Generation and reactivity of sterically hindered iridium carbenes. Competitive α- vs. β-hydrogen elimination in iridium(<scp>iii</scp>) alkyls

Carmona, Ernesto; Paneque, Margarita; Poveda, Manuel L.

doi:10.1039/b303710j

Cited by 65 publications

(34 citation statements)

References 67 publications

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“…The combined organic solvents were dried over Na 2 SO 4 and evaporated. 1 H NMR (CDCl 3 , 258C): d = 6.95, 6.94, 6.74 (d, d, t, 3 JA C H T U N G T R E N N U N G (H,H) = 7.5 Hz, 1 H each; 3 CH ar ); 5.00 (s, 1 H; -OH); 2.62 (q, 3 . The characterization of this compound has been carried out by comparison with literature data.…”

Section: Full Papermentioning

confidence: 99%

“…[a] P. Lara slow b-H elimination. As discussed previously, [3,4] when both a-and b-hydrogen atoms are present in sterically hindered metal environments, a-agostic interactions [4] and a-H eliminations [3] may become more favorable than their b counterparts. In agreement with this line of reasoning, an equilibrium between the two tautomeric structures shown in Scheme 1 could be attained, despite the large energy difference that exists between the free alkene and alkylidene molecules.…”

Section: Introductionmentioning

confidence: 99%

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Synthetic, Mechanistic, and Theoretical Studies on the Generation of Iridium Hydride Alkylidene and Iridium Hydride Alkene Isomers

Lara

Paneque

Poveda

et al. 2009

Chemistry A European J

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Experimental and theoretical studies on equilibria between iridium hydride alkylidene structures, [(TpMe2)Ir(H){C(CH2R)ArO}] (TpMe2=hydrotris(3,5‐dimethylpyrazolyl)borate; R=H, Me; Ar=substituted C6H4 group), and their corresponding hydride olefin isomers, [(TpMe2)Ir(H){R(H)CC(H)OAr}], have been carried out. Compounds of these types are obtained either by reaction of the unsaturated fragment [(TpMe2)Ir(C6H5)2] with o‐C6H4(OH)CH2R, or with the substituted anisoles 2,6‐Me2C6H3OMe, 2,4,6‐Me3C6H2OMe, and 4‐Br‐2,6‐Me2C6H2OMe. The reactions with the substituted anisoles require not only multiple CH bond activation but also cleavage of the MeOAr bond and the reversible formation of a CC bond (as revealed by 13C labeling studies). Equilibria between the two tautomeric structures of these complexes were achieved by prolonged heating at temperatures between 100 and 140 °C, with interconversion of isomeric complexes requiring inversion of the metal configuration, as well as the expected migratory insertion and hydrogen‐elimination reactions. This proposal is supported by a detailed computational exploration of the mechanism at the quantum mechanics (QM) level in the real system. For all compounds investigated, the equilibria favor the alkylidene structure over the olefinic isomer by a factor of between approximately 1 and 25. Calculations demonstrate that the main reason for this preference is the strong Ir–carbene interactions in the carbene isomers, rather than steric destabilization of the olefinic tautomers.

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confidence: 99%

Section: Introductionmentioning

confidence: 99%

Synthetic, Mechanistic, and Theoretical Studies on the Generation of Iridium Hydride Alkylidene and Iridium Hydride Alkene Isomers

Lara

Paneque

Poveda

et al. 2009

Chemistry A European J

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“…Alkene to alkylidene rearrangement is a rare but known event [10] and, similarly, the migratory insertion [11] and the ahydride-elimination [12][13][14] steps find ample literature precedent.…”

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Formation of Iridabenzenes by Coupling of Iridacyclopentadienes and Alkenes

Álvarez¹,

Paneque²,

Poveda³

et al. 2006

Angew Chem Int Ed

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“…It started with hydration of the double bond of 1 through a hydroboration–oxidation sequence and finished with a Wolff rearrangement of a carbene intermediate. The success of this synthesis relied greatly on the well‐known non‐labile nature of the co‐ligands Tp Me2 and CO in the Ir III coordination sphere, which prevented thermal substitution reactions, as well as their kinetic chemical stability towards many reagents, even under forcing conditions (note that the C−H bond of the aromatic pyrazolyl moiety and the B−H and B−N bonds of the Tp Me2 ligand are sterically protected from chemical attack by the 3,5‐Me substituents). Last but not least, the Ir−C bonds of the iridacycle of all the complexes reported herein are very highly stable in the presence of common acids and bases, and this, among other consequences, greatly facilitates the work‐up of many reactions.…”

Section: Introductionmentioning

confidence: 99%

Functionalization of 3‐Iridacyclopentenes

Gómez

Rendón

Álvarez

et al. 2017

Chemistry A European J

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Members of a series of iridacyclopentenes of composition [Tp Ir(k -C,C-CH CR'=CRCH )(CO)] (Tp =hydrotris(3,5-dimethylpyrazolyl)borate; R=R'=H, 1; R=Me, R'=H, 2; R=R'=Me, 3) have been subjected to common organic chemistry procedures for hydrogenation, cyclopropanation, epoxidation, water addition through hydroboration, cis-dihydroxylation, and ozonolysis. The stability of metallacycles 1-3, imparted by the presence of the co-ligands Tp and CO, directs the reactivity towards the C=C double bonds, and furthermore the stereochemistry of the products formed is strongly dictated by the steric demands of the Tp ligand. While the products obtained in some of the above-mentioned reactions are the expected ones from an organic chemistry point of view, in other cases the results differ from the outcomes of similar reactions carried out with the all-carbon counterparts.

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Generation and reactivity of sterically hindered iridium carbenes. Competitive α- vs. β-hydrogen elimination in iridium(iii) alkyls

Cited by 65 publications

References 67 publications

Synthetic, Mechanistic, and Theoretical Studies on the Generation of Iridium Hydride Alkylidene and Iridium Hydride Alkene Isomers

Synthetic, Mechanistic, and Theoretical Studies on the Generation of Iridium Hydride Alkylidene and Iridium Hydride Alkene Isomers

Formation of Iridabenzenes by Coupling of Iridacyclopentadienes and Alkenes

Functionalization of 3‐Iridacyclopentenes

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