Stereoelectronic Effects in Dihapto-Coordinated Complexes of TpW

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Organometallics 2009, 28, 4724–4734 DOI: 10.1021/om900381c

Stereoelectronic Effects in Dihapto-Coordinated Complexes of TpW (NO)(PMe3) and Their Manifestation in Diels-Alder Cycloaddition of Arenes Rebecca J. Salomon,† Edward C. Lis, Jr.,† Monica U. Kasbekar,† Kimberley C. Bassett,† William H. Myers,‡ Carl O. Trindle,† Michal Sabat,† and W. Dean Harman*,† †

Department of Chemistry, University of Virginia, Charlottesville, Virginia 22904, and ‡Department of Chemistry, University of Richmond, Richmond, Virginia 27173 Received May 12, 2009

The addition of singly and doubly activated dienophiles to TpW(NO)(PMe3)(5,6-η2-anisole) and TpW(NO)(PMe3)(5,6-η2-1,3-dimethoxybenzene) to generate dihapto-coordinated [2.2.2]bicyclooctadienes and -trienes is explored. The highly functionalized bicyclic scaffolds are isolated from the metal fragment intact. Although moderate yields hinder their synthetic application, a unique stereoelectronic effect is uncovered. Coordination diastereomers of anisoles with the methoxy substituent distal to the PMe3 ligand have faster reaction rates relative to the proximal diastereomer. DFT calculations reveal the metal fragment possesses a dipole that directs positive charge away from the PMe3 ligand, and a polarized cycloaddition transition state is invoked to explain this observation.

Introduction Under classical reaction conditions, benzenes resist DielsAlder cycloaddition with even the most potent dienophiles, owing to their aromatic stabilization.1-3 Cycloaddition is typically achieved by photochemical means2 or extreme pressures and temperatures.3 For example, at 100 °C and 10-12 kbar, a cycloadduct of naphthalene and maleic anhydride can be obtained in good yield;4 however, such a product is thermodynamically unstable under ambient pressures.3 In earlier studies, our research group found that a chiral rhenium(I) or tungsten(0) complex ([M*]) could be used to promote the cycloaddition of benzene and N-methylmaleimide (NMM), with the metal η2-coordinated to the aromatic ring. The π-basic tungsten or rhenium atom was found to stabilize the cycloadduct with respect to retrocycloaddition and could be removed without degradation of the delicate [2.2.2]bicyclooctadiene (eq 1).5,6 Given the mild conditions under which this reaction occurs and the potential synthetic value of such a process, a follow-up study was initiated to investigate the role of arene substituents on the rate and regio- and stereochemistry of cycloaddition. *Corresponding author. E-mail: [email protected]. (1) Krespan, C. G.; McKusick, B. C.; Cairns, T. L. J. Am. Chem. Soc. 1961, 83, 3428. (2) Al-Jaial, N.; Drew, M. G. B.; Gilbert, A. J. Chem. Soc., Chem. Commun. 1985, 85. (3) Iskhakova, G. G.; Kiselev, V. D.; Kashaeva, E. A.; Potapova, L. N.; Berdnikov, E. A.; Krivolapov, D. B.; Litvinov, I. A. ARKIVOC 2004, 70. (4) Jones, W. H.; Mangold, D.; Plieninger, H. Tetrahedron 1962, 18, 267. (5) Chordia, M. D.; Smith, P. L.; Meiere, S. H.; Sabat, M.; Harman, W. D. J. Am. Chem. Soc. 2001, 123, 10756. (6) Graham, P. M.; Meiere, S. H.; Sabat, M.; Harman, W. D. Organometallics 2003, 22, 4364. pubs.acs.org/Organometallics

Published on Web 07/21/2009

Conventional wisdom dictates that incorporation of electron-donating substituents on the arene will increase the rate of cycloaddition with electron-poor dienophiles. But the effects of substituents on the regio- and stereochemistry of the cycloaddition are less clear. When benzene is monosubstituted, its complexation to an asymmetric dearomatization agent ([M*]) produces two coordination diastereomers for each of three linkage isomers (a-f, Scheme 1).7,8 Hence, six different cycloadduct isomers (g-l ) are possible, neglecting any additional stereocenters resulting from substituents of the dienophile. Given that the rate for both interfacial and intrafacial linkage isomerization (t1/2 ≈ 1 s) is fast relative to cycloaddition (typically t1/2 > 1 h),7 the following question arises: How closely does the isomer ratio for the various cycloadduct complexes (g-l ) correlate to that of their arene complex precursors (a-f )?

Results and Discussion We chose anisole and 1,3-dimethoxybenzene (DMB) as examples of mono- and disubstituted, electron-rich arenes that are known to form stable complexes with {TpW(NO)(PMe3)}.8 The anisole complex TpW(NO)(PMe3)(η2-anisole) (1),8 like its rhenium predecessor,7 exists in solution (7) Brooks, B. C.; Meiere, S. H.; Friedman, L. A.; Gunnoe, T. B.; Harman, W. D. J. Am. Chem. Soc. 2001, 123, 3541. (8) Welch, K. D.; Harrison, D. P.; Lis, E. C.; Liu, W.; Salomon, R. J.; Harman, W. D.; Myers, W. H. Organometallics 2007, 26, 2791. r 2009 American Chemical Society

Article Scheme 1. Possible Isomers of Diels-Alder Cycloaddition for Dihapto-Coordinated Arene Complexes

as a single regioisomer (5,6-η2). However, two coordination diastereomers form a 3.5:1 equilibrium mixture (A:B) in solution, with the methoxy group oriented either proximal (A) or distal (B) to the PMe3 ligand (Scheme 2). Stirring a solution of 1 and N-methylmaleimide (NMM) in dimethoxyethane (DME) at 0 °C overnight results in a tan precipitate. After isolation, proton NMR analysis of this solid revealed a 1:1 mixture of two bicyclo[2.2.2]octadiene complexes, 2A and 2B, with a methoxy group located at a bridgehead carbon (Scheme 2). Analysis by HSQC, HMBC, and NOESY determined that 2A and 2B are both endo cycloaddition products.9 A detailed comparison of chemical shift data for these two isomers identified important differences that facilitated the assignments of other cycloaddition products (vide infra). For example, the B isomer has one of its Tp signals (Tp3A) shifted significantly downfield (∼8.5 ppm) compared to the typical range (6.5-8.0 ppm). Other features that assisted characterization included a large positive shift of the W(0/I) reduction potential, a ∼30 Hz decrease in the 31 P-183W coupling constant from the arene precursor (1),8 and the appearance of alkene resonances between 4 and 6 ppm (vide infra). Although the product regioisomer distribution for this cycloaddition reaction closely parallels that observed for the precursor arene complexes (1, 3), the stereoisomer distribution of products does not. Whereas the anisole complex 1 favors the coordination diastereomer in which the oxygen is oriented toward the PMe3 ligand by a 3.5:1 ratio (A:B), the isolated product was determined to be a 1:1 ratio of diastereomers. In order to establish a more accurate isomer ratio in the crude reaction mixture, the reaction of 1 and NMM was repeated in CH2Cl2 (where all isomers are soluble), and its progress was monitored by 31P NMR. Two experiments were performed, with concentrations of dienophile and arene complex chosen such that the half-life of cycloaddition was 3 h. Under both sets of conditions the ratio of A:B isomers was 1.1:1, with no exo isomer detected. Even under conditions where the equilibrium ratio of 3.5:1 (A:B) (9) endo and exo refer to stereochemistry of dienophile addition relative to the uncoordinated diene fragment of the arene. Thus, the endo isomer of 2 has the succinimide ring extending away from the metal.

Organometallics, Vol. 28, No. 16, 2009

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Scheme 2. Cycloaddition of N-Methylmaleimide (NMM) with Anisole and DMB Complexes

was maintained during the entire course of the reaction (kA, kB . kC[NMM], kD[NMM]; Scheme 2),10 the A and B cycloadducts were formed at virtually identical rates. Hence, in accordance with the Curtin-Hammett principle, the rate of formation of cycloadduct 2B is required to be 3.2 times as fast as that of 2A in CH2Cl2.10 Similar to what was found for anisole, the complex TpW(NO)(PMe3)(5,6-η2-1,3-DMB) 3 can be generated from TpW(NO)Br2 in two steps as a 3.1:1 ratio of coordination diastereomers.11 As with anisole, when the DMB complex was stirred along with an excess of NMM in a DME solution at 0 °C, a white precipitate formed over a period of 24 h. Upon isolation, this compound was determined by proton NMR experiments to be exclusively an endo cycloadduct with the methoxy group oriented away from the PMe3 (4B, 40%). The filtrate was found to contain a 10:1:1 mixture of three bicyclooctadiene complexes, the major species also being an endo cycloadduct (4A; 41%). In methanol, the rate of this cycloaddition reaction is accelerated, reaching completion within 2 min at 20 °C ([NMM]°=1.310-4 M; >99%; isolated yield=75%). Finally, the reaction was carried out in CH2Cl2, in which all of the cycloadduct complexes are soluble. Running under either dilute (0.01 M; 0.02 M) or concentrated (0.14 M; 0.72 M) conditions, the ratio of products was 1.2:1 (endo-4A:endo-4B), with a small amount (∼6%) of what we presume to be an exo cycloadduct isomer also present. As with the anisole-derived analogue 2, several spectral features of 4 helped confirm the formation of the bicyclooctadiene complex shown in Scheme 2. Protons associated with the tungsten-bound carbons (H11 and H10) shift upfield to 2.31 and 1.81 ppm, respectively, and a vinyl ether resonance is present at 4.76 ppm. The 31P NMR spectrum shows a decrease in the JWP coupling constant to 271 Hz for 4A and (10) Eliel, E. L.; Wilen, S. H.; Mander, L. N. Sterochemistry of Organic Compounds; J. Wiley & Sons, Inc.: New York, 1994. (11) The term coordination diastereomers refers herin to two isomers differing in stereochemistry resulting from coordination to the metal.

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Figure 2. ORTEP of cycloadduct complex 7.

Figure 1. Crystal structures of NMM cycloadducts endo-2B (top) and endo-4B (bottom). Table 1

R

R1

R2

conditions

productsa

H CO2Me CO2Me DME, rt L, C, D MeOH, 0 °C C (5) H CN CNb H CN H MeOH, 0 °C L, SM CO2Mec DME, 0 °C L, C, D OMe CO2Me b CO2Me DME, 0 °C L, C, D OMe CO2Me CO2Meb MeOH, 0 °C L, C OMe CO2Me DME, rt C (6) OMe CN CNb H MeOH, 0 °C L, C OMe SO2Ph OMe COMe H MeOH, 0 °C L, D OMe COH H MeOH, 0 °C L, M OMe CN H MeOH, rt L, D OMe CN H MeOH, 0 °C C (7) a L = ligand substitution, C = cycloaddition, D = decomposition, SM = starting material, M = Michael addition upon addition of acid. b trans. c cis.

a b c d e f g h i j k l

264 Hz for 4B (cf. 307 Hz for 3), and the irreversible reduction wave observed at Ep,a=þ0.69 V is positively shifted from the starting material (-0.29 V). Additionally, 4B has the Tp3A pyrazolyl proton shifted downfield to 8.66 ppm. The endo stereochemistry of the cyclooctadiene ligand was assigned using NOESY data, where correlations between H11 and H6 and H10 and H2 (Scheme 2) were observed. Ultimately, X-ray crystal structures of endo-2B and endo-4B were obtained to confirm their stereochemical assignments (Figure 1). We next screened both arene complexes 1 and 3 for reactivity with other singly and doubly activated alkene dienophiles in a variety of solvents. A combination of cyclic voltammetry and 1H NMR was used to monitor these reactions, which are summarized in Table 1. In some cases, the anticipated cycloaddition products (C) were accompanied by products resulting from ligand substitution at the metal (L) (dienophile replacing arene) or decomposition of complexing agent (D). Addition of Lewis acids failed to improve the yield or alter the product ratios of cycloaddition.

Only the reactions with fumaronitrile (entries b, g) and acrylonitrile (entry l) yielded cycloaddition products exclusively, and these were further pursued. Stirring 1 with fumaronitrile in MeOH at 0 °C overnight produces the [2.2.2] bicyclic system as a 1:1 mixture of exo-5A and exo5B.12 The use of MeOH as a solvent was essential to achieving good reaction yields, as ligand substitution occurred in the less polar solvents DME and THF. The reaction of fumaronitrile with DMB complex 3 was also found to be solvent dependent. Stirring 3 with fumaronitrile in a DME/Et2O mixture overnight produces all four stereoisomers of 6 in solution; however, exo-6B spontaneously precipitates out of solution in 26% yield. The yield of the cycloaddition products can be increased to 86% by running the reaction in DME alone; however, the product is a mixture of all four diastereomers. Interestingly, the exo-6A isomer was shown to be the thermodynamically favored product: When a CDCl3 solution of initially pure exo-6B is allowed to stand for 28 h, all four stereoisomers of the cycloaddition are formed. The solution ultimately reaches a 1:2:9.4:2 ratio of endo-A:endo-B:exo-A:exo-B isomers. An identical ratio is reached starting with a solution containing a 1:1 ratio of exo-6A and exo-6B. Addition of acrylonitrile to 1 in MeOH at 0 °C also generates a mixture of four diastereomers; however, the exo isomers precipitate from solution and are isolated as a 1:1 mixture of exo-7A and exo-7B. A crystal structure determination of exo-7B was obtained, and the ORTEP diagram (Figure 2) confirms the stereochemistry of addition. Reaction yield and diastereomer information for other cycloaddition reactions are summarized in Table 2. Arene complexes 1 and 3 were also screened for reactivity with alkynes. Addition of dimethylacetylenedicarboxylate (DMAD) to either complex in THF produced the anticipated barrelene complexes 8 and 9 (Scheme 3; Table 2). The diastereomer ratios in the reaction mixture (CH2Cl2) ranged from 2:1 to 2.8:1 (B:A). Cycloadduct 9 was ultimately obtained in pure form by precipitation from a THF solution as a 12.5:1 ratio of isomers (B:A). Compound 8 was too unstable to be obtained in pure form (∼10% impurities), but 1H NMR data indicated an A:B ratio of 1:4 for the isolated product. Combining 1 or 3 with methyl propiolate or 3-butyne-2-one resulted in decomposition. With several cycloadduct complexes in hand, we next attempted to demetallate and isolate the organic bicyclooctadienes and -trienes. Addition of ceric ammonium nitrate (CAN) to a solution of the NMM cycloadduct 4 in CDCl3 (12) For fumaronitrile, exo refers to the nitrile group alpha to the bridgehead methoxy substituent. A trans stereochemistry is maintained for the two cyano groups in all cycloadducts.

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Table 2. Summary of Cycloaddition Reaction Data product composition CH2Cl2, soln

isolated solid cpd

arene

dienophile

conditions

A:B

exo:endo

yield

A:B

exo:endo

2 4 5 6

anisole DMB anisole DMB

NMM NMM fumaronitrile fumaronitrile acrylonitrile DMAD DMAD

1:>20 1:>20 >20:1 >20:1 1:1.13 >20:1

76% 80% 75% 26% 86% 36% ∼80%b 63%

1:>20 1: 14

DMB anisole DMB

1:1 1:1 1:1 1:>20 1:2.5 1:1 1:4 1:12.5

1:1 1:1.1

7 8 9

DME, 0 °C DME, 0 °C MeOH,0 °C DME/Et2O, rt DME, 0 °C MeOH, 0 °C THF, rt THF, rt

a

1:1

2.5:1

1: 2 1:2.3 1:2.8a

THF solution. b Impure.

Scheme 4. Demetalation (and Hydrolysis) of Dimethoxybicyclooctadienes

Figure 3. ORTEP diagram for compound 11. Scheme 3. Preparation of Barrelene Complexes

followed by chromatography resulted only in a small amount (10%) of the rearomatized product 10 (Scheme 4). However, when the oxidant/solvent combination was switched to CuBr2/acetone, an in situ hydrolysis of the vinyl ether occurred, thus preventing rearomatization or retrocycloaddition, and bicyclooctenone 11 was isolated in 15% yield (Figure 3). By hydrolyzing the vinyl ether moiety present in the complexed bicyclooctadienes prior to oxidation, retrocycloaddition could be minimized. Hence 7 and 6 were converted first to 12 and 13, respectively, then to their organic bicyclooctenones 14 and 15. While compound 14 could be cleanly isolated in 70% yield, compound 15 was unstable to chromatographic conditions and could be isolated only in an impure form. All attempts to remove the organic barrelenes from 8 or 9 were unsuccessful.

The primary goal of the present study is to explore the relationship between the coordination site and stereochemistry of the arene complex and those of the products. An earlier study from our group examined the cycloaddition of a 2-(dimethylamino)pyridine complex (16B; Scheme 6) with various dienophiles.13 In that report, we found that the cycloadduct 17 was derived from a linkage isomer (16D) that made up less than 2% of the pyridine complex (16) at equilibrium. In contrast to those findings, all cycloaddition products reported herein were derived from the dominant constitutional isomer of the η2-arene precursor (1 and 3). However, the distribution of stereoisomers reported in Table 2 for the cycloadduct complexes does not correlate with that of their arene precursors. The prevalence of B isomers can be partly attributed to solubility characteristics (B isomers are (13) Graham, P. M.; Delafuente, D. A.; Liu, W.; Myers, W. H.; Sabat, M.; Harman, W. D. J. Am. Chem. Soc. 2005, 127, 10568.

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Scheme 6. Linkage Isomerization and Cycloaddition of DMAP Complex

generally less soluble than the A isomers; vide supra). However, when these reactions were monitored in methylene chloride, a solvent in which all isomers were soluble, the B isomers proved to be more reactive than their coordination diastereomers (A) in every case. The most illustrative example of this contrasting reactivity is found in the cycloaddition of DMAD and the DMB complex, where an 8.7:1 ratio of rate constants is observed (vide supra). The origin of the bias for formation of B cycloadducts does not appear to be steric strain in the transition state, since the face of the ring that is approached by the dienophile is unencumbered for either coordination diastereomer. Nor can this difference be attributed to thermodynamic differences in the product: When a sample of the fumaronitrile cycloadduct exo-6B is allowed to stand in solution, an equilibrium is established of all four isomers, indicating that the thermodynamic preference is for the exo-A isomer. Rather, there appears to be an electronic bias in the transition states for the cycloaddition of the coordination diastereomers. We postulate that the transition state for these cycloaddition reactions has significant conjugate addition character. Purportedly, the bond between the anisole C4 and the dienophile β-carbon is formed earlier than the C1-R-carbon bond (Scheme 7). This notion is supported by the observation that these cycloaddition reactions occur significantly faster in protic solvents, which can stabilize the buildup of negative charge in the transition state. An asynchronous cycloaddition transition state would result in a buildup of positive charge in either quadrant A or D.14 The preference for B cycloadducts would thus require an energetic preference for the former scenario. The observations described above also led us to reevaluate previous studies with the {TpW(NO)(PMe3)} system in order to determine the extent to which the proposed stereoelectronic effect may have impacted the reactivity of other complexes of carbocations derived from aromatic molecules. Previous studies involving aromatic complexes of {TpW(NO)(PMe3)} and their reactions have reported equilibrium ratios of coordination diastereomers for various cationic π-ligands (Scheme 8). For example, the complex TpW(NO)(PMe3)(5,6-2H-anisolium) (18) was shown to have a strong thermodynamic bias (favored by >2 kcal/mol) for the coordination diastereomer with the methoxy group oriented (14) Harman, W. D. Coord. Chem. Rev. 2004, 853.

Salomon et al. Scheme 7. Asynchronous Transition State for Cycloaddition Reaction

away from the PMe3 (B).15 Similarly, the 2H-thiophenium complex, prepared by protonation of the 2,5-dimethylthiophene complex 19,16 has a coordination diastereomer equilibrium ratio that heavily favors the isomer in which the sp3 ring carbon is oriented toward the PMe3 group. Furthermore, the recent preparation of the acylpyridinium complex 20 shows a thermodynamic preference of 10:1 favoring that isomer with the N-acetyl group oriented away from the PMe3.17 Finally, 13C data for the allyl complex 21 indicate highly asymmetrical allyl binding, where the chemical shift of the terminal allyl carbon in quadrant A (151 ppm) indicates significant carbocation character.18,19 Supporting this notion is an earlier reported crystal structure of the molybdenum congener TpMo(NO)(MeIm)(η3-C6H9), which shows a long C1-Mo bond length of 2.63 A˚ and a 13C resonance for this carbon at 126 ppm.15,20 While steric factors vary widely for the tungsten examples in Scheme 8, common to all is significant π-allyl character and the preference to distort the allyl ligand such that a positive charge buildup occurs in quadrant A rather than quadrant D (quadrants B and C are sterically disadvantageous).21 In order to better understand the origins of the stereoelectronic properties of {TpW(NO)(PMe3)}, an electrostatic (15) Keane, J. M.; Chordia, M. D.; Mocella, C. J.; Sabat, M.; Trindle, C. O.; Harman, W. D. J. Am. Chem. Soc. 2004, 126, 6806. (16) Delafuente, D. A.; Myers, W. H.; Sabat, M.; Harman, W. D. Organometallics 2005, 23, 3772–3779. (17) Harrison, D. P.; Welch, K. D.; Nichols-Nielander, A. C.; Sabat, M.; Myers, W. H.; Harman, W. D. J. Am. Chem. Soc. 2008, 130, 16844. (18) Lis, E. C.; Delafuente, D. A.; Lin, Y.; Mocella, C. J.; Todd, M. A.; Liu, W.; Sabat, M.; Myers, W. H.; Harman, W. D. Organometallics 2006, 25, 5051. (19) DFT calculations for the related system TpRe(CO)(MeIm)(naphthalenium) indicate two conformational energy minima for this type of asymmetric allyl species. See: Lis, E. C.; Delafuente, D. A.; Lin, Y.; Mocella, C. J.; Todd, M. A.; Liu, W.; Sabat, M.; Myers, W. H.; Harman, W. D. Organometllics 2006, 25, 5051. (20) Mocella, C. J.; Delafuente, D. A.; Keane, J. M.; Warner, G. R.; Friedman, L. A.; Sabat, M.; Harman, W. D. Organometallics 2004, 23, 3772. (21) This was first briefly noted in ref 11.

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Figure 4. Electrostatic potential mapped onto an isodensity surface for {TpW(NO)(PMe3)} (red indicates negative charge and blue indicates positive charge). Scheme 8. Equilibrium Ratios (20 °C) of Several Complexes of {TpW(NO)(PMe3)} with Cationic π-Allyl Character

potential map for this fragment was generated by DFT methods (Figure 4). The light blue color about the PMe3 indicates a repulsion with a positive test charge, as would be expected for a phosphonium-like species.22 The charge distribution suggests that a cationic ligand bound to{TpW(NO)(PMe3)}will be oriented such that positive charge is directed away from the phosphorus (i.e., to quadrant A over D). The property of{TpW(NO)(PMe3)} to direct positive charge away from quadrant D (see Figure 4) not only influences the relative rates of cycloaddition for arenes but also appears to have a profound effect on the desymmetrization of other cycloadducts. For example, we recently reported on the ability of furan23 (22) Here GAUSSIAN03W rev D has computed the charge distribution from a LSDA/LANL2DZ wave function; the density isosurface, displayed by GAUSSVIEW 3.09, is 0.0004 electron per cubic Bohr, and the electrostatic potential is evaluated only on that surface. The color coding defines red as the most negative potential (stabilizing to a positive test charge). Only the O atom of NO is so extreme on the molecular periphery. Blue is most positive; intermediate values follow the spectral order; that is, green represents a less positive potential relative to blue. That is, the trimethylphosphine fragment at top is more positive than the scorpionate zone at bottom. The range of potentials is roughly 0.065 atomic unit (hartrees per electron). (23) Bassett, K. C.; You, F.; Graham, P. M.; Myers, W. H.; Sabat, M.; Harman, W. D. Organometallics 2005, 25, 435.


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and 2,5-dimethylpyrrole24 complexes of {TpW(NO)PMe3} to undergo dipolar cycloaddition reactions. In the case of the pyrrole fumarate cycloadduct, two different isomers (22 and 24) of the azabicyclo[2.2.1]heptene ligand were found to undergo retro-Mannich reactions in the presence of methanol. Independent of the stereochemistry at the carbomethoxy-substituted bicyclic carbons, the retro-Mannich occurred in such a way as to form a 2H-pyrrolium intermediate (23 and 25) with the iminium carbon distal to PMe3. What now becomes clear is that this stereoisomer is favored because the partial positive charge of the iminium carbon is in quadrant A. In order to test the generality of this process, we resynthesized the complex (26) of the meso cycloadduct prepared from 2,5-dimethylfuran and N-phenylmaleimide.23 While this complex was stable in methanol, treatment with triflic acid resulted in a single isomer of the 2H-furanium complex 27. As anticipated, the oxonium carbon was determined by extensive spectral data to be in quadrant A. Key spectral features for this complex include an oxonium 13C resonance at 210.8 ppm and a CO stretch at 1708 cm-1. NOESY and gHMBC data confirm that the furan ring is intact and that the methyl group connected to the sp3 ring carbon is oriented toward the PMe3. Also significant are proton and carbon data associated with the bound ring carbons (4.90 (JPH =12.5 Hz), 3.61 ppm; 78.8, 70.2 ppm) that show unambiguously that the metal retains its η2-coordination rather than adopting an η3-geometry. Summary. The arenes anisole and DMB were found to undergo cycloaddition with several dienophiles to generate bicyclooctene and bicyclooctadiene complexes. In some cases these delicate molecules could be removed by oxidation of the metal. Although the limited scope, poor stereocontrol, and modest yields make the present system impractical for organic synthesis, an unexpected stereoelectronic effect was uncovered, resulting in significant differences in cycloaddition rates for the two arene coordination diastereomers. While the stereoelectronic property of {TpW(NO)(PMe3)} only subtlety affects rates of cycloaddition, it can lead to a high degree of stereospecificity in the ring-opening of mesocycloadducts and is potentially able to have a significant ability to desymmetrize other organic ligands involving allylic cation intermediates.

Experimental Section General Methods. NMR spectra were obtained on either a 300 or 500 MHz Varian INOVA spectrometer. All chemical shifts are reported in ppm and are referenced to tetramethylsilane using residual shifts of the deuterated solvent as the internal standard. All coupling constants (J) are in hertz (Hz). 31P NMR spectra are reported using the reported literature value versus H3PO4 for triphenylphosphate (δ=-16.58 ppm) as the internal standard. Infrared spectra (IR) were obtained on a MIDAC Prospect Series spectrometer as a glaze on a horizontal attenuated total reflectance (HATR) cell (Pike Industries). Electrochemical experiments were taken under a dinitrogen atmosphere using a BAS Epsilon EC-2000 potentiostat. Cyclic voltametric (CV) data were obtained at 100 mV/s at ambient temperature in a three-electrode cell from þ1.7 to -1.7 V with a glassy carbon electrode. N,N-Dimethylacetamide (DMA) was the solvent with tetrabutylammonium hexafluorophosphate (TBAH) as the electrolyte. All potentials are reported versus NHE (normal hydrogen electrode) using colbaticinium hexafluorophosphate (E1/2= -0.78 V) as the internal standard. For all reversible waves the (24) Welch, K. D.; Smith, P. L.; Keller, A. P.; Myers, W. H.; Sabat, M.; Harman, W. D. Organometallics 2006, 25, 5067.

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Scheme 9. Desymmetrization of Cycloadducts Using {TpW(NO)(PMe3)}

peak to peak separation was less than 100 mV. High-resolution mass spectrometry data (HRMS) were obtained from the University of Illinois Urbana-Champaign School of Chemical Sciences or the University of Richmond. Elemental analysis (EA) was obtained from Atlantic Microlabs, Inc. All reactions were performed under a dinitrogen atmosphere in a Vacuum Atmospheres glovebox. Chromatography was performed in a hood on 60-325 mesh alumina adsorption available from Fisher Scientific. All solvents were purged thoroughly with nitrogen before being used. CH2Cl2 was purged with nitrogen, then run through a column packed with activated alumina. All deuterated solvents were received from Cambridge Isotopes, and all other reagents were used as received from Sigma-Aldrich or Acros Chemicals. Proton and carbon chemical shift assignments are only in cases where they can be unambiguously assigned with the aid of COSY, HSQC, HMBC, and/or NOESY data. TpW(NO)(PMe3)(10,11-η2-1-methoxy-4-methyl-4-aza-tricyclo[5.2.2.02,6]undeca-8,10-diene-3,5-dione) (2). To a screw-cap test tube were added TpW(NO)(PMe3)(η2-anisole) (0.090 g, 1.47 10-4 mol) and a stirbar. In a second screw-cap test tube NMM (0.034 g, 3.06 10-4 mol) was dissolved in DME (1.921 g). The test tubes were then cooled to 0 °C for 0.5 h. The solution was added to the solid and the reaction stirred at 0° for 25 h. A 10 mL amount of pentane was added to the reaction, whereupon a tan precipitate formed. This was collected on a 15 mL medium-porosity fritted glass funnel and washed with minimal pentane. The tan solid was dried in vacuo and collected as a 1:1 mixture of isomers, endo-A:endo-B (0.081 g, 1.12 10-4 mol, 76.1%). 1H NMR (500 MHz, CDCl3): δ 8.63 (1H, d, J=2, Tp 3,5), 8.09 (1H, d, J=2, Tp 3,5), 8.07 (1H, d, J= 2, Tp 3,5), 7.90 (1H, d, J=2, Tp 3,5), 7.72 (1H, d, J=2, Tp 3,5), 7.69 (3H, m, Tp 3,50 s), 7.55 (1H, d, J=2, Tp 3,5), 7.51 (1H, d, J=2, Tp 3,5), 7.33 (1H, d, J=2, Tp 3,5), 7.27 (1H, d, J=2, Tp 3,5), 6.29 (1H, t, J=2, Tp 4), 6.28 (1H, t, J=2, Tp 4), 6.22 (1H, t, J=2, Tp 4), 6.20 (1H, t, J=2, Tp 4), 6.19 (1H, d, J=2, Tp 4), 6.15 (1H, t, J=2, Tp 4), 6.14 (1H, d, J=8, H9A), 6.09 (1H, d, J=6.5, H9B), 6.06 (1H, dd, J= 8, 6, H8A), 5.82 (1H, dd, J=8, 6, H8B), 3.84 (3H, s, H12A OMe), 3.76 (1H, m, H7A), 3.71 (1H, m, H7B), 3.44 (1H, d, J=8, H2B), 3.41 (1H, d, J=8, H2A), 3.39 (3H, s, H12B OMe), 3.33 (1H, dd, J=8, 3, H6B), 3.15 (1H, dd, H6A), 2.91 (3H, s, H13A NMe), 2.90 (3H, s, H13B NMe), 2.73 (1H, t, J=10, H10A), 2.47 (1H, m, H11B), 1.79 (1H, d, J=10, H10B), 1.48 (1H, dt, J=10, 3, H11A), 1.31 (9H, d, J= 9, PMe3A), 1.26 (9H, d, J=8, PMe3B). 13C NMR (CDCl3): δ 179.0 (C3B), 178.9 (C3A), 177.3 (C5A), 176.3 (C5B), 148.0 (Tp 3,5), 144.1 (Tp 3,5), 143.4 (Tp 3,5), 143.3 (Tp 3,5), 140.9 (Tp 3,5), 140.7 (Tp 3,5), 136.7 (Tp 3,5), 136.5 (Tp 3,5), 135.9 (Tp 3,5), 135.7 (2C, C9B and Tp 3,5), 134.7 (Tp 3,5), 134.5 (Tp 3,5), 131.4 (C9A), 128.0 (C8A), 126.2

(C8B), 106.4 (Tp 4), 106.3 (Tp 4), 105.9 (Tp 4), 105.6 (Tp 4), 105.5 (Tp 4), 105.4 (Tp 4), 89.5 (C1A), 88.9 (C1B), 58.5 (C11A), 58.2 (C10A, d, J=15), 57.3 (C11B, d, J=16), 52.9 (3C, C10B, C6A, and C12A (OMe), 52.3 (C2A), 50.1 (C12B OMe), 48.8 (C2B), 41.4 (C7B), 40.4 (C7A), 24.5 (C13A NMe), 24.4 (C13B NMe), 14.7 (3C, PMe3A, d, J=28), 13.9 (3C, PMe3B, d, J=28). Ep,a=þ0.68 V. IR (HATR): ν(NO) 1558 cm-1, ν(BH) 2485 cm-1, ν(CO) 1690 cm-1. 31 P NMR (CDCl3): δ -12.9 (JPW=275 Hz), -11.5 (B, JPW=264 Hz). Anal. Calcd for C24H32BN8O4PW 3 0.5C4O2H10: C, 40.70; H, 4.86; N, 14.60. Found: C, 41.13; H, 4.72; N, 14.84. TpW(NO)(PMe3)(10,11-η2-1,8-dimethoxy-4-methyl-4-azatricyclo[5.2.2.02,6]undeca-8,10-diene-3,5-dione) (4). To a screw-cap test tube were added TpW(NO)(PMe3)(η2-1,3-dimethoxybenzene) (0.394 g, 6.15 10-4 mol) and a stirbar. In a second screw-cap test tube NMM (0.081 g, 7.3010-4 mol) was dissolved in DME (6.041 g). The test tubes were then cooled to 0 °C for 0.5 h. The solution was added to the solid and the reaction stirred at 0 °C for 24 h. A white precipitate formed in the reaction mixture. This was collected on a 15 mL medium-porosity fritted glass funnel and washed with minimal DME. The white solid was dried in vacuo and collected as a single isomer, B (0.186 g, 2.47 10-4 mol, 40.3%). The filtrate from above was added to 75 mL of stirring hexanes, whereupon a tan precipitate formed. The tan solid was collected on a 15 mL medium-porosity fritted glass funnel and dried in vacuo. The solid was collected as a 10:1:1 ratio of three isomers, A, B, and C (0.193 g, 2.56 10-4 mol, 41.7%). 1H NMR (500 MHz, CDCl3): δ 8.66 (1H, d, J=2, Tp 3,5B), 8.14 (1H, d, J=2, Tp 3,5A), 8.08 (2H, d, J=2, Tp 3,5B and Tp 3,5A), 7.72 (1H, d, J=2, Tp 3,5 B), 7.70 (3H, d, J=2, Tp 3,5 B, Tp 3,50 s A), 7.55 (1H, d, J=2, Tp 3,5A), 7.51 (1H, d, J=2, Tp 3,5B), 7.31 (1H, d, J=2, Tp 3,5B), 7.20 (1H, d, J=2, Tp 3,5A), 6.29 (1H, t, J=2, Tp 4A), 6.28 (1H, t, J=2, Tp 4B), 6.21 (1H, t, J=2, Tp 4B), 6.19 (2H, m, Tp 4’s A), 6.16 (1H, t, J=2, Tp 4B), 4.83 (1H, s, H9A), 4.76 (1H, d, J=2, H9B), 3.82 (3H, s, C1A OMe), 3.62 (3H, s, C8A OMe), 3.52 (3H, s, C8B OMe), 3.50 (2H, dd, J=3, 6, H7A and H7B), 3.45 (1H, d, J=7.5, H10 B), 3.41 (3H, s, C1B OMe), 3.39 (1H, d, J=15, H2A), 3.32 (1H, dd, J=3.5, 7.5, H6B), 3.12 (1H, dd, J=4, 8, H6A), 2.93 (3H, s, NMeA), 2.91 (3H, s, NMeB), 2.82 (1H, t, J= 11, H10A), 2.31 (1H, ddd, J=3, 10.5, 12.5, H11B), 1.81 (1H, dd, J= 2.5, 10.5, H10B), 1.33 (9H, d, J = 9, PMe3A), 1.29 (1H, buried, H11A), 1.27 (9H, d, J=8.5, PMe3B). 13C NMR (CDCl3): δ 178.3 (C3A), 178.2 (C3B), 177.6 (C5A), 176.5 (C5B), 155.8 (C8A), 154.0 (C8B), 148.0 (Tp 3,5B), 144.8 (Tp 3,5A), 142.9 (Tp 3,5B), 142.8 (Tp 3,5A), 140.6 (Tp 3,5A), 140.5 (Tp 3,5B), 136.7 (Tp 3,5B), 136.4 (Tp 3,5A), 135.8 (Tp 3,5A), 135.6 (Tp 3,5B), 134.6 (Tp 3,5A), 134.5 (Tp 3,5B), 106.3 (2C, Tp 4A and Tp 4B), 106.1 (Tp 4A), 105.7 (Tp 4A), 105.6 (Tp 4B), 105.5 (Tp 4B), 98.7 (C9B), 94.3 (C9A), 90.7 (C1A), 90.0 (C1B), 60.5 (C10A, d, J = 14), 58.6 (C11A), 56.4 (C11B, d,

Article J = 16), 55.7 (C8A OMe), 55.6 (2C, C7A and C1B OMe), 55.2 (C10B), 53.9 (C2A), 53.1 (C6B), 53.0 (C1A OMe), 52.1 (C6A), 50.5 (C8B OMe), 50.1 (C2B), 43.9 (C7B), 24.4 (NMeA), 24.3 (NMeB), 14.4 (PMe3A, d, J=28), 13.1 (PMe3B, d, J=28). Ep,a=þ0.69 V. IR (HATR): ν(NO) 1558 cm-1, ν(BH) 2476 cm-1, ν(CO) 1693 cm-1. 31P (CDCl3): δ -13.0 (A, JPW =271 Hz), -12.2 (B, JPW = 264 Hz). HRMS: [M þ H] obsd (%), calcd (%), ppm, 751.2054 (81.3), 751.2043 (86), 1.5; 752.2089 (76.7), 752.2063 (47), 3.5; 753.2081 (100), 753.207 (100), 1.5; 754.2136 (42.5), 754.2104 (27), 4.2; 755.211 (84.6), 755.2105 (93), 0.7. TpW(NO)(PMe3)(7,8-η2-1-methoxybicyclo[2.2.2]octa-5,7diene-2,3-dicarbonitrile) (5). To a screw-cap test tube were added TpW(NO)(PMe3)(η2-anisole) (0.215 g, 3.5210-4 mol) and fumaronitrile (0.053 g, 6.78 10-4 mol), and the mixture was cooled to 0 °C for 0.5 h. MeOH (1.005 g) at 0 °C was added and reaction stirred for 6 days. A white precipitate formed in the reaction. This was collected on a 30 mL fine-porosity fritted glass funnel and washed with minimal hexanes. The white solid was dried in vacuo and collected as a 1:1 mixture of isomers, A and B (0.183 g, 2.65 10-4 mol, 75.4%). 1H NMR (300 MHz, acetone-d6): δ 8.75 (1H, d, J = 1.7, Tp 3,5), 8.17 (1H, d, J = 1.7, Tp 3,5), 8.13 (1H, d, J = 1.8, Tp 3,5), 7.96 (1H, d, J = 2.1, Tp 3,5), 7.93 (3H, d, J = 2.2, Tp 3,5s), 7.91 (1H, d, J = 2.2, Tp 3,5), 7.71 (1H, d, J = 2.2, Tp 3,5), 7.67 (1H, d, J = 2.2, Tp 3,5), 7.65 (1H, d, J = 1.8, Tp 3,5), 7.36 (1H, d, J = 1.8, Tp 3,5), 6.46 (1H, d, J = 8.7, H6B), 6.41 (2H, t, J = 2, Tp 4), 6.33 (1H, t, J = 2.1, Tp 4), 6.28 (3H, m, H6A and 2 Tp 4s), 6.28 (1H, t, J = 2.1, Tp 4), 6.22 (1H, dd, J = 8.7, 6.2, H5A), 6.01 (1H, dd, J = 8.7, 6.3, H5B), 3.78 (1H, br m, H4B), 3.63 (1H, s, OMeA), 3.62 (4H, s, OMeB and H4A), 3.57 (1H, dd, J = 4.6, 2.5, H3B), 3.51 (1H, d, J = 4.6, H2A), 3.49 (1H, d, J = 4.6, H2B), 3.34 (1H, dd, J = 4.6, 2.6, H3A), 2.83 (1H, m, H7A), 2.75 (1H, ddd, J = 10.0, 2.7, 1.2, H8B), 1.78 (1H, ddd, J = 12, 10, 3, H7B), 1.34 (9H, d, J = 9.0, PMe3A), 1.28 (1H, buried, H8A), 1.27 (9H, d, J = 8.5, PMe3B). 13C NMR (acetone-d6): δ 150.3 (Tp 3,5), 146.0 (Tp 3,5), 145.4 (Tp 3,5), 145.2 (Tp 3,5), 143.5 (Tp 3,5), 142.9 (Tp 3,5), 138.9 (Tp 3,5), 138.7 (Tp 3,5), 138.0 (Tp 3,5), 137.9 (Tp 3,5), 136.9 (Tp 3,5), 136.7 (Tp 3,5), 136.3 (C6B), 134.7 (C6A), 131.6 (C5A), 130.3 (C5B), 122.9 (CNA), 122.8 (CNB), 121.3 (CNA), 121.2 (CNB), 108.1 (2C, Tp 4s), 107.8 (2C, Tp 4s), 107.6 (Tp 4), 106.9 (Tp 4), 91.9 (C1B), 90.8 (C1A), 57.6 (C8A), 57.6 (d, J = 15, C8B), 54.7 (d, J = 15, C7A), 53.5 (C7B), 53.0 (OMeA and OMeB), 44.7 (C4B), 43.4 (C4A), 42.1 (C3B), 41.7 (C3A), 41.2 (C2B), 40.8 (C2A), 15.1 (3C, d, J = 29, PMe3A),14.6 (3C, d, J = 29, PMe3B). 31P NMR (acetone-d6): δ -10.6 (JPW=270 Hz), -11.8 (JPW=265 Hz). CV: Ep,a=0.85 V. IR (HATR): ν(NO) 1562 cm-1, ν(BH) 2484 cm-1, ν(CN) 2237 cm-1. HRMS: [M þ H]þ obsd (%), calcd (%), ppm, 688.18184 (82.9), 688.18397 (83.5), 3.1; 689.1866 (79.2), 689.18649 (80.5), 0.2; 690.18475 (100), 690.18638 (100), 2.4; 691.19004 (36), 691.19041 (44.3), 0.5; 692.18901 (86.1), 692.18962 (83.4), 0.9. TpW(NO)(PMe3)(7,8-η2-1,5-dimethoxybicyclo[2.2.2]octa5,7-diene-2,3-dicarbonitrile) (6). Single Isomer: To a 4 dram vial were added TpW(NO)(PMe3)(η2-1,3-dimethoxybenzene) (0.244 g, 3.81 10-4 mol), fumaronitrile (0.155 g, 1.98 10-3 mol), and a stirbar. This was then dissolved in DME (1.018 g), and 8 mL of Et2O was added, producing a yellow precipitate. The heterogeneous mixture was stirred for 19 h, during which the precipitate had become light brown. This was collected on a 15 mL fine-porosity fritted glass funnel. The light brown solid was dried in vacuo and collected as a single isomer, exo-B (0.072 g, 1.0010-4 mol, 26%). All Isomers: To a screw-cap test tube were added TpW(NO)(PMe3)(η2-1,3-dimethoxybenzene) (0.515 g, 8.03 10-4 mol) and fumaronitrile (0.342 g, 4.38 10-3 mol). This was cooled to 0 °C for 45 min. To this a 0 °C solution of DME was added and reaction stirred as a homogeneous brown mixture for 21.5 h. The brown solution was then added to 100 mL of stirring hexanes, whereupon a tan precipitate formed. The precipitate was collected on a 30 mL fine-porosity fritted glass funnel. The tan solid was dried in vacuo and collected as a 3:1:7:3 ratio of isomers exo-B: endo-A:endo-B:exo-A (0.500 g, 6.95 10-4 mol, 86%). NMR characterization for exo-B: 1H NMR (500 MHz, CDCl3): δ 8.74


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(1H, d, J=2, Tp 3,5), 8.14 (1H, d, J=2, Tp 3,5), 7.74 (1H, d, J=2, Tp 3,5), 7,69 (1H, d, J=2, Tp 3,5), 7.50 (1H, d, J=2, Tp 3,5), 7.31 (1H, d, J=2, Tp 3,5), 6.33 (1H, t, J=2, Tp 4), 6.18 (1H, t, J=2, Tp 4), 6.15 (1H, t, J=2, Tp 4), 5.16 (1H, s, H6), 3.71 (3H, s, H10 OMe), 3.61 (3H, s, H9 OMe), 3.41 (2H, buried, H4 and H2), 3.32 (1H, m, H3), 2.21 (1H, dt, J=11, 3, H8), 2.01 (1H, dd, J=11, 2, H7), 1.22 (9H, d, J=8, PMe3). 13C NMR (CDCl3): δ 155.3 (C5), 148.7 (Tp 3,5), 142.7 (Tp 3,5), 140.8 (Tp 3,5), 136.8 (Tp 3,5), 135.7 (Tp 3,5), 134.6 (Tp 3,5), 120. Two (CN), 119.8 (CN), 106.5 (Tp 4), 105.9 (Tp 4), 105.5 (Tp 4), 97.4 (C6), 90.3 (C1), 55.8 (C10 OMe), 55.0 (C8, d, J=16), 54.9 (C7), 51.8 (C9 OMe), 45.7 (C4), 41.0 (C2), 40.5 (C3), 13.4 (3C, PMe3, d, J = 28). 31P NMR (CDCl3): δ -12.8 (JPW = 259 Hz). NMR characterization for exo-A, 1H NMR (500 MHz, CDCl3): δ 8.05 (1H, d, J = 1.7 Hz, Tp 3,5), 8.01 (1H, d, J = 1.7 Hz, Tp 3,5), 7.71 (1H, d, J = 1.9 Hz, Tp 3,5), 7.68 (1H, d, J = 2.1 Hz, Tp 3,5), 7.56 (1H, d, J = 1.9 Hz, Tp 3,5), 7.18 (1H, d, J = 1.8 Hz, Tp 3,5), 6.31 (1H, t, J = 2.2 Hz, Tp 4), 6.2 (1H, t, J = 2.2 Hz, Tp 4), 6.17 (1H, t, J = 2.2 Hz, Tp 4), 4.94 (1H, d, J = 1.4 Hz, H6), 3.75 (3H, s, C5 OMe), 3.57 (3H, s, C1 OMe), 3.37 (1H, d, J = 4.6 Hz, H2), 3.35 (1H, m, H4), 3.07 (1H, dd, J = 4.2, 2.8 Hz, H3), 2.93 (1H, dd, J = 13.3, 10.5 Hz, H7), 1.31 (9H, d, J = 8.9 Hz, PMe3), 1.17 (1H, ddd, J = 10.2, 3.9, 2.4 Hz, H8). 13C NMR (CDCl3): δ 156.9 (C5), 144.4 (Tp 3,5), 142.8 (Tp 3,5), 140.7 (Tp 3,5), 136.5 (Tp 3,5), 135.9 (Tp 3,5), 134.8 (Tp 3,5), 120.4 (CN), 119.6 (CN), 106.5 (Tp 4), 106.2 (Tp 4), 106 (Tp 4), 95.8 (C6), 90.1 (C1), 56 (C5 OMe), 55.8 (C8), 55.4 (d, J = 15, C7), 51.6 (C1 OMe), 44.1 (C4), 40.5 (C2), 39.4 (C3), 13.8 (3C, d, J = 29, PMe3). All isomers: Ep,a=0.87 V. IR (HATR): ν(NO) 1562 cm-1, ν(BH) 2488 cm-1, ν(CN) 2236 cm-1. HRMS: [M þ H]þ obsd (%), calcd (%), ppm, 718.19513 (78.9), 718.19455 (82.8), 0.8; 719.19596 (79.6), 719.19707 (80.7), 1.5; 720.19685 (100), 720.19698 (100), 0.2; 721.19839 (49.2), 721.20096 (45.1), 3.6; 722.19977 (95.3), 722.20021 (83.2), 0.6. TpW(NO)(PMe3)(7,8-η2-1,5-dimethoxybicyclo[2.2.2]octa5,7-diene-2-carbonitrile) (7). To a screw-cap test tube were added TpW(NO)(PMe3)(η2-1,3-dimethoxybenzene) (0.494 g, 7.70 10-4 mol) and a solution of acrylonitrile (0.407 g, 7.67 10-3 mol) in MeOH (2.503 g). Both were cooled to 0 °C for 0.5 h. The solution was added to the solid, and the reaction stirred as a heterogeneous yellow mixture for 7 days. A white precipitate formed in the reaction. This was collected on a 30 mL fine-porosity fritted glass funnel and washed with 3 mL of cold MeOH and minimal hexanes. The white solid was dried in vacuo and collected as 1.1:1 mixture of exo-A:exoB (0.194 g, 2.79 10-4 mol, 36.2%). 1H NMR (500 MHz, acetoned6): δ 8.94 (1H, d, J=2, Tp 3,5), 8.18 (1H, d, J=2, Tp 3,5), 8.12 (1H, d, J=2, Tp 3,5), 8.09 (1H, d, J=2, Tp 3,5), 7.94 (2H, buried, Tp 3,50 s), 7.92 (1H, d, J=2, Tp 3,5), 7.89 (1H, d, J=2, Tp 3,5), 7.76 (1H, d, J=2, Tp 3,5), 7.67 (1H, d, J=2, Tp 3,5), 7.66 (1H, d, J=2, Tp 3,5), 7.32 (1H, d, J=2, Tp 3,5), 6.40 (2H, buried, Tp 4’s), 6.32 (1H, t, J=2, Tp 4), 6.27 (2H, buried, Tp 4’s), 6.16 (1H, t, J=2, Tp 4), 4.94 (1H, d, J=1, H6B), 4.77 (1H, d, J=1, H6A), 3.64 (3H, s, H10A OMe), 3.59 (3H, s, H10B OMe), 3.56 (6H, s, H9A and H9B OMe’s), 3.27 (2H, buried, H2A and H2B), 3.09 (1H, buried, H4B), 3.06 (1H, buried, H7A), 2.93 (1H, m, H4A), 2.53 (1H, ddd, J=12.0, 10.5, 3.5, H8B), 2.45 (2H, buried, H3A and H3B), 2.09 (1H, ddd, J=12.0, 10.5, 2.5, H3B), 1.96 (1H, ddd, J=10, 3, 1, H7B), 1.83 (1H, ddd, J=12.0, 4.0, 3.0, H3A), 1.37 (9H, d, J=9, PMe3A), 1.27 (9H, d, J=9, PMe3B), 1.12 (1H, ddd, J=10, 3.5, 2, H8A). 13C NMR (acetone-d6): δ 161.0 (C5A), 159.7 (C5B), 150.6 (Tp 3,5), 145.9 (Tp 3,5), 144.9 (Tp 3,5), 144.8 (Tp 3,5), 143.5 (Tp 3,5), 142.7 (Tp 3,5), 138.8 (Tp 3,5), 138.5 (Tp 3,5), 137.8 (Tp 3,5), 137.6 (Tp 3,5), 136.5 (Tp 3,5), 124.2 (C11B CN), 124.0 (C11A CN), 108.0 (Tp 4), 107.9 (Tp 4), 107.7 (Tp 4), 107.5 (2C, Tp 4’s), 106.8 (Tp 4), 97.9 (C6B), 96.6 (C6A), 92.4 (C1B), 92.1 (C1A), 60. 0 (C8A), 59.4 (d, J=16, C8B), 58.2 (d, J=15, C7A), 57.7 (C7B), 56.6 (C10A OMe), 56.3 (C10B OMe), 52.4 (C9B OMe), 52.3 (C9A OMe), 43.0 (C4B), 41.0 (C4A), 40.5 (C3B), 39.5 (C3A), 36.4 (C2B), 35.9 (C2A), 15.0 (3C, d, J=29, PMe3A), 14.5 (3C, d, J= 28, PMe3B). 31P NMR (acetone-d6): δ -10.5 (JPW=268 Hz, B), 11.5 (JPW =273 Hz, A). CV: Ep,a =þ0.66 V. IR (HATR): ν(NO) 1554 cm-1, ν(BH) 2484 cm-1, ν(CN) 2229 cm-1. HRMS: [M þ H] obsd (%), calcd (%), ppm, 693.1998 (84.8), 693.1989 (85.7),

4732


1.3; 694.2034 (81.7), 694.2009 (46.6), 3.6; 695.202 (100), 695.2016 (100), 0.6; 696.2069 (45.8), 696.205 (24.8), 2.8; 697.2071 (83.8), 697.205 (93.2), 3. TpW(NO)(PMe3)(5,6-η2-dimethyl-1-methoxybicyclo[2.2.2] octa-2,5,7-triene-7,8-dicarboxylate) (8). In a 4 dram vial a solution of dimethyl acetylene dicarboxylate (0.063 g, 4.44 10-4 mol) in THF (1.018 g) was added to TpW(NO)(PMe3)(η2-anisole) (0.107 g, 1.75 10-4 mol) and stirred for 3 h. The reaction mixture was then added to 50 mL of stirring hexanes, whereupon a tan precipitate formed. This was collected on a 15 mL fine-porosity fritted glass funnel. The tan solid was dried in vacuo and collected as 1:4 ratio of isomers A:B (0.108 g, impure). 1H NMR (500 MHz, CDCl3): δ 8.44 (1H, d, J = 1.5, Tp 3,5), 8.10 (2H, d, J = 1.5, Tp 3,5s), 7.87 (1H, d, J = 1.0, Tp 3,5), 7.70 (2H, d, J = 1.5, Tp 3,5s), 7.66 (1H, d, J = 2.0, Tp 3,5), 7.64 (1H, d, J = 1.0, Tp 3,5), 7.52 (1H, d, J = 2.0, Tp 3,5), 7.47 (1H, d, J = 1.5, Tp 3,5), 7.37 (1H, d, J = 1.5, Tp 3,5), 7.32 (1H, d, J = 1.5, Tp 3,5), 6.76 (1H, d, J = 7.6, H2B), 6.60 (1H, dd, J = 7.5, 6.5, H3A), 6.55 (1H, d, J = 7.5, H2A), 6.29 (1H, buried, H3B), 6.29 (2H, m, Tp 4s), 6.21 (1H, t, J = 2.0, Tp 4), 6.16 (1H, t, J = 2.0, Tp 4), 6.15 (1H, t, J = 2.0, Tp 4), 6.13 (1H, t, J = 2.0, Tp 4), 4.63 (1H, m, H4B), 4.54 (1H, m, H4A), 3.88 (3H, s, C7 CO2MeA), 3.81 (3H, s, C7 CO2MeB), 3.76 (3H, s, C8 CO2MeB), 3.67 (3H, s, C8 CO2MeA), 3.64 (3H, s, C1 OMeA), 3.58 (3H, s, C1 OMeB), 3.14 (1H, dd, J = 12.2, 10.1, H6A), 2.91 (1H, ddd, J = 13.0, 10.0, 3.2, H5B), 2.21 (1H, ddd, J = 10.0, 2.8, H6B), 1.93 (1H, m, H5A), 1.32 (9H, d, J = 8.8, PMe3A), 1.26 (9H, d, J = 8.4, PMe3B). 13C NMR (CDCl3): δ 169.0 (2C, C7 CdO A and B), 165.0 (C8 CdOB), 164.9 (C8 C=OA), 159.7 (C7B), 157.4 (C7A), 147.9 (Tp 3,5), 144.5 (Tp 3,5), 143.5 (Tp 3,5), 143.4 (Tp 3,5), 143.3 (C8A), 141.5 (3C, Tp 3,5s), 141.2 (C8B), 136.5 (Tp 3,5), 136.3 (Tp 3,5), 135.8 (Tp 3,5), 135.0 (C2B), 134.4 (2C, Tp 3,5s), 133.3 (C3A), 131.9 (C2A), 131.5 (C3B), 106.4 (Tp 4), 106.3 (Tp 4), 105.9 (Tp 4), 105.8 (Tp 4), 105.6 (Tp 4), 105.2 (Tp 4), 98.1 (C1A), 97.7 (C1B), 67.7 (C5A), 65.7 (d, J = 18, C5B), 63.2 (C6B), 55.3 (C1 OMeA), 55.1 (C1 OMeB), 54.9 (d, J=18, C6A), 52.1 (C7 CO2MeB), 52 (C7 CO2MeA), 51.9 (C8 CO2MeB), 51.8 (C8 CO2MeA), 47.1 (C4B),45.6 (C4A),14.3 (3C, d, J = 29, PMe3A),13.9 (3C, d, J = 28, PMe3B). 31P NMR (acetone-d6): δ -10.5 (JPW=259 Hz B), -11.5 (JPW = 265 Hz, A). CV: Ep,a = þ0.84 V. IR (HATR): ν(NO) 1562 cm-1, ν(BH) 2495 cm-1, ν(CdO) 1728 cm-1. HRMS: [M þ H]þ obsd (%), calcd (%), ppm, 752.1869 (88.4), 752.1884 (85.7), 2; 753.1916 (85.1), 753.1904 (46.6), 1.6; 754.191 (100), 754.1911 (100), 0.1; 755.1971 (48.3), 755.1982 (24.8), 1.4; 756.1979 (86.2), 756.1945 (93.2), 4.4. TpW(NO)(PMe3)(7,8-η2-1,5-dimethoxybicyclo[2.2.2]octa2,5,7-triene-2,3-dicarboxylic acid dimethyl ester) (9). In a 4 dram vial a solution of dimethyl acetylene dicarboxylate (0.048 g, 3.38 10-4 mol) in THF (4.026 g) was added to TpW(NO)(PMe3)(η2-1,3dimethoxybenzene) (0.198 g, 3.08 10-4 mol) and stirred for 3 h. The reaction mixture was then added to 50 mL of stirring hexanes, whereupon a tan precipitate formed. This was collected on a 15 mL fine-porosity fritted glass funnel. The tan solid was dried in vacuo and collected as 11:1 ratio of isomers B:A (0.153 g, 1.95 10-4 mol, 63.2%). 1H NMR (500 MHz, CDCl3): δ 8.56 (1H, d, J = 1.7 Hz, Tp 3,5B), 8.12 (1H, d, J = 1.7 Hz, Tp 3,5B), 7.7 (1H, d, J = 2.2 Hz, Tp 3,5B), 7.66 (1H, d, J = 2.1 Hz, Tp 3,5B), 7.47 (1H, d, J = 2.2 Hz, Tp 3,5B), 7.39 (1H, d, J = 1.7 Hz, Tp 3,5B), 6.29 (1H, t, J = 2.1 Hz, Tp 4B), 6.15 (1H, t, J = 2.1 Hz, Tp 4B), 6.13 (1H, t, J = 2.2 Hz, Tp 4B), 5.42 (1H, d, J = 2.4 Hz, H6B), 5.2 (1H, d, J = 2.3 Hz, H6A), 4.28 (1H, t, J = 2.9 Hz, H4B), 4.17 (1H, t, J = 3.5 Hz, H4A), 3.91 (3H, s, OMeA), 3.82 (3H, s, C2 CO2MeB), 3.8 (3H, s, OMeA), 3.76 (3H, s, C3 CO2MeB), 3.71 (3H, s, C5 OMeB), 3.66 (3H, s, OMeA), 3.62 (3H, s, OMeA), 3.6 (3H, s, C1 OMeB), 3.27 (1H, dd, J = 13.7, 10.2 Hz, H7A), 2.81 (1H, ddd, J = 3.4, 10.4, 12.0 Hz, H8B), 2.28 (1H, dd, J = 3.1, 10.3 Hz, H7B), 1.86 (1H, ddd, J = 10.0, 4.0, 2.5 Hz, H8A), 1.33 (9H, d, J = 8.9 Hz, PMe3A), 1.26 (9H, d, J = 8.5 Hz, PMe3B). 13 C NMR (CDCl3): δ 169.1 (C2 CdOB), 164.9 (C3 CdOB), 162.4 (C2 or C3B), 161.8 (C5B), 148.2 (Tp 3,5B), 142.9 (Tp 3,5B), 141.4 (Tp 3,5B), 140 (C2 or C3B), 136.4 (Tp 3,5B), 135.6 (Tp 3,5B), 134.3 (Tp 3,5B), 106.3 (Tp 4B), 105.5 (2C, Tp 4B), 98.4 (C6B), 97.9 (C1B), 67 (d, J = 18, C8B), 65.6 (C7B), 56.3 (C5 (OMe)B), 54.9 (C1 (OMe)

Salomon et al. B), 52 (C2 OMeB), 51.9 (C3 OMeB), 48.6 (C4B), 13.7 (d, J = 28, PMe3B). 31P NMR (CDCl3): δ -10.9 (B, JPW=258 Hz), -11.6 (A, JPW=263 Hz). CV: Ep,a=þ0.82 V. IR (HATR): ν(NO) 1557 cm-1, ν(BH) 2488 cm-1, ν(CO) 1703 cm-1. HRMS: [M þ Na]þ obsd (%), calcd (%), ppm, 804.17857 (84.9), 804.18134 (81.5), 3.4; 805.18343 (77.5), 805.18389 (80.5), 0.6; 806.18402 (100), 806.18383 (100), 0.2; 807.18812 (47.7), 807.1878 (46.4), 0.4; 808.1861 (90.9), 808.18704 (83.1), 1.2. 3-(2,4-Dimethoxyphenyl)-1-methylpyrrolidine-2,5-dione (10). To a 4 dram vial were added (TpW(NO)(PMe3)(10,11-η2-1, 8-dimethoxy-4-methyl-4-aza-tricyclo[5.2.2.02,6]undeca-8,10diene-3,5-dione) (0.100 g, 1.33 10-4 mol) and cerric ammonium nitrate (0.168 g, 2.88 10-4 mol). CDCl3 (2.028 g) was added and the reaction stirred as a heterogeneous mixture for 26 h. The reaction mixture was then added to 50 mL of stirring hexanes and the orange precipitate filtered onto a 15 mL fine-porosity fritted glass funnel. The solvent was evaporated from the pale yellow filtrate. The yellow film was dissolved in CH2Cl2 and slowly loaded onto a glasssupported Al2O3 preparatory TLC plate (1000 μm 20 cm 20 cm) and eluted with 20% EtOAc in hexanes. The UV fluorescent band with a Rf=0.18 was removed from the plate. The alumina was stirred in CH3CN for 2 h. The alumina was then filtered over a 15 mL fine-porosity fritted glass funnel. The solvent was evaporated from the filtrate, resulting in a pale yellow film (0.003 g, 1.2 10-5 mol, 9%). Compound 10 has been previously reported.1,2 1H NMR (500 MHz, CDCl3): δ 7.07 (1H, d, J = 8.4, H6Ar), 6.46 (1H, buried, H5Ar), 6.45 (1H, s, H3Ar), 3.88 (1H, dd, J = 5.1, 9.6, H3), 3.80 (3H, s, C4Ar OMe), 3.72 (3H, s, C2Ar OMe), 3.07 (3H, s, NMe), 3.05 (1H, dd, J = 9.6, 18.1, H4syn), 2.72 (1H, dd, J = 5.1, 18.1, H4anti). 13C NMR (CDCl3): δ 179.0 (CdO), 177.0 (CdO), 160.9 (C4Ar), 157.8 (C2Ar), 131.1 (C6Ar), 118.2 (C1Ar), 104.4 (C5Ar), 99.3 (C3Ar), 55.5 (C2Ar OMe), 55.4 (C4Ar OMe), 43.3 (C3), 36.4 (C4), 24.9 (NMe). 1-Methoxy-4-methyl-4-aza-tricyclo[5.2.2.02,6]undec-10-ene3,5,8-trione (11). To a 4 dram vial were added (TpW(NO)(PMe3) (10,11-η2-1,8-dimethoxy-4-methyl-4-aza-tricyclo[5.2.2.02,6]undeca-8,10-diene-3,5-dione) (0.103 g, 1.3710-4 mol) and CuBr2 (0.086 g, 3.85 10-4 mol). Acetone-d6 (3.015 g) was added with 1 drop of H2O and the reaction stirred as a heterogeneous mixture for 3 days. The solvent was then evaporated, leaving a brown residue, which was dissolved in 2 mL of CH2Cl2 added to 50 mL of stirring hexanes. A brown precipitate formed and was filtered onto a 15 mL fine-porosity fritted glass funnel. The solvent was evaporated from the light brown filtrate. The brown film was dissolved in CH2Cl2 and slowly loaded onto a glasssupported Al2O3 preparatory TLC plate (1000 μm 20 cm 20 cm) and eluted with 20% EtOAc in hexanes. The UV fluorescent band with a Rf = 0.08 was removed from the plate. The alumina was stirred in CH3CN for 2 h. The alumina was then filtered over a 15 mL fine-porosity fritted glass funnel. The solvent was evaporated from the resulting filtrate, resulting in a pale yellow film (0.005 g, 2.0 10-5 mol, 15%). 1H NMR (500 MHz, CDCl3): 6.69 (1H, d, J = 8.0, H10), 6.36 (1H, ddd, J = 8.0, 6.0, 0.5, H11), 3.66 (1H, ddd, J = 6.0, 4.0, 1.0, H7), 3.59 (3H, s, OMe), 3.33 (1H, dd, J = 10.0, 2.5, H2), 3.18 (1H, dd, J = 10.0, 4.0, H6), 2.99 (3H, s, NMe), 2.47 (1H, dd, J = 18.0, 2.5, H9’), 2.12 (1H, d, J = 18.0, H9). 13C NMR (CDCl3): δ 202.7 (C8), 175.0 (C5), 174.1 (C3), 139.4 (C10), 127.0 (C11), 79.5 (C1), 52.3 (OMe), 49.1 (C7), 45.1 (C2), 44.1 (C6), 41.7 (C9), 25.0 (NMe). TpW(NO)(PMe3)(5,6-η2-1-methoxy-8-oxo-bicyclo[2.2.2]oct5-ene-2-carbonitrile) (12). TpW(NO)(PMe3)(7,8-η2-1,5-dimethoxybicyclo[2.2.2]octa-5,7-diene-2-carbonitrile) (0.201 g, 2.89 10-4 mol) was dissolved in acetone (2.186 g) in a 4 dram vial with a stirbar. To the heterogeneous tan mixture was added 12 drops of 1 M HClaq and the reaction stirred for 21.5 h. The reaction slowly became a heterogeneous off-white mixture. A white precipitate was collected on a 15 mL fine-porosity fritted glass funnel and dried in vacuo. The white solid was collected as a 1:2 mixture of exo-A:exo-B (0.113 g, 1.66 10-4 mol, 57%). The solvent was evaporated from the brown filtrate. The resulting

Article film was dissolved in CH2Cl2 and added to 50 mL of stirring hexanes, whereupon an off-white precipitate formed and was collected on a 15 mL fine-porosity fritted glass funnel. The solid was dried in vacuo and collected as a 11:1 ratio of exo-A:exo-B (0.043 g, 6.32 10-5 mol, 22%). The overall yield of the reaction was 79%. 1H NMR (500 MHz, CDCl3): δ 8.53 (1H, d, J = 2, Tp 3,5), 8.16 (1H, d, J = 2, Tp 3,5), 8.13 (1H, d, J = 2, Tp 3,5), 8.08 (1H, d, J = 2, Tp 3,5), 7.73 (1H, d, J = 2, Tp 3,5), 7.72 (1H, d, J = 2, Tp 3,5), 7.69 (2H, buried, Tp 3,5), 7.55 (1H, d, J = 2, Tp 3,5), 7.50 (1H, d, J=2, Tp 3,5), 7.3 (1H, d, J=2, Tp 3,5), 7.27 (1H, d, J = 2, Tp 3,5), 6.33 (1H, t, J=2, Tp 4), 6.31 (1H, t, J = 2, Tp 4), 6.20 (3H, m, Tp 4), 6.14 (1H, t, J = 2, Tp 4), 3.46 (2H, m, H2A and H2B), 3.44 (1H, s, OMeB), 3.42 (1H, s, OMeA), 3.1 (1H, buried, H6A), 3.03 (1H, buried, H4A), 3.01 (1H, buried, H4B), 3 (1H, d, J=18.5, H7B), 2.76 (1H, d, J = 18, H7A), 2.55 (1H, buried, H3A), 2.55 (1H, buried, H3B), 2.49 (1H, buried, H7B), 2.47 (1H, buried, H5B), 2.36 (1H, buried, H3B), 2.32 (1H, d, J = 18, H7A), 2.18 (1H, td, J = 3.5, 14.0, H3A), 2.1 (1H, d, J = 11.5, H6B), 1.34 (1H, d, J = 9, PMe3A), 1.23 (1H, buried, H5A), 1.21 (9H, d, J=8.5, PMe3B). 13 C NMR (CDCl3): δ 208.3 (C8B), 208.0 (C8A), 148.3 (Tp 3,5), 144.7 (Tp 3,5), 143.2 (Tp 3,5), 143.0 (Tp 3,5), 140.4 (Tp 3,5), 139.9 (Tp 3,5), 136.8 (Tp 3,5), 136.6 (Tp 3,5), 135.9 (Tp 3,5), 135.8 (Tp 3,5), 134.8 (Tp 3,5), 134.7 (Tp 3,5), 122.6 (CNB), 122.0 (CNA), 106.6 (Tp 4), 106.4 (Tp 4), 106.1 (Tp 4), 106.0 (2C, Tp 4), 105.4 (Tp 4), 86.3 (C1A), 86.0 (C1B), 55.9 (d, J = 15, C6A), 54.2 (C6B), 50.9 (d, J = 15 Hz, C5B), 50.3 (OMeB), 49.8 (C5A), 49.8 (OMeA), 49.0 (C4A), 47.8 (C7B), 46.2 (C4B), 45.6 (C7A), 36.8 (C3B), 35.5 (C3A), 34.5 (C2B), 33.6 (C2A), 14.0 (3C, d, J=29, PMe3A), 13.3 (3C, d, J=28, PMe3B). 31P NMR (acetone-d6): δ -10.7 (JPW =264 Hz, B), -11.8 (JPW =268 Hz, A). CV: Ep,a = þ0.81. IR (HATR): ν(NO) 1556 cm-1, ν(BH) 2488 cm-1, ν(CN) 2236 cm-1, ν(CO) 1724 cm-1. HRMS: [M þ Na]þ obsd (%), calcd (%), ppm, 701.16636 (82.8), 701.16557 (84.1), 1.1; 702.16824 (82.3), 702.16811 (80.2), 0.2; 703.16853 (100), 703.16797 (100), 0.8; 704.1716 (45), 704.17209 (43.4), 0.7; 705.17169 (88.3), 705.17121 (83.8), 0.7. TpW(NO)(PMe3)(7,8-η2-1-methoxy-5-oxobicyclo[2.2.2]oct7-ene-2,3-dicarbonitrile) (13). TpW(NO)(PMe3)(7,8-η2-1,5-dimethoxybicyclo[2.2.2]octa-5,7-diene-2,3-dicarbonitrile) (0.251 g, 3.49 10-4 mol) was dissolved in acetone (5.095 g) in a 4 dram vial with a stirbar. To the homogeneous brown mixture was added 12 drops of 1 M HClaq and the reaction stirred for 21 h. The solvent was evaporated, leaving a brown film, which was dissolved in CH2Cl2 and added to 50 mL of stirring hexanes, whereupon an off-white precipitate formed. The off-white precipitate was collected on a 15 mL fine-porosity fritted glass funnel and dried in vacuo. The offwhite solid was collected as a 1:1.2 mixture of exo-A:exo-B (0.213 g, 3.02 10-4 mol, 86%). 1H NMR (500 MHz, CDCl3): δ 8.47 (1H, d, J = 1.9, Tp 3,5), 8.16 (1H, d, J = 1.8, Tp 3,5), 8.13 (1H, d, J = 1.8, Tp 3,5), 8.03 (1H, d, J = 1.8, Tp 3,5), 7.75 (1H, d, J = 2.4, Tp 3,5), 7.74 (1H, d, J = 2.3, Tp 3,5), 7.72 (2H, m, Tp 3,5), 7.57 (1H, d, J = 2.4, Tp 3,5), 7.52 (1H, d, J = 2.4, Tp 3,5), 7.26 (1H, buried, Tp 3,5), 7.21 (1H, d, J = 2.1, Tp 3,5), 6.36 (1H, t, J=2.2, Tp 4), 6.34 (1H, t, J=2.2, Tp 4), 6.23 (2H, m, Tp 4), 6.21 (1H, t, J=2.2, Tp 4), 6.16 (1H, t, J=2.3, Tp 4), 3.69 (2H, d, J=4.1, H2A and H2A), 3.53 (1H, dd, J=3.3, 4.0, H3B), 3.47 (3H, s, OMe B), 3.46 (3H, s, OMe A), 3.31 (1H, m, H4A and H4B), 3.30 (1H, buried, H3A), 3.14 (1H, d, J= 18.7, H6B), 2.96 (1H, buried, H7A), 2.92 (1H, buried, H6A), 2.62 (1H, dd, J=18.7, 1.5, H6B), 2.46 (1H, d, J=18.5, H6A), 2.32 (1H, td, J=11.6, 3.8, H8B), 2.02 (1H, m, H7B), 1.33 (9H, d, J=8.9, PMe3A), 1.21 (9H, d, J=8.5, PMe3B), 1.16 (1H, ddd, J=2.2, 4.4, 11.6, H8A). 13 C NMR (CDCl3): δ 202.8 (C5B), 202.5 (C5A), 148.5 (Tp 3,5), 144.9 (Tp 3,5), 143.4 (Tp 3,5), 143.2 (Tp 3,5), 140.4 (Tp 3,5), 140.0 (Tp 3,5), 137.3 (Tp 3,5), 137.0 (Tp 3,5), 136.4 (Tp 3,5), 136.3 (Tp 3,5), 135.3 (Tp 3,5), 135.2 (Tp 3,5), 119.7 (CNA), 119.3 (CNB), 118.9 (CNA), 118.6 (CNB), 107.1 (Tp 4), 106.9 (Tp 4), 106.6 (Tp 4), 106.4 (2C, Tp 4), 105.8 (Tp 4), 86.42 (C1A), 86.1 (C1B), 54.8 (d, J=15, C7A), 53.4 (C7B), 52.4 (C4B), 50.8 (OMe B), 50.6 (OMe A), 50.3 (C4A), 49.6 (d, J=16, C8B), 48.1 (C8A), 47.6 (C6B), 45.7 (C6A),


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40.3 (C2B), 39.8 (C2A), 39.0 (C3B), 38.1 (C3A),14.05 (3C, d, J=29, PMe3A),13.5 (3C, d, J=29, PMe3B). 31P NMR (acetone-d6): δ 10.7 (JPW=264 Hz, B), -11.8 (JPW=268 Hz, A). CV: Ep,a=þ1.12 IR (HATR): ν(NO) 1566 cm-1, ν(BH) 2492 cm-1, ν(CN) 2241 cm-1, ν(CO) 1732 cm-1. HRMS: [M]þ obsd (%), calcd (%), ppm, 704.18047 (78.6), 704.17889 (83.4), 2.2; 705.18174 (91.8), 705.18141 (80.5), 0.5; 706.18263 (100), 706.1813 (100), 1.9; 707.18397 (54.5), 707.18532 (44.4), 1.9; 708.18768 (70), 708.18453 (83.5), 4.4. 1-Methoxy-8-oxo-bicyclo[2.2.2]oct-5-ene-2-carbonitrile (14). To a 4 dram vial were added (TpW(NO)(PMe3)(1-methoxy-8-oxobicyclo[2.2.2]oct-5-ene-2-carbonitrile) (0.101 g, 1.48 10-4 mol) and CuBr2 (0.085 g, 3.81 10-4 mol). CD3CN (2.041 g) was added and reaction stirred as a heterogeneous green mixture for 19.5 h. The solvent was evaporated from the reaction mixture. The resulting yellow residue was dissolved in CH2Cl2 and added to 50 mL of stirring hexanes. A yellow precipate was filtered over a 30 mL fineporosity fritted glass funnel. The solvent was evaporated from the filtrate, yielding a brown film. The film was dissolved in 1 mL of CH2Cl2 and purified via basic Al2O3 chromatography (elution with 20% EtOAc/hexanes, Rf = 0.36). After chromatography 0.018 g (1.04 10-4 mol, 70%) was isolated as a colorless oil. 1H NMR (500 MHz, CDCl3): δ 6.61 (1H, dd, J = 8.5, H6), 6.39 (1H, d, J = 8.5, 6.5, H5), 3.5 (3H, s, OMe), 3.26 (1H, m, H4), 3.16 (1H, dd, J = 4.5, 10.5, H2), 2.48 (1H, d, J = 18, H7b), 2.28 (1H, m, H3a), 2.19 (1H, d, J = 18, H7a), 1.97 (1H, td, J = 4.0, 14.0, H3b). 13C NMR (CDCl3): δ 204.7 (C8), 136.1 (C6), 128.0 (C5), 120.4 (CN), 79.2 (C1), 51.9 (OMe), 46.9 (C4), 41.4 (C7), 32.8 (C2), 27.7 (C3). IR (HATR): ν(CO) 1732 cm-1, ν(CN) 2245 cm-1. HRMS (EIþ, [M]þ): calc 177.0790, found 177.0790 1-Methoxy-5-oxobicyclo[2.2.2]oct-7-ene-2,3-dicarbonitrile (15). To a 4 dram vial were added (TpW(NO)(PMe3)(1-methoxy-8oxo-bicyclo[2.2.2]oct-5-ene-2-carbonitrile) (0.076 g, 1.0810-4 mol) and CuBr2 (0.085 g, 3.13 10-4 mol). CD3CN (2.021 g) was added and reaction stirred as a heterogeneous green mixture for 2 days. A yellow precipitate formed and was filtered over a 15 mL F frit. The solvent was evaporated from the brown filtrate. The resulting residue was dissolved in CH2Cl2 and added to 50 mL of stirring hexanes. A yellow precipate was filtered over a 30 mL fine-porosity fritted glass funnel. The solvent was evaporated from the filtrate, yielding a green film. 1H NMR (500 MHz, CDCl3): δ 6.80 (1H, d, J = 8.7, H7 minor (m)), 6.71 (1H, d, J = 8.6, H7 Major (M)), 6.46 (1H, dd, J = 8.7, 6.5, H8 m), 6.41 (1H, dd, J = 8.6, 7.0, H8 M), 3.55 (2H, buried, H4 M and H4 m), 3.54 (3H, s, OMe), 3.52 (3H, s, OMe), 3.42 (1H, d, J=4.2, H2 M), 3.32 (1H, dd, J=5.2,1.7, H2 m), 3.20 (1H, J=5.2, 2.4, H3 m), 3.13 (1H, dd, J=4.2, 3.2, H3 M), 2.61 (3H, m, H6 m, H6 m, H6 M), 2.42 (1H, d, J=18.1). [TpW(NO)(PMe3)(η2-3-(2,5-dimethyl-2,5-dihydrofuran-2yl)-1-phenylpyrrolidine-2,5-dione)] (27). TpW(NO)(PMe3)(η21,4,7-trimethyl-10-oxa-4-aza-tricyclo[5.2.1.02,6]dec-8-ene-3,5dione in benzene (1.04 g, 1.35 mmol) was dissolved in 19 mL of methylene chloride in a 25 mL round-bottom flask and stirred vigorously. Trifluoromethanesulfonic acid (0.780 g, 5.2 mmol) was added to 1.9 mL of methanol. The acidic solution was added to a round-bottom flask and allowed to stir for 20 min. The solution turned brown over time. The reaction mixture was added dropwise to 75 mL of stirring ether in a 125 mL Erlenmeyer flask, and a yellow precipitate was observed. The solid was collected on a 30 mL medium-porosity glass filter and washed with 20 mL of ether, twice. The solid was dried under vacuum for 25 min. [TpW(NO)(PMe3)(η2-3-(2,5-dimethyl-2,5dihydrofuran-2-yl)-1-phenylpyrrolidine-2,5-dione)]þ trifluoromethanesulfonate complex (0.950, 1.03 mmol) was collected in 76% yield. 1H NMR (chloroform-d): δ 8.01 (1H, d, J=1.8, Tp), 7.89 (1H, d, J=2.1, Tp),7.86 (1H, d, J=1.8, Tp), 7.84 (1H, d, J= 1.8, Tp), 7.78 (1H, d, J=2.1, Tp), 7.72 (1H, d, J=2.1, Tp), 7.37 (5H, m, Ph), 6.46 (1H, t, J=2.2, Tp), 6.42 (1H, t, J=2.2, Tp), 6.31 (1H, t, J=2.3, Tp), 4.90 (1H, dd, J=4.0, 12.5, H3), 4.26 (1H, dd, J=5.4, 9.3, H6), 3.61 (1H, d, J=4.0, H4), 3.34 (1H, dd, J= 9.3, 18.9, H7), 3.02 (1H, dd, J=5.4, 18.9, H7), 2.59 (3H, s, Me-5), 1.82 (3H, s, Me-2),1.10 (9H, d, J = 9.2, PMe3). 13C NMR

4734


(chloroform-d): δ 210.8 (s, C5), 176.0 (s, CO), 175.4 (s, CO), 144.4 (s, Tp), 144.3 (s, Tp), 142.1 (s, Tp), 138.6 (s, Tp), 138.5 (s, Tp), 138.2 (s, Tp), 131.8 (s, Ph), 129.5 (s, Tp), 129.4 (s, Ph), 127.0 (s, Ph), 108.5 (s, Tp), 107.3 (s, Tp), 104.7 (s, C2), 78.8 (br, C3), 70.2 (s, C4), 52.9 (s, C6), 32.4 (s, C7), 21.7 (s, Me-5), 21.3 (s, Me2), 14.2 (d, J=31.3, PMe3). IR (HATR): νCdO 1708 cm-1, νNtO 1661 cm-1. HRMS: [M]þ obsd (%), calcd (%), ppm, 771.20921 (74.1), 771.20992 (80.7), 0.9; 772.21215 (78.3), 772.21244 (81.2), 0.4; 773.21193 (100), 773.21243 (100), 0.6; 774.21468 (47.8), 774.21628 (47.7), 2.1; 775.21444 (78.4), 775.21563 (82.4), 1.5.

Salomon et al.

Acknowledgment. This work was supported by the NSF (CHE-0111558 (UVA), 9974875 (UVA), 0116492 (UR), and 0320669 (UR)). Supporting Information Available: Full synthetic details for the preparation of compounds, selected spectra of these compounds, and crystallographic information for compounds 2B, 4B, and 7. This material is available free of charge via the Internet at http://pubs.acs.org.

Stereoelectronic Effects in Dihapto-Coordinated Complexes of TpW

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