Mild and Selective C(CO)–C(α) Bond Activation of Ketones with

Previous Article · Next Article · Table of Contents ... Chun Meng Tam , Ching Tat To , Kin Shing Chan ... Siu Yin Lee , Shiyu Feng , Kin Shing Chan. D...
1 downloads 0 Views 459KB Size
Download PDF
Article pubs.acs.org/Organometallics

Mild and Selective C(CO)−C(α) Bond Activation of Ketones with Rhodium(III) Porphyrin β‑Hydroxyethyl Chung Sum Chan, Siu Yin Lee, and Kin Shing Chan* Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, People’s Republic of China S Supporting Information *

ABSTRACT: Rhodium(III) porphyrin β-hydroxyethyl, RhIII(ttp)CH2CH2OH (ttp = 5,10,15,20-tetratolylporphyrinato dianion), was found to serve as a precursor of the highly reactive RhIII(ttp)OH for the C(CO)−C(α) bond activation (CCA) of ketones under mild and aerobic conditions of 25−50 °C.

■

INTRODUCTION Carbon−carbon bond activation (CCA) has attracted much research interest in recent decades, as it is a fundamentally important step in organic syntheses and industrial applications.1−4 Selective CCA is challenging, as the carbon−carbon bonds in organic compounds are kinetically less accessible than the surrounding carbon−hydrogen bonds. In the past, examples of selective CCA of organic compounds were achieved with the utilization of low-valent transition-metal complexes via oxidative addition.2−4 In contrast, CCA by high-valent transition-metal complexes was less reported, since electronically less accessible high-valent transition-metal intermediates from oxidative addition would be involved.5 We recently reported that high-valent rhodium(III) and iridium(III) porphyrins cleave the C(CO)−C(α) bonds of ketones with the assistance of water at 200 °C.6,7 Initially, rhodium(III) and iridium(III) porphyrins catalyze the aldol condensation of ketones, giving water as a byproduct. The water that forms hydrolyzes the α-carbon−hydrogen bond activation (α-CHA) product of ketones with rhodium(III) and iridium(III) porphyrin complexes (MIII(ttp)CHRCOR′, M = Rh, Ir) to generate RhIII(ttp)OH and IrIII(ttp)OH, respectively (Scheme 1). RhIII(ttp)OH and IrIII(ttp)OH were thus proposed intermediates in cleaving the C(CO)−C(α) bonds of ketones through σ-bond metathesis and oxidization of the alkyl fragments.6,7 In the metalloporphyrin-based CCA of ketones, some limitations exist.6,7 (1) High reaction temperature is required for the generation of MIII(ttp)OH (M = Rh, Ir). (2) The reaction generally requires over 10 days. (3) Solvent-free conditions limit the use of high-boiling substrates. (4) The extensive and competitive aldol condensation of ketones, catalyzed by Lewis acidic metalloporphyrins, converts a large amount of starting material into undesired products.6−8 Hence, the aldol-condensable diethyl ketone gives a lower yield of CCA product with rhodium(III) porphyrins in a slow reaction (eq 1),6 and cyclohexanone is unsuccessful.9 (5) The proposed intermediate RhIII(ttp)OH is highly reactive but extremely thermally unstable toward decomposition to form [RhII(ttp)]2 and unknown rhodium porphyrin complexes.10 Hence, a mild © 2012 American Chemical Society

method to generate RhIII(ttp)OH would be desirable for the facile CCA of ketones. Indeed, mild and selective cleavage of the C(CO)−C(α) bond of isopropyl ketones was recently achieved at 50 °C from the hydrolysis of RhIII(ttp)Me to give RhIII(ttp)OH.6 However, the ketone substrate is limited to non-aldol-condensable isopropyl ketones, since their aldol reactions are reversible without extensive undesirable consumption of ketones. RhIII(ttp)CH2CH2OH (Figure 1) has been used as a RhIII(ttp)OH surrogate in the mild aldehydic CHA with aryl and alkyl aldehydes.11 We now report our findings that RhIII(ttp)CH2CH2OH can also serve as a RhIII(ttp)OH equivalent to selectively undergo CCA of ketones under mild and aerobic conditions.

■

RESULTS AND DISCUSSION Atmosphere Effect. Initially, RhIII(ttp)CH2CH2OH (1a), prepared from the reductive alkylation of Rh(ttp)Cl (1b) with NaBH4/BrCH2CH2OH,11,12 reacted with diisopropyl ketone under solvent-free conditions under N2 at 25 °C in 15 min, giving RhIII(ttp)COiPr (2a) and acetone in 82% and 39% yields (GC-MS), respectively (eq 2). When the reaction was carried

out in air, RhIII(ttp)COiPr (2a) and acetone were formed in 80% and 40% yields (GC-MS), respectively (eq 2). The presence of air did not affect the reactivity or selectivity of the Received: October 11, 2012 Published: December 19, 2012 151

dx.doi.org/10.1021/om3009519 | Organometallics 2013, 32, 151−156

Organometallics

Article

Scheme 1. Mechanism of CCA of Ketones with Metalloporphyrins

Table 2. CCA of Diisopropyl Ketone in Different Solvents

Figure 1. Structure of RhIII(ttp)CH2CH2OH (1a).

reaction. Hence, the more user-friendly aerobic conditions were used for further studies. It was noted that acetone was formed in only half the yield of RhIII(ttp)COiPr (2a). This might be due to the less efficient dehydrogenation of the alcohol formed from the CCA, which will be discussed in the Proposed Mechanism discussion. PPh3 Effect. Though the aldehydic CHA by RhIII(ttp)CH2CH2OH (1a) was significantly accelerated by added PPh3,11 surprisingly, the addition of PPh3 reduced the yield of RhIII(ttp)COiPr (2a) greatly to about 40% yield, even though RhIII(ttp)CH2CH2OH (1a) was completely consumed in 15 min (Table 1, entries 2 and 3). We are unclear of the reason.

amt of PPh3 (equiv)

yield of 2a (%)

1 2 3

0 0.1 1

80 40 38

solvent

time

yield of 2a (%)

1 2 3 4 5 6 7

a benzene tetrahydrofuran acetone acetonitrile dimethylformamide dimethylacetamide

15 min 2d 2d 2d 2d 2d 2d

80 56b 53b 34b tracec tracec tracec

a

Conditions: 480 equiv of diisopropyl ketone, concentration 7.1 M. bA trace amount of 1a was observed by TLC analysis. c1a was recovered quantitatively.

inhibit the reaction. Further studies were thus carried out under solvent-free conditions. CCA of Isopropyl Ketones. RhIII(ttp)CH2CH2OH (1a) selectively cleaved the C(CO)−C(iPr) bond of various isopropyl ketones at 25 °C to give the corresponding rhodium(III) porphyrin acyls (2) (Table 3). The less reactive

Table 1. CCA of Diisopropyl Ketone with Addition of PPh3

entry

entry

Table 3. CCA of Various Isopropyl Ketones with RhIII(ttp)CH2CH2OH (1a)

Solvent Effect. To lower the ketone substrate loading and expand the scope for solid substrates, various solvents were screened in the reaction of RhIII(ttp)CH2CH2OH (1a) with diisopropyl ketone (Table 2). RhIII(ttp)CH2CH2OH (1a) reacted with 100 equiv of diisopropyl ketone in benzene and tetrahydrofuran to give RhIII(ttp)COiPr (2a) in 56% and 53% yields, respectively, in 2 days (Table 2, entries 2 and 3). However, in the more polar solvent acetone, the yield of RhIII(ttp)COiPr (2a) was reduced to 34% (Table 2, entry 4), likely due to the observed poorer solubility of RhIII(ttp)CH2CH2OH (1a) in acetone at room temperature. When the reactions were carried out in acetonitrile, dimethylformamide, and dimethylacetamide solvents, only a trace amount of RhIII(ttp)COiPr (2a) was obtained, and RhIII(ttp)CH2CH2OH (1a) was recovered quantitatively (Table 2, entries 5−7). Coordination of solvent molecules to the rhodium center may 152

dx.doi.org/10.1021/om3009519 | Organometallics 2013, 32, 151−156

Organometallics

Article

illustrates a mechanism to account for the selective C(CO)− C(α) bond activation of ketones by RhIII(ttp)CH2CH2OH (1a). RhIII(ttp)CH2CH2OH (1a) first undergoes reversible βhydroxyl elimination to give the highly reactive RhIII(ttp)OH (eq i).11,14 RhIII(ttp)OH then cleaves the C(CO)−C(α) bond of ketones through σ-bond metathesis, giving RhIII(ttp)COR (2) and an alcohol (eq ii).6 The activation barrier for this CCA step is lower due to the synchronous formation of the Rh− C(CO) and C(alkyl)−O bonds in the four-center transition state (TS1).6 The alcohol then undergoes dehydrogenation catalyzed by RhIII(ttp)OH to give a carbonyl species and RhIII(ttp)H (eq iii).6,15 RhIII(ttp)H possibly reacts with ketones to give α- or β-CHA products (eq iv),6 which are then hydrolyzed to regenerate RhIII(ttp)OH (eq v).6 From the proposed mechanism, the stoichiometry of the formation of RhIII(ttp)COiPr (2a) and acetone should be 1:1 in the CCA of diisopropyl ketone (eq 2). However, acetone was formed in only half the yield of RhIII(ttp)COiPr (2a), probably due to the inefficient dehydrogenation of the alcohol. Isopropyl alcohol formed from the CCA is present in low concentration and is less competitive with the much greater excess of ketone substrate to react with RhIII(ttp)OH. This results in the incomplete conversion to acetone (Scheme 2, eq iii).

methyl isopropyl ketone and isobutyrophenone reacted with RhIII(ttp)CH2CH2OH (1a) for 3 days to give RhIII(ttp)COMe (2b) and RhIII(ttp)COPh (2c) in 28% and 20% yields, respectively, while RhIII(ttp)CH2CH2OH (1a) was recovered in 40% and 33% yields, respectively (Table 3, entries 2 and 3). When RhIII(ttp)CH2CH2OH (1a) reacted with 2,6-dimethylcyclohexanone, Rh III(ttp)COCH(CH 3)(CH 2) 3 COCH3 (2d) was obtained in 68% yield in 4 h (Table 3, entry 4). Cleavage occurred selectively at the C(CO)−C(iPr) bond, placing the alkyl fragment into a carbonyl moiety. Similarly, RhIII(ttp)CH2CH2OH (1a) reacted with the unsymmetrical 2methylcyclohexanone to give RhIII(ttp)CO(CH2)4COCH3 (2e) in 39% yield in 3 days (Table 3, entry 5). Selective CCA at the more hindered C(CO)−C(alkyl) bond was observed, as for RhIII(ttp)Me.6 CCA of Non-Isopropyl Ketones. Some aldol-condensable ketones reacted successfully. RhIII(ttp)CH2CH2OH (1a) reacted with diethyl ketone at 50 °C to give RhIII(ttp)COEt (2f) in 24% yield in 2 days (Table 4, entry 1). Cyclohexanone also reacted with RhIII(ttp)CH2CH2OH (1a) to give a 34% yield of RhIII(ttp)CO(CH2)4CHO (2g) in 2 days (Table 4, entry 2).

■

Table 4. CCA of Non-Isopropyl Ketones with RhIII(ttp)CH2CH2OH (1a)

CONCLUSION In summary, the highly reactive rhodium(III) porphyrin hydroxide was successfully generated from the readily accessible and air-stable RhIII(ttp)CH2CH2OH. The selective CCA of ketones was achieved by RhIII(ttp)CH2CH2OH under solventfree and aerobic conditions at 25−50 °C.

■

a

EXPERIMENTAL SECTION

Unless otherwise noted, all reagents were purchased from commercial suppliers and directly used without further purification. Hexane was distilled from anhydrous calcium chloride. Tetrahydrofuran (THF) was distilled from sodium benzophenone ketyl prior to use. Thin-layer chromatography was performed on precoated silica gel 60 F254 plates. Silica gel (Merck, 70−230 mesh) was used for column chromatography in air. 1 H NMR and 13C NMR spectra were recorded on a Bruker Avance III 400 spectrometer or Bruker Avance III 400Q spectrometer at 400 and 100 MHz, respectively. Chemical shifts were referenced to the residual solvent protons in C6D6 (δ 7.15 ppm), CDCl3 (δ 7.26 ppm), or tetramethylsilane (δ 0.00 ppm) in 1H NMR spectra as the internal standards and referenced to CDCl3 (δ 77.16 ppm) in 13C NMR spectra as the internal standard. Chemical shifts (δ) are reported as parts per million (ppm) in the δ scale downfield from TMS. Coupling constants (J) are reported in Hertz (Hz). High-resolution mass spectra (HRMS) were recorded on a ThermoFinnigan MAT 95 XL mass spectrometer. Fast atom bombardment spectra were performed with 3-nitrobenzyl alcohol (NBA) as the matrix. All samples for microanalysis were recrystallized from CH2Cl2/MeOH and vacuum-dried at room temperature for at least 2 days before submission. GC-MS analysis was conducted on a GCMS-QP2010 Plus system using a Rtx-5MS column (30 m × 0.25 mm). The details of the GC program are as follows. The column oven temperature and injection temperature were 35.0 and 180 °C, respectively. A split injection mode was applied. The carrier gas used was helium with a primary pressure of 500−900 kPa. Linear velocity was applied as the flow control mode. The pressure, total flow, column flow, linear velocity, purge flow, and split ratio were 32.4 kPa, 19.9 mL/min, 0.81 mL/min, 32.3 cm/s, 3.0 mL/min, and 20.0, respectively. The column oven temperature was kept at 35.0 °C for 5 min and then elevated by a rate of 30.0 °C/min up to 200.0 °C. The column oven temperature was then kept at 200.0

Observed by TLC analysis.

The successful CCA results of these two aldol-condensable ketones are encouraging. RhIII(ttp)CH2CH2OH (1a) is therefore a much better precursor of RhIII(ttp)OH than RhIII(ttp)Me and RhIII(ttp)Cl, which could not cleave the C−C bond of cyclohexanone due to extensive aldol condensation.9 The use of mild reaction conditions and the less Lewis acidic RhIII(ttp)CH2CH2OH (1a) can eliminate the aldol condensation, as no aldol condensation product was observed (Table 4, entries 1 and 2). However, RhIII(ttp)CH2CH2OH (1a) reacted with acetone at 50 °C to yield the α-CHA product , RhIII(ttp)CH2COCH3 (3) solely in 17% yield after 2 days without any CCA product (Table 4, entry 3). This is likely due to the stronger C(CO)− C(α) bond of acetone (BDE: C(CO)−C(Me), 84.1 kcal/mol; C(CO)−C(Et), 82.3 kcal/mol; C(CO)−C(iPr), 81.3 kcal/ mol).13 In addition, the less hindered but more abundant α-C− H bonds of acetone favor α-CHA. α-CHA therefore predominates. Proposed Mechanism. On the basis of the above findings and previous proposed mechanisms, 6,11,14,15 Scheme 2 153

dx.doi.org/10.1021/om3009519 | Organometallics 2013, 32, 151−156

Organometallics

Article

Scheme 2. Proposed Mechanism of CCA of Ketones by RhIII(ttp)CH2CH2OH (1a)

°C for 1 min. The ion source temperature and interface temperature were 220 and 270 °C, respectively. RhIII(ttp)CH2CH2OH (1a)11,12 and RhIII(ttp)Cl (1b)16 were synthesized according to the literature methods. Reaction between RhIII(ttp)CH2CH2OH and Diisopropyl Ketone at 25 °C under N2. RhIII(ttp)CH2CH2OH (1a; 18.1 mg, 0.022 mmol) and diisopropyl ketone (1.5 mL) were degassed for three freeze−pump−thaw cycles. The reaction mixture was stirred at 25 °C under N2 for 15 min. The excess solvent was removed by vacuum distillation and collected by a vacuum trap. The red residue was purified by column chromatography on silica gel eluting with a hexane/CH2Cl2 solvent mixture (1/1) as eluent to give RhIII(ttp)COiPr (2a;6 15.3 mg, 0.018 mmol, 82%). The yield of the organic coproduct acetone (39%) was measured by GC/MS using naphthalene as the internal standard. RhIII(ttp)COiPr (2a): Rf = 0.57 (hexane/CH2Cl2 1/1); 1H NMR (CDCl3, 400 MHz) δ −3.67 (sept, 1 H, J = 6.8 Hz), −2.14 (d, 6 H, J = 6.8 Hz), 2.70 (s, 12 H), 7.54 (t, 8 H, J = 8.7 Hz), 7.99 (d, 4 H, J = 7.5 Hz), 8.09 (d, 4 H, J = 7.6 Hz), 8.79 (s, 8 H). Reaction between RhIII(ttp)CH2CH2OH and Diisopropyl Ketone at 25 °C in Air. RhIII(ttp)CH2CH2OH (1a; 18.1 mg, 0.022 mmol) and diisopropyl ketone (1.5 mL) were stirred at 25 °C in air for 15 min. The excess solvent was removed by vacuum distillation and collected by vacuum trap. The red residue was purified by column chromatography on silica gel with a hexane/CH2Cl2 solvent mixture (1/1) as eluent to give RhIII(ttp)COiPr (2a; 14.9 mg, 0.018 mmol, 80%). The yield of the organic coproduct acetone (40%) was measured by GC/MS using naphthalene as the internal standard. Reaction between RhIII(ttp)CH2CH2OH and Diisopropyl Ketone with PPh3 (0.1 equiv) at 25 °C in Air. A stock benzene solution of PPh3 (100 μL, 0.022 M, 0.0022 mmol) was transferred to a Teflon screw capped tube. The benzene solvent was removed by vacuum distillation. RhIII(ttp)CH2CH2OH (1a; 18.1 mg, 0.022 mmol) and diisopropyl ketone (1.5 mL) were then added, and the mixture was stirred at 25 °C in air for 15 min. The excess solvent was removed by vacuum distillation. The red residue was purified by column chromatography on silica gel with a hexane/CH2Cl2 solvent mixture

(1/1) as eluent to give RhIII(ttp)COiPr (2a; 7.5 mg, 0.0089 mmol, 40%). Reaction between RhIII(ttp)CH2CH2OH and Diisopropyl Ketone with PPh3 (1 equiv) at 25 °C in Air. A stock benzene solution of PPh3 (1.0 mL, 0.022 M, 0.022 mmol) was transferred to a Teflon screw capped tube. The benzene solvent was removed by vacuum distillation. RhIII(ttp)CH2CH2OH (1a; 18.1 mg, 0.022 mmol) and diisopropyl ketone (1.5 mL) were then added, and the mixture was stirred at 25 °C in air for 15 min. The excess solvent was removed by vacuum distillation. The red residue was purified by column chromatography on silica gel with a hexane/CH2Cl2 solvent mixture (1/1) as eluent to give RhIII(ttp)COiPr (2a; 7.1 mg, 0.0084 mmol, 38%). Reaction between RhIII(ttp)CH2CH2OH and Diisopropyl Ketone (100 equiv) in Benzene at 25 °C in Air. RhIII(ttp)CH2CH2OH (1a; 9.0 mg, 0.011 mmol) and diisopropyl ketone (160 μL, 1.1 mmol) were mixed in benzene (590 μL) and stirred at 25 °C in air for 2 days. A trace amount of RhIII(ttp)CH2CH2OH (1a) was observed by TLC analysis. The excess solvent was removed by vacuum distillation. The red residue was purified by column chromatography on silica gel with a hexane/CH2Cl2 solvent mixture (1/1) as eluent to give RhIII(ttp)COiPr (2a; 5.2 mg, 0.006 mmol, 56%). Reaction between RhIII(ttp)CH2CH2OH and Diisopropyl Ketone (100 equiv) in THF at 25 °C in Air. RhIII(ttp)CH2CH2OH (1a; 9.0 mg, 0.011 mmol) and diisopropyl ketone (160 μL, 1.1 mmol) were mixed in THF (590 μL) and stirred at 25 °C in air for 2 days. A trace amount of RhIII(ttp)CH2CH2OH (1a) was observed by TLC analysis. The excess solvent was removed by vacuum distillation. The red residue was purified by column chromatography on silica gel with a hexane/CH2Cl2 solvent mixture (1/1) as eluent to give RhIII(ttp)COiPr (2a; 4.9 mg, 0.006 mmol, 53%). Reaction between RhIII(ttp)CH2CH2OH and Diisopropyl Ketone (100 equiv) in Acetone at 25 °C in Air. RhIII(ttp)CH2CH2OH (1a; 9.0 mg, 0.011 mmol) and diisopropyl ketone (160 μL, 1.1 mmol) were mixed in acetone (590 μL) and stirred at 25 °C in air for 2 days. A trace amount of RhIII(ttp)CH2CH2OH (1a) was observed by TLC analysis. The excess solvent was removed by vacuum distillation. The red residue was purified by column chromatography 154

dx.doi.org/10.1021/om3009519 | Organometallics 2013, 32, 151−156

Organometallics

Article

give RhIII(ttp)CO(CH2)4COCH3 (2e;6 7.7 mg, 0.009 mmol, 39%): Rf = 0.04 (hexane/CH2Cl2 1/1); 1H NMR (CDCl3, 400 MHz) δ −3.11 (t, 2 H, J = 7.0 Hz), −1.30 (quin, 2 H, J = 7.3 Hz), −0.58 (quin, 2 H, J = 7.5 Hz), 0.96 (t, 2 H, J = 7.6 Hz), 1.62 (s, 3 H), 2.69 (s, 12 H), 7.53 (d, 8 H, J = 7.8 Hz), 8.04 (t, 8 H, J = 8.3 Hz), 8.80 (s, 8 H). RhIII(ttp)CH2CH2OH (1a; 1.6 mg, 0.002 mmol, 9%) was recovered. Reaction between RhIII(ttp)CH2CH2OH and 3-Pentanone at 50 °C in Air. RhIII(ttp)CH2CH2OH (1a; 18.1 mg, 0.022 mmol) and 3-pentanone (1.5 mL) were heated at 50 °C in air for 2 days. The excess solvent was removed by vacuum distillation. The red residue was purified by column chromatography on silica gel with a hexane/ CH2Cl2 solvent mixture (1/1) as eluent to give RhIII(ttp)COEt (2f;6 4.4 mg, 0.005 mmol, 24%): Rf = 0.52 (hexane/CH2Cl2 1/1); 1H NMR (CDCl3, 400 MHz) δ −3.10 (q, 2 H, J = 7.3 Hz), −1.67 (t, 3 H, J = 7.3 Hz), 2.70 (s, 12 H), 7.54 (d, 8 H, J = 7.6 Hz), 8.06 (d, 8 H, J = 6.4 Hz), 8.80 (s, 8 H). RhIII(ttp)CH2CH2OH (1a; 8.9 mg, 0.011 mmol, 49%) was recovered. Reaction between RhIII(ttp)CH2CH2OH and Cyclohexanone at 50 °C in Air. RhIII(ttp)CH2CH2OH (1a; 18.1 mg, 0.022 mmol) and cyclohexanone (1.5 mL) were heated at 50 °C in air for 2 days. A trace amount of RhIII(ttp)CH2CH2OH (1a) was observed by TLC analysis. The excess solvent was removed by vacuum distillation. The red residue was purified by column chromatography on silica gel with a hexane/CH2Cl2 solvent mixture (1/1) as eluent to give RhIII(ttp)CO(CH2)4CHO (2g; 6.6 mg, 0.007 mmol, 34%): Rf = 0.31 (hexane/ CH2Cl2 1/1); 1H NMR (CDCl3, 400 MHz) δ −3.09 (t, 2 H, J = 6.9 Hz), −1.25 (quin, 2 H, J = 7.2 Hz), −0.60 (quin, 2 H, J = 7.5 Hz), 0.98 (dt, 2 H, J = 1.3, 7.5 Hz), 2.70 (s, 8 H), 7.55 (d, 8 H, J = 7.9 Hz), 8.05 (m, 8 H), 8.81 (s, 8 H), 9.03 (s, 1 H); 13C NMR (CDCl3, 100 MHz) δ 19.3, 21.7, 22.2, 42.0, 42.9, 122.9, 127.6, 131.7, 133.9, 134.2, 137.5, 139.2, 143.2, 201.8 (d, 1JRh−C = 17.2 Hz), 207.7; HRMS (FABMS) calcd for C54H45N4O2Rh+ m/z 884.2592, found m/z 884.2595. Reaction between RhIII(ttp)CH2CH2OH and Acetone at 50 °C in Air. RhIII(ttp)CH2CH2OH (1a; 18.1 mg, 0.022 mmol) and acetone (1.5 mL) were heated at 50 °C in air for 2 days. The excess solvent was removed by vacuum distillation. The red residue was purified by column chromatography on silica gel with a hexane/CH2Cl2 solvent mixture (1/1) as eluent to give RhIII(ttp)CH2COCH3 (3;6 3.1 mg, 0.004 mmol, 17%): Rf = 0.15 (hexane/CH2Cl2 1/1); 1H NMR (CDCl3, 400 MHz) δ −4.63 (d, 2 H, J = 3.8 Hz), −1.79 (s, 3 H), 2.70 (s, 12 H), 7.55 (d, 8 H, J = 7.8 Hz), 8.04 (m, 8 H), 8.79 (s, 8 H). RhIII(ttp)CH2CH2OH (1a; 9.6 mg, 0.012 mmol, 53%) was recovered.

on silica gel with a hexane/CH2Cl2 solvent mixture (1/1) as eluent to give RhIII(ttp)COiPr (2a; 3.2 mg, 0.004 mmol, 34%). Reaction between RhIII(ttp)CH2CH2OH and Diisopropyl Ketone (100 equiv) in Acetonitrile at 25 °C in Air. RhIII(ttp)CH2CH2OH (1a; 9.0 mg, 0.011 mmol) and diisopropyl ketone (160 μL, 1.1 mmol) were mixed in acetonitrile (590 μL) and stirred at 25 °C in air for 2 days. The excess solvent was removed by vacuum distillation. The red residue was purified by column chromatography on silica gel with a hexane/CH2Cl2 solvent mixture (1/1) as eluent to give a trace amount of RhIII(ttp)COiPr (2a). RhIII(ttp)CH2CH2OH (1a) was recovered quantitatively. Reaction between RhIII(ttp)CH2CH2OH and Diisopropyl Ketone (100 equiv) in Dimethylformamide at 25 °C in Air. RhIII(ttp)CH2CH2OH (1a; 9.0 mg, 0.011 mmol) and diisopropyl ketone (160 μL, 1.1 mmol) were mixed in dimethylformamide (590 μL) and stirred at 25 °C in air for 2 days. The excess solvent was removed by vacuum distillation. The red residue was purified by column chromatography on silica gel with a hexane/CH2Cl2 solvent mixture (1/1) as eluent to give a trace amount of RhIII(ttp)COiPr (2a). RhIII(ttp)CH2CH2OH (1a) was recovered quantitatively. Reaction between RhIII(ttp)CH2CH2OH and Diisopropyl Ketone (100 equiv) in Dimethylacetamide at 25 °C in Air. RhIII(ttp)CH2CH2OH (1a; 9.0 mg, 0.011 mmol) and diisopropyl ketone (160 μL, 1.1 mmol) were mixed in dimethylacetamide (590 μL) and stirred at 25 °C in air for 2 days. The excess solvent was removed by vacuum distillation. The red residue was purified by column chromatography on silica gel with a hexane/CH2Cl2 solvent mixture (1/1) as eluent to give a trace amount of RhIII(ttp)COiPr (2a). RhIII(ttp)CH2CH2OH (1a) was recovered quantitatively. Reaction between RhIII(ttp)CH2CH2OH and Methyl Isopropyl Ketone at 25 °C in Air. RhIII(ttp)CH2CH2OH (1a; 18.1 mg, 0.022 mmol) and methyl isopropyl ketone (1.5 mL) were stirred at 25 °C in air for 3 days. The excess solvent was removed by vacuum distillation. The red residue was purified by column chromatography on silica gel with a hexane/CH2Cl2 solvent mixture (1/1) as eluent to give RhIII(ttp)COMe (2b;6 5.0 mg, 0.006 mmol, 28%): Rf = 0.38 (hexane/ CH2Cl2 1/1); 1H NMR (CDCl3, 400 MHz) δ −2.79 (s, 3 H), 2.70 (s, 12 H), 7.54 (t, 8 H, J = 7.8 Hz), 8.06 (dd, 8 H, J = 3.0 Hz, 6.6 Hz), 8.80 (s, 8 H). RhIII(ttp)CH2CH2OH (1a; 7.2 mg, 0.009 mmol, 40%) was recovered. Reaction between RhIII(ttp)CH2CH2OH and Isobutyrophenone at 25 °C in Air. RhIII(ttp)CH2CH2OH (1a; 18.1 mg, 0.022 mmol) and isobutyrophenone (1.5 mL) were stirred at 25 °C in air for 3 days. The excess solvent was removed by vacuum distillation. The red residue was purified by column chromatography on silica gel with a hexane/CH2Cl2 solvent mixture (1/1) as eluent to give RhIII(ttp)COPh (2c;6 3.9 mg, 0.004 mmol, 20%): Rf = 0.43 (hexane/CH2Cl2 1/ 1); 1H NMR (CDCl3, 400 MHz) δ 2.43 (d, 2 H, J = 8.1 Hz), 2.70 (s, 12 H), 5.95−6.00 (m, 2 H), 6.40 (t, 1 H, J = 7.8 Hz), 7.52−7.56 (m, 8 H), 7.95−8.01 (m, 8 H), 8.76 (s, 8 H). RhIII(ttp)CH2CH2OH (1a; 6.0 mg, 0.007 mmol, 33%) was recovered. Reaction between RhIII(ttp)CH2CH2OH and 2,6-Dimethylcyclohexanone at 25 °C in Air. RhIII(ttp)CH2CH2OH (1a; 18.1 mg, 0.022 mmol) and 2,6-dimethylcyclohexanone (1.5 mL) were stirred at 25 °C in air for 4 h. The excess solvent was removed by vacuum distillation. The red residue was purified by column chromatography on silica gel with a hexane/CH2Cl2 solvent mixture (1/1) as eluent to give RhIII(ttp)COCH(CH3)(CH2)3COCH3 (2d;6 13.7 mg, 0.015 mmol, 68%): Rf = 0.03 (hexane/CH2Cl2 1/1); 1H NMR (CDCl3, 400 MHz) δ −3.61 (sext, 1 H, J = 5.6 Hz), −2.34 (d, 3 H, J = 6.8 Hz), −1.65 (q, 1 H, J = 7.8 Hz), −1.39 (m, 2 H), −0.92 (quin, 1 H, J = 8.6 Hz), 1.13 (m, 2 H), 1.72 (s, 3 H), 2.72 (s, 12 H), 7.56 (d, 8 H, J = 7.9 Hz), 8.04 (dd, 8 H, J = 2.0, 7.4 Hz), 8.10 (dd, 8 H, J = 2.1, 7.4 Hz), 8.84 (s, 8 H). Reaction between RhIII(ttp)CH2CH2OH and 2-Methylcyclohexanone at 25 °C in Air. RhIII(ttp)CH2CH2OH (1a ; 18.1 mg, 0.022 mmol) and 2-methylcyclohexanone (1.5 mL) were stirred at 25 °C in air for 3 days. The excess solvent was removed by vacuum distillation. The red residue was purified by column chromatography on silica gel with a hexane/CH2Cl2 solvent mixture (1/1) as eluent to

■

ASSOCIATED CONTENT

S Supporting Information *

Figures giving 1H and 13C NMR spectra for 2g. This material is available free of charge via the Internet at http://pubs.acs.org.

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

■ ■

ACKNOWLEDGMENTS We thank the Direct Grant of CUHK (A/C 2060425) for financial support. REFERENCES

(1) Murai, S., Alper, H., Gossage, R. A., Grushin, V. V., Hidai, M., Ito, Y., Jones, W. D., Kakiuchi, F., van Koten, G., Lin, Y.-S., Mizobe, Y., Murai, S., Murakami, M., Richmond, T. G., Sen, A., Suginome, M., Yamamoto, A., Eds. Activation of Unreactive Bonds and Organic Synthesis; Springer-Verlag: Berlin, Heidelberg, 1999; Topics in Organometallic Chemistry Vol. 3. (2) Murakami, M.; Matsuda, T. Chem. Commun. 2011, 47, 1100− 1105.

155

dx.doi.org/10.1021/om3009519 | Organometallics 2013, 32, 151−156

Organometallics

Article

(3) Rybtchinski, B.; Milstein, D. Angew. Chem., Int. Ed. 1999, 38, 870−883. (4) Jun, C.-H. Chem. Soc. Rev. 2004, 33, 610−618. (5) Anstey, M. R.; Yung, C. M.; Du, J.; Bergman, R. G. J. Am. Chem. Soc. 2007, 129, 776−777. (6) (a) Fung, H. S.; Li, B. Z.; Chan, K. S. Organometallics 2010, 29, 4421−4423. (b) Fung, H. S.; Li, B. Z.; Chan, K. S. Organometallics 2012, 31, 570−579. (7) (a) Li, B. Z.; Song, X.; Fung, H. S.; Chan, K. S. Organometallics 2010, 29, 2001−2003. (b) Li, B. Z.; Fung, H. S.; Song, X.; Chan, K. S. Organometallics 2011, 30, 1984−1990. (8) Aoyama, Y.; Tanaka, Y.; Yoshida, T.; Toi, H.; Ogoshi, H. J. Organomet. Chem. 1987, 329, 251−266. (9) Fung, H. S. Ph.D. Thesis, The Chinese University of Hong Kong, 2012. (10) Choi, K. S.; Lai, T. H.; Lee, S. Y.; Chan, K. S. Organometallics 2011, 30, 2633−2635. (11) Chan, K. S.; Lau, C. M.; Yeung, S. K.; Lai, T. H. Organometallics 2007, 26, 1981−1985. (12) Ogoshi, H.; Setsune, J.; Omura, T.; Yoshida, Z. J. Am. Chem. Soc. 1975, 97, 6461−6466. (13) Luo, Y. R. Comprehensive Handbook of Chemical Bond Energies; CRC Press: Boca Raton, FL, 2007. (14) Wayland, B. B.; Van Voorhees, S. L.; Del Rossi, K. J. J. Am. Chem. Soc. 1987, 109, 6513−6515. (15) (a) Collman, J. P.; Boulatov, R. Inorg. Chem. 2001, 40, 560−563. (b) Liu, L.; Yu, M.; Wayland, B. B.; Fu, X. Chem. Commun. 2010, 46, 6353−6355. (16) (a) Zhou, X.; Li, Q.; Mak, T. C. W.; Chan, K. S. Inorg. Chim. Acta 1998, 270, 551−554. (b) Zhou, X.; Wang, R.-J.; Xue, F.; Mak, T. C. W.; Chan, K. S. J. Organomet. Chem. 1999, 580, 22−25. (c) Zhou, X.; Tse, M. K.; Wu, D.-D.; Mak, T. C. W.; Chan, K. S. J. Organomet. Chem. 2000, 598, 80−86.

156

dx.doi.org/10.1021/om3009519 | Organometallics 2013, 32, 151−156