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The model complex for mononuclear iron(III) enzymes, bearing two His and two Tyr coordinated to the iron(III) center, is investigated to reveal the relationship between the electronic structure and the reactivity of oxidizating intermediates. The model complex employed in the study is the sterically hindered iron salen complex, which well reproduces a coordination environment by His2Tyr2 and most importantly a vacant coordination site on the iron(III) center.

The molecular recognition of carbohydrate by zinc porphyrine was studied to determine the structural motif of its receptors and the roles of polar additives in energetics and selectivity of carbohydrate recognition. The research utilized the nuclear magnetic resonance (NMR) spectroscopy to analyze the complexation-induced shifts of carbohydrate OH proteins. Results show that circular dichroism induced in the porphyrin Soret band exhibited characteristic patterns similar to those from complexation-induced shifts in H NMR.

The condensation of 3,3',4,4'-tetraethyl-2,2'-dipyrrylmethane with 2-hydroxy-7- methoxy-1-naphthaledehyde generate (trans-5,15-bis{2,7-dihydroxy-1-naphthyl} -2,3,7,8,12,13,17,18-octaethylporphyrinato)zinc (1) as a model receptor for dimethyl aspartate. Both the 2-OH and 7-OH groups are involved in hydrogen bonding with the incoming amino group. The complex between the receptor and amino acid ester reveal split type induced CD in the Soret region. The complexation process is mediated by enthalpy changes. The experimental procedure for the synthesis of 1 is discussed.

We have developed a nickel-catalyzed insertion reaction of an alkyne into a 2-(trifluoromethyl)-1,3-benzothiazole to give a seven-membered benzothiazepine that is converted into a 2-(trifluoromethyl)quinoline by thermal desulfidation. This process can be considered a formal substitution of a sulfur atom with an alkyne. The structure of the thianickelacycle intermediate formed through oxidative addition of a C–S bond in the benzothiazole to nickel(0) was confirmed by X-ray single-crystal structure analysis and in situ X-ray absorption fine-structure spectroscopy. [ABSTRACT FROM AUTHOR]

The enantioselective oxa-Diels–Alder reaction of nonactivated substrates by utilizing FeCl3 and a 1,1′-bi-2-naphthol (BINOL) derived chiral phosphoric acid as a multiple activation catalyst is reported. Various oxygen-containing six-membered heterocycles were obtained in high yields and in an enantioselective manner. Density functional theory (DFT) calculations elucidate that both Lewis acidic and Brønsted acidic moieties in the catalyst system synergistically activate two lone pairs of an aldehyde to facilitate enantioselective addition reaction of dienes. [ABSTRACT FROM AUTHOR]

We herein report a new synthetic method for the preparation of α‐hydroxyketones by the dioxygenation of alkynes. The reaction proceeds at room temperature under the action of Fe porphyrin and pinacolborane under air as a green oxidant to produce α‐hydroxyketones. The mild reaction conditions allow chemoselective oxidation with functional group tolerance. Terminal alkynes in addition to internal alkynes are applicable, affording unsymmetrical α‐hydroxyketones that are difficult to obtain by any reported dioxygenation of unsaturated C−C bonds. [ABSTRACT FROM AUTHOR]

An intermolecular nickel-catalyzed addition reaction is developed where salicylic acid ketals have reacted with alkynes to afford substituted chromones. A mechanistic rationale is proposed, which has shown [beta]-elimination of ketone from ring strained seven-membered nickelacycle to generate a five-membered oxa-nickelcycle intermediate.

A series of [Mn.sup.IV](salen)[(L).sub.2] complexes bearing different external axial ligands (L = Cl, N[O.sub.3], [N.sub.3], and OC[H.sub.2]C[F.sub.3]) from chiral salen ligands with trans-cyclohexane-1,2-diamine as a chiral scaffold are prepared in order to understand conformational properties of metal system complexes. The studies have clarified the new finding that the external axial ligands (L) has played a vital role in amplifying the chirality in trans-cyclohexane-1,2-diamine in [Mn.sup.IV](salen0[(L).sub.2] to provide the formation of a chirally distorted conformation, possibly a stepped conformation.

An intermolecular nickel-catalyzed addition reaction is developed in which isatoic anhydrides have reacted with alkynes to produced substituted quinolones. A mechanistic rationale is proposed that has implied oxidative addition of Ni(0) to a carbamate, which has allowed intermolecular addition of alkynes via decarboxylation.

A new nickel-catalyzed [4+2] cycloaddition reaction of enones with alkynes is developed for providing polysubstituted pyrans. The studies have shown that enones are susceptible to oxidative cyclization of nickel(0) and these reactions have allowed inter- or intramolecular cycloaddition with alkynes.

The decarbonylation addition reaction of phthalic anhydrides to alkynes is shown by using a nickel catalyst in association with a Lewis acid as a cocatalyst. The results have shown that reductive elimination is promoted by the addition of Zn[Cl.sub.2].

The [Mn.sup.IV][([N.sub.3]).sub.2] complex from Jacobsen's catalyst is prepared and their X-ray crystal structures along with the starting [Mn.sup.III](salen)([N.sub.3])(C[H.sub.3]OH) complex are determined in order to examine the conformation of the high-valent [Mn.sup.IV](salen) molecule in comparison with that of [Mn.sup.III](salen). The comparison of structural parameters and spectroscopic properties has disclosed key factors for the chiral distortion of Jacobsen's catalyst.

A new nickel-catalyzed reaction of alkynes with N-arylphthalimides is developed for providing isoquinolones. The studies have shown that amide C-H bonds are susceptible to nucleophilic attack of the Ni(0) complex, which has allowed intermolecular addition to alkynes via decarbonylation.

Transient intermediates are examined in order to disclose the structure-reactivity relationships for the high catalytic activity of the epoxidation catalyst Mn(salen). The studies have shown that the high activity of Mn(salen) is the consequence of the favored formation of the reactive O[double bond][Mn.sup.IV](salen) state.

The activation parameters are determined for epoxidation and allylic hydroxylation reactions of cyclohexene with [Fe.sup.IV]O[(TMP).sup.+]Cl. It is shown that chemoselectivity of cyclohexene oxygenation by [Fe.sup.IV]O[(TMP).sup.+]Cl is not controlled by the activation energy but by the entropy of activation value.

The electronic and steric effects that lead to distorted trigonal-bipyramidal geometry using series of sterically hindered mesityl iron salen complexes and another series of less-hindered Xylyl salen complexes is reported. The close inspection of X-ray crystal structures of protocatechuate 3,4-dioxygenase(3,4 PCD) and 3,4-PCD-inhibitor complexes suggests that distorted trigonal-bipyramidal iron site is not preorganized by a 3,4-PCD protein but is electronically induced on binding of an external hydroxide ligand to the iron(III) center.