Selective C=O reduction in phthalimide with nickel(0) compounds

Article abstract of DOI:10.1021/om400164g

The catalytic reduction of phthalimide was achieved using nickel catalysts. The use of catalytic amounts (20% mol) of [Ni(COD)₂] or [(dippe)Ni(μ-H)]₂ (1) allowed the monoreduction of phthalimide to yield isoindolinone and benzamide, at 140-180 C and 750 psi of H₂. When the N-H moiety of phthalimide was protected with a trimethylsilyl group, both C=O groups were reduced to yield (trimethylsilyl)isoindoline. However, when a methyl moiety was used as the protecting group, the C=O groups and the aromatic ring were reduced, using rather similar reaction conditions, due to the formation of 5 A (average) nickel nanoparticles.

Full text of DOI:10.1021/om400164g

Article
pubs.acs.org/Organometallics
Selective CO Reduction in Phthalimide with Nickel(0) Compounds
́ ́
Alma Arevalo, Sebastian Ovando-Segovia, Marcos Flores-Alamo, and Juventino J. Garcıa*
́
Facultad de Quım
́
́ ́
ica, Universidad Nacional Autonoma de Mexico, Circuito Interior, Ciudad Universitaria, Mexico City 04510,
Mexico
*
S Supporting Information
ABSTRACT: The catalytic reduction of phthalimide was achieved using
nickel catalysts. The use of catalytic amounts (20% mol) of [Ni(COD) ] or
2
[
(dippe)Ni(μ-H)] (1) allowed the monoreduction of phthalimide to yield
2
isoindolinone and benzamide, at 140−180 °C and 750 psi of H . When the
2
N−H moiety of phthalimide was protected with a trimethylsilyl group, both
CO groups were reduced to yield (trimethylsilyl)isoindoline. However,
when a methyl moiety was used as the protecting group, the CO groups
and the aromatic ring were reduced, using rather similar reaction conditions,
due to the formation of 5 Å (average) nickel nanoparticles.
INTRODUCTION
yields the corresponding amines, as in the hydrogenation of imides
■
to cyclic amines (50% yield) using Al O −BaO supported on
2
3
The selective reduction of functional groups is an important
task in chemistry and represents a challenge in the industrial
and pharmaceutical arenas. For instance, the catalytic hydro-
genation of CO groups gives important compounds with
biological activity: in particular, derivatives of cyclic amides
9
CuO−ZnO under H pressure (5 MPa) at 250 °C.
2
Closely related systems dealing with lactam production have
been reported, for instance, in the hydrogenation of imides
using a catalyst containing Co, W, Re, and/or Mo in water,
10
under H pressure. However, the specific use of phthalimide
2
have good antifungal, antidepressant, and antitubercular
1
for the preparation of isoindolinone is given in just a handful of
reports; the first was a catalytic synthesis using activated nickel
activities. The use of metal hydrides or H along with metal
2
catalysts has been widely used for the regio- and chemoselective
reduction of CO groups. In this context there are many systems
that use metal hydrides or H along with metal catalysts that
at 200 °C and high pressure of H (200−250 atm), to give
2
11
isoindolinone in 80% yield. The second procedure used
2
12
2
phthalimide in glacial acetic acid with Zn dust under reflux,
have been widely reported for this purpose.
the third method involved the reaction of phthalimide under
similarly harsh conditions with HOAc, HCl, and Sn to give the
Typically, the reduction of CO groups yields the
3
corresponding alcohols, as has been described in some recent
13
product in 47% yield, and the most recent report by Dixneuf
and co-workers used a series of Ru-based catalysts which are
efficient precursors for the monoreduction of cyclic imides in
reports dealing with this type of reduction using a variety of Ru-
based catalysts. It is worth mentioning, for instance, the reduction
of imides in the presence of a base to produce hydroxyamides.
The asymmetric transfer hydrogenation of aromatic ketones
in water with the use of a ruthenium catalyst and HCOONa to
yield the corresponding alcohols has also been reported. The
4
14
water under relatively mild H pressure (60 bar) at 90 °C; of
2
note, with this method octahydroisoindolinone is obtained in 80%
yield. A recent report shows a different reactivity for imides
involved in a nickel-catalyzed cross coupling of phthalimides in the
presence of diorganozinc reagents via a decarbonylative process to
5
catalytic chemoselective hydrogenation of imides into amides and
primary alcohols has also been documented using a Ru−NH
15
6
produce ortho-substituted benzamides in high yields (>70%).
catalyst. The catalytic reduction of aromatic ketones into alcohols
For a number of years our group has been interested in the
activation and functionalization of CO bonds; for instance,
the selective hydrogenation of ketones producing either the
alcohol or the corresponding alkane (yield 70−100%) was
using [Ru(BINAP)(DPEN)Cl ] as precatalyst, at room temper-
2
ature employing ionic liquids, has also been reported, interestingly
using reaction conditions such that the catalyst remains soluble in
the ionic liquid that prevents the leaching of Ru (and Ru catalyst)
into the organic products, yielding pharmaceutical intermediates
16
achieved. Also, we have reported the functionalization of
dienones to produce monoalkylenones in good yields and with
7
free of metal residues. Also worth mentioning is the reported
17
high selectivities, using nickel-based catalysts.
highly enantioselective asymmetric hydrogenation of α-phthali-
mide ketones to form α-phthalimide alcohols under catalytic
conditions using a chiral Ru−TunePhos catalyst in ethanol. In
other cases, the exhaustive CO reduction present in imides
8
Received: February 27, 2013
©
XXXX American Chemical Society
A
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Article
Here we present the metal-mediated decarbonylation
reaction of phthalimide using nickel complexes, to yield
benzamide (2) and isoindolinone (3), the latter as a result of
the monoreduction of one CO group in phthalimide. In
addition, the resulting reactivity when the N−H group in
phthalimide was protected is described.
NMR; this experiment allowed us to identify some key nickel-
containing intermediates, which include the product resulting from
the N−H oxidative addition of phthalimide to yield complex 4 and
the side-on-coordinated carbonyl moiety 4b according to Scheme 2.
The 31P{ H} NMR spectrum for complex 4 displays two
1
doublets, the first at 82.3 ppm and the second located at
2
8
5.6 ppm, both with J = 23 Hz, characteristic for a nickel(II)
P−P
RESULTS AND DISCUSSION
18
1
■
complex. The H NMR spectrum shows a key signal located
at −20 ppm (dd), J = 93 Hz and JP−H(cis) = 15 Hz,
The complexes [Ni(COD) ] and [(dippe)Ni(μ-H)] (1) were
2
2
P−H(trans)
used as catalytic precursors for the phthalimide reduction, under a
variety of reaction conditions; Table 1 summarizes some of the
relevant results derived from the use of [Ni(COD)2].
assigned to the nickel hydride. Closely related N−H oxidative
19
addition at nickel has been reported previously by our group.
Also, in the same spectrum, signals located at 75.6 and 71.2 ppm,
2
both with J = 71 Hz, characteristic of a nickel(0) complex, can
be observed; these signals are assigned to the formation of an
intermediate containing a η -C,O carbonyl moiety coordinated to
P−P
a
18
Table 1. Phthalimide Reduction with [Ni(COD)2]
2
the “dippeNi” fragment, as depicted in Scheme 2 for compound 4b.
Attempts to crystallize complexes 4 and 4b failed several times;
however, crystals suitable for X-ray studies were obtained for the
related complex 4-Cl, containing a chloride anion instead of a
hydride. Crystals of 4-Cl were obtained by slow evaporation
of complex 4 in a toluene/CH Cl mixture. As expected, 4-Cl is
a nickel(II) complex in a square-planar geometry with an
N-coordinated phthalimide (Figure 1). A summary of crystallo-
graphic data for 4-Cl can be found in Table 2. The phthalimide
moiety displays two disordered positions in an approximate ratio
of 55:45; only the major position is depicted.
entry time (days) T (°C) H pressure (psi)
3 (amt (%))
2
1
2
3
3
8
3
140
140
180
750
600
600
isoindolinone (63)
isoindolinone (18)
isoindolinone (40)
2
2
a
Conditions: catalyst load 20 mol % of [Ni(COD) ], 30 mL of THF,
2
in a 300 mL stainless steel Parr reactor.
As can be seen in Table 1, the use of [Ni(COD) ] allowed
A mechanistic proposal for the formation of products 2 and 3 is
depicted in Schemes 3 and 4, respectively, inspired by the closely
related proposals for cross-coupling reactions of phthalimides with
2
the phthalimide monoreduction to yield isoindolinone, in
moderate to low yields, but with high selectivity to the
reduction of only one carbonyl moiety present at phthalimide
and without the formation of any other byproducts. Thereby we
15
diorganozinc. In both mechanisms, the formation of complex 4b
is a common step; in the formation of 2, a ring-opening pathway
leading to the formation of intermediate A followed by a
decarbonylation/hydrogenation step to yield 2 is proposed. On the
other hand, the formation of compound 3 involves a hydrogenation
pathway for the carbonyl moiety via intermediate E, all the way to the
envisaged the use of the reactive complex [(dippe)Ni(μ-H)] (1)
2
as an interesting alternative to evaluate a similar reactivity.
Considering the above, the use of complex 1 was assessed
under reaction conditions similar to those used in entry 1 of
Table 1. The reactivity found is illustrated in Scheme 1.
16
total reduction, probably driven by the formation of H O.
2
In order to further evaluate the reactivity of phthalimide, but
avoiding the N−H oxidative addition product 4, which technically
does not yield a decarbonylation or a carbonyl reduction pathway,
we envisaged the derivatization of such N−H bond at phthalimide
with both methyl and silyl fragments as a protecting groups.
N-methylphthalimide (5) was obtained by reacting the
phthalimide potassium salt with dimethyl sulfate (63% yield)
Scheme 1. Reactivity of Phthalimide with Complex 1
(
Scheme 5).
The reactivity displayed by complex 1 is related to that
Interestingly, on reacting 5 with catalytic amounts of 1 (1% cat.,
presented above for [Ni(COD) ] in terms of the formation of
2
8
70 psi of H , 140 °C, THF, 72 h), 2-methyloctahydro-1H-isoindole
2
isoindoline (3), albeit in lower yield, with benzamide (2) being
the main product in this case (82% yield), for a total conversion
of 93%. Using a mercury drop test for experiments in Table 1
(6) was obtained (33% isolated yield).
(
entry 1) and Scheme 1 did not yield a drop in activity.
This result prompted us to carry out a spectroscopic followup of
the reaction between complex 1 and phthalimide by multinuclear
Scheme 2. Reaction of 1 with Phthalimide
B
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Scheme 3. Mechanistic Proposal for the Formation of 2
Figure 1. ORTEP drawing (50% probability) for 4-Cl·(toluene).
Selected bond lengths (Å) and angles (deg): Ni(1)−N(1) = 1.927(3),
Ni(1)−P(1) = 2.1567(10), Ni(1)−P(2) = 2.1646(10), Ni(1)−Cl(1) =
2.1997(10), N(1)−C(15A) = 1.354(15), N(1)−C(22A) = 1.38(3);
N(1)−Ni(1)−P(1) = 92.38(9), N(1)−Ni(1)−P(2) = 173.63(9),
P(1)−Ni(1)−P(2) = 88.68(4), N(1)−Ni(1)−Cl(1) = 90.87(9),
P(1)−Ni(1)−Cl(1) = 171.88(4), P(2)−Ni(1)−Cl(1) = 88.91(4).
Scheme 4. Mechanistic Proposal for the Formation of 3
Table 2. Summary of Crystallographic Data for
4
-Cl·(toluene)
empirical formula
C H Cl N Ni O P
44 72 2 2 2 4 4
formula wt
1005.24
temp
130(2) K
0.71073 Å
monoclinic
C2/c
wavelength
cryst syst
space group
unit cell dimens
a
31.6164(10) Å
13.6477(5) Å
16.4738(6) Å
92.856(3)°
b
c
β
3
V
7099.5(4) Å
Z
4
3
calcd density
abs coeff
0.940 Mg/m
0.724 mm−
1
Scheme 5. Synthesis of Compound 5
F(000)
2128
crystal size
0.4537 × 0.3183 × 0.0677 mm3
θ range for data collection
index ranges
no. of rflns collected
no. of indep rflns
completeness to θ = 26.05°
refinement method
3.46−26.05°
−39 ≤ h ≤ 31, −14 ≤ k ≤ 16, −18 ≤ l ≤ 20
17035
7005 (R(int) = 0.0395)
99.8%
2
full-matrix least squares on F
1
.6 ppm for the cyclohexane moiety along with a multiplet at
no. of data/restraints/params 7005/122/259
goodness of fit on F2
1.9−2.03 ppm for the N-heterocyclic ring.
1.032
A closely related N-silyl derivative was obtained by reacting
the phthalimide potassium salt with chlorotrimethylsilane to
yield N-(trimethylsilyl)phthalimide (7) (Scheme 6).
The reaction of compound 7 with complex 1 under catalytic
final R indices (I > 2σ(I))
R indices (all data)
R1 = 0.0535, wR2 = 0.1605
R1 = 0.0749, wR2 = 0.1755
1.419, −0.501 e Å−3
largest diff peak, hole
conditions (1%, 870 psi of H , 140 °C, THF, 72 h) gave
2
1
The H NMR spectrum for compound 6 does not show any
signal in the aromatic region, displaying one singlet at 0.84 ppm
assigned to the methyl group and also two multiplets at 1.2 and
product 8 (isolated yield 30%).
1
The corresponding H NMR spectrum displays a singlet at
1.22 ppm assigned to the Si−CH moiety, a multiplet at 4.3 ppm
3
C
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to the participation of nickel nanoparticles, responsible for the
total reduction of the aromatic ring.
EXPERIMENTAL SECTION
■
Scheme 6. Synthesis of Compound 7
General Considerations. Unless otherwise noted, all manipu-
lations were performed under an argon atmosphere in an MBraun
glovebox (<1 ppm of H O and O ) or using standard Schlenk
2
2
techniques. A 300 mL stainless steel Parr 4842 Bench Top Mini
Reactor was used for the hydrogenation reactions. Phthalimide was
purchased from Aldrich, and [Ni(COD) ] was purchased from Strem;
2
both were filtered over silica gel 60 prior to their use. Both substances
were reagent grade and were manipulated in a drybox. All other
solvents used were dried and distilled from sodium/benzophenone
ketyl. Deuterated solvents for NMR experiments were purchased
from Aldrich and stored over 3 Å molecular sieves in the glovebox.
for the methylene proton fraction, and aromatic signals at
7
.83 (m) and 7.75 (m) ppm.
The difference in reactivity observed between the N-substituted
2
0
The nickel(I) complex 1 was prepared from Super-Hydride and
2
1
phthalimides 5 and 7 to yield compounds 6 and 8, respectively,
was indicative of nickel nanoparticles being formed during the
formation of compound 6, as inferred from the complete reduction
of the aromatic ring. Consequently, a mercury drop test was
performed with a consequent drop of yield in the case of 6 (10%),
in contrast with the case for 8, in which no change was registered.
Additionally, a crude sample from the preparation of compound 6
was centrifuged and nickel nanoparticles were found and
characterized by TEM (Figure 2), allowing us to confirm the
nickel-nanocatalyzed formation of 6.
[(dippe)NiCl ] suspended in hexane, similar to the literature
2
22
procedure. All compounds were purified by column chromatog-
1
raphy, and their integrity was verified by the corresponding H and
31
1
P{ H} NMR spectra. All catalytic experiments were loaded in the
reactor inside the glovebox. All the reduction products were recovered
from the reactor, filtered through Celite, purified by column
chromatography, and dried in the vacuum line (P < 10− mmHg)
prior to their quantification and characterization. All NMR spectra of
complexes and products were recorded at room temperature on a
3
1
31
1
3
00 MHz Varian Unity spectrometer. The H and P{ H} NMR spectra
of the compounds were obtained from solutions (∼30 mg) of the pure
1
13
1
compounds in CDCl unless otherwise stated. H and C{ H} NMR
3
chemical shifts (δ, ppm) are reported relative to the residual proton
resonance in the deuterated solvent, and 31P{ H} spectra are reported
relative to external 85% H PO . GC-MS determinations were performed
1
3
4
using an Agilent 5975C system equipped with a 30 m DB-5MS capillary
(
0.32 mm i.d.) column.
Catalytic Reduction of Phthalimide with [(dippe)NiH] . The
2
reactor vessel was loaded in the glovebox with phthalimide (0.274 g,
1
.86 mmol) in 30 mL of THF, and [(dippe)NiH] (0.12 g, 0.186
2
mmol) was added to the solution. The reactor was sealed and charged
with 750 psi of H at room temperature. The mixture was then heated
2
at 140 °C with vigorous stirring for 72 h; after this time the reactor was
cooled and vented into a hood prior to workup (vide supra). GC-MS
•
+
•+
•
for 2: M m/z 121 benzamide; M − NH m/z 105; Ph m/z 77.
2
•+
•+
GC-MS for 3: M m/z 133 isoindolinone; M − CH m/z 104;
Ph m/z 77.
2
•
When this reaction was carried out using stoichiometric amounts of
1
and phthalimide, compounds 4 and 4b were observed in solution.
1
NMR spectra for 4 in THF-d : H, δ −20 (dd, J
= 93 Hz,
8
P−H(trans)
J
6
= 15 Hz), 1.3 (m, CH -phosphine), 2 (d, −CH phosphine),
P−H(cis)
3
2
31
1
2
2
.8−7.4 (m, arom); P{ H}, δ 82.3 (d, J = 23 Hz), 85.6 (d, J
=
P−P
P−P
31
1
2
Figure 2. TEM for nickel nanoparticles involved in the production
of 6.
23 Hz). NMR spectrum for 4b: P{ H}, δ 75.6 (d, J = 71 Hz), 71.2
P−P
2
(d, J = 71 Hz).
P−P
Catalytic Reduction of Phthalimide with [Ni(COD) ]. The reactor
2
was loaded in the glovebox with phthalimide (0.468 g, 3.18 mmol)
CONCLUSIONS
dissolved in 30 mL of THF, and [Ni(COD)
was added to the solution. The reactor was sealed and pressurized with
2
] (0.02g, 0.318 mmol)
■
A nickel-based catalytic system for the monoreduction of a CO
group present in phthalimide to yield isoindoline has been
achieved, using relatively mild reaction conditions and with the
6
50 psi of H at room temperature. The mixture was then heated at
80 °C with vigorous stirring for 72 h; after this time the reactor was
2
1
cooled to room temperature and vented in a hood prior to workup.
1
use of the readily available complex [Ni(COD) ] as the catalyst
Yield: 40% of isoindolinone. NMR data for 3: H, δ 8.2 (s, N−H),
2
precursor. The use of 1 under catalytic conditions allowed both
the monoreduction in low amounts and the ring-opening/
decarbonylation product in good yields. Intermediates bearing a
κ -N-phthalimide and η -C,O-phthalimide are involved during
the homogeneous hydrogenation of phthalimide.
When the N−H group in the phthalimide was protected with
either methyl or trimethylsilyl groups, both CO groups were
reduced; however, the N-methyl derivative was completely
hydrogenated, including the aromatic ring, under relatively mild
reaction conditions. Such reactivity was demonstrated to be due
7.82−7.85 (m, 2H, arom), 7.41−7.46 (m, 2H, arom) 4.4 (s, 2H,
CH-NH); 13C{ H}, δ 172.5 (carbonyl), 143.9 (arom), 132.4 (arom),
1
1
31.8 (arom), 128.1 (arom), 123.8 (arom), 123.3 (arom), 46 (C-NH).
•+
•+
•
1
2
GC-MS: M m/z 133; M − CH NH m/z 104; Ph m/z 77.
2
Synthesis of N-Methylphthalimide (5). A suspension of
phthalimide potassium salt (2.69 mmol) in DMF (10 mL) was reacted
with dimethyl sulfate (0.25 mL, 8.07 mmol) at room temperature, with
vigorous agitation over 24 h. After this time, the reaction mixture was
treated with a saturated aqueous solution of sodium chloride, the product
was extracted with ethyl acetate (3 × 15 mL), and the extracts were
combined, dried over Na SO , evaporated to dryness. A white solid was
2
4
D
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Organometallics
Article
1
obtained. Yield: 62%. Mp: 130−133 °C. NMR data for 5 in CDCl : H, δ
Dedicated to Prof. William D. Jones, a great mentor, colleague, and
friend, on the occasion of his 60th birthday.
3
7
.81−7.77 (q, 2H, arom), 7.68−7.65 (q, 2H, arom), 3.14 (s, 3H, N−
CH ); C{ H}, δ 168.6 (s, CO), 134 (s, CH-arom), 132 (s, C ), 123
13 1
3
ipso
(
s, CH-arom), 24.07 (s, N-CH ).
3
REFERENCES
■
Catalytic Reduction of 5 with [(dippe)NiH] . A reactor was
loaded in the glovebox with 5 (0.46 g, 2.9 mmol) dissolved in 30 mL of
THF, followed by the addition of [(dippe)NiH] (0.018, 0.029 mmol).
The reactor was sealed and charged with 870 psi of H2 at room
temperature. The mixture was then heated to 140 °C with vigorous
stirring for 3 days. After workup (vide supra) 2-methyloctahydroisoindo-
line (6) was obtained. NMR in CDCl : H, δ 0.84 (s, br, N-CH ), 1.2
m, H-cyclohexane), 1.6 (m, cyclohexane), 1.9−2.03 (m, H-pyrrolidone).
Synthesis of Trimethylsilylphthalimide (7). A suspension of
phthalimide potassium salt (1.6g, 8.6 mmol) in THF (15 mL) was
slowly added to CH SiCl (1.31 g, 12 mmol) with vigorous stirring.
2
(
(
(
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The mixture was heated to reflux for 3 h. After this reaction time, the
(
mixture was filtered and the solvent evaporated. A white solid of 7
1
(
yield 72%) was obtained. NMR data: H, δ 0.081 (s, Si-CH ); 7.72
3
(
(
m, H-arom); 7.89 (m, H-arom).
Catalytic Reaction of 7 with [(dippe)NiH] . By a procedure
2
(
entirely similar to the synthesis of 6, compound 8 was obtained. NMR
1
data for 8 in CDCl : H, δ 2.1 (s, Si-CH ), 4.3 (m, methylene), 7.42
3
3
(
2
(
1
(
m, H-arom), 7.5 (m, H-arom).
X-ray Structure Determination. A yellow lamina crystal of 4-Cl
mounted on a glass fiber was studied with an Oxford Diffraction Gemini
A” diffractometer with a CCD area detector (λMoKα = 0.71073 Å,
“
(
(
11) Adkins, H.; Gramer, H. J. Am. Chem. Soc. 1930, 52, 4349−4358.
graphite monochromator) source equipped with a sealed-tube X-ray
source at 130 K. Unit cell constants were determined with a set of 15/3
narrow frame/runs (1° in ω) scans. A data set consisted of 205 frames of
intensity data collected with a frame width of 1° in ω, a counting time of
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Halczenko, W.; Ponticello, G. S.; Shepard, K. L. J. Org. Chem. 1979, 44
(
9), 1519−1533. (b) Feng, S.; Panetta, A.; Graves, D. E. J. Org. Chem.
1
4.9 s/frame, and a crystal-to-detector distance of 55.00 mm. The double-
2001, 66, 612−616.
pass method of scanning was used to exclude any noise. The collected
frames were integrated by using an orientation matrix determined from
the narrow frame scans. CrysAlisPro and CrysAlis RED software
packages were used for data collection and data integration. Analysis
of the integrated data did not reveal any decay. Final cell constants were
determined by a global refinement of 4215 reflections (θ < 26.05°).
Collected data were corrected for absorbance by using analytical numeric
(13) Norman, M. H.; Minick, D. J.; Rigdon, G. C. J. Med. Chem.
1996, 39, 149−157.
(14) Aoun, R.; Renaud, J. L.; Dixneuf, P. H.; Bruneau, C. Angew.
Chem., Int. Ed. 2005, 44, 2021−2023.
23a
(15) Havlik, S. E.; Simmons, J. M.; Winton, V. J.; Johnson, J, B. J. Org.
Chem. 2011, 76 (9), 3588−3593.
(16) Flores-Gaspar, A.; Pinedo-Gonzalez, P.; Crestani, M. G.;
23b
absorption correction
with a multifaceted crystal model based on
̃
Munoz-Hernandez, M.; Morales-Morales, D.; Warsop, B. A.; Jones,
expressions upon the Laue symmetry using equivalent reflections.
J. D.; Garcia, J. J. J. Mol. Catal. A: Chem. 2009, 309, 1−11.
(17) Castellanos-Blanco, N.; Flores-Alamo, M.; Garcia, J. J.
Organometallics 2012, 31, 680−686.
Structure solution and refinement were carried out with the
23c
following program(s): SHELXS97 and SHELXL97. For molecular
2
3d
graphics, ORTEP-3 for Windows was used;
software was used to prepare material for publication.
Full-matrix least-squares refinement was carried out by minimizing
and the : WinGX
(18) (a) Garcia, J. J.; Brunkan, N. M.; Jones, W. D. J. Am. Chem. Soc.
2002, 124, 9547−9555. (b) Garcia, J. J.; Arevalo, A.; Brunkan, N. M.;
Jones, W. D. Organometallics 2004, 23, 3997−4002.
2
3e
2
2 2
(
Fo − F ) . All non-hydrogen atoms were refined anisotropically. H
atoms attached to C atoms were placed in geometrically idealized
(19) Lop
Garcıa, J. J. J. Organomet. Chem. 2002, 664, 170−175.
́
1
̃
́ ́ ́ ́
ez, C.; Baron, G.; Arevalo, A.; Munoz-Hernandez, M. A.;
c
positions and refined as riding on their parent atoms, with C−H =
(20) The quintet at δ −9.81 (J = 24 Hz) in the H NMR spectrum is
0
.95−1.00 Å and U (H) = 1.2[U (C)], or 1.5[U (C)] for aromatic,
characteristic of nickel bisphosphine hydride dimers.
iso
eq
eq
methylene, methyne, and methyl groups.
(21) Scott, F.; Kru
13.
̈
ger, C.; Betz, P. J. Organomet. Chem. 1990, 387,
1
(
22) Jonas, K.; Wilke, G. Angew. Chem., Int. Ed. 1970, 9, 312−313.
ASSOCIATED CONTENT
■
(23) (a) CrysAlis CCD and CrysAlis RED; Oxford Diffraction Ltd,
*
S
Supporting Information
Abingdon, England, 2010. (b) Clark, C.; Ried, J. S. Acta Crystallogr.,
Sect. A: Found. Crystallogr. 1995, 51, 887. (c) Sheldrick, G. M.
SHELXS97 and SHELXL97; University of Go
Germany, 2008. (d) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.
e) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837.
Figures giving NMR and mass spectra and a CIF file giving
crystallographic data for 4-Cl·(toluene). This material is
available free of charge via the Internet at http://pubs.acs.org.
̈ ̈
ttingen, Gottingen,
(
AUTHOR INFORMATION
■
Corresponding Author
*E-mail for J.J.G.: juvent@unam.mx.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank the PAPIIT-DGAPA-UNAM (IN-210613) and
CONACYT (0178265) for their financial support of this work.
E
dx.doi.org/10.1021/om400164g | Organometallics XXXX, XXX, XXX−XXX