Mono(imidazolin-2-iminato) actinide complexes: Synthesis and application in the catalytic dimerization of aldehydes

Article abstract of DOI:10.1021/ja5091436

The synthesis of the mono(imidazolin-2-iminato) actinide(IV) complexes [(Im^RN)An(N{SiMe₃)₂}₃] (3-8) was accomplished by the protonolysis reaction between the respective imidazolin-2-imine (Im^RNH, R = tBu, Mes, Dipp) and the actinide metallacycles [{(Me₃Si)N}₂An{κ²C,N-CH₂SiMe₂N(SiMe₃)}] (1, An = U; 2, M = Th). The thorium and uranium complexes were obtained in high yields, and their structures were established by single-crystal X-ray diffraction analysis. The mono(imidazolin-2-iminato) actinide complexes 3-8 display short An-N bonds together with large An-N-C angles, indicating strong electron donation from the imidazolin-2-iminato moiety to the metal, corroborating a substantial π-character to the An-N bond. The reactivity of complexes 3-8 toward benzaldehyde was studied in the catalytic dimerization of aldehydes (Tishchenko reaction), displaying low to moderate catalytic activities for the uranium complexes 3-5 and moderate to high catalytic activities for the thorium analogues 6-8, among which 8 exhibited the highest catalytic activity. In addition, actinide coordination compounds showed unprecedented reactivity toward cyclic and branched aliphatic aldehydes in the catalytic Tishchenko reaction mediated by the thorium complex [(Im^DippN)Th{N(SiMe₃)₂}₃] (8), exhibiting high activity even at room temperature. Moreover, complex 8 was successfully applied in the crossed Tishchenko reaction between an aromatic or polyaromatic and an aliphatic cyclic and branched aldehyde, yielding selectively the asymmetrically substituted ester in high yields (80-100%).

Full text of DOI:10.1021/ja5091436

Article
pubs.acs.org/JACS
Mono(imidazolin-2-iminato) Actinide Complexes: Synthesis and
Application in the Catalytic Dimerization of Aldehydes
Isabell S. R. Karmel,† Natalia Fridman,† Matthias Tamm,*,‡ and Moris S. Eisen*,†
†Schulich Faculty of Chemistry, Institute of Catalysis Science and Technology, Technion − Israel Institute of Technology, Technion
City, 32000 Israel
‡Institut fur Anorganische und Analytische Chemie, Technische Universitat Braunschweig, Hagenring 30, 38106 Braunschweig,
̈
̈
Germany
S
* Supporting Information
ABSTRACT: The synthesis of the mono(imidazolin-2-
iminato) actinide(IV) complexes [(ImRN)An(N{SiMe3)2}3]
(3−8) was accomplished by the protonolysis reaction between
the respective imidazolin-2-imine (ImRNH, R = tBu, Mes,
Dipp) and the actinide metallacycles [{(Me3Si)N}2An{κ2C,N-
CH2SiMe2N(SiMe3)}] (1, An = U; 2, M = Th). The thorium
and uranium complexes were obtained in high yields, and their
structures were established by single-crystal X-ray diffraction
analysis. The mono(imidazolin-2-iminato) actinide complexes 3−8 display short An−N bonds together with large An−N−C
angles, indicating strong electron donation from the imidazolin-2-iminato moiety to the metal, corroborating a substantial π-
character to the An−N bond. The reactivity of complexes 3−8 toward benzaldehyde was studied in the catalytic dimerization of
aldehydes (Tishchenko reaction), displaying low to moderate catalytic activities for the uranium complexes 3−5 and moderate to
high catalytic activities for the thorium analogues 6−8, among which 8 exhibited the highest catalytic activity. In addition,
actinide coordination compounds showed unprecedented reactivity toward cyclic and branched aliphatic aldehydes in the
catalytic Tishchenko reaction mediated by the thorium complex [(ImDippN)Th{N(SiMe3)2}3] (8), exhibiting high activity even at
room temperature. Moreover, complex 8 was successfully applied in the crossed Tishchenko reaction between an aromatic or
polyaromatic and an aliphatic cyclic and branched aldehyde, yielding selectively the asymmetrically substituted ester in high yields
(80−100%).
donor ligand, which can be described by the limiting resonance
structures shown in Scheme 1. Due to the ability of the
INTRODUCTION
■
The coordination chemistry of the early actinide elements
thorium and uranium has reached a high level of sophistication
over the past three decades.1 The beginning of this field was
marked by ubiquitous cyclopentadienyl-based ligand systems,
and a large variety of uranium and thorium complexes with the
general formula CpnAnX4−n (n = 1−3; An = Th, U; X = halide,
pseudo halide, alkyl) were synthesized and structurally
characterized. Their stoichiometric reactivity and catalytic
activity have been thoroughly investigated.2 Due to their
electronic properties, cyclopentadienyl ligands were further
applied for the stabilization of unusually low oxidation states of
the respective actinide complexes.3 The state of art, however,
includes a large variety of actinide complexes with unique
reactivities,4,5 e.g., with heteroatom-containing ligand systems,
such as amidinates,6 guanidinates,7 hydrotris(3,5-dimethyl-
pyrazolyl)borate scorpionates,8 tris(aryl)oxide chelates,9 larger
macrocyclic systems,10 and tetracoordinate actinide(IV) com-
plexes with sterically demanding ligand systems.11 Special
attention has been attributed to nitrogen-containing ligands,
displaying a higher An−N bond order, such as the imido,12
ketimido,13 and nitrido and azido14 moieties. Similar to the
ketimido systems, the imidazolin-2-iminato system represents a
highly nucleophilic, strongly basic, and monoanionic nitrogen-
Scheme 1. Resonance Structures of Imidazolin-2-iminato
Ligands
imidazolium ring to stabilize a positive charge efficiently (B),
the imidazolin-2-iminato moiety can be regarded as a 2σ,4π-
electron donor and therefore as a cyclopentadienyl analogue, in
particular when coordinated to early transition metals in high
oxidation states.15 The resulting transition metal16 and
lanthanide17 complexes are notorious for their short M−N
bonds and large, almost linear M−N−C angles, suggesting a
higher bond order to the M−N linkage.18
Received: September 4, 2014
Published: November 13, 2014
© 2014 American Chemical Society
17180
dx.doi.org/10.1021/ja5091436 | J. Am. Chem. Soc. 2014, 136, 17180−17192

Journal of the American Chemical Society
Article
Scheme 2. Synthesis of Mono(omidazolin-2-iminato) Actinide(IV) Complexes 3−8
Table 1. Crystallographic Data for Complexes 3−8
3
4
5·3C7H8
6
7
8·3C7H8
empirical formula
C29H74N6Si6U
C39H78N6Si6U
C45H90N6Si6U·
C29H74N6Si6Th
C39H78N6Si6Th
C45H90N6Si6Th·
3C7H8
3C7H8
formula weight/g mol−1
913.51
200(2)
0.71073
orthorhombic
P212121
11.9540(4)
19.2770(8)
19.4130(4)
90
1037.64
200(2)
1398.89
200(2)
0.71073
triclinic
907.52
200(2)
0.71073
orthorhombic
P212121
11.9540(4)
19.2770(8)
19.4130(4)
90
1031.65
200(2)
1392.20
200(2)
0.71073
triclinic
T/K
λ/Å
0.71073
monoclinic
P21/c
0.71073
monoclinic
P21/c
crystal system
space group
a/Å
P1
̅
P1
̅
21.6750(8)
12.2840(11)
20.0070(14)
90
12.0440(2)
14.0560(3)
23.1880(4)
95.5880(18)
92.6530(15)
102.1780(8)
3809.91(12)
2
21.6750(8)
12.2840(11)
20.0070(14)
90
12.0820(4)
14.0920(4)
23.2090(10)
95.8390(11)
92.6290(11)
102.239(2)
3832,5(2)
2
b/Å
c/Å
α/deg
β/deg
90
99.745(4)
90
90
99.745(4)
90
γ/deg
V/Å3
90
90
4473.5(3)
4
5250.1(6)
4
4473.5(3)
4
5250.1(6)
4
Z
ρ/g cm−3
μ(Mo Kα)/mm−1
1.356
1.313
1.198
1.347
1.305
1.185
3.814
3.259
2.262
3.519
3.008
2.077
Θ range for data collection/
2.26−25.03
0.95−24.13
0.88−24.56
2.00−24.18
1.91−24.14
0.88−25.05
deg
F(000)
1864
2120
1408
1856
2112
1404
limiting indices
0 ≤ h ≤ 14
0 ≤ k ≤ 21
0 ≤ l ≤ 23
−4 ≤ h ≤ 23
−13 ≤ k ≤ 0
0 ≤ l ≤ 22
0 ≤ h ≤ 13
−15 ≤ k ≤ 15
−26 ≤ l ≤ 25
0 ≤ h ≤ 13
0 ≤ k ≤ 21
0 ≤ l ≤ 21
−24 ≤ h ≤ 24
−13 ≤ k ≤ 0
0 ≤ l ≤ 22
0 ≤ h ≤ 14
−16 ≤ k ≤ 16
−27 ≤ l ≤ 27
reflections collected/unique
(Rint)
4104/4104
(0.0802)
7372/7372
(0.0650)
11339/11339
(0.0315)
3788/3788
(0.0890)
7788/7788
(0.0968)
12969/12969
(0.0902)
% completeness to Θ
GOF on F2
99.1
88.4
99.7
99.1
93.0
99.5
1.124
1.023
1.073
1.164
1.142
1.060
R1, wR2 [I > 2σ(I)]
R1, wR2 (all data)
0.0351, 0.0713
0.0407, 0.0728
0.0350, 0.0788
0.0522, 0.0837
0.0545, 0.1384
0.0799, 0.1526
0.0423, 0.0608
0.0494, 0.0622
0.0701, 0.0951
0.1047, 0.1029
0.0849, 0.1730
0.1691, 0.2208
largest diff peak and hole/e
0.734 and −0.801 0.939 and −0.817 1.066 and −0.873
0.599 and −0.953 0.740 and −0.536 0.985 and −1.428
Å−3
Recently, we reported the synthesis and structural character-
ization of a series of uranium(IV) imidazolin-2-iminato
complexes, which were obtained by an acid−base reaction
between the homoleptic tetraamido complex [U(NMeEt)4]
and neutral imidazolin-2-imines ImRNH.19 Despite variation of
the stoichiometry of the starting materials and of the reaction
conditions, the uranium(IV) complexes obtained depended on
the steric encumbrance of the R substituent of the imidazolin-2-
iminato ligand, corroborating a thermodynamic control of the
reaction, which did not allow for the preparation of
mono(imidazolin-2-iminato) actinide(IV) complexes. More-
over, an analogous reaction between [Th(NMeEt)4] and the
respective imidazolin-2-imine led to a myriad of products, and a
single complex could not be isolated. In the present study, we
report a strategy for the selective synthesis and characterization
of a series of mono(imidazolin-2-iminato) thorium(IV) and
uranium(IV) complexes, which were obtained in high yields by
protonolysis of the actinide metallacycles [{(Me3Si)N}2An-
{κ2C,N-CH2SiMe2N(SiMe3)}] (1, An = U; 2, M = Th).20 The
large ionic radii and the presence of f-orbitals in the actinide
series, which allow for large coordination numbers and unusual
coordination geometries, gave rise to a unique reactivity in
organic transformations.21 The catalytic activity of actinide
coordination compounds has been investigated in a wide range
of processes, such as the polymerization of α-olefins,22
hydrothiolation,23 hydroalkoxylation,23 hydrosilylation24 and
hydroamination25 of terminal alkynes, isontrile−alkyne cou-
pling,26 coupling of terminal alkynes,27 ring-opening polymer-
17181
dx.doi.org/10.1021/ja5091436 | J. Am. Chem. Soc. 2014, 136, 17180−17192

Journal of the American Chemical Society
Article
a
Table 2. Selected Bond Lengths (Å) and Angles (deg) for Complexes 3−8
3
4
5·3C7H8
6
7
8· 3C7H8
An−N1
An−N2
An−N3
An−N4
N4−Cipso
An−N4−Cipso
N1−An−N2
N2−An−N3
N3−An−N4
N1−An−N3
N1−An−N4
N2−An−N4
cone angle
2.329(8)
2.303(7)
2.318(7)
2.118(8)
1.290(12)
169.5(7)
104.3(2)
118.5(2)
98.3(3)
109.7(3)
122.5(3)
104.5(3)
83
2.328(4)
2.346(6)
2.342(6)
2.313(6)
2.137(6)
1.319(9)
169.5(5)
106.1(2)
104.7(2)
104.8(2)
111.7(2)
115.2(2)
114.0(2)
69
2.401(8)
2.347(7)
2.346(7)
2.176(8)
1.292(12)
166.9(8)
105.2(3)
118.8(3)
100.1(3)
109.6(3)
118.0(3)
105.8(3)
84
2.370(7)
2.350(6)
2.397(8)
2.189(7)
1.308(10)
168.5(6)
118.1(3)
110.2(3)
122.4(3)
101.8(2)
108.0(2)
97.5(2)
71
2.369(10)
2.395(8)
2.418(8)
2.197(10)
1.291(14)
170.7(7)
105.2(3)
106.8(3)
114.4(3)
111.5(3)
105.2(3)
113.4(3)
64
2.319(4)
2.323(4)
2.143(4)
b
1.313(6)
b
169.8(4)
119.53(16)
107.85(15)
126.74(15)
101.04(15)
106.81(15)
96.54(15)
73
a
b
An: U for complexes 3−5; Th for complexes 6−8. Cipso: C19 for complexes 3, 4, 6, 7; C31 for complexes 5 and 8.
ization of cyclic esters,28,6i,19 and the Tishchenko reaction with
aromatic aldehydes.29 Despite the large scope of organic
transformations mediated by actinide complexes, the examples
involving oxygen-containing substrates remain scarce, which
can be attributed to the high oxophilicity of the early actinides
and the resulting formation of thermodynamically stable,
catalytically inactive actinide−oxo species.30 Therefore, an
interesting conceptual question regards the ability to increase
the catalytic activity of actinide compounds toward oxygen-
containing substrates by avoiding the formation of catalytically
inactive actinide−oxo species by decreasing the oxophilicity of
the metal center. This approach can be in principle investigated
by the coordination of strongly nucleophilic ligands, such as the
imidazolin-2-iminato moiety, which might be expected to
increase the electron density of the metal center and therefore
decrease its oxophilicity, which should in turn lead to an
increased catalytic activity toward oxygen-containing molecules,
such as esters and aldehydes. We decided to investigate the
reactivity of the mono(imidazolin-2-iminato) thorium(IV)
complex [(ImDippN)Th{N(SiMe3)2}3] (8) toward aromatic,
cyclic, and branched aliphatic aldehydes. The use of a
thorium(IV) complex, bearing only one sterically encumbering
imidazolin-2-iminato ligand, should ensure an enhanced
catalytic activity, while enabling the substrate to enter the
coordination sphere of the metal, due to the reduced steric bulk
in comparison to bis- and tris(imidazolin-2-iminato) complexes.
Figure 1. ORTEP drawing of [(ImtBuN)U{N(SiMe3)2}3] (3) with
thermal displacement parameters at 20% probability. Hydrogen atoms
are omitted for clarity.
RESULTS AND DISCUSSION
■
Synthesis and Structural Characterization. The mono-
(imidazolin-2-iminato) actinide(IV) complexes 3−8 were
obtained in high yields by treatment of a toluene solution of
the actinide metallacycles 1 and 2 with a toluene solution of 1
equiv of the respective imidazolin-2-imine ImRNH at room
temperature (Scheme 2). Subsequent stirring of the reaction
mixture for 12 h at room temperature, removal of the solvent,
and recrystallization from a concentrated toluene solution at
−35 °C afforded the actinide complexes 3−8 in high yields.
Crystals suitable for X-ray crystallography were obtained from
toluene solutions at −35 °C. Crystallographic data for
complexes 3−8 are presented in Table 1; selected bond
lengths and angles are assembled in Table 2.
Figure 2. ORTEP drawing of [(ImMesN)U{N(SiMe3)2}3] (4) with
thermal displacement parameters drawn at 20% probability. Hydrogen
atoms are omitted for clarity.
(3), and [(ImDippN)U{N(SiMe3)2}3] (5), respectively. X-ray
measurements performed on single crystals of compounds 3−5
show a distorted tetrahedral coordination environment around
the metal, with N−U−N angles of 98.3(3)−122.5(3)°,
96.54(15)−126.74(15)°, and 104.8(2)−111.7(2)°, for com-
plexes 3, 4, and 5, respectively. Moreover, to describe the steric
The mono(imidazolin-2-iminato) uranium(IV) complexes
[(ImRN)U{N(SiMe3)2}3] (3−5) (Figure 1−3) are obtained as
orange powders in high yields of 92%, 94%, and 95% for
[(ImMesN)U{N(SiMe3)2}3] (4), [(ImtBuN)U{N(SiMe3)2}3]
17182
dx.doi.org/10.1021/ja5091436 | J. Am. Chem. Soc. 2014, 136, 17180−17192

Journal of the American Chemical Society
Article
iminato) complexes, showed slightly longer N−Cipso bond
distances for the titanium(IV) compounds with values of
1.331(3), 1.348(4), and 1.330(6) Å, for [(ImtBuN)TiCl3],16a
[(ImMesN)TiCl3],16e and [(ImDippN)TiCl3],16e respectively,
indicating a more covalent bond in the respective mono-
(imidazolin) titanium(IV) complexes than in the respective
lanthanide or actinide complexes.
The mono(imidazolin-2-iminato) thorium(IV) complexes
6−8 (Figure 4−6) were crystallized in a similar fashion from
Figure 3. ORTEP drawing of [(ImDippN)U{N(SiMe3)2}3] (5) with
thermal displacement parameters drawn at 20% probability. Hydrogen
atoms and distorted solvent molecules are omitted for clarity.
demand of phosphine ligands Tolman et al.31 introduced the
ligand cone angle, which is defined as the angle between the
metal at the vertex of the cone formed by the coordinating
ligands and the metal center, and the hydrogen atoms at its
perimeter, which was later adapted to further ligand systems,
such as cyclopentadienyl ligands by Coville et al.32 This
parameter can also be applied for the description of the steric
demand of imidazolin-2-iminato systems, displaying values of
83°, 73°, and 69° for [(ImtBuN)U{N(SiMe3)2}3] (3),
[(ImMesN)U{N(SiMe3)2}3] (4), and [(ImDippN)U{N-
(SiMe3)2}3] (5), respectively. The U−N4 bond distances in
complexes 3−5 are short, with values of 2.118(9), 2.143(4),
and 2.137(6) Å for 3, 4, and 5, respectively, which are on
average 0.20 Å shorter than the U−Namido bond lengths in the
respective uranium compound (Table 2). Moreover, the U−
N4−Cipso angles with values of 169.5(7)°, 169.8(4)°, and
169.5(5)°, for 3, 4, and 5, respectively, are close to linearity, in
comparison to the U−Namido−Si angles, which exhibit as
expected a bent geometry (Table 2). The bonding properties of
imidazolin-2-iminato are comparable to those of the ketimido
moiety, which is also described as a 2σ,4π-electron donor in
actinide complexes.13 The U−N4 bond lengths in the
mono(imidazolin-2-iminato) uranium complexes 3−5 are yet
slightly shorter than the U−N bond distances in uranium(IV)
bis(ketimido) compounds and clearly shorter than the average
U−Namido bond.12 The short U−N4 bond lengths and large U−
N4−Cipso angles indicate a substantial π-character of the U−N4
bond, suggesting a higher bond order of the same. To further
elucidate the bonding properties of the imidazolin-2-iminato
moiety, the N4−Cipso bond distances in complexes 3−5 are
compared with the respective bond distances for lanthanide and
group IV mono(imidazolin-2-iminato) complexes, which have
been investigated in previous studies.16−18 Whereas the
uranium(IV) complexes 3−5 display N4−Cipso bond lengths
of 1.290(12), 1.313(6), and 1.319(9) Å for compounds 3, 4,
and 5, respectively, the rare earth complexes exhibit N−Cipso
bond distances of 1.251(4), 1.266(5), 1.271(10), and 1.254(14)
Å, for [(ImDippN)LuCl2]·3THF, [(ImDippN)GdCl2]·3THF,
[(ImDippN)YbCl2]·3THF,33 and for [(ImDippN)SmCl2]·
3THF33 respectively, showing a slight elongation of the N−
Cipso bond in uranium complexes 3−5, further sustaining a
higher U−N bond order. For group IV metals a comparison of
the N4−Cipso bond distances in the uranium compounds 3−5
with the respective bonds in titanium(IV) mono(imidazolin-2-
Figure 4. ORTEP drawing of [(ImtBuN)Th{N(SiMe3)2}3] (6) with
thermal displacement parameters drawn at 20% probability. Hydrogen
atoms are omitted for clarity.
Figure 5. ORTEP drawing of [(ImMesN)Th{N(SiMe3)2}3] (7) with
thermal displacement parameters drawn at 20% probability. Hydrogen
atoms are omitted for clarity.
Figure 6. ORTEP drawing of [(ImDippN)Th{N(SiMe3)2}3] (8) with
thermal displacement parameters drawn at 20% probability. Hydrogen
atoms and distorted solvent molecules are omitted for clarity.
17183
dx.doi.org/10.1021/ja5091436 | J. Am. Chem. Soc. 2014, 136, 17180−17192

Journal of the American Chemical Society
Article
concentrated toluene solutions at −35 °C. However, the
crystals of the thorium complexes showed a notorious
instability, decomposing at room temperature when submerged
into parathon-N oil, which is commonly used for single-crystal
X-ray measurements of air sensitive compounds.To determine
the crystal structures of the thorium(IV) complexes 6−8, the
single-crystalline material was submerged in cold (−35 °C)
perfluoropolyalkylether oil, the vessel was immediately
submerged in liquid nitrogen, and the single crystals were
fished from the vessel at −78 °C and rapidly mounted on the
diffractometer. Especially, single crystals of complex 8 showed
an exceedingly high instability, losing their transparency within
seconds, when submerged in cold parathion-N oil, or within a
few minutes, when submerged in cold (−35 °C) perfluor-
opolyalkylether oil. The thorium complexes [(ImtBuN)Th{N-
(SiMe3)2}3] (6), [(ImMesN)Th{N(SiMe3)2}3] (7), and
[(ImDippN)Th{N(SiMe3)2}3] (8) are isostructural with the
uranium analogues 3−5, crystallizing in the same crystallo-
graphic space groups, and exhibiting similar imidazolin-2-
iminato cone angles of 84°, 71°, and 64°, for complexes 6, 7,
and 8, respectively (Table 2). The coordination around the
thorium center is distorted tetrahedral, and the N−Th−N bond
angles are comparable to the N−U−N bond angles in
complexes 3−5, displaying values of 100.1(3)−118.8(3)°,
101.8(8)−118.1(3)°, and 105.2(3)−114.4(3)°, for compounds
6, 7, and 8, respectively. The Th−N4−Cipso angles are close to
linearity, displaying values similar to the U−N4−Cipso values, in
the isostructural complexes 3−5, with values of 166.9(8),
168.5(6), and 170.7(7)°, for complexes 6, 7, and 8, respectively.
The Th−N4 bond distances are slightly elongated in
comparison to the U−N4 distances (vide supra), exhibiting
values of 2.176(8), 2.189(7), and 2.197(14) Å for [(ImtBuN)-
Th{N(SiMe3)2}3] (6), [(ImtBuN)Th{N(SiMe3)2}3] (7), and
[(ImDippN)Th{N(SiMe3)2}3] (8), respectively. The difference
of approximately 0.06 Å between the Th−N and U−N bond
lengths is in good agreement with the predicted value of 0.05
Å.34 The Th−N4 bond lengths are on average 0.10 Å shorter
than the Th−N bond distances in thorium bis(ketimido)
complexes, and on average 0.20 Å shorter than Th−Namido
bonds.13,34 The short Th−N4 bond lengths and the large Th−
N−C angles indicate a substantial π-character of the Th−N
bond, comparable to the respective U−N bond (vide supra).
The N4−Cipso bond lengths in the mono(imidazolin-2-iminato)
thorium complexes 6−8 are comparable to the uranium
analogs, displaying values of 1.292(12), 1.308(10), and
1.291(14) Å, for compounds 6, 7, and 8, respectively, indicating
similar interactions in the actinide complexes 3−8. Further-
more, a comparison of the An−Namido bond distances in
complexes 3−8, which range between 2.303(7) and 2.346(6) Å,
for the uranium complexes 3−6, and 2.346(7) and 2.418(8) Å,
for the respective thorium compounds 6−8, are slightly
elongated (0.05−0.1 Å) as compared to those of various
uranium(IV) and thorium(IV) bis(trimethylsilyl) amido
complexes,5n,35 which can be attributed to the steric demand
of the imidazolin-2-iminato ligand.
Scheme 3. General Reaction Scheme for Metal-Catalyzed
Dimerization of Aldehydes
hydrogen atoms in the β-position reduces the scope of
accessible esters and represents a major impediment for the
use of the Tishchenko reaction in organic synthesis.37−39 In
addition, when two different aldehydes are reacted in the
crossed Tishchenko reaction, the selectivity toward the mixed
ester still remains a major challenge and can only be achieved in
particular cases.40 In a previous study, we have reported the
reactivity of Cp*2ThMe2 toward aromatic aldehydes, showing a
high catalytic activity and a tolerance toward several functional
groups.29 Herein, we investigated the reactivity of the
mono(imidazolin-2-iminato) actinide(IV) complexes 3−8
toward aldehydes, addressing the fundamental question
whether postmetallocene actinide catalysts display a reactivity
not only toward aromatic aldehydes but also toward cyclic and
branched aliphatic aldehydes, as well as in the crossed
Tishchenko reaction. To determine the catalyst with the
highest activity, we carried out catalytic studies using
benzaldehyde as the substrate and complexes 3−8 as
precatalysts. Although the uranium complexes 3−5 displayed
moderate to low activities (Table 3), the thorium analogues 6−
Table 3. Catalytic Dimerization of Benzaldehyde Mediated
a
by Complexes 3−8
Yield (%)
complex
6 h
12 h
24 h
48 h
3
4
5
6
7
8
0
3
8
12
9
0
0
5
0
6
12
15
11
100
41
61
96
37
26
19
2
7
0
5
21
13
21
58
61
b
29
,
9
65
85
c
29
,
10
11
d
,
29
a
Reaction conditions: 4.48 μmol of catalyst; cat/PhCHO 1/100; 500
b
μL of C6D6; room temperature (rt). Catalyst: [Cp*2Th(CH3)2] (10
μmol); cat/PhCHO 1/100, rt. Catalyst: [Th(NMeEt)4] (10 μmol);
cat/PhCHO 1/100, rt. Catalyst: ansa-[Me2SiCp″2Th(CH3)2] (10
μmol); cat/PhCHO 1/100, rt.
c
d
8 displayed higher catalytic activities, with [(ImDippN)Th{N-
(SiMe3)2}3] (8) showing the highest catalytic activity among
the mono(imidazolin-2-iminato) complexes 3−8; hence, it was
applied for all further catalytic studies. Despite the notorious
instability displayed by single crystals of complex 8, when
submerged in parathion-N oil, or perfluoropolyalkylether oil,
the thorium compound 8 is stable in solution and can therefore
be applied for catalytic studies, even at elevated temperatures
(90 °C for weeks). The reactivity of a metal coordination
complex depends on the availability of the metal center for
coordination to the incoming substrate moiety. To further
explore the difference in activity of the actinide compounds 3−
8, the steric encumbrance around the respective actinide center
was investigated using space filling models (Figure 7). The
cavities, built by the carbon atoms of the R-substituents of the
imidazolin-2-iminato ligand and the carbon atoms of the
Catalytic Tishchenko Reaction. The dimerization of two
aldehydes to yield the respective ester via a hydride shift, in
which one of the aldehyde monomers acts as a hydride donor
and the other as a hydride acceptor (disproportionation), is
known as the Tishchenko reaction (Scheme 3).36 Despite the
large number of studies carried out with main group,37
transition metal,38 and lanthanide39 catalysts, the tolerance of
the respective metal complexes toward functional groups and
17184
dx.doi.org/10.1021/ja5091436 | J. Am. Chem. Soc. 2014, 136, 17180−17192

Journal of the American Chemical Society
Article
hyde is higher than the activity observed for [Th(NMeEt)4]
(10) and [Cp*2Th(CH3)2] (9) and comparable to the activity
exhibited by ansa-[Me2SiCp″2Th(CH3)2] (11). However, in
contrast to the previously reported actinide complexes, which
catalyzed neither the Tishchenko reaction of aliphatic aldehydes
nor the selective crossed Tishchenko reaction, the mono-
(imidazolin-2-iminato) thorium complex 8, showed an
unprecedented high activity toward cyclic and branched
aliphatic aldehydes, as well as in the crossed Tishchenko
reaction (vide infra).
Important reactions that need to be performed in catalytic
studies are poisoning experiments. The basic idea is to find out
what percentage of the precatalyst is active in the reaction.
Hence, poisoning experiments with isopropanol showed that all
catalyst 8 is active in the catalytic process, and experiments with
stoichiometric amounts of [(ImDippN)Th{N(SiMe3)2}3] (8)
and benzaldehyde showed that two aldehyde units can insert
into the Th−N(SiMe3)2 bonds, leading to the formation of 2
equiv of N(SiMe3)2 α-substituted ester (D), which was
Figure 7. Space filling model of [(ImDippN)Th{N(SiMe3)2}3] (8)
showing the large cavity of ∼5.7 Å. Color code: Th, green; N, blue; Si,
yellow; C, gray. Hydrogen atoms are omitted for clarity.
1
characterized by H NMR, 13C NMR, 29Si NMR, and mass
spectroscopy. A plausible mechanism for the Tishchenko
reaction, mediated by complex 8, is presented in Scheme 4.
After the insertion of an aldehyde unit into the Th−N(SiMe3)2
bond, the thorium alkoxo species A is obtained, which
undergoes a second aldehyde insertion into the Th−O bond
forming the intermediate complex B. Complex B will react with
an additional aldehyde via a six-centered transition state (C),
leading to the active thorium−oxo catalyst E through the
elimination of 1 equivalent of the N(SiMe3)2 α-substituted
ester (D) per trimethylsilylamido ligand. A subsequent
insertion of an incoming aldehyde unit into the Th−O bond
of complex E forms the intermediate complex F, which reacts
bis(trimethylsilyl)amido ligands, display values between 3.6 and
4.5 Å for complexes 3−7; the complex [(ImDippN)Th{N-
(SiMe3)2}3] (8) exhibits a larger cavity (∼5.7 Å), which is in
agreement with the higher activity displayed by this compound.
Recently, we reported the catalytic performance of the
homoleptic amido complex [Th(NMeEt)4] (10), as well as of
[Cp*2Th(CH3)2] (9) and the ansa-bridged thorium(IV)
complex ansa-[Me2SiCp2′′(CH3)2] (11) (Cp′′ = C5(CH3)4),
toward aromatic aldehydes, among which the ansa-bridged
thorium complex displayed the highest catalytic activity (Table
3, entries 9−11).29 The catalytic activity of the mono-
(imidazolin-2-iminato) thorium complex 8 toward benzalde-
Scheme 4. Proposed Mechanism for the Tishchenko Reaction Mediated by Complex 829,41
17185
dx.doi.org/10.1021/ja5091436 | J. Am. Chem. Soc. 2014, 136, 17180−17192

Journal of the American Chemical Society
Article
with another aldehyde via a six-membered transition state (G)
to yield the ester H and regenerating the catalytically active
thorium−oxo species E. To trap the intermediates of the
catalytic cycle shown in Figure 4, experiments with
stoichiometric amounts of benzaldehyde were performed, and
phthalaldehyde, displaying a full conversion to phthalide after
6 h.
When complex 8 is reacted with two different aldehydes, one
of them bearing an aromatic or polyaromatic substituent
(RCHO), the other a cyclic or branched aliphatic substituent
(R1CHO), four possible products can be obtained (Scheme 5).
When a ratio of 1:1 between RCHO and R1CHO is used,
unexpectedly the asymmetrically substituted ester
(RCH2OCOR1) is the first product observed after a reaction
time of 2 h, together with trace amounts of R1CH2OCOR1.
Longer reaction times lead to the formation of the symmetri-
cally substituted esters RCH2OCOR and R1CH2OCOR1, as
well as traces of R1CH2OCOR, after a reaction time 24 h, with
a ratio of 25:5:33:35 for RCH2OCOR1, R1CH2OCOR,
RCH2OCOR, and R1CH2OCOR1, respectively. The formation
of the asymmetrically substituted ester RCH2OCOR1 suggests
that the benzylic thorium alkoxo species E (Scheme 4) reacts
preferentially with an aliphatic aldehyde, which will react again
favorably with another aromatic aldehyde (after hydride
transfer), closing the catalytic cycle. After the reaction proceeds,
the amount of the symmetrically substituted esters increases,
suggesting a competition between the aldehydes in the reaction
mixture. To control the catalytic reaction toward the selective
formation of the asymmetrically substituted ester, we applied an
excess of the aromatic aldehyde (RCHO) (RCHO:R1CHO
200:50) to avoid the competition reactions, resulting in the
formation of symmetrically substituted esters. Owing to the
better hydride-donor ability of aliphatic aldehydes than of
aldehydes bearing electron withdrawing groups (e.g., R = aryl),
which are considered to be better hydride acceptors,40,42 we
were able to control the reaction toward the formation of the
asymmetrically substituted ester. This result indicates that the
hydride transfer is the rate-determining step (rds) in the
catalytic cycle. When all the aliphatic aldehyde (R1CHO) is
consumed after 1.5 h (>95% yield of the asymmetric ester is
obtained), the excess of the aromatic aldehyde yields the
symmetrically substituted ester RCH2OCOR, until full
conversion is reached after 24 h.
1
the intermediates were characterized by H NMR, 13C NMR,
and 29Si NMR spectroscopy. The addition of 2 equiv of
benzaldehyde to complex 8, led to the quantitative formation of
the thorium intermediate A (R = Ph), which after treatment
with an additional 2 equiv of benzaldehyde yielded the
thorium−alkoxo species B (R = Ph). Subsequent addition of
2 equiv of benzaldehyde to the reaction mixture led to the
elimination of 2 equiv of the N(SiMe3)2 α-substituted ester D
(R = Ph), with formation of complex E (R = Ph). The reactivity
of complex 8 was investigated with a variety of substrates
(Table 4), including substituted aromatic, polyaromatic, cyclic,
Table 4. Catalytic Tishchenko Reaction Mediated by
Complex 8
yield (%) RCH2OCOR
a
entry
RCHO
6 h
12 h
24 h
1
2
3
4
5
6
7
8
Ph
21
0
61
100
32
1-naphthyl
2-naphthyl
4-NO2−Ph
cyclohexyl
cyclopentyl
isopropyl
10
0
24
61
39
84
82
94
100
77
100
100
100
100
o-Ph(CHO)2
a
Reaction conditions: 4.48 μmol of catalyst 8; cat/RCHO 1/100; 500
μL of C6D6; rt.
and branched aliphatic aldehydes, exhibiting a higher catalytic
activity toward cyclic and branched aliphatic aldehydes than for
their aromatic counterparts. Therefore, we carried out crossed
Tishchenko experiments (Scheme 5) with two different
aldehydes, one of which was an aromatic or polyaromatic
aldehyde, and the other one being a cyclic or branched aliphatic
aldehyde (Table 5). When the reaction was performed with an
equimolar ratio of both aldehydes, the symmetrically and
asymmetrically substituted esters were obtained in similar
amounts, and no selectivity toward the formation of either one
or the other ester was observed. However, when an excess of
the aromatic aldehyde was applied, the asymmetrically
substituted ester is obtained as the major product and only
small amounts of the homocoupled esters are observed.
The mono(imidazolin-2-iminato) thorium(IV) complex
[(ImDippN)Th{N(SiMe3)2}3] (8) displayed a high activity in
the dimerization of cyclic and branched aliphatic aldehydes
(Table 4, entries 5−7) to yield the respective symmetrically
substituted ester with 100% conversion after 12 h. Mono-
substituted aromatic esters were obtained in moderate to high
yields after the Tishchenko reaction with the respective
aromatic aldehyde proceeds for 24 h at room temperature
(Table 4, entries 1−5). Furthermore, the intramolecular
Tishchenko reaction (Scheme 6) was performed with
CONCLUSIONS
■
The synthesis of mono(imidazolin-2-iminato) actinide(IV)
complexes [(ImRN)An{N(SiMe3)2}3] was performed by the
protonolysis reaction of the actinide metallacycles 1 and 2 with
the respective neutral imidazolin-2-imines (ImRNH) to afford
complexes 3−8 in high yields. Due to the higher reactivity of
the An−CH2 bond in comparison to the An−N bonds in the
actinide metallacycles 1 and 2, the monosubstituted imidazolin-
2-iminato actinide complexes could be obtained selectively,
without a dependence on the steric encumbrance of the
respective imidazolin-2-iminato ligand. The mono(imidazolin-
2-iminato) actinide complexes 3−8 were characterized by X-ray
crystallography, displaying very short An−N bonds and close to
linear An−N−C bond angles, suggesting a substantial π-
character to the An−N bond. The reactivity of complexes 3−8
in the catalytic Tishchenko reaction was investigated, displaying
low to moderate activities for the uranium complexes 3−5 and
moderate to high activities for the thorium complexes 6−8. The
Scheme 5. Crossed Tishchenko Reaction Catalyzed by 8
17186
dx.doi.org/10.1021/ja5091436 | J. Am. Chem. Soc. 2014, 136, 17180−17192

Journal of the American Chemical Society
Article
a
Table 5. Crossed Tishchenko Reaction Mediated by Complex 8
yield (%)
entry
RCHO
Ph
R1CHO
RCH2OCOR
R1CH2OCOR1
RCH2OCOR1
R1CH2OCOR
1
2
3
4
5
C6H11
C5H9
92
84
8
Ph
12
20
Ph
isopropyl
C6H11
C6H11
80
1-naphthyl
5
5
100
2-naphthyl
88
12
a
1
Reaction conditions: 4.48 μmol of catalyst 8; cat/RCHO 1/200; cat/R1CHO 1/50; 750 μL of C6D6; rt; yield was determined by H NMR
spectroscopy of the crude reaction mixture after 1.5 h. The yield is based on the moles of the aromatic aldehyde.
anisotropically. Hydrogen atoms were included using the riding
Scheme 6. Catalytic Lactonization of Phthalaldehyde
Mediated by Complex 8
model. The software used for creating space filling models was
Mercury 3.1.47
General Procedure for the Synthesis of Mono(imidazolin-2-
minato) Actinide(IV) Complexes. A solution of the actinide
metallacycle 1 or 2 (500 mg) in toluene (10 mL) was treated with
a toluene solution of the respective imidazolin-2-imine ImRNH (1.0
equiv in 10 mL) at room temperature. The reaction mixture was
stirred for 12 h at room temperature, and the solvent was subsequently
removed under vacuum to afford crude 3−8. The crude products 3−8
were recrystallized from a concentrated toluene solution at −35 °C to
yield 3−8 as crystalline materials.
mono(imidazolin-2-iminato) thorium(IV) complex
[(ImDippN)Th{N(SiMe3)2}3] (8) exhibited the highest catalytic
activity, and its reactivity toward aromatic, polyaromatic, cyclic,
and branched aliphatic was studied, displaying a moderate to
high activity toward aromatic and polyaromatic aldehydes and a
very high catalytic activity in the dimerization of cyclic and
branched aliphatic aldehydes. The reactivity of 8 was further
studied in the crossed Tishchenko reaction, affording
quantitative yield of the asymmetrically substituted ester, with
only small amounts of the homocoupled aldehydes.
[(ImtBuN)U{N(SiMe3)2}3] (3): yield 94% (598 mg, 0.65 mmol);
1H NMR (300.0 MHz, C6D6) δ 0.01 (s, 54 H, Si(CH3)3), 1.01 (s, 18
H, C(CH3)2), 2.11 (2 H, CH); 13C NMR (75.5 MHz, C6D6) δ 2.63
(Si(CH3)3), 27.96 (C(CH3)3), 33.51 (C(CH3)3), 59.21 (CH), 148.2
(CipsoN); 29Si NMR (59.6 MHz, C6D6) δ −10.14. Anal. Calcd for
C29H74N6Si6U: C, 38.13; H, 8.17; N, 9.20. Found: C, 38.47; H, 8.23;
N, 9.29.
[(ImMesN)U{N(SiMe3)2}3] (4): yield 92% (665 mg, 0.64 mmol);
1H NMR (300.0 MHz, C6D6) δ −13.17 (s, 54 H, Si(CH3)3), −3.87 (s,
6 H, para-CH3), 6.19 (s, 4 H, Har), 17.30 (s, 12 H, ortho-CH3), 27.75
(s, 2 H, CH); 13C NMR (75.5 MHz, C6D6) δ 2.63 (Si(CH3)3), 19.24
(CH3), 32.72 (CH3), 57.32 (CH), 131.68 (CarH), 151.81 (CarC),
158.91 (CipsoN); 29Si NMR (59.6 MHz, C6D6) δ −11.74. Anal.
Calcd for C39H78N6Si6U: C, 45.14; H, 7.58; N, 8.10. Found: C, 44.87;
H, 7.63; N, 7.98.
EXPERIMENTAL SECTION
■
General Considerations. All manipulations of air sensitive
materials were performed with rigorous exclusion of oxygen and
moisture in flamed Schlenk-type glassware on a high vacuum line
(10−5 Torr), or in nitrogen filled MBraun and Vacuum Atmospheres
gloveboxes with a medium capacity recirculator (1−2 ppm oxygen).
Argon and nitrogen were purified by passage through an MnO oxygen
removal column and a Davison 4 Å molecular sieve column.
Analytically pure solvents were dried and stored with Na/K alloy
and degassed by three freeze−pump−thaw cycles prior to use (hexane,
toluene, benzene-d6, toluene-d8). ImDippNH, ImMesNH, ImtBuNH15,
and the metallacycles 1 and 220e were synthesized according to
published literature procedures. Benzaldehyde, cyclohexanecarbalde-
hyde, cyclopentanecarbaldehyde, isobutyraldehyde, and 1-naphthalde-
hyde (Sigma-Aldrich) were distilled over sodium bicarbonate and
stored in a glovebox prior to use. 2-Naphthaldehyde and
phthalaldehyde (Sigma-Aldrich) were dried for 12 h on a high
vacuum line (10−5 Torr) and stored in a glovebox prior to use. NMR
spectra were recorded on Avance 300 and Avance 400 Bruker
spectrometers. Chemical shifts for 1H NMR, 13C NMR, and 29Si NMR
measurements are reported in ppm and referenced using residual
proton or carbon signals of the deuterated solvent relative to
tetramethylsilane. Elemental analyses were carried out by the
microanalysis laboratory at the Hebrew University of Jerusalem. MS
experiments were performed at 200 °C (source temperature) on a
Maxis Impact (Bruker) mass spectrometer with an APCI solid probe
method. For X-ray crystallographic measurements, the single-
crystalline material was immersed in perfluoropolyalkylether oil and
was quickly fished with a glass rod and mounted on a Kappa CCD
diffractometer under a cold stream of nitrogen. Data collection was
performed using monochromated Mo Kα radiation using φ and ω
scans to cover the Ewald sphere.43 Accurate cell parameters were
obtained with the amount of indicated reflections (Table 1).44 The
structure was solved by SHELXS-97 direct methods45 and refined by
the SHELXL-97 program package.46 The atoms were refined
[(ImDippN)U{N(SiMe3)2}3] (5): yield 95% (742 mg, 0.66 mmol);
1H NMR (300.0 MHz, C6D6) δ −9.01 (s, 54 H, Si(CH3)3, −4.96 (s,
12 H CH(CH3)2), 1.28 (s, 12 H, CH(CH3)2), 7.15−7.92 (m, 6 H,
Har), 25.77 (s, 4 H, CH(CH3)2), 26.46 (s, 2 H, CH); 13C NMR (75.5
MHz, C6D6) δ 2.69 (Si(CH3)3), 18.87 (CH(CH3)2), 24.00 (CH-
(CH3)2), 28.95 (CH(CH3)2), 33.64 (CH(CH3)2), 37.93 (CH(CH3)2),
59.27 (CH), 132.97 (CarH), 158.41 (CarC), 163.78 (CipsoN);
29Si NMR (59.6 MHz, C6D6) δ −11.03. Anal. Calcd for C45H90N6Si6U:
C, 48.14; H, 8.09; N, 7.49. Found: C, 48.60; H, 8.15; N, 7.43.
[(ImtBuN)Th{N(SiMe3)2}3] (6): yield 95% (605 mg, 0.67 mmol);
1H NMR (300.0 MHz, C6D6) δ 0.50 (s, 54 H, Si(CH3)3), 1.48 (s, 18
H, C(CH3)2), 5.86 (s, 2 H, CH); 13C NMR (75.5 MHz, C6D6) δ 5.90
(Si(CH3)3), 30.96 (C(CH3)3), 56.06 (C(CH3)3), 108.63 (CH), 145.35
(CipsoN); 29Si NMR (59.6 MHz, C6D6) δ −9.89. Anal. Calcd for
C29H74N6Si6Th: C, 38.38; H, 8.22; N, 9.26. Found: C, 38.56; H, 8.27;
N, 9.33.
[(ImMesN)Th{N(SiMe3)2}3] (7): yield 94% (681 mg, 0.66 mmol);
1H NMR (300.0 MHz, C6D6) δ 0.38 (s, 54 H, Si(CH3)3), 2.18 (s, 6 H,
para-CH3), 2.30 (s, 12 H, ortho-CH3), 5.50 (s, 2 H, CH), 6.76 (s, 4 H,
Har); 13C NMR (75.5 MHz, C6D6) δ 5.63 (Si(CH3)3), 20.25 (CH3),
21.10 (CH3), 112.33 (CH), 136.90 (CarH), 138.63 (CarC),
145.23 (CipsoN); 29Si NMR (59.6 MHz, C6D6) δ −10.12. Anal.
Calcd for C39H78N6Si6Th: C, 45.41; H, 7.62; N, 8.15. Found: C, 45.71;
H, 7.66; N, 8.19.
[(ImDippN)Th{N(SiMe3)2}3] (8) yield 98% (768 mg, 0.69 mmol);
1H NMR (300.0 MHz, C6D6) δ 0.40 (s, 54 H, Si(CH3)3, 1.10 (d, J =
6.71 Hz, 12 H CH(CH3)2), 1.45 (d, J = 6.71 Hz, 12 H, CH(CH3)2),
3.31 (m, 4 H, CH(CH3)2), 5.75 (s, 2 H, CH), 7.14−7.16 (m, 6 H,
Har); 13C NMR (75.5 MHz, C6D6) δ 5.99 (Si(CH3)3), 23.79
17187
dx.doi.org/10.1021/ja5091436 | J. Am. Chem. Soc. 2014, 136, 17180−17192

Journal of the American Chemical Society
Article
(CH(CH3)2), 25.81 (CH(CH3)2), 28.66 (CH(CH3)2), 115.49 (CH),
125.13 (CarH), 136.37 (CarC), 147.61 (CipsoN); 29Si NMR
(59.6 MHz, C6D6) δ −9.79. Anal. Calcd for C45H90N6Si6Th: C, 48.44;
H, 8.13; N, 7.53. Found: C, 48.94; H, 8.19; N, 7.46.
General Procedure for the Catalytic Crossed Tishchenko
Reaction. A sealable J. Young NMR tube was loaded with 5.00 mg
(4.48 μmol) of complex 8 from a stock solution in C6D6 inside the
glovebox. The respective aromatic aldehyde (0.896 mmol, 200 equiv)
and aliphatic aldehyde (0.224 mmol, 50 equiv) were added, and the
reaction was immediately diluted to 750 μL with C6D6. Solid
aldehydes were dissolved in 300 μL of C6D6 before being added to the
General Procedure for the Catalytic Tishchenko Reaction. A
sealable J. Young NMR tube was loaded with 5.00 mg (4.48 μmol) of
complex 3−8 from a stock solution in C6D6 inside the glovebox. The
respective aldehyde (0.448 mmol, 100 equiv) was added, and the
reaction was immediately diluted to 500 μL with C6D6. Solid
aldehydes were dissolved in 300 μL of C6D6 before being added to the
solution of the precatalyst. The progress of the reaction was monitored
by 1H NMR spectroscopy. After 24 h, the tube was opened to air, and
the reaction was quenched with methanol. The products were
identified by 1H NMR spectroscopy and MS analysis, and the
chemical shifts were compared with previously reported literature
data.29,48−55
1
catalyst solution. The progress of the reaction was monitored by H
NMR spectroscopy. After 24 h, the tube was opened to air and the
reaction quenched with methanol. The products were identified by 1H
NMR spectroscopy and MS analysis, and the values were compared to
previous literature.
Cross-Esterification of Benzaldehyde with Cyclohexanecar-
baldehyde. Tthe cross-esterification of benzaldehyde (93.0 μL, 0.896
mmol) and cyclohexanecarbaldehyde (27.0 μL, 0.224 mmol) was
carried out following the general procedure described above.
Benzylcyclohexanecarboxylate53 was obtained in 92% yield after a
Esterification of Benzaldehyde. The esterification of benzalde-
hyde (46.0 μL, 0.448 mmol) was carried out following the general
procedure described above. Benzylbenzoate29 was obtained in 100%
yield after 24 h. 1H NMR (300.00 MHz, C6D6): δ 5.17 (s, 2 H, CH2),
7.06−7.28 (m, 8 H, Har), 8.09 (d, J = 7.66 Hz, Har). MS: m/z 213.11
1
reaction time of 1.5 h. H NMR (300.00 MHz, C6D6): δ 1.10−1.87
(m, 10 H, CH2), 2.29 (m, 1 H, CH), 5.09 (s, 2 H, CH2), 7.20−7.37
(m, 5 H, Har). MS: m/z 219.14 (M+).
Cross-Esterification of Benzaldehyde with Cyclopentane-
carbaldehyde. The cross-esterification of benzaldehyde (93.0 μL,
0.896 mmol) and cyclopentanecarbaldehyde (24.0 μL, 0.224 mmol)
was carried out following the general procedure described above.
Benzylcyclopentanecarboxylate was obtained in 84% yield after a
+
(M+), 92.09 (PhCH2 ).
Esterification of 1-Naphthylaldehyde. The esterification of 1-
naphthylaldehyde (61.0 μL, 0.448 mmol) was carried out following the
general procedure described above. 1-Naphthylmethyl 1-naphthoate48
1
reaction time of 1.5 h. H NMR (300.00 MHz, C6D6): δ 1.51−1.93
1
was obtained in 32% yield, after a reaction time of 24 h. H NMR
(m, 8 H, CH2), 2.73 (m, 1 H, CH), 5.11 (s, 2 H, CH2), 7.26−7.38 (m,
(300.00 MHz, C6D6): δ 5.89 (s, 2 H, CH2), 7.39−7.98 (m, 14 H, Har).
5 H, Har). MS: m/z 205.13 (M+).
+
MS: m/z 312.13 (M+), 141.07 (ArCH2 ).
Cross-Esterification of Benzaldehyde with Isobutyralde-
hyde. The cross-esterification of benzaldehyde (93.0 μL, 0.896
mmol) and isobutyraldehyde (20.0 μL, 0.224 mmol) was carried out
following the general procedure described above. Benzylisobutyrate54
Esterification of 2-Naphthylaldehyde. The esterification of 2-
naphthylaldehyde (70.0 mg, 0.448 mmol) was carried out following
the general procedure described above. 2-Naphthylmethyl 2-
naphthoate48 was obtained in 61% yield after a reaction time of 24
1
was obtained in 80% yield after a reaction time of 1.5 h. H NMR
1
h. H NMR (300.00 MHz, C6D6): δ 5.63 (s, 2 H, CH2), 7.36−8.31
(300.00 MHz, C6D6): δ 1.17 (d, J = 7.30 Hz, 6 H, CH3), 2.51−2.53
(m, 1 H, CH), 5.10 (s, 2 H, CH2), 7.25−7.38 (m, 5 H, Har). MS: m/z
179.17 (M+), 73.08 (CH(CH3)2CO+).
+
(m, 14 H, Har). MS: m/z 312.16 (M+), 141.09 (ArCH2 ).
Esterification of 4-Nitrobenzaldehyde. The esterification of 4-
nitrobenzaldehyde (68.0 mg, 0.448 mmol) was carried out following
the general procedure described above. 4′-(Nitrobenzyl)-4-nitro-
benzoate29 was obtained in 100% yield after a reaction time of 24 h.
1H NMR (300.00 MHz, C6D6): δ 4.78 (s, 2 H, CH2), 6.76−6.79 (m, 2
H, Har), 7.27−7.35 (m, 2 H, Har), 7.56−7.73 (m, 4 H, Har). MS: m/z:
Cross-Esterification of 1-Naphthaldehyde with Cyclohex-
anecarbaldehyde. The cross-esterification of benzaldehyde (112.0
μL, 0.896 mmol) and cyclohexanecarbaldehyde (27.0 μL, 0.224 mmol)
was carried out following the general procedure described above. 1-
Naphthylmethylcyclohexanecarboxylate55 was obtained in 100% yield
after a reaction time of 1.5 h. 1H NMR (300.00 MHz, C6D6): δ 1.21−
2.04 (m, 10 H, CH2), 2.43 (m, 1 H, CH), 5.63 (s, 2 H, CH2), 7.40−
7.90 (m, 6 H, Har), 8.04 (d, J = 8.6 Hz, 1 H, Har) MS: m/z 269.38
(M+).
+
303.23 (M+), 137.9 (ArCH2 ).
Esterification of Cyclohexanecarbaldehyde. The esterification
of cyclohexanecarbaldehyde (54.0 μL, 0.448 mmol) was carried out
following the general procedure described above. Cyclohexylmethyl
cyclohexanecarboxylate49 was obtained in 100% yield after a reaction
Cross-Esterification of 2-Naphthaldehyde with Cyclohex-
anecarbaldehyde. The cross-esterification of benzaldehyde (140.0
mg, 0.896 mmol) and cyclohexanecarbaldehyde (27.0 μL, 0.224
mmol) was carried out following the general procedure described
above. 2-Naphthylmethylcyclohexanecarboxylate55 was obtained in
1
time of 12 h. H NMR (300.00 MHz, C6D6): δ 0.90−2.34 (m, 22 H,
CH2), 3.85 (d, J = 6.87 Hz, 2 H, CH2). MS: m/z 225.18 (M+), 98.15
+
(ChexCH2 ).
Esterification of Cyclopentanecarbaldehyde. The esterifica-
tion of cyclopentanecarbaldehyde (48.0 μL, 0.448 mmol) was carried
out following the general procedure described above. Cyclo-
pentylmethyl cyclopentanecarboxylate50 was obtained in 100% yield
after a reaction time of 12 h. 1H NMR (300.00 MHz, C6D6): δ 1.02−
2.67 (m, 18 H, CH2), 3.89 (d, J = 7.3 Hz, 2 H, CH2). MS: m/z 197.16
(M+), 97.09 (CpentCO+).
Esterification of Isobutyraldehyde. The esterification of
isobutyraldehyde (41.0 μL, 0.448 mmol) was carried out following
the general procedure described above. Isobutylisobutyrate51 was
obtained in 100% yield after a reaction time of 12 h. 1H NMR (300.00
MHz, C6D6): δ 0.87 (d, J = 6.37 Hz, 6 H, CH3), 1.07 (d, J = 6.56 Hz, 6
H, CH3), 2.45−2.55 (m, 2 H, CH), 3.79 (d, J = 6.71 Hz, 2 H, CH2).
MS: m/z 145.11(M+).
Lactonization of Phthalaldehyde. The lactonization of
phthalaldehyde (60.0 mg, 0.448 mmol) was carried out following
the general procedure described above. Phthalide52 was obtained in
100% yield after a reaction time of 6 h. 1H NMR (300.00 MHz,
C6D6): δ 5.21 (s, 2 H, CH2), 7.48−7.55 (m, 1 H, Har), 7.71−7.76 (m,
1 H, Har), 7.81−7.89 (m, 1 H, Har), 8.10 (d, J = 7.59 Hz, 1 H, Har).
MS: m/z 134.95 (M+).
1
88% yield after a reaction time of 1.5 h. H NMR (300.00 MHz,
C6D6): δ 1.25−2.01 (m, 10 H, CH2), 2.40 (m, 1 H, CH), 5.29 (s, 2 H,
CH2), 7.46−7.81 (m, 7 H, Har). MS: m/z 269.33 (M+).
Intermediate Trapping Experiments. A sealable J. Young NMR
tube was loaded with 50.0 mg (44.8 μmol) of complex 8 and dissolved
in 1.0 mL of C6D6 inside the glovebox. Benzaldehyde (10 μL, 89.6
μmol, 2.1 equiv) and the solution of catalyst 8 were added inside the
1
glovebox. The progress of the reaction was monitored by H NMR
spectroscopy. After full consumption of the benzaldehyde after 30 min
to give complex A, benzaldehyde (10 μL, 89.6 μmol, 2.1 equiv) was
added to the reaction mixture inside the glovebox and the progress of
the reaction was monitored by 1H NMR spectroscopy. Complex B was
obtained after 30 min. Then, benzaldehyde (10 μL, 89.6 μmol, 2.1
equiv) was added to the reaction mixture, yielding complex E and ester
D after 30 min.
[(ImDippN)Th{OCHN(SiMe3)2}2{N(SiMe3)2}] (A): 1H NMR
(300.0 MHz, C6D6) δ 0.13 (s, 36 H, Si(CH3)3), 0.41 (s, 18 H,
Si(CH3)3), 1.11 (d, J = 6.44 Hz, 12 H, CH(CH3)2), 1.47 (d, J = 6.44
Hz, 12 H, CH(CH3)2), 3.33−3.36 (m, 4 H, CH(CH3)3), 5.78 (s, 2 H,
CH), 5.90 (s, 2 H, CH(N(SiMe3)2), 7.00−7.11 (m, 10 H, Har), 7.14−
17188
dx.doi.org/10.1021/ja5091436 | J. Am. Chem. Soc. 2014, 136, 17180−17192

Journal of the American Chemical Society
Article
7.55 (m, 6 H, Har); 13C NMR (75.5 MHz, C6D6) δ 5.15 (Si(CH3)3),
5.98 (Si(CH3)3), 23.81 (CH(CH3)2), 25.80 (CH(CH3)2), 28.71
(CH(CH3)2), 68.90 (CH(N(Si(CH3)3)), 115.79 (CH), 124.49−
137.17 (Car), 148.10 (CipsoN); 29Si NMR (59.6 MHz, C6D6) δ
−32.81 (Si(CH3)3), −9.81 (Si(CH3)3).
Stoichiometric Reaction with Cyclohexanecarbaldehyde.
The stoichiometric reaction with cyclohexanecarbaldehyde (28 μL,
0.228 mmol) was carried out following the general procedure
described above. (Bis(trimethylsilyl)amino)(cyclohexyl)methyl cyclo-
hexanecarboxylate (D5) was obtained in 99% yield after a reaction
time of 3 h. 1H NMR (300.0 MHz, C6D6): δ 0.04 (s, 18 H, Si(CH3)3),
1.39−1.60 (m, 20 H, CH2), 1.67−1.84 (m, 2 H, CH), 5.69 (s, 1 H,
CH). 13C NMR (75.5 MHz, C6D6): δ 5.99 (Si(CH3)3), 23.5−49.1
(CH2), 81.5 (CHN(Si(CH3)3)2), 175.8 (CO). 29Si NMR (59.6
MHz, C6D6): δ −0.97. MS: m/z 384.3 (M+).
Stoichiometric Reaction with Cyclopentanecarbaldehyde.
The stoichiometric reaction with cyclopentanecarbaldehyde (24 μL,
0.228 mmol) was carried out following the general procedure
described above. (Bis(trimethylsilyl)amino)(cyclopentyl)methyl cyclo-
pentanecarboxylate (D6) was obtained in 99% yield after a reaction
time of 3 h. 1H NMR (300.0 MHz, C6D6): δ 0.04 (s, 18 H, Si(CH3)3),
1.84−2.01 (m, 18 H, CH2), 2.17−2.59 (m, 2 H, CH), 5.26 (s, 1 H,
CH). 13C NMR (75.5 MHz, C6D6): δ 6.21 (Si(CH3)3), 25.4−45.1
(CH2), 83.5 (CHN(Si(CH3)3)2), 171.6 (CO). 29Si NMR (59.6
MHz, C6D6): δ −0.89. MS: m/z 356.3 (M+).
[(ImDippN)Th{OCHPhOCH2Ph}2{N(SiMe3)2}] (B): 1H NMR
(300.0 MHz, C6D6) δ 0.41 (s, 18 H, Si(CH3)3), 1.13 (d, J = 6.90
Hz, 12 H, CH(CH3)2), 1.44 (d, J = 6.90 Hz, 12 H, CH(CH3)2), 3.31−
3.36 (m, 4 H, CH(CH3)2), 4.20 (s, 2 H, OCHPh), 5.19 (s, 4 H,
OCH2Ph), 7.11−7.70 (m, 26 H, Har); 13C NMR (75.5 MHz, C6D6) δ
5.90 (Si(CH3)3), 23.81 (CH(CH3)2), 25.80 (CH(CH3)2), 28.67
(CH(CH3)2), 61.12 (OCH2Ph), 79.23 (OCHPh), 115.79 (CH),
124.79−137.51 (Car), 147.72 (CipsoN); 29Si NMR (59.6 MHz,
C6D6) δ −9.82.
[(ImDippN)Th{OCH2Ph}2{N(SiMe3)2}] (E): 1H NMR (300.0
MHz, C6D6) δ 0.41 (s, 18 H, Si(CH3)3), 1.14 (d, J = 6.85 Hz, 12
H, CH(CH3)2), 1.44 (d, J = 6.85 Hz, CH(CH3)2), 3.32−3.36 (m, 4 H,
CH(CH3)2), 5.21 (s, 4 H, OCH2Ph), 5.79 (s, 2 H, CH), 7.14−7.68
(m, 16 H, Har); 13C NMR (75.5 MHz, C6D6) δ 5.91 (Si(CH3)3), 23.80
(CH(CH3)2), 25.79 (CH(CH3)2), 28.67 (CH(CH3)2), 55.71
(CH2Ph), 116.00 (CH), 125.16−136.54 (Car), 147.55 (CipsoN);
29Si NMR (59.6 MHz, C6D6) δ −9.81.
Stoichiometric Reaction with Isobutyraldehyde. The stoi-
chiometric reaction with isobutyraldehyde (21 μL, 0.228 mmol) was
carried out following the general procedure described above. 1-
(Bis(trimethylsilyl)amino)-2-methylpropyl isobutyrate (D7) was
General Procedure for Reactions with Stoichiometric
Amounts of Aldehydes. A sealable J. Young NMR tube was loaded
with 50.0 mg (44.8 μmol) of complex 8 from a stock solution in C6D6
inside the glovebox. The respective aldehyde (0.228 mmol, 6.20 equiv)
was added, and the reaction was immediately diluted to 1000 μL with
C6D6. Solid aldehydes were dissolved in 300 μL of C6D6 before being
added to the solution of the precatalyst. The progress of the reaction
1
obtained in 97% yield after a reaction time of 3 h. H NMR (300.0
MHz, C6D6): δ 0.05 (s, 18 H, Si(CH3)3), 1.01 (d, J = 6.56 Hz, 6 H,
CH(CH3)2), 1.03 (d, J = 6.56 Hz, 6 H, CH(CH3)2), 2.26−2.33 (m, 2
H, CH(CH3)2), 5.81 (s, 1 H, CH). 13C NMR (75.5 MHz, C6D6): δ
5.13 (Si(CH3)3), 15.17 (CH(CH3)2), 17.59 (CH(CH3)2), 34.7
(CH(CH3)2), 89.1 (CH), 174.3 (CO). 29Si NMR (59.6 MHz,
C6D6): δ −0.92. MS: m/z 304.3 (M+).
1
was monitored by H NMR spectroscopy. After 3 h, the tube was
opened to air, and the reaction was quenched with methanol. The
1
products (D1−D8) were characterized by H NMR, 13C NMR, and
Stoichiometric Reaction with Phthalaldehyde. The stoichio-
metric reaction with phthalaldehyde (16 mg, 0.114 mmol) was carried
out following the general procedure described above. 3-(Bis-
(trimethylsilyl)amino)isobenzofuran-1(3H)-one (D8) was obtained
29Si NMR spectroscopy and MS analysis.
Stoichiometric Reaction with Benzaldehyde. The stoichio-
metric reaction with benzaldehyde (24 μL, 0.228 mmol) was carried
out following the general procedure described above. ((Bis-
(trimethylsilyl)amino)phenyl)methyl 2-benzoate (D1) was obtained
1
in 99% yield after a reaction time of 3 h. H NMR (300.0 MHz,
C6D6): δ 0.06 (s, 18 H, Si(CH3)3), 5.93 (s, 1 H, CH), 7.09−7.11 (m, 2
H, Har), 7.62−7.64 (m, 2 H, Har). 13C NMR (75.5 MHz, C6D6): δ 5.15
(Si(CH3)3), 91.24 (CH), 121.3−138.4 (Car), 168.3 (CO). 29Si NMR
(59.6 MHz, C6D6): δ −1.31. MS: m/z 294.1 (M+).
1
in 95% yield after a reaction time of 3 h. H NMR (300.0 MHz,
C6D6): δ 0.10 (s, 18 H, Si(CH3)3), 6.15 (s, 1 H, CH), 7.29−7.41 (m,
10 H, Har). 13C NMR (75.5 MHz, C6D6): δ 3.15 (Si(CH3)3), 82.3
(CHN(Si(CH3)3)2), 125.3−132.5 (Car), 169.4 (CO). 29Si NMR
(59.6 MHz, C6D6): δ −1.76. MS: m/z 372.2 (M+).
Stoichiometric Reaction with 1-Naphthylaldehyde. The
stoichiometric reaction with 1-naphthylaldehyde (31 μL, 0.228
mmol) was carried out following the general procedure described
above. (Bis(trimethylsilyl)amino)(naphthalen-1-yl)methyl 1-naphtha-
noate (D2) was obtained in 92% yield after a reaction time of 3 h. 1H
NMR (300.0 MHz, C6D6): δ 0.05 (s, 18 H, Si(CH3)3), 6.98 (s, 1 H,
CH), 7.31−7.43 (m, 8 H, Har), 7.50−7.57 (m, 6 H, Har). 13C NMR
(75.5 MHz, C6D6): δ 5.68 (Si(CH3)3), 84.2 (CHN(Si(CH3)3)2),
121.9−134.5 (Car), 166.5 (CO). 29Si NMR (59.6 MHz, C6D6): δ
−1.98. MS: m/z 472.4 (M+).
Stoichiometric Reaction with 2-Naphthylaldehyde. The
stoichiometric reaction with 2-naphthylaldehyde (36.0 mg, 0.228
mmol) was carried out following the general procedure described
above. (Bis(trimethylsilyl)amino)(naphthalene-2-yl)methyl 2-naph-
thoate (D3) was obtained in 93% yield after a reaction time of 3 h.
1H NMR (300.0 MHz, C6D6): δ 0.05 (s, 18 H, Si(CH3)3), 7.07 (s, 1
H, CH), 7.47−7.51 (m, 14 H, Har). 13C NMR (75.5 MHz, C6D6): δ
5.79 (Si(CH3)3), 87.5 (CHN(Si(CH3)3)2), 124.9−135.8 (Car), 166.5
(CO). 29Si NMR (59.6 MHz, C6D6): δ −2.03. MS: m/z 472.3 (M+).
Stoichiometric Reaction with 4-Nitrobenzaldehyde. The
stoichiometric reaction with 4-nitrobenzaldehyde (35.0 mg, 0.228
mmol) was carried out following the general procedure described
above. (Bis(trimethylsilyl)amino)(4-nitrophenyl)methyl 4-nitroben-
zoate (D4) was obtained in 98% yield after a reaction time of 3 h.
1H NMR (300.0 MHz, C6D6): δ 0.15 (s, 18 H, Si(CH3)3), 7.02 (s, 1
H, CH), 7.57−7.67 (m, 8 H, Har). 13C NMR (75.5 MHz, C6D6): δ
5.59 (Si(CH3)3), 86.7 (CHN(Si(CH3)3)2), 125.4−155.3 (Car), 166.1
(CO). 29Si NMR (59.6 MHz, C6D6): δ −2.36. MS: m/z 462.2 (M+).
ASSOCIATED CONTENT
■
S
* Supporting Information
CIF files and crystallographic information for complexes 3−8
are available free of charge via the Internet at http://pubs.acs.
org.
AUTHOR INFORMATION
■
Corresponding Authors
m.tamm@tu-bs.de
chmoris@tx.technion.ac.il
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the German Israel Foundation
GIF under Contract 1076-68.5/2009.
REFERENCES
■
(1) (a) Batrice, R. J.; Karmel, I. S. R.; Eisen, M. S. Product Class 13:
Organometallic Complexes of the Actinides. In Science Synthesis,
Knowledge Updates 2012/4; Fuerstner, A., Hall, D., Marek, I.,
Oestreich, M., Schaumann, E., Stoltz, B. M., Eds.; Georg Thieme
Verlag KG: Stuttgart, 2013; pp 99−211. (b) Fagan, P. J.; Manriquez, J.
M.; Maata, E. A.; Seyman, A. M.; Marks, T. J. J. Am. Chem. Soc. 1981,
103, 6650−6667.
17189
dx.doi.org/10.1021/ja5091436 | J. Am. Chem. Soc. 2014, 136, 17180−17192

Journal of the American Chemical Society
Article
(2) (a) Ephritikhine, M. Organometallics 2013, 23, 2464−2488 and
references cited therein. (b) Marks, T. J.; Seyam, A. M.; Kolb, J. R. J.
Am. Chem. Soc. 1973, 95, 5529−5539. (c) Secour, C. A.; Day, V. W.;
Ernst, R. D.; Kennelly, W. J.; Marks, T. J. J. Am. Chem. Soc. 1976, 98,
3713−3715. (d) Manriquez, J. M.; Fagan, P. J.; Marks, T. J.; Day, C.
S.; Day, V. W. J. Am. Chem. Soc. 1978, 100, 7112−7114. (e) Baudry,
D.; Charpin, P.; Ephritikhine, M.; Folcher, G.; Lambard, J.; Lance, M.;
Nierlich, M.; Vigner, J. J. Chem. Soc., Chem. Commun. 1985, 1553−
1554. (f) Moloy, K. G.; Marks, T. J. Inorg. Chim. Acta 1985, 110, 127−
(t) Mansell, S. M.; Bonnet, F.; Visseaux, M.; Arnold, P. L. Dalton
Trans. 2013, 42, 9033−9039.
(6) (a) Wedler, M.; Roesky, H. W.; Edelmann, F. J. Organomet. Chem.
1998, 345, C1−C3. (b) Villiers, C.; Thuery, P.; Ephritikhine, M. Eur. J.
Inorg. Chem. 2004, 4624−4632. (c) Evans, W. J.; Walensky, J. R.;
Ziller, W. J.; Rheingold, A. L. Organometallics 2009, 28, 3350−3357.
(d) Evans, W. J.; Walensky, J. R.; Ziller, J. W. Chem. - Eur. J. 2009, 15,
12204−12207. (e) Evans, W. J.; Walensky, J. R.; Ziller, J. W.
Organometallics 2010, 29, 101−107. (f) Evans, W. J.; Walensky, J. R.;
Ziller, W. J. Inorg. Chem. 2010, 49, 1743−1749. (g) Rabinovich, E.;
Aharonovich, S.; Botoshansky, M.; Eisen, M. S. Dalton Trans. 2010, 39,
6667−6676. (h) Hayes, C. E.; Leznoff, D. B. Coord. Chem. Rev. 2014,
266−267. (i) Karmel, I. S. R.; Elkin, T.; Fridman, N.; Eisen, M. S.
Dalton Trans. 2014, 43, 11376−11387.
́
131. (f) Arliguie, T.; Lescop, C.; Ventelon, L.; Leverd, P. C.; Thuery,
P.; Nierlich, M.; Ephritikhine, M. Organometallics 2001, 20, 3698−
3703. (g) Cloke, F. G. N.; Hitchcock, P. B. J. Am. Chem. Soc. 2002,
124, 9352−9353. (h) Cloke, F. G. N.; Green, J. C.; Kaltsoyannis, N.
Organometallics 2004, 23, 832−835. (i) Pool, J. A.; Scott, B. L.;
Kiplinger, J. L. J. Alloys Compd. 2006, 418, 178−183. (j) Kiplinger, J.
L.; Scott, B. L.; Schelter, E. J.; Pool, J. A.; Tournear, D. J. Alloys Compd.
2007, 444−445, 477−482. (k) Evans, W. J.; Miller, K. A.; Kozimor, S.
A.; Ziller, J. W.; DiPasquale, A. G.; Rheingold, A. L. Organometallics
2007, 26, 3568−3576. (l) Evans, W. J.; Montalvo, E.; Kozimor, S. A.;
Miller, K. A. J. Am. Chem. Soc. 2008, 130, 12258−12259. (m) Evans,
W. J.; Miller, K. A.; DiPasquale, A. G.; Rheingold, A. L.; Stewart, T. J.;
Bau, R. Angew. Chem., Int. Ed. 2008, 47, 5075−5078. (n) Montalvo, E.;
Ziller, J.; DiPasquale, A. G.; Rheingold, A. L.; Evans, W. J.
Organometallics 2010, 29, 2104−2110. (o) Montalvo, E.; Miller, K.
A.; Ziller, W. J.; Evans, W. J. Organometallics 2010, 29, 4159−4170.
(p) Castro, L.; Yahia, A.; Maron, L. C. R. Chim. 2010, 13, 870−875.
(q) Castro, L.; Yahia, A.; Maron, L. Dalton Trans. 2010, 39, 6682−
6692.
(7) Villiers, C.; Thuer
2832−2834.
(8) Antunes, M. A.; Ferrence, G. M.; Domingos, A.; McDonald, R.;
Burns, C. J.; Takats, J.; Marques, N. Inorg. Chem. 2004, 43, 6640−
6643.
́
y, P.; Ephritikhine, M. Chem. Commun. 2007,
̂
(9) (a) Castro-Rodriguez, I.; Olsen, K.; Gantzel, P.; Meyer, K. J. Am.
Chem. Soc. 2003, 125, 4565−4571. (b) Schmidt, A.-C.; Nizovtsev, A.
V.; Scheurer, A.; Heinemann, F. W.; Meyer, K. Chem. Commun. 2012,
48, 8634−8636. (c) Halter, D. P.; La Pierre, H. S.; Heinemann, F. W.;
Meyer, K. Inorg. Chem. 2014, 53, 8418−8424.
(10) (a) Barnea, E.; Andrea, T.; Kapon, M.; Eisen, M. S. J. Am. Chem.
Soc. 2004, 126, 5066−5067. (b) Arnold, P. L.; Jones, G. M.; Odoh, S.
O.; Schreckenbach, G.; Magnani, N.; Love, J. B. Nat. Chem. 2012, 4,
221−227. (c) Jones, G. M.; Arnold, P. L.; Love, J. B. Angew. Chem., Int.
Ed. 2012, 51, 12584−12587. (d) Ward, A. L.; Buckley, H. L.; Lukens,
W. W.; Arnold, J. J. Am. Chem. Soc. 2013, 135, 13965−13971.
(e) Arnold, P. L.; Farnaby, J. H.; White, R. C.; Kaltsoyannis, N.;
Gardiner, M. G.; Lovem, J. B. Chem. Sci. 2014, 5, 756−765.
(3) (a) Blake, P. C.; Lappert, M. F.; Atwood, J. L.; Zhang, H. J. Chem.
Soc., Chem. Commun. 1986, 1148−1149. (b) MacDonald, M. R.;
Fieser, M. E.; Bates, J. E.; Ziller, J. W.; Furche, F.; Evans, W. J. J. Am.
Chem. Soc. 2013, 135, 13310−13313.
(11) (a) Rebizant, J.; Spirlet, M. R.; Kanellakopulos, B.; Dornberger,
E. J. Less-Common. Met. 1986, 122, 211−214. (b) Maier, R.;
Kanellakopulos, B.; Apostolidis, C.; Meyer, D.; Rebizant. J. Alloys
Compd. 1993, 190, 269−271. (c) Clark, D. L.; Watkin, J. G. Inorg.
Chem. 1993, 32, 1766−1772. (d) England, A. F.; Burns, C. J.;
Buchwald, S. L. Organometallics 1994, 13, 3491−3495. (e) Radu, N. S.;
Engeler, M. P.; Gerlach, C. P.; Tilley, T. D.; Rheingold, A. L. J. Am.
Chem. Soc. 1995, 117, 3621−3622. (f) Clark, D. L.; Grumbine, S. K.;
Scott, B. L.; Watkin, J. G. Organometallics 1996, 15, 949−957.
(g) Blake, P. C.; Edelman, M. A.; Hitchcock, P. B.; Hu, J.; Lappert, M.
F.; Tian, S.; Muller, G.; Atwood, J. L.; Zhang, H. J. Organomet. Chem.
1998, 551, 261−270. (h) Haskel, A.; Wang, J. Q.; Straub, T.; Neyroud,
T. G.; Eisen, M. S. J. Am. Chem. Soc. 1999, 121, 3025−3034. (I) Evans,
W. J.; Nyce, G. W.; Johnston, M. A.; Ziller, J. W. J. Am. Chem. Soc.
2000, 122, 12019−12020. (j) Trnka, T. M.; Bonanno, J. B.;
Bridgewater, B. M.; Parkin, G. Organometallics 2001, 20, 3255−
3264. (k) Carlson, C. N.; Hanusa, T. P.; Brennessel, W. W. J. Am.
Chem. Soc. 2004, 126, 10550−10551. (l) Monreal, M.; Carver, C. T.;
Diaconescu, P. L. Inorg. Chem. 2007, 46, 7226−7228. (m) Monreal,
M.; Diaconescu, P. L. Organometallics 2008, 27, 1702−1706.
(n) Monreal, M.; Khan, S.; Diaconescu, P. L. Angew. Chem., Int. Ed.
2009, 48, 8352−8355. (o) Broderick, E. M.; Gutswiller, N. P.;
(4) (a) Sharma, M.; Eisen, M. S. Struct. Bonding (Berlin) 2008, 127,
1−85. (b) Eisen, M. S. Top. Organomet. Chem. 2010, 31, 157−184.
(c) Baker, R. J. Chem.- Eur. J. 2012, 18, 16258−16271. (d) Gardner, B.
M.; Stewart, J. C.; Davis, A. L.; McMaster, J.; Lewis, W.; Blake, A. J.;
Liddle, S. T. Proc. Natl. Acad. Sci. U. S. A. 2012, 109, 9265−9270.
(e) La Pierre, H. S.; Meyer, K. Inorg. Chem. 2013, 52, 529−539.
(f) Reznichenko, A. L.; Hultzsch, K. C. Top. Organomet. Chem. 2013,
43, 51−114.
(5) (a) Hayes, C. E.; Leznoff, D. B. Organometallics 2010, 29, 767−
774. (b) Schnaars, D. D.; Wu, G.; Hayton, T. W. Inorg. Chem. 2011,
50, 4695−4697. (c) Fortier, S.; Walensky, J. R.; Wu, G.; Hayton, T. W.
J. Am. Chem. Soc. 2011, 133, 6894−6897. (d) Gardner, B. M.; Patel,
D.; Lewis, W.; Blake, A. J.; Liddle, S. T. Angew. Chem., Int. Ed. 2011,
50, 10440−10443. (e) Hayes, C. E.; Platel, R. H.; Schafer, L. L.;
Leznoff, D. B. Organometallics 2012, 31, 6732−6740. (f) Diaconescu,
P. L.; Cummins, C. C. Inorg. Chem. 2012, 51, 2902−2916. (g) Arnold,
P. L.; Mansell, S. M.; Maron, L.; McKay, D. Nat. Chem. 2012, 4, 668−
674. (h) Hayes, C. E.; Sarazin, Y.; Katz, M. J.; Carpentier, J.-F.;
Leznoff, D. B. Organometallics 2013, 32, 1183−1192. (i) Matson, E.
M.; Forrest, W. P.; Fanwick, P. E.; Bart, S. C. Organometallics 2013, 32,
1484−1492. (j) Cladis, D. P.; Kiernicki, J. J.; Fanwick, P. E.; Bart, S. C.
Chem. Commun. 2013, 49, 4169−4171. (k) Kraft, S. J.; Fanwick, P. E.;
Bart, S. C. Organometallics 2013, 32, 3279−3285. (l) Andreychuk, N.
R.; Ilango, S.; Vidjayacoumar, B.; Emslie, D. J. H.; Jenkins, H. A.
Organometallics 2013, 32, 1466−1474. (m) Lewis, A. J.; Carroll, P. J.;
Schelter, E. J. J. Am. Chem. Soc. 2013, 135, 13185−13192. (n) Lewis,
A. J.; Williams, U. J.; Carroll, P. J.; Schelter, E. J. Inorg. Chem. 2013, 52,
7326−7328. (o) Jilek, R. E.; Spencer, L. P.; Lewis, R. A.; Scott, B. L.;
Hayton, T. W.; Boncella, J. M. J. Am. Chem. Soc. 2013, 134, 9876−
9878. (p) Monreal, M. J.; Wright, R. J.; Morris, D. E.; Scott, B. L.;
Golden, J. T.; Power, P. P.; Kiplinger, J. L. Organometallics 2013, 32,
1423−1434. (q) Nizovtsev, A. V.; Scheurer, A.; Kosog, B.; Heinemann,
F. W.; Meyer, K. Eur. J. Inorg. Chem. 2013, 2538−2548. (r) Camp, C.;
Diaconescu, P. L. Organometallics 2010, 29, 3242−3251. (p) Duhovic,
́
S.; Monreal, M. J.; Diaconescu, P. L. Inorg. Chem. 2010, 49, 7165−
7169. (q) Evans, W. J.; Walensky, J. R.; Ziller, J. W. Organometallics
2010, 29, 945−950. (r) Thomson, R. K.; Scott, B. L.; Morris, D. E.;
Kiplinger, J. L. C. R. Chim. 2010, 13, 790−802. (s) Kraft, S. J.;
Williams, U. J.; Daly, S. R.; Schelter, E. J.; Kozimor, S. A.; Boland, K.
S.; Mikkawa, J. M.; Forrest, W. P.; Christensen, C. N.; Schwarz, D. E.;
Fanwick, P. E.; Clark, D. L.; Conradson, S. D.; Barz, S. C. Inorg. Chem.
2011, 50, 9838−9848. (t) Thomson, R. K.; Graves, C. R.; Scott, B. L.;
Kiplinger, J. L. J. Chem. Crystallogr. 2011, 41, 1241−1244. (u) Scott, B.
L.; Kiplinger, J. L. J. Chem. Crystallogr. 2011, 41, 1301−1304. (v) Ren,
W.; Zi, G.; Fang, D.-C.; Walter, M. D. Chem. - Eur. J. 2011, 17,
́
Andrez, J.; Pecaut, J.; Mazzanti, M. Inorg. Chem. 2013, 52, 7078−7086.
(s) Arnold, P. L.; Turner, Z. R.; Germeroth, A. I.; Casely, I. J.; Nichol,
G. S.; Bellabarba, R.; Tooze, R. P. Dalton Trans. 2013, 42, 1333−1337.
́
12669−12682. (w) Duhovic, S.; Oria, J. V.; Odoh, S. O.;
Schreckenbach, G.; Batista, E. R.; Diaconescu, P. L. Organometallics
17190
dx.doi.org/10.1021/ja5091436 | J. Am. Chem. Soc. 2014, 136, 17180−17192

Journal of the American Chemical Society
Article
2013, 32, 6012−6021. (x) Langeslay, R. R.; Walensky, J. R.; Ziller, J.
W.; Evans, W. J. Inorg. Chem. 2014, 53, 8455−8463.
Batrice, R. J.; Aharonovich, S.; Tumanskii, B.; Botoshansky, M.; Eisen,
M. S. Dalton Trans. 2013, 42, 9096−9078.
(23) (a) Weiss, C. J.; Wobser, S. D.; Marks, T. J. Organometallics
2010, 29, 6308−6320. (b) Weiss, C. J.; Marks, T. J. Dalton Trans.
2010, 39, 6576−6588. (c) Wobser, S. D.; Marks, T. J. Organometallics
2013, 32, 2517−2528.
(24) (a) Dash, A. K.; Wang, J. Q.; Eisen, M. S. Organometallics 1999,
18, 4724−4741. (b) Dash, A. K.; Wang, J. X.; Berthet, J. C.;
Ephritikhine, M.; Eisen, M. S. J. Organomet. Chem. 2000, 604, 83−98.
(25) (a) Haskel, A.; Straub, T.; Eisen, M. S. Organometallics 1996, 15,
3773−3775. (b) Straub, T.; Haskel, A.; Gueta Neyroud, T.; Kapon,
M.; Botoshansky, M.; Eisen, M. S. Organometallics 2001, 20, 5017−
5035. (c) Hayes, C. E.; Platel, R. H.; Schafer, L. L.; Leznoff, D. B.
Organometallics 2012, 31, 6732−3740.
(26) (a) Barnea, E.; Andrea, T.; Kapon, M.; Berthet, J.-C.;
Ephritikhine, M.; Eisen, M. S. J. Am. Chem. Soc. 2004, 126, 10860−
10861. (b) Barnea, E.; Andrea, T.; Berthet, J.-C.; Ephritikhine, M.;
Eisen, M. S. Organometallics 2008, 27, 3103−3012.
(12) (a) Ephritikhine, M. Dalton Trans. 2006, 2501−2516.
(b) Hayton, T. W. Dalton Trans. 2010, 39, 1145−1158. (c) Hayton,
T. W. Chem. Commun. 2013, 49, 2956−2973 and references therein..
(13) (a) Jantunen, K. C.; Burns, C. J.; Castro-Rodriguez, I.; Da Re, R.
E.; Golden, J. T.; Morris, D. E.; Scott, B. L.; Taw, F. L.; Kiplinger, J. L.
Organometallics 2004, 23, 4682−4692. (b) Da Re, R. E.; Golden, J. T.;
Kiplinger, J. L.; Morris, D. E. J. Am. Chem. Soc. 2005, 127, 682−689.
(c) Schelter, E. J.; Yang, P.; Scott, B. L.; Da Re, R. E.; Jantunen, K. C.;
Martin, R. L.; Hay, P. J.; Morris, D. E.; Kiplinger, J. L. J. Am. Chem. Soc.
2007, 129, 5139−5152.
(14) (a) Thomson, R. K.; Cantat, T.; Scott, B. L.; Morris, D. E.;
Batista, E. R.; Kiplinger, J. L. Nat. Chem. 2010, 2, 723−729. (b) King,
D. M.; Tuna, F.; McInnes, E. J. L.; McMaster, J.; Lewis, W.; Blake, A.
J.; Liddle, S. T. Science 2012, 337, 717−720. (c) King, D. M.; Tuna, F.;
McInnes, E. J. L.; McMaster, J.; Lewis, W.; Blake, A. J.; Liddle, S. T.
́
Nat. Chem. 2013, 5, 482−488. (d) Camp, C.; Pecaut, J.; Mazzanti, M.
J. Am. Chem. Soc. 2013, 135, 12101−12111. (e) King, D. M.;
McMaster, J.; Tuna, F.; McInnes, E. J. L.; Lewis, W.; Blake, A. J.;
Liddle, S. T. J. Am. Chem. Soc. 2014, 136, 5619−5622.
(27) (a) Wang, J. Q.; Dash, A. W.; Berthet, J. C.; Ephritikhine, M.;
Eisen, M. S. Organometallics 1999, 18, 2407−2409. (b) Kosog, B.;
Kefalidis, C. E.; Heinemann, F. W.; Maron, L.; Meyer, K. J. Am. Chem.
Soc. 2012, 134, 12792−12797.
(15) Tamm, M.; Petrovic, D.; Randoll, S.; Beer, S.; Bannenber, T.;
Jones, P. G.; Grunenberg, J. Org. Biomol. Chem. 2007, 5, 523−530.
(16) (a) Tamm, M.; Randoll, S.; Bannenberg, T.; Herdtweck, E.
Chem. Commun. 2004, 876−877. (b) Wu, X.; Tamm, M. Coord. Chem.
Rev. 2008, 37, 550−567. (c) Haberlag, B.; Wu, X.; Brandhorst, K.;
Grunenberg, J.; Daniliuc, C. G.; Jones, P. G.; Tamm, M. Chem. - Eur. J.
2010, 16, 8868−8877. (d) Sharma, M.; Yameen, H. S.; Tumanskii, B.;
Filimon, S.-A.; Tamm, M. J. Am. Chem. Soc. 2012, 134, 17234−17244.
(e) Shoken, D.; Sharma, M.; Botoshansky, M.; Tamm, M.; Eisen, M. S.
J. Am. Chem. Soc. 2013, 135, 12592−12595. (f) Lysenko, S.; Daniliuc,
C. G.; Jones, P. G.; Tamm, M. J. Organomet. Chem. 2013, 744, 7−14.
(17) (a) Panda, T. K.; Trambitas, A. G.; Bannenberg, T.; Hrib, C. G.;
Randoll, S.; Jones, P. G.; Tamm, M. Inorg. Chem. 2009, 48, 5462−
5472. (b) Trambitas, A. G.; Panda, T. K.; Tamm, M. Z. Anorg. Allg.
Chem. 2010, 636, 2456−2171. (c) Trambitas, A. G.; Panda, T. K.;
Jenter, J.; Roesky, P. W.; Daniliuc, C.; Hrib, C. G.; Jones, P. G.; Tamm,
M. Inorg. Chem. 2010, 49, 2435−2446. (d) Trambitas, A. G.; Melcher;
Hartenstein, L.; Roesky, P. W.; Daniliuc, C.; Jones, P. G.; Tamm, M.
Inorg. Chem. 2012, 51, 6753−6761.
(28) (a) Barnea, M.; Moradove, D.; Berthet, J.-C.; Ephritikhine, M.;
Eisen, M. S. Organometallics 2006, 25, 320−322. (b) Rabinovich, E.;
Aharonovich, S.; Botoshansky, M.; Eisen, M. S. Dalton Trans. 2010, 39,
6667−6676. (c) Walshe, A.; Fang, J.; Maron, L.; Baker, R. J. Inorg,
Chem. 2013, 53, 9077−9086. (d) Hayes, C. E.; Sarazin, Y.; Katz, M. J.;
Carpentier, J.-F.; Leznoff, D. B. Organometallics 2013, 32, 1183−1192.
(29) (a) Andrea, T.; Barnea, E.; Eisen, M. S. J. Am. Chem. Soc. 2008,
130, 2454−2455. (b) Sharma, M.; Andrea, T.; Brookes, N. J.; Yates, B.
F.; Eisen, M. S. J. Am. Chem. Soc. 2011, 133, 1341−1359.
(30) Lin, Z.; Mark, T. J. J. Am. Chem. Soc. 1987, 109, 7979−7985.
(31) Tolman, C. A. Chem. Rev. 1977, 77, 313−348.
(32) Mohring, P. C.; Coville, N. J. Coord. Chem. Rev. 2006, 250, 18−
̈
35.
(33) Karmel, I. S.; Eisen, M. S. Unpublished results.
(34) Shannon, R. D. Acta Crystallogr. 1976, A32, 751−767.
(35) (a) Barnhart, D. M.; Clark, D. L.; Grumbine, S. K.; Watkin, J. G.
Inorg. Chem. 1995, 34, 1695−1699 and references cited therein.
(b) Korobkov, I.; Gambarotta, S. Inorg. Chem. 2010, 49, 3409−3418
and references cited therein.
(18) Wu, X.; Tamm, M. Coord. Chem. Rev. 2014, 260, 116−138.
(19) Karmel, I. S. R.; Botoshansky, M.; Tamm, M.; Eisen, M. S. Inorg.
Chem. 2014, 53, 694−696.
(36) (a) Claisen, L. Ber. Dtsch. Chem. Ges. 1887, 20, 646−650.
(b) Tischtschenko, W. Zh. Russ. Fiz. Khim. O-va. 1906, 38, 355−418.
(c) Seki, T.; Nakajo, T.; Onaka, M. Chem. Lett. 2006, 35, 824−829.
(20) (a) Simpson, S. J.; Turner, H. W.; Andersen, R. A. J. Am. Chem.
Soc. 1979, 101, 7728−7729. (b) Simpson, S. J.; Andersen, R. A. J. Am.
Chem. Soc. 1981, 103, 4063−4066. (c) Simpson, S. J.; Turner, H. W.;
Andersen, R. A. Inorg. Chem. 1981, 20, 2991−2995. (d) Dormond, A.;
El Bouadili, A. A.; Moïse, C. J. Chem. Soc., Chem. Commun. 1985, 914−
916. (e) Dormond, A.; El Bouadili, A.; Aaliti, A.; Moise, C. J.
Organomet. Chem. 1985, 288, C1−C5. (f) Dormond, A.; El Bouadili,
A. A.; Moïse, C. J. Less-Common Met. 1986, 122, 159−166.
(g) Dormond, A.; Aaliti, A.; Bouadili, A. A.; Moïse, C. Inorg. Chim.
Acta 1987, 139, 171−176. (h) Barnhart, D. M.; Clark, D. L.;
Grumbine, S. K.; Watkin, J. G. Inorg. Chem. 1995, 34, 1695−1699.
(i) Cantat, T.; Scott, B. L.; Kiplinger, J. L. Chem. Commun. 2010, 46,
919−921. (j) Monreal, M. J.; Thomson, R. K.; Cantat, T.; Travia, N.
E.; Scott, B. L.; Kiplinger, J. L. Organometallics 2011, 30, 2031−2038.
(k) Windorff, C. J.; Evans, W. J. Organometallics 2014, 33, 3786−3789.
(21) (a) Barnea, E.; Eisen, M. S. Coord. Chem. Rev. 2006, 250, 855−
899. (b) Burns, C. J.; Eisen, M. S. Homogeneous and Heterogeneous
Catalytic Processes Promoted by Organoactinides. In The Chemistry of
the Actinide and Transactinide Elements; Morss, L. R., Edelstein, N. M.,
Fuger, J., Eds.; Springer: Dordrecht, The Netherlands, 2006; pp 2911−
3012. (c) Andrea, T.; Eisen, M. S. Chem. Soc. Rev. 2008, 37, 550−567.
(d) Fox, A. R.; Bart, S. C.; Meyer, K.; Cummins, C. C. Nature 2008,
455, 341−349.
(37) Tormakangas, O. P.; Koskinen, A. M. P. Recent Res. Dev. Org.
̈
̈
Chem. 2001, 5, 225−255.
(38) (a) Yamashita, M.; Watanabe, Y.; Mitsudo, T.-a.; Takegami, Y.
Bull. Chem. Soc. Jpn. 1976, 49, 3597−3600. (b) Ito, T.; Horino, H.;
Koshiro, Y.; Yamamoto, A. Bull. Chem. Soc. Jpn. 1982, 55, 504−512.
(c) Bergens, S. H.; Fairlie, D. P.; Bosnich, B. Organometallics 1990, 9,
566−571. (d) Barrio, P.; Esteruelas, M. A.; Onate, E. Organometallics
2004, 23, 1340−1348. (e) Suzuki, T.; Yamada, T.; Matsuo, T.;
Watanabe, K.; Katoh, T. Synlett 2005, 1450−1452. (f) Garralda, M. A.
Dalton Trans. 2009, 3635−3645.
(39) (a) Onozowa, S-y.; Sakakura, T.; Tanaka, M.; Shiro, M.
Tetrahedron 1996, 52, 4291−4302. (b) Berberich, H.; Roesky, P. W.
Angew. Chem., Int. Ed. 1998, 37, 1569−1571. (c) Burgstein, M. R.;
Berberich, H.; Roesky, P. W. Chem. - Eur. J. 2001, 7, 3078−3085.
(d) Zuyls, A.; Roesky, P. W.; Deacon, G. B.; Konstas, K.; Junk, P. C.
Eur. J. Org. Chem. 2008, 693−697.
(40) Dzik, W. I.; Gooßen, L. J. Angew. Chem., Int. Ed. 2011, 50,
11047−11049.
(41) (a) Simoes, J. A. M.; Beauchamp, J. L. Chem. Rev. 1990, 90,
629−688. (b) McMillen, D. F.; Golden, D. M. Annu. Rev. Phys. Chem.
1982, 33, 493−532.
(22) (a) He, M. Y.; Xiang, G.; Toscano, P. J.; Burwell, R. L., Jr.;
Marks, T. J. J. Am. Chem. Soc. 1985, 107, 641−652. (b) Hayes, C. E.;
Leznoff, D. B. Organometallics 2010, 29, 767−774. (c) Domeshek, E.;
(42) Ogata, Y.; Kawasaki, A. Tetrahedron 1969, 25, 929−935.
(43) Kappa CCD Server Software; Nonius BV: Delft, The Nether-
lands, 1997.
17191
dx.doi.org/10.1021/ja5091436 | J. Am. Chem. Soc. 2014, 136, 17180−17192

Journal of the American Chemical Society
Article
(44) Otwiniwski, Z.; Minor, W. Methods Enzymol. 1997, 276, 307−
326.
(45) Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467−473.
(46) ORTEP, TEXSAN Structure Analysis Package; Molecular
Structure Corp.: The Woodlands, TX, 1999.
(47) Mercury Software from CCDC, http://www.ccdc.cam.ac.uk/
Solutions/CSDSystem/Pages/Mercury.aspx.
(48) Mojtahedi, M. M.; Akbarzadeh, E.; Sharif, R.; Abaee, S. M. Org.
Lett. 2007, 9, 2791−2793.
(49) Li, L.; Sheng, H.; Xu, F.; Shen, Q. Chin. J. Chem. 2009, 27,
1127−1131.
(50) Mori, N.; Hideo, T. Tetrahedron 2005, 61, 5915−5925.
(51) Cadoret, F.; Six, Y. Tetrahedron Lett. 2007, 98, 5491−5495.
(52) Ji, M.; Wang, X.; Lim, Y. N.; Kang, Y.-W.; Jang, H.-Y. Eur. J. Org.
Chem. 2013, 7881−7885.
(53) Ishihara, K.; Masatoshi, N.; Kasugi, Y. Org. Lett. 2008, 10,
2187−2190.
(54) Mineno, T.; Nikaido, N.; Kansui, H. Chem. Pharm. Bull. 2009,
57, 1167−1174.
(55) Hashimoto, Y.; Ohashi, M.; Ogoshi, S. J. J. Am. Chem. Soc. 2011,
133, 4668−4671.
17192
dx.doi.org/10.1021/ja5091436 | J. Am. Chem. Soc. 2014, 136, 17180−17192