- Photophysical processes in rhenium(I) diiminetricarbonyl arylisocyanides featuring three interacting triplet excited states
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We present a series of four transition-metal complexes based on the rhenium(I) tricarbonyl 1,10-phenanthroline (phen) template, with a lone ancillary arylisocyanide (CNAr) ligand to yield metal-organic chromophores of the generic molecular formula [Re(phen)-(CO)3(CNAr)]+ [CNAr = 2,6-diisopropylphenyl isocyanide (1), 4-phenyl-2,6-diisopropylphenyl isocyanide (2), 4-phenylethynyl-2,6-diisopropylphenyl isocyanide (3), and 4-biphenyl-2,6-diisopropylphenyl isocyanide (4)]. This particular series features varied degrees of π-conjugation length in the CNAr moiety, resulting in significant modulation in the resultant photophysical properties. All molecules possess long-lived [8- 700 μs at room temperature (RT)], strongly blue-green photoluminescent and highly energetic excited states λmax,em = 500-518 nm; Φ = 14-64%). Each of these chromophores has been photophysically investigated using static and dynamic spectroscopic techniques, the latter probed from ultrafast to suprananosecond time scales using transient absorption and photoluminescence (PL). Time-resolved PL intensity decays recorded as a function of the temperature were consistent with the presence of at least two emissive states lying closely spaced in energy with a third nonemissive state lying much higher in energy and likely ligand-field in character. The combined experimental evidence, along with the aid of electronic structure calculations (density functional theory and time-dependent density functional theory performed at the M06/Def2-SVP/SDD level), illustrates that the CNAr ligand is actively engaged in manipulating the excited-state decay in three of these molecules (2-4), wherein the triplet metal-to-ligand charge-transfer (3MLCT) state along with two distinct triplet ligand-centered (3LC) excited-state configurations (phen and CNAr) conspire to produce the resultant photophysical properties. Because the π conjugation within the CNAr ligand was extended, an interesting shift in the dominant photophysical processes was observed. When the CNAr conjugation length is short, as in 1, the phenanthroline 3LC state dominates, resulting in a configurationally mixed triplet excited state of both LC and MLCT character. With more extended π conjugation in the CNAr subunit (2-4), the initially generated 3LC(phen)/3MLCT excited state ultimately migrates to the CNAr 3LC state on the order of tens of picoseconds. Molecules 3 and 4 in this series also feature unique examples of inorganic excimer formation, as evidenced by dynamic self-quenching in the corresponding PL intensity decays accompanied by the observation of a short-lived low-energy emission feature.
- Favale, Joseph M.,Danilov, Evgeny O.,Yarnell, James E.,Castellano, Felix N.
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Read Online
- Carbenes made easy: Formation of unsymmetrically substituted N-heterocyclic carbene complexes of palladium(II), platinum(II) and gold(I) from coordinated isonitriles and their catalytic activity
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From palladium(II) or platinum(II) bis(isonitrile) complexes and from gold(I) isonitrile complexes, both easily available from simple precursors, the corresponding mono-N-heterocyclic carbene (NHC) complexes could be obtained selectively in good yields under very mild conditions. The reagents are simple β-chloroammonium salts in the presence of a weak base. Unsymmetric NHC complexes are accessible. Thus over only two steps from simple metal precursors a broad variety of NHC complexes is available, the method is ideal to quickly assemble catalyst libraries. The palladium complexes are active pre-catalysts in Suzuki cross-coupling even with the additional isonitrile ligand on palladium. Copyright
- Hashmi, A. Stephen K.,Lothschuetz, Christian,Boehling, Constantin,Hengst, Tobias,Hubbert, Christoph,Rominger, Frank
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Read Online
- Palladium-Catalyzed Diarylation of Isocyanides with Tetraarylleads for the Selective Synthesis of Imines and α-Diimines
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Using tetraaryllead compounds (PbAr4) as arylating reagents, isocyanides undergo selective diarylation in the presence of palladium catalysts such as Pd(OAc)2 or Pd(PPh3)4 to afford imines and/or α-diimines based on the isocyanide employed. With aliphatic isocyanides, imines are obtained preferentially, whereas α-diimines are formed in the case of electron-rich aromatic isocyanides. The differences in imine/α-diimine selectivity can be attributed to the stability of imidoylpalladium intermediates formed in this catalytic reaction. Compared with other arylating reagents, tetraaryllead compounds are excellent candidates for use in the selective transformations to imines and/or α-diimines, especially in terms of inhibiting the oligomerization of isocyanides, which results in a lower product selectivity in many transition-metal-catalyzed reactions of isocyanides.
- Tran, Cong Chi,Kawaguchi, Shin-Ichi,Kobiki, Yohsuke,Matsubara, Hitomi,Tran, Dat Phuc,Kodama, Shintaro,Nomoto, Akihiro,Ogawa, Akiya
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p. 11741 - 11751
(2019/10/02)
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- Palladium-catalyzed direct coupling of 2-vinylanilines and isocyanides: An efficient synthesis of 2-aminoquinolines
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Palladium-catalyzed oxidative coupling of 2-vinylanilines and isocyanides constitutes a direct, facile, and efficient approach to 2-aminoquinolines. The procedure, employing palladium acetate and silver carbonate, is attractive in terms of assembly efficiency, functional group tolerance, and operational simplicity. A variety of 2-aminoquinolines were prepared in good to excellent yields.
- Wang, Lijie,Ferguson, Jamie,Zeng, Fanlong
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supporting information
p. 11486 - 11491
(2015/12/04)
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- From isonitriles to unsaturated NHC complexes of gold, palladium and platinum
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In a modular template synthesis, unsaturated NHC complexes of gold, palladium and platinum were synthesized from simple metal salts, isonitriles and amines with acetal or ketal groups. Upon the addition of amines with tethered acetal or ketal moieties to the metal-activated isonitrile, first nitrogen acyclic carbene (NAC) complexes are formed. These undergo ring closure and elimination to the unsaturated NHC complexes upon addition of acid. This simple strategy opens an attractive and fast approach to NHC complexes of gold, palladium and platinum. The modular approach allows a fast modification and is well-suited for the synthesis of unsymetrically and symmetrically substituted unsaturated NHC complexes.
- Riedel, Dominic,Wurm, Thomas,Graf, Katharina,Rudolph, Matthias,Rominger, Frank,Hashmi, A. Stephen K.
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supporting information
p. 1515 - 1523
(2015/05/19)
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- Acyclic aminocarbene-like palladium complex-catalyzed Suzuki-Miyaura reaction at low catalyst loadings
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A series of air-stable aminocarbene-like palladium(II) complexes were easily prepared by the reaction of bis-aromaticisocyanide-dichloropalladium(II) with N-arylbenzamidines. 0.1 mol % of the optimal palladium complex 3a showed excellent catalytic activity for Suzuki-Miyaura cross-coupling reaction at room temperature and the desired products were isolated in up to 98% yields. Moreover, a large-scale reaction showed that 0.01 mol % 3a was enough to catalyze the coupling reaction efficiently at room temperature to give the desired product in 93% yield.
- Fang, Yi,Wang, Shun-Yi,Ji, Shun-Jun
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supporting information
p. 9679 - 9683
(2015/12/04)
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- BLUE LUMINESCENT COMPOUNDS
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There is provided a compound having Formula II. In Formula II: R1 can be alkyl having 1-6 carbons, silyl having 3-6 carbons, or a deuterated analog thereof; R2 can be alkyl, silyl, aryl, or a deuterated analog thereof; a and c are the same or different and are an integer from 0-4; and b is an integer from 0-5.
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Page/Page column 41; 42
(2014/06/23)
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- Generation of powerful tungsten reductants by visible light excitation
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The homoleptic arylisocyanide tungsten complexes, W(CNXy)6 and W(CNIph)6 (Xy = 2,6-dimethylphenyl, Iph = 2,6-diisopropylphenyl), display intense metal to ligand charge transfer (MLCT) absorptions in the visible region (400-550 nm). MLCT emission (λmax ≈ 580 nm) in tetrahydrofuran (THF) solution at rt is observed for W(CNXy)6 and W(CNIph)6 with lifetimes of 17 and 73 ns, respectively. Diffusion-controlled energy transfer from electronically excited W(CNIph) 6 (*W) to the lowest energy triplet excited state of anthracene (anth) is the dominant quenching pathway in THF solution. Introduction of tetrabutylammonium hexafluorophosphate, [Bun4N][PF 6], to the THF solution promotes formation of electron transfer (ET) quenching products, [W(CNIph)6]+ and [anth] ?-. ET from*W to benzophenone and cobalticenium also is observed in [Bun4N][PF6]/THF solutions. The estimated reduction potential for the [W(CNIph)6]+/ *W couple is -2.8 V vs Cp2Fe+/0, establishing W(CNIph)6 as one of the most powerful photoreductants that has been generated with visible light.
- Sattler, Wesley,Ener, Maraia E.,Blakemore, James D.,Rachford, Aaron A.,Labeaume, Paul J.,Thackeray, James W.,Cameron, James F.,Winkler, Jay R.,Gray, Harry B.
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supporting information
p. 10614 - 10617
(2013/08/23)
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- N-Heterocyclic Carbene Complexes, Their Preparation And Use
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Described are N-heterocyclic carbene complexes of the formula I, where n is 0 or 1, M is a metal atom containing group, R1 is selected from hydrogen alkyl, cycloalkyl, heterocycloalkyl, aryl and hetaryl, R2 is selected from hydrogen, alkyl, cycloalkyl, heterocycloalkyl, aryl and hetaryl, wherein R1 and R2 do not both stand for hydrogen. Furthermore, also described are methods for their preparation and their use as catalysts employed in a C—C, C—O, C—N or C—H bond formation reaction.
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Page/Page column 25
(2012/05/07)
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- N-HETEROCYCLIC CARBENE COMPLEXES, THEIR PREPARATION AND USE
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N-heterocyclic carbene complexes of the formula (I) is disclosed, wherein the radicals have the meanings as defined in the invention. The preparation and the use as catalysts employed in a C-C, C-O, C-N or C-H bond formation reaction of said complexes are also disclosed.
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Page/Page column 63-64
(2012/05/19)
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- A short way to switchable carbenes
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A new, one-step route to N-heterocyclic oxo-carbene complexes (NHOCs), representatives of chemo-switchable NHC complexes, is reported. This simple procedure provides an easy access to gold, palladium and platinum complexes of these ligands. Copyright
- Hashmi, A. Stephen K.,Lothschuetz, Christian,Graf, Katharina,Haeffner, Tobias,Schuster, Andreas,Rominger, Frank
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p. 1407 - 1412
(2011/08/07)
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- An umpolung sulfoxide reagent for use as a functionalized benzyl carbanion equivalent
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N-Methyl ortho-carbamoylaryl benzyl sulfoxides can be used as synthetic equivalents for α-hydroxy, α-chloro, and α-acetammido benzyl carbanions by means of a two-step sequence involving highly diastereoselective α-C-alkylation with alkyl halides followed by displacement of the sulfinyl residue (which can be recovered and recycled) by a hydroxyl, a chlorine or an acetamido, respectively, under non-oxidative Pummerer conditions. The scope and limits of the method, including a stereoselective version of the reaction, as well as the mechanism of the process are discussed in detail.
- Pinna, Giovanni,Bellucci, Maria Cristina,Malpezzi, Luciana,Pisani, Laura,Superchi, Stefano,Volonterio, Alessandro,Zanda, Matteo
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p. 5268 - 5281
(2011/08/06)
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- N-heterocyclic carbene stabilized dichlorosilaimine IPr·Cl 2Si=NR
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N-Heterocyclic carbene stabilized dichlorosilaimine IPr·Cl 2Si=N(Diip) (2) has been synthesized by the reaction of dichlorosilylene IPr·SiCl2 (1) with bis(2,6-diisopropylphenyl) carbodiimide (IPr =:C[N(2,6-i-Pr2-C6H3)CH] 2, Diip = 2,6-i-Pr2-C6H3). Reaction of 1 with terphenyl azides also affords dichlorosilaimines IPr·Cl 2Si=N(2,6-Diip2-C6H3) (3) and IPr·Cl2Si=N(2,6-Triip2-C6H3) (4) (Triip = 2,4,6-i-Pr3-C6H2). Compounds 2-4 are stable under an inert atmosphere and were characterized by elemental analysis and NMR spectroscopic studies. The molecular structures of 2-4 were determined by single-crystal X-ray analysis.
- Ghadwal, Rajendra S.,Roesky, Herbert W.,Schulzke, Carola,Granitzka, Markus
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experimental part
p. 6329 - 6333
(2011/02/16)
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- Isonitriles as efficient ligands in Suzuki-Miyaura reaction
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Isonitrile palladium complexes [(RNC)2PdCl2] were prepared and tested in Suzuki reaction of 4-chloroanisol. (AdNC)2PdCl2 was found the most effective catalyst and was used in phenylation of several chloro and bromoaromatic substrates.
- Villemin, Didier,Jullien, Arnaud,Bar, Nathalie
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p. 4191 - 4193
(2008/02/05)
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- An umpolung sulfoxide reagent as α-hydroxy and α-chloro benzyl carbanion equivalents
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ortho-[(N-Methyl)carbamoyl]phenyl benzyl sulfoxide is used as a synthetic equivalent of α-hydroxy and α-chloro benzyl carbanions by means of a two-step sequence involving (1) highly stereoselective α-C-alkylation with alkyl bromides, and (2) displacement of the sulfinyl group by an OH or a Cl under Pummerer or chloro-Pummerer conditions, respectively. The sulfinyl auxiliary can be effectively regenerated and recycled.
- Volonterio, Alessandro,Bravo, Pierfrancesco,Zanda, Matteo
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p. 6537 - 6540
(2007/10/03)
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- Screw Sense Selective Polymerization of Achiral Isocyanides Catalysed by Optically Active Nickel(II) Complexes
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Poly(isocyanides), (RN=Cn, can be prepared from isocyanides, , by the catalytic action of nickel(II) compounds.The main chain of these polymers is a rigid helix.This helical conformation results from a restricted rotation around the single bonds that connect the main-chain carbon atoms.Polymerization of achiral isocyanides generally gives a racemic mixture of left- and right-handed helices, whereas polymerization of optically active isocyanides results in helices with an excess of one screw sense.We describe a procedure for obtaining poly(isocyanides) with predominantly one screw sense, starting from an achiral monomer.A catalyst is prepared by adding an optically active amine to a tetrakis(isocyanide)nickel(II) perchlorate complex.Polymerization of various achiral isocyanides with this catalist yields optically active polymers with an enantiomeric excess up to 83percent.
- Kamer, Paul C. J.,Nolte, Roeland J. M.,Drenth, Wiendelt
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p. 6818 - 6825
(2007/10/02)
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