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Synthetic, Mechanistic, and Theoretical Studies on the Generation of Iridium Hydride Alkylidene and Iridium Hydride Alkene Isomers
Author(s) -
Lara Patricia,
Paneque Margarita,
Poveda Manuel L.,
Santos Laura L.,
Valpuesta José E. V.,
Salazar Verónica,
Carmona Ernesto,
Moncho Salvador,
Ujaque Gregori,
Lledós Agustí,
Maya Celia,
Mereiter Kurt
Publication year - 2009
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200900654
Subject(s) - hydride , iridium , chemistry , alkene , tautomer , medicinal chemistry , olefin fiber , stereochemistry , bond cleavage , photochemistry , computational chemistry , hydrogen , catalysis , organic chemistry
Experimental and theoretical studies on equilibria between iridium hydride alkylidene structures, [(Tp Me2 )I r(H){C(CH 2 R)ArO }] (Tp Me2 =hydrotris(3,5‐dimethylpyrazolyl)borate; R=H, Me; Ar=substituted C 6 H 4 group), and their corresponding hydride olefin isomers, [(Tp Me2 )I r(H){R(H)C C(H)OAr}], have been carried out. Compounds of these types are obtained either by reaction of the unsaturated fragment [(Tp Me2 )Ir(C 6 H 5 ) 2 ] with o ‐C 6 H 4 (OH)CH 2 R, or with the substituted anisoles 2,6‐Me 2 C 6 H 3 OMe, 2,4,6‐Me 3 C 6 H 2 OMe, and 4‐Br‐2,6‐Me 2 C 6 H 2 OMe. The reactions with the substituted anisoles require not only multiple CH bond activation but also cleavage of the MeOAr bond and the reversible formation of a CC bond (as revealed by 13 C 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.