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Quantum chemical calculations of the anions AeF− (Ae=Be−Ba) have been carried out using ab initio methods at the CCSD(T)/def2‐TZVPP level and density functional theory employing BP86 with various basis sets. The detailed bonding analyses using different charge‐ and energy partitioning methods show that the molecules possess three distinctively different dative bonds in the lighter species with Ae=Be, Mg and four dative bonds when Ae=Ca, Sr, Ba. The occupied 2p atomic orbitals (AOs) and to a lesser degree the occupied 2s AO of F− donate electronic charge into the vacant spx(σ) and p(π) orbitals of Be and Mg which leads to a triple bond Ae F−. The heavier Ae atoms Ca, Sr, Ba use their vacant (n‐1)d AOs as acceptor orbitals which enables them to form a second σ donor bond with F− that leads to quadruply bonded Ae F− (Ae=Ca−Ba). The presentation of molecular orbitals or charge distribution using only one isodensity value may give misleading information about the overall nature of the orbital or charge distribution. Better insights are given by contour line diagrams. The ELF calculations provide monosynaptic and disynaptic basins of AeF− which nicely agree with the analysis of the occupied molecular orbitals and with the charge density difference maps. A particular feature of the covalent bonds in AeF− concerns the inductive interaction of F− with the soft valence electrons in the (n)s valence orbitals of Ae. The polarization of the (n)s2 electrons induces a (n)spx hybridized lone‐pair orbital at atom Ae, which yields a large dipole moment with the negative end at Ae. The concomitant formation of a vacant (n)spx AO of atom Ae, which overlaps with the occupied 2p(σ) AO of F−, leads to a strong covalent σ bond. [ABSTRACT FROM AUTHOR]

Carbodicarbene (CDC) has become an emerging ligand in many fields due to its strong σ‐donating ability.

The boron atoms react with carbon monoxide and dinitrogen forming the end‐on bonded NNBCO complex in solid neon or in nitrogen matrices. The NNBCO complex rearranges to the (η2‐N2)BCO isomer with a more activated side‐on bonded dinitrogen ligand upon visible light excitation. (η2‐N2)BCO and its weakly CO‐coordinated complexes further isomerize to the NBNCO and B(NCO)2 molecules with N−N bond being completely cleaved under UV light irradiation. The geometries, energies and vibrational spectra of the molecules are calculated with quantum chemical methods and the electronic structures are analyzed with charge‐ and energy‐partitioning methods. [ABSTRACT FROM AUTHOR]

Two structural isomers containing five second‐row element atoms with 24 valence electrons were generated and identified by matrix‐isolation IR spectroscopy and quantum chemical calculations. The OCBNO complex, which is produced by the reaction of boron atoms with mixtures of carbon monoxide and nitric oxide in solid neon, rearranges to the more stable OBNCO isomer on UV excitation. Bonding analysis indicates that the OCBNO complex is best described by the bonding interactions between a triplet‐state boron cation with an electron configuration of (2s)0(2pσ)0(2pπ)2 and the CO/NO− ligands in the triplet state forming two degenerate electron‐sharing π bonds and two ligand‐to‐boron dative σ bonds. [ABSTRACT FROM AUTHOR]

Homoleptic Group 4 metal carbonyl cation and neutral complexes were prepared in the gas phase and/or in solid neon matrix. Infrared spectroscopy studies reveal that both zirconium and hafnium form eight‐coordinate carbonyl neutral and cation complexes. In contrast, titanium forms only the six‐coordinate Ti(CO)6+ and seven‐coordinate Ti(CO)7. Titanium octacarbonyl Ti(CO)8 is unstable as a result of steric repulsion between the CO ligands. The 20‐electron Zr(CO)8 and Hf(CO)8 complexes represent the first experimentally observed homoleptic octacarbonyl neutral complexes of transition metals. The molecules still fulfill the 18‐electron rule, because one doubly occupied valence orbital does not mix with any of the metal valence atomic orbitals. Zr(CO)8 and Hf(CO)8 are stable against the loss of one CO because the CO ligands encounter less steric repulsion than Zr(CO)7 and Hf(CO)7. The heptacarbonyl complexes have shorter metal−CO bonds than that of the octacarbonyl complexes due to stronger electrostatic and covalent bonding, but the significantly smaller repulsive Pauli term makes the octacarbonyl complexes stable. [ABSTRACT FROM AUTHOR]

The octacarbonyl cation and anion complexes of actinide metals [An(CO)8]+/− (An=Th, U) are prepared in the gas phase and are studied by mass‐selected infrared photodissociation spectroscopy. Both the octacarbonyl cations and anions have been characterized to be saturated coordinated complexes. Quantum chemical calculations by using density functional theory show that the [Th(CO)8]+ and [Th(CO)8]− complexes have a distorted octahedral (D4h) equilibrium geometry and a doublet electronic ground state. Both the [U(CO)8]+ cation and the [U(CO)8]− anion exhibit cubic structures (Oh) with a 6A1g ground state for the cation and a 4A1g ground state for the anion. The neutral species [Th(CO)8] (Oh; 1A1g) and [U(CO)8] (D4h; 5B1u) have also been calculated. Analysis of their electronic structures with the help on an energy decomposition method reveals that, along with the dominating 6d valence orbitals, there are significant 5f orbital participation in both the [An]←CO σ donation and [An]→CO π back donation interactions in the cations and anions, for which the electronic reference state of An has both occupied and vacant 5f AOs. The trend of the valence orbital contribution to the metal–CO bonds has the order of 6d≫5f>7s≈7p, with the 5f orbitals of uranium being more important than the 5f orbitals of thorium. [ABSTRACT FROM AUTHOR]

The lanthanide octacarbonyl anion complexes Ln(CO)8− (Ln=Tm, Yb, Lu) were produced in the gas phase and detected by mass‐selected infrared photodissociation spectroscopy in the carbonyl stretching‐frequency region. By comparison of the experimental CO‐stretching frequencies with calculated data, which are strongly red‐shifted with respect to free CO, the Yb(CO)8− and Lu(CO)8− complexes were determined to possess octahedral (Oh) symmetry and a doublet X2A2u (Yb) and singlet X1A1g (Lu) electronic ground state, whereas Tm(CO)8− exhibits a D4h equilibrium geometry and a triplet X3B1g ground state. The analysis of the electronic structures revealed that the metal‐CO attractive forces come mainly from covalent orbital interactions, which are dominated by [Ln(d)]→(CO)8 π backdonation and [Ln(d)]←(CO)8 σ donation (contributes ≈77 and 16 % to covalent bonding, respectively). The metal f orbitals play a very minor role in the bonding. The electronic structure of all three lanthanide complexes obeys the 32‐electron rule if only those electrons that occupy the valence orbitals of the metal are considered. Follow the rules: The lanthanide anion complexes Ln(CO)8− (Ln=Tm, Yb, Lu) were experimentally observed and spectroscopically characterized in the gas phase. The metal–CO bonds were easily understood in terms of donor–acceptor interactions. The bonding situation follows the 32‐electron rule if the symmetry of the orbitals is taken into account. The dominant valence functions of the lanthanide atoms are the d orbitals, the stabilizing contribution of the f functions is very small. [ABSTRACT FROM AUTHOR]

Abstract: The viability of noble gas axled boron nanowheels NgnM©B10− (Ng=Ar–Rn; M=Nb, Ta; n=1, 2) is explored by ab initio computations. In the resulting Ng2–M complexes, the Ng‐M‐Ng nanorod passes through the center of the B10− ring, providing them with an inverse sandwich‐like structure. While in the singly Ng bound analogue, the Ng binding enthalpy Hb at 298 K ranges from 2.5 to 10.6 kcal mol−1, in doubly Ng bound cases it becomes very low for the Ng2M©B10−→Ng+NgM©B10− dissociation channel, except for the case of Rn, for which the corresponding Hb values are 3.4 (Nb) and 4.0 kcal mol−1 (Ta). For a given Ng, Ta has slightly higher Ng‐binding ability than Nb. The corresponding free‐energy changes indicate that these systems, particularly the Xe and Rn complexes, are good candidates for experimental realization in a low‐temperature matrix. The Ng−M bonds were found to be covalent in nature, as reflected in their large Wiberg bond indices, formation of a 2c–2e σ orbital between Ng and M centers in natural bond orbital and adaptive natural density partitioning (AdNDP) analyses, and the short Ng−M distances. Energy decomposition analysis and a study on the natural orbitals for chemical valence show that the Ng−M contact is supported mainly by the orbital and electrostatic interactions, with almost equal contributions. Although both the Ng→M σ donation and Ng←M π backdonation play roles in the origin of orbital interaction, the former is significantly dominant over the latter. Further, AdNDP analysis indicates that the doubly aromatic character (both σ and π) in MB10− clusters is not perturbed by the interaction with Ng atoms. [ABSTRACT FROM AUTHOR]

Iron(0) pentacarbonyl complexes of gold(I), [Mes3PAu-Fe(CO)5][SbF6] ( 1) and [(IPr*)Au-Fe(CO)5][SbF6] ( 2) (Mes=2,4,6-trimethylphenyl; IPr*=1,3-bis(2,6-bis(diphenylmethyl)-4-methylphenyl)imidazol-2-ylidene) have been synthesized using Mes3PAuCl and (IPr*)AuCl as the gold(I) precursor, AgSbF6 halide ion abstractor, and the Lewis base Fe(CO)5. The Au−Fe bond lengths of these metal-only Lewis pair complexes are significantly shorter than the sum of the experimentally derived covalent radii of Au and Fe. The v̄(CO) bands of the molecules show a notable blueshift relative to those observed for free Fe(CO)5, indicating a substantial reduction in Fe→CO backbonding upon its coordination to gold(I) with either Mes3P or IPr* supporting ligands (L). The analysis of the electronic structure with quantum chemical method suggests that the Au−Fe bond consists mainly of [LAu]+←Fe(CO)5 σ-donation and weaker [LAu]+→Fe(CO)5 π-backdonation. The donor strength of Fe(CO)5 is similar to that of CO. [ABSTRACT FROM AUTHOR]

The parent thioketene S-oxide H2CCSO has been generated in the gas phase through flash vacuum pyrolysis (ca. 1000 K) of vinyl sulfoxide H2CC(Br)−S(O)CF3 via the intermediacy of a novel vinyl sulfinyl radical H2C=C(Br)−SO ( syn and anti conformers). Upon irradiation at 266 nm, H2CCSO decomposes into HCCH/SO and H2CS/CO in cryogenic Ar matrix. Whereas, visible-light irradiations result in syn↔ anti conformational interconversion in H2C=C(Br)−SO. The molecular structures of H2CCSO and isomers are computationally studied at the CCSD(T)-F12/VTZ-F12 level of theory, and the bonding properties of H2CCSO are analyzed with the EDA-NOCV method at the M06-2X/TZ2P level. [ABSTRACT FROM AUTHOR]

The 2-aminophenylaluminum dihydride (2-TMP-C6H4)AlH2 ( 2) has been prepared and characterized for the first time. Compound 2 features an intramolecular N⋅⋅⋅Al donor-acceptor bond. 2 reacted with N-methylpyrrole and N-methylindole (both at 50 °C) by means of the elusive AlH C(sp2)−H dehydroalumination to aluminum heteroaryls ( 3 and 4). Moreover, 2 reacted with PhCCSiMe3 (at room temperature) and Ph2CCNR (R= iPr or 2,6- iPr2C6H3, at −30 to 20 °C ) to yield aluminaindene heterocycle ( 8) and alumina-aza-naphthalene heterocycle ( 9 and 10), respectively. These reactions underwent hydroalumination followed by AlH C(sp2)−H dehydroalumination. The reaction mechanism has been studied by combining experiment and quantum chemical calculations, with the result that the key heteroarene or arene C(sp2)−H bond activation is involved under cooperative interaction by the inherent N/Al donor/acceptor pair. The reported reactions open a straightforward route to heteroaryl and unique heterocyclic aluminum compounds. [ABSTRACT FROM AUTHOR]

Short interatomic distances below standard values for a single bond are usually identified with double or triple bonds. The synthesis and spectroscopic characterization of a molecule is reported where the distance between two beryllium atoms is shorter than a standard double bond but there is no bond. The cyclic diberyllium dioxide Be2O2 molecule, which is coordinated by two noble gas atoms in Ng−Be2O2−Ng′ (Ng, Ng′=Ne, Ar, Kr, Xe) was isolated and spectroscopically identified in low-temperature matrices. The complexes possess very short Be−Be distances, but the analysis of the electronic structure reveals that there is no chemical bond. [ABSTRACT FROM AUTHOR]

Quantum chemical calculations using density functional theory with the TPSS+D3(BJ) and M06-2X+D3(ABC) functionals have been carried out to understand the mechanisms of catalyst-free hydrogermylation/hydrostannylation reactions between the two-coordinate hydrido-tetrylenes :E(H)(L+) (E=Ge or Sn, L+=N(Ar+)(Si iPr3); Ar+=C6H2{C(H)Ph2}2 iPr-2,6,4) and a range of unactivated terminal (C2H3R, R=H, Ph, or tBu) and cyclic [(CH)2(CH2)2(CH2) n, n=1, 2, or 4] alkenes. The calculations suggest that the addition reactions of the germylenes and stannylenes to the cyclic and acyclic alkenes occur as one-step processes through formal [2+2] addition of the E−H fragment across the C−C π bond. The reactions have moderate barriers and are weakly exergonic. The steric bulk of the tetrylene amido groups has little influence on the activation barriers and on the reaction energies of the anti-Markovnikov pathway, but the Markovnikov addition is clearly disfavored by the size of the substituents. The addition of the tetrylenes to the cyclic alkenes is less exergonic than the addition to the terminal alkenes, which agrees with the experimentally observed reversibility of the former reactions. The hydrogermylation reactions have lower activation energies and are more exergonic than the stannylene addition. An energy decomposition analysis of the transition state for the hydrogermylation of cyclohexene shows that the reaction takes place with simultaneous formation of the Ge−C and (Ge)H−C′ bonds. The dominant orbitals of the germylene are the σ-type lone pair MO of Ge, which serves as a donor orbital, and the vacant p(π) MO of Ge, which acts as acceptor orbital for the π* and π MOs of the olefin. Inspection of the transition states of some selected reactions suggests that the differences between the activation energies come from a delicate balance between the deformation energies of the interacting species and their interaction energies. [ABSTRACT FROM AUTHOR]

Quantum chemical calculations of reaction mechanisms for the formal [2+2] addition of ethylene and acetylene to the amido-substituted digermyne and distannyne Ph2NEENPh2 (E=Ge, Sn) have been carried out by using density functional theory at the BP86/def2-TZVPP level. The nature and bonding situations were studied with the NBO method and with the charge and energy decomposition analysis EDA-NOCV. The addition of ethylene to Ph2NEENPh2 takes place through an initial [2+1] addition to one metal atom and consecutive rearrangement to four-membered cyclic species, which feature a weak EE bond. Rotation about the CC bond with concomitant rupture of the EE bond leads to the 1,2-disubstituted ethanes, which have terminal E(NPh2) groups. The overall reaction Ph2NEENPh2+C2H4→(Ph2N)EC2H4E(NPh2) has very low activation barriers and is slightly exergonic for E=Ge but slightly endergonic for E=Sn. The analysis of the electronic structure shows that there is charge donation of nearly one electron to the ethylene moiety already in the first part of the reaction. The energy partitioning analysis suggests that the HOMO(Ph2NEENPh2)→LUMO(C2H4) interaction has a similar strength as the HOMO(C2H4)→LUMO(Ph2NEENPh2) interaction. The [2+2] addition of acetylene to Ph2NEENPh2 also takes place through an initial [2+1] approach, which eventually leads to 1,2-disubstituted olefins (Ph2N)EC2H2E(NPh2). The formation of the energetically lowest lying conformations of cis-(Ph2N)EC2H2E(NPh2), which occurs with very low activation barriers, is clearly exergonic for the germanium and the tin compound. The trans-coordinated isomers of (Ph2N)EC2H2E(NPh2) are slightly lower in energy than the cis form but they are separated by a substantial energy barrier for the rotation about the CC bond. The energy decomposition analysis indicates that the initial reaction takes place under formation of electron-sharing bonds between triplet fragments rather than HOMO-LUMO interactions. [ABSTRACT FROM AUTHOR]

Homoleptic Group 4 metal carbonyl cation and neutral complexes were prepared in the gas phase and/or in solid neon matrix. Infrared spectroscopy studies reveal that both zirconium and hafnium form eight‐coordinate carbonyl neutral and cation complexes. In contrast, titanium forms only the six‐coordinate Ti(CO)6+ and seven‐coordinate Ti(CO)7. Titanium octacarbonyl Ti(CO)8 is unstable as a result of steric repulsion between the CO ligands. The 20‐electron Zr(CO)8 and Hf(CO)8 complexes represent the first experimentally observed homoleptic octacarbonyl neutral complexes of transition metals. The molecules still fulfill the 18‐electron rule, because one doubly occupied valence orbital does not mix with any of the metal valence atomic orbitals. Zr(CO)8 and Hf(CO)8 are stable against the loss of one CO because the CO ligands encounter less steric repulsion than Zr(CO)7 and Hf(CO)7. The heptacarbonyl complexes have shorter metal−CO bonds than that of the octacarbonyl complexes due to stronger electrostatic and covalent bonding, but the significantly smaller repulsive Pauli term makes the octacarbonyl complexes stable. [ABSTRACT FROM AUTHOR]