Role of Siloxides in Transition Metal Chemistry and Homogeneous Catalysis

Abstract

The role of siloxide ligands in the chemistry and catalysis of transition metals is reviewed. The first part deals with recent aspects of low-valent transition metal siloxide chemistry, while the second part describes some developments in the chemistry of transition metal siloxides in high oxidation states, in particular with regard to the stability of the M-OSi

Ceric Ammonium Nitrate and Ceric Ammonium Chloride as Precursors for Ceric Siloxides: Ammonia and Ammonium Inclusion

“…Similar trends were extensively discussed in the case of several transition metal siloxides, with respect to the effects of π‐backbonding into metal d‐orbitals and differing bond lengths (ΔSi–O). Interestingly, relative similar Si–O bond lengths and differences between the tetra‐ and trivalent homoleptic triphenylsiloxides of titanium were reported …”

“…More recently, the heteroleptic complexes [Ce(TriNO x )(OSiMe 3 )] and [Ce(OC 6 H 2 ‐6‐ t Bu‐4‐Me‐2‐PPh 2 ) 3 (OSiMe 3 )] were described, featuring the trimethylsiloxy ligand . Compared to alcohol proligands HOCR 3 , the respective silanols HOSiR 3 display a higher Brønsted acidity, which again is highly dependent on the substituents R and particularly pronounced in alkoxysilanols …”

Yttrium Siloxide Complexes Bearing Terminal Methyl Ligands: Molecular Models for Ln−CH3 Terminated Silica Surfaces

“…[1] Over the years, metals iloxide complexes emerged as important precursors in materials science and catalysis alike. [6][7][8] Versatile, monoanionic tri-tert-butylsiloxy (OSitBu 3 ,s ilox) [5] and tritert-butoxysiloxy (OSi(OtBu) 3 ) [2-4, 9, 10] have attracted particular attention.T he enhanced thermodynamic stability (disfavored SiÀOb ond cleavage) and decreased electron-donating nature compared to alkoxy ligands has provided accesst oi ntriguing metal redox chemistry. [6][7][8] Versatile, monoanionic tri-tert-butylsiloxy (OSitBu 3 ,s ilox) [5] and tritert-butoxysiloxy (OSi(OtBu) 3 ) [2-4, 9, 10] have attracted particular attention.T he enhanced thermodynamic stability (disfavored SiÀOb ond cleavage) and decreased electron-donating nature compared to alkoxy ligands has provided accesst oi ntriguing metal redox chemistry.…”

“…[2][3][4][5] Crucially,t he reactivity of siloxidec omplexes can be efficientlyf ine-tunedb yd istinct organic substituents Ro ft he siloxy ligands( cf.,a lkoxy ligands). [6][7][8] Versatile, monoanionic tri-tert-butylsiloxy (OSitBu 3 ,s ilox) [5] and tritert-butoxysiloxy (OSi(OtBu) 3 ) [2-4, 9, 10] have attracted particular attention.T he enhanced thermodynamic stability (disfavored SiÀOb ond cleavage) and decreased electron-donating nature compared to alkoxy ligands has provided accesst oi ntriguing metal redox chemistry. [5,9] We and others envisaged silanols HOSiR 3 as molecular models of silica surfaces, [10][11][12] with special reference to surfaceo rganometallic chemistry( SOMC).…”

Modern concepts and methods in the chemistry of polyhedral metallasiloxanes

“…Branched silane oligomers with rather rigid disilane Si-Si units instead of flexible disiloxane SiOSi fragments have been used to synthesize PHMSs containing Al [126], Ca [127], Ti (86), and Zr (87) [128] (Scheme 30). These types of compounds are considered to be active catalytic systems [129]. M a n u s c r i p t An original method that uses -R 2 SiO-fragments and a π-complex of titanium as building blocks for PHMS construction was implemented in previous studies [130,131].…”