Well-defined silica supported aluminum hydride: another step towards the utopian single site dream?

Abstract

Reaction of triisobutylaluminum with SBA15700 at room temperature occurs by two parallel pathways involving either silanol or siloxane bridges.

SOMC grafting of vanadium oxytriisopropoxide (VO(OiPr)3) on dehydroxylated silica; analysis of surface complexes and thermal restructuring mechanism

“…The ability of the strained siloxane bridges of highly dehydroxylated silica to participate in graing reactions and in the rearrangement of surface complexes by s-bond metathesis is known. 31,36,39 The rearrangement of 2m to 2b does not generate new silanol moieties in agreement with the lack of such functionalities in 2 as observed by FT-IR (Fig. 1).…”

Tungsten Catalyst Incorporating a Well‐Defined Tetracoordinated Aluminum Surface Ligand for Selective Metathesis of Propane, [(≡Si−O−Si≡)(≡Si−O−)2Al−O−W(≡CtBu) (H)2]

“…The double quanta (DQ) 2D 1 H− 1 H spectrum of [Al−OH], 3 , (Figure ) exhibits a strong autocorrelation on the 2 : 1 diagonal centered at approximately 0.9 ppm in F2 and 1.8 ppm in F1. It corresponds to the proton signal of [≡Si−CH 2 −C H (C H 3 ) 2 ] . The autocorrelation observed at 4.2 ppm is assigned to the [≡SiH 2 ] moiety ( 5′ in the spectrum).…”

“…The band observed at 1945 cm À 1 was assigned to the terminal [AlÀ H], [υ(AlÀ H)]. [5] After the reaction with N 2 O, the IR spectrum of [AlÀ OH], 3, shows a sharp decrease in intensity of this [υ(AlÀ H)] band, accompanied by the appearance of a band at 3783 cm À 1 (Figure 1b). The latter is assigned to the [υ(OHÀ μ 1 À Al IV )] of the [AlÀ OH] species 3.…”

“…The resulting bipodal single‐site supported tetrahedral isobutyl‐aluminum complex, [(≡Si−O−Si≡) (≡Si−O−) 2 Al−iBu], 1 a , was formed on the surface along with silicon hydride, [≡Si−H], 1 b , and silicon isobutyl, [≡Si−CH 2 CH(CH 3 ) 2 ], 1 c . Surprisingly, the data showed that the hydride homologue of 1a, [(≡Si−O−Si≡)(≡Si−O−) 2 Al−H], 2 a , (represented simply as [Al−H]) was not generated from gaseous H2 but rather by a simple thermal treatment of the isobutyl moiety via β‐H elimination and isobutene (Scheme S1, details in SI) …”

“…[2b,4] To design better alkane metathesis catalysts, we were motivated by the idea of creating more electron-deficient metal center, which, might alter the coordination of the tungsten to the AlÀ OÀ ligand and markedly affect the catalytic properties for alkane metathesis. [5] In the work reported here, we focused on the synthesis of an acidic surface ligands by creating well-defined aluminum hydroxyl groups within the mesopores of [(�SiÀ OÀ Si�) (=SiÀ O) 2 AlÀ OH] (represented here simply as [AlÀ OH] (3)) to serve as anchoring sites for tungsten complexes.…”