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Chemistry derived from the tetracarbonylates of group 8, [M(CO)4]2- (M = Fe, Ru, Os): Syntheses, characterization and derivative chemistry of the metalladiboranes, [M(CO )4 (j7 2-B 2 Hs)]~ (M = Ru, Os). Syntheses and structure of the heterobinuclear dianions of the iron triad, [MM'(CO)s]2~ (MM* = FeRu, RuOs, FeOs)

Cofly, Tim Joseph, Ph.D.

The Ohio State University, 1989

300N.ZeebRd. Ann Arbor, MI 48106 Chemistry Derived from the Tetracarbonylates of Group 8,

[M (C O )4]2- (M = Fe, Ru, Os):

Syntheses, Characterization and Derivative Chemistry of the M etalladiboranes, [M(CO)4(-q2-B2H5)]* (M = Ru, Os).

Syntheses and Structure of the Heterobinuclear Dianions of the

Iron Triad, [MM'(CO)8]2- (MM' = FeRu, RuOs, FeOs).

Dissertation

Presented in Partial Fulfillment of the Requirements for the Degree of

Doctor of Philosophy in the Graduate School of The Ohio State University

Tim J. Coffy, B. S.

The Ohio State University

1989

Dissertation Committee

Dr. Bruce E. Bursten

Dr. James A. Cowan A dviser

Dr. Sheldon G. Shore Department of Chemistry To Annamary and Eric

ii Acknowledgements

I would like to acknowledge the Department of Chemistry, the

National Science Foundation and B. P. America for their financial support.

I am grateful to Professor Sheldon G. Shore for his patience, guidence, and support through the duration of this project. I would like to thank the

Shore group members, past and present, for many helpful discussions. I would also like to thank Dr. William Quintana for solving a crystal structure presented in this work and for his invaluable assistance in preparing this dissertation. I am indebted to Ms. Therese Salupo for solving a crystal structure presented in this dissertation.

I am especially grateful to my wife, Annamary, for her love, patience, understanding and unyielding support during this trying time.

Finally, I want to thank my son, Eric Michael, for having impecable timing and for his company during the preparation of this dissertation. V ita

August 5, 1962 Bom - Titisville, FL.

1984 B. S. (Chemistry), The University of Pittsburgh.

1984 - 1986 Graduate Teaching Associate, Department of Chemistry, The Ohio State University, Columbus, OH

1986 - 1988 Graduate Research Associate, Department of Chemistry, The Ohio State University, Columbus, OH

1988 - 1989 Graduate Fellow, B. P. America, Department of Chemistry, The Ohio State University, Columbus, OH

Publications

"Decacarbonyl (t|5-Cyclopentadienyl) Dihydrido Cobalt Triosmium CoOs3(p- H)2Cn^-C5H5)(n-CO)(CO)9. Nonacarbonyl (t\^-Cyclopentadieny 1) Trihydrido and (ri^-Cyclopentadienyl) Tetrahydrido Cobalt Triosmium CoOs3(m-H)3(h5- C5Hs)(CO)9 and CoOs3(|i-H)4(Ti5-C5H5)(CO)9", Jan D.-Y.; Coffy, T.J.; Hsu, W.-L.; Shore, S.G., Inorganic Synthesis, 1989, 25, 195.

"Ruthenium and Osmium Bridged Diborane (6) Derivatives [(p-M(CO)4)B2H5]‘ M=Ru,Os.", Coffy, T.J.; Shore, S.G., Abstracts from the 194th meeting of the American Chemical Society, New Orleans, Inor 158.

"Reactivity of the Metalladiboranes [M(CO)4(ti2-B2H5)]‘ M = Fe, Ru, Os." Coffy, T. J.; Shore, S. G. Abstracts from the 25th regonal Meeting of the American Chemical Society, Cleveland, OH.

iv "Borane Assisted Transition Metal Cluster Chemistry.", Shore, S.G.; Coffy, T.; Jan, D.-Y.; Krause, J.; Workman, D., Abstracts from the 195th meeting of the American Chemical Society, Toronto, Canada, Inor 705.

"Borane Assisted Transition Metal Cluster Chemistry.", Shore, S.G.; Coffy, T.; Jan, D.-Y.; Krause, J.; Workman, D., Abstracts from the First Boron Workshop (BUSA-1), Southern Methodist University, Dallas, Texas, MM4.

Fields of Study

Major Field: Inorganic Chemistry

Studies in Nonmetal and Organometallic Chemistry. Professors Bruce E. Bursten, Daryle H. Busch, Daniel L. Leussing, Devon W. Meek, Eugene P. Schram, Sheldon G. Shore, Andrew Wojcicki.

V Table of Contents

Dedication ...... ii

Acknowledgements ...... iii

Vita...... iv

List of Tables...... x

List of Figures...... xi

Chapter Page

I. Introduction ...... 1

A. Transition Metal Carbonylates ...... 1

1. Synthesis of [M(CO)4]2' (M = Ru, Os) ...... 4

2. Chemistry of [M(CO)4]2' (M = Ru, Os) ...... 5

a. Reactions of [M(CO)4]2* (M = Ru, Os) with Charged Electrophiles...... 5

b. Reactions of [M(CO)4]2‘ (M = Ru, Os) with Neutral Electrophiles...... 13

B. Metallaborane Chemistry ...... 18

1. (n2-B2H5) Compounds ...... 20

2. (n3-B2H5) Compounds ...... 25

3. B2H x (x= 6 or 7) Compounds ...... 27

II. Results...... 35

A. Reactions of Organometallic Anions with Diborane ...... 35

1. Preparation and Characterization of K[M(CO)4(ti2-B2H5)] (M = Ru, Os)...... 35 2. Preparation and Characterization of (n5-C5H5)Ru(CO)2(Tl2-B2H5)] ...... 51

3. Synthesis of K[Cr(CO)4B3Hg] from K2[Cr(CO)s] and THFBH3 59

4. The Reaction of Other Anions with Diborane ...... 62

B. Reactivity of K[M(CO)4Cn2-B2Hs)] (M = Fe, Ru, Os) ...... 63

1. Synthesis of HM(CO)4(ti2-B2H5) (M = Ru, Os) ...... 63

2. Synthesis of (CH3)Os(CO)40l2-B2H5) ...... 74

3. Synthesis of (Ph3PAu)M(CO)4Cn2-B2Hs) M = Fe, Ru, Os ...... 78

4. The Reaction Of [Os(CO)4(ti2-B2H5)]' with Other Organometallic Halides ...... 86

5. The Reaction of PPN[Os(CO)4Cn2-B2H5)] with (p-H)2Os3(CO)io...... 86

6. The reaction of [Os(CO)4(ti2-B2H5)]‘ with Cr(CO)6 ...... 87

7. The reactions of [Os(CO)4(ti2-B2H5)]' with Lewis Bases ...... 88

C. The Synthesis, Characterization and Structure of Group 8 Bimetallic Dianions ...... 91

1. Synthesis of Na2[Os2(CO)s] ...... 91

2. Heterobinuclear Group 8 Dianions [MM’(CO)g]2' (MM' = FeRu, FeOs, RuOs)...... 95

III. Discussion ...... 109

A. (q2-B2H5) Compounds...... 109

1. Synthesis of K[M(CO)4(ti2-B2H5)] (M = Ru, Os) ...... 109

2. Structure and Bonding ...... 115

3. Reactivity of K[M(CO)4(n2-B2H5)] M = Fe, Ru, O s ...... 119

B. Synthesis and Characterization of the Heterobinuclear Dianions [MM'(CO)8]2‘ (MM’ = FeRu, FeOs, RuOs) ...... 127

vii IV. Experimental ...... 133

A. Apparatus...... 133

B. Reagents...... 143

C. Synthesis of Starting Materials ...... 149

D. Reactions of Organometallic Anions with Diborane ...... 157

1. Preparation of K[Ru(CO)4(ti2-B2H5)] ...... 157

2. Preparation of K[Os(CO)4(ti2-B2H5)] ...... 158

3. Synthesis of K[M(CO)4(Tt2-B2D5)] (M = Ru, Os) ...... 159

4. Preparation of (n5-CsH5)Ru(CO)2Cn2-B2H5) ...... 159

5. Preparation of K[Cr(CO)4B3Hs] from K2[Cr(CO)s] and B2H6 160

6. Reaction of K2[H2Ru4(CO)i2] with diborane ...... 161

7. Reaction of K2[0l5-C5H5)V(CO)3] with diborane ...... 161

8. Reaction of K[Cn5-C5H5)Ni(CO)] with diborane ...... 162

E. Reactions of K[M(CO)4(n2-B2H5>] (M = Fe, Ru, Os) ...... 162

1. Preparation of PPN[Ru(CO)4(ti2-B2H5)] ...... 162

2. Preparation of PPN[Os(CO)4(ti2-B2H5)] ...... 163

3...... Formation of HRu(CO)4Cn2-B2H5) ...... 164

4. Formation of DRu(CO)4Cn2-B2H s) ...... 164

5. Formation of HRu(CO)4Cn2-B2D5) ...... 164

6. Decomposition of a mixture of HRu(CO)4(ti 2-B 2D5) and DRu(CO)4(ti2-B2H5)...... 165

7. Formation of HOs(CO)4Cn2-B2H5) ...... 165

8...... Formation of D0 s(C0 )4(ti2-B2H5) ...... 166

9. Formation of HOs(CO)4Cn2-B2D5) ...... 166

10. Reaction of HOs(CO)4Cn2-B2H5) with Br2 ...... 167

v iii 11. Formation of (CH3 )Os(CO)4(ti2-B2H5)...... 167

12. Preparation of Ph3PAuOs(CO)4Cn2-B2H5 ...... 168

13. Preparation of Ph3PAuRu(CO>4Cn2-B2H5) ...... 169

14. Formation of Ph3PAuFe(CO)4(n2-B2H5) ...... 169

15. K[Os(CO)4(n2-B2H5)] with KH ...... 170

16. PPN[Os(CO)4(ti2-B2H5)] with KH...... 170

17. K[Os(CO)4(ti2-B2H5>] with (PPh3>2CuBr l/2C6H6 ...... 171

18. PPN[Os(CO)4(ti2-B2H5)] with (p-H)2Os3(CO )io ...... 172

19. PPN[Os(CO)4(tl2-B2H5)] with Cr(CO)6...... 172

20. K[Os(CO)4(ti2-B2H5)] with (Ti5-C5H5)Fe(CO)2I...... 173

21. K[Os(CO)4(ti2-B2H5)] with Re(CO)5Br...... 173

22. K[Os(CO)40i2-B2H5)] with (CH3)20 BH3...... 174

F. Synthesis of Group 8 Binuclear Dianions ...... 175

1. Synthesis of Na2[Os2(CO)s] ...... 175

2. Synthesis of (PPh4)2[FeRu(CO)g]...... 176

3. Synthesis of (PPh4>2[FeOs(CO)g]...... 177

4. Synthesis of (PPh4>2[RuOs(CO)g]...... 178

IV. References ...... 180

ix List of Tables

Table Page

1 Relative Nucleophilicities of Some Metal Carbonyl Anions ...... 2

2. Infrared Spectra of the Cn2-B2H5) compounds ...... 41

3. Boron-11 NMR Spectra of the (t)2-B2H5) compounds ...... 45

4. *H {^B} NMR Spectra of the (n2-B2H5) compounds ...... 50

5. Carbon-13 NMR Spectra of the Cn2-B2H5) compounds ...... 53

6 Carbon-13 NMR Spectra of (PPh4)2[MM'(CO)8] (MM’ = FeRu RuOs, FeOs) and (PPh4)2[M2(CO)g] (M = Fe, Ru, Os) ...... 99

7. Crystal Data for (PPh4)2FeRu(CO)8 ...... 102

8. Selected Bond Distances for (PPh4)2FeRu(CO)8 ...... 103

9. Selected Bond Angles for (PPh4)2FeRu(CO)8 ...... 103

10. Crystal Data for (PPh4)2Fe2(CO)8 ...... 106

11. Selected Bond Distances for (PPh4)2Fe2(CO)8 ...... 107

12. Selected Bond Angles for (PPh4)2Fe2(CO)8 ...... 107

13. The Reaction of [M(CO)4]2* M = Fe, Ru, Os with B2H6 in Non-Donor Solvents ...... 110

14. Mass Spectrum of the Decomposition Products of HRu(CO)4Cn2-B2D5) + DRu(CO)4Cn2-B2H5) ...... 125

X List of Figures

Figure Page

1. The Molecular Structure of (Ph3PAu)20s(CO)4 ...... 7

2. Reactions of [Fe(CO)4]2‘ for Organic Synthesis ...... 11

3. The Synthesis of Tetranuclear Clusters using [M(CO)4]2" ...... 14

4. Proposed Mechanism for the Synthesis of Heteronuclear Clusters by the addition of [M(CO)4]2' (M = Fe, Ru, Os) (7) ...... 15

5. Proposed Mechanism for the Formation of Ru(CO)s from [Ru(CO)4]2‘.and CO2 ...... 17

6. Representation of the Structures of the Metalladiboranes. a) (Fe(CO)4(Tl2-B2H5)]-. and b) (Ti5-C5H5)Fe(CO)2(Tl2-B2H5) ...... 21

7. Molecular Structures of a) Cn5-C5H5)Fe(CO)2Cn2-B2H5). and b) Cn5-C5H5)2Mo(H)(Ti2-B2H5) ...... 23

8. The Molecular Structure of (ti3-B2H5) Compounds. a) Pt2(PMe2Ph)2(Tl3-B2H5)(Ti3-B6H9). b) (Ti5-C5H5Co)2(H-PPh2)(Tl3-B2H5). c) Topological Sketch of Arachno-’R^H\Q. d) Topological Sketch of M2(p.-L)(ti3-B2H5)...... 26

9. The Molecular Structure of Ligated B2H6 Compounds. a) The Molecular Structure of (Tl^-CsMe5)2Nb2(B2H6)2. b) The Proposed Structure of Fe2(CO)6(B2H6). c) The Molecular Structure of HMn3(CO)io(B2H

10. The Proposed Structure of a) [Fe2(CO )6Cn2-B 2H 5)]‘ and b) [Re(CO)5(BH3)2]-...... 31

11. a) Molecular Structure of (ii^-C5M e5>Ru(PMe3)(Ti2-B 2H 7). b) Representation of the molecular structure of (Tl5-C5Me5)Ru(PMe3)(ii2-B2H7) ...... 34

xi 12. Proposed Structure of [M(CO)4Cn2-B2H5)]’ (M= Ru, Os) ...... 36

13. Infrared Spectrum of K[M(CO)4(t]2-B2H5)]. a) M = Ru. b) M = Os...... 40

14. Boron-11 NMR Spectrum of a) PPN[Ru(CO)4(ti2-B2H5)] in CH3CN. b) K[Ru(CO)4(ti2-B2H5)] in THF. c) K[Ru(CO)4(t12-B2H5)] *H Decoupled in THF ...... 43

15. Boron-11 NMR Spectrum of a) PPN[Os(CO)4(ti2-B2H5)] in CH3CN. b) K[Os(CO)4(ti2-B2H5)] in THF. c) K[Os(CO)4(il2-B2H5)] JH Decoupled in THF ...... 44

16. High Temperature Boron-11 NMR of K[Os(CO)4Cn2-B2H5)] in THF ...... 47

17. Proton NMR of K[Os(CO)4(ti2-B2H5)] in THF a) J1B Coupled, b) 1JB Decoupled ...... 49

18. Carbon-13 NMR Spectra for a) K[Ru(CO)4(ti2-B2H5)] and b) K[Os(CO)4(ti2-B2H5)] in THF ...... 52

19. Representation of the Structure of (ti5-C5H5)Ru(CO)20i2-B2H5).... 55

20. Infrared Spectrum of (t)5-C5H5)Ru(CO)2(ti2-B2H5) ...... 56

21. Boron-11 NMR Spectrum of (ti5-C5H5)Ru(CO)2(ti2-B2H5). a) *H Coupled, b) *H Decoupled ...... 57 22. Proton NMR Spectrum of 0i5-C5H5)Ru(CO)2Cn2-B2H5) a) !H Coupled, b) !H Decoupled ...... 58

23. Representation of the Molecular Structure of [Cr(CO)4B3Hg]' ...... 60 24. Boron-11 NMR of K[Cr(CO)4B3H8] a) *H Coupled. b) *H Decoupled ...... 61

25. Infrared Spectrum of HOs(CO)4Cn2-B2H5> in CH2CI2 ...... 65

26. Boron-11 NMR of HRu(CO)4Cn2-B2Hs) at -10°C in CD2CI2. a) !H Coupled, b) *H Decoupled ...... 67

xii 27. Boron-11 NMR of HOs(CO)4(ti2-B2H5) in CD2CI2. a) *H Coupled, b) *H Decoupled ...... 68

28. Proton NMR of HRu(CO)4(ti2-B2H5) at -70°C in CD2C12. a) 1JB Coupled, b) 1JB Decoupled ...... 69

29. Proton NMR of HOs(CO)4(n2-B2H5) in CD2CI2. a) ^ B Coupled, b) 1JB Decoupled ...... 70

30. Carbon-13 NMR of HRu(CO)4(ti2-B2H5) at -80°C. a) iH Coupled, b) ^ Decoupled...... 72

31. Proposed structure of HM(CO)4Cn2-B2H5) (M = Ru, Os) ...... 73

32. Infrared Spectrum of (CH3)Os(CO)4Cn2-B2Hs) in CH2CI2 ...... 76

33. Boron-11 NMR of (CH3)Os(CO)4Cn2-B2H5) in CD2CI2. a) *H Coupled, b) *H Decoupled...... 77

34. Infrared Spectrum of (Ph3PAu)M(CO)4(ri2-B2H5). a) M = Ru. b) M = Os...... 81

35. Boron-11 NMR of (Ph3PAu)M(CO)4(Tl2-B2H5). a) M = Fe. b) M = Ru. c) M = Os...... 83

36. High Temperature NMR of(Ph3PAu)Os(CO)4(n2-B2H s) in CDCI3...... 84

37. Proton NMR of (Ph3PAu)Os(CO)4(n2-B2H5) in CD2C12...... 85

38. Infrared Spectrum of Na2[Os2(CO)s] in THF ...... 94

39. Infrared Spectrum of (PPh4)2MM’(CO)8 in CH3CN. a) MM’ = FeRu. b) MM' = RuOs. c) MM' = FeOs...... 98

40. The Molecular Structure of (PPh4)2[FeRu(CO)8] ...... 101

41. The Molecular Structure of (PPh4)2[Fe2(CO)8] ...... 105

42. Possible Intermediates in the Formation of K[M(CO)4Cn2-B2Hs)]. a) Bis-Borane Intermediate, b) Intermediate analogous to [B2H7]- ...... 112

43. Possible Mechanism for the Formation of [Cr(CO)4B3Hg]' ...... 114

44. Possible Bonding Modes of [M(CO)4(ti2-B2H5)]\ a) Two Two-Center Two-Electron Bonds, b) Three-Center Two-Electron Bond ...... 114 xiii 45. Bonding Analogy Between a Coordinated C2H4 and B2H5 a) Bonding Based on Pitzers Diborane Model, b) Dewar-Chatt- Duncanson Model for Metal Olefin Bonding ...... 119

46. A Vacuum Line Extractor...... 136

47. Apparatus for Preparing Low Temperature NMR Samples ...... 138

48. Apparatus to Decompose Mixtures of Thermally Sensitive Compounds ...... 139

xiv I. Introduction

A. Transition Metal Carbonylates.

The synthetic utility of transition metal anions in inorganic chemistry is well established (1, 2). The chemistry of carbonylmetallate anions has been the subject of intense research for over thirty years.

Dessy and King (3) were the first to recognize the need to categorize the nucleophilic strength of carbonylmetallate anions. In this classic paper they ranked the nucleophilicities of some transition metal carbonylates through reactions with alkyl halides. Later Pearson (4) added other transition metal anions to the study (Table 1.).

An interesting ranking by Pgarson (4) in Table 1. is the position of

Na2[Fe(CO)4], which is ranked below the nucleophilicity of [Re(CO)5]'. This disagrees with the results of Coleman (5) who coined the term

"supernucleophile" when describing the chemistry of Na2[Fe(CO)4]. His studies advance the idea when Na2[Fe(CO)4] forms a solvent separated ion pair, Na+:S:Fe(CO)42' (S = Solvent), it is at least as nucleophilic as [(t\5-

C5H5)Fe(CO)2]-.

Although there has been no study of the nucleophilicity of the tetracarbonylates [M(CO)4]2_ (M = Ru, Os) it is reasonable to assume they are strong nucleophiles. Norton (6) predicted that the carbonylate [Os(CO)4]2* is more basic than [Fe(CO)4]2’ from the qualitative comparison using the

1 2

Table 1. Relative Nucleophilicity of Some Transition Metal Anions

Anion Relative Nucleophilicitv

(n-C5H5)Fe(CO)2- 65,000,000

(t1-C5H5)Ru(CO)2- 7,000,000

0l-C5H5)Ni(CO)- 5,100,000

Co(dmg)(pyr)- 410000

Re(CO)5- 23,000

Rh(CN)43‘ 18000

Fe(CO)42" 11500

(Tl-C5H5)W(CO)3- 500

Mn(CO)5- 77

(ti-C5H5)Mo(CO)3- 67

(Tl-C5H5)Cr(CO)3- 4

Co(CO)4‘ 1 3

Pka's of the conjugate acids H20s(C0)4 and H2Fe(CO)4. Moreover, Geoffroy

(7) ranked the nucleophilicity in the descending order of Fe > Ru > Os. This

also seems to be the relative ordering of the nucleophilicity for the anions

[(ti5-C5H5)M(CO)2]' (M = Fe, Ru) (Table 1.). Pearson (4) points out, however, that there is no general rule for stating the ordering of whether the first, second or third transition series is more nucleophilic for any series of compounds. Geoffroy (7) also ranked a quantity called "reducing power" for these carbonylates in the order of Os > Ru > Fe. This quantity is presumably the ability of the carbonylmetallate to reduce, rather than form a complex with, a Lewis acid. This quantity is important in the syntheses of the heterobinuclear dianions of group 8 (36).

The chemistry that is described in this dissertation is based on the nucleophilicity of the afore mentioned anions [M(CO)4]2‘ (M = Ru, Os). The large nucleophilicity of these carbonylates observed elsewhere is borne out in this study as well through the reactions with diborane and with the neutral pentacarbonyls of group 8. The following is a brief review of the i synthesis and chemistry of the carbonylates [M(CO)4]2* (M = Ru, Os). Some chemistry of [Fe(CO)4]2‘ will be included when trends or a comparison of the chemistry is warranted. Reviews based on metal carbonylate chemistry have appeared elsewhere (6, 7). 4

1. Synthesis of [M(CO)4]2' (M = Ru, Os)

Stone et.al. (9, 10) first obtained the anions Na2[M(CO)4] (M = Ru, Os)

by the reaction of the trinuclear clusters M3(CO)i2 (M = Ru, Os) with sodium

in liquid ammonia (Equation (1)).

M3(CO)i2 + 6Na ------► 3Na2[M(CO)4] (1)

(M = Ru, Os)

This method was reported not to produce pure mononuclear dianions, but

instead contained a mixture of Na2[M(CO)4] and Na[HM(CO)4] (M = Ru, Os). It

was determined later that the careful control of the stoichiometry of

Equation (1) produces samples whose purity levels are adequate (6).

Analytically pure samples of the anions [M(CO)4]2" (M = Ru , Os) were

prepared using a procedure analogus to Stone’s (Equation (2)).

M3(CO)i2 + 6K ------► 3K2[M(CO)4] (2)

(M = Ru (36), Os (37))

The larger reduction pontential of potassium as compared to sodium may be the reason this reduction is purer than the sodium reduction. The main difference between the potassium and sodium salts is that the potassium salt is insoluble in most common solvents while the sodium salts are slightly soluble in polar solvents. 5

2. Chemistry of [M(CO)4]2* (M = Ru, Os)

The chemistry of the anions [M(CO)4]2' (M = Ru, Os) is largely dictated by their large nucleophilicities and by the stability of the resulting M(CO)4 fragment in the product compound. In general the chemistry can be divided into two catagories: (a) Reactions of [M(CO)4]2‘

(M = Ru, Os) with charged electrophiles, and (b) Reactions of [M(CO)4]2*

(M = Ru, Os) with neutral electrophiles. The charged electrophiles are most often associated with halide, BF4' and PF5' counter ions, while the neutral electrophiles are frequently metal carbonyl compounds and borane (see

Section II. B. 1.).

a. Reactions of [M(CO)4]2* (M = Ru, Os) with Charged Electrophiles.

The anions [M(CO)4]2* (M = Ru, Os) can be monoprotonated to yield the hydrido anions [HM(CO)4]‘ (M = Ru, Os) (11). The osmium compound,

[HOs(CO)4]‘, like the iron compound, [HFe(CO)4]", is moderately stable as the alkali metal salt. The ruthenium compound, [HRu(CO)4]", is unstable as the alkali metal salt but may be isolated as the bistriphenylphosphine imminium (PPN+) salt (11). The hydride in the compound [HFe(CO)4]‘ (12) assumes an axial position in the trigonal bipyramidal arrangement of ligands about the iron center. It is assumed that the hydride in the compounds [HM(CO)4]' (M = Ru, Os) occupies the analogous site of the trigonal bipyramid based on infrared spectroscopic data (11).

The tetracarbonylates can be diprotonated and the volatile compounds cw-H2M(CO)4 (M = Ru, Os) (10, 13) are formed. These compounds 6

are volatile liquids and can be isolated by distillation. The compound cis-

H20s(C0)4 is thermally stable and does not show appreciable amounts of decomposition below 100°C (14). On the other hand, H2Ru(CO)4 is thermally unstable (10) and decomposes above its melting point of -22°C.

The anions [M(CO)4]2‘ (M = Ru, Os) will react with two equivalents of the "pseudo proton" [Ph3PAu]+ to form the compounds M(CO)4(Au(PPh3))2

(M = Ru, Os) (15). The molecular structure of Os(CO)4(Au(PPh3))2 (Figure 1) indicates that [Au(PPh3)]+ does not function as a "pseudo proton" in this case. The structure contains a gold-gold bond which is proposed to donate electron density to a vaccant orbital on the Os(CO)4 fragment. This is considered a closed three-center two-electron bond. The geometry of the carbonyls around the osmium metal center is intermediate between tetrahedral and C2v cis-octahedral.

A survey of the pertinent literature for the chemistry of [M(CO)4]2‘

(M = Ru, Os) reveals that the chemistry of the ruthenium dianion,

[Ru(CO)4]2', is not as well studied as that of the osmium dianion, [Os(CO)4]2'.

Especially lacking are reports of mono-alkylated [Ru(CO)4(R)]‘ or dialkylated Ru(CO)4(R)2 compounds. In contrast, the mononuclear tetracarbonyl osmium dialkyl compound Os(CO)4(CH3)2 (16) and the hydridoalkyl compound Os(CO)4(H)(CH3) (13) had been characterized 19 years ago. Two equivalents of methyl halide react rapidly with [Os(CO)4]2‘ to form the osmium dialkyl compound Os(CO)4(CH3)2 (13).

[Os(CO)4]2- + 2CH3C1 Os(CO)4(CH3)2 + Cl- (3) 7

Figure 1. The Molecular Structure of (Ph3PAu)20s(C0 >4. 8

There has been attempts to isolate the osmium mono alkyl compound

[Os(CO)4(CH3)]* by methods similar to those used to synthesize the analogous

iron mono alkyl compound, [Fe(CO)4(CH3)]‘. Those reactions were not

successful and only Os(CO)4(CH3>2 was isolated (17). This was probably due

to the greater solubility of [Os(CO)4(CH3)]‘ compared to that of [Os(CO)4]2"

coupled with the proposed (13) high nucleophilic character of

[Os(CO)4(CH3)]' thereby favoring disubstitution over monosubstitution. The

anion [Os(CO)4(CH3)]' has been generated (18) by the deprotonation of

Os(CO)4(H)(CH3) according to Equation (4).

Os(CO)4(H)(CH3) + TMG ------► (TMGH)[Os(CO)4(CH3)] (4)

TMG = tetramethylguanidine

The synthesis of tetracarbonyl osmium hydrido alkyls,

[Os(CO)4(H)(R)] (R = alkyl), from [Os(CO)4]2' was more difficult. This is because it was not reasonable to protonate the anion [Os(CO)4(R)]’ due to the lack of a preparative method. The synthesis had to be performed using the stable anion [HOs(CO)4]‘ as the starting compound. The synthesis of

Os(CO)4(H)(CH3) (17) was achieved according to Equation (5). 9

[Os(CO)4l2- + CH3COOH ------► [HOs(CO)4]' + [CH3COO]-

2CH3SO3F

’ r

Os(CO)4(H)(CH3) + CH3COOCH3 + 2 [SO3F]' (5)

The volatile Os(CO)4(H)(CH3) was isolated by distillation. When another methylating agent was used (e. g. methyl tosylate) a mixture of H20s(C0 )4,

Os(CO)4(CH3)2 and Os(CO)4(H)(CH3) was formed. The following reaction sequence was proposed to account for this result (17).

[Os(CO)4]2- + CH3COOH------► [HOs(CO)4J- + [CH3COO]- (6)

[HOs(CO)4]- + CH3X ------► Os(CO)4(H)(CH3) + X ' (7)

[HOs(CO)4]- + Os(CO)4(H)(CH3) ------► H2Os(CO)4 + [Os(CO)4(CH3)]- (8)

[Os(CO)4(CH3)]- + CH3X ------► Os(CO)4(CH3)2 + X’ (9)

X = tosylate, Cl"

The compound Os(CO)4(H)(C2H5) has also been prepared (14). The hydrido alkyls decompose slowly in the absence of light and air at room temperature. The dialkyls are more thermally robust and do not show appreciable decomposition under 100°C (14).

In contrast to [Os(CO)4]2" is the alkylation chemistry of [Fe(CO)4]2".

The mono alkyl compound, [Fe(CO)4R]" (R = Me, Et, PI1CH2, PI1CH2CH2), is stable and readily isolable (19, 20). The alkyl group occupies an axial 10

position in the trigonal bipyramidal arrangement of ligands about the

metal center. The crystal structure of Fe(CO)4(C3Hy) (21) corroborates this

arrangement. The presence of additional carbon monoxide or added phosphine with [Fe(CO)4R]* causes carbon monoxide insertion and acyl compounds are isolated (19).

O ii [Fe(CO)4R]- + L ------► [Fe(CO)3LCR]‘ (10)

L = CO, Phosphine

The compounds Fe(CO)4R2 and Fe(CO)4(H)R (R = alkyl) which would result from the alkylation or the protonation of [Fe(CO)4R]" arc too unstable to be observed. The dialkyl and hydrido alkyl iron compounds, Fe(CO)4R2 and

Fe(CO)4(H)R (R = alkyl), undergo rapid decomposition to yield organic elimination products. Reaction conditions of this decomposition can be modified to yield aldehydes (22), carboxylic acids (23), amides (23), esters

(23) and unsymmetrical ketones (24) as elimination products (Figure (2)).

These results have been extensively reviewed (5, 25) and serve to define the chemistry of [Fe(CO)4]2‘ as the "transition metal analog of a Grignard reag en t".

Compounds M(CO)4(E R 3)2 (M = Ru, Os); ER3 = SnR3 (R = Ph, Me),

PbMe3, GeMe3, SiMe3) have been synthesized (13, 26 - 29). These complexes are the result of the 2:1 addition of the appropriate halide to [M(CO)4]2'

(M = Ru, Os). 11

RX, L L = CO, [Fe(CO)4]2 - RX P(C6H5)3

R'Y O [RFe(CO)4]' ^ ii D'V 9 R'CR x [RCFe(CO)3L]"

RCOH or NaCIO or NaCIO

RCX

HNR’R RD R'OH RCH

O ll O RCNR'R RCOR' RCOH

Figure 2. Reactions of [FefCOkjZ- for Organic Synthesis. 12

[M(CO)4]2- + 2ER3C1 ------► M(CO)4(ER3)2 + Cl’ ( 11)

(M = Ru, Os)

There is little difference between the reactivity of the ruthenium and

osmium tetracarbonylates in Equation (11) with the exception that the

ruthenium compounds are formed in much lower yields. These compounds

have the metal center in the 2+ oxidation state and the ligands are

octahedrally arranged. These compounds may exist in solution as pure cis,

pure trans or a mixture of the two isomers (30). Isomerization at higher

temperatures has been observed. The preferred isomerization mechanism

is the interconversion of the cis- trans isomers by ligand motion. Studies

of this isomerization process indicate no evidence of ligand dissociation.

The activation barrier for the ruthenium and osmium compounds are

similar and both are 6 - 8 Kcal higher than that of the iron analogues (30).

A general route to the synthesis of group 8 mononuclear carbene compounds has been put foreward by Stone (34). The reactions of (I), (II)

and (III) with [M(CO)4]2' M = Fe, Ru, Os produce the mononuclear group 8 thiazolidinylidene and methylpyridinylidene compounds. Yields of the iron complexes in all cases were significantly lower than the yields of the osmium compounds (ruthenium compounds could not be isolated as solids).

This trend may imply the order of nucleophilicity as [Os(CO)4]2' >

[Fe(CO>4]2', which is the opposite of that proposed by Geoffroy (5) . An X- ray structure (35) of tetracarbonyl (1, 3 dimethylimid-azolinylidene) Fe(0) shows that the carbene occupies an axial position of a 13

Me Me Me N Me .N C,^ N^ BF, bf4- )>C I K )>C I bf4- S

(I) (II) (HD

distorted trigonal bipyramid. However, the infrared spectra indicate that the carbene occupies an equatorial position. In all compounds ligand motion inhibited conclusive structural information based on NMR studies.

b. Reactions of [M(CO)4]2‘ (M = Ru, Os) with neutral electrophiles.

Geoffroy (7) found that the anions [M(CO)4]2‘ M = Fe, Ru, Os could be used to synthesize mixed metal tetranuclear clusters. This chemistry is outlined in

Figure 3. It was determined that the greatest purity and the highest yields of the products were associated with the reactions of [Fe(CO)4]2', while reactions of [Ru(CO>4]2- produced products of intermediate purity.

Reactions with [Os(CO)4]2- were the least successful. These results lead to the proposal of the following factors which govern the success of these reactio n s.

1. the order of nucleophilicity for the anions [M(CO)4]2‘, Fe > Ru > Os .

2. The order of the M-C-O bond strength of the Clusters M3(CO)i2, Os > Ru > Fe.

3. The order of the reducing ability of the anions [M(CO)4]2', Os > Ru > Fe. [R u(CO)4]2' / H2Fe2Ru2(CO)13 + H2FeRu3(CO)13 Fe3(CO)12 Os3(CO),2

Fe2Ru(CO)12 [Fe(CO)4]2' ^ H2Fe2Ru2(CO)13 + H2FeRu3(CO)13

FeRu2(CO)12 (Fe(CO)J2- u _ H2Fe2Ru2(CO)13 + H2FeRu3(CO)13

[F e fc o ),]^ H2FeRu3(CO)13 Ru3(0 0 )12 \ fOsfCO^j2' H4RuO s3(CO )12 + H4Ru2O s2(CO )12 + H4Ru3O s(C O )12

Ru2O s (CO)12 _ [Fe(co)4^ H2FeRu2Os(CO)13

[Fe(CO)4]2' RuOs2(CO)12 H2FeRuOs2(CO)13 FejCOUf ^ ^ j L H2FeOs3(CO)13 Os3(CO)12

\ [Ru(CO)4]2'

T h40Cs° C 0 ) 124RU° S4

Figure 3. The Synthesis of Tetranuclear Clusters using [M(CO)4] 2-. Figure 4. Proposed mechanism for the synthesis of heteronuclear clusters by the addition of [M(CO)4]2' (M = Fe, Ru, Os) ( 7 ).

Thus the yields involving [Fe(CO)4]2‘ were the best because in the

above ordering it is the best nucleophile and the least reducing. The

proposed mechanism for this type of cluster build-up is pictured in

Figure 4. The first step of the mechanism involves nucleophillic attack of

the tetracarbonylate at one metal center with subsequent displacement of

carbon monoxide. For the trimers M2M'(CO>2 (IV^M1 = Fe2Ru, Ru2Fe, Ru20s,

Os2Ru) this probably involves attack at the metal with the weakest M-C -0

bond strength. The synthesis of the tetramer is completed by sucessive

attacks by the coordinated anion on the remaining metals in the trimer.

The dinuclear dianions [M2(CO)8]2- M = Fe (38), Ru, Os (32) have been prepared by redox condensation reactions with the anions [M(CO>4]2'

(M = Fe, Ru, Os) according to equation (12).

[M(CO)4]2* + M(CO)5 ► [M2(CO)8]2- + CO ( 12) 16

Synthesis of the pentacarbonyls in Equation ( 7 ), M(CO)s (M = Ru, Os)

(33), involved the reaction of [M(CO)4]2' (M = Ru, Os) with carbon dioxide according to Equation ( 13).

[M(CO)4]2- + 2C0 2 ------► M(CO)5 + [CO3]2- ( 13)

To account for the formation of the pentacarbonyls a mechanism involving two intermediates was proposed by Cooper ( 33) (Figure 5.). Apparently the sodium ion pairs the coordinated CO2 in the intermediate. This reduces the bond order of the C =0 bonds in carbon dioxide and aids in the cleveage of a

C= 0 bond. The result is disproportionation of CO2 into CO and [CO3]2'.

Extensions of this work will be detailed later in the text.

The nucleophilicity of the dianions [M(CO)4]2' (M = Fe, Ru, Os) are undoubtedly the reason for the relatively high yields of the products in

Equation ( 12). Unfortunately the salts Na 2[Ru2(CO)8] and K2[Os2(CO)8] could not be isolated as pure solids. The impurities are, as expected, higher nuclearity cluster carbonylates. It has been suggested ( 36) the purity of the product is dependent upon of the solubility of [M(CO)4]2‘ (M = Ru, Os) in

THF. Since the dinuclear dianions [M2(CO)8]2‘ (M = Ru, Os) are more soluble in THF than is [M(CO)4]2' it can react with M(CO)s to initialize the formation of the higher nuclearity anions. The following series of reactions may account for this result. 17

O O

\ / , o , Na2[Ru(CO)4] + C 02 Na+ O C — Ru — C v( ,'Na

C O

co2

O O C C . Na \ <_ *o" \ Na2C 0 3 + Ru(CO)5 O C Ru — C o | ' o - c j > 3 c ° ’ o

Figure 5. Proposed Mechanism for the Formation of Ru(CO)s from (Ru(CO)4]2- and CO2. 18

[M(CO)4]2" + M(C0)5 — tM2(CO)s)2- + CO (14)

[M2(CO)8]2- + M(C 0)5 - -► [M3(CO)n]2- + 2CO ( 15)

[M3(CO)ii]2- + M(C0)5 p~ [M4(CO)i3]2’ + 3CO ( 16)

This would be especially true for the synthesis of K2[Os2(CO)8] because of

the greater insolubility of K2[Os(CO)4] in THF as compared to the sodium

salt. This was observed, and the resulting salts of K2[Os2(CO)8] were very

impure (36). In the case of the ruthenium compound, Na2[Ru2(CO)8], solids

of reasonable purity were isolated. This may be the result of the higher

solubility of Na2[Ru(CO)4] as compared to the potassium analogs. Also, the

greater nucleophilicity of Na2(Ru(CO)4] compared to that of Na2[Ru2(CO)8]

may be the reason most of the Ru(CO)s reacts with the mononuclear

dianion and limits the production of higher nuclearity cluster anions.

B. Metallaborane Chemistry

Independently, the areas of transition metal cluster chemistry and boron cluster chemistry have experienced rapid expansion. Before the first report of the incorporation of a transition metal into the framework of a boron hydride cluster, the bonding of the boron hydride clusters was considered a oddity. Paralleling the abnormalities in bonding of boron hydride clusters was the bonding in the higher nuclearity transition metal clusters. There had been discoveries of transition metal clusters in 19

which the bonding could not be accounted for using the cluster bonding theory of that time period. It was not until 1971 in which Wade ( 39) and

W illiam s (40) described a different approach to account for the unusual bonding observed in boranes and carboranes. This method was called the

Polyhedral Skeletal Electron Pair Approach and is now affectionately known as "Wade's Rules". It was not long before these rules were applied to the bonding in transition metal clusters ( 3 - 8 metal atoms) (41 - 44), metallaboranes and metallacarboranes ( 52). Since the discovery of "Wade's rules" more sophisticated molecular orbital treatments (45 - 51) have been used to describe cluster bonding with great success. Wade ( 42) refers to the discovery of metallaboranes and metallacarboranes as "The vital link by which boron clusters were seen to be related to metal clusters and metal- hydrocarbon 7T-complexes, paving the way for general theories of cluster bonding". There have been many articles treating the subject of bonding

(39-52) in transition metal, boron hydride, metallaborane and metallacarborane clusters and the basic concepts will not be detailed here.

The number and types of metallaborane compounds is considerable and has been the subject of several review articles ( 53-63) and will not be reviewed in this introduction. Only metallaborane compounds containing two boron atoms in which the borane fragment has the general formula

B2H X (x = 5, 6, 7 ) will be discussed.

In general, there are two modes in which the borane fragment B2HX

(x = 5, 6, 7 ) prefers to bond. The (B2H5) moiety is usually bound to one or two metals in a dihapto On2) or trihapto (i)3) fash on respectively. The 20

(B 2Hx, x = 6 or 7) moiety, however, prefers bonding via a M-H-B mode.

Given below are examples illistrating each bonding arrangement.

1. (ti2-B2H5) compounds.

The first two vertex metallaboranes containing a (q2-B2Hs) moiety reported in the literature were K[Fe(CO)4 ( q 2- B 2H 5)] (64) and

(Ti5-C5H5)Fe(CO)2(,n2"B2H5) (65). These compounds were synthesized according to Equation (17) and (18).

THF K2[Fe(CO)4) +3THF-BH3 ------► K[Fe(CO)4(Tl2-B2H5)] + KBH4 + 3THF (17 )

-78°C, Me20 K[(Ti5-C5H5)Fe(CO)2] + 3Me2OBH3 ------►

(Ti5-C5H5)Fe(CO)2(Tl2-B2H5) + KBH4(18)

The structures of these compounds are based on a diborane(6) structure with a bridge hydrogen replaced by the organometallic fragment

(Figure 6.). They are formally arachno metallaboranes and exist as 18 electron complexes. The specifics of the bonding in Cn2-B2H5) compounds will be given in a later section. The molecular structure of (q5 -

C5H5)Fe(CO)2(q2-B2H5) (Figure 7 a) confirmes that the metal fragment replaces a bridge hydrogen in the diborane (6) structure. 21

0 1 O C o H C \ N H \ / B B a) H \ H c o

H \ B b ) / H

Figure 6. Representations of the Structures of the Mclalladiborancs. a) |Fc(CO)4(n2-B2H5)J-. b) (ti5-C5H5)Fc(CO) 2(ti2-B 2H5). 22

The analogous molybdenum metalladiborane, Cn^-C5H5)2MoH(,n2-B2H5)

(66), was produced from (q5-C5H5)2MoH2 in a 20% yield according to

Equation ( 19).

hv (Tl5-C5H5)2MoH2 + THFBH3 ► (ti5-C5H5)2MoH(ti2-B2H5) ( 19)

Other products which are formed in this reaction 'were not reported. An alternative synthesis of this metallaborane involves the reaction of

(q5-C5H5)2M oC l2 with [B3H8]'.

0l 5-C5H5)2M oCl2 + Na[B3Hg] ------► (ti5-C5H5)2MoH(ii2-B2H5) (20)

This complex is air stable and was isolated by column chromatography. The terminal hydride has a sharp resonance at - 6.65 ppm in the proton NMR spectrum which indicates that there is no exchange between the terminal hydride and the boron ligand. The molecular structure was reported

(Figure 7 b.) and it corroborates that the metal replaces a bridge hydrogen in the diborane (6) structure. The long distance between the terminal hydride and the closest BH2 group of 2.08 A indicates there is no bonding interaction between the two species.

Three complexes which are not metallaboranes but contain the

(ti2-B2H5) moiety are worthy of mention. The first is a metallacarborane

5:l\2'-[l-(Ti5-C5H5)Co-2,3-(Me3Si)2C2B4H3][Ti2-B2H5] (67 ). It was prepared by the reaction of cobalt vapor with cyclopentadiene and 23

b )

Figure 7. The Molecular Structure of (ti2-B 2H s ) Compounds, a) (H5-C5H5)Fe(CO)2(Ti2-B2H5). b) (t\5-C5H5)2Mo(H)(ti2-B2H5). 24

bis(trimethylsilyl)acetylene. A single crystal X-ray diffraction study

indicated that the boron in the 5 position of the closo metallacarborane

fragment l',2'-[l-(Ti5-C5H5)Co-2,3-(Me3Si)2C2B4H3] assumes a bridge

bonding position to the (n2-B2H5) moiety. In this way this compound is

similar to the compounds K[Fe(CO)40n 2-B2H5)], Cn5-C5H5)Fe(CO)20n2-B2H5)

and (ti5-C5H5)2MoH(ti2-B2H5).

T w o other compounds (68), the carborane, 2:r,2'-[l,6-C2B4H5]

[t]2-B2H5], and the borane, 2:r,2'-[B5Hg][ti2-B2H5] have also been reported.

These compounds were prepared according to Equations ( 21) and ( 22).

P tB r2 C2B6H io + B2H6 ------► 2:1^ ,-[1,6-C2B4H5][ii2-B2H5] + H2 (21)

P tB r2 B5H9 + B2H6 ------► 2:1',2,-[B5H8][ti2-B2H5]. + H2 (22)

The reactions depicted in Equations ( 21) and ( 22) have been described as platinum bromide catalyzed dehydrocoupling reactions of diborane. The products have the (q2-B2H5) moiety substituted on the 2 position of the closo [1.6-C2B4H5] and nido [B5H8] cages. The structural assignments were based on spectroscopic data. The compounds are liquids which decompose upon mild heating (ca. 40°C) to yield starting materials. A point to consider is the possibility of the chemistry depicted in Equations ( 21) and ( 22) proceeding through the intermediates PtBr2(H)2(il2-B2H5)(C2B4H5) and

PtBr2(H)20)2-B2H5)(B5H8). These intermediates would yield a platinum atom in the 6+ oxidation state. Such a high oxidation state for platinum 25

would be unstable and reductive elimination of H2 and either of the products 2:r,2'-[l,6-C2B4H5][ii2-B2H5],and 2:1',2'-[B5H8][ti2-B2H5] would be facile. There is precedent for a Pt(VI) metal center in the compound PtF6

(69, 70 ).

2. Cn3-B2H5) compounds

Metallaboranes in which the B2H5 moiety is considered to be trihapto have the boron fragment bound to two metal centers. The first compound of this type, [Pt2(PMe2Ph)20l3-B2H5)(q3-B<5H9)], was reported by

G reenw ood et. al. (71 , 72 ). This diplatinum compound was synthesized according to Equation ( 23).

4-Me2S-7Me20-aracAno-B9H2 + 2PtCl2(PMe2Ph)2 ^

tPt2(PMe2Ph)2(Tl3-B2H5)(Ti3-B6H9)] (23)

The yield in this synthesis was 2-3% and the remaining products were a mixture of other metallaboranes. A single crystal X-ray analysis was reported (Figure (8a)) and the molecular structure is best described as a four vertex arachno Pt2B2 fragment connected by a shared Pt-Pt edge to an arachno eightvertex Pt2B6 cluster. The hydrogens were not located crystallographically.

Another (ti3-B2Hs) compound, (Tl5-C5H5Co)20i-PPh2)(tl3-B2H5) , was reported by Fehlner et. al (73 ). This compound was prepared according to

Equation (24). 26

b )

d ) H

Figure 8. The Molecular Structure of (ti3-B2H5) Compounds. a) Pt 2 (PMe2 Ph)2(Tl3 -B 2 H5 )(Ti3 -B6 H9). b) ((Tl5-C5H5)Co)2(fi-PPh2)(Ti3-B2H5). c) Topological Sketch ofArachno-B^Hio. d) Topological Sketch of M2(|i-L)(n3-B2H5 ). - 27

2(Ti5-C5H5)Co(PPh3)2 + THF-BH3 ► 0l5-C5H5Co)20i-PPh2)0l3-B2H5) (24)

This cobaltaborane was isolated in 18 % yield. The reported crystal structure of this compound (Figure 8 b) is similar to the PL2B 2 core of the platinum compound, [Pt2(PMe2Ph)2(Tl 3-B 2 H 5 )(,n 3-B6H9)], but in this case the hydrogen atoms of the borane fragment were crystallographically located. The structures of both [Pt 2(P M e 2P h )20l 3-B 2H s ) ( ii3-B 6H 9)], and

Cn 5-C5H5Co)2(M.-PPh2)(tl3-B2H5) indicate that these (t| 3-B2H5) compounds are related structurally to the 14 electron arachno boron cluster B 4H jo*

Topological drawings in Figure 8 c. and 8 d. represent a comparison of the proposed multicenter bonding in B4H10 and the 0i3-B2Hs) compounds. This assignment ( 73 ) rationalizes the asymmetry in the metal boron distances observed in the crystal structures.

c. B2Hx (x = 6 or 7 ) Compounds

The complexation of B2H6 in a metallaborane complex is usually accommodated by at least two metal centers and the diborane is formally considered to be an arachno B 2H g2- (62). The diborane ligand would be isostructural and isoelectronic with C2H6 while it bonds in a bidentate fashion through the use of B-H-M bonds. These types of compounds are generally synthesized from the reaction of an organometallic halide with

[BH4]- with the only exception being Fe2(CO)6(B2H6) (see below). 28

The compound 0 l 5 - C 5 M e 5) 2N b 2 (B 2H 6)2 (74 ) was synthesized

according to Equation ( 25).

DME NbCls + Li[C5Me5] + NaBft* ------► 0l 5-C5M e5)2N b2(B 2H 6)2 (25)

This compound was formed in 4 % yield and the molecular structure is

presented in Figure 9a. Each BH3 group is bound in a bidentate fashion to

both niobium metal centers through Nb-H-B bonds. This leaves one B-H

bond exo to the metallaborane cluster.

The diferraborane, Fe2(CO)6(B2H6) ( 85 ), is proposed to have the

diborane ligand bound in a similar manner. The synthesis of

Fe2(CO)6(B2H6) was achieved as in Equation ( 26).

H3PO4 Fe(CO)5 + LiHBEt3 + THFBH3------► Fe2(CO)6(B2H6) (26)

The air sensitive, yellow-brown liquid was formed in 10% yield based on

boron -11 NMR spectroscopy. The proposed structure is presented in

Figure 9b.

The cluster compound HMn3(CO)io(B2H6) was formed as a byproduct in the synthesis of H3Mn3(CO)i2 when an excess of NaBH4 was reacted with

Mn2(CO)io (76 ). The molecular structure of this manganaborane was determined and is also presented in Figure 9c. A reported triruthenium metallaborane, which should be structurally related to HMn3(CO)io(B2H<5), is Ru3(CO)9(B2H6) (77 ). This cluster was formed in very small amounts 29

a) X O

/ I V T ^ b '

Nb, Nb h h-H h \ A - h — Fe OC / \ C C 0 o

M n

Figure 9. The Molecular Structure of Ligated B2H6 Compounds. a) The Molecular Structure of 0i 5-C 5M e5)2N b 2(B 2H 6)2- b) The Proposed Structure of Fe2(CO)6(B2Hg). c) The Molecular Structure of HMn3(CO)io(B2H6). 30

when NaBH4 was reacted with Ru3(CO)i2 in refluxing THF. Unfortunately

the only spectroscopic data reported on this compound is the parent-ion of

the mass spectrum.

Fehlner has shown that one of the M-H-B bonds in the compound

Fe2(CO)6(B2H6) (75 ) can be removed with a base (i. e. deprotonated) to yield a compound which has been spectroscopically identified as [Fe2(CO)g(Ti2-

B2H5)]'. The B2 core is proposed to be equatorially bound to one Fe(CO)3 fragment (the other Fe atom occupies the axial site in the trigonal bipyramid) similar to the compound K[Fe(CO)4(q2-B2H5)]. Two of the B-H bonds of the B2H5 ligand interact with the other Fe(CO)3 group to form B-H-

Fe bonds (Figure 10a). The hydride motion can not be quenched on the

NMR time scale and the resonances are invarient to temperature.

It may be possible that the other (B2H6) complexes may deprotonate in a similar manner to produce the analogous

[(q5.c5Me5)2Nb2(B2H5)(B2H6)]-, [(Tl5-C5Me5)2Nb2(B2H5)2]-, and

[Ru3(CO)9(B2H5)]‘. The cluster HMn3(CO) io(B2H6) should exhibit interesting behavior when deprotonated. The Mn-H-Mn bond could be removed along with a B-H-Mn bond sucessively to form the anions

[Mn3(CO)io(B2H6)]‘ and [Mn3(CO)io(B2H5)]2\ This would be similar to the deprotonation reactions of HFe4(CO)i2BH2 ( 78 ).

A metallaborane that loosely fits into the above category is

[Re(CO)5(BH3)2]". This synthesis was the first reported reaction of a metal carbonylate with diborane ( 80 ) . The carbonylate [Re(CO)5]* was reported 31

a) C O

Figure 10. The Proposed Structure of a) [Fe2(CO)6(n2-B2H j)]‘ b) lRe(CO)5(BH3)2]'.

I 32

to add BH3 to yield the compounds [$e(CO)5(BH3)]' and [Re(CO)5(BH3)2]*

(Equation (27 ) and (28 )).

Re(CO)5- + THFBH3 ► [Re(CO)5(BH3)]- (27 )

Re(CO)5' + 2THFBH3 ------► [Re(CO)5 (BH3)2r (28)

The monoadduct has, presumably, a dative bond from the filled metal

orbital to the empty orbital of the BH3 group. The diadduct was proposed to

have a structure similar to the known structure of [B2H7]' ( 79 ) (Figure 10b)

because the rhenium metal center would have to assume a seven coordinate

geometry to accommodate two dative metal-boron bonds. The

characterization of these species is poor and there is no direct structural

evidence to support either proposed structure. It also can not be ruled out

that the rhenium compound may not be a bis-borane adduct but is

structurally related to the (q^-i^H s) compounds described above.

The last compound in this category is (q5-C5Me5)Ru(PMe3)(q2-B2H7)

(66). This compound was formed in minor amounts from the reaction of

0l5-C5Me5)Ru(PMe3)C l2 with 3,1 excess of NaBH4. The molecular structure

(Figure 11a.) indicates the mode of bonding is through two B-H-Ru bonds.

The B2H7 group can be considered to be formally [B2H7]*. The two B-H

bonds from the [B2H7]" ligand donate two electron each to the ruthenium.

If there is no bonding between the ruthenium and the two boron atoms, the metal center would have 18 electrons. This would place the metal in the 2+ 33

oxidation state and the ruthenium would contain 12 bonding electron pairs.

The Ru-B distance of 2.304(4) A for Cn5-C5Me5)Ru(PMe3)Cq2-B2H7) is long

for a Ru-B single bond but may be an adequate distance if multicenter

bonding is envoked. This distance, of course, may be due to coincidental

approach of the ruthenium and the boron because of the B-H-Ru bonds.

The B-B distance of 1.93( 1) is not indicative of multicenter bonding because

the distance is longer than what would be expected. Therefore, there

should be no bonding interaction between the ruthenium atom and the two boron atoms. A topological sketch depicting this bonding is pictured in figure lib. b ) / \ H H

Figure 11. a) Molecular Structure of (Ti5-C5Me5)Ru(PMe3)(n2-B2H7). b) Representation of the Molecular Structure of (H5-C5Me5)Ru(PMe3)0n2-B2H7). II. Results

A. Reactions of Organometallic Anions with Diborane

1. Preparation and Characterization of K[M(CO)4(q2-B2H 5)]

(M = Ru, Os).

The reaction of THF-BH3 with the nucleophilic tetracarbonylates

K2[M(CO)4] (M = Ru, Os) produce the metalladiboranes K[M(CO)4(ti2-

B 2H 5)].(M = Ru, Os) (Figure 12.) in yields as high as 94% (Equation (29)).

THF K2[M(CO)4] + 3THF-BH3 ------K[M(CO)4(ti2-B2H5)] + KBH4 + 3THF (29)

(M = Ru, Os)

The formation of products is slow at -78°C but the reactions are complete in

less than three hours at room temperature. Qualitatively, the observed

rates of the reactions in Equation (29) (based on reaction time) from fastest

to slowest is Fe > Ru > Os. This is in accord with the proposed nucleophilicity

ordering for the anion [M(CO)4[2' (M = Fe, Ru, Os) (7). When the solvent is

removed from the reaction system in Equation (29), an oily complex

remains in the flask. This oil is probably due to the THF solvating the potassium counter ion of the K[M(CO)4(ti2-B2H5)] complex. The solvate can be removed by pumping in vacuo, for a long period of time or by dissolving

35 Figure 12. Proposed Structure of [M(CO)4(ti2-B2Hs)]' M = Ru, Os.

the oily complex in a more volatile ether and removing the solvent.

Dimethyl ether has the advantage of having a significant vapor pressure at

-78°C and if an intimate mixture of dimethyl ether and hexane are used the dimethyl ether can be removed at low temperature leaving a precipitate in the remaining hexane.

The compounds K[M(CO)40n2-B2H5)] (M = Ru, Os) decompose readily in the presence of air or moisture while in solution or the solid state. The relative stabilities of the K[M(CO)4(t|2-B2H5)] decrease in the order of Fe £ ♦* * - Os » Ru. A similar stability ordering has been observed for the anions

[HM(CO)4]' (M = Fe, Ru, Os) (11). The osmium salt is stable in THF for several days at room temperature and can be stored indefinitely in an inert atmosphere. The ruthenium compound shows noticeable decomposition in

THF at room temperature after two to three hours. The major decomposition products of the ruthenium compound are hydrido ruthenium complexes 37

which do not contain boron. If care is taken during the synthesis of

K[Ru(CO)4(ti2-B2H5)], and the amount of time the product is in solution is kept to a minimum, it can be made in the pure form. The stability of

K[Ru(CO)4(ti2-B2H5)l is enhanced in the solid state and it may be stored as a solid, in an inert atmosphere and at -40°C without noticeable amounts of decomposition after several weeks. The compounds K[M(CO)4(ti2-B2H5)] (M

= Ru, Os) are soluble in ethers and CH3CN while being insoluble in CH2CI2 and hydrocarbon solvents.

As indicated by Equation (29) there is a 1:1 relationship between the metal carbonylate added and the KBH4 recovered and a 3:1 relationship between K2 [M(CO)4] and THF-BH3. This has been demonstrated for the analogous compound K[Fe(CO)4(q2-B2H5)] in an elegant stoichiometry study conducted by Medford (81) in which an excess of THF*BH3 was added to

K2[Fe(CO)4] (Equation (30)). After the reaction was complete the excess

THF-BH3 was measured as the (CH3)3P*BH3 adduct (Equation (31)).

K2[Fe(CO)4] + XTHFBH3 ------►

K[Fe(CO)4(q2-B2H5)] + KBH4 + (X-3)THFBH3 (30)

THFBH3 + P(CH3)3 ------► (CH3)3PBH3 + 3THF (31)

It is interesting to note that the tetracarbonylates of group 8 will not form metallaboranes with more than two boron atoms under the conditions employed in this study. Thus anything in excess of a 3:1 ratio of

THF-BH3 :K2 [M(CO)4] can be recovered. This stoichiometry was also 38

confirmed in the present study. If the ratio of THF-BH3:K2[M(CO>4] is less

than 3:1 the result is diminished yields of K[M(CO)4(i)2-B2 Hs)] and

unreacted K2[M(CO)4] can be detected by infrared spectroscopy.

The driving force for reaction (29) is the precipitation of KBH4. The

KBH4 is insoluble in THF and the anions K[M(CO)4Cn2-B2H5)] (M = Fe, Ru, Os)

are soluble. The salts Na[M(CO)4Cn2-B2H5)] (M = Fe, Ru, Os) can be prepared

from the carbonylates Na2 [M(CO)4] but the compounds are impure because

of the side reactions in Equation (32).

THF Na2[M(CO)4] + THFBH3 ► Na[M(CO)4(Ti2-B2H5)] + NaBILj + 3THF (32a)

THF Na BH4 + 2THF BH3 ------► NaB3Hg + 2THF + H2 (32b)

Since the sodium borohydride formed (Equation (32a)) is soluble in THF, it

reacts with the THF*BH3 to form the sodium octahydrotriborate anion, B3Hs‘

which is also THF soluble. This produces a reaction mixture containing the

soluble salts Na[M(CO)4(ti2-B2H5)], NaBH4 and NaB3H8, thus isolation of the

metalladiborane is difficult to achieve.

The anions K[M(CO)4(ti2-B2H5)] (M = Ru, Os) undergo metathesis

reactions using PPNC1, PPI14X (X = Cl, Br) or AsPh4Cl in CH2CI2 according to

Equation (33). 39

CH2C12 K[M(CO)4(ti2-B2H5)] + PPNC1 ------► PPN[M(CO)4(tl2-B2H5)] + KC1 (33) Room Temp.

Since the alkali metal anions form solvates with THF, performing the

metathesis in CH2C12 prevents the formation of an oil. The metathesis salts

are soluble in CH2C12 but become insoluble in diethyl ether. The stabilities

of these metalladiboranes are enhanced upon metathesis to a large bulky

cation. When the metathesis salts was placed in contact with diethyl ether,

hexane or pentane the crystalline solid became oily and adhered to the

sides of the reaction flask. Thus attempts to grow crystals at room

temperature resulted in this oily solid. There was a modest amount of

success growing crystals at -78°C but when the crystal grower warmed

above -78°C the crystals became opaque and oily.

Infrared Spectra

The solution infrared spectra of K[M(CO)4(q 2-B 2H 5)] and

PPN[M(CO)4 (ti2-B2H 5)] (M = Ru, Os) are shown in Figure 13. and the

absorptions are listed in Table 2. There are two absorbances due to B-H

terminal stretches and two due to B-H-B bridging absorbances. Similar

bands have been observed in compounds [Fe(CO)40l2-B2H5)]* (64, 80),

(Tl5-C5Hs)Fe(CO)2(Ti2-B2H5) (65) and the main group complexes (p.-NR2)B2H5

(82) and (p-Se(CH3)2)B2H5 (83). The compound K[Ru(CO)4(tj2-B2H5)]

exhibits four carbonyl stretches at 2056 (w), 2004 (vs), 1978 (s), and 1956 (s) cm*1. The compound K[Os(CO)40i2-B2H5)], is similar to K[Fe(CO)4(q2-B2H5)], 40

90 —

SO — <0 —

30 — 20 —>

2600 1900 Wovenumbers

Wovenumbers

Figure 13. Infrared Spectrum of K[M(CO)4(t\2-B2H5)J. a) M *Ru b) M s Os. Table 2. Infrared Spectra of Cn2-B 2 H 5 ) compound

Compound v b -h VCD VB-H-B Solvent K[Fe(CO)4d l2-B2H5)] 2450 (m), 2400 (m), 2030 (w), 1943 (vs), 1845 (w), 1655 (w) THF 1927 (s)

K[Ru(CO)4(n 2-B2H5)] 2469 (m), 2426 (m), 2056 (w), 2004 (vs), 1850 (w), 1627 (w) THF 1978 (s), 1956 (s),

K[Os(CO)4(T12-B2H5)] 2433 (m), 2399 (m), 2057 (w), 1961 (vs), 1852 (w), 1688 (w) THF 1921 (s),

CpFe(CO)2(Ti2-B2H5) 2492(m), 2435 (m) 2045 (vs), 1990 (vs) 1892(w), 1698 (w) CH2C12

CpRu(CO)2(ri2-B2H5) 248 8(m), 2432 (m) 2053 (vs), 2001 (vs) 1908 (w), 1722 (w) c h 2c i2

HOs(CO)4Cn2-B2H5) 2498 (m),2433 (m) 2159 (m), 2092 (s) 1929 (w), 1703 (w) c h 2c i2 2073 (vs)

(CH3)Os(CO)4(ti2-B2H5) 2501 (m), 2437 (m) 2150 (m), 2128 (w.sh), 1918 (w), 1728 (w) c h 2c i2 2069 (vs), 2053 (s)

(|)3PAuRu(CO)4(tj2-B2H5) See Text 2104 (w, sh), 2078 (m) 1865 (w), 1678 (w) c h 2c i2 2931 (s)

3PAuOs(CO)4(T12-B2H5) 2462 (m) and 2422 (m), 2106 (m), 2065 (w, sh), 1903 (w), 1684 (w) c h 2c i2 2397 (m,sh) 2030 (vs) 42

in that it exhibits three stretches in the carbonyl region at 2057 (w), 1961

(s) and 1921 (s) cm'1. There is very little change in the infrared spectra

upon metathesis of the anions K[M(CO)4(ti2-B2H5)] (M = Ru, Os) with

PPh4Br, AsPh4Cl and PPNC1.

Nuclear Magnetic Resonance Spectra

The boron-11 NMR spectra of K[M(CO)4(t] 2-B2H 5)] and

PPN [M (C O )4(ti2-B 2H5 )] (M = Ru, Os) are in Figure 14. and Figure 15. and the

shift values have been given in Table 3. The spectra of the potassium salts

in THF yield a triplet at room temperature. This triplet collapses to give a

singlet upon ^ decoupling. When the salts are metathesized (PPN+ in this

case), and the NMR experiment is performed in CH3CN, the spectra show a

triplet of doublets. This is consistent with a structure in which the metal

has replaced a bridge hydrogen in the diborane structure. The triplet

arises from the spin coupling of two terminal hydrogens to one of the

equivalent boron atoms. The spectra are further split into a doublet from

the spin coupling of the bridge hydrogen. Proton decoupling of these

resonances causes the signals to collapse into a singlet. The NMR shifts

move upfield in the boron-11 spectra of [M(CO)4(q2-B2H5)]' upon replacing

the metal (M) with iron, ruthenium, and osmium. This trend might reflect

the electron rich character of the metal center.

The resolution of the boron-11 NMR spectra seems to be a function of counterion because the coupling of the bridge hydrogen can only be resolved in a metathesis salt. This may be rationalized by considering the 43

)

j -10 -15 -20 -25 PPM

L 1 x -5 -10 -15 -20 -25 -30 -35 -40 PPM

Figure 14. Boron-11 NMR Spectrum of ») PPN[Ru(CO)4(ti?-B2H5)] in CH3CN. b) K[Ru(C0 )4(t| 2-B 2H5)] in THF. c) K[Ru(CO)4(ti2-B2H5)] *H Decoupled in THF. 44

-I ------1------1------1------r — 1------1 ------■------T- •5 -*0 *15 -JO -Mppm -JO 05 •« -45

—I______I _ _ i _ _J ______» ______i |______|_ ~5 -JO -15 -20 -25 -30 -35 -40 PPM

Figure 15. Boron- II NMR Spectrum of i) PPN(Os(CO>4

Compound ______Jb -H(Hz)_____ JB-H-BfHzl Jhh(Hz)______Solvent, ______Temp. K[Fe(CO)4(Tl2-B2H5)l -15.4 112 26 26 THF Room

K[Ru(CO)4(7l2-B2H5)] -18.4 100 27 26 THF Room

K[O s(C O )4 (ti2-B 2 H 5 )] -24.0 116 35 35 THF Room

CpFe(CO)2(il2-B2H5) -6.5 117 26 7.0 CH2Cl2 Room

CpRu(CO)2(Tl2-B2H5) -11.2 119 36 6.9 CHCI3 Room

HR u (C O )4 ( ti2 -B 2 H 5 ) -12.4 101 CH2CI2 -10°C

HO s(C O )4 ( t| 2 -B 2 H 5 ) -14.4 104 32 CH2CI2 Room

(C H 3 )O s (C O )4 (t12 -B 2 H 5 ) -8.0 105 26 CH2C12 Room

03PAuFe(CO)4(ti2-B2H5) -12.1 CHCI3 Room

^ 3 P A u R u ( C O )4 (ti2 -B 2 H 5 ) -14.9 CHCI3 Room

4*- 46

nature of boron-11 NMR spectra. Boron-11 NMR is very symmetry

dependent. This is due to the quadrupole moment of the 1 *B nucleus. This

moment gives the boron nucleus an efficient means to relax which results

in very short relaxation times. The faster the relaxation rate, the less

"time" it has to observe the coupling of the surrounding atoms. This also

causes the broadness observed in the 11B NMR spectrum. One way to

increase the resolution in the boron-11 NMR experiment is to perform the

experiment at higher temperatures (84). This essentially enables the

molecules to tumble in solution and reduces the electric field gradient

around the nucleus. This may help explain the resolution observed in the

boron-11 NMR of [M(CO)4(ti2-B2H5)]\ In the compounds K[M(CO)4(ti2-

B2H5)] (M = Ru, Os) the potassium counter ion may be ion paired to a

carbonyl which would result in the reduction of symmetry in the molecule.

This should have an adverse effect on the resolution of the boron-H NMR

spectra. In the compounds (PPN)[M(CO)4Cn2-B2H5)] (M = Ru, Os) the PPN+

counter ion is too large to ion pair, so it should have no effect on the

symmetry of the molecule. This is evident by the boron-11 NMR spectra.

Following this rationale, a high temperature boron-11 NMR spectrum

should resolve the coupling of the bridge hydrogen in the compounds

K[M (CO)4(ti2-B 2H5)] (M = Ru, Os). Since the compound K[Ru(CO)4(i)2-B2H5)]

is somewhat temperature sensitive the anion K[Os(CO)4(tj2-B2H5)] was selected. The results are seen in Figure 16. The observance of the coupling of the bridge hydrogen is evident at 60° C. 47

60*C

-—I------.— .— I------1. — .— I _____ I___ .___ , I .... I . -16.0 -18.0 -20.0 -22.0 -24.0 -26.0 -28.0 PPM

Figure 16. High Temperature Boron-11 NMR of K[Os(CO)4(ti2-B2H5)] in THF. 48

During high temperature boron-11 NMR experiments of the

compounds K[Os(CO)4Cn2-B2H5)] and (PPN)[M(CO)4Cn2-B2H5)] no evidence

was observed for fluxional behavior involving the interconversion of

bridge and terminal hydrogens. This result can be justified by comparison

with the reported boron-11 NMR of the compound (CH3)2NB2H5. It was

determined that the fluxional behavior involving the interconversion of

bridge and terminal hydrogens in the boron-11 NMR of the compound

(CH3>2NB2H5 is solvent assisted (82). The fluxionality is maximized in

solvents which are good Lewis bases. The compounds [M(CO)4(q2-B2H5)]‘

(M = Ru, Os) have a negative charge as a deterant to such solvent assisted

exchange, as well as the strength of the M-B bonding. Additionally, the

resolution of the boron-11 NMR of (PPN)[M(CO)4(q2-B2H5)] is actually

enhanced in CH3CN as compared to CH2CI2.

The proton NMR spectra for [Os(CO)40n2-B2H5)]’ is pictured in

Figure 17 (Table 4.). The spectrum of the ruthenium compound is similar.

The spectra revealed a quartet in the B-H terminal region of relative area

four. The quartet is due to the spin coupling of one boron-11 nucleus to one of the equivalent hydrogens. The broad resonance up field of the quartet is due to the bridge hydrogen and is of relative area one. The bridge hydrogen is spin coupled to two boron-11 nuclei but the septet is not resolved. When these signals are boron-11 decoupled the quartet collapses into a sharp doublet and the broad bridge resonance collapses into a poorly resolved quintet. The doublet originates from the spin coupling of the bridge hydrogen to the terminal hydrogens and the quintet i i i i i i i i i i i i r 3 2 1 0 -1 -2 -3 -4 -5 -6 -7 -8 PPM

i // 1.8 1.6 1.4 1.2 -6.6 -8.8 -7.0 PPM

Figure 17. Proton NMR of K[Os(CO)4(ti2-B2H5)] in THF. a) n B Coupled, b) **B Decoupled. Table 4. ^{^B} NMR Spectra of the Cn2-B 2 H 5 ) Compounds

Compound B-H B-H-B M-R Solvent Temp. K [Fe( CO)4(T] 2-B 2H5)] 1.80 -5.17 -- (CD3)20 -40°C

K[Ru(CO)4(T1 2-B2H5)] 1.56 -6.28 -- THF-D8 Room

K[Os(CO)4(Tl2-B2H5)] 1.45 -6.78 -- THF-D8 Room

CpFe(CO)2(n2-B2H5) 2.73 -5.33 5.0 (R = Cp) CD2C12 Room

CpRu(CO)2(i12-B2H5) 2.53 -6.12 5.39 (R = Cp) c d q 3 Room

HRu(CO)4(tl2-B2H5) 2.22 -5.12 -7.51 (R = H) CD2CI2 -70°C

HOs(CO)4(ti2.B2H5) 2.50 -6.09 -8.56 (R = H) CD2C12 Room

(CH3)Os(CO)4(n2-B2H5) 2.80 -5.51 0.324 (R = CH3) CD2CI2 Room

(j>3PAuRu(CO)4(Tl2-B2H5) 2.49 -3.99 --- CD2CI2 Room

(}>3PAuOs(CO)4(ti 2-B 2H5) 2.31 -4.67 ... CD2CI2 Room 51

arises from the spin coupling of the four terminal hydrogens to the bridge

hydrogen. The proton NMR resonances move upfield for [M(CO)4(ti2-

B2H5)]' upon formally replacing the metal (M) with iron, ruthenium, and

osmium. This trend might reflect the electron rich character of the metal

cen ter.

The Carbon-13 NMR spectra can be seen in Figure 18. and the values

are in Table 5. The spectra consist of single resonances indicating the

equivalence of all carbonyls on the NMR time scale. These resonances are

invariant in the temperature range studied (+30°C - -90°C). The resonances

observed are consistent with that observed for HM(CO)4" (M = Ru (37), Os

(ID).

2. Preparation Cn5-CsH5)Ru(CO)2(Ti2-B2H 5).

The nucleophilic anion K[(ii5-C5H5)Ru(CO)2] reacts with (CH3)20-BH3

to form the metalladiborane (q5-C5H5)Ru(CO)2(tl2-B2H5) according to

Equation (34) (Figure 19.).

K[( ti5 -C 5 H 5 )R u (CO)2] + (CH3)20-BH3 ------►

(ti5 - C 5 H 5 )R u (C O )2 ( ti2 -B 2 H 5 ) + KBH4 (34)

This reaction is slow at -78° C and after 8-10 hours the product

(H5-C5H5)Ru(CO)2(ti2-B2H5) is evident from the spectra but inpurities from side reactions are present. These can be minimized by performing the 52

■— i— ■ 214.0 212.0 2t0.0 208.0 206 0 PPM

b )

200 19 0 100 170 160 PPM

Figure 18. Carbon-13 NMR Spectra for a) K[Ru(CO>4(i]2-B2H5)]. b) K[Os(CO)4(ti2-B2H5)] iu THF.

\ Table 5. 13C NMR Spectra of the (t|2-B2H5) Compounds

Compound 13C Jc .jj Solvent Temp.

K[Fe(CO)4(Tl2-B2H5)] 220 THF-D8 Room

K[Ru(CO)4Cn2-B2H5)] 210 THF-D8 Room

K[Os(CO)4(T12-B2H5)] 192 THF-D8 Room

HRu(CO)4(ti2-B2H5) 190.0,189.7 (d); 188.1; 186.1 17.7 cd2ci2 -80°C

HOs(CO)4(t]2-B2H5) 171.7, 171.5 (d); 169.0; 167.5 9.0 c d 2c i2 -80°C 54

reaction at -38°C for 3-4 hours. The nature of these side reactions is u n k n o w n .

As indicated by Equation (34) there is also 1:1 relationship between the metal carbonylate added and the KBH4 recovered and a 3:1 relationship between K[(ti5-CsH5)Ru(CO)2] and (CH3)20 BH3. As was observed with the tetracarbonylates K2[M(CO)4] (M = Fe, Ru, Os), if the ratio of (CH3)20 BH3 :

K[(ti5-C5H5)Ru(CO)2] is less than 3:1 the result is diminished yields of

(q5-C5H5)Ru(CO)2(Ti^-B2H5). The best yields were observed when the ratio of (CH3)20 BH3 : K[(ti5-C5H5)Ru(CO)2l was greater than 3 : 1.

The stability of (ti5-C5H5)Ru(CO)2(ti2-B2H5) is much less than the iron analog Cn5-C5H5)Fe(CO)20l2-B2H5) (65). The compound is thermally sensitive as well as air and moisture sensitive, and does not readily sublime.

It decomposes in the solid state after several hours. . It is soluble in CHCI3 and CH2CI2 but is insoluble in alkane solvents.

Infrared Spectrum

The solution infrared spectrum of (n5-CsH5)Ru(CO)2Cn^-B2H5) is shown in Figure 20. (Table 2.). There are two absorbances due to B-H terminal stretches at 2488 (m) and 2432 (m) cm"' and two absorptions due to the B-H-B bridge at 1908 (w) and 1722 cm"* (w). Similar bands have been observed in the compound (Ti5-C5H5)Fe(CO)2(n2-B2Hs) (65) (Table 2). There are two carbonyl stretches at 2053 (vs) and 2001 (vs) cm-1. The absorptions at 2025 and 1961 cm-1 which occasionally appear in the infrared spectrum are from unidentified decomposition products. 55

Figure 19. Representation of the structure of (q5-C5H5)Ru(CO)2(Ti2-B2H5)

Nuclear Magnetic Resonance Spectra

The boron-11 NMR spectrum exhibits the triplet of doublets which is characteristic of Cn2-B2H5) compounds. Upon proton decoupling of this signal a singlet is observed centered at -11.05 ppm (Figure 21.). This value is upfield relative to the analogue iron (q5-C5H5)Fe(CO)2(Tl2-B2H5), which resonates at -6.5 ppm (Table 3.). This is consistent with ruthenium being a more electron rich metal than is iron.

The proton NMR spectrum (Figure 22. and Table 4.) consists of a sharp resonance at 5.39 ppm due to the cyclopentadienyl ring (area five), a quartet in the B-H terminal region (area four) and a broad resonance in the B-H-B bridge region (area one). When the spectrum is boron-11 decoupled the quartet collapses into a sharp doublet and the broad resonance in the B-H-B bridge region collapses into a poorly resolved 100

90 —

80 ~

70 — I

60 —

50 —

40 —

30 —

— 20 _ r _ . 2600 2400 2200 2000 1800 Wovenumbers 0 \ Figure 20. Infrared Spectrum of 0t5-C5H5)Ru(CO)20l2-B2H5). 57

Figure 21. Boron-11 NMR Spectrum of a) *H Coupled, b) Decoupled. 58

...... • 'I"’ 4 .0 3 .0 2.0 1.0 -.0 ■1.0 -2.0 -3.0 -4.0 -5.0 -6.0 -7.0 PPM

a . to a.no

Figure 22. Proton NMR Spectrum of (ti5-C5 H5 )Ru(CO)2 Cn2-B2 H5 ). a) n B Coupled, b) 1!B Decoupled.

t 59

quartet. This is from the coupling of the bridge and terminal hydrogens,

Jhh- If the complex is allowed to sit at room temperature in solution for a short period of time signals at -11.08 ppm (the metal hydride region) and at

5.27 ppm (the cyclopentadienyl region) appear in the proton NMR spectrum. These resonances are characteristic of the compound

0l^-C5H5)Ru(CO)2(H). This was confirmed by the proton NMR spectrum of

Cn5-C5H5)Ru(CO)2(H) from an independent synthesis.

3. Synthesis of K[Cr(CO)4B3H8] from K2[Cr(CO)5] and THF-BH3

The reaction of K2[Cr(CO)5] with THF-B H3 does not follow the stoichiometry of the reactions of the group 8 dianions K2[M(CO)4] (M = Fe,

Ru, Os) with THF-B H3. Instead the product K[Cr(CO)4B3Hs] was isolated

(Figure 23, Equation (35)).

K2[Cr(CO)5] + THFBH3 ------►

K[Cr(CO)4B3H8] + KBH4 + CO + 3THF (35)

This reaction is complete in less than two hours at room temperature. The

KBH4 was characterized by infrared spectroscopy and the carbon monoxide was quantitatively evolved and characterized by mass spectrometry. The compound K[Cr(CO)4B3Hg] has been reported previously by Klanberg et. al.

(85) and was originally synthesized according to Equation (36). 60

o H

o O H

Figure 23. Representation of the Molecular Structure of [Cr(CO)4B3H8]

Cr(CO)6 + CsB3H8 ► Cs[Cr(CO)4B3H8] + 2CO (36)

Infrared spectrum

The solution infrared spectrum was taken in THF and is in agreement

with that reported in literature (85). This compound displays bands which

are due to B-H terminal absorptions at 2486, and 2435 cm-1, and carbonyl

absorptions at 2018 (m), 1980 (s), 1899 (vs), 1885 (s, sh), 1846 (s), 1825 (m, sh) and 1785 (w) cm '1.

Nuclear Magnetic Resonance Spectra

The boron-11 NMR spectrum (Figure 24.) consists of two broad singlets up field from (C2H5)20.BF3 (6 = 0.0 ppm). The resonance of area one at -1.8 ppm is assigned to the boron furthest away from the metal center (Bl in Figure 23.) and the resonance of area two at -41.0 ppm is assigned to the two borons which participate in the hydrogen bridge bonds w . A.

...... |.~.r. 20 10 0 -10 -20 -30 -40 -50 PPM

Figure 24. Boron-U NMR of K[CKCO)4B3Hg]. •) iH Coupled, b) l H Decouplfcd. 62

to the metal center (B2 in Figure 23 .). Both signals sharpen upon proton

decoupling, which indicates the fluxionality of all the terminal and bridge

hydrogens on the NMR time scale. These boron -11 NMR values are in

agreement with those reported in literature ( 85 ).

4 . The Reaction of Other Anions with Diborane

The anion K2[(ti5-C5H5) V(CO)3] reacts with THFBH3 at room

temperature and at low temperature to yield KBH4 as a reaction product.

The boron - 11 NMR spectrum of the reaction solution derived from

K2[0l5-C5H5)V(CO)3] does not contain a metallaborane product. Either the

coordination sphere of K2[(ti5-C5H5)V(CO)3] is too restricted to permit the

coordination of a boron to the metal center or the anion is simply too basic

and the KBH4 formed is a charge transfer product.

When the anion K[(Ti^-C5H5)Ni(CO)] reacts with L-BH3 (L = (CH3)20,

(CH3>2S) a borane complex is not formed (by boron -11 NMR). The reaction

appears to form a nickel hydride compound.

LBH3 K[(Ti5-C5H5)Ni(CO)] + L-BH3 ------► (7i5-C5H5)Ni(L)(H) + CO (37 )

L = Me20, Me2S

A mass spectrum of the evolved gas indicated a mixture of CO and H2 was present. Of the remaining boron products only L-BH3 could be identified by boron -11 NMR spectroscopy. The formulation of the compound as (rj5-

C5H5)Ni(L)(H) was assigned based on proton NMR spectroscopy. In the 63

proton NMR spectra the resonances due to the hydride appeared to be solvent dependent. When L = (CH3)20 the hydride resonated at - 14.9 ppm and when L = (CH3)2S the hydride resonated at - 19.6 ppm. The orgin of the hydride was not determined.

The anion K2[H2 R u4 (C O ) i 2] does not react with THFBH3 in THF at room temperature after a period of several days. The infrared spectrum only indicated the presence of starting material. It may be that the anion is not sufficiently basic to react with THF'B H 3 or that a weaker borane adduct is required.

B. Reactivity of K[M(CO)4 (t]2-B2H5)] M = Fe, Ru, Os.

1. Synthesis of HM(CO)4(q2-B2H5) (M = Ru, Os).

The Anions K[M(CO)4(q2-B2H5)] (M = Ru, Os) may be protonated according to Equation ( 38 ).

CH2CI2 K[M(CO)4(ti2-B2H5)] + HC1 ------► HM(CO)4(t12-B2H5) + KC1 (38 )

M = Ru, Os

The reaction was performed in CH2CI2 at - 78 °C or, alternatively, it may be performed in Me 20 at -78 °C. In Me2 0 , the removal of solvent at - 78 °C, after the completion of the reaction, was necessary to prevent decomposition.

Reaction ( 38 ) is heterogeneous and is complete in less then ten minutes. 64

When THF was used in place of CH2CI2 the product HM(CO)4(ti 2-B2H5) was

not observed to be a reaction product. The reaction solution contained

THF-BH3 (as identified by its boron -11 NMR spectrum).

There is a 1 : 1 relationship between the K[M(CO)4(t| 2-B2H5)] and HC 1.

In experiments where an excess of 1 equivalent of HC 1 was added, the

unreacted HC 1 was recovered and measured. This confirmed the

stoichiometry in Equation ( 38 ). Only strong acids could be used for this

protonation, though the acid strength was not the critical factor for a

successful protonation. The strength of the acids conjugate base was most

important. These strong conjugate bases decompose the the protonated

product by attacking either the boron ligand or the metal center. This type

of base attack is discussed in Section III. A. 3.

The compound HOs(CO)4(tj 2-B2H5) slowly decomposes at room

temperature while the compound HRu(CO)4(q 2-B2H5) slowly decomposes

above - 80 °C. The decomposition products are H2 and B2H6. The product of

the reaction of HC 1 and K[Fe(CO)4(t| 2-B2H5)] was reported to decompose

above - 120° C ( 1). Therefore the observed thermal stabilities of the

protonated metalladiboranes are Os » Ru > Fe.

Infrared Spectra

The infrared spectrum of the osmium complex HOs(CO)4(ii 2-B 2H 5) was the only one obtained, due to the thermal sensitivity of these hydrido complexes. The infrared spectrum of HOs(CO)4(t) 2-B2H5) (Figure 25. and

Table 2.) consists of two bands in the B-H terminal region at 2498 (m) and 80 —

70 —

60 —

50 —

40 —

30 — I

20 —

• 2600 2400 2200 2000 1800 1600

Wavenumbers

Figure 25. Infrared Spectrum of HOs(CO)4(ti2-B2H5) in CH2CI2.

ON 66

2433 (m) cm' 1 and two bands in the B-H-B bridge region at 1929 (w) and

1703 (w) cm'1. These bands are consistent with the neutral (ti 2-B 2 H s )

complexes (ti^-C5H5)M(CO)2(i1^-B2H5) M = Fe, Ru. There are three

absorptions which are due to carbonyl stretches at 2159 (m), 2092 (s) and

2073 (vs) c m '1.

Nuclear Magnetic Resonance Spectra

The boron -11 NMR spectra of HM(CO)4(q2-B2H5) (M = Ru, Os) are

shown in Figure 26. and 27 . and the shift values and coupling constants are

given in Table 3. Both spectra exhibit the triplet of doublets that is

characteristic of (ti2-B2Hs) complexes. The fact that a triplet of doublets is

observed indicates that proton occupies a coordination site in which the

symmetry of both borons is conserved. Both borons must be in symmetric

environments to observe a triplet of doublets in the boron - 11 NMR

spectrum. Both signals have shifted down field from the starting anions

K[M(CO)4(ti2-B2H5)] (M = Ru, Os). The compound HOs(CO)4(q 2-B 2 H s)

resonates almost 10 ppm down field from K[Os(CO)4(ti 2-B2H5)] and the

compound HRu(CO)4(t| 2-B2H5) resonates almost 6 ppm down field from

K[Ru(CO)4(tj2-B2H5)]. This is consistent with removing electron density

from the metal center upon protonation.

The proton NMR spectra of HM(CO)4(ti 2-B2H5) (M = Ru, Os) are shown in Figure 28 . and 29. (Table 4.). As expected there is a quartet in the B-H terminal region (area four) and a broad resonance in the B-H-B bridge region (area one). Both signals collapse upon 11B decoupling to give sharp 67

■ ■ j I ■ j ____ i____ -l_-i i i » 1 i.. «- -i—i—t t —l 0 -5 -10 -15 -20 -25 PPM

Figure 26. Boron-11 NMR of HRu(CO)4 (ti2-B2H5) at -10°C in CD 2 CI2 . a) 1H Coupled, b) 'H Decoupled. 68

. 1 I . .. I , . . I. . . I - j . I.. . I . i . I . i ■ I . i - I... i . I > t . K .i . 1 > x -2.0 -4.0 -6.0 -8 .0- 10.0-12.0- 14.0-16.0-10.0-20.0-22.0-24.0-26.0-20.0 PPM

Figure 27. Boron-11 NMR of HOs(CO)4 (ti2-B2 H5 ) in CD2CI2 . a) *H Coupled, b) 'H Decoupled. 69

x xx x x XX 1 j 6,0 6.0 4.0 3 .0 2.0

Figure 28. Proton NMR of HRu(CO)4 (ti^-B2H5 ) at -70°C in CD 2 CI2 . a) 11B Coupled, b) l l B Decoupled. 70

/\ ______/L_

X A L X A X A ___ l _ A X A . ...1. . A X A 8.0 4.0 2.0 oTo - 2 .0 -4.0 - 8.0 PPH

Figure 29. Proton NMR of HOs(CO)4(ti2-B2 H5 ) in CD2 CI2 . ») l l B Coupled, b) U B Decoupled. 71

singlets. There is also a resonance in the mononuclear terminal hydride

region (area one) for both the ruthenium and osmium compounds. These

hydride resonances are consistent with those reported for the neutral

compounds H2M(CO)4, (M = Ru, Os) (6).

The carbon-13 NMR spectrum of HRu(CO)4(q2-B2H5) is shown in

Figure 30. (Table 5.). The proposed structure is pictured in Figure 31. The

carbon-13 NMR spectrum of HRu(CO)4Cn2-B2H5) displays three signals of

relative area 1:2:1. This is consistent with a the hydride being cis to the

(t]2-B2H5) ligand. If the hydride were trans to the Cn2-B2H5) ligand there would be two signals of equal intensity originating from the two sets of inequivalent carbonyls. If the (ti2-B2Hs) ligand is free to rotate there would only be one resonance. In the spectrum of HRu(CO)4(q2-B2H5) the signal furthest down field is a doublet of approximate area one which collapses to give a singlet upon proton decoupling. This is consistent with an axial carbonyl trans to a hydride ligand (87) . Moving upfield, the resonance of approximate area two is from the two chemically equivalent carbonyls which are trans to one another. The final resonance of approximate area 1, which is furthest upfield, is from the carbonyl trans to the (n2-B2H5) ligand. The compound HRu(CO)4(q 2-B2Hs) was found to slowly decompose at -80°C. The resonance that appears at 189.2 ppm in the carbon-13 NMR spectrum of HRu(CO)4(q2-B2H5) is from a decomposition product at which grows in intensity with time -80°C. The carbon-13 NMR spectrum of HOs(CO)4(q2-B2H5) was found to be similar to HRu(CO)4(q2-

B2H5) with the exception that the coupling from the hydride trans to the 72

a) ^ V t v / V

b ) Uf

r™ ’—"T -..... I rT-” ,^ T,| 192.0 190.0 188.0 186.0 184.0 PPM

Figure 30. Caibon-13 NMR of HRu(CO)40l2-B2H5) at -80°C. a) *H Coupled, b) *H Decoupled. Figure 31. Proposed Structure of HM(CO)4(ti2-B2H5> (M = Ru, Os). 74

axial carbonyl was significantly less than that found in the compound

HRu(CO)4(t]2-B2H5). The spectrum of HOs(CO)4(ti2-B2H5) was found to be

static from 30° C to -90° C. The values of the chemical shifts of the

compounds HM(CO)4(ti2-B2H5) (M = Ru, Os) are consistent with other six

coordinate mononuclear ruthenium and osmium tetracarbonyls (e. g.

H2M(CO)4 and M(CO)4l2: (M = Ru, Os) (88)).

2. Synthesis of (CH3)Os(CO)4(ti2-B2H5)

The Anion K[Os(CO)4(ti2-B2H5)) may be methylated according to

Equation (39).

K[Os(CO)4(n2-B2H5)] + XS(CH3)30BF4 ------►

(CH3)Os(CO)4(ti2-B2H5) + KBF4 (39)

The reaction is typically complete in less than four hours with no evolution of a non-condensable gas. The methylating agent in Reaction (39),

(CH3)3OBF4, may be substituted with CH3S 03F. The advantage is CH3S03F is volatile and is efficiently pumped away when an excess is used. There is no difference in methylation efficiency for this system between the two methylating agents.

Unlike the protonation chemistry of K[Os(CO)4(ti2-B2H5)] this system will not react heterogeneously. Neat reactions in CH3S 0 3F do not react appreciably and what does react formed mixtures of products. This may be the result of the methyl group being more sterically bulky than a proton 75

or the methylating agents (CH3)30BF4 and CH3SO3F being more sterically

bulky than HC1. The compound (CH3)Os(CO)4(ti2-B2H5) has similar

solubility as the compound HOs(CO)40n2-B2H5) and is air, moisture and

thermally sensitive.

The stability of (CH3)Os(CO)4(ti 2-B2H5) is less than that of the

protonated analog (H)Os(CO)4(ti2-B2H5). Methylene chloride solutions of

(CH3)Os(CO)4(n2-B2H5) typically decompose in less than one hour at room

temperature to yield CH4 and B2H6.

Infrared Spectrum.

The infrared spectrum of (CH3)Os(CO)4(ti2-B2H5) (Figure 32., Table 2.)

consists of two bands in the B-H terminal region at 2501 (m) and 2437 (m)

cm-1 and two bands in the B-H-B bridge region at 1918 (w) and 1728 (w)

cm '1. These bands are consistent with the neutral (ti2-B2Hs) complex (n5-

C5H5)Ru(CO)2(tl2-B2H5) (Section II. A. 2 ) and with (H)Os(CO)4(ti2-B2H5)

(Section II. B. 1.). There are four carbonyl absorptions at 2150 (m), 2128

w,sh), 2069 (vs) and 2053 (s) cm'1.

Nuclear Magnetic Resonance Spectra

The boron-11 NMR spectrum (Figure 33., Table 3.) consists of a triplet of doublets which upon proton decoupling gives a singlet centered at -8.0 ppm. This represents a 16 ppm shift down field from starting K[Os(CO)40l2-

B2H5)] which is consistent with removing electron density from the osmium upon complexation by the methyl group. It is interesting 100

80 —

70 —

30 — 1

* 20 —

10 “ 2600 2400 2200 2000 1800 Wavenumbers Os Figure 32. Infrared Spectrum of (CH3)Os(CO)4(ti2-B2H5) in CH2CI2. 77

T-T-r T"n i i i | i ■ T 1 < I 1 »'■"■ I 1 ' lT * I ' ■•’ r ' I ’■ 20 is 10 S - 5 -1 0 -1 5 -20 -2 5 -3 0 -35~ PPM

Figure 33. Boron-11 NMR of (CH3)0 «(C0 )4 (Ti2 -B2 H5 ).in CD2CI2 . a) *H Coupled, b) Decoupled. 78

to note that the boron-11 NMR spectrum of the compound HOs(CO)4Cn2-

B2H5) resonates 10 ppm down field from K[Os(CO)4(n2-B2H5)] while the boron-11 NMR spectrum of the compound (CH3)Os(CO)4Cn2-B2H5) resonates

16 ppm down field from K[Os(CO)4(n2-B2Hs)]. This is probably representative of CH3+ being more electron withdrawing than a proton.

The resonance which appears at 18.0 ppm is from B2Hg, which is formed as a decomposition product of (CH3)Os(CO)4Cn2-B2H5) in solution.

The proton NMR spectrum (Table 4.) exhibits resonances in the B-H and B-H-B regions which are similar to (H)Os(CO)4(t]2-B2H5). The **B decoupled proton NMR spectrum consists of a singlet (area four) centered at 2.80 ppm (B-H treminal), a singlet (area three) centered at 0.324 ppm

(CH3) and a singlet (area one) centered at -5.51 ppm.

3. Synthesis of (PPh3)AuM (CO)4(ri2-B2H5) (M = Fe, Ru, Os).

The idea of reacting the compounds K[M(CO)4(t|2-B2H5)] (M = Fe, Ru,

Os) with metal complexes to synthesize metallaboranes with two or more metals is an attractive one. In light of the well behaved protonation chemistry the most logical choice as a starting point for this type of investigation is using the "pseudo proton" reagent, [Ph3PAu]+. Since the compounds K[M(CO)4(ti2-B2H5)] (M = Fe, Ru, Os) protonate at the metal center they should form complexes with PI13PAUCI. Also the inductive effects of a metal-metal bond could make these compounds more stable than the protonated analogues. The Compounds (PPh3)AuM(CO)4(ti2-B2H5) 79

(M = Fe, Ru, Os) can be synthesized from K[M(CO)4(n2-B2H5)] (M = Fe, Ru, Os) according to Equation (40).

K[M(CO)4(ti2-B2H5)] + (PPh3)AuCl ------►

(PPh3)AuM(CO)4(ri2-B2H5) + KC1 (40)

M = Fe, Ru, Os

These triphenyl phosphine gold compounds are more stable than their protonated analogs but have the same stability ordering Os > Ru > Fe. The source of instability seems to be different than those of the protonated analogs. The only decomposition product identified by 11B NMR is

Ph3P*BH3. This also is the only boron containing product when

(PPh3)2CuBr is reacted with K[M(CO)4(q2-B2H5)] (M = Fe, Ru, Os). This is probably the result of ligand exchange on the gold or copper metals. The free PPh3 could attack the boron ligand which would generate Ph3P-BH3.

The compound (PPh3)AuOs(CO)4(q2-B2H5) was synthesized in THF at room temperature. It is a brown-yellow solid which slowly decomposes in solution or in the solid state. The ruthenium compound

(PPh3)AuRu(CO)4Cn2-B2H5) can be synthesized in THF at room temperature but better spectra was obtained if the synthesis was performed in Me20 at

-78°C. The iron compound (PPh3)AuFe(CO)4(Ti2-B2H5) was synthesized in

(CH3)20 at -78°C and was tipped directly into an NMR tube. The yellow- brown osmium compound is moderately stable as a solid, which slowly decomposes over a period of time. The ruthenium compound is red-brown 80

and decomposes at room temperature in solution or in the solid state in less than two hours. The iron compound is a chocolate brown color and rapidly decomposes at room temperature. Solutions of (PPh3)AuFe(CO)4(n2-B2H5) decompose at room temperature in less than 15 minutes.

Infrared Spectra

The infrared spectrum of only the osmium and the ruthenium complexes (Figure 34., Table 2.) were obtained due to the thermal sensitivity of these triphenyl phosphine gold complexes. The infrared spectrum of

PPh3AuOs(CO)4(ii2-B2H5) consists of three bands in the B-H terminal region at 2462 (m) and 2422 (m), and 2397 (m,sh) cm'1 and two bands in the B-H-B bridge region at 1903 (w) and 1684 (w) cm '1. The v b -H a t 2422 cm'1 is from

Ph3P-BH3, which is a decomposition product of PPh3AuOs(CO)4Cn2-B2H5) in solution. There are three carbonyl absorptions at 2106 (m), 2065 (w, sh) and 2030 (vs) cm-1. The infrared spectrum of PPh3AuRu(CO)40i2-B2H5) is similar to the osmium compound but is less resolved probably because of rapid decomposition in solution. A broad ill-resolved absorbance is observed in the B-H terminal region, probably due to overlapping

Ph3P-BH3. There are two resolved absorbancesin the B-H-B bridge region at 1865 (w) and 1678 (w) cm'1. The CO region gives three resolved absorbances at 2104 (w, sh), 2078 (m) and 2931 (s) cm '1. 100

6 0 H

40 — I

3 0 — 1

22 -H

1 r 26 0 0 2400 2200 2000 1800 1600 Wovenumbers

100

8 0

3 0 — !

20 - I

2400 2200 2000 1800 Wovenumbers

Figure 34. Infrared Spectrum of (Ph3 PAu)M

Nuclear Magnetic Resonance Spectra

The boron-11 NMR spectra of (PPh3)AuM(CO)4(,n^-B2H5) (M = Fe, Ru,

Os) (Figure 35., Table 3) consist of a broad, poorly resolved triplet which upon proton decoupling sharpens to give a singlet. The shift values are

down field from starting materials K[M(CO)4(t^2-B2H5)] (M = Fe, Ru, Os)

which is consistent with removing electron density from the metal center upon reaction with the PPh3Au+ fragment. Evidence that this boron-11

NMR resonance is due to the (t]^-B2H5) ligand was provided by the high temperature NMR experiment (Figure 36.) of (PPh3)AuOs(CO)4(q2-B2H5).

The terminal B-H coupling was evident at 60°C. In view of the temperature needed to resolve the B-H terminal coupling, it was not reasonable to assume the compound would survive the high temperature which would be required to resolve the bridge B-H-B coupling. Evidence for the existence of the bridge hydrogen was provided by the proton NMR spectrum (below).

The proton NMR spectrum of PPh3AuOs(CO)4(ri^-B2H5) is shown in

Figure 37. it consists of a large resonance in the phenyl region, a poorly resolves quartet in the B-H terminal region and a broad resonance in the

B-H-B bridge region. The shift values are listed in Table 4. Since the bridge coupling in the boron-11 NMR spectrum could not be resolved the existance of the B-H-B resonance in the proton NMR provides evidence that the 0i2-B2H5) ligand is still in tact. 83

•ii -i* *i •i© -i»

Figure 35. Boron-11 NMR of (Ph3PAu)M(CO>4(ii2-B2Hs). •) M - Fe b) M = Ru. c) M = Os. 84

60«C

40«C

JO«C

r I I ~I— 1 -15 -2 0 -3 0

Figure 36. High Temperature Boron-11 NMR of(Ph3 PAu)Os(CO)4 (n2 >B2 H5 ) in CDCI3. 85

• 7 ■■ — J | ■ 1 ' . ■« > ...... ■I " " . -■ ~ -■ . ■ VI. ! .. I - * m t mm *•* 2*0 l.o -.0 *1.0 -*.0 -J.0 -4.0 -5.0 -5,0 *P*

Figure 37 . Proton NMR of (Pta3PAu)0$(C0)4(fl2-B2H5) in CDjCli. 86

4 . The Reaction of [Os(CO)4(ti2-B2H 5)]* with Other

Organometallic Halides

It was determined that [Os(CO)4(i]2-B2H5)]" would not react with the organometallic halides Cn^-C5H5)Fe(CO)2l or Re(CO)5l at room temperature.

[Os(CO)4(il2-B2H5)]- + (n5-C5H5)Fe(CO)2l ------► No Reaction (41)

[Os(CO)4(ti2-B2H5)]- + Re(CO)sI ------► No Reaction (42)

This may be the result of trying to add a sterically large electrophile to a complex which has a full coordination sphere. There is no doubt that the fragments Cn5-C5Hs)Fe(CO)2+ and Re(CO)s+ have more steric bulk than the electrophiles H+, CH3+ and PPh3Au+ which were shown in earlier sections to react with [Os(CO)4(ti2-B2H5)]". Another reason may be that these organometallic halides may not be electrophilic enough to react with

[Os(CO)4(ti2-B2H5)]\ The compound (i]^-C5H5)Fe(CO)2l does react with

(Os(CO)4(n2-B2H5)]' at elevated temperatures (ca. 60°C in toluene) but the reaction solution consisted of a complex mixture of compounds. Attempts to separate the mixture were unsucessful.

5. The Reaction of PPN[Os(CO)4(ti2-B2Hs)] with (M.-H)20s3(CO)io-

The reaction of (ti-H)20s3(CO)io with PPN[Os(CO)4(ti2-B2Hs)] in

CH2CI2 is slow at room temperature. After 24 hours of reaction time no 87

reaction was observed to occur by boron -11 NMR spectroscopy. When the compounds were reacted for one month starting material had completely disappeared and several resonances were present in the boron -11 NMR including one that could be assigned to the complex HOsg(CO)i7B. This assignment was based on the similarity of the boron -11 and proton NMR spectra to that of the complex HRu6(CO)i7B ( 89 ). The compound

HOs6(CO)i7B has a low-field boron -11 NMR resonance of 187 ppm and a hydride which resonates at - 19.S ppm in the proton NMR. Several attempts to isolate HOs6(CO )nB from the reaction mixture failed.

6. The reaction of [Os(CO)4Cn2-B2Hs)]\with Cr(CO)6*

The octahydrotriborate anion B3H8* can be considered an analog of the metalladiborane anions [M(CO)4(ti 2-B2H5)]-.(M = Fe, Ru, Os). This is based on the similarity in the valence structures of the two types of compounds

(see I and II below). The anion B3H8‘ can be considered a B2H5' anion which is donating electron density from a basic boron-boron bond to a BH3 group. In the case of [M(CO)4Cq2-B2H5)]* (M = Fe, Ru, Os) the fragment

M(CO)4 can formally replace the BH3 group in the B3H8' valence structure.

The reaction of B3Hs‘ with Cr(CO)6 ( 85 ) affords Cr(CO)4B3Hs‘

(Equation (36)). It was therefore of interest to determine if [Os(CO)4 (ti2-

B2H5)]' would function in an analogous manner to B3H8* in a reaction with

Cr(CO)6. 88

H H B (C0)40 s

I II

The compound [Os(CO)4Cn2-B2H5)]' with the potassium or the PPN+

counterion does not react with Cr(CO)6. This may be the result of the anion

[Os(CO)4(t)2-B2H5)]‘ not being nucleophilic enough to displace the

carbonyls on Cr(C0)6.

7. The reaction of [Os(CO)4(t)2.B2Hs)]‘ with Lewis Bases.

The bridge hydrogens of boron hydride compounds behave as

BrOnstead acids (H+) (90). An electron withdrawing Os(CO)4 group bonded

to a B2H5' fragment in the compound [Os(CO)4(t)2-B2H5)]“ should make the

bridge hydrogen somewhat acidic. It would be reasonable to assume that it

could be removed with the base KH to form the complex [Os(CO)4(BH2)2l2'-

An alternative product could be the addition of KH to form the compound

[Os(CO)4(BH3)2]2“. Parshall (11) reported the synthesis of Re(CO)s(BH3)2‘ from the anion Re(CO)s* and diborane (Equation (43)). 89

Re(CO)5- + 2THFBH3 ------► Re(CO)5(BH3)2“ (43)

The formation of the compound [Os(CO)4(BH3)2]2‘ would be interesting

because it is one of the proposed intermediates for the formation of

[Os(CO)4(ti2-B2H5)]' (see Section III. A. 1.). The two possible compounds

would be clearly distinguishable in the boron-11 NMR spectrum.

The anion [Os(CO)4(ti2-B2H5)]‘ with either the potassium or PPN+

counterion was found to be unreactive toward KH.

[Os(CO)4(n2-B2H5)]‘ + KH ------► No reaction (44)

When the reaction time was long (e. g. one week) a small amount of non-

condensable gas evolved. The gas was analyzed as H2 by mass spectrometry.

Unfortunately the boron-11 NMR spectrum indicated only the presence of

the starting material [Os(CO)4(ti2_B2H5)]'. An X-ray powder pattern of a

solid which precipitated from the reaction indicated only the presence of

KH. When the reaction was repeated using KHB(CH3)3, H2 is evolved more

rapidly but the boron-11 NMR spectra did not indicate the formation of

[Os(CO)4(BH2)2]2"- It may be that the B(CH3)3 in the reaction reacts with

[Os(CO)4(BH2)2]2’ because of it's high basicity and facilitates the i decomposition.

The reaction of diborane with sterically small Lewis bases (L) is known to cause symmetric cleavage to form L BH3 adducts (84,91,92). Since 90

the compounds K[M(CO)4(ii 2-B 2H5)] (M = Fe, Ru, Os) are formed in THF, and

B2H6 is cleaved symmetrically in THF, it is reasonable to assume the

presence of the metal in the bridge site strengthens the integrity of the

diboron fragment. The bonding in the (tj2-B2H5) fragment in the

K[M(CO)40n2-B2H5)] (M = Fe, Ru, Os) compounds must be stronger than in

B2H6. This may be due to the inherent strength of the M-B bonds.

Therefore a study of the interactions of K[M(CO)4(tj2-B2H5)] (M = Fe, Ru, Os)

with Lewis bases could give an indication of the degree to which the boron-

boron interaction is enhanced by the bonding of (ii2-B2Hs) to a transition

m etal.

The compounds K[M(CO)4(ti2-B2Hs)] M = Fe, Os arc unreactive toward triphenyl phosphine.

K[M(CO)4Cn2-B2H5)] + PPI13 ------*► No Reaction. (45)

M = Fe, Os

What is more interesting is the compounds K[M(CO)4(ti2-B2H5)] M = Fe, Os can be prepared from Ph3P-BH3.

K2[M(CO)4] + 3Ph3PBH3 ► K[M(C0)4(ti2-B2H5)] + KBH4 + 3PPh3 (46)

M = Fe, Os 91

This is a slow reaction which is typically incomplete after 48 hours. This reaction is the result of the anion [M(CO)4]2' being more nucleophilic than

P P h 3.

The more basic phosphine (CH3)3P was found to be unreactive with

[Os(CO)4(ti2-B2H5)]* with either the potassium or PPN+ counter ion when one equivalent of phosphine was used.

[Os(CO)4(n2-B2H5)]- + (CH3)3P ------► No Reaction (47)

If the reaction time was longer than 24 hours small amounts of

(CH3)3P-BH3 can be detected by boron-11 NMR spectroscopy. If an excess of two equivalents of (CH3)3P were used complete decomposition of starting material occured with reaction times longer than 24 hours.

C. The Synthesis, Characterization and Structure of Group 8

Bimetallic Dianions.

1. Na2[Os2(CO)8]

The synthetic strategy for the synthesis of the homobinuclear octacarbonylates M2(CO)s2' (M = Ru, Os) has been worked out by

Bhattacharyya (Equation (48))(32, 33).

Na2[M(CO)4] + C 02 M(CO)5 + Na2[M(CO)4] + Na2C0 3 (48a) 92

M(CO)s + Na2[M(CO)4] ------► Na2[M2(CO)8] + CO (48b)

(M = Ru, Os)

This method is based on the work of Cooper et. al.(33). When carbon dioxide is reacts with the anion [M(CO)4]2‘ in equimolar amounts, (Equation (48a)) one half equivalent of the anion is converted to M(CO)s (-78°C). The M(CO)s and [M(CO)4]2‘ subsequently react by warming the reaction mixture to room temperature (Equation (48b)). The compounds [M2(CO)8]2' (M = Ru,

Os) have been thoroughly characterized including determination of their molecular structures.

To this point a detailed description of the synthesis of the sodium salt of [Os2(CO)8]2" has not been described. The potassium salt was synthesized at elevated temperatures (60° C) which combined with the marginal solubility of K2[Os(CO)4] in THF provides for impure solutions of

K2[Os2(CO)8]. Since the Na2[Ru2(CO)8] was synthesized as a relatively pure compound using Na2[Ru(CO)4] in THF (according to Equation 21) it was then reasonable to assume the same may be true for the synthesis of

Na2[Os2(CO)8],

Following Equations (48a) and (48b) it was possible to synthesize

Na2[Os2(CO)8]. Comparatively, the synthesis requires less reaction time than does the synthesis of K2[Os2(CO)8] and the salt is more pure. There are still impurities from osmium anions of higher nuclearity but they are in reasonably small amounts. The compound Na2[Os2(CO)s] is soluble in THF 93

and acetonitrile, is insoluble in diethyl ether and hydrocarbon solvents and decomposes in methylene chloride. Through metathesis reactions • with

PPh4Br (in THF) (PPh4)2[Os2(CO)g] can be formed in higher yields than the does the metathesis of solutions of K2[Os2(CO)g], This is the result of the greater purity of Na2[Os2(CO)g] as compared to K2[Os2(CO)g].

S p e c tra

Infrared Spectrum

The solution infrared spectra of Na2[Os2(CO)s] (Figure 38 .) consist of three broad absorptions in the carbonyl region. The band symmetry and relative intensities is quite similar to Na2[Ru2(CO)g] which may be the result of the solution structure of both anions being similar. The broadness of the spectra is probably due to interactions with the polar solvent.

Nuclear Magnetic Resonance Spectrum

The carbon -13 NMR spectrum consists of a resonance at 196 ppm.

The appearance of a singlet is indicative of equivalence of all the carbonyl ligands on the NMR time scale. Other minor resonances appear in the spectrum of Na2[Os2(CO)g] which have been assigned to [Os3(CO)i i]2* and

[Os4(CO)i3]2'. In view of the inability to synthesize spectroscopically pure

Na2[Os2(CO)g], low temperature carbon-13 NMR could not be performed. 2200 2100 2000 1900 1800 1700 1600 Wavenumbers

Figure 38 . Infrared Spectrum of Na2fOs2(CO)8] in THF. 95

2 . Heterobinuclear Group 8 Dianions [MM'(CO)8l2"

(MM' = FeRu, FeOs, RuOs).

Preliminary results of extending the synthesis of the homobinuclear

dianions to include the group 8 heterobinuclear dianions was inconclusive

due to unconvincing spectroscopic evidence (36). Therefore the

development of the synthesis of heterobinuclear dianions of the iron triad

including definitive characterization of the compounds was essential.

The synthesis of the heterobinuclear dianions of the iron triad

[MM'(CO)8]2' (MM’ = FeRu, RuOs, FeOs) is based on a two step procedure. The

first involves the generation of the volatile group 8 pentacarbonyl M(CO)s

by using the method of Cooper et. al (33).

Na2[M(CO)4] +2C 02 ------:— ► M(CO)5 + Na2C03 (49a)

The pentacarbonyl, once generated, is then transferred to a flask

containing a different group 8 tetracarbonylate (in the dark). The

contents react to form the heterobinuclear dianion.

M(CO)5 + Na2[M'(CO)4] ------► Na2[MM'(CO)8] + CO (49b)

The Choice of M and M' is critical to the formation of these heterobinuclear dianions. Geoffroy (7) has determined the order of reducing ability, from highest to lowest, for [M(CO)4]2' is Os > Ru > Fe. Therefore the proper choice of M and M' are those listed below. 96

MM' Os Fe or Ru Ru Fe

This synthesis is never as pure as indicated by Equation (49). The major impurities are higher nuclearity mixed metal cluster dianions. If the synthesis is performed in a suitable vacuum ( < 10'^ Torr ) and care is taken to ensure the complete absence of light, the impurities can be kept to a minimum. The anions Na2[MM'(CO)8] (MM' = FeRu, RuOs, FeOs) are soluble in THF and acetonitrile, while they are insoluble in diethyl ether and hydrocarbon solvents. The anions Na2[MM'(CO)8] (MM' = FeRu, RuOs, FeOs) are sensitive to halogenated solvents. In the presence of halogenated solvents the heterobinuclear dianions decompose rapidly with the evolution of carbon monoxide gas.

The pure heterobinuclear dianions [MM'(CO)s]2* (MM' = FeRu, RuOs,

FeOs) were isolated using the metathesis procedure of Bhattacharyya (36).

The heterobinuclear dianions Na2[MM'(CO)8] (MM' = FeRu, RuOs, FeOs) were metathesized with PPh4Br to yield the pure salts (PPh4)2[MM'(CO)s]

(MM' = FeRu, RuOs, FeOs)

THF Na2[MM'(CO)8] + PPl^Br ------► (PPh4)2[MM’(CO)8] + 2NaBr (50)

MM1 *= FeRu, RuOs, FeOs 97

This metathesis (Equation (50)) in THF causes the precipitation of the salts

(PPh4)2[MM'(CO)8J (MM' = FeRu, RuOs, FeOs) while all other compounds of

nuclearity greater than two remain soluble. A simple filtration of the

reaction solution isolates the solids (PPh4)2[MM'(CO)8] MM' = FeRu, RuOs,

FeOs and NaRr on the frit while the impurities of higher nuclearity are

washed away. The anions (PPh4)2[MM'(CO)8] (MM* = FeRu, RuOs, FeOs) are

separated from NaBr by dissolution in acetonitrile. The anions

(PPh4)2[MM'(CO)8] (MM* = FeRu, RuOs, FeOs) are soluble in acetonitrile and

insoluble in THF, diethyl ether and hydrocarbon solvents.

Infrared Spectra

The solution infrared spectra of (PPh4)2[MM’(CO)8] (MM' = FeRu,

RuOs, FeOs) (Figure 39.) consist of two broad absorptions in the carbonyl region. The similarity of each of the spectra is may be the result of the solution structure being similar. Apparently the change of the metal centers in each of the compounds [MM’(CO)8]2" MM’ = FeOs, RuOs, FeRu may not cause enough of a reduction in symmetry to remove the degeneracy in the infrared spectrum. This observation has been observed in other dinuclear complexes (93). The broadness of the spectra is probably due to interactions with the polar solvent.

Nuclear Magnetic Resonance Spectra.

The shift values from the carbon-13 NMR spectra of the heterobinuclear dianions, (PPh4)2[MM'(CO)8l (MM' = FeRu, RuOs, FeOs), as well as the 98 a)

190O 1000 1700 1600 Vovenumbers ua b )

98 M

7» 88 si

28 2188 Vovenumbers

1600 1700 Vcvenumbers

Figure 39. Infrared Spectra of (PPh 4 ) 2 M M ‘(CO)g in CH 3 CN. a) MM* * FeRu. b) MM* « RuOs. c) MM 1 * F e O s . 99

Table 6. Carbon-13 NMR Spectra of (PPh4)2[M M '(C O )g] (MM' = FeRu,

RuOs, FeOs) and (PPh4)2[M 2(C O )g] (M = Fe, Ru, Os)

Compound ______5cO (CD3CN)______

(PPh4)2[Fe2(CO)8] 225 ppm

(PPh4)2[Ru2(CO)gJ 215 ppm

(PPh4)2[Os2(CO)8] 193.3 ppm

(PPh4)2fFeRu(CO)g] 224.8, 219.3 ppm

(PPh4)2[FeOs(CO)8 ] 224.9, 202.1 ppm

(PPh4)2[RuOs(CO)g]______215.1, 203.0 ppm

homobinuclear dianions, (PPh4)2[M2(CO)8] (M = Fe, Ru, Os), are listed in

Table 6. The values observed in the carbon-13 NMR of the heterobinuclear

dianions, (PPh4)2[MM'(CO)g] (MM’ = FeRu, RuOs, FeOs) remained constant

regardless of whether the enrichement procedure used. That is, whether

anions enriched anion, Na2[M(CO)4] (M = Fe, Ru, Os), were used in the

synthesis or if the impure sodium salts Na2[MM'(CO)8] (MM1 = FeRu, RuOs,

FeOs) were stirred under an atmosphere of carbon-13 carbon monoxide and then metathesized. Assignments were made based on the comparison of the

resonances of the heterobinuclear dianions with the homobinuclear dianions. The resonance furthest down Held in all cases were assigned to the metal center with the lower atomic number (see Section III. B.). 100

Molecular Structures

X-ray quality crystals for structure determination were grown by

slow diffusion of diethyl ether into a concentrated acetonitrile solution at

-10°C. Crystals of suitable size were grown in 5-7 days. Crystals were

separated from the mother liquor by the use of a glass fiber, placed in a

thin walled glass capillary and sealed under a nitrogen atmosphere.

A single crystal X-ray diffraction study of (PPh4)2[FeRu(CO)s] was

performed and the molecular structure is pictured in Figure 40. Crystal

data, selected bond distances and bond angles are listed in Tables 7., 8. and 9.

The structure consists of a four sided pyramidal fragment bonded to a

trigonal bipyramidal fragment. The iron is at the center of the four sided

pyramidal fragment with C(23)-0(23) as the apical ligand and Ru resides at

a basal site. The trigonal bipyramidal unit contains Ru as the central atom

and Fe occupies an equatorial position. There is a small amount of disorder

in the crystal structure of (PPh4)2[FeRu(CO)s] at metal centers. The iron center consists of 78% Fe + 22% Ru and the ruthenium center consists of

78% Ru + 22% Fe.

There are two least squares planes associated with [FeRu(CO)s]2- which are of interest because they show the spatial relationship between the Fe(CO)4 and Ru(CO)4 fragments. The dihedral angle between these two planes is 90.7°. The horizontal plane passes through the equatorial atoms

C(13), C(12), Fe, and the central Ru of the trigonal bipyramidal fragment.

The vertical plane passes through the axial positions C(ll) and C(14), the 101

Figure 40. The Molecular Structure of (PPh4)2[FeRu(C0)gJ. I 102

Table 7. Crystal Data for (PPh 4 )2FeRu(CO>8

Space Group Cc

a, A 19.2334

b,A 16.5347

c, A 16.2506 P. 98.8069

Z 4

v , A 3 5107.1

D (calc.) g cm’3 1.416

Mol. Wt. 1088.85

R adiation MoKa

Diffractometer' CAD4

Mode CO - 20 scan

+h, +k, +1 +22, +19, +19

Lim its 4° < 20 < 50°

No. of Reflections 4502

No. of Variables 613

No of Refl. per Var. 7.3

Abs. Corr , Max, Min, Ave. 99.9, 88.1, 93.9

Rf .049

Rfw .057 103

Table 8. Selected Bond Distances (A) for (PPh4)2FeRu(CO>8<

Fe - Ru 2.827(1)

Fe - C(21) 1.788(11) Ru - C(ll) 1.881(9)

Fe - C(22) 1.810(10) Ru - C(12) 1.826(10)

Fe - C(23) 1.784(12) Ru - C(13) 1.849(11)

Fe - C(24) 1.807(10) Ru - C(14) 1.838(10)

C(21) - 0(21) 1.142(11) C(ll) - 0(11) 1.151(10)

C(22) - 0(22) 1.157(10) C(12) - 0(12) 1.162(11)

C(23) - 0(23) 1.143(11) C(13) - 0(13) 1.151(10)

C(24) - 0(24) 1.147(10) C(14) - 0(14) 1.180(10)

Table 9. Selected Bond Angles (Deg.) for (PPh4)2FeRu(CO)g.

C(21) - Fe - C(23) 103.83(46) C (ll) - Ru - C(12) 96.31(39)

C(23) - Fe - C(24) 110.73(42) C (ll) - Ru - C(13) 98.11(39)

C(23) - Fe - Ru 108.95(31) C (ll) - Ru - C(14) 156.70(37)

C(23) - Fe - C(22) 109.53(39) C(ll) - Ru - Fe 84.89(26)

C(21) - Fe - C(24) 93.65(44) C(12) - Ru - C(13) 111.19(42)

C(24) - Fe - Ru 77.16(29) C(12) - Ru - C(14) 93.37(42)

C(22) - Fe - Ru 74.10(26) C(12) - Ru - Fe 129.43(32)

C(22) - Fe - C(21) 92.95(41) C(13) - Ru - C(14) 98.05(39)

C(21) - Fe - Ru 147.13(35) C(13) - Ru - Fe 118.69(28)

C(22) - Fe - C(24) 136.19(40) C(14) - Ru - Fe 72.64(26) 104

central Ru and the equatorial Fe of the trigonal bipyramidal fragment. The plane also passes through C(23) the central Fe atom and the basal positions

C(21) and Ru of the four sided pyramidal fragment.

The bond angles around the apical carbon, C(23), of the four sided pyramidal fragment are C(23)-Fe-C(24) = 109.3°, C(23)-Fe-C(21) = 102.4°,

C(23)-Fe-C(22) = 108.5° and C(13)-Fe-Ru = 110.9°. The angle between the equatorial carbonyls C(13)-Ru-C(12) is 110.7° in the trigonal bipyramidal fragment. The axial carbonyls on Ru are tipped over the Fe-Ru bond with acute angles of Fe-Ru-C(ll) = 85.4°,and Fe-Ru-C(14) = 71.9°. The respective

Ru-C-0 bond angles of these carbonyls display virtually linear arrangements. Two of the carbonyls on Fe are also tipped over the Fe-Ru bond with the angles of Ru-Fe-C(24) = 77.7° and Ru-Fe-C(22) = 74.6°. Similar tipping of terminal carbonyls was observed in the compound

(PPh4)2tRu2(CO)8] (17).

The bond distance Fe-Ru = 2.828 is 0.108 A shorter than the bond distance in (PPh4)2[Ru2(CO)8] (32) and 0.053 A longer than the bond distance in (PPh4)2[Fe2(CO)8] (vida infra). The Fe-Ru bond distance agrees well with the predicted bond distance based on Pauling covalent radaii (94) of 2.861 A. The Ru-C bond distances range from 1.848-1.903 A and the Fe-C bond distances range from 1.787-1.838 A.

A single crystal X-ray diffraction study of (PPh4)2[Fe2(CO)8] was performed and the molecular structure is shown in Figure 41. Crystal data, selected bond distances and bond angles are listed in Tables 10., 11. and 12.

The structure of (PPh4)2[Fe2(CO)8] is similar to the reported structure Figure 41. The Molecular Structure of (PPh4)2[Fe2(CO)8]. 106

Table 10. Crystal Data for (PPh 4)2F e2(C O )s

Space Group Pi Bar

a, A 9.389 (3) b,A 12.086 (6)

c, A 12.931 (11)

a, deg. 71.37 (4)

0, deg. 76.75(4)

Y, deg. 69.83 (3) Z 1

v, A3 1293.4

D (calc.) g cm-3 1.351

Mol. Wt. 1054.6 Mol. Formula C58 H43Fe2N08 P2 Radiation MoKa (0.71069)

Mode co - 20 scan

+h, +k, +1 +11, 12, +15

Lim its 40 <20 <55°

No. of Measured I's 4534

No. of I's with Fo^ > 3oFo^ 3168

No. of Variables 325

Abs. Corr. , Max, Min, Ave. 99.9, 98.4, 99.1

Abs. Corr.,(p) cm"* 6.74

R f .033

Rfw .048 107

Table 11. Selected Bond Distances (A) for (PPh4)2F e 2(C O )g.

Fel - Fel' 2.929(6)

Fel - C (l) 1.783(3) C(l) - 0(1) 1.160(3)

Fel - C(2) 1.738(3) C(2) - 0(2) 1.157(4)

Fel - C(3) 1.770(4) C(3) - 0(3) 1.155(4)

Fel - C(4) 1.773(3) C(4) - 0(4) 1.163(3)

Table 12. Selected Bond Angles (Deg.) for (PPh4)2Fe2(CO)s.

Fel - F el’ - C(l) 84.9(2) C(2) - Fel - C(3) 93.1(2)

Fel - F el' - C(2) 174.4(2) C(2) - Fel - C(4) 96.5(1)

Fel - F el' - C(3) 81.35(9) C(3) - Fel - C(4) 119.5(1)

Fel - F el' - C(4) 85.5(2) Fel - C(l) - 0(1) 178.1(2)

C(l) - Fel - C(2) 98.9(1) Fel - C(2) - 0(2) 177.4(3)

C(l) - Fel - C(3) 119.6(1) Fel - C(3) - 0(3) 175.9(3)

C(l) - Fel - C(4) 117.6(1) Fel - C(4) - 0(4) 176.7(2) 108

of (PPN)[Fe2(CO>8l (95) and analogous to the reported structure of

(PPh4)2[Os2(CO)8l (32). The unit cell is triclinic with one molecule per unit cell. The space group is PI bar and the center of symmetry is at the mid point of the Fe-Fe bond. It has D3

Fe(CO)4 units with four carbon monoxides occupying four of the vertices of a trigonal bipyramid with the fifth site being common to both Fe(CO)4 fragments. The metals are bound in an axial position of the trigonal bipyramid. As in the case of (PPN)2[Fe2(CO)8l (95) and (PPh4)2[Os2(CO)s]

(32) the equatorial carbonyls are tilted towards the opposite metal center.

The tilt angle, Fe-Fe-C, is in the range of 83.0 - 84.7 A. The carbonyls in the equatorial planes are staggered with respect to one another. The Fe-Fe distance is 2.775 A. The Fe-C bond distances are 1.702 - 1.774 A and the Fe-C-

O bond angles are 174.5 - 178.3 °. The structure contains one acetonitrile molecule which shows a small amount of disorder. III. Discussion

A. (ti2-B 2Hs) Compounds.

1. Synthesis. o f K[M(CO)40l2-B2H5)] (M = Fe, Ru, Os)

The reaction of the nucleophilic tetracarbonylates [M(CO)4]2_

(M = Fe, Ru, Os) with THF BH3 to produce K[M(CO)4(ti2-B2H5)].(M = Fe, Ru, Os)

(Equation (29)) is essentially a heterogeneous reaction and thus it is difficult to gain definitive information about the mechanism of the reaction. A few points can be inferred from experimental observations however. The reaction of the tetracarbonylates K2[M(CO)4] (M = Fe, Ru, Os) with diborane in solvents which do not cleave diborane do not form

K[M(CO)4(q2-B2H5)].(M = Fe, Ru, Os). When the reaction of K2[M(CO)4] (M =

Fe, Ru, Os) and B2H6 is conducted in diethyl ether at -78°C there is no reaction after 24-48 hours (Table 13.). When the reaction was performed at room temperature a slow reaction occured and in all cases (M = Fe, Ru, Os).

The reactions formed KBH4 (identified infrared spectroscopy) as a reaction product. The boron-11 NMR spectra did not indicate the formation of

K[M(CO)4(q2-B2H5)] (M = Fe, Ru, Os) but instead resonances were observed which indicated that a mixture of boron products were formed. Since the reaction of K2(M(CO)4] with B2H6 does does not form the metalladiboranes

K[M(CO)40n2-B2H5)].(M = Fe, Ru, Os) it is reasonable to assume the reactive

1 0 9 110

Table 13. The Results of the Reaction of [M(CO)4]2* M = Fe, Ru, Os with B2H6 in Et20 and THF

A n io n S olv . R e s u lt Rxn. Time Temp.

[Fe(CO)4]2- Et20 No Reaction 28 hours -78°C

[R u ( C O ) 4 ]2 ' Et20 No Reaction 24 hours -78°C

[ O s ( C O ) 4]2 - Et20 No Reaction 30 hours -78°C

[Fe(CO)4]2- Et20 Brown Soln./White Precip. 48 hours Room

[R u ( C O ) 4 ] 2 - Et20 Red-Brown Soln./White Precip. SO hours Room

[ O s ( C O ) 4]2 - Et20 Yellow Soln./White Precip. 28 hours Room

[ F e ( C O ) 4 ]2 - THF Slow Conv. to [Fe(CO) 40 i 2-B 2H 5)] 28 hours -78°C

[ R u ( C O ) 4]2* THF Slow Conv. to [Ru(CO) 4(ti2 -B 2H 5)] 72 hours -78°C

[ O s ( C O ) 4]2 - THF Slow Conv. to [Os(CO) 4( t|2-B 2H 5)] 48 hours -78°C

[Fe(CO)4]2* THF Total Conv. to [Fe(CO) 4(ti2-B 2H 5)] 1 hour Room

[ R u ( C O ) 4]2 - THF Total Conv. to [Ru(CO) 4(ti2-B 2H 5)] 1.5 hours Room

[ O s ( C O ) 4]2 - THF Total Conv. to [Os(CO) 4 (ii2-B 2H 5)] 2 hours Room

V I ll

boron species in the formation of K[M(CO)4(t|2-B2H5)].(M = Fe, Ru, Os) is not

B2H6 and is L*BH3 ( L = solvent). The mechanism most likely is a multi-step

process involving at least three L-BH3 units.

When L-BH3 is reacted with the four electron donor H2S (120, 121)

the bis borane compound [(HS)(BH3)2]* is formed. Other bis borane

compounds prepared following similar procedures are [(CH3Se)(B 113)2]"

(83) and t(C2H5)S(BH3)2]" (96) The presence of an oxidizing agent is

required to facilitate the removal of a hydride (H*) ion to form the bridge

substituted diborane complexes (P-HSKB2H5), (p-(C2H5)S)(B2H5) and

(p-(CH3)S)(B2H5). It is possible that the formation of K[M(CO)4(q2-B2H5)].is

preceeded by the formation of a bis borane intermediate. In general the

iron (-II) d1® configuration can lead to a cubic environment (119) and

could possibly accommodate a bisborane complex [Fe(CO)4(BH3)2]2'. This

may also be true for the ruthenium and osmium (-II) d10 dianions which

would also give the intermediates [M(CO)4(BH3)2]2"(I) (Figure 42a.). The

stability of such a complex would be expected to be small because of the

reducing power of such anions (7). The result could be the donation of

charge to the borons facilitating the removal of a hydride ion thus causing

the oxidation at the metal center from metal (-II) to metal (0). The

substituted bis boranes presented above provide evidence for the donation of electron density to borane (L-BH]), which causes the increase of hydridic character of the hydrogens, which facilitates their removal with

Lewis acids (3). 112

0 2- 0 2 - °c f BH, °c 1 H H s 1 / A* ■ HJ M M—B B—H /1 1 1 0 C' i NBH3 o c C H H 0 0 a) L b)

Figure 42. Possible Intermediates in the Formation of K[M(CO)4(r|2-B2H5)]. a) Bis Borane Intermediate, b) Intermediate Analogous to [B2H7]'.

Another plausible intermediate would be the formation of

[M(CO)4(H2B-H-BH3)]2- (II) (Figure 42b.). This can be considered to be an

analog to [B2H7]~ (79, 97). In this case the metal is still in the -2 oxidation state but it is five coordinate. This may be more likely than the bisborane adduct for the following reasons. Since as stated above group 8 metal (-II) complexes prefer cubic environments, the pentagonalbipyramidal geometry around the metal may induce instability in the (-II) oxidation state. The removal of the hydride would lead to a metal (0) complex which forms stable five coordinate complexes. The hydrides of the bisborane adduct (I) would be less hydridic than intermediate (II). This is because in the former the metal is distributing electron density between two borons and in the latter the donation is solely to one boron. Finally (II) accounts for the removal of [BH4]* by a simple removal of the bridge hydride by the outermost boron. Intermediate (I) either has to eliminate [BH4]* 113

intramolecularly or a third intermediate must be invoked, which would be similar to (II), that would remove the hydride. In both cases the intermediate formation and decomposition must be a fast step in the reaction mechanism because of the lack of observation of either intermediate or the simple adduct [M(CO)4(B H 3)]2' during room temperature or low temperature NMR studies.

It is interesting that the chromium anion K2[Cr(CO)sJ reacts with

THF*BH3 to form K[Cr(CO)4B3Hs], a metallaborane containing three boron atoms (Equation (35)) . This is in contrast to the group 8 tetracarbonylates,

[M(CO)4]2‘ (M = Fe, Ru. Os), which do not react with excess THF*BH3 to form a higher boron containing metallaborane. When a weaker borane adduct is used such as (CH3)20-BH3f there is no reaction with K[Os(CO)4(q2-B2Hs)] after several days (Equation (51).).

K[Os(CO)4(q2-B2H5)] + (CH3)2 0 BH3 ------► No Reaction (51)

This is probably because the compounds K[M(CO)4(q2-B2H5)] (M = Fe, Ru,

Os) are 18 electron species, whereas if K[Cr(CO)4 (Tj2- B 2H 5 )] is an

intermediate in the formation of K[Cr(CO)4B3Hg] it would be a 16 electron

species (figure 43.). Since the metal is electron deficient the ligand can

rearrange to form two hydride bridges. This would break the bond

between the metal and the two borons and leave a electrophilic boron-

boron bond exposed. This boron-boron bond could be attacked by another 114

+bh3 o c H ° c „ [A' b * 'C r \ VH A

oc/IVH c H , o H

18 electron Figuure 43. Possible Mechanism for the Formation of [Cr(CO)4B 3H&]'

H H \ / H H \ ✓ B L*M B /H / \ b) B a ) H H / \ H H

Figure 44. Possible Bonding Modes of the Cn2-B2H5) Ligand, a) Two-Center Two-Electron Bonding, b) Three-Center Two-Electron Bonding. 115

BH j group yielding K[Cr(CO>4B3Hg]. Unfortunately, there is no direct

evidence establishing the intermediacy of K[Cr(CO)4(q2-B2H5)].

2 . Structure and Bonding.

There are two possible bonding modes between the metal center and the

(t]2-B2H5) ligand for [M(CO)4(n2-B2Hs)]* (M = Fe, Ru, Os) which can still

satisfy the symmetry requirements for the observed spectra. Since

[M(CO)4]2' can potentially donate two electron pairs it is possible to have

two two-center two-electron ( 2C-2e) (Figure 44a.) bonds between the metal

center and the two borons, similar to what is observed in the p-ammido

diboranes (82). This would place the metal in the +2 formal oxidation state

and yield a six coordinate d2sp3 hybridized complex. The other bonding

mode could be that the metal is bonded to the two borons via a three-center

two-electron bond (3C-2e) (Figure 44b.). This mode would be analogous to

the bridging hydrogen, the metal center formally replaced in the diborane

structure. This would yield a metal center that is formally M(0), five

coordinate and dsp3 hybridized. Most of the available evidence supports the 3C-2e bonding mode.

The carbon-13 NMR spectrum of the compounds [M(CO)4(q2-B2H5)]‘

(M = Fe, Ru, Os) support the bonding representation in which the metal center is bound to the (n2-B2Hs) ligand through a 3C-2e bond (Figure 44b.).

The appearance of a singlet, which is temperature invariant is 116

characteristic of many penta-coordinate complexes (98). The fluxional

character of the carbonyls in the 13C NMR spectrum and the invariance to

temperature of five coordinate complexes is rarely exhibited in six

coordinate complexes (99, 100). The six coordinate complexes Ru(CO)4X2

(X = H, I) and Os(CO)4X2 (X = H, I) (99) are examples of six coordinate

ruthenium and osmium complexes in which the carbonyl motion has been

arrested at reasonable temperatures.

The metalladiborane compounds (ti5-C5H5)M (CO)2(ti2-B2H5)

M = Fe (65), Ru and 0i5-CsH5)2Mo(H)(ti2-B2H5) (66) appear to have 3C-2e

bonding. This is because the three-center two-electron representation

allows the metals above to have six and eight bonding electron pairs

respectively. Any other valence bond representation in which the metal is

bound to the borons by 2C-2e bonds would require seven and nine bonding

electron pairs, respectively, which is not very likely. There is also data

from Mdssbauer experiments performed on the compounds

(Tt5-C5H5)Fe(CO)2(Tl2-B2H5) and K[Fe(CO)4(Tl2-B2H5)].(101) which support

the 3C-2e bond.

The formation of the compounds HM(CO)40n2-B2H5) (M = Ru, Os),

reported in this dissertation are in favor of 3C-2e bonding. If 3C-2e

bonding is invoked, the compound HM(CO)4(q2-B2H5) has the metal in the

+2 oxidation state. The complex would be six coordinate, d2sp3 hybridized

and the compound would have 12 bonding electron pairs. If 2C-2e bonding

is invoked the compound H[M(CO)4(ti2-B2H5)] would be in the formal oxidation state of +4. This would make the compound "pseudo" seven 117

coordinate and contain 14 bonding electron pairs. The latter possibility is not very likely. Additionally, Bau (12) has determined that the proton in the compound [HFe(CO)4]~ occupies an axial position of a slightly distorted trigonal bipyramid. This provides evidence that the coordinated proton in the compounds HM(CO)4(ti2-B2H5) (M = Ru, Os) most likely occupies a coordination site. Also, the formation of (CH3)M (CO)4Cn2-B2H5) and

(Ph3PAu)M (CO)4(n2~B2H5), where the groups [CH3]+ and [Ph3PAu] + undoubtedly have more steric bulk than a proton, provides evidence that these compounds are six coordinate.

A structural study of [M(CO)4(q2-B2H5)]‘ (M = Fe, Ru, Os) would provide an attractive method for detecting which bonding mode

(Figure 44.) exists. Unfortunately X-ray quality crystals could not be grown.

However, the structures of the (q2-B2H5) complexes 0i5-C5H5)Fe(CO)2(tl2'

B2H5) (101) and (Ti5-C5H5)2M o(H)(q2-B2H5) (66) have been reported

(Figure (7)). In these compounds the metal-boron distances are somewhat longer than that predicted by Pauling's (84) single bond radii. These

"long" distances are consistent with 3C-2e bonding in that the expected bond order of the metal boron bonds, if treated separately, should be less than one. The Fe-B distances of (n^-C5H5)Fe(CO)2(n2-B2H5) are consistent with those reported for [Fe(CO)4B7H i2l’ (109) which has been reported to contain a 3C-2e bond between the iron and two basal borons of the boron hydride cage, [ByH^l*- The B-B distances and the B-H-B angles are similar to that of B2H6 (102). If 2C-2e bonding were invoked these values should be 118

larger than the values in B2 H 6 because the two borons no longer

participate in a common bond.

An alternative bonding description of the interaction between the metal and the borons in [M(CO)4(ti2-B 2H5)]* (M = Fe, Ru, Os) would be to liken

it (qualitatively) to the familiar Dewar-Duncanson-Chatt (103, 104) model of metal olefin bonding (Figure 45b.). Specifically the compounds [M(CO)4(n2-

B2Hs)]‘ (M = Fe, Ru, Os) are the isoelectronic analogs to M(CO)4(q2-C2H4) M =

Fe ( 124, 125), Ru (104), Os (14). To do this Pitzer's protonated double bond model for diborane (106) should be considered (Figure (45a)). One of the bridging protons of diborane, in Pitzer's model, can be replaced with a metal fragment containing an available orbital capable of accepting electron density from the pi cloud of [B2H5]*. Felhner et. al, (107) analyzed the metalladiborane (Ti^-CsH5)Fe(CO)2(H2-B2H5) from photoelectron spectroscopy and Fenske-Hall calculations and tested the validity of such an argument. It was concluded that the bonding is primarily a-donation with very little contribution from 7t-backbonding and that the bonding is best described as a 3C-2e bond. 119

a - Donation 7C* - Back Bonding

L„ L- M M H \ H H ✓ s B a) H > " N + ”0 h. 0 h

M M H N H H C C b ) H H

Figure 45. Bonding Analogy Between a Coordinated (n 2-B 2H 5) a n d C 2H 4. a) Bonding Based on Pitzer's Diborane Model, b) Dewar-Chatt-Duncanson Model for Metal Olefin Bonding.

3. Reactivity of M(CO)4(t]2-B2H5)' (M = Fe, Ru, Os).

Formation of HM(CO)4(n2-B2Hs) (M = Fe, Ru, Os).

Since the C112-B2H5) ligand was proposed by Fehlner et al. ( 107 ) to behave as a bridge deprotonated B2H6 (1. e. [B2H5]-) it was of interest to try to protonate the compounds, K[M(CO)4(ti2-B2H5)J (M = Fe, Ru, Os), and 120

determine whether the proton would react with the boron ligand or the

metal center. Medford reported ( 81 ) the anion K[Fe(CO)4 (tj 2 - B 2 H 5)] could

be protonated at - 110°C when anhydrous HC 1 was used. The complex gave

an ill-resolved broad resonance in the 1 *B NMR at - 120°C centered at - 17.2

ppm. The proposed complex had the site of protonation being the boron

ligand and the proposed product was thought to be Fe(CO)4(BH2-H-BH3>

which decomposes above - 110°C to yield B2H6 and Fe(CO)5. Since the

product of the protonation of K[Fe(CO)4(ri2-B2H5)] was unstable, direct

evidence for the site of protonation does not exist. It was therefore of

interest to attempt the protonation of the ruthenium and osmium analogs.

The compounds K[M(CO)4(ti2-B2H5)] M = Ru, Os protonate at the metal

center to yield the complexes HM(CO)4(tj2-B2H5) M = Ru, Os which have

been characterized (section II. B. 1.). The proton adds to the metal center

cis to the (il^-B2H5) ligand. More important, the stability of the protonated

products of K[M(CO)4(n2-B2H5)] (M = Fe, Ru, Os) decrease in the order Os > Ru

> Fe. Since the proton adds to the metal center in the ruthenium and

osmium cases it only seems logical to extend this to the iron system. The

complex most likely formed during the protonation of K[Fe(CO)4(ri2-B2H5)]

was HFe(CO)4(Ti2-B2H5)].

The chemistry of K[M(CO)4 (ti2-B 2H s )] (M = Fe, Ru, Os) seem to parallel

the chemistry of the compounds [HM(CO)4]- and [M(CO)4R]' (M = Fe, Ru, Os).

This can be rationalized since 0l2-B2H5) is primarily O-donating while being a poor back-bonding ligand ( 107 ). Specifically, the stabilities of the compounds HM(CO)4Cn2-B2H5) (M = Fe, Ru, Os) seem to parallel the stabilities 121

of the compounds HM(CO)4R (R = alkyl, M = Fe, Os). The stability of compounds of the general type HFe(CO) 4 R are well documented in the literature. Collman et.al. (8 , 111) exploited the instability of this Fe(II) compound by noting that the HFe(CO) 4R complex is unstable with respect to elimination of RH. In the case of HFe(CO) 4 ( n 2 -B 2 H 5) Medford noted it's instability and observed the formation of B2H6. This is consistant with the formation of B2H6 being from- the elimination of the unstable Fe(II) com plex.

On the other hand Norton et. al. (6, 112, 113) have worked extensively with the more stable HOs(CO)4R (R = CH3, C2H5) complexes. The Os(II) hydrido alkyl compounds are more stable than the Fe(II) hydrido alkyl analogs. This stability trend is also observed for the compounds

H M ( C O ) 4 ( ti^ - B 2 H 5 ) (M = Fe, Os). The compound HO s ( C O ) 4 ( ti2-B2H5) is less stable with respect to decomposition than is HOs(CO)4R. Solutions of

1108(00)4(112-82115) decompose completely in less than five hours at room temperature. The decomposition products are B2H6 and H2.

The observed inability of K[Os(CO)4(n2-B2H5)] to protonate in donor solvents can be rationalized by considering the analogous HOs(CO)4(CH3) system. It has been demonstrated (6, 112, 113) that the compound

HOs(CO)4(CH3) decomposes by a dinuclear (bimolecular) mechanism.

Simple intramolecular reductive elimination of the compound

HOs(CO)4(CH3) would leave the high energy fragment Os(CO)4 remaining which is not very likely. The compound HOs(CO)4(CH3) can be induced to eliminate CH4 intramolecularly by stabilizing the Os(CO)4 unit remaining. 122

This was done by complexation with a donor ligand (e. g. PEt3) to form

Os(CO)4L. This may be similar to what happens when K[Os(CO)4(q2-B2H5)] is

protonated in a donor solvent. For example, when THF solutions of

K[Os(CO)4(ti2-B2H5)] are protonated in an NMR tube with anhydrous HC1 the

observed product in the llB NMR is THF*BH3. This most likely occurs

because of base induced reductive elimination of B2H6 (Equation (52a)).

HOs(CO)40l2-B2H5) + THF ------► ,,Os(CO)4CrHF)" + B2H6 (52a)

B2Hg + 2THF------► 2THFBH3 (52b)

The second step would be the cleavage of diborane with THF (Equation

(52b)). The Os(CO)4(THF) complex could not be identified in the reaction

products. A more stable osmium product , Os(CO)4Br2, was identified as the

only osmium decomposition product from the reaction of HOs(CO)4(q2-B2H5)

and Br2 (Equation (53)).

HOs(CO)4(n2-B2H5) + Br2 ► Os(CO)4Br2 + boron products (53)

The boron products were not identified Usually Br2 converts the organometallic hydride compounds to the corresponding organometallic bromo compounds (123).

HMLX + 1/2B12 ► BrMLx + HBr (54) 123

Another point that may be addressed is the mechanism for the

decomposition of HOs(CO)4(q2-B2H5). Norton et. al. (6, 112, 113), as stated

earlier, have shown that the compound HOs(CO)4(CH3) does not decompose

by a simple intramolecular reductive elimination. The decomposition is

rather a dinuclear elimination involving an alkyl migration to form an

osmium acyl with a vacant coordination site. It is through the vacant

coordination site in which an Os-H from another osmium interacts to

eliminate CH4 and form the dinuclear complex. If the compound

HO s ( C O ) 4 ( t| 2 - B 2 H 5 ) decomposes in the same manner it would require the

(t)2-B2Hs) ligand to migrate and form a five coordinate osmium intermediate with the Cn2-B2H5) functioning as a alkyl group does in an acyl compound. Intuitively, this does not seem possible. A simple intramolecular reductive elimination of B2H6 from does HM(CO)4(q 2 _ b 2H 5) not seem feasible because of the high energy M(CO)4 fragment remaining

(6, 112, 113).

One reaction which may provide evidence for a dinuclear elimination is the decomposition of a mixture of HM(CO)4(q2-B2D5) and

DM(CO)4Cn2-B2H5). The products B2D5H and B2H5D would be the only products expected if the complex decomposed through a simple intramolecular reductive elimination. If the reaction proceeds through any other mechanism a mixture of B2D6, B2H6, B2D5H and B2H5D would be expected. This experiment was performed using the ruthenium compounds

HRu(CO)4(q2-B2D5) and DRu(CO)4(q2-B2Hs), however the results were 124

inconclusive due to the overlapping envelopes in the mass spectrum of the diborane species involved. There exists an envelope for B2H6 (including parent ion), an envelope for B2D5H (no parent ion), an envelope for B2H5D

(including parent ion) and an envelope for B2D6 (no parent ion)

(Table 14.). Since all the envelopes overlap it is difficult to determine which species are really present.

Another point is that the stability of (CH3)Os(CO)4(ti^-B2H5) is less than that of HOs(CO)4(ti2-B2H5). The decomposition products of

(CH3)Os(CO)4(h2_B2H5) are B2H6 and CH4 (by ^B NMR spectroscopy and mass spectrometry respectively). A dinuclear decomposition mechanism or the decomposition by simple intramolecular elimination can not account for the formation of these decomposition products. The decomposition product expected from either mechanism would be B2Hs(CH3). This was never in the decomposition products. In this case a mechanism that could account for these decomposition products is a radical mechanism in which

CH3* extracts an H* from the coordinated Cn2-B2Hs) to form CH4 and a

(B2H5)* abstracts an H* from a coordinated CH3. Invoking a radical mechanism for the decomposition of HM(CO)4(tj2-B2H5) would also account for the formation of H2 along with B2H6 in the decomposition products.

The evidence presented, however, is not sufficent to draw definitive mechanistic conclusions. 125

Table 13 . Mass spectral data from the Decomposition of a Mixture

H Ru(CO)4(t]2 -B2Ds) and DRu(CO)40i2-B2H5).

Efiakfemu)______Assignment ______Relative intensity

32.33 nB2D5 6.3

31.19 uB2D4H. 10BnB2D5 74.90

30.23 11B2D4, 10B 11B2D4H, 10B2Ds 100

29.19 nB2D3H, 11B2DH5,1°B11BD4,10B2D4H 72.25

28.15 11B2D3(B2H6.10BiiBD3H. 10b2D4 60.8

27.19 11B2H5,11B2D2H, l1B2DH3,l<>B1lBH6, 77.2 ^B^BD* ^B ^H s, 10B2D3H

26.15 nB2H4, HB2D2. nB2DH2, ^B^BHs' 60.29 10Bn BD2H. WB^BDHs, 10B2H6. 10B2D3

25.11 11B2H3,11B2DH, 1°B11BH4.10B11BD2. 21.71 10b11bDH2, MB2H5. 10B2D2H, 10b2DH3

24.15 llB2H2, u B2D, 10Bu BH3, 10B n BDH, 10B2H4 7.00 10B2D2i 10B2DH2

23.19 “B^, ^B^BH^ 10BllBD, 10B2H3, 10B2DH 1.85

22.07 H B 2, iOBllBH, 10b2H2, 10B2D 0.32

21.11 ^B^B, 10B2H 0.32

20.15 !0 b 2 0.86 126

Table 13. (Cont.)

Efiakfemul______Assignment ______Relative intensity

17..27 1JBD3 0.86

16.08 nBD2H, 10BD3 2.76

15.04 nBDH2,11BD2,10BD2H 16.39

14.08 ^BHs.UBDH, 10BDH2.10BD2 39.10

13.12 11BH2, ^BD, ^BHa, ^BDH, 42.79

11.04 n B, 10BH 63.44

2.40 D 46.25

1.27 H 2.5 127

B. Synthesis and Characterization of the

Heterobinuclear dianions [MM'(CO)g]2’ (MM' = FeRu, RuOs,

FeOs) .

The syntheses of the heterobinuclear dianions according to

Equations (49a) and (49b) are more complicated than what is accounted for by that reaction scheme. The alkali salts can not be isolated as pure salts, the major impurities are cluster anions of higher nuclearity. This situation is analogous to the synthesis of the homobinuclear dianions

N a 2 [M 2 (CO)8l (M = Ru, Os) in that the major impurities are higher nuclearity anions (36). The purity of the product may be dependent upon of the solubility of [M'(CO)4]2‘ (M = Fe, Ru) in THF. The heterobinuclear dianions Na2[MM'(CO)s] (MM’ = FeRu, RuOs, FeOs) are more soluble in THF than is Na2 [M'(CO)4], The heterobinuclear dianion can then react with

M(CO)5 to initialize the formation of the higher nuclearity anions. The following series of reactions may account for this result.

[M'(CO)4]2- + M(CO)5 ------► [MM’(CO)8 ]2- + CO (55)

[MM’(CO)8]2- + M(CO)5 ------► [M'M2(CO)ii]2- + 2CO (56)

[M’M2(C O )h]2- + M(CO)5 ------► [M'M3(CO)i3]2- + 3CO (57)

This series of reactions is similar to those proposed to account for the impurities in the reaction solutions of the homobinuclear dianions

Na2[M2(CO)8l (M = Ru, Os) (36). The observation of the lower purity of the 128

heterobinuclear dianions may be the result of the lower stability of bonds between dissimilar metals than is the stability of a bond between the same metals. This may also account for the greater air sensitivity observed for the heterobinuclear dianions as compared to the homobinuclear dianions.

The carbon -13 NMR spectra of the hererobinuclear dianions,

(PPh4)2[MM'(CO>8] (MM' = FeRu, RuOs, FeOs), warrent additional discussion.

Since two resonances are observed in the room temperature carbon - 13

NMR spectra it is apparent that one of two possible situations exist:

(1) There could be a barrier to carbonyl exchange between the

dissimilar metals in these compounds whereby both contain

resonances which are characteristic of that metal center. In this

case the lighter metal of the heterobinuclear dianion,

(PPh4)2[MM'(CO)8 l (MM* = FeRu, RuOs, FeOs), retains almost the exact

chemical shift as the parent homobinuclear dianion,

(PPh4)2tM 2(CO)8 ] (M = Fe, Ru, Os).

(2) It is possible that the formation of the heterobinuclear dianion

(PPh4)2[MM'(CO)8 l (MM’ = FeRu, RuOs, FeOs) and the formation of the

parent homobinuclear dianion (PPh 4)2[M 2(CO)8 J (M = Fe, Ru, Os) are

coincident in this reaction scheme. (Equation ( 49)). Since the

metathesis procedure presented can not discriminate between

different types of dinuclear dianions it is possible that they both

exist in solution. 129

It seems unusual that these compounds would have a barrier to

carbonyl exchange between metal centers. This may be rationalized by

considering that normally the equivalence of carbonyls in polynuclear

clusters is accounted for by the interconversion of terminal and bridge carbonyls (114-117). If a barrier to carbonyl exchange exists then both ends of the dianion may be considered independent (qualitatively) of each other. Both metal centers are five coordinate and fluxionality is characteristic of many pentacoordinate compounds (98). The coincident chemical shifts between the lighter metal atom in the heterobinuclear dianions and the parent homobinuclear dianion may also be rationalized.

Collman et. al. (118) determined that the carbon-13 NMR shifts of some iron carbonyl compounds are only sensitive to the oxidation state of iron and not the particularly sensitive to the ligand environment. Geoffroy et. al.

(31) has observed similar results in the carbon-13 NMR spectra of some heteronuclear carbonyl clusters.

It also can not be ruled out that a complex mixture of dinuclear dianions exist ((2) above). If the reaction solutions contain one heterobinuclear dianion and one homobinuclear dianion it is probably the result of electron transfer. The following reactions could account for the formation of this mixture. 130

M(CO)5 + [M,(CO)4J2 ------► [MM*(CO)8]2- ( 58 )

M(CO)5 + [MXCX))^2------► [M(CO)4]2’ + M(CO)5 (59)

M'(CO)5 + [MXCOHX2* ------► M,2(C 0 >8 ) 2- ( 60)

M(CO)5 + [M(CO)4]2' ------► M2(CO)^]2- ( 61) M M’

Os Fe or Ru Ru Fe

The carbon-13 NMR spectra, if interpe rated as hr (2) above, indicates only

the formation of one homobinuclear dianion. This homodinuclear dianion

impurity is likely to have formed by the electron transfer reactions above.

If this is the case there should also be a resonance: for another

homobinuclear dianion which would have formed in Equation (61). Its

absence may provide evidence that both resonances are due to only the

heterobinuclear dianion.

The molecular structure determination of (PPh4)2[FeRn(CO>8l

provides evidence that the syntheses of the heterobinuclear dianions

(PPh4)2[MM'(CO)«] (MM' = FeRu, RuOs, FeOs) were successful. This unusual

structure described for (PPh4)2[FeRu(CO)g] (Section II. C. 2.) is not without precedent. Shore et. al. (32) reported the molecular structure of

(PPh4)2[M2(GO)8] (M = Ru, Os) in which (FPh4)2[Ru-2(CO)8] has a structure very similar to (PPh4)2{FeRu(CO)8l. If the structures of homobinuclear dianions (PPh4)2[M2(CO)8l (M = Fe, Ru, Os) are considered, the only unique

( not D3d) structure is (PPh4)2[Ru2(CO)8X The fact that the iron assumes the four sided pyramidal geometry and the ruthenium assumes the trigonal 131

bipyramidal geometry in the molecular structure of (PPh4)2[FeRu(CO)g] is

surprising. Since the iron in (PPh4)2[FeRu(CO)g] has four sided pyramidal

geometry and not ruthenium it may be possible that the reason is not of the

chemical nature but of the physical nature (/. e. packing forces). Further

evidence for packing forces is in the 22% disorder at the metal centers in

the structure of (PPh4)2[FeRu(CO)s]. Therefore 22% of the lattice contains

ruthenium in the four sided pyramidal geometry and iron in the trigonal

bipyramidal geometry. If the ligand arrangements in the solid state were

an inherent property of either iron or ruthenium the metals would be

expected to retain the unique geometiy 100% in the crystal lattice. This, of

course, was not the case.

The molecular structures of the compounds [M2(CO)8]2' (M = Ru, Os)

and [FeRu(CO)8]2' all have the same counter ion, [PPh4]+ and the crystals

were grown in the same solvents (CH3CN/Et20). Since the metal-metal bond

distance in the dinuclear group 8 carbonylate compounds decrease in the

order of, Os-Os > Ru-Ru > Fe-Ru, it was of interest to determine the molecular

structure of [Fe2(CO)8]2‘ using the same counter ion and the same solvents of crystallization. Since [Fe2(CO)8l2‘ has the shortest metal-metal bond length the effects of the size of the anion and the effect of the counter ion could be assessed.

The molecular structure of (PPh4)2[Fe2(CO)8l presented in figure 42 is analogous to the reported structure of (PPN)2[Fe2(CO)8l (95) and is similar to (PPh4)2[Os2(CO)8]. This result does not discount crystal packing forces completely. The crystals of (PPh4)2[Fe2(CO)8l and (PPh4)2[Os2(CO)8l 132

are triclinic and belong to the space group PI bar while crystals of

(PPh4)2[Ru2(CO)8l and (PPh4)2[FeRu(CO)8l are monoclinic and belong to the space group Cc. The different unit cells and space groups rules out a direct comparison based on the the structural data. These results however do appear to eliminate the simplistic view that the unusual structures of the compounds (PPh4)2[Ru2(CO)s] and (PPh4)2[FeRu(CO)8] was the direct cause of the counter ion [PPh4]+. IV. Experimental

A. A p p a r a tu s

1. Vacuum System.

Due to the air sensitivity of many of the compounds used in this investigation, the reactions and the manipulation of volatile materials were conducted using a Pyrex glass high vacuum line similar to that described by Shriver (126).

The vacuum line consisted of two reaction manifolds, a calibrated fractionation train, a Mcleod gauge and a calibrated Toeppler system which were interconnected by 8 mm tubing to minimize the volume during the transfer of volatile compounds. The vacuum line was maintained at a vacuum of 10" 5 torr by a Welch Duo-Seal rotary pump and a two stage mercury diffusion pump. The mercury diffusion pump was protected from volatile material by a -196° C (liquid nitrogen) trap and a -78° C (Dry

Ice/isopropanol slush) trap protected the mechanical pump from mercury vapor.

The two reaction manifolds consisted of five and six ports respectively, each of which contained a vacuum stopcock (Kontes or

Fisher-Porter) and either a Fisher-Porter 9 mm Solv-Seal joint or a 14/35 standard taper joint. The center two ports of both manifolds contained

Fisher-porter 9 mm Solv-seal joints and were at a fixed distance apart so a

133 134

trap could be attached for solvent removal. Mercury blowouts were connected to most of the stations to monitor reaction pressure. One reaction manifold contained an isolable mercury manometer.

The fractionation train consisted of four calabrated U-traps. The third U-trap was connected to a mercury manometer. The manifold had two reaction ports on each end. Connections between the U-traps and the manifold were made by Fisher-Porter stopcocks.

The Mcloed gauge connected directly to the main manifold and was isolable. An electrically controlled Toeppler system containing a calibrated volume was used to quantitatively measure non-condensible reaction products ranging from .01 to 8.0 mmoles.

The entire vacuum line could be purged with a prepurified inert gas by the attachment of an inlet stopcock to one of the reaction manifolds.

This permitted the removal of reaction apparatus under a stream of inert gas.

2. D ry Box

Air sensitive solids and liquids of low volitivity were handled in a

Vacuum Atmospheres dry box. The oxygen and moisture in this system was maintained at approximately 10 ppm by the circulation of pre-purified nitrogen (Matheson) through a metal cylinder containing Ridox oxygen scavinger and Linde 13-X molecular sieves. The integrity of the atmosphere was checked by exposing a drop of a THF solution of titanocene in a clean crucible and monitoring the color. A blue color signified clOppm 135

O 2 and H2 O while a yellow color signified a poor atmosphere and

regeneration of the Ridox catalyst was necessary. Access to the box was

obtained through an ante-chamber which was alternately evacuated and

flushed with prepurified nitrogen. The operation and design of this type of

inert atmosphere box has been described elsewhere (126).

Air and thermally sensitive compounds were used in a Vacuum

Atmospheres dry box similar to the one described above with the exception

that a refrigerator maintained at -40° C was mounted inside the dry box.on

the left wall.

3. Glassware

Pyrex or Kimax round bottom flasks fitted with 9 mm or IS mm Solv-

Seal joints served as reaction vessels. Adapters containing a 4 mm Teflon in

line Kontes stopcock with the appropriate Solv-Seal connections on each

end were used to attach the flasks to the vacuum line and to take vessels

into the dry box. Stirring the components of the reaction was

accomplished by the rotation of Teflon coated stirbars with the use of an externally driven magnet.

The filtration of air sensitive compounds was achieved by connecting the reaction flask to a vacuum line extractor (Figure 46). The extractor could be connected to the vacuum line by a horizontal 14/35 standard taper joint. Filtration was achieved by rotating the apparatus 180° and drawing the solvent through the glass frit by using a temperature differential (solvent vapor will condense at the lower temperature and Figure 46. A Vacuum Line Extractor. 137

cooling the receiving flask or the use of a volitile solvent facilitates the

filtration.)- Solids were washed by opening the side stopcock and

condensing the solvent vapor above the frit. This was done by touching a

cotton swab that had been dipped in liquid nitrogen to the inverted

reaction flask. After the condensation was complete, closing the side

stopcock and using the above filtration procedure again washed the solid.

NMR samples were flame sealed under vacuum and waxed as a preventative measure against pinholes. When an NMR spectrum of a thermally sensitive compound was required a flask containing a sidearm was used (Figure 47.). The NMR tube was attached to the side arm and when the reaction was complete the solution was tipped into the NMR tube and flame sealed. Occasionally a two neck flask with a fritted NMR tube adapter was used.

The apparatus used to decompose mixtures of HRu(CO)4(t]2-B2Ds) and

DRu(CO)4(n2-B2H5) is pictured in Figure 48. It consists of two 25 mL flasks containing 9 mm Solv-Seal joints. The flasks were connected by a 0 - 4 mm

Kontes right angle stop cock. The syntheses were performed separately and mixed by opening the Kontes valve and tipping the contents of one flask into the other. Decompositions were then conducted with the Kontes valve closed.

Glassware was cleaned by either using a KOH/ethanol soak or soaking in aqua regia followed by rinsing with distilled water and acetone.

It was dried in an oven maintained at 150°C. 138

NMR sam p le tube

reaction bulb

Figure 47. Apparatus for Preparing Low Temperature NMR Samples. 139

9 mm solv-seal

0 - 4 mm Kontes valve

25 mL* Bulb

Figure 48. Apparatus to Decompose Mixtures of Thermally Sensitive Compounds.. 140

4. Nuclear Magnetic Resonance Spectra

Fourier Transform Nuclear Magnetic Resonance (FT-NMR) spectra were obtained on either a Bruker-WM-300, a Broker AM-250 or a Broker

MSL-300.

The spectrometers were equipped with the capabilities of variable temperature and heteronuclear decoupling. The operating frequencies for the various spectrometers are listed below.

Spectrometer 1*B 3*P

WM-300 75.45 —- 300.0

AM-250 62.88 80.25 250.1 101.26

MSL-300 96.3 300.13

Proton and carbon-13 NMR chemical shifts were measured in ppm using the solvent as the internal standard. Boron-11 spectra were referenced using an external standard of boron trichloride in methylene chloride-d2 which was assigned the chemical shift of 46.8 ppm relative to boron trifluoride at 0.00 ppm. Phosphorus-31 NMR shifts are referenced relative to phosphoric acid which has an assigned value of 0.00 ppm.

5. Infrared Spectra

Fourier transform infrared spectra were recorded on a Mattson

Cygnus-25 infrared spectrometer with internal calibration. The solution spectra were run in Perkin-Elmer cells with .1 mm or .5 mm Teflon spacers 141

with KBr or NaCl windows. Solid samples as Nujol mulls were placed

between two KBr or NaCl windows and sealed in an air tight sample holder.

6 . Mass Spectra

Mass spectra of all gas samples were run on a Balzers 112 Quadrupole

Mass Spectrometer with a Faraday cup detector.

7 . Elemental Analyses

Elemental analyses were obtained from either Oneida Research

Services, One Halsey Road, Whitesboro, NY 11377-2495 of Analytische

Laboratories 5270 Gummersbach 1 Elbach, Germany.

8. Crystal Structure Determination.

For X-ray examination and data collection, each crystal was mounted at the tip of a thin walled capallery in an inert atmosphere and flame sealed. All Xray data were collected on a Enref-Nonius CAD4 diffractometer with graphite-monochromated Mo Ka radiation. All of the crystallographic computations were carried out on a PDP 11/44 computer using SDP (Structure Determination Package) (127).

For each crystal, unit cell parameters were obtained by least squares refinement of the angular setting from 24 reflections, well distributed in reciprocal space and lying in a 20 range of 15-30°. Intensity data were mcollected in the GO-20 mode with a range of 4-50°. Six standard reflections were monitored which indicated no significant decay of the crystals had 142

occured. The crystals were corrected for Lorentz and polarization effects.

The intensities were corrected for absorption by using an empirical

method based on the crystal orientation and measured tjs scans.

9. Solvents

Tetrahydrofuran, diethyl ether, dimethyl ether and glyme were

dried by distillation from sodium benzophenone ketyl after it obtained a

lasting blue color. The solvents were stored in 500 mL bulbs equipped with

4 mm Kontes stopcocks which contained sodium benzophenone ketyl as

both a drying aid and an indicator.

Acetonitrile, dichloromethane and chloroform were dried by

refluxing over P2O5 OR CaH2 and distillation into 500 mL storage bulbs.

Hexane and pentane were purified by stirring over concentrated

sulfuric acid for 2-3 days, extracted with distilled water and dried using the

same procedure as described for dichloromethane. The solvents were stored in 500 mL storage bulbs over sodium.

Deuterated solvents were dried employing the same methods as above. 143

B. Reagents

1. A m m o n ia

Ammonia was obtained from Matheson Scientific Products. It was

dried by condensation on to metallic sodium followed by stirring until the

solution turned the characteristic blue color. Dry ammonia was then

transferred to a thick walled Pyrex tube equipped with a 4 mm Kontes

stopcock and stored at -78°C.

2. Benzophenone

Benzophenone was purchased from Fischer Scientific Company and

used a recieved.

3. Bis(triphenylphosphine)iminium Chloride

Bis(triphenylphosphine)iminium Chloride was purchased from Alfa

Inorganics, recrystallized from CH2Cl2/Et20 and dried at 100° C under vacuum. The pure compound was stored in the drybox prior to use.

4. Boron Trifluoride

Boron Trifluoride was obtained from Matheson Scientific Products. It was purified by fractionation through a -140°C trap and stored in a Pyrex tube with a Kontes stopcock at -196°C. 144

5 . Brom ine

Bromine was obtained from J. T. Baker Chemical Company and distilled prior to use.

6. Carbon Dioxide

Carbon dioxide was obtained from Matheson Scientific Products. It was purified by fractionation through sucessive U-traps of -78°C, -111°C -

129°C and collected at -196°C. It was then transferred to a thick walled

Pyrex tube equipped with a 4 mm Kontes stopcock and stored at -78°C.

7. Carbon Dioxide, 99% *3C

Carbon dioxide,99% 13C enriched was obtained from Isotech, Inc. and was purified and stored using the same procedure as carbon dioxide.

8. Carbon Monoxide, 99% 13C

Carbon monoxode, 99% *3C enriched was purchased from Isotech,

Inc. and was used as recieved.

9. Chromium Hexacarbonyl

Chromium hexacarbonyl was purchased from Strem Chemicals and used without further purification. 145

10. Cyclopentadienyl Vanadium Tetracarbonyl

Cyclopentadienyl Vanadium Tetracarbonyl was purchased from

Strem Chemicals and was used without further purification.

11. Cyclopentadienyl Nickel Carbonyl Dimer

Cyclopentadienyl Nickel Carbonyl Dimer was purchased from

Pressure Chemical Company and stored in the drybox prior to use.

12. Hydrogen Chloride

Hydrogen chloride gas was obtained from Matheson Scientific

Products.and purified by fractionation through sucessive U-traps of -78° C,

-111°C -129°C and collected at -196°C. It was then transferred to a thick walled Pyrex tube equipped with a 4 mm Kontes stopcock and stored at -

78°C.

13. Iron Pentacarbonyl

Iron pentacarbonyl was purchased from Strem Chemicals and was distilled prior to use.

14. Lithium Aluminum Deuteride.

Lithium aluminum deuteride was purchased from Aldrich Chemical

Company and used as received. It was stored in the dry box prior to use. 146

15. Lithium Aluminum Hydride.

Lithium aluminum hydride was purchased from Aldrich Chemical

Company and used as received. It was stored in the dry box prior to use.

16. Osmium Tetroxide

Osmium tetroxide was obtained from Strem Chemicals and used as

recieved.

17. Potassium

Potassium metal was in mineral oil was purchased from Mallinkrodt

Incorporated. It was washed with hexanes, cut into pieces and stored in an

inert atmosphere dry box.

18. Potassium Hydride

Potassium hydride as a 50% mineral oil dispersion was obtained from

Alfa Division, Ventron Corporation. It was freed from oil by repeated washing with hexane under vacuum and stored in the drybox. The activity was determined by methanolysis prior to use.

19. Rhenium Carbonyl

Rhenium carbonyl was purchased from Strem Chemicals and used as recieved. 147

20. Ruthenium (III) Chloride Trihydrate

Ruthenium (III) chloride trihydrate was purchased from Aldrich

Chemical Company and used as recieved.

21 Sodium

Sodium metal in mineral oil was purchased from Mallinkrodt

Incorporated. It was washed with hexanes, cut into pieces and stored in an

inert atmosphere dry box.

2 2. Tetraphenyl Arsonium Chloride

Tetraphenyl arsonium chloride was purchased from Strem

Chemicals. It was recrystallized from a concentrated methylene chloride

solution with diethyl ether and was dried by pumping on the solid using a dynamic vacuum at 100°C for 3-4 hours. It was then stored in the dry box prior to use.

23. Tetraphenyl Phosphonium Bromide

Tetraphenyl phosphonium bromide was purchased from Strem

Chemicals. It was recrystallized from a concentrated methylene chloride solution with diethyl ether and was dried by pumping on the solid using a dynamic vacuum at 100° C for 3-4 hours. It was then stored in the dry box prior to use. 148

24. Triiron Dodecacarbonyl

Triiron dodecacarbonyl was purchased fron Strem Chemicals and

was purified by recrystallization from hot methylene chloride and stored

in the daik at -40°C..

25. Trimethyl Boron

Trimethyl boron was generously donated by Dr. Martin W. Payne.

26. Trimethyl Phosphine Silver Iodide Complex

Trimethyl Phosphine Silver Iodide Complex was purchased from

Aldrich Chemical Company and stored in the refrigerator until needed.

27. Triosmium Dodecacarbonyl

Triosmium dodecacarbonyl was obtained from either Strem

Chemicals or Aldrich Chemical Company and used as received.

28. Triphenyl Phosphine

Triphenyl phosphine was purchased from Aldrich Chemical

Company and used without further purification. 149

C. Synthesis of Starting Materials

1. Diborane

Diborane was synthesized by using one of two literature methods

(128, 129).

2. Diborane-Dg

Diborane-D6 was synthesized by using a modification of Brown's

method by substituting UAID4 for UAIH4 (129).

3. Cyclopentadienyl Ruthenium Dicarbonyl Dimer

Cyclopentadienyl ruthenium dicarbonyl dimer was synthesized from

triruthenium dodecacarbonyl and freshly cracked cyclopentadiene in

refluxing heptane by using a published procedure (130).

4. Bistetraphenylphosphonium Octacarbonyl Diferrate (-2)

In the dry box .506 g (1.33 mmole) Na2[FeRu(CO)s] and 1.10 g (2.62

mmole) PPh4Br was added to a 50 mL bulb containing a teflon coated magnetic stirbar. The flask was connected to a vacuum line extractor.

After evacuation 10 mL of dry THF was added to the flask. The mixture was stirred for three hours. During this time a red solid precipitated from the solution leaving a red solution. The solid was isolated by filtration and was washed with THF. The solvent was removed and a fresh collection flask was connected to the extractor in the dry box. The compound (PPh4)2[Fe2(CO)s] 150

was separated from the precipitate by condensing dry CH3CN into the

reaction flask and washing the precipitate. This left NaBr on the glass frit.

The solvent was then removed and the collection flask was connected to a

fresh extractor in the dry box. The apparatus was evacuated and the solid

was dissolved in a minimum amount of CH3CN. The addition of 10 mL Et20

caused the precipitation of the red (PPh4)2[Fe2(CO)8] as a fine powder. The *

powder was isolated by filtration and dried on the vacuum line. The yield

was 1.08 g (80% based on Na2[Fe2(CO)8]).

5. Deuterium Chloride

Deuterium chloride was synthesized by the reaction of boron trichloride with D2O. The deuterium chloride was then fractionated through a -140°C trap and stored in a Pyrex tube with a Kontes stopcock at -

78°C.

6. Dihydrido Triosmium Decacarbonyl

Dihydrido Triosmium Decacarbonyl was synthesized by the method of

Kaesz et. al. (131).

7. Dipotassium Dihydrido Dodecacarbonyl Tetraruthenium

Dipotassium dodecacarbonyl tetraruthenium (-2) was prepared from

H4Ru4(CO)i2 according to a published procedure (132). 151

8. Dipotassium Pentacarbonyl Chromate (-2)

Dipotassium Pentacarbonyl Chromate was synthesized by the method

of Cooper et. al. (133).

9. Dipotassium Tetracarbonyl Ferrate (- 2).

Dipotassium Tetracarbonyl Ferrate (-2) was synthesized according to

a literature method (139) with the following modifications.

A 920 mg (1.83 mmole) quantity of Fe3(CO)i2 and 449 mg (11.5 mmole)

potassium were placed in a 100 ml flask equipped with a glass coated

magnetic stir bar and a vacuum line adapter. After evacuation

approximately 10 mL of dry ammonia was condensed into the flask at -

196°C. The reaction was warmed to -78°C and stirred for 1 h. At this point

the characteristic blue color of the alkali-ammonia solution changed from blue to yellow. The ammonia was removed and the cream solid was pumped on the line for 2 h. to ensure the removal of ammonia. The yield was 1.28 g

(95% based on Fe3(C O )i2). I. R. (nCO, Nujol): 1720 (br) cm '1.

10. Dipotassium Tetracarbonyl Osmate (- 2).

Dipotassium Tetracarbonyl osmate (-2).was synthesized according to the method of Bhattacharyya and Shore (36) 152

11. Dipotassium Tetracarbonyl Ruthenate (-2).

Dipotassium Tetracarbonyl Ruthenate (-2).was synthesized according

to the method of Bricker and Shore (37).

12. Disodium Octacarbonyi Diferrate (-2)

Disodium octacarbonyi diferrate (-II) was synthesized according to

the method of Collman et. al. (134).

13. Disodium tetracarbonyl Metallate (-2) M = Fe, Ru, Os

Disodium tetracarbonyl Metallate (-2) M = Fe, Ru, Os were synthesized

according to the method of Stone, et. al. (9, 13).

14. Pentacarbonyl Rhenium Bromide

Pentacarbonyl rhenium bromide was prepared from the reaction of

Re2(CO)io and Br2 in methylene chloride. Once the reaction was complete the volatiles were pumped away leaving only Re(CO)sBr in the flask.

15. Potassium Cyclopentadienyl Carbonyl Nickellate (-1)

A 343 mg (2.68 mmole) napthlene and 100 mg (2.56 mmole) potassium were placed in a 50 mL two neck flask containing a Teflon coated magnetic stir bar. The second neck of the flask was stoppered and the apparatus was connected to a vacuum line extractor. After evacuation a 10 mL quantity of

THF was condensed into the flask at -78°C and the solution was stirred until chunks of potassium were no longer visible in the solution. The solution 153

was then frozen to -196°C (liquid N2) and the apparatus was filled with prepurified nitrogen. A tip tube containing 389 mg (1.28 mmole) [(q5-

C5Hs)Ni(CO)]2 was connected to the second neck of the vessel under issuing nitrogen flow. The apparatus was evacuated and warmed to room temperature. The [(q^-CsH5)Ni(CO)]2 was added portion wise over a period of 30 m. The solution was stirred for two hours. The reaction reaction produced no non-condensable gas. The volume of THF was reduced to 2 mL and 10 mL of dry pentane was condensed in the flask at -78°C. This caused the precipitation of a charcoal colored solid and gave a green solution. The solution was filtered and washed several times with fresh pentane until the drippings were colorless. The green solution was identified as (q5_

C5H5>3Ni3(CO)2 by infrared spectroscopy. The volatiles were removed and the solid was dried on the vacuum line for 1 h. The yield was 366 mg (75% based on [(q5-C5H5)Ni(CO)]2). I. R. (vco.THF): 1606 (s) cm’1.

16. Potassium Cyclopentadienyl Dicarbonyl Ruthenate (-1)

Potassium Cyclopentadienyl Dicarbonyl Ruthenate (-1) was prepared in a analogus manner to that of Potassium Cyclopentadienyl Dicarbonyl ferrate (-1) as reported by Shore and Plotkin (135).

A 1.04 g (4.85 mmole) quantity of benzophenone and 223 mg (5.70 mmole) potassium were placed in a 50 mL two neck flask containing a

Teflon coated magnetic stir bar. The second neck of the flask was stoppered and the apparatus was connected to a vacuum line extractor. After evacuation a 10 mL quantity of THF was condensed into the flask at -78°C 154

and the solution was stirred at room temperature until chunks of potassium

were no longer visible in the solution. The solution was then frozen to -

196°C (liquid N2) and the apparatus was filled with prepurified nitrogen. A

tip tube containing 1.20 g (2.70 mmole) [(T]5-C5H5)Ru(CO)2]2 was connected

to the second neck of the vessel under an issuing nitrogen flow. The

apparatus was evacuated and warmed to room temperature. The [(i)5-

C5H5)Ru(CO)2]2 was added portion wise over a period of 15 m. The solution

was stirred for lh giving a light blue solution and a yellow precipitate .

The volume of the THF solution was reduced to 5 mL and then 10 mL of

diethyl ether was condensed into the flask. The solution was filtered and

the solid was washed until the drippings were no longer blue and the

solvent was removed. . The brown-yellow solid was washed twice with fresh

THF to free the solid from the brown inpurity which left a bright yellow solid. The solvent was removed and the solid was dried on the vacuum line for 1 h. The yield was 1.32 g (94.0% based on [(Tl5-C5H5)Ru(CO)2]2)- I. R-

(vCo, THF): 2022 (w), 1959 (w), 1968 (w), 1894 (s), 1811 (s) cm '1.

17. Potassium Tetracarbonyl (q 2-Diborane) Ferrate (0)

Potassium Tetracarbonyl (q 2-Diborane) Ferrate (0) was synthesized according to the method of Shore and Medford (64, 81) with the following modifications.

In the dry box 921 mg (1.88 mmole) of freshly recrystallized

Fe3(CO)i2 and 450 mg (11.5 mmole) of potassium were added to a 100 mL 15 mm Solv-Seal flask. The flask contained a teflon coated magnetic stir bar 155

and was connected to a vacuum line extractor. The apparatus was evacuated

and 20 mL of dry INH3 was added at -78°C. The reaction mixture was stirred

at -78°C until the blue color of the ammonia had dissipated (10-20 minutes).

The ammonia was pumped away leaving cream white K2[Fe(CO)4] in the

flask. The solid was pumped on dynamically for one hour at 50° C to ensure

the removal of all the ammonia. Approximately 25 mL of Dry THF was

condensed into the flask at -78°C and the mixture was cooled to -196°C and

9.0 mmole B2H6 was added. The contents of the flask were warmed to room

temperature and stirred for 2.5 hours. The reaction evolved no non-

condensable gasses. The solution was filtered leaving a white precipitate

(KBH4) on the glass frit and a brown solution. The THF and excess THF-BH3

were pumped away leaving a brown oil in the collection flask. In the dry

box the collection flask was connected to a fresh extractor. The apparatus

was evacuated. 3 mL dry (CH3>20 was added at -78°C to dissolve the

K[Fe(CO)4(T|2-B2H5)] and at -196°C 15 mL of dry hexanes were added. The

mixture was warmed to -78°C and the (CH3)20 was removed while stirring

the contents of the flask. This caused brown K[Fe(CO)40n 2-B2Hs)] to

precipitate. The solid was collected by filtration and dried on the vacuum

line over night. The yield was 1.20 g (94% based on Fe3(CO)i2).

18 Tetrahydrido Dodecacarbonyl Tetraruthenium

Tetrahydrido dodecacarbonyl tetraruthenium was prepared from

Ru3(CO)i2 according to a published procedure (131). 156

19. Trimethyl Phosphine

Trimethyl Phosphine was obtained as the trimethyl phosphine silver iodide salt from Aldrich Chemical Company. It was freed by heating to

100°C while pumping dynamically and collecting the trimethyl phosphine in a -196°C trap. It was stored in a Pyrex tube with a Kontes stopcock at room temperature.

2 0 . Triosmium Dodecacarbonyl

Triosmium dodecacarbonyl was synthesized by using a modification of the method of Sievert and Shapely (136). The details of these modifications are described by Kennedy (137).

21. Triruthenium Dodecacarbonyl

Triruthenium dodecacarbonyl was synthesized by using a modification of a literature Method (138). 157

D. Reactions of Organometallic Anions with Diborane

1. Preparation of K[Ru(CO)4(ti2-B2H5)].

In the drybox a 50 mL flask was charged with 430 mg (1.48 mmole)

K2[Ru(CO)4] and a Teflon coated magnetic stirbar. The flask was connected

to a vacuum line extractor (Figure 47) and was subsequently evacuated on a

high vacuum line. Dry tetrahydrofuran (THF) was condensed into the flask

(Ca. 10 mL) at -78°C. The solution was then stirred at room temperature for

10 - 15 minutes to disperse the insoluble K2[Ru(CO)4]. Added to this

suspension was 2.26 mmole B2H6 by condensation at -196°C (liquid

nitrogen). The reaction mixture was warmed to room temperature and

stirred for two hours. During this time the light tan precipitate was

consumed and a red-brown solution with a white precipitate formed. The

solution was filtered through the extractor leaving the white precipitate on

the frit. The nitrate contained the product K[Ru(CO)4(q2-B2H5)] and excess

THF-BH3. The white precipitate was identified by infrared spectroscopy as

KBH4 and weighed 93.3 mg which represented a 92% yield. The volatiles

were pumped away under a dynamic vacuum through a removable U-trap maintained at -196°C. A red-brown oil remained in the flask. The reaction did not give off non-condensable gases. The collection flask was connected to a fresh extractor in the dry box. After evacuation 2 mL of dry dimethyl ether was added to the flask at -78°C (to dissolve the anion K[Ru(CO)4(n2-

B2H5)]). Dry hexane was condensed in the flask at -196°C and the apparatus 158

was wanned to -78°C. The dimethyl ether was removed dynamically which

caused the precipitation of the red-brown K[Ru(CO>4(t)2-B2H5)]. The solid

was collected by filtration and was dried on the vacuum line for one hour.

The yield was 376 mg which represents a 91% yield based on K2[Ru(CO)4].

Analysis: Calculated for C4H5B2O4RU.I/4THF: C, 20.22; H, 2.38. Found: C,

20.86, H, 2.42.

2. Preparation of K[Os(CO)4(ti2-B2H5)].

In the diybox a 50 mL flask was charged with 406 mg (1.07 mmole)

K2[Os(CO)4] and a Teflon coated magnetic stirbar. The flask was connected to a vacuum line extractor and evacuated on the vacuum line.

Approximately 10 mL of dry THF was condensed into the flask at -78°C. The solution was stilted at room temperature for 10 - 15 minutes to disperse the insoluble K2(Os(CO)4]. Added to this suspension was 1.62 mmole B2H6 by condensation at -196°C . The reaction was warmed to room temperature and stirred for three hours. During this time the yellow-white precipitate was consumed and a bright yellow solution with a white precipitate formed.

The solution was filtered through the extractor and the white solid was collected on the glass frit. The filtrate contained the product and excess

THF.BH3. The white precipitate was identified by infrared spectroscopy as

KBH4 and weighed 0.0582 g which represented a 100% yield. The volatiles were pumped away under a dynamic vacuum through a removable U-trap maintained at -196°C. A bright yellow oil remained in the flask. The reaction did not give off non-condensable gases. The reaction apparatus 159

was brought into the dry box and the collection flask was connected to a

fresh extractor. After evacuation 2 mL of dry dimethyl ether was added to

the flask at -78°C (to dissolve the anion K[Os(CO)4Cn2-B2H5)]). Dry hexane

was condensed in the flask at -196°C and the apparatus was wanned to -78°C.

The dimethyl ether was removed dynamically at -78° C causing the

precipitation of the yellow K[Os(CO)4(ti2-B2H5)]. The solid was collected by

nitration and the solid was dried on the vacuum line. The yield was 366 mg

which represents a 93% yield based on K2[Os(CO)4]. Analysis: Calculated

for C4H5B2O4OS.I/4THF: C, 15.56; H, 1.82. Found: C, 15.03, H, 1.83.

3. Synthesis of K[M(CO)4(ti2-B2D5)] (M = Ru, Os)

K[M(CO)4

procedure as K[M(CO)4(q2-B2H5)] (M = Ru, Os) with the exception of using

B2D6 instead of B2H6.

4. Preparation of (tis-C5H5)Ru(CO)2Oi2-B2H5).

In The Dry box 303 mg (1.16 mmole) of K[Cn5-C5H5)Ru(CO)2] was

added to a 50 mL long neck flask which was equipped with a Teflon coated

magnetic stir bar. The flask was connected to a vacuum line extractor.

After evacuation 5 mL of dry dimethyl ether was added at -78°C along with

2.50 mmole diborane which was added at -196°C. The mixture was wanned to

-3 8°C (acetonitrile/N2) and stirred for 4 h. During this time the color changed from an orange-yellow to a light yellow and the solution contained a white precipitate. The white solid was identified by infrared 160

spectroscopy as KBH4. The solution was filtered through the extractor by

quickly tipping the extractor while cooling the collection flask to -78°C.

The dimethyl ether and unreacted diborane was removed at -78° C by

pumping dynamically through a removable U-trap maintained at -196°C.

This left a yellow solid in the collection flask and a white solid on the frit.

The solid was collected in the dry box and weighed. The yield was 187 mg

(65% based on K[(T15-C5H5)Ru(CO)2]).

5. Preparation of K[Cr(CO>4(B3Hg)] from K2[Cr(CO)5] and

b 2h 6

In the dry box 110 mg (0.407 mmole) of freshly prepared K2[Cr(CO)5]

was added to a 50 mL reaction flask equipped with a Teflon coated magnetic

stir bar. The flask was attached to an extractor. After evacuation 5 mL of

dry THF was condensed into the flask at -78°C along with 1.16 mmole

diborane which was added at -196°C. The reaction was warmed to ambient

temperature and stirred for 2 h. During this time the color of the reaction

solution changed from brown to orange and the solution contained a white

precipitate. The reaction evolved 0.390 mmole CO. The solution was filtered

and the THF was removed. This left a white precipitate on the frit

(identified as KBH4 by infrared spectroscopy) and an orange oil which was

solidified by pumping on it dynamically over night. The yield was 61 mg

(61.5% based on K2[Cr(CO)5]). The spectra are in agreement with those reported in the literature. 161

6 . Reaction of K2[H2RtU(CO)i2] with diborane

In the dry box 110 mg (0.134 mmole) of freshly prepared

K2[H2Ru4(CO)i2] was added to a SO mL reaction flask equipped with a Teflon coated magnetic stir bar. The flask was attached to a vacuum line adapter.

After evacuation 5 mL of dry THF was condensed into the flask at -78° C along with 0.377 mmole of diborane which was added at -196°C. The reaction was warmed to ambient temperature and stirred for 10 days. The reaction evolved 0.25 mmole non condensable gas. An infrared spectrum of the reaction solution indicated that only K2[H2Ru4(CO)i2] was present. The boron-11 NMR spectrum showed onlt THF-BH3.

7 . Reaction of K2[Cn5-CsH5)V(CO)3] with diborane

In the dry box 88.8 mg (0.319 mmole) of freshly prepared K2[(il^-

C5H5)V(CO)3] was added to a SO mL reaction flask equipped with a Teflon coated magnetic stir bar. The flask was attached to a vacuum line extractor.

After evacuation 5 mL of dry THF was condensed into the flask at -78° C along with 0.639 mmole of diborane which was added at -196° C. The reaction was warmed to -23° C and stirred for one hour. The reaction mixture changed from a yellow suspention to a green solution containing a grey precipitate. The reaction evolved a negligible amount non condensable gas. The solution was filtered and the solvent and unreacted

THF.BH3 were removed. An infrared spectrum of the precipitate indicated 162

it was K[BH4]. A boron-11 NMR of the remaining solid did not yield a

resonance due to a boron compound.

8. Reaction of K[(Ti5-C5H5)Ni(CO)] with diborane

In the dry box 114 mg (0.600 mmole) of freshly prepared

K[dl5-C5H5)Ni(CO)J was added to a SO mL reaction flask equipped with a

Teflon coated magnetic stir bar. The flask was attached to a vacuum line

extractor. After evacuation 5 mL of dry Me20 was condensed into the flask

at -78QC along with 1.02 mmole of diborane which was added at -196°C. The

reaction was warmed to -78° C and stirred for 48 hours. The reaction

mixture changed from a brown-black suspention to a burgandy solution

which contained a black precipitate. The reaction evolved 0.520 mmole non

condensable gas which was analyzed by mass spectrometry as a mixture of

CO and H2. The solution was filtered and the solvent and unreacted

Me2 0 -BH3 were removed. A boron-11 NMR of the remaining solid did not

yield a resonance due to a boron compound.

E. Reactions of IM(CO)4(t)2-B2Hs)]- (M = Fe, Ru, Os)

1. Preparation of PPN[Ru(CO)4(q2-B2H5)].

In the dry box, 107 mg (0.384 mmole) of freshly prepared

K[Ru(CO)4(q2-B2H5)] and 207 mg (0.360 mmole) PPNC1 were placed in a 50 mL flask equipped with a stir bar and the flask was connected to a vacuum 163

line extractor. After evacuation 5 mL of dry CH2CI2 was condensed into the

flask at -78°C. The mixture was warmed to ambient temperature and stirred

for 2 h. The insoluble K[Ru(CO)4(t)2-B2H5)] was slowly consumed when the

soluble PPN[Ru(CO)4(h2-B2H5)] was formed. The reaction solution was filtered and the solvent was removed. This left a red-brown solid in the collection flask. This solid was collected and the yield was 235 mg (84% based on PPNC1). A nalysis: Calculated for C40H 35B2 NP2O4 RU: C, 61.72; H,

4.53; N, 1.80; Ru. 13.0; P, 7.96. Found: C, 60.25, H, 3.98; N, 1.94; Ru, 14.91; P,

7.08.

2. Preparation of PPN[Os(CO)4(q2-B2H5)].

In the dry box, 107 mg (0.384 mmole) of K[Os(CO)4(q2-B2H5)] and 152 mg (0.265 mmole) PPNC1 were placed in a 50 mL flask equipped with a stir bar and the flask was connected to a vacuum line extractor. After evacuation 5 mL of dry CH2CI2 was condensed into the flask at -78°C. The mixture was warmed to ambient temperature and stirred for 2 h. The insoluble K[Os(CO)40n2-B2H5)] was slowly consumed when the soluble

PPN[Os(CO)4(ti2-B2H5)] was formed. The reaction solution was filtered and the solvent was removed. This left a yellow solid in the collection flask.

This solid was collected and the yield was 176 mg (77% based on PPNC1).

Analysis: Calculated for C40H35B2NP2O4OS: C, 55.38; H, 4.07; N, 1.61; Os,

21.92; P, 7.14. Found: C, 55.31, H, 4.00; N, 1.59; Os, 21.78; P, 6.91. 164

3. Formation of HRu(CO)40l2-B2H5)

In the dry box, 89.6 mg (0.321 mmole) K[Ru(CO)4(ti2-B2H5)] was

placed in a 15 mL two neck bulb. The bulb contained a Teflon coated

magnetic stir bar, a vacuum adapter and a fritted side arm containing a

NMR tube. The apparatus was evacuated and 1 mL of dry CD2CI2 was

condensed into the flask at -78°C. The flask was frozen with a -196°C trap

and 0.310 mmole HC1 gas was condensed into the flask. The reaction vessel

was warmed to -111°C and stirred for one hour. The brown-red, insoluble

K[Ru(CO)4(h2-B2H5)] reacted immediately at -111°C to form the red, soluble

HRu(CO)4(t]2-B2H5). At -78°C a slow gas evolution was evident. The reaction

was frozen to -196°C and a negligible amount of non-condensible gas was

formed. The reaction solution was tipped into the NMR tube while maintaining the apparatus at -78°C and the NMR tube was flame sealed.

The NMR tube was stored at -196°C until the spectra were recorded.

4. Formation of DRu(CO)4(ti2-B2H5)

The compound DRu(CO)4(tj2-B2H5) was prepared following the procedure for HRu(CO)4Cn2-B2H5) with the exception of using DC1 instead of

HC1.

5. Formation of HRu(CO)40i2-B2D5)

The compound HRu(CO)4(tj2-B2Ds) was prepared following the procedure for HRu(CO)4(n 2-B2H 5) with the exception of using

K[Ru(CO)4(ti2-B2D5)1 instead of K[Ru(CO)4(n2-B2H5)]. 165

6. Decomposition of a mixture of HRu(CO)4(

DRu(CO)4(n2-B2H5)

The compounds DRu(CO)4(q 2-B 2H5) (0.391 mmole) and HRu(CO)4(ti2-

B2D5) (0.358 mmole) were generated as described above in the appararatus pictured in Figure 48. The syntheses were kept independent of eachother by keeping the ajoining stopcock closed and connecting the apparatus to two independent ports on the high vacuum line. After completion of the syntheses HRu(CO)4(q2-B2D5) and DRu(CO)4(t]2-B2H5) the entire apparatus was placed in a -78° C bath. Once thermal equilibrium was attained the contents of one flask was added to the other flask by opening the ajoining stopcock and tipping the contents of one flask.into the other. After the transfer was complete, the ajoining stopcock was closed and the contents were frozen to -196°C. The flask was pumped on for 10 minutes at -196°C to ensure complete evacuation. The mixture was warmed to -111°C and stirred for 20 minutes to attain a homogeneous solution. The contents of the flask were warmed to room temperature and decomposed. This required one hour of reaction time. The flask was frozen to -196°C and the non-condensable gas was pumped away. The diborane mixture was removed at -78°C and condensed into a sample tube for mass spectral analysis.

7 . Formation of HOs(CO)4(q2-B2Hs)

In the dry box, 107 mg (0.291 mmole) K[Os(CO)4(n2-B2H5)] was placed in a 15 mL two neck bulb . The bulb contained a Teflon coated magnetic 166

stir bar, a vacuum adapter and a fritted side arm containing a NMR tube.

The apparatus was evacuated and 1 mL of dry CD2CI2 was condensed into the

flask at -78°C. The flask was frozen with a -196°C trap and 0.538 mmole HC1

gas was condensed into the flask. The reaction vessel was warmed to -78°C

and stirred for one hour. The yellow, insoluble K[Os(CO)4(ti2-B2H5)] reacted

immediately at -78°C to form the yellow, soluble HOs(CO)4(ti2-B2H5). The

reaction was frozen to -196°C and a negligible amount of non-condensible

gas was formed. The excess HC1 was measured by maintaining the reaction

at -111°C and Toeplerizing the volatiles. The unreacted HC1 was measured to

be 0.250 mmole which indicated 0.288 mmole HC1 reacted with K[Os(CO>4 (t)2-

B2H5)]. The solution was wanned to room temperature and tipped into the

NMR tube and the NMR tube was flame sealed. The NMR tube was stored at

-196°C until the spectra were recorded.

8 . Formation of DOs(CO> 4 (t]2 -B 2 H 5 )

The compound DOs(CO)4(t]2-B2H5) was prepared following the

procedure for HOs(CO)4(t]2-B2H5) with the exception of using DC1 instead of

HC1.

9. Formation of HOs(CO) 4 (t)2 -B 2 D 5 )

The compound HOs(CO)4(ti2-B2D5) was prepared following the procedure for HOs(CO)4 (t] 2-B 2H5) with the exception of using K[Os(CO)4 (t]2-

B 2 D 5 )] instead of K[Os(CO)4 (ti2 -B2 H 5 )]. 167

10. Reaction of HOs(CO)4(t)2-B2Hs) with Br2

The compound HOs(CO)4 (ii2-B 2H 5 ) was generated as described above

in a 50 ml flask from the reaction of 105 mg (0.285 mmole) K[Os(CO)40n2-

B2H5)] and 0.376 mmole HC1.. After the formation of HOs(CO)4 (t|2-B 2H 5 ) was

complete the excess HC1 was pumped away at -78° C dynamically into a

removable U-trap maintained at -196°C. Approximately a 5 times molar

excess Br2 was condensed into the flask at -78°C. The reaction mixture was

stirred at room temperature for 15 minutes. The volatiles were pumped

away leaving a cream white solid. This solid was identified as Os(CO)4Br2 by

infrared spectroscopy.

11. Formation of (CH3)Os(CO )40l 2-B2H 5)

In the dry box, 102 mg (0.277 mmole) K[Os(CO)4 (ti2-B2H5)] and 43.0

mg (0.290 mmole) (CH3)30BF4were placed in a 50 mL bulb. The bulb

contained a Teflon coated magnetic stir bar and was connected to a vacuum

line extractor. The apparatus was evacuated and 2 mL of dry (CH3)20 was

condensed into the flask at -78° C. The reaction mixture was stirred at -78° C

for four h. The reaction was frozen to -196°C and no non-condensible gas was formed. The (CH3)20 was removed at -78°C and the yellow residue was pumped on for 1 hour. The remaining solid was dissolved in CH2CI2 which afforded a yellow solution and a white precipitate. The solution was Altered and the CH2CI2 was removed affording a yellow oil. Solution samples for 168

spectra were stored at -196°C until needed. CH3SO3F can be substituted for

(CH3>30BF4 in this synthesis.

12. Preparation of Ph3PAuOs(CO)4(ti2-B2Hs)

In the dry box, 110 mg (0.298 mmole) K[Os(CO)4(t\ 2-B 2H5)] and 134 mg

(0.274 mmole) PI13PAUCI were placed in a 50 mL bulb which contained a

Teflon coated magnetic stir bar. The flask was connected to a vacuum line

extractor. The apparatus was evacuated and 5 mL of dry THF was condensed

into the flask at -78° C. The reaction vessel was warmed to 0°C and stirred

for 15 minutes. The yellow K[Os(CO)4(ii2-B2H5)] reacted immediately at 0°C

and formed the yellow-brown Ph3PAuOs(CO)40i2-B2H5). The reaction

mixture was frozen to -196°C and nonon-condensible gas was formed. The

THF was removed and dry CH2CI2 was condensed into the flask. The solution

was Altered leaving KC1 on the glass frit. The solvent was pumped away

and the collection flask was connected to a fresh extractor in the dry box.

The solid was dissolved in a minimum amount of CH2CI2 and the solid

Ph3PAuOs(CO)4(ii2-B2H5) was precipitated by the addition of 5 mL of dry

hexanes. The solid was isolated by filtration and dried on the vacuum line

for 1 hour. The yield was 162 mg (75% based on PI13PAUCI). A n a ly sis:

Calculated for C22H20AUB2O4OSP: C, 33.50; H, 2.56; P, 3.93. Found: C, 33.43, H,

2.39; P, 4.54. 169

13. Preparation of Ph3PAuRu(CO)4(Ti2-B2H5)

In the diy box, 74.2 mg (0.266 mmole) K[Ru(CO)4(n2-B2H5)] and 124

mg (0.2S0 mmole) PI13PA11CI were placed in a 50 mL bulb which contained

a Teflon coated magnetic stir bar. The vessel was connected to a vacuum

line extractor. The apparatus was evacuated and 5 mL of dry THF was

condensed into the flask at -78°C. The reaction vessel was warmed to 0°C

and stirred for 30 minutes. The red-brown K[Ru(CO)4(ti2-B2H5)] reacted

immediately at 0°C and formed the yellow-brown Ph3PAuRu(CO)4(Ti2-B2H5).

The reaction mixture was frozen to -196°C and a negligible amount of non-

condensible gas was formed. The THF was removed and dry CH2CI2 was

condensed into the flask. The solution was filtered leaving KC1 on the glass

frit. The solvent was pumped away and the collection flask was connected

to a fresh extractor in the dry box. The solid was dissolved in a minimum

amount of CH2CI2 and the solid Ph3PAuRu(CO)4(n2-B2H5) was precipitated

by the addition of 5 mL of dry hexanes. The solid was isolated by filtration

and dried on the vacuum line for 1 hour. The yield was 126 mg (72% based

on Ph3PAuCl).

14. Formation of Ph3PAuFe(CO)4(ii2-B2H5)

In the dry box, 107 mg (0.458 mmole) K[Fe(CO)40l2-B2H5)] and 224 mg

(0.452 mmole) Ph3PAuCl were placed in a 10 mL bulb which contained a

Teflon coated magnetic stir bar and a NMR tube side arm attachment. The apparatus was evacuated and 2 mL of dry (CH3)20 was condensed into the flask at -78° C. The reaction vessel was stirred for 30 minutes. The brown 170

K[Fe(CO)40l2-B2H5>] reacted immediately at -78°C and formed the red-

brown Ph3PAuFe(CO)4(ii2-B2H5). The reaction mixture was frozen to -196°C

and only a negligible amount of non-condensible gas was formed. The

(CH3>20 was removed at -78°C and approximately 1/2 mL of dry CDCI3 was

condensed into the flask at the same temperature. The solution was tipped

into the NMR tube while maintaining the apparatus at -78° C. The NMR tube

was flame sealed and stored at -196°C until spectra were recorded.

1 5 . K[Os(C0)4(112-B2H5)] with KH

In the dry box, 97.5 mg (0.265 mmole) K[Os(CO)4(n2-B2H5)] and 12.0

mg (0.299 mmole) KH were added to a 50 mL flask which contained a Teflon coated magnetic stirbar. The flask was connected to a vacuum line extractor. The apparatus was evacuated and 5 mL of dry THF was condensed into the reaction flask at -78° C. The mixture was warmed to room temperature and stirred for seven days. The reaction mixture evolved 0.100 mmole non-condensable gas which was characterized by mass spectrometry as H2. The solution was yellow with a grey-white precipitate.

The solution was filtered and the solvent was removed. The solid was characterized by X-ray diffraction as KH and the yellow solution was characerized by boron-11 NMR spectroscopy as K[Os(CO)4(n2-B2H5)].

16. PPN[Os(CO)4dl2-B2H5)] with KH

In the dry box, 232 mg (0.267 mmole) PPN[Os(CO)4(tl2-B2H5)] and 13.0 mg (0.324 mmole) KH were added to a 50 mL flask which contained a Teflon 171

coated magnetic stirbar. The flask was connected to a vacuum line extractor. The apparatus was evacuated and 5 mL of diy THF was condensed into the reaction flask at -78° C. The mixture was warmed to room temperature and stirred for three days. The reaction evolved only a negligible amount of non-condensable gas. The color of the solution was yellow with a grey-white precipitate. The solution was filtered and the solvent was removed. The solid was characterized by X-ray diffraction as

KH and the yellow solution was characerized by boron-11 NMR as

PPN[Os(CO)40l2-B2H5)].

17 . K[Os(CO)4(ti2-B2H5)] with (PPh3)2C uBrl/2 C6H 6

In the dry box, 101 mg (0.274 mmole) K[Os(CO)4Cn2-B2H5)] and 198 mg

(0.280 mmole) (PPh3)2CuBr-l/2C6H6 were added to a 50 mL flask which contained a Teflon coated magnetic stirbar. The flask was connected to a vacuum line extractor. The apparatus was evacuated and 5 mL of dry CH2C12 was condensed into the reaction flask at -78°C. The mixture was warmed to room temperature and stirred for 22 hours. The color of the solution changed from yellow to dark orange. The reaction mixture was filtered giving a white precipitate and an orange solution. The boron-11 NMR spectrum of the solution indicated that the only boron containing species was Ph3P*BH3. 172

18 . PPN[Os(CO)4(t12-B2H5)] with H2Os3(CO)io

In the dry box, 48.0 mg (0.130 mmole) PPN[Os(CO)4(ii2-B2H5)] and 103

(0.121 mmole) H20s3(CO)io were added to a 50 mL flask which contained a

Teflon coated magnetic stirbar and connected to a vacuum line adapter.

The apparatus was evacuated and 5 mL of dry CH2CI2 was condensed into the reaction flask at -78°C. The mixture was wanned to room temperature and stirred for 24h. The reaction evolved a negligible amount of non- condensable gas. The color of the solution was dark violet. The boron-11

NMR spectrum of the solution showed PPN[Os(CO)40nB 2H5)] as the only boron containing product. The infrared spectrum indicated a mixture of

H2Qs3(CO)io and PPN[Os(CO)4(h2-B2H5)]. The boron-11 NMR spectrum of the reaction solution was again taken after one month. The spectrum indicated a mixture of boron containing products one being HOs6(CO )i7B which contains resonances 187 ppm. The * H-NMR showed the hydride resonance at -19.5 ppm.

19. P P N [O s(C O )4(ti2-B 2H 5)] with Cr(CO)6

In the dry box, 390 mg (0.450 mmole) PPN[Os(CO)4(ti2-B2H5)] and 99.0

(0.450 mmole) Cr(CO)6 were added to a 50 mL flask which contained a Teflon coated magnetic stirbar. The flask was connected to a vacuum line adapter.

The apparatus was evacuated and 5 mL of dry CH2C12 was condensed into the reaction flask at -78°C. The mixture was warmed to room temperature and stirred for 20 hours. The reaction evolved a negligible amount of non- condensable gas. The color of the solution was yellow. The infrared 173

spectrum indicated that no reaction had occured. The flask was then placed

in an oil bath preheated to 42° C and stirred for two days. A boron-11 NMR

spectrum of the solution showed PPN[Os(CO)4(ti2-B2H5)] as the only boron

containing product. The infrared spectrum indicated that the reaction

solution contained a mixture of Cr(CO)6 and PPN[Os(CO)4(ti2-B2Hs)].

2 0 . K [ O s ( C O ) 4 ( ti2 -B 2 H 5 )] with (n5-C5H5)Fe(CO)2I

In the dry box, 127 mg (0.345 mmole) K[Os(CO)4(n2-B2H5)] and 102

(0.335 mmole) (ti5-C5H5)Fe(CO)2l were added to a 50 mL flask which

contained a Teflon coated magnetic stirbar. It was then connected to a

vacuum line adapter. The apparatus was evacuated and 5 mL of dry toluene

was condensed into the reaction flask at -78°C. The mixture was warmed to

room temperature and stirred for 24 hours. The reaction mixture was

frozen to -196°C and no non-condensable gasses evolved. An infrared

spectrum revealed only starting material. The mixture was then placed in

an oil bath preheated to 40° C and stirred for 24h. The reaction mixture

evolved a 1.20 mmole of non-condensable gas. The color of the solution was

red-brown. The boron-11 NMR spectrum of the solution showed a mixture

of unassignable boron containing products. The reaction was deemed

unsucessful.

21. K[O s(CO)4(ti2-B2H5)] with Re(CO)sBr

In the dry box, 100 mg (0.272 mmole) K[Os(CO)4(ti2-B2H5)J and 110

(0.271 mmole) Re(CO)5Br were added to a 50 mL flask which contained a 174

Teflon coated magnetic stirbar and connected to a vacuum line extractor.

The apparatus was evacuated and 5 mL of dry THF was condensed into the reaction flask at -78°C. The mixture was stirred at room temperature for 36 h. The THF was removed and dry CH2CI2 was condensed into the flask. This gave a yellow precipitate and a clear, colorless solution, which were isolated by filtration. The infrared spectrum of the solution showed only

Re(CO)sBr was present, and the yellow solid was identified as K[Os(CO)4Cn2-

B2H5)] by boron-11 NMR spectroscopy.

2 2 . K[Os(CO)4(ti2-B2H5)] with (CH3)2O B H 3

In the diy box, 100 mg (0.272 mmole) K[Os(CO)4(ti2-B2H5)] was added to a SO mL long neck flask which contained a Teflon coated magnetic stirbar. The flask was attached to a vacuum line extractor. The apparatus was evacuated and 3 mL of dry (CH3)20 was condensed into the reaction flask at -78°C. The mixture cooled to -196°C and 0.592 mmole B2H6 was added to the flask. The mixture was then stirred at -78°C for 24 hours and afforded a yellow solution. The (CH3)20 was removed and dry CH2C12 was condensed into the flask. This gave a yellow precipitate and a clear, colorless solution, which were isolated by filtration. The infrared spectrum and the 11B NMR spectrum of the yellow solid identified it as K[Os(CO)4(ti2-B2H5)]. 175

F. Synthesis of Group 8 Binuclear Diahions

1. Preparation of Na2[Os2(CO)g]

In the dry box, 107 mg (0.307 mmole) Na2[Os(CO)4] was added to a 50

mL long neck flask which contained a Teflon coated magnetic stirbar. The

flask was attached to a vacuum line adapter. The apparatus was evacuated

and 5 mL of dry THF was condensed into the reaction flask at -78° C. The

mixture was frozen to -196°C and 0.308 mmole CO2 was added to the flask.

The entire apparatus was wrapped in aluminum foil to ensure the complete

absence of light. The mixture was stirred at -78° C overnight. The

unreacted CO2 was removed by pumping on the flask at -78° C for one hour.

The mixture was then stirred at room temperature for 5 hours. During this

time 0.15 mmole CO evolved representing 98% theory. The bulb was

connected to an extractor in the dry box and the apparatus was evacuated.

The THF solution was filtered and the solvent was removed. The collection flask was connected to a fresh extractor in the dry box. After evacuation, the yellow Na2[Os2(CO)8l was dissolved in a minimum amount of THF. The addition of 10 mL of dry hexane caused Na2[Os2(CO)8] to precipitate as a fine yellow powder. The powder was collected by filtration and dried on the vacuum line for one hour. The yield was 85 mg (85% yield based on

Na2[Os(CO)4]). 176

2. Preparation of (PPh4 )2 FeRu(CO)g

In the dry box 200 mg (0.772 mmole) Na2[Ru(CO)4] was added to a long neck flask which contained a Teflon coated magnetic stirbar and a vacuum line adapter. Approximately 10 mL dry THF was added to the flask at -78°C.

The apparatus was cooled to -196°C and 1.54 mmole CO2 was added to the flask. The entire apparatus was wrapped in aluminum foil to ensure the complete absence of light. The mixture was stirred at -78°C overnight. The excess CO2 was removed by pumping it away at -78°C for one hour. The contents of the flask were transferred through a U-tube which was connected to a flask containing 85 mg (0.40 mmole) Na2[Fe(CO)4] (the entire system was wrapped in foil). This was done by slowly warming the flask containing the THF solution of Ru(CO)5 to room temperature while maintaining the recieving flask at -196°C. After completion of the transfer the mixture was warmed to room temperature and stirred for 24 hours.

During this time 0.45 mmole CO evolved representing 113% of the theoritical CO evolution. The flask was connected to an extractor in the dry box. After evacuation, the red-brown Na2[FeRu(CO)s] was dissolved in a minimum amount of THF. The addition of 10 mL of dry hexane caused

Na2[FeRu(CO)8] to precipitate as a fine red-brown powder. The powder was collected by filtration and dried on the vacuum line for one hour.

In the dry box 150 mg (0.351 mmole) Na2[FeRu(CO)8] and 205 mg

(0.492 mmole) PPh4Br was added to a 50 mL bulb containing a teflon coated magnetic stirbar. The flask was connected to a vacuum line extractor.

After evacuation 10 mL of dry THF was added to the flask. The mixture was 177

stirred for three hours. During this time a brown solid precipitated from the solution leaving a red-brown solution. The solid was isolated by filtration and was washed with THF. The solvent was removed and a fresh collection flask was connected to the extractor in the dry box. The compound (PPh4)2[FeRu(CO)s] was separated from the precipitate by condensing dry CH3CN into the reaction flask and washing the precipitate.

This left NaBr on the glass frit. The solvent was then removed and the collection flask was connected to a fresh extractor in the dry box. The apparatus was evacuated and the solid was dissolved in a minimum amount of CH3CN. The addition of 10 mL Et20 caused the precipitation of the red- brown (PPh4)2[FeRu(CO)8l as a fine powder. The powder was isolated by filtration and dried on the vacuum line. The yield was 149 mg (50% based on Na2[FeRu(CO)8]).Analysis: Calculated for C56H40P2OsFeRu: C, 63.47; H,

3.80; P. 5.85; Ru, 9.54; Fe, 5.27. Found: C, 64.27, H, 4.25; P, 5.44; Ru, 8.94;

5Fe, 4.91.

3. Preparation of (PPh4)2FeOs(CO)s

The synthesis of this compound was performed following a procedure similar to that of (PPh4)2FeRu(CO)8 Os(CO)s was generated from

163 mg (0.47 mmole) Na2[Os(CO)4] and 0.936 mmole CO2 in THF. The Os(CO)s and the THF were transferred through a U-tube which was connected to a flask containing 103 mg (0.48 mmole) Na2[Fe(CO)4] (the entire system was wrapped in foil). After completion of the transfer the mixture was warmed to room temperature and stirred for 48 hours. During this time 0.43 mmole 178

CO evolved representing 90% of the theoritical CO evolution. The salt was

precipitated with dry hexane and washed thus producing 206 mg of red-

brown, impure Na2[FeOs(CO)8] (83% yield based on Na2[Fe(CO)4]). The

powder was collected by filtration and dried on the vacuum line for one

h o u r.

A metathesis reaction was performed using 206 mg (0.400 mmole)

Na2[FeOs(CO)8] and 300 mg (0.720 mmole) PPh4Br in THF at ambient temperature. After three hours a red-brown solid formed along with a red solution. The solid (PPh4)2[FeOs(CO)s] was isolated using the same procedure as that of (PPh4)2[FeRu(CO)8l- The yield was 229 mg (50% based on Na2[FeOs(CO)8l).AnaIysis: Calculated for C56H4oP20sFeOs: C, 58.54; H,

3.51; P, 5.39; Os, 16.56; Fe, 4.86. Found: C, 64.23, H, 4.47; P, 5.87; Os, 12.90; Fe,

5.62.

4. Preparation of (PPh4)2RuOs(CO)8

The synthesis of this compound was performed following a procedure similar to that of (PPh4)2FeRu(CO)s. Os(CO)s was generated from

297 mg (0.84 mmole) Na2[Os(CO)4] and 1.70 mmole CO2 in THF. The Os(CO)5 and the THF were transfered through a U-tube which was connected to a flask containing 150 mg (0.58 mmole) Na2[Ru(CO)4] (the entire system was wrapped in foil). After completion of the transfer the mixture was warmed to room temperature and stirred for 24 hours. During this time 0.65 mmole

CO evolved representing 112% of the theoritical CO evolution. The salt was precipitated with dry hexane and washed thus producing 283 mg of brown. 179

impure Na2[RuOs(CO)8] (75% yield based on Na2[Fe(CO)4]). The powder was collected by filtration and dried on the vacuum line for one hour.

A metathesis reaction was performed using 283 mg (0.430 mmole)

Na2[RuOs(CO)8] and 303 mg (0.720 mmole) PPh4Br in THF at ambient temperature. After three hours a brown solid formed along with a red- brown solution. The solid (PPh4)2[RuOs(CO)8] was isolated using the same procedure as that of (PPh4)2[FeRu(CO)s]. The yield was 231 mg (45% based on Na2[RuOs(CO)8l). Analysis: Calculated for C56H40P2O8RUOS: C, 56.33; H,

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INFORMATION to USERS the Most Advanced Technology Has Been Used to Photo­ Graph and Reproduce This Manuscript from the Microfilm Master

INFORMATION to USERS the Most Advanced Technology Has Been Used to Photo Graph and Reproduce This Manuscript from the Microfilm Master