Tmtacn

Ru(0)(biqn)(tmtacn)](C10 )2 and [Ru(0)(diopy)(tmtacn)](C10 )2 (biqn=C2 symmetric 1,T-biisoquinoline, diopy=(R,R)-3,3 -(l,2-dimethylethylenedioxy)-2,2 -bipyridine) aremadefrom [RuCl(L)(tmtacn)] + (L=biqn, diopy) and(NH )2[Ce(N03)J with Li(ClO ). Electronic and IR spectra were measured (v(Ru=(0) bands lie at 760 and 795 cm" respectively). The (diopy) complex is paramagnetic with 2.88 B.M. As stoich. [Ru(0)(biqn)(tmtacn)] + and [Ru(0)(diopy)(tmtacn)] VCH3CN they oxidised alkenes (styrene, cis and fran.y-P-methylstyrenes, fran -stilbene, nor-bomene, cyclohexene) to mixtures of aldehydes and epoxides. Conttary to expectation the (diopy) complex did not effect enantioselective epoxidations except with fran -stilbene, for which a moderate e.e. of 33% was observed [623]. 

As stoich. [Ru(0)(bpy)(tmtacn)]VCH3CN it functioned as a competent (sic) epoxidant for alkenes, though the products were often contaminated with by-products (e.g. fran -stilbene gave fran -stilbene oxide and benzaldehyde cw-stilbene gave cis- and trans- epoxides). Kinetics of the epoxidation of norbomene and styrene were reported, with activation parameters measured and discussed [682]. Kinetics of its non-stereospecific, stoicheiometric epoxidation of aromatic alkenes in CH3CN were studied, and the rates compared with those of oxidations effected by other Ru(IV) 0x0 complexes with N-donors, e. g. [Ru(0)(tmeda)(tpy)] ", trans-[Ru(0)(Cl3bpy)(tpy)] " and [Ru(0)Cl(bpy)(ppz )] + [676]. 

For alkynes cw-[Ru(0)3(CF3C00)(tmtacn)]VPhI0 or TBHP/CH Cl (dipheny-lacetylene to benzil) [111]. 

Fig. 3.24 Oxidation of anisoles to p-benzoquinones monoketals catalysed by [Ru(CF3COO)2(Hp)(tmtacn)]+ [261]...

FIGURE 15. Structures proposed for homogeneous and heterogeneous Mn-tmtacn catalysts... 

Berkessel and Sklorz screened a variety of potential co-ligands for the Mn-tmtacn/H202 catalyzed epoxidation reaction and found that ascorbic acid was the most efficient one. With this activator the authors could oxidize the terminal olefins 1-octene and methyl acrylate with full conversion and yields of 83% and 97%, respectively, employing less than 0.1% of the metal complex (Scheme 86). Furthermore, with E- and Z-l-deuterio-1-octene as substrates, it was shown that the oxygen transfer proceeded stereoselectively with almost complete retention of configuration (94 2%). Besides the epoxidation, also the oxidation of alcohols to carbonyl compounds could be catalyzed by this catalytic system (see also Section in.C). 

SCHEME 86. Mn-tmtacn/H202/Na ascorbate catalyzed epoxidation of terminal olefins... 

Taylor and Flood could show that polystyrene-bound phenylselenic acid in the presence of TBHP can catalyze the oxidation of benzylic alcohols to ketones or aldehydes in a biphasic system (polymer-TBHP/alcohol in CCI4) in good yields (69-100%) (Scheme 117) °. No overoxidation of aldehydes to carboxylic acids was observed and unactivated allylic alcohols or aliphatic alcohols were unreactive under these conditions. In 1999, Berkessel and Sklorz presented a manganese-catalyzed method for the oxidation of primary and secondary alcohols to the corresponding carboxylic acids and ketones (Scheme 118). The authors employed the Mn-tmtacn complex (Mn/168a) in the presence of sodium ascorbate as very efficient cocatalyst and 30% H2O2 as oxidant to oxidize 1-butanol to butyric acid and 2-pentanol to 2-pentanone in yields of 90% and 97%, respectively. This catalytic system shows very good catalytic activity, as can be seen from the fact that for the oxidation of 2-pentanol as little as 0.03% of the catalyst is necessary to obtain the ketone in excellent yield. 

SCHEME 118. Mn/tmtacn/Na ascorbate catalyzed alcohol oxidation with H2O2... 

SCHEME 123. Heterogeneous Ru-catalyzed alcohol oxidation with the tmtacn ligand... 

---