Vanadium acetylacetonate

The initiator formed from VCLt and A1(C2H5)2C1 is one of the most efficient means for syndioselective polymerization of propene, especially in the presence of a Lewis base such as anisole (methoxybenzene) [Doi, 1979a,b Natta et al., 1962 Zambelli et al., 1978, 1980], Other vanadium compounds such as vanadium acetylacetonate and various vanadates [VO(OR)xClp x), where x — 1,2,3] can be used in place of VCI4 but are more limited in their stereoselectivity [Doi et al., 1979]. Trialkylaluminum can also be used as a coinitiator, but only for VCI4. Syndiotacticity increases with decreasing temperature most of these syndioselective polymerizations are carried out below —40°C and usually at —78°C. The initiators must be prepared and used at low temperatures since most of them undergo decomposition at ambient and higher temperatures. There is considerable reduction of V(III) to V(II) with precipitation of ill-defined products that are low in activity and do not produce syndiotactic polymer, when the initiators are prepared at or warmed to temperatures above ambient. 

Syndiotactic polypropylene has been made by Zambelli, Natta and Pasquon (75). The anionic catalysts made from dialkylaluminum chloride, vanadium acetylacetonate and anisole reverse the addition to the propylene molecule so that control by an ultimate asymmetric carbon is no longer possible. The formation of syndiotactic polypropylene is shown in Fig. 8 close to the region of inverted reaction of the propylene molecule. 

Reagents i, vanadium acetylacetonate-t-butyl hydroperoxide ii, Me3SiCI-Me3Si NH SiMe3-... 

Epoxidation of allyhc and homoallylic alcohols not part of the diene complex can be achieved using the Sharpless r-butyl hydroperoxide/vanadium acetylacetonate protocol. Dihydroxylation of alkenes adjacent to the diene complex using osmium tetraoxide-r-butyl peroxide has been reported... 

In c -2-cycloocten-l-ol, oxidation with rt-butyl hydroperoxide catalyzed by vanadium acetylacetonate yields almost exclusively the cis epoxide, whereas /n>chloroperoxybenzoic add produces exclusively the trans epoxide. In fra/i5-2-cycloocten-l-ol, both oxidants furnish predominantly the cis epoxide (equation 277) [216]. 

Control of Chemoselectivity. The reaction of allylic alcohols with r-butyl hydroperoxide and vanadium acetylacetonate or titanium tetraisopropoxide provides a highly chemoselective method for the preparation of epoxides, as exemplified below. Catalysis by vanadium is envisioned to involve a complex of r-BuOOH, the OH group of the allylic alcohol, and the metal. 

However, 34 is converted into caprolactam under much milder conditions in the presence of catalytic amounts of vanadium compounds. Rearrangement (88%) is brought about by vanadium acetylacetonate in boiling benzene. ... 

The oxidation of allylic alcohols has been studied thoroughly using a variety of catalysts. The reactivity of the vanadium-tert-butyl hydroperoxide reagents towards the double bond of allylic alcohols makes possible selecfive epoxidation. Thus, reaction of geraniol with t-BuOOH and vanadium acetylacetonate [VO(acac)2] gave the 2,3-epoxide 33 (5.44). With peroxy-acids, reaction takes place preferentially at the other double bond. 

Vanadium catalysts have found particular advantage for stereoselective epoxi-dations. Thus, the acyclic allylic alcohol 34 is oxidized with high selectivity using t-BuOOH and vanadium acetylacetonate, whereas with mCPBA a nearly equal mixture of the diastereomeric epoxides was produced (5.45). 

Numerous methods have been developed for the oxidation of 70 to 68. Transition metal-catalysed oxidation by oxygen, for example with manganese salts in DMF [80] or with vanadium acetylacetonate in pyridine [81] have industrial advantages. Overall yields greater than 80 % are achieved in the two-step reaction from 69 to 68. 

T. Hayakawa, K.-I. Fukukawa, M. Morishima, K. Takeuchi, M. Asai, S. Ando and M. Ueda. Formation of regioregular head-to-tail poly[3-(4-butylphenyl)thiophene] by an oxidative coupling polymerization with vanadium acetylacetonate. J. Polym. Set, Part A Polym. Chem. 39(13), 2287-2295 (2001). 

Liu QH, Sleightholme AES, Shinkle AA, Li YD, Thompson LT. Non-aqueous vanadium acetylacetonate electrolyte for redox flow batteries. Electrochem Commun 2009 11 2312-5. 

Shinkle AA, Sleightholme AES, Thompson LT, Monroe CW. Electrode kinetics in non-aqueous vanadium acetylacetonate redox flow batteries. J Appl Electrochem 2011 41 1191-9. 

In addition to living propylene polymerization, vanadium acetylacetonate complexes have also been shown to be living for 1,5-hexadiene polymerization and 1,5-hexadiene/ propylene copolymerization (Doi et al, 1989). At —78°C, l/Et2AlCl polymerized 1,5-hexadiene to produce a low molecular weight polymer (M = 6600 g/mol, M IM = 1.4) that contained a mixture of MCP and VTM units in a 54 46 ratio. The distribution of these two units varied in 1,5-hexadiene-propylene random copolymers as a function of 1,5-hexadiene incorporation. 

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