Metal complexes (M = Zn, Sn, and Pb) of 2-phosphinobenzenethiolates: Insights into ligand folding and hemilability

Article abstract of DOI:10.1021/ic400990n

The divalent metal complexes M^II{(SC₆H ₄-2-PR₂)-κ²S,P}₂ (3-7, and 9-11) (M = Zn, Sn, or Pb; R = ⁱPr, ^tBu, or Ph), the Sn(IV) complexes Sn{(SC₆H₄-2-PR₂)- κ²-S,P}Ph₂Cl (12 and 13) (R = ⁱPr and ^tBu), and the ionic Sn(IV) complexes [Sn{(SC₆H ₄-2-PR₂)-κ²-S,P}Ph₂][BPh ₄] (14 and 15) (R = ⁱPr and ^tBu) have been prepared and characterized by multinuclear NMR spectroscopy and single crystal X-ray diffraction when suitable crystals were afforded. The Sn(II) and Pb(II) complexes with R = Ph, ⁱPr, or ^tBu (5, 6, 9, and 10) demonstrated ligand folding hinging on the P,S vector - a behavior driven by the repulsions of the metal/phosphorus and metal/sulfur lone pairs and increased M-S sigma bonding strength. This phenomenon was examined by density functional theory (DFT) calculations for the compounds in both folded and unfolded states. The Sn(IV) compound 13 (R = ^tBu) crystallized with the phosphine in an axial position of the pseudotrigonal bipyramidal complex and also exhibited hemilability in the Sn-P dative bond, while compound 12 (R = ⁱPr), interestingly, crystallized with phosphine in an equatorial position and did not show hemilability. Finally, the crystal structure of 15 (R = ^tBu) revealed the presence of an uncommon, 4-coordinate, stable Sn(IV) cation.

Full text of DOI:10.1021/ic400990n

Article
pubs.acs.org/IC
Metal Complexes (M = Zn, Sn, and Pb) of
2‑Phosphinobenzenethiolates: Insights into Ligand Folding and
Hemilability
Brian M. Barry,† Benjamin W. Stein,† Christopher A. Larsen,† Melissa N. Wirtz,† William E. Geiger,‡
Rory Waterman,‡ and Richard A. Kemp*,†,§
†Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, New Mexico 87131, United States
‡Department of Chemistry, University of Vermont, Burlington, Vermont 05405, United States
§Advanced Materials Laboratory, Sandia National Laboratories, Albuquerque, New Mexico 87106, United States
S
* Supporting Information
ABSTRACT: The divalent metal complexes MII{(SC6H4-2-PR2)-κ2S,P}2 (3−7, and 9−11) (M = Zn, Sn, or Pb; R = iPr, tBu, or
i
t
Ph), the Sn(IV) complexes Sn{(SC6H4-2-PR2)-κ2-S,P}Ph2Cl (12 and 13) (R = Pr and Bu), and the ionic Sn(IV) complexes
i
t
[Sn{(SC6H4-2-PR2)-κ2-S,P}Ph2][BPh4] (14 and 15) (R = Pr and Bu) have been prepared and characterized by multinuclear
NMR spectroscopy and single crystal X-ray diffraction when suitable crystals were afforded. The Sn(II) and Pb(II) complexes
i
t
with R = Ph, Pr, or Bu (5, 6, 9, and 10) demonstrated ligand “folding” hinging on the P,S vectora behavior driven by the
repulsions of the metal/phosphorus and metal/sulfur lone pairs and increased M-S sigma bonding strength. This phenomenon
was examined by density functional theory (DFT) calculations for the compounds in both folded and unfolded states. The
Sn(IV) compound 13 (R = tBu) crystallized with the phosphine in an axial position of the pseudotrigonal bipyramidal complex
and also exhibited hemilability in the Sn−P dative bond, while compound 12 (R = iPr), interestingly, crystallized with phosphine
in an equatorial position and did not show hemilability. Finally, the crystal structure of 15 (R = tBu) revealed the presence of an
uncommon, 4-coordinate, stable Sn(IV) cation.
complexes having hemilabile ligands, with only a limited
number of examples in the literature.12−15
INTRODUCTION
■
Unsymmetric, multidentate ligands have garnered significant
attention recently, in particular because of a subset of these
ligands that exhibits hemilability.1−4 In these hemilabile systems
a hybrid ligand containing one strongly binding donor and one
relatively weak donor can be employed to stabilize a metal
center until a substrate is introduced.5 Crucial to this process
are the dynamic interactions between the metal center and the
weak donor, whereby the chelate can open during reactions but
remain closed, suppressing the active metal site, in the ground
state structure.5,6
Transition-metal complexes employing hemilabile ligands
have been well-studied, and have been successfully used, for
example, as homogeneous catalysts for olefin metathesis,7,8 for
small molecule sensing,9 and as catalysts for Suzuki−Miyaura
coupling reactions.10 The majority of the bifunctional ligands
used in such transition-metal complexes are neutral with one
hard and one soft donor, as in phosphine-amine or phosphine-
ether ligand combinations.5,6 N-heterocyclic carbene-substi-
tuted pincer complexes containing hemilabile pendant arms are
also well documented.11 Far less explored are main-group metal
We have previously reported that the Sn(II) complex
Sn[{(iPr2P)2N}-κ2-P,P]2 can form a CO2 “adduct” by formal
insertion of CO2 into a Sn−P bond.16 We have termed this
complex a CO2 adduct as the CO2 molecule is quite labile in
binding to and releasing from the metal fragment. This adduct
formation is dependent upon the complex having an available
Lewis base to form a dative interaction with the electrophilic
central carbon atom of CO2, while one nucleophilic oxygen
atom of CO2 can coordinate to the Lewis acidic metal center.
This interesting reactivity has inspired us to explore alternative
ligands that might behave similarly in their CO2 reactivity. Of
these possible ligands, the unsymmetric 2-phosphinobenzene-
thiolates (Scheme 1) that can chelate to main group metals via
the neutral P and anionic S donor sites seemed particularly
promising. These ligands would also have the potential to
exhibit hemilability with the covalently bound thiolate acting as
Received: April 21, 2013
© XXXX American Chemical Society
A
dx.doi.org/10.1021/ic400990n | Inorg. Chem. XXXX, XXX, XXX−XXX

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Scheme 1. Outline for Reactions Targeting MII Complexes
(3−7 and 9−11)
were measured under argon using a Uni-Melt capillary melting point
apparatus. Infrared spectra were recorded on a Nicolet 6700 FT-IR
spectrometer on KBr plates. Elemental analyses were obtained from
Columbia Analytical Services located in Tucson, Arizona. For metal-
containing compounds WO3 was added to aid in oxidation during the
CHN analyses; however, the C analyses for these Sn and Zn species
were slightly lower than the calculated value, a phenomenon we have
seen previously with a wide range of ligated main group complexes.
Also consistent with our prior results is that the analyzed hydrogen
levels appear not to be affected.
Synthesis of 2-iPr2P(C6H4)SH (1). This synthesis was performed
with slight variation upon the previously reported synthesis of the
analogous 2-Ph2P(C6H4)SH.32 2-iPr2P(C6H4)SH has been previously
prepared,31 but without any synthetic details or characterization data
provided. Thiophenol (8.00 g, 72.6 mmol) diluted to about 10 mL
with cyclohexane was added dropwise to a stirred solution of 1.6 M n-
butyllithium (100 mL, 160 mmol) and TMEDA (18.6 g, 160 mmol) in
about 50 mL of cyclohexane at 0 °C. The solution stirred overnight,
warming gradually to room temperature. The resulting white
precipitate was isolated from the supernatant by filtration, washed
with pentane and dried at atmospheric pressure for 1 h. It was then
dissolved in 75 mL of THF and cooled to −78 °C whereupon a
a strong donor and the phosphine acting as a weaker, more
labile donor. The promise of these ligands was also
substantiated by a recent report in which a related phenolate
analogue was employed in an ionic zirconocene complex,
demonstrating CO2 insertion into the weak Zr−P bond to form
a cyclic Zr phosphinocarbonate.17
i
solution of Pr2PCl (7.75 g, 50.8 mmol) in about 10 mL of THF was
added dropwise over 30 min. After stirring overnight and warming to
room temperature, the resulting red-orange slurry was acidified by the
addition of 0 °C, 1 M H2SO4. The aqueous layer of the resulting
biphasic solution was washed twice with about 50 mL of diethyl ether
and the combined organics (THF/diethyl ether) were then dried over
MgSO4 and concentrated in vacuo to afford a yellow oil. The product
was distilled (ca. 20 mTorr) from the crude oil (80−100 °C) and
collected as a yellow liquid. Yield 7.9 g (48%). 1H (C6D6, 300 MHz): δ
While there have been many reports of complexes containing
2-phosphinobenzenethiolates in transition-metal com-
plexes,1,18−23 the use of this ligand type with main-group
metals24−30 is surprisingly rare. Using transition metals, all of
the known examples are limited to the 2-(diphenylphosphino)-
benzenethiolate ligand with one exception, that exception being
a single report of a 2-phosphinobenzenethiolate complex in
which the phosphine has isopropyl groups and is ligated to Rh
and Ir.31 In this report we expand the number of substituted 2-
phosphinobenzenethiolate ligands and additionally report their
reaction chemistry with several divalent metals (M = Zn(II),
Sn(II) or Pb(II), 3−7 and 9−11). As well, we prepared two
higher-valent neutral Sn(IV) complexes (12−13), leading to
cationic complexes after halide removal (14−15). Unfortu-
nately and quite surprisingly to us, these complexes showed no
tendency to react with CO2. However, despite the lack of
reactivity with CO2 we did observe in the solid-state structure a
unique example of ligand folding, as well as rare examples of
hemilability between phosphine donors and Pb(II) and Sn(IV)
metal centers, and formation of a stable coordinatively
unsaturated Sn(IV) cation.
3
3
0.84 (dd, JP−H = 15 Hz, JH−H = 6.9 Hz, 6H, CH(CH3)2), 1.05 (dd,
3JP−H = 15 Hz, 3JH−H = 6.9 Hz, 6H, CH(CH3)2), 1.88 (sept of d, 2JP−H
3
= 2.4 Hz, JH−H = 6.9 Hz, 2H, CH(CH3)2), 5.10 (s, 1H, SH), 6.82−
7.08 (m, 4H, C6H4). 1H{31P} (C6D6, 300 MHz): δ 0.84 (d, 3JH−H = 6.9
3
Hz, 6H, CH(CH3)2), 1.05 (d, JH−H = 6.9 Hz, 6H, CH(CH3)2), 1.88
3
(sept, JH−H = 6.9 Hz, 2H, CH(CH3)2), 5.10 (s, 1H, SH), 6.82−7.08
(m, 4H, C6H4). 13C{1H} (CDCl3, 75 MHz): δ 19.1 (d, 2JP−C = 10 Hz,
2
1
CH(CH3)2), 24.0 (d, JP−C = 10 Hz, CH(CH3)2), 25.8 (d, JP−C = 21
Hz, CH(CH3)2), 124.3 (s, C6H4), 128.8 (s, C6H4), 129.2 (s, C6H4),
133.0 (s, C6H4). 31P{1H} (C6D6, 121 MHz): δ −2.60 ppm. Anal. Calcd
for C12H19PS: C, 63.68; H, 8.46. Found: C, 64.28; H, 8.37.
Synthesis of 2-tBu2P(C6H4)SH (2). Compound 2 was prepared in
an analogous manner to 1. The product was distilled (ca. 20 mTorr)
from the crude oil (100−115 °C) and collected as a yellow liquid.
Yield 8.9 g (48%). 1H (C6D6, 300 MHz): 1.36 (d, 3JP−H = 12 Hz, 18H,
C(CH3)3), 5.68 (s, 1H, SH), 6.78−7.11 (m, 4H, C6H4). 13C{1H}
(CDCl3, 75 MHz): 30.2 (d, 2JP−C = 13 Hz, C(CH3)3), 33.2 (d, 1JP−C
=
17 Hz, C(CH3)3), 123.3 (s, C6H4), 129.0 (s, C6H4), 131.3 (s,
C6H4),134.9 (s, C6H4). 31P{1H} (C6D6, 121 MHz) 2: δ 18.8 ppm.
Anal. Calcd for C14H23PS: C, 66.10; H, 9.41. Found: C, 66.28; H, 9.46.
Synthesis of MII{(SC6H4-2-PR2)-κ2S,P}2 (3−7, and 9−11). All
divalent metal compounds were prepared in a similar manner in which
the metal chloride, 10−15% molar excess of NEt3, and the
phosphinobenzenethiol were mixed in MeOH, resulting in the
precipitation of pure product. A detailed synthesis of Zn{(SC6H4-2-
PiPr2)-κ2-S,P}2 is given below, and the remaining divalent metal
complexes are prepared in analogous fashion.
EXPERIMENTAL SECTION
■
General Procedures. Standard inert atmosphere and Schlenk
techniques were used, as all reagents and products were presumed to
be air and/or moisture-sensitive. The ligands 2-Ph2P(C6H4)SH and
2-tBu2P(C6H4)OH were prepared as previously reported.32,33 Prior to
use, cyclohexane and tetrahydrofuran (THF) (both Aldrich) were
distilled from P2O5 and Na metal, respectively. Anhydrous methanol
(EMD) was used as received while diethyl ether (Aldrich) was further
dried using an LC Technology Solutions SP-105 purification system.
All other reagents (Aldrich, Alfa-Aesar, or Strem) were used as-
Synthesis of Zn{(SC6H4-2-PiPr2)-κ2-S,P}2 (3). Solid ZnCl2 (0.139
g, 1.02 mmol) was added to a stirred solution of NEt3 (0.237 g, 2.33
mmol) and 1 (0.460 g, 2.03 mmol) in about 25 mL of MeOH at room
temperature. An immediate reaction occurs, resulting in a white
precipitate. The reaction is allowed to stir for 15 h at room
temperature. The white precipitate is then isolated by filtration,
washed twice with diethyl ether (2 × 20 mL), and dried under vacuum
for 1 h. Yield 0.420 g (80.1%). Colorless, single crystals of 3 were
grown from a CH2Cl2/MeOH mixture. 1H NMR (C6D6, 300 MHz): δ
0.87 (s, br, 12H, CH(CH3)2), 1.07 (s, br, 12H, CH(CH3)2), 1.98
(sept, br, 4H, CH(CH3)2), 6.38 (m, 2H, C6H4), 6.70 (m, 2H, C6H4),
6.83 (m, 2H, C6H4), 8.08 (m, 2H, C6H4). 13C{1H} (CH2Cl2, 75
received without further purification. Solution H, H{31P}, 11B{1H},
13C{1H}, 31P{1H}, 119Sn{1H}, and 207Pb{1H} NMR spectra were
obtained on Bruker Avance 500 or Bruker Avance III 300
spectrometers. 1H and 13C{1H} NMR were referenced to residual
solvent peaks downfield of TMS. 11B{1H}, 31P{1H}, 119Sn{1H}, and
207Pb{1H} spectra were referenced to external BF3·Et2O, 85% H3PO4,
SnEt4, and PbCl2(aq), respectively. The solid state 31P{1H} spectrum
was collected on an Avance III 300WB spectrometer. Melting points
1
1
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MHz): δ 16.8 (s, CH(CH3)2), 18.1 (s, CH(CH3)2), 18.4 (s,
reaction occurs, resulting in a white precipitate. The reaction is allowed
to stir for 15 h at room temperature. The white precipitate is then
isolated by filtration, washed twice with diethyl ether (2 × 20 mL), and
dried under vacuum for 1 h. Yield 0.473 g (76.0%). Colorless, single
1
CH(CH3)2), 19.1 (s, CH(CH3)2), 23.4 (d, JP−C = 55 Hz), 121.4 (s,
C6H4), 130.4 (s, C6H4), 131.9 (s, C6H4), 132.9 (s, C6H4). 31P{1H}
(C6D6, 121 MHz) δ 10.9 ppm. Anal. Calcd for C24H36P2S2Zn: C,
55.86; H, 7.03. Found: C, 55.66; H, 6.91. Mp 208−210 °C.
1
crystals of 8 were grown from a CH2Cl2/MeOH mixture. H NMR
Synthesis of Zn{(SC6H4-2-PtBu2)-κ2-S,P}2 (4). ZnCl2 (0.080 g,
0.59 mmol), NEt3 (0.137 g, 1.36 mmol) and 2 (0.300 g, 1.18 mmol)
were reacted in MeOH as previously described, affording a white
powder. Yield 0.205 g (60.8%). Colorless, single crystals of 4 were
grown from a CH2Cl2/MeOH mixture. 1H NMR (CDCl3, 300 MHz):
(C6D6, 300 MHz): δ 1.29 (overlapping doublets, 3JP−H = 6.6 Hz, 36H,
C(CH3)3), 6.66 (m, 2H, C6H4), 7.11 (m, 2H, C6H4), 7.26 (m, 2H,
C6H4), 7.44 (m, 2H, C6H4). 13C{1H} (C6D6, 75 MHz): δ 30.2 (s,
C(CH3)3), 35.4 (s, C(CH3)3), 115.9 (s, C4H6), 121.5 (s, C4H6), 132.5
(s, C4H6), 134.7 (s, C4H6). 31P{1H} (C6D6, 121 MHz) δ 9.41 ppm (s,
Sn satellites, 1JSn−P = 1256 Hz). 119Sn{1H} (C6D6, 112 MHz) δ −301.0
3
δ 1.45 (d, JP−H = 14 Hz, 36H, C(CH3)3), δ 6.90 (m, 2H, C6H4), δ
1
7.11 (m, 2H, C6H4), δ 7.53 (m, 2H, C6H4), δ 7.68 (m, 2H, C6H4).
1H{31P} (CDCl3, 300 MHz): δ 1.45 (s, 36H, C(CH3)3), δ 6.90 (m,
2H, C6H4), δ 7.11 (m, 2H, C6H4), δ 7.53 (m, 2H, C6H4), δ 7.68 (m,
2H, C6H4). 13C{1H} (CH2Cl2, 75 MHz): δ 29.8 (s, C(CH3)3), 35.0
(br, C(CH3)3), 120.6 (s, C6H4), 130.1 (s, C6H4), 133.2 (s, C6H4),
133.8 (s, C6H4). 31P{1H} (CDCl3, 121 MHz) δ 31.7 ppm. Anal. Calcd
for C28H44P2S2Zn: C, 58.78; H, 7.75. Found: C, 58.98; H, 7.77. Mp
>220 °C.
ppm (t, JP−Sn = 1256 Hz). Anal. Calcd for C28H44P2O2Sn: C, 56.68;
H, 7.48. Found: C, 53.97; H, 6.84. Mp 142−145 °C.
Synthesis of Pb{(SC6H4-2-PiPr2)-κ2-S,P}2 (9). PbCl2 (0.123 g,
0.44 mmol), NEt3 (0.103 g, 1.02 mmol), and 1 (0.200 g, 0.88 mmol)
were reacted in MeOH as previously described, affording a light-yellow
powder. Yield 0.172 g (59.0%). Yellow, single crystals of 9 were grown
1
from a CH2Cl2/MeOH mixture. H NMR (C6D6, 300 MHz): δ 0.95
(s, br, 12H, CH(CH3)2), 1.23 (s, br, 12H, CH(CH3)2), 2.26 (sept,
Synthesis of Sn{(SC6H4-2-PiPr2)-κ2-S,P}2 (5). SnCl2 (0.198 g,
1.04 mmol), NEt3 (0.243 g, 2.40 mmol), and 1 (0.473 g, 2.09 mmol)
were reacted in MeOH as previously described, affording a very faintly
yellow powder. Yield 0.450 g (75.7%). Colorless, single crystals of 5
3JH−H = 6.6 Hz, 4H, CH(CH3)2), 6.71 (t, 3JH−H = 7.5 Hz, 2H, C6H4),
3
3
6.91 (d, JH−H = 7.5 Hz, 2H, C6H4), 6.98 (t, JH−H = 7.5 Hz, 2H,
C6H4), 7.85 (d, JH−H = 7.5 Hz, 2H, C6H4). 13C{1H} (CH2Cl2, 75
3
MHz): δ 19.1 (s, br, CH(CH3)2), 24.8 (s, br, CH(CH3)2), 122.8 (s,
C6H4), 129.8 (s, C6H4), 133.6 (s, C6H4), 135.1 (s, C6H4). 31P{1H}
(C7H8, 121 MHz) δ 19.4 ppm, (C7H8, −80 °C, 121 MHz) δ 14.9 ppm
1
were grown from a CH2Cl2/MeOH mixture. H NMR (C6D6, 300
3
3
MHz): δ 0.94 (dd, JP−H = 16 Hz, JH−H = 6.9 Hz, 12H, CH(CH3)2),
3
3
1
1.28 (dd, JP−H = 16 Hz, JH−H = 6.9 Hz, 12H, CH(CH3)2), 2.16 (m,
br, 4H, CH(CH3)2), 6.77 (m, 2H, C6H4), 6.95 (m, 4H, C6H4), 7.88
(m, 2H, C6H4). 1H{31P} (C6D6, 300 MHz): δ 0.94 (d, 3JH−H = 6.9 Hz,
(Pb satellites, JPb−P = 711 Hz). Anal. Calcd for C24H36P2S2Pb: C,
43.82; H, 5.52. Found: C, 44.40; H, 5.06. Mp 212−215 °C.
Synthesis of Pb{(SC6H4-2-PtBu2)-κ2-S,P}2 (10). PbCl2 (0.227 g,
0.82 mmol), NEt3 (0.190 g, 1.88 mmol), and 2 (0.415 g, 1.63 mmol)
were reacted in MeOH as previously described, affording a light-yellow
powder. Pale yellow single crystals were grown by slow diffusion of
3
12 H CH(CH3)2), 1.28 (d, JH−H = 6.9 Hz, 12 H CH(CH3)2), 2.16
(m, br, 4H, CH(CH3)2), 6.77 (m, 2H, C6H4), 6.95 (m, 4H, C6H4),
1
7.88 (m, 2H, C6H4). 13C{1H} (CH2Cl2, 75 MHz): δ 18.6 (d, JP−C
=
1
20 Hz, CH(CH3)2), 23.9 (s, CH(CH3)2), 122.8 (s, C6H4), 129.9 (s,
C6H4), 132.9 (s, C6H4), 133.1 (s, C6H4). 31P{1H} (C6D6, 121 MHz) δ
−2.87 ppm (s, Sn satellites, 1JSn1−P = 892 Hz). 119Sn{1H} (CH2Cl2, 112
MHz) δ −231.4 ppm (t, JP−Sn = 892 Hz). Anal. Calcd for
C24H36P2S2Sn: C, 50.63; H, 6.37. Found: C, 50.86; H, 6.25. Mp
190−192 °C.
pentane into toluene. Yield 0.323 g (55.4%). H NMR (CDCl3, 300
3
MHz): δ 1.41 (s, br, 36H, C(CH3)3), 6.84 (t, JH−H = 7.5 Hz, 2H,
3
3
C6H4), 7.14 (t, JH−H = 7.5 Hz, 2H, C6H4), 7.48 (d, JH−H = 7.5 Hz,
2H, C6H4), 7.59 (d, 3JH−H = 7.5 Hz, 2H, C6H4). 13C{1H} (CH2Cl2, 75
MHz): δ 30.3 (s, C(CH3)3), 36.9 (s, br, C(CH3)3), 121.8 (s, C6H4),
129.8 (s, C6H4), 136.2 (s, C6H4), 136.8 (s, C6H4). 31P{1H} (C7H8, 121
MHz) δ 59.4 ppm, (C7H8, −80 °C, 121 MHz) δ 31.1 ppm (Pb
Synthesis of Sn{(SC6H4-2-PtBu2)-κ2-S,P}2 (6). SnCl2 (0.123 g,
0.65 mmol), NEt3 (0.151 g, 1.49 mmol), and 2 (0.330 g, 1.30 mmol)
were reacted in MeOH as previously described, affording a faintly
yellow powder. Yield 0.358 g (88.2%). Colorless, single crystals of 6
1
satellites, JPb−P = 871 Hz). Anal. Calcd for C28H44P2S2Pb: C, 47.11;
H, 6.21. Found: C, 47.70; H, 5.73. Mp >220 °C.
Synthesis of Pb{(SC6H4-2-PPh2)-κ2-S,P}2 (11). PbCl2 (0.286 g,
1.00 mmol), NEt3 (0.226 g, 2.20 mmol), and 2-Ph2P(C6H4)SH (0.586
g, 1.99 mmol) were reacted in MeOH as previously described,
1
were grown from a CH2Cl2/MeOH mixture. H NMR (CDCl3, 300
MHz) δ 1.41 (m, br, 36H, C(CH3)3), 6.95 (m, 2H, C6H4), 7.15 (m,
2H, C6H4), 7.52 (m, 2H, C6H4), 7.63 (m, 2H, C6H4). 1H{31P}
(CDCl3, 300 MHz): δ 1.41 (s, 36H, C(CH3)3), 6.95 (m, 2H, C6H4),
7.15 (m, 2H, C6H4), 7.52 (m, 2H, C6H4), 7.63 (m, 2H, C6H4).
13C{1H} (CH2Cl2, 75 MHz): δ 27.5 (s, C(CH3)3), 29.8 (br,
C(CH3)3), 122.0 (s, C6H4), 129.5 (s, C6H4), 133.6 (s, C6H4), 135.7
(s, C6H4). 31P{1H} (CH2Cl2, 121 MHz) δ 16.8 ppm (s, Sn satellites,
1JSn−P = 896 Hz). 119Sn{1H} (CH2Cl2, 112 MHz) δ −204.3 ppm (t,
1JP−Sn = 896 Hz). Anal. Calcd for C28H44P2S2Sn: C, 53.77; H, 7.09.
Found: C, 53.97; H, 6.84. Mp >220 °C.
1
affording a yellow powder. Yield 0.414 g (41.2%). H NMR (CDCl3,
300 MHz): δ 6.70−7.70 (m, 28 H, C6H4 and C6H5). 13C{1H} (CDCl3,
75 MHz): δ 124.6, 128.6, 128.7, 129.3, 129.6, 133.4, 133.7, 133.9
(singlets, aromatic C). 31P{1H} (C7H8, 121 MHz) δ 9.73 ppm. Anal.
Calcd for C36H36P2S2Pb: C, 54.46; H, 3.55. Found: C, 55.12; H, 4.00.
Mp > 220 °C.
Synthesis of Sn{(SC6H4-2-PiPr2)-κ2-S,P}Ph2Cl (12). A solution of
Ph2SnCl2 (0.810 g, 2.36 mmol) in about 75 mL of MeOH was cooled
to −78 °C upon which a solution of 1 (0.533 g, 2.36 mmol) and NEt3
(0.274 g, 2.71 mmol) in 30 mL of MeOH was added dropwise over 30
min. Upon complete addition the reaction mixture was allowed to
warm to room temperature, where it stirred for 15 h. The resulting
white precipitate was isolated from the supernatant by filtration and
washed with Et2O (2 × 30 mL) and then dried at atmospheric
pressure for 2 h. Yield 0.752 g (59.8%). Colorless, single crystals of 12
Synthesis of Sn{(SC6H4-2-PPh2)-κ2-S,P}2 (7). SnCl2 (0.188 g,
0.99 mmol), NEt3 (0.228 g, 2.20 mmol), and 2-Ph2P(C6H4)SH (0.583
g, 1.98 mmol) were reacted in MeOH as previously described to afford
an off-white powder. Yield 0.621 g (68.5%). Colorless, single crystals
1
of 7 were grown from a CH2Cl2/MeOH mixture. H NMR (CDCl3,
3
3
300 MHz): δ 6.87 (d, JH−H = 7.4 Hz, 2H, PC6H4S), 6.97 (t, JH−H
=
3
1
7.4 Hz, 2H, PC6H4S), 7.06 (t, JH−H = 7.4 Hz, 2H, PC6H4S), 7.18 (d,
3JH−H = 7.4 Hz, 2H, PC6H4S), 7.35−7.48 (m, 20H, C6H5). 13C{1H}
(CDCl3, 75 MHz): δ 124.2, 128.7, 129.6, 129.9, 131.3, 133.1, 133.5,
133.7, and 149.7 (singlets, aromatic C). 31P{1H} (CDCl3, 121 MHz) δ
were grown from a CH2Cl2/MeOH mixture. H NMR (C6D6, 300
MHz): δ 0.81 (dd, 3JP−H = 16.8 Hz, 3JH−H = 7.2 Hz, 6H, CH(CH3)2),
1.11 (dd, 3JP−H = 16.8 Hz, 3JH−H = 7.2 Hz, 6H, CH(CH3)2), 2.49 (sept
2
3
of d, JP−H = 2.7 Hz, JH−H = 7.2 Hz, 2H, CH(CH3)2), 6.6−6.8 (m,
−2.10 ppm (s, Sn satellites, JSn−P = 640 Hz). 119Sn{1H} (C6H6, 112
1
2H, PC6H4S), 6.93 (m, 1H, PC6H4S) 7.05−7.30 (m, 6H, CPhHm, p),
7.86 (m, 1H, PC6H4S), 8.58 (d, Sn satellites, JH−H = 1.2 Hz, 3JSn−H
=
3
MHz) δ −135.0 (t, 1JP−Sn = 640 Hz). Anal. Calcd for C36H36P2S2Sn: C,
61.30; H, 4.00. Found: C, 60.81; H, 3.94. Mp 163−165 °C.
92 Hz, 4H, CPhHo). 13C{1H} (CH2Cl2, 75 MHz): δ 17.4 (s, C(CH3)2),
1
Synthesis of Sn{(OC6H4-2-PtBu2)-κ2-O,P}2 (8). Solid SnCl2
(0.199 g, 1.05 mmol) was added to a stirred solution of NEt3
(0.244 g, 2.41 mmol) and 2-tBu2P(C6H4)OH (0.500 g, 2.10 mmol)
in about 25 mL of MeOH at room temperature. An immediate
17.9 (s, C(CH3)2), 24.7 (d, JP−C = 18 Hz, C(CH3)2), 123.7, 128.6,
129.6, 131.9, 133.0, 136.0, 142.9 (singlets, all aromatic C). 31P{1H}
(C6D6, 121 Hz) δ 10.8 ppm (s, JSn−P = 637 Hz). 119Sn{1H} (C6D6,
1
1
112 MHz) δ −239.3 ppm (d, JP−Sn = 637 Hz). Anal. Calcd for
C
dx.doi.org/10.1021/ic400990n | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Table 1. Crystallographic Data and Parameters for Divalent Metal Complexes 3−10
3
4
5
6
7
8
9
10
empirical
formula
C24H36P2S2Zn
C28H44P2S2Zn
C24H36P2S2Sn
C28H44P2S2Sn
C36H28P2S2Sn
C28H44O2P2Sn
C24H36P2PbS2
C28H44P2PbS2
FW
515.96
173(2)
572.06
173(2)
569.28
625.38
173(2)
705.33
173(2)
593.26
100(2)
657.78
173(2)
713.88
173(2)
T, K
172(2) K
cryst size (mm) 0.51 × 0.32 ×
0.31 × 0.25 ×
0.15
0.35 × 0.28 ×
0.14
0.30 × 0.21 ×
0.18
0.34 × 0.27 ×
0.20
0.26 × 0.16 ×
0.14
0.65 × 0.48 ×
0.44
0.41 × 0.37 ×
0.31
0.23
cryst syst
space group
a, Å
monoclinic
P2(1)/n
7.9370(2)
15.6717(4)
21.0443(5)
90.00
monoclinic
C2/c
monoclinic
P2(1)/c
11.6509(13)
15.1676(17)
15.5835(19)
90.00.
monoclinic
P2(1)/c
15.6438(7)
12.3176(6)
16.1013(6)
90.00
triclinic
monoclinic
P2(1)/c
17.6554(15)
12.5442(10)
14.4723(11)
90.00
monoclinic
P2(1)/c
11.6851(6)
15.2737(9)
15.4587(9)
90.00
monoclinic
P2(1)/c
12.6418(2)
15.5866(3)
16.0995(3)
90.00
P1
̅
26.861(2)
8.0179(7)
15.7280(13)
90.00
9.7365(11)
9.8591(11)
19.280(2)
100.037(4)
90.502(4)
118.155(4)
1597.9(3)
2
b, Å
c, Å
α, deg
β, deg
γ, deg
vol, Å3
Z
98.8210(10)
90.00
122.853(5)
90.00
96.802(6).
90.00.
103.031(2)
90
113.782(5)
90.00
96.519(3)
90.00
106.7510(10)
90
2586.66(11)
4
2845.6(4)
4
2734.5(5)
4
3022.7(2)
4
2933.1(4)
4
2741.1(3)
4
3037.68(9)
4
calcd density
1.325
1.335
1.383
1.374
1.466
1.343
1.594
1.561
(g/cm3)
μ, mm−1
1.244
1.138
1.213
1.104
1.055
1.002
6.433
5.811
a
R1 [I > 2σ(I)] 0.0312
wR2 0.0749
[I > 2σ(I)]
0.0402
0.1068
0.0237
0.0647
0.0669
0.1803
0.0318
0.0904
0.0618
0.1466
0.0219
0.0527
0.0221
0.0485
b
a
b
2
2
R1 = ∑||Fo| − |Fc||/∑|Fo|. wR2 = {∑[w(Fo − Fc2)2]/∑[w(Fo )2]}1/2
.
C24H28ClPSSn: C, 54.01; H, 5.29. Found: C, 53.07; H, 5.29. Mp 140−
142 °C.
Atmospheric Pressure CO2 Reactions. In separate reactions,
CO2 was bubbled through solutions of 3−7 and 9−15 (ca. 50−150
mg) dissolved in about 20 mL of CH2Cl2 for 1 h. The solutes from the
resulting solutions were deposited on KBr plates by evaporation in an
Ar atmosphere and then examined by FT-IR spectroscopy for the
presence of new stretches in the CO region not seen in samples
prior to CO2 bubbling.
Crystallographic Studies. The crystals (3−10, 12, 13, and 15)
were coated with Paratone-N oil and were mounted on the nylon fiber
of a CryoLoop that had been previously attached to a metallic pin
using epoxy. The data were collected at the temperatures indicated in
the tables using a Bruker X8 Apex II diffractometer using
monochromated Mo Kα radiation (λ = 0.71073 Å). Data collection
and processing were done using the APEX2 software suite.34 The
structures were solved using direct methods and refined with the full-
matrix least-squares method on F2 with SHELXTL.35 The non-
hydrogen atoms were refined anisotropically. Hydrogen atoms were
included at geometrically idealized positions and were not refined. The
isotropic thermal parameters of the hydrogen atoms were fixed at 1.5U
equiv. of parent atom for methyl group hydrogens and 1.2U equiv. for
all others. All final crystallographic figures shown in this document
were generated by Diamond, v. 3.2i.36 Crystallographic data are given
in Tables 1 and 2.
Synthesis of Sn{(SC6H4-2-PtBu2)-κ2-S,P}Ph2Cl (13). Ph2SnCl2
(0.656 g, 1.91 mmol), 2 (0.485 g, 1.91 mmol), and NEt3 (0.222 g, 2.19
mmol) were reacted in MeOH as previously described for the
synthesis of 12, affording a white powder. Yield 0.815 g (76.1%).
Colorless, single crystals of 13 were grown from a CH2Cl2/MeOH
mixture. 1H NMR (CDCl3, 300 MHz): δ 1.32 (d, 3JP−H = 14.7 Hz, 9H,
3
C(CH3)3), 1.36 (d, JP−H = 14.7 Hz, 9H, C(CH3)3) doublets at 1.32
and 1.36 ppm overlap, 7.0−8.3 (m, 14 H, PC6H4S and C6H5). 13C{1H}
(CH2Cl2, 75 MHz): δ 29.5 (s, br, C(CH3)2), 37.1 (s, br, C(CH3)2),
123.3, 128.9, 129.7, 131.1, 134.8, 135.7, 145.6 (singlets, all aromatic
1
C). 31P{1H} (CH2Cl2, 121 Hz): δ 20.5 (s, Sn satellites, JSn−P = 389
Hz), 71.2 (s, Sn satellites, 4JSn−P = 67 Hz). 31P{1H} (solid state) δ 12.9
1
(s, Sn satellites, JSn−P = 1030 Hz). 119Sn{1H} (CH2Cl2, 112 MHz): δ
−260.6 (s, br), −264.4 (s, br). Anal. Calcd for C26H32ClPSSn: C,
55.59; H, 5.74. Found: C, 54.67; H, 5.47. Mp 186−189 °C.
Synthesis of [Sn{(SC6H4-2-PiPr2)- κ2-S,P}Ph2][BPh4] (14). Solid
NaBPh4 (0.277 g, 0.81 mmol) was added to a flask containing a
solution of 12 (0.431 g, 0.81 mmol) dissolved in about 40 mL of
CH2Cl2, resulting in a white slurry. This mixture was stirred for 15h at
room temperature. The mixture was then filtered through Celite filter
aid, and the resulting filtrate had the volatile components removed in
Computational Studies. Density functional theory (DFT)
calculations were performed with ADF 2012.01.37−39 The PBE GGA
functional was used with an all-electron triple-ζ basis set (TZP).40
Scalar relativistic effects were included self-consistently with the ZORA
Hamiltonian .41−43 Computational results were interpreted with the
Natural Bond Order (NBO v5.0) package incorporated into ADF.44,45
1
vacuo, resulting in a white powder. Yield 0.556 g (84.1%). H NMR
(CD2Cl2, 300 MHz): δ 0.87 (m, br, 6H, CH(CH3)2), 1.14 (m, br, 6H,
CH(CH3)2), 2.59 (m, br, 2H, CH(CH3)2), 6.85−7.85 (m, 34H,
aromatic H). 11B{1H} (CH2Cl2, 96 MHz) δ −4.80. 31P{1H} (CH2Cl2,
121 Hz) δ 27.2 (s, Sn satellites, 1JSn−P = 187 Hz). 119Sn{1H} (CH2Cl2,
1
112 MHz) δ −129.7 (d, JP−Sn = 187 Hz). Anal. Calcd for
C48H48BPSSn: C, 70.53; H, 5.92. Found: C, 65.90; H, 5.80. Mp
138−140 °C.
RESULTS AND DISCUSSION
■
Synthesis of [Sn{(SC6H4-2-PtBu2)- κ2-S,P}Ph2][BPh4] (15).
NaBPh4 (0.248 g, 0.72 mmol) and 13 (0.400 g, 0.72 mmol) were
reacted in CH2Cl2 as previously described for 14. Yield 0.516 g
(85.1%). Colorless, single crystals of 15 were grown from a CH2Cl2/
Preparation and Characterization of M(II) Complexes.
The previously uncharacterized 2-iPr2P(C6H4)SH (1) and
unreported 2-tBu2P(C6H4)SH (2) ligands were prepared in
an analogous manner to procedures by Block et al.32 and Figuly
et al.46 for the synthesis of 2-Ph2P(C6H4)SH. Thiophenol can
be ortho-dilithiated by nBuLi in the presence of TMEDA
followed by the addition of the R2PCl species, and the final
product is obtained upon acidification. The literature procedure
1
3
hexanes mixture. H NMR (CD2Cl2, 300 MHz): δ 1.33 (d, JP−H
=
17.4 Hz, 18H, C(CH3)3), 6.80−8.00 (m, 34H, aromatic H). 11B{1H}
(CH2Cl2, 96 Hz) δ −6.91. 31P{1H} (CH2Cl2, 121 MHz) δ 53.9 (s, Sn
satellites, JSn−P = 130 Hz). 119Sn{1H} (CH2Cl2, 112 MHz) δ −66.50
1
(d, 1JP−Sn = 130 Hz). Anal. Calcd for C50H52BPSSn: C, 71.03; H, 6.20.
Found: C, 69.73; H, 6.09. Mp 153−156 °C.
n
followed indicated a 10% excess of BuLi in the first step was
D
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Inorganic Chemistry
Article
after washing. Some product is lost in the filtrate, as all products
have some solubility in MeOH, but given the synthetic ease and
resulting purity of the products, the loss is tolerable. For
complexes 3−7 and 9, suitable crystals for single crystal X-ray
diffraction were grown from a CH2Cl2/MeOH mixed solvent
system at −18 °C, while crystals for complex 10 were grown by
slow vapor diffusion of pentane into a toluene solution.
Although crystalline samples of 11 were obtained, none were of
sufficient quality to allow structure determination.
Table 2. Crystallographic Data and Parameters for Sn(IV)
complexes 12, 13, and 15
12
13
15
empirical formula C24H28 ClPSSn C26H32ClPSSn
C100H104B2P2S2Sn2
1690.89
FW
533.63
173(2)
561.69
173(2)
T, K
173(2)
cryst size (mm)
0.57 × 0.31 × 0.24 × 0.15 ×
0.51 × 0.34 × 0.09
0.18
0.12
cryst syst
space group
a, Å
triclinic
monoclinic
P2(1)/n
9.0291(9)
18.6489(19)
15.7053(14)
90.00
triclinic
Multinuclear NMR data were collected for species 3−7 and
9−11; all showing singlets (−2.87 to 39.5 ppm) in the 31P{1H}
spectra, thus indicating chemically equivalent phosphorus
nuclei on adjacent ligands in the solution phase. For the Sn
P1
̅
P1
̅
9.0010(3)
10.4139(4)
13.3513(5)
87.573(2)
74.666(2)
76.296(2)
1172.31(7)
2
11.4110(16)
17.150(2)
22.365(2)
78.620(7)
89.925(7)
82.993(8)
4257.5(9)
2
b, Å
c, Å
1
complexes 5−7, corresponding JSn−P coupling were observed
α, deg
β, deg
γ, deg
vol, Å3
Z
in both the 119Sn{1H} and the 31P{1H} spectra with values of
892, 896, and 640 Hz, respectively, demonstrating P−Sn
interaction in solution. The relative values of these coupling
constants are congruent with what is expected based on the
relative basicity of the P lone pair interacting with the acidic Sn
center (-PR2: tBu > iPr > Ph). The 119Sn{1H} shifts for 5−7 are
−231.4, −204.3, and −135.0 respectively. The more downfield
position of 7 can be rationalized by the relatively weaker
basicity of the phosphine groups because of the presence of
electron-withdrawing phenyl groups, leading to a more
deshielded Sn center. When comparing 5 and 6, basicity
alone would anticipate a more upfield shift for 6, but with 6
having slightly bulkier alkyl groups, sterics lead to slightly
longer Sn−P bonds and a more deshielded Sn center.
101.863(6)
90.00
2588.0(4)
4
calcd density
1.512
1.442
1.319
(g/cm3)
μ, mm−1
1.369
1.244
0.720
a
R1 [I > 2σ(I)]
0.0326
0.0501
0.0549
b
wR2 [I > 2σ(I)] 0.0780
0.1276
0.1442
a
b
2
2
R1 = ∑||Fo| − |Fc||/∑|Fo|. wR2 = {∑[w(Fo − Fc )2]/
2
∑[w(Fo )2]}1/2
.
needed to produce 1-SLi-2-LiC6H4. Several years later it was
found that the addition of another equivalent of nBuLi to 1-SLi-
2-LiC6H4 produces a trilithiated cluster [Li3{(2-S-C6H4)-
(CH2MeNCH2CH2Me2)(TMEDA)}]2, containing a deproto-
nated TMEDA.47 We suspected that even using the 10% excess
might produce the trilithiated thiophenol as a side product, and
this suspicion was confirmed when crystals of the trilithiated
cluster were grown from the supernatant of our dilithiation
route. While the presence of the trilithiated thiophenol did not
prevent pure products from being obtained, it did lead to
somewhat lowered yields. Isolation of analytically pure
2-iPr2P(C6H4)SH (1) and 2-tBu2(C6H4)SH (2) were achieved
by vacuum distillation while 2-Ph2P(C6H4)SH was purified by
recrystallization.32
Room temperature 31P{1H} NMR spectra of the Pb samples
(9−11) all revealed singlets at 19.4, 59.4, and 9.73 ppm,
respectively, surprisingly devoid of Pb satellites. Additionally,
despite extensive run times, no 207Pb NMR peaks could be
detected for any of the Pb samples. The lack of distinct peaks
could be indicative of a dynamic process between having the P
in the bound and unbound states, which could broaden the
207Pb signals to undetectable levels and is likely why Pb
satellites were not observed. To probe this further, low-
temperature (−80 °C) 31P and 207Pb NMR spectra were
recorded for all three samples. Upon cooling, Pb satellites could
easily be seen in the 31P{1H} NMR spectra for compounds 9
and 10 (1JPb−P 711 and 871 Hz, respectively); however, no
satellites were observed in 11, attributable to the relative
decrease in basicity caused by the electron-withdrawing phenyl
groups. The appearance of Pb satellites upon cooling in 9 and
10 is consistent with ligand hemilability, and is not surprising
given the weak Lewis acidity of Pb(II). Again, even after
extensive run times, no peaks were observed in the 207Pb NMR
spectra.
In the syntheses of the divalent metal complexes reported
here, the addition of MCl2 (M = Zn, Sn, and Pb) to a solution
i
t
of 2-R2P(C6H4)SH (R = Pr, Bu, and Ph) and excess NEt3 in
MeOH at room temperature resulted in an instantaneous
reaction for both ZnCl2 and SnCl2, whereas the PbCl2 reactions
took a few minutes likely because of the relatively low solubility
of PbCl2 in MeOH (Scheme 1). Each product precipitates from
methanol and can be isolated as an analytically pure product
Figure 1. Molecular structures of 5 (a) and 9 (b) (50% ellipsoids). Hydrogen atoms omitted for clarity. Selected bond lengths (Å) and angles (deg).
5 (a): Sn(1)−P(1) 2.7936(5), Sn(1)−P(2) 2.8686(6), Sn(1)−S(1) 2.5481(6), Sn(1)−S(2) 2.5462(5), P(1)−Sn(1)−P(2) 139.340(16), S(1)−
Sn(1)−S(1) 105.516(18). 9 (b): Pb(1)−P(1) 2.8705(5), Pb(1)−P(2) 2.9594(5), Pb(1)−S(1) 2.6344(6), Pb(1)−S(2) 2.6277(5), P(1)−Pb(1)−
P(2) 137.797(15), S(1)−Pb(1)−S(2) 103.103(17). Visualization of the planes used to calculate the fold angle can be seen in (b).
E
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Inorganic Chemistry
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Phosphorus-decoupled proton NMR experiments were
performed on samples 4, 5, and 6 to help assign coupling
constants for the alkyl signals in the nondecoupled spectra. In
both samples 4 and 6, a singlet resulted in the decoupled
spectra indicating that all t-butyl groups are chemically
Figure S3) we observed large fold angles (35−52°), but since
we are dealing with s and p block main-group metals there must
be an alternate explanation for the folding. Full DFT
calculations were performed on compounds 5, 6, 9, and 10
to gain insight on the observed ligand folding. Each of the
calculations revealed identical causality, and as such only
calculation results for compound 5 are discussed here.
3
equivalent and that splitting is in fact due to JP−H coupling.
In the coupled spectrum of 5, the diastereotopic methyl
hydrogens on the isopropyl groups led to two doublets of
doublets, with coupling of the methyl groups to both the
methine hydrogen and the phosphorus. The decoupled spectra
simplified to two doublets, both with coupling constants of 6.9
Hz (3JH−H), revealing that the constant of 16 Hz in the
Ligand folding caused by steric effects from crystal packing
was ruled out as geometry optimized calculations of complex 5
in the gas phase resulted in virtually no change in ligand fold
angles. Using the crystal structure geometry as a template, the
fold angle was changed to zero degrees and a single point DFT
calculation was performed on this unfolded geometry so that
direct comparisons of the electronic structures could be made
between the folded and unfolded forms. Calculations reveal a
total stabilization of 52 kcal/mol upon ligand folding in
compound 5, indicating that ligand folding is thermodynami-
cally favorable. To determine the electronic nature of the
stabilization, the NBOs (natural bond orbitals) were analyzed
to determine individual orbital contributions. Several distinct
contributions to the stabilizations were found to be important.
First, an increase in sulfur/metal p-orbital overlap was seen with
a subsequent 8 kcal/mol stabilization of the sulfur−metal σ
bond. Metal dithiolenes are also known to behave in such a
manner, often with large fold angles and significant metal−
ligand covalency.65 However, unlike metal-dithiolenes this
orbital overlap is not the largest contributor to folding in the
compounds studied here; rather, lone pair repulsion
interactions are found to be most important. The largest
repulsion is due to an interaction between the phosphorus and
metal lone pair orbitals (Figure 2). This repulsion is lowered
upon bending by a rotation of the phosphorus lone pair,
resulting in a surprisingly large ∼30 kcal/mol stabilization. A
smaller stabilization (∼5 kcal/mol) is also found by the
reduction in overlap of the sulfur and metal lone pairs (Figure
2). In summary, NBO analysis of the DFT results leads to a
description in the ligand fold being driven by (1) metal-S
covalency, (2) metal-P lone pair repulsion, and (3) metal-S
lone pair repulsion.
3
nondecoupled spectrum was due to JP−H coupling.
From the crystal structures (Figures 1, 3, Supporting
Information, Figures S2 and S3), the geometry of the metal
centers in the Sn(II) and Pb(II) complexes (5−7, 9, and 10)
can all be similarly described as highly distorted trigonal
bipyramidal with the axial positions being occupied by the P
atoms and the equatorial positions by the two S atoms and one
by the Sn or Pb lone pair. None of the bond lengths or angles
in the structures of 5−7, 9, and 10 are particularly unexpected
or out of the ordinary. Structurally characterized divalent metal
benzenethiolates, particularly with transition metals, are
extremely common, and hundreds of main group metal
benzenethiolates have also been subjected to single crystal X-
ray analysis. The most similar structurally characterized
complexes to 5−7, 9, and 10, in which the benzenethiolate
contains an ortho-PR2 moiety, are the related species reported
by Zubieta et al.25,26 or Morales-Morales et al.30 For our
complexes 5−7, the Sn−S bond lengths fall in the range of
2.47−2.57 Å, quite similar to previous values of 2.473(3),30
2.494(1), and 2.503(1) Å reported earlier.26 As well, our Pb−S
bond lengths for 9 and 10 are in the range of 2.60−2.63 Å,
essentially identical to earlier values of 2.6439(8) and
2.6462(7) Å from Zubieta et al..25
Upon further scrutiny of the crystal structures of these
compounds, it was noticed that significant fold angles,
reminiscent of those found in transition-metal dithiolenes,48−50
were formed in the chelate rings. In these structures, the fold
angle can be described as the acute angle formed between the
M−S−P plane and the least-squares plane formed by S−C
C−P, with folding along the S−P vector (Figure 1). There are
stark differences, however, between the system reported here
and the aforementioned dithiolenes. The most obvious
difference is that the dithiolenes are dianionic with two sulfurs
as opposed to monoanionic with one sulfur and one
phosphorus, as in our system. The other main difference is
the nature of the metal centers: reports of dithiolenes with
significant fold angles (<30°) are limited to early transition
metals (M = Ti, Zr, Hf, V, Nb, Mo, and W),48−62 and
lanthanides/actinides (Ce, Nd, and U),63,64 while our
complexes are based on main-group metals.
To gain more perspective on the significance of the sulfur/
metal lone pair repulsion, the phenolate analogue 8 was
prepared to determine how contracting the chalcogenide lone
pair, and presumably decreasing lone pair repulsion, would
affect the ligand folding. By replacing the S in 6 with O in 8, a
significant average fold angle decrease from 41.02 to 0.29
degrees was observed in the crystal structures (Figure 3). This
dramatic decrease in fold angle is likely due to the oxygen/
metal interaction leading to a relative decrease in metal/
chalcogenide covalency.
With a more ionic chalcogenide/metal interaction one would
expect a relative decrease in electron density and subsequent
increase in Lewis acidity of the Sn center. This increase in
acidity allows for a stronger Lewis acid−base interaction that is
reflected in the shorter Sn−P bond lengths (2.84 and 2.87 Å)
Early transition-metal dithiolenes are reported to be
stabilized by the bonding interaction of the lone pairs in filled
Sπ orbitals with an unoccupied Md orbital that shares the M−
S−S plane, the same interaction that gives rise to the
folding.48−50,59 The availability of a geometrically suited,
unoccupied d orbital is the feature that limits the folding
action to early transition metals (d0 and d1) and f element
metals. Most transition-metal dithiolenes have fold angles less
than 15° because of filled d-orbitals in the M−S−S plane.50
Upon examination of the crystal structures of compounds 5 and
9 (Figure 1), 6 (Figure 3), and 10 (Supporting Information,
1
and the larger JSn−P coupling constant (1256 Hz). Also, the
stronger P lone pair donation shields the Sn center leading to a
more upfield shift in the 119Sn{1H} NMR (−301.0 ppm).
The diphenyl analogue 7 also shows a significant structural
difference from 5, 6, and 8 by exhibiting negative fold angles
(average angle −44.11°). This geometry seen in the crystal
structure can be attributed to π−π interactions between phenyl
rings on adjacent ligands (Supporting Information, Figure S2)
F
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around the Zn atom (Figures 4 and Supporting Information,
Figure S1) and also have relatively small fold angles (28.48 and
Figure 4. Molecular structure of 4 (50% ellipsoids). Hydrogen atoms
omitted for clarity. Selected bond lengths (Å) and angles (deg).
Zn(1)−P(1) 2.4225(9), Zn(1)−S(1) 2.3143(10), S(1)−Zn(1)−P(1)
90.14(3), S(1)−Zn(1)−S(1′) 117.87(6), P(1)−Zn-P(1′) 132.97(5),
S(1)−Zn(1)−P(1′) 114.16(3).
18.78° for 3 and 14.39° for 4). Again, all of the bond distances
seen in 3 and 4, including the directly bound atoms to Zn, fall
in typically seen ranges and as such do not require any further
comment.23 The low fold angles observed in the crystal
structures of 3 and 4 are consistent with our earlier findings
suggesting that metal−sulfur and metal−phosphorus lone pair
repulsions are the driving force behind large ligand fold angles.
Only one fold angle is reported for 4 as it crystallized in the
C2/c space group with a 2-fold rotation axis through the metal
center.
Complexes 3−7 and 9−11 (as well as 12−15 described
later) were reacted with gaseous CO2 to attempt to form either
CO2 adducts or fully inserted products. The main group
complexes were treated with bubbling CO2 in CH2Cl2 solvent
for 1 h at atmospheric pressure. Removal of the solvent
followed by infrared spectroscopic characterization of the
remaining solid product indicated no evidence of CO2 addition
to or reaction with the starting complexes. Characteristic C−O
or CO stretches were not present in the final products. This
lack of reactivity was quite unexpected to us based on our
previous work with other main group complexes,17 but it may
indicate the (undesired, in our case) strengths of the metal-
heteroatom bonds in these various main group heterocyclic
complexes.
Figure 2. Calculated NBO orbitals for the Sn and P lone pairs on
complex 5 in both the unfolded (a) and the folded geometries (b), and
NBO orbitals for the Sn and S lone pairs on complex 5 in both the
unfolded (c) and the folded geometries (d). Stick figure
representations are shown to emphasize the rotation of both the P
and S lone pairs upon ligand folding.
Preparation and Characterization of Neutral Sn(IV)
Complexes. The surprising lack of CO2 reactivity in the
Zn(II), Sn(II), and Pb(II) complexes 3−7 and 9−11 just
mentioned encouraged us to seek alternate complexes using the
same ligands, but with more acidic main group metal centers.
Moving in this direction was prompted by the aforementioned
work of Chapman et al. in which a cationic Zr(IV) complex
employing an analogous phenolate ligand exhibited CO2
reactivity.18 As well, targeting a cationic Sn(IV) complex was
viewed as ideal as it allows for direct comparisons with the
Sn(II) complexes 5−7. To obtain our targeted cationic Sn(IV)
complex, we first needed to synthesize neutral Sn(IV) precursor
complexes with labile chlorine substituents. These precursors
revealed some interesting features meriting discussion separate
from the targeted cationic Sn(IV) complexes.
Figure 3. Molecular structures of 6 (a) and 8 (b) (50% ellipsoids).
Hydrogen atoms omitted for clarity. Selected bond lengths (Å) and
angles (deg). 6 (a): Sn(1)−P(1) 2.9217(19), Sn(1)−P(2) 3.0172(6),
Sn(1)−S(1) 2.521(2), Sn(1)−S(2) 2.513(2), P(1)−Sn(1)−P(2)
152.002(10), S(1)−Sn(1)−S(1) 100.62(13). 8 (b): Sn(1)−P(1)
2.8444(16), Sn(1)−P(2) 2.8697(14), Sn(1)−O(1) 2.082(4),
Sn(1)−O(2) 2.087(5), P(1)−Sn(1)−P(2) 145.00(5), O(1)−Sn(1)−
O(2) 95.79(19).
For the syntheses of monoligated complexes 12 and 13, a
solution of either 1 or 2 in methanol was added dropwise to a
stirred solution of Ph2SnCl2 and excess NEt3, also in methanol,
at −78 °C. An immediate reaction took place, resulting in the
precipitation of the product as a white solid. As compared to
reactions using Sn(II) described above, both lower temper-
with C−C distances between 3.5 and 3.6 Å, well within the
normal range seen for such interactions.
Unlike the Sn(II) and Pb(II) complexes, the Zn(II)
complexes 3 and 4 have no lone pair on the metal and as
such adopt distorted tetrahedral coordination environments
G
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atures and slow addition of the phosphinobenzenethiol were
required to avoid adding two ligands to the tin center.
Interestingly, when targeting the diphenyl analogue of 12 and
13 using 2-Ph2P(C6H4)SH under the same conditions, only the
previously reported27 doubly ligated compound Sn{(SC6H4-2-
PPh2)-κ-S}2Ph2 was formed.
The crystal structures of 12 and 13 revealed in both cases a
distorted trigonal bipyramidal geometry around the tin atom. In
both cases, the Cl occupies an axial position while both phenyl
groups are in equatorial positions. Interestingly, a major
difference occurs in the chelating ligand, as the P in 12 is in
the equatorial position while in 13 it is found in the axial
position (Figure 5).
comparison as its Sn−P interaction is relatively stronger than
that of 13, as indicated by its shorter Sn−P bond length, its
sharp signal in the 31P NMR spectrum, and the absence of a
second resonance in its 119Sn and 31P NMR spectra. The sharp
signal at 71.2 ppm has a small coupling constant of 67 Hz,
4
which if unbound would be a JSn−P coupling. A paper by
Weichmann et al.66 reported JSn−P coupling constants of 35
4
and 53 Hz in two similar Sn(IV) complexes. These complexes
have phosphine ligands that are unbound in solution, but
chelating in the solid state, as in complex 13 described above.
The similarity in these values is additional evidence that the
signal at 71.2 ppm is caused by an unbound P atom. Finally, to
further substantiate the hemilability of the P,S chelate in 13, a
solution 31P NMR spectrum was taken in the presence of a
competing Lewis base. When pyridine was introduced into a
solution of 13 in CH2Cl2, there was a drastic change in the
relative signal intensity ratios (Supporting Information, Figure
S4). The signal at 71.2 ppm became far more intense relative to
the signal at 20.5 ppm after introduction of pyridine, indicative
of an increase in concentration of unbound P. When pyridine
was introduced in solution with 12, no change in the 31P NMR
could be detected, indicating that pyridine could not compete
with the strongly bound chelating phosphine for coordination
to the tin.
Preparation and Characterization of Cationic Sn(IV)
Complexes. Since complexes 12 and 13 had labile chlorine
groups and an ancillary phosphinobenzenethiol ligand, the
opportunity for the formation of stable Sn(IV) cations by
halide abstraction seemed reasonable. Cations of heavier group
14 elements have garnered a lot of attention in recent
years,67−69 and the ability to isolate and characterize these
cations has been aided by the development of robust, weakly
coordinating anions, and/or ligands with high steric bulk.68,70
Sn(IV) compounds, being Lewis acids and with the potential
for hypercoordination, are particularly electrophilic.71−73 This
feature makes isolating cationic, coordinatively- and electroni-
cally unsaturated Sn(IV) species somewhat difficult. As such,
there are only limited examples of isolated tricoordinate
cationic Sn(IV) species,68,69,74 each implementing steric bulk
around the metal center to achieve ion stabilization. Examples
of cationic Sn(IV) species with higher coordination numbers
(>4) are much more common and often occur with stabilizing,
tridentate ligands.71,75,76 Tetracoordinate Sn(IV) cationic
complexes, however, are scarce with only a few structurally
characterized compounds available.77−79 Of these compounds,
only one prior example is monomeric, and with only one metal
center ([LCN(nBu)2Sn]+[Ti2Cl9]−, LCN = 2-(N,N-
dimethylaminomethyl)phenyl).77 We have synthesized and
structurally characterized a second example of this structural
type by reacting 13 with NaBPh4 in CH2Cl2 at room
temperature for 15 h (Scheme 2 and Figure 6).
Figure 5. Molecular structures of 12 (a), and 13 (b) (50% ellipsoids).
Hydrogen atoms omitted for clarity. Selected bond lengths (Å) and
angles (deg). 11 (a): Sn(1)−P(1) 2.5564(3), Sn(1)−S(1) 2.5813(3),
Sn(1)−Cl(1) 2.5438(3), Cl(1)−Sn(1)−S(1) 166.260(11), P(1)−
Sn(1)−S(1) 79.906(10), C(19)−Sn(1)−C(13) 119.61(4), C(19)−
Sn(1)−P(1) 119.54(3), C(13)−Sn(1)−P(1) 120.81(3). 12 (b):
Sn(1)−P(1) 2.869(2), Sn(1)−S(1) 2.4292(17), Sn(1)−Cl(1)
2.5148(18), Cl(1)−Sn(1)−P(1) 159.44(6), S(1)−Sn(1)−P(1)
79.03(5), C(7)−Sn(1)−C(1) 115.3(2), C(7)−Sn(1)−S(1)
115.50(17), C(1)−Sn(1)−S(1) 129.12(19).
This difference in position of the P atom significantly
changes the donor−acceptor characteristics of the Sn−P bond
as evident from the Sn−P bond lengths and from the NMR
spectra. In compound 12, the P atom is in the equatorial plane
with a Sn−P bond length of 2.5564(3) Å and a 1JSn−P coupling
constant of 637 Hz, showing sharp singlets in both the 119Sn
and 31P NMR spectra. This is in clear contrast to 13, which
crystallizes with the P in the axial position and has a
significantly longer Sn−P bond length of 2.869(2) Å. The 31P
NMR spectrum of analytically pure 13 shows two resonances:
one very broad signal at 20.5 ppm and a sharp signal singlet at
71.2 ppm (Supporting Information, Figure S4). To confirm
that the signals were coming from the same compound, a solid
state 31P NMR experiment was performed and revealed only
one resonance at 12.9 ppm, indicating that in solution the Sn−
P interaction is in fact dynamic.
The two signals showed differences in both resolution and in
the Sn−P coupling constants. The broad signal at 20.5 ppm has
a coupling constant of 389 Hz, while the sharp signal at 71.2
ppm has a coupling constant of 67 Hz. This is indicative of
hemilability in the phosphine, where the signal at 20.5 ppm is
consistent with the P in a weakly bound state and the signal at
71.2 ppm being unbound. The broadness of the signal and the
larger coupling constant in the signal at 20.5 ppm supports this
notion. A weakly bound P is more likely to become unbound in
solution, and the coupling constant between P and Sn should
reflect this as smaller in magnitude than a strongly bound P.
The Sn−P coupling constant of 12 (637 Hz) serves as a good
Scheme 2. Reaction Pathway for the Formation of 14 and 15
H
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ASSOCIATED CONTENT
* Supporting Information
■
S
Thermal ellipsoid plots of compounds 3, 7, and 10, and 31P
NMR spectra for compound 13. Crystallographic data in CIF
format for compounds 3−10, 12, 13, and 15 (CCDC 929503−
929513). This material is available free of charge via the
Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: rakemp@unm.edu.
■
Figure 6. Molecular structure of 15 (50% ellipsoids). Hydrogen atoms
omitted for clarity. Selected bond lengths (Å) and angles (deg).
Sn(1)−P(1) 2.522(2), Sn(1)−S(1) 2.401(2), P(1)−Sn(1)−S(1)
87.89(8).
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was financially supported by the National Science
Foundation (Grants CHE09-11110 and CHE12-13529) and in
part by the Laboratory Directed Research and Development
(LDRD) program at Sandia National Laboratories (LDRD
151300). The Bruker X-ray diffractometer was purchased via a
National Science Foundation CRIF:MU award to the
University of New Mexico (CHE04-43580), and the NMR
spectrometers were upgraded via grants from the NSF
(CHE08-40523 and CHE09-46690). Sandia National Labo-
ratories is a multiprogram laboratory managed and operated by
Sandia Corporation, a wholly owned subsidiary of Lockheed
Martin Corporation, for the United States Department of
Energy’s National Nuclear Security Administration under
Contract DE-AC04-94AL85000.
Attempts to grow single crystals suitable for the structure
determination of 14 were not successful; however, NMR data
and elemental analysis are consistent with the targeted product
−
shown in Scheme 2. The choice of BPh4 as an anion in these
syntheses stemmed from its lack of reactivity and weak
coordinating ability, attributes which have made it an effective
counterion in important catalysts in the past.70,80 The crystal
structure of 15, revealed a 4-coordinate Sn complex with no
−
signs of interaction between the metal center and the BPh4
counteranion or solvent (Figure 6).
The closest distance between the Sn and any part of the
−
BPh4 anion is 5.170 Å, well outside the sum of the van der
Waals radii for Sn and H. This complete isolation of the Sn(IV)
cation is uncommon, as even anions with weak coordinating
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