Octahedral alkylbis(phenoxy-imine)tin(IV) complexes: Effect of substituents on the geometry of the complexes and their reactivity toward ionizing species and ethylene

Article abstract of DOI:10.1002/ejic.200700937

The synthesis and characterization of the organo-tin compounds L ₂SnR₂ [L = N-(3,5-dichlorosalicylidene)aniline; R = CH₃ (1), R = CH₂Ph (2)] and L′₂SnR ₂ [3: L′ = N-(3-tert-butylsalicyliden

Full text of DOI:10.1002/ejic.200700937

FULL PAPER
DOI: 10.1002/ejic.200700937
Octahedral Alkylbis(phenoxy-imine)tin(IV) Complexes: Effect of Substituents
on the Geometry of the Complexes and Their Reactivity Toward Ionizing
Species and Ethylene
Liana Annunziata,[a] Daniela Pappalardo,*[b] Consiglia Tedesco,[a] and Claudio Pellecchia[a]
Keywords: Tin / N,O ligands / Cations / Ethylene / Oligomerization
The synthesis and characterization of the organo-tin com-
pounds L2SnR2 [L = N-(3,5-dichlorosalicylidene)aniline; R =
CH3 (1), R = CH2Ph (2)] and LЈ2SnR2 [3: LЈ = N-(3-tert-butyl-
salicylidene)aniline, R = CH2Ph] are described herein. NMR
studies showed a highly symmetric structure for complex 1,
with the alkyl groups in a trans configuration, and the
presence of at least two isomers in fluxional equilibrium for
compounds 2 and 3. Single-crystal X-ray characterization for
compound 2 showed an octahedral geometry with the alkyl
groups in trans relationship. The reactivity of the synthesized
compounds toward ionizing agents was studied by NMR
spectroscopy. For compounds 1 and 2 formation of cationic
species through alkyl abstraction by B(C6F5)3 was observed.
For compound 3, a cationic species was obtained by reaction
with 1 equiv. of [C(C6H5)3]+[B(C6F5)4]–; in this species a ηn
coordination of the benzyl group with the metal centre was
recognized by NMR solution study. All the obtained cationic
species promoted ethylene oligomerization under mild con-
ditions, producing oligomers with saturated end groups and
methyl branches. Oligoethylene end-group NMR analysis
and deuteriolysis experiments excluded the migratory-inser-
tion mechanism.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
interesting features that will be discussed here and com-
pared with the previously reported results.
Introduction
The activity in olefin polymerization of compounds
based on metals beyond group 13 has never been reported
in the literature.[1] Recently we reported the oligomerization
of ethylene in the presence of bis(phenoxy-imine)dialkyl-
tin(IV) complexes.[2] The latter compounds showed octahe-
dral geometry with alkyl groups in a cis configuration and
underwent alkyl abstraction reaction with the carbenium
salt [C(C6H5)3]+[B(C6F5)4]–. The obtained cationic species
exhibited low activity in ethylene oligomerization under
mild conditions, producing oligomers with saturated end
groups and methyl branches. To the best of our knowledge,
the oligomerization of ethylene by a group 14 compound is
unprecedented in the literature.
These results prompted us to persist in exploring the re-
activity of different salicylaldiminatotin(IV) complexes, in
order to ascertain the mechanism involved in the formation
of branched oligoethylenes. Therefore we studied the syn-
thesis and the structural properties of novel dialkyl bis(sal-
icylaldiminato)tin(IV) complexes, bearing electronically and
sterically different ligands. These complexes revealed some
Results and Discussion
Synthesis of the Complexes
The synthesized bis(phenoxy-imine)tin(IV) complexes
are described in Scheme 1. The N-(3-tert-butylsalicylidene)-
aniline[3] and N-(3,5-dichlorosalicylidene)aniline[4] ligands
were synthesized by a condensation reaction between the
aldehyde and the aniline according to literature procedures.
Complexes were prepared by a metathesis reaction of the
sodium salt of the ligands with the corresponding dialkyl-
tin(IV) chloride in tetrahydrofurane, producing compounds
1–3 with high yields (73–91%), as yellow or orange solids.
The products are stable in an inert atmosphere, but easily
underwent hydrolysis with formation of the free ligand in
the presence of traces of adventitious water.
[a] Dipartimento di Chimica, Università di Salerno,
via Ponte don Melillo, 84084 Fisciano (SA), Italy
Fax: +39-089-969603
[b] Dipartimento di Studi Geologici ed Ambientali, Università del
Sannio,
via dei Mulini 59/A, 82100 Benevento, Italy
E-mail: pappalardo@unisannio.it
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
Scheme 1.
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Octahedral Alkylbis(phenoxy-imine)tin(IV) Complexes
NMR Characterization of the Complexes
Nelson equation,[6] from the value of the coupling constant
2JSn,H for the methylene hydrogen atoms (CH2Ph), the cal-
culated angle for the C–Sn–C bonds was of 193° (Ϯ6), in
the expected range for a structure with the benzyl groups
in a trans configuration. As above, of the five possible iso-
mers, the two “trans” ones are compatible with the NMR
spectroscopic data in solution. Single-crystal X-ray diffrac-
tion analysis revealed that compound 2 crystallized in the
“trans-II” isomeric form (vide infra).
In order to investigate the fluxional equilibrium between
different isomers in solution, variable temperature 1H
NMR experiments were performed between 278 and 188 K.
Lowering the temperature, the broad signals split (see elec-
tronic supporting information). At 203 K the signal of the
methylene hydrogen atoms CH2Ph split up into a well de-
fined AB pattern at about 1.9 ppm, two broad signals at δ
= 2.72 ppm (2JSn,H = 27.3 Hz) and 2.93 ppm, and a minor
AB pattern (δ = 2.45 ppm). At lower field three main sing-
lets (δ = 8.00, 7.74 and 7.66 ppm) and a minor one (δ =
7.56 ppm), attributable to the imine protons, were observed.
Such observations are compatible with the presence of at
least two main isomeric species and a minor one involved
in fluxional equilibria.
All the synthesized compounds were characterized by
1H, 13C and 119Sn NMR spectroscopy, and mass spec-
troscopy. Compound 2 was also characterized by single-
crystal X-ray diffraction analysis.
The 119Sn NMR spectrum of the dimethyl compound 1,
bearing the chlorinated phenoxy-imine ligands, showed one
signal at –306.5 ppm, compatible with the presence of a sin-
gle organometallic species. The 1H NMR spectrum showed
very sharp signals and a pattern compatible with the pres-
ence of a highly symmetric structure in solution. Character-
istic signals were the singlet at δ = 0.79 ppm (2JSn,H
=
90.7 Hz) for the methyl groups, and the singlet at δ =
8.02 ppm (3JSn,H = 12.1 Hz) for the imine hydrogen atoms
(CH=N). It is known from the literature that the coupling
constants 2J(119Sn–1H) and 1J(119Sn–13C) can be used to
estimate the methyl–tin–methyl angle.[5,6] For the previously
reported bis(phenoxy-imine)tin(IV) dimethyl complexes, by
using the equation specifically developed by Nelson for oc-
tahedral dialkyltin compounds,[6] we calculated a methyl–
tin–methyl angle of 106(6)°, suggesting a structure with the
methyl groups in a cis configuration; this result was nicely
in agreement with the value disclosed by single-crystal X-
ray analysis (107.4°). For compound 1 the value of the
The dibenzyl compound 3, bearing the N-(3-tert-butyl-
salicylidene)aniline ligands, displayed an intricate 1H NMR
spectrum at room temperature (Figure 1). The compound
must exist in solution in two isomeric forms, as evidenced
by the presence, in the 119Sn NMR spectrum, of two reso-
nances at –456.5 ppm and –457.9 ppm (1:1 molar ratio). In
2
coupling constant JSn,H for the methyl group bonded to
tin is significantly higher than the value observed for pre-
viously reported compounds,[2] and the calculated angle C–
Sn–C is of 160° (Ϯ6), in the expected range for a structure
with the methyl groups in a trans configuration. For octahe-
dral bis(phenoxy-imine) dialkyl complexes, five isomers are
possible, as displayed in Scheme 2. In the present case,
therefore, two isomers, “trans-I” and “trans-II”, are com-
patible with the NMR spectroscopic data in solution.
1
the H NMR spectrum, two sets of signals, attributable to
two different species in a 1:1 ratio, were also recognized.
The first signal set (one singlet at δ = 1.07 ppm for the tBu
group, one signal with AB pattern at 2.5 ppm for the dia-
stereotopic methylene hydrogen atoms CH2Ph and one sin-
3
glet at δ = 7.99 ppm for the imine proton, with a JSn,H of
33.65 Hz) is compatible with a highly symmetric species (I).
The second signal set, compatible with a nonsymmetric spe-
cies (II), consists of two singlets at δ = 1.28 ppm and
1.41 ppm for the tBu groups, two signals with AB pattern
for the CH2Ph at 2.4 ppm and 2.7 ppm and two singlets for
the imine hydrogen atoms at δ = 7.69 ppm and 7.89 ppm.
The 13C NMR spectrum of compound 2 coherently dis-
played two signals sets, one compatible with a symmetric
species I, the second one compatible with a nonsymmetric
species II. Variable-temperature 1H NMR experiments, per-
formed between 273 and 353 K, indicated the presence of a
fluxional equilibrium between species I and II. On increas-
ing the temperature the signals of species II collapsed into
one signal set, attributed to the symmetric species I (Fig-
ure 2). At 333 K only one AB signal set for the CH2Ph hy-
Scheme 2.
The dibenzyl compound 2 showed two broad signals, at drogen atoms, centred at δ = 2.70 ppm, and only one singlet
–425.6 and –426.9 ppm, in the 119Sn NMR spectrum at at δ = 7.83 ppm (3JSn,H = 16.20 Hz) for the imine hydrogen
room temperature, thus indicating the presence of different atoms (CH=N) were observed. Unfortunately, we were not
1
2
tin species in solution. In addition, in the H NMR spec- able to measure the coupling constants J(Sn–H) for the
trum broad signals were also observed. Characteristic reso- methylene H atoms CH2Ph, and consequently to estimate
nances are a singlet at δ = 2.56 ppm (2JSn,H = 105.1 Hz) for the geometry of the benzyl ligands around the tin. We were
the methylene hydrogen atoms (CH2Ph) and a singlet at δ unable to observe the coalescence temperature for the two
= 7.84 ppm for the imine protons (CH=N). By using the species up to 373 K. The 119Sn NMR spectrum, performed
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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L. Annunziata, D. Pappalardo, C. Tedesco, C. Pellecchia
FULL PAPER
at this temperature in C6D5Cl, still showed two resonances ring Sn1–N1–C1–C2–C7–O1 is quite planar (rmsd 0.073)
at –456.2 and –457.6 (in 1:0.45 ratio). We previously ob- with an envelope angle (between the five-atom plane N1–
served a fluxional equilibrium between two different iso- C1–C2–C7–O1 and the Sn1–N1–C1 plane) of 9.39(14)°.
meric species for the analogous bis[N-(3-tert-butylsalicylid-
Table 1. Selected bond lengths [Å], bond angles and torsion angles
ene)anilinato]dimethyltin(IV) compound through NMR
[°] for compound 2. Symmetry equivalent atoms are indicated with
spectroscopy.[2] In that case two species (a C2-symmetric
one and a C1-symmetric one) were frozen out at 195 K,
an asterisk.
Sn1–C14
2.165(3)
2.142(2)
2.339(2)
1.292(3)
93.13(11)
86.87(11)
82.90(8)
97.11(8)
180.00
N1–C8
C1–C2
1.439(3)
1.446(4)
1.415(4)
1.299(3)
92.06(11)
87.93(11)
while the coalescence temperature Tc was observed at 278 K
Sn1–O1
Sn1–N1
1
in the H NMR spectra and at 333 K in the 119Sn NMR
C2–C7
spectra. It is worth noting that the presence of bulkier ben-
zyl ligands in compound 3 instead of methyl groups slows
down the fluxional equilibrium, freezing out the isomers
already at room temperature.[7]
N1–C1
O1–C7
C14–Sn1–N1
C14*–Sn1–N1
C14–Sn1–C14* 179.998(1)
Sn1–C14–C15
N1–Sn1–N1*
C14–Sn1–O1
C14*–Sn–O1
O1–Sn1–N1
O1–Sn1–N1*
O1–Sn1–O1*
116.87(19)
180.00
C1–N1–C8–C13 –49.9(4)
1
Figure 1. H NMR spectrum (CDCl3, 298 K) of compound 3.
Figure 3. Molecular structure of compound 2. Thermal ellipsoids
are drawn at 30% probably level. Hydrogen atoms have been omit-
ted for clarity.
It is worth noting that the analogous bis[N-(3-tert-butyl-
salicylidene)aniline]tin(IV) dialkyl complexes and the bis[N-
(3-tert-butylsalicylidene)-2,3,4,5,6-pentafluoroaniline]tin(IV)
dimethyl compound were crystallized in the cis-I isomeric
structure, displaying the two oxygen atoms trans to each
other and the alkyl ligands and the nitrogen atoms in a cis
relationship.[2] Steric factors could explain the difference in
the coordination environment at the central tin atom. The
presence of chlorine atoms ortho to oxygen atoms of the
phenoxy-imine ligand probably plays a role, and could
favour ligand disposition in the plane.
Notably there are very few structurally characterized oc-
tahedral bis(phenoxy-imine)MR2 compounds (M = any
metal, R = alkyl or halogen atom) presenting the R ligands
in a trans relationship.[8]
1
Figure 2. H NMR spectra of aliphatic regions of compound 3 at
variable temperature (ClC6D5).
Generation of Cationic Species
X-ray Diffraction Analysis
The synthesis of free cationic species of group 14 ele-
Compound 2 was crystallized from methylene chloride/ ments is a tricky task, because of their high reactivity. In
hexane at room temperature. Crystal data are given in the the literature, examples of organotin cations are quite rare.
Experimental Section and selected bond lengths and angles Among them are the remarkable crystal structures of Lam-
are listed in Table 1. A distorted octahedral geometry with bert et al.’s trismesityl stannylium cation displaying a trigo-
the alkyl group in a trans configuration and the two oxygen nal planar geometry around tin,[9] Sekiguchi et al.’s “stable
atoms in trans position was disclosed (Figure 3). The tin and free” tin cation bearing three tris(alkyl)silyl ligands[10]
atom is located on a crystallographic inversion centre and and Michl et al.’s tributylstannylium carboranate.[11] On the
the benzyl moieties coordinated in a η1 mode. The six-atom contrary, organotin cationic compounds stabilized by the
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Octahedral Alkylbis(phenoxy-imine)tin(IV) Complexes
ligand’s intramolecular interactions or by external donor
Compound 3 displayed a different behaviour from com-
atoms are well known and have also been structurally char- pounds 1 and 2. Reaction of compound 3 with B(C6F5)3
acterized.[12]
led to degradation, while reaction with 1 equiv. of [C(C6-
In previous work, in order to mimic the active species in H5)3]+[B(C6F5)4]– produced abstraction of one benzyl group
homogeneous olefin polymerization catalysis, we pursued and formation of the cationic species 3a. Consistently,
cationic species with the formula L2SnR+ (L = phenoxy- in the 1H NMR spectrum (Figure 4), the species
imine; R = alkyl). For this purpose we used ionizing rea- PhCH2C(C6H5)3 was identified as a byproduct.[16] In the
gents, such as [(C6H5)NH(CH3)2]+[B(C6F5)4]–, B(C6F5)3 119Sn NMR only one resonance at –448.7 ppm was ob-
and [C(C6H5)3]+[B(C6F5)4]–, traditionally used in homogen- served. In the 1H NMR spectrum, characteristic resonances
eous Ziegler–Natta catalysis. The alkyl abstraction reaction are one singlet at δ = 1.34 ppm for the tert-butyl hydrogens,
from the dimethyl- and dibutyl-bis(phenoxyimine)tin(IV) one singlet at δ = 3.27 ppm (2JSnH = 118.84 Hz) for the
compounds was successfully obtained by the carbenium methylene H atoms and one singlet at δ = 8.53 ppm (3JSnH
salt [C(C6H5)3]+[B(C6F5)4]–. Reactions with [(C6H5)NH- = 14.92 Hz) for the imine hydrogen CH=N. The signal
(CH3)2]+[B(C6F5)4]– and B(C6F5)3 led instead to degrada- pattern is compatible with the presence of one symmetric
tion products. The obtained cationic species exhibited some species in solution, and shifted at higher frequency, if com-
activity in the oligomerization of ethylene under mild con- pared with the corresponding resonance for the neutral
ditions, producing short-chain oligomers, with saturated compound 3 in the same solvent.
end groups and methyl branches.[2] Now these studies have
been extended to the new synthesized complexes, and are
reported herein.
Reactions of complexes 1–3 with [(C6H5)NH(CH3)2]+-
[B(C6F5)4]– led to decomposition, producing free phenoxy-
imine ligands.
Compounds 1 and 2, bearing the chlorinated phenoxy-
imine ligand, displayed similar reactivity toward ionizing
agents. Actually, reaction with [C(C6H5)3]+[B(C6F5)4]– re-
sulted invariably in mixtures of decomposition products,
while the reaction with B(C6F5)3 produced the abstraction
of an alkyl group. For instance, the reaction of compound
1 with 1 equiv. of B(C6F5)3 rapidly produced a cationic spe-
cies (1a) by methyl abstraction, as indicated by the presence
1
in the H NMR spectrum of a resonance at δ = 0.42 ppm
attributable to the methyl group of the “free” anion
[CH3B(C6H5)3].[13] The 119Sn NMR spectrum of species 1a
showed only one signal at –394.0 ppm. The pattern of sig-
Figure 4. 1H NMR spectrum (CD2Cl2, 298 K) of compound 3a:
nals in the 1H NMR spectrum was compatible with the
presence in solution of one symmetric species, having a li-
(*) “free” ligand impurities; (᭿) C(C6H5)3CH2C6H5.
gand/methyl signals integral ratio consistent with a 2:1 for-
The benzyl ligand can interact with electron-deficient
mulation. According to the formation of a stannylium cat- metal centres also through the π-aromatic system. The ηn
ion, all the resonances were downfield shifted, if compared (n Ͼ 1) coordination is typical of transition metals;[17]
with the corresponding resonances for the neutral com- among main group elements, η3 interaction has been ob-
pound 1 in the same condition. Characteristic resonances served, in the solid state, for benzyl lithium.[18] Latesky et
are the singlet at 1.042 ppm for SnCH3 (2JSnH = 101.8 Hz) al. found NMR spectroscopic evidence to detect this type
and the singlet at δ = 8.54 ppm for the imine proton (3JSnH of interaction in solution.[19] In particular, ηn benzyl ligands
= 22.3 Hz).[14]
are characterized by a high-field shift for the ortho hydrogen
Reaction of compound 2 with 1 equiv. of B(C6F5)3 pro- resonance (δ Ͻ 6.8 ppm) in the 1H NMR, and by large 1JCH
duced a new mono-benzyltin species (2a), characterized by values for the CH2 group (J Ͼ 130 Hz). The increase of the
a signal at –500.0 ppm in the 119Sn NMR spectrum. In the coupling constant can be explained with an increased “sp2”
1H NMR spectrum characteristic resonances are a singlet character of the α-carbon, involving a decrease of the Mt–
at δ = 3.28 ppm for SnCH2Ph (2JSnH = 117.0 Hz) and a C–Ph angle. Interestingly, in the NMR spectra of cationic
singlet at δ = 8.47 ppm due to imine proton (3JSnH
=
species 3a we observed an upfield shift of the ortho benzyl
1
1
18.2 Hz). However, in the H NMR spectrum of species 2a hydrogens’ resonance (δ = 6.44 ppm), and a JCH value for
the signals for the expected byproduct [PhCH2B(C6F5)3]– the methylene carbon of 139.8 Hz. The value observed is
were absent. In addition, the 19F NMR spectrum showed a higher than that observed in tetrabenzyltin (1JCH
=
large number of resonances of comparable intensity, clear 133 Hz), usually taken as a model for a normal σ bond (η1)
indication of the existence of more than one fluorinated benzyl ligand.[20] These spectroscopic features thus suggest
species in solution, probably generated by aryl/alkyl group that in the cationic species 3a the benzyl ligand interacts
exchange reactions.[15]
with the tin also through the π-aromatic system. Therefore
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5755

L. Annunziata, D. Pappalardo, C. Tedesco, C. Pellecchia
FULL PAPER
a ηn (n Ͼ 1) coordination for the benzyl ligand can be hy-
A π interaction of the benzyl group to the tin centre was
pothesized.
previously recognized by NMR for the cationic species
In order to study the influence of the temperature on the Tip2SnBz+ (Tip = 2,4,6-triisopropylphenyl).[21]
coordination of the benzyl to the tin atoms, 1H NMR spec-
tra were recorded at lower temperature (between 278 K and
1
193 K). The aliphatic regions of the H NMR spectra for
Reactivity Toward Ethylene
the cationic species 3a are shown in Figure 5. On decreasing
the temperature, the singlet of the methylene hydrogen
We disclosed that the ethylene oligomerization reaction
atoms SnCH2Ph split up into an AB pattern, indicating that is promoted by dimethyl- and dibutyl-bis(phenoxy-imine)-
they are diastereotopic. At 233 K the doublet attributable tin(IV) complexes, activated by the carbenium salt.[2] The
to the ortho benzyl hydrogen atoms at δ = 6.44 ppm showed obtained oligoethylene oily product had short chains, with
satellite peaks due to the tin–hydrogen spin–spin coupling saturated end groups and methyl branches. This result con-
with JSnH of 33.7 Hz. Similar NMR control experiments stituted the first example of oligomerization of ethylene by
performed for the tetrabenzyltin compound at 233 K dis- a group 14 compound, and prompted us to investigate the
played
a singlet for the methylene hydrogen atoms reactivity of different bis(phenoxy-imine)tin(IV) complexes
SnCH2Ph at δ = 2.16 ppm (1JCH = 132.6 Hz) and a doublet toward ethylene.
for the ortho benzyl hydrogen atoms at δ = 6.60 ppm with
a JSnH of 14.9 Hz.
Compound 3
in combination with [C(C6H5)3]+[B-
(C6F5)4]– and compounds 1 or 2 in combination with
B(C6F5)3 were able to oligomerize ethylene under mild con-
ditions, affording short-chain oligomers (40–60 carbon
atoms, estimated by NMR), with saturated end groups and
methyl branches. The activities were always very low, and
comparable with those observed with previously reported
compounds.[2] These results suggest that the structural and
electronic properties of the salicylidene-aniline ligands,
while influencing the structure of the complexes and their
reactivity toward ionizing agents, do not control the ethyl-
ene oligomerization activity, at least in the presence of the
used catalysts, and under the explored experimental condi-
tions.
Chain end-group analysis was used as a tool to under-
stand the initiation and termination steps of the oligomer-
ization mechanism. Actually, the initiation step is not the
olefin insertion into the Sn–alkyl bond. In fact, the ob-
tained oligomers always had saturated n-propyl end groups,
even when the oligomerization tests were performed in the
presence of compounds 2 and 3, for which a benzyl end
group would have been expected on the basis of the ethylene
insertion in the Sn–CH2Ph bond. Moreover, the absence of
unsaturated end groups in all the sample indicated that the
1
Figure 5. H NMR spectra of aliphatic region of compound 3a at
variable temperature (CD2Cl2).
In conclusion, these observations (i.e., the AB pattern for β-hydrogen elimination mechanism is not involved in the
the methylene hydrogen atoms and the unusually high value termination step.
of JSnH for the ortho benzyl hydrogen atoms) support the
In order to gain deeper insight into the termination step,
hypothesis that ηn coordination of the benzyl to tin is flux- some oligomerization runs were quenched with CH3OD.
ional (probably through a suprafacial metal shifting) and Incorporation of deuterium was not observed; therefore the
slows down at low temperature.
main termination step is not the hydrolysis of the metal–
It is worth nothing that the cationic species 1a and 2a (growing chain) bond.
displayed an upfield shift for the 119Sn NMR signals in
End-group NMR analysis and deuteriolysis experiments
comparison with the resonances of the corresponding neu- therefore seem to exclude the migratory-insertion mecha-
tral compounds 1 and 2. A similar behaviour was pre- nism typical of Ziegler–Natta polymerization catalysis.
viously observed for the analogous bis[N-(3-tert-butylsalicyl-
In order to establish if a different mechanism could be
idene)anilinato]dimethyltin(IV) compound.[2] On the con- involved in the formation of branched oligoethylenes, fur-
trary, the 119Sn NMR resonance for 3a displayed a down- ther oligomerization tests were performed in the presence
field shift (about 10 ppm) in comparison with the resonance of radical additive and proton-trapping agents. The yields
of the corresponding neutral compound 3. This peculiar and nature of the products were unaffected by the presence
feature could be attributed to the different coordination of the radical initiators (dicumyl peroxide, dibenzoyl perox-
sphere, because of the presence in 3a of the intramolecular ide) or of the radical inhibitor 2,2,6,6-tetramethylpiperidine
coordination of the benzyl aromatic ring.
N-oxide. Analogously, the presence of the proton-trapping
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Octahedral Alkylbis(phenoxy-imine)tin(IV) Complexes
CDCl3, 25 °C): δ = 164.8 (N=CH), 159.2, 150.2, 134.2, 132.2,
129.9, 129.1, 127.0, 122.8, 121.6, 120.8 (Ar-C), 8.7 (Sn-CH3) ppm.
119Sn NMR (149 MHz, CDCl3, 25 °C): δ = –306.5 (s) ppm. EI-
MS: m/z (%) 664 (10) [M+ – CH3], 649 (27), 614 (33), 413 (100).
C28H22Cl4N2O2Sn (679.014): calcd. C 49.52, H 3.26, N 4.12; found
C 49.98, H 3.31, N 3.99.
2,6-di-tert-butylpyridine did not have an effect on the oligo-
merization results.
While the insertion mechanism can be definitely ex-
cluded, at the moment a conclusive answer on the origin of
the branched oligoethylenes cannot be given.
Synthesis of Bis[N-(3,5-dichlorosalicylidene)anilinato]dibenzyltin-
(IV) (2): This compound was prepared as illustrated above, but
using Cl2Sn(CH2C6H5)2 (768 mg, 2.06 mmol in 20 mL of dry
THF), 1.1 g of N-(3,5-dichlorosalicylidene)aniline (4.13 mmol in
50 mL of dry THF) and 150 mg of NaH (2.06 mmol) (yield 1.55 g,
43%). Yellow crystals, suitable for single-crystal X-ray diffraction
analysis were grown from dichloromethane/hexane at room tem-
perature. 1H NMR (400 MHz, CD2Cl2, 25 °C): δ = 7.84 (br. s, 2 H,
N=CH), 6.78–7.35 (m, 24 H, ArH), 2.56 (br. s, 2JSnH = 105.1 Hz, 4
H, CH2Ph) ppm. 13C NMR (100 MHz, CD2Cl2, 25 °C): δ = 169.07
(N=CH), 119.6–150.4 (Ar-C), 37.5 (Sn-CH2Ph) ppm. 119Sn NMR
(149 MHz, CDCl3, 25 °C): δ = –425.6 (s), –426.9 (s) ppm. EI-MS:
Conclusions
Three new octahedral bis(phenoxy-imine)tin(IV)dialkyl
complexes have been synthesized and fully characterized by
1H, 13C and 119Sn NMR and mass spectroscopy. Single-
crystal X-ray analysis was obtained for compound 2, show-
ing an octahedral geometry with alkyl groups in trans rela-
tionship. Compounds 1 and 2 reacted with B(C6F5)3 by
alkyl abstraction producing cationic species, identified by
NMR spectroscopy. For complex 3, bearing the N-(3-tert-
butylsalicylidene)aniline ligands, cationic species were in-
stead obtained by reaction with [C(C6H5)3]+[B(C6F5)4]–.
Interestingly, in this latter species ηn coordination of the
benzyl group with the metal centre was recognized by NMR
m/z (%) 740 (35) [M+
– CH2Ph], 565 (43), 530 (100).
C40H30Cl4N2O2Sn (831.209): calcd. C 57.8, H 3.63, N 3.37; found
C 60.05, H 3.70, N 3.45.
Synthesis of Bis[N-(3-tert-butylsalicylidene)anilinato]dibenzyltin(IV)
study. The obtained cationic species promoted ethylene (3):
A solution of N-(3-tert-butylsalicylidene)aniline (1.34 g,
5.28 mmol in 50 mL of THF) was added dropwise to a stirred solu-
tion of NaH (270 mg, 11.4 mmol) in THF (10 mL) at 0 °C. The
mixture was warmed to room temperature and stirred for 3 h. The
resulting light orange solution was added to a stirred solution of
Cl2Sn(CH2C6H5)2 (980 mg, 2.64 mmol) in THF (20 mL) at 0 °C.
The mixture was warmed to room temperature and stirred over-
night. Removal of the solvent in vacuo gave a brown powder. The
crude product was extracted with toluene; the solution was concen-
trated to 10 mL and stored at –20 °C. A yellow solid deposited
overnight (1.55 g, 73%). 1H NMR (400 MHz, CD2Cl2, 25 °C): δ =
7.99 (s, JSnH = 33.65 Hz, 2 H, N=CH), 7.89 (s, JSnH = 22.30 Hz,
1 H, N=CH), 7.69 (s, 1 H, N=CH), 5.25–7.27 (br. m, 32 H, ArH),
2.4–2.7 (3dd, 8 H, CH2Ph), 1.41 (s, 9 H, tBu), 1.28 (s, 9 H, tBu),
1.07 (s, 18 H, tBu) ppm. 13C NMR (100 MHz, CD2Cl2, 25 °C): δ
= 174.3, 172.0, 169.0 (N=CH), 152.5–115.3 (Ar-C), 35.3, 35.1 (C-
CH3), 36.1, 34.8, 33.8 (Sn-CH2Ph), 30.0, 29.6, 29.5 (C-CH3) ppm.
119Sn NMR (149 MHz, CDCl3, 25 °C): δ = –456.5 (s), –457.9 (s)
ppm. EI-MS: m/z (%) 714 (12) [M+ – CH2Ph], 683 (20), 460 (48),
343 (100). C48H50N2O2Sn (805.64): calcd. C 71.56, H 6.25, N 3.47;
found C 71.69, H 6.34, N 3.52.
oligomerization under mild conditions. Mechanistic studies,
based on chain end-group NMR analysis and deuteriolysis
experiments, excluded a migratory-insertion mechanism
typical of Ziegler–Natta olefin polymerization catalysis.
Experimental Section
General Procedure: Manipulation of sensitive materials was carried
out under nitrogen using Schlenk or glove-box techniques. Hexane,
tetrahydrofuran (THF) and toluene were refluxed over sodium/
benzophenone, dichloromethane over calcium hydride, then dis-
tilled under nitrogen prior to use. CDCl3, CD2Cl2 and ClC6D5 were
dried with CaH2 and distilled prior to use. [C(C6H5)3]+[B(C6F5)4]–
was purchased from Boulder SPA Company and B(C6F5)3 from
Strem Chemicals. Cl2Sn(CH2C6H5)2 was synthesized according to
the literature.[20] The phenoxy-imine ligands N-(3-tert-butylsalicyli-
dene)aniline[3] and N-(3,5dichlorosalicylidene)aniline[4] were syn-
thesized according to literature procedures. NMR spectra were re-
corded with a Bruker Advanced 400 MHz spectrometer (1H,
400 MHz; 13C, 100 MHz; 119Sn, 149 MHz; 19F, 376 MHz). The
119Sn NMR were measured relative to Sn(CH3)4. EI-MS data were
obtained with a Finnigan Thermoquest GCQ Plus 200 spectrome-
ter using a direct insertion probe. Elemental analyses were recorded
with a Thermo Finnigan Flash EA 1112 series C,H,N,S Analyzer.
3
3
Generation of {Bis[N-(3,5-dichlorosalicylidene)anilinato]methyl-
tin(IV)}+ [MeB(C6F5)3]– (1a): Compound 1 (15 mg, 22 µmol) was
dissolved in dry CD2Cl2 (0.5 mL). B(C6F5)3 (11 mg, 22 µmol) was
added to the yellow solution. The solution was analyzed by NMR
1
spectroscopy at room temperature. H NMR (400 MHz, CD2Cl2,
3
25 °C): δ = 8.54 (s, JSnH = 22.3 Hz, 2 H, N=CH), 6.9–7.7 (br. m,
Synthesis of Bis[N-(3,5-dichlorosalicylidene)anilinato]dimethyltin-
(IV) (1): A solution of N-(3,5-dichlorosalicylidene)aniline (1.4 g,
5.26 mmol, in 60 mL of THF) was added dropwise to a stirred
solution of NaH (252 mg, 10 mmol) in THF (10 mL) at 0 °C. The
mixture was warmed to room temperature and stirred for 3 h. The
resulting light yellow solution was added to a stirred solution of
Cl2Sn(CH3)2 (577 mg, 2.63 mmol) in 20 mL of THF at 0 °C. The
mixture was warmed to room temperature and stirred overnight.
Removal of the solvent in vacuo gave a brown powder. The crude
product was extracted with toluene; the solution was concentrated
to 15 mL and stored at –20 °C. An orange solid deposited over-
2
14 H, ArH), 1.04 (s, JSnH = 101.8 Hz, 3 H, Sn-CH3), 0.42 (br. s,
3 H, -BCH3) ppm. 13C NMR (100 MHz, CD2Cl2, 25 °C): δ = 171.8
(N=CH), 119–150 (ArC), 10.8 (BCH3 ), 3.73 (Sn-CH3) ppm. 119Sn
–
NMR (149 MHz, CD2Cl2, 25 °C): δ = –394.0 (s) ppm. 19F NMR
(376 MHz, CD2Cl2, 25 °C): δ = –168.2 (t, 2 F, m-F), –165.6 (t, 1 F,
p-F), –133.6 (d, 2 F, o-F) ppm. The side-product Sn(CH3)4 was also
identified.
Generation of {Bis[N-(3,5-dichlorosalicylidene)anilinato]benzyl-
tin(IV)}+ (2a): Compound 2 (15 mg, 18 µmol) was dissolved in dry
CD2Cl2 (0.5 mL). B(C6F5)3 (9 mg, 18 µmol) was added to the yel-
low solution. The resulting solution was analyzed by NMR spec-
troscopy at room temperature. Selected resonances 1H NMR
1
night (1.6 g, 91%). H NMR (400 MHz, CDCl3, 25 °C): δ = 8.01
3
(s, JSnH = 12.1 Hz, 2 H, N=CH) 6.90–7.34 (m, 14 H, ArH), 0.79
2
2
(s, JSnH = 90.7 Hz, 6 H, SnCH3) ppm. 13C NMR (100 MHz,
(400 MHz, CD2Cl2, 25 °C): δ = 1.04 (s, JSnH = 117.0 Hz, 2 H, Sn-
Eur. J. Inorg. Chem. 2007, 5752–5759
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
5757

L. Annunziata, D. Pappalardo, C. Tedesco, C. Pellecchia
FULL PAPER
CH2Ph), 6.5–7.7 (br. m, 14 H, ArH), 8.47 (s, 3JSnH = 18.2 Hz, 2 H,
N=CH) ppm. 119Sn NMR (149 MHz, CD2Cl2, 25 °C): δ = –500.0
(s) ppm. 19F NMR (376 MHz, CD2Cl2, 25 °C): δ = –169 to –123.6
ppm.
least-squares based on F2 using the program SHELXL97.[25] All
non-hydrogen atoms were refined anisotropically. Hydrogen atoms
were positioned geometrically and included in structure factor cal-
culations but not refined.
A total of 223 refinable parameters were finally considered. Maxi-
mum and minimum residual density were respectively 1.20 eÅ–3
and –0.89 eÅ–3. Final disagreement indices: R1 = 0.037 for 4476
reflections with Fo Ͼ 4σ(Fo), wR2 = 0.091 for all 5170 data. Atomic
coordinates, thermal factors, bond lengths and angles have been
deposited with the Cambridge Crystallographic Data Centre (see
below). ORTEP drawings were performed by means of the program
ORTEP32.[26]
Generation of {Bis[N-(3-tert-butylsalicylidene)anilinato]benzyl-
tin(IV)}+ [B(C6F5)4]– (3a): [C(C6H5)3]+[B(C6F5)4]– (25 mg, 27 µmol)
was added to a yellow solution of compound 3 (22 mg, 27 µmol)
in dry CD2Cl2 (0.5 mL). The resulting brown solution was analyzed
1
by NMR spectroscopy at room temperature. H NMR (400 MHz,
3
CD2Cl2, 25 °C): δ = 8.53 (s, JSnH = 14.92 Hz, 2 H, N=CH), 6.9–
4
7.6 (br. m, 19 H, ArH), 6.44 [d, JSnH = 33.75 Hz, 2 H, o-
2
CH2(C6H5)], 3.26 (s, JSnH = 118.84 Hz, 2 H, Sn-CH2Ph), 1.34 (s,
18 H, tBu) ppm. 13C NMR (100 MHz, CD2Cl2, 25 °C): δ = 174.0
(N=CH), 124.2 [o-CH2(C6H5)], 35.5 (C-CH3), 32.0 (Sn-CH2Ph),
29.8 (C-CH3) ppm. 119Sn NMR (149 MHz, CD2Cl2, 25 °C): δ =
–448.7 (s) ppm. 19F NMR (376 MHz, CD2Cl2, 25 °C): δ = –168.0
(t, 2 F, m-F), –164.1 (t, 1 F, p-F), –133.6 (d, 2 F, o-F) ppm.
(C6H5)3CH and (C6H5)3CCH2Ph were also identified as side-prod-
ucts.
CCDC-641608 contains the supplementary crystallographic data
(excluding structure factors) for compound 2. These data can be
obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request.cif/.
Supporting Information (see also the footnote on the first page of
this article): NMR characterization of compounds 1, 2, 3, 1a, 2a,
3a and of the ethylene oligomerization products.
Oligomerization Tests: A typical oligomerization test was carried
out in a 100-mL, magnetically stirred, glass flask, which was condi-
tioned under dynamic vacuum, thermostated at 25 °C and then
charged with a solution of the tin compound (30 µmol) and
[C(C6H5)3]+[B(C6F5)4]– or B(C6F5)3 (30 µmol) in ClC6H5 or
CH3C6H5 (15 mL). Ethylene was fed continuously at a pressure of
1 atm; after 24 h, the reaction mixture was poured into acidified
methanol (50 mL). The solution was treated with water and hexane
(3ϫ30 mL). The organic phase was dried with Na2SO4 and the
solvents distilled off. An oily product was obtained; typically yields
are of 200 mg. The products were analyzed by 13C NMR analysis;
the oligomer structure was determined according to the litera-
ture.[22]
Acknowledgments
The authors are grateful to Dr. Patrizia Oliva for 119Sn NMR ex-
periments. The authors acknowledge financial support by Uni-
versità del Sannio (FAR 2006) and the University of Salerno (Fin-
anziamento grandi e medie attrezzature) for the purchase of a new
glove box.
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1
ence, given by Kc = π∆ν/√2. ∆Gc϶, calculated from H NMR,
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¯
C40H30Cl4N2O2Sn, FW = 831.15, triclinic, space group P1 (no. 2),
Z = 1, a = 9.429(4) Å, b = 12.030(5) Å, c = 8.630(3) Å, α =
90.11(3)°, β = 99.52(3)°, γ = 113.04(3)°, V = 886.0(7) Å3, Dcalcd
1.558 gcm–3, µcalcd = 1.062 mm–1.
=
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5758
www.eurjic.org
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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[14] In the aliphatic region of the H NMR spectrum minor broad
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Published Online: November 20, 2007
Eur. J. Inorg. Chem. 2007, 5752–5759
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
5759