•The difluorine dications [Ph2P(CH2)xPPh2CF2]2+ with x = 2, 3, which are formal adducts of F+ to the carbones [Ph2P(CH2)xPPh2C] with x = 2, 3 have been synthesized and structurally characterized. The bonding situation was analyzed with quantum chemical methods.The difluorine dications [Ph2P(CH2)nPPh2CF2]2+(Br−)2 with n = 2, 3 have been synthesized by reacting Br2CF2 with the chelating ligands Ph2P(CH2)nPPh2 (dppe, n = 2; dppp, n = 3). The dications [Ph2P(CH2)nPPh2CF2]2+ were structurally characterized by x-ray analysis and NMR spectroscopy. The doubly charged species are formally derived from the cyclic carbones [Ph2P(CH2)nPPh2C] where two F+ ions are attached to the divalent C(0) atom. The transient mono addition cations [Ph2P(CH2)nPPh2CF2Br]+ were observed but could not be isolated. The bonding analyses of [Ph2P(CH2)nPPh2CF2]2+ and [Ph2P(CH2)nPPh2CF]+ suggest that the P-C-P bonds should be considered as classical electron-sharing bonds.Download high-res image (51KB)Download full-size imageThe difluorine dications [Ph2P(CH2)nPPh2CF2]2+(Br−)2 with n = 2, 3 have been synthesized and the bonding situation was analyzed with quantum chemical methods, which suggest that the molecules should be described with electron-sharing bonds (model B) rather than dative bonds (model A).

Different model compounds were applied in step-growth condensation reactions with guanidine hydrochloride in order to explore the scope of tri- and oligoamine applicability for phantom ring-closing condensation polymerization processes. The selective formation of five-membered rings was proven by APCI mass spectrometry, different one- and two-dimensional homo- and heteronuclear coupling NMR techniques and investigated via quantum chemical calculations. Furthermore the possibility of ring-closing reactions among guanidine hydrochloride and merely secondary amines was precluded. The obtained oligomers were exposed to antibacterial tests and exhibited a moderate activity towards Escherichia coli.

The structure and stability towards decomposition of eight novel noble gas compounds having a Xe–Xe bond, which have not been experimentally observed so far, have been studied computationally. In addition, the nature of the Xe–Xe interaction has been analysed by a combination of the most popular methods to study the bonding situation of molecules, i.e. Natural Bond Orbital, Atom in Molecules and Energy Decomposition Analysis methods. Two related series of compounds have been considered: HXeXeX (X = F to I) and RXeXeR′ (R = halogen atom). Our calculations indicate that the replacement of the fluorine atom by a heavier group 17 congener in the HXeXeX series leads to a less stable compound, thus making more difficult its experimental observation. The same effect occurs in the RXeXeR′ series, but these species are more kinetically protected against the decomposition reaction and therefore, their experimental detection is more likely.

The synthesis and X-ray structure analysis of the carbodiphosphorane (CDP) complexes [Hg{C(PPh3)2}2][Hg2I6] and [Cu{C(PPh3)2}2]I are reported. The cations [Hg{C(PPh3)2}2]2+ and [Cu{C(PPh3)2}2]+ have approximately linearly coordinated metal atoms. Quantum chemical calculations of model compounds bearing N-heterocyclic carbene (NHC) ligands, [M(NHC)2] and [M{C(PH3)2}2] (M = Cu+, Ag+, Au+, Zn2+, Cd2+, Hg2+), have been carried out at the BP86/TZ2P level. The metal–ligand bonds are very strong, and the bond dissociation energies exhibit a V-shaped trend for first-, second-, and third-row transition metals: Ag+ < Cu+ < Au+ and Cd2+ < Zn2+ < Hg2+. The investigation of the bonding situation in the complexes using an energy decomposition analysis shows that the metal–ligand bonding comes mainly from electrostatic attraction. Inspection of the orbital interactions shows that the Mq←(NHC)2 and Mq←{C(PH3)2}2 σ donation provides between 65 and 75% of the total orbital interactions ΔEorb. The contribution of the Mq→(NHC)2 and Mq→{C(PH3)2}2 π back-donation is very weak. The nature and strength of the donor–acceptor bonds of the two-electron donor ligand NHC and the four-electron donor ligand CDP with the group 11 and group 12 metal cations are very similar.

The equilibrium geometries and bond dissociation energies of the 14 valence electron (VE) complexes [(PMe3)2M−BeCl2], [(PMe3)2M−BeClMe], and [(PMe3)2M−BeMe2] with M = Ni, Pd, and Pt have been calculated using density functional theory at the BP86/TZ2P level. The nature of the M−Be bond was analyzed with the NBO charge decomposition analysis and the EDA energy decomposition analysis. The theoretical results predict the equilibrium structures with a T-shaped geometry at the transition metal where the PMe3 ligands are in the axial positions. The calculated bond dissociation energies show that the M−E bond strengths are in the range of donor−acceptor complexes of divalent beryllium compounds with ammonia. The bond strength decreases when the substituent at beryllium changes from Cl to CH3. The NBO analysis shows a negative charge at the BeX2 fragment, which indicates a net charge flow from the transition metal fragment to the beryllium fragment. The energy decomposition analysis of the M−Be bonds suggests two donor−acceptor bonds with σ and π symmetry where the transition metal fragment is a double donor with respect to the beryllium ligand. The π component of the [Ni]→BeXX′ donation is much smaller than the σ component.

Quantitative evaluations of the aromaticity (antiaromaticity) of neutral exocyclic substituted cyclopropenes (HC)2C═X (X = BH to InH (group 13), CH2 to SnH2 (group 14), NH to SbH (group 15), O to Te (group 16)) by their computed extra cyclic resonance energies (ECRE, via the block-localized wave function method) and by their aromatic stabilization energies (ASEs, via energy decomposition analyses) correlate satisfactorily (R2 = 0.974). Electronegative X-based substituents increase the aromaticity of the cyclopropene rings, whereas electropositive substituents have the opposite effect. For example, (HC)2C═O is the most aromatic (ECRE = 10.3 kcal/mol), and (HC)2C═InH is the most antiaromatic (ECRE = −15.0 kcal/mol). The most refined dissected nucleus-independent chemical shift magnetic aromaticity index, NICS(0)πzz, also agrees with both energetic indexes (R2 = 0.968, for ECRE; R2 = 0.974, for ASE), as do anisotropy of the induced current density plots.

The structure and stability towards decomposition of eight novel noble gas compounds having a Xe–Xe bond, which have not been experimentally observed so far, have been studied computationally. In addition, the nature of the Xe–Xe interaction has been analysed by a combination of the most popular methods to study the bonding situation of molecules, i.e. Natural Bond Orbital, Atom in Molecules and Energy Decomposition Analysis methods. Two related series of compounds have been considered: HXeXeX (X = F to I) and RXeXeR′ (R = halogen atom). Our calculations indicate that the replacement of the fluorine atom by a heavier group 17 congener in the HXeXeX series leads to a less stable compound, thus making more difficult its experimental observation. The same effect occurs in the RXeXeR′ series, but these species are more kinetically protected against the decomposition reaction and therefore, their experimental detection is more likely.