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

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 ).

Yttrium tris(trimethylsilylmethyl) complexes grafted onto MCM-48 mesoporous silica nanoparticles

A series of tris(trimethylsilylmethyl) yttrium donor adduct complexes was synthesized and fully characterized by X-ray diffraction, ¹H/¹³C/²⁹Si/³¹P/⁸⁹Y heteronuclear NMR and FTIR spectroscopies as well as elemental analyses. Treatment of Y(CH₂SiMe₃)₃(thf)_x with various donors Do led to complete (Do = TMEDA, DMAP) and partial displacement of THF (Do = NHC^iPr, DMPE). Exceptionally large ⁸⁹Y NMR shifts to low field were observed for the new complexes. Complexes Y(CH₂SiMe₃)₃(tmeda) and Y(CH₂SiMe₃)₃(dmpe)(thf) were chosen to perform surface organometallic chemistry, due to a comparatively higher thermal stability and the availability of the ³¹P nucleus as a spectroscopic probe, respectively. Mesoporous nanoparticles of the MCM-48-type were synthesized and used as a 3^rd generation silica support. The parent and hybrid materials were characterized using X-ray powder diffraction, solid-state-NMR spectroscopy, DRIFTS, elemental analyses, N₂-physisorption, and scanning electron microscopy (SEM). The presence of surface-bound yttrium alkyl moieties was further proven by the reaction with carbon dioxide. Quantification of the surface silanol population by means of HN(SiHMe₂)₂-promoted surface silylation is shown to be superior to titration with lithium alkyl LiCH₂SiMe₃.