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Considering Fe^(II/IV) Redox Processes as Mechanistically Relevant to the Catalytic Hydrogenation of Olefins by [PhBP^(iPr)_3]Fe-H_x Species

Daida, Erin J. and Peters, Jonas C. (2004) Considering Fe^(II/IV) Redox Processes as Mechanistically Relevant to the Catalytic Hydrogenation of Olefins by [PhBP^(iPr)_3]Fe-H_x Species. Inorganic Chemistry, 43 (23). pp. 7474-7485. ISSN 0020-1669. doi:10.1021/ic0488583. https://resolver.caltech.edu/CaltechAUTHORS:20140731-074557924

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Abstract

Several coordinatively unsaturated pseudotetrahedral iron(II) precursors, [PhBP^(iPr)_3]Fe−R ([PhBP^(iPr)_3] = [PhB(CH2P^(iPr)_2)_3]^-; R = Me (2), R = CH_2Ph (3), R = CH_2CMe_3 (4)) have been prepared from [PhBP^(iPr)_3]FeCl (1) that serve as precatalysts for the room-temperature hydrogenation of unsaturated hydrocarbons (e.g., ethylene, styrene, 2-pentyne) under atmospheric H_2 pressure. The solid-state crystal structures of 2 and 3 are presented. To gain mechanistic insight into the nature of these hydrogenation reactions, a number of [PhBP^(iPr)_3]-supported iron hydrides were prepared and studied. Room-temperature hydrogenation of alkyls 2−4 in the presence of a trapping phosphine ligand affords the iron(IV) trihydride species [PhBP^(iPr)_3]Fe(H)_3(PR_3) (PR_3 = PMe_3 (5); PR_3 = PEt_3 (6); PR3 = PMePh_2 (7)). These spectroscopically well-defined trihydrides undergo hydrogen loss to varying degrees in solution, and for the case of 7, this process leads to the structurally identified Fe(II) hydride product [PhBP^(iPr)_3]Fe(H)(PMePh_2) (9). Attempts to prepare 9 by addition of LiEt_3BH to 1 instead lead to the Fe(I) reduction product [PhBP^(iPr)_3]Fe(PMePh_2) (10). The independent preparations of the Fe(II) monohydride complex [PhBP^(iPr)_3]FeII(H)(PMe_3) (11) and the Fe(I) phosphine adduct [PhBP^(iPr)_3]Fe(PMe_3) (8) are described. The solid-state crystal structures of trihydride 5, monohydride 11, and 8 are compared and demonstrate relatively little structural reorganization with respect to the P_3Fe−P‘ core motif as a function of the iron center's formal oxidation state. Although paramagnetic 11 (S = 1) is quantitatively converted to the diamagnetic trihydride 5 under H_2, the Fe(I) complex 8 (S = 3/2) is inert toward atmospheric H_2. Complex 10 is likewise inert toward H_2. Trihydrides 5 and 6 also serve as hydrogenation precatalysts, albeit at slower rates than that for the benzyl complex 3 because of a rate-contributing phosphine dependence. That these hydrogenations appear to proceed via well-defined olefin insertion steps into an Fe−H linkage is indicated by the reaction between trihydride 5 and ethylene, which cleanly produces the ethyl complex [PhBP^(iPr)_3]Fe(CH_2CH_3) (13) and an equivalent of ethane. Mechanistic issues concerning the overall reaction are described.


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URLURL TypeDescription
http://pubs.acs.org/doi/abs/10.1021/ic0488583PublisherArticle
http://dx.doi.org/10.1021/ic0488583DOIArticle
http://pubs.acs.org/doi/suppl/10.1021/ic0488583Related ItemSupporting Information
ORCID:
AuthorORCID
Peters, Jonas C.0000-0002-6610-4414
Alternate Title:Considering Fe(II/IV) Redox Processes as Mechanistically Relevant to the Catalytic Hydrogenation of Olefins by [PhBP(iPr)3]Fe-Hx Species
Additional Information:© 2004 American Chemical Society. Publication Date (Web): October 14, 2004. Received August 18, 2004. This work was supported by the NSF (CHE-01232216) and the DOE (PECASE). E.J.D. is grateful for the Laszlo Zechmeister Fellowship (Caltech). Lawrence Henling and Theodore A. Betley are acknowledged for crystallographic assistance. We thank Paul J. Chirik for sharing results prior to publication.
Funders:
Funding AgencyGrant Number
NSFCHE-01232216
Department of Energy (DOE) (PECASE)UNSPECIFIED
Caltech Laszlo Zechmeister FellowshipUNSPECIFIED
Issue or Number:23
DOI:10.1021/ic0488583
Record Number:CaltechAUTHORS:20140731-074557924
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20140731-074557924
Official Citation:Considering FeII/IV Redox Processes as Mechanistically Relevant to the Catalytic Hydrogenation of Olefins by [PhBPiPr3]Fe−Hx Species Erin J. Daida and and Jonas C. Peters Inorganic Chemistry 2004 43 (23), 7474-7485
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:47685
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:31 Jul 2014 16:13
Last Modified:10 Nov 2021 17:49

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