Transition Metal-Mimicking Relay Catalysis by a Low-Valent Phosphorus Compound.

Low-valent main group species have been evolving as powerful alternatives to transition metals over the years due to their advantages such as low toxicity and high abundance. However, the inability of main group elements to mimic the redox-switching property of transition metals often limits their role as catalysts. Here, we demonstrate the use of a low-valent phosphorus(I) compound as an efficient metal-free catalyst for the synthesis of biologically relevant γ-butyrolactones through dual activation under ambient reaction conditions.

Bicyclic (alkyl)(amino)carbene (BICAAC) in a dual role: activation of primary amides and CO towards catalytic -methylation.

Herein, we report the first catalytic methylation of primary amides using CO as a C1 source. A bicyclic (alkyl)(amino)carbene (BICAAC) exhibits dual role by activating both primary amide and CO to carry out this catalytic transformation which enables the formation of a new C-N bond in the presence of pinacolborane. This protocol was applicable to a wide range of substrate scopes, including aromatic, heteroaromatic, and aliphatic amides.

Regioselective ring-opening of epoxides towards Markovnikov alcohols: a metal-free catalytic approach using abnormal N-heterocyclic carbene.

Herein we report the first metal-free regioselective Markovnikov ring-opening of epoxides (selectivity up to 99%) using an abnormal N-heterocyclic carbene (aNHC) to yield secondary alcohols. DFT calculations and X-ray crystallography suggest that the Markovnikov selectivity originates from the high nucleophilicity and steric factors associated with the aNHC.

Bicyclic (alkyl)(amino)carbene (BICAAC) as a metal-free catalyst for reduction of nitriles to amines.

Bicyclic (alkyl)(amino)carbene (BICAAC) is introduced as a metal-free catalyst for the reduction of various nitriles to the corresponding amine hydrochloride salts in the presence of pinacolborane. Mechanistic investigations combining experiments and DFT calculations suggest a B-H addition to the carbene center, which acts as a carrier of the hydride source.

From CO activation to catalytic reduction: a metal-free approach.

Over exploitation of natural resources and human activities are relentlessly fueling the emission of CO in the atmosphere. Accordingly, continuous efforts are required to find solutions to address the issue of excessive CO emission and its potential effects on climate change. It is imperative that the world looks towards a portfolio of carbon mitigation solutions, rather than a single strategy.

An NHC-Stabilised Phosphinidene for Catalytic Formylation: A DFT-Guided Approach.

In recent years, the applications of low-valent main group compounds have gained momentum in the field of catalysis. Owing to the accessibility of two lone pairs of electrons, NHC-stabilised phosphinidenes have been found to be excellent Lewis bases; however, they cannot yet be used as catalysts. Herein, an NHC-stabilised phosphinidene, 1,3-dimethyl-2-(phenylphosphanylidene)-2,3-dihydro-1H imidazole (1), for the activation of CO is reported.

Effects of Linkers on the Development of Liposomal Formulation of Cholesterol Conjugated Cobalt Bis(dicarbollides).

Boron neutron capture therapy (BNCT) remains an important treatment arm for cancer patients with locally invasive malignant tumors. This therapy needs a significant amount of boron to deposit in cancer tissues selectively, sparing other healthy organs. Most of the liposomes contain water-soluble polyhedral boron salts stay in the core of the liposomes and have low encapsulation efficiency.

Boron-Containing Lipids and Liposomes: New Conjugates of Cholesterol with Polyhedral Boron Hydrides.

A series of boron-containing lipids were prepared by reactions of cyclic oxonium derivatives of polyhedron boranes and metallacarboranes (closo-dodecaborate anion, cobalt and iron bis(dicarbollides)) with amine and carboxylic acids which are derived from cholesterol. Stable liposomal formulations, on the basis of synthesized boron-containing lipids, hydrogenated soybean l-α-phosphatidylcholine and (HSPC) 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)-2000] (DSPE-PEG) as excipients, were prepared and then characterized by dynamic light scattering (DLS) that revealed the formation of particles to be smaller than 200 nm in diameter. The resulting liposomal formulations showed moderate to excellent loading and entrapment efficiency, thus justifying the design of the compounds to fit in the lipid bilayer and ensuring ease of in vivo use for future application.

Transition metal-free catalytic reduction of primary amides using an abnormal NHC based potassium complex: integrating nucleophilicity with Lewis acidic activation.

An abnormal N-heterocyclic carbene (aNHC) based potassium complex was used as a transition metal-free catalyst for reduction of primary amides to corresponding primary amines under ambient conditions. Only 2 mol% loading of the catalyst exhibits a broad substrate scope including aromatic, aliphatic and heterocyclic primary amides with excellent functional group tolerance. This method was applicable for reduction of chiral amides and utilized for the synthesis of pharmaceutically valuable precursors on a gram scale.

Halo-Bridged Abnormal NHC Palladium(II) Dimer for Catalytic Dehydrogenative Cross-Coupling Reactions of Heteroarenes.

This work describes the dehydrogenative coupling of heteroarenes using a dimeric halo-bridged palladium(II) catalyst bearing an abnormal NHC ( aNHC) backbone. The catalyst can successfully activate the C-H bond of a wide range of heteroarenes, which include benzothiazole, benzoxazole, thiophene, furan, and N-methylbenzimidazole. Further, it exhibited good activity for heteroarenes bearing various functional groups such as CN, CHO, Me, OMe, OAc, and Cl.

Integrating Organic Lewis Acid and Redox Catalysis: The Phenalenyl Cation in Dual Role.

In recent years, merging different types of catalysis in a single pot has drawn considerable attention and these catalytic processes have mainly relied upon metals. However, development of a completely metal free approach integrating organic redox and organic Lewis acidic property into a single system has been missing in the current literature. This study establishes that a redox active phenalenyl cation can activate one of the substrates by single electron transfer process while the same can activate the other substrate by a donor-acceptor type interaction using its Lewis acidity.

A new face of phenalenyl-based radicals in the transition metal-free C-H arylation of heteroarenes at room temperature: trapping the radical initiator C-C σ-bond formation.

The radical-mediated transition metal-free approach for the direct C-H bond functionalization of arenes is considered as a cost effective alternative to transition metal-based catalysis. An organic ligand-based radical plays a key role by generating an aryl radical which undergoes a subsequent functionalization process. The design principle of the present study takes advantage of a relatively stable odd alternant hydrocarbon-based phenalenyl (PLY) radical.