Cyclic (aryl)(amido)carbenes: Pushing the π-acidity of amidocarbenes through benzannulation

Article abstract of DOI:10.1039/c9cc05280a

Cyclic(aryl)(amido)carbenes were synthesized, and studied via a combination of experimental and computational approaches. These carbenes undergo dimerization when isolation is attempted, however, are trapped with sulfur, selenium, and [Ir(cod)Cl]. The π-acidity, measured using ⁷⁷Se NMR, revealed that these are the most electrophilic singlet carbenes reported to date whereas the TEP measured demonstrated that these carbenes are poor σ donors.

Full text of DOI:10.1039/c9cc05280a

Showcasing research from Todd Hudnall’s Laboratory in
the Department of Chemistry and Biochemistry, Texas State
University, San Marcos, Texas, USA
As featured in:
Volume 55 Number 82 21 October 2019 Pages 12269–12414
Cyclic (aryl)(amido)carbenes: pushing the π-acidity of
amidocarbenes through benzannulation
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The π-acidity of amido carbenes can be pushed to the extreme
through annulation to an aromatic ring. This results in a lowering
and raising of the LUMO and HOMO energy levels, respectively,
and provides access to exceptionally electrophilic carbenes
with small singlet–triplet gaps. Such compounds exhibit unique
chemical reactivity as described in the manuscript.
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Cyclic (aryl)(amido)carbenes: pushing the p-acidity
of amidocarbenes through benzannulation†
Cite this: Chem. Commun., 2019,
55, 12300
M. Brenton Gildner
and Todd W. Hudnall
*
Received 10th July 2019,
Accepted 18th September 2019
DOI: 10.1039/c9cc05280a
rsc.li/chemcomm
Cyclic(aryl)(amido)carbenes were synthesized, and studied via a
combination of experimental and computational approaches. These
carbenes undergo dimerization when isolation is attempted, however,
are trapped with sulfur, selenium, and [Ir(cod)Cl]. The p-acidity,
measured using 77Se NMR, revealed that these are the most
electrophilic singlet carbenes reported to date whereas the TEP
measured demonstrated that these carbenes are poor r donors.
The continued interest in novel carbene architectures1 has been
motivated by the versatility of these remarkable compounds in the
stabilization of exotic transition metal2 and main group complexes,3
paramagnetic species,4 nanomaterials,5 in catalysis,6,7 and
more recently as emissive materials for OLED applications.8
The isolation of the first N-heterocyclic carbene (NHC)9 by
Arduengo in 199010 was a landmark achievement; however,
Bertrand’s cyclic(alkyl)(amino)carbenes (CAACs, A, Fig. 1)
which feature higher and lower-lying HOMOs and LUMOs,
respectively, marked a renaissance in the chemistry of stable
carbenes.11 The unique electronic structure of CAACs enables
these carbenes to outperform NHCs for the stabilization of
paramagnetic fragments and in the activation of enthalpically
strong bonds.12,13
In contrast, the introduction of p-withdrawing aryl and/or
amido moieties adjacent to a carbene significantly lowers
the LUMO energy levels when compared to NHCs and CAACs
(B–F).14–17 For example, diamidocarbenes (DACs, D), pioneered
by Bielawski are less nucleophilic yet more electrophilic. While
DACs are adept at stabilizing low-valent main group and
paramagnetic species,18 their ability to activate enthalpically
strong bonds pales in comparison to CAACs,19,20 presumably
due to their low-lying HOMO and poor nucleophilic character.15
Several modifications have been made to the structures of both
CAACs and DACs to further tune their electronic properties.
Fig. 1 HOMO and LUMO energy levels (eV), and singlet–triplet gaps
(DE S/T, kcal molÀ1 calculated at the B3LYP/6-31G+D level) of selected
carbenes. (a) S/T gaps taken from ref. 14, (b) energies taken from ref. 22.
For example, Bertrand has shown that replacement of the alkyl
groups in CAACs with an annulated aryl group affords cyclic
(amino)(aryl) carbenes (CAArCs, B) which are both more
electrophilic and nucleophilic when compared to CAACs.14
Similarly, Bielawski demonstrated the nucleophilicity of DACs
can be increased while retaining their electrophilic character by
replacement of one amido group with an alkyl moiety to give
cyclic(alkyl)(amido) carbenes (C).16
More recently, our group found that DACs can be photolyzed
from their singlet ground state to an excited triplet state which
then undergoes reversible Bu¨chner ring expansion reactions.21
While we believe the low-lying LUMO of DACs is responsible
for the observed photochemistry, there are no other carbenes
which exhibit similar photochemistry. To explore other potentially
photoactive carbene architectures, we have begun an in silico-
guided research program to rationally design and identify novel
carbenes with increasingly electrophilic and nucleophilic properties
relative to DACs. In this vein, computational data indicate that
the replacement of one amido substituent within a DAC by an
aryl group results in enhanced electrophilicity of the carbene
Department of Chemistry and Biochemistry, Texas State University,
601 University Dr, San Marcos, TX, 78666, USA. E-mail: hudnall@txstate.edu
† Electronic supplementary information (ESI) available. CCDC 1939286–1939288.
For ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c9cc05280a
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Scheme 2 (a) Synthesis of carbene dimers 5a, b (crystal structure of 5a
(Ar = Mes) shown, 50% probability ellipsoids, H-atoms removed for clarity);
(b) optimized geometry of carbene Fa; (c) calculated HOMO of Fa;
(d) calculated LUMO of Fa. (Mes = 2,4,6-(CH3)3C6H2, Dipp = 2,6-(iPr)2C6H3).
Scheme 1 Synthesis of carbene precursors 4a–c (yields reported are
over both steps).
and the metrical parameters are consistent with the formation
center, concomitant with increased nucleophilicity. Thus, cyclic of the olefin with a C1–C3 distance of 1.361(3) Å, characteristic
(aryl)(amido)carbenes theoretically represent the most of a CQC double bond. In an attempt to prevent dimerization
F
electrophilic carbenes with the smallest reported singlet–triplet observed with carbenes Fa and Fb, we turned to the bulkier 4c,
(S/T) gap (19.1 kcal molÀ1) to date for any singlet carbene. which features the m-terphenyl N-substituent.23 However, to
During the course of our studies, Lee and co-workers published date, we have not been successful in the deprotonation of 4c
a beautiful paper describing the synthesis of a series of regardless of conditions used (i.e. base, solvent, temperature).
carbenes of type E, which are derived from coumarin.22 Similar
to our predicted results for carbenes of type F, these coumarin- isoindolinone core with an N1–C3–C4 angle of 103.13 which is
derived analogs are very electrophilic species.
smaller than both CAACs (ca. 106.51) and CAArCs (105.01)14 and
The optimized structure of Fa (Scheme 2b) revealed a planar
Encouraged by the in silico data, we attempted the synthesis the C1–O1 distance of 1.207 Å is consistent with what has been
of carbenes of type F (Scheme 1). Carbene precursors could be reported for DACs (1.21 Å)20,24 indicating delocalization of the
readily prepared from commercially available aniline deriva- nitrogen atom lone pair into the carbonyl moiety for Fa. The
tives (1) and 2-carboxybenzaldehyde (2). Simple condensation HOMO is consistent with a lone pair localized in a ns orbital on
reactions of 1 and 2 afford imines (3) good yields, which are the carbene carbon (Scheme 2c) whereas the LUMO (Scheme 2d)
then treated with thionyl chloride in refluxing acetonitrile to is a p-type orbital that is delocalized throughout the isoindolinone
perform a two-step chlorination–cyclization reaction sequence core similar to what Bertrand observed in CAArCs, and consistent
in one reaction flask to give the 3-chloro-2-arylisoindolin-1-ones with the p-accepting nature of the annulated aryl substituent.14 In
(4) in quantitative yields. The commercially-available aniline contrast to the CAArCs, the introduction of the carbonyl moiety in
derivatives, 2,4,6-trimethylaniline (1a) and 2,6-diisopropylphenyl- Fa, results in increased delocalization into the 5-membered ring
aniline (1b) were explored; and, presumably any aniline derivative which spans the N1–C1–C5 linkage.
will work as evidenced by our successful condensation reaction of 2
To verify if the free carbenes Fa and Fb could be accessed at
with the bulky terphenyl-amino derivative, 2,6-bis[3,5-bis(trifluoro- low temperature prior to dimerization, we performed the series
methyl)phenyl]aniline (1c). Note, the final step to provide carbene of trapping experiments described in Scheme 3. First, addition
precursors 4 required no additional workup and compounds 4 of S8 to solutions of 4a or 4b and NaHMDS in THF cooled to
were isolated in quantitative yield without further purification.
À78 1C resulted in the formation of the of thiones 6a or 6b as
The deprotonation of compounds 4a–c with several bases bright pink solids in 49 and 67% yield, respectively, indicating
including: LDA, NaH/KOtBu, and NaHMDS was attempted in
order to isolate the desired free carbenes, Fa–c. Ultimately, it
was found that deprotonation of 4a using NaHMDS in THF at
À78 1C proceeded smoothly, however we were unable to isolate
the free carbene Fa, and instead obtained the carbene dimer 5a
in 86% yield as a bright yellow powder (Scheme 2a, the dimer
5b could also be isolated in a similar fashion in 97% yield, see
ESI,† for full discussion). The identity of 5a was confirmed by a
combination of multinuclear NMR spectroscopy by: (i) the
disappearance of the proton at C3 in compound 4a at 6.5 ppm,
(ii) the appearance of an olefinic carbon at 124.5 ppm, and (iii) by
single crystal X-ray diffraction. Interestingly, only a single isomer,
Scheme 3 Trapping experiments conducted on carbenes Fa and Fb. Iso-
the E-isomer, of carbene dimer 5a is formed presumably due to
large steric compression owing to the large N-mesityl substituents,
lated yields are provided in the scheme. Conditions: (i) NaHMDS, THF, À78 1C,
(ii) S8 or Se, (iii) 0.5 eq. [(cod)IrCl]2, (iv) 1 atm CO in CDCl3, (v) air in CH2Cl2.
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evidenced by 13C NMR and FTIR spectroscopies (ESI†). To our
knowledge, this is the first example where a carbene–Ir(I)
complex becomes oxidized at the carbene center, and is surprising
given singlet carbenes do not react with molecular oxygen. This
unique reactivity may stem from the small calculated S/T gap of Fa.
Despite this instability, we were able to measure the nCO of 9a in
CDCl3, and determined the TEP which was 2065 cmÀ1 and notably
larger than what has been measured for DACs (2057 cmÀ1),
carbene C (2053 cmÀ1),25 and carbenes E (2048 cmÀ1),22 making
it the weakest s-donating carbene reported to date.
Fig. 2 Single crystal X-ray structures of 6a (left) and 7a (right). Rendered
using POV-Ray with 50% probability ellipsoids, and hydrogen atoms
removed for clarity.
that the free carbenes could be prepared as a viable species
In this study we demonstrated that the electrophilicity and
at low temperature. Similarly, the selenones 7a or 7b were singlet–triplet gap of amido carbenes can be increased and
prepared as a sky blue solids in 15 and 28% yield, respectively, decreased, respectively through benzannulation to the carbene
by trapping 4a or 4b with selenium at low temperature. Compound center. The resultant cyclic(aryl)amido carbenes (Fa and Fb)
6a and 6b exhibited characteristic CQS carbon signals in the represent the most electrophilic singlet carbenes reported to
13C NMR spectra (C6D6) at 197 or 198 ppm (6a or 6b, respectively), date. Moreover, these carbenes have the smallest calculated
whereas the corresponding CQSe carbon atoms resonated at singlet–triplet gaps (19.1 kcal molÀ1) for cyclic, singlet ground
201 or 203 ppm (7a or 7b, respectively). To further corroborate state carbenes. Collectively the low-lying LUMO and small S/T
their identity, compounds 6a and 7a were characterized by single gap rendered these carbenes very reactive leading to dimerization.
crystal X-ray diffraction (Fig. 2). The 77Se NMR spectra for com- While the use of a bulky m-terphenyl substitutent at nitrogen was
pounds 7a and 7b exhibited singlets at 1240.9 and 1263.9 ppm explored to prevent dimerization, the deprotonation of the
(CDCl3), respectively. For comparison to other carbene-derived carbene precursor, 4c, was unsuccessful.
selenones,25 the 77Se chemical shifts for 7a and 7b in d6-acetone
To measure the electronic properties of carbens Fa and Fb
were observed at 1204.5 and 1231.1 ppm, respectively. These values experimentally, a series of trapping experiments were performed.
were considerably downfield compared to Lee’s selenones derived The p-acidic nature of these carbenes was interrogated by measuring
from carbenes of type E (values ranging from 1003–1135 ppm the 77Se NMR chemical shift of the corresponding carbene-derived
in d6-acetone)22 and even downfield when compared to what selenones 7a and 7b, which were the most deshielded selenium
Bielawski observed (1179.1 ppm)16 with carbene C. To date, the nuclei reported for these types of compounds. Finally, the measured
observed low field 77Se signals for compounds 7a and 7b are the TEP of Fa revealed that this is the weakest s-donating carbene
most downfield recorded for a selenone derived from a carbene, reported to date. Current efforts to synthesize isolable analogues of
and are consistent with the low-lying LUMO of carbenes of type F carbenes of type F to further interrogate their electronic properties,
and attendant electrophilic nature.
and to explore potential novel photochemistries are underway.
T. W. H. is grateful to the National Science Foundation for
To further interrogate the electronic properties, we attempted
to measure the Tolman electronic parameter (TEP)26 of Fa by supporting this work: CHE-1362140 and CHE-1552359. We also
measuring the carbonyl stretching frequency (nCO) of the complex thank Dr. William Hoffmann for assistance with HRMS samples.
Fa-(Ir(CO)2Cl).27,28 First, carbene Fa was successfully coordinated
to the [Ir(cod)Cl] (cod = 1,5 cyclooctadiene) fragment to give
complex 8a which was isolated as an orange solid in 10% yield.
Conflicts of interest
Complex 8a was found to be very fragile, and all attempts to
recrystallize this compound, improve the yield of the reaction,
or obtain passing elemental analysis resulted in further decom-
position. For this reason, only 1H and 13C NMR spectroscopy as
well as high resolution mass spectrometry (HRMS) were obtained to
confirm the identity of 8a. The most diagnostic data was the
chemical shift of the carbene nucleus in 8a (250.10 ppm, CDCl3)
which was similar to what Lee and Bielawski observed for Rh(cod)Cl
(273.95 ppm, CDCl3)22 and Ir(cod)Cl (286.9 ppm, CDCl3)16
complexes of carbenes E and C, respectively, and in the range
of known carbene-[Ir(cod)Cl] complexes.28,29
Next, 8a was treated with carbon monoxide in CDCl3, to
cleanly release the cyclooctadiene ligand and give the desired
complex, Fa-[(CO)2IrCl] (9a), in quantitative yield by NMR spectro-
scopy. 9a could not be isolated, and was found to decompose even
under inert atmosphere. If isolation is attempted in air, 9a is oxidized
to give N-mesitylphthalimide (10). The liberated [Ir(CO)2Cl] fragment
undergoes disproportionation to give Ir0 and [Ir(CO)6][Cl3] as
There are no conflicts to declare.
Notes and references
1 A. J. Arduengo and G. Bertrand, Chem. Rev., 2009, 109(8), 3209–3210.
2 S. Roy, K. C. Mondal and H. W. Roesky, Acc. Chem. Res., 2016, 49(3),
357–369.
3 T. W. Hudnall, R. A. Ugarte and T. A. Perera, N-Heterocyclic Carbenes: From
Laboratory Curiosities to Efficient Synthetic Tools (2), The Royal Society of
Chemistry, 2017, pp. 178–237, DOI: 10.1039/9781782626817-00178;
J. Brand, H. Braunschweig and S. S. Sen, Acc. Chem. Res., 2014, 47(1),
180–191; M. Arrowsmith, H. Braunschweig, M. A. Celik, T. Dellermann,
R. D. Dewhurst, W. C. Ewing, K. Hammond, T. Kramer, I. Krummenacher,
J. Mies, K. Radacki and J. K. Schuster, Nat. Chem., 2016, 8(9), 890–894;
Y. Wang and G. H. Robinson, Inorg. Chem., 2014, 53(22), 11815–11832;
Y. Wang, M. Chen, Y. Xie, P. Wei, H. F. Schaefer, III, P. V. R. Schleyer and
G. H. Robinson, Nat. Chem., 2015, 7(6), 509–513; R. Kinjo, B. Donnadieu,
M. A. Celik, G. Frenking and G. Bertrand, Science, 2011, 333(6042),
610–613.
4 C. D. Martin, M. Soleilhavoup and G. Bertrand, Chem. Sci., 2013,
4(8), 3020–3030; K. C. Mondal, H. W. Roesky, A. C. Stueckl, F. Ehret,
W. Kaim, B. Dittrich, B. Maity and D. Koley, Angew. Chem., Int. Ed.,
2013, 52(45), 11804–11807; S. Roy, A. C. Stueckl, S. Demeshko,
12302 | Chem. Commun., 2019, 55, 12300--12303
This journal is ©The Royal Society of Chemistry 2019

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Communication
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B. Dittrich, J. Meyer, B. Maity, D. Koley, B. Schwederski, W. Kaim 13 D. R. Tolentino, S. E. Neale, C. J. Isaac, S. A. Macgregor, M. K.
and H. W. Roesky, J. Am. Chem. Soc., 2015, 137(14), 4670–4673.
5 M. J. MacLeod and J. A. Johnson, J. Am. Chem. Soc., 2015, 137(25),
Whittlesey, R. Jazzar and G. Bertrand, J. Am. Chem. Soc., 2019,
141(25), 9823–9826.
7974–7977; J. B. Ernst, C. Schwermann, G.-I. Yokota, M. Tada, 14 B. Rao, H. Tang, X. Zeng, L. Liu, M. Melaimi and G. Bertrand, Angew.
S. Muratsugu, N. L. Doltsinis and F. Glorius, J. Am. Chem. Soc., Chem., Int. Ed., 2015, 54(49), 14915–14919.
2017, 139(27), 9144–9147; C.-Y. Wu, W. J. Wolf, Y. Levartovsky, 15 T. W. Hudnall and C. W. Bielawski, J. Am. Chem. Soc., 2009, 131(44),
H. A. Bechtel, M. C. Martin, F. D. Toste and E. Gross, Nature,
2017, 541, 511; M. R. Narouz, K. M. Osten, P. J. Unsworth,
16039–16041; J. P. Moerdyk, D. Schilter and C. W. Bielawski, Acc.
Chem. Res., 2016, 49(8), 1458–1468.
R. W. Y. Man, K. Salorinne, S. Takano, R. Tomihara, S. Kaappa, 16 Z. R. McCarty, D. N. Lastovickova and C. W. Bielawski, Chem.
S. Malola, C.-T. Dinh, J. D. Padmos, K. Ayoo, P. J. Garrett, M. Nambo, Commun., 2016, 52(31), 5447–5450.
J. H. Horton, E. H. Sargent, H. Hakkinen, T. Tsukuda and 17 G. A. Blake, J. P. Moerdyk and C. W. Bielawski, Organometallics,
¨
C. M. Crudden, Nat. Chem., 2019, 11(5), 419–425.
6 M. P. Wiesenfeldt, Z. Nairoukh, W. Li and F. Glorius, Science, 2017,
2012, 31(8), 3373–3378; M. Braun, W. Frank and C. Ganter, Organo-
metallics, 2012, 31(5), 1927–1934.
357(6354), 908–912; C. M. Crudden and J. M. Praetorius, J. Am. 18 C. L. Dorsey, B. M. Squires and T. W. Hudnall, Angew. Chem., Int.
Chem. Soc., 2007, 129(28), 8923–8924; N. I. Saper and J. F. Hartwig,
J. Am. Chem. Soc., 2017, 139(48), 17667–17676.
Ed., 2013, 52(16), 4462–4465; R. R. Rodrigues, C. L. Dorsey, C. A.
Arceneaux and T. W. Hudnall, Chem. Commun., 2014, 50, 162–164;
C. L. Dorsey, R. M. Mushinski and T. W. Hudnall, Chem. – Eur. J.,
2014, 20(29), 8914–8917; A. D. Ledet and T. W. Hudnall, Dalton
Trans., 2016, 45(24), 9820–9826; C. L. Deardorff, R. Eric Sikma,
C. P. Rhodes and T. W. Hudnall, Chem. Commun., 2016, 52(58),
9024–9027.
`
7 D. Pichon, M. Soleilhavoup, J. Morvan, G. P. Junor, T. Vives,
´
C. Crevisy, V. Lavallo, J.-M. Campagne, M. Mauduit, R. F. R. Jazzar
and G. Bertrand, Chem. Sci., 2019, DOI: 10.1039/C9SC02810B.
8 H. Braunschweig, T. Dellermann, R. D. Dewhurst, B. Hupp, T. Kramer,
J. D. Mattock, J. Mies, A. K. Phukan, A. Steffen and A. Vargas, J. Am.
Chem. Soc., 2017, 139(13), 4887–4893; K. S. Kjær, N. Kaul, O. Prakash, 19 J. P. Moerdyk and C. W. Bielawski, J. Am. Chem. Soc., 2012, 134(14),
´
P. Chabera, N. W. Rosemann, A. Honarfar, O. Gordivska, L. A. Fredin,
6116–6119; J. P. Moerdyk and C. W. Bielawski, Chem. – Eur. J., 2013,
19(44), 14773–14776.
¨
¨
K.-E. Bergquist, L. Haggstrom, T. Ericsson, L. Lindh, A. Yartsev,
¨
S. Styring, P. Huang, J. Uhlig, J. Bendix, D. Strand, V. Sundstrom, 20 T. W. Hudnall, J. P. Moerdyk and C. W. Bielawski, Chem. Commun.,
¨
P. Persson, R. Lomoth and K. Warnmark, Science, 2019, 363(6424),
249–253; D. Di, A. S. Romanov, L. Yang, J. M. Richter, J. P. H. Rivett, 21 T. A. Perera, E. W. Reinheimer and T. W. Hudnall, J. Am. Chem. Soc.,
S. Jones, T. H. Thomas, M. Abdi Jalebi, R. H. Friend, M. Linnolahti, 2017, 139(41), 14807–14814.
M. Bochmann and D. Credgington, Science, 2017, 356(6334), 159–163; 22 H. Song, H. Kim and E. Lee, Angew. Chem., Int. Ed., 2018, 57(28),
R. Hamze, J. L. Peltier, D. Sylvinson, M. Jung, J. Cardenas, R. Haiges, 8603–8607.
M. Soleilhavoup, R. Jazzar, P. I. Djurovich, G. Bertrand and M. E. 23 Bertrand used m-terphenyl substituents to prevent dimerization of
2010, 46(24), 4288–4290.
Thompson, Science, 2019, 363(6427), 601–606; R. Hamze, S. Shi,
S. C. Kapper, D. S. Muthiah Ravinson, L. Estergreen, M.-C. Jung, A. C.
carbenes see: R. Nakano, R. Jazzar and G. Bertrand, Nat. Chem.,
2018, 10(12), 1196–1200.
Tadle, R. Haiges, P. I. Djurovich, J. L. Peltier, R. Jazzar, G. Bertrand, 24 T. W. Hudnall, A. G. Tennyson and C. W. Bielawski, Organometallics,
S. E. Bradforth and M. E. Thompson, J. Am. Chem. Soc., 2019, 141(21),
8616–8626.
9 M. N. Hopkinson, C. Richter, M. Schedler and F. Glorius, Nature,
2014, 510, 485.
10 A. J. Arduengo, III, R. L. Harlow and M. Kline, J. Am. Chem. Soc.,
1991, 113(1), 361–363.
2010, 29(20), 4569–4578.
25 S. V. C. Vummaleti, D. J. Nelson, A. Poater, A. Gomez-Suarez, D. B.
Cordes, A. M. Z. Slawin, S. P. Nolan and L. Cavallo, Chem. Sci., 2015,
6(3), 1895–1904; A. Liske, K. Verlinden, H. Buhl, K. Schaper and
C. Ganter, Organometallics, 2013, 32(19), 5269–5272.
26 C. A. Tolman, Chem. Rev., 1977, 77(3), 313–348.
11 M. Melaimi, R. Jazzar, M. Soleilhavoup and G. Bertrand, Angew. 27 A. R. Chianese, X. Li, M. C. Janzen, J. W. Faller and R. H. Crabtree,
Chem., Int. Ed., 2017, 56(34), 10046–10068; M. Soleilhavoup and Organometallics, 2003, 22(8), 1663–1667.
G. Bertrand, Acc. Chem. Res., 2015, 48(2), 256–266; D. Martin, 28 R. A. Kelly, III, H. Clavier, S. Giudice, N. M. Scott, E. D. Stevens,
M. Melaimi, M. Soleilhavoup and G. Bertrand, Organometallics,
2012, 30(20), 5304–5313; M. Melaimi, M. Soleilhavoup and
G. Bertrand, Angew. Chem., Int. Ed., 2010, 49(47), 8810–8849.
J. Bordner, I. Samardjiev, C. D. Hoff, L. Cavallo and S. P. Nolan,
Organometallics, 2008, 27(2), 202–210.
´
29 C. Vicent, M. Viciano, E. Mas-Marza, M. Sanau´ and E. Peris, Organo-
12 D. Martin, Y. Canac, V. Lavallo and G. Bertrand, J. Am. Chem. Soc.,
2014, 136(13), 5023–5030; G. D. Frey, V. Lavallo, B. Donnadieu,
W. W. Schoeller and G. Bertrand, Science, 2007, 316(5823), 439–441.
metallics, 2006, 25(15), 3713–3720; W. A. Herrmann, D. Baskakov,
E. Herdtweck, S. D. Hoffmann, T. Bunlaksananusorn, F. Rampf and
L. Rodefeld, Organometallics, 2006, 25(10), 2449–2456.
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