Stannylenes: Structures, Electron Affinities, Ionization Energies, and Singlet–Triplet Gaps of SnX2/SnXY and XSnR/SnR2/RSnR′ Species (X; Y = H, F, Cl, Br, I, and R; R′ = CH3, SiH3, GeH3, SnH3)

Fast kinetics studies of the Lewis acid-base complexation of transient stannylenes with σ- and π-donors in solution

The Lewis acid-base complexation chemistry of dimethyl- and diphenylstannylene (SnMe2 and SnPh2, respectively) in hexanes solution has been studied by laser photolysis methods. Complexation of the two stannylenes with a series of nine O-, S-, and N-donors (including cyclic and acyclic dialkyl ethers and sulfides, a primary, secondary, and tertiary amine, ethyl acetate and acetone), two alkenes, and an alkyne proceeds rapidly and reversibly to generate the corresponding stannylene-donor Lewis pairs, which have been detected in each case by time-resolved UV-vis absorption spectroscopy. The complexes exhibit UV-vis absorption maxima in the range of λmax ∼ 310-405 nm depending on the donor and substitution at tin. Bimolecular rate constants for complexation (kC), which could be determined for 14 of the 24 Lewis pairs that were studied, were found to fall within a factor of four of the diffusional limit in all cases, with SnMe2 showing consistently higher reactivity than SnPh2. Equilibrium constants for complexation (KC) could be measured for all but one of the stannylene-π- and O-donor pairs, the values corresponding to (gas phase) binding free energies in the range of +1.1 to -3.9 kcal mol-1. Comparison of the experimental equilibrium constants for complexation of SnMe2 and SnPh2 with methanol and diethyl ether to those measured previously for the homologous silylenes and germylenes indicates that Lewis acidity decreases in the order SiR2 > SnR2 > GeR2 for both the dimethyl- and diphenyltetrylene series, the diphenyl derivatives exhibiting significantly stronger Lewis acidity in all three cases. The experimental trends in the binding energies and UV-vis spectra of the complexes are reproduced well by density functional theory (DFT) calculations, which have been carried out at the (TD)ωB97XD/def2-TZVP level of theory. The experimental data also show evidence of a reaction between tetramethyldistannene (Me2Sn[double bond, length as m-dash]SnMe2, 4a) and amine donors, which is suggested to afford the corresponding amine-stabilized stannylidenestannylene structure. The mechanistic proposal is supported by DFT calculations of the complexation of 4a and SnMe2 with model O-, S- and N-donors.

Toward unsaturated stannylenes Y2ZSn: and related compounds with triplet electronic ground states

Distribution of electrons between the Y₂Z: moiety and the triplet Sn atom in Y₂ZSn: and representations of singlet and triplet Y₂ZSn: and Y₂Z: electronic configurations.

Performance of Møller-Plesset second-order perturbation theory and density functional theory in predicting the interaction between stannylenes and aromatic molecules

The performances of Møller-Plesset second-order perturbation theory (MP2) and density functional theory (DFT) have been assessed for the purposes of investigating the interaction between stannylenes and aromatic molecules. The complexes between SnX2 (where X = H, F, Cl, Br, and I) and benzene or pyridine are considered. Structural and energetic properties of such complexes are calculated using six MP2-type and 14 DFT methods. The assessment of the above-mentioned methods is based on the comparison of the structures and interaction energies predicted by these methods with reference computational data. A very detailed analysis of the performances of the MP2-type and DFT methods is carried out for two complexes, namely SnH2-benzene and SnH2-pyridine. Of the MP2-type methods, the reference structure of SnH2-benzene is reproduced best by SOS-MP2, whereas SCS-MP2 is capable of mimicking the reference structure of SnH2-pyridine with the greatest accuracy. The latter method performs best in predicting the interaction energy between SnH2 and benzene or pyridine. Among the DFT methods, ωB97X provides the structures and interaction energies of the SnH2-benzene and SnH2-pyridine complexes with good accuracy. However, this density functional is not as effective in reproducing the reference data for the two complexes as the best performing MP2-type methods. Next, the DFT methods are evaluated using the full test set of SnX2-benzene and SnX2-pyridine complexes. It is found that the range-separated hybrid or dispersion-corrected density functionals should be used for describing the interaction in such complexes with reasonable accuracy.

A quest for stable 2,5-bis(halobora)cyclopentenylidene and its Si, Ge, Sn and Pb analogs at theoretical levels

Interesting π- and σ-bond hyperconjugations cause the unusual stability of the puckered Arduengo type divalents with electron deficient boron atoms.

2-Adamantylidene and its heavier analogues: hyperconjugation versus lone pair stability and electrophilicity versus nucleophilicity

Too heavy to bend: The Cieplak-type hyperconjugative interaction mainly contributes to the stability of 2C and 2Si whereas the inertness of lone pairs is the major factor for 2Ge and 2Sn. These molecules (2X; X = C–Sn) can be classified as a class of ambiphilic compounds.

Diatomic silylynes, germylynes, stannylynes, and plumbylynes: structures, dipole moments, dissociation energies, and quartet-doublet gaps of EH and EX (E = Si, Ge, Sn, Pb; X = F, Cl, Br, I)

Systematic theoretical studies of the carbyne and halocarbyne analogues E-H and E-X (E = Si, Ge, Sn, Pb; X = F, Cl, Br, I) were carried out with ab initio coupled-cluster methods using very large basis sets. The (2)Π state is the ground electronic state for all these compounds. The quartet-doublet energy separations, equilibrium distances, and dissociation energies for these species are predicted. The quartet-doublet splittings fall in the order EF > ECl > EBr > EI > EH for a given metal E; and PbX > GeX > SnX > SiX for the same halogen atom X. The dipole moments span a large range, from 0.08 debye (GeH) to 3.58 debye (PbCl). The dissociation energies range from 1.84 eV (PbH) to 6.15 eV (SiF).