Synthesis and Resolution of Chiral Ruthenium ... - ACS Publications

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Synthesis and Resolution of Chiral Ruthenium Complexes Containing the 1‑Me-3-PhCp Ligand Yue Hu,† Anthony P. Shaw,‡ Hairong Guan,§ Jack R. Norton,*,∥ Wesley Sattler,⊥ and Yi Rong∥ †

Eastman Chemical Company, Kingsport, Tennessee 37662, United States Pyrotechnics Technology and Prototyping Division, U.S. Army RDECOM-ARDEC, Picatinny Arsenal, New Jersey 07806, United States § Department of Chemistry, University of Cincinnati, Cincinnati, Ohio 45221, United States ∥ Department of Chemistry, Columbia University, New York, New York 10027, United States ⊥ Dow Electronic Materials, The Dow Chemical Company, Marlborough, Massachusetts 01752, United States ‡

S Supporting Information *

ABSTRACT: A new ruthenium chloride complex featuring chirality derived from the face-specific coordination of the 1-Me-3-PhCp ligand has been successfully synthesized and resolved. The resolution has been achieved via the diastereomers of the (S)-α-methylbenzenemethanethiolate complex (1-Me-3-PhCp)Ru(dppm){(S)-C(S)(H)(Ph)(Me)}. The X-ray structures of (SCp,S)-(1-Me-3-PhCp)Ru(dppm){C(S)(H)(Ph)(Me)} and (RCp,S)-(1-Me-3-PhCp)Ru(dppm){C(S)(H)(Ph)(Me)} have been determined. Racemization has been observed at elevated temperatures, but a room-temperature conversion pathway provides access to the corresponding enantiopure acetonitrile, chloride, and hydride complexes.

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earliest reported complexes of this8 kind were racemic 1,2disubstituted ferrocene derivatives,9 while the first enantiopure example was the ferrocene derivative 1, resolved via the menthydrazone diastereomers.10 The first non-ferrocene example to be resolved was the half-sandwich Mn complex 2.11 Although extensive efforts have been directed toward the synthesis and resolution of these kinds of chiral complexes, most have involved exceptionally stable structures such as metallocenes,12 (arene)Cr complexes,13 and CpMn tricarbonyl derivatives.10,14

INTRODUCTION

Chiral transition-metal complexes are widely used for asymmetric catalysis.1 In addition to traditional chiral ligands (chiral phosphines,1h chiral amines,1f etc.), the η5-cyclopentadienyl ligand (Cp) can also be used to introduce chirality.2 Cp-based chirality can have different origins. Chiral centers may be attached to the cyclopentadienyl ring.3 An asymmetrically substituted Cp ligand, although achiral, can induce “face-specific” chirality4 upon coordination to a metal.5 Chirality in Cp-containing complexes may also result from an asymmetric arrangement of ligands around the metal center.6 Many synthetically useful organometallic complexes contain Cp ligands, and the strong coordination (up to 118 kcal/mol)7 of Cp to transition metals diminishes the chance of racemization of complexes with an asymmetrically substituted Cp.2g Different structural modifications are readily available for the Cp ligand.2g Coordination of an asymmetrically substituted Cp ligand to a metal center forms a pair of enantiomers (Scheme 1). The

Chiral complexes of late transition metals formed through face-specific coordination of Cp ligands are limited in the literature. Takahashi has reported a series of such complexes containing a trisubstituted Cp ligand and Ru,6d−f,15 Co,16 Fe,17a and Rh17b centers and has explored the reactivity of the Ru complexes 3 in various asymmetric transformations.6d−f,15 Transition-metal hydride complexes exhibiting Cp-derived face-specific chirality are even rarer. To our knowledge, there is only one example in the literature: the Ir hydride complex 4

Scheme 1. Chiral Transition-Metal Complexes through FaceSpecific Coordination of Disubstituted Cp Ligands

Received: October 9, 2015

© XXXX American Chemical Society

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DOI: 10.1021/acs.organomet.5b00852 Organometallics XXXX, XXX, XXX−XXX

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generation of enantiopure complexes has been achieved by face-selective π complexation (with the help of a chiral auxiliary ligand)23 and through an enzyme-mediated asymmetric reaction.24 In order to separate the enantiomers of 8, we initially prepared the diastereomers 9[BF4] with an enantiopure nitrile ligand (eq 1). Fractional crystallization of 9[BF4] from

reported by Mobley and Bergman in 1998.18 A related Ru hydride complex (5) containing an arene ligand has been reported by Faller and Fontaine in 2007.19 In both cases, the cyclopentadienyl or arene ring is tethered to a coordinated phosphine, inhibiting racemization. CH2Cl2/Et2O (1/2) gave yellow needles which contained a 5/3 ratio of the diastereomers. Fractional crystallization from CH2Cl2/xylenes (1/3) also gave yellow needles, this time containing a 2/1 diastereomer ratio. However, in both cases subsequent crystallizations did not dramatically improve the separation. Additionally, the nitrile ligand is strongly coordinated to the Ru center, making it difficult to remove. We therefore decided to pursue another pathway. Synthesis and Separation of Thiolate Complex Diastereomers. We have previously reported the synthesis of [CpRu(dppe)(rac-α-methylbenzylamine)]+ and [CpRu(dppe)(rac-α-methyl-benzenemethanethiol)]+ complexes as the BPh4− salts.25 The chloride complex 8 did not react with (R)-α-methylbenzylamine but did react with (S)-α-methylbenzenemethanethiol to give a 1/1 mixture of the diastereomers 10[BPh4] (eq 2). With the large tetraphenylborate

This article describes the synthesis and resolution of halfsandwich ruthenium complexes featuring chirality derived from the face-specific coordination of the 1-Me-3-PhCp ligand. Resolution has been achieved via the diastereomeric complexes with the (S)-α-methyl-benzenemethanethiolate ligand, providing access to the enantiopure acetonitrile, chloride, and hydride complexes.

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RESULTS AND DISCUSSION Synthesis of the Racemic Ru Chloride Complex. The synthesis of the racemic Ru chloride complex 8 is shown in Scheme 2. A reported method was used to prepare Li[1-Me-3Scheme 2. Synthesis of the Racemic Ru Chloride Complex 8

anion, these diastereomers cocrystallized from MeOH/CH2Cl2 with essentially no separation. An analogous synthesis of the tetrafluoroborate salts 10[BF4] gave a glassy mass unsuitable for fractional crystallization. Unlike the NH2 group of an amine ligand, which is often difficult to deprotonate,26 the SH groups of thiol ligands are comparatively acidic.27 The counterion associated with 10+ can be removed by deprotonating the thiol ligand, generating the neutral diastereomers 11 (eq 3).28 These diastereomers proved soluble in many polar and nonpolar organic solvents, and slow vapor diffusion of pentane into a saturated Et2O solution of 11 gave excellent separation of the diastereomers (Scheme 3). The orange needles that came out of solution contained 92% of (SCp,S)-11, while the deep orange mother liquor contained 92% of (RCp,S)-11.29 These configurations, shown below, have been confirmed by X-ray crystallography. The separated diastereomers (SCp,S)-11 and (RCp,S)-11 were characterized by 1H and 31P{1H} NMR, circular dichroism

PhCp] (6).20 Refluxing a mixture of 6 and Ru(PPh3)3Cl2 in EtOH generated the bis(triphenylphosphine) complex 7. Replacing the two PPh3 ligands with dppm gave the air-stable Ru complex 8. Synthesis and Attempted Separation of Nitrile Complex Diastereomers. The resolution of enantiomeric complexes that differ through coordination of opposite Cp faces has generally relied on the generation of diastereomers via classical derivatization procedures. A chiral auxiliary must be installed onto either the Cp ligand or the metal.12e,21 The resulting diastereomers can then be separated via fractional crystallization10,11,17,22 or chromatography.16,18 The direct B


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Scheme 3. Separation of 11 by Fractional Crystallization

Figure 2. Structure of (SCp,S)-11 as determined by single-crystal X-ray diffraction. Hydrogen atoms other than the thiolate CH have been omitted for clarity. Selected bond distances (Å) and angles (deg): Ru(1)−P(1) 2.2777(6), Ru(1)−P(2) 2.2598(6), Ru(1)−S(1) 2.4179(6); P(1)−Ru(1)−P(2) 70.09(2), P(1)−Ru(1)−S(1) 83.91(2), P(2)−Ru(1)−S(1) 86.02(2).

(CD) spectroscopy (Supporting Information), and X-ray crystallography. The 31P NMR spectra of both the 1/1 mixture and the separated diastereomers are shown in Figure 1. Both (SCp,S)-11 and (RCp,S)-11 display an AB pattern in their 31P NMR spectra, in accordance with their two inequivalent phosphine atoms.

Figure 3. Structure of (RCp,S)-11 as determined by single-crystal X-ray diffraction. Hydrogen atoms other than the thiolate CH have been omitted for clarity. Selected bond distances (Å) and angles (deg): Ru(1)−P(1) 2.2645(13), Ru(1)−P(2) 2.2589(12), Ru(1)−S(1) 2.3956(11); P(1)−Ru(1)−P(2) 70.91(4), P(1)−Ru(1)−S(1) 82.48 (4), P(2)−Ru(1)−S(1) 86.30(4).

The thiolate diastereomers 11 are unstable in halogenated solvents. For example, at room temperature in CD2Cl2, 11 slowly forms the corresponding chloride complex 8, with approximately 4% conversion observed after 2 days on the basis of the 31P{1H} NMR. The reaction is faster at 40 °C but ultimately gives low yields of the chloride complex (5−10%) along with unidentified decomposition products. Even with more reactive chlorine sources the clean formation of 8 from 11 remained elusive. In CDCl3 at room temperature, 50% conversion was observed after 2 days along with unidentified products. The reaction of 11 with CCl4 was complete within minutes at room temperature, forming a mixture that contained many unidentified products. Attempts to remove the thiolate ligand in other ways were also unsuccessful. When (SCp,S)-11 was dissolved in MeCN, the thiolate ligand was not displaced, even at 70 °C; instead, substantial racemization occurred. The origins of the racemization were not investigated, but dissociation of the

Figure 1. 31P{1H} NMR (121.5 MHz, CD3CN) spectra of the diastereomers 11: (a) the original mixture of diastereomers; (b) (SCp,S)-11; (c) (RCp,S)-11.

The X-ray structures of (SCp,S)-11 and (RCp,S)-11 are shown in Figures 2 and 3, respectively. The S configuration of the chiral center in the thiolate ligand is observed crystallographically in both cases. The configurations of the CpRu system were determined to be SCp in Figure 2 and RCp in Figure 3. In both structures, the phenyl substituent of the 1-Me-3PhCp ligand does not lie in the same plane as the Cp ring. The angle between the two planes is 12.12° in (SCp,S)-11 (Figure 2) and 27.37° in (RCp,S)-11 (Figure 3). Other structural parameters are given in the Supporting Information. C


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therefore, only the thiol complex could be recovered from the mixture.

asymmetrically substituted Cp ring is conceivable under these conditions. Treatment of 11 with NaBH4 in THF at 60 °C did not give any of the corresponding hydride complex. Formation of the Ru(NCMe) Enantiomers. Protonation of 11 with 1 equiv of HCl or HBF4·OMe2 in Et2O regenerates the corresponding thiol complex 10[Cl] or 10[BF 4 ], precipitating from solution. Unlike 11, 10[BF4] reacts with MeCN readily at room temperature, forming the green MeCNcoordinated 12 with retention of the (1-Me-3-PhCp)Ru configuration (eq 4). The CD spectra of (SCp)-12 and (RCp)12 (Figure 4), which do not change over time at room temperature, confirm that the compounds are enantiomeric.

The addition of elemental mercury to the reaction mixture solved the problem nicely. The dissociated thiol ligand was effectively extracted from solution, giving a gray powdery precipitate, presumed to be Hg(SR)n (n = 1, 2, R = CH(Ph)(Me)), although its identity was not confirmed. The elemental Hg was probably oxidized by trace O2, allowing the resulting Hg(II) to capture the thiol due to the well-known Hg−S affinity, although direct oxidation of elemental Hg by organic thiols was also reported.31 This drove the equilibrium all the way to the (SCp)-8 side (eq 6). The enantiopure 8 was

obtained after filtering the reaction mixture through a thin layer of silica gel and removing the THF solvent. The CD spectra of (SCp)-8 and (RCp)-8, shown in Figure 5, confirm that they are

Figure 4. Circular dichroism spectra of enantiomers (SCp)-12 and (RCp)-12.

Acetone solutions of (SCp)-12[BF4] are stable for days when exposed to air. The MeCN ligand, being very strongly coordinated, was not readily replaced by other ligands such as chloride and hydride. For example, 12[Cl] was formed immediately when 1 drop of MeCN was added to a CD2Cl2 solution of the chloride complex 8. The reaction of 12[BF4] with excess NaBH4 in MeOH at room temperature was marked by an immediate color change from green to orange, although the expected Ru hydride complex was just a minor product (accompanied by unidentified products). No reaction occurred when a methanol solution of 12[BF4] and excess NEt3 was stirred under 50 psi of H2a method we had used previously to convert a ruthenium acetonitrile cation to the corresponding hydride complex.30 Formation of Ru Chloride and Hydride Enantiomers. In order to maintain the chiral (1-Me-3-PhCp)Ru configuration, a mild room-temperature pathway was developed to access the chloride complex 8. When (SCp,S)-10[BF4] was mixed with excess LiCl in THF, a ligand exchange equilibrium was established involving the thiol ligand and chloride. However, this equilibrium lies substantially to the left (eq 5);

Figure 5. Circular dichroism spectra of enantiomers (SCp)-8 and (RCp)-8.

enantiomeric. The enantiopurity of the chloride complexes was also confirmed by 31P{1H} NMR after conversion back to the diastereomers (SCp,S)-10[BPh4] and (RCp,S)-10[BPh4]. Treating (SCp)-8 with excess NaOMe in MeOH overnight at room temperature gave the desired hydride complex (SCp)-13 (eq 7). The enantiopurity of (SCp)-13 was confirmed by 31P NMR after it was converted stereospecifically back to (SCp,S)10[BPh4] (Scheme 4 and Figure 6). D


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Scheme 5 provides an overview of the synthetic pathways developed as a part of this work.

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CONCLUSION A racemic mixture of the Ru chloride enantiomers 8 was resolved with enantiopure thiolate ligand via the diastereomers 11. The chiral auxiliary was successfully removed at room temperature, providing access to enantiopure Ru complexes with MeCN, chloride, or hydride ligands. Investigation of the potential of these complexes in asymmetric catalysis is ongoing in our group.

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Figure 6. 31P{1H} NMR spectrum of the thiol complex diastereomer (SCp,S)-10[BPh4] prepared from the corresponding hydride complex (SCp)-13. THF. The mixture was stirred overnight at room temperature. The resulting orange solution was then collected after filtration through a thin layer of silica gel. The orange S product was collected after removing the THF solvent. Method 3. Several drops of CCl4 were added to a THF solution of 13. The pale yellow solution immediately turned orange. The orange racemic product was collected after evaporation of the solvent under vacuum. 1H NMR (300 MHz, CDCl3): δ 1.97 (m, Me, 3H), 4.25−4.37 (m, Ph2PCH2PPh2, 1H), 4.61 (br, Cp, 1H), 4.74 (br, Cp, 1H), 4.83− 4.95 (m, Ph2PCH2PPh2, 1H), 5.26 (br, Cp, 1H), 6.92−7.52 (m, Ar, 25H). 31P{1H} NMR (121.5 MHz, CDCl3): δ 13.13, 13.92 (AB pattern, 2JP−P = 85.8 Hz). Anal. Calcd for C37H33ClP2Ru: C, 65.73; H, 4.92; Cl, 5.24. Found: C, 65.96; H, 4.98; Cl, 5.22. [(1-Me-3-PhCp)Ru(dppm){(R)*C(CN)(H)(Ph)(OCOCH3)}][BF4] (9[BF4]). A mixture of the ruthenium chloride 8 (525 mg, 0.78 mmol), NH4BF4 (105 mg, 1.00 mmol), (R)-cyano(phenyl)methyl acetate (156 mg, 0.89 mmol), and 30 mL of MeOH was refluxed for 48 h. After the orange solution was cooled to room temperature, the solvent was removed under vacuum. The residue was dissolved in 20 mL of CH2Cl2, and a small amount of solid was filtered off. Then, hexanes was added to the filtered solution to cause precipitation of the product. The yellow product was filtered, washed with hexanes several times, and dried under vacuum (480 mg, 68% yield). Data for diastereomer 1 are as follows. 1H NMR (400 MHz, CD2Cl2): δ 1.59−1.60 (m, CpMe, 3H), 1.87 (s, COCH3, 3H), 4.21−4.26 (m, Ph2PCH2PPh2, 1H), 4.48 (br, Cp, 1H), 5.13−5.17 (m, Ph2PCH2PPh2, 1H), 5.48 (br, Cp, 1H), 5.49 (br, Cp, 1H), 5.55 (s, CHCNPh, 1H), 6.49−6.53 (m, Ar, 2H), 7.17−7.58 (m, Ar, 28H). 31P{1H} NMR (161.9 MHz, CD2Cl2): δ 11.36 (s). Data for diastereomer 2 are as follows. 1H NMR (400 MHz, CD2Cl2): δ 1.54−1.55 (m, CpMe, 3H), 1.87 (s, COCH3, 3H), 4.21− 4.26 (m, Ph2PCH2PPh2, 1H), 4.58 (br, Cp, 1H), 5.13−5.17 (m, Ph2PCH2PPh2, 1H), 5.45 (br, Cp, 1H), 5.48 (br, Cp, 1H), 5.54 (s, CHCNPh, 1H), 6.49−6.53 (m, Ar, 2H), 7.17−7.58 (m, Ar, 28H). 31 1 P{ H} NMR (161.9 MHz, CD2Cl2): δ 10.78, 11.88 (AB pattern, 2 JP−P = 81.0 Hz). Anal. Calcd for C47H42BF4NO2P2Ru: C, 62.54; H, 4.69; N, 1.55. Found: C, 62.29; H, 4.62; N, 1.59. [(1-Me-3-PhCp)Ru(dppm){(S)-C(SH)(H)(Ph)(Me)}][BPh 4 ] (10[BPh4]). A solution of racemic 8 (200 mg, 0.29 mmol), (S)-α-

EXPERIMENTAL SECTION

General Procedures. All air-sensitive compounds were prepared and handled under an N2/Ar atmosphere, using standard Schlenk and inert atmosphere box techniques. Hexanes were dried and deoxygenated by two successive columns (activated alumina, Q5 copper catalyst) under Ar. Pentane, Et2O, and THF were distilled from sodium/benzophenone under an N2 atmosphere. Deuterated solvents were dried over CaH2 and then vacuum-transferred to Schlenk tubes. HPLC grade MeCN was sparged with N2 and then stored over 4 Å molecular sieves. Circular dichroism spectra were acquired with an AVIV Model 202SF CD spectrometer. 1-Methyl-3-phenylcyclopentadienyllithium, 2 0 (S)-α-methyl-benzenemethanethiol, 3 2 and RuCl2(PPh3)333 were prepared by literature methods. rac-(1-Me-3-PhCp)Ru(PPh3)2Cl (7). EtOH (absolute, 30 mL) was added to a mixture of RuCl2(PPh3)3 (2.0 g, 2.10 mmol) and 1-methyl3-phenylcyclopentadienyllithium (340 mg, 2.10 mmol). The mixture was refluxed for 3 h, resulting in a red suspension. After the mixture was cooled to room temperature, the red solid was collected by filtration, washed three times with cold absolute EtOH, and dried under vacuum. The red solid was then dissolved in CH2Cl2 to form a saturated solution, and 50 mL of hexanes was added, giving a pale yellow precipitate, which was removed by filtration. Evaporation of the solvent from the remaining solution gave the product, an orange solid (1.11 g, 65% yield). 1H NMR (300 MHz, CD2Cl2): δ 1.18 (s, Me, 3H), 3.50 (br, Cp, 1H), 4.42 (br, Cp, 1H), 4.58 (br, Cp, 1H), 7.08−7.40 (m, Ar, 35H). 31P{1H} NMR (121.5 MHz, CD2Cl2): δ 37.29, 42.20 (AB pattern, 2Jp‑p = 40.76 Hz). Anal. Calcd for C48H41ClP2Ru: C, 70.62; H, 5.06; Cl, 4.34. Found: C, 70.61; H, 5.08; Cl, 4.27. (1-Me-3-PhCp)Ru(dppm)Cl (8). Method 1. Complex 7 (200 mg, 0.25 mmol) and dppm (100 mg, 0.26 mmol) were combined with 30 mL of toluene. The mixture was refluxed overnight to give an orange solution, and then it was cooled to room temperature. The solution was filtered and concentrated. The orange racemic product (105 mg, 64% yield) was purified by flash chromatography with Et2O/hexanes. Method 2. (SCp,S)-10[BF4] (100 mg, 0.115 mmol), excess LiCl (48.5 mg, 1.15 mmol), and 2 drops of Hg were mixed in 10 mL of

Scheme 4. Converting a Hydride Enantiomer Stereospecifically Back to the Thiol Complex Diastereomer

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Organometallics Scheme 5. Synthesis and Resolution of Chiral Ruthenium Complexes Containing the 1-Me-3-PhCp Ligand

methyl-benzenemethanethiol (46 μL, 0.34 mmol), and LiBPh4 (109 mg, 0.34 mmol) in 15 mL of 95% EtOH (5% H2O) was refluxed for 3 h. The reaction mixture was cooled to room temperature, and the resulting solid was filtered and washed with 95% EtOH (3 × 5 mL) and dried under vacuum (135 mg, 0.12 mmol, 42% yield). This material was also made by protonating 11 with HBF4·OMe2 or HCl in Et2O. Anal. Calcd for 10[BPh4] (C69H63BP2RuS): C, 75.47; H, 5.78; S, 2.92. Found: C, 75.18; H, 5.72; S, 2.72. Fractional crystallization and separation of the diastereomers 11 (see below) allowed them to be converted back to (SCp,S)-10[BPh4] and (RCp,S)-10[BPh4]. The configuration of each diastereomer was determined by X-ray crystallography. Data for (SCp,S)-10[BPh4] are as follows. 1H NMR (300 MHz, CD2Cl2): δ 1.04 (d, thiol CH3, JH−H = 6.9 Hz, 3H), 2.05 (m, CpCH3, 3H), 2.35−2.41 (m, SH, 1H), 2.88−2.97 (m, thiol CH, 1H), 4.56− 4.69 (m, Ph2PCH2PPh2, 1H), 4.88−5.02 (m, CpH + Ph2PCH2PPh2, 3H), 5.33 (br, CpH, 1H), 6.88−7.60 (m, Ar, 50H). 31P{1H} NMR (121.5 MHz, CD2Cl2): δ 6.13, 9.16 (AB pattern, JP−P = 84.44 Hz). Data for (RCp,S)-10[BPh4] are as follows. 1H NMR (300 MHz, CD2Cl2): δ 1.13 (d, thiol CH3, JH−H = 6.9 Hz, 3H), 1.69 (m, CpCH3, 3H), 2.27−2.32 (m, SH, 1H), 2.67−2.79 (m, thiol CH, 1H), 4.48− 4.60 (m, Ph2PCH2PPh2, 1H), 4.84−5.07 (m, CpH + Ph2PCH2PPh2, 4H), 6.87−7.60 (m, Ar, 50H). 31P{1H} NMR (121.5 MHz, CD2Cl2): δ 6.02, 8.59 (AB pattern, JP−P = 85.54 Hz). (1-Me-3-PhCp)Ru(dppm){(S)-C(S)(H)(Ph)(Me)} (11). KOH (80 mg, 1.44 mmol) and 10[BPh4] (200 mg, 0.18 mmol) were combined with 20 mL of Et2O, and the suspension was stirred for 4 h at room temperature. The orange solution was collected after filtration and concentrated under vacuum. The addition of hexanes gave an orange precipitate that was collected and dried under vacuum (50 mg, 0.064 mmol, 35% yield).

Fractional crystallization and separation of the diastereomers (see below) allowed them to be characterized independently. The configuration of each diastereomer was determined by X-ray crystallography. Data for (SCp,S)-11 are as follows. 1H NMR (300 MHz, CD2Cl2): δ 0.88 (d, thiolate CH3, JH−H = 6.9 Hz, 3H), 2.18 (m, CpCH3, 3H), 2.45 (q, thiolate CH, 1H), 4.65−4.79 (m, CpH + Ph2PCH2PPh2, 4H), 4.93−5.06 (m, Ph2PCH2PPh2, 1H), 6.92−7.61 (m, Ar, 30H). 31P{1H} NMR (121.5 MHz, CD2Cl2): δ 9.95, 17.17 (AB pattern, JP−P = 91.6 Hz). Data for (RCp,S)-11 are as follows. 1H NMR (300 MHz, CD2Cl2): δ 0.95 (d, thiolate CH3, JH−H = 7.2 Hz, 3H), 1.58 (m, CpCH3, 3H), 2.42 (q, thiolate CH, 1H), 4.64−4.84 (m, CpH + Ph2PCH2PPh2, 4H), 4.97−5.09 (m, Ph2PCH2PPh2, 1H), 7.11−7.40 (m, Ar, 30H). 31P{1H} NMR (121.5 MHz, CD2Cl2): δ 10.75, 16.16 (AB pattern, JP−P = 95.4 Hz). [(S Cp )-(1-Me-3-PhCp)Ru(dppm)(NCMe)][BF 4 ] (12[BF 4 ]). (SCp,S)-10[BF4] (100 mg, 0.115 mmol) was dissolved in 3 mL of acetonitrile. The resulting solution was stirred at room temperature for 2 days. The solvent was evaporated under vacuum, and the resulting solid was washed four times with hexanes to remove the (S)-α-methylbenzenemethanethiol. The solid was dried under vacuum to give a green powder (83 mg, 93% yield). Anal. Calcd for C39H36P2NBF4Ru: C, 60.95; H, 4.72. Found: C, 60.78; H, 4.65. The CD3CN complex was prepared and characterized in situ by an analogous synthesis using CD3CN as the solvent. 1H NMR (500 MHz, CD3CN): δ 1.52 (s, CpCH3, 3H), 4.42−4.50 (m, Ph2PCH2PPh2, 1H), 4.65 (s, CpH, 1H), 5.15−5.22 (m, Ph2PCH2PPh2, 1H), 5.56 (s, CpH, 1H), 5.61 (s, CpH, 1H), 7.24−7.61 (m, Ar, 25H). 31P{1H} NMR (202.5 MHz, CD3CN): δ 10.45, 11.14 (AB pattern, JP−P = 81.0 Hz). F


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Organometallics (SCp)-(1-Me-3-PhCp)Ru(dppm)H ((SCp)-13). MeOH (5 mL) was added to a mixture of (SCp)-8 (100 mg, 0.148 mmol) and NaOMe (42 mg, 0.78 mmol) at room temperature. The resulting mixture was stirred overnight. A yellow precipitate formed, which was collected by filtration and washed three times with cold MeOH. The product was then dried under vacuum (59 mg, 62% yield). 1H NMR (300 MHz, CD2Cl2): δ −10.88 (td, RuH, JP−H = 31.8 Hz, JH−H = 4.2 Hz, 1H), 2.09 (s, CpCH3, 3H), 3.79−3.91 (m, Ph2PCH2PPh2, 1H), 4.68−4.74 (m, Ph2PCH2PPh2, 1H), 5.08 (br, CpH, 1H), 5.51 (br, CpH, 1H), 5.54 (br, CpH, 1H), 7.01−7.72 (m, Ar, 25H). 31P{1H} NMR (121.5 MHz, CD2Cl2): δ 20.58, 19.47 (AB pattern, JP−P = 86.8 Hz). Anal. Calcd for C37H34P2Ru: C, 69.25; H, 5.34. Found: C, 68.29; H, 5.24. Converting (SCp)-13 to (SCp,S)-10[BPh4]. One drop of CCl4 was added to a THF solution (1 mL) of (SCp)-13 (10 mg, 0.015 mmol). The pale yellow solution immediately turned orange. After evaporation of the solvent under vacuum, the orange residue was mixed with (S)-αmethyl-benzenemethanethiol (4 μL, 0.03 mmol) and LiBPh4 (7 mg, 0.02 mmol) in 2 mL of 95% EtOH (5% H2O). The reaction mixture was stirred at 40 °C overnight and then cooled to room temperature. After evaporation of the solvent under vacuum, the crude material was analyzed by 31P{1H} NMR, which only showed the signals of (SCp,S)10[BPh4]. Fractional Crystallization To Separate the Diastereomers 11. The 1/1 mixture of the diastereomers 11 was dissolved in Et2O to form a saturated solution. About 1 mL of the solution was transferred into a small vial. The small vial was placed into a larger vial which contained about 2 mL of pentane. The large vial was capped, allowing vapor diffusion of the pentane into the Et2O solution. After 3 days, orange needle crystals separated from the deep orange mother liquor. The crystals consisted of 92% of the diastereomer (SCp,S)-11, as determined by the 31P{1H} NMR spectrum, and were suitable for Xray crystallography. After the solvent was removed from the mother liquor, the resulting deep orange solid was redissolved in Et2O to form a saturated solution. Vapor diffusion of pentane into this solution gave deep orange crystals that contained 92% of the other diastereomer, (RCp,S)-11, as determined by 31P{1H} NMR. These crystals were also suitable for X-ray crystallography. X-ray Structure Determinations. X-ray diffraction data were collected on a Bruker Apex II diffractometer. The structures were solved using direct methods and standard difference map techniques and were refined by full-matrix least-squares procedures on F2 with SHELXTL (version 6.10).

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(CHE-0840451). The authors are grateful to Prof. G. Parkin (Columbia University) for assistance with the X-ray structure determinations, and to Prof. J. Magyar (Barnard College) and Prof. J. Canary (NYU) for access to their circular dichroism spectrometers.

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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.5b00852. Circular dichroism (CD) spectra of (SCp,S)-11 and (RCp,S)-11, 31P{1H} NMR spectra of (SCp,S)-10[BPh4] and (RCp,S)-10[BPh4], and complete details of the crystallographic study (PDF) Crystallographic data for (SCp,S)-11 and (RCp,S)-11 (CIF)

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REFERENCES

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AUTHOR INFORMATION

Corresponding Author

*E-mail for J.R.N.: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This research was supported by NSF grant CHE-0749537, Boulder Scientific, and OFS Fitel. The National Science Foundation is thanked for acquisition of an X-ray diffractometer (CHE-0619638) and a 400 MHz NMR spectrometer G


Article

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