Preparation and Characterization of Metalloporphyrin Tröger's and Spiro-Tröger's Base Derivatives.

A series of metalloporphyrin dimers as Tröger's bases 1 or spiro-Tröger's bases 2 was prepared starting from five different C4-symmetry porphyrin derivatives substituted in meso-positions by Ph, 3-MeO-Ph, 4-MeO-Ph, 3,4-(MeO)2-Ph, or 3,5-(MeO)2-Ph. Free-base porphyrins were converted to metalloporphyrins, which were subsequently nitrated with nickel(II), copper(II), or zinc(II) nitrate to give ß-nitrometalloporphyrins. These were further reduced to ß-aminometalloporphyrins and treated with a methanal equivalent under acidic conditions to selectively obtain Tröger's base 1, spiro-Tröger's base 2, or a mixture of both, in yields up to 41% of 1 and 45% of 2 depending on the reaction conditions used. The ratio of 1 to 2 was influenced by the methanal equivalent used, the strength of the acid, and, above all, the solvent. The presence of a metal ion within the porphyrin core and the use of a chlorinated solvent were found to be essential for the formation of spiro-Tröger's base 2. The molecular structure of spiroTB 2a-Ni2 was proven by electron diffraction.

Structure and absolute configuration of natural fungal product beauveriolide I, isolated from Cordyceps javanica, determined by 3D electron diffraction.

Beauveriolides, including the main beauveriolide I {systematic name: (3R,6S,9S,13S)-9-benzyl-13-[(2S)-hexan-2-yl]-6-methyl-3-(2-methylpropyl)-1-oxa-4,7,10-triazacyclotridecane-2,5,8,11-tetrone, C27H41N3O5}, are a series of cyclodepsipeptides that have shown promising results in the treatment of Alzheimer's disease and in the prevention of foam cell formation in atherosclerosis. Their crystal structure studies have been difficult due to their tiny crystal size and fibre-like morphology, until now. Recent developments in 3D electron diffraction methodology have made it possible to accurately study the crystal structures of submicron crystals by overcoming the problems of beam sensitivity and dynamical scattering. In this study, the absolute structure of beauveriolide I was determined by 3D electron diffraction. The cyclodepsipeptide crystallizes in the space group I2 with lattice parameters a = 40.2744 (4), b = 5.0976 (5), c = 27.698 (4) Šand ß = 105.729 (6)°. After dynamical refinement, its absolute structure was determined by comparing the R factors and calculating the z-scores of the two possible enantiomorphs of beauveriolide I.

Dicarbonyl[10,10-dimethyl-5,15-bis(pentafluorophenyl)biladiene]ruthenium(II): discovery of the first ruthenium tetrapyrrole cis-dicarbonyl complex by X-ray and electron diffraction.

Dicarbonyl[10,10-dimethyl-5,15-bis(pentafluorophenyl)biladiene]ruthenium(II), [Ru(C33H16F10N4)(CO)2] or Ru(CO)2[DMBil1], is the first reported ruthenium(II) cis-dicarbonyl tetrapyrrole complex. The neutral complex sports two carbonyls and an oligotetrapyrrolic biladiene ligand. Notably, the biladiene adopts a coordination geometry that is well distorted from square planar and much more closely approximates a seesaw arrangement. Accordingly, Ru(CO)2[DMBil1] is not only the first ruthenium cis-dicarbonyl with a tetrapyrrole ligand, but also the first metal biladiene complex in which the tetrapyrrole does not adopt a (pseudo-)square-planar coordination geometry. Ru(CO)2[DMBil1] is weakly luminescent, displaying λem = 552 nm upon excitation at λex = 500 nm, supports two reversible 1 e- reductions at -1.45 and -1.73 V (versus Fc+/Fc), and has significant absorption features at 481 and 531 nm, suggesting suitability for photocatalytic and photosensitization applications. While the structure of Ru(CO)2[DMBil1] was initially determined by X-ray diffraction, a traditionally acceptable quality structure could not be obtained (despite multiple attempts) because of consistently poor crystal quality. An independent structure obtained from electron diffraction experiments corroborates the structure of this unusual biladiene complex.

Reactive Noble-Gas Compounds Explored by 3D Electron Diffraction: XeF2-MnF4 Adducts and a Facile Sample Handling Procedure.

Recent advances in 3D electron diffraction (3D ED) have succeeded in matching the capabilities of single-crystal X-ray diffraction (SCXRD), while requiring only submicron crystals for successful structural investigations. One of the many diverse areas to benefit from the 3D ED structural analysis is main-group chemistry, where compounds are often poorly crystalline or single-crystal growth is challenging. A facile method for loading and transferring highly air-sensitive and strongly oxidizing samples at low temperatures to a transmission electron microscope (TEM) for 3D ED analysis was successfully developed and tested on xenon(II) compounds from the XeF2-MnF4 system. The crystal structures determined on nanometer-sized crystallites by dynamical refinement of the 3D ED data are in complete agreement with the results obtained by SCXRD on micrometer-sized crystals and by periodic density-functional theory (DFT) calculations, demonstrating the applicability of this approach for structural studies of noble-gas compounds and highly reactive species in general. The compounds 3XeF2·2MnF4, XeF2·MnF4, and XeF2·2MnF4 are rare examples of structurally fully characterized xenon difluoride-metal tetrafluoride adducts and thus advance our knowledge of the diverse structural chemistry of these systems, which also includes the hitherto poorly characterized first noble-gas compound, "XePtF6".