Molecular structure and properties of silver (I/II/III) containing organometallics

Table of content

Preface

Acknowledgements

About the contributors

I.Summary

II.Introduction

III.Mononuclear organometallics

IV.Dinuclear organometallics

V.Polynuclear organometallics

VI.–Complexes

VII.Conclusion and outlook

References

Appendix A Multi–isotopic modelling of mass spectra
Appendix B
Appendix C Ab initio effective core potentials

Index

Preface

Despite tremendous number books, monographs, textbooks and review-articles devoted to “organometallic chemistry” largest part of those contributions have been designed into following structure of the content: (i) Manuals, handbooks and encyclopedias summarizing important organometallic reagents in the organic synthesis; (ii) Books, containing synthetic protocols for obtaining of organometallic reagents; and (iii) Manuals on basic organic reactions catalysed by organometallics. However, there are scarce efforts devoted to studies of reaction mechanisms, physical and chemical properties and structure of organometallics. Furthermore largest part of available literature has been organized to serve educational needs of undergraduate and graduate students at different areas of chemist including inorganic, organic and/or physical chemistry, so that it has textbook (or a mixing) style, rather than to represent monographs on advances in organometallic research.

In this context, our book firstly in the literature has treated experimental and theoretical contributions in understanding reaction mechanisms, involving organosilver reagents as well as molecular structure and physical properties, focusing attention on chemical aspects of nature of C–M bond and role of coordination environment of inner coordination sphere of metal ion to effectiveness of mediated organic reactions from a coordination chemistry point of view, rather than to review available chemical reactions. Thus highlighting the main goal of this book to serve as a useful source of information about those molecular factors and properties governing the usefulness of those chemical classes to organic synthesis, which is important for further molecular design of new intermediates having enhanced synthetic efficiency, high enantioselectivity at mild experimental conditions. In other words, we have tried to answer to major challenge in elaboration and implementation of robust organosilver mediating compounds both at laboratory and industrial scale providing molecular level correlation between structure and properties as well as chemical reactivity. Particularly, when we are talking about silver–containing organometallics we should point out that the first group of chemicals having silver–carbon covalent bond are silver–alkynylalkynyl derivatives known since 1865. And nevertheless that those compounds are among the firs reagents in the chemistry there is growing interest to them as catalysing reagents in organic synthesis and/or functional materials recent decades. Long time they did not received much attention due to their, generally, low photochemical stability. The proven catalytic efficiency of those reagents to many important for organic chemistry reactions, however, along with a marked application to many branches of materials research and applied catalysis at an industrial scale, highlighted the search of fictionalized derivatives as challenging and fruitful areas where large number of fundamental aspects on mechanisms of catalysed reactions are often poorly understood and or/even there is a lack of knowledge about them. Given that, as recent trend in silver–containing organometallics it can be pointed out the molecular functionalization, improving their catalytic efficiency and physical properties. The focus of book’s content, thereby, is on crucial for understanding of organic synthetic reactions information obtained both in gas– and condense phase by methods of mass spectrometry and single crystal X–ray diffraction along with indispensable theoretical data about the nature of metal–C bond, structure of organometallics, their kinetic and thermodynamic properties obtained by quantum chemistry. Particularly, we have emphasised on great ability of silver ions to form diverse number of unusual, often unexpected, coordination compounds with covalent metal–ligand bond from a molecular structural point of view. Thus making the coordination chemistry of silver(I/II/III) ions in a general context and the organometallic chemistry of those metal ions, in particular, among promising, prospective and challenging areas in inorganic and metal–organic chemistry with a significant impact to the organic synthesis, catalysis and materials research. In this context the book can be useful to numerous MSci programmes in 'Coordination chemistry', 'Inorganic chemistry', 'Organometallic synthesis and catalysis' and PhD educational and research programmes in organic chemistry, coordination chemistry, catalysis and materials research.

Acknowledgements

The authors thank the Deutsche Forschungsgemeinschaft (DFG, Germany), which has sponsored their study in this research topic within the frame of a project grant 255/22–1; the Alexander von Humboldt Stiftung (Germany) for instrumental equipment (single crystal X-ray diffractometer); as well as central instrumental laboratories for structural analysis at Dortmund University of Technology (Federal State Nordrhein–Westfalia, Germany) and analytical and computational laboratory clusters at Institute of Environmental Research at the same University.

Conflicts of interest

Michael Spiteller has received research grant (255/22–1, DFG); Bojidarka Ivanova has received research grant (255/22–1, DFG).

Address correspondence to the authors:

Lehrstuhl für Analytische Chemie, Institut für Umweltforschung, Fakultät für Chemie und Chemische Biologie, Universität Dortmund, Otto-Hahn-Straße 6, 44221 Dortmund, Nordrhein-Westfalen, Deutschland;

E-Mails: B.Ivanova@web.de, B.Ivanova@infu.uni-dortmund.de (B.Ivanova);

E-Mail: M.Spiteller@infu.uni-dortmund.de (M.Spiteller).

About the contributors

B. Ivanova has received MSc degree in “Chemical physics and theoretical chemistry” (1997) and PhD one in “Inorganic and analytical chemistry” (2001) at Sofia University “St. Kliment Ohridski” (Bulgaria). In 2006 she achieved a Habilitation of “Analytical chemistry” at the same Institution. Ivanova has been “associate professor” of analytical chemistry, and “Head of the group” of “Molecular Spectroscopy and Structural Analysis” (2006–2010). She occupied research position at the Institute of Environmental Research (INFU) of the Faculty of Chemistry and Chemical Biology at the Dortmund University of Technology (Germany) (2010–2011). At the same Institution she hold research positions under projects (2006,2010) sponsored by Deutscher Akademischer Austausch Dienst and Deutsche Forschungsgemeinschaft (Germany). She has been visiting researcher at Ruhr–University Bochum (Germany) under project initiatives sponsored by Alexander von Humboldt Stiftung (Germany) (2003,2007–2009). Ivanova is author and co-author of more than 220 scientific contributions, including books, textbooks and distance–learning eTextbooks, focusing her interest on molecular spectroscopy and structural analysis, inorganic and metal-organic chemistry of d – and f –elements, organometallic synthesis and catalysis. Ivanova has been awarded with Rectors’ Council award “Best young scientist" (Sofia University “St. Kliment Ohridski”, 2003) and “Piagor Award” for “Best young scientist in whole area of sciences” of Bulgarian Ministry of Education (2009).

Michael Spiteller finished his study (1976) and earned a doctoral degree (1979) in Chemistry at Georg–August University (Göttingen, Germany). Habilitation he achieved at Institute for Soil Science and Forest Hygiene (Göttingen) in 1985. After that, he lead “Research Group” at the Institute for Metabolism and Environmental Fate (Bayer Corp., Germany) for 8 years. He has appointed as professor “extraordinarius” at Georg–August University in 1990 and for “full” professor at University of Kassel (Germany). Now, Spiteller is professor and “Head” of the Institute of Environmental Research of the Faculty of Chemistry and Chemical Biology at the Dortmund University of Technology (Germany). In the same Institution, Spiteller holds “Research Group Leader Position” of “Environmental Analytical Chemistry” under the “focus” programme of Deutsche Forschungsgemeinschaft. He is member of numerous expert commissions at German Federal Offices and Councils. He serves also as member of editorial advisory boards of international specialized Journals such as “Fresenius Environmental Bulletin”, “Advances in Food Science”, “Pflanzenschutz Nachrichten” (Bayer), “Journal of Serbian Chemical Society” and the fourth. His work has led to over 500 scientific papers and presentations, review articles and monographs. He has been honoured member of Serbian Chemical Society and Institute of Organic Chemistry at the Bulgarian Academy of Sciences. He has been honoured with doctor title “honoris causa” from the University of Novi Sad (Serbia, 2006) and from the University of Sofia “St. Kliment Ohridski” (Bulgaria, 2009). Spiteller’s scientific interests encompasses environmental analytical chemistry, mass spectrometric methodology and, natural products chemistry.

SUMMARY

As has been pointed out in “Preface” to this book, there are numerous books, textbooks, monographs and review articles along with comprehensive manuals, handbooks and encyclopedias on organometallics, particularly reflecting in mind organosilver compounds, too, focusing the attention on important reagents in the organic synthesis as well as catalysing reactions by silver–containing intermediates. In this respect it is reasonably to argue still here that we have tried to answer to a question which are governing molecular factors determining the efficiency of organosilver substances to the organic synthesis from a coordination chemistry point of view, rather than to present complete review–chapter to known organometallics and their utilization to selected set of important organic reactions. In other words we have chosen to present correlation between molecular structure of silver–containing organometallics and their chemical properties, as useful source of information in further molecular design of more efficient reagents. For this purpose the content involves experimental mass spectrometric and single crystal X–ray diffraction data of know organometallics, highlighting those methods as among most powerful instrumental approaches for structural elucidation encompassing both gas– and condense phase analysis, particularly showing the ability of mass spectrometry to operate up to attomol concentration ranges and providing both kinetic and thermodynamic information about analytes which is indispensable instrumental characteristics studying metal catalysing reactions. In addition we have included contributions of the method of quantum chemistry to this filed allowing to explain known gas–and condense phase phenomena about organosilver intermediate, their structures and properties, including thermodynamics and kinetics data as an excellent base for further theoretical design of new organosilver reagents. It is therefore to be expected that the largest part of content addresses problems in the field of the silver–containing organometallics catalysing organic reactions, nevertheless that it is important to take into consideration that due to diversity of chemical structures organosilver compounds they have found place to many interdisciplinary field of chemistry and materials research, including industrial scale technological application as for example precursors for the non-linear optics, rigid–rode molecular wires, and luminescence materials. In this context this book would represent interest to a wide interdisciplinary audience, having major research topics in the field of organic synthesis; metal–organic and organometallic materials research; coordination chemistry in general; due to fundamental topic in molecular structure, physical and chemical properties of silver–containing species; chemical technology and engineering; chemical kinetics and catalysis, and more.

Keywords

Organosilver intermediates

Mass spectrometry

Quantum chemistry

Single crystal X–ray diffraction

Organic synthesis

Materials research

Abbreviations and acronyms

BDE – Bond dissociation energies; CCSD(T) – Coupled-cluster theory (higher–order); CDA – Charge Decomposition Analysis; CID – Collision-induced dissociation; CN – Coordination number; DFT – Density functional theory; DMSO – Dimethylsulfoxide; EDA – Energy decomposition analysis; ECPs – Effective core potentials; ESI – Electrospray ionization (mass spectrometry); HF – Hartree–Fock (method); HFS – Hartree– Fock–Slater (theory); LANL2DZ – Los Alamos National Laboratory pseudopotentials (doble-); M06 – meta–hybrid GGA DFT functional; MALDI – Matrix – assisted laser desorption ionization (mass spectrometry); MP2 – Møller–Plesset perturbation theory (second order); MP4 – Møller–Plesset perturbation theory (fourth order); MS – Mass spectrometry; NBO – Natural Bond Orbital (analysis); NEC – Natural Electron Configuration; PCM – Polarizable continuum model; rPBE – (revised) Perdew–Burke–Erzerhoff (theory); SDD – Stuttgart–Dresden (pseudopotentials); THF – Tetrahydrofuran; UV – Ultraviolet.

Introduction

In spite of the fact that there is significant interest over the organosilver mediating reactions in the organic synthesis over decades [1,2], the challenge in design of effective organosilver reagents consists of the general thermal and photochemical decomposition properties of those complexes leading to undesirable competitive processes [3–15]. That is why the reported efforts in the implementation of the organosilver reagents are significantly smaller number that those contributions devoted to oranozinc substances. Nevertheless that the topic of this book is mainly addressed to the organic synthesis employing organometallic reagents, those substances, particularly organosilver compounds have wide interdisciplinary interest and application, including catalysis and materials science [16–18]. Among the robustest and in parallel unambiguous methods for structural analysis are the single crystal X–ray diffraction and mass spectrometry, allowing to understand comprehensively molecular structure and nature of Ag–C bond in silver–containing organometallics along with physical and chemical properties, which those substances have. Furthermore the last method allows to obtain experimental kinetic and thermodynamic information about catalytic reactions. By contrast to single crystal X–ray diffraction method where often there is unable to obtain suitable and high quality for measurements single crystal, the methods of mass spectrometry provide crucial structural information about analytes at attomol concentration ranges, which makes those methods irreplaceable to study organometallic catalysing processes both in gas– and in condense phase. Often the method of nuclear magnetic resonance takes place to study the organometallics, however it unable to obtain information about the molecular weight of the studied analytes, furthermore at the concentration ranges typical for the method of the mass spectrometry. On the other hand the nuclear magnetic resonance cannot give accurate information about the fine structure especially investigating paramagnetic species. Those arguments are leading, governing our choice as it was written above, to discuss the structure and properties of the organosilver compounds in the light of available crystallographic and mass spectrometric data. In this respect there is of paramount importance to understand comprehensively the diverse number of the chemical reactions occurring in the gas – phase under the various ionization techniques of the so–called coinage metals such as for example Cu, Ag and relating other ones. Furthermore there are additionally found series parallel process such as for example electrochemical reactions in gas–phase under ESI–ionization conditions; formation of ligand exchange complexes with the solvents of the eluent phase; uni-molecular reactions and the fourth [3–18]. There are determined three fields of employment of the methods of mass spectrometry for inorganics, generally and for organometallics, in particular: (i) Determination of the analyte molecular weight and obtaining of the information about the chemical composition using the isotopic patterns; (ii) Investigation of the relationship structure of the analyte–fragmentation pattern; and (iii) determination of the relative bond energy and the ionization potentials [18]. Particularly the crucial experimental information obtained under point (iv) by mass spectrometry enable a correlation between the experimental and theoretical quantum chemical data in study of the molecular structure of the analytes, and elucidating the nature of metal–C bonds in the organometallics. Given that more specifically we have treated the available theoretical quantum chemical information for silver–containing organometallics as an effort to highlight the excellent correlations found between theoretically modelled structures of the organometallics in gas– and condense phase and experimentally found data about corresponding geometry parameters. So, as already has been said, in this respect it have also treated problems relating structural chemistry of silver–containing organometallic and coordination compounds.

Mononuclear organometallics

From a coordination chemistry point of view the largest class of organosilver intermediates which has received increasing attention over decades enormous efforts in development of the organosilver mediated organic synthetic reactions are mononuclear complexes of AgI/II–ions. They have found application to many organometallic catalysing processes starting this part of he chapter with the reactions of decarboxylation, which have significant importance in the field of the organic chemistry [19,20]. Despite, fact that reactions of decarboxylation can yielded to organometallics, in general, the process not always produce organometallic intermediates [3–10]. To a further understanding of the elementary step of this reaction method of mass spectrometry employed in numerous studies has yielded to important information, regarding the kinetic of the process and the molecular rearrangement at the transition state resulting to formation of the Ag–C bond via breaking of C–C(OOH) bond of corresponding carboxylic acid [3,4,6]. There are found that decarboxylation process is associated with the lowest energy pathway involving decomposition of the organic acid via decarboxylation as well as the elimination of the carboxylate anion and the auxiliary ligand (chemical processes (1) – (3)).

[RCO2Ag(L)n]- ® [RAg(L)n]- + CO2 (1)

[RCO2Ag(L)n]- ® [Ag(L)n]0 + [RCO2]- (2)

[RCO2Ag(L)n]- ® [RAg(L)n-1]- + L- (3)

The mechanism of the reaction proposed via (1) has been additionally supported through the isotope labelled analysis in the case of R = CH3 (chemical process (4)). The MS data have revealed peaks at m/z 150 (relative abundance 4 %) ([RAg]+, R = (CH2)2CH3); 229 ([Ag2CH3]+); 272 ([Ag2CH3R]+, R = (CH2)2CH3) and 368 ([Ag2R2]+, R = C6H5) [3–10].

[CH313CO2AgO2CR]- ® [CH3AgO2CR]- + 13CO2 (4)

In all those reactions of organosilver catalysed decarboxylation and formation of C–X bond (X = O,C) the proposed mechanism has involved a monodentate coordination for the AgI–ions to RCOO-–carboxylate anions at first stage forming a mononucler complex with coordination number CN=2, where deraboxylation has led to RAg product having CN=1 (chemical processes (5) and (6)).

Abbildung in dieser Leseprobe nicht enthalten (5)

Abbildung in dieser Leseprobe nicht enthalten (6)

The decarboxylation has occurred both starting from the carboxylic acid derivative or the corresponding ester via formation of organometallic intermediate in second case ((6)) or mononuclear complex [RAg]0, having CN=1. There is important to point out that reactions of decarboxylation in gas–phase generally can occur employing CID in presence of alkali metal ions as well [4] ((7)).

Abbildung in dieser Leseprobe nicht enthalten (7)

The anion radical formation has been proposed in [13,15], operating under negative MS mode. Thus series of mononuclear anions have been identified at m/z 122 ([CH3Ag]-·), 123 222 ([CH3AgH]-), 151 ([CH3AgCH3CH3]-), 213 ([CH3AgCH2C6H5]-), 184 ([C6H5Ag]-·), and 199 ([CH3AgC6H5]-), respectively. Particularly, operating under positive mode there has been identified as well as a bimetallic [CH3AgCu]+ cation, studying decarboxylative processes [14] as well as AgH and benzylsilver ion formation via reactions shown as (8) [15].

Abbildung in dieser Leseprobe nicht enthalten (8)

The decarboxylation reactions of a set of poly-functional carboxylic acids (Scheme B1, App. B), has shown also a competitive C–H bond activation both involving organosilver, as well as organozinc(II) intermediates [21]. There is shown that interaction of benzene-1,3,5-tricarboxylic acid with AgI–ion has yielded to a MS peak at m/z 419 (Fig. 1) assigned to a cation of biphenyl-2,4,6,2',4',6'-hexacarboxylic acid, which MS/MS experiment has resulted to a MS peak at m/z 293 of cationic 4,8-dioxo-4,8-dihydro-cyclopenta[def]fluorene-2,6-dicarboxylic acid. The structures of organometallic catalysing agent is shown in Schemes 1 and 2. It has been assigned on base of isotopic MS shape at m/z 216/218 (Fig. 2) (App. A) and performed MS/MS experiments.

Abbildung in dieser Leseprobe nicht enthalten

Figure 1. ESI–MS/MS spectra of the system AgI/ benzene-1,3,5-tricarboxylic acid [21]

Abbildung in dieser Leseprobe nicht enthalten

Figure 2. ESI–MS spectrum of mononuclear organosilver intermediate, taking part in a C–H activating process of benzene-1,3,5-tricarboxylic acid [21].

The determination of structure of organometallics within frame of whole series poly–substituted benzoic acids has been carried out, using methods of quantum chemistry, based on DFT approaches complementary employed by ab initio pseudopotentials (see details in App. C) [21–25], thus, supporting experimental data. The theoretical NBO data along with those ones about thermodynamic stability are shown in Schemes 2 and 3.

Abbildung in dieser Leseprobe nicht enthalten

Scheme 1. Thermodynamics, theoretical qC(NBO) data, obtained for most stable geometries of polysubstituted carboxylic acids [21–25].

Abbildung in dieser Leseprobe nicht enthalten

Scheme 2. Thermodynamics of AgIII–containing organometallics obtained via interaction with polyfunctional carboxylic acids (B3PW91/SDD) [21–25].

Abbildung in dieser Leseprobe nicht enthalten

Scheme 3. Energies of d– orbitals of Ag–containing organometallics (B3PW91/SDD) [21–25].

There is important to note, however, that C–H activation reaction discussed above represents an insignificant part comparing with decarboxylation process yielding to [NH4]+ adduct of biphenyl-2,4,6,3',5'-pentacarboxylic acid (m/z 391, Fig. 3).

Abbildung in dieser Leseprobe nicht enthalten

Figure 3. ESI–MS spectrum of a decarboxylation product of AgI–catalysing process in the system AgI/ benzene-1,3,5-tricarboxylic acid [21].

Table. 1. NEC of chromophore atoms of shown silver(III/I)–containing organometallics.

Abbildung in dieser Leseprobe nicht enthalten

Like interaction of AgI–ion with benzene-1,3,5-tricarboxylic acid, system AgI/benzene-1,2,4-tricarboxylic acid has also shown a parallel decarboxylation reactions accompanied with products of C–H activation via formation of mononuclear organometallics (Fig. 4), which has been identified through isotopic MS shape at m/z 374/376 and 316/318, respectively. The formation of AgIIICCl chromophore has occurred, where fragmentation of a Cl–ion is accompanied with redox AgIII®AgI, reaction, yielding to a mononuclear organometallic with CAg chromophore and CN=1. The MS/MS experiment (m/z 316) has shown a peak at m/z 192 assigned to a half of m/z 384 of [C18H8O10]2+ obtained as a result of a reaction of C–C bond formation in gas–phase (F ig. 4).

Abbildung in dieser Leseprobe nicht enthalten

Figure 4. ESI–MS/MS spectrum of mononuclear silver(III)–containing organometallic obtained by C–H activation of 1,2,4–tricarboxylic acid in AgI/1,2,4-tricarboxylic acid system [21]; Chemical diagrams of complex and fragmentation scheme.

The thermodynamic stability of [C9H5O6ClAg]+ and [C9H5O6Ag]+ ions (Scheme 4) shows D(DG) = |0.16| kcal.mol-1, where the second complex appears more stable one. Energies of d– orbitals of those complexes are illustrated in Scheme 4, while corresponding NECs are summarized in Table 1, respectively.

Abbildung in dieser Leseprobe nicht enthalten

Scheme 4. Energies of d–orbitals of AgIII/I–containing organometallics of benzene-1,2,4-tricarboxylic acid [21–25]; Thermodynamics.

Studying organometallic complex formation of 2,3-dihydrpoxybenzoic acid with SnII–, ZnII– and AgI–metal ions [26], there is found that a stabilization of mononuclear AgI–complex with a CN=1 and Ag–C has also occurred. The ESI–MS spectra have shown isotope MS peak at m/z (Fig. 5). The MS/MS data have revealed peak at m/z 143.15 also assigned to a half of weight of a dication [C14H6O7]2+ obtained via C–C bond formation as a result of fragmentation of C–Ag bond in complex discussed above.

Abbildung in dieser Leseprobe nicht enthalten

Figure 5. ESI–MS/MS spectrum of mononuclear silver(II)–containing organometallic obtained by C–H activation of 2,3–dihydroxbenzoic acid in AgI/2,3–dihydroxbenzoic acid system; Chemical diagram of complex.

The results about the thermodynamic stability of the lastly discussed complex have shown DG = –70.99 kcal.mol-1, a value which has agreed to commonly obtained higher thermodynamic stability of the silver containing organometallics with 2,3–dihydroxy–benzoic acid (Compare data with those in Scheme 4). The energies of d–orbitals are dxy = –0.35234, dxz = –0.34993, dyz = –0.34768, dx2-y2 = –0.35014 and dz2 = –0.34836, respectively. Comparing those data with the other shown ones about the studied set of complexes (Figs. 3 and 4) we could highlight that generally higher thermodynamic stability (lower DG values) is associated with higher energies of the corresponding d–orbitals of the metal ion.

A C–Ag bond formation as a result of activation of a C–H bond, and yielding to C–Ag–H chromophore has been reported in [13], while C–Ag–Cl one – in [27], respectively. The corresponding bond lengths r (Ag–C) and r (Ag–Cl) 2.059(9) and 2.306 Å have been obtained using the method of single crystal X – ray diffraction. The formation of mononuclear species of silver–containing organometallic, having Ag–C chromophore and CN=1 has been broadly discussed in the literature as well (See for example references [28–38]).

The homolitic dissociation reactions with participation of mononucler species [RAg] like those reactions discussed in section 3 (see reactions (25)–(27), (28)) have been investigated [12], predicting the bond dissociation energies given by equation (1) (Eq. (1)), where D0 is bond energies of M–C(H3), and R–C(H3) bonds, while IE(R·) and IE(M·) are corresponding ionization energies. E0 is threshold energy given by equation (2) (Eq. (2)), respectively. In equation (2), s0 is scaling factor, while E is relative kinetic energy. The n is a parameter, while Ei – sum of vibrational, rotational and electronic states. The gi is population for which is valid equation (3) (Eq.(3)), respectively.

Abbildung in dieser Leseprobe nicht enthalten Eq.(1)

Abbildung in dieser Leseprobe nicht enthalten Eq.(2)

Abbildung in dieser Leseprobe nicht enthalten Eq.(3)

Employing Eqs. (1)–(3) there is found BDE of Ag–CH3 157 kJ.mol-1 (0 K), using MP2 theoretical level and BDE of 169 kJ.mol-1 by CCSD(T) aug-cc-pVnZ level [12]. The corresponding experimental value is 137 kJ.mol-1, reported in the same reference [12].

Towards accuracy in prediction of D0 of Ag–containing organometallics, Table 2, has provided useful information about this parameter for Ag–CH3, along with the corresponding differences between the theoretical and experimental values (D(D0))

Table 2. The D0 values of Ag–CH3 [kJ.mol-1] at various theoretical levels; D(D0) – Difference between the theoretical and the experimental value [12].

Abbildung in dieser Leseprobe nicht enthalten

The calculated BDE of the RAg at M06/SDD:6-31+G(d) level of theory for different R is shown in Fig. 6.

Abbildung in dieser Leseprobe nicht enthalten

Figure 6. BDE of RAg at M06/SDD:6-31+G(d) at different R [12]

There is important to highlight, also, that interactions of AgI– with organic acids, having stable four-membered ring configuration of the molecular skeleton such as squaric acid prevent formation of the organosilver(I) mediating agents both in solution as well as a result of gas–phase processes [22]. Thus, in polar protic solvents a formation of metal–organic AgI– complex has occurred (Fig. 7), where geometry parameters such as AgI–O bond lengths 2.512(1), 2.352(2), 2.317(3), 2.498(7), 2.613(3) Å; AgI–O–AgI and O–AgI–O angles 93.5(1)o, 90.2(6), 90.8(2), 92.2(9) and 86.9(3)o have been found [22]. The chromatogram has indicated peaks of isolated squaric acid and AgI–complex, where ESI–MS spectra have revealed (Figs. 8 and 9): (a)

Abbildung in dieser Leseprobe nicht enthalten

Figure 8. Crystal structure of AgI–complex of squaric acid [22]

Abbildung in dieser Leseprobe nicht enthalten

Figure 9. Chromatogram of the AgI–complex (Fig. 7) under HPLC–ESI–MS experiment, using mobile phase CH3CN/NH4OH; Electronic absorption spectra to each of the chromatographic peak.

Abbildung in dieser Leseprobe nicht enthalten

Figure 9. ESI–MS spectra of the AgI–complex (Fig. 7) under HPLC–ESI–MS experiment, using mobile phase CH3CN/NH4OH.

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