β-Boration of α,β-unsaturated carbonyl compounds in ethanol and methanol catalyzed by CCC-NHC pincer Rh complexes

CCC-NHC Au(iii) pincer complexes as a reliable platform for isolating elusive species

The reactivity of unprecedented CCC-NHC Au(iii) pincer complexes has been investigated, employing a novel methodology for their preparation. Notably, this marks the inaugural case of CCC-NHC Au(iii) pincer complexes with a central aryl moiety where the two arms of the pincer ligand consist of N-heterocyclic carbenes (NHC). The stability conferred by the CCC-NHC ligand facilitated the isolation of elusive Au(iii) species, encompassing Au(iii)-formate, Au(iii)-F, Au(iii)-Me, and Au(iii)-alkynyl. Our study also unveiled the elusive Au(iii)-H species, offering valuable insights into its formation, stability, and reactivity. While the CCC-NHC Au(iii)-H complex remains stable at room temperature, its decomposition becomes conspicuous at elevated temperatures (>60 °C), exhibiting a more pronounced tendency under acidic conditions compared to basic ones. Through comprehensive experiments, we indirectly demonstrated the potential of Au(iii)-formate to undergo β-hydride elimination, becoming a key step in the dehydrogenation of formic acid. Theoretical calculations revealed variations in the reactivity of Au(iii)-H species towards sodium hydride and formic acid, highlighting a link between σ-donation from the pincer ligand and reaction energetics. Pincers with lower electron donation favored the reaction with sodium hydride but impeded the reaction with formic acid, whereas those with higher electron donation exhibited the opposite behavior. Additionally, the CCC-NHC Au(iii) pincer complex exhibited Lewis acid behavior, catalyzing the synthesis of phenols. In summary, the CCC-NHC Au(iii) pincer complex emerges as a versatile platform for isolating reactive species and unraveling elementary catalytic steps.

Development of Methods to the Synthesis of β-Boryl Acyls, Imines and Nitriles

Organoboron compounds are highly important and versatile synthetic intermediates for the preparation of a wide range of organic molecules. Organoboron compounds have drawn significant attention among organic chemists due to their Lewis acidic property, non-toxicity, and commercial availability. Over the last several decades, there has been a substantial development of new organoboron compounds, useful in organic synthesis. Among all other organoboron compounds, β-boryl carbonyl compounds are the important ones. The β-boryl compounds have appeared as promising intermediates for various synthetic transformations. The 1,4-conjugate addition of diboron reagents to carbon-carbon double bond in the presence of different transition-metal catalysts has been extensively reported by various research groups across the globe. This mini-review outlines the numerous racemic as well as asymmetric β-borylation methods developed to date.

High-Loading Single-Atom Copper Catalyst Supported on Coordinatively Unsaturated Al2 O3 for Selective Synthesis of Homoallylboronates

Single-atom catalysts (SACs) as a bridge between hetero- and homogeneous catalysis have attracted much attention. However, it is still challenging to generate stable single atoms with high metal loadings, and the application of SACs in traditionally homogeneous catalytic reactions is highly desirable. Herein, a Cu SAC with a high Cu loading of 8.7 wt % supported on coordinatively unsaturated Al₂ O₃ was prepared and used in the amine-free synthesis of homoallylboranes. Up to 99 % conversion, 95 % 1,4-selective boration of the enals, and 48-68 % isolated yields of homoallylboranes were achieved, equaling the results of reported homogenous catalysts, and the system was more efficient and stable than nano Cu/γ-Al₂ O₃ . Mechanistic investigation indicated that Cu-Bpin species are the active intermediates of selective boration. The superior catalytic and recycling performance of Cu SAC paves an efficient and green path toward selective synthesis of homoallyborane fine chemicals.

β-Borylation of conjugated carbonyl compounds with silylborane or bis(pinacolato)diboron catalyzed by Au nanoparticles

β-Borylation occurs in the Au/TiO₂-catalysed reaction between the silylborane Me₂PhSiBpin and conjugated carbonyl compounds, in contrast to the so far known analogous reaction catalysed by other metals, where β-silylation occurs instead.

An NHC-CuCl functionalized metal-organic framework for catalyzing β-boration of α,β-unsaturated carbonyl compounds

A microporous metal-organic framework functionalized with in situ generated NHC-CuCl units (1) has been successfully synthesized from a novel imidazolium-containing ligand. In particular, the MOF 1 can catalyze β-boration of α,β-unsaturated carbonyl compounds, while the isoreticular version of 1 (1-im) modified with only imidazolium moiety cannot. This work demonstrates for the first time the heterogeneous catalysis of NHC-Cu(i)Cl within a MOF solid.

Diboron(4) Compounds: From Structural Curiosity to Synthetic Workhorse

Although known for over 90 years, only in the past two decades has the chemistry of diboron(4) compounds been extensively explored. Many interesting structural features and reaction patterns have emerged, and more importantly, these compounds now feature prominently in both metal-catalyzed and metal-free methodologies for the formation of B-C bonds and other processes.

Transmetallation from CCC-NHC pincer Zr complexes in the synthesis of air-stable CCC-NHC pincer Co(iii) complexes and initial hydroboration trials

Development of CCC-NHC pincer Co complexes via transmetalation from Zr is reported. Formation of these air-stable Co(iii) complexes was achieved through use of a CoCl2 or Co(acac)3in situ or with a discrete CCC-NHC pincer Zr transmetallating agent. Preliminary activity in the hydroboration of styrene is reported. This facile methodology will further the development of CCC-NHC pincer first-row transition metal complexes.

Metal complexes with di(N-heterocyclic carbene) ligands bearing a rigid ortho-, meta or para-phenylene bridge

Ag(i) complexes with diNHC ligands are efficient transmetalating agents towards transition metals.