Ni-Catalyzed Site-Selective Dicarboxylation of 1,3-Dienes with CO2

Article abstract of DOI:10.1021/jacs.7b13220

A site-selective catalytic incorporation of multiple CO₂ molecules into 1,3-dienes en route to adipic acids is described. This protocol is characterized by its mild conditions, excellent chemo- and regioselectivity and ease of execution under CO₂ (1 atm), including the use of bulk butadiene and/or isoprene feedstocks.

Full text of DOI:10.1021/jacs.7b13220

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Communication
Ni-Catalyzed Site-Selective Dicarboxylation of 1,3-Dienes with CO2
Ruben Martin, Andreu Tortajada Navarro, and Ryo Ninokata
J. Am. Chem. Soc., Just Accepted Manuscript • Publication Date (Web): 27 Jan 2018
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Ni-Catalyzed Site-Selective Dicarboxylation of 1,3-Dienes with CO2
Andreu Tortajada,† Ryo Ninokata† and Ruben Martin†§*
†Institute of Chemical Research of Catalonia (ICIQ), The Barcelona Institute of Science and Technology, Av. Països Cata-
lans 16, 43007 Tarragona, Spain
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§ ICREA, Passeig Lluïs Companys, 23, 08010, Barcelona, Spain
Supporting Information Placeholder
to complement recent catalytic difunctionalization of
1,3-dienes,10 as raw materials (CO2) would be used as
electrophilic carbon synthons in lieu of nucleophilic
reagents.11 However, such a scenario bears considerable
risk and might seem counterintuitive at first sight due to
(a) the proclivity of 1,3-dienes to trigger telomerization
reactions12 and (b) the fact that statistical mixtures of
monocarboxylic acids were exclusively observed with
hydrocarboxylation conditions previously employed for
either alkynes13 or alkenes, 5b reinforcing the notion that
a multiple, yet controllable, CO2 insertion event would
be particularly problematic. We anticipated that a site-
selective insertion of multiple CO2 units could be ration-
ally controlled in the absence of hydride sources by
exploiting the inherent carbogenic nucleophilicity of I
(Scheme 1, bottom).14 Upon π−σ equilibration, the tar-
geted adipic acids could be obtained by a subsequent
regioselective CO2 incorporation into I that precedes a
final reduction to recover back the catalytic Ni(0)Ln
species. Herein, we report the successful realization of
this goal, culminating in a mild method that operates at
atmospheric pressure of CO2 and is characterized by its
chemo- and regioselectivity profile, including the ability
to use of bulk butadiene and/or isoprene feedstocks.
ABSTRACT: A site-selective catalytic incorporation of
multiple CO2 molecules into 1,3-dienes en route to adip-
ic acids is described. This protocol is characterized by its
mild conditions, excellent chemo- and regioselectivity
and ease of execution under CO2 (1 atm), including the
use of bulk butadiene and/or isoprene feedstocks.
The recent years have witnessed an emerging demand
for catalytic techniques that forge multiple C–C bonds
via the synergistic combination of chemical feedstocks.1
Among various conceivable scenarios, a site-selective
incorporation of carbon dioxide (CO2)2 into olefin feed-
stocks in the absence of stoichiometric organometallic
reagents is of particular relevance,3 holding promise to
streamline the synthesis of industrially-relevant carbox-
ylic acids.4 Despite the elegant advances realized, these
carboxylation protocols remain currently confined to
single CO2 insertions (Scheme 1, paths a & b).5 There-
fore, the ability to expand the catalytic carboxylation
portfolio of C=C bonds beyond single CO2 insertions
would be a worthwhile endeavour, opening up new
strategies for preparing saturated polycarboxylic acids.6
Scheme 1. Carboxylation of Olefinic C=C Bonds.
state-of-the-art catalytic carboxylation of olefinic C=C bonds with CO2
Table 1. Optimization of the Reaction Conditions.a
CO2H
CO2H
C
“H”
+
M
M
C
H
path a
path b
CO2
single CO2
insertion
single CO2
insertion
this work: site-selective multiple catalytic CO2 insertions into 1,3-dienes
O
two CO2
insertions
L
CO2
Ni
Ni
O
CO2H
CO2H
–
δ
reductant
I
no “H”
1,3-dienes
latent
nucleophile
chemo &
regioselective
As part of our ongoing interest in CO2,7 we questioned
whether we could enable a catalytic, site-selective incor-
poration of multiple CO2 motifs into abundant 1,3-dienes
en route to adipic acids,8 building blocks of particular
relevance in the production of plastics and adhesives.9 If
successful, this pathway might also offer an opportunity
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a 1a (0.20 mmol), NiBr4(TBA)2 (5 mol%), L7 (5 mol%),
a As Table 1 (entry 1), followed by exposure to TMSCHN2
and Pd/C (5 mol%), B2(OH)4 (2 equiv) and H2O (5 equiv)
Mn (1.50 equiv), CO2 (1 bar), DMA (0.5 M), 50 ºC. b Z/E =
1
2
3
4
5
6
7
c
b
1.4:1 to 5:1. 1H-NMR yields using fluorene as internal
at rt. Isolated yields, average of two independent runs,
standard. d Isolated yield. e with TBAB (10 mol%). TBAB:
tetrabutylammonium bromide, TBA: tetrabutylammonium.
using 1,3-dienes as E/Z mixtures. c Using E-1a. d dr = 1.5:1.
f
e dr = 1:1. 1 mmol scale. g Using H2 and Pd/C as reduct-
ant. h NiBr4(TBA)2 (10 mol%) and L7 (10 mol%).
We began our investigations by studying the reaction of
1a with CO2 (1 atm). After some experimentation,15
a
Once we established the optimized reaction conditions,
we next studied the generality of our catalytic dicar-
boxylation of 1,3-dienes (Table 2).19 In situ protection of
the carboxylic acid function as the methyl ester and
reduction of the pending alkene was necessary to avoid
unnecessary purification issues of the resulting adipic
acid derivatives.20 As expected, a host of 1,3-dienes
substituted with either aliphatic (1n-1q) or aromatic
backbones (1a-1m) reacted equally well with the
NiBr4(TBA)2/L7 couple. Notably, the outcome of the
latter was found to be insensitive to whether electron-
rich or electron-poor arenes were employed, even in the
presence of ortho-substituents (1i-1k). The site-selective
incorporation of multiple CO2 motifs into 1,3-dienes was
accompanied by an excellent chemoselectivity, as esters
(3j, 3k), nitriles (3m), ketones (3p) or amides (3q) were
well-tolerated. Interestingly, the presence of an organo-
metallic reagent does not interfere with productive for-
mation of 3l, thus demonstrating the complementarity of
our technique with classical nucleophilic/electrophilic
regimes.21,22 Likewise, the reaction could be applied in
the presence of heterocyclic cores (3f). As illustrated by
the successful preparation of 3g and 3h, the reaction
could also be extended to disubstituted 1,3-dienes, albeit
with lower diastereoselectivities. Although C–O electro-
philes are inherently predisposed to nickel-catalyzed C–
C bond-forming reactions,23 we found that 3k could be
obtained in 89% yield, leaving ample room for further
derivatization via cross-coupling technologies.
cocktail consisting of NiBr4(TBA)2, L7 and Mn as re-
ductant in DMA at 50 ºC furnished 2a (Z/E = 2.4:1) in
74% isolated yield. It is worth noting that not even trac-
es of 2a’ or telomerization side-products were observed
in the crude mixtures. Intriguingly, the absence of am-
monium salts resulted in a markedly lower reactivity
(entries 2 and 3).16 A detailed survey of nitrogen-donor
ligands revealed that a seemingly trivial modification at
C2 was critical for success (entries 4 vs 5-6). Unlike
recent reductive carboxylations,17 the presence of sub-
stituents at both 2,2’-positions had a deleterious effect
(entry 9 vs 1), thus showing the subtleties of our proto-
col. The use of other precatalysts (entries 2 and 3), sol-
vents (entry 10) or reductants (entry 11) had a detri-
mental impact on reactivity.18 Notably, identical results
were observed regardless of whether (E)-1a or (Z)-1a
were used, constituting an additional bonus from a syn-
thetic and practical standpoint.19 As expected, control
experiments revealed no product formation when each
parameter was omitted from the mixture (entry 12).15
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Table 2. Ni-catalyzed 1,4-Dicarboxylation of 1,3-Dienes.a,b
Scheme 2. Ni-catalyzed Carboxylation of Diene Feedstocks.
In light of these results, we wondered whether our pro-
tocol could be used for the valorization of butadiene,
isoprene or piperylene, compounds that are obtained in
bulk as byproducts of the steam cracking in the produc-
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tion of ethylene.24 As shown in Scheme 2, this turned out
in the former.28 While one might attribute this finding to
the non-innocent role of COD,29 the reluctance of coor-
dinatively saturated Ni-1 to dissociate L7 prior to 1,3-
diene binding seems more likely. Unfortunately, the
preparation of π-allyl complex I (Scheme 1) in pure
analytical form bearing L7 as ligand proved to be par-
ticularly elusive. Gratifyingly, we could prepare struc-
turally-related Ni-2, and the η3-hapticity of the allyl
motif was finally revealed by X-ray structure analysis
(bottom).15 Interestingly, we found that Ni-2 only fur-
nished 2a in the presence of both L7 and Mn.15,30
Whether these results suggest that single-electron trans-
fer processes come into play via putative Ni(I) species31
or invoke other mechanistic interpretations is the subject
of ongoing studies.
1
2
3
4
5
6
7
8
to be the case, and 7a-9a were all obtained in good
yields from the corresponding 1,3-diene feedstocks after
a subsequent hydrogenolysis event. Strikingly, butadiene
4 resulted in a 93:7 regioselectivity pattern whereas the
presence of a methyl group in either 5 or 6 had a non-
negligible effect on site-selectivity, with 5 providing the
best regiochemical discrimination (8a).25 Although the
1,4–ratio of 7a and 9a could partially be improved by
using either L5 or L2 in lieu of L7, significant lower
yields were observed in these cases.15 Taken together,
the results summarized in Table 2 and Scheme 2 stand as
a testament to the potential of this catalytic technology
for enabling a site-selective incorporation of multiple
CO2 units into abundant 1,3-diene precursors.
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Scheme 3. Mechanistic Experiments.
In summary, we have documented a site-selective, cat-
alytic incorporation of multiple CO2 molecules into
abundant 1,3-dienes, thus giving access to adipic acids
from simple and available precursors. The salient fea-
tures of this method are its excellent regio- and
chemoselectivity, mild conditions and ease of execution.
Further extensions to other hydrocarbons, including
asymmetric transformations, are currently in progress.
stereochemical course of the dicarboxylation event
as Table 1
CO2Me
(entry 1)
CO2Me
then
+
TMSCHN2
60% yield
(91:9)
MeO2C
MeO2C
major
trans-11
10
minor
cis-12
stoichiometric studies with Ni(0)(L7)n
Ph
Ph
Ni(COD)2 (1 equiv)
L7 (1 equiv)
TBAB (1 equiv)
Mn (1 equiv), 50 ºC
56% (E:Z = 69:31)
Ph
Me
N
N
N
N
ASSOCIATED CONTENT
Ni
Ph
Supporting Information. Experimental procedures, crys-
tallographic data and spectral data. This material is availa-
ble free of charge via the Internet at http://pubs.acs.org.
Ni-1
Me
1a
+
2a
CO2
(1 atm)
AUTHOR INFORMATION
Corresponding Author
Ni-1 (1 equiv)
TBAB (1 equiv)
Mn (1 equiv), 50 ºC
0%
Ni-1
* rmartinromo@iciq.es
stoichiometric studies with Ni-2
L7 (1 equiv)
TBAB (1 equiv)
Ph
Funding Sources
2a
O
Ni
Mn (1 equiv), 50 ºC
CO2 (1 atm)
37% (E:Z = 36:64)
No competing financial interests have been declared.
O
Cy3P
Ni-2
ACKNOWLEDGMENT
Ni-2
We thank ICIQ, MINECO (CTQ2015-65496-R & Severo
Ochoa Accreditation SEV-2013-0319) for support. A. T.
thanks MINECO for a FPU fellowship. We sincerely thank
M. Martínez, E. Escudero & E. Martin for X-ray crystallo-
graphic data and Dr. M. Gaydou for helpful discussions.
Next, we decided to gather indirect evidence about the
mechanism by studying the stereochemical course of 10
with CO2 (Scheme 3, top). Interestingly, trans-11 was
preferentially formed over cis-12, suggesting that the
second CO2 unit is inserted into the π-allyl complex I
(Scheme 1) via formal backside attack.26 This seemingly
trivial interpretation, however, does certainly not rule
out a rapid interconversion of the putative π-allyl nickel
complexes upon exposure to Ni(0)(L7) prior to CO2
insertion.27 Although unraveling the mechanistic under-
pinnings of this reaction should await further investiga-
tions, we turned our attention to study the reactivity of
Ni-1 (Scheme 3, middle). This complex was easily pre-
pared by exposure of L7 and Ni(COD)2 in benzene at 40
ºC, the structure of which was univocally determined by
X-ray crystallography.15 Interestingly, the reactivity of
Ni-1 with 1a was not comparable to that observed with
Ni(COD)2/L7, with not even traces of 2a being observed
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(25) Although tentative, these results can be interpreted on the
basis of a subtle influence on both steric and electronic ef-
fects on the reactivity of π-allyl complex I (Scheme 1).
(26) This finding is in excellent agreement with conclusions
previously reached by Sato with stoichiometric amounts of
Ni complexes and pyrophoric reagents. See ref. 8c.
(27) Such interpretation was invoked by Jarvo in non-related
stereospecific Ni-catalyzed reactions. See: Yonova, I. M.;
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(28) Control experiments revealed that the Ni(0)/L7 combination
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erosion in yield was observed when Ni-1 or Ni(COD)2/L7
were exposed to 1a without Mn. See ref 15.
(29) Nett, A. J.; Zhao, W.; Zimmerman, P. M.; Montgomery, J.
J. Am. Chem. Soc. 2015, 137, 7636.
(30) In the absence of L7, Mn or TBAB, low yields of monocar-
boxylic acids were observed in the crude mixtures.
(31) Nickel (I) species have been reported to rapidly react with
CO2: Menges, F. S.; Craig, S. M.; Tötsch, N.; Bloomfield,
A.; Ghosh, S.; Krüger, H. J.; Johnson, M. A. Angew.
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periments with radical inhibitors.
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