Nitrosonium complexes of [2.2]paracyclophane

The reaction of [2.2]paracyclophane with nitrosonium tetrachloroaluminate was studied by NMR (¹H, ¹³C) spectroscopy using deuterium isotopic perturbation technique. The resulting cationic complexes containing one and two nitrosonium ions are involved in fast (on the NMR time scale) interconversion. Quantum-chemical calculations performed on the DFT level (using triple zeta basis set) indicate the higher stability of 2η single-charged π-complexes relative to σ complexes corresponding to the addition of NO⁺ ion at the ipso and ortho positions. The formation of the single-charged π-complex is energetically more favorable, compared to the double-charged π-complex. The affinity of NO⁺ for [2.2]paracyclophane is much greater than for p-xylene, presumably due to stacking interaction between the aromatic rings in the π-complex.     

Nitrosonium complexes of triptycene

According to the ¹H and ¹³C NMR data, triptycene reacts with nitrosonium tetrachloroaluminate to form positively charged π-complexes with one and two nitrosonium ions, which are rapidly (on the NMR time scale) converted into each other. DFT quantum-chemical calculations with Λ02 basis set indicated higher stability of singly charged complexes relative to doubly charged. Addition of three nitrosonium ions to triptycene molecule is unfavorable from the energy viewpoint.     

Quantum-chemical study on cytosine nitrosonium complexes

Cytosine complexes with nitrosonium ion were studied by the RI-MP2/L1 method. Addition of nitrosonium ion to cytosine tautomers leads to formation of a set of nitrosonium complexes with different structures (1η–3η). n-Complexes formed via NO⁺ coordination to the nitrogen and oxygen atoms are energetically more favorable than π-complexes. The complex of cytosine as 4-aminopyrimidin-2(1H)-one tautomer with nitrosonium ion coordinated to the carbonyl oxygen atom occupies the global minimum on the potential energy surface. Structural features of the complexes are discussed.     

Quantum-chemical study on adenine nitrosonium complexes

Adenine complexes with nitrosonium ion have been studied by the RI-MP2/L1 quantum-chemical method. Addition of nitrosonium ion to adenine tautomers produces a set of nitrosonium complexes of different types (1??C3??). n-Complexes involving NO⁺ coordination to nitrogen atoms are more energetically favorable than ??-complexes. The global minimum on the potential energy surface is occupied by the complex of 7H-adenine tautomer with nitrosonium ion coordinated at the N³ atom.     

The Importance of Ligand-Induced Backdonation in the Stabilization of Square Planar d10 Nickel π-Complexes

The electronic nature of Ni π-complexes is underexplored even though these complexes have been widely postulated as intermediates in organometallic chemistry. Herein, the geometric and electronic structure of a series of nickel π-complexes, Ni(dtbpe)(X) (dtbpe=1,2-bis(di-tert-butyl)phosphinoethane; X=alkene or carbonyl containing π-ligands), is probed using a combination of ³¹P NMR, Ni K-edge XAS, Ni K_β XES, and DFT calculations. These complexes are best described as square planar d¹⁰ complexes with π-backbonding acting as the dominant contributor to M−L bonding to the π-ligand. The degree of backbonding correlates with ²J_PP from NMR and the energy of the Ni 1s→4p_z pre-edge in the Ni K-edge XAS data, and is determined by the energy of the π*_ip ligand acceptor orbital. Thus, unactivated olefinic ligands tend to be poor π-acids whereas ketones, aldehydes, and esters allow for greater backbonding. However, backbonding is still significant even in cases in which metal contributions are minor. In such cases, backbonding is dominated by charge donation from the diphosphine, which allows for strong backdonation, although the metal centre retains a formal d¹⁰ electronic configuration. This ligand-induced backbonding can be formally described as a 3-centre-4-electron (3c-4e) interaction, in which the nickel centre mediates charge transfer from the phosphine σ-donors to the π*_ip ligand acceptor orbital. The implications of this bonding motif are described with respect to both structure and reactivity.     

The mechanism of formation of π-allyl complexes: The reaction of PdCl2−4 with isoprene in methanol

A kinetic study of the reaction between PdCl^2?₄ and isoprene is described. The results are interpreted in terms of the formation of two π-complexes between palladium(II) and isoprene, one having only one double bond coordinated to the metal, the other being a chelated diene compound. Nucleophilic attack of solvent methanol on these intermediate complexes gives the methoxy π-allyl complex.     

Vinylidene complexes of transition metals : II. A new method of synthesis of vinylidene complexes. Cymantrene derivatives containing phenylvinylidene ligands

A rearrangement of transition metal acetylenic π-complexes into compounds with vinylidene n-ligands has been established. Compounds CpMn(CCHPh)-(CO)₂ and Cp₂Mn₂(μ-CCHPh)(CO)₄ with terminal and bridging phenylvinylidene (benzylidenecarbene) ligands respectively were obtained from the π-complexes CpMn(CO)₂(PhCCR) where R  H, Ph₃Ge or Ph₃Sn. Reactions leading to conversion of the terminal CCHPh group into a bridging ligand and vice versa were studied. Under the action of L  Ph₃P, (EtO)₃P or (PhO)₃P, substitution of CO groups in vinylidene complexes takes place and compounds CpMn(CCHPh)-(CO)L are formed. IR, ¹H and ¹³C NMR spectra of the novel complexes are discussed. The data obtained indicate an electron-withdrawing property of the CCHPh ligand and stronger bonding of this ligand to the metal as compared with a CO group.     

Synthesis of new binuclear tricarbonylchromium- and -manganese complexes of isoxazolidines by 1,3-dipolar cycloaddition reaction

The reactions of 1,3-dipolar cycloaddition of π-complexes of nitrones of a general formula R²CH=N(O)R¹, where R¹ = Me, Bu^t, Ph, R² = Ph[Cr(CO)₃], C₅H₄[Mn(CO)₃] with (η⁶-styrene)-tricarbonylchromium and vinyl-(η⁵-cyclopentadienyl)tricarbonylmanganese have been investigated. These reactions led to the formation of corresponding isoxazolidines with high regio- and diastereoselectivity. The obtained metal-containing isoxazolidines were identified using UV, IR, ¹H NMR spectroscopy, mass-spectrometry, and X-ray diffraction analysis.     

Gold(III) π-Allyl Complexes

Gold(III) π-complexes have been authenticated recently with alkenes, alkynes, and arenes. The key importance of Pd^II π-allyl complexes in organometallic chemistry (Tsuji–Trost reaction) prompted us to explore gold(III) π-allyl complexes, which have remained elusive so far. The (P,C)Au^III(allyl) and (methallyl) complexes 3 and 3′ were readily prepared and isolated as thermally and air-stable solids. Spectroscopic and crystallographic analyses combined with detailed DFT calculations support tight quasi-symmetric η³-coordination of the allyl moiety. The π-allyl gold(III) complexes are activated towards nucleophilic additions, as substantiated with β-diketo enolates.     

1H- und 13C-NMR-spektroskopische Untersuchungen zur Ladungsverteilung in substituierten 1,3-Dioxan-2-ylium-Salzen

The ¹H and ¹³C NMR spectra of a series of 1,3-dioxan-2-ylium salts substituted at C-2 and C-4, C-5, C-6 have been measured. The atomic charge distribution in 1,3-dioxan- and 1,3-dioxolan-2-ylium cations has been calculated with the MINDO/3 method, leading to a linear correlation between π-charge and ¹³C chemical shift at C-2. The strong C-21-proton downfield shift is caused by the anisotropic influence of the mesomeric cation system. The conformations of substituted 1,3-dioxan-2-ylium cations are discussed.     

Solid-state 23Na, 139La, 27Al and 29Si nuclear magnetic resonance spectroscopic investigations of cation location and migration in zeolites LaNaY

²³Na Magic-angle spinning (MAS), double rotation (DOR) and two-dimensional nutation nuclear magnetic resonance (NMR) and static ¹³⁹La NMR spectroscopy were applied to study the location and migration of sodium and lanthanum cations in faujasites. Generally, ²³Na MAS NMR spectroscopy of as-exchanged and hydrated zeolites LaNaY was used for the quantitative determination of non-localized Na⁺ in the large cavities at a ²³Na NMR shift of −9 ppm and of sodium cations observed at −13 ppm. The latter originate from Na⁺ ions located on position SII in the large cavities, on position SI in the hexagonal prisms and on positions SII′ and/or SI′ in the sodalite cages. The ²³Na MAS NMR signal at about −13 ppm was found to be caused by two coonents. The component that is characterized by a quadrupolar interaction causing a field-dependent shift and a signal at v₁ = 2v_rf in the two-dimensional quadrupolar nutation spectra is attributed to Na⁺ enclosed in the sodalite cages. The ²³Na MAS NMR spectra of dehydrated lanthanum-exchanged faujasites are characterized by a low-field Gaussian line of Na⁺ located on SI positions in the hexagonal prisms and a high-field quadrupole pattern of Na⁺ located on positions SII and SI′. The migration of lanthanum cations from the large cavities to position SI′ in the sodalite cages was monitored by ¹³⁹La NMR spectroscopy and verified by a theoretical estimation of the electric field gradient. The lanthanum migration was found to be coupled with a strain of SiOT and AlOT angles observed by ²⁹Si and ²⁷Al MAS NMR high-field shifts, respectively.     

(η2-Allyl­ammonium)­aqua­bis­(sulfam­ato-N)copper(I)

The Cu^I atom in the title complex, [Cu(NH₂SO₃)₂(C₃H₈N)(H₂O)], is coordinated by the C=C bond of the allyl­ammonium cation, two N atoms of the sulfamate anions and the O atom of the H₂O mol­ecule in the apical position. Thus, the central atom is in a distorted trigonal–pyramidal environment. Strong N—H⃛O and O—H⃛O contacts connect separate moieties of the complex into a three-dimensional framework. The title compound is representative of hitherto unknown copper(I)–sulfamate π-complexes.     

Interaction of diphenylacetylene with chromium salts

The reaction of diphenylacetylene with chromium atoms results in the formation of bisarenechromium π-complexes containing diphenylacetylene and its cyclotrimer as ligands, viz., bis(η⁶-diphenylacetylene)chromium, (η⁶-diphenylacetylene)(η⁶-hexaphenylbenzene)chromium and bis(η⁶-hexaphenylbenzene)chromium. The other reaction products were found to be uncomplexed hexaphenylbenzene and 1,2,3,4-tetraphenylbutadiene-1,3.     

Electronic Effects of para‐Substitution on the Melting Points of TAAILs

Owing to numerous new applications, the interest in “task‐specific” ionic liquids increased significantly over the last decade. But, unfortunately, the imidazolium‐based ionic liquids (by far the most frequently used cations) have serious limitations when it comes to modifications of their properties. The new generation of ionic liquids, called tunable aryl–alkyl ionic liquids (TAAILs), replaces one of the two alkyl chains on the imidazolium ring with an aryl ring which allows a large degree of functionalization. Inductive, mesomeric, and steric effects as well as potentially also π π and π π⁺ interactions provide a wide range of possibilities to tune this new class of ILs. We investigated the influence of electron‐withdrawing and ‐donating substituents at the para‐position of the aryl ring (NO₂, Cl, Br, EtO(CO), H, Me, OEt, OMe) by studying the changes in the melting points of the corresponding bromide and bis(trifluoromethanesulfonyl)imide, (N(Tf)₂⁻), salts. In addition, we calculated (B3LYP/6‐311++G(d,p)) the different charge distributions of substituted 1‐aryl‐3‐propyl‐imidazolium cations to understand the experimentally observed effects. The results indicated that the presence of electron‐donating and ‐withdrawing groups leads to strong polarization effects in the cations.     

Structure Determination of Zinc Complexes of Iminodiacetamide Ionophores in Solution and in the Solid State

It is shown by extensive NMRinvestigation that hexa-coordinatedZn²⁺-complexes containing two tridentateiminodiacetamide ligands adopt a solutionconformation with two different kinds ofZn–O bonds possessing a center ofinversion. In contrast, the complexmolecules are chiral in the solid state asdetermined by CP-MAS ¹³C NMR spectroscopy.     

Über paramagnetische dimerenkomplexe des substituierten triphenylmethylradikals

Highly concentrated frozen solutions of the tri-p-biphenylmethyl doublet radical exhibit ESR triplet spectra with an electron-electron dipolar coupling parameter D of about 300 MHz. This is explained by the formation of intermolecular π-complexes from pairs of doublet radicals resulting in a coupling of the two unpaired electrons to a sufficiently low triplet state. Quant-mechanical model calculations (using a point charge approximation for the p-π AO's) indicate that the π-complexes exist in an ecliptical conformation with a distance of 4·3–4·7 Å between the two doublet moieties.     

Reaction of Nitrosonium Tetrafluoroborate with Nitroxyl Radicals

It was established by means of multinuclear magnetic resonance method (¹H, ^{1 3}C, ^{1 9}F and ^{1 4}N) that reaction of 2,2,6,6-tetramethyl-4-R-piperidin-1-oxyl radicals (R = H, OH, OMe, OCOPh, NHCOMe) with nitrosonium tetrafluoroborate gave rise to the corresponding 2,2,6,6-tetramethyl-1-oxo-4-R-piperidinium tetrafluoroborates. Linear correlations were found between the chemical shifts of atoms H⁴, C⁴ of cations and respectively ₁-constants of substituents R and chemical shifts of C⁴ atom calculated from increments of substitution. The conformational features of the generated nitrosonium cations are considered on the grounds of vicinal coupling constants J _{H H} and quantum-chemical calculations by AM1 method.     

13C, 15N and 113Cd NMR and Molecular Orbital Studies of Novel Bile Acid N-(2-aminoethyl)amides and Their Cd2+-complexes

Lithocholic acid N-(2-aminoethyl)amide (1) and deoxycholic acid N-(2-aminoethyl)amide(2) have been prepared and characterized by¹H, ¹³C and ¹⁵N NMR. The accurate molecular masses of 1 and 2 have been determined by ESI MS. The formation of the Cd²⁺-complexes (1+Cd and 2+Cd) in CD₃OD solution have been detected by ¹H,¹³C, ¹⁵N and ¹¹³Cd NMR. The ¹³C NMR chemical shift assignments of 1 and 2 and their Cd²⁺-complexes are based on DEPT-135 and z-GS ¹H,¹³C HMQC experiments as well as comparison with the assignments of the related structures. The ¹⁵N NMR chemical shiftassignments of the ligands and theirCd²⁺-complexes are based on z-GS¹H,¹⁵N HMBC experiments. ¹³C NMR chemical shift differences between 1and its 1:1 Cd²⁺-complex based on ab initiocalculations at Hartree-Fock SCI-PCM level using3-21G(d) basis set are in agreement with theexperimental shift changes observed onCd²⁺-complexation.     

Quantum-chemical study on nitrosonium complexes of Bi- and polycyclic aromatic compounds

The affinities of bi- and polycyclic aromatic compounds for nitrosonium ion (A_NO⁺ A_{NO^ + } ) were calculated at the RI-MP2/L1 and DFT/PBE/3z levels of theory. Both methods gave generally similar geometric parameters of nitrosonium complexes. The formation of pincer complexes in which the NO⁺ ion is linked to two aromatic rings is more energetically favorable than the formation of analogous complexes through external binding of NO⁺ to one aromatic ring. Linear correlations were found between the calculated A_NO⁺ A_{NO^ + } values of aromatic compounds and experimental equilibrium constants for the reactions of these compounds with nitrosonium ion in solution. Structural peculiarities of the examined nitrosonium complexes are discussed.