TY - JOUR
T1 - Synthetic, mechanistic, and theoretical studies on the generation of iridium hydride alkylidene and iridium hydride alkene isomers
AU - Lara, Patricia
AU - Paneque, Margarita
AU - Poveda, Manuel L.
AU - Santos, Laura L.
AU - Valpuesta, José E.V.
AU - Salazar, Verónica
AU - Carmona, Ernesto
AU - Moncho, Salvador
AU - Ujaque, Gregori
AU - Lledós, Agustí
AU - Maya, Celia
AU - Mereiter, Kurt
PY - 2009/9/14
Y1 - 2009/9/14
N2 - 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 [(TpMs2)Ir(C6H5)2] with o-C6H4(OH)CH2R, or with the substituted anisoles 2,6-Me2C6H3OMe, 2,4,6Me 3C6H2OMe, and 4-Br-2,6-Me2C 6H2OMe. 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. © 2009 Wiley-VCH Verlag GmbH & Co. KGaA.
AB - 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 [(TpMs2)Ir(C6H5)2] with o-C6H4(OH)CH2R, or with the substituted anisoles 2,6-Me2C6H3OMe, 2,4,6Me 3C6H2OMe, and 4-Br-2,6-Me2C 6H2OMe. 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. © 2009 Wiley-VCH Verlag GmbH & Co. KGaA.
KW - Alkenes
KW - C-H activation
KW - Carbenes
KW - Density functional calculations
KW - Iridium
U2 - 10.1002/chem.200900654
DO - 10.1002/chem.200900654
M3 - Article
VL - 15
SP - 9046
EP - 9057
IS - 36
ER -