Theoretical study on the mechanism of cycloaddition reaction between silylene carbene and formaldehyde

Theoretical study on mechanism of cycloaddition reaction between dimethyl methylene carbene and ethylene

The mechanism of the cycloaddition reaction between singlet dichlorosilylene carbene (Cl2Si=C:) 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 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 first dominant reaction pathway consists of two steps: (1) the two reactants (R1, R2) firstly form a four-membered ring intermediate (INT4) through a barrier-free exothermic reaction of 387.9 kJ/mol; (2) intermediate (INT4) then isomerizes to H-transfer product (P4.2) via a transition state (TS4.2) with energy barrier of 4.7 kJ/mol. The second dominant reaction pathway as follows: on the basis of intermediate (INT4) created between R1 and R2, intermediate (INT4) further reacts with formaldehyde (R2) to form the intermediate (INT5) through a barrier-free exothermic reaction of 158.3 kJ/mol. Then, intermediate (INT5) isomerizes to a silicic bis-heterocyclic product (P5) via a transition state (TS5), for which the barrier is 40.1 kJ/mol.

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

The mechanism of the cycloaddition reaction between singlet dimethyl-silylene carbene 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 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 main products of first dominant reaction pathway are a planar four-membered ring product (P4) and its H-transfer product (P4.2). The main product of second dominant reaction pathway is a silicic bis-heterocyclic compound (P5). © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

The mechanism of the sulfur extraction reaction between singlet silylene carbine and its derivatives and thiirane has been investigated with density functional theory (DFT), 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 B3LYP/6-311G(d, p) method. From the potential energy profile, it can be predicted that the reaction pathway of this kind consists in two steps: (1) the two reactants firstly form an intermediate through a barrier-free exothermic reaction; (2) the intermediate then isomerizes to a product via a transition state. This kind of reactions has similar mechanism: when the silylene carbene and its derivatives [X2Si=C: (X = H, F, Cl, CH3)] and thiirane approach each other, the shift of 3p lone electron pair of S in thiirane to the 2p unoccupied orbital of C in X2Si=C: gives a p → p donor-acceptor bond, thereby leading to the formation of intermediate (INT). As the p → p donor-acceptor bond continues to strengthen (that is the C-S bond continues to shorten), the intermediate (INT) generates product (P + C2H4) via transition state (TS). It is the substituent electronegativity that mainly affect the extraction reactions. When the substituent electronegativity is greater, the energy barrier is lower, and the reaction rate is greater.

The mechanism of the cycloadditional reaction between singlet dichloro-germylidene(R1) and (acetaldehyde(R2) has been investigated with MP2/6-31G* method, including geometry optimization, vibrational analysis and energies for the involved stationary points on the potential energy surface. From the potential energy profile, we predict that the cycloaddition reaction between singlet dichloro-germylidene and acetaldehyde has two competitive dominant reaction pathways. Going with the formation of two side products (INT3 and INT4), simultaneously. The two competitive reactions both consist of two steps: (1) two reactants firstly form a three-membered ring intermediate (INT1) and a twisted four-membered ring intermediate (INT2), respectively, both of which are barrier-free exothermic reactions of 44.5 and 63.0 kJ/mol; (2) then INT1 and INT2 further isomerize to a four-membered ring product (P1) and a chlorine-transfer product (P2) via transitions (TS1 and TS2), respectively, with the barriers of 9.3 and 1.0 kJ/mol; simultaneously, P1 and INT2 react further with acetaldehyde(R2) to give two side products (INT3 and INT4), respectively, which are also barrier-free exothermic reaction of 65.4 and 102.7 kJ/mol.

The mechanism of the oxide extraction reaction between singlet silylene carbene and its derivatives [X2Si = C: (X = H, F, Cl, CH3)] and ethylene oxide has been investigated with density functional theory, 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 B3LYP/6-311G(d,p) method. From the potential energy profile, it can be predicted that the reaction pathway of this kind consists two steps, the first step is the two reactants firstly form an intermediate (INT) through a barrier-free exothermic reaction; the second step is the INT then generates a product via a transition state (TS). This kind reaction has similar mechanism, when the silylene carbene and its derivatives [X2Si = C: (X = H, F, Cl, CH3)] and ethylene oxide close to each other, the shift of 2p lone electron pair of O in ethylene oxide to the 2p unoccupied orbital of C in X2Si = C: gives a p → p donor–acceptor bond, thereby leading to the formation of INT. As the p → p donor–acceptor bond continues to strengthen (that is, the CO bond continues to shorten), the INT generates product (P + C2H4) via TS. It is the substituent electronegativity, which mainly affects the extraction reactions. When the substituent electronegativity is greater, the energy barrier is lower, and the reaction rate is greater. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

The mechanism of the sulfur extraction reaction between singlet germylene carbene and its derivatives [X 2 GeC: (X = H, F, Cl, CH 3 )] and thiirane has been investigated with density functional theory, including geometry optimization and vibrational analyses for the involved stationary points on the potential energy surface. The energies of the different conformations are calculated by B3LYP/6‐311G(d,p) method. From the potential energy profile, it can be predicted that the reaction pathway of this kind consists two steps: (1) the two reactants firstly form an intermediate (INT) through a barrier‐free exothermic reaction; (2) the INT then isomerizes to a product via a transition state (TS). This kind reaction has similar mechanism, when the germylene carbene and its derivatives [X 2 GeC: (X = H, F, Cl, CH 3 )] and thiirane get close to each other, the shift of 3 p lone electron pair of S in thiirane to the 2 p unoccupied orbital of C in X 2 Ge = C: gives a p → p donor–acceptor bond, leading to the formation of INT. As the p → p donor–acceptor bond continues to strengthen (that is the CS bond continues to shorten), the INT generates product (P + C 2 H 4 ) via TS. It is the substituent electronegativity that mainly affects the extraction reactions. When the substituent electronegativity is greater, the energy barrier is lower, and the reaction rate is greater. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

Theoretical study on the mechanism of cycloaddition reaction between dimethyl germylidene and formaldehyde

The mechanism of cycloaddition reaction between singlet alkylidene carbene and ethylene has been investigated with second‐order Moller‐Plesset perturbation theory (MP2). By using 6–31G* basis, geometry optimization, vibrational analysis and energetics have been calculated for the involved stationary points on the potential energy surface. The results show that the title reaction has two major competition channels. An energy‐rich intermediate (INT) is firstly formed between alkylidene carbene and ethylene through a barrier‐free exothermic reaction of 63.62 kJ/mol, and the intermediate then isomerizes to a three‐membered ring product (Pl) and a four‐membered ring product (P2) via transition state TS1 and TS2, in which energy barriers are 47.00 and 51.02 kl/mol. respectively. PI is the main product.

The mechanism of the cycloaddition reaction between singlet H2Si=Si: and formaldehyde has been investigated with the CCSD(T)//MP2/6-31G* method. From the potential energy profile, it could be predicted that the reaction has three competitive dominant reaction pathways. The reaction rules presented is that the 3p unoccupied orbital of the Si: atom in H2Si=Si: inserts the π orbital of formaldehyde from the oxygen side, resulting in the formation of an intermediate. Isomerization of the intermediate further generates a four-membered ring silylene (the H2Si–O in the opposite position). In addition, the [2+2] cycloaddition reaction of the two π-bonds in H2Si=Si: and formaldehyde also generates another four-membered ring silylene (the H2Si–O in the syn-position). Because of the unsaturated property of the Si: atom in the two four-membered ring silylenes, the two four-membered ring silylenes could further react with formaldehyde, generating two silicic bis-heterocyclic compounds. Simultaneously, the ring strain of the four-membered ring silylene (the H2Si–O in the syn-position) makes it isomerize to a twisted four-membered ring product.

The mechanism of the cycloaddition reaction of forming a silapolycyclic compound between singlet methylenesilylene 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, we predict that the cycloaddition reaction of forming a silapolycyclic compound between singlet methylenesilylene and acetone has two competitive dominant reaction pathways. First dominant reaction pathway consists of four steps: (I) the two reactants (R1, R2) first form an intermediate (INT1) through a barrier-free exothermic reaction of 46.2 kJ/mol; (II) intermediate (INT1) then isomerizes to a planar four-membered ring product (P3) via transition state (TS3) with an energy barrier of 47.1 kJ/mol; (III) planar four-membered ring product (P3) further reacts with acetone (R2) to form an intermediate (INT4), which is also a barrier-free exothermic reaction of 40.0 kJ/mol; (IV) intermediate (INT4) isomerizes to a silapolycyclic compound (P4) via transition state (TS4) with an energy barrier of 57.0 kJ/mol. Second dominant reaction pathway consists of three steps: (I) the two reactants (R1, R2) first form a four-membered ring intermediate (INT2) through a barrier-free exothermic reaction of 0.5 kJ/mol; (II) INT2 further reacts with acetone (R2) to form an intermediate (INT5), which is also a barrier-free exothermic reaction of 45.4 kJ/mol; (III) intermediate (INT5) isomerizes to a silapolycyclic compound (P5) via transition state (TS5) with an energy barrier of 49.3 kJ/mol. P4 and P5 are isomeric compounds. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010

The mechanism of the cycloaddition reaction between singlet dichloroalkylidenesilylene and ethylene has been investigated with the MP2/6-31G* and B3LYP/6-31G* methods, 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* and CCSD(T)//B3LYP/6-31G* methods. From the surface energy profile obtained with the CCSD(T)//MP2/6-31G* method for the cycloaddition reaction between singlet dichloroalkylidenesilylene and ethylene, it can be predicted that the dominant reaction pathway for this reaction involves the initial formation of an intermediate through a barrier-free exothermic reaction (42.4 kJ mol−1); this intermediate then isomerizes to an active four-membered ring product via a transition state, a second intermediate and a second transition state, for which the energy barriers are 31.2 and 32.2 kJ mol−1, respectively.

The cycloaddition mechanism of forming a polycyclic compound between singlet dimethylmethylene carbene(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 with 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 dimethylmethylene carbene and formaldehyde consists of two steps: (1) the two reactants(R1, R2) firstly form an energy-enricheded intermediate (INT1a) through a barrier-free exothermic reaction of ΔE = 11.3 kJ/mol. (2) Intermediate (INT1a) then isomerizes to a three-membered product (P1) via a transition state (TS1a) with an energy barrier of 20.0 kJ/mol. The dominant reaction has an excellent selectivity and differs considerably from its competitive reactions in reaction rate. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010

The mechanism of the cycloaddition reaction between singlet dichloro-silylene carbene and acetone has been investigated with DFT, 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)//B3LYP/6-31G* method. From the potential energy profile, it can be predicted that the reaction has two competitive dominant reaction pathways. The channel (I) consists of two steps: (1) the two reactants firstly form a four-membered ring intermediate through a barrier-free exothermic reaction of 307.1 kJ/mol; (2) four-membered ring intermediate then isomerizes to a CH3-transfer product via a transition state with energy barrier of 11.3 kJ/mol. The process of channel (II) is as following: on the basis of four-membered ring intermediate created between the two reactants, four-membered ring intermediate further reacts with acetone to form the intermediate through a barrier-free exothermic reaction of 165.8 kJ/mol; Then, intermediate isomerizes to a silicic bis-heterocyclic product via a transition state, for which the barrier is 57.6 kJ/mol.