Supramolecular bulky phosphines comprising 1,3,5-triaza-7-phosphaadamantane and Zn(salphen)s: structural features and application in hydrosilylation catalysis

International audienceThe use of the commercially available, bifunctional phosphine 1,3,5-triaza-7-phosphaadamantane (abbreviated as PN 3) in conjunction with a series of Zn(salphen) complexes leads to sterically encumbered phosphine ligands as a result of (reversible) coordinative Zn–N interactions. The solid state and solution phase behaviour of these supramolecular ligand systems have been investigated in detail and revealed their stoichiometries in the solid state observed by X-ray crystallography, and those determined in solution by NMR and UV-Vis spectroscopy. Also, upon application of these supramolecular bulky phosphines in hydrosilylation catalysis employing 1-hexene as a substrate, the catalysis data infer the presence of an active Rh species with two coordinated, bulky PN 3 /Zn(salphen) assembly units having a maximum of three Zn(salphen)s associated per PN 3 scaffold, with an excess of bulky phosphines hardly affecting the overall activity

Mild formation of cyclic carbonates using Zn(II) complexes based on N2S2-chelating ligands

We have prepared a series of Zn(II) complexes (1-3) based on a versatile N2S2-chelating ligand abbreviated as btsc [btsc = bis-(thiosemicarbazonato)] derived from simple and accessible building blocks. These complexes comprise a Lewis acidic Zn(II) center useful for substrate activation, and we have investigated the potential of these compounds in the cyclo-addition reaction of carbon dioxide to various epoxides yielding cyclic carbonate structures. Initial screening studies with complexes 1-3 showed that complex 3 is most suited for this CO2 fixation reaction under particularly mild conditions (45 °C, pCO2 = 10 bar) and low catalyst loadings (1 mol%). Furthermore, upon examination of the substrate scope, complex 3 shows appreciable catalytic turnover for a range of terminal epoxides, while for the sterically more challenging epoxides almost no conversion was achieved under comparable conditions. Additional experiments indicated that higher yields of cyclic carbonates may be realized by simply increasing the (co)catalyst loading up to 3%, while maintaining mild reaction conditions. The use of a relatively non-toxic and abundant metal and an environmentally benign solvent system (MEK, methyl ethyl ketone) mark this protocol as an attractive way for organic carbonate production