Yttrium and aluminium complexes of two dithiodiolate ligands that feature different bridges (CF3)2C(OH)CH2SRSCH2C(OH)(CF3)2 (L(1)-H2, R = CH2CH2 and L(2)-H2, R = C6H4) were synthesized in good yields by reacting tris(silylamide)yttrium or trimethylaluminium with one equivalent of the proligand. All complexes were characterized by NMR and elemental analysis, and single-crystal X-ray structural analysis was also performed for one of the yttrium complexes. The catalytic activities of the four complexes in the ring-opening polymerization of ε-caprolactone and rac-lactide have been investigated. Furthermore, DOSY experiment and DFT calculations have been carried out to determine the structure of the isopropoxo derivative of the complex L(2)Y amide.

The coordination chemistry of chiral tetradentate dianionic ligands of the diamine-diphenolato and diamine-diolato families having the (R,R)-2,2-bipyrrolidine core around ZnII was investigated. Reactions with diethylzinc led to complexes of the type [{ONNO}Zn] for most ligands and to bridging dinuclear complexes of the type [-Lig4(ZnEt)2] for one of the diamine-diolato ligands. Reactions with bis(hexamethyldisilazide)zinc led to complete conversions. Most complexes were obtained as mononuclear complexes. The least bulky Salan ligand, Lig3, led to an equilibrium between mononuclear and dinuclear complexes in noncoordinating solvents. All ligands were found to wrap around the tetrahedral zinc with very high diastereoselectivities supporting predetermined chiral induction from the bipyrrolidine core to the helical ligand wrapping. Molecular structures determined by single-crystal X-ray diffraction for two complexes of the type [{ONNO}Zn] substantiated the predicted wrapping of the (R,R)-based ligands. In contrast, representative Salan and diamine-diolato ligands assembled around the trans-1,2-diaminocyclohexane core led to diastereomer mixtures of the corresponding complexes.

Dithiodiolate ligands were synthesized by reacting 1,2-ethanedithiol or 1,2-benzenedithiol with 2,2-bis(trifluoromethyl)oxirane, led selectively to mononuclear octahedral group 4 complexes of the type [{OSSO}M(OR)(2)], which features C(2) symmetry and fluxional behavior, and were highly active in the ring-opening polymerization of rac- and L-lactide.

The synthesis of chiral tetradentate dianionic diamine-diolate ligands assembled around either N,N'-dimethyl-trans-1,2-diaminocyclohexane or 2,2'-bipyrrolidine is described. These ligands wrap in a fac-fac helical mode around octahedral titanium and zirconium centers giving chiral-at-metal complexes. Diaminocyclohexane was found to be a poor chiral motif for diastereoselective helical wrapping, and all complexes of this family were obtained as mixtures of stereoisomers. In contrast, bipyrrolidine was found to be a perfect chiral motif for helical wrapping, and the corresponding diamine-diolate complexes were obtained as (enantiomerically pure) single diastereomers.

The first synthesis of Salan ligands assembled around the chiral 2,2'-bipyrrolidine backbone is described; as chelation to a metal can only occur via specific faces of the two pyrrolidine nitrogens, these ligands lead to predetermined chirality at metal centres of octahedral titanium and zirconium complexes.

The coordination chemistry of three tripodal monoanionic amine mono(phenolate) ligands bearing two methoxy side-arm donors with ethylzinc(II) is reported. Reacting diethyl-zinc with the ligand precursor bearing bulky (tBu) phenolate substituents led cleanly to a mono(ethyl) mononuclear C-s-symmetric zinc complex according to spectroscopic data. Xray structure analysis revealed a semi-pentacoordinate complex as one of the methoxy sidearm donors was tightly bound whereas the other one was weakly bound. The ligand precursors bearing less bulky electron-donating (Me) or electron-withdrawing (Br) phenolate substituents led cleanly to dinuclear pentacoordinate complexes, bridged by phenolate oxygens, in which only one of the two sidearm donors was bound, and in a weak manner. (c) Wiley-VCH Verlag GmbH & Co.

AbstractThe cover picture shows the two types of complexes formed by the reaction of diethylzinc and tripodal monoanionic amine mono(phenolate) ligand precursors bearing two methoxy sidearm donors. The ligand precursor bearing bulky (tBu) phenolate substituents leads cleanly to a mono(ethyl) mononuclear zinc complex in which the two methoxy sidearm donors are bound to the metal atom as confirmed by spectroscopic data and X‐ray structure analysis. The ligand precursors bearing less bulky phenolate substituents lead cleanly to dinuclear pentacoordinate complexes that are bridged by phenolate oxygen atoms, and only one of the two sidearm donors is bound. Details are discussed in the article by M. Kol et al. on p. 2739 ff.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An amine mono(phenolate) ligand bearing two side-arm donors led to octahedral trialkoxo and trialkyl group IV metal complexes, in which one of the donors was unbound, and to exceptionally stable cationic complexes in which the two side-arm donors were tightly bound.

The coordination chemistry of tetradentate Salophan ligands with titanium and zirconium alkoxides is described for the first time. Three new Salophan ligand precursors featuring different phenolate substituents (ortho-Me, ortho,para-di-Cl, ortho,para-di-tBu) were synthesized in addition to the known prototypical Salophan precursor, by a sequence of condensation and reduction. All ligand precursors were reacted with the metal alkoxides Ti(OiPr)(4) and Zr(OiBu)(4). The unsubstituted Salophan led to a complex product mixture for both titanium and zirconium. The methyl-substituted ligand led to a clean complex only with zirconium, and the other ligands gave well-defined coordination chemistry with both metals. NMR analysis indicated that these Salophans acted as dianionic ligands, giving rise to hexa-coordinate complexes of C-2-symmetry. X-ray analysis of three complexes supported this view, and revealed that the ligands wrapping mode was fac-fac and that the orientation of the labile groups was cis. A partial hydrolysis of one of the titanium complexes led to a dinuclear bridging oxo complex in which the ligand wrapping mode had changed to fac-mer, as revealed from its crystal structure.

Poly(lactic acid) (PLA), a biodegradable polymer derived from bio-renewable resources is synthesized by the catalyzed ring opening polymerization (ROP) of lactide. Traditionally employed homoleptic complexes catalyze the polymerization of rac-lactide to give stereoirregular polymers, however, catalysts introduced in the last decade that include metal complexes of polydentate ligands enabled the synthesis of stereoregular PLA from raclactide. In comparison to other metals, group 4 metal complexes are relatively less explored in lactide polymerization catalysis. In the few cases that had been described, the complexes of the heavier triad members were found to be more active than the corresponding Ti-complex.