Pentacoordinate Ruthenium(II) Catecholthiolate ... - ACS Publications

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Pentacoordinate Ruthenium(II) Catecholthiolate and Mercaptophenolate Catalysts for Olefin Metathesis: Anionic Ligand Exchange and Ease of Initiation Malte S. Mikus, Sebastian Torker,* Chaofan Xu, Bo Li, and Amir H. Hoveyda* Department of Chemistry, Merkert Chemistry Center, Boston College, Chestnut Hill, Massachusetts 02467, United States S Supporting Information *

ABSTRACT: The investigations disclosed offer insight regarding several key features of Ru-based catecholthiolate olefin metathesis catalysts. Factors influencing the facility with which the two anionic ligands undergo exchange and those that affect the rates of catalyst release are elucidated by examination of more than a dozen new complexes. These studies shed light on how different chelating groups can influence Ru−S bond strength and, as a result, the facility of catecholthiolate rotation. The trans influence series ether < ester ≈ iodide < amine ≈ thioether ≈ olefin < isonitrile ≈ phosphite has been established through X-ray structural analysis and shown to correlate well with the barrier for catecholthiolate rotation (trans effect) determined by variable-temperature NMR experiments and computational studies (DFT). It is found that, apart from electronic factors, chelate geometry has a more notable effect on the rate of catalyst release (five- vs six-membered chelate ring and monovs bidentate ligand). Polytopal processes involving pentacoordinate Ru(II) carbene complexes are shown to be distinct from previously reported fluxional events that involve tetracoordinate species and which are capable of causing diminished polymer syndiotacticity. Ru mercaptophenolate complexes have been synthesized and isolated as a single diastereomer (O−C trans to the NHC). This latter set of species promotes representative olefin metathesis reactions readily and gives Z selectivity levels that are higher than those when the corresponding catecholate systems are used, but less so in comparison to catecholthiolate complexes. A rationale for variations in stereoselectivity is presented.

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stances, and sequence-selective ROMP11,12 is an instance where productive alkene metathesis must be faster than complex isomerization. Regardless of the mechanistic scenario, a greater understanding of the factors that engender non-metathesisbased polytopal rearrangements within a stereogenic-at-metal system is needed for the rational design of efficient and stereoselective olefin metathesis catalysts. Catecholthiolate complexes Ru-4a,b (Scheme 2) are readily accessible and may be used for Z-selective ROMP, ROCM, or cross metathesis.20 A distinct attribute of these systems is the robustness of the Ru−S bonds, which remain intact in the presence of an allylic alcohol, an aldehyde, or a carboxylic acid (in contrast to a Mo−O or Ru−C bond in Mo-1 or Ru-3).20c,d Nonetheless, a σ-donating sulfide ligand that is trans to the NHC can give rise to electronic repulsion/destabilization with tangible influence on complex structure. For example, the trans influence exerted by the comparatively strong σ-electrondonating sulfide that is opposite to the N-heterocyclic carbene (NHC) ligand in catecholthiolate complex Ru-4a in comparison to catecholate Ru-5 leads to a longer Ru−CNHC bond (2.061 vs 2.015 Å; Scheme 2a).20a Electronic effects may affect stereoselectivity as well: because Ru catecholthiolates readily

INTRODUCTION Stereogenic-at-metal complexes have been at the core of recent advances in catalyst-controlled stereoselective olefin metathesis (Scheme 1).1 Ru carbenes such as Ru-1,2 Ru-2,3 and Ru-34 and monoaryloxide pyrrolide (MAP) alkylidenes represented by Mo-15 have been utilized for kinetic control of Z selectivity (Ru-36,7 and Mo-18), enantioselective ring closing (RCM; Mo1) or ring opening/cross metathesis (ROCM; Ru-1, Ru-2,9 and Mo-110), and sequence-selective (i.e., chemo- or syndioselective) ring-opening metathesis polymerization (ROMP).11,12 Stereogenic-at-metal olefin metathesis catalysts undergo stereochemical inversion each time a metallacyclobutane is generated and then cleaved productively to give enantiomeric or diastereomeric species, each of which has distinct characteristics.13 Alternatively, stereoisomeric interconversions may occur without olefin participation (i.e., by polytopal rearrangement) and can perturb the chain of events, causing diminished stereoselectivity.14−17 Depending on the particular case, faster interconversion between the two isomeric forms of the active complex (Curtin−Hammett kinetics) or slower isomerization (fidelity of the chain of events preserved; non-Curtin− Hammett kinetics) may mean high efficiency and stereoselectivity. Mo MAP-catalyzed enantioselective ring-closing metathesis (RCM)18 and ROCM with enol ethers and a complex such as Ru-219 are examples of the earlier circum© XXXX American Chemical Society

Received: October 6, 2016

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DOI: 10.1021/acs.organomet.6b00773 Organometallics XXXX, XXX, XXX−XXX

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resulting ROMP processes can be largely atactic. We recently showed that through controlling catecholthiolate complex isomerization, by means of structural modification and/or adjustment of monomer concentration, ROMP stereoselectivity of 50% to up to ≥95% syndiotacticity can be achieved.17 Another isomerization mode relates to the possible exchange of the two anionic sulfur ligands (see V or VI, Scheme 2c). Such events do not alter a complex’s stereochemical identity (A → A),21 nor do they impact the stereochemical outcome of a ROMP reaction, but they do shed light onto the factors that govern fluxionality and are directly relevant to the processes outlined in Scheme 2b. When dissymmetric dianionic ligands (e.g., a mercaptophenolate) are involved, additional insight regarding the factors that determine the coordination chemistry of Ru carbene complexes can be obtained because diastereomeric complexes VII and VIII are likely to be energetically distinct (cf. Scheme 2d). Herein, we detail the results of our studies aimed at addressing the above matters. The details of how anionic ligand exchange takes place may be probed by gauging the impact of the donor group (e.g., isopropoxy unit in Ru-4a,b; cf. Scheme 2c). This can enhance our appreciation of the factors that can influence the rate of the catecholthiolate ligand rotation in a 16e complex as well as offer several additional advantages: Whereas polytopal rearrangements of tetracoordinate species (Scheme 2b) are difficult to observe and must be inferred from stereochemical outcomes (e.g., polymer tacticity),17 anionic exchange events can be monitored directly (Scheme 2c). More specifically, X-ray crystallographic analysis and variable-temperature (VT) NMR studies will be employed to probe the strength of different neutral chelating groups (tethered (G) or monodentate (L)) and their effect on the robustness of the

Scheme 1. Representative Stereogenic-at-Metal Complexes

and preferentially undergo stereochemical inversion at the fourcoordinate reactive intermediate17 (I → II or III → IV or as stereochemical descriptors C → A or A → C; Scheme 2b),21 the

Scheme 2. Effect of Thiolate Ligands on the Derived Ru-Based Carbenes

B

DOI: 10.1021/acs.organomet.6b00773 Organometallics XXXX, XXX, XXX−XXX

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Organometallics Scheme 3. Synthesis of Modified Ru Catecholthiolate Complexesa

a

Reactions were performed according to the protocols outlined in Scheme 4. Yields (±5%) refer to the lower values obtained for at least two runs and are for products after simple precipitation. See the Supporting Information for experimental and analytical details. Abbreviations: Mes, 2,4,6Me3-C6H2; pyr, pyridine; L, monodentate ligand; G, chelating group.

complexes with diverse chelating (G) and monodentate ligands (L). Two routes were employed, each involving commercially available or easily accessible Ru dichloro precursors (Ru-P; Scheme 3a).23 One procedure entailed salt metathesis with an appropriate Zn-based catecholthiolate reagent (Zn-1; method A);20d reactions were usually complete within 1 h (22 °C, thf), and products were isolated in up to 84% yield. Otherwise, a convenient one-step cross metathesis involving a common intermediate (Ru-4c, prepared by method A) was utilized (method B; Scheme 3a), obviating the need for preparation of each Ru dichloride precursor (Ru-P). Route B relies on the stronger coordinating ability of the chelating ligand in a product, providing the thermodynamic driving force needed for complete conversion of Ru-4c. An assortment of Ru catecholthiolate complexes were accordingly prepared (Scheme 3b), purified by filtration through Celite and/or by

Ru−anionic bond that is trans to the (neutral) group G or L. Further, the effect of a dissymmetric dianionic ligand (i.e., mercaptophenolate) on the structure of Ru−carbene complexes will be probed (Scheme 2d). Insight regarding complexes that release catalytically active 14e species rapidly and those that might serve as latent initiators will also be provided.22,23

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RESULTS AND DISCUSSION We began by examining the impact of Ru−S bond strength in a catecholthiolate complex on the rate of polytopal rearrangement. Our aim was to determine the extent to which the electron donating ability of a neutral ligand might alter the Ru− S2 bond length and affect the swapping of the anionic ligands (Scheme 2c). Synthesis of Complexes with Different Neutral Donor Ligands. We prepared a series of catecholthiolate Ru C

DOI: 10.1021/acs.organomet.6b00773 Organometallics XXXX, XXX, XXX−XXX

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Figure 1. X-ray structures of catecholthiolate Ru complexes arranged by increasing Ru−S2 bond length. The 3σ range (3 times the estimated standard deviation) for the Ru−S2 bond lengths lies within ∼0.002 (Ru-4m) and 0.009 Å (Ru-4q), except for Ru-4r (0.021 Å); see the Supporting Information for details.

Ru-4n is also noteworthy (Ru−S2, 2.328 Å), considering the fact that olefins typically do not exert a strong trans influence; the longer than expected bond length may be the result of the ruthenacyclopropane character of this species, which is reflected in a C−C bond length of 1.374 Å (vs ∼1.300 Å for a monosubstituted alkene26). Donor Ligands and Rates of Catecholthiolate Ligand Rotation. Spectroscopic analysis (VT NMR) reveals that polytopal rearrangement is observable only with Ru-4j,k, which contain strongly σ-donating phosphite groups. Whereas rotation of the catecholthiolate ligand at −10 °C is slow on the NMR time scale (Figure 2), there is coalescence of the peaks for the ortho (Ha1, Ha2) or meta protons (Hb1, Hb2) at slightly higher temperatures (35 °C for coalescence of Ha1 and Ha2 in Ru-4j). Line shape analysis with DNMR3 implemented in the program SpinWorks 427 provided us with the free energy barriers for ligand rotation (ΔG⧧298 K): 14.4 kcal/mol for Ru-4j (ΔH⧧ = 11.6 kcal/mol, ΔS⧧ = −9.2 cal mol−1K−1) and 14.8 kcal/mol for Ru-4k (ΔH⧧ = 13.0 kcal/mol, ΔS⧧ = −6.1 cal mol−1K−1) (Figure 2).24

crystallization, and fully characterized. X-ray crystal structure was secured in many cases.24 Donor Ligand and Length of the Trans Ru−S2 Bond. Among complexes with an aryl ether ligand (Ru-4a−e) the Ru→S2 bond length is shortest in Ru-4c (2.276 vs 2.283 Å in Ru-4a Figure 1); this probably arises from the strongly electron withdrawing p-sulfonamide group, which can minimize the trans influence25 with the opposite S2 unit. Among complexes with an O-based donor group, the Ru−S2 bonds in Ru-4l,m are the most extended (∼2.300 Å) despite the weakly Lewis basic carboxylic ester ligands; this might be because the shorter O→ Ru distances in six-membered chelate structures (vs fivemembered variants) engender a more pronounced electron− electron repulsion along the O−Ru−S2 axis. In complexes with an N-based neutral ligand (cf. Ru-4g−i) the trans influence is stronger and Ru−S2 bonds are longer (2.319−2.330 Å vs Obased variants Ru-4a,c−e). The still more forceful σ-donating phosphite groups (cf. Ru-4j,k) and an isonitrile ligand in Ru-4r displace the S2 atom the farthest away from the Ru center (Ru− S2, 2.342−2.373 Å). The Ru−S2 distance for alkene complex D

DOI: 10.1021/acs.organomet.6b00773 Organometallics XXXX, XXX, XXX−XXX

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facilitates the movement of the anionic S2 ligand located trans to the neutral ligand L (or G) in the transition state.31 It seems that the trans influence between CNHC and S1 together with that involving L/G and S2 elevates the ground state energy of a catecholthiolate complex; the barrier for Ha1/Ha2 exchange via a transition structure wherein the sulfides are nearly trans to the carbene ligands is accordingly diminished.29 Influence of Donor Groups on Initiation Rate. ROMP with Ru-4a,c−e, which contain an aryloxy chelate, was efficient at 22 °C and exceptionally stereoselective (>95% yield, >98% Z; Scheme 5). Reaction with pyridyl system Ru-4g was equally swift (>98:2 Z:E). However, just 5% of the all-Z polymer was generated when bidentate pyridyl complex Ru-4h was used; at 40 °C polynorbornene was generated in 80% yield (>98% Z) with some improvement at 60 °C (98% yield; >98% Z). ROMP efficiency was lower with phosphite-bearing Ru-4j,k (e.g., 45% yield at 40 °C; >98:2 Z:E for Ru-4j). Carboxylate complexes Ru-4l,m were still more reluctant to initiate; heating to 60 °C afforded polynorbornene in only ∼35% yield and somewhat lower selectivity (95:5 Z:E; see the Supporting Information for details). It may be that the more forcing conditions accelerate catalyst decomposition and/or the formation of nonselective Ru carbenes with the somewhat weakly donating neutral ligand (CO2Me). With sulfidecontaining systems Ru-4o,p, styrenyl Ru-4n, or quinolyl Ru4i there was no ROMP even at 80 °C. We were unable to obtain reproducible data with iodide Ru-4q, possibly because of adventitious Ru insertion into the proximal C−I bond. For the most part, there seems to be only modest correlation between trans influence and initiation rates. On the basis of the X-ray data, the chelate ring size (i.e., five- vs six-membered) and the presence of a monodentate neutral donor ligand (vs a chelated system) can be influential as well. Phosphite groups in Ru-4j,k induce a stronger trans influence in comparison to the sulfide unit in Ru-4o (Figure 1) and cause faster initiation (cf. Scheme 5). Conversely, although ester moieties exert a comparatively weak trans influence (vs a phosphite), catalyst initiation requires higher temperatures because the resulting bidentate complexes form relatively stable six-membered chelate rings (Ru-4l,m). Ru Mercaptophenolate Complexes: Stereoselective Synthesis and ROMP Activity. The origin of high Z selectivity in reactions with the catecholthiolate in comparison to those of catecholate Ru complexes is a change in the identity of the stereochemistry-determining/turnover-limiting event.20c With the more donating catecholthiolate complexes the formation of the metallacyclobutane, where steric factors have a stronger influence, is selectivity determining. In the case of the less Lewis basic catecholate complexes, selectivity is determined at the alkene coordination stage with steric factors playing a lesser role (looser, early transition state) and Z:E ratios are therefore much lower. Several intriguing questions thus arise: (1) Can mercaptophenolate complexes be synthesized and isolated as a single diastereomer? The more favored isomer might be the one wherein the strongest and weakest σ-donating ligands (NHC and O−C, respectively) are trans. Would the energy differences be sufficient for high stereoselectivity? (2) Would mercaptophenolate Ru catalysts promote Zselective reactions? Would the kinetics of the catalytic cycle be more similar to that of the highly selective catecholthiolate, the nonselective catecholate system, or somewhere in between?

Figure 2. Determination of the rotational energy barrier for rearrangement of the catecholthiolate ligand in phosphite-containing complex Ru-4j through variable-temperature 1H NMR experiments (CDCl3) and by line-shape analysis.

The above observations are consistent with the scenario that the trans influence/effect28 between CNHC and S1 (cf. Scheme 2) or a donor ligand (monodentate L or chelating G) and S2 can cause ground state destabilization (Scheme 4a) and lowering of the barrier to polytopal rearrangement (without inversion at the metal, A → A).29 The computed energies (M06/Def2QZVPbenzene//BP86/6-31+G(d,p)thf) needed for isomerization of several model catecholthiolate complexes support this hypothesis (Scheme 4b).14b,17,30 The more σ donating and π acidic ligands (phosphites or isonitriles) may thus destabilize Ru−S2 bonds, lowering the energy of the dxy orbitals and facilitating catecholthiolate ligand rotation (Scheme 4c).31 The proposal that an increase in trans influence and weakening/distortion of the Ru−S2 bond accelerates isomerization is in line with the finding that there is fast exchange only in phosphite complexes Ru-4j,k (cf. Figure 2). What is more, the experimentally determined value for the barrier to catecholthiolate ligand rotation for Ru-4j (14.4 kcal/ mol) is similar to that computed for the complex with a P(OMe)3 group (15.2 kcal/mol; Scheme 4b). Also congruent is that the calculated energy barrier for rotation of the dianionic ligand is considerably higher for complexes with N-, O-, or Sbased ligands (19.1−35.9 kcal/mol). Only isonitrile-containing species, reported to be somewhat unstable,32 are predicted to isomerize at a comparable rate (13.2 kcal/mol). We synthesized isonitrile-bound complex Ru-4r, an entity that is stable at ambient temperature. In agreement with the computed trend (Scheme 4b), the 1H NMR of Ru-4r exhibits line broadening for the resonances associated with the catecholthiolate ligand at 25 °C and coalescence at 60 °C; rapid decomposition precluded studies at elevated temperatures.24 Overall, this segment of our investigations indicates that catecholthiolate rotation is favored by strongly σ donating and π acidic ligands (phosphites or isonitriles), which destabilize the Ru−S2 bond and lower the energy of the Ru dxy orbital (cf. Scheme 4c); this E

DOI: 10.1021/acs.organomet.6b00773 Organometallics XXXX, XXX, XXX−XXX

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Organometallics Scheme 4. Computational and Mechanistic Analysis of the Anionic Exchange Processa

a

Rotational energy barriers were calculated at the M06/Def2QZVP//BP86/6-31+G(d,p) level (in benzene). See the Supporting Information for details.

(aryloxy) and π-accepting (phosphite) ligands.33 The destabilization caused by the sulfide unit being trans to the NHC is therefore compensated, countering manifestation of fluxional behavior by the mercaptophenol moiety. The Ru mercaptophenolate complexes promote norbornene ROMP readily and efficiently (typically in >98% yield) but with low Z selectivity (61% Z with Ru-6a, cf. Scheme 6, vs 98% Z with Ru-4a, cf. Scheme 5). With larger N-aryl groups and size differential between the heterocyclic moiety and the oppositely situated O-based ligand, Z selectivity improved (up to 82:18 with Ru-6d) but did not reach the levels that are typically delivered by catecholthiolate systems.34 We did not observe any ROMP activity at temperatures of up to 60 °C with complex Ru-6e, possibly due to the stronger coordination of the phosphite trans to the weakly donating phenol oxygen33 (vs Ru-4j,k; cf. Scheme 5). Comparison of the free energy surfaces (M06/Def2TZVPPbenzene//BP86/Def2SVPthf) indicates that

To answer the above questions, Ru-6a−d were prepared by the Zn/Ru-exchange method described previously (Scheme 6).20d A single diastereomer was obtained in all cases (by analysis of 400 MHz 1H NMR spectra). The oxygen ligand is positioned opposite to the NHC unit, minimizing trans influence, as demonstrated by the X-ray structures for Ru6b,d (Scheme 6). Complex 6b was prepared on the basis of the idea that the methoxy substituent would increase the donor ability of the aryloxy ligand sufficiently so that metallacyclobutane (mcb) formation (vs olefin coordination) would become stereochemistry determining (as with a catecholthiolate20c), resulting in a significant increase in Z selectivity; the observed difference, however, was not substantial (67% vs 61% Z for Ru-6b and Ru-6a, respectively). With a strongly σ donating and π accepting phosphite ligand (Ru-6e) the alternative diastereomer was isolated, a reversal that may be due to synergistic trans alignment of π-donating F

DOI: 10.1021/acs.organomet.6b00773 Organometallics XXXX, XXX, XXX−XXX

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Organometallics Scheme 5. Influence of the Neutral Ligands on the Facility of Catalytic ROMP of Norbornenea

a

Reactions were performed under a N2 atmosphere. Yields (±5%) refer to the lower values obtained for at least two runs. Z:E ratios were determined by analysis of the 400 MHz 1H NMR spectra of unpurified product mixtures. See the Supporting Information for further details.

substrate coordination (ts0), where steric differentiation between E and Z pathways is lower, becomes the energetically more demanding and stereochemistry determining step with an oxygen-based ligand (Figure 3).20c Thus, whereas mcb formation (ts1S,S 11.6 kcal/mol) is predicted to be rate determining with dithiolate complex Ru-4a (vs ts0S,S 8.0 kcal/ mol), ts0S,O (6.4 kcal/mol) is the highest point along the reaction coordinate in the case of Ru-6a (vs ts1S,O 5.1 kcal/ mol). Still, the energy gap is smaller in comparison to catecholate catalyst Ru-5 (5.4 kcal/mol for ts0O,O vs −2.7 kcal/mol for ts1O−O), accounting for the slightly higher Z selectivity (61% Z with Ru-6a vs 58% Z with Ru-5).20a The pathway involving the alternative mercaptophenolate diastereomer (cf. Ru-6e in Scheme 6) was found to be energetically more demanding (6.3 kcal/mol for ts1O,S relative to 14eS,O).

S2 bonds, are prone to polytopal isomerization. Line-shape analysis led us to calculate an energy barrier of 14.4 kcal/mol (ΔG⧧298 K) for ligand rotation in the same phosphite species. Experimental findings are supported by computational studies, pointing to a simulated low-energy barrier for the rearrangement process (ΔΔG⧧298 K = 15.2 kcal/mol vs 27.4 kcal/mol for the thf-bound variant). (3) Strong trans influences/effects that govern Ru catecholthiolate complexes and their transformations lead to fluxional behavior of the catecholthiolate ligand and can cause stereoinversion during ROMP and ROCM reactions (see Scheme 2b). The key consequences of strong trans influence/ effect are as follows. (i) The barrier to olefin metathesis is raised, thus allowing for efficient control over diastereoselectivity (98:2 Z:E) through rate-limiting metallacyclobutane formation. (ii) Promotion of a polytopal rearrangement (see Scheme 2b) allows for loss of sequence selectivity and lowering of syndiotacticity in ROMP. Further investigations to utilize these fluxional properties and development of isotactic ROMP processes are underway. (4) In line with previous investigations on dichloride Ru complexes,22,23 ROMP of norbornene with the above catecholthiolate complexes indicates that initiation rates depend strongly on the identity of the chelating ligand. Those containing an alkoxy chelate are generally most efficient; Ru carbenes chelated to monodentate pyridyl units or those that are part of a six-membered chelate, phosphites and carboxylic esters require heating for high conversion, and those with a fivemembered chelating quinoline, a coordinating alkene, or a sulfide group do not initiate even under forcing conditions.

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CONCLUSIONS The investigations detailed above provide insight regarding several structural and dynamic attributes of the Ru-based catecholthiolate complexes. Notable findings and conclusions are as follows: (1) Sixteen new Ru catecholthiolate complexes containing different types of tethered or monodentate neutral ligands were synthesized and characterized. X-ray crystal structures for 13 of these species offer information regarding the influence of the chelating ligands on the strength of the Ru−S bond that is situated trans to them. (2) Spectroscopic (VT NMR) experiments reveal that only complexes with strongly σ-donating and π-accepting ligands, such as phosphites and isonitriles, resulting in the weakest Ru− G

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Organometallics Scheme 6. Structural Properties and Activity of Ru Mercaptophenolate Complexesa

a

Syntheses of complexes and ROMP reactions were performed under a N2 atmosphere. Yields (±5%) refer to the lower values obtained for at least two runs. Z:E ratios of the ROMP polymers were determined by analysis of the 400 MHz 1H NMR spectra of unpurified product mixtures. See the Supporting Information for further details.

While there is modest correlation between the strength of the Ru−S2 bond trans to the chelating group and the facility of initiation, factors such as the chelate ring size play an important role, as indicated by the reactivity of the two tethered pyridyl structures and the comparison between chelating carboxylate and ether groups. (5) Ru mercaptophenolate complexes can be prepared easily and isolated as a single diastereomer (>98%; NHC trans to oxygen). These species promote ROMP with lower Z selectivity in comparison to the catecholthiolate systems. Although selectivity levels up to 82:18 Z:E were obtained for norbornene ROMP, overall, the data suggest that the energetics of the associated catalytic cycles resemble more those of the catecholate variants. The synergistic relationship between πdonating and π-accepting ligands, sufficiently strong to control catalyst geometry, bear implications for controlling ligand configuration and the development of new stereoselective Rubased catalysts. Application of the mechanistic information secured by the investigations described above to the development of new olefin metathesis catalysts and methods are underway.

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EXPERIMENTAL SECTION

Unless otherwise noted, all reactions were performed with distilled and degassed solvents under an atmosphere of dry N2 in oven-dried (135 °C) or flame-dried glassware with standard drybox or vacuum line techniques. Workup of ruthenium complexes was performed in a glovebox filled with nitrogen using dry and degassed solvents. All other reactions and purification procedures of complex precursors (e.g., styrene derivatives) and ROMP products were carried out with reagent grade solvents (purchased from Fisher) under benchtop conditions. 1 H and 31P NMR spectra were recorded on a 600 MHz VNMRS, a

Figure 3. Comparison of free energy surfaces (ΔG, kcal/mol) for norbornene ROMP with complexes such as Ru-4a, Ru-5, and Ru-6a obtained at the M06/Def2TZVPPbenzene//BP86/Def2SVPthf level; only pathways leading to the Z isomer are shown. See the Supporting Information for details. Abbreviations: 14e, 14-electron species; ts0, transition state for olefin coordination; pc1/pc2, π complex; ts1, transition state for metallacyclobutane formation; mcb, metallacyclobutane; ts2, transition state for metallacyclobutane breakage. H

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Article

Organometallics

Zinc 2-Mercaptophenolate (Zn-2; Scheme 6). A round-bottom flask equipped with a stir bar was charged with Zn(OAc)2·2H2O (5.8 g, 26.4 mmol, 3.3 equiv) and i-PrOH (20 mL). 2-Mercaptophenol (1.0 g, 7.9 mmol) and ethylenediamine (3.2 mL, 47.4 mmol) were added sequentially to the rapidly stirred suspension. After the suspension was stirred for 1 h at 22 °C, the white amorphous solid was filtered, washed with methanol (30.0 mL) and hot chloroform (40.0 mL), and dried under vacuum overnight to afford Zn-2 (1.4 g, 7.7 mmol, 98% yield) as a white solid. Zinc 2-Mercapto-4-methoxyphenolate (Zn-3; Scheme 6). A round-bottom flask equipped with a stir bar was charged with Zn(OAc)2·2H2O (702.4 mg, 3.2 mmol) and i-PrOH (7 mL). 2Mercaptophenol (125 mg, 0.8 mmol) and ethylenediamine (0.5 mL, 4.8 mmol) were added sequentially to the vigorously stirred suspension. After the suspension was stirred for 1 h at 22 °C, the off-white solid was filtered, washed with methanol (8 mL) and hot chloroform (10 mL), and dried under vacuum overnight to afford Zn3 (92 mg, 0.42 mmol, 53% yield) as a white solid. Preparation of Ru Carbene Complexes (General Method A; Scheme 3). A 2 dram vial equipped with a stir bar was charged with zinc catecholthiolate Zn-1 (2.0 equiv) under a N2 atmosphere and a solution of the corresponding Ru dichloride precursor Ru-P (1.0 equiv; see Scheme 3) in tetrahydrofuran (as a 0.3 M solution). The resulting suspension was stirred at 22 °C for 2 h, at which time the solvent was evaporated under reduced pressure. Residual tetrahydrofuran was removed through coevaporation with dichloromethane (2 × 1 mL). The resulting solid was dissolved in a small amount of dichloromethane and filtered through a Celite plug (3 cm in height) in a pipet. The solvent was evaporated in vacuo, and the residue was dissolved in a small amount of dichloromethane (0.5 mL). The complex was precipitated through addition of hexanes (4 mL), filtered over a short plug of Celite in a pipet, and washed with a mixture of dichloromethane and hexane (1/5, 5 mL). The corresponding Ru carbene complex was then eluted with dichloromethane (1 mL) and the solvent removed under reduced pressure. Residual dichloromethane was removed through coevaporation with hexanes. Preparation of Ru Carbene Complexes (General Method B; cf. Scheme 3). In a 2 dram vial charged with a stir bar and Ru-4c (1.0 equiv) under a N2 atmosphere was placed a solution of styrene (2−4 equiv) in dichloromethane (1 mL), and the solution was stirred for 2 h at 22 °C. The solvent was evaporated under reduced pressure; the residue was dissolved in a small amount of dichloromethane (0.5 mL), and the complex was allowed to precipitate through addition of hexanes (4 mL). The brown precipitate was filtered through a short plug of Celite in a pipet and washed with a mixture of dichloromethane and hexanes (1/5, 5 mL). The product was eluted with dichloromethane, and the solvent was removed in vacuo. Residual dichloromethane was removed through coevaporation with hexanes. Complex Ru-4c. Ru catecholthiolate complex Ru-4c was prepared according to method A from the commercially available dichloride precursor Ru-Pc and isolated as a brown solid (78 mg, 97 μmol, 82% yield). Crystals suitable for X-ray analysis were grown through vapor diffusion from a benzene/pentane solution. 1H NMR (400 MHz, CD2Cl2): δ 14.23 (1H, d, J = 0.6 Hz), 7.71 (1H, dd, J = 8.7, 2.3 Hz), 7.48 (1H, dd, J = 7.8, 1.2 Hz), 7.29 (1H, dd, J = 7.7, 1.2 Hz), 7.22 (1H, dd, J = 8.7, 0.6 Hz), 7.06 (1H, d, J = 2.3 Hz), 7.15−6.90 (2H, br s), 6.89−6.54 (1H, br s), 6.78 (1H, ddd, J = 7.8, 7.0, 1.2 Hz), 6.72 (1H, ddd, J = 7.7, 7.0, 1.2 Hz), 6.54−6.14 (1H, br s), 5.26 (1H, septet, J = 6.6 Hz), 4.25−3.67 (4H, br s), 2.55 (6H, s), 2.80−2.39 (6H, br s), 2.29 (6H, s), 1.67 (3H, d, J = 6.6 Hz), 1.55 (3H, d, J = 6.6 Hz), 1.66− 1.34 (3H, br s). 13C NMR (101 MHz, CD2Cl2): δ 246.2, 218.6, 157.8, 152.9, 142.0, 141.0, 139.3 (br), 136.6, 135.2, 130.1, 129.7, 128.4, 127.5, 126.6, 123.8, 122.1, 121.2, 115.2, 82.8, 52.0, 38.3, 34.7, 24.0, 22.9, 22.0, 21.3, 19.7 (br), 17.8 (br), 14.4. Complex Ru-4d. Ru catecholthiolate complex Ru-4d was prepared according to method A from Ru-Pd. The product was isolated as a brown solid (38 mg, 51 μmol, 74% yield). 1H NMR (400 MHz, CD2Cl2): δ 14.24 (1H, d, J = 0.6 Hz), 8.19 (1H, dd, J = 9.2, 2.8 Hz), 7.48 (1H, d, J = 2.8 Hz), 7.47 (1H, ddd, J = 7.8, 1.4, 0.5 Hz), 7.29 (1H, dd, J = 7.6, 1.4, 0.5 Hz), 7.18 (1H, dd, J = 9.2, 0.6 Hz), 7.13−6.86 (2H,

500 MHz VNMRS, a 500 MHz INOVA, or a 400 MHz VNMRS spectrometer. Chemical shifts are reported in ppm from tetramethylsilane with the solvent resonance resulting from incomplete deuterium incorporation as the internal standard (CDCl3, δ 7.26 ppm; C6D6, δ 7.16 ppm; CD2Cl2, δ 5.32 ppm). Data are reported as follows: chemical shift, integration, multiplicity (s = singlet, d = doublet, t = triplet, q = quartet, qu = quintet, sext = sextet, sept = septet, br = broad, m = multiplet), and coupling constants (Hz). 13C NMR spectra were recorded with complete proton decoupling. Chemical shifts are reported in ppm from tetramethylsilane with the solvent resonance as the internal standard (CDCl3, δ 77.16 ppm; CD2Cl2, δ 54.00 ppm). Values for Z:E ratios of products were determined by analysis of 1H NMR spectra or 13C NMR spectra. In general, compound purity was assessed through analysis of 400 MHz 1H NMR spectra. The observed stereoselectivities of the polymers with >98:2 Z:E ratio imply that impurities (e.g., Ru dichloride precursors used in the synthesis of complexes; not detected by 1H NMR analysis) are presumably below the detection limit of elemental analysis; in other words, catecholthiolate complexes are significantly less reactive in comparison to their Ru dichloride analogues. For the more challenging polymerization experiments, such as those with slowly initiating complexes, where potential side reactions catalyzed by Ru carbene impurities are even more likely to be competitive and can cause a lowering of Z selectivity, we also used single crystals in order to rule out such side reactions (e.g., with complexes Ru-4j,k or Ru-4l,m). Every attempt was made to obtain an X-ray structure for each complex; in most cases this proved to be successful. X-ray Data Collection. Selected single crystals suitable for X-ray crystallographic analysis were used for structural determination. The X-ray intensity data were measured at 100(2) K (Oxford Cryostream 700) on a Bruker Kappa APEX Duo diffractometer system equipped with a sealed Mo-target X-ray tube (λ = 0.71073 Å) and a high brightness IμS copper source (λ = 1.54178 Å). The crystals were mounted on a goniometer head with Paratone oil. The detector was placed at a distance of 5.000 or 6.000 cm from the crystal. For each experiment, the data collection strategy was determined by the APEX software package and all frames were collected with a scan width of 0.5° in ω and φ with an exposure time of 10 or 20 s/frame. The frames were integrated with the Bruker SAINT software package using a narrow-frame integration algorithm to a maximum 2θ angle of 56.54° (0.75 Å resolution) for molybdenum data and of 134° (0.84 Å resolution) for copper data. The final cell constants are based upon the refinement of the XYZ centroids of several thousand reflections above 20 σ(I). Analysis of the data showed negligible decay during data collection. Data were corrected for absorption effects using an empirical method (SADABS). The structures were solved and refined by full-matrix least-squares procedures on |F2| using the Bruker SHELXTL (version 6.12) software package. All hydrogen atoms were included in idealized positions for structure factor calculations except for those forming hydrogen bonds or for those on a chiral center. Anisotropic displacement parameters were assigned to all nonhydrogen atoms, except for those that were disordered. Solvents and Reagents. Solvents (dichloromethane, hexane, benzene, and diethyl ether) were purified under a positive pressure of dry argon by a modified Innovative Technologies purification system. Tetrahydrofuran was distilled under a nitrogen atmosphere from sodium/benzophenone. Methanol was distilled from calcium hydride under a nitrogen atmosphere. CDCl3, CD2Cl2, C6D6, and C7D8 were purchased from Cambridge Isotope Laboratories and used as received. Ru-Pa (Aldrich), Ru-Pc (Strem), Ru-Pd (Aldrich), and Ru-Ph (Aldrich) were used as received; Ru-Pe,35 Ru-Pg,36 Ru-Pi,23f RuPl,23b Ru-Pn,37 Ru-Po,23j and Ru-Pp38 were prepared according to published procedures. Zinc catecholthiolate (Zn-1; Scheme 3a) was prepared according to a previously published procedure.20c Mercaptophenol (Aldrich) was used as received, and 2-mercapto-4-methoxyphenol39 was prepared as described in the literature. Styrene derivatives 2-iodostyrene40 and 4-nitro-2-vinylbenzoate41 were prepared according to published procedures; 2-methoxystyrene (Aldrich) was used as received. Norbornene (Aldrich) was sublimed prior to use. I

DOI: 10.1021/acs.organomet.6b00773 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics br s), 6.79 (1H, ddd, J = 7.8, 7.0, 1.4 Hz), 6.72 (1H, ddd, J = 7.6, 7.0, 1.4 Hz), 6.83−6.51 (1H, br s), 5.42 (1H, septet, J = 6.6 Hz), 4.14− 3.68 (4H, br s), 2.67−2.38 (6H, br s), 2.39−2.09 (3H, br s), 2.19 (1H, s), 1.73 (3H, d, J = 6.6 Hz), 1.88−1.41 (3H, br s), 1.56 (3H, d, J = 6.6 Hz). 13C NMR (101 MHz, CD2Cl2): δ 243.1, 217.5, 158.6, 152.3, 142.5, 141.7, 140.2, 138.6, 129.2 (br), 128.9 (br), 127.8, 126.8, 121.5, 121.4, 120.6,118.2, 114.5, 83.4, 51.4, 23.4, 22.6, 21.4, 20.5, 19.0, 14.2, 13.8 (br), 11.8. Complex Ru-4e. This species was prepared according to method A from Ru-Pe and isolated as a brown solid (32 mg, 43 μmol, 76% yield). Crystals suitable for X-ray analysis were grown through vapor diffusion from a dichloromethane/hexanes solution. 1H NMR (500 MHz, C6D6): δ 14.53 (1H, d, J = 0.8 Hz), 8.14 (1H, ddd, J = 8.0, 1.3, 0.4 Hz), 7.93 (1H, ddd, J = 7.8, 1.3, 0.4 Hz), 7.00 (1H, ddd, J = 8.0, 7.0, 1.3 Hz), 6.91 (1H, ddd, J = 7.8, 7.0, 1.3 Hz), 6.79 (2H, s), 6.63 (1H, dd, J = 2.2, 0.8 Hz), 6.59−6.48 (1H, br s), 6.44 (1H, d, J = 8.4 Hz), 6.32−6.18 (1H, br s), 6.19 (1H, dd, J = 8.4, 2.2 Hz), 5.04 (1H, sept, J = 6.5 Hz), 4.21 (1H, sept, J = 6.0 Hz), 3.46−3.18 (4H, br s), 2.71 (3H, br s), 2.45 (3H, br s), 2.25 (3H, br s), 2.07 (6H, br s), 1.50 (3H, br s), 1.41 (3H, d, J = 6.5 Hz), 1.38 (3H, d, J = 6.5 Hz), 1.17 (3H, d, J = 6.0 Hz), 1.15 (3H, d, J = 6.0 Hz). 13C NMR (101 MHz, CD2Cl2): δ 251.7, 219.8, 158.7, 156.4, 153.2, 141.8, 137.1, 129.7, 128.7, 127.4, 125.1, 121.5, 120.7, 108.3, 105.3, 81.5, 71.0, 51.9, 24.2, 22.4, 22.3, 21.8, 21.3, 19.5. Complex Ru-4f. This carbene was prepared according to method B by the use of 2-methoxystyrene (4 equiv) and isolated as brown solid (18 mg, 28 μmol, 87% yield). 1H NMR (400 MHz, CD2Cl2): δ 14.22 (1H, d, J = 0.9 Hz), 7.46 (1H, dd, J = 7.6, 1.3 Hz), 7.41 (1H, ddd, J = 8.4, 7.4, 1.6 Hz), 7.25 (1H, dd, J = 7.6, 1.3 Hz), 7.07 (2H, br s), 7.02 (1H, d, J = 8.4 Hz), 6.90 (1H, td, J = 7.4, 0.9 Hz), 6.79−6.71 (2H, m), 6.70 (1H, ddd, J = 7.5, 7.1, 1.5 Hz), 6.67−6.50 (2H, apparent br s), 4.18 (3H, s), 3.92 (4H, br s), 2.51 (6H, s), 2.31 (6H, s), 2.82−0.91 (6H, apparent br s). 13C NMR (151 MHz, CD2Cl2): δ 250.6, 219.0, 158.9, 153.8, 141.2, 141.0, 137.1, 130.2, 129.9, 129.8, 128.8, 128.6, 128.2, 128.1, 128.0, 127.9, 123.9, 123.9, 123.6, 121.7, 121.0, 111.9, 111.8, 63.3, 63.2, 51.7, 21.4, 21.3, 19.0. Complex Ru-4g. This carbene was prepared according to method A from complex Ru-Pg and isolated as a brown solid (25 mg, 31 μmol, 84% yield). Crystals suitable for X-ray analysis were grown through vapor diffusion from a dichloromethane/hexanes solution. 1H NMR (400 MHz, CD2Cl2): δ 16.24 (1H, s), 7.98 (2H, d, J = 6.4 Hz), 7.54 (1H, tt, J = 7.6, 1.5 Hz), 7.42 (1H, dd, J = 7.6, 1.6 Hz), 7.28 (1H, dd, J = 7.1, 1.9 Hz), 7.16 (1H, t, J = 7.3 Hz), 6.96 (2H, s), 6.89 (4H, t, J = 7.1 Hz), 6.79 (2H, d, J = 7.4 Hz), 6.70−6.60 (2H, m), 3.97 (4H, s), 2.37 (6H, s), 2.60−2.00 (12H, m). 13C NMR (151 MHz, CD2Cl2): δ 285.1, 218.8, 156.4, 154.0, 151.5, 144.8, 139.1, 138.2, 135.66, 130.2, 128.8, 128.6, 128.0, 127.7, 127.7, 124.6, 121.5, 120.5, 52.2, 21.4, 19.6. Complex Ru-4h. This complex was prepared according to method A from Ru-Ph and isolated as a brown solid (40 mg, 60 μmol, 71% yield). Crystals suitable for X-ray analysis were grown through vapor diffusion from a dichloromethane/hexanes solution. 1H NMR (400 MHz, CD2Cl2): δ 16.23−16.18 (1H, m), 7.74 (1H, dd, J = 5.7, 1.2 Hz), 7.60 (1H, td, J = 7.6, 1.6 Hz), 7.48 (1H, dd, J = 7.4, 1.2 Hz), 7.19 (1H, dd, J = 7.4, 1.2 Hz), 7.11 (1H, d, J = 7.6 Hz), 7.06 (1H, s), 7.02 (1H, s), 6.89 (2H, br s), 6.87 (1H, t, J = 6.9 Hz), 6.79 (1H, br s), 6.73 (1H, td, J = 7.4, 1.2 Hz), 6.64 (1H, td, J = 7.4, 1.2 Hz), 3.97−3.66 (4H, m), 3.17−3.04 (1H, m), 2.97 (1H, d, J = 15.2 Hz), 2.75 (3H, s), 2.44 (3H, s), 2.34 (6H, s), 2.11 (3H, s), 1.89 (1H, dq, J = 18.6, 4.1 Hz), 1.56 (3H, s), 1.07−0.92 (1H, m). 13C NMR (101 MHz, CD2Cl2): δ 291.9, 220.5, 162.9, 156.0, 154.4, 145.0, 139.7, 138.9, 138.7, 138.1, 138.0, 136.5, 135.6, 134.9, 130.6, 130.5, 130.2, 130.0, 129.4, 128.7, 128.4, 124.66, 121.7, 121.3, 120.2, 51.9, 51.5, 47.3, 36.8, 30.2, 21.4, 21.3, 20.4, 19.8, 19.7, 18.54, 18.4. Complex Ru-4i. This carbene was prepared according to method A from Ru-Pi and isolated as a black solid (52 mg, 68 μmol, 71% yield). 1 H NMR (400 MHz, CD2Cl2): δ 14.45 (1H, s), 8.53 (1H, dd, J = 4.9, 1.2 Hz), 8.28 (1H, dd, J = 8.3, 1.2 Hz), 7.98 (1H, d, J = 8.1 Hz), 7.60 (1H, d, J = 7.8 Hz), 7.41−7.30 (3H, m), 7.24 (1H, d, J = 7.0 Hz), 7.11 (2H, br s), 6.91−6.74 (1H, br s), 6.79 (1H, ddd, J = 7.9, 7.1, 1.3 Hz), 6.74−6.65 (1H, m), 6.45 (1H, s), 4.11−3.63 (4H, apparent br m),

2.74 (3H, s), 2.37 (6H, s), 2.23 (3H, br s), 1.91 (3H, br s), 0.92 (3H, br s). 13C NMR (101 MHz, CD2Cl2): δ 221.3, 155.9, 154.3, 152.4, 151.5, 146.3, 135.4, 133.0, 130.6, 129.7, 129.5, 122.9, 122.1, 120.9, 119.5, 51.3, 50.7, 30.2, 21.2. Complex Ru-4j. In a 2 dram vial charged with Ru-Pg (1.0 equiv) under a N2 atmosphere was placed a solution of triisopropyl phosphite (1.25 equiv) in dichloromethane (4 mL), and the solution was stirred for 3 h at 22 °C. The solvent was evaporated under reduced pressure. The residue was dissolved in dichloromethane (1 mL) and evaporated under reduced pressure; this was repeated twice. The dark brown solid was taken up in tetrahydrofuran (2 mL) and placed in a 2 dram vial charged with a stir bar and zinc catecholthiolate Zn-1 (1.5 equiv). The suspension was stirred for 3 h at 22 °C and subjected to reduced pressure. Residual tetrahydrofuran was removed through coevaporation with dichloromethane (3 × 1 mL), and the dark residue was taken up in dichloromethane and passed through a short plug of Celite. The solvent was evaporated in vacuo, and the dark green solid was dissolved in a small amount of methanol (0.6 mL), and the solution was kept in the freezer at −50 °C for 3 h. The green precipitate was filtered over a short plug of Celite, washed with a small amount of hexanes (1 mL), and eluted with dichloromethane. After coevaporation with diethyl ether Ru-4j was isolated as an amorphous green solid (25 mg, 29 μmol, 37%). 1H NMR (400 MHz, CD2Cl2): δ 14.23 (1H, d, J = 30.0 Hz), 7.65 (2H, br s), 7.18 (1H, tt, J = 7.6, 1.2 Hz), 6.96 (2H, br s), 6.92 (1H, s), 6.89 (1H, s), 6.79 (2H, tt, J = 7.6, 1.5 Hz), 6.70 (1H, s), 6.28 (2H, dd, J = 7.6, 1.2 Hz), 6.18−6.13 (1H, apparent m), 4.27 (3H, s), 3.96−3.69 (4H, m), 2.75 (3H, s), 2.68 (3H, s), 2.38 (3H, s), 2.19 (3H, s), 2.13 (3H, s), 2.08 (3H, s), 1.10 (9H, d, J = 6.1 Hz), 1.06 (9H, d, J = 6.1 Hz). 13C NMR (101 MHz, CD2Cl2): δ 276.5, 212.4, 212.3, 151.9, 138.3, 138.2, 138.1, 137.9, 137.9, 137.7, 137.6, 136.8, 131.2, 130.5, 130.4, 129.7, 129.5, 129.1, 128.9, 126.9, 121.8, 69.5, 69.4, 54.5, 54.3, 54.0, 53.7, 53.5, 52.4, 52.3, 24.9, 24.8, 24.7, 24.6, 21.3, 21.2, 21.1, 21.0, 20.2, 19.9, 1.3. 31P NMR (202 MHz, CD2Cl2): δ 38.16. Complex Ru-4k. In a 2 dram vial charged with Ru-Pg (1.0 equiv) under a N2 atmosphere was placed a solution of tris(trimethylsilyl) phosphite (1.25 equiv) in dichloromethane (4 mL), and the solution was stirred for 3 h at 22 °C. The solvent was evaporated under reduced pressure. The dark brown solid was dissolved in dichloromethane (1 mL) and evaporated under reduced pressure (repeated twice). The brown solid was taken up in tetrahydrofuran (2 mL) and placed in a 2 dram vial charged with a stir bar and zinc catecholthiolate Zn-1 (1.5 equiv). The suspension was stirred for 3 h at 22 °C and the solvent evaporated in vacuo. Residual tetrahydrofuran was removed by coevaporation with dichloromethane (3 × 1 mL), and the dark residue was taken up in dichloromethane and passed through a short plug of Celite. The solvent was evaporated, the residue was dissolved in a small amount of methanol (0.6 mL), and the solution was kept in the freezer at −50 °C for 3 h. The green precipitate was filtered over a short plug of Celite, washed with a small amount of hexanes (1 mL), and eluted with dichloromethane. After coevaporation with diethyl ether Ru-4k was isolated as an amorphous green solid (11 mg, 12 μmol, 16% yield). Crystals suitable for X-ray crystallographic analysis were grown through vapor diffusion from a diethyl ether/hexanes solution. 1H NMR (500 MHz, CD2Cl2): δ 14.42 (1H, d, J = 34.4 Hz), 7.69 (1H, br s), 7.54 (1H, br s), 7.14 (1H, t, J = 7.3 Hz), 6.97 (1H, s), 7.01−6.84 (2H, apparent br s), 6.88 (1H, s), 6.74 (1H, s), 6.71 (2H, dd, J = 8.1, 7.4 Hz), 6.23 (1H, s), 6.14 (2H, dd, J = 8.3, 1.2 Hz), 3.93− 3.64 (4H, m), 2.75 (3H, s), 2.63 (3H, s), 2.44 (3H, s), 2.05 (3H, s), 0.11 (27H, s). 13C NMR (151 MHz, CD2Cl2): δ 276.5, 213.9, 152.8, 150.6, 148.9, 138.5, 138.3, 138.1, 137.2, 137.0, 131.3, 130.8, 130.1, 130.0, 129.5, 129.3, 129.2, 128.2, 126.7, 121.9, 121.3, 52.6, 21.3, 21.2, 21.1, 21.0, 20.2, 19.8, 2.9. 31P NMR (162 MHz, CD2Cl2): δ 143.09 (d, J = 3.0 Hz). Complex Ru-4l. This carbene was prepared according to method A from Ru-Pl and isolated as a red-brown solid (25 mg, 36 μmol, 61% yield). Crystals suitable for X-ray analysis were grown through vapor diffusion from a dichloromethane/hexanes solution. 1H NMR (400 MHz, CD2Cl2): δ 15.41 (1H, s), 8.09 (1H, dd, J = 6.3, 5.9 Hz), 7.54− 7.44 (2H, m), 7.43 (1H, ddd, J = 7.8, 1.3, 0.3 Hz), 7.24−5.64 (2H, br J

DOI: 10.1021/acs.organomet.6b00773 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics

MHz, CD2Cl2): δ 258.7, 217.4, 156.9, 156.9, 153.6, 148.2, 139.6, 138.3, 138.3, 137.6, 137.4, 135.9, 135.5, 134.4, 134.4, 130.4, 129.9, 129.8, 129.6, 128.9, 128.8, 128.7, 128.6, 128.3, 127.2, 122.1, 121.0, 104.8, 52.0, 51.8, 21.3, 21.3, 20.1, 19.8, 19.5, 18.2. Complex Ru-4r. In a 2 dram vial charged with Ru-Pg (100 mg, 138 μmol) and benzene (2 mL) under a N2 atmosphere was placed a solution of 2,6-dimethylphenylisonitrile (18 mg, 138 μmol) in benzene (2 mL), and the solution was stirred for 1 h at 22 °C, after which glacial acetic acid (100 μL, 1.7 mmol) was added. The solution was then stirred for 10 h at 22 °C, after which the purple precipitate was filtered off over a short plug of Celite and washed with benzene (2 × 4 mL). After elution with dichloromethane (2 mL) and drying under reduced pressure the Ru dichloride isonitrile intermediate Ru-Pr (see Scheme 3) was obtained as a dark purple amorphous solid (18 mg, 26 μmol, 19% yield). Ru-Pr was dissolved in tetrahydrofuran (1 mL) and placed in a 2 dram vial charged with zinc catecholthiolate Zn-1 (11 mg, 52 μmol), and the solution was stirred for 2 h at 22 °C, after which the solvent was coevaporated with hexanes (1 mL). The dark residue was dissolved in a dichloromethane/hexanes mixture (1/1, 2 mL) and passed through a short plug of Celite. The filtrate was concentrated under reduced pressure. The resulting dark brown solid was dissolved in dichloromethane (0.1 mL), followed by addition of hexanes (3 mL). The resulting solution was concentrated to 1 mL, and the resulting brown precipitate was filtered over a short plug of Celite that was washed with hexanes (5 mL) and eluted with dichloromethane (1 mL). After solvent evaporation the product was isolated as a brown amorphous solid (13 mg, 17 μmol, 65% yield (12% yield)). Crystals suitable for X-ray crystallographic analysis were grown through vapor diffusion from a dichloromethane/hexanes solution. 1 H NMR (400 MHz, CD2Cl2): δ 14.86 (1H, s), 7.66 (1H, d, J = 8.0 Hz), 7.42 (1H, d, J = 7.6 Hz), 7.24 (1H, tt, J = 7.1, 1.6 Hz), 7.21−7.11 (4H, m), 7.11−6.97 (5H, m), 6.83 (1H, t, J = 7.7 Hz), 6.78 (1H, t, J = 7.5 Hz), 6.71 (2H, s), 4.22−3.73 (4H, br s), 3.19−2.40 (2H, br s), 2.43−1.85 (9H, br s), 2.28 (6H, s), 2.19 (6H, s). 13C NMR (101 MHz, CD2Cl2): δ 282.9, 215.2, 168.5, 152.6, 151.1, 148.4, 139.0, 137.1, 135.4, 130.5, 130.0, 129.8, 129.4, 129.1, 128.8, 128.3, 127.8, 127.6, 122.1, 121.0, 52.2, 21.3, 19.4. Complex Ru-6a. This carbene was prepared according to method A from Ru-Pa (cf. Scheme 3) and zinc mercaptophenolate Zn-2. The product was isolated as a brown amorphous solid (43 mg, 62 μmol, 62% yield). 1H NMR (500 MHz, benzene-d6): δ 15.86 (1H, s), 7.94 (1H, dd, J = 7.6, 1.6 Hz), 7.09 (1H, dd, J = 7.2, 1.5 Hz), 7.06 (1H, dd, J = 8.1, 1.5 Hz), 7.00 (1H, td, J = 7.7, 1.6 Hz), 6.86 (1H, td, J = 7.2, 1.4 Hz), 6.80 (2H, br s), 6.79 (2H, d, J = 9.0 Hz), 6.69 (1H, t, J = 7.4 Hz), 6.53 (1H, dd, J = 7.5, 1.7 Hz), 6.52−6.24 (2H, br s), 5.03 (1H, hept, J = 6.6 Hz), 3.40−2.87 (7H, br m), 2.69−2.15 (9H, br m), 2.07 (6H, s), 1.60−1.00 (3H, br s), 1.41 (3H, d, J = 6.6 Hz), 1.28 (3H, d, J = 6.6 Hz). 13C NMR (151 MHz, benzene-d6): δ 262.4, 221.8, 167.8, 155.4, 143.6, 137.1, 129.7, 128.3, 128.1, 128.0, 127.4, 126.7, 124.0, 123.0, 122.2, 117.2, 116.3, 116.2, 80.4, 50.8, 23.1, 21.7, 21.0, 21.0, 19.3, 11.7. Complex Ru-6b. This carbene was prepared according to method A from Ru-Pa (cf. Scheme 3) and Zn-3 and isolated as a brown solid (50 mg, 71 μmol, 56% yield). Crystals suitable for X-ray crystallographic analysis were obtained through vapor diffusion from a dichloromethane/hexanes solution. 1H NMR (600 MHz, benzene-d6): δ 15.78 (1H, d, J = 0.9 Hz), 7.55 (1H, d, J = 2.9 Hz), 7.08 (1H, ddd, J = 8.3, 7.2, 1.7 Hz), 6.93 (1H, d, J = 8.5 Hz), 6.81 (2H, s), 6.79 (1H, d, J = 8.3 Hz), 6.71−6.67 (2H, m), 6.62−6.22 (2H, br s, overlapping) 6.55 (1H, dd, J = 7.5, 1.7 Hz), 5.02 (1H, sept, J = 6.4 Hz), 3.49 (3H, s), 3.40− 2.90 (4H, br m), 2.41 (12H, br s), 2.08 (6H, s), 1.41 (3H, d, J = 6.5 Hz), 1.28 (3H, d, J = 6.4 Hz). 13C NMR (151 MHz, benzene-d6): δ 261.1, 222.1, 162.5, 155.4, 152.7, 143.7, 137.7, 129.7, 126.6, 124.0, 123.0, 116.1, 115.3, 112.35, 108.8, 80.4, 55.7, 50.65, 36.4, 35.0, 34.9, 29.4, 25.7, 21.0, 21.0, 20.9, 19.3, 19.0, 11.7. Complex Ru-6c. This carbene was prepared according to method A from the corresponding dichloride precursor42 and Zn-2. The product was isolated as a brown amorphous solid (26 mg, 36 μmol, 73% yield). 1 H NMR (400 MHz, benzene-d6): δ 15.87 (1H, s), 7.96 (1H, dd, J = 7.6, 1.5 Hz), 7.21 (1H, t, J = 7.7 Hz), 7.12 (1H, dd, J = 7.6, 1.6 Hz), 7.09 (1H, dd, J = 7.9, 1.5 Hz), 7.04 (1H, dd, J = 14.7, 1.5 Hz), 6.89

s), 7.14 (1H, ddd, J = 7.6, 1.3, 0.3 Hz), 6.96 (2H, s), 6.90 (1H, ddd, J = 11.5, 4.7, 3.3 Hz), 6.70 (1H, ddd, J = 7.8, 7.0, 1.3 Hz), 6.62 (1H, ddd, J = 7.6, 7.0, 1.3 Hz), 4.17 (3H, s), 3.94 (4H, br s), 2.81−0.98 (6H, br s), 2.53 (6H, s), 2.09 (6H, br s). 13C NMR (101 MHz, CD2Cl2): δ 250.0, 218.7, 175.3, 154.6, 143.6, 143.6, 142.3, 138.7, 137.1, 135.3, 131.0, 129.6, 129.4, 128.8, 128.1, 128.1, 126.5, 121.7, 120.6, 119.9, 119.9, 54.9, 51.8, 21.3, 18.9. Complex Ru-4m. This carbene was prepared according to method B through the use of methyl 4-nitro-2-vinylbenzoate (2 equiv) and isolated as a brown solid (18 mg, 24 μmol, 95% yield). Crystals suitable for X-ray analysis were grown through vapor diffusion from a dichloromethane/hexanes solution. 1H NMR (400 MHz, CD2Cl2): δ 15.27 (1H, s), 8.25−8.23 (2H, m), 7.79 (1H, s), 7.45 (1H, dd, J = 7.8, 1.2 Hz), 7.14 (1H, dd, J = 7.5, 1.2 Hz), 6.98 (2H, s), 6.75 (1H, ddd, J = 7.8, 7.0, 1.2 Hz), 6.65 (1H, ddd, J = 7.5, 7.0, 1.2 Hz), 4.25 (3H, s), 4.08−3.79 (4H, br s), 2.53 (6H, s), 2.23−1.93 (6H, br s), 1.52 (6H, s). Complex Ru-4n. This carbene was prepared according to method A from Ru-Pn and isolated as a brown solid (18 mg, 26 μmol, 53% yield). Crystals suitable for X-ray crystallographic analysis were obtained through vapor diffusion from a dichloromethane/hexanes solution. 1H NMR (400 MHz, CD2Cl2): δ 13.58 (1H, s), 7.69 (1H, dd, J = 8.0, 1.1 Hz), 7.45 (1H, dd, J = 7.7, 1.3 Hz), 7.32 (1H, d, J = 7.6 Hz), 7.27 (1H, td, J = 7.4, 1.1 Hz), 7.22 (1H, s), 6.97 (1H, dd, J = 11.1, 3.8 Hz), 6.90 (2H, ddd, J = 7.8, 5.9, 1.4 Hz), 6.86−6.80 (1H, m), 6.57 (2H, d, J = 11.2 Hz), 6.30 (1H, d, J = 7.7 Hz), 5.94 (1H, dd, J = 12.6, 10.2 Hz), 4.22−4.03 (2H, m), 3.95−3.78 (2H, m), 3.55 (1H, d, J = 12.7 Hz), 3.49 (1H, d, J = 10.2 Hz), 3.06 (3H, s), 2.37 (3H, s), 2.26 (3H, s), 2.22 (3H, s), 1.99 (3H, s), 1.39 (3H, s). 13C NMR (101 MHz, CD2Cl2): δ 275.4, 215.4, 157.4, 152.3, 149.0, 148.1, 139.6, 138.6, 137.9, 137.8, 137.8, 136.3, 135.7, 134.6, 130.7, 130.5, 130.3, 129.2, 129.1, 128.4, 127.8, 126.8, 122.4, 122.0, 121.5, 97.3, 67.2, 52.6, 52.6, 21.3, 21.3, 20.4, 19.2, 19.0, 18.1. Complex Ru-4o. This carbene was prepared according to method A from Ru-Po and isolated as a brown solid (43 mg, 60 μmol, 78% yield). Crystals suitable for X-ray crystallographic analysis were obtained through vapor diffusion from a dichloromethane/hexanes solution. 1H NMR (400 MHz, CD2Cl2): δ 14.42 (1H, d, J = 0.9 Hz), 7.62 (1H, ddd, J = 7.6, 1.3, 0.5 Hz), 7.53 (1H, m), 7.35 (1H, td, J = 7.7, 1.3), 7.30 (1H, ddd, J = 7.8, 1.3, 0.5 Hz), 7.11 (1H, td, J = 7.7, 1.3 Hz), 6.95 (1H, s), 6.92 (1H, s), 6.84 (1H, ddd, J = 7.8, 7.0, 1.3 Hz), 6.72 (1H, ddd, J = 7.6, 7.0, 1.3 Hz), 6.66 (1H, dd, J = 7.8, 1.3 Hz), 6.59 (1H, s), 6.09 (1H, s), 4.03−3.72 (4H, m), 3.57 (1H, sept, J = 6.8 Hz), 2.62 (3H, s), 2.53 (3H, s), 2.24 (3H, s), 2.22 (3H, s), 2.18 (3H, s), 1.56 (3H, s), 1.47 (3H, d, J = 6.9 Hz), 1.07 (3H, d, J = 6.7 Hz). 13C NMR (101 MHz, CD2Cl2): δ 257.9, 216.8, 156.8, 156.8, 153.0, 146.0, 139.3, 138.4, 138.1, 137.4, 137.2, 136.6, 135.8, 134.9, 134.2, 131.2, 129.9, 129.7, 129.6, 129.5, 129.4, 128.6, 128.3, 127.1, 125.0, 122.0, 120.5, 51.9, 51.8, 42.1. Complex Ru-4p. This carbene was prepared according to method A from Ru-Pp and isolated as a brown solid (52 mg, 68 μmol, 61% yield). 1H NMR (400 MHz, CD2Cl2): δ 14.77 (1H, d, J = 0.8 Hz), 8.36 (1H, dd, J = 7.9, 0.9 Hz), 7.95 (1H, dd, J = 7.7, 0.9 Hz), 7.44 (1H, d, J = 7.7 Hz), 7.11 (1H, ddd, J = 8.2, 6.9, 1.3 Hz), 7.01−6.90 (2H, m), 6.79 (1H, s), 6.76−6.68 (2H, m), 6.46 (3H, dd, J = 7.7, 1.3 Hz), 3.33− 3.13 (2H, m), 3.07−2.92 (2H, m), 2.79 (3H, s), 2.47 (3H, s), 2.43 (3H, s), 2.06 (3H, s), 1.99 (3H, s), 1.49 (3H, s), 1.46 (9H, s). 13C NMR (101 MHz, benzene-d6): δ 238.4, 217.6, 156.5, 152.1, 138.8, 138.6, 137.4, 137.4, 137.2, 136.4, 135.7, 135.2, 130.7, 130.0, 129.7, 129.5, 129.3, 129.0, 128.6, 126.1, 125.3, 122.4, 120.8, 53.1, 51.1, 51.1, 31.3, 21.0, 20.9, 20.1, 19.8, 19.7, 17.8. Complex Ru-4q. This carbene was prepared according to method B through the use of 2-iodostyrene (2 equiv) and isolated as a brown solid (52 mg, 68 μmol, 70% yield). Crystals suitable for X-ray analysis were grown through vapor diffusion from a dichloromethane/hexanes solution. 1H NMR (400 MHz, CD2Cl2): δ 15.11 (1H, d, J = 0.7 Hz), 7.70 (1H, dd, J = 7.9, 1.2 Hz), 7.69−7.63 (1H, m), 7.34 (1H, dd, J = 7.7, 1.2 Hz), 7.22−7.15 (2H, m), 7.07 (1H, s), 6.94 (1H, s), 6.85 (1H, ddd, J = 7.7, 7.0, 1.2 H), 6.78−6.72 (2H, m), 6.71 (1H, s), 6.19 (1H, s), 4.10−3.95 (2H, m), 3.90−3.80 (2H, m), 2.73 (3H, s), 2.40 (3H, s), 2.26 (3H, s), 2.25 (3H, s), 2.23 (3H, s), 1.56 (3H, s). 13C NMR (101 K

DOI: 10.1021/acs.organomet.6b00773 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics

amorphous solid washed with methanol (2 × 10 mL). After drying under vacuum the polymer was obtained as an off-white solid. Computational Details. DFT computations44 were performed with the Gaussian 09 suite of programs.45 Methods Applied To Study Catecholthiolate Rotation (Scheme 4). Geometries were optimized by application of the generalized gradient approximation (GGA) functional BP86.46 The 6-31G(d,p) basis set was used for H and C atoms, including additional diffuse functions (+) on heteroatoms (N, O, P, S). A quasi-relativistic effective core potential (ECP) of the Stuttgart−Dresden type47 was used for Ru centers (MWB28 keyword in Gaussian for basis set and ECP); this set is termed “basis1”. Stationary points were probed through vibrational analysis, and Gibbs free energy corrections were performed under standard conditions (298.15 K, 1.0 atm). The effect of a polar medium (benzene) was evaluated by single-point energy calculations at the geometries optimized in the gas phase by means of an integral equation formalism variant of the polarizable continuum model (IEFPCM),48 with three density functionals (ωB97XD49 and M06,50 MN12SX51) and the larger Def2QZVP52 basis set. For further mechanistic details, see the Supporting Information. Methods Applied To Study Norbornene ROMP with Ru-4a, Ru-5, and Ru-6a (Figure 3). Geometries were optimized by application of the density functional BP8646 and the Def2SVP52 basis set for all atoms. A polar medium (thf) was applied within the integral equation formalism variant of the polarizable continuum model (IEFPCM).48 Stationary points were probed through vibrational analysis, and Gibbs free energy corrections were performed under standard conditions (298.15 K, 1.0 atm). We furthermore probed the performance of various density functionals through single-point energy calculations at the geometries optimized at the BP86/Def2SVPthf(PCM) level by means of the SMD solvation model53 with benzene as solvent and the larger Def2TZVPP52 basis set. Since the correct density functional is not known, we tested several state of the art approaches that have been developed over that past decade:44,54 ωB97XD,49 M06,50 MN12SX,51 MN12L,51 M06L,50 BP86-D3BJ,44b and PBE0-D3BJ.44b,55 For further mechanistic details, see the Supporting Information.

(1H, ddd, J = 7.6, 6.8, 1.5 Hz), 6.85 (1H, s), 6.72 (1H, t, J = 7.2 Hz), 6.66 (1H, d, J = 7.7 Hz), 6.58 (1H, d, J = 8.3 Hz), 6.45 (1H, d, J = 2.1 Hz), 4.64 (1H, br s), 3.64 (1H, br s), 3.19 (4H, m), 3.03 (1H, br s), 2.66 (3H, s), 2.13 (3H, s), 1.13−0.94 (12H, m), 0.84 (3H, d, J = 6.4 Hz). 13C NMR (101 MHz, CD2Cl2): δ 264.0, 226.4, 167.9, 155.4, 142.9, 137.1, 136.9, 129.9, 129.6, 127.0, 126.9, 124.6, 123.8, 122.3, 121.8, 116.8, 115.9, 114.4, 77.4, 53.5, 50.6, 34.6, 31.6, 28.0, 26.6, 26.6, 23.5, 22.6, 20.6, 19.7, 19.4, 13.9. Complex Ru-6d. This carbene was prepared according to method A from the corresponding dichloride precursor43 and Zn-2. The product was isolated as a brown amorphous solid (27 mg, 35 μmol, 56% yield). Crystals suitable for X-ray crystallographic analysis were obtained through vapor diffusion from a dichloromethane/hexanes solution. 1H NMR (500 MHz, benzene-d6): δ 15.77 (1H, s), 7.93 (1H, d, J = 7.2 Hz), 7.27 (1H, d, J = 8.0 Hz), 7.23 (1H, t, J = 7.6 Hz), 7.17 (1H, t, J = 8.0 Hz), 7.12 (2H, dt, J = 7.3, 1.7 Hz), 7.07−7.01 (3H, m), 6.94−6.86 (1H, m), 6.74 (1H, dd, J = 7.5, 1.7 Hz), 6.63 (1H, t, J = 7.4 Hz), 6.49 (2H, td, J = 7.1, 1.4 Hz), 4.60 (2H, h, J = 6.5 Hz), 3.85 (1H, q, J = 10.5 Hz, overlapping), 3.80 (1H, sept, J = 6.7 Hz, overlapping), 3.72 (1H, q, J = 9.3 Hz), 3.41 (1H, q, J = 9.8 Hz), 3.30 (1H, q, J = 9.8 Hz), 3.00 (1H, h, J = 6.9 Hz), 2.36 (1H, p, J = 6.8 Hz), 2.02 (3H, d, J = 6.4 Hz), 1.28 (3H, d, J = 6.0 Hz), 1.20 (3H, d, J = 6.4 Hz), 1.19 (3H, d, J = 6.3 Hz), 1.12 (3H, d, J = 6.9 Hz), 1.08 (3H, d, J = 7.0 Hz), 1.05 (3H, d, J = 6.7 Hz), 1.03 (3H, d, J = 6.2 Hz), 0.78 (3H, d, J = 6.7 Hz), 0.09 (3H, d, J = 6.6 Hz). 13C NMR (151 MHz, benzene-d6): δ 265.5, 224.3, 168.1, 156.1, 150.6, 149.1, 147.1, 145.5, 143.0, 138.5, 136.9, 130.3, 128.8, 128.6, 127.6, 127.1, 126.4, 125.5, 125.7, 124.5, 123.9, 122.9, 122.3, 117.3, 116.1, 114.8, 77.1, 53.8, 53.5, 30.3, 28.9, 28.6, 28.5, 27.1, 27.0, 26.6, 25.7, 25.3, 23.9, 23.3, 20.4, 20.3, 19.9. Complex Ru-6e. In a 2 dram vial charged with Ru-Pg (58 mg, 80 μmol; see Scheme 3) under a N2 atmosphere was placed a solution of triisopropyl phosphite (21 mg, 100 μmol) in dichloromethane (4 mL), and the mixture was stirred for 3 h at 22 °C. The solvent was evaporated in vacuo. The dark brown solid was dissolved in dichloromethane (1 mL) and the solvent evaporated under reduced pressure (this was repeated twice). The dark brown solid was taken up in tetrahydrofuran (2 mL) and placed in a 2 dram vial charged with a stir bar and zinc mercaptophenolate Zn-2 (25 mg, 120 μmol). The suspension was stirred for 2 h at 22 °C and the solvent evaporated in vacuo. Residual tetrahydrofuran was then removed through coevaporation with dichloromethane (3 × 1 mL), and the dark solid residue was taken up in a dichloromethane/hexanes mixture (1:1, 1 mL) and passed through a short plug of Celite. Additional hexane was added (3 mL) and the mixture concentrated to 0.5 mL. The resulting browngreen precipitate was filtered through a short plug of Celite and washed with hexanes (5 mL). The complex was eluted with dichloromethane (1 mL). After drying under vacuum the product was isolated as a brown-green amorphous solid (18 mg, 22 mmol, 27% yield). Crystals suitable for X-ray crystallographic analysis were obtained through vapor diffusion from a dichloromethane/hexanes solution. 1H NMR (400 MHz, benzene-d6): δ 14.19 (1H, d, J = 25.9 Hz), 8.07 (1H, dd, J = 7.6, 1.5 Hz), 7.55 (1H, dd, J = 8.0, 1.3 Hz), 7.47 (1H, td, J = 8.2, 1.6 Hz), 7.03−6.95 (2H, m), 6.91 (1H, br s), 6.91 (1H, s), 6.83−6.75 (3H, m), 6.67 (1H, s), 6.33 (1H, s), 6.06 (1H, s), 4.42 (3H, m), 3.30−3.03 (4H, m), 2.53 (6H, s), 2.52 (3H, s), 2.33 (3H, s), 2.00 (3H, s), 1.94 (3H, s), 1.10 (9H, d, J = 6.1 Hz), 1.07 (9H, d, J = 6.1 Hz). 13C NMR (101 MHz, benzene-d6): δ 272.3, 212.0, 171.2, 171.2, 151.4, 143.3, 139.2, 138.9, 137.9, 137.7, 137.7, 136.9, 136.2, 135.7, 134.7, 134.6, 130.6, 130.6, 130.4, 130.3, 129.8, 124.3, 117.4, 117.4, 116.2, 68.7, 68.6, 51.5, 51.1, 24.7, 24.7, 24.6, 24.6, 21.1, 20.9, 20.0, 19.1, 18.4, 18.0. 31P NMR (162 MHz, CD2Cl2): δ 144.31 (d, J = 3.6 Hz). ROMP Reactions. A vial equipped with a stir bar was charged with norbornene (470 mg, 5 mmol) and dichloromethane (10 mL, 0.5 M). After the solution had reached the target temperature (0, 22, 40, 60, or 80 °C), an aliquot (0.0001 equiv) of a stock solution (1 mg/mL) of the corresponding complex in benzene was injected and the mixture was vigorously stirred for 1 h. The polymer was precipitated through the addition of methanol (10 mL), the solvent decanted, and the white

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.6b00773. Combined X-ray structural data (CIF) Computed geometries with the program Mercury 3.3 or higher (XYZ) 1 H, 13C, and 31P NMR data for Ru complexes, variabletemperature NMR experiments for complexes Ru-4j,k,r, and electronic and Gibbs free energies for Scheme 4 and Figure 3 with several density functionals (ωB97XD, M06, MN12SX, MN12L, M06L, BP86-D3BJ, and PBE0D3BJ) (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail for S.T.: [email protected]. *E-mail for A.H.H.: [email protected]. Notes

The authors declare the following competing financial interest(s): The new Ru complexes described herein belong to a set of entities that have been licensed to a company cofounded by A. H. H.

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ACKNOWLEDGMENTS Financial support was provided by the NSF (CHE-1362763). We thank Dr. K. Bergander (Westfälische Wilhelms-Universität Münster) for advice concerning NMR simulation, T. T. L

DOI: 10.1021/acs.organomet.6b00773 Organometallics XXXX, XXX, XXX−XXX

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Organometallics

(9) For development and applications of enantiomerically enriched stereogenic-at-Ru carbene complexes such as Ru-2, see: (a) Ref 3a. (b) Van Veldhuizen, J. J.; Gillingham, D. G.; Garber, S. B.; Kataoka, O.; Hoveyda, A. H. J. Am. Chem. Soc. 2003, 125, 12502−12508. (c) Gillingham, D. G.; Kataoka, O.; Garber, S. B.; Hoveyda, A. H. J. Am. Chem. Soc. 2004, 126, 12288−12290. (d) Ref 3b. (e) Gillingham, D. G.; Hoveyda, A. H. Angew. Chem., Int. Ed. 2007, 46, 3860−3864. (10) For relevant ROCM with Mo MAP complexes, see: (a) Ibrahem, I.; Yu, M.; Schrock, R. R.; Hoveyda, A. H. J. Am. Chem. Soc. 2009, 131, 3844−3845. (b) Yu, M.; Ibrahem, I.; Hasegawa, M.; Schrock, R. R.; Hoveyda, A. H. J. Am. Chem. Soc. 2012, 134, 2788−2799. (c) Ref 8k. (11) For alternating copolymerization processes promoted by complexes represented by Ru-1, see: (a) Ref 2. (b) Bornand, M.; Torker, S.; Chen, P. Organometallics 2007, 26, 3585−3596. (c) Torker, S.; Müller, A.; Sigrist, R.; Chen, P. Organometallics 2010, 29, 2735− 2751. (d) Jovic, M.; Torker, S.; Chen, P. Organometallics 2011, 30, 3971−3980. (e) Torker, S.; Chen, P. Chimia 2011, 65, 106. (12) For alternating copolymerization processes promoted by MAP complexes represented by Mo-1, see: (a) Flook, M. M.; Jiang, A. J.; Schrock, R. R.; Müller, P.; Hoveyda, A. H. J. Am. Chem. Soc. 2009, 131, 7962−7963. (b) Flook, M. M.; Gerber, L. C. H.; Debelouchina, G. T.; Schrock, R. R. Macromolecules 2010, 43, 7515−7522. (c) Flook, M. M.; Ng, V. W. L.; Schrock, R. R. J. Am. Chem. Soc. 2011, 133, 1784−1786. (d) Yuan, J.; Schrock, R. R.; Gerber, L. C. H.; Müller, P.; Smith, S. Organometallics 2013, 32, 2983−2992. (13) The principle of a “side change”, equal to inversion at the metal center in stereogenic-at-metal complexes, was first proposed for a Rubased complex by Chen and co-workers. See: (a) Adlhart, C.; Hinderling, C.; Baumann, H.; Chen, P. J. Am. Chem. Soc. 2000, 122, 8204−8214. (b) Adlhart, C.; Chen, P. Angew. Chem., Int. Ed. 2002, 41, 4484−4487. For a recent overview and analysis, see: (c) Chen, P. Acc. Chem. Res. 2016, 49, 1052−1060. (14) For a recent mechanistic study regarding the effect of anionic ligands on OM-based and non-OM-based polytopal rearrangements, see: (a) Khan, R. K. M.; Zhugralin, A. R.; Torker, S.; O’Brien, R. V.; Lombardi, P. J.; Hoveyda, A. H. J. Am. Chem. Soc. 2012, 134, 12438− 12441. (b) Torker, S.; Khan, R. K. M.; Hoveyda, A. H. J. Am. Chem. Soc. 2014, 136, 3439−3455. (15) For related mechanistic investigations regarding polytopal rearrangements within Ru carbene complexes, see: (a) Benitez, D.; Goddard, W. A. J. Am. Chem. Soc. 2005, 127, 12218−12219. (b) Poater, A.; Ragone, F.; Correa, A.; Szadkowska, A.; Barbasiewicz, M.; Grela, K.; Cavallo, L. Chem. - Eur. J. 2010, 16, 14354−14364. (16) For recent work on mechanistic aspects of polytopal rearrangements in pentacoordinate complexes, see: (a) Couzijn, E. P. A.; Slootweg, J. C.; Ehlers, A. W.; Lammertsma, K. J. Am. Chem. Soc. 2010, 132, 18127−18140. (b) Moberg, C. Angew. Chem., Int. Ed. 2011, 50, 10290−10292. For early work on the mechanism of polytopal rearrangements, see: (c) Berry, R. S. J. Chem. Phys. 1960, 32, 933−938. (d) Mutterties, E. L. J. Am. Chem. Soc. 1969, 91, 1636−1643. (e) Gillespie, P.; Hoffman, P.; Klusacek, H.; Marquarding, D.; Phohl, S.; Ramirez, F.; Tsolis, E. A.; Ugi, I. Angew. Chem., Int. Ed. Engl. 1971, 10, 687−715. (17) Mikus, M. S.; Torker, S.; Hoveyda, A. H. Angew. Chem., Int. Ed. 2016, 55, 4997−5002. (18) Meek, S. J.; Malcolmson, S. J.; Li, B.; Schrock, R. R.; Hoveyda, A. H. J. J. Am. Chem. Soc. 2009, 131, 16407−16409. (19) (a) Khan, R. K. M.; O’Brien, R. V.; Torker, S.; Hoveyda, A. H. J. Am. Chem. Soc. 2012, 134, 12774−12779. (b) Torker, S.; Koh, M. J.; Khan, R. K. M.; Hoveyda, A. H. Organometallics 2016, 35, 543−562. (20) (a) Khan, R. K. M.; Torker, S.; Hoveyda, A. H. J. Am. Chem. Soc. 2013, 135, 10258−10261. (b) Koh, M. J.; Khan, R. K. M.; Torker, S.; Hoveyda, A. H. Angew. Chem., Int. Ed. 2014, 53, 1968−1972. (c) Khan, R. K. M.; Torker, S.; Hoveyda, A. H. J. Am. Chem. Soc. 2014, 136, 14337−14340. (d) Koh, M. J.; Khan, R. K. M.; Torker, S.; Yu, M.; Mikus, M. S.; Hoveyda, A. H. Nature 2015, 517, 181−186. (e) Ref 17. (f) Johns, A. M.; Ahmed, T. S.; Jackson, B. W.; Grubbs, R. H.; Pederson, R. L. Org. Lett. 2016, 18, 772−775.

Nguyen (Boston College) for experimental assistance, Professor J. A. Byers and Dr. Juan del Pozo (Boston College) for helpful discussions, and Boston College Research Services for access to computational facilities.

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REFERENCES

(1) For reviews regarding various aspects of catalyst-controlled stereoselective (enantioselective and/or Z-selective) olefin metathesis reactions, see: (a) Hoveyda, A. H.; Malcolmson, S. J.; Meek, S. J.; Zhugralin, A. R. Angew. Chem., Int. Ed. 2010, 49, 34−44. (b) Hoveyda, A. H. J. Org. Chem. 2014, 79, 4763−4792. (c) Hoveyda, A. H.; Torker, S.; Khan, R. M. K.; Malcolmson, S. J. Handbook of Metathesis, Grubbs, R. H., O’Leary, D. J., Wentzel, A. G., Khosravi, E., Eds.; Wiley-VCH: Weinheim, Germany, 2015; Vol. 2, pp 508−562. (2) For an early narrative regarding this concept, see: Bornand, M.; Chen, P. Angew. Chem., Int. Ed. 2005, 44, 7909−7911. (3) (a) Van Veldhuizen, J. J.; Garber, S. B.; Kingsbury, J. S.; Hoveyda, A. H. J. Am. Chem. Soc. 2002, 124, 4954−4955. (b) Van Veldhuizen, J. J.; Campbell, J. E.; Giudici, R. E.; Hoveyda, A. H. J. Am. Chem. Soc. 2005, 127, 6877−6882. (4) Endo, K.; Grubbs, R. H. J. Am. Chem. Soc. 2011, 133, 8525−8527. (5) Malcolmson, S. J.; Meek, S. J.; Sattely, E. S.; Schrock, R. R.; Hoveyda, A. H. Nature 2008, 456, 933−937. (6) For Z-selective reactions promoted by stereogenic-at-Ru complexes represented by Ru-3, see the following. Cross metathesis: (a) Rosebrugh, L. E.; Herbert, M. B.; Marx, V. M.; Keitz, B. K.; Grubbs, R. H. J. Am. Chem. Soc. 2013, 135, 1276−1279. (b) Herbert, M. B.; Marx, V. M.; Pederson, R. L.; Grubbs, R. H. Angew. Chem., Int. Ed. 2013, 52, 310−314. (c) Miyazaki, H.; Herbert, M. B.; Liu, P.; Dong, X.; Xu, X.; Keitz, B. K.; Ung, T.; Mkrtumyan, G.; Houk, K. N.; Grubbs, R. H. J. Am. Chem. Soc. 2013, 135, 5848−5858. (d) Quigley, B. L.; Grubbs, R. H. Chem. Sci. 2014, 5, 501−506. Ring opening/cross metathesis: (e) Hartung, J.; Grubbs, R. H. J. Am. Chem. Soc. 2013, 135, 10183−10185. (f) Hartung, J.; Grubbs, R. H. Angew. Chem., Int. Ed. 2014, 53, 3885−3888. (g) Hartung, J.; Doornan, P. K.; Grubbs, R. H. J. Am. Chem. Soc. 2014, 136, 13029−13037. Macrocyclic ring-closing metathesis: (h) Marx, V. M.; Herbert, M. B.; Keitz, B. K.; Grubbs, R. H. J. Am. Chem. Soc. 2013, 135, 94−97. (i) Mangold, S. L.; O’Leary, D. J.; Grubbs, R. H. J. Am. Chem. Soc. 2014, 136, 12469−12478. (7) For Ru-based monochloride/sulfide complexes that have been used to promote Z-selective homocoupling and cross-metathesis reactions, see: (a) Occhipinti, G.; Hansen, F. R.; Törnroos, K. W.; Jensen, V. R. J. Am. Chem. Soc. 2013, 135, 3331−3334. (b) Occhipinti, G.; Koudriavtsev, V.; Törnroos, K. W.; Jensen, V. R. Dalton Trans. 2014, 43, 11106−11117. (8) For Z-selective reactions catalyzed by Mo or W MAP complexes, see the following. Cross-metathesis: (a) Meek, S. J.; O’Brien, R. V.; Llaveria, J.; Schrock, R. R.; Hoveyda, A. H. Nature 2011, 471, 461− 466. (b) Kiesewetter, E. T.; O’Brien, R. V.; Yu, E. C.; Meek, S. J.; Schrock, R. R.; Hoveyda, A. H. J. Am. Chem. Soc. 2013, 135, 6026− 6029. (c) Mann, T. J.; Speed, A. W. H.; Schrock, R. R.; Hoveyda, A. H. Angew. Chem., Int. Ed. 2013, 52, 8395−8400. (d) Speed, A. W. H.; Mann, T. J.; O’Brien, R. V.; Schrock, R. R.; Hoveyda, A. H. J. Am. Chem. Soc. 2014, 136, 16136−16139. (e) Koh, M. J.; Nguyen, T. T.; Zhang, H.; Schrock, R. R.; Hoveyda, A. H. Nature 2016, 531, 459− 465. (f) Yu, E. C.; Johnson, B. M.; Townsend, E. M.; Schrock, R. R.; Hoveyda, A. H. Angew. Chem., Int. Ed. 2016, 55, 13210−13214. For efficient and kinetically E selective cross-metathesis reactions, see: (g) Nguyen, T. T.; Koh, M. J.; Shen, X.; Romiti, F.; Schrock, R. R.; Hoveyda, A. H. Science 2016, 352, 569−575. For macrocyclic ringclosing metathesis, see: (h) Yu, M.; Wang, C.; Kyle, A. F.; Jakubec, P.; Dixon, D. J.; Schrock, R. R.; Hoveyda, A. H. Nature 2011, 479, 88−93. (i) Wang, C.; Yu, M.; Kyle, A. F.; Jakubec, P.; Dixon, D. J.; Schrock, R. R.; Hoveyda, A. H. Chem. - Eur. J. 2013, 19, 2726−2740. (j) Zhang, H.; Yu, E. C.; Torker, S.; Schrock, R. R.; Hoveyda, A. H. J. Am. Chem. Soc. 2014, 136, 16493−16496. For an application of Mo/W MAP complexes to natural product synthesis, see: (k) Yu, M.; Schrock, R. R.; Hoveyda, A. H. Angew. Chem., Int. Ed. 2015, 54, 215−220. M

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Organometallics (21) To denote stereogenic centers in compounds that are not tetrahedral, the A/C (vs R/S) nomenclature is used (A = anticlockwise, C = clockwise); see the Supporting Information for details. (22) For a review on latent Ru-based catalysts for olefin metathesis, see: Vidavsky, Y.; Anaby, A.; Lemcoff, N. G. Dalton Trans. 2012, 41, 32−43. (23) The observed trends in reactivity for various chelated Ru complexes are in line with those previously reported for the corresponding dichloro Ru systems; see: (a) Ung, T.; Hejl, A.; Grubbs, R. H.; Schrodi, Y. Organometallics 2004, 23, 5399−5401. (b) Slugovc, C.; Perner, B.; Stelzer, F.; Mereiter, K. Organometallics 2004, 23, 3622−3626. (c) Zirngast, M.; Pump, E.; Leitgeb, A.; Albering, J. H.; Slugovc, C. Chem. Commun. 2011, 47, 2261−2263. (d) Leitgeb, A.; Mereiter, K.; Slugovc, C. Monatsh. Chem. 2012, 143, 901−908. (e) Pump, E.; Fischer, R. C.; Slugovc, C. Organometallics 2012, 31, 6972−6979. (f) Barbasiewicz, M.; Szadkowska, A.; Bujok, R.; Grela, K. Organometallics 2006, 25, 3599−3604. (g) Gstrein, X.; Burtscher, D.; Szadkowska, A.; Barbasiewicz, M.; Stelzer, F.; Grela, K.; Slugovc, C. J. Polym. Sci., Part A: Polym. Chem. 2007, 45, 3494−3500. (h) Barbasiewicz, M.; Michalak, M.; Grela, K. Chem. - Eur. J. 2012, 18, 14237−14241. (i) Barbasiewicz, M.; Blocki, K.; Malinska, M.; Pawlowski, R. Dalton Trans. 2013, 42, 355−358. (j) Ben-Asuly, A.; Tzur, E.; Diesendruck, C. E.; Sigalov, M.; Goldberg, I.; Lemcoff, G. N. Organometallics 2008, 27, 811−813. (k) Diesendruck, C. E.; Tzur, E.; Ben-Asuly, A.; Goldberg, I.; Straub, B. F.; Lemcoff, N. G. Inorg. Chem. 2009, 48, 10819−10825. (l) Tzur, E.; Szadkowska, A.; Ben-Asuly, A.; Makal, A.; Goldberg, I.; Wozniak, K.; Grela, K.; Lemcoff, N. G. Chem. Eur. J. 2010, 16, 8726−8737. (m) Aharoni, A.; Vidavsky, Y.; Diesendruck, C. E.; Ben-Asuly, A.; Goldberg, I.; Lemcoff, N. G. Organometallics 2011, 30, 1607−1615. (n) Bantreil, X.; Schmid, T. E.; Randall, R. A. M.; Slawin, A. M. Z.; Cazin, C. S. J. Chem. Commun. 2010, 46, 7115−7117. (o) Schmid, T. E.; Bantreil, X.; Citadelle, C. A.; Slawin, A. M. Z.; Cazin, C. S. J. Chem. Commun. 2011, 47, 7060−7062. (24) See the Supporting Information for details. (25) For a discussion regarding trans influence, see: (a) Appleton, T. G.; Clark, H. C.; Manzer, L. E. Coord. Chem. Rev. 1973, 10, 335−422. (b) Spessard, G. O.; Miessler, G. L. In Organometallic Chemistry; Oxford University Press: Oxford, U.K., 2016; pp 218−220. (26) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen, A. G.; Taylor, R. J. Chem. Soc., Perkin Trans. 2 1987, S1−S19. (27) Stephenson, D. S.; Binsch, G. J. Magn. Reson. 1978, 30, 625− 626. (28) For a discussion regarding the trans effect, see: Hartwig, J. In Organotransition Metal Chemistry, From Bonding to Catalysis; University Science Books: Sausalito, CA, 2010; pp 228−229. (29) A mechanism for rotation of the catecholthiolate ligand within a five-coordinate Ru catecholthiolate complex is illustrated in the Figure below. The facility of this isomerization is influenced by the ability of the neutral donor group L or G in stabilizing the empty coordination site in the transition state. (30) For selected computational investigations regarding different mechanistic aspects of olefin metathesis reactions catalyzed by Ru carbene complexes, see: (a) Cavallo, L. J. Am. Chem. Soc. 2002, 124, 8965−8973. (b) Adlhart, C.; Chen, P. J. Am. Chem. Soc. 2004, 126, 3496−3510. (c) Straub, B. F. Angew. Chem., Int. Ed. 2005, 44, 5974− 5978. (d) Correa, A.; Cavallo, L. J. Am. Chem. Soc. 2006, 128, 13352− 13353. (e) Occhipinti, G.; Bjorsvik, H. R.; Jensen, V. R. J. Am. Chem. Soc. 2006, 128, 6952−6964. (f) Straub, B. F. Adv. Synth. Catal. 2007, 349, 204−214. (g) Torker, S.; Merki, D.; Chen, P. J. Am. Chem. Soc. 2008, 130, 4808−4814. (h) Yang, H. C.; Huang, Y. C.; Lan, Y. K.; Luh, T. Y.; Zhao, Y.; Truhlar, D. G. Organometallics 2011, 30, 4196− 4200. (i) Minenkov, Y.; Occhipinti, G.; Jensen, V. R. Organometallics 2013, 32, 2099−2111. (j) Ref 19b. (31) The order of ligands that lower the barrier to rotation of the catecholthiolate ligand is largely in agreement with the typical ligand series for the kinetic trans effect observed in associative ligand substitution reactions in square-planar complexes. See ref 28.

(32) The detrimental effect of strongly π accepting ligands on the stability of Ru carbenes has been reported: (a) Galan, B. R.; Gembicky, M.; Dominiac, P. M.; Keister, J. B.; Diver, S. T. J. Am. Chem. Soc. 2005, 127, 15702. (b) Galan, B. R.; Kalbarczyk, K. P.; Szczepankiewicz, S.; Keister, J. B.; Diver, S. T. Org. Lett. 2007, 9, 1203. (c) Galan, B. R.; Pitak, M.; Gembicky, M.; Keister, J. B.; Diver, S. T. J. Am. Chem. Soc. 2009, 131, 6822. (33) A “push-pull” mechanism between a π-donating fluoride and a π-accepting phosphite was proposed to account for the observed trans relationship between F and P-based ligands: Guidone, S.; Songis, O.; Falivene, L.; Nahra, F.; Slawin, A. M. Z.; Jacobsen, H.; Cavallo, L.; Cazin, C. S. J. ACS Catal. 2015, 5, 3932−3939. (34) Consistent with recent studies (see ref 17), the sequence of the Z double bonds in the polymer obtained by Ru-6d is largely atactic. (35) Zaja, M.; Connon, S. J.; Dunne, A. M.; Rivard, M.; Buschmann, N.; Jiricek, J.; Blechert, S. Tetrahedron 2003, 59, 6545−6558. (36) Sanford, M. S.; Love, J. A.; Grubbs, R. H. Organometallics 2001, 20, 5314−5314. (37) Anderson, D. R.; Hickstein, D. D.; O’Leary, D.; Grubbs, R. H. J. Am. Chem. Soc. 2006, 128, 8386−8387. (38) Kost, T.; Sigalov, M.; Goldberg, I.; Ben-Asuly, A.; Lemcoff, N. G. J. Organomet. Chem. 2008, 693, 2200−2203. (39) (a) Chapman, D. D.; Jones, E. T.; Wilgus, H. S., III; Nelander, D. H.; Gates, J. W., Jr. J. Org. Chem. 1965, 30, 1520−1523. (b) Lai, H.W.; Liu, Z.-Q. Eur. J. Med. Chem. 2014, 81, 227−236. (40) Mondal, S.; Basak, A.; Jana, S.; Anoop, A. Tetrahedron 2012, 68, 7202−7210. (41) Zhan, Z.−Y. J.Highly active metathesis catalysis selective for ROMP and RCM. U.S. Pat. Appl. US20110172381A1, Jan 8, 2010. (42) Endo, K.; Herbert, M. B.; Grubbs, R. H. Organometallics 2013, 32, 5128−5135. (43) Courchay, F. C.; Sworen, J. C.; Wagener, K. B. Macromolecules 2003, 36, 8231−8239. (44) For reviews of the application of DFT calculations to transitionmetal chemistry, see: (a) Cramer, C. J.; Truhlar, D. G. Phys. Chem. Chem. Phys. 2009, 11, 10757−10816. (b) Grimme, S.; Ehrlich, S.; Goerigk, L. J. Comput. Chem. 2011, 32, 1456−1465. (c) Peverati, R.; Truhlar, D. G. Philos. Trans. R. Soc., A 2014, 372, 20120476. (45) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; N

DOI: 10.1021/acs.organomet.6b00773 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, Ö .; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09, Revision D.01; Gaussian, Inc., Wallingford, CT, 2009. (46) (a) Becke, A. D. Phys. Rev. A: At., Mol., Opt. Phys. 1988, 38, 3098−3100. (b) Perdew, J. P.; Yue, W. Phys. Rev. B: Condens. Matter Mater. Phys. 1986, 33, 8800−8802. (47) (a) Andrae, D.; Haeussermann, U.; Dolg, M.; Stoll, H.; Preuss, H. Theor. Chim. Acta 1990, 77, 123−141. (b) Bergner, A.; Dolg, M.; Kuechle, W.; Stoll, H.; Preuss, H. Mol. Phys. 1993, 80, 1431−1441. (48) Scalmani, G.; Frisch, M. J. J. Chem. Phys. 2010, 132, 114110. (49) Chai, J.-D.; Head-Gordon, M. Phys. Chem. Chem. Phys. 2008, 10, 6615−6620. (50) Zhao, Y.; Truhlar, D. G. Acc. Chem. Res. 2008, 41, 157−167. (51) Peverati, R.; Truhlar, D. G. Phys. Chem. Chem. Phys. 2012, 14, 16187−16191. (52) Weigend, F.; Ahlrichs, R. Phys. Chem. Chem. Phys. 2005, 7, 3297−3305. (53) Marenich, A. V.; Cramer, C. J.; Truhlar, D. G. J. Phys. Chem. B 2009, 113, 6378−6396. (54) For selected examples highlighting the importance of including treatment of dispersion interactions in modeling olefin metathesis reactions promoted by Ru carbene complexes, see: (a) Ref 30g. (b) Minenkov, Y.; Occhipinti, G.; Singstad, A.; Jensen, V. R. Dalton Trans. 2012, 41, 5526−5541. (c) Ref 30i. (d) Ref 20c. (e) Ref 19b. (f) Ref 17. (55) Adamo, C.; Barone, V. J. Chem. Phys. 1999, 110, 6158−6169.

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DOI: 10.1021/acs.organomet.6b00773 Organometallics XXXX, XXX, XXX−XXX