Chemistry siloxides

The - 0B[0Si(0 Bu)3]2 ligand has provided species of the form L M OB[OSi (0 Bu)3]2 x that are viable molecular precursors to M/B/Si/0 materials. However, the chemistry of this ligand appears to be sensitive to the ancillary ligands on the associated metal, with ligand transfer to the boron center (sometimes accompanied by siloxide transfer from boron to the metal) being a primary pathway for decomposition [64,90]. 

An important area in the chemistry of titanium alkoxides is with the siloxides, Ti(OSiR3)4and their derivatives containing Hal, OR, oxoligands and the related polymers. The latter find rather broad applications as dielectric and isolation materials. They are briefly considered in the book by Feld and Cowe [560], a detailed review being included in the monograph by Andrianov [48]. Table 12.12 presents the properties of only certain simplest derivatives. 

Scheme 5. Siloxide ligands employed in lanthanide chemistry...

An interesting variant of metal-tri(fert-butoxy)siloxide chemistry was described recently. Thus, the thermal... 

Novel chemistry has been developed around binuclear samarium(ll) complexes containing one pentamethylcyclopentadienyl ligand and bulky siloxide ligands. The reaction of Cp 2Sm(TFIF)2 with 1.5equiv. of (BucO)3SiOH in toluene gave the unsymmetrical binuclear Sm(n) complex Cp Sm[/.t-OSi(OBu )3 3Sm as green crystals in 93% yield (Scheme lOO).506... 

The chemistry of transition metal siloxide complexes has continued to attract considerable attention in the field of material science [1] and catalysis [2], particularly since 1980. The synthesis, reactivity, and bonding of such complexes in a wide variety of supporting ligand environments continues to be explored. In this regard numerous silanediols, disilanols and silanetriols have been described in the literature [3,4], which could be used as building blocks for the preparation of novel titanium-containing heterocubanes and titanasiloxanes [4-6]. 

Lanthanides Coordination Chemistry Luminescence Lanthanide Oxide/Hydroxide Complexes Rare Earth Siloxides Organic Syntiiesis. 

The chemistry of rare earth siloxides, also referred to as rare earth silanolates or silyloxides, dates back to 1970,... 

Relatively little is known about the chemistry of divalent rare earth siloxides, primarily because of the sensitivity of these cations to oxidation as reflected in their highly negative standard reduction potentials ... 

There are a number of synthetic pathways to trivalent rare earth siloxides and their Lewis base adducts such as salt metathesis, transesterification, acid-base chemistry, and silanolysis. Less frequently used are insertions of organo rare earth complexes into cychc and linear sUoxanes and CO2 insertion into rare earth silylamides. Transesterification is a common route for the preparation of stericaUy less-hindered early transition metal trialkyl siloxides and involves... 

All bridged dimers feature a central Ln202 core (type I), which in the presence of strong donor molecules such as THF, DME, OPPh3, or pyridine dissociate into mononuclear species with either octahedral (type II) or trigonal bipyramidal structures (type III). Similar structural motifs are found in cyclic silsesquioxane-based rare earth siloxides. In the presence of donors, distorted octahedral (V) or distorted trigonal bipyramidal complexes (IV) are formed, which in solution through loss of donor solvent may be in equilibrium with their respective dimers (see Lanthanides Coordination Chemistry) ... 

There are only a few studies of siloxides serving as spectator ligands in the chemistry of trivalent rare earth metal complexes. In an attempt to design robust precatalysts for the hydrosilylation of olefins, Okuda etal. prepared several rare earth complexes supported by the siloxide ligand, (Bu 0)3Si0 (Scheme 5). Reaction of [Ln(CH2SiMe3)3(THF) ] (Ln = Y, Tb, Lu) with (Bu 0)3Si0H afforded the dimeric siloxides (26). Addition... 

Siloxide ligands are able to coordinate to rare earth metals in various oxidation states and coordination numbers to primarily form mono- and dinuclear complexes. In particular, the synthetic and stmctural chemistry of trivalent rare earth siloxides are well documented in the literature and show analogies with rare earth alkoxides. It is fair to state, however, that the field of divalent and tetravalent rare earth siloxides is poorly developed and that applications pertaining to the design of siloxide-based homogeneous and heterogeneous rare earth metal catalysts as well as the development of novel silicate-based materials are scarce. Although the few results of the catalytic activity of some of the rare earth siloxides in olefin... 

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