Tandem Oligomerization-Hydrogenation Using Brønsted Acidic Iridium Hydride Catalysts.

Cationic iridium complexes bearing the tris-[3,5-bis-(trifluoromethyl)-phenyl]-phosphine ligand unexpectedly give acidic metal hydrides. Net-dihydrogen heterolysis at such complexes provides hydrogenation catalysis by an ionic mechanism. The direct reduction of isobutene competes with cationic oligomerization to give the gasoline additive isooctane (2,4,4-trimethylpentane) as a major product of a tandem oligomerization/hydrogenation sequence.

Unlocking Chromium Decarboxylative Ligand-to-Metal Charge Transfer: Efficient and Redox-Neutral Allylation of Aldehydes Using Carboxylic Acids.

Here, we report the light-induced decarboxylative ligand-to-metal charge transfer (LMCT) of Cr(III) carboxylate complexes and demonstrate its applicability toward stereoselective Nozaki-Hiyama-Kishi (NHK) allylation reactions. The critical design element of our reaction was identifying a bipyridyl ligand scaffold that enables a single Cr catalyst to facilitate both photolytic dissociation and aldehyde addition. This approach allows for the direct utilization of carboxylic acids and eliminates the need for external redox reagents.

Total Synthesis and Pharmacological Evaluation of Phochrodines A-C.

The first syntheses of the -isolated natural products phochrodines A-C are reported. Functional group manipulations on a key 5-chromeno[4,3-]pyridine intermediate, itself synthesized from intramolecular Suzuki-Miyaura coupling, enabled facile and high-yielding syntheses of all three natural products. Additionally, sufficient material was generated to enable detailed pharmacological profiling of each compound.

Photocatalyzed Epimerization of Quaternary Stereocenters.

Quaternary stereocenters play a crucial role in shaping both the molecular topology of small molecules and the outcome of stereoselective transformations. While considerable progress has been achieved in constructing highly substituted carbon centers with varied substitution patterns, the stereoselective synthesis of quaternary carbon centers remains a significant challenge. Here we report a protocol for the precise manipulation of quaternary stereocenters through epimerization.

Synthesis, Structure, and Reactivity of Copper(I) Proazaphosphatrane Complexes.

Copper(I) complexes of isobutyl- () and isopropyl-substituted () proazaphosphatranes have been synthesized. Structural and computational studies of a series of monomeric complexes CuX (X = Cl, Br, I) and dimeric [CuCl] provide insight into the transannulation within and steric properties of the proazaphosphatrane ligand. These halide complexes are competent precatalysts in a model borylation reaction, and the silylamido complex CuN(TMS) catalyzes hydrosilylation of benzaldehyde under mild conditions.

Diastereoselective dearomative cycloaddition of bicyclobutanes with pyridinium ylides: a modular approach to multisubstituted azabicyclo[3.1.1]heptanes.

Diastereoselective (3+3) cycloaddition between bicyclobutanes and pyridinium ylides forms azabicyclo[3.1.1]heptanes pyridine dearomatization.

Five Hypotheses on the Origins of Temperature Dependence of Se NMR Shifts in Diselenides.

Notable thermal shifts in diselenides have been documented in Se NMR for more than 50 years, but no satisfactory explanation has been found. Here, five hypotheses are considered as possible explanations for the large temperature dependence of the Se chemical shifts of diaryl and dialkyl diselenides compared to monoselenides and selenols. Density functional theory calculations are provided to bolster hypotheses and better understand the effects of barrier height and dipole energies.

Bis(bicyclo[1.1.1]pentyl)chlorophosphine as a Precursor for the Preparation of Bis(bicyclo[1.1.1]pentyl)phosphines.

Dialkylchlorophosphines are among the most versatile building blocks for tertiary phosphine ligands, but their synthesis relies on the nucleophilic substitution of PCl, leaving substituents that require P-H precursors largely inaccessible. The primary phosphine reagent iPrNPH·BH can serve as a doubly protected PHCl proxy, enabling the synthesis of bis(bicyclo[1.1.

Rapid sp-Enriched Scaffold Generation via a Selective Aziridine Amide Ring-Opening Reaction.

Sp-enriched small molecules play a critical role in developing drug candidates. While designing analogues with greater sp character, a methodology utilizing a less explored cyclic-aziridine amide ring-opening reaction to generate sp-enriched scaffolds has been developed and reported. This methodology enables rapid access to substructures with higher fsp values, attracting greater attention within the past few decades.

Comparative Analysis of the Donor Properties of Isomeric Pyrrolyl Phosphine Ligands.

Understanding the net donor and electronic properties of pyrrole-based phosphines is critical for guiding their use as ligands. In this study, we compare two isomeric 1- and 2-(diphenylphosphino)methylpyrroles ( and , respectively) to determine the degree to which -(phosphino)pyrroles are distinct from aryl- and 2-pyrrolyl phosphines. Ruthenium, rhodium, platinum, and gold complexes as well as selenide derivatives of these ligands are examined using NMR and IR spectroscopy, X-ray crystallography, and cyclic voltammetry.

Enolate addition to bicyclobutanes enables expedient access to 2-oxo-bicyclohexane scaffolds.

We report the synthesis of 2-oxo-bicyclo[2.1.1]hexanes (2-oxo-BCHs) from bicyclobutanes (BCBs) and readily available enolate precursors.

Vanol-Supported Lanthanide Complexes for Strong Circularly Polarized Luminescence at 1550 nm.

Strong circularly polarized luminescence (CPL) at 1550 nm is reported for lanthanide complexes supported by Vanol; these are the first examples of coordination of Vanol to lanthanides. A change in the ligand design from a 1,1'-bi-2-naphthol (in Binol) to a 2,2'-bi-1-naphthol (in Vanol) results in significantly improved dissymmetry factors for (Vanol) ErNa (|g |=0.64) at 1550 nm.

Tris(bicyclo[1.1.1]pentyl)phosphine: An Exceptionally Small Tri--alkylphosphine and Its Bis-Ligated Pd(0) Complex.

Tris(bicyclo[1.1.1]pentyl)phosphine can be prepared by radical addition of PH to [1.

Reassessment of N activation by low-valent Ti-amide complexes: a remarkable side-on bridged bis-N adduct is actually an arene adduct.

The complex {(TMEDA)Li}{[Ti(N(TMS))](μ-η:η-N)} (5-Li) is the only transition metal N complex ever reported with two side-on N adducts. In this report, the similarity of 5-Li to a new inverse sandwich toluene adduct {(PhMe)K}{[Ti(N(TMS))](μ-PhMe)} (6-K) necessitated a re-examination of the structure of 5-Li. Through a reassessment of the original disordered crystal data of 5-Li and new independent syntheses brought about through revisitation of the original reaction conditions, 5-Li has been re-assigned as an inverse sandwich toluene adduct, {(TMEDA)Li}{[Ti(N(TMS))](μ-PhMe)} (6-Li).

Spinolate Lanthanide Complexes for High Circularly Polarized Luminescence Metrics in the Visible and Near-Infrared.

Analogues of Shibasaki's complexes supported by enantiopure Spinol are synthesized and characterized. The tris(Spinol) Ln complexes are generated either by ligand deprotonation followed by complexation with lanthanide triflate salts or by in situ deprotonation by Ln(N(SiMe)) salts in the presence of additional base. The resulting complexes are found to be luminescent and chiroptically active for both circular dichroism and circularly polarized luminescence (CPL), notably producing strong CPL with dissymmetry factors () of up to 0.

Structure-Activity Relationships for the -Me- Versus -H-Amide Modification to Macrocyclic -Verticilide Antiarrhythmics.

The synthesis of all -Me and -H analogues of -verticilide is described, enabling a structure-activity relationship study based on cardiac ryanodine receptor (RyR2) calcium ion channel inhibition. The use of permeabilized cardiomyocytes allowed us to correlate the degree of -methylation with activity without concern for changes in passive membrane permeability that these modifications can cause. A key hypothesis was that the minimal pharmacophore may be repeated in this cyclic oligomeric octadepsipeptide (a 24-membered macrocycle), opening the possibility that target engagement will not necessarily be lost with a single -Me → -H modification.

Synthesis, characterization and absolute configurations of methyl ladderanoates.

Methyl esters of [5]-ladderanoic acid and [3]-ladderanoic acid were prepared by esterification of the acids isolated from biomass at a wastewater treatment plant. Optical rotations at six different wavelengths (633, 589, 546, 436, 405 and 365 nm) and vibrational circular dichroism (VCD) spectra in the 1800-900 cm region were measured in CDCl solvent and compared with quantum chemical (QC) predictions using B3LYP functional and 6-311++G(2d,2p) basis set with polarizing continuum model representing the solvent. QC predictions gave negative optical rotations at all six wavelengths for (R)-methyl [5]-ladderanoate and positive optical rotations for (R)-methyl [3]-ladderanoate, the same signs as previously reported for the corresponding acids.

Trace Oxygen Affects Osmium Redox Polymer Synthesis for Wired Enzymatic Biosensors.

Electrochemical sensors that utilize enzymes are a sensitive, inexpensive means of detecting biologically relevant analytes. These sensors are categorized based on their construction and method of signal transport. Type I sensors consist of a crosslinked enzyme on an electrode surface and are potentially subject to interference from byproducts and other biological analytes.

Circularly Polarized Luminescence from Uranyl Improves Resolution of Electronic Transitions.

The first reported example of circularly polarized luminescence from a chiral, molecular uranyl (UO) complex in solution is presented. This uranyl chiroptical activity is enabled by complexation with ibuprofen, an enantiopure chiral carboxylate ligand. Salt metathesis between [UOCl(thf)] and the sodium ibuprofenate salts results in the formation of the anionic tris complexes; these complexes are found to be luminescent in solution, both under visible excitation, directly targeting the metal, and through sensitization by UV absorption and energy transfer from the ligand.

Strong Circularly Polarized Luminescence at 1550 nm from Enantiopure Molecular Erbium Complexes.

Circularly polarized luminescence (CPL) in two subregions of the near-infrared (NIR) has been achieved. By leveraging the rigidity and diminishing detrimental vibrations of the heterobimetallic binolate complexes of erbium [(Binol)ErNa], species exhibiting an exceptionally high dissymmetry factor (| |) of 0.47 at 1550 nm were obtained.

Fluorine-induced diastereodivergence discovered in an equally rare enantioselective -aza-Henry reaction.

Attention to the aza-Henry reaction, particularly over the past two decades, has resulted in a wide range of effective catalysts for the enantio- and diastereoselective versions, driven by the versatility of the β-amino nitroalkane products as precursors to secondary amines and -diamines. Despite this broad effort, -diastereoselective variants are exceedingly rare. We have discovered a subset of α-fluoro nitroalkane additions that are characterized by an unusual crossover in diastereoselection, often delivering the products with high selectivities.

Electronic Structure Analysis and Reactivity of the Bimetallic Bis-Titanocene Vinylcarboxylate Complex, [(CpTi)(OCTMS)].

Multimetallic redox cooperativity features heavily in both bioinorganic and synthetic reactions. Here, the electronic structure of the bimetallic Ti/Ti complex , [(CpTi)(OCTMS)] has been revisited with EPR, confirming a predominantly Ti/Ti electronic structure. Reactions of with 2,6-dimethylphenyl isocyanide (CNXyl), TMSCl, MeI, and BnCl were explored, revealing differential redox chemistry of the bimetallic core.

Synthesis and Cytotoxic Evaluation of Arimetamycin A and Its Daunorubicin and Doxorubicin Hybrids.

The arimetamycin A glycan governs the compound's cytotoxicity (IC). To study this branched, deoxy-amino disaccharide, we designed and synthesized a modified acyl donor that underwent glycosylation with three anthracycline aglycones: steffimycinone, daunorubicinone, and doxorubicinone. The result of the approach was a synthesis of arimetamycin A and two novel hybrid anthracyclines.

Di(indenyl)beryllium.

The bonding in beryllocene, [BeCp ], took decades to establish, owing to its unexpected mixed hapticity structure (i.e., [Be(η -Cp)(η -Cp)]).

Selective demethylation of -aryl glycosides by iridium-catalyzed hydrosilylation.

The cleavage of alkyl ethers by hydrosilylation is a powerful synthetic tool for the generation of silyl ethers. Previous attempts to apply this transformation to carbohydrate derivatives have been constrained by poor selectivity and preferential reduction of the anomeric position. O-Aryl glycosides are found to be stable under iridium- and borane-catalyzed hydrosilylation conditions, allowing for alkyl ether cleavage without loss of anomeric functionality.