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The mechanism of the cycloaddition reaction between singlet state unsaturated silylene dichlorosilylenesilylene [Cl2Si = Si:] and ethylene, which generates a silicic bis-heterocyclic compound, has been investigated with the CCSD(T)//MP2/6-31G* method. The calculations show that the dominant reaction pathway consists of three steps. (I) The 3p unoccupied orbital of the Si atom in dichlorosilylenesilylene [Cl2Si = Si:] (R1) and the π-orbital of ethylene (R2) firstly form a π → p donor-acceptor bond, which makes the two reactants generate a three-membered cyclic intermediates (INT) through a barrier-free exothermic reaction of 127.7 kJ mol-1. (II) INT then isomerises to a four-membered cyclic silylene (P1) by the ring-expansion effect, which is via a transition state (TS1) with an energy barrier of 6.4 kJ mol-1. (III) sp3 hybridisation of the Si atom finally makes P1 react directly with ethylene to form a silicic bis-heterocyclic compound (P2) without any intermediates and transition states, and this step is also a barrier-free exothermic reaction of 138.6 kJ mol-1. [ABSTRACT FROM AUTHOR]

The mechanism of the cycloaddition reaction between singlet dichloro-germylene carbene and aldehyde has been investigated with MP2/6-31G* method, including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. The energies of the different conformations are calculated by zero-point energy and CCSD (T)//MP2/6-31G* method. From the potential energy profile, it can be predicted that the reaction has two competitive dominant reaction pathways. The channel (A) consists of four steps: (1) the two reactants (R1, R2) first form an intermediate INT2 through a barrier-free exothermic reaction of 142.4 kJ/mol; (2) INT2 then isomerizes to a four-membered ring compound P2 via a transition state TS2 with energy barrier of 8.4 kJ/mol; (3) P2 further reacts with aldehyde (R2) to form an intermediate INT3, which is also a barrier-free exothermic reaction of 9.2 kJ/mol; (4) INT3 isomerizes to a germanic bis-heterocyclic product P3 via a transition state TS3 with energy barrier of 4.5 kJ/mol. The process of channel (B) is as follows: (1) the two reactants (R1, R2) first form an intermediate INT4 through a barrier-free exothermic reaction of 251.5 kJ/mol; (2) INT4 further reacts with aldehyde (R2) to form an intermediate INT5, which is also a barrier-free exothermic reaction of 173.5 kJ/mol; (3) INT5 then isomerizes to a germanic bis-heterocyclic product P5 via a transition state TS5 with an energy barrier of 69.4 kJ/mol. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 [ABSTRACT FROM AUTHOR]

Abstract: The mechanism of the cycloaddition reaction of forming germanic bis-heterocyclic compound between singlet germylene carbene and acetone has been investigated with MP2/6-31G* method, including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. The energies of the different conformations are calculated by CCSD (T)//MP2/6-31G* method. From the potential energy profile, it can be predicted that the dominant reaction pathway of the cycloadditional reaction of forming germanic bis-heterocyclic compound consists of three steps: (1) the two reactants firstly form an intermediate INT4 through a barrier-free exothermic reaction of 181.4kJ/mol; (2) INT4 further reacts with acetone (R2) to form an intermediate (INT5), which is also a barrier-free exothermic reaction of 148.9kJ/mol; (3) INT5 then isomerizes to a germanic bis-heterocyclic product P5 via a transition state TS5 with an energy barrier of 53.3kJ/mol. [Copyright &y& Elsevier]

The mechanism of cycloaddition reaction between singlet dimethylmethylenesilylene and formaldehyde has been investigated with MP2/6-31G* method, including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. The energies of different conformations are calculated by CCSD(T)//MP2/6-31G* method. From the potential energy surface, it can be considered in thermodynamics and dynamics that reaction (1) and reaction (4) are the two dominant competitive reaction channels of cycloaddition reaction between dimethylmethylenesilylene and formaldehyde. The reaction process of reaction (1) is that: the two reactants (R1, R2) first form intermediates INT1a and INT1b through two reaction paths, a and b, which are barrier-free exothermic reactions of 31.8 and 43.9 kJ/mol; then, INT1a and INT1b isomerize to a four-membered ring product P1 via transition states TS1a and TS1b, with energy barriers of 26.3 and 24.4 kJ/mol. Reaction (4) also has two reaction paths, a and b, each of which consists of three steps are as follows: (i) the two reactants (R1, R2) first form intermediates INT3a and INT3b, which are barrier-free exothermic reactions of 64.5 and 44.2 kJ/mol. (ii) INT3a and INT3b further react with formaldehyde (R2) to form intermediates INT4a and INT4b, through barrier-free exothermic reactions of 22.9 and 22.2 kJ/mol. (iii) INT4a and INT4b then isomerize to form silapolycyclic product P4 via transition states TS4a and TS4b, with energy barriers of 39.7 and 29.3 kJ/mol. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [ABSTRACT FROM AUTHOR]

Mechanism of the cycloadditional reaction between singlet germylidene (R1) and formaldehyde (R2) has been investigated with MP2/6-31G* method, including geometry optimization, and vibrational analysis for the involved stationary points on the potential energy surface. The energies of the different conformations are calculated by CCSD(T)//MP2/6-31G* method. From the potential energy profile, it can be predicted that the dominant reaction pathway of the cycloadditional reaction between singlet germylidene and formaldehyde is reaction (4), which consists of three steps: the two reactants (R1, R2) first form an intermediate INT1b through a barrier-free exothermic reaction of 28.1 kJ/mol; this intermediate reacts further with formaldehyde (R2) to give an intermediate INT4, which is also a barrier-free exothermic reaction of 37.2 kJ/mol; subsequently, the intermediate INT4 isomerizes to a heteropolycyclic germanic compound P4 via a transition state TS4, for which the barrier is 18.6 kJ/mol. The dominant reaction has an excellent selectivity and differs considerably from its competitive reactions in thermodynamic property and reaction rate. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [ABSTRACT FROM AUTHOR]

Abstract: The mechanism of the cycloaddition reaction of forming a silapolycyclic compound between singlet methylenesilylene and ethene has been investigated with the MP2/6-31G∗ method, including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. The energies of the different conformations are calculated by the CCSD(T)//MP2/6-31G∗ method. From the potential energy profile, it can be predicted that, reaction (3) is the dominant channel of cycloaddition reaction between singlet methylenesilylene and ethene. This reaction consists of four steps: (I) the two reactants first form a three-membered ring intermediate INT through a barrier-free exothermic reaction of 13.3kJmol−1; (II) INT then isomerizes to a four-membered ring product P2 via the transition state TS2 with an energy barrier of 32.0kJmol−1; (III) P2 further reacts with ethene(R2) to form a silapolycyclic intermediate INT3, which is also a barrier-free exothermic reaction of 11.8kJmol−1; (IV) INT3 isomerizes to a silapolycyclic compound P3 via the transition state TS3 with an energy barrier of 1.5kJmol−1. This reaction has quite excellent selectivity. [Copyright &y& Elsevier]

7,8,9-Trisubstituted dihydropurine derivatives were prepared from 5-amino-4-(N,N-disubstituted)aminopyrimidines and aromatic aldehydes via a cascade of reactions. The key transformation for the reaction is a [1,6]-hydrogen shift due to a ‘tert-amino effect’. [ABSTRACT FROM AUTHOR]

Abstract: Mechanisms of cycloaddition reaction between singlet dimethyl methylene carbene and ethylene has been investigated with MP2/6-31G∗ method, including geometry optimization and vibrational analysis. Energies for the involved stationary points on the potential energy surface are corrected by zero-point energy and CCSD(T)//MP2/6-31G∗ single-point calculations. From the potential energy surface obtained with the CCSD(T)//MP2/6-31G∗ method for the cycloaddition reaction between singlet dimethyl methylene carbene and ethylene, it can be predicted that reactions (1) and (3) should be two competitive leading channels of cycloaddition reaction between them. The former consists of two steps: (I) the two reactants firstly form an energy-rich intermediate, INT1, which is a barrier-free exothermic reaction; (II) the intermediate INT1 isomerizes to a three-membered ring product P1 via a transition state TS1. The latter proceeds in three steps: (I) the two reactants firstly form a four-membered ring intermediate, INT2, through a barrier-free exothermic reaction; (II) the intermediate INT2 further reacts with ethylene (R2) to form an intermediate, INT3, which is also a barrier-free exothermic reaction; (III) INT3 isomerizes to a polycyclic product P3 via a transition state TS3. [Copyright &y& Elsevier]