Article Cite This: Organometallics XXXX, XXX, XXX−XXX
pubs.acs.org/Organometallics
Cyclometalated Half-Sandwich Iridium Complex for Catalytic Hydrogenation of Imines and Quinolines Zi-Jian Yao,*,†,‡ Nan Lin,† Xin-Chao Qiao,† Jing-Wei Zhu,† and Wei Deng*,† †
School of Chemical and Environmental Engineering, Shanghai Institute of Technology, Shanghai 201418, China Shanghai Key Laboratory of Molecular Catalysis and Innovative Material, State Key Laboratory of Molecular Engineering and Polymers, Fudan University, Shanghai 200433, China
‡
Downloaded via UNIV OF TEXAS AT EL PASO on October 27, 2018 at 07:03:17 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.
S Supporting Information *
ABSTRACT: Several C,N-chelate cyclometalated half-sandwich iridium-based catalysts for imines and quinoline derivatives reduction have been prepared through metalmediated C−H bond activation based on benzothiazole ligands. These iridium complexes exhibited high catalytic activity for hydrogenation of various types of imines with high yields. The most active catalyst was obtained from methoxyl substituted complex 2, showing the catalytic TOF value of 975 h−1 for the reduction of imine 6a. Additionally, these halfsandwich complexes also showed high efficiency for the catalytic hydrogenation of N-heterocyclic quinoline derivatives. Good catalytic activity was displayed for various kinds of substrates with either electron-donating or electron-withdrawing groups. Complexes 1−5 were fully characterized by NMR, IR, and elemental analysis. Molecular structures of complexes 1 and 4 were further confirmed by X-ray diffraction analysis.
■
center is perfectly shielded by the Cp# ligands, minimizing the possibility of undesired side-reactions. (iii) The redox property and solubility of these transition metal complexes can be tuned by introducing various types of substituents to cyclopentadienyl ring. 9 Thus, exploring the synthesis and application of half-sandwich cyclometalated complexes has become one of the most active and exciting areas of organometallic chemistry, because of the useful catalytic reactivity that these ligands impart on complexes.10−23 Amino compounds (including linear and cyclic structure) are widely used as pharmaceuticals and biologically active molecules.24 One of the simplest methods to obtain these compounds is the reduction of the corresponding starting materials containing imine group or nitro group. In the former case, a common method is to use metal borohydride as the reducing reagent because of its selectivity for imine reduction;25 however, the stoichiometric use of reducing reagent limits their large-scale application due to the waste production.26 Thus, the catalytic hydrogenation represents a greener synthetic route has gained great consideration gradually. Thus, various types of catalytic systems based on different metal catalysts have been reported for the imine reduction.27−29 Among these catalysts, cyclometalated iridium complexes attracted our interest because of their high efficiency in the reduction of carbonyls and imines, as well as the reductive amination of ketones with various hydrogen
INTRODUCTION Since the discovery in the early 1960s, cyclometalation has become one of the most studied reactions in organometallic and coordination chemistry, which provides a straightforward route to synthesize organometallic complexes that feature a M−C σ bond. Meanwhile, cyclometalation allows for the investigation of the pertinent aspects governing the metalmediated activation of unreactive bonds, especially the C−H bond.1−3 The generation of cyclometalated compounds often goes through two consecutive reaction steps: The first step is the initial interaction of the metal center with a donor group, and subsequent intramolecular C−H bond activation. The effective bond activation is thus most often a heteroatomassisted process, involving classical donors such as N, P, O, and S atoms. However, the cyclometalation reaction is not very effective until Shaw and co-workers found that the weak base sodium acetate promotes this process. Thus, various types of cyclometalated compounds were synthesized smoothly by using late transition metal precursors.4−6 In contrast, half-sandwich group 9 metal complexes based on Cp#M and (arene)M motifs (arene: η6-C6H6, p-cymene; Cp#: η5-C5H5, η5-C5Me5; M: Co, Ir, Rh, Ru) have been widely used in many catalytic reactions because of their good stability and high catalytic activity.7,8 [(η6-arene)MCl2]2 and [Cp#MCl2]2 are often utilized as the metal precursors to prepare diverse half-sandwich transition-metal complexes due to the following advantages: (i) The transition metal precursors are easily synthesized with high yields by reactions of metal chlorides with conjugated ligands. (ii) The hemisphere of the metal © XXXX American Chemical Society
Received: August 9, 2018
A
DOI: 10.1021/acs.organomet.8b00553 Organometallics XXXX, XXX, XXX−XXX
Article
Organometallics
from downfield range of δ 9.00−7.00 ppm suggested the occurrence of C−H activation in phenyl ring. The chemical shifts at approximately δ 1.70 ppm of these cyclometalated complexes are ascribed to the protons of Cp* group. All the iridium complexes show a characteristic absorption band in the range 1400−1440 cm−1 in their IR spectra, which can be assigned to the vibration of the CN bond of the thiazole ring. These CN absorption bands all shifted to lower frequencies when compared to those of the free benzothiazole ligand (1440−1490 cm −1). The redshift reflected the coordination interaction between the ligand and Cp*Ir moiety. This is consistent with the increase in the electron density on the iridium(III) center caused by the coordination of the C N group, which resulted in increasing the back bonding to the nitrogen and hence a lower CN stretching vibration.35 The elemental analysis and spectroscopic data of these complexes demonstrate that their structures are similar to each other. Crystal Structures of Cyclometalated Half-sandwich Iridium Complexes. To elucidate the structures of the cyclometalated half-sandwich iridium complexes clearly, a single crystal X-ray analysis is desired. Single crystals suitable for X-ray diffraction analysis were obtained by the slow diffusion of hexane into a saturated solution of the iridium complexes in dichloromethane. Both complexes 1 and 3 crystallized in the monoclinic space group P21c (Figure 1). Crystallographic data are summarized in Supporting Information. Both complexes show a typical three-legged piano-stool geometry with the iridium center being coordinated by the η5Cp* and the C and N atoms, as well as a chloride ligand. The metal center has a distorted-octahedral environment, assuming that the η5-Cp* motif occupies three fac coordination sides.36 The air and thermal stability of these half-sandwich iridium complexes is presumably caused by the formation of the cyclometalated structure. The bond lengths of Ir−N bonds in the two complexes (2.105(4) Å (1) and 2.092(5) Å (4)) are within the range of known values for the bond in similar iridium complexes.36 The Ir−C bond distances in complexes 1 and 4 are 2.037(6) and 2.061(6) Å, respectively, also consistent with previous reports.36 The shorter Ir−C bond length compared with the Ir−N distance suggests that the stronger interaction between metal center and carbon atom. The cyclometalated five-membered rings Ir(1)−C(9)−C(8)− C(7)−N(1) of the two complexes are almost planar with the dihedral angle of 5.7 and 5.6°, respectively, between the planes of N(1)−Ir(1)−C(9) and C(9)−C(8)−C(7)−N(1). The sum of the inner angles of the five-membered ring of approximately 540° further confirmed their planarity. Noncovalent intermolecular interactions of Ir−Cl···H(aromatic) in the crystal packing structure of the two complexes are observed. Catalytic Hydrogenation of Imines. Imine hydrogenation process catalyzed by late transition metal complexes using clean H2 as hydrogen source represented the green and sustainable chemical process, when compared with the traditional reduction methods using stoichiometric metal hydrides as reduction reagents.36c Thus, the hydrogenation of imine substrates under catalysis of cyclometalated complexes 1−5 was explored. Reaction conditions optimization of the catalytic hydrogenation process was investigated by using 6a as model substrate at ambient temperature under 10 atm of H2 under catalysis of complex 1 (Table 1). Solvent played an important role in the hydrogenation reaction and results showed that CF3CH2OH was the best choice (Table 1, entries 1−8). This phenomenon is reasonable because the
sources.30,31 We herein report a series of cyclometalated halfsandwich iridium complexes based on benzothiazole ligands which are widely used in the preparation of coordination compounds played important role in catalysis and materials chemistry.32 The easy modification of the ligands helps us elaborate the influences of the electron and steric effects on the catalytic activity of the corresponding iridium catalysts. Moreover, the planar geometry of the ligands facilitates the growth of suitable single crystals of the corresponding halfsandwich iridium complexes. Fortunately, preliminary results exhibit that these complexes can serve as the catalysts for hydrogenation of imines and quinoline derivatives in good yields by using H2 as hydrogen source.
■
RESULTS AND DISCUSSION Synthesis of Cyclometalated Half-Sandwich Iridium Complexes 1−5. Benzothiazole ligands L1−L5 were prepared in high yields through cyclocondensation reaction from aldehydes and thioanilines under air.33 With the ligands in hand, the target products were synthesized by the reactions of benzothiazole ligands with half equivalent iridium precursor [Cp*IrCl2]2 in the presence of sodium acetate (Scheme 1). Scheme 1. Synthesis of Half-Sandwich Iridium Complexes 1−5a
a Reaction condition: (i) toluene, 100 °C, 24 h; (ii) CH3OH, NaOAc, 50 °C, 6 h. Detailed description of the experiments, see the Experimental Section.
Cyclometalated half-sandwich iridium complexes 1−5 were obtained in methanol through metal-induced C−H bond activation34 at elevated temperature in moderate isolated yields. They form air-stable products that are soluble in THF, toluene, and CH2Cl2 but are insoluble in nonpolar solvents such as hexane and diethyl ether. The benzothiazole ligands act as the chelate through the C,N-coordination mode in the products which are supported by various techniques and elemental analysis. No decomposition was observed after refluxing the cyclometalated complexes in toluene for several hours suggested the thermal stability of these complexes. The TGA data further confirmed their thermal stability (see Supporting Information). No C,S-chelate product was found in the reaction. Cyclometalated half-sandwich iridium products 1−5 were characterized by their 1H NMR spectra. In comparison with the free ligand, the disappearance of one proton signal in 1−5 B
DOI: 10.1021/acs.organomet.8b00553 Organometallics XXXX, XXX, XXX−XXX
Article
Organometallics
Figure 1. Molecular structures of 1 (a) and 4 (b) with thermal ellipsoids drawn at the 30% level. All hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg): Complex 1: Ir(1)−N(1), 2.105(4); Ir(1)−C(9), 2.037(6); Ir(1)−Cl(1), 2.3933(13); C(7)−N(1), 1.309(8); C(7)−C(8), 1.449(8); C(9)−Ir(1)−N(1), 77.0(2); Ir(1)−N(1)−C(7), 116.1(4); N(1)−C(7)−C(8), 117.1(5); C(7)−C(8)−C(9), 112.1(5); Ir(1)−C(9)−C(8), 117.2(4). Complex 4: Ir(1)−N(1), 2.092(5); Ir(1)−C(9), 2.061(6); Ir(1)−Cl(1), 2.3920(13); C(7)−N(1), 1.334(8); C(7)−C(8), 1.409(9); C(9)−Ir(1)−N(1), 77.5(2); Ir(1)−N(1)−C(7), 114.6(4); N(1)−C(7)−C(8), 118.6(5); C(7)−C(8)−C(9), 113.0(5); Ir(1)−C(9)−C(8), 115.9(5).
Table 1. Hydrogenation of Imines under Catalysis of Cyclometalated Iridium Complexesa
entry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20c 21 22
cat./mol % 1 1 1 1 1 1 1 1 1 1 1 1 2 3 4 5 2 2 2 2 2 2
(0.1) (0.1) (0.1) (0.1) (0.1) (0.1) (0.1) (0.1) (0.1) (0.1) (0.1) (0.1) (0.1) (0.1) (0.1) (0.1) (0.05) (0.05) (0.01) (0.05) (0.05) (0.01)
time/h
T/°C
P/atm
solvent
3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 2 2 2 2 2 2
rt rt rt rt rt rt rt rt rt rt rt rt rt rt rt rt 50 50 50 50 50 50
10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 6 3 6 6 6 6
THF toluene DMSO DMF 1,4-dioxane CH2Cl2 MeOH CF3CH2OH MeOH MeOH MeOH MeOH MeOH MeOH MeOH MeOH MeOH MeOH MeOH MeOH CF3CH2OH CF3CH2OH
additive
yield/%b
AgOTf AgBF4 AgPF6 AgSbF6 AgOTf AgOTf AgOTf AgOTf AgOTf AgOTf AgOTf AgOTf AgOTf AgOTf
trace trace trace trace trace trace 12 55 78 80 75 77 88 73 79 74 95 72 43 trace 94 48
TON
TOF/h−1
120 550 780 800 750 770 880 730 790 740 1950 1440 4300
40 167 260 267 250 257 293 243 263 247 975 720 2150
1880 4800
940 2400
a
Reaction conditions: substrates 6a (1.0 mmol), solvent (2 mL), silver salt/cat. = 1.2:1. bYield was determined by GC analysis; n-tridecane was used as internal standard. cPMe3 was added (PMe3/cat. = 1:1 in molar ration).
chloride ligand of the coordination saturated cyclometalated iridium complex needs to be dissociated in the first step, so a necessary vacant site is given for the coordination of H2.37 The high polarity, acidity, and low nucleophilicity of CF3CH2OH facilitated the dissociation and solvation of the chloride ligand. Meanwhile, this solvent having minimal interaction with the cationic iridium intermediate.37 Inspired by these results, AgOTf was added in the reaction because the chloride ligand could be easily removed by the silver salt. Fortunately, the corresponding amine was furnished in high yield by using
cheap and readily MeOH as solvent (Table 1, entry 9). No counterion effects were observed when other silver salts were employed in the reactions (Table 1, entries 9−12). The investigation of complexes 1−5 as catalysts suggests that complex 2 shows the best catalytic activity for the imine hydrogenation (Table 1, entries 13−16). Other factors were also screened by using the most active compound, 2, as the catalyst. Higher catalytic activity was observed at elevated temperature, almost quantitative conversion of 6a was found in 2 h with only 0.05 mol % 2 at 6 atm H2 atomsphere (Table 1, C
DOI: 10.1021/acs.organomet.8b00553 Organometallics XXXX, XXX, XXX−XXX
Article
Organometallics Table 2. Scope of the Catalytic Hydrogenation of Iminesa
Reaction conditions: substrates (1.0 mmol), catalyst loading: 0.05 mol %, 50 °C, 2 h, 6 atm, solvent: MeOH (2 mL). Yield was determined by GC analysis; n-tridecane was used as internal standard. Isolated yields (%) are provided in parentheses. a
Figure 2. 1H NMR investigation of the formation of iridium hydride species.
entry 17). Further decreasing the catalyst loading (0.05−0.01 mol %) led to a lower yield of the product (Table 1, entry 18). In the presence of AgOTf, the yields of the reactions use CF3CH2OH as solvent are comparable to that of the reaction by using MeOH as solvent (Table 1, entries 21 and 22). Having established the optimum conditions for the reaction, a variety of substrates were employed in the reaction. Table 2 presents the results of the catalytic hydrogenation of imines. Corresponding amines were furnished in good to high yields by utilization of complex 2 as the catalyst under standard conditions (Table 2). The catalytic system tolerates different kinds of functional groups with either electron-donating or -withdrawing properties (Table 2, 7a−l). However, for the reduction of the imines-derived aliphatic precursors, lower activity of the catalyst was observed compared to that of the ruthenium carbonyl complex (Table 2, 7m−r).27d In the case of nitro-substituted compounds (7j and 7k), the intact of the nitro group indicates the selectivity of this reaction. Although the catalytic activity is comparable to those of the previously
reported iridium and ruthenium complexes used in transfer hydrogenation processes, high reaction temperature and toxic benzene solvent are not essential for the reaction reported here.27d,38 To elucidate the possible mechanism of the hydrogenation process, the reactivity between the catalyst and H2 in the presence of AgOTf was investigated. The NMR tube containing the solution of 2 (in dry d8-toluene) was pressurized with H2 (6 atm). The solution was then kept at 50 °C and characterized by 1H NMR after 20 min. A singlet was observed at δ −9.67 ppm, which indicating that the formation of metal hydride species (Figure 2).39 This step involves the heterolytic splitting of H2 with formation of the hydrido iridium active species. The hydride formation was also indicated by the disappearance of the high-field singlet because of the formation of the Ir−D bond, when H2 was replaced by D2 as starting material. Additionally, the signals of Cp* protons split into two peaks in the H2 heterolytic splitting step (Figure D
DOI: 10.1021/acs.organomet.8b00553 Organometallics XXXX, XXX, XXX−XXX
Article
Organometallics S6). This result may suggest that there are two species ([C∧N]Ir)+ and [C∧N]IrH) in the reaction mixture. The conclusion was further confirmed by the experimental result that little hydrogenation takes place when PMe3 was used as additive to poison the catalyst in the hydrogenation process under standard reaction conditions (Table 1, entry 20). As indicated in the experimental results, the hydrogenation benefits from higher H2 pressure (Table 1, entries 17 and 18), so the reaction was monitored under different pressure. Figure 3 shows that there is almost a linear
Figure 4. Possible mechanism of the catalytic hydrogenation process
h when 0.5 mol % catalyst loading was used (Table 3, entry 7). Further increases of the catalyst loading have little influence on the reaction (Table 3, entry 8). Decreasing H2 pressure to 3 atm did not lead to a decline in productivity (Table 3, entries 9 and 10). With the optimal reaction condition for quinoline hydrogenation in hand, a series of quinoline derivatives were examined in the hydrogenation reaction. The cyclometalated iridium complex showed good catalytic activity for all these substrates employed. The hydrogenation process was found to be tolerant of different functional groups, such as methyl, phenyl, and halide groups and so on (Table 4, 9a−j). No reaction was observed on the ester group of the substrate, indicating the selectivity of the catalyst for the hydrogenation of CN bonds (Table 4, 9k). Compared with a number of waste production of the protocol use NaBH3CN as reducing reagent,41 this method represents an efficient and greener route, although the catalytic efficiency is lower than that of the analogous iridium complexes using HCOOH/HCOONa as hydrogen source.28 We wonder if the catalytic efficiency could be enhanced under harsher conditions. However, only slightly higher yield (48%) was obtained by using 0.1 mol % catalyst at 80 °C and 10 atm (the results have been added in Table 2, entry 11). The recycle of the catalyst was investigated in order to offset the low catalytic efficiency in the reduction of quinolines. The catalyst was separated from the reaction mixture by removing all volatiles under vacuum. Results showed that complex 2 could be reused for at least three cycles without any loss of activity (93, 92, and 89%; Figure 5).
Figure 3. Effect of H2 pressure on the catalytic hydrogenation process. Reaction conditions: 1.0 mmol of imine 6a, 0.05 mol % catalyst 2, AgOTf (0.06 mol %), H2, 50 °C for 20 min. The conversion was determined by 1H NMR.
correlation between the conversions and H2 pressure, indicating that H2 is probably involved in the rate-determining step of the hydrogenation. On the basis of the above experimental results and previous reports, a possible mechanism has been proposed. At high temperature and pressure of H2, cyclometalated half-sandwich iridium catalyst reacted with H2 to give the hydrido iridium intermediate as the catalytic active species. The catalytic cycle is consisted of three steps: reversible interaction of cationic metal center with H2, rate-determining heterolytic cleavage of H2 into a hydride and a proton to be taken up by the imines, and subsequent transfer of the hydride to the resulting iminium cation. Mechanistic studies on the similar ionic pathway have been reported previously (Figure 4).27d Catalytic Hydrogenation of Quinolines. Encouraged by the good activity of the cyclometalated iridium complexes on imine reduction, we turned our attention on the catalytic hydrogenation of unsaturated N-heterocycle compounds.40 Initially, we screened different solvents for the hydrogenation of quinoline 8a by using complex 2 (0.1 mol %) as catalyst at 50 °C (Table 3). To our surprise, the reaction gave the positive results in the CF3CH2OH (47% yield) without any additives over 8 h. However, the catalytic efficiency is not good; only 57% yield of the product was obtained even after 12 h under such conditions (Table 3, entry 6). No reactions were observed in MeOH and other nonprotic solvents, such as toluene, DMF, and so on, with the addition of silver salts (Table 3, entries 1−6). The amount of the catalyst is crucial to the reaction. The product was obtained in 93% yield only in 3
■
CONCLUSIONS In summary, we have described a series of air-stable cyclometalated half-sandwich iridium complexes with the C,N-coordination mode based on benzothiazole ligands. These complexes exhibited good catalytic activity for hydrogenation of imines and quinoline derivatives by using H2 as the hydrogen source. A survey of various kinds of substrates suggested the good tolerance of the catalytic system for the hydrogenation process. In addition, complex 2 could be reused for at least three cycles without any loss of activity in the hydrogenation of quinoline. The good stability and prominent E
DOI: 10.1021/acs.organomet.8b00553 Organometallics XXXX, XXX, XXX−XXX
Article
Organometallics Table 3. Optimization for the Catalytic Hydrogenation of Quinolinea
entry 1 2 3 4 5 6 7c 8c 9c 10c 11
cat./mol % 2 2 2 2 2 2 2 2 2 2 2
(0.1) (0.1) (0.1) (0.1) (0.1) (0.1) (0.5) (1.0) (0.5) (0.5) (0.1)
P/atm
solvent
6 6 6 6 6 6 6 6 3 1 10
MeOH THF Toluene DMF CH2Cl2 CF3CH2OH CF3CH2OH CF3CH2OH CF3CH2OH CF3CH2OH CF3CH2OH
yield/%b
TON
TOF/h−1
430/570 184 93 186 70 480
54/71 61 31 62 23 160
trace
43/57d 92 93 92 35 48e
a Reaction conditions: quinoline (1.0 mmol), solvent (2.0 mL), H2, AgOTf/cat. = 1.2:1, reaction time: 8 h. bYield was determined by GC analysis; n-tridecane was used as internal standard. cReaction time: 3 h, without the addition of silver salt. dReaction time: 12 h. eReaction temperature: 80 °C.
Table 4. Scope of the Catalytic Hydrogenation of Quinoline Derivativesa
Reaction conditions: substrates (1.0 mmol), catalyst loading: 0. Five mol %, 50 °C, 3 h, 3 atm, solvent: CF3CH2OH (2 mL). Yield was determined by GC analysis, n-tridecane was used as internal standard. Isolated yields (%) are provided in parentheses. a
catalytic efficiency of the half-sandwich iridium complexes proved the possibility of their application in industrial production.
■
EXPERIMENTAL SECTION
General Data. All manipulations were performed under an atmosphere of nitrogen using standard Schlenk techniques. Chemicals were used as commercial products without further purification. 1H NMR (500 MHz) spectra were measured with a Bruker DMX-500 spectrometer. Elemental analysis was performed on an Elementar vario EL III analyzer. UV/vis absorption spectra were recorded using a UV 765 spectrophotometer with 1 cm path length quartz cuvettes. IR (KBr) spectra were measured with the Nicolet FT-IR spectrophotometer. Ligands L1−L5 were prepared using the modified method according to the literature.32 Synthesis of Benzothiazole Ligands L1−L5. The mixture of 2aminothiophenol (1 mmol) and corresponding aromatic aldehyde (1.2 mmol, 1.2 equiv) in toluene (5 mL) in a 20 mL Schlenk tube adapted with an air balloon was heated at 100 °C for 24 h. The reaction was then monitored by TLC. Column chromatography of the crude products (PE/EA = 10:1) gave L1−L5 in good yields.
Figure 5. Reuse of catalyst 2 in the quinoline hydrogenation process under optimal conditions.
F
DOI: 10.1021/acs.organomet.8b00553 Organometallics XXXX, XXX, XXX−XXX
Article
Organometallics L1. White solid, 85% isolated yield. 1H NMR (500 MHz, CDCl3): δ 8.11−8.08 (m, Ar−H, 3H), 7.92 (d, 3JHH = 8.0 Hz, Ar−H, 1H), 7.51−7.49 (m, Ar−H, 4H), 7.41 (t, 3JHH = 8.0 Hz, Ar−H, 1H). IR (KBr, disk): υ 1646 (vCC), 1509 (vCC), 1478 (vCN), 1384 (vCC), 1313 (vCC), 1224 (vC−S), 962 (ωC−H), 766 (ωAr−H) cm−1. Elemental analysis calcd (%) for C13H9NS: C 73.90, H 4.29, N 6.63, found: C 73.93, H 4.27, N 6.68. L2. White solid, 83% isolated yield. 1H NMR (500 MHz, CDCl3): δ 8.05 (t, 3JHH = 9.0 Hz, Ar−H, 3H), 7.89 (d, 3JHH = 8.0 Hz, Ar−H, 1H), 7.50 (t, 3JHH = 7.5 Hz, Ar−H, 1H), 7.37 (t, 3JHH = 8.0 Hz, Ar− H, 1H), 7.01 (d, 3JHH = 9.0 Hz, Ar−H, 2H), 3.89 (s, OCH3, 3H). IR (KBr, disk): υ 1605 (vCC), 1521 (vCC), 1485 (vCN), 1310 (vCC), 1302 (vCC), 1225 (vC−S), 968 (ωC−H), 833 (ωAr−H) cm−1. Elemental analysis calcd (%) for C14H11NOS: C 69.68, H 4.59, N 5.80, found: C 69.70, H 4.57, N 5.86. L3. White solid, 80% isolated yield. 1H NMR (500 MHz, CDCl3): δ 8.22 (d, 3J (H,H) = 8.0 Hz, Ar−H, 2H), 8.12 (d, 3JHH = 8.0 Hz, Ar− H, 1H), 7.94 (d, 3JHH = 7.5 Hz,, Ar−H, 1H), 7.76 (d, 3JHH = 8.0 Hz, Ar−H, 2H), 7.55 (t, 3JHH = 8.0 Hz, Ar−H, 1H), 7.45 (t, 3JHH = 7.5 Hz, Ar−H, 1H). IR (KBr, disk): υ 1618 (vCC), 1593 (vCC), 1484 (vCN), 1323 (vCC), 1253 (vC−S), 1173 (vC−F) 971 (ωC−H), 760 (ωAr−H) cm−1. Elemental analysis calcd (%) for C14H8F3NS: C 60.21, H 2.89, N 5.02, found: C 60.23, H 2.83, N 5.06. L4. White solid, 75% isolated yield. 1H NMR (500 MHz, CDCl3): δ 8.08 (d, 3JHH = 8.0 Hz, Ar−H, 1H), 8.04 (d, 3JHH = 8.5 Hz, Ar−H, 2H), 7.92 (d, 3JHH = 7.5 Hz, Ar−H, 1H), 7.52−7.46 (m, Ar−H, 3H), 7.42 (t, 3JHH = 7.5 Hz, Ar−H, 1H). IR (KBr, disk): υ 1643 (vCC), 1589 (vCC), 1474 (vCN), 1399 (vCC), 1251 (vC−S), 1090 (vC−Cl), 972 (ωC−H), 756 (ωAr−H) cm−1. Elemental analysis calcd (%) for C13H8ClNS: C 63.54, H 3.28, N 5.70, found: C 63.55, H 3.30, N 5.60. L5. White solid, 79% isolated yield. 1H NMR (500 MHz, CDCl3): δ 8.23 (t, 3JHH = 5.5 Hz, Ar−H, 1H), 8.15 (d, 3JHH = 8.0 Hz, Ar−H, 2H), 7.96 (d, 3JHH = 7.5 Hz, Ar−H, 1H), 7.53−7.41 (m, Ar−H, 5H). IR (KBr, disk): υ 1656 (vCC), 1579 (vCC), 1479 (vCN), 1386 (vCC), 1239 (vC−S), 1088 (vC−Cl), 978, 762 cm−1. Elemental analysis calcd (%) for C13H8ClNS: C 63.54, H 3.28, N 5.70, found: C 63.59, H 3.22, N 5.64. Synthesis of Half-Sandwich Iridium Complexes 1−5. A mixture of [Cp*IrCl2]2 (0.1 mmol), NaOAc (0.4 mmol), and corresponding ligand L1−L5 (0.2 mmol) was stirred at 50 °C in 10 mL of methanol for 6 h. The mixture was filtered and evaporated to give the crude products which were further purified by silica gel column chromatography (CH2Cl2/EA = 20:1) to afford pure cyclometalated half-sandwich iridium complexes in moderate yields. 1. Dark red solid, 52.6% yield. 1H NMR (500 MHz, CDCl3): δ 7.99−7.95 (m, Ar−H, 2H), 7.84 (d, 3JHH = 8.0 Hz, Ar−H, 1H), 7.72 (d, 3JHH = 7.5 Hz, Ar−H, 1H), 7.55 (t, 3JHH = 7.0 Hz, Ar−H, 1H), 7.43 (t, 3JHH = 7.5 Hz, Ar−H, 1H), 7.22 (t, 3JHH = 7.0 Hz, Ar−H, 1H), 7.08 (t, 3JHH = 7.0 Hz, Ar−H, 1H), 1.72 (s, Cp*, 15H). 13C NMR (100 MHz, CDCl3): 177.9 (CN), 164.9 (CAr(NS)−N = C), 148.3 (Ar(NS)C−S), 139.6 (CAr), 135.2 (CAr), 131.1 (CAr), 130.7 (CAr), 125.9 (CAr), 124.5 (CAr), 124.4 (CAr(NS)), 121.8 (CAr(NS)), 121.3 (CAr(NS)), 120.1 (CAr(NS)), 87.6 (C5(CH3)5), 8.7 (C5(CH3)5). IR (KBr, disk): υ 1656 (vCC), 1542 (vCC), 1430 (vCN), 1394 (vCC), 1325 (ωC−H), 1230 (vC−S), 982 (ωC−H), 763 (ωAr−H) cm−1. Elemental analysis calcd (%) for C23H23ClNIrS: C 48.20, H 4.04, N 2.44, found: C 48.25, H 4.03, N 2.50. MS (ESI, m/z): 538 [M − Cl]+. 2. Orange red solid, 58.0% yield. 1H NMR (500 MHz, CDCl3): δ 7.92 (s, Ar−H, 1H), 7.80 (d, 3JHH = 8.0 Hz, Ar−H, 1H), 7.67 (d, 3JHH = 8.5 Hz, Ar−H, 1H), 7.52−7.48 (m, Ar−H, 2H), 7.37 (t, 3JHH = 7.0 Hz, Ar−H, 1H), 6.65 (dd, 3JHH = 2.5 Hz, 3JHH = 2.5 Hz, Ar−H, 1H), 3.92 (s, OMe, 3H), 1.73 (s, Cp*, 15H). 13C NMR (100 MHz, CDCl3): 178.1 (CN), 168.3 (CAr(NS)−N = C), 161.9 (C−OMe), 149.4 (Ar(NS)C−S), 133.9 (CAr), 131.8 (CAr), 127.1 (CAr), 126.8 (CAr), 124.8 (CAr), 122.7 (CAr(NS)), 120.6 (CAr(NS)), 120.3 (CAr(NS)), 109.4 (CAr(NS)), 88.6 (C5(CH3)5), 55.2 (OMe), 9.7 (C5(CH3)5). IR (KBr, disk): υ 1663 (vCC), 1590 (vCC), 1419 (vCN), 1364 (vCC), 1333 (ωC−H), 1245 (vC−S), 1029 (vC−O), 976 (ωC−H), 743 (ωAr−H) cm−1. Elemental analysis calcd (%) for C24H25ClNOIrS: C
47.79, H 4.18, N 2.32, found: C 47.73, H 4.23, N 2.37. MS (ESI, m/ z): 568 [M − Cl]+. 3. Orange red solid, 49.6% yield. 1H NMR (500 MHz, CDCl3): δ 8.20 (s, Ar−H, 1H), 8.03 (d, 3JHH = 8.0 Hz, Ar−H, 1H), 7.89 (d, 3JHH = 8.0 Hz, Ar−H, 1H), 7.79 (d, 3JHH = 7.5 Hz, Ar−H, 1H), 7.60 (t, 3 JHH = 8.5 Hz, Ar−H, 1H), 7.49 (t, 3JHH = 8.0 Hz, Ar−H, 1H), 7.32 (d, 3JHH = 8.5 Hz, Ar−H, 1H), 1.73 (s, Cp*, 15H). 13C NMR (100 MHz, CDCl3): 177.5 (CN), 165.7 (CAr(NS)−N = C), 149.2 (Ar(NS)C−S), 147.1 (CAr), 143.8 (CAr), 132.6 (CAr), 132.4 (CAr), 127.3 (CAr), 126.1 (CAr), 125.1 (CAr(NS)), 124.2 (q, JFC = 220 Hz, CF3), 123.0 (CAr(NS)), 121.5 (CAr(NS)), 119.4.1 (CAr(NS)), 89.1 (C5(CH3)5), 9.6 (C5(CH3)5). IR (KBr, disk): υ 1651 (vCC), 1556 (vCC), 1439 (vCN), 1375 (vCC), 1319 (ωC−H), 1142 (vC−S), 1110 (vC−F), 983 (ωC−H), 765 (ωAr−H) cm−1. Elemental analysis calcd (%) for C24H22ClF3NIrS: C 44.96, H 3.46, N 2.18, found: C 44.89, H 3.50, N 2.25. MS (ESI, m/z): 606 [M − Cl]+. 4. Orange red solid, 56.3% yield. 1H NMR (500 MHz, CDCl3): δ 7.97 (d, 3JHH = 8.0 Hz, Ar−H, 1H), 7.89 (s, Ar−H, 1H), 7.84 (d, 3JHH = 7.5 Hz, Ar−H, 1H), 7.64 (d, 3JHH = 8.0 Hz, Ar−H, 1H), 7.56 (t, 3 JHH = 7.5 Hz, Ar−H, 1H), 7.44 (t, 3JHH = 7.5 Hz, Ar−H, 1H), 7.32 (d, 3JHH = 8.5 Hz, Ar−H, 1H), 1.72 (s, Cp*, 15H). 13C NMR (100 MHz, CDCl3): 177.7 (CN), 167.4 (CAr(NS)−N = C), 149.2 (Ar(NS)C−S), 139.2 (CAr), 137.6 (CAr), 135.7 (CAr), 132.2 (CAr), 127.1 (CAr), 126.4 (CAr), 125.6 (CAr(NS)), 122.9 (CAr(NS)), 122.7 (CAr(NS)), 121.1 (CAr(NS)), 88.9 (C5(CH3)5), 9.7 (C5(CH3)5). IR (KBr, disk): υ 1655 (vCC), 1550 (vCC), 1436 (vCN), 1354 (vCC), 1329 (ωC−H), 1143 (vC−S), 1069 (vC−Cl), 982 (ωC−H), 772 (ωAr−H) cm−1. Elemental analysis calcd (%) for C23H22Cl2NIrS: C 45.46, H 3.65, N 2.31, found: C 45.53, H 3.70, N 2.22. MS (ESI, m/ z): 572 [M − Cl]+. 5. Orange red solid, 49.8% yield. 1H NMR (500 MHz, CDCl3): δ 8.05 (d, 3J (H,H) = 8.0 Hz, Ar−H, 1H), 7.90−7.85 (m, Ar−H, 2H), 7.59−7.53 (m, Ar−H, 1H), 7.48 (t, 3JHH = 7.0 Hz, Ar−H, 1H), 7.15− 7.08 (m, Ar−H, 2H), 1.70 (s, Cp*, 15H). 13C NMR (100 MHz, CDCl3): 175.2 (CN), 169.2 (CAr(NS)−N = C), 148.0 (Ar(NS)C−S), 138.4 (CAr), 135.0 (CAr), 132.8 (CAr), 132.1 (CAr), 131.3 (CAr), 127.0 (CAr), 125.6 (CAr(NS)), 123.5 (CAr(NS)), 122.5 (CAr(NS)), 121.5 (CAr(NS)), 89.2 (C5(CH3)5), 9.6 (C5(CH3)5). IR (KBr, disk): υ 1671 (vCC), 1538 (vCC), 1429 (vCN), 1352 (vCC), 1328 (ωC−H), 1151 (vC−S), 1065 (vC−Cl), 979 (ωC−H), 762 (ωAr−H) cm−1. Elemental analysis calcd (%) for C23H22Cl2NIrS: C 45.46, H 3.65, N 2.31, found: C 45.60, H 3.73, N 2.32. MS (ESI, m/z): 572 [M − Cl]+. General Procedure for the Hydrogenation of Imine. In a typical run, the substrate (1.0 mmol), catalyst (0.5 mol %), AgOTf (0.6 mol %) and MeOH (2 mL) were charged in a 5 mL vial with a magnetic bar. The vial was then transferred to an autoclave. The autoclave was purged with H2 (6 atm) via three cycles of pressurization/venting, then pressurized with H2 (6 atm) and disconnected from the H2 source. The autoclave was heated to the desired temperature. After stirring for 2 h, the autoclave was cooled and the pressure was slowly released. The resultant mixture extracted with diethyl ether (2 × 5 mL) and dried over anhydrous Na2SO4. Solvent was evaporated under vacuum. The residue was dissolved in hexane and analyzed by GC-MS. Recycle of the Catalyst. After GC analysis of the reaction solution, the reaction mixture was evaporated under vacuum at high temperature until all volatiles were removed. Then, the residue solid was used as the catalyst under standard reaction conditions for the next cycle. X-ray Crystallography. Diffraction data of 1 and 4 were collected on a Bruker Smart APEX CCD diffractometer with graphitemonochromated Mo Kα radiation (λ = 0.71073 Å). All the data were collected at room temperature, and the structures were solved by direct methods and subsequently refined on F2 by using full-matrix least-squares techniques (SHELXL).42 SADABS43 absorption corrections were applied to the data. All non-hydrogen atoms were refined anisotropically, and hydrogen atoms were located at calculated positions. All calculations were performed using the Bruker program Smart. G
DOI: 10.1021/acs.organomet.8b00553 Organometallics XXXX, XXX, XXX−XXX
Article
Organometallics
■
(5) Duff, J. M.; Mann, B. E.; Shaw, B. L.; Turtle, B. Transition metal−carbon bonds. Part XXXVI. Internal metallations of platinum− dimethyl(1-naphthyl)phosphine and − dimethyl(1-naphthyl)arsine complexes and attempts to effect similar reactions with palladium. J. Chem. Soc., Dalton Trans. 1974, 139−145. (6) Dangel, B. D.; Godula, K.; Youn, S. W.; Sezen, B.; Sames, D. C− C Bond Formation via C−H Bond Activation: Synthesis of the Core of Teleocidin B4. J. Am. Chem. Soc. 2002, 124, 11856−11857. (7) (a) Han, Y.-F.; Jin, G.-X. Half-sandwich Iridium- and Rhodiumbased Organometallic Architectures: Rational Design, Synthesis, Characterization, and Applications. Acc. Chem. Res. 2014, 47, 3571− 3579. (b) Yao, Z.-J.; Jin, G.-X. Transition metal complexes based on carboranyl ligands containing N, P, and S donors: Synthesis, reactivity and applications. Coord. Chem. Rev. 2013, 257, 2522−2535. (c) Yao, Z.-J.; Deng, W. Half-sandwich late transition metal complexes based on functionalized carborane ligands. Coord. Chem. Rev. 2016, 309, 21−35. (d) Kumar, P.; Gupta, R. K.; Pandey, D. S. Half-sandwich arene ruthenium complexes: synthetic strategies and relevance in catalysis. Chem. Soc. Rev. 2014, 43, 707−733. (e) Gan, M.-M.; Liu, J.Q.; Zhang, L.; Wang, Y.-Y.; Hahn, F. E.; Han, Y.-F. Preparation and Post-Assembly Modification of Metallosupramolecular Assemblies from Poly(N-Heterocyclic Carbene) Ligands. Chem. Rev. 2018, 118, 9587−9641. (f) Han, Y.-F.; Li, H.; Weng, L.-H.; Jin, G.-X. Efficient One-Pot Approach to Organoiridium Macrocycles via C-H Activation Directed Self-Assembly. Chem. Commun. 2010, 46, 3556−3558. (g) Han, Y.-F.; Li, H.; Hu, P.; Jin, G.-X. Alkyne Insertion Induced Regiospecific C-H Activation with [Cp*MCl2]2 (M = Ir, Rh). Organometallics 2011, 30, 905−911. (h) Zhang, W.-Y.; Lin, Y.-J.; Han, Y.-F.; Jin, G.-X. Facile Separation of Regioisomeric Compounds by a Heteronuclear Organometallic Capsule. J. Am. Chem. Soc. 2016, 138, 10700−10707. (i) Zhang, L.; Yan, T.; Han, Y.-F.; Hahn, F. E.; Jin, G.X. Synthesis of a new type of alkene metal complex using face-capping thione-alkene ligands. Dalton Trans 2015, 44, 8797−8800. (j) Gao, Y.; Lin, Y.-J.; Han, Y.-F.; Jin, G.-X. Efficient synthesis of carborane azo derivatives and their reactivity. Dalton Trans 2017, 46, 1585−1592. (k) Han, Y.-F.; Lin, Y.-J.; Hor, T. S. A.; Jin, G.-X. Efficient Route to Organometallic Cage Formation via C-H Activation-Directed Muticomponent Assembly Accompanying Aromatic Guest Encapsulation. Organometallics 2012, 31, 995−1000. (8) (a) Zhang, R.; Zhu, L.; Liu, G.; Dai, H.; Lu, Z.; Zhao, J.; Yan, H. Cobalt-Promoted B−H and C−H Activation: Facile B−C Coupling of Carboranedithiolate and Cyclopentadienyl. J. Am. Chem. Soc. 2012, 134, 10341−10344. (b) Wang, Z.; Ye, H.; Li, Y.; Li, Y.; Yan, H. Unprecedented Boron-Functionalized Carborane Derivatives by Facile and Selective Cobalt-Induced B−H Activation. J. Am. Chem. Soc. 2013, 135, 11289−11298. (9) (a) Schmitt, F.; Freudenreich, J.; Barry, N. P. E.; JuilleratJeanneret, L.; Süss-Fink, G.; Therrien, B. Organometallic Cages as Vehicles for Intracellular Release of Photosensitizers. J. Am. Chem. Soc. 2012, 134, 754−757. (b) Palmucci, J.; Marchetti, F.; Pettinari, R.; Pettinari, C.; Scopelliti, R.; Riedel, T.; Therrien, B.; Galindo, A.; Dyson, P. J. Synthesis, Structure, and Anticancer Activity of Arene− Ruthenium(II) Complexes with Acylpyrazolones Bearing Aliphatic Groups in the Acyl Moiety. Inorg. Chem. 2016, 55, 11770−11781. (c) Palmucci, J.; Marchetti, F.; Pettinari, R.; Pettinari, C.; Scopelliti, R.; Riedel, T.; Therrien, B.; Galindo, A.; Dyson, P. J. Synthesis, Structure, and Anticancer Activity of Arene−Ruthenium(II) Complexes with Acylpyrazolones Bearing Aliphatic Groups in the Acyl Moiety. Inorg. Chem. 2016, 55, 11770−11781. (d) Gatti, A.; Habtemariam, A.; Romero-Canelón, I.; Song, J.-I.; Heer, B.; Clarkson, G. J.; Rogolino, D.; Sadler, P. J.; Carcelli, M. Half-Sandwich Arene Ruthenium(II) and Osmium(II) Thiosemicarbazone Complexes: Solution Behavior and Antiproliferative Activity. Organometallics 2018, 37, 891−899. (10) Ritleng, V.; Sirlin, C.; Pfeffer, M. Ru-, Rh-, and Pd-Catalyzed C−C Bond Formation Involving C−H Activation and Addition on Unsaturated Substrates: Reactions and Mechanistic Aspects. Chem. Rev. 2002, 102, 1731−1770.
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.8b00553. 1
H NMR spectra of L1−L5, 1H and 13C NMR spectra Complexes 1−5; TGA curves of complex 1−5 (PDF) Accession Codes
CCDC 1859056−1859057 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
[email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
■
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Tel.: +86-21-60877231. Fax: +8621-60873335. ORCID
Zi-Jian Yao: 0000-0003-1833-1142 Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (No. 21601125), the Chenguang Scholar of Shanghai Municipal Education Commission (No. 16CG64), Natural Science Foundation of Shanghai (No. 16ZR1435700), Shanghai Gaofeng & Gaoyuan Project for University Academic Program Development, Shanghai Science and Technology Committee (16DZ2270100), Shanghai Young Teacher Training Program (No. ZZZZyyx16005), the Shuguang Scholar of Shanghai Municipal Education Commission (No. 16SG49).
■
REFERENCES
(1) (a) Kleiman, J. P.; Dubeck, M. The Preparation of Cyclopentadienyl [o-(Phenylazo)Phenyl] Nickel. J. Am. Chem. Soc. 1963, 85, 1544−1545. (b) Cope, A. C.; Siekman, R. W. Formation of Covalent Bonds from Platinum or Palladium to Carbon by Direct Substitution. J. Am. Chem. Soc. 1965, 87, 3272−3273. (2) Trofimenko, S. Cyclopalladation reaction. Inorg. Chem. 1973, 12, 1215−1221. (3) (a) Pfeffer, M. Selected applications to organic synthesis of intramolecular C−H activation reactions by transition metals. Pure Appl. Chem. 1992, 64, 335−342. (b) Bedford, R. B. Palladacyclic catalysts in C−C and C−heteroatom bond-forming reactions. Chem. Commun. 2003, 1787−1796. (c) Dupont, J.; Consorti, C. S.; Spencer, J. The Potential of Palladacycles: More Than Just Precatalysts. Chem. Rev. 2005, 105, 2527−2571. (d) Albrecht, M. Cyclometalation Using d-Block Transition Metals: Fundamental Aspects and Recent Trends. Chem. Rev. 2010, 110, 576−623. (e) Sun, L. Y.; Sinha, N.; Yan, T.; Wang, Y.-S.; Tan, T. T. Y.; Yu, L.; Han, Y.-F.; Hahn, F. E. Template Synthesis of Three-Dimensional Hexakisimidazolium Cages. Angew. Chem., Int. Ed. 2018, 57, 5161−5165. (f) Wang, Y.-S.; Feng, T.; Wang, Y.-Y.; Hahn, F. E.; Han, Y.-F. Homo- and Heteroligand PolyNHC Metal Assemblies: Synthesis by Narcissistic and Social SelfSorting. Angew. Chem., Int. Ed. 2018, DOI: 10.1002/anie.201810010. (4) Duff, J. M.; Shaw, B. L. Complexes of iridium(III) and rhodium(III) with metallated and unmetallated dimethyl(1-naphthyl)- and methylphenyl(1-naphthyl)-phosphine. J. Chem. Soc., Dalton Trans. 1972, 2219−2225. H
DOI: 10.1021/acs.organomet.8b00553 Organometallics XXXX, XXX, XXX−XXX
Article
Organometallics
Hydrogenation Catalyzed by Chiral Ruthenium Complexes. Acc. Chem. Res. 1997, 30, 97−102. (c) Uematsu, N.; Fujii, A.; Hashiguchi, S.; Ikariya, T.; Noyori, R. Asymmetric Transfer Hydrogenation of Imines. J. Am. Chem. Soc. 1996, 118, 4916−4917. (d) Samec, J. S. M.; Backvall, J. E. Ruthenium-Catalyzed Transfer Hydrogenation of Imines by Propan-2-ol in Benzene. Chem. - Eur. J. 2002, 8, 2955− 2961. (e) Mizushima, E.; Yamaguchi, M.; Yamagishi, T. Effective transfer hydrogenation of unsaturated compounds by ruthenium dihydride complex in propan-2-ol. J. Mol. Catal. A: Chem. 1999, 148, 69−75. (f) Nugent, T. C.; El-Shazly, M. Chiral Amine Synthesis − Recent Developments and Trends for Enamide Reduction, Reductive Amination, and Imine Reduction. Adv. Synth. Catal. 2010, 352, 753− 819. (g) Xie, J. H.; Zhu, S. F.; Zhou, Q. L. Recent advances in transition metal-catalyzed enantioselective hydrogenation of unprotected enamines. Chem. Soc. Rev. 2012, 41, 4126−4139. (h) FleuryBregeot, N.; de la Fuente, V.; Castillon, S.; Claver, C. Highlights of Transition Metal-Catalyzed Asymmetric Hydrogenation of Imines. ChemCatChem 2010, 2, 1346−1371. (i) Wang, C.; Villa-Marcos, B.; Xiao, J. L. Hydrogenation of imino bonds with half-sandwich metal catalysts. Chem. Commun. 2011, 47, 9773−9785. (28) (a) Albrecht, M.; Crabtree, R. H.; Mata, J.; Peris, E. Chelating bis-carbene rhodium(III) complexes in transfer hydrogenation of ketones and imines. Chem. Commun. 2002, 32−33. (b) Danopoulos, A. A.; Winston, S.; Motherwell, W. B. Stable N-functionalised ‘pincer’ bis carbene ligands and their ruthenium complexes; synthesis and catalytic studies. Chem. Commun. 2002, 1376−1377. (c) Basu, B.; Bhuiyan, M. H.; Das, P.; Hossain, I. Catalytic transfer reduction of conjugated alkenes and an imine using polymer-supported formats. Tetrahedron Lett. 2003, 44, 8931−8934. (d) Kuhl, S.; Schneider, R.; Fort, Y. Transfer Hydrogenation of Imines Catalyzed by a Nickel(0)/ NHC Complex. Organometallics 2003, 22, 4184−4186. (e) Burling, S.; Whittlesey, M. K.; Williams, J. M. J. Direct and Transfer Hydrogenation of Ketones and Imines with a Ruthenium NHeterocyclic Carbene Complex. Adv. Synth. Catal. 2005, 347, 591− 594. (f) Ros, A.; Magriz, A.; Dietrich, H.; Ford, M.; Fernandez, R.; Lassaletta, J. M. Transfer Hydrogenation of α-Branched Ketimines: Enantioselective Synthesis of Cycloalkylamines via Dynamic Kinetic Resolution. Adv. Synth. Catal. 2005, 347, 1917−1920. (g) Rueping, M.; Antonchick, A. R.; Theissmann, T. Angew. Chem., Int. Ed. 2006, 45, 3683−3686. (h) Storer, R. I.; Carrera, D. E.; Ni, Y.; MacMillan, D. W. C. Enantioselective Organocatalytic Reductive Amination. J. Am. Chem. Soc. 2006, 128, 84−86. (i) Wu, J. S.; Wang, F.; Ma, Y. P.; Cui, X. C.; Cun, L. F.; Zhu, J.; Deng, J. G.; Yu, B. L. Asymmetric transfer hydrogenation of imines and iminiums catalyzed by a water-soluble catalyst in water. Chem. Commun. 2006, 1766−1768. (j) Yang, Q.; Shang, G.; Gao, W.; Deng, J.; Zhang, X. A Highly Enantioselective, Pd-TangPhos-Catalyzed Hydrogenation of N-Tosylimines. Angew. Chem., Int. Ed. 2006, 45, 3832−3835. (k) Mao, J. M.; Baker, D. C. A Chiral Rhodium Complex for Rapid Asymmetric Transfer Hydrogenation of Imines with High Enantioselectivity. Org. Lett. 1999, 1, 841−843. (l) Talwar, D.; Li, H. Y.; Durham, E.; Xiao, J. L. Frontispiece: A Simple Iridicycle Catalyst for Efficient Transfer Hydrogenation of N-Heterocycles in Water. Chem. - Eur. J. 2015, 21, 5370−5379. (29) (a) Iimuro, A.; Yamaji, K.; Kandula, S.; Nagano, T.; Kita, Y.; Mashima, K. Asymmetric Hydrogenation of Isoquinolinium Salts Catalyzed by Chiral Iridium Complexes: Direct Synthesis for Optically Active 1,2,3,4-Tetrahydroisoquinolines. Angew. Chem., Int. Ed. 2013, 52, 2046−2050. (b) Ye, Z. S.; Guo, R. N.; Cai, X. F.; Chen, M. W.; Shi, L.; Zhou, Y. G. Enantioselective Iridium-Catalyzed Hydrogenation of 1- and 3-Substituted Isoquinolinium Salts. Angew. Chem., Int. Ed. 2013, 52, 3685−3689. (c) Werkmeister, S.; Fleischer, S.; Junge, K.; Beller, M. Towards a Zinc-Catalyzed Asymmetric Hydrogenation/Transfer Hydrogenation of Imines. Chem. - Asian J. 2012, 7, 2562−2568. (d) Vaquero, M.; Suárez, A.; Vargas, S.; Bottari, G.; Á lvarez, E.; Pizzano, A. Highly Enantioselective Imine Hydrogenation Catalyzed by Ruthenium Phosphane−Phosphite Diamine Complexes. Chem. - Eur. J. 2012, 18, 15586−15591. (e) Maj, A. M.; Suisse, I.; Meliet, C.; Hardouin, C.; Agbossou-Niedercorn, F. Highly
(11) Suzuki, T. Organic Synthesis Involving Iridium-Catalyzed Oxidation. Chem. Rev. 2011, 111, 1825−1845. (12) Colby, D. A.; Bergman, R. G.; Ellman, J. A. Rhodium-Catalyzed C−C Bond Formation via Heteroatom-Directed C−H Bond Activation. Chem. Rev. 2010, 110, 624−655. (13) Liu, J.; Wu, X.; Iggo, J. A.; Xiao, J. L. Half-sandwich iridium complexesSynthesis and applications in catalysis. Coord. Chem. Rev. 2008, 252, 782−809. (14) Wang, C.; Villa-Marcos, B.; Xiao, J. L. Hydrogenation of imino bonds with half-sandwich metal catalysts. Chem. Commun. 2011, 47, 9773−9785. (15) Patureau, F. W.; Glorius, F. Oxidizing Directing Groups Enable Efficient and Innovative C−H Activation Reactions. Angew. Chem., Int. Ed. 2011, 50, 1977−1979. (16) Colby, D. A.; Tsai, A. S.; Bergman, R. G.; Ellman, J. A. Rhodium Catalyzed Chelation- Assisted C−H Bond Functionalization Reactions. Acc. Chem. Res. 2012, 45, 814−825. (17) Omae, I. Intramolecular five-membered ring compounds and their applications. Coord. Chem. Rev. 2004, 248, 995−1023. (18) Ackermann, L. Carboxylate-Assisted Transition-Metal-Catalyzed C−H Bond Functionaliza- tions: Mechanism and Scope. Chem. Rev. 2011, 111, 1315−1345. (19) Boutadla, Y.; Davies, D. L.; Jones, R. C.; Singh, K. The Scope of Ambiphilic Acetate-Assisted Cyclometallation with Half-Sandwich Complexes of Iridium, Rhodium and Ruthenium. Chem. - Eur. J. 2011, 17, 3438−3448. (20) Arita, S.; Koike, T.; Kayaki, Y.; Ikariya, T. Synthesis and Reactivities of Cp*Ir Amide and Hydride Complexes Bearing C−N Chelate Ligands. Organometallics 2008, 27, 2795−2802. (21) (a) Li, L.; Brennessel, W. W.; Jones, W. D. An Efficient LowTemperature Route to Polycyclic Isoquinoline Salt Synthesis via C−H Activation with [Cp*MCl2]2 (M = Rh, Ir). J. Am. Chem. Soc. 2008, 130, 12414−12419. (b) Li, L.; Brennessel, W. W.; Jones, W. D. C−H Activation of Phenyl Imines and 2-Phenylpyridines with [Cp*MCl2]2 (M = Ir, Rh): Regioselectivity, Kinetics, and Mechanism. Organometallics 2009, 28, 3492−3500. (22) (a) Scheeren, C.; Maasarani, F.; Hijazi, A.; Djukic, J. P.; Pfeffer, M.; Zaric, S. D.; LeGoff, X. F.; Ricard, L. Stereoselective “Electrophilic” Cyclometalation of Planar-Prochiral (η6-Arene) tricarbonylchromium Complexes with Asymmetric Metal Centers: pseudo-T-4 [Cp*RhCl2]2 and [Cp*IrCl2]2. Organometallics 2007, 26, 3336−3345. (b) Boutadla, Y.; Al-Duaij, O.; Davies, D. L.; Griffith, G. A.; Singh, K. Mechanistic Study of Acetate-Assisted C−H Activation of 2-Substituted Pyridines with [MCl2Cp*]2 (M = Rh, Ir) and [RuCl2(p-cymene)]2. Organometallics 2009, 28, 433−440. (c) Sau, Y.K.; Yi, X.-Y.; Chan, K.-W.; Lai, C.-S.; Williams, I. D.; Leung, W.-H. J. Organomet. Chem. 2010, 695, 1399−1404. (d) Hull, J. F.; Balcells, D.; Blakemore, J. D.; Incarvito, C. D.; Eisenstein, O.; Brudvig, G. W.; Crabtree, R. H. Highly Active and Robust Cp* Iridium Complexes for Catalytic Water Oxidation. J. Am. Chem. Soc. 2009, 131, 8730−8731. (23) Kashiwame, Y.; Kuwata, S.; Ikariya, T. Metal−Pyrazole Bifunction in Half-Sandwich C N Chelate Iridium Complexes: Pyrazole−Pyrazolato Interconversion and Application to Catalytic Intramolecular Hydroamination of Aminoalkene. Chem. - Eur. J. 2010, 16, 766−770. (24) Naoi, M.; Maruyama, W.; Nagy, G. M. Dopamine-Derived Salsolinol Derivatives as Endogenous Monoamine Oxidase Inhibitors: Occurrence, Metabolism and Function in Human Brains. NeuroToxicology 2004, 25, 193−204. (25) Carey, F. A.; Sundberg, R. J. Advanced Organic Chemistry, Part B: Reactions and Synthesis, 4th ed.; Kluwer Academic/Plenum Publishers: New York, 2001; p 965. (26) Anastas, P. T.; Kirchhoff, M. M.; Williamson, T. C. Catalysis as a foundational pillar of green chemistry. Appl. Catal., A 2001, 221, 3− 13. (27) (a) Miecznikowski, J. R.; Crabtree, R. H. Transfer hydrogenation reduction of ketones, aldehydes and imines using chelated iridium(III) N-heterocyclic bis-carbene complexes. Polyhedron 2004, 23, 2857−2872. (b) Noyori, R.; Hashiguchi, S. Asymmetric Transfer I
DOI: 10.1021/acs.organomet.8b00553 Organometallics XXXX, XXX, XXX−XXX
Article
Organometallics enantioselective hydrogenation of new 2-functionalized quinoline derivatives. Tetrahedron Lett. 2012, 53, 4747−4750. (f) Hou, C. J.; Wang, Y. H.; Zheng, Z.; Xu, J.; Hu, X. P. Chiral Phosphine− Phosphoramidite Ligands for Highly Efficient Ir-Catalyzed Asymmetric Hydrogenation of Sterically Hindered N-Arylimines. Org. Lett. 2012, 14, 3554−3557. (g) Arai, N.; Utsumi, N.; Matsumoto, Y.; Murata, K.; Tsutsumi, K.; Ohkuma, T. Asymmetric Hydrogenation of N-Arylimines Catalyzed by the Xyl-Skewphos/DPEN-Ruthenium(II) Complex. Adv. Synth. Catal. 2012, 354, 2089−2095. (h) Mrsic, N.; Panella, L.; Ijpeij, E. G.; Minnaard, A. J.; Feringa, B. L.; de Vries, J. G. Methylaluminoxane as an Alternative for BArF in the IridiumCatalyzed Asymmetric Hydrogenation of Imines. ChemCatChem 2011, 3, 1139−1142. (i) Chen, F.; Ding, Z. Y.; Qin, J.; Wang, T. L.; He, Y. M.; Fan, Q. H. Highly Effective Asymmetric Hydrogenation of Cyclic N-Alkyl Imines with Chiral Cationic Ru-MsDPEN Catalysts. Org. Lett. 2011, 13, 4348−4351. (j) Chang, M. X.; Li, W.; Zhang, X. M. A Highly Efficient and Enantioselective Access to Tetrahydroisoquinoline Alkaloids: Asymmetric Hydrogenation with an Iridium Catalyst. Angew. Chem., Int. Ed. 2011, 50, 10679−10681. (30) (a) Talwar, D.; Wu, X.; Saidi, O.; Salguero, N. P.; Xiao, J. L. Versatile Iridicycle Catalysts for Highly Efficient and Chemoselective Transfer Hydrogenation of Carbonyl Compounds in Water. Chem. Eur. J. 2014, 20, 12835−12842. (b) Wu, J.; Barnard, J. H.; Zhang, Y.; Talwar, D.; Robertson, C. M.; Xiao, J. L. Robust cyclometallated Ir(III) catalysts for the homogeneous hydrogenation of N-heterocycles under mild conditions. Chem. Commun. 2013, 49, 7052−7054. (c) Lei, Q.; Wei, Y. W.; Talwar, D.; Wang, C.; Xue, D.; Xiao, J. L. Fast Reductive Amination by Transfer Hydrogenation “on Water. Chem. Eur. J. 2013, 19, 4021−4029. (d) Wang, C.; Pettman, A.; Basca, J.; Xiao, J. L. A Versatile Catalyst for Reductive Amination by Transfer Hydrogenation. Angew. Chem., Int. Ed. 2010, 49, 7548−7552. (e) Villa-Marcos, B.; Tang, W. J.; Wu, X. F.; Xiao, J. L. A highly active cyclometallated iridium catalyst for the hydrogenation of imines. Org. Biomol. Chem. 2013, 11, 6934−6939. (f) Wang, C.; Xiao, J. L. Iridacycles for hydrogenation and dehydrogenation reactions. Chem. Commun. 2017, 53, 3399−3411. (31) (a) Pannetier, N.; Sortais, J. B.; Issenhuth, J. T.; Barloy, L.; Sirlin, C.; Holuigue, A.; Lefort, L.; Panella, L.; de Vries, J. G.; Pfeffer, M. Cyclometalated Complexes of Ruthenium, Rhodium and Iridium as Catalysts for Transfer Hydrogenation of Ketones and Imines. Adv. Synth. Catal. 2011, 353, 2844−2852. (b) Arita, S.; Koike, T.; Kayaki, Y.; Ikariya, T. Synthesis and Reactivities of Cp*Ir Amide and Hydride Complexes Bearing C−N Chelate Ligands. Organometallics 2008, 27, 2795−2802. (32) (a) Roh, S.-G.; Kim, Y.-H.; Seo, K. D.; Lee, D. H.; Kim, H. K.; Park, Y.-L.; Park, J. W.; Lee, J.-H. Synthesis, Photophysical, and Electroluminescent Device Properties of Zn(II)-Chelated Complexes Based on Functionalized Benzothiazole Derivatives. Adv. Funct. Mater. 2009, 19, 1663−1671. (b) Roger, M.; Arliguie, T.; Thuéry, P.; Ephritikhine, M. Homoleptic 2-Mercapto Benzothiazolate Uranium and Lanthanide Complexes. Inorg. Chem. 2008, 47, 3863−3868. (c) Haneda, S.; Gan, Z.; Eda, K.; Hayashi, M. Ligand Effects of 2-(2Pyridyl)benzazole-Pd Complexes on the X-ray Crystallographic Structures, 1H NMR Spectra, and Catalytic Activities in MizorokiHeck Reactions. Organometallics 2007, 26, 6551−6555. (33) Shi, X.; Guo, J.; Liu, J.; Ye, M.; Xu, Q. Unexpectedly Simple Synthesis of Benzazoles by tBuONa-Catalyzed Direct Aerobic Oxidative Cyclocondensation of o-Thio/Hydroxy/Aminoanilines with Alcohols under Air. Chem. - Eur. J. 2015, 21, 9988−9993. (34) (a) Liu, J.; Wu, X.; Iggo, J. A.; Xiao, J. L. Half-sandwich iridium complexes-Synthesis and applications in catalysis. Coord. Chem. Rev. 2008, 252, 782−809. (b) Colby, D. A.; Tsai, A. S.; Bergman, R. G.; Ellman, J. A. Rhodium Catalyzed Chelation-Assisted C−H Bond Functionalization Reactions. Acc. Chem. Res. 2012, 45, 814−825. (c) Han, Y.-F.; Jin, G.-X. Cyclometalated [Cp*M(C∧X)] (M = Ir, Rh; X = N, C, O, P) complexes. Chem. Soc. Rev. 2014, 43, 2799−2823. (35) Govender, P.; Renfrew, A. K.; Clavel, C. M.; Dyson, P. J.; Therrien, B.; Smith, G. S. Antiproliferative activity of chelating N,O-
and N,N-ruthenium(II) arene functionalised poly(propyleneimine) dendrimer scaffolds. Dalton Trans 2011, 40, 1158−1167. (36) Yao, Z.-J.; Li, K.; Li, P.; Deng, W. Mononuclear half-sandwich iridium and rhodium complexes through C−H activation: Synthesis, characterization and catalytic activity. J. Organomet. Chem. 2017, 846, 208−216. (b) Yao, Z.-J.; Li, P.; Li, K.; Deng, W. Synthesis, structure and catalytic polymerization activity of half-sandwich cyclometallated iridium complexes. Appl. Organomet. Chem. 2018, 32, e4239. (c) Yao, Z.-J.; Li, K.; Zhang, J. Y.; Deng, W. [NO]- and [NN]-coordination mode rhodium complexes based on a flexible ligand: synthesis, reactivity and catalytic activity. New J. Chem. 2016, 40, 8753−8759. (37) (a) Wu, J.; Talwar, D.; Johnston, S.; Yan, M.; Xiao, J. L. Acceptorless Dehydrogenation of Nitrogen Heterocycles with a Versatile Iridium Catalyst. Angew. Chem., Int. Ed. 2013, 52, 6983− 6987. (b) Han, Y.-F.; Zhang, L.; Weng, L.-H.; Jin, G.-X. H2-Initiated Reversible Switching Between Two-Dimensional Metallacycles and Three-Dimensional Cylinders. J. Am. Chem. Soc. 2014, 136, 14608− 14615. (38) Gnanamgari, D.; Moores, A.; Rajaseelan, E.; Crabtree, R. H. Transfer Hydrogenation of Imines and Alkenes and Direct Reductive Amination of Aldehydes Catalyzed by Triazole-Derived Iridium(I) Carbene Complexes. Organometallics 2007, 26, 1226−1230. (39) Heiden, Z. M.; Rauchfuss, T. B. Homogeneous Catalytic Reduction of Dioxygen Using Transfer Hydrogenation Catalysts. J. Am. Chem. Soc. 2007, 129, 14303−14310. (40) (a) Glorius, F.; Spielkamp, N.; Holle, S.; Goddard, R.; Lehmann, C. W. Efficient Asymmetric Hydrogenation of Pyridines. Angew. Chem., Int. Ed. 2004, 43, 2850−2852. (b) Kim, J. T.; Gevorgyan, V. Selective Partial Reduction of Various Heteroaromatic Compounds with Bridgehead Nitrogen via Birch Reduction Protocol. J. Org. Chem. 2005, 70, 2054−2059. (c) Wang, T.; Zhuo, L.-G.; Li, Z.; Chen, F.; Ding, Z.; He, Y.; Fan, Q.-H.; Xiang, J.; Yu, Z.-X.; Chan, A. S. C. Highly Enantioselective Hydrogenation of Quinolines Using Phosphine-Free Chiral Cationic Ruthenium Catalysts: Scope, Mechanism, and Origin of Enantioselectivity. J. Am. Chem. Soc. 2011, 133, 9878−9891. (d) Zhou, Y.-G. Asymmetric Hydrogenation of Heteroaromatic Compounds. Acc. Chem. Res. 2007, 40, 1357− 1366. (41) Metallinos, C.; Barrett, F. B.; Wang, Y.; Xu, S.; Taylor, N. J. Reduction of substituted 1,10-phenanthrolines as a route to rigid chiral benzimidazolylidenes. Tetrahedron 2006, 62, 11145−11157. (42) Sheldrick, G. M. SHELXL-97, Program for the Refinement of Crystal Structures; Universität Göttingen: Göttingen, Germany, 1997. (43) Sheldrick, G. M. SADABS 2.01; Bruker AXS: Madison, WI, 1998.
J
DOI: 10.1021/acs.organomet.8b00553 Organometallics XXXX, XXX, XXX−XXX
