Bis(2,4,6-triisopropylphenyl)tin(IV) compounds: Synthesis, single-crystal X-ray characterization and reactivity toward ionizing species and polar monomers

Article abstract of DOI:10.1016/j.jorganchem.2005.12.011

The synthesis of new organotin compounds of general formula Tip ₂SnRR′ (Tip = 2,4,6-triisopropylbenzene; R = R′ = CH ₃ (1); R = R′ = CHCH₂ (2); R = CH₂Ph, R′ = Br (3); R = R′ = CH₂CHCH₂ (4)) is described herein. The compounds have been characterized by ¹H, ¹³C, ¹¹⁹Sn NMR, mass spectroscopy and elemental analysis. Characterization by single-crystal X-ray diffraction analysis has been obtained for compounds 2, 3 and 4. The reactivity with ionizing agents has been studied by NMR spectroscopy. Compounds 2 and 4 underwent alkyl abstraction by [(CH ₃CH₂)₃Si]⁺[B(C₆F ₅)₄]^- affording stable cationic species (2a, 4a). For the cationic specie 4a a π-interaction of the benzyl group to the metal centre was recognized by solution NMR studies. A cationic species (3a) was generated from compound 3 using AgSbF₆ as ionizing agent. The cationic species (2a, 3a) exhibited moderate activity as initiator in the cationic polymerization of 1,4-butadiene and good activity in the ring opening polymerization (ROP) of propylene oxide and ε-caprolactone.

Full text of DOI:10.1016/j.jorganchem.2005.12.011

Journal of Organometallic Chemistry 691 (2006) 1505–1514
www.elsevier.com/locate/jorganchem
Bis(2,4,6-triisopropylphenyl)tin(IV) compounds:
Synthesis, single-crystal X-ray characterization and reactivity
toward ionizing species and polar monomers
a
b,
a
Liana Annunziata , Daniela Pappalardo *, Consiglia Tedesco ,
a
a
Simona Antinucci , Claudio Pellecchia
a
`
Dipartimento di Chimica, Universita degli Studi di Salerno, Via S. Allende, I-84081 Baronissi (SA), Italy
`
Dipartimento di Studi Geologici e Ambientali, Universita del Sannio, Via Port’Arsa, I-82100, Benevento, Italy
b
Received 2 December 2005; accepted 5 December 2005
Available online 19 January 2006
Abstract
The synthesis of new organotin compounds of general formula Tip2SnRR0 (Tip = 2,4,6-triisopropylbenzene; R = R0 = CH3 (1);
R = R0 = CH@CH2 (2); R = CH2Ph, R0 = Br (3); R = R0 = CH2CH@CH2 (4)) is described herein. The compounds have been charac-
1
terized by H, 13C, 119Sn NMR, mass spectroscopy and elemental analysis. Characterization by single-crystal X-ray diffraction analysis
has been obtained for compounds 2, 3 and 4. The reactivity with ionizing agents has been studied by NMR spectroscopy. Compounds 2
and 4 underwent alkyl abstraction by [(CH3CH2)3Si]+[B(C6F5)4]ꢀ affording stable cationic species (2a, 4a). For the cationic specie 4a a p-
interaction of the benzyl group to the metal centre was recognized by solution NMR studies. A cationic species (3a) was generated from
compound 3 using AgSbF6 as ionizing agent. The cationic species (2a, 3a) exhibited moderate activity as initiator in the cationic poly-
merization of 1,4-butadiene and good activity in the ring opening polymerization (ROP) of propylene oxide and e-caprolactone.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Tin; Cationic species; Single crystal X-ray characterization; Polymerization
1. Introduction
et al. [3]. Single-crystal X-ray diffraction analysis displayed
a planar, tricoordinated cation fully free from interactions
with either solvent or anion. Formation of the ‘‘free’’ cat-
ion required hydrocarbon solvents, strong electrophiles to
abstract an appropriate leaving group, and very low nucle-
ophiles anions such as tetrakis(pentafluorophenyl)borate
The chemistry of stable and free cations of heavier
group 14 elements is one of the most attractive topics in
recent years [1]. Very recently tricoordinated stannylium
cations have been obtained using weakly coordinating
anions or strong electrophiles. For instance, in the presence
of bulky weakly coordinating anions such as the permethy-
lated carborane CB11Meꢀ12, Michl et al. reported the crystal
BðC6F5Þꢀ. Moreover, the three bulky aryl groups ‘‘cage’’
4
the central atom preventing access of external nucleophiles
and protecting the positive charge.
structure of the species n-Bu3SnþCB11Meꢀ [2]. Using aryl
ligands with bulky substituents in the ortho positions, such
as 2,4,6-triisopropylphenyl (Tip), the species [(Tip)3Sn]+
[B(C6F5)4]ꢀ was successfully synthesized by Lambert
Our recent research interest was devoted to the synthesis
of octahedral bis(phenoxy-imine)dialkyl tin(IV) complexes
bearing alkyl groups in a cis configuration. The obtained
species underwent alkyl abstraction reaction with the car-
benium salt [C(C6H5)3]+[B(C6F5)4]ꢀ. Interestingly, the
obtained cationic species exhibited some activity in the eth-
ylene oligomerization under mild conditions, producing
oligomers with saturated end groups and methyl branches
12
*
Corresponding author. Tel.: +39 089 965436; fax: +39 089 965296.
E-mail address: pappalardo@unisannio.it (D. Pappalardo).
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.12.011

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L. Annunziata et al. / Journal of Organometallic Chemistry 691 (2006) 1505–1514
[4]. Such results prompted us to persist in exploring the
reactivity of different cationic tin(IV) compounds bearing
at least an alkyl group. Trusting in the protecting effect
of the bulky 2,4,6-triisopropylphenyl ligands against nucle-
ophilic agents, we have investigated the chemistry of di-aryl
tin(IV) compounds of general formula Tip2SnR2 or
Tip2SnXR (Tip = 2,4,6-triisopropylbenzene; R = alkyl,
X = halogen). Herein, we describe their synthesis and
structural characterization, their reactivity with ionizing
agents and the subsequent reactivity with olefins and polar
monomers.
2.2. Characterization
All the synthesized compounds have been characterized
1
by H, 13C, 119Sn NMR, mass spectroscopy and elemental
analysis (see Section 4). For the dialkylcompounds 1, 2 and
4 the 119Sn NMR spectra displayed a single resonance,
appearing between ꢀ114 and ꢀ170 ppm, in the expected
range for tetra-coordinated tin(IV) compounds, thus indi-
cating the existence of a single species in solution. Com-
pound 3 also displayed a single resonance, but at lower
field (ꢀ56.1 ppm), as a consequence of the deshielding
effect of the electron withdrawing bromine atom [5]. The
1H NMR spectra resulted very clear, with useful informa-
tion concerning the coordination deriving from the analysis
of the proton-tin coupling constants. For instance, in all
the compounds the meta hydrogen atoms on the aryl group
2. Results and discussion
2.1. Synthesis
4
The synthesis strategies for the new di-aryl tin(IV) com-
pounds (Chart 1) are described in Scheme 1. Compounds 1
and 2 were synthesized via metathesis reactions of the cor-
respondent di-alkyl tin(IV) dichloride with a THF solution
of TipMgBr in toluene. Reactions proceeded with good
(compound 1) or high (compound 2) yields producing
white solids. Suitable crystals for X-ray crystal structure
determination were obtained for compound 2 from methyl
alcohol at ꢀ20 ꢁC.
exhibited coupling with tin with a J(Sn–H) value ranging
between 17 and 25 Hz. In compound 1 the Sn–CH3 proton
resonance appears as singlet at 0.61 ppm, exhibiting cou-
pling with tin with a 2J(Sn–H) of 53 Hz; using the equation
developed by Lockhart for dimethyltin(IV) compounds the
calculated angle for the C–Sn–C was 108.6ꢁ, in the
expected range for a tetrahedral structure [6]. In the benzyl
derivative compounds, the observed J(Sn–H) for the Sn–
CH2–Ph resonance was 58.7 Hz in compound 3 and
56.4 Hz in compound 4.
2
Compound 3 was prepared by reaction of SnBr4 with
two equivalent of TipMgBr in THF solution; the
(Tip)2SnBr2 product was allowed to react with a solution
of benzylmagnesium bromide, producing compound 3 as
a white solid (Yield: 73%). Suitable crystals for X-ray crys-
tal structure determination were grown from hexane at
ꢀ20 ꢁC. It is worth noting that even in the presence of more
than two equivalent of benzyl Grignard, the only obtained
product was the mono-benzylated tin(IV) derivative 3. We
were instead able to further alkylate compound (3) by
metathesis reaction with allylmagnesiumbromide. The
obtained allylbenzylbis[2,4,6-triisopropylphenyl] tin(IV)
compound (4) was crystallized from methanol/hexane at
ꢀ20 ꢁC.
2.3. Single-crystal X-ray diffraction analysis
The molecular structures of compounds 2–4 are shown
respectively in Figs. 1–3; selected bond lengths and angles
are given in Table 1. The coordination environment about
the Sn atom is approximately tetrahedral. In compounds 2
and 4 the vinyl and allyl ligands show Sn–C distances sim-
ilar to those observed in analogous vinyl and allyl com-
pounds [7]. In compounds 3 and 4 the benzyl moiety
displays g1 coordination with Sn–C1 distances respectively
˚
˚
2.166(8) A and 2.152(11) A and Sn–C1–C2 angles 113.5(6)ꢁ
and 110.2(8)ꢁ [8b].
2.4. Generation of cationic species and their reactivity with
olefins and polar monomers
A main focus of our study has been the search of stanny-
lium cations of general formula Tip2SnR+ (Tip = 2,4,6-
triisopropylphenyl, R = vinyl, benzyl). Therefore, we
studied, via NMR spectroscopy, the reactivity of the
neutral compounds with different ionizing agents such
as [C(C6H5)3]+[B(C6F5)4]ꢀ, B(C6F5)3, [(CH3CH2)3Si]+-
[B(C6F5)4]ꢀ and AgSbF6.
R2
Sn
R1
Compound 1 resulted non-reactive with all the used ion-
izing agents. The species [C(C6H5)3]+[B(C6F5)4]ꢀ and
B(C6F5)3 did not react with all the synthesized compounds,
at least under the explored experimental conditions.
On the contrary, the species [(CH3CH2)3Si]+[B(C6F5)4]ꢀ
was able to remove an alkyl group from compounds 2 or 4,
affording cationic species (2a, 4a) (Scheme 2). These
1
2
3
4
R1= CH3
R1= CH=CH2 R2= CH=CH2
R1= CH2Ph
R1= CH2Ph
R2= CH3
R2= Br
R2= CH2CH=CH2
Chart 1.

L. Annunziata et al. / Journal of Organometallic Chemistry 691 (2006) 1505–1514
1507
MgBr
i)
SnB
r
TH
F
4
Br
ii)
(C
H
)CH
M
gB
r, T
HF
6
5
2
Sn
3
R2SnCl2
Toluene
CH2=CHCH2MgBr
Toluene
R2
R1
CH2CH=CH2
Sn
Sn
1
2
R1= CH3
R1= CH=CH2
R2= CH3
R2= CH=CH2
4
Scheme 1.
Fig. 1. Molecular structure of 2. Thermal ellipsoids are drawn at 20%
probability level. Hydrogen atoms have been omitted for clarity.
Fig. 2. Molecular structure of 3. Thermal ellipsoids are drawn at 20%
probability level. Hydrogen atoms have been omitted for clarity.
reactions were performed in the NMR tube, in C6D6 sol-
vent, and produced two benzene layers. The oily bottom
layer revealed the presence of the cationic species, which
were stable for weeks. This behaviour was already observed
by Lambert for tricoordinated silyl, germyl and stannyl
cations in aromatic solvents, and it is characteristic of the
formation of liquid clathrates [1b]. It is reasonable to
hypothesize that our ionic compounds also exist as liquid
clathrates in benzene solution. It is well known that liquid
clathrates usually present low lattice energy [9]; as matter
of fact, compounds 2a and 4a did not crystallize, even after
prolonged standing at low temperature, and, as a conse-
1
quence, were characterized in situ by H, 13C, and 119Sn
NMR analysis.
As described above, reaction of compound 2 with 1
equiv. of [(CH3CH2)3Si]+[B(C6F5)4]ꢀ in C6D6 (Scheme 2),
produced two layers. In the upper layer, 1H NMR analysis
evidenced the presence of the sideproduct CH2@
1
CHSi(CH2CH3)3. In the bottom layer, H NMR analysis
(Fig. 4) displayed a new organometallic species, different
from the starting compound 2, and characterized by the
upfield shift of the signals and by the aryl signals/vinyl

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L. Annunziata et al. / Journal of Organometallic Chemistry 691 (2006) 1505–1514
1
the H NMR spectrum of the bottom layer the resonances
of the allyl group are absent, with the residual signals
appearing very broad. However, the 119Sn NMR spectrum
showed one signal at 599.9 ppm, thus indicating the exis-
tence of a single tin species in solution. The very high
downfield shift observed is consistent with the formation
of a cationic species. A better resolution of the spectrum
was obtained in the presence of few drops of ClC6D5.
The subsequently recorded 1H NMR spectrum (Fig. 5) dis-
played the benzilic CH2Ph hydrogen atoms at 3.4 ppm
(2J119Sn–1H = 56.2) and an upfield shift of the CH of the
isopropyl substituents on the aryl group in ortho position
at 1.8 ppm, if compared with the corresponding resonances
of the neutral compound 4. Interesting information came
from careful analysis of the aromatic region. As matter
of fact, it is well known that the benzyl ligand differs from
the simple alkyls in its potential ability to interact with elec-
tron-deficient metal centers through the p-aromatic system.
Coordination gn(n > 1) is typical of transition metal and
has been observed in solid state [10]; among main group
elements, g3 interaction has been observed, in solid state,
for benzyl lithium [11]. Latesky found NMR spectroscopic
evidence that also in solution is possible to detect this type
of interaction. In particular, gn benzyl ligands are charac-
terized by an high-field shift for the ortho hydrogen reso-
nance (d < 6.8 ppm) in the 1H NMR spectrum, and by
large 1JCH values for CH2 group (J > 130 Hz). The increase
of the coupling constant can be explained with an increas-
ing ‘‘sp2’’ character of a-carbon, involving a decrease of the
Mt–C–Ph angle. It is worth nothing that in these studies
tetrabenzyltin Sn(CH2C6H5)4 was taken as a model for
Fig. 3. Molecular structure of 4. Thermal ellipsoids are drawn at 20%
probability level. Hydrogen atoms have been omitted for clarity.
signals integrals ratio consistent with a 2:1 formulation. A
very high down-field shift of 119Sn NMR signal (760 ppm)
was observed, which is likely due to tin atom deshielding,
according to literature data concerning free tricoordinate
stannylium cations [1b,3].
Analogously, when compound 4 was reacted with 1
equiv. of [(CH3CH2)3Si]+[B(C6F5)4]ꢀ in C6D6, the allyl
group was abstracted (Scheme 2), and two layers were
formed. In the upper layer, NMR analysis evidenced the
presence of CH2@CHCH2Si(CH2CH3)3. Consequently, in
Table 1
˚
Selected bond lengths (A) and angles (ꢁ) for compounds 2–4
2
3
4
Sn–C(1)
2.163(3)
2.169(4)
2.130(4)
2.144(5)
Sn–C(8)
Sn–C(23)
Sn–C(1)
Sn–Br(1)
2.159(8)
2.157(8)
2.166(8)
2.520(5)
Sn–C(11)
Sn–C(26)
Sn–C(1)
Sn–C(8)
2.174(11)
2.197(11)
2.152(11)
2.188(12)
Sn–C(16)
Sn–C(33)
Sn–C(31)
C(31)–C(32)
C(33)–C(34)
1.201(9)
1.249(7)
C(1)–C(2)
1.486(13)
C(8)–C(9)
C(9)–C(10)
1.43(2)
1.28(3)
Sn–C(31)–C(32)
Sn–C(33)–C(34)
129.7(6)
123.4(4)
Sn–C(1)–C(2)
113.5(6)
Sn–C(1)–C(2)
Sn–C(8)–C(9)
110.2(8)
108.4(10)
-
Et3Si+B(C6F5)4
+
R'
-
Sn R'
B(C6F5)4
Sn
R''
2
2
Et3SiR''
2 R'= R''= CH=CH2
2a R'= CH=CH2
4a R'= CH2Ph
4 R'= CH2Ph R''= CH2CH=CH2
Scheme 2.

L. Annunziata et al. / Journal of Organometallic Chemistry 691 (2006) 1505–1514
1509
+
γ
γ
γ
’
α
β
δ
’
’
’
α’ β’
δ
δ
CH=CH2
-
Et3Si+B(C6F5)4
-
Sn CH=CH22
Sn
B(C6F5)4
ε
’
ε
2
2
CH=CH2
δ’
α
β
Et3SiCH=CH2
γ ’
2a
2
i)
δ’
γ’
ε’
α’
β’
β’
δ
γ
β
β
ii)
α
ε
7.5
7.0
6.0
5.5
5.0
4.5
4.0
3.0
2.5
2.0
1.5
1.0
6.5
3.5
0.5
(ppm)
Fig. 4. 1H NMR spectra (C6D6, 25 ꢁC) of compounds 2 (ii) and 2a (i).
normal r-bound (g1) benzyl [10b]. Interestingly, in the
NMR spectra of cationic specie 4a we observed an upfield
shift of the ortho benzyl hydrogens resonance (6.7 ppm),
was fast and selective. The upper layer was analyzed by 1H,
13C, and 119Sn NMR spectroscopy (Fig. 6). Interestingly,
though the cation in the species 3a had identical formula
to the cation in species 4a, their NMR spectra showed sig-
nificant differences. In order to evaluate the presence of
some gn(n > 1) coordination of the benzyl group to the
1
and a coupling constant JCH for the methylenic carbon
value of 142 Hz. These spectroscopic features thus suggest
that in the cationic species 4a the benzyl ligand interacts, in
some way, with the tin also through the p-aromatic system.
Therefore, a gn(n > 1) coordination for the benzyl ligand
can be hypothesized.
1
metal, we analyzed the NMR spectra. We found a JCH
value for the CH2 group of 136 Hz, which is higher than
usual value for sp3 carbons (125 Hz), but is too close to
that one observed in tetrabenzyltin (133 Hz), usually taken
as a model for a normal r-bound (g1) benzyl groups [10b].
Moreover, the 1H NMR signal of the ortho hydrogen
atoms appeared around 7.0–7.3 ppm (overlapped with the
signals of others aromatic hydrogens), in the expected
range for usual (g1) benzyl ligand. Therefore, we have
not any evidence of gn(n > 1) coordination of the benzyl
group to tin in the cationic species 3a. The 19F NMR anal-
ysis also excluded any interaction with the anion SbFꢀ6 : a
single resonance at 118.7 ppm was in fact observed. It is
worth noting that in the species 4a also the anion does
not interact with the cation. The 119Sn NMR spectrum dis-
plays a single resonance at 257 ppm, at higher field in com-
parison to the resonance observed with 4a, clear indication
of the presence of a different species. As discussed above,
the large upfield shift of d(119Sn) is likely due to the coor-
dinating solvent. It is worth nothing that for the existence
of cationic specie 3a the use of ClC6D5 as solvent seems to
be essential: in fact in CDCl3 or CD2Cl2 as solvent the reac-
tion led quickly to decomposition products. It is reasonable
The 119Sn chemical shift for the species 4a measured in
C6D6 solvent, in the presence of few drops of ClC6D5,
appeared at higher field (535 ppm) in comparison with
the signal measured in neat benzene. For that reason the
effect of the ClC6D5 concentration on the 119Sn chemical
shift was studied: in the presence of ClC6D5 in 1:1 and
65:1 molar ratio with tin the signal appears respectively
at 585 ppm and at 524 ppm. Therefore, the addition of a
stronger coordinating solvent than aromatic hydrocarbons
to the positively charged center leads to the upfield shift of
the tin resonance. It is well established that an increase in
coordination number of the tin atom from four to five,
six or seven produces the upfield shift of d(119Sn) [5]. It is
also known from the literature that chlorobenzene could
coordinate unsaturated species, and recently Jordan
reported the crystal structure of various Zr(IV) cations dis-
playing the chlorobenzene g1-coordinated via chlorine [12].
Compound 3 was reacted with AgSbF6 in ClC6D5
solvent. The reaction proceeded with formation of the
cationic species 3a and precipitation of AgBr. The reaction

1510
L. Annunziata et al. / Journal of Organometallic Chemistry 691 (2006) 1505–1514
+
α
β
γ
ε
CH2CH=CH2
ε’
ε’
η
η
η’
η’
+
-
+
-
[Et Si] [B(C F )]
Et Si B(C F5)
6 5 4
6
δ
3 3
ι
Sn
δ’
-
Sn
ι
’
ο’
B(C6F5)4
2
2
ο’
ε
Et3SiCH2CH=CH2
4
4a
η’
δ’
ε’
i)
ο’
ι’
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
(ppm)
η
ii)
ε
δ
α
ι
γ
β
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
(ppm)
Fig. 5. 1H NMR spectrum (C6D6, 25 ꢁC) of compounds 4 (ii) and H NMR spectrum (mixture of 0.5 ml of C6D6 and 1 ml of ClC6D5, 25 ꢁC) of 4a (i).
1
to hypothesize that a chlorobenzene coordination could be
involved to stabilize the cationic species. This stabilization
in the cationic specie 3a is less significant and in some way
replaced by the stronger (gn) interaction of the benzyl
ligand.
The reactivity of the cationic species 2a, 3a with olefins
and polar monomers was explored. While the species 2a, 3a
did not show any activity with ethylene, preliminary tests
conducted at ambient temperature and pressure showed
that these species exhibited moderate activity as initiator
in the cationic polymerization of 1,4-butadiene. In the
13C NMR spectra (CDCl3, 25 ꢁC) of the obtained polymers
the main resonances are due to 1,4-trans polybutadiene,
while minor resonances were attributed to a 1,2 isolated
units (30.3, 38.4, 43.7, 114.4, 142.9 ppm) [13].
As Lewis acids, the cationic tin compounds should be
useful as catalysts for the polymerization of substrates con-
taining a Lewis basic atom, and therefore were tested in the
polymerization of propylene oxide and e-caprolactone. In
the polymerization of propylene oxide we observed high
reaction rate and absence of stereo- and regioregularity,
clear evidence that an acid catalysed ring opening polymer-
isation mechanism is probably operating in these systems.
The polymerization of e-caprolactone proceeds with good
yields; further work will be addressed to better understand
the mechanism operating in these systems.

L. Annunziata et al. / Journal of Organometallic Chemistry 691 (2006) 1505–1514
1511
Fig. 6. 1H NMR spectra (ClC6D5, 25 ꢁC) of compounds 3 (ii) and 3a (i). (*) Refers to the ‘‘free’’ ligand (1,3,5 triisopropylbenzene) impurities.
3. Conclusions
sevies in a glove box. Reagents were purchased from
Aldrich and used as received. e-Caprolactone and propyl-
ene oxide were distilled in vacuum from CaH2 prior to
use. The carbenium salt [C(C6H5)3]+ [B(C6F5)4]ꢀ was pur-
chased from Boulder and used as received. Butadiene and
ethylene were purchased from SON; butadiene was purified
by distillation from triisopropylaluminium prior to use.
NMR spectra were recorded on a Bruker Advance
400 MHz spectrometer (1H, 400 MHz; 13C, 100 MHz;
119Sn, 149 MHz; 19F, 376 MHz). The 119Sn NMR spectra
were measured relative to Sn(CH3)4. EI MS data were
obtained with a Finnigan Thermoquest GCQ Plus 200
spectrometer using a direct insertion probe. Elemental
analysis were recorded on Thermo Finnigan Flash EA
1112 series C,H,N,S Analyzer.
New Tin(IV) compounds of general formula Tip2SnR2
(Tip = 2,4,6-triisopropylbenzene; R = alkyl, halogen) have
been synthesized and fully characterized by H, 13C, 119Sn
1
NMR, mass spectroscopy and elemental analysis. Charac-
terization by single-crystal X-ray diffraction analysis has
been obtained for compounds 2, 3 and 4, showing the
metal in a distorted tetrahedral geometry. The reactivity
with ionizing agents was studied by NMR spectroscopy.
Compounds 2 and 4 underwent alkyl abstraction by
[(CH3CH2)3Si]+[B(C6F5)4]ꢀ affording stable cationic spe-
cies (2a, 4a), while a cationic species (3a) was generated
from compound 3 using AgSbF6 as ionizing agent. Inter-
estingly, for the cationic specie 4a a p-interaction of the
benzyl group with the metal centre was recognized by solu-
tion NMR studies.
4.2. Synthesis of bis[2,4,6-triisopropylphenyl]dimethyl
tin(IV) (1)
The cationic species (2a, 3a) exhibited moderate activity
as initiator in the cationic polymerization of 1,4-butadiene
and good activity in the ring opening polymerization
(ROP) of propylene oxide and e-caprolactone.
To a stirred solution of Cl2Sn(CH3)2 (504 mg, 2.3 mmol)
in dry toluene (30 ml) at 0 ꢁC was added dropwise a
THF solution of tri-isopropylphenylmagnesiumbromide
(11.1 ml, 5.0 mmol). The mixture was allowed to reflux
for 16 h, then cooled at room temperature, and quenched
with H2O and 10% aqueous HBr. The organic portion
was washed with H2O (2 · 20 ml), NaHCO3 (2 · 20 ml)
and H2O again (2 · 20 ml). The organic solution was dried
over MgSO4, the solvent was removed to give a light yellow
oil. The crude product was dissolved with methyl alcohol
and the solution was stored at ꢀ20 ꢁC. A white solid depos-
4. Experimental section
4.1. General procedure
Manipulation of sensitive materials were carried out
under nitrogen using Schlenk or glove box techniques. Tol-
uene and THF were refluxed over sodium/benzophenone
and distilled under nitrogen prior to use. Diethyl ether
was distilled from LiAlH4, chlorobenzene was dried over
CaH2 and distilled prior to use. CDCl3, CD2Cl2 and
ClC6D5 were distilled from CaH2, C6D6 was distilled from
triisobutylaluminium, and all were stored over molecular
1
ited overnight (730 mg, 60%). H NMR (CDCl3, 293 K):
d = 0.61 (6 H, s, 2J117Sn–1H = 51 Hz, 2J117Sn–1H = 53 Hz,
Sn–CH3), 1.03 (24H, d, J1H–1H = 6.8 Hz, o-CH(CH3)2),
1.19 (12H, d, J1H–1H = 6.9 Hz, p-CH(CH3)2), 2.81 (2H,

1512
L. Annunziata et al. / Journal of Organometallic Chemistry 691 (2006) 1505–1514
m, p-CH(CH3)2), 2.96 (4H, m, o-CH(CH3)2), 6.90 (4H, s,
4J119Sn–1H = 17.4 Hz, ArH). 13C NMR (CDCl3, 293 K):
d = ꢀ0.5 (Sn-CH3), 24.1 (p-CH(CH3)2), 24.8 (o-
CH(CH3)2), 34.4 (p-CH(CH3)2), 37.1 (o-CH(CH3)2), 121.2
(ArCH), 140.5, 149.2, 154.8 (Ar-C). 119Sn (CD2Cl2,
293 K): d = ꢀ113.7. EI MS m/z = 555 [M]+. Anal. Calc.
for C32H52Sn (555.47): C, 69.19; H, 9.44. Found: C,
66.37; H, 9.12%.
ArH). 13C NMR (C6D5Cl, 293 K): d = 24.0 (o-CH(CH3)2),
24.9 (p-CH(CH3)2), 34.5 (p-CH(CH3)2), 34.7 (CH2Ph), 38.1
(o-CH(CH3)2), 122.0 (ArCH), 126–155 (Ph-C + Ar-C).
119Sn (C6D5Cl, 293 K): d = ꢀ56.1. EI MS m/z = 605 [M–
CH2(C6H5)]+. Anal. Calc. for C37H53BrSn (696.43): C,
63.81; H, 7.67. Found: C, 63.59; H, 7.31%.
4.5. Synthesis of allylbenzylbis[2,4,6-triisopropylphenyl]
tin(IV) (4)
4.3. Synthesis of bis[2,4,6-triisopropylphenyl]divinyl
tin(IV) (2)
To a stirred solution of benzylbromobis[2,4,6-triisopro-
pylphenyl] tin(IV) (3) (760 mg, 1.1 mmol) in dry toluene
(60 ml) at 0 ꢁC was added dropwise a THF solution of ally-
lmagnesiumbromide (8 ml, 6.4 mmol). The solution was
refluxed for 2 days. The reaction was then quenched with
H2O and 10% aqueous HBr. The organic portion was
washed with H2O (2 · 50 ml), NaHCO3 (2 · 50 ml) and
H2O again (2 · 50 ml). The organic solution was dried over
MgSO4, the solvent was removed to give a light yellow oil.
The product was crystallized from methanol/hexane 5:1
(509 mg, 70%). Suitable crystals for X-ray crystal structure
determination were grown from methanol/hexane at
ꢀ20 ꢁC. 1H NMR (C6D6, 293 K): d = 1.03 (12H, d,
J1H–1H = 6.6 Hz, CH(CH3)2), 1.15 (12H, d, J1H–1H =
6.8 Hz, CH(CH3)2), 1.19 (12H, d, J1H–1H = 6.9 Hz,
This compound was prepared as above but using
Cl2Sn(CH@CH2)2 (0.900 g, 3.75 mmol) in 60 ml of toluene
and 17 ml of tri-isopropylphenylmagnesiumbromide solu-
tion in THF (0.50 M, 8.5 mmol). (Yield 1.89 g, 87%).
White crystals for X-ray crystal structure determination
were grown from methyl alcohol at ꢀ20 ꢁC. 1H NMR
(C6D6, 293 K): d = 1.17 (24H, d, J1H–1H = 6.8 Hz, o-
CH(CH3)2), 1.22 (12H, d, J1H–1H = 6.9 Hz, p-CH(CH3)2),
2.81 (2H, m, p-CH(CH3)2), 3.20 (4H, m, o-CH(CH3)2), 5.91
(2H, dd, J1H–1H = 2.9, 20.1 Hz, 3J119Sn–1H = 46 Hz,
CH@CH2), 6.25 (2H, dd, J1H–1H = 2.9, 13.5 Hz,
3J119Sn–1H = 90 Hz, CH@CH2), 7.0 (2H, m, CH@CH2),
7.10 (4H, s, 4J119Sn–1H = 18.8 Hz, ArH). 13C NMR
(C6D6, 293 K): d = 24.6 (p-CH(CH3)2), 24.8 (o-CH(CH3)2),
35.0 (p-CH(CH3)2), 38.1 (o-CH(CH3)2), 122.0 (ArCH),
134.1 (CH@CH2), 142.7 (CH@CH2), 139.3, 150.4, 155.8
(Ar-C). 119Sn (C6D6, 293 K): d = ꢀ169.0. EI MS m/
z = 579 [M]+. Anal. Calc. for C34H52Sn (579.49): C,
70.47; H, 9.04. Found: C, 69.81; H, 8.93%.
2
CH(CH3)2), 2.37 (2H, d, J1H–1H = 8.4 Hz, J119Sn–1H =
66.0 Hz, CH2CH2@CH), 2.75 (2H, m, p-CH(CH3)2), 2.87
(4H, m, o-CH(CH3)2), 3.0 (2H, s, 2J119Sn–1H = 56.4
Hz, CH2Ph), 4.83 (1H, dd, J1H–1H = 2.0, 16.9 Hz,
CH2CH@CH2), 5.03 (1H, dd, J1H–1H = 1.9, 16.9 Hz,
CH2CH@CH2), 5.96 (1H, m, CH2CH@CH2), 7.05 (4H, s,
4J119Sn–1H = 18.4 Hz, ArH), 6.8–7.0 (5H, m, Ph). 13C
NMR (C6D6, 293 K): d = 23.5 (CH2CH@CH2), 24.5,
24.8, 25.3 (CH(CH3)2), 25.8 (CH2Ph), 34.9 (p-CH(CH3)2),
38.5 (o-CH(CH3)2), 112.7 (CH2CH@CH2), 122.0 (ArCH),
124.6 (CH2CH@CH2), 137.8 (Ph-C), 141.0, 142.1, 150.3,
155.4 (Ar-C). 119Sn (C6D6, 293 K): d = ꢀ120.6. EI MS
m/z = 617 [M–CH2CH@CH2]+. Anal. Calc. for C40H58Sn
(657.6): C, 73.06; H, 8.89. Found: C, 72.45; H, 8.23%.
4.4. Synthesis of benzylbromobis[2,4,6-triisopropylphenyl]
tin(IV) (3)
To a stirred solution of SnBr4 (2.0 g, 4.5 mmol) in dry
THF (80 ml) was added dropwise a THF solution of triiso-
propylphenylmagnesium bromide (25 ml, 10.8 mmol) at
0 ꢁC. The mixture was allowed to reflux for 16 h. The reac-
tion was then cooled 0 ꢁC and a THF solution of benzyl-
magnesium bromide (12 ml, 10.8 mmol) was added. The
mixture was allowed to reflux for 5 h and then cooled to
room temperature and stirred overnight. The reaction
was quenched with H2O and 10% aqueous HBr. The
organic portion was washed with H2O (2 · 20 ml),
NaHCO3 (2 · 20 ml) and H2O again (2 · 20 ml). The
organic solution was dried over Na2SO4, the solvent was
removed to give a light yellow oil. The crude product was
dissolved in hexane and the solution was stored at
ꢀ20 ꢁC. A white solid deposited overnight (2.3 g, 73%).
Suitable crystals for X-ray crystal structure determination
4.6. Generation of {bis[2,4,6-triisopropylphenyl]vinyl
tin(IV)}+[B(C6F5)4]ꢀ (2a)
The reaction was carried out in a glove box in a 5 mm
NMR tube. To a solution of carbenium salt [C(C6H5)3]+
[B(C6F5)4]ꢀ (160 mg, 0.17 mmol) in 0.5 ml of dry C6D6
was added triethylsilane (25 mg, 0.22 mmol). Addition pro-
duced two layers. The top colorless phase, containing
organic subproduct, was taken off with a syringe and a
brown oil (lower phase) remained in the NMR tube. A
solution of compound 2 (110 mg, 0.19 mmol in 0.5 ml dry
C6D6) was added to create two layer again. The upper
phase was removed and the oil phase, at bottom, was char-
acterized by NMR. 1H NMR (C6D6, 293 K): d = 1.0 (24H,
d, J1H–1H = 6.9 Hz, o-CH(CH3)2), 1.13 (12H, d,
J1H–1H = 6.8 Hz, p-CH(CH3)2), 1.90 (4H, m, o-
CH(CH3)2), 2.70 (2H, m, p-CH(CH3)2), 5.5 (1H, dd,
1
were grown from hexane at ꢀ20 ꢁC. H NMR (C6D5Cl,
293 K): d = 1.16 (12H, d, J1H–1H = 6.5 Hz, CH(CH3)2),
1.24 (12H, d, J1H–1H = 6.6 Hz, CH(CH3)2), 1.30 (12H,
d, J1H–1H = 6.9 Hz, CH(CH3)2), 2.89 (2H, m, p-
CH(CH3)2), 3.19 (4H, m, o-CH(CH3)2), 3.39 (2H, s,
2J119Sn–1H = 58.7 Hz, CH2Ph), 7.03–7.28 (9H, m, Ph +

L. Annunziata et al. / Journal of Organometallic Chemistry 691 (2006) 1505–1514
1513
J1H–1H = 19.6 Hz,
CH@CH2),
6.3
(1H,
dd,
5.2. e-Caprolactone
J1H–1H = 11.8 Hz, CH@CH2), 6.7 (1H, m, CH@CH2),
7.0 (4H, s, ArH). 13C NMR (C6D6, 293 K): d = 23.2 (p-
CH(CH3)2), 24.1 (o-CH(CH3)2), 34.6 (p-CH(CH3)2), 44.1
(o-CH(CH3)2), 124.4 (ArCH), 144.7 (CH@CH2), 145.5
(CH@CH2), 134–158 (Ar-C). 119Sn (C6D6, 293 K):
d = 591.7.
A typical polymerization test was carried out as above
but using 1.5 ml of e-caprolactone. After 1 day the poly-
merization was quenched in heptane. The polymer was fil-
tered, dried in vacuo and characterized by NMR
spectroscopy (Yield = 1.13 g). 1H NMR (CDCl3, 25 ꢁC)
d = 1.37 (m, 2H, –CH2–), 1.65 (m, 4H, –CH2–), 2.29 (t,
2H, –CH2C(O)O–), 4.08 (t, 2H, –CH2OC(O)–).
4.7. Generation of {benzylbis[2,4,6-triisopropylphenyl]
tin(IV)}+[SbF6]ꢀ (3a)
5.3. Butadiene
Compound 3 (19 mg, 27 lmol) was dissolved in dry
ClC6D5 (0.5 ml) and AgSbF6 (9 mg, 27 lmol) was added.
A white solid (AgCl) precipitated. The solution was ana-
A polymerization test was carried out at 25 ꢁC using
100 lmol ofꢀ compound (2) and 100 lmol of
Et3SiþBðC6F5Þ in 30 ml of toluene. The monomer was dis-
1
lysed by NMR spectroscopy. H NMR (C6D5Cl, 293 K):
4
d = 1.23 (36H, d, J1H–1H = 7.5 Hz, CH(CH3)2), 2.58
(4H, m, o-CH(CH3)2), 2.83 (2H, m, p-CH(CH3)2), 3.94
(2H, s, 2J119Sn–1H = 73.6 Hz, CH2Ph), 7.0–7.3 (9H, m,
Ph + ArH). 13C NMR (C6D5Cl, 293 K): d = 23.7
(CH(CH3)2), 34.5 (p-CH(CH3)2), 37.9 (CH2Ph), 40.8 (o-
CH(CH3)2), 123.4 (ArCH), 140–154 (Ph-C + Ar-C). 19F
(C6D5Cl, 293 K): d = ꢀ118.7. 119Sn (C6D5Cl, 293 K):
d = 257.4.
tilled from Al(i-Pr)3 at ꢀ78 ꢁC. After 90 h the polymeriza-
tion was stopped with acidified methanol solution. The
solution was treated with water and hexane (3 · 50 ml).
The organic phase was dried on Na2SO4 and the solvent
removed by rotary evaporation. (Yield = 2.17 g).
A polymerization test in the presence of compound (3)
(100 lmol) and AgSbF6 (100 lmol) was carried out analo-
gously in 30 ml of dry chlorobenzene. After 90 h the poly-
merization was stopped with acidified methanol. The
polymer was filtered and dried in vacuo (Yield = 0.290 g).
The products were characterized by NMR spectroscopy.
13C NMR (CDCl3, 25 ꢁC) d = 32.9, 130.2 (1,4 trans units)
30.3, 38.4, 43.7, 114.4, 142.9 (minor resonances, 1,2 iso-
lated units).
4.8. Generation of {benzylbis[2,4,6-triisopropylphenyl]
tin(IV)}+[B(C6F5)4]ꢀ (4a)
The cationic species 4a was generated as described for
species 2a but using 124 mg of [C(C6H5)3]+ [B(C6F5)4]ꢀ
(0.13 mmol), 24 mg of triethylsilane (0.17 mmol) and
99 mg of allylbenzylbis[2,4,6-triisopropylphenyl]tin (0.15
6. X-ray crystallography
1
mmol) in C6D6 dry. H NMR (mixture of 0.5 ml C6D6
and 1 ml ClC6D5, 293 K): d = 0.93 (24H, d, J1H–1H =
6.3 Hz, o-CH(CH3)2), 1.10 (12H, d, J1H–1H = 6.9 Hz,
p-CH(CH3)2), 1.88 (4H, m, o-CH(CH3)2), 2.70 (2H, m, p-
CH(CH3)2), 3.4 (2H, s, 2J119Sn–1H = 56.2, CH2Ph), 6.7
(2H, d, J1H–1H = 7.7 Hz, o-Ph), 7.04 (4H, s, ArH), 6.9–
7.03 (3H, m, Ph). 13C NMR (C6D6, 293 K): d = 23.7,
24.5 (CH(CH3)2), 35.1 (p-CH(CH3)2), 42.9 (CH2Ph), 46.1
(o-CH(CH3)2), 124.8 (ArCH), 136–157 (Ar-C). 119Sn
NMR (C6D6, 293 K): d = 599.9; 119Sn NMR (mixture of
0.5 ml C6D6 and 15 ll ClC6D5, 293 K): d = 585.3; 119Sn
NMR (mixture of 0.5 ml C6D6 and 1 ml ClC6D5, 293 K):
d = 524.9.
Suitable crystals were selected and mounted in Linde-
mann capillaries under inert atmosphere. Diffraction data
were measured at room temperature with a Rigaku AFC7S
diffractometer using graphite monochromated Mo Ka
˚
radiation (k = 0.71069 A). Data reduction was performed
with the crystallographic package CrystalStructure [14].
The structures were solved by direct methods using the pro-
gram SIR92 [15] and refined by means of full-matrix least-
squares based on F2 using the program SHELXL97 [16]. All
non-hydrogen atoms were refined anisotropically. Hydro-
gen atoms were positioned geometrically and included in
structure factors calculations but not refined. Restraints
were applied to CH–CH3 distances of isopropyl groups.
Crystal data and refinement details are reported in Table
2. Crystal structures are drawn by means of the program
ORTEP32 [17].
5. Polymerization tests
5.1. Propylene oxide
Crystallographic data (excluding structure factors) for
the structures reported in this paper have been deposited
with the Cambridge Crystallographic Data Centre as sup-
plementary publications no. CCDC-287930 (compound
2), CCDC-287931 (compound 3) and CCDC-287929
(compound 4). Copies of data may be obtained free of
charge on application to CCDC, 12 Union Road,
Cambridge CB2 EZ, UK [Fax: +44(1223)336-03; e-mail:
deposit@ ccdc.cam.ac.uk].
A typical polymerization test was carried out at 25 ꢁC
using 60 lmol of neutral compound (2 or 3) and 60 ꢀlmol
of suitable ionizing agent (AgSbF6, Et3SiþBðC6F5Þ ) in
4
15 ml of toluene dry. Propylene oxide (5 ml) was added.
After 5 min, the solvent was removed in vacuo to give an
oily product (Yield = 2.6 g). 1H NMR (CDCl3, 25 ꢁC)
d = 1.04 (d, 3H, CH3), 3.30–3.68 (br m, 3H, OCH(CH3)
and OCH2).

1514
L. Annunziata et al. / Journal of Organometallic Chemistry 691 (2006) 1505–1514
Table 2
(d) K.-C. Kim, C.A. Reed, D.W. Elliott, L.J. Mueller, F. Tham, L.
Lin, J.B. Lambert, Science 297 (2002) 825–827;
Crystal data and structure refinement details for compounds 2–4
(e) A. Sekiguchi, T. Fukawa, V. Ya. Lee, M. Nakamoto, J. Am.
Chem. Soc. 125 (2003) 9250–9251;
(f) T. Muller, C. Bauch, M. Ostermeier, M. Bolte, N. Auner, J. Am.
¨
2
3
4
Formula
SnC34H52
579.47
Triclinic
SnBrC37H53
696.40
Monoclinic
P21/c
12.023(3)
10.264(2)
29.716(6)
SnC40H58
657.55
Monoclinic
C2/c
37.490(15)
11.136(4)
18.267(6)
Formula weight
Crystal system
Space group
Chem. Soc. 125 (2005) 2158–2168.
[2] I. Zharov, B.T. King, Z. Havlas, A. Pardi, J. Milch, J. Am. Chem.
Soc. 122 (2000) 10253–10254.
[3] J.B. Lambert, L. Lin, S. Keinan, T. Muller, J. Am. Chem. Soc. 125
(2003) 6022–6023.
[4] L. Annunziata, D. Pappalardo, C. Tedesco, C. Pellecchia, Organo-
metallics 24 (2004) 1947–1952.
[5] A.G. Davies, P.J. Smith, in: Comprehensive Inorganic Chemistry,
vol. 2, pp. 527–530.
[6] (a) T.P. Lockhart, W.F. Manders, E.O. Schlemper, J. Am. Chem.
Soc. 107 (1985) 7;
(b) T.P. Lockhart, W.F. Manders, Inorg. Chem. 25 (1985) 892–895.
[7] (a) F. Theobald, B. Trimaille, J. Organomet. Chem. 267 (1984) 143;
(b) P. Ganis, D. Furlani, D. Marton, G. Tagliavini, G. Valle, J.
Organomet. Chem. 293 (1985) 207.
[8] (a) G.R. Davis, J.A. Jarvis, B.T. Kilbourn, A.P. Pioli, J. Chem. Soc.
Chem. Commun. (1971) 677;
(b) G.R. Davis, J.A. Jarvis, B.T. Kilbourn, J. Chem. Soc. Chem.
Commun. (1971) 1511–1512.
[9] J.L. Atwood, in: Inclusion Compounds, vol. 1, Academic Press,
London, 1984 (Chapter 9).
ꢀ
P1
˚
a (A)
9.606(4)
12.126(4)
16.853(3)
103.07(2)
96.62(2)
112.53(3)
1721.4(10)
2
1.118
0.76
612
10053
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
93.387(19)
98.99(3)
3
˚
V (A )
3660.8(14)
4
1.264
1.81
1440
3403
7533(5)
8
1.160
0.70
2784
6631
Z
Dcalc (g cmꢀ3
)
l (Mo Ka) (mmꢀ1
F(000)
)
Independent reflections
measured
Parameters/restraints
R1 [Fo > 4r(Fo)]
wR2 (all reflections)
Goodness-of-fit
316/66
352/29
370/66
0.0452 (5771) 0.0461 (2569) 0.0635 (3559)
0.1305
2.473
ꢀ0.68/0.71
0.1303
0.897
ꢀ1.39/0.75
0.2664
1.057
ꢀ1.31/1.27
ꢀ3
˚
Dq min/Dq max (e A
)
[10] (a) E.A. Mintz, K.G. Moloy, T.J. Marks, J. Am. Chem. Soc. 104
(1982) 4692–4695;
(b) S.L. Latesky, A.K. McMullen, G.P. Niccolai, I.P. Rothwell,
Organometallics 4 (1985) 902–908;
Acknowledgements
(c) F.J. Jordan, R.E. La Pointe, C.S. Bajgur, S.F. Echols, R. Willett,
J. Am. Chem. Soc. 109 (1987) 4111–4113;
(d) D.J. Crowther, R.F. Jordan, C. Baenziger, A. Verma, Organo-
metallics 9 (1990) 2574–2580;
(e) P. Legzdins, R. Jones, E. Phillips, V. Yee, J. Trotter, F. Einstein,
Organometallics 10 (1991) 986–1002;
(f) C. Pellecchia, A. Grassi, A. Immirzi, J. Am. Chem. Soc. 115
(1993) 1160–1162;
The authors are grateful to Dr. Carla Scarabino for ele-
mental analysis, to Dr. Patrizia Oliva for 119Sn NMR
experiments, to Dr. Maria Grazia Napoli for EI MS mea-
surements and Dr. Orazio De Vita for some synthetic prep-
arations. This work was supported by the Italian Ministry
of University and Research (PRIN 2004).
(g) C. Pellecchia, A. Immirzi, D. Pappalardo, Peluso, Organomet-
allics 13 (1994) 3773–3775.
Appendix A. Supplementary data
[11] S.P. Patterman, I.L. Karle, G.D. Stucky, J. Am. Chem. Soc. 92
(1970) 1150–1157.
[12] F. Wu, A.K. Dash, R.F. Jordan, J. Am. Chem. Soc. 126 (47) (2004)
15360–15361, and reference therein.
[13] K. Matsuzaki, T. Uryu, T. Asakura, NMR Spectroscopy and
Stereoregularity of Polymers, 1995, pp. 41–46.
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.jorganchem.
2005.12.011.
[14] Crystal Structure, Crystal Structure Analysis Package, Molecular
Structure Corporation.
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