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Diastereoselective Attack on Chiral-at-Metal Ruthenium Allenylidene Complexes To Give Alkynyl Complexes Matthew J. Queensen,† Nigam P. Rath,†,‡ and Eike B. Bauer*,† †

Department of Chemistry and Biochemistry and ‡Center for Nanoscience, University of Missouri−St. Louis, One University Boulevard, St. Louis, Missouri 63121, United States S Supporting Information *

ABSTRACT: New chiral ruthenium(II) allenylidene complexes were synthesized, and their reactivity with nucleophiles to give alkynyl complexes was investigated. The new allenylidene complex (RRu,Rax)-[Ru(Ind)(PPh3)(6){C CC(t-Bu)(2-naphthyl)}]+PF6− was synthesized from the chloro precursor complex (RRu,Rax)-[RuCl(Ind)(PPh3)(6)] and the racemic propargylic alcohol HCCC(OH)(t-Bu)(2naphthyl) and obtained in 96% yield, where (Rax)-6 is a chiral phosphoramidite and Ind an anionic indenyl ligand. The precursor and the allenylidene complex are chiral-at-metal, and the chiral information is completely transferred from the chloro precursor to the product allenylidene complex, both of which show the same absolute configuration, as demonstrated by X-ray diffraction. Together with the known allenylidene complex (RRu,Rax)-[Ru(Ind)(PPh3)(6)(CCCPh2)]+PF6−, the attack of n-BuLi, MeLi, LiCCPh, and lithium 1-phenylethenolate nucleophiles on the allenylidene chain of (RRu,Rax)-[Ru(Ind)(PPh3)(6){CCC(t-Bu)(2-naphthyl)}]+PF6− was investigated. The nucleophiles (Nu) reacted selectively with the gamma carbon of the allenylidene complexes to give the alkynyl complexes (RRu,Rax)-[Ru(Ind)(PPh3)(6)(CC−CPh2Nu)] and (RRu,Rax)[Ru(Ind)(PPh3)(6){CC−C(t-Bu)(2-naphthyl)Nu}] in 40% to 96% isolated yields. In the case of (RRu,Rax)-[Ru(Ind)(PPh3)(6){CC−C*(t-Bu)(2-naphthyl)Nu}], the gamma carbon C* becomes stereogenic upon attack of the nucleophiles. As assessed by 31P{1H} NMR, diastereodifferentiation took place, and the alkynyl complexes were isolated as diastereomeric mixtures with diastereomeric ratios between 60:40 and 84:16. The diastereodifferentiation originated only from the stereogenic metal center and the monodentate, chiral ligand. The study allows for investigation of stereoselective, nucleophilic attack of allenylidene complexes to give optically active, quaternary alkynes, which play a role in potential catalytic versions of nucleophilic substitution reactions of propargylic alcohols.

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INTRODUCTION Allenylidene complexes are cumulene-type structures of the general formula [MCCCR2] (2, Scheme 1).1 This class of complexes has been known since the 1970s.2 Their investigation advanced significantly when Selegue found in 1982 that they can be accessed from corresponding (activated) precursor complexes and propargylic alcohols 1 (Scheme 1).3 Since then, a number of stable allenylidene complexes have been isolated, mainly based on ruthenium,4,5 but also for other metals such as palladium, 6 chromium, 7 molybdenum,8 osmium,9 or iron.10 Allenylidene complexes exhibit interesting optical and electrochemical properties.11 Furthermore, some allenylidene complexes show catalytic activity, e.g., in olefin metathesis,12 etherification of propargylic alcohols,13 ringopening polymerization,14 oxidative coupling,15 or reduction reactions.16 Most significantly, allenylidene complexes have been suggested as catalytic intermediates in the activation of propargylic alcohols toward nucleophilic substitution reactions (Scheme 1 shows a potential catalytic cycle).1,17,18 The Cα and Cγ atoms of the allenylidene chain 2 bear a positive partial charge, as shown by experiment and calculations.19 As such, the © 2014 American Chemical Society

Cα and Cγ atoms can be attacked by nucleophiles to give allenyl or alkynyl complexes, respectively.20 The negatively charged Cβ atom was shown to be protonated by Brønsted acids.21 In a catalytic cycle, a propargylic alcohol could be activated through an allenylidene intermediate 2, which then can be attacked by a nucleophile (Scheme 1). Protonolysis of the resulting alkynyl complex 3 completes the cycle. Accordingly, allenylidene complexes have been suggested as intermediates in a number of catalytic reactions, where the OH functionality of propargylic alcohols (or derivatives thereof) is replaced by nucleophiles.18,22 Copper-catalyzed amination reactions of propargylic acetates have been shown by experiment and calculations to proceed through allenylidene intermediates,23 as has ruthenium-catalyzed replacement of the −OH functionality of propargylic alcohols by a number of nucleophiles.24 Cyclization reactions have also been reported to proceed through allenylidene intermediates.25 In propargylic alcohols of the general formula HC CC*(OH)R1R2 with two different R1R2 groups, the C* carbon Received: June 5, 2014 Published: September 3, 2014 5052

dx.doi.org/10.1021/om500600y | Organometallics 2014, 33, 5052−5065

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As outlined above, the stereoselective attack on allenylidene complexes is crucial in stoichiometric as well as catalytic applications (Scheme 1). The stereoselectivity during the attack can be achieved either through chiral ligands or through stereogenic centers at the substituents of the Cγ atom. Chiral allenylidene complexes have been increasingly investigated in the last two decades,29 but they are not as well explored as their achiral counterparts. Continued research is necessary to better understand and to promote stereoselective attack on chiral allenylidene complexes. As part of our continuous research efforts directed toward the catalytic activation of propargylic alcohols,13,30 we are interested in allenylidene complexes and are investigating new ways as to how they can be reacted with nucleophiles stereoselectively. Chiral-at-metal complexes can provide new pathways to enantioselective reactions.31 Chiral-at-metal allenylidene complexes are rare,29,32 and we speculated that stereogenic metal centers could provide a new method of stereocontrol in the reactions of allenylidene complexes. We have recently synthesized the chiral-at-metal ruthenium(II) complex (RRu,Rax)-[RuCl(Ind)(PPh3)(6)], [(RRuRax)-7] in diastereopure form, where (R)-6 is a chiral phosphoramidite and Ind the indenyl ligand η5-C9H7− (Scheme 2).33 The complex was converted to a series of ruthenium allenylidene complexes of the formula (RRu,Rax)-[Ru(Ind)(PPh3)(6)(C CCR1R2)]+PF6− (R1/R2 = Ph/Ph, Ph/Me, Me/2-furyl) with complete retention of configuration at the stereogenic ruthenium center.33 We hypothesized that these allenylidene complexes would be good candidates to investigate the stereoselectivity of nucleophilic attack. Herein, we present a new chiral-at-metal allenylidene complex, (RRu,Rax)-[Ru(Ind)(PPh3)(6){CCC(t-Bu)(2-naphthyl)}]+PF6−. Together with the previously synthesized allenylidene complex (RRu,Rax)[Ru(Ind)(PPh3)(6)(CCCPh2)]+PF6− [subsequently referred to as (RRu,Rax)-10, Scheme 2], the attack of a number of carbon-centered nucleophiles on the allenylidene chains was investigated.

Scheme 1. Allenylidene Formation and Potential Catalytic Cycle

atom is stereogenic. Replacement of the OH group by a nucleophile results in a chiral alkyne of the general formula HCCC*(Nu)R1R2. In the case that the replacement reaction proceeds through an allenylidene intermediate [MCC CR1R2], it is not relevant whether the propargylic alcohol 1 that is employed is enantiopure or racemic, as the stereogenic center is destroyed upon allenylidene formation. For the enantioselective formation of an alkyne product, the critical step is the stereoselectivity of the attack of the nucleophile on the allenylidene intermediate 2 (Scheme 1). It has been argued that the Cγ atom is relatively distant from the metal center and its (chiral) ligands, making stereodifferentiation upon nucleophilic attack more problematic. Nevertheless, enantiomeric excesses have been reported in catalytic cycles that have been suggested to proceed through allenylidene intermediates.26,27 The stereoselective, nucleophilic attack on the Cγ atom in allenylidene complexes has also been utilized in the stoichiometric formation of optically active alkynes; in this case, the allenylidene chain bore the chiral information in its backbone.28

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RESULTS Our investigation started with the previously synthesized allenylidene complex (RRu,Rax)-[Ru(Ind)(PPh3)(6){C CC(CH3)Ph}]+PF6− [(RRu,Rax)-12],33 which was investi-

Scheme 2. Allenylidene Syntheses

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gated upon its reaction with lithium 1-phenylethenolate, which resulted mainly in deprotonation of the methyl group to give a neutral enynyl complex, (RRu,Rax)-13 (for details see the Supporting Information). It has previously been reported that hydrogens on carbon atoms in a position alpha to the Cγ atom of the allenylidene chain can be considerably acidic.5b Thus, we focused our efforts on allenylidene complexes without hydrogen atoms on the carbon atom in the α position to the Cγ atom. The commercial propargyic alcohol HCCC(OH)(t-Bu)(2naphthyl) (9) seemed to be a good starting material for the synthesis of a corresponding allenylidene complex. Following a protocol previously established in our laboratory,33 the chloro precursor complex (RRu,Rax)-7 was first treated with (Et3O)PF6 to selectively remove the chloro ligand (Scheme 2). Upon addition of the propargylic alcohol 9, the new allenylidene complex (RRu,Rax)-[Ru(Ind)(PPh3)(6){ CCC(t-Bu)(2-naphthyl)}]+PF6− formed, which subsequently will be referred to as (RRu,Rax)-11 without charge and counterion. It was isolated by fractional crystallization as a dark red powder in 96% yield. The complex (RRu,Rax)-11 was isolated in diastereopure form, and its identity was established by NMR, MS, IR, UV− vis, circular-dichroism (CD, vide inf ra), and X-ray diffraction. The 1H NMR spectrum showed three distinct signals for the three protons of the five-membered-ring portion of the indenyl ligand at 6.45, 5.60, and 5.29 ppm, as previously observed.33 The three protons of the five-membered-ring portion of the indenyl ligand might give three signals, because the complex is stereogenic at the metal; typically two of the three protons are magnetically equivalent, and only two signals are observed for these protons.34 The NCHH′ protons of the phosphoramidite ligand are diastereotopic and gave signals between 3.05 and 4.14 ppm, including 2JHH coupling constants of 11 and 13 Hz. The Cα, Cβ, and Cγ atoms were readily identified in the 13 C{1H} NMR spectrum, which exhibited signals at 312.5 (weak), 203.0, and 181.1 ppm. These chemical shifts are diagnostic for allenylidene complexes.1,5o,33 In the 31P{1H} NMR spectrum, the signals arising from the PPh3 and phosphoramidite ligands in (RRu,Rax)-11 are shifted relative to those of the chloro starting material (RRu,Rax)-7 (Δppm ≈ ±4). The spectrum of (RRu,Rax)-11 exhibited two mutually coupled signals at 167.4 and 50.8 ppm (2JPP = 32 Hz) for the two coordinated phosphorus atoms of the PPh3 and phosphoramidite ligand (R)-6, respectively. The NMR spectra exhibited only one set of signals for the complex (RRu,Rax)-11, establishing its diastereopurity. The complex also exhibited a band at 1936 cm−1 for the allenylidene chain in the IR spectrum, which is diagnostic for allenylidene complexes.5o Somewhat surprisingly, the complex did not show a band around λmax = 550 nm in the UV−vis spectrum, as reported for other ruthenium allenylidene complexes.5i To unequivocally establish the structure of the new complex, the X-ray structure was determined. The molecular structure is depicted in Figure 1. Crystallographic details are given in the Supporting Information (Table S1), and key bond lengths and angles are compiled in Table 1. The bond angles for the monodentate ligands about the ruthenium center range from 84.29(15)° to 100.52(4)°. The structure is, thus, best described as a slightly distorted octahedron. The solid-state structure shows that the absolute configurations about the ruthenium center in the precursor (RRu,Rax)-7 and the allenylidene complex (RRu,Rax)-11 are identical. As observed previously for other allenylidene complexes synthesized from the diaster-

Figure 1. Two different views of the molecular structure of (RRu,Rax)11. Hydrogen atoms, the CH2Cl2 solvent molecule, and the PF6− counterion are omitted for clarity. In the bottom view, the indenyl ligand is omitted. Crystallographic parameters are compiled in the Supporting Information (Table S1), and key bond lengths and angles are listed in Table 1.

Table 1. Key Bond Lengths (Å) and Angles (deg)

Ru−CX Ru−P1 Ru−P2 CX−CY CY−CZ CX−Ru−P1 CX−Ru−P2 P1−Ru−P2 CX−CY−CZ CY−CX−Ru CY−CZ−C13 Ru−Ind

(RRu,Rax)-11, X = 1, Y = 2, Z=3

(RRu,Rax)-17, X = 10, Y = 11, Z = 12

1.878(5) 2.2614(12) 2.3152(13) 1.259(7) 1.336(7) 89.50(16) 84.29(15) 100.52(4) 171.4(6) 175.6(5) 119.1(5) 1.943

2.040(5) 2.1897(11) 2.3247(11) 1.187(7) 1.497(7) 93.34(13) 86.22(12) 98.11(4) 178.1(5) 172.9(4) 110.8(4) 1.940

eopure precursor (RRu,Rax)-7, the chiral information was completely transferred from the precursor to the allenylidene 5054


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complex (RRu,Rax)-11.33 The C1−C2−C3 angle of the allenylidene chain in (RRu,Rax)-11 was determined to be 171.4(6)°; this slight deviation from the ideal angle of 180° has frequently been observed previously for allenylidene complexes by us33 and others.5o The internal CαCβ bond is significantly shorter [1.259(7) Å] than the terminal CβCγ bond [1.336(7) Å], a pattern that has been observed for other allenylidene complexes previously,1b,5o,33 and calculations also have corroborated the difference in bond lengths for related systems.35 The Ru−P bond length for the phosphoramidite ligand [2.2614(12) Å] is shorter than that found for the PPh3 ligand [2.3152(13) Å]. We observed this phenomenon previously in the X-ray structures of related allenylidene complexes such as (RRu,Rax)-10 (Scheme 2).33 The positions of the t-Bu and 2-naphthyl substituents at the Cγ carbon atom in the allenylidene complex are oriented almost in a plane formed by the Cα atom of the allenylidene chain, the ruthenium center, and the cyclopentadienyl centroid of the indenyl ligand (schematically shown in structure B, Figure 2),

1-phenylethenolate was generated in solution from LDA and acetophenone and employed without purification or workup, as reported previously by others.28b The other lithium nucleophiles are commercially available and were titrated prior to use.36 The reactions resulted in alkynyl complexes of the general formula (R Ru ,R ax )-[Ru(Ind)(PPh 3 )(6)(CC− CPh 2Nu)] [(RRu ,Rax)-14 to -17], which were isolated chromatographically or by washing of the residue as bright, yellow-orange, air-stable powders in 40% to 74% yields. The complexes were isolated in diastereopure form, and their identity was established by NMR, FAB-MS, UV−vis, IR, and Xray. After reaction with the nucleophiles, the band at 1950 cm−1 in the IR spectrum had disappeared in the new complexes. Instead, new bands between 2082 and 2087 cm−1 were observed in the IR spectra of the new complexes 14−17, which are characteristic for alkynyl ligands.20c,32 The 1H NMR spectrum showed three distinct signals for the three protons of the five-membered-ring portion of the indenyl ligand between 5 and 5.5 ppm, as previously observed for other neutral ruthenium indenyl complexes.20c The NCHH′ protons of the phosphoramidite ligand are again diastereotopic and exhibited signals between 3.3 and 4.8 ppm, including 2JHH couplings of around 11 Hz. The Cα, Cβ, and Cγ atoms of the alkynyl chain were readily identified in the 13C{1H} NMR spectrum, which exhibited signals around 92 ppm for the Cα, around 117 ppm for the Cβ, and around 49 ppm for the Cγ carbon atom. These chemical shifts are diagnostic for neutral ruthenium alkynyl ligands.20c In addition, the Cα carbon atoms exhibited 2JCP couplings around 26 Hz. The 31P{1H} NMR of the alkynyl complexes showed two mutually coupled signals around 180 and 54 ppm (2JPP between 50 and 54 Hz) for the two coordinated phosphorus atoms of the PPh 3 and phosphoramidite ligand, respectively. The 31P{1H} NMR signals of the neutral alkynyl complexes are slightly shifted compared to the cationic allenylidene precursor complex (RRu,Rax)-10, which had exhibited chemical shifts of 171.4 and 53.4 ppm in the 31P{1H} NMR.33 Again, the NMR spectra exhibited only one set of signals for the alkynyl complexes (RRu,Rax)-14 to -17, establishing their diastereopurity. Nucleophilic attack had occurred at the Cγ carbon atom and did not alter the stereochemistry of the ruthenium complexes. To unequivocally establish the structure of the new alkynyl complexes, an X-ray diffraction analysis of the complex (RRu,Rax)-17 was performed. The molecular structure is depicted in Figure 3. Crystallographic details are given in the Supporting Information (Table S1), and key bond lengths and angles are compiled in Table 1. The bond angles for the monodentate ligands about the ruthenium center range from 86.22(12)° to 98.11(4)°. The structure is, thus, again best described as a slightly distorted octahedron. The solid-state structure shows that the absolute configurations about the ruthenium center in the precursor (RRu,Rax)-7, the allenylidene complex (RRu,Rax)-10, and the alkynyl complex (RRu,Rax)-17 are identical. The chiral information was completely transferred from the allenylidene complex (RRu,Rax)-10 to the alkynyl complexes (RRu,Rax)-17. The C10−C11−C12 angle of the alkynyl chain in (RRu,Rax)17 is 178.1(5)°; this slight deviation from the ideal angle of 180° has also been observed for other ruthenium alkynyl complexes.20c The internal CαCβ bond is significantly shorter [1.187(7) Å] than the terminal Cβ−Cγ bond [1.497(7) Å]; these values are typical for CC triple and C−C single bonds, respectively, as expected for an alkynyl complex.20c As

Figure 2. Schematic representation of the conformations of the chloro, allenylidene, and alkynyl complexes.

as previously observed for allenylidene complexes by us33 and others.5o The t-Bu group is pointing toward the indenyl ligand. As schematically shown in Figure 2 (structure C), the aryl ring of the indenyl ligand is oriented along the allenylidene chain, as observed in the structurally related complexes (RRu,Rax)-10 (Scheme 2) and (RRu,Rax)-[Ru(Ind)(PPh3)(6){CCC(CH3)Ph}]+PF6−.33 The geometry differs from the precursor (RRu,Rax)-7, where the indenyl ligand occupies in the solid state an interstitial site between the chloro and PPh3 ligands (Figure 2, structure A).33 The orientation of the indenyl along the allenylidene chain might have an impact on the potential attack of nucleophiles, as the electrophilic Cα carbon atom is sterically more protected than the Cγ carbon. We next investigated the nucleophilic attack of selected reagents on allenylidene complexes. We first employed for test reactions the allenylidene complex (RRu,Rax)-10, which is somewhat easier to access. At temperatures from −20 to −68 °C, (RRu,Rax)-10 was treated with MeLi, n-BuLi, LiCCPh, and lithium 1phenylethenolate nucleophiles (Scheme 3, top). The lithium 5055


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Scheme 3. Synthesis of the Alkynyl Complexes

90 ppm for the Cα, at around 112 ppm for the Cβ, and at around 50 ppm for the Cγ atom.20c The IR spectra exhibited bands between 2071 and 2080 cm−1, as expected for alkynyl complexes.20c,32 Most significantly, as opposed to the alkynyl complexes (RRu,Rax)-14 to -17 described before, the complexes (RRu,Rax)18, (RRu,Rax)-19, and (RRu,Rax)-20 were isolated as mixtures of diastereomers. The 31P{1H} NMR spectra of the three complexes exhibited two sets of signals for both the PPh3 and phosphoramidite ligands. Similar signal doubling was observed in the 13C{1H} NMR spectra and for some distinct signals in the 1H NMR spectra. Extensive efforts to obtain X-ray quality crystals for any of the new alkynyl complexes failed, which we tentatively ascribe to the fact that a mixture of diastereomers has been isolated. All efforts to separate the diastereomers by chromatography or fractional crystallization failed, presumably due to the fact that their physical properties do not differ significantly. Difficulties in separation and crystallization of diastereomeric mixtures of related ruthenium allenylidene complexes have previously been reported by others.32 In order to determine the ratios, we integrated the diastereomeric signals for the phosphorus atoms of the ligands in the 31P{1H} NMR spectra as previously reported by others.20a,32 A representative 31P{1H} NMR spectrum for the alkynyl complex (RRu,Rax)-19 is displayed in Figure 4 (the 31 1 P{ H} NMR spectra for the other two alkynyl complexes are given in the Supporting Information). As can be seen, the phosphorus atoms of the coordinated PPh3 and phosphor-

schematically shown in Figure 2, the position of the indenyl ligand in the solid state changed from the allenylidene complex (RRu,Rax)-11 (structure C) to the alkynyl complex (RRu,Rax)-17 (structure D). In the allenylidene complex, the indenyl ligand is oriented alongside the allenylidene chain, whereas in the alkynyl complex (RRu,Rax)-17, it occupies the interstitial site between the alkynyl chain and the PPh3 ligand. Finally, we employed the allenylidene complex (RRu,Rax)-11 in reactions with nucleophiles (Scheme 3, bottom) with selected reagents. The complex bears two different substituents at the Cγ atom, and a nucleophilic attack on that atom creates a new stereocenter. As complex (RRu,Rax)-11 was employed in diastereopure form, two different diastereomers can form upon the attack, and the diastereomeric ratio of the alkynyl complexes to be formed gives information about the stereoselectivity of the nucleophilic attack, as previously reported for related systems. Accordingly, the allenylidene complex was treated with MeLi, LiCCPh, and lithium 1-phenylethenolate nucleophiles under conditions described previously for the allenylidene complex (RRu,Rax)-10. Chromatographic workup gave the corresponding alkynyl complexes (RRu,Rax)-[Ru(Ind)(PPh3)(6){CC−C(t-Bu)(2-naphthyl)Nu}] (RRu,Rax)-18, (RRu,Rax)-19, and (RRu,Rax)-20 as air-stable, yellow solids in 72% to 96% isolated yields. The new alkynyl complexes (RRu,Rax)-18, (RRu,Rax)-19, and (RRu,Rax)-20 were analyzed by NMR, IR, FAB-MS, and elemental analysis. Their spectroscopic data were similar to those of the other alkynyl complexes 14 to 17 described previously. The alkynyl chain gave again resonances at around 5056


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at 292, 319, and 332 nm, respectively, with positive Cotton effects. The allenylidene complex remotely resembled the spectrum of the chloro precursor at lower wavenumbers below 350 nm; no bands with negative Cotton effects were observed, but two peaks with positive Cotton effects at 293 and 335 nm were present, which are close to the bands for the chloro precursor. However, the allenylidene complex (RRu,Rax)-11 gave a broad, positive band around 404 nm and a negative band at 478 nm, which are both absent in the chloro precursor. Finally, the alkynyl complex (RRu,Rax)-19 exhibited a negative, noisy band around 305 nm and three positive bands at 335, 405, and 451 nm. An absolute configuration cannot be unambiguously derived from the CD spectra, but compounds of opposite configuration show mirror image CD spectra.31,37 All three spectra show mainly positive Cotton effects, and by analogy it can be anticipated that all three complexes have the same configuration, as established for the chloro precursor (RRu,Rax)7 and the allenylidene complex (RRu,Rax)-11 by X-ray diffraction. To the best of our knowledge, CD spectra have not been recorded for allenylidene complexes to date. However, the allenylidene complex shows new bands above 350 nm compared to the chloro precursor, which might be assigned to the allenylidene chain. Allenylidene complexes typically show UV−vis transitions around 500 nm and, as these are in the neighborhood of the stereogenic metal center and the chiral phosphoramidite ligand, could become CD active. Figure 6 displays the CD spectra of the three alkynyl complexes (RRu,Rax)-18, (RRu,Rax)-19, and (RRu,Rax)-20. They resembled each other closely; the three spectra are dominated by a positive band at 333, 335, and 336 nm, respectively, in addition to broad positive bands around 400 and 450 nm. The CD spectra of the three alkynyl complexes show that optically active material was isolated. The similarity of the three CD spectra in Figure 6 suggests that all three complexes do have the same configuration.37 As can be seen from the X-ray structure of complex (RRu,Rax)-17, it appears that the absolute configuration at the metal and at the ligand is not disrupted upon nucleophilic attack at the Cγ atom. Thus, we assigned the (RRu,Rax) configuration to the three alkynyl complexes 18, 19, and 20, and the isolated mixtures of diastereomers are actually mixtures of epimers differing in the absolute configuration at the Cγ atom only. The CD data give some evidence (but no proof) that for all three alkynyl complexes the absolute configurations at the Cγ atom of the major diastereomer are identical.

Figure 3. Two different views of the molecular structure of (RRu,Rax)17. Hydrogen atoms and the toluene solvent are omitted for clarity. In the bottom view, the indenyl ligand is omitted. Crystallographic parameters are compiled in the Supporting Information (Table S1), and key bond lengths and angles are listed in Table 1.

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DISCUSSION The present data show for the first time the diastereoselection upon stoichiometric, nucleophilic attack on an allenylidene complex that is stereogenic at the metal and at one of the ligands and that bears, besides the indenyl, only monodentate, phosphorus-based ligands. The nucleophilic attack resulted in a new, quaternary stereocenter, and the diastereoselection (up to 84:16) originated from the chiral ligand and the stereogenic ruthenium center. The diastereoselectivities in Scheme 3 are moderate and in between those reported by Nakamura and Matsuo for related systems (vide inf ra).32 Still, it is apparent that one face of the Cγ atom of the allenylidene chain that is attacked by the nucleophile is more efficiently shielded than the other face. An examination of the X-ray structure of the allenylidene complex (RRu,Rax)-11 is most instructional, and a schematic representation is given in Figure 7 (left).

amidite ligand (R)-6 are chemically nonequivalent and gave two separate doublets around 55 and 180 ppm in the 31P{1H} NMR spectra. Upon formation of two diastereomers, these two signals further split into two pairs of signals for each diastereomer formed during the reaction. The diastereomeric ratios of the isolated complexes (RRu,Rax)-18, (RRu,Rax)-19, and (RRu,Rax)-20 were calculated from the intensities of these signals to be 40:60, 31:69, and 16:84, respectively (Figure 4 and Scheme 3). The diastereomeric ratios of the isolated products only marginally differed from those of the crude material. The optical activity of the new complexes and their precursors was also analyzed by circular dichroism.37 The CD spectra of the chloro precursor (RRu,Rax)-7, the allenylidene complex (RRu,Rax)-11, and the alkynyl complex (RRu,Rax)-19 are compiled in Figure 5. The chloro complex (RRu,Rax)-7 exhibited a band at 254 nm with a negative Cotton effect and three bands 5057


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Figure 4. Determination of diastereomeric ratios by 31P{1H} NMR, exemplified with complex (RRu,Rax)-19.

Figure 5. Circular dichroism spectra of selected complexes.

The allenylidene chain in (RRu,Rax)-11 is shielded by the phosphoramidite ligand (R)-6 positioned to the left in Figure 7 and by the PPh3 ligand at the right, giving rise to the absolute R configuration around the ruthenium center. Phenyl rings from the two ligands are actually shielding the allenylidene chain from both sides, and the closest atoms to the Cγ atom is an ortho hydrogen atom of the phenyl ring (Figure 7, left). The distance between the ortho hydrogen atom of the phosphor-

amidite ligand to the left and the Cγ atom was determined from the X-ray structure to be 3.5 Å, whereas the distance between the PPh3 ligand to the right and the Cγ atom is 3.8 Å. Furthermore, the ortho hydrogen atoms, the ruthenium center, and the allenylidene chain establish an angle (Figure 7). This angle was determined from the X-ray structures to be 47° for the phosphoramidite ligand to the left and 58° for the PPh3 ligand to the right. 5058


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Figure 6. Circular dichroism of alkyne complexes.

Figure 7. Schematic representation of the conformations of allenylidene complexes in the solid state. Angles and distances are calculated from X-ray data.

Figure 7).27 A schematic representation of the X-ray of the allenylidene complex 21 is shown in Figure 7 (middle). Similar to the complex (RRu,Rax)-11, the face of the allenylidene chain positioned on the left is more efficiently shielded by the ligand than the other face; the closest hydrogen atoms are 3.06 and 3.54 Å apart from the Cγ atom, respectively. The angles drawn by these hydrogen atoms, the ruthenium center, and the allenylidene chain are 32° and 43°, respectively. In Nakamura and Matsuo’s fullerene-based, chiral-at-metal ruthenium complex 22, with a chiral, bidentate phosphine ligand, the situation is similar (Figure 7, right).32 One face is more efficiently shielded than the other. As mentioned above, nucleophilic attack of this allenylidene complex 22 by a series of nucleophiles gave alkynyl complexes with diastereoselectivities ranging from 50:50 to 95:5. Here, the closest atom to the right side is also the ortho hydrogen of an aromatic ring system (3.1

From both the interatomic distances and the angles it can be concluded that the allenylidene chain is more efficiently shielded to the left by the phosphoramidite ligand; the nucleophilic attack presumably takes place from the less shielded side on the right (although there is no experimental proof for this hypothesis). Also, the data presented in Figure 7 are based on the solid-state structures, and the solution behavior could be different. Furthermore, there is some substrate dependency on the diastereomeric ratio, as observed by others before.32 However, examination of related examples from the literature reveals some similarities. Nihibayashi presented chiral, thiolate-bridged ruthenium dimer complexes of the general formula [Cp*RuCl(μ2SR*)]2, which showed catalytic activity in the enantioselective alkylation of propargylic alcohols through allenylidene intermediates.26 One of ruthenium dimer complexes was converted to an allenylidene complex, the assumed intermediate (21, 5059


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Å). To the left side, the closest “atom” is actually the centroid of one of the phenyl rings of the phosphine ligand (4.2 Å). Thus, steric bulk seems to be a common motive for allenylidene complexes to serve either as intermediates in enantioselective catalytic reactions or as target for diastereoselective, nucleophilic attack under stoichiometric conditions. As to whether steric bulk alone serves as the origin for diastereoselection in solution is another question other researchers have raised previously, and π−π interactions have been suggested to increase selectivities in catalytic processes.38 Nishibayashi identified in his allenylidene complex 21 (Figure 7, middle) a T-shaped edge-to-face π−π interaction in the solid state (3.01 Å), which contributes to more efficient shielding of one face of the allenylidene chain.27 Nishibayashi also assigned a similar edge-to-face π−π interaction to be responsible for enantioselective amination reactions to be catalyzed by a chiral copper complex.23b It appears that there is also a (weaker) edge-to-face π−π interaction in Nakamura and Matsuo’s complex 22 of 4.2 Å (indicated by a dotted line in Figure 7, right), which is only slightly shorter than a similar edge-to-face π−π interaction on the left side of the allenylidene chain (4.6 Å, not shown). We could identify in our complex (RRu,Rax)-11 also edge-to-face π−π interactions of 2.8 and 3.8 Å (Figure 7, left). They are, however, not necessarily in line with the shielding of the allenylidene chain (i.e., π−π interactions are in most of the cases shorter for the face that is less shielded). But these interactions might nevertheless provide a steric environment around the Cγ atom to allow for diastereoselection upon nucleophilic attack. In general, there is some consistency among the examples shown above; steric shielding can be quantified by the atom closest to the Cγ atom, and π−π interactions in the solid state can be identified. Further research into the role of those interactions is necessary, e.g., by using substrates that do not bear aromatic ring systems.

noted. Chemicals were treated as follows: THF, distilled from Na/ benzophenone; diethyl ether, distilled from Na/benzophenone; toluene and hexane, used as received. (Et3O)PF6, lithium phenyl acetylide solution, and acetophenone (all Sigma-Aldrich) and RuCl3 (Strem) were used as received. n-BuLi and LDA (Sigma-Aldrich) and MeLi (Acros) were titrated prior to every use against Nbenzylbenzamide according to literature procedures.36 NMR spectra were obtained at room temperature on a Bruker Avance 300 MHz or a Varian Unity Plus 300 MHz instrument and referenced to a residual solvent signal; all chemical shifts (δ) are given in ppm, and all assignments are tentative. FAB and exact masses were recorded on a JEOL MStation [JMS-700] mass spectrometer. UV−vis spectra were recorded on a U-3900 Hitachi double beam spectrophotometer. IR spectra were recorded on a Thermo Nicolet 360 FT-IR spectrometer. Circular dichroism measurements were obtained on a JASCO J-1500 CD spectrophotometer. Melting points were recorded on an Electrothermal MPAPP-S11251 apparatus and are uncorrected. Elemental analyses were performed by Atlantic Microlab Inc., Norcross, GA, USA. Synthesis of (RRu,Rax)-[Ru(Ind)(PPh3)(6){CCC(t-Bu)(2naphthyl)}]+PF6− [(RRu,Rax)-11]. A Schlenk tube was charged with (RRu,Rax)-[RuCl(Ind)(PPh3)(6)] [(RRu,Rax)-7, 0.404 g, 0.394 mmol] and CH2Cl2 (10 mL). The solution was then cooled to 0 °C for 7 min followed by the addition of (Et3O)PF6 (0.977 g, 0.400 mol). The solution was then stirred at 0 °C for 1 h, followed by the addition of 4,4-dimethyl-3-(2-naphthyl)-1-pentyn-3-ol (0.115 g, 0.481 mmol). The solution was then stirred at 0 °C for 30 min and then removed from the ice bath and stirred at room temperature for 30 min. The solvent was removed by oil pump vacuum, and the crude solid was washed with diethyl ether (5 × 4 mL) to yield (RRu,Rax)-11 as a dark red solid (0.515 g, 0.380 mmol, 96%). Mp (capillary): 185−187 °C dec. Anal. Calcd for C78H64NO2P3F6Ru: C, 69.07; H, 4.83. Found: C, 66.66; H, 4.75 (an average of three separate elemental analyses).39 NMR (δ, CDCl3) 1H: 8.47 (d, 1H, 3JHH = 7.6 Hz, aromatic), 8.3 (d, 1H, 3JHH = 8.3 Hz, aromatic), 7.94 (d, 1H, 3JHH = 8.8 Hz, aromatic), 7.87 (d, 1H, 3JHH = 8.2 Hz, aromatic), 7.30 (d, 1H, 3JHH = 8.3 Hz, aromatic), 7.64−7.53 (m, 8H, aromatic), 7.43−7.28 (m, 14H, aromatic), 7.19−7.05 (m, 13H. aromatic), 6.96 (m, 5H, aromatic), 6.65 (t, 2H, 3JHH = 5.91 Hz, aromatic), 6.45 (s, 1H, Ind), 5.60 (s, 1H, Ind), 5.29 (s, 1H, Ind), 4.15 (d, 1H, 2JHH = 10.7 Hz, NCHH′), 4.09 (d, 1H, 2JHH = 10.7 Hz, NCHH′), 3.08 (t, 2H, 2JHH = 13.4 Hz, NCH2), 1.04 (s, 9H, C(CH3)3); 13C{1H}: 312.5 (d, 2JCP = 17.2 Hz, Cα), 203.0 (s, Cβ), 181.8 (s, Cγ), 149.3, 149.1, 147.7, 147.6, 141.6, 136.7, 136.6, 133.6, 133.5, 133.4, 132.4, 132.3, 131.8, 131.5, 131.3, 130.8, 130.7, 130.5, 129.5, 128.9, 128.8, 128.7, 128.5, 128.1, 127.9, 127.5, 127.3, 127.1, 126.9, 126.8, 126.6, 123.5, 122.8, 122.7, 121.9, 121.8, 121.3, 121.2, 120.0 (all s, aromatic), 113.4 (d, 2JCP = 4.3 Hz, Ind), 109.2 (d, 2 JCP = 3.7 Hz, Ind), 95.0 (s, Ind), 84.5 (s, Ind), 83.8 (s, Ind), 50.4 (s, CH2), 50.3 (s, CH2′) 48.0 (s, C(CH3)3), 30.2 (s, CH3); 31P{1H}: 167.4 (d, 2Jpp = 32 Hz, (R)-6), 50.8 (d, 2Jpp = 32 Hz, PPh3), −144.9 (septet, 1 JPF = 711 Hz, PF6−). IR (cm−1, ATR): 2359 (w), 1936 (s), 1463 (m), 1320 (m), 1226 (m) 1090 (s), 953 (s) 833 (s) 748 (s), 694 (s). MS (FAB): 1210 ([(RRu,Rax)-11]+, 100%), 1120 ([(RRu,Rax)-11 − Bn]+, 15%), 1013 ([(RRu,Rax)-11 − NBn2]+, 10%), 946 ([(RRu,Rax)-11 − PPh3]+, 20%), 697 ([(RRu,Rax)-11 − (R)-6]+, 15%). HRMS: calcd for [C78H64NO2P2Ru] 1210.3456, found 1210.3489; corresponds to [(RRu,Rax)-11]+. UV−vis (CH2Cl2): λmax(ε) = 265 nm (3.30 × 103 M−1 cm−1). Synthesis of (R Ru ,R ax )-[Ru (Ind)(PPh 3 )(6){CC−CPh 2 Me}] [(RRu,Rax)-14]. A Schlenk tube was charged with (RRu,Rax)-[Ru(Ind)(PPh3)(6)(CCCPh2)]+PF6− (0.106 g, 0.113 mmol) and THF (5 mL). The solution was then cooled to −68 °C using a dry ice and acetone bath for 10 min, followed by the dropwise addition of freshly titrated MeLi solution (0.262 mL, 0.476 M, 0.124 mmol) over the course of 2 min. The solution was then stirred for 4 h at −60 °C, then stirred at room temperature for 45 min before removing the solvent via oil pump vacuum to yield the crude solid, which was washed with hexanes (5 × 6 mL) and dried under vacuum to yield (RRu,Rax)-14 as a bright orange solid (0.0602 g, 0.0503 mmol, 63%). Mp (capillary): 100−101 °C dec. Anal. Calcd for C77H61NO2P2Ru: C, 77.37; H, 5.14.

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CONCLUSION We have presented herein a new chiral-at-metal and chiral-atligand, cationic ruthenium allenylidene complex [Ru{C CC(t-Bu)(2-naphthyl)}]+, which was isolated in diastereopure form as a salt and which was analyzed by X-ray crystallography. Together with another, previously synthesized allenylidene complex, the attack on the Cγ atom of the allenylidene chain by carbon-centered nucleophiles was investigated. The attacks resulted in the formation of neutral alkynyl complexes [Ru(CC-CRR′R″)], one of which was analyzed by X-ray crystallography. In the case of nucleophilic attack of the complex [Ru{CCC(t-Bu)(2-naphthyl)}]+, a new stereocenter at the Cγ atom resulted, giving rise to the isolation of a diastereomeric mixture of the respective alkynyl complexes. The diastereomeric ratios of the alkynyl complexes ranged from 40:60 to 84:16. Together with literature examples, the origin of the diastereoselective attack was analyzed based on X-ray structures of allenylidene complexes. It appears that, in general, different shielding of the allenylidene chain causes diastereoselection of the nucleophilic attack, and intramolecular π−π interactions seem to play a role in the geometry around the Cγ atoms of the allenylidene complexes.

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EXPERIMENTAL SECTION

General Procedures. All reactions were carried out under an inert N2 atmosphere using standard Schlenk technique unless otherwise 5060


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°C dec. Anal. Calcd for C84H63NO2P2Ru·toluene (the toluene molecule of solvation was also observed in the NMR): C, 79.57; H, 5.21. Found: C, 79.68; H, 5.54. NMR (δ, CDCl3):40 1H 7.97 (t, 2H, 3 JHH = 8.6 Hz, aromatic), 7.95 (d, 4H, 3JHH = 7.4 Hz, aromatic), 7.46− 7.35 (m, 5H, aromatic), 7.20−6.72 (m, 34H, aromatic), 6.48 (m, 5H, aromatic), 6.06 (d, 1H, 3JHH = 8.9 Hz, aromatic), 5.58 (br s, 1H, Ind), 5.00 (br s, 1H, Ind), 4.31 (d, 4H, 2JHH = 11.6 Hz, NCHH′), 4.19 (br s, 1H, Ind), 2.93 (s, 1H, phenyl acetylene), 2.22 (s, 3H, toluene CH3); 13 C{1H}: 151.4, 151.2, 149.5, 149.4, 147.6, 139.6, 138.0, 135.7, 135.5, 133.8, 133.6, 133.0, 132.6, 132.3, 131.7, 131.2, 130.7, 130.5, 129.4, 129.2, 128.6, 128.4, 128.4, 128.2, 128.0, 127.9, 127.8, 127.1, 126.8, 126.5, 126.0, 126.0, 125.8, 125.5, 125.5, 125.3, 124.4, 124.3, 123.6, 123.4, 123.4, 123.2, 121.9 (all s, aromatic), 120.2 (s, Cβ), 110.7 (d, 3 JCP= 4.9 Hz, Ind), 109.17 (s, Ind), 98.0 (t, 3JCP = 26.2 Hz, Cα), 94.7 (s, CγC), 92.9 (s, Ind), 83.2 (s, phenyl acetylene), 81.8 (s, CPh), 74.1 (s, phenyl acetylene), 70.9 (s, Ind), 68.4 (d, 3JCP = 8.3 Hz, Ind), 50.7 (s, NCH2), 50.7 (s, NCH2′), 47.8 (s, Cγ), 21.6 (s, toluene CH3); 31 1 P{ H}: 179.3 (d, 3JPP = 50 Hz, (R)-6), 54.4 (d, 3JPP = 50 Hz, PPh3). IR (cm−1, ATR): 3055 (w), 2082 (w), 1940 (w), 1591 (s), 1487 (m), 1324 (m), 1091 (m), 1071 (s), 949 (s), 823 (s), 745 (s), 691 (s), 641 (s). MS (FAB): 1281 ([(RRu,Rax)-16]+, 20%), 1180 ([(RRu,Rax)-16 − CC-Ph]+, 55%), 728 ([(RRu,Rax)-16 − PPh3 − alkyne]+, 100%). HRMS calcd for [C84H63NO2P2102Ru] 1281.3378, found 1281.3383; corresponds to [(RRu,Rax)-16]+. Synthesis of (RRu,Rax)-[Ru (Ind)(PPh3)(6){CC−CPh2CH2C(O)Ph}] [(RRu,Rax)-17]. An evacuated and flushed two-neck round-bottom flask was charged with acetophenone (0.297 g, 2.47 mmol) and THF (6 mL). The flask was then cooled to −60 °C followed by the rapid addition of freshly titrated LDA (1.64 mL, 1.45 M, 2.38 mmol), and the solution was stirred at −60 °C for 2 h and then warmed to room temperature. To a separate Schlenk tube was added (RRu,Rax)[Ru(Ind)(PPh3)(6)(CCCPh2)]+PF6− (0.735 g, 0.555 mmol) and THF (10 mL), and the solution was cooled to −60 °C for 10 min followed by the dropwise addition of the prepared acetophenone enolate (2.74 mL, 0.302 M, 0.827 mmol) over the course of 3 min. The solution was stirred at −60 °C for 2 h and at room temperature for 2.5 h. The solvent was removed by oil pump vacuum, and the crude solid was purified by flash column chromatography (2 × 30 cm silica, eluted with 3:1 v/v toluene/CH2Cl2). The product was then washed with hexanes (4 × 5 mL) to yield (RRu,Rax)-17 as a bright, orange-yellow solid (0.479 g, 0.369 mmol, 67%). Mp (capillary): 151− 154 °C dec. Anal. Calcd for C84H65NO3P2Ru·toluene (the toluene molecule of solvation was also observed in the NMR and in the X-ray structure): C, 78.54. H, 5.29. Found: C, 78.13; H, 5.39. NMR (δ, toluene-d8): 1H 8.04 (d, 1H, 3JHH = 8.4 Hz, aromatic), 7.95−7.58 (m, 15H, aromatic), 7.35−6.81 (m, 36H, aromatic), 6.57 (d, 4H, 3JHH = 5.5 Hz, aromatic), 5.87 (br s, 1H, Ind), 5.58 (br s, 1H, Ind), 5.12 (t, 2H, 2JHH = 13.8 Hz, NCHH′), 4.69 (br s, 1H, Ind), 3.90 (t, 2H, 2JHH = 13.8 Hz, NCHH′), 3.72 (d, 1H, 2JHH = 16.1 Hz, CHH), 3.41 (d, 1H, 2 JHH = 16.1 Hz, CHH), 2.16 (s, 3H, toluene CH3); 13C{1H}: 193.2 (s, CO), 149.6, 149.3, 149.0, 147.5, 147.4, 146.4, 146.2, 139.7, 139.5, 137.6, 137.0, 136.7, 136.5, 136.4, 135.4, 135.3, 135.1, 133.5, 133.4, 132.2, 132.1, 131.5, 130.8, 130.6, 130.4, 130.1, 129.2, 129.1, 128.6, 128.3, 127.7, 127.5, 127.2, 126.8, 126.6, 126.3, 125.9, 125.6, 125.3, 125.1, 124.7, 124.5, 124.4, 124.0, 123.7, 123.5, 123.2, 122.7, 122.4, 121.8, 121.1, 121.0, 119.7, 119.0 (all s, aromatic), 112.4 (s, Cβ), 109.6 (d, 3JCP = 4.6 Hz, Ind), 108.8 (s, Ind), 92.1 (dd, 3JCP = 27.3, 26.0 Hz, Cα), 91.5 (s, Ind), 68.6 (s, Ind), 65.7 (s, Ind), 48.4 (s, NCH2), 48.4 (s, NCH2), 47.4 (COCH2), 47.1 (s, Cγ), 23.5 (s, toluene CH3); 31 1 P{ H}: 177.3 (d, 3JPP = 53 Hz, (R)-6), 55.0 (d, 3JPP = 53 Hz, PPh3). IR (cm−1, ATR): 3058 (w), 2087 (w), 1691 (s), 1587 (m), 1432 (s), 1325 (s), 1230 (s), 1207 (m), 1072 (m), 951 (s), 821 (s), 743 (s). MS (FAB): 1299 ([(RRu ,Rax )-17]+, 35%), 1180 ([(RRu,Rax )-17 − COCH2Ph]+, 15%), 1036 ([[(RRu,Rax)-17 − PPh3]+, 10%), 728 ([(RRu,Rax)-17 − PPh3 − alkyne]+, 100%). HRMS: calcd for [C84H65NO3P2102Ru] 1299.3483, found 1299.3496; corresponds to [[(RRu,Rax)-17]+. Synthesis of (R Ru ,R ax )-[Ru(Ind)(PPh 3 )(6)−CC−C(t-Bu)(2naphthyl)Me], (RRu,Rax)-18. An evacuated and flushed Schlenk tube

Found: C, 77.12; H, 5.36. NMR (δ, toluene-d8) 1H: 7.59 (d, 2H, 3JHH = 8.1 Hz, aromatic), 7.53 (d, 1H, 3JHH = 8.8 Hz, aromatic), 7.44 (t, 5H, 3 JHH = 7.3 Hz, aromatic), 7.36 (m, 3H, aromatic), 7.15−7.10 (m, 6H, aromatic), 7.04−6.56 (m, 27H, aromatic), 6.41 (m, 3H, aromatic), 6.22 (m, 2H, aromatic), 5.45 (br s, 1H, Ind), 5.16 (br s, 1H, Ind), 4.67 (t, 2H, 2JHH = 13.4 Hz, NCHH′), 4.37 (br s, 1H, Ind), 3.81 (t, 2H, 2 JHH = 12.5 Hz, NCHH′), 1.47 (s, 3H, CH3); 13C{1H}: 150.4, 150.2, 150.1, 148.7, 148.6, 148.5, 138.4, 136.4, 136.0, 135.7, 133.9, 133.7, 132.9, 132.5, 131.8, 131.6, 131.5, 130.2, 129.7, 128.5, 127.9, 127.8, 127.6, 127.5, 127.2, 127.1, 126.94, 126.89, 126.6, 126.4, 126.3, 125.5, 124.8, 124.7, 124.6, 124.5, 124.1, 123.9, 123.7, 123.4, 123.0, 122.1, 120.7, 120.1 (all s, aromatic), 115.8 (s, Cβ), 109.8 (s, Ind), 109.2 (s, Ind), 92.4 (s, Ind), 91.9 (dd, 3JCP = 26.7, 24.4 Hz, Cα), 70.2 (s, Ind), 67.0 (d, 3JCP = 6.3 Hz, Ind), 49.5 (s, CH), 49.5 (s, CH′), 46.1 (s, Cγ), 30.5 (s, CH3); 31P{1H}: 179.9 (d, 3JPP = 53 Hz, (R)-6), 56.3 (d, 3JPP = 53 Hz, PPh3). IR (cm−1, ATR): 3055 (w), 2093 (m), 1583 (m), 1494 (s), 1432 (s), 1326 (s), 1320 (s), 1091 (s), 951 (s), 821 (s), 743 (s), 698 (s). MS(FAB): 1195 ([(RRu,Rax)-14]+, 40%), 990 ((RRu,Rax)-14 − alkyne]+, 45%), 728 ([(RRu,Rax)-14 − alkyne − PPh3]+, 100%). HRMS: calcd for [C77H61NO2P2102Ru] 1195.3221, found 1195.3240; corresponds to [(RRu,Rax)-14]+. Synthesis of (R Ru,Rax)-[Ru (Ind)(PPh3 )(6)(CC−CPh2 n-Bu)] [(RRu,Rax)-15]. A Schlenk tube was charged with (RRu,Rax)-[Ru(Ind)(PPh3)(6)(CCCPh2)]+PF6− (0.522 g, 0.394 mmol) and THF (8 mL). The solution was then cooled to −68 °C for 10 min followed by dropwise addition of freshly titrated n-BuLi solution (1.21 M, 0.359 mL, 0.434 mmol) over the course of 5 min. The solution was then stirred at −68 °C for 3 h and then warmed to room temperature for 30 min before the solvent was removed by oil pump vacuum. The crude solid was purified by flash column chromatography (2 × 30 cm silica, eluted with 3:1 v/v hexanes/toluene). The product was dried under high vacuum to yield (RRu,Rax)-15 as a bright orange solid (0.196 g, 0.159 mmol, 40%). Mp (capillary): 111−112 °C dec. Anal. Calcd for C80H67NO2P2Ru: C, 77.65; H, 5.46. Found: C, 77.98; H, 5.78. NMR (δ, CDCl3): 1H 7.99 (t, 2H, 3JHH = 8.0 Hz, aromatic), 7.62−7.51 (m, 3H, aromatic), 7.40 (t, 1H, 3JHH = 8.0 Hz, aromatic), 7.22−6.86 (m, 40H, aromatic), 6.65−6.60 (m, 6H, aromatic), 6.26 (t, 2H, 3JHH = 9.1 Hz, aromatic), 5.40 (br s, 1H, Ind), 5.22 (br s, 1H, Ind), 4.73 (d, 1H, 2 JHH = 11.3 Hz, NCHH′), 4.67 (d, 1H, 2JHH = 11.3 Hz, NCHH′), 4.58 (br s, 1H, Ind), 3.40 (d, 1H, 2JHH = 11.1 Hz, NCHH′), 3.35 (d, 1H, 2 JHH = 11.1 Hz, NCHH′), 2.25 (s, 3H, toluene), 1.57−1.14 (m, 4H, 2CH2), 0.83 (m, 2H, CH2), 0.59 (t, 3H, 2JHH = 7.4 Hz, CH3); 13 C{1H}: 151.1, 150.9, 149.5, 149.3, 149.3, 139.4, 138.9, 138.4, 138.2, 137.9, 135.3, 135.2, 134.2, 134.0, 133.5, 132., 132.6, 132.4, 131.1, 130.9, 129.6, 126.9, 126.6, 126.1, 126.0, 125.6, 125.3, 125.2, 124.8, 124.7, 124.4, 124.1, 123.1, 121.7, 121.1, 121.0 (all s, aromatic), 114.9 (s, Cβ), 110.7 (s, Ind), 110.1 (d, 3JCP= 4.1 Hz, Ind), 93.4 (s, Ind), 92.6 (dd, 3JCP= 26.6, 25.3 Hz, Cα), 70.7 (d, 3JCP= 4.3 Hz, Ind), 67.8 (d, 3 JCP= 7.0 Hz, Ind), 51.2 (s, Cγ), 50.1 (s, NCH2), 50.0 (s, NCH2′), 41.3 (s, Cγ-CH2), 27.6 (s, CH2), 23.1 (s, CH2), 21.6 (s, toluene CH3), 14.4 (s, CH3); 31P{1H}: 178.0 (d, 3JPP = 54 Hz, (R)-6), 56.0 (d, 3JPP = 54 Hz, PPh3). IR (cm−1, ATR): 3055 (w), 2953 (w), 2863 (w), 2082 (s), 1591 (m), 1494 (m), 1237 (m), 1207 (m), 1091 (s), 952 (s), 821 (s) 743 (s), 693 (s), 640 (m). MS (FAB): 1237 ([(RRu,Rax)-15]+, 80%), 1180 ([(RRu,Rax)-15 − n-butyl]+, 10%), 976 ([(RRu,Rax)-15 − PPh3]+, 15%), 728 ([(RRu,Rax)-15 − PPh3 − alkyne]+, 100%). HRMS: calcd for [C80H66NO2P2102Ru] 1236.3612, found 1236.3617; corresponds to [(RRu,Rax)-15 − H]+. Synthesis of (RRu,Rax)-[Ru (Ind)(PPh3)(6)(CC−CPh2CCPh)] [(RRu,Rax)-16]. A Schlenk tube was charged with (RRu,Rax)-[Ru(Ind)(PPh3)(6)(CCCPh2)]+PF6− (0.350 g, 0.264 mmol) and THF (8 mL). The solution was then cooled to −20 °C for 10 min followed by slow dropwise addition of lithium phenyl acetylide solution (3.44 mL, 1.0 M, 0.344 mmol) over the course of 5 min. The solution was then stirred at −20 °C for 1 h and then warmed to room temperature for 1 h before the solvent was removed by oil pump vacuum. The crude solid was purified by flash column chromatography (2 × 30 cm silica, eluted with 3:1 v/v hexanes/toluene) to yield (RRu,Rax)-16 as a brown powder (0.251 g, 0.196 mmol, 74%). Mp (capillary): 127−129 5061


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JHH = 27.8 Hz, NCHH′), 4.39 (d, 1H, 2JHH = 27.8 Hz, NCHH′), 4.27 (br s, 1H, Ind), 3.81 (t, 2H, 2JHH = 15.1 Hz, NCHH′), 2.38 (s, toluene CH3), 1.19 (s, 6H, C(CH3)3), 1.14 (s, 3H, C(CH3)3*), 0.97 (s, 3H, C(CH3)3), 0.85 (s, 6H, C(CH3)3*); 13C{1H}: 152.0, 151.8, 149.9, 149.8, 140.6, 140.5, 139.2, 136.2, 136.0, 134.3, 134.2, 134.1, 133.9, 133.3, 133.3, 132.9, 132.7, 132.4, 132.2, 132.1, 131.6, 130.9, 129.9, 127.3, 127.1, 127.0, 126.6, 126.5, 126.1, 125.9, 124.3, 123.7, 123.6, 123.3, 123.2, 122.6, 122.3, 121.9, 120.1 (all s, aromatic), 112.7 (s, Cβ), 112.6 (s, Cβ*), 111.6 (s, Ind), 111.5 (s, Ind*), 110.3 (s, Ind*), 110.2 (s, Ind), 96.3 (s, C-C*), 96.0 (s, C-C), 94.5 (t, 3JCP = 25.0 Hz, Cα), 93.1 (s, C-Ph*), 92.9 (s, C-Ph), 83.7 (s, Ind), 82.8 (s, Ind*), 71.6 (s, Ind*), 69.8 (s, Ind), 68.7 (s, Ind*), 68.5 (s, Ind), 53.6 (s, NCH2), 53.5 (s, NCH2*), 51.7 (d, 3JCP = 5.4 Hz, Cγ), 51.2 (d, 3JCP = 6.2 Hz, Cγ*), 41.5 (s, C(CH3)3), 40.9 (s, C(CH3)3*), 27.5 (s, C(CH3)3), 27.1 (s, C(CH3)3*); 31P{1H}: 180.9 (d, 3JPP = 53 Hz, (R)6), 179.1 (d, 3JPP = 51 Hz, (R)-6*), 55.4 (d, 3JPP = 53 Hz, PPh3), 54.8 (d, 3JPP = 51 Hz, PPh3*). IR (cm−1, ATR): 3051 (w), 2945 (w), 2855 (w), 2078 (m), 1587 (s), 1462 (s), 1430 (s), 1321 (s), 1226 (m), 1199 (s), 1089 (s), 943 (s), 817 (s). MS (FAB): 1311 ([(RRu,Rax)-19]+, 5%), 1254 ([(RRu,Rax)-19 − C(CH3)3]+, 100%), 728 ([(RRu,Rax)-19 − PPh3 − alkyne]+, 90%). HRMS: calcd for [C82H60NO2P2102Ru] 1254.3143, found 1254.3176; corresponds to [(RRu,Rax)-19 − C(CH3)3]+. UV−vis (CH2Cl2): λmax (ε) = 417 nm (4.03 × 103 M−1 cm−1), 380 nm (5.15 × 103 M−1 cm−1, 270 nm (2.04 × 104 M−1 cm−1). Synthesis of (R Ru ,R ax )-[Ru(Ind)(PPh 3 )(6){CC−C(t-Bu)(2naphthyl)CH2C(O)Ph}], (RRu,Rax)-20. An evacuated and flushed twoneck round-bottom flask was charged with acetophenone (0.327 g, 2.72 mmol) and THF (6 mL). The flask was then cooled to −68 °C followed by the rapid addition of freshly titrated LDA (1.81 mL, 1.43 M, 2.54 mmol), and the solution was stirred at −68 °C for 2 h and then warmed to room temperature. To a separate Schlenk tube was added (R Ru ,R ax )-[Ru(Ind)(PPh 3 )(6)CCC(t-Bu)(2-naphthyl)]+PF6− [(RRu,Rax)-11, 0.341 g, 0.252 mmol] and THF (10 mL), and the solution was cooled to −68 °C for 17 min followed by the dropwise addition of the prepared acetophenone enolate (0.833 mL, 0.333 M, 0.277 mmol) over the course of 5 min. The solution was then stirred at −68 °C for 2 h and then stirred at room temperature for an additional 2 h before the solvent was removed via oil pump vacuum. The crude solid was then purified by flash column chromatography (2 × 30 cm silica, eluted with 3:1 v/v hexanes/ CH2Cl2) to yield (RRu,Rax)-20 as a bright orange solid as a mixture of diastereomers (0.242 g, 0.182 mmol, 72%). Mp (capillary): 158−162 °C dec. Anal. Calcd for C86H71NO3P2Ru: C, 77.69; H, 5.38. Found: C, 77.70; H, 5.66. NMR (δ, toluene-d8, the asterisks denote the second diastereomer): 1H 7.85 (t, 2H, 3JHH = 10.0 Hz, aromatic), 7.66−7.59 (m, 4H, aromatic), 7.50−7.42 (m, 4H, aromatic), 7.37−7.30 (m, 3H, aromatic), 7.25 (m, 2H, aromatic), 7.10 (m, 4H, aromatic), 7.01−6.55 (m, 32H, aromatic), 6.11−5.96 (m, 4H, aromatic), 5.43 (br s, 1H, Ind*), 5.27 (br s, 1H, Ind), 5.21 (br s, 1H, Ind), 4.64 (br s, 1H, Ind*), 4.47 (br s, 1H, Ind), 4.35 (br s, 1H, Ind*), 4.21 (t, 4H, 2JHH = 9.8 Hz, NCHH′), 3.95 (d, 1H, 2JHH = 18.0 Hz, CH), 3.93 (d, 1H, 2JHH = 18.0 Hz, CH*), 3.23 (d, 1H, 2JHH = 18.0 Hz, CH′*), 3.20 (d, 1H, 2JHH = 18.0 Hz, CH′), 0.83 (s, 6H, C(CH3)3*), 0.77 (s, 6H, C(CH3)3), 0.70 (s, 3H, C(CH3)3), 0.61 (s, 3H, C(CH3)3*); 13C{1H} (CDCl3): 196.5 (s, CO*), 196.1 (s, CO), 151.4, 151.2, 149.6, 149.5, 143.0, 142.1, 139.6, 139.4, 139.3, 136.0, 135.8, 134.4, 134.3, 133.7, 133.0, 132.8, 132.6, 132.5, 132.3, 132.0, 131.8, 131.4, 131.0, 130.0, 129.5, 129.2, 129.1, 128.8, 128.6, 128.3, 128.2, 128.1, 128.0, 127.5, 127.4, 127.3, 127.1, 126.9, 126.8, 126.6, 125.9, 125.8, 125.8, 125.1, 124.9, 124.5, 124.4, 123.3, 122.7, 122.3, 122.2, 122.0 (all s, aromatic), 114.8 (s, Cβ), 114.6 (s, Cβ*), 111.5 (s, Ind), 111.3 (s, Ind), 94.3 (s, Ind*), 94.2 (s, Ind), 89.6 (dd, 3JCP = 20.5, 26.0 Hz, Cα), 89.5 (br s, Cα*), 72.4 (d, 3JCP = 6 Hz, Ind), 70.6 (d, 3JCP = 6 Hz, Ind*), 68.3 (d, 3JCP = 4.5 Hz, Ind*), 66.6 (d, 3JCP = 4.3 Hz, Ind), 52.0 (s, CH2), 51.3 (s, NCH2), 51.3 (s, NCH2′), 50.5 (s, NCH2′*), 50.4 (s, NCH2′*), 45.3 (s, Cγ*), 44.8 (s, Cγ), 39.2 (s, C(CH3)3), 27.3 (s, CH3*), 27.2 (s, CH3); 31P{1H}: 182.6 (d, 3JPP = 59 Hz, (R)-6*), 182.3 (d, 3JPP = 61 Hz, (R)-6), 58.5 (d, 3JPP = 61 Hz, PPh3), 58.3 (d, 3JPP = 59 Hz, PPh3*). IR (cm−1, ATR): 3053 (w), 2960 (w), 2862 (w), 2080 (m), 1678 (s), 1588 (s), 1504 (s),

was charged with (RRu,Rax)-[Ru(Ind)(PPh3)(6){CCC(tBu)(2-naphthyl)}]+PF6− [(RRu,Rax)-11, 0.153 g, 0.113 mmol] and THF (10 mL). The solution was then cooled to −68 °C for 10 min followed by the dropwise addition of MeLi solution (0.26 mL, 0.476 M, 0.124 mmol), during which the solution turned a transparent red. The solution was then stirred at −68 °C for 1 h and then stirred at room temperature for 2 h before the solvent was removed via oil pump vacuum. The crude solid was then extracted with diethyl ether (8 × 4 mL) and filtered through a short pad of silica, and the solvent was removed via rotary evaporator to yield (RRu,Rax)-18 as a bright red solid as a mixture of diastereomers (0.133 mg, 0.108 mmol, 96%). Mp (capillary): 115−117 °C dec. Anal. Calcd for C79H67NO2P2Ru: C, 77.43; H, 5.51. Found: C, 77.65; H, 5.88. NMR (δ, CDCl3, the asterisks denote the second diastereomer): 1H 8.09−7.99 (m, 3H, aromatic), 7.83 (m, 5H, aromatic), 7.74−7.64 (m, 8H, aromatic), 7.54−7.35 (m, 11H, aromatic), 7.20−6.98 (m, 12H, aromatic), 6.79− 6.75 (m, 2H, aromatic), 6.49−6.45 (m, 6H, aromatic), 5.60 (d, 1H, 2 JHH = 2.2 Hz, Ind*), 5.55 (d, 1H, 2JHH = 1.0 Hz, Ind), 5.24 (br s, 1H, Ind*), 5.21 (br s, 1H, Ind), 4.86 (br s, 1H, Ind*), 4.59 (d, 1H, 2JHH = 12.8 Hz, NCHH′), 4.54 (d, 1H, 2JHH = 12.8 Hz, NCHH′), 4.52 (br s, 1H, Ind), 4.41 (d, 1H, 2JHH = 13.5 Hz, NCHH′), 4.36 (d, 1H, 2JHH = 13.5 Hz, NCHH′), 4.21 (d, 1H, 2JHH = 9.4 Hz, NCHH′*), 4.16 (d, 1H, 2JHH = 9.4 Hz, NCHH′*), 3.88 (t, 2H, 2JHH = 9.3 Hz, NCHH′*), 1.57 (s, 3H, CH3), 1.43 (s, 3H, CH3*), 1.37 (s, 3H, C(CH3)3*), 1.13 (s, 3H, C(CH3)3), 0.92 (s, 6H, C(CH3)3*), 0.73 (s, 6H, C(CH3)3). 13 C{1H} (toluene-d8): 151.4, 151.2, 149.6, 145.4, 145.0, 139.5, 139.3, 138.8, 135.6, 135.0, 134.2, 133.7, 133.6, 133.0, 132.8, 132.7, 132.5, 132.0, 131.9, 131.5, 130.8, 130.0, 129.8, 129.5, 129.1, 129.0, 128.4, 128.4, 128.3, 128.2, 128.1, 127.8, 127.3, 126.6, 126.3, 126.2, 126.2, 125.8, 125.3, 124.9, 124.8, 124.7, 124.7, 124.1, 123.7, 122.2, 122.0, 121.5, 121.2, 118.3 (all s, aromatic), 111.7 (s, Cβ), 110.9 (s, Ind*), 110.8 (s, Ind), 110.6 (s, Ind*), 110.5 (s, Ind), 93.8 (s, Ind), 93.5 (s, Ind*), 88.2 (t, 3JCP = 16.6 Hz, Cα), 81.8 (s, Cα*), 70.7 (d, 3JCP = 3.1 Hz, Ind*), 70.6 (d, 3JCP = 4.4 Hz, Ind), 68.2 (d, 3JCP = 5.4 Hz, Ind), 67.8 (d, 3JCP = 6.2 Hz, Ind*), 51.0 (s, NCHH′*), 50.9 (s, NCHH′*), 50.8 (s, NCHH′), 50.6 (s, NCHH′), 50.3 (s, Cγ*), 50.2 (s, Cγ), 38.2 (s, C(CH3)3*), 38.1 (s, C(CH3)3), 27.3 (s, C(CH3)3*), 27.1 (s, C(CH3)3), 24.8 (s, CH3), 24.3 (s, CH3*); 31P{1H}: 181.8 (d, 3JPP = 56 Hz, (R)-6), 181.1 (d, 3JPP = 56 Hz, (R)-6*), 57.3 (d, 3JPP = 56 Hz, PPh3*), 56.7 (d, 3JPP = 56 Hz, PPh3). IR (cm−1, ATR): 3047 (s), 2964 (s), 2356 (s), 2071 (w), 1600 (s), 1425 (m), 1229 (s), 1091 (s), 949 (s), 819 (s), 741 (s), 694 (s). MS (FAB): 1225 ([(RRu,Rax)-18]+, 15%), 1168 ([(RRu,Rax)-18 − C(CH3)3]+, 100%), 728 ([(RRu,Rax)-18 − PPh3 − alkyne]+, 90%). HRMS calculated for [C75H58NO2P2102Ru] 1168.2986, found 1168.3019; corresponds to [(RRu,Rax)-18 − C(CH3)3]+. UV−vis (CH2Cl2): λmax (ε) = 410 nm (1.31 × 103 M−1 cm−1), 263 nm (3.62 × 103 M−1 cm−1). Synthesis of (R Ru ,R ax )-[Ru(Ind)(PPh 3 )(6){CC−C(t-Bu)(2naphthyl)CCPh}], (RRu,Rax)-19. An evacuated and flushed Schlenk tube was charged with (RRu,Rax)-[Ru(Ind)(PPh3)(6){CCC(tBu)(2-naphthyl)}]+PF6− [(RRu,Rax)-11, 0.128 mg, 0.094 mmol] and THF (10 mL). The solution was then cooled to −20 °C for 10 min followed by dropwise addition of lithium phenyl acetylide solution (0.104 mL, 1.0 M, 0.104 mmol). The solution was then stirred at −20 °C for 1 h and then stirred at room temperature for an additional 1 h before the solvent was removed via oil pump vacuum. The crude solid was purified by extraction (4 × 6 mL of 3:1 v/v diethyl ether/toluene) and filtered through a short pad of silica. The solvent was removed via rotary evaporator to yield (RRu,Rax)-19 as a tan solid as a mixture of diastereomers (0.115 mg, 0.088 mmol, 93%). Mp (capillary): 113−115 °C dec. Anal. Calcd for C86H69NO2P2Ru·toluene (the toluene molecule of solvation was also observed in the NMR): C, 79.58. H, 5.53. Found: C, 79.54; H, 5.50. NMR (δ, CDCl3, the asterisks denote the second diastereomer): 1H 8.18−8.08 (m, 4H, aromatic), 7.96 (s, 3H, aromatic), 7.81−7.77 (m, 6H, aromatic), 7.68−7.65 (m, 6H, aromatic), 7.55−6.92 (m, 20H, aromatic), 6.70−6.68 (m, 5H, aromatic), 6.61−6.58 (m, 4H, aromatic), 6.42−6.28 (m, 5H, aromatic), 5.93 (br s, 1H, Ind), 5.90 (br s, 1H, Ind*), 5.73 (br s, 1H, Ind), 5.56 (br s, 1H, Ind*), 5.11(br s, 1H, Ind*), 4.91 (d, 1H, 2JHH = 9.9 Hz, NCHH′), 4.86 (d, 1H, 2JHH = 9.9 Hz, NCHH′), 4.44 (d, 1H, 5062


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thyl)}]+PF6−. Copies of the data can be obtained, free of charge, on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: +44-(0)1223-336033 or e-mail: deposit@ ccdc.cam.ac.uk). Experimental details and spectroscopic data for the generation of (RRu,Rax)-13, Table S1 of crystallographic parameters, UV−vis spectra for selected complexes, 31P{1H} NMR spectra of selected complexes for the determination of diastereomeric ratios, 1H and 13C{1H} NMR of all new complexes. This material is available free of charge via the Internet at http://pubs.acs.org.

1431 (s) 1322 (s), 1226 (s), 1089 (m), 1066 (s), 1026 (s), 946 (s), 819 (s), 800 (s). MS (FAB): 1329 ([(RRu,Rax)-20]+, 10%), 1272 ([(R Ru,Rax )-20 − C(CH3)3]+, 100%), 1212 ([(RRu,Rax )-20 − COCH2Ph]+, 10%), 728 ([(RRu,Rax)-20 − PPh3 − alkyne]+, 90%). HRMS: calcd for [C82H62NO3P2102Ru] 1272.3248, found 1272.3221; corresponds to [(RRu,Rax)-20 − C(CH3)3]+. UV−vis (CH2Cl2): λmax (ε) = 436 nm (1.92 × 103 M−1 cm−1), 263 nm (2.06 × 104 M−1 cm−1). X-ray Crystallography. Crystals of appropriate dimension were obtained for (RRu,Rax)-[Ru(Ind)(PPh3)(6){CCC(t-Bu)(2naphthyl)}]+PF6− by layering a CH2Cl2 solution with diethyl ether at −18 °C and for (RRu,Rax)-[Ru(Ind)(PPh3)(6){CC−CPh2CH2C(O)Ph}] by layering a toluene solution with hexanes at room temperature. Crystals of approximate dimensions were mounted on MiTeGen cryoloops in random orientations. Preliminary examination and data collection were performed using a Bruker X8 Kappa Apex II charge coupled device (CCD) detector system single-crystal X-ray diffractometer equipped with an Oxford Cryostream LT device. All data were collected using graphite-monochromated Mo Kα radiation (λ = 0.71073 Å) from a fine focus sealed tube X-ray source. Preliminary unit cell constants were determined with a set of 36 narrow-frame scans. Typical data sets consist of combinations of ω and Φ scan frames with typical scan width of 0.5° and counting time of 15 s/frame at a crystal to detector distance of 4.0 cm. The collected frames were integrated using an orientation matrix determined from the narrow-frame scans. Apex II and SAINT software packages were used for data collection and data integration.41 Analysis of the integrated data did not show any decay. Final cell constants were determined by global refinement of reflections harvested from the complete data set. Collected data were corrected for systematic errors using SADABS based on the Laue symmetry using equivalent reflections.41 Crystal data and intensity data collection parameters are listed in Table S1 (Supporting Information). Structure solution and refinement were carried out using the SHELXTL-PLUS software package.42 The structure was solved by direct methods and refined successfully in the space groups P212121 and P1 respectively for compounds (RRu,Rax)[Ru(Ind)(PPh3)(6){CC−CPh2CH2C(O)Ph}] and (RRu,Rax)-[Ru(Ind)(PPh3)(6){CCC(t-Bu)(2-naphthyl)}]+PF6−. Full matrix least-squares refinements were carried out by minimizing ∑w(Fo2 − Fc2)2. The non-hydrogen atoms were refined anisotropically to convergence. All hydrogen atoms were treated using an appropriate riding model (AFIX m3). The final residual values and structure refinement parameters are listed in Table S1 (Supporting Information). Two partial occupancy toluene solvates were found in the case of (RRu,Rax)-[Ru(Ind)(PPh3)(6){CC−CPh2CH2C(O)Ph}], which were refined with geometrical restraints. A molecule of CH2Cl2 was located in the case of (RRu,Rax)-[Ru(Ind)(PPh3)(6){ CCC(t-Bu)(2-naphthyl)}]+PF6−). The CH2Cl2 solvent, the PF6− anion, and one of the phenyl rings are disordered in this structure. The disorder was modeled with partial occupancy atoms and geometrical restraints. Absolute structure determination was carried out using Parson’s method for both structures.43 Tables of calculated and observed structure factors are available in electronic format. Circular Dichroism. Circular dichroism spectra of (RRu,Rax)-7 and (RRu,Rax)-11 (both in DMSO) and of (RRu,Rax)-18, (RRu,Rax)-19, and (RRu,Rax)-20 (all in CH3CN) were recorded on a JASCO J-1500 spectropolarimeter at 291 K. The spectra were determined for all samples at a concentration of 0.002 mol/L using a quartz cuvette of 1 mm path length, a scan speed of 100 nm min−1, a 1 nm bandwidth, 0.1 nm data pitch, and 1 s of response time.

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AUTHOR INFORMATION

Corresponding Author

*Tel: +1-314-516-5311. Fax: +1-314-516-5342. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We would like to thank the National Science Foundation (NSF CHE-1300818) for financial support. Further funding from the National Science Foundation for the purchase of the circular dichroism spectropolarimeter (MRI 1337638), the NMR spectrometer (CHE-9974801), the ApexII diffractometer (MRI, CHE-0420497), and the mass spectrometer (CHE9708640) is acknowledged.

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REFERENCES

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ASSOCIATED CONTENT

S Supporting Information *

Crystallographic data (excluding structure factors) for the structures in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication nos. CCDC 1005490, (RRu,Rax)-[Ru(Ind)(PPh3)(6){CC−CPh 2 CH 2 C(O)Ph}], and CCDC 1005491, (R Ru ,R ax )-[Ru(Ind)(PPh 3 )(6){CCC(t-Bu)(2-naph5063


Organometallics

Article

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Organometallics

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