An Antimony(V) Dication as a Z‐Type Ligand: Turning on Styrene Activation at Gold

With the intent to demonstrate that the charge of Z‐type ligands can be used to modulate the electrophilic character and catalytic properties of coordinated transition metals, we are now targeting complexes bearing polycationic antimony‐based Z‐type ligands. Toward this end, the dangling phosphine arm of ((o‐(Ph₂P)C₆H₄)₃)SbCl₂AuCl ( 1 ) was oxidized with hydrogen peroxide to afford [((o‐(Ph₂P)C₆H₄)₂(o‐Ph₂PO)C₆H₄)SbAuCl₂]⁺ ([ 2 a ]⁺) which was readily converted into the dicationic complex [((o‐(Ph₂P)C₆H₄)₂(o‐Ph₂PO)C₆H₄)SbAuCl]²⁺ ([ 3 ]²⁺) by treatment with 2 equiv AgNTf₂. Both experimental and computational results show that [ 3 ]²⁺ possess a strong Au→Sb interaction reinforced by the dicationic character of the antimony center. The gold‐bound chloride anion of [ 3 ]²⁺ is rather inert and necessitates the addition of excess AgNTf₂ to undergo activation. The activated complex, referred to as [ 4 ]²⁺ [((o‐(Ph₂P)C₆H₄)₂(o‐Ph₂PO)C₆H₄)SbAuNTf₂]²⁺ readily catalyzes both the polymerization and the hydroamination of styrene. This atypical reactivity underscores the strong σ‐accepting properties of the dicationic antimony ligand and its activating impact on the gold center.     

Ultrafast Iron‐Catalyzed Reduction of Functionalized Ketones: Highly Enantioselective Synthesis of Halohydrines,Oxaheterocycles, and Aminoalcohols

A molecularly defined chiral boxmi iron alkyl complex catalyzes the hydroboration of various functionalized ketones and provides the corresponding chiral halohydrines, oxaheterocycles (oxiranes, oxetanes, tetrahydrofurans, and dioxanes) and amino alcohols with excellent enantioselectivities (up to >99 %ee) and conversion efficiencies at low catalyst loadings (as low as 0.5 mol %). Turnover frequencies of greater than 40000 h⁻¹ at −30 °C highlight the activity of this earth‐abundant metal catalyst which tolerates a large number of functional groups.     

Hydrostibination

A rigid naphthalenediamine framework has been used to prepare antimony hydrides that feature LUMO shapes and energies similar to those found in secondary boranes. By exploiting this feature, we introduce the first examples of uncatalyzed hydrostibination reactions of robust C≡C, C=C, C=O, and N=N bonds as new elementary hydrometalation reactions analogous to hydroboration. These results endorse the notion of a diagonal relationship between the lightest p‐block element and the heaviest Group 15 elements and may lead to the conception of novel reaction chemistry.     

Redox and Anion Exchange Chemistry of a Stibine–Nickel Complex: Writing the L,X, Z Ligand Alphabet with a Single Element

According to the covalent bond classification (CBC) method, two‐electron donors are defined as L‐type ligands, one‐electron donors as X‐type ligands, and two‐electron acceptors as Z‐type ligands. These three ligand functions are usually associated to the nature of the ligating atom, with phosphine, alkyl, and borane groups being prototypical examples of L‐, X‐ and Z‐ligands, respectively. A new SbNi platform is reported in which the ligating Sb atom can assume all three CBC ligand functions. Using both experimental and computational data, it is shown that PhICl₂ oxidation of (o‐(Ph₂P)C₆H₄)₃SbNi(PPh₃) ( 1 ) into [(o‐(Ph₂P)C₆H₄)₃ClSb]NiCl ( 2 ) is accompanied by a conversion of the stibine L‐type ligand of 1 into a stiboranyl X‐type ligand in 2 . Furthermore, the reaction of 2 with the catecholate dianion in the presence of cyclohexyl isocyanide results in the formation of [(o‐(Ph₂P)C₆H₄)₃(o‐O₂C₆H₄Sb)]Ni(CNCy) ( 4 ), a complex featuring a nickel atom coordinated by a Lewis acidic, Z‐type, stiborane ligand.     

Structure and Bonding in [Sb@In8Sb12]3− and [Sb@In8Sb12]5−

We report the characterization of the compound [K([2.2.2]crypt)]₄[In₈Sb₁₃], which proves to contain a 1:1 mixture of [Sb@In₈Sb₁₂]^3? and [Sb@In₈Sb₁₂]^5?. The tri‐anion displays perfect T_h symmetry, the first completely inorganic molecule to do so, and contains eight equivalent In³⁺ centers in a cube. The gas‐phase potential energy surface of the penta‐anion has eight equivalent minima where the extra pair of electrons is localized on one In⁺ center, and these minima are linked by low‐lying transition states where the electron pair is delocalized over two adjacent centers. The best fit to the electron density is obtained from a model where the structure of the 5? cluster lies close to the gas‐phase transition state.     

Ligand‐Promoted Rhodium(III)‐Catalyzed ortho‐C−H Amination with Free Amines

Ligand development for rhodium(III)‐catalyzed C−H activation reactions has largely been limited to cyclopentadienyl (Cp) based scaffolds. 2‐Methylquinoline has now been identified as a feasible ligand that can coordinate to the metal center of Cp*RhCl to accelerate the cleavage of the C−H bond of N ‐pentafluorophenylbenzamides, providing a new structural lead for ligand design. The compatibility of this reaction with secondary free amines and anilines also overcomes the limitations of palladium(II)‐catalyzed C−H amination reactions.     

Ligand‐Controlled Regiodivergent Enantioselective Rhodium‐Catalyzed Alkene Hydroboration

Regiocontrol in the rhodium‐catalyzed boration of vinyl arenes is typically dominated by the presence of the conjugated aryl substituent. However, small differences in TADDOL‐derived chiral monophosphite ligands can override this effect and direct rhodium‐catalyzed hydroboration of β‐aryl and β‐heteroaryl methylidenes by pinacolborane to selectively produce either chiral primary or tertiary borated products. The regiodivergent behavior is coupled with enantiodivergent addition of the borane. The nature of the TADDOL backbone substituents and that of the phosphite moiety function synergistically to direct the sense and extent of regioselectivity and enantioinduction. Twenty substrates are shown to undergo each reaction mode with regioselectivity values reaching greater than 20:1 and enantiomer ratios reaching up to 98:2. A variety of subsequent transformations illustrate the potential utility of each product.     

Single‐Molecule Force Measurement Guides the Design of Multivalent Ligands with Picomolar Affinity

Interaction of multiple entities and receptors, or multivalency is widely applied to achieve high affinity ligands for diagnostic and therapeutic purposes. However, lack of knowledge on receptor distribution in living subjects remains a challenge for rational structure design. Herein, we develop a force measurement platform to probe the distribution and separation of the cell surface vascular endothelial growth factor receptors (VEGFR) in live cells, and use this to assess the geometry of appropriate linkers for distinct multivalent binding modes. A tetravalent lead ZD‐4, which was developed from an antitumor drug ZD6474 (Vandetanib) with combined hybrid binding effects, yielded a 2000‐fold improvement in the binding affinity to VEGFR with IC₅₀ value of 25 pm . We confirmed the improved affinity by the associated increase of tumor uptake in the VEGFR‐targeting positron emission tomography (PET) imaging using U87 tumor xenograft mouse model.     

Axially Symmetric U−O−Ln‐ and U−O−U‐Containing Molecules from the Control of Uranyl Reduction with Simple f‐Block Halides

The reduction of U^VI uranyl halides or amides with simple Ln^II or U^III salts forms highly symmetric, linear, oxo‐bridged trinuclear U^V/Ln^III/U^V, Ln^III/U^IV/Ln^III, and U^IV/U^IV/U^IV complexes or linear Ln^III/U^V polymers depending on the stoichiometry and solvent. The reactions can be tuned to give the products of one‐ or two‐electron uranyl reduction. The reactivity and magnetism of these compounds are discussed in the context of using a series of strongly oxo‐coupled homo‐ and heterometallic poly(f‐block) chains to better understand fundamental electronic structure in the f‐block.     

PAd2‐DalPhos Enables the Nickel‐Catalyzed C−N Cross‐Coupling of Primary Heteroarylamines and (Hetero)aryl Chlorides

Base‐metal catalysts capable of enabling the assembly of heteroatom‐dense molecules by cross‐coupling of primary heteroarylamines and (hetero)aryl chlorides, while sought‐after given the ubiquity of unsymmetrical di(hetero)arylamino fragments in pharmacophores, are unknown. Herein, we disclose the new “double cage” bisphosphine PAd2‐DalPhos ( L2 ). The derived air‐stable Ni^II pre‐catalyst C2 functions well at low loadings in challenging test C?N cross‐couplings with established substrates, and facilitates the first Ni‐catalyzed C?N cross‐couplings of primary five‐ or six‐membered ring heteroarylamines and activated (hetero)aryl chlorides, with synthetically useful scope that is competitive with Pd catalysis.