Cl Precatalysts - ACS Publications - American Chemical Society

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Base-Free Transfer Hydrogenation of Ketones Using Cp*Ir(pyridinesulfonamide)Cl Precatalysts Andrew Ruff, Christopher Kirby, Benny C. Chan, and Abby R. O’Connor* Department of Chemistry, The College of New Jersey, 2000 Pennington Road, Ewing, New Jersey 08628, United States S Supporting Information *

ABSTRACT: N-(2-(Pyridin-2-yl)ethyl)benzenesulfonamide derivatives and 1,1,1-trifluoro-N-(2-(pyridin-2-yl)ethyl)methanesulfonamide (1−4), along with three-legged piano stool Cp*IrIIICl complexes (5−11) (Cp* = pentamethylcyclopentadienyl) bearing pyridinesulfonamide ligands with varying electronic parameters, were synthesized. These ligands and airstable complexes were characterized by 1H and 13C{1H} NMR spectroscopy, elemental analysis, and single-crystal X-ray diffraction. Precatalysts, 5−11, were assessed for transfer hydrogenation of aryl, diaryl, dialkyl, linear, cycloaliphatic, and α,β-unsaturated ketones, diones, β-ketoesters, and a biomass-derived substrate with 2-propanol, using 1 mol % precatalyst. Catalysis was also efficient using a 0.1 mol % loading. Remarkably, all catalysis experiments can be conducted in air without dried and degassed substrates, and basic additives and halide abstractors are not required for high activity in transfer hydrogenation. Control experiments and a mercury poisoning experiment support a homogeneous catalyzed pathway. Overall, the fastest reactions are observed using electron-poor substrates and precatalysts bearing electron-rich ligands.

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INTRODUCTION The reduction of unsaturated bonds of alkenes, ketones, and imines is a common reaction with importance in both industrial and pharmaceutical applications. Traditionally, reduction of aldehydes and ketones is achieved using stoichiometric reagents, such as NaBH4, LiAlH4, or metal catalysts and H2.1 However, these reagents have drawbacks; for example, NaBH4 and LiAlH4 are air and moisture sensitive and the use of molecular hydrogen for reduction reactions can be dangerous in instances where high pressures of H2 are required.2 Thus, alternatives, such as transfer hydrogenation, have received attention. Transfer hydrogenation involves simultaneous oxidation of a hydrogen source and reduction of an unsaturated acceptor substrate. An organometallic complex is often used to catalyze this reaction;3 however there are organocatalysts for this transformation. 4 Hydrogen donor sources tend to be inexpensive, abundant, derived from renewable feedstocks, and nontoxic. Common donor sources are 2-propanol, azeotropic mixtures of formic acid and triethylamine, and sodium formate in water.5 Hydrogen acceptors include the unsaturated bonds of aliphatic and aromatic ketones,6,7 primary and secondary imines,8,9 internal alkynes,10 alkenes, α,βunsaturated ketones, and nitroarenes.11 Transfer hydrogenation has advantages over other reduction methods, as the reaction conditions are comparatively milder and involve more benign reagents.12 Therefore, transfer hydrogenation provides a greener method for reduction by removing toxic reagents and utilizing safer reaction conditions.13 In addition, reactions using H2 and Pd/C catalysts often impart little selectivity in reductions. In contrast, an example of a selective reduction, © XXXX American Chemical Society

the reduction of ketones and nitroarenes via transfer hydrogenation, was developed by Noyori14 and Beller,15 respectively, and these systems tolerate an array of functional groups. The use of Cp*Ir (Cp* = pentamethylcyclopentadienyl) complexes for transfer hydrogenation has been recently reviewed.3 Cp*Ir fragments containing different classes of ligands, such as NHCs (N-heterocyclic carbenes), triazolyls, cyclometalated imines, and diamines, are active for transfer hydrogenation catalysis (Figure 1). For example, complex A reduces imines and ketones using 1 mol % catalyst in basic solution.16 Complex B, an air- and moisture-tolerant complex, converts 2-cyanoacetophenone to the alcohol product using sodium formate and water as the hydrogen source and

Figure 1. Recently reported Cp*Ir(III) complexes A−E used for transfer hydrogenation. Received: October 14, 2015

A

DOI: 10.1021/acs.organomet.5b00864 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics selectively reduces α-nitroketones to the alcohol without reduction of the nitro group.17 Complex C has one of the largest substrate scopes of recently reported half-sandwich Ir complexes and performs transformations including the conversion of ketones and aldehydes to alcohols,18,19 imines to amines,20 and ketones to secondary20,21 and primary amines22,23 through reductive amination. These reactions were performed using formate at low pH. The Cp*Ir triazolyl complex D was used for the reduction of nitrobenzenes to create aniline, azobenzene, and azoxybenzene derivatives with 2-propanol as a hydrogen source.24 Additionally, it was demonstrated that dinuclear iridium triazolyl complexes exhibit improved reduction compared to mononuclear analogues.25 Crabtree also reported Cp*Ir precatalysts containing NHC ligands (E) and observed quantitative reduction of acetophenone using 10 mol % KOH additive.26 This is one of the most active Cp*Ir precursors known. Although Cp*Ir-based complexes are active for transfer hydrogenation, there are still limitations. For example, many transfer hydrogenation reactions using Cp*Ir complexes require base, KOH or tBuOK, for high catalytic activity. There are however limited examples of Ir complexes that catalyze base-free transfer hydrogenation.27−29 Peris’s Cp*Ir(NHC) catalyst hydrogenates ketones and imines at room temperature without base, but requires a 3-fold excess of AgOTf.27 An in situ generated iridium hydride catalyst, although active for reduction of aromatic ketones without additives, requires an inert atmosphere for high activity.28 Although there are examples of catalysts active under base-free conditions, these drawbacks make the above systems less commercially viable. Another common issue is the inability to reduce unactivated forms of unsaturation. For example, complex B hydrogenates only substrates possessing electron-withdrawing groups, thus limiting the substrate scope. Some systems need extreme reaction conditions in order to force catalysis. Reactions utilizing complex C operate only at low pH. In addition, the catalytic conditions required for transfer hydrogenation using many Cp*Ir complexes require a dry solvent and inert atmosphere. There is a limited number of Cp*Ir complexes that catalyze transfer hydrogenation of an array of substrates without the need for additives and predried solvents and in air. The use of pyridinesulfonamide compounds as ligands in organometallic complexes is an underexplored area in catalysis. These ligands are advantageous for transfer hydrogenation over other typical diamine ligands due to two chemically distinct nitrogen atoms that can act as a proton acceptor during catalysis. Complexes containing a methylene linker between the pyridine and sulfonamide groups (F−I) are more common than those containing ethylene linkers (J) (Figure 2). Complexes using pyridinesulfonamide ligands perform different catalytic reactions. For example, complex F catalyzes αoxygenation of ethers,30 while complex G acts as a catalyst for the A3 coupling of a ketone, terminal alkyne, and secondary amine.23 Methylene-linked pyridinesulfonamides coordinated to Ru (H) catalyze transfer hydrogenation.31,32 A pyridinesulfonamide ligand possessing an ethylene linker coordinated Au (J) catalyzes the addition of methyl furan to methyl vinyl ketone.33 Additionally, coordination complexes of Co containing ethylene-linked pyridinesulfonamides are known.34 There are no reports of Cp*Ir complexes containing pyridinesulfonamides linked by an ethylene bridge.

Figure 2. Complexes F−J containing pyridinesulfonamide ligands.

Here we report the synthesis and NMR characterization of four pyridinesulfonamide ligands containing an ethylene linker (Figure 3, 1−4). Also, X-ray crystal structures for ligands 1 and

Figure 3. Library of pyridinesulfonamide ligands and Cp*Ir(III) precatalysts for transfer hydrogenation.

2 are included. In addition, we describe the synthesis and characterization of air- and moisture-tolerant iridium halfsandwich complexes containing electronically different pyridinesulfonamide ligands (Figure 3, 5−11). These complexes serve as precatalysts for transfer hydrogenation of acetophenone derivatives, diaryl, aliphatic, and α,β-unsaturated ketones, as well as diones, and biomass-derived levulinic acid, using 2propanol, as the hydrogen source. In contrast to other catalysts, base is not required for catalyst activation and catalysis is conducted in air without predried solvents. The electronics of the sulfonamide moiety on the ligand influence the catalytic conversion rate to product, and the electronics of the substrate also impact the conversion of ketone to alcohol. Control and mercury poisoning experiments support a homogeneously catalyzed process.

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RESULTS AND DISCUSSION Synthesis and Characterization of Pyridinesulfonamide Ligands and Cp*Ir(Pyridinesulfonamide)Cl Precatalysts. Different synthetic strategies to prepare pyridinesulfonamide ligands with an ethylene linker have been reported. B


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Organometallics

and base that were not predried. An immediate color change from orange to light orange or yellow was observed upon the addition of base. An aqueous extraction was used to remove the triethylammonium chloride. Upon removal of solvent in vacuo, an orange or yellow oil forms, which turns into an orange or yellow powder upon vigorous stirring in hexanes overnight. The complexes were isolated in high yields and stored at room temperature. The precatalysts are stable in air, and degradation has not been observed. Each complex was characterized by elemental analysis and 1H and 13C{1H} NMR spectroscopy. 1H NMR spectra of the complexes have diagnostic features for each complex. Within the aromatic region (7−9 ppm), four downfield peaks correlate to the hydrogen atoms on the pyridine ring and have integration ratios of 1H:1H:1H:1H. Additionally, two 2H doublets are observed downfield for the sulfonamide moiety for benzenesulfonamide analogues 8−11. A 5H multiplet is observed in the aromatic region for the sulfonamide moiety of 7. Due to the cyclometalation of the pyridinesulfonamide group, the ethylene linker is structurally rigid, and each hydrogen within the ethylene linker generates a unique resonance in the 2.0−4.0 ppm region. The hydrogens of the ethylene backbone for complexes 5−11 are diastereotopic and appear as individual signals with complex coupling patterns (Supporting Information). The absence of a 1H triplet in the 6.0 ppm range indicates metalation at the sulfonamide moiety. X-ray crystal structures were obtained for complexes 5, 9, and 10 to verify the structure of each complex in the solid state (Figure 5). Selected bond distances and angle are found in

However, derivatives that possess a cyano (CN), nitro (NO2), or methoxy (OMe) functional group in the para-position of the benzene ring of the sulfonamide moiety and a CF3 group at the sulfonamide have not been previously characterized in detail. Ligands 1−4 were synthesized using modified literature procedures in good yields.35,36 Compounds 1−3 were characterized via 1H and 13C{1H} NMR spectroscopy and elemental analysis. Elemental analysis for the CF3 derivative 4 has been described elsewhere;37 however 1H, 13C{1H}, and 19 F{ 1 H} NMR for this compound are not reported. Compounds 1−4 possess four unique aromatic resonances for the pyridine and a quartet at ∼3.4 ppm and triplet at ∼2.9 ppm for the CH2 groups of the ethylene linker. X-ray quality crystals were obtained by slow evaporation of 1 in methanol, and X-ray quality crystals of 2 were obtained by vapor diffusion of hexanes into a saturated solution of 2 in CH2Cl2. The ORTEP diagrams for compounds 1 and 2 are seen in Figure 4. Similar X-ray parameters and structures were obtained for other pyridinesulfonamides reported by our group.38

Figure 4. X-ray crystal structures for compounds 1 (NO2, top) and 2 (OMe, bottom). Hydrogen atoms are omitted for clarity.

Synthesis of the iridium half-sandwich precatalysts is achieved via exposure of the [Cp*IrCl2]2 dimer and 2 equiv of the pyridinesulfonamide ligand to excess triethylamine (NEt3) in dichloromethane for 2 h at room temperature (Scheme 1). Synthesis was performed in air, utilizing solvents

Figure 5. X-ray crystal structures of complex 5, 9, and 10. Hydrogen atoms and solvent are omitted for clarity.

Table 1, and all other crystallographic parameters are found in the Supporting Information. X-ray quality crystals of 5, 9, and 10 were obtained via vapor diffusion of hexanes into a saturated solution of the complex in CH2Cl2. Complexes 5, 9, and 10 exhibit three-legged piano stool geometry around the Ir center, where the three legs are the chloride, pyridine, and sulfonamide moiety. A six-membered metallacycle is observed between the metal center and the two nitrogen atoms of the pyridinesulfonamide ligand. The N−Ir−N bond angle is 88.3°, 84.98°, and 83.94°, respectively for 5, 9, and 10. The two Ir−N bond distances were roughly equal for 5 (2.120 vs 2.115 Å), 9 (2.130 vs 2.110 Å), and 10 (2.130 vs 2.114 Å). The Ir to Cp* centroid

Scheme 1. Synthesis of Cp*Ir(pyridinesulfonamide) Halide Precatalysts

C


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Organometallics Table 1. Selected Bond Distances and Angle for Complexes 5, 9, and 10 Distances (Å) Ir1−N1 Ir1−N2 Ir1−Cl1 Ir1−Cp*centroid Angle (deg) N1−Ir1−N2

5

9

10

2.115(3) 2.120(3) 2.4206(8) 1.7864(5)

2.110(5) 2.130(4) 2.4083(15) 1.7912(3)

2.107(2) 2.116(2) 2.4311(7) 1.7929(3)

88.33(11)

84.98(17)

83.94(9)

distances are all approximately equivalent at 1.79 Å, as seen in Table 1. Transfer Hydrogenation Using Cp*Ir(pyridinesulfonamide)Cl Precatalysts. The benchmark reaction for the transfer hydrogenation of ketones is the reduction of acetophenone (Table 2). All catalytic experiments

Figure 6. Plot demonstrating increased conversion vs σ-constant for the reduction for acetophenone derivatives.

conversion in 6 h drops when compared to substrates with electron-poor substituents in the para-position (Table 2, entries 4 and 7 vs 8 and 9). This finding agrees with prior systems reported using iridium and ruthenium precatalysts.5,39,40 From this, it can be concluded that electron-poor substrates are reduced faster under these catalytic conditions. A positional study using ortho-, meta-, and para-methoxyacetophenone was performed in order to determine the effects the substituent position has upon transfer hydrogenation using precatalyst 5. ortho-Methoxyacetophenone showed the highest conversion rate, 98% after 6 h (Table 2, entry 6). metaMethoxyacetophenone was reduced with a slightly lower conversion when compared to 2-methoxyacetophenone, 90% in 6 h (entry 5). para-Methoxyacetophenone displayed the slowest rate and afforded only 56% alcohol product in 6 h (entry 4). This supports the claim that the inductive effects of the substituent play more of a role in influencing reduction rates in comparison to resonance effects, as methoxy is inductively withdrawing and the highest conversion to product is observed when the substituent is in the ortho-position. To verify the high activity of the precatalysts, a catalytic trial was conducted using (Cp*IrCl2)2. Acetophenone was converted to 1-phenylethanol in 12% in 24 h (Table 2, entry 10). Lower conversion was observed using the Ir dimer when compared to trials conducted using Cp*Ir(pyridinesulfonamide)Cl precatalysts (12% vs 88%). In addition, lower conversion was observed using the Ir dimer in conjunction with 2 equiv of a 4-methyl-N-(2-(pyridin-2yl)ethyl)benzenesulfonamide ligand. Only 14% conversion of acetophenone to 1-phenylethanol was observed after 3 h (entry 11). The active catalyst cannot be readily formed in situ from the Ir dimer and ligand. Although the dimer and dimer in conjunction with ligand do show activity, these species are not the cause of the high catalytic activity observed in these systems. The addition of additives was also evaluated (Table 3). Silver triflate, AgOTf, was added in catalytic quantities (1 or 5 mol %) to evaluate the need for precatalyst activation by loss of a chloride. Conversion to product was not improved under standard transfer hydrogenation conditions, as only 3% alcohol product was observed after 1 h using 1 mol % AgOTf, while 5% alcohol was observed at 5 mol % AgOTf (entries 2 and 3). Analogous catalytic conditions without AgOTf afforded 62% conversion in 1 h (entry 1). Addition of KOH did not improve the amount of 1-phenylethanol observed; in fact the conversion

Table 2. Reduction of Acetophenone Derivativesa

entry

X

precat

t (h)

1 2b 3c 4 5 6 7 8 9 10 11d

4-H 4-H 4-H 4-OMe 3-OMe 2-OMe 4-Me 4-Br 4-NO2 4-H 4-H

8 8 8 5 5 5 8 8 8 (Cp*IrCl2)2 (Cp*IrCl2)2/2L

3 3 3 6 6 6 6 6 6 24 3

conv (%) 88 14 28 56 90 98 77 91 99 12 14

± ± ± ± ± ± ± ± ±

1 1 1 2 1 1 1 1 1 (99)

±1

TON 88 14 28 56 90 98 77 91 99 12 14

a1

H NMR spectroscopy used to determine yield. Yields reported as an average of three trials. 1,4-Dimethoxybenzene used as standard. A 1.0 M solution of substrate in 2-propanol. Yield in parentheses was isolated after 3 h. bReaction conducted at 30 °C. cReaction conducted at 50 °C. dL = 4-methyl-N-(2-(pyridin-2 yl)ethyl)benzenesulfonamide.

were conducted in air without dried or degassed reagents at 85 °C. Acetophenone was reduced to 1-phenylethanol in 88% conversion in 3 h using precatalyst 8. At 30 and 50 °C, temperatures below the boiling point of the acetone byproduct, much lower conversions were observed, 14% and 28%, respectively (entries 2 and 3). Both electron-rich (entries 4 and 7) and electron-poor (entries 8 and 9) aromatic ketones were reduced. Additionally, transfer hydrogenation of 4-nitroacetophenone yielded 1-(4-nitrophenyl)ethanol in 99% isolable yield after 3 h (Table 2, entry 9). 4-Nitroacetophenone exhibited the highest conversion to the alcohol product in the shortest time. The plot in Figure 6 demonstrates the electronic effects of the substrate on conversion. On the basis of the positive slope, the addition of electron-withdrawing groups on the substrate increases conversion to product. This is likely due to a weaker carbonyl bond, which is easier to reduce. With electron-donating groups on the para-substituted acetophenone derivative, the observed D


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Organometallics Table 3. Assessing the Effects of Additivesa

entry

additive

mol %

conversion (%)

TON

1 2 3 4 5

none AgOTf AgOTf KOH KOH

N/A 1 5 1 5

62 3 5 17 5

62 3 5 17 5

precatalysts yield more product in less time, as an electronrich precatalyst facilitates reduction. This trend agrees with Noyori’s [RuCl2(η6-benzene)]-N-substituted-1,2-diphenylethylenediamine catalyst system, in which the transfer hydrogenation reactivity decreases with electron-withdrawing groups on the sulfonamide.7 However, this trend contrasts Carriera’s observations that electron-poor substituents on the sulfonamide moiety of a diamine ligand coordinated to Cp*IrIII yield more product in the transfer hydrogenation of α-cyano/nitro-ketones in water using formic acid as the hydrogen source.29 This relationship is verified in Figure 7, where the negative slope

a1

H NMR spectroscopy used to determine yield. Yield reported from one trial. 1,4-Dimethoxybenzene used as standard. A 1.0 M solution of substrate in 2-propanol.

is dramatically reduced. After 1 h, 5−17% product was formed compared to the 62% conversion obtained without the addition of base (entries 1 vs 4 and 5), which is caused by decomposition of the complex under these conditions. In the presence of base, the solutions darken to a purple color, indicative of an inactive complex, and at elevated temperatures in the presence of AgOTf a black precipitate and dark solution form. From these results, base and AgOTf are not necessary for high activity with Cp*Ir(pyridinesulfonamide)Cl precatalysts when reactions are conducted in air. After demonstrating the precatalyst’s ability to reduce aromatic methyl ketones, a study was performed to determine how the electronics of each precatalyst impact conversion under the same reaction conditions (Table 4). For this study, 4-

Figure 7. Plot illustrating the electronic effects of the precatalyst on conversion of 4-nitroacetophenone.

supports that electron-rich precatalysts yield more product than electron-poor precatalysts in the same time period. Reactions were also conducted at 0.1 mol % catalyst loading (Table 4, entries 8 and 9). The ketone starting material is converted 77% in 1 h, and 91% is reduced after 2 h. Lastly, a mercury poisoning experiment was conducted to test for heterogeneous catalysis (entry 10). There was no significant impact on conversion from the addition of Hg(0) (entry 2 vs entry 10); thus it is unlikely that heterogeneous sources of Ir are responsible for the high activity observed. The substrate scope was expanded to include aliphatic, cycloaliphatic, and aromatic ketones. All trials were conducted using precatalyst 5 (Table 5). Benzophenone and methyl isobutyl ketone were reduced in moderate yields, 82% and 52%, respectively, in 24 h (entries 1 and 2). Decanone was reduced to 2-decanol, 65% in 3 h (entry 3). The cycloaliphatic ketones, cyclopentanone, cyclohexanone, and cycloheptanone were also converted to their corresponding alcohols in moderate to high yields, 86%, 99%, and 63%, respectively (entries 4−6). The α,βunsaturated ketone, cyclohex-2-enone, demonstrated selectivity in reduction. After 3 h, cyclohex-2-enone was converted to cyclohexanone (entries 7 and 8). This supports selective reduction of activated alkene bonds over ketones. After 6 h, cyclohexanol was observed in 95% yield, as the major product (entry 8). This reduction may proceed by a 1,4-addition mechanism as seen in other systems.41,42 To further probe this reduction, ketone substrates containing unconjugated alkenes, 2-allyl cyclohexanone and 5-hexen-2-one, were evaluated (entries 9 and 10). Once again selective reduction of the alkene occurred first. However, in these substrates, evidence of isomerization of the alkene to the more stable conjugated isomer is observed by 1H NMR and GCMS. The Ir precatalyst also catalyzes isomerization of olefins. A 1,4-addition

Table 4. Reduction of 4-Nitroacetophenone with Varying Precatalysta

entry

precatalyst

1 2 3 4 5 6 7 8b 9c 10d

8 5 10 7 11 9 6 5 5 5

conversion (%)

TON

± ± ± ± ± ± ±

98 97 97 96 91 86 78 770 910 99

98 97 97 96 91 86 78 77 91 99

1 1 1 1 1 1 1

a1

H NMR spectroscopy used to determine yield. Yields reported as an average of three trials. 1,4-Dimethoxybenzene used as standard. A 1.0 M solution of substrate in 2-propanol. b0.1 mol % catalyst loading. c0.1 mol % catalyst loading for 2 h. dTrial run with Hg.

nitroacetophenone was selected as the substrate due to its fast rate of reduction, and therefore the effects of the precatalyst are more distinguishable. Precatalysts bearing electron-rich substituents on the pyridinesulfonamide (complexes 5, 7, 8, and 10) exhibited the highest conversion to alcohol in 1 h (entries 1−4), while precatalysts 6, 9, and 11, which possess electronpoor substituents on the ligand, afforded only moderate conversion after 1 h (entries 5−7). Thus, electron-rich E


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Organometallics Table 5. Substrate Scopea

precatalyst’s tolerance of acidic functionalities and ability to reduce biomass-relevant substrates selectively.

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CONCLUSION Pyridinesulfonamide ligands containing an ethylene linker with different functional groups were synthesized. These ligands were used to create a library of air- and moisture-stable, halfsandwich Cp*IrIII chloride complexes. The ligands and Cp*IrIII complexes were characterized by NMR, elemental analysis, and X-ray crystallography. The Cp*Ir(pyridinesulfonamide)Cl complexes serve as precatalysts for the transfer hydrogenation of electron-rich and -poor acetophenone derivatives at 1 mol % catalyst loading, with 2-propanol as the hydrogen source in air without predried solvents and reagents. These precatalysts exhibit a wide functional group tolerance. Electron-poor substrates were hydrogenated at a faster rate than electronpoor ketones, whereas, electron-rich precatalysts demonstrated higher conversion rates and favored transfer hydrogenation. A positional study demonstrated that ortho- and meta-methoxyacetophenone isomers were converted to their respective alcohols faster than the para-isomer. KOH and AgOTf were found to have deleterious effects on the reduction of acetophenone and were not needed to see high catalytic conversions. Mercury poisoning experiments support homogeneous catalysts as the active species. Work is currently under way to elucidate the mechanism to determine the active Ir species and to evaluate the role of the linker length upon catalysis. The substrate scope includes diaryl, dialkyl, linear, and cycloaliphatic ketones, diones, β-ketoesters, α,β-unsaturated ketones, and ketones containing alkenes. Lastly, levulinic acid was reduced and underwent lactonization under normal catalytic conditions.

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EXPERIMENTAL SECTION

Materials. Solvents and materials involved in the synthesis of the ligands and all substrates were purchased from Aldrich or Alfa Aesar and used as received. Chloroform-d and dichloromethane-d2 were purchased from Cambridge Isotope Laboratories and dried over molecular sieves. IrCl3·H2O was purchased from Pressure Chemical. The [Cp*IrCl2]2 dimer was prepared according to a literature procedure43 and stored at room temperature. Pyridinesulfonamide ligands were synthesized using a literature procedure.35,36 All iridium precatalysts and ligands were synthesized in air without predried or degassed solvents and reagents. General Methods. A Bruker Biospin Ascend 400 MHz nuclear magnetic resonance spectrometer and a Bruker Biospin Ultra Shield 400 MHz nuclear magnetic resonance spectrometer were used to collect 13C{1H}, 19F{1H}, and 1H NMR spectra. Chemical shifts are referenced to residual CHCl3 (δ 7.24 for 1H), CH(D)Cl2 (δ 5.32 for 1 H), 13CDCl3 (δ 77.0 for 13C), and 13CD2Cl2 (δ 54.0 for 13C). All NMR spectra were collected at 300 K. GCMS was carried out by the Agilent 6890 gas chromatograph/5873 quadrupole mass spectrometer system with a 7683B autoinjector. Elemental analyses were performed by Intertek (Whitehouse Station, NJ, USA). 4-Nitro-N-(2-(pyridin-2-yl)ethyl)benzenesulfonamide (1). An adapted literature procedure was used to prepare this compound.36 4-Nitrobenzenesulfonyl chloride (0.891 g, 4.02 mmol) was dissolved in 4 mL of THF. This solution was added to another solution containing 2-(2-pyridyl)ethylamine (0.502 g, 4.11 mmol), NaOH (0.199 g, 4.98 mmol), 4 mL of THF, and 4 mL of distilled water to produce a cloudy yellow solution with a bilayer. This reaction was stirred for 3 h at room temperature. The solvent was removed in vacuo, and the product was collected by vacuum filtration. The solid precipitate was a light yellow powder (0.752 g, 2.45 mmol, 61%). Compound 1 can be recrystallized from ethanol. X-ray quality crystals of 1 were obtained by slow evaporation of a saturated solution of 4-

a1

H NMR spectroscopy used to determine yield. Yields reported as an average of three trials. 1,4-Dimethoxybenzene used as standard. A 1.0 M solution of substrate in 2-propanol. bGCMS used to determine yield.

mechanism is still likely; however another mechanism could be operative for alkene reduction using these precatalysts. In addition to ketone substrates, the reduction of diones was also examined. Acetylacetone displayed slower rates of conversion when compared to other ketone substrates (Table 5). After 6 h, only 68% conversion to 4-hydroxypentan-2-one, and no diol product, was observed (entries 11 and 12). Ethylacetoacetate exhibited faster rates of reduction (entry 13). Selective reduction of the ketone to form ethyl 3hydroxybutanoate in 100% yield was observed. This supports the trend that substrates that bear electron-withdrawing groups are reduced faster. Reduction of the ester group has not been observed. Lastly, the biomass-derived substrate levulinic acid was reduced and then underwent intramolecular lactonization to form γ-butyrolactone in 69% yield after 12 h (entries 14 and 15). The reduction of levulinic acid demonstrates the F


Article

Organometallics

yield (1.50 g, 5.91 mmol). 1H NMR (400 MHz, CDCl3): δ 8.48 (br d, 1H, 3JH−H = 4.7 Hz, Py-H), 7.90 (br s, 1H, Py-H), 7.69 (dt, 1H, 3JH−H = 7.7 Hz, 4JH−H = 1.8 Hz, Py-H), 7.22 (overlapping signals, 2H, Py-H), 3.70 (t, 2H, 3JH−H = 5.8 Hz, CH2), 3.09 (t, 2H, 3JH−H = 6.0 Hz, CH2). 13 C{1H} NMR (100 MHz, CDCl3): δ 158.6, 148.8, 137.2, 123.7, 122.2, 119.9 (q, 1JC−F = 319 Hz), 43.2, 36.0. 19F{1H} NMR (376 MHz, CDCl3): δ 76.2. Pentamethylcyclopentadienyl(iridium(N-(2-(pyridin-2-yl)ethyl)methanesulfonamide)) Chloride (5). A round-bottom flask was charged with pentamethylcyclopentadienyl iridium dichloride dimer (0.126 g, 0.158 mmol), N-(2-(pyridin-2-yl)ethyl)methanesulfonamide (0.0633 g, 0.316 mmol), and dichloromethane (10 mL). Triethylamine (91.0 μL, 0.509 mmol) was added to the solution. The solution was then stirred for 2 h at room temperature. The solution was then washed with three 10 mL portions of deionized water. The organic phase was then washed with a brine solution. After, the methylene chloride layer was collected and dried over MgSO4 for 30 min. The resultant solution was concentrated in vacuo to yield a yellow oil, which was stirred vigorously in hexanes overnight. The product was isolated through vacuum filtration to form a yellow-orange powder in 94% yield (0.167 g, 0.297 mmol). X-ray quality crystals were grown from vapor diffusion of hexanes into a saturated solution of 5 in dichloromethane at 0 °C. 1H NMR (400 MHz, CDCl3): δ 8.90 (d, 1H, 3 JH−H = 4.7 Hz, Py-H), 7.68 (t, 2H, overlapping, 3JH−H = 7.7 Hz, PyH), 7.31 (d, 1H, 3JH−H = 8.9 Hz, Py-H), 3.57 (apparent dt, 3JH−H = 10.6 Hz, 2,3JH−H = 3.6 Hz, 1H, CH2), 3.01 (m, 1H, CH2), 2.93 (ddd, 1H, 3JH−H = 11.5 Hz, 3JH−H = 10.7 Hz, 2JH−H = 1.5 Hz, CH2), 2.85 (s, 3H, CH3), 2.73 (ddd, 1H, 3JH−H = 13.0 Hz, 3JH−H = 12.1 Hz, 2JH−H = 3.5 Hz, CH2), 1.49 (s, 15H, Cp*). 13C{1H} NMR (100 MHz, CDCl3): δ 162.5, 155.7, 138.6, 132.0, 124.1, 86.9, 43.7, 41.2, 40.9, 9.19. Anal. Calcd for C18H26IrN2O2SCl: C, 38.46; H, 4.66; N, 4.98. Found: C, 38.33; H, 4.85; N, 4.99. Pentamethylcyclopentadienyl(iridium(1,1,1-trifluoro-(N-(2-(pyridin-2-yl)ethyl)methanesulfonamide)) Chloride (6). Complex 6 was synthesized via the same procedure as 5 using pentamethylcyclopentadienyl iridium dichloride dimer (0.104 g, 0.131 mmol), 1,1,1trifluoro-N-(2-(pyridine-2-yl)ethyl)methanesulfonamide (0.0664 g, 0.261 mmol), and triethylamine (110 μL, 0.783 mmol). The product was afforded as a yellow powder in 83% (0.134 g, 0.217 mmol). 1H NMR (400 MHz, CD2Cl2): δ 8.88 (dd, 1H, 3JH−H = 5.8 Hz, 4JH−H = 1.1 Hz, Py-H), 7.75 (dt, 1H, 3JH−H = 7.6 Hz, 4JH−H = 1.6 Hz, Py-H), 7.36 (d, 1H, 3JH−H = 7.8 Hz, Py-H), 7.32 (dt, 1H, 3JH−H = 7.0 Hz, 4 JH−H = 0.9 Hz,), 3.54 (br s, 1H, CH2), 3.04 (m, 2H, CH2), 2.71 (ddd, 1H, 3JH−H = 13.9 Hz, 3JH−H = 13.0 Hz, 2JH−H = 3.9 Hz, CH2), 1.48 (s, 15H, Cp*). 13C{1H} NMR (100 MHz, CD2Cl2): δ 162.1, 155.8, 139.6, 125.0, 124.7, 121.2 (q, 1JC−F = 314 Hz), 87.5, 44.3, 41.5, 9.51. 19F{1H} NMR (376 MHz, CD 2 Cl 2 ): δ −72.6. Anal. Calcd for C18H23F3IrN2O2SCl·0.9CH2Cl2: C, 32.78 H, 3.61; N, 4.04. Found: C, 32.54; H, 3.48; N, 3.96. 1H NMR spectra obtained in CDCl3 for three different samples of 6 submitted for elemental analysis verified the presence of 0.9 equiv of CH2Cl2 per Ir complex (Supporting Information). The samples submitted for elemental analysis were dried in vacuo overnight in attempts to remove the CH2Cl2 from the sample. Pentamethylcyclopentadienyl(iridium(N-(2-(pyridin-2-yl)ethyl)benzenesulfonamide)) Chloride (7). Complex 7 was synthesized via the same procedure as 5 using pentamethylcyclopentadienyl iridium dichloride dimer (0.122 g, 0.153 mmol), N-(2-(pyridin-2-yl)ethyl)benzenesulfonamide (0.0803 g, 0.306 mmol), and triethylamine (92.0 μL, 0.660 mmol). A bright yellow solid was produced (0.172 g, 90%). 1 H NMR (400 MHz, CDCl3): δ 8.94 (d, 1H, 3JH−H = 4.8 Hz, Py-H), 7.94 (m, 2H, Py-H), 7.62 (dt, 1H, 3JH−H = 7.6 Hz, 4JH−H = 1.6 Hz, PyH), 7.22 (m, 5H SO2Ph), 3.53 (apparent dt, 1H, 3JH−H = 10.2 Hz, 2,3 JH−H = 3.9 Hz, CH2), 2.94 (ddd, 3JH−H = 14.0 Hz, 3JH−H = 3.8 Hz, 2 JH−H = 1.7 Hz, 1H, CH2), 2.74 (apparent dt, 1H, 3JH−H = 13.9 Hz, 2,3 JH−H = 3.8 Hz, CH2), 2.63 (ddd, 1H, 3JH−H = 11.3 Hz, 3JH−H = 10.0 Hz, 2JH−H = 1.4 Hz, CH2), 1.58 (s, 15H, Cp*). 13C{1H} NMR (100 MHz, CDCl3): δ 162.2, 155.6, 143.2, 138.7, 129.9, 128.6, 127.9, 124.1, 124.1, 86.8, 43.4, 41.2, 9.6. Anal. Calcd for C23H28IrN2O2SCl: C, 44.26; H, 4.52; N, 4.49. Found: C, 44.18; H, 4.62; N, 4.58.

nitro-N-(2-(pyridin-2-yl)ethylbenzenesulfonamide in methanol. 1H NMR (400 MHz, CDCl3): δ 8.43 (br d, 1H, 3JH−H = 4.9 Hz, PyH), 8.29 (d, 1H, 3JH−H = 8.9 Hz, SO2PhONO2), 8.01 (d, 2H, 3JH−H = 8.9 Hz, SO2PhONO2), 7.57 (dt, 1H, 3JH−H = 7.7 Hz, 4JH−H = 1.8 Hz, Py-H), 7.14 (dd, 1H, 3JH−H = 5.3 Hz, 3JH−H = 7.0 Hz, Py-H), 7.05 (d, 1H, 3JH−H = 7.8 Hz, Py-H), 6.67 (br t, 1H, NH), 3.40 (q, 2H, 3JH−H = 5.9 Hz, CH2−NH), 2.94 (t, 2H, 3JH−H = 5.9 Hz, CH2). 13C{1H} NMR (100 MHz, CDCl3): δ 158.8, 149.9, 148.9, 146.3, 137.0, 128.2, 124.3, 123.6, 122.0, 42.3, 35.5. Anal. Calcd for C13H13N3O4S: C, 50.81; H, 4.26; N, 13.67. Found: C, 50.56; H, 4.18; N, 13.65. 4-Methoxy-N-(2-(pyridin-2-yl)ethyl)benzenesulfonamide (2). An adapted literature procedure was used to prepare this compound.36 4Methoxybenzenesulfonyl chloride (0.830 g, 4.01 mmol) was dissolved in 4 mL of THF. This solution was added to another solution containing 2-(2-pyridyl)ethylamine (0.500 g, 4.09 mmol), NaOH (0.170 g, 4.25 mmol), 4 mL of THF, and 4 mL of distilled water to produce a cloudy yellow solution with a bilayer. This reaction was stirred for 3 h at room temperature. The solvent was removed in vacuo, and the product was collected by vacuum filtration. The solid precipitate was a light yellow powder (0.789 g, 2.70 mmol, 67%). Compound 2 can be recrystallized from ethanol. X-ray quality crystals of 2 were obtained by slow vapor diffusion of hexanes into a saturated solution of 4-methoxy-N-(2-(pyridin-2-yl)ethylbenzenesulfonamide in CH2Cl2. 1H NMR (400 MHz, CDCl3): δ 8.45 (br d, 1H, 3JH−H = 4.1 Hz, Py-H), 7.77 (d, 1H, 3JH−H = 9.0 Hz, SO2PhOMe), 7.58 (dt, 1H, 3 JH−H = 7.7 Hz, 4JH−H = 1.8 Hz, Py-H), 7.17 (dd, 1H, 3JH−H = 5.0 Hz, 3 JH−H = 6.6 Hz, Py-H), 7.09 (d, 1H, 3JH−H = 7.8 Hz, Py-H), 6.92 (d, 2H, 3JH−H = 9.0 Hz, SO2PhOMe), 5.96 (br t, 1H, 3JH−H = 5.8 Hz, NH), 3.83 (s, 3H, OMe), 3.34 (q, 2H, 3JH−H = 6.1 Hz, CH2NH), 2.94 (t, 2H, 3JH−H = 6.2 Hz, CH2). 13C{1H}NMR (100 MHz, CDCl3): δ 162.7, 158.9, 149.0, 136.8, 131.8, 129.2, 123.6, 121.8, 114.2, 55.6, 42.2, 36.1. Anal. Calcd for C14H16N2O3S: C, 57.52; H, 5.52; N, 9.58. Found: C, 57.05; H, 5.31; N, 9.50. 4-Cyano-N-(2-(pyridin-2-yl)ethyl)benzenesulfonamide (3). An adapted literature procedure was used to prepare this compound.36 4-Cyanobenzenesulfonyl chloride (0.412 g, 2.05 mmol) was dissolved in 4 mL of THF. This solution was added to another solution containing 2-(2-pyridyl)ethylamine (243 μL, 2.05 mmol), NaOH (0.0821 g, 2.05 mmol), 4 mL of THF, and 4 mL of distilled water to produce a cloudy yellow solution with a bilayer. This reaction was stirred for 3 h at room temperature. The solvent was removed in vacuo, and the product was collected by vacuum filtration. The solid precipitate was isolated as a light yellow powder (0.399 g, 1.39 mmol, 68%). Compound 3 can be recrystallized from ethanol. 1H NMR (400 MHz, CDCl3): δ 8.43 (br d, 1H, 3JH−H = 4.7 Hz, Py-H), 7.94 (d, 1H, 3 JH−H = 8.2 Hz, SO2PhCN), 7.75 (d, 2H, 3JH−H = 8.3 Hz, SO2PhCN), 7.57 (dt, 1H, 3JH−H = 7.7 Hz, 4JH−H = 1.8 Hz, Py-H), 7.13 (dd, 1H, 3 JH−H = 5.0 Hz, 3JH−H = 7.0 Hz, Py-H), 7.05 (d, 1H, 3JH−H = 7.8 Hz, Py-H), 6.59 (br t, 1H, NH), 3.38 (q, 2H, 3JH−H = 5.8 Hz, CH2NH), 2.93 (t, 2H, 3JH−H = 6.0 Hz, CH2). 13C{1H} NMR (100 MHz, CDCl3): δ 158.8, 148.9, 144.7, 137.0, 132.8, 127.6, 123.6, 122.0, 117.4, 116.1, 42.2, 35.6. Anal. Calcd for C14H13N3O2S: C, 58.52; H, 4.56; N, 14.62. Found: C, 58.01; H, 4.35; N, 14.48. 1,1,1-Trifluoro-N-(2-(pyridin-2-yl)ethyl)methane Sulfonamide (4). This compound has been synthesized via an alternate route, and elemental analysis was previously described.37 An adapted literature procedure was used to prepare this compound for this project.35 A round-bottom flask was charged with 2-(2-pyridyl)ethylamine (735 μL, 6.13 mmol), triethylamine (1.06 mL, 7.64 mmol), and 15 mL of dichloromethane. The solution was cooled to 0 °C. A solution of trifluoromethylsulfonyl chloride (813 μL, 7.63 mmol) in dichloromethane (10 mL) was added dropwise over 5 min. The solution was then stirred for 1 h at 0 °C and warmed to room temperature for 3 h. The solution was washed with two 15 mL portions of a saturated sodium bicarbonate solution and washed twice with a saturated sodium chloride solution (15 mL). The organic phase was reduced in vacuo. To purify, the product was passed through a silica gel plug on a fritted funnel and eluted using 10% methanol/90% ethyl acetate. The solvent was removed in vacuo to yield the product as a tan solid in 96% G


Article

Organometallics 3

JH−H = 12.8 Hz, 2,3JH−H = 3.8 Hz, CH2), 2.57 (ddd, 1H, 3JH−H = 11.6 Hz, 3JH−H = 3.7 Hz, 2JH−H = 1.6 Hz), 1.56 (s, 15H, Cp*). 13C{1H} NMR (100 MHz, CDCl3): δ 161.7, 155.5, 147.87, 133.7, 131.2, 129.1, 124.2, 124.1, 118.6, 113.3, 87.0, 43.4, 41.0, 9.43. Anal. Calcd C24H27IrN3O2SCl: C, 44.40; H, 4.19; N, 6.47. Found: C, 44.24; H, 4.20; N, 6.54. Catalytic Transfer Hydrogenation. A 0.005 mmol (1 equiv) amount of the precatalyst was massed into an empty vial. If a solid substrate was used, 0.500 mmol (100 equiv) of substrate was massed and added to the vial containing the precatalyst. A 500 μL aliquot of a 0.1 M solution of 1,4-dimethoxybenzene in 2-propanol was added to the vial by syringe. If the substrate was a liquid, a 500 μL aliquot of a solution containing 1.0 M substrate and 0.10 M 1,4-dimethoxybenzene in 2-propanol was injected into a vial containing only precatalyst. If necessary, an appropriate amount of additive (Hg, KOH, or AgOTf) was introduced to the reaction mixture. The vials were then heated to 85 °C in an OptiMag-ST aluminum heating plate containing wells fit for the vials for a designated amount of time. After the reaction, the vials were cooled to room temperature. Conversions were determined using 1H NMR spectroscopy by integration of resolved characteristic resonances for ketone starting material and alcohol product. Conversions not determined by 1H NMR were established using GCMS by comparing the peak area to concentration using a standard calibration curve. The final reported values with error are an average of three trials. Isolation of Alcohol Product. This procedure was performed after the transfer hydrogenation catalysis in order to remove the alcohol product from the reaction mixture. The procedure was adapted from a literature procedure.15 The reaction mixture was diluted with a 3:1 mixture of hexanes and ethyl acetate. The resulting solution was then filtered through a fritted funnel containing silica gel. The silica gel was rinsed with 10 mL of the mixture of hexanes and ethyl acetate. The eluent was then collected, and the solvent was removed in vacuo to afford an orange oil. X-ray Crystallography. Single crystals were selected for analysis on a Bruker-AXS SMART Apex II X-ray diffractometer using Mo Kα radiation with a graphite monochromator.44 All samples were mounted using a MiTeGen MicroMount and NVH oil. Data were collected at 100 °C. Unit cells were determined by taking 12 data frames, 0.5° ϕ, in three sections of the Ewald sphere. Full hemispheres were collected on each crystal and integrated using SAINT Plus.45 Data were corrected for absorption correction using SADABS. Structures were solved by the use of direct methods.46 Least squares refinement on F2 was used for all reflections.47 Straightforward structure solution, refinement, and the calculations of measurements were accomplished with the SHELXTL package.48 Non-hydrogen atoms were refined anisotropically. Hydrogen atoms were placed in idealized, theoretical positions. Compounds 1 and 2 and complexes 5 and 10 were solved in centrosymmetric space groups. Complex 9 was solved in a noncentrosymmetric space group, P212121, and refined as an inversion twin using the TWIN and BASF commands. The Flack parameter indicated the crystal was a single enantiomer.

Pentamethylcyclopentadienyl(iridium(4-methyl-N-(2-(pyridin-2yl)ethyl)benzenesulfonamide)) Chloride (8). This was synthesized via the same procedure as 5 using pentamethylcyclopentadienyl iridium dichloride dimer (0.121 g, 0.152 mmol), 4-methyl-N-(2-(pyridin-2yl)ethyl)benzenesulfonamide (0.0839 g, 0.304 mmol), and triethyalmine (90.0 μL, 0.654 mmol). The product was isolated as a bright yellow solid (0.175 g, 90%). 1H NMR (400 MHz, CDCl3): δ 8.93 (dd, 1H, 3JH−H = 6.3 Hz, 4JH−H = 1.7 Hz, Py-H), 7.81 (d, 2H, 3JH−H = 8.2 Hz, CH Ph), 7.61 (dt, 1H, 3JH−H = 7.6 Hz, 4JH−H = 1.6 Hz, Py-H), 7.19 (m, 2H, Py-H), 7.03 (d, 2H, 3JH−H = 8.0 Hz, CH Ph), 3.51 (apparent dt, 1H, 3JH−H = 10.2 Hz, 2,3JH−H = 3.5 Hz, CH2), 2.93 (ddd, 1H, 3JH−H = 14.1 Hz, 3JH−H = 3.3 Hz, 2JH−H = 1.4 Hz, CH2), 2.73 (apparent dt, 1H, 3JH−H = 13.8 Hz, 2,3JH−H = 3.8 Hz, CH2), 2.63 (ddd, 1H, 3JH−H = 11.2 Hz, 3JH−H = 10.3 Hz, 2JH−H = 1.4 Hz, CH2), 2.24 (s, 3H, CH3), 1.58 (s, 15H, Cp*). 13C{1H} NMR (100 MHz, CDCl3): δ 162.3, 155.7, 140.4, 140.0, 138.5, 129.8, 128.7, 127.2, 124.1, 86.9, 43.5, 41.3, 21.4, 9.6. Anal. Calcd for C24H30IrN2O2SCl: C, 45.17; H, 4.74; N, 4.39. Found: C, 44.83; H, 4.52; N, 4.49. Pentamethylcyclopentadienyl(iridium(4-nitro-N-(2-(pyridin-2-yl)ethyl)benzenesulfonamide)) Chloride (9). Complex 9 was synthesized via the same procedure as 5 using pentamethylcyclopentadienyl iridium dichloride dimer (0.122 g, 0.153 mmol), 4-nitro-N-(2(pyridin-2-yl)ethyl)benzenesulfonamide (0.0940g, 0.309 mmol), and triethylamine (92.0 μL, 0.660 mmol) The product was afforded as a bright orange solid (0.203 g, 99%). X-ray quality crystals were grown from vapor diffusion of hexanes into a saturated solution of 9 in 1,2dichloroethane at 0 °C. 1H NMR (400 MHz, CDCl3): δ 8.88 (d, 1H, 3 JH−H = 5.7 Hz, Py-H), 8.10 (roofed doublet, 2H, 3JH−H = 9.0 Hz, CH Ph), 8.04 (roofed doublet, 2H, 3JH−H = 9.0 Hz, CH Ph), 7.65 (dt, 1H, 3 JH−H = 7.6 Hz, 4JH−H = 1.6 Hz, Py-H), 7.23 (m, 2H, Py-H), 3.61 (apparent dt, 1H, 3JH−H = 10.4 Hz, 2,3JH−H = 3.8 Hz, CH2), 2.99 (ddd, 1H, 3JH−H = 14.3 Hz, 3JH−H = 3.7 Hz, 2JH−H = 1.9 Hz, CH2), 2.76 (apparent dt, 1H, 3JH−H = 12.6 Hz, 2,3JH−H = 3.8 Hz, CH2), 2.61 (ddd, 1H, 3JH−H = 11.5 Hz, 3JH−H = 9.6 Hz, 2JH−H = 1.8 Hz, CH2), 1.57 (s, 15H, Cp*). 13C{1H} NMR (100 MHz, CDCl3): δ 161.8, 155.6, 149.6, 148.5, 138.9, 129.7, 124.3, 124.2, 123.2, 87.1, 43.6, 41.2, 9.62. Anal. Calcd for C23H27IrN3O4SCl: C, 41.28; H, 4.07; N, 6.28. Found: C, 41.71; H, 4.05; N, 6.54. Pentamethylcyclopentadienyl(iridium(4-methoxy-N-(2-(pyridin2-yl)ethyl)benzenesulfonamide)) Chloride (10). Complex 10 was synthesized via the same procedure as 5 using pentamethylcyclopentadienyl iridium dichloride dimer (0.108 g, 0.156 mmol), 4methoxy-N-(2-(pyridin-2-yl)ethyl)benzenesulfonamide (0.0792 g, 0.271 mmol), and triethylamine (80.0 μL, 0.574 mmol). The product was yielded as a bright yellow solid (0.170 g, 96%). X-ray quality crystals were grown from vapor diffusion of hexanes into a saturated solution of 9 in 1,2-dichloroethane at 0 °C. 1H NMR (400 MHz, CDCl3): δ 8.93 (dd, 1H, 3JH−H = 6.5 Hz, 4JH−H = 1.5 Hz, Py-H), 7.88 (d, 2H, 3JH−H = 6.9 Hz, CH Ph), 7.62 (dt, 1H, 3JH−H = 7.6 Hz, 4JH−H = 1.5 Hz, Py-H), 7.20 (m, 2H, Py-H), 6.73 (d, 2H, 3JH−H = 8.9 Hz, CH Ph), 3.71 (s, 3H, OCH3), 3.50 (apparent dt, 1H, 3JH−H = 10.3 Hz, 2,3 JH−H = 3.6 Hz, CH2), 2.93 (ddd, 1H, 3JH−H = 14.1 Hz, 3JH−H = 3.4 Hz, 2JH−H = 1.6 Hz, CH2), 2.73 (apparent dt, 1H, 3JH−H = 14.6 Hz, 2,3 JH−H = 3.6 Hz, CH2), 2.62 (ddd, 1H, 3JH−H = 11.3 Hz, 3JH−H = 9.5 Hz, 2JH−H = 1.3 Hz, CH2), 1.58 (s, 15H, Cp*). 13C{1H} NMR (100 MHz, CDCl3): δ 162.3, 160.8, 155.7, 138.6, 135.4, 132.1, 130.5, 124.1, 113.1, 86.8, 55.4, 43.4, 41.3, 9.6. Anal. Calcd for C24H30IrN2O3SCl: C, 44.06; H, 4.62; N, 4.28. Found: C, 43.69; H, 4.57; N, 4.22. Pentamethylcyclopentadienyl(iridium(4-cyano-N-(2-(pyridin-2yl)ethyl)benzenesulfonamide)) Chloride (11). Complex 11 was synthesized via the same procedure as 5 using pentamethylcyclopentadienyl iridium dichloride dimer (0.126 g, 0.158 mmol), 4-cyanoN-(2-(pyridin-2-yl)ethyl)benzenesulfonamide (0.0909 g, 0.316 mmol), and triethylamine (90.0 μL, 0.643 mmol). The product was afforded as a bright yellow solid (0.175 g, 85%). 1H NMR (400 MHz, CDCl3): δ 8.85 (d, 1H, 3JH−H = 5.8 Hz, Py-H), 8.00 (d, 2H, 3JH−H = 8.4 Hz, CH Ph), 7.68 (dt, 1H, 3JH−H = 7.6 Hz, 4JH−H = 1.5 Hz, Py-H), 7.53 (d, 2H, 3 JH−H = 8.4 Hz, CH Ph), 7.25 (m, 2H, Py-H), 3.54 (apparent dt, 1H, 3 JH−H = 10.5 Hz, 2,3JH−H = 3.8 Hz, CH2), 3.00 (ddd, 1H, 3JH−H = 14.4 Hz, 3JH−H = 3.7 Hz, 2JH−H = 1.9 Hz, CH2), 2.75 (apparent dt, 1H,

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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.5b00864. CCDC 1418441−1418445 contain the supplementary crystallographic data for 1, 2, 5, 9, and 10. This material is available free of charge via http://www.ccdc.cam.ac. uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax (+44) 1223-336-033; or e-mail [email protected]. uk. Original representative NMR spectra of the precatalysts and ligands (PDF) X-ray crystallographic data and CIF files of 1, 2, 5, 9, and 10 (CIF) H


Article

Organometallics

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AUTHOR INFORMATION

Corresponding Author

*E-mail (A. R. O’Connor): [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Donors of the American Chemical Society Petroleum Research Fund (ACS PRF UNI#3 53605 to A.R.O’C). X-ray crystallography (#0922931) and NMR data (#1125993) were collected on instruments purchased through MRI grants from the National Science Foundation. We also acknowledge The College of New Jersey for start-up funding. We acknowledge the work of M. Kunitomo, M. Higgins, and K. Webb, who contributed the initial preparation of ligands 1 and 2.

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