Metallabenzenes ebook

Table of Contents

Cover

Title Page

Copyright

List of Contributors

Preface

Chapter 1: Metallabenzenes and Fused-Ring Metallabenzenes of Osmium, Ruthenium and Iridium: Syntheses, Properties and Reactions

1.1 Introduction

1.2 Syntheses and Properties of Metallabenzenes with Methylthiolate Substituents

1.3 Syntheses and Properties of Fused-Ring Metallabenzenes

1.4 Reactions of Metallabenzenes and Metallabenzenoids

1.5 Concluding Remarks

References

Chapter 2: The First Iridabenzenes: Syntheses, Properties, and Reactions

2.1 Introduction

2.2 Basic Theory

2.3 Discovery of the First Stable Metallabenzenes

2.4 Synthesis of Iridabenzene

2.5 Valence Bond Structures and Electron Counting for Iridabenzene

2.6 The Tris(trimethylphosphine) Reaction System

2.7 Structure and Spectroscopy of Iridabenzene 3

2.8 Chemical Reactivity of Iridabenzene 3

2.9 Iridaphenol

2.10 Synthesis and Spectroscopy of Iridapyrylium

2.11 Valence Bond Structures and Electron Counting for Iridapyrylium

2.12 Chemical Reactivity of Iridapyrylium 37

2.13 Comparison of Iridabenzene 3 and Iridapyrylium 37

2.14 Synthesis and Spectroscopy of Iridathiabenzene

2.15 Structure of Iridathiabenzene 50

2.16 Chemical Reactivity of Iridathiabenzene 50

2.17 Comparison of Iridathiabenzene 50 and Iridapyrylium 37

2.18 Synthesis and Structure of a Neutral Iridathiabenzene

2.19 Spectroscopy of Neutral Iridathiabenzene 56

2.20 Chemical Reactivity of Neutral Iridathiabenzene 56

2.21 Related Metal-Coordinated Metallabenzenes

2.22 Aromaticity

2.23 Final Word

References

Chapter 3: Metallabenzenes and Valence Isomers via the Nucleophilic 3-Vinylcyclopropene Route

3.1 Project Origin and Inspiration (A Nod to Binger, Bleeke, Grubbs, Hughes, and Roper)

3.2 Ligand Synthesis (An Exercise in Over-Engineering)

3.3 Iridabenzenes and Valence Isomers (Success after Six Long Years)

3.4 Platinabenzenes (How You Get Your Chemistry on a Beer Coaster)

3.5 Odds and Sods (Ones that Got Away)

3.6 Conclusion (So Long, and Thanks for All the Fish)

3.7 Acknowledgements

References

Chapter 4: Iridabenzenes and Iridanaphthalenes with Supporting Tris(pyrazolyl)borate Ligands

4.1 Introduction

4.2 Synthetic Routes to Iridaaromatic Derivatives with Supporting Tris(pyrazolyl)borate Ligands

4.3 Reactivity of Iridaaromatics with Supporting Tris(pyrazolyl)borate ligands

4.4 Structural Data for Iridaaromatics with Supporting Tris(pyrazolyl)borate Ligands

4.5 Spectroscopic Data for Iridaaromatics with Supporting Tris(pyrazolyl)borate Ligands

4.6 Conclusions

References

Chapter 5: Chemistry of Metallabenzynes and Rhenabenzenes

5.1 Introduction

5.2 Chemistry of Metallabenzynes

5.3 Chemistry of Rhenabenzenes

5.4 Summary

References

Chapter 6: Metallabenzenoid Compounds Bearing Phosphonium Substituents

6.1 Synthesis

6.2 Structure and Bonding

6.3 Reactions

6.4 Physical Properties

6.5 Polycyclic Metallabenzenoid Compounds Bearing Phosphonium Substituents

6.6 Future Prospects

References

Chapter 7: Theoretical Studies of Metallabenzenes: From Bonding Situation to Reactivity

7.1 Introduction

7.2 Structure and Bonding Situation

7.3 Computational Studies on Synthetic Pathways towards Metallabenzenes

7.4 Computational Studies on the Reactivity of Metallabenzenes

7.5 Concluding Remarks and Outlook

7.6 Acknowledgements

References

Index

End User License Agreement

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Guide

Cover

Table of Contents

Preface

Begin Reading

List of Tables

Chapter 3: Metallabenzenes and Valence Isomers via the Nucleophilic 3-Vinylcyclopropene Route

Table 3.1 Product ratios for the synthesis of iridabenzene

22

and iridabenzvalene

23

with varying phosphines.

Table 3.2 Selected NMR data for iridabenzenes

22

,

26

,

30

and

63

a

.

Table 3.3 Selected bond lengths [Å] and bond angles [°] for iridabenzenes.

Table 3.4 Selected bond lengths [Å] and bond angles [°] for iridabenzvalenes.

Table 3.5 Selected bond lengths [Å] and bond angles [°] for platinabenzenes.

Chapter 4: Iridabenzenes and Iridanaphthalenes with Supporting Tris(pyrazolyl)borate Ligands

Table 4.1 Selected bond distances (Å) and other structural data for Tp′-iridabenzenes.

Table 4.2 Selected bond distances (Å) and other structural data for Tp

Me2

-iridanaphthalenes.

Table 4.3 Selected NMR chemical shifts (δ, ppm) for Tp′-iridabenzenes.

Table 4.4 Selected NMR chemical shifts (δ, ppm) for Tp

Me2

-iridanaphthalenes.

Chapter 6: Metallabenzenoid Compounds Bearing Phosphonium Substituents

Table 6.1 Selected bond lengths (Å) and angles (°) of osmabenzene

2

, ruthenabenzene

4

and osmapyridine

24

.

Table 6.2 Selected NMR spectroscopic data of osmabenzene

2

, ruthenabenzene

4

and osmapyridinium

23

.

Table 6.3 Thermal decomposition data of phosphonium-substituted metallabenzenes in solid state.

a

Table 6.4 Selected bond lengths (Å) and angles (°) of osmabenzothiazole

73

and osmabenzoxazole

75

.

Table 6.5 Selected NMR spectroscopic data of osmabenzothiazole

73

and osmabenzoxazole

75

.

Table 6.6 Selected bond lengths (Å) and angles (°) of fused osmabenzene

82

.

Table 6.7 Selected bond lengths (Å) and angles (°) for osmaisoquinoline

85

and osmaisoquinolyne

86

.

Chapter 7: Theoretical Studies of Metallabenzenes: From Bonding Situation to Reactivity

Table 7.1 EDA results for selected metallabenzenes C

5

H

5

and [TM] as fragments calculated at BP86/TZ2P. Energy values in kcal/mol (data taken from reference [20]).

Table 7.2 Computed NICS(0) and NICS(1) (in ppm), magnetic susceptibility anisotropy (Δχ in cgs ppm) values,

a

and ASE values (in kcal/mol)

b

for representative model metallabenzenes.

Metallabenzenes

An Expert View

This edition first published 2017

© 2017 John Wiley & Sons Ltd

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Library of Congress Cataloging-in-Publication Data

Names: Wright, L. James (Leonard James), 1954- editor.

Title: Metallabenzenes : an expert view / edited by L. James Wright, University of Auckland, New Zealand.

Description: Hoboken, NJ : Wiley, 2017. | Includes bibliographical references and index. |

Identifiers: LCCN 2017010554 (print) | LCCN 2017012640 (ebook) | ISBN 9781119068099 (pdf) | ISBN 9781119068082 (epub) | ISBN 9781119068068 (cloth)

Subjects: LCSH: Benzene-Derivatives. | Aromatic compounds.

Classification: LCC QD341.H9 (ebook) | LCC QD341.H9 M51278 2017 (print) | DDC 547/.611-dc23

LC record available at https://lccn.loc.gov/2017010554

Cover image: L. James Wright and Benjamin J. Frogley

Cover design by Wiley

List of Contributors

John R. Bleeke

Department of ChemistryWashington UniversityUSA

Israel Fernández

Departamento de Química Orgánica IFacultad de Ciencias QuímicasUniversidad Complutense de MadridSpain

Gernot Frenking

Fachberich ChemiePhilipps-Universität MarburgMarburgGermany and Donostia International Physics Center (DIPC)Spain

Benjamin J. Frogley

School of Chemical SciencesUniversity of AucklandNew Zealand

Michael M. Haley

Department of Chemistry & Biochemistry and Materials Science InstituteUniversity of OregonUSA

Guochen Jia

Department of ChemistryThe Hong Kong University of Science and TechnologyP. R. China

Margarita Paneque

Instituto de Investigaciones Químicas (IIQ)Departamento de Química Inorgánica and Centro de Innovación en Química Avanzada (ORFEO-CINQA)Consejo Superior de Investigaciones Científicas (CSIC) and Universidad de SevillaSpain

Nuria Rendón

Instituto de Investigaciones Químicas (IIQ)Departamento de Química Inorgánica and Centro de Innovación en Química Avanzada (ORFEO-CINQA)Consejo Superior de Investigaciones Científicas (CSIC) and Universidad de SevillaSpain

Warren R. Roper

School of Chemical SciencesUniversity of AucklandNew Zealand

L. James Wright

School of Chemical SciencesUniversity of AucklandNew Zealand

Haiping Xia

Department of ChemistryXiamen UniversityP. R. China

Hong Zhang

Department of ChemistryXiamen UniversityP. R. China

Preface

Professor Warren R. Roper FRS

(Photo taken in 1989, seven years after his group isolated the first metallabenzene). Source: Image provided courtesy of Professor Warren R. Roper FRS.

Metallabenzenes are a fascinating class of compounds which can be viewed as analogues of benzene in which one of the CH groups has formally been replaced by an isolobal transition metal fragment. Although benzene itself was discovered by Michael Faraday in 1825, it was not until 1982 that the first metallabenzene, an osmabenzene, was isolated by Warren R. Roper and his group at the University of Auckland, New Zealand. Since that time, interest in these compounds has steadily grown, and today it has become a flourishing area of chemistry with new developments and discoveries regularly appearing in the literature. A diverse range of synthetic approaches to these compounds have been developed. The more common of these involve the direct addition to the metal of groups that contain the five carbon atoms that eventually become the metallabenzene ring atoms, the insertion of a carbon atom from an adjacent ligand into the M–C bond of a metallacyclopentadiene, and the ring contraction of metallacycloheptatrienes.

As might be expected, the presence of the transition metal in the metallabenzene ring has a profound effect on the properties of these compounds. Theoretical studies confirm that metallabenzenes are indeed aromatic compounds with aromatic stabilization energies between ca. 20 and 80% that of benzene. However, the delocalized π-system is more complex than that of benzene. Instead of the six π-electrons present in benzene, reported metallabenzenes have either eight or ten π-electrons, depending on whether the p-orbitals of ligands such as chloride participate in the π-bonding scheme of the metallacyclic ring. Some of the occupied metallabenzene π-orbitals have Möbius character and so the standard Hückel (4n + 2) π-electron rule cannot be used as a criterion for aromaticity.

The presence of the metal adds an important dimension to the reaction chemistry of metallabenzenes. Reactions that are not observed (e.g. cycloadditions) or are not even possible for benzene (e.g. coupling of the two Cα atoms to form a cyclopentadienyl ligand) have been reported. At the same time other reactions that are characteristic for benzene such as electrophilic aromatic substitution and π-coordination to metal fragments such as Mo(CO)3 have also been observed. The metal significantly influences the spectral and structural properties of metallabenzenes. For example, in the 1H and 13C NMR spectra the resonances of the Cα (metal-bound) atoms and attached protons appear at very low field values. These resonances are almost invariably observed in between the values observed for related carbene and σ-vinyl complexes and are consistent with partial multiple bond character between the metal and the Cα atoms. The shifts of the remaining three carbon atoms and accompanying protons are in the normal ranges found for benzene derivatives. Structurally, metallabenzenes also display some distinctive features. Although the five-ring carbon atoms are always approximately co-planar, the metal is sometimes found significantly displaced from this plane, while in other cases it sits within this plane. Theoretical studies have shown that both electronic and steric effects are responsible for the location of the metal relative to the five-carbon plane. Unlike the situation for benzene, the energy profile associated with moving the metal out of the five-carbon plane is very shallow since this movement considerably decreases the π-antibonding interactions associated with the ring.

Although major advances have been made, the study of metallabenzenes is still very much in the early stages of development and it can be expected that many important new developments await discovery. The compounds and the reactions they undergo not only are of intrinsic interest but also do much to broaden our understanding of aromaticity. Furthermore, it can be anticipated that, owing to the special properties some of these species exhibit, future applications may be found in areas such as photoelectronics, molecular magnets, conducting polymers, fluorescent molecular probes, and new materials.

The field of metallabenzene chemistry is in the unusual situation that almost all the major synthetic, reaction chemistry, spectroscopic and structural studies have thus far come from just six research groups around the world. Accordingly, this book is arranged so that the work of each of these groups is covered in the form of personal perspectives in the first six chapters. Our own work (Warren R. Roper, L. James Wright and co-workers) from New Zealand, which includes the syntheses of osma-, ruthena- and iridabenzenes (including the first metallabenzene), the electrophilic aromatic substitution and nucleophilic aromatic substitution of hydrogen reactions they undergo, and the synthesis and reactions of fused-ring metallabenzenes, is covered in the first chapter. The research of John R. Bleeke’s group (USA) is presented in Chapter 2, and includes, amongst other things, the synthesis and chemistry of the first iridabenzenes as well as heteroatom-substituted analogues such as iridathiabenzenes and iridapyrylium. The chapter ends with a short summary of metal-coordinated metallabenzenes. Michael M. Haley and co-workers (USA) in Chapter 3 describe the development of new synthetic routes to iridabenzenes and the first platinabenzenes, as well as studies of the mechanisms of synthesis and decomposition. Margarita Paneque and Nuria Rendón (Spain) summarize in Chapter 4 their group’s contributions that include the development of a diverse range of metallaaromatics (including the first metallanaphthalene) which display unique chemistry and utilize supporting tris(pyrazolyl)borate ligands. The work of Guochen Jia and his group (Hong Kong), which has led to many new metallabenzenes incorporating osmium and rhenium as well as the related metallabenzyne species, is covered in Chapter 5. Haiping Xia and Hong Zhang (China) describe, in Chapter 6, the many significant contributions they and their co-workers have made to the field, largely through investigations into osma- and ruthenabenzenes containing one or more triphenylphosphonium ring substituents. These include new synthetic routes, reaction chemistry, bonding interactions, and the formation of fused-ring derivatives. Important computational investigations into the nature of metallabenzenes and the reactions of these compounds have been made by a number of different groups. In the final chapter (Chapter 7), this work is summarized by Israel Fernández and Gernot Frenking (Spain and Germany), who also highlight their own major contributions to this field.

L. James WrightAucklandMay 2017