Generation and spectroscopic characterization of ruthenacyclobutane and ruthenium olefin carbene intermediates relevant to ring closing metathesis catalysis

Article abstract of DOI:10.1021/ja710364e

The reaction of phosphonium alkylidenes [(H₂IMes)RuCl ₂=CHPR₃]⁺[A]^- (R = C ₆H₁₁, A = OTf or B(C₆F₅) ₄, 1-Cy; R = i-C₃H₇, A = CIB(C ₆F₅)₃ or OTf, 1-ⁱPr) with 1 equiv of ethylene at -78°C, in the presence of 2-3 equiv of a trapping olefin substrate, yields intermediates relevant to olefin metathesis catalytic cycles. Dimethyl cyclopent-3-ene-1,1-dicarboxylate gives solutions of a substituted ruthenacy-clobutane 3 of relevance to ring closing metathesis catalysis. ¹H and ¹³C NMR data are fully consistent with its assignment as a ruthenacyclobutane, but ¹J_CC values of 23 Hz for the C_αH₂-C_β bond and 8.5 Hz for the C_αH-C_β bond point to an unsymmetrical structure in which the latter bond is more activated than the former. In contrast, trapping with acenaphthylene leads to an olefin carbene complex (6) in which the putative ruthenacyclobutane has opened; this species was also fully characterized by NMR spectroscopy and compared to related species reported previously.

Full text of DOI:10.1021/ja710364e

Published on Web 03/06/2008
Generation and Spectroscopic Characterization of
Ruthenacyclobutane and Ruthenium Olefin Carbene
Intermediates Relevant to Ring Closing Metathesis Catalysis
Edwin F. van der Eide, Patricio E. Romero, and Warren E. Piers*
Department of Chemistry, UniVersity of Calgary, 2500 UniVersity DriVe NW,
Calgary, Canada T2N 1N4
Received November 15, 2007; E-mail: wpiers@ucalgary.ca
Abstract: The reaction of phosphonium alkylidenes [(H2IMes)RuCl2dCHPR3]+[A]- (R ) C6H11, A ) OTf
or B(C6F5)4, 1-Cy; R ) i-C3H7, A ) ClB(C6F5)3 or OTf, 1-iPr) with 1 equiv of ethylene at -78 °C, in the
presence of 2-3 equiv of a trapping olefin substrate, yields intermediates relevant to olefin metathesis
catalytic cycles. Dimethyl cyclopent-3-ene-1,1-dicarboxylate gives solutions of a substituted ruthenacy-
1
clobutane 3 of relevance to ring closing metathesis catalysis. H and 13C NMR data are fully consistent
1
with its assignment as a ruthenacyclobutane, but JCC values of 23 Hz for the CRH2-Câ bond and 8.5 Hz
for the CRH-Câ bond point to an unsymmetrical structure in which the latter bond is more activated than
the former. In contrast, trapping with acenaphthylene leads to an olefin carbene complex (6) in which the
putative ruthenacyclobutane has opened; this species was also fully characterized by NMR spectroscopy
and compared to related species reported previously.
terization of olefin-carbene complexes,5 but an alternative
Introduction
option for circumvention of this issue was provided by the
Olefin metathesis as catalyzed by ruthenium-based mediators
developed by Grubbs1 and others2 is one of today’s most
versatile chemical reactions, with applications in diverse areas
of chemistry.3 Although there is a relatively sophisticated
understanding of the mechanism by which these catalysts
operate,4 details concerning the actual structures of key inter-
mediates in the catalytic cycle are still emerging. It is important
to determine these details accurately as they inform further
catalyst designs aimed at providing more active, longer lived
and more selective catalysts.
discovery of a related family of catalysts, 1,9 in which a 14
electron phosphonium alkylidene serves as the catalyst precursor
to metathesis. One metathesis event provides access to the
unsaturated intermediates relevant to the Grubbs catalyst
systems, and the phosphine is effectively sequestered in the
vinylphosphonium byproduct, allowing for direct observation
of, for example, the parent ruthenacyclobutane (2) intermediate
via stoichiometric reactions of 1 with ethylene.
Of particular interest are the structures of unsaturated olefin-
carbene5,6 and ruthenacyclobutane7 intermediates. Until recently,
direct observation of these species has been hampered by the
fact that they are generated in the presence of excess PR3,
produced in the initiation step of the process.4 Use of weaker,
more labile donors such as pyridine8 has allowed for charac-
(1) Schwab, P.; Grubbs, R. H.; Ziller, J. W. J. Am. Chem. Soc. 1996, 118,
100.
While this breakthrough provided important insights into the
structure of this family of intermediates, it is desirable to obtain
structuralandspectroscopicdataonsubstitutedruthenacyclobutanes7c
of more direct relevance to productive metathesis reactions. To
this end, we have studied the reactions of catalysts 1 with olefins
germane to the ring closing metathesis (RCM) reaction,10 with
a view toward generating and characterizing more complex
metathesis intermediates. The efficient generation of substituted
(2) (a) Kingsbury, J. S.; Harrity, J. P. A.; Bonitatebus, P. J., Jr.; Hoveyda, A.
H. J. Am. Chem. Soc. 1999, 121, 791. (b) Wakamatsu, H.; Blechert, S.
Angew. Chem., Int. Ed. 2002, 41, 794. (c) Grela, K.; Harutyunyan, S.;
Michrowska, A. Angew. Chem., Int. Ed. 2002, 41, 4038. (d) Conrad, J. C.;
Parnas, H. H.; Snelgrove, J. L.; Fogg, D. E. J. Am. Chem. Soc. 2005, 127,
11882. (e) Bieniek, M.; Bujok, R.; Cabaj, M.; Lugan, N.; Lavigne, G.;
Arlt, D.; Grela, K. J. Am. Chem. Soc. 2006, 128, 13652.
(3) Grubbs, R. H., Ed. Handbook of Metathesis; Wiley-VCH: Weinheim,
Germany, 2003.
(4) (a) Sanford, M. S.; Love, J. A.; Grubbs, R. H. J. Am. Chem. Soc. 2001,
123, 6543. (b) Sanford, M. S.; Ulman, M.; Grubbs, R. H. J. Am. Chem.
Soc. 2001, 123, 749.
(5) Anderson, D. R.; Hickstein, D. D.; O’Leary, D. J.; Grubbs, R. H. J. Am.
Chem. Soc. 2006, 128, 8386.
(6) Tallarico, J. A.; Bonitatebus, P. J., Jr.; Snapper, M. L. J. Am. Chem. Soc.
1997, 119, 7157.
(7) (a) Romero, P. E.; Piers, W. E. J. Am. Chem. Soc. 2005, 127, 5032. (b)
Romero, P. E.; Piers, W. E. J. Am. Chem. Soc. 2007, 129, 1698. (c) Wenzel,
A. G.; Grubbs, R. H. J. Am. Chem. Soc. 2006, 128, 16048.
(8) Sanford, M. S.; Love, J. A.; Grubbs, R. H. Organometallics 2001, 20, 5314.
(9) (a) Romero, P. E.; Piers, W. E.; McDonald, R. Angew. Chem., Int. Ed.
2004, 43, 6161. (b) Dubberley, S. R.; Romero, P. E.; Piers, W. E.;
McDonald, R.; Parvez, M. Inorg. Chim. Acta 2006, 359, 2658.
(10) (a) Villemin, D. Tetrahedron Lett. 1980, 21, 1715. (b) Fu, G. C.; Grubbs,
R. H. J. Am. Chem. Soc. 1992, 114, 5426. (c) Fu, G. C.; Grubbs, R. H. J.
Am. Chem. Soc. 1992, 114, 7324.
9
10.1021/ja710364e CCC: $40.75 © 2008 American Chemical Society
J. AM. CHEM. SOC. 2008, 130, 4485-4491
4485

A R T I C L E S
Scheme 1
van der Eide et al.
Scheme 2
ruthenacyclobutanes of direct relevance to RCM required the
introduction of an even more rapidly initiating species than our
previously reported tricyclohexylphosphonium alkylidene 1-Cy.
Such a compound was found in the tri-iso-propyl-substituted
derivative 1-iPr.
Results
Complex 1-iPr was prepared by the same sequence of
reactions as employed for 1-Cy, starting from the PiPr3-
substituted analogue of the Grubbs generation 2 catalyst
(Scheme 1). Conversion to the carbide complex (H2IMes)(Cl)2-
(PiPr3)RutC was accomplished smoothly using Heppert’s
methodology.11 Protonation of the carbide using gaseous HCl
in CH2Cl2 triggered formation of the phosphonium alkylidene
1-iPr-Cl in which the chloride counteranion coordinates to the
Ru center to form the zwitterionic trichloride, analogous to the
tricyclohexylphosphonium alkylidene recently reported by
Johnson et al.12 These five-coordinate complexes are character-
h, it is the dominant ruthenium-containing product in the system;
3 never comprises more than 55-60% of the solution. This
observation suggests that the parent, unsubstituted ruthenacy-
clobutane, is more thermodynamically stable than substituted
derivatives and that the presence of free ethylene is detrimental
to the generation and stabilization of such compounds.
To minimize the amount of free ethylene in the system, we
developed a route to 3 that begins from the product of RCM
(dimethyl cyclopent-3-ene-1,1-dicarboxylate); here we use the
1
dimethyl ester to simplify H NMR spectra. The chemistry is
summarized in Scheme 2. The success of the experiment relies
on the fact that, at -78 °C, the RCM product exhibits low
reactivity with compounds 1; for R ) Cy, there is no reaction
at room temperature, while for R ) iPr, there is a slow reaction
to yield as yet uncharacterized products which effectively stops
at low temperatures. Therefore, it is possible to mix the RCM
product cyclopentene with 1-Cy or 1-iPr (generated from 1-iPr-
Cl and B(C6F5)3) prior to the introduction of 1 equiv of ethylene.
The ethylene reacts with compounds 1 to form the vinyl
trialkylphosphonium salt and, presumably, the 14 electron
ruthenium methylidene, I, which is not observed.14 Intermediate
I is then rapidly trapped by either ethylene to give 2 or
cyclopentene to yield 3. For 1-Cy, formation of the two products
is competitive, despite the excess of the RCM product, sug-
gesting that the rate of the initial reaction of ethylene with 1-Cy
is comparable to the conversion of I to 2/3. 1-iPr reacts with
ethylene at qualitatively much faster rates than 1-Cy, probably
because of the less sterically bulky phosphonium alkylidene;15
therefore, use of this faster initiator in this experiment results
in a 90% NMR yield of 3, the remaining 10% comprising mainly
2
ized by a somewhat larger JHP coupling constant for the
alkylidene proton (51 Hz for 1-iPr-Cl) than is typically
observed in the four-coordinate complexes (35-37 Hz).9
Complex 1-iPr-Cl was also characterized by X-ray crystal-
lography; full details are given in the Supporting Information.
The Ru-Cl distance for the chloride trans to the NHC ligand
(CNHC-Ru-Cltrans ) 165.04(9)°) is 2.4619(9) Å, more than 0.1
Å longer than the distances of ∼2.33 Å observed for the
chlorides cis to the NHC donor. Zwitterion 1-iPr-Cl is more
thermally stable than the 14 electron analogues where the anion
is weakly coordinating and is conveniently stored in this form
13
prior to activation with, for example, B(C6F5)3 (see below).
Compounds 1 rapidly catalyze the RCM of diethyl diallyl-
malonate at temperatures above 0 °C.9b At -60 °C, the catalytic
reaction is slowed, but phosphonium alkylidene 1-Cy reacts
slowly with an excess of the diolefin substrate to produce a
mixture of products, including [H2CdCHPCy3]+[A]- (charac-
terized by 31P NMR spectroscopy9) the parent, unsubstituted
metallacyclobutane, 2, and a new complex assigned as the
ruthenacyclobutane necessarily involved in this RCM reaction,
3 (Et instead of Me). However, even under these conditions,
the RCM reaction turns over, producing ethylene and cyclo-
pentene product, and the proportion of 2 rises until, after ∼10
(14) (a) We failed to detect a phosphonium-substituted ruthenacyclobutane
intermediate. Given that the vinyl trialkylphosphonium salts appear to be
inert as metathesis substrates, it seems likely that dissociation of this olefin
from the putative ruthenacyclobutane to give I is facile. Consistent with
this is the observation of small amounts of what we currently assign to be
a dimer of I and 1-iPr in addition to 2 in the reaction using 1-iPr in Scheme
2. This assignment is based on observations concerning chemical decom-
position pathways for compounds 114b and the observation of minor
alkylidene proton resonances in the 1H NMR spectra of 3. (b) Leitao, E.
M.; Piers, W. E. Unpublished results.
(11) Carlson, R. G.; Gile, M. A.; Heppert, J. A.; Mason, M. H.; Powell, D. R.;
Vander Velde, D.; Vilain, J. M. J. Am. Chem. Soc. 2002, 124, 1580.
(12) Macnaughtan, M. L.; Johnson, M. J. A.; Kampf, J. W. J. Am. Chem. Soc.
2007, 129, 7708.
(13) Piers, W. E. AdV. Organomet. Chem. 2005, 52, 1.
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4486 J. AM. CHEM. SOC. VOL. 130, NO. 13, 2008

Ruthenacyclobutane and Ru Olefin Carbene Intermediates
A R T I C L E S
reproduced in the CRH and CRH2 doublets,17 and the 8.5 Hz
coupling can thus be assigned to the most substituted CRCâ bond.
The analogous values for the all-carbon bicyclo[3.2.0]heptane
have been calculated by Krivdin18 to be 31 and 27 Hz (the latter
value is for the more substituted CC bond), so the 8.5 Hz
coupling is very small in comparison to the all-carbon bicyclic
ring system; indeed, this is a very low coupling for any C-C
single bond.19 Interestingly, the average of these two coupling
constants is close to the 15 Hz value observed in the sym-
metrically activated parent ruthenacyclobutane complex 2. 1JCH
values were also extracted from this labeling experiment: 167
Hz for CRH, 163 Hz for the CRH2 CH bonds, and 157 Hz for
CâH (cf. 165 Hz for CRH2 and 155 Hz for CâH2 in 2). These
coupling constants are quite large compared to those observed
in, for example, cyclobutane (134 Hz)20 but comparable to those
observed in parent complex 2 (155-164 Hz). The large
magnitude of these coupling constants is likely a consequence
of the kite-shaped geometry of the ruthenacyclobutane arising
from the C-CfRu agostic21 interactions present in these
systems. In any case, given their similarity to the 1JCH couplings
observed in ruthenium carbene olefin complexes,5,6 C-H
coupling constants do not appear to be a useful metric for
distinguishing these two limiting structures.
Figure 1. 13C{1H} NMR resonances for CRH, CRH2, and Câ of 3-13C3
(25%); the singlet at 87.2 ppm is 3-13C1 since CRH2 is 99% 13C labeled
and Câ is only 25% enriched.
2 plus small amounts of what we assign to be a dimer of I and
1-iPr14 (vide infra).
The development of this protocol for the generation of highly
enriched solutions of 3 has allowed us to comprehensively
characterize this species at -60 °C by NMR spectroscopy.
Metallaring 1H NMR signals for 3 were observed at 9.36 (CRH),
6.07, 5.90 (diastereotopic CRH2), and -2.15 (CâH) ppm and
are indicative of a ruthenacyclobutane structure (cf. 6.64, CRH,
and -2.64, CâH, ppm for 2).7a,b An HMQC experiment located
the corresponding 13C signals of CRH, CRH2, and CâH at 144.8,
87.2, and 23.7 ppm, respectively (cf. 94.0 and 2.1 ppm for 2).7a,b
This experiment also confirmed that the 6.07 and 5.90 ppm
resonances are due to the CRH2 group since both show a cross-
peak to the same carbon at 87.2 ppm.
Although most of the key chemical shifts of 3 are similar to
those of 2, both HR and CR of the methine carbon in 3 are shifted
significantly downfield in the 1H and 13C NMR spectra (by 2.72
and 50.8 ppm, respectively) in comparison to 2. Some downfield
shifting is expected upon substitution;16 for example, in the
R-methyl-substituted ruthenacyclobutane derived from 1-Cy and
propene, the CRH resonances appear at 7.76 ppm (proton) and
120.2 ppm (carbon).7c Nevertheless, the magnitude of the
perturbations for CRH in ruthenacyclobutane 3 suggests that they
arise from more than simply substitution and that the CRH-
CâH bond is more activated than the CRH2-CâH bond, rendering
CRH more carbene-like.
The skewed Câ to CR coupling constants in 3 imply a stronger
activation of the CRH-Câ bond than the less substituted CRH2-
Câ bond.22 It suggests that electronic effects are more important
than steric factors in dictating the strength of the C-C agostic
interactions within ruthenacyclobutanes prone to metathesis
activity. Consistent with these data, we have been unable to
detect dynamic exchange on the NMR time scale between CRH
and Câ as might be expected on the basis of the observed
behavior of 2, where CRH2 and CâH2 exchange rapidly on the
NMR time scale.7a,c Furthermore, the diastereotopic CRH2
protons in 3 also do not undergo exchange under these
conditions. If 3 was predisposed to cleave via path b in Scheme
3, these two exchange processes would be expected to be rapid
and observable; the lack of exchange on the NMR time scale
suggests that cleavage via path a is favored over b. In support
of this notion, reaction of 3 with 2 equiv of PMe3 at low
temperature results in rapid formation of the Grubbs-type
ruthenium carbene complex 423 (Scheme 3) in essentially
quantitative NMR yield (98% against an internal standard);24
no trace of the PMe3-stabilized methylidene complex expected
via trapping of the cleavage product arising from path b was
detected. A characteristic resonance at 17.74 ppm for the HR
This notion is supported by the observed one bond 13C-13C
coupling constants in 3, which were determined by preparing
13C3-3, labeled selectively in the three metallaring carbons
(Figure 1). This sample was generated according to Scheme 2,
using ethylene-1,2-13C2 (99%) and dimethyl cyclopent-3-ene-
1,1-dicarboxylate-3,4-13C2 (25% 13C enriched in the 3,4 posi-
tions; see Supporting Information for the synthesis from
acetylene-1,2-13C2).
3
proton exhibits a JHP of 3.5 Hz, suggesting alignment of the
2
(17) The JCC between the R carbons is unresolved in these spectra.
(18) Krivdin, L. B. Magn. Reson. Chem. 2003, 41, 885.
(19) (a) Wray, V.; Hansen, P. E. (Webb, C. A., Ed.) Ann. Rep. NMR Spectrosc.
1981, 32, 789. (b) Wray, V. Prog. Nucl. Magn. Reson. Spectrosc. 1979,
13, 177. (c) Even in cyclopropane, where the C-C bonds have high
p-character, the coupling constant is 12.4 Hz: Hesse, M.; Meier, H.; Zeeh,
B. Spectroscopic Methods in Organic Chemistry; Georg Thieme Verlag:
New York, 1997.
Most informative is the Câ resonance at 23.7 ppm, which
1
appears as a doublet of doublets, with JCC values of 8.5 and
23 Hz (cf. 15 Hz for 2).7b Both coupling constants are
(20) (a) Hansen, P. E. Prog. Nucl. Magn. Reson. Spectrosc. 1981, 14, 175. (b)
Kalinowski, H.O.; Berger, S.; Braun, S. Carbon-13 NMR Spectroscopy;
Wiley: Chichester, U.K., 1988.
(21) Harvey, B. G.; Mayne, C. L.; Arif, A. M.; Ernst, R. D. J. Am. Chem. Soc.
2005, 127, 16426.
(22) Some computational studies support this finding: (a) Adlhart, C.; Chen,
P. J. Am. Chem. Soc. 2004, 126, 3496. (b) Cavallo, L. J. Am. Chem. Soc.
2002, 124, 8965.
(15) The factors influencing the rate of initiation in compounds 1 are poorly
understood, but the steric bulk of the PR3 moiety appears to strongly affect
the rate of reaction of the phosphonium alkylidenes with olefins. Preliminary
calculations suggest that the barrier to rotation of the phosphonium
alkylidene about the RudC double bond is quite sensitive to the bulk of
the PR3 unit.
(16) (a) Wallace, K. C.; Liu, A. H.; Dewan, J. C.; Schrock, R. R. J. Am. Chem.
Soc. 1988, 110, 4964. (b) Gilliom, L. R.; Grubbs, R. H. J. Am. Chem. Soc.
1986, 108, 733. (c) Jennings, P. W.; Johnson, L. L. Chem. ReV. 1994, 94,
2241.
(23) For related PMe3 derivatives of Grubbs catalysts, see: Bolton, S. L.;
Williams, J. E.; Sponsler, M. B. Organometallics 2007, 26, 2485.
(24) Related species have recently been detected but not thoroughly character-
ized: P’Pool, S. J.; Schanz, H.-J. J. Am. Chem. Soc. 2007, 129, 14200.
9
J. AM. CHEM. SOC. VOL. 130, NO. 13, 2008 4487

A R T I C L E S
Scheme 3
van der Eide et al.
Still other olefin substrates give well-defined olefin carbene
complexes5,6 when employed as in Scheme 2. For example,
when 1-Cy is treated with 1 equiv of ethylene in the presence
of acenaphthylene, a product, 6, is generated in >90% NMR
yield with H and 13C NMR data consistent with an olefin-
1
carbene formulation as opposed to a ruthenacyclobutane (Scheme
1
4). Specifically, a sharp singlet at 18.13 ppm in the H NMR
spectrum, accompanied by a resonance at 317.3 ppm in the
13C{1H} NMR trace, is diagnostic for a ruthenium alkylidene
moiety. Also identifiable are the resonances for a coordinated
vinyl group, the data assigned by 2D correlation spectroscopy
(COSY, HMQC) as shown in the Scheme. Unfortunately,
although extensive NMR data on 6 were collected, it is not stable
above temperatures of -20 °C and could not be isolated for
solid state structural characterization.
While the acenaphthylene has clearly undergone ring open-
ing,28 the data do not allow for assignment of the precise
geometry of 6. On the basis of literature precedent,5,6 the
possible isomers are shown in the scheme: two diastereomeric
side-bound isomers related by the face of the vinylic olefin group
presented to the ruthenium center (cis-chlorides), and a bottom-
bound isomer in which the chlorides remain trans disposed (here
coordination of the opposite face gives this isomer’s enanti-
omer). In the reaction of Grubbs’ generation 2 catalyst with
divinyl benzene, an exchanging mixture of side-bound, cis-
chloride diastereomers was observed in solution, and one was
characterized by X-ray crystallography5 (analogous to the top
side-bound isomer depicted in Scheme 4). Conversely, Snapper
apprehended a bottom-bound olefin carbene complex III by
reacting Grubbs generation 1 catalyst with a strained tricyclic
cyclobutene substrate.6
carbene ligand25 with the L-Ru-PMe3 vector as opposed to
the Cl-Ru-Cl vector as is common in Grubbs-type catalysts.
Observed Cs symmetry in the 1H NMR spectrum of 4 down to
-60 °C supports this assignment, which is likely due to the
smaller size of PMe3 relative to PCy3. In any case, the 13C and
1H resonances for the terminal vinyl group indicate it is dangling
with no interaction with the Ru center.
We have also used the methodology in Scheme 2 to trap
“LCl2RudCH2” (I) with other olefins. The generation of another
ruthenacyclobutane related to 3 proceeds smoothly with a related
cyclopentene featuring 1,1-disubstitution. For example, com-
pound 5 was formed from 1-iPr and cyclopent-3-ene-1,1-
diacetyl.
Thus, precedent exists for both types of isomers. In 6, we
observe only one isomer in solution at all temperatures, with
no temperature dependence of the 1H NMR spectrum in ranges
When less reactive olefins,26 such as cyclohexene, tert-butyl
ethylene, and 1,1-difluoroethylene, were employed as trapping
olefins, ruthenacyclobutane products were not observed; here,
only 2 and the dimer formed via trapping of I by 1-iPr14 were
formed. Although dimer II has not been comprehensively
characterized, the NMR data obtained are consistent with this
formulation (see Experimental Section); further studies on these
types of dimers are ongoing.27 Trapping of I by ethylene or
1-iPr is thus more rapid than its trapping with less reactive olefin
substrates. At the other end of the olefin reactivity spectrum,
cyclooctene and norbornene undergo facile ROMP reaction with
1-Cy and 1-iPr, even at low temperatures and cannot be used
as trapping olefins in this protocol.
1
where 6 is stable. A comparison of H and 13C NMR data for
6 and the Grubbs side-bound isomers shows that the alkylidene
proton and carbon resonances for 6 (18.13 and 317.3 ppm) are
downfield of those observed in the side-bound species, which
resonate at 16.34 and 16.17 and 300.3 and 296.9 ppm,
respectively.5 We observe no NOE correlations between the
vinyl protons in 6 and the mesityl methyl or aryl protons of the
NHC ligand, as might be expected in a side-bound structure.
While these observations circumstantially implicate a bottom-
bound structure for 6, in the absence of more definitive data,
we are unable to assign its geometry with a high degree of
certainty; nonetheless, it represents another example of the
family of olefin carbene intermediates relevant to these catalyst
systems.
3
(25) A Karplus-type relationship between the P-Ru-C-H dihedral and JPH
in Grubbs-type ruthenium carbenes has been noted: (a) Lehman, S. E.,
Jr.; Wagener, K. B. Organometallics 2005, 24, 1477. (b) Nguyen, S. T.;
Grubbs, R. H.; Ziller, J. W. J. Am. Chem. Soc. 1993, 115, 9858-9859. (c)
Wu, Z.; Nguyen, S. T.; Grubbs, R. H.; Ziller, J. W. J. Am. Chem. Soc.
1995, 117, 5503-5511.
Conclusions
In summary, we have developed a route from phosphonium
alkylidenes 1 to the 14 electron ruthenium carbene complex I
(26) Chatterjee, A. K.; Choi, T.-L.; Sanders, D. P.; Grubbs, R. H. J. Am. Chem.
Soc. 2003, 125, 11360.
(27) Deactivation of ruthenium-based olefin metathesis catalysts via dimerization
has been previously observed: (a) Amoroso, D.; Yap, G. P. A.; Fogg, D.
E. Organometallics 2002, 21, 3335. (b) Drouin, S. D.; Monfette, S.;
Amoroso, D.; Yap, G. P. A., Fogg, D. E. Organometallics 2005, 24, 4721.
(28) Note that only 1 equiv of the acenaphthylene substrate opens; we do not
observe ROMP of this substrate under any conditions explored.
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4488 J. AM. CHEM. SOC. VOL. 130, NO. 13, 2008

Ruthenacyclobutane and Ru Olefin Carbene Intermediates
A R T I C L E S
Scheme 4
Synthesis of (H2IMes)(Cl)3RudCHPiPr3‚CH2Cl2, 1-iPr-Cl. (H2-
IMes)(Cl)2(PiPr3)RutC (0.300 g, 0.461 mmol) was put in a 50 mL
flask. Dichloromethane (20 mL) was condensed onto the pale yellow
solid at -78 °C. To dissolve all of the carbide, the flask was warmed
to room temperature, after which it was cooled to -78 °C again, giving
a light yellow solution. About 150 mL (∼10-15 equiv) of anhydrous
HCl gas was introduced into the flask at -78 °C through the vacuum
line. This resulted in a red/brown solution, which turned a greenish
yellow color when the reaction mixture was allowed to warm to room
temperature. After 3 h of stirring, all the volatiles were removed in
vacuo, leaving a green waxy residue. Sonication in pentane yielded a
green powder, which was recrystallized by dissolving it in CH2Cl2 and
carefully layering it with two volumes of pentane, affording large
greenish brown/orange prisms (suitable for X-ray diffraction) of the
involving stoichiometric reaction with ethylene. Intermediate I
is extremely reactive and may be trapped by various olefins to
generate stable ruthenacyclobutanes or ruthenium olefin carbene
complexes germane to ring opening and/or ring closing me-
tathesis reactions as catalyzed by Grubbs generation 2 catalyst
platforms. Examples of both types of intermediates were
characterized in detail using low-temperature NMR spectro-
scopy. The data for ruthenacyclobutane 3 suggest that the C-C
bonds of the ring are differentially activated by the ruthenium
center, with the more substituted C-C bond being the most
weakened in the ground state structure of the compound. This
is the opposite to what one would expect for an intermediate
crucial in the ring closing metathesis of such substrates, but
the influence of external olefin on such a product-forming
reaction remains to be studied.
1
title compound: yield 0.288 g (0.373 mmol, 80.9%); H NMR (CD2-
Cl2, 399.6 MHz, 295 K) δ 19.71 (d, 2JHP ) 51 Hz, 1H, RudCH), 7.01
(s, 4H, Mes CH), 3.99 (br, 4H, CH2CH2), 3.21 (d septet, 2JHP ) 15 Hz,
i
3JHH ) 7 Hz, 3H, Pr CH), 2.47 (br, 12H, ortho CH3), 2.34 (s, 6H,
Experimental Section
3
3
i
1
para CH3), 1.19 (dd, JHP ) 16 Hz, JHH ) 7 Hz, 18H, Pr CH3); H
General procedures and synthetic details concerning the preparation
of labeled substrates and starting materials are given in the Supporting
Information.
2
NMR (CD2Cl2, 399.6 MHz, 227 K) δ 19.62 (d, JHP ) 50 Hz, 1H,
RudCH), 7.03 (s, 2H, Mes CH), 6.97 (s, 2H, Mes CH), 4.04-3.83
(m, 4H, CH2CH2), 3.11 (m, 3H, iPr CH), 2.51 (s, 6H, ortho CH3), 2.33
(s, 3H, para CH3), 2.30 (s, 6H, ortho CH3), 2.29 (s, 3H, para CH3),
Synthesis of (H2IMes)(Cl)2(PiPr3)RutC. (H2IMes)(Cl)2(PiPr3)Rud
CHPh (0.740 g, 1.02 mmol) and Feist’s dimethyl ester (0.184 g, 1.08
mmol) were placed in a 50 mL flask. Dichloromethane (20 mL) was
condensed onto the solids at -78 °C, after which the mixture was
warmed to room temperature and stirred for 18 h. During this time,
the color went from dark red to light orange/brown. The volatiles were
removed under reduced pressure, and the dimethyl fumarate byproduct
was sublimed away in vacuo at ca. 50 °C. The residue was washed
three times with 20 mL of pentane. The product was purified by passing
it through a plug of silica (eluent 50:50 EtOAc/hexanes, material loaded
in CH2Cl2), from which it elutes as a yellow band. The volatiles were
removed in vacuo, and the solid was washed with two 20 mL portions
of pentane, after which it was dried in vacuo and isolated: yield 0.540
g (0.830 mmol, 81.7%); 1H NMR (CD2Cl2, 300.1 MHz, 300 K) δ 6.98
(s, 2H, Mes CH), 6.83 (s, 2H, Mes CH), 4.21-4.03 (m, 4H, CH2CH2),
3
3
i
1.13 (dd, JHP ) 16 Hz, JHH ) 7 Hz, 18H, Pr CH3); 13C{1H} NMR
3
(CD2Cl2, 100.5 MHz, 227 K) δ 274.4 (br, RudCH), 201.7 (d, JCP
2-3 Hz, Ru-C(N)2), 138.95, 138.87, 138.3, 137.3, 137.2, 134.6 (all s,
Mes quaternary C), 129.7, 129.1 (both s, Mes CH), 51.9 (s, CH2CH2),
51.4 (s, CH2CH2), 24.3 (d, JCP ) 37 Hz, Pr CH), 21.1 (s, Mes para
CH3), 20.9 (s, Mes para CH3), 20.2 (s, Mes ortho CH3), 18.2 (s, Mes
ortho CH3), 17.6 (d, JCP ) 3 Hz, Pr CH3); 31P{1H} NMR (CD2Cl2,
161.8 MHz, 295 K) δ 42.3 (s), (227 K) δ 40.0 (s). Anal. Calcd for
C32H50Cl5N2PRu: C, 49.78; H, 6.53; N, 3.63. Found: C, 49.75; H,
6.29; N, 3.54.
∼
1
i
2
i
Generation of [(H2IMes)(Cl)2RudCHPiPr3]+[ClB(C6F5)3]-, 1-iPr.
(H2IMes)(Cl)3RudCHPiPr3‚CH2Cl2 (21 mg, 27 µmol) was dissolved
in 0.6 mL of CD2Cl2, cooled to -35 °C in the glove box freezer, and
added to a cooled vial containing B(C6F5)3 (17 mg, 33 µmol). Upon
reaction, the color changed from green/brown to light orange/brown.
The title compound is only present as the monomer, independent of
2
3
i
2.58 (d septet, JHP ) 11 Hz, JHH ) 7 Hz, 3H, Pr CH), 2.48 (12 H,
overlapping inequivalent Mes ortho CH3), 2.29 (s, 3H, Mes para CH3),
3
3
2.23 (s, 3H, Mes para CH3), 1.06 (dd, JHP ) 14 Hz, JHH ) 7 Hz,
18H, iPr CH3); 13C{1H} NMR (CD2Cl2, 75.5 MHz, 300 K) δ 479.6 (s,
RutC), 212.6 (d, 2JCP ) 83 Hz, Ru-C(N)2), 139.1, 139.0, 138.7, 138.0,
135.3 (all s, Mes quaternary C, 2 of them overlapped), 129.7, 129.6
(both s, Mes CH), 52.4 (br d, 4JCP ∼ 2 Hz, CH2CH2), 51.6 (br, CH2CH2),
22.1 (d, 2JCP ) 20 Hz, iPr CH), 21.4 (s, para CH3), 21.2 (s, para CH3),
2
temperature: 1H NMR (CD2Cl2, 399.6 MHz, 285 K) δ 17.77 (d, JHP
) 35 Hz, 1H, RudCH), 7.09 (s, 4H, Mes CH), 4.23 (s, 4H, CH2CH2),
2
3
i
2.61 (d septet, JHP ) 11 Hz, JHH ) 7 Hz, 3H, Pr CH), 2.36 (ps s,
18H, ortho and para CH3), 0.99 (dd, 3JHP ) 16 Hz, 3JHH ) 7 Hz, 18H,
iPr CH3); 1H NMR (CD2Cl2, 399.6 MHz, 213 K) δ 17.72 (d, 2JHP ) 35
Hz, 1H, RudCH), 7.12 (br s, 2H, Mes CH), 7.00 (br s, 2H, Mes CH),
4.20 (app s, 4H, CH2CH2), 2.56 (d septet, 2JHP ) 11 Hz, 3JHH ) 7 Hz,
3H, iPr CH), 2.39 (br, 6H, Mes ortho CH3), 2.32 (app s, 6H, overlapping
inequivalent Mes para CH3), 2.22 (br, 6H, Mes ortho CH3), 0.91 (dd,
20.3 (s, ortho CH3), 19.4 (s, Pr CH3), 18.9 (s, ortho CH3); 31P{1H}
i
NMR (CD2Cl2, 121.5 MHz, 300 K) δ 44.8 (s). Anal. Calcd for C31H47-
Cl2N2PRu: C, 57.22; H, 7.28; N, 4.31. Found: C, 57.21; H, 7.17; N,
4.09.
9
J. AM. CHEM. SOC. VOL. 130, NO. 13, 2008 4489

A R T I C L E S
van der Eide et al.
3
i
3JHP ) 17 Hz, JHH ) 7 Hz, 18H, Pr CH3); 13C{1H} NMR (CD2Cl2,
pentane ring, vicinal to Hâ), -2.15 (m, 1H, Hâ); 13C{HR} NMR (CD2-
Cl2, 100.5 MHz, 213 K) δ 213.5 (s, RuC(N)2), 171.9, 169.7 (both s,
CdO), 144.8 (br s, CR1H, 1JCH ) 167 Hz, 1JCC ) 8.5 Hz), 139.2, 138.9,
137.5, 137.34, 137.30, 137.2, 132.4, 132.2 (all s, Mes quaternary C),
128.98, 128.96 (both s, Mes CH), 128.9 (app s, 2 overlapping Mes
3
100.5 MHz, 285 K) δ 260.1 (br, RudCH), 187.4 (d, JCP ) 2 Hz,
Ru-C(N)2), 141.1, 138.6 (both s, Mes quaternary C), 134.7 (br, Mes
quaternary C), 130.7 (s, Mes CH), 53.1 (s, CH2CH2), 21.3 (s, Mes para
1
i
CH3), 21.2 (d, JCP ) 39 Hz, Pr CH), 19.2 (br, Mes ortho CH3), 17.7
(d, JCP ) 3 Hz, Pr CH3); 13C{1H} NMR (CD2Cl2, 100.5 MHz, 213
CH), 87.2 (s, CR2, JCH ) 163, 163 Hz, JCC ) 23 Hz), 68.9 (s, Od
CCCdO), 53.3 (s, CH3OOC), 52.9 (s, CH3OOC), 52.6 (s, CH2CH2),
51.8 (s, CH2CH2), 39.8 (s, cyclopentane CH2 attached to CR), 26.1 (s,
2
i
1
1
3
K) δ 262.3 (br, RudCH), 186.4 (d, JCP ) 2 Hz, Ru-C(N)2), 139.1,
137.1, 136.1, 132.0 (all br, Mes quaternary C), 130.6 (br, Mes CH),
129.4 (br, Mes CH), 52.6 (br, CH2CH2), 52.2 (br, CH2CH2), 21.0 (br,
Mes CH3), 20.2 (d, JCP ) 39 Hz, Pr CH), 19.9 (br, Mes CH3), 17.7
1
cyclopentane CH2 attached to Câ), 23.7 (s, Câ, JCH ) 157 Hz), 21.0,
1
i
20.9, 19.2, 19.09, 19.05, 19.0 (all s, Mes CH3). Notes regarding
assignments in 1H 3: Signals at 6.07 and 5.90 ppm were assigned based
on the magnitude of NOESY interactions (mixing time ) 0.4 s). Hâ at
-2.15 ppm has a stronger NOESY interaction with the peak at 5.90
ppm than with that at 6.07 ppm. In addition, the peak at 1.69 ppm
(assigned by COSY to a cyclopentane CH2 vicinal to Hâ) has a NOESY
interaction with the 6.07 ppm peak, which lends support to its
assignment as the ruthenacycle CHH anti to Hâ. In the COSY, HR
couples to peaks at 2.31 and 2.04 ppm, and Hâ couples to peaks at
1.81 and 1.69 ppm. These four peaks all appear as doublets of doublets
2
i
(br, Mes CH3), 17.2 (d, JCP ) 2 Hz, Pr CH3). Note: due to H2IMes
fluxional behavior at 213 K, many resonances are broadened and not
all Mes quaternary carbons could be located. In addition, some of the
Mes quaternary carbons may overlap with the anion resonances.
However, most diagnostics in the 13C spectra at both temperatures are
the H2IMes carbene resonance at ∼187 ppm. In these complexes, this
indicates a four-coordinate ruthenium complex with an empty coordina-
tion site opposite the H2IMes ligand. 31P{1H} NMR (CD2Cl2, 161.8
MHz, 285 K): δ 61.0 (s).
Generation of 3 from 1-Cy. In a typical experiment, [(H2IMes)-
(Cl)2RudCHPCy3]OTf (14 mg, 15 µmol) and dimethyl cyclopent-3-
ene-1,1-dicarboxylate (10 mg, 54 µmol) were dissolved in 0.6 mL of
CD2Cl2 in an NMR tube. The tube was placed in a dry ice/acetone
bath and 1 equiv of ethene was added through the septum. The tube
was quickly shaken and re-inserted into the cold bath. After ca. 20 h
of standing at -78 °C, the sample was inserted into the NMR probe
precooled to 223 K, and multinuclear NMR spectroscopy was per-
formed. Typically, the ratio 1-Cy/3/2 was 25:38:38, that is, a 3/2 ratio
of ca. 1:1. This ratio did not change much while the sample was in the
probe for several hours. Among several experiments, the 3:2 ratio varied
from 1:1 to 2:1. See below for a superior procedure starting from 1-iPr,
in which full NMR data for 3 are given.
1
in the H NMR spectrum and are assigned to the cyclopentane CH2
groups.
Generationof(H2IMes)(Cl)2(PMe3)RudC(H)CH2C(CO2Me)2CH2C-
(H)dCH2, 4. In a J-Young tube, 3 was generated using a procedure
similar to that described above. However, in this case, the tube
containing the solution of 1-iPr and dimethyl cyclopent-3-ene-1,1-
dicarboxylate was degassed by three freeze-pump-thaw cycles, after
which 1 equiv of ethene was measured with a calibrated bulb and
transferred into the tube at -196 °C. The tube was placed in a -78 °C
bath, and the contents were allowed to thaw. Careful shaking of the
1
tube at -78 °C resulted in a coloration to red/purple, and H NMR
analysis indicated a 7:1 ratio of 3/2. Then, again using a calibrated
bulb, 2 equiv of PMe3 was measured and transferred into the tube at
-196 °C. The tube was placed in a -78 °C bath, and the contents
were allowed to thaw. After careful shaking of the tube at -78 °C, the
color changed from red/purple to dull orange in the course of several
minutes. The tube was inserted into the NMR probe precooled to -60
°C, and multinuclear NMR experiments were performed. The spectra
indicated formation of 4 in an NMR yield of 98% from 3: 1H NMR
(CD2Cl2, 399.5 MHz, 213 K) δ 17.74 (dt, 3JHP ) 3.5 Hz, 3JHH ) 5 Hz,
1H, RudCH), 6.92 (s, 2H, Mes CH), 6.85 (s, 2H, Mes CH), 5.64 (m,
1H, C(H)dCH2), 4.99-4.92 (m, 2H, inequivalent C(H)dCH2), 4.08-
3.89 (m, 4H, CH2CH2), 3.58 (s, 6H, CH3OOC), 2.48 (s, 6H, Mes ortho
CH3), 2.31 (s, 6H, Mes ortho CH3), 2.22 (s, 3H, Mes para CH3), 2.19
Generation of 3 from 1-iPr. In a glove box, dimethyl cyclopent-
3-ene-1,1-dicarboxylate (15 mg, 81 µmol) was weighed into an NMR
tube and dissolved in 0.1 mL of CD2Cl2. (H2IMes)(Cl)3RudCHPi-
Pr3‚CH2Cl2 (20 mg, 26 µmol) was weighed into a vial and dissolved
in 0.5 mL of CD2Cl2. B(C6F5)3 (15 mg, 29 µmol) was weighed into a
different vial. The vials and the NMR tube were cooled in the glove
box freezer (-35 °C). The ruthenium trichloride compound was added
to the B(C6F5)3 and shaken to form 1-iPr, which was cooled again in
the freezer. Then, quickly, the 1-iPr solution was added to the NMR
tube containing the RCM product, the tube was capped with a septum,
brought out of the glove box, and placed in a dry ice/acetone bath.
One equivalent of ethene was added through the septum, and the tube
was quickly shaken three times, which resulted in a fast color change
to red/purple. This procedure results in a reproducible 3/2 ratio of 9:1
and with ca. 5% of the ruthenium in the form of the [RudCHPiPr3]+/
[RudCH2] dimer: 1H NMR (CD2Cl2, 399.6 MHz, 213 K) δ 9.36 (app
q, 1H, HR, 3JHâ ) 7 Hz), 6.92 (s, 1H, Mes CH), 6.89 (s, 1H, Mes CH),
6.87 (s, 1H, Mes CH), 6.85 (s, 1H, Mes CH), 6.07 (m, 1H, HR′′,
3
(s, 3H, Mes para CH3), 2.11 (d, JHH ) 7 Hz, 2H, CH2C(H)dCH2),
2
1.76 (br, 2H, RudC(H)CH2), 0.83 (d, JHP ) 10 Hz, 9H, P(CH3)3);
31P{1H} NMR (CD2Cl2, 161.7 MHz, 213 K) δ 11.9 (s); 13C{1H} NMR
2
(CD2Cl2, 100.4 MHz, 213 K) δ 303.3 (br, RudCH), 219.7 (d, JCP
)
70 Hz, RuC(N)2), 171.0 (s, CdO), 139.2, 139.1, 138.2, 137.51, 137.46,
136.9, 136.4 (all s, Mes quaternary C), 133.2 (s, C(H)dCH2), 132.7
(s, Mes quaternary C), 129.2 (s, Mes CH), 129.1 (s, Mes CH), 118.7
(s, C(H)dCH2), 57.3 (s, RudC(H)CH2), 56.3 (s, OdCCCdO), 52.4
4
(s, CH3OOC), 51.5 (app s, CH2CH2), 51.2 (d, JCP ) 3 Hz, CH2CH2),
38.3 (s, CH2C(H)dCH2), 20.9 (s, Mes para CH3), 20.8 (s, Mes para
CH3), 19.7 (s, Mes ortho CH3), 18.1 (s, Mes ortho CH3), 11.2 (d, 1JCP
) 30 Hz, P(CH3)3).
Generation of 5 from 1-iPr. The procedure for 3 was followed,
except 14 mg (92 µmol, 3.5 equiv) of cyclopent-3-ene-1,1-diacetyl was
used instead of dimethyl cyclopent-3-ene-1,1-dicarboxylate. Mixing of
1-iPr with the RCM product resulted in a light green solution, indicative
of coordination of the RCM product to 1-iPr, probably through a
3
overlapping with H2CdCHP byproduct), 5.90 (app dd, 1H, HR′, JHâ
) 9 Hz; JHR′′ ) -4.5 Hz), 4.26 (m, 4H, NCH2CH2N), 3.62 (s, 3H,
2
1
2
CH3OOC), 3.55 (s, 3H, CH3OOC), 2.46 (app s, 6H, overlapping
inequivalent Mes CH3), 2.40 (s, 3H, Mes CH3), 2.39 (s, 3H, Mes CH3),
2.31 (app dd, 1H, CHH in cyclopentane ring, vicinal to HR), 2.26 (s,
3H, Mes CH3), 2.24 (s, 3H, Mes CH3), 2.04 (app dd, 1H, CHH in
cyclopentane ring, vicinal to HR1), 1.81 (app dd, 1H, CHH in
cyclopentane ring, vicinal to Hâ), 1.69 (app dd, 1H, CHH in cyclo-
carbonyl oxygen. This was confirmed by H (δ 19.61, d, JHP ) 42
Hz, RudCH) and 31P{1H} (δ 44.3, s) NMR spectroscopy at 213 K,
showing quantitative adduct formation. Nevertheless, addition of 1 equiv
of ethene at -78 °C and shaking resulted in the formation of the
substituted ruthenacyclobutane (red/purple solution), albeit somewhat
slower than with the diester RCM product. The ratio substituted/
9
4490 J. AM. CHEM. SOC. VOL. 130, NO. 13, 2008

Ruthenacyclobutane and Ru Olefin Carbene Intermediates
A R T I C L E S
unsubstituted ruthenacyclobutane is ca. 6:1, with ca. 10% 1-iPr (RCM
product coordinated) and <5% [RudCHPiPr3]+/[RudCH2] dimer: 1H
NMR (CD2Cl2, 399.6 MHz, 213 K) δ 9.17 (app q, 1H, CR1H1), 6.94
(s, 1H, Mes CH), 6.89 (s, 1H, Mes CH), 6.86 (s, 1H, Mes CH), 6.85
(s, 1H, Mes CH), 6.07 (m, 1H, CR2H2, overlapping with H2CdCHP
byproduct), 5.92 (app dd, 1H, CR2H3), 4.26 (m, 4H, NCH2CH2N), 2.46
(app s, 6H, overlapping inequivalent Mes CH3), 2.40 (s, 3H, Mes CH3),
2.38 (s, 3H, Mes CH3), 2.32 (app dd, 1H, CHH in cyclopentane ring,
vicinal to H1), 2.27 (s, 3H, Mes CH3), 2.24 (s, 3H, Mes CH3), 1.97 (s,
3H, CH3CdO), 1.95 (s, 3H, CH3CdO), 1.81 (app dd, 1H, CHH in
cyclopentane ring, vicinal to H4), 1.65 (app dd, 1H, CHH in cyclo-
pentane ring, vicinal to H4), -2.40 (m, 1H, CâH4). One cyclopentane
hydrogen not observed, overlapped by other signals: 13C{1H} NMR
(CD2Cl2, 100.5 MHz, 213 K) δ 213.5 (s, RuC(N)2), 205.5 (s, CdO),
143.9 (overlapped by H2CdCHP byproduct, CR1H, located by HMQC),
139.1, 138.9, 137.6, 137.5, 137.33, 137.26, 132.5, 132.2 (all s, Mes
quaternary C), 129.0, 128.91, 128.86, 128.8 (all s, Mes CH), 87.4 (s,
CR2H2), 83.7 (s, OdCCCdO), 52.6 (s, CH2CH2), 51.8 (s, CH2CH2),
38.6 (s, cyclopentane CH2), 27.1 (s, CH3CdO), 26.1 (s, CH3CdO),
24.4 (s, cyclopentane CH2), 23.3 (s, CâH), 21.0, 20.9, 19.2, 19.10, 19.05,
19.0 (all s, Mes CH3).
245 K) δ 317.3 (s, RudCH), 210.5 (s, RuC(N)2), 149.7, 146.5, 140.6,
139.93, 139.89, 139.1, 138.8, 137.9, 137.8, 136.1, 133.89 (all s, aromatic
quaternary C), 133.86 (s, aromatic CH), 131.0 (s, aromatic quaternary
C), 130.0, 129.9 (both s, aromatic CH), 129.3 (app s, two overlapping
Mes CH), 129.2, 127.1, 126.3, 126.1, 119.8 (all s, aromatic CH), 100.3
(s, H2CdCH), 100.0 (s, H2CdCH), 52.8 (s, CH2CH2), 50.8 (s, CH2CH2),
21.3, 21.2, 20.9, 20.5, 18.7, 17.7 (all s, Mes CH3).
Trapping of I with 1-iPr: Generation of II. 1-iPr was generated
as described before, and 0.5 equiv of ethene was introduced at -78
°C. The tube was quickly shaken, affording an orange/brown solution,
and inserted in the precooled NMR probe. This generates ca. 60% of
dimer, 10-15% of 2, and 25-30% of 1-iPr remains. The dimer is
thermally unstable and decomposes above -30 °C. Partial characteriza-
tion by 1H and 31P NMR spectroscopy was performed, but not all
resonances could be unequivocally assigned: 1H NMR (CD2Cl2, 399.6
2
MHz, 213 K) δ 19.79 (d, JHP ) 43 Hz, 1H, RudCH), 18.01 (s, 2H,
RudCH2), 7.11 (s, 1H, Mes CH), 7.02 (br, overlapping Mes CH), 7.00
(s, 1H, Mes CH), 6.83 (s, 1H, Mes CH, overlapping with HHCdCHP
byproduct), 6.80 (s, 1H, Mes CH, overlapping with HHCdCHP
byproduct), 4.00-3.66 (m, 8H, CH2CH2), 2.50 (s, 3H, Mes CH3), 2.41
(s, 3H, Mes CH3), 2.36 (s, 3H, Mes CH3), 2.34 (s, 3H, Mes CH3), 2.24
(s, 3H, Mes CH3), 2.15 (s, 3H, Mes CH3), 2.09 (s, 3H, Mes CH3), 1.96
(s, 3H, Mes CH3), 1.89 (s, 3H, Mes CH3), 1.1 (br, 18H, iPr CH3); 31P-
{1H} NMR (CD2Cl2, 161.8 MHz, 213 K) δ 43.4 (br).
Trapping of I with Acenaphthalene To Form 6. [(H2IMes)-
(Cl)2RudCHPCy3]OTf (20 mg, 22 µmol) and acenaphthylene (5 mg,
33 µmol) were dissolved in 0.6 mL of CD2Cl2 in an NMR tube. The
tube was placed in a dry ice/acetone bath, and 1 equiv of ethene was
added through the septum. The tube was shaken and inserted in the
precooled (234 K) NMR probe. The reaction was allowed to go to
completion in the NMR probe, which took ca. 5 h. In the data section
below, Np denotes the naphthyl group: 1H NMR (CD2Cl2, 399.6 MHz,
Acknowledgment. Funding was provided by NSERC of
Canada in the form of a Discovery Grant to W.E.P., and the
Alberta Ingenuity Fund for a Studentship to E.F.v.d.E. Dr.
Masood Parvez is acknowledged for the crystal structure
determination of 1-iPr-Cl; Materia Inc. provided ruthenium
catalysts.
3
234 K) δ 18.13 (s, 1H, RudCH), 8.20 (app d, JHH ) 7 Hz, 1H, Np
CH), 7.77 (app d, 3JHH ) 7 Hz, 1H, Np CH), 7.59 (app d, 3JHH ) 7 Hz,
1H, Np CH), 7.34 (app t, 3JHH ) 7 Hz, 1H, Np CH), 7.21 (s, 1H, Mes
3
CH), 7.16 (app t, JHH ) 7 Hz, 1H, Np CH), 7.02 (s, 1H, Mes CH),
3
6.98 (s, 1H, Mes CH), 6.92 (s, 1H, Mes CH), 6.19 (app d, JHH ) 7
Supporting Information Available: General experimental
procedures, details on the syntheses of labeled substrates, and
crystallographic data for 1-iPr-Cl (in .cif format). This material
is available free of charge via the Internet at http://pubs.acs.org.
3
3
Hz, 1H, Np CH), 5.65 (app dd, 1H, Hvinyl, JHcis ) 9.1 Hz, JHtrans
)
14.7 Hz), 5.54 (app dd, 1H, Htrans, 2JHcis ) 2.8 Hz), 4.30-3.93 (m, 4H,
CH2CH2), 3.61 (app dd, 1H, Hcis), 2.86 (s, 3H, Mes CH3), 2.70 (s, 3H,
Mes CH3), 2.49 (s, 3H, Mes CH3), 2.37 (s, 3H, Mes CH3), 2.28 (s, 3H,
Mes CH3), 1.81 (s, 3H, Mes CH3); 13C{1H} NMR (CD2Cl2, 100.5 MHz,
JA710364E
9
J. AM. CHEM. SOC. VOL. 130, NO. 13, 2008 4491