Preface ...................................................... xvii
CHAPTER 1 Introduction and History ............................. 1
CHAPTER 2 Structure and Bonding ................................ 7
2.1 General Perspective ........................................ 7
2.2 Nomenclature and Numbering ................................. 7
2.3 The Localized-bond Approach ................................ 8
2.4 Structural Patterns in Boron Clusters ...................... 9
2.5 Extensions of the Electron-counting Rules ................. 14
2.6 Electron-counting in Classically Bonded Clusters .......... 15
2.7 Isomer Stability and Cage Rearrangement ................... 16
2.8 Cluster Aromaticity ....................................... 16
2.9 "Electron Deficiency" in Polyhedral Boron Clusters ........ 17
CHAPTER 3 Synthesis and Reactivity: An Overview ............... 21
3.1 General Preparative Routes to Carboranes .................. 21
3.1.1 Borane-alkyne Gas Phase Reactions .................. 21
3.1.2 Borane-alkyne Reactions in Solution ................ 22
3.1.3 Carborane-alkyne Reactions ......................... 22
3.1.4 Carbon Insertion via Cyano- and Isocyanoboranes .... 22
3.1.5 Carboranes from Organoboranes ...................... 22
3.2 Interconversion Reactions ................................. 23
3.2.1 Polyhedral Rearrangement ........................... 23
3.2.2 Metal-promoted Cage Fusion ......................... 23
3.2.3 Polyhedral Expansion and Contraction ............... 23
3.3 Substitution at Cage Carbon and Boron Atoms ............... 24
3.4 Carboranes as Substituents and Ligands .................... 25
CHAPTER 4 Small Carboranes: Four- to Six-vertex Clusters ...... 27
4.1 Overview .................................................. 27
4.2 4-Vertex Open Clusters .................................... 27
4.2.1 CB3Hx and C2B2Hx ..................................... 27
4.3 5-Vertex Open Clusters .................................... 28
4.3.1 Nido- and Arachno-CB4 Systems ...................... 28
4.3.2 Nido-l,2-C2B3H7 .................................... 29
4.3.3 Other Open-cage C2B3 Clusters ...................... 32
4.3.4 Nido-C3B2 Clusters ................................. 32
4.4 5-Vertex Closo Clusters ................................... 33
4.4.1 CB4Hx .............................................. 33
4.4.2 1,5-C2B3H5 .......................................... 33
4.4.3 Closo-C3B2H5+ ........................................ 41
4.5 6-Vertex Open Clusters .................................... 41
4.5.1 Nido-2-CB5H9 ........................................ 41
4.5.2 Hypho-CB5H13 ........................................ 44
4.5.3 Nido-2,3-C2B4H8 ..................................... 45
4.5.4 Nido-2,4-C2B4H8 ..................................... 56
4.5.5 Arachno- and Hypho-C2B4Hx Clusters .................. 59
4.5.6 Nido-2,3,4-C3B3H7 ................................... 60
4.5.7 Nido-2,3,5-C3B3H7 ................................... 62
4.5.8 Nido-2,3,4,5-C4B2H6 ................................. 64
4.5.9 Nido-2,3,4,5,6-C5BH6+ ............................... 72
4.6 6-Vertex Closo Clusters ................................... 73
4.6.1 1-CB5H7 and 1-CB5H6- ................................ 73
4.6.2 1,2- and 1,6-C2B4H6 ................................. 75
CHAPTER 5 Intermediate Carboranes: Seven- to Nine-vertex
Clusters ............................................ 93
5.1 Overview .................................................. 93
5.2 7-Vertex Open Clusters .................................... 93
5.2.1 №fifo-C2B5H8- ....................................... 93
5.3 7-Vertex Closo Clusters ................................... 94
5.3.1 2-CB6H7- ............................................ 94
5.3.2 2,3-C2B5H7 .......................................... 96
5.3.3 2,4-C2B5H7 .......................................... 99
5.3.4 C3B4 Clusters ...................................... 111
5.4 8-Vertex Open Clusters ................................... 1ll
5.4.1 Arachno-CB7H13 and CB7H12- .......................... 1ll
5.4.2 Nido-C2B6H10 ....................................... 112
5.4.3 Nido-C2B6H82- ...................................... 114
5.4.4 Arachno-C2B6H12 .................................... 115
5.4.5 Hypho-C2В6H13- ..................................... 116
5.4.6 Nido-C3B5H9 ........................................ 116
5.4.7 Nido-C4B4H8 ........................................ 116
5.5 8-Vertex Closo Clusters .................................. 120
5.5.1 CB7H8- ............................................. 120
5.5.2 1,7-C2B6H8 ......................................... 121
5.6 9-Vertex Open Clusters ................................... 124
5.6.1 Nido-CB8H12, Arachno-CB8H14, and Arachno-B8H13- ..... 124
5.6.2 Nido-C2B7H11 ....................................... 127
5.6.3 Arachno-C2B7H13 .................................... 127
5.6.4 Hypho-C3B6H13- ..................................... 133
5.7 9-Vertex Closo Clusters .................................. 134
5.7.1 4-CB8H9- ........................................... 134
5.7.2 4,5-C2B7H9 ........................................ 134
CHAPTER 6 Ten-vertex Carboranes .............................. 145
6.1 Overview ................................................. 145
6.2 10-Vertex Open Clusters .................................. 145
6.2.1 Nido-CB9H12- and Arachno-CB9B14- .................... 145
6.2.2 Nido-C2B8H12 ....................................... 149
6.2.3 Arachno-C2B8H14 .................................... 155
6.2.4 Nido-C3B7H11 and Arachno-C3B7H13 .................... 158
6.2.5 Nido-C4B6H10 ....................................... 161
6.2.6 Arachno-C4B6H12 .................................... 162
6.3 10-Vertex Closo Clusters ................................. 162
6.3.1 1- and 2-CB9H10- ................................... 162
6.3.2 C2B8H10 ............................................ 171
CHAPTER 7 Eleven-vertex Carboranes ........................... 187
7.1 Overview ................................................. 187
7.2 11-Vertex Open Clusters .................................. 187
7.2.1 Nido-CB10H13- ...................................... 187
7.2.2 Nido-C2B9H13, Nido-C2B9Н12-, and Nido-C2B9H112- ...... 197
7.2.3 Nido-C3B8H12 and Nido-C3B8H11- ...................... 239
7.2.4 Nido-C4B7H11 ....................................... 244
7.2.5 Arachno-C4B7H13 .................................... 245
7.3 11-Vertex Closo Clusters ................................. 246
7.3.1 Closo-CB10H11- ..................................... 246
7.3.2 Closo-C2B9H11 ...................................... 248
CHAPTER 8 Icosahedral Carboranes: Closo-СВ11 Clusters ........ 267
8.1 Overview ................................................. 267
8.2 Synthesis and Structure .................................. 267
8.2.1 Parent СВ11Н12- .................................... 267
8.2.2 Substitution at Carbon ............................ 283
8.2.3 Substitution at Boron by Electrophilic Reagents ... 284
8.2.4 Synthesis of B-substituted Derivatives via Boron
Insertion ......................................... 286
8.2.5 Polyhalogenation at Boron ......................... 286
8.2.6 Polyalkylation at Boron ........................... 287
8.2.7 Mixed Alkyl-halo Derivatives ...................... 288
8.2.8 Acid-base Properties .............................. 289
8.2.9 Metal Complexation ................................ 290
8.2.10 Special Properties of CB11Me12-, НСВ11Ме11-, and
CB11Me12 ........................................... 293
CHAPTER 9 Icosahedral Carboranes: 1,2-C2B10H12 ................ 301
9.1 Overview ................................................. 301
9.2 Synthesis of the 1,2-C2B10 Cage ........................... 301
9.2.1 From B10H14 ........................................ 301
9.2.2 From BH4- Salts ................................... 376
9.2.1 Boron Addition to 11-vertex Nido-carboranes ....... 376
9.2.4 Other o-Carborane-forming Reactions ............... 376
9.3 Structure and Properties ................................. 376
9.4 Substitution at Carbon ................................... 377
9.4.1 Metallation with Group 1 and 2 Metals ............. 377
9.4.2 Substitution via C-metallated Carboranes .......... 381
9.4.3 Substitution at Carbon Without Metallation ........ 394
9.5 Substitution at Boron .................................... 395
9.5.1 Indirect Routes to B-substituted Derivatives ...... 395
9.5.2 Direct Substitution on o-carboranyl Boron Atoms ... 396
9.5.3 Addition of Transition Metals at Boron ............ 404
9.5.4 Metal-promoted Cross-coupling of
B-halo-o-carboranes ............................... 405
9.6 Alkyl, Haloalkyl, and Aryl Derivatives ................... 406
9.6.1 Properties of Alkyl and Haloalkyl Derivatives ..... 406
9.6.2 Properties of Aryl Derivatives .................... 406
9.7 Alkenyl and Alkynyl Derivatives .......................... 411
9.7.1 Properties of Alkenyl Derivatives ................. 411
9.7.2 Properties of Alkynyl Derivatives ................. 417
9.8 Carboxylic Acids and Esters .............................. 418
9.8.1 Synthesis of Carboxylic Acids ..................... 418
9.8.2 Properties of o-carboranyl Carboxylic Acids ....... 425
9.9 Alcohols, Hydroxy Derivatives, and Ethers ................ 427
9.9.1 Synthesis ......................................... 427
9.9.2 Reactions of Alcohols and Ethers .................. 434
9.10 Aldehydes and Ketones .................................... 435
9.10.1 Synthesis of Aldehydes ............................ 435
9.10.2 Synthesis of Ketones .............................. 436
9.10.3 Reactions of o-carboranyl Aldehydes and Ketones ... 440
9.11 Silicon Derivatives ...................................... 442
9.11.1 C-silyl Derivatives ............................... 443
9.11.2 B-organosilyl Derivatives ......................... 454
9.12 Germanium, Tin, and Lead Derivatives ..................... 454
9.12.1 C-germyl and C-stannyl Derivatives ................ 454
9.12.2 B-stannyl Derivatives ............................. 460
9.12.3 C-plumbyl Derivatives ............................. 461
9.13 Nitrogen Derivatives ..................................... 461
9.13.1 Nitrato, Nitro, and Related Compounds ............. 461
9.13.2 Amines, Azides, and Diazonium Salts ............... 463
9.13.3 Nitrogen Heterocycles ............................. 467
9.13.4 Amides and Imides ................................. 471
9.13.5 Nitriles, Isonitriles, and Isocyanates ............ 471
9.13.6 Carbamates and Ureas .............................. 473
9.14 Phosphorus, Arsenic, Antimony, and Bismuth Derivatives ... 475
9.14.1 Phosphino and Related Derivatives ................. 475
9.14.2 Phosphates, Phosphites, and Related Derivatives ... 478
9.14.3 Thiophosphites and Thiophosphates ................. 481
9.14.4 Cyclotriphosphazenes .............................. 483
9.14.5 Metal Complexes ................................... 484
9.14.6 Cage-opening Reactions ............................ 487
9.15 Sulfur, Selenium, and Tellurium Derivatives .............. 488
9.15.1 Thiols, Thioethers, Disulfides, and Related
Compounds ......................................... 488
9.15.2 Metal Complexes ................................... 495
9.16 Halogen Derivatives ...................................... 501
9.16.1 Synthesis ......................................... 501
9.16.2 Properties of B-decahalo-o-carboranes ............. 501
9.16.3 Properties of Partially B-halogenated
o-carboranes ...................................... 502
9.16.4 Properties of C-halo-o-carboranes ................. 505
9.16.5 Properties of C-halomethyl-o-carboranes ........... 506
9.17 Mercury Derivatives ...................................... 506
CHAPTER 10 Icosahedral Carboranes: 1,7-C2B10H12 and
1,12-C2B10H12 ....................................... 541
10.1 Overview ................................................. 541
10.2 Synthesis and Structure .................................. 541
10.2.1 m-Carborane ....................................... 541
10.2.2 p-Carborane ....................................... 603
10.3 Cage Rearrangement Mechanisms ............................ 604
10.4 "Reverse Isomerization": 1,12- → 1,7- → l,2-C2B10H12 ...... 606
10.5 Substitution at Carbon ................................... 607
10.5.1 Metallation with Group 1 and 2 Metals ............. 607
10.5.2 Substitution via C-metallated Carboranes .......... 608
10.6 Substitution at Boron .................................... 617
10.6.1 Boron Insertion into Nido-C2B9 Dianions ........... 617
10.6.2 Nucleophilic Displacement ......................... 617
10.6.3 Electrophilic Alkylation .......................... 617
10.6.4 Electrophilic Halogenation ........................ 618
10.6.5 Photochemical (Radical) Halogenation .............. 619
10.6.6 Fluorination ...................................... 619
10.6.7 Addition of Main-group Elements and Mercury
at Boron .......................................... 620
10.6.8 Addition of Transition Metals at Boron ............ 622
10.6.9 Organosubstitution at Boron ....................... 622
10.7 Alkyl, Haloalkyl, and Aryl Derivatives ................... 625
10.7.1 Properties of Alkyl- and Haloalkyl-substituted
m- and p-carboranes ............................... 625
10.7.2 Properties of Aryl-substituted m- and
p-carboranes ...................................... 625
10.8 Alkenyl and Alkynyl Derivatives .......................... 628
10.8.1 Reactions and Electronic Properties ............... 628
10.9 Carboxylic Acids and Esters .............................. 631
10.9.1 Synthesis ......................................... 631
10.9.2 Properties of m- and p-carboranyl Carboxylic
Acids ............................................. 632
10.10Alcohols, Hydroxy Derivatives, and Ethers ................ 635
10.10.1 Synthesis ........................................ 635
10.10.2 Properties of m- and p-carboranyl Alcohols ....... 637
10.11Aldehydes and Ketones .................................... 638
10.11.1 Synthesis ........................................ 638
10.11.2 Properties ....................................... 639
10.12Silicon, Germanium, Tin, and Lead Derivatives ............ 640
10.12.1 Synthesis ........................................ 640
10.12.2 Properties ....................................... 641
10.13Nitrogen Derivatives ..................................... 641
10.13.1 Nitro, Nitrito, and Related Compounds ............ 642
10.13.2 Amines, Azides, and Diazonium Salts .............. 642
10.13.3 Nitrogen Heterocycles ............................ 644
10.13.4 Amides and Imides ................................ 646
10.13.5 Nitriles, Isonitriles, and Isocyanates ........... 646
10.13.6 Ureas ............................................ 647
10.14Phosphorus Derivatives ................................... 648
10.14.1 Synthesis ........................................ 648
10.14.2 Properties ....................................... 648
10.15Sulfur, selenium, and Tellurium Derivatives .............. 650
10.15.1 Synthesis ........................................ 650
10.15.2 Properties ....................................... 652
10.16Halogen Derivatives ...................................... 653
10.16.1 Synthesis and Properties ......................... 653
10.16.2 C-halo Derivatives ............................... 653
10.16.3 B-halo Derivatives ............................... 653
CHAPTER 11 Open 12-Vertex and Supra-lcosahedral Carboranes .... 675
11.1 Overview ................................................. 675
11.2 Open-Cage C2B10 Anions ................................... 675
11.2.1 Reduction of Neutral C2B10 icosahedra ............. 675
11.2.2 Carbon-bridged Clusters ........................... 682
11.3 Nido- and Arachno-C4B8 Carboranes ........................ 684
11.3.1 Synthesis of Nido-C4B8 cages ...................... 685
11.3.2 Structure and Fluxional Behavior of C4B8
Clusters .......................................... 688
11.3.3 Metal Complexation of Nido-R4C4B8H8 Carboranes ..... 689
11.3.4 Formation and Properties of Arachno-R4C4B8H8n-
mono- and Dianions ................................ 689
11.3.5 Synthesis of Neutral Arachno-C4B8 Clusters ........ 691
11.3.6 Deboronation of Nido-C4B8 Cages ................... 691
11.3.7 General Observations .............................. 692
11.4 Arachno-C6B6 Carboranes .................................. 692
11.5 Supra-Icosahedral Carboranes ............................. 692
11.5.1 13-vertex C2B11 and 14-vertex C2B12 Clusters ....... 692
CHAPTER 12 Heteroatom Carboranes of the Main Group Elements ... 701
12.1 Overview ................................................. 701
12.2 Heterocarboranes of the Group 1 and 2 Elements ........... 701
12.2.1 Lithium, Sodium, Potassium, and Rubidium .......... 701
12.2.2 Beryllium, Magnesium, Calcium, Strontium, and
Barium ............................................ 705
12.3 Heterocarboranes of the Group 13 Elements ................ 707
12.3.1 Aluminum .......................................... 710
12.3.2 Gallium and Indium ................................ 714
12.3.3 Thallium .......................................... 717
12.4 Heterocarboranes of the Group 14 Elements ................ 718
12.4.1 Silicon ........................................... 724
12.4.2 Germanium ......................................... 725
12.4.3 Tin and Lead ...................................... 728
12.5 Heterocarboranes of the Group 15 Elements ................ 732
12.5.1 Nitrogen .......................................... 732
12.5.2 Phosphorus ........................................ 735
12.5.3 Arsenic and Antimony .............................. 755
12.6 Heterocarboranes of the Group 16 Elements ................ 758
12.6.1 Sulfur and Selenium ............................... 761
CHAPTER 13 Metallacarboranes of the Transition and
Lanthanide Elements ................................ 773
13.1 Overview ................................................. 773
13.2 General Synthetic Methods ................................ 773
13.2.1 Insertion of Metal Cations into Open-cage
Carborane Anions .................................. 773
13.2.2 Insertion of Metals into Neutral Carboranes ....... 809
13.2.3 Insertion of Hydrocarbons into Metallaboranes ..... 809
13.2.4 Polyhedral Expansion and Contraction .............. 811
13.2.5 Oxidative Fusion .................................. 812
13.2.6 Metal Displacement and Transfer ................... 813
13.2.7 Metal Atom Reactions .............................. 814
13.2.8 Other Routes to Metallacarboranes ................. 814
13.3 Six- and Seven-Vertex Metallacarboranes .................. 815
13.3.1 Closo six-vertex Cages ............................ 815
13.3.2 Synthesis of Closo-MC2B4 Cages .................... 815
13.3.3 Functionalization and Linkage of Closo-LMC2B4
and Nido-LMC2B3 Clusters .......................... 817
13.3.4 Metal-metal Communication in Linked MC2B4
Clusters .......................................... 822
13.3.5 Thermal Rearrangement of Seven-vertex
Metallacarboranes ................................. 822
13.3.6 Small Metallacarboranes in Organic Synthesis ...... 823
13.3.7 Nido-MC2B3 and Closo-M2C2B3 Cages .................. 828
13.3.8 Nido-MC3B2 and Closo-M2C3B2 Cages .................. 833
13.4 Eight- to Eleven-Vertex Metallacarboranes ................ 839
13.4.1 Monocarbon Cages .................................. 839
13.4.2 Dicarbon Cages .................................... 868
13.4.3 Tricarbon Cages ................................... 878
13.4.4 Tetracarbon Clusters .............................. 880
13.5 Twelve-Vertex Metallacarboranes .......................... 882
13.5.1 Monocarbon Clusters ............................... 882
13.5.2 Dicarbon Clusters ................................. 951
13.5.3 Tricarbon Clusters ................................ 961
13.5.4 Tetracarbon and Pentacarbon Clusters .............. 963
13.6 Supraicosahedral Metallacarboranes ....................... 965
13.6.1 Dicarbon 13-vertex Clusters ....................... 965
13.6.2 Carbon-rich 13- and 14-vertex Clusters ............ 981
CHAPTER 14 Carborane Polymers and Dendrimers ................. 1015
14.1 Overview ................................................ 1015
14.2 Polymers of Subicosahedral Closo-Carboranes ............. 1015
14.3 Polymers of Open-Cage Carboranes ........................ 1016
14.4 Polymers of Closo-CB11 Carboranes ........................ 1016
14.5 Polymers of Closo-C2B10 Carboranes ....................... 1016
14.5.1 Systems with Carborane Units in the Polymeric
Chain ............................................ 1017
14.5.2 Polymers with Pendant Carboranes ................. 1023
14.6 Metallacarborane Polymers ............................... 1026
14.6.1 Metallation of Nido-carboranyl Polymers .......... 1027
14.6.2 Metallacarborane Dendrimers ...................... 1027
14.6.3 Polymerization of Metallacarborane Monomers ...... 1029
14.6.4 Metallacarboranes as Dopants and Inclusion
Compounds in Polymeric Materials ................. 1031
CHAPTER 15 Carboranes in Catalysis ........................... 1037
15.1 Overview ................................................ 1037
15.2 Non-Metallated Carboranes as Catalytic Agents ........... 1037
15.3 Closo-CB11 Anions in Catalysis ........................... 1037
15.3.1 Salts with Main Group Metal Cations .............. 1037
15.3.2 Salts with Transition metal-containing Cations ... 1038
15.4 Ero-Metallated Carboranes in Catalysis .................. 1039
15.4.1 Closo-carborane Systems .......................... 1039
15.4.2 Nido-carborane Systems ........................... 1042
15.5 Metallacarboranes in Catalysis .......................... 1044
15.5.1 Subicosahedral Clusters .......................... 1044
15.5.2 Icosahedral Clusters ............................. 1045
15.5.3 Supraicosahedral Clusters ........................ 1049
CHAPTER 16 Carboranes in Medicine ............................ 1053
16.1 Overview ................................................ 1053
16.2 Carboranes in Drag Development .......................... 1053
16.2.1 Carboranes as Pharmacophores ..................... 1053
16.2.2 HIV Protease Inhibitors .......................... 1057
16.2.3 Anticoagulants ................................... 1058
16.2.4 Antitumor Agents ................................. 1058
16.3 Boron Neutron Capture Therapy ........................... 1062
16.3.1 Background ....................................... 1062
16.3.2 Approaches to BNCT ............................... 1063
16.3.3 Small-molecule Boron Delivery Agents ............. 1063
16.3.4 High Molecular Weight Boron Delivery Agents ...... 1066
16.4 Boron Neutron Capture Synovectomy ....................... 1070
16.5 Photodynamic Therapy .................................... 1070
16.6 Carboranes in Molecular Imaging and Radiotherapy ........ 1071
16.6.1 Radiohalogenation ................................ 1071
16.6.2 Radioastatination ................................ 1072
16.6.3 Radiometal Labeling .............................. 1073
16.6.4 Gadolinium in Imaging and Therapy ................ 1073
16.6.5 Other Carborane-based Imaging Methods ............ 1074
CHAPTER 17 Carboranes in Other Applications .................. 1083
17.1 Overview ................................................ 1083
17.2 Metal Ion Extraction .................................... 1083
17.3 Carborane-Based Materials ............................... 1085
17.3.1 Ionic Liquids .................................... 1085
17.3.2 Liquid Crystals .................................. 1085
17.3.3 Nonlinear Optical Materials ...................... 1086
17.3.4 Electroactive Systems ............................ 1088
17.3.5 Networks and Supramolecular Assemblies ........... 1091
17.3.6 Gas separation and Storage Materials ............. 1093
17.3.7 Films and Monolayers ............................. 1094
17.3.8 Carboranes in Biomaterials ....................... 1095
17.3.9 Carborane-based Ceramics ......................... 1095
17.4 Molecular Machines ...................................... 1096
17.5 Carboranes as Noncatalytic Synthetic Agents ............. 1098
17.6 Carboranes in Analysis .................................. 1099
17.6.1 Gas Chromatography ............................... 1099
17.6.2 Ion-selective Electrodes ......................... 1099
17.7 Into the Future ......................................... 1100
Index ........................................................ 1107
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