Hypercoordinated organotin(IV) compounds containing C,O- and C,N- chelating ligands: Synthesis, characterisation, DFT studies and polymerization behaviour

Article abstract of DOI:10.1016/j.jorganchem.2019.120910

A series of 2-methoxymethyl tetraorganotins [2-(MeOCH₂)C₆H₄]SnR₃ (21: R = Ph; 22: R = n-Bu; 23: R = Me), diorganotin chlorides [2-(MeOCH₂)C₆H₄]R₂SnCl (24: R = Ph; 25a, 25b: R = n-Bu), monoorganotin dichlorides [2-(MeOCH₂)C₆H₄]RSnCl₂ (26: R = Ph; 27: R = n-Bu; 28: R = Me) and the tin trichloride [2-(MeOCH₂)C₆H₄]SnCl₃ (29) were successfully prepared from the reaction of the organolithium, [2-(MeOCH₂)C₆H₄]Li, and the appropriate chlorostannane. Similarly, a series of dimethylamino stannanes including the tetraorganotin [2-(Me₂NCH₂)C₆H₄]SnPh₃ (30), the diorganotin halides [2-(Me₂NCH₂)C₆H₄]Ph₂SnX (34: X = Cl; 35: X = Br), dichlorides [2-(Me₂NCH₂)C₆H₄]RSnCl₂ (38: R = Ph; 39: R = n-Bu; 40: R = Me) and the tribromide [2-(Me₂NCH₂)C₆H₄]SnBr₃ (37) were prepared by reaction of the appropriate organochlorostannane and the organolithium [2-(Me₂NCH₂)C₆H₄]Li followed by selective halogenations in the case of 34–37. 2-Methoxymethyl and dimethylamino diorganotin dichlorides (27, 28 and 39, 40) were hydrogenated with LiAlH₄ to produce new 2-methoxymethyl [2-(MeOCH₂)C₆H₄]RSnH₂ (41: R = n-Bu; 42: R = Me) and dimethylamino [2-(Me₂NCH₂)C₆H₄]RSnH₂ (44: R = n-Bu; 45: R = Me) dihydrides. X-ray structure determination of 30 revealed a nearly tetrahedral stannane, while structural analysis of 24, 29 and 40 display distorted trigonal bipyramidal geometry at Sn with Cl trans to the datively coordinated heteroatom. A selection of DFT methods were assessed for accuracy in predicting the solid-state geometries of the hypercoordinate Sn complexes. Catalytic dehydrocoupling of C,O- (41) and C,N- (44) diorganotin dihydrides was explored using Wilkinson's catalyst at RT leading to the recovery of modest molecular weight polymers (52: M_w = 3.03 × 10⁴ Da, PDI = 1.4, 53: M_w = 3.1 × 10⁴ Da, PDI = 1.86). The new rigid polymers were isolated in moderate (52: 65%) and low yields (53: 18%) and were found to be amorphous by DSC.

Full text of DOI:10.1016/j.jorganchem.2019.120910

Journal of Organometallic Chemistry 900 (2019) 120910
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Hypercoordinated organotin(IV) compounds containing C,O- and C,N-
chelating ligands: Synthesis, characterisation, DFT studies and
polymerization behaviour
Aman Khan b, Jeffrey Pau b, Julie Loungxay b, Timbila Magobenny b, R. Stephen Wylie b,
,
*
Alan J. Lough a, Daniel Foucher b
a Department of Chemistry, X-Ray Laboratory, University of Toronto, Toronto, ON, M5H 3H6, Canada
b Department of Chemistry and Biology, Ryerson University, 350 Victoria Street, Toronto, Ontario, M5B-2K3, Canada
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of 2-methoxymethyl tetraorganotins [2-(MeOCH2)C6H4]SnR3 (21: R ¼ Ph; 22: R ¼ n-Bu; 23:
R ¼ Me), diorganotin chlorides [2-(MeOCH2)C6H4]R2SnCl (24: R ¼ Ph; 25a, 25b: R ¼ n-Bu), mono-
organotin dichlorides [2-(MeOCH2)C6H4]RSnCl2 (26: R ¼ Ph; 27: R ¼ n-Bu; 28: R ¼ Me) and the tin tri-
chloride [2-(MeOCH2)C6H4]SnCl3 (29) were successfully prepared from the reaction of the organolithium,
[2-(MeOCH2)C6H4]Li, and the appropriate chlorostannane. Similarly, a series of dimethylamino stannanes
including the tetraorganotin [2-(Me2NCH2)C6H4]SnPh3 (30), the diorganotin halides [2-(Me2NCH2)C6H4]
Ph2SnX (34: X ¼ Cl; 35: X ¼ Br), dichlorides [2-(Me2NCH2)C6H4]RSnCl2 (38: R ¼ Ph; 39: R ¼ n-Bu; 40:
R ¼ Me) and the tribromide [2-(Me2NCH2)C6H4]SnBr3 (37) were prepared by reaction of the appropriate
organochlorostannane and the organolithium [2-(Me2NCH2)C6H4]Li followed by selective halogenations
in the case of 34e37. 2-Methoxymethyl and dimethylamino diorganotin dichlorides (27, 28 and 39, 40)
were hydrogenated with LiAlH4 to produce new 2-methoxymethyl [2-(MeOCH2)C6H4]RSnH2 (41: R ¼ n-
Bu; 42: R ¼ Me) and dimethylamino [2-(Me2NCH2)C6H4]RSnH2 (44: R ¼ n-Bu; 45: R ¼ Me) dihydrides. X-
ray structure determination of 30 revealed a nearly tetrahedral stannane, while structural analysis of 24,
29 and 40 display distorted trigonal bipyramidal geometry at Sn with Cl trans to the datively coordinated
heteroatom. A selection of DFT methods were assessed for accuracy in predicting the solid-state ge-
ometries of the hypercoordinate Sn complexes. Catalytic dehydrocoupling of C,O- (41) and C,N- (44)
diorganotin dihydrides was explored using Wilkinson's catalyst at RT leading to the recovery of modest
molecular weight polymers (52: Mw ¼ 3.03 ꢀ 104 Da, PDI ¼ 1.4, 53: Mw ¼ 3.1 ꢀ 104 Da, PDI ¼ 1.86). The
new rigid polymers were isolated in moderate (52: 65%) and low yields (53: 18%) and were found to be
amorphous by DSC.
Received 31 May 2019
Received in revised form
15 August 2019
Accepted 20 August 2019
Available online 29 August 2019
Keywords:
Hypercoordinate
Stannanes
Polystannanes
DFT
Dehydropolymerization
© 2019 Elsevier B.V. All rights reserved.
1. Introduction
intermolecular coordination interactions. In recent years, research
interest in hypercoordinate derivatives of silicon [1], germanium
Organotin (IV) compounds possessing
a
flexible or rigid
[3e6] and tin [7e9] with non-classical chemical bonds has
increased largely due to their unusual structural properties and in
the case of tin, their potential suitability as polymerizable mono-
mers. The resulting hypercoordinated metallopolymers are envi-
sioned to be stable towards light and moisture [10].
Hypervalent halogenated organotin derivatives that possess the
C,N-chelating ligand, [2-(Me2NCH2)C6H4]-, were first reported by
van Koten [11] and characterized by NMR (1H, 13C, 15N, 119Sn)
spectroscopy and single-crystal X-ray diffraction studies. The
extent of the donor-acceptor interaction in hypercoordinated
halogenated tin species of this type is readily assessed by the
chelating organic ligand with O or N donor atoms capable of co-
ordination interactions have been extensively investigated both in
solution and in the solid state [1,2]. A common feature of these
hypercoordinated species is the expansion in the coordination
sphere of tin centers facilitated by additional intra- or
* Corresponding author.
E-mail addresses: alough@chem.utoronto.ca (A.J. Lough), daniel.foucher@
ryerson.ca (D. Foucher).
https://doi.org/10.1016/j.jorganchem.2019.120910
0022-328X/© 2019 Elsevier B.V. All rights reserved.

2
A. Khan et al. / Journal of Organometallic Chemistry 900 (2019) 120910
relative proximity of the interacting centers [12]. Consequently, as
the SneN distance decreases in a hypervalent halogenated orga-
notin derivative, the Sn-X (X ¼ F, Cl, Br, I) bond typically elongates
[13].
Along with decreasing SneN distances in these examples there
is also a significant upfield 119Sn NMR chemical shift (>20e30 ppm)
with respect to four coordinate tin analogues [14]. Surprisingly,
there are relatively few reported synthetic and crystallographic
examples for triorganotin monohydrides or diorganotin dihydrides
containing a hypercoordinated ligand (Fig. 1) [15,16]. Organotin
hydrides containing chelating 2-(N,N-dimethylaminomethyl)
phenyl (1, 2, 3) and 2-(4-isopropyl-2-oxazolinyl)-5-phenyl (4e7)
virtually unexplored [24,25]. In 2003, Molloy et al. [25] reported the
Wurtz polymerization behaviour of RBr2Sn(CH2)xOC6H4C6H5
(Fig. 2, 8: R ¼ Ph, x ¼ 3,11: R ¼ Ph, x ¼ 5,12: R ¼ n-Bu, x ¼ 5) bearing
either a flexible propyl- or pentyl-oxy ligand. Moderately high
molecular weight polystannanes [RR’Sn]n (Mw ¼ 2.5e3.0 ꢀ 105 Da;
PDI ¼ 1.30e1.96) were reported for pentyl-oxy derivatives (19, 20),
but no polymer recovered in attempts to polymerize the shorter
propyl-oxy tin dibromide (8). An X-ray structure determination of
dibromo 8 [25] and similar dichloro propyloxy derivatives (9, 10)
[26] indicate a substantial Sn$$$O hypercoordination present,
which may restrict access to one or both of the halogen atoms
during the presumed heterogeneous Na-mediated Wurtz coupling
experiments.
Foucher et al. [26] were able to successfully prepare high mo-
lecular weight (Mw ¼ 1.1 ꢀ 105 Da; PDI ¼ 1.40) asymmetrical poly-
stannanes (15, 16) via the dehydrocoupling of the closely related
propyl-oxy containing dihydrides (13, 14). In this case, the con-
version of hypercoordinated dichlorides to dihydride monomers,
which likely have substantially more limited hypercoordination
with the tin centers due the electronegative nature of the hydrido
ligands, were found to polymerize in the presence of Wilkinson's
catalyst at RT. Interestingly, the 119Sn resonances for these polymers
was found to be similar to other known tin materials (zꢁ195 ppm)
[27], suggestive of a 4-coordinate, rather than 5-coordinate envi-
ronment at Sn centers along the polymer backbone. While these
polymers appear to be indefinitely stable to ambient light, they
degrade within 2 d when exposed to moist air.
ꢀꢁ ꢁ
ꢂ
ligands were reported by the groups of Ruzicka and Stalinski
respectively and are thus rare examples [17,18].
The intramolecular SneO interactions in organotin (IV) com-
pounds with chelating ligands have focused primarily on the use of
pincer type ligands in the stabilization of metal coordination cen-
ters. Several organotin (IV) compounds containing the (o-MeEC6H4)
CH2SnPh3-nCln (where E ¼ O, S) architecture have been reported
[12,19e21]. Structural studies of these compounds reveal, in most
cases, hypercoordinated trigonal bipyramidal geometry (TBP) with
evidence of a significant Sn-E interaction. The number of reports of
hypercoordinate tin benzyl ether compounds LSnR3-nCln {L ¼ [2-
(MeOCH2)]C6H4-} is in general, more limited [22,23].
Unlike four coordinate dichloro- and dihydrostannanes, the
polymerization behaviour of hypercoordinated C,O- and C,N-
dichlorido- or dihydridostannanes by Wurtz coupling or catalytic
dehydrocoupling using early or late transition metal complexes is
The first examples of moisture and light stable (>1 yr), partially
hypercoordinated asymmetrical (alkoxy)arylpolystannanes (Fig. 3)
bearing either a light absorbing diazo moiety [28] (17) or a hydroxyl
substituent [29] (18) were recently identified. Interestingly, poly-
mer 17 displays two 119Sn resonances in C6D6 for polymer prepared
by an uncatalyzed route at
d
¼ ꢁ195 and ꢁ236 ppm, but only one
resonance at ꢁ235 ppm when the polymer was prepared by a
catalyzed process. In C6D6, polymer 18 displays two distinct 119Sn
resonances; one substantially upfield (ꢁ170 to ꢁ180 ppm) and
more reminiscent of other 4-coordinate asymmetric polystannanes
[26], and the other 50e70 ppm downfield (ꢁ110 to ꢁ120 ppm)
suggestive of hypercoordinate tin interactions along the backbone.
Polymer 18 is film forming and appears to be indefinitely stable to
Fig. 1. Organotin hydrides containing a C,N-chelating ligand.
Fig. 2. Flexible tethered propyl- and pentyloxystannanes and polystannanes.

A. Khan et al. / Journal of Organometallic Chemistry 900 (2019) 120910
3
2. Results and discussion
2.1. C,O-stannanes
119Sn NMR chemical shifts of C,O-stannanes 21e24 and 26e29
and comparison to their non-chelating analogues are listed in
Table 1. The 2-methoxymethyl stannanes 21e23 (Scheme 1) were
prepared from the reaction of [2-(MeOCH2)C6H4]Li and the
appropriate trialkyl- or triphenyl chlorostannane. Compounds 21
and 22 were obtained in good yields (73% and 65%) and recovered
as a yellow-brown coloured oil and crystalline white solid (m.p.
95 ꢂC), respectively. Gilman et al. [22] previously synthesized 21 in
a much lower yield (35%) from the reaction of [2-(MeOCH2)C6H4]
MgBr with Ph3SnCl and reported a similar melting point. Com-
pound 23 (Scheme 1) was isolated as clear oil in a 70% yield,
somewhat lower than previously reported for this species (84%)
[30]. The 119Sn resonance of 23 was ꢁ32.5 ppm (CDCl3), slightly
downfield from the reported value (ꢁ38.2 ppm, THF-d8, -78 ꢂC)
[30].
Fig. 3. Recent light and moisture polystannanes.
air and moisture, but will degrade if exposed to chlorinated
solvents.
The monochloride 24 was recovered from the reaction shown in
Scheme 1 as a white coloured solid in 38% yield after precipitation
of the crude product from cold hexanes (ꢁ20 ꢂC) and displayed
a119Sn NMR (CDCl3) resonance of ꢁ127.0 ppm. Access to 24 was also
achieved in a higher yield (81%) by reaction of 21 in C6H6 with an
equimolar equivalent of an ethereal 1.0 M solution of HCl. An
attempt to further convert the monochloride 24 to the dichloride
26 by the reaction of an additional equivalent of the HCl solution
(Scheme 1) resulted in only recovery of the starting material.
The current study is focused on the syntheses and character-
ization of new and known rigid C,O- and C,N- tetraorganotins, tin
chlorides, dichlorides, hydrides and dihydrides (Fig. 4). A progres-
sive DFT modelling study of hypercoordinate stannanes was also
undertaken to compare calculated and experimentally determined
geometries. Finally, a preliminary assessment of the polymerization
behaviour of hypercoordinated C,O- and C,N- tin dichlorides via Na
mediated Wurtz coupling and C,O- and C,N- tin dihydrides by
metal-catalyzed dehydrocoupling is also described.
Fig. 4. Organotin compounds of this study.

4
A. Khan et al. / Journal of Organometallic Chemistry 900 (2019) 120910
Table 1
119Sn NMR (C6D6) chemical shifts of C,O-stannanes.
Compound
119Sn (
d) ppm
Non-chelating analogue
119Sn (
d
) ppm
D d) ppm
119Sn (
21
22
23
24
25 a, b
26
27
28
29
ꢁ133.0
ꢁ40.3
Ph4Sn
ꢁ128.8 [34]a
þ41.7 [35]
ꢁ30.3 [35]
ꢁ44.7 [36]b
ꢁ82.6 [37]
ꢁ33.0 [9]
4.2
82.0
2.2
PhSn(n-Bu)3
PhSnMe3
Ph3SnCl
Ph(n-Bu)2Cl
Ph2SnCl2
Ph(n-Bu)SnCl2
PhMeSnCl2
PhSnCl3
ꢁ32.5
ꢁ127.2
82.2
ꢁ91, ꢁ127
ꢁ28.2
8.7, 65.3
ꢁ3.8
83.1
99.1
119
ꢁ60.9
þ22.2 [38]
ꢁ54.0
55.1 [39]
ꢁ65 [40]
ꢁ184
Note all samples run in CDCl3 unless otherwise noted.
a
Neat.
CCl4.
b
Scheme 1. Syntheses of 21e29.
Crystals of 24 suitable for an X-ray analysis were successfully
grown from DCM:hexanes (1:1) at ꢁ20 ꢂC. Compound 24 (Fig. 5a)
possesses a Sn(1)-O(1) interatomic distance of 2.472 (2) Å which is
substantially longer than for other structures with covalent SneO
bonds (z2.1 Å) [31], but well within van der Waals radii for Sn
and O (3.79 Å). A slightly elongated trans Sn(1)-Cl(1) bond of 2.4345
(8) Å was also present [32], with additional distortion observed
with the O(1)-Sn(1)-Cl(2) bond angle of 169.90 (5)ꢂ.
Reactions of dialkylated dichlorostannanes with [2-(MeOCH2)
C6H4]Li did not yield clean products. The reaction with Me2SnCl2
showed five unassigned resonances by 119Sn NMR spectroscopy,
along with one signal of higher intensity at ꢁ71.0 ppm. No as-
signments of this mixture were made and no further attempts to
purify were undertaken. Similarly, the reaction of [2-(MeOCH2)
C6H4]Li with (n-Bu)2SnCl2 showed six unassigned 119Sn NMR sig-
nals and after extraction with hexane did not yield pure materials.
The oily reaction mixture was stored in a glove box and after 30 d,
an off-white coloured solid material separated from the oil. The
solid was washed with hexane and an accurate mass determination
(HRMS) consistent for a structure with formulae of 25a or 25b was
detected (Fig. 6). The 119Sn NMR (CDCl3) spectrum of the di-
astereomers show resonances at ꢁ91.0 and ꢁ138.0 ppm of unequal
intensities (60/40), likely due to the fluxional exchange of the axial
and equatorial positions of the Cl atom attached to tin. Similar
fluxional behaviour has been observed for other halostannanes
with C,N chelating ligands [33]. We hypothesis that these are the
two conformers present; however NMR assignments to structures
is still required.
The dichlorides 26e28 (Scheme 1) were isolated as brown col-
oured oils by addition of [2-(MeOCH2)C6H4]Li to a pre-cooled
(ꢁ78 ꢂC) hexane/Et2O (1:1) solution of the appropriate organotin
trihalide. Compounds 27 and 28 were purified after extraction of
their crude mixtures with toluene and hot hexane, respectively. The
119Sn NMR (CDCl3) analysis showed a single resonance for both 27

A. Khan et al. / Journal of Organometallic Chemistry 900 (2019) 120910
5
Fig. 5. a (left). Molecular structure of 24. Selected interatomic distances [Å] and angles [º]: Sn(1)-C(1) 2.130(3), Sn(1)-C(9) 2.133(3), Sn(1)-C(15) 2.130(3), Sn(1)-Cl(1) 2.4345(8),
Sn(1)-O(1) 2.472(2), C(1)-Sn(1)-Cl(1) 97.53(10), C(1)-Sn(1)-Ol(1) 72.65(11), C(1)-Sn(1)-C(9) 122.35(12), C(1)-Sn(1)-C(15) 113.80(12), Cl(1)-Sn(1)-O(1) 169.90(5). Fig. 5b (right).
Molecular structure of 29. Selected interatomic distances [Å] and angles [º]: Sn(1)-C(1) 2.104(5), Sn(1)-Cl(1a) 2.3261(10), Sn(1)-Cl(1) 2.3262(10), Sn(1)-O(1) 2.341(4), Sn(1)-Cl(2)
2.3702(15), C(1)-Sn(1)-O(1) 74.29(18), C(1)-Sn(1)-Cl(1a) 123.73(6), C(1)-Sn(1)-Cl(1) 123.73(6), C(1)-Sn(1)-Cl(2) 102.98(16), O(1)-Sn(1)-Cl(2) 177.27(11).
dichloride or direct bromination to the dibromide was attempted.
Compound 30 was previously synthesized by the Holecek group
[43] using [2-(Me2NCH2)C6H4]Li with the appropriate hal-
oorganostannane. Stepwise halogenations of triphenylstannanes
with HCl to the dichloro tin species were first reported by Pannell
et al. [12], while Molloy had reported the conversion of tripheny-
lalkyloxystannanes to dibromides with the addition of Br2 [25].
Compound 30 was synthesized (Scheme 2) in a slightly lower (60%)
yield compared to an earlier report (87%) [43]. Compound 30
(Fig. 7a) was also characterized by single crystal X-ray diffraction
which shows the Sn center adopting a slightly distorted tetrahedral
geometry, with a long SneN distance of 2.917 (3) Å, suggesting a
rather weak or non-existing dative interaction.
Compound 34 was synthesized in a near quantitative yield (99%)
with HCl as shown in Scheme 3 [44]. When a second equivalence of
HCl was added, conversion of 34 to the dichloride 38 was not
observed. HCl appears to be too weak a halogenation source and is
unable to displace a second phenyl group. This result is consistent
with those found for the similarly rigid 2-methoxymethyl mono-
chlorinated diphenylstannane 24. Conversely, the bromination of
30 produced a mixture of mono- (35) and tri-substituted (37)
species instead of the desired dibromide. Increasing the equiva-
lence of Br2 from 2 to 1 also produced a similar result. A dispro-
portionate distribution of bromides was previously observed for
more flexible propyloxyaryl triphenylstannanes [45].
Fig. 6. Exchange of the axial and equatorial positions of Cl atom in 25a and 25b.
(ꢁ61.0 ppm) and 28 (ꢁ54 ppm). The 119Sn NMR spectrum of 26
revealed two unidentified peaks of small intensity (ꢁ48.0
and ꢁ132.0 ppm) along with the main resonance at ꢁ28.0 ppm.
These minor impurities could not be removed even with repeated
extractions with hot hexanes.
Compound 29 was prepared by reacting [2-(MeOCH2)C6H4]Li
with an equimolar amount of SnCl4 and purified by first removing
volatiles from the crude reaction mixture, followed by extraction
with toluene and finally recrystallization of the extracted solid with
DCM:hexanes (1:1) to yield a white coloured crystalline solid. X-ray
analysis of 29 (Fig. 5b) reveals a Sn(1)-O(1) interatomic distance of
2.341 (4) Å which is significantly shorter than that found in 24,
indicative of a stronger intramolecular interaction. The bond angle
of O(1)-Sn(1)-Cl(2) 177.27(11)ꢂ differs only slightly from the ideal
value, suggestive of little induced ring-strain in the molecule. The
5emembered ring formed between Sn(1)-O(1)-C(7)-C(6)-C(1) is
co-planar with the aryl ring.
Compounds 38e40 were obtained by transmetallation reactions
(Scheme 2) of [2-(Me2NCH2)C6H4]Li with either PhSnCl3, n-BuSnCl3
or MeSnCl3 respectively. Compounds 38 and 40 were previously
reported by van Koten et al. [46] from the reaction of [2-(Me2NCH2)
C6H4]Cu with PhSnCl3 or MeSnCl3 in C6H6. Rippstein et al. [47] and
2.2. C,N-stannanes
ꢂ
later Novak et al. [48] have prepared 38 from the reactions [2-
The synthesis of 2-(Me2NCH2)C6H4Br, was prepared in high
yield (88%) and purity by heating 2-(BrCH2)C6H4Br with a large
excess (7.5 eq.) of NHMe2. The product was recovered by an initial
extraction with 3 M HCl, followed by neutralization with 20% NaOH
and finally isolated from DCM [41]. This procedure was found to be
superior with respect to previously reported routes to these ma-
terials [42].
As an alternative to synthesizing tin dihalides by lithiation and
transmetallation with comparatively expensive tin trihalides,
preparation of the triphenyl analogue 30, followed by either
sequential halogenations with HCl leading to the mono- and
(Me2NCH2)C6H4]Li with PhSnCl3 in Et2O or C6H6. The n-butyl de-
rivative 39 was first prepared by Varga et al. [49] in a similar
manner by reacting [2-(Me2NCH2C6H4]Li with n-BuSnCl3 in n-
hexane/Et2O.
The intramolecular SneN interaction and relative change in the
Lewis acidity at the Sn center of hypervalent compounds can be
monitored by 119Sn and 13C NMR spectroscopy. Three parameters
can be used to determine the strength of SneN interaction. These
include a distinct upfield shift of 119Sn NMR signals of these com-
pounds as compared to their analogues before ligand substitution;

6
A. Khan et al. / Journal of Organometallic Chemistry 900 (2019) 120910
Scheme 2. Synthesis of hypercoordinate Sn compounds from [2-(Me2NCH2)C6H4]Li.
Fig. 7. a (left). Molecular structure of 30. Selected interatomic distances [Å] and angles [º]: Sn(1)-C(16) 2.1331(18), Sn(1)-C(10) 2.1422(18), Sn(1)-C(1) 2.1523(18), Sn(1)-C(22)
2.1661(18), Sn(1)$$$N(1) 2.917(5), C(16)-Sn(1)-C(10) 118.23(7), C(16)-Sn(1)-C(1) 114.83(7), C(16)-Sn(1)-C(22) 102.35(7), C(1)-Sn(1)-C(22) 101.49(7). Fig. 7b (right). Molecular
structure of 40. Selected interatomic distances [Å]and angles [º]: Sn(1)-C(10) 2.1146(15), Sn(1)-C(1) 2.1156(15), Sn(1)-Cl(1) 2.3764(4), Sn(1)-N(1) 2.4082(13), Sn(1)-Cl(2) 2.4696(4),
C(10)-Sn(1)-Cl(1) 111.39(5), C(1)-Sn(1)-Cl(1) 107.80(4), C(10)-Sn(1)-N(1) 92.46(6), C(1)-Sn(1)-N(1) 76.60(5), Cl(1)-Sn(1)-N(1) 88.33(3), C(10)-Sn(1)-Cl(2) 93.30(5), C(1)-Sn(1)-Cl(2)
96.42(4), Cl(1)-Sn(1)-Cl(2) 93.273(15), N(1)-Sn(1)-Cl(2) 173.00(3).
Scheme 3. Synthesis of halogenated compounds 34e37.
an increase in the coupling constants (119Sn, 13C); and the presence
of (2J119SneCH3) coupling constant between the tin and amino
methyl groups [41,42,46]. A distorted TBP geometry was expected
for diorganotin dihalides (38e40) having an aryl and R group at
equatorial positions, while the amino ligand occupies an axial po-
sition, leaving one axial and one equatorial position for the two
halogen atoms.
The 1H NMR (CDCl3) spectra of compounds 38 and 39 display a
downfield shift relative to their non-coordinated analogues of
~8 ppm for the ortho protons of the C6H4- ring, which is similar for
other known tin TBP compounds [46]. The increase in the 2J119Sne1H
coupling constant to 80 Hz for 40 also indicates TBP geometry. The

A. Khan et al. / Journal of Organometallic Chemistry 900 (2019) 120910
7
observed upfield chemical shifts in the 119Sn NMR spectroscopy for
2.4. DFT modelling of C,O- and C,N-stannanes
compounds 38e40 when compared to their corresponding
unsubstituted four coordinate analogues (PhSnCl3: 63.0 ppm
[47,48], n-BuSnCl3: 6.0 ppm [22,30,49,50], MeSnCl3: 21.0 ppm
[8,46] respectively) provide strong evidence for a substantive SneN
intramolecular interaction and TBP geometry in the solution phase.
Compound 40 was crystallized from a DCM/hexanes (1:1) solution
by slow evaporation and the molecular structure obtained by single
crystal XRD (Fig. 7b). The geometry at the Sn center is distorted
trigonal bipyramidal, similar to those reported previously for 38
[47] and 39 [51]. A significant N/Sn intramolecular interaction in
40 is revealed by the short SneN distance (2.4082 (13) Å) compared
to 38 (2.444 (3) Å [47]) and 39 (2.428 (3) Å [51]), respectively. The
N(1)-Sn(1)-Cl(2) bond angle is slightly distorted at 173.00 (3)ꢂ.
The molecular structures of hypercoordinated C,O- and C,N- tin
compounds raise interesting questions about the relative impor-
tance of specific hypercoordinating atoms (O, N) and the other li-
gands (alkyl, phenyl, chloro, etc.) in determining the strength of the
hypercoordinate interaction. Computational studies can supple-
ment experiment in addressing these questions. DFT calculations
have proven to be highly effective at predicting molecular struc-
tures and relative energies for a broad range of main group com-
pounds. The results obtained necessarily depend on the basis set(s)
used for the constituent atoms and the density functional selected;
geometry optimized structures are generally similar for different
functionals, but can show significant variations in bond lengths and
angles.
Determining the optimal level of theory requires an assessment
of accuracy by comparison with experimental molecular structures.
Crystallographic structures determined by X-ray diffraction provide
the bulk of experimental structural data [54]. However, direct
comparisons with calculated structures are problematic [55,56].
The experimental structures are thermally-averaged centers of
electron density from molecules in close proximity [55e57] while
the calculated ones correspond to hypothetically motionless iso-
lated molecules at 0 K [55,58,59]. As a result, calculated geometries
are typically more symmetric, with slightly increased metal-ligand
bond lengths in the case of Sn [60]. A more significant challenge is
that solid-state structures may be significantly distorted by inter-
molecular bonding and crystal packing effects [55,60,61]. Never-
theless, such comparisons have been a standard practice [62]
because in most cases there are few if any other options.
The four crystallographic structures determined in this study
(compounds 24, 29, 30, 40) and eight from the earlier literature
(compounds 31 [51], 32 [63], 33 [64], 35 [11], 36 [13], 37 [13], 38
[48], 39 [49]) provide a moderately-sized dataset for evaluating the
performance of selected density functionals in predicting hyper-
coordinate Sn geometries. Previous work has indicated that
LANL08d for Sn and Br, and 6-31 þ G (d,p) for all other atoms are
reasonable basis set choices in balancing accuracy with computa-
tional cost [61,65]; the diffuse functions on non-H atoms signifi-
cantly improve accuracy with respect to predicted hypercoordinate
bond length [66]. Eight functionals were evaluated: one general-
ized gradient approximation (GGA) method (mPWPW91 [67]), six
hybrid-GGAs (B3LYP [68], B3PW91 [69], HSE06 “HSEh1PBE” [70],
MPW1K [71], mPW1PW91 [67], and PBE0 “PBE1PBE” [72]) and one
hybrid-meta-GGA (MPWB1K [73]). Three functionals (B3LYP,
B3PW91, and PBE0) supplemented with Grimme's D3 empirical
dispersion function and Becke-Johnson damping (GD3BJ) were also
evaluated [74].
2.3. Preparation of C,O- and C,N-hydrides
The hydrogenation of the 2-methoxymethyl (27, 28) and
dimethylamino (39, 40) tin dichlorides to their respective dihy-
drides was afforded by reaction with LiAlH4 as shown in Scheme 4.
To the best of our knowledge, only the more rigid oxazoline con-
taining dihydrides (6, 7) [17,18] possess a possible SneN interaction.
The 1H NMR spectrum of 41 (Fig. S52) reveals the expected
distinctly large 119/117SneH coupling constants for the hydride
signals. The 119Sn NMR chemical shifts for 41 and 42 are shifted
upfield compared to four coordinate tin dihydride analogues [35]
without chelating donor atoms.
Dimethylamino containing tin dihydrides 44 and 45 possess a
downfield 1H NMR (C6D6) resonance (5.62 ppm and 5.73 ppm)
compared to tetracoordinated stannyl dihydrides ((n-Bu)2SnH2:
4.78 ppm [52] and Me2SnH2: 4.46 ppm [53]). Another characteristic
of the hypervalent amine diorganotin hydrides is that the 1J119Sne1H
coupling constants for 44 (1760 Hz) and 45 (1824 Hz) are slightly
larger than those observed for tetrahedral coordinated diorganotin
hydride analogues ((n-Bu)2SnH2 1675 Hz, Me2SnH2 1758 Hz) [16].
The 119Sn chemical resonances of trigonal bipyramidal 44 and 45
stannanes are significantly more shielded compared to their
structurally closest tetrahedrally coordinated analogues and are
consistent with other reported chelating amino diorganotin dihy-
drides [16].
When LiAlH4 was used as a hydrogenating agent for 38, a partial
hydrogenation, along with an aryl redistribution reaction (Scheme
5) leading to 43 as the major product, was observed. The 119Sn NMR
spectrum of the product showed a resonance at ꢁ181 ppm, similar
to the value reported earlier by Turek et al. [17] for 43 who prepared
this species from the monochloride 34 and KBEt3H. A softer hy-
drogenating agent, NaBH4, was then used and a yellow coloured oil
obtained (Scheme 5). Once again the main 119Sn NMR (C6D6)
resonance at ꢁ181 ppm corresponded to the presence of the
redistribution product 43 and a second lower intensity unidentified
Calculated and experimental structures were compared by
superimposing Sn centers and then rotating the calculated struc-
ture relative to the experimental one to minimize the distance
between equivalent heavy (non-H) atoms. In the case of 29, the
experimental structure was clearly different than the calculated
resonance (
d
¼ ꢁ223 ppm), possibly the desired dihydride was also
detected. No further characterization of this compound was
attempted at this time.
Scheme 4. Preparation of tin dihydrides containing a C,O- or C,N-chelating ligand.

8
A. Khan et al. / Journal of Organometallic Chemistry 900 (2019) 120910
Scheme 5. Attempted synthesis of an aryltin dihydride containing a C,N-ligand.
ones. The 5-membered ring formed by hypercoordination (Sn(1)-
C(1)-C(6)-C(7)-O(1)) is planar in the solid state structure (Fig. 5b)
and lies in a reflection plane that includes the coplanar aryl ring and
the chloro ligand Cl(2). All the calculated structures for 29 have 5-
membered rings that are puckered to reduce steric strain, forming a
were considered in determining the MSSD values for 24, 30, 31, 35,
38 and 39. Note that the experimental structures for 31, 38, and 39
also exhibit substantial crystallographic disorder [52,66,67].
For each compound, the MSSD varies substantially depending
on the DFT method used, typically by more than 100%. When
comparing methods for different compounds, it is more useful to
compare rankings because the magnitudes of the MSSDs are also
determined by characteristics of the experimental structures.
Table 2 shows the ranking of each DFT method per compound (1 is
lowest MSSD (best), 11 is highest (worst)), as well as an average
rank for the 11 methods considered. Three of the methods,
B3PW91-GD3BJ, MPW1K and PBE0-GD3BJ, perform especially well
by this measure.
The effects of distortions in the experimental structures on the
values of the MSSD are likely reflected in the performance of
B3PW91-GD3BJ. This is the top-ranked method for 8 of the struc-
tures, and second and third-ranked for two more, but there are
three structures for which it performs quite poorly: 24, 30, and 38.
These compounds are the only ones in this study other than 35 that
have two or more phenyl ligands. The large discrepancies in MSSD
arise for two principal reasons. In the case of 30, B3PW91-GD3BJ
significantly underestimates the SneN distance (2.775 Å)
compared to the experimental value (2.917 Å). The latter is un-
usually long for hypercoordinate Sn complexes, comparable to the
SneN distance in 32 (2.904 Å) in which two bulky t-butyl ligands
sterically hinder the hypercoordinate bonding [63]. For every
compound other than 30, B3PW91-GD3BJ is either first- or second-
ranked for predicting the length of the hypercoordinate interaction
(see Supporting Information). It seems likely that the SneN dis-
tance in 30 is lengthened due to crystal packing forces. A second
reason for higher MSSD values is observed in the case of 24. Here,
the poorer performance of B3PW91 eGD3BJ arises due to differ-
ences in the predicted angles between coordinating ligand atoms at
the Sn center. For example, the aryl C(1)-Sn(1)-Cl(1) angle is
calculated as 100.62ꢂ (97.53ꢂ expt.); the angle between phenyl li-
gands, C(9)-Sn(1)-C(15), is 113.44ꢂ (117.87ꢂ expt). These differences
could reflect distortions in the solid state structures but it is also
possible that B3PW91-GD3BJ is not as good as some functionals at
modelling electronic effects due to phenyl ligands.
chiral ring of either d or l handedness. This same structural motif is
observed in the crystallographic structures of the other Sn com-
pounds. The planar form of the 5-membered ring represents a
transition state in the inversion pathway between the two enan-
tiomeric forms. DFT geometric optimizations to this higher energy
transition state result in structures that closely approximate the
experimental structure of 29. Energy differences between the
puckered and planar calculated structures are small, ranging be-
tween 0.15 and 0.5 kJ molꢁ1 for the methods considered here.
Presumably, greater packing efficiency of the planar form in the
solid state compensates for its somewhat higher conformational
energy.
The extent of overlap between the superimposed experimental
and calculated structures can be quantified by summing the
squared distances between equivalent atoms, and then averaging
by the number of atoms (Fig. 8). This mean sum of squared dis-
tances (MSSDs) is a demanding test of accuracy for a calculated
structure, as the impacts of discrepancies in bond angles and/or
lengths proximal to the Sn center will be propagated throughout
the molecular structure, leading to higher values. It is also, how-
ever, sensitive to any distortions in the solid state structure due to
packing forces or intermolecular bonding. Even a slight rotation in
the dihedral angle of a phenyl ligand or a conformational change in
an n-butyl ligand will significantly impact the magnitude of the
MSSD. For this reason, only Ph or n-Bu C atoms directly bound to Sn
Three principal conclusions can be made. First, the commonly
used B3LYP functional significantly underperformed in comparison
with the other methods for modelling hypercoordinate Sn in-
teractions in the solid state. Second, augmenting methods with
empirical dispersion generally improved the performance of the
predictions. Third, B3PW91-GD3BJ, MPW1K, and PBE0-GD3BJ are
the best of the 11 methods for predicting the solid-state geometries
of the hypercoordinate Sn complexes considered in this study.
Additional measures of performance commonly used in DFT
structural benchmarking studies are provided in the Supporting
Information (see Tables S1eS3).
Fig. 8. Overlay of coordinate traces for experimental (blue) and B3PW91-GD3BJ (red)
data for compound 35. Green points indicate coordinates used in calculation and
minimization of MSSD. (For interpretation of the references to colour in this figure
legend, the reader is referred to the Web version of this article.)
2.5. Attempted Na Wurtz coupling of C,N-stannane dichlorides
The polymerization of the dichloride 39 (Scheme 6) was

A. Khan et al. / Journal of Organometallic Chemistry 900 (2019) 120910
9
Table 2
Minimized mean sum of squared distances (MSSDs) between equivalent heavy (non-H) atoms in calculated and experimental molecular structures, with DFT method rank ()
for each compound.
Cmpd
B3LYP
B3LPY-GD3BJ
B3PW91
B3PW91-GD3BJ
HSE06
MPW1K
MPW1PW91
MPWB1K
MPWPW91
PBE0
PBE0-GD3BJ
24a
0.00943
(10)
0.0242
(11)
0.00606
(5)
0.00838
(8)
0.00553
(3)
0.00435
(1)
0.00528
(2)
0.00676
(6)
0.00905
(9)
0.00558
(4)
0.00704
(7)
29b
30c
31d
32
0.00551
(10)
0.00486
(7)
0.0367
(11)
0.0831
(11)
0.00338
(5)
0.00532
(8)
0.0190
(7)
0.0140
(4)
0.00443
(9)
0.00264
(2)
0.0235
(9)
0.0453
(10)
0.00303
(3)
0.0116
(11)
0.0150
(2)
0.00325
(1)
0.00371
(7)
0.00367
(4)
0.0187
(6)
0.0234
(5)
0.00288
(1)
0.00461
(6)
0.0161
(4)
0.0242
(7)
0.00372
(8)
0.00258
(1)
0.0198
(8)
0.0319
(8)
0.00289
(2)
0.00840
(10)
0.0121
(1)
0.0106
(3)
0.00693
(11)
0.0316
(3)
0.0275
(10)
0.0421
(9)
0.00369
(6)
0.00385
(5)
0.0181
(5)
0.0240
(6)
0.00321
(4)
0.00823
(9)
0.0154
(3)
0.00584
(2)
33ae
33be
35f
36
0.0350
(11)
0.0399
(11)
0.0218
(11)
0.01487
(11)
0.0210
(8)
0.0215
(5)
0.0110
(4)
0.00830
(6)
0.0232
(9)
0.0279
(9)
0.0131
(9)
0.00996
(9)
0.0169
(1)
0.0134
(1)
0.00902
(1)
0.00674
(1)
0.0208
(5)
0.0223
(7)
0.0118
(7)
0.00873
(8)
0.0184
(3)
0.0209
(4)
0.00965
(2)
0.00701
(2)
0.0208
(6)
0.0243
(8)
0.0114
(5)
0.00864
(7)
0.0208
(7)
0.0201
(3)
0.0123
(8)
0.00724
(4)
0.0260
(10)
0.0310
(10)
0.0161
(10)
0.0128
(10)
0.0200
(4)
0.0221
(6)
0.0114
(6)
0.00827
(5)
0.0181
(2)
0.0189
(2)
0.00988
(3)
0.00718
(3)
37
0.0176
(11)
0.0356
(11)
0.0288
(11)
0.0313
(11)
0.00896
(6)
0.0301
(10)
0.0138
(3)
0.0185
(5)
0.0106
(9)
0.0276
(6)
0.0200
(9)
0.0222
(9)
0.00683
(1)
0.0278
(8)
0.0102
(1)
0.0145
(1)
0.00928
(8)
0.0263
(3)
0.0168
(7)
0.0196
(7)
0.00804
(3)
0.0251
(1)
0.0162
(5)
0.0175
(4)
0.00921
(7)
0.0263
(4)
0.0177
(8)
0.0199
(8)
0.00874
(4)
0.0129
(10)
0.0299
(9)
0.0220
(10)
0.0254
(10)
0.00885
(5)
0.0259
(2)
0.0164
(6)
0.0189
(6)
0.00753
(2)
0.0273
(5)
0.0122
(2)
0.0160
(2)
38g
39h
40
0.0278i
(7)
0.0154
(4)
0.0171
(3)
Aver. Rank
9.7
5.9
7.3
3.0
5.4
3.0
5.5
4.5
8.5
4.6
3.4
a
For 12 of 22 atoms.
b
c
d
e
f
Calculated structures are for transition state of hypercoordinate ring inversion (see text).
For 13 of 28 atoms.
For 13 of 19 atoms.
Compound 33 has two crystallographically independent molecules in the asymmetric unit.
For 13 of 23 atoms.
For 13 of 18 atoms.
For 13 of 16 atoms.
g
h
i
Structure calculations used “Ultrafine” integration grid.
Scheme 6. Wurtz Coupling of 39 for 4 h and 4 d.
attempted using the soft Na Wurtz coupling conditions first
employed by Molloy et al. [25] However, three non-polymer
products of the reaction mixture were identified by 119Sn NMR
spectroscopy. 119Sn chemical resonances (Fig. S77) for the dis-
tannane [17] 47 and distannoxanes, bis-{[2-(N,N-dimethyamino-
methyl)phenyl]n-butylchloro}tin oxide [17,75] 48 (a,b) and the bis-

10
A. Khan et al. / Journal of Organometallic Chemistry 900 (2019) 120910
{[2-(N,N-dimethyaminomethyl)phenyl]di-n-butyltin (IV) 49, were
obtained in two separate attempts to prepare polymer. Turek et al.
[24] had previously prepared 47 by adding a solution (1:1 hexane/
C6H6) of 39 to a K-mirror initially at ꢁ30 ꢂC, followed by stirring for
one week at RT, resulting in the production of 47 (ꢁ88.1 ppm).
Further, when oxygen was bubbled through a solution containing
47, conversion to the stannoxane (two 119Sn NMR signals at ꢁ134.5
and ꢁ137.5 ppm) existing as two stereoisomers 48a and 48b was
observed, but not assigned [24].
When the reaction time for the Wurtz coupling of 39 was
increased from 4 h to 4 d, the redistributed tetrabutyl distannane
49 was identified as the major product (ꢁ105 ppm). This result
agrees with those observations of Turek et al. [17] who prepared 49
from the reaction of a K-mirror and [2-(Me2NCH2)C6H4](n-Bu)2SnCl
in hexane solution for 5 d. The Wurtz coupling polymerization of
the aryl tin dichloride 38 (Scheme 7) was also attempted using the
soft conditions developed by Molloy et al. [25] After 4 h, the 119Sn
NMR (C6D6) spectroscopy of the reaction mixture showed a reso-
nance at ꢁ173.0 ppm, identified as the hypercoordinated dis-
tannoxane, 51. This compound has been previously isolated and
structurally characterized by Turek and coworkers from the
sequential base hydrolysis and condensation of 34 [17,75]. Addi-
tionally, two other unidentified resonances at ꢁ210.6
and ꢁ212.2 ppm were also present. The absence of any distannane
products in our Wurtz reaction attempt suggests an inadvertent
exposure to either moisture or oxygen sources. After increasing the
reaction time from 4 h to 8 d (Scheme 7), 119Sn NMR spectroscopy
(Fig. S78) showed two resonances at ꢁ145.5 ppm and ꢁ173.0 ppm
along with four smaller unidentified resonances corresponding to
the redistributed tetraphenylated distannane 50 and the dis-
tannoxane 51 respectively, in agreement with assignments pro-
vided by Turek for these species [17].
Scheme 8. Synthesis of rigid polystannanes 52 and 53.
(52: Mw ¼ 3.03 ꢀ 104 Da, PDI ¼ 1.4, 53: Mw ¼ 3.1 ꢀ 104 Da,
PDI ¼ 1.86). The degree of polymerization is approximately 100
monomer units for 52 and 70 for 53. While polymer 52 is clearly a
broad monomodal trace, polymer 53 is more multimodal (Fig. S81).
Analysis by 1H and 13C NMR spectroscopy confirmed the expected
polymer structures. Interestingly, the 119Sn NMR spectroscopy in
two different deuterated solvents (C6D6 and THF-d8) reveals
structural details. Fig. 9 (btm) shows presence of two resonances
for 52, with one substantially downfield (ꢁ49 ppm) and the other
shifted 150 ppm upfield. When 52 was run in THF-d8 (Fig. 9 mid), a
known coordinating solvent, only a single resonance at z ꢁ44 ppm
was observed. This would suggest that large excess of THF mole-
cules were effectively displacing the SneO dative interaction of the
chelating ligand, causing the complex to be effectively in an “open”
position. When the THF-d8 was removed from the solvent and
redissolved in C6D6 (Fig. 9 top), the sample did not return to its
initial closed position, and no resonance at ꢁ195 ppm was detected.
When the same set of experiments were carried out for polymer 53,
only one upfield resonance at ꢁ149 ppm in C6D6 was observed
(Fig. S82 btm), while the same sample in THF-d8 (Fig. S82 mid)
showed two clear resonances similar to 52, but with only a partial
redistribution from the upfield “closed” resonance to the “open”
downfield resonance. When the THF-d8 sample was resuspended in
C6D6, and unlike polymer 52 (Fig. S82 top) all of the “open” struc-
tural isomers returned to the “closed” state. This is good evidence
that the NMe2 functionality of 53 is more strongly donating and
coordinating to Sn than the OMe functionality of 52. This also
suggests that the ability of these rigid dihydride monomers to
undergo dehydrocoupling maybe impacted by the strength of these
dative interactions, which lead to very low yields in the case of 44.
2.6. Dehydrocoupling of C,O- and C,N-monomers
Dehydrocoupling of hypercoordinated compounds 41 and 44
was attempted using Wilkinson's catalyst. The C,O- and C,N- dihy-
dride butyl monomers were selected to ensure good solubility and
processability of any resulting polymer. Polymerization conditions
similar to those used previously for flexible stannanes 13 and 14
were employed for the more rigid C,O and C,N stannanes (Scheme
8) [26,28,29]. The polymerizations were carried out at RT in the
absence of light in Al-foil wrapped Schlenk flasks with 10 mL of
degassed toluene containing 4 mol% of the Wilkinson's catalyst to
which the monomer in the same solvent (6 mL) was slowly added
and stirred for 4 h.
A lightly yellow coloured polymer 52 was recovered from the
dehydrocoupling of 41 in good yield (65%), while a much darker
yellow coloured polymer 53 was recovered from the polymeriza-
tion 44 in poor yield (18%). After several attempts, only modest
absolute molecular weights were obtained for both rigid polymers
2.7. Thermal properties of 52 and 53
A DSC study of 52 and 53 revealed the two polymers to have
amorphous character absent of any crystalline behaviour. As shown
in Figs. S3 and S4, nearly identical Tg's near 11.5 ꢂC were recorded.
The polymers showed nothermal behaviourchanges when annealed
prior to running or after multiple scans. Unfortunately, at these low
molecular weights, polymer film properties were not evident.
Scheme 7. Na Wurtz Coupling of 38.

A. Khan et al. / Journal of Organometallic Chemistry 900 (2019) 120910
11
Fig. 9. 119Sn NMR of 52 in two different solvents: bottom C6D6, middle THF-d8, and THF-d8 sample dried and redispersed in C6D6.
2.8. Conclusion
(239 ppm) using a relaxation delay of 2s, acquisition time 1.36s, 32k
13
points (4096 scans). The C 90ꢂ pulse width was 8.7
m
s. A119Sn
A series of new and known C,O- and C,N- rigid small molecule
stannanes were prepared and characterized. The absence of poly-
mer from Na Wurtz coupling attempts of the dichlorinated dime-
thylamino containing stannanes 38 and 39 suggest a lack of access
of the remaining SneCl bonds to Na surfaces after dimerization. In
these attempts, evidence for redistribution to the tetraalkyl- or
tetraaryldistannanes was observed. Polymerization of C,O- and C,N-
dihydrides 42 and 44 using Wilkinson's catalyst has led to the first
examples of modest molecular weight rigidly hypercoordinated
polystannanes 52 and 53 respectively. Characterization by DSC of
the amorphous polystannanes 52 and 53 display relatively low Tgs.
The polymers appear to be indefinitely stable to both air and
moisture. If higher molecular weights are obtained through
improved catalyst selection and polymerization conditions, these
rigid hypercoordinated polystannanes may be good candidates for
polymeric wires.
pulse width of 30ꢂ was used, 8.75
ms, acquiring a spectral window of
100000 Hz (670 ppm) using a relaxation delay of 1s, acquisition
time 0.33s, 32k points (15360 scans) with inverse gated proton
decoupling. All results were analysed on MestReNova LITE 5.2.5
software. Chemical shifts were calculated using the chemical
deuterated standards as a reference for 1H and 13C. The 119Sn was
referenced to SnMe4 as an internal standard. All J coupling values
are reported as absolute values. Time-of-flight mass spectrometry
analyses were performed at the AIMS Mass Spectrometry Labora-
tory, University of Toronto using a JMS-T1000LC mass spectrometer
(JEOL Inc., Peabody, MA) equipped with a Direct Analysis in Real
Time (DART) ionization source (DART-SVP, Ionsense Inc., Saugus,
MA). The DART source was operated with He gas and the temper-
ature was adjusted in the range 100e400 ꢂC. Isotopic distributions
for the observed ionic species were calculated using the Mass
Center utility (JEOL) and were in good agreement with the
measured mass spectra. Absolute molecular weights of the poly-
mers were determined by GPC using a Viscotek Triple Model 302
Detector system. GPC columns were calibrated versus polystyrene
standards (American Polymer Standards). A flow rate of 1.0 mL/min
was used with ACS grade THF as the eluent. GPC samples were
prepared using 3e10 mg of each polymer per mL THF, and filtered
3. Experimental
3.1. General remarks
1H NMR (400 MHz), 13C NMR (100.6 MHz) and 119Sn NMR
(149.2 MHz) spectra were recorded on a Bruker Advance 400 MHz
NMR spectrometer with a BBFO 5-mm direct probe. A 1H pulse
width of 30ꢂ was used, acquiring a spectral window of 8223 Hz
using a 0.45 mm filter. All samples were run with and without UVA
(conc. z 0.001 M) for comparison. The X-ray diffraction data for
compounds 24, 29, 30 and 40 were collected on a Bruker Kappa
APEX-DUO diffractometer using monochromated Mo-K
(Bruker Triumph) and were measured using a combination of
scans and scans. The data were processed using APEX2 and SAINT
a radiation
(20 ppm) using a relaxation delay of 1s, acquisition time 3.98s, 32k
f
1
points (16 scans). The H 90ꢂ pulse width was 10.4
m
s. A13C pulse
u
width of 30ꢂ was used, acquiring a spectral window of 24038 Hz

12
A. Khan et al. / Journal of Organometallic Chemistry 900 (2019) 120910
[dimethylamino)methyl]phenyl)diphenyltin Bromide, J. Organomet. Chem.
118 (1976) 183e189.
[12] T. Munguia, M. Lo, F. Cervantes-lee, K.H. Pannell, V. Uni, E. Paso, Intra-
molecular chalcogen ꢁ tin interactions, characterized by X-ray diffraction and
119 Sn solution and solid-state NMR, Inorg. Chem. 46 (2007) 1305e1314.
programs. Absorption corrections were carried out using SADAB.
The structures were solved using SHELXT [76] and refined using
SHELXL-2013 [76] for full-matrix least-squares refinement that was
based on F2. For all structures, H atoms were included in calculated
positions and allowed to refine in a riding-motion approximation
with Uiso tied to the carrier atom. All reactions were carried out
under a nitrogen atmosphere using Schlenk techniques unless
otherwise described. LiAlH4 (1.0 M in Et2O), 1.0 M solution of HCl in
Et2O, anhydrous CaCl2, anhydrous MgCl2 and Wilkinson's catalyst
were purchased commercially and used without further purifica-
tion. Solvents were dried by standard procedures prior to use. All
experimental details for all small molecule compounds of this
study can be found in the supplementary material.
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Acknowledgements
Organometallics
om00051a052.
ꢁ ꢁ
10
(1991)
1531e1546,
https://doi.org/10.1021/
This work was supported by the NSERC Discovery Grant pro-
gram. The computational studies were made possible by the facil-
ities of Compute/Calcul Canada. DF is thankful for the editing help
provided by Dr. Robert Gossage.
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Appendix A. Supplementary data
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.jorganchem.2019.120910.
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