Dehydrodechlorination of Methylene Chloride, Chloroform, and

(12) Organochlorine molecules have found numerous applications in the modern world such as pesticides,(13) refrigerants (chlorofluorocarbons, CFCs; hy...
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Dehydrodechlorination of Methylene Chloride, Chloroform, and Chlorodiphenylmethane in the Presence of Ga/N Lewis Pairs Jung-Ho Son, Sem Raj Tamang, Jade I. Fostvedt, and James D. Hoefelmeyer* Department of Chemistry, University of South Dakota, 414 E. Clark Street, Vermillion, South Dakota 57069, United States S Supporting Information *

ABSTRACT: Transmetalation occurs upon addition of GaCl3 to (quinolin-8yl)trimethylstannane. The compound dissolves immediately in pyridine, and recrystallization gives dichloropyridinyl(quinolin-8-yl)gallium(III). In chloroform, the compound bis-μ-(quinolin-8-yl)-μ-chloro-dichlorodigallium(III) tetrachlorogallate could be isolated in small quantities; however, the major product was trichloro(quinolinium-8-yl)gallate(III) zwitterion. The zwitterion also formed upon addition of methylene chloride or chlorodiphenylmethane. We hypothesize that the highly electrophilic digallyl cation abstracts chloride to form a carbocation and that proton transfer from the carbocation to the quinoline nitrogen affords transient carbenes. In particular, diphenyl carbene forms from dehydrodechlorination of chlorodiphenylmethane in toluene/cyclohexene to give a well-defined mixture of products due to cyclopropanation and C−H insertion reactions. Dichloropyridinyl(quinolin-8-yl)gallium(III) undergoes reaction with chloroform only at elevated temperature to yield quinolinium tetrachlorogallate salt as the product. This salt also forms in the reaction of chloroform with GaCl3 and quinoline at elevated temperature. The zwitterion could be converted to quinolinium tetrachlorogallate upon heating, which supports the idea that it was formed initially as an intermediate. Thus, the Ga/N Lewis pairs appear capable of dehydrodechlorination of chloroalkanes.

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INTRODUCTION Frustrated Lewis pairs (FLPs)1 have gained attention due to their remarkable reactivity that includes heterolytic cleavage of stable chemical bonds2 as well as applications in catalytic hydrogenation,1e,3 capture of carbon, nitrogen, and sulfur oxides,4 C−H activation,5 and CO2 reduction.6 There has been recent interest in the use of FLPs to activate carbon−fluorine bonds.7 It is already known that strong electrophiles can abstract halide anion from organohalide molecules, which is the basis for the Friedel−Crafts type reaction.8 For example, BF3 can activate alkylfluoride molecules to generate carbocations.9 The reaction is dependent on strongly electrophilic Lewis acids with high affinity for fluoride anion,10 with a very recent example being the organofluorophosphonium cation, [FP(C6F5)3+], which abstracts fluoride from a variety of organofluorine molecules.11 The resultant carbocation can be treated with a hydride source to afford an overall hydrodefluorination reaction. Potentially, the hydride source could be formed from combination of an FLP with hydrogen; however it is important to note that a catalytic hydrodehalogenation cycle utilizing an FLP catalyst has not yet been fully realized. Additionally, there is potential to develop tailored FLPs that have high affinity for chlorine rather than fluorine, which may be significant due to the wide availability of organochlorine compounds and their lower cost of manufacture. Only very recently, an example of a main-group FLP used for C−Cl cleavage was reported.12 Organochlorine molecules have found numerous applications in the modern world such as pesticides,13 refrigerants (chlorofluorocarbons, CFCs; hydrochlorofluorocarbons, HCFCs),14 solvents, and plastics. Many of © XXXX American Chemical Society

these compounds are toxic, persist in the environment, and contribute to global health problems and climate change. The ill-effects of pesticides in the environment may be fairly obvious; however, some compounds, particularly organochlorine molecules, are persistent and bioaccumulate in organisms.15 The CFCs and HCFCs are especially potent greenhouse gases16 and, when present in the stratosphere, contribute to ozone destruction.17 For these reasons, there is interest in sequestration and degradation of organochlorine compounds. We endeavored to prepare the unimolecular frustrated Lewis pair dichloro(quinolin-8-yl)gallium(III) (1, Scheme 1) in which Scheme 1. Proposed Synthesis of Compound 1

the gallium and nitrogen atoms are separated by a rigid twocarbon spacer in a preorganized geometry that could lead to a reactive site in which heterolytic bond activation in guest molecules may occur. Compound (1) is expected to be highly electrophilic, and the similar sizes of gallium and chlorine could be a basis for high affinity for chloride (the covalent radii of gallium(III) and chlorine are 124 and 99 pm, respectively).18 Received: November 17, 2016

A

DOI: 10.1021/acs.organomet.6b00867 Organometallics XXXX, XXX, XXX−XXX

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Otherwise, the bond distances and angles appear within typical ranges. A similar structure could be obtained upon recrystallization from 2-picoline (3; see the SI). Attempts to obtain an NMR spectrum of the crude product in CDCl3 led to unusual observations. The product was poorly soluble, and within seconds, the crude product was gradually replaced with a colorless precipitate. The NMR spectrum showed a mixture of compounds. Upon allowing the solution in an NMR tube to stand for several days at room temperature, a few tan colored crystals formed along the sides of the tube, though, this was in a much smaller quantity than the colorless crystals that had already formed. Careful selection of the tan crystals allowed us to study the compound with single crystal Xray diffraction from which we determined the structure of the new compound bis-μ-(quinolin-8-yl)-μ-chloro-dichlorodigallium(III) tetrachlorogallate chloroform solvate (4, Figure 2). In the structure, the gallium atoms in the cationic

Thus, we attempted the reaction of GaCl3 and (quinolin-8yl)trimethyltin(IV). Herein, we report the transmetalation reaction products and their remarkable reactivity toward selected chloroalkanes.

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RESULTS AND DISCUSSION Introduction of electrophilic centers to the 8-position of the quinoline ring is a straightforward route to preorganized unimolecular frustrated Lewis pairs. In prior work, lithiation of 8-iodoquinoline, followed by metathesis with organoboronhalide, led to stable (quinolin-8-yl)boranes.19 Similarly, the molecule (quinolin-8-yl)trimethyltin(IV) could be obtained in high yield using Me3SnCl.20 Transmetalation is the preferred route to organometallic compounds with heavy Lewis acids since greater yields can be achieved by avoiding competing reactions such as metal reduction.21 Prior work has established the utility of tin to gallium transmetalation,22 and this rationale led us to attempt the reaction of (quinolin-8-yl)trimethyltin(IV) with GaCl3. The reaction appeared to proceed very quickly even at room temperature. The highest yields were obtained when the reaction was carried out at 65 °C for 2 h. The reaction mixture contained toluene supernatant and insoluble orange viscous residue. The supernatant was decanted away from the residue, and NMR spectra indicated the presence of Me3SnCl. The residue had poor solubility in nonpolar organic solvents and was soluble in polar Lewis base solvents. Clean NMR spectra could be obtained from solutions dissolved in pyridine-d5 in which the six C−H resonances of the quinolinyl ring were clearly observed. Crystals obtained from pyridine solution were suitable quality for single crystal Xray diffraction study, and the solution to the obtained data gave the structure of dichloropyridinyl(quinolin-8-yl)gallium(III) (2), the pyridine adduct of 1, as shown in Figure 1. Interestingly, the Ga(1)−N(1) distance of 3.005 Å is within the sum of the van der Waals radii of the atoms.23 In conjunction with the slight bending of the gallium atom toward N(1), as evidenced by the Ga(1)−C(8)−C(9) angle of 117.7°, there appears to be a weak intramolecular Ga(1)−N(1) bond.

Figure 2. Structure of 4 in the crystal with thermal ellipsoids shown at 50% probability. The solvent molecule and hydrogen atoms were omitted for clarity. Selected bond distances and angles: Ga(1)−N(1) = 2.016 Å, Ga(2)−N(2) = 1.977 Å, Ga(1)−C(17) = 1.968 Å, Ga(2)− C(8) = 1.961 Å, Ga(1)−Cl(2) = 2.346 Å, Ga(2)−Cl(2) = 2.284 Å, Ga(1)−Cl(3) = 2.063 Å, Ga(2)−Cl(1) = 2.135 Å, Ga(1)...Cl(5) = 3.629 Å, Ga(1)...Ga(2) = 3.094 Å, Ga(1)−Cl(2)−Ga(1) = 83.8°, N(1)−Ga(1)−C(17) = 110.3°, N(2)−Ga(2)−C(8) = 112.9°.

digallacycle are in a distorted tetrahedral geometry. The quinoline rings have an approximate dihedral angle of 111°. The tetrachlorogallate anion is slightly closer to the Ga(1) atom and there is a slight asymmetry of the cation (from C2) as a result; e.g., the μ-chloro is slightly shifted toward Ga(2). Conceptually, the salt arises from the head-to-tail dimer of 1 with abstraction of a chloride anion by an equivalent of GaCl3. The NMR spectra of compound 4 in pyridine-d5 were identical to those of the crude product, and compound 2 could be crystallized from solutions of 4 dissolved in pyridine. Thus, we believe the crude product is an amorphous form of compound 4 (Scheme 2). The colorless crystalline precipitate formed in chloroform was found as trichloro(quinolinium-8-yl)gallate(III) zwitterion, 5 (Figure 3). The RGaCl3− moiety is approximately tetrahedral with a weak intramolecular contact between chloride and the quinolinium proton. The zwitterion 5 was soluble in acetonitrile, and in this solvent, the 1H NMR spectrum shows six quinoline C−H resonances and a broad resonance centered at 13.4 ppm that could be assigned to the quinolinium proton. An interesting feature of the work that presented some challenges to the study is that compounds 2, 4, and 5 have very

Figure 1. Structure of 2 in the crystal with thermal ellipsoids shown at 50% probability. Hydrogen atoms were omitted for clarity. Selected bond distances and angles: Ga(1)−C(8) = 1.943 Å, Ga(1)−Cl(1) = 2.219 Å, Ga(1)−Cl(2) = 2.204 Å, Ga(1)−N(2) = 2.205 Å, Ga(1)− N(1) = 3.005 Å, C(8)−Ga(1)−N(2) = 112.7°, Ga(1)−C(8)−C(9) = 117.7°. B

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substantial (≥70% isolated yield) and is evidence of a dehydrodechlorination reaction. For example, from 0.175 g (0.245 mmol) of 4, we observe the formation of 0.143 g (0.47 mmol) of 5 in 5 mL (78.2 mmol) of CH2Cl2. If HCl were present in fresh CH2Cl2 at this concentration, then addition of an equal volume of water should give an aqueous solution with pH ∼ 1; however, equal volume of distilled water in contact with distilled CH2Cl2 gave neutral pH. Interestingly, we did not observe evidence of a neutral tetrachlorodigallacycle (the headto-tail dimer of 1). An MMFF calculation of the hypothetical neutral tetrachlorodigallacycle molecule using the Spartan’10 GUI/computational engine24 shows a highly buckled structure. Conceivably, such a structure could break apart to yield the transient species 1 that would undoubtedly react rapidly with small Lewis acids or Lewis bases. Compound 2 appears to have a considerable barrier toward reaction with chloroform. At room temperature, a reaction was not observed; however, refluxing in chloroform led to formation of 8-quinolinium tetrachlorogallate(III) (7; see the SI). We presume in situ formation of 5 that rapidly decomposed to form compound 7 at elevated temperature. Indeed, separate experiments in which isolated samples of 5 were refluxed in chloroform gave 7 in nearly quantitative yield (Scheme 4).

Scheme 2. Transmetalation Reaction of (Quinolin-8yl)trimethyltin(IV) with GaCl3

Scheme 4. Formation of 7 from 5 upon Heating in Chloroform Figure 3. Structure of 5 in the crystal with thermal ellipsoids shown at 50% probability. Hydrogen atoms (except the quinolinium proton) were omitted for clarity. Selected bond distances and angles: Ga(1)− C(8) = 1.975 Å, Ga(1)−Cl(1) = 2.207 Å, Ga(1)−Cl(2) = 2.179 Å, Ga(1)−Cl(3) = 2.221 Å, Cl(3)···H(99) = 2.463 Å, C(9)−C(8)− Ga(1) = 126.6°.

similar NMR spectra in pyridine-d5. Certainly, it is not surprising that compounds 2 and 4 exhibit similar spectra, given that 2 forms upon addition of pyridine to 4. However, this indicates that, in pyridine, 4 breaks into monomeric units due to the greater abundance and basicity of pyridine relative to quinoline. Additionally, there must be a net chloride transfer from GaCl4− to a (quinolin-8-yl)Ga(III) center to form two neutral equivalents of 1 that may be initiated by py/Cl− ligand exchange at GaCl4−. In order that 5 exhibits a similar NMR spectrum in pyridine-d5, there must be proton transfer from quinoline to the solvent as well as ligand exchange at gallium in which a chloride is displaced by solvent. Interestingly, it was possible to grow crystals from a solution of 5 dissolved in pyridine, which gave the new salt [(py)2H+][(quinolin-8yl)trichlorogallate(III)] (6; see Scheme 3 and the SI).

Interestingly, we observe similar behavior in the reaction of chloroform with GaCl3 and 8-quinoline. The reaction did not proceed at room temperature; however, under refluxing conditions, compound 7 was formed. Dehydrodechlorination of chloroalkanes should give rise to formation of carbene species. Previous work has found that ΔH = 56.9 kcal/mol for the conversion of chloroform to dichlorocarbene and HCl.25 Such a reaction could potentially proceed via chloride abstraction from chloroform, followed by rapid deprotonation of Cl2CH+ carbocation.26 We note this is the opposite sequence of reaction steps in comparison to formation of carbene from deprotonation of Cl3CH with tBuOK.27 Stennet et al. very recently showed that a cationic aluminum(III) nacnac species activates the C−Cl bond of CH2Cl2.12 However, after chloride abstraction, the resultant carbocation was bound by a phosphine Lewis base. We invested considerable effort to detect carbene-derived products. GC−MS analyses of the chloroform supernatant from the reaction with 4 showed traces of CCl4 only slightly elevated compared to fresh chloroform, and tetrachloroethylene was not detected. We attempted several reactions in which cyclohexene was added as a trap for dichlorocarbene;27 however, we could not detect 7,7-dichlorobicyclo[4.1.0]heptane. Upon heating such mixtures to reflux, we found small quantities of bicyclohexane as well as formation of compound 7. We performed experiments in which 4 was combined with methylene chloride, which, by virtue of its larger dipole moment, might more effectively stabilize the highly charged species that form upon dehydrodechlorination. Additionally, the pKa of CH2Cl2 is much higher than that of CHCl3 and

Scheme 3. Formation of 6 from 5 in Pyridine

While the structure of 5 is not extraordinary, its formation suggested an interesting reaction between 4 and chloroform. It is known that small amounts of HCl may form in chloroform solutions as a result of slow decomposition; however, we observed the formation of 5 in chloroform freshly distilled from CaH2. Furthermore, it is important to note that the yield of 5 in reactions of 4 with chloroform (or dichloromethane) is C

DOI: 10.1021/acs.organomet.6b00867 Organometallics XXXX, XXX, XXX−XXX

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quinolinium tetrachlorogallate (7) was formed. The reactions demonstrate dehydrodechlorination of chloroalkanes with geminal H and Cl in the presence of Ga/N Lewis pairs with evidence of concomitant formation of a carbene. Such reactions may serve as fundamental reaction steps in new catalytic processes for the dehydrodechlorination of organochlorine molecules.

could help establish mechanistically whether the dehydrodechlorination proceeds via initial chloride abstraction or deprotonation. Combination of 4 with CH2Cl2 gave faster reaction with formation of 5. Dehydrodechlorination of CH2Cl2 should give chlorocarbene in solution. GC−MS analyses of the supernatant indicated the presence of traces of chloroacetaldehyde and showed dichloroethene at concentrations only slightly greater than the signal from fresh CH2Cl2. We attempted reaction of 4 with CH2Cl2 in the presence of cyclohexene and could not detect 7-chlorobicyclo[4.1.0]heptane. The inability to detect bicycloheptane products was somewhat puzzling, so we performed a control experiment in which GaCl3 was dissolved in CH2Cl2 and cyclohexene. In this case, appreciable quantities of 7-chlorobicyclo[4.1.0]heptane were detected with GC−MS. The result supports the mechanistic concepts of chloride abstraction at the Lewis acidic gallium center as well as the rapid deprotonation of the resultant carbocation to give carbenes. Dehydrodechlorination of chlorodiphenylmethane should yield the more stable diphenylcarbene. The reaction of chlorodiphenylmethane with 4 in toluene/cyclohexene was found to give the zwitterion 5 (95% isolated yield) and a mixture of products arising from reaction of diphenyl carbene with toluene and cyclohexene (Scheme 5). Column chroma-

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EXPERIMENTAL SECTION

General Considerations. 8-Aminoquinoline, n-butyl lithium (1.6 M in hexanes), trimethyltinchloride, gallium(III) chloride, and all solvents were purchased from commercial sources. All preparations were performed under an atmosphere of dry N2 using Schlenk and glovebox techniques unless otherwise noted. Solvents (THF, toluene, pyridine, chloroform, CDCl3, CD3CN, and pyridine-d5) were dried and distilled from CaH2. 8-Iodoquinoline19 and (quinolin-8-yl)trimethyltin(IV)20 were prepared according to the literature. Purity of compounds was assessed as combination of X-ray crystallographic, NMR, and HRMS data. NMR spectra were recorded on a Bruker Avance II 400 MHz spectrometer at 300 K. 1H NMR spectra were referenced to the solvent residual peak (CD3CN, δ 1.93 ppm; CDCl3, δ 7.24 ppm; pyridine-d5, δ 8.74 ppm). 13C NMR spectra were referenced to the solvent residual peak (CD3CN, δ 117.7 ppm; CDCl3, δ 77.0 ppm; pyridine-d5, δ 150.4 ppm). The chemical shifts are reported in ppm, and coupling constants in Hz as absolute values. GC−MS analyses were carried out using a Shimadzu GCMS-QP2010 SE instrument with a 30 m, 0.25 μm inner diameter column coated with SHRXI-5MS and using a temperature profile that ramped from 35 to 250 °C at 15 °C/min and scanning from 50 to 500 m/z. Crystallographic data were collected at 100 K using a Bruker SMART APEX II diffractometer28 with Mo Kα radiation. The data reduction and refinement were completed using the WinGX suite of software.29 SIR9230 was used to solve the structures by direct methods, and SHELXL-9731 was used to refine the structures. Hydrogen atoms were placed in ideal positions and refined as riding atoms with relative isotropic displacement parameters. ORTEP plots were drawn with Mercury software.32 Dichloropyridinyl(quinolin-8-yl)gallium(III) (2) and Bis-μ(quinolin-8-yl)-μ-chloro-dichlorodigallium(III) Tetrachlorogallate (4). A 100 mL round-bottom flask was charged with 0.250 g (0.86 mmol) of (quinolin-8-yl)trimethyltin(IV) dissolved in 6.5 mL of dry toluene, followed by addition of 0.226 g (1.28 mmol) of GaCl3. There was an immediate reaction that gave an orange oily residue and a transparent light-brown supernatant. The mixture was sealed and heated with stirring at 65 °C for 2 h. The mixture was allowed to cool and settle. The supernatant was removed with a pipet, and the product was washed with 3 × 2 mL of dry toluene and then dried under vacuum, yielding an orange viscous residue (0.300 g, 98%). Recrystallization from pyridine/toluene at −20 °C gave crystals of 2 (0.191 g, 65%) suitable for X-ray diffraction (similarly, recrystallization from 2-methylpyridine gave crystals of 3; see the SI). Alternatively, it was found that, while the crude product reacts fairly quickly with chloroform, a small amount of tan crystals could be grown from chloroform under an inert atmosphere over several days to give 4. Melting point of 2: 112−117 °C. 1H NMR (400.1 MHz; [d5]pyridine): δ 7.24−7.30 (dd, 1H, C6-H, 3J = 4.2, 8.2 Hz), 7.60−7.65 (dd, 1H, C3-H, 3J = 6.7, 8.1 Hz), 7.87−7.92 (dd, 1H, C4-H, 3J = 8.1 Hz, 4J = 1.4 Hz), 8.11−8.15 (dd, 1H, C5-H, 3J = 8.2 Hz, 4J = 1.7 Hz), 8.53−8.57 (dd, 1H, C2-H, 3J = 6.7 Hz, 4J = 1.4 Hz), 8.84−8.88 (dd, 1H, C7-H, 3J = 4.2 Hz, 4J = 1.7 Hz). 13C NMR (100.6 MHz; [d5]pyridine): δ 122.0, 127.6, 129.0, 130.3, 137.3, 139.4. ESI-HRMS: m/z = [1H-py]+ calcd33 for C14H12N2Cl2Ga, 346.9633 (35Cl/35Cl/69Ga), 348.9604 (35Cl/37Cl/69Ga), 348.9625 (35Cl/35Cl/71Ga), 350.9595 (35Cl/37Cl/71Ga); found 346.9614, 348.9606, 350.9580. Trichloro(quinolinium-8-yl)gallate(III) (5). A vial was charged with 0.175 g (0.245 mmol) of 4 (crude form, without chloroform solvate molecule). To the vial was added 5 mL of dry methylene chloride, causing a white powder to precipitate out of solution (similar reaction was observed with chloroform or chlorodiphenylmethane).

Scheme 5. Reaction of 4 with Ph2CHCl Leads to Formation of Zwitterion 5 and a Mixture of Organic Products

tography gave two fractions. GC−MS and NMR analyses showed one fraction consisted of three compounds identified as a mixture of the cyclohexene-trapped diphenylcarbene isomers in a 7.4:2.4:1 ratio, 1,1′-(1-cyclohexen-1-ylmethylene)bisbenzene (CAS 83605-32-7), 1,1′-(cyclohexylidenemethylene)bis-benzene (CAS 30125-24-7), and 7,7-diphenylbicyclo[4.1.0]heptane (CAS 145630-02-0), respectively. The other fraction consisted of two compounds identified as the ortho and para products of diphenylcarbene addition to toluene in an 11:1 ratio, 1-(diphenylmethyl)-4-methyl-benzene (CAS 603-37-2), and 1-(diphenylmethyl)-2-methyl-benzene (CAS 17016-20-5), respectively. The products obtained from reaction of diphenylcarbene with cyclohexene and toluene account for 10% and 50% yields, respectively, based on Ph2CHCl.

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CONCLUSIONS We report a transmetalation route for the preparation of bis-μ(quinolin-8-yl)-μ-chloro-dichlorodigallium(III) tetrachlorogallate (4), in which the cation is a head-to-tail dimer of (1) minus a chloride. Solutions of 4 in Lewis base solvents yield base stabilized forms of 1 (compounds 2 and 3). In the presence of CHCl3, CH2Cl2, or chlorodiphenylmethane, 4 was converted to the zwitterion 5. However, the Ga/N Lewis pairs, 2 or GaCl3/8-quinoline undergo reaction with chloroalkanes only at elevated temperatures, and in those cases, 8D

DOI: 10.1021/acs.organomet.6b00867 Organometallics XXXX, XXX, XXX−XXX

Organometallics The solvent was separated from the precipitate using a pipet, and the solid product was allowed to dry on a Kim-wipe, leaving a chalky white powder. Yield: 0.143 g (96%). Crystals were obtained upon dissolution of the powder in ether, followed by vapor diffusion of CH2Cl2 into the solution, to give colorless crystals. Melting point: 117−119 °C. 1H NMR (400.1 MHz; CD3CN): δ 7.93−7.99 (dd, 1H, C6-H, 3J = 6.9, 8.3 Hz), 7.98−8.04 (dd, 1H, C3-H, 3J = 5.6, 8.2 Hz), 8.26−8.30 (dd, 1H, C5/7-H, 3J = 8.3 Hz, 4J = 1.4 Hz), 8.42−8.46 (dd, 1H, C5/7-H, 3J = 6.8 Hz, 4J = 1.3 Hz), 9.08−9.11 (dd, 1H, C4-H, 3J = 5.6 Hz, 4J = 1.6 Hz), 9.11−9.15 (dd, 1H, C2-H, 3J = 8.3 Hz, 4J = 1.6 Hz), 13.3−13.5 (br, s, 1H, N-H). 13C NMR (100.6 MHz; CD3CN) δ 121.7, 130.2, 130.3, 144.1, 145.3 (br, C2), 149.7. ESI-HRMS: m/z = [3-H]− calcd33 for C9H6NCl3Ga−, 301.8822 (35Cl/35Cl/35Cl/69Ga), 303.8792 (35Cl/ 35 Cl/37Cl/69Ga), 303.8813 (35Cl/35Cl/35Cl/71Ga), 305.8763 (35Cl/ 37 Cl/37Cl/69Ga), 305.8783 (35Cl/35Cl/37Cl/71Ga); found 301.8818, 303.8801, 305.8795. 1,1′-(Cyclohexylidenemethylene)bis-benzene, 1,1′-(1-Cyclohexen-1-ylmethylene)bis-benzene, 7,7-Diphenylbicyclo[4.1.0]heptane, 1-(Diphenylmethyl)-2-methyl-benzene, and 1(Diphenylmethyl)-4-methyl-benzene. Inside the glovebox, a 100 mL Schlenk flask was charged with 851 mg (1.19 mmol) of 4 and 20 mL of dry toluene; this led to a dense orange oil phase-separated from the supernatant. To this mixture were added 242 μL (2.38 mmol) of cyclohexene, 423 μL (2.38 mmol) of chlorodiphenylmethane, and a small magnetic stir bar. The mixture was sealed and stirred in the glovebox for 14 h. Over the course of the reaction, a pale orange precipitate formed under a yellow supernatant. The supernatant was transferred to a 100 mL Schlenk flask. The orange residue was washed with 3 × 2 mL of dry toluene; the washings were added to the toluene supernatant above. The residue was subjected to additional washings with 10 × 2 mL of dry ether, resulting in a white powder identified as 3 (mass 690 mg, yield 95%). The toluene solution was subjected to vacuum to remove solvent, resulting in an impure mixture of red and yellow oils. GC−MS analysis of the mixture gave evidence of five products. Three peaks eluting at 16.38, 16.51, and 16.81 min were identified as a mixture of the cyclohexene-trapped diphenylcarbene isomers in a 7.4:2.4:1 ratio, 1,1′-(1-cyclohexen-1-ylmethylene)bisbenzene (A) (CAS 83605-32-7), 1,1′-(cyclohexylidenemethylene)bisbenzene34 (B) (CAS 30125-24-7), and 7,7-diphenylbicyclo[4.1.0]heptane35 (C) (CAS 145630-02-0), respectively. Two peaks eluting at 16.97 and 17.24 min were identified as the ortho and para products of diphenylcarbene addition to toluene in an 11:1 ratio, 1-(diphenylmethyl)-4-methyl-benzene36 (D) (CAS 603-37-2) and 1-(diphenylmethyl)-2-methyl-benzene36 (E) (CAS 17016-20-5), respectively. The product mixture was purified and separated via column chromatography with a silica (63-200 μm) stationary phase and a hexane mobile phase. The first eluent was a mixture of A, B, and C (mass 57.5 mg, isolated yield 9.7%). The second eluent was a mixture of D and E (mass 309 mg, isolated yield 50.2%). NMR spectra were simulated using software from nmrdb.org37, and our data (see the SI) matched well with the literature.

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ACKNOWLEDGMENTS

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REFERENCES

We acknowledge the support of the National Science Foundation (NSF) for purchase of the single crystal X-ray diffractometer, glovebox (EPS-0554609), NMR (CHE1229035), and student support (EPS-0903804 and DGE0903685). We acknowledge the support of the U.S. Department of Energy under contracts DE-FG02-08ER64624 and DEEE0000270. We are grateful to Ron New at the UC Riverside High Resolution Mass Spectrometry Facility for obtaining the HRMS data. The HRMS equipment was obtained within the NSF CHE-0541848 grant.

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S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.6b00867. Crystallographic data for 2−7 (CIF) NMR spectra, HRMS data, and ORTEP drawings (PDF)

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AUTHOR INFORMATION

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*E-mail: [email protected]. ORCID

James D. Hoefelmeyer: 0000-0002-5955-8557 Notes

The authors declare no competing financial interest. E

DOI: 10.1021/acs.organomet.6b00867 Organometallics XXXX, XXX, XXX−XXX

Article

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DOI: 10.1021/acs.organomet.6b00867 Organometallics XXXX, XXX, XXX−XXX