Density Functional Theory Study on Mechanism of Forming Spiro-Geheterocyclic Ring Compound from Me 2 Ge=Ge: and Acetaldehyde

CHINESE JURNAL F CHEMICAL PHYSICS VLUME 26, NUMBER 1 FEBRUARY 27, 2013 ARTICLE Density Functional Theory Study on Mechanism of Forming Spiro-Geheterocyclic Ring Compound from Me 2 Ge=Ge: and Acetaldehyde Xiu-hui Lu, Yong-qing Li, Wei-jie Bao, Dong-ting Liu School of Chemistry and Chemical Engineering, University of Ji nan, Ji nan 250022, China (Dated: Received on November 12, 2012; Accepted on December 10, 2012) The H 2 Ge=Ge:, as well as and its derivatives (X 2 Ge=Ge:, X=H, Me, F, Cl, Br, Ph, Ar,...) is a kind of new species. Its cycloaddition reactions is a new area for the study of germylene chemistry. The mechanism of the cycloaddition reaction between singlet Me 2 Ge=Ge: and acetaldehyde was investigated with the B3LYP/6-31G method in this work. From the potential energy profile, it could be predicted that the reaction has one dominant reaction pathway. The reaction rule is that the two reactants firstly form a four-membered Ge-heterocyclic ring germylene through the [2+2] cycloaddition reaction. Because of the 4p unoccupied orbital of Ge: atom in the four-membered Ge-heterocyclic ring germylene and the π orbital of acetaldehyde forming a π p donor-acceptor bond, the four-membered Ge-heterocyclic ring germylene further combines with acetaldehyde to form an intermediate. Because the Ge atom in intermediate happens sp 3 hybridization after transition state, then, intermediate isomerizes to a spiro-ge-heterocyclic ring compound via a transition state. The research result indicates the laws of cycloaddition reaction between Me 2 Ge=Ge: and acetaldehyde, and lays the theory foundation of the cycloaddition reaction between H 2 Ge=Ge: and its derivatives (X 2 Ge=Ge:, X=H, Me, F, Cl, Br, Ph, Ar,...) and asymmetric π-bonded compounds, which are significant for the synthesis of small-ring and spiro-ge-heterocyclic ring compounds. Key words: Me 2 Ge=Ge:, Four-membered Ge-heterocyclic ring germylene, Spiro-Geheterocyclic compound, Potential energy profile I. INTRDUCTIN Unsaturated germylenes is a kind of quite unstable active intermediates. In 1997, Clouthier et al. observed the first unsaturated germylene germylidene (H 2 C=Ge:) [1], which was produced by striking an electric discharge in a high-pressure argon pulse using the tetramethylgermane (TMG) vapor as the precursor. At the same time, ab initio calculations made predictions of its molecular structure, electronic spectrum, and oscillatory fluorescence decay of jet-cooled germylidene (H 2 C=Ge:) [2], the ground state structure of H 2 C=Ge: and D 2 C=Ge: [3] and the stimulated emission pumping (SEP) spectroscopy of the first excited singlet state of germylidene [4]. Stogner and Grev have done a lot of ab initio calculations on both germylidene and the trans-bent germyne HC GeH isomer [5]. They found that germylidene was the global minimum on the H 2 C=Ge: potential energy surface, with germyne some 43 kcal/mol higher in energy. The barrier to germyne isomerization was predicted to be only 7 kcal/mol and no stable linear germyne structures could be found. With regard to the cycloadditon reaction of the unsaturated germylene, we have done some elementary discussion [6 9]. But these studies are limited to the cycloaddition reaction of H 2 C=Ge: and its derivatives (X 2 C=Ge:, X=H, Me, F, Cl, Br, Ph, Ar,...). There are no reports on the cycloaddition reaction of H 2 Ge=Ge: and its derivatives (X 2 C=Si:, X=H, Me, F, Cl, Br, Ph, Ar,...) until now, it is a new branch of unsaturated germylene s cycloaddition reaction. It is quite difficult to investigate mechanisms of cycloaddition reaction directly by experimental methods due to the high activity of unsaturated germylene, therefore, the theoretical study is more practical. To explore the rules of cycloaddition reaction between H 2 Ge=Ge: (include its derivatives) and the asymmetric π-bonded compounds, Me 2 Ge=Ge: and acetaldehyde were selected as model molecules, the cycloaddition reaction mechanism (considering the H and Me transfer simultaneously) was investigated and analyzed theoretically. The results show that the cycloaddition reaction consists of four possible pathways, as follows: Author to whom correspondence should be addressed. E-mail: lxh@ujn.edu.cn DI:10.1063/1674-0068/26/01/43-50 43

44 Chin. J. Chem. Phys., Vol. 26, No. 1 Xiu-hui Lu et al. II. CMPUTATINAL METHDS B3LYP/6-31G implemented in the Gaussian 03 package [10] is employed to locate all the stationary points along the reaction pathways. Full optimization and vibrational analysis are done for the stationary points on the reaction profile. Zero point energy (ZPE) corrections are included for the energy calculations. In order to explicitly establish the relevant species, the intrinsic reaction coordinate (IRC) [11, 12] is also calculated for all the transition states appearing on the cycloaddition energy surface profile. Density functional theory (DFT) has become one of the most important theories in the computational chemistry field due to moderate amount of calculation and high calculation accuracy. B3LYP method is the most widely used DFT method. Compared with other methods, B3LYP not only has higher calculation accuracy of the molecular ground state, but also considers the interrelation between the electronic effect, thus, the energy is more accurate. Now, B3LYP is the most commonly used calculation method of quantum chemistry. In addition, B3LYP is quite accurate when dealing with clusters of small molecular systems, and has got general recognition of the chemists. This is also the reason that we select B3LYP method in this work. III. RESULTS AND DISCUSSIN A. Reaction (1): channels of forming the four-membered Ge-heterocyclic ring germylene (P1), Me-transfer Products (P1.1 and P1.2), and H-transfer products (P1.3) Theoretical researchs show that the ground state of Me 2 Ge=Ge: is a singlet state. The geometrical parameters of the intermediate (INT1), transition states (TS1, TS1.1, TS1.2, and TS1.3), and products (P1, P1.1, P1.2, and P1.3) which appear in reaction (1) between Me 2 Ge=Ge: and acetaldehyde are given in Fig.1, the energies are listed in Table I, and the potential energy profile for the cycloaddition reaction is shown in Fig.2. According to Fig.2, it can be seen that the reaction (1) consists of five steps: the first one is that the two reactants (R1, R2) form an intermediate (INT1), which is a barrier-free exothermic reaction of 77.3 kj/mol; DI:10.1063/1674-0068/26/01/43-50

Chin. J. Chem. Phys., Vol. 26, No. 1 Spiro-Ge-heterocyclic Ring Compound 45 2.316 2.330 125.2 2.290 120.3 1.224 89.7 128.3 2.077 1.241 87.4 108.6 2.091 1.257 R1 R2 =51.6 =64.4 INT1 TS1 2.510 1.829 74.0 112.6 1.458 2.496 1.897 113.1 71.9 1.416 2.409 79.9 1.814 103.1 2.507 71.4 1.951 84.1 1.351 =2.6 =-0.2 =19.3 =-44.7 P1 TS1.1 P1.1 TS1.2 2.534 69.3 2.205 105.4 1.246 2.512 70.2 1.984 82.5 1.353 2.512 69.5 2.178 106.6 1.251 =5.5 =46.3 =-3.6 P1.2 TS1.3 P1.3 FIG. 1 ptimized B3LYP/6-31G geometrical parameters and the atomic numbering for the species in cycloaddition reaction (1). Bond lengths are in Å, bond angles and dihedral angles are in ( ). the second step is INT1 isomerizes to a four-membered Ge-heterocyclic ring germylene (P1) through transition state (TS1) with an energy barrier of 6.1 kj/mol; the third, fourth, and fifth steps are that the P1 undergoes Me and H transfer via transition states TS1.1, TS1.2, and TS1.3 with energy barriers of 118.8, 180.9, and 116.2 kj/mol, respectively, resulting in the formation of products P1.1, P1.2, and P1.3. Because the energies of P1.1, P1.2, and P1.3 are 55.6, 56.2, and 38.5 kj/mol higher than that of P1, so the reactions of P1 P1.1, P1 P1.2, and P1 P1.3 are prohibited in thermodynamics at the normal temperature and pressure, reaction (1) will end in product P1. B. Reaction (2): channel of forming a spiro-ge-heterocyclic ring compound (P2) In reaction (2), the four-membered Ge-heterocyclic ring germylene (P1) further reacts with acetaldehyde (R2) to form a spiro-ge-heterocyclic ring compound (P2). The geometrical parameters of intermediate (INT2), transition state (TS2) and product (P2) which appear in reaction (2) are given in Fig.3. The energies are listed in Table I, and the potential energy profile for the cycloaddition reaction is shown in Fig.2. According to Fig.2, it can be seen that the process of reaction (2) as follows: on the basis of P1 formed from the reaction (1) between R1 and R2, the P1 further reacts with acetaldehyde to form an intermediate (INT2), which is a barrier-free exothermic reaction of 58.0 kj/mol; next, the intermediate (INT2) isomerizes to a spiro-ge-heterocyclic ring compound (P2) via a transition state (TS2) with an energy barrier of 23.8 kj/mol. The reaction of INT2 P2 is endothermic reaction, because the energie of P2 is 10.3 kj/mol higher than that of INT2. C. Reaction (3): channels of forming four-membered Ge-heterocyclic ring germylene (INT3), Me-transfer products (P3 and P3.1), H-transfer product (P3.2) The geometrical parameters of four-membered Geheterocyclic ring germylene (INT3), transition states (TS3, TS3.1, and TS3.2) and products (P3, P3.1, and DI:10.1063/1674-0068/26/01/43-50

/ (kj/mol) R DI:10.1063/1674-0068/26/01/43-50 -250-200 -150-100 0 0.0 R1+R2 INT3-127.2-50 -116.2 TS3.2-92.2 TS3-70.3 TS3.1-161.2 P3.2-125.8 P3-139.8 P3.1-77.3 INT1 0.0 P1+R2-71.2 TS1-58.0 INT2 TS2-181.3 P1-34.2 TS1.3-61.5-62.5 P1.1 P1.2 INT4 * -142.8 P1.3-125.7-125.1-88.9 TS4-49.2 P2 0.0 INT3+R2-47.7 TS1.1-0.4 TS1.2 P4-93.8 Chin. J. Chem. Phys., Vol. 26, No. 1 FIG. 2 The potential energy profile for the cycloaddition reactions between Me 2 Ge=Ge: and MeHC= with B3LYP/6-31G. E 46 Xiu-hui Lu et al. c 2013 Chinese Physical Society

Chin. J. Chem. Phys., Vol. 26, No. 1 Spiro-Ge-heterocyclic Ring Compound 47 TABLE I Zero point energy (ZPE), total energies (E T) and relative energies (E R) for the species from B3LYP/6-31G method. Reaction Species ZPE/a.u E T a /a.u E R b /(kj/mol) Reaction (1) R1+R2 0.12994 4383.47311 0.0 INT1 0.13212 4383.50254 77.3 TS1 (INT1-P1) 0.13174 4383.50023 71.2 P1 0.13404 4383.54216 181.3 TS1.1 (P1-P1.1) 0.13129 4383.49692 62.5 P1.1 0.13319 4383.52098 125.7 TS1.2 (P1-P1.2) 0.13062 4383.47328 0.4 P1.2 0.12971 4383.52076 125.1 TS1.3 (P1-P1.3) 0.12842 4383.49791 65.1 P1.3 0.12832 4383.52750 142.8 Reaction (2) P1+R2 0.18985 4537.31647 0.0 INT2 0.19202 4537.33857 58.0 TS2 (INT2-P2) 0.19112 4537.32951 34.2 P2 0.19318 4537.33462 47.7 Reaction (3) R1+R2 0.12994 4383.47311 0.0 INT3 0.13269 4383.52155 127.2 TS3 (INT3-P3) 0.13224 4383.50821 92.2 P3 0.13317 4383.52101 125.8 TS3.1 (INT3-P3.1) 0.13060 4383.49987 70.3 P3.1 0.13066 4383.52637 139.8 TS3.2 (INT3-P3.2) 0.12789 4383.51738 116.2 P3.2 0.12801 4383.53451 161.2 Reaction (4) INT3+R2 0.18849 4537.29588 0.0 INT4 0.19156 4537.32975 88.9 TS4 (INT4-P4) 0.19001 4537.31462 49.2 P4 0.19246 4537.33161 93.8 a E T=E Species+ZPE. b E R=E T E (R1+R2) for reaction (1) and reaction (3), E R=E T E (P1+R2) for reaction (2), and E R=E T E (INT3+R2) for reaction (4). P3.2) which appear in reaction (3) between Me 2 Ge=Ge: and acetaldehyde are given in Fig.4. The energies are listed in Table I, and the potential energy profile for the cycloaddition reaction is shown in Fig.2. According to Fig.2, it can be seen that reaction (3) consists of four steps: the first step is that the two reactants (R1, R2) form a four-membered Ge-heterocyclic ring germylene (INT3), which is a barrier-free exothermic reaction of 127.2 kj/mol. The second and third step is that the INT3 undergoes Me-transfer and via transition states TS3 and TS3.1 with energy barriers of 35.0 and 56.9 kj/mol, resulting in the formation of products P3 and P3.1. The fourth step is that the INT3 undergoes H-transfer via transition state TS3.2 with energy barrier of 11.0 kj/mol, resulting in the formation of product P3.2. Because the enegies of P3 are 1.4 kj/mol higher than that of INT3 and the energy barrier of TS3.1 is 45.9 kj/mol higher than that of TS3.2, so INT3 P3.2 is the dominant reaction pathway of reaction (3). According to Fig.1, Fig.2, and Fig.4, it can be seen that INT1 and INT3 are isomerides, the equilibrium distributions of INT1 and INT3 are P r INT1 =K INT1 /K INT1 +K INT3 0.0 P r INT3 =K INT3 /K INT1 +K INT3 1.0 So, INT3 is the main distribution. D. Reaction (4): channel of forming spiro-ge-heterocyclic ring compound (P4) In reaction (4), the four-membered Ge-heterocyclic ring germylene (INT3) further reacts with acetaldehyde (R2) to form a spiro-ge-heterocyclic ring compound (P4). The geometrical parameters of intermediate (INT4), transition state (TS4) and product (P4) which appear in reaction (4) are given in Fig.5. The energies are listed in Table I, and the potential energy DI:10.1063/1674-0068/26/01/43-50

48 Chin. J. Chem. Phys., Vol. 26, No. 1 Xiu-hui Lu et al. 1.235 2 1.843 1 123.3 2.200 2 2.698 90.8 1.838 1 2 1.447 1.858 69.4 1.848 1 1=-4.9 1=-5.8 1=-8.6 2=-91.9 2=-91.6 2=-102.8 2=-90.4 2=165.7 2=-160.4 INT2 TS2 P2 FIG. 3 ptimized B3LYP/6-31G geometrical parameters of INT2, TS2, P2, and the atomic numbering for cycloaddition reaction (2). Bond lengths are in Å, bond angles and dihedral angles are in ( ). 2.497 1.851 80.3 102.5 1.432 2.357 86.2 98.2 1.817 1.456 2.412 79.7 1.815 103.3 1.453 1.927 2.528 77.3 98.6 1.330 =-1.3 =-5.3 =17.5 =0.0 INT3 TS3 P3 TS3.1 2.476 75.2 2.00 98.8 1.299 2.514 78.1 99.1 1.324 2.481 76.5 99.9 1.990 1.285 =-18.1 =-0.7 =12.2 P3.1 TS3.2 P3.2 FIG. 4 ptimized B3LYP/6-31G geometrical parameters of INT3, TS3, P3, TS3.1, P3.1, TS3.2, P3.2, and the atomic numbering for cycloaddition reaction (3). Bond lengths are in Å, bond angles and dihedral angles are in ( ). profile for the cycloaddition reaction is shown in Fig.2. According to Fig.2, it can be seen that the process of reaction (4) as follows: on the basis of the two reactants (R1, R2) to form INT3, it further reacts with acetaldehyde (R2) to form an intermediate (INT4), which is a barrier-free exothermic reaction of 88.9 kj/mol. And then intermediate (INT4) isomerizes to a spiro-geheterocyclic ring compound (P4) via a transition state (TS4) with an energy barrier of 39.7 kj/mol. Comparing reaction (4) with reaction (3), it is realized that the two reactions compete mutually due to scrambling for INT3 together. In reaction (4), INT3+R2 INT4 can directly reduce the system energy of 88.9 kj/mol. In reaction (3), the energy barrier of INT3 P3.2 is 11.0 kj/mol, therefore, reaction (4) is the dominant reaction channel. E. Theoretical analysis and explanation of the dominant reaction channel According to the above analysis, there is only one dominant reaction channel of the cycloaddition reaction between singlet Me 2 Ge=Ge: and acetaldehyde as follows: R1+R2 INT3 +R2 INT4 TS4 P4 (4) In the reaction, the frontier molecular orbitals of R2 and INT3 are shown in Fig.6. According Fig.6, the frontier molecular orbitals of R2 and INT3 can be expressed in schematic diagram (Fig.7). The mechanism of the reaction could be explained with the molecular orbital diagram (Fig.7) and Fig.1, Fig.4, and Fig.5. According to Fig.1 and Fig.4, as Me 2 Ge=Ge: initially interacts with acetaldehyde, the [2+2] cycload- DI:10.1063/1674-0068/26/01/43-50

Chin. J. Chem. Phys., Vol. 26, No. 1 Spiro-Ge-heterocyclic Ring Compound 49 126.7 2.490 1 1.245 2 2.060 1.230 2 97.6 2.439 2.488 1 1.422 70.2 2 1.878 2.412 1 1=18.4 1=-1.9 1=2.3 21=-106.1 21=-85.7 21=-113.0 2=-80.5 2=-128.8 2=-143.9 INT4 TS4 P4 FIG. 5 ptimized B3LYP/6-31G geometrical parameters of INT4, TS4, P4 and the atomic numbering for cycloaddition reaction (4). Bond lengths are in Å, bond angles and dihedral angles are in ( ). π HM of R2 HM of INT3 LM of INT3 FIG. 6 The frontier molecular orbitals of R2 and INT3. dition of the bonding π-orbitals firstly results in a fourmembered Ge-heterocyclic ring germylene (INT3). Because the INT3 is an active intermediate, INT3 further reacts with acetaldehyde (R2) to form a spiro-geheterocyclic ring compound (P4). The mechanism of the reaction could be explained with Fig.5 and Fig.7, according to orbital symmetry matching condition, when INT3 interacts with acetaldehyde (R2), the 4p unoccupied orbital of the atom in INT3 will insert the π orbital of acetaldehyde from oxygen side, then the shift of π-electrons to the p unoccupied orbital from a π p donor-acceptor bond, leading to the formation of intermediate (INT4). As the reaction goes on, the 2 (INT4: 80.5, TS4: 128.8, P4: 143.9 ) gradually increase, 2 (INT4: 126.7, TS4: 97.6, P4: 70.2 ) gradually decrease, the in INT4 happens sp 3 hybridization after the transition state (TS4), forming a spiro-ge-heterocyclic ring compound (P4). IV. CNCLUSIN n the basis of the potential energy profile the cycloaddition reaction between singlet Me 2 Ge=Ge: and acetaldehyde obtained with the B3LYP/6-31G method can be predicted. This reaction has one dominant chan- sp 4p Me H π 2 R2 4p + sp Me _ H Me 1 Me INT3 FIG. 7 A schematic interaction diagram for the frontier orbitals of INT3 and MeHC= (R2). nel. It consists of three steps: the first step is that the two reactants (R1, R2) form a four-membered Geheterocyclic ring germylene (INT3), which is a barrierfree exothermic reaction of 127.2 kj/mol; the second step is that INT3 further reacts with acetaldehyde (R2) to form an intermediate (INT4), which is also a barrierfree exothermic reaction of 88.9 kj/mol; the third step is that intermediate (INT4) isomerizes to a spiro-geheterocyclic ring compound (P4) via a transition state (TS4) with an energy barrier of 39.7 kj/mol. The π orbital of X 2 Ge=Ge: (X=H, Me, F, Cl, Br, Ph, Ar,...) and the 4p unoccupied orbital of Ge: in X 2 Ge=Ge: (X=H, Me, F, Cl, Br, Ph, Ar,...) are the object in cycloaddition reaction of X 2 Ge=Ge: and the asymmetric π-bonded compounds. The [2+2] cycloaddition reaction between the π orbital of X 2 Ge=Ge: and the bonding π orbital of the asymmetric π-bonded compounds leads to the formation of the four-membered Ge-heterocyclic ring germylene. The 4p unoccupied orbital of Ge: atom in the four-membered Ge-heterocyclic ring germylene further reacts with the bonding π orbital of the asymmetric π-bonded compounds to form DI:10.1063/1674-0068/26/01/43-50

50 Chin. J. Chem. Phys., Vol. 26, No. 1 Xiu-hui Lu et al. an intermediate. The Ge: atom in the intermediate happens sp 3 hybridization, the intermediate isomerizes to a spiro-ge-heterocyclic ring compound. V. ACKNWLEDGMENT This work was supported by the National Natural Science Foundation of China (No.51102114). [1] W. H. Harper, E. A. Ferrall, R. K. Hilliard, S. M. Stogner, R. S. Grev, and D. J. Clouthier, J. Am. Chem. Soc. 119, 8361 (1997). [2] D. A. Hostutler, T. C. Smith, H. Y. Li, and D. J. Clouthier, J. Chem. Phys. 111, 950 (1999). [3] D. A. Hostutler, D. J. Clouthier, and S. W. Pauls, J. Chem. Phys. 116, 1417 (2002). [4] S. G. He, B. S. Tackett, and D. J. Clouthier, J. Chem. Phys. 121, 257 (2004). [5] S. M. Stogner and R. S. Grev, J. Chem. Phys. 108, 5458 (1998). [6] X. H. Lu, Y. H. Xu, H. B. Yu, and W. R. Wu, J. Phys. Chem. 109, 6970 (2005). [7] X. H Lu, Y. H Xu, P. P Xiang, and X. Che, Int. J. Quant. Chem. 108, 75 (2008). [8] C. L Tian, Y. H Xu, and X. H Lu, Int. J. Quant. Chem. 110, 1675 (2010). [9] X. H. Lu, Y. H. Xu, L. Y. Shi, J. F. Han, and Z. X. Lian, J. rganomet. Chem. 694, 4062 (2009). [10] C. Lee, W. Yang, and R. G. Parr, Phys. Rev. B 37, 785 (1988). [11] K. Fukui, J. Phys. Chem. 74, 4161 (1970). [12] K. Ishida, K. Morokuma, and A. Komornicki, J. Chem. Phys. 66, 2153 (1981). DI:10.1063/1674-0068/26/01/43-50