The insertion reactions of the germylenoid H2GeLiF with CH3X (X = F, Cl, Br)

Journal of Organometallic Chemistry 724 (2013) 163e166

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The insertion reactions of the germylenoid H2GeLiF with CH3X (X ¼ F, Cl, Br) Wen-Zuo Li*, Bing-Fei Yan, Qing-Zhong Li, Jian-Bo Cheng The Laboratory of Theoretical and Computational Chemistry, College of Chemistry and Chemical Engineering, Yantai University, Yantai 264005, PR China

a r t i c l e i n f o

a b s t r a c t

Article history: Received 24 August 2012 Received in revised form 30 October 2012 Accepted 8 November 2012

The insertion reactions of the germylenoid H2GeLiF with CH3X (X ¼ F, Cl, Br) were studied for the first time by using the DFT B3LYP and QCISD methods. The theoretical calculations predicted that along the potential energy surface, there are one precursor complex, one transition state, and one intermediate which connect the reactants and the products. The elucidations of the mechanism of these insertion reactions provide a new reaction mode of germaniumecarbon bond formation. Ó 2012 Elsevier B.V. All rights reserved.

Keywords: H2GeLiF CH3X (X ¼ F, Cl, Br) Insertion reaction B3LYP QCISD

1. Introduction Germylenoid, which can be denoted as R1R2GeMX, are analogous to carbenoid [1,2] and silylenoid [3,4]. In 1991, Gaspar and Lei [5] firstly pointed out that germylenoid might be the intermediate in the reaction of dichlorodimethylgermane with substituted butadiene. Some other subsequent organic experimental works [6e9] also indicated that germylenoids might be important active intermediates. Very recently, Filippou et al. [10] synthesized some compounds containing metal-germanium triple bonds. They considered that the germylenoid should be an important reactant. Today the understanding on the germylenoid is not so much as the carbenoid [1,2] and silylenoid [3,4]. The germylenoid is active and it is difficult to be synthesized and stabilized. Therefore, it is necessary to carried out systemic theoretical study on germylenoids to penetrate their structures, properties, and reactions. There were a few theoretical works on the structures and properties of some kind of germylenoid H2GeMX (M ¼ Li, Na; X ¼ F, Cl) [11e15], H2C ¼ GeMX [16], H2GeClBeCl [17], H2GeClMgCl [18], H2GeClAlCl2 [19], and HB ¼ GeLiF [20]. However, we noted that theoretical studies on the reactions of the germylenoids were few and only some reactions of germylenoids with HF, H2O, NH3, and CH4 [12,13,21e23] have been calculated. As far as we know the insertion reactions of germylenoid into CeX (X ¼ F, Cl, Br) have not been systematically studied yet. In order to fill this gap and extend the reactions of the germylenoid,

* Corresponding author. Tel./fax: þ86 535 6902063. E-mail address: [email protected] (W.-Z. Li). 0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jorganchem.2012.11.012

recently, we performed theoretical study on the insertion reactions of the simplest germylenoid H2GeLiF with CH3X (X ¼ F, Cl, Br) and the calculations would (1) reveal the structures and energies of all stationary points, (2) determine the thermodynamics of the insertion reactions, (3) estimate their activation barriers, (4) clarify the reaction mechanisms, and (5) investigate the solvent effects on the insertion reactions of H2GeLiF with CH3X (X ¼ F, Cl, Br). 2. Computational details The computational details have been described elsewhere [23]. The geometries of all the stationary points were fully optimized by using the density functional theory (DFT) B3LYP (Becke’s three-parameter hybrid function with the non-local correlation of LeeeYangeParr) [24,25] method with the 6-311 þ G(d, p) [26] basis set. The geometries were first optimized and then the harmonic vibrational frequencies were calculated at the same level of theory to confirm the nature of the stationary points. The nature of a given transition state was analyzed by IRC (intrinsic reaction coordinate) [27] computations at the same level. The B3LYP/6-311 þ G(d, p) natural bond order analysis calculations were performed at the optimum geometries. In order to improve the treatment of electron correlation the single-point calculations were made at the QCISD [28,29] level using the 6-311þþG(d, p) basis set for all species. Unless otherwise noted, relative energies given in the text are those determined at QCISD/6-311þþG(d, p)//B3LYP/6-311 þ G(d, p) and include vibrational zero-point energy (ZPE, without scale) corrections determined at B3LYP/6-311 þ G(d,p) level. To consider solvent effects on the insertion reactions, the polarized continuum model

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(PCM) [30e32] was applied to the calculations and the solvent cyclohexane (C6H12) was used. All of the calculations were carried out using the Gaussian 09 program suits [33]. 3. Results and discussion The previous study [12,23] indicated that H2GeLiF had three equilibrium configurations, in which the p-complex structure was the lowest in energy and was the most stable structure. Therefore, we selected the p-complex structure as the reactant when we researched the insertion reactions of H2GeLiF and CH3X (X ¼ F, Cl, Br). In present paper, the H2GeLiF is just the p-complex structure. The insertion reactions of H2GeLiF with CH3X (X ¼ F, Cl, Br) could be described as the following formula: H2GeLiF þ CH3X / H2XGeeCH3 þ LiF (X ¼ F, Cl, Br) Based on the calculated results, we found that along the potential energy surface, there are one precursor complex (Q), one transition state (TS), and one intermediate (IM) which connect the reactants and the products. The geometries of the stationary points calculated at the B3LYP/6-311 þ G(d, p) level are shown in Fig. 1 and the relative energies of the stationary points are listed in Table 1. 3.1. The structures and energies of the precursor complexes When CH3X approaches H2GeLiF, the initial formation of the precursor complexes Q1, Q2, and Q3 are facilitated by the interaction between the p orbital on Ge and the negative X atom of CH3X. Compared with the structures of CH3X and H2GeLiF molecules, the CH3X and H2GeLiF moieties in Q1, Q2, and Q3 change little, respectively. From Fig. 1, it can be seen that the GeeX (X ¼ F, Cl, Br) bond lengths in Q1, Q2, and Q3 are very long. As listed in Table 1, the relative energies of the precursor complexes Q1, Q2, and Q3 are small. The long GeeX bond lengths and the small relative energies of the precursor complexes Q1, Q2, and Q3 indicate that the GeeX interaction is very weak. 3.2. The structures and energies of the transition states From Fig. 1 we can see that the three transition states (TS1, TS2, and TS3) have the similar structures. There is a three-membered ring (CGeX, X ¼ F, Cl, Br) in each TS. The CeX bond lengths of the TSs are longer than that of CH3X. For example, for TS1, the CeF2 bond length (1.935  A) is about 0.540  A longer than the CeF bond length (1.395  A) of CH3F. Compared with the respective precursor complexes, the GeeC and GeeX (X ¼ F, Cl, Br) bond lengths of TSs become shorter and the CGeX bond angles of TSs become larger. The changes of the bond lengths and CGeX bond angles imply the fracturing of the CeX bond and the forming of the GeeX and GeeC bonds. The frequency analysis calculations indicated that the three TSs have unique imaginary frequency. The B3LYP/6-311 þ G(d, p) calculated imaginary frequency of TS1, TS2, and TS3 is 549.9i, 434.8i,and 419.8i cm1, respectively. The IRC calculations displayed that the TSs connected the precursor complexes and the intermediates. As listed in Table 1, the relative energies of TS1, TS2, and TS3 to their reactants are 220.06, 229.43, and 207.69 kJ/mol, respectively. Therefore the reaction barriers are 226.58, 238.01, and 216.2 kJ/mol when X ¼ F, Cl, and Br, respectively. 3.3. The structures and energies of the intermediates and products As shown in Fig. 1, IM1, IM2, and IM3 are the three intermediates of the three insertion reactions. From Fig. 1, we can see that

the XGeC (X ¼ F, Cl, Br) bond angles of IMs are much larger than that of TSs. For example, for IM1, the F2GeC (101.0 ) bond angle is about 53.8 larger than the F2GeC (47.2 ) bond angle of TS1. In the IMs, the CeX bonds have been fractured completely. The GeeC and GeeX (X ¼ F, Cl, Br) bond lengths of IMs are shorter than those of TSs respectively. For example, for IM1, the GeeC bond length is about 0.652  A shorter than that of TS1 and the GeeF2 bond length is about 0.277  A shorter than that of TS1. The short of the GeeC and GeeX (X ¼ F, Cl, Br) bond lengths imply that the GeeC and GeeX (X ¼ F, Cl, Br) bond have been almost formed. As listed in Table 1, the relative energies of IM1, IM2, and IM3 to their reactants are 180.87, e172.47, and 173.89 kJ/mol, respectively. The B3LYP/6-311 þ G(d, p) calculations indicated that the IMs could dissociate to H2XGeeCH3 and LiF, which were the products of the insertion reactions of H2GeLiF and CH3X (X ¼ F, Cl, Br). The dissociations of IMs are monotonously energy increasing process. As listed in Table 1, the relative energies of the products (H2XGee CH3 þ LiF) of the three insertion reactions of X ¼ F, Cl, and Br to their reactants are 124.34, e124.69, and 127.31 kJ/mol, respectively. The three insertion reactions are all exothermic. 3.4. The mechanisms of the insertion reactions Taking the insertion reaction of H2GeLiF þ CH3F as an example, IRC calculations have been performed on the basis of the calculated TS1 to investigate the interaction between two reactants in the insertion process. The total energy change and the variations of CeF2, GeeF2, GeeC, and GeeF1 bond distances along the IRC path are shown in Fig. 2. From Fig. 2, it can be seen that as the reaction coordinate passes from point 5.0 to 0.0, the total energy increases sharply and reaches its maximum. In this region, the Ce F2 and GeeF1 distances increase and the GeeC and GeeF2 distances decrease evidently. The GeeC and GeeF2 distances then approach a constant, and GeeC and GeeF2 bonds form at around point 10.0 with the decomposition of the CeF2 and GeeF1 bonds. We think other insertion reactions of H2GeLiF with CH3X (X ¼ Cl, Br) have the same mechanism with H2GeLiF þ CH3F reaction. It is well known that the germylenes undergo characteristic chemical reactions such as insertion into a single bond [34]. The simplest germylene H2Ge can also react with CH3X (X ¼ F, Cl, Br) and the products are same as those from H2GeLiF. We also calculated the insertion reactions of H2Ge þ CH3X (X ¼ F, Cl, Br) using the B3LYP and QCISD methods. The calculated results indicated that along the reaction pathways of H2Ge þ CH3X / H2XGeeCH3, there were no intermediates, which is different from H2GeLiF þ CH3X / H2XGee CH3 þ LiF. 3.5. The solvent effect To consider the solvent effects on the reactions, using the PCM model and the C6H12 solvent, the B3LYP/6-311þG(d, p) geometry optimizations were carried out, and then the QCISD/6-311þþG(d, p) single-point calculations were performed at the B3LYP/6311þG(d, p) optimized geometries. The calculated relative energies are also listed in Table 1. It can be seen from Table 1 that the relative energies of the TSs, IMs, and products for the three insertion reactions calculated in THF are lower respectively than those calculated in gas phase. The energy barriers of the three insertion reactions calculated in C6H12 are 218.12, 221.48, and 204.29 kJ/mol, respectively. Compared with those in gas phase, the barrier heights in C6H12 are lower, implying insertion reactions are easier to occur in C6H12. It is apparent that the three insertion reactions in C6H12 are thermodynamically exothermic.

W.-Z. Li et al. / Journal of Organometallic Chemistry 724 (2013) 163e166

Li

Li H 2.448 2.037

C

H

H

F2 2.099

Cl 2.525

2.169

H H

TS1

1.639

2.786

101.0 Ge

H H

C

2.331

H

H Ge

Ge

Br

H

Ge

H

H

H

IM3

H Ge

H

1.957

2.025

H

P3

Cl

1.395

H

H

P2

F

F

C

H

H

P1

F

2.357

2.356 108.2

C

H

1.636

2.824

Li

C H

Li

H

C H

IM2

1.955

1.950

H

102.3

H

2.203 107.6

H

TS3

1.950

H

Cl

1.784 106.3

2.353

H

H

H H

Br 2.434

C

H IM1

F

F

1.948

H

H

1.637

H

C

H

H

2.816

1.946

2.135

Li

Ge

101.9

Ge

2.999

C

TS2

F

57.6

2.758

H

Cl 2.272

F1

Br 2.696

2.153

3.029

H

1.674 2.665

H

F Ge

Li

H

F2 1.822

2.671

55.6

2.598

C

Li H

1.670

H

2.629

1.935

H

H

F1

H

H

Li

2.650

47.2

C

H

1.669

Ge

4.069

Q3

Li H

2.035

28.9

1.967

H

H

H

Ge

Q2

C

H

H

F

3.597

2.030

4.040

Q1

1.724 2.451

H

Br

1.809

3.829

F

26.6

Cl

F2 1.401

H

2.452

Ge

3.560

19.5

Li

1.725

H

F1 Ge

3.032

H

1.724

H

165

LiF

Br

1.806

Li

H1 H2

1.965

2.454

C

C

H

C

H

Ge

H H

CH3F

F

H

H H

1.729

2.016

H H

CH3Cl

CH3Br

H2GeLiF

Fig. 1. The geometries of the stationary points of the insertion reactions of the germylenoid H2GeLiF with CH3X (X ¼ F, Cl, Br) in gas phase calculated at B3LYP/6-311 þ G(d, p) level (Bond lengths are given in angstroms and angles in degrees).

3.6. The substituent effect We also calculated the insertion reactions of some substituent germylenoids HXGeLiF (X ¼ F, Cl, Br) with CH3F. The calculated results indicated that the mechanisms of the insertion reactions of

HXGeLiF (X ¼ F, Cl, Br) with CH3F are similar to the insertion reaction of H2GeLiF with CH3F. And along the reaction path, there are also one precursor complex (Q), one transition state (TS), and one intermediate (IM) which connect the reactants and the products. The relative energies of the stationary points are listed in

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Table 1 Relative energiesa (kJ/mol) of precursor complexes (Qs), transition states (TSs), intermediates (IMs), and productsb. Species

X¼F

X ¼ Cl

X ¼ Br

H2GeLiF þ CH3X Q TS IM H2GeXeCH3 þ LiF

0.00 6.52 (2.59) 220.06 (215.53) 180.87 (193.30) 124.34 (152.36)

0.00 8.58 (4.07) 229.43 (217.41) 172.47 (189.63) 124.69 (150.97)

0.00 8.51 (4.38) 207.69 (199.91) 173.89 (192.41) 127.31 (153.16)

a Calculated at the QCISD/6-311þþG(d, p)//B3LYP/6-311 þ G(d, p) level and include vibrational zero-point energy (ZPE, without scale) corrections determined at B3LYP/6-311 þ G(d, p) level. b Values in parentheses were calculated in C6H12.

to occur in C6H12. The three insertions are thermodynamically exothermic both in gas phase and in C6H12. The insertion reactions of some substituent germylenoids HXGeLiF (X ¼ F, Cl, Br) with CH3F were also calculated, and the results indicated that the substituent effect is small on this kind of reaction. The elucidations of the mechanism of these insertion reactions provide a new reaction mode of germaniumecarbon bond formation. Acknowledgments This research was supported by the National Natural Science Foundation Committee of China (No. 21103145), the Natural Science Foundation of Shandong Province (No. ZR2009BQ006) and the Fund for Doctor of Yantai University (No. HY05B30). Professor Cheng acknowledges support by the Open fund (sklssm201216) of the State Key Laboratory of Supramolecular Structure and Materials, Jilin University. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]

Fig. 2. The changes of energies and bond distances along the reaction coordinates.

Table 2 Relative energiesa (kJ/mol) of precursor complexes (Qs), transition states (TSs), intermediates (IMs), and products of the insertion reactions of HXGeLiF (X ¼ F, Cl, Br) with CH3F. Species

X¼F

X ¼ Cl

X ¼ Br

HXGeLiF þ CH3F Q TS IM HXGeFeCH3 þ LiF

0.00 6.32 225.28 171.45 107.59

0.00 7.45 227.23 157.42 118.49

0.00 7.01 229.44 149.19 117.62

a

Calculated at the QCISD/6-311þþG(d, p)//B3LYP/6-311 þ G(d, p) level and include vibrational zero-point energy (ZPE, without scale) corrections determined at B3LYP/6-311 þ G(d, p) level.

Table 2. It can be seen from Table 2 that energy barriers of the three insertion reactions are 231.60, 234.68, and 236.45 kJ/mol, respectively. Comparing to the energy barrier of the insertion reaction of H2GeLiF with CH3F 226.58 kJ/mol, the change of the energy barriers is little. On the other hand, when the X ¼ F, Cl, and Br, the energy barriers of the three insertion reactions are much near to each other, indicating that the substituent effect is small on this kind of reaction.

[11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33]

4. Conclusions The insertion reactions of the germylenoid H2GeLiF with CH3X (X ¼ F, Cl, Br) were studied for the first time by using the DFT B3LYP and QCISD methods. The theoretical calculations predicted that along the potential energy surface, there are one precursor complex, one transition state, and one intermediate which connect the reactants and the products. The energy barriers in gas phase are higher than those in C6H12, indicating insertion reactions are easy

[34]

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