Experimental and computational studies on a three-membered diphosphido thorium metallaheterocycle [η5-1,3-(Me3C)2C5H3]2Th[η2-P2(2,4,6-iPr3C6H2)2]

Article abstract of DOI:10.1039/c9dt01160a

A three-membered thorium metallaheterocycle [η⁵-1,3-(Me₃C)₂C₅H₃]₂Th[η²-P₂(2,4,6-ⁱPr₃C₆H₂)₂] (4) is readily prepared besides H₂ from [η⁵-1,3-(Me₃C)₂C₅H₃]₂Th(PH-2,4,6-ⁱPr₃C₆H₂)₂ (3) upon heating in toluene solution. Density functional theory (DFT) studies were performed to elucidate the 5f orbital contribution to the bonding within Th-(η²-P-P) revealing more covalent bonds between the [η⁵-1,3-(Me₃C)₂C₅H₃]₂Th²⁺ and [η²-P₂(2,4,6-ⁱPr₃C₆H₂)₂]^2- fragments than those in the related thorium metallacyclopropene. Consequently, distinctively different reactivity patterns emerge, e.g., while 4 reacts with pyridine derivatives such as 4-dimethyaminopyridnie (DMAP) and forms the DMAP adduct [η⁵-1,3-(Me₃C)₂C₅H₃]₂Th[η²-P₂(2,4,6-ⁱPr₃C₆H₂)₂](DMAP) (5), it may also act as a [η⁵-1,3-(Me₃C)₂C₅H₃]₂Th(ii) synthon when reacted with bipy, Ph₂S₂ or Ph₂Se₂. Nevertheless, no reaction of complex 4 with alkynes is observed, but it reacts as a nucleophile towards nitriles and aldehydes resulting in five- or seven-membered metallaheterocycles, respectively. DFT computations provide some additional insights into the experimental observations.

Full text of DOI:10.1039/c9dt01160a

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Experimental and computational studies on
a three-membered diphosphido thorium
metallaheterocycle [η5-1,3-(Me3C)2C5H3]2Th
[η2-P2(2,4,6-iPr3C6H2)2]†
Cite this: DOI: 10.1039/c9dt01160a
Congcong Zhang,a Yongsong Wang,a Guohua Hou, a Wanjian Ding,a
Guofu Zi *a and Marc D. Walter
*
b
A three-membered thorium metallaheterocycle [η5-1,3-(Me3C)2C5H3]2Th[η2-P2(2,4,6-iPr3C6H2)2] (4) is
readily prepared besides H2 from [η5-1,3-(Me3C)2C5H3]2Th(PH-2,4,6-iPr3C6H2)2 (3) upon heating in
toluene solution. Density functional theory (DFT) studies were performed to elucidate the 5f orbital con-
tribution to the bonding within Th-(η2-P-P) revealing more covalent bonds between the [η5-1,3-
(Me3C)2C5H3]2Th2+ and [η2-P2(2,4,6-iPr3C6H2)2]2− fragments than those in the related thorium metallacy-
clopropene. Consequently, distinctively different reactivity patterns emerge, e.g., while 4 reacts with pyri-
dine derivatives such as 4-dimethyaminopyridnie (DMAP) and forms the DMAP adduct [η5-1,3-
(Me3C)2C5H3]2Th[η2-P2(2,4,6-iPr3C6H2)2](DMAP) (5), it may also act as a [η5-1,3-(Me3C)2C5H3]2Th(II)
synthon when reacted with bipy, Ph2S2 or Ph2Se2. Nevertheless, no reaction of complex 4 with alkynes is
observed, but it reacts as a nucleophile towards nitriles and aldehydes resulting in five- or seven-mem-
bered metallaheterocycles, respectively. DFT computations provide some additional insights into the
experimental observations.
Received 19th March 2019,
Accepted 16th April 2019
DOI: 10.1039/c9dt01160a
rsc.li/dalton
study thorium and uranium metallacycles.5 In the course of
these investigations, the thorium metallacyclopropene
Introduction
Metal phosphido complexes are interesting starting materials [η5-1,2,4-(Me3C)3C5H2]2Th(η2-C2Ph2)5a,b and the uranium
for new phosphorus containing materials, molecules and metallacyclopropene
(η5-C5Me5)2U[η2-C2(SiMe3)2]
were
organometallic compounds. This also extends to their poten- prepared.5f,g Reactivity studies revealed complementary reactiv-
tial applications in phosphorus–element bond formations and ity patterns: the thorium metallacyclopropene [η5-1,2,4-
catalytic transformation.1 As a result, numerous phosphido (Me3C)3C5H2]2Th(η2-C2Ph2) reacts as a nucleophile toward
complexes of transition metals have been isolated and hetero-unsaturated molecules or as a strong base inducing
thoroughly characterised, whereas related actinide compounds intermolecular C–H bond activations,5a,b whereas the uranium
have only sporadically been explored leaving many new metallacyclopropene (η5-C5Me5)2U[η2-C2(SiMe3)2] constitutes a
avenues in this area to be explored.2 This includes not only useful synthon for the (η5-C5Me5)2U(II) fragment when treated
novel reactivity patterns including small molecule activation,3 with unsaturated organic substrates.5f,g As a consequent exten-
but also addresses the questions of how 6d and 5f orbitals sion of these studies, we moved from all-carbon metallacycles
effect the reactivity patterns of actinide compounds in to metallaheterocycles. Herein, we report on the synthesis,
general.4 These inherent questions also led us to prepare and electronic structure, and structure–reactivity relationship of
the three-membered diphosphido thorium metallaheterocycle
complex [η5-1,3-(Me3C)2C5H3]2Th[η2-P2(2,4,6-iPr3C6H2)2] (4). In
addition, the reactivity pattern of 4 is compared to that of the
aDepartment of Chemistry, Beijing Normal University, Beijing 100875, China.
E-mail: gzi@bnu.edu.cn
related thorium metallacyclopropenes.5a,b
bInstitut für Anorganische und Analytische Chemie, Technische Universität
Braunschweig, Hagenring 30, 38106 Braunschweig, Germany.
E-mail: mwalter@tu-bs.de
Results and discussion
†Electronic supplementary information (ESI) available: Crystal parameters.
Cartesian coordinates of all stationary points optimized at the B3PW91-PCM
level. CCDC 1899191–1899195. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/c9dt01160a
The reaction of [η5-1,3-(Me3C)2C5H3]2ThCl2 (1) with 1 equiv. of
2,4,6-iPr3C6H2PHK in benzene affords [η5-1,3-(Me3C)2C5H3]2Th
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(Cl)(PH-2,4,6-iPr3C6H2) (2) in 90% yield (Scheme 1). The mole- 2,4,6-iPr3C6H2PHK in benzene to yield [η5-1,3-(Me3C)2C5H3]2Th
cular structure of 2 is shown in Fig. 1, and the selected bond (PH-2,4,6-iPr3C6H2)2 (3) in 80% yield (Scheme 1). Contrary to
distances and angles are listed in Table 1. The Th–P distance the reaction of [η5-1,2,4-(Me3C)3C5H2]2ThCl2 with 2,4,6-
of 2.865(3) Å is ca. 0.2 Å longer than the Th–Cl distance of (Me3C)3C6H2PHK,2t complex 3 can also be prepared in 70% yield
2.637(3) Å, and the angle of P–Th–Cl is 99.7(1)°. In a subsequent when [η5-1,3-(Me3C)2C5H3]2ThCl2 (1) is treated with 2 equiv. of
salt metathesis step, 2 is exposed to a second molecule of 2,4,6-iPr3C6H2PHK (Scheme 1). It is noteworthy that no thorium
phosphinidene [η5-1,3-(Me3C)2C5H3]2ThvP-2,4,6-iPr3C6H2 is
formed under these conditions. Complex 3 was structurally auth-
enticated (Fig. 2) and relevant bond distances and angles are
given in Table 1. The Th–P distances of 2.891(4) and 2.808(3) Å
are in the same range as that found in 2, while the P–Th–P angle
is 94.6(1)°. Finally, heating of [η5-1,3-(Me3C)2C5H3]2Th
(PH-2,4,6-iPr3C6H2)2 (3) in toluene at 75 °C affords the desired
three-membered diphosphido thorium metallaheterocycle
complex [η5-1,3-(Me3C)2C5H3]2Th[η2-P2(2,4,6-iPr3C6H2)2] (4) in
85% yield and with concomitant H2 release (Scheme 2). We
anticipate that the reaction mechanism is analogous to that
proposed for the related zirconium complex (η5-C5Me5)2Zr(η2-
P2Mes2):6 heating of the bis(phosphido) compound 3 elimin-
ates 2,4,6-iPr3C6H2PH2 to give a phosphinidene intermediate,
which immediately forms a phosphido hydride complex with
Scheme 1 Synthesis of complexes 2 and 3.
Fig. 1 Molecular structure of 2 (thermal ellipsoids drawn at the 35%
Fig. 2 Molecular structure of 3 (thermal ellipsoids drawn at the 35%
probability level).
probability level).
Table 1 Selected distances (Å) and angles (°) for compounds 2–3, 5 and 9–10a
Compound C(Cp)–Thb C(Cp)–Thc Cp(cent)–Thb Th–X
Cp(cent)–Th–Cp(cent) X–Th–X/Y
2
3
5
9
2.801(14)
2.811(12)
2.853(3)
2.829(4)
2.863(3)
2.695(14) to 2.849(11) 2.528(12)
2.711(12) to 2.875(10) 2.540(10)
Cl1: 2.637(3), P1: 2.865(3)
P1: 2.891(4), P2: 2.808(3)
P1: 2.934(1), P2: 2.778(1), N1: 2.620(3) 124.6(1)
N1: 2.227(3), P2: 2.906(1)
O1: 2.175(2), O2: 2.138(2)
127.0(3)
125.9(4)
99.7(1)
94.6(1)
44.5(1)d
67.4(1)
84.8(1)
2.757(3) to 2.965(3)
2.786(4) to 2.864(4)
2.808(3) to 2.945(3)
2.587(3)
2.560(4)
2.598(3)
119.3(1)
116.1(1)
10
a Cp = cyclopentadienyl ring. b Average value. c Range. d The angle defined by P1–Th–P2.
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ΔG‡(298 K) = 27.9 kcal mol−1, which is consistent with the
experimental observations. In contrast, the computed reaction
barrier for the alternative reaction mechanism of a direct H2
elimination from the bis(phosphido) 3 to form 4 via transition
state TS4d is much larger (ΔG‡(298 K) = 70.9 kcal mol−1
)
(Fig. S1, ESI†). This is not in line with experimental findings
and can therefore be discounted. To fully characterize
complex 4, various spectroscopic techniques and elemental
analysis were employed. Its 31P{1H} NMR spectrum features a
singlet at δ = 81.9 ppm, corresponding to the coordinated
[η2-P2(2,4,6-iPr3C6H2)2] diphosphido moiety.2 Consistent with a
strong coordination of the diphosphido {[2,4,6-iPr3C6H2P]2}2−
fragment, no dissociation is observed when 4 is heated to
100 °C as established by variable-temperature 1H NMR spec-
troscopy (20–100 °C). Furthermore, no exchange of dipho-
sphene (2,4,6-iPr3C6H2P)2 with internal alkynes such as
MeCuCMe, PhCuCMe and PhCuCPh was observed at elev-
ated temperatures on a chemical time scale, which is analogy
to the observations on thorium metallacyclopropene
complexes.5a
Scheme 2 Synthesis of complex 4.
2,4,6-iPr3C6H2PH2, which further releases H2 to yield
4
To further evaluate the interaction between the thorium
atom and the [(2,4,6-iPr3C6H2)2P2] moiety, a computational
study was undertaken at the DFT level of theory (B3PW91).
Consistent with the experimental molecular structure, the
computed gas-phase structure features an asymmetric Th[η2-
P2(2,4,6-iPr3C6H2)2] fragment with two in-plane Th–P σ-bonds
and two out-of-plane π-bonds interacting with the metal centre
(Fig. 4). Based on a natural localized molecular orbital (NLMO)
analysis, the P–P σ-bond is formed by two phosphorus hybrid
orbitals (43.5%; 9.3% 3s and 90.7% 3p; and 46.3%; 13.5% 3s
and 86.5% 3p) along with a minor contribution from a
thorium hybrid orbital (8.6%; 51.4% 5f and 43.6% 6d and
2.3% 7p and 2.7% 7s). The asymmetry in the Th–P bond dis-
tances is also reflected in different orbital contributions based
on the NLMO analysis. The σ1(Th–P) bond is composed of a
phosphorus hybrid orbital (72.5%; 27.3% 3s and 72.7% 3p)
(Scheme 2). Alternatively, complex 4 may also be directly
formed by the elimination of H2 from the bis(phosphido)
species 3 upon heating (Scheme 2). To differentiate between
these two potential reaction pathways, DFT computations were
performed. These computational studies suggest that indeed 3
initially eliminates 2,4,6-iPr3C6H2PH2 to give the phosphini-
dene intermediate INT4a via the transition state TS4a (Fig. 3).
In the next step, the phosphinidene intermediate INT4a reacts
with 2,4,6-iPr3C6H2PH2 to afford a phosphido hydride inter-
mediate INT4b via the transition state TS4b. Finally, H2 is
eliminated from the phosphido hydride species INT4b to yield
4 via the transition state TS4c. Overall, the formation of 4 + H2
from
3 is energetically favourable (ΔG(298 K) = −11.0
kcal mol−1) and occurs with a moderate reaction barrier of
Fig. 3 Energy profile (kcal mol−1) for the formation of 4 + H2 (com-
puted at T = 298 K). [Th] = [η5-1,3-(Me3C)2C5H3]2Th. Ar = 2,4,6-iPr3C6H2.
Fig. 4 Plots of HOMOs for 4 (the hydrogen atoms have been omitted
for clarity).
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and a thorium hybrid orbital (23.3%; 15.5% 5f and 72.0% 6d
and 4.0% 7p and 8.5% 7s), whereas the σ2(Th–P) bond consists
of a phosphorus hybrid orbital (74.1%; 9.9% 3s and 90.1% 3p)
and a thorium hybrid orbital (21.3%; 28.7% 5f and 68.9% 6d
and 1.4% 7p and 1.0% 7s). This asymmetry also carries on to
the Th–P π bonds. The π1(Th–P) bond is composed of a phos-
phorus hybrid orbital (88.3%; 47.3% 3s and 52.7% 3p) with a
thorium hybrid orbital (7.6%; 44.5% 5f and 28.1% 6d and
20.4% 7p and 7.0% 7s), whereas the π2(Th–P) bond is based on
a phosphorus hybrid orbital (80.0%; 53.2% 3s and 46.8% 3p)
and a thorium hybrid orbital (18.1%; 22.9% 5f and 54.7% 6d
and 10.3% 7p and 12.1% 7s). These computations imply that
6d and 5f orbital contributions are easily modulated and
that electron density from the π-orbitals of the
[η2-P2(2,4,6-iPr3C6H2)2] fragment can be readily transferred to
the Lewis-acidic thorium atom. In contrast to the related
thorium metallacyclopropene complexes,5a,f more covalent
bonds
between
the
[1,3-(Me3C)2C5H3]2Th2+
and
[η2-P2(2,4,6-iPr3C6H2)2]2− fragments are realized. This also
causes larger Wiberg bond orders for the Th–P bonds (1.06
and 1.29) than those found for the Th–C bond in the thorium
metallacyclopropene
complex
[1,2,4-(Me3C)3C5H2]2Th(η2-
C2Ph2) (0.53). Consequently, 4 forms the DMAP adduct [η5-1,3-
(Me3C)2C5H3]2Th[η2-P2(2,4,6-iPr3C6H2)2](DMAP) (5) with 4-di-
methylaminopyridine (DMAP) in 95% yield (Scheme 3),
whereas upon the addition of pyridine derivatives to the
thorium
metallacyclopropene
[1,2,4-(Me3C)3C5H2]2Th(η2-
C2Ph2), pyridine deprotonation is observed.5b Fig. 5 shows the
molecular structure of 5, and the interested reader may refer to
Table 1 for the selected bond distances and angles. The Th–N
distance is 2.620(3) Å, whereas the Th–P distances are signifi-
cantly different with 2.934(1) and 2.778(1) Å as a direct result
of the DMAP coordination, but still comparable to that found
in [1,2,4-(Me3C)3C5H2]2Th(η2-P2Ph2) (2.877(1) Å).2t
Scheme 3 Synthesis of complexes 5–10.
Similar to the reactivity of the bis(phosphido) thorium
complex [H2B(3-Mes-C3H2N2)2]2Th(PHMes)2 (Mes
= 2,4,6-
Me3Ph) toward bipy,2m reductive elimination occurs in the
reaction of complex 4 and bipy, that is, the coordinated dipho-
sphene (2,4,6-iPr3C6H2P)2 in 4 is replaced by bipy to give
[η5-1,3-(Me3C)2C5H3]2Th(bipy) (6) in quantitative conversion
(Scheme 3). This contrasts the reactivity of the thorium
metallacyclopropene [1,2,4-(Me3C)3C5H2]2Th(η2-C2Ph2), but
resembles that of the uranium metallacyclopropene
(η5-C5Me5)2U[η2-C2(SiMe3)2] towards bipy.5f Nevertheless, in
contrast to the reactivity of the bis(phosphido) thorium
complex [H2B(3-Mes-C3H2N2)2]2Th(PHMes)2 toward bipy,2m
complex 6 was not formed when 3 was exposed to bipy. In
addition, the replacement of the coordinated diphosphene
may also be achieved on the addition of Ph2S2 or Ph2Se2,
yielding the disulfido and diselenido complexes [η5-1,3-
(Me3C)2C5H3]2Th(EPh)2 (E = S (7), Se (8)), respectively, in
quantitative conversions (Scheme 3).
Fig. 5 Molecular structure of 5 (thermal ellipsoids drawn at the 35%
probability level).
Nevertheless, despite some differences, there are also simi-
larities with the reactivity observed for the thorium metallacyclo- (η2-P2Mes2) towards hetero-unsaturated molecules,6 complex 4
propene [1,2,4-(Me3C)3C5H2]2Th(η2-C2Ph2).5a For example, in also inserts hetero-unsaturated organic substrates. The addition
analogy to the reactivity of the zirconium complex (η5-C5Me5)2Zr of 1 equiv. of PhCN to 4 yields the mono-insertion product
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[η5-1,3-(Me3C)2C5H3]2Th[NCPh{P2(2,4,6-iPr3C6H2)2}] (9) in quanti-
tative conversion (Scheme 3). DFT computations imply that this
reaction is exergonic (ΔG(298 K) = −15.0 kcal mol−1), and occurs
via the transition state TS9 with a low activation barrier
(ΔG‡(298 K) = 17.4 kcal mol−1) (Fig. 6). This is consistent with
the rapid formation of 9 at ambient temperature. The molecular
structure of 9 is shown in Fig. 7, and the selected bond distances
and angles are provided in Table 1. The Th–N and Th–P dis-
tances of 2.227(3) Å and 2.906(1) Å, respectively, are comparable
to those found in 5 (Table 1). However, when complex 4 is
exposed to p-ClPhCHO, only the seven-membered metallahetero-
cycle [η5-1,3-(Me3C)2C5H3]2Th[OCH(p-ClPh){P2(2,4,6-iPr3C6H2)2}
CH(p-ClPh)O] (10) (Scheme 3) is isolated irrespective of the
amount of aldehyde (p-ClPhCHO) added to the reaction mixture.
Presumably, as in the case of PhCN, complex 4 converts initially
with p-ClPhCHO to a five-membered metallaheterocycle, in
which a second molecule of p-ClPhCHO can insert to yield
complex 10. Fig. 8 depicts the molecular structure of 10, while
Table 1 lists assorted bond distances and angles. The Th–O dis-
Fig. 8 Molecular structure of 10 (thermal ellipsoids drawn at the 35%
probability level).
tances of 2.175(2) and 2.138(2) Å are close to those found in
(η5-C5Me5)2Th[OCH(p-ClPh)(C4Ph2)CH(p-ClPh)O] (2.157(4) and
2.150(4) Å).5d
Conclusions
In conclusion, the synthesis, electronic structure and reactivity
of the three-membered diphosphido thorium metallaheterocycle
complex [η5-1,3-(Me3C)2C5H3]2Th[η2-P2(2,4,6-iPr3C6H2)2] (4) were
comprehensively studied. Similar to the related thorium
metallacyclopropenes,5a,f density functional theory (DFT) studies
reveal that 5f and 6d orbitals contribute to the bonding within
the metallaheterocycle Th-(η2-P-P) moiety, but the bonds
between [η5-1,3-(Me3C)2C5H3]2Th2+ and [η2-P2(2,4,6-iPr3C6H2)2]2−
fragments and their contribution to the bonding are modulated.
Fig. 6 Energy profile (kcal mol−1) for the reaction of 4 + PhCN (com-
puted at T = 298 K). [Th] = [η5-1,3-(Me3C)2C5H3]2Th. Ar = 2,4,6-iPr3C6H2.
While
the
thorium
metallacyclopropene
[η5-1,2,4-
(Me3C)3C5H2]2Th(η2-C2Ph2) reacts as a strong base inducing
intermolecular C–H bond activations with pyridine derivatives,5b
the coordinated [η2-P2(2,4,6-iPr3C6H2)2] diphosphido ligand in 4
is inert towards DMAP and only the adduct [η5-1,3-
(Me3C)2C5H3]2Th[η2-P2(2,4,6-iPr3C6H2)2](DMAP) (5) is isolated.
Furthermore, whereas the coordinated alkyne in the thorium
metallacyclopropene [η5-1,2,4-(Me3C)3C5H2]2Th(η2-C2Ph2) is inert
towards ligand exchange,5a,f complex 4 may serve as a synthetic
equivalent for [η5-1,3-(Me3C)2C5H3]2Th(II) in the reaction with
bipy, Ph2S2 or Ph2Se2, which results in the displacement of the
coordinated diphosphene. However, in analogy to the reactivity
of the related thorium metallacyclopropenes,5a complex 4 shows
no reactivity towards alkynes, but it behaves as a nucleophile
toward hetero-unsaturated molecules such as nitriles and alde-
hydes, resulting in five- or seven-membered metallaheterocycles.
Further investigations dealing with the intrinsic reactivity of acti-
nide metallaheterocycles are currently in progress.
Fig. 7 Molecular structure of 9 (thermal ellipsoids drawn at the 35%
probability level).
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removed. The residue was extracted with n-hexane (10 mL × 3)
and filtered. The volume of the filtrate was reduced to 10 mL
and orange crystals of 3 were isolated when this solution was
Experimental
General methods
All reactions and product manipulations were carried out stored at room temperature for two days. Yield: 423 mg (80%)
under an atmosphere of dry dinitrogen with rigid exclusion of (found: C, 63.69; H, 8.51. C56H90P2Th requires C, 63.61; H,
1
air and moisture using standard Schlenk or cannula tech- 8.58%). M.p.: 167–169 °C (dec.). H NMR (C6D6): δ 7.23 (s, 4H,
niques, or in a glovebox. All organic solvents were freshly dis- phenyl), 6.54 (s, 2H, ring CH), 6.23 (d, J = 1.3 Hz, 4H, ring CH),
tilled from sodium benzophenone ketyl immediately prior to 4.71 (d, JP–H = 233 Hz, 2H, PH), 4.06 (m, 4H, CH(CH3)2), 2.91
use. [η5-1,3-(Me3C)2C5H3]2ThCl2 (1),4g 2,4,6-iPr3C6H2PH2 and (m, 2H, CH(CH3)2), 1.49 (d, J = 6.7 Hz, 24H, CH(CH3)2), 1.31 (d,
7
2,4,6-iPr3C6H2PHK8 were prepared according to literature J = 6.9 Hz, 12H, CH(CH3)2), 1.25 (s, 36H, C(CH3)3) ppm. 13C
methods. All other chemicals were purchased from Aldrich {1H} NMR (C6D6): 151.3 (d, JP–C = 6.6 Hz, phenyl C), 150.8
Chemical Co. and Beijing Chemical Co. and used as received (phenyl C), 147.3 (phenyl C), 139.1 (d, JP–C = 12.7 Hz,
unless otherwise noted. Infrared spectra were recorded in KBr phenyl C), 120.6 (d, JP–C = 2.6 Hz, ring C), 115.7 (ring C), 112.4
pellets on an Avatar 360 Fourier transform spectrometer. 1H, (ring C), 34.6 (CH(CH3)2), 34.0 (d, JP–C = 12 Hz, C(CH3)3), 33.6
13C{1H} and 31P{1H} NMR spectra were recorded on a Bruker (CH(CH3)2), 32.4 (C(CH3)3), 24.6 (CH(CH3)2), 24.3 (CH(CH3)2)
AV 400 spectrometer at 400, 100 and 162 MHz, respectively. All ppm. 31P{1H} NMR (C6D6): δ 9.8 ppm. IR (KBr, cm−1): ν
chemical shifts are reported in δ units with reference to the 2958 (s), 1599 (m), 1460 (s), 1359 (s), 1249 (s), 1057 (s), 802 (s).
residual protons of the deuterated solvents, which served as
internal standards, for proton and carbon chemical shifts, and added to
Method B. Solid 2,4,6-iPr3C6H2PHK (274 mg, 1.0 mmol) was
a
benzene (20 mL) solution of [η5-1,3-
to external 85% H3PO4 (0.00 ppm) for phosphorus chemical (Me3C)2C5H3]2ThCl2 (1; 329 mg, 0.5 mmol) with stirring at
shifts. Melting points were measured on X-6 melting point room temperature. After the solution was stirred at room temp-
apparatus and were uncorrected. Elemental analyses were per- erature overnight, the solvent was removed. The residue was
formed on a Vario EL elemental analyzer.
extracted with n-hexane (10 mL × 3) and filtered. The volume
of the filtrate was reduced to 10 mL and orange crystals of 3
were isolated when this solution was kept at room temperature
Syntheses
Preparation of [η5-1,3-(Me3C)2C5H3]2Th(Cl)(PH-2,4,6-iPr3C6H2)· for two days. Yield: 370 mg (70%).
0.5C6H6 (2·0.5C6H6). Solid 2,4,6-iPr3C6H2PHK (274 mg,
Preparation of [η5-1,3-(Me3C)2C5H3]2Th[η2-P2(2,4,6-iPr3C6H2)2]
1.0 mmol) was added to a benzene (20 mL) solution of [η5-1,3- (4). Method A. After a toluene (15 mL) solution of [η5-1,3-
(Me3C)2C5H3]2ThCl2 (1; 657 mg, 1.0 mmol) with stirring at (Me3C)2C5H3]2Th(PH-2,4,6-iPr3C6H2)2 (3; 529 mg, 0.5 mmol)
room temperature. After the solution was stirred at room temp- was stirred at 75 °C for 3 days, the solvent was removed. The
erature overnight, the solvent was removed. The residue was residue was extracted with THF (10 mL × 3) and filtered. The
extracted with n-hexane (10 mL × 3) and filtered. The volume volume of the filtrate was reduced to 10 mL and orange micro-
of the filtrate was reduced to 10 mL, yellow crystals of crystals of 4 were isolated when this solution was stored at
2·0.5C6H6 were isolated when this solution was stored at room room temperature for two days. Yield: 448 mg (85%) (found: C,
temperature for two days. Yield: 806 mg (90%) (found: C, 63.79; H, 8.39. C56H88P2Th requires C, 63.74; H, 8.41%). M.p.:
1
58.91; H, 7.81. C44H69ClPTh requires C, 58.95; H, 7.76%). M.p.: 176–178 °C (dec.). H NMR (C6D6): δ 7.27 (s, 4H, phenyl), 6.62
1
111–113 °C (dec.). H NMR (C6D6): δ 7.22 (s, 2H, phenyl), 7.15 (s, 2H, ring CH), 6.29 (d, J = 1.3 Hz, 4H, ring CH), 4.63 (br s,
(s, 3H, C6H6), 6.60 (s, 2H, ring CH), 6.18 (s, 2H, ring CH), 6.16 4H, CH(CH3)2), 2.90 (m, 2H, CH(CH3)2), 1.47 (d, J = 6.7 Hz,
(s, 2H, ring CH), 4.78 (d, JP–H = 227 Hz, 1H, PH), 3.93 (m, 2H, 24H, CH(CH3)2), 1.29 (d, J = 6.9 Hz, 12H, CH(CH3)2), 1.28 (s,
CH(CH3)2), 2.89 (m, 1H, CH(CH3)2), 1.50 (d, J = 6.4 Hz, 12H, 36H, C(CH3)3) ppm. 13C{1H} NMR (C6D6): 152.8 (phenyl C),
CH(CH3)2), 1.34 (s, 18H, C(CH3)3), 1.29 (s, 18H, C(CH3)3), 1.29 149.8 (phenyl C), 146.1 (phenyl C), 120.8 (ring C), 117.3
(d, J = 5.8 Hz, 6H, CH(CH3)2) ppm. 13C{1H} NMR (C6D6): 151.4 (ring C), 113.1 (ring C), 34.4 (CH(CH3)2), 33.4 (C(CH3)3), 31.4
(d, JP–C = 7.7 Hz, phenyl C), 151.3 (phenyl C), 151.0 (ring C), (C(CH3)3), 25.8 (CH(CH3)2), 25.0 (CH(CH3)2), 24.5 (CH(CH3)2)
147.2 (phenyl C), 137.8 (d, JP–C = 16.5 Hz, phenyl C), 128.5 ppm; one carbon of phenyl overlapped. 31P{1H} NMR (C6D6):
(C6H6), 120.5 (d, JP–C = 4.5 Hz, ring C), 118.3 (ring C), 112.7 δ 81.9 ppm. IR (KBr, cm−1): ν 2962 (s), 1404 (s), 1257 (s),
(ring C), 112.6 (ring C), 34.6 (C(CH3)3), 34.2 (d, JP–C = 12.0 Hz, 1087 (s), 1018 (s), 802 (s).
C(CH3)3), 33.6 (CH(CH3)2), 33.5 (CH(CH3)2), 32.2 (C(CH3)3),
Method B. NMR scale. After a J. Young NMR tube charged
32.1 (C(CH3)3), 24.6 (CH(CH3)2), 24.1 (CH(CH3)2) ppm. 31P{1H} with [η5-1,3-(Me3C)2C5H3]2Th(PH-2,4,6-iPr3C6H2)2 (3; 21 mg,
NMR (C6D6): δ −2.6 ppm. IR (KBr, cm−1): ν 2960 (s), 2902 (s), 0.02 mmol) and C6D6 (0.5 mL) was stored at 75 °C for 3 days,
1462 (s), 1396 (s), 1249 (s), 1097 (s), 1020 (s), 800 (s).
Preparation of [η5-1,3-(Me3C)2C5H3]2Th(PH-2,4,6-iPr3C6H2)2 (3). observed by 1H NMR spectroscopy (100% conversion).
Method A. Solid 2,4,6-iPr3C6H2PHK (137 mg, 0.5 mmol) was Preparation of [η5-1,3-(Me3C)2C5H3]2Th[η2-P2(2,4,6-iPr3C6H2)2]
added to
resonances of 4 and H2 (1H NMR (C6D6): δ 4.47 ppm) were
a
benzene (20 mL) solution of [η5-1,3- (DMAP) (5). A benzene (5 mL) solution of DMAP (31 mg,
(Me3C)2C5H3]2Th(Cl)(PH-2,4,6-iPr3C6H2) (2; 429 mg, 0.5 mmol) 0.25 mmol) was added to a benzene (10 mL) solution of [η5-
with stirring at room temperature. After the solution was 1,3-(Me3C)2C5H3]2Th[η2-P2(2,4,6-iPr3C6H2)2] (4; 263 mg,
stirred at room temperature overnight, the solvent was 0.25 mmol) with stirring at room temperature. After this solu-
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tion was stirred at room temperature for 1 h, the solution was n-hexane solution by a similar procedure to that in the synthesis
filtered. The volume of the filtrate was reduced to 5 mL and of 6. Yield: 173 mg (86%). 1H NMR (C6D6): δ 7.79 (d, J = 8.1 Hz,
orange crystals of 5 were isolated when this solution was 4H, phenyl), 7.11 (t, J = 7.7 Hz, 4H, phenyl), 6.92 (t, J = 7.4 Hz,
stored at room temperature for 3 days. Yield: 280 mg (95%) 2H, phenyl), 6.22 (d, J = 2.7 Hz, 4H, ring CH), 6.13 (t, J = 1.8 Hz,
(found: C, 64.29; H, 8.31; N, 2.40. C63H98N2P2Th requires C, 2H, ring CH), 1.34 (s, 36H, C(CH3)3) ppm. These spectroscopic
64.26; H, 8.39; N, 2.38%). M.p.:195–197 °C (dec.). 1H NMR data agreed with those reported in the literature.2t
(C6D6): δ 9.01 (br s, 2H, DMAP), 7.35 (s, 2H, phenyl), 7.26 (s,
Method B. NMR scale. A C6D6 (0.3 mL) solution of Ph2S2
2H, phenyl), 7.01 (s, 1H, ring CH), 6.86 (s, 1H, ring CH), 6.43 (4.4 mg, 0.02 mmol) was slowly added to a J. Young NMR tube
(br s, 2H, DMAP), 6.16 (br s, 2H, ring CH), 6.08 (s, 1H, ring charged with [η5-1,3-(Me3C)2C5H3]2Th[η2-P2(2,4,6-iPr3C6H2)2]
CH), 5.91 (s, 1H, ring CH), 5.13 (br s, 2H, CH(CH3)2), 4.90 (br s, (4; 21 mg, 0.02 mmol) and C6D6 (0.2 mL). Resonances of 7
2H, CH(CH3)2), 2.94 (br s, 2H, CH(CH3)2), 1.97 (s, 6H, along with those of (2,4,6-iPr3C6H2P)4 were observed by NMR
N(CH3)2), 1.81 (br s, 12H, CH(CH3)2), 1.54 (br s, 12H, CH spectroscopy (100% conversion) after the sample was stored at
(CH3)2), 1.36 (br s, 24H, CH(CH3)2 and C(CH3)3), 0.97 (br s, room temperature overnight.
24H, CH(CH3)2 and C(CH3)3) ppm. 13C{1H} NMR (C6D6): δ
Preparation of [η5-1,3-(Me3C)3C5H2]2Th(SePh)2 (8). Method A.
171.1 (aryl C), 150.3 (aryl C), 137.8 (aryl C), 129.3 (aryl C), 128.5 This compound was isolated as yellow crystals from the reac-
(aryl C), 128.3 (aryl C), 125.6 (ring C), 121.8 (ring C), 38.0 tion of [η5-1,3-(Me3C)2C5H3]2Th[η2-P2(2,4,6-iPr3C6H2)2] (4;
(NCH3), 34.6 (C(CH3)3), 34.5 (C(CH3)3), 34.1 (CH(CH3)2), 32.9 263 mg, 0.25 mmol) and Ph2Se2 (78 mg, 0.25 mmol) in
(CH(CH3)2), 32.6 (C(CH3)3), 32.5(C(CH3)3), 25.8 (CH(CH3)2), benzene (15 mL) at room temperature and recrystallization
24.5 (CH(CH3)2), 24.2 (CH(CH3)2), 21.4 (CH(CH3)2) ppm; other from an n-hexane solution by a similar procedure to that in
carbons were not observed. 31P{1H} NMR (C6D6): 14.4 (d, JP–P
=
the synthesis of 6. Yield: 189 mg (84%). 1H NMR (C6D6): δ 8.00
233.0 Hz), −2.6 (d, JP–P = 233.0 Hz) ppm. IR (KBr, cm−1): ν 2960 (d, J = 5.2 Hz, 4H, phenyl), 7.08 (s, 4H, phenyl), 6.98 (d, J = 5.2
(s), 1384 (s), 1259 (s), 1091 (s), 1020 (s), 800 (s).
Hz, 2H, phenyl), 6.18 (s, 6H, ring CH), 1.33 (s, 36H, (CH3)3C).
Preparation of [η5-1,3-(Me3C)2C5H3]2Th(bipy) (6). Method A. These spectroscopic data agreed with those reported in the
A benzene (5 mL) solution of bipy (39 mg, 0.25 mmol) was literature.9
added to
a
benzene (10 mL) solution of [η5-1,3-
Method B. NMR scale. A C6D6 (0.3 mL) solution of Ph2Se2
mg, (6.2 mg, 0.02 mmol) was slowly added to a J. Young NMR tube
(Me3C)2C5H3]2Th[η2-P2(2,4,6-iPr3C6H2)2]
(4;
263
0.25 mmol) with stirring at room temperature. After the solu- charged with [η5-1,3-(Me3C)2C5H3]2Th[η2-P2(2,4,6-iPr3C6H2)2]
tion was stirred at ambient temperature overnight, the solvent (4; 21 mg, 0.02 mmol) and C6D6 (0.2 mL). Resonances of 8
was removed. The residue was extracted with n-hexane (10 mL along with those of (2,4,6-iPr3C6H2P)4 were observed by NMR
× 3) and filtered. The volume of the filtrate was reduced to spectroscopy (100% conversion) after the sample was stored at
4 mL and purple crystals of 6 were isolated when this solution room temperature overnight.
was kept at room temperature for two days. Yield: 152 mg
Preparation of [η5-1,3-(Me3C)2C5H3]2Th[NCPh{P2(2,4,6-iPr3
1
(82%). H NMR (C6D6): δ 7.29 (d, J = 6.4 Hz, 2H, bipy), 6.89 (d, C6H2)2}]·C6H6·0.5C6H14 (9·C6H6·0.5C6H14). Method A. This
J = 9.6 Hz, 2H, bipy), 6.20 (d, J = 2.4 Hz, 4H, ring CH), 6.14 (m, compound was isolated as green crystals from the reaction of
2H, bipy), 5.95 (t, J = 2.4 Hz, 2H, ring CH), 5.30 (t, J = 6.0 Hz, [η5-1,3-(Me3C)2C5H3]2Th[η2-P2(2,4,6-iPr3C6H2)2] (4; 263 mg,
2H, bipy), 1.22 (s, 36H, (CH3)3C) ppm. These spectroscopic 0.25 mmol) and PhCN (26 mg, 0.25 mmol) in benzene (15 mL)
data agreed with those reported in the literature.9
at room temperature and recrystallization from an n-hexane
Method B. NMR scale. A C6D6 (0.3 mL) solution of bipy solution by a similar procedure to that in the synthesis of 6.
(3.1 mg, 0.02 mmol) was slowly added to a J. Young NMR tube Yield: 253 mg (79%) (found: C, 67.59; H, 8.32; N, 1.07.
charged with [η5-1,3-(Me3C)2C5H3]2Th[η2-P2(2,4,6-iPr3C6H2)2] C72H106NP2Th requires C, 67.58; H, 8.35; N, 1.09%). M.
1
(4; 21 mg, 0.02 mmol) and C6D6 (0.2 mL). Resonances of 6 p.:180–182 °C (dec.). H NMR (C6D6): δ 7.99 (d, J = 7.6 Hz, 2H,
along with those of (2,4,6-iPr3C6H2P)2 (1H NMR (C6D6): δ 7.12 phenyl), 7.15 (s, 6H, C6H6), 6.99 (m, 7H, phenyl), 6.71 (s, 4H,
(s, 2H, phenyl), 3.44 (m, 2H, CH(CH3)2), 2.83 (m, 1H, ring CH), 6.54 (s, 2H, ring CH), 4.53 (br s, 1H, CH(CH3)2), 4.05
CH(CH3)2), 1.31 (d, J = 6.9 Hz, 12H, CH(CH3)2), 1.18 (d, J = 6.9 (br s, 2H, CH(CH3)2), 3.64 (m, 1H, CH(CH3)2), 2.77 (m, 1H,
Hz, 6H, CH(CH3)2) ppm; 31P{1H} NMR (C6D6): 517.9 ppm)10a CH(CH3)2), 2.63 (m, 1H, CH(CH3)2), 1.53 (s, 18H, C(CH3)3),
were observed by NMR spectroscopy (40% conversion in 2 h), 1.42 (s, 18H, C(CH3)3), 1.26 (d, J = 7.5 Hz, 6H, CH(CH3)2), 1.23
and conversion to 6 was completed after the sample was stored (m, 16H, CH2 and CH(CH3)2), 1.20 (d, J = 7.4 Hz, 6H, CH
at room temperature overnight. Nevertheless, diphosphene (CH3)2), 1.16 (d, J = 7.2 Hz, 6H, CH(CH3)2), 1.09 (d, J = 7.4 Hz,
(2,4,6-iPr3C6H2P)2 is unstable, which dimerizes to cyclotetra- 6H, CH(CH3)2), 0.88 (t, 3H, J = 7.8 Hz, CH3) ppm. 13C{1H} NMR
phosphane (2,4,6-iPr3C6H2P)4 (31P{1H} NMR (C6D6):
δ
(C6D6): δ 156.0 (phenyl C), 153.9 (phenyl C), 153.4 (phenyl C),
150.4 (phenyl C), 149.9 (d, JP–C = 21.2 Hz, NvC), 147.9 (phenyl
−35.9 ppm)10 during the course of the reaction.
Preparation of [η5-1,3-(Me3C)2C5H3]2Th(SPh)2 (7). Method A. C), 139.1 (d, JP–C = 41.0 Hz, phenyl C), 138.2 (d, JP–C = 56.8 Hz,
This compound was isolated as colourless crystals from the phenyl C), 132.6 (phenyl C), 130.0 (phenyl C), 129.3
reaction of [η5-1,3-(Me3C)2C5H3]2Th[η2-P2(2,4,6-iPr3C6H2)2] (4; (phenyl C), 129.0 (phenyl C), 128.6 (phenyl C), 128.5 (C6H6),
263 mg, 0.25 mmol) and Ph2S2 (55 mg, 0.25 mmol) in benzene 125.6 (ring C), 123.8 (ring C), 122.2 (ring C), 121.8 (ring C),
(15 mL) at room temperature and recrystallization from an 111.9 (ring C), 34.7 (C(CH3)3), 34.5 (C(CH3)3), 33.9 (CH(CH3)2),
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33.6 (C(CH3)3), 33.3 (CH(CH3)2), 32.7 (C(CH3)3), 32.2 (CH X-ray crystallography
(CH3)2), 31.9 (CH2), 31.0 (CH(CH3)2), 25.8 (CH(CH3)2), 24.5 (CH
Single-crystal X-ray diffraction measurements were carried out
on a Rigaku Saturn CCD diffractometer at 100(2) K using
Cu Kα radiation (λ = 1.54184 Å). An empirical absorption cor-
rection was applied using the SADABS program.11 All struc-
tures were solved by direct methods and refined by full-matrix
least squares on F2 using the SHELXL program package.12 All
the hydrogen atoms were geometrically fixed using the riding
model. The crystal data and experimental data for 2–3, 5 and
9–10 are summarized in the ESI.† Selected bond distances and
angles are listed in Table 1.
(CH3)2), 24.2 (CH(CH3)2), 24.2 (CH(CH3)2), 23.0 (CH2), 14.3
(CH3) ppm. 31P{1H} NMR (C6D6): δ 104.2 (br s, ThP), −0.9 (br s,
ThPP) ppm. IR (KBr, cm−1): ν 2960 (s), 1460 (s), 1388 (s),
1259 (s), 1093 (s), 1022(s), 800 (s).
Method B. NMR scale. A C6D6 (0.3 mL) solution of PhCN
(2.1 mg, 0.02 mmol) was slowly added to a J. Young NMR tube
charged with [η5-1,3-(Me3C)2C5H3]2Th[η2-P2(2,4,6-iPr3C6H2)2]
(4; 21 mg, 0.02 mmol) and C6D6 (0.2 mL). Resonances of 9
were observed by 1H NMR spectroscopy (100% conversion in
10 min).
Preparation
of
[η5-1,3-(Me3C)2C5H3]2Th[OCH(p-ClPh)
(10·0.5C6H6).
Computational methods
{P2(2,4,6-iPr3C6H2)2}CH(p-ClPh)O]·0.5C6H6
Computations were carried out with the Gaussian 09 program
(G09),13 employing the B3PW91 functional, plus a polarizable
continuum model (PCM) (denoted as B3PW91-PCM), with
standard 6-31G(d) basis set for C, H, N and P elements, and a
Method A. This compound was isolated as colourless
crystals from the reaction of [η5-1,3-(Me3C)2C5H3]2Th[η2-
P2(2,4,6-iPr3C6H2)2] (4; 263 mg, 0.25 mmol) and p-ClPhCHO
(70 mg, 0.50 mmol) in benzene (15 mL) at room temperature
and recrystallization from an n-hexane solution by a similar
procedure as that in the synthesis of 6. Yield: 292 mg (85%)
(found: C, 63.71; H, 7.45. C73H101Cl2O2P2Th requires C, 63.74;
quasi-relativistic
5f-in-valence
effective-core
potential
(ECP60MWB) treatment with 60 electrons in the core region
for Th and the corresponding optimized segmented
((14s13p10d8f6g)/[10s9p5d4f3g]) basis set for the valence
shells of Th,14 to fully optimize the structures of reactants,
complexes, transition states, intermediates, and products, and
also to mimic the experimental toluene-solvent conditions
(dielectric constant ε = 2.379). All stationary points were sub-
sequently characterized by vibrational analyses, from which
their respective zero-point (vibrational) energy (ZPE) was
extracted and used in the relative energy determinations.
Furthermore, frequency calculations were performed to ensure
that the reactant, complex, intermediate, product and tran-
sition state structures remained at minima and 1st order
saddle points, respectively, on their potential energy
hypersurfaces.
1
H, 7.40%). M.p.: 155–157 °C (dec.). H NMR (C6D6): δ 7.34 (d,
J = 7.9 Hz, 4H, phenyl), 7.15 (s, 3H, C6H6), 7.08 (s, 2H, ring
CH), 7.00 (s, 2H, phenyl), 6.98 (s, 2H, phenyl), 6.74 (d, J =
7.8 Hz, 4H, phenyl), 6.54 (s, 2H, ring CH), 6.45 (s, 2H, ring
CH), 6.30 (s, 2H, CHO), 4.53 (br s, 2H, CH(CH3)2), 3.92 (br s,
2H, CH(CH3)2), 2.60 (m, 2H, CH(CH3)2), 1.78 (d, J = 5.7 Hz, 6H,
CH(CH3)2), 1.54 (s, 18H, C(CH3)3), 1.40 (d, J = 5.7 Hz, 12H, CH
(CH3)2), 1.24 (s, 18H, C(CH3)3), 1.06 (d, J = 6.7 Hz, 12H, CH
(CH3)2), 0.69 (d, J = 6.8 Hz, 6H, CH(CH3)2) ppm. 13C{1H} NMR
(C6D6): δ 155.0 (phenyl C), 150.7 (phenyl C), 148.7 (phenyl C),
143.0 (d, JP–C = 25.0 Hz, phenyl C), 132.8 (phenyl C), 129.8
(phenyl C), 128.6 (phenyl C), 128.5 (C6H6), 124.0 (phenyl C),
121.9 (ring C), 114.4 (ring C), 113.0 (ring C), 112.1 (d, JP–C
=
30.0 Hz, OCH), 110.7 (ring C), 109.9 (ring C), 33.6 (C(CH3)3),
33.3 (C(CH3)3), 33.0 (CH(CH3)2), 32.6 (C(CH3)3), 32.2 (C(CH3)3),
26.9 (CH(CH3)2), 25.5 (CH(CH3)2), 24.2 (CH(CH3)2), 23.9 (CH
(CH3)2), 23.8 (CH(CH3)2) ppm. 31P{1H} NMR (C6D6): −6.8 ppm.
IR (KBr, cm−1): ν 2960 (s), 1560 (s), 1400 (s), 1384 (s), 1259 (s),
1089 (s), 1058 (s), 1016 (s), 800 (s).
Conflicts of interest
There are no conflicts to declare.
Method B. NMR scale. A C6D6 (0.3 mL) solution of
p-ClPhCHO (5.6 mg, 0.04 mmol) was slowly added to a
J. Young NMR tube charged with [η5-1,3-(Me3C)2C5H3]2Th[η2-
P2(2,4,6-iPr3C6H2)2] (4; 21 mg, 0.02 mmol) and C6D6 (0.2 mL).
Resonances of 10 were observed by 1H NMR spectroscopy
(100% conversion) after the sample was kept at room tempera-
ture overnight.
Acknowledgements
This work was supported by the National Natural Science
Foundation of China (Grant No. 21871029, 21573021, and
21672024), and the Deutsche Forschungsgemeinschaft (DFG)
through the Heisenberg program (WA 2513/6 and WA 2513/8).
Reaction of [η5-1,3-(Me3C)2C5H3]2Th[η2-P2(2,4,6-iPr3C6H2)2]
(4) with p-ClPhCHO. NMR scale. A C6D6 (0.2 mL) solution of
p-ClPhCHO (2.8 mg, 0.02 mmol) was slowly added to a
J. Young NMR tube charged with [η5-1,3-(Me3C)2C5H3]2Th[η2-
P2(2,4,6-iPr3C6H2)2] (4; 21 mg, 0.02 mmol) and C6D6 (0.3 mL).
Notes and references
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2000, 39, 314–329; (c) F. Mathey, Angew. Chem., Int. Ed., 2003,
42, 1578–1604; (d) S. Greenberg and D. W. Stephan, Chem.
Soc. Rev., 2008, 37, 1482–1489; (e) R. Waterman, Dalton
Trans., 2009, 18–26; (f) L. Weber, Eur. J. Inorg. Chem., 2007,
Resonances of 10 along with those of unreacted
4
were observed by 1H NMR spectroscopy (50% conversion
based on 4) after the sample was kept at room temperature
overnight.
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