Interconverting Lanthanum Hydride and Borohydride Catalysts for C=O Reduction and C−O Bond Cleavage

Grignard Reagent-Catalyzed Hydroboration of Esters, Nitriles, and Imines

The reduction in esters, nitriles, and imines requires harsh conditions (highly reactive reagents, high temperatures, and pressures) or complex metal-ligand catalytic systems. Catalysts comprising earth-abundant and less toxic elements are desirable from the perspective of green chemistry. In this study, we developed a green hydroboration protocol for the reduction in esters, nitriles, and imines at room temperature (25 °C) using pinacolborane as the reducing agent and a commercially available Grignard reagent as the catalyst. Screening of various alkyl magnesium halides revealed MeMgCl as the optimal catalyst for the reduction. The hydroboration and subsequent hydrolysis of various esters yielded corresponding alcohols over a short reaction time (~0.5 h). The hydroboration of nitriles and imines produced various primary and secondary amines in excellent yields. Chemoselective reduction and density functional theory calculations are also performed. The proposed green hydroboration protocol eliminates the requirements for complex ligand systems and elevated temperatures, providing an effective method for the reduction in esters, nitriles, and imines at room temperature.

t BuOLi-Promoted Hydroboration of Esters and Epoxides

Commercially available and inexpensive lithium tert-butoxide ( ^t BuOLi) acts as a good precatalyst for the hydroboration of esters, lactones, and epoxides using pinacolborane as a borylation agent. Functional groups such as cyano-, nitro-, amino-, vinyl, and alkynyl are unaffected under the presented hydroboration process, representing high chemoselectivity. This transformation has also been effectively applied to the synthesis of key intermediates of Erlotinib and Cinacalcet. Preliminary investigations of the mechanism show that the hydroboration proceeds through the in situ formed BH₃ species.

Supported Lanthanum Borohydride Catalyzes CH Borylation Inside Zeolite Micropores

The zeolite‐supported lanthanide La(BH₄)_x‐HY₃₀ catalyzes C−H borylation of benzene with pinacolborane (HBpin), providing a complementary approach to precious, late transition metal‐catalyzed borylations. The reactive catalytic species are generated from La grafted at the Brønsted acid sites (BAS) in micropores of the zeolite, whereas silanoate‐ and aluminoate‐grafted sites are inactive under the reaction conditions. During typical catalytic borylations, conversion to phenyl pinacolborane (PhBpin) is zero‐order in HBpin concentration. A turnover number (TON) of 167 is accessed by capping external silanols, selectively grafting at BAS sites, and adding HBpin slowly to the reaction.

Rh-Catalyzed Coupling of Aldehydes with Allylboronates Enables Facile Access to Ketones

We present herein a novel strategy for the preparation of ketones from aldehydes and allylic boronicesters. This reaction involves the allylation of aldehydes with allylic boronicesters and the Rh-catalyzed chain-walking of homoallylic alcohols. The key to this successful development is the protodeboronation of alkenyl borylether intermediate via a tetravalent borate anion species in the presence of KHF 2 and MeOH. This approach features mild reaction conditions, broad substrate scope, and excellent functional group tolerance. Mechanistic studies also supported that the tandem allylation and chain-walking process was involved.

Recent advances in the carbon-phosphorus (C-P) bond formation from unsaturated compounds by s- and p-block metals

Researchers around the globe have witnessed several breakthroughs in s- and p-block metal chemistry. Over the past few years, several applications in catalysis associated with these main group metals have been established, and owing to their abundance and low cost and they have proved to be essential alternatives to transition metal catalysts. In this review, we present a detailed discussion on the catalytic addition of P-H bonds from various phosphine reagents to multiple bonds of unsaturated substrates for the synthesis of organophosphorus compounds with C-P bonds promoted by various s- and p-block metal catalysts, as published in the last decade.

Manganese-Catalyzed Hydroborations with Broad Scope

Reductive transformations of easily available oxidized matter are at the heart of synthetic manipulation and chemical valorization. The applications of catalytic hydrofunctionalization benefit from the use of liquid reducing agents and operationally facile setups. Metal‐catalyzed hydroborations provide a highly prolific platform for reductive valorizations of stable C=X electrophiles. Here, we report an especially facile, broad‐scope reduction of various functions including carbonyls, carboxylates, pyridines, carbodiimides, and carbonates under very mild conditions with the inexpensive pre‐catalyst Mn(hmds)₂. The reaction could be successfully applied to depolymerizations.

Trivalent Rare-Earth Metal Amide Complexes as Catalysts for the Hydrosilylation of Benzophenone Derivatives with HN(SiHMe2 )2 by Amine-Exchange Reaction

The rare-earth metal complexes Ln(L1 )[N(SiHMe2 )2 ](thf) (Ln=La, Ce, Y; L1 =N,N''-bis(pentafluorophenyl)diethylenetriamine dianion) were synthesized by treating Ln[N(SiHMe2 )2 ]3 (thf)2 with L1 H2 . The lanthanum and cerium derivatives are active catalysts for the hydrosilylation of benzophenone derivatives with HN(SiHMe2 )2 . An amine-exchange reaction was revealed as a key step of the catalytic cycle, in which Ln-Si-H β-agostic interactions are proposed to promote insertion of the carbonyl moiety into the Si-H bond.