Polymerization of rac-Lactide Using Achiral Iron Complexes: Access to Thermally Stable Stereocomplexes.

Enantiopure poly(lactic acid) (PLA) can form stereocomplexes when enantiomeric PLA chains are mixed in equivalent amounts. Such materials provide interesting features that might be suitable for numerous applications. Despite several advantages, the main drawback of PLA is its narrow window of processing, thus limiting its use for industrial applications.

Mechanistic Aspects of the Polymerization of Lactide Using a Highly Efficient Aluminum(III) Catalytic System.

We report here a unique example of an in situ generated aluminum initiator stabilized by a C-symmetric salen ligand which shows a hitherto unknown high activity for the ROP of rac-lactide at room temperature. Using a simple and robust catalyst system, which is prepared from a salen complex and an onium salt, this convenient route employs readily available reagents that afford polylactide in good yields with narrow polydispersity indices, without the need for time-consuming and expensive processes that are typically required for catalyst preparation and purification. In line with the experimental evidence, DFT studies reveal that initiation and propagation proceed via an external alkoxide attack on the coordinated monomer.

Replacing tin in lactide polymerization: design of highly active germanium-based catalysts.

Most germane: Hexacoordinate germanium(IV) species exhibit unprecedented activities, yet controlled behavior, as initiators for the ring-opening polymerization of rac-lactide to form polylactide polymers.

Chemically engineered papain as artificial formate dehydrogenase for NAD(P)H regeneration.

Organometallic complexes of the general formula [(η(6)-arene)Ru(N⁁N)Cl](+) and [(η(5)-Cp*)Rh(N⁁N)Cl](+) where N⁁N is a 2,2'-dipyridylamine (DPA) derivative carrying a thiol-targeted maleimide group, 2,2'-bispyridyl (bpy), 1,10-phenanthroline (phen) or ethylenediamine (en) and arene is benzene, 2-chloro-N-[2-(phenyl)ethyl]acetamide or p-cymene were identified as catalysts for the stereoselective reduction of the enzyme cofactors NAD(P)(+) into NAD(P)H with formate as a hydride donor. A thorough comparison of their effectiveness towards NAD(+) (expressed as TOF) revealed that the Rh(III) complexes were much more potent catalysts than the Ru(II) complexes. Within the Ru(II) complex series, both the N⁁N and arene ligands forming the coordination sphere had a noticeable influence on the activity of the complexes.

(Eta6-arene) ruthenium(II) complexes and metallo-papain hybrid as Lewis acid catalysts of Diels-Alder reaction in water.

Covalent embedding of a (eta(6)-arene) ruthenium(II) complex into the protein papain gives rise to a metalloenzyme displaying a catalytic efficiency for a Lewis acid-mediated catalysed Diels-Alder reaction enhanced by two orders of magnitude in water.

Synthesis and structural characterization of well-defined anionic aluminum alkoxide complexes supported by NON-type diamido ether tridentate ligands and their use for the controlled ROP of lactide.

The tridentate proligands (RNH-o-C6H4)2O (1a, R = C5H9; 1b, R = Cy) were found to readily react with LiAlH4 to yield the corresponding lithium aluminium dihydrido salt species [eta(2)-N,N-{(RN-o-C6H4)2O}AlH(mu-H)Li(THF)]2 (2a, R = C5H9; 2b, R = Cy) in 50% and 42% yield, respectively. The solid-state structure of both complexes 2a and 2b were determined by X-ray crystallographic studies. Compounds 2a and 2b readily react with one equivalent of benzaldehyde to afford the corresponding mono-benzyloxide species eta(2)-N,N-{RN-o-C6H4)2O}Al(H)(mu-OCH2Ph)Li(THF)2 (4a, R = C4H9; 4b, R = Cy), as confirmed by X-ray studies in the case of 4b.

Cysteine-specific, covalent anchoring of transition organometallic complexes to the protein papain from Carica papaya.

Site-directed and covalent introduction of various transition metal-organic entities to the active site of the cysteine endoproteinase, papain, was achieved by treatment of this enzyme with a series of organometallic maleimide derivatives specially designed for the purpose. Kinetic studies made it clear that time-dependent irreversible inactivation of papain occurred in the presence of these organometallic maleimides as a result of Michael addition of the sulfhydryl of Cys25. The rate and mechanism of inactivation were highly dependent on the structure of the organometallic entity attached to the maleimide group.

A new optically pure half-sandwich Cp-Ru diphosphine complex with a chiral metal centre, (S)-Ru(eta 5-C5H5)(EPHOS)Cl [EPHOS is (+)-(1R,2S)-2-[(diphenylphosphino)methylamino]-1-phenylpropyl diphenylphosphinite].

The crystal structure of the title compound, chloro(eta(5)-cyclopentadienyl)[(1R,2S)-2-[(diphenylphosphino)methylamino]-1-phenylpropyl diphenylphosphinite-kappa(2)P,P']ruthenium(II), [Ru(C(5)H(5))Cl(C(34)H(33)NOP(2))], is reported. The pseudo-octahedral complex is chiral and the configuration at the Ru atom is S. The seven-membered metallacycle adopts a boat-like conformation.