The decarboxylation of pyrrole-2-carboxylic acid in acid solutions was elucidated by full optimization with the CPCM solvation model at the B3LYP/6-31 l＋＋G（d,p） level. Compared with the single-point energy calculation, CPCM full optimization is better to model solvent environments to gain reasonable reaction mechanisms. The π interactions play a significant role in the decarboxylation of pyrrole-2-carboxylic acid （R）. Firstly, the a hydrogen is protonated, but all of the carbonyl hydration pathways bear relatively higher energy barriers. The carbonyl group can rove over the pyrrole ring, but it does not lead to the speciation of pyrrole and protonated carbon dioxide for the latter is an energy-rich species. The decarboxylation mechanism proposed here is that, the protonated pyrrole-2-carboxylic acid （RH） decarboxylates via direct C-C bond cleavage with the aid of a water molecule to accommodate the proton on the carbonyl group.
The chemistry of silylene-transition-metal complexes LnM（=SiR2）SiR3 is one of the attractive synthetic targets in organometallic chemistry for such complexes are key intermediates in many transition metal-catalyzed systems.In the present work,the novel insertion reactions of an isocyanide into the Cp＊Mo（CO）2（=SiMe2）（SiMe3） Si-C bond were investigated extensively by using the DFT method.The effective core potentials（ECP） with a double-ζ valence basis set（LanL2DZ） were employed for Mo and Si and the standard 6-31G basis set for all other atoms.Polarization functions[22] were added for Si（ζd = 0.262）,C（ζd = 0.8） and N（ζd = 0.8）.The effect of solvent was evaluated with the standard PCM model.Our calculations show that the two-step channel is energetically favorable,and the solvation mode has minor influence on the relative energies.
The reaction mechanisms of Ti（~3F） ＋ CH2C12→CH2=TiCl2 and Ti（~3F） ＋ CHC13→HC÷TiCl3 were investigated with Gaussian 03 program package at the B3PW91/6-311＋＋G（d,p）level.The computational results revealed that：1） Both reaction systems are initiated by Ti（~3F） atom attacking the C atom of CH2C12 and CHCl3 to activate a C-Cl bond;2） Both reaction systems were carried out via triplet reaction channels;3） CH2=TiCl2 has singlet and triplet isomers,and the singlet one is more stable;4） The HOMO of CH2=TiCl2（S） illustrates a π-bonding interaction between C and Ti;5） Only singlet HC÷TiCl3 was located,and the Mulliken atomic spin densities show that the two single electrons are mostly on the C atom.
The catalytic activation of carbon dioxide by metals and non-metals is one of the attractive scientific challenges in scientific community. In this work, the conversion mechanisms of CO2 to CO by B, Al and Si were elucidated extensively at the B3LYP/6-311＋＋G（d,p） basis set level. Our theoretical mode testifies that the reaction mechanisms of these three systems are significantly different from each other, and both boron and silicon have good performance in the conversion of CO2 to CO.
The pyrolysis of 1-hexene can act as a prototype of pyrolytic mechanism in petro- leum processing. Details of C-C bond cleavage in the 1-hexene pyrolysis were investigated at the MP2/6-31 I＋＋G^＊＊ basis set level. The equilibrium geometries and key thermodynamic parameters such as Gibbs free energies and thermal enthalpies were gained. Our theoretical results show that the entropy effect plays a significant role in dissociative processes. The dissociation of 1-hexene-4-yl radical into C4H6 and C2H5 is not an H-transfer and C-C rupture elementary reaction, but a process involving H-transfer and C-C rupture.
