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Download fileStereoselective Oxidative Additions of Iodoalkanes and Activated Alkynes to a Sulfido-Bridged Heterotrinuclear Early−Late (TiIr2) Complex
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posted on 2003-05-21, 00:00 authored by Miguel A. Casado, Jesús J. Pérez-Torrente, Miguel A. Ciriano, Isabel T. Dobrinovitch, Fernando J. Lahoz, Luis A. OroThe reactions of the early−late trinuclear complex [Cp(acac)Ti(μ3-S)2Ir2(CO)4] (1) with electrophiles have been
found to occur on the iridium atoms with no other involvement of the early metal than in electronic effects. The
reaction with iodine gave two isomers of the diiridium(II) complex [Cp(acac)Ti(μ3-S)2Ir2I2(CO)4] differentiated by the
relative positions of the iodo ligands on the iridium atoms. The reactions with iodoalkanes are highly stereoselective
to give one sole isomer of formula [Cp(acac)Ti(μ3-S)2Ir2(R)(I)(CO)4] (R = CH3, CH2I, CHI2) with a carbonyl and the
iodo ligand trans to the metal−metal bond. The structures of the symmetrical isomer with the iodo ligands trans to
the metal−metal bond and that of the compound with R = CHI2 have been solved by X-ray diffraction methods.
The stereoselectivity of the oxidative-addition reactions can be rationalized assuming the influence of steric effects
of the groups on the titanium center and a radical-like mechanism. Reactions of 1 with the activated acetylenes,
dimethylacetylenedicarboxylate and methylacetylenecarboxylate, gave the complexes [Cp(acac)Ti(μ3-S)2Ir2(μ-η1-RCCCO2Me)(CO)4] (R = CO2Me, H), with the alkyne bridging the two iridium centers as a cis-dimetalated olefin
and the CC bond parallel to the Ir−Ir axis. Two isomers resulting from the disposition of the alkyne along the
Ir−Ir vector were observed in solution for the compound with the nonsymmetrical alkyne (R = H), while only one
was observed for the compound with R = CO2Me. An exchange, fast in the NMR time scale, of the apical with the
equatorial carbonyls occured in the complexes [Cp(acac)Ti(μ3-S)2Ir2(μ-η1-RCCCO2Me)(CO)4], producing their
equivalence in the 13C{1H} NMR spectra.