Facial (methyl)(hydrido)(silyl) complexes of iridium: Synthesis, X-ray structures, and reductive elimination reactions. Facile formation of silametallacycles by metalation of silyl ligands

Michael Aizenberg, David Milstein

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Abstract

Facial complexes L3Ir(CH3)(H)(SiR3) (L = PMe3; R = EtO (2), Ph (3), Et (4)) result from oxidative addition of the corresponding silanes to MeIrL4. The three compounds are fully characterized spectroscopically and the mutual cis arrangement of H, CH3, and SiR3 groups is confirmed by X-ray crystallographic studies of 3 and 4. Crystal data for 3: monoclinic, P21/n, a = 10.050(2) Å, b = 31.459(6) Å, c = 10.325(2) Å, β = 114.61(3)°, Z = 4. Crystal data for 4: triclinic, P1, a = 8.653(2) Å, b = 10.090(2) Å, c = 14.988(3) Å, α = 92.43(3)°, β = 94.53(3)°, γ = 113.69(3)°, Z = 2. Based on the X-ray structural data, the following order of increasing trans influence is deduced: CH3 <H <SiPh3 <SiEt3. On heating to 100 °C, 2 and 3 reductively eliminate methane exclusively. The resulting Ir(I) silyls quantitatively cyclometalate to produce novel iridasilacycles L3Ir(H)(CH2CH2OSi(OEt)2) (5) and L3Ir(H)(o-C6H4SiPh2) (6). 5 and 6 are fully characterized spectroscopically and complex 6 also crystallographically. Compound 4 on heating eliminates C-H, C-Si, and H-Si bonds competitively (the latter one reversibly). The upper limit of the relative rates of C-H and C-Si bond formation is estimated as kC-H/kC-Si ≈ 4. The resulting highly reactive intermediate complexes [HIrL3], [MeIrL3], and [Et3SiIrL3] react further with the solvent benzene and triethylsilane to yield a mixture of C-H and Si-H addition products. These were identified by carrying out independent oxidative addition reactions of HSiEt3, H2, and C6H6 to HIrL4 and PhIrL3. A plausible scheme accounting for the formation of the observed complexes is proposed.

Original languageEnglish
Pages (from-to)6456-6464
Number of pages9
JournalJournal of the American Chemical Society
Volume117
Issue number24
Publication statusPublished - Jun 21 1995

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ASJC Scopus subject areas

  • Chemistry(all)

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