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Horitani M, Grubel K, McWilliams SF, Stubbert BD, Mercado BQ, Yu Y, Gurubasavaraj PM, Lees NS, Holland PL, Hoffman BM. ENDOR characterization of an iron-alkene complex provides insight into a corresponding organometallic intermediate of nitrogenase. Chem Sci 2017; 8:5941-5948. [PMID: 28989623 PMCID: PMC5620524 DOI: 10.1039/c7sc01602f] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2017] [Accepted: 06/17/2017] [Indexed: 12/16/2022] Open
Abstract
Comparison of an iron(I)–alkene complex to a nitrogenase intermediate using ENDOR reveals details of the binding geometry.
A bio-organometallic intermediate, denoted PA, was previously trapped during the reduction of propargyl alcohol to allyl alcohol (AA) by nitrogenase, and a similar one was trapped during acetylene reduction, representing foundational examples of alkene binding to a metal center in biology. ENDOR spectroscopy led to the conclusion that these intermediates have η2 binding of the alkene, with the hydrogens on the terminal carbon structurally/magnetically equivalent and related by local mirror symmetry. However, our understanding of both the PA intermediate, and of the dependability of the ENDOR analysis on which this understanding was based, was constrained by the absence of reference iron–alkene complexes for EPR/ENDOR comparison. Here, we report an ENDOR study of the crystallographically characterized biomimetic iron(i) complex 1, which exhibits η2 coordination of styrene, thus connecting hyperfine and structural parameters of an Fe-bound alkene fragment for the first time. A tilt of the alkene plane of 1 from normal to the crystallographic Fe–C2–C1 plane causes substantial differences in the dipolar couplings of the two terminal vinylic protons. Comparison of the hyperfine couplings of 1 and PA confirms the proposed symmetry of PA, and that the η2 interaction forms a scalene Fe–C–C triangle, rather than an isosceles triangle. This spectroscopic study of a structurally characterized complex thus shows the exceptional sensitivity of ENDOR spectroscopy to structural details, while enhancing our understanding of the geometry of a key nitrogenase adduct.
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Affiliation(s)
- Masaki Horitani
- Department of Chemistry , Northwestern University , Evanston , Illinois 60208 , USA . .,Department of Applied Biochemistry and Food Science , Saga University , Saga , 840-8502 , Japan
| | - Katarzyna Grubel
- Department of Chemistry , Yale University , New Haven , CT 06520 , USA .
| | - Sean F McWilliams
- Department of Chemistry , Yale University , New Haven , CT 06520 , USA .
| | - Bryan D Stubbert
- Department of Chemistry , University of Rochester , Rochester , New York 14627 , USA
| | - Brandon Q Mercado
- Department of Chemistry , Yale University , New Haven , CT 06520 , USA .
| | - Ying Yu
- Department of Chemistry , University of Rochester , Rochester , New York 14627 , USA
| | | | - Nicholas S Lees
- Department of Chemistry , Northwestern University , Evanston , Illinois 60208 , USA .
| | - Patrick L Holland
- Department of Chemistry , Yale University , New Haven , CT 06520 , USA .
| | - Brian M Hoffman
- Department of Chemistry , Northwestern University , Evanston , Illinois 60208 , USA .
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Stubbert BD, Vela J, Brennessel WW, Holland PL. A Sulfide-Bridged Diiron(II) Complex with a cis-N 2H 4Ligand. Z Anorg Allg Chem 2013; 639:1351-1355. [PMID: 24678131 PMCID: PMC3963182 DOI: 10.1002/zaac.201300163] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2013] [Accepted: 05/24/2013] [Indexed: 11/07/2022]
Abstract
A sulfide-bridged diiron(II) complex bearing a cis-N2H4 (hydrazine) ligand has been prepared by reaction of LFeII(μ-S)FeIIL (1; L = sterically encumbered βdiketiminate ligand) with 2 molar equivalents of N2H4. The metastable diiron(II) hydrazine complex LFeII(μ-S)(μH N-NH2)FeII (3) is formed, as shown by crystallography, and NMR, vibrational, and electronic absorption spectroscopies. Compound 3 has been crystallographically characterized as its DBU (1,8-diazabicyclo[5.4.0]undec-7$ene) adduct, which exhibits weak N-H···DBU hydrogen bonding. The synthetic process evolves roughly 2 equivalents of NH3. The cis-N2H4 bridge in 3 may be relevant to the structure and function of intermediates on the FeMoco of nitrogenase.
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Affiliation(s)
- Bryan D. Stubbert
- Department of Chemistry University of Rochester Rochester, NY, USA 14627
| | - Javier Vela
- Department of Chemistry University of Rochester Rochester, NY, USA 14627
| | | | - Patrick L. Holland
- Department of Chemistry University of Rochester Rochester, NY, USA 14627
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Rodriguez MM, Stubbert BD, Scarborough CC, Brennessel WW, Bill E, Holland PL. Isolation and characterization of stable iron(I) sulfide complexes. Angew Chem Int Ed Engl 2012; 51:8247-50. [PMID: 22821816 PMCID: PMC3970908 DOI: 10.1002/anie.201202211] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2012] [Indexed: 11/11/2022]
Affiliation(s)
| | - Bryan D. Stubbert
- Department of Chemistry University of Rochester Rochester, NY 14627 (USA)
| | | | | | - Eckhard Bill
- Max-Planck-Institut für Bioanorganische Chemie 45470 Mülheim an der Ruhr (Germany)
| | - Patrick L. Holland
- Department of Chemistry University of Rochester Rochester, NY 14627 (USA)
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Rodriguez MM, Stubbert BD, Scarborough CC, Brennessel WW, Bill E, Holland PL. Isolation and Characterization of Stable Iron(I) Sulfide Complexes. Angew Chem Int Ed Engl 2012. [DOI: 10.1002/ange.201202211] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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Affiliation(s)
- Bryan D. Stubbert
- Department of Chemistry, California Institute of Technology, Pasadena, California 91125, United States
| | - Jonas C. Peters
- Department of Chemistry, California Institute of Technology, Pasadena, California 91125, United States
| | - Harry B. Gray
- Department of Chemistry, California Institute of Technology, Pasadena, California 91125, United States
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Stubbert BD, Marks TJ. Mechanistic Investigation of Intramolecular Aminoalkene and Aminoalkyne Hydroamination/Cyclization Catalyzed by Highly Electrophilic, Tetravalent Constrained Geometry 4d and 5f Complexes. Evidence for an M−N σ-Bonded Insertive Pathway. J Am Chem Soc 2007; 129:6149-67. [PMID: 17441716 DOI: 10.1021/ja0675898] [Citation(s) in RCA: 184] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A mechanistic study of intramolecular hydroamination/cyclization catalyzed by tetravalent organoactinide and organozirconium complexes is presented. A series of selectively substituted constrained geometry complexes, (CGC)M(NR2)Cl (CGC = [Me2Si(eta5-Me4C5)(tBuN)]2-; M = Th, 1-Cl; U, 2-Cl; R = SiMe3; M = Zr, R = Me, 3-Cl) and (CGC)An(NMe2)OAr (An = Th, 1-OAr; An = U, 2-OAr), has been prepared via in situ protodeamination (complexes 1-2) or salt metathesis (3-Cl) in high purity and excellent yield and is found to be active precatalysts for intramolecular primary and secondary aminoalkyne and aminoalkene hydroamination/cyclization. Substrate reactivity trends, rate laws, and activation parameters for cyclizations mediated by these complexes are virtually identical to those of more conventional (CGC)MR2 (M = Th, R = NMe2, 1; M = U, R = NMe2, 2; M = Zr, R = Me, 3), (Me2SiCp' '2)UBn2 (Cp' ' = eta5-Me4C5; Bn = CH2Ph, 4), Cp'2AnR2 (Cp' = eta5-Me5C5; R = CH2SiMe3; An = Th, 5, U, 6), and analogous organolanthanide complexes. Deuterium KIEs measured at 25 degrees C in C6D6 for aminoalkene D2NCH2C(CH3)2CH2CHCH2 (11-d2) with precatalysts 2 and 2-Cl indicate that kH/kD = 3.3(5) and 2.6(4), respectively. Together, the data provide strong evidence in these systems for turnover-limiting C-C insertion into an M-N(H)R sigma-bond in the transition state. Related complexes (Me2SiCp' '2)U(Bn)(Cl) (4-Cl) and Cp'2An(R)(Cl) (R = CH2(SiMe3); An = Th, 5-Cl; An = U, 6-Cl) are also found to be effective precatalysts for this transformation. Additional arguments supporting M-N(H)R intermediates vs M=NR intermediates are presented.
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Affiliation(s)
- Bryan D Stubbert
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208-3113, USA
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Stubbert BD, Marks TJ. Constrained Geometry Organoactinides as Versatile Catalysts for the Intramolecular Hydroamination/Cyclization of Primary and Secondary Amines Having Diverse Tethered C−C Unsaturation. J Am Chem Soc 2007; 129:4253-71. [PMID: 17371022 DOI: 10.1021/ja0665444] [Citation(s) in RCA: 151] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A series of "constrained geometry" organoactinide complexes, (CGC)An(NMe)2 (CGC = Me2Si(eta5-Me4C5)(tBuN); An = Th, 1; U, 2), has been prepared via efficient in situ, two-step protodeamination routes in good yields and high purity. Both 1 and 2 are quantitatively converted to the neutrally charged, solvent-free dichlorides (1-Cl2, 2-Cl2) and slightly more soluble diiodides (1-I2, 2-I2) with excess Me3Si-X (X = Cl, I) in non-coordinating solvents. The new complexes were characterized by NMR spectroscopy, elemental analysis, and (for 1 and 2) single-crystal X-ray diffraction, revealing substantially increased metal coordinative unsaturation vs the corresponding Me2SiCp' '2AnR2 (Cp' ' = eta5-Me4C5; An = Th, R = CH2(SiMe3), 3; An = U, R = CH2Ph, 4) and Cp'2AnR2 (Cp' = eta5-Me5C5 ; An = Th, R = CH2(SiMe3), 5; An = U, R = CH2(SiMe3), 6) complexes. Complexes 1-6 exhibit broad applicability for the intramolecular hydroamination of diverse C-C unsaturations, including terminal and internal aminoalkenes (primary and secondary amines), aminoalkynes (primary and secondary amines), aminoallenes, and aminodienes. Large turnover frequencies (Nt up to 3000 h-1) and high regioselectivities (>/=95%) are observed throughout, along with moderate to high diastereoselectivities (up to 90% trans ring closures). With several noteworthy exceptions, reactivity trends track relative 5f ionic radii and ancillary ligand coordinative unsaturation. Reactivity patterns and activation parameters are consistent with a reaction pathway proceeding via turnover-limiting C=C/CC insertion into the An-N sigma-bond.
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Affiliation(s)
- Bryan D Stubbert
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208-3113, USA
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Seyam AM, Stubbert BD, Jensen TR, O’Donnell JJ, Stern CL, Marks TJ. Organolanthanide constrained geometry complexes modified for catalysis: synthesis, structure, and aminoalkene hydroamination properties of a pyrrolidine-substituted constrained geometry organolutetium complex. Inorganica Chim Acta 2004. [DOI: 10.1016/j.ica.2004.08.018] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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Stubbert BD, Stern CL, Marks TJ. Synthesis and Catalytic Characteristics of Novel Constrained-Geometry Organoactinide Catalysts. The First Example of Actinide-Mediated Intramolecular Hydroamination. Organometallics 2003. [DOI: 10.1021/om034093f] [Citation(s) in RCA: 104] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Bryan D. Stubbert
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208-3113
| | - Charlotte L. Stern
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208-3113
| | - Tobin J. Marks
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208-3113
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