A new type of palladium-pincer complexes generated via hydrolytic ring-opening of imidazole-2-ylidenes

Article abstract of DOI:10.1021/om500362x

The reaction of a series of pyridine-appended imidazolium salts with Pd(COD)Cl₂ in the presence of KO^tBu as base led to hydrolytic ring-opening followed by a new type of pincer tridentate (N,C,O) bonding of the in situ generated formamide-based new ligands toward the metal center. This unprecedented type of bonding resulted from a vinylic C-H activation by palladium stabilized with coordination from the pyridine nitrogen and aldehyde oxygen donors in a pincer fashion. The new stable, square-planar palladium(II) complexes (1-3) were characterized by 1D and 2D NMR spectroscopic and high-resolution mass spectrometric (HRMS) methods. The single-crystal X-ray structure of a representative complex (2) confirmed the above interesting bonding features.

Full text of DOI:10.1021/om500362x

Note
pubs.acs.org/Organometallics
A New Type of Palladium-Pincer Complexes Generated via
Hydrolytic Ring-Opening of Imidazole-2-ylidenes
Suraj K. Gupta, Debasish Ghorai, and Joyanta Choudhury*
Organometallics & Smart Materials Laboratory, Department of Chemistry, Indian Institute of Science Education and Research
Bhopal, Bhauri, Indore By-pass Road, Bhopal 462 066, India
S
* Supporting Information
ABSTRACT: The reaction of a series of pyridine-appended
imidazolium salts with Pd(COD)Cl2 in the presence of KOtBu
as base led to hydrolytic ring-opening followed by a new type
of pincer tridentate (N,C,O) bonding of the in situ generated
formamide-based new ligands toward the metal center. This
unprecedented type of bonding resulted from a vinylic C−H
activation by palladium stabilized with coordination from the
pyridine nitrogen and aldehyde oxygen donors in a pincer
fashion. The new stable, square-planar palladium(II) com-
plexes (1−3) were characterized by 1D and 2D NMR
spectroscopic and high-resolution mass spectrometric (HRMS) methods. The single-crystal X-ray structure of a representative
complex (2) confirmed the above interesting bonding features.
ring was hydrolytically opened via a C−N bond-breaking
process to result in a new type of tridentate ligand that was
coordinated to iron and cobalt, as reported by Xue et al.
(Scheme 1).6 Herein, we present another unique and
unprecedented bonding chemistry of an imidazolium ring
after its hydrolytic ring-opening reaction induced by traces of
moisture under basic conditions. This chemistry reveals that the
pyridine-appended imidazolium salts generated a new type of
(N,C,O) tridentate pincer complexes with palladium(II) that
featured a vinylic C−H activation along with coordination from
pyridine nitrogen and aldehyde oxygen donors (Scheme 1).
INTRODUCTION
■
Recently, N-heterocyclic carbenes (NHCs) undoubtedly placed
themselves on the front rows of the ligand matrix as developed
and utilized successfully in the fields of fundamental organo-
metallic chemistry, catalysis, and materials.1 Their unique
stereoelectronic features, such as strong metal−CNHC bonding,
electronic/steric tunability via the wingtips, and excellent
stability of the metal−NHC complexes toward heat, air, and
moisture, are considered as the key to the observed success of
this versatile class of ligands. To date, a number of successful
methods have been developed to synthesize NHC complexes
with different metal centers. One such common and easy
strategy involves the use of a base (mild/strong, inorganic/
organic) with the parent imidazolium salt, generating the free
carbene in situ for efficient coordination with the metal
(Scheme 1).2 Although this method has been employed quite
successfully with many imidazolium salts, the risk of slow
hydrolysis and subsequent decomposition of the in situ
generated free carbenes with traces of moisture should not be
ignored (Scheme 1).3 Interestingly, beyond this general
caution, some unconventional and unique chemistry was
observed very recently that can enhance the fundamental
knowledge-base in this research area: specifically the diversity of
metal−ligand bonding. For example, Braunstein et al. found
hydrolytic cleavage of an uncoordinated imidazolium ring
within an iridium-based complex without any further
coordination of the resulting iminoformamide derivative
(Scheme 1).4 On the other hand, Peris et al. observed an
unusual postcleavage bonding of a similar hydrolyzed, ring-
opened fragment with two iridium centers where an additional
transformation (decarbonylation of the formyl group) took
place (Scheme 1).5 In another surprising chemistry, a triazolyl
RESULTS AND DISCUSSION
■
The reaction of the imidazolium salts [L1H]PF6, [L2H]PF6, and
[L3H]PF6, with 1.9 equiv of KOtBu in tetrahydrofuran at
ambient temperature for a short time (∼20 min), followed by
stirring with Pd(COD)Cl2 for ∼1 h under the same conditions,
and a suitable workup with a solvent mixture of acetonitrile−
diethyl ether resulted in the air- and moisture-stable complexes
1, 2, and 3, respectively, in good yields (Scheme 2).
1
The H NMR spectra of all the complexes showed the
presence of a single palladium complex with an indication of an
unusual coordination environment as compared to an expected
∧
bidentate Npyridine Ccarbene mode of bonding of the ligand to the
metal center.7 Three characteristic peaks were observed at
9.23−10.23 ppm (doublet, J = 4.8−5.6 Hz) corresponding to
the NH proton, at 7.87−8.03 ppm (singlet) corresponding to
the CHO proton, and at 5.74−6.25 ppm (doublet, J = 5.5−5.8
Hz) corresponding to the vinylic Pd−CCH proton, in
Received: April 5, 2014
Published: June 10, 2014
© 2014 American Chemical Society
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Organometallics
Note
∼124.9−129.8 ppm assigned to the Pd-C carbon atom. The
vinylic CCH carbon appeared at 106.4−108.9 ppm. The
1H−13C HSQC spectrum (Figure 1B) of 2 displayed the
expected correlation, confirming the above assignment for the
vinylic CCH and the CHO carbons. In the infrared spectra of
the complexes, we observed peaks at ∼1620 and ∼3430 cm−1
characteristic for −N-C(H)O and −N−H groups, respec-
tively. The positive ion high-resolution electrospray ionization
mass spectra (HR-ESIMS) of all the complexes exhibited a
major intense peak (at m/z = 281.9874 for 1, 324.0342 for 2,
and 344.0038 for 3) with the expected isotopic pattern assigned
to the solvent-dissociated molecular ion [M − CH3CN]+.
To unambiguously confirm the above-suggested structural
arrangement in these new complexes, a single-crystal X-ray
diffraction study of complex 2 was accomplished. Figure 2
Scheme 1. Conventional and Unconventional Reactions of
Imidazolium Salts
Figure 2. ORTEP diagram of complex 2 (30% ellipsoid probability
level). Selected bond lengths (Å) and bond angles (deg): C7−Pd1 =
1.867(10), O1−Pd1 = 2.094(8), N1−Pd1 = 2.052(8), N4−Pd1 =
2.116(9), C5−N2 = 1.304(16), C6−N2 = 1.349(16), C6−C7 =
1.368(18), C7−N3 = 1.42(2), C8−N3 = 1.279(16), C8−O1 =
1.253(15), C7−Pd1−N1 = 92.1(6), C7−Pd1−O1 = 81.8(7), N1−
Pd1−N4 = 97.5(4), O1−Pd1−N4 = 88.6(4). Only one molecule is
shown here.
Scheme 2. Synthesis of the Complexes 1−3
represents the ORTEP diagram illustrating the molecular
structure of 2 along with important bond lengths and bond
angles. The structure shows the formation of two uneven,
dissimilar, fused palladacycles where one is six-membered and
another is five-membered, leading to a distorted square planar
geometry around the Pd(II) metal center with a tridentate
(N,C,O) pincer type of bonding. The (N,C,O) donors resulting
from a vinylic carbon, the pyridine nitrogen, and an aldehyde
oxygen center established the in situ generation of a formamide-
based new ligand motif possibly via base-promoted hydrolytic
ring-opening of the imidazolium salts during the reaction. The
Pd−C bond length, 1.867(10) Å, is unusually shorter than
normal and abnormal Pd−Ccarbene bonds8 or a Pd−Cvinylic bond
with electron-withdrawing C-substituents.9 Due to the strong
trans influence of the vinylic ligand, the Pd−NCMe bond
(2.116(9) Å) is relatively longer in comparison to a similar type
of bond in reported palladium complexes.10
addition to the expected peaks for the coordinated pyridine
ring. 2D NMR spectroscopy of the complexes was performed
to confirm the connections.
1
Thus, for complex 2, the H−1H COSY spectrum (Figure
1A) suggested the correlation between the two doublet peaks at
10.17 and 6.25 ppm, whereas the singlet peak at 8.03 ppm did
not show any correlation. The 13C{1H} NMR spectra of the
complexes showed the CHO signal at ∼167 ppm and a signal at
The reactivity of NHC ligands displaying a ring-opening-type
rearrangement around the metal-coordination sphere has been
reported in the literature, but with preformed metal−NHC
complexes, via organometallic migratory insertion of an
adjacent anionic (typically methyl, phenyl) ligand to the
coordinated CNHC.
11 Although the exact mechanism in our case
is not fully clear, at this juncture it is noteworthy to mention
that we observed the formation of the above formamide-based
free ligand when the imidazolium salts were reacted with
KOtBu in THF. This indicates the plausibility of a prior ring-
cleaving hydrolysis of the in situ generated free NHC by
Figure 1. Expanded regions of 1H−1H COSY (A) and 1H−13C HSQC
(B) NMR spectra of complex 2 (DMSO-d6, 300 K).
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Organometallics
Note
1H, NCHN of Im), 8.65 (dd, JH−H = 4.8, 0.9 Hz, 1H, pyrH), 8.49 (t,
JH−H = 1.8 Hz, 1H, ImH), 8.22 (dt, JH−H = 8.1, 1.8 Hz, 1H, pyrH), 8.00
(d, JH−H = 8.2 Hz, 1H, pyrH), 7.95 (t, JH−H = 1.6 Hz, 1H, ImH), 7.64
(dd, JH−H = 7.1, 4.9 Hz, 1H, pyrH), 3.97 (s, 3H, NCH3) ppm. HRMS
(ESI, positive ion): m/z 160.0880 (calcd for [C9H12N3]+ 160.0869).
adventitious water before the reaction with the palladium
precursor, leading to the desired complexes after coordination
and subsequent C−H activation steps (Scheme 3).
Scheme 3. Plausible Mechanistic Steps
1
[L2H]PF6. Yield: 1.5 g (44%). H NMR (400 MHz, DMSO-d6): δ
10.08 (t, JH−H = 1.6 Hz, 1H, NCHN of Im), 8.65 (ddd, JH−H = 4.8, 1.8,
0.8 Hz, 1H, pyrH), 8.53 (t, JH−H = 1.9 Hz, 1H, ImH), 8.22 (ddd, JH−H
= 8.2, 7.5, 1.8 Hz, 1H, pyrH), 8.05 (m, 1H, ImH), 8.01 (dt, JH−H = 8.3,
0.8 Hz, 1H, pyrH), 7.64 (ddd, JH−H = 7.5, 4.8, 0.8 Hz, 1H, pyrH), 4.29
n
n
(t, JH−H = 7.2 Hz, 2H,CH2 of Bu), 1.88 (m, 2H, CH2 of Bu), 1.32
n
n
(m, 2H, CH2 of Bu), 0.93 (t, JH−H = 7.4 Hz, 3H, CH3 of Bu) ppm.
13C{1H} NMR (100 MHz, DMSO-d6): δ 149.2 (d), 146.4, 140.5,
135.1 (d), 125.2, 123.5, 119.3, 114.2, 49.3, 31.1, 18 8, 13.3 ppm.
HRMS (ESI, positive ion): m/z 202.1355 (calcd for [C12H16N3]+
202.1339).
1
[L3H]PF6. Yield: 0.64 g (43%). H NMR (400 MHz, DMSO-d6): δ
10.59 (s, 1H, NCHN of Im), 8.75 (m, 1H, ImH), 8.71 (dd, JH−H = 4.7,
0.9 Hz, 1H), 8.57 (m, 1H, ImH), 8.28 (dt, J = 8.1, 1.7 Hz, 1H), 8.16
(d, JH−H = 8.2 Hz, 1H), 7.94 (d, JH−H = 7.9 Hz, 2H), 7.69 (m, 3H),
7.65 (m, 1H) ppm. 13C{1H} NMR (100 MHz, DMSO-d6): δ 149.3
(d), 146.3, 140.6, 134.7, 134.3 (d), 130.2, 130.2, 125.5, 122.3, 120.1,
119.9, 114.7 ppm. The 13C{1H} NMR chemical shift values for this
compound matched satisfactorily with the reported values for the
bromide salt of the compound.15 HRMS (ESI, positive ion): m/z
222.1027 (calcd for [C14H12N3]+ 222.1026).
CONCLUSIONS
■
In conclusion, the above result highlights an unusual but
fascinating coordination chemistry emerging from the other
side of the conventional transition metal−NHC research. The
possibility of often-ignored hydrolytic ring-opening of NHC
ligands has been realized with our new findings, resulting in an
unprecedented type of palladium-pincer complexes.
Typical Procedure for the Synthesis of Complexes 1, 2, and
3. [L1H]PF6 (38.1 mg, 0.125 mmol), [L2H]PF6 (43.4 mg, 0.125
mmol), or [L3H]PF6 (45.9 mg, 0.125 mmol) and KOtBu (26.6 mg,
0.24 mmol) were mixed in a Schlenk tube under a stream of nitrogen
gas in a Schlenk line; 5 mL of THF was added and the mixture was
stirred under a nitrogen atmosphere at ambient temperature for 20
min. Pd(COD)Cl2 (31.4 mg, 0.11 mmol) was added into the solution;
an additional 2 mL of THF was added and the reaction mixture was
again stirred at the same conditions for 50 min. After that 3 mL of
CH3CN was added to the mixture, and the resulting yellow-red
solution was filtered. The volume of the solvent was reduced to 0.5−1
mL. Diethyl ether was added to precipitate out a yellow solid, which
was filtered, washed thoroughly with diethyl ether, and dried under
high vacuum to afford the desired product. The product was purified
by recrystallization via ether diffusion into a CH3CN solution of the
compound.
EXPERIMENTAL SECTION
■
General Methods and Materials. 1H and 13C{1H} NMR spectra
were recorded on Bruker AVANCE III 400 and 500 MHz NMR
spectrometers. Chemical shifts (δ) are expressed in ppm using the
residual proton resonance of the solvent as an internal standard
(DMSO: δ = 2.50 ppm for 1H spectra, 39.5 ppm for 13C{1H} spectra;
CH3COCH3: δ = 2.05 ppm for H spectra, 29.8 ppm for 13C{1H}
1
spectra). All coupling constants (J) are expressed in hertz (Hz) and
only given for 1H−1H couplings unless mentioned otherwise. The
following abbreviations were used to indicate multiplicity: s (singlet), d
(doublet), t (triplet), q (quartet), dd (doublet of doublets), dt
(doublet of triplets), ddd (doublet of doublet of doublets), m
(multiplet). ESI mass spectrometry was performed on a Bruker
microTOF QII spectrometer. Single-crystal X-ray diffraction data were
collected using a Bruker SMART APEX II CCD diffractometer with
graphite-monochromated Mo Kα (λ = 0.71073 Å) radiation at 202 K.
Structure was solved with direct methods using SHELXS-97 and
refined with full-matrix least-squares on F2 using SHELXL-97.12 FTIR
spectra were recorded on a PerkinElmer N3896 instrument. Solvents
(Spectrochem; water content 0.1−0.5%), reagents (Aldrich), deu-
terated solvents (Aldrich), and PdCl2 (Johnson Matthey) were
obtained from commercial suppliers and used without further
purification. [Pd(COD)Cl2] was synthesized according to a reported
procedure.13
Synthetic Procedures. Typical Procedure for the Synthesis of
[L1H]PF6, [L2H]PF6, and [L3H]PF6. N-Methyl imidazole (0.82 g, 10
mmol), N-butyl imidazole (1.24 g, 10 mmol), or N-phenyl imidazole
(0.57 g, 4.0 mmol) and 2-bromopyridine (equivalent amount) were
mixed in a pressure tube and stirred for 60 h at 150−160 °C in neat
conditions. After that the reaction mixture was cooled to room
temperature, and diethyl ether was added to the oily material, which
was washed with diethyl ether (3 × 20 mL) to remove unreacted
starting materials. The oily compound was dissolved in a minimum
volume of water; an aqueous NH4PF6 solution was added and stirred
for 30 min, which resulted into a solid precipitate. The precipitate was
filtered, washed with water and diethyl ether, and dried in high vacuum
to afford the light brown desired product.
1
Complex 1. Yield: 32 mg (∼70%). H NMR (400 MHz, DMSO-
d6): δ 10.23 (d, JH−H = 4.8 Hz, 1H, N-H), 9.36 (s, br [note: an H/D
exchange was observed for this proton with the deuterated solvent,
which sometimes leads to decreased peak integration], 1H, pyrH),
7.98 (s, 1H, CHO), 7.64 (m, 1H, pyrH), 7.12 (d, JH−H = 8.5 Hz, 1H,
pyrH), 6.67 (t, JH−H = 6.3 Hz, 1H, pyr), 6.19 (d, JH−H = 5.8 Hz, 1H,
Pd-CCH), 3.40 (s, 3H, NCH3), 2.07 (s, CH3CN) ppm. 13C{1H}
NMR (125 MHz, DMSO-d6): δ 167.4 (CHO), 150.8 (pyrC), 144.8
(pyrC), 136.3 (pyrC), 126.4 (Pd−C), 114.5 (pyrC), 113.0 (pyrC),
106.4 (Pd−CCH), 30.6 (NCH3), ppm. HRMS (ESI, positive ion):
m/z 281.9874 (calcd for [C9H10N3OPd]+ 281.9857). Anal. Found: C,
28.83; H, 3.17; N, 12.30. Calcd for C11H13N4OPF6Pd·0.5CH3CN·
H2O: C, 28.43; H, 3.28; N, 12.44.
1
Complex 2. Yield: 39 mg (∼75%). H NMR (500 MHz, DMSO-
d6): δ 10.17 (d{sometime s}, JH−H = 5.6 Hz, 1H, N-H), 9.43 (d, {ill-
defined} [note: an H/D exchange was observed for this proton with
the deuterated solvent, which sometimes leads to decreased peak
integration], 1H, pyrH), 8.03 (s, 1H, CHO), 7.62 (m, 1H, pyrH), 7.11
(d, JH−H = 8.5 Hz, 1H, pyrH), 6.65 (m, 1H, pyrH), 6.25 (d, JH−H = 5.8
Hz, 1H, Pd-CCH), 3.90 (t, JH−H = 7.0 Hz, 2H, CH2 of nBu), 2.07 (s,
CH3CN), 1.64 (m, 2H, CH2 of nBu), 1.26 (m, 2H, CH2 of nBu), 0.90
n
(t, JH−H = 7.3 Hz, 3H, CH3 of Bu) ppm. 13C{1H} NMR (125 MHz,
DMSO-d6): δ 167.3 (CHO), 150.7 (pyrC), 144.7 (pyrC), 136.3
(pyrC), 124.9 (Pd-C), 118.1 (CH3CN), 114.5 (pyrC), 113.0 (pyrC),
106.6 (Pd-CCH), 43.3 (nBuC), 29.7 (nBuC), 19.2 (nBuC), 13.5
(nBuC), 1.1 (CH3CN) ppm. HRMS (ESI, positive ion): m/z 324.0342
(calcd for [C12H16N3OPd]+ 324.0328). Anal. Found: C, 33.06; H,
[L1H]PF6. Yield: 0.95 g (31%). The NMR chemical shift values for
this compound were compared with reported values14 and were found
1
to match satisfactorily. H NMR (400 MHz, DMSO-d6): δ 10.02 (s,
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Organometallics
Note
3.82; N, 11.29. Calcd for C14H19N4OPF6Pd: C, 32.94; H, 3.75; N,
10.98.
Complex 3. Yield: 40 mg (∼71%). H NMR (500 MHz, acetone-
d6): δ 9.79 (d, JH−H = 5.5 Hz, 1H, PyrH), 9.23 (d {ill-defined}, 1H, N-
(7) Loch, J. A.; Albrecht, M.; Peris, E.; Mata, J.; Faller, J. W.;
Crabtree, R. H. Organometallics 2002, 21, 700.
(8) Lebel, H.; Janes, M. K.; Charette, A. B.; Nolan, S. P. J. Am. Chem.
1
Soc. 2004, 126, 5046.
H), 7.87 (s, 1H, CHO), 7.58 (m, 6H, pyrH and PhH), 7.13 (d, JH−H
8.5 Hz, 1H, pyrH), 6.64 (t, JH−H = 6.4 Hz, 1H, pyrH), 5.74 (d, JH−H
=
=
(9) van Belzen, R.; Elsevier, C. J.; Dedieu, A.; Veldman, N.; Spek, A.
L. Organometallics 2003, 22, 722.
(10) Khlebnikov, V.; Meduri, A.; Mueller-Bunz, H.; Montini, T.;
Fornasiero, P.; Zangrando, E.; Milani, B.; Albrecht, M. Organometallics
2012, 31, 976.
(11) (a) Waltman, A. W.; Ritter, T.; Grubbs, R. H. Organometallics
2006, 25, 4238. (b) Pugh, D.; Boyle, A.; Danopoulos, A. A. Dalton
Trans. 2008, 1087. (c) Danopoulos, A. A.; Tsoureas, N.; Green, J. C.;
Hursthouse, M. B. Chem. Commun. 2003, 756.
5.5 Hz, 1H, Pd-CCH) ppm. 13C{1H} NMR (125 MHz, acetone-d6):
δ 167.6 (CHO), 152.9 (pyrC), 146.3 (pyrC), 137.3 (pyrC), 134.8
(PhC), 13o.7 (PhC), 130.7 (PhC), 129.8 (Pd-C), 128.6 (PhC), 115.3
(pyrC), 114.0 (pyrC), 108.9 (Pd-CCH) ppm. HRMS (ESI, positive
ion): m/z 344.0038 (calcd for [C14H12N3OPd]+ 344.0015). Anal.
Found: C, 37.19; H, 3.14; N, 11.69. Calcd for C16H15N4OPF6Pd·
0.5CH3CN: C, 37.06; H, 3.02; N, 11.45.
(12) Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, 64, 112.
(13) Wiedermann, J.; Mereiter, K.; Kirchner, K. J. Mol. Catal. A:
Chem. 2006, 257, 67.
(14) Barbante, G. J.; Francis, P. S.; Hogan, C. F.; Kheradmand, P. R.;
Wilson, D. J. D.; Barnard, P. J. Inorg. Chem. 2013, 52, 7448.
(15) Vaughan, J. G.; Reid, B. L.; Ramchandani, S.; Wright, P. J.;
Muzzioli, S.; Skelton, B. W.; Raiteri, P.; Brown, D. H.; Stagni, S.;
Massi, M. Dalton Trans. 2013, 42, 14100.
ASSOCIATED CONTENT
■
S
* Supporting Information
1H, 13C{1H}, 1H−1H COSY, and 1H−13C HSQC NMR
spectra; ESI-HR mass spectra; FT-IR spectra; CIF file of
complex 2 (CCDC 995442). This material is available free of
charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail (J. Choudhury): joyanta@iiserb.ac.in.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
J.C. sincerely thanks DAE, BRNS (Young Scientist Research
Award grant no. 2011/20/37C/14/BRNS/1728), DST (Fast
Track research grant no. SR/FT/CS-49/2011), and IISER
Bhopal for financial support. A doctoral fellowship from CSIR
(to S.K.G.) and a postdoctoral fellowship from IISER Bhopal
(to D.G.) are gratefully acknowledged. This work is dedicated
to Professor Sujit Roy on the occasion of his 55th birthday.
REFERENCES
■
(1) For reviews, see: (a) Melaimi, M.; Soleilhavoup, M.; Bertrand, G.
Angew. Chem., Int. Ed. 2010, 49, 8810. (b) Poyatos, M.; Mata, J. A.;
Peris, E. Chem. Rev. 2009, 109, 3677. (c) Hahn, F. E.; Jahnke, M. C.
Angew. Chem., Int. Ed. 2008, 47, 3122. (d) Kaufhold, O.; Hahn, F. E.
́
Angew. Chem., Int. Ed. 2008, 47, 4057. (e) Díez-Gonzalez, S.; Marion,
N.; Nolan, S. P. Chem. Rev. 2009, 109, 3612. (f) Clavier, H.; Grela, K.;
Kirschning, A.; Mauduit, M.; Nolan, S. P. Angew. Chem., Int. Ed. 2007,
46, 6786. (g) Herrmann, W. A. Angew. Chem., Int. Ed. 2002, 41, 1290.
(2) (a) Balof, S. L.; P’Pool, S. J.; Berger, N. J.; Valente, E. J.; Shiller,
A. M.; Schanz, H.-J. Dalton Trans. 2008, 5791. (b) Boydston, A. J.; Xia,
Y.; Kornfield, J. A.; Gorodetskaya, I. A.; Grubbs, R. H. J. Am. Chem.
Soc. 2008, 130, 12775. (c) Luan, X.; Mariz, R.; Gatti, M.; Costabile, C.;
Poater, A.; Cavallo, L.; Linden, A.; Dorta, R. J. Am. Chem. Soc. 2008,
130, 6848. (d) Peng, H. M.; Webster, R. D.; Li, X. Organometallics
2008, 27, 4484. (e) Scheele, U. J.; Dechert, S.; Meyer, F. Chem.Eur.
J. 2008, 14, 5112. (f) McGuinness, D. S.; Suttil, J. A.; Gardiner, M. G.;
Davies, N. W. Organometallics 2008, 27, 4238. (g) Poyatos, M.; Mas-
Marza,
́
E.; Sanau, M.; Peris, E. Inorg. Chem. 2004, 43, 1793.
(h) Viciano, M.; Mas-Marza,
́
E.; Poyatos, M.; Sanau, M.; Crabtree,
R. H.; Peris, E. Angew. Chem., Int. Ed. 2005, 44, 444. (i) Vogt, M.;
Pons, V.; Heinekey, D. M. Organometallics 2005, 24, 1832. (j) Yang,
L.; Kruger, A.; Neels, A.; Albrecht, M. Organometallics 2008, 27, 3161.
(3) Holloc
D.; Nyulaszi, L. J. Am. Chem. Soc. 2011, 133, 780.
(4) Zuo, W.; Braunstein, P. Dalton Trans. 2012, 41, 636.
(5) Segarra, C.; Mas-Marza, E.; Benítez, M.; Mata, J. A.; Peris, E.
́
zki, O.; Terleczky, P.; Szieberth, D.; Mourgas, G.; Gudat,
́
́
Angew. Chem., Int. Ed. 2012, 51, 10841.
(6) Wang, G.-F.; Song, X.-J.; Chen, F.; Li, Y.-Z.; Chen, X.-T.; Xue, Z.-
L. Dalton Trans. 2012, 41, 10919.
3218
dx.doi.org/10.1021/om500362x | Organometallics 2014, 33, 3215−3218