Breaking C-O Bonds with Uranium: Uranyl Complexes as Selective Catalysts in the Hydrosilylation of Aldehydes

Article abstract of DOI:10.1021/acscatal.9b01408

We report herein the possibility to perform the hydrosilylation of carbonyls using actinide complexes as catalysts. While complexes of the uranyl ion [UO₂]²⁺ have been poorly considered in catalysis, we show the potentialities of the Lewis acid [UO₂(OTf)₂] (1) in the catalytic hydrosilylation of a series of aldehydes. [UO₂(OTf)₂] proved to be a very active catalyst affording distinct reduction products depending on the nature of the reductant. With Et₃SiH, a number of aliphatic and aromatic aldehydes are reduced into symmetric ethers, while ⁱPr₃SiH yielded silylated alcohols. Studies of the reaction mechanism led to the isolation of aldehyde/uranyl complexes, [UO₂(OTf)₂(4-Me₂N-PhCHO)₃], [UO₂(μ-κ²-OTf)₂(PhCHO)]_n, and [UO₂(μ-κ²-OTf)(κ¹-OTf)(PhCHO)₂]₂, which have been fully characterized by NMR, IR, and single-crystal X-ray diffraction.

Full text of DOI:10.1021/acscatal.9b01408

Subscriber access provided by ECU Libraries
Article
Breaking C-O Bonds with Uranium: Uranyl Complexes as
Selective Catalysts in the Hydrosilylation of Aldehydes
Louis Monsigny, Pierre Thuery, Jean-Claude Berthet, and Thibault Cantat
ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.9b01408 • Publication Date (Web): 20 Aug 2019
Downloaded from pubs.acs.org on August 20, 2019
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a service to the research community to expedite the dissemination
of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in
full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully
peer reviewed, but should not be considered the official version of record. They are citable by the
Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore,
the “Just Accepted” Web site may not include all articles that will be published in the journal. After
a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web
site and published as an ASAP article. Note that technical editing may introduce minor changes
to the manuscript text and/or graphics which could affect content, and all legal disclaimers and
ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or
consequences arising from the use of information contained in these “Just Accepted” manuscripts.
is published by the American Chemical Society. 1155 Sixteenth Street N.W.,
Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 10
ACS Catalysis
1
2
3
4
5
6
7
8
9
Breaking CO Bonds with Uranium: Uranyl Complexes as Selective
Catalysts in the Hydrosilylation of Aldehydes
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Louis Monsigny, Pierre Thuéry, Jean-Claude Berthet* and Thibault Cantat*.
NIMBE, CEA, CNRS, Université Paris-Saclay, CEA Saclay, 91191 Gif-sur-Yvette, France
ABSTRACT: We report herein the possibility to perform the hydrosilylation of carbonyls, using actinide complexes as
catalysts. While complexes of the uranyl ion [UO2]2+ have been poorly considered in catalysis, we show the potentialities of
the Lewis acid [UO2(OTf)2] (1) in the catalytic hydrosilylation of a series of aldehydes. [UO2(OTf)2] proved a very active
catalyst affording distinct reduction products depending on the nature of the reductant. With Et3SiH, a number of aliphatic
i
and aromatic aldehydes are reduced into symmetric ethers, while Pr3SiH yielded silylated alcohols. Studies of the reaction
mechanism led to the isolation of aldehyde/uranyl complexes, [UO2(OTf)2(4-Me2N-PhCHO)3], [UO2(-2-OTf)2(PhCHO)]n
and [UO2(-2-OTf)(OTf)2(PhCHO)2]2 which have been fully characterized by NMR, IR and single crystal X-ray diffraction.
KEYWORDS: Homogenous catalysis, Uranium, Uranyl, Hydrosilylation, Reduction, Aldehydes, Mechanisms.
Actinides have aroused considerable fundamental researches to
better understand their fascinating chemical and physical
properties. The last decades have witnessed a profuse literature of
the chemistry of the 5f-elements revealing unprecedented
structures and reactivities including the isolation of new
coordination motifs or unusual activation of small molecules
(such as N2, CO or CO2).1 Translating these chemical features in
the realm of catalysis remains shy and catalytic applications have
been mainly achieved with the organometallic An4+ species (Th,
In contrast to hydroboranes, hydrosilanes (R3SiH) have never
been used for the reduction of carbonyl or heterocumulene
compounds with actinide catalysts. Hydrosilanes are milder
reductants compared to hydroboranes14 or diboranes15. Yet, the
slight polarization of the Si-H bond offers appealing advantages
for the development of selective reduction processes in organic
chemistry,10,11 the valorization of biomass,16 and the recycling of
plastics.17
U) for the hydroamination, hydrosilylation and polymerization of
2
alkenes and alkynes.1b,
The transformation of oxygenated
A) Proton-Transfer Esterification of Aldehydes catalyzed by An4+
N'' N''
Th
=
O
compounds with actinide catalysts represents a difficult task, as
the strength of actinide-oxygen bonds may preclude efficient
catalytic turnover.1d, 3 Nonetheless, the group of Eisen recently
challenged this vision by unveiling the ability of some
uranium(IV) and thorium(IV) complexes to promote the catalytic
dimerization of aldehydes (Tishchenko reaction).4 These authors
thus paved the way to developments in this field, substantiated by
the subsequent reports of key examples of hydroalkoxylation,5
addition of alcohols on heterocumulene,6 ring opening
polymerization of epoxides7 and esters8 and dehydration of
amides.9
R'
[Th]4+
[Th]4+
+
O
HO
H
HO
+
R
H
N
Si
R'
An = Th
O
Ph
CF3
R
O
Me3Si
+
N" = N(SiMe3)2
Ph
CF3
B) Hydroboration of aldehydes and ketones catalyzed by An4+
LH =
Bpin
O
iPr
O
R = alkyl, aryl
R' = H, alkyl, aryl
[(L)Th{N"}3]
C6D6
+ HBpin
N
H
R'
R
R'
R
HN
N
iPr
2+
C) This work: hydrosilylation of aldehydes catalyzed by UO2
[UO2]2+ (1 mol%)
H
0.5
R
O
R
R'3SiH (1.2 equiv.)
and/or
The reduction of oxygenated substrates, involving the cleavage
of CO and/or C=O bonds, is of fundamental importance, for
instance in the conversion of carbonyl or bio-based substrates10
and CO2.11 The utilization of actinide based catalysts in this area
is extremely rare, as the metal ion must cope with the strength of
the An-O bonds and tolerate the reductant.12 Eisen et al. showed
that aldehydes could undergo esterification reactions in the
presence of alcohols, in the presence of ,,,trifluoro-
benzophenone as a sacrificial hydride acceptor (Error! Reference
source not found., A).13 In this example, the thorium(IV)
complex favors a hydrogen transfer that formally results in the
reduction of ,,,trifluoro-benzophenone. Very recently the
same group reported the first catalytic reduction of carbonyl
compounds (aldehydes and ketones) with hydroboranes (R2BH),
in the presence of thorium complexes able to generate reactive
[Th]-H species as catalytically active intermediates, thereby
unlocking new opportunities in catalysis with actinides (Error!
Reference source not found., B).12a
R
OSiR'3
R
O
20°C, CD2Cl2
+ 0.5 R'3SiOSiR'3
Scheme 1. Exhaustive overview of the catalytic reduction of
oxygenated compounds using actinide complexes.
These recent successes in catalytic reduction chemistry have
been achieved with An4+ (An=U, Th) organometallic complexes,
and the catalysts are in consequence sensitive to air and moisture.
In contrast, the uranyl cation [UO2]2+ is the most abundant form
of uranium in the environment and it is ubiquitous in the nuclear
industry. Although the use of uranyl in reductive transformations
would be novel and attractive, it also poses significant questions:
indeed, a handful of reports describe the reduction of [UO2]2+
species into U(V) or U(IV) compounds by hydrosilanes in the
presence of the Lewis acid (B(C6F5)3)18 or a catalytic quantity of
bases (MX = KNSiMe3, KOtBu, etc).15a These findings prompted
us to investigate, in anhydrous conditions, the potentialities of
ACS Paragon Plus Environment

ACS Catalysis
Page 2 of 10
uranyl species as catalysts in the reductive hydrosilylation of
carbonyls.
The reduction of benzaldehyde (2) with a uranyl catalyst
and a hydrosilane was initially investigated as a model
reaction (Eqn (1)). Because [{UO2Cl2(THF)}2]2 is an efficient
pre-catalyst for the ring opening polymerization of epoxides,7
To probe the influence of the nature of the hydrosilane on
1
2
3
4
the reduction of 2, different reagents were used.
Phenyldimethylsilane (PhMe2SiH) and triphenylsilane
(Ph3SiH) behaved similarly to Et3SiH affording 2a
quantitatively, although a longer reaction time (6 h) was
necessary with Ph3SiH (Table 1, entries 5 and 6). The use of
5
i
it was first tested with
a 2.5 mol% charge for the
the sterically hindered Pr3SiH induced a considerable change
6
7
8
9
hydrosilylation of 2 with 1.2 equivalent of triethylsilane
(Et3SiH), at room temperature in dichloromethane (Table 1,
entry 1). Poorly soluble in dichloromethane, the dimeric
complex dissolved upon addition of excess 2 to give a clear
yellow solution, but proved inactive. In similar conditions, the
iodide analogue [{UO2I2(THF)}3] (5 mol%) displayed a weak
activity with a low conversion of 2 into the symmetric ether
PhCH2OCH2Ph (2a), obtained in ca 23% yield within 19 h
(Table 1, entry 2).
with the selective formation of the silylated alcohol
PhCH2OSiiPr3 (2c) in nearly quantitative yield within 12 h
(Table 1, entry 7).
The reductive etherification of aldehydes proved general and a
number of benzaldehyde derivatives were successfully
transformed into the corresponding dibenzylethers 3-10 in
excellent yields, ranging from 83 to 99% (
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
). Depending on the nature of the substituents, the reactions
required 0.5-10 h at room temperature to go to completion, with
the release of Et3SiOSiEt3 as by-product. More precisely, p-
substituted benzaldehydes 3-7, featuring electron withdrawing
(EW) halogen atoms (Cl, Br, I) or electron donating alkyl (ED)
groups (Me, tBu) were readily reduced into the symmetrical ethers
3a-7a (
Such reductive etherification of aldehyde has been reported
with various Lewis acid such as Me3SiX (X = I19, OTf),
Fe(III)20, M(OTf)3 (M = In21, Sc, Bi, Ga, Al22), M(OTf)2 (M=
Cu23, Zn24) as well as several Sb(III)25 and Sb(V)26
compounds.27 Several reports describe the reductive coupling
of aldehydes and ketones to ethers with organosilicon reagents
in the presence of Lewis acid activators.
). Surprisingly, the increased steric congestion in 9 –
possessing an ortho-methyl group – or in the anthracene
derivative 8 did not affect the rate of the reaction. Importantly,
ketone groups were tolerated and the hydrosilylation of 4-
acetylbenzaldehdye 10 led chemoselectively to ether 10a with
excellent yields and a longer reaction time (10 h). This
selectivity was confirmed with the absence of reaction with
ketones (acetophenone or benzophenone). Furthermore, the
carboxylic functionality in ortho position of 11 was
maintained upon hydrosilylation of the formyl moiety with 2.4
equiv. of Et3SiH and 1 mol% of uranyl 1, and it led to an
intramolecular cyclization to phthalide 11a. Benzaldehyde
derivatives with EW para-substituents (CN or NO2) afforded,
after long reaction times (12 and 24 h, respectively), a 1:1
mixture of ether 12a and silyl ether 12b or only the silylated
alcohol 13b, respectively. While no reaction was observed
The high Lewis acidity of metal triflates has been
extensively used in recent years in a number of organic
transformations since they enhance reactivity of substrates
through electrophilic activation.28 Accordingly, we tested a
stronger Lewis acid, e.g. uranyl triflate [UO2(OTf)2] (1), in the
hydrosilylation of 2. Yellow complex 1 is quite soluble in
polar organic solvents, such as THF (which undergoes rapid
polymerization), pyridine and acetonitrile, but is insoluble in
toluene and dichloromethane. Addition of 1.2 equiv. Et3SiH to
a slurry of complex 1 in toluene or CH2Cl2 did not induce
solubilization of 1 or its reaction at 20 or 65 °C. However,
addition of benzaldehyde (2) to 1 mol% of catalyst 1 at room
1
temperature led to an immediate clear yellow solution. H
NMR monitoring of the reaction showed the quantitative
conversion of benzaldehyde, within 1 hour, into ether 2a and
the siloxane Et3SiOSiEt3 (Table 1, entry 3). Interestingly, a
somewhat different outcome was observed when an excess
Et3SiH (> 4 equiv.) was used, since ether 2a along with the
silylated alcohol PhCH2OSiEt3 (2b) were formed in a ~75:25
ratio (Table 1, entry 4).
with
p-dimethylaminobenzaldehyde
(15),
p-
methoxybenzaldehyde led to
a
complex mixture of
deoxygenated and Friedel-Craft products. Pyridine-, furan-,
and thiophene-2-carboxaldehyde derivatives were also found
unreactive, a trend that may be related to a deleterious
chelation of the catalyst by the substrate.
Table 1: Optimization of the hydrosilylation of benzaldehyde (2), catalyzed by uranyl(VI) complexes
H
OSiR3
O
Cat (1-5 mol%)
O
and/or
0.5
+ R3SiH
(1)
2b-c
20°C, CH2Cl2
Time
Hydrosilane
2
2a
2b
2c
R3= Et3
R3 = iPr3
+ 0.5 R3SiOSiR3
Entry
Cat (mol%)
[{UO2Cl2(THF)}2] (5)
[{UO2I2(THF)}3] (5)
[UO2(OTf)2] 1 (1)
1 (1)
Hydrosilane (n eq.)
Et3SiH (1.2)
Time
24 h
19 h
1 h
Conversion (%)
< 5%
2a (%)
2b-c (%)
1
2
3
4
5
6
7
-
-
Et3SiH (1.2)
39 %
23%
> 99%
73%
> 99%
> 99%
-
13%
Et3SiH (1.2)
> 99%
-
Et3SiH (4)
1 h
> 99%
24%
1 (1)
PhMe2SiH (1.2)
Ph3SiH (1.2)
iPr3SiH (1.2)
1 h
> 99%
-
1 (1)
6 h
> 99%
-
1 (1)
12 h
> 99%
2c > 99%
ACS Paragon Plus Environment

Page 3 of 10
ACS Catalysis
8
-
Et3SiH (1.2)
24 h
[UO2(OTf)2] (1 mol%)
CD2Cl2, time, 20 °C
0%
-
-
1
2
H
(2)
+ 1.2 eq. Et3SiH
0.5 Et3SiOSiEt3
+
R
0.5 R
O
R
O
3
4
5
6
Aromatic aldehydes
No reaction with
R
O
O
O
N
O
O
NC
: 1/1
R
R
X
X
O
12a 12b
12a
/
12 h, Full conversion
2a
3a
4a
5a
6a
7a
(R = H)
1 h, 97%*
(X = Cl)
(X = Br)
0.5 h, 99 %*
0.5 h, 99 %
0.5 h, 83 %
Me2N
12b
R = SiEt3
R = CH2(4-C6H4CN),
15
16
(R = Me)
2 h, 92 %*
7
t
t
8a
1 h, 99%
(R = Bu)
0.5 h, 97%*
(X = I)
O
X
8
9
O
OSiEt3
OSiEt3
O
CO2H
O
O
O
R
from
O2N
13b
MeS
14b
O
X = S, thiophene
X = O, furan
Me Me
24h, 63%
24h, 96%
10
11
12
13
14
15
R = Me, Ph or CF3
10a
10 h, 86%
9a
O
O
0.5 h, 97%
11a
11
3 h, 99%
Aliphatic aldehydes
O
O
O
O
O
O
O
n
n
Ph
Ph
0.1 h, 98%
17a
18a
19a
(n = 3) 0.1 h, 97%
(n = 4) 0.1 h, 97%
(n = 8) 0.1 h, 97%*
24a
20a
0.1 h, 98%
0.1 h, 98%
21a
25a
2 h, 71%
40 °C
23a
22a
0.1 h, 99%
0.1 h, 97%
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Scheme 2. Scope of the catalytic reductive etherification of aromatic and aliphatic aldehydes with Et3SiH and [UO2(OTf)2] (1). Reaction
conditions: aldehyde (0.2 mmol); 0.24 mmol Et3SiH; CD2Cl2 (0.4 mL; 0.5 M). Yields determined by 1H NMR using mesitylene (10 mL) as
an internal standard. *Yields of isolated products from scaled-up experiments (2 mmol scale).
The divergent selectivities in these reactions can be
tentatively explained by considering the Hammett
aldehydes 20-22 displayed a similar reactivity with respect to
the uranyl catalyzed hydrosilylation. It is noteworthy that the
double bond in cyclohexene 23 was left untouched. ,-
unsaturated aldehydes

parameters of the substituents.29 (Scheme 3) For strong ED
groups, characterized by negative  constants (NMe2, –0.83),
no reaction occurs. The formation of symmetric ethers is
favored for  constants in the range -0.3 to 0.5. More electron
deficient substrates, characterized by higher  constants,
30
100
25
80
60
40
20
require longer reaction times and exhibit
a different
20
selectivity, with the formation of silylated alcohols
ArCH2OSiR3 being facilitated.
15
10
5
The
behavior
of
the
p-MeS-benzaldehyde
(para(SMe) = (H) = 0.00) is intriguing. Instead of the
expected dibenzylether derivative 14a, only 14b was obtained,
albeit with a low 63 % yield, after 24 h. This result may
suggest a peculiar influence of sulfur although thioethers are
weak ligands for the hard uranium(VI) ion.
0
0
-1
-0.5
0
0.5
1
 (Hammett Parameters)
2-13a
2-13b
Time
The formation of ethers RCH2OCH2R or silylethers
RCH2OSiR3 from aromatic and aliphatic aldehydes has been
previously reported with Zn(OTf)2 in the presence of TMDS
(TMDS = tetramethyldisiloxane) or Et3SiH, and the selectivity
strongly correlated to the electron–donating or electron–
withdrawing properties of the aldehyde substituents.24 Similar
results have been observed with Cu(OTf)2 and this catalyst
was also able to reduce ketones into the corresponding
symmetrical ether and carboxylic acids into the corresponding
alcohols.23 Altogether, these observations may suggest that the
uranyl cation can follow catalytic paths similar to Lewis acids
based on the transition metals.
Scheme 3. Correlation of the yields of ethers 2-13a (red
line) and silylated alcohols 2-13b (blue line) and reaction time
(green line) of the reaction of hydrosilylation of aldehydes 4-
R-PhCHO (R = NMe2, Me, H, Cl, MeC(O), CN, NO2) with the
Hammett parameters
led to a rapid degradation of the starting materials as
observed
with
1-cyclohexene-1-carboxaldehyde
and
cinnamaldehyde. In contrast, hydrocinnamaldehyde was
efficiently reduced to 24a at room temperature, while the
reductive etherification of phenylacetaldehyde (25) required a
longer reaction time and a smooth heating to 40 °C. 1H and 13
C
In the presence of Lewis acidic complexes, a common side
reaction of aliphatic aldehydes is the homo-aldol
condensation, relying on the keto-enol tautomerism catalyzed
NMR monitoring of the later catalytic run showed well
separated resonances assignable to free aldehyde 25 and its
trimeric form (PhCH2CHO)3 which are in equilibrium
(K(20 °C) = 0.77, Eqn. 3, Scheme 4). Formation of the
trioxane is catalyzed by uranyl 1, as observed in a subsequent
experiment by mixing only uranyl triflate and 25 in CD2Cl2.
While the trioxane is favored at low temperatures, moderate
heating at 40 °C gave back the genuine aldehyde 25 which can
then be reduced into the ether 25a.
28a, 30
by Lewis acids such as lanthanide triflates.
Gratifyingly,
in the conditions of eqn. 2, the aliphatic aldehydes 17-24 were
rapidly converted into the corresponding ethers 17a-24a in
excellent yields (97 - 99% in 0.1 h) without any side-product
observed. Aldol condensation only occurred at elevated
temperature (> 70 °C) with longer reaction time (>2 h, see SI).
Linear aldehydes 17-19 as well as branched aliphatic
ACS Paragon Plus Environment

ACS Catalysis
Page 4 of 10
The activation energy (Ea), the enthalpy (ΔH‡), and the
The thermodynamic parameters measured for the equilibrium
entropy (∆S‡) of activation for the rate-determining step were
found to be 11.4 ± 0.40 kcal/mol, 10.8 ± 0.5 kcal/mol, and -
43.2 ± 0.5 eu, respectively. (ΔG‡ = 23.7 ± 0.6 kcal/mol). The
high negative entropy values would indicate a highly ordered
transition state at the rate-determining step (RDS). Studies of
the isotopic effect by using deuterated hydrosilanes yielded a
KIE value of 2.3 ± 0.1, revealing that the H atom transfer was
involved in the RDS. A secondary kinetic isotope effect
(SDKIE) of 0.90 was determined for Et3SiH with the
deuterated substrate PhCDO. This low value (< 1) is indicative
of a purely ionic mechanism, excluding a radical pathway.36
1
2
3
4
5
6
7
8
depicted in eqn. (3) revealed an exothermic (ΔH = –54 ± 0.3
kJ/mol) and entropically unfavorable reaction (ΔS = –184.6 ± 1.2
J/K.mol) with an overall reaction free energy of ΔG = +84.2 J/mol
at 20 °C (see SI). The cyclotrimerisation of 25 is reminiscent of
the cyclisation of methanal (CH2O) to 1,3,5-trioxane. Such a
reactivity has been widely reported with different Lewis acids
(incl. Ru,31 Me3SiCl,32 InCl3,33 FeCl3,34 etc35). If the other
aldehydes with -hydrogen atoms are left untouched by 1 in
CH2Cl2, in neat condition they were transformed into the
corresponding 1,3,5-trioxanes which often solidified in the flask.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Ph
UO2(OTf)2
The inverse kinetic order observed for the aldehyde
underlines a progressive deactivation of the catalyst with
increasing concentrations of aldehyde, likely by saturation of
the coordination sphere of uranium which may impede an
access to the metal center for the reductant or a decreased
Lewis acidity on the UVI cation. Such interpretation is
supported by the acceleration noted in the hydrosilylation of
bulky aldehydes derivatives (0.5 h for p-tBu or o-Me-
compounds 4 and 9 vs 2 h for p-MePhCHO (3)), which may
favor the occurrence of unsaturated uranium centers. Influence
of the triflate ion is also notable. Thus addition of 1 eq.
[nBu4N]OTf proved deleterious with a dramatic decrease of the
rate of the reaction which is reflected by a kinetic constant kobs
of 6.0.10-6 M.s-1 while it is 2.5.10-5 M.s-1 without [nBu4N]OTf.
O
(1 mol%)
O
Ph
3
(3)
O
O
K = 0.77 at 20 °C
in CD2Cl2
H
Ph
25
Scheme 4: Equilibrium reaction between phenylacetaldehyde
and its trioxane form catalyzed by uranyl complex 1 in CD2Cl2
Thus, in presence of uranyl catalyst 1, the aldehydes 21, 22,
24, 25, rapidly stiffened as white solid trimers within 10 min-
30 min while compounds 17, 18 gave colorless oils. These
trioxanes have been readily isolated in quantitative yields (see
SI).
i
Replacing Et3SiH with Pr3SiH considerably altered the
In order to better apprehend the mechanism of Eqns 2 and 4,
we turned our attention on the uranium species that might be
formed when complex 1 is treated with either hydrosilanes or
aldehydes, or under the catalytic conditions.
course of the reaction and aromatic and aliphatic aldehydes
were transformed into the corresponding silylated alcohols
(Eqn (4)). The reaction required 12 h to reach completion in
CH2Cl2, and showed quantitative conversions, excellent
selectivity and yields (92-98%) (Scheme 5).
The insolubility of [UO2(OTf)2] in CD2Cl2 disfavors the
observation by 1H NMR of a possible contact between Et3SiH and
the amphoteric uranyl complex.37 However, when suspended in
neat PhSiH3, a stronger reductant than Et3SiH, the yellow powder
of 1 turned green after 1h at 100°C. Addition of pyridine gave an
immediate orange solution upon which slow addition of pentane
afforded green crystals of the hexanuclear U(IV) oxide cluster
[U6O8(OTf)8(py)10] previously obtained from reduction of
uranyl.38 The reduction of 1 into uranium(IV) is reminiscent of the
instability of uranyl borohydride compounds, which likely results
from H2 loss from putative uranyl hydride intermediates.39
H
[UO2(OTf)2] (1mol%)
CD2Cl2, 12 h, 20°C
+ 1.2 eq. iPr3SiH
OSiiPr3
4)
R
OSiiPr3
R
O
OSiiPr3
OSiiPr3
tBu
X
2c
4c
5c
6c
93%
95%
(X = Cl) 96%
(X = Br) 92%
OSiiPr3
OSiiPr3
OSiiPr3
n
O2N
13c
While complexation of uranium ions with ketones has given
rise to numerous studies related to nuclear fuel reprocessing,
similar investigations with aldehydes are rare. Only two
18c (
19c
24c (
98%)
24h, 96%
n = 4) 94%
(n = 8) 98%
Scheme 5. Reduction of aldehydes into silylated alcohols
[UO2(2-CSAL)(1-
catalyzed by [UO2(OTf)2] in presence of iPr3SiH.Quantitative
conversion for all the reactions. Yields determined by 1H
NMR using mesitylene (10 µL) as internal standard.
species,
CSAL)(DMSO)2]
e.g.
the
uranyl(VI)
(CSAL-H =
3,5-dichloro-2-
hydroxybenzaldehyde)40 and [UO2(2-ALAC)2(H2O)] (ALAC-
H =
2-dimethylacetal-4-chloro-2-hydroxybenzaldehyde)
compounds have been crystallographically characterized.41 It
is noteworthy that the ALAC and CSAL ligands are
derivatives of salicylaldehyde (2-hydroxybenzaldehyde), for
which the coordination of the formyl moiety to uranium is
facilitated by a chelation effect ensured by bonding of the
phenoxide group.
In order to gain insights into the mechanism of this reaction
and to better apprehend the role of the uranyl catalyst, kinetic
1
measurements were carried out by H NMR for the reductive
coupling of p-MePhCHO with Et3SiH (see ESI for details).
These investigations revealed a complex rate law for the
reaction presented in Eqn. 5. with a third order for the catalyst,
3
In presence of a series of aldehydes reported in
a first order in hydrosilane and an inverse
aldehyde.
/ order in
2
, suspension of 1 in CH2Cl2 immediately gave clear yellow
to orange solutions. Most attempts at crystallization failed, but
crystals suitable for X-ray diffraction were grown with
benzaldehyde (2) and p-Me2NPhCHO (16), by slow diffusion
of pentane into a CH2Cl2 solution of 1 with a large excess of
ligand.
∂푝
∂푡
[ퟏ]3 × [ℎ푦푑푟표푠푖푙푎푛푒]1
= k ×
(5)
3
2
[푎푙푑푒ℎ푦푑푒]
ACS Paragon Plus Environment

Page 5 of 10
ACS Catalysis
Yellow crystals of the polymer [UO2(-2-OTf)2(PhCHO)]n
(26) (Figure 1) and the dimer [UO2(-2-OTf)(1-
OTf)(PhCHO)2]2 (27) (Figure 2 and 3) were obtained from
distinct batches prepared under the same conditions.42
Attempts at isolation of powdery samples of the uranyl(VI)
compound, by precipitation from a mixture of 1 with 10 equiv.
of 2, gave a dry product formulated as [UO2(OTf)2(PhCHO)2]
(according to NMR and elemental analyses) in 74% yield. The
1H NMR spectra in CH2Cl2-d2 revealed a thin CHO signal at
 = 10.1 slightly shifted downfield in comparison with that of
free benzaldehyde 2 (10.0 ppm).
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
With p-Me2NPhCHO, dark-orange crystals of the
monometallic complex [UO2(1-OTf)2(Me2N-PhCHO)3] (28)
were readily collected (Figure 3). Dried powder samples have
the same formula and displayed a 1H NMR signal at  = 10.31
for the CHO group and a singlet at  = 3.24 for the Me2N
group (vs  = 9.70 and  = 3.07 for the free aldehyde 15).
The three structures evidence that the aldehydes are weak
ligands for the [UO2]2+ ion as triflate bridges are sometimes
maintained and not displaced towards the formation of
cationic species as in [UO2(OPPh3)4][OTf]2.43 Moreover, the
monomeric form of 28 confirms the stronger coordinating
ability of the more electron rich p-Me2NPhCHO, compared to
benzaldehyde.
Figure. 2 View of complex 27 with 50% probability
displacement ellipsoids. Hydrogen atoms are omitted for
clarity. Symmetry code: i = 2 – x, 2 – y, 2 – z.
Complexes 26 and 27 both display an inversion center
located at the center of the U2S2 square entity. The three
complexes display the usual pentagonal-bipyramidal uranium
coordination environment with the equatorial plane, defined
by the uranium atom and five oxygen
Figure 3 View of complex 28 with 40% probability displacement
ellipsoids. Hydrogen atoms are omitted for clarity.
donors of the aldehyde and triflate ligands, perpendicular to
the linear UO2 moiety (O–U–O > 178.6°). To our knowledge,
26 is the first [UO2(OTf)2] species with a polymeric structure.
Connections between the neighboring uranyl entities in 26 and
27 are ensured by bidentate bridging triflate anions and these
compounds are unique uranyl species with (2--OTf) ligands.
The U–O(uranyl), U–O(aldehyde) and U–OTf (bridging
bidentate and monodentate) distances in 26, 27 and 28 are
unexceptional, with mean values of 1.743(4) / 1.762(1) /
1.748(5) Å, 2.391(4) / 2.413(2) / 2.403(9) Å and 2.410 (1) /
2.38(2) / 2.397(3) Å, respectively. These values can be
compared to the mean values of 2.410(1) Å for the
monodentate triflates in [UO2(1-OTf)2(THF)3] and 2.45(2) Å
for the U-O(ArCH=O) bond length in [UO2(ALAC)2(H2O)]
and in [UO2(CSAL)2(DMSO)2]. Finally, the C=O bond lengths
in 28 of 1.196(7), 1.235(7) and 1.269(7) Å can be compared to
that in the free aldehyde 15 (1.204(2) Å).44 The N-C(aromatic)
bond lengths are slightly shorter in complex 28 than in the free
aldehyde (1.338(7) (twice) and 1.340(6) Å vs 1.366(2) Å)
which seems to confirm the existence of a charge transfer of
the ligand 15 to the metal center.
Figure. 1 Views of complex 26 with 50% probability
displacement ellipsoids. Hydrogen atoms are omitted for
clarity. Symmetry codes: i = 2 – x, –y, –z; j = 1 – x, 1 – y, –z.
To gain further information on how the catalytic
hydrosilylation proceeds (Eqns. 2 and 4), stoichiometric
reactions from isolated uranyl species, labeling experiments,
and concomitant addition of a 1:1 mixture of an aldehyde and
the derived silylated alcohol were carried out (Eqns 6-10,
Scheme 6). When reacted with a stoichiometric amount of
ACS Paragon Plus Environment

ACS Catalysis
Et3SiH (1 equiv.) in dichloromethane, complex 27 did not
afford any observable intermediate, and only the dibenzyl
ether 2a was produced quantitatively (with respect to Et3SiH)
along with siloxane.
Page 6 of 10
[UO2(OTf)2] (1mol%)
Et3SiD (1.2 eq.)
O
D
D
1
2
3
4
5
6
7
8
O
(6)
0.5
CD2Cl2, 1h, 20 °C
Quantitive
X
X
X
2a-d
5a-d
X = H (
X = Cl (
)
)
2
X = H ( )
2
5
= Cl ( )
2
Catalytic hydrosilylation of 2 and p-chlorobenzaldehyde 5
with Et3SiD and 1 mol% 1 evidenced, in both cases, the
quantitative formation of the corresponding deuterated
dibenzylether 2a-d2 and 5a-d2 formed within 1 h (Scheme 6,
Eqn 6). 13C{1H} NMR spectra revealed clearly the presence of
+ 0.5 Et3SiOSiEt3
[UO2(OTf)2] (1 mol%)
Ph
OSiEt3
(7)
No reaction
2b
CD2Cl2
a
single deuterium atom on each methylene moiety
2
Ph
Ph
OSiEt3
O
9
[UO2(OTf)2] (1 mol%)
2b
2
Ph
O
2a
Ph
(CHD = 71.8 ppm and CHD = 71.6 ppm, respectively with the
+ Ph
O
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
2
CD2Cl2
- Et3SiOSiEt3
3
same JC-D = 21.5 Hz values). This result confirms a net
+
transfer of the hydride group from silicon to the aldehyde.
Ph
(8)
In the catalytic formation of ethers (Eqn 2), silylated
alcohols were systematically observed in low quantities (1-
5%), whatever the nature of the hydrosilane (Et3SiH,
PhMe2SiH and Ph3SiH), before they were fully consumed by
the end of the reaction. To evaluate their potential role as
intermediates in the formation of ethers, PhCH2OSiEt3 (2b)
was added to 1 (1 mol%) in CH2Cl2 (Scheme 6, Eqn 7).
Ph
O
O
Ph
- Et3SiOSiEt3
29
[U]
Ph
Ph
H
[U]
Ph
O
O
H
More plausible than
O
Ph
O
Ph
Ph
Although no reaction occurred, addition of
1 equiv.
[UO2(OTf)2] (1 mol%)
CD2Cl2, 20 °C
benzaldehyde led to the rapid and incomplete formation of the
benzaldehyde dibenzyl acetal (29), in ca. 50 % yield, and
Et3SiOSiEt3 as byproduct (Scheme 6, Eqn 8). Compound 29
was not observed in the catalytic experiments with
hydrosilanes but its formation in Eqn 8 was shown
unambiguously by NMR.45 From this mixture, 29 slowly
degraded into the corresponding ether 2a and benzaldehyde 2
within 1 week. To understand this evolution, a labeling
experiment with PhCDO was performed, which unveiled a -
bonds metathesis of 29 catalyzed by the uranium complex. A
1,3-H shift pathway is unlikely, as PhCHO was absent
(Scheme 6, see SI).
2
Ph
OSiiPr3
(9)
+
Ph
No reaction
O
2c
2
Ph
One-pot
[UO2(OTf)2]
(1 mol%)
2
Ph
Ph
OSiEt3
Ph
O
Ph
O
Et3SiH (1.2 eq.)
2b
2
2a
(10)
Ph
Neat, 0.5 h, 0 °C
quantitive
CD2Cl2
quantitive
O
Ph
OSiEt3
2b
+
O
Ph
29
Scheme 6: Reaction of silylated benzyl alcohol 2b and 2c with
benzaldehyde and deuterium labeling experiments
Based on the above experiments and kinetic results, a
plausible mechanism is proposed in Scheme 7, for the uranyl-
catalyzed hydrosilylation of aldehydes. At the onset, the
insoluble polymeric uranyl triflate is coordinated by the
As depicted in Eqn 9, replacing the silyl ether PhCH2OSiEt3
with its sterically congested analogue PhCH2OSiiPr3 2c
prevented the reaction, and 2a was not detected after one week
at 20 °C. At last, cleavage of 29 into the ether 2a is
considerably accelerated in presence of the reductant:
treatment of 29 with a mixture of Et3SiH (1.2 equiv.) and 1
(1 mol%) at 20°C, led within minutes to the ether 2a and the
silylated alcohol 2b (Scheme 6, eqn 10). These two important
points evidence the key role of acetal intermediates, such as
29, in the reductive coupling of aldehydes into symmetric
ethers.
aldehydes
to
yield
soluble
oligomeric
adducts
[UO2(OTf)2(aldehyde)n]y, likely engaged in equilibria, as
reflected in the distinct structures of 26 and 27. The active
uranyl catalyst A is expected to be unsaturated to enter in the
catalytic cycle. The first step of the cycle is the hydrosilylation
of the aldehyde RCHO to the silylated alcohol RCH2OSiR3.
The latter reacts with a molecule of aldehyde to give the
transient silylated acetal complex C (step 2) which was not
detected. Hydrosilylation of the coordinated acetal affords the
desired ether (RCH2)2O and the by-product (Et3Si)2O, while
catalyst A is regenerated (steps 3 and 4). Complex C can also
react with RCH2OSiR3 to provide the acetal analogue of 29
which, as seen in Eqn 8, is readily transformed into the
symmetric ether and the silylated alcohol. This mechanism
highlights the key role of acetal intermediates.
ACS Paragon Plus Environment

Page 7 of 10
ACS Catalysis
x RCHO + 1
R
O
[U]y
[U]n = [UO2(OTf)2]n
The following files are available free of charge. Supplementary
x
1
2
3
4
5
6
7
equations, detailed descriptions of experimental methods, kinetic
and mechanism studies are provided in the Supporting
Information.
- RCHO
R
O
Et3SiH
Et3Si
SiEt3
Accession Codes
O
[U]y
x-1
A
CCDC
1904787−1904789
contain
the
supplementary
Step 4
Step 1
crystallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
RCHO
RCH2OSiEt3
SiEt3
[U]y
R
O
x-2
R
O
SiEt3
O
8
9
RCHO
R
O
x-2
SiEt3
[U]y
D
B
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
R
O
R
Step 3
Step 2
O
Rx-2
O
R
O
R
R
SiEt3
[U]y
O
ACKNOWLEDGMENT
Et3SiH
Et3SiH
R
O
R
For financial support of this work, we acknowledge the CEA,
CNRS, CHARMMMAT Laboratory of Excellence and the
European Research Council (ERC Starting Grant Agreement
n.336467). T.C. thanks the Fondation Louis D. – Institut de
France for its support. We thank CINES for the allowance of
computer time (Project No. c2017086494).
C
Not observed
O
R
R
O
+
O
R
SiEt3
R
O
Et3Si
SiEt3
+ [U]
Scheme 7: Plausible mechanism of the uranyl catalyzed
REFERENCES
reductive coupling of aldehydes into ethers
1.
(a) Liddle, S. T., The Renaissance of Non-Aqueous
In conclusion, treatment of uranyl(VI) triflate 1 in the
presence of hydrosilanes induced the reduction of C=O bonds
in a large range of aromatic and aliphatic aldehydes.
Symmetric ethers and silylated alcohols could be selectively
obtained, depending on the nature of the hydrosilane. With
PhMe2SiH, Ph3SiH and Et3SiH, reductive coupling of the
aldehydes into the symmetric ethers was observed, while the
choice of a more sterically congested hydrosilane, e.g. iPr3SiH,
leads to the silylated alcohol RCH2OSiiPr3 in excellent yield.
Uranium Chemistry. Angew. Chem. Int. Ed. 2015, 54, 8604-8641; (b)
Liu, H.; Ghatak, T.; Eisen, M. S., Organoactinides in Catalytic
Transformations: Scope, Mechanisms and Quo Vadis. Chem.
Commun. 2017, 53, 11278-11297; (c) Liu, H.; Kulbitski, K.; Tamm,
M.; Eisen, M. S., Organoactinide-Catalyzed Monohydroboration of
Carbodiimides. Chemistry 2018, 24, 5738-5742; (d) Arnold, P. L.;
Turner, Z. R., Carbon Oxygenate Transformations by Actinide
Compounds and Catalysts. Nat. Rev. Chem. 2017, 1, 0002; (e)
Mullane, K. C.; Ryu, H.; Cheisson, T.; Grant, L. N.; Park, J. Y.;
Manor, B. C.; Carroll, P. J.; Baik, M.-H.; Mindiola, D. J.; Schelter, E.
J., C–H Bond Addition Across a Transient Uranium–Nitrido Moiety
and Formation of a Parent Uranium Imido Complex. J. Am. Chem.
Soc. 2018, 140, 11335-11340; (f) Coughlin, E. J.; Qiao, Y.; Lapsheva,
E.; Zeller, M.; Schelter, E. J.; Bart, S. C., Uranyl Functionalization
Mediated by Redox-Active Ligands: Generation of O–C Bonds via
Acylation. J. Am. Chem. Soc. 2019, 141, 1016-1026.
This work provides a new and rare example of a catalytic
transformation of oxygen-containing molecules with the
highly oxophilic actinide ions. Above all, it shows the first use
of an actinide complex to carry out catalytic hydrosilylation of
C=O bonds and clearly evidences that high oxidation state
species derived from the ubiquitous uranyl(VI) ion are stable
and able to carry out reduction reactions in presence of
reducing agents. Despite the uranyl ion contains oxidizing
U=O bonds, reduction of the C=O group and CO bond
cleavage are possible without compromising the integrity of
the uranyl moiety.
2.
Towards Uranium Catalysts. Nature 2008, 455, 341.
3. Lin, Z.; Marks, T. J., Metal, Bond Energy, and Ancillary
Fox, A. R.; Bart, S. C.; Meyer, K.; Cummins, C. C.,
Ligand Effects on Actinide-Carbon .Sigma.-Bond Hydrogenolysis. A
Kinetic and Mechanistic Study. J. Am. Chem. Soc. 1987, 109, 7979-
7985.
4.
Andrea, T.; Barnea, E.; Eisen, M. S., Organoactinides
Promote The Tishchenko Reaction: The Myth of Inactive Actinide-
Alkoxo Complexes. J Am Chem Soc 2008, 130, 2454-2455.
AUTHOR INFORMATION
Corresponding Author
5.
Wobser, S. D.; Marks, T. J., Organothorium-Catalyzed
Hydroalkoxylation/Cyclization of Alkynyl Alcohols. Scope,
Mechanism, and Ancillary Ligand Effects. Organometallics 2012, 32,
2517-2528.
* E-mail: jean-claude.berthet@cea.fr; thibault.cantat@cea.fr; Fax:
+33 1 6908 6640; Tel: +33 1 6908 4338
† NIMBE, CEA, CNRS, Université Paris-Saclay, CEA Saclay,
91191 Gif-sur-Yvette, France.
6.
Batrice, R. J.; Kefalidis, C. E.; Maron, L.; Eisen, M. S.,
Actinide-Catalyzed Intermolecular Addition of Alcohols to
Carbodiimides. J Am Chem Soc 2016, 138, 2114-2117.
7.
Baker, R. J.; Walshe, A., New Reactivity of the Uranyl Ion:
Author Contributions
Ring Opening Polymerisation of Epoxides. Chem. Commun. 2012, 48,
985-987.
The manuscript was written with contributions of all authors. All
authors have given approval to the final version of the manuscript.
8.
Walshe, A.; Fang, J.; Maron, L.; Baker, R. J., New
Mechanism for the Ring-Opening Polymerization of Lactones?
Uranyl Aryloxide-Induced Intermolecular Catalysis. Inorg. Chem.
2013, 52, 9077-9086.
Funding Sources
Any funds used to support the research of the manuscript should
be placed here (per journal style).
9.
Enthaler,
S.,
Straightforward
Uranium-Catalyzed
Dehydration of Primary Amides to Nitriles. Chemistry 2011, 17,
9316-9319.
ASSOCIATED CONTENT
ACS Paragon Plus Environment

ACS Catalysis
Page 8 of 10
10.
(a) Fedorov, A.; Toutov, A. A.; Swisher, N. A.; Grubbs, R.
18.
Pedrick, E. A.; Wu, G.; Kaltsoyannis, N.; Hayton, T. W.,
H., Lewis-Base Silane Activation: From Reductive Cleavage of Aryl
Ethers to Selective Ortho-Silylation. Chem. Sci. 2013, 4, 1640-1645;
(b) Zheng, J.; Chevance, S.; Darcel, C.; Sortais, J.-B., Selective
Reduction of Carboxylic Acids to Aldehydes Through Manganese
Catalysed Hydrosilylation. Chem. Commun. 2013, 49, 10010-10012;
(c) Rauch, M.; Parkin, G., Zinc and Magnesium Catalysts for the
Hydrosilylation of Carbon Dioxide. J. Am. Chem. Soc. 2017, 139,
18162-18165.
Reductive Silylation of a Uranyl Dibenzoylmethanate Complex: an
Example of Controlled Uranyl Oxo Ligand Cleavage. Chem. Sci.
2014, 5, 3204-3213.
1
2
3
4
5
6
7
8
19.
Sassaman, M. B.; Kotian, K. D.; Prakash, G. K. S.; Olah,
G. A., General Ether Synthesis under Mild Acid-Free Conditions.
Trimethylsilyl Iodide Catalyzed Reductive Coupling of Carbonyl
Compounds with Trialkylsilanes to Symmetrical Ethers and
Reductive Condensation with Alkoxysilanes to Unsymmetrical
Ethers. J. Org. Chem. 1987, 52, 4314-4319.
11.
(a) Das, S.; Bobbink, F. D.; Laurenczy, G.; Dyson, P. J.,
Metal-Free Catalyst for the Chemoselective Methylation of Amines
Using Carbon Dioxide as a Carbon Source. Angew Chem Int Edit
2014, 53, 12876-12879; (b) Bobbink, F. D.; Menoud, F.; Dyson, P. J.,
Synthesis of Methanol and Diols from CO2 via Cyclic Carbonates
under Metal-Free, Ambient Pressure, and Solvent-Free Conditions.
ACS Sustainable Chem. Eng. 2018, 6, 12119-12123; (c) Lalrempuia,
R.; Iglesias, M.; Polo, V.; SanzꢀMiguel, P. J.; Fernández-Alvarez, F.
J.; Pérez-Torrente, J. J.; Oro, L. A., Effective Fixation of CO2 by
Iridium-Catalyzed Hydrosilylation. Angew. Chem. Int. Ed. 2012, 51,
12824-12827.
20.
Leino, R.; Savela, R., Synthesis of Ethers from Carbonyl
9
Compounds by Reductive Etherification Catalyzed by Iron(III) and
Silyl Chloride. Synthesis 2015, 47, 1749-1760.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
21.
Mineno, T.; Tsukagoshi, R.; Iijima, T.; Watanabe, K.;
Miyashita, H.; Yoshimitsu, H., Reductive Coupling Reaction of
Aldehydes Using Indium(III) Triflate as the Catalyst. Tetrahedron
Lett. 2014, 55, 3765-3767.
22.
Bach, P.; Albright, A.; Laali, K. K., Influence of Lewis
Acid and Solvent in the Hydrosilylation of Aldehydes and Ketones
with Et3SiH; Tris(pentafluorophenyl)borane B(C6F5)3 versus Metal
Triflates [M(OTf)3; M = Sc, Bi, Ga, and Al] - Mechanistic
Implications. Eur. J. Org. Chem. 2009, 2009, 1961-1966.
12.
(a) Ghatak, T.; Makarov, K.; Fridman, N.; Eisen, M. S.,
Catalytic Regeneration of a Th-H Bond from a Th-O Bond Through a
Mild and Chemoselective Carbonyl Hydroboration. Chem. Commun.
2018, 54, 11001-11004; (b) Mullane, K. C.; Cheisson, T.; Nakamaru-
Ogiso, E.; Manor, B. C.; Carroll, P. J.; Schelter, E. J., Reduction of
Carbonyl Groups by Uranium(III) and Formation of a Stable Amide
Radical Anion. Chem. Eur. J. 2018, 24, 826-837.
23.
Zhang, Y.-J.; Dayoub, W.; Chen, G.-R.; Lemaire, M.,
Copper(II) Triflate-Catalyzed Reduction of Carboxylic Acids to
Alcohols and Reductive Etherification of Carbonyl Compounds.
Tetrahedron 2012, 68, 7400-7407.
24.
Sakai, N.; Nonomura, Y.; Ikeda, R.; Konakahara, T., Zinc-
13.
Liu, H.; Eisen, M. S., Selective Actinide-Catalyzed
catalyzed Reduction of Aldehydes with a Hydrosilane Leading to
Symmetric Ethers and Silyl Ethers. Chem. Lett. 2013, 42, 489-491.
Tandem Proton-Transfer Esterification of Aldehydes with Alcohols
for the Production of Asymmetric Esters. Organometallics 2017, 36,
1461-1464.
25.
Baek, J.-Y.; Lee, S.-J.; Han, B.-H., Direct Synthesis of
Symmetric Ethers from Carbonyl Compounds Using SbI3/PhSiH3. J.
Korean Chem. Soc. 2004, 48, 220-224.
14.
(a) Stachowiak, H.; Kaźmierczak, J.; Kuciński, K.;
Hreczycho, G., Catalyst-Free and Solvent-Free Hydroboration of
Aldehydes. Green Chem. 2018, 20, 1738-1742; (b) Lortie, J. L.;
Dudding, T.; Gabidullin, B. M.; Nikonov, G. I., Zinc-Catalyzed
Hydrosilylation and Hydroboration of N-Heterocycles. ACS Catal.
2017, 7, 8454-8459; (c) Obligacion, J. V.; Chirik, P. J., Earth-
Abundant Transition Metal Catalysts for Alkene Hydrosilylation and
Hydroboration. Nat. Rev. Chem. 2018, 2, 15-34.
26.
Arias Ugarte, R.; Devarajan, D.; Mushinski, R. M.;
Hudnall, T. W., Antimony(v) Cations for the Selective Catalytic
Transformation of Aldehydes into Symmetric Ethers, Alpha, Beta-
Unsaturated Aldehydes, and 1,3,5-Trioxanes. Dalton Trans. 2016, 45,
11150-11161.
27.
(a) Komatsu, N.; Ishida, J.-y.; Suzuki, H., Bismuth
Bromide-Catalyzed Reductive Coupling of Carbonyl Compounds and
its Application to the Synthesis of Novel Crownophanes. Tetrahedron
Lett. 1997, 38, 7219-7222; (b) Gellert, B. A.; Kahlcke, N.; Feurer, M.;
Roth, S., Triflic Acid Catalyzed Reductive Coupling Reactions of
Carbonyl Compounds with O-, S-, and N-Nucleophiles. Chemistry
2011, 17, 12203-12209; (c) Yadav, J. S.; Subba Reddy, B. V.; Shiva
Shankar, K.; Swamy, T., The Reductive Etherification of Carbonyl
Compounds using Polymethylhydrosiloxane Activated by Molecular
Iodine. Tetrahedron Lett. 2010, 51, 46-48; (d) Zhao, C.; Sojdak, C.
A.; Myint, W.; Seidel, D., Reductive Etherification via Anion-
Binding Catalysis. J. Am. Chem. Soc. 2017, 139, 10224-10227.
15.
(a) Cowie, B. E.; Nichol, G. S.; Love, J. B.; Arnold, P. L.,
Double Uranium Oxo Cations Derived from Uranyl by Borane or
Silane Reduction. Chem. Commun. 2018, 54, 3839-3842; (b)
Chauvier, C.; Cantat, T., A Viewpoint on Chemical Reductions of
Carbon–Oxygen Bonds in Renewable Feedstocks Including CO2 and
Biomass. ACS Catal. 2017, 7, 2107-2115.
16.
(a) Feghali, E.; Carrot, G.; Thuéry, P.; Genre, C.; Cantat,
T., Convergent Reductive Depolymerization of Wood Lignin to
Isolated Phenol Derivatives by Metal-Free Catalytic Hydrosilylation.
Energy Environ. Sci. 2015, 8, 2734-2743; (b) Monsigny, L.; Feghali,
E.; Berthet, J.-C.; Cantat, T., Efficient Reductive Depolymerization of
Hardwood and Softwood Lignins with Brookhart's Iridium(III)
Catalyst and Hydrosilanes. Green Chem. 2018, 20, 1981-1986; (c)
Adduci, L. L.; McLaughlin, M. P.; Bender, T. A.; Becker, J. J.;
Gagne, M. R., Metal-Free Deoxygenation of Carbohydrates. Angew.
Chem. Int. Ed. 2014, 53, 1646-1649; (d) McLaughlin, M. P.; Adduci,
L. L.; Becker, J. J.; Gagne, M. R., Iridium-Catalyzed Hydrosilylative
Reduction of Glucose to Hexane(s). J Am Chem Soc 2013, 135, 1225-
1227; (e) Zhang, J.; Chen, Y.; Brook, M. A., Reductive Degradation
of Lignin and Model Compounds by Hydrosilanes. ACS Sustainable
Chem. Eng. 2014, 2, 1983-1991.
28.
(a) Kobayashi, S.; Sugiura, M.; Kitagawa, H.; Lam, W. W.
L., Rare-Earth Metal Triflates in Organic Synthesis. Chem. Rev. 2002,
102, 2227-2302; (b) Ladziata, V., Recent Applications of Rare-Earth
Metal(III) Triflates in Cycloaddition and Cyclization Reactions.
Arkivoc 2014, 2014, 307; (c) Ghosh, R.; Maiti, S., Advances in
Indium Triflate Catalyzed Organic Syntheses. J. Mol. Catal. A: Chem.
2007, 264, 1-8; (d) Gaspard-Iloughmane, H.; Le Roux, C.,
Bismuth(III) Triflate in Organic Synthesis. Eur. J. Org. Chem. 2004,
2004, 2517-2532; (e) Deuss, P. J.; Lahive, C. W.; Lancefield, C. S.;
Westwood, N. J.; Kamer, P. C.; Barta, K.; de Vries, J. G., Metal
Triflates for the Production of Aromatics from Lignin. ChemSusChem
2016, 9, 2974-2981.
17.
(a) Feghali, E.; Cantat, T., Room Temperature
Organocatalyzed Reductive Depolymerization of Waste Polyethers,
Polyesters, and Polycarbonates. ChemSusChem 2015, 8, 980-984; (b)
Monsigny, L.; Berthet, J.-C.; Cantat, T., Depolymerization of Waste
Plastics to Monomers and Chemicals Using a Hydrosilylation
Strategy Facilitated by Brookhart’s Iridium(III) Catalyst. ACS
Sustainable Chem. Eng. 2018; (c) Li, A. Y.; Segalla, A.; Li, C.-J.;
Moores, A., Mechanochemical Metal-Free Transfer Hydrogenation of
Carbonyls Using Polymethylhydrosiloxane as the Hydrogen Source.
ACS Sustainable Chem. Eng. 2017, 5, 11752-11760.
29.
Hansch, C.; Leo, A.; Taft, R. W., A Survey of Hammett
Substituent Constants and Resonance and Field Parameters. Chem.
Rev. 1991, 91, 165-195.
30.
by Bismuth(III) Triflate. Eur. J. Org. Chem. 2017, 2017, 761-780.
31. Sorkau, A.; Schwarzer, K.; Wagner, C.; Poetsch, E.;
Ondet, P.; Lemière, G.; Duñach, E., Cyclisations Catalysed
Steinborn, D., Dimerization and Cyclotrimerization of Aldehydes:
Ruthenium Catalyzed Formation of Esters, 1,3,5-Trioxanes, and Aldol
Condensation Products from Aldehydes. J. Mol. Catal. A: Chem.
2004, 224, 105-109.
ACS Paragon Plus Environment

Page 9 of 10
ACS Catalysis
32.
1,3,5-Trioxanes. Tetrahedron Lett. 2002, 43, 7919-7920.
33. Elamparuthi, E.; Ramesh, E.; Raghunathan, R., InCl3 as an
Efficient Catalyst for Cyclotrimerization of Aldehydes: Synthesis of
1,3,5‐Trioxane Under Solvent‐Free Conditions. Synth. Commun.
2006, 35, 2801-2804.
Augé, J.; Gil, R., A Convenient Solvent-Free Preparation of
Cluster: Synthesis and Crystal Structure of the First F-Element Oxide
with a M6(µ3-O)8 Core. Chem. Commun. 2005, 3415-3417.
39. (a) Villiers, C.; Thuéry, P.; Ephritikhine, M., Synthesis and
Crystal Structure of [UO2(BH4)2(hmpa)2], a Novel Uranyl Complex
and the First Metal Oxoborohydride. Inorg. Chem. Commun. 2007,
10, 891-893; (b) Ephritikhine, M., Synthesis, Structure, and Reactions
of Hydride, Borohydride, and Aluminohydride Compounds of the f-
Elements. Chem. Rev. 1997, 97, 2193-2242.
1
2
3
4
5
6
7
8
34.
Arias-Ugarte, R.; Wekesa, F. S.; Findlater, M., Selective
Aldol Condensation or Cyclotrimerization Reactions Catalyzed by
FeCl3. Tetrahedron Lett. 2015, 56, 2406-2411.
40.
Majumder, I.; Chatterjee, S.; Fischer, R. C.; Neogi, S. K.;
35.
Bromide in Organic Synthesis:
Cyclotrimerization of Aldehydes. Tetrahedron 2001, 57, 6181-6188.
36. (a) Gomez-Gallego, M.; Sierra, M. A., Kinetic Isotope
Hon, Y.-S.; Lee, C.-F., Acetonyltriphenylphosphonium
Mautner, F. A.; Chattopadhyay, T., Syntheses of U3O8 Nanoparticles
form Four Different Uranyl Complexes: Their Catalytic Performance
for Various Alcohol Oxidations. Inorg. Chim. Acta 2017, 462, 112-
122.
a
Useful Catalyst in the
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Effects in the Study of Organometallic Reaction Mechanisms. Chem.
Rev. 2011, 111, 4857-4963; (b) Christensen, N. J.; Fristrup, P.,
Kinetic Isotope Effects (KIE) and Density Functional Theory (DFT):
A Match Made in Heaven? Synlett 2015, 26, 508-513.
41.
Graziani, R.; Faraglia, G., Synthesis, Characterization and Crystal
Structure of 2-dimethylacetal-4-chloro-6-formylphenol and
aquabis(2-dimethylacetal-4-chloro-6-
formylphenolato)dioxouranium(VI). Inorg. Chim. Acta 1986, 121,
103-111.
Sitran, S.; Fregona, D.; Casellato, U.; Vigato, P. A.;
37.
(a) Pagano, J. K.; Dorhout, J. M.; Waterman, R.;
Czerwinski, K. R.; Kiplinger, J. L., Phenylsilane as a Safe, Versatile
Alternative to Hydrogen for the Synthesis of Actinide hydrides.
Chem. Commun. 2015, 51, 17379-17381; (b) Erickson, K. A.; Scott,
B. L.; Kiplinger, J. L., Ca(BH4)2 as a Simple Tool for the Preparation
of Thorium and Uranium Metallocene Borohydride Complexes: First
Synthesis and Crystal Structure of (C5Me5)2Th(η3-H3BH)2. Inorg.
Chem. Commun. 2017, 77, 44-46; (c) Pagano, J. K.; Dorhout, J. M.;
Czerwinski, K. R.; Morris, D. E.; Scott, B. L.; Waterman, R.;
Kiplinger, J. L., Tuning the Oxidation State, Nuclearity, and
Chemistry of Uranium Hydrides with Phenylsilane and Temperature:
The Case of the Classic Uranium(III) Hydride Complex
[(C5Me5)2U(μ-H)]2. Organometallics 2016, 35, 617-620; (d) Altman,
A. B.; Brown, A. C.; Rao, G.; Lohrey, T. D.; Britt, R. D.; Maron, L.;
Minasian, S. G.; Shuh, D. K.; Arnold, J., Chemical Structure and
Bonding in a Thorium(III)–Aluminum Heterobimetallic Complex.
Chem. Sci. 2018, 9, 4317-4324.
42.
These compounds were always contaminated with a few
green crystals of a hexanuclear U(IV) oxide cluster with a central
[U6O4(OH)4(OTf)7(PhCO2)5(PhCHO)5] core, the crystal structure of
which could not be refined in a completely satisfying manner due to
considerable disorder..
43.
(a) Berthet, J. C.; Nierlich, M.; Ephritikhine, M., Oxygen
and Nitrogen Lewis Base Adducts of [UO2(OTf)2]. Crystal Structures
of polypyridine complexes with Out-Of-Plane Uranyl Equatorial
Coordination. Dalton Trans. 2004, 2814-2821; (b) Berthet, J. C.;
Nierlich, M.; Ephritikhine, M., Isolation of a Uranyl [UO2]+ Species:
Crystallographic Comparison of the Dioxouranium(V) and (VI)
Compounds [UO2(OPPh3)4](OTf)n (n=1, 2). Angew. Chem. Int. Ed.
2003, 42, 1952-1954.
44.
Gao, B.; Zhu, J. L., 4-(Dimethyl-amino)benzaldehyde. Acta
crystallographica. Section E, Structure reports online 2008, 64,
o1182.
38.
(a) Berthet, J.-C.; Thuéry, P.; Ephritikhine, M., Formation
of Uranium(IV) Oxide Clusters from Uranocene [U(η8-C8H8)2] and
Uranyl [UO2X2] Compounds. Inorganic Chemistry 2010, 49, 8173-
8177; (b) Berthet, J. C.; Thuéry, P.; Ephritikhine, M., Unprecedented
Reduction of the Uranyl Ion [UO2]2+ into a Polyoxo Uranium(IV)
45.
Tsunoda, T.; Suzuki, M.; Noyori, R., A Facile Procedure
for Acetalization Under Aprotic Conditions. Tetrahedron Lett. 1980,
21, 1357-1358.
ACS Paragon Plus Environment

ACS Catalysis
Page 10 of 10
graphic
SYNOPSIS
TOC
1
2
3
4
R
O
R
5
6
7
8
+ R'3SiOSiR'3
O
2+
+ R'3SiH
[UO2
]
R
H
SiR'3
R
O
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
ACS Paragon Plus Environment