Dimeric dioxo

They include the hydrolysis to form the (i-dioxo dimer 49, and the products derived from the formal insertion of nitriles, ketones, and Bu NC into the Zr-C ct bonds. In the case of hydrolysis, butenes have been identified. The occurrence of the zirconyl ( Zr=0 ) group in a monomeric zirconium compound remains... 

Introduction of mesityl groups at the porphyrin ring can prevent the formation of the dimeric products and the reaction with dioxygen now leads to ruthenium(VI)-dioxo complexes of TMP (tetramesitylporphyrin) [35], The tram-Ru(VI)02-TM P species can catalyse the epoxidation of alkenes as well as whole range of other oxidation reactions. After transfer of one oxygen atom to an organic substrate Ru(IV)0-TMP is formed, which disproportionates to an equilibrium of Ru02 and llu ). 

Succinylcholine Succinylcholine, 2,2 -[(l,4-dioxo-l,4-butanediyl)fcw(oxy)]few[Af,Af,Af-trimethylethanaminium(diacetylcholine)] dichloride, which can be viewed as a dimeric molecule of acetylcholine (diacetylcholine), is synthesized by reacting succinic acid dichloride with 2-dimethylaminoethanol and subsequent transformation of the resulting bM-(2-dimethy-laminoethyl)succinate (15.1.13) into a quaternary salt, succinylcholine (15.1.14) [20-24]. 

The formal transfer of an oxygen atom is one way of describing the function of the Mo site in molybdoenzymes.5 The formation of dinuclear reduction products is a complication that causes difficulty in trying to model the mononuclear site.5,165 This difficulty can be overcome by the use of sterically demanding ligands that prevent the formation of the dinuclear complex,73 79,125 176 177 For example, the cycle shown in Scheme 3 can be effected without dimerization. Further, in this case DMSO and the enzyme substrate biotin sulfoxide, can serve as the oxo donor to form the Movl dioxo complex during the catalytic cycle.79,177 The Movl complex involved is discussed structurally above (Figure 7). 

The Criegee mechanism originally proposed involves the formation of an osmium(VI)-ester complex (106) from the [4+2] cycloaddition of the Osvul cis-dioxo moiety with an alkene, followed by the hydrolysis or reduction of (106) to cis-glycol and reduced osmium species. In support of this mechanism a variety of Osvl cyclic esters such as (107) or (108) (L = quinuclidine) have recently been synthesized from Os04 and the alkene, and characterized by an X-ray crystal structure.290,343 In solution the dimeric complex (108) dissociates to give the monomeric dioxo trigonal-bipyramidal complex (109), which is similar to (106).344... 

Under the action of Ph3P/pyridine in an atmosphere of oxygen, tellura-pyrylium and tellurachromylium salts undergo oxidative dimerization, affording l,l-dioxo(tellurapyranylidene)tellurapyrans 113 and 1,1 -dioxo(benzo[6]pyranilidene)tellurapyrans 114, the yields of each compound approaching 25% (87JOC2123). 

The iron catalysis of vinylogous Michael reactions is not only restricted to dimerizations. The y-donor 46b can be converted with MVK (41a) to give the 1,7-dioxo-constituted product 49 when the catalyst is Fe(III) (Scheme 8.21) [75]. If NaOMe in MeOH is applied as the catalyst, reaction of the dienolate of donor 46b in the a-position with acceptor 41a proceeds via a normal Michael reaction and 1,5-dioxo-constituted product 50 is obtained. 

Based on the interpretation of luminescence measurements and pH titration results, the formation of a /t-dioxo dimer (see Fig. 16) at high pH has been proposed to account for this original pH behavior as this dimer does not possess any coordinated water molecule or hydroxyl ion. 

Of the complexes studied, those with ancillary ligands that contain sulfur atoms have received the most attention. Among the most studied are the bis(dial-kyldithiocarbamate) molybdenum oxido complexes [196,197], Unfortunately, although these complexes react with certain enzyme substrates, their common problem as models for Moco active sites involves the propensity of the Movl dioxo and MoIV monoxo complexes to form a comproportionated Mov p-oxido dimer (Eq. 13 dtc = diethyldithiocarbamate). 

The self condensation of a-carbonyl ketenes also constitutes a type (i) synthesis of 2//-pyran-2-oncs. Cyclophanes 627 are synthesized by the thermal decomposition of bis(4,6-dioxo-l,3-dioxanes) 628 and dimerization of the resulting bis(a-carbonyl ketenes) 629 (Scheme 141) <1999JA8270>. Similarly, thermal decomposition of 4,5-diarylfuran-2,3-diones 630 forms the intermediate a-carbonyl ketenes, which dimerize to afford 3,4,5-aryl-2//-pyran-2-ones (Scheme 142) <2003RJ0103>. 

Ethyl 2-(phenylhydrazino)acetoacetate (4) with malononitrile (5) (as its dimer) gave 7-hydroxy-2,5-dioxo-3-phenylhydrazino-1,2,5,6-tetrahydro-1,6-naphthyridine-8-carbonitrile (6) (reactants, AcONH4, 160°C, 1 h 88%).1360... 

The thermal polymerization of /3-carboxymethyl caprolactam results in a novel polyimide which has been identified as a poly(2,6-dioxo-l, 4-piperidinediyl)trimethylene. The formation of this structure is explained by a mechanism that consists in an initial isomerization of the caprolactam derivative to 3-(3-aminopropyl)glutaranhydride or its linear dimer and subsequent polymerization by condensation involving the terminal amino group and the anhydride moiety. Suggested reaction schemes and corresponding kinetic equations are based upon the premise that the extent of polymerization is represented by the concentration of imide linkages. Results of rate studies carried out at 210°-290°C. support the proposed mechanism. 

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