Metathesis between E−C(spn) and H−C(sp3) σ‐Bonds (E=Si, Ge; n=2, 3) on an Osmium‐Polyhydride

• Published in: Angewandte Chemie International Edition 2022-07, Vol.61 (29), p.e202204081-n/a
• Main Authors: Esteruelas, Miguel A., López, Ana M., Oñate, Enrique, Raga, Esther
• Format: Article
• Language: English
• Subjects: Activation energy; Entropy; Entropy of activation; Ethane; Germanes; Germanium; Hydrogen bonds; Metathesis; Osmium; Phosphine; Phosphines; Polyhydrides; Selectivity; Silanes; Silicon; σ-Bond Metathesis
• ISSN: 1433-7851; 1521-3773; 1521-3773
• DOI: 10.1002/anie.202204081

The silylation of a phosphine of OsH6(PiPr3)2 is performed via net‐metathesis between Si−C(spn) and H−C(sp3) σ‐bonds (n=2, 3). Complex OsH6(PiPr3)2 activates the Si−H bond of Et3SiH and Ph3SiH to give OsH5(SiR3)(PiPr3)2, which yield OsH4{κ1‐P,η2‐SiH‐[iPr2PCH(Me)CH2SiR2H]}(PiPr3) and R−H (R=Et, Ph), by displacement of a silyl substituent with a methyl group of a phosphine. Such displacement is a first‐order process, with activation entropy consistent with a rate determining step occurring via a highly ordered transition state. It displays selectivity, releasing the hydrocarbon resulting from the rupture of the weakest Si‐substituent bond, when the silyl ligand bears different substituents. Accordingly, reactions of OsH6(PiPr3)2 with dimethylphenylsilane, and 1,1,1,3,5,5,5‐heptamethyltrisiloxane afford OsH5(SiR2R′)(PiPr3)2, which evolve into OsH4{κ1‐P,η2‐GeH‐[iPr2PCH(Me)CH2SiR2H]}(PiPr3) (R=Me, OSiMe3) and R′−H (R′=Ph, Me). Exchange reaction is extended to Et3GeH. The latter reacts with OsH6(PiPr3)2 to give OsH5(GeEt3)(PiPr3)2, which loses ethane to form OsH4{κ1‐P,η2‐GeH‐[iPr2PCH(Me)CH2GeEt2H]}(PiPr3). A series of pentahydride‐silyl/germyl‐osmium(VI) derivatives was prepared. These d2‐species of a late transition metal undergo a novel metathesis reaction between non‐activated E−C(spn) and H−C(sp3) σ‐bonds (E=Si, Ge; n=2, 3) affording new osmium(IV) tetrahydride complexes bearing phosphino‐silane and phosphino‐germane chelate ligands.