Studies in Inorganic Chemistry 19

Molybdenum: An Outline of its Chemistry and Uses

E.R. Braithwaite 5 Downside, St John's Avenue, Putney, London SW15 2AE, England

J. Haber y

Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, UI Niezapominajek 1, 30-239 Krakow, Poland

1994 ELSEVIER Amsterdam-Lausanne-New York-Oxford-Shannon-Tokyo

Contents

Preface v List of Contributors vii

Chapter 1. Occurrence, Extraction, Production and Uses of Molybdenum by E.R. BRAITHWAITE

1. Introduction 1 2. Geological Origin 1

2.1 Hydrothermal deposits 2 3. Geochemistry of Porphyries 3

3.1 Molybdenum rieh porphyries 3 3.2 The copper porphyries 6

4. Distribution 7 5. Mining 7

5.1 Underground mining 8 5.2 Surface or 'Open Pit' mining 8

6. Benefication 9 6.1 Mo-porphyries (Climax) 9 6.2 Cu-porphyries 10

7. Technical Grade M o 0 3 12 7.1 Ferromolybdenum 13

8. Pure MoO, and Molybdates 14 8.1 Sublimation process 14

9. Wet Chemical Process 15 9.1 Introduction 15 9.2 Ammonium dimolybdate 17 9.3 Ammonium (hepta) paramolybdate 18 9.4 Ammonium oetamolybdate 18 9.5 Ammonium dodecamolybdate 18 9.6 Sodium molybdate 19

10. Molybdenum Disulphide 19 10.1 Introduction 19 10.2 Preparation 19

11. Molybdenum Metal 20 11.1 Introduction 20 11.2 Theory of oxide reduetion 20

12. Production of Mo Metal 22 12.1 Introduction 22 12.2 Double reduetion process 22 12.3 Single reduetion process 23 12.4 Sintering 24

13. Chemical and Physical Properties of Mo 25 14. Molybdenum Hexacarbonyl 26 15. The Industrial Uses of Mo and its Basic Compounds 29

15.1 Introduction 29 16. Lubrication (Solid) 30

16.1 Introduction 30 16.2 Structural and electronic factors 31 16.3 Chemical environment and surface properties 31

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16.4 Operating conditions 32 17. Oil Soluble Mo Compounds (E.P. Lubricants) 34

17.1 Surface attachment 36 17.2 Role of sulphur 36

18. Incorporation in Plastics 37 19. Batteries 38 20. Corrosion Inhibition 40

20.1 Introduction 40 20.2 Surface films on steel 42 20.3 Inhibition of molybdate of the corrosion of other metals 43 20.4 Molybdate inhibition 44 20.5 Inorganic additives 47 20.6 Organic film formers 47 20.7 Corrosion inhibition in aqueous Systems 48 20.8 Corrosion inhibiting molybdate pigments 49

21. Basic Dye Complex Pigments 49 22. Pigments and Inks 51 23. Fire Retardance and Smoke Suppression of Plastics 51

23.1 Introduction 51 23.2 PVC Systems 52 23.3 Polyester thermosets 56

24. Applications of Mo Metal 58 25. Molybdenum Metal and its Alloys 59

25.1 Introduction 59 25.2 Alloying principles 60

26. The Binary Alloys 61 26.1 Mo-Re alloys 63

27. Mo(Solute)Alloying Metal in Steels 65 27.1 Introduction 65 27.2 Stainless steels 66 27.3 High Strength low alloy steels 66 27.4 High temperature steels 67 27.5 Ultra high strength steels 67 27.6 Tool steels 68

28. Interstitial Compounds 68 28.1 Introduction 68 28.2 Crystallography 70 28.3 Structure and bonding 70 28.4 Surface properties 72

29. Molybdenum Carbide 73 30. Molybdenum Nitrides 75 31. Molybdenum Borides 77 32. Molybdenum Silicides 80 33. Agriculture and Horticulture 84

33.1 Introduction 84 33.2 Role of molybdenum 85 33.3 Applications 85 References 87

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Chapter 2. An Introduction to the Chemistry of Molybdenum by M.L.H. GREEN

2.1 Introduction 94 2.2 Properties of the dement 94 2.3 Classiciation of molybdenum Compounds 96

2.3.1 Definition of the class of a ligand 98 2.3.2 Definition of the class of a molybdenum Compound 99 2.3.3 Determination of MLX class of a molybdenum Compound

containing non-innocent ligands and related aspects 107 2.3.4 Definition of electron number, valency number, and

ligand bond number 109 2.4 The construction of E.N. versus V.N. plots (called MLX

plots) 110 2.4.1 The construction of the MLX plot for molybdenum 110 2.4.2 General comments on the MLX plot for molybdenum 111 2.4.3 The relationship between the MLX plot and properties

of ligands 112 2.4.4 A Classification of reactions and the use of MLX

plots for discussing reaction pathways 113 2.4.5 Further interpretation of the population density pattern

in MLX plot for molybdenum 115 2.5 Discussion of individual MLX classes of molybdenum Compounds 117

2.5.1 Zerovalent molydenum Compounds, MoL, ' 117

2.5.2 Monovalent molybdenum Compounds, MoL.X 120 2.5.3 Divalent molybdenum Compounds, MoL.X^ 120 2.5.4 Trivalent molybdenum Compounds, MoL.XX 122 2.5.5 Tetravalent molybdenum Compounds, MoL.X, 122 2.5.6 Pentavalent molybdenum Compounds, MoL.Xc 194

2.5.7 Hexavalent molybdenum Compounds, MoL,Xß ^ 4

2.6 A Discussion of the chemistry of molybdenum in various ligand environments 127 2.6.1 The aqueous Solution and other oxygen chemistry of

molybdenum 127 2.6.2 Molybdenum-oxo-chloro chemistry 132 2.6.3 Molybdenum Compounds with sulphur ligand

environments 135 2.7 Comparison of general trends in the chemistries of chromium,

molybdenum and tungsten 135 2.8 Conclusion 137 Appendix 138

Chapter 3. The Oxide Chemistry of Molybdenum by A.M. CHIPPINDALE and A.K. CHEETHAM

3.1 Introduction 146 3.2 Binary Oxides 147

3.2.1 Molybdenum trioxide 147 3.2.2 Magneli and related phases 148 3.2.3 Molybdenum dioxide 150

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3.3 Molybdenum Oxide Hydrates 151 3.4 Ternary Oxides of Molybdenum 153

3.4.1 Metal molybdates 153 3.4.2 Molybdenum-oxide bronzes and ambient-temperature

insertion Compounds 157 3.4.3 Molybdenum-molybdenum bonding and oxide Cluster

Compounds 168 3.5 Suggestions for further reading 176 3.6 References 177

Chapter 4. Molybdenum Sulphur Chemistry by J.R. DILWORTH

1. Introduction 185 2. Thioether Chemistry 185

2.1 Introduction 185 2.2 Thioether complexes 185

3. Dithiolene Chemistry 187 3.1 Introduction 187 3.2 Dithiolene complexes 188 3.3 Dithiolene-related complexes 189

4. 1,1-Dithiolate Complexes 190 4.1 Introduction 190 4.2 Dithiocarbamato-complexes 191 4.3 Dithiophosphato- and dithiophosphinato- complexes 197 4.4 Other 1,1-dithiolato-complexes 199

5. Thiolato-Complexes 200 5.1 Introduction 200 5.2 Complexes of mono- and bi-dentate thiolates 201 5.3 Polydentate thiolato-complexes 205 5.4 Sterically hindered thiolato-complexes 207

6. Molybdenum Sulphido- and Disulphido-Complexes 210 6.1 Introduction 210 6.2 Mononuclear sulphido- and disulphido-complexes 210 6.3 Thiomolybdates 211 6.4 Homonuclear, linear molybdenum Clusters 211 6.5 Heteronuclear molybdenum sulphido-clusters 216

6.5.1 Introduction 216 6.5.2 Iron-molybdenum-sulphur Clusters 217

6.5.2.1 Linear Clusters 217 6.5.2.2 Other Clusters 217

6.5.3 Copper-molybdenum-sulphide Clusters 222 6.5.4 Clusters with other metals 224

6.6 MooS., Mo-iS-, and Mo^S, core Clusters 225 6.7 Nitrosyl andcyano-sulphido-clusters 227 6.8 Cyclopentadienyl molybdenum sulphido-clusters 228

7. Molybdenum Sulphides 229 8. Applications of Molybdenum Sulphur Complexes 230 9. Postscript 230

References 231

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Chapter 5. The Halides of Molybdenum by R.L. RICHARDS

1. Introduction 251 2. Molybdenum Fluorides 251

2.1 Molybdenum hexafluoride 251 2.2 Molybdenum pentafluoride 253 2.3 Molybdenum tetrafluoride 254 2.4 Molybdenum trifluoride 254 2.5 Molybdenum difluoride 254

3. Molybdenum Chlorides 255 3.1 Molybdenum hexachloride 255 3.2 Molybdenum pentachloride 255 3.3 Molybdenum tetrachloride 257 3.4 Molybdenum trichloride 259 3.5 Molybdenum dichloride 261

3.5.1 Amorphous molybdenum dichloride (ß-MoCU) 261 3.5.2 Hexanuclear molybdenum dichloride (a-MoCX?) 262

4. Molybdenum Bromides 265 4.1 Molybdenum tetrabromide 265 4.2 Molybdenum tribromide 265 4.3 Molybdemnum dibromide 266

5. Molybdenum Iodides 266 5.1 Molybdenum triiodide 266 5.2 Molybdenum diiodide 266

6. Oxide Halides of Molybdenum 267 6.1 Oxide-fluorides of molybdenum 267 6.2 Oxide-chlorides of molybdenum 268 6.3 Oxide-bromides of molybdenum 270

7. Oxide-Iodides of Molybdenum 271 8. Sulphide-Halides of Molybdenum 271

8.1 Sulphide-chlorides of molybdenum 271 8.2 Sulphide-bromides and sulphide-iodides of molybdenum 272

9. Selenide-Chlorides of Molybdenum 273 References 273

Chapter 6. The Organometallic and Metal-Organic Chemistry of Molybdenum by J.A. McCLEVERTY

1. Introduction 277 1.1 Organometallic chemistry 277 1.2 Metal-organic chemistry 278

2. Molybdenum Carbonyl 278 2.1 Carbonylate anions 279 2.2 Carbonyl halides 280 2.3 Carbonyl hydrides and hydrogen complexes 280 2.4 Carbonyl complexes containing Lewis base ligands 281

2.4.1 Particular nitrogen donor ligands 282 2.4.2 Tertiary phosphine, phosphido, arsine and related

complexes 288 2.4.3 Particular oxygen donor Compounds 289 2.4.4 Selected sulphur ligand complexes 289

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2.5 Carbonyl Cyanide complexes 291 3. Isocyanide Complexes 292 4. Carbene, Alkylidene, Vinylidene, Carbyne and Alkylidyne

Complexes 293 4.1 Introduction 293 4.2 Molybdenum Alkylidene Complexes 294

4.2.1 Low-oxidation State species 294 4.2.2 High-oxidation State species 297

4.3 Alkylidyne complexes 298 4.3.1 Low-oxidation State species 298 4.3.2 High-oxidation State species 299 4.3.3 Bi- and tri-metallic alkylidyne species 301

5. Compounds Containing Molybdenum-Carbon erBonds 300 5.1 Monomeric alkyl and aryl Compounds 300 5.2 Dimeric alkyls and related Compounds of Mo(II) and Mo(III) 302

5.2.1. Molybdenum(II) species, [Mo2R4] 302 5.2.2 Morybdenum(III) species, [Mo2R6] 303 5.2.3 Other bimetallic species 304 5.2.4 Cluster Alkyls 304

6. Alkene, Polyene and Simple Alkyne Complexes 304 6.1 Simple alkene complexes 304

6.1.1 7>OTK-[Mo(C2H4)2(diphos)2] and related species 304 6.1.2 Alkene Jjgands as part of polydentate ligands 305 6.1.3 Other r) -complexes 306

6.2 Diene Complexes 306 6.2.1 Homoleptic diene complexes 306 6.2.2 Diene carbonyl complexes 307

6.3 Cyclic Triene and Tetraene Complexes 307 6.3.1 Homoleptic cyclic triene complexes 308 6.3.2 Cycloheptatriene molybdenum tricarbonyl 308 6.3.3 Cyclooctatetraene complexes 308 6.3.4 Other cyclic polyalkene complexes 309

6.4 Simple alkyne complexes 309 7. Allyl Complexes 310

7.1 Homoleptic allyl complexes 310 7.2 Pseudo-octahedral carbonyl derivatives [Mo^O^Lo^-a l ly^X] 311 7.3 Pyrazolylborato and related allyl complexes 312 7.4 Cyclopentadienyl carbonyl allyl complexes 313 7.5 Other allyl complexes 315 7.6 Cyclopentadienyl nitrosyl allyl complexes 315 7.7 Bis-cyclopentadienyl allyl complexes 317 7.8 Arene allyl complexes 318

8. Cyclopropenyl, Cyclobutadiene and Trimethylenemethane Complexes 319 8.1 Cyclopropenyl and oxocyclobutenyl complexes 319 8.2 Cyclobutadiene complexes 319 8.3 Trimethylenemethane complexes 320

9. Cyclopentadienyl Complexes 320 9.1 Cyclopentadienyl carbonyl and related complexes 320

9.1.1 Bimetallic species,[{Mo(CO)3Cp}2] 320 9.1.2 Bimetallic species,[{Mo(CO)2Cp}2] 322 9.1.3 Alkene, allene and alkyne derivatives of [{Mo^O^Cp}. , ] 324 9.1.4 Monocyclopentadienyl alkyne complexes 326

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9.1.5 Monocyclopentadienyl alkylidene, vinylidene and alkylidyne Compounds 328

9.2 [Mo(CO)4Cp] and related cations 331 9.2.1 Cyclopentadienyl carbonyl alkene cations 331 9.2.2 Nitrosyl alkene complexes 331 9.2.3 Cyclopentadienyl diene cations 332

9.3 The [Mo(CO)3Cp]"anion 332 9.4 [Mo(CO)3CpX] 334

9.4.1 [Mo(CO)3CpH] 334 9.4.2 [Mo(CO)3CpR] (R = alkyl, allyl, etc.) and their reactions 335 9.4.3 [Mo(CO)3CpX] (X = halide) and related Compounds 336 9.4.4 Metal derivatives of [Mo(CO)3Cp]" 336

9.5 Monocyclopentadienyl Carbonyl Complexes Containing Nitrogen-based Ligands 337 9.5.1 Nitrosyl Compounds 337 9.5.2 Analogues of NO 338 9.5.3 Imido Compounds 339 9.5.4 Analogues of allyl ligands 339 9.5.5 Chiral Systems, [Mo(CO)(L-L')Cp] 339

9.6 Bimetallic cyclopentadienyl carbonyl Compounds bridged by P-, As-, and S-containing ligands 340

9.7 Monocyclopentadienyl arsenido, oxo, sulphido, halo and related complexes 340

9.8 Electrochemically-active monocyclopentadienyl complexes 343 9.9 Bis(cyclopentadienyl) complexes 343

9.9.1 Activation of the C<-H5rings 344 9.9.2 Bis(cyclopentadienyl)dihydridomolybdenum, [MoCp^l^] 345 9.9.3 Bis(cyclopentadienyl) alkene complexes 345 9.9.4 Dihalobis(cyclopentadienyl)molybdenum and related complexes . 346 9.9.5 Metallo-derivatives of bis(cyclopentadienyl)molybdenum 347 9.9.6 Bis(cyclopentadienyl)nitrosyl complexes 349

9.10 Bis(cyclopentadienyl) Compounds containing dihapto- and related hetero-atom ligands 349

9.11 Cyclopentadienyl complexes containing other hydrocarbon ring Systems 350

9.12 Triple-decker "sandwich" Compounds 351 9.13 Cyclohexadienyl complexes 351 Arene and Related Complexes 351 10.1 Bis(arene) molybdenum 352 10.2 Tricarbonyl(arene) complexes 353 10.3 Other arene complexes 355

10.3.1 Arene molybdenum tertiary phosphine species 355 10.3.2 Complexes of ^ e t e r o c y c M 3 £

10.4 Cycloheptatrienyl complexes 355 10.4.1 Tricarbonyl (ri -cycloheptatrienyl) molybdenum cation 355 10.4.2 Cycloheptatrienyl complexes [Mo(r/ -arene)(i7 -C„H7)]+ and

related species 356 10.5 Cyclooctatetraene complexes 357 Nitrosyl Complexes 357 11.1 Mononitrosyl complexes 357

11.1.1 Complexes of Mo(0) 358 11.1.2 Complexes of Mo(I) 358

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11.1.3 Complexes of Mo(II) 358 11.1.4 Tris(pyrazolyl)borato and related complexes 359

11.2 Dinitrosyl molybdenum complexes 367 11.3 Diazenido complexes 368 11.4 Other analogues of nitrosyl complexes 368

12. Dialkylamido, Alkoxy and Related Complexes 368 12.1 Molybdenum dialkylamides 369

12.1.1 Molybdenum (III) dialkylamides 369 12.1.2 Molybdenum(IV) dialkylamides 370 12.1.3 Molybdenum(IV) imido species 370

12.2 Molybdenum alkoxides 372 12.2.1 Molybdenum (II) alkoxides 372 12.2.2 Molybdenum(III) alkoxides 372 12.2.3 Molybdenum(IV) alkoxides 374 12.2.4 Alkylidene alkoxides 374 12.2.5 Phenoxides 374

12.3 Imido alkoxide and related species 375 12.4 Molybdenum thiolates 376

13. The Metal-Metal Bond, and Molybdenum Clusters 376 13.1 Quadruple bonds 377 13.2 Triple bonds 378 13.3 Double bonds 379 13.4 Single bonds 379 13.5 Clusters 380

13.5.1 Trimeric units 380 13.5.2 Tetrameric units 381 13.5.3 Pentameric units 383 13.5.4 Hexameric units 383 13.5.5 Clusters of higher nuclearity 383

14. References 383

Chapter 7. The Chemical Nature of the Molybdenum Centres in Enzymes by C D . GARNER

1. Introduction 403 2. The iron-molybdenum cofactor FeMoco 404 3. The molybdenum cofactor, Moco 411 4. Conclusions 415 5. Acknowledgements 415

References 416

Chapter 8. The Biochemistry of Molybdenum by R.-J.P. WILLIAMS

1. Introduction 419 2. Molybdenum in Evolution 420 3. Geographical Distribution of Molybdenum 422 4. Molybdenum Enzymes: General Information 422 5. Physical Methods for Enzyme Study 425 6. General Relevant Chemistry of Molybdenum 426

6.1 Structures of molybdenum complexes 426 6.2 Thermodynamics of molybdenum complexes: general principles and the

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elementary aqueous chemistry of molybdenum 428 6.3 Acid/base properties of molybdenum 429 6.4 Molybdenum complexes: relative stability compared to other metal

complexes 430 6.5 Condensation or complexation 432 6.6 The stability constants of MO, complexes 434 6.7 The special ligand for M o 0 2

2 + 435 6.8 Polynuclear complexes 437

7. Rates of Reaction 437 8. Biological Problems: General Considerations 438

8.1 Uptake of molybdate 438 8.2 General acid/base properties of amino-acid side-chains in proteins 439 8.3 Oxidation State diagram and metal-protein complexes 439 8.4 The M(II)/M(III) couples in enzymes 441 8.5 Molybdenum redox potentials in proteins 442 8.6 Redox reactions of molybdenum proteins and cofactors 443

9. Mechanistic Considerations in Proteins: General Considerations 444 9.1 Electron transfer 444 9.2 Oxo/hydroxy reactions 444 9.3 The reactions with dioxygen 445

10. Molybdenum Enzymes 446 10.1 Nitrogenase and FeMoco 446 10.2 The mechanism of nitrogenase 447 10.3 The oxygen transfer reaction 448 10.4 The evolutionary importance of molybdenum enzymes 448

11. Substitution for Molybdenum 450 12. Conclusion 450

References 450

Chapter 9. Molybdenum Requirements, Toxicity and Nutritional Limits for Man and Animals

by G.M. WARD

1. Introduction 452 1.1 Molybdenum toxicity 453 1.2 Diagnosis of potential Mo problems 457 1.3 Metabolism of molybdenum 459

1.3.1 Dietary factors 458 1.4 Treatment of molybdenosis 462 1.5 Data for Mo in irrigation water, alfalfa and milk in Colorado 463 1.6 Summary of literature relative to toxicity 464

2. Conclusions 471 References 472

Chapter 10. Molybdenum Compounds in Heterogeneous Catalysis by J. HABER

1. Introduction 477 2. Catalytic Properties of MoO-, and Molybdates 481

2.1 Electrophilic and nucleophilic oxidation reactions 481 2.2 Surface properties of MoO-, 488 2.3 Nucleophilic addition of oxygen 496

4.

2.4 Oxidation of methanol to formaldehyde 504 2.5 Bismuth molybdates 508 2.6 Addition of nitrogen 522 2.7 Transition metal molybdates 526 2.8 Dynamics of the catalyst surface 535

3. Catalytic Properties of Heteropolymolybdates 539 3.1 Primary and secondary structure of heteropolymolybdic acid and salts . . . . 539 3.2 Acid-base catalysis on heteropolymolybdates 547 3.3 Oxidation over heteropolymolybdates 549 Supported MoOj Catalysts 559 4.1 Impregnation of the carrier in molybdate solutions 559 4.2 Molybdenum oxides grafted at the surface of the support 566 4.3 Spreading of MoOo over surfaces of oxide carriers 570 4.4 Structure of the molybdenum oxide monolayer catalysts 573 4.5 Transformations of surface molybdenum oxide 575

5. Molybdenum Sulphides as Catalysts 577 5.1 Catalytic hydrodesulfurization 577 5.2 Structure and properties of M0S2 578 5.3 Catalytically active sites at M0S9 surface 579 5.4 Defect structure of MoS2 583 5.5 Mechanism of desulfurization 589 5.6 Promotional effect of other transition metal cations 594 5.7 Surface structure of HDS catalysts 599 5.8 Origin of the Synergy 602

6. References 608

Chapter 11. Homogeneous Coordination Catalysis with Molybdenum Complexes by A. KELLER, J.M. SOBCZAK and J.J. ZIOLKOWSKI

1. Introduction 618 2. Molybdenum Catalyzed Epoxidations 618 3. Oxomolybdenum Complexes as Catalysts for Oxygen Transfer 621 4. Heteropolycompounds as Catalysts 623

4.1 Acid properties and acid catalysis by heteropolyacids 623 4.2 Redox properties and oxidation catalysis by HPC 624 4.3 Wacker's type catalytic Systems 625

5. Molybdenum Catalyzed Olefin Metathesis 628 5.1 Introduction 628 5.2 Homogeneous Systems 628

5.2.1 Nitrosyl molybdenum complexes 629 5.2.2 Carbonyl molybdenum complexes 630

5.3 High-valent molybdenum complexes 632 5.4 Molybdenum based heterogeneous Systems 634 5.5 Mechanism of olefin methathesis reaction 634 5.6 Carbene and carbyne molybdenum complexes 638 Abbreviations 640 References 642

Index 651