Novel tin complexes containing an oximato ligand: Synthesis, characterization, and computational investigation

Article abstract of DOI:10.1002/hlca.201200259

Organotin complexes 1-6 of the general formula [SnR₂L] and [(SnR₃)₂L] (L=phenanthrenequinone dioximato - a bidentate ligand, R=Me, Bu, and Ph) were synthesized by the reaction of the sodium salt of the ligand H₂L (prepared in situ with MeONa) and SnR₂Cl₂/SnR₃Cl in 1: 1 and 1: 2 molar ratios. The physical and spectral properties of the newly synthesized complexes 1-6 are described. DFT and HF Calculations were performed to confirm the proposed structures. Copyright

Full text of DOI:10.1002/hlca.201200259

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Helvetica Chimica Acta – Vol. 96 (2013)
Novel Tin Complexes Containing an Oximato Ligand: Synthesis,
Characterization, and Computational Investigation
by Raji Thomasa), Joseph P. Nelsona), Ramchand T. Pardasanib), Pushpa Pardasani*a),
and Tulsi Mukherjeec)
a) Department of Chemistry, University of Rajasthan, Jaipur-302055, India
(e-mail: pushpa.pardasani@gmail.com)
b) Department of Chemistry, Central University of Rajasthan, Bandarsindri, Ajmer-305802, India
c) Chemistry Division, BARC, Mumbai-400085, India
Organotin complexes 1 – 6 of the general formula [SnR2L] and [(SnR3)2L] (L ¼ phenanthrenequi-
none dioximato – a bidentate ligand, R ¼ Me, Bu, and Ph) were synthesized by the reaction of the sodium
salt of the ligand H2L (prepared in situ with MeONa) and SnR2Cl2/SnR3Cl in 1:1 and 1:2 molar ratios.
The physical and spectral properties of the newly synthesized complexes 1 – 6 are described. DFTand HF
Calculations were performed to confirm the proposed structures.
Introduction. – Since Ziese synthesized in 1827 the first organometallic compound
K[PtCl3(CH2¼CH2)] [1], the organometallic chemistry has grown enormously although
most of its applications have only been developed in recent decades. Coordination
chemistry of oxime precursors is a fascinating area which has attracted the attention of
inorganic chemists due to its variety of versatile electronic distribution [2]. The
chemistry of (vicinal-dioximato)metal complexes has been studied and has been the
subject of several reviews [3]. Oxime ligands and oximato complexes show an
impressively rich variety of reactivity modes which leads to various unusual types of
chemical compounds. Coordination compounds of vicinal dioximes are interesting for
many applications in a variety of high-technology fields, such as analytical reagents, as
models for biological systems, in medicines, catalysis, electro optical sensors, liquid
crystals, and trace metal analysis [4].
Organotin complexes of bidentate oxime ligands have been of great interest due to
their pharmacological relevance. Because of the large size of the Sn-atom and
availability of low lying empty 5d atomic orbitals, a coordination number greater than
four is frequently encountered in organotin structures. Although organotin compounds
have been known since the 1850s, the commercial application of organotin for the use
as PVC stabilizers [5] in the 1940s promoted extensive studies in this area. Organo-
tin(IV) complexes are put to use in various fields [6][7] and exhibit potential biological
application such as insecticidal, fungicidal, and antitumor activities. N-, O-, and S-
Donor ligands have been used to enhance the biological activity of organotin
derivatives [8][9]. Also organotin compounds with N- and O-donor ligands have
widely been tested for their possible use in cancer chemotherapy [10].
Thus, in view of the synthetic and pharmacological significance of organotin
complexes and in continuation of our interest in organotin and organotitanium chelates
ꢀ 2013 Verlag Helvetica Chimica Acta AG, Zꢁrich

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[11][12], we report herein the synthesis and spectrophotometric characterization of
novel methyl-, butyl- and phenyltin complexes of 9,10-phenanthrenequinone dioxime
(¼ phenanthrene-9,10-dione 9,10-dioxime). The structures of alkyl/aryltin complexes
can be either monomeric, dimeric [13], oligo- and polymeric [14], or cyclooligomeric
which are mainly formed through intermolecular Sn O and Sn N bonds. Besides
the synthesis, computational methods were applied to validate the proposed structures
and determine the structural parameters.
Results and Discussion. – The ligand 9,10-phenanthrenequinone dioxime (H2L)
was prepared by the reaction of the vicinal diketone with hydroxylamine hydrochloride
in the presence of sodium acetate (Scheme 1). The dioxime was then converted to its
sodium salt Na2L by refluxing with sodium methoxide in methanol.
Scheme 1. Preparation of Ligand
The reaction of the sodium salt of H2L with dichlorodialkyl- or dichlorodiphenyl-
stannane and chlorotrialkyl- or chlorotriphenylstannane (SnR2Cl2 and SnR3Cl) in 1:1
and 1:2 molar ratios, respectively, produced organotin complexes 1 – 6 of the general
formula [SnR2L] and [(SnR3)2L] (Scheme 2). Their structures (cf. Fig. 1) were
established by spectroscopic means.
Scheme 2. Preparation of Complexes 1 – 6

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Fig. 1. Proposed structures of complexes 1 – 6
In the IR spectrum of the ligand H2L, no characteristic C¼O absorption appeared at
1675 cmꢀ1 indicating the formation of the dioxime. The characteristic ˜n(OH) of the
¼NOH group and n(C¼N) , and ˜n(NO) stretching vibrations were observed at 3140 – 3122,
1600, and 951 cmꢀ1, respectively. The formation of the complexes 1 – 6 was ascertained
by the disappearance of ˜n(OH) band as well as by the appearance of medium-intensity
peaks in the regions 524 – 570 and 485 – 570 cmꢀ1 assignable to ˜n(SnꢀO) and ˜n(SnꢀC)
,
respectively [15] (Table 1). While the ˜n(NO) stretching vibrations of H2L was shifted to
slightly lower frequencies, the ˜n(C¼N) stretching vibrations remained almost unchanged
upon complexation. The low-frequency shift of the (NꢀO) vibration in the IR spectra
of the tin(IV) complexes as compared to that of the ligand is an evidence for the
coordination through O-atoms. There was no characteristic peak for Sn N which is
usually observed in the region 300 – 400 cmꢀ1 [16].
1
The H-, 13C-, and 119Sn-NMR spectra of all the complexes 1 – 6 were recorded in
1
CDCl3 and (D6)DMSO (Table 1). In the H-NMR spectrum ((D6)DMSO) of the
ligand H2L, the exchangeable protons of the OH groups appeared as a s at d(H) 12.24.
On complexation, this signal disappeared indicating deprotonation of the ¼NOH
groups and complexation with the tin metal, along with subsequent formation of SnꢀO
bonds. The resonances of the aromatic protons of the phenanthrene moiety of H2L
appeared at d(H) 8.63 – 7.36 and remained almost unchanged in the complexes. The
butyltin protons of 2 and 5 were observed in the region d(H) 0.06 – 1.92: Awell-defined
t at d(H) 0.933 was attributed to the Me protons of the butyl group, whereas the
resonances of the CH2 protons were observed as m at d(H) 1.131 – 1.747. The Me
protons of the methyltin derivatives 1 and 4 appeared as s at d(H) 0.43 – 0.38.
In the 13C-NMR spectrum of H2L, the C¼NOH group was observed at d(H) 144.64;
other signals in the range d(C) 141.2 – 121.6 were assigned to the aromatic C-atoms. A
downfield shift of the signals of different C-atoms on complexation confirmed the
formation of complexes 1 – 6 with SnꢀO bonds (Table 1). In complexes 2 and 5, the
butyl resonances in the range d(H) 13.51 – 13.63 were assigned to the Me groups and
those at d(C) 28.05 – 32.88 to the CH2 groups [17]. Besides there was only a downfield

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shift Dd(C) of 3 – 4 of the C¼N signal, thus confirming the absence of Sn N
coordination.
The 119Sn-NMR chemical shifts of organotin compounds cover a range of 600 ppm.
Besides, as the electron-releasing power of the alkyl group bonded to Sn in 1, 2, 4, and 5
increased, the Sn-atom became more shielded, thus shifting the d(Sn) towards higher
field (Table 1). Even though Ph groups have a huge electron-withdrawing effect, upon
replacement of the alkyl groups with the Ph group (see 3 and 6), the d(Sn) moved
towards lower frequencies [18]. Another important factor about 119Sn-NMR is that the
value of the 119Sn-NMR chemical shift is proportional to the coordination number of
the central Sn-atom. Thus, the s at d(Sn) 139.72 and 106.41 of 4 and 5, respectively,
were diagnostic for a tetra-coordination of the Sn-atom suggesting the bonding of the
deprotonated O-atom of the oxime groups to the Sn-atom. Complex 6 in (D6)DMSO
gave a signal at d(Sn) ꢀ 254.21, indicating that the Sn-atom was five-coordinated in
solution due to the presence of coordinated solvent. In the 119Sn-NMR spectra of
complexes 2 and 1 in CDCl3, a sharp signal at d(Sn) ꢀ 137.70 and ꢀ 135.50,
respectively, was observed, both these chemical-shift values being in the range of a
penta-coordinated Sn-atom, thus suggesting the formation of dimer complexes. In these
complexes, one of the O-atoms from each monomer unit is involved in an
ꢂintermolecularꢃ bond (Sn O) and becomes tri-coordinate (O1, O2), while the other
remains di-coordinate (O). The d(Sn) of complex 3 at ꢀ 307.41 was also in the range of
penta-coordinated organotin chelates as given by Otera [19]. The more upfield value of
3 as compared to those of 1 and 2 was due to the presence of the Ph groups. Thus, it may
be concluded that in 1:1 complexes, the Sn-atom is penta-coordinated, and in 1:2
complexes, the Sn-atom is tetra-coordinated. However, in both types of complexes,
there is the possibility of penta-coordination in the solid state.
The structures of the complexes were also confirmed by the coupling constants
1J(Sn,C) and 2J(Sn,H), both being directly linked to the CꢀSnꢀC angle (q) as given in
1
the equations J(Sn,C) ¼ 11.4 q(CꢀSnꢀC) ꢀ 875 and q(CꢀSnꢀC) ¼ 0.0161[2J(Sn,H)]2
ꢀ 1.32[2J(Sn,H)] þ 133.4. The 1J(Sn,C) value observed for the dibutyl derivative 2 was
640 Hz, and that for the dimethyl derivative 1 was 590 Hz, these values being in the
range of penta-coordinated Sn-atoms [20][21]; the corresponding 2J(Sn,H) values were
78 and 81 Hz, respectively, consistent with penta-coordinated Sn-atoms [22]. Com-
1
2
pounds 4 and 5 had J values of 396.11 and 377.25 Hz and J values of 59 and 57 Hz,
respectively, indicating the tetra-coordinated nature of their Sn-atom. Applying the
above equations, the CꢀSnꢀC bond angles calculated for the trimethyl and tributyl
derivatives 4 and 5 were 111.5 and 109.8, respectively, while for the dimethyl and
dibutyl derivatives 1 and 2, the values were 128.5 and 132.8, respectively.
Theoretical Calculations. The ground-state geometry of the ligand 9,10-phenan-
threnequinone dioxime was optimized for three types of isomers namely syn, anti, and
anti-amphi. The energy values showed that the anti (E,E) isomer is the most stable.
Frequency calculations gave zero imaginary frequency, that is, all were real. Parallel
calculations on oxime derivatives were carried out to get more structural information.
For the dialkyl and diphenyl dimeric complexes 1 – 3, we first studied the structure
of their monomeric units. To obtain information regarding the electron rich centers, the
molecular electrostatic potential of the monomer units was analyzed. MESP
(molecular electrostatic potential) analysis brings about the effective localization of

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electron-rich regions in a molecular system. The minimum points are often located at
lone-pair regions and p-bonded regions, and they represent centers of negative charge
in the molecule. In the case of the methyl and butyl complexes, the minimum value was
found at the O-atoms and the phenanthrene moiety. In the case of the phenyl complex,
besides these minimum points, an additional minimum was also observed at the phenyl
ligand. The MESP plot for the monomer units of 1 – 3 is given in Fig. 2. In this particular
case, regions of attractive potential are shown in dark grey and those of repulsive
potential in white. The MESP plot led to the conclusion that the lone-pair strength of
the O-atoms was greater than that of the N-atoms. This caused the formation of a
coordinate bond between an O-atom of one monomer unit and the Sn-atom of another
monomer unit resulting in a dimer.
In the atomic-charge distribution, the Sn-atoms bore a high positive charge and the
Fig. 2. Electronic features of the monomer units of 1 – 3. Vmin points (considering only the lone-pair
region) with isosurface value ꢀ 38.22 – 32.33 kcal/mol.
O-atoms a high negative charge. The population analysis also led to the same
conclusion that a dimer was formed. Mulliken and NPA (natural population analysis)
charge distribution at selected atoms of the monomer units of 1 – 3 are given in Table 2.
In performing NBO (natural bond orbitals) analysis of dimers 1 – 3, molecules were
again treated as two monomer subunits bound through donorꢀacceptor interactions.
NPA Charges at the O-atoms, associated with the SnꢀO short and long bonds in dimers,
were ꢀ 0.75 and ꢀ 0.74, ꢀ 0.741 and ꢀ 0.74, and ꢀ 0.742 and ꢀ 0.745 for methyl,
butyl, and phenyl complexes, respectively. This indicated that relatively little charge
was transferred from the O-atoms as compared to the monomer units (Table 2).
Nonvalent interactions in dimers were analyzed in terms of the second-order-

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Table 2. Mulliken and NPA (values in parantheses) Charge Distribution at Selected Atoms of the 1 : 1
Monomer Units of 1 – 3
Atom
Monomer unit of
1 (R ¼ Me)
2 (R ¼ Bu)
3 (R ¼ Ph)
C (C¼N)
0.362421 (0.21179)
0.178233 (0.21181)
0.363009 (0.21143)
0.361826 (0.21023)
0.358787 (0.21036)
0.358793 (0.21036)
C (C¼N)
N
N
O
O
Sn
ꢀ 0.277016 (ꢀ 0.12109)
ꢀ 0.276971 (ꢀ 0.12104)
ꢀ 0.676879 (ꢀ 0.75812)
ꢀ 0.676852 (ꢀ 0.75810)
1.843269 (2.29145)
ꢀ 0.277953 (ꢀ 0.12076)
ꢀ 0.276801 (ꢀ 0.12045)
ꢀ 0.673223 (ꢀ 0.76024)
ꢀ 0.676707 (ꢀ 0.76139)
1.840732 (2.31710)
ꢀ 0.269567 (ꢀ 0.11515)
ꢀ 0.269565 (ꢀ 0.11515)
ꢀ 0.681803 (ꢀ 0.76138)
ꢀ 0.681804 (ꢀ 0.76138)
2.015735 (2.35388)
perturbation theory with the Fock matrix constructed in the NBO basis set. Most
important nonvalent interactions in dimers 1 – 3 are presented in Table 3. The vacant pz
orbitals of the metal atoms, LP*Sn, interacted with the lone pairs (LPs) of covalently
bound O-atoms of the other fragment, leading to LP O ! LP*Sn. It is clear from
Table 3 that LP O1 ! LP*Sn2 and LP O2 ! LP*Sn1 were strong interactions in
comparison to LP N1 ! LP*Sn2 and LP N2 ! LP*Sn1. Thus, each Sn-atom formed an
ꢂintermolecularꢃ coordination bond with the O-atom of the second subunit.
Table 3. Most Important Nonvalent Interactions in Dimers 1 – 3 in the NBO Basis. LP ¼ lone pair.
Compound
Donor
Acceptor
E(2) [kcal/mol]
1 (R ¼ Me)
LP O1
LP N1
LP O2
LP N2
LP O1
LP N1
LP O2
LP N2
LP O1
LP N1
LP O2
LP N2
LP*Sn2
LP*Sn2
LP*Sn1
LP*Sn1
LP*Sn2
LP*Sn2
LP*Sn1
LP*Sn1
LP*Sn2
LP*Sn2
LP*Sn1
LP*Sn1
87.55
2.55
73.79
3.41
70.68
1.58
56.89
2.67
30.03
3.07
21.18
2.19
2 (R ¼ Bu)
3 (R ¼ Ph)
Compared to the structures of monomer units, the MꢀO covalent bonds in dimers
1 – 3 were 0.12 ꢄ longer. The tricoordinated O-atoms from the two monomer units
created a four-membered Sn2O2 ring. The Sn ··· O’ coordination bond was the longest
one in the dimers (Table 4). Due to this coordination, intramonomer SnꢀO bonds had
unequal lengths. In the central Sn2O2 ring, the length of the Sn ··· O’ bonds were less
than the sum of the covalent radii of Sn and O (2.13 ꢄ). Relevant geometrical
parameters of the dimers 1 – 3 are given in Table 4.
Frequency calculations were done with the optimized structures of the trialkyl/
triphenyl complexes to evaluate the thermodynamic stability of the complexes. The
stability constants of the complexes were then derived from the equation DG ¼

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Table 4. Gas-Phase-Optimized Parameters of 1 : 1 Complexes 1 – 3
Compound r(Sn1ꢀO) r(Sn1ꢀO1) r(O1 ··· Sn2) q(O1ꢀSn1ꢀO2) q(OꢀSn1ꢀO1) q(CꢀSnꢀC) q(Sn1ꢀO1ꢀSn2)
1 (R ¼ Me) 1.980
2 (R ¼ Bu) 1.979
3 (R ¼ Ph) 1.972
2.043
2.051
2.034
2.122
2.126
2.130
65.89
65.74
65.68
80.42
80.28
77.84
119.14
115.64
113.17
110.28
111.85
113.01
ꢀRTlnK. Theoretical calculations of the tin complexes 4 – 6 indicated that in all
complexes, the central atom existed in a tetrahedral geometry. The data of optimized
geometries and thermochemistry at 298.15 K of these complexes are given in Table 5.
Table 5. Gas-Phase-Optimized Parameters and Thermal Data of 1 : 2 Complexes 4 – 6 at 298.15 K
Compound r(Sn1ꢀO1) r(SnꢀC) r(Sn2ꢀO2) q(CꢀSnꢀC) DE [kJ/mol] DH [kJ/mol] DG [kJ/mol] Log K
4 (R ¼ Me) 2.134
5 (R ¼ Bu) 2.012
6 (R ¼ Ph) 2.010
2.174
2.164
2.075
2.016
2.012
2.131
112.07
109.69
112.05
ꢀ 468.50
ꢀ 71.09
ꢀ 91.18
ꢀ 464.75
ꢀ 64.88
ꢀ 73.36
ꢀ 465.95
ꢀ 45.75
ꢀ 59.27
81.62
8.01
10.38
Conclusions. – A series of methyl, butyl, and phenyl complexes of the general
formula [SnR2L] and [(SnR3)2L] were prepared from the ligand and the corresponding
chlorostannane in a 1:1 and 1:2 molar ratio, respectively. The proposed structures of
the complexes based on experimental results were also confirmed by computational
methods. The thermodynamic stability of the complexes 4 – 6 were in the order
[(SnMe3)2L] > [(SnPh3)2L] > [(SnBu3)2L]. The NBO analysis clearly revealed the
coordination bond between the O-atom of one monomer fragment and the Sn-atom of
another monomer fragment in the 1:1 complexes leading to the formation of dimers
1 – 3. The Sn-atoms in the 1:1 complexes were penta-coordinated and in the 1:2
complexes tetra-coordinated. The optimized structures of complexes 2 and 5 are given
in Fig. 3, and the remaining ones can be obtained as supporting information1).
The financial support of this work by the Department of Atomic Energy/Board of Research in
Nuclear Sciences (DAE/BRNS) (2009/37/31/BRNS/2099) is hereby gratefully acknowledged.
Experimental Part
General. All the chemicals were purchased from Merck and Aldrich and used without further
purification. All the reactions were carried out under dry conditions. Solvents were dried by standard
methods [23]. M.p.: Perfit apparatus; uncorrected. IR Spectra: Nicolet-Shimadzu spectrometer (range
1
4000 – 200 cmꢀ1); KBr pellets and CCl4 solns. H-, 13C-, and 119Sn-NMR Spectra: Jeol-300AL-FT-NMR
spectrometer; at 300, 75.5, and 111.9 Hz, resp.; in CDCl3 and (D6)DMSO (1H- and 13C) and in C6D6
(
119Sn), with Me4Si as internal standard and Me4Sn as external standard, resp. Elemental analyses:
estimation of the Sn-content as tin oxide, and of the N-content as reported in [24].
Computational Details. The gas-phase calculations of the structural and electronic properties of the
metal complexes and the ligand were performed with the Gaussian 03 suite of programs [25]. Restricted
1
)
Electronic supplementary material is available from the corresponding author P. Pardasani.

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Helvetica Chimica Acta – Vol. 96 (2013)
Fig. 3. Optimized geometries of complexes 2 and 5
density-functional calculations were carried out by means of this package, with the B3LYP hybrid
method that employs the Becke three parameters exchange functional and the LeeꢀYangꢀParr
correlation functional. This functional has been established to be effective for the determination of the
optimal geometries, harmonic frequencies, and electronic properties of complexes. Considering the size
of the dimeric complexes and our calculation tools, HF/3-21G was also used for calculation of the 1:1
complexes.
Phenanthrene-9,10-dione 9,10-Dioxime (H2L). Ligand H2L was prepared by the reaction of
phenanthrene-9,10-dione (0.8328 g, 4 mmol) and hydroxylamine hydrochloride (1.042 g, 15 mmol) in
EtOH (25 ml) with sodium acetate (0.8203 g, 10 mmol) and reflux for 12 h (red ! yellow during
refluxing). Then, the mixture was filtered and the filtrate concentrated to half the volume and kept
overnight at r.t. yielding shining yellowish green crystals which were collected and dried under vacuum:
H2L (83%). M.p. 197 – 2028 ([26]: m.p. 2028).
Phenanthrene-9,10-dione 9,10-Dioxime Sodium Salt (1:2) (Na2L). To the freshly prepared MeOH
soln. (5 ml) of MeONa (0.1728 g, 3 mmol), a soln. of H2L (0.3573 g, 1.5 mmol) in benzene (15 ml) was
added dropwise (yellowish green ! dark brown during the addition). Subsequently, the mixture was
refluxed for 5 h.
Bis{m-{[phenanthrene-9,10-dione 9,10-Di(oximato-kO,kO’:kO’)](2ꢀ)}}tetraphenylditin (3). To the
MeOH/benzene soln. (10 ml) of Na2L (0.2095 g, 0.8 mmol), the benzene soln. of dichlorodiphenyl-
stannane (0.2751 g, 0.8 mmol) was added slowly dropwise at r.t. under N2 (dark brown ! light yellow).
The mixture was then refluxed for 5 h to ensure completion of the reaction. The precipitated NaCl was
filtered off, the filtrate concentrated, and the light yellow residue washed with hexane and dried under
vacuum: 3 (0.3418 g, 42%). Data: Table 6.
Table 6. Physical and Analytical Data of Organotin(IV) Complexes
Compound Physical
appearance
Yield [%] M.p. [8C] Elemental analysis: found (calc.) [%]
C
H
N
Sn
203 (dec.) 51.54 (51.92) 3.80 (3.78) 5.46 (5.82) 30.87 (30.46)
176 57.66 (57.88) 5.70 (5.33) 4.48 (4.81) 25.33 (25.38)
1
2
3
4
brown solid
red solid
yellow solid
greenish yellow 68
solid
60
75
42
280 (dec.) 62.57 (62.51) 3.67 (3.33) 4.13 (4.16) 23.34 (23.76)
195 (dec.) 42.60 (41.52) 4.65 (4.10) 4.97 (4.92) 42.11 (42.18)
5
6
red solid
brown solid
60
50
104
55.91 (55.27) 7.66 (7.18) 3.43 (3.56) 29.08 (29.19)
235 (dec.) 64.14 (63.98) 4.09 (3.54) 2.99 (2.80) 25.36 (25.22)

Helvetica Chimica Acta – Vol. 96 (2013)
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Tetrabutylbis{m-{[phenanthrene-9,10-dione 9,10-Di(oximato-kO,kO’:kO’)](2ꢀ)}}ditin (2). As de-
scribed for 3. Data: Table 6.
Tetramethylbis{m-{[phenanthrene-9,10-dione 9,10-Di(oximato-kO,kO’:kO’)](2ꢀ)}}ditin (1). Di-
chlorodimethylstannane was added to Na2L at r.t. under stirring within 5 h. Workup as described for
3: light brown crystalline 1 (60%). Data: Table 6.
Hexamethyl{m-{[phenanthrene-9,10-dione 9,10-Di(oximato-kO :kO’)](2ꢀ)}}ditin (4), Hexabutyl{m-
{[phenanthrene-9,10-dione 9,10-Di(oximato-kO :kO’)](2ꢀ)}}ditin (5), and {m-{[Phenanthrene-9,10-
dione 9,10-Di(oximato-kO:kO’)](2ꢀ)}}hexaphenylditin (6). As described for 3, with Na2L and the
chloroorganostannane SnR3Cl (R ¼ Me, Bu, and Ph) in a 1:2 molar ratio. Data: Table 6.
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Received May 15, 2012