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 OsH₆ (Pⁱ Pr₃ )₂ is performed via net-metathesis between Si-C(spⁿ ) and H-C(sp³ ) σ-bonds (n=2, 3). Complex OsH₆ (Pⁱ Pr₃ )₂ activates the Si-H bond of Et₃ SiH and Ph₃ SiH to give OsH₅ (SiR₃ )(Pⁱ Pr₃ )₂ , which yield OsH₄ {κ¹ -P,η² -SiH-[ⁱ Pr₂ PCH(Me)CH₂ SiR₂ H]}(Pⁱ Pr₃ ) 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 (Pⁱ Pr₃ )₂ with dimethylphenylsilane, and 1,1,1,3,5,5,5-heptamethyltrisiloxane afford OsH₅ (SiR₂ R')(Pⁱ Pr₃ )₂ , which evolve into OsH₄ {κ¹ -P,η² -GeH-[ⁱ Pr₂ PCH(Me)CH₂ SiR₂ H]}(Pⁱ Pr₃ ) (R=Me, OSiMe₃ ) and R'-H (R'=Ph, Me). Exchange reaction is extended to Et₃ GeH. The latter reacts with OsH₆ (Pⁱ Pr₃ )₂ to give OsH₅ (GeEt₃ )(Pⁱ Pr₃ )₂ , which loses ethane to form OsH₄ {κ¹ -P,η² -GeH-[ⁱ Pr₂ PCH(Me)CH₂ GeEt₂ H]}(Pⁱ Pr₃ ).

Keywords: Germanes; Osmium; Polyhydrides; Silanes; σ-Bond Metathesis.

Scheme 1

Metathesis reactions between σ‐bonds mediated by transition metal complexes.

Scheme 2

σ‐Activation/cross‐coupling metathesis according to Equation (c) applied to R₃SiH: Preparation of complexes 2–4.

Figure 1

X‐ray structure of complex 3 with 50 % probability ellipsoids. Hydrogen atoms (except hydrides) are omitted for clarity. Selected bond lengths [Å] and angles [deg] for the X‐ray and DFT optimized (in square brackets) structures: Os−H(01) 1.581(10) [1.662], Os−H(02) 1.582(10) [1.635], Os−H(03) 1.593(10) [1.629], Os−H(04) 1.593(10) [1.657], Os−H(05) 1.582(10) [1.638], Os−P(1) 2.3996(8) [2.448], Os−P(2) 2.3965(8) [2.442], Os−Si 2.4312(9) [2.458], Si−H(02) [2.174], Si−H(05) [2.123]; P(1)‐Os‐P(2) 110.92(3) [109.84], Si‐Os‐P(1) 109.70(3) [106.95], Si‐Os‐P(2) 133.72(3) [134.04].

Figure 2

X‐ray structure of complex 5 with 50 % probability ellipsoids. Hydrogen atoms (except hydrides) are omitted for clarity. Selected bond lengths [Å] and angles [deg] for the X‐ray and DFT optimized (in square brackets) structures: Os−H(01) 1.584(9) [1.666], Os−H(02) 1.577(9) [1.667], Os−H(03) 1.580(9) [1.674], Os−H(04) 1.592(9) [1.648], Os−H(05) 1.590(9) [1.641], Os−P(1) 2.3512(6) [2.376], Os−P(2) 2.3449(6) [2.377], Os−Si 2.4645(6) [2.512], Si−H(01) 1.91(2) [1.847]; P(1)‐Os‐P(2) 157.56(2) [164.01], Si‐Os‐P(1) 80.98(2) [80.29], Si‐Os‐P(2) 121.302(19) [115.56].

Figure 3

³¹P{¹H} NMR spectra (161.98 MHz) showing the transformation of 3 into 5 in toluene at 378 K.

Figure 4

Plot of Equation (1) at different temperatures.

Figure 5

Eyring plot for the transformation of 3 into 5 in toluene.

Scheme 3

σ‐Activation/cross‐coupling metathesis according to Equation (c) extended to R'R₂SiH: preparation of complexes 6–9.

Scheme 4

σ‐Activation/cross‐coupling metathesis according to Equation (c) extended to Et₃GeH: preparation of complexes 10 and 11.