- Cytochrome Oxidase Models. 2. μ-Bipyrimidyl Mixed-Metal Complexes as Synthetic Models for the Fe/Cu Binuclear Active Site of Cytochrome Oxidase
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μ-Bipyrimidyl (bipym) mixed-metal complexes, with II(bipym)MII> cores (MII = Cu and Zn), have been synthesized to model the proposed imidazolate-bridged 33+(imid)CuU2+> active site structure of cytochrome oxidase where -J(FeIII-CuII) > 200 cm-1.The binuclear compounds have been prepared from a six-coordinate II(C18H18N6)(bipym)>2+ species (B) (C18H18N6 = a folded macrocycle) by reaction with the appropriate bis(acetylacetonato)M(II) compound in CH2Cl2 to yield II(C18H18N6)(bipym)CuII(acac)2>2+ (C) and II(C18H18N6)(bipym)ZnII(acac)2>2+ (D) as ClO4- salts.Compound B contains low-spin iron(II), whereas C and D are high-spin species in both the solid and solution states at room temperature.Comparative variable-temperature (10-300 K) magnetic susceptibility measurements for C and D indicate C to contain magnetically isolated S = 2 (FeII) and S = 1/2 (CuII) centers with J ca. 0 through the bipym bridge.The 57Fe Moessbauer spectra of C and D and the CuII EPR spectrum of C at 8 K are also supportive of this interpretation.In solution, the redox activity of B, C, and D has been examined by cyclic voltammetry in CH2Cl2 where E1/2 for the FeII/FeIII couple of high-spin C and D are identical at +0.60 V (SCE) and 700 mV lower in potential than for the low-spin monomer compound (B).The CuII/CuI couple for C appears to occur at E1/2 = -0.24 V (SCE).Finally, the μ-bipyrimidyl Cu2 compound, II(bipym)CuII(hfa)2> (hfa- = hexafluoroacetylacetonato anion), has been prepared and found to exhibit an antiferromagnetic exchange interaction with -J = 7.9 cm-1.The ramifications of these results as they pertain to the magnetically coupled 33+-Cuu2+> active site of resting cytochrome oxidase are discussed, and an oxo-bridged alternative to the imidazolate-bridge possibility is also considered in view of the findings from the present model study.
- Petty, Randall H.,Welch, Byron R.,Wilson, Lon J.,Bottomley, Lawrence A.,Kadish, Karl M.
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- One-electron Reduction of 2,2'-Bipyrimidine in Aqueous Solution
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Pulse-radioloysis studies on the one-electron reduction of 2,2'-bipyrimidine (bpym) have allowed us to establish pKa values for dissociation of bpymH2.+ and bpymH. of 4.5 and 12.5, respectively.
- Barqawi, Khaled,Akasheh, Talal S.,Parsons, Barry J.,Beaumont, Paul C.
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Read Online
- Inverse electron demand diels-alder reactions of 1,2,3-triazines: Pronounced substituent effects on reactivity and cycloaddition scope
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A systematic study of the inverse electron demand Diels-Alder reactions of 1,2,3-triazines is disclosed, including an examination of the impact of a C5 substituent. Such substituents were found to exhibit a remarkable impact on the cycloaddition reactivity of the 1,2,3-triazine without altering, and perhaps even enhancing, the intrinsic cycloaddition regioselectivity. The study revealed not only that the reactivity may be predictably modulated by a C5 substituent (R = CO2Me > Ph > H) but also that the impact is of a magnitude to convert 1,2,3-triazine (1) and its modest cycloaddition scope into a heterocyclic azadiene system with a reaction scope that portends extensive synthetic utility, expanding the range of participating dienophiles. Significantly, the studies define a now powerful additional heterocyclic azadiene, complementary to the isomeric 1,2,4-triazines and 1,3,5-triazines, capable of dependable participation in inverse electron demand Diels-Alder reactions, extending the number of complementary heterocyclic ring systems accessible with implementation of the methodology.
- Anderson, Erin D.,Boger, Dale L.
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supporting information; experimental part
p. 12285 - 12292
(2011/09/16)
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- Scope of the inverse electron demand Diels-Alder reactions of 1,2,3-triazine
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Chemical equations presented. An examination of the scope of the inverse electron demand Diels-Alder reactions of the parent unsubstituted 1,2,3-triazine is described including the first report of its unique capabilities for participating in previously unexplored [4 + 2] cycloaddition reactions with heterodienophiles.
- Anderson, Erin D.,Boger, Dale L.
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supporting information; experimental part
p. 2492 - 2494
(2011/07/09)
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- BIPYRIDINE COMPOUND, TRANSITION METAL COMPLEX, AND METHOD FOR PRODUCTION OF CONJUGATED AROMATIC COMPOUND USING THE TRANSITION METAL COMPLEX
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A bipyridine compound represented by the formula (1): wherein R1, R2 and R3 each independently represent a C1-C10 alkyl group which may be substituted etc., and R4, R5, R6, R7 and R8 each independently represent a hydrogen atom etc., a transition metal complex obtained by contacting a bipyridine compound represented by the formula (1) with a compound of a transition metal belonging to Group 9, 10 or 11, and a method for production of a conjugated aromatic compound comprising reacting an aromatic compound (A) wherein one or two leaving groups are bonded to an aromatic ring with an aromatic compound (A) having the same structure as that of the above-mentioned aromatic compound (A) or an aromatic compound (B) being structurally different from the above-mentioned aromatic compound (A) and having one or two leaving groups bonded to an aromatic ring, in the presence of the transition metal complex.
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Page/Page column 43
(2010/04/25)
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- Aryl-aryl bonds formation in pyridine and diazine series. Diazines part 41
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The synthesis of several symmetrical polyaromatic compounds with pyridine or diazine units has been achieved by homocoupling of aryl halides with Pd(OAc)2 as catalyst. Cross-coupling reactions of aryl Grignard reagents with Fe(acac)3 as catalyst allowed the synthesis of various unsymmetrical polyaryl- or polyheteroaryl compounds with π-deficient rings.
- Boully, Ludovic,Darabantu, Mircea,Turck, Alain,Ple, Nelly
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p. 1423 - 1428
(2007/10/03)
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- Preparation of 5-brominated and 5,5′-dibrominated 2,2′-bipyridines and 2,2′-bipyrimidines
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Efficient syntheses of 5-brominated and 5,5′-dibrominated 2,2′-bipyridines and 2,2′-bipyrimidines, useful for the preparation of metal-complexing molecular rods, have been developed. 5-Bromo-2,2-bipyridine, 5-bromo-5′-n-butyl-2,2′-bipyridine, and 5-bromo-5′-n-hexyl-2,2′-bipyridine were obtained by Stille coupling of 2,5-dibromopyridine with 2-trimethylstannylpyridine or the requisite 5-alkyl-2-trimethylstannylpyridine, obtained via regioselective zincation of a 3-alkylpyridine. BF3 complex in the less hindered of the two reactive positions with lithium di-tert-butyl-(2,2,6,6-tetramethyl-piperidino)zincate. 5,5′-Dibromo-2,2′-bipyridine was obtained by the reductive symmetric coupling of 2,5-dibromopyridine with hexa-n-butyldistannane. The yields of these coupling reactions ranged from 70 to 90%. 5-Bromo- and 5,5′-dibromo-2,2′-bipyrimidines were obtained in yields of 30 and 15%, respectively, by bromination of 2,2′-bipyrimidine, prepared from 2-chloropyrimidine in 80% yield by an improved reductive symmetric coupling procedure.
- Schwab, Peter F.H.,Fleischer, Frank,Michl, Josef
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p. 443 - 449
(2007/10/03)
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- Improved synthesis of 2,2′-bipyrimidine
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A high-yield synthesis was developed for the preparation of 2,2′-bipyrimidine (1) using the Ullmann coupling of 2-iodopyrimidine. The new procedure was also used for the preparation of 4,4′,6,6′-tetramethyl-2,2′-bipyrimidine (2) and 5,5′-dibromo-2,2′-bipyrimidine (3).
- Vlad, Gabor,Horvath, Istvan T.
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p. 6550 - 6552
(2007/10/03)
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- A Convenient Synthetic Route to bis-Heteroaromatic and bis-Heterocyclic Compounds Promoted by Liganded Nickel Complex Reducing Agents.
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A number of nitrogen, sulfur or oxygen containing bis-heteroaromatic or bis-heterocyclic derivatives have been synthesized in good to excellent yields by homocoupling of the corresponding halogenated compounds in the presence of liganded (triphenylphosphine or 2,2'-bipyridine) nickel Complex Reducing Agents in THF or DME at 63 deg C.
- Forst, Yves,Becker, Sandrine,Caubere, Paul
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p. 11893 - 11902
(2007/10/02)
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- Efficient coupling of 2-halopyrimidines to 2,2'-bipyrimidines
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2-chloropyrimidine, 2-chloro- and 2-bromo-4,6-dimethylpyrimidines, 2-chloro- and 2-bromo-4,6-diphenylpyrimidines have been dimerized to the corresponding 2,2'-bipyrimidines in good yields by Tiecco's method using NiCl2, triphenylphosphine and zinc in DMF.
- Nasielski,Standaert,Nasielski-Hinkens
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p. 901 - 906
(2007/10/02)
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