Enantioselective Catalysts for the DielsâAlder Reaction between

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Enantioselective Catalysts for the Diels−Alder Reaction between Methacrolein and Cyclopentadiene Based on the Chiral Fragment (η5-C5Me5)M(chiral diphosphane) (M = Rh, Ir) Daniel Carmona,* Fernando Viguri, Ainara Asenjo, M. Pilar Lamata, Fernando Lahoz, ́ Pilar Garcıa-Ordun ̃a, and L. A. Oro ́ Instituto de Sı ́ntesis Quı ́mica y Catálisis Homogénea (ISQCH), CSIC - Universidad de Zaragoza, Departamento de Qui mica Inorgánica, Pedro Cerbuna 12, 50009 Zaragoza, Spain S Supporting Information *

ABSTRACT: The aqua complexes [(η 5-C5Me5)M(PP*)(H2O)][SbF6]2 (M = Rh, Ir; PP* = chiral diphosphane) (1− 10) are prepared and characterized. These complexes efficiently catalyze the Diels−Alder reaction between methacrolein and HCp with enantioselectivities of up to 96% e.e. The norphos complexes 9 and 10, which are obtained as diastereomeric mixtures of the two epimers at the metal, afford the highest e.e. values. The intermediate complexes [(η 5-C5Me5)M(PP*)(methacrolein)][SbF6]2 (11−20) are also isolated and characterized, including the molecular structure determination of the [(η 5C5Me5)M(benphos)(methacrolein)][SbF6]2 (M = Rh (13), Ir (14)) derivatives. An NMR study of the reactivity of the metallic intermediates under catalytic conditions explains the high enantioselectivities achieved with the norphos systems.

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enantiopure (R)-prophos ligand renders, in a completely diastereoselective manner, only S at the metal derivatives when, for example, a molecule of water or methacrolein occupies the vacant position depicted in Scheme 1.7b Moreover, although, in some instances, epimerization at the metal in half-sandwich complexes is a low-demanding energy process,8 we have not detected changes in the configuration of the metal from −90 to +20 °C for our fragment. Second, the five-membered metallacycle M−P1−C−C−P2 adopts a λ conformation, this way allowing the methyl group of the (R)prophos ligand to occupy the less-hindered pseudoequatorial position (Scheme 2A). This conformation together with the S configuration at the metal determines the chiral bias of the catalyst pocket in which catalysis occurs. Third, when methacrolein coordinates at the vacant site, it adopts a planar geometry with an E configuration with respect its CO double bond and an s-trans conformation around the single OC−C bond (Scheme 2B). Finally, the methacrolein rotamer around the M−O bond is set, in both the solid state and solution, by CH/π attractive interactions between the CHO aldehyde proton and the pro-S phenyl ring connected to the P1 phosphorus atom. All these features make the chiral fragment (η 5C5Me5)M{(R)-prophos} depicted in Scheme 1 a privileged structure for cycloadditions to methacrolein. In fact, enantioselectivities ≥ 90% e.e. have been achieved in DA reactions between methacrolein and HCp6j as well as in 1,3-dipolar cycloadditions of enals to nitrones.7a−c With all these concerns in mind, we envisaged the possibility of extending these studies to other related chiral diphosphanes. In this paper, we report on the synthesis and characterization of new rhodium or iridium complexes of the formula [(η 5-C5Me5)M-

INTRODUCTION One of the most powerful strategies for synthesizing enantioenriched compounds by asymmetric catalysis involves the use of metal-based catalysts. The metal catalyst function is two-fold: it activates the substrates with concomitant acceleration of the catalytic process, and simultaneously, it provides them with the chiral environment capable of generating enantioselectivity.1 Among the wide variety of metalcatalyzed asymmetric processes, the Diels−Alder (DA) reaction is one of the most versatile synthetic transformations for the construction of the cyclohexane framework, allowing the formation of up to four contiguous stereocenters in a concerted fashion.2 Recently, one-point-binding half-sandwich complexes of Rh(III), Ir(III), Ru(II), or Os(II) have been developed as catalysts for this reaction by the groups of Kündig,3 Faller,4 Davies,5 and ourselves.6 In particular, we have shown that a chiral rhodium or iridium fragment containing the diphosphane (R)-propane-1,2-diylbis(diphenylphosphane) ((R)-prophos) (Scheme 1) is well suited for Scheme 1. The Chiral Fragment (η 5-C 5 Me 5 )M{(R)prophos)}

generating very active and selective catalysts for cycloaddition reactions.6a,j,7 This fragment presents some peculiar features. First, the metal is a stereogenic center. Fortunately, induction from the © 2011 American Chemical Society

Received: September 13, 2011 Published: November 21, 2011 6661

dx.doi.org/10.1021/om200859z | Organometallics 2011, 30, 6661−6673

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Scheme 2. (A) Conformation of the M−P1−C−C−P2 Metallacycle and (B) Geometry of Coordinated Methacrolein

(PP*)(H2O)][SbF6]2 (M = Rh, Ir), where PP* represents one of the chiral diphosphanes outlined in Scheme 3, and on their

prepared. For complexes 1−8, the reaction is completely diastereoselective: from −90 °C to RT, only one set of sharp resonances was observed in the 1H, 13C, and 31P NMR spectra. However, the norphos derivatives 9 and 10 are isolated as 79/ 21 (9) or 76/24 (10) molar ratio mixtures of the two epimers at the metal. As these ratios do not change after several hours in dichloromethane solution, we assume that they are thermodynamic equilibrium compositions, in this solvent. Complexes 1−10 were characterized by analytical and spectroscopic means. Assignment of the NMR signals was verified by two-dimensional homonuclear (COSY, NOESY) and heteronuclear (13C−1H, 31P−1H) correlations. In particular, the 31P NMR spectra reveal the presence of the coordinate diphosphane. The spectra consist of two doublets of doublets for the rhodium compounds (Rh−P and P−P couplings) and of two doublets (only P−P coupling) for the iridium ones. Typical Rh(III)−P couplings of about 130 Hz are measured, and as a reflection of the stronger electron-releasing character of the iridium, the phosphorus resonances of the iridium compounds appear around 30 ppm shifted to higher energies. Additionally, 31P−1H correlation spectra allow us to assign the downfield resonance to the phosphorus nucleus nearest to the asymmetric carbon atom, for complexes 1−8. In the 1H NMR spectra, a broad two-proton peak in the 2.61−4.81 ppm region denotes the presence of water coordinated to the metal. In complexes 1−8, a NOE correlation between the H11 proton (see Scheme 3 for labeling) and the water protons indicates an S configuration for the metal12 in a λ conformation for the M−P1−C1−C2−P2 metallacycle. Similarly, in complexes 9 and 10, a NOE correlation of the H2 proton with the water protons is indicative of an S configuration at the metal for the major epimers. Finally, one of the methyl groups of the 2propyl substituent of the valphos complexes 5 and 6 is shifted about 1 ppm toward higher field. Most probably, this shift is due to the shielding of this methyl by the electronic ring current of the pro-R phenyl group bonded to the nearest phosphorus atom. Catalytic Reactions. The water complexes [(η 5-C5Me5)M(PP*)(H2O)][SbF6]2 (1−10) efficiently catalyze the Diels−Alder reaction of methacrolein with cyclopentadiene. Table 1 lists a selection of the results together with the reaction conditions employed. The collected results are the average of at least two comparable reaction runs. Catalyst precursors have to be treated with methacrolein in the presence of 4 Å MS before the addition of cyclopentadiene. Both rhodium and iridium systems perform similarly, the iridium system being a little more reactive and enantioselective. Although the catalytic system remains active, Table 1 lists the conversions achieved after reactions were quenched by addition of excess Me4NCl after 1 h of treatment at −20 °C. e.e.'s ≥ 70% for the exo isomer were obtained, the S at the C2 enantiomer being the most abundant in all cases.13 In particular, the Ir/cyphos complex 8 (entry 8) and the M/norphos

Scheme 3. Chiral Diphosphanes Employed

application as catalyst precursors for the DA reaction between methacrolein and HCp. The corresponding catalytic intermediates containing coordinated methacrolein [(η 5-C5Me5)M(PP*)(methacrolein)][SbF6]2 are also isolated and characterized, including the molecular structure determination by X-ray diffraction methods of two of them, namely, (SM,RC)-[(η 5-C5Me5)M(benphos)(methacrolein)][SbF6]2 (M = Rh, Ir). The origin of the high enantioselectivity achieved with the M(norphos) systems (norphos = (1S,2R,3R,4R)-(−)-2,3-bis(diphenylphosphane)bicyclo[2.2.1]hept-5-ene]) (Scheme 3) is also discussed.

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RESULTS AND DISCUSSION The Aqua Compounds [(η 5-C5Me5)M(PP*)(H 2O)][SbF6]2. Aqua complexes of the general formula [(η 5-C5Me5)M(PP*)(H2O)][SbF6]2 (M = Rh, Ir) have been prepared by treating the corresponding dimer9 [{(η 5-C5Me5)MCl}2μ(Cl)2] in acetone with AgSbF6 and subsequent addition of the corresponding diphosphane (eq 1). The intermediate tris(acetone) solvates10 have not been isolated. The presence of trace amounts of water in the solvent is enough to afford pure aqua complexes 1−10.4e,5c,6e,g,11

During the reaction, the metal becomes a stereogenic center, and therefore, two diastereomers, epimers at the metal, can be 6662


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(19a/19b) or 67/33 (20a/20b) molar ratio. The new complexes were characterized by analytical and spectroscopic means (see the Experimental Section). Assignment of the NMR signals was verified by NOE experiments and by twodimensional homonuclear and heteronuclear ( 13 C− 1 H, 31 P−1H) correlations. The 1H NMR spectra denote the presence of the C5Me5, PP*, and methacrolein ligands in a 1/1/1 molar ratio. In particular, the CHO functionality originates a medium intensity ν(CO) absorption around 1600 cm−1 in the IR spectra and a 13C resonance at δ = 208−210 ppm. NOE correlations between the H11, H21, or H22 protons of the diphosphane (see Scheme 3) and the CHO, Me (methacrolein), or C5Me5 protons strongly suggest an S configuration for the metal in a λ conformation for the M−P1−C1−C2−P2 metallacycle for complexes 11−18. NOE correlations between the CHO and H2 protons indicate an S configuration at the metal for the most abundant epimer of compounds 19 and 20. Notably, a general feature of compounds 11−20 is that the CHO proton resonates in the 7.2−8.0 ppm interval, that is, 2.3−1.5 ppm shifted toward higher energies, with respect to the corresponding free enal. It has been previously reported that, for [(η 5-C5Me5)M{(R )prophos}(enal)]2+ cations, the electronic ring current of the proS phenyl group connected to the P1 atom of the diphosphane, related to the existence of CH/π attractive interactions between the CHO proton and this phenyl ring, are in the origin of such a strong shielding.7a−c The molecular structures of the benphos rhodium (13) and iridium (14) complexes reveal a comparable set of interactions in the solid state. Molecular Structures of Compounds 13 and 14. The molecular structures of complexes 13 and 14 have been determined by X-ray diffraction methods.14 Selected bond lengths and angles are reported in Table 2. Figure 1 shows an ORTEP diagram of the cation of complex 13 (for a similar view of the cation of 14, see the Supporting Information). Both structures resulted to be isostructural with analogous structural features. Although we will comment on some structural data of complex 14, we are going to center the discussion on complex 13. In both structures, the metal atom is pseudotetrahedral, being coordinated to a C5Me5 ring, to the two phosphorus atoms of the benphos chelate, and to the oxygen atom of the methacrolein ligand. Also, for both complexes, the configuration at the metal is S and the five-membered metallacycle M−P(1)−C(36)−C(35)−P(2) presents a λ conformation (Cremer and Pople parameters: Q2 = 0.579(9) Å and ϕ2 = 75.0(5)° (complex 13) and Q2 = 0.572(4) Å

Table 1. Enantioselective DA Reaction between Methacrolein and Cyclopentadiene Catalyzed by Complexes 1−10a

entry

complex

diphosphane

conv.b,c (%)

isomer ratioc (exo/ endo) (%)

1 2 3 4 5 6 7 8 9 10

1 (Rh) 2 (Ir) 3 (Rh) 4 (Ir) 5 (Rh) 6 (Ir) 7 (Rh) 8 (Ir) 9 (Rh) 10 (Ir)

phenphos phenphos benphos benphos valphos valphos cyphos cyphos norphos norphos

88 88 95 95 85 90 85 93 82 93

98/2 96/4 99/1 98/2 96/4 96/4 98/2 98/2 98/2 98/2

e.e.d (%) 79 80 79 89 70 74 88 96 93 96

(S) (S) (S) (S) (S) (S) (S) (S) (S) (S)

a

Reaction conditions: catalyst, 0.025 mmol (5 mol %); methacrolein, 0.5 mmol; HCp, 3 mmol; 4 mL of CH2Cl2; 100 mg of 4 Å molecular sieves; temperature, −20 °C; reaction time, 1 h. bBased on methacrolein. cDetermined by GC. dIn the exo isomers. Determined by 1H NMR with the chiral shift reagent (+)−Eu(hfc)3.

complexes 9 and 10 (entries 9 and 10) give e.e.’s greater than 90%. These e.e. values are among the highest achieved for onepoint-binding catalysts of the half-sandwich type.3−6 The Methacrolein Compounds [(η 5-C5Me5)M(PP*)(methacrolein)][SbF6]2. Addition of an excess of methacrolein to dichloromethane solutions of the aqua complexes [(η 5C5Me5)M(PP*)(H2O)][SbF6]2 affords the corresponding methacrolein complexes 11−20 (eq 2).

Again, the norphos complexes 19 and 20 are isolated as diastereomeric mixtures of both epimers at the metal in a 63/37

Table 2. Selected Bond Lengths (Å) and Angles (°) for Complexes 13 and 14 M−P(1) M−P(2) M−O M−Ga O−C(38) C(38)−C(39) C(39)−C(40) C(39)−C(41) P(1)−M−P(2) P(1)−M−O P(1)−M−Ga P(2)−M−O P(2)−M−Ga O−M−Ga a

13

14

2.331(2) 2.360(2) 2.163(2) 1.854(9) 1.254(11) 1.396(16) 1.292(17) 1.561(17) 83.20(9) 85.04(18) 131.3(3) 86.2(2) 131.3(3) 123.9(3)

2.320(3) 2.337(3) 2.152(6) 1.869(11) 1.259(12) 1.432(16) 1.304(16) 1.436(17) 83.2(1) 84.9(2) 131.7(3) 84.6(2) 131.8(3) 124.0(3)

P(1)−C(11) P(1)−C(17) P(1)−C(36) P(2)−C(29) P(2)−C(23) P(2)−C(35) C(35)−C(36) C(36)−C(37) C(37)−C(50) M−O−C(38) O−C(38)−C(39) C(38)−C(39)−C(40) C(38)−C(39)−C(41) C(40)−C(39)−C(41)

13

14

1.804(9) 1.767(10) 1.848(10) 1.825(9) 1.799(10) 1.806(11) 1.552(12) 1.547(14) 1.517(13) 131.2(7) 124.3(10) 118.2(9) 116(1) 125(1)

1.794(10) 1.810(9) 1.847(11) 1.821(10) 1.827(10) 1.797(12) 1.574(14) 1.540(16) 1.501(15) 128.4(6) 121.9(9) 115(1) 118(1) 125(1)

G represents the centroid of the η 5-C5Me5 ligand. 6663


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values around 0° or 180° correspond to perpendicular planes. An in-between value of −55.8(9)° has been found for 13, pointing to an intermediate relative orientation. This situation is only slightly different from that observed in the related prophos complex [(η 5 -C 5 Me 5 )Rh{(R)-prophos}(methacrolein)][SbF6]2, where a dihedral angle of −64.6(6)° was found.7b In the resulting Rh−O rotamer, the methacrolein plane is almost parallel to the pro-S phenyl ring connected to the P(1) atom (dihedral angle between the mean planes, 14.5(5)°) and quasiorthogonal to the pro-S phenyl ring connected to the P(2) atom (dihedral angle, 87.5(4)°). This rotamer allows for the establishment of CH/π interactions (Figure 2) between the

Figure 1. ORTEP diagram of the cation of complex 13. H atoms are omitted for clarity.

and ϕ2 = 77.2(5)° (complex 14)).15 As it has been established that both complexes present the same configuration and conformation in solution (see above), it can be concluded that both features are retained on going from the solid state to solution and vice versa. The two M−P distances are slightly different from each other, specially in the cation of 13 where the Rh−P(1) and Rh−P(2) bond lengths differ by 0.029(2) Å. A similar dissymmetry has been observed in other Rh complexes containing (η 5-C5Me5)Rh(PP*) fragments,16,17 which has been associated with the different steric requirements of dissimilarly substituted P atoms. The methacrolein ligand exhibits a planar s-trans conformation with an E configuration around the carbonylic double bond, in agreement with related chiral half-sandwich Lewis acid− methacrolein complexes previously reported.3c,6b,7b The partial delocalization of the π-electron density in the conjugated system O−C(38)−C(39)−C(40) is evidenced by the shortening of the C(38)−C(39) single bond (1.396(16) Å (13), 1.432(16) Å (14)) and the elongation of the O−C(38) double bond (1.254(11) Å (13), 1.259(12) Å (14)) distances, when compared with the mean values of these bond distances in related uncoordinated organic systems (C−C, 1.464(18) Å; OC, 1.192(5) Å).18 From a catalytic point of view, an important feature of these complexes is the conformation of the methacrolein into the chiral pocket generated by the C5Me5 and chiral diphosphane ligands. The G−Rh−O−C(38) torsion angle (G represents the centroid of the η 5-C5Me5 ligand) characterizes the relative disposition of the methacrolein and pentamethylcyclopentadienyl planes, as well as the rotamer around the Rh−O bond. A value of 90° places both planes in a parallel disposition, and

Figure 2. CH/π interactions in complex 13.

CHO methacrolein proton (H(38)) and the C(17)−C(22) bond of the pro-S phenyl ring of the P(1)Ph2 group, as well as between a hydrogen of the CH3 group of the methacrolein, H(41A), and the C(27)−C(28) bond of the pro-S phenyl ring of the P(2)Ph2 group. These interactions are characterized by short H···phenyl plane ring separations (2.99 and 2.79 Å) and H···C interatomic distances (2.91−3.08 Å), clearly shorter than the sum of the van der Waals radii (Table 3).19 Notably, these interactions set the methacrolein M−O rotamer and, therefore, are responsible for the high enantioselectivities achieved in the Diels−Alder reaction investigated. In fact, the sign of the enantioselectivity obtained (exo-(S) enantiomer) corresponds to a preferential attack of HCp to the Re-face of the coordinated methacrolein. Accordingly, in the X-ray structure of the cations of complexes 13 and 14, this face is exposed to the attack, whereas the Si-face is shielded by the pro-S phenyl ring of the P(1)Ph2 group. On the Origin of the Enantioselectivity for M/norphos Systems (M = Rh, Ir). As we stated above, the norphoscontaining complexes [(η 5 -C 5 Me 5 )M(norphos)(H 2 O)] [SbF6]2 (M = Rh (9), Ir (10)) and [(η 5-C5Me5)M(norphos)(methacrolein)][SbF6]2 (M = Rh (19), Ir (20)) are obtained as diastereomeric mixtures of both epimers at the metal in molar ratios of SRh-9/RRh-9, 79/21; SIr-10/RIr-10, 76/24;

Table 3. Selected Structural Parameters (Å, °) Concerning CH/π Interactions for Complex 13a,b H···G′

H···Ph (plane)

γ angle

C(38)−H(38)···C(17)/C(22)

3.160

2.986

19.1

C(41)−H(41A)···C(27)/C(28)

2.833

2.788

10.2

C−H···C C(17): C(22): C(27): C(28):

3.082 3.059 2.913 3.007

C−H···C(Ph) 3.453−3.812 3.100−3.339

a For the corresponding parameters of the cation of complex 14, see the Supporting Information. bH···G′ represents the distance from the H atom to the centroid of the phenyl ring of the reported C−H···π interaction. H···Ph is the separation from the H atom to the mean plane of the phenyl ring. γ angle: angle between the H−G′ vector and the normal of the phenyl ring. C−H···C: contact distances between H atom under the assumed criterion (3.05 Å). C−H···C(Ph): separation between H and the rest of the carbon atoms of the phenyl ring.

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SRh-19/RRh-19, 63/37; and SIr-20/RIr-20, 67/33.20 All the remaining related compounds of the formula [(η 5-C5Me5)M(PP*)(methacrolein)][SbF6]2 (11−18) are obtained as pure SM epimers. In a recent study, we have shown that the two epimers at the metal of the related nitrile-containing compounds (SM,RC and R M ,R C )-[(η 5 -C 5 Me 5 )M{(R)-prophos}(α,β-unsaturated nitrile)][SbF6]2 (M = Rh, Ir) induce divergently in the catalytic 1,3-dipolar cycloaddition between methacrylonitrile and 3,4dihydroisoquinoline N-oxide: the SM isomer preferentially gives the S3C,R5C cycloadduct and the RM, the R3C,S5C one.7d Taking into account these results, an erosion of the enantioselectivity would be expected when mixtures of epimers at the metal were used as catalysts. However, the e.e. values collected in Table 1 show that the opposite is true because the highest values of enantioselectivity were achieved with the norphos systems. To try to explain this unexpected catalytic outcome, we studied, as a model, the reaction between methacrolein and cyclopentadiene catalyzed by the mixture of iridium epimers SIr-20/RIr-20, generated in situ from the corresponding aqua complexes SIr-10/RIr-10. At this point, it is useful to remember that (i) in this reaction, four adducts, namely, exo-(S), exo-(R), endo-(S), and endo-(R), can be formed, as specified in Figure 3, and (ii) the commonly

complex 20 instantaneously produces the quantitative formation of a mixture of new metallic complexes. Thus, the two pairs of doublets assigned to the two epimers of complex 20 (trace a, Figure 5) disappear and two new iridium complexes,

Figure 5. 31P NMR spectra, in CD2Cl2, at −20 °C, of compound [(η 5C5Me5)Ir(norphos)(methacrolein)][SbF6]2 (a) and after addition of HCp (b).

labeled as I and II, are formed (trace b). Minute quantities of some other complexes are also detected. A Diels−Alder adduct with an exo/endo molar ratio of 98/2 and an e.e. of 96% (exo) was obtained when an excess of NMe4Cl was added to a solution of spectrum b. Figure 5 also reveals that the chemical shift of the P1 and P2 phosphorus atoms of the RIr-20 and SIr-20 isomers, respectively, are much more sensible to the metal environment than the two remaining phosphorus nuclei are. For this reason, from now on, we will only show the high-field doublet for the complexes we discuss. To ascertain the actual nature of the new species I and II, we monitored, by 31P NMR, the addition of mixtures of adducts of two compositions, A and B21 (see Scheme 4), to a 76/24 = SIr10/RIr-10 molar ratio mixture of the aqua complex [(η 5C5Me5)Ir(norphos)(H2O)][SbF6]2, in the presence of 4 Å molecular sieves as a water scavenger. Under these conditions, the formation of Ir-adduct species is plausible. Mixture A is a racemate with an exo/endo molar ratio of 86/14, and B represents a 98/2, exo/endo mixture with 96% e.e. in the major component (Scheme 4). Addition of an equimolar amount of A to complex 10 affords four new complexes, labeled I−IV in trace a of Figure 6, together with other minor metallic species. In an independent experiment, an equimolar amount of B was added to complex 10, mostly rendering complexes I, II, and IV (Figure 6, trace b). Compounds I and II are formed in the three experiments, and taking into account the performed reactions, the isomeric compositions of the iridium complexes involved, and the reagents and conditions employed, they have to be the SIr and RIr isomers of the Ir-adduct complex [(η 5-C5Me5)Ir(norphos)(adduct)]2+ with the exo-(S) adduct coordinated to the metal.

Figure 3. Possible cycloadducts for the DA reaction between methacrolein and cyclopentadiene.

assumed pathway for this reaction (Figure 4) involves the cyclopentadiene attack to coordinated methacrolein (step 1),

Figure 4. Plausible catalytic cycle.

followed by the displacement of the coordinated adduct by methacrolein (step 2). According to step 1, 31P NMR measurements reveal that the addition of an equimolar amount of HCp to the methacrolein 6665


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Scheme 4. Reaction of Complex 10 with Mixtures A and B

Formation of almost only I and II from an SIr-20/RIr-20 mixture (Figure 5) implies that, with high selectivity, an exo attack through the Re-face of the methacrolein takes place in both iridium epimers (see Figure 3). That is, both epimers are active Diels−Alder catalysts for the reaction studied and both induce the preferential formation of the same Diels−Alder stereoisomer. Therefore, as a whole, high selectivities are achieved because the stereochemistry of the adducts is governed by the configuration of the chiral diphosphane. The selectivity values obtained with the rhodium system point to a similar explanation. On the other hand, we assign the resonances III and IV (Figure 6) to the [(η 5-C5Me5)Ir(norphos)(adduct)]2+ species

doublets, attributed to the two epimers at the metal of the methacrolein complex [(η 5-C5Me5)Ir(norphos)(methacrolein)][SbF6]2 (20), increased at the expense of the Ir-adduct complexes. We have also recorded the spectra corresponding to addition of 0.4, 0.6, and 0.9 equiv of methacrolein (spectra not shown in Figure 7). Figure 8 shows

Figure 7. High-field 31P NMR resonances, in CD2Cl2, at −40 °C, of mixtures of Ir-adduct complexes: before methacrolein addition (a) and after addition of 0.3 (b), 0.5 (c), or 0.7 equiv (d) of methacrolein. Figure 6. Fragments of the 31P NMR spectra, in CD2Cl2, at −70 °C, after addition of equimolar amounts of A (a) or B (b) to complex 10.

in which the exo-(R) adduct is coordinated to the iridium with RIr and SIr configurations, respectively. The remaining minor doublets detected stand for the Ir-adduct complexes with endo(S) and endo-(R) adducts coordinated to the metal. Finally, taking advantage of the availability of solutions containing mixtures of Ir-adduct complexes, we studied the dissociation of adducts from them by addition of methacrolein, according to step 2 of the catalytic cycle depicted in Figure 4. Trace a in Figure 7 corresponds to the high-field part of the 31P NMR spectrum, at −40 °C, of the CD2Cl2 solution obtained after addition of an equimolar amount of mixture A (Scheme 4) to the aqua complex [(η 5-C5Me5)Ir(norphos)(H2O)][SbF6]2 (10). Traces b, c, and d (Figure 7) show the same spectral zone after the subsequent addition of 0.3, 0.5, or 0.7 equiv of methacrolein. Before the addition of methacrolein (trace a), nine doublets are detected. As we have previously shown, doublets I, II, III, and IV correspond to the four Ir-adduct complexes in which the exo adducts are coordinated to the metal. We tentatively assign the doublets labeled A, B, C, and D to the four Ir-adduct complexes with coordinated endo adducts. The remaining doublet, centered at 5.35 ppm, corresponds to residual aqua complex 10. As methacrolein was added, two

Figure 8. Variation of the concentration of Ir-adduct complexes I−IV with the addition of methacrolein.

the decreasing of the concentration of the Ir-adducts I−IV with respect to the amount of methacrolein added. The rate of dissociation of the exo-(R) adducts from complexes III and IV is greater than that of the exo-(S) adducts from complexes I and II. No equilibria are established between the metallic species during the recording time of the spectra. Therefore, only the preferential formation of the exo-(S) adducts for both epimers at the metal in step 1 accounts for the observed enantioselectivity. Thus, step 1 is the enantio-determining step. 6666


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corresponding solid PP* ligand (0.800 mmol) was added. The solution was stirred at −25 °C for 1 h (3 h when PP* = norphos) and then vacuum-concentrated to ca. 5 mL. Addition of 20 mL of n-hexane gave orange oils. Vigorous stirring in n-hexane affords orange (Rh) or yellow (Ir) solids. The solutions were poured off and the solids washed with n-hexane (3 × 10 mL) and then vacuum-dried. The solids were recrystallized three times, at −25 °C, from CH2Cl2/n-hexane (1/5, v/v). (SRh,RC)-[(η 5-C5Me5)Rh(phenphos)(H2O)][SbF6]2 (1).

Finally, Figure 9 shows the relative concentration of complexes SIr-20 and RIr-20 formed by the addition of

Figure 9. Relative concentration of the methacrolein epimers SIr-20 and RIr-20 with respect to the amount of methacrolein added.

methacrolein. Notably, during the addition, the molar ratio of SIr-20/RIr-20 is almost constant (straight lines) and its value is about 2. This value is very similar to the 67/33 equilibrium ratio attained when these compounds are prepared (see above). Thus, after formation of these stereoisomers from the Ir-adduct species, the equilibrium composition is achieved by, if necessary, instantaneous epimerization at the metal.

Yield: 80%. Anal. Calcd for C42H45F12RhOP2Sb2: C, 42.0; H, 3.8. Found: C, 41.9; H, 3.9. IR (solid, cm −1): ν(H2O) 3519 (w), ν(SbF6) 650 (s). 1H NMR (400.16 MHz, CD2Cl2, −25 °C): δ = 7.96−6.64 (25H, Ph), 4.18 (m, 1H, H11), 3.44 (dt, J = 52.8, 12.9 Hz, 1H, H22), 3.14 (bs, 2H, H2O), 3.01 (ddd, J = 22.3, 15.1, 6.9 Hz, 1H, H21), 1.40 ppm (t, J = 3.1 Hz, 15H, C5Me5). 13C NMR (100.61 MHz, CD2Cl2, −25 °C): δ = 135.94−128.47 (30C, Ph), 106.01 (bs, C5Me5), 42.02 (dd, J (P,C) = 24.8, 12.8 Hz, C1), 29.96 (dd, J (P,C) = 35.7, 19.8 Hz, C2), 14.20 ppm (C5Me5).31P NMR (161.96 MHz, CD2Cl2, −25 °C): δ = 77.74 (dd, J (Rh,P1) = 130.5 Hz, J (P2,P1) = 43.6 Hz, P1), 41.52 ppm (dd, J (Rh,P2) = 131.5 Hz, P2).

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CONCLUSION The new diphosphane complexes [(η 5-C5Me5)M(PP*)(H2O)][SbF6]2 (M = Rh, Ir) generate very efficient systems for the Diels−Alder reaction between methacrolein and cyclopentadiene with an e.e. up to 96%. The stereochemistry of coordinated methacrolein in the metallic intermediates [(η 5C5Me5)M(PP*)(methacrolein)][SbF6]2 accounts for the encountered enantioselectivity. The M/norphos complexes are obtained as a mixture of epimers at the metal. However, they give rise to the most enantioselective systems because this selectivity is not governed by the configuration at the metal, but by that of the diphosphane ligand.

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(SIr,RC)-[(η 5-C5Me5)Ir(phenphos)(H2O)][SbF6]2 (2).

EXPERIMENTAL SECTION

Yield: 85%. Anal. Calcd for C42H45F12IrOP2Sb2: C, 39.1; H, 3.5. Found: C, 39.2; H, 3.7. IR (solid, cm−1): ν(H2O) 3497 (w), ν(SbF6) 653 (s). 1H NMR (400.16 MHz, CD2Cl2, −25 °C): δ = 7.96−7.64 (25H, Ph), 4.08 (m, 1H, H11), 3.86 (bs, 2H, H2O), 3.44 (dddd, J = 48.4, 15.7, 11.4, 4.2 Hz, 1H, H22), 2.98 (m, 1H, H21), 1.45 ppm (s, 15H, C5Me5). 13C NMR (100.61 MHz, CD2Cl2, −25 °C): δ = 135.55−128.37 (30C, Ph), 99.93 (s, C5Me5), 42.64 (dd, J (P,C) = 30.4, 9.3 Hz, C1), 30.05 (dd, J (P,C) = 37.7, 16.1 Hz, C2), 8.66 ppm (C5Me5). 31P NMR (161.96 MHz, CD2Cl2, −25 °C): δ = 48.78 (d, J (P2,P1) = 17.1 Hz, P1), 17.43 ppm (d, P2).

All solvents were treated in a PS-400-6 Innovative Technologies Solvent Purification System (SPS) and degassed prior to use. All preparations have been carried out under argon. Infrared spectra were obtained as net solids with a PerkinElmer Spectrum 100 spectrophotometer. Carbon, hydrogen, and nitrogen analyses were performed using a PerkinElmer 2400 CHNS/O microanalyzer. Proton NMR spectra were recorded on Bruker Avance-300 (300.13 MHz), 400 (400.16 MHz), or 500 (500.13 MHz) spectrometers. Chemical shifts are expressed in parts per million upfield from SiMe4 or 85% H3PO4 (31P). NOEDIFF and 13C, 31P, and 1H correlation spectra were obtained using standard procedures. Gas chromatography was performed on a Hewlet-Packard 3398 gas chromatograph equipped with a split-mode capillary injection system and a flame ionization detector. (R)-phenphos, (R)-benphos, (R)-valphos, and (R)-cyphos were synthesized from (S)-mandelic acid (Aldrich), L-phenylalanine (Acros), L-valine (Acros) and (S)-hexahydromandelic acid (Fluka), respectively, and NaPPh2 or LiPPh2 according to the literature procedures.22 (1S,2R,3R,4R)-norphos was purchased from Strem Chemical Co. Preparation of the Complexes [(η 5-C5Me5)M(PP*)(H2O)][SbF6]2 (1−10). To a suspension of the appropriate [{(η 5-C5Me5)MCl}2(μ-Cl)2] dimer (0.400 mmol), in acetone (20 mL), was added AgSbF6 (551.3 mg, 1.604 mmol). The resulting suspension was stirred at room temperature for 4 h. The mixture was filtered through a cannula and the precipitate washed with 3 × 2 mL of acetone. The filtrate was concentrated to ca. 10 mL and cooled to −25 °C, and the

(SRh,RC)-[(η 5-C5Me5)Rh(benphos)(H2O)][SbF6]2 (3).

Yield: 82%. Anal. Calcd for C43H47F12RhOP2Sb2: C, 42.5; H, 3.9. Found: C, 42.5; H, 3.7. IR (solid, cm −1): ν(H2O) 3552 (w), ν(SbF6) 654 (s). 1H NMR (500.13 MHz, CD2Cl2, −25 °C): δ = 8.00−7.13 (25H, Ph), 3.26 (d, J = 12.3 Hz, 1H, H31), 6667


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3.00 (dt, J = 53.4, 14.6 Hz, 1H, H22), 2.86 (m, 1H, H11), 2.61 (bs, 2H, H2O), 2.29 (ddd, J = 19.8, 14.5, 5.2 Hz, 1H, H21), 2.00 (m, 1H, H32), 1.44 ppm (s, 15H, C5Me5). 13C NMR (125.77 MHz, CD2Cl2, −25 °C): δ = 137.92−127.71 (30C, Ph), 105.95 (s, C5Me5), 37.36 (dd, J (P,C) = 30.2, 9.5 Hz, C1), 35.66 (d, J = 12.3 Hz, C3), 27.60 (dd, J (P,C) = 33.0, 16.7 Hz, C2), 9.20 ppm (C5Me5). 31P NMR (202.48 MHz, CD2Cl2, −25 °C): δ = 70.78 (dd, J (Rh,P1) = 131.7 Hz, J(P2,P1) = 41.9 Hz, P1), 44.09 ppm (dd, J (Rh,P2) = 132.6 Hz, P2).

Yield: 91%. Anal. Calcd for C39H47F12IrOP2Sb2: C, 37.25; H, 3.8. Found: C, 36.8; H, 3.7. IR (solid, cm −1): ν(H2O) 3480 (w), ν(SbF6) 651 (s). 1H NMR (500.13 MHz, CD2Cl2, −25 °C): δ = 7.91−7.23 (20H, Ph), 4.31 (bs, 2H, H2O), 3.20 (dt, J = 50.55, 15.1 Hz, 1H, H22), 2.65 (m, 1H, H11), 2.40 (m, 1H, H21), 2.21 (m, 1H, H3), 1.45 (s, 15H, C5Me5), 1.19 (d, J = 6.5 Hz, 3H, CH3), 0.09 ppm (d, J = 6.3 Hz, 3H, CH3). 13C NMR (125.77 MHz, CD2Cl2, −25 °C): δ = 134.80−119.95 (24C, Ph), 99.73 (s, C5Me5), 40.67 (dd, J (P,C) = 34.6, 7.0 Hz, C1), 26.47 (dd, J = 14.5, 4.2 Hz, C3), 24.74 (d, J = 10.0 Hz, CH3), 24.17 (dd, J(P,C) = 40.8, 12.5 Hz, C2), 17.03 (s, CH3), 8.72 ppm (C5Me5). 31P NMR (202.48 MHz, CD2Cl2, −25 °C): δ = 46.95 (d, J (P2,P1) = 14.2 Hz, P1), 22.58 ppm (d, P2).

(SIr,RC)-[(η 5-C5Me5)Ir(benphos)(H2O)][SbF6]2 (4).

(SRh,RC)-[(η 5-C5Me5)Rh(cyphos)(H2O)][SbF6]2 (7).

Yield: 77%. Anal. Calcd for C43H47F12IrOP2Sb2: C, 39.4; H, 4.1. Found: C, 39.6; H, 3.6. IR (solid, cm−1): ν(H2O) 3542 (w), ν(SbF6) 653 (s). 1H NMR (500.13 MHz, CD2Cl2, −25 °C): δ = 7.99−7.09 (25H, Ph), 3.25 (d, J = 12.5 Hz, 1H, H31), 3.07 (bs, 2H, H2O), 2.98 (m, 1H, H22), 2.78 (m, 1H, H11), 2.27 (ddd, J = 21.4, 15.2, 6.1 Hz, 1H, H21), 1.91 (dt, J = 14.2, 6.6 Hz, 1H, H32), 1.49 ppm (s, 15H, C5Me5). 13C NMR (125.77 MHz, CD2Cl2, −25 °C): δ = 138.20−127.73 (30C, Ph), 99.71 (s, C5Me5), 37.59 (dd, J (P,C) = 34.1, 8.6 Hz, C1), 34.91 (d, J = 16.3 Hz, C3), 27.76 (dd, J (P,C) = 38.3, 15.5 Hz, C2), 8.81 ppm (C5Me5). 31P NMR (202.48 MHz, CD2Cl2, −25 °C): δ = 42.95 (d, J(P2,P1) = 14.7 Hz, P1), 19.35 ppm (d, P2).

Yield: 94%. Anal. Calcd for C42H51F12RhOP2Sb2: C, 41.9; H, 4.75. Found: C, 41.75; H, 4.25. IR (solid, cm−1): ν(H2O) 3538 (w), ν(SbF6) 650 (s). 1H NMR (300.13 MHz, CD2Cl2, −25 °C): δ = 7.93−6.97 (20H, Ph), 3.28 (dt, J = 57.3, 13.2 Hz, 1H, H22), 2.75 (bs, 2H, H2O), 2.49 (m, 1H, H11), 2.41 (m, 1H, H21), 1.74−0.70 (m, 11H, cy), 1.41 ppm (t, J = 3.0 Hz, 15H, C5Me5). 13C NMR (75.48 MHz, CD2Cl2, −25 °C): δ = 134.93−120.70 (24C, Ph), 105.87 (s, C5Me5), 40.34 (dd, J (P,C) = 28.1, 9.0 Hz, C1), 37.23− 22.94 (6C, cy), 25.00 (m, C2), 9.16 ppm (C5Me5). 31P NMR (121.48 MHz, CD2Cl2, −25 °C): δ = 75.33 (dd, J (Rh,P1) = 129.5 Hz, J (P2,P1) = 41.3 Hz, P1), 47.04 ppm (dd, J (Rh,P2) = 132.8 Hz, P2).

(SRh,RC)-[(η 5-C5Me5)Rh(valphos)(H2O)][SbF6]2 (5).

(SIr,RC)-[(η 5-C5Me5)Ir(cyphos)(H2O)][SbF6]2 (8).

Yield: 83%. Anal. Calcd for C39H47F12RhOP2Sb2·CH2Cl2: C, 38.3; H, 3.9. Found: C, 38.0; H, 3.9. IR (solid, cm −1): ν(H2O) 3531 (w), ν(SbF6) 653 (s). 1H NMR (500.13 MHz, CD2Cl2, −25 °C): δ = 7.95−7.29 (20H, Ph), 3.25 (dt, J = 55.5, 13.5 Hz, 1H, H22), 2.78 (bs, 2H, H2O), 2.57 (m, 1H, H11), 2.42 (m, 1H, H21), 2.20 (m, 1H, H3), 1.42 (m, 15H, C5Me5), 1.15 (d, J = 6.3 Hz, 3H, CH3), 0.13 ppm (d, J = 6.3 Hz, 3H, CH3). 13C NMR (125.77 MHz, CD2Cl2, −25 °C): δ = 134.86−119.68 (24C, Ph), 105.89 (s, C5Me5), 40.55 (dd, J (P,C) = 28.7, 9.7 Hz, C1), 27.49 (dd, J = 15.4, 5.3 Hz, C3), 24.48 (d, J = 9.1 Hz, CH3), 24.22 (dd, J (P,C) = 34.0, 14.3 Hz, C2), 17.20 (CH3), 9.16 ppm (C5Me5). 31P NMR (202.48 MHz, CD2Cl2, −25 °C): δ = 74.71 (dd, J (Rh,P1) = 129.6 Hz, J(P2,P1) = 41.7 Hz, P1), 46.80 ppm (dd, J (Rh,P2) = 133.0 Hz, P2).

Yield: 88%. Anal. Calcd for C42H51F12IrOP2Sb2: C, 38.9; H, 4.0. Found: C, 39.1; H, 4.1. IR (solid, cm −1): ν(H2O) 3524 (w), ν(SbF6) 652 (s). 1H NMR (500.13 MHz, CD2Cl2, −25 °C): δ = 7.91−7.26 (20H, Ph), 3.99 (bs, 2H, H2O), 3.23 (dt, J = 51.6, 11.6 Hz, 1H, H22), 2.52 (m, 1H, H11), 2.39 (m, 1H, H21), 1.75−0.70 (11H, cy), 1.44 ppm (s, 15H, C 5Me5). 13 C NMR (125.77 MHz, CD2Cl2, −25 °C): δ = 134.81−119.81 (24C, Ph), 99.72 (s, C5Me5), 40.60 (dd, J (P,C) = 33.8, 7.1 Hz, C1), 36.41−22.87 (6C, cy), 25.19 (dd, J (P,C) = 40.8, 12.6 Hz, C2), 8.75 ppm (C5Me5). 31P NMR (202.48 MHz, CD2Cl2, −25 °C): δ = 47.47 (d, J (P2,P1) = 14.2 Hz, P1), 23.22 ppm (d, P2).

(SIr,RC)-[(η 5-C5Me5)Ir(valphos)(H2O)][SbF6]2 (6).

[(η 5-C5Me5)Rh(norphos}(H2O)][SbF6]2 (9). Yield: 99%. Molar ratio of S at the metal (9a) to R at the metal (9b) epimer: 79/21. Anal. Calcd for C41H45F12RhOP2Sb2: C, 41.4; H, 3.8. Found: C, 41.9; H, 3.9. IR (solid, cm−1): ν(H2O) 3547 (w), ν(SbF6) 653 (s). 6668


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S at Metal Epimer (9a).

(m, 1H, H2), 3.11 (s, 1H, H4), 3.08−2.89 (m, 1H, H3), 2.28 (s, 1H, H72), 1.96 (bd, J = 9.0 Hz, 1H, H71), 1.46 ppm (s, 15H, C5Me5). 13C NMR (100.61 MHz, CD2Cl2, −25 °C): δ = 140.57 (d, J = 7.5 Hz, C5), 134.78−116.04 (24C, Ph), 130.16 (d, J = 9.0 Hz, C6), 98.58 (s, C5Me5), 53.11−52.84 (m, C7), 49.07 (dd, J (P,C) = 20.0, 1.8 Hz, C3), 42.79−42.57 (m, C1), 43.66 (dd, J (P,C) = 42.4, 15.2 Hz, C2), 40.77−40.47 (m, C4), 9.07 ppm (C5Me5). 31P NMR (161.96 MHz, CD2Cl2, −25 °C): δ = 12.30 (d, J (P2,P1) = 28.2 Hz, P1), 5.42 ppm (d, P2). R at Metal Epimer (10b).

1

H NMR (500.13 MHz, CD2Cl2, −25 °C): δ = 7.86−7.18 (20H, Ph), 6.07 (dd, J = 5.4, 3.2 Hz, 1H, H5), 4.96 (dd, J = 5.5, 2.7 Hz, 1H, H6), 3.88 (s, 1H, H1), 3.28 (bs, 2H, H2O), 3.20 (m, 1H, H2), 3.11 (s, 1H, H4), 2.96 (m, 1H, H3), 2.03 (bd, 1H, H72), 1.90 (d, J = 9.2 Hz, 1H, H71), 1.43 ppm (t, J = 3.6 Hz, 15H, C5Me5). 13C NMR (125.77 MHz, CD2Cl2, −25 °C): δ = 140.64 (d, J = 7.0 Hz, C5), 134.68−117.08 (24C, Ph), 130.65 (m, C6), 104.61 (d, J = 5.8 Hz, C5Me5), 52.47 (d, J = 9.2 Hz, C7), 49.34 (dd, J = 27.0, 17.6 Hz, C3), 43.64 (d, J = 18.6 Hz, C2), 43.42−42.83 (m, C1), 41.65 (dd, J = 12.7, 7.4 Hz, C4), 9.52 ppm (C5Me5). 31P NMR (202.48 MHz, CD2Cl2, −25 °C): δ = 40.14 (dd, J(Rh,P1) = 132.4 Hz, J (P2,P1) = 44.3 Hz, P1), 30.91 ppm (dd, J (Rh,P2) = 137.6 Hz, P2).

1

H NMR (400.16 MHz, CD2Cl2, −25 °C): δ = 7.19−7.85 (20H, Ph), 6.65 (m, 1H, H5), 6.08 (m, 1H, H6), 4.81 (bs, 2H, H2O), 3.41 (m, 1H, H2), 3.23 (s, 1H, H1), 2.75 (s, 1H, H4), 2.62 (m, 1H, H3), 1.90 (m, 1H, H72), 1.46 (s, 15H, C5Me5), 0.26 ppm (bd, J = 8.9 Hz, 1H, H71). 13C NMR (100.61 MHz, CD2Cl2, −25 °C): δ = 142.08 (m, C5), 132.93 (m, C6), 98.71 (s, C5Me5), 52.20 (m, C7), 9.34 ppm (C5Me5). 31P NMR (161.96 MHz, CD2Cl2, −25 °C): δ = 12.44 (d, J (P2,P1) = 27.9 Hz, P2), 5.10 ppm (d, P1).

R at Metal Epimer (9b).

Catalytic Procedure. The corresponding metallic complex [(η 5C5Me5)M(PP*)(H2O)][SbF6]2 (0.025 mmol, 5 mol %) was dissolved in 3 mL of dry CH2Cl2 under argon at −20 °C, and 100 mg of 4 Å molecular sieves and freshly distilled methacrolein (41.4 μL, 0.500 mmol) were added. After 15 min of reaction, cyclopentadiene (247.2 μL, 3.0 mmol) in 1 mL of CH2Cl2 was added. The reaction was quenched by addition of excess Me4NCl in CH2Cl2, after 1 more hour of reaction, and the conversion and exo/endo ratio were determined by GC. The suspension was then concentrated to ca. 0.3 mL, filtered through silica gel, and washed with CH2Cl2/n-hexane (1/1, v/v), before the determination of the enantiomeric purity. Enantiomeric excesses were determined by integration of the aldehyde proton of both enantiomers in the NMR spectra, using Eu(hfc)3, in a 0.3 molar ratio, as a chiral shift reagent. The absolute configuration of the major adduct was assigned by comparing the sign of [α]D with that in the literature.13 Preparation of the Complexes [(η 5 -C 5 Me 5 )M(PP*)(methacrolein)][SbF6]2 (11−20). At −25 °C, under argon, to a solution of [(η 5-C5Me5)M(PP*)(H2O)][SbF6]2 (0.120 mmol) in CH2Cl2 (4 mL) were added methacrolein (33.0 μL, 0.395 mmol) and 4 Å molecular sieves (200.0 mg). The resulting suspension was stirred for 20 min and then was filtered through a cannula. The filtrate was concentrated to ca. 3 mL. The addition of 20 mL of dry n-hexane afforded orange (Rh) or yellow (Ir) solids that were filtered off, washed with 3 × 2 mL of dry n-hexane, and vacuum-dried. (S Rh ,R C )-[(η 5 -C 5 Me 5 )Rh(phenphos)(methacrolein)][SbF 6 ] 2 (11).

1

H NMR (500.13 MHz, CD2Cl2, −25 °C): δ = 6.60 (dd, J = 5.5, 3.3 Hz, 1H, H5), 6.02 (dd, J = 5.6, 2.5 Hz, 1H, H6), 3.47 (bs, 2H, H2O), 3.37 (m, 1H, H2), 3.16 (m, 1H, H1), 2.78 (m, 1H, H4), 2.56 (m, 1H, H3), 1.69 (m, 1H, H72), 1.67 (s, 15H, C5Me5), 0.28 ppm (d, J = 8.7 Hz, 1H, H71). 13C NMR (125.77 MHz, CD2Cl2, −25 °C): δ = 142.19 (d, J = 6.0 Hz, C5), 132.76 (m, C6), 100.49 (d, J = 9.8 Hz, C5Me5), 52.06 (d, J = 12.9 Hz, C7), 8.72 ppm (C5Me5). 31P NMR (202.48 MHz, CD2Cl2, −25 °C): δ = 40.34 (dd, J(Rh,P2) = 131.9 Hz, J (P2,P1) = 36.6 Hz, P2), 31.10 ppm (dd, J (Rh,P1) = 147.2 Hz, P1). [(η 5-C5Me5)Ir(norphos}(H2O)][SbF6]2 (10). Yield: 98%. Molar ratio of S at the metal (10a) to R at the metal (10b) epimer: 76/24. Anal. Calcd for C41H45F12IrOP2Sb2: C, 38.5; H, 3.5. Found: C, 38.6; H, 3.6. IR (solid, cm−1): ν(H2O) 3548 (w), ν(SbF6) 653 (s). S at Metal Epimer (10a).

1

H NMR (400.16 MHz, CD2Cl2, −25 °C): δ = 7.19−7.85 (20H, Ph), 6.07 (dd, J = 5.0, 3.0 Hz, 1H, H5), 4.91 (dd, J = 5.3, 2.6 Hz, 1H, H6), 4.52 (bs, 2H, H2O), 3.28 (s, 1H, H1), 3.24 6669


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(SIr,RC)-[(η 5-C5Me5)Ir(benphos)(methacrolein)][SbF6]2 (14).

Yield: 59%. Anal. Calcd for C 46H49F12RhOP2Sb2·CH2Cl2: C, 42.15; H, 3.8. Found: C, 41.7; H, 3.9. IR (solid, cm −1): ν(CO) 1620 (m), ν(SbF6) 652 (s). 1H NMR (500.13 MHz, CD2Cl2, −25 °C): δ = 7.94−7.08 (25H, Ph), 7.67 (s, 1H, CHO), 6.66 (bs, 1H, H b), 6.13 (bs, 1H, Ha), 3.87 (m, 1H, H11), 3.55 (dt, J = 52.55, 12.7 Hz, 1H, H 22), 3.18 (m, 1H, H21), 1.40 (s, 15H, C 5Me5), 1.13 ppm (s, 3H, Me). 13 C NMR (125.77 MHz, CD 2Cl2, −25 °C): δ = 208.56 (CHO), 149.41 (C5), 145.06 (C4), 135.15−120.25 (30C, Ph), 106.57 (s, C5Me5), 43.14 (m, C1), 31.78 (dd, J (P,C) = 45.8, 24.0 Hz, C2), 13.35 (Me), 9.41 ppm (C 5Me5). 31P NMR (202.48 MHz, CD2Cl2, −25 °C): δ = 77.49 (dd, J (Rh,P1) = 130.9 Hz, J (P2,P1) = 43.3 Hz, P1), 43.61 ppm (dd, J (Rh,P2) = 132.4 Hz, P2).

Yield: 82. %. Anal. Calcd for C47H51F12IrOP2Sb2: C, 41.6; H, 3.8. Found: C, 42.1; H, 4.1. IR (solid, cm−1): ν(CO) 1600 (m), ν(SbF6) 654 (s). 1H NMR (400.16 MHz, CD2Cl2, −25 °C): δ = 7.9−6.9 (25H, Ph), 7.39 (s, 1H, CHO), 6.45 (s, 1H, Hb), 5.87 (s, 1H, Ha), 3.22 (d, J = 14.7 Hz, 1H, H32), 3.15 (dt, J = 49.3, 13.4 Hz, 1H, H22), 2.62 (m, 1H, H11), 2.53 (m, 1H, H21), 2.00 (m, 1H, H31), 1.44 (s, 15H, C5Me5), 0.97 ppm (s, 3H, Me). 13C NMR (100.61 MHz, CD2Cl2, −25 °C): δ = 209.51 (CHO), 150.47 (C5), 144.87 (C4), 136.52−119.51 (30C, Ph), 100.46 (bs, C5Me5), 37.79 (dd, J (P,C) = 34.2, 8.2 Hz, C1), 35.48 (d, J (P,C) = 13.6 Hz, C3), 29.56 (dd, J (P,C) = 41.5, 11.5 Hz, C2), 12.98 (Me), 8.84 ppm (C5Me5). 31 P NMR (161.96 MHz, CD2Cl2, −25 °C): δ = 42.90 (d, J (P2,P1) = 12.3 Hz, P1), 22.76 ppm (d, P2).

(SIr,RC)-[(η 5-C5Me5)Ir(phenphos)(methacrolein)][SbF6]2 (12).

(SRh,RC)-[(η 5-C5Me5)Rh(valphos)(methacrolein)][SbF6]2 (15).

Yield: 83%. Anal. Calcd for C46H49F12IrOP2Sb2: C, 41.1; H, 3.7. Found: C, 41.1; H, 3.7. IR (solid, cm−1): ν(CO) 1622 (m), ν(SbF6) 654 (s). 1H NMR (400.16 MHz, CD2Cl2, −25 °C): δ = 7.90−6.53 (25H, Ph), 7.75 (s, 1H, CHO), 6.63 (s, 1H, H b), 6.15 (s, 1H, Ha), 3.79 (m, 1H, H11), 3.55 (dddd, J = 48.3, 15.5, 11.0, 4.4 Hz, 1H, H22), 3.15 (m, 1H, H21), 1.43 (t, J(P,H) = 2.2 Hz, 15H, C5Me5), 1.10 ppm (s, 3H, Me). 13C NMR (100.61 MHz, CD2Cl2, −25 °C): δ = 210.13 (CHO), 150.96 (C5), 145.45 (C4), 136.93−119.11 (30C, Ph), 100.46 (s, C5Me5), 43.32 (dd, J (P,C) = 31.1, 9.0 Hz, C1), 31.40 (dd, J (P,C) = 39.3, 14.9 Hz, C2), 13.28 (Me), 8.85 ppm (C5Me5). 31P NMR (161.96 MHz, CD2Cl2, −25 °C): δ = 48.98 (d, J (P2,P1) = 16.3 Hz, P1), 20.00 ppm (d, P2).

Yield: 84%. Anal. Calcd for C43H51F12RhOP2Sb2: C, 42.3; H, 4.2. Found: C, 42.3; H, 4.3. IR (solid, cm−1): ν(CO) 1614 (m), ν(SbF6) 652 (s). 1H NMR (500.13 MHz, CD2Cl2, −25 °C): δ = 7.93−7.34 (20H, Ph), 7.19 (s, 1H, CHO), 6.45 (s, 1H, Hb), 5.79 (s, 1H, Ha), 3.46 (dt, J = 56.0, 13.5 Hz, 1H, H22), 2.61 (m, 1H, H21), 2.33 (m, 1H, H11), 2.12 (m, 1H, H3), 1.38 (t, J = 3.1 Hz, 15H, C5Me5), 1.16 (d, J = 6.7 Hz, 3H, CH3), 0.93 (s, 3H, Me), 0.34 ppm (d, J = 6.5 Hz, 3H, CH3). 13 C NMR (125.77 MHz, CD2Cl2, −25 °C): δ = 207.75 (s, CHO), 148.28 (C5), 144.64 (C4), 135−120 (24C, Ph), 106.6 (s, C5Me5), 40.67 (dd, J (P,C) = 28.9, 8.6 Hz, C1), 28.49 (dd, J (P,C) = 15.1, 5.3 Hz, C3), 26.36 (dd, J (P,C) = 36.9, 17.2 Hz, C2), 24.37 (d, J(P,C) = 8.1 Hz, CH3), 17.90 (d, J(P,C) = 8.1 Hz, CH3), 13.14 (Me), 9.31 ppm (C5Me5). 31P NMR (202.48 MHz, CD2Cl2, −25 °C): δ = 74.43 (dd, J (Rh,P1) = 130.4 Hz, J (P2,P1) = 40.7 Hz, P1), 49.16 ppm (dd, J (Rh,P2) = 133.6 Hz, P2).

(SRh,RC)-[(η 5-C5Me5)Rh(benphos)(methacrolein)][SbF6]2 (13).

Yield: 90%. Anal. Calcd for C47H51F12RhOP2Sb2: C, 44.5; H, 4.05. Found: C, 44.0; H, 3.65. IR (solid, cm−1): ν(CO) 1614 (m), ν(SbF6) 653 (s). 1H NMR (500.13 MHz, CD2Cl2, −25 °C): δ = 7.96−7.02 (25H, Ph), 7.28 (s, 1H, CHO), 6.49 (s, 1H, Hb), 5.84 (s, 1H, Ha), 3.23 (d, J = 14.9 Hz, 1H, H32), 3.16 (dt, J = 52.55, 12.7 Hz, 1H, H22), 2.66 (m, 1H, H11), 2.58 (m, 1H, H21), 2.04 (m, 1H, H31), 1.41 (t, J = 2.7 Hz, 15H, C5Me5), 0.98 ppm (s, 3H, Me). 13C NMR (125.77 MHz, CD2Cl2, −25 °C): δ = 207.93 (CHO), 148.73 (C5), 144.65 (C4), 135−120 (30C, Ph), 106.71 (s, C5Me5), 37.49 (dd, J (P,C) = 27.7, 11.3 Hz, C1), 36.23 (d, J (P,C) = 15.9 Hz, C3), 29.33 (dd, J (P,C) = 35.3, 15.9 Hz, C2), 13.04 (Me), 9.37 ppm (C5Me5). 31P NMR (202.48 MHz, CD2Cl2, −25 °C): δ = 69.85 (dd, J (Rh,P1) = 132.4 Hz, J(P2,P1) = 40.7 Hz, P1), 46.46 ppm (dd, J (Rh,P2) = 133.2 Hz, P2).

(SIr,RC)-[(η 5-C5Me5)Ir(valphos)(methacrolein)][SbF6]2 (16).

Yield: 60%. Anal. Calcd for C43H51F12IrOP2Sb2: C, 39.4; H, 3.9. Found: C, 39.9; H, 4.2. IR (solid, cm−1): ν(CO) 1588 (m), ν(SbF6) 653 (s). 1H NMR (500.13 MHz, CD2Cl2, −25 °C): δ = 7.91−7.15 (20H, Ph), 7.34 (s, 1H, CHO), 6.41 (s, 1H, H b), 6670


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S at Metal Epimer (19a).

5.83 (s, 1H, Ha), 3.40 (ddd, J = 50.1, 14.9, 4.8 Hz, 1H, H22), 2.56 (m, 1H, H21), 2.26 (m, 1H, H11), 2.12 (m, 1H, H3), 1.40 (s, 15H, C5Me5), 1.19 (d, J = 6.7 Hz, 3H, CH3), 0.91 (s, 3H, Me), 0.31 ppm (d, J = 6.6 Hz, 3H, CH3). 13C NMR (125.77 MHz, CD2Cl2, −25 °C): δ = 209.37 (CHO), 150.12 (C5), 144.93 (C4), 135.97−119.32 (24C, Ph), 100.56 (s, C5Me5), 41.07 (dd, J (P,C) = 34.4, 6.3 Hz, C1), 27.45 (dd, J (P,C) = 14.2, 3.9 Hz, C3), 26.29 (dd, J (P,C) = 40.7, 12.2 Hz, C2), 24.69 (d, J(P,C) = 8.7 Hz, CH3), 17.71 (CH3), 12.85 (Me), 8.81 ppm (C5Me5). 31P NMR (202.48 MHz, CD2Cl2, −25 °C): δ = 46.84 (d, J(P2,P1) = 12.6 Hz, P1), 25.14 ppm (d, P2).

1

H NMR (500.13 MHz, CD2Cl2, −25 °C): δ = 7.93−7.29 (20H, Ph), 7.77 (s, 1H, CHO), 6.60 (s, 1H, Hb), 6.18 (dd, J = 5.4, 3.2 Hz, 1H, H5), 5.99 (s, 1H, Ha), 4.87 (d, J = 2.3 Hz, 1H, H6), 3.34 (s, 1H, H1), 3.19 (m, 1H, H3), 3.15 (s, 1H, H4), 2.85 (m, 1H, H2), 2.10 (bd, J = 10.9 Hz, 1H, H72), 1.96 (d, J = 9.4 Hz, 1H, H71), 1.44 ppm (s, 15H, C5Me5), 1.13 ppm (s, 3H, Me). 13C NMR (125.77 MHz, CD2Cl2, −25 °C): δ = 208.47 (CHO), 149.14 (C10), 145.43 (C9), 141.23 (d, J = 7.2 Hz, C5), 137.16−116.77 (24C, Ph), 129.98 (m, C6), 104.54 (s, C5Me5), 52.90 (d, J = 8.8 Hz, C7), 50.07 (dd, J = 26.0, 17.5 Hz, C3), 43.69 (d, J = 17.7 Hz, C2), 43.41 (dd, J = 12.7, 4.9 Hz, C1), 41.67 (dd, J = 12.7, 7.4 Hz, C4), 13.59 (Me), 9.67 ppm (C5Me5). 31P NMR (121.46 MHz, CD2Cl2, −25 °C): δ = 39.48 (dd, J (Rh,P1) = 132.7 Hz, J (P2,P1) = 45.1 Hz, P1), 32.09 ppm (dd, J (Rh,P2) = 136.9 Hz, P2).

(SRh,RC)-[(η 5-C5Me5)Rh(cyphos)(methacrolein)][SbF6]2 (17).

Yield: 97%. Anal. Calcd for C46H55F12RhOP2Sb2: C, 43.8; H, 4.4. Found: C, 43.6; H, 4.3. IR (solid, cm−1): ν(CO) 1613 (m), ν(SbF6) 653 (s). 1H NMR (500.13 MHz, CD2Cl2, 0 °C): δ = 7.9−7.3 (20H, Ph), 7.23 (s, 1H, CHO), 6.45 (s, 1H, H b), 5.81 (s, 1H, Ha), 3.45 (dt, J = 56.4, 13.9 Hz, 1H, H22), 2.57 (m, 1H, H21), 2.23 (m, 1H, H11), 1.53−0.81 (m, 11H, cy), 1.38 (t, J = 3.3 Hz, 15H, C5Me5), 0.89 ppm (s, 3H, Me). 13C NMR (125.77 MHz, CD2Cl2, −25 °C): δ = 207.78 (CHO), 148.34 (C5), 144.80 (C4), 134.93−120.68 (24C, Ph), 106.71 (s, C5Me5), 40.84 (dd, J (P,C) = 28.1, 8.8 Hz, C1), 37.33−22.54 (6C, cy), 26.70 (dd, J (P,C) = 31.8, 17.8 Hz, C2), 13.01 (Me), 9.44 ppm (C5Me5). 31P NMR (202.48 MHz, CD2Cl2, 0 °C): δ = 74.96 (dd, J(Rh,P1) = 130.2 Hz, J (P2,P1) = 40.7 Hz, P1), 49.32 ppm (dd, J (Rh,P2) = 133.5 Hz, P2).


(SRh,RC)-[(η 5-C5Me5)Ir(cyphos)(methacrolein)][SbF6]2 (18).

1

H NMR (400.16 MHz, CD2Cl2, −25 °C): δ = 7.99 (s, 1H, CHO), 6.73 (s, 1H, Hb), 6.55 (m, 1H, H5), 6.17 (s, 1H, Ha), 6.08 (dd, J = 5.3, 2.0 Hz, 1H, H6), 3.49 (m, 1H, H2), 3.30 (s, 1H, H1), 2.82 (s, 1H, H4), 2.14 (m, 1H, H3), 1.73 (m, 1H, H72), 1.44 (s, 15H, C5Me5), 1.25 (s, 3H, Me), 0.4 ppm (d, J = 8.8 Hz, 1H, H71). 13C NMR (125.77 MHz, CD2Cl2, −25 °C): δ = 208.70 (CHO), 149.65 (C10), 145.74 (C9), 141.68 (d, J = 6.9 Hz, C5), 137.16−116.77 (24C, Ph), 133.20 (m, C6), 104.45 (s, C5Me5), 51.98 (d, J = 10.1 Hz, C7), 47.30 (m, C3), 45.43 (d, J = 26.1 Hz, C2), 43.49 (m, C1), 40.69 (m, C4), 13.59 (Me), 9.60 ppm (C5Me5). 31P NMR (202.46 MHz, CD2Cl2, −25 °C): δ = 39.75 (dd, J (Rh,P2) = 131.7 Hz, J (P2,P1) = 46.2 Hz, P2), 29.87 ppm (dd, J (Rh,P1) = 136.1 Hz, P1).

Yield: 99%. Anal. Calcd for C46H55F12IrOP2Sb2: C, 40.9; H, 4.1. Found: C, 41.2; H, 4.2. IR (solid, cm−1): ν(CO) 1622 (m), ν(SbF 6 ) 654 (s). 1 H NMR (500.13 MHz, CD 2 Cl 2 , −25 °C): δ = 7.92−7.29 (20H, Ph), 7.40 (s, 1H, CHO), 6.43 (s, 1H, Hb), 5.87 (s, 1H, Ha), 3.40 (dddd, J = 51.8, 15.4, 11.9, 4.2 Hz, 1H, H22), 2.53 (m, 1H, H21), 2.16 (m, 1H, H11), 1.50−0.84 (m, 11H, cy), 1.42 (t, J = 2.2 Hz, 15H, C5Me5), 0.87 ppm (s, 3H, Me). 13C NMR (75.50 MHz, CD2Cl2, −25 °C): δ = 209.83 (CHO), 150.67 (C5), 145.48 (C4), 135.4−129.7 (24C, Ph), 100.69 (s, C5Me5), 41.46 (dd, J(P,C) = 33.2, 7.2 Hz, C1), 37.43−23.31 (6C, cy), 26.68 (dd, J (P,C) = 19.5, 10.4 Hz, C2), 13.30 (Me), 9.25 ppm (C5Me5). 31P NMR (121.48 MHz, CD2Cl2, −25 °C): δ = 47.59 (d, J (P2,P1) = 13.6 Hz, P1), 25.53 ppm (d, P2).

[(η 5-C5Me5)Ir(norphos)(methacrolein)][SbF6]2 (20). Yield: 77%. Molar ratio of S at the metal (20a) to R at the metal (20b) epimer: 67/33. Anal. Calcd for C45H49F12IrOP2Sb2: C, 40.6; H, 3.7. Found: C, 40.6; H, 3.9. IR (solid, cm−1): ν(CO) 1583 (m), ν(SbF6) 656 (s). S at Metal Epimer (20a).

[(η 5-C5Me5)Rh(norphos)(methacrolein)][SbF 6]2 (19). Yield: 95%. Molar ratio of S at the metal (19a) to R at the metal (19b) epimer: 63/37. Anal. Calcd for C45H49F12RhOP2Sb2·CH2Cl2: C, 41.6; H, 3.9. Found: C, 41.7; H, 4.2. IR (solid, cm−1): ν(CO) 1599 (m), ν(SbF6) 654 (s). 6671


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1

H NMR (500.13 MHz, CD2Cl2, −25 °C): δ = 7.92−7.30 (20H, Ph), 7.76 (s, 1H, CHO), 6.55 (s, 1H, H b), 6.19 (dd, J = 5.4, 3.2 Hz, 1H, H5), 5.98 (s, 1H, Ha), 4.85 (dd, J = 4.9, 2.3 Hz, 1H, H6), 3.34 (s, 1H, H1), 3.16 (m, 1H, H3), 3.15 (s, 1H, H4), 2.88 (m, 1H, H2), 2.33 (m, 1H, H72), 1.98 (d, J = 9.0 Hz, 1H, H71), 1.45 (s, 15H, C5Me5), 1.13 ppm (s, 3H, Me). 13C NMR (100.61 MHz, CD2Cl2, −25 °C): δ = 209.99 (CHO), 150.75 (C10), 145.70 (C9), 141.07 (d, J = 6.5 Hz, C5), 135.93−115.61 (24C, Ph), 129.88 (m, C6), 98.74 (s, C5Me5), 52.64 (m, C7), 49.80 (m, C3), 43.91 (d, J = 15.3 Hz, C2), 43.11 (m, C1), 40.65 (dd, J = 11.8, 6.2 Hz, C4), 14.26 (Me), 9.18 ppm (C5Me5). 31 P NMR (161.98 MHz, CD2Cl2, −25 °C): δ = 12.41 (d, J (P2,P1) = 28.0 Hz, P1), 6.95 ppm (d, P2).

and an ORTEP diagram and structural parameters concerning the CH/π interactions for the cation of 14. This material is available free of charge via the Internet at http://pubs.acs.org.

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ACKNOWLEDGMENTS We thank the Ministerio de Educación y Ciencia (Grant CTQ 2009-10303/BQU) and Gobierno de Aragón (Grupo Consolidado: Catalizadores Organometálicos Enantioselectivos) for financial support. A.A thanks the IUCH for a grant. P.G.-O. acknowledges financial support from the CSIC, ″JAE-Doc″ program, contract cofunded by the ESF.

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(1) (a) Jacobsen, E. N., Pfaltz, A., Yamamoto, H., Eds. Comprehensive Asymmetric Catalysis; Springer: New York, 1999; Vol. I−III. (b) Jacobsen, E. N., Pfaltz, A., Yamamoto, H., Eds. Comprehensive Asymmetric Catalysis: Supplement 1; Springer: New York, 2004. (c) Jacobsen, E. N., Pfaltz, A., Yamamoto, H., Eds. Comprehensive Asymmetric Catalysis: Supplement 2; Springer: New York, 2004. (d) Ojima, I., Ed. Catalytic Asymmetric Synthesis; VCH: Weinheim, Germany, 2000. (e) Noyori, R. Asymmetric Catalysis in Organic Synthesis; John Willey and Sons: New York, 1994. (2) (a) Fringuelli, F.; Taticchi, A. The Diels-Alder Reaction. Selected Practical Methods; Wiley, New York, 2002. (b) Carmona, D.; Lamata, M. P.; Oro, L. A. Coord. Chem. Rev. 2000, 200−202, 717−772. (c) Dias, L. C. J. Braz. Chem. Soc. 1997, 8, 289−332. (d) Hollis, T. K.; Oderdink, W.; Robinson, J. W.; Bosnich, B. Tetrahedron 1993, 49, 5415−5430. (e) Kobayashi, S. Pure Appl. Chem. 1998, 70, 1019−1026. (f) Corey, E. J.; Guzmán-Pérez, A. Angew. Chem., Int. Ed. 1998, 37, 389−401. (g) Johannsen, M.; Yao, S.; Graven, A.; Jørgensen, K. A. Pure Appl. Chem. 1998, 70, 1117−1122. (h) Jørgensen, K. A.; Johannsen, M.; Yao, S.; Audrian, H.; Thorhauge, J. Acc. Chem. Res. 1999, 32, 605−613. (3) (a) Kündig, E. P.; Bourdin, B.; Bernardinelli, G. Angew. Chem., Int. Ed. Engl. 1994, 33, 1856−1858. (b) Bruin, M. E.; Kündig, E. P. Chem. Commun. 1998, 2635−2636. (c) Kündig, E. P.; Saudan, C. M.; Bernardinelli, G. Angew. Chem., Int. Ed. 1999, 38, 1219−1223. (d) Kündig, E. P.; Saudan, C. M.; Viton, F. Adv. Synth. Catal. 2001, 343, 51−56. (e) Kündig, E. P.; Saudan, C. M.; Alezra, V.; Viton, F.; Bernardinelli, G. Angew. Chem., Int. Ed. 2001, 40, 4481−4485. (f) Alezra, V.; Bernardinelli, G.; Corminboeuf, C.; Frey, U.; Kündig, E. P.; E. Merbach, A.; Saudan, C. M.; Viton, F.; Weber, J. J. Am. Chem. Soc. 2004, 126, 4843−4853. (g) Anil Kumar, P. G.; Pregosin, P. S.; Vallet, M.; Bernardinelli, G.; Jazzar, R. F.; Viton, F.; Kündig, E. P. Organometallics 2004, 23, 5410−5418. (h) Rickerby, J.; Vallet, M.; Bernardinelli, G.; Viton, F.; Kündig, E. P. Chem.Eur. J. 2007, 13, 3354−3368. (i) Thamapipol, S.; Bernardinelli, G.; Besnard, C.; Kündig, E. P. Org. Lett. 2010, 12, 5604−5607. (4) (a) Faller, J. W.; Parr, J. Organometallics 2000, 19, 1829−1832. (b) Faller, J. W.; Lavoie, A. J. Organomet. Chem. 2001, 630, 17−22. (c) Faller, J. W.; Parr, J. Organometallics 2001, 20, 697−699. (d) Faller, J. W.; Grimmond, J. B. Organometallics 2001, 20, 2454−2458. (e) Faller, J. W.; Grimmond, J. B.; D’Alliessi, D. G. J. Am. Chem. Soc. 2001, 123, 2525−2529. (f) Faller, J. W.; Lavoie, A. R.; Grimmond, B. J. Organometallics 2002, 21, 1662−1666. (g) Faller, J.; D’Alliessi, D. G. Organometallics 2003, 22, 2749−2757. (h) Faller, J. W.; Fontaine, P. P. Organometallics 2005, 24, 4132−4138. (5) (a) Davies, D. L.; Fawcett, J.; Garratt, S. A.; Russell, D. R. Chem. Commun. 1997, 1351−1352. (b) Davenport, A. J.; Davies, D. L.; Fawcett, J.; Garratt, S. A.; Lad, L.; Russell, D. R. Chem. Commun. 1997, 2347−2348. (c) Davenport, A. J.; Davies, D. L.; Fawcett, J.; Krafczyk, R.; Russell, D. R. J. Chem. Soc., Dalton Trans. 2000, 4432−4441. (d) Davenport, A. J.; Davies, D. L.; Fawcett, J.; Russell, D. R. J. Chem. Soc., Perkin Trans. 1 2001, 1500−1503. (e) Davies, D. L.; Fawcett, J.; Garratt, S. A.; Russell, D. R. Organometallics 2001, 20, 3029−3034. (f) Davies, D. L.; Fawcett, J.; Garratt, S. A.; Russell, D. R. J. Organomet. Chem. 2002, 662, 43−50. (g) Davenport, A. J.; Davies, D. L.; Fawcett,

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H NMR (400.16 MHz, CD2Cl2, −25 °C): δ = 7.96 (s, 1H, CHO), 7.92−7.30 (20H, Ph), 6.67 (s, 1H, Hb), 6.61 (dd, J = 5.5, 3.2 Hz, 1H, H5), 6.19 (s, 1H, Ha), 6.06 (dd, J = 5.5, 2.7 Hz, 1H, H6), 3.50 (m, 1H, H2), 3.31 (s, 1H, H1), 2.79 (s, 1H, H4), 2.17 (m, 1H, H3), 1.95 (m, 1H, H72), 1.45 (s, 15H, C5Me5), 1.26 (s, 3H, Me), 0.38 ppm (d, J = 8.8 Hz, 1H, H71). 13C NMR (100.61 MHz, CD2Cl2, −25 °C): δ = 210.21 (CHO), 151.29 (C10), 145.88 (C9), 141.59 (d, J = 7.8 Hz, C5), 133.28 (m, C6), 98.67 (s, C5Me5), 52.22 (m, C7), 47.52 (m, C3), 46.01 (m, C2), 44.33 (d, J = 15.4 Hz, C1), 39.86 (m, C4), 14.19 (Me), 9.12 ppm (C5Me5). 31P NMR (161.98 MHz, CD2Cl2, −20 °C): δ = 12.73 (d, J (P2,P1) = 28.6 Hz, P2), 4.36 ppm (d, P1). Structural Analysis of Complexes 13 and 14. The X-ray diffraction data were collected at 100(2) K on a Bruker SMART APEX CCD area detector diffractometer with graphite-monochromated Mo Kα radiation (λ = 0.71073 Å) using narrow ω rotations (0.3°). Intensities were integrated with APEX2 and SMART programs and corrected of absorption effects with SADABS.23 The structures were solved by direct methods SHELXS-9724 and refined using SHELXL97.25 Anisotropic displacement parameters were used for all non-H atoms. Hydrogen atoms were observed in the Fourier difference maps and refined with a riding model from calculated positions. Additionally, to the internal configuration reference of the (R)-benphos ligand, the Flack parameter was refined as a check on the correct absolute configuration determination.26 An analysis of the solvent region has been performed using the SQUEEZE program.27 Complex 14 tends to form twinned crystals, not very appropriate for X-ray diffraction data collection; unfortunately, several crystals were tested with no success. Finally, a tiny crystal allows us to solve the structure, although the presence of a high value of the second parameter of the weighting scheme points to the fact that the chosen sample was also twinned. Residual density peaks of 7.22 and 7.19 e·Å−3 were observed at the end of the refinement. Both peaks were located close to the metal atom (closer than 1 Å), at both sides to the Ir atom. They have no chemical sense.

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REFERENCES

ASSOCIATED CONTENT

S Supporting Information *

X-ray crystallographic information files containing full details of the structural analysis of complexes 13 and 14 (CIF format) 6672


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0.09 × 0.07 mm3; orthorhombic; P212121; a = 11.1076(3) Å, b = 15.9002(7) Å, c = 30.7680(10) Å; V = 5434.0(3) Å3; Z = 4; Dc = 1.870 g/cm3; μ = 3.561 mm−1; min and max. transmission factors, 0.509 and 1.0; 2θ max = 57.88°; 104 944 reflections collected, 13 644 unique [Rint = 0.103]; number of data/restrains/parameters, 13 644/ 0/592; final GOF, 1.100; R1 = 0.069 [13 644 reflns, I > 2 σ(I)]; wR(F 2) = 0.156 for all data; Flack parameter: x = 0.034(8). (15) Cremer, D.; Pople, J. A. J. Am. Chem. Soc. 1975, 97, 1354−1358. (16) Totev, D.; Salzer, A.; Carmona, D.; Oro, L. A.; Lahoz, F. J.; Dobrinovitch, I. T. Inorg. Chim. Acta 2004, 357, 2889−2898. (17) Brunner, H.; Winterm, A.; Breu, J. J. Organomet. Chem. 1998, 553, 285−306. (18) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen, A. G.; Taylor, R. J. Chem. Soc., Perkin Trans. 1987, S1−S19. (19) Takahashi, O.; Kohni, Y.; Nishio, M. Chem. Rev. 2010, 110, 6049−6076. (20) To simplify the stereochemical notation, we will use SM to denote the (SM,S1C,R2C,R3C,R4C)-[(η 5-C5Me5)M(norphos)(ligand)] [SbF6]2 isomer and RM for the corresponding epimer at the metal (RM,S1C,R2C,R3C,R4C)-[(η 5-C5Me5)M(norphos)(ligand)][SbF6]2; thus, for example, 9a ≡ SRh-9 and 20b ≡ RIr-20. (21) Racemic mixture A was obtained in the reaction between HCp and methacrolein catalyzed by the achiral complex [(η 5-C5Me5) Ir(dppe)(H2O)][SbF6]2 (dppe = ethane-1,2-diylbis(diphenylphosphane). Mixture B was obtained according to entry 10, Table 1. (22) (a) King, R. B.; Bakos, J.; Hoff, C. D.; Markó, L. J. Org. Chem. 1979, 44, 1729−1731. (b) Riley, D. P.; Shumate, R. E. J. Org. Chem. 1980, 45, 5187−5193. (c) Bergstein, W.; Kleemann, A.; Martens, J. Synthesis 1981, 76−78. (23) Blessing, R. H. Acta Crystallogr. 1995, A51, 33−38. (24) Sheldrick, G. M. Acta Crystallogr. 1997, A46, 467−473. (25) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112−122. (26) Flack, H. D. Acta Crystallogr. 1983, A39, 876−881. (27) der Luis, P. V.; Spek, A. L. Acta Crystallogr. 1990, A46, 194− 201.

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