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Base-Promoted Silicon−Hydrogen Bond Activation of Silanes by Iridium(III) Porphyrin Complexes

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journal contribution
posted on 25.08.2008, 00:00 by Baozhu Li, Kin Shing Chan
Iridium(III) porphyrin silyls were synthesized in moderate to high yields conveniently from the reactions of iridium(III) porphyrin carbonyl chloride and methyl with silanes, via silicon−hydrogen bond activation (SiHA) in solvent-free conditions and nonpolar solvents. Base was found to promote the SiHA reactions. Specifically, K3PO4 accelerated the SiHA with iridium porphyrin carbonyl chloride, while KOAc promoted the SiHA by iridium porphyrin methyl. Mechanistic experiments suggested that iridium(III) porphyrin carbonyl chloride initially formed iridium porphyin cation, which then reacted with silanes likely via heterolysis to give iridium porphyrin hydride. Iridium porphyrin hydride further reacted with silanes to yield iridium porphyrin silyls. On the other hand, iridium(III) porphyrin methyl and silyls underwent either oxidative addition or σ-bond metathesis to form the products. In the presence of base, a pentacoordinated silicon hydride species likely formed and reacted with iridium porphyrin methyl to form iridium porphyrin anion, which could further react with silanes to yield iridium porphyrin hydride after protonation. Ir(ttp)H finally reacted with excess silanes to give iridium porphyrin silyl complexes.