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A series of neutral lanthanide alkoxide complexes stabilized by a new salen-type Schiff-base ligand were synthesized, and their catalytic behaviors for the ring-opening polymerization of lactide were explored. Amine elimination reactions of N -methyl- N ′, N ″-bis(3,5-di- tert -butylsalicylidene)-2,2′-diaminodiethylamine (LH 2 ) with Ln[N(SiMe 3 ) 2 ] 3 (Ln = Sm, Nd, La) in a 1:1 M ratio in THF, followed by reactions with 1 equiv of alcohols ( t BuOH, EtOH and CH 3 OCH 2 CH 2 OH), produced lanthanide alkoxide complexes LLn(O t Bu)(THF) (Ln = Sm ( 1 ), Nd ( 2 ), La ( 3 )), [LSm( μ -OEt)] 2 ( 4 ) and [LSm( μ -OCH 2 CH 2 OCH 3 )] 2 ( 5 ), respectively, whereas the same reaction with Yb[N(SiMe 3 ) 2 ] 3 gave an unexpected homoleptic complex L 2 Yb 2 ( μ -L) ( 6 ). X-ray structural determination showed that complexes 1 – 3 have a THF-solvated monomeric structure, whereas complexes 4 – 6 have an unsolvated dimeric structure. All lanthanide alkoxide complexes can efficiently initiate the ring-opening polymerization (ROP) of L -LA and rac -LA. The polymerization kinetics of L -LA initiated by complex 1 has been studied in detail and the first-order kinetic dependence on both l -lactide concentration and initiator concentration was found. Furthermore, all complexes showed moderate stereoselectivity for rac -LA polymerization to afford heterotactic-rich polylactides. [ABSTRACT FROM AUTHOR]

Abstract: Three aluminium salophen and two aluminium salen complexes were synthesised, characterised and screened in the ring-opening polymerisation (ROP) of rac-lactide and rac-β-butyrolactone. The focus was on controlling the apparent polymerisation rate (k p) and stereoselectivity of poly(lactic acid) and poly(3-hydroxybutyrate) by modulating the electron density at the aluminium centre or by switching from an alkyl backbone (salen complex) to an aryl backbone (salophen complex). The salen complexes generally showed higher k p as well as isoselectivity compared to the salophen complexes. For instance, salophen and salen complexes biased the microstructure of poly(3-hydroxybutyrate) towards syndiotacticity and isotacticity, respectively. Electron-withdrawing or electron-donating backbones on a salophen complex tuned k p, with electron-donating backbones offering faster k p. [Copyright &y& Elsevier]

Abstract: A new chiral salen ligand based on two ferrocenyl groups is designed. Unlike known salen ligands, of which chirality originates from central and axial chiral centers, the chirality of this ligand comes from the planar chiral ferrocenyl groups. The ligand is synthesized stereoselectively using a novel aromatization strategy starting from a ferrocene derivative, which was readily prepared using a known chiral auxiliary approach. [Copyright &y& Elsevier]

Abstract: Four different ligands of the Salan class have been prepared and reacted with boric acid. Reaction of saleanH4 (saleanH4 = N,N′-bis(o-hydroxybenzyl)-1,2-diaminoethane) with three equivalents of boric acid gave a neutral trinuclear boron complex containing two four-coordinate and one three-coordinate boron atom involved in a system of four heterocyclic rings of the composition {C3BNO}, {C2B2N2O} and {B3O3}. The salceanH4 ligand (salceanH4 = N,N′-bis(o-hydroxybenzyl)-trans-1,2-diaminocyclohexane) gave a so far unknown mononuclear boronium complex of the general formula [(RO)2B(NR′R′′)2]+. Both compounds might have applications, the trinuclear species as Lewis acid catalyst and the borocation as positively charged counterion for voluminous anions. With salpanH4 (salpanH4 = N,N′-bis(o-hydroxybenzyl)-1,3-diaminopropane) and salophanH4 (salophanH4 = N,N′-bis(o-hydroxybenzyl)-1,2-diaminobenzene) only unseparable product mixtures of oligo- and/or polymeric boron complexes could be obtained. [Copyright &y& Elsevier]

Abstract: Rigid spacer-chelator with the framework of 3 has been prepared. Building units with two parallel coordination sites such as salen and oxazoline units have also been synthesized. The spacer-chelators, 11 and 15, readily self-assembled with metal complexes such as Zn++ and Co++ to form molecular rectangles. The overall dimensions of the rectangles, 13 and 17, are 6.2Å×23.5Å. The characterization of the supramolecules by NMR, mass spectroscopy, and X-ray crystal structures is also reported. [Copyright &y& Elsevier]

Abstract: The reduction of [Co(III)(tmsalen)(py)2]+ with NaBH4/PdCl2 and the successive oxidative addition of CH2ClI, carried out in neutral methanolic solution and followed by the addition of NaOH, afford a new dinuclear complex. The molecular structure reveals that it is formed by an octahedral [Co(tmsalen)(py)(OH)] unit connected to a β-folded [Co(tmsalenCH2)]+ fragment, in such a way that the latter metal completes the coordination sphere with the hydroxo group and a tmsalen oxygen from the former unit. [Copyright &y& Elsevier]

Abstract: The reaction of a chiral cis-β-organocobalt salen-type complex, 1, racemic mixture of Δ and Λ enantiomers, with enantiomerically pure l-histidine and a non-chiral monocationic cobalt complex, 3, resulted quite unexpectedly in the cocrystallization of diastereomers. Each diastereomer is a dicobalt monocationic complex, where four positions around one metal center are occupied by the tetradentate ligand in a cis fashion, the remaining two positions being occupied by l-histidinate. Histidinate further axially coordinates the other Co atom through the nitrogen of the imidazole residue. The two diastereomers are related by a quasi-symmetry center. In this case, the opposite helical chirality of the metal complex 1 prevails over the identical configuration of the asymmetric carbon in the crystallization process and the diastereomers behave as if they were enantiomers. The reaction of the same cobalt complexes 1 and 3 with dl-histidine led to the formation of two pairs of enantiomers, which crystallized separately as racemic compound. Therefore, in this case, the chirality of the asymmetric center is the property that allows the mutual selective recognition of the “true” enantiomers and drives their cocrystallization. [Copyright &y& Elsevier]

Abstract: The reaction of 2-fluoronitrobenzene with 2,2′-biphenol or (R)-binaphthol, followed by reduction and subsequent reaction of the resulting diamine with two equivalents of a salicylaldehyde, affords expanded salen-type ligands having backbones based on biphenol or binaphthol: salbipH2, (R)-salbinH2 and (R)-salbin(t-Bu)4H2. Deprotonation of these ligands with sodium methoxide or potassium hydride, followed by metallation with M(OAc)2 (M=Mn, Co, Ni, or Cu), affords the corresponding metal complexes in good yield (61–85%). The species containing Mn, Co, and Ni all have distorted octahedral geometry, as determined by X-ray crystallography. The ethereal oxygen atoms occupy two coordination sites with metal–oxygen distances ranging from 2.19 to 2.36 Å. The imine nitrogen atoms are trans to each other in the solid state, an impossible geometry in traditional salen-type complexes. The species containing Cu are distorted square planar and show much longer metal–ethereal oxygen distances ranging from 2.79 to 3.22 Å. The manganese complexes are competent catalysts for the epoxidation of olefins. [Copyright &y& Elsevier]

2,4-Pentanedione (=acetylacetone) has been reacted with 2-aminoethanol, 1,2-diaminoethane and 1,3-diaminopropane to give the NO2 and N2O2 type ligands named acacaminolH2, acacenH2 and acpenH2, which are structurally and electronically related to the corresponding ligands derived from salicylaldehyde (salaminolH2 and salenH2). On reaction of acacaminolH2 with phenylboronic acid a dinuclear monomeric complex has been obtained containing one three- and one four-coordinate boron atoms as well as one six-membered and one seven-membered heterocyclic ring. Since with salaminolH2 a dimeric complex with a central 10-membered heterocycle had been reported, it becomes apparent that there may be differences in reactivity when comparing 2,4-pentanedione and salicylaldehyde derived ligands. The molecular compositions of the boron complexes prepared from acacenH2 and acacpenH2 are analogous to the corresponding salen and salpen derivatives, however, the presence of two methyl groups in the six-membered chelate rings generates some structural changes, the most important being the distortion of the boat conformation of the central heterocyclic ring. This was predicted by computational methods and confirmed experimentally for one of the complexes. A further important observation was that the products described in here are much more soluble than the salicylaldehyde derivatives. As lateral product the adduct of acacenH2 with 1,3,5-triphenylboroxine was crystallized. Elemental analysis, IR and NMR (1H, 13C, 11B) spectroscopy, mass spectrometry, ab intio theoretical calculations and X-ray crystallography have been applied to carry out this study. [Copyright &y& Elsevier]

The first examples of five coordinate aluminum acetylide compounds chelated by a single ligand are reported in this paper. The combination of L(tBu)AlCl (where L=Salen (1), Salpen (2), Salophen (3), Salomphen (4)) with LiC&z.tbnd6;CPh in THF at −78 °C leads to the formation of the four acetylides (5–8), LC&z.tbnd6;CPh. These are extremely moisture sensitive and readily hydrolyze to form aluminum hydroxides and with condensation form compounds of formula [L(tBu)Al]2O. The hydrosylate [Salophen(tBu)Al]2O (9) has been structurally characterized. [Copyright &y& Elsevier]

Six boron compounds have been synthesized through the combination of phenylboronic acid and various Salen (N,N′-ethylenebis(2-hydroxy)benzylidenimine) ligands. They contain seven- and eight-membered heterocycles with a bridging oxygen and have the formula: L[(PhB)2(μ-O)] (L=Acmen (1), Salen(tBu) (2), Sal(2-OH)pen (3), Salpen(tBu) (4), Acpen (5)) and L[B2(μ-O)(O2BPh)] (L=Acen (6), Salmen (7)). Compounds 6 and 7 are interesting trinuclear boron derivatives with two four-coordinate and one three-coordinate boron atoms. The compounds have been characterized by MP, MS, IR, EA and 1H- and 11B-NMR, by 11B-MAS for 6 and 7 and by X-ray crystallography for 2, 4–7. [Copyright &y& Elsevier]

• Two aluminium methyl complexes and three aluminium alkyloxide complexes stabilized by a new thioether-bridged salen ligand were synthesized. • Aluminium alkoxide complexes exhibited higher activity and better controllability for the homopolymerization of ε-caprolactone than aluminium methyl complexes. • Aluminium alkoxide complexes could serve as efficient initiators for the copolymerization of ε-caprolactone and L - lactide to give practically random copolymers. Several aluminium alkyl and alkyloxide complexes supported by a thioether-bridged salen ligand were synthesized by the protonolysis reaction. Reactions of N,N '-bis(3,5-di- tert -butylsalicylidene)-2,2'-diaminophenylsulfide (H 2 L) with one or two equivalents of AlMe 3 in toluene at 100 °C afforded the corresponding mono- and binuclear aluminium methyl complexes L AlMe (1) and L (AlMe 2) 2 (2). Treatment of the in situ generated complex 1 with one equivalent of ROH (R = PhCH 2 , i Pr, CH 3 OCH 2 CH 2) produced the desired aluminium alkyloxide complexes L AlOCH 2 Ph (3), L Al(O i Pr) (4) and L AlO(CH 2) 2 OCH 3 (5). All the molecular structures were established by single crystal X-ray diffraction studies. It was found that aluminium alkyloxide complexes 3 - 5 showed higher catalytic activity for the homopolymerization of ε -caprolactone (ε- CL) than corresponding aluminium methyl complexes 1 and 2. Furthermore, these alkyloxide complexes were also efficient initiators for the copolymerization of L -lactide and ε -CL to give practically random copolymers. Several aluminium alkyl and alkyloxide complexes supported by a thioether-bridged salen ligand were synthesized and characterized. The aluminium alkoxide complexes could serve as efficient initiators for the ε -caprolactone homopolymerization and copolymerization wth L - lactide. [Display omitted] [ABSTRACT FROM AUTHOR]