A bromonium oxidizing agent was used to produce a ring-oxidized zinc phthalocyanine (PcZn), [PcZn(solvent)][BAr] (1·solvent), in good yield. This material is dimeric in the solid state with one axially coordinated solvent [tetrahydrofuran (THF) or 1,2-dimethoxyethane (DME)] and close intradimer ring-ring distances of 3.18 and 3.136 Å (THF and DME respectively); this proximity facilitates strong antiferromagnetic coupling to yield diamagnetic dimers. 1·THF is present in solution as a monomer and a dimer. In CHCl, the dimer is favored above 0.1 mM, and it is almost exclusively present in solvents with a high dielectric constant such as acetonitrile. The material 1·THF/DME decomposes in DME to a meso-nitrogen-protonated species, [HPcZn(DME)][BAr] (2), which was isolated and represents the first example of such a structurally characterized, protonated, unsubstituted PcM complex. A partially oxidized dimer or "pimer" [(PcZn(DME))][BAr] (3) was also structurally characterized and has a intradimer ring-ring distance of 3.192 Å, similar to 1·THF/DME. Dimer 3 also represents the first isolated PcM-based pimer. Electron paramagnetic resonance analysis of a 1.0 mM solution of 1·DME in DME showed the production of 3 over hours by the combination of 1·DME and 2 in solution.

Hydrolyses of cyclohexenyl-based carbasugars that mimic either α-Dglucose or α-D-galactose were explored with two Bacteroides thetaiotaomicron enzymes from glycoside hydrolase family 97: an inverting α-glucosidase (BtGH97a) and a retaining αgalactosidase (BtGH97b). Both enzymes yield nucleophilic substitutions at the pseudoanomeric center of the carbasugar substrates, giving significantly different linear energy relationships for the catalytic rate constant as a function of the leaving group ability. Specifically, the kinetic data for the inverting α-glucosidase is consistent with the reaction giving a hydrolyzed inverted carbaglucose product by a mechanism that proceeds with little nucleophilic participation by the bound water molecule at the reaction transition state. In contrast, the reaction of carbagalactose substrates with the retaining GH97 enzyme involves a rate-limiting nonchemical step, likely a conformational change, followed by rapid substitution involving a nucleophilic amino acid residue to give a covalently bound intermediate. Considering the structural similarities between these two GH97 enzymes, the kinetic data nonetheless reveal a significant (>10 6 ) difference in the rates of nucleophilic attack between the unique enzymatic nucleophileswith the less nucleophilic species being H 2 O in the inverting α-glucosidase and the better nucleophile being a carboxylate in the retaining αgalactosidase. The enzymatic rate constant ratio for the phenyl carbasugars contrasts with the corresponding kinetic data obtained using natural substrate phenyl glycopyranosides. Last, for the galactocarbasugar with a phenol leaving group, the second-order rate constant for alkylation of the GH97 α-galactosidase is only ∼10-fold lower than that for glycosylation of this enzyme by the parent carbohydrate phenyl α-D-galactopyranoside. This modest difference in rate constants underscores our conclusion that retaining glycoside hydrolases may not have optimized the nucleophilicity of their active site nucleophiles with the result that the transition state free energies for formation and hydrolysis of the covalent enzyme intermediate are matched.

Here we describe the synthesis of two specifically labelled carbon-13 isotopologues of cis-2-(4-nitrophenoxy)bicyclo[4.1.0]heptane and their solvolysis reactions in trifluoroethanol. By using 1D and 2D 1 H-and 13 C-NMR spectroscopy we characterized the pathways for the rearrangement of these isotopologues to give 13 C-labelled 4-(2,2,2-trifluoroethoxy)cycloheptene. We show that the initially formed cationic intermediate undergoes a degenerate rearrangement, which does not reach equilibrium before nucleophilic capture of the cation. Moreover, we show that the nonclassical carbocation, cyclohept-3-ene(3,1,4-deloc)ylium, gives an approximate 6:1 ratio of the cis-to trans-diastereomeric 2-(2,2,2-trifluoroethoxy)bicyclo[4.1.0]heptane as reaction intermediates that subsequently solvolyze to the 4-(2,2,2-trifluoroethoxy)cycloheptene product.

The preparation and structural characterization of a pair of scandium(III) phthalocyanine hydroxide complexes were achieved by reaction of PcScCl with alkali metal alkoxides, likely via hydrolysis of soluble PcSc-alkoxide intermediates. A Sc[Formula: see text]Li[Formula: see text]-OH)[Formula: see text] cubane supported by two distorted Pc rings of the form (PcSc)[Formula: see text]-OH)[Formula: see text]Li[Formula: see text](THF)(DME) was isolated from the reaction of PcScCl with LiO[Formula: see text]Pr, while a simpler alkali-metal-free [Pc[Formula: see text]Sc[Formula: see text]-OH)[Formula: see text](THF)] was obtained from addition of NaO[Formula: see text]Bu; both structures are reminiscent of bent metallocenes, with dihedral angles between the two Pc rings of 50.8 and 37.7[Formula: see text]respectively. A soluble PcScOH material can also be obtained directly via hydrolysis of insoluble PcScCl in approximately 95:5 THF:water. Reduction of the Pc ring of PcScCl using KC[Formula: see text] is reversible and generates Pc[Formula: see text] and Pc[Formula: see text]-containing materials that were characterized via UV-vis spectroscopy and, where appropriate EPR and [Formula: see text]H NMR spectroscopy; analogous reductions of the PcScOH-based species were irreversible. Exposure of the air-sensitive, reduced PcScCl-based species to ambient atmosphere generated PcScOH materials analogous to the direct hydrolysis route.

Sterically congested chiral alcohol and amines have gained tremendous attention in the design of asymmetric catalysts. Herein, the synthesis of a sterically congested bis-adamantane framework-based chiral alcohol, (1R,2S,3S,4R)-4-(2-adamantyl)adamantan-2-ol, and amine, (1R,2S,3S,4R)-4-(2-adamantyl)adamantan-2-amine, is described. Access to these sterically encumbered compounds is found via the preparation of an enantioenriched 4-adamantyladamantan-2-one intermediate, which was synthesized in 6 steps from adamantan-2-one. The key step involved enzyme-catalyzed ester hydrolysis in giving unsaturated alcohol with an enantiomeric excess of >95%. This adamantylidene adamantanol was subjected to an acid-catalyzed intramolecular [1,4] shift to give the key chiral intermediate without racemization. This ketone intermediate was transformed into the target compounds via reduction and reductive amination protocols.