Microwave-assisted Synthesis, Characterization, And .
MICROWAVE-ASSISTED SYNTHESIS, CHARACTERIZATION, ANDPHOTOPHYSICAL PROPERTIES OF NEWRHENIUM(I) PYRAZOLYL-TRIAZINE COMPLEXESGustavo Adolfo Salazar Garza, B. S.Thesis Prepared for the Degree ofMASTER OF SCIENCEUNIVERSITY OF NORTH TEXASMay 2010APPROVED:Mohammad A. Omary, Major ProfessorW. Justin Youngblood, Committee MemberWilliam E. Acree Jr., Chair of the Department ofChemistryMichael Monticino, Dean of the Robert B.Toulouse School of Graduate Studies
Salazar Garza, Gustavo Adolfo. Microwave-assisted synthesis, characterization,and photophysical properties of new rhenium(I) pyrazolyl-triazine complexes. Master ofScience (Chemistry), May 2010, 48 pp., 11 tables, 22 figures, references, 25 titles.The reaction of the chelating ligand zin-2-yl]-N,N-diethyl-benzenamine, L, with pentacarbonylchlororhenium byconventional heating method produces the complexes fac-[ReL(CO)3Cl2] and fac[Re2L(CO)6Cl2] in a period of 48 hours. The use of microwaves as the source of heat andthe increase in the equivalents of one of the reactants leads to a more selective reactionand also decreases the reaction time to 1 hour. After proper purification, thephotophysical properties of fac-[ReL(CO)3Cl] were analyzed. The solid-statephotoluminescence analysis showed an emission band at 628 nm independent oftemperature. However, in the solution studies, the emission band shifted from 550 nm infrozen media to 610 nm when the matrix became fluid. These results confirm that thiscomplex possess a phenomenon known as rigidochromism.
Copyright 2010byGustavo Adolfo Salazar Garzaii
TABLE OF CONTENTSLIST OF TABLES . .vLIST OF FIGURES . .viCHAPTER 1 SYNTHESIS AND CHARACTERIZAION OF RHENIUM CARBONYLCOMPLEXES . 11.1Introduction . .11.2Synthetic Methods . .61.2.1 Conventional Method . .71.2.2 Microwave-assisted Synthesis . . .71.2.3 Characterization Procedures . 81.3 Results and Discussions. . . .81.3.1 ] . . .101.3.2 2] . . 211.4 Conclusions . . 331.5References . 34iii
CHAPTER 2 LUMINESCENCE PROPERTIES OF RHENIUMCARBONYL COMPLEXES . 362.1 Introduction 362.2 Photophysical Measurements . 392.3 Results and Discussions .402.3.1 Free Ligand Photoluminescence .402.3.2 Rhenium Complexes Photoluminescence . 422.4 Conclusions and Future Directions . . 472.5 References .48iv
LIST OF TABLESTable 1.1 1H-NMR data and assignment of the complex fac-[ReL(CO)3Cl] andcomparison with the free ligand signals . 11Table 1.2 13C-NMR data and assignment of the complex fac-[ReL(CO)3Cl] andcomparison with the free ligand signals . 13Table 1.3 IR data assignment from the complex fac-[ReL(CO)3Cl] and thecomparison with the free ligand L. . . .14Table 1.4 Crystal data for the fac-[ReL(CO)3Cl] . .17Table 1.5 Bond lengths [Å] and angles [ ] of fac-[ReL(CO)3Cl] . . 18Table 1.6 1H-NMR data and assignment of the complex fac-[Re2L(CO)6Cl2]and comparison with the free ligand signals . . 23Table 1.7 13C-NMR data and assignment of the complex fac-[Re2L(CO)6Cl2]and comparison with the free ligand signals . 25Table 1.8 IR data assignment from the complex fac-[Re2L(CO)6Cl2]and the comparison with the free ligand L and the complex fac-[ReL1(CO)3Cl]. .27Table1.9 Crystal data for the fac-[Re2L(CO)6Cl2] . 29Table 1.10 Bond lengths [Å] and angles [ ] for fac-[Re2L(CO)6Cl2] . . . .30Table 2.1 Lifetime measurements from each emission peak in the frozen solutionanalysis of fac-[ReL(CO)3Cl] in 2-methyltetrahydrofuran. . 47v
LIST OF FIGURESFigure 1.1 Typical complex geometry of a rhenium tricarbonyl species . . .1Figure 1.2 Ligand azin-2-yl] -N,Ndiethyl-benzenamine, L. . 2Figure 1.3 Schematic representation of the comparison between a) conventionalheating, and b) microwave-assisted heating methods . . .5Figure 1.4 Synthesis of the ligand, L1. a) reflux under Ar atmosphere;b) potassium 5,5-dimethylpyrazolate . . .7Figure 1.5 Products obtained from the reaction between L1 andpentacarbonylchlororhenium(I) using equimolar quantities; a) fac-[ReL(CO)3Cl]and b) fac-[Re2L(CO)6Cl2] . .9Figure 1.6 1H-NMR spectrum of the complex fac-[ReL(CO)3Cl] . . 10Figure 1.7 1H-NMR signal assignment in the complex fac-[ReL(CO)3Cl] . 11Figure 1.8 lR spectrum of the complex fac-[ReL(CO)3Cl] . . 12Figure 1.9 IR spectrum of the complex fac-[ReL(CO)3Cl] . .14Figure 1.10 A view of the fac-[ReL(CO)3Cl] complex showing the numberingemployed 16Fig. 1.11 1H-NMR spectrum of the complex fac-[Re2L(CO)6Cl2] . .22Figure 1.12 Structure and proton assignation from the 1H-NMR Spectrum of thecomplex fac-[Re2L(CO)6Cl2] . . .23Figure 1.13 1H-NMR spectrum of the complex fac-[Re2L(CO)6Cl2] . . .24Figure 1.14 IR spectrum of the complex fac-[Re2L(CO)3Cl2] . . . 26vi
Figure 1.15 A view of the fac-[ReL(CO)3Cl] and the numbering employed . .28Figure 2.1 Simplified Jablonski diagram for rhenium complexes of the[Re(diimine)(CO)3L] . .37Figure 2.2 Energy level diagram of the lowest occupied excited state ofa) [(CH3CN)Re(CO)3(phen)] and b) [(quinoline)Re(CO)3(bpy)] .37Figure 2.3 UV-VIS absorption spectra of the solvent-dependent study for theligand L .41Figure 2.4 Photoluminescence Study of the Free Ligand L1 in a 10-5 M tetrahydrofuransolution .42Figure 2.5 UV-VIS absorption spectra of the solvent-dependent Study for thecomplex fac-[ReL(CO)3Cl] . .43Figure 2.6 Emission and excitation of the complex fac-[ReL(CO)3Cl] in thesolid state .44Figure 2.7 Temperature-dependent study of the complex fac-[ReL(CO)3Cl] in 2methyltetrahydrofuran 10-4 M frozen solution . . 46vii
CHAPTER 1SYNTHESIS AND CHARACTERIZAION OF RHENIUM CARBONYL COMPLEXES1.1 IntroductionThe complexes treated in this thesis have a metal center of rhenium(I) andpyrazolyl triazines as ligands. Rhenium metal was originally discovered in 1925, and isnaturally found in molybdenite and other ores.1 Rhenium (I) metal is known to form alarge variety of tricarbonyl complexes with the coordination of two or more π-donatingligands and one halide to form a neutral species.2 These complexes have an octahedralgeometry (Figure 1) where the three carbonyl groups are in the facial arrangement iespentacarbonylchlororhenium(I), Re(CO)5Cl.LLReXCOCOCOFigure 1.1 Typical complex geometry of a rhenium tricarbonylspecies.Rhenium(I) tricarbonyl complexes can be either neutral or cationic based on theother ligands.3 In addition, a large variety of photochemical and photophysical properties1
can be achieved and modified using different types of ligands.4 For instance, therigidochromism phenomenon of the complexes fac-[ReX(α-diimine)] /0, which isexplained in detail in chapter 2, has a very unique excited state nature base on the αdiimine ligand.4b In addition the complex [ReCl(CO)3(phen)]* has remarkable oxidationreduction properties.4cTherefore, the synthesis of a rhenium complex with theappropriate choice of ligands controls the final desired photochemical and/orphotophysical properties.For the synthesis of the rhenium complex reported in this thesis, ligand zin-2-yl]-N,N-diethyl-benzenamine,[L1],(Figure 1.2) was used, having been first prepared by Yang et al.5 The ligand, L1, containsa 1,3,5-triazine ring core, two pyrazolyl groups and one benzene ring with an aminegroup. Each of these components plays a very specific role in the electronic mechanismof the final complex.NNNNNNNNFigure 1.2 Ligand azin-2-yl]-N,Ndiethyl-benzenamine, L1.2
The core of the ligand is the heterocyclic molecule 1,3,5-triazine. Thesecompounds have been used extensively in syntheses due to the large variety ofadvantages they offer6; in fact, the very inexpensive precursor, 2,4,6-trichloro-1,3,5triazine allows the production of many different derivatives with an extensive use insynthesis.7The coordination properties of the pyrazolyl group in the ligand aids in theattachment to the rhenium metal.8 The relatively easy synthesis of a large variety ofpyrazole derivatives, as well as multiple coordination possibilities has led to a plethora ofcomplexes with remarkable properties.9Combining the advantages of the two groups, triazines and pyrazoles, aninteresting ligand can be formed. Two pyrazole ligands, along with the triazine core,create a very electron poor species. In addition, attachment of an electron-rich group,such as a benzene ring with an amine group in the para-position to the free carbon in thetriazine, forms an ambipolar molecule. This species has been employed in the formationof lanthanide complexes with remarkable luminescence properties,5 and the use of thisligand with transition metals, like rhenium, can potentially produce similar or enhancedphotophysical properties. For instance, lanthanides complexes have an emission with afixed wavelength, for its atomic transition nature. On the other hand, the use of transitionmetals allows tuning this emission since it is more ligand base. Change in the ligand willchange its luminescence properties.3
The complex formed with the ligand L and Europium reported by Yang, Chi etal.5 was made by simply mixing the two reactants in dry tetrahydrofuran at roomtemperature.However, in the case of pentacarbonylchlororhenium(I), the substitutionrequires the addition of energy because two of the carbonyl groups need to be replaced.Thus, the use of microwave as a source of heat was employed not only to achieve thedesired complex, but also in order to reduce the reaction time.Microwave-assisted organic synthesis (MAOS), was first employed in the 1980sin organic synthesis10. The use of conventional microwave ovens to accelerate organicreactions gained popularity, yet these instruments were not designed for the syntheticlaboratory where acids and corrosive solvent quickly destroyed the internal cavities. Bythe late 1980s, several industries started manufacturing microwave ovens specifically forchemical synthesis. Finally, in the last 5 years, MAOS has increased drastically due tothe different advantages they offer such as higher yields, cleaner reactions, and shortenedreaction times.The reason why MAOS works better than conventional methods is due to theimproved heat transfer process. The conventional method uses an external source toproduce the heat needed in the reaction (Figure 1.3a). In this case the heat has to betransferred from the source through the container wall to reach the reaction mixture. Thisprocess takes longer; the heat transfer time makes the material’s temperature uneven.Decreasing the reaction temperature requires the heat source to be removed. On the otherhand, the heating process using microwaves interacts directly with the reaction mixture,4
creating instantaneous localized heating with either the solvent and/or the reactantsbecause of interactions with dipole rotation or ionic conduction (figure 1.3b). The heatingis more even, and since the instrumentation contains an air cooling system, thetemperature can be easily controlled.11abFigure 1.3 Schematic representation of the comparison between a) conventionalheating, and b) microwave-assisted heating methods.Though the use of microwaves as a source of heating has been utilized widely inorganic chemistry, its application to inorganic reactions has not been well developed.12 Itshould be noted that at a specific wavelength, the microwaves can easily penetrate theexternal part of a material affecting some molecules in the surface, and some in the insideof the material. If the wavelength is changed to one where it interacts 100% with thesample treated, only the surface area will be heated and it will resemble the conventional5
heating. This is called the “skin effect”. Inorganic species have more drastic skin effectthan organic compounds.13 The reported rhenium complexes possess large organicligands, which overcomes the skin effect. Thus, microwaves can be employed to carryout the reaction.1.2 Synthetic MethodsThe methodology used by the conventional method was carried out under argonatmosphere, using standard Schlenk techniques. Glassware was oven-dried at 300 C for3 hours. Chemicals were purchased from Sigma Aldrich and used as received. Solventswere distilled using standard procedures.14 A CEM Discover Class-S system was utilizedfor microwave-enhance synthesis. A 10 ml reaction tube was used for the first tries and30 mL tube after setting the best conditions, was re3)usingdimethylphenylaniline that had been distilled twice14. The complex formation was doneby both, the conventional and microwaves-enhanced methods described in the nextsection.6
NNNClNNClNClabNNNClNNNNNClNNFigure 1.4 Synthesis of the ligand, L1: a) reflux under Ar atmosphere; b) potassium5,5-dimethylpyrazolate.1.2.1 Conventional MethodFor the conventional method, 0.86 g (0.24 mmol) of Re(CO)5Cl was added to asolution of 0.1g (0.24
Thus, the use of microwave as a source of heat was employed not only to achieve the desired complex, but also in order to reduce the reaction time. Microwave-assisted organic synthesis (MAOS), was first employed in the 1980s in organic synthesis10. The use of conventional microwave ovens to accelerate organic
the advantages of microwave assisted synthesis in com-parison to conventional heating. First, we will discuss the microwave synthesis of 2-pyridones. In the second part, microwave assisted synthesis of 2-quionolones will be given. At the end of the review, examples of microwave synthesis of ring fused N-substituted 2-pyri-dones will be discussed.
thermal synthesis, microwave-assisted synthesis offers rapid processing speed, homogeneous heating, and simple control of processing conditions, and thus has attracted much attention in the past few years.25 Ding et al.26 reported the synthesis TiO 2 nanocrystals via a microwave-assisted process and demon-
Microwave Assisted Organic Synthesis had developed in now years which has been considered superior to traditional . Journal of University of Shanghai for Science and Technology ISSN: 1007-6735 Volume 22, Issue 11, November - 2020 Page-1096. heating. Microwave assisted organic synthesis has as a new “lead” in the organic synthesis.
Conventional and microwave-assisted SPPS approach: a comparative synthesis of PTHrP(1– 34)NH 2, October 2011 Journal of Peptide Science, Volume 17, Issue 10, pages 708–714, Direct Solid-Phase Synthesis of the β-Amyloid (1-42) Peptide Using Controlled Microwave Heating J. Org. Chem. Vol. 75, No. 6, 2010 Solid-Phase Peptide Synthesis in .
MICROWAVE-ASSISTED SYNTHESIS OF MESOPOROUS SILICA NANOPARTICLES AS A DRUG DELIVERY VEHICLE . Indeed, the microwave synthesis of MCM-41 has been reported earlier [10]. In the report, the MCM-41 was synthesized by the composition of synthesis materials of CTAB, TMAOH, TEOS and H 2
The conventional synthesis gave a 56.5% yield and a 90.3% purity of acetaminophen. These results were used as a point of comparison for microwave and ultrasound-assisted methods. The microwave-assisted synthesis yield was 88.9%, and the purity was 98.7%. The yield for the ultrasound-assisted synthesis was 80.3% and the purity was 95.3%.
2- en-1-ones were synthesised by microwave assisted method as well as conventional method. When the reaction durations were compared among microwave assisted synthesis (4–6 min) and the conventional method (12 h) again to prove the reduced reaction
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