Osmium Models of Intermediates Involved in Catalytic Reactions of

Article pubs.acs.org/Organometallics

Osmium Models of Intermediates Involved in Catalytic Reactions of Alkylidenecyclopropanes Miguel A. Esteruelas,*,† Ana M. López,*,† Fernando López,‡ José L. Mascareñas,*,§ Silvia Mozo,† Enrique Oñate,† and Lucıá Saya§ †

Departamento de Quı ́mica Inorgánica-Instituto de Sı ́ntesis Quı ́mica y Catálisis Homogénea (ISQCH), Universidad de Zaragoza-CSIC, 50009 Zaragoza, Spain ‡ Instituto de Quı ́mica Orgánica General-CSIC, Juan de la Cierva 3, 28006 Madrid, Spain § Departamento de Quı ́mica Orgánica e Centro de Investigación en Quı ́mica Biolóxica e Materiais Moleculares (CIQUS), Universidade de Santiago de Compostela, 15782 Santiago de Compostela, Spain S Supporting Information *

ABSTRACT: The complex [OsCp{κ 3 -P,C,C-P i Pr 2 [C(CH3)CH2]}(CH3CN)]PF6 (1) reacts with (2-pyridyl)methylenecyclopropane, at room temperature, to give initially the cyclobutylidene derivative [Os(η 5 -C 5 H 5 )(CCH2CH2CH-o-C5H4N){PiPr2[C(Me)CH2]}]PF6 (2), as a result of the ring expansion of the alkylidenecyclopropane unit. Over time complex 2 rearranges into the cyclobutene derivative [Os(η5-C5H5){η2-C(CHCH2CH2)-o-C5H4N}{PiPr2[C(Me)CH2]}]PF6 (3). The reaction of 1 with (2pyridyl)methylenecyclopropane at room temperature also affords the phosphinomethanide metallacycle [Os(η5-C5H5){κ4-P,Ca,Cb,N-PiPr2[Ca(Me)CH2CH)(CbCH2CH2-o-C5H4N]}]PF6 (4) as a minor product, which becomes the major product of the reaction at 45 °C. This osmacyclopentane results from the C−C coupling of the isopropenyl substituent of the phosphine ligand and the organic substrate. In acetone at 75 °C, the reaction of 1 with (2-pyridyl)methylenecyclopropane leads to the 2-alkylidene-1-osmacyclobutane [Os(η5-C5H5){κ3-N,Ca,Cb-Ca(CH2CbH2)(CH-o-C5H4N)}{PiPr2[C(Me)CH2]}]PF6 (5), as a consequence of the oxidative addition of one of the C(sp2)−C(sp3) bonds of the cyclopropane unit of the substrate to the osmium atom, along with 6, a diastereomer of 4. Complexes 3−5 have been characterized by X-ray diffraction analysis. DFT calculations suggest that all of the reaction products are derived from a common key 1-osma-2-azacyclopent-3-ene intermediate (D).

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INTRODUCTION

Scheme 1

Alkylidenecyclopropanes are very useful building blocks in organic synthesis1 and, because of the simultaneous presence of a double bond and a strained cycle, have provided for the development of a variety of metal-catalyzed processes, including ring-opening, cycloaddition, and isomerization reactions.2 Thus, the groups of Fürstner3 and Shi4 have independently described the isomerization of alkylidenecyclopropanes to cyclobutenes promoted by platinum3 and palladium4 catalysts. The authors suggested that the reaction takes place via cyclopropylmethyl cations, which undergo ring expansion to give cyclobutylidene intermediates. Subsequent 1,2-hydrogen shift and elimination reactions give rise to the corresponding cyclobutenes (Scheme 1a). With regard to cycloadditions, it has been suggested that many of these metal-promoted reactions involve the proximal or distal cleavage of the cyclopropane ring, to generate metallacyclobutane species of either type A or B (Scheme 1b).2,5 © 2013 American Chemical Society

Most of the mechanistic studies on these processes rely on isotopic labeling or DFT calculations, but intermediates have not been isolated. This is not surprising, since transition-metal complexes derived from alkylidenecyclopropanes are extremely Received: June 21, 2013 Published: August 21, 2013 4851

dx.doi.org/10.1021/om400597q | Organometallics 2013, 32, 4851−4861

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rare,5l,6 as a consequence of the fact that the stoichiometric reactions of metal complexes with these organic substrates have been scarcely investigated. We have recently observed that the triisopropylphosphine complex [OsTp(κ1-OCMe2)2(PiPr3)]BF4 (Tp = hydridotris(pyrazolyl)borate) promotes the cleavage of both C(sp3)−C(sp2) bonds of the three-membered ring of benzylidenecyclopropane and 3-phenylpropylidenecyclopropane to give ethylene−osmium−vinylidene species (Scheme 2a).7 In

This paper shows the formation and characterization of several novel osmium complexes of mechanistic significance. In addition to the osmium counterparts of the cyclobutylidene and cyclobutene intermediates proposed by Fürstner and Shi for the isomerization of alkylidenecyclopropanes into cyclobutenes, we also report the first alkylidenemetallacyclobutane of type A for a late transition metal and novel phosphinomethanide derivatives resulting from the addition of the C−C double bond of the phosphine to the organic substrate. Furthermore, we present DFT calculations that propose an explanation of the different experimental results obtained depending on the reaction conditions, in particular on the reaction temperature.

Scheme 2

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RESULTS AND DISCUSSION 1. Cyclobutylidene and Cyclobutene Species. The reactions of the isopropenyldiisopropylphosphine complex [OsCp{κ3-P,C,C-PiPr2[C(CH3)CH2]}(CH3CN)]PF6 (1) with (2-pyridyl)methylenecyclopropane, at room temperature, in dichloromethane and acetone was followed by 31P{1H}NMR spectroscopy, and the resulting products were characterized by spectroscopy and/or X-ray diffraction analysis. Figure 1 shows the composition of the reaction mixtures, as a function of time. As observed in Figure 1, the reaction gives initially the cyclobutylidene derivative [Os(η5-C5H5)(CCH2CH2CH-o-C5H4N){PiPr2[C(Me)CH2]}]PF6 (2), as a result of the ring expansion of the alkylidenecyclopropane unit (Scheme 3). The presence of 2 in the mixtures, which reaches a maximum amount of about 70% in dichloromethane and 40% in acetone with regard to the total amount of osmium, is strongly supported by the 13C{1H} and 31 1 P{ H} NMR spectra of the mixtures. In accordance with the triisopropylphosphine counterpart,8 the 13C{1H} NMR spectrum shows at δ 281.6 a doublet with a C−P coupling constant of 8 Hz, corresponding to the carbene carbon atom. Resonances due to the remaining carbon atoms of the four-membered cycle appear at δ 86.8 (CH), 62.1 (CCH2), and 14.0 (CCH2CH2). In agreement with the uncomplexed nature of the isopropenyl substituent of the phosphine,9 its C(sp2) atoms display resonances at δ 137.8 (PC) and 130.7 (CH2), shifted 94.5 (PC) and 99 (CH2) ppm toward lower field with regard to those of 1.10 In the 31P{1H} NMR spectrum, this ligand gives rise to a singlet at δ 25.6.

contrast, (2-pyridyl)methylenecyclopropane reacts at room temperature with [OsCp(CH3CN)2(PiPr3)]PF6 (Cp = cyclopentadienyl) and [MTp(κ1-OCMe2)2(PiPr3)]BF4 (M = Ru, Os) to give cyclobutylidene derivatives (Scheme 2b) related to those proposed by Fürstner and Shi for the case of platinum- or palladium-promoted isomerizations.8 Because the kinetics and thermodynamics of the equilibria involving transition-metal complexes and organic molecules depend not only on the substituents of the substrates but also on the nature of the metal center, which is a function of the ligands of the complexes, we decided to further explore the reactivity of (2pyridyl)methylenecyclopropane with other related osmium complexes that could lead to the isolation of mechanistically relevant intermediates. In particular, we have now studied the reactivity with the complex [OsCp{κ3-P,C,C-PiPr2[C(CH3)CH2]}(CH3CN)]PF6 (1), which features an isopropenyldiisopropylphosphine ligand.

Figure 1. Composition of the reaction mixtures of 1 (blue ◆) with (2-pyridyl)methylenecyclopropane vs time, at room temperature, in dichloromethaned2 (a) and acetone-d6 (b). Complexes 2 (pink ◆), 3 (green ▲), and 4 (orange ▲). 4852


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Scheme 3

The formation of complex 2 is in agreement with the previous result using the triisopropylphosphine complex [OsCp(CH3CN)2(PiPr3)]PF68 and most probably arises from the initial coordination of the nitrogen atom and the C−C double bond of the substrate to the osmium atom of 1, which leads to intermediate C (Scheme 3).11 The subsequent oxidation of the metal center promotes sp2 to sp3 rehybridizations of the nitrogen atom and the C(sp2) atom of the three-membered ring to afford the 1-osma-2-azacyclopent-3-ene intermediate D. Then, the CH2 group cis-disposed to the pyridyl group in the free substrate undergoes a concerted shift from position 5 to 4 of the fivemembered metalla ring. The expansion is accompanied by the reduction of the metal center and the sp3 to sp2 retrohybridization of the initially rehybridized atoms.8 Interestingly, in addition to osmium carbene, we also observe the formation of the cyclobutene derivative

Figure 2. Molecular diagram of the cation of 3-BArF4 with ellipsoids at the 30% probability level. Selected bond lengths (Å) and angles (deg): Os−N(1) = 2.105(9), Os−C(6) = 2.306(17), Os−C(7) = 2.114(16), Os−P(1) = 2.332(3), C(6)−C(7) = 1.346(15); N(1)−Os−P(1) = 97.0(3), N(1)−Os−C(6) = 59.9(4), N(1)−Os−C(7) = 84.7(4), P(1)− Os−C(6) = 111.1(5), P(1)−Os−C(7) = 84.7(4).

[Os(η 5 -C 5 H 5 ){η 2 -C(CHCH 2 CH 2 )-o-C 5 H 4 N}{P i Pr 2 [C(Me)CH2]}]PF6 (3; 2:3 = 1:1.4 after 40 h in acetone or 74 h in dichloromethane), which in all probability arises from the rearrangement of 2 (Scheme 3). A few crystals of the tetrakis(3,5bis(trifluoromethyl)phenyl)borate (BArF4) salt of 3, suitable for X-ray diffraction analysis, were obtained by slow diffusion of pentane into a dichloromethane solution of the reaction mixture enriched in 3, after PF6/BArF4 anion exchange. Figure 2 shows a view of the cation, which is highly disordered (see the Experimental Section). As a consequence, the structural parameters show a significant standard deviation and should be considered carefully. The structure proves the alkylidene to olefin rearrangement. The geometry around the metal center is close to octahedral with the Cp ligand occupying one of the faces. The metal coordination sphere is completed by the phosphorus atom of the phosphine ligand and the chelate 2-pyridylcyclobutene molecule, which coordinates through the nitrogen atom and the C(6)−C(7) double bond with Os−N(1), Os−C(6), and Os−C(7) distances of 2.105(9), 2.306(17) and 2.114(16) Å, respectively.11 The 1H and 13C{1H} NMR spectra of 3 are consistent with the structure shown in Figure 2. In the 1H NMR spectrum, the resonance due to the olefinic C(7)−H hydrogen atom appears at δ 4.92 as a double doublet with H−H and H−P coupling constants of 4.3 and 19.8 Hz, respectively, while in the 13 C{1H} NMR spectrum the resonances corresponding to the coordinated carbon atoms C(6) and C(7) are observed at δ 50.9 and 56.7. The first of them appears as a doublet with a C−P coupling constant of 3 Hz, while the second is a broad signal. In

accordance with the noncoordination of the isopropenyl unit of the phosphine ligand to the metal center, the resonances of its C(sp2) atoms appear at δ 140.2 (PC) and 126.6 (CH2) as doublets with C−P coupling constants of 36 and 3 Hz, respectively. A singlet at δ 12.5 in the 31P{1H} NMR spectrum is also characteristic of this complex. The formation of the cyclobutene 3 by rearrangement of the carbene 2 supports the mechanistic proposals of Furstner and Shi for the isomerization of alkylidenecyclopropanes into cyclobutenes promoted by Pt or Pd catalysts.3,4 The M−alkylidene to M−olefin rearrangement is the key step in other catalytic transformations.12 Indeed, conversions of alkylidene complexes into the corresponding alkene derivatives have been known for some time,13 in particular for cationic electrophilic species containing an alkylidene ligand with β-CH bonds.14 On the basis of an investigation of cationic rhenium complexes, Gladysz and Hatton have rationalized the transformation as an organometallic Wagner−Meerwein rearrangement in reference to its carbocationlike hydrogen migration.15 In agreement with this, the isomerization is faster in acetone than in dichloromethane (Figure 1). In the reaction of 1 with (2-pyridyl)methylenecyclopropane we also observe the minor formation of another product that was identified as the osmacycle [Os(η 5 -C 5H 5 ){κ4 -P,Ca ,Cb ,NP i Pr 2 [C a (Me)CH 2 CH)(C b CH 2 CH 2 -o-C 5 H 4 N]}]PF 6 (4), 4853


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The coupling is diastereoselective because of the two possible diastereoisomers; due to the chirality of the carbon atoms C(6) and C(11) and the metallic center, only one of them is observed, that containing the phosphorus atom transoid disposed to N(1) (P−Os−N(1) = 120.6(2)°). The angles around the osmium atom in the five-membered metalla rings are 75.2(4)° (C(7)− Os−N(1)) and 79.4(4)° (C(7)−Os−C(11)). As expected for an Os−P−C(11) phosphinomethanide unit, the C(11)−Os−P angle of 44.9(3)° is significantly smaller than the P−Os−C(7) angle (90.0(3)°) and is similar to those found in other M(κ2-P,CR2PCHR) derivatives.16f,17 The Os−P distance of 2.278(3) Å compares well with those found in the complexes Os(η6-1,3,5C6H3Me3)Cl{κ2-P,C-PiPr2[CHCO2Me]} (2.287(2) Å)17a and [OsCp{κ 5 -P,C a ,C b ,C c ,C d -P i Pr 2 [C a (CH 3 )CH 2 C b (C c H 2 )CdHCy]}]PF6 (2.3021(14) Å),16f whereas the P−C(11) bond length of 1.734(11) Å is about 0.1 Å shorter than the distances P−C(13) (1.826(11) Å) and P−C(16) (1.831(12) Å), suggesting some double-bond character.18 In agreement with this, the Os−C(11) bond length of 2.263(10) Å lies in the upper part of the range reported for metal−olefin distances in Os− olefin compounds (2.13−2.28 Å).19 The Os−C(7) bond length of 2.088(10) Å supports an Os−C(sp3) bond.20 The 13C{1H} NMR spectrum of 4 is consistent with the structure shown in Figure 4. Thus, it shows at δ 15.4 and 34.0 doublets with C−P coupling constants of 6 and 15 Hz, which were assigned to the metalated C(11) and C(7) atoms, respectively. In the 31P{1H} NMR spectrum, the phosphinomethanide ligand gives rise to a singlet at δ −8.8, shifted 34 and 21 ppm toward higher field with regard to those of 2 and 3, respectively. 2. 2-Alkylidene-1-osmacyclobutane Species. Figure 3 shows that, in addition to the carbene 2, cyclobutane 3, and osmacyclopentane 4, the osmacyclobutane [Os(η5-C5H5){κ3N,C a ,C b -C a (CH 2 C b H 2 )(CH-o-C 5 H 4 N)}{P i Pr 2 [C(Me) CH2]}]PF6 (5) (Scheme 4) is also formed as a minor species,

which accounts for less than 10% of the mixture after 40 h at room temperature (Figure 1). This phosphinomethanide metallacycle results from the coupling of the terminal C(sp2) atom of the isopropenyl substituent of the phosphine and the C(sp2) atom adjacent to the six-membered heterocycle of intermediate D (Scheme 3).16 Interestingly, when the reaction is carried out at 45 °C instead of at room temperature, we observe the fast formation of 2 and its isomerization into 3, but over time there is a decrease in the proportion of both isomers along with the concomitant formation of 4, which becomes the main product (about 55% of the mixture) after 40 h (Figure 3).

Figure 3. Composition of the reaction mixtures of 1 (blue ◆) with (2pyridyl)methylenecyclopropane vs time, at 45 °C, in acetone-d6. Complexes 2 (pink ◆), 3 (green ▲), 4 (orange ▲), and 5 (olive ▲).

A few crystals of the BArF4 salt of 4, suitable for X-ray diffraction analysis, were obtained by slow diffusion of pentane into a dichloromethane solution of the reaction mixture enriched in 4, after PF6/BArF4 anion exchange. Figure 4 shows a view of

Scheme 4

about 7% after 40 h. When the reaction is carried out at 75 °C, this product reaches about 40% of the mixture (Figure 5). A few crystals of the BArF4 salt of 5, suitable for X-diffraction analysis, were obtained by slow diffusion of pentane into a dichloromethane solution of 5 and 6, after PF6/BArF4 anion exchange. Figure 6 shows a view of the cation, which similarly to that of 3 is also highly disordered (see the Experimental Section). The structure proves the insertion of the metal fragment into one of the C(sp2)−C(sp3) bonds of the three-membered ring of the substrate. The Os−C(7) bond length of 2.052(11) Å compares well with the Os−C(sp2) single-bond distance found in osmium−alkenyl complexes,21 whereas the C(6)−C(7) bond length of 1.36(2) Å is consistent with a C−C double bond. The Os−C(9) distance of 2.240(13) Å, which is about 0.15 Å longer than the Os−C(7) bond length in 4, reflects the tension of the four-membered metallacycle. The C(9)−Os−C(7) angle in the latter is 61.6(5)°, whereas the C(7)−Os−N(1) angle in the fivemembered metalla ring is 76.6(4)°. The 13C{1H} NMR spectrum of 5 also supports the presence of Os−C(sp2) and

Figure 4. Molecular diagram of the cation of 4-BArF4. Selected bond lengths (Å) and angles (deg): Os−N(1) = 2.134(10), Os−P = 2.278(3), Os−C(7) = 2.088(10), Os−C(11) = 2.263(10), P−C(11) = 1.734(12), P−C(13) = 1.826(11), P−C(16) = 1.831(12), C(5)−C(6) = 1.486(15), C(6)−C(7) = 1.524(15), C(6)−C(10) = 1.561(15), C(10)−C(11) = 1.529(15); P−Os−N(1) = 120.6(2), P−Os−C(7) = 90.0(3), P−Os−C(11) = 44.9(3), N(1)−Os−C(7) = 75.2(4), N(1)− Os−C(11) = 75.7(4), C(7)−Os−C(11) = 79.4(4), C(10)−C(11)− C(12) = 113.4(10).

the cation. The structure proves the C(sp2)−C(sp2) coupling, which gives rise to a tetradentate ligand (P, C(11), C(7), N(1)). 4854


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alkylidenecyclopropane.6k It should be mentioned that these types of metallacyclobutanes have been proposed as key intermediates in several nickel-catalyzed [3 + 2], [3 + 3], and [3 + 2 + 2] cycloadditions of alkylidenecyclopropanes.5k,l As observed in Figure 5, the major product of the reaction of 1 and (2-pyridyl)methylenecyclopropane, in acetone at 75 °C, is the phosphinomethanide metallacycle 6 (60% of the mixture after 20 h), a diastereomer of 4 (Scheme 4). In contrast to the latter, the phosphorus and nitrogen atoms lie cisoid disposed in the four-membered face of the four-legged piano-stool structure. Thus, in the 13C{1H} NMR spectrum, the resonance corresponding to the metalated carbon atom Cb transoid disposed to the phosphorus atom appears at δ 32.8 as a doublet with a C−P coupling constant of 4 Hz, significantly lower than that observed for the C(7) resonance of 4 (Chart 1). This value agrees well with those Chart 1. Selected 13C{1H} NMR Chemical Shifts (δ) and Coupling Constants (Hz) for 4 and 6 Figure 5. Composition of the reaction mixture of 1 (blue ◆) with (2pyridyl)methylenecyclopropane vs time, in acetone-d6 at 75 °C. Complexes 2 (pink ◆), 3 (green ▲), 4 (orange ▲), 5 (olive ▲), and 6 (brown ●).

reported for other osmium complexes with C−P transoid dispositions in four-legged piano-stool structures.9b,14i,22 In contrast to Cb, the Ca resonance appears at δ 21.1 as a doublet with the same C−P coupling constant as in 4 (6 Hz). In agreement with the latter, the phosphinomethanide phosphorus atom displays a singlet at δ −13.6 in the 31P{1H} NMR spectrum. 3. DFT Calculations. In an effort to shed light into the wide range of products resulting from the reaction of 1 with (2pyridyl)methylenecyclopropane, we have carried out DFT calculations (M06/631g**/Lanl2dz). The changes in free energy (ΔG) have been computed at 298.15 K and P = 1 atm and corrected using dichloromethane as solvent. Figure 7 shows

Figure 6. Molecular diagram of the cation of 5-BArF4. Selected bond lengths (Å) and angles (deg): Os−N(1) = 2.182(9), Os−P(1) = 2.395(3), Os−C(7) = 2.052(11), Os−C(9) = 2.240(13), C(5)−C(6) = 1.40(2), C(6)−C(7) = 1.36(2), C(7)−C(8) = 1.433(19), C(8)−C(9) = 1.51(2); P(1)−Os−N(1) = 85.3(2), P(1)−Os−C(7) = 104.6(4), P(1)− Os−C(9) = 82.5(4), N(1)−Os−C(7) = 76.6(4), N(1)−Os−C(9) = 131.3(4), C(7)−Os−C(9) = 61.6(5).

Os−C(sp3) single bonds in the cation. Thus, it shows at δ 180.9 and −36.8 doublets with C−P coupling constants of 3 and 8 Hz, which were assigned to C(7) and C(9), respectively. The resonances corresponding to C(6) and C(8) are observed at δ 124.6 and 44.2, respectively, while those due to the C(sp2) atoms of the isopropenyl group of the phosphine appear at δ 134.4 (PC) and 130.6 (CH2) as doublets with coupling constants of 38 and 5 Hz, respectively. The 31P{1H} NMR spectrum contains a singlet at δ 6.5, corresponding to the phosphine ligand. The formation of the osmacyclobutane 5 implies the cleavage of one of the OsC−CH2 bonds of the three-membered ring of the coordinated organic substrate in intermediate D by means of an α-carbon elimination reaction, which results in a formal oxidative addition of the proximal C−C bond of the alkylidenecyclopropane to the metal center (Scheme 4). To the best of our knowledge, 5 is the first isolated example of a 2alkylidene-1-metallacyclobutane complex for a late transition metal formed by proximal insertion of the metal into an

Figure 7. Energy profile (ΔGdichloromethane, kcal mol−1) for the transformation of intermediate C in 2 and 4−6.

the resulting energy profile for the transformations, whereas Chart 2 and Table 1 collect the optimized structures of products, 4855


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Chart 2. Optimized Structures of Products, Intermediates, and Transition Statesa

a

Hydrogen atoms of cyclopentadienyl, isopropyl, and pyridyl groups have been omitted for clarity.

contains the isopropenyl group anti disposed to the organic substrate, while in conformers D2 and D3 the isopropenyl group is syn disposed, with the terminal C(10)H2 group situated under the C6 carbon atom of the five-membered metallacycle. The difference between D2 and D3 is the disposition of the methyl C(12)H3 substituent of the isopropenyl group with regard to the pyridine ring: in D2 it is syn disposed, while in D3 it lies in an anti position. The position of the isopropenyl substituent of the phosphine determines the reaction product. Thus, conformer D1 with the isopropenyl group away from the substrate rearranges to afford the carbene 2 and the alkylideneosmacyclobutane 5 through transition states TSD1‑2 and TSD1‑5, respectively. However, conformers D2 and D3 with the C6 carbon atom of the substrate over the C(10)H2 group of the isopropenyl substituent undergo C−C coupling between the fragments to give the osmacyclopentanes 4 and 6 via the transition states TSD2‑4 and TsD3‑6, respectively. In agreement with the experimental observations (Figures 1, 3, and 5), the activation energies for the formation of the reaction products and their respective stabilities increase in the sequence 2 < 4 < 5 < 6. The formation of 2, 4, and 6 occurs directly from D; however, that of 5

intermediates, and transition states and important bond distances and angles. The DFT results are qualitatively consistent with the diversity of products observed in the reaction and reveal that the versatility of the reaction is a consequence of the existence of at least three conformers of the 1-osma-2-azacyclopent-3-ene intermediate D (Schemes 3 and 4), which is generated from an η2-methylenecyclopropane species stabilized by coordination of the pyridine nitrogen atom (C). These intermediates are analogous to those that we had previously proposed for the formation of the cyclobutylidene derivatives [Os(η5-C5H5)(CCH2CH2CH-o-C5H4N)(PiPr3)]PF6 and [OsTp(CCH2CH2CH-o-C5H4N)(PiPr3)]BF4 (Scheme 2b) related to 2.8 The key intermediates D1−D3 differ by only 1.0 kcal mol−1 and are about 16 kcal mol−1 less stable than the η2-olefin species C. The transition state TSC‑D connecting intermediates C and D lies 16.5 kcal mol−1 above C. Conformers D result from different orientations of the substituents of the phosphine with regard to the coordinated organic substrate. Conformer D1 4856


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considered as models of intermediates proposed in catalytic reactions involving alkylidenecyclopropanes. In addition, the presence of an isopropenyldiisopropylphosphine as an osmium ligand has allowed us to characterize the novel derivatives 4 and 6 resulting from the addition of the terminal CH2 group of the isopropenyl substituent of isopropenyldiisopropylphosphine to (2-pyridyl)methylenecyclopropane. In agreement with the mechanistic proposals of Fürstner and Shi for the isomerization of alkylidenecyclopropanes to cyclobutenes catalyzed by platinum and palladium species,3,4 the isopropenyldiisopropylphosphine complex 1 initially promotes the ring expansion of the three-membered ring of the organic substrate to afford the cyclobutylidene 2, which isomerizes into the cyclobutane 3. In acetone at 75 °C, the formation of the osmacyclobutane 5 takes also place as a consequence of the oxidative addition of one of the C(sp2)−C(sp3) bonds of the cyclopropane unit of the substrate to the osmium atom, in a manner similar to the formation of the nickelacyclobutanes proposed for the nickel-catalyzed [3 + 2] and [3 + 2 + 2] cycloadditions of alkylidenecyclopropanes.5k,l The formation of these models competes with the C−C coupling reactions resulting from the presence of an isopropenyl substituent in the phosphine. DFT calculations suggests that the wide range of products in this reaction is a consequence of the disposition of the isopropenyl substituent of the phosphine with regard to the coordinated alkylidenecyclopropane in the key intermediate of the reaction. The experimental observation of the formation of complexes 2, 3, and 5 might be relevant for future developments and mechanistic studies in metal-catalyzed reactions of alkylidenecyclopropanes. However, the generalization of the mechanisms should be done carefully, since the products of the stoichiometric reactions, the elemental steps of the catalysis, depend not only upon the substituents of the substrates but also upon the ligands of the metal complexes. In this context we note the differences in behavior between 1 and its triisopropylphosphine counterpart.8

Table 1. Selected Bond Lengths (Å) and Angles (deg) for the Optimized Structures Collected in Chart 2 C Os−C6 = 2.242 Os−C7 = 2.143 Os−N = 2.129 N−C5 = 1.352 C5−C6 = 1.474

TSC‑D Os−C7 = 2.195 Os−N = 2.033 N−C5 = 1.384 C5−C6 = 1.400 N−C5−C6−C7 = −13.4

D1

D2

Os−C7 = 2.137 Os−N = 2.022 N−C5 = 1.392 C5−C6 = 1.392 N−C5−C6−C7 = −6.2

Os−C7 = 2.110 Os−N = 2.037 N−C5 = 1.386 C5−C6 = 1.397 P−C11 = 1.829

N−C5−C6−C7 = −61.1

D3 Os−C7 = 2.096 Os−N = 2.051 N−C5 = 1.388 C5−C6 = 1.400 P−C11 = 1.832

C10−C11 = 1.341 N−C5−C6−C7 = −6.0 TSD2‑4

TSD1‑2

2

Os−C7 = 2.065 N−C5 = 1.378 C5−C6 = 1.418 C7−C8 = 1.686 C6−C9 = 2.186

Os−C7 = 1.899 N−C5 = 1.360 C5−C6 = 1.484 C6−C9 = 1.563

C6−C10 = 2.263 P−C11 = 1.799

C10−C11 = 1.338 N−C5−C6−C7 = −3.6 4

Os−C7 = 2.110 N−C5 = 1.376 C5−C6 = 1.415

C10−C11 = 1.370 P−Os−N = 98.9 TSD1‑5

Os−C7 = 2.166 Os−C11 = 2.259 Os−C9 = 2.651 C6−C10 = C7−C9 = 1.538 1.614 P−C11 = 1.762 C10−C11 = 1.529 P−Os−N = 122.2 C7−Os−C11 = 79.2 5a

E

Os−C7 = 2.113

TSE‑5a

Os−C7 = 2.093

Os−C7 = 2.089

Os−C9 = 2.257

Os−C9 = 2.254

C7−Os−C9 = 53.3

C7−Os−C9 = 55.8

N−Os−C9 = 95.6 C6−C7−C8−C9 = 104.5

N−Os−C9 = 110.4 C6−C7−C8−C9 = 122.1

5

Os−C7 = 2.013

Os−C7 = 2.011

Os−C9 = 2.198

Os−C9 = 2.205

C7−Os−C9 = 62.9

C7−Os−C9 = 63.1

N−Os−C9 = 130.4

N−Os−C9 = 132.0

C6−C7−C8−C9 = −156.2

C6−C7−C8−C9 = −158.5

TSD3‑6 Os−C7 = 2.082 N−C5 = 1.371 C5−C6 = 1.429 C6−C10 = 2.203 P−C11 = 1.796 C10−C11 = 1.377 P−Os−N = 98.4

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EXPERIMENTAL SECTION

General Methods and Instrumentation. All reactions were carried out under argon with rigorous exclusion of air using Schlenk tube, sealed tube,23 or glovebox techniques. Solvents were dried by the usual procedures and distilled under argon prior to use or obtained oxygen- and water-free from an MBraun solvent purification apparatus. The starting materials [OsCp{κ3-P,C,C-PiPr2[C(CH3)CH2]}(CH3CN)]PF6 (1),10 (2-pyridyl)methylenecyclopropane,24 and NaBArF4 (BArF4 = tetrakis(3,5-bis(trifluoromethyl)phenyl)borate)25 were prepared as previously reported. 1H, 31P{1H}, and 13C{1H} NMR spectra were recorded on a Bruker Avance 400 MHz instrument. Chemical shifts (δ) are referenced to residual solvent peaks (1H, 13 C{1H}) or external H3PO4 (31P{1H}). Coupling constants, J, are given in hertz. Spectral assignments were achieved by 1H−1H COSY, 1H{31P}, 13 C APT, 1H−13C HSQC, and 1H−13C HMBC experiments. Infrared spectra were recorded on a Spectrum One spectrometer as neat solids. C, H, and N analyses were carried out in a Perkin-Elmer 2400 CHNS/O analyzer. High-resolution electrospray mass spectra were acquired using a MicroTOF-Q hybrid quadrupole time-of-flight spectrometer (Bruker Daltonics, Bremen, Germany). Characterization of [Os(η5-C5H5)(CCH2CH2CH-o-C5H4N)-

6 Os−C7 = 2.145 Os−C11 = 2.223 C6−C10 = 1.534 P−C11 = 1.773 C10−C11 = 1.534 P−Os−N = 85.6 C7−Os−C11 = 72.3

takes place through the intermediate E, which is a conformational isomer of 5 with a C6−C7−C8−C9 dihedral angle of 104.5°. Intermediate E isomerizes into 5a, which has a C6−C7−C8−C9 dihedral angle of −156.2°, with a very low activation energy of 0.1 kcal mol−1 through the transition state TSE‑5a. The rotation of the phosphine around the Os−P bond of 5a finally affords 5.

{P i Pr 2 [C(Me)CH 2 ]}]PF 6 (2) and [Os(η 5 -C 5 H 5 ){η 2 -C(

■

CHCH2CH2)-o-C5H4N}{PiPr2[C(Me)CH2]}]PF6 (3). A mixture enriched in complex 2 was prepared as follows. A solution of 1 (144 mg, 0.24 mmol) in 6 mL of dichloromethane was treated with (2pyridyl)methylenecyclopropane (47 mg, 0.36 mmol). After it was stirred for 14 h at room temperature, the red solution was filtered through Celite and concentrated to ca. 1 mL. The addition of pentane

CONCLUDING REMARKS This study shows the formation and characterization, including X-ray diffraction analysis, of three osmium complexes (cyclobutylidene 2, cyclobutene 3, and alkylidenemetallacyclobutane 5) that could be 4857


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at −75 °C caused the precipitation of a pink solid, which according to its NMR spectra was a 82:11:7 mixture of 2−4. Yield: 125 mg (76%). Anal. Calcd for C23H33NF6OsP2: C, 40.05; H, 4.82; N, 2.03. Found: C, 39.70; H, 4.50; N, 1.95. HRMS (electrospray, m/z): calcd for C23H33NOsP [M]+ 546.1965, found 546.1999. IR (ATR, cm−1): ν(PF6) 832 (s). Spectroscopic data for 2: 1H NMR (400 MHz, CD2Cl2, 298 K) δ 8.94 (dd, JH−H = 5.9, JH−H = 1.6, 1H, H6 py), 7.63 (ddd, JH−H = 7.6, JH−H = 7.5, JH−H = 1.6, 1H, H4 py), 7.58 (dd, JH−H = 7.6, JH−H = 1.6, 1H, H3 py), 6.99 (ddd, JH−H = 7.5, JH−H = 5.9, JH−H = 1.6, 1H, H5 py), 5.68 (dd, JH−P = 35.8, JH−H = 1.3, 1H, CHHtrans to P), 5.38 (s, 5H, C5H5), 5.22 (dd, JH−P = 16.1, JH−H = 1.3, 1H, CHHcis to P), 2.87−2.81 (m, 1H, OsCCH2), 2.46 (ddd, JH−H = 15.4, JH−H = 10.4, JH−H = 9.7, 1H, OsCCH2), 2.15 (m, 1H, PCH), 2.09 (m, 1H, PCH), 1.84 (overlapped signal, 1H, OsCCH), 1.83 (d, JH−P = 9.1, 3H, PC(CH3)), 1.82 (overlapped signal, 2H, Os CCH2CH2), 0.94 (dd, JH−P = 15.1, JH−H = 6.9, 3H, PCHCH3), 0.93 (dd, JH−P = 15.2, JH−H = 6.8, 3H, PCHCH3), 0.91 (dd, JH−P = 15.8, JH−H = 6.7, 3H, PCHCH3), 0.75 (dd, JH−P = 15.4, JH−H = 7.0, 3H, PCHCH3); 31P{1H} NMR (161.98 MHz, CD2Cl2, 298 K) δ 25.6 (s), −144.1 (sept, JP−F = 708, PF6); 13C{1H} NMR (100.63 MHz, CD2Cl2, 298 K) δ 281.6 (d, JC−P = 8, OsC), 168.7 (s, C2 py), 159.7 (s, C6 py), 138.9 (s, C4 py), 137.8 (d, JC−P = 36, PC(CH3)), 130.7 (d, JC−P = 9, CH2), 124.3 (s, C5 py), 121.0 (s, C3 py), 86.8 (s, OsCCH), 84.2 (s, C5H5), 62.1 (s, OsCCH2), 27.9 (d, JC−P = 30, PCH), 27.4 (d, JC−P = 41, PCH), 23.0 (d, JC−P = 10, PC(CH3)), 19.7 (d, JC−P = 1, PCHCH3), 19.0 (d, JC−P = 1, PCHCH3), 19.0 (s, PCHCH3), 18.9 (s, PCHCH3), 14.0 (d, JC−P = 1, Os CCH2CH2). A mixture enriched in complex 3 was prepared as follows. A solution of 1 (86 mg, 0.14 mmol) in 6 mL of dichloromethane was treated with (2-pyridyl)methylenecyclopropane (27 mg, 0.21 mmol). After it was stirred for 72 h at room temperature, the red solution was filtered through Celite and concentrated to ca. 1 mL. The addition of pentane at −75 °C caused the precipitation of a pinkish solid, which according to its NMR spectra was a 40:47:13 mixture of 2−4. Yield: 70 mg (72%). Spectroscopic data for 3: 1H NMR (400 MHz, (CD3)2CO, 273 K) δ 8.34 (dd, JH−H = 5.0, JH−H = 1.3, 1H, H6 py), 7.80 (ddd, JH−H = 7.9, JH−H = 7.8, JH−H = 1.3, 1H, H4 py), 7.76 (dd, JH−H = 7.9, JH−H = 1.3, 1H, H3 py), 7.10 (ddd, JH−H = 7.8, JH−H = 5.0, JH−H = 1.3, 1H, H5 py), 5.77 (dd, JH−P = 31.6, JH−H = 1.0, 1H, CHHtrans to P), 5.44 (dd, JH−P = 13.7, JH−H = 1.0, 1H, CHHcis to P), 5.40 (s, 5H, C5H5), 4.92 (dd, JH−P = 19.8, JH−H = 4.3, 1H, CH), 3.26 (dddd, JH−H = 13.2, JH−H = 7.5, JH−P = JH−H = 2.8, 1H, CHCH2CH2), 2.88 (dddd, JH−H = JH−H = 7.5, JH−H = 4.3, JH−H = 2.8, 1H, CHCH2CH2), 2.75 (m, 1H, PCH), 2.63 (m, 1H, PCH), 2.32−2.26 (m, 1H, CHCH2CH2), 1.82 (d, JH−P = 9.4, 3H, PC(CH3)), 1.75−1.70 (m, 1H, CHCH2CH2), 1.32 (dd, JH−P = 14.2, JH−H = 7.1, 3H, PCHCH3), 1.22 (dd, JH−P = 13.4, JH−H = 7.3, 3H, PCHCH3), 0.95 (dd, JH−P = 15.1, JH−H = 7.0, 3H, PCHCH3), 0.90 (dd, JH−P = 15.0, JH−H = 7.5, 3H, PCHCH3); 31P{1H} NMR (161.98 MHz, (CD3)2CO, 273 K) δ 12.5 (s), −144.1 (sept, JP−F = 708, PF6); 13 C{1H} NMR (100.63 MHz, (CD3)2CO, 273 K) δ 167.5 (s, C2 py), 153.4 (s, C6 py), 140.2 (d, JC−P = 36, PC(CH3)), 136.5 (s, C4 py), 126.6 (d, JC−P = 3, CH2), 122.4 (s, C5 py), 119.7 (s, C3 py), 84.2 (s, C5H5), 56.7 (br, CH), 50.9 (d, JC−P = 3, CCH), 38.8 (d, JC−P = 41, PCH), 32.9 (s, CHCH2CH2), 28.4 (d, JC−P = 30, PCH), 27.7 (s, CHCH2CH2), 23.1 (d, JC−P = 10, PC(CH3)), 21.1 (s, PCHCH3), 20.4 (d, JC−P = 2, PCHCH3), 19.1 (d, JC−P = 4, PCHCH3), 18.8 (s, PCHCH3). Characterization of [Os(η5-C5H5){κ4-P,Ca,Cb,N-PiPr2[Ca(Me)CH2CH{Cb(CH2CH2)}-o-C5H4N]}]PF6 (4). A mixture enriched in complex 4 was prepared as follows. Method a. A solution of 1 (115 mg, 0.19 mmol) and (2pyridyl)methylenecyclopropane (38 mg, 0.29 mmol) in 6 mL of dichloromethane was heated at 45 °C in a Schlenk flask equipped with a Teflon stopcock for 7 days. The resulting orange solution was filtered through Celite and evaporated to dryness. The addition of dichloromethane (0.5 mL) and pentane (4 mL) afforded an orange solid, which according to its NMR spectra was a 6:21:66:7 mixture of 2−5. Yield: 115 mg (88%). Method b. The same result was obtained starting from a 82:11:7 mixture of 2−4 (100 mg, 0.14 mmol) and following the procedure described in method a. Yield: 85 mg (85%). Spectroscopic data for 4: 1H

NMR (400 MHz, (CD3)2CO, 298 K) δ 9.21 (dd, JH−H = 6.0, JH−H = 1.4, 1H, H6 py), 8.06 (ddd, JH−H = JH−H = 7.6, JH−H = 1.4, 1H, H4 py), 7.83 (dd, JH−H = 7.6, JH−H = 1.4, 1H, H3 py), 7.23 (ddd, JH−H = 7.6, JH−H = 6.0, JH−H = 1.4, 1H, H5 py), 5.56 (s, 5H, C5H5), 3.02 (d, JH−H = 3.9, 1H, CHpy), 2.99 (m, 1H, PCH), 2.75 (m, 1H, PCH), 2.26 (ddd, JH−H = 13.5, JH−P = 11.0, JH−H = 3.9, 1H, CaCH2), 1.78 (dd, JH−P = 16.3, JH−H = 7.2, 3H, PCHCH3), 1.72 (dd, JH−P = 16.2, JH−H = 7.4, 3H, PCHCH3), 1.71 (dd, JH−P = 18.3, JH−H = 7.5, 3H, PCHCH3), 1.53 (dd, JH−P = 18.6, JH−H = 7.5, 3H, PCHCH3), 1.35 (d, JH−P = 10.0, 3H, CaCH3), 1.34 (overlapped signal, 1H, CaCH2), 0.34−0.27 (m, 2H, CbCHHCHH), 0.15−0.09 (m, 2H, CbCHHCHH); 31P{1H} NMR (161.98 MHz, (CD3)2CO, 298 K) δ −8.8 (s), −144.1 (sept, JP−F = 708, PF6); 13C{1H} NMR (100.63 MHz, (CD3)2CO, 298 K) δ 171.9 (s, C2 py), 159.4 (s, C6 py), 140.3 (s, C4 py), 124.1 (s, C5 py), 120.9 (s, C3 py), 84.5 (s, C5H5), 76.4 (s, CH-py), 39.9 (d, JC−P = 3, CaCH2), 39.2 (d, JC−P = 41, PCH), 34.0 (d, JC−P = 15, Cb), 27.9 (s, CaCH3), 24.5 (d, JC−P = 29, PCH), 24.3 (d, JC−P = 6, PCHCH3), 20.6 (d, JC−P = 5, PCHCH3), 20.1 (s, PCHCH3), 19.6 (d, JC−P = 1, PCHCH3), 17.1 (d, JC−P = 1, CH2CH2), 15.6 (s, CH2CH2), 15.4 (d, JC−P = 6, Ca). Preparation of BArF4 Salts of 2−4. Method a. NaBArF4 (160 mg, 0.18 mmol) was added to a 40:47:13 mixture of 2−4 (62 mg, 0.09 mmol). Acetone (7 mL) was added, and the solution was stirred overnight. Then, the solvent was evaporated and 5 mL of dichloromethane was added. The suspension was filtered through Celite and concentrated to ca. 0.5 mL. The addition of pentane at 198 K caused the precipitation of a pink solid. Yield: 45 mg (36%). Anal. Calcd for C55H45BF24NOsP: C, 46.92; H, 3.22; N, 0.99. Found: C, 46.50; H, 3.21; N, 0.93. The 31P and 1H NMR data were identical with those reported for the initial mixture of 2−4 except for the additional 1 H signals of BArF4 and the absence of the signal at δP −144 due to the PF6 anion. A small amount of crystals of 3-BArF4, suitable for X-ray diffraction analysis, were obtained by slow diffusion of pentane into a dichloromethane solution of this solid at 225 K. Method b. Starting from a 6:21:66:7 mixture of 2−5 (76 mg, 0.11 mmol) and NaBArF4 (196 mg, 0.22 mmol), and following the procedure described in method a, an orange solid was obtained. Yield: 59 mg (38%). A small amount of crystals of 4-BArF4, suitable for X-ray diffraction analysis, were obtained by slow diffusion of pentane into a dichloromethane solution of this solid at 255 K. Characterization of [Os(η5-C5H5){κ4-N,Ca,Cb-Ca(CH2CbH2)( CH-o-C5H4N)}{PiPr2[C(Me)CH2]}]PF6 (5) and [Os(η5-C5H5){κ4N,Ca,Cb,N-PiPr2[Ca(Me)CH2CH{Cb(CH2CH2)}-o-C5H4N]}]PF6 (6). A 1:1 mixture of 5 and 6 was prepared as follows. A 6:21:66:7 mixture of 2−5 (200 mg, 0.29 mmol) was dissolved in 8 mL of acetone and heated at 75 °C for 48 h in a Schlenk flask equipped with a Teflon stopcock.23 The resulting orange solution was filtered through Celite and evaporated to dryness. The addition of dichloromethane (0.5 mL) and pentane (4 mL) afforded an orange solid, which according to its NMR spectra was a 1:1 mixture of 5 and 6. Yield: 180 mg (90%). A mixture enriched in complex 6 was prepared as follows. A solution of 1 (110 mg, 0.18 mmol) and (2-pyridyl)methylenecyclopropane (36 mg, 0.27 mmol) in 8 mL of acetone was heated at 75 °C in a Schlenk flask equipped with a Teflon stopcock for 5 days. The resulting orange solution was filtered through Celite and evaporated to dryness. The addition of dichloromethane (0.5 mL) and pentane (4 mL) afforded an orange solid, which according to its NMR spectra was a 31:69 mixture of 5 and 6. Yield: 88 mg (71%). Anal. Calcd for C23H33NF6OsP2: C, 40.05; H, 4.82; N, 2.03. Found: C, 39.55; H, 4.44; N, 1.63. HRMS (electrospray, m/z): calcd for C23H33NOsP [M]+ 546.1965, found 546.2002. IR (ATR, cm−1): ν(PF6) 833 (s). Spectroscopic data for 5: 1H NMR (400 MHz, CD2Cl2, 310 K) δ 8.38 (dd, JH−H = 6.0, JH−H = 1.4, 1H, H6 py), 7.59 (ddd, JH−H = 8.0, JH−H = 7.4, JH−H = 1.4, 1H, H4 py), 7.44, (dd, JH−H = 8.0, JH−H = 1.4, 1H, H3 py), 7.30 (s, 1H, OsCCH), 6.69 (ddd, JH−H = 7.4, JH−H = 6.0, JH−H = 1.4, H5 py), 6.02 (dd, JH−P = 33.7, JH−H = 1.4, 1H, CHHtrans to P), 5.39 (d, JH−P = 14.7, JH−H = 1.4, 1H,  CHHcis to P), 5.20 (s, 5H, C5H5), 4.52 (dd, JH−H = 16.9, JH−H = 8.0, 1H, OsCH2CH2), 3.98−3.89 (m, 1H, OsCH2CH2), 2.51 (m, 1H, PCH), 2.39 (ddd, JH−H = 10.2, JH−H =8.0, JH−H = 2.4, 1H, OsCbH2), 2.14 (m, 1H, PCH), 1.91 (d, JH−P = 10 Hz, PC(CH3)), 1.66 (dd, JH−P = 17.2, JH−H = 7.3, 3H, PCHCH3), 1.60 (overlapped signal, 1H, OsCbH2), 1.36 (dd, JH−P = 15.2, JH−H = 7.3, 3H, PCHCH3), 1.29 (dd, JH−P = 15.6, 4858


Organometallics

Article

JH−H = 7.2, 3H, PCHCH3), 0.88 (dd, JH−P = 13.4, JH−H = 6.4, 3H, PCHCH3); 31P{1H} NMR (161.98 MHz, CD2Cl2, 310 K) δ 6.5 (br s), −144.3 (sept, JP−F = 710, PF6); 13C{1H} NMR (100.63 MHz, CD2Cl2, 310 K) δ 180.9 (d, JC−P = 3, OsCaCH), 172.4 (s, C2 py), 157.8 (s, C6 py), 138.7 (s, C4 py), 134.4 (d, JC−P = 38, PC(CH3)), 130.6 (d, JC−P = 5, CH2), 124.6 (s, OsCCH), 121.3 (s, C3 py), 117.3 (s, C5 py), 90.7 (s, C5H5), 44.2 (s, OsCH2CH2), 31.5 (d, JC−P = 33, PCH), 26.3 (d, JC−P = 25, PCH), 24.6 (d, JC−P = 10, PC(CH3)), 22.9 (d, JC−P = 6, PCHCH3), 20.1 (d, JC−P = 4, PCHCH3), 19.7 (s, PCHCH3), 17.3 (d, JC−P = 3, PCHCH3), −36.8 (d, JC−P = 8, OsCbH2); 13C{1H} NMR (100.63 MHz, (CD3)2CO, 323 K) δ 182.1 (d, JC−P = 3, OsCaCH), 172.2 (s, C2 py), 159.5 (s, C6 py), 139.5 (s, C4 py), 136.0 (d, JC−P = 38, PC(CH3)=), 131.0 (d, JC−P = 5, CH2), 122.6 (s, OsC=CH), 121.2 (s, C3 py), 118.0 (s, C5 py), 92.1 (d, JC−P = 2, C5H5), 44.6 (s, OsCH2CH2), 32.0 (d, JC−P = 33, PCH), 27.2 (d, JC−P = 28, PCH), 25.1 (d, JC−P = 10, PC(CH3)), 23.4 (d, JC−P = 6, PCHCH3), 20.9 (d, JC−P = 4, PCHCH3), 20.8 (s, PCHCH3), 18.1 (d, JC−P = 3, PCHCH3), −36.5 (d, JC−P = 8, OsCbH2). Spectroscopic data for 6: 1H NMR (400 MHz, CD2Cl2, 310 K) δ 8.65 (dd, JH−H = 6.0, JH−H = 1.4, 1H, H6 py), 7.65 (ddd, JH−H = 7.6, JH−H = 7.4, JH−H = 1.4, 1H, H4 py), 7.36 (dd, JH−H = 7.6, JH−H = 1.4, 1H, H3 py), 6.93 (ddd, JH−H = 7.4, JH−H = 6.0, JH−H = 1.4, 1H, H5 py), 5.46 (s, 5H, C5H5), 3.01 (dd, JH−H = 5.9, JH−P = 5.8, 1H, CH-py), 2.74 (m, 1H, PCH), 2.12 (overlapped signal, 1H, CaCH2), 2.11 (m, 1H, PCH), 1.96 (d, JH−P = 10.4, 3H, CaCH3), 1.65 (dd, JH−P = 16.3, JH−H = 7.1, 3H, PCHCH3), 1.62 (overlapped signal, 1H, CaCH2), 1.19 (dd, JH−P = 17.9, JH−H = 7.5, 3H, PCHCH3), 1.13 (dd, JH−P = 14.4, JH−H = 7.1, 3H, PCHCH3), 0.77−0.68 (m, 2H, CH2CH2), 0.49 (dd, JH−P = 15.2, JH−H = 7.1, 3H, PCHCH3), 0.36 (ddd, JH−H = 9.0, JH−H = 5.5, JH−H = 5.2, 1H, CH2CH2), 0.27 (ddd, JH−H = 9.0, JH−H = 5.8, JH−H = 5.5, 1H, CH2CH2); 31 1 P{ H} NMR (161.98 MHz, CD2Cl2, 310 K) δ −13.6 (s), −144.3 (sept, JP−F = 710, PF6); 13C{1H} NMR (100.63 MHz, CD2Cl2, 310 K) δ 172.6 (s, C2 py), 159.8 (s, C6 py), 139.7 (s, C4 py), 123.7 (s, C5 py), 120.6 (s, C3 py), 85.1 (s, C5H5), 76.7 (d, JC−P = 3, CH-py), 34.4 (s, CaCH2), 32.5 (s, CaCH3), 32.3 (d, JC−P = 4, Cb), 31.5 (d, JC−P = 33, PCH), 28.3 (d, JC−P = 31, PCH), 21.3 (d, JC−P = 6, PCHCH3), 20.7 (d, JC−P = 6, Ca), 19.9 (d, JC−P = 5, PCHCH3), 18.3 (s, PCHCH3), 17.5 (s, PCHCH3), 16.3 (s, CH2CH2), 14.3 (s, CH2CH2);13C{1H} NMR (100.63 MHz, (CD3)2CO, 323 K): δ 173.9 (s, C2 py), 160.9 (s, C6 py), 140.7 (s, C4 py), 124.5 (s, C5 py), 121.7 (s, C3 py), 86.4 (s, C5H5), 77.7 (d, JC−P = 2, CH-py), 35.3 (s, CaCH2), 33.0 (s, CaCH3), 32.8 (d, JC−P = 4, Cb), 32.0 (d, JC−P = 33, PCH), 29.0(d, JC−P = 30, PCH), 21.6 (d, JC−P = 6, PCHCH3), 21.1 (d, JC−P = 6, Ca), 20.6 (d, JC−P = 4, PCHCH3), 19.1 (s, PCHCH3), 16.8 (s, PCHCH3), 16.8 (s, CH2CH2), 14.8 (s, CH2CH2). Preparation of BArF4 Salts of 5 and 6. A 1:1 mixture of 5 and 6 (65 mg, 0.09 mmol) and NaBArF4 (167 mg, 0.18 mmol) in 7 mL of acetone was stirred at room temperature overnight. Then, the solvent was evaporated and 5 mL of dichloromethane was added. The suspension was filtered through Celite and concentrated to ca. 0.5 mL. The addition of pentane at 198 K caused the formation of an orange solid. Yield: 55 mg (43%). Anal. Calcd for C55H45BF24NOsP: C, 46.92; H, 3.22; N, 0.99. Found: C, 47.20; H, 3.50; N, 1.25. The 31P and 1H NMR data were identical with those reported for the initial mixture of 2−4 except for the additional 1H signals of BArF4 and the absence of the signal at δP −144 due to the PF6 anion. A small amount of crystals of 5-BArF4, suitable for X-ray diffraction analysis, were obtained by slow diffusion of pentane into a dichloromethane solution of this solid at 255 K. Structural Analysis of Complexes 3−5. X-ray data were collected on a Bruker Smart APEX or Smart APEX DUO diffractometer equipped with a fine or normal focus, respectively, 2.4 kW sealed-tube source (Mo radiation, λ = 0.71073 Å). Data were collected over the complete sphere. Data were corrected for absorption by using a multiscan method applied with the SADABS program.26 The structures were solved by direct methods. Refinement was performed by full-matrix least squares on F2 with SHELXL97,27 including isotropic and subsequently anisotropic displacement parameters. The three compounds are very difficult to crystallize. Slow diffusion of pentane or diethyl ether into saturated solutions of [BF4]−, [PF6]−, [BPh4]−, or [BArF4]− salts of cations of 3−5 in dichloromethane was tried at room temperature or in the refrigerator (−20 °C). Most attempts ended giving oily residues. Finally, small crystals were obtained with [BArF4]−, although with very poor quality.

However, the significance of the crystallographic study in this work prompted us to go ahead. The presence of the large [BArF4]− anions in the crystal packing allow disorder in the smaller organometallic cations. In 3 and 5 it was observed that the top residual peaks in the least difference Fourier has no chemical sense and seems to indicate disordered osmium and/or phosphorus atoms. This disorder can be interpreted by the presence of a second cation in the asymmetric unit. The crystals were carefully checked, and nonmerohedral twinning was discarded. The problem could be a rotational disorder or enantiomer packing disorder. These complexes are all chiral, and both enantiomers are present in the centrosymmetric crystals. A small amount of disorder between the two enantiomers could produce the observed results. The intensities of the peaks suggested low occupancy of this disordered molecules (about 5−10% each). They were isotropically refined as an Os atom witha fixed multiplicity of 7% for 3 and as Os and P atoms with a multiplicity of 5% for 5. No attempt was made to locate disordered positions for lighter atoms. In this way, only the 93% in 3 and the 95% in 5 of complete cations were refined and included in the corresponding CIF files, similarly to previously reported disordered structures.28 In all complexes, the [BArF4]− anions were found to be severely disordered. The terminal CF3 groups were refined in one, two, or three moieties with restrained geometry and displacement parameters (isotropic or/and anisotropic). In 3 the isopropenyldiisopropylphosphine ligand was also disordered in two positions by rotation about the metal−phosphorus bond and was isotropically refined with restrained geometry and relative occupancies about 62:31. In 4, we can also see disordered dichloromethane molecules in the last cycles of refinement, treated in the same way. In 5, the C(CH3)CH2 group of the phosphine is disordered in two positions (60:40) related by a rotation of about 180° over the P−C bond, refined with restrained geometry and isotropic thermal parameters. Crystal data for 3: C23H33NOsP, C32H12BF24, mol wt 1407.90, irregular block, orange (0.20 × 0.12 × 0.08), monoclinic, space group P21/n, a = 16.4170(18) Å, b = 13.7633(15) Å, c = 24.548(3) Å, β = 104.3710(10)°, V = 5373.2(10) Å3, Z = 4, Dcalcd = 1.740 g cm−3, F(000) = 2776, T = 100(2) K, μ = 2.526 mm−1. 48421 measured reflections (2θ = 3−58°, ω scans 0.3°), 12643 unique (Rint = 0.0673), minimum/ maximum transmission factors 0.862/0.682, final agreement factors R1 = 0.0917 (8896 observed reflections, I > 2σ(I)) and wR2 = 0.2160, data/ restraints/parameters 12643/98/697, GOF = 1.088, largest peak and hole 3.185 and −1.909 e/Å3. Crystal data for 4: C23H33NOsP, C32H12BF24·CH2Cl2, mol wt 1492.83, irregular block, orange (0.14 × 0.09 × 0.01), monoclinic, space group C2/c, a = 19.056(2) Å, b = 17.482(2) Å, c = 34.820(5) Å, β = 91.2683(19)°, V = 11597(3) Å3, Z = 8, Dcalcd = 1.710 g cm−3, F(000) = 5888, T = 100(2) K, μ = 2.435 mm−1. 46134 measured reflections (2θ = 3−58°, ω scans 0.3°), 10788 unique (Rint = 0.0618), minimum/ maximum transmission factors 0.862/0.665, final agreement factors R1 = 0.0837 (9190 observed reflections, I > 2σ(I)) and wR2 = 0.1819, data/restraints/parameters 10788/416/1040, GOF = 1.098, largest peak and hole 3.117 and −1.686 e/Å3. Crystal data for 5: C23H33NOsP, C32H12BF24, mol wt 1407.90, irregular block, yellow (0.25 × 0.19 × 0.03), orthorhombic, space group Pna21, a = 33.789(9) Å, b = 12.687(4) Å, c = 12.974(4) Å, V = 5562(3) Å3, Z = 4, Dcalcd = 1.681 g cm−3, F(000) = 2776, T = 100(2) K, μ = 2.440 mm−1. 44614 measured reflections (2θ = 3−58°, ω scans 0.3°), 14904 unique (Rint = 0.0428), minimum/maximum transmission factors 0.636/0.862, final agreement factors R1 = 0.0788 (11629 observed reflections, I > 2σ(I)) and wR2 = 0.2244, Flack parameter 0.056(13), data/restraints/parameters 14904/104/704, GOF = 1.046, largest peak and hole 4.686 and −2.587 e/Å3. Computational Details and Cartesian Coordinates of Model Complexes. The theoretical calculations were carried out on the model complexes by optimizing the structures at the M06-DFT29 levels with the Gaussian 09 program.30 The basis sets used were LANL2DZ basis and pseudopotentials for Os and 6-31G(d,p) for the rest of the atoms. We fully optimized these structures and calculated Gibbs free energies. All stationary points were confirmed by having only positive vibrational frequencies for intermediates or one negative frequency for transition states. The transition state search was performed in a two-stage process: first, a relaxed PES scan of 4859


Organometallics

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5609. (e) Gulı ́as, M.; Garcı ́a, R.; Delgado, A.; Castedo, L.; Mascareñas, J. L. J. Am. Chem. Soc. 2006, 128, 384. (f) Trillo, B.; Gulı ́as, M.; López, F.; Castedo, L.; Mascareñas, J. L. Adv. Synth. Catal. 2006, 348, 2381. (g) Garcı ́a-Fandiño, R.; Mascareñas, J. L.; Gulı ́as, M.; Castedo, L.; Granja, J. R.; Cárdenas, D. J. Chem. Eur. J. 2008, 14, 272. (h) Evans, P. A.; Inglesby, P. A. J. Am. Chem. Soc. 2008, 130, 12838. (i) Villarino, L.; López, F.; Castedo, L.; Mascareñas, J. L. Chem. Eur. J. 2009, 15, 13308. (j) Bhargava, G.; Trillo, B.; Araya, M.; López, F.; Castedo, L.; Mascareñas, J. L. Chem. Commun. 2010, 46, 270. For Ni-catalyzed cycloadditions involving proximal cleavage of the cyclopropane, see: (k) Saya, L.; Bhargava, G.; Navarro, M. A.; Gulı ́as, M.; López, F.; Mascareñas, J. L. Angew. Chem., Int. Ed. 2010, 49, 9886. (l) Ohashi, M.; Taniguchi, T.; Ogoshi, S. Organometallics 2010, 29, 2386. (m) Yamasaki, R.; Terashima, N.; Sotome, I.; Komagawa, S.; Saito, S. J. Org. Chem. 2010, 75, 480 and references therein. (6) (a) Noyori, R.; Nishimura, T.; Takaya, H. Chem. Commun. 1969, 89. (b) Green, M.; Howard, J. A. K.; Hughes, R. P.; Kellett, S. C.; Woodward, P. J. Chem. Soc., Dalton Trans. 1975, 2007. (c) Pinhas, A. R.; Samuelson, A. G.; Risemberg, R.; Arnold, E. V.; Clardy, J.; Carpenter, B. K. J. Am. Chem. Soc. 1981, 103, 1668. (d) Isaeva, L. S.; Peganova, T. A.; Petrovskii, P. V.; Furman, D. B.; Zotova, S. V.; Kudryasev, A. V.; Bragin, O. V. J. Organomet. Chem. 1983, 258, 367. (e) Allen, S. R.; Barnes, S. G.; Green, M.; Moran, G.; Trollope, L.; Murrall, N. W.; Welch, A. J.; Sharaiha, D. M. J. Chem. Soc., Dalton Trans. 1984, 1157. (f) Mashima, K.; Takaya, H. Organometallics 1985, 4, 1464. (g) Osakada, K.; Takimoto, H.; Yamamoto, T. Organometallics 1998, 17, 4532. (h) Osakada, K.; Takimoto, H.; Yamamoto, T. J. Chem. Soc., Dalton Trans. 1999, 853. (i) Nishihara, Y.; Yoda, C.; Osakada, K. Organometallics 2001, 20, 2124. (j) Tantillo, D. J.; Carpenter, B. K.; Hoffmann, R. Organometallics 2001, 20, 4562. (k) Binger, P.; Müller, P.; Podubrin, S.; Albus, S.; Krüger, C. J. Organomet. Chem. 2002, 656, 288. (l) Itazaki, M.; Yoda, C.; Nishihara, Y.; Osakada, K. Organometallics 2004, 23, 5402. (m) Kozhushkov, S. I.; Foerstner, J.; Kakoschke, A.; Stellfeldt, D.; Yong, L.; Wartchow, R.; de Meijere, A.; Butenschön, H. Chem. Eur. J. 2006, 12, 5642. (n) Yamasaki, R.; Ohashi, M.; Maeda, K.; Kitamura, T.; Nakagawa, M.; Kato, K.; Fujita, T.; Kamura, R.; Kinoshita, K.; Masu, H.; Azumaya, I.; Ogoshi, S.; Saito, S. Chem. Eur. J. 2013, 19, 3415. (7) Castro-Rodrigo, R.; Esteruelas, M. A.; López, A. M.; López, F.; Mascareñas, J. L.; Oliván, M.; Oñate, E.; Saya, L.; Villarino, L. J. Am. Chem. Soc. 2010, 132, 454. (8) Castro-Rodrigo, R.; Esteruelas, M. A.; Fuertes, S.; López, A. M.; López, F.; Mascareñas, J. L.; Mozo, S.; Oñate, E.; Saya, L.; Villarino, L. J. Am. Chem. Soc. 2009, 131, 15572. (9) (a) Baya, M.; Buil, M. L.; Esteruelas, M. A.; Oñ ate, E. Organometallics 2004, 23, 1416. (b) Esteruelas, M. A.; González, A. I.; López, A. M.; Oñate, E. Organometallics 2004, 23, 4858. (10) Castro-Rodrigo, R.; Esteruelas, M. A.; López, A. M.; Mozo, S.; Oñate, E. Organometallics 2010, 29, 4071. (11) For related osmium complexes with a pyridyl−olefin chelate ligand see: Castro-Rodrigo, R.; Esteruelas, M. A.; López, A. M.; López, F.; Mascareñas, J. L.; Mozo, S.; Oñate, E.; Saya, L. Organometallics 2010, 29, 2372. (12) (a) Grubbs, R. H.; Coates, G. W. Acc. Chem. Res. 1996, 29, 85. (b) Schrock, R. R. Chem. Rev. 2002, 102, 145. (c) Carmona, E.; Paneque, M.; Poveda, M. L. Dalton Trans. 2003, 4022. (d) Bielawski, C. W.; Grubbs, R. H. Prog. Polym. Sci. 2007, 32, 1. (13) Freudenberger, J. H.; Schrock, R. R. Organometallics 1985, 4, 1937. (14) See for example: (a) Cutler, A.; Fish, R. W.; Giering, W. P.; Rosenblum, M. J. Am. Chem. Soc. 1972, 94, 4354. (b) Casey, C. P.; Albin, L. D.; Burkhardt, T. J. J. Am. Chem. Soc. 1977, 99, 2533. (c) Brookhart, M.; Tucker, J. R. J. Am. Chem. Soc. 1981, 103, 979. (d) Marsella, J. A; Folting, K.; Huffman, J. C.; Caulton, K. G. J. Am. Chem. Soc. 1981, 103, 5596. (e) Casey, C. P.; Miles, W. H.; Tukada, H.; O’Connor, J. M. J. Am. Chem. Soc. 1982, 104, 3761. (f) Kremer, K. A. M.; Kuo, G.-H.; O’Connor, E. J.; Helquist, P.; Kerber, R. C. J. Am. Chem. Soc. 1982, 104, 6119. (g) Casey, C. P.; Miles, W. H.; Tukada, H. J. Am. Chem. Soc. 1985, 107, 2924. (h) Alías, F. M.; Poveda, M. L.; Sellin, M.; Carmona, E. J. Am. Chem. Soc. 1998, 120, 5816. (i) Castro-Rodrigo, R.; Esteruelas, M. A.;

the key bonds broken or formed, or key angles moved, was performed with steps of 0.1 Å for bonds or 0.5° for angles and then the highest energy structure was optimized as the transition state by the default Gaussian algorithms. The chemical correctness of the transition states found was confirmed by visual inspection of the normal mode having the negative vibrational frequency, followed by moving the TS geometries toward the minima along the reaction path using the GaussView program utilities and reoptimizing to verify the nature of products. Solvent effects (CH2Cl2, ε = 8.930) were introduced in the refinement by means of a continuum method, the PCM approach31 implemented in Gaussian09. The relative Gibbs energies in dichloromethane shown throughout this present work (ΔGCH2Cl2) were obtained by employing the following scheme: ΔGCH2Cl2 = ΔECH2Cl2 + (ΔGgas − ΔEgas). For the calculations of Gibbs free energies, we used the standard ideal gas− rigid rotor−harmonic oscillator approximation. All the Gibbs energies collected in the text are at 298.15 K and 1 atm.32

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ASSOCIATED CONTENT

* Supporting Information S

Figures giving 1H, 31P{1H}, and 13C{1H} NMR spectra for complexes 2−6, text giving the complete ref 30 and computational details, tables giving optimized coordinates and energies of all optimized complexes, and CIF files giving crystallographic data for 3−5. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (M.A.E.); [email protected] (A.M.L.); [email protected] (J.L.M.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Financial support from the Spanish MICINN (Projects CTQ2011-23459, SAF2010-20822-C02, and Consolider Ingenio 2010 (CSD2007-00006)), the Diputación General de Aragón (E35), the Xunta de Galicia INCITE09 209 084PR, GRC2010/ 12, and the European Social Fund (FEDER) is acknowledged. L.S. thanks the Xunta de Galicia for a grant. We thank the Centro de Supercomputación de Galicia (CESGA) for generous allocation of computational resources.

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REFERENCES

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