Comparison of reactivity of phosphagermaallene Tip(t-Bu)GeCPMes* towards sulfur ylides

Article abstract of DOI:10.1016/j.jorganchem.2014.01.003

Phosphagermaallene 1, Tip(t-Bu)GeCPMes* (Tip = 2,4,6- triisopropylphenyl, Mes* = 2,4,6-tri-tert-butylphenyl), reacts with diphenylsulfoniumylide (Ph₂SCH₂) leading to adduct 2, through a nucleophilic attack of the negatively charged carbon atom of the ylide on the positively charged germanium atom followed by a migration of one of the phenyl groups. By contrast, dimethyloxosulfoniummethylide (Me ₂S(O)CH₂) appears much less reactive towards 1: it preferentially undergoes an in-situ oxidation of THF leading to a γ-butyrolactone intermediate which gives a [2+2] cycloaddition by the CO group with the GeC double bond to form 3. The new compounds 2 and 3 were completely characterized by multinuclear NMR spectroscopy and by single crystal X-ray structural analysis.

Full text of DOI:10.1016/j.jorganchem.2014.01.003

Journal of Organometallic Chemistry 755 (2014) 120e124
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Comparison of reactivity of phosphagermaallene
Tip(t-Bu)Ge]C]PMes* towards sulfur ylides
,
,
,
*
Tibor-Gabor Kocsor a b, Noemi Deak a b, Dumitru Ghereg a, Gabriela Nemes b
,
Jean Escudié a, Heinz Gornitzka c
a Université de Toulouse, UPS, CNRS, LHFA, UMR 5069, 118 Route de Narbonne, F-31062 Toulouse Cedex 09, France
, Sonia Ladeira , Annie Castel
,
d,
e
a
**
b
ꢀ
ꢀ
Universitatea Babes¸-Bolyai, Facultatea de Chimie s¸i Inginerie Chimica, Departamentul de Chimie, Str. M. Kogalniceanu, Nr: 1, RO-400084 Cluj-Napoca,
Romania
c CNRS, LCC (Laboratoire de Chimie de Coordination), 205 route de Narbonne, BP 44099, F-31077 Toulouse Cedex 4, France
d Université de Toulouse, UPS, INPT, F-31077 Toulouse Cedex 4, France
e Université de Toulouse, UPS, Service Commun Rayons X, ICT-FR2599, 118 Route de Narbonne, F-31062 Toulouse Cedex 09, France
a r t i c l e i n f o
a b s t r a c t
Article history:
Phosphagermaallene 1, Tip(t-Bu)Ge]C]PMes* (Tip ¼ 2,4,6-triisopropylphenyl, Mes* ¼ 2,4,6-tri-tert-
butylphenyl), reacts with diphenylsulfoniumylide (Ph2S]CH2) leading to adduct 2, through a nucleo-
philic attack of the negatively charged carbon atom of the ylide on the positively charged germanium
atom followed by a migration of one of the phenyl groups. By contrast, dimethyloxosulfoniummethylide
(Me2S(O)]CH2) appears much less reactive towards 1: it preferentially undergoes an in-situ oxidation of
Received 14 November 2013
Received in revised form
19 December 2013
Accepted 7 January 2014
THF leading to a
g
-butyrolactone intermediate which gives a [2þ2] cycloaddition by the C]O group with
Keywords:
the Ge]C double bond to form 3. The new compounds 2 and 3 were completely characterized by
multinuclear NMR spectroscopy and by single crystal X-ray structural analysis.
Ó 2014 Elsevier B.V. All rights reserved.
Heteroallene
Sulfur ylide
Phosphagermaallene
Adduct
1. Introduction
now. Besides the transient phosphagermaallene Mes2Ge]C]
PMes* [22], the first stable phosphagermaallene Tip(t-Bu)Ge]C]
In the last three decades, a new research field about low coor-
dinated compounds containing one or two elements of Groups 14
and 15 was developed [1e10]. It began with the synthesis of the first
stable diphosphene Mes*P]PMes* (Mes* ¼ 2,4,6-tri-tert-butyl-
phenyl) by Yoshifuji [11], disilene Mes2Si]SiMes2 by West [12] and
silene (Me3Si)2Si]C(OSiMe3)Ad by Brook [13] in 1981. Besides the
study of such highly reactive double bonded alkene analogs, com-
pounds containing two cumulative double bonds of the type E]C]
E0 (E, E0 ¼ group 14, 15) became also the focus of recent researches
[14e20]. Among such cumulenic systems, the most intensively
studied are phosphaheteroallenes P]C]E (E ¼ Si, Ge) presenting
two different double bonds and multiple reaction centers. In the case
of phosphasilaallenes eP]C]Si<, only a transient system was
evidenced [21] and in the case of tin, no such a system is known up to
PMes* (1) (Tip ¼ 2,4,6-triisopropylphenyl) was obtained in 2002
[23]. The reactivity of phosphagermaallene 1 has been extensively
studied in the last decade. Most of the reactions occur on the Ge]C
double bond which appears much more reactive than the P]C
double bond. Various types of cycloadditions were observed: [2þ1]
with chalcogens [24], and [2þ2] and [2þ4] with various types of
carbonyl derivatives [25e28] and multiply bonded nitrogen com-
pounds [29], [2þ3] with nitrones and nitrile oxides [29]. However, in
some cases, (dimethyl acetylenedicarboxylate [30], diphenylketene
[31], carbon disulfide and phenylisothiocyanate [26], benzonitrile
[29], methylacrylate [25]) the phosphagermaallene 1 shows an un-
precedented 1,3-dipole behavior that involves the whole Ge]C]P
unit leading by a [3þ2] cycloaddition with various double or triple
bonds to new types of carbenes, the phosphagerma heterocyclic
carbenes, analogs of the well-known N-heterocyclic carbenes
(NHC). Ene reactions have also been evidenced in some cases [27,29].
In conclusion, phosphagermaallene 1 shows a great versatility in
reactivity.
ꢀ
* Universitatea Babes¸ -Bolyai, Facultatea de Chimie s¸ i Inginerie Chimica, Depar-
ꢀ
tamentul de Chimie, Str. M. Kogalniceanu, Nr: 1, RO-400084 Cluj-Napoca, Romania
** Corresponding author. CNRS, LCC (Laboratoire de Chimie de Coordination), 205
route de Narbonne, BP 44099, F-31077 Toulouse Cedex 4, France.
E-mail addresses: sgabi@chem.ubbcluj.ro (G. Nemes), heinz.gornitzka@lcc-
toulouse.fr (H. Gornitzka).
In this context we were curious to study the reactivity of 1 to-
wards other dipolar compounds such as ylides. It has been shown
that ylides react with double bond containing systems of type E]C
0022-328X/$ e see front matter Ó 2014 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2014.01.003

T.-G. Kocsor et al. / Journal of Organometallic Chemistry 755 (2014) 120e124
121
(E ¼ C, N, O, S,.) leading to three-membered heterocyclic com-
pounds [32e36]. The present study is focused on the reactivity
study of phosphagermaallene 1, Tip(t-Bu)Ge]C]PMes*
(Tip ¼ 2,4,6-triisopropylphenyl, Mes* ¼ 2,4,6-tri-tert-butylphenyl),
toward diphenylsulfoniumylide (Ph2S]CH2) and dimethylox-
osulfoniummethylide (Me2S(O)]CH2), respectively.
2. Results and discussion
Diphenylsulfoniumylide has been obtained in-situ by deproto-
nation of the methyldiphenylsulfoniumtriflate with n-BuLi in THF
at low temperature [37]. The addition of one equivalent of phos-
phagermaallene 1 in Et2O at ꢀ80 ꢁC led to the formation of a unique
compound as proved by the 31P NMR spectrum of the reaction
mixture (277.1 ppm). After evaporation of the solvents and crys-
Scheme 1. Synthesis of compound 2.
The molecular structure of compound 2 is shown in Fig. 1. The
germanium atom is in a slightly distorted tetrahedral geometry.
The carbon atom of the P]C double bond is almost planar (sum of
angles: 359.8 ) and the GeeC bond lengths (1.990(2) to 2.033(2) A)
lie at the upper limit for the GeeC single bond (2.00 A) [43], due to
the large steric hindrance. The torsion angles (C34eP1eC1e
Ge1 ¼ 176ꢁ and C34eP1C1eC2 ¼ 1.8ꢁ) involving the P]C double
bond are in good agreement with a planar classical double bonded
system.
In sharp contrast, the reaction of the dimethyloxosulfonium
ylide (obtained by deprotonation of the trimethylsulfoxonium io-
dide with NaH in THF [36]) with 1 was more complex. The 31P NMR
spectrum of the crude mixture revealed the presence of several
products including a major signal at 263 ppm. A slow crystallization
in pentane at ꢀ30 ꢁC allowed isolation of the corresponding com-
pound in a low yield. The X-ray structure analysis proved the un-
expected formation of the spiro-compound 3 which corresponds to
the cycloadduct between the phosphagermaallene 1 and g-butyr-
olactone (see Fig. 2). The latter was formed in-situ by the oxidation
of THF.
THF is routinely used as solvent in the formation and the re-
actions of such kind of organometallic compounds and is consid-
ered as an inert solvent in this case. However, it is known that
sometimes it can display some reactivity: strong organolithium
bases can extract a proton from THF, usually initiating one or two
ring fragmentation reactions [44]. Moreover, some oxidative re-
tallization from pentane, compound
2 (Mes*P]C(Ph)eGe(t-
ꢁ
ꢁ
Bu)(Tip)(CH2SPh)) was isolated as colorless crystals in a good yield
(70%). The low-field chemical shift of the phosphorus atom in-
dicates that the P]C double bond was still present [38] and that
only the Ge]C double bond was involved in the reaction. More-
over, in the 13C NMR spectrum, a low-field shift of the carbon atom
bonded to the phosphorus was observed (185.24 ppm,
1JCP ¼ 88.1 Hz), which is in good agreement with the presence of the
P]C unsaturation. In the 1H and 13C NMR spectra, the most
important point to be mentioned is the presence of a singlet at
ꢁ
3.15 ppm (1H NMR) and a doublet at 27.69 ppm (3JCP ¼ 8.3 Hz) (13
C
NMR), respectively, corresponding to the CH2S group. A free rota-
tion of the Tip group was observed in the 1H NMR spectrum as
i
proved by the equivalence of the two Pr groups; however, two
doublets were observed for the diastereotopic Me groups of these
iPr groups. Compound 2 was unambiguously characterized by a
single crystal X-ray structure analysis which confirms the addition
of the ylide on the Ge]C bond with a transfer of one phenyl group
to the carbon atom (see Fig. 1).
Thus, although the sulfur ylides have been reported as potential
precursor of carbenes [39e42], the cycloaddition of the transient
carbene on the Ge]C double bond to give a germirane has not been
observed (Scheme 1).
actions of THF leading to g-butyrolactone have been reported, for
Fig. 1. Solid state structure of 2. Thermal ellipsoids are drawn at the 50% probability
level. Tip, Mes* and t-Bu groups have been simplified, hydrogen atoms and disorders
ꢁ
ꢁ
have been omitted for clarity. Selected bond lengths (A) and angles ( ): Ge1eC1
1.990(2), Ge1eC8 1.984(2), Ge1eC15 2.033(2), Ge1eC19 2.002(2), C8eS1 1.808(2), S1e
C9 1.778(2), C1eC2 1.481(2), C1eP1 1.682(2), P1eC34 1.851(2), C1eGe1eC8 102.04(6),
C1eGe1eC15 115.44(6), C1eGe1eC19 113.85(6), C8eGe1eC15 100.21(6), C8eGe1eC19
118.93(7), C15eGe1eC19 106.02(7), Ge1eC1eP1 108.78(7), Ge1eC1eC2 120.48(10),
C2eC1eP1 130.52(11), C1eP1eC34 110.01(7), Ge1eC8eS1 117.66(8), C8eS1eC9
99.84(7).
Fig. 2. Solid state structure of 3. Thermal ellipsoids are drawn at the 50% probability
level. Tip, Mes* and t-Bu groups have been simplified andꢁhydrogen atoms have been
ꢁ
omitted for clarity. Selected bond lengths (A) and angles ( ): Ge1eC19 1.964(3), Ge1e
O2 1.835(2), Ge1eC24 1.986(4), Ge1eC28 1.959(3), P1eC19 1.650(4), P1eC1 1.845(3),
C19eC20 1.545(5), C20eO2 1.453(4), C1eP1eC19 103.24, P1eC19eGe1 133.44, Ge1e
O2eC20 95.79, C19eC20eO2 101.12, O1eC20eO2 108.37, C1eP1eC19eGe1 177.52,
P1eC19eGe1eC28 77.33.

122
T.-G. Kocsor et al. / Journal of Organometallic Chemistry 755 (2014) 120e124
example using calcium hypochlorite [45], zinc dichromate [46] and
unsaturation and the C]O double bond of a g-butyrolactone
zinc permanganate [47]. In order to verify the hypothesis that 3 was
formed by oxidation of THF by the ylide. Thus, whereas diphe-
nylsulfoniumylide reacts rapidly with 1 without formation of side
products, dimethyloxosulfonium ylide reacts faster with the
solvent.
formed by a reaction between 1 and
g-butyrolactone, trime-
thylsulfoxonium iodide was reacted with NaH in THF under
described conditions and then the reaction mixture was stirred at
room temperature for two additional hours. After filtration and
distillation,
g-butyrolactone was isolated in low yield. Furthermore,
4. Experimental section
the direct reaction of phosphagermaallene and the lactone was
carried out. Treatment of 1 with a slight excess of lactone in diethyl
ether at ꢀ80 ꢁC yielded as expected the desired cycloadduct 3 as
colorless crystals in a moderate yield (49%) (Scheme 2).
4.1. General
All manipulations were performed in a dry and oxygen-free
atmosphere of argon by using standard Schlenk-line and glove
box techniques. Solvents were purified with the MBRAUN SBS-800
purification system. NMR spectra were recorded with a Bruker
Avance II 300 apparatus: 1H (300.13 MHz), 13C (75.48 MHz), 31P
(121.50 MHz). Chemical shifts are expressed in parts per million
with residual solvent signals as internal reference (1H and 13C{1H})
or with an external reference (H3PO4 for 31P). In the case of the new
compounds, the assignments of 1H signals together with those in
13C NMR spectra were obtained from 2D heteronuclear experi-
ments (HSQC and HMBC). Melting points were measured in a
sealed capillary using the Stuart automatic melting point SMP40
The 31P NMR spectrum displayed, like in compound 2, the for-
mation of a sole compound with the chemical shift at 263.4 ppm
proving that the [2 þ 2] cycloaddition between the Ge]C and C]O
double bonds occurred in this case. The presence of non-equivalent
OCH2 groups in the 1H NMR spectrum at 3.11 and 3.84 ppm was in
good agreement with such a bi-cyclic structure. However, this
cycloadduct was unstable in solution and the 13C NMR analysis
could not be performed. It rapidly led to the formation of a new
derivative which could not be identified. The reaction of dimethy-
loxosulfoniummethylide with 1 in other solvents like CHCl3 and
CH2Cl2 was not possible due to the instability of 1 in this
environment.
apparatus. The phosphagermaallene
1 [23] and the methyl-
The formation of the cycloadduct 3 was confirmed by a single
crystal X-ray structural analysis.
diphenylsulfoniumtriflate [48] were prepared according to litera-
ture procedures. The phosphagermaallene 1 could be prepared in-
situ or kept in a glove box in solid form. Trimethylsulfoxonium
iodide Me3S(O)I was purchased from Aldrich and used without
further purification.
The four-membered cycle Ge1eO2eC20eC19 is almost planar,
with the germanium atom slightly outside of the four-membered
cycle (the distance between the germanium atom and the plane
ꢁ
O2, C20 and C19 is 0.017 A and the angle between the planes O2,
C20, C19 and O2, Ge1, C19 is only 4.39ꢁ. The C]P double bond is
located in the same plane as O2, C20 and C19 atoms. The five-
4.2. Acyclic compound (2)
ꢁ
membered cycle is distorted with the C21 carbon atom at 0.599 A
To a solution of Ph2(Me)SOTf (182 mg, 0.519 mmol) in THF
(2 mL), a solution of n-BuLi 1.6 M in 0.34 mL, 0.545 mmol was added
dropwise at ꢀ80 ꢁC. The mixture in hexane (0.34 mL, 0.545 mmol)
was stirred for 20 min at this temperature. The formed ylide was
used without isolation and further purification. The phospha-
germaallene 1 was prepared from the previously formed Tip(t-
Bu)(F)GeeC(Cl)]PMes*(350 mg, 0.518 mmol) in diethyl ether
(3 mL) by adding a solution of t-BuLi 1.7 M in pentane (0.32 mL,
0.544 mmol) at ꢀ80 ꢁC. After stirring for 30 min at this tempera-
ture, the red reaction mixture was allowed to warm up to room
temperature to get phosphagermaallene 1 from the previously
formed Tip(t-Bu)(F)GeeC(Li)]PMes* and became redebrown; af-
ter 10 min, it was cooled again to ꢀ80 ꢁC and the solution con-
taining the ylide was slowly added. The cooling bath was removed
after 10 min and the solution was allowed to warm up to room
temperature, while its color became brownish red. The solvents
were evaporated under low pressure and replaced by pentane. The
mixture was filtered to eliminate LiF. Compound 2 was crystallized
from pentane (0.3 g, 0.364 mmol, yield 70%), m.p.: 177e178 ꢁC.
of the mean plane constituted by the other four atoms; the angle
between the plane containing the C20, C21, C22 atoms and the
plane containing C20, C22, C23, and O1 atoms is 38.72ꢁ. The Ge-O2
ꢁ
bond length (1.834(2) A) is comparable to that measured in ger-
ꢁ
maoxetanes (1.826(2) A [23]. Otherwise, the bond lengths and
angles are comparable to those reported in the literature [43]. Only
the E isomer relative to the P]C double bond was formed.
3. Conclusions
The reactivity of phosphagermaallene 1 towards sulfur con-
taining ylides has been studied. With diphenylsulfoniumylide, a
nucleophilic attack of the negatively charged carbon atom of the
ylide on the positively charged germanium atom, followed by a
migration of one of the phenyl group, led exclusively to acyclic
adduct 2. A three-membered germanium compound, which could
be expected, was not formed. In the case of the dimethylox-
osulfonium ylide, among a complex mixture, the cycloadduct 3 was
surprisingly obtained as main product. This reaction can only be
1H NMR (CDCl3)
d
¼ 0.71 (broad s, 6H, o-CHMeMe0, Tip), 1.17 (d,
3JHH ¼ 6.9 Hz, 6H, p-CHMe2, Tip), 1.18 (d, JHH ¼ 6.6 Hz, 6H, o-
CHMeMe0, Tip), 1.23 (s, 9H, o-CMe3, Mes*), 1.36 (s, 9H, p-CMe3,
Mes*), 1.50 (s, 9H, GeeCMe3), 1.70 (s, 9H, o-CMe3, Mes*), 2.77 (sept,
3
explained by
a
[2þ2] cycloaddition between the Ge]C
3JHH ¼ 6.9 Hz, 1H, p-CHMe2, Tip), 3.10 (sept, JHH ¼ 6.6 Hz, 2H, o-
3
CHMeMe0, Tip), 3.15 (s, 2H, CH2eS), 6.23 (d, 3JHH ¼ 7.8 Hz, 2H, o-CH,
PheC), 6.58 (t, 3JHH ¼ 7.8 Hz, 2H, m-CH, PheC), 6.70e6.77 (m, 1H, p-
CH, PheC), 6.85 (s, 2H, m-CH, Tip), 7.09e7.14 (m, 1H, p-CH, PheS),
7.24e7.34 (m, 5H, o- and m-CH, PheS, m-CH, Mes*), 7.43 (s, 1H, m-
CH, Mes*).
13C NMR (CDCl3)
d
¼ 23.74 and 23.83 (2s, p-CHMeMe0, Tip), 25.14
3
and 26.87 (2s, o-CHMeMe0, Tip), 27.69 (d, JCP ¼ 8.3 Hz, CH2eS),
30.32 (s, GeeCMe3), 31.47 (s, p-CMe3, Mes*), 32.67 and 32.79 (2s, o-
CMe3, Mes*), 33.76 (s, p-CHMeMe0, Tip), 34.42 (s, o-CHMeMe0, Tip),
34.97 (s, p-CMe3, Mes*), 37.96 (d, 3JCP ¼ 0.8 Hz, o-CMe3, Mes*), 38.06
Scheme 2. Synthesis of the cycloadduct 3.

T.-G. Kocsor et al. / Journal of Organometallic Chemistry 755 (2014) 120e124
123
Table 1
(s, o-CMe3, Mes*), 121.12 and 123.30 (2s, m-CH, Mes*), 121.74 (s, m-
CH, Tip), 124.61 (s, p-CH, PheS) 126.08 (d, 5JCP ¼ 3.6 Hz, p-CH, Phe
C), 126.48 and 128.60 (2s, o-CH and m-CH, PheS), 126.62 (d,
Selected crystallographic data and collection parameters.
2
3
3
4JCP ¼ 1.7 Hz, m-CH, PheC), 129.17 (d, JCP ¼ 11.1 Hz, o-CH, PheC),
Formula
fw
Temp (K)
C51H73GePS
821.71
180(2)
0.71073
Triclinic
C42H67GeO2P
707.54
193(2)
0.71073
Monoclinic
P21/n
10.135(2)
16.120(4)
25.137(5)
e
132.29 (d, 3JCP ¼ 13.2 Hz, ipso-C, Tip), 138.09 (d, 1JCP ¼ 82.8 Hz, ipso-
2
C, Mes*), 141.17 (d, JCP ¼ 17.9 Hz, ipso-C, PheC), 141.69 (s, ipso-C,
ꢁ
Wavelength (A)
Crystal system
Space group
PheS), 148.98 (s, p-C, Tip), 150.44 and 153.58 (2s, o-C, Mes*), 154.10
4
(d, JCP ¼ 4.0 Hz, p-C, Mes*), 154.58 (s, o-C, Tip), 185.24 (d,
P1
1JCP ¼ 88.1 Hz, P]C]Ge).
ꢁ
a (A)
9.9717(4)
15.5744(7)
15.9957(7)
105.247(2)
100.413(2)
93.703(2)
2340.76(17)
2
1.166
0.765
884
0.40 ꢂ 0.20 ꢂ 0.20
5.12e28.28
64,192
31P NMR (CDCl3)
d
¼ 277.1 ppm.
ꢁ
b (A)
ꢁ
c (A)
a
b
g
(ꢁ)
(ꢁ)
(ꢁ)
94.175(12)
e
4.3. Cycloadduct (3)
3
ꢁ
V [A ]
4095.9(15)(3)
4
1.147
0.818
1528
0.08 ꢂ 0.04 ꢂ 0.04
5.12e26.37
44,499
4.3.1. Starting from the sulfoxonium ylide
Z
dcalcd (Mg mꢀ3
)
To a solution of sodium hydride (21 mg, 0.88 mmol, 60%
dispersion in mineral oil washed with pentane) in THF (3 mL),
trimethylsulfoxonium iodide (88 mg, 0.4 mmol) was added at 0 ꢁC.
At this mixture, after stirring 5 min, a solution of Tip(t-Bu)Ge]C]
PMes* 1 (250 mg, 0.4 mmol) in diethyl ether (3 mL) was added at
m
(mmꢀ1
)
F(000)
Crystal size [mmꢀ1
range (ꢁ)
]
q
No of rflns collected
No of indep rflns
GOF on F2
R1, wR2 (I > 2
R1, wR2 (all data)
0
ꢁC. The mixture was allowed to warm up to room temperature
11,497 (Rint ¼ 0.0375)
8307 (Rint ¼ 0.1346)
1.018
0.988
and all solvents were evaporated under reduced pressure. Ac-
cording to the 31P NMR studies, compound 3 was formed in low
yield (15e20%). The crystals of this cycloadduct 3 were obtained
from pentane.
s
(I))
0.0320, 0.0731
0.0458, 0.0790
0.0536, 0.1034
0.1203, 0.1258
Acknowledgments
4.3.2. Starting from the
The phosphagermaallene
described from a solution 1.7 M of t-BuLi (0.457 mL, 0.777 mmol) in
g
-butyrolactone
We are grateful to the CNRS (ANR-08-BLAN-0105-01) and
Romanian Agency UEFISCDI (PCCE-140/2008) for financial support
of this work.
1
was prepared as previously
pentane to
a solution of Tip(t-Bu)(F)GeeC(Cl)]PMes*(0.5 g,
0.74 mmol) in diethyl ether (6 mL) at ꢀ90 ꢁC. To the solution of 1
cooled at ꢀ80 ꢁC, freshly distilled
g-butyrolactone (0.12 g,
Appendix A. Supplementary material
1.394 mmol) was added dropwise. After 15 min a yellow precipitate
was formed. All solvents were evaporated under low pressure and
pentane (18 mL) was added; the reaction mixture was then filtered
and concentrated. After 12 h at ꢀ24 ꢁC, compound 3 was isolated as
a pale yellow powder (0.26 g, 0.367 mmol, yield 49%).
CCDC 952746 (2) and 952747 (3) contain the supplementary
crystallographic data for this paper. This data can be obtained free
of charge from The Cambridge Crystallographic Data Center via
www.ccdc.cam.ac.uk/data_request/cif.
1H NMR (C6D6) 1.14 (d, 3JHH ¼ 6.9 Hz, 3H, CHMeMe0, Tip), 1.15 (d,
3JHH ¼ 6.9 Hz, 3H, CHMeMe0, Tip), 1.32 (d, JHH ¼ 6.6 Hz, 3H,
3
References
3
CHMeMe0, Tip), 1.41 (d, JHH ¼ 6.6 Hz, 3H, CHMeMe0, Tip), 1.49 (d,
3JHH ¼ 6.3 Hz, 3H, CHMeMe0, Tip), 1.54 (d, JHH ¼ 6.9 Hz, 3H,
3
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CHMeMe0, Tip), 1.24, 1.44, 1.53 and 1.71 (4s, 4 ꢂ 9H, CMe3 of Mes*
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