A New Route to Ruthenium Thiolate Alkylidene Complexes

Figure 1. POV-ray depiction of the molecular structure of 1: Ru, dark green; S, yellow; O, red; Cl, green; N, aquamarine; C, black. H atoms are omitte...
0 downloads 0 Views 580KB Size
Download PDF
Communication pubs.acs.org/Organometallics

A New Route to Ruthenium Thiolate Alkylidene Complexes Fatme Dahcheh and Douglas W. Stephan* Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario, Canada M5S 3H6 S Supporting Information *

A BS T R A CT : ( I m ( O Me ) 2 ) ( S I M e s ) ( P P h 3 ) R u H C l ( I m ( O M e ) 2 = (C3H2(NCH2CH2OMe)2) reacts with aryl vinyl sulfides (PhSCHCH2 and (C6F5)SCHCHPh) to give the Ru thiolate alkylidene complexes (Im(OMe)2)(SIMes)(PhS)RuCl(CHCH3) and (Im(OMe)2)(SIMes)(F5C6S)RuCl( CHCH2Ph), which are shown to be effective olefin metathesis catalysts upon activation with BCl3.

O

conversion of Ru hydride species to Ru alkylidene species employing aryl vinyl sulfides.17 This provides a safe and cheap route to thiolate-containing Ru alkylidene species. Reaction of (Im(OMe)2)(SIMes)(PPh3)RuHCl16 with phenyl vinyl sulfide in CH2Cl2, for 4 h at room temperature, gave the new red solid 1 in 92% yield (Scheme 1). The 1H NMR of

lefin metathesis has become a synthetic tool for the modification of organic substrates that is exploited across the discipline in natural product synthesis, polymer, pharmaceutical, and industrial chemistry.1 Catalysts based on W and Mo developed by Schrock and co-workers show superb activities, and recent advances have improved their functional group tolerance.2 Nonetheless, they are used to a lesser extent in industrial applications. Indeed, the commercially available Grubbs catalysts, (Cy3P)2Cl2RuCHPh and (Cy3P)Cl2RuCHPh(SIMes), are most commonly employed.3 Since their discovery, efforts to modify the catalysts to improve activity and stability have been pursued. Such efforts have employed a variety of strategies, including replacement of phosphine donors with Nheterocyclic carbenes (NHCs),4 tuning the NHCs, and functionalizing the alkylidene to incorporate pendant donors (Hoveyda−Grubbs).5 Several modifications to the anionic ligands have also been reported.5a For example, Fogg and coworkers6 have developed active systems in which the halides are replaced with either mono- or bidentate aryloxide ligands. In seeking avenues to new metathesis catalysts, a key facet involves strategies to install Ru alkylidene moieties. The variety of known methods have been comprehensively reviewed by Fogg and Foucault.7 These include reactions of cyclopropene,8 sulfur ylides,9 dihalomethanes,10 and diazomethanes.11 Alternatively, reactions of Ru synthons with alkynes, propargyl chlorides,6a,12 and propargyl alcohols13 offer routes to Ru-based complexes incorporating allenylidene, indenylidene,14 vinylidene,10c or cumulenylidene15 fragments. While these developments offer interesting variants, these strategies are generally more expensive and yield less active catalysts. As a result, the use of diazomethane remains the most commonly used method for installing alkylidene fragments, in spite of the problematic nature of diazomethanes. In initiating our efforts to uncover new routes to alkylidenes, we have focused our attention on the reactivity of a Ru bis-carbene hydride complex, which we have previously shown to be a selective hydrogenation catalyst.16 Herein, we describe a new synthetic route for the facile © XXXX American Chemical Society

Scheme 1. Synthesis of 1 and 2

1 revealed signals arising from carbene and thiolate ligands as well as a broad singlet at 18.29 ppm corresponding to one proton and assigned to the RuCH fragment. The corresponding carbon signal was seen at 313.7 ppm. A singlecrystal X-ray analysis of compound 1 confirmed the formulation as (Im(OMe)2)(SIMes)(PhS)RuCl(CHCH3) (Figure 1). The geometry at the metal center is distorted square pyramidal in nature. Unlike the precursor, but similar to related biscarbene complexes,4 the two carbenes are positioned trans to each other with a C−Ru−C angle of 158.23(6)°. The two anionic groups are also in a trans disposition, with the Received: July 26, 2013

A

dx.doi.org/10.1021/om400740p | Organometallics XXXX, XXX, XXX−XXX

Organometallics

Communication

Figure 1. POV-ray depiction of the molecular structure of 1: Ru, dark green; S, yellow; O, red; Cl, green; N, aquamarine; C, black. H atoms are omitted for clarity.

Figure 2. POV-ray depiction of the molecular structure of 2: Ru, dark green; S, yellow; O, red; Cl, green; N, aquamarine; F, deep pink; C, black. H atoms are omitted for clarity.

alkylidene fragment occupying the pseudoaxial position. The Ru−C distances for the NHCs were found to be 2.084(2) Å and 2.100(2) Ǻ for SIMes and (Im(OMe)2), respectively, while the Ru−C distance for the alkylidene was found to be 1.820(2) Ǻ . The corresponding Ru−Cl distance was found to be 2.4744(4) Ǻ , while the Ru−S distance was found to be 2.3595(5) Ǻ . Interestingly, efforts to utilize this method to react (Im(OMe)2)(PPh3)2RuHCl16 or (PPh3)3RuHCl with vinyl sulfides did not afford alkylidene complexes. However, the addition of pentafluorophenyl benzyl sulfide to a solution of (Im(OMe)2)(SIMes)(PPh3)RuHCl in C6H5Br at room temperature gave rise to a brown solution upon stirring overnight. Isolation of compound 2 as a pink-red solid was achieved in 70% yield (Scheme 1). The 1H NMR spectrum of 2 revealed a doublet of doublets at 15.65 ppm with coupling constants of 8 and 3 Hz. This signal integrates to one proton and was assigned to the RuCH fragment. The corresponding carbon signal for this fragment was identified via 2-D NMR experiments (HSQC) and was found at 309.6 ppm. The 19F{1H} NMR spectrum of 2 showed five signals, indicating a dissymmetric environment for the (C6F5)S moiety. A single-crystal X-ray analysis of compound 2 confirmed the formulation as (Im(OMe)2)(SIMes)(F5C6S)RuCl(CHCH2Ph), where the geometry around the metal center is best described as distorted square pyramidal. In contrast to 1, the two carbenes adopt a cis arrangement (Figure 2), similar to that observed in previous compounds when a tridentate bis-carbene ligand is used.18 The SIMes ligand is trans to the chloride, whereas the Im(OMe)2 carbene is trans to the thiolate moiety. The alkylidene occupies the pseudoaxial position of the square-pyramidal coordination sphere. The Ru−C distances for the NHCs were found to be 2.047(4) ́ and 2.062(4) Ǻ for SIMes and Im(OMe) 2 , respectively, while the Ru−C distance for the alkylidene was found to be 1.815(4) Ǻ . The corresponding Ru−Cl distance was found to be 2.4660(9) Ǻ , while the Ru−S distance was found to be 2.360(1) Ǻ . This route follows a general insertion−elimination pathway where initial insertion of olefin into the Ru−H followed by αthiolate migration to the Ru center allows for the generation of the Ru alkylidene. This methodology of reaction of a Ru−H with a vinyl sulfide is reminiscent of a report by Caulton and co-workers,19 in which they demonstrate that the reaction of

vinyl chloroformate converts Ru−H species into Ru ethylidene complexes with concurrent loss of CO2. It also brings to mind the work of Grubbs and co-workers in which the reactions of alkenyl chlorides12a with Ru hydride complexes yield reactive alkylidenes, although it is noteworthy that this avenue generates a number of byproducts, making this route not very synthetically useful. The present route, described herein, provides the incorporation of both a thiolate ligand and an alkylidene fragment. This synthetic route is particularly intriguing in light of recent work from Jensen and co-workers,20 who have shown that an Ru thiolate derivative affords a highly Z-selective olefin metathesis catalyst. The utility of 1 and 2 as metathesis catalysts was assessed by employing standard metathesis tests,21 including ring-opening metathesis polymerization (ROMP) of 1,5-cyclooctadiene, ring-closing metathesis (RCM) of diethyl diallylmalonate, and cross-metathesis (CM) of 5-hexenyl acetate with methyl acrylate. Compound 1 was ineffective as a catalyst for these transformations at room temperature; however, it did catalyze ROMP at 45 °C, producing 93% conversion after 24 h. On the other hand, compound 2 is more active, catalysis of ROMP yielding 79% conversion at room temperature after 24 h and 93% conversion after 6 h at 45 °C. Nonetheless, this species was only marginally operative in RCM and inactive in CM under similar conditions. Interestingly, the addition of 1 equiv of BCl3 to 1 resulted in increased activity in ROMP, affording 100% product yield after 6 h at room temperature. This reaction was accelerated at 45 °C, affording 98% conversion after 2 h. In the case of RCM, similar BCl3 addition resulted in an 88% yield of product at 45 °C after 24 h, whereas for CM under similar conditions, conversions to the heterocoupled product was 53% with some homocoupled product observed. Similarly, addition of 1 equiv of BCl3 to 2 resulted in increased activity in ROMP, yielding 100% product conversions after 8 h at room temperature and 100% after 30 min at 45 °C. RCM conversions are increased to 93% after 24 h at room temperature and 100% after 2 h at 45 °C, while for CM, 50% conversion to the heterocoupled product is seen after 4 h at 45 °C. B

dx.doi.org/10.1021/om400740p | Organometallics XXXX, XXX, XXX−XXX

Organometallics

Communication

11882−11883. (c) Monfette, S.; Fogg, D. E. Organometallics 2006, 25, 1940−1944. (d) Monfette, S.; Camm, K. D.; Gorelsky, S. I.; Fogg, D. E. Organometallics 2009, 28, 944−946. (7) Fogg, D. E.; Foucault, H. M. Comprehensive Organometallic Chemistry II; Wiley: New York, 2007; pp 623−652 (8) (a) Binger, P.; Muller, P.; Benn, R.; Mynott, R. Angew. Chem., Int. Ed. 1989, 28, 610−611. (b) Gagne, M. R.; Grubbs, R. H.; Feldman, J.; Ziller, J. W. Organometallics 1992, 11, 3933−3935. (c) Nguyen, S. T.; Johnson, L. K.; Grubbs, R. H.; Ziller, J. W. J. Am. Chem. Soc. 1992, 114, 3974−3975. (9) Gandelman, M.; Rybtchinski, B.; Ashkenazi, N.; Gauvin, R. M.; Milstein, D. J. Am. Chem. Soc. 2001, 123, 5372−3. (10) (a) Belderrain, T. R.; Grubbs, R. H. Organometallics 1997, 16, 4001−4003. (b) Olivan, M.; Caulton, K. G. Inorg. Chem. 1999, 38, 566−570. (c) Wolf, J.; Stuer, W.; Grunwald, C.; Werner, H.; Schwab, P.; Schulz, M. Angew. Chem., Int. Ed. 1998, 37, 1124−1126. (11) Schwab, P.; Grubbs, R. H.; Ziller, J. W. J. Am. Chem. Soc. 1996, 118, 100−110. (12) (a) Wilhelm, T. E.; Belderrain, T. R.; Brown, S. N.; Grubbs, R. H. Organometallics 1997, 16, 3867−3869. (b) Volland, M. A. O.; Rominger, F.; Eisentrager, F.; Hofmann, P. J. Organomet. Chem. 2002, 641, 220−226. (13) Dorta, R.; Kelly, R. A.; Nolan, S. P. Adv. Synth. Catal. 2004, 346, 917−920. (14) (a) Castarlenas, R.; Fischmeister, C.; Bruneau, C.; Dixneuf, P. H. J. Mol. Catal.: Chem. 2004, 213, 31−37. (b) Fürstner, A.; Guth, O.; Duffels, A.; Seidel, G.; Liebl, M.; Gabor, B.; Mynott, R. Chem. Eur. J. 2001, 7, 4811−4820. (15) Louie, J.; Grubbs, R. H. Angew. Chem., Int. Ed. 2001, 40, 247− 249. (16) (a) Lund, C. L.; Sgro, M. J.; Cariou, R.; Stephan, D. W. Organometallics 2012, 31, 802−805. (b) Wang, T. E.; Pranckevicius, C.; Lund, C. L.; Sgro, M. J.; Stephan, D. W. Organometallics 2013, 32, 2168−2177. (17) Dahcheh, F.; Lund, C. L.; Sgro, M. J.; Stephan, D. W. Multidentate Carbene-Ru-Based Metathesis Catalysts. May 24, 2013. (18) Lund, C. L.; Sgro, M. J.; Stephan, D. W. Organometallics 2012, 31, 580−587. (19) Ferrando, G.; Coalter, J. N.; Gerard, H.; Huang, D. J.; Eisenstein, O.; Caulton, K. G. New J. Chem. 2003, 27, 1451−1462. (20) Occhipinti, G.; Hansen, F. R.; Tornroos, K. W.; Jensen, V. R. J. Am. Chem. Soc. 2013, 135, 3331−4. (21) Ritter, T.; Hejl, A.; Wenzel, A. G.; Funk, T. W.; Grubbs, R. H. Organometallics 2006, 25, 5740−5745. (22) Hartman, J. S.; Yuan, Z.; Fox, A.; Nguyen, A. Can. J. Chem. 1996, 74, 2131−2142. (23) Hansen, S. M.; Volland, M. A. O.; Rominger, F.; Eisentrager, F.; Hofmann, P. Angew. Chem., Int. Ed. 1999, 38, 1273−1276. (24) McKinty, A. M.; Lund, C.; Stephan, D. W. Organometallics 2013, 17, 4730−4732.

The role of BCl3 as an activator was probed. Monitoring reactions of 1 or 2 with BCl3 by 11B NMR spectroscopy showed resonances at 6.9 ppm attributable to the formation of the [BCl4] anion.22 Nonetheless, efforts to either isolate the corresponding cation or its complex with a series of donor molecules were unsuccessful. In spite of this, these data suggest that the borane abstracts the halide to generate a site of unsaturation on Ru, presumably accounting for the enhanced catalytic activity. Similarly, halide abstraction has been used with Ru alkylidene precursors to enhance metathesis activity, as was demonstrated by Hofmann and co-workers.23 In addition, it is noteworthy that we have recently documented the activation of Ru dithiolate alkylidene complexes with BCl3, where halide abstraction yields the activate catalyst.24 In conclusion, we have reported a safe, high-yielding, and cheap route to thiolate-containing Ru alkylidene species starting with Ru hydride complexes. These species were shown to yield moderately active metathesis catalysts upon activation with BCl3. Nonetheless, this finding offers a new strategy to Ru alkylidenes, and we are continuing to probe the generality of this route and explore the reactivity of these species in olefin metathesis. The results of these studies will be reported in due course.

■

ASSOCIATED CONTENT

* Supporting Information S

Text, tables, figures, and CIF files giving synthetic methods and spectroscopic, catalytic and crystallographic data. This material is available free of charge via the Internet at http://pubs.acs.org.

■

AUTHOR INFORMATION

Corresponding Author

*E-mail for D.W.S.: [email protected]. Notes

The authors declare no competing financial interest.

■ ■

ACKNOWLEDGMENTS We are grateful for the support of the NSERC of Canada, and D.W.S. acknowledges the support of a Canada Research Chair. REFERENCES

(1) (a) Van de Weghe, P.; Eustache, J.; Cossy, J. Curr. Top. Med. Chem. 2005, 5, 1461−1472. (b) Bielawski, C. W.; Grubbs, R. H. Prog. Polym. Sci. 2007, 32, 1−29. (c) Grubbs, R. H. Angew. Chem., Int. Ed. 2006, 45, 3760−3765. (d) Schrock, R. R. Angew. Chem., Int. Ed. 2006, 45, 3748−3759. (2) Sinha, A.; Schrock, R. R. Organometallics 2004, 23, 1643−1645. (3) (a) Schwab, P.; France, M. B.; Ziller, J. W.; Grubbs, R. H. Angew. Chem., Int. Ed. 1995, 34, 2039−2041. (b) Scholl, M.; Ding, S.; Lee, C. W.; Grubbs, R. H. Org. Lett. 1999, 1, 953−956. (4) (a) Weskamp, T.; Schattenmann, W. C.; Spiegler, M.; Herrmann, W. A. Angew. Chem., Int. Ed. 1998, 37, 2490−2493. (b) Trnka, T. M.; Morgan, J. P.; Sanford, M. S.; Wilhelm, T. E.; Scholl, M.; Choi, T. L.; Ding, S.; Day, M. W.; Grubbs, R. H. J. Am. Chem. Soc. 2003, 125, 2546−58. (c) Vorfalt, T.; Leuthausser, S.; Plenio, H. Angew. Chem., Int. Ed. 2009, 48, 5191−4. (d) Sashuk, V.; Peeck, L. H.; Plenio, H. Chem. Eur. J. 2010, 16, 3983−93. (e) Bantreil, X.; Randall, R. A. M.; Slawin, A. M. Z.; Nolan, S. P. Organometallics 2010, 29, 3007−3011. (5) (a) Vougioukalakis, G. C.; Grubbs, R. H. Chem. Rev. 2010, 110, 1746−87. (b) Garber, S. B.; Kingsbury, J. S.; Gray, B. L.; Hoveyda, A. H. J. Am. Chem. Soc. 2000, 122, 8168−8179. (6) (a) Conrad, J. C.; Amoroso, D.; Czechura, P.; Yap, G. P. A.; Fogg, D. E. Organometallics 2003, 22, 3634−3636. (b) Conrad, J. C.; Parnas, H. H.; Snelgrove, J. L.; Fogg, D. E. J. Am. Chem. Soc. 2005, 127, C

dx.doi.org/10.1021/om400740p | Organometallics XXXX, XXX, XXX−XXX