Steric and electronic parameters of a bulky yet flexible N-heterocyclic carbene: 1,3-bis(2,6-bis(1-ethylpropyl)phenyl)imidazol-2-ylidene (IPent)

Article abstract of DOI:10.1021/om400168b

The free N-heterocyclic carbene IPent (1; IPent = 1,3-bis(2,6-bis(1- ethylpropyl)phenyl)imidazol-2-ylidene) was prepared from the corresponding imidazolium chloride salt (2). The steric and electronic parameters of 1 were determined by synthesis of the gold(I) chloride complex [Au(IPent)Cl] (3) and the nickel-carbonyl complex [Ni(IPent)(CO)₃] (4), respectively. 3 and 4 were fully characterized by NMR spectroscopy, elemental analysis, and X-ray diffraction studies on single crystals.

Full text of DOI:10.1021/om400168b

Article
pubs.acs.org/Organometallics
Steric and Electronic Parameters of a Bulky yet Flexible
N‑Heterocyclic Carbene: 1,3-Bis(2,6-bis(1-
ethylpropyl)phenyl)imidazol-2-ylidene (IPent)
Alba Collado,† Janos Balogh,† Sebastien Meiries,† Alexandra M. Z. Slawin,† Laura Falivene,‡
́
Luigi Cavallo,‡,§ and Steven P. Nolan*,†
†EaStCHEM School of Chemistry, University of St Andrews, St Andrews KY16 9ST, U.K.
‡Dipartimento di Chimica e Biologia, Universita
̀
degli Studi di Salerno, Via Ponte Don Melillo, I-84084 Fisciano, SA, Italy
§Physical Sciences and Engineering, Catalysis Center, King Abdullah University of Science and Technology (KAUST), Thuwal
23955-6900, Saudi Arabia
S
* Supporting Information
ABSTRACT: The free N-heterocyclic carbene IPent (1;
IPent = 1,3-bis(2,6-bis(1-ethylpropyl)phenyl)imidazol-2-yli-
dene) was prepared from the corresponding imidazolium
chloride salt (2). The steric and electronic parameters of 1
were determined by synthesis of the gold(I) chloride complex
[Au(IPent)Cl] (3) and the nickel−carbonyl complex [Ni-
(IPent)(CO)3] (4), respectively. 3 and 4 were fully
characterized by NMR spectroscopy, elemental analysis, and
X-ray diffraction studies on single crystals.
uring the last few decades, N-heterocyclic carbenes
D(NHCs) have become a well-established tool in organic
and organometallic chemistry.1,2 They can participate in a wide
range of catalytic processes as ancillary ligands in transition-
metal catalysis1,3 or as organocatalysts.4 Due to their strong σ-
donor properties and usually large steric demand, NHC ligands
are able to stabilize low-valent transition-metal complexes that
can be used in many catalytic processes.3d,5 In this context,
significant efforts have targeted the development and character-
ization of new NHC ligands. One of the structural parameters
that can be modified to tune the ligand electronic and steric
Figure 1. Examples of NHC ligands with “flexible sterics”.
properties is the N-substituent of the imidazolium ring.1a
Recently, bulky NHCs with “flexible sterics”, i.e. ligands capable
bulky ligand (1). To synthesize the IPent·HCl salt11 (2), the
of adjusting their steric bulk as a function of incoming
substrates such as IBiox5-12,6 CAAC (cyclic (alkyl)(amino)-
carbenes),7 IBiox[(−)menthyl],8 and IPr*9 (Figure 1), have
drawn significant attention because of their spectacular
reactivity.
required aniline can be prepared following Steele’s method.12
This compound was converted to 2 following standard
procedures for the synthesis of NHC·HX salts (Scheme 1,
Supporting Information).13
The free carbene IPent (1) was easily generated by treatment
of 2 with NaH and KOtBu for 16 h (unoptimized reaction
time) at room temperature in THF. 1 was isolated as a white
solid in 65% yield (eq 1) and characterized by 1H and 13C{1H}
NMR spectroscopy and elemental analysis. The most salient
spectroscopic feature of this compound is the presence of a
singlet at 220.5 ppm corresponding to the carbenic carbon in
the 13C{1H} NMR spectrum.14
Organ and co-workers have recently reported the excellent
activity of palladium complexes containing the hindered yet
flexible IPent ligand (1). This ligand is a bulkier analogue of IPr
(IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene), one
of the most common NHC ligands, and has been shown to
significantly increase the activity of the [Pd-PEPPSI-NHC]
systems in challenging cross-coupling reactions.10 As part of our
ongoing research into the development of new catalysts
containing NHC ligands, we were interested in the isolation
and characterization of free IPent. Herein, we report the
synthesis and the steric and electronic characterization of this
Received: February 28, 2013
© XXXX American Chemical Society
A
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of the conformers of 3 was calculated using the SambVca17
software. These values (49.0 (3a), 48.6 (3b)) show that IPent
is a bulky ligand, presenting a steric demand significantly higher
than that reported for IMes or IPr and closer to that for IPr*
(Table 1).
Scheme 1. Synthetic Steps Leading to 2
Table 1. Comparison of 3 with [Au(NHC)Cl] Analogues
a
NHC
Au−C1 (Å)
1.998(5)
%Vbur
36.5
b
IMes
b
IPr
1.942(3)
44.5
c
IPr*
1.987(7)
50.4
IPent
1.968(11), 1.979(10)
48.6, 49.0
a
Parameters used for SambVca calculations: sphere radius, 3.50 Å;
Au−C1, 2.00 Å; mesh spacing, 0.05; Bondi radius, 1.17. H atoms are
b
c
To better understand the reactivity and use of NHCs in
catalytic processes, the quantification of their steric and
electronic properties is of fundamental importance. Therefore,
we set out to evaluate these parameters for 1. To determine the
steric demand of NHC ligands, our group, in collaboration with
Cavallo, have proposed the “percent buried volume” model.
This value (%Vbur) is defined as the percentage of the total
volume of a sphere centered upon the metal atom that is
occupied by the ligand.5c,15 The gold(I) [Au(NHC)Cl] family
of complexes is a useful metal-based model to quantify the
steric properties of different ligands.5c Therefore, [Au(IPent)-
Cl] (3) was synthesized by treatment of 1 with 1 equiv of
[Au(DMS)Cl] (DMS = dimethyl sulfide) in THF (eq 2).
excluded. Taken from ref 16. Taken from ref 9c.
To better characterize the bulkiness of IPent, the steric map
of the square-planar standard model complex [Ir(IPent)Cl-
(CO)2] was first calculated (Figure 3).18 This map shows a top
Complex 3 was fully characterized by 1H and 13C{1H} NMR
spectroscopy, elemental analysis, and X-ray diffraction analysis.
The carbene peak in the 13C{1H} NMR spectrum appears at
174.2 ppm and compares well with signals for related
[Au(NHC)Cl] complexes.16 Crystals of 3 were grown by
slow vapor diffusion of pentane into a saturated dichloro-
methane solution. Interestingly, two variants of complex 3 were
found in the crystal lattice. These two low-energy conformers
can be considered as indicative of the high degree of flexibility
of the ligand (Figure 2).
Figure 3. Steric mapping for the model complex [Ir(IPent)Cl(CO)2]
and [Pd-PEPPSI-IPent].
view of the complex and represents the space IPent occupies
around the iridium atom, which is not homogeneously
distributed. Two quadrants appear to be very bulky, while the
two others show much lower steric hindrance. We hypothesized
that this map would be a good qualitative model for the [Pd-
PEPPSI-IPent] complex, which also presents a square-planar
geometry. Therefore, we retrieved the crystal data from the
CCDC database reported by Organ for this complex and
calculated its steric map. We were pleased to observe similar
steric occupations in both cases (Figure 3). This distribution
might very well explain the high catalytic activity of the [Pd-
PEPPSI-IPent] complex in cross-coupling reactions.10 The less
hindered quadrant could facilitate the entrance of substrates
into the metal coordination sphere, whereas the bulkier
direction might promote the reductive elimination of the
coupling products, as has been previously postulated for
[Pd(NHC)(cinnamyl)Cl] complexes.18a,b
Complex 3 presents the expected linear geometry with C−
Au−Cl angles of 175.9(4)° (3a) and 177.2(3)° (3b). The Au−
Ccarbene distances found for the conformers are 1.979(10) Å
(3a) and 1.968(11) Å (3b). The %Vbur value of IPent for each
Once the steric parameters of IPent were determined, we
next looked at its electronic properties. One established method
to determine the electronic parameters of two-electron ligands
is by IR measurements of the carbonyl stretching frequencies
(ν) of the related [Ni(L)(CO)3] complexes.19,20 The A1
carbonyl stretching frequency of CO ligands in these
compounds is known as the Tolman electronic parameter
Figure 2. ORTEP representation of the conformer 3a showing
thermal ellipsoids at the 50% probability level.
B
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(TEP) and is directly correlated to the electron-donating ability
of the ligand: a lower TEP corresponds to a more σ-donating
ligand.19 Therefore, the nickel derivative [Ni(IPent)(CO)3] (4)
was synthesized (eq 3).
Figure 4. ORTEP representation of [Ni(IPent)(CO)3] (4) showing
thermal ellipsoids at the 50% probability level.
Treatment of a THF solution of 1 with a slight excess of
[Ni(CO)4] (see the Experimental Section for safety informa-
tion) for 3 h led to the desired nickel complex 4, which was
isolated as a beige microcrystalline solid in 92% yield (eq 3).
The color of compound 4 hinted at its saturated character.20d
This was also supported by its IR spectra in solution, where the
positions of the carbonyl bands, 2049.3 (A1) and 1959.8 (E)
cm−1 in dichloromethane solution and 2053.1 (A1) and 1977.8
and 1970.7 (E) cm−1 in hexane solution, are consistent with the
existence of the tricarbonyl complex (Table 2). Thus, the TEP
In summary, the free IPent carbene (1) has been obtained
from the corresponding imidazolium chloride salt (2) and its
steric and electronic properties have been evaluated. The %Vbur
value of IPent in [Au(IPent)Cl] (3) was calculated and
compared to the reported values for other [Au(NHC)Cl]
complexes. The steric mapping of a square-planar model
complex containing 3 is also reported. The electronic
properties of IPent were evaluated by means of IR measure-
ments of [Ni(IPent)(CO)3] (4). These parameters show that
IPent is a flexible ligand, bulkier and more σ-donating than IPr.
Table 2. Comparison of 4 with [Ni(NHC)(CO)3]
a
Analogues
a
EXPERIMENTAL SECTION
NHC
Ni−C1 (Å)
TEPDCM (cm−1
)
TEPhex (cm−1
)
%Vbur
■
b
Preparation of IPent (1). In a glovebox, 2 (200 mg, 0.372 mmol),
NaH (13.4 mg, 0.558 mmol), and the tip of a spatula of KOtBu were
dissolved in THF (15 mL). The mixture was stirred at room
temperature for 16 h and filtered. Then, the solvent was removed in
vacuo. The residue was redissolved in pentane and filtered through
Celite. The solvent was removed in vacuo, affording a white solid.
IMes
1.971(3)
1.979(2)
1.971(3)
1.973(4)
2050.7
2051.5
2052.7
2049.3
2054.0
2055.1
d
34.0
38.1
38.8
39.4
b
IPr
c
IPr*
IPent
2053.1
a
SambVca parameters: sphere radius, 3.50 Å; Ni−C1, 2.00 Å; mesh
b
1
spacing, 0.05; Bondi radius, 1.17. H atoms are excluded. Reference
Yield: 120 mg (65%). H NMR (400 MHz, C6D6): δ 7.32 (t, J = 7.8
20d. For comparison, the published CIF file was retrieved23 and the %
c
Hz, 2H, CHAr), 7.11 (d, J = 7.8 Hz, 4H, CHAr), 6.73 (s, 2H, CH4,5),
2.67−2.53 (m, 4H, Et2CH), 1.46−1.76 (m, 16 H, CH3CH2), 0.93 (t, J
= 7.6 Hz, 12H, CH3), 0.83 (t, J = 7.6 Hz, 12H, CH3). 13C{1H} NMR
(100 MHz, C6D6): δ 220.5 (Ccarb), 143.3 (CAr), 141.4 (CAr), 128.2
(CHAr), 123.8 (CHAr), 122.2 (CH4,5), 42.0 (Ar-CHEt2), 29.2
(CH2CH3), 28.9 (CH2CH3), 12.5 (CH3), 11.9 (CH3). Anal. Calcd
for C35H52N2 (733.22): C, 83.94; H, 10.47; N, 5.59. Found: C, 83.85;
H, 10.49; N, 5.69.
Vbur recalculated using the parameters described in footnote a.
d
[Ni(IPr*)(CO)3] is insoluble in hexane.
for this ligand, 2049.3 cm−1 in DCM and 2053.1 cm−1 in
hexane, shows that IPent (1) is slightly more σ-donating than
IMes, IPr and IPr*. The TEP value obtained in DCM solution
agrees with the value recently reported by Organ of 2049.6
cm−1,21 which was calculated from the CO stretching
frequencies of the [Ir(IPent)Cl(CO)2] complex by applying
the correlation we previously established between the Ir and Ni
systems.22
Preparation of [Au(IPent)Cl] (3). In a glovebox, [Au(DMS)Cl]
(60.0 mg, 0.204 mmol) was added to a solution of 1 (102 mg, 0.204
mmol) in THF (10 mL). The mixture was kept in the dark and stirred
at room temperature for 16 h. Then, the reaction mixture was filtered
through silica outside the glovebox. The solvent was concentrated, and
pentane (4 mL) was added to the solution. A white solid was obtained,
which was washed with pentane and dried under vacuum. Yield: 121
Complex 4 was also characterized by 1H and 13C{1H} NMR
spectroscopy and elemental analysis. The resonance due to the
carbenic carbon appears at 196.8 ppm in the 13C{1H} NMR
spectrum and confirms the coordination of the ligand to the
nickel atom.20d 4 was structurally characterized by single-crystal
diffraction studies. Crystals of 4 were grown by slow cooling of
a saturated hexane solution to −40 °C (Figure 4).
The structure of 4 confirms the presence of three carbonyl
groups coordinated to the metal center. 4 presents the expected
tetrahedral geometry around the Ni atom with C−Ni−C angles
between 108 and 111°.20d The percent buried volume for 4 was
also calculated using SambVca and compared with those for
other [Ni(NHC)(CO)3] complexes (see Table 2). Interest-
ingly, IPent presents the largest %Vbur value for this family of
complexes, even larger than that calculated for IPr*. The
remarkable difference between the percent buried volume
computed for the linear complex 3 (48.8) and for 4 (39.4)
highlights the degree of flexibility of the IPent ligand.
1
mg (81%). H NMR (400 MHz, CD2Cl2): δ 7.55 (t, J = 7.8 Hz, 2H,
CHAr), 7.26 (d, J = 7.8 Hz, 4H, CHAr), 7.11 (s, 2H, CH4,5), 2.24−2.08
(m, 4H, Et2CH), 1.45−1.85 (m, 16 H, CH3CH2), 0.93 (t, J = 7.6 Hz,
12H, CH3), 0.79 (t, J = 7.6 Hz, 12H, CH3). 13C{1H} NMR (100 MHz,
C6D6): δ 174.2 (Au−C), 143.4 (CAr), 136.8 (CAr), 130.2 (CHAr),
124.7 (CHAr), 123.7 (CH4,5), 42.8 (Ar−CHEt2), 29.2 (CH2CH3), 28.1
(CH2CH3), 12.7 (CH3), 12.2 (CH3). Anal. Calcd for C35H52AuClN2
(733.22): C, 57.33; H, 7.15; N, 3.82. Found: C, 57.29; H, 7.06; N,
3.85.
Preparation of [Ni(CO)3(IPent)] (4). In a glovebox, [Ni(CO)4]
(50.0 μL, 0.381 mmol) was chilled to −40 °C and added via syringe to
a THF (10 mL) solution of 1 (127 mg, 0.254 mmol) at −40 °C.
(Caution! [Ni(CO)4] is an extremely toxic substance and should be
handled with appropriate safety measures.) All the glassware and syringes
used in this synthetic procedure were washed with a PPh3 solution in
THF to neutralize any remaining [Ni(CO)4]. After 3 h, the solvent
was removed under vacuum. The residue was dissolved in pentane and
filtered through Celite. The solvent was evaporated, affording a beige
solid. Yield: 148 mg (76%). 1H NMR (300 MHz, C6D6): δ 7.27 (t, J =
C
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Organometallics
Article
7.8 Hz, 2H, CHAr), 7.21 (d, J = 7.8 Hz, 4H, CHAr), 6.62 (s, 2H,
CH4,5), 2.46−2.38 (m, 4H, Et2CH), 1.97−1.83 (m, 4H, CH3CH2),
1.82−1.62 (m, 4 H, CH3CH2), 1.56−1.38 (m, 8H, CH3CH2), 1.08 (t, J
= 7.6 Hz, 12H, CH3), 0.73 (t, J = 7.6 Hz, 12H, CH3). 13C{1H} NMR
(100 MHz, C6D6): δ 197.9 (CO), 196.8 (NCN), 144.1 (CAr), 139.2
(CAr), 129.3 (CHAr), 125.5 (CHAr), 123.9 (CH4,5), 41.7 (Ar-CHEt2),
28.2 (CH2CH3), 26.4 (CH2CH3), 12.6 (CH3), 11.3 (CH3). IR νCO
(hexane, cm−1): 2053.1 (s), 1977.9, 1970.7 (vs). IR νCO (DCM,
cm−1): 2049.3 (s), 1959.8 (vs). Anal. Calcd for C38H52N2NiO3
(643.52): C, 70.92; H, 8.14; N, 4.35. Found: C, 70.80; H, 8.23; N,
4.41.
Organometallics 2011, 30, 5463−5470. (d) Chartoire, A.; Frogneux, X.;
Nolan, S. P. Adv. Synth. Catal. 2012, 354, 1897−1901.
(10) (a) Organ, M. G.; Çalimsiz, S.; Sayah, M.; Hoi, K. H.; Lough, A.
J. Angew. Chem., Int. Ed. 2009, 48, 2383−2387. (b) Valente, C.;
C
̧
alimsiz, S.; Hoi, K. H.; Mallik, D.; Sayah, M.; Organ, M. G. Angew.
Chem., Int. Ed. 2012, 51, 3314−3332. (c) Hoi, K. H.; Coggan, J. A.;
Organ, M. G. Chem. Eur. J. 2013, 19, 843−845.
(11) To the best of our knowledge, the detailed syntheses of
IPentHCl and free IPent have never been reported.
(12) Steele, B. R.; Georgakopoulos, S.; Micha-Screttas, M.; Screttas,
C. G. Eur. J. Org. Chem. 2007, 19, 3091−3094.
(13) Benhamou, L.; Chardon, E.; Lavigne, G.; Bellemin-Laponnaz, S.;
́
Cesar, V. Chem. Rev. 2011, 111, 2705−2733.
ASSOCIATED CONTENT
* Supporting Information
Text, figures, and CIF files giving full characterization data,
crystallographic data for 3 and 4, details of the synthesis of 2,
and steric maps of 3 and 4. This material is available free of
charge via the Internet at http://pubs.acs.org.
■
(14) Tapu, D.; Dixon, D. A.; Roe, C. Chem. Rev. 2009, 109, 3385−
3407.
S
(15) Hillier, A. C.; Sommer, W. J.; Yong, B. S.; Petersen, J. L.;
Cavallo, L.; Nolan, S. P. Organometallics 2003, 22, 4322−4326.
́
(16) de Fremont, P.; Scott, N. M.; Stevens, E. D.; Nolan, S. P.
Organometallics 2005, 24, 2411−2418.
(17) This software is available free of charge at http://www.molnac.
unisa.it/OMtools.php.
AUTHOR INFORMATION
Corresponding Author
*E-mail for S.P.N.: snolan@st-andrews.ac.uk.
Notes
■
(18) (a) Chartoire, A.; Lesieur, M.; Falivene, L.; Slawin, A. M. Z.;
Cavallo, L.; Cazin, C. S. J.; Nolan, S. P. Chem. Eur. J. 2012, 18, 4517−
4521. (b) Wu, L.; Drinkel, E.; Gaggia, F.; Capolicchio, S.; Linden, A.;
Falivene, L.; Cavallo, L.; Dorta, R. Chem. Eur. J. 2011, 17, 12886−
12890. (c) Poater, A.; Ragone, F.; Mariz, R.; Dorta, R.; Cavallo, L.
Chem. Eur. J. 2010, 16, 14348−14353. (d) Ragone, F.; Poater, A.;
Cavallo, L. J. Am. Chem. Soc. 2010, 132, 4249−4258.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
(19) Tolman, C. A. Chem. Rev. 1977, 77, 313−348.
(20) (a) Herrmann, W. A.; Goossen, L. J.; Artus, G. R. J.; Kocher, C.
The ERC (Advanced Investigator Award-FUNCAT), Umicore,
Syngenta and the EPSRC are thanked for support of this work.
We thank the EPSRC National Mass Spectrometry Service
Center in Swansea for mass analyses. S.P.N. is a Royal Society
Wolfson Research Merit Award holder.
̈
Organometallics 1997, 16, 2472−2477. (b) Dorta, R.; Stevens, E. D.;
Hoff, C. D.; Nolan, S. P. J. Am. Chem. Soc. 2003, 125, 10490−10491.
(c) Scott, N. M.; Nolan, S. P. Eur. J. Inorg. Chem. 2005, 2005, 1815−
1828. (d) Dorta, R.; Stevens, E. D.; Scott, N. M.; Costabile, C.;
Cavallo, L.; Hoff, C. D.; Nolan, S. P. J. Am. Chem. Soc. 2005, 127,
2485−2495. (e) Gusev, D. G. Organometallics 2009, 28, 6458−6461.
(21) Pompeo, M.; Froese, R. D. J.; Hadei, N.; Organ, M. G. Angew.
Chem., Int. Ed. 2012, 51, 11354−11357.
(22) Kelly, R. A., III; Clavier, H.; Giudice, S.; Scott, N. M.; Stevens,
E. D.; Bordner, J.; Samardjiev, I.; Hoff, C. D.; Cavallo, L.; Nolan, S. P.
Organometallics 2007, 27, 202−210.
(23) Balogh, J.; Slawin, A. M. Z.; Nolan, S. P. Organometallics 2012,
31, 3259−3263.
REFERENCES
■
(1) (a) N-Heterocyclic Carbenes in Synthesis; Nolan, S. P., Ed.; Wiley-
VCH: New York, 2006. (b) Cazin, C. S. J. N-Heterocyclic Carbenes in
Transition Metal Catalysis; Springer: Berlin, 2011.
(2) (a) De Vreese, R.; D’hooghe, M. Beilstein J. Org. Chem. 2012, 8,
398−402. (b) Lin, J. C. Y.; Huang, R. T. W.; Lee, C. S.; Bhattacharyya,
A.; Hwang, W. S.; Lin, I. J. B. Chem. Rev. 2009, 109, 3561−3598.
́
(c) de Fremont, P.; Marion, N.; Nolan, S. P. Coord. Chem. Rev. 2009,
253, 862−892.
(3) (a) Gaillard, S.; Cazin, C. S. J.; Nolan, S. P. Acc. Chem. Res. 2011,
45, 778−787. (b) Nolan, S. P. Acc. Chem. Res. 2011, 44, 91−100.
́
(c) Dıez-Gonzal
́
ez, S.; Marion, N.; Nolan, S. P. Chem. Rev. 2009, 109,
3612−3676. (d) Wurtz, S.; Glorius, F. Acc. Chem. Res. 2008, 41, 1523−
̈
1533. (e) Kantchev, E. A. B.; O’Brien, C. J.; Organ, M. G. Angew.
Chem., Int. Ed. 2007, 46, 2768−2813.
(4) (a) Enders, D.; Niemeier, O.; Henseler, A. Chem. Rev. 2007, 107,
5606−5655. (b) Marion, N.; Díez-Gonzal
Chem., Int. Ed. 2007, 46, 2988−3000.
(5) (a) Cavallo, L.; Correa, A.; Costabile, C.; Jacobsen, H. J.
́
ez, S.; Nolan, S. P. Angew.
́
́
Organomet. Chem. 2005, 690, 5407−5413. (b) Dıez-Gonzalez, S.;
Nolan, S. P. Coord. Chem. Rev. 2007, 251, 874−883. (c) Clavier, H.;
Nolan, S. P. Chem. Commun. 2010, 46, 841−861. (d) Droge, T.;
̈
Glorius, F. Angew. Chem., Int. Ed. 2010, 49, 6940−6952.
(6) Altenhoff, G.; Goddard, R.; Lehmann, C. W.; Glorius, F. J. Am.
Chem. Soc. 2004, 126, 15195−15201.
(7) Lavallo, V.; Frey, G. D.; Donnadieu, B.; Soleilhavoup, M.;
Bertrand, G. Angew. Chem., Int. Ed. 2008, 47, 5224−5228.
(8) Wurtz, S.; Lohre, C.; Frohlich, R.; Bergander, K.; Glorius, F. J.
̈
̈
Am. Chem. Soc. 2009, 131, 8344−8345.
(9) (a) Berthon-Gelloz, G.; Siegler, M. A.; Spek, A. L.; Tinant, B.;
Reek, J. N. H.; Marko, I. E. Dalton Trans. 2010, 39, 1444−1446.
(b) Laskowski, C. A.; Miller, A. J. M.; Hillhouse, G. L.; Cundari, T. R.
J. Am. Chem. Soc. 2010, 133, 771−773. (c) Gom
́ ́ ́
ez-Suarez, A.; Ramon,
R. S.; Songis, O.; Slawin, A. M. Z.; Cazin, C. S. J.; Nolan, S. P.
D
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