Vanadium Acetylacetonate Catalysts

Utilizing the living nature of l/Et2AlCl, Doi and coworkers were able to synthesize block copolymers of propylene and ethylene (Doi et al., 1982). Specifically, a jPP-h/ocA -poly(E-co-P)-fc(ocfe-iPP triblock copolymer was synthesized via sequential monomer addition and exhibited a narrow molecular-weight distribution (Af M = 1.24) with Mn = 94000 g/mol and a propylene content of 70mol%. 

Beyond block copolymer synthesis, one of the important applications of living olefin polymerization is in the synthesis of end-functionalized polymers, which is typically achieved by reaction of the living chain end with an electrophile. The vanadium-based living olefin polymerization catalysts discovered by Doi and coworkers proved to be particularly amenable to this application (Doi et al, 1983 Doi et ai, 1984 Doi and Keii, 1986 Doi et al, 1987a Ueki et al, 1995). In addition to end-functionalized polymers, one challenging goal in polymer 

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. 

---

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. 

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). 

Neyertz, C. and Volpe, M. (1998). Preparation of Binary Palladium-vanadium Supported Catalysts from Metal Acetylacetonates, Colloids Surf. A, 136, pp. 63-69. 

V0x/Zr02 catalysts were designated as ZVx(y)pHz, where x gives the analytical vanadium content (weight percent), y specifies the preparation method (a, adsorption, i, impregnation or acac, acetylacetonate) and z the AV solution pH. The V-content was determined by atomic absorption (Varian Spectra AA-30) after the sample had been dissolved in a concentrated (40%) HF solution. 

Table VI summarizes important homogeneous Ziegler catalysts. The best known are the systems based on bis(cyclopentadienyl)titanium(IV), titanium alcoholates, vanadium chloride, or chromium acetylacetonate with trialkylaluminum or alkylaluminum halides.

In reporting a Ziegler-Natta catalyst, the kind of transition metal compound should not be omitted. Group 4-8 transition metal compounds, such as halides, oxyhalides, alkoxides, acetylacetonates, etc., have been used as catalyst precursors with activators such as alkyl derivatives or hydrides of group 1-4 metals. Titanium chlorides and triethylaluminium are most commonly applied for the preparation of heterogeneous catalysts in an aliphatic hydrocarbon medium. Also, vanadium oxychloride or acetylacetonate and dialkyaluminium chloride are often used for the preparation of homogeneous catalysts in an aliphatic hydrocarbon or an aromatic hydrocarbon medium. 

Other catalysts effective in the conversion of isocyanates into carbodiimides include the naphthenates of Mn, Fe, Co, Cu and Pb, derivatives of metallic acetylacetonates, the alkoxides of titanium, zirconium and niobium and vanadium oxides or chlorides. Sterically hindered isocyanates are readily converted into carbodiimides upon heating in the presence of a catalytic amount of a strong base. For example, heating of... 

Because oxidations with oxygen are free-radical reactions, free radicals should be good initiators. Indeed, in the presence of hydrogen bromide at high enough temperatures, lower molecular weight alkanes are oxidized to alcohols, ketones, or acids [5 7]. Much more practical are oxidations catalyzed by transition metals, such as platinum [5, 6, 55, 56], or, more often, metal oxides and salts, especially salts soluble in organic solvents (acetates, acetylacetonates, etc.). The favored catalysts are vanadium pent-oxide [3] and chlorides or acetates of copper [2, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66], iron [67], cobalt [68, 69], palladium [60, 70], rhodium [10], iridium [10], and platinum [5, 6, 56, 57]. 

The most direct way to prepare VO(acac)2 is by the reaction of vanadyl sulfate with a source of the ligand. Vanadium(V), such as V205, can be reduced to vanadium(IV) by ethanol solvent in the presence of sulfuric acid. Reaction with acetylacetone in sodium carbonate yields the desired product. The synthesis we will use produces the complex in high yield directly in a system that can visually shed light on the active catalyst species in the epoxidation of olefins, Figure 9.4. 

Highly syndiotactic polypropylene was prepared by Natta et al. [38] with homogeneous catalysts formed from VCI4 or fi om vanadium tri-acetylacetonate, aluminum dialkyl halide, and anisole at —48 to 78°C. 

The asymmetric synthesis of florfenicol (104) from the oxidation of 4-methylthiobenzaldehyde by TBHP in the presence of Yamamoto s vanadium catalyst resulted in 37% overall yield intermediate formation of aUyUc alcohol (105) and its epoxidation to (25, 35)-epoxide (106) in 75% yield and 90% ee was involved. TBHP oxidation of jS-dicarbonyls in the presence of vanadyl acetylacetonate in benzene involved the activated methylene group in formation of intermediate trioxo derivatives and is accompanied by decomposition of the carbon skeleton... 

---