The Role of Electron Transfer in Copper-Mediated C(sp)-H Trifluoromethylation.

We report copper(II) and copper(III) trifluoromethyl complexes supported by a pyridinedicarboxamide ligand (L) as a platform for investigating the role of electron transfer in C(sp)-H trifluoromethylation. While the copper(II) trifluoromethyl complex is unreactive towards (hetero)arenes, the formal copper(III) trifluoromethyl complex performs C(sp)-H trifluoromethylation of a wide range of (hetero)arenes. Mechanistic studies using the copper(III) trifluoromethyl complex suggest that the mechanism of arene trifluoromethylation is substrate-dependent.

Tuning Secondary-Sphere Lewis Acidity via Late-Stage Modification of an Appended Borane.

To develop synthetic strategies to construct ligands containing secondary-sphere acids, we demonstrate that an appended borane of low Lewis acidity (-BPin) can be upgraded to a strong Lewis acid (-BF). Using a pyridine-pyrazole ligand coordinated to Mo(CO), we show that a pendent -BPin group undergoes exhaustive fluorination to -BFK, a precursor to a highly acidic -BF unit (acceptor number ∼15× greater than that of -BPin).

Synthesis of heteroleptic bis-phosphine bis-NHC iron (0) complexes: a strategy to enhance small molecule activation.

We report the synthesis of heteroleptic iron complexes supported by both a bis-phosphine ligand (depe) and a bis-NHC ligand. The mixed ligand sets provide access to iron (0) adducts of N and CO that are highly activated, in comparison to homoleptic ( Fe(depe)L) variants. Computational and experimental studies revealed the mixed ligand set distorts the geometric and electronic structure to yield an unusually basic iron.

Additive Effects in Metal/Lewis Acid Cooperativity Assessed in a Tetrahedral Copper Hydrazine Complex Featuring an Appended Borane.

Within metal/ligand cooperative systems employing acidic groups, studies that empirically assess distance relationships are needed to maximize cooperative interactions with substrates. We report the formation of two Cu(I)-NH complexes using 1,4,7-triazacyclononane ligand frameworks bearing two -butyl groups and either a Lewis acidic trialkylborane or an inert alkyl group. Metal/Lewis acid cooperativity imparts heightened acidification of the hydrazine substrate and plays a key role in the release of substrate to a competitive Lewis acidic group.

Lewis Acid-Tethered (cAAC)-Copper Complexes: Reactivity for Hydride Transfer and Catalytic CO Hydrogenation.

We present a series of borane-tethered cyclic (alkyl)(amino)carbene (cAAC)-copper complexes, including a borane-capped Cu(I) hydride. This hydride is unusually hydridic and reacts rapidly with both CO and 2,6-dimethylphenol at room temperature. Its reactivity is distinct from variants without a tethered borane, and the underlying principles governing the enhanced hydricity were evaluated experimentally and theoretically.

Catalytic Olefin Transpositions Facilitated by Ruthenium N,N,N-Pincer Complexes.

In this report, we demonstrate olefin transposition/isomerization reactions catalyzed by a series of -pincer (1,3-bis(2-pyridylimino)isoindoline) Ru-hydride complexes. The protocol proceeds at room temperature for most substrates, achieving excellent yields, regioselectivity, and diastereoselectivity in short reaction times. The air-stable Ru-chloride derivatives of these complexes exhibit comparable reactivity enabling benchtop setup and synthetic versatility.

Appended Lewis Acids Enable Dioxygen Reactivity and Catalytic Oxidations with Ni(II).

We disclose a suite of Ni(II) complexes featuring secondary sphere Lewis acids of varied Lewis acidity and tether lengths. Several of these complexes feature atypical behavior of Ni(II): reactivity with O that occurs only in the presence of a tethered Lewis acid. In situ UV-vis spectroscopy revealed that, although adducts are stable at -40 °C, complexes containing 9-borabicyclo[3.

Iron-Catalyzed C-H Oxygenation Using Perchlorate Enabled by Secondary Sphere Hydrogen Bonds.

Perchlorate (ClO) is a groundwater pollutant that is challenging to remediate. We report a strategy to use Fe(II) tris(2-pyridylmethyl)amine (TPA) complexes featuring appended aniline hydrogen bonds (H-bonds) to promote ClO reduction. These complexes facilitate oxygen atom transfer from ClO to PPh and C-H oxygenation reactions of organic substrates.

A metal-free strategy to construct fluoroalkyl-olefin linkages using fluoroalkanes.

We present a metal-free strategy to access fluoroalkyl-olefin linkages from fluoroalkane precursors and vinyl-pinacol boronic ester (BPin) reagents. This reaction sequence is templated by the boron reagent, which induces C-C bond formation upon oxidation. We developed this strategy into a one-pot synthetic protocol using RCFH precursors directly with vinyl-BPin reagents in the presence of a Brønsted base, which tolerated oxygen- and nitrogen-containing heterocycles, and aryl halogens.

A Bidentate Ligand Featuring Ditopic Lewis Acids in the Second Sphere for Selective Substrate Capture and Activation.

We present a ligand platform featuring appended ditopic Lewis acids to facilitate capture/activation of diatomic substrates. We show that incorporation of two 9-borabicyclo[3.3.

Nucleophilic strategies to construct -CF- linkages using borazine-CFAr reagents.

Using a Lewis acid-quenched CFPh reagent, we show C-C bond formation through nucleophilic addition reactions to prepare molecules containing internal -CF- linkages. We demonstrate C(sp)-C(sp) coupling using both SAr reactions and Pd-catalysis. Finally, C(sp)-C(sp) bonds are forged using operationally simple S2 reactions that tolerate medicinally-relevant motifs.

A Borane Lewis Acid in the Secondary Coordination Sphere of a Ni(II) Imido Imparts Distinct C-H Activation Selectivity.

Two borane-functionalized bidentate phosphine ligands that vary in tether length have been prepared to examine cooperative metal-substrate interactions. Ni(0) complexes react with aryl azides at low temperatures to form structurally unusual κ-()-NAr adducts. Warming these adducts affords products of N extrusion and in one case, a Ni-imido compound that is capped by the appended borane.

Distinct Reactivity Modes of a Copper Hydride Enabled by an Intramolecular Lewis Acid.

We disclose a 1,4,7-triazacyclononane (TACN) ligand featuring an appended boron Lewis acid. Metalation with Cu(I) affords a series of tetrahedral complexes including a boron-capped cuprous hydride. We demonstrate distinct reactivity modes as a function of chemical oxidation: hydride transfer to CO in the copper(I) state and oxidant-induced H evolution as well as alkyne reduction.

Hydrazone and Oxime Olefination via Ruthenium Alkylidenes.

We describe the development of an efficient method for the olefination of hydrazones and oximes. The key design approach that enables this transformation is tuning of the energy/polarity of C=N π-bonds by employing heteroatom functionalities (NR , OR). The resulting hydrazones or oximes facilitate olefination with ruthenium alkylidenes.

Modulation of H/H exchange in iridium-hydride 2-hydroxypyridine complexes by remote Lewis acids.

A series of iridium hydride complexes featuring dihydrogen bonding are presented and shown to undergo rapid H/H exchange (1240 s at 25 °C). We demonstrate that the H/H exchange rate can be modified by post-synthetic modification at a remote site using BH, Zn(CF), and [MeO][BF]. This route provides a complementary strategy to traditional methods that rely on pre-metalation modifications to a metal's primary sphere.

Substrate Specific Metal-Ligand Cooperative Binding: Considerations for Weak Intramolecular Lewis Acid/Base Pairs.

Metal-ligand cooperative binding modes were interrogated in a series of zinc bis(thiophenoxide) complexes. A weak B-S binding interaction is observed in solution between the weakly Lewis basic thiophenoxide ligands and an appended trialkylborane. The energy of this binding event is dependent upon the strength of the Lewis acid and its proximity to the zinc thiophenoxide.

Late-stage ligand functionalization the Staudinger reaction using phosphine-appended 2,2'-bipyridine.

The ability of a phosphine-appended-2,2'-bipyridine ligand ((Ph2P)2bpy) to serve as a platform for late-stage ligand modifications was evaluated using tetrahedral (Ph2P)2bpyFeCl2. We employed a post-metalation Staudinger reaction to install a series of functionalized arenes, including those containing Brønsted and Lewis acidic groups. This reaction sequence represents a versatile strategy to both tune the ligand donor properties as well as directly incorporate appended functionality.

Hydrogen-bonded nickel(I) complexes.

A series of nickel(ii) tris(2-pyridylmethyl)amine (TPA) complexes featuring appended hydrogen bonds (H-bonds) to halides (F, Cl, Br) was synthesized and charcterized. Reduction to the nickel(i) state provided access to an unusual nickel(i) fluoride complex stabilized by H-bonds, enabling structural and spectroscopic characterization.

Defluorinative Functionalization of Pd(II) Fluoroalkyl Complexes.

When subjected to arylboranes, anionic trifluoromethyl and difluorobenzyl palladium(II) complexes undergo fluoride abstraction followed by 1,1-migratory insertion. The resulting intermediate fluoroalkyl species can be induced to undergo a subsequent transmetalation and reductive elimination from either an formed fluoroboronate (FB(Ar)) or an exogenous boronic acid/ester (ArB(OR)) and nucleophilic activator, representing a net defluorinative arylation reaction. The latter method enabled a structurally diverse substrate scope to be prepared from either an isolated palladium-CF complex, or from Pd(PPh) and other commercially available reagents.

Mobility of Lewis acids within the secondary coordination sphere: toward a model for cooperative substrate binding.

Distance dependence of appended Lewis acids in NH binding and deprotonation was evaluated within a series of zinc complexes. Variation of spacer-length to a tethered trialkylborane Lewis acid revealed distinct preferences for binding and stabilization of the resulting deprotonated NH unit.

Examining the Generality of Metal-Ligand Cooperativity Across a Series of First-Row Transition Metals: Capture, Bond Activation, and Stabilization.

We outline the generality and requirements for cooperative NH capture, N-N bond scission, and amido stabilization across a series of first-row transition metal complexes bearing a pyridine(dipyrazole) ligand. This ligand contains a pair of flexibly tethered trialkylborane Lewis acids that enable hydrazine capture and M-NH stabilization. While the Lewis acids are required to bind NH, the identity of the metal dictates whether N-N bond scission can occur.

Reductively Stable Hydrogen-Bonding Ligands Featuring Appended CF-H Units.

We present the development of ligands featuring the unconventional hydrogen bond donor, -CFH, within a metal's secondary coordination sphere. When metalated with palladium, CFH-functionalized 1,10-phenanthroline provides highly directed H-bonding interactions with Pd-coordinated substrates. Spectroscopic and computational analyses with a series of -type ligand acceptors (-F, -Cl, -Br, -OR) establish the H-bonding interaction strength for the -CFH group (∼3 kcal/mol).

A Critically Appraised Topic on the Tuck Jump Assessment: Does the Tuck Jump Assessment Demonstrate Interrater and Intrarater Reliability in Healthy Individuals?

Clinical Scenario: Lower-extremity injuries in the United States costs millions of dollars each year. Athletes should be screened for neuromuscular deficits and trained to correct them. The tuck jump assessment (TJA) is a plyometric tool that can be used with athletes.

Tetrahedral iron featuring an appended Lewis acid: distinct pathways for the reduction of hydroxylamine and hydrazine.

We present the preparation of a nitrogen-based bidentate ligand featuring an appended boron Lewis acid as well as its tetrahedral Fe2+ and Zn2+ complexes. These complexes act as platforms for hydrazine and hydroxylamine capture and reduction chemistry.