Extreme π-Loading as a Design Element for Accessing Imido Ligand Reactivity. A CCC-NHC Pincer Tantalum Bis(imido) Complex: Synthesis, Characterization, and Catalytic Oxidative Amination of Alkenes

Article abstract of DOI:10.1021/acs.organomet.6b00216

A rare Ta bis(imido) complex, which has unique reactivity, was prepared by manipulating the coordination sphere of a CCC-NHC pincer Ta complex. The reaction of lithium tert-butylamide with complex 1 yielded (1,3-bis(3′-butylimidazol-2′-yl-1′-idene)-2-phenylene)bis(tert-butylimido)tantalum(V) (2) as a lithium iodide bridged dimer, as determined by the X-ray structure. Complex 2 catalytically cyclized α,ω-aminoalkenes to effect an oxidative amination of alkenes (dehydrogenation by C-H activation) and produced a cyclic imine, an equivalent of reduced substrate, and varying proportions of hydroamination. Various additives and concentration impact the catalytic results. Computational and experimental observations have led to an initial mechanistic hypothesis. Based upon it, precatalyst 2 appears to be the first example of a bifunctional catalyst (MH-NHR) that is highly selective for nonpolar C=C bonds in preference to polar C=X bonds for outer-sphere hydrogenation.

Full text of DOI:10.1021/acs.organomet.6b00216

Article
pubs.acs.org/Organometallics
Extreme π‑Loading as a Design Element for Accessing Imido Ligand
Reactivity. A CCC-NHC Pincer Tantalum Bis(imido) Complex:
Synthesis, Characterization, and Catalytic Oxidative Amination of
Alkenes
Theodore R. Helgert,†,‡,⊥,# Xiaofei Zhang,†,# Hannah K. Box,†,# Jason A. Denny,† Henry U. Valle,†
Allen G. Oliver,§ Gopalakrishna Akurathi,† Charles Edwin Webster,*,† and T. Keith Hollis*,†,‡
†Department of Chemistry and Center for Computational Sciences, Mississippi State University, Mississippi State, Mississippi 39762,
United States
‡Department of Chemistry and Biochemistry, The University of Mississippi, Oxford, Mississippi 38655, United States
§Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, United States
S
* Supporting Information
ABSTRACT: A rare Ta bis(imido) complex, which has unique
reactivity, was prepared by manipulating the coordination sphere of
a CCC-NHC pincer Ta complex. The reaction of lithium tert-
butylamide with complex 1 yielded (1,3-bis(3′-butylimidazol-2′-yl-
1′-idene)-2-phenylene)bis(tert-butylimido)tantalum(V) (2) as a
lithium iodide bridged dimer, as determined by the X-ray structure.
Complex 2 catalytically cyclized α,ω-aminoalkenes to effect an
oxidative amination of alkenes (dehydrogenation by C−H
activation) and produced a cyclic imine, an equivalent of reduced
substrate, and varying proportions of hydroamination. Various additives and concentration impact the catalytic results.
Computational and experimental observations have led to an initial mechanistic hypothesis. Based upon it, precatalyst 2 appears
to be the first example of a bifunctional catalyst (MH-NHR) that is highly selective for nonpolar CC bonds in preference to
polar CX bonds for outer-sphere hydrogenation.
early transition metal imido complexes has been and continues
to be an area of interest.17 The metal−ligand multiple-bond
chemistry of Ta18 contains such notable examples as the first
alkylidene carbene,19 N2,20 and CO2 activation.21 C−H
activation with TaNR complexes of sterically congested
substituents was extensively studied,22 and these iconic reports
provide a detailed kinetic and thermodynamic analysis of Ta.23
More recently, group 5 imido and bis(imido)s have been
exploited for hydrogenation13c and hydroamination.24
INTRODUCTION
■
Metal−ligand multiple bonds are becoming ubiquitous in
modern chemistry and play critical roles as both ancillary and
reactive moieties.1 Much fundamental inorganic chemistry work
continues in the area,2 including the recent example of a single,
double, and triple M−N bond in one complex.3 A few of the
many applications that have become especially noteworthy
include olefin metathesis,4 dihydroxylation,5 epoxidation,6
aziridination,7 and aminohydroxylation8 for the synthesis of
complex and biologically active compounds and functional
materials.
The selective functionalization of unactivated C−H bonds,
such as in methane to methanol, is of critical importance for
developing sustainable energy resources.9 C−H bond activia-
tion remains one of the Holy Grails of modern organometallic
research.10 Parallel efforts in C−H activation have led to the
achievement of selective borylation of aliphatic and arene
hydrocarbons11 and alkane dehydrogenation/transfer hydro-
genation yielding alkenes.12
The availability of three in-plane vacant orbitals in d0 bent
metallocene fragments, Cp2M, can be traced back to Ballhausen
and Dahl’s analysis in 1961 and to Lauher and Hoffmann’s
construction in 1976.25 The incredible versatility of this
chemical fragment across the periodic table and with different
types of reactivity has generated much interest in drawing the
isolobal analogy between the bent Cp2M fragment and the bent
bis(imido) fragment, (RN)2M (Figure 1).26 Recently, this
analogy has been exploited in the design of group 5 bis(imido)
complexes and their reactivity by Bergman and Arnold.13c,27
These three frontier orbitals (Figure 1) are aligned in a
meridional fashion. It was hypothesized a ligand that could
Recently a number of workers in the field have reexamined
the “π-loading” hypothesis.13 This strategy, which leads to a
systematic approach to developing complexes for the activation
of C−H bonds, was proposed by Wigley,14 examined by
Cundari,15 and exploited by others.13b,16 Work in the area of
Received: March 17, 2016
© XXXX American Chemical Society
A
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NMR spectrum of 2. The 13C NMR spectrum contained a
carbene peak at δ 201.8 and an aryl (Ta−C) signal at δ 170.3.
These data were consistent with the synthesis of a CCC-NHC
pincer Ta bis(imido) complex, which was confirmed by X-ray
analysis.
An ORTEP plot of complex 2 is presented in Figure 2 along
with selected metric data. X-ray quality crystals of complex 2
Figure 1. Isolobal frontier orbitals of a bent d0 [(RN)2Ta]+ fragment
that is analogous to a bent Cp2M fragment.
interact with all three orbitals and maintain its geometric
integrity would push up the energy of the (RN)2M fragment
orbitals and make them accessible for chemical reactivity. Thus,
the π-loading aspect of the complex would be maximized as it is
fully coordinatively saturated and there are no more orbital
interactions to be gained, which is termed “extreme π-
loading”.28 A pincer-type ligand that is rigidly meridional and
contains three strong donors (such as the monoanionic CCC-
NHC pincer ligands with two NHC donors) might be ideally
suited and produce more reactive imido groups. We have been
exploiting CCC-NHC pincer ligands that are rigidly meridional
and contain an anionic central donor and two NHC donors,29
for which we recently reported the first examples for Ta.30 We
report herein the synthesis, characterization, and molecular
structure of [(BuCiCiCBu)Ta(NtBu)2·LiI]2,31 2, determined by
X-ray crystallography, and its initial reactivity with α,ω-
aminoalkenes that resulted in oxidative amination (OA),
which involved a C−H bond activation and transfer hydro-
genation reduction of an alkene.
Figure 2. ORTEP representations of 2 with the n-butyl groups and
hydrogens omitted for clarity of (a) the molecular dimer and (b) the
asymmetric unit. Thermal ellipsoids are shown at 50% probability.
Bond distances (Å): Ta1−N5 = 1.799(6); Ta1−N6 = 1.856(4); Ta1−
C7 = 2.248(8); Ta1−C13 = 2.260(7); Ta1−C16 = 2.307(8). Angles
(deg): N5−Ta1−N6 = 116.8(2); C7−Ta1−C13 = 68.7(4); C13−
Ta1−C16 = 69.4(4); C7−Ta1−C16 = 137.7(3); Ta1−N5−C21 =
176.8(6); Ta1−N6−C25 = 151.0(5).
RESULTS AND DISCUSSION
■
Synthesis. Following a slight modification of the procedure
by Wigley,32 complex 1 was treated with lithium tert-butylamide
in toluene at 100 °C for 9 h (Scheme 1). The most obvious
were grown by layering hexanes onto the reaction solution of 1
and lithium tert-butylamide. A distorted trigonal bipyramidal
geometry along with the tridentate binding of the CCC-NHC
pincer ligand was confirmed by X-ray analysis. The NHC
carbon donors occupied coordination sites trans to each other,
which yielded a CNHC−Ta−CNHC bond angle of 137.7° due to
the length of the Ta−C bonds. With lengths of 2.248(8) and
2.307(8) Å, the Ta−NHC bonds were similar ( 0.02 Å) to the
bond lengths of the previously reported Ta NHC complex-
es.30f,33 At 2.260(7) Å the Ta−Caryl bond was similar to other
aryl ligands flanked by neutral donors with values of 2.250(2),
2.248(5), and 2.270(3) Å.30f,34 The non-lithium iodide bound
imido ligand had a Ta−N bond length of 1.799(5) Å, while the
imido ligand bound to Li had a Ta−N bond length of 1.856(5)
Å. Regardless of binding to Li, both imido bond lengths were
similar to the imido bond lengths of Wigley’s Ta bis(imido)
( 0.1 Å) complexes.32 Also the Li−I bond was 2.705(11) Å,
shorter than the sum of ionic radii of Li+ and I− (0.90 + 2.20 =
2.90 Å).35
Scheme 1. Synthesis of Ta(V) Bis(imido) Dimer 2
change in the 1H NMR spectrum of the product was the loss of
the diastereotopic dimethylamido signals at δ 4.24 and 3.89 for
starting complex 1. The signal corresponding to the methylene
group adjacent to the nitrogen (−NCH2Pr) shifted from a
diastereotopic multiplet at δ 4.13 in 1 to a pseudotriplet at δ
4.18 in 2. A signal at δ 1.06 with an integration of 18H
The DFT geometry-optimized structure of 2 compares well
to that determined by X-ray crystallography. The resulting
1
corresponded to the two tert-butylimido ligands in the H
B
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molecular orbitals of the complex revealed that the HOMO of
the dimer is, in fact, a mostly N-centered (∼45%) π-type orbital
of the imido ligand as illustrated in Figure 3a. Thus, the goal of
Table 1. Scope of Catalytic Oxidative Amination Activity of
Complex 2 at 2.5 and 5 mol %
Figure 3. Illustration of select molecular orbitals of 2 with n-butyl
groups and hydrogens omitted for clarity. (a) HOMO of 2. (b)
Localized molecular orbital illustrating the interaction between Li and
N.
“extreme π-loading”, making the imido orbitals the frontier and,
therefore reactive orbitals, was achieved. HOMO−1 is the
degenerate partner of that depicted in Figure 3a. A Boys
localized molecular orbital indicates the bonding between the
Li and N as illustrated in Figure 3b.36
VT-NMR of 2 from −70 to 95 °C on a 500 MHz NMR in
THF-d8 did not give sharp signals at low or high temperature
(see Figure S36) for the pseudotriplet (δ 4.18) corresponding
to the −N−CH2Pr protons. The monomer−dimer equilibrium,
exchange of the lithium iodide between imidos, coordination of
THF, decomplexation, and dynamic tumbling issues all
combined to complicate the system. Recourse to DFT
computation indicated that the free energy of activation for
LiI exchange between the imidos was 16.7 kcal/mol with THF
coordinated (see Figure S54).
Catalysis. A Ta imido complex has been reported to
catalyze the hydroamination (HA) of alkynes.37 Intramolecular
HA substrates (Table 1) were on hand since their reactivity
under the influence of CCC-NHC pincer Ta monoamido
complex 1 had been evaluated without observing any
reactivity.30f When bis(imido) complex 2 was combined with
the diphenyl-substituted substrate 3a (Table 1, entry 1, method
A) and heated in toluene, a mixture of products was obtained
with no starting material remaining after 12 h at 120 °C. After
some work deconvoluting the data, the major products were
determined to be the cyclic imine (pyrroline), 4a (R = Ph, R′ =
Me) from oxidative amination and the “saturated” product 5a
(R = Ph), which resulted from hydrogenation of the alkene in
the substrate. Thus, a net transfer oxidation/reduction process
had occurred with reduction of ∼1 equiv of starting material
(3) for each equivalent of oxidized product 4. Careful
examination of the data revealed the presence of a small
amount (∼8%) of cyclic amine 6a from hydroamination.
Interestingly, the amount of HA product 6 (∼8%) plus the
amount of reduction product 5 (42%) matched the amount of
OA product 4 (50%). The spectral data of the products (1H
NMR, 13C NMR, and high-resolution mass spectral data; see
a
b
1
Determined by H NMR analysis. Method A: toluene-d8 at 120 °C
c
[3] = 0.023 M, [2] = 0.0011 M (5 mol %). Method B: benzene-d6 at
80 °C [3] = 0.21 M, [2] = 0.005 M (2.5 mol %). R′ = Me. 10 mol %
2 used. R′ = Bn. With 1.0 equiv of benzyl amine.
d
e
f
g
the SI) matched the literature reports for the products using the
diphenyl-substituted substrate.38 A variety of late transition
metal catalysts have been reported to catalyze the oxidative
amination of vinyl arenes.39 However, the oxidative amination
of unactivated alkenes at the more substituted position as the
major product was found in only one prior report by
Mitsudo38a and as a minor side product.40
Examination of additional substrates (3b and 3c) was carried
out under method A conditions. The major products observed
were again OA 4 and reduction 5 with minor amounts of
hydroamination 6 as listed in Table 1, entries 3 and 5. Again,
the amount of OA vs (reduction + HA) was 1:1, as observed in
entry 1. These data could imply a competitive reduction
process that transfers the hydrogen selectively to the alkene
over the more polar CN double bond, after formation of the
OA product 4 (Scheme 2, 13 to 7). This type of selectivity is
the reverse of normal selectivity.41 While these results were
interesting and seemed to have mechanistic implications, for
practicality attempted optimization using less catalyst, less-
expensive C6D6, lower temperatures, and higher substrate
concentrations (method B: Table 1, entries 2, 4, 6, 7, 8) led to a
considerably different outcome. Thus, when method B was
employed in the catalytic trials, two significant observations
were made. First, significantly more hydroamination product 6
was observed, as may be noted in entries 2 (24%), 4 (30%), 6
(49%), 7 (36%), and 8 (19%). Second, and most importantly,
the ratio of OA to (reduction + HA) is no longer 1:1.
C
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a
Scheme 2. Working Hypothesis for a Proposed Catalytic Pathway
a
[Ta] = (BuCiCiCBu)Ta.
Table 2. Catalytic Oxidative Amination Activity of Complex 2 with Additives and at Various Concentrations
a
b
c
1
The concentration of additive was 0.063 M. Determined by H NMR analysis. At low conversion greater accuracy was not obtained, and HA
d
product was not detected. Entry 12 was carried out in tol-d8.
Subjecting the substrate to reaction conditions in the presence
of LiI gave no reaction.
The substrates evaluated are collected in Table 1 for
convenient viewing of the results. Thus far, complex 2 was
found to have activity for the formation of pyrroline rings. The
OA was found to occur with substrates containing a
spirocyclohexane (Table 1, entries 3 and 4), a spirocyclopen-
tane (entry 7), a phenyl (entries 5 and 6), and a diallyl
substituent (entry 8). No signals for these substrates were
1
observed in the H NMR spectrum after catalysis. A signal
D
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Figure 4. Schematic representation of the free energy diagram (kcal mol−1, in red) for the proposed pathway from 7 to 8 to 10 to 13 from DFT
computations. The diagrammatic structures represent the computed transition states. The n-butyl groups of complex 2 and the phenyl groups of 3a
were replaced with methyl groups for the computations.
around δ 173 was observed in the 13C NMR spectra of all these
substrates (entries 1−8) after catalysis. These data were
consistent with pyrroline formation. The mass spectrum of
the substrate with the phenyl and allyl substituent at the C-2
position of the substrate (entry 8) had signals at 200.1, 202.1,
and 204.1, which is consistent with the [M + H+]+ products of
catalysis as suggested. The mass spectrum of the spirocyclo-
hexyl-substituted substrate (entry 4) had a signal at 152.1,
which corresponded to the cyclic imine product. Complex 2
catalyzed the cyclization of an amino-alkyne substrate to
produce the cyclic imine (entry 9). Furthermore, no reactivity
was observed in substrates that would form a six-membered
ring (entry 10), had an internally substituted double bond
(entry 11), or had a secondary amine (Table 1, entries 12 and
13).
Inspired by the uncommon activity of complex 2, the
catalysis was investigated more carefully and for mechanistic
insight using 3a (Table 2) under a variety of conditions related
to method B. The OA reaction is favored under a variety of
conditions. It benefits from high temperature (entries 1−3) and
short reaction times (entries 3−5). Most importantly, it was
found that the lower the concentration of the substrate, the
higher the proportion of OA (entries 5, 6, and 8). As seen in
entry 7 at 0.21 M substrate and 0.0005 M 2, no reaction was
observed. This concentration dependence provides insight into
the mechanism of the reaction (vide infra). The addition of
9,10-dihydroanthracene had little effect on the overall rate of
reaction and minimal impact on the ratio of products (entries 6
vs 9). This observation and the lack of observable anthracene
(entry 9) are consistent with the absence of radicals during the
reaction. The presence of a sacrificial alkene tert-butylethylene
(tbe) impeded the reaction (78% vs 100% in 10 h, entries 10 vs
6) with little impact on the product ratios. The steric
congestion of tbe was considered as a possible issue. Therefore,
1-hexene was evaluated as a sacrificial hydrogen acceptor. 1-
Hexene dramatically reduced the rate of reaction (11% vs
100%, entries 11 vs 6), but OA and reduced-alkene products
were observed, ∼1:1. At this low conversion HA product was
not detectable. Significantly, under slightly altered conditions
complete conversion was obtained in the presence of 1-hexene
(entry 12). With complete conversion, it was possible to
identify all three products 4a, 5a, and 6a, but no reaction of the
1-hexene was observed. Thus, presumably the high selectivity
for the alkene of the substrate is due to an interaction with the
amino group in 3a or an as yet unidentified reaction pathway.
Computational and Mechanistic Analysis. The exper-
imental data in Tables 1 and 2 combined with computations
(substrate 3a was modeled as the dimethyl analogue to simplify
the computations) led to a working hypothesis for a proposed
catalytic cycle as depicted in part in Scheme 2 and Figure 4.
The lack of reactivity of 2° amines with and without the
presence of benzylamine (Table 1, entries 12 and 13)42
implicates the formation of a Ta imido. Partitioning between
the OA (k2) vs the HA (k1) pathways can occur at intermediate
8, which contains an azatantallacyclobutane. At this point the
HA/OA ratio will be dependent upon k1[subst]/k2, i.e., the
ratio 9:10. The conversion from 8 to 10 involves a C−H
activation at the α-carbon that is similar to that of hydro-
aminoalkylation.24,43 Alternatively, if 8 is converted to 9,
partitioning can occur at 9 via path k3 or k4. If partitioning
occurred here, the ratio of products would be dependent only
on the ratio of k3/k4, explicitly with no substrate dependence.
As the data in Table 2 illustrate, the amount of HA product
diminishes as the initial concentration of substrate is reduced
(Table 2, entries 5, 6 vs 8). Further, HA product 6a was not
observed to interconvert to OA product 4a upon extended
reaction times. Reversibility of the 9 to 7 interconversion might
be expected to convert it over time. These observations are
consistent with 9 and 11 not being on the active pathway for
OA. Thus, the 8 vs 9 partitioning determines the HA/OA ratio.
Complex 10 can be the intermediate to form OA and reduced
products via several pathways. For instance, it may undergo a
ligand exchange (10 → 13) or a hydride shift (10 → 12).
E
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Intermediate 13 may lead to the reduced product through an
inter- or intramolecular diimide-like hydrogen transfer.44
The computed transition-state free energy for 8 → 10 was
23.3 kcal mol−1 (Figure 4), contributing to the plausibility of
this pathway. The pathways that remained were 8 → 10 → 12
and 8 → 10 → 13. While 13 may react with alkene to produce
the reduced product, 12 may account for the formation of OA
product. Figure 4 demonstrates a proposed pathway of 7 → 8
→ 10 → 13. The computed free energies of activation are
reasonable, and the isomerization to the pyrroline product at
the end provides a thermodynamic driving force that is
exergonic.
An alternative to β-hydride elimination would be for the N in
the imido ligand of 8 to abstract the hydrogen, producing 14
(pictured in Figure S57), a bis(amido)Ta(III) “isomer” of 10.
This pathway would be analogous to the mechanism of
hydroaminoalkylation.45 Structure 14 was computed to be 26.8
kcal mol−1 relative to 7 (at 0 kcal mol−1), which is 22.8 kcal
mol−1 higher in energy than 10. It is, therefore, higher in energy
than the computed transition state TS-8-10 (see Figure 4).
Thus, the pathway involving 10, with its Ta−H, seems the most
plausible pathway at present.
Intermediate 10 is another potential point of bifurcation in
the mechanism to produce the two different products. It can
undergo exchange with substrate 3a, yielding directly the
enamine isomer 4i (i = isomer), which isomerizes to pyrroline
4a and produces intermediate 13. It could also potentially
undergo a “five-center reductive elimination” via a transition
state illustrated in TS-10-12 below, which would produce
Ta(III) intermediate 12. Preliminary computations indicate
that the pathways involving Ta(III) are much higher in energy
(see Figure S56). Complete details of these computations will
be reported separately.
herein, intermediate 13 seems to be highly selective for
nonpolar CC bonds over polar CX bonds. An observation
that is the reverse of a typical bifunctional catalyst results.41,49
A
hypothesized outer-sphere hydrogenation transition state in
depicted in TS-13-7. If this mechanism occurs, this catalytic
system appears to be the first that has such high selectivity for
CC bonds. Future experimental and computational work will
examine this possibility in detail. It should be noted that
recently a report appeared describing selectivity for CC
bonds over CX bonds for an analogue50 of the Shvo
system.51 To our knowledge 2 is the first such system (MH-
NHR) that is selective for CC over CX bonds.
CONCLUSIONS
■
We have synthesized a CCC-NHC pincer Ta bis(imido)
lithium iodide dimer, 2, which contains Nimido−Li bonds
consitent with extreme π-loading. It reacts catalytically with
aminoalkenes to form a mixture of the corresponding cyclic
imine, the reduced substrate (aminoalkane), and cyclic amine.
Thus far, when attempting to employ a sacrificial hydrogen
acceptor, it was not consumed and did not change the product
distribution significantly. A preliminary mechanistic proposal
accounts for the HA/OA dependence on the initial substrate
concentration via pathway 8 to 10 to 13. Reactivity has been
achieved even with the sterically congested t-BuN ligands; thus,
use of less sterically demanding substituents is expected to
produce even more reactive systems. Further reactivity studies
of CCC-NHC pincer Ta bis(imido) complexes, particularly for
C−H activation, oxidative amination exclusively by employing a
more reactive hydrogen scavenger, a full kinetic and isotopic
labeling analysis, and in different oxidation states, are under
evaluation and will be reported in due course.
EXPERIMENTAL SECTION
■
General Considerations. Standard inert atmosphere techniques
were used. Complex 1 and lithium tert-butyl amide were prepared
following previously reported literature procedures.30f,52 Toluene,
CH2Cl2, and hexanes were degassed with Ar and passed through two
columns of activated alumina.53 CD2Cl2, C6D6, and d8-toluene were
purchased from Cambridge Isotopes and passed through a column of
activated basic alumina prior to use. No-D NMR experiments were
conducted using procedures similar to Hoye’s work.54 1H and 13C
NMR spectra were collected on either a Bruker Avance 300, 500, or
600 MHz NMR at ambient temperatures unless otherwise specified.
The transfer of hydrogen to produce the reduced substrate 5
is hypothesized to occur via a transition state much like that for
the Noyori bifunctional catalysis in the reduction of polar C
X bonds.46 It is illustrated in TS-13-7 below. Preliminary
computations using ethylene as a model for the substrate and a
t-BuNH for the amido ligand are consistent with an accessible
transition state for this transformation (see SI, p. S73).
1
The H NMR spectra were internally referenced from the residual
protio-solvent signal: CD2Cl2 (δ 5.32), C6D6 (δ 7.16), and d8-toluene
(δ 2.09). The 13C NMR spectra were referenced internally using the
signal from the deuterated solvent: CD2Cl2 (δ 53.84).
Procedures: Preparation of (1,3-Bis(3′-butylimidazol-1-yl-2-
idene)-2-phenylene)bis(tert-butylimido) tantalum(V) Lithium
Iodide Bridged Dimer (2). 1,3-Bis(3′-butylimidazol-1-yl-2-idene)-2-
phenylene)(tert-butylimido)(dimethylamido)iodotantalum(V) (1;
0.200 g, 0.270 mmol) was suspended in toluene (10 mL) in a vial
with a Teflon-lined cap, lithium tert-butylamide (0.047 g, 0.59 mmol),
in toluene (2 mL) was added dropwise. The mixture was heated at 100
°C for 9 h and then cooled to room temperature. The volume was
reduced to ∼7 mL. Hexanes (∼15 mL) was then added dropwise
precipitating an off-white solid. The mother liquor was decanted from
the precipitate. The precipitate was washed with hexanes (3 × 3 mL),
and the volatiles removed to yield an off-white solid (0.051 g, 30%). X-
ray quality crystals were obtained from layering hexanes onto a
reaction solution. 1H NMR (600 MHz, CD2Cl2): δ 7.52 (broad s, 2H,
CH imidazolyl), 7.30 (t, 3J = 7.6 Hz, 1H, CH arom), 7.15 (broad s, 2H,
CH imidazolyl), 7.14 (d, 3J = 7.7 Hz, 2H, CH arom), 4.36
A reaction manifold intrinsic to the catalytic cycle may
produce hydroamination product (7 → 8 → 9). In addition, the
outer-sphere hydrogenation mechanism of bifunctional catalysis
(MH-NHR),46a,47 which is related to the diimide hydro-
genation mechanism,48 is also a potential pathway for the
reduction of oxidative amination product (4 to produce the
hydroamination product 6). On the basis of the observations
3
(pseudotriplet, J = 8.0 Hz, 4H, NCH2CH2CH2CH3), 1.93 (m, 4H,
NCH2CH2CH2CH3), 1.56 (m, 4H, NCH2CH2CH2CH3), 1.16 (s, 18H,
F
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3
HNCMe3) 1.02 (t, J = 7.4 Hz, 6H, NCH2CH2CH2CH3). 13C NMR
NMR spectra, tables giving full crystallographic data of 2,
and further computational details (PDF)
Crystallographic data for 2 (CIF)
(300 MHz, CD2Cl2): δ 200.0, 149.2, 129.3, 128.4, 121.9, 116.4, 109.8,
64.2, 52.9, 36.7, 32.9, 20.5, 14.1. Anal. Calcd for 2, C28H43ILiN6Ta: C,
43.20; H, 5.57; N, 10.80. Found: C, 38.65; H, 5.30; N, 9.42. Calculated
for hydrolysis with loss of one t-BuNH2 and addition of two −OH’s,
C24H36ILiN5O2Ta: C, 38.72; H, 5.28; N, 9.42.
Optimized Cartesian coordinates (XYZ)
AUTHOR INFORMATION
Corresponding Authors
*E-mail: ewebster@chemistry.msstate.edu.
*E-mail: khollis@chemistry.msstate.edu.
Oxidative Amination: General Procedure for the NMR-Scale
Catalytic Oxidative Aminations (Tables 1 and 2). Method A:
(1,3-Bis(3′-butylimidazol-1-yl-2-idene)-2-phenylene)bis(tert-
butylimido)tantalum(V) lithium iodide bridged dimer (2, 0.0031 g,
0.0020 mmol), amine (0.041 mmol), and C7D8 (1.75 mL) were
combined in an NMR tube. The reaction was heated at 120 °C. The
■
Present Address
⊥T.R.H., Chemical Sciences and Engineering Division, Argonne
National Laboratory, 9700 S. Cass Avenue, Argonne, Illinois
60439, United States.
1
yield was determined by H NMR spectroscopy analysis. Method B:
(1,3-Bis(3′-butylimidazol-1-yl-2-idene)-2-phenylene)bis(tert-butylimi-
do) tantalum(V) lithium iodide bridged dimer (2, 0.0043 g, 0.0028
mmol), amine (0.126 mmol), and C6D6 (0.6 mL) were combined in
an NMR tube. The reaction was heated at 80 °C. The yield was
Author Contributions
#T.R.H., X.Z., and H.K.B. each contributed significant portions
1
determined by H NMR spectroscopy analysis.
to this work.
Time-Dependence of the Yields of Oxidative Amination,
Reduction, and Hydroamination Products (Table 2, Entries 3, 4,
and 5). (1,3-Bis(3′-butylimidazol-1-yl-2-idene)-2-phenylene)bis(tert-
butylimido)tantalum(V) lithium iodide bridged dimer (2, 0.0078 g,
0.0050 mmol, [2] = 0.005 M), (2,2-diphenyl-4-pentenyl)amine
(0.0500 g, 0.21 mmol, [amine] = 0.21 M), and C6D6 (1.0 mL) were
combined in an NMR tube. The reaction was heated at 100 °C and
Notes
The authors declare no competing financial interest.
Crystallographic data are also available from Cambridge
Crystallographic Data Centre (CCDC 1480842) for 2.
ACKNOWLEDGMENTS
1
■
monitored by H NMR spectroscopy.
This work is dedicated to the memory of Professor Brice
Bosnich for his formative contributions to chemistry and
rigorous standards for science and training. We gratefully
acknowledge partial support from the Mississippi State
University Office of Research and Economic Development
and the National Science Foundation (CHE-0809732,
-0955723; OIA-1539035). T.R.H. and H.K.B. also acknowledge
the DoEd GAANN-P200A120046 and GAANN-P200A120066.
Concentration-Dependence of the Yields of Oxidative Amina-
tion, Reduction, and Hydroamination Products (Table 2, Entries 3,
6, 7, and 8). To four screw-capped NMR tubes were added complex 2
(tubes 1 and 2: 0.5 mg, 0.0003 mmol, [2] = 0.0005 M; tubes 3 and 4:
5.0 mg, 0.003 mmol, [2] = 0.005 M), (2,2-diphenyl-4-pentenyl)amine
(tubes 1 and 3: 3.0 mg, 0.0126 mmol, [amine] = 0.021 M; tubes 2 and
4: 30.0 mg, 0.126 mmol, [amine] = 0.21 M), and C6D6 (0.6 mL). The
reaction was heated at 100 °C and monitored by 1H NMR
spectroscopy.
Additive-Dependence of the Yields of Oxidative Amination,
Reduction, and Hydroamination Products (Table 2, Entries 9, 10,
and 11). To a screw-capped NMR tube complex were added 2 (0.5
mg, 0.0006 mmol, [2] = 0.001 M), (2,2-diphenyl-4-pentenyl)amine
(3.0 mg, 0.0126 mmol, [amine] = 0.021 M), additive (0.0378 mmol,
[additive] = 0.063 M), and C6D6 (0.6 mL). The reaction was heated at
REFERENCES
■
(1) (a) Nugent, W. A.; Mayer, J. M. Metal-Ligand Multiple Bonds;
John Wiley & Sons: New York, 1988. (b) Odom, A. L. Dalton Trans.
2011, 40, 2689. (c) Whited, M. T. Beilstein J. Org. Chem. 2012, 8, 1554.
(d) Tomson, N. C.; Arnold, J.; Bergman, R. G. Organometallics 2010,
29, 5010. (e) Cundari, T. R. Chem. Rev. 2000, 100, 807. (f) Saouma, C.
T.; Peters, J. C. Coord. Chem. Rev. 2011, 255, 920.
(2) (a) Schwarz, A. D.; Nielson, A. J.; Kaltsoyannis, N.; Mountford,
P. Chem. Sci. 2012, 3, 819. (b) Searles, K.; Fortier, S.; Khusniyarov, M.
M.; Carroll, P. J.; Sutter, J.; Meyer, K.; Mindiola, D. J.; Caulton, K. G.
Angew. Chem., Int. Ed. 2014, 53, 14139. (c) Tran, B. L.; Krzystek, J.;
Ozarowski, A.; Chen, C.-H.; Pink, M.; Karty, J. A.; Telser, J.; Meyer,
K.; Mindiola, D. J. Eur. J. Inorg. Chem. 2013, 2013, 3916. (d) Mindiola,
D. J.; Waterman, R.; Iluc, V. M.; Cundari, T. R.; Hillhouse, G. L. Inorg.
Chem. 2014, 53, 13227. (e) Harrold, N. D.; Hillhouse, G. L. Chem. Sci.
2013, 4, 4011. (f) Smeltz, J. L.; Lilly, C. P.; Boyle, P. D.; Ison, E. A. J.
Am. Chem. Soc. 2013, 135, 9433.
1
100 °C and monitored by H NMR spectroscopy.
X-ray Crystallography. A suitable crystal was selected and
analyzed on a Bruker APEX-II CCD diffractometer. The crystal was
kept at 100.0 K during data collection. Using Olex2,55 the structure
was solved with the ShelXT56 structure solution program using direct
methods and refined with the ShelXL57 refinement package using least
squares minimization.
Computational Details. In the case of the mechanistic proposal,
for computational convenience, the n-butyl groups were trimmed to
methyl groups. In the case of the fluxional behavior in 2, the full CCC-
NHC ligand was utilized. Geometries were optimized using the
Gaussian0958 implementation of PBEPBE59 density functional
theory.60 The LANL2DZ basis set and effective core potential,61a as
modified by Couty and Hall,62 were utilized for tantalum. The
LANL2DZ(d,p) basis set61b and effective core potential61c were
utilized for iodine. The 6-31G(d′) basis sets63 were utilized for carbon,
nitrogen, and oxygen, and the 6-31G basis set64 was utilized for
hydrogen. Each geometry was optimized in the gas phase and
determined to be a minimum energy conformation or a transition state
using an analytical frequency calculation. Standard statistical mechanics
relationships for an ideal gas at 1 atm and 298 K were used to
determine thermodynamic corrections.
(3) Beaumier, E. P.; Billow, B. S.; Singh, A. K.; Biros, S. M.; Odom, A.
L. Chem. Sci. 2016, 7, 2532.
(4) (a) Marx, V. M.; Sullivan, A. H.; Melaimi, M.; Virgil, S. C.; Keitz,
B. K.; Weinberger, D. S.; Bertrand, G.; Grubbs, R. H. Angew. Chem.,
Int. Ed. 2015, 54, 1919. (b) Koh, M. J.; Khan, R. K. M.; Torker, S.; Yu,
M.; Mikus, M. S.; Hoveyda, A. H. Nature 2015, 517, 181. (c) Nelson,
D. J.; Manzini, S.; Urbina-Blanco, C. A.; Nolan, S. P. Chem. Commun.
2014, 50, 10355. (d) Schrock, R. R. Chimia 2015, 69, 388.
(5) Kolb, H. C.; VanNieuwenhze, M. S.; Sharpless, K. B. Chem. Rev.
1994, 94, 2483.
(6) (a) Zhang, W.; Loebach, J. L.; Wilson, S. R.; Jacobsen, E. N. J.
Am. Chem. Soc. 1990, 112, 2801. (b) Martin, V. S.; Woodard, S. S.;
Katsuki, T.; Yamada, Y.; Ikeda, M.; Sharpless, K. B. J. Am. Chem. Soc.
1981, 103, 6237. (c) Katsuki, T.; Sharpless, K. B. J. Am. Chem. Soc.
1980, 102, 5974.
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.6b00216.
(7) (a) Pellissier, H. Adv. Synth. Catal. 2014, 356, 1899.
(b) Degennaro, L.; Trinchera, P.; Luisi, R. Chem. Rev. 2014, 114, 7881.
G
DOI: 10.1021/acs.organomet.6b00216
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(8) Li, G.; Chang, H. T.; Sharpless, K. B. Angew. Chem., Int. Ed. Engl.
1996, 35, 451.
(9) Gonsalvi, L.; Bertini, F.; Guerriero, A.; Mellone, I.; Wong, W. Y.
Organometallics and Related Molecules for Energy Conversion: Green
Chemistry and Sustainable Technology 2015, 395.
(26) (a) Williams, D. S.; Schofield, M. H.; Anhaus, J. T.; Schrock, R.
R. J. Am. Chem. Soc. 1990, 112, 6728. (b) Williams, D. S.; Schofield, M.
H.; Schrock, R. R. Organometallics 1993, 12, 4560.
(27) La Pierre, H. S.; Arnold, J.; Bergman, R. G.; Toste, F. D. Inorg.
Chem. 2012, 51, 13334.
(10) (a) Bergman, R. G. Nature 2007, 446, 391. (b) Crabtree, R. H.
Chem. Rev. 2010, 110, 575.
(28) “Extreme π-loading” is suggested as a term for bent (bis)imido
complexes for which all potential orbital interactions between the
metal and additional ligands are spacially maximized. Thus, “extreme
π-loading” represents maximal orbital loading of the system. It is
different from conventional π-loading, wherein all of the remaining
orbitals at the metal center may not have been fully occupied.
Compare, for instance, the bidentate β-diketiminato ligands of ref 16
to the rigid, meridional, tridentate ligands herein. Extreme π-loading
may be fine-tuned with stronger or weaker donors, but there remain
no additional orbital interactions to be had.
(29) (a) Sattler, A.; Parkin, G. Organometallics 2015, 34, 1828.
(b) Sattler, A.; Parkin, G. J. Am. Chem. Soc. 2012, 134, 2355.
(30) (a) Reilly, S. W.; Webster, C. E.; Hollis, T. K.; Valle, H. U.
Dalton Trans. 2016, 45, 2823. (b) Reilly, S. W.; Akurathi, G.; Box, H.
K.; Valle, H. U.; Hollis, T. K.; Webster, C. E. J. Organomet. Chem.
2016, 802, 32. (c) Zhang, X.; Wright, A. M.; DeYonker, N. J.; Hollis,
T. K.; Hammer, N. I.; Webster, C. E.; Valente, E. J. Organometallics
2012, 31, 1664. (d) Bauer, E. B.; Andavan, G. T. S.; Hollis, T. K.;
Rubio, R. J.; Cho, J.; Kuchenbeiser, G. R.; Helgert, T. R.; Letko, C. S.;
Tham, F. S. Org. Lett. 2008, 10, 1175. (e) Rubio, R. J.; Andavan, G. T.
S.; Bauer, E. B.; Hollis, T. K.; Cho, J.; Tham, F. S.; Donnadieu, B. J.
Organomet. Chem. 2005, 690, 5353. (f) Helgert, T. R.; Hollis, T. K.;
Oliver, A. G.; Valle, H. U.; Wu, Y.; Webster, C. E. Organometallics
2014, 33, 952.
(11) (a) Radano, C. P.; Baker, G. L.; Smith, M. R., III. J. Am. Chem.
Soc. 2000, 122, 1552. (b) Cho, J. Y.; Tse, M. K.; Holmes, D.;
Maleczka, R. E., Jr.; Smith, M. R., III. Science 2002, 295, 305. (c) Chen,
H.; Schlecht, S.; Semple, T. C.; Hartwig, J. F. Science 2000, 287, 1995.
(d) Hartwig, J. F.; Cook, K. S.; Hapke, M.; Incarvito, C. D.; Fan, Y.;
Webster, C. E.; Hall, M. B. J. Am. Chem. Soc. 2005, 127, 2538.
(e) Mkhalid, I. A. I.; Barnard, J. H.; Marder, T. B.; Murphy, J. M.;
Hartwig, J. F. Chem. Rev. 2010, 110, 890. (f) Hartwig, J. F. J. Am.
Chem. Soc. 2016, 138, 2. (g) Schaefer, B. A.; Margulieux, G. W.; Small,
B. L.; Chirik, P. J. Organometallics 2015, 34, 1307. (h) Cook, A. K.;
Schimler, S. D.; Matzger, A. J.; Sanford, M. S. Science 2016, 351, 1421.
́
(i) Smith, K. T.; Berritt, S.; Gonzalez-Moreiras, M.; Ahn, S.; Smith, M.
R.; Baik, M.-H.; Mindiola, D. J. Science 2016, 351, 1424.
(12) (a) West, J. G.; Huang, D.; Sorensen, E. J. Nat. Commun. 2015,
6, 1. (b) Haibach, M. C.; Kundu, S.; Brookhart, M.; Goldman, A. S.
Acc. Chem. Res. 2012, 45, 947. (c) Gupta, M.; Hagen, C.; Flesher, R. J.;
Kaska, W. C.; Jensen, C. M. Chem. Commun. 1996, 2083. (d) Gupta,
M.; Hagen, C.; Kaska, W. C.; Cramer, R. E.; Jensen, C. M. J. Am.
Chem. Soc. 1997, 119, 840. (e) Dobereiner, G. E.; Crabtree, R. H.
Chem. Rev. 2010, 110, 681.
(13) (a) Webb, J. R.; Burgess, S. A.; Cundari, T. R.; Gunnoe, T. B.
Dalton Trans. 2013, 42, 16646. (b) Kriegel, B. M.; Bergman, R. G.;
Arnold, J. J. Am. Chem. Soc. 2016, 138, 52. (c) Gianetti, T. L.; La
Pierre, H. S.; Arnold, J. Eur. J. Inorg. Chem. 2013, 2013, 3771.
(14) Chao, Y. W.; Rodgers, P. M.; Wigley, D. E.; Alexander, S. J.;
Rheingold, A. L. J. Am. Chem. Soc. 1991, 113, 6326.
(15) Cundari, T. R. Organometallics 1994, 13, 2987.
(16) Tomson, N. C.; Arnold, J.; Bergman, R. G. Organometallics
2010, 29, 2926.
(17) (a) Cummins, C. C.; Baxter, S. M.; Wolczanski, P. T. J. Am.
Chem. Soc. 1988, 110, 8731. (b) Walsh, P. J.; Hollander, F. J.;
Bergman, R. G. J. Am. Chem. Soc. 1988, 110, 8729. (c) Wicker, B. F.;
Fan, H.; Hickey, A. K.; Crestani, M. G.; Scott, J.; Pink, M.; Mindiola,
D. J. J. Am. Chem. Soc. 2012, 134, 20081.
(31) To simplify the representation of the ligands in the text, we have
adopted the shorthand whereby the atoms bonded to the metal are
represented with capital letters, CCC; the outer superscripts represent
the groups on the nitrogens, BuCCCBu, and the NHC being imidazole-
based is represented by the inner superscript “i”, CiCiC. Thus complex
1 would be represented [(BuCiCiCBu)Ta(Nt-Bu)(NMe2)I].
(32) (a) Baldwin, T. C.; Huber, S. R.; Bruck, M. A.; Wigley, D. E.
Inorg. Chem. 1993, 32, 5682. (b) Chao, Y. W.; Wexler, P. A.; Wigley,
D. E. Inorg. Chem. 1990, 29, 4592.
(33) Spencer, L. P.; Beddie, C.; Hall, M. B.; Fryzuk, M. D. J. Am.
Chem. Soc. 2006, 128, 12531.
(34) (a) Abbenhuis, H. C. L.; Faiken, N.; Grove, D. M.; Jastrzebski, J.
T. B. H.; Kooijman, H.; Van Der Sluis, P.; Smeets, W. J. J.; Spek, A. L.;
Van Koten, G. J. Am. Chem. Soc. 1992, 114, 9773. (b) Abbenhuis, H.
C. L.; Feiken, N.; Haarman, H. F.; Grove, D. M.; Horn, E.; Kooijman,
H.; Spek, A. L.; van Koten, G. Angew. Chem., Int. Ed. Engl. 1991, 30,
996.
(35) Shannon, R. Acta Crystallogr., Sect. A: Cryst. Phys., Diffr., Theor.
Gen. Crystallogr. 1976, 32, 751.
(36) (a) Foster, J. M.; Boys, S. F. Rev. Mod. Phys. 1960, 32, 300. For
an example of MO interactions altering the geometry, see: (b) Tonks,
I. A.; Henling, L. M.; Day, M. W.; Bercaw, J. E. Inorg. Chem. 2009, 48,
5096.
(18) Wigley, D. E. Prog. Inorg. Chem. 1994, 42, 239.
(19) Schrock, R. R. J. Am. Chem. Soc. 1974, 96, 6796.
(20) (a) Hulley, E. B.; Bonanno, J. B.; Wolczanski, P. T.; Cundari, T.
R.; Lobkovsky, E. B. Inorg. Chem. 2010, 49, 8524. (b) Avenier, P.;
Taoufik, M.; Lesage, A.; Solans-Monfort, X.; Baudouin, A.; De
Mallmann, A.; Veyre, L.; Basset, J. M.; Eisenstein, O.; Emsley, L.;
Quadrelli, E. A. Science 2007, 317, 1056. (c) Hirotsu, M.; Fontaine, P.
P.; Epshteyn, A.; Zavalij, P. Y.; Sita, L. R. J. Am. Chem. Soc. 2007, 129,
9284. (d) Hirotsu, M.; Fontaine, P. P.; Zavalij, P. Y.; Sita, L. R. J. Am.
Chem. Soc. 2007, 129, 12690. (e) Yonke, B. L.; Keane, A. J.; Zavalij, P.
Y.; Sita, L. R. Organometallics 2011, 31, 345.
(21) Rankin, M. A.; Cummins, C. C. J. Am. Chem. Soc. 2010, 132,
10021.
(22) Wolczanski, P. T. Chem. Commun. 2009, 740.
(23) (a) Miller, R. L.; Toreki, R.; LaPointe, R. E.; Wolczanski, P. T.;
Van Duyne, G. D.; Roe, D. C. J. Am. Chem. Soc. 1993, 115, 5570.
(b) Hirsekorn, K. F.; Veige, A. S.; Marshak, M. P.; Koldobskaya, Y.;
Wolczanski, P. T.; Cundari, T. R.; Lobkovsky, E. B. J. Am. Chem. Soc.
2005, 127, 4809. (c) Bennett, J. L.; Wolczanski, P. T. J. Am. Chem. Soc.
1994, 116, 2179. (d) Schaller, C. P.; Wolczanski, P. T. Inorg. Chem.
1993, 32, 131.
(37) (a) Anderson, L. L.; Arnold, J.; Bergman, R. G. Org. Lett. 2004,
6, 2519. (b) Anderson, L. L.; Arnold, J.; Bergman, R. G. Org. Lett.
2006, 8, 2445.
(38) (a) Kondo, T.; Okada, T.; Mitsudo, T. A. J. Am. Chem. Soc.
2002, 124, 186. (b) Bexrud, J. A.; Li, C.; Schafer, L. L. Organometallics
2007, 26, 6366.
(39) Beller, M.; Trauthwein, H.; Eichberger, M.; Breindl, C.; Herwig,
J.; Muller, T. E.; Thiel, O. R. Chem. - Eur. J. 1999, 5, 1306.
̈
(40) (a) Julian, L. D.; Hartwig, J. F. J. Am. Chem. Soc. 2010, 132,
13813. (b) Sevov, C. S.; Zhou, J.; Hartwig, J. F. J. Am. Chem. Soc. 2014,
136, 3200. (c) Utsunomiya, M.; Kuwano, R.; Kawatsura, M.; Hartwig,
J. F. J. Am. Chem. Soc. 2003, 125, 5608. (d) Kitahara, H.; Sakurai, H.
Chem. Lett. 2010, 39, 46. (e) Beller, M.; Breindl, C.; Eichberger, M.;
Hartung, C. G.; Seayad, J.; Thiel, O. R.; Tillack, A.; Trauthwein, H.
Synlett 2002, 2002, 1579. (f) Specht, Z. G.; Grotjahn, D. B.; Moore, C.
E.; Rheingold, A. L. Organometallics 2013, 32, 6400. (g) Bernoud, E.;
(24) (a) Zhang, F.; Song, H.; Zi, G. Dalton Trans. 2011, 40, 1547.
(b) Reznichenko, A. L.; Emge, T. J.; Audorsch, S.; Klauber, E. G.;
̈
Hultzsch, K. C.; Schmidt, B. Organometallics 2011, 30, 921.
(25) (a) Ballhausen, C. J.; Dahl, J. P. Acta Chem. Scand. 1961, 15,
1333. (b) Lauher, J. W.; Hoffmann, R. J. Am. Chem. Soc. 1976, 98,
1729.
H
DOI: 10.1021/acs.organomet.6b00216
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Oulie,
Ed. 2014, 53, 4930.
́
P.; Guillot, R.; Mellah, M.; Hannedouche, J. Angew. Chem., Int.
Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.;
Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.;
Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.;
Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian09;
Revision D.01; Gaussian, Inc.: Wallingford, CT, 2009.
(59) (a) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. Rev. Lett. 1996,
77, 3865. (b) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. Rev. Lett.
1997, 78, 1396.
(60) Parr, R. G.; Yang, W. Density-Functional Theory of Atoms and
Molecules; Oxford University Press, Clarendon Press: New York and
Oxford, England, 1989.
(61) (a) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 270.
(b) Check, C. E.; Faust, T. O.; Bailey, J. M.; Wright, B. J.; Gilbert, T.
M.; Sunderlin, L. S. J. Phys. Chem. A 2001, 105, 8111. (c) Wadt, W. R.;
Hay, P. J. J. Chem. Phys. 1985, 82, 284.
(62) Couty, M.; Hall, M. B. J. Comput. Chem. 1996, 17, 1359.
(63) Hariharan, P. C.; Pople, J. A. Theor. Chim. Acta 1973, 28, 213.
The 6-31G(d′) basis sets were utilized for carbon and nitrogen (which
have the d polarization functions taken from the 6-311G(d) basis sets,
rather than the default value of 0.8 used in the 6-31G(d) basis sets).
(64) Hehre, W. J.; Ditchfield, R.; Pople, J. A. J. Chem. Phys. 1972, 56,
2257.
(41) Bullock, R. M. Angew. Chem., Int. Ed. 2007, 46, 7360.
(42) Manna, K.; Xu, S.; Sadow, A. D. Angew. Chem., Int. Ed. 2011, 50,
1865.
(43) (a) Chong, E.; Brandt, J. W.; Schafer, L. L. J. Am. Chem. Soc.
2014, 136, 10898. (b) Herzon, S. B.; Hartwig, J. F. J. Am. Chem. Soc.
2008, 130, 14940. (c) Hamzaoui, B.; Pelletier, J. D. A.; El Eter, M.;
Chen, Y.; Abou-Hamad, E.; Basset, J.-M. Adv. Synth. Catal. 2015, 357,
3148. (d) Luhning, L. H.; Brahms, C.; Nimoth, J. P.; Schmidtmann,
M.; Doye, S. Z. Anorg. Allg. Chem. 2015, 641, 2071. (e) Dorfler, J.;
Bytyqi, B.; Huller, S.; Mann, N. M.; Brahms, C.; Schmidtmann, M.;
Doye, S. Adv. Synth. Catal. 2015, 357, 2265. (f) Eisenberger, P.; Ayinla,
R. O.; Lauzon, J. M. P.; Schafer, L. L. Angew. Chem., Int. Ed. 2009, 48,
8361. (g) Eisenberger, P.; Schafer, L. Pure Appl. Chem. 2010, 82, 1503.
(h) Reznichenko, A. L.; Hultzsch, K. C. J. Am. Chem. Soc. 2012, 134,
3300. (i) Payne, P. R.; Garcia, P.; Eisenberger, P.; Yim, J. C. H.;
Schafer, L. L. Org. Lett. 2013, 15, 2182. (j) Garcia, P.; Payne, P. R.;
Chong, E.; Webster, R. L.; Barron, B. J.; Behrle, A. C.; Schmidt, J. A.
R.; Schafer, L. L. Tetrahedron 2013, 69, 5737. (k) Garcia, P.; Lau, Y. Y.;
Perry, M. R.; Schafer, L. L. Angew. Chem., Int. Ed. 2013, 52, 9144.
(44) (a) Corey, E. J.; Pasto, D. J.; Mock, W. L. J. Am. Chem. Soc.
̈
̈
̈
1961, 83, 2957. (b) Hunig, S.; Muller, H. R.; Thier, W. Angew. Chem.,
̈
̈
Int. Ed. Engl. 1965, 4, 271. (c) Smit, C.; Fraaije, M. W.; Minnaard, A. J.
J. Org. Chem. 2008, 73, 9482.
(45) Chong, E.; Garcia, P.; Schafer, L. L. Synthesis 2014, 46, 2884.
(46) (a) Hashiguchi, S.; Fujii, A.; Takehara, J.; Ikariya, T.; Noyori, R.
J. Am. Chem. Soc. 1995, 117, 7562. (b) Eisenstein, O.; Crabtree, R. H.
New J. Chem. 2013, 37, 21.
(47) (a) Nova, A.; Taylor, D. J.; Blacker, A. J.; Duckett, S. B.; Perutz,
R. N.; Eisenstein, O. Organometallics 2014, 33, 3433. (b) Hamilton, R.
J.; Bergens, S. H. J. Am. Chem. Soc. 2008, 130, 11979.
(48) (a) Corey, E. J.; Pasto, D. J.; Mock, W. L. J. Am. Chem. Soc.
1961, 83, 2957. (b) Pasto, D. J.; Chipman, D. M. J. Am. Chem. Soc.
1979, 101, 2290. (c) Pasto, D. J.; Taylor, R. T. Org. React. 1991, 91.
(49) Bullock, R. M. Chem. - Eur. J. 2004, 10, 2366.
(50) Kamitani, M.; Nishiguchi, Y.; Tada, R.; Itazaki, M.; Nakazawa,
H. Organometallics 2014, 33, 1532.
(51) (a) Shvo, Y.; Goldberg, I.; Czerkie, D.; Reshef, D.; Stein, Z.
Organometallics 1997, 16, 133. (b) Shvo, Y.; Czarkie, D.; Rahamim, Y.;
Chodosh, D. F. J. Am. Chem. Soc. 1986, 108, 7400. (c) Blum, Y.;
Czarkie, D.; Rahamim, Y.; Shvo, Y. Organometallics 1985, 4, 1459.
(d) Casey, C. P.; Strotman, N. A.; Beetner, S. E.; Johnson, J. B.; Priebe,
D. C.; Vos, T. E.; Khodavandi, B.; Guzei, I. A. Organometallics 2006,
25, 1230. (e) Comas-Vives, A.; Ujaque, G.; Lledos
2008, 27, 4854.
́
, A. Organometallics
(52) Tay, B.-Y.; Wang, C.; Stubbs, L. P.; Jacob, C.; van Meurs, M. J.
Organomet. Chem. 2011, 696, 3431.
(53) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518.
(54) Hoye, T. R.; Eklov, B. M.; Ryba, T. D.; Voloshin, M.; Yao, L. J.
Org. Lett. 2004, 6, 953.
(55) Dolomanov, O. V.; Bourhis, L. J.; Gildea, R. J.; Howard, J. A. K.;
Puschmann, H. J. Appl. Crystallogr. 2009, 42, 339.
(56) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Adv. 2015, 71,
3.
(57) Sheldrick, G. M. Acta Crystallogr., Sect. C: Struct. Chem. 2015, 71,
3.
(58) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci,
B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H.
P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.;
Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima,
T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.;
Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin,
K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.;
Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega,
N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.;
Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.;
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DOI: 10.1021/acs.organomet.6b00216
Organometallics XXXX, XXX, XXX−XXX