Showing papers by "Arnold L. Rheingold published in 2020"
TL;DR: Remarkably, this chemistry tolerates various electronic environments, providing access to facile substitution chemistry at both electron-rich and electron-poor B-H vertices in carboranes.
Abstract: We report the first indirect observation and use of boron vertex-centered carboranyl radicals generated by the oxidation of modified carboranyl precursors. These radical intermediates are formed by...
38 citations
TL;DR: The utility of the fluorous soluble pentamethine cyanine dye is showcased for tracking the localization of perfluorocarbon nanoemulsions in macrophage cells and for measurements of mechanical forces in multicellular spheroids and zebrafish embryonic tissues.
Abstract: The bioorthogonal nature of perfluorocarbons provides a unique platform for introducing dynamic nano- and microdroplets into cells and organisms. To monitor the localization and deformation of the droplets, fluorous soluble fluorophores that are compatible with standard fluorescent protein markers and applicable to cells, tissues, and small organisms are necessary. Here, we introduce fluorous cyanine dyes that represent the most red-shifted fluorous soluble fluorophores to date. We study the effect of covalently appended fluorous tags on the cyanine scaffold and evaluate the changes in photophysical properties imparted by the fluorous phase. Ultimately, we showcase the utility of the fluorous soluble pentamethine cyanine dye for tracking the localization of perfluorocarbon nanoemulsions in macrophage cells and for measurements of mechanical forces in multicellular spheroids and zebrafish embryonic tissues. These studies demonstrate that the red-shifted cyanine dyes offer spectral flexibility in multiplexed imaging experiments and enhanced precision in force measurements.
37 citations
TL;DR: This report introduces stimuli-responsive decomplexation as an additional consideration in the design of high-affinity host-guest complexes by prepared boron-functionalized 9-amino-ortho-carborane that binds to CB[7] with a Ka ≈ 1010 M-1.
Abstract: High-affinity guests have been reported for the macrocyclic host cucurbit[7]uril (CB[7]), enabling widespread applications, but hindering CB[7] materials from being returned to their guest-free sta...
27 citations
TL;DR: The implementation of strongly coordinating dianionic carboranyl N-Heterocyclic Carbenes (NHCs) to create organometallic ate complexes of Au(I) that serve both as WCAs and functional catalysts are described.
Abstract: Weakly coordinating anions (WCAs) are generally tailored to act as spectators with little or no function. Here we describe the implementation of strongly coordinating dianionic carboranyl N-heteroc...
24 citations
TL;DR: It is shown that azide, sulfonamide, cyanate, and phosphoramidate nucleophiles can be straightforwardly cross-coupled onto the B(9) vertices of the o- and m-carborane core from readily accessible precursors without significant deboronation by-products, laying the groundwork for further study into the utility and properties of these new B-aminated carborane species.
17 citations
TL;DR: In this paper, the synthesis of unsymmetrically trisubstituted bismuthanes of the general formula Ar12Ar2Bi has been studied in the context of organobismuthane dismutation.
14 citations
TL;DR: This work reports the synthesis and characterization of a new C^N-based cycloplatinated(II) fluoride complex, [Pt(ppy)(PPh3)F] (2; ppy = 2-phenylpyridinate), involving a Pt-F bond, which is highly luminescent in the green area with a high quantum yield.
Abstract: This work reports the synthesis and characterization of a new C^N-based cycloplatinated(II) fluoride complex, [Pt(ppy)(PPh3)F] (2; ppy = 2-phenylpyridinate), involving a Pt-F bond. The new complex is highly luminescent in the green area with a high quantum yield of 94.6% at 77 K. A comparison study of the heavier halogen derivatives reveals a descending emission quantum yield order of F > Cl > Br > I. Time-dependent density functional theory calculations ascribe the decreased emission efficiency to the decreasing trend of an intraligand (IL) transition from F to I, which accounts for the major radiative pathway. In addition, 2 is capable of the fluorinating alkyl halides, leading to Csp3-F bond formation at room temperature.
13 citations
TL;DR: X-ray structures are reported for the first time for tolyporphin A, R, R (8), E (9), revealing unexpected stereochemical variation within the series.
Abstract: Tolyporphins L–R (2–8) have been isolated from a mixed cyanobacterium-microbial culture. The structures of tolyporphins L and M have been revised to four constitutional isomers, isolated as two mix...
11 citations
TL;DR: This work establishes a foundation for the development of new catalysts for stereoselective electrocyclizations by utilizingPF 6 as a precatalyst for the disrotatory 6π electrocyclization of highly substituted trienes that are resistant to thermal cyclization.
Abstract: Triene 6π electrocyclization, wherein a conjugated triene undergoes a concerted stereospecific cycloisomerization to a cyclohexadiene, is a reaction of great historical and practical significance. In order to circumvent limitations imposed by the normally harsh reaction conditions, chemists have long sought to develop catalytic variants based upon the activating power of metal-alkene coordination. Herein, we demonstrate the first successful implementation of such a strategy by utilizing [(C5 H5 )Ru(NCMe)3 ]PF6 as a precatalyst for the disrotatory 6π electrocyclization of highly substituted trienes that are resistant to thermal cyclization. Mechanistic and computational studies implicate hexahapto transition-metal coordination as responsible for lowering the energetic barrier to ring closure. This work establishes a foundation for the development of new catalysts for stereoselective electrocyclizations.
11 citations
TL;DR: It was found that spectroscopy-oriented configuration interaction as applied to a simplified model in which the free-ion lanthanide was embedded in ligand-centered Löwdin point charges performed as well or better than canonical NEVPT2 calculations, when the ligand orbitals were included in the treatment.
Abstract: Four groups of rare-earth complexes, comprising 11 new compounds, with fluorinated O-donor ligands ([K(THF)6][Ln(OC4F9)4(THF)2] (1-Ln; Ln = Ce, Nd), [K](THF)x[Ln(OC4F9)4(THF)y] (2-Ln; Ln = Eu, Gd, Dy), [K(THF)2][Ln(pinF)2(THF)3] (3-Ln; Ln = Ce, Nd), and [K(THF)2][Ln(pinF)2(THF)2] (4-Ln; Ln = Eu, Gd, Dy, Y) have been synthesized and characterized Single-crystal X-ray diffraction data were collected for all compounds except 2-Ln Species 1-Ln, 3-Ln, and 4-Ln are uncommon examples of six-coordinate (Eu, Gd, Dy, and Y) and seven-coordinate (Ce and Nd) LnIII centers in all-O-donor environments Species 1-Ln, 2-Ln, 3-Ln, and 4-Ln are all luminescent (except where Ln = Gd and Y), with the solid-state emission of 1-Ce being exceptionally blue-shifted for a Ce complex The emission spectra of the six Nd, Eu, and Dy complexes do not show large differences based on the ligand and are generally consistent with the well-known free-ion spectra Time-dependent density functional theory results show that 1-Ce and 3-Ce undergo allowed 5f → 4d excitations, consistent with luminescence lifetime measurements in the nanosecond range Eu-containing 2-Eu and 4-Eu, however, were found to have luminescence lifetimes in the millisecond range, indicating phosphorescence rather than fluorescence The performance of a pair of multireference models for prediction of the Ln = Nd, Eu, and Dy absorption spectra was assessed It was found that spectroscopy-oriented configuration interaction as applied to a simplified model in which the free-ion lanthanide was embedded in ligand-centered Lowdin point charges performed as well (Nd) or better (Eu and Dy) than canonical NEVPT2 calculations, when the ligand orbitals were included in the treatment
8 citations
TL;DR: It is shown that expansion of the [CNArMes2]2 scaffold with a central phenylene spacer allows for the formation of a robust Cu(I)-based framework with a distinct and solvent accessible channel structure, thereby signifying the robust nature of materials produced from metal-isocyanide M-C linkages.
Abstract: Isocyanide coordination networks (ISOCNs), which consist of multitopic isocyanide linker groups and transition-metal-based secondary building units (SBUs), are a promising class of organometallic f...
TL;DR: The advances described demonstrate the value that programs in natural product total synthesis have in advancing organic chemistry, here through the design and realization of an annulation reaction that accom-plishes what previously established reactions do not.
Abstract: A stereoselective entry to ryanoids is described that culminates in the synthesis of anhydroryanodol and thus the formal total synthesis of ryanodol. The pathway described features an annulation re...
TL;DR: In this article, single crystal X-ray structures of the complexes reveal that in all the three complexes the Ln(III) ions are in a distorted dodecahedral geometry with N4O4-coordination environment provided by two coordinated ligands.
TL;DR: A new cytotoxic thiodepsipeptide, verrucosamide (1), was isolated along with the known, related cyclic peptide thiocoraline, from the extract of a marine-derived actinomycete, a Verrucosispora sp.
Abstract: A new cytotoxic thiodepsipeptide, verrucosamide (1), was isolated along with the known, related cyclic peptide thiocoraline, from the extract of a marine-derived actinomycete, a Verrucosispora sp., our strain CNX-026. The new peptide, which is composed of two rare seven-membered 1,4-thiazepane rings, was elucidated by a combination of spectral methods and the absolute configuration was determined by a single X-ray diffraction study. Verrucosamide (1) showed moderate cytotoxicity and selectivity in the NCI 60 cell line bioassay. The most susceptible cell lines were MDA-MB-468 breast carcinoma with an LD50 of 1.26 µM, and COLO 205 colon adenocarcinoma with an LD50 of 1.4 µM. Also isolated along with verrucosamide were three small 3-hydroxy(alkoxy)-quinaldic acid derivatives that appear to be products of the same biosynthetic pathway.
TL;DR: Calculations confirm that the Sn(ii) lone pair is localized within the 5s orbital and reveal that theSn 5px LUMO is energetically inaccessible, which effectively abates reactivity.
Abstract: The synthesis and characterization of a series of Sn(II) and Sn(IV) complexes supported by the highly electron-withdrawing dianionic perfluoropinacolate (pinF) ligand are reported herein. Three analogs of [SnIV(pinF)3]2− with NEt3H+ (1), K+ (2), and {K(18C6)}+ (3) counter cations and two analogs of [SnII(pinF)2]2− with K+ (4) and {K(15C5)2}+ (5) counter cations were prepared and characterized by standard analytical methods, single-crystal X-ray diffraction, and 119Sn Mossbauer and NMR spectroscopies. The six-coordinate SnIV(pinF) complexes display 119Sn NMR resonances and 119Sn Mossbauer spectra similar to SnO2 (cassiterite). In contrast, the four-coordinate SnII(pinF) complexes, featuring a stereochemically-active lone pair, possess low 119Sn NMR chemical shifts and relatively high quadrupolar splitting. Furthermore, the Sn(II) complexes are unreactive towards both Lewis bases (pyridine, NEt3) and acids (BX3, Et3NH+). Calculations confirm that the Sn(II) lone pair is localized within the 5s orbital and reveal that the Sn 5px LUMO is energetically inaccessible, which effectively abates reactivity.
14 Jan 2020
TL;DR: Two Cu(II)-malonate complexes with 2-amino-4-methylpyridine and 2-aminopyrimidine auxiliary ligands were synthesized, and their single-crystal X-ray diffraction structures were established.
Abstract: Two Cu(II)-malonate complexes with 2-amino-4-methylpyridine (complex 1) and 2-aminopyrimidine (complex 2) auxiliary ligands were synthesized, and their single-crystal X-ray diffraction structures w...
TL;DR: In this paper, the authors investigated the hydrogen bond strength of symmetric and asymmetric ditopic secondary amines with 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr), a representative NHC.
Abstract: Hydrogen bonding plays a critical role in maintaining order and structure in complex biological and synthetic systems. N-heterocyclic carbenes (NHCs) represent one of the most versatile tools in the synthetic chemistry toolbox, yet their potential as neutral carbon hydrogen bond acceptors remains underexplored. This report investigates this capability in a strategic manner, wherein carbene-based hydrogen bonding can be assessed by use of ditopic NH-containing molecules. N–H bonds are unique as there are three established reaction modes with carbenes: non-traditional hydrogen bonding adducts (X–H⋯:C), salts arising from proton transfer ([H–C]+[X]−), or amines from insertion of the carbene into the N–H bond. Yet, there are no established rules to predict product distributions or the strength of these associations. Here we seek to correlate the hydrogen bond strength of symmetric and asymmetric ditopic secondary amines with 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr, a representative NHC). In symmetric and asymmetric ditopic amine adducts both the solid-state (hydrogen bond lengths, NHC interior angles) and solution-state (1H Δδ of NH signals, 13C signals of carbenic carbon) can be related to the pKa of the parent amine.
TL;DR: Rec reproducing oxidative alcohol dehydrogenation (OAD) chemistry known for VOx surfaces and demonstrating, in air, the thermodynamically challenging selective oxidation of alcohols to aldehydes/ketones.
Abstract: A new air-stable catalyst for the oxidative dehydrogenation of benzylic alcohols under ambient conditions has been developed. The synthesis and characterization of this compound and the related monomeric and dimeric V(IV)- and V(V)-pinF (pinF = perfluoropinacolate) complexes are reported herein. Monomeric V(IV) complex (Me4N)2[V(O)(pinF)2] (1) and dimeric (μ-O)2-bridged V(V) complex (Me4N)2[V2(O)2(μ-O)2(pinF)2] (3a) are prepared in water under ambient conditions. Monomeric V(V) complex (Me4N)[V(O)(pinF)2] (2) may be generated via chemical oxidation of 1 under an inert atmosphere, but dimerizes to 3a upon exposure to air. Complexes 1 and 2 display a perfectly reversible VIV/V couple at 20 mV (vs Ag/AgNO3), whereas a quasi-reversible VIV/V couple at -865 mV is found for 3a. Stoichiometric reactions of 3a with both fluorenol and TEMPOH result in the formation of (Me4N)2[V2(O)2(μ-OH)2(pinF)2] (4a), which contains two V(IV) centers that display antiferromagnetic coupling. In order to structurally characterize the dinuclear anion of 4a, {K(18C6)}+ countercations were employed, which formed stabilizing K···O interactions between the counterion and each terminal oxo moiety and H-bonding between the oxygen atoms of the crown ether and μ-OH bridges of the dimer, resulting in {K(18C6)}2[V2(O)2(μ-OH)2(pinF)2] (4b). The formal storage of H2 in 4a is reversible and proton-coupled electron transfer (PCET) from crystals of 4a regenerates 3a upon exposure to air over the course of several days. Furthermore, the reaction of 3a (2%) under ambient conditions with excess fluorenol, cinnamyl alcohol, or benzyl alcohol resulted in the selective formation of fluorenone (82% conversion), cinnamaldehyde (40%), or benzaldehyde (7%), respectively, reproducing oxidative alcohol dehydrogenation (OAD) chemistry known for VOx surfaces and demonstrating, in air, the thermodynamically challenging selective oxidation of alcohols to aldehydes/ketones.
TL;DR: The rhodium benzyl complexes Rh(diphos*)(η3-CH2Ph) (1, 14, diphos = chiral bis(phosphine), potential precursors for asymmetric catalysis, were prepared either by treatment of Rh(COD) (η 3-CH 2Ph).
TL;DR: 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.
Abstract: Kinetic separation of the commercially available cis/trans-(+)-limonene oxide mixture by ring opening with primary phosphido nucleophiles LiPHR (R = ferrocenyl, Ph, Cy, t-Bu, Mes* (Mes* = 2,4,6-(t-Bu)3C6H2)), followed by treatment with aqueous NH4Cl and H2O2, gave unreacted cis-(+)-limonene oxide and diastereoenriched mixtures of the secondary phosphine oxides (SPOs) PHR(trans-(+)-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.
TL;DR: A series of heteroleptic mixed phosphine/alkoxide 3d complexes was designed to evaluate PPh3 as a protecting group, stabilizing the metal coordination sphere prior to O2 exposure, but oxidatively dissociating in the presence of O2 to allow facile O2 reduction by low coordinate metal centers as mentioned in this paper.
TL;DR: Magnetic characterization confirms slow magnetic relaxation behaviour and suggests antiferromagnetic coupling across {Ln-O[double bond, length as m-dash]V} in all four complexes, with variations tunable as a function of Ln and R.
TL;DR: In this article, an IrIIICp* complex bearing a triazenide ligand functionalized with pyrazole was synthesized and fully characterized by spectroscopic methods and the structure confirmed by X-ray diffraction studies.
TL;DR: The crystal structures of the oxidized states of three of the most common biochemical reducing agents have been determined, by crystallization from aqueous solution where possible: tris(2-carboxyethyl)phosphine oxide (TCEP oxide, 1), bis (2-hydroxyethyl) disulfide (2MESS, 3), and tributylphosphines oxide (Bu4PO, 4) as mentioned in this paper.
TL;DR: In this paper, the structure of the platinum selenolate complex along with an organo-oxotin cage compound in the same lattice were characterized by elemental analyses, NMR (1H, 31P, 77Se, 119Sn) spectroscopy and scalar relativistic density functional theory calculations.
Abstract: The reaction of [PtCl2(P–P)] (P–P = PPh3, dppp) with [R2Sn(SeC5H4N)2] (R = Me, Et) afforded an orange co-crystallized product [{Pt(κ2-SeC5H4N)(P–P)}{R10Sn5(μ-O)3Cl5}] (P–P = PPh3, dppp; R = Me, Et). The latter complexes can also be obtained by the treatment of [Pt(SeC5H4N)2(dppp)] with R2SnCl2 (R = Me, Et). These co-crystallized complexes displayed a completely separated core of the platinum selenolate complex along with an organo-oxotin cage compound in the same lattice. These complexes were characterized by elemental analyses, NMR (1H, 31P, 77Se, 119Sn) spectroscopy and scalar relativistic density functional theory (DFT) calculations. The crystal structures of compounds [{Pt(κ2-SeC5H4N)(dppp)}{Me10Sn5(μ-O)3(μ-Cl)Cl4}]HCONMe2 (2a) and [{Pt(Cl)(SeC5H4N)(P–P)}{Et10Sn5(μ-O)3Cl5}] (2b) were established by single crystal X-ray diffraction analyses. Natural bond orbital (NBO) and energy decomposition analysis (EDA) were carried out in detail to establish the nature of bonding in both cocrystals. Their molecular structure contains nearly the same platinum fragment; however, the only variation that can be observed with the organo-oxotin cage fragment is that the methyl-substituted oxotin compound 2a is Cl-capped and the ethyl substituted one 2b is an O-capped type cluster.
TL;DR: The first intermediate in chemical reactions mediated by Fe(CO)5 is considered in this paper, and it has long been recognized that the first intermediate is Fe( CO)5.
25 Nov 2020
TL;DR: X-ray analysis revealed unconventional C–H···N hydrogen bonding between two quinolyls of neighboring molecules, pointing to a new strategy for the development of non-planar molecular semiconductors with stronger intermolecular interactions.
Abstract: Zinc(II) complexes of tetraphenylazadipyrromethenes are potential non-planar n-type conjugated materials. To tune the properties, we installed 5-quinolylethynyl groups at the pyrrolic positions. Co...
TL;DR: The trigermanes ButMe2GeGePh2GeMe2But and Bun3GeGePH2GeBun3 were synthesized via the hydrogermolysis reaction.
TL;DR: The synthetic factors governing access to tris(β-diketimine) cyclophanes versus tripodal tri-β-aminoenones are discussed, and a modified condensation method produced α-Me β-Me cyclophane.
Abstract: Tris(β-diketimine) cyclophanes are an important ligand class for investigating cooperative multimetallic interactions of bioinorganic clusters. Discussed herein are the synthetic factors governing ...