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The coordination chemistry of an amine-rich CpN3 ligand has been explored with cobalt. We demonstrate that in the presence of NaCo(CO)4, the cationic precursor [CpN3]+ yields the complex CpN3CoI(CO)2. While 2e− oxidation generates new CoIII complexes such as [CpN3Co(NCMe)3]2+ and CpN3CoI2(CO), subsequent ligand loss is facile, generating free [CpN3]+ or the protonated dication [CpN3H]2+. We have structurally characterized both these ligand release products via single crystal X-ray diffraction and obtained thermochemical C–H bond strengths via experiment and density functional theory (DFT). Upon reversible 1e− reduction, the radical cation [CpN3H]˙+ has a weak C–H BDFE of 52 kcal mol−1 in acetonitrile. Mechanistic analysis shows that [CpN3H]˙+ undergoes radical–radical disproportionation in the absence of exogenous H-atom acceptors, which is supported by deuterium isotope labelling experiments. Structural comparison of these organic molecules shows a high degree of iminium-like electron delocalization over the C–N bonds connected to the central five-membered ring. [ABSTRACT FROM AUTHOR]

The introduction of fluorine atom has attracted considerable interest in molecular design owing to the high electronegativity and the resulting polarization of carbon–fluorine bonds. Simultaneously, sterically‐hindered N‐heterocyclic carbenes (NHCs) have received major interest due to high stabilization of the reactive metal centers, which has paved the way for the synthesis of stable and reactive organometallic compounds with broad applications in main group chemistry, inorganic synthesis and transition‐metal‐catalysis. Herein, we report the first class of sterically‐hindered, fluorinated N‐heterocyclic carbenes. These ligands feature variable fluorine substitution at the N‐aromatic wingtip, permitting to rationally vary steric and electronic characteristics of the carbene center imparted by the fluorine atom. An efficient, one‐pot synthesis of fluorinated IPr*F ligands is presented, enabling broad access of academic and industrial researchers to the fluorinated ligands. The evaluation of steric, electron‐donating and π‐accepting properties as well as coordination chemistry to Au(I), Rh(I) and Se is presented. Considering the unique properties of carbon–fluorine bonds, we anticipate that this novel class of fluorinated carbene ligands will find widespread application in stabilizing reactive metal centers. [ABSTRACT FROM AUTHOR]

Acenes are attractive as building blocks for low gap organic materials with applications, for example, in organic light emitting diodes, solar cells, bioimaging and diagnostics. Previously, we have shown that modification of dipyridylanthracene via B–N Lewis pair fusion (BDPA) strongly redshifts the emission, while facilitating self‐sensitized reactivity toward O2 to reversibly generate the corresponding endoperoxides. Herein, we report on the further expansion of the π‐system of BDPA to a vinyl‐substituted monomer, vinylene‐bridged dimer, and a polymer with an average of 20 chromophores. The extension of π‐conjugation results in largely reduced band gaps of 1.8 eV for the dimer and 1.7 eV for the polymer, the latter giving rise to NIR emission with a maximum at 731 nm and an appreciable quantum yield of 7 %. Electrochemical and computational studies reveal efficient delocalization of the lowest unoccupied molecular orbital (LUMO) along the pyridyl‐anthracene‐pyridyl axis, which results in effective electronic communication between BDPA units, selectively lowers the LUMO, and ultimately narrows the band gap. Time‐resolved emission and transient absorption (TA) measurements offer insights into the pertinent photophysical processes. Extension of π‐conjugation also slows down the self‐sensitized formation of endoperoxides, while significantly accelerating the thermal release of singlet oxygen to regenerate the parent acenes. [ABSTRACT FROM AUTHOR]

The chiral ligand (R)-sirtinol and its ferric derivative, compound (I), have been used in a wide range of chemical and biological studies which should be sensitive to their chirality inasmuch as enantioselectivity is of primordial importance in such processes. It is, therefore, imperative that the chiral nature of the iron-containing molecule should be recognized; and, if the metal is chiral, the expectation is that its function(s) may be stereospecific. Surprisingly enough, until now little or nothing has been elucidated concerning its stereochemical character, probably because the chiral nature of a seven-fold coordinated environment is often overlooked and not commonly encountered in 3d compounds. Below, we address these issues because (I) crystallizes with Z′ = 2.0; thus, the chiral nature of its two diastereoisomers must be clearly understood in order to properly interpret the results of future chemical and biochemical investigations. We found that there is a novel form of crystallization in (I) characterized by: (1) there are two distinct diastereoisomeric species in the asymmetric unit differing in the magnitude and/or sign of relevant torsional angles; (2) the sirtinol ligand itself bears an (R) carbon in both, as expected from Z′ = 2.0. Thus, if the chirality of the ligand carbon is momentarily ignored, the crystals are simple examples of a kryptoracemate. If not, we have discovered a new crystalline form for which we propose a suitable nomenclature as this is now needed. In analogy to the classical example of "racemic mimics" recognized a long time ago, we name it kryptoracemic mimic. In essence, there are two different conditions to consider: the kryptoracemic character of the iron (in this case), and the pure enantiomeric character of the sirtinol ligand, and they must be properly described in the name of such species. [ABSTRACT FROM AUTHOR]

Sirtinol is a known inhibitor of sirtuin proteins – a family of deacetylases involved in the physiology of aging. Its crystalline structure has never been determined except when bound to Fe(III) where it participates in the seven-fold coordination of the metal or to Cu(II) where it acts as a bidentate or tridentate ligand. Herein, we describe the structure of this important molecule, as follows: (a) the prevalent form of the keto-enol tautomerism in the solid state, and (b) in solution. Do they match? If not, how? The crystals of (R)-sirtinol are characterized by a large number of π–π bonded interactions linking molecules in infinite ribbons, which, in turn, are linked by additional π–π interactions of a variety of types, and by hydrogen bonds. In the latter case, we confirm by NMR that the X-ray determined position of an important H atom is on a N atom rather than on an O, which is how the molecule is usually depicted. [ABSTRACT FROM AUTHOR]

A confiscated package of street drugs was characterized by the usual mass spectral (MS) and FT–IR analyses. The confiscated powder material was highly crystalline and was found to consist of two very different species, accidentally of sizes convenient for X-ray diffraction. Thus, one each was selected and redundant complete sets of data were collected at 100 K using Cu Kα radiation. The selected crystals contained: (a) 1,2-diphenyl-2-(pyrrolidin-1-yl)ethanone hydrochloride hemihydrate or 1-(2-oxo-1,2-diphenylethyl)pyrrolidin-1-ium chloride hemihydrate, C18H20NO+ ·Cl-·0.5H2O, (I), a synthetic cathinone called ‘α-D2PV’, and (b) the sugar myo-inositol, C6H12O6, (II), probably the only instance in which the drug and its diluent have been fully characterized from a single confiscated sample. Moreover, the structural details of both are rather attractive showing: (i) interesting hydrogen bonding observed in pairwise interactions by the drug molecules, mediated by the chloride counter-anions and the waters of crystallization, and (ii) π–π interactions in the case of the phenyl rings of the drug which are of two different types, namely, π–π stacking and edge-to-π. Finally, the inositol crystallizes with Z′ = 2 and the resulting diastereoisomers were examined by overlay techniques [ABSTRACT FROM AUTHOR]

Two-electron oxidation of a NiIIPh(PCP) pincer complex initiates phosphine ligand insertion, generating an η6-arylphosphonium moiety coordinated to NiII. The reaction is fully reversible under reducing conditions. X-ray crystallography, NMR/EPR spectroscopy, electrochemistry, and DFT calculations support the proposed Ni–C–P bond reorganization mechanisms, which access oxidation states from Ni0 to NiIV. [ABSTRACT FROM AUTHOR]

Herein we report the results of preparing metal compounds (where the metal ions are Co2+, Ni2+, Cu2+, Zn2+) with the cyclic ligand 1,4,8,11-tetraazacyclotetradecane [cyclam] under a variety of conditions of metal-ligand ratios and solvent media. In all cases, we used metal Cl2·nH2O salts (except for anhydrous CoCl2), as specified. Outcome: we isolated species with a four-coordinate metal in the N4 cavity of the ligand alone, and also with either one or two additional axial ligands. Those axial ligands can be (a) a single chloride, leading to penta-coordinated moncationic products; (b) two chlorides, leading to octahedral-neutral compounds; (c) two waters, giving rise to hexa-coordinated [(cyclam)metal(H2O)2]2+ species. Finally, in the case of HCl added to the reaction medium, the cyclam can be di-protonated and appears as [(cyclam)H2]2+ in the crystals. With such a variety of products, it is not surprising that since the metal coordination numbers vary, the cyclam ligand stereochemistries are thereby affected. Interestingly, the [(cyclam)metal] species are invariably hydrogen-bonded to one another in infinite strings of two kinds: (1) those for which the crystal's Z′ = 1 have single strings; (2) when Z′ = 2, there is a pair of homogeneous strings attached to one another by a variety of hydrogen-bonding linkages. Finally, we observed an interesting pair of hydroxonium cations: the first is hydoxonium cations in a pleated 2-D sheet consisting of fused pentagons located between sheets of [(cyclam)metal] moieties; the second one is an infinite string of composition {(H3O+)-(H2O)-(H3O+)-(H2O)-(H3O+)-(H2O)-(H3O+)}∞. [ABSTRACT FROM AUTHOR]