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Labrum NS, Cabelof AC, Caulton KG. A Dimeric Chromium(II) Pincer as an Electron Shuttle for N=N Bond Scission. Chemistry 2020; 26:13915-13926. [PMID: 32428366 DOI: 10.1002/chem.202001749] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2020] [Revised: 05/12/2020] [Indexed: 01/08/2023]
Abstract
Reduction of the bis-pyrazolyl pyridine complex [CrL]2 with 4 KC8 , followed by addition of one azobenzene (overall mole ratio 1:4:1), PhNNPh, transfers reducing equivalents to three azobenzenes, to form [K3 Cr(PhNNPh)3 ]. This has three κ2 PhNNPh2- ligands and K+ bound to nitrogen atoms of azobenzene. When the stoichiometry is modified to 1:4:3, the product is changed to [K2 CrL(PhNNPh)2 ], which has C2 symmetry except for the intimate ion pairing of two K+ ions to reduced azobenzene nitrogen atoms, and to pyrazolate and phenyl rings. The origin of the observed delivery of reducing equivalents to several, not to a single N=N bond, is traced to the resistance of the one-electron-reduced substrate to receiving a second electron, and is thus a general phenomenon. [CrL]2 alone is shown to be a two-electron reductant towards benzo[c]cinnoline (BCC) resulting in a product of formula [Cr2 L2 (BCC)], in which the reducing equivalents originate purely from CrII . An analogous study of the reaction of [CrL]2 with azobenzene yields [Cr2 L2 (PhNNPh)(THF)], an adduct in which one THF has displaced one of four hydrazide nitrogen/Cr bonds. Together these illustrate different modes for the Cr2 L2 unit to bind and reduce the N=N bond. Collectively, these results show that two divalent Cr, without added K0 , have the ability to reduce the N=N bond. Further KC8 reduction of preformed Cr2 L2 (RNNR) inevitably gives products in which K+ stabilizes the charge in the increasingly electron-rich nitrogen atoms, in a phenomenon which mimics proton coupled electron transfer: K+ performs the role of H+ . A least-squares fit of the two singly reduced DFT structures shows that the only major change is a re-orientation of one of the two phenyl rings in order to avoid repulsion with potassium but to still allow interaction of that phenyl π system with K+ . This shows both the impact of K+ , being modest to nitrogen/chromium interactions, but nevertheless accommodating some π donation of phenyl to potassium. Finally, delivering increasing equivalents of KC8 leads to complete cleavage of the N=N bond, and both N bind to three CrII . The varied impacts of the K+ electrophile on NN multiple bond reduction is discussed.
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Affiliation(s)
- Nicholas S Labrum
- Department of Chemistry, Indiana University, 800 E. Kirkwood Ave., Bloomington, IN, 47405-7102, USA
| | - Alyssa C Cabelof
- Department of Chemistry, Indiana University, 800 E. Kirkwood Ave., Bloomington, IN, 47405-7102, USA
| | - Kenneth G Caulton
- Department of Chemistry, Indiana University, 800 E. Kirkwood Ave., Bloomington, IN, 47405-7102, USA
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Wang W, Tan G, Feng R, Fang Y, Chen C, Ruan H, Zhao Y, Wang X. Stable, yet "naked", azo radical anion ArNNAr - and dianion ArNNAr 2- (Ar = 4-CN-2,6- iPr 2-C 6H 2) with selective CO 2 activation. Chem Commun (Camb) 2020; 56:3285-3288. [PMID: 32073045 DOI: 10.1039/c9cc07382e] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Azo radical anion 1˙- and dianion 12- have been isolated by one- and two-electron reduction of the azo compound 1 (ArNNAr, Ar = 4-CN-2,6-iPr2-C6H2) with alkali metals, respectively. The reduced species have been characterized by single-crystal X-ray analysis, EPR, UV and FT-IR spectroscopy, as well as SQUID measurements. The filling of one and two electrons in the π* orbital of the N-N double bond of 1 leads to a half-double N-N bond in 1˙- and a single N-N bond in 12-. The uncoordinated nature of these reduced species enables them to activate CO2. The exposure of 1˙- solution to CO2 led to the formation of oxalate anion C2O42-, while that of 12- solution to CO2 afforded the hydrazine dicarboxylate dianion [1-2CO2]2-, which reversibly dissociated back to 1 and CO2 upon oxidation.
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Affiliation(s)
- Wenqing Wang
- College of Chemistry and Material Science, Key Laboratory of Functional Molecular Solids, Ministry of Education, Anhui Laboratory of Molecule-Based Materials, Anhui Normal University, Wuhu, Anhui 241002, China and State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China.
| | - Gengwen Tan
- State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China.
| | - Rui Feng
- State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China.
| | - Yong Fang
- State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China.
| | - Chao Chen
- State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China.
| | - Huapeng Ruan
- State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China.
| | - Yue Zhao
- State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China.
| | - Xinping Wang
- State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China.
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Vaddypally S, McKendry IG, Tomlinson W, Hooper JP, Zdilla MJ. Electronic Structure of Manganese Complexes of the Redox‐Non‐innocent Tetrazene Ligand and Evidence for the Metal‐Azide/Imido Cycloaddition Intermediate. Chemistry 2016; 22:10548-57. [DOI: 10.1002/chem.201600531] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2016] [Revised: 05/12/2016] [Indexed: 11/06/2022]
Affiliation(s)
- Shivaiah Vaddypally
- Department of Chemistry Temple University 1901 N. 13th St. Philadelphia PA 19122 USA
| | - Ian G. McKendry
- Department of Chemistry Temple University 1901 N. 13th St. Philadelphia PA 19122 USA
| | - Warren Tomlinson
- Department of Physics Naval Postgraduate School 833 Dyer Rd. Monterey CA 93943 USA
| | - Joseph P. Hooper
- Department of Physics Naval Postgraduate School 833 Dyer Rd. Monterey CA 93943 USA
| | - Michael J. Zdilla
- Department of Chemistry Temple University 1901 N. 13th St. Philadelphia PA 19122 USA
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Levin JR, Cheisson T, Carroll PJ, Schelter EJ. Accessing relatively electron poor cerium(iv) hydrazido complexes by lithium cation promoted ligand reduction. Dalton Trans 2016; 45:15249-58. [DOI: 10.1039/c6dt03154d] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A series of substituted N,N′-diarylhydrazines (ArNHNHAr) were reacted with Ce(iii)[N(SiMe3)2]3 and LiN(SiMe3)2 to form complexes of general formula Li4(OEt2)4 [Ce(iv)(ArNNAr)4] where the spectroscopic and redox properties were affected by the ligand substitution.
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Affiliation(s)
- Jessica R. Levin
- P. Roy and Diana T. Vagelos Laboratories
- Department of Chemistry
- University of Pennsylvania
- Philadelphia
- USA
| | - Thibault Cheisson
- P. Roy and Diana T. Vagelos Laboratories
- Department of Chemistry
- University of Pennsylvania
- Philadelphia
- USA
| | - Patrick J. Carroll
- P. Roy and Diana T. Vagelos Laboratories
- Department of Chemistry
- University of Pennsylvania
- Philadelphia
- USA
| | - Eric J. Schelter
- P. Roy and Diana T. Vagelos Laboratories
- Department of Chemistry
- University of Pennsylvania
- Philadelphia
- USA
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Levin JR, Dorfner WL, Carroll PJ, Schelter EJ. Control of cerium oxidation state through metal complex secondary structures. Chem Sci 2015; 6:6925-6934. [PMID: 29861931 PMCID: PMC5951102 DOI: 10.1039/c5sc02607e] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2015] [Accepted: 08/10/2015] [Indexed: 12/20/2022] Open
Abstract
A series of alkali metal cerium diphenylhydrazido complexes, M x (py) y [Ce(PhNNPh)4], M = Li, Na, and K, x = 4 (Li and Na) or 5 (K), and y = 4 (Li), 8 (Na), or 7 (K), were synthesized to probe how a secondary coordination sphere would modulate electronic structures at a cerium cation. The resulting electronic structures of the heterobimetallic cerium diphenylhydrazido complexes were found to be strongly dependent on the identity of the alkali metal cations. When M = Li+ or Na+, the cerium(iii) starting material was oxidized with concomitant reduction of 1,2-diphenylhydrazine to aniline. Reduction of 1,2-diphenylhydrazine was not observed when M = K+, and the complex remained in the cerium(iii) oxidation state. Oxidation of the cerium(iii) diphenylhydrazido complex to the Ce(iv) diphenylhydrazido one was achieved through a simple cation exchange reaction of the alkali metals. UV-Vis spectroscopy, FTIR spectroscopy, electrochemistry, magnetic susceptibility, and DFT studies were used to probe the oxidation state and the electronic changes that occurred at the metal centre.
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Affiliation(s)
- Jessica R Levin
- Roy and Diana T. Vagelos Laboratories , Department of Chemistry , University of Pennsylvania , 231 South 34th St. , Philadelphia , Pennsylvania 19104 , USA . ; Tel: +1 215-898-8633
| | - Walter L Dorfner
- Roy and Diana T. Vagelos Laboratories , Department of Chemistry , University of Pennsylvania , 231 South 34th St. , Philadelphia , Pennsylvania 19104 , USA . ; Tel: +1 215-898-8633
| | - Patrick J Carroll
- Roy and Diana T. Vagelos Laboratories , Department of Chemistry , University of Pennsylvania , 231 South 34th St. , Philadelphia , Pennsylvania 19104 , USA . ; Tel: +1 215-898-8633
| | - Eric J Schelter
- Roy and Diana T. Vagelos Laboratories , Department of Chemistry , University of Pennsylvania , 231 South 34th St. , Philadelphia , Pennsylvania 19104 , USA . ; Tel: +1 215-898-8633
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Hamilton CR, Gau MR, Baglia RA, McWilliams SF, Zdilla MJ. Mechanistic elucidation of the stepwise formation of a tetranuclear manganese pinned butterfly cluster via N-N bond cleavage, hydrogen atom transfer, and cluster rearrangement. J Am Chem Soc 2014; 136:17974-86. [PMID: 25424971 DOI: 10.1021/ja508244x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A mechanistic pathway for the formation of the structurally characterized manganese-amide-hydrazide pinned butterfly complex, Mn4(μ3-PhN-NPh-κ(3)N,N')2(μ-PhN-NPh-κ(2)-N,N')(μ-NHPh)2L4 (L = THF, py), is proposed and supported by the use of labeling studies, kinetic measurements, kinetic competition experiments, kinetic isotope effects, and hydrogen atom transfer reagent substitution, and via the isolation and characterization of intermediates using X-ray diffraction and electron paramagnetic resonance spectroscopy. The data support a formation mechanism whereby bis[bis(trimethylsilyl)amido]manganese(II) (Mn(NR2)2, where R = SiMe3) reacts with N,N'-diphenylhydrazine (PhNHNHPh) via initial proton transfer, followed by reductive N-N bond cleavage to form a long-lived Mn(IV) imido multinuclear complex. Coordinating solvents activate this cluster for abstraction of hydrogen atoms from an additional equivalent of PhNHNHPh resulting in a Mn(II)phenylamido dimer, Mn2(μ-NHPh)2(NR2)2L2. This dimeric complex further assembles in fast steps with two additional equivalents of PhNHNHPh replacing the terminal silylamido ligands with η(1)-hydrazine ligands to give a dimeric Mn2(μ-NHPh)2(PhN-NHPh)2L4 intermediate, and finally, the addition of two additional equivalents of Mn(NR2)2 and PhNHNHPh gives the pinned butterfly cluster.
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Affiliation(s)
- Clifton R Hamilton
- Department of Chemistry, Temple University , 1901 North 13th Street, Philadelphia, Pennsylvania 19122, United States
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Vaddypally S, Kondaveeti SK, Roudebush JH, Cava RJ, Zdilla MJ. Formation of the tetranuclear, tetrakis-terminal-imido Mn4IV(NtBu)8cubane cluster by four-electron reductive elimination oftBuNNtBu. The role of the s-block ion in stabilization of high-oxidation state intermediates. Chem Commun (Camb) 2014; 50:1061-3. [DOI: 10.1039/c3cc42165a] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Kondaveeti SK, Vaddypally S, McCall JD, Zdilla MJ. Electronic structure and solution behavior of a tris(N,N′-diphenylhydrazido)manganese(iv) propeller complex. Dalton Trans 2012; 41:8093-7. [DOI: 10.1039/c2dt30493g] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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