Carbon-13, 1H spin-spin coupling. V—π-benzenechromium tricarbonyl and the π-tropyliumchromium tricarbonyl cation

The ¹³C, ¹H spin-spin coupling constants have been determined for π-benzenechromium tricarbonyl (3) and the π-tropyliumchromium tricarbonyl cation using the ¹³C{²H}double resonance technique described in a previous paper. In addition, conventional analysis of the ¹H-coupled ¹³C NMR spectrum of 3 was carried out and the ¹H NMR spectrum of 3 partially oriented in the nematic phase was analysed. Both treatments also allowed the determination of the ¹H, ¹H coupling constants for this compound. The ⁿJ(CH) results are discussed on the basis of structural data and the theoretical results available. The complexation effects for ¹J(CH) are found to correlate with the C? H overlap population and hybridization changes, and those for ³J(CH) with the CC bond lengths and π-bond orders. The dependence of ²J(CH) on CC bond length as well as on the CCH bond angle is indicated. The liquid crystal results are compared with those of related studies.     

Arsenites and antimonites as ligands toward π-cyclopentadienylmanganese tricarbonyl

π-Cyclopentadienyldicarbonylmanganese(I) complexes of methyl, ethyl, butyl and phenyl arsenites and antimonites have been prepared for comparison with the analogous phosphite systems. The carbonyl IR spectra suggest that the order of decresaing electron density on the manganese atom is Sb(OR)₃ P(OR)₃ As(OR)₃, and E(O-alkyl)₃ E(O-aryl)₃ where E = P, As, and Sb.     

A novel route to bicyclic iron tricarbonyl complexes involving π-allyl and σ-components

Nucleophilic attack of CN⁻ on bicyclo[3.2.1]octadienyl-, bicyclo[3.2.2]- nonadienyl-, and 6,7-benzobicyclo[3.2.2]nonadienyliron tricarbonyl tetrafluoroborates, results in mixed-type complexes containing both σ and π-allyl bonds. The cyano group in the products is located exo to the bicyclic ring.In contrast, the three cations react smoothly with I⁻; carbon monoxide is displaced to give iron complexes containing covalently-bound halogen.     

Mass spectral studies of some β-diketones and their beryllium complexes

Detailed comparison of the fragmentation behavior of a series of beryllium β-diketonates with that of the corresponding series of β-diketones reveals a number of striking differences. A-typical fragmentations are observed for diketones and diketonates with trifluoromethyl and α-phenyl substituents.     

Nachweis von π → σ-Umlagerungen bei Ligandenverdrängungsreaktionen von π-Allyl-π-cyclopentadienyl-Palladiumkomplexen

It has been proved by NMR. measurements at low temperatures that the ligand displacement reactions of (π-all)Pd(π-C₅H₅) and Lewis bases L yielding PdL₄ proceed by a π → σ rearrangement of the allylic group as the primary step. The organic reaction product is the 1-isomer of the corresponding allylcyclopentadiene but in the reactions of (π-1,1,2-Me₃C₃H₂)Pd(π-C₅H₅) with L besides the isomeric allylcyclopentadienes also 2,3-dimethylbutadiene and cyclopentadiene are formed. The reaction mechanism will be discussed.     

Mass spectral studies of some aryl and aroyl derivatives of glyoxime

Mass spectra of two diaroylglyoximes (Ia and Ib) are reported and compared with those of the corresponding dehydration products, 3,4-diaroyl-1,2,5-oxadiazoles (IIIa and IIIb, respectively). In Ia and Ib, unlike in diarylglyoximes (Id and Ie), the largest ion is [M — 18]⁺, but this does not form in the ion source by a simple thermal dehydration. Similar spectra have been obtained for an alkyl aroyl derivative of glyoxime (Ic) and an isonitroso-β-diketone (II). A specific electron-impact-induced rearrangement leading to the formation of carboxylic acids has been observed in the mass spectra of all the acylated oximes under investigation.     

Tricarbonyl(η5‐formylcyclopentadienyl)manganese(I) and tricarbonyl(η5‐formylcyclopentadienyl)rhenium(I) containing short π(CO)...π(CO) and π(CO)...π interactions

The structures of tricarbonyl(formylcyclopentadienyl)manganese(I), [Mn(C₆H₅O)(CO)₃], (I), and tricarbonyl(formylcyclopentadienyl)rhenium(I), [Re(C₆H₅O)(CO)₃], (II), were determined at 100 K. Compounds (I) and (II) both possess a carbonyl group in a trans position relative to the substituted C atom of the cyclopentadienyl ring, while the other two carbonyl groups are in almost eclipsed positions relative to their attached C atoms. Analysis of the intermolecular contacts reveals that the molecules in both compounds form stacks due to short attractive π(CO)...π(CO) and π(CO)...π interactions, along the crystallographic c axis for (I) and along the [201] direction for (II). Symmetry‐related stacks are bound to each other by weak intermolecular C—H...O hydrogen bonds, leading to the formation of the three‐dimensional network.     

Understanding the Fundamental Role of π/π, σ/σ, and σ/π Dispersion Interactions in Shaping Carbon‐Based Materials

Noncovalent interactions involving aromatic rings, such as π‐stacking and CH/π interactions, are central to many areas of modern chemistry. However, recent studies proved that aromaticity is not required for stacking interactions, since similar interaction energies were computed for several aromatic and aliphatic dimers. Herein, the nature and origin of π/π, σ/σ, and σ/π dispersion interactions has been investigated by using dispersion‐corrected density functional theory, energy decomposition analysis, and the recently developed noncovalent interaction (NCI) method. Our analysis shows that π/π and σ/σ stacking interactions are equally important for the benzene and cyclohexane dimers, explaining why both compounds have similar boiling points. Also, similar dispersion forces are found in the benzene???methane and cyclohexane???methane complexes. However, for systems larger than naphthalene, there are enhanced stacking interactions in the aromatic dimers adopting a parallel‐displaced configuration compared to the analogous saturated systems. Although dispersion plays a decisive role in stabilizing all the complexes, the origin of the π/π, σ/σ, and σ/π interactions is different. The NCI method reveals that the dispersion interactions between the hydrogen atoms are responsible for the surprisingly strong aliphatic interactions. Moreover, whereas σ/σ and σ/π interactions are local, the π/π stacking are inherently delocalized, which give rise to a non‐additive effect. These new types of dispersion interactions between saturated groups can be exploited in the rational design of novel carbon materials.     

The proton spectrum including 13C-satellites of π-benzenechromium tricarbonyl in a nematic solvent

The proton spectrum of π-benzenechromium tricarbonyl with ¹³C-satellites due to ring- and carbonyl-carbons at natural abundance has been investigated in a nematic solvent. The structural data are found to be in agreement with those from electron and neutron diffraction measurements. The proton–proton indirect coupling constants have also been determined.     

Mass spectral studies of some carbohydrate enones

A study of the mass spectra of ethyl 2,3-dideoxy-α-d-glycero-hex-2-enopyranosid-4-ulose1a, its 6-0-acetyl derivative1b, and methyl 3,4-dideoxy-α-d-glycero-hex-3-enopyranosidulose2a indicates that the main fragmentation of these compounds occurs by a retro-Diels-Alder type cleavage. Recognition of the ions produced by this cleavage provides a means of allocating the position of the α,β-unsaturated chromophore in carbohydrate enones. Fragmentation of molecular ions of1a and1b also occurred by direct loss of individual ring substituents to give ions which retain the pyranoid nucleus. The fragmentation pathways suggested are supported by accurate mass measurements of the salient fragment ions of1a.