The structure of the inclusion compound of 1-(3-hydroxy-4-{(E)-[(2-hydroxyphenyl)methylidene]amino}phenyl)ethan-1-one - a light-sensitive guest molecule, with 4,4 '-cyclohexylidenebisphenol as light-stable host molecule was studied at 293 and 200 K. At room temperature the crystal structure may be described in space group P-1, with one of the two guest molecules disordered occupying a crystallographic inversion center or in space group P1, avoiding the need for disorder description. One of the ordered guest molecules is connected by H-bonds to a water molecule and a host molecule. The other guest molecule has the role of filling space. The distinction between the structures in the two space groups is discussed from a crystallographic and from chemical interactions point of view. The crystal structure at low temperature justifies the chemical arguments regarding the true space group.

Flat corannulene has been considered so far only as a transition state of the bowl-to-bowl inversion process. This study was driven by the prediction that substituents with strong steric repulsion could destabilize the bowl-shaped conformation of this molecule to such an extent that the highly unstable planar geometry would become an isolable molecule. To examine the substituents' effect on the corannulene bowl depth, optimized structures for the highly-congested decakis(t-butylsulfido)corannulene were calculated. The computations, performed with both the M06-2X/def2-TZVP and the B3LYP/def2-TZVP methods (the latter with and without Grimme's D3 dispersion correction), predict that this molecule can achieve two minimum structures: a flat carbon framework and a bowl-shaped structure, which are very close in energy. This rather unusual compound was easily synthesized from decachlorocorannulene under mild reaction conditions, and X-ray crystallographic studies gave similar results to the theoretical predictions. This compound crystallized in two different polymorphs, one exhibiting a completely flat corannulene core and the other having a bowl-shaped conformation.

Our previous experimental report showed a switching behavior from ethylene polymerization to nonselective oligomerization by a novel triphenylsiloxy complex of chromium(II) [(Ph3SiO)Cr·(THF)]2(μ-OSiPh3)2 (1) together with methylaluminoxane (MAO) as a cocatalyst. In this work, combined experimental and computational studies were carried out to shed some light on the nature of the active species and their fascinating switching mechanism. The experimental results and DFT calculations suggested that (i) the chain propagation and chain transfer processes proceed via a Cossee–Arlman mechanism and β-hydrogen transfer to the chromium center, respectively; (ii) the trivalent cationic model [(Ph3SiO)CrIIIMe]+ and [(η6-toluene)CrIIIMe2]+, which could be generated by a disproportionation reaction, are the most plausible active species for ethylene polymerization, and the divalent cationic model [(η6-toluene)CrIIMe]+ might be responsible for ethylene nonselective oligomerization. A switching mechanism from ethylene po...

Comprehensive studies on the coordination properties of tridentate nitrenium-based ligands reveal general and versatile binding abilities to various transition metals. The generality of N-heterocyclic nitrenium as a ligand and its electronic properties have been investigated both experimentally and computationally, as discussed by M. Gandelman et al. in their Full Paper on page 7099 ff. The cover picture shows how a wide variety of transition metals in various oxidation states can be “picked up” by tridentate nitrenium ligands to form complexes with potentially interesting properties (cover design by Igor Armiach). Comprehensive studies on the coordination properties of tridentate nitrenium-based ligands reveal general and versatile binding abilities to various transition metals. The generality of N-heterocyclic nitrenium as a ligand and its electronic properties have been investigated both experimentally and computationally, as discussed by M. Gandelman et al. in their Full Paper on page 7099 ff. The cover picture shows how a wide variety of transition metals in various oxidation states can be “picked up” by tridentate nitrenium ligands to form complexes with potentially interesting properties (cover design by Igor Armiach). Challenging Polymers The controlled radical polymerization of “more active” unsaturated monomers such as styrenics, (meth)acrylates, acrylonitrile and others can now be easily achieved by various moderating methods, but challenges remain in the control of “less active” monomers. Organometallic-mediated radical polymerization (OMRP) has made high impact contributions in this area. The Concept article by R. Poli on page 6988 ff. highlights the advantages and pitfalls of the OMRP technique and highlights the remaining problems to be solved in order to further push the frontiers of controlled polymerization. 1 Hydrogen Sulfide Sensing In their Communication on page 7002 ff., M. Licchelli, R. Martínez-Máñez, et al. report the synthesis, characterization, and sensing behavior of a new hybrid material functionalized with a CuII-macrocyclic derivative that is capped, through electrostatic interactions, with the bulky anion hexametaphosphate. Of all the chemicals tested, only HS− was able to induce pore opening and dye release. The fluorogenic response obtained was ascribed to a demetallation reaction, selectively induced by HS− ion.1 Diboron Compounds In their Full Paper on page 7082 ff., T. Marder et al. report the isolation and detailed structural characterization of a series of anionic adducts of B2pin2 (bis(pinacolato)diborane) with hard Lewis bases such as alkoxides and fluoride. Such sp2–sp3 adducts have been implicated as intermediates in both metal-catalyzed and metal-free borylations. The ability of the isolated adducts to transfer a nucleophilic boryl anion directly to electrophilic aromatic substrates in the absence of a transition metal was demonstrated in several stoichiometric reactions with aryl halides and diazonium salts.1

Comprehensive studies on the coordination properties of tridentate nitrenium-based ligands are presented. N-heterocyclic nitrenium ions demonstrate general and versatile binding abilities to various transition metals, as exemplified by the synthesis and characterization of Rh(I) , Rh(III) , Mo(0) , Ru(0) , Ru(II) , Pd(II) , Pt(II) , Pt(IV) , and Ag(I) complexes based on these unusual ligands. Formation of nitrenium-metal bonds is unambiguously confirmed both in solution by selective (15) N-labeling experiments and in the solid state by X-ray crystallography. The generality of N-heterocyclic nitrenium as a ligand is also validated by a systematic DFT study of its affinity towards all second-row transition and post-transition metals (Y-Cd) in terms of the corresponding bond-dissociation energies.

Reaction of the f-element complexes ThCl4(THF)(3), Cp*Sm-2(mu-Cl)(2)MgCl(THF)(2), NdCl3, Cp*2UMe2, and Cp*2ZrMe2 with an excess of catecholborane (HBCat) yields macrocyclic complexes where the metal is encapsulated inside a 15-membered, hexaoxo, trianionic macrocycle built from alternating catechol and catecholborate fragments. With ThCl4(THF)(3) as the starting material, the reaction produced a macrocyclic complex with one chloride ligand and three solvent molecules in the apical positions; however, for the zirconium and uranium complexes the apical positions are occupied by one C5Me5 ligand and a THF solvent molecule. In the samarium and neodymium complexes, only solvent molecules occupy the apical positions. Transmetalation of the ligand among different complexes in refluxing THF were performed. When the zirconium macrocycle was treated with a slight excess of ThCl4 or NdCl3, the corresponding (eta(2)-catechol-mu-catecholborate)(3)ThCl(C4H8O)(3)center dot C4H8O (2) and (eta(2)-catechol-mu-catecholborate)(3)Nd(C4H8O)(3)center dot C4H8O (4) macrocycles were obtained in 87% and 79% yields, respectively. In addition, the reaction of the samarium macrocycle complex (eta(2)-catechol-mu-catecholborate)(3)Sm(C4H8O)(3)center dot C4H8O (3) with a slight excess of ThCl4 allowed the formation of complex 2 in 76% yield. While some of the pentamethylcyclopentadienyl (Cp*)-containing inclusion complexes were found to be catalytically inactive in the polymerization of epsilon-caprolactone, the lanthanides and thorium complexes were found to be active, yielding only short chains of polycaprolactone. The X-ray molecular structures for all of the complexes are presented and discussed. Experiments performed with Cp*2ThMe2 and catecholborane allowed us to trap the intermediate Cp*(H)BH2BH2 complex, which was trapped in situ and characterized by B-11 NMR, allowing us to propose a possible mechanism for the formation of the macrocycle.

Stable nitroxides (nitroxyl radicals) have many essential and unique applications in chemistry, biology and medicine. However, the factors influencing their stability are still under investigation, and this hinders the design and development of new nitroxides. Nitroxides with tertiary alkyl groups are generally stable but obviously highly encumbered. In contrast, α-hydrogen-substituted nitroxides are generally inherently unstable and rapidly decompose. Herein, a novel, concept for the design of stable cyclic α-hydrogen nitroxides is described, and a proof-of-concept in the form of the facile synthesis and characterization of two diverse series of stable α-hydrogen nitroxides is presented. The stability of these unique α-hydrogen nitroxides is attributed to a combination of steric and stereoelectronic effects by which disproportionation is kinetically precluded. These stabilizing effects are achieved by the use of a nitroxide co-planar substituent in the γ-position of the backbone of the nitroxide. This premise is supported by a computational study, which provides insight into the disproportionation pathways of α-hydrogen nitroxides.

Nitroxides (nitroxyl radicals) hold a unique place in science due to their stable radical nature. We have recently reported the first design concept providing a general solution to the problem of designing and preparing monocyclic α-hydrogen nitroxides. The initial studies were limited to aryl derivatives. We now report a wider study showing that alkyl substituents may be employed as well. In addition, we report several additional examples of aryl substituents and reveal some of the structural limitations with regard to nitroxide stability as a function of the α-carbon substituent.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

The thermally stable [(tBuMe2 Si)2 M] (M=Zn, Hg) generate R3 Si(.) radicals in the presence of [(dmpe)Pt(PEt3 )2 ] at 60-80 °C. The reaction proceeds via hexacoordinate Pt complexes, (M=Zn (2 a and 2 b), M=Hg (3 a and 3 b)) which were isolated and characterized. Mild warming or photolysis of 2 or 3 lead to homolytic dissociation of the Pt-MSiR3 bond generating silyl radicals and novel unstable pentacoordinate platinum paramagnetic complexes (M=Zn (5), Hg (6)) whose structures were determined by EPR spectroscopy and DFT calculations.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Nitrenium ligands provide an excellent platform for the straightforward and efficient synthesis of extremely rare complexes that possess positively charged ligands coordinated to positively charged metals. Examples of stable cation-cation and cation-dication coordination bonds are demonstrated. Computational studies show that such bonding is greatly stabilized by its incorporation into a tridentate frame, as well as the use of polar solvents.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

A series of asymmetric formamidine ligands bearing different substituents with various steric and electronic properties on the nitrogen of the N-C-N motif were synthesized. Group 4 bis(formamidinate) dimethylamido, chloride, and benzyl complexes were studied using these asymmetric ligands and their solid-state structures and their behavior in solution were determined. These complexes were activated with MAO (methylalumoxane) or a combination of cocatalysts and tested in the polymerization of ethylene and propylene. A noticeable influence of the formamidine nitrogen substituents on the activity of the catalyst and properties of the obtained polymers was observed. Further, a plausible mechanism for the polymerization of propylene is presented derived from a combination of ESR-C-60 and MALDI-TOF trapping experiments which shed light on the nature of the active catalytic species.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

The very high stability of cucurbiturils under harsh acidic conditions and their reported prolific chemistry over more than three decades pose a question: why has no thiocucurbituril been reported to date? Furthermore, although glycoluril is a highly stable, easily accessible precursor of all cucurbiturils, its sulfur analog represents a yet unmet synthetic challenge. The reaction between glyoxal and thiourea was found to stop at the level of dihydroxyimidazolidine-2-thione, which is quite unstable under various acidic conditions. In an attempt to answer these questions, several stable analogs of thioglycoluril, that is, monothioglycoluril, ditolylthioglycoluril, and its diether derivative were prepared and characterized in the hope that they could be employed as building blocks for the synthesis of thiocucurbiturils. Several side products were also obtained that highlight the complex reactivity of thiourea in these reactions. The crystal structures of the above-mentioned thioglycolurils are dominated by networks of hydrogen-bonding interactions. Attempts to co-oligomerize these compounds with formaldehyde clearly suggest that it is impossible to synthesize thiocucurbiturils by the methods commonly used for the preparation of cucurbiturils. Given that thiocucurbiturils are expected to be stable molecules, alternative synthetic strategies that are different from the thermodynamically controlled approaches must be designed.