Molecular Understanding of the Formation of Surface Zirconium Hydrides upon Thermal Treatment under Hydrogen of [(⋮SiO)Zr(CH₂tBu)₃] by Using Advanced Solid-State NMR Techniques

Abstract

The reaction of [([triple bond]SiO)Zr(CH(2)tBu)(3)] with H(2) at 150 degrees C leads to the hydrogenolysis of the zirconium-carbon bonds to form a very reactive hydride intermediate(s), which further reacts with the surrounding siloxane ligands present at the surface of this support to form mainly two different zirconium hydrides: [([triple bond]SiO)(3)Zr-H] (1a, 70-80%) and [([triple bond]SiO)(2)ZrH(2)] (1b, 20-30%) along with silicon hydrides, [([triple bond]SiO)(3)SiH] and [([triple bond]SiO)(2)SiH(2)]. Their structural identities were identified by (1)H DQ solid-state NMR spectroscopy as well as reactivity studies. These two species react with CO(2) and N(2)O to give, respectively, the corresponding formate [([triple bond]SiO)(4-x)Zr(O-C(=O)H)(x)] (2) and hydroxide complexes [([triple bond]SiO)(4-x)Zr(OH)(x)] (x = 1 or 2 for 3a and 3b, respectively) as major surface complexes.

Mesoporous Silica-Supported Amidozirconium-Catalyzed Carbonyl Hydroboration

“…Previously, a signal at 1638 cm −1 was assigned to the ν ZrH in (SiO) 3 ZrH. 41 Importantly, the 1592 cm −1 peak was not detected in the IR spectrum of the ZrH/Bpin@MSN exposed to D 2 , and this change is taken as evidence for the formation of ZrD/Bpin@MSN ( Figure 7C). Unfortunately, the expected location of a ν ZrD at 1125 cm…”

Silica‐Alumina‐Supported, Tungsten‐Based Heterogeneous Alkane Metathesis Catalyst: Is it Closer to a Silica‐ or an Alumina‐Supported System?

“…[1,2] Since the early 1990s, we have developed a series of oxidesupported metal hydrides [3][4][5][6] for the low temperature alkane transformation. [7][8][9] In contrast to hydrogenolysis, alkane metathesis allows both lower and higher homologues to be obtained, and we have shown recently through a combination of structure-reactivity [10] and kinetic [11] studies that the key carbon-carbon cleavage and formation process involves olefin metathesis.…”

“…[6] Similarly, the band at 2270 cm À1 is not affected by this treatment, and can be assigned to a n (SiÀH) . [3][4][5] Additionally, the band at 2961 cm À1 associated with the residual alkyl ligands (5 %, Figure 1 c) are modified, while a weak band at 2214 cm…”

“…Moreover, in contrast to the tungsten hydride supported on alumina, [6] the IR spectrum of this supported tungsten hydride on silica-alumina, [W À H/SiO 2 -Al 2 O 3 ] SA (3) show several tungsten hydride bands, residual surface alkyl species as well as both Si À H and Al À H species. These latter hydride species are probably formed by the reaction of tungsten hydride intermediates with adjacent ( Si À O À Si ) and ( Si À O À Al s ) bridges, [3][4][5] thus providing bisgrafted species, [( SiO) 2 WH n ] and [( SiO)A C H T U N G T R E N N U N G (Al s O)WH n ] along with ( Si À H) and (Al s À H). The absence of SiH 2 species (not observed in the IR spectrum) [4] suggests the absence of formation of trisgrafted species.…”

“…These latter hydride species are probably formed by the reaction of tungsten hydride intermediates with adjacent ( Si À O À Si ) and ( Si À O À Al s ) bridges, [3][4][5] thus providing bisgrafted species, [( SiO) 2 WH n ] and [( SiO)A C H T U N G T R E N N U N G (Al s O)WH n ] along with ( Si À H) and (Al s À H). The absence of SiH 2 species (not observed in the IR spectrum) [4] suggests the absence of formation of trisgrafted species.…”