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Guanidine-Functionalized Rhenium Cyclopentadienyl Carbonyl Complexes: Synthesis and Cooperative Activation of H–H and O–H Bonds

Teets, Thomas S. and Labinger, Jay A. and Bercaw, John E. (2014) Guanidine-Functionalized Rhenium Cyclopentadienyl Carbonyl Complexes: Synthesis and Cooperative Activation of H–H and O–H Bonds. Organometallics, 33 (15). pp. 4107-4117. ISSN 0276-7333. http://resolver.caltech.edu/CaltechAUTHORS:20140804-164958436

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Abstract

Catalytic reactions utilizing carbon monoxide as a substrate are numerous, and they typically involve selective functionalization of a metal-bound CO. We have developed group 7 carbonyl complexes where secondary coordination sphere, Lewis acidic functionalities can assist in the activation of substrate molecules, mainly in the context of syngas conversion. This work describes a new class of cyclopentadienyl (Cp) rhenium carbonyl compounds of the type [Re(η^5-C_5H_4DMEG)(CO)_(3–n)(NO)_n]^n (DMEG = dimethylethyleneguanidine, n = 0, 1), where a tethered guanidine base is appended to the Cp ring to participate in cooperative substrate activation with the electrophilic carbonyl. A reliable synthetic route for these complexes is presented, with crystallographic characterization of the free-base and protonated forms for both the carbonyl and mixed carbonyl-nitrosyl complexes. The latter are employed as platforms to study heterolytic H–H and O–H bond cleavage reactions that result in nucleophilic CO functionalization. The corresponding formyl complex is prepared by hydride transfer, and by measuring its hydricity (ΔG^°_(H–)) and pK_a of the protonated base, the free energy of H_2 cleavage is found to be +3.3(6) kcal/mol. The activation of methanol to form methoxycarbonyl complexes is found to be more favorable, with ΔG^° ≈ 0 for the intramolecular addition of methanol to the guanidine-appended carbonyl complex. A detailed thermodynamic study is described for both the intramolecular methanol activation reaction and related intermolecular reactions with external bases. The results highlight some tangible thermodynamic benefits of tethering the base in the secondary coordination sphere.


Item Type:Article
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http://dx.doi.org/10.1021/om500650bDOIArticle
http://pubs.acs.org/doi/abs/10.1021/om500650bPublisherArticle
http://pubs.acs.org/doi/suppl/10.1021/om500650bPublisherSupporting Information
ORCID:
AuthorORCID
Labinger, Jay A.0000-0002-1942-9232
Additional Information:© 2014 American Chemical Society. Received: June 18, 2014; Publication Date (Web): July 30, 2014. We acknowledge BP for their support of this work through the XC^2 program. Dr. Glenn J. Sunley (BP) and Dr. Aaron Sattler (Caltech) are thanked for helpful discussions.
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Record Number:CaltechAUTHORS:20140804-164958436
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20140804-164958436
Official Citation:Guanidine-Functionalized Rhenium Cyclopentadienyl Carbonyl Complexes: Synthesis and Cooperative Activation of H–H and O–H Bonds Thomas S. Teets, Jay A. Labinger, and John E. Bercaw Organometallics 2014 33 (15), 4107-4117
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:47951
Collection:CaltechAUTHORS
Deposited By: Joanne McCole
Deposited On:05 Aug 2014 18:35
Last Modified:19 Sep 2017 22:04

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