C-H Activation and Sequential Addition to Dienes and Imines: Synthesis of Amines with -Quaternary Centers and Mechanistic Studies on the Complex Interplay Between the Catalyst and Three Reactants.

A Rh(III)-catalyzed sequential C-H bond addition to dienes and in situ formed aldimines was developed, allowing for the preparation of otherwise challenging to access amines with quaternary centers at the -position. A broad range of dienes were effective inputs and installed a variety of aryl and alkyl substituents at the quaternary carbon site. Aryl and alkyl sulfonamide and carbamate nitrogen substituents were incorporated by using different formaldimine precursors.

Complexes of Iron(II), Cobalt(II), and Nickel(II) with DOTA-Tetraglycinate for pH and Temperature Imaging Using Hyperfine Shifts of an Amide Moiety.

Paramagnetic complexes of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate (DOTA) derivatives have shown potential for molecular imaging with magnetic resonance. DOTA-tetraglycinate (DOTA-4AmC) coordinated with lanthanide metal ions (Ln) demonstrates pH/temperature sensing with Biosensor Imaging of Redundant Deviation in Shifts (BIRDS) and Chemical Exchange Saturation Transfer (CEST), respectively, detecting nonexchangeable (e.g.

Bridging Carbonyl and Carbyne Complexes of Weak-Field Iron: Electronic Structure and Iron-Carbon Bonding.

Carbon monoxide inhibited forms of nitrogenases have carbonyl (CO) and carbide (C) bridges, which are common in synthetic iron complexes with strong-field ligand environments but rare in iron sites with weak-field ligand environments analogous to the enzyme. Here, we explore the fundamental bonding description of bridging CO in high-spin iron systems. We describe the isolation of several diiron carbonyls and related species, and elucidate their electronic structures, magnetic coupling, and characteristic structural and vibrational parameters.

Inserting Three-Coordinate Nickel into [4Fe-4S] Clusters.

Metalloenzymes can efficiently achieve the multielectron interconversion of carbon dioxide and carbon monoxide under mild conditions. Anaerobic carbon monoxide dehydrogenase (CODH) performs these reactions at the cluster, a unique nickel-iron-sulfide cluster that features an apparent three-coordinate nickel site. How nature assembles the [NiFeS]-Fe cluster is not well understood.

Linear Free Energy Relationships Associated with Hydride Transfer From [(6,6'-R-bpy)Re(CO)H]: A Cautionary Tale in Identifying Hydrogen Bonding Effects in the Secondary Coordination Sphere.

Six rhenium hydride complexes, [(6,6'-R-bpy)Re(CO)H] (bpy = 2,2'-bipyridine, R = OEt, OMe, NHMe, Me, F, Br), were synthesized. These complexes insert CO to form rhenium formate complexes of the type [(6,6'-R-bpy)Re(CO){OC(O)H}]. All the rhenium formate species were characterized using X-ray crystallography, which revealed that the bpy ligand is not coplanar with the metal coordination plane containing the two nitrogen donors of the bpy ligand but tilted.

Exfoliation of a metal-organic framework enabled by post-synthetic cleavage of a dipyridyl dianthracene ligand.

The synthetic tunability and porosity of two-dimensional (2D) metal-organic frameworks (MOFs) renders them a promising class of materials for ultrathin and nanoscale applications. Conductive 2D MOFs are of particular interest for applications in nanoelectronics, chemo-sensing, and memory storage. However, the lack of covalency along the stacking axis typically leads to poor crystallinity in 2D MOFs, limiting structural analysis and precluding exfoliation.

Rh(II)-Catalyzed Enantioselective -Alkylation of Sulfenamides with Acceptor-Acceptor Diazo Compounds Enables the Synthesis of Sulfoximines Displaying Diverse Functionality.

The Rh(II)-catalyzed enantioselective -alkylation of sulfenamides with α-amide diazoacetates at 1 mol % catalyst loading to obtain sulfilimines in high yields and enantiomeric ratios of up to 99:1 is reported. The enantioenriched sulfilimine products incorporate versatile amide functionality poised for further elaboration to diverse sulfoximines with multiple stereogenic centers, including by highly diastereoselective sulfilimine and sulfoximine α-alkylation with alkylating agents and epoxides and by interconversion of the amide to --butanesulfinyl aldimines, followed by diastereoselective additions.

Tuning Energetics of 2 e/2H PCET Properties with Model Ru-bisamido Complexes.

Most redox processes that break/form bonds involve net 2e changes, and many are coupled to protons. Yet most proton-coupled electron transfer (PCET) studies focus on 1e/1H reactions. Reported here is a family of molecular models that undergo tunable 2e/2H redox changes.

Effect of 6,6'-Substituents on Bipyridine-Ligated Ni Catalysts for Cross-Electrophile Coupling.

A family of 4,4'-Bu-2,2'-bipyridine (bpy) ligands with substituents in either the 6-position, 4,4'-Bu-6-Me-bpy (bpy), or 6 and 6'-positions, 4,4'-Bu-6,6'-R-bpy (bpy; R = Me, Pr, Bu, Ph, or Mes), was synthesized. These ligands were used to prepare Ni complexes in the 0, I, and II oxidation states. We observed that the substituents in the 6 and 6'-positions of the bpy ligand impact the properties of the Ni complexes.

Scaffold-Oriented Asymmetric Catalysis: Conformational Modulation of Transition State Multivalency during a Catalyst-Controlled Assembly of a Pharmaceutically Relevant Atropisomer.

A new class of superbasic, bifunctional peptidyl guanidine catalysts is presented, which enables the organocatalytic, atroposelective synthesis of axially chiral quinazolinediones. Computational modeling unveiled the conformational modulation of the catalyst by a novel phenyl urea N-cap, that preorganizes the structure into the active, folded state. A previously unanticipated noncovalent interaction involving a difluoroacetamide acting as a hybrid mono- or bidentate hydrogen bond donor emerged as a decisive control element inducing atroposelectivity.

Iron(iv) alkyl complexes: electronic structure contributions to Fe-C bond homolysis and migration reactions that form N-C bonds from N.

High-valent iron alkyl complexes are rare, as they are prone to Fe-C bond homolysis. Here, we describe an unusual way to access formally iron(iv) alkyl complexes through double silylation of iron(i) alkyl dinitrogen complexes to form an NNSi group. Spectroscopically validated computations show that the disilylehydrazido(2-) ligand stabilizes the formal iron(iv) oxidation state through a strongly covalent Fe-N π-interaction, in which one π-bond fits an "inverted field" description.

An oxidative photocyclization approach to the synthesis of alkaloids.

Securines and securamines are cytotoxic alkaloids that contain reactive alkene and heterocyclic residues embedded in skeletons comprising four to six oxidized rings. This structural complexity imparts a rich chemistry to the isolates but has impeded synthetic access to the structures in the nearly three decades since their isolation. We present a flexible route to eight isolates that exemplify the three skeletal classes of metabolites.

Three-Coordinate Nickel and Metal-Metal Interactions in a Heterometallic Iron-Sulfur Cluster.

Biological multielectron reactions often are performed by metalloenzymes with heterometallic sites, such as anaerobic carbon monoxide dehydrogenase (CODH), which has a nickel-iron-sulfide cubane with a possible three-coordinate nickel site. Here, we isolate the first synthetic iron-sulfur clusters having a nickel atom with only three donors, showing that this structural feature is feasible. These have a core with two tetrahedral irons, one octahedral tungsten, and a three-coordinate nickel connected by sulfide and thiolate bridges.

Studies of κ- and κ-tripyridylamine complexes of ruthenium and π-stacking by pyridyls.

The reaction of tris(pyridin-2-yl)amine with [CyRuCl] (Cy = p-isopropyltoluene or cymene) in refluxing diglyme led to the formation of cis-[RuCl{κ-(2-py)N}]·CHCl (1a) after recrystallization from chloroform/pentane, or cis-dichloridobis[tris(pyridin-2-yl)amine-κN,N']ruthenium(II) dichloromethane disolvate, [RuCl(CHN)]·2CHCl or cis-[RuCl{κ-(2-py)N}]·2CHCl (1b). Treatment of 1a with one equivalent of silver(I) hexafluoridoantimonate in dichloromethane gave [RuCl{κ-(2-py)N}{κ-(2-py)N}][SbF]·CHCl (2a). Crystallization of 2a from chloroform provided chlorido[tris(pyridin-2-yl)amine-κN,N'][tris(pyridin-2-yl)amine-κN,N',N'']ruthenium(II) hexafluoridoantimonate chloroform monosolvate, [RuCl(CHN)][SbF]·CHCl or [RuCl{κ-(2-py)N}{κ-(2-py)N}][SbF]·CHCl (2b).

An Asymmetric Aromatic Finkelstein Reaction: A Platform for Remote Diarylmethane Desymmetrization.

A first-of-its-kind enantioselective aromatic Finkelstein reaction is disclosed for the remote desymmetrization of diarylmethanes. The reaction operates through a copper-catalyzed C-I bond-forming event, and high levels of enantioselectivity are achieved through the deployment of a tailored guanidinylated peptide ligand. Strategic use of transition-metal-mediated reactions enables the chemoselective modification of the aryl iodide products; thus, the synthesis of a diverse set of otherwise difficult-to-access diarylmethanes with excellent levels of selectivity is realized from a common intermediate.

Knowledge and identity antecedents of COVID-19 vaccine status: a study of South Carolina residents.

Introduction: Despite over three years of learning about SARS-CoV-2 and extensive work to develop vaccines, vaccination rates remain suboptimal, thereby preventing our society from reaching herd immunity.

Purpose: Extant literature on vaccine hesitancy led us to hypothesize that specific socio/political variables may be contributing to low vaccination rates, particularly in South Carolina.

Methods: By use of Qualtrics surveys, we collected data from people across all counties in South Carolina regarding vaccine status, plans to vaccinate, and a host of demographics.

Valence Delocalization and Metal-Metal Bonding in Carbon-Bridged Mixed-Valence Iron Complexes.

The carbide ligand in the iron-molybdenum cofactor (FeMoco) in nitrogenase bridges iron atoms in different oxidation states, yet it is difficult to discern its ability to mediate magnetic exchange interactions due to the structural complexity of the cofactor. Here, we describe two mixed-valent diiron complexes with C-based ketenylidene bridging ligands, and compare the carbon bridges with the more familiar sulfur bridges. The ground state of the [Fe (μ-CCO) ] complex with two carbon bridges (4) is S= , and it is valence delocalized on the Mössbauer timescale with a small thermal barrier for electron hopping that stems from the low Fe-C force constant.

Comparative study of CO insertion into pincer supported palladium alkyl and aryl complexes.

The insertion of CO into metal alkyl bonds is a crucial elementary step in transition metal-catalyzed processes for CO utilization. Here, we synthesize pincer-supported palladium complexes of the type (PBP)Pd(alkyl) (PBP = B(NCHPBu)CH; alkyl = CHCH, CHCHCH CHCH, and CH-4-OMe-CH) and (PBP)Pd(CH) and compare the rates of CO insertion into the palladium alkyl bonds to form metal carboxylate complexes. Although, the rate constant for CO insertion into (PBP)Pd(CHCH) is more than double the rate constant we previously measured for insertion into the palladium methyl complex (PBP)Pd(CH), insertion into (PBP)Pd(CHCHCH) occurs approximately one order of magnitude slower than (PBP)Pd(CH).

A Guide to Tris(4-Substituted)-triphenylmethyl Radicals.

Triphenylmethyl (trityl, PhC•) radicals have been considered the prototypical carbon-centered radical since their discovery in 1900. Tris(4-substituted)-trityls [(4-R-Ph)C•] have since been used in many ways due to their stability, persistence, and spectroscopic activity. Despite their widespread use, existing synthetic routes toward tris(4-substituted)-trityl radicals are not reproducible and often lead to impure materials.

Independent Tuning of the p or the in a Family of Ruthenium Pyridine-Imidazole Complexes.

Two series of Ru(acac)(py-imH) complexes have been prepared, one with changes to the acac ligands and the other with substitutions to the imidazole. The proton-coupled electron transfer (PCET) thermochemistry of the complexes has been studied in acetonitrile, revealing that the acac substitutions almost exclusively affect the redox potentials of the complex (|Δ| ≫ |Δp|·0.059 V) while the changes to the imidazole primarily affect its acidity (|Δp|·0.

Dinitrogen Binding and Functionalization from a Low-Coordinate Alkynyliron Complex.

Alkynyl complexes of low-coordinate transition metals offer a sterically open environment and interesting bonding opportunities. Here, we explore the capacity of iron(I) alkynyl complexes to bind N and isolate a N complex including its X-ray crystal structure. Silylation of the N complex gives an isolable, formally iron(IV) complex with a disilylhydrazido(2-) ligand, but natural bond orbital analysis indicates that an iron(II) formulation is preferable.

Aspartyl β-Turn-Based Dirhodium(II) Metallopeptides for Benzylic C(sp)-H Amination: Enantioselectivity and X-ray Structural Analysis.

Amination of C(sp)-H bonds is a powerful tool to introduce nitrogen into complex organic frameworks in a direct manner. Despite significant advances in catalyst design, full site- and enantiocontrol in complex molecular regimes remain elusive using established catalyst systems. To address these challenges, we herein describe a new class of peptide-based dirhodium(II) complexes derived from aspartic acid-containing β-turn-forming tetramers.