Tuning the Properties of Hydrazone/Isosorbide-Based Switchable Chiral Dopants.

The long-range supramolecular interactions in liquid crystals (LCs) can be used to amplify and subsequently propagate microscopic structural changes into macroscopic events. Here, we report on a systematic structure-property analysis using 16 chiral photoswitchable dopants composed of bistable hydrazones and chiral isosorbide moieties. Our findings showcase the relationship between the dopant's structure and its helical twisting power (β), and hence, the photophysical properties of the host LC.

Ethylene Polymerizations Catalyzed by Fluorinated "Sandwich" Diimine-Nickel and Palladium Complexes.

Nickel and palladium complexes bearing "sandwich" diimine ligands with perfluorinated aryl caps have been synthesized, characterized, and explored in ethylene polymerization reactions. The X-ray crystallographic analysis of the precatalysts and shows differences from their nonfluorinated analogues and , with the perfluorinated aryl caps centered precisely over the nickel and palladium centers, which results in higher buried volumes of the metal centers relative to the nonfluorinated analogues. The sandwich diimine-palladium complexes and containing perfluorinated aryl caps polymerize ethylene in a controlled fashion with activities that are substantially increased compared with their nonfluorinated analogues.

Tripodal Organic Cages with Unconventional CH···O Interactions for Perchlorate Remediation in Water.

Perchlorate anions used in industry are harmful pollutants in groundwater. Therefore, selectively binding perchlorate provides solutions for environmental remediation. Here, we synthesized a series of tripodal organic cages with highly preorganized C-H bonds that exhibit selectively binding to perchlorate in organic solvents and water.

Regiodivergent (3 + 2) annulation reactions of oxyallyl cations.

We report a new method for the regiodivergent dearomative (3 + 2) reaction between 3-substituted indoles and oxyallyl cations. Access to both regioisomeric products is possible and is contingent on the presence or absence of a bromine atom on the substituted oxyallyl cation. In this way, we are able to prepare molecules that contain highly-hindered, stereodefined, vicinal, quaternary centers.

Protonation of P-Stereogenic Phosphiranes: Phospholane Formation via Ring Opening and C-H Activation.

Protonation of cyclopropanes and aziridines is well-studied, but reactions of phosphiranes with acids are rare and have not been reported to result in ring opening. Treatment of -Mes*PCHCHR (Mes* = 2,4,6-(-Bu)CH, R = Me or Ph, --) or -Mes*PCHCHPh (-) with triflic acid resulted in regiospecific -Markovnikov C-protonation with ring opening and cyclophosphination of a Mes* --Bu group to yield the phospholanium cations [PH(CHCHR)(4,6-(-Bu)-2-CMeCHCH)][OTf] (R = Me or Ph, -), which were deprotonated with NEt to give phospholanes -. Enantioenriched or racemic - both gave racemic .

Nickel-Catalyzed Homologation of Vinylidene Difluoride (CH═CF): Selective β-F β-H Elimination.

Hydrofluoroolefins (HFOs) constitute the newest generation of fluorocarbon refrigerants and foam-blowing agents due to their reduced global warming potential their saturated analogues. To identify new synthetic routes to HFOs, we show that reactions of bulky Ni(0) phosphine and -NHC complexes with vinylidene difluoride (VF2) afford μ-fluoro-1,1,3-trifluorobut-3-enyl Ni complexes. Moreover, addition of triisopropylsilane allows for reductive elimination of the reduced product─2,4,4-trifluoro-1-butene─demonstrating the Ni-catalyzed hydrodefluorodimerization of VF2.

Configurational Lability at Tetrahedral Phosphorus: syn/anti-Isomerization of a P-Stereogenic Phosphiranium Cation by Intramolecular Epimerization at Phosphorus.

Tetrahedral main-group compounds are normally configurationally stable, but P-epimerization of the chiral phosphiranium cations syn- or anti-[Mes*P(Me)CH CHPh][OTf] (Mes*=2,4,6-(t-Bu) C H ) occurred under mild conditions at 60 °C in CD Cl , resulting in isomerization to give a syn-enriched equilibrium mixture. Ion exchange with excess [NBu ][Δ-TRISPHAT] (Δ-TRISPHAT=Δ-P(o-C Cl O ) ) followed by chromatography on silica removed [NBu ][OTf] and gave mixtures of syn- and anti-[Mes*P(Me)CH CHPh][Δ-TRISPHAT]⋅x[NBu ][Δ-TRISPHAT]. NMR spectroscopy showed that isomerization proceeded with epimerization at P and retention at C.

Comparing Properties of Common Bioinorganic Ligands with Switchable Variants of Cytochrome .

Ligand substitution at the metal center is common in catalysis and signal transduction of metalloproteins. Understanding the effects of particular ligands, as well as the polypeptide surrounding, is critical for uncovering mechanisms of these biological processes and exploiting them in the design of bioinspired catalysts and molecular devices. A series of switchable K79G/M80X/F82C (X = Met, His, or Lys) variants of cytochrome (cyt) was employed to directly compare the stability of differently ligated proteins and activation barriers for Met, His, and Lys replacement at the ferric heme iron.

P-Alkynyl functionalized benzazaphospholes as transmetalating agents.

Exposure of 10π-electron benzazaphosphole 1 to HCl, followed by nucleophilic substitution with the Grignard reagent BrMgCCPh afforded alkynyl functionalized 3 featuring an exocyclic -C[triple bond, length as m-dash]C-Ph group with an elongated P-C bond (1.7932(19) Å). Stoichiometric experiments revealed that treatment of trans-Pd(PEt3)2(Ar)(i) (Ar = p-Me (C) or p-F (D)) with 3 generated trans-Pd(PEt3)2(Ar)(CCPh) (Ar = p-Me (E) or p-F (F)), 5, which is the result of ligand exchange between P-I byproduct 4 and C/D, and the reductively eliminated product (Ar-C[triple bond, length as m-dash]C-Ph).

Diastereoselective Synthesis of P-Stereogenic Secondary Phosphine Oxides (SPOs) Bearing a Chiral Substituent by Ring Opening of (+)-Limonene Oxide with Primary Phosphido Nucleophiles.

Kinetic separation of the commercially available /-(+)-limonene oxide mixture by ring opening with primary phosphido nucleophiles LiPHR (R = ferrocenyl, Ph, Cy, -Bu, Mes* (Mes* = 2,4,6-(-Bu)CH)), followed by treatment with aqueous NHCl and HO, gave unreacted -(+)-limonene oxide and diastereoenriched mixtures of the secondary phosphine oxides (SPOs) PHR(-(+)-Lim-OH)(O), which could be separated by chromatography and/or recrystallization. This one-pot synthesis uses a cheap chiral material and commercially available primary phosphines to control the configuration of the new P-stereogenic SPOs, which are potentially useful as ligands for metal complexes in asymmetric catalysis.

-Selective Synthesis and Coordination Chemistry of Pyridine-Phosphaalkenes: Five Ligands Produce Four Distinct Types of Ru(II) Complexes.

Pyridine-phosphaalkene (PN) ligands were prepared in an -selective fashion using phospha-Wittig methodology. Treatment of these five ligands, varying only in their 6-substituent with RuCl(PPh), produced four distinct types of coordination complexes: pyridine-phosphaalkene-derived , cyclized , and six-coordinate and . Prolonged heating of in THF resulted in C-H activation of the Mes* group and cyclization to give featuring a bidentate pyridine-phospholane ligand bound to the metal center.

Comment on "Observation of alkaline earth complexes M(CO) (M = Ca, Sr, or Ba) that mimic transition metals".

Wu (Reports, 31 August 2018, p. 912) claim that recently characterized octacarbonyls of Ca, Sr, and Ba mimic the classical Dewar-Chatt-Duncanson bonding motif of transition metals. This claim, which contradicts known chemistry and computed electron density distributions, originates in the assumption of a flawed reference state for energy decomposition analyses.

Diastereoselective Coordination of P-Stereogenic Secondary Phosphines in Copper(I) Chiral Bis(phosphine) Complexes: Structure, Dynamics, and Generation of Phosphido Complexes.

Diastereoselective coordination of racemic secondary phosphines (PHRR') to Cu(I) precursors containing chiral bis(phosphines) (diphos*) was explored as a potential route to P-stereogenic phosphido complexes. Reaction of [Cu(NCMe)][PF] with chiral bis(phospholanes) gave [Cu(diphos*)][PF] (diphos* = ( R, R)-Me-DuPhos (1), ( R, R)-Et-DuPhos (2), or ( R, R)-Me-FerroLANE) (3)) or the mono(chelates) [Cu(diphos*)(NCMe) ][PF] (diphos* = ( R, R)- i-Pr-DuPhos, n = 2 (4); diphos* = ( R, R)-Me-FerroLANE, n = 1 (5)). Treatment of [Cu(NCMe)][PF] with diphos* and PHMe(Is) (Is = 2,4,6-( i-Pr)CH) gave mixtures of diastereomers of [Cu(( R, R)- i-Pr-DuPhos)(PHMe(Is))(NCMe)][PF] (6) and [Cu(( R, R)-Me-FerroLANE)(PHMe(Is))][PF] (7); two of the three expected isomers of the bis(secondary phosphine) complexes [Cu(( R, R)- i-Pr-DuPhos)(PhHP(CH) PHPh)][PF] ( n = 2 (8); n = 3 (9)) were formed preferentially in related reactions.

Topochemical Synthesis of Single-Crystalline Hydrogen-Bonded Cross-Linked Organic Frameworks and Their Guest-Induced Elastic Expansion.

Covalently linked single-crystalline porous organic materials are highly desired for structure-property analysis; however, periodically polymerizing organic entities into high dimensional networks is challenging. Here, we report a series of topologically divergent single-crystalline hydrogen-bonded cross-linked organic frameworks (HOFs) with visible guest-induced elastic expansions, which mutually integrate high structural order and high flexibility into one framework. These HOFs are synthesized by photo-cross-linking molecular crystals with alkyldithiols of different chain lengths.

Building Strain with Large Macrocycles and Using It To Tune the Thermal Half-Lives of Hydrazone Photochromes.

Strain has been used as a tool to modulate the reactivity (e.g., mechanochemistry) and thermal isomerization kinetics of photochromic compounds.

Inversion of Configuration at the Phosphorus Nucleophile in the Diastereoselective and Enantioselective Synthesis of P-Stereogenic syn-Phosphiranes from Chiral Epoxides.

Nucleophilic substitution results in inversion of configuration at the electrophilic carbon center (S 2) or racemization (S 1). The stereochemistry of the nucleophile is rarely considered, but phosphines, which have a high barrier to pyramidal inversion, attack electrophiles with retention of configuration at P. Surprisingly, cyclization of bifunctional secondary phosphine alkyl tosylates proceeded under mild conditions with inversion of configuration at the nucleophile to yield P-stereogenic syn-phosphiranes.

Synthetic nat- or ent-steroids in as few as five chemical steps from epichlorohydrin.

Today, more than 100 Food and Drug Administration-approved steroidal agents are prescribed daily for indications including heart failure, inflammation, pain and cancer. While triumphs in organic chemistry have enabled the establishment and sustained growth of the steroid pharmaceutical industry, the production of highly functionalized synthetic steroids of varying substitution and stereochemistry remains challenging, despite the numerous reports of elegant strategies for their de novo synthesis. Here, we describe an advance in chemical synthesis that has established an enantiospecific means to access novel steroids with unprecedented facility and flexibility through the sequential use of two powerful ring-forming reactions: a modern metallacycle-mediated annulative cross-coupling and a new acid-catalysed vinylcyclopropane rearrangement cascade.

Synthesis, Structure, and Luminescence of Copper(I) Halide Complexes of Chiral Bis(phosphines).

For investigation of structure-property relationships in copper phosphine halide complexes, treatment of copper(I) halides with chiral bis(phosphines) gave dinuclear [Cu((R,R)-i-Pr-DuPhos)(μ-X)] [X = I (1), Br (2), Cl (3)], [Cu(μ-((R,R)-Me-FerroLANE)(μ-I)] (5), and [Cu((S,S)-Et-FerroTANE)(I)] (6), pentanuclear cluster CuI((S,S)-Et-FerroTANE) (7), and the monomeric Josiphos complexes Cu((R,S)-CyPF-t-Bu)(I) (8) and Cu((R,S)-PPF-t-Bu)(I) (9); 1-3, 5, and 7-9 were structurally characterized by X-ray crystallography. Treatment of iodide 1 with AgF gave [Cu((R,R)-i-Pr-DuPhos)(μ-F)] (4). DuPhos complexes 1-4 emitted yellow-green light upon UV irradiation at room temperature in the solid state.

Fluorocarbene, fluoroolefin, and fluorocarbyne complexes of Rh.

The manuscript reports the synthesis, characterization, and analysis of electronic structure in a series of complexes of small perfluorocarbon ligands with the (PNP)Rh fragment (where PNP is a diarylamido/bis(phosphine) pincer ligand). Reactions of (PNP)Rh(TBE) as the source of (PNP)Rh with CHF and CHF produced perfluoroalkylidene complexes (PNP)Rh[double bond, length as m-dash]CF and (PNP)Rh[double bond, length as m-dash]C(F)(CF). (PNP)Rh[double bond, length as m-dash]CF could also be obtained the reaction of (PNP)Rh(TBE) with MeSiCF/CsF, with an admixture of (PNP)Rh(CF), where TBE = -butylethylene.

Generation of Hydrofluoronickelacycles from Trifluoroethylene and Ni(0): Ligand Effects on Regio-/Stereoselectivity and Reactivity.

Treatment of Ni(0) complexes 1a-e with sub-atmospheric pressures of trifluoroethylene (TrFE) affords hydrofluoronickelacyclopentanes LNi(CFH) 2a-e (L = PPh, P(O-o-tol), PPhMe, PPhMe, PMe). Fluorine NMR analysis of 2a-e demonstrates predominant formation of three (of the possible six) isomers upon oxidative cycloaddition of TrFE: the cis and trans head-tail isomers and the trans head-head isomer, where the CHF group is defined as the TrFE "head". The respective ratios of LNi(CFH) isomers are influenced by the nature of L, with smaller phosphines favoring the thermodynamically preferred (from DFT calculations) trans head-head isomer (cf.

A Masked Phosphinidene Trapped in a Fluxional NCN Pincer.

The trapping of a phosphinidene (R-P) in an NCN pincer is presented. Stabilized phosphinidene 1 was characterized by P{ H}, H, and C{ H} NMR spectroscopy, exhibiting an averaged C symmetry in solution between -60 and 60 °C. In the solid state, the phosphinidene is coordinated by one adjacent N atom featuring a formal P-N bond (1.

Coordination contributions to protein stability in metal-substituted carbonic anhydrase.

Contributions of the active site metal to the stability of carbonic anhydrase (CA) were quantified by differential scanning calorimetry and complementary unfolding measurements of CA substituted with Co(2+), Cd(2+), Cu(2+), Ni(2+) and Mn(2+). The metal ions stabilize the protein to different extent, with the highest stability provided by the native Zn(2+). This additional stability does not correlate with the enthalpy of the three metal-imidazole (His) bonds at the active site or other properties of the metal ions (charge density, hydration enthalpy).

Dearomative Indole (3 + 2) Reactions with Azaoxyallyl Cations--New Method for the Synthesis of Pyrroloindolines.

Herein, we report the first examples of the synthesis of pyrroloindolines by means of (3 + 2) dearomative annulation reactions between 3-substituted indoles and highly reactive azaoxyallyl cations. Computational studies using density functional theory (DFT) (B3LYP-D3/6-311G**++) support a stepwise reaction pathway in which initial C-C bond formation takes place at C3 of indole, followed by ring closure to give the observed products. Insights gleaned from these calculations indicate that the solvent, either TFE or HFIP, can stabilize the transition state through H-bonding interactions with oxygen of the azaoxyallyl cation and other relevant intermediates, thereby increasing the rates of these reactions.

Synthesis, structure, and reactivity of iridium perfluorocarbene complexes: regio- and stereo-specific addition of HCl across a metal carbon double bond.

Reductive activation of an α-fluorine in the perfluoroalkyl complexes Cp*(L)(i)Ir-CF2RF using Mg/graphite leads to perfluorocarbene complexes Cp*(L)Ir[double bond, length as m-dash]CFRF (L = CO, PMe3; RF = CF3, C2F5, C6F5). New complexes E-Cp*(PMe3)Ir[double bond, length as m-dash]CFC2F5 and E-Cp*(CO)Ir[double bond, length as m-dash]CFC6F5 have been characterized by single crystal X-ray diffraction studies, and a comparison of metric parameters with previously reported analogues is reported. Experimental NMR and computational DFT (B3LYP/LACV3P**++) studies agree that for Ir[double bond, length as m-dash]CFRF complexes (RF = CF3, CF2CF3) the thermodynamic preference for the E or Z isomer depends on the steric requirements of ligand L; when L = CO the Z-isomer (F cis to Cp*) is preferred and for L = PMe3 the E-isomer is preferred.

A (pentafluoroethyl)(trifluoromethyl)carbene complex of iridium and reductive activation of its sp(3)α, β, and γ carbon-fluorine bonds to give perfluoro-2-butyne, perfluoro-1,2,3-butatriene and perfluoro-1-irida-2-methyl-2-cyclobutene) complexes.

The (pentafluoroethyl)(trifluoromethyl)carbene complex Cp*Ir(CO)[[double bond, length as m-dash]C(CF3)(C2F5)] was synthesized by the reductive activation of the α-C-F bond in the perfluoro-sec-butyl-iridium complex Cp*Ir(CO)[CF(CF3)(C2F5)](I) with Na/Pb alloy. This compound exists as two geometric isomers in solution; the structure of one isomer has been determined by a single crystal X-ray diffraction study and contains two independent molecules in the asymmetric unit. Further reduction of this carbene complex with Na/Pb alloy afforded the perfluoro-2-butyne iridium complex Cp*Ir(CO)(η(2)-CF3C[triple bond, length as m-dash]CCF3) by an overall 2-electron reduction and elimination of two β-fluorides.