Palladium-Catalysed C?H Bond Zincation of Arenes: Scope, Mechanism, and the Role of Heterometallic Intermediates

Article abstract of DOI:10.1002/anie.202014960

Catalytic methods that transform C?H bonds into C?X bonds are of paramount importance in synthesis. A particular focus has been the generation of organoboranes, organosilanes and organostannanes from simple hydrocarbons (X=B, Si, Sn). Despite the importan

Full text of DOI:10.1002/anie.202014960

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Accepted Article
Title: Palladium-Catalysed C–H Bond Zincation of Arenes: Scope,
Mechanism and the Role of Heterometallic Intermediates
Authors: Martí Garçon, Nicolette Wee Mun, Andrew J P White, and
Mark Richard Crimmin
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10.1002/anie.202014960
Angewandte Chemie International Edition
RESEARCH ARTICLE
Palladium-Catalysed C–H Bond Zincation of Arenes: Scope,
Mechanism and the Role of Heterometallic Intermediates
Martí Garçon, Nicolette Wee Mun, Andrew J. P. White, Mark R. Crimmin*[a]
[a]
Martí Garçon, Nicolette Wee Mun, Dr. Andrew J. P. White, Dr. Mark R. Crimmin
Molecular Sciences Research Hub,
Imperial College London
White City Campus, 82 Wood Lane, Shepherds Bush, London, W12 0BZ, UK
E-mail: m.crimmin@imperial.ac.uk
Supporting information for this article is given via a link at the end of the document.
Abstract: Catalytic methods that transform C–H into C–X bonds are
of paramount importance in synthesis. A particular focus has been the
generation of organoboranes, organosilanes and organostannanes
from simple hydrocarbons (X = B, Si, Sn). Despite the importance of
organozinc compounds (X = Zn), their synthesis by the catalytic
functionalisation of C–H bonds remains unknown. Here we show that
a palladium catalyst and zinc–hydride reagent can be used to
transform C–H into C–Zn bonds. The new catalytic C–H zincation
protocol has been applied to a variety of arenes – including
fluoroarenes, heteroarenes, and benzene – with high chemo- and
regioselectivity. A mechanistic study shows that heterometallic Pd---
Zn complexes play a key role in catalysis. The conclusions of this work
are twofold; the first is that valuable organozinc compounds are finally
accessible by catalytic C–H functionalisation, the second is that
heterometallic complexes are intimately involved in bond-making and
bond-breaking steps of C–H functionalisation.
others have developed families of mixed Zn/M (M = Mg, Li) bases
to achieve the direct zincation of electron deficient arenes.[12–17]
The current understanding of these systems is that both metals
are crucial to reactivity.[18,19] As such these methods rely on a
stoichiometric equivalent of an s-block metal. In contrast, the new
catalytic method we report uses a palladium catalyst for C–H
zincation. Our approach is highly efficient, forming only H2 as a
by-product. This reaction gives access to organozinc compounds
which are robust, easy to handle and are active partners for
Negishi cross-coupling reactions.
We have conducted a detailed analysis of the mechanism of C–H
zincation, which shows that heterometallic complexes involving
both Pd and Zn play a vital role in the catalytic cycle. We show for
the first time that heterometallic Pd---Zn compounds can engage
in a series of steps required for catalytic turnover (oxidative
addition, ligand exchange, reductive coupling). While there is
pioneering work demonstrating some of these steps in
isolation,[20],[21] this is the first time they have been integrated into
an efficient catalytic cycle.
Introduction
Catalytic methods to transform C–H bonds to C–C or C–X (X =
heteroatom) bonds are an essential component of modern
synthesis.[1],[2] Methods for C–H functionalisation can be applied
on scale for upgrading simple hydrocarbons or more precisely in
late-stage functionalisation of complex organic molecules and
materials. Arguably, one of the most successful approaches in C–
H functionalisation catalysis has been C–H borylation.[3] This
reaction involves the transformation of C–H to C–B bonds and is
typically catalysed by a transition metal complex.[4,5] The key
advantage of C–H borylation is that it allows the preparation of
boronic esters, compounds that find widespread use in synthesis
due to their ease of handling and application in Suzuki-Miyaura
cross-couplings. Related protocols involving the transformation of
C–H bonds into C–Si and C–M bonds (M = Mg, Al, and Sn) have
also been reported and are a powerful means to access potential
partners for Hiyama, Kumada and Stille cross-coupling
reactions.[6–11] Organozinc compounds, like organoboranes are
widely applied in synthesis including Negishi couplings and are
often versatile, mild and functional group tolerant partners. It is
surprising then that a catalytic method for the transformation of
C–H bonds into C–Zn bonds is unknown.
Results and Discussion
Reaction Scope: The reaction of C6F5H and 1.1 – 1.2 equiv. of
the β-diketiminate supported zinc hydride complex 1 in the
presence of 2 mol% [Pd(PCy3)2] afforded 2a in excellent yield
after 1 day at 50 °C. A control reaction between 1 and C6F5H gave
only trace amounts of the product (<2%) after 3 days at 50 °C. In
the absence of substrate and catalyst, 1 is thermally stable under
reaction conditions. We believe the primary role of b-diketiminate
ligand is to provide kinetic stability to this species and onward
reaction intermediates. The reaction scope was investigated and
a range of fluoroarenes and heteroarenes were amenable to C–
H zincation forming 2a-t (Table 1 and 2). High chemoselectivity
was observed despite the fact that [Pd(PCy3)2] is known to
catalyse the functionalisation of C–F bonds of fluoroarenes.[22],[23]
For fluoroarenes, the regiochemistry appears to be dictated by the
ortho-fluorine effect, with substitution occurring at sites adjacent
to at least one fluorine substituent. Similar trends have been
observed in the C–H silylation and borylation of these
substrates.[8],[24],[25] For highly fluorinated substrates the reaction
operates under mild conditions even when using the fluoroarene
as the limiting reagent.[26] Halogen, trifluoromethyl, and methoxy
functional groups are all tolerated.
In this paper, we report the first catalytic method for the
transformation of C–H to C–Zn bonds. The work complements
modern approaches to C–H zincation which rely on specialist
main group bases. For example, Knochel, Hevia, Mulvey and
1
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Table 1. Scope of the C–H zincation of fluorocarbons catalysed by [Pd(PCy3)2] along with (inset) structures of 2b and 2e determined by single crystal X-ray
diffraction.
Arenes with lower fluorine content react slower. Using an excess
of fluoroarene (10 equiv.), however, it was possible to achieve
good yields for even the most challenging substrates. Under the
optimised conditions, fluorobenzene (C6H5F) only reacted
sluggishly (<30 % conversion, 3d, 80 °C). The scope can even be
expanded to the C–H zincation of benzene, provided the
substrate is used as a solvent and the reaction is conducted under
static vacuum to remove the H2 by-product. Furthermore, the
reaction scope is not limited to fluoroarenes. Heteroarenes were
found to engage in these reactions under mild conditions and high
selectivity. C–H zincation is observed to occur selectively at the
2-position of oxygen- and sulfur-containing heterocycles. In
contrast, indoles favoured functionalisation at the 3-position. The
products could be isolated cleanly despite the precedent for
related C–H alumination products to undergo ring-expansion
reactions under similar conditions.[27]
Compounds 2a-t could be crystallised from crude reaction
mixtures and fully characterised by multinuclear NMR and IR
spectroscopy, high-resolution mass spectrometry and single
crystal X-ray diffraction. These products proved to be remarkably
robust. In hydrocarbon solutions they can survive exposure to air
for short periods of time (1.5 - 4 h) without decomposing. The
solid-state structures of 2a-t resemble known β-diketiminate
supported zinc aryl complexes and do not warrant detailed
comment.[28] Single crystal X-ray diffraction data show two main
conformations based on the aryl ring existing either approximately
coplanar or orthogonal to the plane created by the b-diketiminate
ligand (see SI for details).
2
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Table 2. Scope of the C–H zincation of heteroarenes and arenes catalysed by [Pd(PCy3)2] along with (inset) structures of 2n and 2o determined by single crystal
X-ray diffraction.
Curious as to the mechanism of C–H zincation catalysed by
[Pd(PCy3)2], we undertook a series of stoichiometric experiments
between the different components of the reaction. These
experiments unveiled several reactions of direct relevance to
catalysis. This information, in combination with DFT calculations,
was used to build a mechanistic and kinetic model which was
further interrogated through kinetics experiments. We detail these
findings below.
1JPt–H = 719 Hz) allowing unambiguous assignment of the number
of hydride ligands on Pt. In the infrared spectrum, a stretch at
1708 cm-1 is assigned to a n(Pt–H) vibration. The structure of 3b
was determined by single crystal X-ray diffraction (Figure 1d).
While the position of the hydride ligands could not be located from
the Fourier difference map, they almost certainly lie in the plane
of the molecule, trans disposed to one another, forming a T-
shaped motif with Pt and the PCy3 ligand. A closely related
magnesium analogue of 3b has been reported by our group and
the hydride locations of this complex have been confirmed by
neutron diffraction.[30] The Pt–Zn distances of 3b of 2.4816(6) and
2.4848(7) Å are close to the sum of the covalent radii (Pyykkö,
2.41 Å; Pauling, 2.54 Å; Alvarez, 2.58 Å).[31–33] The Pt–P distance
of 2.316(1) Å is unremarkable.
Coordination of (Zn–H) Bonds to Pd: The reaction between 1
s
and [Pd(PCy3)2] allowed the identification of the reversible binding
of the zinc hydride to the catalyst. 1 and [Pd(PCy3)2] react to form
the bis(s-zincane) complex [Pd(PCy3)(1)2] (3a) and PCy3 at 253
K. At 193 K, [Pd(PCy3)3] could also be identified as part of this
reaction mixture.[29] This reaction is reversible and the equilibrium
is completely displaced towards the starting materials at 298 K.
At 233 K, 3a demonstrates a characteristic resonance at d = 29.3
ppm in the 31P NMR spectrum.
Considering the stepwise ligand substitution of [M(PCy3)2] (M =
Pd, Pt) to form 3a-b, it is likely that the first step involves
association of 1 equiv. of 1 to form a 3-coordinate, 16-electron s-
zincane complex. Reaction of 2 equiv. of 1 with [Pd(dcpe)]2 (dcpe
= bis(dicyclohexylphosphino)ethane) supports this hypothesis
and allows the isolation of 4, a s-zincane complex bearing a
chelating diphosphine ligand (Figure 1c). 4 is characterised by a
Although 3a could not be isolated, the reaction of 2 equiv. of 1
with [Pt(PCy3)2] allowed isolation of 3b, a direct platinum analogue
(Figure 1b). 3b is stable at 298 K in hydrocarbon solutions and
demonstrates diagnostic resonances at d = –4.97 ppm, 39.4 ppm
and –5797 ppm in the 1H-, 31P- and 195Pt-NMR, respectively. The
hydride resonance appears as a doublet (2JP–H = 7.7 Hz) and has
clearly resolved Pt satellites (1JPt–H = 719 Hz). The 195Pt NMR
spectrum is resolved into a doublet of triplets (1JPt–P = 2516 Hz,
1H resonance at d = –0.80 ppm (t, 2JP–H = 56 Hz) and a single 31
P
NMR resonance at d = 52.8 ppm. A single crystal X-ray diffraction
experiment on 4 reveals a Pd–Zn distance of 2.4499(7) Å that is
again close to the sum of the covalent radii (Pyykkö, 2.38 Å;
Pauling, 2.53 Å; Alvarez, 2.61 Å).[34]
3
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Figure 1. Reaction of 1 with (a) [Pd(PCy3)2], (b) [Pt(PCy3)2], and (c) [Pd(dcpe)]2. (d) Crystal structures of 3b and 4.
The Pd–H and Zn–H distances of 1.59(4) and 1.79(3) Å and the
Pd–H–Zn angle of 93° are consistent with the description of this
complex as a σ-zincane complex.[35] The Pd–P distances are
slightly asymmetric, taking values of 2.3382(8) and 2.287(1) Å
respectively, with that trans to the hydride moiety being longer
(Figure 1d).[36]
A
stoichiometric reaction between [Pd(PCy3)2] and C6F5H
revealed trace amounts of trans-[Pd(PCy3)2(F)(p-C6F4H)] derived
from the oxidative addition of the C–F bond to Pd(0).[39],[40] There
was no spectroscopic evidence for trans-[Pd(PCy3)2(H)(C6F5)]
formed from oxidative addition of the C–H bond. In contrast, the
reaction of the heterometallic Pt---Zn complex 3b with C6F5H
allowed the identification of the C–H oxidative addition product
(Figure 2b). The reaction of 3b with 5 equiv. of C6F5H at 60 ºC for
3 h gave a mixture of products including platinum complex 5,
fluoroarenes derived from the hydrodefluorination of C6F5H and a
zinc compound assumed to be the fluoride analogue of 1.
Fractional crystallisation resulted in isolation of a few single
crystals of 5. 5 can be viewed as a Pt(II) complex bearing a
phosphine ligand and hydrides that bridge to a zinc center.
Diagnostic resonances are observed in the 1H-NMR spectrum at
δH-trans= –7.59 ppm (1JH–Pt = 581 Hz – satellites) and δH-cis = –4.39
ppm (dd, JH–P = 113 Hz, JH–H = 6.5 Hz, JH–Pt = 671 Hz –
satellites) and the 31P-{1H}-NMR spectrum at δ = 30.9 ppm (1JP–Pt
= 2877 Hz). In the solid-state, 5 adopts a geometry that is
approximately square planar at platinum and tetrahedral at zinc.
The hydride and s-zincane ligands organise themselves in a cis
arrangement such that both hydrides can interact and bridge
between both metal centres. The Pt---Zn distance of 2.5184(8) Å
is similar to those recorded for 3b. The Pt–C bond length of
2.067(4) Å is consistent with known Pt(II) fluoroaryl complexes,[41]
while the C---H1 separation is ~2.5 Å. The Pt–H and Zn–H
distances are similar across both hydride positions, and these
take values of 1.59(4), 1.66(6), 1.81(4) and 1.78(5) Å for Pt–H1,
Pt–H2, Zn–H1 and Zn–H2 respectively.
The bonding in 3b and 4 was interrogated with DFT calculations.
The bonding in complex 4 is consistent with that of a σ-complex;
NBO analysis shows donation from the σ-(Zn–H) orbital into an
empty Pd orbital and backdonation of a filled Pd d-orbital into the
σ*-(Zn–H) orbital, as the most characteristic bonding features of
this complex. The bonding in 3b was more complex. We have
characterised in detail a number of compounds involving Zn–H
bonds coordinated to transition metals;[35],[37] and the Zn---H
distances typically range from ~ 1.7 to 2.2 Å. The Zn---H distance
in 3b was calculated to be 1.9 Å. These data, in combination with
Wiberg Bond Indices, indicate that 3b contains stretched Zn---H
bonds (see Supporting Information). In combination, these
experiments demonstrate the reversible binding of the Zn–H bond
of 1 to Pd. This binding event plays an important role in both on-
cycle and off-cycle steps during catalysis (vide infra).
2
2
1
Oxidative Addition: Based on their facile formation and ease of
ligand exchange, Pd---Zn heterometallic complexes likely play a
key role in catalytic C–H zincation. To interrogate this idea further,
reactions between the substrate C6F5H and the Pd and Pt
complexes described above were undertaken. These
experiments were designed to probe the key C–H bond breaking
step; the oxidative addition to M(0) (M = Pd, Pt). For partially
fluorinated substrates, chemoselectivity for C–H or C–F bond
functionalisation becomes an important consideration.[38]
4
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Figure 2. Reaction of C6F5H with (a) [Pd(PCy3)2] and (b) 3b. (c) Crystal structure of 5.
Based on the current understanding, we suggest that the
oxidative addition of both the C–H and C–F bonds of C6F5H to
Pd(0) may be reversible (SI, Figure S23).[40] Unique insight into
the C–H oxidative addition step could be gained by trapping an
Despite the relocation of the hydrogen atom to a bridging hydride
in Int-2, the Zn atom does not interact directly with the hydrogen
atom in TS-1 and it would not be accurate to classify this reaction
as a 4-centered ligand-assisted oxidative addition.[44–46]
analogue of the C–H oxidative addition product as
heterometallic Pt---Zn complex.
a
A ligand exchange reaction of a further equivalent of 1 with Int-2
forms Int-3. A subsequent concerted rearrangement of this
complex forms Int-4 which contains both 2a and H2 within the
coordination sphere of Pd. TS-2 involves the reorganisation of
electron density between the equatorial ligands of palladium.
Simultaneous migration of the perfluorinated s-aryl ligand from Pd
to Zn is accompanied by reductive coupling of the hydride
ligands.[21] This concerted process involves a reduction in the
formal oxidation state at the transition metal from Pd(II) back to
Pd(0). The catalytic cycle is closed by further ligand exchange
reactions of Int-4 by coordination of PCy3 and liberation of
DFT Calculations: To better understand the mechanism of
catalytic C–H zincation, series of DFT calculations
a
(ωB97x/BS1)[42] were undertaken (see SI for details). A low
energy pathway was identified involving Pd---Zn heterometallic
complexes. Specifically, [Pd(PCy3)(1)] was identified as a key
catalytic intermediate. The reaction sequence is initiated by the
oxidative addition of the C–H bond of C6F5H to this 14-electron
Pd(0) intermediate (see SI for alternative pathways).[43],[10] From
[Pd(PCy3)(1)] and C6F5H, formation of Int-1, a weakly associated
complex of the fluoroarene and active catalyst, is mildly exergonic. dihydrogen and 2a to reform [Pd(PCy3)(1)]. Overall the C–H
Oxidative addition occurs through TS-1 (DG‡ = +1.9 kcal mol-1)
and is expected to reversibly form Int-2 based on the extremely
low barrier for the forward reaction and modest stabilisation of the
product (DGº298K = –7.8 kcal mol-1). Int-2 is a direct isostructural
analogue of the crystallographically characterised complex 5. TS-
1 involves a 3-centered Pd···H···C interaction and population of
the s*-orbital of the C–H bond of the fluoroarene with electrons
from a d-orbital of Pd. This transition state is palladium centred.
zincation reaction is slightly exergonic (DGº298K = –1.4 kcal mol-1).
The pathway predicts that C–H activation should be fast and
reversible while the C–H functionalisation (formation of the C–Zn
bond) is slow. The calculated Gibbs activation energy required for
catalyst turnover is DG‡ = 23.0 kcal mol-1.
Figure 3. DFT calculated reaction pathway for catalytic C–H zincation.
5
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Figure 4. (a) Catalytic cycle. (b) Kinetic model and rate law (derived from steady-state approximation).
Catalytic Cycle, Kinetic Model and Kinetics: Based on the
combination of the stoichiometric experiments and the DFT
calculations a comprehensive catalytic cycle can be proposed
(Figure 4a). A simpler catalytic cycle involving monometallic
palladium complexes can be excluded based on not only the facile
formation of Pd---Zn heterometallics, but also as independently
prepared trans-[Pd(PCy3)2(H)(4-C5F4N)] was not catalytically
competent (see SI). The pre-catalyst equilibria are off-cycle
events, while the on-cycle species all involve Pd---Zn
heterometallic complexes. Considering the most important off-
cycle equilibria and approximating the transformation of Int-2 to
products by TS-2 as a single kinetically relevant non-reversible
step, the kinetic model in Figure 4b can be derived. The
associated rate law determined using the steady state
approximation predicts complex kinetic behaviour but broadly
suggests that the reaction should be 1st order in catalyst, partial
order (0 to 1) in fluoroarene, and variable order in 1.[47] It is clear
from this analysis that 1 can potentially act as an inhibitor of
catalytic turnover.
plot of ln[C6F5H] versus ln(vinitial) gave an order in C6F5H of 0.6
consistent with the partial order predicted by the kinetic model
(Figure 5b). A similar approach was used to determine the order
in 1 and complex behaviour was revealed (Figure 5c). Two
regimes were apparent. At low initial concentrations, vinitial
increases with increasing concentration of 1. This reaches a
maximum however and further increasing the [1]initial leads to vinitial
becoming smaller with increasing [1]initial. These results indicate
that the order in 1 changes when changing the concentration of
1; this is not a simple case of saturation kinetics. In combination
with curvature of the plots of ln[1] versus time away from a linear
fit at high conversion (>2 half-lives), the proposed catalytic cycle,
and derived kinetic model, the finding suggests that while 1 is
involved in the turnover limiting step it also acts as an inhibitor of
catalysis. At low [1]initial the reaction runs in a regime with weak
catalytic inhibition and a hence a partial positive order is obtained
for [1], whereas at high [1]initial catalyst inhibition becomes a
dominant effect and a negative order is obtained for [1].
An Eyring analysis provided the activation parameters of the
reaction, ΔHǂ = 16.8 ± 1.1 kcal mol-1, ΔSǂ = –22 ± 4 cal mol-1·K-1.
These values provide a reasonable barrier for a reaction that
occurs at 298 K, ΔGǂ = 23.3 ± 2.2 kcal·mol-1, which is in excellent
agreement with that predicted by DFT calculations on the
proposed pathway of DG‡ = 23.0 kcal mol-1.
To interrogate the model a series of kinetics experiments were
undertaken. The reaction between 1 and C6F5H with [Pd(PCy3)2]
as catalyst in C6H6 was investigated. Under pseudo-first order
conditions, the reaction was found to be 1st order in catalyst (see
SI, Figure S29). At high conversion the data sets for ln[1] versus
time show slight deviation from linearity (Figure 5a). Initial rate
methods were used to determine the orders in 1 and C6F5H. The
6
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Figure 5. Plots of (a) ln([10]–[2a]] vs. time with a linear fit over 2 half-lives and evidence of substrate inhibition at high conversions. (b) partial order in [ArH] from
initial rates. (c) variable order in [1] from initial rates. (d) Eyring analysis.
A Hammett analysis was undertaken by performing experiments
with para-substituted tetrafluorobenzenes (C6F4HR, R = F, H, Me,
OMe, Cl) under pseudo-first order conditions. Although there was
not a quantitative correlation between the kobs and Hammett σ
parameters,[48] there was a clear trend that showed reaction
acceleration with electron-withdrawing groups and deceleration
with electron-donating groups on the para position of the
fluoroarene (see SI for details). This trend likely arises due to a
stabilisation of the accumulating negative charge on the fluoroaryl
group and is consistent with a turnover-limiting catalytic sequence
involving migration of the fluoroaryl ligand from the less
electropositive Pd site to the more electropositive Zn site in TS-2.
Synthetic Application of Organozinc Complexes: The
products of C–H zincation possess reactive C–Zn bonds with
enormous potential in synthesis.[51] In order to showcase this, their
performance as coupling partners in C–C bond formation
reactions was investigated. 2a undergoes Negishi cross-coupling
reactions in high yields under mild conditions. Preliminary
reactions with a series of aryl bromides and aryl chlorides resulted
in high yield (determined by 19F-NMR spectroscopy) of the biaryl
products (71–100%), using [Pd(PCy3)2] as a catalyst. The
reaction could be conducted either from the isolated organozinc
intermediates or in
a one-pot procedure from 1 and the
corresponding fluoroarene (see SI for details). While the resulting
products can be prepared by other well-established
methodologies,[52–55] these reactions importantly show that these
organozinc compounds can engage in onwards chemistry and act
as a point of synthetic diversification. In this regard, 2a was also
found to engage in allylation reactions[56] through catalytic
palladium p-allyl intermediates (see SI for further details).
While hindered by H/D exchange, a significant KIE could be
observed for the reaction, kH / kD ~ 2.5 to 3.5. These values are
small compared to those arising from non-reversible oxidative
addition of a C–H bond to a transition metal on the turnover
limiting step.[10] Rather based on the mechanistic proposal, the
KIE can be qualitatively assigned to a combination of an
equilibrium isotope effect originating from the reversible oxidative
addition of the C–H bond to Pd, and a KIE resulting from the
subsequent steps that lead to C–H zincation.[49],[50]
Conclusions
In summary, we report
a new catalytic reaction for the
transformation of C–H bonds to C–Zn bonds. Catalytic C–H
zincation has been achieved for a wide variety of arenes with high
7
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efficiency and selectivity. The reaction mechanism has been
interrogated and heterometallic complexes identified as key
intermediates. The new catalytic reaction not only provides
access to high-value organozinc compounds for use in synthesis,
it also showcases a remarkable role for heterometallic complexes
and metal---metal cooperativity in the catalytic functionalisation of
C–H bonds. Heterometallic cooperativity is an emerging design
approach in catalysis. The mechanistic insight we provide has the
potential to inspire further studies and provides a unique
perspective on transmetallation events involving Pd and Zn.[57],[58]
Mulvey, Chem. Commun. 2008, 2638–2640.
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Acknowledgements
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13016–13027.
We are grateful to the European Research Council
(FluoroFix:677367) and the Royal Society (UF090149). Johnson
Matthey are thanked for generous donation of PdCl2. Pete
Haycock is gratefully acknowledged for assistance with NMR
spectroscopy. M.G. thanks “la Caixa” Foundation (ID 100010434)
for a postgraduate scholarship (LCF/BQ/EU19/11710077).
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Entry for the Table of Contents
Insert text for Table of Contents here. A palladium catalyst and zinc–hydride reagent can be used to transform C–H into C–Zn bonds.
The reaction scope includes fluoroarenes, heteroarenes, and benzene. Heterometallic Pd---Zn complexes play a key role in catalysis.
Institute and/or researcher Twitter usernames: @crimmingroup
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