Ruthenium complexes of an abnormally bound, anionic N-heterocyclic carbene

Article abstract of DOI:10.1002/chem.201402080

The abnormally bound, anionic NHC-borane complex [Ru(IDipp-BF ₃)(p-cymene)Cl]₂ (4; IDipp-BF₃=1,3-(2,6- iPr₂C₆H₃)₂-2-BF₃(C ₃HN₂)-4-yl) was synthes

Full text of DOI:10.1002/chem.201402080

DOI: 10.1002/chem.201402080
Communication
&
Synthetic Methods
Ruthenium Complexes of an Abnormally Bound, Anionic
N-Heterocyclic Carbene
Conor Pranckevicius and Douglas W. Stephan*[a]
Our initial investigation involved examining the reactions of
Abstract: The abnormally bound, anionic NHC–borane
complex [Ru(IDipp-BF3)(p-cymene)Cl]2 (4; IDipp-BF3 =1,3-
(2,6-iPr2C6H3)2-2-BF3(C3HN2)-4-yl) was synthesized by trans-
metalation from Li[(IDipp-BF3)2Ag]. Addition of donors
gave species of the form [Ru(IDipp-BF3)(p-cymene)(L)Cl],
whereas halide abstraction with Ag(Et2O)[B(C6F5)4] gave CÀ
H activation of the methine position of the IDippÀBF3
ligand.
the lithiated IDipp-BF3 adduct (2), with a number of common
Ru starting materials; however, this led only to intractable mix-
tures. A strategy frequently used in the synthesis of Ru–NHC
complexes is the use of an NHC–Ag complex as a transmetalat-
ing agent,[11] and we next investigated whether this strategy
could be extended to anionic abnormal carbenes. It was found
that stirring suspension of Li(IDipp-BF3) with AgCl in THF clean-
ly generated a species of the formula Li[(IDipp-BF3)2Ag] (3). No
reduction to Ag metal was observed. Crystals of the THF sol-
vate [(THF)3Li][(IDipp-BF3)2Ag] were grown from THF/pentane,
and were analyzed by single-crystal X-ray diffraction. The ge-
ometry at Ag is linear with coordination by two NHCs through
the abnormal positions. The average AgÀC distance is
2.090(3) ꢀ. There is a FÀLi dative interaction in the solid state
with a bond length of 1.882(6) ꢀ. In [D8]THF solution, C–109Ag
and C–107Ag coupling to the a carbon is apparent in the
N-heterocyclic carbenes (NHCs) have been responsible for sig-
nificant advances in transition-metal, organic, and main-group
chemistry.[1] Their tunable steric demands together with their
strong donor ability have proven to be useful in numerous cat-
alytic transformations, notably, in olefin metathesis[2] and in
cross-coupling reactions.[3] The utility of NHCs as organometal-
lic ligands is often due to their ability to stabilize highly coordi-
natively unsaturated transition-metal species. In this vein, an
interesting extension to this ligand class involves the notion of
generating anionic NHCs. Anionic dicarbenes were first isolated
by Robinson and co-workers in 2010 by lithiation of 1,3-(2,6-
iPr2C6H3)2(C3H2N2) (IDipp) at the abnormal position.[4] Selective
coordination of a neutral electrophile to the abnormal position
allows isolation of the anionic NHC as its Li salt.[1k,4–5] To date,
anionic NHCs and their metal complexes have been accessed
by deprotonation of neutral N-heterocycles,[6] incorporating
anionic functionalities in the NHC backbone,[7] CÀH activa-
tion,[8] and by reduction of a NHC in the presence of a metal
source.[9] These reactions often require that the metals in-
volved are either stable to reducing conditions, or are tolerant
of the strong basicity of the anionic NHC alkali salt. Seeking to
explore the strong electron-donor properties offered by anion-
ic NHCs, we envisioned binding a metal at the abnormal posi-
tion[6g,h,10] of an anionic carbene would further enhance the
donor ability. Herein, we report first examples of mono- and di-
nuclear RuII complexes containing abnormally bound anionic
NHCs. These species were obtained by a convenient and
gentle transmetalation route employing an Ag complex. The
subsequent reactivity of the Ru-anionic NHC complex with
donors and a halide abstractor is also described.
Scheme 1. Synthesis of compounds 2–4.
[a] C. Pranckevicius, Prof. Dr. D. W. Stephan
Department of Chemistry, University of Toronto
80 St. George St., Toronto, Ontario, M5S3H6 (Canada)
E-mail: dstephan@chem.utoronto.ca
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201402080.
Figure 1. Molecular structure of 3. iPr groups and hydrogens atoms were
removed for clarity.
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13C NMR spectrum with coupling constants of 184 and 159 Hz,
respectively (Scheme 1 and Figure 1).
Stirring equimolar amounts of 3 and [Ru(p-cymene)Cl2]2 in
THF for 16 h resulted in a dark red solution, which upon purifi-
cation gave crystals of dark red [Ru(IDipp-BF3)(p-cymene)Cl]2
(4) in 63% yield. Compound 4 is a rare example of an abnor-
mally bound Ru NHC species,[8,12] and the first example of a Ru
complex containing a nonbridging anionic NHC. In [D8]THF so-
lution, four doublets were observed in the alkyl region of the
1H NMR spectrum, corresponding to the four inequivalent iPr
1
Figure 3. Variable-temperature H NMR (CD2Cl2) spectrum of 4, aromatic
region.
Figure 2. Molecular structure of 4. iPr groups and hydrogens atoms were re-
moved for clarity.
groups. Broad resonances are attributable to p-cymene pro-
tons. A single-crystal X-ray analysis (Figure 2) confirmed the di-
meric nature of 4, in which the two Ru centers are bridged by
chloride atoms. The coordination sphere is completed by the
p-cymene and the anionic carbene ligand. The RuÀC distance
for the carbene donor was determined to be 2.119(2) ꢀ, slight-
ly longer than the length of 2.084(7) reported for the abnormal
NHC complex [Ru(p-cymene)(1,3-dimethyl-2-phenylimidazol-4-
yl)Cl2].[12a] This lengthening may be attributed to steric factors.
Interestingly, a CD2Cl2 solution of 4 at room temperature
gave rise to a broad, largely featureless 1H NMR spectrum.
Upon cooling to 08C, the signals sharpen to reveal the pres-
ence of two species in a 1:0.66 ratio. Further cooling to À20
and À408C altered this ratio to 1:0.60 and 1:0.50, respectively,
consistent with an equilibrium between two species. Each spe-
cies contains an h6 p-cymene ring and an abnormally bound
IDipp-BF3 ligand. Upon further cooling to À808C, signals for
the minor component broaden into the baseline of the NMR
spectrum, whereas sharper resonances were observed for the
major component (Figure 3 and the Supporting Information).
This behavior is believed to be the result of monomer/dimer
equilibrium with the dominant species being the dimer. The
observed broadening an À808C in the minor species is attrib-
uted to the wagging of the chloride ligand in monomeric [Ru-
(IDippBF3)(p-cymene)Cl] between two magnetically inequiva-
lent positions on the NMR timescale. However, the possibility
Scheme 2. Synthesis of compounds 5–7.
of conformational isomers of dimeric 4 giving rise to the ob-
served equilibrium cannot be ruled out (Scheme 2).
The dimeric 4 readily reacted with monodentate ligands in-
cluding PPh3 and CO to give the compounds [Ru(IDipp-BF3)(p-
cymene)(PPh3)Cl] (5) and [Ru(IDipp-BF3)(p-cymene)(CO)Cl] (6),
respectively, which were characterized crystallographically (see
the Supporting Information). Complex 5 displayed ten dou-
1
blets in the aliphatic region of the H NMR spectrum, indicative
of restricted rotation of all five iPr groups, presumably result-
ing from steric congestion in the ligand field. The carbonyl
complex 6 displayed a CO stretching frequency at u˜ =
2008 cmÀ1. RuÀC bond lengths are 2.118(3) and 2.0682(13) ꢀ in
5 and 6, respectively.
Compound 4 also reacted with Ag(Et2O)[B(C6F5)4] in CH2Cl2,
resulting in an immediate color change from dark red to
orange, and the precipitation of AgCl from solution. The fil-
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tered reaction mixture was layered with hexamethyldisiloxane,
and pale orange crystals of a new species 7 were formed over
a 24 hour period. The 19F NMR spectrum was consistent with
in this case by the basicity of the anionic carbene and the par-
tial coordination of the arene ring to Ru. Bertrand and co-
workers have observed that their free abnormal NHC decom-
posed by a related proton-transfer reaction in the presence of
a Lewis acid or by heating.[10b]
1
the 1:1 ratio of B(C6F5)4 and IDipp-BF3 moieties. H NMR data
for 7 revealed protonation of the IDipp-BF3 ligand at the ab-
normal position had occurred, although the two backbone
protons remained inequivalent, as are all of the aryl and alkyl
protons in the IDipp-BF3 ligand. Notably, one of the iPr meth-
ine protons of the ligand was absent. A doublet was observed
at d=2.66 ppm integrating to 1H, and was observed to
couple to a doublet of doublets at d=7.61 ppm, also 1H, as
indicated by a correlation spectroscopy (COSY) experiment.
Additionally, there is a broad upfield singlet at À3.30 ppm inte-
grating to 3H, suggesting an agostic interaction between Ru
and one of the iPr methyl groups. Collectively, these data sug-
gest that proton transfer had occurred between the abnormal
position on the NHC and one of the iPr methine positions, and
part of one of the Dipp rings has now coordinated to Ru. A
molecular structure of 7 revealed that cationic Ru center is co-
ordinated to h6 to a p-cymene ligand and an iPr group depro-
In conclusion, this work has demonstrated that transmetala-
tion of an anionic NHC ligand from Ag provides a viable access
to a Ru dimer containing the anionic NHC ligand. Subsequent
reactions with donors effect dimer scission, whereas abstrac-
tion of halide results in a unique binding mode of the carbene
by deprotonation of the iPr fragment of the N-aryl substituent.
This new reactivity stands in contrast to neutral NHCs and
other carbene donors, and suggests that anionic NHC com-
plexes may provide access to further unique reactivity.
Experimental Section
General comments
All manipulations were carried out under an atmosphere of dry,
O2-free N2 employing
a Vacuum Atmospheres glovebox or
a Schlenk vacuum line. Solvents were purified with a Grubbs-type
column system manufactured by Innovative Technology and dis-
pensed into thick-walled Straus flasks equipped with Teflon-valve
stopcocks. Deuterated dichloromethane was distilled under re-
duced pressure from CaH2 and degassed by successive freeze/
pump/thaw cycles. Deuterated THF was distilled from purple
sodium benzophenone ketyl. 1 H, 13C, 19F, 11B, 31P, and 7 Li NMR spec-
tra were recorded at 258C on Bruker 400 MHz, Agilent DD2
500 MHz, or Agilent DD2 600 MHz spectrometers, unless otherwise
noted. Chemical shifts are reported in parts per million are given
relative to SiMe4 and referenced to the residual solvent signal. Ele-
mental analyses were performed in house employing a PerkinElmer
CHN Analyzer. In some cases, elemental analyses were reproducibly
low on carbon content, presumably due to the formation of metal
carbides during combustion. IR spectra were collected on a Perkin-
Elmer Spectrum One FTIR instrument. Compound [Ru(p-cyme-
ne)Cl2]2, nBuLi solution, BF3(OEt)2, PPh3, and CO were purchased
from Sigma–Aldrich or Strem chemicals and used without further
purification. Complex Ag(Et2O)[B(C6F5)4][13] and IDipp[14] were syn-
thesized according to literature procedures.
Figure 4. Molecular structure of the cation of 7. Hydrogen atoms shown
were located in the electron-density map and freely refined, other hydrogen
atoms were removed for clarity.
tonated at the methine position on IDipp-BF3 (Figure 4). This
unusual binding is stabilized by an h2-interaction with the adja-
cent phenyl ring and an agostic interactions with the adjacent
CH3 group. The crystallographic data revealed the RuÀC dis-
tance for the deprotonated carbon is 2.104(3) ꢀ, whereas the
corresponding distances to the adjacent aryl and methyl car-
bons are 2.236(3), 2.234(3), and 2.342(3) ꢀ, respectively. The
CarylÀCaryl bond length on the h2-coordianted ring is elongated
to 1.448(4) ꢀ. The hydrogens on the agostically coordinated
methyl group were located in the electron-density map and
give rise to a RuÀH distance of 1.85(5) ꢀ.
Synthesis of IDippÀBF3 (1)
IDipp (1.045 g, 2.69 mmol) was dissolved in diethyl ether (10 mL),
and BF3(Et2O) (0.362 mL, 2.93 mmol) was added to the solution in
a dropwise fashion with stirring. A white crystalline precipitate
formed immediately, and n-pentane (10 mL) was added to the mix-
ture. After stirring for 10 min, the precipitate was collected by fil-
tration, washed with pentane (2ꢂ10 mL), and dried under vacuum
1
(1.165 g, 95%). H NMR (400 MHz, [D8]THF): d=7.52 (s, 2H, NCHꢂ
2), 7.44 (t, 3JHÀH =8 Hz, 2H, p-Dipp), 7.29 (d, 3JHÀH =8 Hz, 4H, m-
3
3
Dipp), 2.57 (septet, JHÀH =7 Hz, 4H, CH(CH3)2), 1.27 (d, JHÀH =7 Hz,
6H, CH(CH3)2), 1.17 ppm (d, 3JHÀH =7 Hz, 6H, CH(CH3)2); 13C NMR
(125 MHz, [D8]THF): 146.28 (ipso-iPr), 134.88 (ipso), 130.76 (p-Dipp),
124.93 (NCH), 124.27(m-Dipp), 29.70 (CH(CH3)), 25.10 (CH(CH3)),
23.17 ppm (CH(CH3)); 19F NMR (376.5 MHz, [D8]THF): d=
À140.01 ppm (1:1:1:1 q, 1JBÀF =33 Hz, BF3); 11B NMR (128.4 MHz,
[D8]THF): d=À0.89 ppm (q, 1JBÀF =33 Hz, BF3); elemental analysis
calcd for (456.39): C, 71.05; H, 7.95; N, 6.14; found: C, 71.35; H,
7.93; N, 6.14.
The formation of 7 suggests that upon abstraction of the
halide from Ru by Ag(Et2O)[B(C6F5)4], the cationic Ru center
mediates proton migration from the methine carbon to the
carbene carbon. The iPr-deprotonated carbene is trapped by
coordinatively unsaturated Ru, affording the unique binding
mode observed. Presumably, this rearrangement is facilitated
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LiCl. The mixture was concentrated in vacuo, and Et2O (10 mL)
added to cause the precipitation of red microcrystals. The solid
was washed with Et2O (3ꢂ5 mL) and dried. To remove final traces
of LiCl, the solid was dissolved in dichloromethane, filtered, the
product precipitated with n-pentane, and dried under high
vacuum (124 mg, 63%). Crystals suitable for X-ray diffraction analy-
sis were grown from slow diffusion of n-pentane in to a CH2Cl2 so-
Synthesis of (THF)xLi(IDippBF3) (2)
A solution of 1 (1.163 g, 2.55 mmol) in THF (10 mL) was cooled to
À408C, and a pre-cooled nBuLi solution (1.70 mL, 1.6m in hexane,
2.72 mmol) was added. The stirred mixture was allowed to warm
to RT over the course of 1 h to give a white precipitate. n-Pentane
(10 mL) was then added, the mixture was shaken, and the superna-
tant decanted. The white solid obtained was washed with n-pen-
tane (4ꢂ10 mL) and dried under vacuum (1.540 g, 97%). The prod-
uct was stored in a À408C freezer under N2. 1H NMR (400 MHz,
1
3
lution. H NMR (600 MHz, [D8]THF): d=7.45 (t, JHÀH =7 Hz, 1H, p-
3
3
Dipp), 7.34 (d, JHÀH =7 Hz, 2H, m-Dipp), 7.28 (t, JHÀH =7 Hz, 1H, p-
3
Dipp), 7.13 (d, JHÀH =7 Hz, 2H, m-Dipp), 6.85 (br s, 1H, NCH), 5.50
3
3
[D8]THF): d=7.27 (t, JHÀH =8 Hz, 1H, p-Dipp), 7.20 (dd, JHÀH =7 Hz,
(br, 2H, p-cymeneAr), 4.60 (br, 2H, p-cymeneAr), 2.90 (br, 2H,
CH(CH3)2), 2.71–2.53 (br m, 3H, CH(CH3)2), 1.66 (s, 3H, p-cymeneMe),
1.41 (d, 3JHÀH =7 Hz, 6H, CH(CH3)2), 1.27 (d, 3JHÀH =7 Hz, 6H,
3
3
8 Hz, 1H, p-Dipp), 7.15 (d, JHÀH =8 Hz, 2H, m-Dipp), 7.11 (d, JHÀH
=
3
8 Hz, 2H, m-Dipp), 6.27 (s, 1H, NCH), 2.79 (septet, JHÀH =7 Hz, 2H,
3
3
CH(CH3)2), 2.70 (septet, JHÀH =7 Hz, 2H, CH(CH3)2), 1.22 (d, JHÀH
=
3
3
CH(CH3)2), 1.21 (d, JHÀH =7 Hz, 6H, CH(CH3)2), 1.09 (d, JHÀH =6.8 Hz,
6H, CH(CH3)2), 0.97 ppm (br, 6H, p-cymene CH(CH3)2); 13C NMR
(125 MHz, CD2Cl2): d=130.05 (p-Dipp), 130.00 (p-Dipp), 124.49 (br,
m-Dipp), 124.19, 124.10 (br, m-Dipp), 30.60, 29.23, 28.97, 25.15,
23.25 ppm (br); 19F NMR (376.5 MHz, [D8]THF): d=À136.4–
À137.0 ppm (br m, BF3); 11B NMR (128.4 MHz, [D8]THF): d=
À0.51 ppm (br q, 1JBÀF =35 Hz, BF3); elemental analysis calcd for
C74H98B2Cl2F6N4Ru2·2(CH2Cl2) (1622.12): C, 56.27; H, 6.35, N, 3.45;
found: C, 56.12; H, 6.12; N, 3.41.
7 Hz, 6H, CH(CH3)2), 1.21 (d, 3JHÀH =7 Hz, 6H, CH(CH3)2), 1.13 (d,
3JHÀH =7 Hz, 6H, CH(CH3)2), 1.10 ppm (d, JHÀH =7 Hz, 6H, CH(CH3)2);
3
13C NMR (125 MHz, [D8]THF): d=146.42 (ipso Ar-iPr), 146.11 (ipso
Ar-iPr), 142.30 (ipso), 137.16 (ipso), 129.80 (NCH), 128.57 (p-Dipp),
127.43 (p-Dipp), 123.14 (m-Dipp), 122.80 (m-Dipp), 28.90 (CH(CH3)),
28.81 (CH(CH3)), 25.46 (CH(CH3)), 24.89 (CH(CH3)), 23.48 (CH(CH3)),
23.18 ppm (CH(CH3)); 19F NMR (376.5 MHz, [D8]THF): d=
1
À141.29 ppm (1:1:1:1 br q, JBÀF =36 Hz, BF3); 11B NMR (128.4 MHz,
1
7
[D8]THF): d=À2.26 ppm (q, JBÀF =38 Hz, BF3); Li NMR (155.5 MHz,
[D8]THF): d=À1.25 ppm (s); elemental analyses was not possible
due to the extreme air sensitivity of 2.
Synthesis of [Ru(IDippBF3)(p-cymene)(PPh3)Cl] (5)
PPh3 (16 mg, 0.061 mmol) was added to a dark red solution of 3
(43 mg, 0.030 mmol) in CH2Cl2 (2 mL), resulting in an immediate
color change to orange. The mixture was filtered and concentrated
to 1 mL. n-Pentane (15 mL) was added to cause the precipitation
of an orange-brown solid, which was collected, washed with n-
pentane (3ꢂ5 mL), and dried under high vacuum (45 mg, 76%).
Crystals suitable for X-ray diffraction analysis were grown from
Synthesis of Li[Ag(IDippBF3)2] (3)
To a suspension of 2 (1.180 g, 1.90 mmol) in THF (10 mL) was
added anhydrous AgCl (0.245 g, 1.72 mmol), and the mixture was
stirred for 16 h in the dark. The resulting suspension was filtered
through Celite pad, and the solvent was removed in vacuo. Tolu-
ene (10 mL) was added and stirred for 10 min, the mixture was
then filtered from LiCl, and concentrated under vacuum. The re-
sulting colorless oil was triturated in n-pentane, giving a white
solid, which was dried in vacuo (0.806 g, 83%). Crystals of [Ag-
(IDippBF3)2][Li(THF)3] were grown from slow diffusion of n-pentane
slow diffusion of pentane in to
a
CH2Cl2 solution. 1H NMR
(400 MHz, CD2Cl2): d=7.46–7.26 (m, 18H, PPh3 +p-Dippꢂ2+m-
Dippꢂ1), 7.18 (dd, 3JHÀH =8 Hz, 4JHÀH =1.3 Hz, 1H, m-Dipp), 7.13
(dd, 3JHÀH =8 Hz, 4JHÀH =2 Hz, 1H, m-Dipp), 7.10 (dd, 3JHÀH =8 Hz,
3
4JHÀH =2 Hz, 1H, m-Dipp), 6.03 (s, 1H, NCH), 5.81 (d, JHÀH =6 Hz, p-
1
3
cymeneAr), 5.47 (apparent t, 3JHÀH =5 Hz), 4.91 (d, 3JHÀH =6 Hz, p-
cymeneAr), 3.92 (d, 3JHÀH =6 Hz, p-cymeneAr), 2.65 (septet, 2H,
into a THF solution. H NMR (400 MHz, [D8]THF): d=7.30 (t, JHÀH
=
=
=
3
3
8 Hz, 2H, p-Dipp), 7.17 (d, JHÀH =8 Hz, 2H, m-Dipp), 7.02 (d, JHÀH
3
3
3JHÀH =7 Hz, 2H, CH(CH3)2), 2.53 (septet, JHÀH =7 Hz, 1H, CH(CH3)2),
8 Hz, 2H, m-Dipp), 6.33 (d, J=2 Hz, 1H, NCH), 2.60 (septet, JHÀH
7 Hz, 2H, CH(CH3)2), 2.56 (septet, 3JHÀH =7 Hz, 2H, CH(CH3)2), 1.18
(d, 3JHÀH =7 Hz, 6H, CH(CH3)2), 1.13 (d, 3JHÀH =7 Hz, 6H, CH(CH3)2),
1.10 (d, 3JHÀH =7 Hz, 6H, CH(CH3)2), 1.00 ppm (d, 3JHÀH =7 Hz, 6H,
CH(CH3)2); 13C NMR (125 MHz, [D8]THF): d=161.54 (pseudo dd,
2.45 (septet, 3JHÀH =7 Hz, 1H, CH(CH3)2), 2.32 (septet, 3JHÀH =7 Hz,
1H, CH(CH3)2), 2.12 (s, 3H, p-cymeneMe), 1.61 (d, 3JHÀH =7 Hz, 3H,
3
3
CH(CH3)2), 1.33 (d, JHÀH =7 Hz, 3H, CH(CH3)2), 1.31 (d, JHÀH =7 Hz,
3
3
3H, CH(CH3)2), 1.24 (d, JHÀH =7 Hz, 3H, CH(CH3)2), 1.09 (d, JHÀH
=
1JCÀ Ag =184 Hz, JCÀ Ag =159 Hz, NCAg), 146.39 (ipso Ar-iPr),
145.92 (ipso Ar-iPr), 140.59 (ipso), 136.16 (ipso), 129.39 (pseudo d,
2JCÀAg =15 Hz, NCH), 129.25 (p-Dipp), 128.41 (p-Dipp), 123.46 (m-
Dipp), 123.13 (m-Dipp), 28.99 (CH(CH3)), 28.94 (CH(CH3)), 25.45
(CH(CH3)), 25.27 (CH(CH3)), 23.33 (CH(CH3)), 23.21 ppm (CH(CH3));
19F NMR (376.5 MHz, [D8]THF): d=À139.5–À139.9 ppm (br m, BF3);
11B NMR (128.4 MHz, [D8]THF): d=1.0–À1.6 ppm (br m, BF3); 7Li
NMR (155.5 MHz, [D8]THF): d=À0.96 ppm (s); elemental analysis
calcd for C54H70AgB2F6LiN4 (1025.58): C, 63.24; H, 6.88; N 5.46;
found: C, 63.48; H, 6.80; N, 5.28.
109
1
107
7 Hz, 3H, CH(CH3)2), 1.08 (d, 3JHÀH =7 Hz, 3H, CH(CH3)2), 0.96 (d,
3JHÀH =7 Hz, 3H, CH(CH3)2), 0.92 (apparent t, 3JHÀH =6 Hz, 6H,
CH(CH3)2), 0.31 ppm (d, 3JHÀH =7 Hz, 3H, CH(CH3)2); 13C NMR
(125 MHz, CD2Cl2): d=149.20 (ipso Ar-iPr), 146.92 (ipso Ar-iPr),
146.74 (ipso Ar-iPr), 145.56 (ipso Ar-iPr), 138.40 (ipso), 134.26 (br,
PPh3), 133.70 (ipso), 130.74 (br, PPh3), 129.63 (p-Dipp), 129.26 (p-
3
3
Dipp), 128.92 (d, JPÀC =8.9 Hz, NCH), 128.82 (d, JPÀC =1.3 Hz, ipso
cymeneiPr), 128.33 (br, PPh3), 124.03 (m-Dipp), 123.49 (m-Dipp),
123.24 (m-Dipp), 122.43 (m-Dipp), 99.71 (d, 3JPÀC =5 Hz, p-cyme-
3
neAr), 88.99 (d, JPÀC =20 Hz, p-cymeneAr), 87.77 (p-cymeneAr), 79.95
(d, 3JPÀC =13 Hz, p-cymeneAr), 31.11 (CH(CH3)2), 30.00 (CH(CH3)2),
29.54 (CH(CH3)2), 29.98 (CH(CH3)2), 28.83 (CH(CH3)2), 27.45
(CH(CH3)2), 27.25 (CH(CH3)2), 26.93 (CH(CH3)2), 24.73 (CH(CH3)2),
24.69 (CH(CH3)2), 24.24 (CH(CH3)2), 22.61 (CH(CH3)2), 22.36
(CH(CH3)2), 22.05 (CH(CH3)2), 21.26 (CH(CH3)2), 17.45 ppm (p-cyme-
neMe); 31P NMR (162.0 MHz, CD2Cl2): d=30.27 ppm (s); 19F NMR
(CD2Cl2): À134.04 ppm (1:1:1:1 br q, 1JBÀF =33 Hz, BF3); 11B NMR
(128.4 MHz, CD2Cl2): d=À0.66 ppm (br q, 1JBÀF =37 Hz, BF3); ele-
mental analysis calcd for C55H64BClF3N2Ru (988.41): C, 66.83; H, 6.53,
N, 2.83; found: C, 66.12; H, 6.24; N, 2.80.
Synthesis of [Ru(p-cymene)(IDippBF3)Cl]2 (4)
To a solution of 3 (145 mg, 0.141 mmol) in THF was added [Ru(p-
cymene)Cl2]2 (75 mg, 0.122 mmol), and the mixture was stirred for
16 h at 258C, resulting a dark red solution and the precipitation of
AgCl. The solution was filtered and concentrated under vacuum.
The red oil obtained was dissolved in toluene (10 mL) and stirred
for 2 h, affording a red precipitate. CH2Cl2 (8 mL) was added, and
the resultant suspension was stirred for 2 h and then filtered from
Chem. Eur. J. 2014, 20, 6597 – 6602
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ꢁ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
1
Ar-iPr), 145.29 (ipso Ar-iPr), 140.54 (p-Dipp), 138.6 (br d, JCÀF
=
Synthesis of [Ru(IDippBF3)(p-cymene)(CO)Cl] (6)
1
243 Hz, p-C6F5), 136.7 (br d, JCÀF =246 Hz, m-C6F5), 132.85, 131.44
(p-Dipp), 127.04, 125.32 (NCH), 125.07 (NCH), 124.49 (m-Dipp),
124.45 (m-Dipp), 124.2 (br, ipso-C6F5), 124.03 (m-Dipp), 114.90 (ipso-
cymeneiPr), 104.54 (ipso-cymeneMe), 100.54 ([Ru]CC(CH3)2), 89.72 (q,
A deep red solution of 3 (53 mg, 0.036 mmol) in CH2Cl2 (2 mL) was
backfilled with 1 atm of CO, resulting in an immediate color
change to orange. The mixture was filtered and concentrated to
1 mL. n-Pentane (15 mL) was added to precipitate the product
from solution as a pale yellow solid, which was collected, washed
with n-pentane (3ꢂ5 mL), and dried under high vacuum (38 mg.
69%). Crystals suitable for X-ray diffraction analysis were grown
from slow diffusion of n-pentane into a CH2Cl2 solution. 1H NMR
(400 MHz, CD2Cl2): d=7.47 (t, 3JHÀH =8 Hz, 2H, p-Dipp), 7.30 (d,
3JHÀH =8 Hz, 1H, m-Dipp), 7.27 (d, 3JHÀH =7 Hz, 1H, m-Dipp), 7.24
(d, 3JHÀH =8 Hz, 1H, m-Dipp), 7.23 (d, 3JHÀH =8 Hz, 1H, m-Dipp),
J
CÀF =3 Hz, cymeneAr), 86.95 (q, JCÀF =3 Hz, p-cymeneAr), 81.07 (m,
p-cymeneAr), 80.88 (p-cymeneAr), 69.48 ([Ru]CC(CH3)2), 65.31 ([Ru] m-
Dipp), 30.87 (CH(CH3)2), 29.67 (CH(CH3)2), 29.23 (CH(CH3)2), 25.34
(CH(CH3)2), 25.28 (CH(CH3)2), 24.26 (CH(CH3)2), 23.38 (CH(CH3)2),
22.61 (CH(CH3)2), 22.38 (CH(CH3)2), 22.05 (CH(CH3)2), 21.06
(CH(CH3)2), 20.88 ([Ru]CCH3), 17.73 (p-cymeneMe), 2.51 ppm
([Ru]CH3); 19F NMR (376.5 MHz, CD2Cl2): d=À133.09 (m, 8F, o-C6F5),
1
3
À137.56 (1:1:1:1 q, JBÀF =34 Hz, 3F, BF3), À163.63 (t, JFÀF =20.1 Hz,
4F, p-C6F5), À167.48 (t, 3JFÀF =17.9 Hz, 8F, m-C6F5); 11B NMR
(128.4 MHz, CD2Cl2): d=À0.66 (q, 1JBÀF =34 Hz, BF3), À16.69 ppm
(s, B(C6F5)4); elemental analysis for C61H49B2F23N2Ru (1369.71): C,
53.49; H, 3.61; N, 2.05; found: C, 53.31; H, 3.58; N, 2.41.
3
6.67 (s, 1H, NCH), 6.28 (d, JHÀH =7 Hz, 1H, p-cymeneAr), 5.88 (ap-
3
3
parent t, JHÀH =8 Hz, 2H, p-cymeneAr), 5.37 (d, JHÀH =6 Hz, 1H, p-
cymeneAr), 2.84 (septet, 3JHÀH =7 Hz, 1H, CH(CH3)2), 2.67 (septet,
3JHÀH =7 Hz, 1H, CH(CH3)2), 2.54–2.42 (m, 2H, 2ꢂCH(CH3)2), 2.31
3
(septet, JHÀH =7 Hz, 1H, CH(CH3)2), 2.13 (s, 3H, p-cymeneMe), 1.33–
3
1.19 (m, 21H, 7ꢂCH(CH3)), 1.15 (d, JHÀH =7 Hz, 3H, CH(CH3)2), 1.12
(d, 3JHÀH =7 Hz, 3H, CH(CH3)2), 1.07 ppm (d, 3JHÀH =7 Hz, 3H,
CH(CH3)2); 13C NMR (125 MHz, CD2Cl2): d=193.60 (CO), 148.72 (ipso
Ar-iPr), 147.30 (ipso Ar-iPr), 146.16 (ipso-Ar-iPr), 145.09 (ipso Ar-iPr),
137.80 (ipso), 134.35 (ipso), 130.54 (p-Dipp), 130.16 (NCH), 130.15
(p-Dipp), 124.99 (m-Dipp), 123.94 (m-Dipp), 123.74 (m-Dipp), 123.37
(m-Dipp), 121.82 (ipso-cymeneiPr), 116.83 (ipso-cymeneMe), 108.49
(p-cymeneAr), 99.27 (p-cymeneAr), 95.05 (p-cymeneAr), 90.24 (p-cym-
eneAr), 31.84 (CH(CH3)2), 29.17 (CH(CH3)2), 29.14 (CH(CH3)2), 29.01
(CH(CH3)2), 26.84 (CH(CH3)2), 26.30 (CH(CH3)2), 24.73 (CH(CH3)2),
24.63 (CH(CH3)2), 24.16 (CH(CH3)2), 23.90 (CH(CH3)2), 22.81
(CH(CH3)2), 22.70 (CH(CH3)2), 22.63 (CH(CH3)2), 22.49 (CH(CH3)2),
19.52 ppm (p-cymeneMe); 19F NMR (376.5 MHz, CD2Cl2): d=
À137.11 ppm (1:1:1:1 q, 1JBÀF =34 Hz, BF3); 11B NMR (128.4 MHz,
Acknowledgements
The authors gratefully acknowledge the financial support of
NSERC of Canada. D.W.S. is also grateful for the award of
a Canada Research Chair. C.P. would like to gratefully acknowl-
edge a Queen Elizabeth II/Edwin Walter and Margery Warren
Scholarship in Science and Technology for funding.
Keywords: abnormal NHCs · anionic NHCs · CÀH activation ·
carbenes · ruthenium
1
CD2Cl2): d=À0.75 (q, JBÀF =37 Hz, BF3); IR (KBr): u˜ =2008 cmÀ1 (s,
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60.52; H, 6.55; N, 3.71; found: C, 58.82; H, 6.16; N, 3.55.
Synthesis of [Ru(IDippBF3)(p-cymene)][B(C6F5)4] (7)
Compound 3 (44 mg, 0.030 mmol) was dissolved in CH2Cl2 (2 mL),
and Ag(Et2O)[B(C6F5)4] (52 mg, 0.061 mmol) was added, causing an
immediate color change to orange and the precipitation of AgCl.
The mixture was stirred for 30 min at 258C and was filtered. The
solution was concentrated in vacuo to 2 mL, and (Me3Si)2O (2 mL)
was layered on top. After 24 h, pale orange needles of 7 separated
from solution. The solid was collected by filtration, washed with
Et2O, and dried under high vacuum (36 mg, 43%). Crystals suitable
for X-ray diffraction analysis were grown from slow diffusion of
Et2O in to a CH2Cl2 solution. 1H NMR (600 MHz, CD2Cl2): d=7.61
(dd, 3JHÀH =6, 9 Hz, 1H, p-Dipp), 7.59 (t, 3JHÀH =8 Hz, 1H, p-Dipp),
4
7.47 (d, 3JHÀH =9 Hz, 1H, m-Dipp), 7.39 (dd, 3JHÀH =8 Hz, JHÀH
=
3
4
1 Hz, 1H, m-Dipp), 7.37 (dd, JHÀH =8 Hz, JHÀH =1 Hz, 1H, m-Dipp),
7.29 (d, JHÀH =2 Hz, 1H, NCH), 7.21 (d, JHÀH =2 Hz, 1H, NCH), 6.35
3
3
3
3
(d, JHÀH =6 Hz, 1H, p-cymeneAr), 6.29 (d, JHÀH =6 Hz, 1H, p-cyme-
neAr), 4.59 (d, 3JHÀH =6 Hz, 1H, p-cymeneAr), 4.51 (d, 3JHÀH =6 Hz,
1H, p-cymeneAr), 2.67 (septet, 3JHÀH =7 Hz, 2H, CH(CH3)2), 2.66 (d,
3JHÀH =6 Hz, 1H, [Ru]m-Dipp), 2.53 (septet, 3JHÀH =7 Hz, 1H,
CH(CH3)2), 2.32 (septet, 3JHÀH =7 Hz, 1H, CH(CH3)2), 2.29 (s, 3H,
[Ru]CCH3), 2.05 (s, 3H, p-cymeneMe), 1.41 (d, 3JHÀH =7 Hz, 3H,
3
3
CH(CH3)2), 1.35 (d, JHÀH =7 Hz, 3H, CH(CH3)2), 1.32 (d, JHÀH =7 Hz,
3
3
3H, CH(CH3)2), 1.30 (d, JHÀH =7 Hz, 3H, CH(CH3)2), 1.21 (d, JHÀH
=
7 Hz, 3H, CH(CH3)2), 1.20 (d, 3JHÀH =7 Hz, 3H, CH(CH3)2), 1.17 (d,
3JHÀH =7 Hz, 3H, CH(CH3)2), 1.04 (d, 3JHÀH =7 Hz, 3H, CH(CH3)2),
À3.30 ppm (br s, 3H, [Ru]CH3); 13C NMR (200 MHz, CD2Cl2): d=
ˇ
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ꢁ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
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Received: February 7, 2014
Published online on April 29, 2014
Chem. Eur. J. 2014, 20, 6597 – 6602
www.chemeurj.org
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ꢁ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim