Acrylate Metathesis via the Second-Generation Grubbs Catalyst: Unexpected Pathways Enabled by a PCy3-Generated Enolate

Article abstract of DOI:10.1021/jacs.5b04524

The diverse applications of acrylate metathesis range from synthesis of high-value α,β-unsaturated esters to depolymerization of unsaturated polymers. Examined here are unexpected side reactions promoted by the important Grubbs catalyst GII. Evidence is presented for attack of PCy₃ on the acrylate olefin to generate a reactive carbanion, which participates in multiple pathways, including further Michael addition, proton abstraction, and catalyst deactivation. Related chemistry may be anticipated whenever labile metal-phosphine complexes are used to catalyze reactions of substrates bearing an electron-deficient olefin.

Full text of DOI:10.1021/jacs.5b04524

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Communication
Acrylate Metathesis via the Second-Generation Grubbs Catalyst:
Unexpected Pathways Enabled by a PCy3-Generated Enolate
Gwendolyn A Bailey, and Deryn Elizabeth Fogg
J. Am. Chem. Soc., Just Accepted Manuscript • Publication Date (Web): 01 Jun 2015
Downloaded from http://pubs.acs.org on June 2, 2015
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Acrylate Metathesis via the Second-Generation Grubbs Catalyst:
Unexpected Pathways Enabled by a PCy3-Generated Enolate
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Gwendolyn A. Bailey and Deryn E. Fogg*
Center for Catalysis Research and Innovation and Department of Chemistry, University of Ottawa, Ottawa, Canada K1N6N5
Supporting Information Placeholder
An influential report by Meier and coꢀworkers described
50ꢀfold higher productivity for the Hoveyda catalyst HII
in oleate–acrylate CM, relative to the secondꢀgeneration
Grubbs catalyst GII (Chart 1).9,13 Related catalysts
(Zhan1B, M51) likewise show improved performance.14
Phosphineꢀfree catalysts are now the standard for acryꢀ
late metathesis applied to renewable feedstocks, altꢀ
hough GII remains commonly used in targetꢀdirected
synthesis of α βꢀunsaturated carbonyl derivatives.15
ABSTRACT: The diverse applications of acrylate meꢀ
tathesis range from synthesis of highꢀvalue α,βꢀ
unsaturated esters to depolymerization of unsaturated
polymers. Examined here are unexpected sideꢀreactions
promoted by the important Grubbs catalyst GII. Eviꢀ
dence is presented for attack of PCy3 on the acrylate
olefin to generate a reactive carbanion, which particiꢀ
pates in multiple pathways, including further Michael
addition, proton abstraction, and catalyst deactivation.
Related chemistry may be anticipated whenever labile
metalꢀphosphine complexes are used to catalyze reacꢀ
tions of substrates bearing an electronꢀdeficient olefin.
Chart 1. Key catalysts used in acrylate metathesis, and
the restingꢀstate species GIIm for the Grubbs catalyst.
Olefin metathesis offers powerful methodologies for the
synthesis of α,βꢀunsaturated carbonyl compounds.1ꢀ4
Highꢀprofile targets accessed via acrylate metathesis
range from the highꢀvalue antioxidant 1a to natural
products of medicinal relevance (Scheme 1).5,6 Crossꢀ
metathesis (CM) of acrylates with plantꢀoil triglycerides
or fatty acid esters is likewise key to the transformation
of unsaturated fats and oils into renewable platform
chemicals, including novel building blocks for highꢀ
performance surfactants.2ꢀ4,7 In materials applications,
related strategies have recently been deployed for depolꢀ
ymerization of polybutadiene,8 or, alternatively, assemꢀ
bly of bioꢀbased polyesters9 and polyamides.10ꢀ12
While several explanations for the superiority of phosꢀ
phineꢀfree catalysts have been advanced,16,17 the mechaꢀ
nistic basis remains speculative. Given the large number
of metathesis catalysts now based on the archetypal
structures GII and HII,18 and the limited understanding
of the factors governing relative performance, this sysꢀ
tem affords an important target for study. Here we
demonstrate that the performance of GII in acrylate meꢀ
tathesis is undermined by Michael addition pathways
enabled by free PCy3, which limit yields, promote sideꢀ
reactions, and cause catalyst decomposition. These findꢀ
ings offer informed insight into catalyst choice for acryꢀ
late metathesis. In the broader context, they highlight
hazards in the use of metalꢀphosphine complexes to
promote reactions of electronꢀdeficient olefins.
Scheme 1. Acrylate metathesis and selected products.
We recently noted that the excellent performance of HII
in acrylateꢀanethole metathesis is completely suppressed
by added PCy3 (Figure 1a).19 Here we use the combinaꢀ
tion of fastꢀinitiating HII and midꢀmetathesis addition of
PCy3 to simulate highlyꢀinitiated GII. By amplifying the
concentration of the metallacyclobutane (MCB) interꢀ
mediate relative to the offꢀcycle species GII and GIIm
which otherwise dominate, this experimental approach
permits us to dissect out the impact of PCy3 on the MCB
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intermediate: that is, on the active species central to the initial attack of PCy3 on the electronꢀdeficient olefin,
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olefin metathesis reaction.
forming zwitterionic A, which can participate in multiꢀ
ple subsequent pathways (Scheme 2). Ample precedent
exists for this phosphonium enolate, both in phosphineꢀ
catalyzed Michael reactions,22ꢀ25 and in the Moritaꢀ
BaylisꢀHillman reaction, in which A participates in furꢀ
ther nucleophilic attack on aldehyde substrates.26,27
To confirm that the rapid knockdown seen in Figure 1a
is due to the electronꢀwithdrawing ester moiety, we reꢀ
peated the reaction with styrene in the absence of acryꢀ
late (Figure 1b). Styrene was chosen in place of anethole
to ensure formation of the key methylidene species
GIIm (the dominant species observed on treating GII
with methyl acrylate), while subtracting esterꢀ
functionalized intermediates. In sharp contrast with the
acrylate experiment, the ultimate yield of stilbene 2 was
unaffected. That is, addition of PCy3 merely slowed the
reaction, by trapping the catalyst as the offꢀcycle species
GIIm and GII (ratio 2:3 at 0.5 h). This experiment pinꢀ
points the acrylate ester functionality as key to the deacꢀ
tivating effect of PCy3, and we therefore examined the
companion reaction, in which acrylate is retained but its
coupling partner is omitted.
Scheme 2. Proposed mechanism for acrylate-induced
catalyst decomposition (E = CO2Me).
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In the present context, the dominant reaction involves
attack of A on further acrylate, followed by proton abꢀ
straction to liberate [B]X. No reaction is seen in the abꢀ
sence of HII, indicating that the ruthenium species preꢀ
sent supplies the required proton and counterꢀanion.28
Chloride abstraction may provide the anion, given the
absence of additional signals in NMR spectra of isolated
B+. A metallacyclobutane (MCB) intermediate is sugꢀ
gested as the likely target of attack. We recently reported
that MCB intermediates formed during styrene metatheꢀ
sis are rapidly deprotonated by base, including amines.29
Competing attack on GIIm is not unequivocally excludꢀ
ed, but is sterically less favourable.
Coꢀformation of A+ indicates competing reaction of the
carbon nucleophile in A with a proton source. MCB speꢀ
cies are again candidates for attack. Adventitious water
is another, and indeed the proportion of A+ was inꢀ
creased on use of acrylate that was not dried over moꢀ
lecular sieves.30 Stronger acids promote this reaction:
thus, treating PCy3 with methyl acrylate in the presence
of HCl (Scheme 3) resulted in quantitative formation of
[A]Cl. This behaviour offers a new explanation for the
longꢀestablished capacity of phenols to improve the
productivity of the Grubbs catalysts in acrylate metatheꢀ
sis:31ꢀ35 in short, the phenol functions as a proton source,
protecting the catalyst.
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0
time (min)
0
time (min)
90
0
30
Figure 1. (a) Termination of CM by added PCy3 in aneꢀ
thole–acrylate CM. (b) Rate retardation by added PCy3
for CM in the absence of acrylate (0.5 mol% Ru, 70 °C,
C7H8).
In these experiments, HII and PCy3 were added to exꢀ
cess acrylate in C6D6, and the reaction was heated open
to N2 to permit ethylene loss.20 Periodic analysis reꢀ
vealed formation of the phosphonium salts B+ and A+, in
parallel with loss of HII and its PCy3 adduct HII’.21 The
simplicity of the 31P{1H} NMR spectrum (Figure 2b)
suggests that one decomposition process predominates.
(a)
100
(b)
31P{1H} NMR
HII + HII'
B+
B+
(82%)
A+
GIIm
(3%)
(5%)
Scheme 3. Formation of [A]Cl in the presence of HCl,
with no metal species present.
A+
0
0
5
time (h)
Figure 2. (a) Rate of loss of HII/HII’ (1H NMR analyꢀ
sis) and formation of phosphonium salts (31P NMR analꢀ
ysis); curve for GIIm omitted for clarity (<5%). (b)
31P{1H} NMR spectrum of the reaction mixture at 5 h.
The relevance of this chemistry to GII is supported by
analysis of the anethole–acrylate CM reaction shown in
We propose that the phosphonium salts are generated by
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Scheme 4a. Four species account for ca. 90% of the total
31P NMR integration at 1 h, and for the three major ESIꢀ
ACKNOWLEDGMENT
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8
This work was funded by NSERC of Canada. NSERC is
thanked for a CGSꢀD fellowship to GB. Nikita Panov is
thanked for technical assistance.
MS signals. Of these species, B+ and A+ account for
60%. The balance is due to the new diastereomers C+,
generated by attack of A on the re and si faces of methyl
fumarate (Scheme 4b). Fumarate formation is due in part
to the higher temperatures employed: C+ is likewise obꢀ
served at 70 °C in acrylate metathesis using the HII /
PCy3 system (16%, vs. <2% at 50 °C). Also notable is
the higher proportion of A+, which may suggest that
both the MCB and the restingꢀstate species GIIm are
deprotonated by A. Precedents for the accessibility of
the methylidene ligand of GIIm were noted above.17
REFERENCES
(1)
For recent reviews, see: (a) Prunet, J.; Grimaud, L., Crossꢀ
metathesis in Natural Products Synthesis. In Metathesis in Natural
Product Synthesis: Strategies, Substrates and Catalysts, Cossy, J.;
Arseniyadis, S.; Meyer, C., Eds. WileyꢀVCH: Weinheim, 2010; pp.
287–312. (b) van Lierop, B. J.; Lummiss, J. A. M.; Fogg, D. E., Ringꢀ
Closing Metathesis. In Olefin Metathesis-Theory and Practice, Grela,
K., Ed. Wiley: Hoboken, NJ, 2014; pp 85–152. (c) Żukowska, K.;
Grela, K., Cross Metathesis. In Olefin Metathesis-Theory and
Practice, Grela, K., Ed. Wiley: Hoboken, NJ, 2014; pp 39–84. For
tandem catalysis routes to heteroaromatics, beginning with metathesis
of vinyl ketones, see: (d) Donohoe, T. J.; Bower, J. F. Proc. Natl.
Acad. Sci. U.S.A. 2010, 107, 3373–3376. For an analysis of the
context and opportunities of these methodologies, see: (e) Krische, M.
J. Proc. Natl. Acad. Sci. U.S.A. 2010, 107, 3279–3280. For a tandem
intramolecularꢀhydroarylation sequence enabled by metathesis of α,βꢀ
unsaturated carbonyl compounds, see: (f) Chen, J.ꢀR.; Li, C.ꢀF.; An,
X.ꢀL.; Zhang, J.ꢀJ.; Zhu, X.ꢀY.; Xiao, W.ꢀJ. Angew. Chem. Int. Ed.
2008, 47, 2489–2492.
9
10
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12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
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46
47
48
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50
51
52
53
54
55
56
57
58
59
60
Scheme 4. (a) Decomposition of GII during anethole–
acrylate CM. (b) Formation of C+.
(2)
Chikkali, S.; Mecking, S. Angew. Chem., Int. Ed. 2012, 51,
5802−5808.
(3)
Biermann, U.; Bornscheuer, U.; Meier, M. A. R.; Metzger,
J. O.; Schafer, H. J. Angew. Chem. Int. Ed. 2011, 50, 3854–3871.
(4)
Marshall, A.ꢀL.; Alaimo, P. J. Chem. - Eur. J. 2010, 16,
4970ꢀ4980.
(5)
Lummiss, J. A. M.; Oliveira, K. C.; Pranckevicius, A.;
Santos, A.; dos Santos, E. N.; Fogg, D. E. J. Am. Chem. Soc. 2012,
134, 18889–18891.
The foregoing demonstrates that the superiority of HII
over GII in acrylate metathesis reactions is due to elimiꢀ
nation of reaction pathways triggered by the ancillary
PCy3 ligand. The potent nucleophilicity of the latter enꢀ
ables efficient reaction with electronꢀdeficient olefins,
leading to unwanted byproducts and to catalyst deactivaꢀ
tion. The wellꢀestablished versatility of nucleophilic
phosphines in organocatalysis points toward the broad
scope of this pathway. Substrates at risk, where a phosꢀ
phine ligand is liberated – whether in metathesis or other
catalytic chemistry – include those bearing α,βꢀ
unsaturated carbonyl and cyano functionalities, includꢀ
ing acrylates, acrylamides, acrylonitriles, and α,βꢀ
unsaturated ketones. In all of these cases, a phosphineꢀ
free catalyst is likely to offer the simplest means of
achieving the desired selectivity and catalyst productiviꢀ
ty.
(6)
For recent applications in the synthesis of natural products
of medicinal relevance, see: (a) Plummer, C. W.; Wei, C. S.;
Yozwiak, C. E.; Soheili, A.; Smithback, S. O.; Leighton, J. L. J. Am.
Chem. Soc. 2014, 136, 9878–9881; (b) Chatterjee, S.; Ghadigaonkar,
S.; Sur, P.; Sharma, A.; Chattopadhyay, S. J. Org. Chem. 2014, 79,
8067–8076; (c) Xiao, Q.; Jackson, J. J.; Basak, A.; Bowler, J. M.;
Miller, B. G.; Zakarian, A. Nature Chem. 2013, 5, 410–416; (d)
Willwacher, J.; Fürstner, A. Angew. Chem. Int. Ed. 2014, 53, 4217–
4221; (e) Fuwa, H.; Saito, A.; Sasaki, M. Angew. Chem. Int. Ed. 2010,
49, 3041–3044; (f) Brewitz, L.; Llaveria, J.; Yada, A.; Fürstner, A.
Chem. Eur. J. 2013, 19, 4532–4537.
(7)
Corma, A.; Iborra, S.; Velty, A. Chem. Rev. 2007, 107,
2411–2502.
(8)
Schulz, M. D.; Ford, R. R.; Wagener, K. B. Polym. Chem.
2013, 4, 3656–3658.
(9)
Rybak, A.; Meier, M. A. R. Green Chem. 2007, 9, 1356–
1361.
(10) Miao, X.; Fischmeister, C.; Dixneuf, P. H.; Bruneau, C.;
Dubois, J. L.; Couturier, J. L. Green Chem. 2012, 14, 2179–2183.
(11) Malacea, R.; Fischmeister, C.; Bruneau, C.; Dubois, J.ꢀL.;
Couturier, J.ꢀL.; Dixneuf, P. H. Green Chem. 2009, 11, 152–155.
(12) Winkler, M.; Meier, M. A. R. Green Chem. 2014, 16,
3335–3340.
(13) The superior performance of HII relative to GII for
acrylate metathesis has since been confirmed in multiple reports. See,
for example, Refs. 8, 10, and: (a) Schweitzer, D.; Snell, K. D. Org.
Process Res. Dev. 2015, Advance article. DOI: 10.1021/op5003006;
(b) Lafaye, K.; Nicolas, L.; Guérinot, A.; Reymond, S. b.; Cossy, J.
Org. Lett. 2014, 16, 4972−4975; (c) Meng, X.; Matson, J. B.; Edgar,
K. J. Biomacromolecules 2014, 15, 177–187; (d) Bilel, H.; Hamdi,
N.; Zagrouba, F.; Fischmeister, C.; Bruneau, C. Green Chem. 2011,
13, 1448–1452; (e) Djigoué, G. B.; Meier, M. A. R. Appl. Catal. A
2009, 368, 158ꢀ162.
ASSOCIATED CONTENT
Supporting Information. Experimental procedures and
NMR spectra. This material is available free of charge via
the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
* Email dfogg@uottawa.ca.
Notes
The authors declare no competing financial interest.
(14) See, for example, Refs. 10, 13a,dꢀe, and: (a) Vignon, P.;
Vancompernolle, T.; Couturier, J.ꢀL.; Dubois, J.ꢀL.; Mortreux;
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Gauvin, R. M. ChemSusChem 2015, 8, 1143–1146; (b) Ho, T. T.;
multiplicity of the 13C{1H} NMR signal for PCH2 (C5: 17.5 ppm, d,
Jacobs, T.; Meier, M. A. R. ChemSusChem 2009, 2, 749–754.
(15) For selected noteworthy examples, see: Refs. 1a, 6e, and:
(a) Cash, B. M.; Prevost, N.; Wagner, F. F.; Comins, D. L. J. Org.
Chem. 2014, 79, 5740–5745; (b) Kinzurik, M. I.; Hristov, L. V.;
Matsuda, S. P. T.; Ball, Z. T. Org. Lett. 2014, 16, 2188–2191; (c)
Beemelmanns, C.; Gross, S.; Reissig, H.ꢀU. Chem. Eur. J. 2013, 19,
17801–17808; (d) Trost, B. M.; Aponick, A.; Stanzl, B. N. Chem.
Eur. J. 2007, 13, 9547–9560; (e) Marjanovic, J.; Kozmin, S. A.
Angew. Chem. Int. Ed. 2007, 46, 8854–8857. Additional examples
appear in a recent review of RCM methods for the synthesis of
lactones from acrylates. See: (f) Bassetti, M. D. A., Andrea Curr.
Org. Chem. 2013, 17, 2654–2677.
(16) Early suggestions centered on the limited capacity of the
electronꢀdeficient olefin to compete with PCy3 for binding to the
metal. See: (a) Love, J. A.; Morgan, J. P.; Trnka, T. M.; Grubbs, R. H.
Angew. Chem. Int. Ed. 2002, 41, 4035–4037. (b) Hoveyda, A. H.;
Gillingham, D. G.; Van Veldhuizen, J. J.; Kataoka, O.; Garber, S. B.;
Kingsbury, J. S.; Harrity, J. P. A. Org. Biomol. Chem. 2004, 2, 8–23.
Conversely, excessively strong binding of PCy3 to electronꢀdeficient
Ru intermediates has been proposed: see Ref. (b).
(17) Also potentially plausible is nucleophilic attack of PCy3 on
the electronꢀdeficient alkylidene, by analogy to the pathway
established for the methylidene complexes RuCl2(L)(PCy3)(=CH2).
Crystallographic evidence demonstrating attack of PCy3 on the
methylidene ligand was recently reported. See: (a) Lummiss, J. A. M.;
McClennan, W. L.; McDonald, R.; Fogg, D. E. Organometallics
2014, 33, 6738–6741. Abstraction of the methylidene moiety from
isolated GIIm liberates [MePCy3]Cl. See: (b) Hong, S. H.; Wenzel,
A. G.; Salguero, T. T.; Day, M. W.; Grubbs, R. H. J. Am. Chem. Soc.
2007, 129, 7961–7968. For evidence of this pathway during catalysis,
see: (c) Lummiss, J. A. M.; Ireland, B. J.; Sommers, J. M.; Fogg, D.
E. ChemCatChem 2014, 6, 459–463. While nucleophilic attack of
phosphine on Ruꢀalkylidene species is rare, Diver has demonstrated
such a pathway where CO binding rendered the alkylidene carbon
more electrophilic. See: Galan, B. R.; Pitak, M.; Keister, J. B.; Diver,
S. T. Organometallics 2008, 27, 3630–3632.
1JPC = 44 Hz; see SI). This signal exhibits the expected HMQC
correlation to two diastereotopic methylene protons (δ 2.84, ddd, JHH
= 16 Hz, 2JPH = 12 Hz, JHH = 10 Hz, 1H; δ 2.35, m, 1H). The 13C{1H}
NMR doublet at 38.2 for the PCH2CH methine carbon also exhibits
the expected HMBC correlations with the adjacent methylene protons
(H5, H9, and H10); see SI.
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(22) Fan, Y. C.; Kwon, O. Chem. Commun. 2013, 49, 11588–
11619.
(23) Methot, J. L.; Roush, W. R. Adv. Synth. Catal. 2004, 346,
1035–1050.
(24) Gimbert, C.; Lumbierres, M.; Marchi, C.; MorenoꢀMañas,
M.; Sebastián, R. M.; Vallribera, A. Tetrahedron 2005, 61, 8598–
8605.
(25) GómezꢀBengoa, E.; Cuerva, J. M.; Mateo, C.; Echavarren,
A. M. J. Am. Chem. Soc. 1996, 118, 8553–8565.
(26) Morita, K.ꢀI.; Suzuki, Z.; Hirose, H. Bull. Chem. Soc.
Japan 1968, 41, 2815–2815.
(27) Basavaiah, D.; Rao, A. J.; Satyanarayana, T. Chem. Rev.
2003, 103, 811–892.
(28) The Ru center may also act as a Lewis acid, complexing
the carbonyl group of A, and thus favouring subsequent Michael
addition reactions. Such behaviour was reported for a related Ruꢀ
hydride complex. See Ref. 25.
(29) Ireland, B. J.; Dobigny, B. T.; Fogg, D. E. ACS Catal.
2015, submitted.
(30) The phenol inhibitors present in methyl acrylate are not
significant contributors. The maximum level of 100 ppm 4ꢀ
methoxyphenol cited in the supplier’s specification sheet (Sigmaꢀ
Aldrich; 99% purity reagent) would account for just 0.5% yield of A+.
(31) Adding a phenol (the renewable phenol guaiacol) to the
reaction resulted in selective formation of [A]Cl: see SI.
(32) Forman, G. S.; Tooze, R. P. J. Organomet. Chem. 2005,
690, 5863–5866.
(33) Forman, G. S.; McConnell, A. E.; Tooze, R. P.; Van
Rensburg, W. J.; Meyer, W. H.; Kirk, M. M.; Dwyer, C. L.;
Serfontein, D. W. Organometallics 2005, 24, 4528–4542.
(34) Schmidt, B.; Hauke, S. Org. Biomol. Chem. 2013, 11,
4194–4206.
(35) Scavenging of phosphine offers an alternative solution. CuI
has recently been employed to enhance yields in GIIꢀpromoted
acrylate metathesis. See: (a) Nair, R. N.; Bannister, T. D. J. Org.
Chem. 2014, 79, 1467–1472; (b) Voigtritter, K.; Ghorai, S.; Lipshutz,
B. H. J. Org. Chem. 2011, 76, 4697–4702. As expected, adding CuI
during the anetholeꢀacrylate CM reaction completely suppressed
formation of the phosphonium salts. Instead visible in the 31P{1H}
NMR spectrum were a sharp singlet for [MePCy3]Cl (34.0 ppm) and a
broad singlet at 12.89 ppm, likely corresponding to a copperꢀ
phosphine adduct.
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(18) (a) Vougioukalakis, G.C. RutheniumꢀBenzylidene Olefin
Metathesis Catalysts. In Olefin Metathesis-Theory and Practice,
Grela, K., Ed. Wiley: Hoboken, NJ, 2014; pp 397–416. (b) Ginzburg,
Y.; Lemcoff, N. G. HoveydaꢀType Olefin Metathesis Complexes. In
Olefin Metathesis-Theory and Practice, Grela, K., Ed. Wiley:
Hoboken, NJ, 2014; pp 437–451.
(19) Bates, J. M.; Lummiss, J. A. M.; Bailey, G. A.; Fogg, D. E.
ACS Catal. 2014, 4, 2387−2394.
(20) These experiments were carried out at 50 °C, to permit
interception of lowꢀenergy organometallic pathways, rather than
downstream events. At higher temperatures, attack of A on additional
CM products is observed; see text.
(21) The cation B+ was identified by mass spectrometric and
NMR analysis of material isolated by aqueous extraction. The cation
is unperturbed by isolation, as confirmed by spiking a reaction aliquot
with the isolated salt and assessing the 31P{1H} NMR spectrum.
Diagnostic for the structure of B+ is the upfield location and doublet
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