A local density functional study of the structure and vibrational frequencies of molecular transition-metal compounds

Sosa, Carlos; Andzelm, Jan; Elkin, Brad C.; Wimmer, E.; Dobbs, Kerwin D.; Dixon, David A.

doi:10.1021/j100195a022

Cited by 753 publications

(504 citation statements)

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“…Based on these discoveries we propose a mechanism similar to that of Pearson and Waymouth (40) (64); spin unrestricted orbitals and exchange correlation was treated at the B3LYP (Becke, threeparameter, Lee-Yang-Par) hybrid functional level (65,66); DGDZVP (density Gauss double-zeta with polarization functions) (67) full electron basis set was used with the density Gaussian fitting basis set DGA1 (67,68)], indicating that the proposed structures for these intermediates are feasible (see SI Appendix for DFT parameters). Optimized structures for Fig.…”

Section: Resultsmentioning

confidence: 99%

Transient Ru-methyl formate intermediates generated with bifunctional transfer hydrogenation catalysts

Perry

Brownell

Chingin

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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Desorption electrospray ionization (DESI) coupled to high-resolution Orbitrap mass spectrometry (MS) was used to study the reactivity of a (β-amino alcohol)(arene)RuCl transfer hydrogenation catalytic precursor in methanol (CH 3 OH). By placing ½ðp-cymeneÞ RuCl 2 2 on a surface and spraying a solution of β-amino alcohol in methanol, two unique transient intermediates having lifetimes in the submillisecond to millisecond range were detected. These intermediates were identified as Ru (II) and Ru (IV) complexes incorporating methyl formate (HCOOCH 3 ). The Ru (IV) intermediate is not observed when the DESI spray solution is sparged with Ar gas, indicating that O 2 dissolved in the solvent is necessary for oxidizing Ru (II) to Ru (IV). These proposed intermediates are supported by high-resolution and high mass accuracy measurements and by comparing experimental to calculated isotope profiles. Additionally, analyzing the bulk reaction mixture using gas chromatography-MS and nuclear magnetic resonance spectroscopy confirms the formation of HCOOCH 3 . These results represent an example that species generated from the (β-amino alcohol)(arene)RuCl (II) catalytic precursor can selectively oxidize CH 3 OH to HCOOCH 3 . This observation leads us to propose a pathway that can compete with the hydrogen transfer catalytic cycle. Although bifunctional hydrogen transfer with Ru catalysts has been well-studied, the ability of DESI to intercept intermediates formed in the first few milliseconds of a chemical reaction allowed identification of previously unrecognized intermediates and reaction pathways in this catalytic system. organometallic catalysis | reaction intermediates | ruthenium | kinetics C atalytic transfer hydrogenation (CTH) is an efficient method for the enantioselective reduction of multiple bonds (e.g., C═O and C═NR) in chemical and pharmaceutical syntheses (1-4). Typically, a hydrogen donor such as isopropanol is used as a convenient reducing agent and is oxidized to its corresponding ketone (5). As a catalytic version of the classical MeerweinPondorf-Verley reduction/Oppenaur oxidation (6-10), CTH provides a mild method for both ketone reduction and alcohol oxidation. Previous studies show that methanol (CH 3 OH) can serve as a hydrogen donor for (arene)Ru complexes ligated by β-amino alcohols (11), but the nature of the oxidized products from CH 3 OH has not been previously characterized (12). Additionally, some Pd and Ru (13, 14) catalysts can oxidize CH 3 OH to methyl formate (HCOOCH 3 ), but selective oxidation to methyl formate has not been observed previously for a transfer hydrogenation catalysis. Fig. 1 shows the mechanism proposed by Kenney, Heck, Walgrove, and Wills (15) for CTH when Fig. 1, 1 is treated with β-amino alcohol ligands in the presence of a base. Ligation of the cymene dimer Fig. 1, 1 with ligand Fig. 1, 2 generates the Ru-Cl catalyst precursor Fig. 1, 3, which undergoes dehydrohalogenation to form the Ru-amide Fig. 1, 4. An outer-sphere concerted hydrogen transfer of α-C─H to Ru and ─O─H t...

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Section: Resultsmentioning

confidence: 99%

Transient Ru-methyl formate intermediates generated with bifunctional transfer hydrogenation catalysts

Perry

Brownell

Chingin

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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“…20 Theoretical Calculations. Full geometry optimizations of compounds LP225 and LP227 in their singlet ground state were performed with density functional theory (DFT) using the M06 functional 21 with the DGDZVP basis set 22,23 for all the atoms (double-ζ and polarizations), an ultrafine integration grid, and tight geometrical convergence criteria with the Gaussian 09 package. 24 All calculations were carried out including implicit solvent effects.…”

Section: ■ Introductionmentioning

confidence: 99%

Unravelling the Potential for Dithienopyrrole Sensitizers in Dye-Sensitized Solar Cells

et al. 2013

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Two D−π−A dyes based on the dithieno[3,2-b:2′,3′-d]pyrrole π-bridge (DTP) were synthesized, characterized using UV−vis absorption spectroscopy and electrochemistry, modeled using quantum chemical calculations, and used as sensitizers in dye-sensitized solar cells (DSCs). The photoelectrochemical properties and DSC performance are thoroughly compared with their cyclopenta[1,2-b:5,4-b′]dithiophene (CPDT) analogues. The use of DTP results in a small increase in the zero−zero transition energy reflecting the higher lying lowest unoccupied molecular orbital that is commonly reported for DTP relative to CPDT systems. This increased optical gap manifests in slightly blue-shifted incident photon-to-collected electron conversion efficiency (IPCE) responses; however, increased opencircuit photovoltage values and improved charge-transfer kinetics relative to the CPDT systems result in comparable power conversion efficiencies. The present report highlights the potential of DTP for the development of tailored sensitizers employing stronger acceptors. KEYWORDS: dye-sensitized solar cells, D−π−A, dithienopyrrole ■ INTRODUCTIONOver the past two decades, considerable research efforts have been devoted to dye-sensitized solar cells (DSCs) due to their potential as a low-cost photovoltaic technology. 1 The basic working principle, which relies on a delicate energetic balance between the anode, sensitizer, and electrolyte, is comprehensively described in a review by Hagfeldt et al. 2 The most efficient cells are based on relatively expensive or synthetically challenging ruthenium(II) and porphyrin sensitizers that have provided efficiencies up to 11.7% and 11.9%, respectively. 3,4 More accessible organic dyes take the form of a D−π−A structure, which is reminiscent of push−pull chromophores used in nonlinear optics. 5 In this context, oligothiophenes and their fused derivatives are intensively exploited as π-bridges. 6 The two highest performing organic dyes, Y123 and JF419 (Chart 1), incorporate cyclopenta[1,2-b:5,4-b′]dithiophene (CPDT), reaching power conversion efficiencies of up to 10.3%. 7,8 The success of CPDT is attributed to (i) the advantageous steric effect of the alkyl groups placed in the 4,4-position, which helps to prevent aggregation of the dyes on the surface, and (ii) the effective electronic communication between the donor (D) and acceptor (A), which enables efficient charge transfer.Contrary to the CPDT bridge, which is synthetically costly (35% yield over five steps), 9,10 dithieno[3,2-b:2′,3′-d]pyrrole (DTP) is more accessible (up to 80% yield in one step) as showcased by Rasmussen et al. 11,12 Notably, N-substituted DTP possesses similar electronic properties with respect to CPDT 13 but also has the potential to incorporate a variety of N-substituents. As a result, this position offers greater versatility toward the control of dye aggregation, which makes it particularly attractive for DSC applications. 14,15 The only direct comparison between CPDT and DTP π-bridges in sensitizers for DSCs concluded...

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“…In this sense, we have designed a proper molecular LC having a triple bond inserted between two aryl rings and at least one terminal short alkyl chain, such as a methoxy group. To investigate the origin of this behavior a theoretical study was performed using a DFT/B3LYP calculations with Becke's three-parameter hybrid method 17 using the Lee-Yang-Parr correlation functional 18 (B3LYP) with DGDZVP 19 basis set. All quantum chemical calculations were performed with the Gaussian package.…”

Section: Resultsmentioning

confidence: 99%

An evaluation of the chalcogen atom effect on the mesomorphic and electronic properties in a new homologous series of chalcogeno esters

Rampon¹,

Rodembusch²,

Gonçalves³

et al. 2010

J. Braz. Chem. Soc.

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Uma série de calcogeno ésteres, 1a, 6a e 6b foi obtida em uma rota sintética conveniente. A análise de microscopia óptica de luz polarizada (POM) e calorimetria diferencial de varredura (DSC) mostrou que estes calcogeno ésteres apresentam uma ampla faixa de mesofase nemática. Além disso, espectros de absorção na região do UV-Vis em solução (ca.10 -5 mol L -1 ) também foram obtidos de maneira a se obter a diferença de energia entre os orbitais moleculares HOMO-LUMO, para posterior comparação com os resultados teóricos. Os valores calculados para o gap de HOMO-LUMO estão de acordo com os valores experimentais obtidos, onde a eletronegatividade do heteroátomo (O, S e Se) deve ser o principal fator para a localização do máximo de absorção. Um estudo teórico foi realizado utilizando cálculos de DFT/B3LYP com método híbrido de Becke aplicando uma correlação funcional de Lee-Yang-Parr (B3LYP) com a base DGDZVP a fim de avaliar algumas propriedades físico-químicas relacionadas com o mesomorfismo e as propriedades eletrônicas espectrais. Através da síntese destes compostos, a influência do átomo de calcogênio nas propriedades fotofísicas e mesomórficas pôde ser avaliada de uma forma mais precisa.A series of chalcogeno esters 1a, 6a and 6b have been synthesized in a straightforward manner. Polarized-light optical microscopy (POM) and differential scanning calorimetry (DSC) showed that these chalcogeno esters displayed a wide nematic range of mesophase. In addition, UV-Vis in solution (ca.10 -5 mol L -1 ) was applied in order to obtain the HOMO-LUMO gap for further comparison with the theoretical results. The calculated values to the HOMO-LUMO gap are in excellent agreement with the experimental results, where the electronegativity of the heteroatom (O, S and Se) seems to play a fundamental role in the absorption maxima location. A theoretical study was performed using a DFT/B3LYP calculations with Becke's three-parameter hybrid method applying the Lee-Yang-Parr functional correlation (B3LYP) with DGDZVP basis set in order to evaluate some physical chemistry data related with mesomorphic and spectral eletronic properties. By synthesizing these compounds we were able to get a more precise description about the influence of the chalcogen atom on the mesomorphic and photophysical properties. Rampon et al. 2101 Vol. 21, No. 11, 2010 The biological and medicinal properties of selenium and organoselenium compounds are increasingly appreciated, mainly due to their antioxidant, antitumor, antimicrobial and antiviral properties. 4 Besides, the synthesis of peptides containing selenocysteine is rapidly gaining interest with the discovery of an increasing number of proteins containing this aminoacid. Keywords 5Chalcogeno esters (thiol, selenol and tellurol esters) are useful synthetic intermediates that have been employed, for example, as acylating reagents, building blocks for heterocyclic compounds, precursors of acyl radicals and anions, as well asymmetric aldol reactions. However, rare are the examples where these compounds a...

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A local density functional study of the structure and vibrational frequencies of molecular transition-metal compounds

Cited by 753 publications

References 2 publications

Transient Ru-methyl formate intermediates generated with bifunctional transfer hydrogenation catalysts

Transient Ru-methyl formate intermediates generated with bifunctional transfer hydrogenation catalysts

Unravelling the Potential for Dithienopyrrole Sensitizers in Dye-Sensitized Solar Cells

An evaluation of the chalcogen atom effect on the mesomorphic and electronic properties in a new homologous series of chalcogeno esters

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