Catalyst transition metal 3-diketonates

Several combinatorial approaches to the discovery of transition metal based catalysts for olefin polymerization have been described. In one study Brookhart-type polymer-bound Ni- and Pd-(l,2-diimine) complexes were prepared and used in ethylene polymerization (Scheme 3).60,61 A resin-bound diketone was condensed with 48 commercially available aminoarenes having different steric properties. The library was then split into 48 nickel and 48 palladium complexes by reaction with [NiBr2(dme)] and [PdClMe(COD)], respectively, all 96 pre-catalysts being spatially addressable. 

Interestingly, the mild reaction conditions of the CIR are fully compatible with the Stetter reaction. As a result a sequence of transition metal, base and organoca-talysis can be easily conceived. Upon CIR of electron-deficient (hetero)aryl halides 11 and (hetero)aryl propargyl alcohols 12, and after subsequent addition of aliphatic or aromatic aldehydes 92 and catalytic amounts of thiazolium salt 93 1,4-diketones 94 are obtained in moderate to excellent yields in a one-pot procedure (Scheme 50) [259, 260]. For aromatic aldehydes the catalyst precursor of choice is 3,4-dimethyl-5-(2-hydroxyethyl) thiazolium iodide (93a) (R = Me), and for aliphatic aldehydes 3-benzyl-4-methyl-5-(2-hydroxyethyl)-thiazolium chloride (93b) (R = CH2Ph) is applied. 

The formation of equilibrium between carbonyl compounds and alcohols is general for this reaction, except for the reduction of trifluoromethyl phenyl ketone. The Meerwein-Ponndorf-Verley reduction has advantages of chemoselectivity, mild reaction conditions, operational simplicity, low cost, and scalability." " In addition, this reaction does not affect other double bonds or triple bonds as well as other enolizable carbonyl compounds (e.g., j8-keto ester, j8-diketone). The catalysts suitable for this reaction include aluminum alkoxide and some transition-metal alkoxides (e.g., zirconium," " iron, ... 

Scheme 2.3 Examples of transition metal catalyst precursors for the peroxidative oxidation of alkanes, bearing (a) a C-scorpionate [16-20], (b) an azoderivative of a 8-diketone [21], (c) an aminopolyalcohol derivative (tea = deprotonated form of triethanolamine, Hjtea) [33, 34], and (d) a benzene dicarboxylate [33, 34] hgand.

The sulfur-containing polymers are synthesized by a method similar to that described above for the polyurethane-semicarbazides V in donor solvents (DMF, DMSO, HMF, dioxane, etc.). Tertiary amines, organotin compounds, and transition metal /3-diketonates are active catalysts in this synthesis, leading to the obtaining of polymers with a maximal molecular mass of 50 000-60000 [4]. 

Polyurethanes with a desired set of physico-chemical properties can be prepared by varying their chemical structure, as well as by the proper choice of catalysts for urethane formation and modifiers in this respect, the ideal choice would be a single substance combining these two functions. By the addition of various transition metal /3-diketonates, hydrazine-containing polyurethanes with specific properties were prepared [25-27]. 

It is well known that transition metal 3-diketonates are involved in various substitution reactions. Methine protons of chelate rings in 3-diketonates complexes can be substituted by different electrophiles. Formally, these reactions are analogous to the Michael addition reactions [15, 16], This is a metal-controlled process of the C-C bond formation [17], The complex Ni Xacac) is the most efficient catalyst of such reactions. 

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