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Do TH, Haungs DA, Chin WY, Jerit JT, VanderZwaag A, Brown SN. Modulation of Isomerization and Ligand Exchange Rates by π Bonding in Bis(iminoxolene)iridium Pyridine Complexes. Inorg Chem 2023. [PMID: 37437186 DOI: 10.1021/acs.inorgchem.3c01717] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/14/2023]
Abstract
The bis(iminoxolene)iridium complex (Diso)2IrCl (Diso = N-(2,6-diisopropylphenyl)-4,6-di-tert-butyl-2-imino-o-benzoquinone) reacts with pyridine to give trans-(Diso)2Ir(py)Cl as the kinetic product, with cis-(Diso)2Ir(py)Cl formed as the exclusive thermodynamic product upon heating. Electronic spectra and density functional theory calculations point to very similar electronic structures for the cis and trans isomers, with a nonbonding iminoxolene-centered HOMO and a metal-iminoxolene π* LUMO. The triplet states of cis-(Diso)2Ir(py)Cl and cis-[(Diso)2Ir(py)2]+ (but not trans-(Diso)2Ir(py)Cl) are unusually low in energy (1000-1500 cm-1 above the singlets), as shown by variable-temperature NMR spectroscopy. The low-energy triplets are attributed to a change in dihedral angle in the iminoxolenes, which allows a partial π interaction that cannot be achieved in the trans octahedral compounds. Mechanistic studies of the trans-cis isomerization in toluene indicate that the reaction proceeds via isomerization of the five-coordinate species to a form with cis iminoxolene ligands and an apical oxygen. This form is high in energy due to the loss of a secondary iminoxolene-to-iridium π-donor interaction that is possible in the trans form but not in the cis form for the square pyramidal structures. This stereoelectronic effect, combined with the poorer binding of pyridine in trans-(Diso)2Ir(py)Cl due to the interactions of the N-aryl substituents with the pyridine, makes the pyridine dissociate faster from the trans isomer by a factor of 108 at room temperature.
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Affiliation(s)
- Thomas H Do
- Department of Chemistry and Biochemistry, University of Notre Dame, 251 Nieuwland Science Hall, Notre Dame, Indiana 46556-5670, United States
| | - David A Haungs
- Department of Chemistry and Biochemistry, University of Notre Dame, 251 Nieuwland Science Hall, Notre Dame, Indiana 46556-5670, United States
| | - William Y Chin
- Department of Chemistry and Biochemistry, University of Notre Dame, 251 Nieuwland Science Hall, Notre Dame, Indiana 46556-5670, United States
| | - Jack T Jerit
- Department of Chemistry and Biochemistry, University of Notre Dame, 251 Nieuwland Science Hall, Notre Dame, Indiana 46556-5670, United States
| | - Analena VanderZwaag
- Department of Chemistry and Biochemistry, University of Notre Dame, 251 Nieuwland Science Hall, Notre Dame, Indiana 46556-5670, United States
| | - Seth N Brown
- Department of Chemistry and Biochemistry, University of Notre Dame, 251 Nieuwland Science Hall, Notre Dame, Indiana 46556-5670, United States
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Haungs DA, Brown SN. Slicing the π in Three Unequal Pieces: Iridium Complexes with Alkyne, Iminoxolene, and Dioxolene Ligands. Organometallics 2022. [DOI: 10.1021/acs.organomet.2c00431] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- David A. Haungs
- Department of Chemistry and Biochemistry, University of Notre Dame, 251 Nieuwland Science Hall, Notre Dame, Indiana 46556-5670, United States
| | - Seth N. Brown
- Department of Chemistry and Biochemistry, University of Notre Dame, 251 Nieuwland Science Hall, Notre Dame, Indiana 46556-5670, United States
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Do TH, Brown SN. Mono- and Bis(iminoxolene)iridium Complexes: Synthesis and Covalency in π Bonding. Inorg Chem 2022; 61:5547-5562. [PMID: 35357169 DOI: 10.1021/acs.inorgchem.1c04005] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
N-(2,6-Diisopropylphenyl)-4,6-di-tert-butyl-o-iminobenzoquinone (Diso) reacts with the (cyclooctadiene)iridium chloride dimer to form a monoiminoxolene complex, (Diso)Ir(cod)Cl. Reaction of 2 equiv of the iminoquinone with chlorobis(cyclooctene)iridium dimer affords the bis-iminoxolene (Diso)2IrCl. This five-coordinate complex adopts a distorted square pyramidal structure with an apical chloride ligand and undergoes halide exchange to form an air-stable iodide complex. (Diso)2IrCl can be reduced by one electron to form neutral, square planar (Diso)2Ir, while oxidation with PhICl2 gives octahedral trans-(Diso)2IrCl2. The cis isomer can be prepared by air oxidation of (Diso)2IrCl; cis/trans isomerization is not observed even on prolonged heating. Structural and spectroscopic features of the complexes are consistent with the presence of strong, covalent π bonding between the metal and the iminoxolene ligands, with structural data suggesting between 45 and 60% iridium character in the π bonding orbitals, depending on the ancillary ligands. The spectroscopic similarity of (Diso)2Ir and (Diso)2IrCl to their cobalt congeners suggests that the first-row metal complexes likewise have appreciably covalent metal-iminoxolene π bonds.
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Affiliation(s)
- Thomas H Do
- Department of Chemistry and Biochemistry, University of Notre Dame, 251 Nieuwland Science Hall, Notre Dame, Indiana 46556-5670, United States
| | - Seth N Brown
- Department of Chemistry and Biochemistry, University of Notre Dame, 251 Nieuwland Science Hall, Notre Dame, Indiana 46556-5670, United States
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Nguyen HT, Bui TQ, Nhat PV, Lan DTP, Nhung NTA. A DFT study of the molecular and electronic structures of cis-dioxidomolybdenum (VI) complex of 8-hydroxyquinoline and 4-benzoyl-3-methyl-1-phenyl-2-pyrazolin-5-one with water. Theor Chem Acc 2022. [DOI: 10.1007/s00214-022-02868-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Erickson AN, Gianino J, Markovitz SJ, Brown SN. Amphiphilicity in Oxygen Atom Transfer Reactions of Oxobis(iminoxolene)osmium Complexes. Inorg Chem 2021; 60:4004-4014. [PMID: 33657323 DOI: 10.1021/acs.inorgchem.1c00068] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Oxobis(iminoxolene)osmium(VI) compounds (Rap)2OsO (Rap = 2-(4-RC6H4N)-4,6-tBu2C6H2O) are readily deoxygenated by phosphines and phosphites to give five-coordinate (Rap)2Os(PR'3) or six-coordinate (Rap)2Os(PR'3)2. Structural data indicate that this net two-electron reduction is accompanied by apparent oxidation of the iminoxolene ligands due to their greater ability to engage in π donation to the reduced deoxy form of the osmium complex. In (Rap)2Os(PR'3)2, the HOMO is a ligand-based combination of the iminoxolene redox-active orbitals, while the LUMO is a highly covalent metal-iminoxolene π* orbital. In the trans isomer, the HOMO is required to be ligand-localized by symmetry, while in the cis isomer, the ligands adopt a conformation that minimizes metal-ligand π* interactions in the HOMO. Kinetic studies indicate that the deoxygenations involve the rate-determining attack of the phosphorus(III) reagent on the five-coordinate oxo complexes. Varying the substituents of the aryl groups on the iminoxolene ligands or on the triarylphosphines has little effect on the rate of oxygen atom transfer, with the best correlation shown between oxygen atom transfer rates and the HOMO-LUMO gap of the oxo complexes. This suggests that the osmium oxo group shows a balance between electrophilic and nucleophilic character in its oxygen atom transfer reactions with phosphorus(III) reagents.
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Affiliation(s)
- Alexander N Erickson
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556-5670, United States
| | - Jacqueline Gianino
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556-5670, United States
| | - Sean J Markovitz
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556-5670, United States
| | - Seth N Brown
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556-5670, United States
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Gianino J, Erickson AN, Markovitz SJ, Brown SN. High-valent osmium iminoxolene complexes. Dalton Trans 2020; 49:8504-8515. [PMID: 32525176 DOI: 10.1039/d0dt01735c] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
2-(Arylamino)-4,6-di-tert-butylphenols containing 4-substituted phenyl groups (RapH2) react with oxobis(ethylene glycolato)osmium(vi) in acetone to give square pyramidal bis(amidophenoxide)oxoosmium(vi) complexes. A mono-amidophenoxide complex is observed as an intermediate in these reactions. Reactions in dichloromethane yield the diolate (Hap)2Os(OCH2CH2O). Both the glycolate and oxo complex are converted to the corresponding cis-dichloride complex on treatment with chlorotrimethylsilane. The novel bis(aminophenol) ligand EganH4, containing an ethylene glycol dianthranilate bridge, forms the chelated bis(amidophenoxide) complex (Egan)OsO, where the two nitrogen atoms of the tetradentate ligand bind in the trans positions of the square pyramid. Structural and spectroscopic features of the complexes are described well by an osmium(vi)-amidophenoxide formulation, with the amount of π donation from ligand to metal increasing markedly as the co-ligands change from oxo to diolate to dichloride. In the oxo-bis(amidophenoxides), the symmetry of the ligand π orbitals results in only one effective π donor interaction, splitting the energy of the two osmium-oxo π* orbitals and rendering the osmium-oxo bonding appreciably anisotropic.
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Affiliation(s)
- Jacqueline Gianino
- Department of Chemistry and Biochemistry, 251 Nieuwland Science Hall, University of Notre Dame, Notre Dame, IN 46556-5670, USA.
| | - Alexander N Erickson
- Department of Chemistry and Biochemistry, 251 Nieuwland Science Hall, University of Notre Dame, Notre Dame, IN 46556-5670, USA.
| | - Sean J Markovitz
- Department of Chemistry and Biochemistry, 251 Nieuwland Science Hall, University of Notre Dame, Notre Dame, IN 46556-5670, USA.
| | - Seth N Brown
- Department of Chemistry and Biochemistry, 251 Nieuwland Science Hall, University of Notre Dame, Notre Dame, IN 46556-5670, USA.
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Gianino J, Brown SN. Highly covalent metal-ligand π bonding in chelated bis- and tris(iminoxolene) complexes of osmium and ruthenium. Dalton Trans 2020; 49:7015-7027. [PMID: 32367103 DOI: 10.1039/d0dt01287d] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The bis(aminophenol) 2,2'-biphenylbis(3,5-di-tert-butyl-2-hydroxyphenylamine) (ClipH4) forms trans-(Clip)Os(py)2 upon aerobic reaction of the ligand with {(p-cymene)OsCl2}2 in the presence of pyridine and triethylamine. A more oxidized species, cis-β-(Clip)Os(OCH2CH2O), is formed from reaction of the ligand with the osmium(vi) complex OsO(OCH2CH2O)2, and reacts with Me3SiCl to give the chloro complex cis-β-(Clip)OsCl2. Octahedral osmium and ruthenium tris-iminoxolene complexes are formed from the chelating ligand tris(2-(3',5'-di-tert-butyl-2'-hydroxyphenyl)amino-4-methylphenyl)amine (MeClampH6) on aerobic reaction with divalent metal precursors. The complexes' structural and electronic features are well described using a simple bonding model that emphasizes the covalency of the π bonding between the metal and iminoxolene ligands rather than attempting to dissect the parts into discrete oxidation states. Emphasizing the continuity of bonding between disparate complexes, the structural data from a variety of Os and Ru complexes show good correlations to π bond order, and the response of the intraligand bond distances to the bond order can be analyzed to illuminate the polarity of the bonding between metal and the redox-active orbital on the iminoxolenes. The osmium compounds'π bonding orbitals are about 40% metal-centered and 60% ligand-centered, with the ruthenium compounds' orbitals about 65% metal-centered and 35% ligand-centered.
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Affiliation(s)
- Jacqueline Gianino
- Department of Chemistry and Biochemistry, 251 Nieuwland Science Hall, University of Notre Dame, Notre Dame, IN 46556-5670, USA.
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Credendino L, Sproules S. Modulating Iron Spin States with Radical Ligands: A Density Functional Theoretical Study. ASIAN J ORG CHEM 2020. [DOI: 10.1002/ajoc.201900626] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
| | - Stephen Sproules
- WestCHEM School of ChemistryUniversity of Glasgow Glasgow G12 8QQ UK
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Do TH, Brown SN. Mono- and bimetallic pentacoordinate silicon complexes of a chelating bis(catecholimine) ligand. Dalton Trans 2019; 48:11565-11574. [PMID: 31297499 DOI: 10.1039/c9dt02475a] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Schiff base condensation of 4,5-diamino-9,9-dimethylxanthene with 4,6-di-tert-butylcatechol-3-carboxaldehyde affords the bis(catecholimine) ligand XbicH4, which can bind metals in both a square bis(catecholate) upper pocket and a pentagonal N2O3 lower pocket. Metalation with PhSiCl3 results in [(XbicH2)SiPh][HCl2], where the silicon adopts a five-coordinate, square pyramidal geometry in the upper pocket and the lower pocket binds to two protons on the imine nitrogens. Deprotonation of the imines with LiOtBu, NaN[SiMe3]2, or AgOAc results in binding of the univalent metal ion in the lower pocket, where it adopts an unusual pentagonal monopyramidal geometry in the solid state. The complexes show irreversible electrochemistry, with oxidations taking place at relatively high potentials.
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Affiliation(s)
- Thomas H Do
- Department of Chemistry and Biochemistry, University of Notre Dame, 251 Nieuwland Science Hall, Notre Dame, IN 46556-5670, USA.
| | - Seth N Brown
- Department of Chemistry and Biochemistry, University of Notre Dame, 251 Nieuwland Science Hall, Notre Dame, IN 46556-5670, USA.
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Marshall-Roth T, Yao K, Parkhill JA, Brown SN. On the border between localization and delocalization: tris(iminoxolene)titanium(iv). Dalton Trans 2019; 48:1427-1435. [DOI: 10.1039/c8dt04528c] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
An air-stable tris(iminoxolene)titanium(iv) complex is a ground state singlet best described as intermediate between fully localized and fully delocalized.
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Affiliation(s)
| | - Kun Yao
- Department of Chemistry and Biochemistry
- University of Notre Dame
- Notre Dame
- USA
| | - John A. Parkhill
- Department of Chemistry and Biochemistry
- University of Notre Dame
- Notre Dame
- USA
| | - Seth N. Brown
- Department of Chemistry and Biochemistry
- University of Notre Dame
- Notre Dame
- USA
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