Re(CO)3 TEMPLATE FORMATION OF DIIMINOISOINDOLINE BASED CHELATES
A Dissertation Presented to The Graduate Faculty at The University of Akron
In Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy
Allen Jordan Osinski May 2018
Re(CO)3 TEMPLATE FORMATION OF DIIMINOISOINDOLINE BASED CHELATES
Allen Jordan Osinski
Dissertation
Approved: Accepted:
______Advisor Department Chair Dr. Christopher J. Ziegler Dr. Christopher J. Ziegler
______Committee Member Dean of the College Dr. Claire A. Tessier Dr. John C. Green
______Committee Member Dean of the Graduate School Dr. Wiley J. Youngs Dr. Chand K. Midha
______Committee Member Date Dr. Yi Pang ______Committee Member Dr. Chrys Wesdemiotis
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ABSTRACT
Over the last century, in the field of coordination chemistry, the number of template reactions has expanded into a diverse collection which can produce a variety of compounds. These template reactions have been used to afford compounds that would be difficult to obtain otherwise. One of the most famous template reactions is the synthesis of phthalocyanine, which was investigated by Linstead. After exploring the chemistry of phthalocyanine, Linstead synthesized hemiporphyrazines and bis(2- iminopyridyl)isoindolines from 1,3-diiminoisoindoline and various primary amines. Later, Siegl improved the synthesis of the hemiporphyrazines and the bis(2- iminopyridyl)isoindolines by employing a calcium ion as a templating agent. The template formation of isoindoline based macrocyclic compounds has been explored, however, the template formation of isoindoline based chelates is relatively unexplored. Due to its restrictive facial arrangement of carbonyl ligands and propensity to coordinate nitrogenous bases, the Re(CO)3-unit is a prime candidate for templating the formation of isoindoline based chelates.
The second and third chapters in this thesis present the template synthesis of semihemiporphyrazines, “half” hemiporphyrazine like chelates, and α-amidino azadi(benzopyrro)methenes using the Re(CO)3-unit as a templating agent in a one-step reaction. In both cases, the complexes have terminal amine groups and do not experience hydrolysis as seen with the Re(CO)3-templated azadi(benzopyrro)methenes. Additionally, in the α-amidino azadi(benzopyrro)methene case, a rhenium bound nitrile is activated by a diiminoisoindoline unit to afford a rhenium bound amidine and one diiminoisoindoline sp2 carbon is converted to a sp3 carbon by attack of another diiminoisoindoline unit disrupting conjugation. The spectroscopy of the semihemiporphyrazines was investigated along with DFT and TDDFT calculations. Whereas, the conjugation in the α-amidino azadi(benzopyrro)methenes is disrupted resulting in yellow crystalline products that lack
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a metal-to-ligand charge transfer band. In the third chapter, 2,6-diacetylpyridine dihydrazone is coordinated to middle and late first row transition metals and their magnetic susceptibilities are explored via Evans NMR method. In the fourth chapter, neutral and deprotonated anionic complexes of the tetrakis(perfluorophenyl)-N-confused porphyrin are prepared and investigated by UV-visible and magnetic circular dichroism spectroscopies as well as by DFT and TTDFT calculation methods.
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ACKNOWLEDGEMENTS
First of all, I would like to say thank you to my advisor Christopher J. Ziegler. Your support and leadership was an integral part of my journey through graduate school.
Additionally, I would like to say thank you to my current and previous colleagues in lab. “Lab Mom” Ingrid took me in the first years of graduate school. I can’t say thank you enough to Kullapa and Ingrid for their patience and guidance during the first few years. Laura, Abed, Dan, and Briana- your friendship and support is greatly appreciated.
Thank you to the members of my committee: Dr. Claire Tessier, Dr. Wiley Youngs, Dr. Yi Pang and Dr. Chrys Wesdemiotis. I am appreciative of your support and time spent serving on my committee. I would also like to thank the University of Akron and the department of Chemistry for accepting me into the program and financially supporting me during my Ph.D. career.
Lastly, I would like to thank my family for putting up with me during the stressful times of graduate school and giving me the confidence to stay in school. Without their love and support, none of this would be possible.
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TABLE OF CONTENTS
LIST OF TABLES...... viii
LIST OF FIGURES...... ix
LIST OF SCHEMES...... xvii
LIST OF ABBREVIATIONS...... xix
CHAPTER
I. INTRODUCTION AND BACKGROUND...... 1
1.1 Template Reactions...... 1
Phthalocyanine...... 6
Hemiporphyrazine...... 15
Bis(2-iminopyridyl)isoindoline...... 32
“Helmet” and Bicyclic Phthalocyanines...... 46
1.2 Amidine Formation and Metal Mediated Nitrile and Activation...... 51
Re(CO)3 diimine complexes...... 55
II. Re(CO)3-TEMPLATED SYNTHESIS OF SEMIHEMIPORPHYRAZINES...... 62 Introduction...... 62 Experimental...... 64
Results and Discussion...... 69
Conclusions...... 79
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III. Re(CO)3-TEMPLATED SYNTHEIS OF α-AMIDINOAZADI(BENZOPYRRO)METHENES...... 80 Introduction...... 80
Experimental...... 82
Results and Discussion...... 91
Conclusion...... 106
IV. COMPLEXES OF 2,6-DIACETYLPYRIDINE DIHYDRAZONE WITH MIDDLE AND LATE FIRST ROW TRANSITION METALS...... 107
Introduction...... 107
Experimental...... 109
Results and Discussion...... 122 Conclusion...... 127
V. MAGNETIC CIRCULAR DICHROISM OF TRANSITION-METAL COMPLEXES OF PERFLUOROPHENYL-N-CONFUSED PORPHYRINS: INVERTING ELECTRONIC STRUCTURE THROUGH A PROTON...... 128
Introduction...... 128
Experimental...... 132
Results and Discussion...... 133 Conclusions...... 151
VI. SUMMARY...... 152
REFERENCES...... 155
APPENDIX: PERMISSIONS ...... 183
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LIST OF TABLES
2.1: X-ray crystal data and structure parameters for compounds 2.1-2.3...... 68
2.2: X-ray crystal data and structure parameters for compounds 2.4 and 2.6...... 69
3.1: X-ray crystal data and structure parameters for compounds 3.1-3.3...... 89
3.2: X-ray crystal data and structure parameters for compounds 3.5-3.7...... 90
3.3: X-ray crystal data and structure parameters for compounds 3.8-3.10...... 91
4.1: X-ray crystal data and structure parameters for compounds 4.1-4.3...... 117
4.2: X-ray crystal data and structure parameters for compounds 4.4-4.6...... 118
4.3: X-ray crystal data and structure parameters for compounds 4.7-4.8...... 119
4.4: Evans NMR method data and parameters for 4.2-4.5...... 121
4.5: Evans NMR method data and parameters for 4.6-4.8...... 122
4.6: Selected bond lengths and angles for 4.2–4.8 and related DAPH compounds...... 126
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LIST OF FIGURES
1.1.1: Molecular structures of porphyrin and phthalocyanine...... 7
1.1.2: α- and β-benzo positions on the Pc skeleton...... 10
1.1.3: C4h, D2h, C2v, and Cs isomers of a cyclotetramerization from a single precursor with one substitution on the periphery...... 11
1.1.4: Alternative Hps using diaryl diamines other than 2,6-diaminopyridine...... 16
1.1.5: Peripheral substitution of Hps...... 17
1.1.6: Incorporation of naphthalene and anthracene rings into Hps...... 18
1.1.7: An example of a water soluble Hp...... 19
1.1.8: Structure of NiHp with a top view (left) and a side view (right). Hydrogen atoms have been omitted for clarity. Redrawn from CSD data code NIPHCA11...... 19
1.1.9: Structures of NiHp(py)2 (left) and Li(HHp)(py) (right). Hydrogen atoms and solvent molecules have been omitted for clarity. Redrawn from CSD data code CIFDAW and CCDC number 729564...... 20
1.1.10: Structures of Fe(Hp)OFe(Hp)H2O (left) and [Fe(butyloxy)2Hp]2O (right). Hydrogen atoms and solvent molecules have been removed for clarity. Redrawn from CSD data codes DIMWEB10 and XECHAP...... 21
1.1.11: Structures of cobalt (top left), nickel (top right), lithium (bottom left), and zinc (bottom right) bzpc. Hydrogen atoms except ionizable protons and internal hydrogens, and solvent molecules have been omitted for clarity. Redrawn from CCDC numbers 641690, 726132, 729564, and 750085...... 23
1.1.12: Structures of silver (left), cobalt (middle), and zinc (right) dchp. Hydrogen atoms except ionizable protons and internal hydrogens and solvent molecules have been omitted for clarity. Redrawn from CCDC numbers 603062, 661972, and 750084...... 24
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1.1.13: Structures of copper (left), nickel (middle), and nickel ring oxidation (right) dchp. Hydrogen atoms except ionizable protons and internal hydrogens, and solvent molecules have been omitted for clarity. Redrawn from CCDC numbers 603063, 726130, and 726131...... 25
1.1.14: Structures of resorcinol bzpc (left) and phenol dchp (right). Hydrogen atoms except for ionizable protons and internal protons, and solvent molecules have been omitted for clarity. Redrawn from CCDC numbers 762392 and 747403...... 26
1.1.15: Structures of anti-phenol dchp (left), syn-phenol dchp (middle), and resorcinol dchp (right)...... 27
1.1.16: Structures of nonaromatic resorcinol dchp (top) and aromatic resorcinol dchp (bottom). Hydrogen atoms except ionizable and internal protons, solvent molecules, and peripheral aryl ether groups have been omitted for clarity. Redrawn from CCDC numbers 848549 and 848550...... 28
1.1.17: Structures of aromatic bzpc (top) and O-dimethylated bzpc (bottom). Hydrogens atoms except ionizable and internal protons, solvent molecules, and peripheral aryl ether groups have been omitted for clarity. Redrawn from CCDC numbers 975640 and 975641...... 29
1.1.18: Structure cyclohexylcyanine (right). Hydrogen atoms except for ionizable protons and solvent molecules have been omitted for clarity. Redrawn from CCDC number 790317...... 30
1.1.19: Triazolehemiporphyrazine (left) and triazolephthalocyanine (right)...... 31
1.1.20: Structures of triazinehemiporphyrazine (left), azaphenalene Pc (middle), and azepiphthalocyanine (right). Hydrogen atoms, peripheral groups, and solvent molecules have been omitted for clarity. Redrawn from CCDC numbers 767425 and 79148...... 32
1.1.21: Structure of BPI. Redrawn from CCDC number 218623...... 33
1.1.22: Structures of [Cu(BPI)]2CO3 (left) and the oxidized tetramer (right) Hydrogen atoms and solvent molecules have been omitted for clarity. Redrawn from CSD data codes MPICCU and HXCUIM...... 34
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2+ 1.1.23: Structures of Mn(3-MeBPI)2 (top left), Mo2(BPI)(OAc)2 (top right), trimeric Zn
BPI complex (bottom left), and Cd(BPI)2(NO3)2 (bottom right). Hydrogen atoms and solvent molecules have been omitted for clarity. Redrawn from CSD data codes CEMSAO and JEZCEW and CCDC numbers 613797 and 253849...... 36
1.1.24: 1,3-bis(2-thiazolylimino)isoindoline (BTI) (left) and bis(2-2’- benzimidazolylimino)isoindoline (bimimd) (right)...... 37
1.1.25: Structures of a Pd(BTI) complex with the abnormal N,N,S coordination mode (left) and Mn(bimimd)Cl2 (right). Hydrogen atoms have been omitted for clarity. Redrawn from CCDC numbers 677874 and 688573...... 38
1.1.26: Structures of phthalazine (left) and a bis copper complex of phthalazine (right). Hydrogen atoms have been omitted for clarity. Redrawn from CCDC numbers 187625 and 1129164...... 38
1.1.27: Structures of Co(BPI)(OBz)(OO-tert-Bu) (left) and Cu2+ catecholato BPI complex (right). Hydrogen atoms and solvent molecules have been omitted for clarity. Redrawn from CCDC numbers 1136466 and 151528...... 39
1.1.28: Structures of the Ir(COD)BPI complex (left) and the Ru2+ hydride BPI complex (right). Hydrogen atoms except the hydride proton have been omitted for clarity. Redrawn from CCDC numbers 847562 and 951887...... 40
1.1.29: Structures of the alkynylated Pd(BPI) complexes. Hydrogen atoms have been omitted for clarity. Redrawn from CCDC numbers 232254 and 232255...... 41
1.1.30: Structures of BPI ligands derived from myrtenal (top left), (–)-β-pinene (top right), (+)-2-carene (bottom left), and cyclopropyl methyl ether (bottom right)...... 43
1.1.31: Structures of pyridine adducts of Mn2+ (left) and Fe2+ (right) bis(oxazolinyl- methylidene)isoindoline complexes. Hydrogen atoms have omitted for clarity. Redrawn from CCDC numbers 1539151 and 1427737...... 43
1.1.32: Structures of a BPI Co2+ five coordinate acetato complex (left) and a BPI Ru2+ pyridine adduct (right). Hydrogen atoms and solvent molecules have been omitted for clarity. Redrawn from CCDC numbers 693092 and 802588...... 45
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1.1.33: Structures of Fe3+ “helmet” Pc (left and middle) and Ni2+ Pc with alkoxy substituents (right). Hydrogen atoms, solvent molecules, and 6th position ligands have been omitted for clarity. Redrawn from CCDC numbers 606957 and 174008...... 47
1.1.34: Structures of the proposed high-valent iron oxo species based on experimental data from a cryospray mass spectrometry study...... 48
1.1.35: Structure of the first bicyclic Pc. Hydrogen atoms have been omitted for clarity. Redrawn from CCDC number 1195852...... 49
1.1.36: Structures of In3+ (left), Gd3+ (middle), and Tl3+ (right) bicyclic Pcs. Hydrogen atoms have been omitted for clarity. Redrawn from CCDC numbers 1206913, 125805, and 1314592...... 49
1.1.37: Structure of Cd2+ bicyclic Pc. Hydrogen atoms except on the meso nitrogen position and solvent molecules have been omitted for clarity. Redrawn from CCDC number 953713...... 50
1.1.38: Three forms of the bicyclic Pcs...... 51
1.2.1: Structures of Co3+ (left), Ir3+ (middle), and Pt2+ (right) amidine complexes. Hydrogen atoms and solvent molecules have been omitted for clarity. Redrawn from CCDC numbers 1250298 and 1242676...... 52
1.2.2: Structures of heterocyclic amidines coordinated to Ru2+ (left), Re3+ (middle), and an osmium cluster (right). Hydrogen atoms and solvent molecules have been omitted for clarity. Redrawn from CCDC numbers 1191449, 1278672, and 1239533...... 53
1.2.3: Structures of rhenium bound amidines from a primary amine (left) and a cyclic secondary amine (right). Hydrogen atoms and solvent molecules have been omitted for clarity. Redrawn from CCDC numbers 1103269 and 902159...... 54
1.2.4: Structures of rhenium bound amidines from a triamine (left) and a pyrazole (right). Hydrogen atoms and solvent molecules have been omitted for clarity. Redrawn from CCDC numbers 830222 and 299803...... 55
1.2.5: Jablonski Diagram...... 57
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1.2.6: Structures of Re pyca complexes with an ester protected amino acid (left), a phenylene linked dimer (middle), and a hydrazine linked dimer (right). Hydrogens atoms have been omitted for clarity. Redrawn from CCDC numbers 246099, 979434, and 1414735...... 58
1.2.7: Structures of Re pyca complexes with an azobenzene moiety (left) and an aminophenol moiety (right). Hydrogen atoms have been omitted for clarity. Redrawn from CCDC numbers 1409716 and 929877...... 58
1.2.8: Structures of Re(CO)3-templated ADBMs terminated by bis(imino) (left), mixed imino/oxo (middle), and bis(oxo) (right) groups. Hydrogen atoms have been omitted for clarity. Redrawn from CCDC numbers 1042791, 1042792, and 1042793...... 60
1.2.9: Structures of various ADBMs coordinated to a BF2-unit. Hydrogen atoms and solvent molecules have been omitted for clarity. Redrawn from CCDC numbers 992707, 691385, and 1047636...... 61
1.2.10: Structures of a Re dipyrrinato complex (left) and a Re azadipyrromethene complex (right). Hydrogen atoms have been omitted for clarity. Redrawn from CCDC numbers 760502 and 768868...... 61
2.1: Semihemiporphyrazine and related compounds...... 63
2.2: X-ray structure of 2.1 (left) and 2.4 (right) with 35% thermal ellipsoids. Hydrogen atoms except on the terminal amines and solvent molecules have been omitted for clarity...... 71
2.3: X-ray structure of 2.2 (top), 2.3 (bottom left), and 2.6 (bottom right) with 35% thermal ellipsoids. Hydrogen atoms except on the terminal amines and solvent molecules have been omitted for clarity...... 71
1 2.4: H NMR spectrum (300 MHz) of 2.1 in d6 – DMSO. * represents residual THF,
DMSO, DCM, and H2O...... 73
1 2.5: H NMR spectrum (300 MHz) of 2.2 in d6 – DMSO. * represents residual THF,
DMSO, and H2O...... 74
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1 2.6: H NMR spectrum (300 MHz) of 2.3 in d6 – DMSO. * represents residual THF,
DMSO, and H2O...... 75
2.7: Experimental (top) and TDDFT-predicted (bottom) UV-visible spectra for compounds 2.1-2.3...... 76
2.8: Top: The DFT-predicted energies of the frontier orbitals of compounds 2.1-2.6. Bottom: The representative examples of frontier orbitals for 2.1-2.6...... 78
3 3.1: Re(CO)3 A DBM and related compounds...... 81
3.2: Elucidated X-ray structures of compounds 3.1 (left), 3.2 (middle), and 3.3 (right) with 35% thermal ellipsoids. Anions, solvent molecules, and hydrogen atoms except on nitrogen atom positions have been omitted for clarity...... 93
3.3: Elucidated X-ray structures of compounds 3.9 (left) and 3.5 (right) with 35% thermal ellipsoids. Anions, solvent molecules, and hydrogen atoms except on nitrogen atom positions have been omitted for clarity...... 93
1 3.4: H NMR spectrum (750 MHz) of 3.1 in d6 – DMSO. * represents residual DMSO,
DMF, H2O, and Et2O...... 95
1 3.5: H NMR spectrum (750 MHz) of 3.2 in d6 – DMSO. * represents residual DMSO,
DMF, H2O, Et2O, and DCM...... 96
1 3.6: H NMR spectrum (750 MHz) of 3.3 in d6 – DMSO. * represents residual DMSO,
DMF, H2O, and Et2O...... 97
1 3.7: H NMR spectrum (750 MHz) of 3.4 in d6 – DMSO. * represents residual DMSO,
DMF, and H2O...... 98
1 3.8: H NMR spectrum (750 MHz) of 3.5 in d6 – DMSO. * represents residual DMSO,
DMF, and H2O...... 99
13 3.9: C NMR spectrum (500 MHz) of 3.1 in d6 – DMSO. * represents residual DMSO...... 100
13 3.10 C NMR spectrum (500 MHz) of 3.2 in d6 – DMSO. * represents residual DMSO...... 101
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13 3.11: C NMR spectrum (500 MHz) of 3.3 in d6 – DMSO. * represents residual DMSO and DMF...... 102
13 3.12: C NMR spectrum (500 MHz) of 3.4 in d6 – DMSO. * represents residual DMSO...... 103
13 3.13: C NMR spectrum (500 MHz) of 3.5 in d6 – DMSO. * represents residual DMSO...... 104
4.1: The structure of 4.1 with 35% thermal ellipsoids...... 123
4.2: The structures of compounds 4.2–4.6 with 35% thermal ellipsoids. Hydrogen atoms and non-coordinating anions have been omitted for clarity...... 124
4.3: The structures of compounds 4.7 and 4.8 with 35% thermal ellipsoids. Hydrogen atoms and non-coordinating anions have been omitted for clarity...... 125
5.1: Structures of porphyrin, N-confused porphyrin (showing both inner and outer tautomers), and complexes 5.1 – 5.4...... 130
5.2: The UV-Vis and MCD spectra of 5.1 (top left), 5.2 (top right), 5.3 (bottom left), and 5.4 (bottom right) in dichloromethane...... 136
5.3: Transformation of 5.3 into 5.4 (top) with DDQ in dichloromethane...... 136
5.4: Transformation of 5.1 (top left) into 5.1-, 5.2 (top right) into 5.2-, and 5.3 (bottom) into 5.3- during titration with tetrabutylammonium hydroxide in dichloromethane...... 138
5.5: The UV-Vis and MCD spectra of 5.1- (top), 5.2- (bottom left), and 5.3- (bottom right) in dichloromethane...... 139
5.6: DFT-predicted (B3LYP) partial energy diagram NCPs 5.1 – 5.4 and 5.1- - 5.3-...... 141
5.7: DFT-predicted (TPSSh) molecular orbital energy diagram for 5.1 – 5.4 and 5.1- - 5.3...... 141
5.8: DFT-predicted (B3LYP) Gouterman’s type frontier orbitals for 5.1, 5.2, 5.1-, and 5.2...... 142
5.9: DFT-predicted (B3LYP) Gouterman’s type and copper-centered “dx2-y2” frontier orbitals for 5.3, 5.3-, and 5.4...... 143
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5.10: DFT-predicted (B3LYP) generalized molecular orbital diagrams...... 145
5.11: DFT-predicted (TPSSh) generalized molecular orbital diagrams...... 146
5.12: Comparison of DFT-predicted (B3LYP) Gouterman’s type orbital energy levels and orbital diagrams for previously reported NCP and TPP compounds and compounds 5.1 and 5.4...... 147
5.13: Experimental and TDDFT-predicted UV-Vis spectra of 5.1 – 5.4 using B3LYP exchange-correlation functional in dichloromethane...... 149
5.14: Experimental and TDDFT-predicted UV-Vis spectra of 5.1- - 5.3- using B3LYP exchange-correlation functional in dichloromethane...... 150
5.15: Experimental and TDDFT-predicted (TPSSh) UV-vis spectra of complexes 5.1 – 5.4 in dichloromethane...... 150
5.16: Experimental and TDDFT-predicted (TPSSh) UV-vis spectra of complexes 5.1- – 5.3- in dichloromethane...... 151
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LIST OF SCHEMES
1.1.1: Demonstration of the thermodynamic coordination template effect...... 2
1.1.2: Demonstration of the kinetic coordination template effect...... 2
1.1.3: Reaction of Ni2+ α-diketobismercaptoethylimine and a monofunctionalized alkylating agent...... 3
1.1.4: Self-condensation of o-aminobenzaldehyde in the absence and in the presence of transition metal ions...... 4
1.1.5: The nickel mediated synthesis of cyclam...... 5
1.1.6: Synthesis of Pc from various starting materials...... 8
1.1.7: Products from the cyclotetramerization of two different precursors...... 13
1.1.8: Selective synthesis of the ABAB type Pc structure...... 14
1.1.9: Selective synthesis of the AABB type structure...... 14
1.1.10: The synthesis of the bis-pyridine variant of Hp...... 16
1.1.11: Synthesis of bzpc...... 22
1.1.12: Synthesis of BPI using Siegl’s template procedure...... 33
1.1.13: Metallation of BPI and bis(oxazolinyl-methylidene)isoindoline with rare-earth metals...... 45
2.1: Synthesis of semihemiporphyrazines...... 70
3 3.1: Synthesis of Re(CO)3 A DBM complexes...... 92
3.2: Synthesis of the nitrate salts...... 105
3.3: Postulated reaction steps for the formation of the nitrate salts...... 106
4.1: The synthesis of the metal complexes of DAPH (4.1)...... 108
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4.2: Synthesis of 4.1...... 110
4.3: Synthesis of 4.2...... 111
4.4: Synthesis of 4.3...... 111
4.5: Synthesis of 4.4...... 112
4.6: Synthesis of 4.5...... 113
4.7: Synthesis of 4.6...... 114
4.8: Synthesis of 4.7...... 115
4.9: Synthesis of 4.8...... 116
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LIST OF ABBREVIATIONS
Pc- phthalocyanine
MPc- metallophthalocyanine
DII- 1,3-diiminoisoindoline
Hp- hemiporphyrazine dchp- dicarbahemiporphyrazine bzpc- benziphthalocyanine
DDQ- 2,3-dichloro-5,6-dicyano-1,4-benzoquinone
BPI- bis(2-iminopyridyl)isoindoline
BTI- 1,3-bis(2-thiazolylimino)isoindoline bimimd- bis(2-2’-benzimidazolylimino)isoindoline
DMF- dimethylformamide
THF- tetrahydrofuran
LC- ligand centered
MLCT- metal-to-ligand charge transfer pyca- pyrdine-2-carboxaldehyde
ADBM- aza(dibenzopyrro)methene
DFT- density functional theory
TDDFT- time dependent density functional theory
TDDFT-PCM- time dependent density functional theory-polarized continuum model
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DMSO- dimethylsulfoxide
DCM- dichloromethane
LUMO- lowest unoccupied molecular orbital
HOMO- highest occupied molecular orbital
A3DBM- α-amidino azadi(benzopyrro)methene
DAPH- 2,6-diacetylpyridine dihydrazone
MCD- magnetic circular dichroism
NCP- N-confused porphyrin
PF-NCP- tetra(perfluorophenyl)-N-confused porphyrin
TPP- tetraphenylporphyrin
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CHAPTER I
INTRODUCTION AND BACKGROUND
1.1 Template Reactions
In the field of coordination chemistry, the number of template reactions has expanded into a diverse collection of compounds over the last hundred years.1 However, the term “template” was not used in the scientific literature until 1964, when it was coined by Busch and Thompson.1 In their manuscript, a template reaction was described as a reaction in which a metal ion holds reactive ligands in a geometric position that can facilitate further stereochemical selective multistep reactions.1,2 In addition to defining a template reaction and synthesizing a new macrocyclic complex, Busch and Thompson described the thermodynamic and kinetic effects that are present during coordination mediated template reactions.3
To illustrate the importance of the metal ion coordination geometry, Busch et al. selected the Ni2+ ion due to its preference to form square planar complexes. In their report, divalent nickel acetate was reacted with β-mercaptoethylamine and α-diketone to form a
Schiff base square planar complex with a yield over 70% (Scheme 1.1.1).2,4,5 Without the presence of the metal ion, thiazolines form, which are in competition with the Schiff base species.6 This reaction demonstrates the thermodynamic or equilibrium coordination template effect. In the reaction, the desired Schiff base ligand is in equilibrium with other
1
competing species but due to its higher metal binding affinity shifts the equilibrium towards the desired complex.3
Scheme 1.1.1: Demonstration of the thermodynamic coordination template effect.1–5
Once the Ni2+ α-diketobismercaptoethylimine complex was synthesized, it was recognized that the thiolate sulfur atoms are positioned in a geometric manner that they can react with a dialkylating agent. The complex was reacted with one equivalent of 1,2- bis(bromomethyl)benzene to form a new macrocyclic complex with a yield of 60%
(Scheme 1.1.2). Without the presence of the metal center, the reaction would form an assortment of cyclic and polymeric products. The cyclization process involves the stepwise irreversible nucleophilic attack of the thiolates on the methylene carbon atom positions.1,3,7
Scheme 1.1.2: Demonstration of the kinetic coordination template effect.1,3,7
The second step in this reaction sequence demonstrates the kinetic coordination template effect. The reaction takes advantage of the organization of the ligands bound to the metal center. Since the adjacent terminal sulfur atoms can act as nucleophiles, they are favored to react with the same dialkylating agent. When the Ni2+ α- diketobismercaptoethylimine complex is reacted with a monofunctionalized alkylating agent, the first nucleophilic attack is much faster than the second nucleophilic attack, and
2
the monofunctionalized intermediate complex can be isolated (Scheme 1.1.3) and can engage in unwanted side reactions. However, when the Ni2+ α- diketobismercaptoethylimine complex reacts with 1,2-bis(bromomethyl)benzene, only the desired cyclization product is isolated (Scheme 1.1.2), meaning the second nucleophilic attack is faster than the first nucleophilic attack.3
Scheme 1.1.3: Reaction of Ni2+ α-diketobismercaptoethylimine and a monofunctionalized alkylating agent.7
An additional reaction that illustrates the thermodynamic template effect is the self- condensation of o-aminobenzaldehyde. In 1954, Eichhorn and Latif showed that in the presence of Cu2+, Ni2+, Co2+, Zn2+, Pd2+, Co3+, and Fe2+, o-aminobenzaldehyde would self- condense into a tridentate ligand and a tetradentate ligand.8–10 The tetradentate ligand contains a tetraaza[16]annulene ring which upon a two-electron reduction generates a dianion. The dianion is a structural analog of porphyrin and phthalocyanine.11 In the absence of the metal center, the self-condensation forms polycyclic structures including two polycyclic trimers that do not contain any imine bonds (Scheme 1.1.4).12 The metal centers sequester the tridentate and tetradentate ligands from the reaction and shift the
3
equilibrium toward the Schiff base complexes, rather than the polycyclic structures, thus showing the thermodynamic template effect.3
Scheme 1.1.4: Self-condensation of o-aminobenzaldehyde in the absence and in the presence of transition metal ions.3
Another important reaction that displays the kinetic coordination template effect is the Ni2+ templated synthesis of cyclam.1,13 In 1937, cyclam or 1,4,8,11- tetraazacyclotetradecane was synthesized by van Alphen by reacting 1,3-dibromopropane with 1,4,8,11-tetraazaundecane in the presence of an alkali metal. In 1961, Stetter and
Mayer synthesized cyclam by another route and showed that van Alphen only synthesized cyclam as a small portion of the product.14 In 1965, Bosnich et al. would metallate cyclam with Co3+ and investigate its absorption spectra in the presence of various metal binding anions.15 However, Barefield would synthesize cyclam in a more convenient method using
Ni2+ as a template agent with a percent yield of 65%, as compared to van Alphen (5% yield)
4
and Stetter and Mayer (24% yield).16 In this template reaction, 1,5,8,12-tetraazadodecane was reacted with Ni2+ perchlorate to form a square planar complex where all the nitrogen atoms of the tetraamine are bound to the metal center. Afterwards, glyoxal is added to the reaction to form a Schiff base complex where both terminal amines undergo condensation with the carbonyls of glyoxal. No monofunctionalized intermediates were isolated and in the absence of the metal center holding the terminal amines in close proximity, various cyclic and polymeric species would be possible. Subsequently, the Schiff bases can undergo hydrogenation by sodium borohydride or hydrogen and Raney nickel catalyst to form the Ni2+ cyclam complex. Finally, the desired product formed by the addition of excess cyanide to remove the nickel center (Scheme 1.1.5).13
Scheme 1.1.5: The nickel mediated synthesis of cyclam.1,13
5
Phthalocyanine
One of the most famous template reactions is the synthesis of phthalocyanine (Pc).
The first synthesis of Pc occurred in 1907 when Braun and Tcherniac, working at the South
Metropolitan Gas Company in London, heated o-cyanobenzamide in refluxing ethanol.17
The reaction resulted in a dark blue insoluble powder which was recovered in low yield.18
Several years later, in 1928, Scottish Dyes Ltd were preparing phthalimide from phthalic anhydride which, during a failed attempt, saw the glass-lined reaction vessel crack exposing the reaction to the outer steel casing. This exposure resulted in the formation of a blue-green pigment which researchers hypothesized was an iron based by-product.19
Later in 1928, Imperial Chemical Industries would acquire Scottish Dyes Ltd and sent some of the pigment to Jocelyn F. Thorpe at Imperial College in London to learn more about the structure and properties of the sample, who would then gave the sample to
Reginald P. Linstead. Linstead correctly predicted the structure of the pigment through various synthetic studies, which would be confirmed later by Robertson using X-ray diffraction.20–22 Linstead would note that Pc is an aromatic 18π electron macrocycle which can accommodate metal ions in the pore of the structure similar to porphyrin (Figure 1.1.1).
The differences between the two macrocycles are the presence of benzo-units on the pyrrole rings and nitrogen atoms at the meso positions of Pc.23–28
Linstead, in an experiment that agreed with the observations on the initial synthesis, showed that the yield of Pc could be increased to 40% if magnesium metal, magnesium oxide, magnesium carbonate, or antimony metal were mixed with o-cyanobenzamide when heated at 230ᵒC. The resulting metallophthalocyanine (MPc) could be demetallated with cold concentrated sulfuric acid to form the desired metal-free Pc. Since the early work in
6
this area, the use of o-cyanobenzamide to form various Pcs has not been common.24
Instead, Linstead and his coworkers used phthalonitrile or 1,3-diiminoisoindoline (DII) as the starting material.25,29 DII is prepared from phthalonitrile by bubbling gaseous ammonia into a solution of phthalonitrile in the presence of sodium methoxide in methanol.30 Due to
Linstead’s investigations using phthalonitrile and DII, these two materials would become the most common precursors for synthesizing Pc.
Figure 1.1.1: Molecular structures of porphyrin and phthalocyanine.23–28
Phthalocyanine often forms a dianion (Pc2-) that binds many transition metal ions in the pore so tightly that they cannot be recovered without destruction of the macrocycle.
The stability of the these MPcs has allowed researchers to add a simple transition metal salt as a template for cyclotetramerization to either phthalonitrile or DII to form the desired
Pc in a high boiling solvent. Even though phthalonitrile and DII are the most common precursors, Pcs have been synthesized from a variety of other starting materials as shown in Scheme 1.1.6.31
Many transition metal ions such as Zn2+, Co2+, Cu2+, Fe2+, and Mn2+ do not distort the macrocycle and lead to square planar complexes. However, transition metal ions like
7
Pt2+ and Pb2+ are too large for the pore and therefore coordinate to the nitrogen atoms above the Pc plane.32,33 Additionally, reactions with the rare-earth metal ions such as the lanthanides lead to the formation of the sandwich complexes where the metal ion complexes to two Pc rings.34 Also, the large uranyl ion templates the formation of superphthalocyanine where the macrocycle around the metal center contains five DII moieties instead of the normal four.35,36 In contrast, the small boron ion templates the formation of subphthalocyanine where the macrocycle only has three DII units around the boron center.37
Scheme 1.1.6: Synthesis of Pc from various starting materials.31
8
Phthalocyanines and MPcs have strong absorptions called Q bands in the visible spectrum between 670 and 690 nm.38 In addition, they have strong absorptions in the ultra- violet region between 320 and 370 nm known as Soret bands. The Q-band is responsible for the color of the compounds and can be bathochromically or hypsochromically shifted by substitution on the periphery of the isoindoline units or by the electronic properties of the central metal ion.31 Typically, the Q-bands have extinction coefficients of ~105 M-1 cm-
1 and can be split if the macrocycle is asymmetric.39 In general, when electron donating functional groups such as alkoxy and thioether are substituted on the α-benzo positions of
Pc, the Soret and Q-bands undergo a bathochromic shift. However, substitution of these same groups on the β-benzo positions cause the Q-band to undergo a hypsochromic shift
(Figure 1.1.2). When electron withdrawing functional groups such as nitro and sulfonyl are substituted on the α-benzo positions and β-benzo positions of Pc, the Q-band undergoes a hypsochromic and bathochromic shift, respectively.40
Additionally, the Q-band absorption energies can be affected by metal identity.
Closed shell metal ions like Li+, Mg2+, and Zn2+ show absorption maxima at 670 nm, whereas open shell metal ions like Fe2+, Co2+, and Ru2+ hypsochromically shift the Q-band to lower wavelengths between 630 and 650 nm.41,42 However, some bathochromic shifts have been observed for Fe2+ and VO2+ MPcs reaching absorption maxima values of 700 nm, and red Mn3+ Pcs have been reported to shift the Q-band absorption maxima values to 808 and 828 nm.41,43 Alternatively, the Q-band absorption can undergo a bathochromic shift when the π-system is extended. When naphthalene units are used instead of the benzopyrrole units, Q-band absorptions shift to between 750 and 840 nm. Anthracene units also cause bathochromic shift of the Q-bands to values between 830 and 935 nm. The
9
general trend is that the Q-bands bathochromically shift by about 20 to 30 nm per benzene unit that has been integrated into the π-system.44–46 Also, the Q-bands can undergo bathochromic shifts when the symmetry of the macrocycle is reduced.47
Figure 1.1.2: α- and β-benzo positions on the Pc skeleton.48
The synthesis of lower symmetry Pcs can be achieved via a variety of different ways. Low symmetry macrocycles can be synthesized by the cyclotetramerization of a single precursor with only one substitution on the periphery. This cyclotetramerization leads not only to the C4h isomer but to the D2h, C2v, and Cs isomers as well (Figure 1.1.3).
The separation of isomers is possible by chromatography, however, is a laborious task.49,50
One of the most common ways to synthesize a low symmetry Pc is by cyclotetramerization with two different precursors. These condensations afford the AAAA, AAAB, AABB,
ABAB, ABBB, and BBBB structures (Scheme 1.1.7).48 The yield of the AAAB type structures can be improved statistically by adjusting the amount of each precursor and are relatively easy to chromatographically separate from the other structures. However, the
10
AABB and ABAB type structures are difficult to separate due to their similar molecular properties and identical molecular weight.51–54 Although, separation and complete characterization of all type of structures for peripheral substituted and fused rings isomers have been achieved.55–58
Figure 1.1.3: C4h, D2h, C2v, and Cs isomers of a cyclotetramerization from a single precursor with one substitution on the periphery.48
11
The AAAB, AABB, ABAB, and ABBB type structures have also been selectively synthesized in a variety of different ways. Subphthalocyanine has also been used to selectively synthesize the AAAB type structures. When subphthalocyanine reacts with a
DII unit, it undergoes a macrocyclic ring expansion that can form a low symmetry Pc.59,60
The ABAB and AABB type structures are more difficult to selectively synthesize than the
AAAB type structures, however, researchers have accomplished this endeavor.61–64 To selectively synthesize the ABAB type structures, Young et al. used a cross-condensation of two different precursors where six of the eight interior nitrogen atoms of the macrocycle come from one precursor. In the reaction, 1,3,3,-trichloro-6-nitro-isoindolenine was reacted with a DII unit with a ether group on the β-benzo position in the presence of CuCl2 or CoCl2 and the products were isolated with yields ranging from 17 to 72% (Scheme
1.1.8).65 To selectively synthesize the AABB type structures, Kobayashi et al. employed the lithium method. The reaction of 3,6-diphenylphthalonitrile and lithium hexyl oxide at
170ᵒC leads to the formation of a half-Pc intermediate. The cyclotetramerization of this intermediate is disfavored due to the steric bulk at the α-benzo positions. Afterwards, the intermediate is reacted with another phthalonitrile precursor in the presence of NiCl2 to afford the desired AABB type structure (Scheme 1.1.9).66
12
Scheme 1.1.7: Products from the cyclotetramerization of two different precursors.48
13
Scheme 1.1.8: Selective synthesis of the ABAB type Pc structure.48,65
Scheme 1.1.9: Selective synthesis of the AABB type structure.48,66
14
In recent years, the use of Pcs has moved away from their established roles as colorants and dyes. The ability to tune the electronic and physical properties of Pcs has allowed for the preparation of materials with applications in the fields of semiconductors,67,68 liquid crystals,69–71 nonlinear optics,72 photovoltaic and solar cells,73–
75 sensors,76 catalysis,77 polymers,78 and photodynamic theory.79 Changing the electronics and physical properties of Pcs not only derives from the capability to preform peripheral substitutions but also from the capacity to insert about seventy different elements into the
Pc pore.31,40
Hemiporphyrazines
Hemiporphyrazines (Hps) are 20π electron nonaromatic Pc analogs which were defined by Campbell in 1956 as four-unit macrocycles where two units are pyrrole-like and the other two units are heterocycles that are oppositely faced. The units are bound by aza bridges at the meso positions.80 In 1952, Elvidge and Linstead were the first to synthesize the new macrocyclic class by condensing DII with 2,6-diaminopyridine (Scheme 1.1.10).81
After the initial synthesis, Linstead would expand the Hp class by altering the diamine used in the reaction. Instead of using 2,6-diaminopyridine, a variety of aryl diamines would be used including m-phenylenediamine, 2,7-diaminonaphthalene, 2,8-diaminoacridine, and
3,5-diaminopyridine.82 The 3,5-diaminopyridine derivative led to the first confused Pc analog, where the nitrogen atom faces the outside the Pc ring and a carbon atom faces the interior of the Pc pore and is considered an analog of N-confused porphyrin83–85. The m- phenylenediamine derivative generated a core-modified Pc analog where two benzene rings were inserted into the backbone which is considered as a carbaphthalocyanine or more recently named dicarbahemiporphyrazine.86 The 2,7-diaminonaphthalene and 2,8-
15
diaminoacridine derivatives were the first examples of a core expanded Hp (Figure 1.1.4).
In all cases, the Hp class of molecules are 20π electron nonaromatic macrocycles due to the π systems being localized on the DII and pyrrolic units. Hemiporphyrazines exhibit neither low energy absorptions in the UV-visible spectrum like Pc nor exhibit ring current effects derived from an 18π electron aromatic or a 20π electron antiaromatic system in the
NMR spectrum.87
Scheme 1.1.10: The synthesis of the bis-pyridine variant of Hp.81
Figure 1.1.4: Alternative Hps using diaryl diamines other than 2,6-diaminopyridine.82
Like Pc, the peripheral substitution of Hp has also been explored. The peripheral modification occurs on the DII units or at the 4th position of the pyridine rings. The solubility of Hps in organic solvent is low and much of the peripheral substitution chemistry has been explored to remedy this problem. Many alkyl and alkoxy functionalized
Hps have been synthesized (Figure 1.1.5). However, due to the steric bulk of these groups, condensation does not occur unless in the presence of a metal template.88,89 Additionally,
16
Hps with naphthalene and anthracene rings incorporated into the DII moiety have been synthesized (Figure 1.1.6).89 Furthermore, a water soluble Hp has been synthesized using
2,3-dicyanopyridine.90 Starting from this precursor, a pyridine ring is placed in the DII moiety which can undergo subsequent alkylation with CH3I. The dicationic macrocycle can then metallated with either Cu2+ or Ni2+ (Figure 1.1.7).90
Figure 1.1.5: Peripheral substitution of Hps.88,89
Hemiporphyrazine, like Pc, is an avid metal binder. The first examples of metallated Hp were synthesized by Elvidge and Linstead when prepared the Ni2+ and Pb2+
17
complexes.81 The structure nickel complex was elucidated by X-ray crystallography by
Speakman in 1953 (Figure 1.1.8). The elucidated structure showed that during metallation the macrocycle loses the two ionizable protons on the DII units and becomes a dianionic tetradentate chelate. The Ni2+ center adopts a square planar geometry and the ligand adapts a saddle shape around the metal center.91 Unlike Pc, Hps have a higher susceptibility towards axial substitution due to the asymmetrical binding of the macrocycle pore, where the DII units bind more tightly to the metal center than the pyridine units.92,93 This gives rise to 1:1 and 1:2 adducts in coordinating solvents like water and pyridine.94,95
Figure 1.1.6: Incorporation of naphthalene and anthracene rings into Hps.89
18
Figure 1.1.7: An example of a water soluble Hp.90
Figure 1.1.8: Structure of NiHp with a top view (left) and a side view (right). Hydrogen atoms have been omitted for clarity. Redrawn from CSD data code NIPHCA11.91
The addition of pyridine to Ni(Hp) causes two equivalents of pyridine to coordinate to the axial positions forming the resultant Ni(Hp)(py)2 compound producing a 1:2 complex (Figure 1.1.9).95,96 Whereas, the addition of pyridine in the presence of lithium bis(trimethylsilyl)amide to Hp causes one equivalent of pyridine to coordinate to the axial position of the metal center forming the Li(HHp)(py) compound generating the 1:1 adduct
(Figure 1.1.9). Charge balance is achieved with one proton in the meso position.97 In addition to the pyridine adducts, Peng et al. synthesized the five coordinate Mn2+, Co2+,
Cu2+, and Zn2+ Hp complexes with water molecules in the axial positions.98 In addition to
19
water and pyridine, Clemente et al. synthesized a 1:2 adduct with N-methylimidazole occupying the axial positions of a Co3+ metal center.99 Besides producing adducts with bases like water, pyridine and N-methylimidazole, Kenney et al. synthesized the
Ge(Hp)Cl2 and Sn(Hp)Cl2 complexes in which the axial positions could be converted to the hydroxide, fluoride, bromide, iodide, and alkoxide analogs.92,93 The germanium and tin hydroxide complexes can undergo polymerization when heated in chloronaphthalene. The reactions produced µ-oxo structures where oxygen atoms are in the axial positions bridging each macrocyclic unit.92,93 In addition to µ-oxo polymeric structures, Collamati et al. and
3+ Hanack et al. synthesized Fe µ-oxo Hp dimers Fe(Hp)OFe(Hp)H2O and
100,101 [Fe(butyloxy)2Hp]2O, respectively. The crystal structure of Fe(Hp)OFe(Hp)H2O is a symmetric µ-oxo dimer whereas the crystal structure of [Fe(butyloxy)2Hp]2O is an asymmetric µ-oxo dimer where the monomeric structures are not in parallel orientation
(Figure 1.1.10).100,101
Figure 1.1.9: Structures of NiHp(py)2 (left) and Li(HHp)(py) (right). Hydrogen atoms and solvent molecules have been omitted for clarity. Redrawn from CSD data code CIFDAW and CCDC number 729564.95–97
20
Figure 1.1.10: Structures of Fe(Hp)OFe(Hp)H2O (left) and [Fe(butyloxy)2Hp]2O (right). Hydrogen atoms and solvent molecules have been removed for clarity. Redrawn from CSD data codes DIMWEB10 and XECHAP.100,101
As previously described, the reaction of DII and m-phenylenediamine was the first example of a core modified Hp called dicarbahemiporphyrazine (dchp).82,86 After the synthesis of dicarbahemiporphyrazine, Elvidge created a new Pc analog. This compound, which was later called benziphthalocyanine by Ziegler,102 due to it also being an analog of benziporphyrin, where only one of the DII moieties is replaced with a benzene ring.103–105
Benziphthalocyanine (bzpc) is generated by two consecutive reactions: first, one equivalent of 1,3-diaminebenzene reacts with two equivalents of DII at 0ᵒC to produce a chelate-like intermediate compound that can be isolated and second, the chelate-like compound then reacts with another equivalent of DII in a 3+1 condensation (Scheme
1.1.11).103,106 Elvidge originally believed that bzpc only had one ionizable proton in the pore but believed an alternative structure could exist with three ionizable protons in the pore. Later structural elucidation by X-ray crystallography showed that there is only one ionizable proton in the pore, however, there are two ionizable protons on the two meso nitrogen atom positions neighboring the benzene unit.107 Like dchp, bzpc is non-aromatic due to the lack of a ring current as seen in the 1H NMR spectrum.106 However, dchp is a
21
non-planar macrocycle whereas bzpc is a planar macrocycle due to the two protons in the pore instead of the four proton sites seen in the former case.107
Scheme 1.1.11: Synthesis of bzpc.103
Due to its poor solubility, the metal chemistry of bzpc is limited. Only cobalt, nickel, lithium, and zinc have been inserted into the pore of bzpc.96,102,108,109 Cobalt and nickel are inserted into the pore by the reaction of bzpc with Co2(CO)8 and Ni(COD)2 respectively (Figure 1.1.11).96,102 These reactions lead to C-H activation and a direct M-C bond in the pore of the macrocycle with each metal having an oxidation state of +2.96,102
Lithium and zinc are inserted into the pore by the reaction of bzpc with lithium
22
bis(trimethylsilyl)amide and diethyl zinc respectively.108,109 Instead of direct M-C bonds, these reactions lead to agostic-type interactions (Figure 1.1.11).108,109 The zinc metalation reaction leads to the alkylation of one of the α-carbons on the DII unit opposite to the benzene ring leading to an sp3 hybridized carbon.109
Figure 1.1.11: Structures of cobalt (top left), nickel (top right), lithium (bottom left), and zinc (bottom right) bzpc. Hydrogen atoms except ionizable protons and internal hydrogens, and solvent molecules have been omitted for clarity. Redrawn from CCDC numbers 641690, 726132, 729564, and 750085.96,102,108,109
Like the metal chemistry of bzpc, the metalation of dchp results in M-C interactions. The first elucidated X-ray structure of a metallated dchp was in 2006 by the
+ 110 insertion of Ag into the macrocyclic pore using AgNO3 in pyridine (Figure 1.1.12). The silver ion is formally three-coordinate by being bound to the two nitrogen atoms of the
23
macrocycle and one nitrogen atom of a pyridine solvent molecule. However, the silver ion does form two agostic-type interactions with the internal carbons. The manganese, iron, and cobalt derivatives have been synthesized using the metal carbonyl compounds
111 Mn2(CO)10, Fe(CO)5, and Co2(CO)8 (Figure 1.1.12). These resultant products are paramagnetic but diamagnetic compounds including the lithium and zinc have been synthesized from lithium bis(trimethylsilyl)amide and diethyl zinc respectively (Figure
1.1.12).108,109
Figure 1.1.12: Structures of silver (left), cobalt (middle), and zinc (right) dchp. Hydrogen atoms except ionizable protons and internal hydrogens and solvent molecules have been omitted for clarity. Redrawn from CCDC numbers 603062, 661972, and 750084.109–111
The above structures do not lead to C-H activation, however, the reaction of Cu2+ salts with dchp in the presence of pyridine leads to a formally three coordinate Cu+ species.110 The copper center is bound by the two DII nitrogen atoms and one axial pyridine nitrogen atom with one agostic-type bond. Interestingly, the internal benzene C-H moiety across from the agostic-type interaction has been activated. The activation affords a reaction with pyridine generating a new C-N bond and the reduction of the Cu2+ metal center to Cu+ (Figure 1.1.13) which previously has been seen with carbaporphyrins.112
Additionally, the first stable metal complex of dchp with a direct M-C bond was
24
96 structurally elucidated with the insertion of nickel using Ni(COD)2 (Figure 1.1.13). The reaction leads to a diamagnetic complex with a square planar Ni2+ metal center. The metal center is electron rich due to the two direct M-C bonds and reacts with dioxygen. This reaction leads to the oxidation of one of the two internal carbon positions to produce a phenol (Figure 1.1.13). One possible mechanism is that dioxygen reacts with the nickel center to transiently produce a Ni3+ ion, which then transfers an oxygen atom to one of the two internal carbon positions. This process is uncommon but a few Ni2+ complexes have reacted with dioxygen to generate Ni3+ metal centers in the presence of electron donating ligands.113
Figure 1.1.13: Structures of copper (left), nickel (middle), and nickel ring oxidation (right) dchp. Hydrogen atoms except ionizable protons and internal hydrogens, and solvent molecules have been omitted for clarity. Redrawn from CCDC numbers 603063, 726130, and 726131.96,110
In addition to dchp and bzpc, other analogs of Hp have been synthesized. Phenol and resorcinol groups have been incorporated into the backbones of dchp as well as bzpc
(Figure 1.1.14).106,114 The modification of these Hps were performed to try to induce electron delocalization via oxidation. The phenol and resorcinol dchps are synthesized from the condensation of DII and 3,5-diaminophenol and 4,6-diaminoresorcinol respectively.114 The phenol dchps reaction generates two isomers, an anti- and a syn- arrangement (Figure 1.1.15).114 The structures of the phenol and resorcinol dchps have
25
been elucidated. The crystal structures show that the macrocycles are planar with the ionizable protons on the external meso nitrogen positions.114 The phenol and resorcinol bzpcs are synthesized in two steps. First, the trimeric chelate-like compounds are generated and then reacted with DII in a 3+1 condensation.106 The structure of the resorcinol bzpc derivative has been elucidated by X-ray crystallography. The structure shows that the macrocycle is planar with one ionizable proton in the pore with two ionizable protons on the external meso nitrogen positions of the resorcinol ring.106 The resorcinol dchp and the phenol and resorcinol bzpcs reveal visible absorptions. The macrocycles are not aromatic and the low energy absorptions do not come from π to π* transitions.106 The transitions have been hypothesized as either a intramolecular charge transfer transition or an excited state intramolecular proton transfer transition.106,115
Figure 1.1.14: Structures of resorcinol bzpc (left) and phenol dchp (right). Hydrogen atoms except for ionizable protons and internal protons, and solvent molecules have been omitted for clarity. Redrawn from CCDC numbers 762392 and 747403.106,114
26
Figure 1.1.15: Structures of anti-phenol dchp (left), syn-phenol dchp (middle), and resorcinol dchp (right).106,114
Recently, Muranaka et al. have incorporated resorcinol rings into the backbone of dchp with aryl ether groups on the periphery on the DII units.116 Upon oxidation with 2,3- dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), the first 18π electron aromatic dchp was generated.116 Before and after oxidation macrocycle structures were elucidated by X-ray crystallography (Figure 1.1.16). Before oxidation, the macrocycle displays the usual nonplanar saddle conformation. However, after oxidation, the structure becomes planar.
Upon oxidation, the chemical shift of the internal C-H appears at -0.49 ppm indicating that a diatropic ring current is present. Additionally, after oxidation, two Q band absorptions were observed at 852 and 653 nm.116
27
Figure 1.1.16: Structures of nonaromatic resorcinol dchp (top) and aromatic resorcinol dchp (bottom). Hydrogen atoms except ionizable and internal protons, solvent molecules, and peripheral aryl ether groups have been omitted for clarity. Redrawn from CCDC numbers 848549 and 848550.116
Based on the preparation of the first aromatic dchp, Muranaka and coworkers would incorporate resorcinol rings into the backbone of bzpc with aryl ether groups on the periphery of the DII units.117 The resultant product is the first 18π aromatic bzpc. The structure was elucidated showing that the macrocycle is planar and one of the O-H protons on the resorcinol ring is transferred to a meso nitrogen position (Figure 1.1.17).117 In the unsubstituted resorcinol bzpc, two meso nitrogen positions are protonated.106 The chemical shift of the internal C-H appears at 1.89 ppm displaying a weak diatropic ring current which is ascribed to a fast exchange on the NMR timescale of a phenol and quinoidal form. The resorcinol bzpc was methylated with MeI to capture the phenol and quinoidal tautomeric
28
structures. The O-dimethylated compound shows a chemical shift of the internal C-H at
5.78 ppm which is assigned to the phenol form. Whereas, the C-dimethylated compound shows a chemical shift of the internal C-H at -1.87 ppm which indicates a strong diatropic ring current and is assigned to the quinoidal form. The structure of the O-dimethylated compound was elucidated which shows its saddle-like conformation. Furthermore, the C- dimethylated compound displays two Q-band absorptions at 740 and 684 nm. Whereas, the
O-dimethylated compound only displays a weak broad absorption in the 600-700 nm region.117
Figure 1.1.17: Structures of aromatic bzpc (top) and O-dimethylated bzpc (bottom). Hydrogens atoms except ionizable and internal protons, solvent molecules, and peripheral aryl ether groups have been omitted for clarity. Redrawn from CCDC numbers 975640 and 975641.117
In 2011, the first Hp with an aliphatic ring incorporated into the backbone was synthesized using 1,3-cyclohexanediamine. The resulting compound was titled
29
cyclohexylcyanine (Figure 1.1.18).118 In cyclohexylcyanine, the cyclohexane rings take on the chair conformation and the macrocycle exists in an external tautomeric form where the ionizable protons are found on the meso nitrogen atoms rather than in the core of the compound. Besides pyridine and benzene rings, triazole rings have incorporated in to the backbone of Hp called triazolehemiporphyrazines (Figure 1.1.19).80 Campbell first described triazolehemiporphyrazines in his patent with the reaction of phthalonitrile and guanazole.80 Studies have been conducted on the free base and its metal complexes but no structures have been elucidated by X-ray crystallography.119–121 In addition to Hps, the triazole moiety has been incorporated in to the backbone of bzpc called triazolephthalocyanine (Figure 1.1.19).122 The macrocycle is synthesized either by a metal template or by the 3+1 condensation seen with the bzpcs.122,123 Triazolephthalocyanine does not exhibit the 18π annulene ring structure and is not aromatic, however, Torres et al. believe that the electronic structure is intermediary between triazolehemiporphyrazine and
Pc.124 Regardless, the structure of triazolephthalocyanine has not been elucidated.
Figure 1.1.18: Structure cyclohexylcyanine (right). Hydrogen atoms except for ionizable protons and solvent molecules have been omitted for clarity. Redrawn from CCDC number 790317.118
30
Figure 1.1.19: Triazolehemiporphyrazine (left) and triazolephthalocyanine (right).80,122
Continuing with alternative Hp structures, Borodkin synthesized the first asymmetric Hp called triazinehemiporphyrazine in the 1970s (Figure 1.1.20).125–127
Triazinehemiporphyrazine was synthesized by a 3+1 condensation. First, the triazine chelate-like compound is generated by reacting 2 equivalents of DII with 2-hydroxy-4,6- diamino-1,3,5-triazine. Afterwards, one equivalent of an aryl diamine such as 1,3- diaminobenzene is reacted with the triazine chelate-like compound to form the triazinehemiporphyrazine. Borodkin would synthesize other asymmetric Hps by assimilating other rings structures like benzene and triazole, benzene and thiophene, benzene and thiadiazole, as well as pyridine and thiadiazole into the backbone.127–132 As in triazolehemiporphyrazines and triazolephthalocyanine, the structure of triazinehemiporphyrazine has not been elucidated by X-ray crystallography.
Expanded Hps have also been synthesized. Torres and Islyaikin generated a new
Hp analog where three equivalents of DII reacted with three equivalents of 2,5-diamino-
1,3,4-dithiadiazole.133 The structure was fully characterized and showed that the sulfur atoms faced the exterior of the macrocycle. Furthermore, structural elucidation showed that
31
the macrocycle is planar with single and double bonds that indicated a lack of aromaticity which is supported by the 1H NMR spectra.134 Torres would also generate another expanded Hp that composed of four DII units and two triazole units. The structure resulted from taking the triazole-like chelate compound, previously used to make triazolephthalocyanine, and fusing it with another equivalent in the absence of DII.135
Kobayashi would also generate expanded Hps with a naphthalene unit in the periphery or a seven-membered ring included in the macrocyclic backbone (Figure 1.1.20).136,137 These macrocycles were named azaphenalene Pc and azepiphthalocyanine respectively.136,137
Figure 1.1.20: Structures of triazinehemiporphyrazine (left), azaphenalene Pc (middle), and azepiphthalocyanine (right). Hydrogen atoms, peripheral groups, and solvent molecules have been omitted for clarity. Redrawn from CCDC numbers 767425 and 791481.125–127,136,137
Bis(2-iminopyridyl)isoindoline
Along with the synthesis of Hp, Elvidge and Linstead would further explore the chemistry of DII by reacting the precursor with two equivalents of an aryl amine such as
2-aminopyridine.138 The resultant product is a tridentate pincer ligand called bis(2- iminopyridyl)isoindoline (BPI) which can be considered a three-quarter unit of Hp (Figure
1.1.21).138 Later, Siegl would report an alternative synthesis that used phthalonitrile instead of DII (Scheme 1.1.12). In Siegl’s procedure, phthalonitrile was reacted with an aryl amine in the presence of CaCl2 as the template. This reaction affords a high yield of BPI-like
32
compounds without the need to isolate DII and avoids undesired Pc byproducts.139 The crystal structure of BPI was not elucidated until 2004.140 The structure shows that the pyridine units face the center of the compound probably due to hydrogen bonding with the
NH of the DII unit. The N-H proton resonance is seen between 13.55 and 14.20 ppm in the
NMR spectrum confirming the hydrogen bonding.140
Figure 1.1.21: Structure of BPI. Redrawn from CCDC number 218623.140
Scheme 1.1.12: Synthesis of BPI using Siegl’s template procedure.139
As Elvidge and Linstead predicted, BPI is an avid metal chelate.138 However, the first detailed study of the metal chemistry of BPI was not until 1967 when performed by
33
Hurley et al.141 In this work study, the authors would react BPI with divalent salts of Fe,
Co, Ni, Zn, and Cd using coordinating anions (chloride and acetate) and non-coordinating anions.141 However, the study did not produce any structural data. The first BPI metal complex elucidated by X-ray crystallography would not be until 1979.142 In the report,
Gagne et al. reacted Cu(OAc)2 and CuCl in the presence of CO and triethylamine with a modified BPI to generate Cu(BPI)(OAc) and Cu(BPI)CO respectively. The Cu+ complex is air sensitive and reacts with dioxygen to form a carbonate bridged dimer [Cu(BPI)]2CO3
(Figure 1.1.22).142 The crystal structure would confirm that BPI binds metals in a tridentate planar manner with the DII nitrogen atom binding more tightly than the pyridine rings as seen with Hps.91 The exposure of the Cu+ complex would also generate a hydroxide bridged complex which was elucidated and shows the similar binding features as the dimer.142
Figure 1.1.22: Structures of [Cu(BPI)]2CO3 (left) and the oxidized tetramer (right) Hydrogen atoms and solvent molecules have been omitted for clarity. Redrawn from CSD data codes MPICCU and HXCUIM.142
In addition to BPI binding to metal ions in 1:1 tridentate planar fashion, alternative binding modes have been observed. While studying the paramagnetic 1H NMR spectra,
34
EPR, and magnetic susceptibility of BPI complexes, Ittel et al. prepared 2:1 BPI complexes
2+ 2+ 2+ 143 of Fe , Co , and Ni (Figure 1.1.23). Additionally, when BPI reacts with Mo2(OAc)4, the ligand replaces one of the acetate anions and binds the metals in an unusual fashion
(Figure 1.1.23).144–146 The DII nitrogen atom and one of the pyridines bind to one molybdenum center, while the other pyridine ring rotates around the imine bond and the meso nitrogen atom binds to the other molybdenum center. Similar to the reaction with
Mo2(OAc)4, when BPI reacts with Zn(ClO4)2, the resultant product is a trimeric species with four BPI units and three zinc metal centers (Figure 1.1.23).147 In this structure, the terminal metal centers bind to two BPI ligands acting as bidentate ligands where one pyridine ring and the central DII nitrogen coordinate to the terminal metal ion. For the central zinc metal center, the remaining pyridine rings coordinate. Furthermore, Wicholas et al. explored the effects of steric crowding around the BPI ligand by methylating the 6th position of the pyridine rings.148 When the authors reacted the modified BPI ligand with
Cd2+, an alternative binding mode was observed which was not seen with BPI (Figure
1.1.23).148 The ligand binds in a bidentate fashion where one of the pyridine rings rotates around the imine bond then binds to the metal center with one of the meso nitrogen positions.
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Figure 1.1.23: Structures of Mn(3-MeBPI)2 (top left), Mo2(BPI)(OAc)2 (top right), trimeric 2+ Zn BPI complex (bottom left), and Cd(BPI)2(NO3)2 (bottom right). Hydrogen atoms and solvent molecules have been omitted for clarity. Redrawn from CSD data codes CEMSAO and JEZCEW and CCDC numbers 613797 and 253849.143–148
In addition to using pyridyl rings, alternative BPI-like compounds have been generated by using aryl amines such as 2-aminothiazole and 2-aminobenzimidazole. The resultant chelates are called 1,3-bis(2-thiazolylimino)isoindoline (BTI) and bis(2-2’- benzimidazolylimino)isoindoline (bimimd) respectively (Figure 1.1.24).149,150 Modified
BTI compounds have been structurally elucidated and show similar structural features to the BPI class of compounds and the nitrogen atoms of the thiazole rings face the center of the compound and the compound is planar.151 However, adding bulky groups to the thiazole ring has been shown to cause rotation around the imine bond, where the sulfur atom faces the center of the compound instead of the nitrogen atom.151 Not only has Brӧring et al.
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elucidated the structure of the normal N,N,N, coordination mode of BTI using Cu2+, the researchers have also elucidated a structure with the abnormal N,N,S coordination mode using Pd2+ that also leads to C-H activation of one of the methyl groups (Figure
1.1.21).149,152,153 Less work has been performed on the bimimd ligand, however, Speier et al. has structurally characterized a Mn2+ complex where the ligand binds as a neutral species with a proton on the meso nitrogen position (Figure 1.1.25).150 Additionally, ring expanded BPI have been synthesized called phthalazines.154 To generate this ligand, BPI is reacted with excess hydrazine hydrate which expands the skeleton by one nitrogen atom on the DII moiety.155,156 Like BPI, phthalazines are avid metal chelates but they can bind to two metal centers instead of the usual one (Figure 1.1.26).157
Figure 1.1.24: 1,3-bis(2-thiazolylimino)isoindoline (BTI) (left) and bis(2-2’- benzimidazolylimino)isoindoline (bimimd) (right).149,150
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Figure 1.1.25: Structures of a Pd(BTI) complex with the abnormal N,N,S coordination mode (left) and Mn(bimimd)Cl2 (right). Hydrogen atoms have been omitted for clarity. Redrawn from CCDC numbers 677874 and 688573.150,153
Figure 1.1.26: Structures of phthalazine (left) and a bis copper complex of phthalazine (right). Hydrogen atoms have been omitted for clarity. Redrawn from CCDC numbers 187625 and 1129164.154,157
One of the major applications of the BPI class of compounds is their use in catalysis.
The first application of BPI compounds for this application was when Co2+ BPI complexes were used in the aerobic oxidation of cyclohexane to afford cyclohexanol and cyclohexanone after the decomposition of cyclohexyl hydroperoxide.158,159 Using the same
Co2+ BPI catalysts, Mimoun et al. observed the catalytic hydroxylation of alkanes and
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alkenes in the presence of organic peroxides. The Co(BPI)(OBz)(OO-tert-Bu) complex was isolated and structurally elucidated (Figure 1.1.27). The structure was revealed to be a
Co3+ complex with a peroxide bound to the axial position with a bidentate benzoate ligand.160 Additionally, Spier et al. generated various Cu2+ catecholato and carboxylato
BPI complexes as enzyme mimics (Figure 1.1.27).161–163 These Cu2+ BPI complexes react with dioxygen to catalytically generate benzoylsalicylic acid and its hydrolysate
163 derivatives. Other dioxygenase models have prepared including [(4’-Me-BPI)-FeCl2] which reacts with 3,5-di-tert-butylcatechol which in the presence of triethylamine forms a catechol adduct which in turn reacts with dioxygen in DMF to trigger intradiol-cleavage.164
Figure 1.1.27: Structures of Co(BPI)(OBz)(OO-tert-Bu) (left) and Cu2+ catecholato BPI complex (right). Hydrogen atoms and solvent molecules have been omitted for clarity. Redrawn from CCDC numbers 1136466 and 151528.160,162
Iridium has also been bound to BPI for oxidation catalysis. Substituted BPIs have been reacted with [Ir(µ-Cl)(COD)]2 and [Ir(µ-Cl)(C2H2)2]2 to afford a square planar species with one pyridine ring rotated around the imine bond and an expected trigonal bipyramidal species respectively.165 Structure of the Ir(COD)BPI complex was elucidated (Figure
39
1.1.28). The addition of the Ir+ BPI compounds in the presence of 3-phenyl-2-
(phenylsulfonyl)-1,2-oxaziridine to non-electron-rich olefins lead to catalytic epoxidation.165 More recently, Fe3+ BPI complexes have been found to be catalysts for the oxidative decarboxylation and deamination of α-aminoisobutyric acid and cyclic amino acids in a DMF/H2O solution with H2O2 to afford ethylene or the desired carbonyl compounds.166 Additionally, a Ru2+ hydride BPI complex has been synthesized and elucidated by X-ray crystallography (Figure 1.1.28).167 The BPI ligand is deprotonated, metallated with Ru(PPh3)3Cl2, and the hydride product is generated by the addition of
NaHEt3B and of PPh3 in THF. The product was found to catalyze the alcohol oxidation of primary alcohols and diols to esters and lactones without base and acceptor additives.167
Figure 1.1.28: Structures of the Ir(COD)BPI complex (left) and the Ru2+ hydride BPI complex (right). Hydrogen atoms except the hydride proton have been omitted for clarity. Redrawn from CCDC numbers 847562 and 951887.165,167
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In addition to oxidation catalysis, BPI complexes have also been used in reduction catalysis. Brominated pyridyl rings of BPI can undergo alkynylation by a Sonogashira coupling reaction and then metallated with Pd2+; the structures were determined by X-ray crystallography (Figure 1.1.29).168 The resultant products have been appended to polyether and carbosilane dendrimers and tested in catalytic hydrogenation reactions of alkenes.169,170
The catalysts were shown to work best when catalytically hydrogenating styrene under
168 atmospheric H2 pressure.
Figure 1.1.29: Structures of the alkynylated Pd(BPI) complexes. Hydrogen atoms have been omitted for clarity. Redrawn from CCDC numbers 232254 and 232255.168
Continuing with BPI catalysis, chiral BPI ligands have been prepared where chiral groups are introduced on the pyridyl ring. These ligands are generated for enantioselective catalysis. The ligands are procured from myrtenal, (–)-β-pinene and (+)-2-carene (Figure
1.1.29).171,172 The metal chemistry and asymmetric catalysis of these ligands have been explored. It was found that the carene BPI derivative preformed best in the asymmetric Fe catalyzed hydrosilylation and Co catalyzed cyclopropanation.171 The Fe catalyzed
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hydrosilylation was found to produce alcohols from diaryl ketones and aryl alkyl ketones with enantioselectivities up to 60% and 93% respectively.171 However, using the ligand with appended ether groups (Figure 1.1.30), generated enantioselectivity up to 91% in a
Co catalyzed hydrosilylation of aryl alkyl ketones.173 The Co catalyzed cyclopropanation produced the desired cyclopropyl compounds from a diazoalkane and an aryl alkene without diazoalkane dimerization. The reaction generated the cyclopropyl compounds with enantioselectivities up to 94%.171 Recently, Gade et al. have coordinated a chiral derivative of BPI called bis(oxazolinyl-methylidene)isoindoline to a Mn2+ alkyl metal center (Figure
1.1.31). The complex was found to catalyze the hydroboration of ketones to chiral alcohols in the presence of pinacolborane. The reaction generates chiral alcohols with enantioselectivities up to 99%.174 The ligand has also been coordinated to an alkyl Fe2+ metal center (Figure 1.1.31).175 The complex has been observed to catalyze the hydrosilylation of aryl alkyl ketones to chiral alcohols in the presence of (EtO)2MeSiH with enantioselectivities up to 99%.175
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Figure 1.1.30: Structures of BPI ligands derived from myrtenal (top left), (–)-β-pinene (top right), (+)-2-carene (bottom left), and cyclopropyl methyl ether (bottom right).171–173
Figure 1.1.31: Structures of pyridine adducts of Mn2+ (left) and Fe2+ (right) bis(oxazolinyl- methylidene)isoindoline complexes. Hydrogen atoms have omitted for clarity. Redrawn from CCDC numbers 1539151 and 1427737.174,175
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In addition to their use in small molecule catalysis, BPI compounds have been used to catalyze various polymerization reactions. The previously mentioned chiral bis(oxazolinyl-methylidene)isoindoline has been coordinated to scandium, lutetium, and yttrium dialkyl metal centers (Scheme 1.1.13).176 It was observed that in the presence of borate and AlR3 in a toluene solution at room temperature, the rare-earth metal complexes catalyzed the polymerization of isoprene with cis-1,4 selectivities up to 97% affording cis-
1,4-polyisoprenes with polydispersities of 2.0-4.5.176 Whereas, normal BPI has been coordinated to scandium and lutetium dialkyl metal centers and has been found to also catalyze the polymerization of isoprene in the presence of borate and AlR3 in a toluene solution at room temperature (Scheme 1.1.13). These rare-earth metal complexes have cis-
1,4 selectivities up to 99% affording cis-1,4-polyisoprenes with polydispersities in the range of 1.26-2.08.177 Additionally, Gade et al. coordinated various BPIs to Co2+ centers to afford [Co(BPI)(OAc)] and [Co(acac)(BPI)(MeOH)] complexes.178 Upon heating the acetato complexes to 100ᵒC, the methanol ligand was removed generating the corresponding five coordinate Co2+ species (Figure 1.1.32).178 In the presence of the radical source 2,2’-azobis-(4-methoxy-2,4-dimethylvaleronitrile) initiator, the Co2+ BPI complexes were observed to catalyze the radical polymerization of methyl acrylate. The acetate complexes controlled the radical polymerization with polydispersities of 1.12-1.40.
The five coordinate acetato complexes performed better with polydispersities around
1.13.178 Gade and coworkers also have coordinated various BPI type ligands to Ru2+
(Figure 1.1.32). In the presence of triethylamine, the BPI ligands were reacted with Ru(µ-
Cl)2(cod)]x in coordinating solvents such as pyridine, dimethyl sulfoxide, and acetonitrile.
The complexes were tested for their catalytic activity in the atom transfer radical
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polymerization of styrene using (1-bromoethyl)benzene as a radical initiator. The complexes were found to have polydispersities on the order of 1.32-1.57.179
Scheme 1.1.13: Metallation of BPI and bis(oxazolinyl-methylidene)isoindoline with rare- earth metals.176,177
Figure 1.1.32: Structures of a BPI Co2+ five coordinate acetato complex (left) and a BPI Ru2+ pyridine adduct (right). Hydrogen atoms and solvent molecules have been omitted for clarity. Redrawn from CCDC numbers 693092 and 802588.173,178
The Hp class of macrocycles are nonaromatic analogs of Pc which therefore lack the optical properties of Pc.87 Hps as well as the BPI-like compounds can be readily
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synthesized from aryl diamines in Schiff base condensation reactions with DII. The resultant products are usually isolated in large yields unlike various other porphyrinoids.82
Like Pc, Hps and BPIs are potent metal binders, however unlike Pc, many elements have not been inserted into the core of Hps and the metal chemistry of these classes of compounds have not been fully explored.87 Even though, Hps have been examined as polymeric materials and BPIs have been examined as organic catalysts, biologically active compounds, and enzymatic model complexes many other areas have not been studied.162,180–184 Due to the unexplored chemistry of these compounds, many open areas of investigation for researchers remain.
“Helmet” and Bicyclic Phthalocyanines
Although many examples of Pc analogs exist where the backbone has been modified, fewer cases occur where an isoindoline ring has been altered. In 2006, McGaff and coworkers synthesized the first examples of a new type of modified Pc: a chiral pentadentate “helmet” Pc.185 In these structures, two inner positions of the Pc ligand are bridged by another DII unit at the 14 and 28 carbon positions while coordinating a metal center (Figure 1.1.33). The DII unit in the bridging positions results in the formation of two sp3 hybridized carbon atoms and loss of planarity in the Pc ring. The chirality arises from the formation of the sp3 carbon atoms now having four different substituents. The interruption of the conjugation in the Pc ring results in the disappearance of the Q band found in other Pc complexes. Other inner substituted Pc complexes do exist, however,
McGaff based this study off a previous observation where alkoxy substituted Pcs at the 14 and 28 positions were synthesized by reacting Ni2+ acetate tetrahydrate with phthalonitrile in methanol or ethanol at 70ᵒC or 90ᵒC respectively (Figure 1.1.33).186–189
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Figure 1.1.33: Structures of Fe3+ “helmet” Pc (left and middle) and Ni2+ Pc with alkoxy substituents (right). Hydrogen atoms, solvent molecules, and 6th position ligands have been omitted for clarity. Redrawn from CCDC numbers 606957 and 174008.186,190
In this study, the complexes were synthesized in one pot by reacting Fe2+ or Co2+ acetate tetrahydrate as templating agents with phthalonitrile in methanol at 130 or 70ᵒC respectively in solvothermal reactions.185 The resultant products oxidize the metal centers from the +2 to the +3 states and the 6th position of the metal centers are occupied either by a methanol or a water solvent molecule. The products do not form if either Fe3+ or Co3+ are used instead of the divalent oxidation states. Additionally, the products do not decompose to unsubstituted Pcs complexes like the analogous alkoxy derivatives.186 Furthermore, reacting Fe2+ or Co2+ Pc with phthalonitrile in methanol at 70ᵒC does not generate the
“helmet” Pcs.
3+ The Fe “helmet” Pc complex has been used in oxidation catalysis with H2O2 to generate epoxides from olefins, alcohols from cycloalkanes, and ketones and aldehydes
191–193 th from benzylic alcohols. The ligand in the 6 position is labile, allowing H2O2 to react with the metal center to afford proposed high valent iron oxo species.191 The high-valent
ᵒ iron oxo species were detected in a cryospray mass spectrometry study with H2O2 at -40 C in a methanol acetone mixture (Figure 1.1.34).191 The generation of these species is
47
believed to be the reason why the “helmet” Pc is able to oxidize various substrate with similarities to heme oxidations.191,192
Figure 1.1.34: Proposed structures of the high-valent iron oxo species based on experimental data from a cryospray mass spectrometry study.191
In addition to “helmet” Pc, other bridgehead modified Pcs have been synthesized such as the bicyclic Pcs. In 1990, Strähle and Gingl synthesized the first bicyclic Pc as a byproduct from the reaction of phthalonitrile and NbOC13 acting as a templating agent
(Figure 1.1.35).194 The resultant product is a metallated modified Pc with a half-Pc bridgehead at two pyrrole carbons. The half-Pc bridgehead generates two sp3 hybridized carbon atoms which interrupts conjugation within the macrocycle and is responsible for the disappearance of a Q band as seen with the “helmet” Pcs.185,194,195 In the complex, the modified Pc acts as a hexadentate ligand while a chloride completes the coordination sphere for the niobium metal center.194
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Figure 1.1.35: Structure of the first bicyclic Pc. Hydrogen atoms have been omitted for clarity. Redrawn from CCDC number 1195852.194
Later, Janczak and Kubiak would react phthalonitrile with indium, gadolinium, and thallium at 210ᵒC in a sealed tube to afford different bicyclic Pcs (Figure 1.1.36).196–198 The structures of the trivalent metal centers coordinated by the bicyclic Pc were elucidated by
X-ray crystallography. In this study, the elucidation lead to the modified Pc being described as a tetradentate Pc ligand bridged by an additional bidentate half-Pc unit.195–198 Unlike what Strähle and Gingl observed, these bicyclic Pcs were bridged at the 14 and 28 pyrrole carbon positions similar to the “helmet” Pcs.190,194,196–198
Figure 1.1.36: Structures of In3+ (left), Gd3+ (middle), and Tl3+ (right) bicyclic Pcs. Hydrogen atoms have been omitted for clarity. Redrawn from CCDC numbers 1206913, 125805, and 1314592.196–198
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Recently, Fukuda et al. generated a new bicyclic Pc by reacting phthalonitrile with lithium methoxide for 30 minutes at 70ᵒC and then adding cadmium acetate to the reaction mixture (Figure 1.1.37).195 The structure revealed that the ligand was hexadentate with a bridgehead at the 14 and 28 pyrrole carbon positions. However, the cadmium metal center was divalent and the ligand was only a dianionic species instead of the normally trianionic state. Additionally, there was a hydrogen atom bound to a meso nitrogen position. The hydrogen position allows this new bicyclic Pc to form around the cadmium metal center due to this metal’s exclusive +2-oxidation state. The cadmium complex affords the third form of the bicyclic Pcs (Figure 1.1.38).194–198
Furthermore, it is believed that effective ionic radius is responsible for the formation of either the “helmet” Pcs or the bicyclic Pcs.195 The effective ionic radii of Fe3+ and Co3+ are inadequate to support the hexadentate bicyclic Pc skeleton and thus form the
“helmet” Pcs.195 However, the effect ionic radius of Tl3+ is the lower limit for the formation of the bicyclic Pcs and Cd2+ has the largest radius of the reported bicyclic Pcs.195
Figure 1.1.37: Structure of Cd2+ bicyclic Pc. Hydrogen atoms except on the meso nitrogen position and solvent molecules have been omitted for clarity. Redrawn from CCDC number 953713.195
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Figure 1.1.38: Three forms of the bicyclic Pcs.195
1.2 Amidine Formation from Metal Mediated Nitrile Activation
In organic chemistry, nucleophilic addition to the nitrile, R-C≡N, triple bond is an appealing direction for the generation of new C-N functional groups.199 However, nucleophilic additions to nitriles can be sometimes difficult due to the poor electrophilic activation of the R groups even when using strong electron withdrawing substituents.199
This chemistry can be facilitated by the coordination of the nitriles to metal ions as nucleophilic addition activators.200,201 The coordination activates the nitrile and enhances addition as shown by the 106-108 fold rate increase of nucleophilic addition as compared to non-coordinated nitriles.202–204
The nucleophilic addition of an amine to a nitrile generates a new C-N bond and a functional group called an amidine, RC(=NH)NR’R’’. Amidines can be synthesized in a pure organic reaction by reacting an amine with a nitrile only when the R group is a strong
199 electron withdrawing group like CCl3. However, in metal mediated synthesis, amidines can form when the R group is a simple alkyl or aryl group.205
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The simplest amidines form when liquid ammonia reacts with an alkyl or aryl nitrile. Jackson et al. observed the formation of amidines by the reaction of liquid ammonia
3+ ᵒ and [Co(NH3)5(NCR)] (R = Me and Ph) at -76 C to generate the resultant products
3+ 206 [Co(NH3)5{NH= C(NH2)R}] (R = Me and Ph) (Figure 1.2.1). Primary and even secondary amines have been used to synthesize metal mediated amidines. Chin and
3 coworkers reacted [Cp*Ir(η -CH2-CHCHPh)(MeC≡N)](SO3CF3) with a series of primary and secondary amines R2NH [R2 = Me2, Me(H), i-Pr(H), (CH2)5] to afford the
3 corresponding products [Cp*Ir(η -CH2CHCHPh){NH=C(NR2)Me}](SO3CF3) (Figure
1.2.1).207 The amidine ligands were removed from the metal center by the addition of triphenylphosphine in dry solvents.207 Additionally, the cyclic secondary amine, aziridine
2+ 208 adds to the carbon position of nitriles in the Pt complex [PtCl2(PhCN)2] (Figure 1.2.1).
Like the previous reaction, the newly formed amidines can be removed from the metal
208 center with the addition of a phosphine such as Ph2PCH=CHPPh2.
Figure 1.2.1: Structures of Co3+ (left), Ir3+ (middle), and Pt2+ (right) amidine complexes. Hydrogen atoms and solvent molecules have been omitted for clarity. Redrawn from CCDC numbers 1250298 and 1242676.206–208
Furthermore, the addition of heterocyclic amines such as pyrazole to coordinated nitriles has led to heterocyclic amidines. Pyrazole and its derivatives were added to
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+ ruthenium bound nitriles, [RuX(CO)(RCN)2(PPh3)2] (X = H, CH=CHR’’; R = Me, CH2-
Ph), to form heterocyclic amidines (Figure 1.2.2).209 In the reaction, one of the coordinated nitriles is substituted by a pyrazole followed by intramolecular nucleophilic attack of the
209 NH on the neighboring nitrile. In addition to pyrazole, amino alkylated adenines, R2AdH
(R = Me, Et), were added to cis-[ReCl4(MeCN)2] which afforded the substitution of one nitrile and the formation of a coordinated heterocyclic amidine (Figure 1.2.2).210 Similarly, the reaction of [Os6(CO)16(NCMe)2 and 7-azaindole leads to the formation of
1 2 211 [Os6(CO)14(µ-CO)(µ-H)(µ-η :η C9H8N3)] (Figure 1.2.2). The resultant product shows the substitution of one of the acetonitrile ligands and the formation of a coordinated heterocyclic amidine. However, the structure also shows the loss of a CO ligand, the formation of a M-C bond, and a bridging hydride.211
Figure 1.2.2: Structures of heterocyclic amidines coordinated to Ru2+ (left), Re3+ (middle), and an osmium cluster (right). Hydrogen atoms and solvent molecules have been omitted for clarity. Redrawn from CCDC numbers 1191449, 1278672, and 1239533.209–211
Recently, Marzilli et al. coordinated bipyridines to fac-[Re(CO)3(CH3CN)3]PF6 and then reacted the resultant products with various primary and cyclic secondary amines to form rhenium bound amidines (Figure 1.2.3).212,213 The ratio of E and Z isomers and their interchange were measured by NMR experiments. Additionally, Marzilli and coworkers
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reacted fac-[Re(CO)3(CH3CN)3]PF6/BF4 with triamines, which caused two acetonitrile ligands to be substituted for two nitrogen positions of the triamine (Figure 1.2.4).214 The transformation caused the intramolecular nucleophilic attack of the non-coordinated terminal amine position on the bound nitrile, generating an amidine. It was observed that the bound amidine could be removed from the metal center with the addition of HF.214 In the study, the authors hypothesize that the amidine forms in two steps; first, the amine adds to the nitrile and second, a proton is transferred from the original amine position to the nitrile nitrogen position.214 This hypothesis is in contrast to a theorized concerted transition
214,215 step. Similarly, Riera et al. reacted fac-[ReBr(CO)3(NCMe)2] with pyrazoles (Figure
1.2.4).216 As seen with the formation of the other metal mediated heterocyclic amidines, one acetonitrile ligand was substituted with a pyrazole and the NH of the pyrazole underwent intramolecular nucleophilic attack on the adjacent bound nitrile to form an heterocyclic amidine.216
Figure 1.2.3: Structures of rhenium bound amidines from a primary amine (left) and a cyclic secondary amine (right). Hydrogen atoms and solvent molecules have been omitted for clarity. Redrawn from CCDC numbers 1103269 and 902159.212,213
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Figure 1.2.4: Structures of rhenium bound amidines from a triamine (left) and a pyrazole (right). Hydrogen atoms and solvent molecules have been omitted for clarity. Redrawn from CCDC numbers 830222 and 299803.214,216
Re(CO)3 diimine complexes
The majority of rhenium(I) organometallic complexes contain a octahedral rhenium metal center with a low spin d6 electron configuration and some kind of direct M-C bond.217
This chemistry is expansive, and there are many examples of the carbonyl variants of the
0/+ formula [Re(X)(CO)3diimine] where the ligand is a bidentate diamine such as 2,2’- bipyridine or 1,10-phenanthroline. This chemistry has drawn much attention for many decades due to their rich photochemistry.218 In these complexes, photoexcitation causes either a 1π→1π* or a 1dπ→1π* transition to occur originating from the orbitals on the diimine ligand or the metal center respectively.219 The first type of transition occurs in the
UV-visible spectrum around 300 to 350 nm and is called a ligand centered (1LC) excited state charge transfer. The LC transition appears as a sharp band in the UV-visible spectrum.
However, the second type of transition occurs at lower energy, and has been observed to occur at wavelengths out to 550 nm with a molar absorptivities in the range of 2000 to
6000 M-1 cm-1.220 This second type of transition is called a metal-to-ligand charge transfer
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(1MLCT) and appears as a broad band in the UV-visible spectrum.219 The 1MLCT band is sensitive to polarity and displays solvatochromism in which the band red shifts with decreasing solvent polarity.218 Additionally, the 1MLCT excited state allows the complexes
II 0/+ to be depicted as charge separated species with the formula [Re (X)(CO)3(diimine•−)] .
Many of these complexes are capable of emission after photoexcitation. They emit from the transition from the lowest 3MLCT state to the ground state as a broad band (Figure
1.2.5). After photoexcitation, the 1LC and 1MLCT band can undergo intersystem crossing to reach the 3LC and 3MLCT states (Figure 1.2.5). The 3LC state can also reach the 3MLCT state by internal conversion (Figure 1.2.5).221 Intersystem crossing to the triplet state is possible due to the heavy atom effect of rhenium which results in spin-orbit coupling interactions. Typically, the 3MLCT excited state lifetime is around 10 ns to 1 µs with luminescence quantum yields ranging from 0.0001 to 0.1.222–226 The lifetime of the 3MLCT excited state is long enough to allow energy transfer or electron transfer to nearby acceptors.227 Due to the above described photochemistry, rhenium(I) tricarbonyl diimine complexes have been employed as emission sensitizers, photosensitizers, photooxidants, photocatalysts and electrocatalysts.228–231
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Figure 1.2.5: Jablonski Diagram.232
There are a number of ways to prepare rhenium diamine complexes, including the use of the rhenium(I) tricarbonyl unit a templating unit to generate a variety
233–236 compounds. The carbonyls bound to the rhenium center in the Re(CO)3 unit are in a restrictive facial arrangement and are not displaced without considerable amount of back- bonding, which prevents macrocycle formation. Additionally, nitrogenous ligands are
234–236 characteristicly nonlabile when chelated to the Re(CO)3 unit.
The most extensively explored templating reaction with Re(CO)5X uses pyrdine-2- carboxaldehyde (pyca) with a primary amine. This has led to the formation of
0/+ 237–242 [Re(X)(CO)3diimine] complexes where the diamine is a pyridine -2-imine. These reactions have allowed the functionalization of biomolecules via conjugate formation with ester protected amino acids, including H-L-Ala-OEt, H-β-Ala-OEt, H-L-Val-OMe, H-
GABA-OMe, H-L-Asp(OMe)-OMe, and H-L-Met-OMe, and the N of lysine. The last
57
complex was used in the solid phase synthesis of peptides incorporating neurotensin, bombesin, leutenizing hormone releasing hormone, and a nuclear localization sequence
237,238 (Figure 1.2.6). Additionally, Re(CO)5X and pyca have been reacted with hydrazine and various phenylenediamine compounds to generate dimeric Re(CO)3 species where the metal centers are electronically coupled with one another (Figure 1.2.6).241,242 Furthermore, similar conditions have been employed to incorporate an azobenzene moiety into a
Re(CO)3 complex which undergoes photoinduced E/Z isomerization via excitation of the
MLCT band (Figure 1.2.7).240 Pyca complexes have also been synthesized with different aminophenols which showed pH-dependent UV-visible transitions (Figure 1.2.7).239
Figure 1.2.6: Structures of Re pyca complexes with an ester protected amino acid (left), a phenylene linked dimer (middle), and a hydrazine linked dimer (right). Hydrogens atoms have been omitted for clarity. Redrawn from CCDC numbers 246099, 979434, and 1414735.237,241,242
Figure 1.2.7: Structures of Re pyca complexes with an azobenzene moiety (left) and an aminophenol moiety (right). Hydrogen atoms have been omitted for clarity. Redrawn from CCDC numbers 1409716 and 929877.239,240
58
Recently in our laboratory, the Re(CO)3-unit has been used to template the
236 formation of aza(dibenzopyrro)methene (ADBM). In the reaction, Re(CO)5Cl was reacted with two equivalents of DII in the presence of pyridine or N-methylimidazole due to the ligand having a negative charge (Figure 1.2.8). The planar ADBM ligand coordinates to the rhenium center in a bidentate fashion and resembles that of a half-Pc. Additionally, the terminal bis(imino)groups can be hydrolyzed to either a bis(oxo)-terminated species or a mixed oxo/imino chelate depending on the presence of water in the reaction solution. The
Re(CO)3-templated ADBMs have MLCT absorption bands ranging from ~425 to ~525 nm with extinction coefficients in the range of 1500 to 2000 M-1 cm-1 which are typical for
0/+1 other [Re(X)(CO)3diimine] complexes.
The synthesis of the Re(CO)3-templated ADBMs are related to the prior work done by Cammidge, Lukyanets, and You et al.243–245 Cammidge and coworkers took various aminoisoindolines and self-condensed them in refluxing toluene to generate the desired
243 ADBMs which afterwards were coordinated to a BF2-unit (Figure 1.2.9). Lukyanets et al. reacted phthalonitrile with a variety of arylmagnesium bromides in dry benzene to
244 afford ADBMs which then were coordinated to a BF2-unit (Figure 1.2.9). You and coworkers reacted phthalonitrile with potassium tert-butoxide in DMF to afford an ADBM with an amino terminal group which would also be coordinated to a BF2-unit (Figure
1.2.9).245
Additionally, the Re(CO)3-templated ADBMs are structurally similar to the
Re(CO)3 dipyrrinato and azadipyrromethene complexes synthesized by Telfer et al. and
Gray et al respectively (Figure 1.2.10).246,247 In these complexes, the ligands have a negative charge which causes the halide in the 6th position to be replaced by a neutral
59
coordinating ligand such as triphenylphosphine or pyridine. Unlike other
0/+ [Re(X)(CO)3diimine] complexes, these complexes have strong visible absorptions between 500 and 600 nm with extinction coefficients in the range of 40,000 to 50,000 M-1 cm-1.246,247 The strong transitions are not from a MLCT band but rather ligand centered
246,247 transitions which have been observed with the BF2 derivatives. Based on the synthesis of the Re(CO)3-templated ADBMs, the Re(CO)3-unit could be employed as a templating agent to synthesize other DII based chelates.234–236
Figure 1.2.8: Structures of Re(CO)3-templated ADBMs terminated by bis(imino) (left), mixed imino/oxo (middle), and bis(oxo) (right) groups. Hydrogen atoms have been omitted for clarity. Redrawn from CCDC numbers 1042791, 1042792, and 1042793.236
60
Figure 1.2.9: Structures of various ADBMs coordinated to a BF2-unit. Hydrogen atoms and solvent molecules have been omitted for clarity. Redrawn from CCDC numbers 992707, 691385, and 1047636.243–245
Figure 1.2.10: Structures of a Re dipyrrinato complex (left) and a Re azadipyrromethene complex (right). Hydrogen atoms have been omitted for clarity. Redrawn from CCDC numbers 760502 and 768868.246,247
61
CHAPTER II
Re(CO)3-TEMPLATED SYNTHESIS OF SEMIHEMIPORPHYRAZINES
The text of this chapter is a reprint of the material as it appears in: Allen J. Osinski,
Tanner Blesener, Abed Hasheminasab, Cole Holstrom, Victor N. Nemykin, Richard S.
Herrick and Christopher J. Ziegler. Inorg. Chem., 2016, 55 (24), 12527–12530. Copyright
© 2016 American Chemical Society.
DOI: 10.1021/acs.inorgchem.6b02558
Introduction
In the early 1950s, Linstead first synthesized diiminoisoindoline (DII, Figure 2.1) as a precursor for phthalocyanines.23,138 Linstead showed that when DII reacts with a diamine such as 2,6-diaminopyridine, a modified phthalocyanine is produced, which was later termed hemiporphyrazine (Figure 2.1).80,82 A hemiporphyrazine is a modified phthalocyanine where one or two of the isoindoline rings are replaced with other aromatic rings such as pyridine or benzene.108,109 At the same time, Linstead developed chelates using DII that could be considered as ¾ of a hemiporphyrazine ring; these systems, known as bis(pyridylimino)isoindolines (BPI, Figure 2.1), can be synthesized either from DII and a primary amine or via reaction of phthalonitrile and an amine in the presence of a templating metal.138,139 However, the synthesis of chelates that can be considered as half
62
of a hemiporphryazine has been limited.248 In this report, we present the rhenium templated synthesis of a semihemiporphyrazine (Figure 2.1). Using Re(CO)5X (X = Cl,
Br) as our template precursor, we have been able to generate half-hemiporphyrazine type chelates using pyridine, thiazole and benzimidazole as the alternate heterocycle to isoindoline.
Figure 2.1: Semihemiporphyrazine and related compounds.
The interest in half macrocycle structures has been driven by the chemistry of dipyrromethene, azadipyrromethene and azadi(benzopyrro)methene chelates, and in
244,249–257 particular their BF2 adducts. These compounds can be considered as half porphyrin, half azaporphyrin and half phthalocyanine type ligands respectively. In spite of
63
extensive work on these systems, the synthesis of semihemiporphyrazines has only been presented in a few reports.139,258 This results from the difficulty in isolating the 1:1 condensation products from the BPI-like chelates and the products of these reactions have been reported as complex mixtures. Recently, Brӧring has produced a BPI-like precursor in which DII condensed with only one thiazole unit, which was then used to generate asymmetric BPI- type chelates.248 In 2016, we reported the synthesis of aza(dibenzopyrro)methene chelates from DII using either the Re(CO)3 moiety or BPh2 as templating agents.236,259 We surmised that a semihemiporphyrazine could similarly be produced from DII and a simple amine modified heterocycle using the Re(CO)3 moiety as
I a templating agent. Re (CO)3 based compounds are typically non-labile when chelated by nitrogenous ligands, and the three carbonyls form a structurally limiting facial
241,242,260 geometry. Thus, the Re(CO)3 group prevents the formation of metal centered macrocycles and instead facilitates chelate formation.
Experimental
General Information
All reagents and starting materials were purchased from commercial vendors and used without further purification. 1,3-diiminoisoindoline (DII) was synthesized according to a previously published procedure.261 Chlorobenzene and bromobenzene were stored over 3 Å molecular sieves. Deuterated solvents were purchased from Cambridge Isotope
Laboratories and used as received.
NMR spectra were recorded on a 300 MHz spectrometer and chemical shifts were given in ppm relative to residual solvent resonances (1H NMR spectra). High resolution mass spectrometry experiments were performed on a Bruker MicroTOF-III instrument.
64
Infrared spectra were collected on Thermo Scientific Nicolet iS5 which was equipped with an iD5 ATR. UV-Vis spectra were recorded on a Hitachi UV-Vis spectrophotometer (U-
3010).
X-ray intensity data were measured on a Bruker CCD-based diffractometer with dual Cu/Mo ImuS microfocus optics (Cu Kα radiation, λ = 1.54178 Å, Mo Kα radiation, λ
=0.71073 Å). Crystals were mounted on a cryoloop using Paratone oil and placed under a steam of nitrogen at 100 K (Oxford Cryosystems). The detector was placed at a distance of
5.00 cm from the crystal. The data were corrected for absorption with the SADABS program. The structures were refined using the Bruker SHELXTL Software Package
(Version 6.1) and were solved using direct methods.
DFT and TDDFT calculations: The starting geometries of all compounds were taken from X-ray structures. They were optimized using the B3LYP exchange-correlation functional262 coupled with the relativistic DZP basis set for the Re atom263 and the 6-
311G(d)264 basis set for the remaining atoms. Energy minima in optimized geometries were confirmed by frequency calculations. THF was used as a solvent in all of the single point
DFT-PCM and TDDFT-PCM calculations; solvent effects were calculated using the polarized continuum model (PCM).265 The first 30 states of each compound were calculated in all TDDFT-PCM calculations. All DFT calculations were conducted using the Gaussian 09 software package,266 and the QMForge program267 was used for the molecular orbital analysis.
65
Syntheses
Synthesis of 2.1-2.6. The procedure for generating 2.1 is representative for these syntheses except bromobenzene is used for the solvent in 2.4-2.6. Also, the reactions to make 2.4-2.6 are based on Re(CO)5Br (0.25 mmol). Re(CO)5Cl (0.28 mmol), DII (0.28 mmol), and the amine heterocycle (0.28 mmol) were refluxed in 5 mL of chlorobenzene for 18 hours. Once the mixture cooled to room temperature, 16 mL of hexane was added and the mixture was placed in an ice bath. After reaching 0°C, the mixture was filtered and with a clean vacuum flask the dark red powder was washed with hot THF until no more solid would dissolve. The solvent was removed under reduced pressure which afforded a dark red powder. To the dark red powder, 5 mL of THF was added. The mixture was then heated and put in ice bath. Afterwards, the mixture was filtered which afforded a bright red powder. The bright red powder was washed with hexane and dried in vacuo. Crystals of
2.1 suitable for X-ray diffraction were grown by slow evaporation of a DMSO solution.
Crystals of 2.2-2.4 and 2.6 suitable for X-ray diffraction were grown by vapor diffusion of hexane into a THF solution.
-1 C14H8ClN4O3ReS (2.1). Yield: 73 mg (49%). IR (CO stretch, cm ): 2021(s),
1906(s), 1855(vs). ESI MS (negative mode) calcd for C14H7ClN4O3ReS m/z 532.9480,
4 3 -1 -1 found 532.9484. λmax = 363 nm, ε = 1.5x10 , λmax = 435 nm, ε = 5.2x10 M cm (THF).
1 H NMR (300 MHz, d6 - DMSO): δ = 10.98 (s br, 1 H, NH), 9.30 (s br, 1 H, NH), 8.27-
8.21 (m, 1 H, α1-CH), 7.99-7.91 (m, 1 H, α2-CH), 7.88 (d, 1 H, 5-CHTh), 7.81-7.72 (m, 3
H, β,β-CH and 4-CHTh).
-1 C18H11ClN5O3Re (2.2). Yield: 51 mg (32%). IR (CO stretch, cm ): 2021(s),
1897(s), 1868(vs). ESI MS (negative mode) calcd for C18H10ClN5O3Re m/z 566.0021,
66
4 3 -1 -1 found 565.9932. λmax = 379 nm, ε = 1.4x10 , λmax = 460 nm, ε = 6.0x10 M cm (THF).
1 H NMR (300 MHz, d6 – DMSO): δ = 13.54 (s br, 1 H, NHbenz), 10.91 (s, br, 1 H, NH),
9.24 (s br, 1 H, NH), 8.31-8.24 (m, 1 H, α1-CH), 7.99-7.92 (m, 1 H, α2-CH), 7.85 (d, 1 H,
8-CHbenz) 7.82-7.73 (m, 2 H, β,β-CH), 7.52 (d, 1 H, 5-CHbenz), 7.48-7.33 (m, 2 H, 6,7-
CHbenz).
-1 C16H10ClN4O3Re (2.3). Yield: 42 mg (28%). IR (CO stretch, cm ): 2015(s),
1872(vs). ESI MS (negative mode) calcd for C16H9ClN4O3Re m/z 526.9917, found
4 3 -1 -1 1 526.9920. λmax = 352 nm, ε = 1.2x10 , λmax = 415 nm, ε = 3.6x10 M cm (THF). H
NMR (300 MHz, d6 – DMSO): δ = 10.78 (s br, 1 H, NH), 8.98 (s br, 1 H, NH), 8.95-8.81
(m, 1 H, 6-CHpy), 8.30-8.21 (m, 1 H, α1-CH), 8.20-8.05 (m, 1 H, 4-CHpy), 8.04-7.92 (m, 1
H, α2-CH), 7.91-7.72 (m, 2 H, β,β-CH), 7.71-7.58 (m, 1 H, 3-CHpy), 7.50-7.28 (m, 1 H, 5-
CHpy).
-1 C14H8BrN4O3ReS (2.4). Yield: 82 mg (57%). IR (CO stretch, cm ): 2022(s),
1907(s), 1855(vs). ESI MS (negative mode) calcd for C14H7BrN4O3ReS m/z 576.8967,
4 3 -1 -1 found 576.8976. λmax = 363 nm, ε = 1.3x10 , λmax = 440 nm, ε = 4.5x10 M cm (THF).
1 H NMR (300 MHz, d6 – DMSO): δ = 10.97 (s br, 1 H, NH), 9.21 (s br, 1 H, NH), 8.29-
8.22 (m, 1 H, α1-CH), 7.99-7.93 (m, 1 H, α2-CH), 7.90 (d, 1 H, 5-CHTh), 7.83-7.75 (m, 3
H, β,β-CH and 4-CHTh).
-1 C18H11BrN5O3Re (2.5). Yield: 60 mg (39%). IR (CO stretch, cm ): 2014(m),
1882(br). ESI MS (negative mode) calcd for C18H10BrN5O3Re m/z 609.9513, found
4 3 -1 -1 1 609.9510. λmax = 380 nm, ε = 1.2x10 , λmax = 460 nm, ε = 5.3x10 M cm (THF). H
NMR (300 MHz, d6 – DMSO): δ = 13.58 (s br, 1 H, NHbenz), 10.94 (s br, 1 H, NH), 9.26
(s br, 1 H, NH), 8.32-8.24 (m, 1 H, α1-CH), 8.01-7.94 (m, 1 H, α2-CH), 7.86 (d, 1 H, 8-
67
CHbenz), 7.83-7.73 (m, 2 H, β,β-CH), 7.54 (d, 1 H, 5-CHbenz), 7.50-7.34 (m, 2 H, 6,7-
CHbenz).
-1 C16H10BrN4O3Re (2.6). Yield: 68 mg (48%). IR (CO stretch, cm ): 2022(s),
1904(s), 1857(vs). ESI MS (negative mode) calcd for C16H9BrN4O3Re m/z 570.9404,
4 3 -1 -1 found 570.9405. λmax = 351 nm, ε = 1.3x10 , λmax = 415 nm, ε = 4.0x10 M cm (THF).
1 H NMR (300 MHz, d6 – DMSO): δ = 10.77 (s br, 1 H, NH), 9.31 (s br, 1 H, NH), 8.98-
8.85 (m, 1 H, 6-CHpy), 8.27-8.19 (m, 1 H, α1-CH), 8.18-8.07 (m, 1 H, 4-CHpy), 8.04-7.92
(m, 1 H, α2-CH), 7.87-7.72 (m, 2 H, β,β-CH), 7.71-7.60 (m, 1 H, 3-CHpy), 7.47-7.29 (m, 1
H, 5-CHpy).
Table 2.1: X-ray crystal data and structure parameters for compounds 2.1-2.3.
Compound 2.1 2.2 2.3 Empirical formula C14H8ClN4O3ReS C22H19ClN5O4Re C20H18ClN4O4Re Formula weight 533.95 639.07 600.03 Crystal system Monoclinic Triclinic Monoclinic Space group P21/n P-1 I2/a a/ Å 13.6015(8) 11.2046(10) 13.820(8) b/ Å 7.9204(5) 14.4386(14) 13.687(8) c/ Å 22.5448(13) 14.7316(13) 21.516(16) α(°) 90 68.906(3) 90 β(°) 103.904(2) 79.798(3) 93.216(5) γ(°) 90 79.828(4) 90 Volume (Å3) 2357.6(2) 2171.8(3) 4063(4) Z 4 4 8 Dc (Mg/m3) 1.504 1.955 1.962 µ (mm-1) 12.093 12.434 6.148 F(000) 1008 1240 2320 reflns collected 14156 21088 13615 indep. reflns 4014 6643 3610 GOF on F2 1.109 1.035 1.097 2 R1(on Fo ,I>2σ(I)) 0.0475 0.0245 0.0296 2 wR2(on Fo ,I>2σ(I)) 0.1270 0.0626 0.0730 R1(all data) 0.0496 0.0261 0.0333 wR2(all data) 0.1289 0.0647 0.0753
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Table 2.2: X-ray crystal data and structure parameters for compounds 2.4 and 2.6.
Compound 2.4 2.6 Empirical formula C18H16BrN4O4ReS C20H18BrN4O4Re Formula weight 650.52 644.49 Crystal system Triclinic Monoclinic Space group P-1 C2/c a/ Å 7.5308(5) 25.0765(12) b/ Å 10.2739(7) 13.8489(7) c/ Å 13.1559(9) 13.8250(8) α(°) 80.679(3) 90 β(°) 85.321(4) 120.778(2) γ(°) 89.679(4) 90 Volume (Å3) 1001.06(12) 4125.0(4) Z 2 8 Dc (Mg/m3) 2.158 2.076 µ (mm-1) 8.203 14.103 F(000) 620 2464 reflns collected 11997 11998 indep. reflns 3544 3237 GOF on F2 1.042 1.043 2 R1(on Fo ,I>2σ(I)) 0.0406 0.0258 2 wR2(on Fo ,I>2σ(I)) 0.0957 0.0623 R1(all data) 0.0450 0.0287 wR2(all data) 0.0986 0.0643
Results and Discussion
Re(CO)5X (X = Cl, Br) was reacted with one equivalent of DII and one equivalent of an amine modified heterocycle (pyridine, thiazole, or benzimidazole) in refluxing chlorobenzene or bromobenzene, depending on the halide, as shown in Scheme 2.1. Upon refluxing the mixture, the solution turned red in color. We were able to isolate the products as crystalline materials, and characterization (Figures 2.2 and 2.3) revealed that a half hemiporphyrazines, or semihemiporphyrazines, were produced via a metal-based template reaction. Five of the six compounds were elucidated by X-ray crystallography and their structures are shown in Figures 2.2 and 2.3. In all cases, the rhenium(I) ion adopts an octahedral geometry and is coordinated by a neutral bidentate semihemiporhryazine unit.
69
The remaining positions are occupied by three facially coordinated carbonyl ligands and either a bromide or a chloride ligand. The metal-nitrogen bond lengths in these complexes range from 2.148(4) Å in 2.3 to 2.216(3) Å in 2.6. Rhenium-carbonyl bond lengths are as expected for these compounds, ranging from 1.900(6) Å in 2.3 to 1.944(8) Å in 2.1. The rhenium-halide bond lengths are observed to be ~2.62 Å and ~2.49 Å for the bromide and chloride variants respectively. All are comparable to lengths seen in compounds such as
268,269 (bpy)Re(CO)3Cl and (6,6’-Me2bpy)Re(CO)3Br. The mean plane of the semihemiporphyrazine ligand tilts in relation to the CCO-Re-CCO plane by ~28ᵒ in 2.1 to
~35ᵒ in 2.2 which are similar to the tilts found in tricarbonyl rhenium(I) azadipyrromethene complexes and transition metal dipyrrinato complexes.246,247,270,271 The terminal amine carbon-nitrogen bond lengths vary from 1.289(8) Å in 2.1 to 1.312(7) Å in 2.3, which are longer than the carbon-nitrogen double bond lengths (1.222(7) Å to 1.249(10) Å) found in
236 the recently synthesized Re(CO)3 templated aza(dibenzopyrro)methenes.
Scheme 2.1: Synthesis of semihemiporphyrazines.
70
Figure 2.2: X-ray structure of 2.1 (left) and 2.4 (right) with 35% thermal ellipsoids. Hydrogen atoms except on the terminal amines and solvent molecules have been omitted for clarity.
Figure 2.3: X-ray structure of 2.2 (top), 2.3 (bottom left), and 2.6 (bottom right) with 35% thermal ellipsoids. Hydrogen atoms except on the terminal amines and solvent molecules have been omitted for clarity.
71
As expected for Re(I)(CO)3 compounds, the semihemiporphyrazine complexes are diamagnetic and can be characterized by NMR even though their solubilities can be limited
(Figures 2.4-2.6 for 2.1-2.3). In the 1H NMR spectrum, we observed the complex splitting of the isoindoline resonances that Brӧring noted with the asymmetric BPI-type chelates.248
Additionally, we observed two resonances for the terminal amine at ~10.90 and ~9.30 ppm for each compound. In the IR spectra, the Re(CO)3 unit shows a1- and e-type CO stretches produced by the pseudo C3V environment of the facial carbonyls units with frequencies that range from ~2014 to 2022 cm-1 and from ~1855 to 1907 cm-1, respectively. The semihemiporphyrazines absorb light in the visible region and their UV-visible spectra in
THF are shown for compounds 2.1-2.3 in Figure 2.7. Each compound exhibits a band above 400 nm and a band near 360 nm. The bands can be characterized as predominantly ligand based π-π* and predominantly metal-to-ligand charge transfer (MLCT) transitions
236,241,242,260,268 respectively, which are seen with other Re(CO)3 compounds. The extinction coefficients for the semihemiporphyrazines’ MLCT bands are observed to be between 3600 and 6000 M-1cm-1 (Figure 2.7). In all cases, solvatochromic effects in the low-energy bands can be clearly seen, confirming their predominantly MLCT character.
72
β, β, 4-CHTh
5-CHTh 5-CHTh α1 4-CHTh
β α1 α2 β α2 *
0.98 1.02 0.98 2.97
8.40 8.35 8.30 8.25 8.20 8.15 8.10 8.05 8.00 7.95 7.90 7.85 7.80 7.75 7.70 7.65 7.60 Chemical Shift (ppm)
* * *
*
0.57 0.68 0.98 1.02 0.98 2.97
13 12 11 10 9 8 7 6 5 4 3 2 1 0 Chemical Shift (ppm)
1 Figure 2.4: H NMR spectrum (300 MHz) of 2.1 in d6 – DMSO. * represents residual THF, DMSO, DCM, and H2O.
73
β, β
8-CHbenz 5-CHbenz 8-CHbenz 6,7-CH benz α2 6,7-CHbenz α1 α1
5-CHbenz β
α β 2
1.02 1.17 1.36 1.83 1.13 2.16
8.5 8.4 8.3 8.2 8.1 8.0 7.9 7.8 7.7 7.6 7.5 7.4 7.3 7.2 Chemical Shift (ppm) *
*
*
*
0.69 0.79 0.92 1.02 1.17 1.36 1.83 1.13 2.16
13 12 11 10 9 8 7 6 5 4 3 2 1 0 Chemical Shift (ppm)
1 Figure 2.5: H NMR spectrum (300 MHz) of 2.2 in d6 – DMSO. * represents residual THF, DMSO, and H2O.
74
6-CH py 5-CHpy α1
4-CHpy β
α 3-CHpy β 2 β, β *
α1 6-CHpy 5-CHpy α2 3-CHpy
0.94 0.98 1.19 1.02 2.00 0.71 0.82
8.9 8.8 8.7 8.6 8.5 8.4 8.3 8.2 8.1 8.0 7.9 7.8 7.7 7.6 7.5 7.4 7.3 Chemical Shift (ppm)
* * *
0.55 0.72 0.94 0.98 1.191.02 2.00 0.71 0.82
13 12 11 10 9 8 7 6 5 4 3 2 1 0 Chemical Shift (ppm)
1 Figure 2.6: H NMR spectrum (300 MHz) of 2.3 in d6 – DMSO. * represents residual THF, DMSO, and H2O.
75
Figure 2.7: Experimental (top) and TDDFT-predicted (bottom) UV-visible spectra for compounds 2.1-2.3.
76
We carried out DFT and TDDFT calculations on compounds 2.1-2.6. The structures of the frontier orbitals (LUMO, HOMO, HOMO-1, and HOMO-2) for compounds 2.1-2.6 can be seen in Figure 2.8. The LUMO orbitals are primarily ligand π antibonding in character, the HOMOs have mixed ligand and metal orbital character, and the HOMO-1 orbitals are clearly d orbital based. The energy levels of the frontier orbitals for 2.1-2.6 are also shown in the Figure 2.8; the LUMO is well separated from other unoccupied orbitals, and the HOMO and HOMO-1 are close in energy. The HOMO- LUMO gaps range between ~5.16 to ~5.42 eV for 2.1-2.3. Compounds 2.4-2.6 exhibit identical trends as seen for the chloride compounds; the HOMO-LUMO gaps in 2.4-2.6 are slightly less than in
2.1-2.3. We were able to calculate the excited state energies of the semihemiporphyrazine compounds using TDDFT methods; the predicted spectra for compounds 2.1-2.3 are shown along with the observed spectra in Figure 2.7. The bromides variants exhibit identical behavior. The two TDDFT-predicted excited states with the highest oscillator strengths correlate well with two major UV-visible absorption bands and can be characterized as predominantly HOMO to LUMO transitions and predominantly HOMO-2 to LUMO transitions for the bands above and below 400 nm, respectively.
77
Figure 2.8: Top: The DFT-predicted energies of the frontier orbitals of compounds 2.1-2.6. Bottom: The representative examples of frontier orbitals for 2.1-2.6.
78
Conclusions
In conclusion, we have shown that half hemiporphyrazines compounds
“semihemiporphyrazines” can be produced by condensing one equivalent of DII and an amino heterocycle with Re(CO)5X as a templating agent. The UV-visible absorption spectra of the products show MLCT-type absorptions comparable to other Re(CO)3 diimine complexes. The elucidated X-ray crystal structures of the semihemiporphyrazines show that the ligand tilts out of the plane of coordination and that the terminal amine carbon- nitrogen bond is longer than the recently synthesized Re(CO)3 templated aza(dibenzopyrro)methenes. We are continuing our work on developing new template reactions for isoindoline and Schiff base chelates including structures similar to the ¾ of a hemiporphyrazine comprised of two isoindoline units and one pyridyl unit proposed by
Elvidge.272 Similar compounds, incorporating benzene rather than pyridine, can be synthesized without a template.106
79
CHAPTER III
Re(CO)3-TEMPLATED SYNTHESIS OF α-
AMIDINOAZADI(BENZOPYRRO)METHENES
The text of this chapter is a reprint of the material as it appears in: Allen J. Osinski,
Daniel L. Morris, Richard S. Herrick, and Christopher J. Ziegler. Inorg. Chem., 2017, 56
(24), 14734–14737. Copyright © 2017, American Chemical Society.
DOI: 10.1021/acs.inorgchem.7b02140
Introduction
The unusual chemistry of the Re(I)(CO)3 fragment continues to attract significant attention in inorganic synthesis.273–278 This interest arises from both its notable properties as a non-labile unit with a rigid facial geometry as well as its use as a synthon for a wide
240–242,260 variety of functional inorganic complexes. Recently, we have used the Re(CO)3 moiety as a template to produce isoindoline based chelates that can be considered as half of a phthalocyanine or a hemiporphyrazine (a “semihemiporphyrazine”) (Figure 3.1).234,236
The limited geometry options and inert nature of this metal unit in both cases prevent larger macrocycles or chelates from forming. In our continuing studies on the templating behavior of the Re(CO)3 unit, we have uncovered a new nitrile-activating reaction that
80
affords an α-amidino azadi(benzopyrro)methene (A3DBM) which is a tridentate complex that has similar connectivity to the “helmet” and bicyclic phthalocyanines (Figure
3.1).190,193,196,197,279–283 In these reactions, two equivalents of diiminoisoindoline (DII) react with Re(CO)5X to produce a bis-isoindoline ligand with an appended amidine; the template reaction adds a nitrile-derived “tail” to the axial position.
3 Figure 3.1: Re(CO)3 A DBM and related compounds.
The activation of a nitrile to undergo nucleophilic attack at the Re(CO)3 unit has been previously observed. Recently, Marzilli et al. have activated a bound acetonitrile ligand on rhenium(I)(diimine) tricarbonyl complexes with various amines and alcohols.212–
214 The nucleophiles attack the carbon of the nitrile, forming a new C-N bond followed by an intramolecular proton transfer to complete the reaction. Similarly, Riera et al. reacted
Re(CO)3(CH3CN)2(ClO4) with pyrazoles in refluxing acetonitrile affording pyrazolylamidino complexes where the pyrazoles attacked a rhenium-bound acetonitrile.216 Additionally, Bengali et al. reacted rhenium(I)(β-diimine) tricarbonyl complexes with nitriles where the diimine ligand attacks the nitrile after it binds to the rhenium. The reaction forms a new C-C bond followed by proton transfer to the cyano nitrogen.284
81
In addition to the Re(CO)3-unit, other transition metal containing compounds have been used to activate nitriles at an sp carbon position. Kukushkin et al. has shown that aryl ketonitrones can activate platinum bound nitriles to form oxadiazoles via 1,3-dipolar cycloaddition;285 Pombeiro and coworkers have shown similar reactions to occur with palladium.286 Additionally, Cho et al. has shown that a peroxocobalt(III) complex can activate nitriles to form hydroximatocobalt(III) complexes via oxidation by the peroxo group while Lee and coworkers have activated nitriles using a Ni(II)-(2- mercaptophenyl)phosphine complex to form a thioiminium moiety by nucleophilic attack of a thiol.287,288
Experimental
General Information
All reagents and starting materials were purchased from commercial vendors and used without further purification. 1,3-diiminoisoindoline (DII) was synthesized according to a previously published procedure.261 Deuterated solvents were purchased from
Cambridge Isotope Laboratories and used as received.
NMR spectra were recorded on a 750 MHz and a 500 MHz spectrometer and chemical shifts were given in ppm relative to residual solvent resonances (1H NMR and
13C NMR spectra). High resolution mass spectrometry experiments were performed on a
Bruker MicroTOF-III instrument. Infrared spectra were collected on Thermo Scientific
Nicolet iS5 which was equipped with an iD5 ATR.
X-ray intensity data were measured on a Bruker CCD-based diffractometer with dual Cu/Mo ImuS microfocus optics (Cu Kα radiation, λ = 1.54178 Å, Mo Kα radiation, λ
=0.71073 Å). Crystals were mounted on a cryoloop using Paratone oil and placed under a
82
steam of nitrogen at 100 K (Oxford Cryosystems). The detector was placed at a distance of
5.00 cm from the crystal. The data were corrected for absorption with the SADABS program. The structures were refined using the Bruker SHELXTL Software Package
(Version 6.1) and were solved using direct methods.
Syntheses
Synthesis of 3.1-3.8. The procedure for generating 3.1 is representative for these syntheses except propionitrile is used for the solvent in 3.2 and 3.7, butyronitrile is used for the solvent in 3.3 and 3.8, cyclohexanecarbonitrile is used for solvent in 3.4, and benzonitrile is used for the solvent in 3.5. Additionally, the reactions to make 3.6-3.8 employ Re(CO)5Br (0.25 mmol). Re(CO)5Cl (0.28 mmol), DII (0.56 mmol), and 8 mL of the nitrile were mixed together and heated to 70ᵒC for 18 hrs. After cooling to room temperature, the mixture was filtered through a fine frit and washed with acetonitrile, hexane, and Et2O to afford a yellow powder. The powder was dissolved in a minimal amount of DMF and gravity filtered to remove small insoluble particulates. Afterwards,
Et2O was added to the solution until a yellow precipitate formed. The solution was decanted and the solid was washed with Et2O then placed in the vacuum oven. Crystals suitable for
X-ray diffraction were grown by vapor diffusion of Et2O into a DMF solution.
Synthesis of 3.9-3.10. The procedure for generating 3.9 is the same as 3.10 except for 3.10 benzonitrile is used for the solvent and 0.12 mmol of AgNO3 was added in 3.10.
Re(CO)5Br (0.25 mmol), DII (0.50 mmol), and 8 mL of cyclohexanecarbonitrile were mixed together and heated to 70ᵒC for 18 hrs. After cooling to room temperature, the mixture was filtered through a fine frit and washed with acetonitrile, hexane, and Et2O to afford a yellow powder. The powder was dissolved in a minimal amount of DMF and
83
gravity filtered to remove small insoluble particulates. AgNO3 (0.14 mmol) was added to solution and the reaction was allowed to stir for 18 hrs. The mixture was filtered to remove
AgBr then Et2O was added to the solution until a yellow ppt formed. The solution was decanted and the solid was washed with Et2O then placed in the vacuum oven. Crystals suitable for X-ray diffraction were grown by vapor diffusion of Et2O into a DMF solution.
-1 C21H17ClN7O3Re (3.1). Yield: 68 mg (38%). IR (CO stretch, cm ): 2007(s),
1889(br, vs). IR (amidine stretch, cm-1): 1635(s). ESI MS (positive mode) calcd
1 C21H17N7O3Re 602.0923 m/z, found 602.0916. H NMR (750 MHz, d6 - DMSO): δ = 10.35
(s br, 1H, NH), 9.20 (s, 1H, amidine NH-Re), 9.17 (s br, 1H, NH), 8.46 (s br, 1H, NH),
8.30-8.26 (m, 1H, α1), 8.17 (d, 1H, α3), 8.12 (s, 1H, amidine -NH-), 8.05 (d, 1H, α4), 7.78
(t, 1H, β3), 7.74-7.71 (m, 1H, α2), 7.68-7.63 (m, 3H, β1, β2, β4), 7.28 (s br, 1H, NH), 2.06
13 (s, 3H, 1). C NMR (500 MHz, d6 – DMSO): δ = 196.36 (CO), 196.12 (CO), 195.54 (CO),
170.27 (8), 164.92 (1), 164.92 (16), 156.76 (17), 148.31 (10), 138.11 (15), 132.96 (7),
132.06 (4), 131.82 (12), 131.62 (14), 130.14 (5), 129.30 (6), 124.15 (3), 122.59 (11),
122.22 (13), 121.57 (2), 86.45 (9), 21.97 (18).
-1 C22H19ClN7O3Re (3.2). Yield: 65 mg (35%). IR (CO stretch, cm ): 2006(s),
1899(br, vs). IR (amidine stretch, cm-1): 1635(s). ESI MS (positive mode) calcd
1 C22H19N7O3Re 616.1079 m/z, found 616.0867. H NMR (750 MHz, d6 - DMSO): δ = 10.34
(s br, 1H, NH), 9.18 (s, 1H, amidine NH-Re), 9.16 (s br, 1H, NH), 8.45 (s br, 1H, NH),
8.28-8.25 (m, 1H, α1), 8.17 (d, 1H, α3), 8.06-8.02 (m, 2H, α4, amidine -NH-), 7.78 (t, 1H,
β3), 7.73-7.71 (m, 1H, α2), 7.68-7.63 (m, 3H, β1, β2, β4), 7.28 (s br, 1H, NH), 2.36-2.27 (m,
13 2H, 1), 1.02 (t, 3H, 2). C NMR (500 MHz, d6 – DMSO): δ = 196.32 (CO), 196.14 (CO),
195.63 (CO), 170.24 (8), 170.15 (1), 164.82 (16), 156.79 (17), 148.19 (10), 138.18 (15),
84
132.95 (7), 132.08 (4), 131.80 (12), 131.59 (14), 130.16 (5), 129.40 (6), 124.29 (3), 122.55
(11), 122.20 (13), 121.49 (2), 86.55 (9), 29.05 (18), 12.48 (19).
-1 C23H21ClN7O3Re (3.3). Yield: 70 mg (37%). IR (CO stretch, cm ): 2010(s),
1905(s), 1860(vs). IR (amidine stretch, cm-1): 1652(s). ESI MS (positive mode) calcd
1 C23H21N7O3Re 630.1235 m/z, found 630.1168. H NMR (750 MHz, d6 - DMSO): δ = 10.35
(s br, 1H, NH), 9.16 (s br, 2H, amidine NH-Re, NH), 8.45 (s br, 1H, NH), 8.29-8.24 (m,
1H, α1), 8.17 (d, 1H, α3), 8.08-8.02 (m, 2H, amidine -NH-, α4), 7.77 (t, 1H, β3), 7.73-7.70
(m, 1H, α2), 7.68-7.63 (m, 3H, β1, β2, β4), 7.28 (s br, 1H, NH), 2.35-2.24 (m, 2H, 1), 1.55-
13 1.43 (m, 2H, 2), 0.76 (t, 3H, 3). C NMR (500 MHz, d6 – DMSO): δ = 196.34 (CO), 196.16
(CO), 195.62 (CO), 170.23 (8), 168.73 (1), 164.81 (16), 156.86 (17), 148.16 (10), 138.16
(15), 133.00(7), 132.08 (4), 131.79(12), 131.58 (14), 130.17 (5), 129.42 (6), 124.34 (3),
122.59 (11), 122.21 (13), 121.46 (2), 86.59 (9), 37.15 (18), 20.82 (19), 12.71 (20).
-1 C26H25ClN7O3Re (3.4). Yield: 54 mg (28%). IR (CO stretch, cm ): 2008(s),
1901(s), 1868(vs). IR (amidine stretch, cm-1): 1645(s). ESI MS (positive mode) calcd
1 C26H25N7O3Re 670.1548 m/z, found 670.1514. H NMR (750 MHz, d6 - DMSO): δ = 10.39
(s br, 1H, NH), 9.18 (s br, 1H, NH), 9.01 (s, 1H, amidine NH-Re), 8.40 (s br, 1H, NH),
8.31-8.26 (m, 1H, α1), 8.18 (d, 1H, α3), 8.05 (d, 1H, α4), 7.77 (t, 1H, β3), 7.74-7.69 (m, 1H,
α2), 7.67-7.63 (m, 3H, β1, β2, β4), 7.26 (s br, 1H, NH), 2.44-2.36 (m, 1H, 1), 1.74-1.64 (m,
2H, 2), 1.63-1.54 (m, 2H, 3), 1.53-1.43 (m, 3H, 4), 1.18-1.07 (m, 3H, 5). 13C NMR (500
MHz, d6 – DMSO): δ = 196.12 (2 CO), 195.69 (CO), 172.54 (8), 170. 23 (1), 164.79 (16),
156.82 (17), 148.08 (10), 138.27 (15), 132.96 (7), 132.15 (4), 131.72 (12), 131.59 (14),
130.18 (5), 129.49 (6), 124.52 (3), 122.55 (11), 122.17 (13), 121.44 (2), 86.79 (9), 44.71
(18), 28.84 (19), 28.76 (20), 25.53 (21), 25.33 (22), 24.76 (23).
85
-1 C26H19ClN7O3Re (3.5). Yield: 74 mg (37%). IR (CO stretch, cm ): 2011(s),
1877(br, vs). IR (amidine stretch, cm-1): 1645(s). ESI MS (positive mode) calcd
1 C26H19N7O3Re 664.1079 m/z, found 664.0959. H NMR (750 MHz, d6 - DMSO): δ = 10.39
(s br, 1H, NH), 9.60 (s, 1H, amidine NH-Re), 9.21 (s br, 1H, NH), 8.56 (s, 1H, amidine -
NH-), 8.46 (s br, 1H, NH), 8.31-8.25 (m, 1H, α1), 8.18 (d, 1H, α3), 8.14 (d, 1H, α4), 7.79-
7.73 (m, 2H, α2, β3), 7.70-7.63 (m, 3H, β1, β2, β4), 7.56-7.52 (m, 1H, 1), 7.51-7.47 (m, 2H,
13 2), 7.47-7.42 (m, 2H, 3), 7.34 (s br, 1H, NH). C NMR (500 MHz, d6 – DMSO): δ = 196.14
(CO), 195.78 (CO), 195.66 (CO), 170.36 (8), 165.37 (1), 164.97 (16), 157.22 (17), 147.96
(10), 138.23 (15), 133.67 (21), 133.00 (7), 132.12 (4), 131.69 (12), 131.64 (14), 131.40
(18), 130.40 (18), 130.15 (5), 129.48 (6), 128.13 (20), 127.94 (19), 124.88 (3), 122.59 (11),
122.06 (13), 121.55 (2), 87.17 (9).
-1 C21H17BrN7O3Re (3.6). Yield: 46 mg (27%). IR (CO stretch, cm ): 2007(s),
1895(br, vs). IR (amidine stretch, cm-1): 1635(s). ESI MS (positive mode) calcd
1 C21H17N7O3Re 602.0923 m/z, found 602.0925. H NMR (750 MHz, d6 - DMSO): δ = 10.18
(s br, 1H, NH), 9.15 (s, 1H, amidine NH-Re), 9.07 (s br, 1H, NH), 8.47 (s br, 1H, NH),
8.21-8.16 (m, 1H, α1), 8.15-8.10 (m, 2H, amidine -NH-, α3), 8.04 (d, 1H, α4), 7.78 (t, 1H,
β3), 7.75-7.70 (m, 1H, α2), 7.9-7.64(m, 3H, β1, β2, β4), 7.29 (s br, 1H, NH), 2.05 (s, 3H, 1).
13 C NMR (500 MHz, d6 – DMSO): δ = 196.38 (CO), 196.15 (CO), 195.55 (CO), 170.23
(8), 164.89 (1), 164.81 (16), 156.80 (17), 148.36 (10), 138.14 (15), 132.91 (7), 132.10 (4),
131.83 (12), 131.60 (14), 130.17 (5), 129.28 (6), 124.13 (3), 122.35 (11), 122.12 (13),
121.57 (2), 86.39 (9), 22.03 (18).
-1 C22H19BrN7O3Re (3.7). Yield: 59 mg (34%). IR (CO stretch, cm ): 2011(s),
1873(br, vs). IR (amidine stretch, cm-1): 1634(s). ESI MS (positive mode) calcd
86
1 C22H19N7O3Re 616.1079 m/z, found 616.0866. H NMR (750 MHz, d6 - DMSO): δ = 10.17
(s br, 1H, NH), 9.14 (s, 1H, amidine NH-Re), 9.05 (s br, 1H, NH), 8.46 (s br, 1H, NH),
8.20-8.16 (m, 1H, α1), 8.12 (d, 1H, α3), 8.08-8.00 (m, 2H, amidine -NH-, α4), 7.78 (t, 1H,
β3), 7.75-7.70 (m, 1H, α2), 7.69-7.63 (m, 3H, β1, β2, β4), 7.30 (s br, 1H, NH), 2.36-2.25 (m,
13 2H, 1), 1.02 (t, 3H, 2). C NMR (500 MHz, d6 – DMSO): δ = 196.35 (CO), 196.18 (CO),
195.66 (CO), 170.21 (8), 170.09 (1), 164.78 (16), 156.84 (17), 148.22 (10), 138.21 (15),
132.90 (7), 132.16 (4), 131.81 (12), 131.58 (14), 130.19 (5), 129.38 (6), 124.25 (3), 122.33
(11), 122.09 (13), 121.49 (2), 86.59 (9), 28.98 (18), 12.50 (19).
-1 C23H21BrN7O3Re (3.8). Yield: 55 mg (31%). IR (CO stretch, cm ): 2011(s),
1910(s), 1868(vs). IR (amidine stretch, cm-1): 1651(s). ESI MS (positive mode) calcd
1 C23H21N7O3Re 630.1235 m/z, found 630.1177. H NMR (750 MHz, d6 - DMSO): δ = 10.17
(s br, 1H, NH), 9.11 (s, 1H, amidine NH-Re), 9.05 (s br, 1H, NH), 8.45 (s br, 1H, NH),
8.20-8.15 (m, 1H, α1), 8.12 (d, 1H, α3), 8.06 (s, 1H, amidine -NH-), 8.03 (d, 1H, α4), 7.78
(t, 1H, β3), 7.73-7.70 (m, 1H, α2), 7.69-7.64 (m, 3H, β1, β2, β4), 7.30 (s br, 1H, NH), 2.34-
13 2.23 (m, 2H, 1), 1.54-1.42 (m, 2H, 2), 0.76 (t, 3H, 3). C NMR (500 MHz, d6 – DMSO):
δ = 196.35 (CO), 196.18 (CO), 195.64 (CO), 170.22 (8), 168.70 (1), 164.76 (16), 156.90
(17), 148.18 (10), 138.16 (15), 132.91 (7), 132.10 (4), 131.79 (12), 131.60 (14), 130.17 (5),
129.40 (6), 124.27 (3), 122.34 (11), 122. 11 (13), 121.46 (2), 86.59 (9), 37.17 (18), 20.89
(19), 12.65 (20).
-1 C26H25N8O6Re (3.9). Yield: 12 mg (7%). IR (CO stretch, cm ): 2011(s), 1912(s),
1879(vs). IR (amidine stretch, cm-1): 1652(s). ESI MS (positive mode) calcd
1 C26H25N7O3Re 670.1548 m/z, found 670.1470. H NMR (500 MHz, d6 - DMSO): δ = 10.16
(s br, 1H, NH), 9.03 (s br, 1H, NH), 8.97 (s, 1H, amidine NH-Re), 8.43 (s br, 1H, NH),
87
8.19-8.15 (m, 1H, α1), 8.10 (d, 1H, α3), 8.04 (d, 1H, α4), 7.78 (t, 1H, β3), 7.74-7.71 (m, 1H,
α2), 7.68-7.64 (m, 3H, β1, β2, β4), 7.30 (s br, 1H, NH), 2.40-2.34 (m, 1H, 1), 1.72-1.65 (m,
2H, 2), 1.63-1.55 (m, 2H, 3), 1.52-1.44 (m, 3H, 4), 1.18-1.08 (m, 3H, 5). 13C NMR (500
MHz, d6 – DMSO): δ = 196.08 (2 CO), 195.64 (CO), 172.52 (8), 170.23 (1), 164.78 (16),
156.75 (17), 148.00 (10), 138.20 (15), 133.00 (7), 132.03 (4), 131.73 (12), 131.65 (14),
130.21 (5), 129.49 (6), 124.50 (3), 122.31 (11), 122.01 (13), 121.50 (2), 86.79 (9), 44.76
(18), 28.82 (19), 28.75 (20), 25.53 (21), 25.32 (22), 24.75 (23).
-1 C26H19N8O6Re (3.10). Yield: 21 mg (12%). IR (CO stretch, cm ): 2010(s), 1872(br,
-1 vs). IR (amidine stretch, cm ): 1653(s). ESI MS (positive mode) calcd C26H19N7O3Re
1 664.1079 m/z, found 664.1107. H NMR (500 MHz, d6 - DMSO): δ = 10.20 (s br, 1H, NH),
9.59 (s, 1H, amidine NH-Re), 9.08 (s br, 1H, NH), 8.56 (s, 1H, amidine -NH-), 8.47 (s br,
1H, NH), 8.21-8.17 (m, 1H, α1), 8.15 (d, 1H, α3), 8.12 (d, 1H, α4), 7.79-7.73 (m, 2H, α2,
β3), 7.70-7.64 (m, 3H, β1, β2, β4), 7.56-7.52 (m, 1H, 1), 7.51-7.48 (m, 2H, 2), 7.47-7.43 (m,
13 2H, 3), 7.35 )s br, 1H, NH). C NMR (500 MHz, d6 – DMSO): δ = 196.15 (CO), 195.76
(CO), 195.65 (CO), 170.38 (8), 165.38 (1), 164.96 (16), 157.14 (17), 147.96 (10), 138.21
(15), 133.64 (21), 133.02 (7), 132.06 (4), 131.71 (12), 131.70 (14), 131.41 (18), 130.20 (5),
129.47 (6), 128.14 (20), 127.93 (19), 124.90 (3), 122.36 (11), 121.91 (13), 121.59 (2),
87.16 (9).
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Table 3.1: X-ray crystal data and structure parameters for compounds 3.1-3.3.
Compound 3.1 3.2 3.3 Empirical formula C30H38ClN10O6Re C31H40ClN10O6Re C29H35ClN9O5Re Formula weight 856.35 870.38 811.31 Crystal system Triclinic Triclinic Triclinic Space group P-1 P-1 P-1 a/ Å 11.9846(13) 11.9969(8) 11.9524(7) b/ Å 12.2128(13) 12.2558(8) 12.2255(6) c/ Å 14.2147(16) 14.1455(10) 14.5199(8) α(°) 65.187(4) 65.955(4) 65.623(3) β(°) 72.517(4) 73.288(4) 86.237(3) γ(°) 63.826(4) 64.804(4) 63.657(2) Volume (Å3) 1677.8(3) 1702.2(2) 1713.82(17) Z 2 2 2 Dc (Mg/m3) 1.695 1.698 1.572 µ (mm-1) 3.760 3.707 3.673 F(000) 856 872 808 reflns collected 65623 43268 28891 indep. reflns 5951 8213 8467 GOF on F2 1.111 1.065 0.984 2 R1(on Fo ,I>2σ(I)) 0.0220 0.0523 0.0559 2 wR2(on Fo ,I>2σ(I)) 0.0550 0.1196 0.1261 R1(all data) 0.0232 0.0719 0.0696 wR2(all data) 0.0557 0.1276 0.1328
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Table 3.2: X-ray crystal data and structure parameters for compounds 3.5-3.7.
Compound 3.5 3.6 3.7 Empirical formula C32H33ClN9O5Re C21H17BrN7O3Re C22H19BrN7O3Re Formula weight 845.32 681.53 695.55 Crystal system Monoclinic Triclinic Triclinic Space group P21/c P-1 P-1 a/ Å 11.8894(5) 11.9475(12) 11.3325(7) b/ Å 12.5424(6) 12.4778(12) 12.1328(6) c/ Å 23.4462(11) 14.2234(14) 13.0606(7) α(°) 90 64.865(5) 85.193(4) β(°) 95.244(2) 72.151(5) 83.365(4) γ(°) 90 63.474(5) 80.783(4) Volume (Å3) 3481.7(3) 1699.6(3) 1756.80(17) Z 4 2 2 Dc (Mg/m3) 1.613 1.332 1.315 µ (mm-1) 3.620 4.776 4.622 F(000) 1680 652 668 reflns collected 87185 56002 31910 indep. reflns 8747 8574 8751 GOF on F2 1.053 1.010 0.900 2 R1(on Fo ,I>2σ(I)) 0.0475 0.0488 0.0507 2 wR2(on Fo ,I >2σ(I)) 0.0907 0.1068 0.1003 R1(all data) 0.0799 0.0631 0.0825 wR2(all data) 0.0995 0.1113 0.1083
90
Table 3.3: X-ray crystal data and structure parameters for compounds 3.8-3.10.
Compound 3.8 3.9 3.10 Empirical formula C23H21BrN7O3Re C38H53N12O10Re C32H33N10O8Re Formula weight 709.58 1024.12 871.88 Crystal system Triclinic Triclinic Monoclinic Space group P-1 P-1 P21/c a/ Å 11.7984(3) 12.2733(10) 11.0375(5) b/ Å 12.1082(3) 12.2807(11) 26.7858(12) c/ Å 13.0157(4) 15.7207(14) 12.4180(6) α(°) 86.035(2) 107.188(6) 90 β(°) 82.409(2) 102.917(5) 109.646(2) γ(°) 82.220(2) 95.887(6) 90 Volume (Å3) 1823.64(9) 2169.9(3) 3457.6(3) Z 2 2 4 Dc (Mg/m3) 1.292 1.567 1.675 µ (mm-1) 4.454 2.869 3.580 F(000) 684 1040 1736 reflns collected 32588 37058 60732 indep. reflns 8962 10750 8623 GOF on F2 0.918 1.009 1.072 2 R1(on Fo ,I>2σ(I)) 0.0464 0.0610 0.0490 2 wR2(on Fo ,I>2σ(I)) 0.0854 0.1401 0.1077 R1(all data) 0.0731 0.0936 0.0816 wR2(all data) 0.0909 0.1584 0.1217
Results and Discussion
In our work, Re(CO)5X (X = Cl, Br) was reacted with two equivalents of DII and an excess of a nitrile (acetonitrile, propionitrile, butyronitrile, cyclohexanecarbonitrile, and benzonitrile) as the solvent. Scheme 3.1 shows the reactions and the structures of the
3 resultant yellow crystalline Re(CO)3 A DBM products. All compounds were characterized via spectroscopic methods and elucidated by single crystal X-ray diffraction.
Characterization revealed that nitrile activation occurred which afforded a neutral tridentate A3DBM ligand where one DII sp2 carbon was converted to a sp3 carbon interrupting conjugation through the bis-DII fragment. Similar conversions have been seen in the “helmet” and bicyclic phthalocyanines.190,193,196,197,279–283 The structures of
91
compounds 3.1-3.3, 3.5, and 3.9 are shown in Figures 3.2 and 3.3. In all cases, the rhenium(I) ion adopts an octahedral geometry and is coordinated by a neutral tridentate
A3DBM ligand and the remaining positions are occupied by the expected three facially coordinated carbonyl ligands. The tridentate A3DBM ligand is neutral, and in all cases charge balance is provided by a non-coordinating anion. The two isoindoline units form a bidentate fragment similar to the systems we observed upon the templated reaction of
236,259 diiminoisoindoline with Re(CO)5X and BPh3. The axial ligand is composed of an amidine produced from activation of the nitrile solvent.
3 Scheme 3.1: Synthesis of Re(CO)3 A DBM complexes.
92
Figure 3.2: Elucidated X-ray structures of compounds 3.1 (left), 3.2 (middle), and 3.3 (right) with 35% thermal ellipsoids. Anions, solvent molecules, and hydrogen atoms except on nitrogen atom positions have been omitted for clarity.
Figure 3.3: Elucidated X-ray structures of compounds 3.9 (left) and 3.5 (right) with 35% thermal ellipsoids. Anions, solvent molecules, and hydrogen atoms except on nitrogen atom positions have been omitted for clarity.
93
From the reactions with Re(CO)5X and from additional chemical methodologies
(vide infra), nine products (3.1-3.3 and 3.5-3.10) were elucidated by X-ray crystallography.
The metal-nitrogenDII bond lengths are ~2.15 Å while the metal nitrogenamidino bond lengths are also ~2.15 Å. Rhenium-carbonyl bond lengths are ~1.92 Å which are similar to those seen in rhenium(I)(diimine) tricarbonyl complexes.268,269 The mean plane of the DII
3 ᵒ moieties in the A DBM ligand tilts in relation to the CCO-Re-CCO plane by ~36 which is similar to the tilts seen in the semihemiporphyrazines and other transition metal containing azadipyrromethene complexes.234,246,247,270,271 The terminal amine and carbonyl oxygen distances are ~3.5 Å or longer, indicating hydrogen bonding is not present and the tilt is due to other effects. The terminal amine carbon-nitrogen bond lengths are ~1.31 Å which is longer than the carbon-nitrogen double bonds in the Re(CO)3-templated aza(dibenzopyrro)methenes and are comparable to the single bond terminal amine carbon- nitrogen bond lengths in the semihemiporphyrazines.234,236 Additionally, the double bonds of the axial amidines are ~1.29 Å, whereas the single bonds of these groups are ~1.35 Å.
The bond lengths of the amidines are consistent with those observed in the work of Marzilli et al. and Riera et al.212–214,216
3 As in other rhenium tricarbonyl complexes, the Re(CO)3 A DBM complexes are diamagnetic and were characterized by NMR even though their solubilities are very limited
(Figures 3.4-3.8 for 1H NMR and Figures 3.9-3.13 for 13C NMR of compounds 3.1-3.5).
In the 1H spectrum, we observed complex splitting of the DII moieties, one DII moiety had resonances similar to that which Kleeberg and Bröring noted with the asymmetric BPI- type chelates, while the other DII moiety differed due to the presence of the amidine group.248 Additionally, we observed four broad resonances for the terminal amines at
94
~10.20, ~9.10, ~8.45, and ~7.25 ppm while we typically observed two strong resonances for the amidine at ~9.20 and ~8.10 ppm except for 3.4 and 3.9 which only had one amidine resonance. In the IR spectra, the Re(CO)3 unit shows a1- and e-type CO stretches produced by the pseudo-C3v environment of the facial carbonyl units with frequencies that range from
∼2006 to 2011 cm−1 and from ∼1872 to 1912 cm−1, respectively. Furthermore, the amidine shows a strong stretch with frequencies that range from ~1634 cm-1 to 1653 cm-1.
1
β2 β4 α2 α4
β1 β3
α1 α3
β1, β2, β4
α3 β3 α4 α1 α2 *
*
1.00 1.01 0.98 0.86 0.95 0.85 2.64
8.30 8.25 8.20 8.15 8.10 8.05 8.00 7.95 7.90 7.85 7.80 7.75 7.70 7.65 7.60 Chemical Shift (ppm) *
* *
* *
1.06 2.14 1.10 1.00 1.01 0.98 0.86 0.95 0.85 2.64 1.05 2.82
10.0 9.5 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 Chemical Shift (ppm)
1 Figure 3.4: H NMR spectrum (750 MHz) of 3.1 in d6 – DMSO. * represents residual DMSO, DMF, H2O, and Et2O.
95
2
1
β2 α2 α4 β4
β1 β3
α1 α3
β1, β2, β4 α4 β4
α3 α4 β3 * α1 α2
* *
1.00 1.02 1.94 0.98 0.86 2.73
8.30 8.25 8.20 8.15 8.10 8.05 8.00 7.95 7.90 7.85 7.80 7.75 7.70 7.65 7.60 Chemical Shift (ppm)
* *
* * * *
1.06 2.05 0.89 1.00 1.02 1.94 0.98 0.86 2.73 1.03 2.14 3.12
10 9 8 7 6 5 4 3 2 1 Chemical Shift (ppm)
1 Figure 3.5: H NMR spectrum (750 MHz) of 3.2 in d6 – DMSO. * represents residual DMSO, DMF, H2O, Et2O, and DCM.
96
3
2 1
β2 α2 α4 β4
β1 β3
α1 α3
β1, β2, β4
α3 β3 α4 * α2 * α1 * *
*
1.01 1.07 0.940.90 0.96 0.89 2.69
8.30 8.25 8.20 8.15 8.10 8.05 8.00 7.95 7.90 7.85 7.80 7.75 7.70 7.65 7.60 Chemical Shift (ppm)
*
* *
1.23 2.31 1.21 1.01 1.07 0.94 0.90 0.96 0.89 2.69 1.16 2.25 2.30 3.25
10 9 8 7 6 5 4 3 2 1 Chemical Shift (ppm)
1 Figure 3.6: H NMR spectrum (750 MHz) of 3.3 in d6 – DMSO. * represents residual DMSO, DMF, H2O, and Et2O.
97
4;5 4;5 4;5
2;3 1 2;3
β2 α2 α4 β4
β1 β3
α1 α3 β1, β2, β4
α3 β3 α4 α1 α2
* * 1.01 1.00 0.92 0.97 0.92 3.23 8.30 8.25 8.20 8.15 8.10 8.05 8.00 7.95 7.90 7.85 7.80 7.75 7.70 7.65 7.60 Chemical Shift (ppm) *
* *
*
1.22 1.03 1.09 0.92 1.01 1.00 0.92 0.97 0.92 3.23 1.08 1.07 2.15 2.15 3.043.14
10 9 8 7 6 5 4 3 2 1 Chemical Shift (ppm)
1 Figure 3.7: H NMR spectrum (750 MHz) of 3.4 in d6 – DMSO. * represents residual DMSO, DMF, and H2O.
98
1
3
2
β2 α2 α4 β4
β1 β3
α1 α3
2
3
β1, β2, β4
α2, β3
α3 1
α1 α4 * *
*
1.00 0.98 0.91 1.71 2.71 1.09 1.87 1.96
8.30 8.25 8.20 8.15 8.10 8.05 8.00 7.95 7.90 7.85 7.80 7.75 7.70 7.65 7.60 7.55 7.50 7.45 Chemical Shift (ppm)
*
*
*
1.01 1.091.07 1.07 0.88 1.00 0.98 0.91 1.71 2.71 1.09 1.87 1.96 0.89
10.5 10.0 9.5 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 Chemical Shift (ppm)
1 Figure 3.8: H NMR spectrum (750 MHz) of 3.5 in d6 – DMSO. * represents residual DMSO, DMF, and H2O.
99
196.36 196.12 195.54 170.27 164.92 156.76 148.31 138.11 132.96 132.06 131.82 131.62 130.14 129.30 124.15 122.59 122.22 121.57 86.45 21.97 *
190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 Chemical Shift (ppm)
13 Figure 3.9: C NMR spectrum (500 MHz) of 3.1 in d6 – DMSO. * represents residual DMSO.
100
196.32 196.14 195.63 170.24 170.15 164.82 156.79 148.19 138.18 132.95 132.08 131.80 131.59 130.16 129.40 124.29 122.55 122.20 121.49 86.55 29.05 12.48 *
190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 Chemical Shift (ppm)
13 Figure 3.10: C NMR spectrum (500 MHz) of 3.2 in d6 – DMSO. * represents residual DMSO.
101
196.34 196.16 195.63 170.24 168.73 164.80 156.85 148.16 138.17 132.07 131.78 131.59 130.16 129.41 124.32 122.57 122.22 121.47 86.59 37.13 20.82 12.69
*
* * *
190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 Chemical Shift (ppm)
13 Figure 3.11: C NMR spectrum (500 MHz) of 3.3 in d6 – DMSO. * represents residual DMSO and DMF.
102
196.13 195.69 172.52 170.24 164.79 156.82 148.06 138.27 132.96 132.13 131.71 131.58 130.17 129.49 124.55 122.55 122.16 121.45 86.71 44.72 28.84 28.76 25.53 25.33 *
190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 Chemical Shift (ppm)
13 Figure 3.12: C NMR spectrum (500 MHz) of 3.4 in d6 – DMSO. * represents residual DMSO.
103
196.14 195.78 195.66 170.36 165.35 164.98 157.21 147.98 138.22 133.65 132.13 131.69 131.64 131.40 129.48 128.13 127.94 124.88 122.59 122.06 87.14 *
190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 Chemical Shift (ppm)
13 Figure 3.13: C NMR spectrum (500 MHz) of 3.5 in d6 – DMSO. * represents residual DMSO.
Even though the chloride analogs were synthesized without complication, only the straight chain alkyls (3.6-3.8) of the bromides could be isolated without a subsequent reaction. The cyclohexyl and phenyl derivatives could not be synthesized as pure materials with the bromide as the halide. We surmised that this was due to the reduced lability of the bromide complex relative to that of the chloride.289 To remove the halide from the metal and drive the reaction to completion, we employed AgNO3 as a halide metathesis agent.
The addition of 1.2 equivalents of AgNO3 in DMF to the initial reaction product from
Re(CO)5Br for these two compounds (Scheme 3.2) afforded the cyclohexyl and phenyl derivatives (compounds 3.9-3.10) as pure materials as the nitrate salts. The bromide and nitrate compounds 3.6-3.10 exhibited identical spectroscopic features as the chloride
104
analogues. Compound 3.9 was elucidated by single crystal X-ray methods (Figure 3.3) and the structure of this compound reveals similar structural parameters as seen in 3.1-3.3 and
3.5. We can hypothesize on the sequence of ligand formation based on the observed bromide effect, shown in Scheme 3.3. Upon the dissolution of Re(CO)5X, the nitrile replaces two equivalents of carbonyl and is subsequently activated by an equivalent of DII.
A second DII then forms an additional linkage at the α-carbon position to produce the bis-
DII chelate. Halide loss can then occur to allow the final chelate to form, which can be promoted via the use of silver nitrate at the last step. Support for this possible mechanism could be established through isolation of the mono-DII intermediate.
Scheme 3.2: Synthesis of the nitrate salts.
105
Scheme 3.3: Postulated reaction steps for the formation of the nitrate salts.
Conclusions
In conclusion, we have shown that yellow crystalline α-amidino azadi(benzopyrro)methenes can be produced by condensing two equivalents of DII and a
2 nitrile with Re(CO)3 as a templating agent. In the reaction, one DII sp carbon is converted to a sp3 carbon interrupting conjugation through the bis-DII fragment. Similar conversions have seen in the “helmet” and bicyclic phthalocyanines.190,193,196,197,279–283 The elucidated
X-ray crystal structures of the α-amidino azadi(benzopyrro)methenes show that the bidentate DII fragment tilts out of the plane of coordination and that the carbon-nitrogen bonds lengths are longer than the Re(CO)3-templated azadi(benzopyrro)methenes but comparable to the semihemiporphyrazines.234,236 We are continuing our work on rhenium- based templating reactions.
106
CHAPTER IV
COMPLEXES OF 2,6-DIACETYLPYRIDINE DIHYDRAZONE WITH MIDDLE AND
LATE FIRST ROW TRANSITION METALS
The text of this chapter is a reprint of the material as it appears in: Allen J. Osinski,
Bradley A. Hough, Laura A. Crandall, Ingrid-Suzy Tamgho and Christopher J. Ziegler.
Inorg. Chem. Commun. 2015, 59, 76–79. Copyright © 2015, Elsevier B.V.
DOI: 10.1016/j.inoche.2015.07.005
Introduction
Planar tridentate chelates, such as the bis(2-iminopyridyl)isoindolines, Louie’s bisiminopyridine ligands, and pincer type systems, have been explored both for their fundamental metal binding properties and as ligands for transition metal catalysts.159,290–296
One advantage of many of these ligand systems is their ease of synthesis and ready modification at the periphery, resulting in both bulky and chiral systems that can be used as effective ligands for effecting specific organic transformations.297–304 We have been working for several years on the chemistry of Schiff bases and their complexes and have turned our attention to hydrazine based ligand systems.305–308 Hydrazines will react rapidly with aldehydes and ketones to generate hydrazones, which have strong affinity as ligands for transition metal ions.309–315 The reaction of 2,6-diacetylpyridine with excess hydrazine
107
results in a tridentate chelate shown in Scheme 4.1, known as 2,6-diacetylpyridine dihydrazone (4.1, DAPH). Although this ligand has been previously synthesized, its transition metal chemistry has not been greatly explored.309–312 Additionally, the structure of DAPH can be considered as an analog of more sterically bulky substituted hydrazones, which have been explored as catalysts for organic transformations and polymerizations.313–
315 In this report, we present a study that completes the middle and late first row transition metal chemistry of DAPH, including reactions with manganese, iron, cobalt, copper and zinc, with a focus on the structures of the resultant complexes. In all cases, DAPH binds as a neutral, planar, tridentate ligand, with both 1:1 and 2:1 homoleptic ligand to metal stoichiometries.
Scheme 4.1: The synthesis of the metal complexes of DAPH (4.1).
108
Experimental
General information
Materials and Methods. Reagents were purchased from Strem, Matrix Scientific,
Acros Organics, TCI AMERICA or Sigma-Aldrich and used as received without further purification. All solvents were purified by alumina and copper columns in the Pure Solv solvent system (Innovative Technologies, Inc.); dried solvents were stored over molecular sieves.
NMR spectra were recorded on Varian Mercury 300 MHz and 400 MHz instruments. Chemical shifts were reported with respect to residual solvent peaks as
1 internal standard ( H: d6-DMSO, δ = 2.50 ppm; d4-Methanol, δ = 4.78 ppm and 3.31 ppm; d2-Deuterium Oxide, δ = 4.80 ppm). Infrared spectra were collected on Thermo Scientific
Nicolet iS5 which was equipped with iD5 ATR. Electronic absorption spectra were recorded on Hitachi U-2000 UV-vis spectrophotometer. Elemental Analyses were performed by Atlantic Microlab of Norcross, GA 30091. Mass Spectrometric analyses were carried out at the Mass Spectrometry center at The University of Akron in Akron,
OH.
X-ray Data Collection and Structure Determination. X-ray Data Collection and
Structure Determination: X-ray intensity data for compounds 4.2-4.4 and 4.6-4.7 were measured at 100 K on a CCD-based X-ray diffractometer system equipped with a Mo- target X-ray tube (Mo Kα radiation, λ = 0.71073 Å) operated at 2000 W power. Data for
4.1, 4.5, and 4.8 were collected on a CCD-based diffractometer with dual Cu/Mo ImuS microfocus optics (Cu Kα radiation, λ = 1.54178 Å). Crystals were mounted on a cryoloop using Paratone oil and placed under a steam of nitrogen at 100 K. The detector was placed
109
at a distance of 5.009 cm from the crystal. Crystals data and structures refinement parameters are summarized in Table 4.1-4.3.
Synthesis of 2,6-diacetylpyridinedihydrazone (DAPH, 4.1) (Scheme 4.2). This compound was prepared as previously described.309 Single crystals that were suitable for
X-ray diffraction were grown from a diffusion of hexanes into a chloroform solution.
Scheme 4.2: Synthesis of 4.1.
(Synthesis of 4.2 Fe(DAPH)Cl3 (Scheme 4.3). FeCl3٠6H2O (0.141 g, 0.52 mmol dissolved in 1.5 mL of methanol was added to DAPH (0.100 g, 0.52 mmol) dissolved in 7 mL of boiling acetonitrile. The reaction mixture was allowed to stir at room temperature for 1 hr. After stirring, a black solid was filtered and washed with acetonitrile and Et2O.
The powder was dried in vacuo. Crystals suitable for X-ray diffraction were prepared by slow diffusion of Et2O into a methanol solution. Yield: 125 mg (68%). CHN Anal. Calc.
,for FeC9H13Cl3N5٠0.4 CH3OH٠0.4 H2O: C, 30.23; H, 4.16; N, 18.75. Found: C, 30.17; H
4.12; N, 18.83. FTIR ν/cm-1: 3189 (NH); 1589, 1534 (C=N). MS (ESI): m/z = calc. for
+ FeC9H13Cl2N5 [M-Cl] : 317.0 found 316.6. UV-Vis spectrum in CH3OH λmax 269 nm (ɛ =
1.8 × 104 M-1 cm-1).
110
Scheme 4.3: Synthesis of 4.2.
(Synthesis of 4.3 Cu(DAPH)Cl2 (Scheme 4.4). CuCl2٠2H2O (0.089 g, 0.52mmol dissolved in 1 mL of methanol was added to DAPH (0.100 g, 0.52 mmol) dissolved in 7 mL of boiling acetonitrile. The reaction mixture was allowed to stir at room temperature for 1 hr. After stirring, the green solid was filtered and washed with acetonitrile and Et2O.
The powder was dried in vacuo. Crystals suitable for X-ray diffraction were prepared by slow diffusion of Et2O into a methanol solution. Yield: 168 mg (99%). CHN Anal. Calc.
;for CuC9H13Cl2N5٠1.20 CH3OH: C, 33.64; H, 4.93; N, 19.23. Found: C, 33.16; H, 3.88
N, 18.17. FTIR ν/cm-1: 3112 (NH); 1590, 1540 (C=N). MS (ESI): m/z = calc. for
+ CuC9H13ClN5 [M-Cl] : 289.0 found 288.7. UV-Vis spectrum in CH3OH λmax 223 nm (ɛ =
4 -1 -1 3 -1 -1 3 1.2 × 10 M cm ), λmax 283 nm (ɛ = 5.7 × 10 M cm ), and λmax 338 nm (ɛ = 3.7 × 10
M-1 cm-1).
Scheme 4.4: Synthesis of 4.3.
111
Synthesis of 4.4 Zn(DAPH)Cl2 (Scheme 4.5). ZnCl2 (0.071 g, 0.52 mmol) was dissolved in 1 mL of methanol and was added to DAPH (0.100 g, 0.52 mmol) dissolved in
6 mL of boiling acetonitrile. The reaction mixture was allowed to stir at room temperature for 1 hr. After stirring, a yellow solid was filtered and washed with acetonitrile and Et2O.
The yellow solid was dissolved in hot DMSO and allowed to cool in an ice bath. An off- white solid was filtered and washed with cold DMSO and Et2O. The powder was dried in vacuo. Crystals suitable for X-ray diffraction were prepared by slow diffusion of Et2O into
1 a methanol solution. Yield: 166 mg (98%). H NMR (400 MHz, d6-DMSO, δ (ppm) at
90ºC): 2.24 (s, 6H, methyl), 6.87 (s, 4H, NH), 7.78 (d, J = 8.31 Hz, 2H phenyl), 8.12 (s,
1H, phenyl). CHN Anal. Calc. for ZnC9H13Cl2N5: C, 33.00; H, 4.00; N, 21.38. Found: C,
32.92; H, 3.87; N, 21.21. FTIR ν/cm-1: 3187 (NH); 1603, 1550 (C=N). MS (ESI): m/z =
+ calc. for ZnC9H13ClN5 [M-Cl] : 290.0 found 289.7. UV-Vis spectrum in CH3OH λmax 278
4 -1 -1 3 -1 -1 nm (ɛ = 1.6 × 10 M cm ) and λmax 356 nm (ɛ = 2.5 × 10 M cm ).
Scheme 4.5: Synthesis of 4.4.
112
(Synthesis of 4.5 Mn(DAPH)Cl2 (Scheme 4.6). MnCl2٠4H2O (0.103 g, 0.52 mmol dissolved in 2 mL of methanol was added to DAPH (0.100 g, 0.52 mmol) dissolved in 7 mL of boiling acetonitrile. The reaction mixture was allowed to stir at room temperature for 1 hr. After stirring, an orange solid was filtered and washed with acetonitrile and Et2O.
The resultant orange powder was dried in vacuo. Crystals suitable for X-ray diffraction were prepared by slow diffusion of Et2O into a methanol solution. Yield: 159 mg (96%).
,CHN Anal. Calc. for Mn2C18H26Cl4N10٠1.3 H2O: C, 32.88; H, 4.38; N, 21.30. Found: C
32.88; H, 4.26; N, 21.16. FTIR ν/cm-1: 3199 (NH); 1590, 1540 (C=N). MS (ESI): m/z =
+ calc. for Mn2C18H26Cl3N10 [M-Cl] : 597.0 found 598.8. UV-Vis spectrum in CH3OH λmax
4 -1 -1 3 -1 -1 282 nm (ɛ = 1.9 × 10 M cm ) and λmax 353 nm (ɛ = 5.2 × 10 M cm ).
Scheme 4.6: Synthesis of 4.5.
113
Synthesis of 4.6 [Co2(DAPH)2(MeOH)2Cl2][CoCl4] (Scheme 4.7). CoCl2٠6H2O
(0.185 g, 0.78 mmol) dissolved in 1.5 mL of methanol was added to DAPH (0.100 g, 0.52 mmol) dissolved in 7 mL of boiling acetonitrile. The reaction mixture was allowed to stir at room temperature for 1 hr. After stirring, the dark green solid was filtered and washed with acetonitrile and Et2O. The powder was dried in vacuo. Crystals suitable for X-ray diffraction were prepared by slow diffusion of Et2O into a methanol solution. Yield: 124
.mg (62%). CHN Anal. Calc. for Co3C20H34Cl6N10٠1.6 CH3CN: C, 32.04; H, 4.50; N, 18.68
Found: C, 32.09; H, 4.17; N, 18.95. FTIR ν/cm-1: 3203 (NH); 1595, 1532 (C=N). MS (ESI):
+ m/z = calc. for Co3C18H26Cl5N10 [M-Cl-(2 MeOH)] : 733.9 found 735.7. MS (ESI): m/z =
+ calc. for Co2C18H26Cl3N10 [M-CoCl3-(2 MeOH)] : 605.0 found 604.8. UV-Vis spectrum in
5 -1 -1 4 -1 -1 CH3OH λmax 275 nm (ɛ = 1.1 × 10 M cm ) and λmax 356 nm (ɛ = 1.5 × 10 M cm ).
Scheme 4.7: Synthesis of 4.6.
114
Synthesis of 4.7 [Fe(DAPH)2][FeCl4] (Scheme 4.8). FeCl2٠4H2O (0.10 g, 0.52 mmol) dissolved in 5 mL of methanol was added to DAPH (0.100 g, 0.52 mmol) dissolved in 10 mL of boiling acetonitrile. The reaction mixture was allowed to stir at room temperature for 1 hr. After stirring, a dark red solid was filtered and washed with Et2O. The powder was dried in vacuo. Crystals suitable for X-ray diffraction were prepared by slow diffusion of Et2O into a methanol solution. Yield: 109 mg (66%). CHN Anal. Calc. for
,Fe2C18H26Cl4N10٠0.2 CH3OH٠4 H2O: C, 30.60; H, 4.91; N, 19.60. Found: C, 30.17; H
4.22; N, 18.90. FTIR ν/cm-1: 3205 (NH); 1551, 1517 (C=N). MS (ESI): m/z = calc. for
+ Fe2C18H26Cl3N10 [M-Cl] : 599.0 found 598.8. UV-Vis spectrum in CH3OH λmax 260 nm (ɛ
4 -1 -1 4 -1 -1 3 - = 2.8 × 10 M cm ), λmax 278 nm (ɛ = 2.3 × 10 M cm ), λmax 327 nm (ɛ = 9.3 × 10 M
1 -1 3 -1 -1 3 -1 -1 cm ), λmax 427 nm (ɛ = 5.3 × 10 M cm ), and λmax 517 nm (ɛ = 4.1 × 10 M cm ).
Scheme 4.8: Synthesis of 4.7.
115
,Synthesis of 4.8 [Co(DAPH)2](NO3)2 (Scheme 4.9). Co(NO3)2٠6H2O (0.076 g
0.26 mmol) dissolved in 1.5 mL of methanol was added to DAPH (0.100 g, 0.52 mmol) dissolved in 7 mL of boiling acetonitrile. The reaction mixture was allowed to stir at room temperature for 1 hr. After stirring, the brown solid was filtered and washed with Et2O.
The powder was dried in vacuo. Crystals suitable for X-ray diffraction were prepared by slow diffusion of Et2O into a methanol solution. Yield: 131 mg (89%). CHN Anal. Calc.
,for CoC18H26N12O6٠0.9 CH3OH: C, 38.20; H, 5.02; N, 28.28. Found: C, 38.47; H, 4.70; N
-1 28.04. FTIR ν/cm : 3174 (NH); 1602, 1550 (C=N); 1317 (NO3). MS (ESI): m/z = calc. for
2+ CoC18H26N10 [M-2(NO3)] : 220.6 found 220.0. UV-Vis spectrum in CH3OH λmax 280 nm
4 -1 -1 4 -1 -1 (ɛ = 5.0 × 10 M cm ) and λmax 340 nm (ɛ = 1.4 × 10 M cm ).
Scheme 4.9: Synthesis of 4.8.
116
Table 4.1: X-ray crystal data and structure parameters for compounds 4.1-4.3.
Compound 4.1 4.2 4.3 Empirical formula C9H13N5 C10H17Cl3FeN5O C9H13Cl2CuN5 Formula weight 191.24 385.49 325.68 Crystal system Orthorhombic Monoclinic Monoclinic Space group Pnma P2(1)/n C2/c a/ Å 10.4929(4) 8.4488(10) 17.7365(13) b/ Å 19.7480(8) 9.8289(12) 7.6502(6) c/ Å 4.6435(2) 18.435(2) 19.5265(15) α(°) 90 90 90 β(°) 90 97.7860(10) 95.526(3) γ(°) 90 90 90 Volume (Å3) 962.20(7) 1516.8(3) 2637.2(3) Z 4 4 8 Dc (Mg/m3) 1.320 1.688 1.641 µ (mm-1) 0.699 1.524 2.046 F(000) 408 788 1320 reflns collected 3108 5254 14651 indep. reflns 823 2697 2305 GOF on F2 1.106 1.063 1.376 2 R1(on Fo ,I>2σ(I)) 0.0477 0.0317 0.0953 2 wR2(on Fo ,I>2σ(I)) 0.1413 0.0783 0.2252 R1(all data) 0.0497 0.0369 0.0977 wR2(all data) 0.1449 0.0832 0.2262
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Table 4.2: X-ray crystal data and structure parameters for compounds 4.4-4.6.
Compound 4.4 4.5 4.6 Empirical C9H13Cl2N5Zn C9H13Cl2MnN5 C10H17Cl3Co1.50N5O Formula Formula weight 327.51 317.08 418.03 Crystal system Monoclinic Monoclinic Monoclinic Space group P2(1)/n C2/c C2/c a/ Å 8.0114(8) 18.0309(10) 15.860(3) b/ Å 10.8477(10) 7.5296(4) 14.501(2) c/ Å 15.2629(15) 21.8536(13) 15.384(3) α(°) 90 90 90 β(°) 104.2630(10) 113.872(3) 115.277(2) γ(°) 90 90 90 Volume (Å3) 1285.5(2) 2713.1(3) 3199.4(9) Z 4 8 8 Dc (Mg/m3) 1.692 1.553 1.736 µ (mm-1) 2.311 11.430 2.077 F(000) 664 1288 1692 reflns collected 9105 8367 10843 indep. reflns 2271 2251 2826 GOF on F2 0.896 0.827 1.043 2 R1(on Fo ,I>2σ(I)) 0.0273 0.0423 0.0455 2 wR2(on Fo ,I>2σ(I)) 0.0977 0.1112 0.1117 R1(all data) 0.0287 0.0443 0.0629 wR2(all data) 0.1008 0.1131 0.1218
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Table 4.3: X-ray crystal data and structure parameters for compounds 4.7-4.8.
Compound 4.7 4.8 Empirical C9H13Cl2FeN5 C18H26CoN12O6 Formula Formula weight 317.99 565.44 Crystal system Monoclinic Tetragonal Space group Cc P-42(1)c a/ Å 14.804(4) 7.3607(2) b/ Å 10.695(3) 7.3607(2) c/ Å 15.978(4) 21.1507(10) α(°) 90 90 β(°) 100.49(2) 90 γ(°) 90 90 Volume (Å3) 2487.6(11) 1145.94(7) Z 8 2 Dc (Mg/m3) 1.698 1.639 µ (mm-1) 1.626 6.446 F(000) 1296 586 reflns collected 8642 11792 indep. reflns 4309 951 GOF on F2 1.056 1.115 2 R1(on Fo ,I>2σ(I)) 0.0314 0.0273 2 wR2(on Fo ,I>2σ(I)) 0.0729 0.0687 R1(all data) 0.0335 0.0287 wR2(all data) 0.0746 0.0693
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Equation 4.1: Evans NMR method calculation for effective magnetic moment.316 ______
3 퓀Β 푃 휇푒푓푓 = √ 2 (휒푀푇) 푁퐴β kB = Boltzmann constant NA = Avogadro’s number β = Bohr magneton 픁P = molar susceptibility T = absolute temperature (K)
Equation 4.2: Evans NMR method calculation for mass susceptibility.317
훿휈푝 휒 = 푝 + 휒표 휐표푆푓푚
δvp = Shift in frequency for an internal inert reference; t-butanol (Hz) vo = frequency of the NMR spectrometer (Hz) Sf = Shape factor of the NMR spectrometer; 4π/3 sample axis parallel to magnetic field mp = concentration of solute (g/mL) 픁° = mass susceptibility of the deuterated solvent (mL/g)
Equation 4.3: Evans NMR method calculation for molar susceptibility.317
푝 푝 푃 훿휈 푀 푑푖푎 휒푀 = 푝 − 휒푀 푣표푆푓푚
δvp = Shift in frequency for an internal inert reference; t-butanol (Hz) MP = Molecular weight of solute (g/mol) vo = frequency of the NMR spectrometer (Hz) Sf = Shape factor of the NMR spectrometer; 4π/3 sample axis parallel to magnetic field mp = concentration of solute (g/mL) 푑푖푎 휒푀 = diamagnetic constant (mL/mol)
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Table 4.4: Evans NMR method data and parameters for 4.2-4.5.
Compound 4.2 4.3 4.4 4.5 Mass (mg) 1.0 1.1 2.1 2.5
Volume (mL) 1 0.5 1 0.5 Deuterated Methanol Methanol Water Methanol Solvent Mass 5.3x10-7 5.3x10-7 -7.2x10-7 5.3x10-7 Susceptibility of solvent (mL/g) Shift in 53.86 8.84 0 307.78 frequency (Hz) Temperature (K) 303.15 303.15 303.15 303.15 Molecular 353.44 325.68 327.51 634.16 weight of solute (g/mol) Frequency of 2.9975x108 2.9975x108 2.9975x108 2.9975x108 NMR spectrometer (Hz) μeff (μβ) 6.10 1.71 0 8.73 Mass 4.34x10-5 3.73x10-6 -7.203x10-7 4.96x10-5 Susceptibility (mL/g) Molar 1.53x10-2 1.20x10-3 -1.45x10-4 3.14x10-2 Susceptibility (mL/mol) Diamagnetic -1.83x10-4 -1.61x10-4 -1.45x10-4 -3.27x104 constant (mL/mol)
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Table 4.5: Evans NMR method data and parameters for 4.6-4.8.
Compound 4.6 4.7 4.8 Mass (mg) 3.6 5.0 2.0 Volume (mL) 1 0.5 0.5 Deuterated Solvent Methanol Methanol Water Mass Susceptibility of solvent (mL/g) 5.3x10-7 5.3x10-7 -7.2x10-7 Shift in frequency (Hz) 96.18 103.87 76.36 Temperature (K) 303.15 303.15 303.15 Molecular weight of solute (g/mol) 771.98 635.97 565.41 Frequency of NMR spectrometer (Hz) 2.9975x108 2.9975x108 2.9975x108 μeff (μβ) 6.38 3.68 4.63 Mass Susceptibility (mL/g) 2.18x10-5 8.80x10-6 1.45x10-5 Molar Susceptibility (mL/mol) 1.68x10-2 5.59x10-3 8.85x10-3 Diamagnetic constant (mL/mol) -3.82x10-4 -3.25x10-4 -2.56x10-4
Results and Discussion
The DAPH ligand 4.1 was first synthesized by Lukes and Pergal, and recently a more detailed procedure was presented by Datta and coworkers.309,318 The ligand can be readily prepared via the reaction of 2,6-dacetylpyridine with excess hydrazine in ethanol.
Compound 4.1 precipitates as a pure product directly from solution, and can be used immediately in metalation reactions. We were able to grow single crystals of 4.1 from a diffusion of hexanes into a chloroform solution, and its structure is shown in Figure 4.1.
Unlike in its metal complexes (vide infra), the C–N bonds are turned away from the central nitrogen atom. The C–N bonds of the imines measure 1.2851 (19) Å while the N–N bonds of the hydrazine units measure 1.3812 (18) Å. The hydrazine units engage in complementary hydrogen bonding with neighboring molecules in the solid state.
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Figure 4.1: The structure of 4.1 with 35% thermal ellipsoids.
The chemistry of this ligand has been sporadically investigated. Early work was carried out in the 1960s with minimal characterization.319 More recently, several compounds have been structurally characterized including Ni(II), Zn(II), Cd(II), Hg(II) and
Pb(II).309–312 The DAPH ligand readily reacts with a variety of transition metal salts in methanol. Depending on the metal salts used and the ratio of ligand to metal, we could obtain 1:1 ligand:metal complexes (Figure 4.2) or 2:1 ligand metal complexes (Figure 4.3).
Reaction of one equivalent of the DAPH ligand with FeCl3, CuCl2 and ZnCl2 results in monomeric compounds (4.2, 4.3 and 4.4), whereas reactions with MnCl2 and CoCl2 afford dimeric species (4.5 and 4.6). For the monomeric compounds, the remainder of the coordination sphere is occupied by chlorides, producing neutral species. For the dimeric compounds 4.5 and 4.6, two bridging chlorides form a M2Cl2 diamond core; in the case of
4.5 two additional chlorides complete the coordination environment in apical positions,
2− whereas in 4.6 the charge is balanced by an equivalent of CoCl4 . For the 2:1 ligand:metal ratio reactions, homoleptic complexes 4.7, and 4.8 are obtained, from FeCl2, and Co(NO3)2 respectively. The structures of the cations for these compounds are shown in Figure 4.2, and the two are similar in structure to each other and the previously elucidated Ni(II) and
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Zn(II) complexes.309,310 Since the ligand is neutral, and since the identity and number of the anions in each of the structure can be clearly determined, the oxidation states of these compounds are unambiguous. With the exception of compound 4.4, all of the complexes are paramagnetic. All of the compounds exhibit divalent metals with the exception of 4.2, which has a trivalent metal ion. We measured the magnetic susceptibility of all of the compounds via the Evans method (see Experimental Section Table 4.3 and Equations 4.1-
4.3).316,317,320 Compounds 4.5 and 4.6 are dimeric, and compound 4.7 has a paramagnetic anion, so their susceptibilities are not readily interpretable with a single measurement, but compounds 4.2, 4.3 and 4.8 exhibit susceptibilities of 6.1, 1.7 and 4.6 BM, corresponding to spins of 5/2, 1/2 and 3/2 respectively.
Figure 4.2: The structures of compounds 4.2–4.6 with 35% thermal ellipsoids. Hydrogen atoms and non-coordinating anions have been omitted for clarity.
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Figure 4.3: The structures of compounds 4.7 and 4.8 with 35% thermal ellipsoids. Hydrogen atoms and non-coordinating anions have been omitted for clarity.
In both the mono and bis DAPH complexes, the ligand binds as a tridentate, planar species. The M–N bond lengths, shown in Table 4.4, reveal that the M–Npyr bond lengths are shorter than the adjacent M–Nimine bond lengths. Similar trends are observed in bis(iminopyridyl)isoindoline compounds and related bis(iminoazolyl)isoindoline complexes.159,171,172,292,293,297,298,300,301,307,308 Another feature of the DAPH ligand is the acute angle formed by the Nimine–M–Nimine bonds. These angles range from ~142°
(compound 4.5) to ~160° (compound 4.7). The magnitude of this angle is affected by two parameters: the radius of the metal ion, and the degree of displacement from the tridentate chelate. Another aspect of the metal complexes of the DAPH ligand is the effect of metal binding on the imine bond lengths; due to metal to ligand backbonding effects, the C-N bond can be lengthened. Table 4.3 shows these metal bound imine bond lengths, and we observe a range of behavior ranging from no effective change to the bond (such as in complex 4.4) to appreciable lengthening of ~0.03 Å in complex 4.3.
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Table 4.6: Selected bond lengths and angles for 4.2–4.8 and related DAPH compounds.
Compound M-Nimine M-Npyr (Å) Nimine-M- C-Nimine (Å) Nimine (º) (Å) 4.2 2.143(2) 2.076(2) 149.37(8) 1.300(3) 2.150(2) 1.298(3) 4.3 2.026(8) 1.923(8) 154.3(3) 1.313(13) 2.048(8) 1.314(13) 4.4 2.1947(18) 2.0624(17) 146.96(7) 1.288(3) 2.1813(18) 1.296(3) 4.5 2.270(3) 2.203(3) 141.63(9) 1.289(4) 2.296(3) 1.289(4) 4.6 2.135(3) 2.053(3) 150.08(13) 1.301(5) 2.133(3) 1.293(5) 4.7 1.957(3) 1.882(3), 159.97(13), 1.292(5) 1.963(3) 1.876(3) 159.12(13) 1.303(5) 1.949(3) 1.297(5) 1.950(3) 1.320(5) 4.8 2.1967(19) 2.034(3) 149.85(10) 1.294(3)
[Zn(DAPH)2](ClO4)2 2.187(3) 2.040(3) 150.62(12) 1.287(4) 2.206(3) 2.036(3) 150.06(12) 1.282(5) 2.244(3) 2.037(3) 150.64(12) 1.282(6) 2.161(3) 2.039(3) 150.77(11) 1.290(5) 2.192(3) 1.298(5) 2.242(3) 1.289(5) 2.202(3) 1.292(5) 2.183(3) 1.304(6) [Cd(DAPH)2](ClO4)2 2.350(3) 2.285(2) 137.75(9) 1.281(4) 2.430(3) 2.300(2) 129.90(8) 1.279(3) 2.470(3) 1.284(4) 2.529(3) 1.293(4)
[Hg(DAPH)2](ClO4)2 2.362(4) 2.274(3) 132.17(12) 1.290(6) 2.495(4) 2.305(4) 137.35(12) 1.290(5) 2.455(4) 1.286(6) 2.569(4) 1.297(6)
[Ni(DAPH)2](NO3)2 2.164(3) 1.995(3) 152.39(14) 1.300(4)
[Pb(DAPH)(MeOH)2](NO3)2 2.59(2) 2.49(3) 128.9(8) 1.28(5) 2.50(2) 1.30(4)
[Pb(DAPH)(N3)2 2.524(8) 2.484(9) 127.7(3) 1.28(1)
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Conclusions
In conclusion, we present a study on the middle and late first row transition metal chemistry of the DAPH ligand. All new complexes have been fully characterized, including by single crystal X-ray diffraction. We observe both 1:1 and 2:1 ligand to metal ratio compounds, and the 2:1 compounds are homoleptic. In all cases, the DAPH ligand acts as a neutral tridentate ligand, exhibits shorter M–Npyr bonds than M–Nimine bonds, and adopts an acute Nimine–M–Nimine bond angle. We are continuing our work on multidentate Schiff base ligands and their metal binding properties.
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CHAPTER V
MAGNETIC CIRCULAR DICHROISM OF TRANSITION-METAL
COMPLEXES OF PERFLUOROPHENYL-N-CONFUSED PORPHYRINS:
INVERTING ELECTRONIC STRUCTURE THROUGH A PROTON
The text of this chapter is a reprint of the material as it appears in: Samantha
Doble, Allen J. Osinski, Shelby M. Holland, Julia M. Fisher, G. Richard Geier, III,
Rodion V. Belosludov, Christopher J. Ziegler, and Victor N. Nemykin. J. Phys. Chem. A
2017, 121, 3689−3698. Copyright © 2017, American Chemical Society.
DOI: 10.1021/acs.jpca.7b02908
Introduction
The electronic structure of normal porphyrins have been extensively studied,321–323 but much work remains in the investigation of the electronic structures of isomers and analogs of porphyrins. Isomers of porphyrins include rings re-arranged macrocycles, such as porphycene, while analogs of porphyrins are skeletal modified macrocycles such as expanded, contracted or ring modified systems.324–337 Both types of macrocycles share many of the characteristics of normal porphyrin. However, modification of the ring alters the electronic structure of the isomers and analogs of porphyrin, and we have been investigating these systems for the past several years.338–342 In particular, when asymmetry
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is incorporated into the macrocycle skeleton, an inversion of the magnitude of the
ΔHOMO versus the ΔLUMO is observed (within the borders of Gouterman’s four-orbital model343–345 and Michl’s perimeter model346–349, ΔHOMO is the energy difference between the macrocycle-centered HOMO and HOMO-1, while ΔLUMO is the energy difference between the macrocycle-centered LUMO and LUMO+1). In normal metal-containing porphyrins, the ΔLUMO is zero (the orbitals are degenerate as the effective symmetry of such porphyrins is D4h or C4v) and the ΔHOMO is non-zero, which results in the typical
LUMO < HOMO relationship. In the low-symmetry porphyrinoids such as chlorins and bacteriochlorins, the LUMO and LUMO+1 are non-degenerate and in many cases the
LUMO > HOMO energy relationship is observed, which results in readily observable spectroscopic changes in the magnetic circular dichroism (MCD) spectra.343–349
N-confused porphyrin (NCP, Figure 5.1) or 2-aza-21-carbaporphyrin is one of the most thoroughly studied isomers of porphyrin.350,351 In NCP, one of the pyrrole rings is inverted compared to normal porphyrin; a carbon atom occupies the internal binding position while a nitrogen atom is located on the periphery of the pyrrole ring. Although modified from normal porphyrin, NCP retains an 18-electron annulene ring structure. Even though the overall structures of normal porphyrin and NCP are similar, the inversion of one of the pyrrole rings alters the electronics of NCP which results in different chemical and physical properties.83,84,352–355 In particular, NCP exhibits two isolable tautomers: an internal tautomer with three hydrogen atoms in the core of the ring and an external tautomer with a hydrogen atom on the external nitrogen atom and only two hydrogen atoms in the core.356,357
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Figure 5.1: Structures of porphyrin, N-confused porphyrin (showing both inner and outer tautomers), and complexes 5.1 – 5.4.
Based on the MCD spectra and theoretical calculations on cis- and trans-isomers of Cu(III) complexes of doubly N-confused porphyrins, in 2008, Kobayashi and co- workers suggested that the formation of N-confused macrocycle should result in LUMO
> HOMO energy relationship. This would lead to a positive-to-negative in ascending energy sequence of the MCD signals in Q-band region.358 Later, we showed that the MCD spectra of the metal-free meso-phenyl340 and meso-(4-methoxycarbonyl)phenyl359 NCPs
(CO2Me) (H2NCP and H2NCP , respectively) have a typical for porphyrins LUMO <
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HOMO relationship in the Q-band region, which is not altered by protonation or deprotonation of the nitrogen or NH centers or by the polarity of the solvent. In contrast, we showed that the nickel meso-phenyl NCP (NiNCP) and its externally methylated variant
(NiNCPMe) exhibit sign-reversed MCD spectra in the Q-band region, indicating that the
ΔHOMO ˂ ΔLUMO condition is observed.341 Although the sign-reversed MCD spectrum is seen with other porphyrinoids including corroles and reduced porphyrins,338,339,360 the
MCD spectrum of NiNCP can be reverted to the typical for porphyrins ΔHOMO ˃
ΔLUMO relationship by simple deprotonation of the external NH proton; this cannot occur in the methylated form.341 Thus, MCD spectra available on NCPs studied so far are indicative of a complex interplay between type of the NCP core (external versus internal tautomer) as well as type of the central ion (proton versus nickel). The small set of NCPs studied by MCD spectroscopy to date, however, precludes observation of general trends in this class of porphyrinoids. In this report, we expand the range of studied NCPs, with an
MCD study of the nickel, palladium and copper complexes of tetra(perfluorophenyl)-N- confused porphyrin (PF-NCP, Figure 5.1).361 By introducing strongly electron- withdrawing meso-perfluorophenyl groups, we sought to determine whether the sign- reversed MCD spectrum of NiNCP was maintained or whether the spectrum was restored to the typical ΔHOMO ˃ ΔLUMO relationship. We investigated the Ni(II) (5.1) and Pd(II)
(5.2) complexes of PF-NCP in both their protonated and deprotonated states. Additionally, we investigated the Cu(II) complex (5.3) of PF-NCP in both forms, and were able to probe the effect of metal oxidation state on the MCD spectra via the Cu(III) complex (5.4, Figure
5.1). DFT calculations on the new MPF-NCP systems as well as previously reported
- NiNCP, [NiNCP] , and H2NCP were conducted at the same level of theory us to generalize
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to some extent general trends in electronic structures and spectroscopic signatures of these systems.
Experimental
Materials and Instrumentation. All solvents were purchased from commercial sources and dried using standard approaches prior to experiments. DDQ and a methanol solution of (NBu4)OH were purchased from Aldrich used without future purification.
Metal-free perfluorophenyl-N-confused porphyrin was synthesized using a two-step, one- flask method recently described by Geier.362 Metallation of perfluorophenyl-N-confused porphyrin by copper and palladium was performed using a modified method developed by
Furuta.361 Nickel complex 5.1 was prepared using a modification of a method initially reported by Chen, Tung and coworkers for a different NCP.363 UV-vis-NIR data were obtained on a JACSO V-670 spectrometer with dichloromethane as the solvent. MCD data were recorded using an OLIS DCM 17 CD spectropolarimeter using a permanent 1.4 T
DeSa magnet. The spectra were recorded twice for each sample, once with a parallel field and again with an antiparallel field, and their intensities were expressed by molar ellipticity per tesla.
Computational aspects. All computations were performed using the Gaussian 09 software package running under Windows or UNIX OS.266 Molecular orbital contributions were compiled from single point calculations using the QMForge program.267 All geometries were optimized without any symmetry restrictions. Frequencies were calculated for all optimized geometries in order to ensure that final geometries represent minima on the potential energy surface. In all calculations, the hybrid B3LYP exchange- correlation functional364 and 6-31G(d) basis set264 were used for all atoms. In addition, DFT
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and TDDFT calculations of all MPF-NCP and [MPF-NCP]- complexes were conducted using hybrid TPSSh exchange-correlation functional to study an exchange-correlation functional dependence. TDDFT calculations were conducted for the first 50 excited states in order to ensure that all π-π* transitions of interest were accounted for. Solvent effects were modeled using PCM approach using DCM as a solvent.365
Results and Discussion
Comparing the absorption spectra of both free base and the metal complexes of PF-
TPP to normal TPP and its metal adducts, the most significant changes are blue shifts of
366,367 the absorption bands in the former compound. H2TPP exhibits an intense B-band at
~420 nm and four weak Q-band absorptions at 515, 550, 591, and 647, while in H2PF-TPP these same bands shift to ~410 nm for the B-band with the Q-band absorptions at 504, 539,
582, and 638 nm.368,369 For hypso-type porphyrins, observed in metalloporphyrins with transition metals that have six or more d-orbital electrons, the absorption bands are also blue shifted relative to the freebase; in Ni(TPP) at the B-band appears at 415 nm with one
Q-band absorption at 524 nm.370 For the perfluoronated variant Ni(PF-TPP), the bands are further blue shifted, with a B-band at 407 nm with two Q-band absorptions at 526 and 559 nm.371
The confusion of the pyrrole ring in H2NCTPP significantly impacts the spectra
356 versus normal H2TPP as well as induces tautomer-depended spectroscopic properties.
We have discussed the absorption spectroscopy of both tautomeric forms previously.357
Upon metal insertion, the absorption profile depends greatly on whether the macrocycle is acting as a trianion (internal tautomer) or a dianion (external tautomer). NCP compounds have red shifted B-bands relative to normal porphyrins.340,372,373 For instance, NiNCP,
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where the ring is acting as a dianion, has a B-band at 425 nm with a shoulder at 458 nm, and multiple Q-band absorptions at 555, 594, 655, 716, and 789 nm.341 When deprotonated, the bands shift as the macrocycle becomes trianionic type, and the B-band appears at 424 nm along generally red shifted Q bands at 537, 590, 667 and 719 nm.341
Figure 5.2 shows the UV-visible spectra of PF-NCP complexes 5.1 – 5.4 along with their MCD spectra. Compared to NiNCP, in Ni(II) complex 5.1, the B-band shifts to 419 nm, as do the higher energy transitions in Q-band region (564 nm with a 592 nm shoulder compared to 594 nm with a 665 nm in NiNCP).341 The lower energy transitions in Q-band region appear shifted to the red: 735 and 808 nm compared to 716 and 789 nm for
NiNCP.341 The other metal complexes 5.2 – 5.4 exhibit quite different absorption spectra in spite of the fact that complexes 5.2 and 5.3 have divalent d8 and d9 transition metal ions and complex 5.4 has a trivalent d8 central ion. In Pd(II) complex 5.2, we observe a split B- band (422 and 442 nm) and five transitions in Q-band region at 537, 578, 638, 695, and
761 nm. Unlike in Ni(II) complex 5.1, all transitions in Q-band region are of comparable intensity. In Cu(II) complex 5.3, the B-band region is dominated by broad red shifted (440 nm) band, while four clear transitions can be observed in the Q-band region at 543, 587,
676, and 735 nm. We also sought to investigate an N-confused porphyrin system where the macrocycle acts as a trianion without deprotonation of the external nitrogen position. This can occur when N-confused porphyrin binds trivalent metal ions in its internally protonated form. The earliest form of this type of binding was seen in the Ag(III) adduct, where the metal ion resides in the core of ring.374 An analogous structure can be achieved for copper upon oxidation of the Cu(II) complex 5.3. Osuka reported that the Cu(III) complex is produced upon oxidation of the Cu(II) compound with DDQ.375 As shown in Figure 5.3,
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titration of DDQ into a solution of Cu(II) complex 5.3 affords the oxidized complex 5.4.
The B-band region in 5.4 is dominated by three overlapping transitions at 446, 409, and
378 nm with band at 446 nm bathochromically shifted compared to complex 5.3. The Q- band region in 5.4 is dominated by transitions observed at 521, 554, 633, and 724 nm.
Overall, UV-vis spectra of the neutral complexes 5.1 – 5.4 are clearly indicative of their central-metal dependency.
The MCD spectra of the neutral complexes 5.1 – 5.4 can be seen in Figure 5.2. For
Ni(II) complex 5.1, MCD spectrum in the Q-band region can be described by four Faraday
B-terms observed at 560, 594, 738, and 811 nm. The two lowest energy signals are very weak and have positive amplitude, while bands at 594 and 560 nm are much stronger and have positive and negative amplitudes. The MCD spectrum of 5.1 in the B-band region is dominated by an intense positive signal at 430 nm. Similarly, for the Pd(II) complex 5.2, low-energy Q-band region of MCD spectrum can be described as a superposition of three positive signals observed at 643, 697, and 761 nm along with two negative signals at 543 and 578 nm (Figure 5.2). Again, the MCD spectrum of 5.2 in B-band region is dominated by positive signal at 447 nm. Cu(II) complex 5.3 has MCD spectrum close to that in compound 5.2 with positive bands observed at 676 and 738 nm and negative signals detected at 541 and 588 nm. Because of the extremely low intensity for the Cu(III) complex
5.4, we were not able to clearly define a sign of the MCD transitions associated with the broad, low-energy band at 724 nm observed in the UV-vis spectrum. In contrast, a clear positive signal at 631 nm and negative bands at 583 and 552 nm were clearly observed in the MCD spectrum in the Q-band region of 5.4, which resembles the spectroscopic signature of complex 5.1 with a similar d8 configuration. Overall, MCD spectra of the
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complexes 5.1 – 5.4 are indicative of the unusual ΔHOMO < ΔLUMO energy relationship as evidenced by reverse sign sequence (positive to negative in ascending energy) features.
Figure 5.2: The UV-Vis and MCD spectra of 5.1 (top left), 5.2 (top right), 5.3 (bottom left), and 5.4 (bottom right) in dichloromethane.
Figure 5.3: Transformation of 5.3 into 5.4 (top) with DDQ in dichloromethane.
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Titration of the neutral complexes 5.1 – 5.3 with a strong organic base removes the external proton from the inverted pyrrole ring and leads to formation of anionic 5.1-, 5.2-, and 5.3- complexes. These anionic complexes have significantly different UV-vis spectra
(Figure 5.4). Spectroscopic changes associated with the formation of anionic species have clear central-metal dependence. In case of the Ni(II) complex 5.1, the most intense peak in
B-band region increases in shifts to 419 nm and a prominent shoulder at ~480 nm appears in the spectrum. The Q-band region also alters significantly with all observable peaks shifting to higher energies at 537, 587, 683 and 739 nm. Similar changes were observed for Cu(II) complex 5.3 upon its deprotonation. In particular, the most intense peak in the
B-band region increases in intensity and shifts slightly to 452 nm with a formation of clear shoulder at ~485 nm. In the Q-band region the most intense bands shift to higher energies
(540, 583, 651, and 684 nm) although a broad low intensity shoulder appears at ~760 nm in this case. Upon deprotonation of Pd(II), the initial split B-band converts to three peaks
(399, 440, 462 nm) and the five initial peaks in the Q-band region undergo red shifts and transform into four bands at 528, 568, 654, and 703 nm. This behavior is significantly different from that of the nickel and copper analogs. If there is a common trend to the changes of these spectra upon deprotonation, it is a general hypsochromic shift of the Q band transitions.
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Figure 5.4: Transformation of 5.1 (top left) into 5.1-, 5.2 (top right) into 5.2-, and 5.3 (bottom) into 5.3- during titration with tetrabutylammonium hydroxide in dichloromethane.
MCD spectra of anionic complexes 5.1- - 5.3- are shown in Figure 5.5 and are indicative of the normal for porphyrins ΔHOMO > ΔLUMO energy relationship, which was also observed in [NiNCP]-.341 Indeed, in all cases examined in this study, anionic transition-metal PF-NCPs have negative MCD signal associated with the lowest energy band in corresponding UV-vis spectra. Thus, all divalent transition-metal NCPs studied so far exhibit the same behavior, i.e. they possess the rarely observed inverse (ΔHOMO <
ΔLUMO) relationship in neutral state and normal for porphyrins (ΔHOMO > ΔLUMO) relationship in anionic state.
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Figure 5.5: The UV-Vis and MCD spectra of 5.1- (top), 5.2- (bottom left), and 5.3- (bottom right) in dichloromethane.
To further elucidate the electronic structures in 5.1 – 5.4 and anionic 5.1- - 5.3- complexes, we carried out theoretical investigations on these systems using hybrid B3LYP and TPSSh exchange-correlation functionals, which have proven to be reliable for determining the vertical excitation energies of porphyrins, phthalocyanines, and their analogues.338–342,376 The B3LYP-predicted energy diagram for all target compounds is shown in Figure 5.6, while representative frontier orbital images are pictured in Figures
5.8 and 5.9. Figure 5.7 depicts the energy diagram for TPSSh calculations on the same systems. Both exchange-correlation functionals give very similar results for NCPs 5.1 –
5.4 and anions 5.1- - 5.3-. In particular, both functionals indicative of the presence of
Gouterman’s type frontier orbitals in diamagnetic Ni(II) and Pd(II) compounds 5.1, 5.2,
- - 5.1 , and 5.2 . Indeed, DFT-predicted HOMO resembles Gouterman’s “a2u” orbital (“s”
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orbital in Michl’s perimeter model for porphyrins), HOMO-1 resembles Gouterman’s “a1u” orbital (“a” orbital in Michl’s notation), while LUMO and LUMO+1 resemble
Gouterman’s “eg” orbitals (pair of “-a” and “-s” orbitals in Michl’s notation) with
LUMO+1 orbital having node at the N-confused nitrogen atom (Figure 5.8). In case of the copper-containing complexes 5.3, 5.3-, and 5.4, the expected frontier in-plane orbital with significant contribution from the copper ion “dx2-y2” orbital was predicted by DFT calculations. For the diamagnetic Cu(III) complex 5.4 such orbital was predicted to be
LUMO (Figure 5.9), which correlates well with the metal-centered oxidation of the Cu(II) complex 5.3. In case of the paramagnetic complexes 5.3 and 5.3-, copper-centered orbital was predicted to be LUMO+2 (-set) and HOMO-1 (-set) or HOMO (TPSSh for 5.3 only), which reflects a large spin-polarization in 5.3 and 5.3- (Figure 5.7 and Figure 5.9).
Independently of the exchange-correlation functional that was used, DFT predicts major spin density localization at the Cu(II) center, which agree well with the experimental EPR spectra available for CuNCPs. In case of all divalent complexes, DFT predicts rather minor influence of the central metal on the energies of Gouterman’s type frontier, NCP-centered
-orbitals. DFT calculations also predict correctly the ΔHOMO < ΔLUMO relationship for the neutral complexes 5.1 – 5.4 and the ΔHOMO > ΔLUMO relationship for anionic complexes 5.1- - 5.3-.
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Figure 5.6: DFT-predicted (B3LYP) partial energy diagram NCPs 5.1 – 5.4 and 5.1- - 5.3- .
Figure 5.7: DFT-predicted (TPSSh) molecular orbital energy diagram for 5.1 – 5.4 and 5.1- - 5.3-.
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Figure 5.8: DFT-predicted (B3LYP) Gouterman’s type frontier orbitals for 5.1, 5.2, 5.1-, and 5.2-.
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Figure 5.9: DFT-predicted (B3LYP) Gouterman’s type and copper-centered “dx2-y2” frontier orbitals for 5.3, 5.3-, and 5.4.
To gain insight into the general trends of MCD spectroscopy of NCPs, we have conducted DFT calculations on NiNCP, NiTPP, NiPF-TPP, H2TPP, H2NCP-i, and H2NCP- e compounds (TPP = 5,10,15,20-tetraphenylporphyrinato(2-), PF-TPP = 5,10,15,20- tetra(perfluorophenyl)porphyrinato(2-), NCP-i = “internal” tautomer of N-confused porphyrin, and NCP-e = “external” tautomer of N-confused porphyrin) at the same level of theory (B3LYP and TPSSh exchange-correlation functionals). The generalized energy diagrams for such comparative calculations are shown in Figures 5.10 and 5.11. First, it should be noted that independent of the exchange-correlation functional used, all DFT
143
calculations were able correctly predict HOMO/LUMO relationship and sign of the
MCD transitions in Q-band region, which proves validity of calculations. Second, it seems that introduction of the perfluorophenyl groups instead of phenyl substituents into porphyrin and N-confused core has a simple electron-withdrawing effect. Indeed, the energy differences between respective s (“a2u”), a (“a1u”), -a (“eg”), and –s (“eg”) orbitals in NiNCP and 5.1 (0.49, 0.35, 0.43, and 0.42 eV) as well as NiTPP and NiPF-TPP (0.53,
0.36, 0.43, and 0.43 eV) are very close to each other. The only difference between frontier orbitals in NiTPP and NiPF-TPP is the order of the occupied s (“a2u”), a (“a1u”) orbitals as the former orbital is the HOMO in NiTPP and HOMO-1 in NiPF-TPP. Next, according to the perturbation theory approach, introduced in application to MCD spectroscopy of doubly N-confused porphyrins by Kobayashi and co-workers,358 inversion of the pyrrole ring in the porphyrin core should result in destabilization of Gouterman’s a2u and one of eg orbitals (s and –s orbitals in Michl’s notation) and stabilization of Gouterman’s a1u and another eg orbitals (a and –a orbitals in Michl’s notation, Figure 5.12).
144
Figure 5.10: DFT-predicted (B3LYP) generalized molecular orbital diagrams.
145
Figure 5.11: DFT-predicted (TPSSh) generalized molecular orbital diagrams.
146
Figure 5.12: Comparison of DFT-predicted (B3LYP) Gouterman’s type orbital energy levels and orbital diagrams for previously reported NCP and TPP compounds and compounds 5.1 and 5.4.
Our DFT calculations and measurements of spectroscopic properties of N-confused porphyrins indicate that such simplified approach can be misleading. For instance, DFT calculations at both B3LYP and TPSSh levels suggest that the unoccupied Gouterman’s
“eg” (-a and –s in Michl’s notation) orbitals in H2NCP-i and Cu(III) NCP 5.4 are stabilized compared to the parent H2TPP and NiPF-TPP. Simple perturbation theory predicts that
Gouterman’s “a1u” (a in Michl’s notation) orbital should be more stable in N-confused systems compared to the parent porphyrins, but DFT predicts that such stabilization in
H2TPP/H2NCP-e, NiTPP/NiNCP, and NiPF-TPP/5.1 is negligibly small (0.02 – 0.05 eV).
147
Thus, to explain observed trends in electronic structure and spectroscopy of N-confused porphyrins, we need consider additional factors such as influence of the central ion and the nature of N-confused nitrogen atom (pyrrolic N-H type versus aromatic N: type of the nitrogen atom). Indeed, when H2TPP/H2NCP-e, NiTPP/NiNCP, and NiPF-TPP/5.1 pairs with external N-H fragments in N-confused ring are compared, the destabilization of
Gouterman’s “a2u” (s in Michl’s notation) orbital and stabilization of one of “eg” (-a in
Michl’s notation) orbital is significantly larger in the case of nickel complexes, which can be traced back to the central ion contribution to these orbitals. As a result, HOMO <
LUMO in all nickel systems, while HOMO > LUMO relationship holds for all metal- free NCPs studied so far. Transformation of the external pyrrolic type N-H fragment into aromatic-type N: nitrogen atom (H2TPP/H2NCP-i and NiTPP/5.4 pairs) dramatically reduces LUMO value compared to all other NCPs studied so far. The HOMO gap in
NCP 5.4 with trivalent central ion is very small compared to the same gap in H2NCP-i tautomer. Finally, destabilization of the –a orbital (one with non-zero contribution from the external N-confused nitrogen), upon deprotonation of NiNCP and 5.1 is about twice as large compared to the destabilization of –s orbital (one with node at the external N- confused nitrogen), which reduces LUMO gap in these complexes and inverts the MCD signals to the normal porphyrin trend.377–379
We also used TDDFT methods to predict the UV-vis spectra of the compounds investigated in this study with the results shown in Figures 5.13 and 5.14 (B3LYP calculations) and Figures 5.15 and 5.16 (TPSSh calculations). For both the B3LYP and
TPSSh calculations, we observe good agreement between theory and experiment. The
TDDFT-predicted B-band region in complexes 5.1 – 5.3 and 5.1- - 5.3- should be primarily
148
dominated by the HOMO-1 → LUMO, HOMO-1 → LUMO+1, and HOMO → LUMO+1 single-electron excitations which fits well within the borders of Gouterman’s four-orbital model. For Cu(III) compound 5.4, the B-band region is primarily dominated by single- electron excitations from the HOMO-1 → LUMO+2, HOMO-1 → LUMO+1, HOMO →
LUMO+2, and HOMO → LUMO+1 as the LUMO in this compound is copper-centered
“dx2-y2” orbital. All transitions listed above can be characterized as π-π* transitions and adhere to the Gouterman four orbital paradigm. For both functionals, the TDDFT-predicted energies in the Q-band region for 5.1 – 5.4 and 5.1- - 5.3- are slightly overestimated.
However, as expected from the Gouterman’s four-orbital model, TDDFT predicts that the
Q-band region in respective complexes should be dominated by the HOMO → LUMO
(complexes 5.1 – 5.3 and 5.1- - 5.3-) or HOMO → LUMO+1 (compound 5.4) single- electron excitations.
Figure 5.13: Experimental and TDDFT-predicted UV-Vis spectra of 5.1 – 5.4 using B3LYP exchange-correlation functional in dichloromethane.
149
Figure 5.14: Experimental and TDDFT-predicted UV-Vis spectra of 5.1- - 5.3- using B3LYP exchange-correlation functional in dichloromethane.
Figure 5.15: Experimental and TDDFT-predicted (TPSSh) UV-vis spectra of complexes 5.1 – 5.4 in dichloromethane.
150
Figure 5.16: Experimental and TDDFT-predicted (TPSSh) UV-vis spectra of complexes 5.1- – 5.3- in dichloromethane.
Conclusions
In conclusion, the transition-metal perfluorophenyl-N-confused porphyrin complexes 5.1 – 5.4 exhibit the unusual reversed sign sequence MCD spectra as compared to other porphyrinoid variants. The deprotonation of the external pyrrolic hydrogen in complexes 5.1- 5.3, changes the electronic structure from ΔLUMO ˃ ΔHOMO to the usual
ΔLUMO ˂ ΔHOMO relationship which we have previously shown to occur with the deprotonation of NiNCP.341 DFT calculations on all NCPs studied by MCD spectroscopy so far are in agreement with the experimental data and are indicative of the important role of not only the central metal ion but also tautomeric type of the N-confused π-system (i.e., external versus internal tautomer).
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CHAPTER VI
SUMMARY
In Chapter II, half-hemiporphyrazine macrocycles, which can be called
“semihemiporphyrazines,” were synthesized using the Re(CO)3 unit as a templating agent.
The products of these template reactions are six-coordinate Re complexes, with a facial arrangement of carbonyls, a halide, and a bidentate semihemiporphyrazine chelate that tilts out of the plane of coordination. Three types of semihemiporphyrazines can be produced from these reactions, depending on the alternate heterocycle to the isoindoline unit; structures including pyridine, thiazole and benzimidazole were formed. The electronic structures of these compounds were probed using spectroscopy as well as density functional theory methods.
In Chapter III, α-amidino azadi(benzopyrro)methenes were synthesized using the
Re(CO)3 unit as a templating agent. The products of these template reactions are six- coordinate Re complexes, with a facial arrangement of carbonyls, a non-coordinating anion, and a tridentate α-amidino azadi(benzopyrro)methene ligand. The tridentate ligand shows the conversion of one diiminoisoindoline sp2 carbon to a sp3 carbon which has been seen in the “helmet” and bicyclic phthalocyanines. The bidentate diiminoisoindoline fragment tilts out of the plane of coordination. Five examples of α-amidino azadi(benzopyrro)methenes were produced from these reactions using different nitrile
152
solvents, including the nitrile activation of acetonitrile, propionitrile, butyronitrile, cyclohexanecarbonitrile, and benzonitrile were formed.
In Chapter IV, a study of the transition metal chemistry with the planar tridentate ligand 2,6-diacetylpyridine dihydrazone (4.1, DAPH) is presented, expanding the chemistry of this ligand across the first row of the transition metals. Ligand 4.1 forms both
1:1 and homoleptic 2:1 complexes with transition metal ions, depending on the metal salt used and reaction conditions, and seven new complexes with Mn, Fe, Co, Cu, and Zn are presented. All compounds, including the ligand, have been characterized by X-ray crystallography. DAPH (4.1) binds to metal ions in an asymmetric fashion, with a M-Npyr bond that is shorter than the flanking M-Nimine bonds. Additionally, the Nimine-M-Nimine bonds form acute angles ranging from ~140 to 160°, depending on the identity of the metal ion and ligand environment. All compounds are compared to previously elucidated DAPH structures from the literature.
Finally, in Chapter VI, neutral and deprotonated anionic Ni(II), Pd(II), Cu(II), and
Cu(III) complexes of the tetrakis(perfluorophenyl)-N-confused porphyrin (PF-NCP) were prepared and investigated by UV-visible and magnetic circular dichroism (MCD) spectroscopies. As in the previously reported Ni(II) adduct of tetraphenyl N-confused porphyrin, we observe sign reverse (positive to negative intensities with increasing energy) features in the MCD spectra of the neutral Ni(II), Pd(II), and Cu(II) complexes of PF-NCP, which is indicative of rare ΔHOMO < ΔLUMO relationships. Upon deprotonation of
Ni(II), Pd(II), and Cu(II) complexes, these features revert to those of more typical porphyrinic MCD spectra consistent with a ΔHOMO > ΔLUMO condition. The Cu(III)
PF-NCP complex shows features similar to those of the deprotonated divalent metal
153
systems. Spectroscopic features in all target complexes as well as previously published metal-free and Ni(II) NCP systems were correlated with the Density Functional Theory
(DFT) and Time-Dependent DFT (TDDFT) calculations. Calculation results are consistent with the tautomeric rearrangement of the electronic structures of NCP cores playing dominant roles, with smaller contribution from the central metal ions in the observed optical and magneto-optical properties. This is true for all described NCP systems to date, as they affect the stabilization/destabilization of the N-confused porphyrin centered
Gouterman’s orbitals.
154
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