C-H Nickelation of Naphthyl Phosphinites: Electronic and Steric Limitations, Regioselectivity, and Tandem C-P Functionalization

Article abstract of DOI:10.1021/acs.organomet.9b00660

This report describes the results of a study on the C-H nickelation of phosphinites derived from variously substituted 1- and 2-naphthols, as well as the C-P functionalization of the Ni-naphthyl moiety arising from the C-H cyclonickelation. Refluxing 4-X-1-naphthyl phosphinites (X = H, 1a; MeO, 1b; Cl, 1c) with {(i-PrCN)NiBr2}n and Et3N in acetonitrile gave the nickelacyclic complexes {(κP,κC-4-X-1-OP(i-Pr)2-naphth-2-yl)Ni(μ-Br)}2, 2a-c, resulting from cyclonickelation at the C2-H, whereas cyclonickelation of the 2-naphthyl phosphinite analogue 1e under the same conditions occurred at C3-H. Placing a Me substituent at the C3 position of a 2-naphthyl phosphinite (1f) led to a very sluggish nickelation at the C1-H position, whereas 2-ethyl-1-naphthyl phosphinite (1d) failed to nickelate at C8-H. H/D scrambling tests conducted on the deuterated analogue of 1a (1a-d7) confirmed that nickelation occurs exclusively at C2. Similar tests conducted on deuterated analogues of alkyl-substituted 1- and 2-naphthyl phosphinites showed that no nickelation takes place at Csp3-H sites of the alkyl substituents. In contrast, very facile C-H nickelation was observed with 2-allyl-1-naphthyl phosphinite 1g to give a product featuring a π-allyl-Ni moiety. A series of tests have shown that the nickelation of substrates 1a, 1e, and 1f can be accelerated dramatically at 120-160 °C. On the other hand, conducting the high temperature reaction of 1a in the absence of Et3N resulted in an unanticipated and interesting C-P functionalization of the C2-H site, thus generating a i-Pr2P-substituted bidentate phosphine-phosphinite. A similar tandem C-H nickelation/C-P(O) functionalization was also observed at the C8-H position of substrate 1d. The mechanisms of these functionalization reactions have been probed and outlined.

Full text of DOI:10.1021/acs.organomet.9b00660

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Cite This: Organometallics XXXX, XXX, XXX−XXX
C−H Nickelation of Naphthyl Phosphinites: Electronic and Steric
Limitations, Regioselectivity, and Tandem C−P Functionalization
Loïc P. Mangin and Davit Zargarian*
Departement de Chimie, Universite de Montreal, Montreal, Quebec H3C 3J7, Canada
́ ́ ́ ́ ́
*
S Supporting Information
ABSTRACT: This report describes the results of a study on the C−H nickelation of phosphinites derived from variously
substituted 1- and 2-naphthols, as well as the C−P functionalization of the Ni-naphthyl moiety arising from the C−H
cyclonickelation. Refluxing 4-X-1-naphthyl phosphinites (X = H, 1a; MeO, 1b; Cl, 1c) with {(i-PrCN)NiBr } and Et N in
2
n
3
P
C
acetonitrile gave the nickelacyclic complexes {(κ ,κ -4-X-1-OP(i-Pr) -naphth-2-yl)Ni(μ-Br)} , 2a−c, resulting from
2
2
cyclonickelation at the C2−H, whereas cyclonickelation of the 2-naphthyl phosphinite analogue 1e under the same conditions
occurred at C3−H. Placing a Me substituent at the C3 position of a 2-naphthyl phosphinite (1f) led to a very sluggish
nickelation at the C1−H position, whereas 2-ethyl-1-naphthyl phosphinite (1d) failed to nickelate at C8−H. H/D scrambling
tests conducted on the deuterated analogue of 1a (1a-d ) confirmed that nickelation occurs exclusively at C2. Similar tests
7
conducted on deuterated analogues of alkyl-substituted 1- and 2-naphthyl phosphinites showed that no nickelation takes place
3
at C −H sites of the alkyl substituents. In contrast, very facile C−H nickelation was observed with 2-allyl-1-naphthyl
sp
phosphinite 1g to give a product featuring a π-allyl-Ni moiety. A series of tests have shown that the nickelation of substrates 1a,
1
e, and 1f can be accelerated dramatically at 120−160 °C. On the other hand, conducting the high temperature reaction of 1a
in the absence of Et N resulted in an unanticipated and interesting C−P functionalization of the C2−H site, thus generating a i-
3
Pr P-substituted bidentate phosphine-phosphinite. A similar tandem C−H nickelation/C−P(O) functionalization was also
2
observed at the C8−H position of substrate 1d. The mechanisms of these functionalization reactions have been probed and
outlined.
INTRODUCTION
substituted derivatives. In an initial report, we showed that
■
orthometalation of ArOP(i-Pr) is feasible with the Ni(II)
2
Catalytic processes based on non-redox-type C−H metalation
and tandem functionalization have gained increasing prom-
inence in the drive toward sustainable chemical synthesis.
Historically, the early success of these processes was due in
large part to the use of noble metal-based precursors, and to
4
precursor {(i-PrCN)NiBr } . The isolation and structural
2
n
1
characterization of the resulting cyclonickelated species have
allowed us to gain some understanding of their thermal
stabilities and reactivities in C−C and C−heteroatom
functionalization (Scheme 1, A).
2
some extent the supremacy of these metals persists today.
We have also delineated the impact of reaction solvent,
However, the past decade has witnessed the development of
many efficient C−H functionalization processes that are
catalyzed by precursors based on the more abundant 3d
external base, and aryl substituents on the kinetics and
5
energetics of C−H nickelation. It was found, for instance, that
3
C−H bond rupture is rate determining (k /k ≈ 11), and that
metals. In addition to the potential cost advantages of the
H
D
nickelation proceeds faster with substrates bearing electron-
latter relative to their 4d and 5d congeners, continued
investigations of C−H metalation-functionalization chemistry
based on 3d metals also open the door to the discovery of new
and complementary reactivity patterns, which can be exploited
to create exciting opportunities in commercial developments.
Our group’s contributions to this field have focused on the
C−H nickelation of phosphinites derived from phenol and its
6
releasing substituents. Significantly, D-labeling studies and
rate measurements indicated that the C−H nickelation step
occurs reversibly and independently of the presence of an
Received: October 7, 2019
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.9b00660
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Scheme 1. C−H Nickelation with Aryl Phosphinites
RESULTS AND DISCUSSION
■
C−H Nickelation of 1-Naphthyl Phosphinites. Our
studies began by examining the reactivities of 1-naphthyl
phosphinites under the reaction conditions optimized for the
C−H nickelation of substrates derived from substituted
phenols. Thus, the substrate being studied was refluxed in
acetonitrile in the presence of {(i-PrCN)NiBr } and Et N, the
2
n
3
latter serving the purpose of quenching the HBr generated in
situ at the C−H nickelation step. Scheme 2 shows the
acetonitrile adducts of the cyclonickelated products generated
from 1-naphtyl phosphinites 1a−1c.
Scheme 2. Nickelation of 4-X-1-Naphthyl Phosphinites
external base (Scheme 1, B). On the other hand, isolation of
the nickelacyclic complex resulting from the C−H metalation
step requires a sufficiently strong external base, because the
acid generated during the nickelation step protonates the
5
newly formed Ni-aryl moiety to reverse the C−H nickelation.
Finally, studying the C−H nickelation of aryl phosphinites
based on 3-substituted phenols has revealed that the
regiochemistry of orthonickelation is strongly influenced by
6
steric factors.
In continuation of our previous investigations, we have
begun to examine the C−H nickelation of phosphinites
derived from 1- and 2-napththols. These substrates offer two
potentially reactive C−H sites, but the steric and electronic
properties of these sites of reactivity are more dissimilar than in
phosphinites derived from phenol. For instance, nickelation of
1
-naphthyl phosphinite at C2 would give a 5-membered
Complete conversions took place over 16−30 h, which was
3
1
nickelacycle, whereas reaction at C8 would generate a 6-
membered nickelacycle. In the case of 2-naphthyl phosphinite,
nickelation at both ortho C−H sites (C1 and C3) would
generate 5-membered nickelacycles, but these two products
would be reasonably expected to display different reactivities
based on their steric and electronic differences.
There is scant literature on the metalation of naphthyl
phosphinites, but the few precedents that do exist offer us an
indication of which C−H site might be more favorable to
metalation. Bedford has shown, for example, that metalation of
confirmed by the P NMR spectra of the final reaction
mixtures displaying new singlet resonances at 194−197 ppm,
the chemical shift region characteristic of cyclonickelated
5
ArOP(i-Pr)
.
2
The green reaction mixtures containing the
cyclonickelated products were then worked up in toluene to
give the target dimeric complexes as orange powders in 74−
84% isolated yields. Complete characterization of 2a−2c by
NMR and single crystal XRD confirmed that the desired
cyclonickelation had taken place at the C2 to give 5-membered
nickelacycles (Figure 1); the putative compounds arising from
nickelation at the C8 position and featuring 6-membered
nickelacycles were not observed.
1
-naphthyl phosphinites with Rh occurs mainly at the C2−H
site, but it can also take place to a lesser extent at the C8 site to
give a 6-membered rhodacycle. The analogous reactivity with
7
The solid-state structures of 2a−c will be discussed in the
last section of this report, but the reaction times required for
their formation and the isolated yields merit some comment
2
-naphthyl phosphinites takes place at both C1−H and C3−H
9
sites. In the case of Pd, metalation of 1-naphthoxide (as
opposed to its phosphinite) has been reported to occur at C8−
H, whereas palladation of 2-naphthoxides takes place
exclusively at C1, presumably generating a 4-membered
8
palladacycle. The above considerations prompted us to
study the nickelation of naphthyl phosphinites and compare
the results to the nickelation of phenyl phosphinites.
The present contribution reports the cyclonickelation of 1-
and 2-naphthyl phosphinites and some of their substituted
derivatives. We have found that nickelation of 1-naphthyl
phosphinites occurs at C2 in preference over C8, whereas the
C3 site is favored over C1 for 2-naphthyl phosphinites. In the
latter case, blocking the favored pathway allowed us to induce
nickelation at the less favored C1−H site, but a similar strategy
was much less successful for 1-naphthyl phosphinite. In some
cases, conducting the reactions at high temperatures led to
accelerated C−H nickelation rates and a potentially useful
tandem C−P functionalization.
Figure 1. Top view of the molecular diagram for complex 2a. Thermal
ellipsoids are shown at the 50% probability level; hydrogens are
omitted for clarity.
B
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here. The yields obtained for complexes 2a−2c are somewhat
higher than those obtained for the analogous dimeric
complexes derived from phenol (67%), 3-MeO-phenol
Scheme 4. Testing D/H Scrambling in 1-Naphthyl
Phosphinite
(
60%), and 3-Cl-phenol (71%). We believe that these higher
yields are due to the lower solubility of these complexes in
Et O and hexanes, which facilitates product isolation by
2
precipitation from these solvents.
As for the different reaction times required for the formation
of 2a−2c, although we have not made systematic measure-
3
1
ments of reaction rates in this study, monitoring the P NMR
spectra of the reaction mixtures showed that the nickelation
times varied as a function of substituents X, going to
completion within 20 h for X = H and OMe, but requiring
longer times for X = Cl. The observation of faster nickelation
for 2a and 2b echoes our previous results on the faster
nickelation of aryl phosphinites bearing electron-rich substrates
even after 3 days of heating. This establishes that the formation
of the expected 6-membered nickelacycle is either kinetically
not allowed in these conditions or, if nickelation does take
place at C8−H, the in situ generated DBr reacts with the
resulting Ni−C moiety to reverse nickelation faster than D/H
exchange with the solvent.
6
(
Hammett slope of ca. −4).
The observation of exclusive nickelation at C2 for 1a−1c
prompted us to ask if the nickelation can be forced to occur at
the alternative C8 site. This was examined by testing the C−H
9
nickelation of 2-Et-1-naphthyl phosphinite, 1d, in which the
C2 site is blocked by a substituent. This substrate was
subjected to the standard cyclonickelation conditions at 80 °C
for 3 days, to no avail: analysis of the final reaction mixture by
C−H Nickelation of 2-Naphthyl Phosphinites. Cyclo-
nickelation of 2-naphthyl phosphinite, 1e, proceeded even
more sluggishly than the analogous nickelation of 1-naphthyl
phosphinites 1a−1c, requiring 60 h at 80 °C to go to
3
1
P NMR spectroscopy showed no signal in the 190−210 ppm
range, implying no nickelation (Scheme 3).
31
completion (Scheme 5). Nevertheless, the P NMR spectrum
Scheme 3. Inertness of 2-Ethyl-1-Naphthyl Phosphinite
toward Nickelation
Scheme 5. Nickelation of 2-Naphthyl Phosphinite
The issue of cyclonickelation regioselectivity with 1-
naphthyl phosphinites, i.e., reactivity at C2 vs C8 sites, was
further examined using H/D scrambling experiments. This
idea was inspired from H/D scrambling experiments we
carried out in a previous study on the cyclonickelation
6
mechanism of aryl phosphinites. Thus, heating C D OPR
6
5
2
and {(i-PrCN)NiBr } in CH CN or protio-toluene in the
2
n
3
absence of external base led to partial incorporation of H into
the ortho C−D sites of the phosphinite (Scheme 1, B). This
allowed us to conclude that nickelation occurs independently
of external base, but the in situ generated DBr can undergo D/
H exchange with the solvent to generate HBr, which then
protonates the cyclonickelated species to generate 2-H-
C D OPR (reversible nickelation).
By analogy to the above approach, we set out to conduct a
D/H scrambling experiment aimed at establishing whether
nickelation of 1-naphthyl phosphinite might be taking place at
of the final reaction mixture confirmed a clean conversion of 1e
to a new species displaying a singlet at 197 ppm. Cooling the
reaction mixture to room temperature gave yellow crystals,
which were identified by XRD analysis as the acetonitrile
adduct of the cyclonickelated compound (2e-NCMe in
Scheme 5).
On the other hand, isolation of the corresponding dimeric
complex 2e by the usual workup protocol was hampered by its
limited solubility in toluene. Conducting the extraction process
using hot toluene dissolved more of 2e-NCMe, thus allowing
us to isolate 2e with ca. 54% yield. However, despite multiple
attempts to purify the crops of 2e obtained from this approach,
they always contained residual toluene impurities, whereas
pure samples of the acetonitrile adduct 2e-NCMe could be
obtained from these in 80% yield.
6
4
2
the C8−H position. To do this, we prepared 1-naphthyl-d -
7
9
OP(i-Pr) (1a-d ) and used it to prepare the precursor
2
7
complex trans-{(1-naphthyl-d -OP(i-Pr) } NiBr (3a-d ),
7
2
2
2
7
which was subsequently heated in CH CN for 1 day at 80
3
°
C (Scheme 4).
Cooling the final reaction mixture to −35 °C allowed us to
1
isolate the product by crystallization, and H NMR analysis in
C−H nickelation of 1e could, in principle, occur at one of
the two ortho C−H positions C1 and C3, but NMR
characterization and XRD analyses of 2e and 2e-NCMe
CDCl revealed 53% H-incorporation into the C2 position
3
1
0
(Figure S137). H-incorporation into C8 was not detected
C
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revealed C3 to be the only site of reactivity (Scheme 5, Figure
formation of a new species, but complete conversion was not
achieved even after 10 days. NMR monitoring of the reaction
2
).
3
1
progress showed a new P singlet at ca. 192 ppm, which we
tentatively assign to 2f-NCMe (Scheme 6). Integrating this
peak against that of the internal standard [n-Bu N][PF ]
4
6
showed conversions of about 10% and 16% after 3 and 7 days,
respectively. Unfortunately, the standard workup of the
reaction mixture in toluene was complicated by the presence
of significant quantities of the unreacted starting material; as a
result, we obtained only a small quantity of crystals.
Nevertheless, XRD analysis conducted on these crystals
showed that this reaction generated a phosphinite adduct of
the cyclonickelated species 2f-L wherein nickelation of 1f had
taken place at C1 (Scheme 6).
Comparison of the C−H nickelation regioselectivities
observed for the 2-naphthyl phosphinites 1e and 1f and the
relative facility/sluggishness of these reactions inform us on the
relative importance of sterics and electronics for these
reactions. Thus, in substrate 1e wherein C−H nickelation is,
in principle, possible at both sites, reactivity takes place at C3
in preference over the more electron-rich C1 site; moreover,
the nickelation of this substrate required 60 h. In contrast, with
substrate 1f wherein the C3 site is blocked by the Me
substituent, the nickelation occurred at the alternative C1 site,
but at a very sluggish pace.
Figure 2. Top view of the molecular diagram for complex 2e.
Thermal ellipsoids are shown at the 50% probability level; hydrogens
are omitted for clarity.
This raised the question of whether the observed preference
for nickelation at C3 vs C1 originates from steric or electronic
factors. Our previous investigations on the nickelation of
phosphinites derived from 3-R-phenols had demonstrated that
electronic factors can influence nickelation rates but not
regioselectivity, whereas steric hindrance is the main
We believe that the sluggishness of nickelation with 1f
results from the steric congestion at the C1 site. Consistent
with this, the molecular diagram of 2f-L (Scheme 6) revealed a
very distorted structure in which the steric repulsion between
C8−H and the phosphinite has caused a significant twist
around the Ni−C1 axis. Indeed, the tetrahedral distortion
11,12
determinant of which C−H is nickelated.
By analogy, it
seems reasonable to conclude that the observed preference for
nickelation of 1e at C3 must be due to lower steric hindrance
at this site relative to C1. On the other hand, the much slower
nickelation of this substrate compared to the analogous
reactions with 1-naphthyl phosphinites 1a−1c is likely caused
by unfavorable electronic factors, the C3 position in 2-
14
4
parameter τ
around the Ni center was found to be 0.30−
0.35, caused primarily by the out-of-plane displacement of the
non metalated naphthyl phosphinite ligand. As a result, the
dihedral angle of ca. 50° for C10A−C1A−Ni1−P2 represents a
significant out-of-plane rotation of the nickelated naphthyl
ring.
13
naphthols being less electron-rich relative to the C1 position.
Similarly to the above-described probe of regioselectivity
with substrate 1d (Scheme 3), we examined the C−H
nickelation of 3-Me-2-naphthyl phosphinite, 1f, in which the
more reactive C3 site has been blocked in order to see if C−H
nickelation can be forced to occur at the less favored C1 site
Reactivity of Ortho Substituents. In the above
discussions on the regioselectivity of C−H nickelation with
alkyl-substituted 1- and 2-naphthyl phosphinites, the possibility
of nickelation at the alkyl substituents was not considered.
Discounting this possibility might be justified, because
(
Scheme 6).
Refluxing the emerald green acetonitrile mixture resulting
from mixing 1f with {(i-PrCN)NiBr2}n and Et N led to
3
3
metalation of C −H bonds is usually more difficult, and the
sp
3
resulting Ni−C bonds are known to be less stable than Ni−
Scheme 6. Nickelation of the 3-Me-2-Naphthyl Phosphinite
sp
a
2
C
bonds arising from metalation of C −H. Nevertheless, it
1
f and Molecular Diagram of 2f-L
sp
sp2
3
seemed important to determine if C −H nickelation can be
sp
kinetically accessible in naphthyl phosphinites bearing ortho-
alkyl substituents. We have probed this possibility by using a
H/D scrambling test analogous to the one shown in Scheme 4
for studying C−H nickelation at C8 in 1a.
Stirring the deuterated analogue of 1d with {(i-PrCN)-
NiBr } in dichloromethane at r.t. gave the target compound
2
n
9
{
2-CH CD -1-naphthyl-OP(i-Pr) } NiBr , 3d-d (Scheme 7).
3 2 2 2 2 2
Refluxing the latter in acetonitrile or toluene over extended
reaction times (up to 3 days), followed by gradual cooling to
−
35 °C gave crystals after 1 day. Analysis of these crystals by
1
H NMR (CDCl ) confirmed that no H-incorporation had
3
3
sp
taken place into the α C −D positions (Scheme 7). The
analogous scrambling test was also conducted for the
deuterated analogue of 1f, with the same results: H NMR
9
1
analysis of crystals of 3f-d obtained after heating showed no
3
a
3
Thermal ellipsoids are shown at the 50% probability level; hydrogens
H-incorporation into the α C −D site (Scheme 7). We
sp
3
and P-substituents are omitted for clarity.
conclude, therefore, that nickelation of the C H(D) sites in
sp
D
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Scheme 7. D/H Scrambling Tests with 1- and 2-
Phosphinites Bearing α-Deuterated Alkyl Substituents
symmetrical than in “free” π-allyl complexes of Ni(II)Br, and
the naphthalene ring bends out of the mean plane around Ni
by 25−37°.
Evidently, C−H nickelation at a methylenic C−H in 1g is
feasible and fairly facile, presumably due to the binding of the
terminal olefin moiety of the substituent to the Ni(II) center;
this would be akin to the C−H nickelation of a LXL′ pincer
ligand, which is often more facile than a simple cyclo-
16
nickelation. Unfortunately, efforts to isolate the putative
bidentate phosphinite-olefin intermediate shown in Scheme 8
from 1:1 mixtures of 1g:{(i-PrCN)NiBr } yielded only the
2
n
bis-phosphinite L NiBr complex (3g).
2
2
Acceleration of C−H Nickelation at High Temper-
atures. The generally sluggish rate of C−H nickelation for 1-
and 2-naphthyl phosphinites (16 h of refluxing in MeCN in the
most favorable case) spurred us to find a way to accelerate
these reactions. Tests showed that much faster C−H
nickelation is possible with some substrates by conducting
the reactions in a thermostated autoclave that allows us to
safely attain reaction temperatures above the boiling point of
the solvent. For instance, using this approach led to near
complete nickelation of 1a in only 30 min at 160 °C, which is
significantly faster than the 16 h required for the analogous
nickelation to occur in a Schlenk tube at 80 °C (Scheme 9).
alkyl-substituted 1- or 2-naphthyl phosphinites is either not
happening in our system or, if it is, the resulting nickelated
product is simply too high in energy and reverts back to its
starting form faster than the competing H/D exchange with
the solvent.
The observed inertness of the alkyl substituents in 1d and 1f
prompted us to ask if a more activated allylic/benzylic CH2
moiety would get nickelated. To answer this question, we
9
prepared substrate 1g and tested its C−H nickelation with
{
h).
(i-PrCN)NiBr } and Et N (Scheme 8: acetonitrile, 80 °C, 2
2 n 3
Scheme 9. C−H Nickelation of 1- and 2-Naphthyl
Phosphinites at 160 °C
Scheme 8. C−H Nickelation of 2-Allyl-1-Naphthyl
a
Phosphinite 1g and Molecular Diagram of 2g
Driving the nickelation of 1a to completion necessitated a
larger excess of the precursor {(i-PrCN)NiBr } , because this
2
n
compound decomposes partially at 160 °C to give Ni black
deposition on the walls of the reaction flask and on the stir
17
bar. Thus, using 1.5 equiv of both {(i-PrCN)NiBr } and
2
n
Et N led to complete nickelation of 1a within 1 h at 160 °C.
3
An even greater acceleration was noted for the much more
sluggish nickelation of 2-naphthyl phosphinite 1e: applying the
above reaction conditions (i.e., 50% excess Ni precursor, 160
a
Thermal ellipsoids are shown at the 50% probability level; hydrogens
°
C) led to complete conversion to the nickelation product 2e
and P substituents are omitted for clarity.
in 1 h, much faster than the 60 h required for complete
nickelation of this substrate at 80 °C (Scheme 9).
This reaction did give a new species represented by a 31P
singlet at 201 ppm, which we ascribed to a nickelated species.
However, there were also significant amounts of Ni black
deposited on the walls of the reaction flask, implying that some
of the putative nickelated complexes are prone to decom-
position. Repeating the reaction at lower temperatures allowed
us to promote the nickelation while avoiding thermal
degradation. For instance, conducting the reaction with 1
equiv of Ni precursor and 2 equiv of Et N at r.t. over 16 h led
to a cleaner nickelation. Workup of the final reaction mixture
followed by crystallization in Et O/pentane gave orange
crystals that were shown by XRD to be the monomeric
Having identified optimal conditions for the high temper-
ature nickelation of 1a and 1e, we conducted a few small scale
test reactions (ca. 0.2 mmol) to see if the very sluggish
nickelation of 1f (>10 d at 80 °C, Scheme 6) can be
accelerated at higher temperatures. Unfortunately, these
attempts were unsuccessful as we obtained mostly Ni black
and other undesired side-products (Figure S127). For instance,
conducting the reaction at 160 °C over 2 h gave a mixture in
which the desired cyclonickelated species 2f-NCMe showed
3
3
1
only a minor P signal at 192 ppm. Numerous additional
signals were also observed, including some in the 50−100 ppm
range believed to be phosphinite and phosphine oxides (Ni-
bound or free) and an unassigned sharp signal at 123 ppm, in
addition to signals around 135 ppm attributed to adducts of
the unreacted phosphinite.
2
3
complex 2g featuring an η -π-allyl moiety (Scheme 8).
Complex 2g features a 6-membered nickelacycle with
1
5
significantly longer Ni−C11 (1.983 and 1.972 Å) and Ni−
P bonds (2.145 and 2.134 Å) relative to other dimers featuring
5
On the other hand, lowering the reaction temperature
reduced the extent of thermal degradation and gave higher
-membered nickelacycles. Moreover, the allyl moiety is less
E
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conversions to the target product over shorter reaction times
different impacts on the C−H nickelation of different
substrates. With substrates such as 1a and 1e that undergo
slow C−H nickelation at 80 °C, high temperatures accelerated
the cyclonickelation significantly. On the other hand, with a
substrate such as 1d that does not undergo C−H nickelation at
(Scheme 10). For instance, conducting the reaction at 120 °C
Scheme 10. Nickelation of Phosphinite 1f at 160 °C and
Protonation of 2f-L in Toluene
8
0 °C, high temperatures resulted in a great deal of
decomposition. This observation suggested that disrupting
the formation of stable cyclonickelated products at high
temperatures might open new reactivity pathways. To test this
assertion, we set out to conduct the high temperature
nickelation of 1a in the absence of base, which we reasoned
would suppress formation of the normal nickelation product
2
a-NCMe and divert the reaction toward alternative pathways.
Thus, heating an acetonitrile solution of 1-naphthyl-
phosphinite 1a and 1.2 equiv of {(i-PrCN)NiBr } at 160 °C
2
n
over 4 h in the absence of Et N gave a red mixture that
3
3
1
displayed two major sets of P NMR resonances not observed
previously, namely: a set of AB doublets at 180 and 30 ppm
(
JPP ∼ 69 Hz), and a singlet at 121 ppm. A few other species
were also detected, including the non-nickelated phosphinite
adduct 3a represented by a broad signal at ca. 135 ppm.
Cooling the mixture to r.t. caused the precipitation of
unreacted starting material, 3a, which was removed by
filtration. Cooling the filtrate to −35 °C overnight afforded
red crystalline blocks, which were shown via XRD analysis to
(
1.2 equiv each of {(i-PrCN)NiBr } and Et N) gave 2f-
2 n 3
18
NCMe in 43% after 3 h (Figure S135). These results should
be compared to ca. 16% yield for the same nickelated product
when the reaction is conducted over 7 days at 80 °C. The
above encouraging results prompted us to see if conducting
mmol scale reactions at 120 °C would allow us to isolate the
cyclonickelated MeCN adduct 2f-NCMe and eventually work
it up into its corresponding dimeric complex 2f. Indeed,
heating 1f with 1.2 equiv of both Et N and {(i-PrCN)NiBr }
P
P
contain the new compound cis-(κ ,κ ′-2-P(i-Pr)
-1-naphhtyl-
2
OP(i-Pr) )NiBr , 4, shown in Scheme 11.
2
2
Scheme 11. C−P Functionalization of 1a
3
2 n
at 120 °C for 16 h gave mostly the desired 2f-NCMe, as
inferred from the observation of a very major peak at 192 ppm
assigned to this compound.
An initial attempt to isolate the dimeric species 2f failed,
however, because the workup in toluene led to reprotonation
of the nickelated species with Et N·HBr, giving back the non-
3
nickelated complex (Scheme 10). To circumvent this reversal
of the nickelation step, the crude reaction mixture was cooled
to −35 °C to allow crystallization of unreacted 3f and of some
The unanticipated formation of the new phosphinite/
phosphine compound 4 can be viewed as the formal insertion
+
of [i-Pr P] into the C−Ni bond generated from C−H
2
Et N·HBr. The green supernatant was then evaporated,
nickelation of ligand 1a. It occurred to us that the presence of
an excess of substrate might favor this pathway, because
transformation of 1a to 4 requires a 2:1 molar ratio of 1a:Ni.
Indeed, repeating the above reaction with twice as much 1a as
3
extracted with toluene, and evaporated to give an orange
solid, which was recrystallized from Et O to give orange
2
crystals that were identified as 2f. As will be discussed below,
this compound displayed a strong structural distortion.
Lastly, we conducted a few experiments to see if substrate
3
1
before gave a red mixture for which the P NMR spectrum
seemed cleaner than the spectrum obtained from the first
reaction, even though the reaction was not complete after 4 h.
Increasing the reaction temperature to 200 °C resulted in
1
d, which could not be induced to undergo nickelation under
the standard reaction conditions at 80 °C, might be nickelated
31
19
at high temperatures. Unfortunately, the P NMR spectrum of
complete consumption of the starting material within 1 h.
the final mixture obtained from the 160 °C reaction of 1d with
Cooling the final reaction mixture overnight to −35 °C
yielded a crop of thin needles consisting of elongated plates
stuck together. XRD analysis of a crystal obtained from this
batch showed it to be poorly diffracting and twinned;
nevertheless, the data allowed us to establish that it contained
compound 4 and 1/2 molecule of free 1-naphthol (Scheme 11,
Figure S182). As will be discussed below, the in situ formation
of 1-napththol in this reaction is significant, because it provides
a significant clue for the reaction mechanism.
{
(i-PrCN)NiBr } and Et N did not show the anticipated
2 n 3
signals for a nickelation product. We found instead a major
species at 123 ppm as well as a number of minor signals in the
9
0−110 and 160−170 ppm regions. Moreover, much Ni black
was found deposited on the walls of the reaction vial, and this
after only 1 h of reaction. As before, control experiments
showed that no degradation of 1d occurs after 1 h of heating at
1
60 °C in MeCN, implying that the degradation likely involves
the putative nickelated product. Lowering the nickelation
temperature to 120 °C led to less thermal degradation, but the
makeup of the reaction mixture remained fairly unchanged.
Interception of Unanticipated C−P Functionalized
Products. The results discussed in the previous section
showed us that high temperatures can have dramatically
Another mechanistically relevant observation was that
heating a MeCN solution of the cocrystals isolated from this
3
1
reaction to 160−200 °C showed only the P resonances
3
1
assigned to 4 (two P doublets at 180 and 30 ppm), no trace
of the unidentified peak at 121 ppm being detected. This
implied that the unidentified species is the product of a
F
DOI: 10.1021/acs.organomet.9b00660
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Organometallics
Article
different side reaction and does not arise from thermal
degradation of 4.
Combining the above clues suggested that the conversion of
[R P]+ from cationic imidazoliophosphines coordinated to
2
Pd(II) and Ni(II) to generate the corresponding NHC-
21
carbenes.
1
a to 4 proceeds by the following sequence of steps: (a)
cyclonickelation would initially generate HBr and 2a-NCMe;
b) substitution of MeCN in the latter species by the non
nickelated phosphinite 1a would give the phosphinite adduct
Having identified complex 4 and proposed a plausible
mechanism for its formation from 1a, we set out to identify the
other product observed during this transformation, i.e., the
(
3
1
minor species represented by the P singlet at 121 ppm. As
mentioned above, we concluded that this species does not arise
from the thermal degradation of 4. We posited that it might
also be a C−P functionalization product, but one that arises via
a competing C−H nickelation at C8. To test this possibility,
we examined the analogous reaction of substrate 1d at 160 °C
2
0
2
a-L; (c) this intermediate would then undergo a rearrange-
ment to initiate the C−P bond forming process; (d) the
naphthoxide leaving group generated in this last step would
capture the proton produced at the nickelation step (a) to give
the naphthol molecule cocrystallized with 4.
To test the validity of the above postulate, we generated 2a-
NCMe in situ by dissolving the independently prepared
dimeric complex 2a in MeCN, and heated it in the presence of
and in the absence of Et N, based on the reasoning that the
3
ethyl substituent in 1d would block C−H nickelation at C2,
thereby suppressing the reactivity pathway leading to 4. Thus,
heating a 1:1.2 MeCN mixture of 1d and {(i-PrCN)NiBr } at
1
equiv of the phosphinite 1a at 160 °C for 1 h. Analysis of the
2
n
31
final red mixture by P NMR showed only a trace of the
diagnostic AB doublet for 4, in addition to broadened signals
for unreacted 2a-NCMe and 1a, as well as minor peaks in the
region of phosphine and phosphinite oxides. This experiment
showed that the formation of 4 does not proceed to any
appreciable extent from the treatment of 2a-NCMe with 1a.
Upon reflection, it occurred to us that the main difference
between the reaction depicted in Scheme 11 and the above test
is the use of independently prepared 2a-NCMe in the latter
case vs its formation via in situ cyclonickelation in the former
case. Given that in situ cyclonickelation generates HBr as a
coproduct, we reasoned that this might be an important factor
for transformation of 2a-NCMe into 4. For instance, the
presence of in situ generated HBr might convert the
160 °C for 1 h gave an emerald green suspension and a Ni
22
mirror on the reactor walls. Filtration of this suspension gave
a mixture of Ni black and a mass of light green/yellowish solid,
which was identified as {NiBr (NCMe) } . Analysis of the
2
2 n
3
1
emerald green filtrate by P NMR spectroscopy showed a
major singlet at 123 ppm, plus very minor resonances at 135,
95, and ca. 45 ppm.
The above filtrate was cooled and filtered to remove more of
{NiBr (NCMe) } in addition to a few deep-red crystals,
2
2 n
which were revealed by XRD analysis to be cis-(i-
23
Pr PH) NiBr . Evaporation of the supernatant gave a green
2
2
2
oil, which was washed with toluene and analyzed by NMR
3
1
(CD CN, Figure S151). The P NMR spectrum of this
3
1
sample showed the expected singlet at 123 ppm, whereas its H
phosphinite 1a into BrP(i-Pr) , and this might be more
reactive for transforming 2a-NCMe into 4.
NMR spectrum showed two components, the minor one being
identified as 2-Et-1-naphthol and the major one displaying the
characteristic signals for the P(i-Pr)2 moiety and the Et
substituent in addition to only 5 resonances in the aromatic
region (instead of 6 that would be expected for a
2
9
To test the above possibility, we prepared BrP(i-Pr)2 and
heated it with independently prepared 2a-NCMe (MeCN, 160
3
1
°C, 1 h). The P NMR spectrum of the resulting red mixture
showed complete disappearance of the starting material and
formation of the anticipated AB signals of 4 as the major
component of the mixture (Figure S146). This result supports
the putative mechanism shown in Scheme 12. We speculate
monosubstituted naphthol derivative). Adding Et O to this
NMR sample afforded colorless crystals that were identified by
2
XRD analysis as 2-Et-8-(i-Pr P(O))-1-naphthol (compound 5
2
in Scheme 13), cocrystallized with 1/2 molecule of 2-Et-1-
naphthol itself. It should be mentioned that we also obtained
crystals for 5·HBr (Figure S189).
Scheme 12. Postulated Mechanism for Formation of 4
Scheme 13. Tandem C−H Nickelation/C−P
a
Functionalization at C8−H of 1d
a
For molecular diagrams of (i-Pr PH) NiBr and 5·(2-Et-1-
2
2
2
naphthol) , see Figures S187 and S188.
0
.5
that the C−P bond formation step involves a nucleophilic
attack by the Ni-bound aryl moiety on the P nucleus of the
coordinated BrP(i-Pr) , but other pathways can also be
The question arises whether the 31P resonance at 123 ppm
detected for the side-product of the high temperature reaction
of 1d represents the phosphine oxide 5 or its Ni complex. To
shed some light on this question, we repeated the reaction of
1d with {(i-PrCN)NiBr } (1:1; MeCN, 160 °C, 1h), added 2
2
envisaged. It should be added that we are not aware of a
precedent for the formal insertion of a phosphenium fragment
into a Ni-aryl bond as shown in Scheme 12, but a closely
related inverse of this reactivity has been observed previously.
Indeed, a number of reports have documented the extrusion of
2
n
equiv of PPh to the crude reaction mixture, and then recorded
3
G
DOI: 10.1021/acs.organomet.9b00660
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Organometallics
Article
3
1
its P NMR spectrum. This showed only the peak at 123 ppm
and no new peak for free PPh , which implies the in situ
3
formation of the tetrahedral (and NMR-silent) (PPh ) NiBr
3
2
2
from the reaction of free NiBr with added PPh . We infer,
2
3
therefore, that the phosphine oxide 5 generated in this reaction
is not Ni-bound. Moreover, solubility tests showed that 5 is
soluble in MeCN but insoluble in toluene; the same pattern of
solubility was found for the unidentified species generated
3
1
from the reaction of 1a (Scheme 11) and represented by a P
singlet at 121 ppm. The latter has also been analyzed by GC−
MS, thus allowing us to identify it as 8-(i-Pr P(O))-1-
2
naphthol.
We propose, therefore, that the formation of the phosphine
oxides discussed above, 5 from 1d and the unidentified species
in Scheme 11, involves C−H nickelation at C8, followed by the
+
formal insertion of a “[i-Pr P] ” into the C−Ni bond. The 7-
2
membered nickelacycles present in the resulting species would
likely be thermally unstable and prone to decomposition. The
main aspect that still remains obscure is how the phosphinite
moiety at C1 is transformed into (i-Pr PH) NiBr (Scheme
2
2
2
1
4).
Figure 3. Side views of the molecular diagrams for complexes 2a
(
top), 2b (middle), and 2c (bottom). Thermal ellipsoids are shown at
Scheme 14. Postulated Mechanism for Formation of 5
the 50% probability level; hydrogens and P-substituents are omitted
for clarity.
The data in Table 1 also show fairly narrow ranges for the
bond distances C−Ni (1.908−1.921(2) Å) and P−Ni
(
2.099(1) − 2.111(1)), and also for the C−Ni−P bite angles
82°−83°); evidently, the different electronic character of the
(
naphthol substituents appears to have little or no impact on
these parameters. The Ni−Br bonds also showed a fairly
narrow range of distances in complexes 2a, 2c, and 2e: 2.365−
2
.398 Å over all 14 bonds trans or cis to the C−Ni bonds. The
outlier in this category is complex 2b, the only “flat” dimer not
generated by a symmetry element, which shows greater
differences for the Ni−Br distances trans or cis to Ni−C
bond: 2.342 vs 2.413 Å; 2.402 vs 2.375 Å respectively.
2
4
Solid State Structures of Dimers and Complex 4.
One structure that justifies some additional discussion here
is that of 2f (Figure 4), the naphthyl phosphinite adduct of the
cyclometalated complex derived from 1f, because it can help
rationalize the C3/C1 regioselectivity observed in the C−H
nickelation of 2-naphthyl phosphinite 1e. The solid state
structure of 2f displays a significantly acute trans angle for P−
The solid state structures of the dimeric complexes 2a, 2b, 2c,
and 2e (Figure 3) share some of the main features found in the
structures of the analogous dimeric complexes derived from
5
phenyl phosphinites. Thus, the Ni centers in all dimers adopt
1
4
a geometry that is very close to square planar, with τ values
4
ranging from 0.05−0.07 for dimers sitting on an inversion
center (2c and 2e) and 0.08−0.13 for those not generated by a
symmetry operation (2a and 2b). However, the Ni−μ-Br−Ni
angle in 2a was found significantly smaller than the others
Ni−Br (156°), a tetrahedral distortion with a τ value of 0.22,
4
and a naphthalene ring that bends out of the ideal plane
around Ni to give a C10−C1−Ni−Br dihedral of ca. 47° (as
opposed to an aromatic plane twisted by less than 10° in
similar dimeric compounds).
(
85−87° vs <92°), which translates into a noncoplanarity of
the two halves of the dimer (Table 1).
We believe that the tetrahedral distortion referred to above
serves the purpose of minimizing any steric contact of the C8−
H moiety of the rigid naphthalene ring with the ligand cis to
C1−Ni (μ-Br for 2f and P for 2f-L). Moreover, it is reasonable
to conclude that this steric hindrance would lead to a higher
energy barrier for the nickelation of 1e at C1−H, thus
explaining the observed preference for nickelation at C3−H.
Finally, the structure of the bis-phosphine/phosphinite
complex 4 is worth discussing because the bidentate ligand
creates a 6-membered chelating environment around Ni.
Although the P1−Ni1−P2 bite angle of 94° is close to the ideal
value, this brings about a significant tetrahedral distortion with
Indeed, the hinge angle between the two halves (the
dihedral angle Ni1−Br1−Br2−Ni2) was found to be ca. 140°
with 2a, which strongly deviates from the 180° observed in
symmetric structures 2c and 2e, and from the ca. 177°
observed in 2b. The two Ni centers in 2a are thus brought
closer to each other with a Ni−Ni distance of less than 3.3 Å,
shorter than the Ni−Ni distance of 3.4 Å in the planar
complexes. These features have already been observed in
5
cyclometalated phenyl phosphinite complexes of Ni and
cyclometalated phosphines of Pd; in the case of Ni, this
bent” conformation is thought to be more stable in solution
25
“
than the planar one observed in crystallized centrosymmetrical
complexes.
a τ of ca. 0.29, and the naphthalene ring is pushed out of the
mean plane around Ni by 46° (Figure 5).
4
H
DOI: 10.1021/acs.organomet.9b00660
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Organometallics
Article
Table 1. Selected Structural Parameters, Bond Distances (Å), and Bond Angles (°) for Cyclonickelated Dimers
a
a
space group
Ni−C
Ni−P1
trans-Ni−Br
cis-Ni−Br
C−Ni−P1
Br−Ni−L
τ4
2
a
Pca21
1.914(5)
2.1050(14)
2.1031(15)
2.1006(15)
2.1028(14)
2.1063(7)
2.1105(7)
2.1036(11)
2.1062(11)
2.0992(6)
2.0872(5)
2.3868(9)
2.3975(9)
2.3810(9)
2.3819(9)
2.3854(9)
2.4133(4)
2.3751(5)
2.3642(7)
2.3714(7)
2.390
81.8
81.8
82.0
82.1
83.1
82.1
82.1
82.6
82.8
80.7
87.0
87.5
87.2
86.9
86.9
86.4)
87.4
87.4
86.9
88.3
0.098
0.126
0.114
0.116
0.101
0.080
0.074
0.054
0.052
0.224
1
1
1
.908(5)
.911(5
.917(5)
2.3818(10)
2.3853(10)
2.3978(9)
2.34241(4)
2.4021(4)
2.3685(8)
2.3647(7)
2.3862(4)
2.3880(3)
2
b
c
Pbca
1.908(2)
.915(2)
1.912(4)
.914(4)
1
2
P1
̅
1
2
2
e
f
P2 /n
1
1.921(2)
1.9232(16)
P2 /n
1
2.408
a
cis and trans positions are relative to the Ni−C bond.
significantly longer than those in trans-(phosphinite) NiBr
2
2
complexes characterized throughout this study.
CONCLUSION
■
This study has established that phosphinites derived from 1-
and 2-naphthol undergo C−H nickelation when treated with
II
the Ni precursor {(i-PrCN)NiBr } . When these reactions are
2
n
conducted in the presence of Et N, the cyclonickelated
3
products can be isolated in the form of bromo-bridged dimers
or adducts of either acetonitrile or the phosphinite ligand itself.
Experimentation allowed us to optimize these reactions as a
function of phosphinite:Ni:Et N molar ratios, reaction temper-
3
ature, and also the electronic properties of substituents placed
at the para position of 1-naphthol. The results of these studies
showed that reaction temperature has a great influence on C−
H nickelation rates. For instance, the 2-naphthyl phosphinite
1e is quantitatively converted to the dimeric cyclonickelated
complex 2e in 1 h at 160 °C, whereas the analogous reaction at
Figure 4. Side view of the molecular diagram for complex 2f. Thermal
ellipsoids are shown at the 50% probability level; hydrogens and P-
substituents are omitted for clarity.
80 °C requires 60 h.
Another major issue that was addressed in this study was the
regioselectivity of C−H nickelation in our system. Of the two
potential C−H sites in 1- and 2-naphthyl phosphinites not
bearing substituents in the ortho positions, the favored site for
cyclonickelation is C2 (not C8) with 1-naphthyl phosphinite
and C3 (not C1) in 2-naphthyl phosphinite. It is also
important to emphasize that a 2-naphthyl phosphinite bearing
a Me substituent at the C3 position can undergo nickelation at
the alternative C1−H site at the same temperature (albeit
more sluggishly), whereas blocking the favored site in 1-
naphthyl phosphinite by an alkyl substituent at the C2 position
does not facilitate cyclonickelation at C8.
The observation of exclusive nickelation at the C2 site of 1-
naphthyl phosphinites is in contrast to the regioselectivity of 1-
naphthyl metalation-functionalization with other metals. With
Rh, for instance, these substrates react preferentially at C2, but
Figure 5. Molecular diagram for complex 4. Thermal ellipsoids are
shown at the 50% probability level; hydrogens are omitted for clarity.
7
metalation also occurs to some extent at C8. We speculate
The Ni1−P1 distance of 2.1247(5) Å is longer than in the
corresponding ortho-nickelated phosphinites, but still much
shorter than the Ni-phosphinite distances of ≥ 2.23 Å observed
in L NiBr complexes featuring non cyclonickelated phosphin-
ites; this is presumably due to the chelate effect in 4. Similarly,
the Ni1−P2 distance of 2.1767(5) Å is longer than P1−Ni1,
but still shorter than the corresponding Ni−P distances of ca.
that the observed inertness of the C8 site toward nickelation
can be attributed to two factors. First, the shorter Ni(II) radius
(relative to Rh(III)) likely results in a Ni−C8 distance that
would be longer than optimal for initiating the C→Ni
2
2
6
interaction and the ensuing deprotonation step. Alternatively
(or additionally), the putative 6-membered nickelacycle
intermediate that would result from C−H nickelation at C8
might be thermodynamically less stable (especially at high
temperatures) relative to the 5-membered metalacyclic
transition state that leads to the observed products 2a−2c.
Perhaps the most unexpected result of the present study has
been the serendipitous discovery of a tandem C−P
2
.23−2.33 Å seen for monodentate (i-Pr) PPh; it is also
2
comparable to the Ni−P distances in cis-(diphosphine)NiX
2
complexes (2.137−2.176 Å). The two cis Ni−Br bonds were
found to be 2.3390(3) and 2.3405(3) Å, and thus not
significantly different; on the other hand, these distances are
I
DOI: 10.1021/acs.organomet.9b00660
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
functionalization reaction that leads to the “insertion” of a [i-
solution cooled to −35 °C for 3f-L; from slow diffusion of pentane
+
+
into an Et O solution at −35 °C for 2g.
Pr P] or [i-Pr P(O)] moiety into the Ni−C site generated by
2
2
2
Synthesis of the Dimers Derived from Naphthols. To a
solution of the desired naphthol (2.00 mmol) in 20 mL dry THF was
cyclonickelation of the phosphinites derived from 1-naphthol
or 2-Et-1-naphthol, respectively. In the first case, the
functionalization requires conducting the C−H nickelation at
added 1.10 equiv Et N (2.20 mmol, 307 μL), followed by 1.05 equiv
3
ClP(i-Pr) (2.10 mmol, 334 μL); salt precipitation started almost
2
high temperatures (160−200 °C) and in the absence of Et N.
3
instantaneously. The mixture was stirred at room temperature for 0.5
The available mechanistic information indicates that the C−P
31
to 4 h until reaction was complete (monitoring by P NMR). The
bond formation in this case proceeds via a nucleophilic attack
solvent was then removed under vacuum, and the residues were
by the Ni−C moiety on in situ generated BrP(i-Pr) . This C−
extracted with Et O (3 × 15 mL) and evaporated to yield a colorless
2
2
P functionalization reaction product provides further support
for the conclusions we have drawn from our earlier studies,
namely: (a) C−H nickelation can take place in the absence of
external base, and (b) HBr generated in situ in the C−H
nickelation step can leave the coordination sphere of the Ni
center and linger in the reaction medium long enough to allow
it to react with other species, including H/D exchange with the
solvent.
to pale yellow oil, to which was added 15 mL dry MeCN, 1.2 equiv
{
(i-PrCN)NiBr } (2.40 mmol, 691 mg) and 1.2 equiv Et N (2.40
2
n
3
mmol, 335 μL). The brownish-green homogeneous mixture was
stirred at 80 °C until the reaction was complete (monitored by the
3
1
disappearance of the P signal for the starting material at ca. 135
ppm). The solvent was then removed under vacuum, and the residues
were extracted with toluene through filtration on Celite. The filtrate
was evaporated under vacuum, the residues were extracted into a few
mL Et O (sonication), hexanes added to precipitate the product,
2
A more complex “insertion”-type C−P functionalization
occurs during the high temperature C−H nickelation of the
phosphinite derived from 2-Et-1-naphthol. In this case, the
followed by filtration and washing with a minimum of hexanes to
complete removal of unreacted material/toluene. The solid was dried
under vacuum to yield an orange powder. Single crystals were
obtained from slow evaporation in Et O under N .
“insertion” takes place at C8 and the product is 2-Et-8-(i-
2
2
P
C
{
(κ ,κ -1-OP(i-Pr) -naphth-2-yl)Ni(μ-Br)} (2a). Yield: 587 mg
2
2
Pr P(O))-1-naphthol, 5. A related though not identical side-
2
1
of an orange powder (0.738 mmol, 74%). H NMR (500 MHz, 20 °C,
CD CN) δ 1.37 (dd, 6H, CH(CH )(CH ), J = 7.0, J = 14.9),
.50 (dd, 6H, CH(CH )(CH ), J = 7.2, J = 17.6), 2.55 (oct,
reaction also takes place during the high temperature C−H
nickelation of 1-naphthyl phosphinite, but the product of this
insertion at C8 is a minor component of the final mixture.
Future investigations will aim to improve our understanding
of these interesting functionalization reactions. We will also
explore the potential reactivities of the cyclonickelated
compounds described herein for oxidation-induced C−
heteroatom functionalization reactions. These studies will
draw inspiration from recently reported model systems based
3
3
3
3
3
HH
HP
3
3
1
2
7
3 3 HH HP
3
2
3
H, CH(CH ) , J ≈ J = 7.2), 7.23 (d, 1H, C4 −H, J = 8.3),
3
2
HH
HP
Ar
HH
3
4
.33 (dd, 1H, C3 −H, J = 8.5, J = 1.3), 7.36−7.40 (m, 2H,
Ar
HH
HP
C6 −H and C7 −H), 7.72−7.78 (m, 1H, C5 −H), 7.87−7.92 (m,
Ar
Ar
Ar
1
3
1
1H, C8 −H). C{ H} NMR (125.7 MHz, 20 °C, CD CN) δ 16.82
Ar
3
2
(d, 2C, CH(CH
)(CH ), JCP = 2.0), 18.43 (d, 2C, CH(CH )(CH ),
3
3
3
3
2
1
JCP = 2.8), 29.14 (d, 2C, CH(CH )(CH ), J = 28.8), 120.28 (d,
3
3
CP
4
4
1
C, C4 −H, J = 1.6), 121.54 (d, 1C, Cquat, J = 12.5), 122.50 (d,
Ar
CP
CP
III
1C, C8 −H), 125.69 (s, 2C, C6 −H and C7 −H), 127.70 (s, 1C,
on NCN-type pincer-Ni complexes that promote C−N, C−
Ar
Ar
Ar
2
26
C5 −H), 127.68 (d, 1C, C2 −Ni, J = 34.7), 134.03 (s, 1C, C ),
Ar
Ar
CP
quat
O, and C−halide bond formation reactions.
3
3
1
1
34.87 (d, 1C, C3 −H, J = 2.7), 161.95 (d, 1C, C1 −OP, J
=
Ar
CP
Ar
CP
3
1
1
2.6). P{ H} NMR (202.4 MHz, 20 °C, CDCl ) δ 195.77. Anal.
3
EXPERIMENTAL SECTION
Calc. for C H Br Ni O P : C, 48.30; H, 5.07. Found: C, 47.73; H,
■
32 40 2 2 2 2
5
.00; N, 0.06.
General Considerations. All manipulations were carried out
under a nitrogen atmosphere using standard Schlenk techniques and
an inert-atmosphere glovebox. The reactions conducted in acetonitrile
at temperatures above its boiling point (120−200 °C) were carried
out in a conductively heated, sealed vessel autoclave with a reaction
volume of ca. 5 mL (Anton-Paar Monowave 50). The heating
program allowed the reaction mixtures to rapidly attain the target
temperature and maintain it for the desired reaction time. Solvents
were dried by passage over a column of activated alumina, collected
under nitrogen, and stored over 3 Å molecular sieves. Triethylamine
P
C
{
(κ ,κ -4-MeO-1-OP(i-Pr) -naphth-2-yl)Ni(μ-Br)} (2b). Yield:
2
2
1
7
21 mg of an orange powder (0.842 mmol, 84%). H NMR (500
3
MHz, 20 °C, CD CN) δ 1.36 (dd, 6H, CH(CH )(CH ), J = 7.0,
3
3
3
HH
3
3
3
JHP = 14.9), 1.49 (dd, 6H, CH(CH )(CH ), J = 7.2, J = 17.6),
3
2
3
HH
HP
3
27
2.52 (oct, 2H, CH(CH ) , J ≈ J = 7.2), 3.93 (s, 3H, C4 −
3
2
HH
HP
Ar
OCH ), 6.69 (s, 1H, C3 −H), 7.35−7.45 (m, 2H, C6 −H and
3
Ar
Ar
3
4
3
C7 −H, J ≈ 7.0, J ≈ 1.6), 7.81 (dm, 1H, C8 −H, J = 7.6),
Ar
HH
HH
Ar
HH
3
13
1
8
.03 (dm, 1H, C5 −H, J = 7.6). C{ H} NMR (125.7 MHz, 20
Ar
HH
2
°
C, CD CN) δ 17.05 (d, 2C, CH(CH )(CH ), J = 2.0), 18.69 (d,
3 3 3 CP
2
1
2
C, CH(CH )(CH ), J = 2.7), 29.36 (d, 2C, CH(CH )(CH ), J
was dried over CaH . Synthesis of the nickel precursor {(i-
3
3
CP
3
3
CP
2
3
=
3
1
28.9), 56.04 (s, 1C, C4 −OCH ), 113.30 (d, 1C, C3 −H, J
=
PrCN)NiBr } used throughout this study has been described
Ar
3
Ar
CP
2
n
4
2
8
.0), 121.89 (d, 1C, C , J = 12.7), 122.38 (s, 1C, C5 −H),
previously. 1-Naphthol-d8 was purchased from CDN Isotopes,
whereas other reagents were purchased from Sigma-Aldrich or Fisher
Scientific and used without further purification.
quat
CP
Ar
22.72 (s, 1C, C8 −H), 125.18 (s, 1C, C6 −H), 125.69 (s, 1C,
Ar
Ar
2
C
), 126.50 (s, 1C, C7 −H), 124.18 (d, 1C, C2 −Ni, J = 35.2),
quat
Ar
Ar
CP
4
1
148.71 (d, 1C, C4 −OCH , J = 2.6), 156.38 (d, 1C, C1 −OP,
The NMR spectra were recorded at 500 MHz ( H), 125.72 MHz
Ar
3
CP
Ar
3
31 1
(13
31
J
= 12.3). P{ H} NMR (202.4 MHz, 20 °C, CDCl ) δ 193.60.
C), and 202.4 MHz ( P). Chemical shift values are reported in
C
P
3
1
ppm (δ) and referenced internally to the residual solvent signals ( H
Anal. Calc. for C34
H44Br Ni O P : C, 47.71; H, 5.18. Found: C,
2 2 4 2
and 13C: 1.94 and 118.26 ppm for CD CN; 7.26 and 77.16 for
47.19; H, 5.18; N, 0.12.
{(κ ,κ -4-Cl-1-OP(i-Pr)
mg of an orange powder (0.767 mmol, 77%). H NMR (500 MHz, 20
3
3
1
P
C
CDCl ; 7.16 and 128.06 for C D ) or externally ( P: H PO in D O,
-naphth-2-yl)Ni(μ-Br)} (2c). Yield: 633
2 2
3
6
6
3
4
2
1
δ = 0). J coupling values are given in Hz. The NMR spectroscopic
3
3
data for the dimers correspond to the monomeric NCCD adducts in
°C, CD
15.1), 1.50 (dd, 6H, CH(CH )(CH ), JHH = 7.2, JHP = 17.8), 2.56
3 3
3
CN) δ 1.37 (dd, 6H, CH(CH )(CH ), JHH = 7.0, JHP =
3
3
3
3
3
CD CN. The elemental analyses were performed by the Laboratoire
3
3
2
4
́
(oct, 2H, CH(CH ) , J ≈ J = 7.2), 7.36 (d, 1H, C3 −H, J
d’Analyse Elementaire, Dep
Montreal.
́
artement de Chimie, Universite
́
de
3
2
HH
HP
Ar
HH
3 3 4
= 0.9), 7.47 (ddd, 1H, C7Ar−H, JHH = 8.3, JHH′ = 7.6, JHH = 1.4),
3 3 4
Single crystals of the structurally characterized complexes were
7.53 (tm, 1H, C6Ar−H, JHH = 8.2, JHH′ = 7.6, JHH = 1.4), 7.94 (dm,
3 3
grown as follows: by slow evaporation of an Et O solution under inert
1H, C8Ar−H, JHH = 8.4), 8.07 (dm, 1H, C5Ar−H, JHH = 8.4).
2
1
3
1
atmosphere for the dimeric complexes 2a, 2b, 2c, 2e and 2f; from hot
acetonitrile for 2e-NCMe, 3a, 3d, 3f, 3g, and 4; from an acetonitrile
solution cooled to −35 °C for (i-Pr PH) NiBr ; from a toluene
C{ H} NMR (125.7 MHz, 20 °C, CD
3
CN) δ 17.15 (d, 2C,
2
2
CH(CH )(CH ), J = 2.2), 18.74 (d, 2C, CH(CH )(CH ), J
=
3
3
CP
3
3
CP
1
2.6), 29.64 (d, 2C, CH(CH )(CH ), J = 28.8), 122.54 (d, 1C, Cquat
2
2
2
3
3
CP
J
DOI: 10.1021/acs.organomet.9b00660
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
or C4 −Cl, J = 3.1), 122.66 (d, 1C, Cquat, 4J = 12.2), 123.70 (s,
4
room temperature, kept in a fridge at −10 °C for 4 h to induce
gradual crystallization, and subsequently kept at −35 °C overnight.
The resulting yellow crystals were isolated and washed with cold
MeCN (2 × 2.5 mL) and dried under vacuum. Yield: 168 mg of
yellow crystals (383 μmol, 77%).
Ar
CP
CP
1
1
1
1
2
4
C, C8 −H), 124.73 (s, 1C, C5 −H), 127.01 (s, 1C, C7 −H),
Ar
Ar
Ar
2
27.28 (s, 1C, C6 −H), 128.48 (d, 1C, C2 −Ni, J = 33.7),
Ar
Ar
CP
3
30.71 (s, 1C, C or C4 −Cl), 135.31 (d, 1C, C3 −H, J = 2.5),
quat
Ar
Ar
CP
3
31
1
61.66 (d, 1C, C1 −OP, J = 12.5). P{ H} NMR (202.4 MHz,
Ar
CP
0 °C, CDCl ) δ 196.48. Anal. Calc. for C H Br Cl Ni O P : C,
Method B. 200 mg (250 μmol) of 1e containing ca. 2−5% w/w
3
32 38
2
2
2
2 2
4.45; H, 4.43. Found: C, 44.57; H, 4.49.
residual toluene were suspended in 10 mL Et O. Addition of 130 μL
2
P
C
{
(κ ,κ -2-OP(i-Pr) -naphth-3-yl)Ni(μ-Br)} (2e). This compound
MeCN (2.5 mmol, 10 equiv) turned the orange suspension yellow.
The mixture was stirred at room temperature for 30 min and the
residues were isolated by cannula filtration, washed with 2 × 5 mL
2
2
required a modified workup procedure for optimal yields. After
evaporation of the crude reaction mixture, 25 mL toluene was added,
the mixture stirred at 80 °C for 30 min, followed by filtration (while
hot), evaporation, and washing of the solids with Et O and hexanes.
Yield: 431 mg of an orange powder (0.542 mmol, 54%). The H
NMR of the final powder showed that it still contained toluene (ca.
−5% w/w). Even after extended drying in vacuo at 80 °C, trituration
in hexanes, and trituration in Et O or Et O:CH Cl 1:1, traces of
Et
crystalline material (396 μmol, 79%). Anal. Calc. for C18
C, 49.25; H, 5.28; N, 3.19. Found: C, 49.13; H, 5.44; N, 3.15.
O, and dried under vacuum. Yield: 174 mg of yellow micro-
2
H
23BrNiOP:
2
1
P
Cα Cγ
(
κ ,κ ,κ -2-CH CHCH-1-naphtyl-OP(i-Pr) )NiBr (2g). To
2
2
a solution of 600 mg 1g (2.00 mmol) in 10 mL acetonitrile were
added 575 mg {(i-PrCN)NiBr } (2.00 mmol, 1.00 equiv) and 558
2
2
n
2
2
2
2
μL Et3N (4.00 mmol, 2.00 equiv), and the green mixture was stirred
overnight at room temperature The resulting red mixture was
evaporated, the residues were redissolved in 6 mL THF, and 10 mL
hexanes added to induce precipitation. Filtration and evaporation gave
toluene were still found, although it decreased to ca. 1% w/w (5 mol
vs. Ni). The elemental analysis of this solid showed fair purity.
Conversion into the MeCN adduct removed all toluene and resulted
%
1
in higher NMR purity. H NMR (500 MHz, 20 °C, CD CN) δ 1.33
3
3
3
residues, which were treated with 10 mL Et O, filtered and
(
dd, 6H, CH(CH )(CH ), J = 7.0, J = 15.0), 1.48 (dd, 6H,
CH(CH )(CH ), J = 7.2, J = 17.6), 2.50 (oct, 2H, CH(CH ) ,
2
3
3
HH
HP
3
3
evaporated. The resulting residues were dissolved in 2 mL Et O,
2
3
3
HH
HP
3 2
3
2
diluted with 2 mL pentane, filtered, and kept at −35 °C overnight.
The mixture of orange crystals and other precipitate was evaporated,
washed with cold pentane (2 × 2 mL), and dried under vacuum.
NMR characterization showed some impurities. Elemental analysis
JHH ≈ J = 7.1), 7.01 (s, 1H, C1 −H), 7.25 (ddd, 1H, C6 −H,
HP
Ar
Ar
3J
8
(
(
2
3
4
3
= 8.1, J
= 6.8, J = 1.3), 7.32 (ddd, 1H, C7 −H, J
=
HH
HH′
HH
Ar
HH
3
4
3
.1, J
= 6.8, J = 1.3), 7.61 (d, 1H, C8 −H, J = 8.1), 7.66
HH′
HH
Ar
HH
13
3
1
s, 1H, C4 −H), 7.71 (d, 1H, C1 −H, J = 8.1). C{ H} NMR
Ar
Ar
HH
1
2
was not performed on this sample. H NMR (500 MHz, 20 °C,
125.7 MHz, 20 °C, CDCl ) δ 17.18 (d, 2C, CH(CH )(CH ), J
=
3
3
3
CP
CD CN) δ 0.88 (dd, 3H, P[CH(CH )(CH )][CH(CH )(CH )],
2
3
3
3
3
3
.0), 18.79 (d, 2C, CH(CH )(CH ), JCP = 2.7), 29.54 (d, 2C,
3
3
3
3
JHH = 7.1, J = 13.6), 0.99 (dd, 3H, P[CH(CH )(CH )][CH-
CH )(CH )], J = 7.2, J = 17.1), 1.24 (dd, 3H, P[CH(CH )-
1
4
HP
3
3
3
CH(CH )(CH ), J = 29.2), 104.98 (d, 1C, C1 −H, J = 13.1),
3
3
CP
Ar
CP
3
(
3
3
HH
HP
3
1
24.18 (s, 1C, C6 −H), 126.14 (s, 1C, C7 −H), 127.03 (s, 1C,
Ar
Ar
3
3
4
(CH
3
)][CH(CH
3
)(CH
)][CH(CH
(hept, 1H, P[CH(CH ][CH(CH
P[CH(CH ) ][CH(CH ) ], J ≈ J = 7.7), 3.16−3.26 (m, 2H,
3
)], JHH = 7.0, JHP = 14.7), 1.55 (dd, 3H,
C8 −H), 127.73 (s, 1C, C5 −H), 130.36 (d, 1C, C , J = 2.1),
Ar
Ar
quat
CP
3
3
2
P[CH(CH
3
)(CH
3
)(CH )], JHH = 7.2, JHP = 17.4), 2.32
3 3
1
34.60 (s, 1C, C ), 138.10 (d, 1C, C3 −Ni, J = 36.0), 138.99
quat
Ar
CP
3
3
3
3
)
3
2
3 2
) ], JHH = 7.1), 2.47 (oct, 1H,
(
d, 1C, C4 −H, J = 2.7), 166.62 (d, 1C, C1 −OP, J = 12.1).
Ar
CP
Ar
CP
3
2
3
1
1
3
2
2
HH
HP
P{ H} NMR (202.4 MHz, 20 °C, CDCl ) δ 197.33. Anal. Calc. for
3
Ar−C H(Ni) and Ar−C H(Ni)-C H = C(Ha)(Hb) cis to C H), 4.36
dd, 1H, Ar−C H(Ni)-C H = C(Ha)(Hb) trans to C H), J = 7.2,
α
α
β
β
C H Br Ni O P : C, 48.30; H, 5.07. Found: C, 48.25; H, 5.21.
3
3
2
{
40
2
2
2 2
(
P
C
α
β
β
HH
(κ ,κ -3-Me-2-OP(i-Pr) -naphth-1-yl)Ni(μ-Br)} (2f). To a
2
2
2
J
= 4.3), 4.95 (ddd, 1H, Ar−C H(Ni)-C H=CH ), 7.13 (d, 1H,
HH′
α
β
2
solution of 274 mg 3-Me-2-naphthyl-OP(i-Pr) (1.00 mmol) in 5
3
2
C3 −H, J = 8.4), 7.22−7.28 (m, 2H, C4 −H and C6 −H), 7.32
Ar
HH
Ar
Ar
mL MeCN were added 345 mg {(i-PrCN)NiBr } (1.20 mmol, 1.2
3
3
2
n
(
(
t, 1H, C7 −H, J = 7.4), 7.59 (d, 1H, C5 −H, J = 8.1), 8.19
Ar
HH
Ar
HH
equiv) and 167 μL Et N (1.20 mmol, 1.2 equiv). The resulting dark
3 13 1
3
d, 1H, C4 −H, J = 8.3). C{ H} NMR (125.7 MHz, 20 °C,
Ar
HH
greenish solution that contained a red precipitate of 3f was heated at
2
CDCl ) δ 15.72 (d, 1C, P[CH(CH )(CH )][CH(CH )(CH )], J
3
3
3
3
3
CP
1
20 °C for 16 h in the Monowave 50. The crude mixture was cooled
=
1.8), 17.72 (s, 1C, P[CH(CH )(CH )][CH(CH )(CH )]), 17.99
3 3 3 3
at −35 °C overnight resulting in crystallization of unreacted 3f and
2
(
1
d, 1C, P[CH(CH )(CH )][CH(CH )(CH )], J = 3.6), 18.10 (d,
C, P[CH(CH )(CH )][CH(CH )(CH )], J = 6.3), 29.48 (d, 1C,
3 3 3 3 CP
Et N·HBr. The green supernatant was evaporated, extracted with
2
3
3 3 3 3 CP
toluene, and the volatiles removed under vacuum at 60 °C. The
1
P[CH(CH ) ][CH(CH ) ], JCP = 26.6), 30.41 (d, 1C, P[CH-
3
2
3 2
orange residues were treated with 3 mL Et O and filtered, and then
1
2
2
(
5
1
CH ) ][CH(CH ) ], J = 15.9), 59.07 (d, 1C, Ar-C H(Ni), J
.5), 77.48 (d, 1C, Ar−C H(Ni)-C H = CH , J = 20.8), 110.92 (d,
C, Ar−C H(Ni)-C H = CH , J = 2.5), 120.62 (d, 1C, C2 −
=
3
2
3
2
CP
α
CP
the dark orange filtrate cooled at −35 °C overnight to give some
orange precipitate. These were removed manually and dried under
vacuum to allow NMR characterization, which showed some
impurities. Elemental analysis was not performed on this sample.
2
α
β
2
CP
3
α
β
2
CP
Ar
3
C H(Ni), J = 6.5), 122.23 (s, 1C, C8 −H), 122.61 (s, 1C, C4 −
α
CP
Ar
Ar
5
H), 126.03 (d, 1C, Cquat, J = 2.9), 126.61 (s, 2C, C6 −H and
CP
Ar
1
H NMR (500 MHz, 20 °C, CD CN) δ 1.24 (dd, 6H, CH(CH )-
3
3
C7 −H), 126.92 (s, 1C, C3 −H), 128.27 (s, 1C, C5Ar−H, hidden
Ar
Ar
3
3
3
(
CH ), J = 7.0, J = 14.7), 1.48 (dd, 6H, CH(CH )(CH ), J
3 HH HP 3 3 HH
under the peak for C D ), 134.46 (s, 1C, C ), 151.41 (s, 1C, C1 −
6
6
quat
Ar
3
6
31 1
=
7.2, J = 17.7), 2.29 (d, 3H, Ar−CH , J = 0.7), 2.44 (oct, 2H,
HP
3
HH
OP). P{ H} NMR (202.4 MHz, 20 °C, CDCl ) δ 199.72.
3
3
2
3
CH(CH ) , J ≈ J = 7.2), 7.21 (ddd, 1H, C6 −H, J = 8.0,
3
2
HH
HP
Ar
HH
Synthesis of Bis-phosphinite-NiBr2 Complexes 3. To a
solution of 2.00 mmol of the desired naphthyl phosphinite in 15
mL CH Cl was added 403 mg of {(i-PrCN)NiBr } (1.40 mmol, 0.7
3
4
JHH′ = 6.8, J = 1.2), 7.28 (s, overlapping with δ 7.29, 1H, C4 −
HH
Ar
3
3
H), 7.29 (ddd, overlapping with δ 7.28, C7 −H, 1H, J = 8.3, J
=
Ar
HH
HH′
2
2
2 n
4
3
6.8, J = 1.4), 7.57 (d, 1H, C5 −H, J = 8.3), 8.19 (d, 1H,
equiv). The resulting dark red mixture was stirred at room
HH
Ar
HH
3
13
1
C8 −H, J = 8.6). C{ H} NMR (125.7 MHz, 20 °C, CDCl ) δ
1
1
temperature for 30 min. The excess NiBr was separated by cannula
Ar
HH
3
2
2
7.22 (d, 2C, CH(CH )(CH ), J = 2.5), 17.60 (s, 1C, Ar-CH3),
8.76 (d, 2C, CH(CH )(CH ), JCP = 2.8), 29.71 (d, 2C,
filtration and the residues extracted with an extra 2 × 15 mL CH Cl .
3
3
CP
2
2
2
The combined extracts were evaporated to give orange to red
brownish powders that were crystallized from hot MeCN, cooled to
room temperature first and then to −10 °C for 3−4 h, and finally
placed overnight in a freezer at −35 °C. The resulting dark red
crystals were washed with cold MeCN (3 × 5−10 mL), and dried
under vacuum. Their purity was established by elemental analysis,
3
3
1
4
CH(CH )(CH ), JCP = 27.5), 123.22 (d, 1C, C3 −Me, JCP
=
3
3
Ar
1
1
1.4), 123.65 (s, 1C, C6 −H), 124.36 (s, 1C, C7 −H), 127.65 (d,
Ar
Ar
2
C, C1 −Ni, J = 36.6), 128.29 (s, 1C, C4 −H), 128.32 (s, 1C,
Ar
CP
Ar
C5 −H), 130.09 (s, 1C, C8 −H), 131.85 (s, 1C, C ), 141.09 (d,
1
Ar
Ar
quat
3
3
31
1
C, C , J = 4.1), 161.65 (d, 1C, C2 −OP, J = 10.1). P{ H}
quat
CP
Ar
CP
3
1
1
NMR (202.4 MHz, 20 °C, CDCl ) δ 189.85.
whereas P and H NMR spectra in CDCl suggested they exist as 2
3
3
P
C
(
κ ,κ -2-OP(i-Pr) -naphth-3-yl)NiBr(NCMe) (1e-NCMe). Meth-
isomers in solution in a ca. 1:9 ratio; we infer that the
centrosymmetric structure is the major isomer while the minor one
is a C2-symmetric structure or else the cis isomer. For instance, in
compound 3f, both isomers have also been detected in the solid state
2
od A. 200 mg (250 μmol) of 1e containing ca. 2−5% w/w residual
toluene were dissolved in a minimum amount of MeCN at 80 °C (ca.
1
2 mL). The resulting yellow solution was slowly cooled down to
K
DOI: 10.1021/acs.organomet.9b00660
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
31P NMR (see Figure S103) at δ 137.10 (major) and 132.45 ppm
trans-{1-naphthyl-d -OP(i-Pr) } NiBr (3a-d ). 1-Naphthol-d
8
7
2 2
2
7
(
minor). In the case of deuterated ligands, the complexes were used as
(152 mg, 1.00 mmol) was converted to the corresponding
phosphinite, and all of the recovered ligand was used to prepare the
title complex. Yield: 348 mg of an orange powder (0.462 mmol, 92%).
powders in H/D scrambling experiments without crystallization.
trans-{1-Naphthyl-OP(i-Pr) } NiBr ·CH CN (3a·CH CN). This
2
2
2
3
3
trans-{2-CH CD -1-naphthyl-OP(i-Pr) } NiBr ·CH CN (3d-d ).
complex cocrystallized with 1 molecule of MeCN per nickel center,
yielding 618 mg of dark red crystals (0.79 mmol, 79%). H NMR
3
2
2 2
2
3
2
1
2
-CH CD -1-naphthol (348 mg, 2.00 mmol) was converted to the
3 2
3
corresponding phosphinite, and all of the recovered ligand was used
to prepare the title complex. Yield: 727 mg of a dark red powder
(0.910 mmol, 91%).
(500 MHz, 20 °C, CDCl ) δ 1.48 (m, 6H, CH(CH )(CH ), J
=
3
3
3
HH
3
6
.3), 1.59 (3, 6H, CH(CH )(CH ), J = 6.3), 2.1.99(br s, 1.5H,
3 3 HH
3
CH CN), 2.84 (hept, 2H, CH(CH )(CH ), J = 7.0, minor), 2.92
3
3
3
HH
3
trans-{3-CD -2-naphthyl-OP(i-Pr) } NiBr (3f-d ). 3-CD -2-
(
hept, 2H, CH(CH )(CH ), J = 7.2, major), 7.40−7.48 (m, 2H,
3
2 2
2
3
3
3
3
HH
3
3
naphthol (322 mg, 2.00 mmol) was converted to the corresponding
phosphinite, and all of the recovered ligand was used to prepare the
title complex. Yield: 681 mg of a red powder (0.881 mmol, 88%).
H/D Scrambling Experiments. In Acetonitrile. Deuterated
C6 −H and C7 −H, J ≈ 6.9), 7.50 (t, 1H, C3 −H, J = 7.9),
7
8
Ar
Ar
HH
Ar
HH
3
3
.59 (d, 1H, C4 −H, J = 8.2), 7.81 (d, 1H, C5 −H, J = 7.2),
.10 (d, 1H, C8 −H, J = 7.5), 8.42 (d, 1H, C2 −H, J = 7.5,
Ar
HH
Ar
HH
3
3
Ar
HH
Ar
HH
3
13
1
major), 8.46 (d, 1H, C2 −H, J = 7.6, minor). C{ H} NMR
(
CH(CH )(CH ), minor), 18.48 (s, 2C, CH(CH )(CH ), major),
1
Ar
HH
complexes (ca. 100 mg) were heated at 80 °C in 2 mL CH CN for
3
125.7 MHz, 20 °C, CDCl ) δ 2.06 (s, 0.5C, CH CN), 18.19 (s, 2C,
3 3
the required time (1 or 3 days). The final mixtures were cooled down
to room temperature and placed overnight in a freezer at −35 °C. The
3
3
3
3
9.26 (s, 2C, CH(CH )(CH ), minor), 19.77 (s, 2C, CH(CH )-
3
3
3
resulting crystals were collected, washed with cold CH CN (2 × 1.5
3
(CH ), major), 28.91 (s, 2C, CH(CH )(CH ), minor), 29.98 (s, 2C,
1
3
3
3
mL), and dried under vacuum. The material was analyzed by H
CH(CH )(CH ), major), 113.78 (s, 1C, C2 −H, minor), 113.95 (s,
1
H), 122.59 (s, 1C, C4 −H), 125.11 (s, 1C, C3 −H, major), 125.3
3
3
Ar
NMR in CDCl , and the integration of the incorporated protons into
3
C, C2 −H, major), 116.53 (s, 1C, CH CN), 122.16 (s, 1C, C8 −
Ar
3
Ar
D positions (if any) was compared to the integration of the methyne
Ar
Ar
in P(CH(CH ) ) to determine the amount of protons at D positions.
3
2 2
(
s, 1C, C3 −H, minor), 125.76 (s, 1C, C7 −H), 126.51 (s, 1C,
Ar
Ar
In Toluene. Deuterated complexes (ca. 100 mg) were heated at 100
C6 −H), 126.60 (s, 1C, C ), 127.78 (s, 1C, C5 −H), 134.79 (s,
1
Ar
quat
Ar
°
C in 2 mL C H CH for the required time (1 or 3 days).
3
1
1
6
5
3
C, C ), 150.84 (s, 1C, C1 −OP). P{ H} NMR (202.4 MHz, 20
quat
Ar
Evaporation of the solvent under a vacuum, redissolution in CH CN
3
°
C, CDCl ) δ 130.37 (s, 1P, minor), 135.65 (s, 1P, major). Anal.
3
at room temperature, filtration, and cooling overnight in a freezer at
−35 °C afforded crystals, which were collected, washed with cold
Calc. for C H Br NNiO P : C, 52.34; H, 5.81; N, 1.80. Found: C,
34
45
2
2 2
5
2.64; H, 5.97; N, 1.75.
CH CN (2 × 1.5 mL), and dried under vacuum. The material was
3
trans-{2-Et-1-naphthyl-OP(i-Pr) } NiBr (3d). Yield: 439 mg of
1
2
2
2
analyzed by H NMR, and the integration of the incorporated protons
1
dark red crystals (0.55 mmol, 55%). H NMR (500 MHz, 20 °C,
CDCl ) δ 1.08 (m, 6H, CH(CH )(CH ), J = 8.0), 1.21 (t, 3H,
Ar−CH CH , J = 7.6), 1.33 (m, 6H, CH(CH )(CH ), J
6
into D positions (if any) was compared to the integration of the
3
3
3
3
HH
methyne in P(CH(CH ) ) to determine the ratio of protons at D
3
2 2
3
3
=
2
3
HH
3
3
HH
positions.
3
P
P
.6), 2.91 (q, 2H, Ar−CH CH , JHH = 7.6), 3.04 (m, 2H,
2
3
cis-(κ ,κ ′-2-P(i-Pr) -1-naphtyl-OP(i-Pr) )NiBr (4). To a sol-
2
2
2
CH(CH )(CH ), J = 7.0, minor), 3.19 (m, 2H, CH(CH )(CH ), J
ution of 260 mg of 1-naphthyl-OP(i-Pr) (1.00 mmol) in 4 mL
3
3
3
3
2
3
=
6.7, major), 7.27 (d, 1H, C3 −H, J = 8.5), 7.43 (t, 1H, C6 −H,
acetonitrile was added 288 mg of {(i-PrCN)NiBr } (0.50 mmol, 0.50
Ar
HH
Ar
2 n
3
3
JHH = 7.4), 7.53 (t, 1H, C7 −H, J = 7.6), 7.56 (d, 1H, C4 −H,
equiv). This gave a red mixture containing an orange precipitate of 3a
which was subsequently heated at 200 °C for 1 h in the Monowave
Ar
HH
Ar
3
3
JHH = 8.5), 7.79 (d, 1H, C5 −H, J = 8.1), 8.33 (d, 1H, C8 −H,
Ar
HH
Ar
3J = 8.3). C{ H} NMR (125.7 MHz, 20 °C, CDCl ) δ 14.76 (s,
13
1
50. The resulting dark red solution was evaporated, and the residues
HH
3
were treated in 6 mL toluene and filtered to remove the insoluble
residues. Evaporation of the filtrate gave a red, sticky material that was
redissolved in 3 mL acetonitrile, filtered and placed in a freezer at −35
1
2
C, Ar−CH CH ), 17.59 (s, 2C, CH(CH )(CH ), minor), 17.74 (s,
2
3
3
3
C, CH(CH )(CH ), major), 17.98 (s, 2C, CH(CH )(CH )), 24.54
3
3
3
3
(s, 1C, Ar-CH CH , minor), 25.67 (s, 1C, Ar-CH CH , major), 29.97
2 3 2 3
°
C for 48 h. The red crystals were isolated and washed with cold
(
m, 2C, CH(CH )(CH ), minor), 31.34 (vt/pt, 2C, CH(CH )(CH ),
3
3
3
3
1
acetonitrile (3 × 1.5 mL) and dried under vacuum to give 56 mg of
JCP = 10.3,major), 123.44 (s, 1C, C8 −H), 123.91 (s, 1C, C4 −H),
1
Ar
Ar
1
crystalline material. H NMR (500 MHz, 20 °C, C D ) δ 1.00−1.14
(
6
6
25.42 (s, 1C, C6 −H), 126.18 (s, 1C, C7 −H), 127.36 (s, 1C,
Ar
Ar
m, 12H, C1 −OP[CH(CH )(CH )] and C2 −P[CH(CH )-
Ar
3
3
2
Ar
3
C3 −H), 127.84 (s, 1C, C ), 127.92 (s, 1C, C5 −H), 131.29 (s,
1
NMR (202.4 MHz, 20 °C, CDCl ) δ 131.50 (s, 1P, minor), 136.10 (s,
1
Found: C, 54.58; H, 6.67; N, 0.05.
trans-{3-Me-2-naphthyl-OP(i-Pr) } NiBr (3f). Yield: 465 mg of
dark red crystals (0.61 mmol, 61%). H NMR (500 MHz, 20 °C,
CDCl ) δ 1.35 (m, 6H, CH(CH )(CH ), J = 6.8), 1.52 (m, 6H,
CH(CH )(CH ), J = 6.8), 2.34 (s, 3H, Ar−CH ), 2.76 (hept, 2H,
CH(CH )(CH ), J = 7.0, minor), 2.84 (hept, 2H, CH(CH )-
3
Ar
quat
Ar
(
CH )] ), 1.40 (dd, 6H, C1 −OP[CH(CH )(CH )] , J = 6.9,
3
1
1
3
2
Ar
3
3
2
HH
C, C ), 133.78 (s, 1C, C ), 149.16 (s, 1C, C1 −OP). P{ H}
3
3
quat
quat
Ar
J
= 16.8), 1.66 (dd, 6H, C2 −P[CH(CH )(CH )] , J = 7.0,
HP
Ar
3
3
3
2
HH
3
3
JHP = 15.7), 2.61 (hept, 2H, C2 −P[CH(CH ) ] , J = 7.0), 2.83
Ar
3
2
2
HH
P, major). Anal. Calc. for C H Br NiO P : C, 54.37; H, 6.34.
36 50 2 2 2
3
2
(
oct, 2H, C1 −OP[CH(CH ) ] , J ≈ J = 7.2), 6.93 (d, 1H,
Ar
3
2
2
HH
HP
3
3
C3 −H, J = 8.2), 7.19 (d, 1H, C4 −H, J = 8.7), 7.21−7.26
Ar
HH
Ar
HH
2
2
2
1
(m, 2H, C6Ar−H and C7Ar−H), 7.46−7.52 (m, 1H, C5Ar−H), 8.03−
13 1
3
8.09 (m, 1H, C8Ar−H). C{ H} NMR (125.7 MHz, 20 °C, C
D ) δ
6 6
3
3
3
HH
1
8.80 (s, 2C, C1 −OP[CH(CH )(CH )] or C2 −P[CH(CH )-
3
Ar
3
3
2
Ar
3
3
3
HP
3
(
CH )] ), 18.86 (s, 2C, C1 −OP[CH(CH )(CH )] or C2 −
3
3
2
Ar
3
3
2
Ar
3
3
HH
3
P[CH(CH )(CH )] ), 20.04 (s, 2C, C1 −OP[CH(CH )(CH )] ),
2
3
3
3
2
Ar
3
3
2
(
CH ), J = 7.2, major), 7.33−7.42 (m, 2H, C6 −H and C7 −H,
3
HH
Ar
Ar
1.00 (s, 2C, C2 −P[CH(CH )(CH )] ), 26.31 (d, 2C, C1 −
3
4
Ar
3
3
2
Ar
JHH ≈ 7.8, J ≈ 1.9), 7.57 (s, 1H, C4 −H), 7.72 (d, 1H, C5 −H,
2
HH
Ar
Ar
OP[CH(CH ) ] , J = 27.7), 34.50 (d, 2C, C2 −P[CH(CH ) ] ,
3
2
2
CP
Ar
3 2 2
3J = 8.0), 7.75 (d, 1H, C8 −H, J = 8.1), 8.51 (s, 1H, C1 −H,),
3
2
HH
Ar
HH
Ar
JCP = 26.5), 122.86 (d, 1C, C4 −H), 122.96 (d, 1C, C8 −H),
Ar
Ar
1
3
1
major), 8.55 (s, 1H, C1 −H,), minor). C{ H} NMR (125.7 MHz,
Ar
126.57 (d, 1C, C3 −H), 127.41 (d, 1C, C6 −H or C7 −H), 128.26
Ar
Ar
Ar
2
0 °C, CDCl ) δ 17.58 (s, 1C, Ar-CH ), 18.01 (s, 2C, CH(CH )-
3
3
3
(s, 1C, C5 −H, hidden under the peak for C D ), 129.12 (s, 1C,
Ar
6
6
(CH ), minor), 18.28 (s, 2C, CH(CH )(CH ), major), 19.12 (s, 2C,
3
3
3
C6 −H or C7 −H), 135.98 (s, 1C, C2 −P), 157.20 (s, 1C, C1 −
Ar
Ar
Ar
Ar
3
1
1
CH(CH )(CH ), minor), 19.67 (s, 2C, CH(CH )(CH ), major),
2
3
3
3
3
OP). P{ H} NMR (202.4 MHz, 20 °C, C D ) δ 29.33 (d, 1P,
6
6
8.56 (s, 2C, CH(CH )(CH ), minor), 29.59 (s, 2C, CH(CH )-
3
3
3
C2 −P, 64.8), 176.77 (d, 1P, C1 −OP, 65.4).
Ar
Ar
(
CH ), major), 114.43 (s, 1C, C1 −H), 124.43 (s, 1C, C6 −H or
3
Ar
Ar
(i-Pr PH) NiBr . To a solution of 288 mg of 2-Et-1-naphthyl-OP(i-
2 2 2
C7 −H), 125.55 (s, 1C, C6 −H or C7 −H), 126.94 (s, 1C, C8 −
Pr) (1.00 mmol) in 4 mL acetonitrile was added 316 mg of {i-
Ar
Ar
Ar
Ar
2
H), 127.05 (s, 1C, C5 −H), 129.10 (s, 1C, C4 −H), 129.60 (s, 1C,
PrCN)NiBr } (1.10 mmol, 1.10 equiv). The resulting dark greenish
Ar
Ar
2 n
C
), 130.14 (s, 1C, C ), 132.74 (s, 1C, C ), 152.35 (s, 1C,
solution that contained a red precipitate of 3d was heated at 160 °C
for 1 h in the Monowave 50. The resulting emerald green solution was
left to stand at room temperature for 1 h during which time a pale
green precipitate formed. The solution was separated by filtration and
quat
quat
quat
31
1
C2 −OP). P{ H} NMR (202.4 MHz, 20 °C, CDCl ) δ 129.30 (s,
1
C, 53.23; H, 6.04. Found: C, 53.36; H, 6.35.
Ar
3
P, minor), 134.55 (s, 1P, major). Anal. Calc. for C H Br NiO P :
34 46 2 2 2
L
DOI: 10.1021/acs.organomet.9b00660
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
kept overnight in a −35 °C freezer to give red crystals and some
Complementary Tool in the Total Synthesis of Complex Natural
Products. Chem. - Eur. J. 2012, 18 (31), 9452−9474.
additional precipitate {NiBr (MeCN) } . The latter was removed by
2
x n
washing the solid residues with 3 × 2 mL H O, and the water was
(2) (a) Klei, S. R.; Tan, K. L.; Golden, J. T.; Yung, C. M.; Thalji, R.
K.; Ahrendt, K. A.; Ellman, J. A.; Tilley, T. D.; Bergman, R. G. C−H
Bond Activation by Iridium and Rhodium Complexes: Catalytic
Hydrogen−Deuterium Exchange and C−C Bond-Forming Reactions.
In Activation and Functionalization of C−H Bonds; American Chemical
Society, 2004; Vol. 885, pp 46−55. (b) Colby, D. A.; Bergman, R. G.;
Ellman, J. A. Rhodium-Catalyzed C−C Bond Formation via
Heteroatom-Directed C−H Bond Activation. Chem. Rev. 2010, 110
(2), 624−655. (c) Rouquet, G.; Chatani, N. Catalytic Functionaliza-
tion of C(sp2)−H and C(sp3)−H Bonds by Using Bidentate
Directing Groups. Angew. Chem., Int. Ed. 2013, 52 (45), 11726−
11743. (d) Arockiam, P. B.; Bruneau, C.; Dixneuf, P. H. Ruthenium-
(II)-Catalyzed C−H Bond Activation and Functionalization. Chem.
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Palladium-Catalyzed Ligand-Directed C−H Functionalization Reac-
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Yang, Z.; Shi, Z.-J. Organopalladium(iv) chemistry. Chem. Soc. Rev.
2
removed by washing with 3 × 1.5 mL cold acetonitrile. After drying
under vacuum, 44 mg of red crystals were collected. While the crystal
3
1
structure discloses the cis isomer of the complex (with a solid state
P
NMR with δ 30.34 ppm, see Figure S122), the solution NMR of the
complex in C D is rather in accordance with the trans isomer, as
6
6
proven by the correlation between the experimental spectrum and the
v
1
simulation realized with a J
coupling constant of 300−400 Hz. H
P−H
NMR (500 MHz, 20 °C, C D ) δ 1.09 (br s, 12H, CH(CH )(CH )),
6
6
3
3
1
(
.50 (br s, 12H, CH(CH )(CH )), 2.07 (br s, 4H, CH(CH ) ), 3.79
3 3 3 2
v
13
1
br m, 2H, P-H, J = 345). C{ H} NMR (125.7 MHz, 20 °C, C D )
6 6
δ 20.59 (s, CH(CH )(CH )), 21.25 (s, CH(CH )(CH )), 21.98 (br
3
3
3
3
31
1
s, CH(CH ) ). P{ H} NMR (202.4 MHz, 20 °C, C D ) δ 41.74.
3
2
6
6
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.organomet.9b00660.
■
*
S
2
010, 39 (2), 712−733. (g) Sehnal, P.; Taylor, R. J. K.; Fairlamb, I. J.
S. Emergence of Palladium(IV) Chemistry in Synthesis and Catalysis.
Additional synthetic procedures, NMR spectra; addi-
tional ORTEPs/figures and crystallographic details
Chem. Rev. 2010, 110 (2), 824−889.
(3) (a) Castro, L. C. M.; Chatani, N. Nickel Catalysts/N,N′-
Bidentate Directing Groups: An Excellent Partnership in Directed C−
H Activation Reactions. Chem. Lett. 2015, 44 (4), 410−421.
(PDF)
Accession Codes
(b) Gandeepan, P.; Mu
Ackermann, L. 3d Transition Metals for C−H Activation. Chem. Rev.
019, 119 (4), 2192−2452. (c) Beattie, D. D.; Grunwald, A. C.;
̈
ller, T.; Zell, D.; Cera, G.; Warratz, S.;
CCDC 1952151−1952167 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
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
2
Perse, T.; Schaefer, L. L.; Love, J. A. Understanding Ni(II)-Mediated
C(sp3)-H Activation: Tertiray Ureas as Model Substrates. J. Am.
Chem. Soc. 2018, 140, 12602−12610. (d) Roy, P.; Bour, J. R.; Kampf,
J. W.; Sanford, M. S. Catalytically Relevant Intermediates in the Ni-
Catalyzed C(sp2)−H and C(sp3)−H Functionalization of Amino-
quinoline Substrates. J. Am. Chem. Soc. 2019, 141, 17382−17387.
(4) Vabre, B.; Deschamps, F.; Zargarian, D. Ortho Derivatization of
Phenols through C−H Nickelation: Synthesis, Characterization, and
Reactivities of Ortho-Nickelated Phosphinite Complexes. Organo-
metallics 2014, 33 (22), 6623−6632.
AUTHOR INFORMATION
Corresponding Author
E-mail: zargarian.davit@umontreal.ca.
ORCID
■
*
(
5) Mangin, L. P.; Zargarian, D. C−H nickellation of phenol-derived
Davit Zargarian: 0000-0002-0207-7007
phosphinites: regioselectivity and structures of cyclonickellated
Notes
complexes. Dalton Transactions 2017, 46 (46), 16159−16170.
(
6) Mangin, L. P.; Zargarian, D. C−H Nickelation of Aryl
The authors declare no competing financial interest.
Phosphinites: Mechanistic Aspects. Organometallics 2019, 38 (7),
479−1492.
7) Bedford, R. B.; Limmert, M. E. Catalytic Intermolecular Ortho-
1
(
ACKNOWLEDGMENTS
■
The authors gratefully acknowledge financial support provided
by NSERC of Canada (Discovery grants to D. Z.); Centre in
Green Chemistry and Catalysis (CGCC/CCVC, summer
Arylation of Phenols. J. Org. Chem. 2003, 68 (22), 8669−8682.
(8) Satoh, T.; Inoh, J.-i.; Kawamura, Y.; Kawamura, Y.; Miura, M.;
Nomura, M. Regioselective Arylation Reactions of Biphenyl-2-ols,
Naphthols, and Benzylic Compounds with Aryl Halides under
Palladium Catalysis. Bull. Chem. Soc. Jpn. 1998, 71 (9), 2239−2246.
research stipends and travel awards); Universite
graduate scholarships to L. P. M.). We also thank our
colleague, Dr. Pedro Aguiar, for his availability and discussions
de Montreal
́ ́
(
(9) This compound was prepared in-house. For synthetic details see
3
1
the SI.
upon NMR related topics, for P solid state NMR of
compounds 3f and (i-Pr PH) NiBr and simulation of the H
NMR spectrum of the latter.
1
(10) It should be noted here that a lower H-incorporation had been
observed with the C D OPR analogue mentioned above, indicating a
2
2
2
6
5
2
smoother reaction with 1a-d7.
(
11) For instance, C−H nickelation of 3-R-C H OP(i-Pr) occurs at
6
4
2
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v
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PH
(13) The contention that the C1 position is more electron-rich is
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4
angles in the given structure. This approach generates values ranging
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1
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9
55−964. (b) Rosiak, D.; Okuniewski, A.; Chojnacki, J. Copper(I)
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(
(
26) (a) Cloutier, J.-P.; Zargarian, D. Functionalization of the Aryl
15) The mounted crystal of 2g was found to be a 2-component twin
Moiety in the Pincer Complex (NCN)NiIIIBr2: Insights on NiIII-
Promoted Carbon−Heteroatom Coupling. Organometallics 2018, 37
and the Br ligand was found disordered in both the complexes of the
asymmetric unit.
(
9), 1446−1455. (b) Cloutier, J.-P.; Rechignat, L.; Canac, Y.; Ess, D.
(16) (a) Spasyuk, D. M.; Gorelsky, S. I.; van der Est, A.; Zargarian,
H.; Zargarian, D. C−O and C−N Functionalization of Cationic,
NCN-Type Pincer Complexes of Trivalent Nickel: Mechanism,
Selectivity, and Kinetic Isotope Effect. Inorg. Chem. 2019, 58 (6),
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the Chemical and Electrochemical Oxidation of a Dimeric Pincer
Complex of Nickel. Inorg. Chem. 2011, 50 (6), 2661−2674.
3
(
861−3874.
(
b) Lefev
Pincer Complexes of Nickel(II). J. Organomet. Chem. 2011, 696 (4),
64−870.
17) In contrast, control experiments showed no decomposition at
60 °C for the free phosphinite 1a or the cyclonickelated product 2a.
18) Quantification of this C−H nickelation reaction was done by
̀
re, X.; Spasyuk, D. M.; Zargarian, D. New POCOP-Type
27) Obermayer, D.; Znidar, D.; Glotz, G.; Stadler, A.; Dallinger, D.;
Kappe, C. O. Design and Performance Validation of a Conductively
Heated Sealed-Vessel Reactor for Organic Synthesis. J. Org. Chem.
8
(
2
(
016, 81 (23), 11788−11801.
1
28) (a) Vabre, B.; Spasyuk, D. M.; Zargarian, D. Impact of
(
31
Backbone Substituents on POCOP-Ni Pincer complexes: A
Structural, Spectroscopic and Electrochemical Study. Organometallics
2012, 31 (24), 8561−8570. (b) Vabre, B.; Lindeperg, F.; Zargarian,
D. Direct, one-pot synthesis of POCOP-type pincer complexes from
metallic nickel. Green Chem. 2013, 15 (11), 3188−3194.
integrating the P singlet at 192 ppm against the signal for [n-Bu N]
4
[
PF ] used as an internal standard.
6
3
1
1
(19) The major resonances present in the P{ H} NMR spectrum
of this mixture were the same as in the spectrum for the analogous
reaction with 1 equiv of 1a (i.e., AB doublets arising from compound
4
and the singlet at 121 ppm), but in this case we observed an
additional minor resonance, a set of doublets at 167 and 150 ppm
with J ≈ 27 ppm.
(20) Recall that isolation and full characterization of phosphinite
adducts of the cyclonickelated complexes has been reported
previously: See ref 4.
(21) For primary reports and a review describing this type of
reactivity see the following sources: (a) Abdellah, I.; Lepetit, C.;
Canac, Y.; Duhayon, C.; Chauvin, R. Imidazoliophosphines are True
N-Heterocyclic Carbene (NHC)−Phosphenium Adducts. Chem. Eur.
J. 2010, 16 (44), 13095−13108. (b) Abdellah, I.; Boggio-Pasqua, M.;
Canac, Y.; Lepetit, C.; Duhayon, C.; Chauvin, R. Towards the Limit
of Atropochiral Stability: H-MIOP, an N-Heterocyclic Carbene
Precursor and Cationic Analogue of the H-MOP Ligand. Chem.
Eur. J. 2011, 17 (18), 5110−5115. (c) Vabre, B.; Canac, Y.; Duhayon,
C.; Chauvin, R.; Zargarian, D. Nickel(II) Complexes of the New
Pincer-Type Unsymmetrical Ligands PIMCOP, PIMIOCOP, and
NHCCOP: Versatile Binding Motifs. Chem. Commun. 2012, 48 (84),
1
0446−10448. (d) Vabre, B.; Canac, Y.; Lepetit, C.; Duhayon, C.;
Chauvin, R.; Zargarian, D. Charge Effects in PCP Pincer Complexes
of Ni bearing Phosphinite and Imidazol(i)ophosphine Coordinating
II
Jaws: From Synthesis to Catalysis through Bonding Analysis. Chem.
Eur. J. 2015, 21 (48), 17403−17414. (e) Canac, Y. Carbeniophos-
phines versus Phosphoniocarbenes: The Role of the Positive Charge.
Chem. Asian J. 2018, 13 (15), 1872−1887.
(22) Monitoring the thermal profile of this reaction revealed an
exothermic reaction as soon as it reached 150 °C.
1
(
23) It is worth noting that the H NMR (C D ) spectrum of (i-
6 6
Pr PH) NiBr crystals indicated that it adopts a trans conformation in
2
2
2
N
DOI: 10.1021/acs.organomet.9b00660
Organometallics XXXX, XXX, XXX−XXX