A cationic terminal methylene complex of Ir(I) supported by a pincer ligand

Article abstract of DOI:10.1021/om400383s

A rare example of a cationic methylene complex of Ir(I), [(PONOP)Ir(CH ₂)]⁺, 2 (PONOP = 2,6-bis(di-tert-butylphosphinito) pyridine), has been prepared by α-hydride abstraction from the previously described neutral methyl complex [(PO

Full text of DOI:10.1021/om400383s

Note
pubs.acs.org/Organometallics
A Cationic Terminal Methylene Complex of Ir(I) Supported by a
Pincer Ligand
Jesus Campos,†,§ Riccardo Peloso,† Maurice Brookhart,‡ and Ernesto Carmona*,†
†Instituto de Investigaciones Químicas-Departamento de Química Inorgan
́
ica, Universidad de Sevilla-Consejo Superior de
́
Investigaciones Científicas, Avda. Americo Vespucio 49, 41092 Sevilla, Spain
‡Department of Chemistry, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States
S
* Supporting Information
ABSTRACT: A rare example of a cationic methylene complex of Ir(I), [(PONOP)-
Ir(CH2)]+, 2 (PONOP = 2,6-bis(di-tert-butylphosphinito)pyridine), has been
prepared by α-hydride abstraction from the previously described neutral methyl
complex [(PONOP)Ir(CH3)]. The intrinsic high reactivity of the compound
prevented both the isolation of a pure solid and its full characterization in the solid
state. Nevertheless, the proposed molecular structure finds unequivocal support in
multinuclear NMR spectroscopy and in reactivity studies that include reactions with
Lewis bases, dihydrogen, and ethyl diazoacetate. An ylide compound, 3, resulted from
the reaction between [(PONOP)Ir(CH2)]+ and PMe3, while the η2-alkene complex 5 formed in a CC coupling reaction
involving the methylene ligand of 2 and ethyl diazoacetate. Hydrogenolysis of the IrCH2 linkage of 2 led to several, previously
known, hydride and dihydrogen iridium complexes.
ince the original report by Fischer and Maasbol of the first
demonstrated utility in stabilizing elusive species such as σ-
̈
Sheteroatom carbene complex, transition metal carbenes CH421 complexes or related σ-H2 derivatives.22 Moreover, they
1
have provided relevant mechanistic information regarding C−H
bond activation, metal−carbon bond hydrogenolysis, and other
important organometallic transformations.23 The high level of
steric protection provided by this ligand is believed to be
responsible for the kinetic stabilization of its complexes, which
allows detecting and studying reactive intermediates often
invoked as key participants in catalytic and stoichiometric
reactions.
have become one of the most prominent families of
organometallic compounds.2,3 The past 15 years have witnessed
remarkable advances in the chemistry of carbene complexes of
rhodium and iridium, both with and without stabilizing
heteroatoms,3−12 including the accessibility of O- and N-
substituted carbenes by double C−H bond activation
reactions.4,5,8−11
It was early recognized that metal alkylidene compounds,
that is, carbene complexes that possess only hydrogen or
hydrocarbyl substituents, were of special interest due to their
higher reactivity compared to heteroatom-stabilized carbene
complexes.13 Schrock’s discovery of an isolable nucleophilic
TaCH2 complex14 called attention to the simple methylene
ligand, in both mononuclear and binuclear systems.15,16
Terminal methylene ligands may exhibit nucleophilic or
electrophilic reactivity at the carbene carbon atom.13−15
Whereas, as already indicated, a wealth of experimental and
theoretical information has accumulated concerning Rh and Ir
carbene complexes over the years, only a few examples of their
methylene derivatives are known to date. Following initial
studies by Thorn and Tulip17 and by Roper and co-
workers,13b,15a,18 a major advance in this field was the structural
characterization by Fryzuk’s group of an isolable Ir(I)-
methylene complex.19 In all these early examples the Ir
CH2 moiety featured electrophilic reactivity, whereas the
complex (η5-C5Me5)Ir(CH2)(PMe3) described in 1989 by
Bergman and Klein exhibited nucleophilic character.20
We have recently discussed the generation of electrophilic
cationic alkylidene complexes of Ir(III)24a and Pt(II)24b by α-
hydride abstraction reactions from the appropriate metalacyclic
precursor. The alkylidene functionality of these complexes was
part of a sterically protected five-membered ring originally
derived from the facile metalation of a xylyl phosphine,
24a
PMeXyl2 and PiPr2Xyl,24b respectively (Xyl = 2,6-dimethyl-
phenyl). Accordingly, we envisaged that the bulky PONOP
ligand might stabilize a fleeting cationic Ir(I) methylene species,
[(PONOP)Ir(CH2)]+, obtained by α-hydride abstraction from
the methyl terminus of (PONOP)Ir(CH3).23a
In agreement with expectations, we found that treatment of a
C6D5Br solution of 1 with 1 equiv of [Ph3C][B(C6F5)4] at −20
°C resulted in a rapid color change from orange to dark green.
Investigation of the reaction by NMR spectroscopy showed the
selective formation of the desired complex (Scheme 1) and
concomitant disappearance of its precursor 1. No other
products were detected. In the 31P{1H} NMR spectrum of 2,
the singlet at 186.4 ppm corresponding to the starting methyl
Rhodium and iridium complexes bearing the ancillary
tridentate pincer ligand 2,6-bis(di-tert-butylphosphinito)-
pyridine (PONOP, in shorthand notation) have recently
Received: May 2, 2013
© XXXX American Chemical Society
A
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Note
independently prepared by treatment of (PONOP)IrCl with
Scheme 1. Synthesis of Compound 2
NaBArF and PMe3. The fate of the ylide ligand of 3 was not
1
investigated. In the H NMR spectrum of the latter complex, a
doublet of triplet resonance centered at 2.56 ppm and featuring
1
two- and three-bond H−31P couplings of 17.0 and 5.8 Hz,
respectively, replaced the deshielded triplet at 18.6 ppm
characteristic of the IrCH2 unit of 2. In accordance with
expectations, the 31P{1H} NMR spectrum of 3 consisted of two
singlets at δ 182.0 (PONOP) and 32.5 ppm (PMe3). The
methylene carbon atom of 2 resonating at 252.2 ppm
undergoes, upon ylide formation, a remarkable shift to lower
frequencies, appearing in 3 as a doublet of triplets centered at
−27.9 ppm, with corresponding 13C−31P coupling constants of
27 and 5 Hz. The NMR spectra of the cationic adduct 4 are
unexceptional. As expected, its 31P{1H} NMR spectrum
consists of a doublet and a triplet centered at 194.6 and
−46.2 ppm, due respectively to the PONOP and the PMe3 31P
nuclei, with a two-bond JPP value of 16 Hz.
complex was replaced by a new, also sharp singlet at 180.2 ppm,
suggesting that the integrity of the [(PONOP)Ir]+ moiety was
maintained in the new compound 2. At the same time, the H
1
and 13C{1H} NMR signals due to the iridium-bound methyl
group in 1 experienced a remarkable shift to higher frequencies,
from 2.1 (1H) and −24.8 (13C) in 1, to 18.6 and 252.2 ppm
(1JCH = 138 Hz) in 2, respectively, in agreement with the
formation of [(PONOP)Ir(CH2)]+. These NMR data compare
well with those reported25 for the few cationic alkylidenes of
iridium known to date.
The dark green solutions of the iridium methylene complex 2
were thermally stable at −20 °C but slowly decomposed at
room temperature with a half-life of ca. 4 days (C6D5Br). In
addition, they exhibited high reactivity toward oxygen and
water, which, along with the presence of the triphenylmethane
reaction byproduct and of small amounts of unidentified
impurities resulting from partial thermal decomposition,
precluded isolation of 2 with analytical purity. Evaporation of
the solvent or precipitation by addition of hexane led invariably
to a dark oily material. It is worth mentioning in this regard that
attempts to produce a cationic RhCH2 analogue starting
from (PONOP)Rh(CH3)21a proved unsuccessful. NMR studies
of the reaction of the latter compound with [Ph3C][B(C6F5)4]
at −80 °C indicated the formation of a complex mixture of
products, among them the quinoid dimer of the triphenyl-
methyl radical,26 probably as a result of a radical reaction
pathway.
To provide additional support for the formulation of 2 as a
cationic methylene complex, we investigated its reactivity. The
first indication of its electrophilic character was a result of
serendipity, since performing the reaction of complex 1 and
[Ph3C][B(C6F5)4] in tetrahydrofuran produced a viscous
solution interpreted as originating from the cationic polymer-
ization of THF.27 However, the alkylidene nature of 2 was
unequivocally demonstrated by its reaction with PMe3 (Scheme
2) that afforded an orange crystalline solid characterized by
The molecular structures of the two PMe3 complexes, 3 and
4, were unequivocally confirmed by X-ray crystallography, with
the results represented in Figure 1. For the two compounds, the
coordination environment around the Ir center presents little
distortion from an ideal square-planar geometry. In the ylide
complex 3, the Ir(1)−C(22) bond distance of 2.135(2) Å is
only slightly longer than the 2.091(4) Å value reported for the
cationic methyl hydride23a [(PONOP)Ir(CH3)(H)]+ and
comparable to that in other pincer methyl derivatives of
Ir(III).28 The ylidic carbon has a distorted tetrahedral
environment, with an Ir(1)−C(22)−P(3) angle of 125.2(1) °.
We also studied the reactivity of 2 toward ethyl diazoacetate,
N2CHCO2Et (EDA). A smooth C−C coupling reaction
occurred at −20 °C, accompanied by a marked color change
from dark green to intense red. From the resulting solutions,
red crystals of an also cationic alkene complex, 5, that contains
a coordinated molecule of ethyl acrylate, were isolated (Scheme
3). In addition to resonances due to the ester terminus,
1
−CO2Et, the H and 31C NMR spectra of 5 contained signals
revealing η2-coordination of a CH2CH fragment. In
particular, the coordinated 13C nuclei resonate at δ 39.9
1
1
(CH2; JCH = 162 Hz) and 34.7 ppm (CH; JCH = 157 Hz).
The solid state molecular structure of 5 was also determined
by X-ray crystallography, and it is shown in Figure 2. Suitable
crystals were grown by slow diffusion of pentane into Et2O
solutions of 5. Whereas the pincer ligand was well-refined to its
specific positions, the ethyl acrylate ligand presented a
substitutional disorder between two equivalent, symmetry-
related orientations (ca. 85:15 ratio). As expected, the acrylate
ester skeleton has a nearly orthogonal orientation with respect
to the (PONOP)Ir backbone and exhibits a C(22)−C(23)
bond length of 1.394(8) Å, typical for a coordinated alkene.
Recent studies on the hydrogenation of square-planar
hydrocarbyl complexes of Ir(I) have provided interesting
results.23b,29 In particular, Brookhart’s group analyzed the
reactivity of the methyl complex 1 toward H2, leading to a
methyl bis(hydride) species (PONOP)Ir(CH3)(H)2. This
compound, which possesses trans hydride ligands, formed in
a proton catalyzed reaction that proceeded through the
intermediacy of the previously characterized [(PONOP)Ir-
(CH3)(H)]+ cation, 6.23a In view of the obvious formal
connection that exists between the Ir(I) methylene complex 2
and the latter Ir(III) hydride methyl cation by means of H2
interplay, we set out to probe it experimentally. The
hydrogenation of 2 was performed at low temperatures (from
Scheme 2. Synthesis of the Ylide 3 and Its Conversion into
the Trimethyl Phosphine Adduct 4
NMR spectroscopy and X-ray crystallography as the ylide
[(PONOP)Ir(CH2PMe3)][B(C6F5)4], 3. On the basis of
detailed low-temperature NMR studies on the analogous
reaction of the neutral methylene complex Ir(CH2)[N-
(SiMe2CH2PPh2)2], Fryzuk and co-workers19 identified the
corresponding ylide, Ir(CH2PMe3)[N(SiMe2CH2PPh2)2], as a
low-temperature intermediate in a process ultimately yielding
the corresponding phosphine adduct, Ir(PMe3)[N-
(SiMe2CH2PPh2)2]. Indeed, as shown in Scheme 2, the use
of an excess of PMe3 furnished the cationic adduct 4, which was
B
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Note
Figure 1. ORTEP view of the cationic complexes 3 (left) and 4 (right) with ellipsoids set at 50% probability. Counteranions, solvent molecules, and
hydrogen atoms have been omitted for clarity. Only the major disordered components of compound 4 are shown in the displacement ellipsoid plot.
Scheme 3. Synthesis of the η2-Alkene Complex 5
Scheme 4. Reactions of 2 with Dihydrogen at Low
Temperature
a
a
Spectroscopic molar yields based on 2 are indicated in parentheses.
Figure 2. ORTEP view of the cationic complex 5 with ellipsoids set at
50% probability. Only the major disordered components are shown in
the displacement ellipsoid plot. Counteranion and hydrogen atoms
have been omitted for clarity.
ASSOCIATED CONTENT
* Supporting Information
Experimental details and procedures, NMR data, and crystallo-
graphic data for complexes 3, 4, and 5 (CIF). This material is
available free of charge via the Internet at http://pubs.acs.org.
■
S
−120 to −60 °C) using 3 equiv of H2 and CDCl2F as the
1
solvent (Scheme 4). Monitoring of the process by H and
31P{1H} NMR spectroscopy evinced no reaction until −60 °C,
when the [(PONOP)Ir(CH3)(H)]+ cation formed selectively,
albeit with a conversion of only ca. 10% (Scheme 4). Since this
low reaction yield was most probably due to slow hydrogen
diffusion into the Freon solvent, H2 was then bubbled through
this solution maintained at −60 °C, with frequent shaking of
the NMR tube. Under these conditions full consumption of 2
was observed, with two other, previously known complexes, 7
and 8, adding to this reaction manifold, in agreement with
previous studies.21c,23a
In short, the cationic methylene complex [(PONOP)Ir-
(CH2)]+, 2, produced by α-hydride abstraction from the neutral
methyl derivative (PONOP)Ir(CH3), 1, exhibits the expected
high electrophilicity and undergoes facile C−C coupling and
hydrogenolysis reactions, as well as ylide formation by action of
PMe3.
AUTHOR INFORMATION
Corresponding Author
*E-mail: guzman@us.es.
■
Present Address
§Department of Chemistry, Yale University, 225 Prospect
Street, New Haven, Connecticut 06520, United States.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Financial support (FEDER contribution and Subprograma Juan
de la Cierva) from the Spanish Ministry of Science and
Innovation (Projects CTQ2010-17476 and Consolider-Ingenio
2010 CSD2007-00006), the Junta de Andalucia (Projects
FQM-119 and P09-FQM-4832), and the National Science
Foundation (CHE-1010170) is gratefully acknowledged. J.C.
́
C
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Note
(13) (a) Dotz, K. H.; Fischer, H.; Hofmann, P.; Kreissl, F. R.;
̈
thanks the Spanish Ministry of Education for a research grant
(AP-20080256).
Schubert, U.; Weiss, K. Transition Metal Carbene Complexes; VCH
Verlag Chemie: Weinheim, 1983. (b) Gallop, M. A.; Roper, W. R. Adv.
Organomet. Chem. 1986, 25, 121. (c) Aguero, A.; Osborn, J. A. New J.
Chem. 1988, 12, 111.
(14) (a) Schrock, R. R. J. Am. Chem. Soc. 1975, 97, 6577.
(b) Guggenberger, L. J.; Schrock, R. R. J. Am. Chem. Soc. 1975, 97,
6578. (c) Schrock, R. R.; Sharp, P. R. J. Am. Chem. Soc. 1975, 100,
2389.
REFERENCES
■
(1) Fischer, E. O.; Maasbol, A. Angew. Chem., Int. Ed. 1964, 3, 580.
̈
(2) (a) Chauvin, Y. Angew. Chem., Int. Ed. 2006, 45, 3740.
(b) Schrock, R. R. Angew. Chem., Int. Ed. 2006, 45, 3748. (c) Grubbs,
R. H. Angew. Chem., Int. Ed. 2006, 45, 3760.
(15) For early examples see: (a) Roper, W. R. In Advances in Metal
Carbene Chemistry; Schubert, U., Ed.; Kluwer Academic Publishers:
Norwell, MA, 1989; p 27. (b) Brookhart, M.; Liu, Y. In Advances in
Metal Carbene Chemistry; Schubert, U., Ed.; Kluwer Academic
Publishers: Norwell, MA, 1989; p 251. See also: (c) Gunnoe, T. B.;
White, P. S.; Templeton, J. L.; Casarrubios, L. J. Am. Chem. Soc. 1997,
119, 3171 and references therein. (d) Gunnoe, T. B.; Surgan, M.; P. S.
White, P. S.; Templeton, J. L; Casarrubios, L. Organometallics 1997,
16, 4865.
(16) (a) Herrmann, W. A. Angew. Chem., Int. Ed. 1978, 17, 800.
(b) Herrmann, W. A. Adv. Organomet. Chem. 1982, 20, 159.
(17) Thorn, D. L.; Tulip, T. H. J. Am. Chem. Soc. 1981, 103, 5984.
(18) Clark, G. R.; Roper, W. R.; Wright, A. H. J. Organomet. Chem.
1984, 273, C17.
(19) (a) Fryzuk, M. D.; MacNeil, P. A.; Rettig, S. J. J. Am. Chem. Soc.
1985, 107, 6708. (b) Fryzuk, M. D.; Gao, X.; Joshi, K.; MacNeil, P. A.;
Massey, R. L. J. Am. Chem. Soc. 1993, 115, 10581.
(20) Klein, D. P.; Bergman, R. G. J. Am. Chem. Soc. 1989, 111, 3079.
(21) (a) Bernskoetter, W. H.; Schauer, C. K.; Goldberg, K. I.;
Brookhart, M. Science 2009, 326, 553. (b) Walter, M. D.; White, P. S.;
Schauer, C. K.; Brookhart, M. New J. Chem. 2011, 35, 2884.
(c) Campos, J.; Kundu, S.; Pahls, D. R.; Brookhart, M.; Carmona,
E.; Cundari, T. R. J. Am. Chem. Soc. 2013, 135, 1217.
(3) (a) Maitlis, P. M.; Zanotti, V. Chem. Commun. 2009, 1619.
(b) Jellema, E.; Jongerius, A. L.; Reek, J. N. H.; de Bruin, B. Chem. Soc.
Rev. 2010, 39, 1706. (c) Arduengo, J. A.; Bertrand, G. Chem. Rev.
2009, 109, 3209. Special issue dedicated to carbenes: (d) Herndon, J.
W. Coord. Chem. Rev. 2011, 255, 3 (annual survey covering the year
2009; see references therein for previous years).
(4) (a) Werner, H. Angew. Chem., Int. Ed. 2010, 49, 4714.
(b) Conejero, S.; Paneque, M.; Poveda, M. L.; Santos, L. L.;
Carmona, E. Acc. Chem. Res. 2010, 43, 572. (c) Whited, M. T.; Grubbs,
R. H. Acc. Chem. Res. 2009, 42, 1607.
(5) (a) Luecke, H. F.; Arndtsen, B. A.; Burger, P.; Bergman, R. G. J.
Am. Chem. Soc. 1996, 118, 2517. (b) Luecke, H. F.; Bergman, R. G. J.
Am. Chem. Soc. 1998, 120, 11008. (c) Klei, S. R.; Golden, J. T.; Burger,
P.; Bergman, R. G. J. Mol. Catal. A: Chem. 2002, 189, 79.
(6) (a) Werner, H. Organometallics 2005, 24, 1036. (b) Ortmann, D.
A.; Weberndorfer, B.; Ilg, K.; Laubender, M.; Werner, H. Organo-
̈
metallics 2002, 21, 2369. (c) Pechmann, T.; Brandt, C. D.; Werner, H.
Organometallics 2003, 22, 3004.
(7) (a) Gandelman, M.; Naing, K. M.; Rybtchinski, B.; Poverenov, E.;
Ben-David, Y.; Ashkenazi, N.; Gauvin, R. M.; Milstein, D. J. Am. Chem.
Soc. 2005, 127, 15265. (b) Poverenov, E.; Milstein, D. Chem. Commun.
2007, 3189.
(8) Clot, E.; Chen, J.; Lee, D.-H.; Sung, S. Y.; Appelhans, L. N.;
Faller, J. W.; Crabtree, R. H.; Eisenstein, O. J. Am. Chem. Soc. 2004,
126, 8795.
(22) Findlater, M.; Schultz, K. M.; Bernskoetter, W. H.; Cartwright-
Sykes, A.; Heinekey, D. M.; Brookhart, M. Inorg. Chem. 2012, 51,
4672.
(9) (a) Whited, M. T.; Grubbs, R. H. J. Am. Chem. Soc. 2008, 130,
5874. (b) Whited, M. T.; Grubbs, R. H. J. Am. Chem. Soc. 2008, 130,
16476. (c) Brookes, N. J.; Ariafard, A.; Stranger, R.; Yates, B. F. J. Am.
Chem. Soc. 2009, 131, 5800. (d) Whited, M. T.; Zhu, Y.; Timpa, S. D.;
Chen, C.-H.; Foxman, B. M.; Ozerov, O. V.; Grubbs, R. H.
Organometallics 2009, 28, 4560. (e) Brookes, N. J.; Whited, M. T.;
Ariafard, A.; Stranger, R.; Grubbs, R. H.; Yates, B. F. Organometallics
2010, 29, 4239.
(23) (a) Bernskoetter, W. H.; Hanson, S. K.; Buzak, S. K.; Davis, Z.;
White, P. S.; Swartz, R.; Goldberg, K. I.; Brookhart, M. J. Am. Chem.
Soc. 2009, 131, 8603. (b) Findlater, M.; Bernskoetter, W. H;
Brookhart, M. J. Am. Chem. Soc. 2010, 132, 4534. For related
chemistry with PCP ligands, see: (c) Choi, J.; Wang, D. Y.; Kundu, S.;
Choliy, Y.; Emge, T. J.; Krogh-Jespersen, K.; Goldman, A. S. Science
2011, 332, 1545.
́
(24) (a) Campos, J.; Lopez-Serrano, J.; Alvarez, E.; Carmona, E. J.
́
Am. Chem. Soc. 2012, 134, 7165. (b) Campos, J.; Peloso, R.; Carmona,
E. Angew. Chem., Int. Ed. 2012, 51, 8255.
́
́ ́
(10) (a) Gutierrez-Puebla, E.; Monge, A.; Nicasio, M. C.; Perez, P. J.;
Poveda, M. L.; Carmona, E. Chem.Eur. J. 1998, 4, 2225.
(b) Carmona, E.; Paneque, M.; Poveda, M. L. Dalton Trans. 2003,
4022. (c) Slugovc, C.; Mereiter, K.; Trofimenko, S.; Carmona, E.
Angew. Chem., Int. Ed. 2000, 39, 2158. (d) Lara, P.; Paneque, M.;
Poveda, M. L.; Salazar, V.; Santos, L. L.; Carmona, E. J. Am. Chem. Soc.
2006, 128, 3512. (e) Lara, P.; Paneque, M.; Poveda, M. L.; Santos, L.
(25) Alías, F. M.; Poveda, M. L.; Sellin, M.; Carmona, E. J. Am. Chem.
Soc. 1998, 120, 5816. (b) Alías, F. M.; Poveda, M. L.; Sellin, M.;
Carmona, E.; Gutier
(c) Besora, M.; Vyboishchikov, S. F.; Lledos
Carmona, E.; Poveda, M. L. Organometallics 2010, 29, 2040.
(26) McBride, J. M. Tetrahedron 1974, 30, 2009.
́
rez, E.; Monge, A. Organometallics 1998, 17, 4124.
, A.; Maseras, F.;
́
́
L.; Valpuesta, J. E. V.; Carmona, E.; Moncho, S.; Ujaque, G.; Lledos,
́
A.; Alvarez, E.; Mereiter, K. Chem.Eur. J. 2009, 15, 9034.
(27) (a) Kang, J. W.; Han, Y.-K. Bull. Korean Chem. Soc. 1997, 18,
433. (b) Borkowsky, S. L.; Jordan, R. F.; Hinch, G. D. Organometallics
1991, 10, 1268.
(28) Ghosh, R.; Emge, T. J.; Krogh-Jespersen, K.; Goldman, A. S. J.
Am. Chem. Soc. 2008, 130, 11317.
(29) (a) Ben-Ari, E.; Leitus, G.; Shimon, L. J. W.; Milstein, D. J. Am.
Chem. Soc. 2006, 128, 15390. (b) Iron, M. A.; Ben-Ari, E.; Cohen, R.;
Milstein, D. Dalton Trans. 2009, 9433.
(f) Conejero, S.; Lop
́
ez-Serrano, J.; Paneque, M.; Petronilho, A.;
́
Poveda, M. L.; Vattier, F.; Alvarez, E.; Carmona, E. Chem.Eur. J.
́
2012, 18, 4644. (g) Valpuesta, J. E. V.; Alvarez, E.; Lop
́
ez-Serrano, J.;
Maya, C.; Carmona, E. Chem.Eur. J. 2012, 18, 13149.
́
(11) (a) Alvarez, E.; Conejero, S.; Paneque, M.; Petronilho, A.;
Poveda, M. L.; Serrano, O.; Carmona, E. J. Am. Chem. Soc. 2006, 128,
13060. (b) Conejero, S.; Lara, P.; Paneque, M.; Petronilho, A.; Poveda,
́
M. L.; Serrano, O.; Vattier, F.; Alvarez, E.; Maya, C.; Salazar, V.;
́
Carmona, E. Angew. Chem., Int. Ed. 2008, 47, 4380. (c) Alvarez, E.;
Hernandez, Y. A.; Lopez-Serrano, J.; Maya, C.; Paneque, M.;
́
́
Petronilho, A.; Poveda, M. L.; Salazar, V.; Vattier, F.; Carmona, E.
Angew. Chem., Int. Ed. 2010, 49, 3496.
(12) (a) Meiners, J.; Friedrich, A.; Herdtweck, E.; Schneider, S.
Organometallics 2009, 28, 6331. (b) Surawatanawong, P.; Ozerov, O.
V. Organometallics 2011, 30, 2972. (c) Burford, R. J.; Piers, W. E.;
Parvez, M. Organometallics 2012, 31, 2949. (d) O’Neill, M.; Addy, D.
A.; Riddlestone, I.; Kelly, M.; Phillips, N.; Aldridge, S. J. Am. Chem. Soc.
2011, 133, 11500.
D
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