Metal halide alkoxides

Lanthanide alkoxide complexes can be prepared using a number of methods. The key difference lies in the nature of lanthanide starting materials. These include elemental metals, halides, alkoxides, amides, carboxylates, hydrides, and organometallic species [1, 11], The organic ligands come from aliphatic alcohols, phenols, or their metal salts. 

From Metal Halides. The reaction of metal chlorides with alcohols can give metal chloride alkoxides (67—69), eg... 

Mixed Halide Alkoxides. Metal chlorides, hydrogen chloride, and carboxyUc acid chlorides convert metal alkoxides to metal chloride alkoxides. 

See related alkylaluminium alkoxides and hydrides, metal halides... 

Amphoteric molecules of this type, where the acidic and basic sites are relatively close to each other but cannot interact directly, can heterolytically cleave H-X and C-X bonds where X is a halide, alkoxide, amide, alcohol, thiol, trimethylsilyl, or alkyl group.18,18a The ability to effect changes in the reactivity of borollide complexes by adjusting metal oxidation states and ligands allows fine-tuning of catalytic and other properties, which in turn advances the application of these compounds in synthesis. 

Above all, the discovery that some organometallic compounds are effective in the synthesis of high molecular weight PCL [7] promoted a renewed interest in the ROP of lactones, particularly with alkyl metals, metal halides, oxides, car-boxylates, and alkoxides. These metal compounds were first classified as anionic... 

Two different mechanisms have been proposed for the ROP of (di)lactones depending on the nature of the organometalhc derivatives. Metal halides, oxides, and carboxylates would act as Lewis acid catalysts in an ROP actually initiated with a hydroxyl-containing compound, such as water, alcohol, or co-hydroxy acid the later would result more hkely from the in-situ hydrolysis of the (di)lac-tone [11]. Polymerization is assumed to proceed through an insertion mechanism, the details of which depends on the metal compound (Scheme la). The most frequently encountered Lewis acid catalyst is undoubtedly the stannous 2-ethylhexanoate, currently referred to as stannous octoate (Sn(Oct)2). On the other hand, when metal alkoxides containing free p-, d-, or f- orbitals of a favo-... 

Bismuth is an important element in many of the new high-temperature, oxide superconductors and in a variety of heterogeneous mixed oxide catalysts. Some of the methods employed in the preparation of these materials, namely sol-gel and chemical vapor deposition processes, require bismuth alkoxides as precursors and a number of papers on these compounds have recently been published.1 One synthetic route to bismuth alkoxides, which avoids the more commonly used trihalide starting materials and the often troublesome separation of alkali metal halides, involves the reaction between a bismuth amide and an alcohol according to the following equation ... 

The addition of a base, typically ammonia, to mixtures of transition metal halides and alcohols allows the synthesis of homoleptic alkoxides and phenoxides for a wide range of metals. Anhydrous ammonia was first used in the preparation of titanium alkoxides where the reaction is forced to completion by the precipitation of ammonium chloride.41 Although useful for the synthesis of simple alkoxides and phenoxides of Si, Ge, Ti, Zr, Hf, V, Nb, Ta and Fe, as well as a number of lanthanides,42-47 the method fails to produce pure /-butoxides of a number of metals.58 Presumably, secondary reactions between HC1 and Bu OH take place. However, mixing MC14(M = Ti, Zr) with the Bu OH in the presence of pyridine followed by addition of ammonia proves successful, giving excellent yields of the M(OBul)4 complexes.59... 

An in-depth study of the industrially important hydrolysis of titanium alkoxides has been carried out by Bradley.234,235 A number of intermediate complexes were isolated and characterized. The alcohol exchange reaction has been discussed previously. The addition of hydrohalous acids to alkoxides is clearly related to the reverse reaction, the addition of alcohols to metal halides. In general, the products of these two reactions will be the same (equation 59). Hence, complete substitution will occur to give metal halides that are known to form only alcoholates with alcohols (equations 60 and 61),31,236... 

An important advantage of the electrochemical technique lies in its simplicity because metals are much easier to handle than metal halides and are always commercially available the consumption of the solvents is also much smaller than for conventional techniques [1639, 1612]. The electrochemical method allows the creation of a highly efficient, low-waste continuous process for commercial production of metal alkoxides [948]. 

The synthesis of bimetallic alkoxides can be achieved using the 2 routes first described by Meerwein and Bersin [1101] complex formation of2 alkoxides and the methathesis of a metal halide with an alkali metal alkoxide. 

See related ALKYLALUMINIUM ALKOXIDES AND HYDRIDES, METAL HALIDES... 

With the exception of nitrogen, all of the Group Vb elements are expected to form pentacoordinate compounds in their 5+ oxidation state, and this is, indeed, the case with some of the halides, alkoxides, etc. It was not until the pioneering work of Georg Wittig and his collaborators, however, that the first examples of pentaorganyls of these borderline elements between metals and metalloids were reported (95-99, 102, 104). In this early investigation, a complete set of the pentaphenyls could be obtained and characterized (95-99, 102), but apart from the pentamethyl-antimony case, all attempts for the preparation of pentaalkyl derivatives failed (104). 

Allyl silanes will also attack carbonyl compounds when they are activated by coordination of the carbonyl oxygen atom to a Lewis acid. The Lewis acid, usually a metal halide such as TiCLj or ZnCl2, activates the carbonyl compound by forming an oxonium ion with a metal-oxygen bond. The allyl silane attacks in the usual way and the (3-silyl cation is desilylated with the halide ion. Hydrolysis of the metal alkoxide gives a homoallylic alcohol. 

Photoelectron spectroscopy (PES) has been shown to provide a convenient probe of metal ion effective nuclear charge and the nature of the metal-ligand bond via the energy of valence-electron photoionizations (16, 20, 22, 284, 285, 312, 332-334). Recently, PES spectroscopy has been employed in the study of oxo-molybdenum compounds of the type (L-A5)MoE(X,Y) [E = O, S, NO X, Y = halide, alkoxide, or thiolate] in order to evaluate the synergy between the axial (E) and equatorial (X,Y) donors in affecting the ionization energy of the HOMO localized on the Mo center (16, 284, 334). These studies have conclusively shown that equatorial dithiolene coordination electronically bulfers the Mo center in (L-A pMoEttdt) (Fig. 13) from the severe electronic perturbations associated with the enormous variation in the Ji-donor/acceptor properties... 

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