Dehydrogenation of (Di)amine-Boranes by Highly Active Scandocene Alkyl Catalysts

Article abstract of DOI:10.1021/acs.organomet.9b00461

The scandocene alkyl complexes (C₅Me₅)₂ScR (1, R = CH(SiMe₃)₂; 5, R = CH₂SiMe₃) were found to be highly active catalysts for the dehydrogenation of dimethylamine-borane (DMAB), e

Full text of DOI:10.1021/acs.organomet.9b00461

Article
pubs.acs.org/Organometallics
Cite This: Organometallics XXXX, XXX, XXX−XXX
Dehydrogenation of (Di)amine−Boranes by Highly Active
Scandocene Alkyl Catalysts
Pengfei Xu and Xin Xu*
Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry, Chemical Engineering and Materials Science,
Soochow University, Suzhou 215123, People’s Republic of China
*
S Supporting Information
ABSTRACT: The scandocene alkyl complexes (C Me ) ScR (1, R =
5
5 2
CH(SiMe ) ; 5, R = CH SiMe ) were found to be highly active catalysts
3
2
2
3
for the dehydrogenation of dimethylamine−borane (DMAB), exhibiting
turnover frequencies up to 100 min− at ambient temperature. The β-B-
agostic scandium amidoborane intermediate 6 was isolated from a
stoichiometric reaction of complex 5 with DMAB. In contrast, treatment of
complex 5 with sterically bulky diisopropylamine−borane led to isolation of
the aminoborane-coordinated scandocene hydride 7 via a complete β-H
elimination. Scandium amidoborane complex 6 showed scandium hydride
like reactivity toward dicyclohexylcarbodiimide (DCC) and 4-dimethylami-
nopyridine (DMAP), affording DCC insertion product 8 and DMAP ortho-borylation product 9, respectively. In addition,
complexes 1 and 5 also showed remarkably high activity for the catalyzed dehydrogenative cyclization of diamine−boranes to
give N-heterocyclic boranes.
1
7
INTRODUCTION
β-H elimination from metal alkyl complexes is a fundamental
process in organometallic chemistry and plays an essential role
in a variety of transition-metal-catalyzed reactions. These
transformations proceed via a β-agostic interaction (e.g. I,
Scheme 1). However, the resulting metal hydride alkene
pling of amine−boranes. However, the isolation of key
intermediates in the dehydrogenation reaction, particularly in
highly active systems, is challenging and only a few active β-B-
■
8
1
agostic metal amidoboranes have been characterized. Herein,
we have found that scandocene alkyls (Cp* ScR; Cp* =
C Me , R = CH(SiMe ) , CH SiMe ) are remarkably active
2
2
5
5
3 2
2
3
catalysts for the dehydrogenation of Me NH·BH (DMAB)
2
3
and diamine−boranes, with a turnover frequency (TOF) of up
Scheme 1. β-H Eliminations of β-Agostic Metal Alkyl and β-
B-Agostic Metal Amidoborane
−
1
a
to 100 min at room temperature. Furthermore, a β-B-agostic
scandium amidoborane intermediate was successfully isolated
from the corresponding stoichiometric reaction.
RESULTS AND DISCUSSION
■
Although a number of transition-metal and main-group
catalysts have been investigated for the catalytic dehydrogen-
ation of amine−boranes, examples using rare-earth (RE)
a
Ln, ligand; M, metal.
9
0
catalysts are limited. We have examined a series of well-known
intermediate (II) is difficult to observe, especially for d metal
10
RE metallocene alkyl complexes for the catalytic dehydro-
genation of DMAB (Scheme 2). The dehydrogenation reaction
was initially performed using 0.5 mol % Cp* ScCH(SiMe )
complexes because of weak alkene−metal π bonding and the
3
tendency for further migratory insertion reactions to occur.
−
2
3 2
Amidoborane ligands (NR -BH ) are isoelectronic with alkyl
ligands (CR -CH ) , and so the β-B-agostic metal amidobor-
2
3
−
(1) in C D at room temperature (Table 1, entry 1).
6 6
2
3
Remarkably, a vigorous evolution of H gas was observed
2
ane (III, Scheme 1) is expected to exhibit chemical behavior
similar to that of I. However, the direct observation of metal
4
and subsequent analysis of the quenched reaction mixture
1
1
using B NMR spectroscopy indicated that the DMAB was
completely consumed within 2 min. Thus, the TOF for the
hydride aminoborane intermediates (e.g. IV) that result from
5
β-H elimination remains elusive.
−
1
scandium complex 1 reached 100 min , which is comparable
The catalytic dehydrogenation of amine−boranes has been
explored extensively because of their potential for hydrogen
storage and as precursors for BN-based ceramics and
to those of the most active catalyst for DMAB dehydrogen-
11,12
ation.
After the reaction, the starting amine−borane was
6
polymeric materials. β-H elimination of a β-B-agostic metal
amidoborane is thought to be a key step in many early-
transition-metal- or main-group-metal-catalyzed dehydrocou-
Received: July 5, 2019
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.9b00461
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Scheme 2. Catalytic Dehydrogenation of DMAB with
Complexes 1−5
(Table 1, entry 5). Thus, it is plausible that the sterically bulky
pentamethylcyclopentadienyl ligand might be crucial for
achieving high catalytic activity. The influence of different
alkyl initiating groups on the catalyst was also examined, with
Cp* ScCH SiMe (5) that contained the less sterically
2
2
3
hindered −CH SiMe group showing reactivity similar to
2
3
that of complex 1 (Table 1, entry 6).
To gain more insight into the reaction mechanism, a
stoichiometric reaction between the scandocene complex 5
and an equimolar amount of DMAB was performed at −30 °C.
Workup of the reaction mixture at low temperature resulted in
the precipitation of pale yellow crystals that were identified as
the β-B-agostic scandium amidoborane complex 6 by single-
crystal X-ray diffraction (70% yield; Scheme 3 and Figure 1).
Table 1. Catalytic Dehydrogenation of DMAB with Rare-
a
Earth Metallocene Alkyls 1−5
cat. loading
(mol %)
time
(min)
conversn
(%)
TOF
A (%) B (%) (min 1)
−
entry cat.
1
2
3
4
5
6
1
1
2
3
4
5
0.5
0.2
0.5
0.5
0.5
0.5
2
6
6
6
10
2
100
97
98
95
20
93
38
60
41
0
2
56
34
53
100
10
100
81
33
32
4
100
81
100
a
Conditions: reactions were performed in C D at room temperature
6
6
in an unsealed vial. Conversion and product distribution were
1
1
determined by integration of B NMR spectra.
largely converted into the cyclic borazane [Me N-BH ] (A)
2
2 2
(
93%), along with trace amounts of other borane-containing
species. Even with a very small catalyst loading (0.2 mol %),
the reaction still achieved 97% conversion within 6 min.
However, these reaction conditions resulted in the linear
diborazane Me NH·BH −NMe ·BH (B) as the major
2
2
2
3
Figure 1. Molecular structure of complex 6. Hydrogen atoms (except
BH) are omitted for clarity, and ellipsoids are drawn at the 30%
probability level. Selected bond lengths (Å) and angles (deg): Sc1−
N1, 2.3116(17); Sc1−H1, 1.97(3); N1−B1, 1.577(3); B1−H1,
product (Table 1, entry 2), presumably because the
concentration of DMAB has a strong effect on the formation
13
of different dehydrogenation products. The effect of the
metal ionic radius on the dehydrogenation of DMAB was
examined by using larger RE metals, including lutetium and
1
.27(2); B1−H2, 1.15(2); B1−H3, 1.17(2); Sc1−N1−B1,
2.84(11); N1−B1−H1, 103.9(12); B1−H1−Sc1, 106.906(152);
8
H1−Sc1−N1, 62.8(7).
yttrium. Under the same reaction conditions, Cp* LuCH-
2
(
SiMe3)2 (2) and Cp* YCH(SiMe ) (3) exhibited poor
2 3 2
1
−
−
reaction selectivity and lower TOFs of 33 and 32 min ,
respectively (Table 1, entries 3 and 4). Thus, the reaction
activity decreased as the ionic radii of the central metal ion
increased (Sc > Lu ≈ Y). The reactivity of RE metal complexes
is highly dependent on the size of the ancillary ligand. The less
The structure showed that the [NMe BH ] ligand was bound
2 3
to the scandium metal center via a relatively long Sc−N (Sc1−
9
a,14
N1 2.3116(17) Å) bond
and an agostic Sc−H−B (Sc1−
H1 1.97(3) Å, B1−H1 1.27(2) Å) interaction. The N1−B1
bond distance was 1.577(3) Å which was comparable to other
well-defined main-group and transition-metal β-B-agostic
sterically encumbered scandocene alkyl complex Cp ScCH-
2
4
,5,8
(
SiMe ) (Cp = C H ; 4) was prepared and used for the
amidoborane complexes.
Remarkably, the Sc−N−B bond
3
2
5
5
dehydrogenation reaction. Complex 4 exhibited dramatically
lower activity, exclusively affording the linear borazane B when
the reaction was performed using our standard conditions
angle (Sc1−N1−B1 82.84(11)°) in complex 6 was quite
similar to those of the recently reported rare-earth β-agostic
ethyl complexes (Cp* YEt;
1
5
Y−C −Cβ 82.6(2)°;
2
α
i
Scheme 3. Stoichiometric Reactions of Complex 5 with DMAB and Pr NH·BH
2
3
B
DOI: 10.1021/acs.organomet.9b00461
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
1
6
solution 11B NMR spectrum of complex 7 featured a broad
signal at 23.3 ppm, which was significantly shifted to lower
field in comparison with the signal from complex 6 (−8.7
ppm). Variable-temperature NMR spectroscopy of complex 7
showed that it was the product of an irreversible β-H
elimination product, with the reinsertion reaction most likely
Cp* ScEt, Sc−C −C 85.6(2)°). In addition, the IR
2
α
β
spectrum of complex 6 contained bonds that were character-
istic of terminal and bridging BH bonds at 2365 and 1688
cm , respectively.
Complex 6 was dissolved in toluene-d at room temperature
for NMR analysis. Two singlets at 2.57 ppm (NMe ) and 1.92
ppm (Cp*) were present in the H NMR spectrum. Peaks
from BH or ScH were not observed clearly, likely because of
−
1
4a,8
8
2
20
1
hampered by the sterically hindered N atom.
Additional experiments were carried out to provide further
information for the β-H elimination of complex 6 in solution.
The stoichiometric reaction of 6 with an equimolar amount of
dicyclohexylcarbodiimide (DCC) was examined because of its
3
quadrupole broadening and/or the rapid exchange of
1
7,18
11
hydrides.
However, the B NMR spectrum showed two
broad signals at 5.2 and −8.7 ppm (Figure S10), which
indicated that two species existed in the solution state. The
scandium amidoborane complex 6 may have caused the signal
at −8.7 ppm, which would be consistent with other metal
amidoborane complexes that have been reported.
have tentatively assigned the peak at 5.2 ppm, which has
21
tendency to undergo insertion reactions into RE−H bonds.
As expected, the reaction clearly gave DCC insertion product 8
in 76% isolated yield with the concomitant formation of the
cyclic borazane A (Scheme 4 and Figure 3; for details, see the
Experimental Section and Supporting Information). The
scandocene hydride is also reported to react with heterocyclic
4a,5,9a,9
c
We
2
19
considerable sp character, to another borane unit from the
compounds (e.g. pyridine) to afford the ortho C−H activation
β-H elimination product that contains a Me NBH
2
2
18
product with the release of H . Thus, the reaction of 6 with
2
coordinated scandocene hydride (6′). Unfortunately, attempt
to isolate complex 6′ failed because it slowly converted to the
cyclic borazane A and other unidentified species in solution at
ambient temperature. Thus, the structure of 6′ currently
remains undetermined. Variable-temperature NMR experi-
ments of the sample were investigated and showed a
4
-dimethylaminopyridine (DMAP) was also investigated. The
evolution of H gas was observed during the reaction, which
was confirmed by in situ H NMR spectroscopy. Workup of
2
1
the reaction mixture gave complex 9 as a yellow crystalline
solid in 79% yield. The molecular structure of complex 9
determined by single-crystal X-ray diffraction is depicted in
Figure 3. It has a contact ion pairing framework in which the
cationic scandium center is coordinated by both B−H and N
atoms of the former DMAP ring. We propose that the
formation of complex 9 resulted from ortho C−H activation of
DMAP followed by an alkide abstraction by a borane Lewis
1
decoalescence of the H resonances at 253 K. Notably, the
ratio of complex 6 in the mixture increased as the temperature
was decreased (for details, see the Supporting Information).
To elucidate the structure of 6′, we performed a controlled
i
reaction of scandocene alkyl 5 with 1 equiv of Pr NH·BH ,
2
3
which contained a sterically bulky amino group. Following the
acid (for details, see Scheme S6 in the Supporting
i
reaction, an Pr NBH coordinated scandium hydride (7;
22,23
2
2
Information).
Both of the reactions that have been
Scheme 3) was obtained in 75% yield. Therefore, it is likely
that a similar β-B-agostic scandium amidoborane intermediate
formed initially, which was followed by a rapid β-H elimination
to afford the final product. The crystal structure of complex 7
described may represent typical scandocene hydride like
behavior and possibly indicate the existence of a β-H
elimination product in solution.
As both scandocene alkyls 1 and 5 exhibited excellent
performances in dehydrogenation of DMAB, we examined
their use in the catalytic dehydrogenation of diamine−borane
substrates to form cyclic diaminoboranes, which are nitrogen-
containing analogues of widely used pinacol− or catechol−
borane reagents. To date, there have only been three other
catalysts that were reported to be active for such a
transformation, each having a low activity (TOF < 0.4
(
Figure 2) revealed that the B−N bond (1.491(3) Å) was
considerably shorter than that in complex 6 (1.577(3) Å). The
−
1
24
min ) even at elevated temperatures. Using complex 1 as
the catalyst (2 mol %), the diamine−borane substrate 10a was
converted to the corresponding cyclic product 11a in 92%
yield in 20 min at room temperature (Table 2, entry 1). When
complex 5 was used as the catalyst, a significantly higher
activity was observed in transforming 10a into 11a (95% yield
−
1
within 5 min, TOF = 9.5 min ; Table 2, entry 2). Scandocene
alkyl 5 also showed high activity for the dehydrogenative
cyclization of other challenging diamine−borane substrates
such as 10b,c. This resulted in the five-membered N-
−
1
heterocyclic borane 11b (TOF = 9.7 min ) and the six-
−
1
membered N-heterocyclic borane 11c (TOF = 4.9 min ),
respectively (Table 2, entries 3 and 4).
CONCLUSION
■
Figure 2. Molecular structure of complex 7. Hydrogen atoms (except
BH) are omitted for clarity, and ellipsoids are drawn at the 30%
probability level. Selected bond lengths (Å) and angles (deg): Sc1−
H1B, 2.02(2);Sc1−H1C, 1.95(2); B1−H1A, 1.18(2); B1−H1B,
In summary, a series of rare-earth metallocene alkyls were
examined for the catalytic dehydrogenation of DMAB. The
catalytic activity was found to be dependent on both the metal
ion and the surrounding ligands. The scandocene alkyls 1 and
5 showed extremely high activity, affording TOFs of up to 100
1
5
.22(3); B1−H1C, 1.22(3); B1−N1, 1.491(3); H1B−Sc1−H1C,
3.4(11); H1B−B1−H1C, 94.4(17).
C
DOI: 10.1021/acs.organomet.9b00461
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Scheme 4. Stoichiometric Reactions of Complex 6 with DCC and DMAP
Figure 3. Molecular structures of complexes 8 (left) and 9 (right). Hydrogen atoms (except BH) are omitted for clarity, and ellipsoids are drawn at
the 30% probability level. Selected bond lengths (Å) and angles (deg) for 8: N1−C1, 1.324(3); N2−C1, 1.324(3); N1−Sc1, 2.2268(17); N2−Sc1,
2
.2424(18); C1−N1−C2, 115.40(17); C1−N1−Sc1, 88.99(13); C2−N1−Sc1, 153.72(14); C1−N2−Sc1, 88.32(12). Selected bond lengths (Å)
and angles (deg) for 9: Sc1−N1, 2.228(2); B1−N2, 1.506(4); B1−C1, 1.620(4); N2−B1−C1, 116.0(2); C1−N1−Sc1, 110.17(16); N1−C1−B1,
1
18.2(2).
Table 2. Catalyzed Dehydrogenative Cyclization of
Diamine−Boranes by Scandocene Alkyls
scandocene alkyls are highly active catalysts for the
dehydrogenation of (di)amine−boranes and gives a deeper
understanding of the β-H elimination of β-agostic metal
complexes.
a
EXPERIMENTAL SECTION
For general information and the characterization data of the new
compounds see the Supporting Information.
■
time
(min)
yield
(%)
TOF
entry
substrate
cat.
(min 1)
−
Preparation of Complex 4. LiCH(SiMe ) (118 mg, 0.71 mmol,
3
2
1
2
3
4
10a (n = 1, R = Me)
10a (n = 1, R = Me)
10b (n = 1, R = Pr)
1
5
5
5
20
5
5
92
95
97
98
2.3
9.5
9.7
4.9
in 2 mL of toluene) was added to a solution of [Cp ScCl] (150 mg,
2
2
0.36 mmol) in toluene (2 mL). The reaction mixture was stirred at
room temperature for 1 h. After filtration, the volatiles were removed
under vacuum and the residue was dissolved in hexane. After standing
at −30 °C overnight, a large amount of pale yellow crystalline solid
was formed, which was collected and washed with hexane (2 × 0.5
mL) to finally give complex 4 (152 mg, 64%).
i
10c (n = 2, R = Me)
10
a
Conditions: reactions were performed in C D with 2 mol % catalyst
loading at room temperature in an unsealed vial. Yields were
determined by H NMR using hexamethylbenzene as an internal
standard.
6
6
1
General Procedure for Dehydrogenation of DMAB. A 20 mL
oven-dried glass reactor was charged with rare-earth-metal complex
−
3
(
3.0 × 10 mmol) inside the glovebox. DMAB was dissolved in the
min− at room temperature. The stoichiometric reaction of
complex 5 with DMAB led to the isolation of the scandocene
β-B-agostic amidoborane complex 6, which probably under-
went a β-H elimination in solution to react with DCC and
DMAP. However, the reaction of scandocene alkyl 5 with
1
solvent (0.5 mL) and added to the catalyst at room temperature. A
vigorous evolution of H gas was immediately observed. The mixture
2
was allowed to react uncapped and unstirred. After the measured time
interval, a 0.2 mL aliquot was taken out and quickly quenched into a 4
mL vial containing 0.5 mL of undried “wet” C D . The quenched
6
6
i
reaction mixture was immediately frozen in liquid N
2
and was
Pr NH·BH gave an aminoborane-coordinated scandocene
2
3
defrosted just before NMR analysis.
hydride through a complete β-H elimination process. In
addition, complexes 1 and 5 also exhibited very high activities
for the catalyzed dehydrogenative cyclization of diamine−
boranes to give N-heterocyclic boranes. This work shows that
Preparation of Complex 6. DMAB (22 mg, 0.37 mmol, in 1 mL
of toluene) was added to a solution of complex 5 (150 mg, 0.37
mmol) in hexane (1 mL) at −30 °C. The volatiles were immediately
removed under vacuum, and the residue was dissolved in cold hexane.
D
DOI: 10.1021/acs.organomet.9b00461
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
After standing at −30 °C overnight, a large amount of pale yellow
crystalline solid was formed, which was collected and washed with
cold hexane (0.5 mL) to finally give complex 6 (97 mg, 70%).
Crystals suitable for a single-crystal X-ray structure analysis were
grown from a solution of 6 in hexane at −30 °C. In solution, complex
Crystals suitable for an X-ray single-crystal structure analysis were
grown from a solution of 9 in hexane at −30 °C.
X-ray Crystal Structure Analysis of Complex 9: formula
−
1
C
H
47BN
Sc, M
monoclinic, space group P2
= 31.4224(13) Å, β = 94.5270(10)°, V = 5589.7(4) Å , ρcalc = 1.173 g
= 493.47 g mol , yellow, 0.25 × 0.18 × 0.15 mm,
29
3
r
/c, a = 10.0262(5) Å, b = 17.7978(8) Å, c
1
3
6
was partially converted to complex 6′ (molar ratio of 6:6′ = ca.
−
3
−1
0
.85:1, Tol-d , 253 K). Note: complexes 6 and 6′ are not stable at
cm , μ = 0.285 mm , empirical absorption correction (0.6624 ≤ T
≤ 0.7460), Z = 8, λ = 0.71073 Å, T = 120(2) K, 93919 reflections
collected (−14 ≤ h ≤ 14, −25 ≤ k ≤ 25, −43 ≤ l ≤ 44), 16397
8
room temperature in solution and will slowly convert to the cyclic
borazane A and other undefined species.
independent (R = 0.1084) and 9797 observed reflections (I >
X-ray Crystal Structure Analysis of Complex 6: formula
int
−
1
2
σ(I)), 641 refined parameters, final R1 = 0.0616 (I > 2σ(I)) and final
C H BNSc, M = 373.31 g mol , colorless, 0.20 × 0.15 × 0.05 mm,
2
2
39
r
wR2 = 0.2048 (all data), maximum (minimum) residual electron
triclinic, space group P1
̅
, a = 8.4624(17) Å, b = 9.2052(18) Å, c =
4.534(3) Å, β = 89.9975(121)°, V = 1083.3(4) Å , ρ = 1.145 g
cm , μ = 0.344 mm , empirical absorption correction (0.8197 ≤ T
1.0000), Z = 2, λ = 0.71073 Å, T = 123.1500 K, 10529 reflections
collected (−10 ≤ h ≤ 10, −11 ≤ k ≤ 11, −18 ≤ l ≤ 17), 4854
independent (R = 0.0377) and 3794 observed reflections (I >
−
3
3
density 0.598 (−0.629) e Å . Hydrogen atoms were placed in
calculated positions and refined using a riding model.
1
calc
−
3
−1
General Procedure for Dehydrogenation of Diamine−
≤
Borane. A 20 mL oven-dried glass reactor was charged with rare-
−
3
earth-metal complex (2.5 × 10 mmol) inside the glovebox.
Diamine−borane and hexamethylbenzene (internal standard) were
dissolved in the solvent (0.5 mL) and added to the catalyst at room
int
2σ(I)), 250 refined parameters, final R1 = 0.0459 (I > 2σ(I)), final
wR2 = 0.1175 (all data), maximum (minimum) residual electron
−
3
temperature. A vigorous evolution of H gas was immediately
2
density 0.427 (−0.345) e Å . Hydrogen atoms were placed in
calculated positions and refined using a riding model.
observed. The mixture was allowed to react uncapped and unstirred.
After the measured time interval, a 0.2 mL aliquot was taken out and
quickly quenched into a 4 mL vial containing 0.5 mL of undried “wet”
C D . The quenched reaction mixture was immediately frozen in
Preparation of Complex 7. Following the procedure described
i
for 6, reaction of complex 5 (100 mg, 0.25 mmol) with Pr NH·BH
2
3
6
6
(
29 mg, 0.25 mmol) gave 7 as orange crystals (81 mg, 75%). Crystals
liquid N and was defrosted just before NMR analysis.
2
suitable for an X-ray single crystal structure analysis were grown from
a solution of 7 in hexane at −30 °C.
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.9b00461.
X-ray Crystal Structure Analysis of Complex 7: formula
■
−
1
S
*
C H BNSc, M = 429.41 g mol , yellow, 0.25 × 0.16 × 0.12 mm,
26
47
r
monoclinic, space group P1 1/c1, a = 14.6104(11) Å, b = 11.8168(8)
2
3
Å, c = 15.3319(12) Å, β = 100.813(2)°, V = 2600.0(3) Å , ρ
=
calc
−
3
−1
1
4
.097 g cm , μ = 0.295 mm , empirical absorption correction (0.
789 ≤ T ≤ 0.7456), Z = 4, λ = 0.71073 Å, T = 120 K, 46380
General procedures, characterization data, and NMR
spectra of the compounds (PDF)
reflections collected (−17 ≤ h ≤ 17, −14 ≤ k ≤ 14, −18 ≤ l ≤ 18),
839 independent (R = 0.1072) and 3448 observed reflections (I >
4
int
2
σ(I)), 345 refined parameters, final R1 = 0.0524 (I > 2σ(I)) final
Accession Codes
wR2 was 0.1690 (all data), maximum (minimum) residual electron
density 0.479 (−0.509) e Å . Hydrogen atoms were placed in
calculated positions and refined using a riding model.
CCDC 1915434−1915437 contain the supplementary crys-
tallographic 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.
−
3
Preparation of Complex 8. Dicyclohexylcarbodiimide (DCC; 37
mg, 0.18 mmol, in 0.5 mL of toluene) was added to a solution of
complex 6 (67 mg, 0.18 mmol) in toluene (0.5 mL) at room
temperature. The reaction mixture stood at room temperature for 30
min. The volatiles were removed under vacuum, and the residue was
dissolved in hexane. After standing at −30 °C overnight, a large
amount of colorless crystalline solid was formed which was collected
and washed with hexane (2 × 0.5 mL) to finally give complex 8 (72
mg, 77%). Crystals suitable for an X-ray single-crystal structure
analysis were grown from a solution of 8 in hexane at −30 °C.
X-ray Crystal Structure Analysis of Complex 8: formula
AUTHOR INFORMATION
Corresponding Author
*E-mail for X.X.: xinxu@suda.edu.cn.
■
ORCID
Xin Xu: 0000-0003-2426-9816
Notes
The authors declare no competing financial interest.
−
1
C H N Sc, M = 522.73 g mol , colorless, 0.26 × 0.15 × 0.12 mm,
tetragonal, space group I4 /a, a = 35.6027(14) Å, b = 35.6027(14) Å,
c = 9.9827(4) Å, β = 90°, V = 12653.6(11) Å , ρ = 1.098 g cm , μ
=
33
53
2
r
1
3
−3
calc
−1
0.254 mm , empirical absorption correction (0.5617 ≤ T ≤
ACKNOWLEDGMENTS
■
0
.7456), Z = 16, λ = 0.71073 Å, T = 120(2) K, 102778 reflections
This work was supported by the National Natural Science
Foundation of China (21871204), 1000-Youth Talents Plan,
PAPD, and the project of scientific and technologic infra-
structure of Suzhou (SZS201708).
collected (−46 ≤ h ≤ 46, −46 ≤ k ≤ 45, −12 ≤ l ≤ 12), 7275
independent (R = 0.1168) and 5448 observed reflections (I >
int
2σ(I)), 339 refined parameters, final R1 = 0.0485 (I > 2σ(I)) and final
wR2 = 0.1639 (all data), maximum (minimum) residual electron
density 0.306 (−0.518) e Å . Hydrogen atoms were placed in
calculated positions and refined using a riding model.
−
3
REFERENCES
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E
DOI: 10.1021/acs.organomet.9b00461
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DOI: 10.1021/acs.organomet.9b00461
Organometallics XXXX, XXX, XXX−XXX