High H Solubility of Perfluorocarbon Solvents and Their Use in Reversible Polarization Transfer from -Hydrogen.

This research uses perfluorocarbons (PFCs) as effective alternatives to traditional toxic solvents in reversible -hydrogen-induced polarization (PHIP) for NMR signal enhancement. Hydrogen solubility in PFCs is shown here to be an order of magnitude higher than in typical organic solvents by determination of Henry's constants. We demonstrate how this high H solubility enables the PFCs to deliver substantial polarization transfer from -hydrogen, achieving up to 2400-fold signal gains for H NMR detection and 67,000-fold (22% polarization) for N NMR detection at 9.

Solid/Gas Reactivity of an Ir(I) Methylidene Complex.

stabilization of known, but solution unstable, methylidene complex [Ir(Bu-PONOP)(=CH)][BAr ] allows single-crystal to single-crystal solid/gas reactivity associated with the {Ir=CH} group to be studied. Addition of H results in [Ir(Bu-PONOP)(H)][BAr ]; exposure to CO forms iridium(I) carbonyl [Ir(Bu-PONOP)(CO)][BAr ], and reaction with NH gas results in the formation of methylamine complex [(Bu-PONOP)Ir(NHMe)][BAr ] via an aminocarbene intermediate. Periodic density functional theory and electronic structure analyses confirm the Ir=CH bond character but with a very low barrier to rotation around the Ir=CH bond.

The ubiquitous P(-tol) ligand promotes formation of catalytically-active higher order palladacyclic clusters.

The Herrmann-Beller catalyst, Pd[(C^P)(μ-OAc)], is readily formed by reaction of the cyclic trimer of 'Pd(OAc)' with P(-tol). In the presence of hydroxide, Pd(C^P)(μ-OAc)] converts to [Pd(C^P)(μ -OH)]. Here, we report how this activated Pd precatalyst species, and related species, serve as a conduit for formation of higher order Pd clusters containing multiple cyclopalladated P(-tol) ligands.

Ligand-to-metal charge transfer facilitates photocatalytic oxygen atom transfer (OAT) with -dioxo molybdenum(vi)-Schiff base complexes.

Systems incorporating the -Mo(O) motif catalyse a range of important thermal homogeneous and heterogeneous oxygen atom transfer (OAT) reactions spanning biological oxidations to platform chemical synthesis. Analogous light-driven processes could offer a more sustainable approach. The -Mo(O) complexes reported here photocatalyse OAT under visible light irradiation, and operate a non-emissive excited state with substantial ligand-to-metal charge-transfer (LMCT) character, in which a Mo[double bond, length as m-dash]O π*-orbital is populated transfer of electron density from a chromophoric salicylidene-aminophenol (SAP) ligand.

Revealing the Hidden Complexity and Reactivity of Palladacyclic Precatalysts: The P(-tolyl) Ligand Enables a Cocktail of Active Species Utilizing the Pd(II)/Pd(IV) and Pd(0)/Pd(II) Pathways for Efficient Catalysis.

The ligand, P(-tolyl), is ubiquitous in applied synthetic chemistry and catalysis, particularly in Pd-catalyzed processes, which typically include Pd(OAc) (most commonly used as Pd(OAc)) as a precatalyst. The Herrmann-Beller palladacycle [Pd(C^P)(μ-OAc)] (where C^P = monocyclopalladated P(-tolyl)) is easily formed from reaction of Pd(OAc) with P(-tolyl). The mechanisms by which this precatalyst system operates are inherently complex, with studies previously implicating Pd nanoparticles (PdNPs) as reservoirs for active Pd species in arylative cross-coupling reactions.

Pyrazine-bridged polymetallic copper-iridium clusters.

Single crystals of the mol-ecular compound, {CuIrCl(CHN)(CHN)]·3.18CHOH or [({CuIr}Cl(IMes)(pyrazine))(pyrazine)]·3.18CHOH [where IMes is 1,3-bis-(2,4,6-trimethylphen-yl)imidazol-2-yl-idene], with a unique heterometallic cluster have been prepared and the structure revealed using single-crystal X-ray diffraction.

Deciphering complexity in Pd-catalyzed cross-couplings.

Understanding complex reaction systems is critical in chemistry. While synthetic methods for selective formation of products are sought after, oftentimes it is the full reaction signature, i.e.

Stereoselective synthesis of an advanced -decalin intermediate towards the total synthesis of anthracimycin.

Progress towards the total synthesis of the macrolide natural product anthracimycin is described. This new approach utilises an intermolecular Diels-Alder strategy followed by epimeirsation to form the key -decalin framework. The route culminates in the stereoselective synthesis of an advanced tricyclic lactone intermediate, containing five contiguous sterogenic centres with the correct relative and absolute stereochemistry required for the anthracimycin core motif.

Gold(III), Mercury(II), and Palladium(II) Complexes of a Series of Isomeric Bis(mono- and dialkoxyphenyl)pyridines: Introduction of Gold through Transmetalation and Catalysis.

A series of isomeric bis-2,6-(monoalkoxyphenyl)pyridine and bis-2,6-(dialkoxyphenyl)pyridine ligands were synthesized and characterized. In order to prepare their chlorogold(III) complexes, intermediate chloromercury(II) complexes were first prepared, but unlike observations from previous studies where they were obtained impure and at best in moderate yield, here pure complexes were synthesized, many in rather high yields. Depending on the substitution pattern of the alkoxy chains on the ligands, mono- and/or dimercurated complexes were obtained, characterized by H, C{H}, and Hg NMR spectroscopy as well as, in several cases, by X-ray crystallography.

Correction: On the mercuration, palladation, transmetalation and direct auration of a C^N^C pincer ligand.

Correction for 'On the mercuration, palladation, transmetalation and direct auration of a C^N^C pincer ligand' by Alice Jane McEllin , , 2023, , 872-876, https://doi.org/10.1039/d2dt04114f.

Expanding the scope of the successive ring expansion strategy for macrocycle and medium-sized ring synthesis: unreactive and reactive lactams.

New methods are described that expand the scope of the Successive Ring Expansion (SuRE) with respect to synthetically challenging lactams. A protocol has been developed for use with 'unreactive' lactams, enabling SuRE reactions to be performed on subsrates that fail under previously established conditions. Ring expansion is also demonstarted on 'reactive' lactams derived from iminosugars for the first time.

A Modular Strategy for the Synthesis of Macrocycles and Medium-Sized Rings via Cyclization/Ring Expansion Cascade Reactions.

Macrocycles and medium-sized rings are important in many scientific fields and technologies but are hard to make using current methods, especially on a large scale. Outlined herein is a strategy by which functionalized macrocycles and medium-sized rings can be prepared using cyclization/ring expansion (CRE) cascade reactions, without resorting to high dilution conditions. CRE cascade reactions are designed to operate exclusively via kinetically favorable 5-7-membered ring cyclization steps; this means that the problems typically associated with classical end-to-end macrocyclization reactions are avoided.

Effect of Ligand Substituents on Spectroscopic and Catalytic Properties of Water-Compatible Cp*Ir-(pyridinylmethyl)sulfonamide-Based Transfer Hydrogenation Catalysts.

Transition-metal-based hydrogenation catalysts have applications ranging from high-value chemical synthesis to medicinal chemistry. A series of (pyridinylmethyl)sulfonamide ligands substituted with electron-withdrawing and -donating groups were synthesized to study the influence of the electronic contribution of the bidentate ligand in Cp*Ir piano-stool complexes. A variable-temperature NMR investigation revealed a strong correlation between the electron-donating ability of the substituent and the rate of stereoinversion of the complexes.

Metal-Mediated Catalytic Polarization Transfer from Hydrogen to 3,5-Dihalogenated Pyridines.

The neutral catalysts [IrCl(H)(NHC)(substrate)] or [IrCl(H)(NHC)(substrate)(sulfoxide)] are used to transfer polarization from hydrogen (H) to 3,5-dichloropyridine and 3,5-dibromopyridine substrates. This is achieved in a rapid, reversible, and low-cost process that relies on ligand exchange within the active catalyst. Notably, the sulfoxide-containing catalyst systems produced NMR signal enhancements between 1 and 2 orders of magnitude larger than its unmodified counterpart.

Divergent Cascade Ring-Expansion Reactions of Acryloyl Imides.

Macrocyclic and medium-sized ring ketones, lactones and lactams can all be made from common acryloyl imide starting materials through divergent, one-pot cascade ring-expansion reactions. Following either conjugate addition with an amine or nitromethane, or osmium(VIII)-catalysed dihydoxylation, rearrangement through a four-atom ring expansion takes place spontaneously to form the ring expanded products. A second ring expansion can also be performed following a second iteration of imide formation and alkene functionalisation/ring expansion.

Mechanically Robust Hybrid Gel Beads Loaded with "Naked" Palladium Nanoparticles as Efficient, Reusable, and Sustainable Catalysts for the Suzuki-Miyaura Reaction.

The increase in demand for Pd and its low abundance pose a significant threat to its future availability, rendering research into more sustainable Pd-based technologies essential. Herein, we report Pd scavenging mechanically robust hybrid gel beads composed of agarose, a polymer gelator (PG), and an active low-molecular-weight gelator (LMWG) based on 1,3:2,4-dibenzylidenesorbitol (DBS), . The robustness of the PG and the ability of the LMWG to reduce Pd(II) to generate naked Pd(0) nanoparticles (PdNPs) combine within these gel beads to give them potential as practical catalysts for Suzuki-Miyaura cross-coupling reactions.

Ir(η-diene) precatalyst activation by strong bases: formation of an anionic Ir tetrahydride.

The reaction between [IrCl(COD)] and dppe in a 1 : 2 ratio was investigated in detail under three different conditions. [IrCl(COD)(dppe)], 1, is formed at room temperature in the absence of base. In the presence of a strong base at room temperature, hydride complexes that retain the carbocyclic ligand in the coordination sphere are generated.

Ring Expansion Strategies for the Synthesis of Medium Sized Ring and Macrocyclic Sulfonamides.

Two new ring expansion strategies are reported for the synthesis of medium sized ring and macrocyclic sulfonamides. Both methods can be performed without using classical protecting groups, with the key ring expansion step initiated by nitro reduction and amine conjugate addition respectively. Each method can be used to make diversely functionalised cyclic sulfonamides in good to excellent yields, in a range of ring sizes.

On the mercuration, palladation, transmetalation and direct auration of a C^N^C pincer ligand.

The C^N^C ligand 2,6-bis(2,3-dialkoxyphenyl)pyridine forms dimercury and orthopalladated complexes, both of which may be transmetallated to gold(III) complexes; the gold complexes may also be formed directly in a Rh(III)-catalysed process, hence it is possible to circumvent the use of organomercury intermediates in the synthesis of this important class of compound.

Coumarin C-H Functionalization by Mn(I) Carbonyls: Mechanistic Insight by Ultra-Fast IR Spectroscopic Analysis.

Mn(I) C-H functionalization of coumarins provides a versatile and practical method for the rapid assembly of fused polycyclic pyridinium-containing coumarins in a regioselective manner. The synthetic strategy enables application of bench-stable organomanganese reagents in both photochemical- and thermal-promoted reactions. The cyclomanganated intermediates, and global reaction system, provide an ideal testing ground for structural characterization of the active Mn(I) carbonyl-containing species, including transient species observable by ultra-fast time-resolved spectroscopic methods.

Enhancing the Air Stability of Dimolybdenum Paddlewheel Complexes: Redox Tuning through Fluorine Substituents.

The optical and electrochemical properties of quadruply bonded dimolybdenum paddlewheel complexes (MoPWCs) make them ideal candidates for incorporation into functional materials or devices, but one of the greatest bottlenecks for this is their poor stability toward atmospheric oxygen. By tuning the potential at which the Mo core is oxidized, it was possible to increase the tolerance of MoPWCs to air. A series of homoleptic MoPWCs bearing fluorinated formamidinate ligands have been synthesized and their electrochemical properties studied.

Synthesis of medium-ring lactams and macrocyclic peptide mimetics conjugate addition/ring expansion cascade reactions.

A novel conjugate addition/ring expansion (CARE) cascade reaction sequence is reported that enables medium-sized ring and macrocyclic bis-lactams to be prepared from primary amines and cyclic imides. The reactions are simple to perform, generally high yielding, and very broad in scope, especially with respect to the primary amine component. CARE reactions can also be performed iteratively, enabling β-peptoid-based macrocyclic peptide mimetics to be 'grown' well controlled, sequential 4-atom ring expansion reactions, with the incorporation of varied functionalised amines during each iteration.

Inverse Isotope Effects in Single-Crystal to Single-Crystal Reactivity and the Isolation of a Rhodium Cyclooctane σ-Alkane Complex.

The sequential solid/gas single-crystal to single-crystal reaction of [Rh(CyP(CH)PCy)(COD)][BAr ] (COD = cyclooctadiene) with H or D was followed in situ by solid-state P{H} NMR spectroscopy (SSNMR) and ex situ by solution quenching and GC-MS. This was quantified using a two-step Johnson-Mehl-Avrami-Kologoromov (JMAK) model that revealed an inverse isotope effect for the second addition of H, that forms a σ-alkane complex [Rh(CyP(CH)PCy)(COA)][BAr ]. Using D, a temporal window is determined in which a structural solution for this σ-alkane complex is possible, which reveals an η,η-binding mode to the Rh(I) center, as supported by periodic density functional theory (DFT) calculations.

MicroED characterization of a robust cationic σ-alkane complex stabilized by the [B(3,5-(SF)CH)] anion, on-grid solid/gas single-crystal to single-crystal reactivity.

Microcrystalline (∼1 μm) [Rh(CyPCHCHPCy)(norbornadiene)][S-BAr], [S-BAr] = [B(3,5-(SF)CH)], reacts with H in a single-crystal to single-crystal transformation to form the σ-alkane complex [Rh(CyPCHCHPCy)(norbornane)][S-BAr], for which the structure was determined by microcrystal Electron Diffraction (microED), to 0.95 Å resolution, an on-grid hydrogenation, and a complementary single-crystal X-ray diffraction study on larger, but challenging to isolate, crystals. Comparison with the [BAr] analogue [Ar = 3,5-(CF)(CH)] shows that the [S-BAr] anion makes the σ-alkane complex robust towards decomposition both thermally and when suspended in pentane.

Indole-ynones as Privileged Substrates for Radical Dearomatizing Spirocyclization Cascades.

Indole-ynones have been established as general substrates for radical dearomatizing spirocyclization cascade reactions. Five distinct and varied synthetic protocols have been developed─cyanomethylation, sulfonylation, trifluoromethylation, stannylation and borylation─using a variety of radical generation modes, ranging from photoredox catalysis to traditional AIBN methods. The simple and easily prepared indole-ynones can be used to rapidly generate diverse, densely functionalized spirocycles and have the potential to become routinely used to explore radical reactivity.