Lone-Pair-π Bond Strength Unveiled by a Combined Experimental and Computational Study.

A series of naphthalene-diimide (NDI) and perylene-diimide (PDI) connected bis-N-heterocyclic carbene complexes of iridium(III) have been prepared and fully characterized. The analysis of their NMR spectroscopic features, together with their molecular structures show that these species display lone-pair-π interactions between the chloride ligands of the Ir(III) complex and the heterocycles of the NDI/PDI moieties. The detection of this type of interaction in solution is due to the formation of two atropisomers, which are formed as a result of the restricted rotation about the Ir-Ccarbene bond imposed by the (Cl)lp⋅⋅⋅π interaction. Variable-temperature 1H NMR analysis allowed the determination of the strength of this non-covalent interaction, which lies between ΔH=6.6 and 10 kcal/mol. The computational studies performed fully support the experimental findings.

Reversible Coupling of Germylone with Isocyanates.

The germylone dimNHCGe (5, dimNHC=diimino N-heterocyclic carbene) undergoes a [2+2] cycloaddition with isocyanates RNCO (R=4-tolyl or 3,5-xylyl) to furnish novel alkyl carboxamido germylenes 7 (R=4-tolyl) and 8 (R=3,5-xylyl), featuring a C-C bond between the former carbene carbon and the isocyanate moiety. Heating a mixture of 8 with 4-tolyl isocyanate to 100 °C results in isocyanate metathesis, demonstrating reversible C-C bond formation on the reduced germanium compound. DFT calculations suggest that this process occurs via the reductive dissociation of isocyanate from 8 that regenerates the parent Ge(0) compound 5.

Tuning the Catalytic Activity of a Pincer Complex of Rhodium(I) by Supramolecular and Redox Stimuli.

We report the rhodium(I) complex [Rh(CNC-NDI)(CO)]+ , in which CNC-NDI refers to a pincer-CNC ligand decorated with a naphthalenediimide moiety. Due to the presence of the planar CNC ligand and the naphthalenediimide moiety, the electronic nature of the complex can be modulated by means of supramolecular and redox stimuli, respectively. The metal complex shows a strong π-π-stacking interaction with coronene. This interaction has an impact on the electron-richness of the metal, as demonstrated by the shifting of the ν(CO) stretching band to a lower frequency. The addition of tetrabutylammonium fluoride facilitates the sequential one- and two-electron reduction of the NDI moiety of the ligand, thus resulting in a situation in which the ligand can increase its electron-donor strength in two levels. The nature of the interaction with the fluoride anion was studied computationally. The catalytic activity of the [Rh(CNC-NDI)(CO)]+ complex was tested in the cycloisomerization of alkynoic acids, where it is observed that the activity of the catalyst can be modulated between four levels of activity, which correspond to i) the use of the unmodified catalyst, ii) catalyst+coronene, iii) catalyst+2 equivalents of fluoride, and iv) catalyst+5 equivalents of fluoride.

A Guanidine-Supported π-Complex of Germanium Amenable to Intramolecular C-C Cleavage in Arene and Ge Atom Transfer.

The germylone dimNHCGe (dimNHC=diimino N-heterocyclic carbene) reacts with azides N3 R (R=SiMe3 or p-tolyl) to furnish the first examples of germanium π-complexes, i. e. guanidine-ligated compounds (dimNHI-SiMe3 )Ge (NHI=N-heterocyclic imine, R=SiMe3 ) and (dimNHI-Tol)Ge (R=p-tolyl). DFT calculations suggest that these species are formed by a Staudinger type replacement of dinitrogen in the azide by a nucleophilic germylone, leading to a transient carbene adduct of iminogermylidene. Heating a solution of compound (dimNHI-SiMe3 )Ge to 70 °C results in extrusion of the iminogermylidene that further aggregates to produce the known [Me3 SiNGe]4 tetramer, whereas the imidazolylidene fragment transforms into an unusual heptatriene species that can be considered as a product of carbene insertion into the C-C bond of a pendant Ar substituent at the imidazolylidene nitrogen of the dimNHC. Reaction of (dimNHI-SiMe3 )Ge with tetrachloro-o-benzoquinone results in the net transfer of a germanium atom and formation of the free diimino-guanidine ligand. This ligand also forms when (dimNHI-SiMe3 )Ge is treated with azide N3 (p-Tol), with the germanium product being [(p-Tol)NGe]n.

Cyclization of arylhydrazones of cross-conjugated enynones: synthesis of luminescent styryl-1H-pyrazoles and propenyl-1H-pyrazoles.

Condensation of 1,5-disubstituted pent-1-en-4-yn-1-ones with arylhydrazines in acidified alcohol results mainly in the formation of the corresponding arylhydrazones with traces of the side products of cyclization at the double bond - 1,5-diaryl-3-(arylethynyl)-4,5-dihydro-1H-pyrazoles (pyrazolines). Arylhydrazones are cyclized only by refluxing in high-boiling polar solvents (DMF and ethylene glycol), with the selective formation of 1,5-disubstituted 3-styrylpyrazoles in up to 77-95% yields. Thermodynamically, the cyclization of arylhydrazones at the triple bond is the most preferable pathway, as shown by DFT calculations and preparative synthesis experiments. Thus, we demonstrate that the reactions of arylhydrazines with 1,5-disubstituted pent-1-en-4-yn-1-ones lead to the formation of arylhydrazones and side pyrazoline impurities in a parallel (not consecutive) manner. 2-Hydrazinylpyridine interacts with 1,5-disubstituted pent-1-en-4-yn-1-ones in some other way, giving not pyridinylhydrazones but 2-(5-styryl-3-phenyl-1H-pyrazol-1-yl)pyridines (despite the acidity of the medium). The authors have developed a gram-scale synthesis method for these compounds, which were obtained in up to 60-82% yields. Besides, we have developed the synthesis method for certain styrylpyrazoles, which are quite promising substances for use as fluorescent probes. Their spectral-luminescence characteristics were examined as well as their complexing with Hg2+, Cd2+, and Pb2+ ions.

Hemolytic Performance in Two Generations of the Sputnik Left Ventricular Assist Device: A Combined Numerical and Experimental Study.

BACKGROUND: Currently, left ventricular assist devices (LVADs) are a successful surgical treatment for patients with end-stage heart failure on the waiting list or with contraindicated heart transplantation. In Russia, Sputnik 1 LVAD was also successfully introduced into clinical practice as a bridge-to-transplant and a destination therapy device. Development of Sputnik 2 LVAD was aimed at miniaturization to reduce invasiveness, optimize hemocompatibility, and improve versatility for patients of various sizes. METHODS: We compared hemolysis level in flow path of the Sputnik LVADs and investigated design aspects influencing other types of blood damage, using predictions of computational fluid dynamics (CFD) and experimental assessment. The investigated operating point was a flow rate of 5 L/min and a pressure head of 100 mm Hg at an impeller rotational speed of 9100 min-1. RESULTS: Mean hemolysis indices predicted with CFD were 0.0090% in the Sputnik 1 and 0.0023% in the Sputnik 2. Averaged values of normalized index of hemolysis obtained experimentally for the Sputnik 1 and the Sputnik 2 were 0.011 ± 0.003 g/100 L and 0.004 ± 0.002 g/100 L, respectively. CONCLUSIONS: Obtained results indicate obvious improvements in hemocompatibility and sufficiently satisfy the determined miniaturization aim for the Sputnik 2 LVAD development.

An Isolable Gallium-Substituted Nitrilimine and its Reactivity with B-H, Si-H and B-B Bonds.

Reaction of the Ga(I) compound NacNacGa (9) with the diazo compound N2 CHSiMe3 affords the nitrilimine compound NacNacGa(N-NCSiMe3 )(CH2 SiMe3 ) (10). Carrying out this reaction in the presence of pyridine does not lead to C-H activation on the transient alkylidene NacNacGa=CHSiMe3 but generates a metallated diazo species NacNacGa(NHN=CHSiMe3 )(CN2 SiMe3 ) (13) that further rearranges into the isonitrile compound NacNacGa(NHN=CHSiMe3 )(N(NC)SiMe3 ) (15). Reactions of 10 with the silane H3 SiPh and the borane HBcat furnished products of 1,3 addition to the nitrilimine moiety NacNacGa{N(ERn )NCSiMe3 }(CH2 SiMe3 ), whereas reaction with the diborane B2 cat2 gave the product of formal nitrene insertion into the B-B bond. DFT calculations suggest that the interaction of 9 with N2 CHSiMe3 proceeds through intermediate formation of an alkylidene compound that undergoes CH activation with a second molecule of N2 CHSiMe3 . Insertion into the B-B bond likely proceeds through an initial 1,3-addition of the diborane, followed by boryl migration to the former nitrene center.

Reactivity of Cross-Conjugated Enynones in Cyclocondensations with Hydrazines: Synthesis of Pyrazoles and Pyrazolines.

The cyclocondensation of cross-conjugated enynones, dienynones, and trienynones (easily available due to low-cost starting compounds) with arylhydrazines leads to the regioselective synthesis of pyrazole derivatives (dihetaryl-substituted ethens, buta-1,3-diens, and hexa-1,3,5-triens) or results in 4,5-dihydro-1H-pyrazoles in good yield. The reaction path is controlled by the character of the substituent in enynone: the pyrazoles are obtained from the reaction of substrates that contain five-membered heteroaromatic substituents with arylhydrazines, and the 4,5-dihydro-1H-pyrazoles are obtained from the reaction of 1,5-diphenylpent-1-en-4-yn-3-one with arylhydrazines consistently. Despite the presence of a substituent, cyclocondensation of 2-hydrazinylpyridine with all of examined cross-conjugated enynones leads to the formation of pyrazoles. The reaction does not require special conditions (temperature, catalyst, inert atmosphere). The cyclocondensation pathways are determined by the electronic effect of an electron-rich five-membered heteroaromatic ring in the substrate. The synthesis allows use of various substituents and functional groups in enynone and hydrazine. The present method features high yields and simplicity of the product purification. The obtained pyrazoles possess fluorescent properties with a quantum yield up to 31%.

Ion Mobility Mass Spectrometry Uncovers Guest-Induced Distortions in a Supramolecular Organometallic Metallosquare.

The encapsulation of the tetracationic palladium metallosquare with four pyrene-bis-imidazolylidene ligands [1]4+ with a series of organic molecules was studied by Electrospray ionization Travelling Wave Ion-Mobility Mass Spectrometry (ESI TWIM-MS). The method allowed to determine the Collision Cross Sections (CCSs), which were used to assess the size changes experienced by the host upon encapsulation of the guest molecules. When fullerenes were used as guests, the host is expanded ΔCCS 13 Å2 and 23 Å2 , for C60 or C70 , respectively. The metallorectangle [1]4+ was also used for the encapsulation of a series of polycyclic aromatic hydrocarbons (PAHs) and naphthalenetetracarboxylic diimide (NTCDI), to form complexes of formula [(NTCDI)2 (PAH)@1]4+ . For these host:guest adducts, the ESI IM-MS studies revealed that [1]4+ is expanded by 47-49 Å2 .. The energy-minimized structures of [1]4+ , [C60 @1]4+ , [C70 @1]4+ , [(NTCDI)2 (corannulene)@1]4+ in the gas phase were obtained by DFT calculations.Introduction.

The Milstein Bipyridyl PNN Pincer Complex of Ruthenium Becomes a Noyori-Type Catalyst under Reducing Conditions.

Hydrogenation of the dearomatized PNN ligand of the Milstein bipyridyl complex RuH(CO)[PNN] (2) gives a square-pyramidal Ru(II) product RuH(CO)[pPNN] (5). The central ring of the pPNN ligand is a piperidine. A minor byproduct of the hydrogenation reaction is complex 6 which has a dimeric structure made of two Ru(II) fragments each possessing a partly hydrogenated PNN ligand. The structures of 5 and 6 have been elucidated by NMR spectroscopy and X-ray crystallography. The PNN ligand of 2 is also hydrogenated under the conditions of the catalytic dehydrogenative coupling of ethanol to ethyl acetate. No direct evidence of the aromatized dihydride RuH2(CO)[PNN] (4) was found in this study. However, treating RuHCl(CO)[PNN] with Li[HBEt3] or reacting 2 with H2 at low temperature resulted in a structurally characterized hydride-bridged dimer (7) bearing intact aromatized bipyridyl ligands. M06-L/def2-QZVP DFT calculations provided insights into the thermodynamics of the stoichiometric reactions of this work and into the nature of the intermediates of the catalytic ester hydrogenation facilitated by RuH2(CO)[pPN(H)N] (8) formed from 5 under H2.

Ge(0) Compound Stabilized by a Diimino-Carbene Ligand: Synthesis and Ambiphilic Reactivity.

The germylone dimNHCGe (5, dimNHC = diimino N-heterocyclic carbene) was successfully prepared via the reduction of the germanium cation [dimNHCGeCl]+ with KC8. The molecular structure of 5 was unambiguously established by both NMR spectroscopy and single-crystal X-ray diffraction. The reactivity of 5 was investigated, revealing that it undergoes oxidative addition of HCl, CH3I, and PhI, accompanied by an unusual migration of the H, Me, and Ph groups from germanium to the carbene ligand. Related chemistry was also observed with C5F5N, which results in the migration of the fluorinated pyridine moiety to the carbene ligand. Compound 5 also undergoes cycloaddition with tetrachloro-o-benzoquinone to afford a Ge(IV) adduct.

A Shape-Adaptable Organometallic Supramolecular Coordination Cage for the Encapsulation of Fullerenes.

The development of three-dimensional supramolecular coordination complexes (SCCs), with cavities suitable for guest binding, is of great interest because these materials are useful in a large number of applications. Herein, a nickel-conjoined organometallic molecular prism is described, which has been fully characterized. The X-ray diffraction structure of the molecule reveals that the cage possesses an internal cavity with a volume of 1028 Å3 , thus suitable for the encapsulation of large 3D-molecules, such as fullerenes. This cage shows highly selective complexation of C70 over C60 , thus being potentially useful for fullerene separation and purification. The combined experimental and computational studies suggest that the complexation process is largely entropically-driven, and DFT calculations suggest that the cage is flexible and can adapt the size and the shape of the cavity to maximize the face-to-face interaction with the fullerenes.

Gold(I) Metallo-Tweezers for the Recognition of Functionalized Polycyclic Aromatic Hydrocarbons by Combined π-π Stacking and H-Bonding.

Two gold(I)-based metallo-tweezers with bis(Au-NHC) pincers and a carbazole connector have been obtained and used for the recognition of polycyclic aromatic hydrocarbons (PAHs). In the case of the tweezer with pyrene-NHC ligands, the presence of the pyrene fragment and the N-H bond in the carbazole linker enable the receptor to show significant enhanced binding abilities toward PAHs functionalized with H-bonding groups, through combined π-π stacking and H-bonding.

Cationic, Neutral, and Anionic Hydrides of Iridium with PSiP Pincers.

This work describes synthetic routes from the known precursor [IrClH{κP,P,Si-Si(Me)(C6H4-2-PiPr2)2}] (1) to new hydride and polyhydride derivatives. Substituting the chloride ligand with triflate leads to the five-coordinate complex [IrH{κO-O3S(CF3)}{κP,P,Si-Si(Me)(C6H4-2-PiPr2)2}] (2), which can undergo reversible coordination of water (H2O) or dihydrogen (H2) to generate respectively the cationic derivative [IrH{κP,P,Si-Si(Me)(C6H4-2-PiPr2)2}(OH2)2](CF3SO3) (3) or the neutral trans-hydride-dihydrogen [IrH{κO-O3S(CF3)}{κP,P,Si-Si(Me)(C6H4-2-PiPr2)2}(η2-H2)] (6) in equilibrium. The use of acetonitrile or carbon monoxide (CO) excess instead of water produces stable analogues of 3 (complexes 4 or 5, respectively). The reaction between 1 and NaBH4 affords the tetrahydroborate derivative [IrH{κ2H-H2BH2}{κP,P,Si-Si(Me)(C6H4-2-PiPr2)2}] (7), which can be protonated with triflic acid to form 2 or with HBF4 to give the dinuclear cationic derivative [(µ:κ2H,κ2H-BH4)[IrH{κP,P,Si-Si(Me)(C6H4-2-PiPr2)2}]2](BF4) (8). The reactions of 7 with alcohols afford either the dihydride-carbonyl [IrH2{κP,P,Si-Si(Me)(C6H4-2-PiPr2)2}(CO)] (9) or the known tetrahydride [IrH4{κP,P,Si-Si(Me)(C6H4-2-PiPr2)2}] (10), depending on the ease of alcohol decarbonylation. NMR observations and density functional theory calculations on the fluxional behavior of 10 indicate that the spatial contour of the mer PSiP framework conditions hydride-ligand exchanges. Complex 10 reacts with NaH in tetrahydrofuran to form the anionic trihydride [IrH3{κP,P,Si-Si(Me)(C6H4-2-PiPr2)2}]Na (11), which exists as a mixture of fac and mer isomers in equilibrium.

Self-Assembly of Di-N-Heterocyclic Carbene-Gold-Adorned Corannulenes on C60.

The deprotonation of a corannulene-based bisazolium salt allowed the preparation of a corannulene-based NHC di-AuI complex. The prepared di-AuI -complex was tested in the recognition of fullerene-C60 , demonstrating good binding affinity in toluene solution, and producing a host-guest complex with 3:1 stoichiometry, as evidenced by a combination of NMR spectroscopy and ITC titrations. The experimental results are fully supported by DFT calculations. The binding of C60 with the di-AuI complex in toluene solution is enthalpically and entropically favoured. Remarkably, the entropic term is the dominant parameter in the binding process. The good complementarity that exists between the concave shape of the corannulene-di-gold complex and the convex surface of the fullerene, together with the presence of tBu groups and the AuCl fragment are key factors for the measured high affinity between host and guest. The obtained results indicate that fullerene may be acting as a template for the formation of a self-assembled aggregate involving up to three molecules of the di-AuI complex.

Rethinking the Claisen-Tishchenko Reaction.

Pincer-type complexes [OsH2 (CO){PyCH2 NHCH2 CH2 NHPtBu2 }] and [OsH2 (CO){HN(CH2 CH2 PiPr2 )2 }] catalyze the disproportionation reaction of aldehydes via an outer-sphere bifunctional mechanism achieving turnover frequencies up to 14 000 h-1 . The N-H group of the catalysts is a key player in this process, elucidated with the help of DFT calculations.

First homoleptic MIC and heteroleptic NHC-MIC coordination cages from 1,3,5-triphenylbenzene-bridged tris-MIC and tris-NHC ligands.

The preparation of a triphenylbenzene-bridged tris-(1,2,3-triazolium) salt allowed us to obtain the first homoleptic tris-MIC cylinder-like cages of Ag and Au. The silver MIC-based cage reacts with the tris-NHC-Ag analogue to form the corresponding heteroleptic NHC-MIC silver cage in an unusual reaction involving the simultaneous exchange of the tris-NHC and tris-MIC ligands.

Chemoselective hydrogenation of carbonyl compounds and acceptorless dehydrogenative coupling of alcohols.

OsHCl(CO)[κ(3)-PyCH2NHC2H4NHPtBu2] is the first efficient catalyst for chemoselective reduction of challenging unsaturated esters to enols and for acceptorless coupling of amines with MeOH and EtOH affording formamides and acetamides. The NMR, ESI-MS, and DFT data indicate a mechanism proceeding in the metal coordination sphere and producing no free organic intermediates.

Replacing phosphorus with sulfur for the efficient hydrogenation of esters.

Catalyst tune-up: A readily available, air-stable amino-sulfide catalyst, [RuCl(2)(PPh(3)){HN(C(2)H(4)SEt)(2)}], has been developed. This complex displays outstanding efficiency for the hydrogenation of a broad range of substrates with C=X bonds (esters, ketones, imines), as well as for the acceptorless dehydrogenative coupling of ethanol to ethyl acetate.

The Tolman electronic parameter (TEP) and the metal-metal electronic communication in ditopic NHC complexes.

Whereas the electronic communication between metals in dimetallic organometallic compounds is often assessed through cyclic voltammetric measurements, we have found that the variations in the Tolman electronic parameter (TEP) can also be an alternative and effective way of determining this type of interaction. The TEP values of several (CO)3Ni-NHC-X systems with five different ditopic NHC ligand systems [triazolyldiylidene (A), bis(imidazolylidene) (B), benzobis(imidazolylidene) (C), cyclopenta[f,g]acenaphthylenebis(imidazolylidene) (D) and bis(imidazolidinylidene) (F)] were determined by means of DFT calculations. Based on these values, the electron-withdrawing character of the X metal fragments employed in this study was found to increase in the order IrCp(CO) → RhCl(COD) → Ni(CO)3 → Cr(CO)5 → RhCl(CO)2. We found that the degree of electronic interaction through the ditopic NHC ligands is the strongest in A, followed by B and F, while being weak in B and C. The TEP values and the quantitative analysis of the upper molecular orbitals of A and F and their (CO)3Ni-NHC-Ni(CO)3 complexes strongly suggest that the principal electronic interaction between the metal centres of the M-NHC-M' complexes is of σ-type, via the delocalized HOMO and HOMO - 1 orbitals of the NHC ligands.