Facile Synthesis of an Octagermacubane with Two Three-Coordinate Germanium(0) Atoms and its Unique Radical Anion.

Thermolysis of a 1 : 1 mixture of tris(di-tert-butylmethylsilyl)germane 9 and bis(di-tert-butylmethylsilyl)germane 17 at 100 °C produces unexpectedly octagermacubane 18, having two 3-coordinate Ge0 atoms (40 % yield). 18 was characterized by X-ray crystallography and it is a singlet biradical (according to DFT quantum mechanical calculations and the absence of an EPR signal). Reactions of 18 with CH2 Cl2 and H2 O yield the novel dichloro-octagermacubane 24 and hydroxy-octagermacubane 25, respectively. Reduction of 18 with tBuMe2 SiNa in THF produces an isolable octagermacubane radical anion 26-Na. Based on X-ray crystallography, EPR spectroscopy and DFT quantum mechanical calculations, 26-Na is classified as a Ge-centered radical anion.

Multimodal Reactivity of N-H Bonds in Triazanes and Isolation of a Triazinyl Radical.

The employment of nitrogen Lewis acids based on nitrenium cations has been increasingly featured in the fields of main group chemistry and catalysis. A formally reduced form of nitrenium D─cyclic triazanes E─are intriguing chemical compounds, the chemistry of which is completely unexplored. In this work, we reveal that N-H-triazanes exhibit unusual N-H bond properties; namely, they can serve as protons, hydrides, or hydrogen atom donors. This unique multimodal reactivity provides an N-cation, N-anion, or N-radical from the same species. It allowed us to isolate, for the first time, a stable naphto[1,2,3]triazinyl radical, which was fully characterized both computationally and experimentally, including its monomeric X-ray structure. Moreover, this radical can be prepared directly from the nitrenium cation by a single electron reduction (E = -0.46 V), and this process is reversible. We envision versatile uses of this radical in synthetic and materials chemistry.

Hydroxide Chemoselectivity Changes with Water Microsolvation.

Solvent molecules are known to affect chemical reactions, especially if they interact with one or more of the reactants or catalysts. In ion microsolvation, i.e., solvent molecules in the first solvation sphere, strong electronic interactions are created, leading to significant changes in charge distribution and consequently on their nucleophilicity/electrophilicity and acidity/basicity. Despite a long history of research in the field, fundamental issues regarding the effects of ion microsolvation are still open, especially in the condensed phase. Using reactions between hydroxide and relatively stable quaternary ammonium salts as an example, we show that water microsolvation can change hydroxide's chemoselectivity by differently affecting its basicity and nucleophilicity. In this example, the hydroxide reactivity as a nucleophile is less affected by water microsolvation than its reactivity as a base. These disparities are discussed by calculating and comparing oxidation potentials and polarizabilities of the different water-hydroxide clusters.

Mechanistic Insights on the Selectivity of the Tandem Heck-Ring-Opening of Cyclopropyldiol Derivatives.

The preparation of a new class of alkenyl cyclopropyl diols, easily available through a copper-catalyzed carbometalation reaction of cyclopropenes, has enabled the study of key mechanistic aspects of the tandem Heck-cyclopropane ring-opening reaction. Utilizing these substrates containing two distinct hydroxyl groups allowed us to examine parameters affecting the reaction outcome and selectivity. The combination of these experimental results with detailed DFT studies shed light on the mechanism governing the regio- and stereoselectivity of the cyclopropane ring-opening. A thorough investigation displayed the dual roles fulfilled by the hydroxyl group during the reaction, which is key to this remarkable transformation. In addition to its mechanistic implication, the reaction granted access to various lactones possessing up to four stereocenters as a single diastereomer, conveniently prepared in only two catalytic steps from easily accessible achiral cyclopropenes.

Isoindolinium Groups as Stable Anion Conductors for Anion-Exchange Membrane Fuel Cells and Electrolyzers.

Anion-exchange membrane (AEM) fuel cells (AEMFCs) and water electrolyzers (AEMWEs) have gained strong attention of the scientific community as an alternative to expensive mainstream fuel cell and electrolysis technologies. However, in the high pH environment of the AEMFCs and AEMWEs, especially at low hydration levels, the molecular structure of most anion-conducting polymers breaks down because of the strong reactivity of the hydroxide anions with the quaternary ammonium (QA) cation functional groups that are commonly used in the AEMs and ionomers. Therefore, new highly stable QAs are needed to withstand the strong alkaline environment of these electrochemical devices. In this study, a series of isoindolinium salts with different substituents is prepared and investigated for their stability under dry alkaline conditions. We show that by modifying isoindolinium salts, steric effects could be added to change the degradation kinetics and impart significant improvement in the alkaline stability, reaching an order of magnitude improvement when all the aromatic positions are substituted. Density functional theory (DFT) calculations are provided in support of the high kinetic stability found in these substituted isoindolinium salts. This is the first time that this class of QAs has been investigated. We believe that these novel isoindolinium groups can be a good alternative in the chemical design of AEMs to overcome material stability challenges in advanced electrochemical systems.

The porphyrin ring rather than the metal ion dictates long-range electron transport across proteins suggesting coherence-assisted mechanism.

The fundamental biological process of electron transfer (ET) takes place across proteins with common ET pathways of several nanometers. Recent discoveries push this limit and show long-range extracellular ET over several micrometers. Here, we aim in deciphering how protein-bound intramolecular cofactors can facilitate such long-range ET. In contrast to natural systems, our protein-based platform enables us to modulate important factors associated with ET in a facile manner, such as the type of the cofactor and its quantity within the protein. We choose here the biologically relevant protoporphyrin molecule as the electron mediator. Unlike natural systems having only Fe-containing protoporphyrins, i.e., heme, as electron mediators, we use here porphyrins with different metal centers, or lacking a metal center. We show that the metal redox center has no role in ET and that ET is mediated solely by the conjugated backbone of the molecule. We further discuss several ET mechanisms, accounting to our observations with possible contribution of coherent processes. Our findings contribute to our understanding of the participation of heme molecules in long-range biological ET.

Facile H/D Exchange at (Hetero)Aromatic Hydrocarbons Catalyzed by a Stable Trans-Dihydride N-Heterocyclic Carbene (NHC) Iron Complex.

Earth-abundant metal pincer complexes have played an important role in homogeneous catalysis during the last ten years. Yet, despite intense research efforts, the synthesis of iron PCcarbeneP pincer complexes has so far remained elusive. Here we report the synthesis of the first PCNHCP functionalized iron complex [(PCNHCP)FeCl2] (1) and the reactivity of the corresponding trans-dihydride iron(II) dinitrogen complex [(PCNHCP)Fe(H)2N2)] (2). Complex 2 is stable under an atmosphere of N2 and is highly active for hydrogen isotope exchange at (hetero)aromatic hydrocarbons under mild conditions (50 °C, N2). With benzene-d6 as the deuterium source, easily reducible functional groups such as esters and amides are well tolerated, contributing to the overall wide substrate scope (e.g., halides, ethers, and amines). DFT studies suggest a complex assisted σ-bond metathesis pathway for C(sp2)-H bond activation, which is further discussed in this study.

The Reactions of Carbon Monoxide with Silyl and Silenyl Lithium - Synthesis and Isolation of the First Stable Tetra-Silyl Di-Ketyl Biradical and 1-Silaallenolate Lithium.

Reactions of carbon monoxide (CO) with tBu2 MeSiLi and (E)-(tBu2 MeSi)(tBuMe2 Si)C=Si(SiMetBu2 )Li⋅2 THF (4) were studied both experimentally and computationally. Reaction of tBu2 MeSiLi with CO in hexane yields the first stable tetra-silyl di-ketyl biradical [(tBu2 MeSi)2 COLi]. 2 (3). Reaction of 4 with CO yields selectively and quantitatively the first reported 1-silaallenolate, (tBu2 MeSi)(tBuMe2 Si)C=C=Si(SiMetBu2 )OLi⋅THF (5). Both 3 and 5 were characterized by X-ray crystallography and biradical 3 also by EPR spectroscopy. Silaallenolate 5 reacts with Me3 SiCl to produce siloxy substituted 1-silaallene (tBu2 MeSi)(tBuMe2 Si)C=C=Si(SiMetBu2 )OSiMe3 . The reaction of 4 with CO provides a new route to 1-silaallenes. The mechanisms of the reactions of tBuMe2 SiLi and of 4 with CO were studied by DFT calculations.

First α-deuterium nitroxides; synthesis and EPR study.

Herein is reported the first preparation of stable α-deuterium nitroxides of the IAPNO family. The confirmation and characteristics of the α-deuterium nitroxides and their α-hydrogen analogues are compared and analyzed. Such α-deuterium nitroxides may find use in biology, medicine and physical chemistry.

Synthesis of an Isolable Bis(silylene)-Stabilized Silylone and Its Reactivity Toward Small Gaseous Molecules.

The first bis(N-heterocyclic silylene)-stabilized zero-valent silicon compound, [SiII(Xant)SiII]Si0 (4, Xant = 9,9-dimethyl-xanthene-4,5-diyl), has been synthesized via the reduction of the corresponding chlorosilyliumylidene chloride precursor {[SiII(Xant)SiII]SiCl}+Cl- (2). The electronic structure of silylone 4, whose molecular structure is confirmed spectroscopically and crystallographically, is investigated by DFT calculations and Natural Bond Orbital analysis, showing two perpendicular lone-pairs of electrons on the central Si0 atom, i.e., an sp0.41-type lone-pair and a delocalized p lone-pair. With the electron-rich and oxophilic Si0 center, silylone 4 exhibits a striking reactivity toward small gaseous molecules. Remarkably, the oxidation of silylone 4 by N2O can be controlled to generate distinct products by regulating the amount of added N2O. Exposing 4 to an excess or two molar equivalents of N2O yields the unexpected oxidation product 5, bearing a central six-membered Si4O2 ring. When 4 is mixed with one molar equivalent of N2O, the unique compound 6 is obtained, resulting from a rare 1,4-addition of two central silicon atoms to a phenyl ring of an amidinate ligand coordinated to the SiII atom. In addition, cleavage of the strong N-H bond in ammonia is also readily accomplished by silylone 4, representing the first example of NH3 activation in silylone chemistry. In the presence of the Lewis acid BPh3, silylone 4 achieves heterolytic dihydrogen cleavage and ethylene addition to form the corresponding hydridosilyliumylidene hydroborate salt 8 and the zwitterionic compound 9, respectively, which represent a new type of frustrated Lewis pair based on an electron-rich Si0 donor and a borane acceptor.

Diastereoselective ring opening of fully-substituted cyclopropanes via intramolecular Friedel-Crafts alkylation.

We herein disclose a diastereoselective ring opening of non-donor-acceptor cyclopropanes via an intramolecular Friedel-Crafts alkylation en route to functionalized dihydronaphthalene scaffolds possessing quaternary carbon stereocentres. The transformation proceeds through a selective bond breaking at the most alkylated carbon centre with a pure retention of configuration. Mechanistic investigations and computational studies revealed that alkoxy functionality is the key for selective bond breaking leading to a complete retention of configuration.

Rhodium Complexes of a New-Generation Sapphyrin: Unique Structures, Axial Chirality, and Catalysis.

Rhodium insertion into the new 5,10,15,20-tetrakis(trifluoromethyl)sapphyrin was found to be much more facile than for other analogues, owing to NH⋅⋅⋅F hydrogen-bonding interactions that stabilise the pyrrole-inverted structure characteristic of the metallated product. The thus-obtained rhodium(I) complexes have axial chirality, and the enantiomers were resolved. The latter were found to interconvert quite rapidly in a process that involves a tautomerisation-like movement of the metal fragment between the five N atoms. The rhodium sapphyrins were investigated as catalysts for organic synthesis, by studying their carbene-transfer activity in the cyclopropanation of styrene with ethyl diazoacetate and comparing it to that of rhodium corroles.

α-Sila-Dipeptides: Synthesis and Characterization.

The first two α-sila-dipeptides, 7 and cyclo-sila-dipeptide 8, were synthesized and characterized by several methods, including X-ray crystallography. Bulky t-BuMe2 Si substituents provide some kinetic stabilization to the synthesized molecules. 7 and 8 are the first examples of a "Si for C switch" in the central α-position of an amino acid or a peptide, in which silicon is bonded to both the amino and the carbonyl groups.

Generation and Characterization of the First Persistent Platinum(I)-Centered Radical.

The first persistent platinum(I)-centered radical was generated by homolytic cleavage of a Pt-HgSiR3 bond of a mercury-substituted platinum(II) complex. The PtI radical was characterized by EPR spectroscopy, chemical trapping experiments, and density functional theory (DFT) calculations.

Isolation and Characterization, Including by X-ray Crystallography, of Contact and Solvent-Separated Ion Pairs of Silenyl Lithium Species.

Reaction of bromoacylsilane 1 (pink solution) with tBu2 MeSiLi (3.5 equiv) in a 4:1 hexane:THF solvent mixture at -78 °C to room temperature yields the solvent separated ion pair (SSIP) of silenyl lithium E-[(tBuMe2 Si)(tBu2 MeSi)C=Si(SiMetBu2 )](-) [Li⋅4THF](+) 2 a (green-blue solution). Removal of the solvent and addition of benzene converts 2 a into the corresponding contact ion pair (CIP) 2 b (violet-red solution) with two THF molecules bonded to the lithium atom. The 2 a⇌2 b interconversion is reversible upon THF⇌ benzene solvent change. Both 2 a and 2 b were characterized by X-ray crystallography, NMR and UV/Vis spectroscopy, and theoretical calculations. The degree of dissociation of the Si-Li bond has a large effect on the visible spectrum (and thus color) and on the silenylic (29) Si NMR chemical shift, but a small effect on the molecular structure. This is the first report of the X-ray molecular structure of both the SSIP and the CIP of any R2 E=E'RM species (E=C, Si; E'=C, Si; M=metal).

Correction of combined angular and rotational deformities by the Ilizarov method.

Deformities of the lower extremities are often a combination of angular and rotational components. The rotational component of combined deformities may be difficult to measure using plain radiography. Based on the current study, the computed tomography rotational malalignment test was developed. Evaluation of lower extremity alignment was done on 56 patients. Rotational malalignment was diagnosed in 14 limbs of nine patients. In all patients, correction of angular and rotational deformities was done simultaneously using an Ilizarov external fixator. The frame included a standard angular distraction system and a derotation block interconnected via an additional empty ring. In all cases, successful correction of angular and rotational deformities was achieved. The pain was eliminated in all seven patients having preexisting chronic joint pain. There were no cases of deep infection or nonunion. This simple and reliable method allowed precise analysis of the deformity in the transverse plane. Preoperative frame construction incorporating the derotational module decreased the time of the operation and allowed one-stage correction of rotational and angular deformities without additional manipulations.