Electronic Effect of Ligands on the Stability of Nickel-Ketene Complexes

Article abstract of DOI:10.1021/acs.organomet.8b00484

Electronically variant (dppf)Ni(ketene) complexes were synthesized and characterized to perform kinetic analysis on their decomposition through a decarbonylation/disproportion process to Ni-CO complexes and alkenes. Ligands containing electron-donating groups stabilized such complexes, whereas an electron-withdrawing group was found to destabilize them. Hammett analysis on the decomposition reaction revealed the buildup of negative charges in the rate-determining step, which corroborates past computational models.

Full text of DOI:10.1021/acs.organomet.8b00484

Article
pubs.acs.org/Organometallics
Cite This: Organometallics XXXX, XXX, XXX−XXX
Electronic Effect of Ligands on the Stability of Nickel−Ketene
Complexes
Noman Al, Ryan M. Stolley, Nicholas D. Staudaher,‡ Ryan T. Vanderlinden, and Janis Louie*
Department of Chemistry, The University of Utah, 315 S. 1400 E, Rm. 2020, Salt Lake City, Utah 84112, United States
S
* Supporting Information
ABSTRACT: Electronically variant (dppf)Ni(ketene) complexes were
synthesized and characterized to perform kinetic analysis on their
decomposition through a decarbonylation/disproportion process to Ni−
CO complexes and alkenes. Ligands containing electron-donating groups
stabilized such complexes, whereas an electron-withdrawing group was
found to destabilize them. Hammett analysis on the decomposition
reaction revealed the buildup of negative charges in the rate-determining
step, which corroborates past computational models.
(dppf) as the ligand (Scheme 2).8 Key to the stability of these
complexes versus previous complexes is the more robust
INTRODUCTION
Despite a long history of coordination complexes of
heterocumulenes, Ni−ketene complexes are often overlooked
in the field of organometallics. Literature reports of these
■
Scheme 2. Synthesis of (Dppf)Ni(Ketene) Complexes8
compounds are limited,1 primarily owing to their instability
and rapid decomposition via decarbonylation.2 Generally,
insufficient reactivity between potential transition metal
catalysts and ketenes is not the problem, as ketenes readily
form η2-complexes with various metals (Ni, Pd, Pt, Co, Rh, Ir,
etc.).3 The inability of these η2-complexes to undergo further
useful reactions lies in their propensity to decarbonylate and
form stable, unreactive 18-electron carbonyl complexes (2).4
Carbonyls, being good π-acceptor ligands, also hinder further
reactivity by forming strong Ni−CO bonds5 as products of the
ligation of a chelating ligand compared to that of the previously
decarbonylation process (Scheme 1). In addition, ketenes
used monodentate phosphines.
Kinetic analysis on the thermal decomposition of (dppf)-
Scheme 1. Decarbonylation of the Ni−Ketene Complex1
Ni(ketene) complexes (4) has shown that ketenes appended
with electron-donating moieties further stabilized the com-
plexes by resisting the formation of the catalytically inert nickel
carbonyl complex.8 DFT modeling on the mechanism of
decomposition revealed a buildup of negative charges on the β
carbon of the ketene moiety during the rate-determining step
(TS2, Figure 1). The presence of an electron-donating ketene
can destabilize the buildup of this negative charge, which lends
to the observed stability.
With the electronic effects of the ketenes on the stability of
often undergo homodimerization under thermal conditions,6
limiting the effective concentrations of ketene to generate Ni−
ketene complexes. Despite these pitfalls, several nickel-
mediated reactions utilizing ketenes directly or containing
proposed Ni−ketene complex intermediates are known.7
their respective Ni−ketene complexes previously elucidated,
we hypothesize that, in a similar manner, electron-donating
These results suggest certain Ni−ketene complexes may
actually be quite robust, yet still reactive. This potential to
generate such Ni−ketene complexes has inspired us to
investigate what factors govern both the stability as well as
the reactivity of Ni−ketene complexes.
Past efforts from our research group have led to a synthesis
chelating phosphines would also stabilize such complexes. By
increasing the electron density on the nickel center through a
highly donating ligand, the buildup of negative charge that
occurs during the rate-determining step (RDS) of the
of stable and isolable Ni−ketene complexes using various
ketenes and chelating 1,1′-bis(diphenylphosphino)ferrocene
Received: July 13, 2018
© XXXX American Chemical Society
A
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Scheme 4. Synthesis of (Dppf)Ni(Ketene) Complexes
Figure 1. DFT modeling of the decomposition of (dppf)Ni(ketene)
complexes using BP86/tzvp-svp for optimizations and BLYP/6-31G*
for single-point energies. Number in parentheses corresponds to the
trans-alkene species.8
deficient nickel center, which hinders the lability of the COD
ligand, thereby affecting the ketene coordination to the nickel.
When ketene is added to an equimolar mixture of a substituted
dppf ligand and Ni(COD)2, the formation of the Ni−ketene
complex is observed as an appearance of two doublets in the
31P NMR. X-ray crystal structures of the Ni−ketene complexes
have shown that a square planar geometry exists around the
nickel center, which, along with past Mayer bond analysis,8 is
decarbonylation may be negated, thereby leading to higher
stability. The formation of a nickel carbonyl carbene
intermediate species (5, Figure 1) in the RDS of the
decarbonylation can be strongly influenced by the electronic
parameter of the ligand. Through Hammett analysis, the
electronic effects of the ligand that pertain to the RDS can be
obtained, which can be corroborated to stability imparted to
the complexes. This would subsequently allow the insight into
electronic tuning of the phosphine ligand to increase the
stability of Ni−ketene complexes. Ketene-dependent stability
on such complexes may also be mitigated, which would further
open the possibility of using a variety of ketenes regardless of
their electronic nature, a critical property for the general use of
Ni−ketene complexes or intermediates. In this report, we
present the synthesis of (dppf)−Ni−ketene complexes in
which the electronic parameter of the phosphine substituent is
systematically varied and perform NMR-based kinetic analysis
studies to investigate effects in their rates of decomposition.
indicative of a Ni(II) species. The two doublets seen in the 31
P
NMR corresponds to the two inequivalent phosphine atoms
on the complex. This observation is critical as it is used to
gauge the completion of the reaction and to monitor any other
coordination modes of the ketene8 (Figure 2, 9b C,C) and
RESULTS AND DISCUSSION
■
As our group has previously shown, dppf remains the optimal
ligand in the synthesis of stable Ni−ketenes complexes.
Henceforth, the synthesis of the modified dppf ligands
(Scheme 3) was generally carried out via modified literature
Scheme 3. Synthesis of Substituted Dppf Ligands9
Figure 2. 31P NMR of the formation of 9b.
undesired products such as possible ketene dimer adducts
being formed. Furthermore, the ratio of the two observed
coordination modes (C,O and C,C) did not change
significantly among the ligands employed in this study.
Despite numerous attempts, Ni−ketene complexes contain-
ing highly electron-withdrawing substituents such as chloro
(7f) and trifluoromethyl (7g) could not be synthesized. By
monitoring through 31P NMR, we found that the Ni−ketene
complexes of these ligands decomposed to unidentifiable
paramagnetic products upon the formation of appreciable
amounts of the respective ketene complexes. An alternate
synthetic pathway using (glyme)NiCl2 and performing an in
situ reduction in the presence of COD and/or ketene was also
attempted (Scheme 5). However, repeated trials of this
method did not yield the desired product either.
procedures9 to generate common intermediate 6, which was
treated with the appropriate Grignard reagent to afford the
ligands in moderate to high yields (7a−g).
The corresponding Ni−ketene complexes were obtained by
reaction with Ni(COD)2 and variable molar equivalents of
phenyl n-butyl ketene (Scheme 4). A higher equivalence of
ketene was required to synthesize the electron-withdrawing
Ni−ketene complex 9e. This can be attributed to an electron-
The decomposition of the electronically substituted (dppf)-
Ni(ketene) (9a−e) complexes to the corresponding (dppf)-
Ni(CO)2 (9a−e) complexes was performed by NMR at 100
B
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Scheme 5. Attempted Synthesis of (dEWGppf)Ni(Ketene)
The data obtained from the kinetic analysis indicate that
electronic substitution at the ligand does indeed influence the
kobs of the decomposition via decarbonylation of Ni−ketene
complexes. It revealed that complexes bearing electron-
donating dppf (9a−c) demonstrated a kobs that is lower than
that containing an electronically neutral ligand (9d).
Conversely, the complex containing the electron-withdrawing
dppf (9e) has a kobs that is higher than the neutral species
(9d). This highlights the trend that electron-donating
phosphines stabilize Ni−ketene complexes, whereas electron-
withdrawing phosphines destabilize them. Performing a
Hammett analysis on the rate data reveals a positive ρ value
of 1.285, which indicates that the stability of the Ni−ketene
complex is strongly influenced by the electronic substituent on
the phosphine ligands (Figure 4). The positive slope also
corroborates computational studies that indicate negative
charge is being built up in the transition state (TS2) during
the rate-determining step.
°C (Scheme 6) in toluene-d8. Using 1,3,5-trimethoxybenzene
as an internal standard, the relative concentration of the
Scheme 6. Decomposition of Substituted (Dppf)Ni(Ketene)
Complex and Their Observed Rate Constant
Figure 4. Hammett analysis of the decomposition of the substituted
(dppf)Ni(ketene) complex.
complex was monitored upon heating through 1H NMR
(Figure 3). Over time, the resonances that corresponded to the
The crystal structures obtained for the complexes 9a−e
(Figure 5) reveal Ni−O and Ni−C bond lengths that are very
similar to each other across the series (Table 1). Additionally,
Figure 3. 1H NMR of decomposition of 9e, where four singlets in the
Cp region (3.5δ− 4.25δ) collapses to two singlets.
Ni−ketene complex decreased and gave rise to resonances that
aligned with olefinic protons. The observation of such
resonance confirmed that the Ni−ketene complex was
decomposing to form olefin byproducts. The decomposition
was performed until all of the Ni−ketene complex fully
converted to its dicarbonyl counterparts (10).
Figure 5. ORTEP diagrams of substituted (dppf)Ni(Ketene)
complexes 9b−e. Ellipsoids are set at 30% probability.
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Table 1. Selected Bond Lengths (Å), Angles, and Torsions (deg) of (Dppf)Ni(ketene) Complexes
complex
P1−Ni
P2−Ni
O1−Ni
C1−Ni
O1−C1
C1C2
O1−Ni−C1
P1−Ni−P2
O1−C1−C2−C3
9b
9c
9d
9e
2.151
2.155
2.183
2.153
2.225
2.218
2.183
2.232
1.887
1.880
1.862
1.881
1.877
1.872
1.862
1.885
1.265
1.275
1.383
1.284
1.358
1.350
1.291
1.369
39.29
39.73
43.60
39.88
106.53
107.80
108.13
106.16
−2.47
−5.26
−19.00
6.53
the solid-state structure of 9d was previously found to be
disordered, with random orientation of the ketene with respect
to the nickel center.8 In light of these, no discernible
correlation between the bond lengths of the metallacycle and
their observed rate constant of decomposition can be made.
However, the observed electronic trend can be explained using
past computational modeling of the decomposition pathway of
the Ni−ketene complex. DFT models have shown that the
rate-determining step of the decomposition is the formation of
the nickel carbonyl complex (5). This occurs through a
transition state (TS2) where a buildup of negative charge on
the β carbon occurs, as observed through the Hammett
analysis and previous computational studies. When an
electronically donating ligand is used (15a−c), the nickel
center becomes higher in electron density. This causes a
resistance for additional electron donation via the carbene
formation (Scheme 7). Conversely, the opposite occurs if an
complexes. Such complexes which were previously found to be
too unstable could potentially be accessed now through the
judicious use of electron-donating phosphine ligands. Their
characterizations would reveal valuable insight into such
complexes, which would allow further probes into their
reactivity.
EXPERIMENTAL SECTION
■
General Considerations. All reactions were carried out under an
atmosphere of N2 in a glovebox or using standard Schlenk techniques.
All glassware was oven-dried. Benzene and pentane were sparged with
nitrogen, dried over neutral alumina, and deoxygenated over Q5
under N2 using a Grubbs-type solvent purification system. Dppf, PCl3,
HCl in ether solution (2 M), nBuLi, ferrocene, diethylamine, 4-
methoxyphenyl magnesium bromide, 4-fluorophenyl magnesium
bromide, 4-methylphenyl magnesium bromide, and 1,3,5-trimethox-
ybenzene were purchased from Sigma-Aldrich and used without any
further purification. Ni(COD)2 was purchased from Strem and used
without any further purification. P(NEt2)2Cl10 and phenyl n-butyl
ketene11 were prepared according to literature procedure. 4-
(Dimethylamino)phenyl magnesium bromide,12 4-chlorophenyl
magnesium bromide,13 and 4-(trifluoromethyl)phenyl magnesium
bromide14 were prepared according to literature procedure.
Deuterated benzene (Sigma), deuterated toluene, and THF (Cam-
bridge Isotope) were distilled from CaH2 and degassed by three
freeze−pump−thaw cycles. Screw-cap NMR tubes were used for all
NMRs. The tubes were cleaned by rinsing with acetone, sonicating
with 1:1 THF/concentrated HCl for 1 h to remove residual Ni, and
Scheme 7. Ligand Effects on the Rate-Determining Step of
the Decomposition of (Dppf)Ni(ketene) Complexes
1
rinsed with water. H NMR spectra were acquired at 500 MHz. 13C
spectra were recorded at 100 or 125 MHz. 31P spectra were recorded
at 121 MHz. All 13C and 31P NMR spectra were proton decoupled.
1H and 13C spectra were referenced to residual solvent peaks (C6D6 δ
7.15 and δ 128.6). 31P NMR shifts were reported with respect to
external 85% H3PO4 (0 ppm). X-ray crystallography data were
collected and analyzed.
electron-withdrawing ligand (9e) is used, which facilitates the
formation of the intermediate 5, thereby further enabling
transformation toward the decomposed product.
Bis(dichlorophosphino)ferrocene (6). At all times during this
reaction, an inert atmosphere of Nitrogen was maintained. To an
oven-dried 500 mL RBF with a side arm equipped with a stir bar and
a septum was quickly added 2.76 g Ferrocene (14.78 mmol, 1 equiv).
The flask was then purged and backfilled 3x under N2. Pentane (150
mL) was added, followed by 4.65 mL TMEDA (31 mmol, 2.1 equiv),
and 12.42 mL nBuLi (31 mmol, 2.1 equiv). This slurry was stirred
overnight, after which, an orange color formed. The reaction was
cooled to −78 °C, and a solution of P(NEt2)2Cl (7.16 g, 34.1 mmol,
2.3 equiv) in 20 mL THF was added dropwise. After the addition was
completed, the reaction was warmed to room temperature, and left to
stir overnight. The reaction was cooled to −78 °C again, and HCl in
ether (60.6 mL, 2M, 121.20 mmol, 8.2 equiv) was added dropwise.
The reaction was warmed to room temperature and stirred overnight.
The following day, the precipitates were filtered out, and the solvent
was removed in vacuo. A brown viscous oil was left, to which was
added 15 mL of pentane. An orange-yellow solid precipitated out,
which was filtered and washed with 2x 5 mL of cold pentane to yield 6
(5.04 g, 88%). NMR of product matches literature values.15
CONCLUSION
■
Ni−ketene complexes were previously found to be thermally
unstable upon isolation, yet they would partake in a variety of
reactions, which is indicative of their utilitarian nature. Past
research from our group found that the dppf yielded stable
derivatives of Ni−ketene complexes, with further studies
showing that electron-donating ketenes aid in the stability. In
this report, we have demonstrated the electronic effects the
phosphine ligands have on the stability of Ni−ketene
complexes. NMR-based kinetic analysis on the decomposition
of dppf−Ni−ketene complexes with electronically substituted
phosphine ligands indicates that ligands bearing electron-
donating groups afford stability to the complexes. Meanwhile,
phosphine ligands containing an electron-withdrawing group
destabilize such complexes, leading to a higher rate of
decomposition. Hammett analysis of the data provided insight
that the electronic parameters of the phosphine ligand strongly
influence the stability, while confirming the buildup on
negative charges in the transition state. This information, in
conjunction with previous works, presents a more complete
profile as to how electronics factor into stabilizing Ni−ketene
General Procedure for the synthesis of substituted Dppf
(7a−g). At all times during this reaction, an inert atmosphere of
nitrogen was maintained. An oven-dried 200 mL RBF with a side arm
equipped with a stir bar and septum was purged and backfilled 3×
under N2. The Grignard reagent (15.47 mmol, 6 equiv) was added via
syringe. A solution of 6 (1 g, 2.58 mmol, 1 equiv) in 50 mL of THF
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was then added dropwise into the reaction over 10 min. The reaction
was left to stir overnight. Water (10 mL) was added, and the organic
layer dried using MgSO4, and the solvent removed. The viscous
leftover oil was redissolved in minimum diethyl ether, layered with 15
mL of pentane, and left in the freezer at −38 °C overnight. A yellow
powder precipitated out, which was filtered and washed with 3 × 5
mL of cold pentane to yield 7a (412.3 mg, 22%), 7b (679.4 mg, 39%),
7c (708.5 mg, 45%), 7e (710.8 mg, 44%), 7f (302.1 mg, 17%), and 7g
(255.7 mg, 12%). NMR of product matches literature values.9
General Procedure for Synthesis of Substituted (Dppf)Ni-
(Ketene) Complexes. In the N2-filled glovebox, Ni(COD)2 (50 mg,
0.182 mmol, 1 equiv) and ligand (7a−g) (0.182 mmol, 1 equiv) were
weighed into a 20 mL scintillation vial and dissolved in 3 mL of
benzene. The solution was stirred for 2 min, at which point ketene
was added directly.
D(NMe2)ppf−Ni−Ketene (9a). Complex 9a was synthesized
according to the general procedure, using 7a (132.2 mg) and phenyl-
n-butyl ketene (63.4 mg, 0.36 mmol, 2 equiv). The reaction was left
unstirred overnight, and then 15 mL of pentane was layered and left
overnight. The solids were filtered and washed 3× with 5 mL of
pentane and dried under vacuum: δH (500 MHz, C6D6) 8.47 (2 H, d),
8.21 (4 H, d), 8.19 (4 H, d), 7.49 (2 H, t), 7.04 (1 H, t), 6.50 (4 H,
d), 6.46 (4 H, d), 4.57 (2 H, s), 4.15 (2 H, s), 4.03 (2 H, s), 3.83 (2
H, s), 2.42 (12 H, s), 2.32 (12 H, s), 1.46 (2 H, m), 1.37 (2 H, s),
0.69 (2 H, m), 0.63 (3 H, m); 31P NMR (121 MHz, benzene) δ 36.37
(d), 12.01 (d); 13C NMR (500 MHz, DMSO-d6) δ 161.62 (s), 137.50
(s), 129.12−128.15 (ddd), 127.95 (s). 125.46−125.09 (t), 93.26 (s),
67.48 (s), 55.59 (s), 46.43 (s), 44.76 (s), 34.40 (s), 25.58 (s), 20.70−
20.40 (d), 6.33 (s).
D(OMe)ppf−Ni−Ketene (9b). Complex 9b was synthesized
according to the general procedure, using 7b (153.1 mg) and phenyl-
n-butyl ketene (190.2 mg, 1.09 mmol, 6 equiv). The reaction was left
unstirred overnight, and then 15 mL of pentane was layered and left
overnight. The solids were filtered and washed 3× with 5 mL of
pentane and dried under vacuum: δH (500 MHz, C6D6) 8.38 (2 H, d),
8.09 (8 H, m), 7.49 (2 H, t), 7.05 (1 H, t), 6.72 (8 H, t), 4.40 (2 H,
s), 3.98 (2 H, s), 3.92 (2 H, s), 3.78 (2 H, s), 3.23 (6 H, s), 3.11 (6 H,
s), 0.87 (6 H, dd, J = 9.5, 4.7 Hz), 0.65 (3 H, d, J = 2.9 Hz); δP (121
MHz, C6D6) 32.54 (d), 7.75 (d); δC (500 MHz, C6D6) 160.65 (s),
136.50 (d), 135.94 (d), 134.86 (s), 128.209 (s), 127.966 (d), 127.68
(d), 127.49(d), 126.75 (s), 126.0 (s), 125.22 (s), 114.14 (d), 113.83
(t), 74.07 (s), 70.851 (d), 54.37 (d), 34.061 (s), 29.86 (s), 23.18(s),
22.35 (s), 14.08 (s), 13.91 (s).
D(Me)ppf−Ni−Ketene (9c). Complex 9c was synthesized
according to the general procedure, using 7c (111.0 mg) and
phenyl-n-butyl ketene (190.2 mg, 1.09 mmol, 6 equiv). The reaction
was left unstirred overnight, and then 15 mL of pentane was layered
and left overnight. The solids were filtered and washed 3× with 5 mL
of pentane and dried under vacuum: δH (500 MHz, toluene-d8) 8.17
(2 H, d), 8.08 (4 H, t), 7.94 (4 H, t), 7.41 (2 H, t), 7.14 (1 H, s), 6.96
(4 H, d), 6.89 (4 H, d), 4.40 (2 H, s), 4.00 (2 H, s), 3.84 (2 H, s),
3.75 (2 H, s), 2.09 (6H, s, slight overlap with solvent peak), 1.97 (6
H, s), 1.26 (6 H, m), 0.88 (3 H, t); δP (121 MHz, toluene-d8) 39.96
(d), 14.97 (d); 13C NMR (500 MHz, C6D6) δ 167.98−167.67 (d),
140.39 (s), 139.91(s), 18.93 (s), 134.96−134.85 (d), 134.41 (s),
134.30 (s), 133.76−133.54 (d), 132.46−132.21 (d), 131.93 (s),
131.50−131.30 (d), 131.19 (s), 129.15 (s), 127.96 (s), 127.87 (s),
127.68 (s), 127.58 (s), 127.48 (s), 127.09 (s), 126.75 (s), 126.04 (s),
125.24 (s), 125.23 (s), 121.33 (s), 85.56 (s), 85.17 (s), 78.62−78.52
(d), 77.80 (s), 76.80 (s), 76.44 (s), 74.36 (s), 73.92 (s), 72.38 (s),
70.92−70.66 (d), 32.55 (s), 32.06 (s), 29.85 (s), 23.13 (s), 22.49−
22.35 (d), 20.90−20.80 (d), 14.73 (s), 14.13 (s).
D(F)ppf−Ni−Ketene (9e). Complex 9e was synthesized accord-
ing to the general procedure, using 7d (114.0 mg) and phenyl-n-butyl
ketene (317.1 mg, 1.82 mmol, 10 equiv). The reaction was left
unstirred overnight, and then 15 mL of pentane was layered and left
overnight. The solids were filtered and washed 3× with 5 mL of
pentane and dried under vacuum: δH (500 MHz, C6D6) 8.20 (2 H, d),
7.88 (4 H, q), 7.77 (4 H, q), 7.48 (2 H, d), 7.06 (1 H, t), 6.77 (4 H,
t), 6.68 (4 H, t), 4.16 (2 H, s), 3.95 (2 H, s), 3.73 (2 H, s), 3.61 (2 H,
s), 2.06 (1 H, m), 1.37 (1 H, m), 0.87 (1 H, t), 0.65 (3 H, t), 0.57 (2
H, m); δP (121 MHz, C6D6) 39.64 (d), 14.68 (d); δF (282 MHz,
C6D6) 67.47 (s), 67.25 (s); 13C NMR (500 MHz, C6D6) δ 167.36−
167.03 (d), 165.42−167.13 (d), 163.42−163.13 (d), 139.26 (s),
136.87−136.74 (d), 136.18−136.06 (d), 130.40 (s), 130.09 (s),
129.80 (s), 129.47 (s), 127.96 (s), 127.86 (s), 127.77 (s), 127.67 (s),
127.58 (s), 127.48 (s), 127.14 (s), 126.74 (s), 126.03 (s), 125.42 (s),
125.29 (s), 122.01 (s), 115.70−115.23 (d), 84.58 (s), 84.22 (s), 81.11
(s), 78.38 (s), 76.01−75.74 (d), 74.08 (s), 73.991−73.71 (d), 72.73
(s), 70.98 (s), 37.13 (s), 35.03 (s), 32.33 (s), 31.90−31.90 (t), 29.85
(s), 26.62 (s), 23.08 (s), 22.49−2.26 (d), 13.82 (s), 13.49−1.17 (d).
Kinetic Analyses of the Decomposition of Substituted
(Dppf)Ni(Ketene) Complexes. The procedure was adapted from a
previous literature source.8 In the N2-filled glovebox, the substituted
(dppf)Ni(ketene) complex (0.01 mmol) and 1,3,5-trimethoxybenzene
(0.008 mmol) standard were measured into a 4 mL scintillation vial
with stir bar in the glovebox and dissolved in toluene-d8 (0.75 mL)
with vigorous stirring. The solution was then transferred through a
pipet filter with glass wool to screw cap NMR tubes and analyzed by
1H NMR (500 MHz). The tubes were immersed in a 100 °C oil bath
for 10 min and cooled to room temperature, and the exterior was
cleaned to remove any oil residue and the mixture analyzed again by
1H NMR. The heating/NMR cycles were repeated until 25 time
points had been obtained. Two kinetic data sets were collected for
each complex (Table 2). In some trials, significant line broadening
Table 2. Kinetic Analysis Data for the Decomposition of
Substituted Ni−Ketene Complexes
complex
kobs (×10−5
)
R2
average kobs
9a
4.15
4.14
5.90
5.918
7.89
7.75
8.00
7.98
9.39
9.40
0.9965
0.9933
0.9959
0.9945
0.9923
0.99100
0.9900
0.9970
0.9911
0.9985
4.15
9b
9c
9d
9e
5.91
7.82
8.00
9.35
was observed after a few time points. We believe this is due to oxygen
contamination through seepage into the NMR tube. Such trials were
omitted and repeated with a fresh sample.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.8b00484.
■
S
NMR spectra and crystallographic data (PDF)
Crystal structure (XYZ)
D(H)ppf−Ni−Ketene (9d). Complex 9d was synthesized
according to the general literature procedure,3 using dppf (100.8
mg) and phenyl-n-butyl ketene (95 mg, 0.55 mmol, 3 equiv). The
reaction was left unstirred overnight, and then 15 mL of pentane was
layered and left overnight. The solids were filtered and washed 3×
with 5 mL of pentane and dried under vacuum. NMR matches those
of literature report.8
Accession Codes
CCDC 1843712−1843714 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
E
DOI: 10.1021/acs.organomet.8b00484
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Organometallics
Article
Approach to Aromatic Boronic Esters. Angew. Chem., Int. Ed. 2011,
50, 2769−2772. (d) Huffman, M. A.; Liebeskind, L. S. Nickel(0)-
catalyzed synthesis of substituted phenols from cyclobutenones and
alkynes. J. Am. Chem. Soc. 1991, 113, 2771−2772. (e) Kumar, P.;
Troast, D. M.; Cella, R.; Louie, J. Ni-Catalyzed ketene cycloadditions:
A System that Resists the Formation of Decarbonylation Side
Products. J. Am. Chem. Soc. 2011, 133, 7719−7721. (f) Rofer-
DePoorter, C. K. A comprehensive mechanism for the fischer-
Tropsch Synthesis. Chem. Rev. 1981, 81, 447−474.
(8) Staudaher, N. D.; Arif, A. M.; Louie, J. Synergy between
Experimental and Computational Chemistry Reveals the mechanism
of Decomposition of Nickel-Ketene Complexes. J. Am. Chem. Soc.
2016, 138, 14083−14091.
(9) (a) Qin, L.; Hirao, H.; Zhou, J. Regioselective Heck reaction of
aliphatic olefins and aryl halides. Chem. Commun. 2013, 49, 10236−
10238. (b) Ogasawara, M.; Takizawa, K.; Hayashi, T. Effects of
Bidentate Phosphine Ligands on syn-anti Isomerizations in π
Allylpalladium complexes. Organometallics 2002, 21 (22), 4853−
4861.
(10) Coyle, E. E.; Doonan, B. J.; Holohan, A. J.; Walsh, K. A.;
Lavigne, F.; Krenske, E. H.; O’Brien, C. Catalytic Wittig Reactions of
Semi- and Nonstabilized Ylides Enabled by Ylide Tuning. Angew.
Chem., Int. Ed. 2014, 53, 12907−12911.
(11) Staudaher, N. D.; Lovelace, J.; Johnson, M. P.; Louie, J.
Preparation of aryl alkyl ketenes. Organic Syntheses; John Wiley &
Sons, Inc.: Hoboken, NJ, 2018; Vol. 94, pp 1−15.
(12) Zhu, C.; Oliveira, J. C. A.; Shen, Z.; Huang, H.; Ackermann, L.
Manganese (II/III/I)-Catalyzed C-H Arylations in continuous Flow.
ACS Catal. 2018, 8, 4402−4407.
(13) Liu, X.; Liang, Y.; Ji, J.; Luo, J.; Zhao, X. Chiral Selenide
-catalyzed Enantioselective Allylic reaction and intermolecular
Difunctionalization of Alkenes: Efficient Construction of C-SCF3
Stereogenic Molecules. J. Am. Chem. Soc. 2018, 140, 4782−4786.
(14) Guha, S.; Kazi, I.; Mukherjee, P.; Sekar, G. Halogen-bonded
iodonium ion catalysis: a route to α-hydroxy ketone via domino
oxidations of secondary alcohols and aliphatic C-H bonds with high
selectivity and control. Chem. Commun. 2017, 53, 10942−10945.
(15) Nagahora, N.; Sasamori, T.; Watanabe, Y.; Furukawa, Y.;
Tokitoh, N. Kinetically Stabilized 1,1′-Bis[(E)-diphosphenyl]-
ferrocenes; Syntheses, Structures, Properties, and Reactivity. Bull.
Chem. Soc. Jpn. 2007, 80 (10), 1884−1900.
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
Corresponding Author
*E-mail: louie@chem.utah.edu.
■
ORCID
Nicholas D. Staudaher: 0000-0002-5720-0949
Janis Louie: 0000-0003-3569-1967
Present Address
‡Department of Chemistry, The University of Wisconsin, 1101
University Avenue, Madison, WI 53706.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We gratefully acknowledge the National Science Foundation
(CHE1213774) and the National Institutes of Health
(GM076125) for financial support. The authors would like
to gratefully acknowledge Andrew Clevenger from the
University of Utah for his invaluable insights on Ni−ketene
complexes and for discussion and interpretation of kinetics
data.
REFERENCES
■
(1) (a) Hoberg, H.; Korff, J. Durch nickel (0) ausgeloste
dimerisierung von diphenketen. J. Organomet. Chem. 1978, 152,
C39−C41. (b) Hofmann, P.; Perez-Moya, L. A.; Steigelmann, O.;
Riede, J. Eta.2-(C,O) Ketene coordination at nickel(O). Synthesis,
bonding, and molecular structure of (dtbpm)Ni[.eta.2-(C,O)-
Ph2C2O] [dtbpm = bis(di-tert-butylphosphino)methane]. Organo-
metallics 1992, 11 (3), 1167−1176. (c) Curley, J.; Kitiachvili, K. D.;
Waterman, R.; Hillhouse, G. L. Sequential Insertion Reactions of
Carbon Monoxide and Ethylene into the Ni-C Bond of a Cationic
Nickel (II)Alkyl Complex. Organometallics 2009, 28, 2568−2571.
(2) Miyashita, A.; Sugai, R.; Yamamoto, J. Synthesis and reactivities
of novel eta2-(C,O) alkylphenylketene complexes of nickel.
Coordination-mode switching reaction of the ketene ligand. J.
Organomet. Chem. 1992, 428, 239−247.
(3) (a) Grotjahn, D. B.; Collins, L. S. B.; Wolpert, M.; Bikzhanova,
G. A.; Lo, H. C.; Combs, D.; Hubbard, J. L. First Direct Structural
Comparision of Complexes of the Same Metal Fragment to Ketenes
in both C,C- and C,O-Bonding Modes. J. Am. Chem. Soc. 2001, 123,
8260−8270. (b) Grotjahn, D. B.; Bikzhanova, G. A.; Concolino, T.;
Lam, K.; Rheingold, A. L. J.; Collins, L. S. B. Controlled, Reversible,
Conversion of a Ketene Ligand to Carbene and CO Ligands on a
Single Metal Center. J. Am. Chem. Soc. 2000, 122, 5222−5223.
(c) Urtel, H.; Bikzhanova, G. A.; Grotjahn, D. B.; Hofmann, P.
Reversible Carbon-Carbon Double Bond Cleavage of a Ketene Ligand
at a Single Iridium (I) Center: A theoretical Study. Organometallics
2001, 20, 3938−3949.
(4) Ellgen, P. C. Kinetics and mechanism of the reactions od the
di.mu.-carbonyl-bis(cyclopentadienyl)dinickel(0) with monodentate
ligands. Inorg. Chem. 1971, 10, 232−239.
(5) Sunderlin, L. S.; Wang, D.; Squires, R. R. Metal (iron andnickel)
carbonyl bond strengths in Fe(CO)n- and Ni(CO)n-. J. Am. Chem.
Soc. 1992, 114, 2788−2796.
(6) Hurd, C. D.; Roe, A. S. Ketene and its Dimer. J. Am. Chem. Soc.
1939, 61, 3355−3359.
(7) (a) Zhang, Z.; Zhang, Y.; Wang, J. Carbonylation of Metal
Carbene with Carbond Monoxide: Generation of Ketene. ACS Catal.
2011, 1, 1621−1630. (b) Ruchardt, C.; Schrauzer, G. N. Uber die
Carbonylierung von Carbenen und die katalytische Zersetzung von
Diazoalkanen mit Nickelcarbonyl. Chem. Ber. 1960, 93, 1840−1848.
(c) Auvinet, A. L.; Harrity, J. P. A Nickel-Catalyzed Benzannulation
F
DOI: 10.1021/acs.organomet.8b00484
Organometallics XXXX, XXX, XXX−XXX