Selective C−O Bond Cleavage of Sugars with Hydrosilanes Catalyzed by Piers’ Borane Generated In Situ

Described herein is the selective reduction of sugars with hydrosilanes catalyzed by using Piers’ borane [(C₆F₅)₂BH] generated in situ. The hydrosilylative C−O bond cleavage of silyl‐protected mono‐ and disaccharides in the presence of a (C₆F₅)₂BH catalyst, generated in situ from (C₆F₅)₂BOH, takes place with excellent chemo‐ and regioselectivities to provide a range of polyols. A study of the substituent effects of sugars on the catalytic activity and selectivity revealed that the steric environment around the anomeric carbon (C1) is crucial.     

Neodymium(III) Complexes Capable of Multi‐Electron Redox Chemistry

A family of neodymium complexes featuring a redox‐active ligand in three different oxidation states has been synthesized, including the iminoquinone (L⁰) derivative, (^dippiq)₂NdI₃ ( 1‐iq ), the iminosemiquinone (L¹⁻) compound, (^dippisq)₂NdI(THF) ( 1‐isq ), and the amidophenolate (L²⁻) [K(THF)₂][(^dippap)₂Nd(THF)₂] ( 1‐ap ) and [K(18‐crown‐6)][(^dippap)₂Nd(THF)₂] ( 1‐ap crown ) species. Full spectroscopic and structural characterization of each derivative established the +3 neodymium oxidation state with redox chemistry occurring at the ligand rather than the neodymium center. Oxidation with elemental chalcogens showed the reversible nature of the ligand‐mediated reduction process, forming the iminosemiquinone metallocycles, [K(18‐crown‐6)][(^dippisq)₂Nd(S₅)] ( 2‐isq crown ) and [K(18‐crown‐6)(THF)][(^dippisq)₂Nd(Se₅)] ( 3‐isq crown ), which are characterized to contain a 6‐membered twist‐boat ring.     

Catalytic Reduction of Alkyl and Aryl Bromides Using Propan‐2‐ol

Milstein's complex, (PNN)RuHCl(CO), catalyzes the efficient reduction of aryl and alkyl halides under relatively mild conditions by using propan‐2‐ol and a base. Sterically hindered tertiary and neopentyl substrates are reduced efficiently, as well as more functionalized aryl and alkyl bromides. The reduction process is proposed to occur by radical abstraction/hydrodehalogenation steps at ruthenium. Our research represents a safer and more sustainable alternative to typical silane, lithium aluminium hydride, and tin‐based conditions for these reductions.