Isomeric structures, isomerization and decomposition of silylenoids H2SiMX(MX=KF,KCl LiBr,NaBr and KBr)

The isomeric structures, isomerization and decomposition of silylenoids H(2)SiMX (MX=KF, KCl, LiBr, NaBr and KBr) have been investigated by ab initio molecular orbital theory. These silylenoids have four kinds of very similar equilibrium structures. The three-membered ring and p-complex structures should be stable and experimentally detectable. The lifetime of sigma-complex and tetrahedral structures would be very short and experimentally undetectable.

Effect of substituents (NH_2,OH,F) on structures and stability of lithofluorosilylenoids

Isomeric structures and energies of three kinds of lithofluorosilylenoids, R\-2SiLiF (R=NH\-2, OH, F) were studied using the ab initio molecular orbital theory. The calculations show that thermal stability of the three membered ring structures of these three kinds of silylenoids decreases in the order of substituents NH\-2>OH>F because of the conjugation between NH\-2, OH or F and Si atom. The interaction of substituents R with Li atom makes R\-2SiLiF have a structure with two Li A Si F (A=N, O, F) four membered rings, which is the most stable of the isomers of each of three kinds of silylenoids and whose stability decreases in the order of substituents F>OH>NH\-2. Inductive effect of substituents influences the thermal stability of the linear structure of silylenoids.

THEORETICAL STUDIES ON THE STRUCTURES AND REACTIVITY OF SILYLENOIDS (Ⅰ)——STRUCTURES AND ISOMERIZATION OF SILYLENOID H_2SiLiCl

The structures of silylenoid H2SiLiCl have been studied by RHF/3-21G gradient method. Three equilibrium states and two isomerization transition states are located. The electronic energy, Mulliken populations, dipole moments and frontier molecular orbitals （FMO） of every structure and the isomeric barriers are also given and analyzed. Further single point calculations on the 3-21G optimum geometries were performed using 6-21G basis set. The calculations show that three-membered ring structure of H2SiLiCl is the most stable and detectable, and the "classical" tetrahedral form is not the local minimum on the potential energy surface.

Structures of silylenoids and effects of metallic and haloid atoms on their stability

The structural characteristics of silylenoids, H2SiMX, where M = Li or Na and X = F or Cl, have been studied by ab initio calculations. H2SiMX can be represented as adducts of silylene H2Si with alkali metal halogenides, MX. The associative energies at different calculational levels of various structures of H2SiMX are given. Effects of metallic and haloid atoms on the stability of various structures of H2SiMX are also discussed in this paper.

Mechanism of Insertion Reactions between Silylenoid H_2SiLiF and GeH_3R(R=F,OH,NH_2):a Theoretical Study

Theoretical investigations on the insertion reaction mechanisms of three- membered-ring silylenoid H2 Si Li F with GeH 3R（R = F, OH, NH2） have been systematically carried out by combined density functional theory（DFT） and ab initio quantum chemical calculations. The geometries of all stationary points for these reactions were optimized using the B3 LYP method and then the QCISD method was used to calculate the single-point energies. The calculated results indicate that, there are one precursor complex（Q）, one transition state（TS）, and one intermediate（IM） which connect the reactants and the products along the potential energy surface. The insertion reactions of three-membered-ring silylenoid with Ge H3 R proceed in a concerted manner, forming H2RSi-Ge H3 and Li F. The calculated potential energy barriers of the three reactions are 29.17, 30.90, and 54.07 k J/mol, and the reaction energies for the three reactions are –127.05, –116.91, and –103.31 k J/mol, respectively. The insertion reactions in solvents are similar to those in vacuum. Under the same situation, the insertion reactions should occur easily in the following order： GeH 3-F GeH 3-OH GeH 3-NH2. The elucidations of the mechanism of these insertion reactions provided a new mode of silicon-germanium bond formation.

Isomers and [2,3]-Sila-wittig Rearrangement of [(Allyloxy)silyl]lithium Silylenoid in the Gas Phase and THF Solvent

Theoretical calculations of the [2,3]-sila-wittig rearrangement of isomers of [（allyloxy）silyl]lithium （C3H5O）HzSiLi have been performed in the gas phase and THF solvent using the G3MP2B3 method. Seven isomers of silylenoid （C3H5O）H2SiLi, 1-7, are found. The [2,3]-silawittig rearrangement paths are followed using two isomers, 2 and 4, to yield the transition states as well as the products. In the transition state, the silicon center functions as a nucleophile and the aUyl as an electrophile. The interaction between the silicon and allylic sites leads to the formation of SiC（3） bond and the break of O-C（1） bond. Finally, the （allylsilyl）oxylithium （C3H5）H2SiOLi is obtained. The rearrangement paths are confirmed by the intrinsic reaction coordinate （IRC） calculations. The rearrangement mechanisms of reactions of 2 and 4 are similar, and the latter reaction is more favored in the gas phase and THF solvent. Also, the solvent effects are analyzed in this work.