Herein, we wish to describe the efficient three-step synthesis of a novel highly hindered, but flexible, N-heterocyclic carbene and its coordination chemistry to Ag(i) and Rh(i).

The two-step spin crossover of a new mononuclear iron(ii) complex is studied by magnetic, crystallographic and calorimetric methods revealing two successive first-order phase transitions and an ordered intermediate phase built by the repetition of the unprecedented [HS-LS-LS] motif.

A new cupric-superoxo complex [LCu II (O 2 •− )] + , which possesses particularly strong O-O and Cu-O bonding, is capable of intermolecular C-H activation of the NADH analogue 1-benzyl-1,4-dihydronicotinamide (BNAH). Kinetic studies indicate a first-order dependence on both the Cucomplex and BNAH with a deuterium kinetic isotope effect (KIE) of 12.1, similar to that observed for certain copper monooxygenases.Copper(I) reactions with molecular oxygen play fundamental roles in many chemical and biological processes.1 , 2 Copper-dependent proteins perform a diverse array of oxidative and oxygenative reactions. This has inspired considerable efforts in the design of novel ligands and copper coordinated complexes as well as the study of ligand-copper(I) dioxygen adducts to elucidate their structures, electronic characteristics and substrate reactivity.2 -4 Compared to binuclear copper-dioxygen derived species, mononuclear analogues have been synthetically challenging and hence are less understood.3 , 5 However, they are fundamentally important and are directly relevant to copper proteins including dopamine-β-monooxygenase (DβM) and peptidlyglycine-α-hydroxylating monooxygenase (PHM).6 These enzymes possess a so-called non-coupled binuclear active site,7 which comprises two Cu centers separated by ~11Å. Dioxygen binding and substrate hydroxylation occur at one of the copper sites (designated Cu M ). In an important PHM X-ray structure, a dioxygen derived species presumed to be an end-on bound cupric superoxide species (i.e., Cu II -O-O •− ) resides adjacent to an inhibitory substrate analog.6c Along with biochemical,6a,b , 8 chemical and computational studies,5 , 9 the cupric-superoxo species is thought by many to be the reactive intermediate responsible for initiating oxidation via hydrogen-atom abstraction. However, other species have been considered as important intermediates in enzymatic turnover, either prior to or following substrate attack, including cuprichydroperoxo (Cu II -− OOH)10 and high-valent cupryl (Cu II -O• <-> Cu III =O) (1) is unreactive toward a number of commonly employed C-H substrates, such as dihydroanthracene, xanthene and 10-methyl-9,10-dihydroacridine -substrates possessing C-H bonds significantly weaker than those found for DBM and PHM substrates (dopamine, 85 kcal/mol; hippuric acid, 87 kcal/mol).6b However, the addition of an excess of 1-benzyl-1,4-dihydronicotinamide (BNAH) -an NADH analogue, which is both a strong H-atom (H (Figure 3b). This gives a kinetic isotope effect (KIE) of 12.1. This KIE value is comparable to that (KIE = 10) reported for C-H bond cleavage of BNAH by a trans-dioxomanganese(V) porphyrin.20 Product analysis of the [LCu II (O 2 •− )] + /BNAH reaction (following quenching with HCl at −130 °C)15 confirms that BNAH has undergone oxidation by 1. The substrate's 4' C-H bond has been oxidatively cleaved to form 1-benzylnicotinamidium ion (BNA + ) in 42% yield ( 1 H-NMR), based on the initial copper concentration (Scheme 1). Additionally, upon acidification, ...

The rebound mechanism for alkane hydroxylation was invoked over 40 years ago to help explain reactivity patterns in cytochrome P450, and subsequently has been used to provide insight into a range of biological and synthetic systems. Efforts to model the rebound reaction in a synthetic system have been unsuccessful, in part because of the challenge in preparing a suitable metal-hydroxide complex at the correct oxidation level. Herein we report the synthesis of such a complex. The reaction of this species with a series of substituted radicals allows for the direct interrogation of the rebound process, providing insight into this uniformly invoked, but previously unobserved process.

We describe a novel and straightforward route to all stereoisomers of 1,10-bisaboladien-3-ol and 10,11-epoxy-1-bisabolen-3-ol via the rhodium-catalyzed asymmetric addition of trimethylaluminum to diastereomeric mixtures of cyclohex-2-enones 1 and 2. The detailed stereoisomeric structures of many natural sesquiterpenes with the bisabolane skeleton were previously unknown because of the absence of stereoselective syntheses of individual stereoisomers. Several of the bisabolenols are pheromones of economically important pentatomid bug species. Single-crystal X-ray crystallography of underivatized triol 13 provided unequivocal proof of the relative and absolute configurations. Two of the epoxides, (3S,6S,7R,10S)-10,11-epoxy-1-bisabolen-3-ol (3) and (3R,6S,7R,10S)-10,11-epoxy-1-bisabolen-3-ol (4), were identified as the main components of a male-produced aggregation pheromone of the brown marmorated stink bug, Halyomorpha halys, using GC analyses on enantioselective columns. Both compounds attracted female, male, and nymphal H. halys in field trials. Moreover, mixtures of stereoisomers containing epoxides 3 and 4 were also attractive to H. halys, signifying that the presence of additional stereoisomers did not hinder attraction of H. halys and relatively inexpensive mixtures can be used in monitoring, as well as control strategies. H. halys is a polyphagous invasive species in the U.S. and Europe that causes severe injury to fruit, vegetables, and field crops and is also a serious nuisance pest.

Mononuclear nonheme iron(III)-superoxo species (FeIII-O2−•) have been implicated as key intermediates in the catalytic cycles of dioxygen activation by nonheme iron enzymes. Although nonheme iron(III)-superoxo species have been trapped and characterized spectroscopically in enzymatic and biomimetic reactions, no structural information has yet been obtained. Here we report for the first time the isolation, spectroscopic characterization, and crystal structure of a mononuclear side-on (η2) iron(III)-superoxo complex with a tetraamido macrocyclic ligand (TAML), [FeIII (TAML) (O2)]2− (1). The nonheme iron(III)-superoxo species undergoes both electrophilic and nucleophilic oxidation reactions as well as O2-transfer between metal complexes. In the O2-transfer reaction, 1 transfers the bound O2 unit to a manganese(III) analogue, resulting in the formation of a manganese(IV)-peroxo complex, [MnIV(TAML)(O2)]2− (2); 2 is characterized structurally and spectroscopically as a mononuclear side-on (η2) manganese(IV)-peroxo complex. The difference in the redox distribution between the metal ions and O2 in 1 and 2 is rationalized using density functional theory calculations.

Synthetic protocols were developed for the gram-scale preparation of two isomeric dithienoborepins (DTBs), boron-containing polycyclic aromatics featuring the fusion of borepin and thiophene rings. DTBs exhibit reversible cathodic electrochemistry and boron-centered Lewis acidity in addition to enhanced electronic delocalization relative to benzo-fused analogues. Boron's precise position within the conjugation pathway of DTBs significantly affected electronic structure, most clearly demonstrated by the variation in spectroscopic responses of each isomer to fluoride ion binding. In addition to excellent stability in the presence of air and moisture, DTBs could also be subjected to electrophilic aromatic substitution and metalation chemistry, the latter enabling the direct, regiospecific functionalization of the unsubstituted thiophene rings. Subsequent tuning of molecular properties was achieved through installation of donor and acceptor π-substituents, leading to compounds featuring multistep electrochemical reductions and polarizable electronic structures. As rare examples of directly functionalizable, π-conjugated, boron-containing polycyclic aromatics, DTBs are promising building blocks for the next generation of organoboron π-electron materials whose development will demand broad scope for molecular diversification in addition to chemical robustness.

The new iron(II)-thiolate complexes [(iPrBIP)FeII(SPh)(Cl)] (1) and [(iPrBIP)FeII(SPh)(OTf)] (2) (BIP = bis(iminopyridine)) were prepared as models for cysteine dioxygenase (CDO), which converts Cys to Cys-SO2H at a (His)3FeII center. Reaction of 1 and 2 with O2 leads to Fe-oxygenation and S-oxygenation, respectively. For 1 + O2, the spectroscopic and reactivity data, including 18O isotope studies, are consistent with an assignment of an iron(IV)-oxo complex as the product of oxygenation ([(iPrBIP)FeIV(O)(Cl)] (3)). In contrast, 2 + O2 results in direct S-oxygenation to give a sulfonato product (PhSO3−). The positioning of the thiolate ligand in 1 versus 2 appears to play a critical role in determining the outcome of O2 activation. The thiolate ligands in 1 and 2 are essential for O2 reactivity, and exhibit an important influence over the FeIII/FeII redox potential.