Salt additives as activity boosters: a simple strategy to access heterometallic cooperativity in lactide polymerisation

Salt addition to homometallic initiators gives similar catalyst enhancements to isolated heterometallic complexes, resulting in exceptional activities in lactide polymerisation.

MIXED-LIGAND HETEROMETALLIC COMPLEXES OF Ge(IV)-M2+ (Mn, Fe, Co, Ni, Zn) WITH 1,3-DIAMINO-2-HYDROXYPROPANE N,N,N',N'-TETRAACETIC ACID

There have been developed a novel synthetic method that allowed to obtain raw of mixed-ligand heterometallic binuclear complexes of Ge(IV)-M2+ (Mn, Fe, Co, Ni, Zn) with 1,3-diamino‑2-hydroxypropane N, N, N’, N’-tetraacetic acid (H5hpdta). Compounds have been characterized by the set of methods: elemental analysis, thermogravimetry, IR‑spectroscopy, spectrum of diffuse reflection, magnetic suspensibility. According to the elemental analysis, the molar ratio Ge: M: H5hpdta: bipy= 1:1:1:1 in the obtained compounds 1‑5 corresponds to the formula [(H2O)(OH)Ge(m-hpdta)M(bipy)]·nН2О (M=Mn n=3 (1), Fe n=2 (2), Co n=4 (3), Ni n=4 (4), Zn n=3 (5). Complexes have yellow (1), red (2), orange (3), violet (4) and pink (5) colors and are stable on air. Compounds 1‑5 exist in the form of crystal hydrates, that contain certain amount of water molecules, that are eliminated into the gas phase while heating in the wide range of temperatures (t=80‑250 °C), which is accompanied with the low-temperature endothermic effect. This indicates the presence of a system of stable hydrogen bonds in their crystal structure. Analysis of the IR‑spectra 1‑5 revealed that form and coordination of ligands is similar. Deprotonation of all carboxylic groups in the ligands (H5hpdta) and their bonding to germanium and d-metal is confirmed with the absence in the IR‑spectra 1‑5 absorption bands characteristic for the free СООН H5hpdta (1716 сm‑1) and nas(СОО-) і ns(СОО-) bands. Disappearance of the ν(С-OН)-1210 сm‑1 and appearance of the ν(С-O)alk., νas(Ge-O-M), νs(Ge-O- M) absorption band indicates that OH‑group of H5hpdta is deprotonated and performs bridging function. 2,2`-bipyridine bidentatly coordinates to the d-metal, binds to the O, N‑atoms of hpdta5- ligand and reaches coordination number 6. The last ligand plays the bringing role between Ge-dmetal, shows itself as ditopic, octadentate in total. According to the magnetic moments of 3, 4 and their diffuse reflection spectra, polyhedrons of Co (II), Ni (II) are octahedrons, which are realized due to the bidentate coordination of bipyridine and four bonds with nitrogen and oxygen of hpdta5-. Structure of heterometallic binuclear complexes 1‑5 is similar. Ligand hpdta5- shows itself as octadentate ditopic, all carboxylate groups monodentatly coordinate to metals, oxygen atom of the deprotonated OH‑group performs the bridging function.

Polyoxometalate-like structure of new potassium triphenylsiloxides: [K6(OSiPh3)6(C3H7OH)(H2O)]·2C6H5CH3 and [K6(OSiPh3)6(H2O)2]

The synthesis and structural characterization of two new potassium triphenylsiloxides, namely, aqua(propan-2-ol)hexakis(triphenylsilanolato)hexapotassium toluene disolvate, [K6(C18H15OSi)6(C3H8O)(H2O)]·2C7H8, and diaquahexakis(triphenylsilanolato)hexapotassium, [K6(C18H15OSi)6(H2O)2], are reported. Both compounds crystallize in the triclinic space group P-1. The structure in each case resembles an alkali metal polyoxometalate-like structure, in which electrostatic interactions are observed in the metal–oxygen core. Furthermore, both compounds also resemble a reverse micelles-like architecture, in which the hydrophilic core is enclosed in a hydrophobic shell. The cores of the complexes are flanked by hydrophobic aromatic rings derived from Ph3SiO− anions, where intramolecular π-interactions between the aromatic rings and potassium cations stabilize the cores of the crystals. Moreover, in both structures, the presence of hydrogen bonds is observed; until now, no crystal structures have been described containing K atoms and triphenylsiloxide molecules in which the presence of hydrogen bonds was confirmed. Thus, these coordination entities could be considered as attractive reagents for further synthetic protocols towards heterometallic complexes.