| 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 |
| Contributors: |
Engineering & Physical Science Research Council (EPSRC) |
| Source: |
956 ; 949 |
| Publisher Information: |
American Chemical Society |
| Publication Year: |
2017 |
| Collection: |
Imperial College London: Spiral |
| Subject Terms: |
Science & Technology; Physical Sciences; Chemistry; Inorganic & Nuclear; Organic; 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 |
| Description: |
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. |
| Document Type: |
article in journal/newspaper |
| Language: |
English |
| Relation: |
Organometallics; http://hdl.handle.net/10044/1/58877; https://dx.doi.org/10.1021/acs.organomet.7b00908; EP/L011514/1 |
| DOI: |
10.1021/acs.organomet.7b00908 |
| Availability: |
http://hdl.handle.net/10044/1/58877; https://doi.org/10.1021/acs.organomet.7b00908 |
| Rights: |
© 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). |
| Accession Number: |
edsbas.CBF2B335 |
| Database: |
BASE |