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

Abstract

The silylation of a phosphine of OsH 6 (P i Pr 3 ) 2 is performed via net-metathesis between SiÀ C(sp n ) and HÀ C(sp 3 ) σ-bonds (n = 2, 3). Complex OsH 6 (P i Pr 3 ) 2 activates the SiÀ H bond of Et 3 SiH and Ph 3 SiH to give OsH 5 (SiR 3 )(P i Pr 3 ) 2 , which yield OsH 4 {k 1 -P,η 2 -SiH-[ i Pr 2 PCH(Me)CH 2 SiR 2 H]}(P i Pr 3 ) and RÀ 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 OsH 6 (P i Pr 3 ) 2 with dimethylphenylsilane, and 1,1,1,3,5,5,5-heptamethyltrisiloxane afford OsH 5 (SiR 2 R')(P i Pr 3 ) 2 , which evolve into OsH 4 {k 1 -P,η 2 -GeH-[ i Pr 2 PCH(Me)CH 2 SiR 2 H]}(P i Pr 3 ) (R = Me, OSiMe 3 ) and R'À H (R' = Ph, Me). Exchange reaction is extended to Et 3 GeH. The latter reacts with OsH 6 (P i Pr 3 ) 2 to give OsH 5 (GeEt 3 )(P i Pr 3 ) 2 , which loses ethane to form OsH 4 {k 1 -P,η 2 -GeH-[ i Pr 2 PCH(Me)CH 2 GeEt 2 H]}(P i Pr 3 ).

Silyl-Osmium(IV)-Trihydride Complexes Stabilized by a Pincer Ether-Diphosphine: Formation and Reactions with Alkynes

“…Complexes with two triisopropylphosphine ligands instead of ether-diphosphine resembling to b 3 have been recently isolated and fully characterized, including the X-ray analysis structure of one of them in our laboratory. 29 …”

Dehydrogenation of Formic Acid Catalyzed by an Osmium-Polyhydride: Relevance of Acid Assistance in the CO2 Formation Stage

“…Instrumental methods, X-ray information, and DFT computational details are provided in the Supporting Information. Complex 1 was prepared according to the published method . Chemical shifts are expressed in ppm and coupling constants are given in hertz.…”

“…The transformation involves the displacement of one of the substituents of the germyl ligand by a methyl group of an isopropyl substituent of the phosphine involved (Scheme ). Unlike the germanium atom of germylenephosphine of II , the germanium atom of this other bidentate (η 2 -GeH)-phosphine ligand has the electrons necessary to achieve electronic saturation. In search for the differences between both systems and trying to delve deeper into the role of acid-assistance during the CO 2 release process, we decided to investigate the catalytic performance of the σ-complex 1 in the dehydrogenation of formic acid.…”

Structurally Well-Defined PC(sp3)P Osmium Pincer Catalysts for Methylation of Alcohols, Indoles, Phenols, and Sulfonamides Using Methanol as a C1 Source

“…Recent findings spot homogeneous osmium-based catalysts as superior in a broad spectrum of synthetically valuable transformations, such as dihydroxylation reactions, regioselective hydroformylation, olefin metathesis, Tichenko reaction via C–H α activation–hydroxylation of aldehydes, transfer hydrogenation, acceptorless dehydrogenation, and others . Despite this progress, osmium is the least catalytically studied metal from the platinoid group, mainly because it is redox and coordination flexiblethe metal center easily changes the oxidation state and primary coordination sphere, especially in the presence of molecular hydrogen .…”