Xerox University Microfilms, Ann Arbor, M Ichigan 48106

I I I 77-2394

EDWARDS, Robert Charles, 1949- SYNTHESES AND CHARACTERIZATION OF CHROMIUM COMPLEXES WITH TETRAAZA MACROCYCLIC LIGANDS.

The Ohio State University, Ph.D., 1976 Chemistry, inorganic

Xerox University Microfilms, Ann Arbor, Michigan 48106 SYNTHESES AND CHARACTERIZATION OF CHROMIUM COMPLEXES WITH TETRAAZA MACROCYCLIC LIGANDS

DISSERTATION

Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University

By Robert Charles Edwards, B.S.

The Ohio State University 1976

Reading Committee: Approved by Professor Daryle H. Busch Professor Devon W. Meek Professor Eugene P. Schram Advised Department of Chemistry To Debra and Marie

& # 5J: aj: % # # # ACKNOWLEDGEMENTS

I would like to acknowledge the help given to me by fellow graduate students, post-doctoral fellows in Dr. Busch's group, and the staff in the Department of Chemistry. I want to especially thank Professor Daryle H„ Busch for his guidance and understanding,,

iii CURRICULUM VITAE

March 2, 1949...... Born, Marion, Ohio

1971 ...... B .S., Heidelberg College Tiffin, Ohio

1971-1974...... Teaching Associate, Dept, of Chemistry, The Ohio State University, Columbus, Ohio

1974-197 5 ...... Allied-Chemical Fellow The Ohio State University, Columbus, Ohio

1975-1976 ...... Research Associate, Dept, of Chemistry, The Ohio State University, Columbus, Ohio

1976 ...... Ph. D ., The Ohio State University, Columbus, Ohio

PUBLICATIONS

Robert C. Edwards and Daryle H. Busch, "Synthesis and Properties of Chromium(I), (III), and (IV) Complexes", American Chemical Society Centennial Meeting, New York City, New York, April, 1976, Abstr. INOR-153.

FIELD OF STUDY

Major Field: Chemistry

Specialization—Inorganic Coordination Chemistry Professor Daryle H. Busch, adviser

iv TABLE OF CONTENTS Page. Acknowledgements ...... iii

Curriculum Vitae...... iv

List of Tables ...... vii

List of Figures ...... x

Introduction, ...... 1

Experimental...... 19

P hysical ^Measurements...... co.o...... 0. 00. 0. .0. 00...... 19 S yntheses ...... 21

Results and Discussion...... 37

Preparation of [Cr(Me 2[l4]tetraenatoN 4)(py) 2]PFG, [Cr(Me2[i5 ]- tetraenatoN4) (py) 2]PFG> [Cr(Me2[ l6]tetraenatoN 4)(py) 2]PFG, and [Cr(M e4[l4]tetraenatoN 4)(py) 2]PF6o ...... 37 Preparation of [Cr(Me 2[Z]tetraenatoN 4)(L)2]PF 6 (Z = 14, 15, or 16) and [Cr(Me4[l4]tetraenatoN 4)(L)2]PFG (L = dimethylformamide, 1-methylimidazole, thiocyanate, or cyanide)...... 40 Characterization of [Cr(Me 2[Z]tetraenatoN 4)(L)2jPFG (Z = 14, 15, or 16) and [Cr(Me4[l4]tetraenatoN 4)(L)2]PFG (L = pyridine, dimethylforma mide, and 1-methylimidazole) ...... 43 Characterization of Cr(Me 2[Z]tetraenatoN 4)(NCS)(py), Cr(Me 4[l4]- tetraenatoN 4)(NCS)(py), and Cr(Me 2[Z]tetraenatoN4)CN (Z = 14, 15, o r 1 6 )...... 57 Oxidation and Other Reactions of the Chromium!HI) Complexes ...... 63 Preparation of Cr(Me 2[Z]tetraenatoN 4)(CGH5)(py) (Z = 14, 15, or 16) and Cr(Me2[14]tetraenatoN4) (L)(py) (L = Me or n-Bu) 67 Characterization of Cr(Me 2[Z]tetraenatoN 4)(C6H5)(py) (Z = 14, 15, or 16) and Cr(Me 2[l4]tetraenatoN 4)(L)(py) (L = CH 3 or n-B u) ...... 68 Electronic Spectra of the Chromium!HI) Complexes ...... 75 Electrochemistry of the Chromium(III) Complexes...... 86 ESR Spectra of the Chromium(IU) Complexes...... 91 Preparation of [Cr(Me 2[l4]tetraenatoN 4) (CGH5)]X (X = I or SCN) ...... 100

v TABLE OF CONTENTS

Page

Characterization of [Cr(Me 2[i4 ]tetraenatoN 4)(C 6H5)]X (X = I and SCN) ...... io i Preparation of Cr(Me 2[l4]tetraenatoN 4)(NO) and [Cr(Me6[i4]- 4, il-dieneN 4)(NO)(N02)]PFG...... 112 Characterization of Cr(Me 2[i4]tetraenatoN 4)(NO) and [Cr(Mee[i4j4, ll-dieneN 4)(N 0)(N 02)]P F s...... 113 Syntheses and Characterization of Chromium(Il) and (III) Complexes with MeG[l4]4, ll-dieneN4„ ...... „ ...... 123 Preparation of the Chromium (II) and Chromium(III) Complexes 0 ...... 123 Characterization of the Chromium(H) and Chromium(IU) C omplexe s ...... 124

AppendlXo ...... •o...oao....«ooo...«o*...... a..aoo.o..e...... 133

BeferenCeSo 138

vi LIST OF TABLES Page Table 1. Analytical Data for the Complexes, [Cr(Me [ZjtetraenatoN^- (L)2]PF 6 ...... *...... 44

Table 2. Selected Infrared Absorptions of the Complexes, [Cr(Me [ZjtetraenatoN^lL^ ]PFG ...... : ...... 48

Table 3. Physical Properties of the Complexes, [Cr(Me [ZJtetraenato- N4)(L)2]P F 6...... * 49

Table 4. Temperature Dependence of the Magnetic Susceptibility of [Cr(Me2{44]tetraenatoN4)(py)2]PF6o 51

Table 5. Temperature Dependence of the Magnetic Susceptibility of [C r (Me2115] te tr aenatoN4) (py) 2] PF 6...... 52

Table 6. Temperature Dependence of the Magnetic Susceptibility of [Cr(M e2[ l6]tetraenatoN 4)(py) 2]PFG...... 53

Table 7. Temperature Dependence of the Magnetic Susceptibility of [Cr(Me4[l4]tetraenatoN 4)(py)2]PFg ...... 54

Table 8 . Magnetic Moments and Weiss Constants Calculated from the Variable Temperature Magnetic Susceptibility Data of the Bis- physical Complexes ...... 56

Table 9. Analytical Data for the Complexes, Cr(Me [ZjtetraenatoN^- (A)(B)...... ? ...... 58

Table 10. Selected Infrared Absorption Bands of the Complexes, Cr(Me [Z]tetraenatoN 4)(A )(B )...... 61 x Table 11. Physical Properties of the Complexes, Cr(Me [Zjtetraenato- N4)(A)(B)...... X...... 62

Table 12. Analytical Data for the Complexes with Aryl and Alkyl Ligands... 69

vii Page

Table 13. Selected Infrared Absorptions for the Complexes with Aryl and Alkyl Ligands...... 72

Table 14. Physical Properties of the Complexes with Alkyl and Aryl L ig a n d s...... 74

Table 15. Comparison of Calculated and Observed Spectral Band Positions of Chromium (HI)—Ethylene diamine Complexes. „...... 78

Table 16. Electronic Spectral Data for Chromium(HI) Complexes with; the Ligands Me 6[i4]aneN 4 and Me6[i4]4, ll-dieneN 4 ...... 79

Table 17. Electronic Spectral Data for the Complexes, [Cr(Me [Z]- tetraenatoN 4)(L)2]PF 6...... X...... 80

Table 18. Electronic Spectral Data for the Complexes, Cr(Me [Z]- tetraenatoN ^ (A) (B) ...... X...... 81

Table 19. Electronic Spectral Data for the Complexes, Cr(Me 2[Z]- tetraenatoN 4) (R) (py)...... 82

Table 20. Electrochemical Data for the Complexes, [Cr(Me [Z]- tetraenatoN 4) (L) 2]P F e...... 87

Table 21. Electrochemical Data for the Complexes, Cr(Mex[Z]- tetraenatoN^ (A) (B) ...... 88

Table 22. Electrochemical Data for the Complexes, Cr(Me 2[Z]- tetraenatoN4) (R) (py) ...... 89

Table 23. Physical Properties of the Chromium(IV) Complexes...... 108

Table 24. Electronic Spectral Data for the Chromium(IV) Complexes...... 108

Table 25. Analytical Data for the Chromium (I) Nitrosyl Complexes ...... 116

Table 26. Physical Properties of the Chromium(l) Nitrosyl Complexes.... 116

Table 27. Electronic Spectral Data for the Chromium(I) Nitrosyl C o m p lex es ...... 116

v iii Page

Table 28. Analytical Data for the Chromium(II) Complexes with Me6[l4]4, ll-dieneN 4 ...... 125

Table 29. Physical Properties of the Complexes with Me 6[l4]4, ii-d ie n e N 4. . 126

Table 30. Electrochemical Data for the Cliromium(Il) Complexes ...... 127

Table 31. Electronic Spectral Data for the Chromium(II) Complexes with Me6[l4]4, il-dieneN 4...... 128

Table 32. Physical Properties of the Complexes, [Cr(Me 6[l4]4, 11-diene- N^XglPFg...... 130

Table 33. Analytical Data for the Complexes, [Cr(Me 6[l4]4,11-dieneN^- X2]PFg...... 131

Table 34. Electronic Spectral Data for the Complexes, [Cr(Mee[l4]4,11- dieneN 4)X]PF6...... 132

ix LIST OF FIGURES

Page

Figure 1. Infrared Spectrum of [Cr(Me 2[i4]tetraenatoN 4)(py) 2]PFG...... 45

Figure 2. Infrared Spectrum of [Cr(Me 2[l4]tetraenatoN 4)(dmf)2]PFG...... 46

Figure 3. Infrared Spectrum of [Gr(Me 4[l4]tetraenatoN 4)(M e-Im )2]PF6...... 47

Figure 4. Variation of 1 / xm with Temperature for: #» - [C r (Me4 [ 14 JtetraenatoN 4) (py) 2 ]PFG; & - [C r(M e2 [ 14 JtetraenatoN 4) (py) 2 ]PFg; ® -[C r(M e2[l5]tetraenatoN 4)(py) 2]PF6; and ^ -[C r(M e2[l6]tetraenatoN 4)(py) 2]P F e...... 55

Figure 5. Infrared Spectrum of Cr(Me 2f l 6]tetraenatoN 4)(NCS)(py) ...... 59

Figure 6 . Infrared Spectrum of Cr(Me 2[ l 5]tetraenatoN 4)CN...... 60

Figure 7. Infrared Spectrum of Cr(Me 2[l4]tetraenatoN 4)(C6H5)(py) ...... 70

F igure 8 . Infrared Spectrum of Cr(Me 2[l4]tetraenatoN 4) (CH3) (py)...... 71

Figure 9. Term Splitting Diagram for a d 3 Metal Ion in and S ym m etries ...... 76

Figure 10. Electronic Spectra o f : -----[Cr(Me2[l4]tetraenatoN 4)(M e-Im )2J- PFe; • ° • [Cr(Me4[l4]tetraenatoN 4)(M e-Im )2]PFs; -• [Cr(Me2[l5]tet- raenatoN 4)(M e-Im )2]PF6; [Cr(Me2[l6]tetraenatoN4)(Me-Im)]PF6.....83

Figure 11. Electronic Spectra o f: -----[Cr(Me2[i5]tetraenatoN 4)(py) 2]PFG; [Cr(Me2[ l 5]tetraenatoN 4) (dmf)2]P F 6; • *0 tCr(M e2[l5]tetraenatoN4)- (M e-Im )2]PFG; Cr(Me2[l5]tetraenatoN 4)(NCS)(py); and -• -• Cr(Me2[l5]tetraenatoN4)CN ...... 85

Figure 12. Energy Levels of a d 3 Ion in Tetragonal Symmetry ...... 92

Figure 13. ESR Spectra of: A, [Cr(Me4[l4]tetraenatoN 4)(py) 2]PFG; B, [Cr(Me2[ l6]tetraenatoN 4)(py) 2]PFG; C, [Cr(Me2[l4]tetraenato- N4)(py) 2]PFg; D, [Cr(Me 2[l5]tetraenatoN 4)(py) 2]PFG...... 95 Page

Figure 14. ESR Spectra of: A , [Cr(Me2[i5]tetraenatoN,j) (Me-Im) 2]PFG; B, [Cr(Me2[i4 ]tetraenatoN 4)(M e-Im )2]PF6; C , [C r (Me4 [l4]tetraenatoN4) (Me -Ini) 2 ] PF 6; D, [Cr(Me2[ l6]tetraenatoN 4)(M e-Im )2]PF 6 ...... 96

Figure 15. ESR Spectra of : A , [Cr(M e2[ i 6]tetraenatoN 4) (dmf) 2]PFG; B , [Cr(M e2 [i4]tetraenatoNit) (dmf) 2]PFG; C , [Cr(Me2 [i5]tetraenatoN4) (dmf) 2]PFG; D, [Cr(Me4[14]tetraenatoN4)(dmf)2]PFG ...... 97

Figure 16. ESR Spectra of: A , Cr(M e4[i4 ]tetraenatoN 4) (NCS)(py); B, Cr(M e2[ i6]tetraenatoN 4) (NCS) (py); C, Cr(M e2[i4]tetraenatoN 4)(NCS)(py) ; D, Cr(M e2[i5]tetraenatoN 4)(NCS)(py); ...... 98

Figure 17. ESR Spectra of: A, Cr(M e2[l4]tetraenatoN 4)CN; B, Cr(M e2[l5]tetraenatoN 4)CN; C, Cr(M e2[l6]tetraenatoN 4)CN...... 99

Figure 18. Infrared Spectrum of [Cr(Me 2[l4]tetraenatoN 4)(CGH5)]I...... 102

Figure 19. Infrared Spectrum of [Cr(Me 2[i4jtetraenatoN 4)(CGH5)]SCN 104

Figure 20. Electronic Spectrum of [Cr(Me 2[l4]tetraenatoN 4)(CGH5)]I: Mull; CH3N02 S o l'n ...... 106

Figure 21. Electronic Spectrum of [Cr(Me 2[l4jtetraenatoN 4)(CGH5)]SCN: Mull; CH2N 02 S ol'n ...... 107

Figure 22. ESR Spectrum of (Cr(Me 2[l4]tetraenatoN 4)(CGH5)]I...... 110

Figure 23. Infrared Spectrum of Cr(Me 2[l4jtetraenatoN 4)NO...... 114

Figure 24. Infrared Spectrum of [Cr(MeG[l4]4, ll-dieneN^ (NO)(N0 2)]P F G. . 115

Figure 25. ESR Spectrum of Cr(Me 2[l4]tetraenatoN 4)NO„...... 117

xi Page

Figure 26. ESR Spectrum of [Cr(MeG[i4]4, li-dieneN 4)(NO)(N02)JPF 6...... 118

Figure 27. Schematic Molecular Orbital Diagram for the Chromium(l) Nitrosyl Complexes ...... <.120

Figure 28. Ortep Drawing of [Cr(MeG[i4]4, ii-dieneN 4)(N0 )(N0 2)]PF 6...... 121

Figure 29. X-ray Crystallographic Bond Distances for [Cr(MeG[l4]4,11- dieneN4) (NO) (NOz) ] P F G ...... 122

Figure 30. Diagram of the Dry Train ...... 135

Figure 31. Diagram of the Furnace ...... 136

Figure 32. Wiring Diagram for the Switches„ ...... 137

xii INTRODUCTION

During the last ten to fifteen years there has been a great deal of interest in the synthesis and study of metal complexes containing macrocyclic ligands . 1-4 These metal complexes are related structurally to important natural products, such as heme proteins, chlorophyll, and vitamin B12. Many of these macrocyclic ligand coinplexes exhibit unusual properties (e.g., they can contain metal ions in unusual oxidation states) due to the steric and electronic constraints imposed on the metal ion by the ligand. In addition to the biochemical implications these results have led to a greater understanding of the chemistry of metal ions in general and are of fundamental significance to the understanding of metal ion cataly sis. Although some macrocyclic ligands have b een reported with ether5’G or thioether donors , 7-9 the vast majority of these complexes have ligands with only nitrogen donor atoms. These tetraaza macrocycles have proven to be very versatile as they can be constructed to incorporate a wide variety of features, such as varying ring size, degree of unsaturation, type and number of substituents, and charge. Most of the tetraaza macrocyclic ligands produced have 14-membered rings because in some cases ligands with ring sizes of 13, 15, and 16 members are more difficult to synthesize and commonly the 14-mem bered cyclic ligands are the most effective at coordination. Despite the long known natural anionic ligands (e.g., the porphyrin and corrin ligands) relatively few synthetic macrocyclic ligands bearing negative charges have been reported until recently. The bulk of the early studies'on metal complexes having tetraaza macrocyclic ligands were done with the metal ions of iron, cobalt, and nickel. Since the preparation and study of nickel complexes is not particularly difficult and iron and cobalt complexes with macrocycles are directly related to biological systems 1 2 the use of these metal ions for early study was entirely logical. A sa direct result of the rich chemistry displayed by these iron, cobalt, and nickel complexes, these studies have been expanded to include many other transition metal ions in recent years. To further extend the chemistry of metal complexes with macrocyclic ligands, it is appropriate to synthesize and characterize a series of macrocyclic comp lexes having macrocycles with different ring sizes and negative charges and having a metal ion whose macrocyclic complexes are unknown or have received little previous attention. This thesis is concerned with the synthesis and study of a number of chromium complexes with tetraaza macrocyclic ligands. It attempts to add to the previous work done by Sperati 10 with chromium(H) mid (III) complexes containing the ligands of structures I and II. The major portion of this thesis is devoted to the preparation and properties of a new group of chromium complexes.with the ligands shown in structures JH-VI.

I II

III IV 3

Investigations of metal complexes with these macrocycles and other structurally similar species have demonstrated that in a basic environment the macrocycles lose two ring protons becoming dianionic in nature upon coordination to metal ions. With metal ions in the dipositive oxidation state these ligands form neutral planar complexes as shown in structures VII-X . 11-18 Most of these complexes possess

MIT Y M il Y

VII VIII 4

i — i

IX X

x = "(c h 2)2- =y

X= -(CH2)r , Y= -(CH2)3=

X= - ( c h 2)3- =Y

relatively facile oxidation potentials which allow them to undergo ligand oxidative dehydrogenation reactions or metal ion oxidation . 15 >1G ,l8 ,19 Since tlie axial sites of the chromium(II]) complexes with ligands III-VI proved to be labile to ligand substitution reactions, a number of derivatives were produced and characterised having neutral or anionic axial ligands. Thermally stable aryl and alkyl derivatives were also synthesized via axial ligand substitution and characterized. Electrochemical investigations of these derivatives led directly to the production and characterization of the first chromium(IV) complexes having a chelating ligand. In addition, the reaction of sodium nitrite with one of the chromium(ffl) derivatives afforded a chromium (I), nitrosyl complex. In general, the coordination chemistry of chromium is dominated by the di- and tripositive oxidation states, although numerous compounds are known having the oxidation states of 0 through VI. A large var iety of ligands form complexes 5

with chromium(U) and (III) but since the amine complexes are closely related to those with tetraaza macrocyclic ligands, they are of special interest. In compari son to many of the transition metal ions the preparation of chromium(D) and (III)

amine complexes is not trivial . 20 Chromium(H) is easily oxidized by molecular oxygen; therefore, complexes having chromium in this oxidation state must be prepared in an oxygen-free environment. Chromium(III) is very air-stable but its inertness toward ligand substitution reactions is a genuine handicap. Also chromium ions in both oxidation states are known to readily form chromium(HI)

hydroxo- or oxo-bridged species in basic aqueous solution . 20 In spite of these difficulties, many amine complexes of chromium(II) and (HI) have been prepared. Using hydrated chromium(D) salts, alcoholic solvents, and

an inert atmosphere, chromium(H) complexes with the ligands pyridine , 21

acetonitrile , 22 ethylene diamine , 23 diethylene triam ine , 24 2 , 2 '-bipyridyl ,25 and

i, iO-phenanthroline 25 have been prepared. All of these complexes are air-sensi tive and, in most cases, they have spectral and magnetic properties which are characteristic of high-spin chromium(D). The magnetic moments of the complexes

C r dienX2 where X is Cl~, Br , or I- are 4.28-4.38 B.M. which are well below the spin-only value at room temperature of 4.90 B.M. These low magnetic moments are believed to result from the halide bridged, binuclear structure shown in structure XI in which there is interaction between the chromium ions . 24

C l

C r

C l C t

XI 6

The tris-2,2'-bipyridyl and tris-1, iO-phenanthroline diacido complexes are assumed to be low-spin as they have magnetic moments of 2„77-3.24 B.M. indicating two impaired electrons . 25

A wide variety of amine complexes with chromium(IH) have been prepared . 20 They include complexes having monoamines, diamines, triamines, and tetramines in various numbers and combinations. Several methods were used to prepare these amine complexes, such as the reaction of anhydrous chromium(ni) salts with anhydrous amines, the reaction of CrX 3Cl3 (X = py, dmf, dmso, thf) with amines, the reaction of diperoxochromium(IV) amines with acids, and the oxidation of the corresponding chromium(U) complexes . 20 The physical and chemical properties of the chromium(III) amine complexes are not unusual. They are stable and unreactive and have effective magnetic moments of 3. 5-4.1 B.M. which agree generally with the spin-only value for three unpaired electrons of 3.87 B.M . 20 The first reported chromium complexes containing macrocyclic ligands were those formed with derivatives of the porphine ring (structure XII) and with phthalocyanine (structure XIII). The reaction of chromium(III) acetate with phthalonitrile at 270° C afforded the sublimable product phthalocyanine-chromium- (IB) hydroxide. Using this complex as a starting material, a number of octahedral

XII XIII 7

chromium(ID) derivatives were prepared along with four- and six-coordinate chromium(IJ) complexes. The chromium(IU) complexes had typical magnetic moments of 3.69-4.06 B.M. The magnetic moments for the chromium(U) complexes were considerably lower than the spin-only value for high-spin chromium(D) indicating that metal-metal interaction may occur in the planar complex and that electron pairing takes place in the six-coordinate complex,

resulting in two unpaired electrons .26 Several chromium complexes with porphyrins have been prepared and

characterized. 27-32 The preparation of these chromium porphyrins involves

reactions of Cr(CO )6 o r C rC l 2 with the porphyrin ligand in high boiling solvents, such as decalin, n-decane, or dimethylformamide. Depending on the reaction conditions, either chromium(II) or chromium(IIT) derivatives can be obtained. Tsutsui and coworkers prepared meso-porphyrin-IX-dimethylesterchromium(Il) which is reported to be square planar in die solid-state. This compound has a solid-state magnetic moment of 2.84 B. M. and a solution moment of 5.19 B.M. The solid-state magnetic moment indicates interaction between metal centers resulting in electron pairing but this interaction is destroyed when the complex is in solution and a magnetic moment consistent with high-spin chromium! II) re su lts.

Fleischer and coworkers 29-31 prepared several chromium(III) porphyrin complexes and studied the axial substitution reactions of chromium(III) tetra- (p-sulfonatophenyl)porphine in detail. The magnetic moment of 3.87 B.M. for this complex agrees with the assigned oxidation state. Rates for the replacement of axial water molecules by CN , F , and py were found to be 10 3-104 faster than rates previously determined for other chromium(HI) complexes. There is assumed to be extensive electron delocalization in this complex which results from the rr-bonding between the ligand t t * orbitals and the metal dyz and dxz orbitals. By this mechanism electron density is transferred from the electron rich dianionic porphyrin to the chromium ion, thereby malting the complex labile toward substitution. Furhop and coworkers 32 have studied the electrochemistry of octaethylpor- phinatochromium(IH) hydroxide in butyronitrile using a SCE reference electrode. The oxidations that occur at 1.22 volts and 0.99 volts have been assigned to ligand oxidations and the cathodic process at -1.35 volts has been assigned to a ligand reduction. Although oxidations of chromium(HI) are very rarely observed electrochemically, an oxidation talcing place at 0.79 volts was assigned to the chromium(Itt)- chromium(IV) couple. The cathodic process observed at -1.14 volts was desig nated as the chromium(III) to chromium(D) reduction. Sperati synthesized both chromium(U) and chromium(III) complexes with the ligands Me 6[l4]aneN 4 (structure H) and Me6[14]4,11-dieneN,^10^ (structure 1), while

Tobe and Ferguson 33 prepared only chromium(ILO complexes with cyclam ([l4]ane- N4, structure XIV). Working in a dry box with an inert atmosphere, the chromium(IJ) complexes with Me 6[l4]aneN 4 and Me6[l4]4, ll-dieneN 4 were prepared by the

XIV

reaction of the acetonitrile adducts of the chromium(D) halides with the ligands in ethanol solutions. The reaction with the saturated ligand produced only trans-dihalide complexes while the diene ligand formed five-coordinate complexes having only one axial halide. Other chromium(II) derivatives were prepared by metathesis of die halide complexes. Although these chromium(II) complexes are air-sensitive in both solution and the solid-state, solid samples of the complexes containing the diene ligand 9 can be exposed to air for a short time without noticeable oxidation. The solid- state magnetic moments for these complexes indicate that the chromium(II) is high-spin in nature, as the moments deviate only slightly from the spin-only value of 4.90 B. M. The conductivity data support the six coordination of the saturated complexes and the five coordination of the diene complexes. Five coordination is rare for chromium(II) complexes as the only other reported examples are complexes containing the tripod ligands tris( 2-dimethylaminoethyl)- am ine, 34 tris ( 2-diphenylphosphinoethyl)amine, and bis( 2-diethylaminoethyl)-

(2-diphenylphosphinoethyl)amine . 35 The electronic spectra of these macrocyclic complexes have been assigned using the crystal field model for tetragonal high- spin d 4 sy stem s. A number of chromium(Hl) complexes were also prepared with these two macrocyclic ligands. Working on the benchtop, halogens were used to oxidize the appropriate chromium(H) complex. Metathesis was then used to prepare other derivatives that did not contain halide ligands. All of these chromium(lll) complexes were found to be quite stable, being high-spin, six-coordinate species with tetragonal structures. Magnetic susceptibility measurements confirmed the tripositive oxidation state for these complexes. The electronic spectra were assigned for these complexes on the basis of the crystal field model for tetragonal d3 sy stem s. Since the preparation of the first pure cr-bonded organochromium compound,

[CeH5CH2Cr(H 20 )5]2+, by Anet and Leblanc in 1957, 36 a number of complexes which have alkyl or aryl groups covalently bonded to chromium!ID or (III) have been prepared and characterized . 37’38 However, no organochromium complex has previously been prepared containing a macrocyclic ligand. The interaction of certain organometallic compounds and chromium(n) or chromium(HD halides in ethereal solvents leads to the corresponding solvated cr-bonded organochromium(in) and (H) compounds provided particular attention is paid to solvent, temperature, and stoichiometry of the reaction. By varying reaction conditions, it is possible to produce organochromium compounds having 10 from one to three alkyl or aryl groups and varying amounts and types of solvation. The most convenient and perhaps cleanest route to cr-bonded organochromium compounds is by the action of organomagnesium halides on chromium halides in tetrahydrofuran or diethyl ether (equations 1-5).

t h f RMgX + CrCl 3(THF)3 - R C rC l2(THF)3 (1)

R = m ethyl ,39 p -to ly l , 40 benzyl ,39 and others

THF 2 RMgX + CrCl 3(THF)3 R2CrCl(THF) (2)

R = benzyl , 40 eth y l ,38 m ethyl 3,8 propyl , 38 and others

THF 3RMgX + CrCl 3(THF)3 - R3Cr(TH F)3 (3)

R = phenyl , 41 benzyl , 40 a - and ^-naphthyl , 42 m ethyl 43 and others

THF RMgBr + CrCl 2 =* RCrBr(THF) (4)

IT - 1-naphthyl , 44 l-(2-methylnaphthyl ) , 44 and others

RMgBr + CrCl 2 E t 2 ° R2Cr(TH F)3 or [R 2C r ]2 (5)

R = mesityl , 44 o-methoxyphenyl , 45 phenyl , 48 and others

The tetrahydrofuran of solvation in these complexes may be displaced by pyi-idine, 2,2'-bipyridyl, or 1,10-phenanthroline. These nitrogen donor ligands are known to stabilize carbon-metal cr-bonds 38 and this has permitted the isolation of otherwise unstable organochromium species (equations 6 and 7).

CGH5CH2C rC l2(THF) c 6H5CIi2C rC l2(py )3 (6)

CgH5MgBr + C rB r 2(THF)2 THE/blPy (c 6H5)2Cr(bipy )2 (7) i i

The reaction between triaryl- or trialkylaluminum compounds and chromium-

(III) chloride in tetrahydrofuran results in only one organic group being introduced 37

(equation 8 ).

THF RgAl + CrCl 3(THF)3 R C rC l2(THF)3 (8)

R = phenyl , 37 m ethyl , 47 ethyl , 47 p ro p y l ,47 and others

Reactions of organolithium and organosodium compounds with chromium(II) and chromium(III) salts can lead to the formation of lithium or sodium poly(organo)- chromate complexes of the type M 3Cr(III)Rg, M 2Cr(III)R5, MCr(IH)R4, and MCr(II)-

R3 (M = Li or Na). However, the specific products formed in these reactions depend critically upon the nature of the organic group in the organometallic reagent, the stoichiometry of the reagents, the ligands associated with the final product, and the solvent employed for the reaction (equations 9-12).

6LiR + C rC l3 E-^ ° Li3 [CrReHEtjjO] (9)

R = p h en y l , 38 p -to ly l ,38 m ethyl ,38 and others

5NaCgH 5 + CrCl; Ei 20 Na2[Cr(C6H5)5][Et20]3(48) ( 10)

4Li(2-CH 3OC6H4) + C rC l3 E^° Li[Cr(2-CH30 C6H4)4][Et20]3(38^ (11)

THF 8 CH3Li + 2CrCl2 E-^ ° [Li2Cr(CH3)4]2[Et20]n

Li4[(CII3)4Cr - Cr(CH3)4][THF]4(49) (12)

In some cases organolithium reagents give neutral complexes (equation 13).49

’(gjCtfCI*,), - CrCl3(THF)3 E3° d3) 12

Another interesting route to organochromium species is based on the reaction of chromium(I]) salts with certain organic halides 36’50 (equation 14).

2C r2+ + RC1 H4° [RCr(H20 )5]2+ (14)

R = CgH 5CH2, 2-CH 3C6H,tCH2, and others

A modification of this method (equation 15) has been used to prepare the crystal line monoorganochromium compounds RCrCl 2(py)3^51^ (R = benzyl, o-chlorobenzyl, and p-chlorobenzyl).

CgH 5CH2C1 + 2C rC l2(py )2 C6H5CH2C rC l2(py )3 (15)

Organochromium compounds differ markedly in their stabilities. The water soluble species [RCr(H 20)5]2+ are sensitive to oxygen and have not been isolated as solids. The majority of the isolatable organochromium compounds are sensi tive to both oxygen and protic solvents although there are some (e.g., [(C6H5)2-

Cr(bipy)2)+] that are stable in air and water .38 Their thermal stabilities also vary depending upon the type and number of organo groups present. Broadly speaking, the complexes having aryl groups (e.g., (CGH5)3Cr(TH F)3 and 4-CH3-

CGH4C rC l2(THF)3) are more stable than species having alkyl groups 38 (e.g.,

(CgH 5CH2)3C r(THF)3 and (CH3CH2)3Cr(TH F)3). Organochromium compounds undergo a variety of reactions in which the chromium ion acts as a coordination center or as center for hydrogen transfer. All of the known cr-bonded organochromium compounds react with mercuric chloride to give quantitatively the organomercuric halide and a chromium(HD sp e c ie s .38 These species react with oxygen, iodine, andwater, as well as thermally resulting in the homolytic or heterolytic cleavage of the chromium- carbon bond; therefore, they can serve as sources of radicals or carbanions. Their reactions with alkenes, alkynes, and ketones have been investigated. Acetylenes react with tris(organo)chromium compounds to produce products 13

formed from one, two, or three acetylenic units and one or two of the organic

groups originally bonded to chromium (equation 16 ) . 52 The reactions with

C CH3 (C6H5)3C r(TH F )3 + CH3GeCCH3 C H ( 16)

enolizable ketones yield aryl or alkyl carbinols formed by the transfer of one of the organic groups bonded to chromium to complexed ketone and products formed from one of the groups bonded to chromium and two molecules of ketone (equation 17).53 Polymers or addition products are obtained when olefins react with these

(C6II5)3Cr(TH F)3 + (17)

chromium compounds . 38 Aryl chromium compounds are known to undergo

rearrangements to form n-arenechromium complexes . 37’38 This thesis will report the synthesis and properties of the first organochromium(IH) complexes with macrocyclic ligands. Although the chemistry of chromium is centered around the di- and tripositive oxidation states, complexes containing chromium(I) and (IV) are known. The most common chromium(I) species are the ■p-bis(arene) chromium(I) compounds which are formed by oxidizing the n-bis(arene) chromium(O) compounds . 38 These compounds are air- and water-stable and form salts with a variety of anions. The ESR spectra of r-bis(arene) chromium(i) compounds show g values of slightly less than 2 and have magnetic moments of 1.70-1.80 B.M. which indicate a low- spin d 5 electron configuration.

The tris ( 2 , 2 '-bipyridyl)chromium(I) complex (structure XV) has been synthe sized and characterized . 54’55 It has a magnetic moment of 2.05 B.M. and a solu tion ESR spectrum showing a g value of 1.9971. 14

The other well-known chromium(I) complexes are nitrosyl derivatives. Several complexes having the CrN02+ moiety have been isolated and characterized, e.g ., [Cr(CN) 5(NO)J3- , [Cr(NH3)5(NO)]2+, [Cr(H20)5(NO)]2+ , and [Cr(Cl)(NO)

(d ia rs)2]+. 5G_G0 The coordination of an NO+ group to chromium has been accomplished using NO, N02", N03~, and NH 2OH. The nitrosyl complexes are all air-stable solids exhibiting N-0 infrared absorptions at 1645-1747 cm-1, which are consistent with the NO+ formulation of the nitrosyl ligand. The magnetic moments range from 1.70 B.M. to 2.30 B.M. indicating the presence of one unpaired electron and a low -spin d 5 electron configuration. The room temperature solution ESR spectra of these compounds have g values slightly lower than 2 and in most cases show 53Cr hyperfine and 14N superhyperfine splitting. The low temperature, frozen solution spectra appear axially symmetric with g^ larger than . 59~62 15

Gray and coworkers have reported molecular orbital calculations for

[Cr(CN)5(NO)]3_ which resulted in an energy level diagram with the lowest-lying unoccupied level being derived mainly from the nitrosyl antibonding orbital.

The electronic spectra for the complexes with CN" and NH 3 ligands have been

assigned using the results of these molecular orbital calculations. 59, 63,64,65

The crystal structure of [Cr(CN) 5(NO) ]3- was determined by Enemark and

co w o rk ers . 66 The molecule has a Cr-N distance of 1.71 A, an N-O distance of 1.21 A, and a Cr-N-O angle of 176°. To this date only two chromium nitrosyl complexes with macrocyclic ligands have been reported. The reaction of nitric oxide with chromium(II) phthalocyanine is reported to give a nitrosyl complex but very little data has been offered in

support of this claim . 67 Wayland and coworkers have recently prepared nitrosyl- tetraphenylporphyrinchromium(l) (CrTPP(NO)) by the reaction of nitric oxide with either tetraphenylporphyrinchromium(II) or tetraphenylporphyrinchromium(ni) methoxide.68 CrTPP(NO) can be isolated as a red solid having a N-O stretching frequency at 1700 cm-1. The ESR spectrum of the complex in frozen solution is anisotropic with g^ > gjj while the room temperature spectrum is isotropic and complicated by nitrogen-14 superhyperfine splitting from both nitric oxide and porphyrin pjurole nitrogens. CrTPP(NO) behaves as a low-spin d 5 species with the ESR g values indicating that the odd electron is in the molecular orbital derived from the chromium d orbital. xy The preparation and properties of two chromium(I) nitrosyl complexes with different tetraaza macrocyclic ligands will be presented and discussed. The crystal structure of the chromium(I) nitrosyl complex with a diene macrocyclic ligand [Cr(Me 6[l4]4, il-dieneN 4)(N 02)(N 0)]P F 6 has been performed by Dr. Dennis W ester. Although several organochromium(IV) complexes have been reported recently, compounds with chromium in the tetrapositive oxidation state are uncommon.

The halides are reported and CrF 4 has been isolated while CrCl 4 and C rB r4 ex ist only as gaseous materials . 69 The complex mixed oxides M 4CrO e, M3C r0 5, and 16

M2C r0 4 (M = Sr or Ba )70 and the K, Rb, and Cs salts of CrF62“ are known . 69 Several air-sensitive dialkylamides have been prepared but only the piperidinato

derivative (structure XVI) was isolated as a solid material . 71

XVI

A few Cr(OR)4 compounds (R = t-Bu, CMe 2Et, CMeEl^, CEt3, and SiEt3) have been synthesized and found to be relatively stable due to the absence of a-CH bonds . 12,73 The predominant method used for making these compounds was the reaction of the tertiary alcohol or triethylsilanol with Cr(NEt2)4, which results in a color change from green to blue and the liberation of diethylamine. These air- sensitive compounds are royal blue in color and all of them are liquids except for

C r(0 -t-B u )4 which is a low melting solid. The electronic spectra of these com pounds displayed several bands which were provisionally assigned based on tetrahedral symmetry. The magnetic moments for the chromium(IV) alkoxides are close to the spin-only value of 2.83 B„M. for a d 2 system. A weak peak assignable to the parent ion was found (m/e = 344 for Cr(0-t-Bu)4+) in the mass spectrum of Cr(0-t~Bu)4. Attempts to prepare primary or secondary alkoxides led to the oxidation of the ligand and formation of the chromium(Hl) alkoxide. Similarly, attempts to synthesize chromium(IV) compounds in higher coordination states by exchange reactions with chelating ligands (e.g ., acetylacetone and hexafluoroacetylacetone) consistently led to redox reactions and the formation of tris-chelates of chromium(ID). 17

The previously mentioned chromium(IV) compounds all contain a heteroatom bonded to chromium but recently a number of chromium(IV) compounds have been prepared which have carbon bonded to chromium and are tetrahedral in structure. Compounds have been prepared and isolated containing the alkyl groups Me*

CH2CPh3, CH2CMe2Ph, CH2CMe3, CH2SiMe3, i-camphyl, i-norbornyl, and t-

butyl . 74-77 The stabilities of these compounds have been attributed to the

absence of hydrogen atoms on the carbon beta to the metal center. 76 ,78 ,79 This obviates two of the low-energy fragmentation routes characteristic of

CT-bonded alkyl transition metal compounds; i.e ., concerted / 3-metal-hydride elimination (equation 18) and /2-hydrogen abstraction (equation 19).

R - CH - CH, RCH = CH, + MH (18) II H M

R - CH - CH? R - CII = CIi2 + R'H + M (19) I J H M / r '

In addition to the two fragmentation routes mentioned above and simple homolytic bond cleavage, there are a variety of other low-energy fragmentation routes whereby the carbon to metal bond may be destroyed. There are three ways in which these low-energy paths may be blocked thereby stabilizing the a-bonded alkyl chromium compound . 38 Alkyl groups can be used which lack hydrogen or other readily transferrable groups on the carbon atom /? to the metal. The coordi nation sites on the metal center which are required for the metal-hydride elimination process can be blocked with some suitable ligand, e .g ., 2 , 2 '-bipyridyl. Finally, the geometry of the molecule can be altered so that not only are there no coordination sites on the metal center available for participation in the metal- hydride elimination process but also that the bulk of the organic groups are such 18

as to prevent both concerted / 3-hydrogen abstraction and / 3-metal-hydride elimination. IV The species Cr (R )4 were prepared either by the interaction of Grignard or lithium reagents with CrCl 3(THF)3 or by an exchange reaction between lithium reagents and chromium(IV) t-butoxide. In the syntheses using the CrCl3-

(THF)3 and Grignard or lithium reagents the chromium!Ill) is oxidized to chromium!Ill) via a disproportionation reaction or by air oxidation . 74-77 Depending on the type of organic group coordinated to the metal, the properties of these compounds vary. Some are crystalline, air-stable solids

(e.g., Cr(i-norbornyl )4 and Cr(CH2CPh3)4) while others are unstable liquids

(e.g., Cr(CH 3)4 and Cr(n-Bu)4). These compounds have magnetic moments of 2.6-3.0 B. M. which correspond to two unpaired electrons as is expected for chromium(IV). Their electronic and variable temperature ESR spectra have been investigated and discussed in terms of their tetrahedral configurations . 76 >77 »80 »81 This data indicates that these compounds possess slightly distorted tetrahedral structures. Mass spectrometry has been used to characterize tetra!alkyl)chromium(IV) compounds and, of the compounds studied, Cr(i-camphyl)4,

Cr(l-norbornyl)4, and Cr(neopentyl )4 showed peaks at m/e values corresponding to the tetraalkyls. 74, 75 A preliminary report of a single crystal X-ray structure analysis confirms the tetrahedral array of the organic ligands in Cr(CH 2C(CH3)2- c gh 5)4. 82 The synthesis and characterization of the first chromium(IV) complexes with a chelating ligand and a non-tetrahedral configuration will be presented and discussed in this thesis. EXPERIMENTAL

Physical Measurements

NMR Spectra. — Varian A-60 and A-60A spectrometers were used to perform all nmr measurements,, To determine the probe temperature of the instruments, a calibration curve based on the chemical shift of methanol was used. All chemical shifts were determined using external tetramethylsilane (TMS) as the reference. Air-sensitive samples were prepared in a glove box and sealed with tight-fitting caps which were then wrapped with parafilm. The spectra of the samples were immediately recorded upon removal of the samples from the glove box.

Electronic Spectra. — Both visible and near infrared spectra were obtained using a Cary Model 14R recording spectrophotometer. The preparation of air- sensitive samples was accomplished in a glove box by first weighing the samples on a Cahn Model RTL Electrobalance and then preparing solutions using volumetric flasks. These samples were loaded into one cm. matching quartz cells and tightly sealed with teflon stoppers. After removal of these samples from the glove box, their spectra were immediately recorded. Solid-state spectra were obtained from mulls prepared hi the glove box using filter paper impregnated with Halocarbon 25-55 grease.

Infrared Spectra. — Infrared spectra were acquired with Perkin-Elmer Model 337 and Model 457 recording spectrophotometers using Nujol mulls between potassium bromide plates. Mulls of air-sensitive complexes were prepared hi a glove box and their spectra were recorded directly upon removal from the box.

19 20

M a g n e t i c Susceptibilities. — Solid-state magnetic susceptibilities were measured by the Faraday method 83 at room temperature under a helium pressure of 35 mm using a Cahn electrobalance and a Varian electromagnet operating at a current of 3. 5 amps. For magnetic susceptibilities in the temperature range

90-350° K, the technique and apparatus used were as described in the literature . 83

Solution susceptibilities were measured by the Evans method 84 using Varian A-60 and A-60A spectrometers. The samples were prepared in the glove box employing the Cahn electrobalance to accurately determine the mass of the samples and volumetric flasks to make up the solutions. Solvents commonly used for this type of measurement were chloroform, acetonitrile, nitromethane, and acetone. For both solid-state and solution susceptibilities diamagnetic corrections were made using Pascal's constants . 85

Conductivities. — Conductance measurements were made with an industrial Instruments Model RC 16B conductivity bridge. The conductance cell was the

Sproule type having a cell constant of 0 .100 cm-1. The sample solutions were prepared in the glove box utilizing the Calm electrobalance and volumetric flasks.

The measurements were carried out in the glove box on 1.0 x 10 -3 M solutions at room temperatui’e and at 1000 cps. Nitromethane and acetonitrile were commonly used as solvents for these measurements.

Mass Spectra. — The mass spectra were obtained by Mr. Richard Weisenberger of this Department employing an MS-9 spectrometer at an ionizing potential of 70 eV.

Elemental Analyses. — Elemental analyses were performed by Galbraith and Schwarzkopf Laboratories. Nitrogen analyses for most of the complexes were done by the author or by Mr. Wayne Schammel of this Department using a Model 29 Coleman Nitrogen Analyzer. 21

ESR Spectra. — The esr spectra were obtained using a Varian V4500-10A spectrometer operating on the X band at a frequency of approximately 9300 MHz. Since the instrument was equipped with a dual cavity, the free radical diphenyl- pieralhydrazyl (g = 2.0037) was placed in the rear cavity and used as a reference

for all measurements. Samples having concentrations approximately i0 -2 - 10“3 M in complex and containing a small amount of tetra-n-butylammonium tetrafluoro-

borate 86 were prepared in the glove box, placed in quartz cells stoppered with ground glass joints, and frozen with liquid nitrogen immediately upon removal from the glove box. In order to maintain the samples at a constant temperature while their spectra were being recorded, the cell was placed in a small quartz dewar containing liquid nitrogen which was then inserted into the front cavity of the instrument.

Electrochemistry. — Polarography and cyclic voltammetry were performed by Miss Kathy Holter of this Department and in some cases by the author using an Indiana Instrument and Chemical Corporation Controlled Potential and Derivative Voltammeter Model ORNL-1988A. The current-potential curves were recorded on a Hewlett-Packard/Moseley Division X-Y recorder. The polarographic cell was a three compartment H-type cell utilizing a rotating platinum wire working electrode and a reference electrode consisting of a silver wire

immersed in a 0 .1 M acetonitrile solution of silver nitrate. All measurements were carried out in a Vacuum Atmospheres Dry Lab using acetonitrile as the solvent and tetra-n-butylammonium tetrafluoroborate as the supporting electro lyte.

Syntheses

General Procedures. — Unless otherwise indicated all manipulations involving chromium(II) salts and metal complexes were carried out in a Vacuum Atmospheres Dry Lab equipped with a recirculation and purification system which is later described in detail. 22

Materials. — Only reagent grade chemicals and solvents were employed in carrying out syntheses and obtaining physical measurements. The solvents used in the glove box were dried and degassed before they were taken into the dry box. Acetonitrile, diethyl ether, ethanol, methanol, tetrahydrofuran, and benzene were refluxed for at least one hour over calcium hydride before being distilled under nitrogen. Chloroform, dimethylformamide, nitromethane, and acetone were stored several days over Linde molecular sieves and then distilled under nitrogen. After being stored over potassium hydroxide for several days pyridine and triethylamine were distilled under nitrogen. Chromium metal, 9.9$ and 140 mesh, and alkyl and aryl lithium reagents were purchased from Alfa Inorganics, Beverly, Massachusetts.

Tetraaquochromium(II) chloride, CrCl? • 4 H?Q. — Following the method

of Lux and Illman , 87 this chromium(Il) salt was prepared on the benchtop under a blanket of nitrogen. To a flask containing 10.4 g (0.2 mole) of very pure

chromium metal was added 100 ml of 20$ hydrochloric acid under a nitrogen stream. The flask was warmed and stirred under a purge of nitrogen until all of the metal dissolved. After the volume of the blue solution was reduced to near dryness under vacuum, the flask was taken into the glove box. Upon the addition of acetone to the flask the blue crystals were collected by filtration, washed with acetone and diethyl ether, and dried under vacuum.

Hexaaquochromium(D) bromide, CrBr? • 6H?Q and Hexaaquochromium(II)

iodide, CrL> • 6H?Q. — These chromium(H) salts were prepared as in the preceding procedure using the appropriate acid.

Chromium(II) acetate, CrAc2. — Again following the method of Lux and

Illm an, 87 on the benchtop under nitrogen hydrated chromium(U) acetate was

prepared from a water solution of chromium(II) chloride by the addition of sodium acetate. After transferring the flask containing the red chromium(H) acetate to the glove box, the red material was collected by filtration and washed with ethanol and ether. The chromium(n) acetate was placed in a tube equipped 23

with a vacuum stopcock, removed from the dry box, and heated under vacuum at approximately 200° C overnight causing the bright red solid to become light orange in color. The tube was taken into the dry box where the anhydrous chromium(II) acetate was washed with ethanol and diethyl ether and dried under vacuum .

Bis(pyridine)chromium(H) chloride, CrCl? • 2py. — This green chromium(II)

salt was prepared by a method similar to that of Holah and Fackler . 20 An

excess of pyridine was added to a hot ethanolic solution of CrCl 2 • 4H20 resulting in the formation of a light green precipitate. The green solid was collected by filtration, washed with ethanol and diethyl ether, and dried under vacuum.

Hexakis(pyridine)chromium(H> bromide, CrBr? • 6py and hexakis(p.yridine)- chromium(II) iodide, CrI? • Gpy. — These two chromium(U) halides were prepared according to the above procedure employing the appropriate hydrated chromium(IJ) halide.

Tetrakis(pyridine)chromium(II) trifluoromethylsulfonate, Cr(CF^SO ^)9 • 4py. —

To a slurry of 4.0 g (11.1 mmol) of [Cr(Ac )2]2 in 50 ml of acetonitrile was added dropwise an excess of trifluoromethanesulfonic acid. As the acid was added, the fumes were removed by vacuum. The bright blue solution was filtered and then the volume reduced to near dryness. The addition of 30 ml of diethyl ether caused the precipitation of a bright blue solid. This blue solid was collected by filtration and washed with diethyl ether. To a hot stirring solution of the above blue solid in ethanol was slowly added approximately 20 ml of pyridine. After the solution cooled to room temperature, the blue crystalline product was collected by filtration, washed with ethanol and diethyl ether, and dried under vacuum. The product was re crystallized from pyridine and ethanol. Based on chromous acetate, the yield was 81^. Anal. Calcd. for Cr(CF 3S03)2 • 4py: C, 39.65; H, 3.05; N, 8.42. Found: C, 39.37; H, 3.11; N, 8.31. 24

trans-[(5,14-Dimethyl-1,4,8> li-tetraazac.yclotetradeca-4,6,11,13-tetraenato)bis( pyridine) chromium(II])]hexafluorophosphate, [Cr(Me?[14]tetraenatoN^)~ (py)?]PFR. — To a solvent mixture containing 50 ml of acetonitrile and 10 ml of

pyridine was added 5.12 g (0.01 mol) of H 2[Me2[l4 ]tetraeneN 4](PFg) 215 and 2.81 g

(0 .01 mol) of CrCl 2 • 2py. When the mixture was heated and stirred the ligand salt dissolved but the chromium(II) salt did not. To this warm stirring solution was added dropwise 4.04 g (0.04 mol) of triethylamine causing the solution to turn a bright green color. The solution was refluxed for 30 min and then allowed to cool to room temperature. The green solution was filtered to remove the insoluble white salts and any unreacted chromium(II) salt. The volume was reduced under vacuum to approximately 10 ml, after which 40 ml of ethanol was added to the hot stirring solution resulting in the formation of green crystals. After the solution had cooled to room temperature, the green crystals were collected by filtration, washed with ethanol and diethyl ether, and dried under vacuum. This complex was recrystallized by first dissolving the complex in pyridine and filtering and then causing it to crystallize by adding ethanol. Yields obtained ranged from 50-60$ based on the ligand salt.

trans-[(7, 13-Dimeth.yl-l,4, 8 ,12-tetraazacyclopentadeca-4,6,12,14-tetraenato)bis(pyridine) chromium( ttljJhexafluorophosphate, [Cr(Me?[ 15]tetraenatoNt1) - (py),]PFfi. — The procedure for this complex was the same as the preceding one except that 5.26 g (0.01 mol) of H 2[Me2[ l 5]tetraeneN 4](PF 6)215 was the ligand salt used. The crystalline product was dark brown in color and the yields obtained were 45-55$ based on the ligand salt.

trans-[(2,12-Dimethyl-l, 5, 9 ,13-tetraazacyclohexadeca-l, 3, 9,11- tetraenato)bis(pyridine)chromium(UD]hexafluorophosphate, [Cr(Me 7[ l6]te tra e - natoN^)(py)c>]PFfi. — This complex was prepared by a procedure similar to the one used for the above complex except in this case 5.40 g (0.01 mole) of

H2[Me2[ l6]tetraeneN 4](PF6)10 was used as the ligand source. Also the solvent volume was reduced to approximately 5 ml before the addition of the ethanol. 25

The complex was orange in color and typical yields were 35-45$ based on the ligand salt.

trans-[(5, 7,12,14-Tetramethyl-l,4,8, ll-tetraazacyclotetradeca-4,6,11,13- tetr aenato) bi s( pyr idine) chr omium (III) ]hexafluor ophosphate, [C r (Me,t [ 14 ]te tr aenatoN^ -

(py) 2]PFR. — To a solvent mixture consisting of 50 ml of acetonitrile and 10 ml of pyridine was added 3.1 g (0.0125 mol) of Me 4[l4jtetraeneN 417 and 3.51 g (0.0125 mol) of CrCl 2 • 2py. Stirring and heating the solution caused it to become green in color. After refluxing the green solution for 15 min, 4.08 g (0.025 mol) of

NH4PFg was added to the hot solution with stirring. The solution was filtered and the volume was reduced under vacuum to 10 ml. Then 40 ml of ethanol were added to this hot solution. When the solution cooled, the green crystals were collected by filtration, washed with ethanol and diethyl ether, and dried under vacuum. This complex was recrystallized by dissolving it in a minimum amount of pyridine and then adding ethanol to cause the product to crystallize. Yields obtained were 70-85$ based on the ligand.

trans-[(5,14-Dimethyl-1,4, 8 , ll-tetraazacyclotetradeca-4,6,11,13-tetraenato)bis(dimethylformamide)chromium(III)]hexafluorophosphate, [Cr(Me?[l4j- tetraenatoN 4)(dmf)?]PFR. — To 50 ml of dimethylformamide was added 2.0 g

(3.49 mmol) of [Cr(Me 2[i4]tetraenatoN 4)(py) 2]PF6. The volume of this solution was reduced under vacuum to near dryness resulting in removal from the complex the lower boiling pyridine and leaving only dimethylformamide as a possible axial ligand. As the pyridine was removed, the color of the solution changed from green-brown to red-orange. To this hot solution (about 5 ml) 50 ml of ethanol was added with stirring. This resulted in the precipitation of a red- orange solid which was collected by filtration after the solution had cooled to room temperature. This solid was washed with ethanol and diethyl ether and dried under vacuum. The compound was recrystallized by dissolving it in a minimum amount of dimethylformamide, filtering the solution, and then adding ethanol causing the product to precipitate. The yield was 82$ based on the starting complex. 26

trans-[(7, 13-Dimethyl-1,4, 8 , l2-tetraazacyclopentadeca-4,6,12,14-tetraenato)bis(dimethylformamide)chromium(HI)]hexafluorophosphate, [Cr(Me 9 [l5]- tetraenatoN 4)(dmf) ;]PFR. — The above procedure was employed to prepare this complex starting with [Cr(Me 2[i5]tetraenatoN 4)(py) 2]PF6. The yield of this orange complex was 65$ based on 2.0 g (3.4 mmol) of starting complex.

trans-[(2,12-Dimethyl-l, 5, 9 ,13-tetraazacyclohexadeca-l, 3, 9 ,11-tetraenato)bis( dimethylformamide) chromium(HI)]hexafluorophosphate, [Cr(Me?[l 6]~ tetraenatoHd (dmf) 9 ]PFR. — This orange complex was prepared in the same manner as the preceding complex. Based on 1. 5 g (2. 5 mmol) of [Cr(Me 2[ l6]- tetraenatoN 4)(py) 2]PFG, the yield was 55$.

trans-[(5, 7,12,14-Tetramethyl~l,4,8, ll-tetraazacyclotetradeca-4,6,11,13- tetraenato)bis(dimethylformamide)chromium(n])]hexafluorophosphate, [Cr(Me^~

[i 4 jtetraenatoN,1) (dmf),] PFR. — The preparation of this orange complex was similar to the preparation of the above complex. Employing 1.0 g (1.66 mmol) of [Cr(Me 4[l4]tetraenatoN 4)(py) 2]PFG, the yield was 82$ based on that complex.

trans-[(5, 14-Dimethyl-1,4, 8 , ll-tetraazacyclotetradeca-4,6,11,13-tetraenato)bis( l-methylimidazole)chromium(HI)]hexafluorophosphate, [Cr(Me 9 [l4]~ te tr ae natoISh) (Me - Im) 9 ] P FR. — Approximately 0.5 ml of 1-methylimidazole was added to a stirring solution of 1.0 g (1.74 mmol) of [Cr(Me 2[l4]tetraenatoN 4)(py)2]- PFg in 50 ml of acetone. Immediately following this addition, the color of the solution turned from green to red indicating replacement of the axial pyridine by 1-methylimidazoles. The volume was reduced to 15 ml under vacuum and 30 ml of ethanol was added. Upon again reducing the volume to 15 ml, red crystals were produced. The product was collected by filtration, washed with several portions of ethanol and diethyl ether, and dried under vacuum. This product was recrystallized by dissolving it in acetone and then adding ethanol causing the product to crystallize. Based on the starting complex, the yield was 79$. 27

trans-[(7,13-Dimethyl-1,4,8, l2-tetraazacyclopentadeca-4,6,12,14-tetraenato)bis( 1 -methylimidazole)chromium( HI) jhexailuorophosphate, [Cr(Me?[15]- tetraenatoINh) (Me-Im)?]PFft. — This red complex was prepared in the same

manner as the preceding complex. Based on 1.5 g (2.55 mmol) of [Cr(Me 2[l5]-

tetraenatoN 4) (py) 2]PF6, the yield was 89$.

trans-[(2,12-Dimethyl-l, 5, 9 ,13-tetraazacyclohexadeca-l, 3 ,9 ,11-tetraenato)- bis(l-methylimidazole)chromium(III) Jhexailuorophosphate, [Cr(Me?{l 6]tetraenato-

N4)(M e-Im )9 ]PFR. — This orange complex was synthesized using the same procedure as for the above complex. The yield was 92$ starting with 1. 5 g

(2. 5 mmol) of [Cr(Me 2[ l6]tetraenatoN 4)(py) 2]P F e.

trans-[(5, 7,12,14-Tetramethyl-l,4,8, ll-tetraazacyclotetradeca-4,6,11,13- tetraenato)bis( l-methylimidazole)chromium(III) Jhexafluorophosphate, [Cr(Me^ [14]- tetraenatoN^) (Me-Im) 9 ]PFR. — The synthesis of this red complex was the same as the one described previously. The yield was 79$ based on 1.0 g (1.66 mmol) of [Cr(Me 4[l4]tetraenatoN 4)(py) 2]P F 6„

trans-Thiocyanato(5,14-dimethyl-1,4,8, ll-tetraazacyclotetradeca-4, 6 ,11, - l3-tetraenato)pyridinechromium(IlI), Cr(Me?[l4]tetraenatoN 4)(NCS)(p.y). — To a stirring solution of 3.0 g (5.23 mmol) of [Cr(Me 2[i4]tetraenatoN 4)(py) 2]PF 6 in 50 ml of acetonitrile was added 0.5 g (49.4 mmol) of NaSCN. After the green solution was heated to reflux, the volume was reduced under vacuum to 10 ml resulting in the formation of dark green crystals. Upon adding 40 ml of ethanol to insure precipitation of all the complex and cooling to room temperature, the product was collected by filtration, washed with ethanol and diethyl ether, and dried under vacuum. The complex was recrystallized by dissolving it in a minimum amount of hot pyridine and then adding ethanol causing the product to precipitate. The yield was 94$ based on the starting complex. 28

trans-Thiocyanato(7, l3-dim ethyl-l,4, 8 , l2-tetraazacyclopentadeca-4, 6 ,12, -

l4-tetraenato)pyridineehromium(UI), Cr(Me 9 [l5]tetraenatoN/i)(NCS)(py). — The procedure for making this dark brown complex was similar to the one used above. Since the solubility of this complex in acetonitrile is substantial, the volume of

the solution was reduced to 20 ml after the addition of the ethanol in order to

remove most of the acetonitrile. Using 1.5 g (2.56 mmol) of [Cr(Me 2[l5]tetrae-

natoN,i)(py) 2]PF6, the yield was 84$,

trans-Thioc.yanato(2,12-dimethyl-1, 5,9 ,13-tetraazacyclohexadeca-l, 3,9,11-

tetraenato)pyridineehromium(IU), Cr(Me?[l 6 ]tetraenatoN^)(NCS)(py). — The preparation of this orange complex was the same as that used for the preceding}

complex. Starting with 1.5 g (2.5 mmol) of [Cr(Me 2[ l 6]tetraenatoN 4)(py) 2]PF6,

the yield was 83$.

trans-Thioc.yanato(5,7,12, l4-tetram ethyl-l,4, 8 , 11-tetraazac.yclotetradeca-

4 ,6 ,1 1 , l 3-tetraenato)pyridinechromium(III), Cr(MeA[14]tetraenatoNJ(NCS)(p.y). — The procedure for producing this green complex was the same as that used for the above complex. Based on 1.0 g (1.66 mmol) of [Cr(Me 4[l4 ]tetraenatoN 4)(py)2]- PFG, the yield was 83$,

C.yano(5,14-dimethyl-1,4,8, ll-tetraazacyclotetradeca-4, 6,11,13-tetraenato)- chi-omium(IU), Cr(Me 2[l4]tetraenatoN 4)CN. — To 50 ml of methanol were added 0.2 g (4.1 mmol) of NaCN and a solution containing 1.0 g (1.74 mmol) of [Cr(Me2-

[l4 ]tetraenatoN 4)(py) 2]PF 6 dissolved hi 10 ml of acetonitrile. This solution was refluxed for one hour and then filtered. The volume was reduced under vacuum to 10 ml and after adding 50 ml of dimethylformamide the volume was again reduced to 10 ml producing a green precipitate. A small portion of ethanol was added to the solution and the green powder was collected by filtration, washed with ethanol and diethyl ether, and dried under vacuum. For purification the complex was dis solved hi a minimum amount of hot pyridine. After the solution was filtered, 50 ml of dimethylformamide were added and the volume reduced under vacuum until the solid precipitated. The yield based on the starting complex was 77$. 29

Cyano(7,13-dimethyl-1,4,8, l2-tetraazacyclopentadeca-4, 6,12,14-tetraenato)chromium(III), Cr(Me?[l5]tetraenatoN)1)CNo — The synthesis of this green complex was the same as for the preceding complex. Using 1.0 g

(1.7 mmol) of [Cr(Me 2[l5]tetraenatoN 4)(py) 2]PF6, the yield was 75^. 30

Cyano(2,12-dimethyl-1,5,9,13-tetraazacyclohexadeca-l, 3,9,11-tetraenato)- chromium(III), Cr(Me 9 [ l 6]tetraenatoN;1)CN. — This orange complex was prepared using the same procedure as for the above complex. The yield was 50$ using

1.5 g (2.5 mmol) of [Cr(Me 2[ l 6]tetraenatoN 4)(py) 2]P F 8.

trans-Phenyl(5, 14-dimethyl-1,4,8, ll-tetraazacyclotetradeca-4,6,11,13- tetraenato)pyridinechromium(ni), [Cr(Me 9 [l4]tetraenatoN^)(CRHR)(py). — To a slurry of 1.45 g (2.53 mmol) of [Cr(Me 2[ l4]tetraenatoN 4)(py) 2]PF 6 hi 50 ml of tetrahydrofuran was added an excess of phenyllithium reagent (Alfa Inorganics,

2 M in 70:30 benzene :diethyl ether). As the addition of the phenyllithium reagent proceeded, the solution turned red-brown hi color and some of the lavender product started to precipitate. After the solution was heated to redissolve all of the product and filtered, 25 ml of ethanol were added and the volume was reduced under vacuum to 20 ml. The lavender crystals were collected by filtration, washed with ethanol and diethyl ether, and dried under vacuum. This complex was recrystallized by first dissolving it in a minimum amount of hot benzene, filtering the solution, and then adding ethanol causing the product to crystallize. The yield was 79$ based on the starting complex.

trans-Phenyl(7, l3-dim ethyl-l,4,8, l2-tetraazacyclopentadeca-4,6,12,14- tetraenato)pyridmechromium(III), Cr(Me?[l5]tetraenatoN 4)(CKHR)(py). — This red complex was prepared in the same manner as the previous complex. The yield was 88 $ starting with 2.5 g (4.26 mmol) of [Cr(Me 2[ l 5]tetraenatoN 4)(py) 2jP F G.

trans-Phenyl(2,12-dimethyl-1, 5,9,13-tetraazacyclohexadeca-l, 3,9,11- tetraenato)pyridinechromium(IIl), Cr(Me?[f 6]tetraenatoN^)(CRHR)(p,y). — This orange complex was synthesized using a procedure similar to that used for the above complex. After adding the ethanol the volume was reduced to approxi mately 5 ml since this complex has good solubility in ethanol. The complex was recrystallized from diethyl ether. The yield was 62$ based on 1. 5 g (2. 5 mmol) of

[C r (Me2 [ i 6 ] te tr aenatoN4) (py) 2 ] PF G. 31

(5, 14-Dimethyl-1,4,8, ll-tetraazacyclotetradeca-4,6,11,13-tetraenato)- nitrosylchromium(]), Cr(Me 9 [l4 ]tetraenatoISb)NO.— To 50 ml of methanol were added 2.0 g (3.49 mmol) of [Cr(Me 2[l4 ]tetraenatoN 4)(py) 2]PF 6 and 0. 5 g (7.25 mmol) of sodium nitrite. After the mixture was refluxed for one hour, the volume was reduced to dryness under vacuum and the solid was then extracted with hot benzene. The green benzene solution was filtered and the volume reduced to 10 ml under vacuum. After adding 50 ml of ethanol to the solution, the volume was again reduced to io ml causing the green solid to precipitate. The complex was collected by filtration, washed with ethanol and diethyl ether, and dried under vacuum. The compound was recrystallized by dissolving it in a minimum amount of hot benzene, filtering the solution, and adding ethanol causing the complex to precipitate. Based on the starting complex, the yield was 48$.

trans-Methyl( 5 ,14-dimethyl-l, 4 , 8 , ll-tetraazacyclotetradeca-4,6,11,13- tetraenato)pyridinechromium(III), C r(Me? [ 14]tetraenatoN.i) (CHa) (p.y). — To a solution consisting of 1.5 g (2.62 mmol) of [Cr(Me 2[i4 ]tetraenatoN 4) (py) 2]PF 6 in 50 ml of pyridine was added an excess of methyllithium reagent (Alfa Inorganics, 1.3 M in diethyl ether). The addition of the methyllithium reagent caused the color of the solution to change from bright green to dark brown. After the solution was stirred for 15 minutes, the green crystalline complex was collected by filtration, washed with a small portion of pyridine and a liberal amount of ether, and dried under vacuum. The complex was recrystallized from a minimum amount of hot benzene. The yield was 78$ based on the starting material.

trans-n-Butyl(5, l4-dim ethyl-l,4, 8 , ll-tetraazacyclotetradeca-4,6,11,13- tetraenato)pyridinechromium(ID), Cr(Me 9 [l4 ]tetraenatoN/1)(CH^(CH?)^)(py). — This green complex was synthesized using the same method as above. In this synthesis excess n-butyllithium (Alfa Inorganics, 2 M in hexane) was employed as the alkyl source. Based on 1.45 g (2.53 mmol) of [Cr(Me 2[l4]tetraenatoN 4)(py) 2jP F G, the yield was . 32

[Phenyl(5,14-dimethyl-l,4,8, ll-tetraazacyclotetradeca-4,6,11,13-tetraenato)-

chi-omium(IV)]iodide, [Cr(Me 2[l4jtetraenatoN/t)(CfiHQ jl. — A tetrahydrofuran solution of 0.35 g (1.38 mmol) of iodine was added slowly to a hot stirring solution

containing 1.2 g (2.82 mmol) of Cr(Me 2[l4 ]tetraenatoN 4)(C6H5)(py) in 50 m l of tetrahydrofuran. As the addition of the iodine solution proceeded, the solution became dark green in color and solid began to precipitate. After the solution cooled to room temperature, the dark greenish-brown crystals were collected by filtration, washed with tetrahydrofuran and diethyl ether, and dried under vacuum. For purification the complex was passed through a column of cellulose

15 cm long using ethanol as the eluant. The yield was 86 % based on the starting com plex.

[Phenyl(5,14-dimethyl-l,4, 8 , ll-tetraazacyclotetradeca-4,6,11,13-tetraenato)- chromium(IV)]thiocyanate, [Cr(Me? [MJtetraenatoISb)(CfiHfl)]SCN. — To a solution

composed of 0.5 g (1.05 mmol) of [Cr(Me 2[l4]tetraenatoN 4)(CGH5)]I dissolved in 50 ml of ethanol was added 0.25 g (3.09 mmol) of NaSCN. The solution was stirred until green crystals formed and precipitated. These crystals were collected by filtration, washed with ethanol and diethyl ether, and dried under a vacuum. Based on the starting complex, the yield was 82%.

[Chloro(5, 7, 7,12,14, l4-hexamethyl-l,4,8, ll-tetraazacyclotetradeca-4,11- diene)chromium(II)]hexafluorophosphate, [Cr(MeR[14]4, ll-dieneNJCl ]PFfi . — To

a slurry of Me 6[l4]4, ll-dieneN 4 • 2CF3S03H88 (2.9 g, 5.0 mmol) and CrCl 2 • 2py (2.81 g, 5.0 mmol) in 50 ml of ethanol was added an excess of triethylamine causing the solution to become brown in color. After being brought to reflux the solution

was filtered and 3.0 g (18.4 mmol) of NII 4PFG was added to the hot stirring solution. As the solution cooled.to room temperature with stirring, the red-brown product precipitated. The complex was collected by filtration, washed with ethanol and diethyl ether, and dried under vacuum. It was recrystallized by dissolving it in a minimum of acetonitrile, filtering the solution, and then adding ethanol until the product precipitated. Based on the ligand salt, the yields were 65-88%. 33

[Bromo(5, 7,7,12,14, l4-hexamethyl-l,4,8, ll-tetraazacyclotetradeca-4,11- diene)chromium(II) jhexafluorophosphate, [Cr(MeR[14]4,ll-dieneNJBrjPFe and [Iodo(5,7,7,12,14,14-hexamethyl-1,4,8, ll-tetraazacyclotetradeca-4,11-diene)- chromium(H) jhexafluorophosphate, [Cr(MeR[l4]4, ll-dieneN^IjPFfi. — These

two i’ed-brown complexes were prepared by the above method using CrBr 2 • 6py

and C rl2 • 6py as the metal sources. The yields were 66jo and 68 $ respectively, based on the ligand salt.

[Thjocyanato(5,7,7,12,14, i4-hexamethyl-l,4,8,11-tetraazacyclotetradeca- 4,11-diene)chromium(II)Jhexafluorophosphate, [Cr(MeR[l4j4, ll-dieneN,i)NCS]PFR. — To a slurry of 1.25 g (2.44 mmol) of [Cr(MeG[l4]4, ll-dieneN^CljPFg in 50 ml of hot ethaiol was added 0.4 g (4.93 mmol) of NaSCN. The brown solution was refluxed for 5 min and then filtered. The volume was reduced under vacuum until the brown product precipitated. Tt was collected by filtration, washed with ethaiol and diethyl ether, and dried under vacuum. The complex was recrystallized

from ethaiol. The yield was 68 f0 based on the starting complex.

[Pyridine(5,7,7, 12,14, l4-hexamethyl-l,4,8, ll-tetraazacyclotetradeca-4,11-

diene)chromium(II)Jhexafluorophosphate, [Cr(MeR[14]4, li-dieneN. 4)pyj(PFfi)?. — To

50 ml of ethanol containing 5.8 g (10 mmol) of Me 6[l4]4, ll-dieneN /1 • 2CF3S03H

aid 6 . 7 g (10 mmol) of Cr(CF 3S03)2 • 4py was added an excess of triethylamine causing the solution to turn brown. The solution was refluxed for a short time and

then filtered hot. To the hot filtrate was added 5.0 g (31 mmol) of NH 4PF 6 and the solution was again brought to reflux. The brown solution was allowed to cool with stirring resulting in the precipitation of a brown product. The complex was collected by filtration, washed with ethaiol aid diethyl ether, and dried under vacuum. The complex was recrystallized by dissolving it in a minimum amount of hot pyridine, filtering the hot solution, aid then adding ethaiol to cause crystallization. The yield was 83$ based on the ligand salt. 34

[Nitro(5,7, 7,12,14,14-hexamethyl-l,4,8, ll-tetraazacyclotetradeca-4,11- diene)nitrosylchromium(3) Jhexafluorophosphate, [Cr(MeK[14j4, ll-dieneN/)(NO)- (NO?)]PFfi. — To a solution consisting of 1.0 g (1.43 mmol) of [Cr(Mee[i4j4,11-

dieneN4)pyJ(PF 6)2 dissolved in a mixture of 35 ml of acetonitrile and 15 ml of ethanol was added 0.25 g (3.62 mmol) of sodium nitrite. The solution was stirred for 30 min at room temperature and then filtered. After the volume had been reduced under vacuum to 10 ml, 30 ml of ethanol were added and the volume was again reduced until the green product crystallized. The complex was collected by filtration, washed with diethyl ether and ethanol, and dried under vacuum. It was recrystallized by dissolving it in a minimum amount of acetonitrile, filtering the solution, and then adding ethanol to cause the product to precipitate. The yield was 43$ based on the starting complex. The halogen complexes could also be used to prepare the complex.

[Dichloro(5, 7,7,12,14,14-hexamethyl-l,4,8, ll-tetraazacyclotetradeca-4,11-

diene)chromium(HI)Jhexafluorophosphate, [Cr(MeR[l4]4,11 -dieneNJC1 9 ]PF R and [Dibromo(5, 7, 7,12,14,14-hexamethyl-l,4,8, ll-tetraazacyclotetradeca-4,11-

diene)chromium(III) jhexafluorophosphate, [Cr(M eJl4]4,11-dieneISh)Br 9 ] PF fi. — A sealed vial containing the chromium(U) complex was removed from the glove box and dissolved under nitrogen in 50 ml of acetonitrile. When a slight excess

of the appropriate halogen (Cl 2 or Br2) was introduced to the brown solution, the color of the solution immediately changed indicating oxidation of the metal ion. A large excess of ammonium hexafluorophosphate was added to this solution. The solution volume was reduced under vacuum to about 10 ml and then 80 ml of ethanol was added. The volume of the solution was again reduced until the product crystallized. The complex was collected by filtration, washed with water, ethanol, and diethyl ether, and dried under vacuum. Both complexes were recrystallized by dissolving them in a minimum amount of acetonitrile, filtering the solution, and then adding ethanol causing the complexes to crystallize. The yields for the purple dichloro complex and the pink dibromo complex were 60-80$ based on the starting complex. 35

[Dicyano(5,7, 7,12,14,14-hexamethyl-l, 4 , 8 , 11-tetraazacyclotetradeca-

4-, ll-diene)chromium(III)]hexafluorophosphate, [Cr(Mefi[l4]4, ll-dieneN 4)(CN)?]- PF(; and [Dithiocyanato{5,7, 7,12,14,14-hexamethyl-l,4 ,8 ,11-tetraazacyclotetradeca-4, ll-diene)chromium(III) jhexafluorophosphate, [Cr(Mefi[l4]4, ll-dieneNA)-

(NCS)?]PFfi. — To 100 ml of water were added 2 mmol of [Cr(Me 6[l4 ]4 ,11- dieneN4)Cl2]PFG and 6 mmol of NaSCN or NaCN. This was heated on a steam bath for 30 min resulting in the dissolution of the starting complex and a color change of purple to orange. A large excess of ammonium hexafluorophosphate was added to the hot solution and as the solution cooled to room temperature, the product crystallized. It was collected by filtration, washed with water, ethanol, and diethyl ether, and dried under vacuum. The complexes were recrystallized by dissolving them in a minimum amount of acetonitrile, filtering the solution, and adding ethanol causing them to precipitate. The yields of the yellow cyanide and orange thiocyanate complexes were 35-50$ based on the starting complex.

Di(chloro or bromo)(meso-5, 5, 7,12,12,14-hexamethyl-l,4 ,8 ,11-tetraaza- c.yclote trade cane) chromium(Il), Cr(MeR[l 4 ]aneN/i)X9 , (X- Cl or Br). — These complexes were prepared using the. method of Sperati . 10

Bis(thiocyanato)(meso-5, 5,7,12,12,14-hexamethyl-l,4 ,8 ,11-tetraazac.yclo- tetradecane)chromium(II), Cr(MeR[!4]aneN,i)(NCS)2. — To 1.0 g (2.45 mmol) of

Cr(M e6[l4 janeN4)Cl2 dissolved hi 50 ml of ethanol was added 0.4 g (4.94 mmol) of NaSCN. The solution was stirred and heated causing the color of the solution to change from blue to pink. After the solution had cooled to room temperature, the pink complex was collected by filtration, washed with ethanol and diethyl ether, and dried imder vacuum. The yield was 88 $ based on the starting material. 36

[Bis(acetonitrile)(meso-5> 5,7,12,12,14-hexamethyl-l, 4 , 8 , 11-tetraaza- cyclotetradecane)chromium(II)jhexafluorophosphate, [Cr(MeJl4]aneN,d (CIljCN)?]-

(PFk)?. — To a solution of 1.0 g (2.04 mmol) of [Cr(Me 6[l4janeN4)(CH3CN)2]C1210

in 50 ml of acetonitrile was added 2. 5 g (15,3 mmol) of NH 4PF6. After the volume of the solution had been reduced to 15 ml, 40 ml of ethanol were added and the volume was again reduced resulting in the precipitation of the pink product. The product was collected by filtration, washed with ethanol and diethyl ether, and dried under vacuum. The yield based on the starting complex was 84^. RESULTS AND DISCUSSION

Syntheses and Characterization of Chromium(IIi) Complexes with Me?[l4]tetraene-

Nd, Me?[l5]tetraeneNii, Me?[l6]tetraeneNA> and Me/t[l4]tetraeneNA.

Preparation of [Cr(Me 7[l4]tetraenatoNf))(py) 9 ]PF(;, [CiiMe?[l5jteti-aenatoN^-

(py)?]PFR, [Cr(Me 9 [l6 ]tetraenatoNA)(p.y)?]PFR, and [Cr(MeA[14]tetraenatoNft)(p,y)9]- PFRo — Several methods can be used to prepare the complexes XVII-XX. Since the methods involve the use of air-sensitive chromium(II) salts as starting

+ +

PR: PF o

p ;

XVII XVIII +

CrH PPC PR.

XIX XX 37 38

materials, all of the preparations were carried out in a glove box under a nitrogen atmosphere. Although chromium complexes have been synthesized employing chromium species in the oxidation states of 0, II, and III, chromium(H) starting materials were selected because of their reactivity. Chromium(II) is known to be very labile to ligand substitution reactions while chromium(III) is substitution inert. When the rate constants for the exchange of water molecules from the first coordination sphere of the metal ions is considered, the magnitude of the difference in their reactivity becomes readily apparent. The rate constant for chromium(H) is 7 x 10 9 se c -1 while the rate constant for chromium(IIl) is 3 x 10 ~6 se c -1. 89 Since macrocyclic ligands are known to coordinate more slowly by a few orders of magnitude than similar open chained ligands , 90 it would seem that a labile metal ion is necessary to insure complexation within a reasonable time period. These complexes were first prepared by refluxing anhydrous chromium(Il) acetate and H2[Me2[Z]tetraeneN 4](PF 6)2 (Z = 14, 15, or 16) in pyridine overnight with either the acetate or the pyridine deprotonating the ligand salts. This method proved to be unsatisfactory as the products were produced in low yields and an excessive reaction time was required. The ligand salts and Cr(CF 3S03)2 ° 4py were found to react readily in hot pyridine upon adding triethylamine to depro- tonate the ligand salts. This method resulted in good yields of highly crystalline products in relatively short times. The preferred method for the preparation of these complexes was the reaction of the ligand salts, CrCl 2 * 2py, and triethyl amine in a refluxing solvent mixture of pyridine and acetonitrile (equation 20).

(F ) xE Nr l2 • 2py + Y (PFe)2 + xsE%NCrC *Cr \ P F 6(20)

Py 39

R = HorCHg, X = -(CH2)2- = Y R = H, X = -(CH2)2-, Y = -(CH2)3- R = H, X = -(CH2)3- = Y

This reaction gave slightly lower yields and less pure products than the previous reaction but this chromium(II) starting material was much easier to obtain. Complexes XVII-XX were isolated as their hexafluorophosphate salts by reducing the volume of the reaction mixture to near dryness and then adding a copious amount of ethanol to induce crystallization. These complexes were recrystallized by dissolving them in a minimum amount of pyridine and inducing crystallization by adding ethanol. They can also be purified by dissolving them in pyridine and then passing the solutions through a 10-15 cm length column of neutral alumina. All manipulations must be performed in an inert atmosphere. In view of the conditions used for preparing these complexes, it is unusual that they contain chromium in the tripositive oxidation state. Calderazzo et al have prepared tris(N-methylsalicylideneiminato)chromium(II3) by the reaction of hexacarbonylchromium and N-methylsalicylideneimine in refluxing toluene for

6.5 h o u rs . 91 Tsutsui and coworkers allowed hexacarbonylchromium and mesoporphyrin-IX-dimethylester to react in refluxing decalin for 1.5 hours obtaining mesoporphyrin-IX-dimethylesterchromium(II ) . 28 Since both of these complexes were prepared under nitrogen, it was postulated that the acidic protons on the ligands were responsible for the oxidation of the chromium. The macrocyclic ligands are related to the N-methylsalicylideneimine and the porphyrin in that they too have acidic protons; therefore, it seems likely that these protons immediately oxidize the initially formed chromium(II) complex giving the chromium(HI) complex that is subsequently isolated. In addition, when the complexation reaction was carried out at room temperature, gas evolution was observed indicating that the protons do indeed act as the oxidizing agent and are reduced to hydrogen. 40

Preparation of [Cr(Me?[Z]tetraenatoNA)(L)9]PFfi (Z = 14, 15, or 16) and [CrCMe^ [l4]tetraenatoN/t) (L)9]PF(; (L - dimeth.ylformamide, 1-methylimidazole, thiocyanate, or cyanide). — As has been previously discussed, chromium(IQ) complexes are considered to be relatively substitution inert but the chromium(II]) complexes, XVII-XX, were found to readily undergo axial ligand substitution. Fleischer and coworkers found that the axial sites of the chromium(IH) complex with tetra(p-sulfonatophenyl)porphine, XXI, were substitutionally labile.29’30 Reaction rates were measured for the replacement of axially coordinated water

•scy

XXI molecules by fluoride, cyanide, and pyridine. These rates were found to be 103-104 faster than substitution rates of chromium(IIt) complexes that did not contain porphyrin ligands. This enhanced reactivity is thought to be a result of extensive n-bonding between the d and d metal orbitals and the rr porphyrin yz xz orbitals. This rr-bonding allows significant electron delocalization which results in greatly enhanced electron density on the chromium(M) and this, in turn, enhances the substitution lability of that metal containing species. Since the chromium(III) complexes, XVII-XX, are structurally similar to the chromium(HI) tetra(p-sulfonatophenyl)porphyrin complexes, these complexes should also involve extensive n-interaction which would result in labilization of groups in the axial sites. 41

Making use of the lability of the axial pyridine ligands, a number of simple derivatives were prepared in the dry box utilizing relatively mild conditions. Employing metathesis reactions, complexes were isolated containing 1-methyl imidazole, dimethylformamide, thiocyanate, and cyanide as axial ligands (equa tions 21-23). The bis-l-methylimidazole derivatives were prepared by adding an excess of 1-methylimidazole to acetone solutions of the respective bis-pyridine complexes in a minimum amount of acetone and adding ethanol to induce crystal lization.

XVH-XX + L (21)

L = Me-Im or dmf NCS

XXII XVII-XX + NaSCN S5 lC.» (22) N

Me OH x x i n XVII-XIX + NaCN & (23)

XXIV To prepare the dimethylformamide derivatives, the respective bis-pyridine complexes were dissolved in dimethylformamide (equation 21). After the volumes of the solutions were reduced to near dryness, ethanol was added precipitating the cationic complexes as their hexafluorophosphate salts, A large volume of dimethylformamide was used to guarantee the removal of all the pyridine from the reaction solutions when die volume was reduced under vacuum. Since pyridine is a stronger donor than dimethylformamide, mixtures of the starting complex and the desired derivative will be obtained if all the pyridine is n

Adding excess NaSCN to acetonitrile solutions of the cationic bis-pyridine complexes resulted in the formation of neutral thiocyanate complexes with one thiocyanate replacing one of the axial pyridine ligands (equation 22). The thio cyanate complexes with the 14-membered macrocycles are not very soluble in acetonitrile and they crystallize upon formation. The derivatives with the 15- and 16-membered macrocycles have better solubility; therefore, it is necessary to reduce the volume of the acetonitrile solutions and add ethanol to isolate the crystalline products. These complexes were recrystallized from ethanol-pyridine mixtures. Since their solubility was not good in cold pyridine, they were not subjected to chromatography on alumina. The cyanide derivatives were prepared by refluxing methanol solutions containing the pyridine complexes dissolved in acetonitrile and excess NaCN (equation 23). Extended reflux is necessary because neither the pyridine complex nor the NaCN are very soluble in methanol. The volume of the reaction solutions was reduced to near dryness, dimethylformamide was added, and the volume was again reduced until the product precipitated. These complexes are extremely soluble in a variety of solvents when any pyridine is present and extremely insoluble when it is absent. Therefore, the addition of the dimethyl formamide and the subsequent volume reduction is required to insure the removal of the pyridine and to allow solid products to be isolated. The cyanide derivatives are neutral complexes which have a cyanide molecule in one axial coordination site but, unlike the thiocyanate complexes, they do not have a pyridine molecule in the other site. These complexes can also be prepared by the reaction of the dimethylformamide derivative with NaCN in methanol. As no pyridine is present, the cyanide complex precipitates immediately upon formation. They were recrystallized by dissolving them in a minimum of pyridine, adding a large quantity of dimethylformamide, and reducing the volume until the complexes precipitated. Pyridine solutions of these complexes can be passed through alumina columns (10-15 cm in length) for further purification. 43

Characterization of [Cr(Me?[Z]tetraenatoN,i)(L)9]PFfl (Z = 14, 15, or 16) and [Cr(Me,t[ 14]tetraenatoN^)(L)? j PFR (L = pyridine, dimethylformamide, and 1-methyl imidazole) . — The six-coordinate cationic chromium(III) complexes, [Cr(Me2- [Z]tetraenatoN4)(L)2]PFe (Z = 14, 15, or 16) and [Cr(Me4[l4]tetraenatoN4)(L)2]PFG (L = py, dmf, and Me-Im), have been assigned structures XVII-XX and XXII. The compositions of these complexes are consistent with the given formulations as shown by their analytical data (Table 1) „ The infrared spectra of these complexes indicates the presence of the macrocyclic ligands, the type of axial ligands present, and the presence of the hexafluorophosphate anion. Sample infrared spectra are presented in Figures 1-3 and selected infrared absorptions for all of the complexes are given in Table 2. The infrared spectra of the chromium complexes have bands occurring in the double bond region which are very similar to those observed in the infrared spectra of iron(II) complexes with the same ligands.15 An incomplete crystal structure on Fe(Me6[l5]tetraenatoN4) shows that the complex is essentially square-planar.92 Also, these macrocyclic ligands have been reported to form square-planar complexes with a number of other divalent metal ions.15-16 In view of this evidence the macrocyclic ligands of the chromium complexes are assumed to be in an essentially planar arrangement around the chromium metal ion and to have two negative charges. Knowing that the chromium(III) ion and the ligand are in a planar configuration, all of the monodentate ligands must therefore be trans to. each other occupying coordination sites above and below the plane of the ring. The molar conductivities (Table 3) of these complexes are indicative of 1:1 electrolytes93 which supports the formulation of the complexes as univalent cationic species. Magnetic susceptibility measurements and ESR spectra were used to substantiate that the chromium ion is in the tripositive oxidation state. The solid-state magnetic moments of these complexes (Table 3) range from 3. 79- 3.97 B.M. and are in good agreement with the spin-only value of 3.87 B.M. for 3 unpaired electrons. Due to spin-orbit coupling the magnetic moments Table 1 Analytical Data for the Complexes, [Cr(Mex[Z]tetraenatoN4)(L) 2 ] PF6. Calc.

2 14 Py 46.08 4.92 14.65 45.76 5.02 14.76

2 15 Py 47.02 5,15 14.30 47.08 5.21 14.14

2 16 Py 47.92 5.36 13.97 48.17 5.22 13.78

4 14 Py 47.92 5.36 13.97 48.01 5.45 13.95

2 14 dmf 38.51 4.75 14.97 38.50 5.64 15.01

2 15 dmf 39.66 5.96 14.60 39.57 5.90 14.23

2 16 dmf 40.75 6.16 14.26 40.52 6.18 14.23

4 14 dmf 40.75 6.16 14.26 40.84 6.14 14.16

2 14 M e-Im 41.45 5.22 19.34 41.20 5.30 19.25

2 15 M e-Im 42.50 5.43 18.88 42.57 5.42 18.87

2 16 M e-Im 43.49 5.64 18.44 43.42 5.64 18.34

4 14 M e-Im 43.49 5.64 18.44 43.38 5.65 18.37 16 00 1400 1200 1000 800 600 400 Frequency (cm *)

Figure 1. Infrared Spectrum of [Cr(Me2[l4]tetraenatoN4)(Py)2]PF6. _ l___ _J— 1 —I__ 1600 1400 1Z00 1000 800 600 400 Frequency (cm-1)

Figure 2. Infrared Spectrum of [Cr(Me2[l4]tetraenatoN4)(Dmf)2]PF6„

C5 3000 1600 1400 1200 1000 800 600 Frequency(cm""1)

Figure 3„ Infrared Spectrum of [Cr(Me4[l4]tetraenatoN4)(Me-Im)2]PF6. Table 2

Selected Infrared Absorptions of the Complexes [Cr(Mex[Z]tetraenatoN 4) (L)2]PF6. a x_ Z_ L Double Bond Region L P F fi

2 14 py 1569, 1502 1608 840, 560

2 15 py 1574, 1510 1604 840, 560

2 16 py 1582, 1518 1608 840, 560

4 14 py 1535, 1515 1605 840, 560

2 14 dmf 1572 1642 840, 560

2 15 dmf 1580 1645 840, 560

2 16 dmf 1576 1646 840, 560

4 14 dmf 1550, 1517, 1497 1650 840, 560

2 14 M e-Im 1570, 1532, 1499 3120 840, 560

2 15 M e-Im 1585, 1535, 1510 3120 840, 560

2 16 M e-Im 1575, 1535, 1512 3122 840, 560

4 14 M e-Im 1558, 1540, 1521 3125 840, 560 aUnits are cm-1. oo Table 3 Physical Properties of the Complexes, [Cr(Mex[Z]tetraenatoN4)(L)2]PFG„ x_ Z_ JL_ Color (B.M.) A]vi(cm2ohm

2 14 py green 3.90 80 2 15 py brown 3.83 86 2 16 py orange 3.87 82 4 14 py green 3.87 86

2 14 dmf red 3.82 89 2 15 dmf orange 3.84 82 2 16 dmf orange 3.97 87 4 14 dmf red 3.79 91

2 14 M e-Im red 3.84 75 2 15 M e-Im red 3.87 85 2 16 M e-Im orange 3.87 81 4 14 M e-Im red 3.82 95 determ ined by the Faraday method at room temperature. Determined at room temperature using 1 x 10-3M CH3N02 solutions.

CD 50 for chromium(IH) complexes are expected to be reduced below the spin-only value (|i = (1-4 A/10 Dq)fj, spin-only). Since the spin-orbit coupling constant (A.) for chromium(IQ) is small and positive, the reduction in the moments is rather small, often approximately 4$.94 Variations due to such difficulties as uncertainties in diamagnetic corrections often exceed this value. The magnetic susceptibilities of the bis-pyridine complexes, XVII-XX, were measured over the temperature range from 98°K to 330°K. The data from these measurements is presented in Tables 4-7. As shown by the straight line graphs in Figure 4, these complexes obey the Curie-Weiss law (V x m = C /- (T + 9)) over the temperature range studied. Magnetic moments appropriate to the entire temperature range can be calculated from the slopes of the straight lines from the graphs of 1 / x m versus temperature. The moments and Weiss constants (Table 8) for the bis-pyridine complexes were calculated from the slopes which were determined using a least squares calculation. The complicated frozen solution ESR spectra of these complexes are indicative of a chromium (III) ion in a tetragonal environment. No nitrogen or chromium hyperfine splittings were observed in these spectra. These spectra will be discussed in greater detail in a later section of the thesis. The electronic spectra of these cationic complexes have a large number of absorptions with large molar-extinction coefficients indicating an extensive amount of mixing between the ligand and metal orbitals. The electronic spectra of the complexes having 14- and 15-membered macrocycles are similar in nature but the spectra of the complexes with the 16-membered macrocycle are markedly different as they possess fewer bands and no bands lower in energy than 18 kK. Polarographic measurements on these complexes show, in general, two oxidations and one reduction. One of the oxidations occurs near 0.0 volts vs Ag/AgNOg in acetonitrile and this causes these complexes to be air-sensitive. Both the electronic spectra and the electrochemistry of the cationic complexes will be the subject of further discussion. 51

Table 4 Temperature Dependence of the Magnetic Susceptibility of [Cr(Me2[i4]tetraenatoN4) (py)2]PF6. a

T(K) 1 /x m ’ Heff(B,M*)

98.1 61.1 3.59

134.8 79.1 3.69

152.9 87.8 3.74

189.3 104.3 3.81

210.9 114.9 3.83

240.1 129.2 3.86

270.5 144.4 3.87

302.8 155.5 3.95

329.6 168.1 3.96

determ ined by the Faraday method. ^Units are x iO6 cgs. diamagnetic cor- rection of 335 * x 10 "“6 'cgsu using Pascal's constants. 52

Table 5 Temperature Dependence of the Magnetic Susceptibility of [Cr(Me2[i5]tetraenatoN4) (py)2]PF6. a

T (K) V x m *3’ 0 Meff

103.2 61.9 3.65

137.7 80.7 3.70

155.7 89.7 3.73

188.3 109.6 3.71

213.0 121.8 3.74

242.4 133.4 3.81

268.5 146.9 3.82

300.2 162.1 3.85

328.8 173.1 3.90

a Determined by the Faraday Method. Units are x l06cgs. CDiamagnetic cor rection of 347 x i0~6cgsu using Pascal's constants. 53

Table 6 Temperature Dependence of the Magnetic Susceptibility of [Cr(Me2 [!6]tetraenatoN4) (py)2]PFG.a

T (k) VXM b ’ C Ueff (B

103.8 62.4 3.65

137. 5 78.1 3.74

164.6 91.6 3.79

195.7 107.6 3.81

217.2 117.9 3.84

243.3 130.7 3.86

264.6 141.6 3.87

303.6 159.4 3.90

329.5 171.9 3.92

determined by the Faraday method. dnits are x 106 cgs. diamagnetic cor rection of 359 x 10-Gcgsu using Pascal's constants. 54

Table 7

Temperature Dependence of the Magnetic Susceptibility of [Cr (Me4 [!4]tetraenatoN4) (py)2|P F G.a

T(K) . / D ,C X_M ..... ■ Feff (B: 101.6 63.0 3.59

132.4 77.4 3.70

164.2 96.8 3.68

195.2 114.1 3.70

222. 5 127.5 3.74

247.9 141.2 3.75

273. 5 155.0 3.76

301.6 167. 5 3.79

330. 1 175.7 3.88

aDetermined by the Faraday Method,, Units are x 10G cgs. CDiamagnetic cor rection of 359 x iO-(fcgsu using Pascal's constants. 55

170

160

150

140

130

120

100 150 200 250 300 Temperature (°K)

Figure 4„ Variation of 1/x with Temperature for : ® - [Cr(M e4[ 14]tetraenatoN4)( Py^] PF(,/^-[C r(M e2[ 14 ]tetraenatoN4)( Py)2]- PF6s° @ -[Cr(M e2[l5]tetraenatoN4)(Py)2]PF6; and ^ -[Cr(Me2[l6 ]- tetraenatoN4)(Py)2]PF6. 56

Table 8 Magnetic Moments and Weiss Constants Calculated from the Variable Temperature Magnetic Susceptibility Data of the Bis-pyridine Complexes.

Complex p. (B. M.) 8 (K)

[Cr(Me2[l4]tetraenatoN4)(py)2]PF6 4. 17 36

[Cr(Me2[l5]tetraenatoN4)(py)2]PF6 4.03 27

[Cr(Me2[i6]tetraenatoN4)(py)2]PFG 4.06 24

[Cr(Me4[l4]tetraenatoN4)(py)2]PF6 3.97 24 57

Characterization of Cr(Me?[Z]tetraenatoN,i)(NCS)(py), Cr(M eJl4jtetraenato- N^)(NCS)(py), and Cr(Me9[Z]tetraenatoN4)CN (Z = 14, 15, or 16). — These neutral complexes are assigned structures XXIII and XXIV. As is the case with the cationic complexes, these complexes are assumed to have the ligand in an essentially planar configuration about the metal ion. The elemental analyses for these complexes are given in Table 9 and they confirm the assigned formula tions. Representative infrared spectra are presented in Figures 5 and 6 and selected infrared absorption bands for all of these complexes are reported in Table 10. Infrared spectroscopy proved very useful in establishing the presence of pyridine in the thiocyanate complexes and its absence in the cyanide complexes. Elemental analyses suggest that the thiocyanate complexes are six-coordinate and that the cyanide complexes may be five-coordinate in the solid-state. The neutrality of these species was established by their molar conductivity measure ments (Table 11) which are well below values for electrolytes.93 The oxidation state of the chromium ion in these complexes was established by the magnetic susceptibility data in Table 11. The solid-state magnetic moments for the thiocyanate complexes agree quite well with accepted values for d3 metal ions but the moments for the cyanide complexes are about 0.5 B. M. below the spin-only value of 3.87 B.M. Even by taking into account experimental error and spin-orbit coupling the measured magnetic moments are still too low. The solubility behavior of these complexes and their low solid state moments imply that in the solid-state the cyanide complexes are probably polymeric in nature having Cr(IH)-CN-Cr(III) bridges but while in solution are six-coordinate having a pyridine ligand trans to the cyanide ligand. To substantiate this hypothesis, solution susceptibility measurements were performed on pyridine-nitromethane solutions of these complexes. The moments obtained from these measurements (Table 11) are much higher than the solid-state moments and agree quite well with expected values for chromium(HI) complexes. Table 9 Analytical Data for the Complexes, Cr(Mex[Z]tetraenatoN4)(A)(B).

Calc, j Found <%> X Z_ A_ B_ c_ _H_ A A J L A

2 14 NCS py 53.06 5.69 20.63 53.11 5.44 20.46

2 15 NCS py 54.14 5.98 19.94 54.26 5.92 19.83

2 16 NCS py 55.15 6.25 19.30 55.20 6.37 19.24

4 14 NCS py 55.15 6.25 19.30 55.34 6.32 19.40

2 14 CN — 52.69 6.12 23.63 52.40 6.09 23.51

2 15 CN — 54.18 6.50 22.57 53.81 6.71 22.34

2 16 CN _ — 55.54 6.84 21.59 55.39 6.68 21.45

Cl 00 2000 1800 1600 1400 1200 1000 800 F re q u e n c y (c m “ )

Figure 5. Infrared Spectrum, of Cr(Me2[l6]tetraenatoN4)(NCS)(Py).

Co l L _ _ _J___ I 2000 1800 1600 1400 1200 1000 800 Frequency (cm.-1)

Figure 6. Infrared Spectrum of Cr(Me2[l5]tetraenatoN4)CN. Table 10 cl Selected Infrared Absorption Bands of the Complexes, Cr(Mex[Z]tetraenatoN4)(A)(B).

X Z_ A_ B_ Double Bond Region CN m . c s

2 14 NCS py 1570, 1500 2082 1602 770

2 15 NCS py 1580, 1508 2092 1597 772

2 16 NCS py 1575, 1505 2090 1608 775

4 14 NCS py 1560, 1525 2090 1685 775

2 14 CN — 1580, 1503 2140 — —

2 15 CN — 1585, 1509 2145 . — —

2 16 CN 1582, 1515, 1493 2155 — - _____

aUnits are cm-1. Table 11 Physical Properties of the Complexes, Cr(Me [Z]tetraenatoN|)(A)(B). X

X Z_ A_ B_ Color Ueff (B.M .)a A ]yj(cm2ohm-1mor

2 14 NCS py green 3.93 I2b

2 15 NCS py brown 3.80 2b

2 16 NCS py orange 3.78 9b

4 14 NCS py green 3.92 I2b

2 14 . CN — green 3.38 (3.88)d i C

2 15 CN — green 3.39 (3.84)d 1C

2 16 CN — orange 3.22 (3.80)d 1C

3. b Determined by the Faraday method at room temperature. Determined at room temperature on lO^M CH3N02 solutions. °Determined at room temperature on 10-3M pyridine solutions. Determined by the Evans method at room temperature in CH3N02-pyridine solution. 63

The frozen solution ESR spectra of the thiocyanate and cyanide complexes are much the same as those of the cationic complexes. The low temperature solid-state ESR spectra of the cyanide complexes has a very broad intense absorption at about g = 2. A ll of the other complexes studied gave no absorptions in the solid-state. This indicates the solid-state structure of the cyanide complex differs significantly from the others. The oxidation potentials for the neutral complexes are lower than are those of the corresponding cationic complexes with the same macrocycle. The electronic spectra also resemble those obtained with the cationic complexes. The ESR spectra, electrochemical measurements and electronic spectra of these neutral complexes will be discussed later in more detail.

Oxidation and Other Reactions of the Chromium(IU) Complexes. — In view of the low oxidation potentials exhibited by these complexes, chemical oxidations were attempted with a variety of oxidizing agents. The reaction of [Cr(Me2[l4]- tetraenatoN,j)(py)2jPF6 with Cl2, 02, and (NH4)Ce(N03)6 in a variety of solvents produced no characterizable compounds. From these reactions only insoluble dark-brown or black powders were obtained indicating that the macrocycle was probably destroyed. The less powerful oxidizing agents I2 and K3Fe(CN)6 were tried on the same complex. The K3Fe(CN)e is probably too weak an oxidizing agent as only starting material was recovered from the system. The reaction of the green complex with excess I2 or I3“ in refluxing pyri dine resulted in the formation of an air-sensitive, dark-brown crystalline product. The infrared spectrum of this complex is similar to that of the starting material suggesting that the ligand is still present. The elemental analysis of the complex agrees well with that calculated for the starting complex. (Found C, 46.04; H, 5.02; N, 14.79; Calcd. f . C, 46.08; H, 4.92; N, 14.65.) The molar conductance value in CH3N02 of 82 cm2ohm-1mol-1 is consistent with the presence of a 1:1 electrolyte,93 and the solid-state magnetic moment of 3.82 B. M. indicates that the chromium ion is in the .tripositive oxidation state. 64

The electronic spectrum in acetonitrile is as follows: 8.3 kK (sh, 84), 14.7 (670), 19.6 (sh, 1690), 23.3 (sh, 2330), and 29.8 (sh, 3000). As would be expected from the color change, this electronic spectrum is quite different from that of the starting complex. A plausible explanation for these observations is that the macrocycle has been altered by oxidative dehydrogenation resulting in a greater degree of unsaturation. Holm and coworkers have reported oxidative dehydrogena tion reactions with similar Fe, Ni, Co, and Cu macrocyclic complexes.19 If indeed oxidative dehydrogenation has occurred, the complex may have structure XXV.

XXV

The reactions of the ckromium(IH) complexes with nitric oxide and carbon monoxide were investigated. No reaction was observed when carbon monoxide was bubbled through an acetonitrile solution of [Cr(Me2[l4]tetraenatoN4)(py)2]PFe. A reaction was observed when an acetonitrile solution of the same complex was exposed to nitric oxide. The green solution turned brown, but only tars or insoluble dark-brown powders could be isolated suggesting extensive decomposi tion. 65

In addition to the reported derivatives having various axial ligands, the preparations of other simple derivatives such as azide and the halides were attempted. The reactions of sodium azide and lithium chloride with [Cr(Me2[l4]- tetraenatoN4)(py)2]PF6 in various polar solvents resulted only in isolation of the starting complex. It was suspected that since pyridine is a strong ligand, perhaps azide and chloride ions might not be strong enough ligands to displace it.95 Therefore, these ions were allowed to react with [Cr(Me2[i4]tetraenatoN4)(dmf)2]- PFG in acetone or alcohols. Again, only the starting complex was isolated from the reactions. These results seem to suggest that these complexes will coordinate neutral ligands but will only coordinate strong anionic ligands. The complexes [Cr(Me2[i4]tetraenatoN4)(py)2]PF6 and [Cr(Me2[i5]tetraenato- N4)(py)2]PFG react with potassium t-butoxide in diethyl ether or tetrahydrofuran solvents to give brown crystalline products. These products are very air-sensi tive and are soluble in non-polar solvents such as benzene, diethyl ether, and tetrahydrofuran. This solubility behavior and the absence of hexafluorophosphate in their infrared spectra indicate they are probably neutral compounds having a coordinated t-butoxide in place of a pyridine as shown in structures XXVI and XXVII. Mass spectral measurements on these complexes gave parent ions at 270 m/e for the complex with the 14-membered ring and 284 m/e for the complex with the 15-membered ring which in both cases corresponded to the presence of only the chromium atom and the macrocycle although their infrared spectra show the presence of pyridine. Elemental analyses obtained on these complexes were not satisfactory but they indicate that the above formulations are possible. '•t-Bu

A I j

XXVI XXVII 66

Another class of reactions attempted with the chromium(ffl) complexes involved protonation of [Cr(Me 2[l4 ]tetraenatoN 4)(py) 2]PFg and [Cr(Me 2 [i4]tetrae- natoN, 1)(dm f)2 ]PFG. Tr if luorome thane sulfonic acid was added to an acetonitrile solution of the bis-pyridine complex and to a dimethylformamide solution of the bis-dimethylformamide derivative. A pale yellow crystalline compound was isolated from the acetonitrile solution and a light pink crystalline compound was isolated from the dimethylformamide solution. The infrared spectrum of the yellow complex showed no N-H absorption, a huge absorption due to hexafluorophosphate, and a C=N absorption, along with bands attributable to the macrocycle. Since pyridine is a fair base, the acid protonated the pyridine along with the ligand; therefore, acetonitriles became the axial ligands in place of the pyridines. The spectrum of the pink complex showed no N-H absorption, a large absorption from hexafluorophosphate, and absorptions from dimethylformamide and the macrocycle. From this evidence and protonation reactions of Fe(II) complexes with the same ligands 15 the complexes have been assigned the probable structures XXVIII and XXIX. These complexes did not appear to be air-sensitive, but it was extremely difficult to keep them protonated as they are extremely acidic. Satisfactory elemental analyses were not obtained for these complexes because the solvents used for recrystallization and the exposure to the dry box atmosphere tended to deprotonatc the complexes. 3+

XXVIII L= acetonitrile

XXIX Li= dimethylformamide 67

Preparation of Cr(Me?[Z]tetraenatoN^)(CnHs)(py) (Z = 14, 15, or 16) and Cr-

(Me9 [l4]tetraenatoN,i)(L)(py) (L = Me or n-Bu). — Excess phenyllithium reagent was added to a slurry of a bis-pyridine complex in tetrahydrofuran resulting in the formation of a cr-bonded phenyl derivative that is soluble in tetrahydrofuran (equation 24). The volume of the solution was reduced to near dryness and ethanol Eh

THF [Cr(Me2 [Z]tetraenatoN 4)(py) 2]PF 6 + CGH5Li (24)

XXX was added to cause crystallization. Since the phenyl complex with the 16-membered ring has good solubility in ethanol, the volume of this ethanol solution was reduced to facilitate precipitation. The addition of the ethanol not only precipi tated the complexes but also destroyed any excess phenyllithium reagent. The complexes with the 14- and 15-membered macrocycles were recrystallized by dissolving them in a minimum amount of hot benzene, filtering the benzene solutions, and adding ethanol. The complex with the 16-membered macrocycle was recrystal lized from diethyl ether.

n-Butyl and methyl derivatives of [Cr(Me 2[ l4 ]tetraenatoN 4)(py) 2 ]PF 6 w ere p r e pared by the addition of excess n-butyllithium reagent or methyllithium reagent to a pyridine solution of the complex (equation 25). The products crystallized from

p r(M e 2 [l4]tetraenatoN 4)(py) 2 ]PF 6 + RLi ———^ (25)

R = CH3 or n-B u P y XXXI the pyridine solutions and were collected by filtration and recrystallized from a minimum amount of hot benzene. The reactions with the alkyllithium reagents were tried with the bis-pyridine complexes having the 15- and 16-membered rings 68 in a variety of solvents and under a variety of reaction conditions, but in each instance no product was isolated. The solubility properties of the 14-membered ring derivatives in pyridine probably facilitated their isolation whereas useful solvent systems for the derivatives of the other ring sizes were not found. All manipulations with the aryl and alkyl complexes were performed in the dry box as these species proved to be the most air-sensitive group of chromium(IU) complexes encountered in these studies.

Characterization of Cr(Me?[ZJtetraenatoN,i)(CRHR)(py) (Z = 14, 15, or 16) and

Cr(M e9 [l4 ]tetraenatoNd)(L)(py) (L = CH^ or n-Bu). — These complexes with the aryl and alkyl ligands have been assigned structures XXX and XXXI. They are crystalline compounds containing thermally stable chromium-carbon cr-bonds. As in the other derivatives, the metal and macrocycle are in a planar arrangement with the pyridine and aryl ligands occupying the coordination positions above and below this plane. The analytical data for these complexes in Table 12 indicate that the formulations for the phenyl derivatives are correct; however, the analyses for the alkyl complexes are not very good indicating that impurities are present. Repeated recrystallizations did not result in better analytical data for the alkyl complexes. The impurities present are probably lithium compounds of some type which have solubilities in benzene similar to those of the complexes. A possible solution to this problem may be to synthesize these alkyl complexes using Grignard reagents instead of lithium reagents because they have been reported to give much cleaner products . 37’ 96 The infrared spectra of these complexes proved useful as they show the absence of hexafluorophosphate and the presence of pyridine, the macrocycle, and the aryl and alkyl groups. Representative infrared spectra of these complexes are given in Figures 7 and 8 and selected absorptions for all of the complexes are reported in Table 13. Since these complexes are neutral, their mass spectra were measured. As no parent ions were observed in these spectra, values for the highest molecular Table 12 Analytical Data for the Complexes with Aryl and Alkyl Ligands.

Calc. % Found 4, C omplex C H N C HN

Cr(M e2 [l4]tetraenatoN 4) (py) (Ph) 64.77 6.62 16.42 64.47 6 .8 8 16.33

C r (Me2 [ 15 ] tetraenatoN 4) (py) (Ph) 65.43 6 .8 6 15.90 65.38 6.96 15.84

Cr(M e2 [!6 ]tetraenatoN 4)(py) (Ph) 66.06 7.10 15.41 66.39 7.02 15.49

Cr(M e2[l4]tetraenatoN 4)(py)(CH3) 59.32 7.19 19.22 60.47 6.54 18.73

Cr(M e2 [l4]tetraenatoN 4) (py) (n-Bu) 62.05 7.93 17.23 62.16 7.43 18.54

C5 to 1600 1400 1200 1000 800 400 Frequency (cm*'1)

Figure 7. Infrared Spectrum of Cr(Me2[l4]tetraenatoN4)(C6H5)(Py)0

o 3000 1600 1400 1200 1000 800 Frequency {cm"1)

Figure 8. Infrared Spectrum of Cr(Me2[l4]tetraenatoN4)(CH3)(Py)« Table 13 cL Selected Infrared Absorptions for the Complexes with Alkyl and Aryl Ligands.

Complex Double Bond Region Aromatic C-H Bend Alkyl C

C r (Me2 [ 14 ] tc tr aenatoN4) (py) (Ph) 1575, 1568, 1501 1595 763, 732, 722, 713, 700 -----

C r (Me2 [ 15 ] te tr ae natoN4) (py) (Ph) 1583, 1504 1596 755, 725, 693 -----

Cr(M e2 [!6 ]tetraenatoN 4) (py) (Ph) 1576, 1511 1600 750, 738, 725, 703, 692 -----

C r(M e2 [14 ]tetraenatoN 4) (py) (CH3) 1518, 1488 1585 762, 725, 692 3028

C r (Me2 [ 14 ] te tr aenatoN4) (py) (n-Bu) 1516, 1486 1583 760, 723, 691 3025

aUnits are cm-1.

to-q 73

weight fragments are reported in Table 14 and compared to the calculated molecular weights for the complexes. For the three aryl complexes the highest mass peak found corresponds to the complex with the pyridine ligand removed. The alkyl complexes, on the other hand, have high mass peaks that are equivalent in mass to the complexes minus the alkyl ligands. It is not surprising that parent peaks were not observed for these complexes at the ionizing voltages used, but the information gained from the highest mass fragments do help support the assigned structures. As before the tripositive oxidation state is assigned to the chromium ion in these complexes on the basis of magnetic susceptibility measurements (Table 14). The solid-state magnetic moments of the aryl derivatives are close to the spin-only value for three unpaired electrons. Solution moments were obtained for the alkyl complexes because their extreme air-sensitivity would not permit the short exposure to air required for a solid-state magnetic susceptibility measurement. These magnetic moments are slightly low due to error in the measurements and the presence of the previously discussed impurities. The alkyl complexes are destroyed by alcohols and water. The reactions with water were very vigorous with definite evolution of gas which probably was methane or butane depending on the complex used. They also reacted with HgCl 2 in tetrahydrofuran which probably resulted in cleavage of the Cr-C bond to give the alkyl mercury species, RHgCl. The alkyl and aryl species have good thermal stabilities which undoubtedly result from the presence of the dianionic tetraaza macrocyclic and pyridine ligands. As discussed earlier, pyridine, 2,2'~bipyridyl, and 1, 10-phenanthroline ligands are known to stabilize chromium-carbon cr-bonds . 38 For these complexes the macrocyclic ligands can act in a similar manner to the nitrogen donor ligands mentioned above by blocking coordination sites and donating electron density to the metal ion which helps stabilize the chromium-carbon cr-bonds. Table 14 Physical Properties of the Complexes with Alkyl and Aryl Ligands.

Complex Color Meff Calc. Mol. Wt. Highest Mass Found (m/e) Cr(M e2[l4]tetraenatoN 4)(py)(Ph) lavendar 3.S2a 426 347

C r(M e2 [15 ]tetraenatoN 4) (py) (Ph) red 3.83a 440 361°

Cr(M e2 [l6 ]tetraenatoN 4) (py) (Ph) orange 3 .8 5 a 454 375°

Cr(M e2 [14 ItetraenatoN ^ (py) (CH3). green 3.52b 364 349d

Cr(M e2[l4]tetraenatoN 4)(py) (n-Bu) green 3.74b 406 349d

o Q Determined by the Faraday method at room temperature. Determined by the Evans method in CHC1 3 solvent. Corresponds to m/e calculated for Cr(Me 2[Z]tetraenatoN 4)(Ph). Corresponds to the m/e calculated for Cr(Me 2[l4 ]- tetraenatoN4) (py). 75

The oxidation potentials of these organo-chromiura(LD) complexes are very cathodic explaining their extreme sensitivity to air although the aryl species in the solid-state can be exposed to air for a short period of time without noticeable oxidation. The electronic and ESR spectra of these complexes are similar to the spectra observed for the other derivatives. The polarography, electronic spectra, and ESR spectra of these aryl and alkyl species will be discussed later in conjunction with the other derivatives.

Electronic Spectra of the Chromium(3J]) Complexes. — Since these chromium(HI) complexes with tetraaza macrocyclic ligands have pseudo D4h or C.lv symmetry, their electronic spectra are expected to show features consistent with these configurations. The crystal field theory for D4h complexes including chromium (ID) complexes has been given by Ballhausen . 97 Octahedral chromium- (III) complexes should exhibit three transitions, each of which, upon descending in symmetry to D 4it, should be split into two components (Figure 9). The split ting of the bands is expressed in terms of two parameters, Ds and Dt. Making the energy of the ground state ( 4Bjg) zero, the energies of the first four excited states are

E (4B2g) = 10 Dq

E (4Eg) = 10 Dq - 35/4 Dt

E (4A2g) - 10 Dq + 12B - 4Ds + 5 Dt

E (4E g') = 10 Dq + 12B + 2 Ds - 25/4 Dt Thus, the splitting of the first band is 35/4 Dt and that of the second band is CDs - 5/4 Dt. The splitting of the first band can provide a direct estimation of the axial ligand field strength. The magnitude of splitting is also a function of the geometry about the metal as trans complexes are expected to have twice the splitting of the corresponding c-is complexes. In general, the d-d electronic spectrum of a chromium(III) complex with tetragonal symmetry contains two, three, or four absorptions with molar extinction coefficients of 10-100 . 98-100 The first absorption occurs at about 76

4E, 4T\ M g

^ g

4E g 4rp T lg / / y "" ______4a , / ^ 2g / / / /

4 JP I S 4 g

\ \ 4 \ E g \ ^ \ *Azg 4 b 1d

F r e e Ion 0 4 ^

Figure 9° Term. Splitting Diagram for a d 3 Metal Ion in and D4^ S y m m e trie s o 77

17-19 kK, the next appears at about 20-21 kK, the third band at approximately 25 kK, and the last in the range 28-30 kK„ The second absorption is usually observed while the fourth is always ill-resolved and often not detected. The bands are assigned to the transitions from the 4B4g ground state to the excited states 4Eg, 4B2g, 4A2g, and 4Eg ( 4T 1g(F)) successively. The transition to the components of the ( 4Tjg(P)) states are assumed to occur at very high energies and therefore are not observed. The predicted positions of the absorptions bands in the spectra of tetragonal disubstituted amine and ethylene diamine complexes have been calculated using appropriate Dt values . 98 Table 15 shows the calculated band positions for several ethylenediamine complexes and compares them with the observed spectra for the same complexes. These spectra are of interest because the ethylene- diamines approximate the ligand field strength of the tetraaza macrocycles studied. In addition, the tians-diacido ethylenediamine complexes have a geometry similar to that of the macrocyclic ligand complexes. Spectral data (Table 16) for the chromium(IH) complexes with the ligands Me6[14]aneN4 and

Me6|l4]4, ll-dieneN 4 provide an.even better source for comparison . 10 The spectral data obtained for the chromium(III) complexes with the dianionic tetraaza macrocyclic ligands are shown in Tables 17-19. These spectra do not resemble any of the previous examples, i.e ., the ethylenediamine and macrocyclic ligand complexes, as they exhibit numerous intense bands between 16-30 kK with molar extinction coefficients of 400 to 20, 000. The spectra of the complexes having the 14- and 15-membered macrocycles are similar to each other while the spectra of the complexes with the 16-membered ring are quite different. Figure 10 shows how the spectra of the bis-l-methylimidazole comp lexes change as a function of the macrocyclic ligand. Depending on the type of axial ligands present, the spectra for the 14- and 15-membered rings have from two to three absorptions between 16-20 kK having molar extinction coefficients between 400-1000. The spectra of the complexes with the 16-membered macrocycle show only an ill-resolved shoulder before 20 kK. Although the 78

Table 15 Comparison of Calculated and Observed Spectra Band Positions of cl Chromium( Ill) —Ethylenediam ine C om plexes.

[Cr(en)2Cl2]+ [Cr(en)2(H20)2]3+ [Cr(en)2(NCS)2]+ Assignment Calc. Obs. (e) Calc. Obs. (e) Calc. Obs. (£)

4E 17.0 17.3 (25) 19.4 19.7 (22) 19.5 g 20. 7 (93) 4B2 . 21.6 22.1 (23) 21.6 22.6 (30) 21.6 ‘g

4A2o.S2g 23.6 25.3 (34) 25.8 25.9 2 7 .7 (39) 27.5 (6 7 ) 4E„ 26.2 27.3 (23) 27.0 27.1 ]g c lUnits are kK. 79

Table 16 Electronic Spectral Data for Chromium(lll) Complexes with the Ligands M eJl^anehh and MeR[i4]4, 11-dieneN,,.

C omplex ^ (e)

[Cr(MeG[l4]aneN 4)C l2]Cl 17.3 (29), 23.8 (sh, 31), 26.0 (42)

[Cr(MeG [MJaneN^ B r2]Br 16.4 (29), 23,9 (sh, 48), 25„8 (53)

[Cr(MeG[l4]aneN 4)(CH3CN)2](C104)3 18.7 (39), 23.5 (sh, 52), 27.4 (130)

[Cr(Mee[l4]4, ll-dieneN 4)Cl2]Cl 17. 5 (26) ,2 5 . 1 (sh, 23), 27. 5 (58)

[C r (MeG [ 14 ]4, 11 -dieneN4) B r 2 ]Br 16.2 (28), 25.2 (sh, 35), 27.3 (22)

[C r (MeG [ 14 ]4,11 -dieneN 4) (CH3C N) 2 ] - (C104)3 18.5 (39), 25.0 (sh, 36), 27.9 (148)

aUnits are kK. Table 17 3, Electronic Spectral Data for the Complexes, [Cr(Me [Z]tetraenatoN4)(L)2]PF6. X x . Z_ L_ Solvent V a x ^

2 14 py py 15.3(922), l6.4(sh), 20.4(5810), 21.7(4110), 23.3(sh), 27.4(sh)

2 15 py py 16.0(820), 16.9(sh). 21.5(5800), 22.8(sh), 23. 0(5100),. 31. 3(16, 700)

2 16 py py 17. 5(sh), 22.6(5000), 25.3(6400), 30. 1(15,700)

4 14 py py 16.1(1000), I7.2(sh), 21.2(5300), 22.5(3800), 23.9(sh), 27.3(sh)

2 14 dmf dmf 17.5(sh), 18.5(660), I9.8(sh), 21.8(9200), 23.1(6600), 24.4(sh), 32.3(22,000)

2 15 dmf dmf l8.2(sh), I9.4(sh), 23.1(6700), 24.3(6000), 25.3(sh), 31.7(18,300)

2 16 dmf dmf 18. 5(sh), 26.2(12,700)

4 14 dmf dmf I8.4(sh), 19.3(837), 22.5(10,700), 23.7(sh), 32.7(25,300)

2 14 Me-Im acetone 16.5(960), 17.8(975), I9.2(sh), 21.0(8500), 22.4(6200), 23.8(sh), 28.2(sh)

2 15 Me-Im acetone 17.3(850), 18.6(870), 20.0(790), 22.3(8800), 23.5(5800), 27.4(5800)

2 16 M e-Im acetone 18.5(sh), 23. 5(sh), 25.8(9200)

4 14 Me-Im acetone 17.3(990), 18.5(820), 21.8(6970), 23.2(4830), 24.6(sh), 28.6(sh)

oo aUnits are kK. o Table 18 Electronic Spectral Data for the Complexes, Cr(Me [Z]tetraenatoN4)(A)(B). X

a (e) X JZ_ A B Solvent max

2 14 NCS py CHClg 16„ 2(738), 17.2(sh), 20.6(4470), 21.8(3480), 23.3(sh),32. (19,400)

2 15 NCS py CHC13 16.8(600), 17.9(sh), I9.0(sh), 21.6(3600), 23.2(3000), 25, 31.4 (15,600)

2 16 NCS py CHClg 18. l(sh), 24.0(6210), 25.6(7420), 31.6(15,100)

4 14 NCS py CHC13 16.2(700), 22.4(5700), 23.7(4700), 25.2(sh), 30.0(20,000)

2 14 CN — py 15.4(1300), 17.0(1050), 20.0(8400), 21.2(5800), 23.0(sh), 27. l(sh)

2 15 CN -- py 16.3(600), 17. 5(sh), I9.5(sh), 21.5(4000), 22.8(sh), 26.4 (4000), 31.7 (13,400)

2 16 CN — py I8.2(sh), 23.2(6200), 26.0(5100), 31.4(13,500)

aUnits are kK. >

Table 19 cl Electronic Spectral Data for the Complexes, Cr(Me 2[Z]tetraenatoN 4)(R) (py). z_ _R_ Solvent '''•max (s)

14 c 6h 5 CHC13 12.9(490), 17.8(400), 20.2(sh), 22.2(5000), 27.3(sh)

15 C6H5 CHCI3 13.3(600), 17. 6 (sh), 22.8(5000)

16 c 6h 5 CHCI3 19. 3(sh), 25.0(7800), 26.9(12,300)

14 c h 3 CHCI3 16.4(570), 17.6(540), 20.6(4800), 21.9(3400), 27.7(sh), 32.0 (17,300) 14 n-B u CHCI3 16.3(540), 17.6(510), 20.6(4500), 21.9(3700), 27.7(sh), 32.0 (16,500) aUnits are kK.

00to 900C 900

8000- 800

/ \ • / 7 .-^ ' 700

6000 600 4

5000 500 H- < 4000 ±00^

3000 300

2000 200

100 1000 •T ----

400 500 500 600 Wavelength (nm) Figure 10. Electronic Spectra of:--- [Cr(Me2[l4]tetraenatoN4)(Me-Im)2]PF6J 0 • * [Cr(Me4[14]- tetraenatoN 4)(M e-Im)2]PF£,; -•-•[Cr(M e2[l5]tetraenatoN 4)(Me-Im.)2]PF6i —=— [Cr(M e2[l6]tetraenatoN 4)(Me-Im.)} p p . oc 84

complexes with the two different 14-membered macrocycles differ by only two methyl groups, their spectra are found to be different indicating that methyl substituents can effect the electronic structure substantially.15 From two to four absorptions with molar extinction coefficients of greater than 1000 occur at energies higher than 20 kK! in the spectra of these complexes with the 16-mem bered derivatives having fewer bands than the complexes with the 14- and 15-mem bered rings. The axial ligands present also result in spectral differences. Figure 11 shows how the spectra of the complexes having the macrocyclic ligand Me2[i5]- tetraenatoN4 are affected by the axial ligands present. No systematic changes in the spectra are observed as a function of the axial ligands but different axial ligands result in varying numbers of bands and variations in intensity for comp lexes having the same macrocyclic ligand. Assignments for the absorptions in these spectra were not attempted using the theory discussed earlier as all the bands observed are too intense to be pure d-d transitions. These spectra resemble those reported for metal comp lexes with the same15’16 or sim ilar macrocyclic ligands18’19 and of chromium(JII) complexes with porphyrin31 and phthalocyanine26 ligands. The macrocyclic ligands p re se n t in these com plexes are capable of substantial TT-bonding with the metal orbitals due to the conjunction of the ligand double bonds. The molecular o rb itals that re su lt fro m the TT-bonding between the m etal and the ligand a re low enough in energy that low-energy transitions can occur between occupied and unoccupied molecular orbitals which are derived mainly from either the ligand or the metal, i.e ., low-energy metal to ligand tt* transitions, ligand rr to metal transitions, or ligand tt to ligand tt* transitions can occur. Thus, the combination of these low-energy charge transfer processes and the d-d transitions results in the observed spectra for the chromium!Ill) macrocyclic ligand complexes and at this time the separation of only the d-d transitions seems impossible. 8 0 0 C 800

700C 700

600C V 600 ity tiv rp o s b A Molar

500 500

000 400

3000 / • < - 300

2000 200

1000 100 s

"— i r ~ — Wavelength (nm) Figure 11, Electronic Spectra o f[C r(M e 2[15]tetraenatoN4)(Py)2]PF£,;—-[Cr(Me2[l5]tetraenatoN4)(Dmf)2- ]P F 6j— [Cr(Me2[l5]tetraenatoN 4)(Me-Im)2]PF6t——[Cr(M e2[l5]tetraenatoN 4)(NCS)(Py)f and — * —. Cr(Me2[l5]tetraenatN4)CN. oo U1 86

Electrochemistry of the Chromium(II]) Complexes, — The electrochemical behavior of these chromium(III) complexes with the dianionic tetraaza macrocyclic ligands is quite unusual. The electrochemical data obtained for these complexes is reported in Tables 20-22. The bis-dimethylformamide derivatives (Table 20) would probably be better represented as bis-acetonitrile derivatives since the data was obtained in acetonitrile which is a stronger donor than dimethylformamide and most certainly replaces it in solution. The thiocyanate (Table 21) derivatives have polarograms which show other processes that are not included in the table. These processes are attributed to the replacement of the thiocyanate ligand by a solvent molecule as the same waves are present in the polarograms of the bis- dimethylformamide complexes. In general, these chromium(m) complexes have two oxidation processes and one reduction process. The less anodic oxidation process occurs at relatively low moderate potentials and is responsible for the air-sensitivity of these comp lexes. For the cationic and neutral aryl complexes this oxidation process is reversible or quasi-reversible in nature as the cyclic voltammogram of these complexes give AEp values of 50-100 millivolts while for the other neutral comp lexes this oxidation process is irreversible. For a completely reversible one- electron process a eP should have a value of 60 m v.86 The other oxidation process for these chromium(ffl) complexes is always irreversible except for the bis-1- methylimidazole derivatives in winch the process is quasi-reversible. The reduction process exhibited by these complexes occurs at very negative potentials and is for the most part irreversible in nature. Although oxidations of chromium(EI) that can be detected electrochemically are extremely rare, the oxidation with the lower potential occurring in these chromium(III) complexes with the dianionic tetraaza macrocyclic ligands is assigned as a Cr(IH) -» Cr(IV) oxidation. A Cr(ID) - Cr(IV) oxidation occurs at 0.79 v vs SCE in butyronitrile (about 0.43 v vs Ag/AgN03) for octaethylporphi- natochromium(Hl) hydroxide.32 Iron complexes with the same15 and sim ilar18 dianionic macrocyclic ligands have very cathodic reversible Fe(II) Fe(III) Table 20 Electrochemical Data for the Complexes, [Cr(Mex [Z ]tetraenatoN 4) (L) 2]PF6. Oxidations Reductions ci b E i /,, Ligand ( aE p) E 1 /,, aCr(ffl) /Cr(II) (AEp) x_ Z L E,/o,a Cr(III)/Cr(IV) (AEp) /

4 14 dmf -0.11 (70) -0.78 (HO) -1.71 (irr) 2 14 dmf 0.02 (60) -0 .9 4 (irr) -1.69 (240) 2 15 dmf 0.12 (100) 0.79 (irr) -1 .8 0 (irr) 2 16 dmf 0.09 (70) 0.46 (irr) -1.89 (irr)

4 14 py -0.03 (80) 0.83 (irr) -1 .7 7 (irr)

2 14 py 0.03 (60) 0.99 (irr) -1.62 (90) 2 15 py 0.13 (100) 0.80 (irr) -1.73 (irr) 2 16 py 0.20 (180) 0.69 (irr) -1 .9 (irr) iH c— O 1 4 14 M e-Im • (60) 0.73 (60) -2 .2 4 (irr) 2 14 M e-Im -0 .1 1 (90) 0.85 (100) -2 .1 0 (irr) 2 15 Me-Im 0.02 (90) 0.66 (irr) -2.11 (irr) 2 16 M e-Im 0.05 (90) 0.49 (HO) -2.30 (irr)

a b Volts vs Ag/AgNOg (0.1 M) reference electrode, in acetonitrile with 0.1 M (n-Bu)4NBF4. Millivolts. Table 21 Electrochemical Data for the Complexes, Cr(Me [ZjtetraenatoNJ (A)(B). X Oxidations Reductions x_ Z_ A B Ef/„a Cr(IH)/Cr(IV)

4 14 NCS py -0.28 (irr) 0.50 (irr) -2.08 (irr)

2 14 NCS py -0.21 (irr) 0.32 (irr) -1.98 (irr)

2 15 NCS py -0.13 (irr) 0.45 (irr) -2.05 (irr)

2 16 NCS py 0.0 (irr) . 0.48 (irr) -2.27 (irr)

2 14 CN — -0.26 (irr) 1.24 (irr) -2.40 (irr)C

2 15 CN — -0.15 (irr) 0.63 (irr) -2.60 (irr)C

2 16 CN _ _ -0.02 (irr) 0.46 (irr) -2.40 (irr)C

a b e Volts vs Ag/AgN03 (0.1 M) reference electrode, in acetonitrile with 0.1 M (n-Bu)4NBF4. Millivolts. Pyridine solu tion of complex added to acetonitrile.

oo oo Table 22 Electrochemical Data for the Complexes, Cr(Me2[Z]tetraenatoN4)(R)(py). Oxidations Reductions a . , z_ R Ei /?, aCr(IU)/Cr(IV) (AEp)b E i/,, Ligand (AEp)b E1/,,aCr(IU)/Cr(II) (AEp)b

14 cgh5 -0.60 (50) 0.62 (irr) -2.43 (50)

15 C6H5 -0. 50 (50) 0.41 (irr) -2.55 (irr)

----- 16 c6h5 -0.42 (60) 0.32 (irr)

14 ch3 -1.45 (irr)° 0.90 (irr) -2.54 (irr)

14 n-B u -1.45 (irr)C 0.85 (irr) -----

aVolts vs Ag/AgNOg (0.1 M) reference electrode, in acetonitrile. with 0.1M (n-Bu)4NBF4. Millivolts. °Very broad w aves.

OO CO

\ 90

oxidationso The alternative to the assignment of this oxidation process as a metal ion oxidation is to assign it to a ligand process. The quasi-reversible behavior of the oxidation in most of the complexes and the absence of a free radical signal in the ESR spectrum of the electrochemical oxidation product of [Cr(Me2U4]tetraenatoN4)(py)2]PFG do not support a ligand oxidation assignment. The most convincing evidence for this process being a metal oxidation is that the iodine oxidation of Cr(Me2[14]tetraenatoN4)(C6H5)(py) produces a characterized chromium(IV) complex (vida infra). The dianionic tetraaza macrocyclic ligands of these complexes physically constrain the chromium(HI) ion and they also can donate a large amount of electron density to the metal by both or- and Tr-bonding making the chromium(III) ion electron rich. Both of these effects would tend to lower the oxidation potential of the chromium(HJ) ion, thereby promoting the occurrence of higher oxidation states of the chromium complexes with these macrocyclic ligands. Electroche mical studies of nickel complexes with anionic macrocyclic ligands demonstrated that negative charge does promote the formation of higher oxidation states of the complexes and causes their reductions to be more difficult.86 The irreversible oxidation that occurs at more anodic potentials is most likely a ligand oxidation process which involves the removal of an electron from

the tt system of the ligand to form a free radical species. The irreversible reduction process which appears at very cathodic potentials may be the Cr(III) -> Cr(Il) reduction at -1.14 v vs SCE in butyronitrile (about -1.50 v vs Ag/AgNQJ. This low reduction potential would be expected for a complex having a negatively charged ligand. These chromium(III) complexes exhibit changes in their metal ion and ligand oxidation potentials which are a function of both the ring size of the macrocycle and the axial ligands. Keeping the axial ligands constant, the metal ion oxidation potential becomes more positive as the ring size increases while the ligand oxida tion shows the reverse behavior becoming less positive. These trends can be explained using charge density arguments. As the ring size of the macrocyclic 91

ligand increases, the interaction between the metal ion and the ligand decreases. Thus, the larger macrocyclic ligand donates less electron density to the chromium(IIl) ion than do the smaller rings. This causes the metal ion in the comp lexes with the smaller rings to be more electron rich and therefore to be more easily oxidized. The reverse trend occurs when the ligand oxidation is considered because as the ligand donates more electron density, it, in turn, becomes less electron rich and more difficult to oxidize. The order of increasing axial ligand donor strength is dimethylformamide (actually acetonitrile) < pyridine < 1-methylimidazole < thiocyanate < cyanide. This oraer is reflected by the metal and ligand oxidation processes of complexes having the same macrocyclic ligand. In general, as the donor strength of the axial ligand increases the metal and ligand oxidations become more facile. Charge density arguments can again be invoked to explain this behavior. Ligands of greater donor strength can donate more electron density to a metal ion, thereby making the metal ion easier to oxidize. This increase in electron density on the metal ion is passed on to the ligand also making it more oxidizable. It is interest ing to note that the derivatives which have the aryl and alkyl ligands exhibit the lowest (most cathodic) metal ion oxidation potentials (Table 22), indicating that these ligands are more effective at donating electron density than even cyanide for these chromium(III) macrocyclic ligand complexes.

ESR Spectra of the Chromium (III) Complexes. — Investigations of the ESR spectra of chromium(ni) compounds with tetragonal and lower symmetry recently have been reported for several series of complexes in the solid-state and in frozen solution.101-106 The conventional spin-Hamiltonian operator for S = 3/2 is

H - g.jgH S + g.,3(H S + H S ) + D[S 2- i/3S(S+l)] + If z z XL x x y y z

E(S 2- S 2) (26) x y 92

At zero magnetic field the quartet ground state is split into doublets separated in ■energy by 2[D2+ 3E2]1/2. These pairs, which reflect the degeneracy of an ion with an odd number of electrons, are called Kramer's doublets . 107 The axial zero-field splitting parameter, D, measures the difference between the spin- orbit mixing about the Z axis and that about an axis in the xy plane. The rhombic zero-field splitting parameter, E, measures differences in the spin-orbit mixing about the x and y directions and, therefore, should vanish for tetragonal comp lexes (Figure 12).

3 /2

1/2

/ S 2D

- 1/2

3 /2

Figure 12. Energy Levels of a d 3 Ion in Tetragonal Symmetry. 93

The frozen solution spectra of chromium(IIl) complexes with appreciable zero-field splitting are broad and have a number of features at low field. In these frozen solution spectra, interactions of the complex with randomly oriented counterions and solvent molecules contribute to the widths of absorption lines. The interpretation of spectra for randomly oriented species is complicated by the fact that features in addition to those at resonance positions for the magnetic field along a symmetry axis of the system can be expected in certain situations. These include transitions for which the maximum or minimum effective g value does not correspond to the x, y, or z resonance position (e.g., a AM = 2 transi tion). It is also possible that transitions which cannot occur for a specific value of hv when the magnetic field is along one or more symmetry axes do occur for intermediate orientations of the magnetic field with respect to the symmetry axes. X, y, and z transitions correspond to maxima, minima, or inflection points. Features corresponding to z transitions are characteristically less intense than the associated x and y transitions. Intensities of spectral features are functions of how the absorption lines for each paramagnetic complex in the randomly oriented array superimpose and the relative transition probability for each transition and orientation involved . 101 In order to interpret the random orientation spectra of chromium(HI) comp lexes computer simulations of the spectra must be performed based on the spin- Ilamiltonian (equation 26). These calculations result in graphs showing resonance field positions as functions of the various spin-Hamiltonian parameters. Using the se graphs prominent peaks or inflections in the spectra can be located which correspond to x, y, z, or intermediate orientations of the static magnetic field relative to the molecular magnetic axes. Using this process one can obtain good estimates of the spin-Hamiltonian parameters. Detailed computer simulations based on these preliminary parameters can then be performed, followed by small adjustments of the param eters . 101-104 94

The frozen solution ESR spectra of the chromium! HI) complexes with the dianionic tetraaza macrocyclic ligands are presented in Figures 13-17. All are X-band spectra of frozen dimethylformamide solutions of the complexes taken at liquid nitrogen temperature. As expected for chromium(m) complexes they have numerous broad bands with many of them occurring at low field. There seems to be no drastic change in the spectra as the axial ligands are varied but the complexes with the 16-membered macrocycle definitely show the best resolution. The purpose of presenting these spectra is in establishing that these macrocyclic ligand complexes contain a chromium!ID) ion in a tetragonal environment. No further interpretation of the spectra was attempted as this would require detailed computer simulation of the spectra. In addition, the ESR instrument used to obtain these spectra would not operate above a magnetic field strength of 4500 gauss; therefore, some important features that may occur above this field strength could not be detected. ^jb-g=2.0036

=2.0036

1 2 H(kG) 3 4.

Figure 13. ESR Spectra of: A, [Cr(Me4[14]tetraenatoN4)(Py)2]PFe, * B, [C r(M e 2[ l 6 ]tetraenatoN4)( Py) 2]PF 6>° C, [Cr(Me2[14]tetraenatoN4)(Py)2]PF6J D, [Cr(Me2[15]tetraenatoN4)( Py) 2]PF 6 . 96

*Tg =2. 0036

1 2 H (kG) 3 4 Figure 14. ESR Spectra of: A, [Cr(Me2[15]tetraenatoN4)(M.e-Irn)2]PF6; B, [C r(M e 2[l4]tetraenatoN 4 )(M e -Im )2] P F 6; C, [Cr(Me4[14]tetraenatoN4)(Me-Im)2]PF£,; D, [C r(M e 2[ l 6 ]tetraenatoN 4 )(M e-lm .)2] P F 6. 97

1 2 H (kG) 3 4

Figure 15. ESR Spectra of: A, [Cr(Me 2[ l 6 ]tetraenatoN 4 )(D m f)2]P F 6; B, [Cr(Me2[14]tetraenatoN4)(Dmf)2]PF6; C, [C r(M e 2[l5]tetraenatoN 4 )(D m f)2]P F 6; D, [C r(M e 4[l4]tetraenatoN 4 )(D m f)2]P F 6 . 98

1 2 H(kG) 3 4

Figure 16. ESR Spectra of: A, Cr(Me4[14]tetraem toN4)(NCS)(Py),* B, C r(M e 2[ l 6 ]tetraenatoN 4)(NCS)(Py),° C, Cr(M e2[ 14]tetraenatoN4)(NCS)(Py),° D, Cr(Me2[15]tetraenatoN4)(NCS)(Py). 99

g=2.0036

Figure 17 „ ESR Spectra of: A, Cr(M e2[ 14 ]tetraenatoN 4)CN ; Bs C r(M e 2[1 5 ]te tra e n a to N 4)CN,° C , C r(M e 2[ l 6 ]tetraenatoN 4)CN. 100

Syntheses and Characterization of the Complexes, [Cr(Me^[l 4-jtetraenatoN/i)- (CfiHg)]X (X = I or SCN).

Preparation of [Cr(Me 9 [l4 ]tetraenatoNJ (CRHS)JX (X = I or SCN). — Since

the complex Cr(Me 2[l4]tetraenatoN 4)(C6H5)(py) possesses a highly reversible metal oxidation at a fairly cathodic potential, the treatment of this complex with a mild oxidizing agent should result in the formation-of a chromium(IV) complex. The starting complex was dissolved in hot tetrahydrofuran and a tetrahydrofuran solution containing one equivalent of iodine was added to the hot stirring solution of the complex causing it to darken immediately. After the solution cooled to

room temperature, the green-brown product, [Cr(Me 2tl4]tetraenatoN 4)(C6H5)]I, crystallized and was collected by filtration (equation 27). This chromium(IV) Ph “1

Cr(M e2[l4]tetraenatoN 4)(C6H5)(py) + 1/21^ ■—

(27)

XXXII

complex was then dissolved in ethanol and an excess of sodium thiocyanate was

added causing the dark green complex LCr(Me 2[i4 ]tetraenatoN 4)(C6H5)jSCN, to crystallize (equation 28).

EtOH SCN XXXII + NaSCN (28)

The oxidation of Cr(Me 2[i5]tetraenatoN 4)(C6H5)(py) was attempted using the same procedure with iodine as the oxidizing agent. A brown product was obtained which contained axially bound pyridine and chromium(HI). This compound was not characterized further but the preliminary data indicate that a different type of reaction occurred. 101

The chromium(IV) complexes are air-sensitive with the thiocyanate derivative being more air-sensitive than the iodide derivative and they dissolve in such polar solvents as nitromethane, acetonitrile, and ethanol. After an ethanol solution of [Cr(Me2[i4]tetraenatoN4) (C6H5)]I was passed through a 15 cm column of cellulose, an acceptable elemental analysis was obtained- (Calcd. $ for

C rC 18H23N4I: C, 45.58; H, 4.89; N, 11.81. Found $: C, 45.23; H, 4.98; N, 11.60.) Neutral alumina and silica gel proved to be unsatisfactory column supports as they caused the iodide complex to decompose. Since alumina, silica gel, and cellulose caused [Cr(Me2[l4]tetraenatoN4)(CGH5)]SCN to decompose that compound was not successfully purified. An elemental analysis was obtained on the crude complex and although it was unsatisfactory, it does help support the assigned formulation of the complex- (Calcd- fa for C rC i9H23N5S: C, 56.28; H, 5.72; N, 17.27. Founder C, 54.27; H, 5.70; N, 16.80.)

Characterization of [Cr(Me?[l4]tetraenatoN/<)(CfiHr,)]X (X = I and SCN). — The two chromium(IV) complexes are assigned structures XXXII and XXXIII. The infrared spectra of these complexes (Figures 18 and 19) indicate the presence of the macrocycle, the aryl group, and for the one complex, thiocyanate. It is interesting to note that the infrared bands due to the double bonds in the macrocycle are shifted to lower frequencies for the chromium(IV) complexes. The five-coordinate structure for these complexes is established by the conductivity measurements (Table 23) in nitromethane which indicate that the compounds are 1:1 electrolytes-93 This type of stereochemistry is rare for chromium(IV) complexes as most of them have distorted tetrahedral geometries. The electronic solution and mull spectra for the chromium(IV) complexes are shown in Figures 20 and 2l and the spectral data is summarized in Table 24. These spectra are quite different from the spectra reported for the chromium(III) complexes with the same macrocyclic ligand. They contain a large number of intense bands with several occurring below 15 kK. The intensities of these bands imply that they are mainly charge transfer in nature; I—______I______I______I______t___ 4000 3000 2000 1500 1300 1200 Frequency (cm"1)

Figure 18. Infrared Spectrum of [Cr(Me2[14]tetraenatoN4)(C6H5)]l. J ______I ______!______I______s______I 1300 1000 800 600 500 400 Frequency (cm"1) Figure 18 (cont.). Infrared Spectrum of [Cr(Me2[l4]tetraenatoN4)(C6H5)]l.

o CO I___ I______I______5______S______I 4000 3000 2000 1500 1300 1200 Frequency (cm-1)

Figure 19. Infrared Spectrum of [Cr(Me2[14]tetraenatoN4)(C6H5)]SCN„ J ------1______I______1______S______! 1300 1000 800 600 500 400 Frequency (cm-1)

Figure 19 (cont. ). Infrared Spectrum of [Cr(Me2[14]tetraenatoN4)(C6H5)]SCN. 8______i______s______i______i______i______i______i______i______■ 400 600 800 1000 1200 Wavelength (nm)

Figure 20. Electronic Spectrum of [Cr(Me2[14]tetraenatoN4)(Q,H5)]l:- Mull; —— CH3N02 Sol'n.

o C5 A I 400 600 800 1000 1200 1400 Wavelength, (nm)

Figure 21. Electronic Spectrum of [Cr(Me2[14]tetraenatoN4)(C6H5)]SCN: ----M ull; - “ CH3N02 Sol'n. 108

Table 23 Physical Properties of the Chromium(IV) Complexes.

Complex Color M.)a Ajyj(cm2ohm''1mol_1)b

[Cr(Me2[14]tetraenatoN4)(CGH5)]I brown 2.85 95

[Ci'(Me2[i4]tetraenatoN4)(CGH5)]SCN green 3.29 75 c Determined by the Faraday method at room temperature. Determined using 10-3 M CH3N02 solutions at room temperature.

Table 24 a Electronic Spectral Data for the Chromium(IV) Complexes.

Complex Solvent ^ max.....—

[Cr(Me2[ l4]tetraenatoN4)(C6H5)]I CH3N02 10.0(sh, 430), 12.8(4000), 14.7(5400), 16.7(sh, 3500), 20.0(sh, 1200), 23.8(sh, 3200) Mull 10.0(sh), 12.5, 15.1, I7.2(sh), 22.7(sh), 25.0(sh) [Cr(Me2 [i4]tetraenatoN4) (C6H5) ]- SCN CH3N 02 l0.4(sh,400), 13.0(2800), 14.8(4000), 16. 7(sh, 3000), 22.2(sh, 3280), 23.5 (sh, 4280) Mull 7.7, 13.2, 16.1, 20.8(sh), 26.3(sh) aUnits are kK. 109

therefore, no assignments were attempted,, The spectrum of [Cr(Me2ll4]tetrae- natoN4)(CGH5)]I in solution is essentially the same as in the solid-state. This indicates that there is little interaction with the iodide or with the solvent and confirms five-coordination for this complex. Differences are apparent in the solution and mull spectra of the thiocyanate derivative demonstrating that the thiocyanate does interact with the complex in the solid-state. The tetrapositive oxidation state of the chromium ion in these complexes is established by ESR, magnetic, and electrochemical measurements. The frozen solution ESR spectrum of [Cr(Me2[l4]tetraenatoN4)(C6H5)]I (Figure 22) is sim ilar to the reported spectra of other chromium(IV) compounds.77’80’81 The magnetic moments for these complexes (Table 23) indicate the presence of two unpaired electrons. The magnetic moment of the iodide complex agrees well with the spin-only value for a d2 system while the higher value of the thio cyanate derivative probably reflects its impure state. The polarogram of [Cr(Me2[l4]tetraenatoN4)(C6H5)JI has three irreversible oxidations at 0.66 v, and -0.15 v , a reversible reduction at -0.55 v (AEp= 60 mv), and an irreversible reduction at -2.41 v all vs the Ag/AgNQj reference electrode in acetonitrile. The oxidation processes at -0.15 v and 0.23 v are due to iodide and the oxidation at 0.66 v corresponds to potentials previously observed for the ligand oxidation. The reversible reduction at -0.55 v indicates that the chromium(in) ion of the starting complex has indeed been oxidized to chromium(IV) as the starting complex has a reversible oxidation at -0.60 v. These chromium(IV) complexes with the dianionic tetraaza macrocyclic ligands are the first fully obnracterized chromium(IV) complexes having a chelating ligand. Wilkinson and coworkers77 reported the complex bis(i,3- dimethylezietetramethyldisiloxane)chromium(IV) but it was only partially characterized by its ESR and electronic spectra. The special features of this dianionic tetraaza macrocycle allow the existence of these chromium(IV) complexes. The encompassing nature of the macrocycle and its associated g=2.0036

H (kG)

Figure 22. ESR Spectrum of [Cr(Me2[14]tetraenatoN4)(C6H5)]l.

o i l l

kinetic inertness protect the metal ion by effectively blocking coordination sites. The anionic character of the ligand enables it to stabilize high metal oxidation states by donation of electron density. The cyclic planar nature of this macrocyclic ligand also accounts for the unique stereochemistry of these chromium(IV) complexes. Since the ring cannot fold to assume even a pseudo-tetrahedral configuration, the five-coordinate structure results. 112

Syntheses and Characterization of the Complexes, Cr(Me?[l4]tetraenatoNJ(.NO) and [Cr(MeR[l4j4, ll-dieneN,)(NO)(NQ>)]PFR.

Preparation of Cr(Me9[l4]tetraenatoN/1)(NO) and [Cr(MeR[l4]4,11-dieneN^)- (NQ)(N09)]PFRo -- The complexes Cr(Me2[l4]tetraenatoN4)(NO) and [Cr(Mee[i4]- 4, ii-dieneN4)(N0)(N02)]PF6 were prepared in essentially the same manner (equations 29 and 30) „ A large excess of sodium nitrite was added to alcoholic

Me 01 [Cr(Me2[i4]tetraenatoN4)(py)2]PF6 + xsNaN02 (29)

XXXIV n q I +

[Cr(Me6[i4]4, il-dieneN4)(py)](PF6)2 + xsNaNt^

solutions of [Cr(Me2[l4]tetraenatoN4)(py)2]PF6 or [Cr(MeG[l4]4, il-dieneN4)(py)]- (PFg)2. Since neither the starting complexes nor the sodium nitrite are very soluble in the alcoholic media, the solutions were refluxed for a period of time. The neutral complex, XXXIV, was extracted with benzene from the residue which remained after the reaction solution was taken to dryness. The cationic complex, XXXV, was isolated as a hexafluorophosphate salt by reducing the volume of the reaction solution. After the recrystallization of the neutral complex from benzene and the cationic complex from acetonitrile-ethanol, satisfactory elemental analyses (Table 25) were obtained for both complexes. The same reaction procedure was used with [Cr(Me2[l5]tetraenatoN4)(py)2]PF6 but only starting complex was obtained. It is interesting to note that the neutral complex was prepared from a chromium(III) complex while the cationic complex was prepared from a chromium- (H) complex. Wayland et al.68 reported the preparation of CrTPP(NO) from both 113

Cr^TPP and Cr^TPP(OMe). The preparation of a chromium(l) nitrosyl species from a chromium(Il) complex can be viewed as simply the transfer of the NO n* electron to the metal. Using a chromium(III) complex, however, requires another type of mechanism which at this time is not understood.

Characterization of Cr(Me?[l4]tetraenatoN,i) (NO) and [Cr(MeR[l4]4,11-diene- N,i) (NQ)(NQ9) ]PF,;0 — The two chromium(I) nitrosyl complexes are assigned the structures XXXIV and XXXV. The infrared spectra of these complexes (Figures 23 and 24) indicate the presence of the nitrosyl groups, the macrocycles, and hexafluorophosphate for the cationic complex. The nitrosyl absorptions for the neutral, XXXIV, and cationic, XXXV, complexes are 1620 cm-1 and 1640 cm-1, respectively, which are indicative of NO „108 The conductivity data in Table 26 demonstrates the neutrality of Cr(Me2[l4]tetraenatoN4)(NO) and the ionic nature of [Cr(MeG[l4]4, ll-dieneN4)(N0)(N02)]PF6.93 Since Cr(Me2[l4j- tetraenatoN4) (NO) is a neutral complex, its mass spectrum was obtained giving a parent ion at m/e = 300 which is the same as the calculated molecular weight of the complex. The ESR spectra and magnetic moments of these complexes confirmed the monopositive oxidation state of the chromium ion. The magnetic moments of these chromium(I) nitrosyl complexes in the solid state (Table 26) indicate the presence of one unpaired electron; therefore, the d5 chromium(l) ion must be low- spiiio The frozen solution ESR spectra of both complexes (Figures 25 and 26) show axial symmetry with gj_> gjj while the room temperature solution spectrum of both complexes have only one signal that averages gj^and gjj. No 53Cr hyperfine or 14N superhyperfine splitting is observed at either room or liquid nitrogen temperatures. The low-temperature ESR spectra of these complexes are in complete agreement with the low-temperature spectra reported for other clrro- mium(I) nitrosyl complexes59*61>62>68 but usually hyperfine or superhyperfine splitting was observed in the room temperature solution spectra for the other com plexes. 1600 1400 1200 1000 800 600 400 Frequency (cm”1)

Figure 23. Infrared Spectrum of Cr(Me2[l4]tetraenatoN4)NO. J. I i i 1 —I__ 3000 1600 1400 1200 1000 800 600 Frequency (cm-1)

Figure 24. Infrared Spectrum of [Cr(Me6[l4]4, 11 -dieneN4)(NO)(NC>2)]PF6.

cn 116

Table 25 Analytical Data for the Chromium(l) Nitrosyl Complexes. C alc. % Found 4> C omplex C HNC H N

Cr(Me2 [l4]tetraenatoN4)(NO) 47.99 6.04 23.32 47.74 6.01 23.38 [Cr(MeG[l4]4, ii-dieneN4)(NO)- (NG>)]PFe 34.75 5.83 15.19 34.94 5.87 15.28

Table 26 Physical Properties of Chromium(I) Nitrosyl Complexes. Com plex Color (B.M.)a A(cm2ohm-1 Cr(M e2[l4]tetraenatoN 4)(NO) green 1.81 <1

[Cr(Me6[i4]4, li-dieneN4)- (N0)(N02)]PF6 green 1.72 87

3- b ' Determined by the Faraday method at room temperature. Determined using 10-’ M CH3N02 solutions at room temperature.

Table 27 0. Electronic Spectral Data for the Chromium(I) Nitrosyl Complexes. C omplex ^ m ax’ ^ C r (Me2 [ 14 ] tetraenatoN 4) (N O)'0 15.3(1330), 22.2(sh,2l00), 26.0(7100) 32.6(16,000) [Cr(MeG[l4j4, ll-dieneN4)- (N0)(N02)]PFGc 15.4(45), 22.2(99), 27.7(340) aUnits are kK. ^THF solvent. CCH3CN solvent. i 17

g =

Figure 25. ESR Spectrum of Cr(Me2[14]tetraenatoN4)NO. £ rcr(Me,,[14]4, H-dieneN4)(N0)(N02)]PFt. F igure 26. ESR Spectrum o£ [Cr(M e6l 119

A schematic MO diagram for these chromium(I) nitrosyl complexes with macrocyclic ligands appears in Figure 27 which focuses on the metal d and nitric oxide n' levels that are the principal valence orbitals.68’109 The Cr*(NO ) units are expected to be linear in order to maximize d r r -T T * bonding which is consistent with the axially observed g tensors for these complexes, hi analogy to the complex CrTPP(NO) the odd electron for these macrocyclic ligand complexes is placed in the d ^ molecular orbital since gj^> gjj. The electronic spectral data for the chromium(I) nitrosyl complexes are presented in Table 27. If band intensities are not taken into account, the similarity of these spectra is striking considering that the two complexes have different coordination numbers and very different macrocyclic ligands. This seems to indicate the molecular orbital scheme in Figure 27 is applicable to both complexes and that the nitrosyl ligand does dominate the electronic configurations of chromium(I) nitrosyl complexes. The first three bands observed for these complexes may be assigned to the 2B2g-»2Ai, the 2B2 -» 2 B j, and the 2B2 -> 2E transitions, respectively. Dr. Dennis Wester solved the crystal structure of [Cr(Me6[l4]4, ii-dieneN4)- (N0)(N02)]PF6 which unequivocally proves the previously assigned structure. The ortep diagram of this complex is presented in Figure 28 showing that the complex is six-coordinate with axial nitrosyl and nitro ligands. The N3-Cr-N4 bond angle is 180° and this bond axis also constitutes a C2 axis for the complex which makes one-half of the macrocycle equivalent to the other. The chromium atom is displaced out of the plane of the macrocycle toward the nitrosyl ligand. A diagram of the complex in Figure 29 presents pertinent bond distances. The chromium-nitrosyl nitrogen bond distance of i.679 A is very short for a Cr-N bond but it is not unusual for metal-nitrosyl complexes.109 The Cr-N, C-C, and C-N bonds have normal lengths and the imine function is readily distinguishable having a C-N distance of 1.272 A compared to the C-N distance of 1. 500 A for the am ine. 120 (NO tT + dxz.dyz) 3E— ±2\ / / \ \ Bj (dx2- y 2)- \ “ T Bl \ (NO n )E / - + I (d z2 + NO d) j / 3A, / A 1 (d z2) — }- / / E (dxz, dyz)— A / \ B2 (dxy) “ — b 2 / \ / \ \ '+/ *. (dx^, dyz+NOdyz+h TT )

-H— (NO a)Aj

1 E q p Z ± T ------"Tpfr- (NOrr)E

Cr(ll)L Cr(l) L(NO) NO

Figure 27« Schematic Molecular Orbital Diagram for the Chromium(l) Nitrosyl Complexes,, 121

c *

Figure 28„ Ortep Drawing of [Cr(Me6[14]4, 1 l-dieneN4)(N0)(N02)]PF6. 492

Figure 29. X-Ray Crystallographic Bond Distances for [Cr(Me6[14]4, 11 -dieneN4)(N0)(N02)]PF6. 123

Syntheses and Characterization of Chromium(II) and Chromium(III) Complexes with Mefi[l4]4, ll-dieneN^.

Preparation of the Chromium(Ip and Chromium(IH) Complexes. — The chromium(II) complexes with MeG[14]4, il~dieneN4, I, were prepared first and then oxidized to yield the chrOmium(IU) complexes. Sperati10 initially prepared cationic chloride, bromide, and thiocyanate chromium(II) and chromium(II]) complexes with Me6[l4]4, ii-dieneN4 and isolated them as perchlorate salts. Since perchlorates are hazardous materials, these complexes were again prepared in the present work as their hexafluorophosphate salts and pyridine and iodide derivatives were also prepared. Instead of using the perchlorate salt of the ligand in the syntheses of the complexes, the trifluoromethylsulfonate salt was employed since complexes with this anion can be easily metathesized to the corresponding hexafluorophosphate s. The halide complexes were prepared using CrCl2 ° 2py, CrBr2 - 6py, and Crl^ • 6py as the metal sources. The thiocyanate complex was prepared from the chloride derivative by metathesis and the pyri dine complex resulted from employing Cr(CF3S03)2 • 4py as the metal source. The preparation of a cyanide derivative was also attempted and resulted in an extremely air-sensitive green material which was not characterized. The chromium(ll) chloride and bromide derivatives were oxidized on the benchtop with Cl2 and Br2, respectively, to give [Cr(Mee[i4]4, ii-dieneN4)Cl2]PFG and [Cr(Me6[i4]4, ll-dieneN4)Br2]PFG. The dicyanide and dithiocyanate complexes' were prepared by metathesis from [Cr(Mee[l4]4, ll-dieneN4)Cl2]PFG. The pre paration of the cliiodo complex of chromium(III) was attempted but these attempts failed to give a characterizable complex. 124

Characterization of the ChrQmium(II) and Chromium(III) Complexes. — The air-sensitive chromium(II) complexes with Me6[l4]4, ll-dieneN4 are five-coordi nate and high-spin as were those prepared by Sperati.10 Satisfactory elemental analyses (Table 28) for these complexes indicate that their formulations are correct. The infrared spectra of these complexes show the presence of the macrocycle, the hexafluorophosphate anion, and pyridine or thiocyanate for those particular derivatives. The N-H and C=N absorptions for these complexes are summarized in Table 29. The N-H stretching frequencies for these comp lexes occur about 100 cm-1 higher in energy than the corresponding perchlorate derivatives and the C=N absorptions are about 20 cm-1 higher in energy. The hexafluorophosphate derivatives are also much more air-sensitive in the solid- state than are the perchlorate complexes. Since these complexes are extremely air-sensitive, their solution moments (Table 29) were measured by the Evans method and solid-state measurements were not attempted. These magnetic moments are somewhat below those expected for high-spin d4 configurations which may be due to experimental error or slight metal-metal interaction between species in solution. The conductivity data (Table 29) is consistent with the assigned five coordination of these complexes demonstrating that they are 1:1 electrolytes.93 Electrochemical data for these chromium(II) complexes with the diene macrocyclic ligand'and for several chromium(II) complexes with MeG[i4]aneN4, II, prepared previously by Sperati10 are presented in Table 30. The very cathodic metal oxidation potentials displayed by these complexes are responsible for their extreme air-sensitivity. The electronic spectral data for these complexes are given in Table 31. Sperati observed two d-d bands and one charge transfer band for the perchlo rate complexes but only one d-d band and one charge transfer band were detected in the electronic spectra of the hexafluorophosphate complexes. Curve analysis of these spectra may possibly resolve another d-d band at lower energy. Following Sperati1 s reasoning, this d-d band which occurs at about 20 kK in these complexes is assigned to the 5B4g-* 5B2g transition. Table 28 Analytical Data for the Chromium(II) Complexes with Me6[l4]4, ll-dieneN4. Calc. Found € Complex _C_ _N _C_ H_ _N_

[Cr(Mee[l4]4, ii-dieneN4) I]PF6 31.79 5.34 9.27 31.41 5.48 9.21

[Cr(Me6[i4]4, il-dieneN4)Br]PF6 34.48 5.79 10.05 34.09 5.71 10.05

[Cr(Mee[14]4, ll-dieneN4)Cl]PF6 37.47 6.29 1Q092 37.12 6.16 10.74 'rH 00 [Cr(Mee[l4]4, il-dieneN4)SCN]PF6 38.13 6.02 CO o 38.61 6.37 13.35

[C r (Me6 [ 14 ]4,11 -diene N4) py ](P F 6) 2 35.96 5.32 9.98 35.87 5.61 9.61

to Ol Table 29 Physical Properties of the Chromium(II) Complexes with Me6[l4]4, li-dieneN4.

Ajvf(cm2ohm-1m ol ^ Complex Color Meff (B .M .)a vC=N(c-m'^ VN-H^cm

[Cr(Me6[l4]4, ll-dieneN4)I]PF6 brown 4.68 185 1660 3250

[Cr(Me6[l4]4, il-dieneN4)Br]PF6 brown 4.50 181 1663 3255

[Cr(Mee[l4]4, ll-dieneN4)Cl]PF6 brown 4.64 172 1660 3250

[Cr(Me6[l4]4, ii-dieneN4)SCN]PF6 tan 4.58 167 1648 3270

[C r (Me6 [ 14 ]4,11 -diene N4) py ] (P F 6) 2 tan 4.70 317 1658 3265

determ ined by the Evans method in acetone solution. Determined using 10 3 M acetonitrile solutions at room tempera tu re.

to Ci Table 30 a Electrochemical Data for the Chromium(II) Complexes.

Complex Oxidations Reductions

[Cr(Me@[l4]4, ll-dieneN^pyKPFg^ -0.30 ir r -2.36 i r r

[Cr(Me6[l4]4, ll-dieneN4)NCS]PF6 -0.20 irr, 1.37 irr -2 .3 5 ir r

[Cr(Me6[l4]4, ll-dieneN4)Cl]PF6 -0.80 irr, 0.36 irr -2 .3 2 ir r

[Cr(Me6[l4]4, li-dieneN4)Br]PF6 -0.75 irr, 1.01 irr -2 .3 5 ir r

[Cr(Mes[l4]4, U-dieneN4)I]PF6 -0. 59 irr, 0.77 irr -2 .3 3 ir r

Cr(Me6[l4]aneN4) (NCS)2 -0.77 irr, 0.38 irr, 1.83 irr -2 .3 7 i r r

Cr(Mes[i4]aneN4)(CH3CN)2 -0.86 irr, 0.82 irr -1 .4 2 i r r

Cr(M e6[l4]aneN4)Cl2 -1.37 rev, -0.76 irr, 0.75 irr -2 .7 6 i r r

Cr(Me6[i5]aneN4)Br2 -1.45 irr, -0.98 irr, -0.70 irr 0.33 i r r , 0. 61 ir r -2 .4 6 i r r

^Volts vs Ag/AgN03 (0.1 M) reference electrode in acetonitrile. Table 31 cl Electronic Spectral Data for the Chromium(II) Complexes with Me6[l4]4, ll-dieneN4.

Complex Solvent ^m ax’ ^

[Cr(Me6[i4]4, ll-dieneN4)(py)2](PF6)2 CH3CN 21.6 (sh, 65), 30.7 (1960)

[Cr(Mee[l4]4, ll-dieneN4)NCS]PF6 CHgCN 20.0 (sh, 70), 29.6 (2200)

[Cr(Mee[i4]4, ll-dieneN4)Cl]PF6 CH3CN 19.5 (sh, 60), 28.6 (1900)

[Cr(Mee[l4]4, H -dieneN 4)B rjP F 6 CHgCN 19.0 (sh, 63), 28.6 (1600)

[Cr(Me6[l4]4, ll-dieneN4)I]PF6 CHgCN 20.0 (sh, 95), 28.6 (1950)

a Units are kK.

to 00 129

The cationic chromium(II]) complexes with Me6[i4]4, ll-dieneN4 and the hexafluorophosphate anion are very unreactive and air-stable species. They are trans six-coordinate complexes having magnetic moments (Table 32) that are consistent with a high-spin d3 electron configuration. The conductivity data presented in Table 32 demonstrates that they are six-coordinate complexes in solution as the values correspond to those reported for 1:1 electrolytes.93 In addition, the analytical data (Table 33) for these complexes show good agree ment with the assigned formulations. The N-H and C=N infrared absorptions for the macrocycle in these complexes are summarized in Table 32. Infrared bands for the cyanide and thiocyanate ligands are observed in the spectra of those derivatives and hexafluorophosphate bands appear in the spectra for all the complexes. The electronic spectral data for the chromium(III) complexes appear in Table 34. The dihalo complexes have a typical chromiura(HI) spectrum with three absorptions. The cyanide and thio cyanate complexes, however, show only two bands and one band, respectively. The other bands at higher energy are probably obscured by the charge transfer region. Using the same band assignments as Sperati,10 the three bands observed for the dihalo complexes are assigned successively to the 4Blg -* 4Eg, the

4B4g - 4B 2g, and the 4Blg 4A2g transitions (see Figure 9). Table 32 Physical Properties of the Complexes, [Cr(Mee[l4]4,1 l-dieneN1)X2]PF6o x_ Color ueff (B. M.)a A m (cm2°hm“im°l“1)b VC=N VN-H (crn~^

CN yellow 3.88 145 1650 3170

SCN yellow 3.87 149 1650 3190

Cl purple 3.74 148 1649 3234

B r pink 3,96 175 1660 3240

aDetermined by the Faraday method at room temperature. Determined using 10 3M CH3CN solutions at room tempera tu re. Table 33 Analytical Data for the Complexes, [Cr(Me6[i4]4, ii-dLeneN4)X2]PFg.

Calc. Found 4 x_ C_ H N CHN

CN 40.83 6.09 15.96 40.76 6.22 15.85

SCN 36.42 5.43 14.16 36.43 5.35 14.13

Cl 35.05 5.88 10.22 35.28 6.07 10.05

B r 30.16 5.06 8.79 30.43 5.34 9.02

CO Table 34 Electronic Spectral Data for the Complexes, [Cr(Mee[14]4, H-dieneN^XojPFg.a

X Solvent ^m ax1

CN CH3CN 19. 8(sh, 6), 24.5(58)

SCN CH3CN 2 0 .5 (91)

Cl CH3CN 17.5(26), 23.9(sh, 22), 27.1(52)

B r CH3CN 18.4(32), 23.5(sh, 19), 26.7(44) aUnits are kK.

DOCO 133

APPENDIX

Dry Train Description

When manipulations involving air-sensitive materials are carried out inside a glove box, it is necessary to maintain an inert atmosphere that is free from moisture and oxygen. The most effective way to accomplish this task is through the use of an attached dry train that continuously removes oxygen, moisture, and solvents from the glove box atmosphere. Vacuum Atmospheres of California can provide such a unit that is almost completely automatic but the cost of this commercial unit is prohibitive. Therefore, a unit costing approximately one- fourth as much as the commercial one was designed and built to provide the desired inert atmosphere purification. The dry train in conjunction with the dry box is a completely enclosed system with the glove box atmosphere being continuously recirculated through the purification system. The dry train (Figure 30) consists of a blower for circulating the atmosphere and a furnace containing oxygen removal catalyst and molecular sieves for purifying the glove box atmosphere. The box, blower, and furnace are joined by an assembly of 1 inch copper tubing and ball valves. Valves one, two, and three are 1 inch Lunkenheimer ball valves which allow either part of or the entire dry train to be isolated from the glove box. The M.D. light duty blower is belt driven and powered by a i/2 h.p. electric motor. To reduce vibration, the blower and motor assembly is mounted on a platform which is separated from the one that houses tire rest of the dry train. Also, the copper tubing is connected to the blower using bellows. The furnace (Figure 31) is a brass drum containing 10 lbs. of Ridox oxygen removal catalyst sandwiched between layers of Linde 13X molecular sieves (12 lbs. total). To heat the furnace, current is passed through a nichrome wire 134

that is wrapped around the brass drum. A Temcometer (Thermolyne Corp.) supplies current to the heater and also monitors the temperature of the furnace via a thermocouple. The drum is wrapped with several layers of asbestos and mounted in a box filled with vermiculite in order to minimize heat loss. Following the furnace is a water jacket which helps cool the circulating atmosphere of the d ry box. An assembly of 1/2 inch copper tubing, 1/2 inch Lunkenheimer ball valves, and A sco solenoid valves is used to supply nitrogen and vacuum to the dry box during normal operation and regeneration gas and vacuum for regeneration of the sieves and Ridox. The pressure of the box atmosphere is controlled either manually by footswitches or automatically by a photohelic switch which activates the nitrogen or vacuum solenoid valves. The switches are connected to the solenoid valves through a three-way switch that allows either the footswitches or the photohelic to activate the solenoids. The wiring diagram for these controls is shown in Figure 32. The sieves and oxygen removal catalyst should be regenerated at least once a month to insure a good glove box atmosphere. After the blower is turned off, valves 2, 3, 5, and 6 are closed and the furnace is heated to 200-225°C which requires about five hours. When the required furnace temperature is attained, valves 5 and 6 are opened, solenoids 3 and 4 are activated, and a mixture of 95$ N2 and 5$ H2 is passed through the furnace and vented into a fume hood. A total of sixty cubic feet of the gas mixture is passed through the furnace during one hour. Then solenoids 3 and 4 are deactivated and valve 5 is closed. A vacuum is connected to solenoid 4 and it is activated for two hours to remove any remaining water or solvent. Finally, solenoid 4 is deactivated, valve 6 is closed, valves 2, 3, and 5 are opened, and the blower is restarted. Out .In

K VI X V2 B ello \ rs n 2 -®c SI EC V4 VaCo<-“ S2

Nz/HzC S3 E le c tr ic V6 M o to r B lo w er V ent &=■ O^4- ^ r □EE

W a te r V5 J a c k e t

Bellow ;

F u rn a c e M. V3

Figure 3 0. Diagram of the Dry Train. 136

Thermocouple Well

Ridoc£ 10 lbs

.ec xe

Figure 31. Diagram of the Furnace. Photohelic Switch

Three -Way Switch

N2 V a c . Footswitch Footswitch

32. Wiring Diagrain for the Switches. 138

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