1 An Innovative Method to Generate Iodine(V and III)-Fluorine Bonds and Contributions to the Reactivity of Fluoroorganoiodine(III) Fluorides and Related Compounds Vom Fachbereich Chemie der Universität Duisburg-Essen zur Erlangung des akademischen Grades eines Doktors der Naturwissenschaften genehmigte Dissertation von Anwar Abo-Amer aus Irbid / Jordanien Referent: Prof. Dr. H.-J. Frohn Korreferent: Prof. Dr. G. Geismar Tag der mündlichen Prüfung:
2 Die experimentellen Arbeiten wurden in der Zeit von Juli 2001 bis April 2004 unter Anleitung von Herrn Prof. Dr. H.-J. Frohn im Fach Anorganische Chemie des Fachbereiches Chemie am Campus Duisburg der Universität Duisburg-Essen durchgeführt.
3 ACKNOWLEDGMENTS I would like to thank my supervisor Prof. Dr. Hermann-Josef Frohn (Distinguished Professor Inorganic Chemistry), for his guidance, encouragement, support throughout my graduate study, his willingness to share his technical knowledge and for having patience with me. He acted as the driving force behind this research. He provided his knowledge and expertise. He spent many time for constructive discussion, which enriched my knowledge, skill and my experience. I sincerely thank Prof. Dr. G. Geismar, the Korreferent, for his encouragement, support and constructive discussion. Also, I m very grateful to Prof. Dr. Vadim Bardin for many fruitful discussions concerning topics in fluorine and boron chemistry. I have to thank my colleague Dr. Nicolay Adonin for helpful discussions. He provided not only scientific, but also moral support, and most of all friendship, throughout my study and research. I am also grateful to many other persons and I would like to acknowledge their significant contributions to my study: - Karsten Koppe, who has provided me with constant support, kind guidance and significant contribution, not only on my academic life but also on my personal life. - Wassef Al Sekhaneh, who inspired my research with his incredible knowledge. - Dietmar Jansen, Petra Fritzen, Christoph Steinberg, Andre Wenda, and Oliver Brehm, which all inspired my research with their incredible knowledge and helped for a warm and supportive environment. Special thanks are given to many faculty and staff members of the chemistry department (Duisburg-Essen Universität) for their assistance during my graduate study. In particular, thanks are pressed to Dr. Ulrich Flörke for the X-Ray crystallographic work. Special thanks to Mrs. Beate Römer and Mr. Manfred Zähres for NMR spectrometric measurements. My utmost appreciation and thanks are given to my wife, Eman Abu-Jadoua, for her love and support throughout my graduate career. I also thank my daughter, Mimas, and my son, Yamen, for bringing so much joy the moment they joined into my life in Germany. I warmly thank my parents, brothers and sisters for continuous inspiration and encouragement. The support of many friends through out my research (Prof. Dr. Alaa Hassan, Prof. Dr. Mohammad Shabat) has also been much appreciated.
4 After great pain, a formal feeling comes Emily Dickinson
5 Dedicated to My Daughter Mimas, My Son Yamen, My Wife Eman, My Mother and Father
6 Table of Contents I Table of Contents 1 Introduction Bonding and Structure in Polyvalent Iodine Compounds (Difluoroiodo)arenes (Tetrafluoroiodo)arenes and (Difluorooxoiodo)arenes (Tetrafluoroiodo)arenes (Difluorooxoiodo)arenes Iodine Pentafluoride Iodonium Salts Diaryliodonium Salts Alkenyl(aryl)iodonium Salts 12 2 Objectives Preparative Aspects Iodine Pentafluoride (Tetrafluoroiodo)arenes (Difluorooxoiodo)arenes (Difluoroiodo)arenes Iodonium Salts Reactivity, Structure, and Spectroscopy 17 3 Results and Discussion Preparation of Iodine Pentafluoride (IF 5 ) by a New Methodological Approach Introduction Relevant Reactivities of I(V)-F and I(V)-O Bonds The Reaction of I(V)-O Compounds with ahf in a Two Phase System The Important Steps in the Preparation of IF The Influence of the HF Concentration on the IF 5 Formation 21
7 Table of Contents II Fluoro-1-(tetrafluoroiodo)benzene by Oxygen-Fluorine Substitution Fluoro-1-(difluorooxoiodo)benzene (p-c 6 H 4 FIOF 2 ) by Treat- ment of 4-Fluoro-iodylbenzene with Hydrofluoric Acid (Difluoroiodo)arenes (ArIF 2 ) by Oxygen-Fluorine Substitution on ArIO with Hydrofluoric Acid as Reagent 25 The Influence of the HF Concentration on the Formation of (Difluoroiodo)arenes (ArIF 2 ) A Convenient Route to (Difluoroiodo)benzenes (ArIF 2 ) Directly from (Diacetoxyiodo)benzenes Iodonium Salts The Synthesis of Diaryliodonium Salts Starting from (Difluoroiodo)arenes The Synthesis of Alkenyl(aryl)iodonium Salts Starting from (Difluoroiodo)arenes trans-1,2,3,3,3-pentafluoroprop-1-enyl(fluorophenyl)iodonium Tetrafluoroborates trans-1,2,3,3,3-pentafluoroprop-1-enyl(pentafluorophenyl)iodonium Tetrafluoroborate Preparation of Trifluorovinyl(fluorophenyl)iodonium Tetrafluoroborates Preparation of Trifluorovinyl(pentafluorophenyl)iodonium Tetrafluoroborate Selected Reactivities of Fluoro(difluoroiodo)benzenes C 6 H 4 FIF Reactivities with Nucleophiles and Lewis Bases The Reaction of p-c 6 H 4 FIF 2 with Trimethylsilylacetate The Interaction of ArIF 2 with 2,2 -Bipyridine The Interaction of ArIF 2 with (C 6 H 5 ) 3 PO The Reaction of ArIF 2 with [NMe 4 ]F 37
8 Table of Contents III The Reaction of p-c 6 H 4 FIF 2 with [N(CH 3 ) 4 ]F (1 : 1) in Dichloromethane The 1 : 2 Reaction of p-c 6 H 4 FIF 2 with [N(CH 3 ) 4 ]F in Dichloromethane The 1 : 0.5 Reaction of p-c 6 H 4 FIF 2 with [N(CH 3 ) 4 ]F in Dichloromethane The Reaction of p-c 6 H 4 FIF 2 with [N(CH 3 ) 4 ]F (1 : 1) in Acetonitrile The Reaction of p-c 6 H 4 FIF 2 with [N(CH 3 ) 4 ]F (1 : 3) in Dichloromethane The 1 : 2 Reaction of o-c 6 H 4 FIF 2 with [N(CH 3 ) 4 ]F in Dichloromethane The 1 : 2 Reaction of m-c 6 H 4 FIF 2 with [N(CH 3 ) 4 ]F in Dichloromethane The Reaction of p-c 6 H 4 FIF 2 with CsF The Reaction of p-c 6 H 4 FIF 2 with CsF (1 : 1) in Acetonitrile The Reaction of p-c 6 H 4 FIF 2 with CsF (1 : 2) in Acetonitrile Reactions of C 6 H 4 FIF 2 with Lewis and Brønsted Acids The Reaction of p-c 6 H 4 FIF 2 with C 6 H 5 PF The Reactions of p-c 6 H 4 FIF 2 with Alcohols (MeOH, EtOH, CF 3 CH 2 OH) The Reaction of p-c 6 H 4 FIF 2 with CF 3 CO 2 H The Reaction of p-c 6 H 4 FIF 2 with ahf Selected Reactivities of Iodonium Salts Reactions with Lewis Bases The Reaction of [p-c 6 H 4 F(CF 2 =CF)I][BF 4 ] with Naked Fluoride The Reaction of [p-c 6 H 4 F(C 6 H 5 )I][BF 4 ] with Naked Fluoride The 1 : 1 Reaction of [p-c 6 H 4 F(C 6 H 5 )I]F with Naked Fluoride in Dichloromethane Reactions with Nucleophiles The Reaction of [p-c 6 H 4 F(trans-CF 3 CF=CF)I][BF 4 ] with (p-c 6 H 4 F) 3 As in CH 2 Cl The Reaction of [p-c 6 H 4 F(trans-CF 3 CF=CF)I][BF 4 ] with (p-c 6 H 4 F) 3 P in CH 2 Cl The Reaction of [p-c 6 H 4 F(trans-CF 3 CF=CF)I][BF 4 ] with 2,2 -Bipyridine in CH 2 Cl The Attempted Reaction of [p-c 6 H 4 F(CF 2 =CF)I][BF 4 ] with (p-c 6 H 4 F) 3 P in ahf 58
9 Table of Contents IV 3.9 The Results of 1 H, 13 C, and 19 F NMR Spectroscopic Studies F NMR Spectroscopic Studies of IF The NMR Spectroscopic Studies of 4-Fluoro-1-(tetrafluoroiodo)benzene (p-c 6 H 4 FIF 4 ) The NMR Spectroscopic Studies of 4-Fluoro-1-(difluorooxoiodo)benzene (p-c 6 H 4 FIOF 2 ) The NMR Spectroscopic Comparison of C 6 H 4 XI, C 6 H 4 XI(OAc) 2, and C 6 H 4 XIF 2 (X = o-, m-, and p-f) The Temperature Dependence of 19 F NMR Chemical Shifts in Monofluoro(difluoroiodo)benzenes NMR Spectroscopic Studies on Iodonium Salts Asymmetric Diaryliodonium Tetrafluoroborates trans-1,2,3,3,3-pentafluoroprop-1-enyl(fluorophenyl)iodonium Tetrafluoroborates Trifluorovinyl(fluorophenyl)iodonium Tetrafluoroborates Alkenyl(pentafluorophenyl)iodonium Tetrafluoroborates Thermal Stabilities of Selected (Difluoroiodo)benzenes and Aryl-Containing Iodonium Salts X-Ray Crystal Structure Analysis The Crystal Structures of p-c 6 H 4 FIF 2 and o-c 6 H 4 FIF The Crystal Structure of [m-c 6 H 4 F(C 6 H 5 )I][BF 4 ] The Crystal Structure of [p-c 6 H 4 F(trans-CF 3 CF=CF)I][BF 4 ] The Crystal Structure of p-c 6 H 4 FIOF The Inductive and Resonance Parameters of Selected I(III)- Substituents in Iodonium Salts Using Taft`s Method Experimental Section Materials, Apparatus, and Methods General Methods Spectroscopic, Physical, and Analytical Measurements 105
10 Table of Contents V NMR Spectroscopy H NMR Spectroscopy B NMR Spectroscopy F NMR Spectroscopy C NMR Spectroscopy Differential Scanning Calorimetry (DSC) Measurements Melting Point Measurements X-Ray Single Crystal Measurements Weighing of Electrostatic Materials Solvents, Chemicals, and Starting Compounds Solvents Chemicals Available in the Laboratory Commercially Available Chemicals Starting Compounds The Preparation of (Diacetoxyiodo)arenes ArI(O 2 CCH 3 ) The Preparation of Iodosylbenzenes ArIO The Preparation of p-fluoroiodylbenzene p-c 6 H 4 FIO The Preparation of Phenyldifluoroborane The Preparation of Perfluorovinyldifluoroborane The Preparation of Potassium Perfluorovinyltrifluoroborate The Preparation of Lithium Perfluorovinyltrimethoxyborate The Preparation of trans-1,2,3,3,3-pentafluoroprop-1-enyldifluoroborane The Preparation of Potassium trans-1,2,3,3,3-pentafluoroprop-1- enyltrifluoroborate The Preparation of Lithium trans-1,2,3,3,3-pentafluoroprop-1- enyltrimethoxyborate The Preparation of trans-1,2,3,3,3-pentafluoropropene Synthetic Procedures and Spectroscopic Data An Innovative Preparation of Iodine Pentafluoride Starting from Iodine(V) Oxide Starting from Sodium Iodate 124
11 Table of Contents VI The Influence of the HF Concentration on the IF 5 Formation: Reaction of NaIO 3 with ahf The Preparation of 4-Fluoro-1-(tetrafluoroiodo)benzene The Preparation of 4-Fluoro-1-(difluorooxoiodo)benzene The Preparation of (Difluoroiodo)benzenes from Iodosylbenzenes 128 The Influence of the HF Concentration on the Formation of (Difluoroiodo)arenes (ArIF 2 ) A Convenient Route to (Difluoroiodo)benzenes ArIF 2 Directly from (Diacetoxyiodo)benzenes The Preparation of Monofluorophenyl(phenyl)iodonium Tetrafluoroborates The Preparation of trans-1,2,3,3,3-pentafluoroprop-1-enyl(monofluorophenyl)iodonium Tetrafluoroborates The Preparation of trans-1,2,3,3,3-pentafluoroprop-1-enyl(pentafluorophenyl)iodonium Tetrafluoroborate The Preparation of Trifluorovinyl(monofluorophenyl)iodonium Tetrafluoroborates The Preparation of Trifluorovinyl(pentafluorophenyl)iodonium Tetrafluoroborate Selected Reactivities of Fluoro(difluoroiodo)benzenes C 6 H 4 FIF Reactivities with Nucleophiles and Lewis Bases The Reaction of p-c 6 H 4 FIF 2 with Trimethylsilylacetate The Interaction of ArIF 2 with 2,2 -Bipyridine The Interaction of ArIF 2 with (C 6 H 5 ) 3 PO The Reaction of p-c 6 H 4 FIF 2 with [NMe 4 ]F The Reaction of p-c 6 H 4 FIF 2 with [N(CH 3 ) 4 ]F (1 : 1) in Dichloromethane The Reaction of p-c 6 H 4 FIF 2 with [N(CH 3 ) 4 ]F (1 : 2) in Dichloromethane The Reaction of p-c 6 H 4 FIF 2 with [N(CH 3 ) 4 ]F (1 : 0.5) in Dichloromethane The Reaction of p-c 6 H 4 FIF 2 with [N(CH 3 ) 4 ]F (1 : 1) in Acetonitrile The Reaction of p-c 6 H 4 FIF 2 with [N(CH 3 ) 4 ]F (1 : 3) in CH 2 Cl The Reaction of m-c 6 H 4 FIF 2 with [N(CH 3 ) 4 ]F (1 : 2) in Dichloromethane 154
12 Table of Contents VII The Reaction of o-c 6 H 4 FIF 2 with [N(CH 3 ) 4 ]F (1 : 2) in Dichloromethane The Reaction of p-c 6 H 4 FIF 2 with CsF The Reaction of p-c 6 H 4 FIF 2 with CsF (1 : 1) in Acetonitrile The Reaction of p-c 6 H 4 FIF 2 with CsF (1 : 2) in Acetonitrile Reactions of C 6 H 4 FIF 2 with Lewis and Brønsted Acids The Reaction of p-c 6 H 4 FIF 2 with C 6 H 5 PF The Reactions of ArIF 2 with Alcohols (MeOH, EtOH, CF 3 CH 2 OH) The Reaction of p-c 6 H 4 FIF 2 with CF 3 CO 2 H The Reaction of p-c 6 H 4 FIF 2 with ahf Selected Reactivities of Iodonium Salts Reactions with Lewis Bases The Reaction of [p-c 6 H 4 F(CF 2 =CF)I][BF 4 ] with Naked Fluoride in CH 2 Cl The Reaction of [p-c 6 H 4 F(C 6 H 5 )I][BF 4 ] with Naked Fluoride in CH 2 Cl The 1 : 1 Reaction of [p-c 6 H 4 F(C 6 H 5 )I]F with Naked Fluoride in CH 2 Cl Reactions with Nucleophiles The Reaction of [p-c 6 H 4 F(trans-CF 3 CF=CF)I][BF 4 ] with (p-c 6 H 4 F) 3 As in CH 2 Cl The Reaction of [p-c 6 H 4 F(trans-CF 3 CF=CF)I][BF 4 ] with (p-c 6 H 4 F) 3 P in CH 2 Cl The Reaction of [p-c 6 H 4 F(trans-CF 3 CF=CF)I][BF 4 ] with 2,2 -Bipyridine in CH 2 Cl The Attempted Reaction of [p-c 6 H 4 F(CF 2 =CF)I][BF 4 ] with (p-c 6 H 4 F) 3 P in ahf The Determination of the Inductive and Resonance Parameters of Selected I(III)-Substituents in Iodonium Salts Using Taft`s Method Summary Generation of Iodofluorides and Organoiodofluorides Iodine Pentafluoride (Tetrafluoroiodo)arenes 171
13 Table of Contents VIII (Difluorooxoiodo)arenes (Difluoroiodo)arenes The First Synthesis of Perfluoroalkenyl(aryl)iodonium Tetrafluoroborate Salts Reactivity, Structure, and Spectroscopy of Monofluoro(difluoroiodo)benzenes General Reactivities of Perfluoroalkenyl(aryl)iodonium Tetrafluoroborate Salts References Appendix NMR Spectroscopic Data of I-F and Related Compounds Solubility of ArIF 2 in Different Solvents Solubility of HF in Methylene Chloride The Interatomic Distances and Angles of p-c 6 H 4 FIF 2, o-c 6 H 4 FIF 2, [m-c 6 H 4 F(C 6 H 5 )I][BF 4 ], p-c 6 H 4 FIOF 2 [p-c 6 H 4 F(trans-CF 3 CF=CF)I][BF 4 ] List of Figures List of Schemes List of Tables List of Symbols and Abbreviations List of Publications, Presentations and Conferences 201 Curriculum Vitae
14 Introduction 1 1 Introduction 1.1 Bonding and Structure in Polyvalent Iodine Compounds The concept of hypervalency was introduced by Musher  in By definition in hypervalent molecules the octet rule is not obeyed, that means that there are more than four pairs of electrons around the central atom in the conventional Lewis formula. More simply, hypervalent molecules or ions are containing central atoms of group 15 18, non-metals of groups V VIII of the main groups, in a higher valency than the stable one given by the valency rule 8 group number. In such compounds the central atom uses a p-orbital to form a linear bond to two ligands. Such bonds, termed "hypervalent", are longer and weaker than [2, 3, 4, 5] (normal) two-centre two-electron covalent bonds. The description of such bonding systems by molecular orbital theory led to the concept of 3- [6, 7] center-4-electron or similar poly-centre bonds (hypervalent bonds). Supported by [8, 9] computational work this concept is now accepted. The most common hypervalent iodine compounds are aryl λ 3 iodanes (ArIL 2 ) with a decet structure and pseudotrigonal bipyramidal geometries (T-shaped molecules) and aryl-λ 5 iodanes (ArIL 4 ) with a dodecet structure and square pyramidal geometries. Bonding in ArIL 2 compounds uses essentially a pure 5p orbital in the linear L-I-L bond, the hypervalent three-centre-four-electron bond (3c-4e bond), with two electrons from the doubly occupied 5p orbital of iodine and one electron from each p-orbital of the ligands L. The least electronegative ligand in ArIL 2, the aryl group, is bound by a normal two-centre-two-electron covalent bond with C(sp 2 ) hybridization in the C Ar I σ-bond. [10, 11] In the MO-scheme of the IL 2 subunit with three molecular orbitals the two molecular orbitals of lower energy, bonding and nonbonding orbitals, are filled (Fig. 1). Partial positive charge has to be assigned to the central iodine atom (ca a.u.),  while partial negative charge on both apical heteroatom ligands (L = F: ca. 0.5 a.u.).  The filled nonbonding molecular orbital has a node at the central iodine atom. The partial positive charge on iodine in the highly polarised 3c 4e bond makes the aryl-λ 3 -iodane an electrophilic agent. The inherent nature of the 3c 4e bond explains the preferred orientation of more electronegative ligands in the apical positions. For non-metals of the same group more electropositive central atoms are energetically favoured for hypervalent species: thus in general, λ 3 -iodanes are more stable than analogous λ 3 - bromanes and λ 3 [10, 11] -chloranes.
15 Introduction 2 L antibonding : Ar I nonbonding : L bonding L I L Figure 1: Molecular orbital scheme for the three centre-four electron bond in the IL 2 group. For the designation of hypervalent compounds the Martin Arduengo [N-X-L] notation is usually used , in which N is the number of valence electrons surrounding the central atom X and L is the number of ligands bonded to the X-atom. According to this designation, six structural types of polyvalent iodine species (1 6) are the most common. The first two species, 8-I-2 (1) and 10-I-3 (2), called λ 3 -iodanes, are conventionally considered as derivatives of iodine(iii), whereas the next two, 10-I-4 (3) and 12-I-5 (4) λ 5 -iodanes, represent the most typical structural types of pentavalent iodine. .. L L L O L : L L L L L L L I R I : I I I L I.. L L : L L L L L L L L L.. L L 8-I-2 10-I-3 10-I-4 12-I-5 14-I-6 14-I Species 1 4 are common in organic chemistry. The 10-I-3 species have an approximately T- shaped structure with a collinear arrangement of the most electronegative ligands. Including the free electron pairs, the ψ-geometry of iodine is a distorted trigonal bipyramide. 8-I-2 species (iodonium cations) (1) are usually considered as cationic part of salts with pseudotetrahedral geometry of the central I-atom. Caused by the positive partial charge on iodine and the open moiety of iodine, additional contacts to basic sites of the anion are observed. [14, 15] The I-C distances in both species 1 and 2 are approximately equal to the sum of the covalent radii of iodine and carbon, ranging generally from 2.00 to 2.10 Å. Compounds of iodine(iii) with one carbon ligand are represented by organic iodosyl compounds (RIO, where R is usually aryl) and their derivatives (RIX 2, where X represents an electronegative ligand). The second iodine(iii) class with two carbon ligands on iodine includes various iodonium salts (R 2 I + X ). The overwhelming majority of known, stable organic compounds of polyvalent iodine belong to these two classes. The two heteroatom ligands X attached to iodine in RIX 2 are commonly represented by fluorine, chlorine, O-, N-, and strongly electronegative C-substituents. In general, only RIX 2 derivatives bearing the
16 Introduction 3 [13, 14] most electronegative substituents X are sufficiently stable. The bonding in iodine(v) compounds containing divalent ligands such as oxygen may also be described in terms of hypervalency. Two singly occupied atomic orbitals of oxygen interact with a doubly occupied 5p orbital of iodine forming three molecular orbitals: one bonding (doubly occupied), one nonbonding localised on oxygen (doubly occupied), and one antibonding (unoccupied). The result is a highly polarised I O bond with considerable positive partial charge on iodine and negative partial charge on oxygen. Such hypervalent bonds are designated as 2c 4e bonds (fig. 2).  On the other hand, compounds of the IOL 3 type are constructed from three different bonds. In PhIOF 2 there is one 2c 2e I C bond, one 3c 4e IF 2 bond, and one 2c 4e I O bond.  C... O. : I C O.... I : ψ 3 antibonding ψ 2 ψ 1 nonbonding bonding I O Figure 2: The molecular orbital scheme for the hypervalent 2c-4e I-O bond. The bonding in iodine(v) compounds, IL 5, with a square pyramidal structure may be described in terms of one 2c 2e bond between iodine and the ligand in the apical position, trans to the lone pair, and two orthogonal, hypervalent 3c 4e bonds, accommodating four [17, 18a] ligands. Aryl-λ 5 -iodanes ArIL 4 have a square pyramidal structure with the aryl group in the apical position and four ligands in basal positions. L L Ar I..: L L A very high fugalibility (leaving group ability) of iodanyl groups (λ 1 ) is among the most
17 Introduction 4 important features of iodonium salts, often describes as λ 3 -iodanes [18b], which makes it possible to generate highly reactive species such as carbenes, nitrenes, cations, and arynes under mild conditions. Furthermore λ 3 -iodanes, RIX 2, are suitable oxidizing agents and allow the transformation of a wide range of functionalities such as alcohols, amines, sulfides, alkenes, alkynes, and carbonyl groups.  1.2 (Difluoroiodo)arenes Actually (difluoroiodo)arenes have received a widespread practical application in organic synthesis as versatile fluorination reagents. Generally, they are more reactive than the analogous bromides and chlorides.  There is a considerable number of different methods of synthesis for this widely applied class.  (Difluoroiodo)arenes were synthesised for the first time by Dimroth and Bockemüller from iodosylbenzenes and 40 % aqueous hydrogen fluoride as impure products in 1931:  ArIO + 2 HF K[HF 2 ] CHCl 3 ArIF 2 + H 2 O Garvey, Halley, and Allen used a mixture of 46 % aqueous HF and glacial acetic acid:  (1) ArIO + 2 HF / CH 3 CO 2 H ArIF 2 + H 2 O (2) In 1966, Carpenter reported a method, which can be described as chlorine-fluorine substitution on (dichloroiodo)arene using HF in the presence of mercury(ii) oxide:  ArICl HF / HgO ArIF 2 + HgCl 2 + H 2 O (3) The isolation of readily hydrolysible (difluoroiodo)arenes is the mean problem in all above mentioned methods owing to the fact that the reaction mixture contains water. To overcome this disadvantage, Schmidt and Meinert proposed the electrochemical oxidation of iodoarenes in acetonitrile solution in the presence of silver fluoride as supporting electrolyte and fluoride source giving the pure (difluoroiodo)arenes.  For a high yield the electrochemical preparation of para-substituted (difluoroiodo)arenes [25, 26] Et 3 N n HF was recently used as reagent. Moreover, (difluoroiodo)arenes are formed readily when the corresponding iodosyl or bis(trifluoracetoxy)iodoarenes are treated with sulfur tetrafluorid at 20 C.  All the by-
18 Introduction 5 products in this reaction are volatile and can be removed by evaporation. (Difluoroiodo)arenes are afforded in high purity: ArIO + SF 4-20 C ArIF 2 + SOF 2 (4) ArI(O 2 CCF 3 ) SF 4-20 C ArIF SOF CF 3 COF (5) Schmeißer reported for the first time the oxidative addition of fluorine to C 6 F 5 I. C 6 F 5 IF 2 was [28, 29] obtained by using elemental fluorine at low temperature: -100 C Ar f I + F 2 CCl 3 F Ar f IF 2 (6) Xenon difluoride was also used to obtain (difluoroiodo)arenes:  ArI + XeF C ArIF 2 + Xe (7) The fluorination of various iodoarenes with elemental fluorine, diluted with nitrogen to avoid the fluorination of the aromatic ring which contained donating substituents, have been [31, 32] published: -100 C ArI + F 2 CCl 3 F ArIF 2 (8) A modified three step method for preparing (difluoroiodo)arenes from iodoarenes in a pure form was reported parallel to this work. (Dichloroiodo)arenes were prepared by the reaction of iodoarenes with chlorine gas (eq. 9). The products were hydrolysed to form the corresponding iodosylarenes (eq. 10), which were treated after purification with 46 % aqueous HF to produce (difluoroiodo)arenes (eq. 11):  ArI + Cl 2 ArICl NaOH ArIO + 2 HF ArICl 2 ArIO + H 2 O + 2 NaCl ArIF 2 + H 2 O (9) (10) (11)
19 Introduction (Tetrafluoroiodo)arenes and (Difluorooxoiodo)arenes (Tetrafluoroiodo)arenes The chemistry of iodine(v) compounds or λ 5 -iodanes is substantially less developed in comparison with the chemistry of I(III). Recently there has been an increasing interest in I(V) especially in their fluorinated compounds.  Iodine(V) compounds may have the general formula IL 5, IZL 3, and IZ 2 L where L is a monovalent and Z a divalent ligand. The bonding system of IL 5 can be described in terms of one 2c 2e bond I L apical and two orthogonal 3c 4e bonds, accommodating the basal IF 2 subunits. In the case of RIF 4, the R-ligand is placed in [19, 35] the apical position. The oxidative fluorination of organoiodides can be used to prepare (tetrafluoroiodo)arenes (RIF 4 ). This method produces very often RIF 4 in mixtures with (difluoroiodo)arenes, and their separation is difficult. The first reported method for the preparation of ArIF 4 used the fluorination of ArI by nitrogen-diluted F 2 in CCl 3 F. In the first step ArI reacts with F 2 at 100 C giving slightly soluble ArIF 2 in CCl 3 F, which can - as far as dissolved - further interact with F 2 at 40 C and form ArIF 4. [36-38] Fluorination of iodoarenes with an excess of one of the following fluorinating agents XeF 2, ClF 3, BrF 3, BrF 5, C 6 F 5 BrF 2 and C 6 F 5 BrF 4 led to the corresponding (tetrafluoroiodo)arene compounds: [27, 30, 37, 39 41] C 3 ArI + 4 ClF 3 3 ArIF Cl 2 (12) Another approach to ArIF 4 preferentially developed for aryl groups with electronwithdrawing substituents is the nucleophilic substitution on IF 5. Arylsilanes and arylmetal [19a, 42 46] compounds of thalium, lead, bismuth, and cadmium have been used: PhSiF 3 + IF Py PhIF 4 + SiF 4 2 Py (13) Si(C 6 F 5 ) IF Py 4 C 6 F 5 IF 4 + SiF 4 2 Py (14) Cd(C 6 F 5 ) IF 5 2 C 6 F 5 IF 4 + CdF 2 (15) Ar f IF 4 can be produced by electrophilic substitution using the highly electrophilic [IF 4 ] + cation [47a]. No Ar f IF 4 was formed by oxidative fluorination between iodoarenes Ar f I and IF 5 under non-acidic conditions: [47b]
20 Introduction 7 Ar f H + [IF 4 ] + Ar fif 4 + H + (16) (Tetrafluoroiodo)arenes were obtained in quantitive yield also by heating iodylarenes with [48, 49] sulphur tetrafluoride: ArIO SF 4 ArIF SOF 2 (17) (Difluorooxoiodo)arenes react in the same manner with SF 4, moreover their use is safer [27, 37, 45, 50] because they are less explosive than iodylarenes: ArIOF 2 + SF 4 ArIF 4 + SOF 2 (18) (Difluorooxoiodo)arenes (Difluorooxoiodo)arenes were obtained by dissolving iodylarenes in hot 40 % aqueous [51 53] hydrofluoric acid: ArIO HF ArIOF 2 + H 2 O (19) Alternative procedures are the reaction of (tetrafluoroiodo)arenes with equivalent amounts of hexamethylsiloxane (eq. 20) or simply with water (eq. 21) or iodylarenes (eq. 22):  ArIF 4 + ( (CH 3 ) 3 Si) 2 O ArIOF (CH 3 ) 3 SiF (20) ArIF 4 + H 2 O ArIOF HF (21) ArIF 4 + ArIO 2 2 ArIOF 2 (22) 1.4 Iodine Pentafluoride Iodine pentafluoride, IF 5, is the only known binary interhalogen compound of iodine(v). Iodine pentafluoride is a colourless liquid with a melting point of 9.6 C and a boiling point of 98 C.
21 Introduction 8 Iodine pentafluoride is a versatile and well-known fluorinating agent. It can be used, for example, to prepare fluorohydrocarbons and fluoroalkyl sulfides, to form adducts with oxides of nitrogen and to convert metals to fluorides.  IF 5 was first prepared in 1862 by heating of iodine with silver fluoride:  3 I AgF IF AgI (23) Thirty years later, Moissan reported the direct synthesis using iodine and elemental fluorine.  It has been found that iodine(v) fluoride can be prepared by reacting iodine oxygen compounds with sulfur tetrafluoride. Such I-O starting materials are iodine oxides (I 2 O 5 ), alkali metal iodates (NaIO 3, KIO 3 ) and alkaline earth metal iodates (Mg(IO 3 ) 2, Ca(IO 3 ) 2, Ba(IO 3 ) 2 ). The reactants must be used in anhydrous form, because water reacts as well with sulfur tetrafluoride as with iodine pentafluoride:  I 2 O SF 4 2IF SOF 2 (24) In 1963, Fawcett reported a new method of preparing iodine pentafluoride by fluorinating anhydrous iodine pentaoxide (I 2 O 5 ) with pure carbonyl fluoride at high temperature:  I 2 O COF 2 2IF CO 2 (25) The reaction between iodine and fluorine is primarily a heterogeneous solid-gas reaction. Because of the high reaction enthalpy iodine sublimates and reacts instantaneously with fluorine in the gas phase. At a temperature above 250 C IF 7 becomes the favoured product. Therefore it is useful in the direct synthesis of IF 5 to look for homogeneous and moderate temperature conditions. Principally the presence of an inert solvent may be useful. In the technical process IF 5 itself is used as slightly dissolving medium for I 2 :  IF 5 as solvent I F 2 2 IF C (26) In a modified method molten iodine was reacted with gaseous fluorine at C (eq. [59, 60] 27):