(Eta6-naphthalene)Mn(CO)(3)(+) is reduced reversibly by two electrons in CH(2)Cl(2) to afford (eta4-naphthalene)Mn(CO)(3)(-). The chemical and electrochemical reductions of this and analogous complexes containing polycyclic aromatic hydrocarbons (PAH) coordinated to Mn(CO)(3)(+) indicate that the second electron addition is thermodynamically easier but kinetically slower than the first addition. Density functional theory calculations suggest that most of the bending or folding of the naphthalene ring that accompanies the eta6 --> eta4 hapticity change occurs when the second electron is added. As an alternative to further reduction, the 19-electron radicals (eta6-PAH)Mn(CO)(3) can undergo catalytic CO substitution when phosphite nucleophiles are present. Chemical reduction of (eta6-naphthalene)Mn(CO)(3)(+) and analogues with one equivalent of cobaltocene affords a syn-facial bimetallic complex (eta4,eta6-naphthalene)Mn(2)(CO)(5), which contains a Mn-Mn bond. Catalytic oxidative activation under CO reversibly converts this complex to the zwitterionic syn-facial bimetallic (eta4,eta6-naphthalene)Mn(2)(CO)(6), in which the Mn-Mn bond is cleaved and the naphthalene ring is bent by 45 degrees . Controlled reduction experiments at variable temperatures indicate that the bimetallic (eta4,eta6-naphthalene)Mn(2)(CO)(5) originates from the reaction of (eta4-naphthalene)Mn(CO)(3)(-) acting as a nucleophile to displace the arene from (eta6-naphthalene)Mn(CO)(3)(+). Heteronuclear syn-facial and anti-facial bimetallics are formed by the reduction of mixtures of (eta6-naphthalene)Mn(CO)(3)(+) and other complexes containing a fused polycyclic ring, e.g., (eta5-indenyl)Fe(CO)(3)(+) and (eta6-naphthalene)FeCp(+). The great ease with which naphthalene-type manganese tricarbonyl complexes undergo an eta6 --> eta4 hapticity change is the basis for the formation of both the homo- and heteronuclear bimetallics, for the observed two-electron reduction, and for the far greater reactivity of (eta6-PAH)Mn(CO)(3)(+) complexes in comparison to monocyclic arene analogues.

Reactions involving methyl b-cellobioside and several oxygen species were used to investigate cleavage of glycosidic linkages in cellulose by reaction with photochemical hydroxyl radicals. The intent is not to reproduce delignification conditions, but rather to study the specific behavior of carbohydrate models toward hydroxyl radical. Experiments show that hydroxyl radicals are responsible for the degradation of glycosidic linkages in methyl b-cellobioside by substitution reactions displacing cellobiose, D-glucose, methyl b-D-glucoside, and methanol. Once the glycosidic linkages are broken, the reducing carbohydrates undergo a series of reactions forming 67

The reduction of (η6-benzothiophene)Mn(CO)3 + with cobaltocene under CO leads to insertion of the Mn(CO)4 - fragment into the C(aryl)−S bond to afford a neutral bimetallic complex. When there are methyl substituents at the 2,3-, 2,7-, or 3,7-positions, the regioselectivity and product distribution in the reductive insertion reactions are significantly affected, and several new types of complexes are formed. Low-temperature chemical reduction of (η6-benzothiophene)Mn(CO)3 + complexes affords unstable η4-species, (η4-BT)Mn(CO)3 -, which do not react with the η6-cation to give insertion products. Similarly, electrochemical reduction of (η6-benzothiophene)Mn(CO)3 + changes from a one-electron chemically irreversible process at room temperature to a two-electron chemically reversible but electrochemically irreversible process at −90 °C. It is concluded from these results that the room-temperature reductive cleavage of a C−S bond in (η6-benzothiophene)Mn(CO)3 + occurs by a radical mechanism. Crystallographic data and density function theory (DFT) calculations indicate that insertion into the C(aryl)−S and not the C(vinyl)−S bond of (η6-benzothiophene)Mn(CO)3 + is favored. A redetermination of the crystal structure of the η1-S complex (η1-3-MeBT)Re(Cp*)(CO)2 revealed that the C(aryl)−S and C(vinyl)−S bonds are of similar lengths, suggesting that an η1-S intermediate is not predisposed to insert into the latter bond, as was previously thought. DFT calculations of (η6-BT)Mn(CO)3 + bonded in an η1-S fashion to Mn(CO)4 - indicated that an intermediate of this sort is viable in the C−S insertion reactions.

The relative rates of iron pentacarbonyl‐catalyzed photo‐induced isomerization of allyl alcohol to propanal in various solvents have been measured using 1H NMR spectroscopy. The reactions were run in linear and cyclic alkanes, alcohols, and amines in order to investigate solvent effects on the isomerization mechanism upon ultraviolet irradiation. The isomerization was efficient in nonane, hexane, cyclohexane, and benzene. The isomerization was very slow or completely suppressed in ethanol, propanol, isopropanol, triethylamine, and pyridine. Density functional theory calculations predicted thermodynamically favorable (ΔGo < 0) formation of Fe(CO)4–solvent compounds in the suppressing alcohol/amine solvents and unfavorable (ΔGo > 0) formation in the hydrocarbon solvents. The strong solvent ligation likely prevents formation of Fe(CO)3●(η2‐alkene) necessary for isomerization. Copyright © 2013 John Wiley & Sons, Ltd.