English

• 1. INTRODUCTION

  Carbon-carbon bonds are the most common chemical bonds, and constitute the frameworks of organic molecules^[1-5]. Nowadays, direct activation of C–C bonds to initiate sequential reactions is a long-pursued goal of synthetic chemists. Compared with the on-going C–H bond activation, the catalytic activation of C–C bonds is still an under-developed domain in synthetic organic chemistry^{[6, 7]}.

  The C–C bond activation is divided into two main subsets involving strained rings^[8-12] and unstrained C–C bonds^[13-17]. Most of these cyclic compounds are generally activated with the aid of transition metals or their organometallic complexes. In contrast with the few reports on activation of unstrained rings^[12], the catalytic activation and ring expansion of strained rings have attracted much attention for decades. However, with regard to strained carbocycles, investigations on cyclobutane derivatives lagged behind the three-membered-ring compounds. In 2012, Xu and coworkers^{[18, 19]} reported the Rh(Ⅰ)-catalyzed olefin carboacylation as well as the high regioselectivity and enantioselectivity in the formation of poly-fused rings, where the four-membered rings of benzocyclobutenone derivatives were activated by chiral Rh(Ⅰ) complexes to generate Rh–C covalent bonds, followed by recyclization and formation of poly-fused rings with five- and six-membered carbocycles. Metal-carbon bonds are the foundation of entire organometallic chemistry^[20-22], and cyclization as well as ring expansion from strained rings to larger five- and six-membered rings has received systematic attention and becomes an important synthetic technology^[23-26]. In the present work, the activation of C–C bond of a benzocyclobutenone derivative and the bonding characters of the newly-formed Ph–C bond as well as the recylization and ring-expansion mechanisms will be explored with density functional theory (DFT) methods.

  Chirality is a fundamental chemical property in nature and in living systems^[27-29]. Based on the experimental results^{[18, 19]}, the same workgroup has investigated the reaction mechanisms of the Rhcatalyzed carboacylation of benzocyclobutenones using B3LYP and M06 density functionals with the Ph₂P(CH₂)_nPPh₂ (n = 1~4) and R-SEGPHOS ligands in 2015^[30], and our workgroup has carried out DFT calculations on this Rh(Ⅰ)-catalyzed activation and recyclization mechanism with (4R,5R)-trans-4,5-bis(diphenylphosphino)-2,2-dime-thyl-1,3-dioxolane as the ligand^[31]. We also have reported the reaction mechanism and chiral enantioselectivity of Rh(Ⅰ)-catalyzed olefin carboacylation in the formation of poly-fused rings in gas phase, THF and water^[32]. In the present work, to investigate the reaction characteristics of chiral reactant, the methyl on vinyl group is moved to the adjacent carbon atom to create a chiral center (Scheme 1). In contrast with the experimental study using the 2,3-O-isopropylidene-2,3-dihydroxy-1,4-bis(diphen-ylphosphino)butane (DIOP) ligand, a different chiral (4R, 5S)-trans-4,5-bis(diphenylphosphino)-2,2-dime-thyl-1,3-dioxolane ligand (termed R,S-L in this work) was employed. After introducing an extraordinary stereogenic center in the reactant, the catalytic system becomes very complicated. With the aid of the chiral catalysts [Rh(R,S-L)]⁺, the R-reactant can be catalyzed to R,S- and R,R-products, and the S-one will be recyclized to S,R- and S,S-products. The formation mechanisms of these 4 optical isomers will be discussed from the view of thermodynamics based on full optimization by using the BP86 functional in gas phase and in tetrahydrofuran (THF) as solvent, and the M06-2X functional in THF. The role of solvent THF to the catalytic mechanisms will also be considered. This work can provide new insights into the enantioselectivity and regioselectivity in asymmetric synthesis.

  Scheme 1

  

  Scheme 1.  C–C activation and ring expansion in this work.

  The Arabic numerals besides atoms are sequence numbers for the selected atoms

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  2. COMPUTATIONAL DETAILS

  All molecular structures were fully optimized with G09 program package^[33] without any constraints, and frequency verification was performed to identify whether a stationary point was a transition state or a local minimum according to the number of imaginary frequency (0 or 1)^[34]. Then the vibrational analyses on the imaginary frequencies were used to preliminarily confirm transition states. The standard 6-31G(d,p) basis set^[35-37] was applied for C, P, O and H, and the Hay and Wadt effective core potentials with a double-ζ valence basis set (LanL2DZ)^[38-42] was used to describe Rh atoms. The BP86 functional has shown computational efficiency and better agreement with experimental spectra^{[43, 44]}. So, originally, the reaction mechanisms were elucidated on the basis of full optimization at the BP86/6-31G(d,p) level without any solvent, then discussed again based on full optimization at the same level in THF by using the polarized continuum model (PCM)^[45-48] to describe the solvation effect. Subsequently, as the more computationally expensive M06-2X functional^[49-51] has good performance to describe noncovalent interactions in the main-group thermochemistry^[52-55], all species in THF were fully re-optimized at the PCM//M06-2X/6-31G(d,p) level to clarify the role of the solvent and the discrepancies between these two functionals in investigating reaction mechanisms. In the BP86 and M06-2X calculations with THF as the solvent, intrinsic reaction coordinate (IRC) calculations^[56-60] were also carried out to confirm the connections of transition states.

  In gas phase, the counterpoise=2 keyword was employed to estimate the Basis Set Superposition Error (BSSE)^[61-63] between reactants/products and the chiral catalyst at the BP86/6-31G(d,p) level. To obtain natural population analysis (NPA) charges^[64-66], the natural bond orbital (NBO) analysis was performed at the same basis set level. The frontier orbitals (HOMOs and LUMOs) were read from the check point files.

  3. RESULTS AND DISCUSSION

  The R- and S-enantiomers of the reactant coordinate to the catalyst [Rh(R,S-L)]⁺ to yield R,S-, R,R- and S,R- and S,S-products. The lowest frequencies and their vibrational mode assignments, the electronic and zero-point energies E, thermal enthalpies H, and thermal free energies G as well as their relative values for all species involving these 4 reaction channels obtained by the BP86 method in gas phase and in THF, and by the M06-2X method in THF are listed in Tables S1~S3 of Supporting Information, and the Cartesian coordinates of all species involved the R,S-, S,R-, R,R- and S,S-reaction pathways obtained at the BP86/6-31G(d,p) level in THF are shown in Table S4. The optimized structural parameters of the reactant and catalyst in gas phase and THF are shown in Fig. S1 of Supporting Information, and the optimized R,S-P, S,R-P, R,R-P and S,S-P are depicted in Fig. 1.

  Figure 1

  

  Figure 1.  Optimized structures of the product in this work obtained by the BP86 functional in gas phase and THF (in brackets) as well as by M06-2X in THF (in square brackets). Bond lengths are in Å. Cyan balls denote the methyl

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  From the BP86 calculations in gas phase and THF it can be seen that the THF just slightly alters the bond lengths except some strained bonds in five-membered rings, such as the C–C bond in the catalyst and C–O bond in the products, which may imply that THF will influence the molecular geometries of intermediates and transition states and further the reaction mechanisms. Fig. 1 and Fig. S1 also show that, in THF the M06-2X bond distances are generally shorter than the BP86 ones. However, all above-mentioned methods correctly predict that the racemate pairs (R-R and S-R, R,S-P and S,R-P, and R,R-P and S,S-P) bear the same structures and energies. The BP86 method estimates that R,S-P/S,R-P is more stable than R,R-P/S,S-P by a free energy difference of 6.5 kJ/mol in gas phase and 6.3 kJ/mol in THF because in R,R-P/S,S-P the methyl group and hydrogen atom stand in the same side of the five-membered tetrahydrofuran ring and avoid steric hindrance. The optimized geometrical parameters of the intermediates and transition states producing the diastereomeric pair of R,S-P and S,R-P are illustrated in Figs. 2 an 3, and the optimized structures of transition states in the formation of R,R-P and S,S-P are schematically represented in Fig. 4. Moreover, the detailed structural parameters involving the R,R- and S,S-pathways are depicted in Figs. S2 and S3 of Supporting Information.

  Figure 2

  

  Figure 2.  Optimized structural parameters of all intermediates and transition states involving the [Rh(R,S-L)]⁺-catalyzed reaction channel of R-R → R,S-P obtained by BP86 functionals in gas phase and in THF (in brackets) as well as by M06-2X in THF (in square brackets). Bond lengths are in Å. Except that R,S-P is based on the M06-2X skeleton, the other molecular frameworks are drawn from the gas-phase results. Symbols: = -CH₃, = Ph

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  Figure 3

  

  Figure 3.  Optimized structural parameters of all intermediates and transition states involving the [Rh(R,S-L)]⁺-catalyzed reaction channel of S-R → S,R-P obtained by BP86 functionals in gas phase and in THF (in brackets) as well as by M06-2X in THF (in square brackets). Bond lengths are in Å. The molecular frameworks are drawn from the gas-phase results. Symbols: = –CH₃, = Ph

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  Figure 4

  

  Figure 4.  Optimized schematic structures of the transition states in the R,R- and S,S-channels obtained by the BP86 functional in gas phase and in THF (in brackets). Bond lengths are in Å. The molecular frameworks are drawn from the gas-phase results. stands for the catalyst of [Rh(R,S-L)]⁺

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  3.1 Catalytic mechanism in gas phase

  The solvent will affect the configurations of the catalyst, intermediates and transition states, so in comparison with those in THF, the catalytic mechanisms in gas phase are also discussed. The potential energy surface (PES) profiles obtained with the BP86 functional in gas phase are illustrated in Fig. 5.

  Figure 5

  

  Figure 5.  Potential energy surfaces (PES) for the 4 [Rh(R,S-L)]⁺-catalyzed reaction pathways obtained from the BP86 method in gas phase. The black, red, green and blue lines represent the reaction channels leading to S,R-P, R,S-P, R,R-P and S,S-P, respectively. All relative Gibbs free energies in kJ/mol are compared with [Rh(R,S-L)]⁺ + R/S-R

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  The Rh atom of [Rh(R,S-L)]⁺ initially coordinates to the active sites surrounded by the ether oxygen atom, the vinyl group, the C=O bond and the strained C(3)–C(4) bond to yield R,S-IM1, S,R-IM1, R,R-IM1 and S,S-IM1. However, their coordination modes are different, and the complexation with the C–C bonds in R,S-IM1 and S,S-IM1 is relatively weak, as illustrated by the highest occupied molecular orbitals (HOMOs) in Fig. 6. Fig. 6 also shows that the HOMOs of IM1 are mainly the lone-pair electrons on Rh influenced by the coordination bonds. The noncovalent interactions (NCI)^[67] in the 4 conformations of IM1, which were simulated by the reduced density gradient (RDG) functions presented in the medium quality grid with Multiwfn 3.6^{[68, 69]} and visualized by VMD 1.9.2^[70], are illustrated in Fig. 7. Fig. 7 shows that the 4 isomers of IM1 have complex van der Waals interactions and steric repulsion, especially a distinct π-π stacking between a benzene ring of the ligand and the benzocyclobutenone moiety. Moreover, there are van der Waals interactions of Rh with the C(3) atom (2.452 Å) in S,R-IM1 and the C(4) atom (2.845 Å) in R,R-IM1, so the breaking C(3)–C(4) bond in S,R-IM1 and R,R-IM1 is effectively activated. However, in R,S-IM1 and S,S-IM1, Rh is covalently bonded to the C=C bond, and links to the ether O atom with a very strong van der Waals interaction. Via TS1, the Rh atom is inserted into the breaking C(3)–C(4) bond, which is extended to 1.773, 1.757, 1.684 and 1.844 Å in R,S-TS1, S,R-TS1, R,R-TS1 and S,S-TS1, respectively, forming two Rh–C covalent bonds with the activated C(3) and C(4) atoms. Then via TS2, the vinyl C(1) atom links the benzene ring to generate a five-membered ring, and the terminal vinyl C(2) atom is covalently connected to the Rh atom. Finally, C(2) is bonded to C(4) to yield intermediate IM4, followed by the departure of the catalyst.

  Figure 6

  

  Figure 6.  The highest occupied molecular orbitals (HOMO) of IM1 obtained at the BP86/6-31G(d,p)//LanL2DZ level in gas phase and in THF

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  Figure 7

  

  Figure 7.  Noncovalent interaction (NCI) isosurfaces (isovalue = 0.05 e) for the 4 isomers of IM1 obtained with Multiwfn 3.6 and VMD 1.9.2. The complex van der Waals interactions are filled in green, and the steric interactions at the centers of the ring structures are marked in red

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  When the products coordinate to the catalyst, the BSSE values of R,S-IM1, S,R-IM1, R,R-IM1 and S,S-IM1 are 39.0, 33.7, 33.7 and 35.0 kJ/mol, and those of R,S-IM4, S,R-IM4, R,R-IM4 and S,S-IM4 are 32.8, 21.7, 21.2 and 21.2 kJ/mol, respectively. All of them are lower than 40 kJ/mol, and have no influence to calculate the energy barriers. So in the present work, the BSSE values will not discussed. The PES profiles demonstrate that, along the reaction coordinates, the relative free energies of intermediates decrease gradually. For the C–C bond activation, the energy barriers of R,S- and S,S-channels are 52.3 and 49.6 kJ/mol, much higher than those of S,R- and R,R-channels. The reason may be that the hydrogen atom on C1 atom lying above the molecular plane leads to weaker complexation between Rh and the vinyl group but a stronger coordination bond between Rh and C(3)–C(4). The rate-determining steps of R,S- and S,S-channels are the formation of the six-membered rings via TS3 with barriers of 61.7 and 79.4 kJ/mol, but S,R- and R,R-channels are dominated by the formation of five-membered rings via TS2 with barriers of 65.8 and 113.6 kJ/mol, respectively. The energy barriers suggest that, although the reaction pathway leading to R,S-P is energetically more favorable, the products are a mixture of S,R-P, R,S-P, and even a little S,S-P. According to the relative free energy values^[71] at T = 298.15 K, Boltzmann conformational population p_i can be estimated from $ {p_i} = \frac{{{e^{ - {G_i}/RT}}}}{{\sum\limits_j {{e^{ - {G_j}/RT}}} }} = \frac{{{e^{ - \Delta {G_i}/RT}}}}{{\sum\limits_j {{e^{ - \Delta {G_j}/RT}}} }} $, where ΔG_i is the relative Gibbs free energy of the ith conformer compared with the most stable one. As a result, if just determining the relative free energy between S,R-P/R,S-P and R,R-P/S,S-P, the S,R-P and R,S-P pair equally constitutes about 93.2% of the outcome optical isomers in gas phase. However, due to the existence of poly-fused rings, one configuration cannot be transformed to the other ones, so the conformational population may mainly depend on the rate-determining steps. The rate-determining barriers of the S,S- and R,S-channels are much lower than those of the R,R- and S,R-pathways, so they are the candidates for the energetically most favorable reaction channel. According to the energy vertexes along the reaction coordinates, the relative energy of S,S-TS1 is lower than that of R,S-TS1 by 16.8 kJ/mol, so the S,S-channel may proceed more rapidly. However, the R,S-channel has lower rate-limiting barrier toward the more stable product, so it is energetically more favorable.

  3.2 Catalytic mechanism in THF

  Then based on the gas-phase molecular geometries, all species of the 4 reaction pathways were re-optimized at the BP86/6-31G(d,p) level in THF. The optimized geometrical parameters are also illustrated in Figs. 2~4, and the PES profiles are shown in Fig. 8. Compared with the gas-phase molecular structures, THF alters some weak interactions. For example, in R,S-IM1 the coordination bond of Rh–C(1) is extended from 2.207 to 2.223 Å. For S,S-IM1, the interactions between the catalyst and S-R are dominated by the coordination linkage between Rh and the vinyl group, as illustrated in Fig. 6. However, the coordination mode of IM4 changes significantly. For S,R-IM4, R,R-IM4 and S,S-IM4, Rh terminally coordinates to the C=O oxygen atoms of the product moieties in gas phase, but Rh coordinates to the C=O double bonds in THF. So in THF, these solvent molecules will disturb the interactions of Rh with the reactant enantiomers to elevate the relative energies of IM1, and further hoist the whole potential energy surfaces.

  Figure 8

  

  Figure 8.  Potential energy surfaces (PES) for the 4 [Rh(R,S-L)]⁺-catalyzed reaction pathways obtained from the BP86 method in THF. The black, red, green and blue lines represent the reaction channels leading to S,R-P, R,S-P, R,R-P and S,S-P, respectively. All relative Gibbs free energies in kJ/mol are compared with [Rh(R,S-L)]⁺ + R/S-R

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  Adding a monodentate THF molecule to the catalyst [Rh(R,S-L)]⁺ is an energetically favorable (ΔG = –7.3 kJ/mol) and exothermic (ΔH = –56.9 kJ/mol) process, as shown in Fig. S4. The interaction between THF and the catalyst with a Rh···O coordination bond of 2.172 Å is comparable with or much stronger than the interactions in S,R-, R,S-, R,R- and S,S-IM1. Thus, on the whole, the displacement of a solvent molecule by S-R or R-R elevates the relative energies of all species. THF only marginally influences the free-energy barriers, and does not change the rate-determining steps of these 4 channels. The energy barriers of the rate-determining steps of the S,R-, R,S-, S,S- and R,R-channels are 64.0, 67.0, 78.0 and 112.1 kJ/mol, respectively. The S,R-channel is also energetically most favorable. However, without regard to energy barriers, the Boltzmann conformational population of S,R-P and R,S-P is 92.7% in THF according to an energy difference of 6.3 kJ/mol.

  3.3 Catalytic mechanism in THF with the M06-2X method

  The M06-2X functional can better describe weak interactions. To validate the reaction mechanisms in this work, the two energetically most preferable reaction pathways (R,S- and S,R-channels) in THF were reinvestigated at the M06-2X/6-31G(d,p) level. The optimized structures are depicted in Figs. 2 and 3, and the PES profiles are displayed in Fig. 9. The theoretical results show that the coordination bonds and weak interactions in transition states are slightly different from those obtained by the BP86 functional. Fig. 9 indicates that R,S-IM1 and S,R-IM1 are much more stable than the corresponding ones optimized by the BP86 functional. In fact, compared with the optimized results by the BP86 functional, in IM1, TS1 and IM2, the bond lengths of Rh–C(1) and Rh–C(2) coordination bonds are much longer, but from TS2 via IM3 to TS3, the Rh–C(2) bond is stronger.

  Figure 9

  

  Figure 9.  Potential energy surfaces (PES) for the S,R- (black line) and R,S- (red line) reaction pathways catalyzed by [Rh(R,S-L)]⁺ obtained from the M06-2X method in THF. All relative Gibbs free energies in kJ/mol are compared with [Rh(R,S-L)]⁺ + R/S-R

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  The varieties on optimized structures lead to the decline of relative energies of R,S-IM1 and S,R-IM1, which are much more stable under the M06-2X theoretical model. In the M06-2X results, the 3 energy barriers of S,R- and R,S-channels are 63.5, 94.4, 44.0 kJ/mol and 88.0, 77.0, 44.1 kJ/mol, so the R,S-channel are energetically favorable. Compared with the BP86 results in THF, except for R,S-TS3, the barriers of other transition states are higher than the BP86 ones, and the rate-determining barriers are also elevated.

  3.4 Electron population analysis of the S,R- and R,S-channels

  Electron population analysis is a mathematical way of partitioning electron density into charges on the nuclei, bond orders, and other related information^{[72, 73]}. There are no dependable experimental tools to observe electron population. Electron population analysis may mirror the structural variation, so the NPA charges are employed to elucidate the reaction mechanisms of the S,R- and R,S-channels. The NPA charges obtained by the BP86 functional in gas phase and in THF as well as by the M06-2X functional in THF are listed in Table 1.

  Table 1

  

  Table 1.  NPA Charges for C(1), C(2), C(3) and C(4) Atoms Involving the S,R- and R,S-Channels Obtained by the BP86 Functional in Gas Phase and in THF as well as by the M06-2X Functional in THF

  DownLoad: CSV

  Species	BP86 in gas phase				BP86 in THF				M06-2X in water
  	C(1)	C(2)	C(3)	C(4)	C(1)	C(2)	C(3)	C(4)	C(1)	C(2)	C(3)	C(4)
  R,S-IM1	–0.325	–0.463	–0.182	0.574	–0.302	–0.466	–0.183	0.571	–0.281	–0.447	–0.205	0.631
  R, S-TS1	–0.249	–0.467	–0.255	0.509	–0.251	–0.464	–0.256	0.507	–0.254	–0.444	–0.268	0.597
  R,S-IM2	–0.272	–0.457	–0.134	0.601	–0.272	–0.450	–0.132	0.603	–0.265	–0.432	–0.143	0.660
  R,S-TS2	–0.226	–0.540	–0.175	0.604	–0.225	–0.532	–0.170	0.603	–0.204	–0.539	–0.193	0.680
  R,S-IM3	–0.309	–0.589	–0.133	0.586	–0.311	–0.587	–0.128	0.580	–0.311	–0.579	–0.142	0.658
  R,S-TS3	–0.312	–0.602	–0.109	0.490	–0.311	–0.601	–0.107	0.489	–0.309	–0.610	–0.126	0.591
  R,S-IM4	–0.308	–0.576	–0.077	0.589	–0.306	–0.573	–0.068	0.598	–0.303	–0.556	–0.100	0.692
  S,R-IM1	–0.295	–0.450	–0.315	0.561	–0.295	–0.453	–0.314	0.565	–0.289	–0.435	–0.328	0.621
  S,R-TS1	–0.274	–0.436	–0.253	0.525	–0.273	–0.436	–0.251	0.523	–0.267	–0.429	–0.271	0.623
  S,R-IM2	–0.261	–0.491	–0.192	0.551	–0.263	–0.484	–0.201	0.549	–0.250	–0.459	–0.221	0.634
  S,R-TS2	–0.224	–0.507	–0.137	0.610	–0.223	–0.506	–0.139	0.611	–0.188	–0.522	–0.163	0.697
  S,R-IM3	–0.312	–0.579	–0.088	0.565	–0.314	–0.586	–0.083	0.558	–0.313	–0.570	–0.093	0.638
  S,R-TS3	–0.313	–0.575	–0.094	0.517	–0.314	–0.601	–0.087	0.488	–0.310	–0.623	–0.095	0.584
  S,R-IM4	–0.300	–0.555	–0.102	0.621	–0.304	–0.563	–0.095	0.635	–0.276	–0.549	–0.180	0.629

  The C(4) atom is one of the positive charge centers. In gas phase, along with the elongation of the breaking C(1)–C(2) bond, from IM1 via TS1 to IM2, the NPA charge on C(1) changes from –0.325 via –0.249 to –0.272 e in the R,S-channel, and from –0.295 via –0.274 to –0.261 e in the S,R-channel, implying that the coordination of catalyst with the C=C bond is weakened. The same tendency also occurs on the C(3) atom. However, the negative charge on C(3) of these two intermediates in the S,R-channel is much higher than that in the R,S-channel, suggesting they are more stable than those in R,S-channel and may have a more higher energy barrier. From IM2 via TS2 to IM3, when C(1) links to C(3) in these 2 reaction pathways, the negative charge on C(2) increases gradually, but the C(2) atom in the R,S-channel has more negative charge than the one in the S,R-channel. Then from IM3 to IM4, the negative charge on C(2) decreases gradually, but in the R,S-channel, C(2) bears more negative charge, which may suggest that it will be more inclined to combine with the C(4) atom.

  In THF, the BP86 functional predicts that the NPA charges only change slightly, so the free energy barriers also alter marginally. However, the structurally large variations obtained by M06-2X are also reflected on the NPA charges. Compared with the BP86 results in THF, from IM1 via TS1 to IM2, the C(4) atom has more positive charge, C(3) bears more negative charge, and C(2) has less negative charge. After the formation of IM2, the positive charge on C(4) is increased, but the negative charge on C(3) is decreased, so there is a larger charge difference in the S,R-channel with a lower barrier. After C(1) is bonded to C(3) via TS2, the negative charge on C(1) is increased from –0.265 to –0.311 e in the R,S-channel and from –0.250 to –0.313 e in the S,R-channel. In the formation of the six-membered ring, C(2) is one of the negative charge centers, and C(4) is one of the positive centers, so it is not surprising that these 2 pathways have relatively low barriers.

  4. CONCLUSION

  In the beginning, the enantioselectivity and reaction mechanisms of the olefin carboacylation in the formation of poly-fused rings catalyzed by [Rh(R,S-L)]⁺ were investigated at the BP86/6-31G(d,p) level in gas phase and THF. The strained C–C bond in the benzocyclobutenone derivatives with a vinyl group is activated, and then the vinyl group is bonded to this activated C–C bond to form a five- and a six-membered rings. The chiral center in the reactant and the newly-formed asymmetric center in the formation of the six-membered ring lead to 4 configurations of the products, viz. R,S-, S,R-, R,R- and S,S-products. THF as the solvent can influence the molecular structures and energy barriers, and increase the enantioselectivity in this reaction system. In gas phase and THF, the rate-determining steps of S,R- and R,R-channels are the formation of five-membered rings, but those of R,S- and S,S-channels are the formation of six-membered rings. The energy barriers of R,S-, S,R-, R,R- and S,S- rate-determining steps are 61.7, 65.8, 113.6 and 79.4 kJ/mol in gas phase and 67.0, 64.0, 112.1 and 78.0 kJ/mol in THF. Then the R,S- and S,R-pathways were re-investigated at the M062X/6-31G(d,p) level in THF. However, the M062X functional elevates the relative energies of intermediates and transition states except for IM1. The electron population analysis based on the NPA charges is also carried out. The change of NPA charges can reflect the variation of molecular structures to interpret reaction mechanisms to some extent.

  
  
• 1. [1]

     Jun, C. H. Transition metal-catalyzed carbon-carbon bond activation. Chem. Soc. Rev. 2004, 33, 610−618. doi: 10.1039/B308864M

  2. [2]

     Chen, F.; Wang, T.; Jiao, N. Recent advances in transition-metal-catalyzed functionalization of unstrained carbon-carbon bonds. Chem. Rev. 2014, 114, 8613−8661. doi: 10.1021/cr400628s

  3. [3]

     Zhu, B.; Guan, W.; Yan, L. K.; Su, Z. M. Two-state reactivity mechanism of benzene C−C activation by trinuclear titanium hydride. J. Am. Chem. Soc. 2016, 138, 11069−11072. doi: 10.1021/jacs.6b02433

  4. [4]

     Hartwig, J. F. Evolution of C−H bond functionalization from methane to methodology. J. Am. Chem. Soc. 2016, 138, 2−24. doi: 10.1021/jacs.5b08707

  5. [5]

     Kim, D. S.; Park, W. J.; Jun, C. H. Metal-organic cooperative catalysis in C–H and C–C bond activation. Chem. Rev. 2017, 117, 8977–9015. doi: 10.1021/acs.chemrev.6b00554

  6. [6]

     Wentzel, M. T.; Reddy, V. J.; Hyster, T. K.; Douglas, C. J. Chemoselectivity in catalytic C–C and C–H bond activation: controlling intermolecular carboacylation and hydroarylation of alkenes. Angew. Chem. Int. Ed. 2009, 48, 6121−6123. doi: 10.1002/anie.200902215

  7. [7]

     Obenhuber, A.; Ruhland, K. Activation of an unstrained C(sp²)–C(sp²) single bond using chelate-bisphosphinite rhodium(Ⅰ) complexes. Organometallics 2011, 30, 4039−4051. doi: 10.1021/om200288e

  8. [8]

     Namyslo, J. C.; Kaufmann, D. E. The application of cyclobutane derivatives in organic synthesis. Chem. Rev. 2003, 103, 1485−1537. doi: 10.1021/cr010010y

  9. [9]

     Rubin, M.; Rubina, M.; Gevorgyan, V. Transition metal chemistry of cyclopropenes and cyclopropanes. Chem. Rev. 2007, 107, 3117−3179. doi: 10.1021/cr050988l

  10. [10]

      Shi, M.; Shao, L. X.; Lu, J. M.; Wei, Y.; Mizuno, K.; Maeda, H. Chemistry of vinylidenecyclopropanes. Chem. Rev. 2010, 110, 5883–5913. doi: 10.1021/cr900381k

  11. [11]

      Seiser, T.; Saget, T.; Tran, D. N.; Cramer, N. Cyclobutanes in catalysis. Angew. Chem. Int. Ed. 2011, 50, 7740–7752. doi: 10.1002/anie.201101053

  12. [12]

      Mack, D. J.; Njardarson, J. T. Recent advances in the metal-catalyzed ring expansions of three- and four-membered rings. ACS Catal. 2013, 3, 272−286. doi: 10.1021/cs300771d

  13. [13]

      Suggs, J. W.; Jun, C. H. Synthesis of a chiral rhodium alkyl via metal insertion into an unstrained C–C bond and use of the rate of racemization at carbon to obtain a rhodium-carbon bond dissociation energy. J. Am. Chem. Soc. 1986, 108, 4679–4681. doi: 10.1021/ja00275a086

  14. [14]

      Müller, C.; Iverson, C. N.; Lachicotte, R. J.; Jones, W. D. Carbon-carbon bond activation in Pt(0)-diphenylacetylene complexes bearing chelating P,N- and P,P-ligands. J. Am. Chem. Soc. 2001, 123, 9718–9719. doi: 10.1021/ja016675z

  15. [15]

      Ruhland, K.; Obenhuber, A.; Hoffmann, S. D. Cleavage of unstrained C(sp²)–C(sp²) single bonds with Ni⁰ complexes using chelating assistance. Organometallics 2008, 27, 3482–3495. doi: 10.1021/om800054m

  16. [16]

      Sun, M.; Shen, G.; Bao, W. Regioselective cleavage of unstrained C–C bond and C–H bond: palladium-copper catalyzed deacetophenonylative arylation of coumarin derivatives. Adv. Synth. Catal. 2012, 354, 3468–3474. doi: 10.1002/adsc.201200539

  17. [17]

      Zhou, W.; Fan, W.; Jiang, Q.; Liang, Y. F.; Jiao, N. Copper-catalyzed aerobic oxidative C–C bond cleavage of unstrained ketones with air and amines. Org. Lett. 2015, 17, 2542–2545. doi: 10.1021/acs.orglett.5b01114

  18. [18]

      Xu, T.; Ko, H. M.; Savage, N. A.; Dong, G. Highly enantioselective Rh-catalyzed carboacylation of olefins: efficient syntheses of chiral poly-fused rings. J. Am. Chem. Soc. 2012, 134, 20005–20008. doi: 10.1021/ja309978c

  19. [19]

      Xu, T.; Dong, G. Rhodium-catalyzed regioselective carboacylation of olefins: a C–C bond activation approach for accessing fused-ring systems. Angew. Chem. Int. Ed. 2012, 51, 7567–7571. doi: 10.1002/anie.201202771

  20. [20]

      Lyon, J. T.; Andrews, L. An infrared spectroscopic and theoretical study of group 4 transition metal CH₂=MCl₂ and HC÷MCl₃ complexes. Organometallics 2007, 26, 332–339. doi: 10.1021/om0608399

  21. [21]

      Cheng, X. Density functional theory investigation on the reaction mechanisms of Ti (³F) with CH₂Cl₂ and CHCl₃ to CH₂=TiCl₂ and HC÷TiCl₃. Chin. J. Struct. Chem. 2016, 35, 193–198.

  22. [22]

      Sberegaeva, A. V.; Zavalij, P. Y.; Vedernikov, A. N. Oxidation of a monomethylpalladium(Ⅱ) complex with O₂ in water: tuning reaction selectivity to form ethane, methanol, or methylhydroperoxide. J. Am. Chem. Soc. 2016, 138, 1446−1455. doi: 10.1021/jacs.5b12832

  23. [23]

      Dowd, P.; Zhang, W. Free radical-mediated ring expansion and related annulations. Chem. Rev. 1993, 93, 2091–2115. doi: 10.1021/cr00022a007

  24. [24]

      Zsoldos-Mády, V.; Ozohanics, O.; Csámpai, A.; Kudar, V.; Frigyes, D.; Sohár, P. Ferrocenyl pyrazolines: preparation, structure, redox properties and DFT study on regioselective ring-closure. J. Organomet. Chem. 2009, 694, 4185–4195. doi: 10.1016/j.jorganchem.2009.09.007

  25. [25]

      Yasui, E.; Ootsuki, R.; Takayama, K.; Nagumo, S. Unique ring expansion of a 6-3 bicyclic ring system forming a functionalized 7-membered ring accelerated by nitrogen functional groups. Tetra. Lett. 2017, 58, 3092–3095. doi: 10.1016/j.tetlet.2017.06.061

  26. [26]

      Chen, X.; Xu, J. Synthesis of 3-acyl-5,6-dihydro-1,4-oxathiines through ring expansion of thiiranes. Tetra. Lett. 2017, 58, 1651–1654. doi: 10.1016/j.tetlet.2017.03.039

  27. [27]

      Chen, Q.; Zhou, J.; Han, Q.; Wang, Y.; Fu, Y. Electrochemical enantioselective recognition of tryptophane enantiomers based on chiral ligand exchange. Colloid. Surface B 2012, 92, 130–135. doi: 10.1016/j.colsurfb.2011.11.031

  28. [28]

      Liu, M.; Zhang, L.; Wang, T. Supramolecular chirality in self-assembled systems. Chem. Rev. 2015, 115, 7304–7397. doi: 10.1021/cr500671p

  29. [29]

      Sanganyado, E.; Lu, Z.; Fu, Q.; Schlenk, D.; Gan, J. Chiral pharmaceuticals: a review on their environmental occurrence and fate processes. Water Res. 2017, 124, 527–542. doi: 10.1016/j.watres.2017.08.003

  30. [30]

      Lu, G.; Fang, C.; Xu, T.; Dong, G.; Liu, P. Computational study of Rh-catalyzed carboacylation of olefins: ligand-promoted rhodacycle isomerization enables regioselective C–C bond functionalization of benzocyclobutenones. J. Am. Chem. Soc. 2015, 137, 8274−8283. doi: 10.1021/jacs.5b04691

  31. [31]

      Cheng, X.; Li, F.; Zhao, Y.; Wang, Z.; Wang, C. A. Activation and recyclization of a benzocyclobutenone derivative catalyzed by a chiral Rh(Ⅰ) complex based on DFT investigations. Chem. Pap. 2019, 73, 995–1001. doi: 10.1007/s11696-018-0641-1

  32. [32]

      Cheng, X.; Li, Y.; Zhao, Y.; Liu, Y. Reaction mechanism of Rh(Ⅰ)-catalyzed olefin carboacylation: chiral enantioselectivity in the formation of poly-fused rings. Chem. J. Chin. U. 2018, 39, 521–529.

  33. [33]

      Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery Jr., J. A.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Keith, T.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09, Revision C. 01, Gaussian, Inc., Wallingford CT 2010.

  34. [34]

      Prince, B. M.; Cundari, T. R. Computational study of methane C−H activation by earth-abundant metal amide/aminyl complexes. Organometallics 2017, 36, 3987−3994. doi: 10.1021/acs.organomet.7b00600

  35. [35]

      Krompiec, S.; Bujak, P.; Malarz, J.; Krompiec, M.; Skórka, Ł.; Pluta, T.; Danikiewicz, W.; Kania, M.; Kusz, J. An isomerization-1,3-dipolar cycloaddition tandem reaction towards the synthesis of 3-aryl-4-methyl-5-O-substituted isoxazolines from O-allyl compounds. Tetrahedron 2012, 68, 6018−6031. doi: 10.1016/j.tet.2012.05.027

  36. [36]

      Cheng, X.; Zhao, Y.; Liu, Y.; Li, F. Role of F^- in the hydrolysis-condensation mechanisms of silicon alkoxide Si(OCH₃)₄: a DFT investigation. New J. Chem. 2013, 37, 1371–1377. doi: 10.1039/c3nj41140k

  37. [37]

      Cheng, X. Cyclization mechanisms of the cyclic dimer of aziridine aldehyde with vinyl aldehyde. Comput. Theor. Chem. 2017, 1113, 105–109. doi: 10.1016/j.comptc.2017.05.013

  38. [38]

      Wadt, W. R.; Hay, P. J. Ab initio effective core potentials for molecular calculations. Potentials for main group elements Na to Bi. J. Chem. Phys. 1985, 82, 284–298. doi: 10.1063/1.448800

  39. [39]

      Wadt, W. R.; Hay, P. J. Ab initio effective core potentials for molecular calculations. Potentials for K to Au including the outermost core orbitals. J. Chem. Phys. 1985, 82, 299–310. doi: 10.1063/1.448975

  40. [40]

      Petrović, Z. D.; Petrović, V. P.; Simijonović, D.; Marković, S. Insight into hydrolytic reaction of N-acetylated L-histidylglycine dipeptide with novel mechlorethamine platinum(Ⅱ) complex. NMR and DFT study of the hydrolytic reaction. Dalton Trans. 2011, 40, 9284–9288. doi: 10.1039/c1dt10593k

  41. [41]

      Andrada, D. M.; Granados, A. M.; Solà, M.; Fernández, I. DFT study of thermal 1,3-dipolar cycloaddition reactions between alkynyl metal(0) Fischer carbene complexes and 3H-1,2-dithiole-3-thione derivatives. Organometallics 2011, 30, 466–476. doi: 10.1021/om1007105

  42. [42]

      Liu, R.; Zhang, J.; Han, L.; Liu, T. Mechanistic insight into the ruthenium-catalyzed cycloaddition of diynes with 2,3-diphenyl-2H-azirines: a theoretical study. Comput. Theor. Chem. 2018, 1127, 16–21. doi: 10.1016/j.comptc.2018.02.002

  43. [43]

      Wang, H.; Xie, Y.; King, R. B.; Schaefer Ⅲ, H. F. Binuclear cyclopentadienylcobalt carbonyls: comparison with binuclear iron carbonyls. J. Am. Chem. Soc. 2005, 127, 11646−11651. doi: 10.1021/ja051554a

  44. [44]

      Darmon, J. M.; Stieber, S. C. E.; Sylvester, K. T.; Fernández, I.; Lobkovsky, E.; Semproni, S. P.; Bill, E.; Wieghardt, K.; DeBeer, S.; Chirik, P. J. Oxidative addition of carbon-carbon bonds with a redox-active bis(imino)pyridine iron complex. J. Am. Chem. Soc. 2012, 134, 17125−17137. doi: 10.1021/ja306526d

  45. [45]

      Ke, Z.; Abe, S.; Ueno, T.; Morokuma, K. Rh-catalyzed polymerization of phenylacetylene: theoretical studies of the reaction mechanism, regioselectivity, and stereoregularity. J. Am. Chem. Soc. 2011, 133, 7926−7941. doi: 10.1021/ja2012565

  46. [46]

      Suarez-Bertoa, R.; Saliu, F.; Bruschi, M.; Rindone, B. Reaction products and mechanism of the regioselective oxidation of N-phenylmorpholine by ozone. Tetrahedron 2012, 68, 8267–8275. doi: 10.1016/j.tet.2012.07.055

  47. [47]

      Raczyńska, E. D.; Michalec, P.; Zalewski, M.; Sapuła, M. Effects of ionization on stability of 1-methylcytosine — DFT and PCM studies. J. Mol. Model. 2016, 22, 146–14. doi: 10.1007/s00894-016-3020-2

  48. [48]

      Santos, C. I. A. V.; Ramos, M. L.; Justino, L. L. G.; Burrows, H. D.; Valente, A. J. M.; Esteso, M. A.; Leaist, D. G.; Ribeiro, A. C. F. Effect of pH in the structure and mass transport by diffusion of theophylline. J. Chem. Thermodyn. 2017, 110, 162−170. doi: 10.1016/j.jct.2017.02.019

  49. [49]

      Gadžurić, S.; Tot, A.; Armaković, S.; Armaković, S.; Panić, J.; Jović, B.; Vraneš, M. Uncommon structure making/breaking behaviour of cholinium taurate in water. J. Chem. Thermodyn. 2017, 107, 58–64. doi: 10.1016/j.jct.2016.12.025

  50. [50]

      Shi, Q.; Wang, Y.; Wei, D. Theoretical study on DABCO-catalyzed ring expansion of cyclopropyl ketone: mechanism, chemoselectivity, and role of catalyst. Comput. Theor. Chem. 2018, 1123, 20−25. doi: 10.1016/j.comptc.2017.11.013

  51. [51]

      Cheng, X. Structures, bonding and thermodynamics of extracting U(Ⅵ) from aqueous nitric acid solutions with N-methyl-N-decyl-octanamide and its amide derivatives: an M06-2X investigation. J. Chem. Thermodyn. 2019, 132, 470−475. doi: 10.1016/j.jct.2017.11.001

  52. [52]

      Zhao, Y.; Truhlar, D. The M06 suite of density functionals for main group thermochemistry, thermochemical kinetics, noncovalent interactions, excited states, and transition elements: two new functionals and systematic testing of four M06-class functionals and 12 other functionals. Theor. Chem. Acc. 2008, 120, 215−241. doi: 10.1007/s00214-007-0310-x

  53. [53]

      Schenker, S.; Schneider, C.; Tsogoeva, S. B.; Clark, T. Assessment of popular DFT and semiempirical molecular orbital techniques for calculating relative transition state energies and kinetic product distributions in enantioselective organocatalytic reactions. J. Chem. Theory Comput. 2011, 7, 3586−3595. doi: 10.1021/ct2002013

  54. [54]

      Tot, A.; Armaković, S.; Armaković, S.; Gadžurić, S.; Vraneš, M. Kosmotropism of newly synthesized 1-butyl-3-methylimidazolium taurate ionic liquid: experimental and computational study. J. Chem. Thermodyn. 2016, 94, 85–95. doi: 10.1016/j.jct.2015.10.026

  55. [55]

      Salehi, Y.; Hamzehloueian, M. The strain-promoted alkyne-nitrone and alkyne-nitrile oxide cycloaddition reactions: a theoretical study. Tetrahedron 2017, 73, 4634–4643. doi: 10.1016/j.tet.2017.06.038

  56. [56]

      Gonzalez, C.; Schlegel, H. B. An improved algorithm for reaction path following. J. Chem. Phys. 1989, 90, 2154–2161. doi: 10.1063/1.456010

  57. [57]

      Gonzalez, C.; Schlegel, H. B. Reaction path following in mass-weighted internal coordinates. J. Phys. Chem. 1990, 94, 5523–5527. doi: 10.1021/j100377a021

  58. [58]

      Zheng, W.; Ariafard, A.; Lin, Z. Understanding the highly regioselective cyanothiolation of 1-alkynes catalyzed by palladium phosphine complexes. Organometallics 2008, 27, 246–253. doi: 10.1021/om7009446

  59. [59]

      Naka, A.; Takase, S.; Shimada, A.; Kobayashi, H.; Ishikawa, M. Platinum-catalyzed reactions of 2,3-bis(dimethylsilyl)furan with alkynes. J. Organomet. Chem. 2017, 853, 13–17. doi: 10.1016/j.jorganchem.2017.10.016

  60. [60]

      Zhang, X.; Liu, Y.; Chen, G.; Pei, G.; Bi, S. Theoretical insight into C(sp³)−F bond activations and origins of chemo- and regioselectivities of ″tunable″ nickel-mediated/-catalyzed couplings of 2-trifluoromethyl-1-alkenes with alkynes. Organometallics 2017, 36, 3739–3749. doi: 10.1021/acs.organomet.7b00514

  61. [61]

      Boys, S. F.; Bernardi, F. The calculation of small molecular interactions by the differences of separate total energies. Some procedures with reduced errors. Mol. Phys. 1970, 19, 553−566. doi: 10.1080/00268977000101561

  62. [62]

      Simon, S.; Duran, M.; Dannenberg, J. J. How does basis set superposition error change the potential surfaces for hydrogen-bonded dimers? J. Chem. Phys. 1996, 105, 11024−11031. doi: 10.1063/1.472902

  63. [63]

      Zhu, R.; Zhang, D.; Wu, J.; Liu, C. Theoretical study of the bifunctional-urea catalyzed Michael reaction of 1,3-dicarbonyl compounds and nitroolefins: reaction mechanism and enantioselectivity. Tetrahedron: Asymmetr. 2006, 17, 1611–1616. doi: 10.1016/j.tetasy.2006.05.033

  64. [64]

      Reed, A. E.; Weinstock, R. B.; Weinhold, F. Natural population analysis. J. Chem. Phys. 1985, 83, 735−746. doi: 10.1063/1.449486

  65. [65]

      Uggla, R.; Sundberg, M. R.; Nevalainen, V. Boronic acids as molecular sensors NBO analysis and ¹³C chemical shifts as tools for evaluation of DFT geometry optimization of complexes of diphenylmethane 3, 3'-diboronic acids and glucose. Tetrahedron: Asymmetr. 1996, 7, 1741−1748. doi: 10.1016/0957-4166(96)00208-X

  66. [66]

      Uggla, R.; Nevalainen, V.; Sundberg, M. R. On the role of π-stacking in aldehyde complexes of N-sulphonylated oxazaborolidinones used as chiral catalysts. Tetrahedron: Asymmetr. 1996, 7, 2725−2732. doi: 10.1016/0957-4166(96)00351-5

  67. [67]

      Johnson, E. R.; Keinan, S.; Mori-Sánchez, P.; Contreras-García, J.; Cohen, A. J.; Yang, W. Revealing noncovalent interactions. J. Am. Chem. Soc. 2010, 132, 6498–6506. doi: 10.1021/ja100936w

  68. [68]

      Lu, T.; Chen, F. Multiwfn: a multifunctional wavefunction analyzer. J. Comput. Chem. 2012, 33, 580−592. doi: 10.1002/jcc.22885

  69. [69]

      Keerthi, A.; Geim, A. K.; Janardanan, A.; Rooney, A. P.; Esfandiar, A.; Hu, S.; Dar, S. A.; Grigorieva, I. V.; Haigh, S. J.; Wang, F. C.; Radha, B. Ballistic molecular transport through two-dimensional channels. Nature 2018, 558, 420–424. doi: 10.1038/s41586-018-0203-2

  70. [70]

      Humphrey, W.; Dalke, A.; Schulten, K. VMD: visual molecular dynamics. J. Mol. Graphics 1996, 14, 33−38. doi: 10.1016/0263-7855(96)00018-5

  71. [71]

      Amesty, Á.; Burgueño-Tapia, E.; Joseph-Nathan, P.; Ravelo, Á. G.; Estévez-Braun, A. Benzodihydrofurans from cyperus teneriffae. J. Nat. Prod. 2011, 74, 1061−1065. doi: 10.1021/np200020t

  72. [72]

      Cheng, X. L.; Li, G. X.; Wang, Z. M.; Zhao, Y. Y.; Sun, Y. F. Theoretical investigation of CH₃CF₂O₂ + HOO reaction. Chin. J. Chem. Phys. 2007, 20, 243−248. doi: 10.1088/1674-0068/20/03/243-248

  73. [73]

      Cheng, X. L.; Zhao, Y. Y.; Li, F.; Li, L. Q.; Tao, X. J. Reaction mechanism of the multi-channel decomposition reactions of 1-pentenyl free radicals. Chin. J. Chem. 2008, 26, 44−50. doi: 10.1002/cjoc.200890036

• 

  Scheme 1  C–C activation and ring expansion in this work.

  The Arabic numerals besides atoms are sequence numbers for the selected atoms

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  Figure 1  Optimized structures of the product in this work obtained by the BP86 functional in gas phase and THF (in brackets) as well as by M06-2X in THF (in square brackets). Bond lengths are in Å. Cyan balls denote the methyl

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  Figure 2  Optimized structural parameters of all intermediates and transition states involving the [Rh(R,S-L)]⁺-catalyzed reaction channel of R-R → R,S-P obtained by BP86 functionals in gas phase and in THF (in brackets) as well as by M06-2X in THF (in square brackets). Bond lengths are in Å. Except that R,S-P is based on the M06-2X skeleton, the other molecular frameworks are drawn from the gas-phase results. Symbols: = -CH₃, = Ph

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  Figure 3  Optimized structural parameters of all intermediates and transition states involving the [Rh(R,S-L)]⁺-catalyzed reaction channel of S-R → S,R-P obtained by BP86 functionals in gas phase and in THF (in brackets) as well as by M06-2X in THF (in square brackets). Bond lengths are in Å. The molecular frameworks are drawn from the gas-phase results. Symbols: = –CH₃, = Ph

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  Figure 4  Optimized schematic structures of the transition states in the R,R- and S,S-channels obtained by the BP86 functional in gas phase and in THF (in brackets). Bond lengths are in Å. The molecular frameworks are drawn from the gas-phase results. stands for the catalyst of [Rh(R,S-L)]⁺

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  Figure 5  Potential energy surfaces (PES) for the 4 [Rh(R,S-L)]⁺-catalyzed reaction pathways obtained from the BP86 method in gas phase. The black, red, green and blue lines represent the reaction channels leading to S,R-P, R,S-P, R,R-P and S,S-P, respectively. All relative Gibbs free energies in kJ/mol are compared with [Rh(R,S-L)]⁺ + R/S-R

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  Figure 6  The highest occupied molecular orbitals (HOMO) of IM1 obtained at the BP86/6-31G(d,p)//LanL2DZ level in gas phase and in THF

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  Figure 7  Noncovalent interaction (NCI) isosurfaces (isovalue = 0.05 e) for the 4 isomers of IM1 obtained with Multiwfn 3.6 and VMD 1.9.2. The complex van der Waals interactions are filled in green, and the steric interactions at the centers of the ring structures are marked in red

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  Figure 8  Potential energy surfaces (PES) for the 4 [Rh(R,S-L)]⁺-catalyzed reaction pathways obtained from the BP86 method in THF. The black, red, green and blue lines represent the reaction channels leading to S,R-P, R,S-P, R,R-P and S,S-P, respectively. All relative Gibbs free energies in kJ/mol are compared with [Rh(R,S-L)]⁺ + R/S-R

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  Figure 9  Potential energy surfaces (PES) for the S,R- (black line) and R,S- (red line) reaction pathways catalyzed by [Rh(R,S-L)]⁺ obtained from the M06-2X method in THF. All relative Gibbs free energies in kJ/mol are compared with [Rh(R,S-L)]⁺ + R/S-R

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  Table 1.  NPA Charges for C(1), C(2), C(3) and C(4) Atoms Involving the S,R- and R,S-Channels Obtained by the BP86 Functional in Gas Phase and in THF as well as by the M06-2X Functional in THF

  Species	BP86 in gas phase				BP86 in THF				M06-2X in water
  	C(1)	C(2)	C(3)	C(4)	C(1)	C(2)	C(3)	C(4)	C(1)	C(2)	C(3)	C(4)
  R,S-IM1	–0.325	–0.463	–0.182	0.574	–0.302	–0.466	–0.183	0.571	–0.281	–0.447	–0.205	0.631
  R, S-TS1	–0.249	–0.467	–0.255	0.509	–0.251	–0.464	–0.256	0.507	–0.254	–0.444	–0.268	0.597
  R,S-IM2	–0.272	–0.457	–0.134	0.601	–0.272	–0.450	–0.132	0.603	–0.265	–0.432	–0.143	0.660
  R,S-TS2	–0.226	–0.540	–0.175	0.604	–0.225	–0.532	–0.170	0.603	–0.204	–0.539	–0.193	0.680
  R,S-IM3	–0.309	–0.589	–0.133	0.586	–0.311	–0.587	–0.128	0.580	–0.311	–0.579	–0.142	0.658
  R,S-TS3	–0.312	–0.602	–0.109	0.490	–0.311	–0.601	–0.107	0.489	–0.309	–0.610	–0.126	0.591
  R,S-IM4	–0.308	–0.576	–0.077	0.589	–0.306	–0.573	–0.068	0.598	–0.303	–0.556	–0.100	0.692
  S,R-IM1	–0.295	–0.450	–0.315	0.561	–0.295	–0.453	–0.314	0.565	–0.289	–0.435	–0.328	0.621
  S,R-TS1	–0.274	–0.436	–0.253	0.525	–0.273	–0.436	–0.251	0.523	–0.267	–0.429	–0.271	0.623
  S,R-IM2	–0.261	–0.491	–0.192	0.551	–0.263	–0.484	–0.201	0.549	–0.250	–0.459	–0.221	0.634
  S,R-TS2	–0.224	–0.507	–0.137	0.610	–0.223	–0.506	–0.139	0.611	–0.188	–0.522	–0.163	0.697
  S,R-IM3	–0.312	–0.579	–0.088	0.565	–0.314	–0.586	–0.083	0.558	–0.313	–0.570	–0.093	0.638
  S,R-TS3	–0.313	–0.575	–0.094	0.517	–0.314	–0.601	–0.087	0.488	–0.310	–0.623	–0.095	0.584
  S,R-IM4	–0.300	–0.555	–0.102	0.621	–0.304	–0.563	–0.095	0.635	–0.276	–0.549	–0.180	0.629

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