Surface Organobarium and Organomagnesium Chemistry on Periodic Mesoporous Silica MCM‐41: Convergent and Sequential Approaches Traced by Molecular Models

Abstract

The alkaline earth metal alkyl complexes [Ba(AlEt(4))(2)](n) and Mg(AlMe(4))(2) were directly grafted onto periodic mesoporous silica MCM-41, which had been dehydroxylated at 270 °C (specific surface area a(s): 1023 m(2) g(-1); pore volume V(p): 1.08 cm(3) g(-1); main pore diameter 3.4 nm). Alternatively, barium alkyl surface species were generated by sequential grafting of MCM-41 with Ba[N(SiHMe(2))(2)](2)(thf)(4) and AlEt(3) to yield the hybrid material AlEt(3)@Ba[N(SiHMe(2))(2)](2)(thf)(4)@MCM-41. For a better understanding of the surface chemistry, AlEt(3)@MCM-41 was also accessed. All hybrid materials were analyzed by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, elemental analysis, nitrogen physisorption, and solid-state NMR spectroscopy; this clearly revealed distinct surface chemistry for the alkylaluminate-treated materials [Ba(AlEt(4))(2)]@MCM-41 and Mg(AlMe(4))(2)@MCM-41. In an attempt to mimic the surface chemistry, the organometallic precursors were treated with HOSi(OtBu)(3). The reaction of equimolar amounts of {Ba[N(SiHMe(2))(2)](2)}(n) and HOSi(OtBu)(3) produced a mixed silylamido/siloxide cluster of Ba(3)[OSi(OtBu)(3)](3)[N(SiHMe(2))(2)](3) with bridging-only siloxide ligands as well as one bridging and two terminal silylamido ligands. The Schlenk equilibrium was found to govern the [Ba(AlEt(4))(2)](n)-HOSi(OtBu)(3) and Mg(AlMe(4))(2)-HOSi(OtBu)(3) reactions, leading to the isolation of complexes of [Ba(AlEt(4))(2) (toluene)](2) and Mg[OSi(OtBu)(3))](2)(AlMe(3))(2), respectively. Allowing for a donor-induced cleavage of Mg(AlMe(4))(2), the reaction of [MgMe(2)] with one or two equivalents of HOSi(OtBu)(3) was studied. While putative Mg[OSi(OtBu)(3)](Me) and Mg[OSi(OtBu)(3)](2) could not be crystallized from the reaction mixtures, cluster complexes Mg(5)(O)[OSi(OtBu)(3)](5)Me(3) and Mg(4)(OH)(2)[OSi(OtBu)(3)](6) could be unambiguously identified by X-ray crystallography.

Barium‐Catalysed Dehydrocoupling of Hydrosilanes and Borinic Acids: A Mechanistic Insight

“…Unusually, the arrangement about Ba1 is trigonal planar (Σ θ (Ba1)=360.0°), using the centroid of the aromatic ring (Ba1‐Ct=3.1778(5) Å) to represent the coordinated toluene. The Ba1−C interatomic distances in 2 ⋅(tol), within 3.341(2)–3.5152(25) Å, compare well to those in known toluene adducts …”

Mechanisms of Silicon Alkoxide Hydrolysis–Oligomerization Reactions: A DFT Investigation

“…[8] Silica aerogels are ideal candidates for various applications, such as thermal superinsulators, adsorbents, sensors, catalyst carriers, and inorganic fillers. [12][13][14][15][16][17] The hydrolysis and condensation of the precursor silicon alkoxide, Si(OR) 4 , is the initial step to prepare silica aquasols. [12][13][14][15][16][17] The hydrolysis and condensation of the precursor silicon alkoxide, Si(OR) 4 , is the initial step to prepare silica aquasols.…”

“…[3,[9][10][11] The fabrication, morphologies, and applications of silica aerogels have received sustained attention in recent years in both chemistry and physics. [12][13][14][15][16][17] The hydrolysis and condensation of the precursor silicon alkoxide, Si(OR) 4 , is the initial step to prepare silica aquasols. The Si atoms in Si(OR) 4 carry a reduced partial positive charge [e.g.…”

Inorganic heterocycles based on alumosilicate-sulfide ligand

“…1 ,9.27;N,3.16. Found: C,61.4;H,9. A solution of 1 (0.50 g, 0.73 mmol) in toluene (10 mL) was prepared inside a glove box and kept for at least 30 min. at À35°C in an integrated freezer.…”