Journey through the potential energy surfaces for the isomerization and decomposition reactions of the telluroformaldehyde analogues: H2A═Te and HFA═Te (A = C, Si, and Ge).

The unavailability of monomeric heavy ketone analogues has been ascribed to the evanescence of the very reactive A═E double bond (A and E are the heavier group 14 and group 16 elements, respectively). Can the isolation of any of the monomeric telluro-ketones be assisted by an energetic favorability on its potential energy surface (PES)? In this light, the reaction pathways for the isomerization and decomposition reactions of H2A═Te and HFA═Te (A = C, Si, and Ge) molecules on their singlet state PES have been studied using second-order Møller-Plesset perturbation theory (MP2). The barrier heights reported suggest that telluroformaldehyde, silanetellone, and germatellone are kinetically more resistant to unimolecular reactions than the corresponding lighter chalcogen analogues. However, upon replacing a hydrogen atom by fluorine, the barrier heights of most of the isomerization and decomposition reactions are lowered. Among the unimolecular reactions studied for the H2A═Te and HFA═Te (A = C, Si, and Ge) molecules, the decomposition of cis-FGeTeH into HF and GeTe is found to be the most facile reaction, with a barrier height of only 4.6 kcal/mol. We also predict the ground state telluro-ketones to be viable molecules, as they have no imaginary vibrational frequencies and their lowest vibrational frequencies are always >100 cm(-1). In view of the scarcity of information on the chemistry of the mentioned telluro-ketones, the molecular parameters of various isomers and decomposition products have been reported, and should be useful for future experimental investigations.

Novel germanetellones: XYGe=Te (X, Y = H, F, Cl, Br, I and CN) - structures and energetics. Comparison with the first synthetic successes.

No stable germanetellone was described until Tbt(Dis)Ge=Te and Tbt(Tip)Ge=Te (Tbt = 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl, Dis = bis(trimethylsilyl)methyl and Tip = 2,4,6-triisopropylphenyl) were reported in 1997. Following these initial experiments, there has arisen considerable interest in Ge[double bond, length as m-dash]Te systems. An obvious question is: why have the simple XYGe=Te (X, Y = H, F, Cl, Br, I and CN) molecules not yet been isolated? In view of the present situation, theoretical information may be of great help for further advances in germanetellone chemistry. A systematic investigation of the XYGe=Te molecules is carried out using the second order Møller-Plesset perturbation theory (MP2) and density functional theory (DFT). The structures and energetics, including ionization potentials (IPad and IPad(ZPVE)), four different forms of neutral-anion separations (EAad, EAad(ZPVE), VEA and VDE) and the singlet-triplet gaps, are reported. The electronegativity (χ) reactivity descriptor for the halogens (F, Cl, Br and I) and the natural charge separations of the Ge=Te moiety are used to assess the interrelated properties of germanetellone and its derivatives. The results are analyzed, discussed and compared with analogous studies of telluroformaldehyde, silanetellone and their derivatives. The thermodynamic viabilities of some of the novel germanetellones have also been evaluated in terms of the bond dissociation enthalpies of Tbt(Dis)Ge=Te and Tbt(Tip)Ge=Te. The simple mono-substituted germanetellones appear to be slightly more thermodynamically favored than Tbt(Dis)Ge=Te and Tbt(Tip)Ge=Te, since the bond dissociation enthalpies of these kinetically stabilized germanetellones are about 28 and 51 kcal mol(-1) lower, respectively.

Bonding analysis of telluroketones H2A = Te (A = C, Si, Ge).

Quantum chemical calculations using density functional theory BP86/def2-TZVPP and ab initio methods at CCSD(T)/def2-TZVPP have been carried for the telluroketones H2A=Te (A = C, Si, Ge). DFT calculations have also been carried out for the ketones H2C=E (E = O, S, Se, Te) and for the complexes NHC → [H2A=Te] → B(C6F5)3. The nature of the bonding has been investigated with charge- and energy decomposition analyses. The calculated bond dissociation energies for the double bonds of the H2C = E and H2A = Te molecules show the expected trends O > S > Se > Te for atom E and C > Si > Ge for atom A. Complexation of the telluroketones in NHC → [H2A = Te] → B(C6F5)3 leads to longer and weaker A-Te bonds which exhibit the surprising trend for the bond dissociation energy Si > Ge > C. The contribution of the π bonding in H2A = Te increases for the heavier atoms with the sequence C < Si < Ge.