Theoretical Study on the Reaction Mechanism of Ti with CH3CN in the

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Theoretical Study on the Reaction Mechanism of Ti with CHCN in the Gas Phase 3

Xiaoli Wang, Yongcheng Wang, Shuang Li, Yuwei Zhang, and Panpan Ma J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/acs.jpca.6b04733 • Publication Date (Web): 01 Jul 2016 Downloaded from http://pubs.acs.org on July 3, 2016

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The Journal of Physical Chemistry

Theoretical Study on the Reaction Mechanism of Ti with CH3CN in the Gas Phase

Xiaoli Wang, Yongcheng Wang*, Shuang Li, Yuwei Zhang, and Panpan Ma

College of Chemistry and Chemical Engineering, Northwest Normal University

Lanzhou, Gansu 730070, P.R. China

*

Corresponding author: E-mail: [email protected]; Fax: + 86-13893691912

ACS Paragon Plus Environment


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ABSTRACT: To gain a deeper understanding of the reaction mechanisms of Ti with acetonitrile molecules, the triplet and singlet spin-state potential energy surfaces (PESs) has been investigated at B3LYP level of density functional theory (DFT). Crossing points between the different PESs and possible spin inversion processes are discussed by spin-orbit coupling (SOC) calculation. In addition, the bonding properties of the species along the reaction were analyzed by electron localization function (ELF), atoms in molecules (AIM) and natural bond orbital (NBO). The results showed that acetonitrile activation by Ti is a typical spin-forbidden process,


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larger SOC (by 220.12cm-1) and possibility of crossing between triplet and singlet imply that intersystem crossing (ISC) would occur near the minimum energy crossing point (MECP) during the transfer of hydrogen atom.

1. INTRODUCTION ACS Paragon Plus Environment


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The transition metals play an important role in the catalysis, so it is very necessary to further study the catalytic mechanism and potential chemical value. The special nature of the electronic structure of d orbital is the essential reason for having transition metal catalysis. According to the Hund’s rule,1-3 the transition metal d electrons on the orbital share orbitals by spin parallel to make energy lowest, the ground state of their atoms and ions as well as weak ligands coordination complex are high spin states. However, during the reaction of the transition metal participated,4-9 due to the rearrangement of d electronic, metal center may form different electronic configuration so as to accommodate different bonding abilities to avoid high energy barrier and make the reaction proceed along the low-energy pathway. Thus, spin-forbidden reaction without conserved total spin may form with the change of the total spin of the system before and after. That is to say, the reaction accompanied with spin flip possibly occurs on two or more potential energy surfaces, the two-state/multiple-state reaction (TSR/MSR), which has been confirmed and reported by Schroder et al.10-14 Recently, the Andrew’s group15 carried out a detailed experiment and theoretical research for group 4 transition metal atoms with acetonitrile. Although the lowest energy product, CH2=M(H)NC, was supported by theory, the detailed theoretical study about the spin inversion process of the reaction path have not been taken into account. After that, Wang’s group also made a prediction on the reaction. However, it did not come to a detailed and precise conclusion. In this study, the reaction of Ti with CH3CN was as research subjects in order to clearly understand the theoretical


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mechanism of the reaction system of transition metal with acetonitrile. The geometries and energies of all intermediates and transition states were optimized and calculated in the single and triplet state, we determined the crossing points (CP) and the minimum energy crossing point (MECP), calculated the spin-orbit coupling (SOC) constant and the probability of intersystem crossing to obtain useful kinetic information. In addition, we also analyzed the evolution of the bonds along the reaction process by diverse methods including electronic localization function (ELF), atoms in molecules (AIM) and natural bond orbital (NBO) to better explain the reaction path.

2. CALCULATION METHOD 2.1 Geometrical Optimization Density function theory (DFT)16 in terms of the applicability for the reaction of Ti with CH3CN has been confirmed.15,18 In this paper, stationary points of single, triplet and part of quintet states in the reaction system were full optimized using (U)B3LYP19-20 method (the Becke’s three-parameter hybrid functional (B3)21 combined with the Lee-Yang-Parr(LYP)20 correlation functional), 6-311++G(3df, 3pd) basic set. Vibrational analysis confirmed that transition states have only one negative eigenvalue, the energy of other stationary points local minimum on the PESs (without any imaginary frequency). The intrinsic reaction coordinate (IRC) was then calculated to check if the correct transition state was located and further verify the reliability of elementary reaction steps. The single point calculation were performed at the



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(U)CCSD(T)22-26 level, cc-PVTZ27 basic sets to obtain more accurate relative energy. The crossing point (CP) between the two PESs was approximately located using the method of vertical excitation, presented by Yoshizawa,28 which main idea is to achieve single-point energy calculations (in spin state) as a function of the structural change along the IRC of the other spin state and vice versa. The minimum energy crossing point (MECP) was further defined using the method of energy gradient optimization by virtue of Crossing 2004 packages, which was also applied by Harvey29 et al.

The investigation of the bonding evolution along the pathway is relied on the analysis of the electron localization function (ELF),30-32 which shows maxima at the most probable positions of localized electron pairs and each special position is surrounded by a basin in which there is an increased probability of finding an electron pair. It was performed with the Multiwfn33 package. The topological properties of the (3,-1) bond critical points (bcp) in the gradient field of the electron density were analyzed using the atoms-in-molecules (AIM) theory34-35 as applied in the Multiwfn code.

2.2 Spin-Orbit Coupling Calculations According to the non-adiabatic theory, intersystem crossing may occur at the crossing point between different spin potential surfaces, which degree of difficulty depends on the degree of spin-orbit coupling at the point. Therefore, we estimated the spin-orbit coupling constant at the MECP with the help of GAMESS36-37 package,


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which based on the approximation one-electron spin-coupled Hamiltonian operator38-39 given in Equation 1, at the same time, according to the Landau-Zener theory40-41, we calculated the PLZ, which is the probability for hopping from one adiabatic surface to another during a single pass through the crossing region; P1ISC, which is the probability of hopping from one diabatic state to other on the first pass through the crossing region; and P2ISC, the probability of hopping during a potential double pass, which is given by (1-PLZ) plus PLZ(1-PLZ)(the probability of not hopping on the first pass, then hopping on the second pass). As are shown in Equation(2),(3) and (4).

H SO

α2

 Z k*   3 (Si ⋅ Lik ) = ∑ hi Z * = ∑∑ 2 i k  rik  i

α2

( )

− 2pH 2 SOC PLZ = exp( [∆F ]

P1 P2

ISC

ISC

e2 h = 2 4π me2 c 2

µ 2( E − EMECP )

= 1 − PLZ

= (1 − PLZ )(1 + PLZ )

(1)

) (2)

(3) (4)

Here, Si and Lik are the orbital and spin angular momentum operators for electron i in the framework of the nuclei indexed k, Zk* is the effective charge. HSOC is the Hamiltonian matrix element between the two different spin states, ∆F is the gradient change between the two spin potential energy surfaces, μ is the reduced mass, E is the total energy of stable point, and EMECP is the relative energy at the MECP.



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3. RESULTS AND DISCUSSION The valence shell electron configuration of Ti atom is 3d24s2, indicating that there are three different spin states (singlet, triplet and quintet). Since the energy barrier of 5IM2→5IM3 needed to overcome is too high in quintet state, which is not discussed in detail herein. The optimized geometries and main parameters of all stationary and transition points in triplet and singlet state are depicted in Figure 1 and Figure S1 (Supplementary Materials). In addition, bonding analysis of all complex involved in the reaction were performed, the results are shown in Figure 2 and Table S1(Supplementary Materials). The relative energies and schematic reaction mechanism and possible CP are presented in Table S2 and Figure 3. The detailed analysis will be gradually given in the following. (All energy mentioned in this article at the level of B3LYP, unless specially stated)


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Figure 1. Geometric parameter of the stationary and transition points on the triplet at the UB3LYP/6-311++G(3df,3pd) level (bond lengths are in angstroms and angles are in degrees)

3.1 Bonding Analysis The bonding evolution of the species for single and triplet state along the reaction pathway have been performed using three different analysis methods (ELF, AIM and NBO) to have a deeper understanding of the reaction mechanism, which were carried out using the formchk files (.fch) obtained by the Gaussian 09 programs



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were used as input files of the Multiwfn package.

The ELF localization domains (η=0.7) of the lowest-energy minima and transition states of Ti+CH3CN are shown in Figure 2. The AIM parameters42-43 of bond critical points (bcp) for all species are depicted in Table S1, which include the electron density ρ(r) and its Laplacian ▽2ρ(r) at the critical points, the potential energy density V(r), which indicates the degree of the electrons are localized in the regions, the kinetic electron energy density G(r), which positively correlated with the speed of the electrons move, and the total electron energy density H(r) or E(r), E(r) = G(r) +V(r) = H(r). A positive E(r) implies the closed-shell interaction, whereas negative E(r) is regarded as the standard of covalent character.6,42 The E(r) standard was proved to be very appropriate to characterize the nature of a bond for heavy-atom systems.44-45


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V(Ti)

V(Ti) V(Ti)

V(C-H) V(C-H) IM1(3A1)

V(C-H) TS2(3A″)

V(Ti-C1)

V(C-H)

TS1(3A)

V(Ti,C2,H)

V(Ti)

V(Ti-N)

V(Ti-H) V(Ti) V(C-H) IM3(3A)

V(Ti,C1,H)

V(Ti,N,C2) IM2(3A″) V(Ti,H,C1) V(Ti) V(C-H) TS3(3A″)

V(Ti-H)

V(C-H) V(C-H) IM4(3A″)

V(C-H) TS4(1A)

IM5(1A′)

Figure 2. ELF localization domains (η=0.70) of the lowest energy minima and transition states of the Ti+CH3CN reaction path. 1. IM1. The ELF analysis of the complex presents absence of a disynaptic valence basin between the Ti atom and N atom, indicating that the interaction between CH3CN and Ti is an electrostatic interaction. The fact is also confirmed by AIM analysis, which shows a bcp (3,-1) exists between the Ti and N atom, but the corresponding electrons density is very low (3ρ(bcp) = 0.075au, 1ρ(bcp) = 0.127au); the energy density |E(r)| is very small, although E(r) is negative (3E(r) = -0.009au, 1

E(r) = -0.046au). All of the above have proven that no bond formed between Ti and



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CH3CN, which are consistent with the results of NBO. 2. IM2. In this phase, ρ(bcp) of the Ti and N atom increases to a maximum value of the entire process, especially triplet with a relatively large amplitude (triplet state increased to 0.155au, and the singlet at 0.197au). |E(r)| also has a marked increase (3E(r) reaches -0.081au, and 1E(r) reaches -0.122au). ELF analysis reveals that the disynaptic V(Ti, N ) basin replaced by the trisynaptic V(Ti,N,C2), as indicated that the formation of the Ti-N. NBO analysis also showed that Ti forms two covalent bonds, one with N atom, and the other with C2.

3. IM3. At this stage, a V(Ti, H3) basin formed, which is consistent with the NBO analysis, that is, the C1-H3 bond is completely broken with the formation of Ti-H3 bond.

4. IM4. The existence of the V(C1,H3) and V(Ti,C1) basins by ELF, the formation of the single Ti-C1 bond and the absence of the C1-C2 bond by NBO, proving that the C1-C2 bond is completely broken, Ti fully inserted into C-CN at this step.

5. IM5. The ELF analysis shows that the V(Ti,C1,H) basin replaced by the V(Ti,H3). According to the AIM, the ρ(bcp) and |E(r)| of Ti-H3 bond have stable increase. The final product, CH2Ti(H)NC is generated with the transferring of H3 from the C1 to Ti. NBO calculations show that the C1-Ti bond is a double bond for singlet state, which is composed of σ and π bond (σ (C1-Ti) = 0.818(sp1.78) C1 + 0.575(sd5.60) Ti, π (C1-Ti) = 0.735(p) C1 + 0.678(pd20.79) Ti), while triplet state


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remains a single bond. The results show that the singlet is more stable than triplet state for the IM5.

Figure 3. The potential energy profiles including the relative energies and possible CP of the reaction Ti +CH3CN in the singlet and triplet states.

3.2 Reaction Mechanism 3.2.1 Mechanism in the Triplet State Ti (3F).

We first discuss the reaction of Ti+CH3CN on the ground state triplet in which the relatively stabilized 3

3

IM1 is formed initially. The non-bonded species of

TiNCCH3 has C3v structures and its relative energy to the reactant is -49.1 kJ/mol,

lower than that of the reactant, as is shown in Figure 3. Then, 3TiNCCH3 would instantly convert over 3TS1 across a negligible barrier, the Ti atom moving to above the C-N bond with the continuous decrease of the bond angle of Ti-N-C2, forming the



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π complex 3Ti-η2-(NC)-CH3 (3IM2) and releasing energy about 94.8 kJ/mol. Notably, the relative energy of 3IM2 is -143.9 kJ/mol, the further reduction of energy, making 3

IM2 more stable.

The next step is the insertion of Ti into the NC-CH3 bond. According to Andrew's hypothesis, it is a directly insertion motion that 3Ti from 3Ti-η2-(NC)-CH3 (3IM2 ) into the C-C bond forming the specie 3IM4.15 Our IRC research showed detailed PESs and rearrangement processes for this motion in two spin states. First, a cluster structure 3

Ti-η3-(N-C2-C1H2) (3IM3) will be formed through a higher transition-state barrier of

3

TS2 with 130.8 kJ/mol. In this step, the Ti gradually approaching the methyl group

and capturing the H3 atom from C1. The IRC calculation confirms that 3TS2 is connected to 3IM3 in the forward direction and to 3IM2 in the backward direction. Then the 3Ti atom continues to move toward C1 and eventually breaks the C1-C2 bond. Noticeably, the nitrile group is turned around while the C1-Ti bond is formed and H3 returns to the methylene (That is, 3IM4 is formed). The N≡C2 nitrile triple bond remains substantially intact during the rearrangement. The energy barrier of 3

TS3 is as high as 124.2 kJ/mol, while the exothermicity of 3IM3→3IM4 is only 47.7

kJ/mol. The last step is the H3 transfer of 3IM4 from C1 to Ti to generate 3IM5. The complex 3IM5 relative to the 3Ti+CH3CN is exothermic by 56.1 kJ/mol, remarkably, this process of hydrogen transfer has to overcome the barrier by 160.4 kJ/mol and endothermic by 153.3 kJ/mol, indicating that 3IM5 is unstable in dynamics and the last step on the triplet PES seems less likely. 3.2.2 Mechanism in the Singlet State Ti (1D).


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According to Figure 3, the singlet reaction pathway is somewhat similar to the triplet state discussed above. Compared to the triplet, 1IM1 does not maintain the C3v symmetry as 3IM1 due to the intervention of 1Ti with d3s2 configuration. The singlet transition barriers at 1TS1 by 13.7 kJ/mol, higher than 3TS1, while 1TS4 by 47.0 kJ/mol, lower than 3TS4. The complex 1IM5 relative to the 1Ti+CH3CN is exothermic by 257.5 kJ/mol, much higher than triplet, the last step just overcome the barrier by 47.0 kJ/mol and exothermic 14.1 kJ/mol, showing that 1IM5 more stable than 1IM4. The overall reaction on the singlet is hugely exothermic by 257.5 kJ/mol.

3.3 The Spin-Orbit Coupling and Probability of Intersystem Crossing The reaction starts on the triplet PES and ends on the singlet PES, which is a typical two-state reaction. Thus, the minimum energy path would go on the two PESs and a spin crossing might occur. As is shown in Figure 3, the energy crossing point (CP) for the reaction is involved among the two non-adiabatic paths. Since the energy- difference of TS4 is relatively small (only 3.6 kJ/mol), the precise single-point calculation have been done for all species in singlet and triplet to determine the presence of the energy crossing phenomena, As Table S2 shown, the energy of 1IM4

is higher than 3IM4 by 99.7 kJ/mol while 1TS4 is lower than 3TS4

by 27.0 kJ/mol, which indirectly implies that the CP exists between 1/3IM4 and 1/3TS4 and in the vicinity TS4. The CP meet the spin coupling law,46 indicating that the singlet and triplet may be mixed, the effective intersystem crossing may occur under the effect of spin-orbit coupling nearby the CP, which result is to make reaction proceed along the lower energy potential energy surface.



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Figure 4. Potential energy curve-crossing point diagram along the Intrinsic reaction coordinate.

In order to more accurately locate the position of the CP, we found the corresponding minimum energy crossing point (MECP) by Crossing 2004 packages, the corresponding structural parameters as shown in Figure 4. We also depicted the frontier molecular orbital interaction diagram of MECP structure. In Figure 5, the a″ orbital is mostly the dyz orbital of Ti, which is the highest occupied molecular orbital (HOMO) in the triplet state, but is the lowest unoccupied molecular orbital (LUMO) in the singlet state. The a′ orbital is mainly composed of the dz2 orbital of Ti, which is the lowest single occupied orbital in the triplet state, but is the highest double occupied orbital in the singlet state. In this case, the α single electron in the dyz orbital will undergo spin inversion and complete the leap from the dyz orbital to the dz2 orbital.


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As noted above, the spin-flip may occur between IM4 and TS4, when the H3 migrates from CH3 group to the Ti atom. In the singlet state, the doubly occupied orbital (instead of single-occupied orbital in the triplet) can better interact with the CH2 group to form a carbon-metal double bond.17 Besides, the spin hopping easily takes place from 3A″ to 1A′ in term of symmetry. Many theoretical studies38,46-51 have demonstrated that the mixing and the degree of difficulty between different spin states depends on the spin-orbit coupling (SOC).

Figure 5. Frontier molecular orbital interaction analysis for MECP (energies are in hartree)

It is known, the power of intersystem crossing stems from the spin-orbit coupling, in an ideal case, large SOC occurs when the spin inversion makes the spin angular momentum change, accompanied by the change of the orbital angular momentum.52 For MECP, the SOC constant is 220.12 cm-1. However, in some situations, even much larger values of SOC do not guarantee spin crossing activation, which has been



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confirmed by Cimas et al.51,53 Thus, the estimate of the probability of ISC for the reaction becomes very necessary. Using the Landau-Zener model given in the calculation methods section, the probability of single (P1ISC) and double (P2ISC) at the MECP are approximately 0.0316 and 0.0611, respectively. The high probability in the vicinity of the crossing indicates that ISC will be very efficient between the triplet and the singlet state. In other words, the effective spin flip will reduce the barrier of the reaction energy and make the reaction occurs along the lower potential energy surface.

4. CONCLUSIONS In this paper, a specific theoretical calculation has been performed to study the mechanism of the gas phase reaction of the Ti atom with CH3CN. The bonding properties of all species involved in the reaction were analyzed by ELF, AIM and NBO calculation. The singlet and triplet PESs have been studied to explore the whole reaction process at DFT-B3LYP/CCSD(T) level. Some conclusions can be summarized as follows:

(1) For the reaction, all species were optimized and analyzed, among them, some stationary states (italics in reaction formula) have been recognized by Andrews et al.7 experimentally. The initial complex, CH3CN-Ti, is formed by electrostatic interaction, because no bond formed between Ti and CH3CN at first. In the process of capturing the hydrogen, from IM4 to IM5, the C1-Ti double bond is formed in the singlet state, while triplet state remains a single bond, which better verified the crossing


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mechanism.

(2) The reaction is a typical TSR reaction. Starting with the triplet ground state of the Ti atom and the respective, very unstable 3

3

TiNCCH3 of CH3CN,

Ti-η2-(NC)-CH3 are formed at first. Then the insertion process of Ti into C-C bond

crossed two high barrier to form 3Ti-η3-(N-C2-C1H2) and CN-3Ti-CH3. Hereafter, a spin inversion and a crossing in the vicinity of TS4 make the reaction access to the lower potential energy surface, singlet state. That is to say, from 3IM4, after crossing region, the more stable 1IM5 generated. Thus, the transformation from triplet to singlet state is completed. The minimum energy reaction path can be described as follows: 1/3

3

Ti + NCCH3 →

Ti-η3-(N-C2-C1H2) →

3

TiNCCH3 → 3

3

TS1 →

3

Ti-η2-(NC)-CH3 →

TS3 → CN-3Ti-CH3 →

1/3

MECP →

3

1

TS2 →

TS4 →

CN-1TiH=CH2 (3) The constant of spin-orbit coupling and the possibility of intersystem crossing at MECP have been calculated. The high probability provides support for the spin-forbidden reaction, as discussed above that the reaction of Ti and CH3CN occurs in two different spin states from the entrance channel to the exit channel.

Supporting Information Geometries and main parameters of all stationary and transition points in singlet state. Parameters of bonding analysis at the bcp. The total and relative energy on both spin states.



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ACKNOWLEDGMENTS We greatly acknowledge financial support from the National Natural Science Foundation of China (Grant No. 21263023) and support from the Supercomputing Center of Gansu Province.

REFERENCES [1] Haule, K.; Kotliar, G. Coherence–Incoherence Crossover in the Normal State of Iron Oxypnictides and Importance of Hund's Rule Coupling. New J. Phys. 2009, 11, 025021.

[2] Ji, W.; Yan, X. W.; Lu, Z.-Y. Pressure-and Temperature-Induced Structural Phase Transitions of CaFe2As2 and BaFe2As2 Studied in the Hund’s Rule Correlation Picture. Phys. Rev. B. 2011, 83, 132504.

[3] Liu, S.; Langenaeker. W. Hund’s Multiplicity Rule: A Unified Interpretation. Theor. Chem. Acc. 2003, 110, 338-344.

[4] Si, Y.; Zhang, W.; Zhao, Y. Theoretical Investigations of Spin–Orbit Coupling and Kinetics in Reaction W+ NH3→ N≡WH3. J. Phys. Chem. A. 2012, 116, 2583-2590. [5] Cho, H. G.; Andrews, L. Infrared Spectra of the Complexes Os← NCCH3, Re← NCCH3, CH3–ReNC, CH2=Re(H)NC, and CH≡Re(H)2NC and their Mn Counterparts Prepared by Reactions of Laser-Ablated Os, Re, and Mn Atoms with Acetonitrile in Excess Argon. Organometallics. 2012, 31, 6095-6105. [6] Niu, W.; Zhang, H.; Li, P.; Gao, T. Gas ‐Phase Ammonia Activation by Th, Th+,


Page 20 of 28

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and Th2+: Reaction Mechanisms, Bonding Analysis, and Rate Constant Calculations. Int. J. Quantum Chem. 2015, 115, 6-18.

[7] Li, Q.; Qiu, Y. X.; Chen, X.-Y.; Schwarz, W. E.; Wang, S. G. Investigation of Spin-Flip Reactions of Nb + CH3CN by Relativistic Density Functional Theory. Phys. Chem. Chem. Phys. 2012, 14, 6833-6841.

[8] Cho, H. G. Matrix Infrared Spectra and DFT Computations of CH2CNH and CH2NCH Produced from CH3CN by Laser-Ablation Plume Radiation. Bull. Korean Chem. Soc. 2013, 34, 1361-1365.

[9] Roithová, J.; Schroder, D. Selective Activation of Alkanes by Gas-Phase Metal Ions†. Chem. Rev. 2009, 110, 1170-1211.

[10] Shaik, S. Danovich, D.; Fiedler, A.; Schwarz, H. Two-State Reactivity in Organometallic Gas-Phase Ion Chemistry. Helv. Chim. Acta. 1995, 78, 1393-1407.

[11] Shaik, S.; Filatov, M.; Schröder, D.; Schwarz, H. Electronic Structure Makes a Difference: Cytochrome P-450 Mediated Hydroxylations of Hydrocarbons as a Two-State Reactivity Paradigm. Chem. Eur. J. 1998, 4, 193-199.

[12] Shaik, S.; de Visser, S. P.; Ogliaro, F.; Schwarz, H.; Schröder, D. Two-State Reactivity Mechanisms of Hydroxylation and Epoxidation by Cytochrome P-450 Revealed by Theory. Curr. Opin. Chem. Biol. 2002, 6, 556-567

[13] Schröder, D.; Shaik, S.; Schwarz, H. Two-State Reactivity as a New Concept in Organometallic Chemistry §. Acc. Chem. Res. 2000, 33, 139-145.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

[14] Shaik, S. An Anatomy of the Two-State Reactivity Concept: Personal Reminiscences in Memoriam of Detlef Schröder. Int. J. Mass Spectrom. 2013, 354, 5-14. [15] Cho, H. G.; Andrews, L. IR Spectra and DFT Calculations of M-η2-(NC)-CH3, CH3-MNC, and CH2= M (H) NC Prepared by Reactions of Laser-Ablated Hf and Ti Atoms with Acetonitrile. Eur. J. Inorg. Chem. 2015, 2015, 4379-4387.

[16] Su, M. D.; Chu, S. Y. Density Functional Study of some Germylene Insertion Reactions. J. Am.Chem. Soc. 1999, 121, 4229-4237.

[17] Li, Q.; Chen, X. Y.; Qiu, Y. X.; Wang, S. G. Investigation of Spin–Flip Reactions of Zr+ CH3CN by Relativistic Density Functional Theory. J. Phys.Chem. A. 2012, 116, 5019-5025.

[18] Harvey, J. N. On the Accuracy of Density Functional Theory in Transition Metal Chemistry. Annu. Rep. Prog. Chem.,Sect. C: Phys. Chem. 2006, 102, 203-226

[19] Lee, C.; Yang, W.; Parr, R. G. Development of the Colle-Salvetti Correlation-Energy Formula into a Functional of the Electron Density. Phys. Rev. B. 1988, 37, 785.

[20] Raghavachari, K.; Trucks, G. W. Highly Correlated Systems. Excitation Energies of First Row Transition Metals Sc–Cu. J. Chem. Phys. 1989, 91, 1062-1065.

[21] Becke, A. D. Density-Functional Exchange-Energy Approximation with Correct Asymptotic Behavior. Phys. Rev. A. 1988, 38, 3098.


Page 22 of 28

Page 23 of 28

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


[22] Scuseria, G. E.; Schaefer III, H. F. Is Coupled Cluster Singles and Doubles (CCSD) more Computationally Intensive than Quadratic Configuration Interaction (QCISD)? J. Chem. Phys. 1989, 90, 3700-3703.

[23] Scuseria, G. E.; Janssen, C. L.; Schaefer Iii, H. F. An Efficient Reformulation of the Closed ‐Shell Coupled Cluster Single and Double Excitation (CCSD) Equations. J. Chem. Phys. 1988, 89, 7382-7387. [24] Purvis III, G. D.; Bartlett, R. J. A Full Coupled ‐Cluster Singles and Doubles Model: The Inclusion of Disconnected Triples. J. Chem. Phys. 1982, 76, 1910-1918. ‐Gordon, M .; Raghavachari, K Configuration

[25] Pople, J. A.; Head

Interaction. A General Technique for Determining Electron Correlation Energies. J. Chem. Phys. 1987, 87, 5968-5975.

[26] De Jong, G. T.; Geerke, D. P.; Diefenbach, A.; Bickelhaupt, F. M. DFT Benchmark Study for the Oxidative Addition of CH4 to Pd. Performance of Various Density Functionals. Chem. Phys. 2005, 313, 261-270.

[27] Dunning Jr, T. H. Gaussian Basis Sets for Use in Correlated Molecular Calculations. I. The Atoms Boron through Neon and Hydrogen. J. Chem. Phys. 1989, 90, 1007-1023.

[28] Yoshizawa, K.; Shiota, Y.; Yamabe, T. Intrinsic Reaction Coordinate Analysis of the Conversion of Methane to Methanol by an Iron–Oxo Species: A Study of Crossing Seams of Potential Energy Surfaces. J. Chem. Phys. 1999, 111, 538-545.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

[29] Harvey, J. N.; Aschi, M.; Schwarz, H.; Koch, W. The Singlet and Triplet States of Phenyl Cation. A Hybrid Approach for Locating Minimum Energy Crossing Points between Non-Interacting Potential Energy Surfaces. Theor. Chem. Acc. 1998, 99, 95-99.

[30] Becke, A. D.; Edgecombe, K. E. A Simple Measure of Electron Localization in Atomic and Molecular Systems. J. Chem. Phys. 1990, 92, 5397-5403.

[31] Gillespie, R. J.; Robinson, E. A. Gilbert N. Lewis and the Chemical Bond: The Electron Pair and the Octet Rule from 1916 to the Present Day. J. Comput. Chem. 2007, 28, 87-97.

[32] Alikhani, M. E.; Michelini, M. d. C.; Russo, N.; Silvi, B. Topological Analysis of the Reaction of Uranium Ions (U+, U2+) with N2O in the Gas Phase†. J. Phys. Chem. A. 2008, 112, 12966-12974.

[33] Lu, T.; Chen, F. Multiwfn: A Multifunctional Wavefunction Analyzer. J. Comput. Chem. 2012, 33, 580-592. [34] Li, P.; Niu, W.; Gao, T. Investigation of the Reactions of U, U+ and U2+ with Ammonia: Mechanisms and Topological Analysis. RSC Adv. 2014, 4, 29806-29817.

[35] Bader, R. A Quantum Theory; Clarendon: Oxford, England, 1990.

[36] Granovsky, A. A. www http://classic.chem.msu.su/gran/gamess/index.html. Schmidt. MW

[37] Gaenko, A.; DeFusco, A.; Varganov, S. A.; Martínez, T. J.; Gordon, M. S.


Page 24 of 28

Page 25 of 28

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Interfacing the Ab Initio Multiple Spawning Method with Electronic Structure Methods in GAMESS: Photodecay of Trans-Azomethane. J. Phys. Chem. A. 2014, 118, 10902-10908.

[38] Danovich, D.; Marian, C. M.; Neuheuser, T.; Peyerimhoff, S. D.; Shaik, S. Spin-Orbit Coupling Patterns Induced by Twist and Pyramidalization Modes in C2H4: A Quantitative Study and a Qualitative Analysis. J. Phys. Chem. A. 1998, 102, 5923-5936.

[39] Isobe, H.; Yamanaka, S.; Kuramitsu, S.; Yamaguchi, K. Regulation Mechanism of

Spin-Orbit

Coupling

in

Charge-Transfer-Induced

Luminescence

of

Imidazopyrazinone Derivatives. J. Am.Chem. Soc. 2008, 130, 132-149.

[40] Harvey, J. N.; Aschi, M. Modelling Spin-Forbidden Reactions: Recombination of Carbon Monoxide with Iron Tetracarbonyl. Faraday Discuss. 2003, 124, 129-143.

[41] Harvey, J. N. Understanding the Kinetics of Spin-Forbidden Chemical Reactions. Phys. Chem. Chem. Phys. 2007, 9, 331-343.

[42] Cremer, D.; Kraka, E. Chemical Bonds without Bonding Electron

‐Density of Analysis Su

Density—Does the Difference Electron the Chemical Bond ? Angew. Chem. Int. Ed. 1984, 23, 627-628.

[43] Di Santo, E.; Michelini, M. d. C.; Russo, N. Methane C− H Bond Activation by Gas-Phase

Th+

and

U+:

Reaction

Mechanisms

Organometallics 2009, 28, 3716-3726.


and

Bonding

Analysis.


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 28

[44] De Almeida, K.; Ramalho, T.; Neto, J.; Santiago, R.; Felicíssimo, V.; Duarte, H. Methane Dehydrogenation by Niobium Ions: a First-Principles Study of the Gas-Phase Catalytic Reactions. Organometallics. 2013, 32, 989-999. [45] Du, J.; Sun, X.; Chen, J.; Zhang, L.; Jiang, G. An Icosahedral Ta12 2+ Cluster with Spherical Aromaticity. Dalton Trans. 2014, 43, 5574-5579.

[46] Danovich, D.; Shaik, S. Spin-Orbit Coupling in the Oxidative Activation of H-H by FeO+. Selection Rules and Reactivity Effects. J. Am. Chem. Soc. 1997, 119, 1773-1786.

[47] Ermler, W. C.; Ross, R. B.; Christiansen, P. A. Spin-Orbit Coupling and. Adv. Quantum. Chem. 1988, 19, 139.

[48] Kennedy, C. J.; Siviloglou, G. A.; Miyake, H.; Burton, W. C.; Ketterle, W. Spin-Orbit Coupling and Quantum Spin Hall Effect for Neutral Atoms without Spin Flips. Phys. Rev. Lett. 2013, 111, 225301.

[49] Graham, M. J.; Zadrozny, J. M.; Shiddiq, M.; Anderson, J. S.; Fataftah, M. S.; Hill, S.; Freedman, D. E. Influence of Electronic Spin and Spin–Orbit Coupling on Decoherence in Mononuclear Transition Metal Complexes. J. Am. Chem. Soc. 2014, 136, 7623-7626.

[50] Fedorov, D. A.; Pruitt, S. R.; Keipert, K.; Gordon, M. S.; Varganov, S. A. Ab Initio

Multiple

Spawning

Method

for

Intersystem

Crossing

Dynamics:

Spin-Forbidden Transitions between 3B1 and 1A1 States of GeH2. J. Phys. Chem. A.


Page 27 of 28

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


2016, DOI: 10.1021/acs.jpca.6b01406.

[51] Cimas, A.; Rayón, V. M.; Aschi, M.; Barrientos, C.; Sordo, J. A.; Largo, A. Computational Study of the Reaction of N(D2) Atoms with CH2F Radicals: An Example of a Barrier-Free Reaction Involving very High Internal Energies. J. Chem. Phys. 2005, 123, 114312.

[52] Nian, J. Y.; Wang, Y. C.; Ma. W. P.; et al. Theoretical Investigation for the Cycle Reaction of N2O (x1∑+) with CO (1∑+) Catalyzed by IrOn+(n= 1, 2) and Utilizing the Energy Span Model to Study Its Kinetic Information. J. Phys. Chem. A. 2011, 115, 11023-11032.

[53] Cimas, A.; Rayón, V.; Barrientos, C.; Aschi, M.; Sordo, J.; Largo, A. Reaction of N(2D) Atoms with Bromomethyl Radicals: A Theoretical Study. Chem. Phys. 2006, 328, 45-52.



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Table of Contents:

In order to obtain the spin-flip mechanism of Ti with CH3CN, the two spin-state PESs have been investigated. Crossing points between the different PESs and possible spin inversion processes are discussed by spin-orbit coupling (SOC) calculation. The frontier molecular orbital of MECP structure is analyzed. The results showed that acetonitrile activation by Ti is a typical spin-forbidden process.


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Theoretical Study on the Reaction Mechanism of Ti with CH3CN in the

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