Electrocatalytic Transfer Hydrogenation of 1-Octene with [(tBuPCP)Ir(H)(Cl)] and Water.

Electrocatalytic hydrogenation of 1-octene as non-activated model substrate with neutral water as H-donor is reported, using [(tBuPCP)Ir(H)(Cl)] (1) as the catalyst, to form octane with high faradaic efficiency (FE) of 96% and a kobs of 87 s-1. Cyclic voltammetry with 1 revealed that two subsequent reductions trigger the elimination of Cl- and afford the highly reactive anionic Ir(I) hydride complex [(tBuPCP)Ir(H)]- (2), a previously merely proposed intermediate for which we now report first experimental data by mass spectrometry. In absence of alkene, the stoichiometric electrolysis of 1 in THF with water selectively affords the Ir(III) dihydride complex [(tBuPCP)Ir(H)2] (3) in 88% FE from the reaction of 2 with H2O. Complex 3 then hydrogenates the alkene in classical fashion. The presented electro-hydrogenation works with extremely high FE, because the iridium hydrides are water stable, which prevents H2 formation. Even in strongly alkaline conditions (Bu4NOH added), the electro-hydrogenation of 1-octene with 1 also proceeds cleanly (89% FE), suggesting a highly robust process that may rely on H2O activation, reminiscent to transfer hydrogenation pathways, instead of classical H+ reduction. DFT calculations confirmed oxidative addition of H2O as a key step in this context.

Introducing Benzene-1,3,5-tri(dithiocarboxylate) as a Multidentate Linker in Coordination Chemistry.

Benzene-1,3,5-tri(dithiocarboxylate) (BTDTC3-), the sulfur-donor analogue of trimesate (BTC3-, benzene-1,3,5-tricarboxylate), is introduced, and its potential as a multidentate, electronically bridging ligand in coordination chemistry is evaluated. For this, the sodium salt Na3BTDTC has been synthesized, characterized, and compared with the sodium salt of the related ditopic benzene-1,4-di(dithiocarboxylate) (Na2BDDTC). Single-crystal X-ray diffraction of the respective tetrahydrofuran (THF) solvates reveals that such multitopic aromatic dithiocarboxylate linkers can form both discrete metal complexes (Na3BTDTC·9THF) and (two-dimensional) coordination polymers (Na2BDDTC·4THF). Additionally, the versatile coordination behavior of the novel BTDTC3- ligand is demonstrated by successful synthesis and characterization of trinuclear Cu(I) and hexanuclear Mo(II)2 paddlewheel complexes. The electronic structure and molecular orbitals of both dithiocarboxylate ligands as well as their carboxylate counterparts are investigated by density functional theory computational methods. Electrochemical investigations suggest that BTDTC3- enables electronic communication between the coordinated metal ions, rendering it a promising tritopic linker for functional coordination polymers.

Thermal Defect Engineering of Precious Group Metal-Organic Frameworks: A Case Study on Ru/Rh-HKUST-1 Analogues.

A methodology is introduced for controlled postsynthetic thermal defect engineering (TDE) of precious group metal-organic frameworks (PGM-MOFs). The case study is based on the Ru/Rh analogues of the archetypical structure [Cu3(BTC)2] (HKUST-1; BTC = 1,3,5-benzenetricarboxylate). Quantitative monitoring of the TDE process and extensive characterization of the samples employing a complementary set of analytical and spectroscopic techniques reveal that the compositionally very complex TDE-MOF materials result from the elimination and/or fragmentation of ancillary ligands and/or linkers. TDE involves the preferential secession of acetate ligands, intrinsically introduced via coordination modulation during synthesis, and the gradual decarboxylation of ligator sites of the framework linker BTC. Both processes lead to modified Ru/Rh paddlewheel nodes. These nodes exhibit a lowered average oxidation state and more accessible open metal centers, as deduced from surface-ligand IR spectroscopy using CO as a probe and supported by density functional theory (DFT)-based computations. The monometallic and the mixed-metal PGM-MOFs systematically differ in their TDE properties and, in particular in the hydride generation ability (HGA). This latter property is an important indicator for the catalytic activity of PGM-MOFs, as demonstrated by the ethylene dimerization reaction to 1-butene.

Mixed precious-group metal-organic frameworks: a case study of the HKUST-1 analogue [RuxRh3-x(BTC)2].

This work presents the first full series of mixed precious-group metal-organic frameworks (MPG-MOFs) using ruthenium and rhodium. The obtained crystalline, highly porous and thermally robust materials were characterized by means of powder X-ray diffraction, N2/CO2 sorption isotherms, thermogravimetry, spectroscopy methods (IR, Raman, UV/VIS-, NMR and XPS) and as well by high resolution transmission electron microscopy (HR-TEM) with elemental mapping (HAADF-EDS). Additionally, the assignment of spectroscopic data is supported by computational (time dependent)-density functional theory methods. The materials turned out to consist of homogeneously dispersed Ru2 and Rh2 paddlewheel units being linked by benzenetricarboxylate (BTC) to yield a framework that is isoreticular to [Cu3(BTC)2] (HKUST-1, Hong Kong University of Science and Technology). However, acetate (OAc) is incorporated as an intrinsic component which compensates for missing BTC-linker defects and some Cl is coordinated to the Ru centre at an apical position. The exact empirical formula of the MPG-MOFs is derived as [RuxRh3-x(BTC)2-a(OAc)b(Cl)c].

Single-Site, Organometallic Aluminum Catalysts for the Precise Group Transfer Polymerization of Michael-Type Monomers.

Unlike different types of Lewis pairs as polymerization catalysts for acrylic monomers, organometallic aluminum(III) compounds are reported that show a surprisingly high polymerization activity even without an additional Lewis base. DFT calculations, end group analysis and kinetic investigations clearly suggest a main group element (MGE) group transfer polymerization (GTP) mechanism analogous to the known metal-mediated GTP mechanism. The novel catalysts perform a precision polymerization of a broad variety of monomers, ranging from 2-isopropenyl-2-oxazoline to tert-butylmethacrylate and N,N-dimethylacrylamide. Additionally, extended Michael-type structures like 4-vinyl pyridine are accessible. Especially the Al(III) half-metallocenes show an almost quantitative initiator efficiency, and, combined with the living character of the polymerization reactions, they enable the synthesis of block copolymers, even with unconventional monomers like vinyl phosphonates.

Acylation of Homoatomic Ge9 Cages and Subsequent Decarbonylation.

The direct acylation of Ge9 Zintl clusters by the reaction of K[Ge9 {Si(SiMe3 )3 }3 ] with acyl chlorides in hexane or toluene solutions is presented, leading to the neutral, carbonyl-derivatized products [{Si(SiMe3 )3 }3 Ge9 (CO)R'] (R'=Me, iPr, tBu, Ph, Bz, cyclopropylmethyl, phenethyl, 4-vinylphenyl). This reaction is applicable to a wide range of acyl chlorides and allows for diverse functionalization of Ge9 Zintl clusters. [{Si(SiMe3 )3 }3 Ge9 (CO)tBu] readily releases CO at ambient conditions under formation of [{Si(SiMe3 )3 }3 Ge9 tBu]. This temperature-dependent decarbonylation most likely proceeds via a radical Norrish-type I α-bond cleavage. Except for R'=tBu and Bz all obtained acyl-derivatized Ge9 cluster compounds do not release CO even at elevated temperatures. All compounds were characterized by NMR spectroscopy. [{Si(SiMe3 )3 }3 Ge9 (CO)R'] (R'=tBu, Ph, Me, iPr) as well as [{Si(SiMe3 )3 }3 Ge9 tBu] were further structurally characterized by single crystal X-ray diffraction.

NXS, Morpholine, and HFIP: The Ideal Combination for Biomimetic Haliranium-Induced Polyene Cyclizations.

In contrast to Nature that accomplishes polyene cyclizations seemingly with ease, such transformations are difficult to conduct in the lab. In our program dealing with the development of selective halogenations of alkenes, we now asserted that standard X+ reagents are perfectly suited for the biomimetic cation-π cyclization of both electron rich and poor linear polyenes in the presence of the Lewis base morpholine and the Lewis acid HFIP. The method stands out due to its broad substrate scope and practicability together with high chemical yields and excellent selectivities, even for highly challenging chloriranium-induced polyene cyclizations.

Sphenoid sinus barotrauma in diving: case series and review of the literature.

About 50% of scuba divers have suffered from barotrauma of the ears and about one-third from barotrauma of paranasal sinuses. The sphenoid sinuses are rarely involved. Vital structures, as internal carotid artery and optic nerve, adjoin the sphenoid sinus. Thus, barotrauma could lead to serious neurologic disorders, including blindness. After searching the literature (Medline) and other sources (Internet), we present some cases of sphenoid sinus barotrauma, because these injuries may be underreported and misdiagnosed due to the lack of awareness and knowledge. Therefore, information is provided, e.g. on anatomical and pathophysiological features. Divers and physicians should have in mind that occasional headache during or after diving sometimes signals serious neurological disorders like vision loss. We show that injuries can develop from both negative and positive pressures in the sinuses. Because visual recovery depends on prompt diagnosis and proper therapy, physicians like otolaryngologists, ophthalmologists and neurologists need to closely collaborate.

Synthesis of Lactones via C-H Functionalization of Nonactivated C(sp3)-H Bonds.

An electron-deficient amide is utilized as a directing group to functionalize nonactivated C(sp3)-H bonds through radical 1,5-hydrogen abstraction. The γ-bromoamides formed are subsequently converted to γ-lactones under mild conditions. The method described is not limited to tertiary and secondary positions but also allows functionalization of primary nonactivated sp3-hybridized positions in a one-pot sequence. In addition, the broad functional group tolerance renders this method suitable for the late-stage introduction of γ-lactones into complex carbon frameworks.

Hydrogen Production and Storage on a Formic Acid/Bicarbonate Platform using Water-Soluble N-Heterocyclic Carbene Complexes of Late Transition Metals.

The synthesis and characterization of two water-soluble bis-N-heterocyclic carbene (NHC) complexes of rhodium and iridium is presented. Both compounds are active in H2 generation from formic acid and in hydrogenation of bicarbonate to formate. The rhodium derivative is most active in both reactions, reaching a TOF of 39 000 h-1 and a TON of 449 000 for H2 production. The catalytic hydrogenation reactions were carried out in an autoclave system and analyzed using the integrated peak areas in the 1 H NMR spectra. Decomposition of formic acid was investigated using a Fisher-Porter bottle equipped with a pressure transducer. Long-term stability for hydrogen evolution was tested by surveillance of the gas flow rate. The procedure does not require any additives like amines or inert gas conditions. Density functional theory calculations in agreement with experimental results suggest a bicarbonate reduction mechanism involving a second catalyst molecule, which provides an external hydride acting as reducing agent.

Supramolecular exo-functionalized palladium cages: fluorescent properties and biological activity.

Metallosupramolecular systems are promising new tools for pharmaceutical applications. Thus, novel self-assembled Pd(ii) coordination cages were synthesized which were exo-functionalized with naphthalene or anthracene groups with the aim to image their fate in cells. The cages were also investigated for their anticancer properties in human lung and ovarian cancer cell lines in vitro. While the observed cytotoxic effects hold promise and the cages resulted to be more effective than cisplatin in both cell lines, fluorescence emission properties were scarce. Therefore, using TD-DFT calculations, fluorescence quenching observed in the naphthalene-based system could be ascribed to a lower probability of a HOMO-LUMO excitation and an emission wavelength outside the visible region. Overall, the reported Pd2L4 cages provide new insights into the chemical-physical properties of this family of supramolecular coordination complexes whose understanding is necessary to achieve their applications in various fields.

Dynamics of the NbCl5-catalyzed cycloaddition of propylene oxide and CO2 : assessing the dual role of the nucleophilic Co-catalysts.

A mechanistic study on the synthesis of propylene carbonate (PC) from CO2 and propylene oxide (PO) catalyzed by NbCl5 and organic nucleophiles such as 4-dimethylaminopyridine (DMAP) or tetra-n-butylammonium bromide (NBu4 Br) is reported. A combination of in situ spectroscopic techniques and kinetic studies has been used to provide detailed insight into the reaction mechanism, the formation of intermediates, and interactions between the reaction partners. The results of DFT calculations support the experimental observations and allow us to propose a mechanism for this reaction.

Fluoridonitrosyl complexes of technetium(I) and technetium(II). Synthesis, characterization, reactions, and DFT calculations.

A mixture of [Tc(NO)F5](2-) and [Tc(NO)(NH3)4F](+) is formed during the reaction of pertechnetate with acetohydroxamic acid (Haha) in aqueous HF. The blue pentafluoridonitrosyltechnetate(II) has been isolated in crystalline form as potassium and rubidium salts, while the orange-red ammine complex crystallizes as bifluoride or PF6(-) salts. Reactions of [Tc(NO)F5](2-) salts with HCl give the corresponding [Tc(NO)Cl4/5](-/2-) complexes, while reflux in neat pyridine (py) results in the formation of the technetium(I) cation [Tc(NO)(py)4F](+), which can be crystallized as hexafluoridophosphate. The same compound can be synthesized directly from pertechnetate, Haha, HF, and py or by a ligand-exchange procedure starting from [Tc(NO)(NH3)4F](HF2). The technetium(I) cation [Tc(NO)(NH3)4F](+) can be oxidized electrochemically or by the reaction with Ce(SO4)2 to give the corresponding Tc(II) compound [Tc(NO)(NH3)4F](2+). The fluorido ligand in [Tc(NO)(NH3)4F](+) can be replaced by CF3COO(-), leaving the "[Tc(NO)(NH3)4](2+) core" untouched. The experimental results are confirmed by density functional theory calculations on [Tc(NO)F5](2-), [Tc(NO)(py)4F](+), [Tc(NO)(NH3)4F](+), and [Tc(NO)(NH3)4F](2+).

Cleavage of C-O bonds in lignin model compounds catalyzed by methyldioxorhenium in homogeneous phase.

Methyldioxorhenium (MDO)-catalyzed C-O bond cleavage of a variety of lignin ß-O-4-model compounds yields phenolic and aldehydic compounds in homogeneous phase under mild reaction conditions. MDO is in situ generated by reduction of methyltrioxorhenium (MTO) and is remarkably stable under the applied reaction conditions allowing its reuse for least five times without significant activity loss. Based on the observed and isolated intermediates, 17 O- and 2 H-isotope labeling experiments, DFT calculations, and several spectroscopic studies, a reaction mechanism is proposed.

Synthesis and characterisation of chelated cationic ReI(CO)3bis(NHC)(WCA) complexes.

Twelve novel Re(I) acetonitrile complexes of the type [Re(CO)3(L)(MeCN)][WCA], with L being a chelating bis(NHC) ligand with alkylene-bridged and N-substituted bis(imidazolineylidene) moieties, and WCA (WCA = weakly coordinating anion) representing PF6(-) and [Al(OC(CF3)3)4](-), have been synthesized. 1D and 2D NMR spectroscopy as well as IR spectroscopy, elemental analysis and X-ray crystallography have been applied in characterization. The propylene-bridged complex, displaying mesitylene groups R, is discussed in depth revealing interesting chemical behaviour both in solid state and in solution. DFT calculations were undertaken to better understand the properties of such compounds. In addition, the X-ray molecular structure of the first rhenium CCC pincer complex is reported.

The mechanism of borane-amine dehydrocoupling with bifunctional ruthenium catalysts.

Borane-amine adducts have received considerable attention, both as vectors for chemical hydrogen storage and as precursors for the synthesis of inorganic materials. Transition metal-catalyzed ammonia-borane (H3N-BH3, AB) dehydrocoupling offers, in principle, the possibility of large gravimetric hydrogen release at high rates and the formation of B-N polymers with well-defined microstructure. Several different homogeneous catalysts were reported in the literature. The current mechanistic picture implies that the release of aminoborane (e.g., Ni carbenes and Shvo's catalyst) results in formation of borazine and 2 equiv of H2, while 1 equiv of H2 and polyaminoborane are obtained with catalysts that also couple the dehydroproducts (e.g., Ir and Rh diphosphine and pincer catalysts). However, in comparison with the rapidly growing number of catalysts, the amount of experimental studies that deal with mechanistic details is still limited. Here, we present a comprehensive experimental and theoretical study about the mechanism of AB dehydrocoupling to polyaminoborane with ruthenium amine/amido catalysts, which exhibit particularly high activity. On the basis of kinetics, trapping experiments, polymer characterization by (11)B MQMAS solid-state NMR, spectroscopic experiments with model substrates, and density functional theory (DFT) calculations, we propose for the amine catalyst [Ru(H)2PMe3{HN(CH2CH2PtBu2)2}] two mechanistically connected catalytic cycles that account for both metal-mediated substrate dehydrogenation to aminoborane and catalyzed polymer enchainment by formal aminoborane insertion into a H-NH2BH3 bond. Kinetic results and polymer characterization also indicate that amido catalyst [Ru(H)PMe3{N(CH2CH2PtBu2)2}] does not undergo the same mechanism as was previously proposed in a theoretical study.

Synthesis and comparison of transition metal complexes of abnormal and normal tetrazolylidenes: a neglected ligand species.

To date, only few examples of tetrazolylidene carbenes coordinated to transition metal complexes have been described. A direct comparison of "normal" tetrazolylidenes (1,4-substitution pattern) and "abnormal" tetrazolylidenes (also referred to as "mesoionic carbenes"; 1,3-substitution pattern) has not been performed at all. In this work, we describe coordination of both ligand types to a row of transition metals. For example, the first examples of tetrazolylidene Mo, Ag, or Ir complexes have been isolated and fully characterized. The mesoionic tetrazolylidene Ag compound 2d is shown to be a viable carbene transfer reagent. By means of NMR, IR, and Raman spectroscopy, as well as X-ray crystallography and computational results, the pronounced differences between the two ligand substitution patterns are highlighted. It is shown that simply changing the position of a methyl group from N3 to N4 in the heterocycle can cause enormous differences in ligand characteristics.

N-Heterocyclic carbenes via abstraction of ammonia: 'normal' carbenes with 'abnormal' character.

A new ammonia adduct of a N-heterocyclic carbene (NHC) has been isolated, which can be used as a reagent for the synthesis of transition metal carbene complexes. It represents the first example of a 1,2,3-triazolylidene with a 1,2,4-substitution pattern, thus opening a new subclass ('normal' 1,2,3-triazolylidenes) of sterically and electronically tunable NHCs.

The Étard reaction: a DFT study.

The mechanism of the Étard reaction of chromylchloride in toluene, discovered more than a century ago, has been investigated by DFT calculations (B3LYP/6-31G(d)). The formation of the experimentally observed product can be rationalized by multiple CH-abstraction reactions.