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Heterobimetallic rebound: a mechanism for diene-to-alkyne isomerization with M-Zr hydride complexes (M = Al, Zn, and Mg)

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Title: Heterobimetallic rebound: a mechanism for diene-to-alkyne isomerization with M-Zr hydride complexes (M = Al, Zn, and Mg)
Authors: Butler, MJ
White, AJP
Crimmin, MR
Item Type: Journal Article
Abstract: The reaction of a series of M·Zr heterobimetallic hydride complexes with dienes and alkynes has been investigated (M = Al, Zn, and Mg). Reaction of M·Zr with 1,5-cyclooctadiene led to diene isomerization to 1,3-cyclooctadiene, but for M = Zn also result in an on-metal diene-to-alkyne isomerization. The resulting cyclooctyne fragment is trapped between Zr and Zn metals in a heterobimetallic species that does not form for M = Mg or Al. The scope of diene isomerization and alkyne trapping has been explored leading to the isolation of three new heterobimetallic slipped metallocyclopropene complexes. The mechanism of diene-to-alkyne isomerization was investigated through kinetics. While the reaction is first-order in Zn·Zr at high diene concentration and proceeds with ΔH‡ = +33.6 ± 0.7 kcal mol−1 , ΔS‡ = +23.2 ± 1.7 cal mol−1 K−1 , and ΔG⧧ 298 K = +26.7 ± 1.2 kcal mol−1 , the rate is dependent on the nature of the diene. The positive activation entropy is suggestive of involvement of a dissociative step. On the basis of DFT calculations, a heterobimetallic rebound mechanism for diene-to-alkyne isomerization has been proposed. This mechanism explains the origin of heterobimetallic control over selectivity: Mg---Zr complexes are too strongly bound to generate reactive fragments, while Al---Zr complexes are too weakly bound to compensate for the contrathermodynamic isomerization process. Zn---Zr complexes have favorable energetics for both dissociation and trapping steps.
Issue Date: 26-Mar-2018
Date of Acceptance: 26-Dec-2017
URI: http://hdl.handle.net/10044/1/58877
DOI: https://dx.doi.org/10.1021/acs.organomet.7b00908
ISSN: 0276-7333
Publisher: American Chemical Society
Start Page: 949
End Page: 956
Journal / Book Title: Organometallics
Volume: 37
Issue: 6
Copyright Statement: © 2018 American Chemical Society. This is an open access article published under an ACS AuthorChoice License, which permits copying and redistribution of the article or any adaptations for non-commercial purposes (https://pubs.acs.org/page/policy/authorchoice_termsofuse.html).
Sponsor/Funder: Engineering & Physical Science Research Council (EPSRC)
Funder's Grant Number: EP/L011514/1
Keywords: Science & Technology
Physical Sciences
Chemistry, Inorganic & Nuclear
Chemistry, Organic
Chemistry
ZIEGLER-NATTA POLYMERIZATION
BETA-HYDROGEN ELIMINATION
ACTIVATION STRAIN MODEL
C-H BORYLATION
AB-INITIO
INSERTION
KINETICS
DERIVATIVES
OLEFINS
ETHYLENE
0302 Inorganic Chemistry
0305 Organic Chemistry
0399 Other Chemical Sciences
Organic Chemistry
Publication Status: Published
Open Access location: https://pubs.acs.org/doi/pdf/10.1021/acs.organomet.7b00908
Online Publication Date: 2018-02-28
Appears in Collections:Chemistry



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