1
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Horrer G, Luff MS, Radius U. N-Heterocyclic carbene and cyclic (alkyl)(amino)carbene ligated half-sandwich complexes of chromium(II) and chromium(I). Dalton Trans 2023; 52:13244-13257. [PMID: 37667868 DOI: 10.1039/d3dt02123h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/06/2023]
Abstract
The synthesis and characterization of a series of Cr(II) N-Heterocyclic Carbene (NHC) complexes of the type [{Cr(NHC)Cl(μ-Cl)}2] and [(Cyp)Cr(NHC)X] (Cyp = η5-C5H5, cyclopentadienyl; η5-C5Me5, pentamethylcyclopentadienyl; X = Cl, η3-C3H5; NHC = IMeMe, IiPrMe, IMes, IDipp) as well as the cyclic (alkyl)(amino)carbene cAACMe ligated complexes [(η5-C5H5)Cr(cAACMe)X] (X = Cl, NPh2), [(η5-C9H7)Cr(cAACMe)Cl] (C9H7 = Ind, indenyl) and [(η5-C13H9)Cr(cAACMe)Cl] (C13H9 = Fl, fluorenyl) are reported. The reduction of [(η5-C5Me5)Cr(IMeMe)Cl] with KC8 in the presence of CO afforded the NHC ligated Cr(I) metallo-radical [(η5-C5Me5)Cr(IMeMe)(CO)2]. Quantum chemical calculations performed on [(η5-C5Me5)Cr(IMeMe)(CO)2] confirm for this complex a predominantly chromium centered radical.
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Affiliation(s)
- Günther Horrer
- Institut für Anorganische Chemie, Julius-Maximilians-Universität Würzburg, Am Hubland, 97074 Würzburg, Germany.
| | - Martin S Luff
- Institut für Anorganische Chemie, Julius-Maximilians-Universität Würzburg, Am Hubland, 97074 Würzburg, Germany.
| | - Udo Radius
- Institut für Anorganische Chemie, Julius-Maximilians-Universität Würzburg, Am Hubland, 97074 Würzburg, Germany.
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2
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Ju MY, Fan ZH, Ma Y, Jing Y, Chen XM, Chen X. Syntheses, Structures, and Reactivities of N-Heterocyclic Carbene-Coordinated Aminoborane Complexes. Inorg Chem 2023. [PMID: 37224452 DOI: 10.1021/acs.inorgchem.3c00930] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Recent research has attracted considerable attention toward N-heterocyclic carbene-coordinated boranes (NHC-borane) and their B-substituted derivatives because of their unique characteristics. In the present work, we focused on the syntheses, structures, and reactivities of such types of amine complexes, [NHC·BH2NH3]X ((NHC = IPr (1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) and IMe (1,3-dimethylimidazol-2-ylidene); X = Cl, I, OTf). We have developed a synthetic method to access NHC·BH2NH2 through the reaction of NaH with [IPr·BH2NH3]I, which was synthesized by the reaction of IPr·BH2I with NH3. As a Lewis base, NHC·BH2NH2 could further react with HCl or HOTf to produce the corresponding salts of [IPr·BH2NH3]+. IPr·BH2NH2BH2X (X = Cl, I) were synthesized by the reaction of HCl/I2 with IPr·BH2NH2BH3 and then converted to [IPr·BH2NH2BH2·IPr]X (X = Cl, I) by reacting with IPr. The IMe-coordinated boranes reacted quite similarly. The preliminary results revealed that the introduction of the NHC molecule has a considerable impact on the solubility and reactivities of aminoboranes.
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Affiliation(s)
- Ming-Yue Ju
- Henan Key Laboratory of Boron Chemistry and Advanced Energy Materials, School of Chemistry and Chemical Engineering, Henan Normal University, Xinxiang, Henan 453007, China
| | - Zi-Heng Fan
- Henan Key Laboratory of Boron Chemistry and Advanced Energy Materials, School of Chemistry and Chemical Engineering, Henan Normal University, Xinxiang, Henan 453007, China
| | - Yubin Ma
- Henan Key Laboratory of Boron Chemistry and Advanced Energy Materials, School of Chemistry and Chemical Engineering, Henan Normal University, Xinxiang, Henan 453007, China
| | - Yi Jing
- College of Chemistry, Zhengzhou University, Zhengzhou, Henan 450001, China
| | - Xi-Meng Chen
- Henan Key Laboratory of Boron Chemistry and Advanced Energy Materials, School of Chemistry and Chemical Engineering, Henan Normal University, Xinxiang, Henan 453007, China
| | - Xuenian Chen
- Henan Key Laboratory of Boron Chemistry and Advanced Energy Materials, School of Chemistry and Chemical Engineering, Henan Normal University, Xinxiang, Henan 453007, China
- College of Chemistry, Zhengzhou University, Zhengzhou, Henan 450001, China
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3
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Takebayashi S, Fayzullin RR, Bansal R. Direct observation of reversible bond homolysis by 2D EXSY NMR. Chem Sci 2022; 13:9202-9209. [PMID: 36093009 PMCID: PMC9383717 DOI: 10.1039/d2sc03028d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2022] [Accepted: 07/07/2022] [Indexed: 11/21/2022] Open
Abstract
Bond homolysis is one of the most fundamental bond cleavage mechanisms. Thus, understanding of bond homolysis influences the development of a wide range of chemistry. Photolytic bond homolysis and its reverse process have been observed directly using time-resolved spectroscopy. However, direct observation of reversible bond homolysis remains elusive. Here, we report the direct observation of reversible Co-Co bond homolysis using two-dimensional nuclear magnetic resonance exchange spectroscopy (2D EXSY NMR). The characterization of species involved in this homolysis is firmly supported by diffusion ordered NMR spectroscopy (DOSY NMR). The unambiguous characterization of the Co-Co bond homolysis process enabled us to study ligand steric and electronic factors that influence the strength of the Co-Co bond. Understanding of these factors will contribute to rational design of multimetallic complexes with desired physical properties or catalytic activity.
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Affiliation(s)
- Satoshi Takebayashi
- Science and Technology Group Okinawa Institute of Science and Technology Graduate University 1919-1 Tancha Onna-son Okinawa 904-0495 Japan
| | - Robert R Fayzullin
- Arbuzov Institute of Organic and Physical Chemistry, FRC Kazan Scientific Center, Russian Academy of Sciences 8 Arbuzov Street Kazan 420088 Russian Federation
| | - Richa Bansal
- Science and Technology Group Okinawa Institute of Science and Technology Graduate University 1919-1 Tancha Onna-son Okinawa 904-0495 Japan
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4
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Sinclair J, Dai G, McDonald R, Ferguson MJ, Brown A, Rivard E. Insight into the Decomposition Mechanism of Donor-Acceptor Complexes of EH 2 (E = Ge and Sn) and Access to Germanium Thin Films from Solution. Inorg Chem 2020; 59:10996-11008. [PMID: 32686404 DOI: 10.1021/acs.inorgchem.0c01492] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Electron-donating N-heterocyclic carbenes (Lewis bases, LB) and electron-accepting Lewis acids (LA) have been used in tandem to yield donor-acceptor complexes of inorganic tetrelenes LB·EH2·LA (E = Si, Ge, and Sn). Herein, we introduce the new germanium (II) dihydride adducts ImMe2·GeH2·BH3 (ImMe2 = (HCNMe)2C:) and ImiPr2Me2·GeH2·BH3 (ImiPr2Me2 = (MeCNiPr)2C:), with the former complex containing nearly 40 wt % germanium. The thermal release of bulk germanium from ImMe2·GeH2·BH3 (and its deuterated isotopologue ImMe2·GeD2·BD3) was examined in solution, and a combined kinetic and computational investigation was undertaken to probe the mechanism by which Ge is liberated. Moreover, the thermolysis of ImMe2·GeH2·BH3 in solution cleanly affords conformal nanodimensional layers of germanium as thin films of variable thicknesses (20-70 nm) on silicon wafers. We also conducted a computational investigation into potential decomposition pathways for the germanium(II)- and tin(II)-dihydride complexes NHC·EH2·BH3 (NHC = [(HCNR)2C:]; R = 2,6-iPr2C6H3 (Dipp), Me, and H; and E = Ge and Sn). Overall, this study introduces a mild and convenient solution-only protocol for the deposition of thin films of Ge, a widely used semiconductor in materials research and industry.
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Affiliation(s)
- Jocelyn Sinclair
- Department of Chemistry, University of Alberta, 11227 Saskatchewan Drive, Edmonton, Alberta, Canada T6G 2G2
| | - Guoliang Dai
- School of Chemistry, Biology and Materials Engineering, Suzhou University of Science and Technology, 2215009 Suzhou, P. R. China
| | - Robert McDonald
- Department of Chemistry, University of Alberta, 11227 Saskatchewan Drive, Edmonton, Alberta, Canada T6G 2G2
| | - Michael J Ferguson
- Department of Chemistry, University of Alberta, 11227 Saskatchewan Drive, Edmonton, Alberta, Canada T6G 2G2
| | - Alex Brown
- Department of Chemistry, University of Alberta, 11227 Saskatchewan Drive, Edmonton, Alberta, Canada T6G 2G2
| | - Eric Rivard
- Department of Chemistry, University of Alberta, 11227 Saskatchewan Drive, Edmonton, Alberta, Canada T6G 2G2
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5
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Shapovalov SS, Tikhonova OG, Grigor’eva MO, Skabitskii IV, Simonenko NP. Metal Complexes with the N-Heterocyclic Ligand: Synthesis, Structures, and Thermal Decomposition. RUSS J COORD CHEM+ 2019. [DOI: 10.1134/s1070328419100063] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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6
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Huang T, Rountree ES, Traywick AP, Bayoumi M, Dempsey JL. Switching between Stepwise and Concerted Proton-Coupled Electron Transfer Pathways in Tungsten Hydride Activation. J Am Chem Soc 2018; 140:14655-14669. [PMID: 30362720 DOI: 10.1021/jacs.8b07102] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Catalytic processes to generate (or oxidize) fuels such as hydrogen are underpinned by multiple proton-coupled electron transfer (PCET) steps that are associated with the formation or activation of metal-hydride bonds. Fully understanding the detailed PCET mechanisms of metal hydride transformations holds promise for the rational design of energy-efficient catalysis. Here we investigate the detailed PCET mechanisms for the activation of the transition metal hydride complex CpW(CO)2(PMe3)H (Cp = cyclopentadienyl) using stopped-flow rapid mixing coupled with time-resolved optical spectroscopy. We reveal that all three limiting PCET pathways can be accessed by changing the free energy for elementary proton, electron, and proton-electron transfers through the choice of base and oxidant, with the concerted pathway occurring exclusively as a secondary parallel route. Through detailed kinetics analysis, we define free energy relationships for the kinetics of elementary reaction steps, which provide insight into the factors influencing reaction mechanism. Rate constants for proton transfer processes in the limiting stepwise pathways reveal a large reorganization energy associated with protonation/deprotonation of the metal center (λ = 1.59 eV) and suggest that sluggish proton transfer kinetics hinder access to a concerted route. Rate constants for concerted PCET indicate that the concerted routes are asynchronous. Additionally, through quantification of the relative contributions of parallel stepwise and concerted mechanisms toward net product formation, the influence of various reaction parameters on reactivity are identified. This work underscores the importance of understanding the PCET mechanism for controlling metal hydride reactivity, which could lead to superior catalyst design for fuel production and oxidation.
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Affiliation(s)
- Tao Huang
- Department of Chemistry , University of North Carolina at Chapel Hill , Chapel Hill , North Carolina 27599-3290 , United States
| | - Eric S Rountree
- Department of Chemistry , University of North Carolina at Chapel Hill , Chapel Hill , North Carolina 27599-3290 , United States
| | - Andrew P Traywick
- Department of Chemistry , University of North Carolina at Chapel Hill , Chapel Hill , North Carolina 27599-3290 , United States
| | - Magd Bayoumi
- Department of Chemistry , University of North Carolina at Chapel Hill , Chapel Hill , North Carolina 27599-3290 , United States
| | - Jillian L Dempsey
- Department of Chemistry , University of North Carolina at Chapel Hill , Chapel Hill , North Carolina 27599-3290 , United States
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7
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Hui Z, Watanabe T, Tobita H. Synthesis of Base-Stabilized Hydrido(hydroborylene)tungsten Complexes and Their Reactions with Terminal Alkynes To Give η3-Boraallyl Complexes. Organometallics 2017. [DOI: 10.1021/acs.organomet.7b00723] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Zeping Hui
- Department of Chemistry,
Graduate School of Science, Tohoku University, Aoba-ku, Sendai 980-8578, Japan
| | - Takahito Watanabe
- Department of Chemistry,
Graduate School of Science, Tohoku University, Aoba-ku, Sendai 980-8578, Japan
| | - Hiromi Tobita
- Department of Chemistry,
Graduate School of Science, Tohoku University, Aoba-ku, Sendai 980-8578, Japan
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8
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Sunada Y, Ishida S, Hirakawa F, Shiota Y, Yoshizawa K, Kanegawa S, Sato O, Nagashima H, Iwamoto T. Persistent four-coordinate iron-centered radical stabilized by π-donation. Chem Sci 2016; 7:191-198. [PMID: 28758000 PMCID: PMC5515065 DOI: 10.1039/c5sc02601f] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2015] [Accepted: 09/25/2015] [Indexed: 11/21/2022] Open
Abstract
Dinuclear iron carbonyl complex 2, which contains an elongated unsupported Fe-Fe bond, was synthesized by the reaction between Fe2(CO)9 and phosphinyl radical 1. Thermal Fe-Fe bond homolysis led to the generation of a four-coordinate carbonyl-based iron-centered radical, 3, which is stabilized by π-donation. Complex 3 exhibited high reactivity toward organic radicals to form diamagnetic five-coordinate Fe(ii) complexes.
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Affiliation(s)
- Yusuke Sunada
- Institute for Materials Chemistry and Engineering , Kyushu University , 6-1 Kasugakoen , Kasuga , Fukuoka 816-8580 , Japan
| | - Shintaro Ishida
- Department of Chemistry , Graduate School of Science , Tohoku University , Aoba-ku , Sendai 980-8578 , Japan
| | - Fumiya Hirakawa
- Department of Chemistry , Graduate School of Science , Tohoku University , Aoba-ku , Sendai 980-8578 , Japan
| | - Yoshihito Shiota
- Institute for Materials Chemistry and Engineering , Kyushu University , Nishi-ku , Fukuoka 819-0395 , Japan
| | - Kazunari Yoshizawa
- Institute for Materials Chemistry and Engineering , Kyushu University , Nishi-ku , Fukuoka 819-0395 , Japan
| | - Shinji Kanegawa
- Institute for Materials Chemistry and Engineering , Kyushu University , Nishi-ku , Fukuoka 819-0395 , Japan
| | - Osamu Sato
- Institute for Materials Chemistry and Engineering , Kyushu University , Nishi-ku , Fukuoka 819-0395 , Japan
| | - Hideo Nagashima
- Institute for Materials Chemistry and Engineering , Kyushu University , 6-1 Kasugakoen , Kasuga , Fukuoka 816-8580 , Japan.,CREST , Japan Science and Technology Agency (JST) , 6-1 Kasugakoen , Kasuga , Fukuoka 816-8580 , Japan
| | - Takeaki Iwamoto
- Department of Chemistry , Graduate School of Science , Tohoku University , Aoba-ku , Sendai 980-8578 , Japan
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9
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Fang H, Jing H, Ge H, Brothers PJ, Fu X, Ye S. The Mechanism of E–H (E = N, O) Bond Activation by a Germanium Corrole Complex: A Combined Experimental and Computational Study. J Am Chem Soc 2015; 137:7122-7. [DOI: 10.1021/jacs.5b01121] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Huayi Fang
- Beijing
National Laboratory for Molecular Sciences, College of Chemistry and
Molecular Engineering, Peking University, Beijing 100871, China
| | - Huize Jing
- Beijing
National Laboratory for Molecular Sciences, College of Chemistry and
Molecular Engineering, Peking University, Beijing 100871, China
| | - Haonan Ge
- Beijing
National Laboratory for Molecular Sciences, College of Chemistry and
Molecular Engineering, Peking University, Beijing 100871, China
| | - Penelope J. Brothers
- School
of Chemical Sciences, University of Auckland, Private Bag 92019, Auckland 1042, New Zealand
| | - Xuefeng Fu
- Beijing
National Laboratory for Molecular Sciences, College of Chemistry and
Molecular Engineering, Peking University, Beijing 100871, China
| | - Shengfa Ye
- Max-Planck Institute for Chemical Energy Conversion, Stiftstraße 34-36, D-45470 Mülheim an der Ruhr, Germany
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10
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11
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Giner EA, Santiago A, Gómez-Gallego M, Ramírez de Arellano C, Poulten RC, Whittlesey MK, Sierra MA. Mono- and Bimetallic Zwitterionic Chromium(0) and Tungsten(0) Allenyls. Inorg Chem 2015; 54:5450-61. [DOI: 10.1021/acs.inorgchem.5b00492] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Elena A. Giner
- Departamento de
Química Orgánica, Facultad de Ciencias Químicas, Universidad Complutense, 28040 Madrid, Spain
- Centro de Innovación
en Química
Avanzada, ORFEO−CINQA, Madrid, Spain
| | - Alicia Santiago
- Departamento de
Química Orgánica, Facultad de Ciencias Químicas, Universidad Complutense, 28040 Madrid, Spain
- Centro de Innovación
en Química
Avanzada, ORFEO−CINQA, Madrid, Spain
| | - Mar Gómez-Gallego
- Departamento de
Química Orgánica, Facultad de Ciencias Químicas, Universidad Complutense, 28040 Madrid, Spain
- Centro de Innovación
en Química
Avanzada, ORFEO−CINQA, Madrid, Spain
| | - Carmen Ramírez de Arellano
- Departamento de Química Orgánica, Facultad
de Química, Universidad de Valencia, 46100-Valencia, Spain
- Centro de Innovación
en Química
Avanzada, ORFEO−CINQA, Madrid, Spain
| | - Rebecca C. Poulten
- Department of Chemistry, University of Bath, Claverton Down, Bath BA2
7AY, U.K
| | | | - Miguel A. Sierra
- Departamento de
Química Orgánica, Facultad de Ciencias Químicas, Universidad Complutense, 28040 Madrid, Spain
- Centro de Innovación
en Química
Avanzada, ORFEO−CINQA, Madrid, Spain
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12
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Zhang X, Meng D, Li X, Meng L, Sun Z. Nature of the M–M bonding (M = Cr, Mo, and W) in [CpM(CO)3]2: Covalent single bond or noncovalent interaction? J Organomet Chem 2014. [DOI: 10.1016/j.jorganchem.2014.07.015] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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13
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Bellemin-Laponnaz S, Dagorne S. Group 1 and 2 and early transition metal complexes bearing N-heterocyclic carbene ligands: coordination chemistry, reactivity, and applications. Chem Rev 2014; 114:8747-74. [PMID: 25144918 DOI: 10.1021/cr500227y] [Citation(s) in RCA: 251] [Impact Index Per Article: 25.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Affiliation(s)
- Stéphane Bellemin-Laponnaz
- IPCMS (Institut de Physique et Chimie des Matériaux de Strasbourg), CNRS-Université de Strasbourg , 23 rue du Loess BP 43, F-67034 Strasbourg, France
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14
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Eide EFVD, Hou GL, Deng SHM, Wen H, Yang P, Bullock RM, Wang XB. Metal-Centered 17-Electron Radicals CpM(CO)3• (M = Cr, Mo, W): A Combined Negative Ion Photoelectron Spectroscopic and Theoretical Study. Organometallics 2013. [DOI: 10.1021/om3011454] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Edwin F. van der Eide
- Chemical and Materials Sciences
Division and ‡Environmental Molecular
Sciences Laboratory, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352,
United States
| | - Gao-Lei Hou
- Chemical and Materials Sciences
Division and ‡Environmental Molecular
Sciences Laboratory, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352,
United States
| | - S. H. M. Deng
- Chemical and Materials Sciences
Division and ‡Environmental Molecular
Sciences Laboratory, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352,
United States
| | - Hui Wen
- Chemical and Materials Sciences
Division and ‡Environmental Molecular
Sciences Laboratory, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352,
United States
| | - Ping Yang
- Chemical and Materials Sciences
Division and ‡Environmental Molecular
Sciences Laboratory, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352,
United States
| | - R. Morris Bullock
- Chemical and Materials Sciences
Division and ‡Environmental Molecular
Sciences Laboratory, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352,
United States
| | - Xue-Bin Wang
- Chemical and Materials Sciences
Division and ‡Environmental Molecular
Sciences Laboratory, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352,
United States
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15
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van der Eide EF, Helm ML, Walter ED, Bullock RM. Structural and spectroscopic characterization of 17- and 18-electron piano-stool complexes of chromium. Thermochemical analyses of weak Cr-H bonds. Inorg Chem 2013; 52:1591-603. [PMID: 23343354 DOI: 10.1021/ic302460y] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The 17-electron radical CpCr(CO)(2)(IMe)(•) (IMe = 1,3-dimethylimidazol-2-ylidene) was synthesized by the reaction of IMe with [CpCr(CO)(3)](2), and characterized by single crystal X-ray diffraction and by electron paramagnetic resonance (EPR), IR, and variable temperature (1)H NMR spectroscopy. The metal-centered radical is monomeric under all conditions and exhibits Curie paramagnetic behavior in solution. An electrochemically reversible reduction to 18-electron CpCr(CO)(2)(IMe)(-) takes place at E(1/2) = -1.89(1) V vs Cp(2)Fe(+•/0) in MeCN, and was accomplished chemically with KC(8) in tetrahydrofuran (THF). The salts K(+)(18-crown-6)[CpCr(CO)(2)(IMe)](-)·½THF and K(+)[CpCr(CO)(2)(IMe)](-)·(3)/(4)THF were crystallographically characterized. Monomeric ion pairs are found in the former, whereas the latter has a polymeric structure because of a network of K···O((CO)) interactions. Protonation of K(+)(18-crown-6)[CpCr(CO)(2)(IMe)](-)·½THF gives the hydride CpCr(CO)(2)(IMe)H, which could not be isolated, but was characterized in solution; a pK(a) of 27.2(4) was determined in MeCN. A thermochemical analysis provides the Cr-H bond dissociation free energy (BDFE) for CpCr(CO)(2)(IMe)H in MeCN solution as 47.3(6) kcal mol(-1). This value is exceptionally low for a transition metal hydride, and implies that the reaction 2 [Cr-H] → 2 [Cr(•)] + H(2) is exergonic (ΔG = -9.0(8) kcal mol(-1)). This analysis explains the experimental observation that generated solutions of the hydride produce CpCr(CO)(2)(IMe)(•) (typically on the time scale of days). By contrast, CpCr(CO)(2)(PCy(3))H has a higher Cr-H BDFE (52.9(4) kcal mol(-1)), is more stable with respect to H(2) loss, and is isolable.
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Affiliation(s)
- Edwin F van der Eide
- Chemical and Materials Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, USA
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16
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Li G, Han A, Pulling ME, Estes DP, Norton JR. Evidence for formation of a Co-H bond from (H2O)2Co(dmgBF2)2 under H2: application to radical cyclizations. J Am Chem Soc 2012; 134:14662-5. [PMID: 22897586 DOI: 10.1021/ja306037w] [Citation(s) in RCA: 98] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Under H(2), the radical cyclization of appropriate dienes can be catalyzed by cobaloximes. H• can be abstracted from an intermediate (presumably a cobalt hydride) by trityl radicals (Ar(3)C•) or by TEMPO. The rate-determining step in these reactions is the uptake of H(2), which is second order in cobalt and first order in hydrogen; the third-order rate constant is 106(3) M(-2)·s(-1).
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Affiliation(s)
- Gang Li
- Department of Chemistry, Columbia University, 3000 Broadway, New York, New York 10027, USA
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17
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Fischer PJ, Neary MC, Avena L, Sullivan KP, Hackbarth KC. Dicarbonyl{[2-(diphenylphosphino)ethyl]cyclopentadienyl} Group VI Metal Hydrides, Halides, and Anions: Precursors for Olefin Epoxidation Catalysts. Organometallics 2012. [DOI: 10.1021/om300057n] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Paul J. Fischer
- Department of Chemistry, Macalester College, Saint Paul, Minnesota
55105-1899, United States
| | - Michelle C. Neary
- Department of Chemistry, Macalester College, Saint Paul, Minnesota
55105-1899, United States
| | - Laura Avena
- Department of Chemistry, Macalester College, Saint Paul, Minnesota
55105-1899, United States
| | - Kevin P. Sullivan
- Department of Chemistry, Macalester College, Saint Paul, Minnesota
55105-1899, United States
| | - Kent C. Hackbarth
- Department of Chemistry, Macalester College, Saint Paul, Minnesota
55105-1899, United States
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