Light- and Manganese-Initiated Borylation of Aryl Diazonium Salts: Mechanistic Insight on the Ultrafast Time-Scale Revealed by Time-Resolved Spectroscopic Analysis

Article abstract of DOI:10.1002/chem.202004568

Manganese-mediated borylation of aryl/heteroaryl diazonium salts emerges as a general and versatile synthetic methodology for the synthesis of the corresponding boronate esters. The reaction proved an ideal testing ground for delineating the Mn species responsible for the photochemical reaction processes, that is, involving either Mn radical or Mn cationic species, which is dependent on the presence of a suitably strong oxidant. Our findings are important for a plethora of processes employing Mn-containing carbonyl species as initiators and/or catalysts, which have considerable potential in synthetic applications.

Full text of DOI:10.1002/chem.202004568

Accepted Article
Accepted Article
Title: Light- and Manganese-Initiated Borylation of Aryl Diazonium
Salts: Mechanistic Insight on the Ultrafast Time-Scale Revealed
by Time-Resolved Spectroscopic Analysis
Authors: Ian Fairlamb, James D. Firth, L. Anders Hammarback,
Thomas J. Burden, Jonathan B. Eastwood, James R.
Donald, Chris S. Horbaczewskyj, Matthew T. McRobie, Adam
Tramaseur, Ian P. Clark, Michael Towrie, Alan Robinson,
Jean-Philippe Krieger, and Jason M. Lynam
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Chem. Eur. J. 10.1002/chem.202004568
Link to VoR: https://doi.org/10.1002/chem.202004568
01/2020

10.1002/chem.202004568
Chemistry - A European Journal
FULL PAPER
Light- and Manganese-Initiated Borylation of Aryl Diazonium
Salts: Mechanistic Insight on the Ultrafast Time-Scale Revealed
by Time-Resolved Spectroscopic Analysis
James D. Firth,[a] L. Anders Hammarback,[a] Thomas J. Burden,[a] Jonathan B. Eastwood,[a] James R.
Donald,[a] Chris S. Horbaczewskyj,[a] Matthew T. McRobie,[a] Adam Tramaseur,[a] Ian P. Clark,[b] Michael
Towrie, [b] Alan Robinson,[c] Jean-Philippe Krieger,[c] Jason M. Lynam*[a] and Ian J. S. Fairlamb*[a]
[a]
Prof. Dr. I. J. S. Fairlamb, Drs. J. M. Lynam, J. D. Firth, L. A. Hammarback, J. R. Donald, C. S. Horbaczewskyj, Mr. T. J. Burden, Mr. J. B. Eastwood, Mr.
M. T. McRobie, Mr. A. Tramaseur
Department of Chemistry
University of York
Heslington, York, YO10 5DD, United Kingdom
E-mail: ian.fairlamb@york.ac.uk; jason.lynam@york.ac.uk (joint corresponding authors)
[b]
[c]
Dr. I. P. Clark, Prof. M. Towrie,
Central Laser Facility
Research Complex at Harwell, STFC Rutherford Appleton Laboratory, Harwell Campus, Didcot, Oxfordshire, OX11 0QX, United Kingdom.
Drs. A. Robinson, J.-P. Krieger
Syngenta Crop Protection AG
Münchwilen, Breitenloh 5, 4333, Switzerland.
Supporting information for this article is given via a link at the end of the document (full experimental details).
Abstract: Manganese-mediated borylation of aryl/heteroaryl
diazonium salts emerges as a general and versatile synthetic
methodology for the synthesis of the corresponding boronate esters.
The reaction proved an ideal testing ground for delineating the Mn
species responsible for the photochemical reaction processes, i.e.
involving either Mn radical or Mn cationic species, which is dependent
on the presence of a suitably strong oxidant. Our findings are
important for a plethora of processes employing Mn-containing
carbonyl species as initiators and/or catalysts, which have much
potential in synthetic applications.
radicals can be simply achieved using a photo-initiator, resulting
in many reports over the past decade of the photoredox-catalysed
arylation of unsaturated systems.[14] For example, Yan and co-
workers demonstrated the eosin Y catalysed borylation of aryl
diazonium salts to generate aryl pinacol boronates (Scheme 1).[16]
In some cases, such processes proceed via photoinitiated radical
chain mechanisms, as was observed for arylation with aryl
diazonium salts.[17] However, it has been shown that the use of
broadband visible light irradiation can lead to the direct photolysis
of aryl diazonium salts, generating the aryl boronates via aryl
cations.[13,18,19] These findings therefore show that it is critical to
understand how the photochemical activation is being executed,
under specific conditions, as radical and cationic pathways might
be similarly energetically feasible. Furthermore, other research
teams have developed non-photoinduced processes for the
synthesis of aryl boronates from aryl diazonium salts,[20–25]
including the one-pot diazotization/borylation of anilines,[26–30]
proceeding via both radical and cationic intermediates.
Introduction
Aryl boronates are important building blocks within organic
synthesis, without question due to the ubiquity of the Suzuki-
Miyaura reaction, which ranks in the top-five most used reactions
in target-orientated synthesis,[1] across the pharmaceutical and
agrochemical industries.[2,3] The most common methods for their
preparation involve either the stoichiometric metalation (to
organo-lithium or Grignard reagents) or the Miyaura borylation[4]
of aryl halides. The former approach suffers from limited
functional group tolerance and the need for anhydrous conditions
and controlled reagent addition, whereas the latter requires Pd
catalysis. Inexpensive and abundant transition metals including
Cu, Ni, Zn and Fe can also be employed.[5,6]
Alternative practical approaches to aryl boronates include
C-H activation / borylation, often using earth abundant metals[7,8]
and the visible light-induced borylation of aryl radical precursors,
including aryl iodides,[9] aryl N‑hydroxyphthalimido esters,[10] and
aryl azo-sulfones.[11] Indeed, aryl diazonium salts have been
employed extensively as aryl radical precursors[12–15] due to their
relatively low reduction potential and the ease of synthesis from
widely available anilines. Photoreduction to the desired aryl
Scheme 1. Light mediated borylation of aryl diazoniums.
A versatile Mn precursor complex, namely dimanganese(0)
decacarbonyl, Mn2(CO)10, readily undergoes photo-induced
1
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homolysis to generate a manganese-centered radical [Mn(CO)5]●
(BDE of Mn-Mn bond ~15 kcal mol-1).[31] Facile generation of this
reactive species has been employed in several distinctive organic
transformations, which often proceed through the abstraction of a
halogen from an alkyl halide in reactions involving light.[32–41]
Despite this precedent there has been little reported confirming
that Mn2(CO)10 generates reactive aryl radicals.[42]
Given our interest in initiating chemical transformations with
MnI-carbonyl complexes,[43–45] we envisaged that the facile
reduction of aryl diazonium salts to aryl radicals could be achieved
with Mn2CO10, leading to generation of aryl pinacol boronates
upon treatment with B2pin2. Credibility for this proposal comes
from Ackermann and co-workers’ recent study, with the synthesis
of an exemplar aryl boronate (Scheme 1), using Mn2(CO)10 and
blue LEDs through a MnI-mediated process.[42] We recognized
that this single example could be broadened out into a general
synthetic methodology, but that the reaction manifold allowed us
to ask arguably a more fundamentally important question about
the involvement of Mn species in a raft of low oxidation state Mn-
mediated transformations,[42,46,55–62,47–54] particularly those
invoking redox neutral MnI species.
entries 8-13). We found that use of acetone resulted in full
conversion of 1a, however isolation was complicated by the
presence of minor unknown side products. Interestingly, when
methanol was used as solvent, gas evolution was observed prior
to irradiation, pointing to the involvement of alcohol in the
mechanism, perhaps in initiation.[19,25,26]
With optimal reaction conditions in hand, we investigated
the robustness and reproducibility of the protocol (for the
synthesis of 2a) using a Glorius sensitivity assessment (Scheme
2, top right, for full details see Supporting Information).[66] This
method is a quick means to gain an overview of the reaction
condition based sensitivity of a given synthetic method. Our
protocol showed little sensitivity to water content, concentration or
light intensity and only a moderate sensitivity to the presence of
oxygen. Furthermore, the reaction was easily scaled, giving 2a in
90% yield (2.10 g) on a 10 mmol scale (Scheme 2).
Table 1. Optimisation of Reaction Conditions.[a]
It is evident that initiators derived from Mn2(CO)10 could be
either radical (Mn0), cationic (MnI) or anionic (Mn-I) in nature.
Knowing which species form, particularly under activation by light,
and under what reaction conditions, is vitally important in
exploiting downstream breakthroughs in synthetic chemistry,
particularly with an eye on cascade processes. Answering this
question is not straight-forward. However, in recent years we have
demonstrated exactly how time-resolved multiple probe
spectroscopy (TRMPS) with infra-red detection can be used to
interrogate reaction steps pertinent to catalysis, from the pico-
Entry
1
Deviation from above
none
Yield of 2a / %[b]
100 (96)
2
2% Mn2(CO)10
81
3
1% Mn2(CO)10
44
4
1 equivalent of B2pin2
without Mn2(CO)10
without light[c]
51 (47)
2
second
to
micro-second
timescale.[43,63–65]
Following
5
photochemical activation of the pre-catalyst, the vibrational
modes of the Mn-CO moiety provide the perfect spectroscopic
handle for monitoring the accumulation of new species and
intermediates as well as their final fate. Thus, in this paper we
firstly describe the innovation of the Mn-mediated borylation of
6
3
7
2.5 mL MeCN
96
8
acetone instead of MeCN
MeOH instead of MeCN[d]
THF instead of MeCN
H2O instead of MeCN
DMA instead of MeCN[d]
DMSO instead of MeCN[d]
100 (85)
87
aryl/heteroaryl diazonium salts into
a
general synthetic
methodology. The reaction proved ideal for generating
mechanistic detail and extraordinary insight into the Mn species
involved in the photochemical reaction processes, the findings of
which are globally important for a plethora of processes
employing Mn-containing carbonyl initiators / catalysts.
9
10
11
12
13
32
Trace
90
58
Results and Discussion
[a] Reaction Conditions: 1a (0.5 mmol), B2pin2 (1.5 mmol) and Mn2(CO)10 (4
mol%) in MeCN (0.5 mL) were irradiated with 60W blue LEDs at room
temperature under Ar for 2 h. [b] Yield determined by GC using mesitylene (0.25
mmol) as an internal standard. Isolated yield in parentheses. [c] Vial wrapped in
foil. [d] 1.0 mL of solvent used.
Our investigation began with the borylation of aryl diazonium
tetrafluoroborate salt 1a with B2pin2 and Mn2(CO)10 initiator in
MeCN, irradiating with a 60 W blue LED lamp (Table 1 and Table
S1 in the Supporting Information). Aryl boronate 2a was formed
in quantitative yield and isolated in 96% yield when 4 mol%
Mn2(CO)10 and 3 equivalents of B2pin2 were irradiated in MeCN,
for 2 h (Table 1, entry 1). Reducing the stoichiometry of the
Mn2(CO)10 or B2pin2 resulted in lower yields (Table 1, entries 2-4).
Control experiments without either Mn2(CO)10 or light confirmed
the essential role of both the former (presumed to be the initiator
vide infra) and latter (Table 1, entries 5-6). Further reaction
optimisation studies showed that reducing reaction concentration
by five-fold had a negligible effect on product 2a yield (96%, Table
1, entry 7) and that acetonitrile was the optimal solvent (Table 1,
Next, the substrate scope of the transformation was investigated
(Scheme 2). The Mn-initiated borylation tolerated ethers giving 2a
(vide supra) and biaryl ether 2b in excellent yield. Simple alkyl
groups were also tolerated giving 2c–f in moderate yield (43–
75%). Sterically demanding mesityl and ortho-biphenyl substrates
gave 2g and 2h in 63% and 61% yield respectively. Potentially
reactive functional groups were also found compatible;
halogenated aryl diazonium salts gave borylated haloarenes (2i–
m) in moderate to excellent yields (44–99%), as well as
trifluoromethyl aryl boronate 2n in 71% yield. Ester (2o), amide
2
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and TEMPO indicated that this reaction proceeds via an aryl
radical (see Supporting Information for further details).
(2p) and ketone (2q) functionality were tolerated, as were phenol
(2r) and nitro groups (2s and 2t), albeit in poorer yields.
Furthermore, heteroaryl substituents gave the corresponding
pinacol boronates in moderate yield, including quinoline (2u),
pyridine (2v) and benzofuran (2w). Pleasingly, more complex
drug-derived substrates were accommodated well by the
methodology, with boronates 2x and 2y being formed in 88% and
63% yield respectively.
Mechanistic insight provided by TRMPS. Previous work on the
photochemistry of [Mn2(CO)10] (summarized in Figure 1) has
demonstrated that irradiation at low energy ( ≥ 400 nm) results
in Mn–Mn bond cleavage to give [Mn(CO)5]● .[67] The radical may
.
undergo different fates in non-donor solvents including (a)
dimerization to regenerate Mn2(CO)10 (b) in MeCN strong
oxidising agents result in the conversion to 18-electron
[Mn(CO)5(NCMe)]+,[68] and (c) in the absence of an exogenous
oxidant,
CO-substitution
by
MeCN
affords
[Mn(CO)3(NCMe)3][Mn(CO)5]. This latter process likely proceeds
via 19-electron [Mn(CO)3(NCMe)3]● which is then oxidised by
Mn2(CO)10 to [Mn(CO)3(NCMe)3][Mn(CO)5], with concomitant
formation of [Mn(CO)5]●.[69,70]
hn, 400 nm
(b)
½ Mn2(CO)10
[Mn(CO)5]
[Mn(CO)5(NCMe)]+
(a)
oxidant / NCMe
(c)
+ 2CO, - 3NCMe
- 2CO, + 3NCMe
[Mn(CO)3(NCMe)3]
+ Mn2(CO)10
-[Mn(CO)5]
[Mn(CO)3(NCMe)3][Mn(CO)5]
Figure 1. Previously reported fates of photochemically generated [Mn(CO)5]●.
(a) dimerization to reform Mn2(CO)10 (b) oxidation and solvent addition to form
[Mn(CO)5(NCMe)]+ (c) formation of [Mn(CO)3(NCMe)3][Mn(CO)5] corresponding
for a formal disproportionation of Mn2(CO)10
.
TRMPS was used to gain insight into the mechanistic process
underpinning the formation of pinacol boronates 2. In these
experiments, the sample was irradiated with an ultrafast laser
pulse ( = 400 nm) to activate the Mn2(CO)10. Insight into the
nature and dynamic behavior of the photoproducts was obtained
by monitoring the subsequent changes in the infra-red spectrum
between 1900 and 2100 cm-1 with pump-probe delays between 1
ps and 1 ms.[71] The resulting data are shown in Figures 2 and 3
as difference spectra, with negative peaks corresponding to
material consumed on photolysis, typically Mn2(CO)10, and
positive peaks due to the photoproducts.
Photolysis of Mn2(CO)10 in MeCN solution (ca. 1.36 mmol
dm-3) resulted in the formation of [Mn(CO)5]● in ca. 100 ps (Figure
2a). As expected, the majority of the Mn-radical recombined to
give Mn2(CO)10 as evidenced by the decrease in intensity of the
negative bleach bands for the dimer. A single long-lived
photoproduct, identified as [Mn(CO)3(NCMe)3]+ by comparison to
literature data,[72] was formed (kobs = (1.88 ± 0.09) x105 s-1).
Experiments performed in the presence of PhN2BF4 1c
showed concentration-dependent behavior. At a PhN2BF4 1c
concentration of 40.7 mmol dm-3 the initially formed [Mn(CO)5]●
converted to [Mn(CO)5(NCMe)]+ (Figure 2b) and evidence for the
reformation of Mn2(CO)10 was again obtained. However,
experiments performed at lower concentrations of PhN2BF4 1c
afforded [Mn(CO)3(NCMe)3]+ as the sole long-lived photoproduct
(Figure 2d). Furthermore, experiments performed with PhN2BF4
1c at high concentrations of Mn2(CO)10 resulted in the formation
of [Mn(CO)5(NCMe)]+ whereas at lower dimer concentrations
[Mn(CO)3(NCMe)3]+ was formed (Figure 1e).
Scheme 2. Borylation of (hetero)aryl diazonium salts 1.
We examined the feasibility of a continuous photo-flow method;
irradiating a 0.35 M solution of 1a, with 4 mol% of initiator
Mn2(CO)10 and 3 equivalents of B2pin2 for 2.5 h led to a 93%
conversion to aryl boronate 2a. A preliminary mechanistic
investigation involving irradiating 1n in the presence of Mn2(CO)10
3
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(a)
(b)
(c)
(e)
(d)
(f)
Figure 2 TRMPS-IR data for the reaction between Mn2(CO)10 and PhN2BF4 1c and/or B2pin2. Top: Reaction scheme showing proposed mechanistic pathways.
Bottom: TRMPS-IR data in the metal carbonyl region. The y-axis shows the change in absorbance (mOD, milli-optical density). The negative peaks correspond to
the bleach of the bands for Mn2(CO)10. The positive bands show the growth and change of intermediates. Data were acquired in a sealed flow system under ambient
conditions. (a) Mn2(CO)10 (1.36 mmol dm-3 ) in MeCN (10 mL), (b) Mn2(CO)10 (1.36 mmol dm-3) in MeCN (10 mL) and PhN2BF4 1c (40.7 mmol dm-3), (c) Mn2(CO)10
(1.36 mmol dm-3) in MeCN (10 mL) and 3.1 equiv. B2pin2, (d) effect of changing concentration of PhN2BF4 1c on the extent of the formation of [Mn(CO)5(NCMe)]+
and [Mn(CO)3(NCMe)3]+, spectra recorded after 8.8 s; (e) effect of changing concentration of Mn2(CO)10 on the extent of the formation of [Mn(CO)5(NCMe)]+ and
[Mn(CO)3(NCMe)3]+, spectra recorded after 8.8 s; (f) effect of changing concentration of B2pin2 on the extent of the formation of [Mn(CO)3(NCMe)3]+, spectra
recorded after 8.8 s;.
These data are consistent with the mechanism outlined in
Figure 2. At high concentrations, one-electron oxidation of
[Mn(CO)5]● by the diazonium salt results in the formation
[Mn(CO)5]+, which undergoes rapid solvation to give
[Mn(CO)5(NCMe)]+. Reduction of the diazonium salt results in the
formation of phenyl radicals and dinitrogen. In the synthetic
reaction the phenyl radicals then react with B2pin2 to give 2c. The
irreversible reduction of PhN2BF4 1c occurs at a potential of –0.16
V (versus SCE in MeCN),[73] given that the corresponding
reduction of [Mn(CO)5(NCMe)]+ has a potential of –0.455 V then
this process is clearly thermodynamically viable.[74] At lower
concentrations of PhN2BF4 1c the data are consistent with solvent
substitution of [Mn(CO)5]● to give [Mn(CO)3(NCMe)3]● and
subsequent oxidation by the diazonium salt to give
[Mn(CO)3(NCMe)3]+ – a viable process as [Mn(CO)3(NCMe)3]● is
a strong reducing agent (E < –3 V[69]).
Consistent with the Marcus theory of electron transfer which
predicts faster reduction of the diazonium salt by
[Mn(CO)3(NCMe)3]● than by [Mn(CO)5]●. These data show that
PhN2BF4 1c can be reduced through two different pathways,
following the photochemical activation of Mn2(CO)10.
a
Photolysis of Mn2(CO)10 in the presence of B2pin2 resulted
in the initial formation of [Mn(CO)5]● followed by conversion to
[Mn(CO)3(NCMe)3]+ (Figure 2c). Experiments performed at
variable concentrations of B2pin2 demonstrated that at higher
concentrations of B2pin2 more [Mn(CO)3(NCMe)3]+ was formed at
the expense of the recovery of Mn2(CO)10. The observation of
[Mn(CO)3(NCMe)3]+ in these experiments is remarkable, for which
two explanations are possible. Firstly, the presence of B2pin2
increases the rate of solvent substitution at [Mn(CO)5]● to give
greater amounts of [Mn(CO)3(NCMe)3]● which is then quenched
by Mn2(CO)10 to give [Mn(CO)3(NCMe)3]+. Secondly, and more
plausibly, [Mn(CO)3(NCMe)3]● reduces B2pin2. The reduction of
B2pin2 is predicted to occur at a potential of < –3 V[75] supported
by the ability of the 19-electron [Mn(CO)3(NCMe)3]● species to act
At lower concentration conditions, the second order rate of
oxidation of [Mn(CO)5]● by PhN2BF4 1c is slower than the rate of
solvent substitution and oxidation of [Mn(CO)3(NCMe)3]●.
4
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as a powerful reducing agent. No evidence was obtained for the
known boryl complex, Mn(CO)5(Bpin) (bands at 2012.06 and
1959.74 cm-1).[76]
(a)
In order to gain insight into the mechanistic process which
occurred under the reaction conditions used in the development
of the synthetic methodology vide supra, the TRMPS experiments
were performed with Mn2(CO)10 in the presence of both PhN2BF4
1c and B2pin2. When the experiment was performed with a
concentration of Mn2(CO)10 used in the previous experiments, but
the ratio of reagents used in Table 1, then [Mn(CO)3(NCMe)3]+
was the dominant product formed from [Mn(CO)5]● (Figure 3a). A
related experiment performed at the same concentration as the
synthetic chemistry showed more complicated behavior (Figure
3b) with evidence for the formation of both [Mn(CO)3(NCMe)3]+
and [Mn(CO)5(NCMe)]+. While an additional unassigned band at
2071 cm-1 was also present in this experiment, these results
support the conclusion that photochemically generated
[Mn(CO)5]● may either act as reducing agent directly or, following
solvent substitution, through [Mn(CO)3(NCMe)3]●. It is likely that
subsequent to initiation, the reaction proceeds through a chain
propagation process whereby trapping of the aryl radical results
in the formation of a boryl radical anion that can reduce another
molecule of aryl diazonium 1.[15] Of note, even though the reaction
is thought to proceed through a chain propagation process,
constant irradiation is required due to the facile recombination of
[Mn(CO)5]● to regenerate Mn2(CO)10.
(b)
FT-IR analysis of a reaction mixture performed using the
conditions in Table 1, entry 1, demonstrated that
[Mn(CO)5(NCMe)]+ was the dominant metal carbonyl-containing
species at the end of the reaction (see Supporting Information).
This is consistent with the primary activation pathway involving
reduction of 1c by [Mn(CO)5]● and provides an important link
between the data obtained by TRMPS and the synthetic chemistry.
Figure 3 TRMPS-IR data for the reaction between Mn2(CO)10 and PhN2BF4 1c
and B2pin2 (a) Mn2(CO)10 (0.1 equiv. 0.70 mmol dm-3), and B2pin2 (3 equiv., 21.1
mmol dm-3) (b) Mn2(CO)10 (0.04 equiv., 2.29 mmol dm-3)PhN2BF4 1c(1.7 equiv.,
90.6 mmol dm-3) and B2pin2 (3 equiv., 156.9 mmol dm-3) in MeCN (10 mL).
Conclusion
In this paper we have innovated a robust borylation reaction for
aryl/heteroaryl diazonium salts involving Mn2(CO)10 as an initiator.
The reaction proved the ideal manifold for state-of-the-art
mechanistic work, through a study on the behavior of the MnI-
carbonyl species utilizing time-resolved multiple probe
spectroscopy (TRMPS-IR). This enabled the transient species
pertinent to the chemistry and their fates to be mapped out. Our
findings indicate that Mn radical species of the type, [Mn(CO)5]●
are formed, which is then susceptible to oxidation at the Mn centre
(Figure 4). A clean reaction is seen upon treatment of [Mn(CO)5]●
with high concentrations of PhN2BF4 1c to give [Mn(CO)5(S)]+
species, where S = CH3CN (we expect polar aprotic solvents to
behave similarly). At lower concentrations of PhN2BF4 1c
[Mn(CO)3(S)3]+ is generated through oxidation of 19-electron
[Mn(CO)3(S)3]●. In both cases, reduction of the 1c will result in the
generation of aryl radicals which then react with B2pin2 to give 2c.
We presume that this results in the concomitant generation of
boron-based radicals which propagate the reaction, highlighting
the role of the Mn-carbonyl complex as a photo-initiator. In the
presence of the B2pin2 we also see that [Mn(CO)3(S)3]+ is formed,
5
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[Mn(CO)5(S)]+ and [Mn(CO)3(S)3]+ are both cationic MnI species,
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chemistries.
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Acknowledgements
We thank the EPSRC for funding (EP/S009965/1: ‘A Fully-
Automated Robotic System for Intelligent Chemical Reaction
Screening’), in addition, the EPSRC for an iCASE award involving
Syngenta, EP/N509413/1, for funding the PhD studentship to L.
A. H. The STFC (access to the ULTRA facility) is gratefully
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Keywords: Manganese • Photocatalysis • Mechanism •
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Entry for the Table of Contents
Mn-mediated borylation of aryl/heteroaryl diazonium salts emerges as a general and versatile synthetic methodology for the
synthesis of aryl/heteroaryl boronate esters. The MnI-carbonyl species generated under the reaction conditions has been revealed by
time-resolved multiple probe spectroscopy (TRMPS-IR).
Institute and/or researcher Twitter usernames: @Ian_Fairlamb @ChemistryatYork @legosnail1
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