Bismuth alkoxides

The electrochemical route (2) can be applied only for the synthesis of Bi(OMe)3, which is insoluble in the parent alcohol (in the other alcohols it was the electrochemical refinement of metal that took place) [967], The glycolates and derivatives of polyatomic phenols stable to hydrolysis have been obtained on alcoholysis ofBi203 [1808, 1352, 684, 559]. 

This high sensitivity ofbismuth derivatives to traces of water often leads to a situation where the results of the synthesis are dependent on the origin of the reactants. Thus, Whitmire [1742] has shown that on application of the phenol purchased from Aldrich in the reaction of BiCl3 with NaOC6F5, the 

All Bi(OAlk)3 derivatives of n- and z -alcohols are volatile, which permits their purification by distillation, but the yields of the sublimates are low as the processes are accompanied by partial decomposition. A much higher thermal stability is demonstrated by Bi(OBu )3. According to the mass-spectrometry data the first members of the homologous series are dimeric in the gas phase, while Bi(OR% and Bi(0C2H40Me)3 are monomeric [967], However the solid state structure of the latter contains the polymer chains and its solutions in benzene — the dimeric molecules. The NMR spectra indicate the equilibrium in solution of aggregates with different number of chelated ligands [1069]. This obstacle hinders the crystallization of 2-methoxyethoxide from solutions (Table 12.15). 

The coordination of bismuth atoms varies considerably in the structures described in the literature, but as for all other derivatives of Bi(III) these are the geometries with a localized electron pair [Bi ] that are dominating. The minimal CN 3 and 4 ( /-tetrahedron and -trigonal bipyramid) are present in the molecule ofBi(OBu )3 (in the gas phase) and in the polymeric structure of [KBi(ji-OBu,)4] . There are also present the structures with 5-coordinated Biatom (tetragonal pyramid = y-octahedron). Its representatives are the structure 

Chemical composition. Structure Synth. route Properties Investig. methods Ref. 

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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 ... 

Bismuth alkoxide complexes are easily hydrolyzed and complex bismuth oxo-aUcoxide compounds may result as intermediates to full hydrolysis. A number of examples of these are known for the pentafluorophenox-ide system and include Bi4(/u.4-0)(/u.-0C6F5)6 /x3-0Bi(/x-0C6F5)3 2 2(C6H5CH3), Bi8(/r,4-0)2(M-3-0)2(M,-OC6F5)l6,... 

The most common procedure for preparing bismuth alkoxides is the substitution reaction of bismuth halides with alkali metal alkoxides. The alternative is treatment of bismuth amides with alcohols. Bismuth alkoxides such as trimethoxide, triethoxide and triisopropoxide were first prepared in 80-93% yields by the reaction between BiCl3 and alkali metal alkoxides by Mehrotra et al. in 1966. Bismuth alkoxides are less soluble in organic solvents and the yields after purification by sublimation are generally very low (10-20%) [66IJC537]. Known aliphatic alkoxides include Bi(OEt)3... 

Bismuth catecholates may be classified better as bismuth alkoxides, but the known compound examples are not pure eatecholates. These eompounds are discussed in Section 4.2.4.1. 

Oxabismoles refer to a type of bismuth alkoxide in which the bismuth-oxygen bond is incorporated into the bismole ring system. Most known oxabismoles are benzoxabismoles as reported by Akiba et al., the unique ring system being stabilized by the Martin ligand. The general synthetic pathway to benzoxabismoles and their derivatives is shown below [930M1857]. 

The oxidation of alcohols is proposed to proceed via a pentavalent bismuth alkoxide, which is prone to undergo reductive elimination to carbonyl compound and triorganylbismuth. From the tracer study, two mechanistic pathways are postulated as shown in Scheme 5.18 [80CC246, 81T73], The intermediate formation of a bismuth(V) compound with the covalent Bi-O bond is confirmed by H-NMR [87JCS(P1)251]. 

Recently, Vuorinen et al. have used simple bismuth alkoxides, Bi(OR)j (R Tr, Bu, and CMe Tr), in LA ROP [27]. Their results showed these alkoxides had acceptable activity (Table 7.2, entry 60-62) except Bi(OTr)j which made aggregate and decreased solubility. They also showed that the reactivity of bismuth t-butoxide was higher than 2,3-dimethyl-2-butoxide and both had higher activity than tin octanoate. In addition, their kinetic studies revealed the linear relationship between monomer/catalyst ratio and polymer molecular weight through a classical coordination-insertion mechanism. According to their report, Bi(0 Bu)j also showed good reactivity in CL ROP reaction. 

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