Zwitterionic forms of salicylaldimine donor ligands in unusual adduct formation with organotin(IV) Lewis acids

Article abstract of DOI:10.1021/om030540f

The focus of this investigation was on adduct formation, and its consequences, between organotin(IV) Lewis acids and the tetradentate salicylaldimine ligands H₂3-MeOsalen [N,N′-bis(3-methoxysalicylidine)1,2-ethane diamine] and H₂3-MeOsalbiphen [N,N′-bis(3-methoxysalicylidine)2,2′-biphenyl diamine]. SnBuⁿ₂Cl₂ reacted with H₂3-MeOsalen to give a 1/1 adduct, A, containing a dangling salicylaldimine ligand but failed to yield a solid state adduct with H₂3-MeOsalbiphen, even though it exists in dynamic equilibrium with the latter ligand in solution. The stronger Lewis acids SnPh₂Cl₂ and SnBuⁿCl₃ yielded 2/1 solid state adducts D and E, respectively, with H₂3-MeOsalbiphen in each of which the ligand bridges to six-coordinated tin centers and donor bonds are via phenolic and methoxy oxygen atoms. SnBuⁿ₂-(NCS)₂ reacted with H₂3-MeOsalen to give an adduct, B, having a solid state ionic structure of formulation {[SnBuⁿ₂(NCS)(H₂3-MeOsalen)]₂(μ-H ₂3-MeOsalen)} [SnBuⁿ₂(NCS)₄]. The cation of B displays both bridging and dangling ligands and seven-coordinated tin. The ionic structure gives way to a nonionic symmetric cyclic trimeric structure of formulation [SnBuⁿ₂-(NCS)₂(μ-H₂ 3-MeOsalen)]₃ in solution. The latter reacted with NaCl and SnBuⁿ₂Cl₂ to yield a new adduct, C, which in the solid state has an the ionic formulation [SnBuⁿ₂ Cl(μ-H₂3-MeOsalen)]₂ [SnBuⁿ₂ (NCS)₄], the cation of which has a centrosymmetric structure and seven-coordinated tin. The solid state ionic structure of C is not retained in solution. Crystallographic data are also reported for the free ligands H₂3-MeOsalen and H₂3-MeOsalbiphen (two crystal modifications of the latter were identified). The structural data clearly identify that donor bond formation through the salicylaldimine phenolic oxygen has the concomitant effect of phenolic hydrogen transfer to the imine nitrogen, a process that accounts for the imine hydrolysis which frequently occurs when the salicylaldimine ligands react with Lewis acids. Salicylaldehyde does not assume a switterionic form in its 1/1 adduct, F, with SnMe₂- Cl₂ (the structure of this adduct was reinvestigated in the present study), and consequently the role of the phenolic oxygen is reduced to that of a very weak donor, participating merely in secondary bonding.

Full text of DOI:10.1021/om030540f

984
Organometallics 2004, 23, 984-994
Zw itter ion ic F or m s of Sa licyla ld im in e Don or Liga n d s in
Un u su a l Ad d u ct F or m a tion w ith Or ga n otin (IV) Lew is
Acid s
Des Cunningham,* Karon Gilligan, Martina Hannon, Cathal Kelly,
Pat McArdle, and Ann O’Malley
Department of Chemistry, National University of Ireland, Galway, Ireland
Received J uly 17, 2003
The focus of this investigation was on adduct formation, and its consequences, between
organotin(IV) Lewis acids and the tetradentate salicylaldimine ligands H23-MeOsalen [N,N′-
bis(3-methoxysalicylidine)1,2-ethane diamine] and H23-MeOsalbiphen [N,N′-bis(3-methoxy-
salicylidine)2,2′-biphenyl diamine]. SnBun Cl2 reacted with H23-MeOsalen to give a 1/1
2
adduct, A, containing a dangling salicylaldimine ligand but failed to yield a solid state adduct
with H23-MeOsalbiphen, even though it exists in dynamic equilibrium with the latter ligand
in solution. The stronger Lewis acids SnPh2Cl2 and SnBunCl3 yielded 2/1 solid state adducts
D and E, respectively, with H23-MeOsalbiphen in each of which the ligand bridges to six-
coordinated tin centers and donor bonds are via phenolic and methoxy oxygen atoms. SnBun -
2
(NCS)2 reacted with H23-MeOsalen to give an adduct, B, having a solid state ionic structure
of formulation {[SnBun (NCS)(H23-MeOsalen)]2(µ-H23-MeOsalen)}[SnBun (NCS)4]. The cation
2
2
of B displays both bridging and dangling ligands and seven-coordinated tin. The ionic
structure gives way to a nonionic symmetric cyclic trimeric structure of formulation [SnBun -
2
(NCS)2(µ-H23-MeOsalen)]3 in solution. The latter reacted with NaCl and SnBun Cl2 to yield
2
a new adduct, C, which in the solid state has an the ionic formulation [SnBun Cl(µ-H23-
2
MeOsalen)]2[SnBun (NCS)4], the cation of which has a centrosymmetric structure and seven-
2
coordinated tin. The solid state ionic structure of C is not retained in solution. Crystallo-
graphic data are also reported for the free ligands H23-MeOsalen and H23-MeOsalbiphen
(two crystal modifications of the latter were identified). The structural data clearly identify
that donor bond formation through the salicylaldimine phenolic oxygen has the concomitant
effect of phenolic hydrogen transfer to the imine nitrogen, a process that accounts for the
imine hydrolysis which frequently occurs when the salicylaldimine ligands react with Lewis
acids. Salicylaldehyde does not assume a zwitterionic form in its 1/1 adduct, F , with SnMe2-
Cl2 (the structure of this adduct was reinvestigated in the present study), and consequently
the role of the phenolic oxygen is reduced to that of a very weak donor, participating merely
in secondary bonding.
In tr od u ction
been employed for the synthesis of diorganotin com-
plexes, but problems have been encountered that are
attributed to tin hydrolysis resulting in stannoxane
formation.4-10 The use of a diorganotin dihalide in the
presence of a HCl scavenger is generally not an ap-
propriate synthetic route since the Lewis-base scavenger
can catalyze stannoxane formation. In the absence of
the base, simple adducts of 1/1 stoichiometry are formed,
and several such adducts were isolated.4 Closely related
adducts SnR2Cl2‚H2acacen [H2acacen ) N,N′-bis(acetyl-
ecetenato)ethane 1,2-diamine] have also been isolated
and their structures studied in detail by Mo¨ssbauer
Transition metal salicylaldimine complexes have been
intensively investigated. They are complexes that dis-
play a wide diversity of properties embracing such
important phenomena as high-spin-low-spin equilib-
rium and reversible uptake of both dioxygen and carbon
dioxide.1 Their ability to act as chiral oxidation catalysts
is of greatest current interest, prime examples being
J acobson’s manganese(III) salicylaldimine chiral epoxi-
dation catalysts.2 Significantly less attention has fo-
cused on p-block salicylaldimine complexes.3 One of the
attractive features of the salicylaldimine complexes is
their ease of synthesis, generally from the metal acetate,
acetylacetonate, or, in some cases, the freshly precipi-
tated hydroxide. A number of synthetic methods have
(4) Kawakami, K.; Miya-Uchi, M.; Tanaka, T. J . Inorg. Nucl. Chem.
1971, 33, 3733.
(5) Honnick, W. D.; Zuckerman, J . J . Inorg. Chem. 1979, 18, 1437.
(6) Kawakami, K.; Miya-Uchi, M.; Tanaka, T. J . Organomet. Chem.
1974, 70, 67.
* Corresponding author. Fax: 353-91-525700. E-mail: des.
cunningham@nuigalway.ie.
(1) Aly, M. M. J . Coord Chem. 1998, 43, 89.
(2) J acobsen, E. N.; Loebach, J . L.; Wilson, S. R. J . Am. Chem. Soc.
1990, 112, 2801.
(7) Cozens, R. J .; Murray, K. S.; West, B. O. Aust. J . Chem. 1970,
23, 683.
(8) Dey, K. J . Inorg. Nucl. Chem. 1970, 32, 3125.
(9) Barbieri, R.; Herber, R. H. J . Organomet. Chem. 1972, 42, 65.
(10) Ruddick, J . N. R.; Sams, J . R. J . Organomet. Chem. 1973, 60,
233.
(3) Atwood, D. A.; Harvey, M. J . Chem. Rev. 2001, 101, 37.
10.1021/om030540f CCC: $27.50 © 2004 American Chemical Society
Publication on Web 01/30/2004

Adduct Formation with Organotin(IV) Lewis Acids
Organometallics, Vol. 23, No. 5, 2004 985
the literature.15 Salicylaldehyde, ethylenediamine, and 1,3-
diaminopropane (Aldrich Chemical Co.) and 3-methoxy sali-
cylaldehyde (J annsen Chimica) were used as supplied. 2,2′-
Diaminobiphenyl was obtained from the reduction of 2,2′-
dinitrobiphenyl.16
Sch em e 1. Sa licyla ld im in e Liga n d s
Syn th esis of Sa licyla ld im in e Liga n d s a n d Cr ysta lliza -
tion of H23-MeOsa len (G) a n d H23-MeOsa lbip h en (H). The
salicylaldimine ligands were prepared by standard proce-
dures.17 Crystals of H23-MeOsalen (mp 170-172 °C) were
grown from an acetonitrile solution that had been saturated
at
a temperature approximately 5 °C higher than room
temperature. Ruby red needlelike crystals of H23-MeOsalbi-
phen (H) (mp 178-180 °C) can be grown likewise. Crystals of
the same polymorph were obtained from an acetonitrile
solution containing SnBunCl2 and H23-MeOsalbiphen in equimo-
lar quantities, and from this solution slightly paler colored
crystals (mp 184-186 °C) with a more blocklike morphology
belonging to another crystal modification were also obtained.
Syn th esis a n d Cr ysta lliza tion of Sn Bu n 2Cl2‚H23-Me-
Osa len (A). SnBun2Cl2 (1.21 g) was dissolved in 40 cm3 of
acetonitrile. An equimolar quantity of H23-MeOsalen was
added and the resulting solution stirred over gentle heat for
1 h. On cooling, the yellow 1/1 adduct precipitated (yield 80%).
After removal of the solid by filtration, the solution was left
to stand for approximately 12 h, after which time good quality
crystals were obtained (dec at ca. 170 °C). The crystals had
limited lifetime in solution and were totally unstable out of
solution. A crystal for the crystal structure determination was
sealed in a capillary tube, with residual solvent and data
collection was undertaken without delay. Anal. Calcd for
spectroscopy, from which it was concluded that they
possessed chain polymeric structures with bridging H2-
acacen ligands and trans alkyl octahedral tin coordina-
tion geometries.11-13 The structure of SnMe2Cl2‚H2salen
(see Scheme 1 for ligand nomenclature) was subse-
quently determined, and although the data were of low
quality (due to crystal twinning), they confirmed this
type of polymeric structure.14 No further interest has
been expressed in adducts of this type. Interest in this
laboratory in salicylaldimine complexes having methoxy
substituents in the 3,3′-positions led to the investigation
of adducts of organotin tin species with H23-MeOsalen
and related ligands (see Scheme 1). The study revealed
an unexpected and fascinating structural chemistry as
well as important zwitterionic behavior of salicylaldi-
mine ligands, the latter behavior accounting for the
catalytic role of Lewis acids in the hydrolysis of the
imine functional group.
C
26H38N2O4Cl2Sn: C, 49.40; H, 6.06; N, 4.43. Found for initial
precipitate: C, 49.74; H, 5.83; N, 4.85. Found for the crystals:
C, 49.51; H, 5.84; N, 4.61.
Syn th esis a n d Cr ysta lliza tion of {[Sn Bu n 2(NCS)(H23-
MeOsa len )]2(µ-H23-MeOsa len )}[Sn Bu n 2(NCS)4] (B). To a
solution of 1.4 g (4 mmol) of SnBun2(NCS)2 in methanol (40
cm3) was added an equimolar quantity of H23-MeOsalen. The
suspension was stirred over gentle heat for 1 h to yield a clear
yellow solution. On cooling, the microcrystalline adduct was
obtained (yield 70%). Recrystallization from acetonitrile gave
air-stable crystals (dec at ca. 170 °C) suitable for crystal-
lography. Anal. Calcd for C84H114N12O12S6Sn3: C, 49.64; H,
5.65; N, 8.27. Found for the microcrystalline material: C,
49.36; H, 5.26; N, 8.03. Found for the crystals: C, 49.43; H,
5.54; N, 8.11.
Syn t h esis a n d Cr yst a lliza t ion of [Sn Bu n 2Cl(µ-H23-
MeOsa len )]2[Sn Bu n 2(NCS)4] (C). To a solution of 3.1 g (1.5
mmol) of B in methanol (60 cm3) was added equimolar
quantities of SnBun2Cl2 and NaCl. After stirring over gentle
heat for 3 h a clear yellow solution was obtained. On cooling,
C was obtained as a yellow solid (yield 60%). Crystallization
of the yellow solid from acetonitrile yielded crystals of C (dec
at ca. 160 °C). Anal. Calcd for C64H94N8O8S4Cl2Sn3: C, 46.34;
H, 5.71; N, 6.76. Found for the precipitate: C, 45.89; H, 5.13;
N, 6.23. Found for the crystals: C, 46.11; H, 5.45; N, 6.63.
Syn t h esis a n d Cr yst a lliza t ion of (Sn P h 2Cl2)2‚H 23-
MeOsa lbip h en (D). To a solution of 0.96 g (2.1 mmol) of H2-
MeOsalbiphen in acetonitrile (20 cm3) was added 1.46 g (4.2
mmol) of SnPh2Cl2. The resulting orange solution was left aside
for 1 day, after which time air-stable orange crystals of the
adduct D were obtained (yield 60%). Anal. Calcd for C52H44N2O4-
Cl4Sn2: C, 54.78; H, 3.87; N, 2.46. Found for the crystals: C,
54.65; H, 3.81; N, 2.39.
Exp er im en ta l Section
Infrared spectra, recorded on a Perkin-Elmer 1600 spectro-
photometer, were obtained for Nujol mulls between KBr plates.
NMR spectra were recorded on a J EOL Lambda 400 spec-
trometer. Sn-119 Mo¨ssbauer spectra were recorded on a
spectrometer supplied by J & P Engineering, Reading, U.K.
Spectra were recorded with the sample at liquid nitrogen
temperature and the source, Ca119SnO3 (the Radiochemical
Centre Amersham, U.K), at room temperature. Spectra were
analyzed using the program Peakfit (J andel Scientific). Mo-
lecular weights in chloroform (distilled from calcium hydride
immediately before use) were determined using a Perkin-
Elmer 115 molecular weight machine employing the vapor
pressure (isopiestic) method. Naphthalene was employed as
calibrant. Conductivity measurements in solution were deter-
mined using a conductivity meter (EDT instruments).
Butyltin halides (Aldrich Chemical Co.) were used as
supplied. Diphenyltin dichloride (Aldrich Chemical Co.) was
recrystallized prior to use. SnBun2(NCS)2 was prepared as in
Syn t h esis a n d Cr yst a lliza t ion of (Sn Bu n Cl3)2‚H 23-
MeOsa lbip h en (E). To a solution of 2.44 g (5 mmol) of H23-
MeOsalbiph in acetonitrile (20 cm3) was added 3.05 g (10
(11) Smith, P. J .; Dodd, D. J . Organomet. Chem. 1971, 32, 195.
(12) Barbieri, R.; Cefalu, R.; Chandra, S. C.; Herber, R. H. J .
Organomet. Chem. 1971, 32, 97.
(15) Chow, Y. M. Inorg. Chem. 1970, 9, 794.
(13) Barbieri, R.; Pellerito, L.; Cefalu, R. J . Organomet. Chem. 1971,
32, 107.
(14) Randaccio, L. J . Organomet. Chem. 1973, 55, C58.
(16) Smith, W. B. J . Heterocycl. Chem. 1987, 24, 745.
(17) (a) Curtis, N. F. Coord. Chem. Rev. 1968, 3, 3. (b) Goeden, V.
L.; Kildohl, N. K.; Bush, D. H. J . Coord. Chem. 1977, 7, 89.

986 Organometallics, Vol. 23, No. 5, 2004
Cunningham et al.
mmol) of SnBunCl3. A yellow precipitate of the adduct rapidly
formed in the resulting orange solution (yield 85%). A satu-
rated solution of the yellow solid in acetonitrile at ap-
proximately 40 °C yielded crystals of adduct E after slow
cooling. Anal. Calcd for C36H42N2O4Cl6Sn2: C, 42.52; H, 4.16;
N, 2.75. Found for the precipitate: C, 42.11; H, 3.74; N, 2.52.
Found for the crystals: C, 42.44; H, 3.78; N, 2.61.
Sch em e 2. P ossible Str u ctu r es of Dior ga n otin
Dich lor id e Ad d u cts w ith Sa licyla ld im in e Liga n d s
Syn th esis a n d Cr ysta lliza tion of Sn Me2Cl2‚sa licyl-
a ld eh yd e (F ). A large excess of salicylaldehyde was added to
a hot solution of SnMe2Cl2 (1.0 g) in hexane (40 cm3). On
cooling, crystals of SnMe2Cl2 formed. When 1.0 g of SnMe2Cl2
was dissolved in 15 cm3 of hot salicylaldehyde and the
resulting solution allowed to cool, crystals of SnMe2Cl2‚
salicylaldehyde were obtained (yield 90%). Anal. Calcd for
C9H12O2Cl2Sn: C, 31.63; H, 3.54. Found: C, 31.44; H, 3.50.
Cr ysta llogr a p h y. Crystal data are in Table 1. Diffraction
data for A, B, F , G, and H were collected on an image plate
(Marr Research). Data for C, D, and E were collected on a
four-circle diffractometer (Enraf-Nonius CAD 4). Unit cell
parameters, in all cases, were determined from four-circle
diffractometer data. Data were corrected for Lorentz and
polarization effects but not for absorption. All structures were
solved by direct methods, SHELXS-97,18 and refined by full
matrix least squares using SHELXL-97.19 SHELX operations
were automated using ORTEX, which was also used to obtain
the drawings.20 The non-hydrogen atoms were refined aniso-
tropically. With the exception of the phenolic hydrogen, all
other hydrogen atoms were included in calculated positions
with thermal parameters 30% larger than the atom to which
they were attached. At this point of refinement, the difference
map in each case, with the exception of that for C, revealed a
peak close to either the phenolic oxygen or the imine nitrogen.
Generally these peaks were the highest intensity peaks in the
difference maps (in the case of E higher intensity peaks were
found around the butyl group, which did not refine very
satisfactorily, and in the case of D, high-intensity peaks were
found very close to tin, thus accounting for the high residual
electron density following final refinement). In no case was a
peak found close to both the nitrogen and oxygen. In the case
of C a peak was found close to nitrogen at one end of the
ligand, but no peak was found at the other end. In the case of
H23-MeOsalen, data were collected for a second crystal from
a different crystallization, and in this case the peak in the
difference map was found close to the phenolic oxygen precisely
as it was found in the first structure determination. These
peaks were taken to represent the positions of the phenolic
hydrogens, and in the final refinement the positions were
refined isotropically. All calculations were performed on a
Pentium PC.
oxygens. On the other hand, their likely involvement
in bonding to tin may result in simple monomeric
structures of either 1/1 or 2/1 stoichiometry (Scheme 2b
and 2c, respectively), in which tin achieves a coordina-
tion number of six without recourse to a polymeric
structure. In fact, it would be anticipated that a 2/1
adduct would form if sufficient tin Lewis acid (e.g.,
SnBun2Cl2) was available.
As it transpires, the reaction of SnBun2Cl2 with H23-
MeOsalen led exclusively to the formation of a 1/1
addition complex (A), irrespective of the quantity of
SnBun2Cl2 used in the synthesis, and this suggested that
an adduct of type 2a was being formed. The crystal
structure of the adduct (see Figure 1 and Table 2)
however revealed that the salicylaldimine ligand was
acting as a dangling ligand with only one phenolic and
one methoxy oxygen coordinating to tin, thus giving an
adduct of type b in Scheme 2. An examination of the
lattice structure did not reveal any bonding features
that would tend to add stability to the lattice and hence
favor a 1/1 rather than a 2/1 adduct. For example, there
are no intermolecular hydrogen-bonding interactions
involving the free end of the ligands and the phenyl
rings are not involved in significant π-interactions.
119Sn NMR solution state spectra suggest that the
failure to isolate the 2/1 adduct is largely, if not totally,
a consequence of ligand hydrolysis reactions, which
become more extensive as the acid/base ratio increases.
A dry chloroform solution of adduct A gave a 119Sn NMR
spectrum displaying two tin signals, a broad peak (peak
width of 638 Hz at half peak height) at -115.6 and a
sharp peak at -185.5 ppm. The ratio of the integrated
intensities of broad peak to sharp peak was approxi-
Resu lts a n d Discu ssion
SnMe2Cl2‚H2salen has a chain polymeric structure
resulting from the formation of trans phenolic oxygen
donor bonds to tin, as shown schematically in Scheme
2a.14 In this way tin achieves octahedral geometry with
trans methyl groups. A noteworthy feature is the lack
of participation of the imine nitrogen in donor bond
formation; the lack of participation of the nitrogen atoms
necessitated the involvement of all of the phenolic
oxygen atoms in bonding such as to produce six-
coordinated tin in the polymeric structure. The intro-
duction of methoxy groups in the 3,3′-positions provides
alternative bonding possibilities. Polymeric structures
such as that observed in SnMe2Cl2‚H2salen may still
result with little or no participation of the methoxy
mately 3.1. These are not attributable to the ClSnBun
-
2
OSnBun2Cl or ClSnBun2OSnBun2OH, nor is either peak
attributable to the presence of the free tin Lewis acid.
The broad peak is attributable to a tin that is involved
in dynamic behavior on the NMR time scale. Progressive
addition of further dibutyltin dichloride had the effect
of shifting this latter peak to lower field (as expected)
while the sharp peak position remained static. Further-
more, with addition of the extra tin Lewis acid, the
intensity of the sharp peak increased very significantly
relative to that of the broad peak. When a solution
containing excess dibutyltin dichloride was left aside for
a number of hours, a precipitate fell from solution. This
precipitate contained some of the 1/1 adduct but also
contained a complex (or complexes) that gave rise to a
(18) Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467.
(19) Sheldrick, G. M. SHELXL-97 a computer program for crystal
structure determination; University of Gottingen, 1997.
(20) McArdle, P. J . Appl. Crystallogr. 1995, 28, 65.

Adduct Formation with Organotin(IV) Lewis Acids
Organometallics, Vol. 23, No. 5, 2004 987

988 Organometallics, Vol. 23, No. 5, 2004
Cunningham et al.
tion of SnBun2Cl2, relative to that of the stationary peak
at -185.5 ppm is explicable on the basis of increased
hydrolysis of the salicylaldimine ligand.
Ligand hydrolysis was also observed in other reac-
tions. For example, the 119Sn NMR spectrum of a
solution containing equimolar quantities of SnBu2Cl2
and H23-MeOsal1,3pn again showed a broad peak (at
-123.0 ppm) and the sharp peak (at 188.0 ppm), but in
this case the intensity of the latter peak (resulting from
ligand hydrolysis) was very low. Reaction of BunSnCl3
with H23-MeOsalen in chloroform yielded an oily prod-
uct, which was not identified, but a product from the
reaction of SnBunCl3 with H23-MeOsal1,3pn was iso-
lated and identified as 1,3propylenediamine bishydro-
chloride, showing that in this case complete hydrolysis
of the ligand occurs. Reaction of SnBunCl3 with H23-
MeOsal1,2pn in ethanol at room temperature resulted
in the precipitation of SnBunCl2(3-MeOsal1,2pnNH2) in
high yield.21 However, ligand hydrolysis was not ob-
served when H23-MeOsalphen and H23-MeOsalbiphen
were employed as donor ligands. A chloroform solution
containing SnBun2Cl2 and H23-MeOsalphen, in 1:1
molar ratio, showed only a broad peak at -44.08 ppm,
and the position of this peak moved with increasing
ratio of Lewis acid to base. Likewise, a chloroform
solution containing SnBun2Cl2 and H2salbiphen showed
a single broad peak, the position of which was dictated
by the acid/base ratio.
F igu r e 1. ORTEX20 view A (30% ellipsoids).
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for A
Sn(1)-O(1)
Sn(1)-Cl(1)
Sn(1)-C(19)
2.293(4)
2.4252(17)
2.122(7)
Sn(1)-O(2)
Sn(1)-Cl(2)
Sn(1)-C(23)
3.177(4)
2.527(2)
2.130(8)
C(19)-Sn(1)-C(23) 145.1(3)
C(23)-Sn(1)-O(1) 89.3(3)
C(23)-Sn(1)-Cl(1) 105.8(3)
C(19)-Sn(1)-O(1)
87.6(3)
C(19)-Sn(1)-Cl(1) 107.5(2)
O(1)-Sn(1)-Cl(1)
C(23)-Sn(1)-Cl(2) 96.7(2)
78.53(10)
C(19)-Sn(1)-Cl(2)
O(1)-Sn(1)-Cl(2)
C(19)-Sn(1)-O(2)
O(1)-Sn(1)-O(2)
Cl(2)-Sn(1)-O(2)
94.4(2)
166.23(11) Cl(1)-Sn(1)-Cl(2)
87.89(6)
70.7(2)
79.0(2)
C(23)-Sn(1)-O(2)
55.66(13) Cl(1)-Sn(1)-O(2) 133.74(9)
138.09(10)
Ligand hydrolysis had not been considered in early
synthetic studies or in 13C and 1H NMR studies of
complex formation between organotin Lewis acids and
salicylaldimine ligands. On the other hand, the pos-
sibility of hydrolysis of the organotin Lewis acid leading
to stannoxane formation was clearly recognized.6,9 In
actual fact, if solutions of SnBun2Cl2 and H23-MeOsalen
are not rigorously protected from water, two extra sharp
strong band at 2060 cm-1 and other weaker bands at
2282, 2441, and 2519 cm-1 in the infrared spectrum.
These bands do not occur in the spectrum of the adduct
but are typically observed in adducts of ethylenediamine
and in complexes containing the partially hydrolyzed
salicylaldimine ligand H3-MeOsalenNH2 (see Scheme
1). They are found, for example, in the spectrum of
SnBunCl2(3-MeOsalenNH2), which has been character-
ized crystallographically in this laboratory.21 The com-
plexities of the 119Sn NMR spectra are thus almost
certainly a consequence of ligand hydrolysis, which will
introduce 3-methoxysalicylaldehyde, ethylenediamine
(resulting from total hydrolysis), and/or H3-MeOsalen-
NH2 (resulting from partial hydrolysis) as potential
donor ligands. Since the ethylenediamine adduct of
dibutyltin dichloride is insoluble in chloroform, its
involvement in solution is ruled out. Furthermore, a
119Sn NMR spectrum of an equimolar chloroform solu-
tion of dibutyltin dichloride and 3-methoxysalicylalde-
hyde showed a single sharp peak that was only 5 ppm
upfield from the peak due to dibutyltin dichloride, and
thus the involvement of the free 3-methoxysalicylalde-
hyde is also eliminated. This leaves the presence of H3-
MeOsalenNH2 as the most likely source of the NMR
complexities. Chelation between H3-MeOsalenNH2 and
SnBun2Cl2 could account for the sharp peak that re-
mains invariant at -185.5 ppm [SnBunCl2(salenNH2)
shows a single sharp peak in its 119Sn NMR spectrum],
whereas the other peak may be attributable to a
dynamic interaction between SnBun2Cl2 and the phe-
nolic oxygen of H23-MeOsalen. The loss of intensity of
this latter peak, occurring on increasing the concentra-
bands located at -90 and -140 ppm due to ClSnBun
-
2
OSnBun2Cl are found in the NMR spectrum.
Reaction of SnBu2(NCS)2 with H23-MeOsalen again
leads exclusively to the formation of what appears from
analytical data to be a 1/1 addition complex (complex
B). However, the crystallographic study revealed a
considerably more complicated structure than that
of A. It is an ionic adduct having the formulation
{[SnBu2(NCS)(H23-MeOsalen)]2(µ-H23-MeOsalen)}-
[SnBu2(NCS)4]; analytical data correspond to those
expected for a simple 1/1adduct formulation. The struc-
ture of the centrosymmetric ditin cation is shown in
Figure 2a and that of the anion in Figure 2b. Selected
bonding parameters are in Table 3. The presence of
dangling ligands is again a surprising feature.
The 119Sn Mo¨ssbauer spectrum of the complex re-
vealed the existence of two tin environments with
quadrupole splitting values of 4.59 and 3.69 mm.s-1 and
associated isomer shifts of 2.30 and 1.85 mm.s-1, respec-
tively. The larger quadrupole splitting is clearly associ-
ated with the anionic tin with the much greater C-Sn-C
bond angle.22 Rather surprisingly, however, the 119Sn
NMR spectrum of B (measured in dry chloroform)
showed a single sharp signal at -294 ppm, and further-
more, the 13C NMR spectrum was simple, showing
evidence for only one type of salicylaldimine ligand and
(21) Timmins, B. Ph.D. Degree Thesis, National University of
Ireland, 1995.
(22) Bancroft, T. M.; Platt, R. H. Adv. Inorg. Radiochem. 1972, 15,
159.

Adduct Formation with Organotin(IV) Lewis Acids
Organometallics, Vol. 23, No. 5, 2004 989
F igu r e 2. Structure of B. (a) Centrosymmetric ditin cation. (b) Chain arrangement of the anions resulting from short
S-S contacts of 3.4 Å (30% ellipsoids).
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for B
Sn(1)-C(39)
Sn(1)-N(6)
Sn(2)-C(35)
Sn(2)-O(3)
Sn(2)-O(6)
2.134(7)
2.284(7)
2.097(4)
2.913(3)
2.946(3)
Sn(1)-N(5)
Sn(2)-C(31)
Sn(2)-O(1)
Sn(2)-O(5)
Sn(2)-N(4)
2.271(5)
2.121(3)
2.193(3)
2.205(3)
2.139(5)
C(39)-Sn(1)-N(5) 90.9(2)
N(5)-Sn(1)-N(6) 91.3(2)
C(39)-Sn(1)-N(6)
87.7(3)
C(35)-Sn(2)-C(31) 149.2(2)
C(35)-Sn(2)-N(4) 106.49(17) C(35)-Sn(2)-O(1)
C(35)-Sn(2)-O(3) 80.22(12) C(35)-Sn(2)-O(5)
91.40(14)
95.60(13)
C(35)-Sn(2)-O(6) 76.94(13) C(31)-Sn(2)-N(4) 104.30(17)
C(31)-Sn(2)-O(1) 94.36(14) C(31)-Sn(2)-O(3)
C(31)-Sn(2)-O(5) 91.50(12) C(31)-Sn(2)-O(6)
76.23(12)
80.92(13)
61.21(11)
59.94(10)
N(4)-Sn(2)-O(1)
O(3)-Sn(2)-O(6)
N(4)-Sn(2)-O(5)
78.06(14) O(1)-Sn(2)-O(3)
83.54(10) O(5)-Sn(2)-O(6)
77.55(13)
F igu r e 3. Centrosymmetric ditin cation of C (30% el-
lipsoids).
this being a ligand symmetrically involved in bonding
interactions. The conductivity of chloroform and aceto-
nitrile was only marginally altered by the addition of
the complex. For example, the conductivity of a 0.003
M chloroform solution was 0.0 µs, and that of a 0.012
M solution 0.9 µs. It can thus be safely concluded that
the ionic structure does not persist in solution. Molec-
ular weight measurements in chloroform solutions were
consistent with the existence of trimeric units of SnBu2-
(NCS)2‚H23-MeOsalen. For example, measured molec-
ular weights for 1.11, 1.44, and 2.16 M (based on the
monomeric formulation) chloroform solutions were
1828.2, 1817.0, and 1755.3, respectively, and these
values compare with a theoretical molecular weight of
1780.14 for a trimeric formulation. Taken as a whole,
the data point to the existence of a complex of formula
[SnBu2(NCS)2(µ-H23-MeOsalen)]3 in chloroform having
a symmetrical cyclic structure such as that in Scheme 4.
When equimolar quantities of {[SnBu2(NCS)(H23-
MeOsalen)]2(µ-H23-MeOsalen)SnBu2}[SnBu2(NCS)4],
SnBu2Cl2, and NaCl are stirred together in warm
methanol (approximately 50 °C), a new complex C is
obtained which can be crystallized from acetonitrile.
This is also an ionic adduct and has the formulation
[SnBu2Cl(µ-H23-MeOsalen)]2[SnBu2(NCS)4]. The inter-
esting cyclic centrosymmetric ditin cation of this com-
plex is in Figure 3, and selected bonding parameters
are in Table 4. In this instance there are no dangling
salicylaldimine ligands. As in the case of B, its addition
to chloroform or acetonitrile had essentially no impact
on conductivity measurements, and a 119Sn NMR spec-
trum of a chloroform solution showed two signals, a
sharp intense band at -182.5 ppm and a very broad
low-intensity band at -294 ppm. A major difficulty
associated with the interpretation of the NMR spectrum

990 Organometallics, Vol. 23, No. 5, 2004
Cunningham et al.
Sch em e 3. Sch em a tic Rep r esen ta tion s of th e Solid Sta te Str u ctu r es of A-F
in this instance stems from the ratio of tin to ligands;
to every three tin atoms in solution there are two
chloride, four thiocyanate, and two salicylaldimine
ligands.
MeOsalbiphen (D) and (SnBunCl3)2‚H23-MeOsalbiphen
(E). For each adduct, crystallographic data confirmed
straightforward bisbidentate behavior of the ligand as
in Scheme 2c, with the phenolic and methoxy atoms
alone involved in donation to tin (see Figures 4 and 5
for views of the asymmetric units and Tables 5 and 6
for selected bonding parameters).
There are several features of the crystallographic
structural data that merit comment. The cationic tin
species of B and C have very similar tin coordination
geometries. Methoxy and phenolic oxygen atoms from
two separate salicylaldimine ligands form donor bonds
to tin of a dibutyltin monothiocyanato cation in B and
to a dibutyltin monochloro cation in C. The phenolic
oxygen donor bonds to tin are strong, whereas the
Although SnBun2Cl2 is involved in dynamic equilib-
rium with both H23-MeOsalphen and H23-MeOsalbi-
phen in solution (see earlier discussion), it did not prove
possible to isolate adducts in the solid state. Acetonitrile
and chloroform solutions of SnBun2Cl2 and H23-MeOsal-
phen (equimolar quantities) yielded intractable oils after
slow removal of solvent. Acetonitrile and chloroform
solutions containing either SnBun2Cl2 or SnBun2(NCS)2,
along with H23-MeOsalbiphen, invariably yielded crys-
tals of the free ligand. On the other hand, this latter
ligand readily yielded the 2/1 adducts (SnPh2Cl2)2‚H23-

Adduct Formation with Organotin(IV) Lewis Acids
Organometallics, Vol. 23, No. 5, 2004 991
F igu r e 4. ORTEX20 view of D (30% ellipsoids).
Sch em e 4. Solu tion Sta te Str u ctu r e for
[Sn Bu n 2(NCS)2‚H23-MeOsa len ]3 Con sisten t w ith
Molecu la r Weigh t a n d NMR Da ta
F igu r e 5. ORTEX20 view of E (30% ellipsoids). Phenyl
rings C(1)-C(6) and C(21)-C(26) are nonparallel, having
a centroid-centroid separation of 3.95 Å and a closest C-C
contact of 3.36 Å.
Ta ble 5. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for D
Sn(1)-C(14)
Sn(1)-O(1)
Sn(1)-Cl(1)
2.140(3)
2.206(2)
2.3999(10)
Sn(1)-C(20)
Sn(1)-O(2)
Sn(1)-Cl(2)
2.148(3)
2.594(3)
2.5287(10)
C(14)-Sn(1)-C(20) 164.40(15) C(14)-Sn(1)-O(1)
87.45(12)
C(20)-Sn(1)-O(1)
C(20)-Sn(1)-Cl(1)
C(14)-Sn(1)-Cl(2)
C(14)-Sn(1)-O(2)
O(1)-Sn(1)-O(2)
Cl(2)-Sn(1)-O(2)
89.07(12) C(14)-Sn(1)-Cl(1) 97.79(10)
97.54(11) O(1)-Sn(1)-Cl(1) 92.45(7)
90.65(10) C(20)-Sn(1)-Cl(2) 88.80(10)
84.32(12)
67.34(9) Cl(1)-Sn(1)-Cl(2) 102.47(4)
97.75(6)
80.31(11) C(20)-Sn(1)-O(2)
Ta ble 6. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for E
Sn(1)-C(29)
Sn(1)-O(3)
Sn(1)-Cl(4)
Sn(2)-C(33)
Sn(2)-O(4)
Sn(2)-Cl(3)
2.131(5)
2.447(3)
2.4748(11)
2.124(4)
2.444(3)
2.4710(11)
Sn(1)-O(1)
Sn(1)-Cl(1)
Sn(1)-Cl(6)
Sn(2)-O(2)
Sn(2)-Cl(2)
Sn(2)-Cl(5)
2.116(2)
Ta ble 4. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for th e Ca tion of C
2.4215(12)
2.3888(11)
2.115(2)
2.4209(12)
2.3888(11)
Sn(1)-C(19)
Sn(1)-O(1)
Sn(1)-O(3)
Sn(1)-Cl(1)
2.096(4)
2.232(3)
3.150(4)
2.4233(8)
Sn(1)-C(23)
Sn(1)-O(2)
Sn(1)-O(4)
2.105(4)
2.155(3)
3.035(3)
O(1)-Sn(1)-C(29) 100.23(15) C(29)-Sn(1)-Cl(6) 104.01(14)
C(19)-Sn(1)-C(23) 144.2(2)
C(19)-Sn(1)-O(1)
C(19)-Sn(1)-O(3)
91.1(2)
74.3(2)
O(1)-Sn(1)-Cl(1)
Cl(6)-Sn(1)-Cl(1)
86.18(7) C(29)-Sn(1)-Cl(1) 104.83(16)
91.12(4) O(1)-Sn(1)-O(3)
C(19)-Sn(1)-O(2)
C(19)-Sn(1)-O(4)
C(23)-Sn(1)-O(1)
C(23)-Sn(1)-O(3)
96.5(2)
71.22(9)
84.34(7)
83.89(7)
89.78(4)
76.74(19) C(19)-Sn(1)-Cl(1) 107.09(18)
C(29)-Sn(1)-O(3) 170.70(15) Cl(6)-Sn(1)-O(3)
94.0(2)
C(23)-Sn(1)-O(2)
92.2(2)
Cl(1)-Sn(1)-O(3)
C(29)-Sn(1)-Cl(4) 96.39(16) Cl(6)-Sn(1)-Cl(4)
O(3)-Sn(1)-Cl(4)
O(2)-Sn(2)-Cl(5) 155.31(7) O(2)-Sn(2)-Cl(2)
O(2)-Sn(2)-O(4) 70.94(9) O(2)-Sn(2)-Cl(3)
78.74(7) O(1)-Sn(1)-Cl(4)
79.23(19) C(23)-Sn(1)-O(4)
C(23)-Sn(1)-Cl(1) 108.68(13) O(1)-Sn(1)-O(3)
78.01(16)
56.45(9)
59.50(10)
78.40(7)
79.33(7) O(2)-Sn(2)-C(33) 100.80(15)
O(4)-Sn(1)-O(3)
O(2)-Sn(1)-Cl(1)
86.53(9) O(2)-Sn(1)-O(4)
79.16(8) O(1)-Sn(1)-Cl(1)
86.19(7)
83.86(7)
C(33)-Sn(2)-Cl(5) 103.62(14) C(33)-Sn(2)-Cl(3) 96.62(16)
C(33)-Sn(2)-Cl(2) 104.62(16) Cl(2)-Sn(2)-O(4)
78.70(7)
79.40(7)
89.80(4)
methoxy oxygens bonds to tin are very weak (contrast-
ing with the much stronger methoxy-tin interactions in
D and E); essentially they are van der Waals interac-
tions. When the latter are considered, the coordination
geometry about tin in each case is most aptly described
as distorted pentagonal bipyramidal with axial alkyl
groups. Within the equatorial plane the largest angle
subtended at tin is by the methoxy oxygens, and not
surprisingly, as a result of this and the weakness of the
methoxy oxygen-tin interactions, the butyl groups fall
away from the true axial positions toward the methoxy
oxygens. In the case of the centrosymmetric ditin cation
of C, the tin and chlorine atoms are essentially collinear
and chlorine-chlorine separation within the ring is
3.99 Å.
Cl(5)-Sn(2)-Cl(2)
Cl(5)-Sn(2)-O(4)
91.07(4) O(4)-Sn(2)-Cl(3)
84.46(7) Cl(5)-Sn(2)-Cl(3)
Both B and C contain centrosymmetric dibutyltetra-
thiocyanato tin(IV) anions. The geometries of the anions
do not differ in any significant manner, but in the case
of B, but not C, they are arranged in linear arrays in
the lattice as in Figure 2b such that there are very short
S-S contacts of 3.4 Å. S-S interactions are found in
many structures,23 but they are particularly noteworthy
(23) See for example: Turner, S. S.; Day, P.; Gelbrich, T.; Hurst-
house, M. B. J . Solid State Chem. 2001, 159, 385. Or: Kepert, C. J .;
Kurmoo, M.; Truter, M. R.; Day, P. J . Chem. Soc., Dalton Trans. 1997,
607.

992 Organometallics, Vol. 23, No. 5, 2004
Cunningham et al.
Ta ble 7. P h en olic C-O a n d Im in e C-N Bon d
Len gth s (Å) for H23-MeOsa len , H23-MeOsa lbip h en ,
a n d Th eir Ad d u cts
uncomplexed end of ligand complexed end of ligand
complex
C-O
C-N
C-O
C-N
G
A
B
1.349(2)
1.351(7)
1.341(5)
1.266(3)
1.267(8)
1.260(6)
1.296(7)
1.311(5)
1.307(5)
1.302(4)
1.312(4)
1.286(6)
1.285(8)
1.287(6)
1.290(6)
1.290(5)
1.289(5)
1.300(7)
C
La
Hb
1.352(4)
1.352(4)
1.355(4)
1.357(4)
1.280(4)
1.281(4)
1.284(4)
1.272(4)
D
E
1.304(4)
1.322(4)
1.310(4)
1.365(8)
1.295(5)
1.301(4)
1.294(4)
F igu r e 6. Structure of G. (a) Asymmetric unit (30%
ellipsoids). The phenolic hydrogen is positioned as found.
(b) Aromatic π-stacking of molecules. Opposing phenyl ring
planes are parallel with a centroid-centroid separation of
3.73 Å.
F
a
b
L ) [La(H2salen)(NO3)3(MeOH)2]n (see ref 23). The first two
and last two rows of data are for molecules 1 and 2, respectively
(see Figure 7).
bond distances under consideration are very similar to
those of the free ligand (G). At the complexed end of
the ligands the C-O bond lengths are considerably
shorter (despite the fact that the oxygen forms a bond
to tin) and the CdN bond distances considerably longer
than the corresponding uncomplexed ligand bond lengths.
It is now clear from the data in Table 7 that in the case
of La(H2salen)(NO3)3(MeOH)2]n not only is the phenolic
C-O bond length shortened as a result of adduct
formation (as previously suggested) but the imine Cd
N bond length is lengthened as observed in the present
case. In the case of C, only one of the phenolic hydrogens
was located with certainty from the difference map.
Significantly, it is bonded to the imine nitrogen, and in
general C-O and CdN bond lengths point clearly to the
presence of zwitterionic forms of the ligands.
in the present case where they have the effect of
shortening the separation between the doubly charged
anions.
The ability of salicylaldimine ligands to exist in
zwitterionic forms in their adducts with lanthanide
metals has already been demonstrated both by NMR
spectroscopy and crystallographically.24-26 In the case
of Dy(LH)3(NO3)3 (LH ) 4-methoxy-N-n-butyl-2-hy-
droxybenzaldimine) the phenolic hydrogen was located
bonded to the imine nitrogen and hydrogen-bonded to
the phenolic oxygen; this is probably the case also for
the Nd(III) and Tb(III) analogues.25 In the case of La(H2-
salen)(NO3)3(MeOH)2]n the crystallographic data did not
reveal the position of the phenolic hydrogen, but the
transfer of this hydrogen to the imine nitrogen was
suggested on the basis of the shortened C-O bond
length compared to that of the C-O bond length in a
related free ligand.26
The present crystallographic data provide the most
complete description of zwitterion formation since crys-
tallographic data are included for the free ligands as
well as those for their adducts. Furthermore, in practi-
cally all cases the phenolic hydrogen position was clearly
identified from the difference maps.
Crystallographic data for A, B, and G (H23-MeOsalen)
revealed the positions of all phenolic hydrogen atoms.
In the case of G, these hydrogens, as expected, are
bonded to the phenolic oxygens. Both A and B have
dangling salicylaldimine ligands, and at the free end of
these ligands the phenolic hydrogen atoms were also
located bonded to the phenolic oxygens. However, at the
complexed end of the ligands the phenolic hydrogens
were located bonded to the imine nitrogen atoms. The
effect of zwitterion formation is clearly evident from the
phenolic C-O and imine CdN bond lengths (see Table
7). At the uncomplexed end of the dangling ligands the
Acetonitrile solutions containing SnBun2Cl2 and H23-
MeOsalbiphen yielded crystals of two triclinic poly-
morphs of H23-MeOsalbiphen. One polymorph, H, con-
tained two slightly different molecules per asymmetric
unit, whereas the other contained only one molecule per
asymmetric unit. The only significant difference be-
tween the molecules existing in these polymorphs is
seen in the angle between phenyl planes of the biphenyl
bridge. In the case of H, the angles are 62.6° and 63.3°
(these compare with angles of 60.3° and 57.4° in D and
E, respectively, the latter smaller angle probably being
a consequence of the aromatic interactions indicated in
Figure 5), whereas for the other polymorph the angle
is 71.6°. It should be noted that neither of the structures
feature the strong aromatic interactions that dictate the
lattice structure of H23-MeOsalen (see Figure 6).
Corresponding bond lengths were virtually identical
for the molecules of the two crystal modifications of H23-
MeOsalbiphen. The data in Table 7 are for the structure
with two molecules per asymmetric unit (see Figure 7).
In general, while there does not appear to be a signifi-
cant difference between the phenolic C-O bond lengths
of H23-MeOsalen and H23-MeOsalbiphen, the CdN
bond lengths of the latter are longer than those of the
former, an observation that can clearly be related to the
delocalization of the CdN bonds next to the phenyl
groups. On formation of the adducts D and E, the C-O
bond lengths decrease quite dramatically, whereas the
(24) Costes, J .-P.; Laussac, J .-P.; Nicode`me, F. J . Chem. Soc., Dalton
Trans. 2002, 2731.
(25) Binnemans, K.; Galyametdinov, Y. G.; Van Deun, R.; Bruce,
D. W.; Collinson, S. R.; Polishchuk, A. P.; Bikchantaev, I.; Haase,
W.; Prosvirin, A. V.; Tinchurina, L.; Litinov, I.; Gubajdullin, A.;
Rakhmatullin, A.; Uytterhoeven, K.; Van Meervelt, L. J . Am. Chem.
Soc. 2000, 122, 4335.
(26) Xie, W.; Heeg, M. J .; Wang, P. G. Inorg. Chem. 1999, 38, 2541.

Adduct Formation with Organotin(IV) Lewis Acids
Organometallics, Vol. 23, No. 5, 2004 993
F igu r e 7. ORTEX20 view of the asymmetric unit of H (30% ellipsoids).
CdN bond lengths increase, and this, once again, is
indicative of zwitterion formation (in the cases of D and
E all of the phenolic hydrogen atoms were located
bonded to the imine nitrogen atoms).
It would appear that on adduct formation, salicyl-
aldimine ligands, in general, assume zwitterionic forms.
The catalytic role of tin(IV) Lewis acids and FeCl3 (see
ref 27) in promoting ligand hydrolysis can clearly be
related to the protonation of the imine nitrogen, thus
facilitating electrophilic attack of the imine carbon by
water as the initial hydrolysis step.
In an attempt to observe the extent to which phenolic
hydrogen transfer to the imine nitrogen would occur in
the presence of a weak tin Lewis acid, trimethyltin
chloride and H23-MeOsalen were added in equimolar
quantities to warm acetonitrile. However, as the solu-
tion cooled, the only crystals that grew from solution
were those of the starting materials.
F igu r e 8. Section of a chain in the crystal structure of F
(30% ellipsoids). Phenyl groups within each chain are
coplanar. Each phenyl group is flanked by two phenyl
groups from neighboring chains giving rise to centroid-
centroid separations of 3.64 Å.
Ta ble 8. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for F
In light of zwitterion formation by the salicylaldimine
ligands, attention is drawn to the behavior of salicyl-
aldehyde as a ligand, the latter differing from salicyl-
aldimines in having a carbonyl group in place of the
imine group. Preliminary details of the crystal struc-
ture of the adduct SnMe2Cl2‚salicylaldehyde based on
Weissenberg data have been reported.28 The structure
was redetermined in the course of the present study
using image plate data, and this yielded much more
accurate structural parameters. Furthermore, the phe-
nolic hydrogen was located in the difference map.
The most significant feature of the structure of this
adduct (F ) (see Figure 8 for a view of the structure and
Table 8 for selected bonding parameters) is the fact that
it is the carbonyl oxygen rather than the phenolic
oxygen that forms the intramolecular donor bond to tin,
and this is a very weak bond [Sn-O ) 2.702(4) Å]. The
formation of a weak donor bond through the carbonyl
group rather than a strong donor bond through the
phenolic oxygen, as occurs in all of the salicylaldimine
Sn(1)-C(1)
Sn(1)-Cl(1)
Sn(1)-O(2)
2.097(7)
2.4028(16)
2.702(4)
Sn(1)-C(2)
Sn(1)-Cl(2)
2.110(6)
2.3522(16)
C(1)-Sn(1)-C(2) 132.0(3)
C(1)-Sn(1)-Cl(1) 101.30(19)
81.2(2)
C(1)-Sn(1)-Cl(2) 110.65(19) C(1)-Sn(1)-O(2)
C(2)-Sn(1)-Cl(1) 101.22(18) C(2)-Sn(1)-Cl(2) 108.91(19)
C(2)-Sn(1)-O(2)
Cl(2)-Sn(1)-O(2)
79.70(19) Cl(2)-Sn(1)-Cl(1)
80.34(9) Cl(1)-Sn(1)-O(2) 175.29(10)
95.02(6)
adduct structures, is a result of the fact that zwitterion
formation does not occur; the phenolic hydrogen was
located bonded to the phenolic oxygen. The inability to
form the zwitterion also accounts for the fact that,
whereas the salicylaldimine ligands exist in dynamic
equilibrium with SnBun2Cl2 in solution, there is es-
sentially no such interaction between either salicylal-
dehyde or 3-methoxysalicylaldehyde and SnBun2Cl2.
The phenolic C-O bond length [1.365(8) Å] is longer
than that of H23-MeOsalen [1.349(2) Å] (presumably
this latter bond length is very similar to that of free
salicylaldehyde), this being a consequence of the fact
that the phenolic oxygen forms a weak intermolecular
donor bond to a neighboring tin [Sn-O ) 3.383(5) Å],
thus generating the chain structure of Figure 8. Within
the chain, the phenyl groups are perfectly coplanar and
(27) Marini, P. J .; Murray, K. S.; West, B. O. J . Chem. Soc., Dalton
Trans. 1983, 143.
(28) Cunningham, D.; Douek, I.; Frazer, M. J .; McPartlin, M.;
Mathews, J . D. J . Organomet. Chem. 1975, 90, C23.

994 Organometallics, Vol. 23, No. 5, 2004
Cunningham et al.
Su p p or tin g In for m a tion Ava ila ble: Tables giving de-
tails of crystal data, data collection and structure refinement,
atomic coordinates, isotropic and anisotropic thermal param-
eters, and all bond lengths and angles. This material is
available free of charge via the Internet at http://pubs.acs.org.
each is flanked on each side by phenyl groups of
neighboring chains. In this fashion each chain is zipped
to four neighboring chains via significant aromatic
π-interactions.
Ack n ow led gm en t. One of us (C.K.) is grateful to
Enterprise Ireland for financial support.
OM030540F