- O -Functionalization of a cobalt carbonyl generates a terminal cobalt carbyne
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Despite efforts toward extending multiple bonding motifs to late metal systems, examples of late transition metal carbynes remain scarce. Herein, we describe the synthesis of a series of L3Co(CO) complexes supported by a trisphosphine ligand framework, with the most reduced of these complexes being amenable to O-functionalization. This transformation provides access to the second reported example of a terminal Co-carbyne complex, in this case stabilized in a pseudotetrahedral geometry (i.e., L3CoC-OSiR3). Its geometry makes its electronic structure suitable for comparison to structurally-related examples of terminal Co-imido and oxo species.
- Deegan, Meaghan M.,Peters, Jonas C.
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supporting information
p. 9531 - 9534
(2019/08/15)
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- Exploiting Charge-Transfer States for Maximizing Intersystem Crossing Yields in Organic Photoredox Catalysts
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A key feature of prominent transition-metal-containing photoredox catalysts (PCs) is high quantum yield access to long-lived excited states characterized by a change in spin multiplicity. For organic PCs, challenges emerge for promoting excited-state intersystem crossing (ISC), particularly when potent excited-state reductants are desired. Herein, we report a design exploiting orthogonal π-systems and an intermediate-energy charge-transfer excited state to maximize ISC yields (ΦISC) in a highly reducing (E0? = -1.7 V vs SCE), visible-light-absorbing phenoxazine-based PC. Simple substitution of N-phenyl for N-naphthyl is shown to dramatically increase ΦISC from 0.11 to 0.91 without altering catalytically important properties, such as E0?.
- Sartor, Steven M.,McCarthy, Blaine G.,Pearson, Ryan M.,Miyake, Garret M.,Damrauer, Niels H.
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supporting information
p. 4778 - 4781
(2018/04/17)
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- A Gold Carbene Manifold to Prepare Fused γ-Lactams by Oxidative Cyclisation of Ynamides
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Gold-catalysed oxidative cyclisation reactions of ynamides offer great promise in γ-lactam synthesis but are limited by preferential over-oxidation to form α-keto imides. Evaluating the factors that might limit N-cyclisation pathways led to effective gold-catalysed conditions that allow access to different fused γ-lactams on changing the ynamide N-substituent and accommodate previously incompatible substitution patterns. New and efficient methods for the synthesis of functionalised 3-aryl indoles and cyclohepta[c]pyrrol-1-one derivatives are presented. These conditions illustrate the complementarity of gold catalysis to other metals.
- Sánchez-Cantalejo, Fernando,Priest, Joshua D.,Davies, Paul W.
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supporting information
p. 17215 - 17219
(2018/11/10)
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- Formal Synthesis of Bioactive Indole Alkaloids Eburnamonine, Eburnaminol, and Vindeburnol
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Starting from (±)-3-acetoxyglutarimide, diastereoselective formal synthesis of indole alkaloids (±)-eburnamonine, (±)-eburnaminol, and (±)-vindeburnol have been demonstrated via a common intermediate (±)-1-hydroxy-12-tosyl-2,3,6,7,12,12b-hexahydroindolo[2,3-a]quinolizin-4(1H)-one in very good overall yields. The acetoxy group from (±)-3-acetoxyglutarimide was first used to induce the diastereoselectivity and also as a latent source of ketone carbonyl group. The stereoselective eliminations, reductions, and intramolecular cyclizations were the involved key steps.
- Mondal, Pravat,Argade, Narshinha P.
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p. 1849 - 1856
(2017/04/06)
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- Structures, Interconversions, and Spectroscopy of Iron Carbonyl Clusters with an Interstitial Carbide: Localized Metal Center Reduction by Overall Cluster Oxidation
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The syntheses, interconversions, and spectroscopic properties of a set of iron carbonyl clusters containing an interstitial carbide are reported. This includes the low temperature X-ray structures of the six-iron clusters (Y)2[Fe6(μ6-C)(μ2-CO)4(CO)12] (1a-c; where Y = NMe4, NEt4, PPh4); the five-iron cluster [Fe5(μ5-C)(CO)15] (3); and the novel formulation of the five-iron cluster (NMe4)2[Fe5(μ5-C)(μ2-CO)(CO)13] (4). Also included in this set is the novel charge-neutral cluster, [Fe6(μ6-C)(CO)18] (2), for which we were unable to obtain a crystallographic structure. As synthetic proof for the identity of 2, we performed a closed loop of interconversions within a family of crystallographically defined species (1, 3, and 4): [Fe6]2- → [Fe6]0 → [Fe5]0 → [Fe5]2- → [Fe6]2-. The structural, spectroscopic, and electronic properties of this "missing link" cluster 2 were investigated by IR, Raman, XPS, and M?ssbauer spectroscopies - as well as by DFT calculations. A single νCO feature (1965 cm-1) in the IR spectrum of 2, as well as a prominent Raman feature (νsymm = 1550 cm-1), are consistent with the presence of terminal carbonyls and a {(μ6-C)Fe6} arrangement of iron centers around the central carbide. The XPS of 2 exhibits a higher energy Fe 2p3/2 feature (707.4 eV) as compared to that of 1 (705.5 eV), consistent with the two-electron oxidation induced by treatment of 1 with two equivalents of [Fc](PF6) under CO atmosphere (for the two added CO ligands). DFT calculations indicate two axial and four equatorial Fe sites in 1, all of which have the same or similar oxidation states, for example, two Fe(0) and four Fe(+0.5). These assignments are supported by M?ssbauer spectra for 1, which exhibit two closely spaced quadrupole doublets with δ = 0.076 and 0.064 mm s-1. The high-field M?ssbauer spectrum of 2 (4.2 K) exhibits three prominent quadrupole doublets with δ = -0.18, -0.11, and +0.41 mm s-1. This indicates three pairs of chemically equivalent Fe sites. The first two pairs arise from irons of a similar oxidation state, while the last pair arises from irons in a different oxidation state, indicating a mixed-valent cluster. Variable field M?ssbauer spectra for 2 were simulated assuming these two groups and a diamagnetic ground state. Taken together, the M?ssbauer results and DFT calculations for 2 indicate two axial Fe(II) sites and four equatorial sites of lower valence, probably Fe(0). In the DFT optimized pentagonal bipyramidal structure for 2, the Fe(II)-Ccarbide distances are compressed (~1.84 ?), while the Fe(0)-Ccarbide distances are elongated (~2.05 ?). Analysis of the formulations for 1 (closo-square bipyramid) and 2 (nido-pentagonal bipyramid) is considered in the context of the textbook electron-counting rules of 14n+2 and 14n+4 for closo and nido clusters, respectively. This redox-dependent intracluster disproportionation of Fe oxidation states is concluded to arise from changes in bonding to the central carbide. A similar phenomenon may be promoted by the central carbide of the FeMoco cluster of nitrogenase, which may in turn stimulate N2 reduction.
- Kuppuswamy, Subramaniam,Wofford, Joshua D.,Joseph, Chris,Xie, Zhu-Lin,Ali, Azim K.,Lynch, Vincent M.,Lindahl, Paul A.,Rose, Michael J.
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p. 5998 - 6012
(2017/05/22)
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- A Straightforward Synthesis of 5-Methylaaptamine from Eugenol, Employing a 6π-Electrocyclization Reaction of a 1-Azatriene
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Aaptamine, isolated from tropical marine sponges of the Demospongiae class, is the most prominent member of a growing family of natural products. Many aaptaminoids have been shown to have interesting biological activity. The efficient access to 5-methylaaptamine, an unnatural analogue of aaptamine, was achieved by using economic and naturally-occurring eugenol as the starting material. The synthesis involved the preparation of a 5-aminoeugenol derivative through successive nitration, O-methylation, and nitro group reduction reactions. An Elderfield-Johnson sequence was employed to synthesize the N-tosyl-5-allyl-7,8-dimethoxydihydro-1H-quinolin-4-one ring system. A catalytic double-bond isomerization followed by a carbonyl methoximation and 6-π electrocyclization of the 1-azatriene motif afforded the 2,3-dihydro-1H-benzo[de][1,6]naphthyridine tricyclic intermediate, which underwent a reductive desulfonylation and catalytic dehydrogenation to afford the target product.
- Heredia, Daniel A.,Larghi, Enrique L.,Kaufman, Teodoro S.
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p. 1397 - 1404
(2016/03/19)
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- Palladium-catalyzed cyclization of bromoenynamides to tricyclic azacycles: Synthesis of trikentrin-like frameworks
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Palladium-catalyzed cascade cyclization of bromoenynamides equipped with an additional alkyne or ynamide substituent affords azatricyclic products. Using 5- to 7-membered ring tethers, this chemistry offers a regiospecific route to highly-functionalized azacycles. Elaboration to the trikentrin B skeleton is achieved from the arylsilane cyclization products. the Partner Organisations 2014.
- Campbell, Craig D.,Greenaway, Rebecca L.,Holton, Oliver T.,Chapman, Helen A.,Anderson, Edward A.
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supporting information
p. 5187 - 5189
(2014/05/06)
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- Oxidation and reduction of bis(imino)pyridine iron dinitrogen complexes: Evidence for formation of a chelate trianion.
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Oxidation and reduction of the bis(imino)pyridine iron dinitrogen compound, (iPrPDI)FeN2 (iPrPDI = 2,6-(2,6- iPr2-C6H3-N=CMe)2C 5H3N) has been examined to determine whether the redox events are metal or ligand based. Treatment of (iPrPDI)FeN 2 with [Cp2Fe][BArF4] (BAr F4 = B(3,5-(CF3)2-C 6H3)4) in diethyl ether solution resulted in N2 loss and isolation of [(iPrPDI)Fe(OEt 2)][BArF4]. The electronic structure of the compound was studied by SQUID magnetometry, X-ray diffraction, EPR and zero-field 57Fe M?ssbauer spectroscopy. These data, supported by computational studies, established that the overall quartet ground state arises from a high spin iron(II) center (SFe = 2) antiferromagnetically coupled to a bis(imino)pyridine radical anion (SPDI = 1/2). Thus, the oxidation event is principally ligand based. The one electron reduction product, [Na(15-crown-5)][(iPrPDI)FeN2], was isolated following addition of sodium naphthalenide to (iPrPDI)FeN2 in THF followed by treatment with the crown ether. Magnetic, spectroscopic, and computational studies established a doublet ground state with a principally iron-centered SOMO arising from an intermediate spin iron center and a rare example of trianionic bis(imino)pyridine chelate. Reduction of the iron dinitrogen complex where the imine methyl groups have been replaced by phenyl substituents, (iPrBPDI)Fe(N2)2 resulted in isolation of both the mono-and dianionic iron dinitrogen compounds, [( iPrBPDI)FeN2]- and [(iPrBPDI) FeN2]2-, highlighting the ability of this class of chelate to serve as an effective electron reservoir to support neutral ligand complexes over four redox states.
- Tondreau, Aaron M.,Stieber, S. Chantal E.,Milsmann, Carsten,Lobkovsky, Emil,Weyhermüller, Thomas,Semproni, Scott P.,Chirik, Paul J.
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p. 635 - 646
(2013/03/13)
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- One-pot galvanic formation of ultrathin-shell Sn/CoOx nanohollows as high performance anode materials in lithium ion batteries
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The thermolysis of a heterobimetallic Sn-Co organometallic precursor resulted in the formation of hollow Sn/CoOx nanomaterials through galvanic reaction between metal species. The Sn/CoOx nanohollows with 6.1 nm diameter and ~1.5 nm shell thickness showed excellent lithium storage capacity of up to 857 mA h g-1 after 30 cycles.
- Xu, Juan,Jin, Jaewon,Kim, Kyeongyeol,Shin, Young Jun,Kim, Hae Jin,Son, Seung Uk
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supporting information
p. 5981 - 5983
(2013/07/19)
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- NK1 ANTAGONIST
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The invention is to a compound exhibiting neurokinin inhibitory properties, a pharmaceutical composition comprising same and a method of treatment for neurokinin-meditated conditions.Formula (I)
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Page/Page column 22; 24-25; 41-42
(2010/02/09)
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- A Facile One Pot Synthesis of 1-Alkylbenzimidazoline-2-thiones
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Reactions of benzimidazoline-2-thione with alkyl halides in the presence of sodium naphthalenide in tetrahydrofuran at room temperature under a nitrogen atmosphere afforded 1-alkyl-2-alkylthiobenzimidazoles in excellent yields, which underwent a bond cleavage between S and C of alkyl group to give excellent yields of 1-alkylbenzimidazoline-2-thiones by the treatment with an additional amount of sodium naphthalenide.
- Lee, Tae Ryong,Kim, Kyongtae
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p. 747 - 751
(2007/10/02)
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- Paramagnetic Solvent Nuclear Magnetic Resonance Shifts in Radical Anion Solutions. 2. Some Cation-Dependent Phenomena in Concentrated Solutions of Aromatic Hydrocarbon Radical Anions and Dianions
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The molar paramagnetic solvent shifts (MPSS's) of (biphenyl)(1-)Li(1+), (p-terphenyl)(1-)M(1+) (M = Li, Na), (naphthalene)(1-)M(1+) (M = Li, Na, K), (2-tert-butylnaphthalene)(1-)Li(1+), (2,6-di-tert-butylnaphthalene)(1-)Li(1+), (phenanthrene)(1-)M(1+) (M = Li, Na, K), (anthracene)(1-)M(1+) (M = Li, Na, K), (pyrene)(1-)M(1+) (M = Li, Na, K),(chrysene)(1-)M(1+) (M = Li, Na, K), (cis-stilbene)(1-)Li(1+), and (trans-stilbene)(1-)Li(1+) have been measured in tetrahydrofuran (THF) at 60 MHz and at 35 +/- 1 deg C.These parameters, which are more or less cation as well as anion dependent, may reflect structural properties of the ion pairs in solution such as covalency in the ion-pair bond or aggregation to diamagnetic species.The effect of alkyl substitution on the magnitude of the MPSS has been studied in the case of lithium napthalene radical anion.A tert-butyl group in the 2-position has no effect on the molar shift.Two tert-butyl groups in the 2,6-positions, however, cause a dramatic drop in the magnitude of the MPSS.It has been shown that this change is due to extensive spin pairing.A double internal reference technique has been used in order to separate contributions due to the bulk paramagnetism and the contact shift.Contrary to previous belief that THF protons undergo only negative contact shifts, it was shown that they may undergo positive contact shifts as well.Thus the α protons of THF in the presence of lithium naphthalene radical anion exhibit a contact shift of -0.25 ppm/mol, whereas in the presence of lithium (p-biphenyl)phenylketyl they exhibit a contact shift of 0.25 ppm/mol.These contact shifts correspond to coupling constants of the order of 10-3 G.Attention is called, however, to the possibility that in strongly cation-complexing agents such as glymes, the contact shift could correspond to a coupling constant of the order of 0.1 G.In such a case, line broadening in the ESR spectra could be caused by additional small splitting due to the interaction of the unpaired spin with the protons of the coordinated-to-cation ligands.The effect of adding poorly solvating cosolvents, Et2O and Et3N, on the structure of (naphthalene)(1-)M(1+) (M = Li, Na, K) has been studied.Three patterns of behavior have been observed. (1) The added cosolvent does not perturb the structure of the radical anion-cation pair. (2) A change occurs after the composition of the medium reaches a certain point, and the change varies gradually as the medium becomes enriched in cosolvent. (3) An abrupt change occurs at a certain composition of the medium.The above phenomena are strongly cation dependent.Dianions of polynuclear aromatic hydrocarbons, particularly those with angularly condensed rings, are chemically unstable in THF, causing cleavage of the ethereal solvent.Instability appears to depend markedly on the cation and increases in the order K, Na, Li.
- Screttas, Constantinos G.,Micha-Screttas, Maria
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p. 153 - 158
(2007/10/02)
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- Thermochemistry of Solid Naphthalene Anion Salts and Their Interaction with Water
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Calorimetric studies have been used to determine that the solid sodium salt of the naphthalene anion radical lies at about the same energy level as does sodium metal and naphthalene, while the tetrahydrofuran (THF) solvated anion radical lies 13 kcal/mol lower in energy.The solid potassium naphthalenide lies about 9.6 kcal/mol lower than solid potassium metal and naphthalene.The calorimetric results have been placed into a thermochemical cycle to yield the crystal lattice energy and the heat of solvation of the sodium salt.ESR has been used to monitor the decomposition of the solid anion radical salt into the sodium-naphthalene mixture
- Stevenson, Gerald R.,Wledrich, Charles R.,Zigler, Steven S.,Echegoyen, Luis,Maldonado, Rene
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p. 4995 - 4998
(2007/10/02)
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