Electronic Structure Control of the Nucleophilicity of Transition Metal-Thiolate Complexes: An Experimental and Theoretical Study.
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| Title: | Electronic Structure Control of the Nucleophilicity of Transition Metal-Thiolate Complexes: An Experimental and Theoretical Study. |
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| Authors: | Fox, Derek C.1, Fiedler, Adam T.2, Halfen, Heather L.1, Brunold, Thomas C.2 brunold@chem.wisc.edu, Halfen, Jason A.1 halfenja@uwec.edu |
| Source: | Journal of the American Chemical Society. 6/23/2004, Vol. 126 Issue 24, p7627-7638. 12p. |
| Subjects: | Spectrum analysis, Crystals, Crystallography, Ligands (Chemistry), Biochemistry, Nitrogen, Transition metal thiolates |
| Abstract: | New metal(II)-thiolate complexes supported by the tetradentate ligand 1 ,5-bis(2-pyridylmethyl)- 1 ,5-diazacyclooctane (L8py2) have been synthesized and subjected to physical, spectroscopic, structural, and computational characterization. The X-ray crystal structures of these complexes, [L8py2M(S-C6H4-p- CH3)}BPh4 (M = Co, Ni, Zn), reveal distorted square-pyramidal divalent metal ions with four equatorial nitrogen donors from L8py2 and axial p-toluenethiolate ligands. The reactions of the complexes with benzyl bromide produce isolable metal(II)-bromide complexes (in the cases of Co and Ni) and the thioether benzyl- p-tolylsulfide. This reaction is characterized by a second-order rate law (v = k2[L8py2M(SAr)+][PhCH2Br]) for all complexes (where M = Fe, Co, Ni, or Zn). Of particular significance is the disparity between k2 for M = Fe and Co versus k2 for M = Ni and Zn, in that k2 for M = Ni and Zn is ca. 10 times larger (faster) than k2 for M = Fe and Co. An Eyring analysis of k2 for [L8py2Co(SAr)]+ and [L8py2Ni(SAr)]+ reveals that the reaction rate differences are not rooted in a change in mechanism, as the reactions of these complexes with benzyl bromide exhibit comparable activation parameters (M = Co: ΔH‡ = 45(2) kJ mol-1, ΔS† = -144(6) J mol-1 K-1 M = Ni: ΔH‡ = 43(3) kJ mol-1, ΔS‡ = -134(8) J mol-1 K-1). Electronic structure calculations using density functional theory (DFT) reveal that the enhanced reaction rate for [L8py2Ni-(SAr)]+ is rooted in a four-electron repulsion (or a "filled/filled interaction") between a completely filled nickel-(II) dx orbital and one of the two thiolate frontier orbitals, a condition that is absent in the Fe(II) and Co(II) complexes. The comparable reactivity of [L8py2Zn(SAr)]+ relative to that of [L8py2Ni(SAr)]+ arises from a highly ionic zinc(I)-thiolate bond that enhances the negative charge density on the thiolate sulfur. DFT calculations on putative thioether-coordiriated intermediates reveal that the Co(II)- and Zn(II)-thioethers exhibit weaker M-S bonding than Ni(II). These combined results suggest that while Ni(II) may serve as a competent replacement for Zn(II) in alkyl group transfer enzymes, turnover may be limited by slow product release from the Ni(II) center. [ABSTRACT FROM AUTHOR] |
| Copyright of Journal of the American Chemical Society is the property of American Chemical Society and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.) | |
| Database: | Engineering Source |
| FullText | Text: Availability: 0 |
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| Header | DbId: egs DbLabel: Engineering Source An: 13612985 AccessLevel: 6 PubType: Academic Journal PubTypeId: academicJournal PreciseRelevancyScore: 0 |
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| Items | – Name: Title Label: Title Group: Ti Data: Electronic Structure Control of the Nucleophilicity of Transition Metal-Thiolate Complexes: An Experimental and Theoretical Study. – Name: Author Label: Authors Group: Au Data: <searchLink fieldCode="AR" term="%22Fox%2C+Derek+C%2E%22">Fox, Derek C.</searchLink><relatesTo>1</relatesTo><br /><searchLink fieldCode="AR" term="%22Fiedler%2C+Adam+T%2E%22">Fiedler, Adam T.</searchLink><relatesTo>2</relatesTo><br /><searchLink fieldCode="AR" term="%22Halfen%2C+Heather+L%2E%22">Halfen, Heather L.</searchLink><relatesTo>1</relatesTo><br /><searchLink fieldCode="AR" term="%22Brunold%2C+Thomas+C%2E%22">Brunold, Thomas C.</searchLink><relatesTo>2</relatesTo><i> brunold@chem.wisc.edu</i><br /><searchLink fieldCode="AR" term="%22Halfen%2C+Jason+A%2E%22">Halfen, Jason A.</searchLink><relatesTo>1</relatesTo><i> halfenja@uwec.edu</i> – Name: TitleSource Label: Source Group: Src Data: <searchLink fieldCode="JN" term="%22Journal+of+the+American+Chemical+Society%22">Journal of the American Chemical Society</searchLink>. 6/23/2004, Vol. 126 Issue 24, p7627-7638. 12p. – Name: Subject Label: Subjects Group: Su Data: <searchLink fieldCode="DE" term="%22Spectrum+analysis%22">Spectrum analysis</searchLink><br /><searchLink fieldCode="DE" term="%22Crystals%22">Crystals</searchLink><br /><searchLink fieldCode="DE" term="%22Crystallography%22">Crystallography</searchLink><br /><searchLink fieldCode="DE" term="%22Ligands+%28Chemistry%29%22">Ligands (Chemistry)</searchLink><br /><searchLink fieldCode="DE" term="%22Biochemistry%22">Biochemistry</searchLink><br /><searchLink fieldCode="DE" term="%22Nitrogen%22">Nitrogen</searchLink><br /><searchLink fieldCode="DE" term="%22Transition+metal+thiolates%22">Transition metal thiolates</searchLink> – Name: Abstract Label: Abstract Group: Ab Data: New metal(II)-thiolate complexes supported by the tetradentate ligand 1 ,5-bis(2-pyridylmethyl)- 1 ,5-diazacyclooctane (L8py2) have been synthesized and subjected to physical, spectroscopic, structural, and computational characterization. The X-ray crystal structures of these complexes, [L8py2M(S-C6H4-p- CH3)}BPh4 (M = Co, Ni, Zn), reveal distorted square-pyramidal divalent metal ions with four equatorial nitrogen donors from L8py2 and axial p-toluenethiolate ligands. The reactions of the complexes with benzyl bromide produce isolable metal(II)-bromide complexes (in the cases of Co and Ni) and the thioether benzyl- p-tolylsulfide. This reaction is characterized by a second-order rate law (v = k2[L8py2M(SAr)+][PhCH2Br]) for all complexes (where M = Fe, Co, Ni, or Zn). Of particular significance is the disparity between k2 for M = Fe and Co versus k2 for M = Ni and Zn, in that k2 for M = Ni and Zn is ca. 10 times larger (faster) than k2 for M = Fe and Co. An Eyring analysis of k2 for [L8py2Co(SAr)]+ and [L8py2Ni(SAr)]+ reveals that the reaction rate differences are not rooted in a change in mechanism, as the reactions of these complexes with benzyl bromide exhibit comparable activation parameters (M = Co: ΔH‡ = 45(2) kJ mol-1, ΔS† = -144(6) J mol-1 K-1 M = Ni: ΔH‡ = 43(3) kJ mol-1, ΔS‡ = -134(8) J mol-1 K-1). Electronic structure calculations using density functional theory (DFT) reveal that the enhanced reaction rate for [L8py2Ni-(SAr)]+ is rooted in a four-electron repulsion (or a "filled/filled interaction") between a completely filled nickel-(II) dx orbital and one of the two thiolate frontier orbitals, a condition that is absent in the Fe(II) and Co(II) complexes. The comparable reactivity of [L8py2Zn(SAr)]+ relative to that of [L8py2Ni(SAr)]+ arises from a highly ionic zinc(I)-thiolate bond that enhances the negative charge density on the thiolate sulfur. DFT calculations on putative thioether-coordiriated intermediates reveal that the Co(II)- and Zn(II)-thioethers exhibit weaker M-S bonding than Ni(II). These combined results suggest that while Ni(II) may serve as a competent replacement for Zn(II) in alkyl group transfer enzymes, turnover may be limited by slow product release from the Ni(II) center. [ABSTRACT FROM AUTHOR] – Name: AbstractSuppliedCopyright Label: Group: Ab Data: <i>Copyright of Journal of the American Chemical Society is the property of American Chemical Society and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.) |
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| RecordInfo | BibRecord: BibEntity: Identifiers: – Type: doi Value: 10.1021/ja039419q Languages: – Code: eng Text: English PhysicalDescription: Pagination: PageCount: 12 StartPage: 7627 Subjects: – SubjectFull: Spectrum analysis Type: general – SubjectFull: Crystals Type: general – SubjectFull: Crystallography Type: general – SubjectFull: Ligands (Chemistry) Type: general – SubjectFull: Biochemistry Type: general – SubjectFull: Nitrogen Type: general – SubjectFull: Transition metal thiolates Type: general Titles: – TitleFull: Electronic Structure Control of the Nucleophilicity of Transition Metal-Thiolate Complexes: An Experimental and Theoretical Study. Type: main BibRelationships: HasContributorRelationships: – PersonEntity: Name: NameFull: Fox, Derek C. – PersonEntity: Name: NameFull: Fiedler, Adam T. – PersonEntity: Name: NameFull: Halfen, Heather L. – PersonEntity: Name: NameFull: Brunold, Thomas C. – PersonEntity: Name: NameFull: Halfen, Jason A. IsPartOfRelationships: – BibEntity: Dates: – D: 23 M: 06 Text: 6/23/2004 Type: published Y: 2004 Identifiers: – Type: issn-print Value: 00027863 Numbering: – Type: volume Value: 126 – Type: issue Value: 24 Titles: – TitleFull: Journal of the American Chemical Society Type: main |
| ResultId | 1 |
