Computational Investigation of Scandium-Based Catalysts for Olefin

Article Cite This: Organometallics XXXX, XXX, XXX−XXX

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Computational Investigation of Scandium-Based Catalysts for Olefin Hydroaminoalkylation and C−H Addition Gen Luo,‡ Fan Liu,‡ Yi Luo,*,‡ Guangli Zhou,‡ Xiaohui Kang,‡,§ Zhaomin Hou,*,∥ and Lun Luo*,‡,†

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Hubei Key Laboratory of Wudang Local Chinese Medicine Research, School of Pharmaceutical Sciences, Hubei University of Medicine, Shiyan 442000, China ‡ State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of Technology, Dalian 116024, China § College of Pharmacy, Dalian Medical University, Dalian, Liaoning 116044, China ∥ Organometallic Chemistry Laboratory, RIKEN Cluster for Pioneering Research, and Advanced Catalysis Research Group, RIKEN Center for Sustainable Resource Science, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan S Supporting Information *

ABSTRACT: Great progress has been achieved in the olefin hydroaminoalkylation by using amines, which is an atom-efficient route for the synthesis of alkylated amine derivatives. However, success in the catalytic olefin hydroaminoalkylation with a simple tertiary amine is hitherto very limited. In this study, density functional theory was applied to investigate the hydroaminoalkylation of olefins with tertiary amines, catalyzed by a series of homoleptic tris(benzyl) scandium complexes. It is found that the catalytic performance can be improved via substitution of electron-withdrawing groups and modifying ligand frameworks to reduce their steric hindrance. In addition, the potential applications of scandium catalysts in the α-C(sp3)−H alkylation of various heteroatomcontaining (P, As, O, S, and Se) substrates were explored. The results suggest that alkyl sulfides and selenides are promising substrates to undergo α-C(sp3)−H addition to olefins. Importantly, the effects of ligand backbone and substituent on catalytic performance and the different reactivities of the heteroatom-containing substrates were elucidated by frontier orbital, natural charge, topographic steric map, and distortion−interaction analyses, which give considerable insight into catalytic systems. This work provides useful information for developing new olefin hydroaminoalkylation reactions by using simple tertiary amines and for the addition of α-C(sp3)−H bond of heteroatom-containing substrates to alkenes.

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INTRODUCTION Amine motifs are important functional groups, which are involved in a large number of agrochemicals, pharmaceuticals, and fine chemicals. Therefore, the development of effective approaches toward amine functionalization has attracted considerable interests in the past few decades.1 Of the possible approaches, the catalytic olefin hydroaminoalkylation by using amines is an atom-efficient method to synthesize alkylated amine derivatives.2−4 Significant advances have been made in early-transition-metal-catalyzed hydroaminoalkylation.4−6 These reactions are generally thought to initially go through the formation of metal amido intermediates via deprotonation of an N−H bond, which limits the amine substrates to primary and secondary amines.4 Although olefin hydroaminoalkylation by using tertiary amines can be accomplished through latetransition-metal catalysts,7,8 the reactions are often limited to the amines having a directing group such as pyridyl.7 The development of new systems for the catalytic olefin hydroaminoalkylation with simple tertiary amines is therefore still of great interest and significance. Hou et al. recently reported that a homoleptic tris(benzyl) scandium complex was an excellent © XXXX American Chemical Society

catalyst working for the addition of C−H bond of various aliphatic tertiary amines into olefins (Scheme 1).9 Remarkably, Scheme 1. Sc-Catalyzed Hydroaminoalkylation9

that work demonstrated the first catalytic olefin hydroaminoalkylation using simple aliphatic tertiary amines without a directing group.9,10 Subsequent theoretical work revealed that such a reaction generally follows the sequential events: active species formation, olefin insertion, and C−H activation of another molecule of amine (Scheme 2).11,12 Furthermore, electronic factors were found to be responsible for the regioselectivity experimentally observed.11 To date, however, Received: December 15, 2018

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DOI: 10.1021/acs.organomet.8b00906 Organometallics XXXX, XXX, XXX−XXX

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Organometallics

series of proposed homoleptic tris(benzyl) scandium catalysts for the hydroaminoalkylation of olefins to systematically compare their catalytic performances. The effects of the substituents and the ligand framework of these Sc-based catalysts were elucidated, providing useful information for catalyst design. In addition, the α-C(sp3)−H alkylation reactivities of various model substrates, that is, PMe3, AsMe3, OMe2, SMe2, and SeMe2, were also investigated. It is theoretically predicted that the alkyl sulfides and selenides are promising substrates for achieving the addition of α-C(sp3)−H to alkenes.

Scheme 2. Mechanistic Synopsis of Sc-Catalyzed Hydroaminoalkylation11

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COMPUTATIONAL METHODS

The Gaussian 09 program15 was applied in all calculations. The geometry optimizations were carried out by using B3PW91 functional.16 In these optimizations, the 6-31G* basis set was used for nonmetallic atoms and the Stuttgart/Dresden relativistic effective core potentials17 as well as the associated valence basis sets were used for Sc atom. All structures were subsequently characterized, at the same level theory, by harmonic vibrational frequency analysis. Each stationary point was characterized as a minimum (no imaginary frequency) or transition state (one imaginary frequency). Single-point calculations were carried out at the M06/6-311+G** level with the CPCM model18 to consider the solvation effect of toluene. The free energy in solution is reported here, which includes the Gibbs free-energy correction calculated in the gas phase. Considering the overestimation of the entropy contribution, the free energies were corrected by +2.6 (or −2.6) kcal/mol for one-to-two (or two-to-one) molecular conversions, based on the free-volume theory.19 This empirical value is on the basis of energy of activation experimentally determined for the collision frequency Z′AB in liquids. Similar corrections were also applied in many earlier computational studies.20 The theoretical method used here was successfully applied to a similar system in our previous studies.11 The three-dimensional pictures of optimized structures were generated by using CYLview.21

factors governing the catalytic performance of the homoleptic tris(benzyl) scandium complex in hydroaminoalkylation, such as the effects of substituents and ligand frameworks with various heteroatoms, are not well understood. Because of the importance of this reaction, continuous efforts toward the development of more efficient catalysts are still highly desired in this field. Theoretical calculations are an effective approach for assessing various factors of a catalyst, such as the metal center, substituents, and ligand backbone, at the molecular level. This tool can facilitate the design of new catalysts with better catalytic performances.13 To identify more efficient catalytic systems for olefin hydroaminoalkylation, a deep theoretical understanding of the effects of the metal center, substituents, and ligand framework would be helpful. In addition, the exploration of αC(sp3)−H alkylation of various heteroatom (e.g., phosphorus, arsenic, oxygen, sulfur, and selenium)-containing substrates is also of much interest and significance. Similar to the addition of α-C(sp3)−H bond of amines, the direct addition of α-C(sp3)− H of other heteroatom-containing substrates into simple olefins is also challenging and still underexplored.14 In this work, density functional theory calculations were utilized to study a

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RESULTS AND DISCUSSION Overview of the Catalytic Cycle. Regarding rare-earthcatalyzed hydroaminoalkylation, some analogous complexes

Scheme 3. Detailed Mechanism for the Sc-Catalyzed n-Hexene Hydroaminoalkylation with N-Methylpiperidine11

B


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another molecule of N-methylpiperidine coordinates to the metal center to form complex G.23 Subsequently, G undergoes σ-BM via TS3 to give complex H with the coordinating alkylation product P. Finally, the catalytic cycle completed via ligand exchange between a1 and H23 to yield the product P and regenerate D. It is obvious that the σ-BM (C−H activation) is the rate-determining step with an energy barrier of 28.3 kcal/ mol.11 Hereafter, the exploration of catalyst designs and αC(sp3)−H alkylation of the other heteroatom-containing substrates is discussed based on this mechanism. Effects of the Substituents. To the base scandium catalyst Sc-1,9 electron-donating group (EDG) NH2 and electronwithdrawing group (EWG) NO2 substitute the para position of NMe2, respectively (Sc-NH2 and Sc-NO2, Figure 1). The calculated energy profiles of the hydroaminoalkylation of nhexene with N-methylpiperidine catalyzed by Sc-NH2 or ScNO2 are indicated in Figure 2. The previously reported energy profile of Sc-1-catalyzed reaction is also shown in this figure for a comparison.11 The coordination complex BSc‑NO2 with NO2 group is lower in energy than BSc‑1 by 4.1 kcal/mol, whereas the complex BSc‑NH2 with the NH2 EDG is higher in energy than BSc‑1 by 1.7 kcal/mol. For the active species generation, all three systems have moderate energy barriers of 25−27 kcal/mol, which is kinetically accessible under typical experimental conditions. It is noted that the active species DSc‑NO2 is significantly more stable than the corresponding species DSc‑1 and DSc‑NH2, and its formation is exergonic by 22.2 kcal/mol. In the catalytic cycle, the olefin insertion energy barriers for all three cases are similar (ΔG2⧧ = 21−23 kcal/mol). The subsequent C−H activation becomes the rate-determining step of catalytic cycle and has energy barriers of 28.3, 27.8, and 27.5 kcal/mol for Sc-1, Sc-NH2, and Sc-NO2, respectively. It should be noted that although the newly designed Sc-NH2 has a slightly lower energy barrier than Sc-1 (27.8 vs 28.3 kcal/mol for the rate-determining steps), the stationary points involved in the Sc-NH2 system are obviously higher in energy than the corresponding stationary points in the Sc-1 system. Therefore, modifying the Sc catalyst by introducing EDGs is thermodynamically unfavorable for this reaction. In contrast, the reaction

Figure 1. Sc-based catalysts with different substituents and their corresponding cationic species A showing selected bond distances (Å).

(e.g., Y, Lu, Gd, and Sm) were demonstrated experimentally to be inactive;9 thus, various metal centers are not considered in this work. Before discussing the effects of the substituents and ligand backbone, the features of the catalytic cycle are described.11 As shown in Schemes 1 and 2, the combination of [Ph3C][B(C6F5)4] and a neutral complex [Sc] can generate a cationic species A by loss of one alkyl group.22 In addition, the hydroaminoalkylation reaction includes the generation of the active species and the subsequent catalytic cycle (Scheme 3). In the step of active species generation, N-methylpiperidine (a1) coordinates to A, yielding the more stable complex B.23 Then, B transforms through the σ-bond metathesis (σ-BM)24,25 transition state (TS1) to give C with a coordinating N,Ndimethyl-o-toluidine part. Subsequently, C could undergo a ligand exchange process23 to generate the N-methylpiperidinecoordinated η2-azametallacyclic species D, which is the catalytically active species. In the catalytic cycle, D undergoes ligand exchange23 to yield π-complex E. Thereafter, the coordinating n-hexene in E inserts to the Sc−C bond through a conventional four-center transition state TS2, producing the ring-expanded azametallocyclic species F. Once olefin inserted,

Figure 2. Calculated energy profiles for the hydroaminoalkylation of n-hexene with N-methylpiperidine catalyzed by Sc-1, Sc-NH2, and Sc-NO2. The energies (kcal/mol) in the profiles include the energies of all species involved in the corresponding reactions. C


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Figure 3. Frontier molecular orbital analyses of the cationic scandium species A (ASc‑1, ASc‑NH2, and ASc‑NO2) and N-methylpiperidine a1 (orbital energies in eV).

Figure 4. Sc-based catalysts with different ligands and their corresponding cationic species A showing selected bond distances (Å).

Figure 5. Energy profiles of the hydroaminoalkylation of n-hexene with N-methylpiperidine catalyzed by Sc-1, Sc-P, Sc-O, and Sc-S. The energies (kcal/mol) shown in the profiles include those of all species involved in the corresponding reactions.

catalyzed by Sc-NO2 is thermodynamically more favorable than that catalyzed by Sc-1, and the energy barrier of C−H activation in the former system is slightly lower (27.7 vs 28.3 kcal/mol, Figure 2). Therefore, introducing an EWG into the ligand could improve the catalytic activity13i and stabilize the reaction intermediates. The small differences in the bond lengths of Sc−N (2.18− 2.20 Å) and Sc−C (2.26−2.27 Å) in the three cationic species A

(Figure 1) suggest that the substituents NH2 and NO2 have little influence on the steric environment around the metal center (see also the topographic steric map analysis26,27 in Figure S1), and thus, steric factors should not have an obvious effect on the performance of the proposed catalysts. Therefore, the electronic effects of the substituents were investigated. Accordingly, a natural charge analysis was performed. It is found that the EWG increases the Lewis acidity of the Sc center, whereas the EDG D


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Figure 6. Topographic steric maps of the cationic scandium species A with different heteroatom-containing frameworks. % VBur denotes the percent of buried volume of Sc atom.

Scheme 4. α-C(sp3)−H Alkylation of Various HeteroatomContaining Substrates

In addition, the frontier orbitals of catalysts and Nmethylpiperidine (a1) were analyzed. During the reaction, the LUMO (lowest unoccupied molecular orbital) of the electrophilic Sc catalyst could interact with the HOMO (the highest occupied molecular orbital) of the nucleophilic amine substrate. As illustrated in Figure 3, the LUMO of A mostly consists of the Sc 3dZ2 orbital and the HOMO of N-methylpiperidine is dominated by a sp-hybrided lone pair orbital of the N atom. Compared to ASc‑1, NH2 substitution clearly increases the LUMO energy from −3.14 to −2.85 eV, whereas NO2 substitution reduces the LUMO energy from −3.14 to −4.19 eV. Therefore, introducing an electron-withdrawing substituent (e.g., NO2) could effectively reduce the energy gap of E(LUMO,A) − E(HOMO,a1). In short, the electron-withdrawing substituent increases the Lewis acidity of Sc center and decreases the energy gap of E(LUMO,A) − E(HOMO,a1) (Figure 3), resulting in tighter binding between the catalyst and the substrate/product and thus stabilizing the reaction intermediates in this catalytic system. To verify this finding, the binding energies (ΔE) of the catalyst−substrate (complex D) and catalyst−product (complex H) complexes involved in both the Sc-1 and Sc-NO2 systems were calculated. As expected, the results clearly indicate that the binding between the catalyst and the substrate/product is stronger in the Sc-NO2 system than that in the Sc-1 system. Furthermore, the binding (in H) between the catalyst and product is stronger than that (in D) between the catalyst and amine substrate (ΔED(Sc‑1) = −48.5 kcal/mol; ΔED(Sc‑NO2) = −50.0 kcal/mol; ΔEH(Sc‑1) = −50.1 kcal/mol; ΔEH(Sc‑NO2) = −52.4 kcal/mol). Effects of the Heteroatom-Containing Ligand Framework. In addition to the substituents, the heteroatom of the ligand framework probably affects the catalytic performance as well. In this study, the N atom of the ligand framework was replaced with several common heteroatoms (O, S, and P). As shown in Figure 4, all of the cationic scandium analogues were successfully optimized and have similar structural characteristics. The energy profiles of the hydroaminoalkylation of hexene with N-methylpiperidine catalyzed by Sc[CH2C6H4XMen-o]3 [X = P (Sc-P); X = O (Sc-O); and X = S (Sc-S)] are shown in Figure 5, which also includes the results for the reaction catalyzed by Sc-1 for comparison. It is found that during active

Figure 7. Energy profiles for the generation of catalytically active species via various heteroatom-containing substrates XMe3 (X = P and As) and XMe2 (X = O, S, and Se). The energies (kcal/mol) shown in the profiles include those of all species involved in the corresponding reactions.

decreases the Lewis acidity, as revealed by the calculated natural charges on the Sc center of 1.70, 1.67, and 1.74 in ASc‑1, ASc‑NH2, and ASc‑NO2, respectively. This result explains the relative stability of the corresponding stationary points in the three systems (Figure 2); the more positive metal center binds the ligand more strongly, resulting in its higher stability. E


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Figure 8. Optimized geometrical structures of the coordination complexes and transition states in the C(sp3)−H activation of heteroatom-containing substrates by the cationic scandium species ASc‑1 and the distortion−interaction analysis for corresponding transition states (energies in kcal/mol).

Figure 9. Topographic steric maps of the TSs for α-C(sp3)−H activation of heteroatom-containing substrates. The % VBur denotes the percent of buried volume of the heteroatom.

for improving the catalytic performance of this type of hydroaminoalkylation reaction. To obtain better understanding of the higher thermodynamic stability of the stationary points in the Sc-P/Sc-O/Sc-S systems compared to those in the Sc-1 system, the electronic effects of these catalysts were analyzed. The natural charges on the Sc atom of A suggest that only the O atom substitution (charge of 1.80 on Sc of ASc‑O) increases the Lewis acidity of the Sc center, and the P and S ligands (charges of 1.38 and 1.43 on Sc of ASc‑P and ASc‑S, respectively) decrease the Lewis acidity compared to the catalyst with N ligands (1.70 on Sc of ASc‑1). This result does not explain the relative thermodynamic stabilities of the stationary points indicated in Figure 5. Besides, the frontier orbital analyses of these catalysts do not provide a rational explanation as well (see Figure S2). These results indicate that

species generation, the coordination complex B and the active species D in the Sc-P/Sc-O/Sc-S systems are significantly more stable than those in the Sc-1 system. Although the energy barriers of TS1 (ΔG⧧1 ) in the newly designed Sc-P/Sc-O/Sc-S catalyst systems are slightly higher than that in the Sc-1 system, the reaction should be kinetically accessible under experimental conditions in all of the systems. The energy barriers of olefin insertion and C−H activation in the three newly designed systems are moderate (less than 28 kcal/mol).28 It is noteworthy that all of the stationary points in the three systems (Sc-P, Sc-O, and Sc-S) are more stable than that in the Sc-1 system. The energy barriers are energetically accessible, especially for the ScS system having the lowest energy barrier (ca. 26 kcal/mol). On the basis of these comparisons, the S-containing complex is the most promising candidate of the three newly designed catalysts F


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performed.29 In Figure 8, ΔEdist(cat) is the energy required to distort the cationic scandium species structure in coordination complex B to that in transition state TS1, whereas ΔEdist(XMen) is the energy needed to distort the coordinated XMen in coordination complex B to that in TS1. The difference in the interaction energies between the distorted Sc active species and XMen in complex B and transition state TS1 is denoted ΔEint. The activation energy ΔE⧧ is the sum of ΔEdist(cat), ΔE dist (XMe n ), and ΔE int . As shown in Figure 8, the distortion−interaction analysis reveals that the activation energies (ΔE⧧) of the five TS1 transition states are consistent with the trends in their corresponding free-energy barriers (ΔG⧧). Small variations in ΔEdist(cat) (+7.8 to +8.9 kcal/mol) and ΔEint (−12.2 to −15.4 kcal/mol) are clearly observed between all five systems. However, the values of ΔEdist(XMen) for the SMe2 (+31.7 kcal/mol) and SeMe2 (+31.9 kcal/mol) systems are significantly smaller than those for the other three systems (+38.2, +36.0, and +37.1 kcal/mol for PMe3, OMe2, and AsMe3, respectively). The differences between ΔEdist(XMen) of the SeMe2 system and those of the other three systems (PMe3, OMe2, and AsMe3) are nearly equivalent to the differences between related activation energies (ΔE⧧). Therefore, the differences in distortion energy of the XMen moiety in transition states are the origin of energy barrier differences of these systems. The relatively small values of ΔEdist(XMen) for SMe2 and SeMe2 suggest that the steric effects in TS1(SMe2) and TS1(SeMe2) are smaller than those in the other transition states. To confirm these steric effects, the topographic steric map analysis of the five TS1 was carried out (Figure 9).26,27 As expected, the percent of buried volume of the heteroatom center in TS1(PMe3) (% VBur = 75.3), TS1(AsMe3) (% VBur = 73.8), and TS1(OMe2) (% VBur = 71.7) is significantly larger than those in TS1(SMe2) (% VBur = 62.3) and TS1(SeMe2) (% VBur = 59.2), which is in line with the results of distortion−interaction analyses. The results of the distortion−interaction and topographic steric map analyses can elucidate the origin of the energy barrier differences of the reactions with various substrates. To further explore the feasibility of the catalytic cycle for the SMe2 and SeMe2 substrates, the reaction pathways of the C−H activation and olefin insertion were also calculated (Figure 10). It is found that the energy barriers of the olefin insertion are 21.4 and 23.1 kcal/mol for SMe2 and SeMe2, respectively. In addition, the energy barriers of corresponding C−H activation are 22.2 and 24.3 kcal/mol, respectively. Such moderate energy barriers are kinetically accessible under typical experimental conditions. In this sense, alkyl sulfides and selenides are promising candidates for α-C(sp3)−H alkylation.

Figure 10. Energy profiles of XMe2 (X = S and Se) in the catalytic cycle. The free energies are relative to A and the substrates and include the energies of all species involved in the corresponding reactions (energy in kcal/mol).

electronic factors might not be the origin of the differences in the catalytic performances of these catalysts. Because the differences in the sizes of heteroatoms (N, O, P, and S) and the number of methyl groups of the ligands might result in differences in the steric hindrance of these catalysts, the topographic steric maps of the four cationic scandium species (ASc‑1, ASc‑O, ASc‑P, and ASc‑S) were analyzed (Figure 6).26,27 The percent of buried volume (% VBur) of the Sc atom demonstrates the differences in the steric bulkiness of these four ligands; the N ligand in ASc‑1 (% VBur = 81.5) is clearly more bulky than the heteroatom-containing ligands in ASc‑P (% VBur = 74.3), ASc‑O (% VBur = 72.2), and ASc‑S (% VBur = 76.3). Thus, the stationary points involved in the former system are less thermodynamically favorable than those in the latter three systems. This steric effect correlates well with the differences in the thermodynamics of the stationary points in the systems shown in Figure 5. The results obtained indicate that the catalytic performance could be improved through modifying the catalyst with less sterically bulky ligands. Reactivities of the Substrates with Various Heteroatoms. Similarly, to hydroaminoalkylation, the direct αC(sp3)−H alkylation of various heteroatom-containing (e.g., P, As, O, S, and Se) substrates with simple olefins is also a highly desirable but underexplored methodology (Scheme 4).14 To computationally explore the application scope of the Sc-based catalyst, α-C(sp3)−H alkylation of model substrates XMe3 (X = P and As) and XMe2 (X = O, S, and Se) with n-hexene was investigated (Scheme 4 and Figure 7). As shown in Figure 7, the generation of the active species through the reaction of ASc‑1 with PMe3 or AsMe3 has energy barrier of up to 33 kcal/mol. Besides, the formation of active species D is endothermic, which is 15.4 and 20.0 kcal/mol higher in energy compared with B in PMe3 and AsMe3 systems, respectively. Therefore, the C−H activation of PMe3 or AsMe3 by ASc‑1 is difficult to achieve under typical experimental conditions. Regarding the group VIA substrates (XMe2, X = O, S, and Se), the reaction for the OMe2 substrate also shows high-energy barrier (32.4 kcal/mol), whereas moderate energy barriers are observed for SeMe2 (28.4 kcal/mol) and SMe2 (28.2 kcal/mol), suggesting that αC(sp3)−H bonds in SeMe2 and SMe2 can be activated by ASc‑1. Therefore, the alkyl sulfides and selenides are promising substrates for generating active species via α-C(sp3)−H activation under appropriate conditions. To explore the origin of the differences in free-energy barriers of transition states, distortion−interaction analyses were

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CONCLUSIONS In summary, a series of homoleptic tris(benzyl) scandium complexes were computationally investigated as potential catalysts for olefin hydroaminoalkylation with simple tertiary amines to determine the effects of the substituents and heteroatoms. The key discoveries and insights are as follows. (1) The catalytic performance of the Sc-based catalyst could be improved by the introduction of EWGs because they increase the Lewis acidity of the metal atom and reduce the energy gap between the LUMO of the catalyst and the HOMO of the amine substrate. (2) Modifying the ligand framework by heteroatom substitution is also a promising approach for improving the catalytic performance. By these means, the steric hindrance G


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transition-metal dialkylamides and alkoxides. Organometallics 1983, 2, 161−162. (4) For reviews, see (a) Roesky, P. W. Catalytic hydroaminoalkylation. Angew. Chem., Int. Ed. 2009, 48, 4892−4894. (b) Chong, E.; Garcia, P.; Schafer, L. L. Hydroaminoalkylation: Early-transition-metal-catalyzed α-alkylation of amines. Synthesis 2014, 46, 2884−2896. (c) Ryken, S. A.; Schafer, L. L. N,O-Chelating Four-Membered Metallacyclic Titanium(IV) Complexes for Atom-Economic Catalytic Reactions. Acc. Chem. Res. 2015, 48, 2576−2586. (d) Edwards, P. M.; Schafer, L. L. Early transition metal-catalyzed C−H alkylation: hydroaminoalkylation for Csp3−Csp3 bond formation in the synthesis of selectively substituted amines. Chem. Commun. 2018, 54, 12543−12560. (e) Hannedouche, J.; Schulz, E. Hydroamination and hydroaminoalkylation of alkenes by group 3−5 elements: Recent developments and comparison with late transition metals. Organometallics 2018, 37, 4313−4326. (5) Examples of group 4 metal catalysts, see: (a) Bielefeld, J.; Doye, S. Dimethylamine as a substrate in hydroaminoalkylation reactions. Angew. Chem., Int. Ed. 2017, 56, 15155−15158. (b) Manßen, M.; Lauterbach, N.; Dörfler, J.; Schmidtmann, M.; Saak, W.; Doye, S.; Beckhaus, R. Efficient access to titanaaziridines by C−H activation of N-methylanilines at ambient temperature. Angew. Chem., Int. Ed. 2015, 54, 4383−4387. (c) Dörfler, J.; Preuß, T.; Schischko, A.; Schmidtmann, M.; Doye, S. A 2,6-Bis(phenylamino)pyridinato titanium catalyst for the highly regioselective hydroaminoalkylation of styrenes and 1,3butadienes. Angew. Chem., Int. Ed. 2014, 53, 7918−7922. (d) Chong, E.; Schafer, L. L. 2-Pyridonate titanium complexes for chemoselectivity. Accessing intramolecular hydroaminoalkylation over hydroamination. Org. Lett. 2013, 15, 6002−6005. (e) Bexrud, J. A.; Eisenberger, P.; Leitch, D. C.; Payne, P. R.; Schafer, L. L. Selective C−H activation α to primary amines. Bridging metallaaziridines for catalytic, intramolecular α-alkylation. J. Am. Chem. Soc. 2009, 131, 2116−2118. (f) Preuß, T.; Saak, W.; Doye, S. Titanium-catalyzed intermolecular hydroaminoalkylation of conjugated dienes. Chem.Eur. J. 2013, 19, 3833−3837. (g) Dörfler, J.; Doye, S. Aminopyridinato titanium catalysts for the hydroaminoalkylation of alkenes and styrenes. Angew. Chem., Int. Ed. 2013, 52, 1806−1809. (h) Prochnow, I.; Zark, P.; Müller, T.; Doye, S. The mechanism of the titanium-catalyzed hydroaminoalkylation of alkenes. Angew. Chem., Int. Ed. 2011, 50, 6401−6405. (i) Jaspers, D.; Saak, W.; Doye, S. Dinuclear titanium complexes with sulfamide ligands as precatalysts for hydroaminoalkylation and hydroamination reactions. Synlett 2012, 23, 2098−2102. (j) Kubiak, R.; Prochnow, I.; Doye, S. Titanium-catalyzed hydroaminoalkylation of alkenes by C−H bond activation at sp3 centers in the α-position to a nitrogen atom. Angew. Chem., Int. Ed. 2009, 48, 1153−1156. (k) Kubiak, R.; Prochnow, I.; Doye, S. [Ind2TiMe2]: A catalyst for the hydroaminomethylation of alkenes and styrenes. Angew. Chem., Int. Ed. 2010, 49, 2626−2629. (l) Stelter, L.; Teusch, T.; Bielefeld, J.; Doye, S.; Klüner, T. Theoretical studies on the hydroaminoalkylation of alkenes with primary and secondary amines. Chem.Eur. J. 2018, 24, 12485−12489. (6) Examples of group 5 metal catalysts, see: (a) DiPucchio, R. C.; Roşca, S.-C.; Schafer, L. L. Catalytic and atom-economic Csp3-Csp3 bond formation: Alkyl tantalum ureates for hydroaminoalkylation. Angew. Chem., Int. Ed. 2018, 57, 3469−3472. (b) Chong, E.; Brandt, J. W.; Schafer, L. L. 2-Pyridonate tantalum complexes for the intermolecular hydroaminoalkylation of sterically demanding alkenes. J. Am. Chem. Soc. 2014, 136, 10898−10901. (c) Garcia, P.; Lau, Y. Y.; Perry, M. R.; Schafer, L. L. Phosphoramidate tantalum complexes for room-temperature C−H functionalization: hydroaminoalkylation catalysis. Angew. Chem., Int. Ed. 2013, 52, 9144−9148. (d) Reznichenko, A. L.; Hultzsch, K. C. The mechanism of hydroaminoalkylation catalyzed by group 5 metal binaphtholate complexes. J. Am. Chem. Soc. 2012, 134, 3300−3311. (e) Eisenberger, P.; Ayinla, R. O.; Lauzon, J. M. P.; Schafer, L. L. Tantalum-amidate complexes for the hydroaminoalkylation of secondary amines: Enhanced substrate scope and enantioselective chiral amine synthesis. Angew. Chem., Int. Ed. 2009, 48, 8361−8365. (f) Herzon, S. B.; Hartwig, J. F. Hydroaminoalkylation of unactivated olefins with dialkylamines. J. Am. Chem. Soc. 2008, 130, 14940−14941. (g) Herzon, S. B.; Hartwig, J. F. Direct, catalytic hydroaminoalkylation of unactivated olefins with N-alkyl arylamines. J.

surrounding the metal atom could be effectively decreased. Of the N-, P-, O-, and S-containing ligand frameworks, the Scontaining catalyst exhibits the best catalytic performance. (3) To explore the application scope of the catalysts, the α-C(sp3)− H addition of various heteroatom-containing substrates to olefins was calculated. It is found that P-, As-, and O-containing substrates are inert because of steric factors in the transition state of C−H activation. In contrast, alkyl sulfides and selenides are calculated to be promising candidates for α-C(sp3)−H alkylation. These results provide valuable information on catalyst design and the application of these catalysts in the alkylation of α-C(sp3)−H of heteroatom-containing compounds.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.8b00906. Topographic steric maps and frontier orbital analysis (PDF) Cartesian coordinates of all optimized structures and their single-point energies (XYZ)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (Y.L.). *E-mail: [email protected] (Z.H.). *E-mail: [email protected] (L.L.). ORCID

Gen Luo: 0000-0002-5297-6756 Yi Luo: 0000-0001-6390-8639 Xiaohui Kang: 0000-0003-2793-7111 Zhaomin Hou: 0000-0003-2841-5120 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Financial supports from the NSFC (nos. 21429201, 21674014, and 21704011), the Fundamental Research Funds for the Central Universities (DUT18GJ201 for Y.L. and DUT18RC(3) 002 for G.L.), the State Key Laboratory of Fine Chemicals for a research grant (KF1713 for X.K.), and a Faculty Development Grant from Hubei University of Medicine (2018QDJZR13 for L.L.) are gratefully acknowledged. We also thank the RIKEN’s HOKUSAI system and the Network and Information Center of Dalian University of Technology for computational support.

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REFERENCES

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Organometallics

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Computational Investigation of Scandium-Based Catalysts for Olefin

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