PPh2)-NC(CH3)3}, {(BH3)2(PPh)2N(CH2)C6H5}, and {(BH3)2(PPh2)2N-(BH3)CH2C6H4N} as reducing agents. These compounds were synthesized to replace more commonly used borane reagents. Solid amidophosphine boranes, which were synthesized with ease, demonstrated excellent reactivity and functional group tolerance toward a wide variety of nitriles, alkynes, and carboxylic acids, affording the corresponding ammonium salts, alkenes, and alcohols in good yield.

Aluminium(iii) and zinc(ii) complexes of azobenzene-containing ligands for ring-opening polymerisation of ε-caprolactone and rac-lactide

The ability to control the outcome of polymerisations using an external stimulus remains a formidable challenge.

Diverse Coordinative Zinc Complexes Containing Amido-Pyridinate Ligands: Structural and Catalytic Studies

In this work, zinc complexes containing amidopyridinate ligands substituted with different pendant arms have been described. Treatment of ligand precursors with ZnEt₂ at a 1:1 ratio in THF yields zinc ethyl complexes (PyNC1Py)₂(ZnEt)₂ (1) and (PyNC2NMe2)₂(ZnEt)₂ (2), respectively. Complexes 1 and 2 show the same geometry as a distorted tetrahedron, but adopt different coordination behaviors supported by the ligands. Complex 1 represents a rare and a non-centrosymmetric mode, which the amido group bridges two zinc centers to form a six-membered ring. However, complex 2 shows a centrosymmetric mode, which the pyridine group links to the zinc centers to form an eight-membered ring. Recrystallization of complex 2 gives an additional complex (PyNC2NMe2)₄Zn₃(μ³-O) (3). We attempted to prepare zinc benzyl oxide complexes but afforded only a self-assembly cubane complex Zn₇Et₆(OBn)₈(4). All molecular structures 1–4 are characterized depending on both single-crystal X-ray and spectroscopic data. Furthermore, their catalytic properties toward the ring opening polymerization of ε-caprolactone and L-lactide, using benzyl alcohol as the initiation reagent, are under investigation.

Aluminium complexes containing salicylbenzothiazole ligands and their application in the ring-opening polymerisation of rac-lactide and ε-caprolactone

This paper is the first report on the use of aluminium salicylbenzothiazole complexes for the ROP of rac-LA and ε-CL.

Synthesis of Ti, Zr, and Hf complexes with a new tetra-azane ligand by one-pot HCl-elimination and their properties as catalysts for production of UHMWPE

The first example for the HCl-elimination reaction being applied in the attachment of an amido-containing ligand to Zr and Hf.

Immortal ring-opening polymerization of ε-caprolactone by a neat magnesium catalyst system: an approach to obtain block and amphiphilic star polymers in situ

Building of various functional and topological microstructured PCLs via the immortal catalyst system of MgⁿBu₂/ROH and click reaction.

Ring-opening polymerization of ε-caprolactone by lithium piperazinyl-aminephenolate complexes: synthesis, characterization and kinetic studies

A series of lithium complexes were prepared from 2(N-piperazinyl-N'-methyl)-2-methylene-4-R'-6-R-phenols ([ONN](RR')) and characterized through elemental analysis, (1)H and (13)C{(1)H} NMR spectroscopy, and X-ray crystallography. Treatment of the ligands with n-butyllithium afforded {Li[ONN](RR')}(3) [R = Me, R' = (t)Bu, (1); R = R' = (t)Bu (2); R = R' = (t)Am, (3), (t)Am = C(CH(3))(2)CH(2)CH(3)], with trimetallic structures in the solid-state as shown by single-crystal X-ray diffraction. The reactivity of these complexes in the ring-opening polymerization of ε-caprolactone (ε-CL), as well as the influences of monomer concentration, monomer/Li molar ratio, polymerization temperature and time, was studied. Rates of polymerization were first order with respect to both monomer and lithium concentrations, and activation energies for the reactions were determined. MALDI-TOF MS analysis revealed that transesterification had occurred during the polymerization.

[(E)-10-(2,6-Dimethyl-phenyl-imino)-9-methyl-9,10-dihydro-phenanthren-9-olato]penta-methyl-dialuminum(III)

The two Al atoms in the title compound, [Al₂(CH₃)₅(C₂₃H₂₀NO)], are four-coordinated in a distorted tetra­hedral environment. The coordination of one Al atom includes three methyl-C atoms and the O atom from the ligand, whereas the second Al atom is surrounded by the O atom and one N atom from the ligand as well as by two methyl-C atoms. In the ligand, the dihedral angle between the two phenyl rings in the 9,10-dihydro­phenanthren unit is 20.64 (12)°.

[N-((E)-2-{[2-(Dimethyl-amino)-eth-yl]imino-meth-yl}phen-yl)-N-(2,6-dimethyl-phen-yl)anilinido-κN,N',N'']ethyl-zinc

The title eth­yl–zinc complex, [Zn(C₂H₅)(C₁₉H₂₄N₃)], bears a tridentate anilinide–aldimine ligand and features one long Zn—N(amine) bond length, attributable to the crowded environment of the coordinated metal, arising from the dimethyl­phenyl group. The Zn^II ion adopts a distorted tetra­hedral geometry, the dihedral angle between the two benzene rings being 86.05 (16)°.

Simple generation of neutral bimetallic aluminium and zinc alkyls Schiff bases bridged by a central resorcinol moiety

Aluminium and zinc complexes bearing the N,O-chelating Schiff base ligand 4,6-bis-1-(2-(dimethylamino)ethylimino)ethyl)benzene-1,3-diol, (C6H2(OH)2(NCH2CH2NMe2)2) (1a), have been synthesized. Bimetallic aluminium and zinc alkyl complexes (2a–4a) were prepared by treatment of the hexadentate 1a with the appropriate amount of AlMe3, ZnMe2 and ZnEt2, respectively. 2a has been characterized crystallographically, it lies on a crystallographic two-fold rotation axis and each aluminium centre adopts a five coordinate geometry. Complex 2a was tested as a catalyst in the ring-opening polymerisation of ɛ-caprolactone. We describe here the synthesis of two neutral ligands (1a and (C6H2(OH)2(C6H5NH2) (C=O(CH3)) (1b)) and demonstrate their application in the synthesis of molecular aluminium and zinc derivatives.

Synthesis of polycaprolactone: a review

Polycaprolactone (PCL) is an important polymer due to its mechanical properties, miscibility with a large range of other polymers and biodegradability. Two main pathways to produce polycaprolactone have been described in the literature: the polycondensation of a hydroxycarboxylic acid: 6-hydroxyhexanoic acid, and the ring-opening polymerisation (ROP) of a lactone: epsilon-caprolactone (epsilon-CL). This critical review summarises the different conditions which have been described to synthesise PCL, and gives a broad overview of the different catalytic systems that were used (enzymatic, organic and metal catalyst systems). A surprising variety of catalytic systems have been studied, touching on virtually every section of the periodic table. A detailed list of reaction conditions and catalysts/initiators is given and reaction mechanisms are presented where known. Emphasis is put on the ROP pathway due to its prevalence in the literature and the superior polymer that is obtained. In addition, ineffective systems that have been tried to catalyse the production of PCL are included in the electronic supplementary information for completeness (141 references).