Unexpected Reactivity Patterns of Ruthenium Alkylidenes with N

Article pubs.acs.org/Organometallics

Unexpected Reactivity Patterns of Ruthenium Alkylidenes with N‑Phosphino-Functionalized N‑Heterocyclic Carbene Ligands (NHCPs) Christopher C. Brown,† Philipp N. Plessow,†,‡ Frank Rominger,∥ Michael Limbach,†,§ and Peter Hofmann*,†,∥ †

Catalysis Research Laboratory (CaRLa), Im Neuenheimer Feld 584, D-69120 Heidelberg, Germany Quantum Chemistry, BASF SE, Carl-Bosch-Straße 38, D-67056 Ludwigshafen, Germany § Synthesis & Homogeneous Catalysis, BASF SE, Carl-Bosch-Straße 38, D-67056 Ludwigshafen, Germany ∥ Organisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 270, D-69120 Heidelberg, Germany ‡

S Supporting Information *

ABSTRACT: N-phosphino-functionalized N-heterocyclic carbene (NHCP) ligands have been evaluated as potential supporting ligands in ruthenium-catalyzed olefin metathesis. Initial density functional theory (DFT) calculations suggested that these NHCP ligands may allow access to neutral 14 valence electron (VE) species equivalents of the active 14 VE species formed by phosphine dissociation from Grubbs II precatalystsvia facile decoordination of the NHCP phosphino donor of the strained four-membered [RuPNC] chelate systems. Their attempted synthesis from NHCPs and Grubbs-type Ru carbenes revealed addition of an NHCP donor atom (P or C) to the alkylidene fragment, forming a new C−P or C−C bond in five-membered chelate structures. DFT investigations showed that these reactions are controlled kinetically and must not be neglected as important possible deactivation routes in olefin metathesis.

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INTRODUCTION Since the discovery of Schrock and Grubbs catalysts, intense interest has evolved in the field of catalytic olefin metathesis. Widespread research efforts have led to the preparation of an extensive number of variations of ruthenium(II) olefin metathesis catalysts with a broad variation of the phosphine ligands, introduction of N-heterocyclic carbene (NHC) and Schiff base ligands, variation of the alkylidene functionality, and introduction of non-halide anionic ligands.1−5 Functionalized NHC ligands capable of chelate coordination at Ru(II), however, have received relatively little attention. Notable examples include the reports of Z-selective systems6,7 as well as a report concerning N-phosphino-functionalized NHC (NHCP) ligands.8 NHCPs represent a new class of ligands recently introduced by our group and others.8−11 The bidentate NHCP ligand framework incorporates both a phosphine donor and an NHC carbene donor, either directly bound or separated via a carbon bridge, resulting in four- or five-membered chelate NHCP coordination at Ru, respectively. NHCP ligands have since been applied in a variety of applications.10,12,13 NHC ligands have been shown to provide greater stability and activity to Grubbs-type olefin metathesis catalysts than phosphines.1,14 Furthermore, phosphine ligands have been found to be involved more extensively in catalyst decomposition than NHCs.15,16 In particular, it has been demonstrated that phosphine addition to a ruthenium © XXXX American Chemical Society

methylidene unit is facile, resulting in alkylidene−ruthenium bond cleavage.17 On the other hand, NHC ligands have not hitherto been disclosed to undergo catalyst deactivation in Grubbs-type systems via their C donor atom, as decomposition occurs primarily via activation of the N-aryl group. The omethyl groups of both IMes and SIMes, typical NHC ligands, are particularly susceptible to activation leading to decomposition. There are few examples of NHC activation with respect to ruthenium−carbon bonds.18 Most notably, a series of reports by Kirchner and co-workers detail the migratory insertion of NHCs into a ruthenium−carbon double bond.19,20 Previously we have reported the synthesis of cationic ruthenium alkylidene complexes based on the bidentate, bulky, electron-rich bis(di-tert-butylphosphino)methane (dtbpm) ligand21 which display exceptionally high activity in ROMP reactions even in the ppm range of catalyst loadings. Neutral (dtbpm)RuCl2 alkylidenes have shown low activity in metathesis, as well as, a unique dtbpm P-addition to a Ru alkylidene.21,22 Herein, we report an experimental investigation into NHCP ruthenium alkylidene chemistry, an unexpected alkylidene decomposition pathway, and a computational study into the unexpected reactivity. Received: May 21, 2014

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dx.doi.org/10.1021/om5005429 | Organometallics XXXX, XXX, XXX−XXX

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RESULTS AND DISCUSSION Computational Investigation of the Proposed Catalytic Cycle. In this study, we set out to utilize NHCP ligands capable of forming four-membered chelate units at Ru for catalytic olefin metathesis as analogues to dtpbm. Initially we sought to assess the applicability of such NHCP ligands for catalytic olefin metathesis with a preliminary density functional theory (DFT) investigation into the catalytic competency of A, a computational model for the synthetic target B (Figure 1).

instant reaction that produced new compounds 1a and 1b in 86% yield (Scheme 2). When the reaction was followed by Scheme 2. Synthesis of 1 and 2

NMR spectroscopy, the liberation of PCy3 and complete consumption of NHCPMe were observed. Analysis of the purified sample by NMR spectroscopy did not display a 1H NMR signal downfield of 10 ppm, indicating the lack of formation of a new ruthenium alkylidene-bearing species. The 31 P NMR spectrum displayed new signals, including one signal at 172 ppm and several centered about 95 ppm, suggesting the formation of more than one new product. These unexpected spectroscopic results were explained via crystallographic studies of three data sets: one for pure isomer 1b (Figure 2), one for a crystal predominantly composed of 1a

Figure 1. Computational model complex A and the synthetic target B.

A computationally proposed reaction pathway, as shown in Scheme 1 for the methylidene complex A, illustrates that the Scheme 1. Computational Study of the Catalytic Competency of NHCP-Based Olefin Metathesis Catalystsa

Figure 2. ORTEP plot of complex 1b (hydrogen atoms omitted for clarity; ellipsoids at 30% probability).

A5 denotes the most stable conformer of the κ1-P-coordinated methylidene complex. The barrier for equilibration of the conformers is negligible and has been omitted for brevity (see the SI for more details). a

(Figure 3), and one for a crystal composed predominantly of 2b (Figure 4). The crystallographic studies were complicated by finding disorder between 1a and 1b or 2a and 2b in many attempts to obtain high-quality data. The molecular structure of the pure isomer 1b revealed that the ruthenium center adopts a distorted octahedral geometry with two cis-coordinated pyridines and two trans-disposed chlorides. The Cl−Ru−Cl bond angle was found to be 170.47(3)°, with Ru−Cl bond distances of 2.4172(7) and 2.4308(7) Å. It was determined that the NHCP carbene carbon underwent a formal addition to the ruthenium alkylidene carbon to form a new C−C bond. This C−C bond was found to have a bond distance of 1.477(4) Å, indicating a significantly shortened single bond. The Ru−C bond lengthened to 2.179(2) Å compared with the Ru−C bond distance of 1.834(4) Å in the first-generation Grubbs catalyst.34 Additional crystals from an identical reaction were further examined via X-ray crystallography to reveal an additional insertion isomer, 1a, where the alkylidene addition occurred via C−P bond formation (Figure 3). These crystals of 1a were found to be disordered in a 85:15 ratio of 1a to 1b.

phosphine arm of the NHCP ligand should readily dissociate to create a free coordination site for, e.g., an olefin. We here refer to gas-phase free energies at the M06/def2-TZVP/BP86/def2SV(P)23−30 level of theory at 1 bar and 298.15 K (see the Supporting Information (SI) for details). The phosphine dissociation to yield A2 (ΔG = 34 kJ/mol above A1) is facile (ΔG⧧ = 70 kJ/mol) and could provide access to a direct analogue of the putative four-coordinate active species of second-generation Grubbs catalysts.31,32 Coordination of ethylene is then downhill in energy by 30 kJ/mol, followed by a low barrier to give a metallocyclobutane. Dissociation of the NHC side would lead to A5, which is 61 kJ/mol more endergonic than dissociation of the phosphine arm and is therefore not expected to be relevant. On the basis of these results, we sought to prepare neutral ruthenium complexes of, e.g., type B possessing NHCP supporting ligands. Synthesis of Ruthenium Complexes. Mixing RuCl2(PCy3)py2(CHPh)33 with NHCPMe resulted in a nearly B


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Computational Investigation of the Unexpected Reactivity. Since a mixture of products of the attack of the NHC and the phosphine arm of NHCPMe at the Ru alkylidene carbon is found experimentally, either the activation products must be in thermodynamic equilibrium or their formation is kinetically controlled. According to our DFT calculations, C−C bond formation by attack of the NHC is favored thermodynamically by 51 kJ/mol, from which we conclude that the formation of 1b is kinetically controlled (Scheme 3, B5 vs B7). The elemental steps that lead to the experimentally observed products could be attack of the phosphine or NHC donor center on the alkylidene followed by coordination of the other donor to a vacant coordination site at ruthenium, vice versa, concerted, or initial coordination of the NHCP followed by migratory insertion. Preliminary calculations suggest that all of these processes are realistic, and we did not attempt to further clarify the exact course of this reaction. The most important question is whether the addition to the alkylidene is reversible so that the isolated complexes 1a,b and 2a,b are catalytically competent, as envisioned in the preliminary calculations. If the κ1-P-coordinated NHCP is bound adjacent to the alkylidene unit, attack of the NHC at the alkylidene occurs without barrier (Scheme 3). Additionally, a local minimum for a complex with a pendant uncoordinated NHC (B4, ΔG = 209 kJ/mol) was located only for the NHC pointing away so that its coordination is hindered by a small rotational barrier (Scheme 3). However, if the attack of the NHC occurs, a thermodynamically stable C−C bond is irreversibly formed (Scheme 3, B2 and B5). We also studied whether cleavage of the C−C bond is possible without generating the unfavorable uncoordinated dangling NHC. This should be possible if a pyridine ligand is dissociated first, forming a vacant coordination site (B2). We located such a transition state that goes directly from the C−C-activated product to the complex with κ2-P,C-bound NHCP (B3). The barrier is again prohibitively high (ΔG⧧ = 199 kJ/mol), even without taking into account the energy required for pyridine dissociation. On the basis of the preceding evidence, we may conclude that C−C bond formation is not reversible. In the case of the formation of 1a and 2a, the complexes have a surviving thermodynamically stable NHC−Ru bond, as supported by experimental evidence and our calculations. At the same time, the formation of the P−C bond is definitely

Figure 3. ORTEP plot of octahedral complex 1a with a five-membered chelate structure (hydrogen atoms omitted for clarity; ellipsoids at 30% probability).

Mixing of RuCl2(PCy3)py2(CHPh) with NHCPMes produced an analogous result. NMR spectroscopy revealed primarily the formation of one new species. The 31P NMR spectrum displayed a peak at 167.1 ppm, while integration of the 1H NMR spectrum showed a greater than 90% yield of a single product. X-ray crystallography unambiguously confirmed the synthesis of 2b, wherein the primary bond formation occurred by addition of the NHC carbene center to the benzylidene carbon (Figure 4). The molecular structure displayed metrical parameters similar to those found for 1b.

Figure 4. ORTEP plot of complex 2b (hydrogen atoms omitted for clarity; ellipsoids at 30% probability).

Scheme 3. Free Energy Diagram for NHCP Activation of a Ruthenium Benzylidene; The Solid Line Denotes That for the Corresponding Reaction Path, and All Intermediates and Transition States Are Shown

C


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of the NHC in an active conformation pointing toward the alkylidene.

reversible with a modest barrier of 55 kJ/mol (Scheme 3, B7 to B6). Therefore, complexes 1a and 2a may lead to a catalytically active species while 1b and 2b would be catalytically inactive. Catalytic Implications. These experimental findings prompted us to revisit the initial calculations because the observed addition of the NHCP carbon to the alkylidene moiety could be an important general deactivation route in olefin metathesis catalysis. Indeed, we found that in the initially studied model complex A, the NHC arm readily undergoes migratory addition to the methylidene (ΔG⧧ = 77 kJ/mol) in the absence of an olefin (Scheme 4), as pictured in Figure 5.

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CONCLUSION We have investigated the potential of four-membered Nphosphino-functionalized NHC (NHCP)-based chelate complexes as ruthenium olefin metathesis precatalysts. Initial DFTbased screening indicated that NHCP ligands may be a suitable choice for a new type of olefin metathesis catalysts. However, the reaction of such NHCPs (NHCPMe, NHCPMes) with a Grubbs-type catalyst unexpectedly revealed the attack of the Ru alkylidene moiety by the donor atoms of the NHCP ligand. We have found a unique example of the direct addition of an NHC carbene carbon to a Grubbs-type alkylidene carbon. Our computational study suggests that the reaction is controlled kinetically and that it might also be a relevant deactivation path for actual catalysis experiments with N-phosphino-functionalized NHC ligands. Consideration of these results is important for the structural design of more robust and active catalysts. Further investigation into the scope of this reaction is currently underway. Our results also make it clear that for the new family of Ru alkylidenes with modified four-membered chelating units and variable alkylidene units, as represented by B, alternative synthetic pathways other than ligand substitution of Grubbs systems with NHCP have to be developed. Our continuing efforts will be reported in due course.

Scheme 4. Intramolecular NHC Alkylidene Activation as a Function of the Alkylidene Substituent

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EXPERIMENTAL SECTION

General Considerations. All manipulations were carried out under an atmosphere of dry argon using standard Schlenk techniques or in an MBraun glovebox. Solvents were either dried over appropriate drying agents, distilled under an atmosphere of argon, purchased dry from Aldrich, or dispensed from an MBraun SPS-800 solvent system. Solvents were stored over either sodium ingots or molecular sieves (3 Å). Solvents were degassed via either three freeze−pump−thaw cycles or sparging with argon. Phosphorylated NHCs and the Grubbs pyridine complex were prepared according to literature procedures. All solvents and reagents were purchased from Aldrich or prepared from literature procedures.10,33 NMR spectra were recorded using a Bruker 200 or a Bruker AVANCE III 600 spectrometer. Chemical shifts are given in parts per million referenced to solvent for 1H and 13C NMR and relative to 85% H3PO4 for 31P NMR. Abbreviations used are s = singlet, d = doublet, br = broad. Coupling constants (J) are reported in hertz. Elemental analysis was performed by the Mikroanalytisches Laboratorium der Chemischen Institute der Universität Heidelberg. Computational Details. Molecular structures were optimized at the BP86/def2-SV(P)23,25−29 level of theory. Calculations were carried out using the resolution of the identity approximation and appropriate auxiliary basis functions24 with TURBOMOLE.36 Single-point energies at the M06/def2-TZVP//BP86/def2-SV(P)30 level were computed with GAMESS-US.37 Gas-phase Gibbs free energies were obtained within the usual rigid-rotator, harmonic-oscillator approximation at 1 bar and 298.15 K. Ru(NHCPMe-CHPh)Cl2py2 (1a and 1b). A solution of NHCPMe (68 mg, 0.300 mmol, 1.05 equiv) in THF (2 mL) was added to RuCl2(PCy3)(py)2(CHPh) (200 mg, 0.286 mmol, 1 equiv) in THF (5 mL). The reaction mixture was stirred for 30 min. The solvent volume was reduced in vacuo. The reaction mixture was filtered through Celite, washed from the frit with dichloromethane (15 mL), and layered with pentane. Slow mixing gave compound 1 as red crystals (144 mg, 0.222 mmol, 78% yield). X-ray-quality single crystals obtained via slow mixing of pentane and toluene contained a mixture of two superimposed isomers. X-ray-quality single crystals obtained via slow mixing of pentane and THF contained predominantly the NHC− benzylidene insertion product.

Figure 5. Transition state for NHC addition to the methylidene carbon. Bond formation is shown as a dashed line. C, gray; H, light gray; Ru, dark green; Cl, green; P, orange; N, blue. Non-alkylidene hydrogens have been omitted for clarity.

The reaction is expected to be irreversible (ΔG = −50 kJ/mol). In contrast to this, aryl- or alkyl-substituted Ru carbenes should be kinetically inert at room temperature (in both cases ΔG⧧ ≈ 120 kJ/mol). On the other hand, if a Ru methylidene is formed as an intermediate in metathesis, one can expect that the computed deactivation reaction becomes important. The possibility of the attack of an NHC at an alkylidene has already been pointed out by Straub.35 In a theoretical investigation of a Grubbs-II model compound, the activation barrier was found to be somewhat too high to be relevant at room temperature (ΔG⧧ = 111 kJ/mol). Straub noted that the equilibrium orientation of real NHCs is usually inactive with respect to attack at the alkylidene. It is therefore interesting to note that in complex A the NHCP chelate fixes the orientation D


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19.070(3) Å, b = 12.8411(17) Å, c = 15.932(2) Å, α = 90°, β = 109.153(3)°, γ = 90°, V = 3685.6(8) Å3, ρ = 1.165 g/cm3, T = 200(2) K, θmax = 21.124°, 0.5° ω scans with the CCD area detector, covering the asymmetric unit in reciprocal space with a mean redundancy of 3.12 and a completeness of 92.5% to a resolution of 0.99 Å, 12 912 reflections measured, 3723 unique (Rint = 0.0697), 2617 observed (I > 2σ(I)), intensities were corrected for Lorentz and polarization effects, an empirical absorption correction was applied using SADABS1 based on the Laue symmetry of the reciprocal space, μ = 0.63 mm−1, Tmin = 0.70, Tmax = 0.96, structure refined against F2 with a full-matrix leastsquares algorithm using the SHELXL software (version 2014-3),2 369 parameters refined, hydrogen atoms were treated using appropriate riding models, goodness of fit 1.09 for observed reflections, final residual values R1(F) = 0.069, wR(F2) = 0.154 for observed reflections, residual electron density −0.35 to 0.66 e Å−3. 2b: orange crystal (cuboid), dimensions 0.26 mm × 0.16 mm × 0.10 mm, crystal system triclinic, space group P1̅, Z = 2, a = 8.9978(6) Å, b = 14.2563(10) Å, c = 14.5573(11) Å, α = 105.448(1)°, β = 93.863(1)°, γ = 100.488(1)°, V = 1756.5(2) Å3, ρ = 1.419 g/cm3, T = 200(2) K, θmax= 26.73°, 0.5° ω scans with the CCD area detector, covering the asymmetric unit in reciprocal space with a mean redundancy of 3.18 and a completeness of 99.6% to a resolution of 0.79 Å, 23 714 reflections measured, 7439 unique (Rint = 0.0285), 6426 observed (I > 2σ(I)), intensities were corrected for Lorentz and polarization effects, an empirical absorption correction was applied using SADABS38 based on the Laue symmetry of the reciprocal space, μ = 0.68 mm−1, Tmin = 0.84, Tmax = 0.94, structure solved by direct methods and refined against F2 with a full-matrix least-squares algorithm using the SHELXTL39 software package, 437 parameters refined, hydrogen atoms were treated using appropriate riding models, goodness of fit 1.09 for observed reflections, final residual values R1(F) = 0.038, wR(F2) = 0.082 for observed reflections, residual electron density −0.50 to 0.58 e Å−3.

All of the solution NMR spectra showed a complex mixture of isomers. Complex 1 was only sufficiently soluble in pyridine-d5 to obtain informative NMR spectra. 1H NMR (MHz, C5D5N, 298 K): δ 0.93 (d, 3J(H,P) = 15.7 Hz, tBu), 0.94 (d, 3J(H,P) = 15.5 Hz, tBu), 1.05 (d, 3J(H,P) = 15.2 Hz, tBu), 1.09 (d, 3J(H,P) = 15.2 Hz, tBu), 1.45, 1.46, 1.47, 1.48, 1.48, 1.49, 1.57 (d, 3J(H,P) = 12.9 Hz, tBu), 1.64 (d, 3J(H,P) = 12.7 Hz, tBu), 3.21 (Me), 3.53 (Me), 3.62 (Me), 3.73 (Me), 4.04 (Me), 4.07 (Me), 5.23 (d, 2J(H,P) = 16.5 Hz PCHPh), 5.60 (s, PCHPh), 5.82 (d, 2J(H,P) = 21.7 Hz, PCHPh), 6.71 (br), 6.85, 6.93, 6.94, 6.95, 7.05, 7.25−7.36 (m), 7.45 (br), 7.53 (CHimdazole), 7.54, 7.57, 7.63 (CHimdazole), 7.96, 8.08, 8.10, 8.12, 8.56, 8.74, 8.85. 31 1 P{ H} NMR: δ 94.7, 96.1, 98.5, 98.6, 173.4. 13C{1H} NMR (partial): δ 21.4 (d, J(C,P) = 11.3 Hz, tBu), 22.0 (d, J(C,P) = 8.5 Hz, tBu), 26.9, 27.0, 28.2, 28.3, 28.2, 28.7, 29.2, 30.2 (d, J(C,P) = 5.1 Hz, tBu), 33.1 (d, J(C,P) = 5.5 Hz, tBu), 36.4, 37.3, 37.5, 37.7, 38.0, 39.2, 40.3, 40.5, 43.5 (d, J = 7.5 Hz, tBu), 46.2 (d, J = 7.2 Hz, tBu), 119.6, 119.7, 121.3, 122.9, 123.6, 123.8, 125.5, 126.9, 127.0, 127.9, 129.7, 132.0, 132.1, 135.6, 135.8, 150.0, 150.1, 152.0, 171.9 (d, J = 23.4 Hz, Ccarbene). Elemental analysis for C29H39Cl2N4PRu·THF: calcd C 55.15, H 6.59, N 7.80; found C 54.89, H 6.93, N 7.98. Note: one molecule of THF was found in the molecular structure. Ru(NHCPMes-CHPh)Cl2py2 (2a and 2b). A solution of NHCPMes (94 mg, 0.286 mmol) in THF (2 mL) was added to RuCl2(PCy3)(py)2(CHPh) (200 mg, 0.286 mmol) in THF (5 mL). The reaction mixture was stirred for 30 min. The solvent volume was reduced in vacuo. The reaction mixture was filtered through Celite, washed from the frit with dichloromethane (15 mL), and layered with pentane. Slow mixing gave compound 2 as red crystals (87 mg, 0.232 mmol, 81% yield). X-ray-quality crystals were obtained via slow mixing of pentane and toluene. 1 H NMR (MHz, CD2Cl2, 298 K): δ 1.43 (d, 9H, 3J(H,P) = 13.3 Hz, t Bu), 1.62 (d, 9H, 3J(H,P) = 13.1 Hz, tBu), 1.95 (s, 3H, CH3), 2.07 (s, 3H, CH3), 2.11 (s, 3H, CH3), 5.43 (s, 1H, CHPh), 6.45 (s, 1H, CHMes), 6.65 (s, 1H, CHMes), 6.91 (s, 1H, CHimidazole), 6.97 (br, 1H, Ar), 7.39 (s, 1H, CHimidazole), 7.47 (s, 1H, Ar), 8.63 (br, 2H, Ar), 9.07 (br, 2H, Ar). 31P{1H} NMR: δ 167.1. 13C{1H} NMR: δ 18.7 (o-CH3), 18.8 (o-CH3), 20.9 (p-CH3), 22.8 (m, CHPh), 30.8 (d, 2J(C,P) = 4.9 Hz, PC(CH3)3), 33.3 (d, 2J(C,P) = 5.3 Hz, PC(CH3)3), 44.7 (d, 2 J(C,P) = 6.0 Hz, PC(CH3)3), 46.7 (d, 2J(C,P) = 8.3 Hz, PC(CH3)3), 119.1 (CHimidazole), 121.5, 123.3, 124.6 (CHimidazole), 129.0 (CHMes), 129.4 (CHMes), 133.6, 134.2, 135.1, 139.3, 148.1, 156.0, 173.3 (d, 26.0 Hz, Cimidazole). Elemental analysis for C37H47Cl2N4PRu: calcd C 59.19, H 6.31, N 7.46; found C 59.42, H 6.60, N 7.23. X-ray Diffraction Studies. For the X-ray diffraction studies, data sets were collected on a Bruker APEX CCD diffractometer with Mo Kα radiation (λ = 0.71073 Å). CCDC 992988 (1b), 992989 (1a), and 992990 (2b) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/ cif. 1b: red crystal (plate), dimensions 0.21 mm × 0.08 mm × 0.06 mm, crystal system monoclinic, space group P21/n, Z = 4, a = 14.2635(12) Å, b = 14.8790(12) Å, c = 16.2613(13) Å, α = 90°, β = 101.753(2)°, γ = 90°, V = 3378.7(5) Å3, ρ = 1.413 g/cm3, T = 200(2) K, θmax = 25.95°, 0.5° ω scans with the CCD area detector, covering the asymmetric unit in reciprocal space with a mean redundancy of 8.72 and a completeness of 99.7% to a resolution of 0.81 Å, 58 598 reflections measured, 6586 unique (Rint = 0.0659), 5361 observed (I > 2σ(I)), intensities were corrected for Lorentz and polarization effects, an empirical absorption correction was applied using SADABS38 based on the Laue symmetry of the reciprocal space, μ = 0.70 mm−1, Tmin = 0.87, Tmax = 0.96, structure solved by direct methods and refined against F2 with a full-matrix least-squares algorithm using the SHELXTL39 software package, 386 parameters refined, hydrogen atoms were treated using appropriate riding models, goodness of fit 1.05 for observed reflections, final residual values R1(F) = 0.032, wR(F2) = 0.061 for observed reflections, residual electron density −0.37 to 0.40 e Å−3. 1a: orange crystal (plate), dimensions 0.170 mm × 0.150 mm × 0.030 mm, crystal system monoclinic, space group P21/c, Z = 4, a =

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ASSOCIATED CONTENT

S Supporting Information *

Experimental data for compounds 1 and 2, tables of crystallographic data (CIF), full computation details, references, atomic coordinates, and a text file of all computed molecule Cartesian coordinates in .xyz format for convenient visualization. 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]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS C.C.B., P.N.P., M.L., and P.H. work at the Catalysis Research Laboratory (CaRLa) of Heidelberg University, which is cofinanced by the University of Heidelberg, the State of Baden-Württemberg, and BASF SE. We gratefully acknowledge generous support from these institutions.

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REFERENCES

(1) Vougioukalakis, G. C.; Grubbs, R. H. Chem. Rev. 2010, 110, 1746−1787. (2) Lozano-Vila, A. M.; Monsaert, S.; Bajek, A.; Verpoort, F. Chem. Rev. 2010, 110, 4865−4909. (3) Nguyen, S. T.; Trnka, T. M. In Handbook of Metathesis; WileyVCH: Weinheim, Germany, 2008; pp 61−85. (4) Hoveyda, A. H.; Zhugralin, A. R. Nature 2007, 450, 243−251. (5) Weskamp, T.; Schattenmann, W. C.; Spiegler, M.; Herrmann, W. A. Angew. Chem., Int. Ed. 1998, 37, 2490−2493. E


Organometallics

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