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Despite a few decades of intense study, a full description of tautomers of one-electron-oxidized guanine remains to be achieved. Here we show that two of these tautomers are produced by the protonation of an 8-haloguanine electron adduct. The rate constants for the reactions of hydrated electrons (eaq -) with a variety of 8-substituted guanine derivatives have been measured by a pulse radiolysis technique and correlated with both inductive and resonance components of the substituents. The fate of electron adducts was investigated by radiolytic methods coupled with product studies and addressed computationally by means of time-dependent DFT (TD-B3LYP/6-311G**//B1B95/6-31+G**) calculations. The reaction of eaq - with 8-haloguanosine or 8-halo-2‘-deoxyguanosine produces the first observable transient species that decay unimolecularly (k = 1 × 105 s-1 at 22 °C) to give the one-electron oxidized guanosine or 2‘-deoxyguanosine. Theory suggests that the electron adducts of 8-bromoguanine derivatives protonated at C8 form a π-complex, with the Br atom situated above the molecular plane, that is prompt to eject Br-. The two short-lived intermediates, which show a substantial difference in their absorption spectra, are recognized to be the two purine tautomers (i.e., iminic 7 and aminic 3 forms). The spin density distributions of the two tautomers are quite different at the O6 and N10 positions, whereas they are very similar at the N3, C5, and C8 positions. The resonance structures of the two tautomers are discussed in some detail. B1B95/6-31+G** calculations show also that the tautomerization from the iminic (7) to the aminic (3) arrangement is a water-assisted process.

Open-cage fullerene derivatives have excited organic chemists' creativity over the past decade. These adducts, generated via consecutive cleavage of sigma- and pi-carbon-carbon bonds on the fullerene cage, allow small atoms or molecules to pass through their opening and be placed inside the cavity. Restoration of the ruptured fullerene back to the pristine fullerene cage affords the corresponding endohedral complexes. This "molecular surgery" approach has been proposed as an alternative to the synthesis of endohedral fullerenes via the conventional physical methods of production, which restrict the availability of endohedral fullerenes to milligram quantities after laborious isolation procedures. In this critical review, we survey all published techniques for the creation of an orifice, as well as for the expansion of an existing one, on the fullerene framework. Successful encapsulation experiments employing cage-opened fullerene derivatives are also comprehensively discussed (160 references).

Two novel open-cage fullerene derivatives bearing a 12-membered-ring orifice on the fullerene cage have been isolated. Removal of the N-MEM protective group leads to the first open-cage [60]fullerene derivative without organic addends on the rim of the orifice. [structure: see text]

Olefin metathesis has revolutionized the way chemists design and synthesize molecules, mostly due to the development of well-defined ruthenium catalysts with high oxygen-, moisture-, and functional-group tolerance. However, the complete removal of residual ruthenium after the end of a metathesis reaction often imposes significant challenges. This Minireview summarizes the strategies for the sequestration of ruthenium impurities from olefin metathesis post-reaction mixtures, thus comprising a practical guide for synthetic chemists employing ruthenium-catalyzed metathesis reactions in the synthesis of organic or polymeric materials.

A series of ruthenium-based olefin metathesis catalysts coordinated with unsymmetrical N-heterocyclic carbene (NHC) ligands has been prepared and fully characterized. These complexes are readily accessible in one or two steps from commercially available [(PCy(3))(2)Cl(2)Ru==CHPh]. All of the complexes reported herein promote the ring-closing of diethyldiallyl and diethylallylmethallyl malonate, the ring-opening metathesis polymerization of 1,5-cyclooctadiene, and the cross metathesis of allyl benzene with cis-1,4-diacetoxy-2-butene, in some cases surpassing in efficiency the existing second-generation catalysts. Especially in the cross metathesis of allyl benzene with cis-1,4-diacetoxy-2-butene, all new catalysts demonstrate similar or higher activity than the second-generation ruthenium catalysts and, most importantly, afford improved E/Z ratios of the desired cross-product at conversion above 60 %. The influence of the unsymmetrical NHC ligands on the initiation rate and the activation parameters for the irreversible reaction of these ruthenium complexes with butyl vinyl ether were also studied. Finally, the synthesis of the related chlorodicarbonyl(carbene) rhodium(I) complexes allowed for the study of the electronic properties of the new unsymmetrical NHC ligands that are discussed in detail.

A new family of ruthenium-based olefin metathesis catalysts bearing a series of thiazole-2-ylidene ligands has been prepared. These complexes are readily accessible in one step from commercially available (PCy3)2Cl2RudCHPh or (PCy3)Cl2RudCH(o-iPrO-Ph) and have been fully characterized. The X-ray crystal structures of four of these complexes are disclosed. In the solid state, the aryl substituents of the thiazole-2-ylidene ligands are located above the empty coordination site of the ruthenium center. Despite the decreased steric bulk of their ligands, all of the complexes reported herein efficiently promote benchmark olefin metathesis reactions such as the ring-closing of diethyldiallyl and diethylallylmethallyl malonate and the ring-opening metathesis polymerization of 1,5-cyclooctadiene and norbornene, as well as the cross metathesis of allyl benzene with cis-1,4-diacetoxy-2-butene and the macrocyclic ring-closing of a 14-membered lactone. The phosphine-free catalysts of this family are more stable than their phosphinecontaining counterparts, exhibiting pseudo-first-order kinetics in the ring-closing of diethyldiallyl malonate. Upon removing the steric bulk from the ortho positions of the N-aryl group of the thiazole-2-ylidene ligands, the phosphine-free catalysts lose stability, but when the substituents become too bulky the resulting catalysts show prolonged induction periods. Among five thiazole-2-ylidene ligands examined, 3-(2,4,6-trimethylphenyl)and 3-(2,6-diethylphenyl)-4,5-dimethylthiazol-2-ylidene afforded the most efficient and stable catalysts. In the cross metathesis reaction of allyl benzene with cis-1,4-diacetoxy-2-butene increasing the steric bulk at the ortho positions of the N-aryl substituents results in catalysts that are more Z-selective.