Hydrogen Activation by an Iridium(III) Complex Bearing a Bidentate Protic NH,NR-NHC^Phosphine Ligand

Article abstract of DOI:10.1021/acs.organomet.5b00799

Benzimidazole 2 bearing an N1-(biscyclohexylphosphine)ethyl tether cleaves [IrCpCl₂]₂ to yield the mononuclear phosphine complex [3]. Heating of [3] yields via a formal C/N tautomerization complex [4]Cl with a protic NHC. Complex [4]

Full text of DOI:10.1021/acs.organomet.5b00799

Article
pubs.acs.org/Organometallics
Hydrogen Activation by an Iridium(III) Complex Bearing a Bidentate
Protic NH,NR-NHC∧Phosphine Ligand
Steffen Cepa, Christian Schulte to Brinke, Florian Roelfes, and F. Ekkehardt Hahn*
Institut fur Anorganische und Analytische Chemie, Westfalische Wilhelms-Universitat Munster, Corrensstraße 30, D-48149 Munster,
̈
̈
̈
̈
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Germany
S
* Supporting Information
ABSTRACT: Benzimidazole 2 bearing an N1-(biscyclohexylphosphine)-
ethyl tether cleaves [IrCp*Cl2]2 to yield the mononuclear phosphine
complex [3]. Heating of [3] yields via a formal C/N tautomerization
complex [4]Cl with a protic NHC. Complex [4]Cl can be N3-
deprotonated to give its conjugate base [6]. Complex [6] is able to
activate molecular hydrogen under mild conditions, leading to complex
[5]BF4. The molecular structures of complexes [3], [4]Cl, [5]Cl, and [5]BF4 have been determined by X-ray diffraction studies.
tethered to one of the ring nitrogen atoms of the azole. This
donor function precoordinates, thereby bringing the C2−H
bond into close proximity to the metal center, allowing for its
subsequent oxidative addition. The initially formed hydrido
complex often reacts by reductive elimination of a proton and
protonation of the ring nitrogen atom. Various complexes of
type C featuring different donor groups have been prepared.12
The protic NHC ligands in complexes of type B can be easily
N-alkylated by N-deprotonation followed by addition of an
alkylating agent. This has enabled the preparation of various
macrocycles featuring only NHC13 or NHC and phosphine
donors.8c,14 In addition, the N−H function of the protic NHC
ligands can act as a molecular recognition unit by forming
hydrogen bonds with selected substrates.15 We became
interested in the reactivity of complexes of type C after N-
deprotonation. The resulting complexes D are potential
candidates for bifunctional substrate activation due to the
presence of a Lewis base (the deprotonated ring nitrogen
atom) and a Lewis acid (the metal center).
INTRODUCTION
■
N-Heterocyclic carbenes (NHCs) and their metal complexes
have been studied intensively over the last two decades.1 Due
to their useful electronic and steric properties, NHCs have
found various applications in coordination chemistry,1,2 as
building blocks for metallosupramolecular complexes,3 and as
organocatalysts,4 and their transition metal complexes are used
as efficient catalysts.5
“Classical” NHC complexes A (Figure 1) feature NHC
ligands normally derived from azolium cations bearing alkyl or
Here we describe the preparation of some new iridium(III)
complexes of types C and D featuring a benzimidazole-derived
NHC and a dicyclohexylphosphine tether. Intermediates
formed during the synthesis of C and D and the reactivity of
complexes of type D toward dihydrogen have also been studied.
The results are compared to preliminary reports on some
related iridium(III)16 and ruthenium(II)17 complexes bearing
imidazole-derived NHCs and an N-2-(bistriphenylphosphine)-
ethyl tether.
Figure 1. Different types of NHC complexes.
aryl substituents at both ring nitrogen atoms.1 Over the last
years new NHC types such as abnormal, mesoionic, P-
heterocyclic or cyclic alkyl-amino-carbenes have been
described.6 We became interested in complexes bearing “protic”
NHC ligands B (Figure 1),7 which can be obtained via the
template-controlled cyclization of β-amino-functionalized iso-
cyanides8 or, more conveniently, by the oxidative addition of
C2-halogeno-substituted N-alkylazoles9 or azoles10 to low-
valent transition metals. Some alternative, occasionally
serendipitous, syntheses leading to complexes bearing protic
NHCs have also appeared.11 While the oxidative addition of 2-
halogenoazoles to low-valent transition metals is often
unproblematic, the oxidative addition of the C2−H bond of
azoles normally requires the presence of a donor function
RESULTS AND DISCUSSION
■
The N-2-(biscyclohexylphosphine)-ethyl-substituted 5,6-
dimethylbenzimidazole 2 (the 5,6-dimethyl derivative was
selected owing to its improved solubility in most solvents)
was prepared by treatment of 112b,c with in situ prepared
Received: September 22, 2015
© XXXX American Chemical Society
A
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lithium biscyclohexylphosphide (Scheme 1) in 62% yield.
1
Formation of 2 was confirmed by H, 13C{1H}, and 31P{1H}
Scheme 1. Synthesis of the N-PCy2-Functionalized
Benzimidazole 2 and Its Metal Complexes [3] and [4]Cl
Figure 2. Molecular structure of [3] in [3]·0.5CH2Cl2 (molecule A is
depicted, 50% displacement ellipsoids, hydrogen atoms have been
omitted). Selected bond lengths (Å) and angles (deg) for molecule A
[molecule B]: Ir−Cl1 2.4072(6) [2.4203(6)], Ir−Cl2 2.4127(6)
[2.4035(6)], Ir−P 2.3492(6) [2.3229(6)], range Ir−CCp 2.171(2)−
2.238(3) [2.155(3)−2.236(3)], N1−C1 1.362(4) [1.366(3)], N2−C1
1.311(4) [1.311(3)]; Cl1−Ir−Cl2 90.28(2) [87.95(3)], Cl1−Ir−P
87.18(2) [89.21(2)], Cl2−Ir−P 88.38(2) [88.45(2)], N1−C1−N2
114.4(3) [113.9(2)].
Å) and a rather large N1−C1−N2 angle (molecule A:
114.4(3)°) confirm the presence of a normal N-monoalkylated
benzimidazole unit. Comparable metric parameters for [3] fall
in the range previously observed for related iridium(III)
complexes.16
NMR spectroscopy in addition to microanalytical data. Due to
31P−1H coupling the resonances for the protons of the ethylene
bridge were observed as multiplets at δ = 4.18−4.25 ppm
(H12) and δ = 1.86−1.93 ppm (H13) in the 1H NMR
spectrum. The 31P{1H} NMR spectrum of 2 shows a resonance
at δ = −7.7 ppm significantly downfield from the resonance
recorded for free biscyclohexylphosphine (δ = −14.4 ppm).18
Reaction of 2 with 0.5 equiv of [IrCp*Cl2]2 in toluene for 12
h at 25 °C resulted in cleavage of the dinuclear iridium complex
and exclusive coordination of the phosphine donor to give the
orange mononuclear complex [3] in 99% yield (Scheme 1).
The C2−H bond is not involved in this reaction. The 13C{1H}
NMR spectrum of complex [3] features the resonance for the
Heating of a toluene solution of complex [3] to 130 °C in a
pressure tube gave within 24 h the yellow NHC complex [4]Cl,
bearing a protic NH,NR-NHC ligand (Scheme 1). We assume
that the formation of [4]Cl proceeds by an initial oxidative
addition of the C2−H bond to the iridium atom, leading to an
unstable iridium(V) hydrido complex, which rapidly loses HCl
via a reductive elimination. The liberated HCl then protonates
the ring nitrogen atom to give [4]Cl. While we cannot produce
experimental evidence for this reaction sequence, it is very
likely based on previous observations12 and due to the fact that
no base was present for a deprotonation at the C2 position.
Formation of complex [4]Cl was confirmed by 1H, 13C{1H},
and 31P{1H} NMR spectroscopy. In the 1H NMR spectrum the
resonance for the N−H proton was detected at δ = 12.37 ppm.
The resonance at δ = 7.80 ppm for the proton bound to C2 in
complex [3] is missing. A new resonance for the NHC carbene
carbon atom was observed at δ = 150.5 ppm in the 13C{1H}
NMR spectrum. This resonance was observed as a doublet
(2JC,P = 20.0 Hz) due to coupling between the CNHC carbon
atom and the phosphorus atom, confirming that both donors
are coordinated to the same metal center. Coordination of the
phosphine donor hinders the rotation about the CH2−CH2
bond of the tether. Consequently, diastereotopic behavior is
observed for the hydrogen atoms of the ethylene bridge and
four multiplets are found for these hydrogen atoms at δ =
4.98−5.14 (1H, H12), 3.93−4.11 (1H, H12), 2.23−2.33 (1H,
H13), and 2.11−2.23 ppm (1H, H13).
Cp* ring carbon atoms as a doublet at δ = 92.4 ppm (d, 2JC,P
=
2.6 Hz) due to the coupling with the phosphorus atom. The
resonance for the C13 carbon atom of the ethylene bridge was
also observed as a doublet at δ = 21.5 ppm (d, 1JC,P = 27.4 Hz).
The 31P{1H} NMR spectrum exhibits a resonance at δ = 1.1
ppm, which is shifted downfield (Δδ = 8.8 ppm) upon complex
formation compared to the free ligand 2 (δ = −7.7 ppm). The
1H NMR resonance at δ = 7.80 ppm can be assigned to the H2
proton, indicating that the C2 position is still protonated and
only the phosphorus atom coordinates to the metal center.
Crystals of [3]·0.5CH2Cl2, suitable for an X-ray diffraction
study, were obtained by slow diffusion of pentane into a
saturated solution of [3] in dichloromethane at ambient
temperature. The asymmetric unit of [3]·0.5CH2Cl2 contains
two essentially identical molecules of [3] and one disordered
CH2Cl2 molecule. Only the metric parameters for molecule A
will be discussed here. A listing of selected bond lengths and
angles for both molecules can be found in the caption of Figure
2.
The conclusions drawn from the spectroscopic data have
been confirmed by an X-ray diffraction study with crystals of
[4]Cl, obtained by diffusion of pentane into a CH2Cl2 solution
of the compound. Complex cation [4]+ (Figure 3) features a
C(NHC)∧PCy2 chelate ligand in addition to a chloro and an η5-
C5Me5 ligand. The Ir−CNHC bond length (2.010(2) Å) is
slightly shorter than found in the related iridium(III) complex
bearing an imidazolylidene ligand with an N-(2-
The structure analysis (Figure 2) confirmed the conclusions
drawn from the NMR spectra. The iridium atom is coordinated
by an η5-C5Me5, two chloro ligands, and the phosphine donor
tethered to the benzimidazole group. The diazaheterocycle is
protonated at the C2 position. Two different C1−N bond
distances (molecule A: N1−C1 1.362(4) Å, N2−C1 1.311(4)
B
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Figure 4. Molecular structure of [5]+ in [5]Cl·CH2Cl2·0.5C5H12 (50%
displacement ellipsoids, hydrogen atoms have been omitted except for
H1 bonded to N1 and H bound to Ir). Selected bond lengths (Å) and
angles (deg): Ir−P 2.2731(5), Ir−C1 2.006(2), Ir−H 1.55(2), range
Ir−CCp 2.244(2)−2.267(2), N1−C1 1.361(2), N2−C1 1.363(2); P−
Ir−C1 87.64(6), P−Ir−H 82.3(9), C1−Ir−H 83.5(9), N1−C1−N2
105.2(2).
Figure 3. Molecular structure of [4]+ in [4]Cl (50% displacement
ellipsoids, hydrogen atoms have been omitted except for H1 bound to
N1). Selected bond lengths (Å) and angles (deg): Ir−Cl 2.4034(4),
Ir−P 2.3283(5), Ir−C1 2.010(2), range Ir−CCp 2.188(2)−2.261(2),
N1−C1 1.353(2), N2−C1 1.362(2); Cl−Ir−P 88.29(2), Cl−Ir−C1
91.39(5), P−Ir−C1 84.06(5), N1−C1−N2 106.2(2).
for a hydrido ligand in [5]Cl. This substitution influences most
metric parameters within the two complex cations only
marginally. The Ir−CNHC distances are identical within
experimental error ([4]Cl: 2.010(2) Å; ([5]Cl: 2.006(2) Å).
A noticeable difference is the larger P−Ir−C bite angle in [5]Cl
(87.64(6)°) compared to 84.06(5)° in [4]Cl. This expansion of
the bite angle is most likely caused by the substitution of the
sterically demanding chloro ligand for a sterically much less
demanding hydrido ligand.
diphenylphosphine)ethylene tether (2.026(2) Å).16 Two al-
most identical N−CNHC bond lenghts (1.353(2) and 1.362(2)
Å) and a N−CNHC−N angle of 106.2(2)° confirm the presence
of a protic NHC ligand and fall in the range previously
observed for transition metal complexes bearing NH,NR-NHC
ligands.9,12
Treatment of compound [4]Cl with an equimolar amount of
NaOMe in methanol formally led to substitution of the chloro
ligand and formation of the hydrido complex [5]Cl (Scheme
2). The mechanism for the formation of the hydrido complex
Treatment of complex [4]Cl with an excess of KOtBu leads
to the benzimidazol-2-yl complex [6] or [7] depending on the
solvent used (Scheme 3). In both cases, the KOtBu
Scheme 2. Synthesis of Hydrido Complex [5]Cl, Bearing a
Bidentate NH,NR-NHC∧Phosphine Ligand
Scheme 3. N-Deprotonation of Complex [4]Cl and Synthesis
of the Hydrido Complex [5]BF4
cation [5]+ is currently not known. On the basis of previous
investigations16 on related compounds it is likely that cation
[4]+ initially reacts in a substitution reaction with displacement
of the chloro ligand for a methanolate ligand. A subsequent β-
hydride elimination from the coordinated methanolate
subsequently yields [5]+ and formaldehyde.
Complex [5]Cl still bears the protic NH,NR-NHC ligand.
The resonance for the N−H proton was detected at δ = 12.16
ppm, slightly upfield from the N−H resonance in [4]Cl (δ =
12.37 ppm). The presence of the hydrido ligand can be
concluded from the doublet at δ = −17.03 ppm (d, 2JH,P = 28.5
Hz) due to coupling with the phosphorus nucleus. The
13C{1H} NMR spectrum exhibits a resonance for the carbene
carbon atom as a doublet at δ = 152.0 ppm (d, 2JC,P = 14.4 Hz).
The resonance for the phosphorus atom in [5]Cl at δ = 19.2
ppm is significantly downfield shifted compared to the
equivalent resonance in [4]Cl (δ = 0.3 ppm).
Crystals of [5]Cl·CH2Cl2·0.5C5H12 were obtained by
diffusion of pentane into a dichloromethane solution of
[5]Cl. The structure analysis with these crystals (Figure 4)
confirms the composition of [5]Cl proposed on the basis of the
NMR spectra. The chloro ligand in [4]Cl has been substituted
deprotonates the ring nitrogen atom, generating an anionic
heterocycle. If this reaction is carried out in methanol, the
chloro ligand can be substituted for a methanol or methanolate
ligand. This ligand can subsequently react under β-hydride
elimination to give [7], similar to the reaction [4]Cl → [5]Cl.
In the presence of a solvent not capable of coordination/β-
hydride elimination, such as toluene, only the chloro complex
[6], bearing the N-deprotonated heterocycle, is obtained.
1
The H NMR spectra of [6] and [7] exhibit no resonances
that can be assigned to a N−H proton, indicative for the N-
deprotonation and the formation of the neutral complexes. The
C
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hydrido ligand in [7] gives rise to a resonance at δ = −17.69
2
ppm (d, JH,P = 30.5 Hz). Compared to [4]Cl (δ = 150.5 ppm
2
d, JC,P = 20.0 Hz) the resonance of the CNHC atoms is shifted
upfield in the 13C{1H} NMR spectra of [6] (δ = 143.8 ppm, d,
2
2JC,P = 21.8 Hz) and [7] (δ = 148.0 ppm, d, JC,P = 16.5 Hz).
Complex [6] dissolved in CD2Cl2 reacts with molecular
hydrogen (2 bar) at 25 °C in the presence of NaBF4 to give the
hydrido complex [5]BF4. The reaction goes to completion over
5 d (100% by NMR). The chloro salt [5]Cl has previously been
described and was obtained from [4]Cl (Scheme 2).
Alternatively, [5]BF4 can be obtained by N-protonation of
the ligand in [7] using NH4BF4. Similar N-protonation
reactions of azol-2-yl ligands have been described.9,10
Figure 5. Molecular structure of [5]BF4 (50% displacement ellipsoids,
hydrogen atoms have been omitted except for H1 bonded to N1 and
H bonded to Ir). Selected bond lengths (Å) and angles (deg): Ir−P
2.2818(7), Ir−C1 1.991(2), Ir−H 1.53(3), range Ir−CCp 2.238(3)−
2.297(2), N1−C1 1.371(3), N2−C1 1.373(3), N1−H1···F 2.084(2);
P−Ir−C1 85.48(7), N1−C1−N2 104.9(2).
The CNHC resonance in [5]BF4 was observed at δ = 152.8
2
ppm (d, JC,P = 15.2 Hz), which constitutes a downfield shift
compared to [6] (δ = 143.8 ppm) and [7] (δ = 148.0 ppm).
The doublet resonance at δ = −17.00 ppm (d, 2JH,P = 28.5 Hz)
was assigned to the hydride proton. While this resonance
appears at the same chemical shift as the hydride resonance in
[5]Cl, the resonance of the N−H proton in [5]BF4 at δ = 9.58
ppm appears significantly high-field shifted compared to the
equivalent resonance in [5]Cl (δ = 12.16 ppm). Given the fact
Table 2. Selected Bond Lengths [Å] and Angles [deg] of
Complexes [3], [4]Cl, [5]Cl, and [5]BF4
Ir−C1
N1−C1
N2−C1
Ir−P
N1−C1−N2
1
that the H NMR spectra for both [5]BF4 and [5]Cl were
[3]
1.362(4)
1.353(2)
1.361(2)
1.371(3)
1.311(4)
1.362(2)
1.363(2)
1.373(3)
2.3492(6)
2.3283(5)
2.2731(5)
2.2818(7)
114.4(3)
106.2(2)
105.2(2)
104.9(2)
recorded in the same solvent (CD2Cl2), the difference in the
chemical shift of the N−H protons would indicate differing
interactions of the complex cation with the anions present. The
presence of N−H and Ir−H resonances in the 1H NMR
spectrum of [5]BF4 confirms that dihydrogen has been cleaved
(starting from [6]) or that a proton has been added to the ring
nitrogen atom (starting from [7]).
[4]Cl
[5]Cl
[5]BF4
2.010(2)
2.006(2)
1.991(2)
identical irrespective of the protonation state of the heterocycle
and the coligands present.
The 31P{1H} NMR resonances also provide information
regarding the protonation state of the NH,NR-
NHC∧phosphine chalate ligand and the coligands present.
Starting from the free ligand precursor 2 a first downfield shift
is observed for the complex with the protic NHC ligand, [4]Cl.
Further downfield shifts have been recorded for the hydrido
complexes [7], [5]Cl, and [5]BF4 (see Table 1).
CONCLUSIONS
■
We have shown that benzimidazole 2, bearing a N1-
(biscyclohexylphosphine)ethyl tether, cleaves [IrCp*Cl2]2 to
yield the mononuclear phosphine complex [3]. Upon heating
of [3], complex [4]Cl was obtained by a currently unknown
reaction mechanism. It is conceivable that the reaction proceeds
by an initial oxidative addition of the C2−H bond to
iridium(III), but alternative procedures have also been
described.12h Complex [4]Cl can be deprotonated at the N3
ring nitrogen atom with KOtBu in toluene to give [6], still
bearing the chloro ligand at the metal center. If this
deprotonation is carried out in methanol, substitution of the
chloro ligand for a hydrido ligand to give complex [7] was
observed, most likely by coordination of a methanolate ligand
followed by β-hydride elimination. Both chloro complex [6]
and hydrido complex [7] feature a diazaheterocycle with an
unsubstituted ring nitrogen atom. Complex [6] reacts with
molecular hydrogen to yield [5]BF4, featuring a hydrido ligand
and a protonated ring nitrogen atom. Further studies are
directed toward the use of complexes of type [5]BF4 in catalytic
transfer hydrogenations.
Table 1. 31P{1H} NMR Shifts of Selected Compounds
compound
2
[4]Cl
[5]Cl, [5]BF4
[6]
[7]
a
b
b
b
a
b
δ/ppm
−7.7
0.3
19.2, 18.9
−0.9
17.8
a
b
Recorded in CDCl3. Recorded in CD2Cl2.
Crystals of [5]BF4 were studied by X-ray diffraction. The
molecular structure of the compound is depicted in Figure 5.
Comparable molecular parameters for the cations [5]+ in [5]Cl
and [5]BF4 do not differ significantly. The major difference
between the molecular structures of [5]Cl and [5]BF4 can be
found in the interaction of cations and anions. While the chloro
anion in [5]Cl does not interact with the cation [5]+, a
hydrogen bond is found between the N−H proton and the
−
BF4 anion in [5]BF4 (Figure 5). The N−H···F distance of
EXPERIMENTAL SECTION
2.084(2) Å is indicative of a strong hydrogen bond. Related
hydrogen bonds between fluorinated anions and N−H groups
of protic NHC ligands have been described.9b
■
General Procedures. All preparations were carried out under an
argon atmosphere using conventional Schlenk techniques or in a
glovebox. Solvents were dried and degassed by standard methods prior
Selected metric parametes for compounds [3], [4]Cl, [5]Cl,
and [5]BF4 are listed in Table 2. All complexes show the typical
piano stool conformation of Cp*-IrIII complexes. Upon
formation of the NHC complexes, the expected changes within
the five-membered heterocycle are observed (N−C1 bond
lengths become longer and almost equidistant; the N1−C1−
N2 angle becomes smaller). The Ir−CNHC distances are almost
19
to use. [IrCp*Cl2]2 and N-2-chloroethyl-5,6-dimethylbenzimidazo-
le12c (1) were prepared as described in the literature. NMR spectra
were recorded on a Bruker Avance I 400 or Bruker Avance III 400
NMR spectrometer. Chemical shifts (δ) are expressed in ppm
downfield from tetramethylsilane or using the residual protonated
solvent signal as internal standard. Coupling constants are expressed in
hertz. ESI-HRMS spectra were obtained with an OrbitrapXL
D
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spectrometer. For assignment of the NMR resonances see the
numbering at the molecular plots. Satisfactory elemental analyses of
compounds 3, [5]Cl, [5]BF4, [6], and [7] were difficult to obtain due
to the sensitivity of the compounds toward oxygen and moisture and
−
the presence of the BF4 anion in [5]BF4. A complete set of NMR
spectra is provided in the Supporting Information instead.
N1-2-(Bistricyclohexylphosphine)ethyl-5,6-dimethyl-
benzimidazole, 2. A sample of LiPCy2 was prepared by the addition of
toluene (5 mL), giving an orange solution. This mixture was heated for
1 d at 130 °C. Over this time a yellow powder precipitated, which was
filtered off, washed with pentane (2 × 5 mL), and dried in vacuo. The
powder was identified to be complex [4]Cl. Yield: 70 mg (0.09 mmol,
1
90%). H NMR (400 MHz, CD2Cl2): δ 12.37 (s, 1H, NH), 8.11 (s,
1H, H5), 7.23 (s, 1H, H8), 5.14−4.98 (m, 1H, H12), 4.11−3.93 (m,
1H, H12), 2.38 (s, 3H, H10), 2.34 (s, 3H, H11), 2.33−2.23 (m, 1H,
H13), 2.23−2.11 (m, 1H, H13), 1.89 (d, 4JH,P = 1.6 Hz, 15H, Cp*-H),
1.85−1.01 (m, 22H, Cy-H). 13C{1H} NMR (101 MHz, CD2Cl2): δ
nBuLi (1.30 mmol, 0.13 mL of a 10 M solution in hexane) to a
solution of dicyclohexyl phosphine (242 mg, 1.22 mmol) in THF (10
mL) at ambient temperature. After 30 min this solution was added to a
solution of N1-2-chloroethyl-5,6-dimethylbenzimidazole (1) (220 mg,
1.05 mmol) in THF (8 mL). The resulting solution was stirred at
ambient temperature for 3 d. The reaction mixture was then quenched
by addition of methanol (2 mL), and all solvents were subsequently
removed in vacuo. The solid residue was suspended in degassed water
(20 mL), and compound 2 was extracted with dichloromethane (3 ×
10 mL). The combined organic phases were dried over Na2SO4, and
all volatiles were removed in vacuo, giving 2 as a beige air-sensitive
solid. Yield: 240 mg (0.65 mmol, 62%). 1H NMR (400 MHz, CDCl3):
δ 7.83 (s, 1H, H2), 7.56 (s, 1H, H5), 7.13 (s, 1H, H8), 4.25−4.18 (m,
2H, H12), 2.40 (s, 3H, H10), 2.38 (s, 3H, H11), 1.93−1.86 (m, 2H,
H13), 1.82−1.12 (m, 22 H, Cy-H). 13C{1H} NMR (101 MHz,
CDCl3): δ 142.6 (s, C4), 141.8 (s, C2), 132.0 (s, C9), 131.9 (s, C7),
2
150.5 (d, JC,P = 20.0 Hz, C2), 134.0 (s, C4), 133.5 (s, C6), 133.0 (s,
2
C9), 132.9 (s, C7), 115.2 (s, C5), 109.8 (s, C8), 97.9 (d, JC,P = 2.2
Hz, Cp*-C), 42.9 (d, 2JC,P = 1.5 Hz, C12), 37.4 (d, JC,P = 30.1 Hz, Cy-
C), 37.1 (d, JC,P = 29.8 Hz, Cy-C), 28.6−28.5 (m, Cy-C), 28.2 (d, JC,P
= 1.6 Hz, Cy-C), 27.6−27.3 (m, Cy-C), 27.3−27.0 (m, Cy-C), 26.3 (s,
1
Cy-C), 26.2 (s, Cy-C), 20.5 (s, C10), 20.2 (s, C11), 17.5 (d, JC,P
=
34.7 Hz, C13), 10.2 (s, Cp*-CH3). 31P{1H} NMR (162 MHz,
CD2Cl2): δ 0.3. MS (ESI, HRMS): m/z = 733.3019 [4 − Cl]+ (calcd
for [4 − Cl]+ 733.3023). Anal. Calcd for C33H50Cl2IrN2P: C, 51.55; H,
6.56; N 3.64. Found: C, 51.81; H, 6.53; N, 3.65.
Complex [5]Cl. Complex [4]Cl (78.0 mg, 0.10 mmol) was dissolved
in methanol (4 mL), and NaOMe (0.10 mmol, 1 mL of a 0.1 M
2
130.9 (s, C6) 120.4 (s, C5), 109.6 (s, C8), 44.9 (d, JC,P = 34.2 Hz,
C12), 33.2 (d, JC,P = 12.0 Hz, Cy-C), 30.2 (d, JC,P = 14.5 Hz, Cy-C),
29.0 (d, JC,P = 7.6 Hz, Cy-C), 27.2 (d, JC,P = 11.5 Hz, Cy-C), 27.1 (d,
1
JC,P = 7.3 Hz, Cy-C), 26.4 (s, Cy-C), 22.7 (d, JC,P = 20.3 Hz, C13),
20.6 (s, C10), 20.2 (s, C11). 31P{1H} NMR (162 MHz, CDCl3): δ
−7.7. MS (ESI, HRMS): m/z = 371.2604 [2 + H]+ (calcd for [2 + H]+
371.2616). Anal. Calcd for C23H35N2P: C, 74.56; H, 9.52; N 7.56.
Found: C, 74.07; H, 9.56; N, 7.18.
solution in methanol) was added. The brown reaction mixture was
stirred for 24 h at ambient temperature. Then, the solvent was
removed in vacuo and the residue dissolved in dichloromethane (1
mL). Addition of pentane (5 mL) led to precipitation of a colorless
solid, which was isolated by filtration, washed with pentane (2 × 5
Complex [3]. Compound 2 (37.0 mg, 0.10 mmol) and [IrCp*Cl2]2
(40.0 mg, 0.05 mmol) were dissolved in toluene (5 mL) to give an
1
mL), and dried in vacuo. Yield: 65 mg (0.09 mmol, 90%). H NMR
(400 MHz, CD2Cl2): δ 12.16 (s, 1H, NH), 8.20 (s, 1H, H5), 7.02 (s,
1H, H8), 4.44−4.27 (m, 1H, H12), 3.82−3.69 (m, 1H, H12), 2.32 (s,
3H, H10), 2.29 (s, 3H, H11), 2.24 (s, 15H, Cp*-H), 1.99−0.74 (m,
2
24H, H13 + Cy-H), − 17.03 (d, JH,P = 28.5 Hz, 1H, Ir-H). 13C{1H}
NMR (101 MHz, CD2Cl2): δ 152.0 (d, 2JC,P = 14.4 Hz, C2), 134.2 (s,
C4), 132.1 (s, C6), 131.6 (s, C9), 131.5 (s, C7), 115.0 (s, C5), 109.0
(s, C8), 97.0 (d, 2JC,P = 2.1 Hz, Cp*-C), 45.9 (s, C12), 37.2 (d, JC,P
=
34.4 Hz, Cy-C), 35.1 (d, JC,P = 31.0 Hz, Cy-C), 28.7−26.4 (m, Cy-C),
1
20.4 (s, C10), 20.1 (s, C11), 20.0 (d, JC,P = 40.3 Hz, C13), 11.4 (s,
Cp*-CH3). 31P{1H} NMR (162 MHz, CD2Cl2): δ 19.2. MS (ESI,
HRMS): m/z = 699.3414 [5 − Cl]+ (calcd for [5 − Cl]+ 699.3421).
Complex [5]BF4. A pressure tube was charged with complex [6]
(83.0 mg, 0.11 mmol), NaBF4 (0.14 mg, 0.13 mmol), and CD2Cl2 (2.5
orange solution. The reaction mixture was stirred at ambient
temperature for 12 h. Then the solvent was removed in vacuo, and
the resulting solid residue was dissolved in dichloromethane (1 mL).
Addition of pentane (5 mL) led to precipitation of the orange, air-
1
stable complex [3]. Yield: 76 mg (0.10 mmol, 99%). H NMR (400
MHz, CD2Cl2): δ 7.80 (s, 1H, H2), 7.44 (s, 1H, H5), 7.43 (s, 1H,
H8), 4.72−4.61 (m, 2H, H12), 2.64−2.52 (m, 2H, H13), 2.39 (s, 3H,
H10), 2.35 (s, 3H, H11), 1.63 (d, 4JH,P = 1.8 Hz, 15H, Cp*-H) 2.10−
1.19 (m, 22H, Cy-H). 13C{1H} NMR (101 MHz, CD2Cl2): δ 142.9 (s,
C4), 142.6 (s, C2), 132.7 (s, C9), 132.1 (s, C7), 130.9 (s, C6), 120.1
mL). The reaction mixture was stirred at ambient temperature for 5
days in a hydrogen atmosphere (2 bar). The solvent was removed
under reduced pressure. Yield: 83 mg, 0.11 mmol, 100% (also
2
(s, C5), 111.1 (s, C8), 92.4 (d, JC,P = 2.6 Hz, Cp*-C), 42.6 (s br,
C12), 36.8 (d, JC,P = 27.4 Hz, Cy-C), 29.4 (s, Cy-C), 29.1 (d, JC,P = 3.8
Hz, Cy-C), 27.8 (d, JC,P = 11.3 Hz, Cy-C), 27.7 (d, JC,P = 9.9 Hz, Cy-
C), 26.6 (s, Cy-C), 21.5 (d, 1JC,P = 27.4 Hz, C13), 20.8 (s, C10), 20.3
(s, C11), 9.5 (s, Cp*-CH3). 31P{1H} NMR (162 MHz, CD2Cl2): δ 1.1.
MS (ESI, HRMS): m/z = 769.2763 [3 + H]+ (calcd for [3 + H]+
769.2783). Anal. Calcd for [3]·C33H50Cl2IrN2P: C, 51.55; H, 6.56; N
3.64. Found: C, 50.51; H, 6.59; N, 2.72.
1
determined by NMR). H NMR (400 MHz, CD2Cl2): δ 9.58 (s, 1H,
NH), 7.53 (s, 1H, H5), 7.09 (s, 1H, H8), 4.53−4.31 (m, 1H, H12),
3.78−3.64 (m, 1H, H12), 2.35 (s, 3H, H10), 2.34 (s, 3H, H11), 2.14
(s, 15H, Cp*-H), 2.05−0.95 (m, 24H, H13 + Cy-H), − 17.00 (d, 2JH,P
= 28.5 Hz, 1H, Ir-H). 13C{1H} NMR (101 MHz, CD2Cl2): δ 152.8 (d,
2JC,P = 15.2 Hz, C2), 133.1 (s, C6), 132.9 (s, C9), 132.4 (s, C7), 131.6
(s, C4), 112.8 (s, C5), 109.7 (s, C8), 97.0 (d, 2JC,P = 2.2 Hz, Cp*-C),
45.9 (d, 2JC,P = 2.4 Hz, C12), 36.8 (d, JC,P = 34.5 Hz, Cy-C), 35.0 (d,
Complex [4]Cl. A pressure tube was charged with compound 2
(37.0 mg, 0.10 mmol), [Cp*IrCl2]2 (40.0 mg, 0.05 mmol), and
E
DOI: 10.1021/acs.organomet.5b00799
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
JC,P = 31.3 Hz, Cy-C), 28.7 (s, Cy-C), 28.1 (s, Cy-C), 27.8 (s, Cy-C),
27.4 (s, Cy-C), 27.1 (d, JC,P = 12.9 Hz, Cy-C), 26.9 (d, JC,P = 4.6 Hz,
Cy-C), 26.8 (s, Cy-C), 26.8 (d, JC,P = 10.3 Hz, Cy-C), 26.5 (s, Cy-C),
Crystal Data for [3]·0.5CH2Cl2. Crystals suitable for an X-ray
diffraction study were obtained by slow diffusion of pentane into a
solution of [3] in dichloromethane. Formula C33.5H51N2Cl3IrP, M =
811.28, orange plates, 0.32 × 0.23 × 0.05 mm3, monoclinic, space
group P21/n, a = 16.6119(7) Å, b = 14.9729(6) Å, c = 27.5702(12) Å,
β = 95.786(2)°, V = 6822.6(5) Å3, Z = 8, ρcalcd = 1.580 g cm−3, μ =
4.221 mm−1, ω- and φ-scans, 124 604 intensities measured in the
range 4.9° ≤ 2θ ≤ 62.0°, semiempirical absorption correction (0.417 ≤
T ≤ 0.552), 21 556 independent intensities (Rint = 0.0387), 18 558
observed intensities [I ≥ 2σ(I)], refinement of 742 parameters against
all |F2| with anisotropic thermal parameters for all non-hydrogen atoms
and hydrogen atoms on calculated positions, R = 0.0265, wR = 0.0603,
Rall = 0.0351, wRall = 0.0635. The asymmetric unit contains two
molecules of [3] and one disordered CH2Cl2 molecule.
1
26.4 (s, Cy-C), 20.4 (s, C10), 20.2 (s, C11), 19.8 (d, JC,P = 40.6 Hz,
C13), 11.0 (s, Cp*-CH3). 31P{1H} NMR (162 MHz, CD2Cl2): δ 18.9.
11B{1H} NMR (128 MHz, CD2Cl2): δ −0.9. 19F{1H} NMR (377
MHz, CD2Cl2): δ −151.4. MS (ESI, HRMS): m/z = 699.3401 [5 −
BF4]+ (calcd for [5 − BF4]+ 699.3421).
Alternatively, compound [5]BF4 can be obtained by stirring a
mixture of [7] (73.0 mg, 0.10 mmol) and NH4BF4 (21.0 mg, 0.20
mmol) in toluene or CD2Cl2 (5 mL) for 12 h at ambient temperature.
Complex [6]. Complex [4]Cl (93.0 mg, 0.12 mmol) and KOtBu
(17.0 mg, 0.15 mmol) were dissolved in toluene (5 mL). The mixture
Crystal Data for [4]Cl. Crystals suitable for a X-ray diffraction study
were obtained by slow diffusion of pentane into a solution of [4]Cl in
dichloromethane. Formula C33H50N2Cl2IrP, M = 768.82, yellow
prisms, 0.14 × 0.13 × 0.06 mm3, monoclinic, space group P21/n, a
= 14.8310(2) Å, b = 15.9517(2) Å, c = 15.0123(2) Å, β =
114.8010(10)°, V = 3224.04(7) Å3, Z = 4, ρcalcd = 1.584 g cm−3, μ
= 4.382 mm−1, ω- and φ-scans, 38 843 intensities measured in the
range 3.9° ≤ 2θ ≤ 62.0°, semiempirical absorption correction (0.579 ≤
T ≤ 0.779), 10 110 independent intensities (Rint = 0.0295), 8702
observed intensities [I ≥ 2σ(I)], refinement of 359 parameters against
all |F2| with anisotropic thermal parameters for all non-hydrogen atoms
and hydrogen atoms (including the N−H hydrogen atom) on
was stirred for 1 day at ambient temperature. The solvent was removed
in vacuo, and the residue was dissolved in dichloromethane (2 mL).
Addition of pentane (8 mL) led to precipitation of [6], which was
isolated by filtration, washed with pentane (2 × 3 mL), and dried in
vacuo. Yield: 55 mg, (0.08 mmol, 67%). 1H NMR (400 MHz, CDCl3):
δ 7.32 (s, 1H, H8), 6.87 (s, 1H, H8), 5.03−4.89 (m, 1H, H12), 4.25−
4.08 (m, 1H, H12), 2.34 (s, 3H, H10), 2.32 (s, 3H, H11), 2.09−0.93
(m, 24H, H13 + Cy-H) 1.83 (s, 15H, Cp*-H). 13C{1H} NMR (101
2
MHz, CDCl3): δ 145.6 (s, C4), 143.8 (d, JC,P = 21.8 Hz, C2), 135.9
calculated positions, R = 0.0205, wR = 0.0437, Rall = 0.0278, wRall
=
(s, C9), 127.0 (s, C6), 126.3 (s, C7), 117.0 (s, C5), 107.3 (s, C8), 96.1
(d, 2JC,P = 2.0 Hz, Cp*-C), 39.4 (s, C12), 38.7 (d, JC,P = 28.7 Hz, Cy-
C), 35.6 (d, JC,P = 32.7 Hz, Cy-C), 28.4 (s, Cy-C), 28.3 (s, Cy-C)
27.4−26.5 (m, Cy-C), 26.3 (s, Cy-C), 25.9 (s, Cy-C), 20.3 (s, C10),
0.0461. The asymmetric unit contains one formula unit.
Crystal Data for [5]Cl·CH2Cl2·0.5C5H12. Crystals suitable for an X-
ray diffraction study were obtained by slow diffusion of pentane into a
solution of [5]Cl in dichloromethane. Formula C36.5H59N2Cl3IrP, M =
855.38, light yellow sticks, 0.40 × 0.25 × 0.21 mm3, monoclinic, space
group P21/n, a = 13.1256(11) Å, b = 13.7279(12) Å, c = 21.138(2) Å,
β = 98.471(4)°, V = 3767.2(6) Å3, Z = 4, ρcalcd = 1.508 g cm−3, μ =
3.827 mm−1, ω- and φ-scans, 66 479 intensities measured in the range
6.6° ≤ 2θ ≤ 62.3°, semiempirical absorption correction (0.509 ≤ T ≤
0.746), 11 870 independent intensities (Rint = 0.0387), 10 346
observed intensities [I ≥ 2σ(I)], refinement of 401 parameters against
all |F2| with anisotropic thermal parameters for all non-hydrogen atoms
and hydrogen atoms (including the N−H hydrogen atom) on
1
20.1 (s, C11), 18.4 (d, JC,P = 35.8 Hz, C13), 9.6 (s, Cp*-CH3).
31P{1H} NMR (162 MHz, CDCl3): δ −0.9. MS (ESI, HRMS): m/z =
733.2999 [6 + H]+ (calcd for [6 + H]+ 733.3023).
Complex [7]. Complex [4]Cl (69.0 mg, 0.09 mmol) and KOtBu
(12.0 mg, 0.11 mmol) were dissolved in methanol (5 mL). The
calculated positions, R = 0.0212, wR = 0.0497, Rall = 0.0280, wRall
=
0.0523. The positional parameters for the hydridic hydrogen atom
were identified in a difference Fourier map and were refined with an
isotropic thermal parameter. The asymmetric unit contains one
molecule of [5]Cl, one molecule of CH2Cl2, and a pentane molecule
with SOF = 0.5. No hydrogen positions have been calculated for the
pentane molecule.
reaction mixture was stirred at ambient temperature for 12 h. The
solution was filtered over Celite, and the solvent was removed in vacuo,
giving complex [7] as a brown solid. Yield: 23 mg (0.03 mmol, 33%).
1H NMR (400 MHz, CD2Cl2): δ 7.15 (s, 1H, H5), 6.80 (s, 1H, H8),
4.21−4.02 (m, 1H, H12), 3.76−3.62 (m, 1H, H12), 2.31 (s, 3H, H10),
2.30 (s, 3H, H11), 2.10 (s, 15H, Cp*-H), 2.02−0.81 (m, 24H, H13 +
Crystal Data for [5]BF4. Crystals suitable for an X-ray diffraction
study were obtained by slow diffusion of pentane into a solution of
[8]BF4 in dichloromethane. Formula C33H51N2BF4IrP, M = 785.78,
colorless needles, 0.40 × 0.35 × 0.23 mm3, monoclinic, space group
Cc, a = 21.8788(8) Å, b = 13.5847(5) Å, c = 12.4615(5) Å, β =
115.7590(4)°, V = 3335.7(2) Å3, Z = 4, ρcalcd = 1.565 g cm−3, μ =
4.098 mm−1, ω- and φ-scans, 29 615 intensities measured in the range
5.7° ≤ 2θ ≤ 62.1°, semiempirical absorption correction (0.500 ≤ T ≤
0.746), 10 449 independent intensities (Rint = 0.0258), 10 303
observed intensities [I ≥ 2σ(I)], refinement of 390 parameters against
all |F2| with anisotropic thermal parameters for all non-hydrogen atoms
and hydrogen atoms (including the N−H hydrogen atom) on
2
Cy-H), −17.69 (d, JH,P = 30.5 Hz, 1H, Ir-H). 13C{1H} NMR (101
MHz, CD2Cl2): δ 148.0 (d, 2JC,P = 16.5 Hz, C2), 146.6 (s, C4), 135.1
(s C9), 126.8 (s, C6), 125.5 (s, C7), 116.2 (s, C5), 107.3 (s, C8), 95.5
(d, 2JC,P = 2.4 Hz, Cp*-C), 43.8 (s, C12), 37.9 (d, JC,P = 34.8 Hz, Cy-
C), 34.3 (d, JC,P = 30.3 Hz, Cy-C), 27.8−26.5 (m, Cy-C), 21.7 (d, 1JC,P
= 39.8 Hz, C13), 20.3 (s, C10), 20.2 (s, C11), 10.8 (s, Cp*-CH3).
31P{1H} NMR (162 MHz, CD2Cl2): δ 17.8. MS (ESI, HRMS): m/z =
699.3406 [7 + H]+ (calcd for [7 + H]+ 699.3421).
X-ray Diffraction Studies. X-ray diffraction data were collected
with a Bruker APEX-II CCD diffractometer equipped with a micro
source at 153(2) K using graphite-monochromated Mo Kα (λ =
0.710 73 Å) radiation. Diffraction data were collected over the full
sphere and were corrected for absorption. Structure solutions were
found with the SHELXS-97 package20 using the heavy-atom method
and were refined with SHELXL-9720 against F2 using first isotropic
and later anisotropic thermal parameters for all non-hydrogen atoms.
Hydrogen atoms were added to the structure models on calculated
positions.
calculated positions, R = 0.0231, wR = 0.0584, Rall = 0.0235, wRall
=
0.0587. The positional parameters for the hydridic hydrogen atom
were identified in a difference Fourier map and were refined with an
isotropic thermal parameter. The asymmetric unit contains one
formula unit.
F
DOI: 10.1021/acs.organomet.5b00799
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(10) (a) Das, R.; Daniliuc, C. G.; Hahn, F. E. Angew. Chem., Int. Ed.
2014, 53, 1163−1166. (b) Das, R.; Hepp, A.; Daniliuc, C. G.; Hahn, F.
E. Organometallics 2014, 33, 6975−6987.
(11) (a) Burling, S.; Mahon, M. F.; Powell, R. E.; Whittlesey, M. K.;
Williams, J. M. J. J. Am. Chem. Soc. 2006, 128, 13702−13703.
(b) Wang, X.; Chen, H.; Li, X. Organometallics 2007, 26, 4684−4687.
(c) Ruiz, J.; Perandones, B. F. J. Am. Chem. Soc. 2007, 129, 9298−
9299. (d) Lewis, J. C.; Bergman, R.; Ellman, J. A. Acc. Chem. Res. 2008,
41, 1013−1025.
ASSOCIATED CONTENT
■
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.5b00799.
1H, 13C{1H}, and 31P{1H} NMR spectra of all
compounds (PDF)
(12) (a) Araki, K.; Kuwata, S.; Ikariya, T. Organometallics 2008, 27,
2176−2178. (b) Hahn, F. E.; Naziruddin, A. R.; Hepp, A.; Pape, T.
Organometallics 2010, 29, 5283−5288. (c) Naziruddin, A. R.; Hepp,
A.; Pape, T.; Hahn, F. E. Organometallics 2011, 30, 5859−5866.
X-ray crystallographic files for complexes [3]·0.5CH2Cl2,
[4]Cl, [5]Cl·CH2Cl2·0.5C5H12, and [5]BF4 (CIF)
́
́
(d) Viciano, M.; Mas-Marza, E.; Poyatos, M.; Sanau, M.; Crabtree, R.
AUTHOR INFORMATION
■
H.; Peris, E. Angew. Chem., Int. Ed. 2005, 44, 444−447. (e) Mas-Marza,
́
Corresponding Author
*Tel: +49-(0)251-83-33111. Fax: +49-(0)251-833-3108. E-
mail: fehahn@uni-muenster.de.
E.; Sanau, M.; Peris, E. Inorg. Chem. 2005, 26, 9961−9967. (f) Flowers,
́
S. E.; Cossairt, B. M. Organometallics 2014, 33, 4341−4344. (g) Toda,
T.; Kuwata, S.; Ikariya, T. Chem. - Eur. J. 2014, 20, 9539−9542.
(h) Marelius, D. C.; Darrow, E. H.; Moore, C. E.; Golen, J. A.;
Rheingold, A. L.; Grotjahn, D. B. Chem. - Eur. J. 2015, 21, 10988−
10992. (i) He, F.; Braunstein, P.; Wesolek, M.; Danopoulos, A. A.
Chem. Commun. 2015, 51, 2814−2817.
Notes
The authors declare no competing financial interest.
(13) Hahn, F. E.; Langenhahn, V.; Lugger, T.; Pape, T.; Le Van, D.
̈
REFERENCES
■
Angew. Chem., Int. Ed. 2005, 44, 3759−3763.
(1) (a) Kirmse, W. Angew. Chem., Int. Ed. 2004, 43, 1767−1769.
(14) (a) Kaufhold, O.; Stasch, A.; Pape, T.; Hepp, A.; Edwards, P. G.;
Newman, P. D.; Hahn, F. E. J. Am. Chem. Soc. 2009, 131, 306−317.
(b) Edwards, P. G.; Hahn, F. E. Dalton Trans. 2011, 40, 10278−10288.
(15) (a) Meier, N.; Hahn, F. E.; Pape, T.; Siering, C.; Waldvogel, S.
Eur. J. Inorg. Chem. 2007, 2007, 1210−1214. (b) Hahn, F. E.
ChemCatChem 2013, 5, 419−430.
(b) Díez-Gonzal
́
ez, S.; Nolan, S. P. Coord. Chem. Rev. 2007, 251, 874−
883. (c) Hahn, F. E.; Jahnke, M. C. Angew. Chem., Int. Ed. 2008, 47,
3122−3172. (d) Hopkinson, M. N.; Richter, C.; Schedler, M.; Glorius,
F. Nature 2014, 510, 485−496.
(2) (a) Arduengo, A. J., III; Bertrand, G., Eds. Chem. Rev. 2009, 109,
3209−3884, this is a themed issue dedicated to NHC
chemistry.10.1021/cr900241h (b) Hahn, F. E., Ed. Dalton Trans.
2009, 6893−7313, this is a themed issue dedicated to NHC
chemistry.
(16) Miranda-Soto, V.; Grotjahn, D. B.; DiPasquale, A. G.;
Rheingold, A. L. J. Am. Chem. Soc. 2008, 130, 13200−13201.
(17) (a) Miranda-Soto, V.; Grotjahn, D. B.; Cooksy, A. L.; Golen, J.
A.; Moore, C. E.; Rheingold, A. L. Angew. Chem., Int. Ed. 2011, 50,
631−635.
(3) (a) Hahn, F. E.; Radloff, C.; Pape, T.; Hepp, A. Chem. - Eur. J.
2008, 14, 10900−10904. (b) Hahn, F. E.; Radloff, C.; Pape, T.; Hepp,
A. Organometallics 2008, 27, 6408−6410. (c) Radloff, C.; Weigand, J.
J.; Hahn, F. E. Dalton Trans. 2009, 9392−9394. (d) Conrady, F. M.;
(18) Busacca, A. A.; Lorenz, J. C.; Grinberg, N.; Haddad, N.;
Hrapchak, M.; Latli, B.; Lee, H.; Sabila, P.; Saha, A.; Sarvestani, M.;
Shen, S.; Varsolona, R.; Wie, X.; Senayake, C. H. Org. Lett. 2005, 7,
4277−4280.
Frohlich, R.; Schulte to Brinke, C.; Pape, T.; Hahn, F. E. J. Am. Chem.
̈
Soc. 2011, 133, 11496−11499. (e) Schmidtendorf, M.; Pape, T.; Hahn,
F. E. Angew. Chem., Int. Ed. 2012, 51, 2195−2198. (f) Schmidtendorf,
M.; Pape, T.; Hahn, F. E. Dalton Trans. 2013, 42, 16128−16141.
(4) (a) Enders, D.; Niemeier, O.; Henseler, A. Chem. Rev. 2007, 107,
́
(19) Vazquez-Villa, H.; Reber, S.; Ariger, M. A.; Carreira, E. M.
Angew. Chem., Int. Ed. 2011, 50, 8979−8981.
(20) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Crystallogr.
2008, A64, 112−122.
́
5606−5655. (b) Marion, N.; Díez-Gonzalez, S.; Nolan, S. P. Angew.
Chem., Int. Ed. 2007, 46, 2988−3000. (c) Grossmann, A.; Enders, D.
Angew. Chem., Int. Ed. 2012, 51, 314−325.
(5) (a) Herrmann, W. A. Angew. Chem., Int. Ed. 2002, 41, 1290−
́
1309. (b) Díez-Gonzalez, S.; Marion, N.; Nolan, S. P. Chem. Rev. 2009,
109, 3612−3676. (c) Poyatos, M.; Mata, J. A.; Peris, E. Chem. Rev.
2009, 109, 3677−3707.
(6) (a) Albrecht, M. Chem. Commun. 2008, 3601−3610. (b) Schuster,
O.; Yang, L.; Raubenheimer, H. G.; Albrecht, M. Chem. Rev. 2009, 109,
3445−3478. (c) Melaimi, M.; Soleilhavoup, M.; Bertrand, G. Angew.
Chem., Int. Ed. 2010, 49, 8810−8849.
(7) (a) Jahnke, M. C.; Hahn, F. E. Chem. Lett. 2015, 44, 226−237.
(b) Jahnke, M. C.; Hahn, F. E. Coord. Chem. Rev. 2015, 293−294, 95−
115.
(8) (a) Tamm, M.; Hahn, F. E. Coord. Chem. Rev. 1999, 182, 175−
209. (b) Hahn, F. E.; Langenhahn, V.; Meier, N.; Lugger, T.;
̈
Fehlhammer, W. P. Chem. - Eur. J. 2003, 9, 704−712. (c) Flores-
Figueroa, A.; Kaufhold, O.; Feldmann, K.-O.; Hahn, F. E. Dalton
Trans. 2009, 9334−9342.
(9) (a) Kosterke, T.; Pape, T.; Hahn, F. E. J. Am. Chem. Soc. 2011,
̈
133, 2112−2115. (b) Kosterke, T.; Pape, T.; Hahn, F. E. Chem.
̈
Commun. 2011, 47, 10773−10775. (c) Kosterke, T.; Kosters, J.;
Wurthwein, E.-U.; Muck-Lichtenfeld, C.; Schulte to Brinke, C.; Lahoz,
F.; Hahn, F. E. Chem. - Eur. J. 2012, 18, 14594−14598. (d) Herve,
Jahnke, M. C.; Pape, T.; Hahn, F. E. Z. Anorg. Allg. Chem. 2013, 639,
2450−2454. (e) Brackemeyer, D.; Herve, A.; Schulte to Brinke, C.;
Jahnke, M.; Hahn, F. E. J. Am. Chem. Soc. 2014, 136, 7841−7844.
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DOI: 10.1021/acs.organomet.5b00799
Organometallics XXXX, XXX, XXX−XXX