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The coordination chemistry of phenoxide ligands, such as [C.sub.6] [H.sub.5][O.sup.-], 4-(C[H.sub.3])-[C.sub.6][H.sub.4][O.sup.-], 3,5-[(C[H.sub.3]).sub.2]-[C.sub.6][H.sub.3][O.sup.-], 2,6-[(tert-butyl).sub.2]-[C.sub.6][H.sub.3][O.sup.-]-, 2,6-[(C[H.sub.3]).sub.2]-[C.sub.6][H.sub.3]0-, to Mn(II) has been investigated because of the possible implication of Mn(II)-phenoxide complexes as intermediates in the phenylphosphate carboxylase enzyme, a protein which catalyses the selective carboxylation of phenylphosphate to 4-OH-benzoic acid using C[O.sub.2]. We report here the synthesis and characterization of [[CpMn([[eta].sup.5]-OAr)(THF)].sub.2] (ArO = [C.sub.6][H.sub.5] [O.sup.-], 4-(C[H.sub.3])-[C.sub.6][H.sub.4][O.sup.-], 3,5-[(C[H.sub.3]).sub.2]-[C.sub.6][H.sub.3][O.sup.-], 2,6-[(C[H.sub.3]).sub.2]-[C.sub.6][H.sub.3][O.sup.-]) and [CpMn([[eta].sup.5]-ArO)] (ArO = 2,6-[(tert-butyl).sub.2]-[C.sub.6] [H.sub.3][O.sup.-] and 2,6-[(CH.sub.3]).sub.2]-[C.sub.6][H.sub.3] [O.sup.-]) complexes, the first examples of mixed-sandwich complexes with Cp and phenate as [pi]-ligands. The latter bear the 2,6-substituted phenoxide [pi]-coordinated to the [[Mn(Cp)].sup.+] moiety. The different mode of bonding of the phenoxide ligands to Mn(II), substantiated by [sup.1]H NMR and electron spin resonance (ESR) spectroscopy, is controlled by the steric hindrance of substituents at the 2- and 6-position. The reactivity of the [pi]-bonded ligand towards C[O.sub.2] is also reported as a quite rare example of nucleophilic attack at the cumulene by the ring-carbon of the phenoxide, which is driven by electron density localization at the 4-position generated upon [pi]-coordination to Mn(II). Key words: Mn(II)-complexes, phenoxide ligands, [sup.1]H NMR spectroscopy, ESR spectroscopy, reaction with carbon dioxide.

The anaerobic degradation of phenolic compounds depends greatly on their molecular structure. We have undertaken a systematic study on several phenol derivatives which are commonly found in industrial waters with the aim of investigating the structure–biodegradation relationship for bacteria in anaerobic conditions. The Thauera aromatica strain was used; this bacterium is able to use phenol as a sole carbon source in liquid cultures in the absence of molecular oxygen. Nitrate is the electron sink with complete reduction to N 2 . A systematic study has demonstrated the ability of this bacterial strain to use 3,4-dihydroxybenzoic acid, 4-hydroxycinnamic acid ( p -coumaric acid), 4-hydroxy-3-methoxycinnamic acid (ferulic acid), 3,4-dimethoxybenzoic acid (veratric acid), and 3,4,5-trihydroxybenzoic acid (gallic acid) as substrate. The matching of the depletion of the concentration of such compounds with the increment in bacterial growth in the cultures demonstrates that the substrates are used as the sole carbon source. Also, a correlation between the rate of growth of bacteria and nitrite concentration has been observed. The progressive reduction in nitrate into nitrite and N 2 is monitored through analyses. The protein pattern extracted from bacteria grown on methylated substrates is now being compared with that of bacteria grown on non-methylated polyphenols that are structurally analogous in order to identify specific enzymes for demethylation processes. [ABSTRACT FROM AUTHOR]

We present an overview of possible biotechnological applications for using carbon dioxide for the synthesis of chemicals. These approaches are very appealing as they contribute to the implementation of new synthetic methodologies that reduce waste and make a better use of carbon and energy. Several synthetic approaches will be considered including both the incorporation of the whole COO moiety or its reduction to other C1 molecules. Each option will be discussed making a comparison between the natural and artificial process in order to highlight the possibility to learn from Nature and develop useful mimetic or enzymatic systems. [ABSTRACT FROM AUTHOR]

The coordination chemistry of phenoxide ligands, such as C[sub 6] H[sub 5] O[sup –] , 4-(CH[sub 3] )-C[sub 6] H[sub 4] O[sup –] , 3,5-(CH[sub 3] )[sub 2] -C[sub 6] H[sub 3] O[sup –] , 2,6-(tert-butyl)[sub 2] -C[sub 6] H[sub 3] O[sup –] , 2,6-(CH[sub 3] )[sub 2] -C[sub 6] H[sub 3] O[sup –] , to Mn(II) has been investigated because of the possible implication of Mn(II)–phenoxide complexes as intermediates in the phenylphosphate carboxylase enzyme, a protein which catalyses the selective carboxylation of phenylphosphate to 4-OH-benzoic acid using CO[sub 2] . We report here the synthesis and characterization of [CpMn(µ-OAr)(THF)][sub 2 ] (ArO = C[sub 6] H[sub 5] O[sup –] , 4-(CH[sub 3] )-C[sub 6] H[sub 4] O[sup –] , 3,5-(CH[sub 3] )[sub 2] -C[sub 6] H[sub 3] O[sup –] , 2,6-(CH[sub 3] )[sub 2] -C[sub 6] H[sub 3] O[sup –] ) and [CpMn(η[sup 5] -ArO)] (ArO = 2,6-(tert-butyl)[sub 2] -C[sub 6] H[sub 3] O[sup –] and 2,6-(CH[sub 3] )[sub 2] -C[sub 6] H[sub 3] O[sup –] ) complexes, the first examples of mixed-sandwich complexes with Cp and phenate as π-ligands. The latter bear the 2,6-substituted phenoxide π-coordinated to the [Mn(Cp)][sup +] moiety. The different mode of bonding of the phenoxide ligands to Mn(II), substantiated by [sup 1] H NMR and electron spin resonance (ESR) spectroscopy, is controlled by the steric hindrance of substituents at the 2- and 6-position. The reactivity of the π-bonded ligand towards CO[sub 2] is also reported as a quite rare example of nucleophilic attack at the cumulene by the ring-carbon of the phenoxide, which is driven by electron density localization at the 4-position generated upon π-coordination to Mn(II).Key words: Mn(II)-complexes, phenoxide ligands, [sup 1] H NMR spectroscopy, ESR spectroscopy, reaction with carbon dioxide.On a étudié la chimie de coordination des ligands phénolates, tels que C[sub 6] H[sub 5] O[sup –] , 4(CH[sub 3] )-C[sub 6] H[sub 4] O[sup –] , 3,5-(CH[sub 3] )[sub 2] -C[sub 6] H[sub 3] O[sup –] , 2,6-(tert-butyl)[sub 2] -C[sub 6] H[sub 3] O[sup –] et 2,6-(CH[sub 3] )[sub 2] -C[sub 6] H[sub 3] O[sup –] , avec le Mn(II) en raison de l'implication possible des complexes Mn(II)-phénolates comme intermédiaires dans l'enzyme carboxylase du phosphate de phényle, une protéine qui catalyse la carboxylation sélective du phosphate de phényle en 4-HO-C[sub 6] H[sub 4] -C(O)OH à l'aide de CO[sub 2] . On a synthétisé et caractérisé les complexes [CpMn(µ-OAr)(THF)][sub 2] (ArO = C[sub 6] H[sub 5] O[sup –] , 4(CH[sub 3] )-C[sub 6] H[sub 4] O[sup –] , 3,5-(CH[sub 3] )[sub 2] -C[sub 6] H[sub 3] O[sup –] et 2,6-(CH[sub 3] )[sub 2] -C[sub 6] H[sub 3] O[sup –] ) et [CpMn(η[sup 5] -ArO)] (ArO = 2,6-(tert-butyl)[sub 2] -C[sub 6] H[sub 3] O[sup –] et 2,6-(CH[sub 3] )[sub 2] -C[sub 6] H[sub 3] O[sup –] ), le premier exemple d'un complexe sandwiche mixte comportant un Cp et un phénate comme ligands π. Dans le dernier, le phénolate 2,6-disubstitué est fixée par une coordination π à la partie [Mn(Cp)][sup +] . Les différents modes de fixation des ligands phénolates au Mn(II), tels que confirmés par RMN du [sup 1] H et par spectroscopie RPE, sont contrôlés par l'encombrement stérique des substituants en positions 2 et 6. On a aussi déterminé la réactivité des ligands fixés d'une façon π vis à vis du CO[sub 2] ; il s'agit d'un rare exemple d'attaque nucléophile au niveau du cumulène par l'atome de carbone du cycle du phénolate alors que celle-ci est amenée par la localisation de la densité électronique en position 4 sous l'influence d'une coordination π avec le Mn(II).Mots clés : complexes du Mn(II), ligands phénolates, spectroscopie RMN du [sup 1] H, spectroscopie RPE, réaction avec le bioxyde de carbone.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

The mitigation of carbon dioxide is one of the scientific and technological challenges of the 2000s. Among the technologies that are under assessment, the recovery of carbon dioxide from power plants or industrial flue gases plays a strategic role. Recovered carbon dioxide can be either disposed in natural fields or used. The availability of large amounts of carbon dioxide may open new routes to its utilisation in biological, chemical and innovative technological processes. In this paper, the potential of carbon dioxide utilisation in the short-, medium-term is reviewed.