Nucleophilicity of Neutral versus Cationic Magnesium Silyl Compounds

Charge and ancillary ligands affect the reactivity of monomeric tris(trimethylsilyl)silyl magnesium compounds. Diamine-coordinated (tmeda)Mg{Si(SiMe3)3}Me (tmeda = tetramethylethylenediamine; 2-tmeda) and (dpe)Mg{Si(SiMe3)3}Me (dpe =1,2-N,N-dipyrrolidenylethane; 2-dpe) are synthesized by salt elimination reactions of L2MgMeBr and KSi(SiMe3)3. Compounds 2-tmeda or 2-dpe react with MeI or MeOTf to give MeSi(SiMe3)3 as the product of Si–C bond formation. In contrast, 2-tmeda and 2-dpe undergo exclusively reaction at the magnesium methyl group with electrophiles such as Me3SiI, B(C6F5)3, HB(C6F5)2, and [Ph3C][B(C6F5)4]. These reactions provide a series of neutral, zwitterionic, and cationic magnesium silyl compounds, and from this series we have found that silyl group transfer is less effective with cationic magnesium compounds than neutral complexes

Enantiopure Isotactic PCHC Synthesized by Ring-Opening Polymerization of Cyclohexene Carbonate

International audienceThe ring-opening polymerization (ROP) of racemic trans-cyclohexene carbonate (rac-CHC) and enantiopure trans-(R,R)-CHC is successfully carried out with various catalyst systems. Poly(cyclohexene carbonate) (PCHC) with a slight isotactic bias (Pm = ca. 60–76%) is obtained by ROP of rac-CHC catalyzed by zinc diaminophenolate, zinc β-diketiminate, yttrium bis(phenolate), or 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) in combination with an alcohol as a co-initiator. Purely isotactic PCHC is synthesized for the first time via ROP of enantiopure (R,R)-CHC with a zinc/benzyl alcohol catalyst system. All reactions proceed without decarboxylation, affording well-defined PCHCs with Mn,NMR up to 17 000 g mol–1 and ĐM = ca. 1.2. Purely isotactic PCHC is semicrystalline, with Tg = 130 °C, Tc = 162 °C, and Tm = 248 °C. DFT computations further highlight the significant favorable impact of the trans-cyclohexane ring-strain to enable the ROP of CHC, as opposed to meso-CHC which is unreactive