Octahedral Bis(phenoxy-imine)tin(IV) alkyl complexes: Synthesis, characterization, and reactivity toward ionizing species and ethylene

Article abstract of DOI:10.1021/om0491084

The synthesis of new organotin compounds of the general formula L ₂SnR₂ (L = N-(3-tert-butylsalicylidene)-2,3,4,5,6- pentafluoroaniline; R = CH₃ (1), n-C₄H₉ (3)) and L′₂SnR₂ (L′ = Ar-(3-tert- butylsalicylidene)aniline; R = CH₃ (2), n-C₄H₉ (4)) is described herein. The compounds were characterized by ¹H, ¹³C, and ¹¹⁹Sn NMR in solution; in some cases a fluxional behavior was observed by variable-temperature experiments. Characterization by single-crystal X-ray diffraction analysis has been obtained for compounds 1, 2, and 4. The reactivity of the synthesized compounds toward ionizing agents was studied by an NMR-tube reaction. Compounds 2 and 4 underwent an alkyl abstraction reaction with the carbenium salt [C(C₆H₅) ₃]⁺[B(C₆F₅)₄] . The obtained cationic species exhibited some activity in the oligomerization of ethylene under mild conditions, producing short-chain oligomers, with saturated end groups and methyl branches.

Full text of DOI:10.1021/om0491084

Organometallics 2005, 24, 1947-1952
1947
Octahedral Bis(phenoxy-imine)tin(IV) Alkyl Complexes:
Synthesis, Characterization, and Reactivity toward
Ionizing Species and Ethylene
Liana Annunziata,† Daniela Pappalardo,*,‡ Consiglia Tedesco,† and
Claudio Pellecchia†
Dipartimento di Chimica, Universita` di Salerno, Via S. Allende, I-84081 Baronissi (SA), Italy,
and Dipartimento di Studi Geologici ed Ambientali, Universita` del Sannio, Via Port’Arsa 11,
I-82100, Benevento, Italy
Received November 18, 2004
The synthesis of new organotin compounds of the general formula L2SnR2 (L ) N-(3-tert-
butylsalicylidene)-2,3,4,5,6-pentafluoroaniline; R ) CH3 (1), n-C4H9 (3)) and L′2SnR2 (L′ )
N-(3-tert-butylsalicylidene)aniline; R ) CH3 (2), n-C4H9 (4)) is described herein. The
1
compounds were characterized by H, 13C, and 119Sn NMR in solution; in some cases a
fluxional behavior was observed by variable-temperature experiments. Characterization by
single-crystal X-ray diffraction analysis has been obtained for compounds 1, 2, and 4. The
reactivity of the synthesized compounds toward ionizing agents was studied by an NMR-
tube reaction. Compounds 2 and 4 underwent an alkyl abstraction reaction with the
carbenium salt [C(C6H5)3]+[B(C6F5)4]-. The obtained cationic species exhibited some activity
in the oligomerization of ethylene under mild conditions, producing short-chain oligomers,
with saturated end groups and methyl branches.
Chart 1
Introduction
The field of olefin polymerization catalysis has expe-
rienced a great momentum in the past few years, with
many new catalyst systems being reported across and
also beyond the transition series.1 Actually, the polym-
erization of ethylene has been achieved in the presence
of transition-metal-free homogeneous Al catalysts, albeit
with low activity.2 In this regard, for instance, we
recently described new neutral and cationic salicylaldi-
minato3 and 2-anilinotroponato4 aluminum alkyl com-
plexes and investigated their ethylene polymerization
activity.
To our knowledge, however, no examples have been
reported in the literature concerning the activity in
olefin polymerization of compounds based on metals
beyond group 13. In this regard, bearing in mind the
similarities between titanium and tin,5 we thought to
explore this potentiality. In general, olefin polymeriza-
tion catalytic precursors consist of a metal center,
bearing ancillary ligand(s) and two alkyl groups located
in mutually cis positions; the active species are obtained
from the precursors by reactions with suitable ionizing
agents. Following the recent results in olefin polymer-
ization with bis(phenoxy-imine) group 4 transition-
metal catalysts,6 our first goal was the synthesis of
analogous bis(phenoxy-imine)tin complexes carrying two
alkyl groups in cis positions.
Although the tetradentate Schiff base Salen ligands
have been largely used for the preparation of several
complexes of group 14,7 no reports concerning related
bis(salicylaldiminato)tin(IV) compounds have appeared
in the literature. Murray et al. described the formation
of a 1:2 adduct of tin tetrachloride with N-p-tolylsali-
cylaldimine; attempts to deprotonate the Schiff base
with triethylamine were unsuccessful.8 Using a metath-
esis reaction approach, however, we succeeded in the
preparation of new octahedral organotin compounds of
the general formula L2SnR2 (L ) phenoxy-imine; R )
alkyl) (Chart 1). In this paper we report on their
synthesis and structural characterization and some
* To whom correspondence should be addressed. Fax: +39 089
965296. Tel.: +39 089 965254. E-mail: pappalardo@unisannio.it.
† Universita` di Salerno.
‡ Universita` del Sannio.
(1) Gibson, V. C.; Spitzmesser, S. K. Chem. Rew. 2003, 103, 283-
315.
(6) (a) Tian, J.; Hustad, D.; Coates, G. W. J. Am. Chem. Soc. 2001,
123, 5134-5135. (b) Saito, J.; Mitani, M.; Mohri, J.; Ishii, S.; Yoshida,
Y.; Matsugi, T.; Kojoh, S.; Kashiwa, N.; Fujita, T. Chem. Lett. 2001,
576-577.
(7) (a) Yearwood, B.; Parkin, S.; Atwood, D. A. Inorg. Chim. Acta
2002, 124-131. (b) Jing, H.; Edulji, S. M.; Gibbs, J. M.; Stern, C. L.;
Zhou, H.; Nguyen, S. T. Inorg. Chem. 2004, 43, 4315-4327.
(8) Van den Bergen, A.; Cozens, R. J.; Murray, K. S. J. Chem. Soc.
A 1970, 3060-3064.
(2) See ref 1 and references therein.
(3) Pappalardo, D.; Tedesco, C.; Pellecchia, C. Eur. J. Inorg. Chem.
2002, 621-628.
(4) Pappalardo, D.; Mazzeo, M.; Montefusco, P.; Tedesco, C.;
Pellecchia, C. Eur. J. Inorg. Chem. 2004, 1292.
(5) Cotton, F. A.; Wilkinson, G. Advanced Inorganic Chemistry, 5th
ed.; Wiley: New York, 1988; p 652.
10.1021/om0491084 CCC: $30.25 © 2005 American Chemical Society
Publication on Web 03/15/2005

1948 Organometallics, Vol. 24, No. 8, 2005
Annunziata et al.
Chart 2
preliminary data on their reactivity with ion-generating
activators and toward ethylene.
Results and Discussion
Synthesis of the Complexes. The bis(phenoxy-
imine)tin complexes were prepared via metathesis reac-
tion of the sodium salt of the ligand with the corre-
sponding dialkyltin(IV) chloride in rigorously dry
tetrahydrofurane solvent. Reaction proceeds cleanly
with good yields, producing compounds 1-4 as yellow
or orange solids. The products are very stable as solids
in an inert atmosphere, but easily underwent hydrolysis
reaction with formation of the free ligand in the pres-
ence of traces of adventitious water.
Figure 1. ORTEP diagram of compound 1. Hydrogen
atoms have been omitted for clarity. Ellipsoids are drawn
at the 30% probability level.
NMR Characterization of the Complexes. Com-
be also excluded, the two possible isomers in solution
remaining cis-I and cis-III.
1
pounds 1-4 were characterized via H, 13C, and 119Sn
NMR in solution, exhibiting interesting spectroscopic
features.
The structure was finally elucidated by single-crystal
X-ray analysis (Figure 1; vide infra), showing an octa-
hedral arrangement around the tin atom, with the
methyl groups in a cis configuration (angle C-Sn-C )
107.4°), and the oxygen atoms in trans positions.
The tin methyl compound 2, bearing the nonfluori-
nated N-(3-tert-butylsalicylidene)aniline ligand, showed,
at variance with compound 1, very broad 1H NMR
signals. In addition, in the 119Sn NMR spectrum two
broad signals at -352.8 and -342.7 ppm were observed.
These observations suggested the existence of different
tin species in dynamic equilibrium in solution at room
temperature and prompted us to explore the behavior
of the compound at lower temperatures. Consequently,
several 1H and 119Sn NMR spectra were recorded
between 25 and -85 °C in CD2Cl2 solution. Upon a
temperature decrease, the two resonances in the 119Sn
NMR spectra become sharper; at -85 °C the relative
ratio is about 3:2.11 More information came from the 1H
NMR spectra (Figure 2); actually, upon lowering the
temperature, the broad signals split up. At -85 °C the
1H NMR spectrum of compound 2 exhibited two sets of
signals, attributable to two different isomeric species,
a C2-symmetric one and a C1-symmetric one, respec-
tively, in about a 3:2 ratio. Diagnostic signals for the
C2-symmetric isomer are the singlet relative to the Sn-
1
Compound 1 showed a clear H NMR spectrum in
CDCl3 at room temperature, with very sharp peaks: one
signal for the SnCH3 protons at 0.37 ppm, one singlet
for the tBu protons at 1.16 ppm, one signal for the iminic
proton at 8.06 ppm, and finally two doublets and one
triplet in the aromatic region, accounting for the re-
maining Ar H protons, were observed. The 13C NMR
spectrum coherently displayed only one signal for the
methyl groups bound to Sn and only one signal for the
t
methyl groups of the Bu substituents on the aromatic
rings. The 119Sn NMR spectrum showed one signal at
-309 ppm, thus indicating the existence of a single tin
species in solution. Additional information came from
the observations of the proton-tin and carbon-tin
3
coupling constants. For the iminic protons a J(Sn-H)
value of 15.9 Hz was measured, thus indicating the
coordination of the nitrogen atoms to tin. This picture
is compatible with a highly symmetric structure in
solution. It is worth noting that for octahedral bis-
(phenoxy-imine) dialkyl complexes five isomers are
possible, as displayed in Chart 2. On the basis of the
1H and 13C NMR signal patterns, the C1-symmetric
structure cis-II can be definitely ruled out. According
to the equations developed by Lockhart9 and by Nel-
son,10 the coupling constants 2J(119Sn-1H) and 1J(119Sn-
13C) can be used to estimate the methyl-tin-methyl
angle. In our case the methyl groups bound to Sn
2
CH3 groups (6H, J(Sn-H) ) 68.12 Hz) at 0.16 ppm,
the tBu singlet (18 H) at 0.97 ppm, and the CHdN
singlet at 8.11 ppm (3J(Sn-H) ) 30.8 Hz). According
to the Nelson equation,10 the measured 2J(Sn-H) value
is compatible with a structure showing the methyl
groups bound to Sn in mutually cis positions.
2
exhibited a J(119Sn-1H) value of 67.1 Hz; using the
equation specifically developed by Nelson for octahedral
dialkyltin complexes,10 the calculated angle for C-Sn-C
is 106(6)°, in the expected range for a structure with
the methyl groups in a cis configuration. Therefore, the
“trans-I” and “trans-II” isomeric forms of Chart 2 can
For the C1-symmetric isomer, instead, we observed
two signals belonging to the Sn-CH3 groups, respec-
tively, at 0.33 ppm (3H, 2J(Sn-H) ) 65.5 Hz) and -0.21
2
(9) (a) Lockhart, T. P.; Manders, W. F.; Schlemper, E. O. J. Am.
Chem. Soc. 1985, 107, 7. (b) Lockhart, T. P.; Manders, W. F. Inorg.
Chem. 1985, 25, 892-895.
(10) Howard, W. F.; Crecely, R. W.; Nelson, W. H. Inorg. Chem.
1985, 24, 2204-2208.
ppm (3H, J(Sn-H) ) 65.9 Hz) and two signals (over-
(11) In the 119Sn NMR spectrum at -85 °C a minor resonance at
-368 ppm was also detected, but it accounts for less than 5%.

Bis(phenoxy-imine)tin(IV) Alkyl Complexes
Organometallics, Vol. 24, No. 8, 2005 1949
Table 1. Selected Bond Lengths (Å) and Angles
(deg) for Compounds 1, 2, and 4
1
2
4
Sn-N1
2.397(3)
2.366(3)
2.083(2)
2.077(2)
2.124(3)
2.137(4)
1.291(4)
1.294(4)
1.429(4)
1.428(4)
1.434(4)
1.430(5)
2.349(3)
2.386(3)
2.086(2)
2.080(2)
2.143(4)
2.144(4)
1.291(4)
1.289(4)
1.436(3)
1.441(4)
1.438(4)
1.443(4)
2.378(4)
2.373(4)
2.092(3)
2.086(3)
2.157(5)
2.156(4)
1.288(6)
1.290(6)
1.440(5)
1.439(6)
1.431(6)
1.431(6)
Sn-N2
Sn-O1
Sn-O2
Sn-C35
Sn-C36/C39
N1-C1/C7
N2-C18/C24
N1-C12/C8
N2-C29/C25
C1-C2/C7-C6
C18-C19/C23-C24
N1-Sn-N2
78.06(9)
155.71(9)
107.39(15)
79.89(9)
161.24(9)
108.79(15)
80.03(13)
159.06(12)
111.1(2)
O1-Sn-O2
C35-Sn-C36/C39
nated phenoxyimine ligand, displayed at room temper-
ature a single 119Sn NMR resonance at -337.4 ppm and
clean 1H and 13C NMR spectra, compatible with the
existence, in solution, of a single C2-symmetric species.
As in the case of the previously analyzed compounds,
the CHdN hydrogen atoms appear as a singlet at 8.02
3
ppm, accounting for two H, with a J(Sn-H) value of
14.3 Hz, thus indicating the coordination of the N atoms
to the tin center.
The tin dibutyl compound 4, instead, displayed at
room temperature two resonances in the 119Sn NMR
spectrum and very broad signals in the 1H NMR
spectrum. As observed for compound 2, variable-tem-
perature 1H NMR experiments evidenced the presence
of at least two isomeric species, in fluxional equilibrium,
while a single-crystal X-ray structure determination
revealed that compound 4 crystallizes in the C2-sym-
metric form cis-I.
X-ray Diffraction Analysis. Suitable crystals for
X-ray analysis were obtained from hexane at -20 °C
for compounds 1, 2, and 4. The three compounds have
a similar molecular structure, displaying a distorted-
octahedral geometry; the two oxygen atoms are trans
to each other, while the alkyl ligands and the nitrogen
atoms are in a cis relationship. Selected bond lengths
and angles are listed in Table 1. Notably, the O1-Sn-
O2 angle deviates substantially from 180° and the
largest deviation is observed in compound 1 (155.71-
(9)°). This means that in compound 1 the Sn atom is
more exposed away from the ligand coordination sphere.
The same deviation effect can be observed for the
analogous bis(phenoxy-imine)titanium complexes; in
particular the angle O1-Ti-O2 is significantly smaller
if the N-aryl group is perfluorinated.12
To determine if the cis-I isomeric structure belonged
merely to the particular analyzed crystals or, rather,
to all the crude solids, an X-ray powder diffraction
analysis was performed on a sample of compound 4. The
Rietveld analysis, based on the single-crystal X-ray
structure of compound 4, disclosed the same structure
also for the powder sample, thus indicating the existence
of a single isomer in the solid state.
Figure 2. 1H NMR spectra in the aliphatic regions of
compounds 2 at variable temperature (CD2Cl2).
lapped, 18 H) for the tBu groups at 1.35 and 1.34 ppm.
The resonances for the CHdN hydrogen atoms, instead,
at -85 °C still appear as a broad singlet and account
for two hydrogen atoms. Several 1H NMR experiments
were also performed between 25 and 60 °C: when the
temperature is increased, the signals sharpen, indicat-
ing a faster equilibrium between the C2 and the C1
species.
The equilibrium between the two isomers does not
seem to be concentration dependent: integration of
119Sn NMR signals measured at different concentrations
(0.3 and 0.05 M) gave identical results.
For compound 2, crystals suitable for an X-ray crystal
structure determination were grown from hexane at
-20 °C and displayed a distorted-octahedral geometry
with the alkyl group in a cis configuration and the two
oxygen atoms in trans positions.
The tin dibutyl compounds 3 and 4 displayed NMR
behavior similar to that of the corresponding dimethyl
compounds (1 and 2). Compound 3, bearing the fluori-
(12) Cf.: (a) Mitani, M.; Mohri, J.; Yoshida, Y.; Saito, J.; Ishii, S.;
Tsuru, K.; Matsui, S.; Furuyama, R.; Nakano, T.; Tanaka, H.; Kojoh,
S.; Matsugi, T.; Kashiwa, N.; Fujita, T. J. Am. Chem. Soc. 2002, 124,
3327-3336. (b) Makio, H.; Kashiwa, N.; Fujita, T. Adv. Synth. Catal.
2002, 344, 477-493. (c) Tohi, Y.; Makio, H.; Matsui, S.; Onda, M.;
Fujta, T. Macromolecules 2003, 36, 523-525 and references therein.

1950 Organometallics, Vol. 24, No. 8, 2005
Annunziata et al.
Similar results were obtained by Coates for analogous
bis(phenoxy-imine)titanium compounds: while X-ray
data always indicated a C2-symmetric structure in the
solid state, in some cases both C2- and C1-symmetric
isomers were observed in solution by NMR analysis. The
factors influencing the C2/C1 ratio were not fully un-
derstood, but it was observed that C1 species were
disfavored by the presence of fluorine substituents at
the ortho position of the N-aryl rings.13 These observa-
tions nicely agree with our experimental results con-
cerning the closely related tin compounds. We have not
explored the mechanism responsible for the isomeriza-
tion in solution, but it probably operates via a nitrogen
dissociation mechanism, as hypothesized for related bis-
(phenoxy-imine) group 4 transition-metal compounds.12c
Generation of Cationic Species and Their Re-
activity toward Ethylene. The search for free cations
of heavier group 14 elements has recently achieved
important results. Lambert et al., for instance, reported
the crystal structure of a remarkable triphenylstan-
nylium cation displaying a trigonal-planar geometry
around tin.14 Almost contemporaneously, Sekiguchi also
reported the crystal structure of a “stable and free” tin
cation bearing three bulky tris(alkyl)silyl ligands.15
To mimic the active species in homogeneous olefin
polymerization, we were instead interested in generat-
ing cationic species with the formula L2SnR+ (L )
phenoxy-imine; R ) alkyl). Actually, the active species
in homogeneous olefin polymerization catalysts are
believed to be cationic complexes of group 4 metals
bearing at least an alkyl group σ-bonded to the metal
center, where the polymer chain can grow via olefin
insertion. Therefore, we explored the reactivity of the
synthesized compounds toward ionizing reagents,
such as [(C6H5)NH(CH3)2]+[B(C6F5)4]-, B(C6F5)3, and
[C(C6H5)3]+[B(C6F5)4]-, traditionally used in homoge-
neous Ziegler-Natta catalysis, via NMR tube reactions.
Reactions of compounds 1 and 3 with any ionizing
reagent resulted invariably in mixtures of decomposition
products. In the case of 2 and 4, reaction with [(C6H5)NH-
(CH3)2]+[B(C6F5)4]- and B(C6F5)3 also led to degradation,
while the use of [C(C6H5)3]+[B(C6F5)4]- produced ab-
straction of an alkyl group.
Figure 3. 1H NMR spectra (ClC6D5, 25 °C) of compounds
2 (i) and 2a (ii): (*) “free” ligand impurities; (O) C(C6H5)3-
CH3; (9) Sn(CH3)4 impurities.
The reactivity of the synthesized compounds toward
ethylene was explored in preliminary tests. Interest-
ingly, compounds 2 and 4, in combination with 1 equiv
of [C(C6H5)3]+[B(C6F5)4]-, displayed some activity, al-
though very low, in the oligomerization of ethylene
under mild conditions. In contrast, control experiments,
performed under identical conditions but in the presence
of compound 2 alone, or in the presence of [C(C6H5)3]+-
[B(C6F5)4]- alone, did not give any product.
The obtained oily products were analyzed by13C NMR
spectroscopy in CDCl3 solution. Interestingly, in addi-
tion to the main resonance of polyethylene sequences
at 29.98 ppm, minor resonances are detected at 19.97,
24.73, 33.01, and 37.36 ppm. According to literature
data, these resonances are diagnostic of the presence
of methyl branches.18 Resonances for saturated end
groups are also observed. From the 13C NMR spectrum,
the amount of branching was estimated to be 1.5-3
units per chain, while the chain length was between 40
and 60 carbons.
The mechanism responsible of the methyl branches
is presently unknown. Formation of methyl-branched
polyethylene was previously observed, e.g. with R-di-
imine Ni and Pd catalysts, for which a “chain walking”
mechanism was hypothesized,19 or with supported
vanadium-magnesium catalysts, for which an intramo-
lecular isomerization mechanism of a growing chain was
posited.20
For instance, the reaction of compound 2 with
[C(C6H5)3]+[B(C6F5)4]- clearly proceeded by methyl
abstraction, as indicated by the presence, in the 1H
NMR spectrum, of a resonance at 2.2 ppm attributable
to the methyl group of CH3C(C6H5)3 (Figure 3). Char-
acteristic resonances for the cationic species are a
+
singlet at 0.60 ppm for SnCH3 and a singlet at 8.16
ppm due to CHdN. The imine resonance shows a
downfield shift, if compared with the corresponding
resonance of compound 2 in the same solvent (7.75
ppm). It is worth noting that in analogous experiments
performed with bis(phenoxy-imine) group 4 transition-
metal compounds, a cationic character was attributed
to the species displaying a similar downfield shift of the
imine hydrogen.16,17
(17) The NMR 119Sn spectrum showed a resonance at 394.26 ppm,
upfield in comparison with the neutral compound 2. An opposite
behavior, observed by Ruzˇicˇka et al. in five-coordinated Sn cationic
compounds, could be probably ascribed to the different coordination
environment of tin. Cf.: Ruzˇicˇka, A.; Jambor, R.; C´ısarˇova´, I.; Holecˇek,
J. Chem. Eur. J. 2003, 9, 2411-2418.
(18) De Pooter, M.; Smith, P. B.; Dohrer, K. K.; Bennet, K. F.;
Meadows, M. D.; Smith, C. G.; Schouwenaars, H. P.; Geerards, R. A.
J. Appl. Polym. Sci. 1991, 42, 399-408.
(19) Johnson, L. K.; Killian, C. M.; Brookhart, M. J. Am. Chem. Soc.
1995, 117, 6414-6415.
(13) Mason, A. F.; Tian, J.; Hustad, P. D.; Lobkovsky, E. B.; Coates,
G. W. Isr. J. Chem. 2002, 42, 301-306.
(14) Lambert, J. B.; Lin, L.; Keinan, S.; Muller, T. J. Am. Chem.
Soc. 2003, 125, 6022-6023.
(15) Sekiguchi, A.; Fukawa, T.; Lee, V. Ya.; Nakamoto, M. J. Am.
Chem. Soc. 2003, 125, 9250-9251.
(16) Makio, H.; Fujita, T. Macromol. Symp. 2004, 213, 221-233.

Bis(phenoxy-imine)tin(IV) Alkyl Complexes
Organometallics, Vol. 24, No. 8, 2005 1951
NMR (CDCl3, 293 K): δ 6.7 (1J(Sn-C) ) 645 Hz, Sn-CH3),
29.2 (C-CH3), 35.1 (C-CH3), 116.9, 119.1, 134.0, 134.8, 142.4,
167.8 (Ar C), 176.4 (NdCH). 119Sn NMR (CD2Cl2, 293 K): δ
-308.9. EI MS m/z 818 [M - CH3] +. Anal. Calcd for
C36H32F10N2O2Sn (833.35): C, 51.89; H, 3.87; N, 3.36. Found:
C, 51.7; H, 3.67; N, 3.49.
It is worth noting that with our system ethylene
oligomers were produced only in the presence of the tin
compounds 2 and 4, for which the formation of relatively
stable cationic species has been detected. Further work
is in progress in order to ascertain the mechanism
responsible for ethylene oligomerization and for the
branch formation.
Synthesis of Bis[N-(3-tert-butylsalicylidene)anilinato]-
dimethyltin(IV) (2). This compound was prepared as il-
lustrated above, but using Cl2Sn(CH3)2 (1.75 g, 7.9 mmol in
15 mL of dry THF), 4.04 g of N-(3-tert-butylsalicylidene)aniline
(15 mmol in 45 mL of dry THF) and 0.57 g of NaH (24 mmol)
(yield 4.7 g, 91%). Crystals suitable for an X-ray crystal
structure determination were grown from hexane at - 20 °C.
Conclusions
A new family of octahedral bis(phenoxy-imine)tin(IV)
dialkyl complexes has been synthesized. These com-
pounds have been fully characterized by NMR and
single-crystal X-ray analysis. For the compounds bear-
ing the nonfluorinated N-(3-tert-butylsalicylidene)-
aniline ligands, the formation of cationic species via
alkyl abstraction by [C(C6H5)3]+[B(C6F5)4]- has been
detected by NMR monitoring. Interestingly, the ob-
tained cationic species promote ethylene oligomerization
under mild conditions. To our knowledge, the oligomer-
ization of ethylene by a group 14 compound is unprec-
edented in the literature.
2
1H NMR (CDCl3, 293 K): δ 0.30 (6H, br s, J(Sn-H) ) 67.3
Hz, Sn-CH3), 1.27 (18H, br s, t-Bu), 6.58-7.34 (16H, br m,
1
Ar H), 7.95 (2H, br s, NdCH). C2 isomer: H NMR (CD2Cl2,
188 K) δ 0.15 (6H, s, 2J(Sn-H) ) 68.1 Hz, Sn-CH3), 0.96 (18H,
s, t-Bu), 6.54-7.45 (16H, br m, ArH), 8.11 (2H, s, 3J(Sn-H) )
30.8 Hz, NdCH). C1 isomer: 1H NMR (CD2Cl2, 188 K) δ -0.21
(3H, s, 2J(Sn-H) ) 65,9 Hz, Sn-CH3), 0.33 (3H, s, 2J(Sn-H)
) 65,5 Hz, Sn-CH3), 1.34 and 1.35 (18H, two singlets
overlapped, t-Bu), 6.54-7.45 (16H, br m, Ar H), 7.86 (2H, br
s, NdCH). 13C NMR (CDCl3, 293 K): δ 7.4 (Sn-CH3), 29.5 (C-
CH3), 35.1 (C-CH3), 115.4, 118.5, 123.4, 126.2, 128.9, 132.1,
134.1, 142.4, 151.7, 167.4 (Ar-C), 170.5 (NdCH). 119Sn NMR
(CD2Cl2, 293 K): δ -352.8 (s), -342.7 (s). EI MS m/z 654 [M]+.
Anal. Calcd for C36H42N2O2Sn (653.44): C, 66.17; H, 6.48; N,
4.29. Found: C, 67.0; H, 6.80; N, 4.50.
Experimental Section
General Procedure. Manipulations of sensitive materials
were carried out under nitrogen using Schlenk or glovebox
techniques. Hexane and THF were refluxed over sodium/
benzophenone and distilled under nitrogen prior to use. CDCl3,
CD2Cl2, and ClC6D5 were dried over CaH2 and distilled prior
to use. The carbenium salt [C(C6H5)3]+[B(C6F5)4]- was pur-
chased from Boulder SPA Co. and used as received. The
phenoxy-imine ligands N-(3-tert-butylsalicylidene)aniline21 and
N-(3-tert-butylsalicylidene)-2,3,4,5,6-pentafluoroaniline22 were
synthesized according to literature procedures. 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. Elemen-
tal analysis were recorded on a Thermo Finnigan Flash EA
1112 series C,H,N,S analyzer.
Synthesis of Bis[N-(3-tert-butylsalicylidene)-2,3,4,5,6-
pentafluoroanilinato]dibutyltin(IV) (3). This compound
was prepared as above but using Cl2Sn[(CH2)3CH3]2 (1.27 g,
4.2 mmol) in 10 mL of dry THF, N-(3-tert-butylsalicylidene)-
2,3,4,5,6-pentafluoroaniline (2.87 g, 8.4 mmol) in 45 mL of
1
THF, and NaH (0.30 g, 12 mmol) (yield 3.0 g, 80%). H NMR
(CDCl3, 293 K): δ 0.75 (6H, t, -CH3), 1.20 (30 H, br s, 3 CH2
and t-Bu), 6.64 (2H, t, Ar H), 6.96 (2H, d, Ar H), 7.36 (2H, d,
Ar H), 8.02 (2H, s, 3J(Sn-H)) 14.3 Hz, NdCH). 13C NMR
(CDCl3, 293 K): δ 13.7 (Sn(CH2)3CH3), 26.3, 27.2, 28.3 (Sn-
(CH2)3CH3), 29.5 (C-CH3), 35.2 (C-CH3), 116.6, 119.8, 134.0,
135.0, 141.9 (Ar C), 176.8 (NdCH). 119Sn NMR (CD2Cl2, 293
K): δ -337.4 (s). EI MS m/z 917 [M]+. Anal. Calcd for
C42H44F10N2O2Sn (917.51): C, 54.98; H, 4.83; N, 3.05. Found
C, 54.62; H, 5.12; N, 3.24.
Synthesis of Bis[N-(3-tert-butylsalicylidene)anilinato]-
dibutyltin(IV) (4). This compound was prepared as above but
using Cl2Sn[(CH2)3CH3]2 (2.7 g, 8.9 mmol) in 20 mL of dry
THF, N-(3-tert-butylsalicylidene)aniline (4.5 g, 17.5 mmol) in
45 mL of THF, and NaH (0.70 g, 29 mmol) (yield 5.9 g, 90%).
Crystals suitable for an X-ray crystal structure determination
were grown from dried hexane at -20 °C. 1H NMR (CDCl3;
293 K): δ 0.74 (6H, br t, -CH3), 1.15-1.40 (30 H, br m, 3 CH2
and t-Bu), 6.55-7.30 (16H, br m, Ar H), 7.90 (2H, br s, Nd
CH). 13C NMR (CDCl3; 293 K): δ 13.7 (Sn(CH2)3CH3), 26.4, 27.3,
28.5 (Sn(CH2)3CH3), 29.6 (C-CH3), 35.2 (C-CH3), 115.1, 119.9,
123.3, 126.1, 128.8, 132.1, 134.3, 152.2 (Ar C), 170.6 (NdCH).
119Sn NMR (CD2Cl2, 293 K): δ -369.7 (s), -375.8 (s). EI MS
m/z 737 [M]+. Anal. Calcd for C42H54N2O2Sn (737.6): C, 68.39;
H, 7.38; N, 3.80. Found: C, 69.12; H, 7.79; N, 3.40.
Synthesis of Bis[N-(3-tert-butylsalicylidene)-2,3,4,5,6-
pentafluoroanilinato]dimethyltin(IV) (1). To a stirred
solution of NaH (155 mg, 6.45 mmol) in THF (10 mL) at 0 °C
was added dropwise a solution of N-(3-tert-butylsalicylidene)-
2,3,4,5,6-pentafluoroaniline (1.0 g, 3.23 mmol) in 35 mL of
THF. 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(CH3)2 (350 mg, 1.62 mmol) in 10
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 hexane, and the solution was concentrated to 15 mL and
stored at -20 °C. A yellow solid deposited overnight (yield 1.14
g, 85%). Crystals suitable for an X-ray crystal structure
1
determination were grown from hexane at -20 °C. H NMR
(CDCl3, 293 K): δ 0.37 (6H, s, 2J(Sn-H) ) 67.1 Hz, Sn-CH3),
1.16 (18H, s, t-Bu), 6.68 (2H, t, Ar H), 7.03 (2H, d, Ar H), 7.39
Generation of Bis[N-(3-tert-butylsalicylidene)anili-
nato]methyltin(IV) Tetrakis(perfluorophenyl)borate (2a).
Compound 2 (10 mg, 15 µmol) was dissolved in dry ClC6D5
(0.5 mL). To the yellow solution was added [C(C6H5)3]+-
[B(C6F5)4]- (14 mg, 15 µmol). An orange solution was obtained
3
(2H, d, Ar H), 8.06 (2H, s, J(Sn-H) ) 15.9 Hz, NdCH). 13C
(20) (a) Kissin, Y. V.; Nowlin, T. E.; Mink, R. I. Macromolecules 1993,
26, 2151-2158. (b) Echevskaya, L.; Zakharov, V. A.; Golovin, A. V.;
Mikenas, T. B. Macromol. Chem. Phys. 1999, 200, 1434-1438.
(21) Fujita, T.; Tohi, Y.; Mitani, M.; Matsui, S.; Saito, J.; Nitabaru,
M.; Sugi, K.; Maiko, H.; Tsutsui, T. (Mitsui Chemicals Inc.) EP Patent
0874005, 1998; Chem. Abstr. 1998, 129, 331166.
(22) Mitani, M.; Mohri, J.; Yoshida, Y.; Saito, J.; Ishii, S.; Tsuru,
K.; Matsui, S.; Furuyama, R.; Nakano, T.; Tanaka, H.; Kojoh, S.;
Matsugi, T.; Kashiwa, N.; Fujita, T. J. Am. Chem. Soc. 2002, 124(13),
3327-3336.
1
and analyzed by NMR spectroscopy at room temperature. H
NMR (ClC6D5, 293 K): δ 0.60 (3H, s, Sn-CH3), 1.23 (18H, s,
3
t-Bu), 6.78-7.39 (16H, br m, Ar H), 8.16 (2H, s, J(Sn-H) )
14,9 Hz, NdCH). 13C NMR (ClC6D5, 293 K): δ 3.8 (Sn-CH3),
29.2 (C-CH3), 35.0 (C-CH3), 172.3 (NdCH). 119Sn NMR (CD2-
Cl2, 293 K): δ -394.26. 19F NMR (ClC6D5, 293 K): δ -131.9
(2F, d, o-F), -162.6 (1F, t, p-F), -166.4 (2F, t, m-F). The

1952 Organometallics, Vol. 24, No. 8, 2005
Annunziata et al.
the crystallographic package TEXSAN.24 Absorption and
intensity decay corrections were applied to the data.
The structures were solved by direct methods using the
program SIR9225 and refined by means of full-matrix least
squares based on F2 using the program SHELXL97.26
For all compounds non-hydrogen atoms were refined aniso-
tropically and hydrogen atoms were positioned geometrically
and included in structure factor calculations but not refined.
Crystal structures were drawn by means of the program
ORTEP32.27
Crystal data and refinement details are listed in Table 2.
X-ray Powder Diffraction. A 0.5 mm Lindemann capillary
was filled with the air-sensitive powder of 4 and sealed in a
drybox under an argon atmosphere.
X-ray powder diffraction data of 4 were collected by means
of a Bruker D8 diffractometer equipped with a Goebel mirror
using Cu KR radiation, step size 0.05° in 2θ, and step time
40 s.
Table 2. Crystal Data and Refinement Details for
Compounds 1, 2, and 4
1
2
4
mol formula
C
36H32F10N2- C36H42N2-
C
42H54N2-
O2Sn
O2Sn
O2Sn
mol wt
cryst syst
space group
a (Å)
b (Å)
c (Å)
833.33
monoclinic
P21/c
8.757(5)
25.021(3)
16.603(5)
97.49(4)
3606.6(2)
4
653.43
737.59
monoclinic orthorhombic
P21/n
P212121
13.265(6)
9.651(4)
26.01(1)
94.18(4)
3320(2)
4
1.31
1352
8.0
16.551(6)
18.233(5)
12.590(3)
â (deg)
V (Å3)
3799(2)
4
1.29
1544
7.1
Z
Dc (g/cm3)
F(000)
1.53
1672
7.9
abs coeff (cm-1
)
(λ ) 0.7107 Å)
transmissn factors
decay (%)
0.753-0.853 0.749-0.786 0.66-0.753
7.7 8.5
polynomial polynomial
Data reduction was performed using the program GUFI.28
The background was modeled manually using GUFI. Rietveld
refinement was accomplished with the program GSAS.29 The
peak profile was described by a pseudo-Voigt function, in
combination with a special function that accounts for the
asymmetry due to axial divergence.30 No absorption correction
was applied to the data. The atomic parameters were taken
from the structure model obtained from the single-crystal
X-ray diffraction data and were not refined. Final indices are
Rp ) 0.035 and Rwp ) 0.046.
decay cor
scan type
2θmax (deg)
ω
55
ω
50
ω/2θ
55
no. of rflns
no. of rflns (I > 2σ(I)) 4990
8299
6130
5854
370
0.027
0.081
1.02
4829
3792
424
0.028
0.076
1.02
no. of variables
R1 (I > 2σ(I))
wR2 (all data)
goodness of fit
max, min diff
Fourier (e/Å3)
460
0.031
0.082
0.98
0.39, -0.39 0.34, -0.55 0.38, -0.39
Acknowledgment. We are grateful to Dr. Carla
Scarabino for elemental analysis, to Dr. Patrizia Oliva
for 119Sn NMR experiments, to Mr. Raffaele Miranda
for EI MS measurements, and Dr. Angela Alfano for
some synthetic preparations. This work was supported
by the Italian Ministry of University and Research
(PRIN 2002).
byproduct (C6H5)3CCH3 was identified according to the litera-
ture.23 The side product Sn(CH3)4 was also identified.
Polymerization Tests. A typical polymerization test was
carried out in a 500 mL magnetically stirred glass autoclave,
which was conditioned under dynamic vacuum, thermostated
at 25 °C, and then charged with a solution of the tin compound
(45 µmol) and [C(C6H5)3]+[B(C6F5)4]- (45 µmol) in ClC6H5 (50
mL). Ethylene was fed continuously at a pressure of 6 atm;
after 6 h, the autoclave was vented and the reaction mixture
was poured into acidified methanol. The solution was treated
with water and hexane (3 × 30 mL). The organic phase was
dried on Na2SO4, and the solvents were stilled off. An oily
product was obtained; typically yields are about 200 mg. The
products were analyzed by 13C NMR analysis; the oligomer
structure was assigned according to the literature.18
X-ray Diffraction Analysis. Single-Crystal X-ray Crys-
tallography. Suitable crystals were selected and mounted in
Lindemann capillaries under an inert atmosphere. Diffraction
data were measured at room temperature with a Rigaku
AFC7S diffractometer using graphite-monochromated Mo KR
radiation (λ ) 0.710 69 Å). Data reduction was performed with
1
Supporting Information Available: Figures giving H
1
and 13C NMR spectra of compounds 1-4, H and 119Sn NMR
spectra of compound 2 at variable temperature, 1H NMR
spectra of compound 4 at variable temperature, ORTEP
diagrams of compounds 2 and 4, observed and calculated X-ray
powder diffraction pattern of compound 4, and a 13C NMR
spectrum of the ethylene oligomers and CIF files giving
crystallographic data for compounds 1, 2, and 4. This material
is available free of charge via the Internet at http://pubs.acs.org.
OM0491084
(26) Sheldrick, G. M. SHELXL97, a Program for Refining Crystal
Structures; University of Go¨ttingen, Go¨ttingen, Germany, 1997.
(27) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.
(28) Dinnebier, R. E.; Finger, L. Z. Kristallogr. Suppl. 1998 15, 148
(available at www.fkf.mpg.de/xray/html/body_gufi_software.html).
(29) Larson, A. C.; Von Dreele, R. B. (2001). GSAS-General Struc-
ture Analysis System; Los Alamos National Laboratory. Los Alamos.
NM, 2001; LANL Report LAUR 86-748 (available by anonymous FTP
from mist.lansce.lanl.gov).
(23) Korolev, A. V.; Delpech, F.; Dagorne, S.; Guzei, I. A.; Jordan,
R. F. Organometallics 2001, 20, 3367-3369.
(24) TEXSAN, Crystal Structure Analysis Package; Molecular Struc-
ture Corp., The Woodlands, TX, 1985-1992.
(25) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Gagliardi, A.;
Burla, M. C.; Polidori, G.; Camalli, M. J. Appl. Crystallogr. 1994, 27,
435.
(30) (a) Thompson, P.; Cox, D. E.; Hastings, J. B. J. Appl. Crystal-
logr. 1987, 20, 79-83. (b) Finger, L. W.; Cox, D. E.; Jephcoat, A. P. J.
Appl. Crystallogr. 1994, 27, 892-900.