Application of iridium pincer complexes in hydrogen isotope exchange reactions
作者:Annika Träff、Göran N. Nilsson、Kálmán J. Szabó、Ludvig Eriksson
DOI:10.1016/j.jorganchem.2007.09.009
日期:2007.12
Iridium pincer complex catalyzed hydrogen to deuterium exchange could be achieved using aromatic and heteroaromatic substrates. The reactions proceed under mild conditions and with high regioselectivity. The efficiency of the hydrogenisotopeexchange reaction depends on the electronic properties of the pincer complexcatalyst.
Mechanistic Studies of the Transfer Dehydrogenation of Cyclooctane Catalyzed by Iridium Bis(phosphinite) <i>p</i>-XPCP Pincer Complexes
作者:Inigo Göttker-Schnetmann、Maurice Brookhart
DOI:10.1021/ja048393f
日期:2004.8.1
Reaction of bis(phosphinite) PCP iridium pincer complexes (p-XPCP)IrHCl (5a-f) [X = MeO (5a), Me (5b), H (5c), F (5d), C6F5 (5e), Ar-F(= 3,5-bis(trifluoromethyl)phenyl) (5f)] with NaOtBu in neat cyclooctane (COA) generates 1:1 mixtures of the respective (p-XPCP)IrH2 complexes 4a-f and the cyclooctene (COE) olefin complexes (p-XPCP)lr(COE) (6a-f) at 23 degreesC. At higher temperatures, complexes 4 and 6 are equilibrated because of the degenerate transfer dehydrogenation of COA with free COE (6 + COA = 4 + 2COE), as was shown by temperature-dependent equilibrium constants and spin saturation transfer experiments at 80 degreesC. At this temperature, the COE complexes 6 exchange with free COE on the NMR time scale with the more electron-deficient complexes 6 exchanging COE faster. The exchange is dissociative and zero order in [COE]. Further analysis reveals that the stoichiometric hydrogenation of COE by complex 4f, and thus the separated back reaction 4f + 2COE --> 6f + COA proceeds at temperatures as low as - 100 degreesC with the intermediacy of two isomeric complexes (p-(ArPCP)-P-F)lr(H)(2)(COE) (8f, 8f'). COE deuteration with the perdeuterated complex 4f-d(38) at -100 degreesC results in hydrogen incorporation into the hydridic sites of complexes 8f,8f'-d(38) but not in the hydriclic sites of complex 4f-d(38), thus rendering COE migratory insertion in complexes 8f,8f' reversible and COE coordination by complex 4f rate-determining for the overall COE deuteration.