Selective Dehydrogenative Coupling of Ethylene to Butadiene via an Iridacyclopentane Complex

Article abstract of DOI:10.1021/jacs.7b11689

An iridium complex is found to catalyze the selective dehydrogenative coupling of ethylene to 1,3-butadiene. The key intermediate, and a major resting state, is an iridacyclopentane that undergoes a surprisingly facile β-H elimination, enabled by a partial dechelation (κ³-κ²) of the supporting 3,5-dimethylphenyl-2,6-bis(oxazolinyl) ligand.

Full text of DOI:10.1021/jacs.7b11689

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Article
Selective Dehydrogenative Coupling of Ethylene
to Butadiene via an Iridacyclopentane Complex
Yang Gao, Thomas J Emge, Karsten Krogh-Jespersen, and Alan S. Goldman
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.7b11689 • Publication Date (Web): 16 Jan 2018
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Journal of the American Chemical Society
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Selective Dehydrogenative Coupling of Ethylene to Butadiene
via an Iridacyclopentane Complex
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0
Yang Gao, Thomas J. Emge, Karsten Krogh-Jespersen* and Alan S. Goldman*
Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, New Brunswick, New
Jersey 08903, United States
Supporting Information Placeholder
ABSTRACT: An iridium complex is found to catalyze the selective dehydrogenative coupling of ethylene to 1,3-butadiene. The
key intermediate, and a major resting state, is an iridacyclopentane that undergoes a surprisingly facile β-H elimination, enabled
3
2
by a partial dechelation (κ -κ ) of the supporting Phebox ligand.
■
INTRODUCTION
of C
products (entry 1, Table 1) as determined by gas chro-
4
matography.
1,3-Butadiene is a "platform chemical", with ca. 10 M tons per
(Phebox)Ir(C
2 4 2
H )
annum produced for the manufacture of rubbers, polymers
and chemicals. Until recently demand for butadiene was
1
3
2 6
+ C H
(1)
1
00 °C, toluene-d
8
largely met through its production as a side-product from
the cracking of naphtha, driven primarily by demand for
ethylene. The recent abundance of ethane-rich shale gas,
When an identical solution was heated for a longer time
(16 h) the yield of butadiene was higher but the amount of
butene as a percentage of C4 products was significantly
greater at 21% (entry 2, Table 1). The latter observation indi-
cates that the butadiene observed at the shorter reaction
time was not a secondary product formed by the dehydro-
genation of butene; it is instead consistent with the converse
possibility that the butenes observed are formed as second-
ary products from butadiene hydrogenation.
2
however, has shifted the production of ethylene toward the
cracking of ethane; this has led to tightening supplies of bu-
tadiene while demand continues to increase with growth of
the global economy. As a result there is renewed interest in
the development of methods for the on-purpose production
3
of butadiene from inexpensive feedstock. On the supply side
of this calculus, the same abundance of ethane that has led
to decreased butadiene production from naphtha makes eth-
ylene an attractive potential feedstock for butadiene.
Table 1. Dehydrogenative Ethylene Coupling Catalyzed
a
by 1
Herein we report the discovery of a catalyst for the selec-
tive formation of butadiene from ethylene, a reaction with
little if any precedent. We show that this dehydrogenative
coupling proceeds via an iridacyclopentane intermediate that
undergoes β-H elimination, a reaction step which also has
limited precedent.
temp
butadiene/mM butenes
6
C /
mM
entry
time
P
2
C H
4
/ °C
(% total olefins)
/mM
1
2
3
4
5
6
7
8
9
100
100
100
100
4 h
16 h
12 h
12 h
6 h
2 atm
2 atm
8 atm
12 atm
8 atm
8 atm
12 atm
12 atm
12 atm
8.0 (92%)
15 (70%)
23 (88%)
20 (90%)
6.1 (47%)
65 (62%)
70 (71%)
67 (62%)
101 (76%)
<1.0
4.1
2.1
2.2
6.2
28
0
2.2
1.3
0
b
100
■ RESULTS AND DISCUSSION
0.7
12
110
110
110
18 h
18 h
21 h
21 h
As part of our studies of pincer-ligated iridium catalysts for
the dehydrogenation of alkanes we recently reported the
20
8.2
12
30
synthesis of
a
new Phebox complex (Phebox
=
3,5-
c
4
110
21
11
dimethylphenyl-2,6-bis-(oxazolinyl)) (Phebox)Ir(C H ) (1).
2
4 2
a
8
1 (5 mM) in toluene-d . To promote gas-liquid mixing the NMR tube
was shaken periodically (entries 1-5, sealed NMR tube in an oven
equipped with an internal rotator; entries 6-9, high-pressure J-Young
tube manually shaken every 1 h). 73 mM added butadiene. Volatiles
removed every 5.5 h followed by recharging with toluene-d
ethylene.
In the course of testing this complex for activity for catalytic
alkane dehydrogenation (which was not detected), using
ethylene as a potential hydrogen acceptor, the formation of
butadiene was observed. For example, upon heating a tolu-
b
c
8
and
ene-d solution of 1 (5.0 mM) under ethylene (2 atm) at 100
8
°C for 4 h, 1,3-butadiene (8.0 mM) and ethane (3.0 mM) were
observed in solution by H NMR spectroscopy (eq 1). Surpris-
1
Under higher pressures of ethylene (8 atm and 12 atm; en-
tries 3 and 4) greater yields of butadiene were obtained, with
a relatively lower yield of butenes. When butadiene was add-
ed initially to the solution (entry 5), the net production of
butadiene was much less, while the production of butene was
ingly, only a minimal concentration of butenes (<1.0 mM)
1
was observed in the H NMR spectrum, comprising only 8%
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Journal of the American Chemical Society
Page 2 of 6
significantly greater, consistent with the proposal that the
butene is formed from butadiene. Accordingly, when the
reaction is taken to higher conversion (with slightly longer
times and a slightly higher temperature of 110 °C) significant
yields of butenes are obtained (entries 6-8). The formation of
O
O
O
O
N
N
N
N
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
O
O
6 6
C D
Ir
+
Ir
+ HOAc
Ir
O
+
Ir
O
r.t.
Et
N
N
N
N
O
O
O
O
1
(3.0 mM)
2
(7.0 mM)
3
(3.0 mM)
4
(7.0 mM)
C olefins is also observed at later times suggesting that these
6
are also secondary products.
C
6
D
6
, r. t. CO (1 atm)
By removing the volatiles periodically (every 5.5 h) and re-
placing solvent and ethylene, greater total yields of butadi-
ene and selectivity were achieved. After 21 h (4 cycles) a total
of 101 mM butadiene had been produced, comprising 76% of
the total olefins (entry 9, Table 1).
To our knowledge the direct catalytic coupling of ethylene
to butadiene under mild conditions (or perhaps under any
conditions) is effectively unprecedented. We therefore con-
sidered alternative pathways proceeding through dimeriza-
tion and subsequent butene dehydrogenation . In that con-
text we prepared a toluene-d solution of 1 and isotopically
unlabeled 1-butene (30 mM) to which 2 atm ethylene-d was
O
O
N
N
Ir CO
+
Ir
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
CO
N
N
O
O
5
3.0 mM)
6
(7.0 mM)
(
5
Figure 1. Characterization of 2 by reaction with HOAc to
yield 4 and reaction with CO to yield 6. Solid-state molecular
structure of complex 6. H atoms other than those of the iri-
dacyclopentane ring omitted for clarity.
6
8
4
added. After 2 h at 100 °C, 3.2 mM butadiene had formed all
of which was butadiene-d , while the concentration of unla-
6
When a mixture of 1 (3.0 mM) and 2 (7.0 mM) in p-xylene-
d10 solution was heated under argon (1 atm) at 90 °C, 1 was
observed as the major species after 1 h. Further heating led to
the decomposition of 1 with release of ethylene and the for-
beled 1-butene was unchanged. An analogous experiment
was conducted with ethylene- C and 3.6 mM unlabeled 1-
butene. After 3 h at 100 °C, 7.1 mM butadiene had formed of
which 7.0 mM was butadiene- C as determined by H NMR
spectroscopy. Thus the formation of butadiene does not pro-
ceed via free 1-butene.
Speciation of the Catalyst. In the course of the catalytic
runs (5 mM 1, ethylene, toluene-d , 100 °C), H NMR spec-
troscopy revealed the presence of a new species 2, along with
13
2
1
3
1
4
mation of only trace amounts (< 0.5 mM) of C hydrocarbons
4
(
eq 2).
1
O
O
O
8
N
N
N
p-xylene
Ir
+
Ir
Ir
+
1. The ratio of 2 to 1 reached a steady state within ca. 4 h. It
90 °C, 1 h
argon atm
N
N
N
was found to be independent of ethylene pressure over a
O
O
O
range from 2 atm – 8 atm, with [2]/[1] = 1.6 ± 0.1.
(
2)
1
1
(3.0 mM)
2
(7.0 mM)
1
(9.1 mM)
The H NMR spectral data for 2 indicates C symmetry, in
s
contrast with the C symmetry of 1. A set of four multiplets
2v
1
is observed in the H NMR spectrum; their assignment to a
1,4-butanediyl ligand is supported by HCOSY NMR spectros-
copy. A broad singlet indicative of an ethylene ligand, is ob-
served at δ 2.86 ppm (4H) with a corresponding signal at δ
Intermediacy of the Iridacyclopentane. The formation
of a metallacyclopentane represents a coupling of ethylene
units, obviously suggesting the possibility that the iridacy-
clopentane is an intermediate in the catalytic formation of
butadiene (eq 1). Nonetheless, a priori it remained quite
plausible that 2 is an out-of-cycle species rather than an ac-
tual intermediate in the catalytic cycle for butadiene for-
mation. To test this possibility, we synthesized a mixture of 1
1
3
13
53.19 ppm in the C NMR spectrum. Signals in the C NMR
spectrum at δ 40.6, δ 36.4, δ 29.9 and δ 2.7 ppm are attribut-
able to the butanediyl group. Based on this data, complex 2 is
proposed to be an iridacyclopentane ethylene complex. We
were unable to isolate 2 from the mixture with 1, and at-
tempts to grow X-ray-quality crystals directly from the mix-
ture were unsuccessful.
13
13
and 2 with
C H , which resulted in full C-labeling of the
2 4
1,4-butanediyl unit of 2 and the ethylene ligands of both 1
13
13
and 2. The mixture of 1- C
(3.0 mM) and 2- C (7.0 mM) in
6
p-xylene-d10 was then exposed to unlabeled ethylene (2 atm)
4
Addition of acetic acid (20 mM) to the C D solution of 1
6
6
1
3
and 2 (3:7), immediately afforded a 3:7 mixture of (Phe-
at room temperature. The ethylene- C
ligands of both com-
2
plexes were rapidly substituted by unlabeled ethylene ligand.
No loss of C labeling of the 1,4-butanediyl group was ob-
served, consistent with the higher temperatures required for
interconversion of 1 and 2. Upon heating this mixture of un-
4
box)Ir(OAc)(ethyl) (3) and (Phebox)Ir(OAc)(n-butyl) (4)
1
3
(Figure 1). When an identical solution of 1 and 2 was exposed
to 1 atm CO, the signals attributable to the ethylene ligands
of both compounds quickly disappeared from the H NMR
1
1
3
spectrum. The products were identified, on the basis of their
labeled 1 and
under an atmosphere of unlabeled C H , fully labeled ( C )
2 4 4
C -butanediyl labeled 2 at 100 °C for 30 min
4
1
13
13
H and C NMR spectra, as (Phebox)Ir(CO) (5) and 6, the
1
product of substitution of the ethylene ligand of 2 by CO. We
were able to obtain X-ray-quality crystals of 6 from this mix-
ture, which confirmed our assignment of 6 (Figure 1), and by
inference, our assignment of 2.
butadiene (1.7 mM) was observed in the H NMR spectrum,
along with some unlabeled butadiene (0.6 mM). The for-
13
mation of the
unlabeled C
C
-labeled butadiene under an atmosphere of
, particularly as the major product, rules out
the possibility that this butadiene formed via conversion of 2
to 1, as the latter undergoes rapid exchange with free eth-
ylene.
4
H
2
4
The formation of metallacyclopentanes from reactions of
transition metal complexes with ethylene and other
7
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Journal of the American Chemical Society
7
f,8
olefins is well precedented. Metallacyclopentanes are be-
lieved to be critical intermediates in the selective trimeriza-
tion and tetramerization of ethylene to give 1-hexene and 1-
to catalytic transformations we are aware only of Bercaw’s
report of a titanocene complex affording extremely slow
rates, 1-2 turnovers/year at 25 °C.
1
2
3
4
5
6
7
8
9
5
9
octene respectively. They have been reported to decompose
to give 1-butene, or even to catalyze the dimerization of
ethylene to give 1-butene.
very limited examples of reactions of metallacyclopentanes
to give butadiene. Gas-phase cationic metallacyclopentanes
have been reported to give the corresponding metal butadi-
ene complexes. Whitesides reported decomposition of plat-
inacyclopentanes to give primarily butenes but also traces of
DFT Calculations and the Mechanism of Formation of
Butadiene. To determine the mechanism of eq 1, and in
particular the formation of butadiene derived from the 1,4-
butanediyl unit of 2, we have conducted a computational
investigation (DFT) employing the M06-L functional, the
SDD effective core potential on Ir, and valence basis sets of
triple-zeta plus polarization quality (M06-L/SDD(+f+spdf)/6-
311G(d,p)); bulk solvation effects were included via a contin-
uum dielectric model (CPCM/p-xylene; see SI for full compu-
tational details). Complex 1 was calculated to undergo con-
version to iridacyclopentane 2 via a concerted mechanism
1
0
7c,11
We are aware, however, of only
12
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
10b,10c
4
butadiene.
Itoh observed formation of Ru(II) η -
butadiene complexes, and proposed it to proceed via the
decomposition of in-situ generated ruthena(IV)cyclopentane
1
3
‡
‡
intermediates. Berke and Chirik have reported reactions
with ethylene to give Re and Mo butadiene complexes re-
spectively; both reactions were proposed to proceed via a
metallacyclopentane intermediate. Most closely related to
the present chemistry, Carmona has reported the apparent
interconversion of a butene-1-yl iridium hydride with an iri-
dacyclopentane, and formation of small amounts (<10%) of
with activation parameters ꢀH = 26.7 kcal/mol and ꢀS = -
‡
1.7 eu (ꢀG = 27.2 kcal/mol at T = 298 K) to afford the 16-
electron iridacyclopentane 7, followed by rapid coordination
1
4
of ethylene to give 2 (Figure 2). At 100 °C these activation
-
4
-1
parameters correspond to a rate of 7.6 x 10 s or a half life of
ca. 900 s, in good agreement with the observation, noted
above, that the reaction of 1 at 100 °C took several hours to
4
15
an η -butadiene complex after 2 days at 150 °C. With respect
reach
a
steady
state
ratio
of
1
to
2.
N
+
N
O
H
N
N
C
Ir
H
C
Ir
H
C
Ir
≡
Ir
+
H
H
TS1
7.2
H
N
N
H
N
2
N
H
TS2
N
O
H
24.4
C
Ir
H
H
2
0.8
N
H
H
N
O
H
N
H
H
H
N
C
Ir + 3
H
N
H
8
17.2
C
Ir
+
H
1
5.3
Ir
≡
C
Ir
N
H
H
N
+
H
9.4
N
O
H
N
N
N
7.8
7.8
N
Ir
9
H
H
H
H
C
Ir
C
Ir
C
H
N
+
+
N
10
H
N
H
H
0.0
N
7
7
C
Ir
+
N
-1.9
1
N
M06-L/SDD(+f+spdf)/6-311G(d,p)
CPCM(p-xylene)
+
C
Ir
2
N
T = 298.15 K P = 1.0 atm
Figure 2. Free energy profile for ethylene coupling and β-H elimination of the resulting iridacyclopentane
1
0a,10b
As first noted by Whitesides,
a key, characteristic,
Figures 2 and 3) would be sterically prohibitive but for an
accompanying rotation around an oxazoline-aryl bond and
property of metallacyclopentanes is their resistance toward
undergoing β-hydride elimination. Nevertheless, systems in
which butene is apparently formed via metallacyclopentanes
have been reported, consistent with the occurrence of β-H-
3
2
thus loss of an N-Ir bond, i.e. κ -κ partial dechelation of the
Phebox ligand. The free energy of 8 is 17.2 kcal/mol above 1,
or 9.4 kcal/mol above the non-agostic iridacyclopentane 7
(note that this energy includes the loss of an Ir-N bond).
It is perhaps noteworthy that upon dechelation to give 8
the resulting "open" coordination site is not in fact very
"open". The pendant oxazolinyl group necessarily remains
close to the metal center, probably too close to allow coordi-
nation of another ligand (even one as small as ethylene), but
not so close as to prevent puckering of the iridacyclopentane
ring or slippage of the resulting butenyl vinyl group into the
vacant coordination site.
1
0a,10b,16
elimination, followed by C-H elimination.
In the case of iridacyclopentane 2, DFT calculations re-
vealed an unanticipated pathway for β-H-elimination. Loss of
ethylene from 2 returns the 16-electron intermediate 7, which
shows signs of steric crowding including a short distance of
.97 Å between the H atoms at C2 of the iridacyclopentane
ring and an oxazoline methyl group. This is followed by the
1
formation of an agostic interaction with a C(2)-H bond (d
2.11 Å) , requiring the formation of a strongly puckered
Ir-H
1
7
=
iridacyclopentane ring. Formation of this agostic complex (8,
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Journal of the American Chemical Society
Page 4 of 6
‡
ꢀ
G
for β-H elimination from agostic complex 8 is 7.2
Figure 3. DFT structures of complex 7, agostic iridacyclopen-
tane complex 8, TS for β-H-elimination TS2, and initial
product of β-H-elimination 9, highlighting the distortion
required to allow the agostic interaction and the geometrical
similarity of 8, TS2, and 9. (H atom undergoing migration to
Ir shown in green, other 1,4-butanediyl H atoms shown in
yellow.)
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
kcal/mol (TS2), corresponding to an overall barrier of 26.3
kcal/mol from 2. The β-H elimination from 8, which requires
surprising little geometric rearrangement (Figure 3), leads to
a 3-buten-1-yl hydride complex, 9, with the Phebox ligand
2
still bound in a κ configuration. Intermediate 9 may be de-
scribed as approximately square pyramidal with C1 of the 3-
buten-1-yl group in the apical position and the C3-C4 double
bond positioned trans to the bound Phebox N atom (Figure
Decoordination of the C-C double bond of 10, or decoor-
3
). Migration of the hydride to the vacant coordination site
dination of the C-C double bond and re-coordination of the
3
trans to C1, accompanied by migration of the C-C double
bond to the position formerly occupied by the hydride, along
with coordination of the dangling oxazolinyl N atom, would
oxazoline N atom directly from 9, gives κ -Phebox complex 11
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(
Figure 4). Complex 11 could then undergo C-H elimination
to give 1-butene. However, the calculations predict that the
C-H elimination transition state TS3 is 4.6 kcal/mol higher in
free energy than TS4 for β-H elimination (Pathway B, shown
in blue, Figure 4). An even more favorable pathway, however,
is calculated to proceed via insertion of ethylene into the Ir-
H bond of 11 (following ethylene coordination via TS5 to give
12; Pathway A, shown in red). The free energies of TS4 and
TS5 are probably not significantly different within the accu-
racy limits of the calculation, and the relative probability of
3
give the 18-electron κ -Phebox complex 10 with a free energy
.6 kcal/mol above 7.
1
1
1 undergoing ethylene coordination and insertion (Pathway
A), as opposed to β-H-elimination (Pathway B), may depend
on ethylene concentration. Regardless, via either Pathway A
or B, butadiene is formed via β-H-elimination of the 3-buten-
7
8
1-yl group. By Pathway B, (Phebox)IrH (14) is produced,
2
which is expected to undergo facile insertion of ethylene into
an Ir-H bond. The two pathways thereby converge at (Phe-
box)IrH(Et) (15). Elimination of ethane from 15 and coordina-
tion of two ethylene molecules then completes the catalytic
cycle.
TS2
9
C-H elimination
yielding
-butene + [Ir]
H
Pathway B
+
O
β-H elimination to yield
[Ir]H plus butadiene
2
[
Ir]
1
N
TS3
[
Ir] =
Ir
H
H
H
28.1
N
+
[Ir]
H
H
O
[Ir]
[
Ir]
TS4
~
±
25
3
2
2.2
TS5
23.5
20.8
H
H
9
+
[Ir]
TS7
H
+
H
H
H
H
[Ir]
H
TS6
17.7
H
2
H
[Ir]
[κ -Ir]
H
17.8
TS8
14
[
Ir]
H
15.2
H
1
1
14.1
(30.4)
H
+
12.4
[
Ir]
Pathway A
H
9.4
H
1
0.0
H
10
[Ir]
H
ethylene insertion
prior to β-H
elimination to
6.1
2
H
H
H
[κ -Ir]
5.7
H
[Ir]
H
H
5.6
(8.0)
15
yield butadiene
1
2
H
+
H
[Ir]
[
Ir]
H
M06-L/SDD(+f+spdf)/6-311G(d,p)
CPCM(p-xylene) T = 298.15 K P = 1.0 atm
1
3
+
Figure 4. Free energy profile for butadiene formation following β-H elimination by iridacyclopentane 2.
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A caveat to the above discussion is that Pathway B, by pro-
ACKNOWLEDGEMENTS
1
2
3
4
5
6
7
8
9
ceeding via dihydride 14, allows the possibility that 14 will
hydrogenate the butadiene product to give 1-butene. This is
consistent with the observation discussed above that higher
pressures of ethylene lead to higher ratios of butadiene to 1-
butene.
This work was supported by NSF under the CCI Center for
Enabling New Technologies through Catalysis (CENTC)
Phase II Renewal, CHE-1205189.
REFERENCES
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in accord with our experimental results demonstrating that
the iridacyclopentane is a true intermediate. We also consid-
ered that α-elimination by iridacyclopentane 7 might lead to
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above 1. Finally, the free energy of the TS for β-H-elimination
(
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from 7 with κ -Phebox coordination maintained was located
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1
(
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■
CONCLUSION
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In summary, catalytic dehydrogenative coupling of eth-
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mation of an iridacyclopentane that undergoes a surprisingly
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3
2
facile β-H elimination. A κ -κ dechelation of the Phebox
ligand affords a vacant coordination site cis to both binding
sites of the 1,4-butanediyl unit, which allows room for severe
puckering of the iridacyclopentane and then β-H migration.
The ability of Phebox to act as a hemi-labile ligand, yet while
still blocking the vacated coordination site from exogenous
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1
884 (f) Blom, B.; Clayton, H.; Kilkenny, M.; Moss, J. R. Adv.
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ASSOCIATED CONTENT
Supporting Information
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The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/jacs.xxxxx. Crystal-
lographic data are also deposited as CCDC no. 1581264.
Experimental details, characterization data, computa-
tional details, table of energetic quantities and opti-
mized structures (as .mol2 formatted files) for all path-
ways considered, and X-ray crystallographic information
for 6.
K. Catal. Sci. Technol. 2016, 6, 8234 (e) Tobisch, S.; Ziegler, T.
Organometallics 2005, 24, 256.
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Crystallographic data for 6 (CIF)
AUTHOR INFORMATION
Corresponding Authors
Organomet. Chem. 1991, 406, 189.
(14) (a) Dudle, B.; Blacque, O.; Berke, H. Organometallics 2012, 31,
1
832 (b) Joannou, M. V.; Bezdek, M. J.; Al-Bahily, K.; Korobkov, I.;
Chirik, P. J. Organometallics 2017, 4215.
15) Padilla-Martinez, I. I.; Poveda, M. L.; Carmona, E.; Monge, M. A.;
* kroghjes@rutgers.edu
* alan.goldman@rutgers.edu
(
Ruiz-Valero, C. Organometallics 2002, 21, 93.
(16) Schaefer, B. A.; Margulieux, G. W.; Tiedemann, M. A.; Small, B.
L.; Chirik, P. J. Organometallics 2015, 34, 5615.
ORCID
Alan S. Goldman: 0000-0002-2774-710X
Karsten Krogh-Jespersen: 0000-0001-6051-1791
(
2
17) Brookhart, M.; Green, M. L. H.; Parkin, G. Proc. Natl. Acad. Sci.
007, 104, 6908.
Notes
The authors declare no competing financial interest.
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Table of Contents Graphic
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• Catalytic dehydrogenative
O
O
O
dimerization of ethylene to
N
N
butadiene
3
2
Ir
Ir
• Enabled by κ -κ -Phebox
interconversion
X-ray
N
N
O
CO
structure
O
O
O
N
N
H
+
Ir
Ir
CO
3
N
N
O
2
κ -Phebox
6
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