Expedient Hydrofunctionalisation of Carbonyls and Imines Initiated by Phosphacyclohexadienyl Anions

Article abstract of DOI:10.1002/cctc.202100651

The ability of phosphacyclohexadienyl anions [Li(1-R-PC₅Ph₃H₂)] [R=Me (1 a), nBu (1 b), tBu (1 c), Ph (1 d) and CH₂SiMe₃ (1 e)] to initiate hydrofunctionalisation reactions was investigated and compar

Full text of DOI:10.1002/cctc.202100651

The European Society Journal for Catalysis
Supported by
Accepted Article
Title: Expedient Hydrofunctionalisation of Carbonyls and Imines
Initiated by Phosphacyclohexadienyl Anions
Authors: Matthew J Margeson, Felix Seeberger, John A Kelly, Julia
Leitl, Peter Coburger, Robert Szlosek, Christian Müller, and
Robert Wolf
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: ChemCatChem 10.1002/cctc.202100651
Link to VoR: https://doi.org/10.1002/cctc.202100651
0
1/2020

ChemCatChem
10.1002/cctc.202100651
COMMUNICATION
Expedient Hydrofunctionalisation of Carbonyls and Imines
Initiated by Phosphacyclohexadienyl Anions
[a]
[a]
[a]
[a]
[a]
Matthew J. Margeson, Felix Seeberger, John A. Kelly, Julia Leitl, Peter Coburger, Robert
[
a]
[b]
[a]
Szlosek, Christian Müller* and Robert Wolf*
Abstract: The ability of phosphacyclohexadienyl anions
Li(1-R-PC Ph )] [R = Me (1a), nBu (1b), tBu (1c), Ph (1d) and
CH SiMe (1e)] to initiate hydrofunctionalisation reactions was
reduction of ketones with pinacolborane in solvent-free conditions
at elevated temperatures.[11]
[
5
3 2
H
2
3
Compared to hydroboration, hydrosilylation reactions
catalysed by main group compounds are much less common.
investigated and compared with simple, commercially available
compounds, such as LiOtBu, KOtBu and nBuLi. All compounds are
expedient catalysts for the hydroboration of a wide scope of
substrates, ranging from aldehydes to imines and esters. In the
hydroboration of carbon dioxide, however, only our system was
observed to efficiently produce the desired methanol equivalents.
Noteworthy examples include the highly Lewis acidic borane
6 5 3
F )
,[12] and phosphemium cations as well as commercially
[13]
B(C
available bases, such as KOtBu,
[
14,15]
KOH,[15] and Cs .[16]
CO
2 3
Although promising, main groups systems still do not match the
efficiency and scope of many transition metal catalysts in terms of
the hydrosilylation of carbonyl compounds, thus the demand for
more effective main group catalysts remains high.
The past few decades have seen considerable strides in main
group chemistry, both from a fundamental and applied point of
view. One of the more attractive prospects is the utilisation of main
group compounds as precious metal mimics, especially in terms
of catalytic applications.[1] The main goal is the eventual
replacement of rare transition metal catalysts with an effective and
more abundant main group counterpart.
The hydroelementation of unsaturated organic compounds, in
particular hydroboration and hydrosilylation, is a reaction that
traditionally was firmly in the remit of precious metal catalysts.[2]
Hydrofunctionalisation processes are highly prevalent in industry;
products from these reactions are used extensively in the
production of fine chemicals, pharmaceuticals, lubricants,
[
3]
adhesives and insulation. The past decade has witnessed an
influx of main group compounds capable of such transformations
and in the case of hydroboration reactions, actually surpassing
transition metal catalysts.[4] Beside these rather sophisticated
catalysts, recent years have also seen a plethora of reports with
more easily accessible and commercially available compounds,
which are able to effectively catalyse hydroelementation reactions.
Figure 1. Catalytic hydrofunctionalisation of carbonyl compounds using
phosphacyclohexadienyl salts 1a-e [R = Me (1a), nBu (1b), tBu (1c), Ph (1d),
CH
2 3
SiMe (1e)] and [a] Turnover frequency – average value for complete
reaction.
Alkoxides,[5,6]
potassium
fluoride/carbonate,[7]
Grignard
reagents[8] as well as n-butyl lithium[9,10] all were able to
hydroborate ketones to their respective alkoxyborane.
Furthermore, Leung and co-workers reported the catalyst-free
Our efforts to devise new main group element based catalysts
involved investigating phosphacyclohexadienyl anions 1a-e
(
2
Figure 1), which are readily synthesised by treatment of
,4,6-triphenylphosphinine with alkyl lithium reagents.[ These
17]
[
a]
M. J. Margeson,[+] F. Seeberger,[+] Dr. J. Leitl, Dr. P. Coburger, R.
Szlosek, Dr. J. A. Kelly, Prof. Dr. R. Wolf
Institute of Inorganic Chemistry, University of Regensburg
4
species (typically referred to as λ -phosphinine anions) are best
described as anionic tertiary phosphines, although they display
distinct chemical properties. We envisioned that the highly
reactive nature of these anions would lend themselves to small
molecule activation/catalysis. Here we show that such anions
have excellent properties for the hydrofunctionalisation of ketones,
imines and esters. We also compared our findings with
commercially available catalysts such an nBuLi, LiOtBu and
KOtBu.
93040 Regensburg (Germany)
E-mail: robert.wolf@chemie.uni-regensburg.de
[+
]
These author contributed equally to this work.
[
b]
Prof. Dr. C. Müller
Freie Universität Berlin, Institut für Chemie und Biochemie
Fabeckstr. 34/36, 14195 Berlin, Germany
E-Mail: c.mueller@fu-berlin.de
Supporting information for this article is given via a link at the end of
this article
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.202100651
COMMUNICATION
To test the catalytic potential of anions 1a-e, we performed a
series of hydroboration/silylation reactions. Acetophenone
hydrofunctionalisation was chosen as the benchmark reaction to
probe the capability of 1a-e, and to compare their catalytic activity
especially for n-butyl lithium. Benzophenone was used as a
sterically more demanding substrate to give a more manageable
reaction timeframe. Both alkoxides achieved a conversion of at
least 50% within 105 seconds, while 1c and n-butyl lithium only
required 60 and 30 seconds, respectively. These short reaction
times translate into an approximate turnover frequency (TOF) of
(
Table 1). While all compounds displayed high efficiency, the tBu
derivative, 1c performed the best (see Table 1, entry 3) and thus
was chosen for further optimisation in both hydroboration and
hydrosilylation reactions. Using 1c at a loading of 0.01 mol%,
acetophenone was fully converted to 1-phenylethan-1-ol in less
-1
-1
-1
-1
64 800 h , 35 000 h , 34 300 h and 153 500 h for 1c, LiOtBu,
KOtBu and nBuLi, respectively. To our knowledge, the best
known main group based catalyst for hydroboration reactions is
Okuda’s lithium triphenylborohydride complex containing
tris[2-(dimethylamino)ethyl]amine, which was reported to achieve
°
than 8 minutes at T = 23 C. This equates to a TOF of ≥ 75 000
−
1
h , which is among the most rapid of any reductions employing
pinacolborane to date.
-1 [18]
a TOF of at least 66 666 h . This TOF, however, was calculated
after the reaction was completed, meaning the actual TOF could
be much higher. Taken altogether, it is clear that nBuLi possesses
great catalytic activity, rivalling even the most active main group
hydroboration catalysts.
The catalyst was able to readily hydroborate a wide array of
substrates, including aldehydes, ketones, esters, ald- and
ketimines as well as benzoic acid (see Table S1 and S2, SI for
details). Besides its good functional group tolerance, 1c also
showed exceptional chemoselectivity in the presence of other
reducible moieties such as nitro, nitrile, pyridyl, and alkenyl
groups. In the hydrosilylation reactions, 1c showed a similar
substrate scope, excluding only esters, benzoic acid and
ketimines (see SI).
Table 2. ReactIR monitored catalyst comparison in the hydroboration of
[a]
benzophenone.
Table
1.
Acetophenone
hydrofunctionalisation
catalysed
by
phosphacyclohexadienyl anions in comparison to literature-known alkoxides and
time50% [s][c]
[
a]
time [s][b]
conversion
%]
−1 [d]
nBuLi.
Entry
cat.
TOF [h
]
[
1
2
3
4
1c
480
1155
2895
105
>99
>99
91
60 (54%)
105 (51%)
105 (50%)
30 (64%)
64 800
LiOtBu
KOtBu
nBuLi
34 971
34 286
153 600
>99
Red. Agent
eq]
TOF
[103
−1 [c]
h ]
Entry
cat. [mol%]
T [°C]
Time [h][b]
[
[
a] Reducing agent = 0.511 mmol, benzophenone = 0.500 mmol. [b] Time until
the given conversion was observed. [c] Time until a conversion of at least 50%
was reached. [d] Turnover frequency – calculated at the first point when the
conversion was greater than 50%.
1
2
1a (0.01)
1b (0.01)
HBpin (1.0)
HBpin (1.0)
HBpin (1.0)
HBpin (1.0)
HBpin (1.0)
HBpin (1.3)
HBpin (1.1)
HBpin (1.1)
23
23
23
23
23
rt
0.40
0.25
<0.13
0.17
0.17
0.5
25
40
3
1c (0.01)
≥75
60
A similar trend was also observed for the hydroboration of
octan-2-one, N-benzylidenaniline and ethyl acetate with
pinacolborane (Table 3). Low catalyst loadings are sufficient to
achieve high conversions in the course of 5 – 30 min. While in
most cases KOtBu was observed to be slightly slower, especially
in the hydroboration of the ethyl acetate, there was no major
difference between 1c, nBuLi and LiOtBu.
4
1d (0.01)
5
1e (0.01)
60
6[d]
7[e]
8[f]
LiOtBu (1.0)
NaOtBu (5.0)
nBuLi (0.1)
0.2
22
rt
3
< 0.007
5.8
0.17
[
a] Reducing agent = 0.20 mmol, substrate = 0.20 mmol, 0.1 mL solvent. [b] Time
for complete substrate conversion, detected by GC-FID using n-pentadecane as
an internal standard. [c] Turnover frequency - average value for complete Table 3. Comparison of 1c, LiOtBu, KOtBu and nBuLi in the reduction of
reaction. [d] See ref. 6. [e] See ref. 7. Reaction performed in toluene. [f] See different substrates using pinacolborane.
ref. 12. Reaction performed without solvent.
It is known that simple inorganic bases such as alkali metal
tert-butoxides and n-butyllithium can also catalyse the
hydroboration of acetophenone, but with comparatively higher
catalyst loadings and longer reaction times.[5,6,9,10] Considering
these results, we were interested in how well our catalytic system
compares to such commercially available catalysts. With
previously reported results in mind, we anticipated to see 1c to be
faster than these compounds. Surprisingly, initial tests using 2-
methylacetophenone gave similar activity for all catalysts (see SI).
In order to better compare the catalytic activities, ReactIR
measurements were conducted, revealing high activities that
surpassed expectations for these commercial compounds,
Solvent
mL]
time
[min]
conversion
[%]
Entry
Substrate
cat. [mol-%]
[b]
[
1
2
3
4
1c (0.05)
THF (0.5)
THF (0.5)
THF (0.5)
THF (0.5)
5
5
5
5
82
87
73
83
LiOtBu (0.05)
KOtBu (0.05)
nBuLi (0.05)
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.202100651
COMMUNICATION
5
6
7
8
9
1c (0.05)
LiOtBu (0.05)
KOtBu (0.05)
nBuLi (0.05)
1c (0.5)
THF (0.5)
THF (0.5)
THF (0.5)
THF (0.5)
THF (0.2)
THF (0.2)
THF (0.2)
THF (0.2)
THF (0.1)
THF (0.1)
THF (0.1)
THF (0.1)
5
70
59
52
77
49
63
55
64
49
44
15
45
These species have been previously proposed as intermediates
in certain reductions mediated by main group catalytic systems.[
19]
5
5
Table 5. Borane reduction of CO
2
catalysed by 1a-e.[a]
5
15
15
15
15
30
30
30
30
1
0
1
2
LiOtBu (0.5)
KOtBu (0.5)
nBuLi (0.5)
1c (3.0)
1
1
-1 [c]
Entry
cat. [mol%]
BR
2
Time [h][b]
TOF [h ]
3[c]
4[c]
5[c]
6[c]
1
2
3
4
5
1c (2)
Bpin
Bpin
Bpin
Bpin
Bcat
16
72[d]
72[d]
16
3.1
1
1
1
1
LiOtBu (5)
KOtBu (5)
nBuLi (5)
1c (0.5)
-
-
LiOtBu (3.0)
KOtBu (3.0)
nBuLi (3.0)
<0.2[e]
13
16
[
a] HBpin = 0.26 mmol, substrate = 0.25 mmol. [b] Conversion detected via
GC-FID using n-pentadecane as internal standard. [c] HBpin = 0.66 mmol, ethyl
acetate = 0.30 mmol, conversion detected via 1H NMR integration using
[a] Borane = 0.20 mmol, ~1 bar CO
complete substrate conversion, followed by 1H and B NMR spectroscopy.
c] Turnover frequency - average value for complete reaction. [d] Reaction
2
, 0.2 mL THF-d , T = 25 °C. [b] Time for
8
11
[
mesitylene as internal standard.
performed at 60 °C. [e] Yield < 15 %.
As potassium tert-butoxide has been reported as an efficient
hydrosilylation catalyst,[14,15] we went on to also test 1c, LiOtBu,
and n-butyl lithium in the hydrosilylation of acetophenone. In these
reactions, however, none of the lithium salts was able to compete
with potassium tert-butoxide hinting at a more pronounced cation
effect on the activity in hydrosilylation reactions (see Table 4).
Studies of 2'-methylacetophenone hydroboration in THF and
5 3 2 4
benzene using [K(1-tBu-PC Ph H )] (3) and [N(nBu) ][1-tBu-
PC Ph ] (4) revealed similar catalytic activities as observed for
5
3 2
H
1c (Table S5, SI). This was also observed for the alkoxides MOMe
and MOtBu (M = Li, Na, K). Therefore, it can be inferred that the
cation only has a minor influence on the reactivity. Similar
conversions of 73-89% were observed for all alkoxides with the
exception of NaOMe, which gave a conversion of only 30% (see
SI).
Table
4.
Acetophenone [ hydrofunctionalisation
catalysed
by
a]
phosphacyclohexadienyl anions.
In order to shed light onto the mechanism, further ReactIR
kinetic measurements were conducted. The reaction order was
determined using the method of initial rates and the time
normalisation approach (see SI for details).[20] The results clearly
suggest a zero-order dependence on ketone concentration and a
first order dependence on 1c and HBpin. Furthermore, a
stoichiometric reaction between 1c, ketone and HBpin was
performed. The full consumption of HBpin was observed and
upon comparing the integrals of the methyl signals of the ketone
(δ = 2.26 ppm) with the signals of the product (δ = 2.30 ppm) the
yield of the desired borolane can be estimated to be >95%. The
TOF
Time [h][b]
Entry
cat. [mol%]
T [°C]
[
h−
1 [c]
]
1[d]
2
1c (0.5)
23 (40)
23
3 (1)
1
67 (200)
200
LiOtBu (0.5)
KOtBu (0.1)
nBuLi (0.5)
3
23
<0.17
1
6000
200
4
23
1
1
1
B{ H} NMR spectrum has a major signal (δ = 22.2 pm) that can
be assigned to the borolane (5) with two minor signals (<10%) at
[
a] Reducing agent = 0.20 mmol, substrate = 0.20 mmol, 0.1 mL solvent. [b] Time
for complete substrate conversion, detected by GC-FID using n-pentadecane as δ = 6.3 and 5.8 ppm that could not be identified. The 31P{ H} NMR
1
an internal standard. [c] Turnover frequency - average value for complete
reaction. [d] Solvent free.
shows 1c to be the main component (86%) with the formation of
a new signal at δ = -24.3 ppm (11%). The signal at δ = -24.3 ppm
was also observed, when reacting 1c with the ketone in the
As all tested catalysts displayed the ability to reduce very
demanding substrates, we went on to test their ability to catalyse
the hydroboration of CO . With LiOtBu and KOtBu, no conversion
2
absence of borane. Therefore, we propose this to be an adduct of
the ketone with 1c. Although we can isolate the presumed adduct
(2), we were unable as of yet to crystallographically characterise
it. Upon testing 2 in the hydroboration of 2’-methylacetophenone,
only a slight decrease in catalytic activity was observed when
compared to 1c (Table S5, SI). When stoichiometric amounts of
HBpin were added to 2, the desired product (5) as well as the
released catalyst 1c could be observed as the main products.
Altogether, these experiments suggest the mechanism starts with
the formation of an adduct between the ketone and 1c, which then
was observed even at elevated temperatures. 1c and nBuLi both
1
were able to fully consume pinacolborane, as observed in the H
and 1 B NMR spectra. However, in the case of nBuLi a mixture of
1
products was observed. The hydroboration of CO
2
worked
significantly better with 1c, leading to the clean formation of
methanol equivalent (MeOBpin). The hydrofunctionalisation of
2
CO could be further optimised by using catechol borane (HBcat),
-1
giving TOFs of 13 h . Throughout the reaction with pinacolborane, reacts with the reducing agent. The catalytic cycle is subsequently
the formate equivalent HCO
C(OBpin)
2
1
Bpin and acetal equivalent
were identified by H and B NMR spectroscopy.
closed by the release 5 and the reformation of 1c.
11
H
2
2
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.202100651
COMMUNICATION
6268–6271; f) M. Arrowsmith, M. S. Hill, G. Kociok-Köhn, Chem. Eur. J.
2013, 19, 2776–2783; g) M. S. Hill, D. J. Liptrot, C. Weetman, Chem.
Soc. Rev. 2016, 45, 972–988.
[
[
[
[
[
[
[
5]
6]
7]
8]
9]
J. H. Kim, A. K. Jaladi, H. T. Kim, D. K. An, Bull. Korean Chem. Soc.
2019, 40, 971–975.
I. P. Query, P. A. Squier, E. M. Larson, N. A. Isley, T. B. Clark, J. Org.
Chem. 2011, 76, 6452–6456.
D. H. Ma, A. K. Jaladi, J. H. Lee, T. S. Kim, W. K. Shin, H. Hwang, D. K.
An, ACS Omega 2019, 4, 15893–15903.
W. Wang, K. Lu, Y. Qin, W. Yao, D. Yuan, S. A. Pullarkat, L. Xu, M. Ma,
Tetrahedron 2020, 76, 131145.
S. J. Yang, A. K. Jaladi, J. H. Kim, S. Gundeti, D. K. An, Bull. Korean
Chem. Soc. 2018.
10] Z. Zhu, X. Wu, X. Xu, Z. Wu, M. Xue, Y. Yao, Q. Shen, X. Bao, J. Org.
Chem. 2018, 83, 10677–10683.
11] W. Wang, M. Luo, W. Yao, M. Ma, S. A. Pullarkat, L. Xu, P.-H. Leung,
New J. Chem. 2019, 43, 10744–10749.
[
[
12] Blackwell, Sonmor, Scoccitti, Piers, Org. Lett. 2000, 2, 3921–3923.
13] a) T. Lundrigan, E. N. Welsh, T. Hynes, C.-H. Tien, M. R. Adams, K. R.
Roy, K. N. Robertson, A. W. H. Speed, J. Am. Chem. Soc. 2019, 141,
1
4083–14088; b) J. Zhang, J.-D. Yang, J.-P. Cheng, Nat Commun
Scheme 1. Proposed Mechanistic pathway of the hydroboration of ketones
initiated by 1c.
2021, 12, 2835..
[
14] D. Addis, S. Zhou, S. Das, K. Junge, H. Kosslick, J. Harloff, H. Lund, A.
Schulz, M. Beller, Chem. Asian J. 2010, 5, 2341–2345.
[
[
[
15] K. Revunova, G. I. Nikonov, Chem. Eur. J. 2014, 20, 839–845.
16] M. Zhao, W. Xie, C. Cui, Chem. Eur. J. 2014, 20, 9259–9262.
17] a) A. J. Ashe, T. W. Smith, Tetrahedron Lett. 1977, 18, 407–410; b) M.
Bruce, G. Meissner, M. Weber, J. Wiecko, C. Müller, Eur. J. Inorg.
Chem. 2014, 2014, 1719–1726; c) G. Märkl, F. Lieb, A. Merz, Angew.
Chem. Int. Ed. 1967, 6, 87-88; d) G. Märkl, C. Martin, Angew. Chem.
Int. Ed. 1974, 13, 408–409; e) G. Märkl, A. Merz, Tetrahedron Lett.
When
comparing
the
anions
effectiveness
hydroboration
of
and
phosphacyclohexadienyl
in
hydrosilylation catalysis of polar substrates with those for
commercially available bases LiOtBu, KOtBu and nBuLi, we have
found that these catalysts also show a remarkable efficiency,
rivalling the most active catalysts available to date. All of these
catalysts can reduce very challenging substrates, such as imines
and esters. However, LiOtBu, KOtBu and nBuLi were ineffective
1
968, 9, 3611–3614.
18] D. Mukherjee, H. Osseili, T. P. Spaniol, J. Okuda, J. Am. Chem. Soc.
016, 138, 10790–10793.
[19] T. J. Hadlington, C. E. Kefalidis, L. Maron, C. Jones, ACS Catal. 2017,
, 1853–1859.
[
2
7
[
20] a) J. Burés, Angew. Chem. Int. Ed. 2016, 55, 16084–16087; b) C. D.-T.
Nielsen, J. Burés, Chem. Sci. 2019, 10, 348–353.
in the hydroboration of CO
e which were able to efficiently reduce CO
2
. This is in contrast to compounds 1a-
to the corresponding
2
methanol equivalent under ambient conditions with HBpin and
HBcat. On-going work in our group concerns the utilisation of this
methodology
and
the
development
of
asymmetric
hydrofunctionalization reactions.
Acknowledgements
We thank Robert Kretschmer for access to a ReactIR instrument.
Vasily Korotenko, Hendrik Zipse, Robert Kretschmer and an
anonymous reviewer are thanked for valuable suggestions.
Funding by the Deutsche Forschungsgemeinschaft (MU1657/5-1,
WO1496/9-1, and RTG 2620 Ion Pair Effects) is greatfully
acknowledged.
Keywords: phosphinine • main group catalysis •
hydrofunctionalisation • carbon dioxide reduction • phosphorus
[
[
1]
2]
P. P. Power, Nature 2010, 463, 171–177.
a) J.-F. Carpentier, V. Bette, Curr. Org. Chem 2002, 6, 913–936; b) C.
C. Chong, R. Kinjo, ACS Catal. 2015, 5, 3238–3259; c) S. Díez-
González, S. P. Nolan, Org. Prep. Proced. Int. 2007, 39, 523–559; d) K.
Kuciński, G. Hreczycho, Green Chem. 2020, 22, 5210–5224.
a) E. P. Beaumier, A. J. Pearce, X. Y. See, I. A. Tonks, Nat. Rev. Chem.
[
[
3]
4]
2
2
019, 3, 15–34; b) J. Magano, J. R. Dunetz, Org. Process Res. Dev.
012, 16, 1156–1184; c) Z. Rappoport, Y. Apeloig, The Chemistry of
Organic Silicon Compounds, John Wiley & Sons, Ltd, Chichester, UK,
998.
1
a) M. L. Shegavi, S. K. Bose, Catal. Sci. Technol. 2019, 9, 3307–3336;
b) C. Weetman, S. Inoue, ChemCatChem 2018, 10, 4213–4228; c) Q.
Yin, Y. Soltani, R. L. Melen, M. Oestreich, Organometallics 2017, 36,
2381–2384; d) M. Oestreich, J. Hermeke, J. Mohr, Chem. Soc. Rev.
2015, 44, 2202–2220; e) M. R. Adams, C.-H. Tien, B. S. N. Huchenski,
M. J. Ferguson, A. W. H. Speed, Angew. Chem. Int. Ed. 2017, 56,
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.202100651
COMMUNICATION
Entry for the Table of Contents
Hydrofunctionalisations of various substrates, including, imines, esters and CO
2
are effectively initiated by lithium
phosphacyclohexadienyl compounds. High selectivities and excellent TOFs were found, rivalling those of previously reported organyl
and alkoxide anions.
This article is protected by copyright. All rights reserved.