Heterocyclic Carbene-Catalyzed Hydride Transfer in the Hydroboration of Carbonyl Compounds

Article abstract of DOI:10.1002/cjoc.201900139

N-Heterocyclic carbene (NHC) enabled the highly efficient catalytic hydroboration of a wide range of ketones and aldehydes under mild conditions, and a new mechanism of catalytic hydroboration reaction which involves direct hydride transfer is proposed.

Full text of DOI:10.1002/cjoc.201900139

Accepted Article
Title: Heterocyclic Carbene-Catalyzed Hydride Transfer in the Hydroboration of
Carbonyl Compounds
Authors: Tianhao Li, Jianying Zhang, and Chunming Cui*
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Heterocyclic Carbene-Catalyzed Hydride Transfer in the Hydroboration
of Carbonyl Compounds
Tianhao Li,a Jianying Zhang,a and Chunming Cui*,a
a State Key Laboratory of Elemento-Organic Chemistry, Nankai University, 94 Weijin Road, Tianjin 300071, P.R. China.
Cite this paper: Li, T.; Zhang, J.; Cui, C. Chin. J. Chem. 2019, 37, XXX—XXX. DOI: 10.1002/cjoc.201900XXX
Summary of main observation and conclusion N-heterocyclic carbene (NHC) enabled the highly efficient catalytic hydroboration of a wide range of
ketones and aldehydes under mild conditions, and a new mechanism of catalytic hydroboration reaction which involves direct hydride transfer is
proposed.
of the hydride in the absence of catalysts is quite slow and not
Background and Originality Content
suitable for synthetic purpose. To our delight, the hydroboration
of acetophenone in the presence of 1.0 mol% IiPr in CH3CN at
N-heterocyclic carbene-borane (NHC-BH3) complexes have
emerged as powerful hydrogen donors and hydride transfer
room temperature led to a single product in over 99% yield in 2 h
reagents because of the increased reactivity of the B-H bonds.1
(Table 1, entry 2). These experiments indicated that the NHC is a
NHC-boranes have also been employed as reagents for
potential catalyst for the hydroboration reaction. The other NHCs
hydroboration of alkenes and alkynes in the presence of initiators
have also been tested under the same conditions, and the results
or catalysts.2 Although significant advances have been achieved
with NHC-borane reagents in stoichiometric hydroboration, the
complexation of the NHC in the final products is problematic for
synthetic purpose, and generally requires additional steps for its
removal. We, therefore, are interested in the development of
catalytic approach for hydroboration enabled by NHCs.
are summarized in Table 1 (entries 2-6). It can be seen that IiPr
gave the best yield while the other less or more bulkier NHCs led
to low yields, indicating the catalytic reaction is sensitive to the
steric effects of NHCs.
Scheme 1 N-heterocyclic carbenes tested in the studies
Catalytic hydroboration of unsaturated compounds
represents the most atom-economic and selective protocol for
the synthesis of organoboranes, which are significant synthetic
intermediates in a variety of organic transformations.3 However,
the hydroboration of carbonyl compounds is much less studied
compared to alkenes. Recent studies have shown that transition
metal,4,5 rare-earth6 and main group catalysts7,8 could mediate
this transformation but most of them are only efficient for
aldehydes. NHC-catalyzed hydroboration can be considered to be
practical and mechanistically distinctive from metal-catalyzed
reactions since NHCs are strong bases and easily available either
from commercial sources or bench scale synthesis. Herein, we
report the first NHC-catalyzed hydroboration of carbonyl
compounds, which involves the direct hydride transfer from
HBpin to carbonyl compounds and exhibits high efficiency to both
aldehydes and ketones.
Table 1 Optimization of the reaction conditions
Entrya
cat. (mol%)
-
IiPr (1)
Solvent
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
Toluene
THF
Time (h)
Yields (%)b
< 10
> 99
75
1
2
10
2
3
IMe (1)
ItBu (1)
IMes (1)
IDipp (1)
IiPr (1)
2
4
2
81
5
2
49
Results and Discussion
Results
6
2
75
7
2
60
At the outset, we were aware that the choice of boranes and
N-heterocyclic carbenes are critically important for the catalytic
process. Pinacol borane (HBpin) is commercially available and has
been widely used as hydroboration reagents under transition
metal catalysis. On the other hand, several NHCs with different
steric effects (Scheme 1) have been synthesized and employed for
the studies. Thus, we commenced our studies with acetophenone
as the model substrate and HBpin as the hydroboration reagent
to test various reaction conditions. In the absence of NHCs, the
reaction in acetonitrile at room temperature resulted in less than
10% yield in 10 h (Table 1, entry 1), indicating the direct transfer
8
IiPr (1)
2
42
9
IiPr (0.5)
IiPr (0.2)
CH3CN
CH3CN
2.5
10
> 99
50
10
a
Reaction conditions: acetophenone (1.0 mmol), HBpin (1.2 mmol),
b
solvent (2 mL) and catalyst at room temperature.
Yields were
determined by 1H NMR spectroscopy.
On the basis of the initial success, the catalytic reactions with
IiPr as catalyst in toluene and THF as solvents were also examined
(Table 1, entries 7-8) under the same conditions. It is clear that
*E-mail: cmcui@nankai.edu.cn
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Li et al.
Report
reactions in THF and toluene are much slow compared to that in
acetonitrile. The loadings of the NHC catalyst were also optimized
under the similar conditions, and 0.5 mol% loading was found to
be the best (Table 1, entries 9 and 10).
11
12
< 1
13
2k
2l
> 99
> 99
> 198
With the optimized conditions, the scope of the
hydroboration was investigated using a variety of ketones and
aldehydes. Both aromatic and aliphatic ketones led to almost
complete conversions. However, aromatic ketones undergo faster
hydroboration than aliphatic ketones (Table 2, entries 1-3, and 5),
and sterically hindered ketones resulted in slow reaction (Table 2,
entry 4). Ketones with electron-withdrawing groups were
converted rapidly (Table 2, Entries 6 and 11), whereas the ketones
with electron-donating groups led to long reaction time (Table 2,
entries 7 and 12). Functional groups on the different positions of
aromatic ketones have little effects on the catalytic reaction
(Table 2, entries 8-10). 2-acetylfuran and 2-acetylthiophene can
also achieve complete hydroboration (Table 2, entries 13 and 14).
Hydroboration of aldehydes using IiPr as catalyst required longer
time under the same reaction conditions (Table 3)
> 15.2
13
14
3
4
2m
2n
> 99
> 99
> 66
> 49.5
a Reaction conditions: ketone (1 mmol), HBpin (1.2 mmol), CH3CN (2 mL),
and catalyst IiPr (0.005 mmol) at room temperature. Yields were
b
determined by 1H NMR spectroscopy.
Table 3 Hydroboration of aldehydes catalyzed by IiPr
Table 2 Hydroboration of ketones catalyzed by IiPr
TOF
Entrya
1
Substrate
Time (h) Product Yields (%)b
TOF
Entrya
1
Substrate
Time (h) Product Yields (%)b
(hr-1)
(hr-1)
3
4
4a
4b
4c
> 99
> 99
> 99
> 66
2.5
3.5
3
2a
2b
2c
2d
2e
> 99
> 99
> 99
> 99
> 99
> 79.2
2
3
> 49.5
> 19.8
2
3
4
5
> 56.6
> 66
10
4
5
6
7
8
9
6
4d
4e
4f
> 99
> 99
> 99
> 99
> 99
> 99
> 33
> 16.5
> 18
5
> 39.6
> 198
< 1
12
11
11
10
3
6
7
< 1
5
2f
2g
2h
2i
> 99
> 99
> 99
> 99
> 99
> 198
> 39.6
> 56.6
> 56.6
> 66
4g
4h
4i
> 18
8
3.5
3.5
3
> 19.8
> 66
9
10
2j
10
5
4j
> 99
> 39.6
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Heterocyclic Carbene-Catalyzed Hydride Transfer in the Hydroboration of Carbonyl Compounds
Chin. J. Chem.
a Reaction conditions: aldehyde (1 mmol), HBpin (1.2 mmol), CH3CN (2 mL), transition state TS to form the ion pair Int-2 is the rate limiting
b
and catalyst IiPr (0.005 mmol) at room temperature. Yields were
step with the relative low energy barrier of 20.88 kcal/mol. The
Int-2 could spontaneously combine to form the NHC complex
Int-3 without any energy barrier, leading to the favorable
equilibrium to the final product via the dissociation of IiPr from
Int-3. The overall reaction is highly exothermic, consistent with
the experiment observation in the large scale reaction of
benzophenone (1e, 50 mmol) with HBpin. The relatively high
reactivity observed for ketones probably resulted from the
relatively higher stability of the Int-2 (alkoxide intermediate,
Scheme 2) for a ketone than that for an aldehyde.
determined by 1H NMR spectroscopy.
The NHC-catalyzed hydroboration can be scaled up to 50
mmol of substrate without the noticeable decay of the activity. A
high dosage reaction of benzophenone (1e, 9.1 g. 50 mmol) with
60 mmol of HBpin in acetonitrile in the presence of 0.5 mol% of
IiPr led to the immediate exothermic hydroboration, which was
completed within 1 h to give the pure hydroboration product up
to 99% yield.
Compared with the previous reports,4-8 the present NHC
catalyzed hydroboration of carbonyl compounds is highly efficient
for both ketones and aldehydes and suitable for large scale
synthesis. In addition, the complete conversion of bulky
substrates was observed for this system.
Conclusions
In summary, we have demonstrated that the efficient
hydroboration of carbonyl compounds could be achieved under
the catalysis of IiPr. The reaction is scalable and might be practical.
Mechanistic studies disclosed that the combination of the
commercially HBpin with IiPr not only resulted in facile hydride
transfer but also exhibited high activity for both ketones and
aldehydes. Further studies on NHC-catalyzed hydride transfer to
other substrates are currently undertaken in our group.
To gain further insight into the hydroboration mechanism,
several controlled experiments and Density Functional Theory
(DFT) calculations were carried out. When large excess (10
equivalents) of acetophenones was employed, the reaction rate
was significantly increased. In contrast, large excess (10
equivalents) of HBpin significantly suppressed the hydroboration
reaction (Table S1). In addition, the reaction rate increased
linearly along with the increase of the loadings of the catalyst
(Table S2) within 0.7 mol% loadings. When the loadings of the
NHC are more than 0.7 mol%, the reaction rates deviate from the
linearity and are slowly increased (Figure S1). The NMR scale
reaction of the equal amounts of HBpin and IiPr in CD3CN
Experimental
General Consideration
All operations were carried out under an atmosphere of argon
by using modified Schlenk line and glovebox techniques. All
solvents were freshly distilled from Na or P2O5. The NMR spectra
were recorded at room temperature on Bruker AMX 400
spectrometers. The N-heterocyclic carbenes IiPr, IMe,S1 ItBu,S2
IMes,S3 and IDippS4 were synthesized as described in literature.
disclosed the coordination of IiPr to HBpin as indicated by the H
1
and 11B NMR spectroscopy, indicating the initial activation of
HBpin with the NHC (Figure S2). The NMR experiments of the
reaction of HBpin with IiPr also showed that IiPr could be
hydrogenated at the carbene center to give a mixture containing
H2IiPr (Figures S3). The mechanism for this side reaction is not
clear at current state. We reasoned that the side reaction might
be responsible for the observation that a large excess of HBpin
suppressed the hydroboration reaction.
General Procedure for Catalytic Hydroboration of Ketones
and Aldehydes
Ketone or aldehyde (1 mmol), pinacolborane (HBpin, 1.2
mmol), CH3CN (2 ml) and IiPr (0.5 mol%, 0.005 mmol) were
charged in a Schlenk reaction tube with a magnetic bead inside
the glove box. The reaction mixture was allowed to stir at room
temperature for a period of time. The progress of the reaction
was monitored by 1H NMR. The results were given in Tables 1-3 in
the manuscript. Chalcone, 4-acetylbenzaldehyde and methyl
4-acetylbenzoate were also tested for the hydroboration, a
mixture was obtained for these reactions.
Scheme 2 Calculated energy profiles for the catalytic hydroboration
Supporting Information
The supporting information for this article is available on the
WWW under https://doi.org/10.1002/cjoc.2018xxxxx.
Acknowledgement
This work was supported by the National Natural Science
Foundation of China (grant nos. 21632006 and 21472098).
References
[1] For selected references, see (a) Curran, D. P.; Solovyev, A.; Brahmi, M.
M.; Fensterbank, L.; Malacria M.; Lacôte, E. Synthesis and Reactions
of N-Heterocyclic Carbene Boranes. Angew. Chem, Int. Ed. 2011, 50,
10294-10317; (b) McFadden, T. R.; Fang, C.; Geib, S. J.; Merling, E.;
Liu P.; Curran D. P.; Synthesis of Boriranes by Double Hydroboration
Reactions of N-Heterocyclic Carbene Boranes and Dimethyl
Acetylenedicarboxylate. J. Am. Chem. Soc. 2017, 139, 1726-1729; (c)
Ren, S. –C.; Zhang, F. –L.; Qi, J.; Huang, Y. –S.; Xu, A. –Q.; Yan H. –Y.;
Wang, Y. –F. Radical Borylation/Cyclization Cascade of 1,6-Enynes for
DFT
calculations
at
the
M06/6-311+G(d,p)/CPCM(acetonitrile)//B3LYP/6-31G(d) level of
the theory (Scheme 2) disclosed that the initial activation of
HBpin by IiPr to form the intermediate Int-1 is exothermic with
the very small energy barrier of 2.79 kcal/mol, in line with the
facile formation of the NHC-borane complex observed in the
above mentioned NMR experiment. The hydride transfer via the
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Li et al.
Report
the Synthesis of Boron-Handled Hetero- and Carbocycles. J. Am.
[5] (a) Bandini, M.; Cozzi, P. G.; Angelis M.; Umani-Ronchi, A. Zinc
triflate-bis-oxazoline complexes as chiral catalysts: enantioselective
reduction of α-alkoxy-ketones with catecholborane. Tetrahedron Lett.
2000, 41, 1601-1605; (b) Roh, S. –G.; Park, Y. –C.; Park, D. –K.; Kim T.
–J.; Jeong, J. H. Synthesis and characterization of a Zn(II) complex of
Chem. Soc. 2017, 139, 6050-6053; (d) Allen, T. H.; Kawamoto, T.;
Gardner, S.; Geib S. J.; Curran, D. P. N-Heterocyclic Carbene Boryl
Iodides Catalyze Insertion Reactions of N-Heterocyclic Carbene
Boranes and Diazoesters. Org. Lett. 2017, 19, 3680-3683; (e)
Supranovich, V. I.; Levin, V. V.; Struchkova, M. I.; Korlyukov A. A.;
Dilman, A. D. Radical Silyldifluoromethylation of Electron-Deficient
Alkenes. Org. Lett. 2017, 19, 3215-3218; (f) McGough, J. S.; Cid J.;
Ingleson, M. J. Catalytic Electrophilic C-H Borylation Using
NHC⋅Boranes and Iodine Forms C2-, not C3-, Borylated Indoles. Chem.
Eur. J. 2017, 23, 8180-8184; (g) Bolt D. A.; Curran, D. P.
a pyrazole-based ligand bearing
a chiral L-alaninemethylester.
Polyhedron 2001, 20, 1961-1965; (c) Locatelli M.; Cozzi, P. G.
Effective Modular Iminooxazoline (IMOX) Ligands for Asymmetric
Catalysis: [Zn(IMOX)]-Promoted Enantioselective Reduction of
Ketones by Catecholborane. Angew. Chem. Int. Ed. 2003, 42,
4928-4930; (d) Roh, S. G.; Yoon J. U.; Jeong, J. H. Synthesis and
1-Butyl-3-methylimidazol-2-ylidene Borane:
A
Readily Available,
characterization of
a
chiral Zn(II) complex based on
a
Liquid N-Heterocyclic Carbene Borane Reagent. J. Org. Chem. 2017,
82, 13746-13750.
trans-1,2-diaminocyclohexane derivative and catalytic reduction of
acetophenone. Polyhedron 2004, 23, 2063-2067; (e) Koren-Selfridge,
L.; Londino, H. N.; Vellucci, J. K.; Simmons, B. J.; Casey C. P.; Clark, T.
B. A Boron-Substituted Analogue of the Shvo Hydrogenation Catalyst:
Catalytic Hydroboration of Aldehydes, Imines, and Ketones.
Organometallics 2009, 28, 2085-2090; (f) Lummis, P. A.; Momeni, M.
R.; Lui, M. W.; McDonald, R.; Ferguson, M. J.; Miskolzie, M.; Brown A.;
Rivard, E. Accessing Zinc Monohydride Cations through Coordinative
Interactions. Angew. Chem. Int. Ed. 2014, 53, 9347-9351; (g) Kaithal,
A.; Chatterjee B.; Gunanathan, C. Ruthenium Catalyzed Selective
Hydroboration of Carbonyl Compounds. Org. Lett. 2015, 17,
4790-4793; (h) Drover, M. W.; Schafer L. L.; Love, J. A. Capturing
HBCy2: Using N,O-Chelated Complexes of Rhodium(I) and Iridium(I)
for Chemoselective Hydroboration. Angew. Chem. Int. Ed. 2016, 55,
3181-3186; (i) Bagherzadeh S.; Mankad, N. P. Extremely efficient
hydroboration of ketones and aldehydes by copper carbene catalysis.
Chem. Commun. 2016, 52, 3844-3846; (j) King, A. E.; Stieber, S. C. E.;
Henson, N. J.; Kozimor, S. A.; Scott, B. L.; Smythe, N. C.; Sutton A. D.;
Gordon, J. C. Ni(bpy)(cod): A Convenient Entryway into the Efficient
Hydroboration of Ketones, Aldehydes, and Imines. Eur. J. Inorg.
Chem. 2016, 1635-1640; (k) Tamang S. R.; Findlater, M. Iron
Catalyzed Hydroboration of Aldehydes and Ketones. J. Org. Chem.
2017, 82, 12857-12862; (l) Khoo, S.; Cao, J.; Ng, F.; So, C. –W.
[2] (a) Prokofjevs, A.; Boussonnière, A.; Li, L.; Bonin, H.; Lacôte, E.;
Curran D. P.; Vedejs, E. Borenium Ion Catalyzed Hydroboration of
Alkenes with N-Heterocyclic Carbene-Boranes. J. Am. Chem. Soc.
2012, 134, 12281-12288; (b) Boussonnière, A.; Pan, X.; Geib S. J.;
Curran, D. P. Borenium-Catalyzed Hydroborations of Silyl-Substituted
Alkenes and Alkynes with
a Readily Available N-Heterocyclic
Carbene–Borane. Organometallics 2013, 32, 7445-7450; (c)
Taniguchi T.; Curran, D. P. Hydroboration of Arynes with
N-Heterocyclic Carbene Boranes. Angew. Chem. Int. Ed. 2014, 53,
13150-13154; (d) Watanabe, T.; Curran D. P.; Taniguchi, T.
Hydroboration of Arynes Formed by Hexadehydro-Diels-Alder
Cyclizations with N-Heterocyclic Carbene Boranes. Org. Lett. 2015,
17, 3450-3453.
[3] (a) Burgess, K.; Ohlmeyer, M. J. Transition-metal promoted
hydroborations of alkenes, emerging methodology for organic
transformations. Chem. Rev. 1991, 91, 1179-1191; (b) Thomas, S. P.;
Aggarwal, V. K. Asymmetric Hydroboration of 1,1-Disubstituted
Alkenes. Angew. Chem. Int. Ed. 2009, 48, 1896-1898; (c) Chong C. C.;
Kinjo, R. Catalytic Hydroboration of Carbonyl Derivatives, Imines, and
Carbon Dioxide. ACS Catal. 2015, 5, 3238-3259.
[4] (a) Giffels, G.; Dreisbach, C.; Kragl, U.; Weigerding, M.; Waldmann H.;
Wandrey, C. Chiral Titanium Alkoxides as Catalysts for the
Enantioselective Reduction of Ketones with Boranes. Angew. Chem.
Int. Ed. Engl. 1995, 34, 2005-2006; (b) Almqvist, F.; Torstensson, L.;
Gudmundsson A.; Frejd, T. New Ligands for the Titanium (IV)-Induced
Asymmetric Reduction of Ketones with Catecholborane. Angew.
Chem. Int. Ed. Engl. 1997, 36, 376-377; (c) Sarvary, I.; Almqvist F.;
Frejd, T. Asymmetric Reduction of Ketones with Catecholborane
Using 2,6-BODOL Complexes of Titanium(IV) as Catalysts. Chem. Eur.
J. 2001, 7, 2158-2166; (d) Fernandes A. C.; Romão, C. C. Reduction of
sulfoxides with boranes catalyzed by MoO2Cl2. Tetrahedron Lett.
2007, 48, 9176-9179; (e) Khalimon, A. Y.; Farha, P.; Kuzmina, L. G.;
Nikonov, G. I. Catalytic hydroboration by an imido-hydrido complex
of Mo(IV). Chem. Commun. 2012, 48, 455-457; (f) Oluyadi, A. A.; Ma
S.; Muhoro, C. N. Titanocene(II)-Catalyzed Hydroboration of Carbonyl
Compounds. Organometallics 2013, 32, 70-78; (g) Huang L.; Wei, H.
Mechanistic insights into B-H bond activation with the high-valent
oxo-molybdenum complex MoO2Cl2. New J. Chem. 2014, 38,
5421-5428; (h) Khalimon, A. Y.; Farha P. M.; Nikonov, G. I.
Imido-hydrido complexes of Mo(IV): catalysis and mechanistic
aspects of hydroboration reactions. Dalton Trans. 2015, 44,
18945-18956; (i) Vasilenko, V.; Blasius, C. K.; Wadepohl H.; Gade, L. H.
Mechanism-Based Enantiodivergence in Manganese Reduction
Catalysis: A Chiral Pincer Complex for the Highly Enantioselective
Hydroboration of Ketones. Angew. Chem. Int. Ed. 2017, 56,
8393-8397; (j) Huang, Z.; Liu, D.; Camacho-Bunquin, J.; Zhang, G.;
Yang, D.; López-Encarnación, J. M.; Xu, Y.; Ferrandon, M. S.; Niklas, J.;
Poluektov, O. G.; Jellinek, J.; Lei, A.; Bunel E. E.; Delferro, M.
Supported Single-Site Ti(IV) on a Metal-Organic Framework for the
Hydroboration of Carbonyl Compounds. Organometallics 2017, 36,
3921-3930.
Synthesis of
a Base-Stabilized Silicon(I)-Iron(II) Complex for
Hydroboration of Carbonyl Compounds. Inorg. Chem. 2018, 57,
12452-12455; (m) Tamang, S. R.; Bedi, D. Shafier-Haghighi, S.; Smith,
C. R. Crawford, C. Findlater, M. Cobalt-Catalyzed Hydroboration of
Alkenes, Aldehydes, and Ketones. Org. Lett. 2018, 20, 6695-6700; (n)
Wu, J.; Zeng, H.; Cheng, J.; Zheng, S.; Golen, J. A.; Manke, D. R.;
Zhang, G. Cobalt(II) Coordination Polymer as a Precatalyst for
Selective Hydroboration of Aldehydes, Ketones, and Imines. J. Org.
Chem. 2018, 83, 9442-9448.
[6] (a) Weidner, V. L.; Barger, C. J.; Delferro, M.; Lohr T. L.; Marks, T. J.
Rapid, Mild, and Selective Ketone and Aldehyde Hydroboration
/Reduction Mediated by a Simple Lanthanide Catalyst. ACS Catal.
2017, 7, 1244-1247; (b) Chen, S.; Yan, D.; Xue, M.; Hong, Y.; Yao Y.;
Shen, Q. Tris(cyclopentadienyl)lanthanide Complexes as Catalysts for
Hydroboration Reaction toward Aldehydes and Ketones. Org. Lett.
2017, 19, 3382-3385; (c) Wang, W.; Shen, X.; Zhao, F.; Jiang, H.; Yao,
W.; Pullarkat, S. A.; Xu, L.; Ma, M. Ytterbium-Catalyzed
Hydroboration of Aldehydes and Ketones. J. Org. Chem. 2018, 83,
69-74.
[7] (a) Blake, A. J.; Cunningham, A.; Ford, A.; Teat S. J.; Woodward, S.
Enantioselective Reduction of Prochiral Ketones by Catecholborane
Catalysed by Chiral Group 13 Complexes. Chem. Eur. J. 2000, 6,
3586-3594; (b) Arrowsmith, M.; Hadlington, T. J.; Hill M. S.;
Kociok-Köhn, G. Magnesium-catalysed hydroboration of aldehydes
and ketones. Chem. Commun. 2012, 48, 4567-4569; (c) Hadlington, T.
J.; Hermann, M.; Frenking G.; Jones, C. Low Coordinate Germanium(II)
and Tin(II) Hydride Complexes: Efficient Catalysts for the
Hydroboration of Carbonyl Compounds. J. Am. Chem. Soc. 2014, 136,
3028-3031; (d) Yang, Z.; Zhong, M.; Ma, X.; De, S.; Anusha, C.;
Parameswaran P.; Roesky, H. W. An Aluminum Hydride That
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Heterocyclic Carbene-Catalyzed Hydride Transfer in the Hydroboration of Carbonyl Compounds
Chin. J. Chem.
Functions like a Transition-Metal Catalyst. Angew. Chem. Int. Ed.
2015, 54, 10225-10229; (e) Mukherjee, D.; Osseili, H.; Spaniol T. P.;
Okuda, J. Alkali Metal Hydridotriphenylborates [(L)M][HBPh3] (M = Li,
Na, K): Chemoselective Catalysts for Carbonyl and CO2 Hydroboration
J. Am. Chem. Soc. 2016, 138, 10790-10793; (f) Jakhar, V. K.; Barman
M. Kr.; Nembenna, S. Aluminum Monohydride Catalyzed Selective
Hydroboration of Carbonyl Compounds. Org. Lett. 2016, 18,
4710-4713; (g) Fohlmeister L.; Stasch, A. Ring-Shaped
2018, 83, 10677-10683.
[8] (a) Corey, E. J.; Bakshi, R. K.; Shibata, S. Highly enantioselective
borane reduction of ketones catalyzed by chiral oxazaborolidines.
Mechanism and synthetic implications. J. Am. Chem. Soc. 1987, 109,
5551-5553; (b) Chong, C. C.; Hirao H.; Kinjo, R. Metal-Free σ-Bond
Metathesis in 1,3,2-Diazaphospholene-Catalyzed Hydroboration of
Carbonyl Compounds. Angew. Chem. Int. Ed. 2015, 54, 190-194; (c)
Lawson,
J.
R.;
Wilkins
L.
C.;
Melen,
R.
L.
Phosphinoamido-Magnesium-Hydride
Complexes:
Syntheses,
Tris(2,4,6-trifluorophenyl)borane: An Efficient Hydroboration
Catalyst. Chem. Eur. J. 2017, 23, 10997-11000; (d) Bisai, M. K.; Pahar,
S.; Das, T.; Vanka K.; Sen, S. S. Transition metal free catalytic
hydroboration of aldehydes and aldimines by amidinato silane.
Dalton Trans. 2017, 46, 2420-2424; (e) Wu, Y.; Shan, C.; Ying, J.; Su, J.;
Zhu, J.; Liu L. L.; Zhao, Y. Catalytic hydroboration of aldehydes,
ketones, alkynes and alkenes initiated by NaOH. Green Chem. 2017,
19, 4169-4175; (f) Ould, D. M. C.; Melen, R. L. Arsenic Catalysis:
Structures, Reactivity, and Catalysis. Chem. Eur. J. 2016, 22,
10235-10246; (h) Mukherjee, D.; Shirase, S.; Spaniol, T. P.; Mashima
K.; Okuda, J. Magnesium hydridotriphenylborate [Mg(thf)6][HBPh3]2:
a versatile hydroboration catalyst. Chem. Commun. 2016, 52,
13155-13158; (i) Wu, Y.; Shan, C.; Sun, Y.; Chen, P.; Ying, J.; Zhu, J.;
Liu L.; Zhao, Y. Main group metal-ligand cooperation of
N-heterocyclic germylene: an efficient catalyst for hydroboration of
carbonyl compounds. Chem. Commun. 2016, 52, 13799-13802; (j)
Schneider, J.; Sindlinger, C. P.; Freitag, S. M.; Schubert H.; Wesemann,
L. Diverse Activation Modes in the Hydroboration of Aldehydes and
Ketones with Germanium, Tin, and Lead Lewis Pairs. Angew. Chem.
Int. Ed. 2017, 56, 333-337; (k) Yadav S.; Pahar S.; Sen, S. S.
Benz-amidinato calcium iodide catalyzed aldehyde and ketone
hydroboration with unprecedented functional group tolerance.
Chem. Commun. 2017, 53, 4562-4564; (l) Zhu, Z.; Wu, X.; Xu, X.; Wu,
Z.; Xue, M.; Yao, Y.; Shen, Q.; Bao, X. n-Butyllithium Catalyzed
Selective Hydroboration of Aldehydes and Ketones. J. Org. Chem.
Hydroboration
of
Aldehydes
Using
aꢀBenzo-Fused
Diaza-benzyloxy-arsole. Chem. Eur. J. 2018, 24, 15201-15204.
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Manuscript received: XXXX, 2019
Manuscript revised: XXXX, 2019
Manuscript accepted: XXXX, 2019
Accepted manuscript online: XXXX, 2019
Version of record online: XXXX, 2019
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N-Heterocyclic Carbene-Catalyzed Hy-dride
Transfer in the Hydroboration of Carbonyl
Compounds
N-heterocyclic carbene (NHC) catalytically enabled the highly efficient hydroboration of various
ketones and aldehydes in high conversions under mild conditions, and a new mechanism of
catalytic hydroboration reaction which involves direct hydride transfer is proposed.
Tianhao Li, Jianying Zhang, Chunming Cui*
This article is protected by copyright. All rights reserved.