Dispersion forces and counterintuitive steric effects in main group molecules: Heavier group 14 (Si-Pb) dichalcogenolate carbene analogues with sub-90 interligand bond angles

Article abstract of DOI:10.1021/ja403802a

The synthesis and spectroscopic and structural characterization of an extensive series of acyclic, monomeric tetrylene dichalcogenolates of formula M(ChAr)₂ (M = Si, Ge, Sn, Pb; Ch = O, S, or Se; Ar = bulky m-terphenyl ligand, including two new

Full text of DOI:10.1021/ja403802a

Article
pubs.acs.org/JACS
Dispersion Forces and Counterintuitive Steric Effects in Main
Group Molecules: Heavier Group 14 (Si−Pb) Dichalcogenolate
Carbene Analogues with Sub-90° Interligand Bond Angles
Brian D. Rekken,† Thomas M. Brown,† James C. Fettinger,† Felicitas Lips,† Heikki M. Tuononen,§
Rolfe H. Herber,‡ and Philip P. Power*,†
†Department of Chemistry, University of California, Davis, One Shields Avenue, Davis, California, 95616, United States
‡Racah Institute of Physics, Hebrew University of Jerusalem, 91904, Jerusalem, Israel
§Department of Chemistry, University of Jyvaskyla, P.O. Box 35, FI-40014 Jyvaskyla, Finland
̈
̈
̈
̈
S
* Supporting Information
ABSTRACT: The synthesis and spectroscopic and structural
characterization of an extensive series of acyclic, monomeric
tetrylene dichalcogenolates of formula M(ChAr)2 (M = Si,
Ge, Sn, Pb; Ch = O, S, or Se; Ar = bulky m-terphenyl ligand,
including two new acyclic silylenes) are described. They were
found to possess several unusual featuresthe most notable
of which is their strong tendency to display acute interligand,
Ch−M−Ch, bond angles that are often well below 90°.
Furthermore, and contrary to normal steric expectations, the interligand angles were found to become narrower as the size of
the ligand was increased. Experimental and structural data in conjunction with high-level DFT calculations, including cor-
rections for dispersion effects, led to the conclusion that dispersion forces play an important role in stabilizing their acute
interligand angles.
species (metallylenes) of formula MR2 (M = Si, Ge, Sn, or Pb;
R = alkyl, aryl, silyl, amido, phosphido, alkoxo, etc.) which are
analogous to carbenes and for which more than 250 stable
examples are currently known.6 They possess V-shaped
geometries with interligand angles that are usually well below
120°, but generally >90°. The angles decrease with increasing
atomic number of the group 14 element and increasing
electronegativity of the ligand in accordance with Bent’s rule.7
In isolated cases, interligand angles below the expected lower
limit of 90° (on the basis of the 90° angle between the valence
p-orbitals) have been observed, as in Sn(OC6H2-2,6-But2-
4-Me)2 (O−Sn−O = 88.8(2)°),8 Sn(SMes*)2 (Mes* = C6H2-
2,4,6-But3; S−Sn−S = 85.4(1)°),9 or the bis primary amides
INTRODUCTION
■
The use of sterically crowding ligands to influence chemical
reactivity, to protect reactive sites, and to stabilize molecules with
unusual bonding or low coordination numbers is a well-
established and powerful technique in molecular chemistry.
Such ligands have been crucial for the synthesis of numerous new
molecular classes throughout the periodic table.1 For example,
a considerable portion of modern main group chemistry is
sustained by their employment in the isolation of compounds
with previously unknown oxidation states or bonding, where
stability is achieved by blocking decomposition routes that often
involve disproportionation or polymerization reactions.2 The
crowded environments produced by the ligands introduce some
degree of steric strain due to overlapping electron clouds. The
presence of strain is usually manifested in the distortion of
structural parameters and may result in bond lengthening and the
widening of interligand angles to reduce the congestion.3 The
distortions can, in extreme instances, lead to bond cleavage or
dissociation4 or molecular rearrangement.5 In such cases, the
cause and effect relationship between the strain and geometrical
distortion appears to be intuitively obvious. However, in this
paper we shall describe the synthesis and characterization of a
series of compounds (the dichalcogenolates of divalent group 14
elements) where such trends are apparently reversed, so that
increasing the size of the ligand leads to a decrease, rather than
an increase, in the interligand angles.
M{N(H)ArMe }2 (N−M−N = 88.6(2)°, Ge; 87.07(8)°, Sn;
6
87.47(9)°, Pb; ArMe = C6H3-2,6(C6H2-2,4,6-Me3)2).10 Recently,
6
we demonstrated that the terphenyl chalcogenolate ligands,
i
i
i
-OArPr and -SArPr (ArPr = C6H3-2,6-(C6H3-2,6-Pri2)2)
4
4
4
produced very different interligand angles in their divalent lead
i
4
derivatives Pb(OArPr )2 (O−Pb−O = 99(1)° average value) and
i
Pb(SArPr )2 (S−Pb−S = 77.21(4)°).11 The latter angle was the
4
narrowest reported for a group 14 element metallylene
derivative. We also showed that the use of the somewhat less
crowding chalcogenolate ligand −SArMe (ArMe = C6H3-2,6,-
6
6
12
(C6H2-2,4,6-Me3)2) stabilized an acyclic silylene, Si(SArMe )2,
6
The neutral bis-chalcogenolate derivatives of the heavier group
14 elements form part of a wider class of stable, monomeric
Received: April 16, 2013
© XXXX American Chemical Society
A
dx.doi.org/10.1021/ja403802a | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Article
hexanes solutions in 3.5 mL quartz cuvettes using a HP 8452 diode-array
spectrophotometer. Melting points were determined on a Meltemp II
apparatus using glass capillaries sealed with vacuum grease and are
uncorrected.
(reported essentially simultaneously to the acyclic silylene,
Si{N(SiMe3)(Dipp)}{BN(Dipp)CHCHN(Dipp)} (Dipp =
C6H3-2,6-Pri2) by Aldridge and Jones)13 which possesses a
relatively narrow interligand angle 90.52(2)°.1,14 These unusual
angular variations suggested that a more extensive study on a
larger range of compounds was warranted to explain their origin.
We now describe our experimental and computational studies of
an extensive series (a total of 20 compounds, of which 14 are
newly described, including 2 new acyclic silylenes) of low-valent
dichalocogenolate, ChAr (Ch = O, S, Se; Ar = terphenyl),
derivatives of Si, Ge, Sn, and Pb. The data show that interligand
angles as low as 73.09(2)° can be obtained and that the Ch−M−
Ch angle depends on a variety of factors, including steric
interactions across the 2-fold axis bisecting the ChMCh bond.
DFT calculations employing a correction for dispersion effects
provide further insight to the bonding and show that attractive
dispersion forces between the alkyl substituents of the terphenyl
ligands play an important role in narrowing the interligand
angles. All of the compounds are stabilized by chalcogenolate
ligands bearing the terphenyl substituents illustrated in Figure 1.
i
Pri4
Si(SArPr )2 (2). Si(Br)2(SAr )2 (1.698 g, 1.62 mmol; see compound
4
27, SI) in THF (45 mL) was added over 10 min to a chilled suspension
of Rieke’s magnesium (0.0493 g, 2.03 mmol), freshly prepared in
40 mL of THF, and sonicated with a catalytic amount of anthracene for
3 h. The solution became red and, after 30 min, was allowed to warm to
ambient temperature and stirred for a further 5 days. All the volatile
components were removed under reduced pressure, and ca. 60 mL of
hexanes and ca. 12 mL of 1,4-dioxane were added. The resultant solution
was stirred for 24 h and filtered to give a clear, red solution. All of the
volatile components were removed under reduced pressure, and the
residue was redissolved in hexanes (12 mL), which were concentrated to
ca. 3 mL storage in a ca. −18 °C refrigerator. This afforded small yellow
needles of 2 after 1 week. Yield: (0.243 g, 0.27 mmol, 16.9%); mp 203−
207 °C. Calcd for C60H74S2Si: C, 81.2; H, 8.41. Found: C, 80.4; H, 8.23.
1H NMR (399.8 MHz, C6D6, 295 K): δ = 1.07 (d, 24H, o-CH(CH3)2,
3JH,H = 6.80 Hz), 1.19 (d, 24H, o-CH(CH3)2, 3JH,H = 7.20 Hz), 2.69 (m,
3
3
8H, o-CH(CH3)2, JH,H = 6.80 Hz), 6.97 (t, 2H, p-C6H3, JH,H = 6.80
Hz), 7.05 (d, 4H, m-C6H3, JH,H = 7.2 Hz), 7.10 (d, 8H, m-C6H3Pri2,
3
3JHH = 6.80 Hz), 7.20 (t, 4H, p-C6H3Pri2, JHH = 7.20 Hz); 13C{1H}
3
NMR (100.5 MHz, C6D6, 296 K): δ =23.34 (o-CH(CH3)2), 25.39
(o-CH(CH3)2), 31.23 (o-CH(CH3)2), 123.55 (m-C6H3Pri2), 125.41
(p-C6H3), 128.97 (m-C6H3), 129.78 (o-C6H3), 137.38 (p-C6H3Pri2),
138.87 (o-C6H3Pri2), 141.85 (i-C6H2Pri2), 147.05 (i-C6H3Pri2); 29Si
NMR (119.1 MHz, C6D6, 295 K): δ = 270.4; UV−vis: [λ, nm
(ε, M−1cm−1)] 405 (3700), 318 (7400), 290 (11 200). IR (cm−1): The
Si−S stretching band tentatively assigned to an absorption at 648 cm−1.
A small portion of the silylene (0.05 g) was mixed with the potassium
i
thiolate, K2(SArPr )2 (see SI) and dissolved in a mixture of 1,4-dioxane
4
(ca. 2 mL) and hexanes (ca. 2 mL) and placed in a ca. 7 °C refrigerator to
yield X-ray quality crystals of 2 after 3 days.
i
Pri6
Si(SArPr )2 (3). Si(Br)2(SAr )2 (1.141 g, 0.94 mmol; see compound
6
Figure 1. The terphenyl group substituent anions display increasing
bulk moving from left to right. The ipso carbon is bonded to O, S, or Se.
28, SI) in THF (45 mL) was added over 10 min to a chilled suspension
of Rieke’s magnesium (0.0285 g, 1.17 mmol), freshly prepared in 40 mL
of THF, and sonicated with a catalytic amount of anthracene for 3 h. The
solution became red and was allowed to warm to ambient temperature
and stirred for a further 3 days. All the volatile components were
removed under reduced pressure, and hexanes (ca. 65 mL) and
1,4-dioxane (ca. 8 mL) were added and stirred for 24 h. Filtration yielded
a clear, red solution which was concentrated to ca. 8 mL and placed in
a ca. 7 °C refrigerator. Small yellow crystalline blocks of 3 (0.201 g)
were obtained and isolated after 3 days. The supernatant liquid was
evaporated to dryness, and the yellow residue was redissolved in toluene
(ca. 15 mL). The resultant solution was concentrated to ca. 8 mL under
reduced pressure and placed in a ca. 7 °C refrigerator to yield X-ray
quality yellow crystals of 3. Yield: (0.422 g total weight, 0.40 mmol,
42.6%); mp: 254−257 °C. Calcd for C72H98S2Si: C, 81.91; H, 9.36.
Found: C, 81.01; H, 9.08. 1H NMR (599.7 MHz, C6D6, 295 K): δ = 1.12
EXPERIMENTAL SECTION
■
General Procedures. All manipulations were performed with the
use of modified Schlenk techniques under an N2 atmosphere or in a
Vacuum Atmospheres drybox under N2 except the magnesium
reductions, which were performed under argon. Solvents were distilled
over a potassium mirror and degassed immediately prior to use via
freeze−pump−thaw cycles. Unless otherwise noted, all chemicals were
obtained from commercial sources and used without further purification.
Pri4
Pri6
Rieke’s magnesium15,16 and the thiols ArMe SH, Ar SH, and Ar SH as
6
well as their alkali metal salts were prepared by literature procedures.17
i
8
The thiol, ArPr SH (see Supporting Information (SI), 30), was prepared
3
(d, 24H, o-CH(CH3)2, JH,H = 6.99 Hz), 1.25 (d, 24H, o-CH(CH3)2,
i
8
by reaction of ArPr Li(OEt2)18 with sulfur employing the same synthetic
3JH,H = 6.99 Hz), 1.33 (d, 24H, p-CH(CH3)2, 3JH,H = 7.00 Hz), 2.75 (m,
i
i
8H, o-CH(CH3)2, 3JH,H = 6.99 Hz), 2.89 (m, 4H, p-CH(CH3)2, 3JH,H
=
17c
procedure as that used for ArPr SH. The MSeArPr (M = Li, K) salts
6
4
6.99 Hz), 6.93 (t, 2H, p-C6H3, 3JH,H = 7.63 Hz), 7.05 (d, 4H, m-C6H3,
3JH,H = 7.63 Hz), 7.12 (s, 8H, m-C6H2Pri3); 13C{1H} NMR (C6D6, 150.8
MHz, 295 K): δ = 23.62 (o-CH(CH3)2), 24.50 (o-CH(CH3)2), 25.56
(o-CH(CH3)2), 31.28 (p-CH(CH3)2), 34.81 (p-CH(CH3)2), 121.48
(p-C6H3), 125.36 (m-C6H2Pri3), 130.11 (m-C6H3), 136.87 (o-C6H3),
138.04 (o-C6H2Pri3), 141.66 (p-C6H2Pri3), 146.84 (i-C6H2Pri3), 148.92
(i-C6H3); 29Si NMR (119.1 MHz, C6D6, 295 K): δ = 270.9; UV−vis:
[λ, nm (ε, M−1cm−1)] 411 (4400), 331 (7500), 290 (10 500). IR
(cm−1): The Si−S stretching band was tentatively assigned to an
absorption at 645 cm−1.
were prepared by addition of either LiBun or K metal to the air-stable
i
19
triselenine, Se(SeArPr )2 (see SI). 1H NMR and 13C NMR spectra were
4
recorded on either a Varian 300, 400, or 600 MHz instrument and
referenced internally to either protio benzene or trace silicon grease (δ =
0.29 in C6D6). 29Si NMR spectra were acquired on a Varian 600 MHz
(operating at 119.14 MHz) instrument referenced to an external
standard of SiMe4 (TMS) (δ = 0) in C6D6. 77Se NMR spectra were
acquired on a Varian 600 MHz (operating at 114.4 MHz) instrument and
were externally referenced to a saturated solution of selenous acid in D2O
(δ = 1300). 119Sn (223.63 MHz) and 207Pb (125.53 MHz) NMR spectra
were acquired on a Varian 600 MHz instrument and were referenced to
SnBun4 in C6D6 (δ = −11.7) or PbMe4 in C6D6 (δ = 0). IR spectra were
recorded as Nujol mulls between KBr or CsI plates on a Perkin-Elmer
1430 spectrophotometer. UV−vis spectra were recorded as dilute
i
Pri4
Ge(SArPr )2 (5). A solution of LiSAr (1.253 g, 2.87 mmol) in diethyl
4
ether (60 mL) was added dropwise over 45 min to a diethyl ether slurry
(5 mL) of GeCl2(1,4-dioxane) (0.332 g, 1.43 mmol) cooled to ca. 0 °C.
The solution became yellow, and after 30 min, was allowed to warm to
B
dx.doi.org/10.1021/ja403802a | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Article
i
Pri6
Pri8
ambient temperature and stirred for a further 12 h. All volatile
components were removed under reduced pressure, and the residue was
extracted with hexanes (50 mL) and filtered. The solution was con-
centrated to ca. 4 mL and cooled to −17 °C to give 5 as a micro-
crysystalline, threadlike solid. A small amount of 5 (ca. 0.04 g) was
dissolved in a concentrated THF solution and stored at −17 °C for
3 days to yield X-ray yellow quality crystals of 5. Yield: (0.943 g, 1.01
mmol, 70.5%). mp 203−206 °C. 1H NMR (399.8 MHz, C6D6, 294 K):
δ = 1.07 (d, 24H, CH(CH)2, 3JHH = 6.83 Hz), 1.20 (d, 24H, CH(CH)2,
3JHH = 6.83 Hz), 2.72 (m, 8H, CH(CH)2, 3JHH = 6.83 Hz), 6.94 (t, 2H,
p-C6H3, 3JHH = 7.51 Hz), 7.04 (d, m-C6H3, 4H, 3JHH = 7.41 Hz), 7.10
The stannylenes, Sn(SArPr )2 (9), Sn(SAr )2 (10), and Sn(SAr
)
4
2
(11) were prepared by a similar method to that used for 8, see
Supporting Information for details.
i
Pri8
Pb(SArPr )2 (14). LiSAr (0.952 g, 1.56 mmol; see compound 33, SI)
8
and PbBr2 (0.289 g, 0.79 mmol) were placed in a flask, and diethyl ether
(60 mL) cooled to ca. −78 °C was added. The resulting solution was
stirred at ca. −78 °C for 2 h and warmed to ca. 25 °C. It was stirred for a
further 24 h to give an orange-red solution and a white precipitate. All of
the volatile components were removed under reduced pressure. The
product was extracted with pentane (100 mL) and filtered. The filtrate
was concentrated under reduced pressure to a ca. 20 mL and placed in a
3
3
(d, 8H, m-C6H3Pri2, JHH = 7.41 Hz), 7.20 (t, 4H, p-C6H3Pri2, JHH
=
ca. −17 °C freezer, which afforded a small quantity of X-ray quality
crystals of the disulfide, (SArPr )2 as yellow rods after 3 days. The
i
6.84 Hz); 13C{1H} NMR (100.5 MHz, C6D6, 296 K): δ = 23.46
(o-CH(CH3)2), 25.23 (o-CH(CH3)2), 31.16 (o-CH(CH3)2), 123.81
(m-C6H2Pri3), 124.64 (p-C6H3), 128.89 (m-C6H3), 129.44 (o-C6H3),
139.39 (p-C6H2Pri2), 139.97 (o-C6H2Pri2), 141.12 (i-C6H2Pri2), 147.12
(i-C6H3); UV−vis: [λ, nm (ε, M−1cm−1)] 410 (3100), 330 (3600), 278
(5600).
8
supernatant liquid was decanted and further concentrated to 8 mL and
placed in a ca. −17 °C freezer for 2 weeks to afford X-ray quality crystals
of 14 as orange rods. Yield: 0.450 g (0.321 mmol 40.8%); mp 246−
1
249 °C; H NMR (599.7 MHz, C6D6, 295 K): δ = 1.14 (d, 24H,
3
3
o-CH(CH3)2, JH,H = 6.63 Hz), 1.25 (d, 24H, m-CH(CH3)2, JH,H
=
6.96 Hz), 1.34 (d, 24H, p-CH(CH3)2, 3JH,H = 6.97 Hz), 1.41 (d, 24H,
i
Pri6
Ge(SArPr )2 (6). A flask containing LiSAr (1.518 g, 2.91 mmol) and
6
3
3
o-CH(CH3)2, JH,H = 6.63 Hz), 2.60 (m, 8H, o-CH(CH3)2, JH,H
=
GeCl2(1,4-dioxane) (0.338 g, 1.43 mmol), was cooled to ca. −78 °C.
Diethyl ether (65 mL) was added slowly over 20 min to afford a solution
which, after 2 h, was allowed to warm to ambient temperature, after
which time stirring was continued for 24 h. All volatile components were
removed under reduced pressure and the residue was extracted with
toluene (40 mL) and filtered. The solution was concentrated to ca. 4 mL
and cooled to ca. −17 °C to give 6 as a yellow microcrystalline solid.
Crystals of 6 suitable for X-ray diffraction were obtained by cooling their
hexane solutions at ca. −17 °C. Yield: 0.836 g (0.76 mmol, 52.0%); mp
273−276 °C; 1H NMR (599.7 MHz, C6D6, 295 K): δ = 1.12 (d, 24H,
3
6.64 Hz), 2.88 (m, 8H, p-CH(CH3)2, JH,H = 6.97 Hz), 2.90 (m, 8H,
o-CH(CH3)2, JH,H = 6.63 Hz), 7.18 (s, 2H, p-C6H3), 7.24 (s, 8H,
3
m-C6H3,); 13C{1H} NMR (C6D6, 150.8 MHz, 295 K): δ = 24.29
(CH(CH3)2), 24.42 (CH(CH3)2), 24.83 (CH(CH3)2), 25.07 (CH-
(CH3)2), 26.43 (CH(CH3)2), 26.55 (CH(CH3)2), 31.21 (CH(CH3)2),
121.89 (p-C6HPri2), 122.12 (m-C6H2Pri3), 136.94 (m-C6HPri2), 140.29
(o-C6HPri2), 141.30 (p-C6H2Pri3), 146.69 (o-C6H2Pri3), 147.73
(i-C6H2Pri3), 149.13 (i-C6HPri2); 207Pb{1H} NMR (125.53 MHz,
C6D6, 295 K): δ = 4335; UV−vis: [λ, nm (ε, M−1cm−1)] 446 (4200),
372 (2500), 292 (6600); IR (cm−1): The Pb−S stretching band was
tentatively assigned to an absorption at 302 cm−1.
3
3
o-CH(CH3)2, JH,H = 7.04 Hz), 1.27 (d, 24H, o-CH(CH3)2, JH,H
=
i
3
Pb(SArPr )2 (13) was prepared by a similar method to 14, see SI for
7.04 Hz), 1.32 (d, 24H, p-CH(CH3)2, JH,H = 7.04 Hz), 2.78 (m, 8H,
6
o-CH(CH3)2, 3JH,H = 6.75 Hz), 2.90 (m, 4H, p-CH(CH3)2, 3JH,H = 7.04
details.
Hz), 6.91 (t, 2H, p-C6H3, 3JH,H = 7.49 Hz), 7.04 (d, 4H, m-C6H3, 3JH,H
=
i
4
Pri4
Ge(SeArPr )2 (15). LiSeAr (1.21 g, 2.50 mmol) in diethyl ether
7.63 Hz), 7.12 (s, 8H, m-C6H2Pri3); 13C{1H} NMR (C6D6, 150.8 MHz,
295 K): δ = 23.69 (o-CH(CH3)2), 24.47 (o-CH(CH3)2), 25.50
(o-CH(CH3)2), 31.23 (p-CH(CH3)2), 34.75 (p-CH(CH3)2), 121.59
(p-C6H3), 124.64 (m-C6H2Pri3), 129.90 (m-C6H3), 137.25 (o-C6H3),
138.82 (o-C6H2Pri3), 141.19 (p-C6H2Pri3), 146.99 (i-C6H2Pri3), 148.91
(i-C6H3); UV−vis: [λ, nm (ε, M−1cm−1)] 414 (3600), 338 (3700), 286
(4100); IR (cm−1): The Ge−S stretching band was tentatively assigned
to an absorption at 438 cm−1.
(40 mL) was added dropwise over 15 min to a diethyl ether slurry
(5 mL) of GeCl2(1,4-dioxane) (0.290 g, 1.25 mmol) cooled to −72 °C.
The solution became a bright-orange color immediately, and after 1 h, it
was allowed to warm to ambient temperature and was stirred overnight.
All the volatile components were removed under reduced pressure,
and the residue was extracted with n-pentane (50 mL) and filtered. The
solution was concentrated to ca. 3 mL, warmed gently, and allowed to
sit at ambient temperature overnight to produce X-ray quality amber
crystals of 15. Calcd for C60H74GeSe2: C, 70.26; H, 7.27. Found: C, 70.7;
Pri8
The germylenes Ge(SArMe )2 (4) and Ge(SAr )2 (7) were prepared
6
H, 7.27. Yield: 0.710 g (0.690 mmol, 53.7%); mp 205−207 °C; 1H NMR
by a similar method to that used for 5. See Supporting Information for
3
(599.7 MHz, C6D6, 295 K): δ = 1.05 (d, 24H, o-CH(CH3)2, JH,H
=
details.
3
Me6
Sn(SArMe )2 (8). LiSAr (1.120 g, 3.18 mmol) was dissolved in ca.
6.75 Hz), 1.22 (d, 24H, o-CH(CH3)2, JH,H = 6.75 Hz), 2.77 (m, 8H,
6
o-CH(CH3)2, 3JH,H = 7.04 Hz), 6.99 (t, 2H, p-C6H3, 3JH,H = 8.22 Hz),
60 mL of diethyl ether and added dropwise over 30 min to a diethyl ether
(5 mL) slurry of SnCl2 (0.301 g, 1.59 mmol) cooled to ca. −78 °C. The
solution immediately became yellow and was stirred at ca. −78 °C for a
further 30 min and then allowed to warm slowly to a room temperature.
The solution was stirred for 24 h to give a yellow solution and a white
precipitate. All the volatile components were removed under reduced
pressure. Toluene (50 mL) was added and filtration afforded a clear,
yellow solution. The filtrate was concentrated under reduced pressure to
a ca. 12 mL and placed in a ca. −17 °C freezer to afford X-ray quality
crystals of 8 as pale-yellow blocks after 3 days. Yield: 0.404 g (0.50 mmol,
31.4%); mp 194−196 °C. Calcd for C48H50S2Sn: C, 71.20; H, 8.74.
Found: C, 70.93; H, 8.49. 1H NMR (300.1 MHz, C6D6, 298 K): δ = 2.06
(s, 24H, o-CH3), 2.17 (s, 12H, p-CH3), 6.78 (s, 8H, C6H2Me3), 6.85 (d,
7.02 (d, 4H, m-C6H3, 3JH,H = 7.92 Hz), 7.09 (d, 8H, m-C6H2Pri2, 3JH,H
=
7.63 Hz), 7.19 (t, 4H, p-C6H2Pri2, JH,H = 7.63 Hz); 13C{1H} NMR
(C6D6, 150.8 MHz, 295 K): δ = 23.73 (o-CH(CH3)2), 25.16
(o-CH(CH3)2), 31.15 (o-CH(CH3)2), 123.92, (m-C6H2Pri3), 125.36
(p-C6H3), 129.02 (m-C6H3), 129.47 (o-C6H3), 138.38 (p-C6H2Pri2),
140.43 (o-C6H2Pri2), 142.77 (i-C6H2Pri2), 146.74 (i-C6H3); 77Se NMR
(114.4 MHz, C6D6, 295 K): δ = 657.5; UV−vis: [λ, nm (ε, M−1cm−1)]
3
435 (7700), 358 (9000), 303 (8900).
i
Sn(SeArPr )2 (16). Stannylene 16 was prepared by a similar method to
that of 15, except that potassium selenolate was used instead of the
lithium selenolate, see SI for details.
4
X-ray Crystallography. Crystals of 2, 7−11, 13−16, 27, 28, and
30−35 were removed from a Schlenk tube under N2 and covered with a
layer of hydrocarbon oil. A suitable crystal was selected, attached to a
glass fiber, and quickly placed in low temperature N2 stream. The data
for 2−11, 13−16, 27, 28, and 30−35 were collected at ca. 90 K on a
Bruker APEX II CCD or Bruker DUO APEX II CCD diffractometers
with Mo Kα (λ = 0.71073 Å) radiation or Cu Kα (λ = 1.5418 Å).
The crystal structures were solved by direct methods using SHELX
version 6.1 program package.20,21 All nonhydrogen atoms were refined
anisotropically. Absorption corrections were applied using SADABS
3
3
4H, m-C6H3, JH,H = 7.50 Hz), 7.00 (t, 2H, p-C6H3, JH,H = 7.50 Hz);
13C{1H} NMR (C6D6, 75.45 MHz, 298 K): δ = 20.27 (p-CH3), 21.23
(o-CH3) 124.78 (p-C6H3), 125.46 (m-C6H2Me3), 129.35(m-C6H3),
136.31 (o-C6H3), 137.11 (o-C6H2Me3), 137.47 (p-C6H2Me3), 140.03
(i- C6H2Me3), 142.58 (i-C6H3); 119Sn NMR (223.6 MHz, C6D6, 295 K):
δ = 763.8; UV−vis: [λ, nm (ε, M−1cm−1)] 400 (1100), 298 (5300),
292 (5300); IR (cm−1): Sn−S stretching band tentatively assigned to an
absorption at 393 cm−1.
C
dx.doi.org/10.1021/ja403802a | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Article
Tsi = C(SiMe3)3) was assigned a shift of δ = 140.5 in the 29Si
program (SADABS, an empirical absorption correction programs, part
of the SAINTPlus NT version 5.0 package; Bruker AXS: Madison, WI,
1998). All crystallographic calculations were performed on an iMac with
2.80 GHz i7 quad core processor and 8GB of memory. Data collected
were corrected for Lorentz and polarization effects and absorption using
Blessing’s method and merged as incorporated into the program
Twinabs. Structures were drawn using the program OLEX2.22a Details
NMR spectrum.30 The upfield shift of SiBr(MgBr)(SArMe )2 is
6
probably due to the more electronegative thiolate substituents.
The silylenoid is likely an intermediate in the synthesis of silylenes
2 and 3; however, in those systems, the MgBr2 is apparently
eliminated, possibly due to increased steric crowding of the
bulkier ligands (SI).
The syntheses of most of the Ge−Pb aryloxo and arylthiolato
complexes were carried out primarily by a salt metathesis of the
lithium or potassium chalcogenolates with the corresponding
metal dihalide. An exchange reaction using Sn{N(SiMe3)2}2 with
of the data collections and refinements are given in the SI (Tables S3-
i
4
S6). For 2, the potassium thiolate salt (KSArPr )2 (31; see SI) was used
i
4
in a cocrystallization with the silicon dithiolate Si(SArPr
) (2) to
2
facilitate the structural determination of 2, although we later found that
crystals of 2 suitable for X-ray crystallography could also be obtained
from toluene solvent. The structure of the potassium salt (31) was also
determined from an independently synthesized sample, as was the
2 equiv of the corresponding thiol was also used as an alternative
i
8
synthetic route to Sn(SArPr )2. Previous work by Clyburne to
Pri4
6
determine the structure of the complex Ge(OArMe )2 proved
structure of the Si(Br)2(SAr )2 (27), which was a 5% contaminant.
Pri6
unsuccessful due to poor crystallinity, although a structure of
X-ray data for the Ar substituted thiolate derivatives 3 and 6 were also
31
Sn(OArMe )2 was obtained. An overview of the synthesis of
6
obtained. The data refinement for these two structures could not be
performed to low residual values, although the key structural parameters
2−20 is given in Scheme 1.
i
8
Pri4
During the synthesis of M(SArPr )2 or M(SeAr )2, (M = Sn,
for the core atoms could be obtained without difficulty. It is noteworthy
i
that the ArPr terphenyl substituent has also been associated with
6
i
Pb) small amounts of the disulfide (ArPr S)2 and diselenide
8
difficulties in the refinement of X-ray data for other systems.22b Some
key structural data for the core atoms in these structures are given in Table 2,
where it can be seen that their structural parameters conform to the pattern
established by the structures of the other compounds in the series.
i
4
(ArPr Se)2 were observed as coproducts. Furthermore, solutions
i
8
Pri8
of Sn(SArPr )2 deposit tin metal and the disulfide (SAr )2 upon
standing at ca. 25 °C over a period of several months. This is
similar to reports of other group 14 dithiolate oligomers that have
been shown to decompose over time, although those resulted in
the formation of the metal sulfide and diaryl sulfide.32 The
decomposition pathways may differ because of the greater steric
hindrance associated with the terphenyl ligands.
̈
Mossbauer Spectroscopy. Experimental samples were shipped in
sealed ampules, transferred (ca. 45 s) to O-ring-sealed sample holders in
an inert atmosphere glovebox, and quenched to liquid nitrogen
temperature prior to mounting in the precooled cryostat. They were
examined in transmission geometry using a 10 mCi CaSnO3 source at
room temperature as previously described, as was the spectrometer
calibration.23 The Mossbauer effect (ME) data were collected over the
̈
Structures. Dithiolates. The most numerous of the divalent
species discussed in this paper are the dithiolato derivatives of Si,
Ge, Sn and Pb, 1−14, and their structures are described first.
Important structural data for 1−14 are given in Table 1 which
also includes data for the stannylene, Sn(SMes*)2, (Mes* =
C6H2-2,4,6-But3, 26) for comparison.9 The most notable feature
temperature range ∼90 < T < 220 K. Sample temperature was
monitored using the Daswin program,23b and the transmission data were
monitored (to ensure no sample loss) before and after each temperature
data point acquisition.
Computational Details. All calculations were performed with the
Turbomole 6.3 program package24a and the results were visualized with
gOpenMol.24b,c The geometries of R−Ch−M−Ch−R, where M = Si,
of the structures is that with the exception of Si(SArMe )2, (S−Si−
6
i
8
S = 90.52(2)°),12 they all possess S−M−S bond angles below
90°. Furthermore, and in contrast to the usual expectation,6,33
as the bulk of the aryl substituents increases in the silicon,
germanium, and tin dithiolates, the S−M−S bond angle
decreases. In contrast, the S−Pb−S angles change little when
the size of the substituents is varied. The data in Table 1 also
show that, as the crowding of the terphenyl ligand increases, as in
Ge, Sn, Pb; Ch = O, S, Se; and R = H, Ph, C6H3-2,6-Ph2, ArPr were
optimized with the hybrid PBE1PBE density functional25 in
combination with the TZVP basis sets.26 Due to the size of the systems
in question, frequency calculations were performed only for R = H, Ph
derivatives to assess the nature of stationary points found. The struc-
i
tures with R = ArPr substituents were also optimized using Grimme’s
8
empirical dispersion correction scheme (DFT-D3).27
i
i
6
i
8
SArMe < SArPr < SArPr < SArPr , the angle (M−S−C−C)
between the plane of the central aryl ring of the terphenyl ligand
and the M−S−C(ipso) plane decreases. (this is accompanied by
decreased interligand distances between the Pri substituents;
Table 33, SI). This is also contrary to steric expectations.
However, the torsion angle between the S−C(ipso) bond and the
S−M−S plane (C−S−M−S) does not display a correlation with
the size of the terphenyl ligand, with the majority of the angles
having values between 20° and 30°. The structures of the
6
4
RESULTS AND DISCUSSION
■
Synthesis. As recently shown, the silylene, Si(SArMe )2 (1)
6
was synthesized by reduction of Br2Si(SArMe )2 with (IMesMg)2
6
(IMes = [(2,4,6-trimethylphenyl)NC(CH3)]2CH).12 However,
attempts to extend this method to the more sterically crowded
Pri4
Pri6
silylenes Si(SAr )2 (2) and Si(SAr )2 (3) were unsuccessful.
This is likely due to the increased steric hindrance of the bulkier
terphenyl ligands. Instead, the dibromo-bisthiolato Si(IV) pre-
compounds of the thiolate series are illustrated by the tin
i
4
Pri6
cursors, Br2Si(SArPr )2 and Br2Si(SAr )2, were reduced using
derivatives shown in Figure 2 as well as the silylenes Si(SArMe
)
6
2
magnesium (as prepared by Rieke)15 with a catalytic amount of
i
and Si(SArPr )2 in Figure 3.
4
i
4
anthracene to yield the new acyclic silylenes, Si(SArPr )2 (2) and
The average Si−S distance in silylenes 2 (2.137(1) Å) and 3
(2.089(9) Å) is slightly shorter than that in 1 (2.158(3) Å) and is
comparable to those found in Tilley’s bisthiolatosilylene
platinum complex, trans-(Cy3P)2Pt(H)Si(SEt)2OTf (2.092(4)
and 2.074(4) Å),34a whereas the S−Si−S angles in 1−3 are all
significantly narrower by more than 17°. Likewise, the Ge−S
distances and S−Ge−S angles in germylenes 4−7 are both longer
i
6
Si(SArPr )2 (3). Attempts to synthesize Si(SAr )2, by reduction
Me6
using only Rieke’s magnesium, were unsuccessful. Based on 29Si
NMR evidence (signal at δ = 50.5), we believe that a magnesium
bromide-bisthiolato-bromosilylenoid, SiBr(MgBr)(SArMe )2,
6
was formed instead.12,28,29 A previously reported magnesium
silylenoid, SiBr(Mes)(Tsi)(MgBr) (Mes = 2,4,6-C6H2-Me3,
D
dx.doi.org/10.1021/ja403802a | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Article
a
Scheme 1. Overview of the Synthesis of 2−20
a
(a) Reduction of dibromo-bisthiolato-silanes with magnesium anthracenide gives the silylene analogues (i, ii). Reduction by Rieke’s magnesium is
believed to proceed through a magnesium silylenoid intermediate (iii). (b) A general overview of the synthetic routes for the synthesis of very bulky
germylene, stannylene, and plumbylene dichalcogenolates.
Table 1. Selected Distances (Å) and Angles (°) for M(SAr)2 (M = Si, Ge, Sn, Pb) Dithiolato Compounds
compound
S−M
S−M−S
M−C−S
M−S−C−C
C−S−M−S
C−S
M-centroid
S···S
ref
a
a
a
a
a
a
a
(1) Si(SArMe
)
2.158(3)
2.137(1)
2.089(9)
2.265(1)
2.284(4)
90.52(2)
85.08(5)
102.93(6)
113.80(9)
44.9(1)
15.5/11.3
26.6
1.791(2)
1.775(2)
1.77(1)
3.431
3.0666(4)
2.8903(9)
12
6
2
i
(2) Si(SArPr
)
)
38.2(2)
3.249
this work
this work
this work
this work
this work
this work
9
4
2
i
b
a
a
a
a
a
a
a
(3) Si(SArPr
84.8(1)
118.(1)
29(7)
29.9/30.0
23.0
3.31(6)
2.817(3)
6
2
a
a
a
(4) Ge(SArMe
)
88.68(2)
81.26(2)
79.6(2)
103(3)
40(6)
1.785(1)
1.778(1)
3.28(5)
3.1656(6)
2.9749(6)
2.867(7)
6
2
i
(5) Ge(SArPr
(6) Ge(SArPr
(7) Ge(SArPr
)
113.58(5)
32.3(1)
28.0
3.094
4
6
8
2
2
2
i
i
b
a
a
a
a
a
)
)
2.24(4)
114(1)
27(7)
25.5/26.1
27.3
1.79(3)
3.3(1)
2.2940(6)
2.4356(3)
77.01(2)
85.4(1)
119.42(6)
101.64
3.6(2)
86.34
1.782(2)
3.302
2.8566(6)
3.3034(5)
3.3677(4)
3.130(1)
(26) Sn(SMes*)2
9.6
1.8087(2)
1.7815(9)
4.383
a
a
a
a
(8) Sn(SArMe
)
2.479(5)
85.555(3)
78.63(3)
104(5)
38(10)
19.6/20/7
29.3
3.22(9)
this work
this work
this work
this work
11
6
2
i
a
a
a
a
(9) Sn(SArPr
)
2.470(1)
113.8(1)
31.2(3)
1.778(4)
3.082
4
2
i
a
a
a
a
a
a
a
(10) Sn(SArPr
(11) Sn(SArPr
(12) Pb(SArPr
(13) Pb(SArPr
(14) Pb(SArPr
)
)
2.46(6)
78.2(2)
113(1)
34(6)
23.4−31.1
27.5
1.774(2)
3.3(2)
3.10(2)
6
2
2
i
8
2.5009(6)
2.5656(9)
73.09(2)
77.21(4)
77.27(2)
80.07(2)
119.15(8)
3.8(2)
1.776(2)
1.771(3)
3.220
3.046
2.9783(8)
3.202(1)
i
4
6
8
)
113.42(11)
31.0(1)
29.8
2
2
2
i
i
a
a
a
a
a
)
)
2.579(5)
114.9(7)
28(8)
27.1/33.8
30.2/34.7
1.772(2)
3.12(5)
3.2207(7)
3.3281(7)
this work
this work
a
a
a
a
a
2.587(7)
117.4(9)
29(4)
1.782(1)
3.08(2)
a
b
Averaged values. Data for these two structures could not be refined to a low residual value.
(ca. 2.24- 2.29 Å) and narrower (ca. 89−77°) than those of Jutzi’s
bisthiolatogermylene chromium complex, Cr(CO)5Ge(SC6H2-
2,4,6-Me3)2, that has Ge−S distances of 2.181(4) and 2.192(6) Å
angles become narrower in the bulkier stannylenes 9
(78.63(3)°), 10 (78.2(2)°), and 11 (73.09(2)°). The Ge−S
distances in 4−7 (range: 2.265(1)−2.2940(6) Å) are ca. 0.05−
0.07 Å longer than the ca. 2.22 Å typically observed in Ge(IV)
thiolates.35a The Sn−S bond lengths in 8−11 (2.46(6)−
2.5009(6) Å) are longer than those in Sn(IV) thiolates (e.g.,
2.382(1) Å in Sn(SC6H11)4 and 2.397(1) Å in Sn(SBut)4.35b
and a S−Ge−S angle of 102.4(2)°.34b The S−Sn−S angle in
Sn(SArMe
) (8, 85.553(3)°) is similar to the 85.4(1)° in
2
6
Lappert’s Sn(SMes*)2 (26) (where the sub-90° angle was
deemed not to be due to steric effects),9 but the interligand
E
dx.doi.org/10.1021/ja403802a | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Article
Pri4
Pri6
Figure 2. Thermal ellipsoid drawings (30% probability ellipsoids without hydrogen atoms) of the Sn(II) derivatives of the SArMe (8), SAr (9), SAr
6
i
Pri8
(10), and SArPr (11) thiolato ligands, showing that the bulkiest ligand, SAr , yields a narrower (73.09(2)°) S−Sn−S bond angle in comparison to the
8
85.553(3)° observed for the smallest SArMe ligand. The essential coplanarity of the central aryl ring of the terphenyl substituents within the SnS2 core
6
structure is apparent in the structure of 11.
Figure 3. Thermal ellipsoid (30%) drawings of the structures of 1 and 2;
hydrogens are not shown for clarity. The structure of 2 features the
narrowest R−Si−R angle (84.72(5)°) for a two-coordinate silylene
(cyclic or acyclic).
Figure 4. Drawings of the core atoms in the bisthiolato tetrylenes
i
M(SArPr )2 (M = Si, 2; Ge, 5; Sn, 9; Pb, 12) (30% probability ellipsoids)
4
i
which feature identical SArPr ligands and show that the S−M−S angle
4
becomes narrower with increasing atomic number.
Presumably the longer distances in 4−11 are mainly due to the
larger sizes of the Ge2+ and Sn2+ ions and the changed polar
character of the bonds.
(3) The M−S−C(ipso) bending angles of the thiolate ligands
increase as the size of the terphenyl substituents increases
for all compounds including those of lead.
In contrast to the silylene, germylene, and stannylene
derivatives, the plumbylene dithiolates displayed only minor
variation (ca. 2.9°) in their S−M−S angles with the different
terphenyl substituent sizes. The M−S−C−C torsion angles,
of the lead thiolates, also remain relatively constant at ca. 29°.
We attribute the lower angular/substituent dependence to the
larger size of lead in comparison to the lighter elements. In
the lead derivatives, the Pb−S bonds lengthen slightly with
increasing substituent size and in all cases,11 the Pb−S distances
in plumbylenes 12−14 are longer than the Pb−S distance found
in Tokitoh’s monothiolato plumbylene, Pb(Tbt)(STbt), (Tbt =
C6H2-2,4,6-(CH(SiMe3)2)3) (2.498(10) Å).36 The C−S bond
lengths are very similar to those seen in the lighter analogues
with an almost negligible average decrease of about 0.01 Å upon
descending the group.37
(4) The M−S−C−C torsion angles decrease with increasing
size of the terphenyl substituents except in the lead
derivatives where it changes little. This results in the
opposition of flanking ring isopropyl substituents from the
two terphenyl substituents across the axis of the molecule,
contrary to steric expectations.
(5) The M−S bond lengths for each element display only
minor variation with terphenyl substituent size.
(6) The C(ipso)−S bond lengths vary little throughout the series.
The most striking features of the structural data are the
decreasing interligand Ch−M−Ch and M−Ch−C−C angles as
the terphenyl substituent size increases for the Si, Ge, and Sn
derivatives. These trends are counterintuitive from the point
of view of purely steric considerations. Clearly, other factors
influence the structures, and these will be discussed below.
Aryloxo and Selenolato Derivatives. Selected structural data
Although not all of the structures of the compounds of the
thiolate series are currently known, the structural data clearly
display patterns that can be summarized as follows:
for aryloxo and selenolato derivatives are given in Tables 2 and 3.
i
Pri4
The tetrylenes, Ge(SeArPr )2 (15, Figure 5) and Sn(SeAr
)
2
4
(1) The S−M−S interligand angles for M = Si, Ge and Sn
derivatives decrease as the bulk of the terphenyl
substituents increases.
(16), are the first structurally characterized two-coordinate
Ge(II) and Sn(II) selenolates and rare examples of two-
coordinate metallylenes stabilized by ligands bonded through
fourth row elements.6,38
(2) The S−M−S interligand angles decrease in the order
M = Si > Ge > Sn > Pb (Figure 4).
F
dx.doi.org/10.1021/ja403802a | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Article
Table 2. Selected Distances (Å) and Angles (°) for M(OAr)2 (M = Ge, Sn, Pb) Compounds
b
compound
O−M
O−M−O
C−O−M
M−O−C−C
C−O
M-centroid
O···O
ref
i
a
a
a
a
a
a
a
a
a
a
(17) Ge(OArPr
)
1.8271(16)
92.54(6)
87.32(11)
92.18(6)
128.03(13)
36.9(4)
1.378(3)
1.343(6)
1.360(3)
1.354(2)
3.377
2.640(2)
2.818(5)
3.13
40
31
40
11
8a
8a
8b
8c
8c
4
2
a
a
a
a
(18) Sn(OArMe
)
2.041(3)
126.7(3)
30.0
2.961
6
2
i
a
a
(19) Sn(OArPr
)
2.0472(17)
129.25(15)
30.6
3.163
4
2
i
a
a
a
a
a
(20) Pb(OArPr
)
2
2.216(8)
99(1)
127(2)
26(5)
2.95(3)
3.38(3)
4
a
a
a
(21) Ge(OAr*Me)2
(22) Sn(OAr*Me)2
(23) Pb(OAr*Me)2
(24) Ge{OC6H3-2,6-Ph2}2
1.807(9)
92.0(4)
88.8(2)
86.2(4)
92.10(5)
91.09(7)
124.7(7)
1.44(2)
a
a
a
2.009(5)
125.2(5)
1.371(7)
a
a
a
2.14(2)
124(2)
1.36(1)
a
1.820(3)
117.2(2)
124.1(1)
(25) Ge{OC6H-2,3,5,6-Ph4}2
1.820(1)
a
b
Average value. Ar*Me = C6H2But2-2,6-Me-4.
Table 3. Selected Distances (Å) and Angles (°) for Compounds M(SeAr)2, M = Ge, Sn
compound
Se−M
Se−M−Se
C−Se−M
M−Se−C−C
C−Se
M-centroid
Se···Se
ref
i
a
a
a
a
a
a
a
(15) Ge(SeArPr
(16) Sn(SeArPr
)
2.396(5)
2.594(3)
84.715(1)
78.60(3)
108.8(5)
36(1)
1.939(4)
1.935(9)
3.17(3)
3.2301(6)
3.286(1)
this work
this work
4
2
i
a
a
a
4
)
112.1(3)
26(7)
3.17(7)
2
a
Average value.
Figure 5. X-ray structures of the bisphenoxo and bisselenolato germylenes 17 and 15 (30% probability ellipsoids) without hydrogen atoms. The
Ch−Ge−Ch angles are: O1−Ge1−O2 = 92.54(6)°; Se1−Ge1−Se2 = 84.75(1)°. Other structural data are given in Table 4.
The structural data for the selenolates are necessarily limited
because of their lower stability in comparison to the aryloxides or
thiolates which is presumably a result of the decreased M−Se
significantly wider than the corresponding S−M−S and Se−M−
Se angles.8,31,40
Table 4 gives structural details of all the available divalent,
Pri4
Pri4
bond strengths.39a The compounds, Ge(SeAr )2 and Sn(SeAr )2,
have group 14 element−selenium bonds that are 0.11 and 0.12 Å
longer than their thiolate counterparts. The increase corresponds
roughly to the 0.13 Å difference in the single bond covalent radii of
group 14 element aryloxo, thiolate and selenolato metallylenes
i
4
that carry the common terphenyl substituent (ArPr ). A similar
range of structural data is not currently available for the other
terphenyl substituents. The Ch−M−Ch angles for the
terphenyloxo complexes are wider than those of the thiolato
and selenolato derivatives by ca. 11.3° for germanium, ca. 1.77−
13.55° for tin, and ca. 22° for lead complexes. The deviation of
the Ch−M−Ch angle from 90° is largest for S and Se derivatives.
The more electronegative aryloxide derivatives feature the
widest interligand angles that are seemingly in contradiction of
Bent’s rule.7
Pri4
S and Se.37 The Se−Ge−Se angle in Ge(SeAr )2 is about 3.5°
Pri4
wider than the S−Ge−S angle in Ge(SAr )2, and the Ge−Se−C
Pri4
angle is about 4.8° narrower. In the tin complexes, Sn(SAr )2 and
Pri4
Sn(SeAr )2, the Ch−Sn−Ch and Sn−C−Ch angles are very
i
4
similar (78.63(3) and 31.2(3) for SArPr vs 78.60(3) and 26(7)°).
As in the Ge(II) thiolates discussed above, the Ge−Se bond length
in 15 is longer than those seen in the Ge(IV) selenolates (e.g.,
Ge(SeMes)4, 2.37(1) Å).8c,39b
In Table 2, it can be seen that the aryloxo derivatives are
characterized by O−M−O angles (cf. 17 in Figure 5) that are
Pri6
The structure of Sn(SAr )2 (10) is worthy of further comment:
it contains two molecules in the asymmetric unit possessing similar
S−Sn−S angles of 78.27(1)° and 78.1(2)° and Sn−S−C-C torsion
angles of 30(2)° and 36(7)°, respectively, but one of the molecules
G
dx.doi.org/10.1021/ja403802a | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Article
i
i
δ = 814.8 and 827.4, respectively, and the signal of Sn(SArPr
)
Table 4. Selected Distances (Å) and Angles (°) for ChArPr
8
4
2
has the furthest downfield shift at δ = 919.4. The 119Sn
Substituted Derivatives, M = Ge, Sn, Pb
Pri4
i
4
NMR chemical shifts of Sn(SArPr )2 (δ = 814.8), Sn(SeAr
)
i
i
4
i
4
OArPr
(17) 1.827(16)
Ch−Ge−Ch (17) 92.54(6)
SArPr
SeArPr
4
2
i
(δ = 1148.1), and the previously reported Sn(OArPr )2 (δ =
−289.7)40 clearly illustrate the very large effects of the different
chalcogenolate ligands. The trend is opposite of what one would
expect based on σ-inductive effects. The more electropositive
substituents decrease the HOMO−LUMO gap, and as a result,
increase the paramagnetic deshielding which augments the
applied field and causes a downfield chemical shift on the 119Sn
NMR signal.43,44
A comparison of the chemical shifts for stannylene
dichalcogenolates with other two coordinate stannylenes shows
their 119Sn NMR signal to be downfield of stannylene diamides,
such as Sn{N(SiMe3)2}2 (δ = 746),44 and upfield of dialkyl
or diaryl stannylenes, such as Sn{CH(SiMe3)2}2 (δ = 2328)45
4
Ge
Sn
Pb
Ge−Ch
(5) 2.284(4)
(5) 81.26(2)
(15) 2.396(5)
(15) 84.75(1)
(15) 108.8(5)
(16) 2.594(3)
(16) 78.60(3)
(16) 112.1(3)
Ge−Ch−C
Sn−Ch
(17) 128.03(13) (5) 113.58(5)
(19) 2.0472(17) (9) 2.470(1)
Ch−Sn−Ch (19) 92.18(6)
(9) 78.63(3)
Sn−Ch−C
Pb−Ch
(19) 129.25(15) (9) 113.8(1)
(20) 2.216(8)
(12) 2.5656(9)
(12) 77.21(4)
(12) 113.42(11)
Ch−Pb−Ch (20) 99(1)
Pb−Ch−C (20) 127(2)
in the asymmetric unit has two tin sites, A and B, with 71/29%
occupancy. The main difference in the two sites is the disparity
of the S−Sn bond lengths. For site A, the S−Sn bond lengths are
2.4919(6) Å and 2.4114(6) Å, whereas for site B, the lengths are
2.3530(12) Å and 2.5235(12) Å. The Sn-centroid distances for
site A are 3.160 Å (centroid 1) and 3.492 Å (centroid 2). For site B,
the distances between the centroids are similar at 3.498 Å
(centroid 1) and 3.151 Å (centroid 2). The shorter Sn-centroid
distances in the mixed occupancy molecule are comparable to the
Sn-centroid distances in the other molecule in the asymmetric unit
at 3.126 and 3.155 Å.
i
46
and Sn(ArMe )2 (δ = 1971). The signals of Sn(SArPr )2 and
Sn(SeArPr )2 are close to that observed for the diarylstannylene
6
8
i
4
Sn(Mes*)2 (δ = 980) (Mes* = C6H2-2,4,6-But3).3
The 207Pb NMR spectra of the lead thiolates demonstrated
only small shift differences upon varying the thiolate ligands
(in comparison to the very wide dispersion range of 207Pb NMR
shifts in general).47 Plumbylenes Pb(SArPr )2, Pb(SAr )2, and
i
Pri6
4
i
Pb(SArPr )2 have signals in the narrow range of 4283−4335 ppm.
8
A possible explanation of the two different tin sites in
Sn(SArPr )2 (10) (Figure 6) as observed by X-ray crystallography
and Mossbauer spectroscopy (see below) is that at low
i
These are comparable to other monomeric plumbylenes, such as
Pb{N(SiMe3)2}2, which has a chemical shift at δ = 4916,47
though they are much further downfield of that of the previously
6
̈
temperatures the structures, which are related by the asymmetric
b2 vibration of the SnS2 moiety, are close in energy and are
stabilized by steric, dispersion, and packing forces. When the
crystals are dissolved at ambient temperature, only one 119Sn
NMR signal is observed; indicating that the structures are
indistinguishable by the slower time scale of the NMR technique,
or that there is only one structure. Although this complex
displays some of the characteristics of bond-stretch isomerism,41
several attempts to model the two environments resulted in only
one minimum on the potential energy surface corresponding to a
symmetric S−Sn−S moiety.
reported Pb{N(H)ArMe }2 (δ = 2871).10 The difference between
6
these two amido plumbylenes is believed to be due to the interac-
tion of flanking aryl rings of Pb{N(H)ArMe }2 with the lead atom.
6
Pri4
i
4
The 77Se NMR spectra for Ge(SeArPr )2 and Sn(SeAr
)
2
display signals that have a greater downfield shift for the
germylene (δ = 657.5) in comparison to the stannylene analogue
(δ = 526.9). The difference is likely due to an inductive effect
since germanium is more electronegative than tin. The region
of 77Se NMR shifts for both metals is characteristic of organic
selenides.48 The JSeSn coupling observed in the 77Se NMR
1
i
4
29Si, 77Se, 119Sn, and 207Pb NMR Spectroscopy. The 29Si
spectrum of Sn(SeArPr )2 is 516 Hz, which represents an average
spectrum of Si(SArMe )2 features a downfield singlet at δ =
6
of the 119Sn or 117Sn couplings due to broad signals. This is
similar to the 1JSeSn coupling observed in the triselenolato Sn(II)
complex, NaSn(SePh)3 (1JSeSn ≈ 400 Hz) (no reported
structure), which has a chemical shift (δ = 164) significantly
i
285.5.12 Signals for the bulkier silylenes Si(SArPr
) and
2
4
i
Si(SArPr )2 were located at similar chemical shifts but slightly
upfield at δ = 270.4 and 270.9, respectively. The very similar
shifts obtained for the silylenes show that the relatively small
(≤6°) angular changes at silicon have a minor effect on the
chemical shift of the thiolate derivatives.
6
upfield of 15 and 16.49 A weak signal corresponding to the
i
4
diselenide, (SeArPr )2, was also located at δ = 480.2. Chemical
shifts for the 29Si, 77Se, 119Sn, and 207Pb NMR spectra are shown
The 119Sn NMR spectra indicate a progressive downfield shift
in Table 5.
as the interligand angle decreases.42 Sn(SArMe )2 has a signal at
Sn Mossbauer Spectroscopy. The isomer shifts of
stannylenes Sn(SArMe )2 (8), Sn(SAr )2 (9), Sn(SAr )2 (10),
119
6
̈
Pri6
Pri4
Pri6
i
4
δ = 763.8, whereas Sn(SArPr )2 and Sn(SAr )2 display signals
6
i
6
Figure 6. A drawing showing the two tin sites in the structure of Sn(SArPr )2. For clarity, flanking arene groups are not shown.
H
dx.doi.org/10.1021/ja403802a | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Article
Pri8
Pri4
Pri4
Pri4
Pri6
Sn(SAr )2 (11), Sn(SeAr )2 (16), and Sn(OAr )2 (19) all
Sn(II).50 For the stannylenes Sn(SAr )2 (9) and Sn(SAr )2
(10), two tin sites are present, in approximately a 2:1 ratio at 90 K
(Figure 7). While the isomer shift difference between the two sites
is relatively small, the quadrupolar splitting is significantly
different. The two signals can be assigned to a change in the
geometry of the tin sites leading to a large difference in the electric
field gradient tensor at the metal site. As mentioned earlier, in the
X-ray crystal structure, one of the two molecules of 10 at 90 K
reveals two tin sites with occupancies of 71 and 29%. While this
appear above 2.65 mm/sec−1, so clearly all of these correspond to
Table 5. 29Si, 77Se, 119Sn, and 207Pb Heteronuclear NMR
Chemical Shifts for Tetrylene Dichalcogenolates
δ: 29Si
δ: 77Se
δ: 119Sn
δ: 207Pb
(1) Si(SArMe
(2) Si(SArPr
(3) Si(SArPr
(8) Sn(SArMe
(9) Sn(SArPr
(10) Sn(SArPr
(11) Sn(SArPr
)
285.5
270.4
270.9
6
2
i
4
)
2
i
ratio does not match that seen in the Mossbauer effect (ME)
6
̈
)
2
6
spectra (is ca. 50% of the ratio), it does show that two tin sites with
similar electronic but different geometric structures can coexist in
the solid state. All of the 119Sn ME data are summarized in Table 6,
in which the hyperfine parameters (IS and QS) are those observed
at 90 K. The IS values are reported with respect to a room
temperature absorber spectrum of BaSnO3. The data relating to
the mean-square amplitude-of-vibration (msav) of the tin atoms
in the various compounds are noteworthy. The msav is most
readily expressed in terms of the parameter F = −k2 < x2 > k2.
)
2
763.8
814.8
827.4
919.4
i
4
)
6
2
i
)
)
2
2
i
8
i
(12) Pb(SArPr
(13) Pb(SArPr
(14) Pb(SArPr
)
4283
4299
4335
4
6
8
2
2
i
i
)
)
2
i
(15)Ge(SeArPr
)
657.5
4
2
Pri4
a
(16)Sn(SeAr
(18) Sn(OArMe
(19) Sn(OArPr
(20) Pb(OArPr
)
526.9
1148
2
This parameter can be evaluated from the 119Sn ME data (F X,T
)
)
6
)
−344
2
i
4
)
−289.7
2
as well as the Ui,j values determined in the X-ray studies (F X,T
i
all at temperatures T.51 The 119Sn ME F parameters were cal-
4
)
1070
2
a
1JSeSn = 516 Hz.
culated from the temperature dependence of the logarithm of the
i
Pri6
Figure 7. Mossbauer spectrum for Sn(SArPr )2 (9) at 93 K, with tabular data for Sn(SAr )2 (10) also included. Two signals, in an almost identical ratio,
4
̈
i
Me6
Pri8
are also observed for Sn(SArPr )2. Only one tin site is observed for compounds Sn(SAr )2 and Sn(SAr )2.
6
a
Table 6. Summary of the 119Sn Mossbauer Effect Results cited in the Text
̈
8
9
10
11
16
19
units
IS1(90)
3.08(1)
2.03(1)
3.34(1)
2.71(1)
3.45(1)
1.38(1)
∼indep
∼indep
∼indep
∼indep
25.13(16)
21.31(16)
2.22(6)
2.99(6)
1.89(6)
0.74
3.23(1)
2.67(1)
3.36(1)
1.40(1)
1.4(3)
3.34(1)
2.60(1)
3.30(2)
2.59(2)
3.15(1)
2.10(1)
mm sec−1
QS1(90)
IS2(90)
mm sec−1
mm sec−1
mm sec−1
QS2(90)
-dIS1/dT
-dIS2/dT
-dQS1/dT
-dQS2/dT
-d ln A1/dT
∼4.6(1)
∼8.(1)
mm sec−1/K × 10−4
mm sec−1/K × 10−4
mm sec−1/K × 10−4
mm sec−1/K × 10−4
K−1 × 10−3
∼indep
3.4(3)
2.2(4)
∼indep
24.93(9)
19.53(9)
2.19(5)
2.86(9)
18.94(21)
17.55(41)
25.7(21)
-d lnA2/dT
K−1 × 10−3
k12 < xave
k12 < xave
k22 < xave
>
>
1.68(8)
2.77(4)
1.55(13)
2.63(2)
2.27(9)
3.94(2)
1.83(4)
2.79(1)
2
M,88
X,88
M,88
2
2
>
ME/X-ray
0.61
0.76
0.59
0.58
0.66
a
The parenthetical values are the experimental errors in the last significant figure(s). The subscripts on the cited F parameters indicate M for the
Mossbauer experiment results and X for the X-ray derived values.
̈
I
dx.doi.org/10.1021/ja403802a | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Article
recoil-free fraction, which in turn, for an optically thin absorber,
is equal to the temperature dependence of the logarithm of the
area under the resonance curve. An assumption underlying this
calculation is that f→1 as T→0, that is, that the zero point
vibration is negligibly small compared to the msav in the cited
temperature regime. The F values are smaller than the F
Table 7. Experimental Data for the Electronic Spectra of 1−16
a
and 20
i
i
(1) Si(SArMe
)
2
(2) Si(SArPr
405 (3700)
318 (7400)
)
(3) Si(SArPr
411 (4400)
331 (7500)
)
2
(4) Ge(SArMe
396 (3000)
276 (7700)
)
2
6
4
6
6
2
382 (8300)
318 (23 000)
291 (20 000)
269 (25 000)
M
X
290 (11 200)
290 (10 500)
values, the ratios ranging from 0.59 to 0.76. As has been shown in
a number of recent studies involving iron and/or tin containing
organometallics, the difference in the F factors is especially
large when the metal atom (in this case Sn) is ligated to its
nearest-neighbor environment by single σ, rather than multiple,
bonds.52 Such ligated atoms are sensitive to low-frequency
rotational/librational motions, which are recorded in the X-ray
i
i
i
(5) Ge(SArPr
410 (3100)
330 (3600)
278 (5600)
)
(6) Ge(SArPr
414 (3600)
338 (3700)
286 (4100)
)
(7) Ge(SArPr
430 (7200)
362 (6100)
282 (10 400)
)
(8) Sn(SArMe
400 (1100)
298 (5300)
292 (5300)
)
2
4
6
8
6
2
2
)
8
2
determination but not in the 119Sn Mossbauer data. This
i
i
i
8
i
̈
(9) Sn(SArPr
406 (1300)
330 (1500)
276 (3700)
)
(10) Sn(SArPr
414 (1400)
342 (1700)
276 (4900)
(11) Sn(SArPr
430 (2400)
366 (2500)
286 (4900)
)
(12) Pb(SArPr
422 (1300)
354 (1100)
292 (5800)
)
4
6
4
2
2
2
2
bonding feature is clearly evident in the structures of compound
8 and 11.
The temperature dependence of the logarithm of the recoil-
free fraction, − d ln f/dT, for both 8 and 11, inter alia, is well
fitted by a linear regression, and thus the F̵ parameter permits
the evaluation of the root-mean-square amplitude-of-vibration
(rmsav) of the tin atoms over the range 90 < T < 225 K in the
two structures. These rmsav values are summarized graphically in
Figure 8, from which it is seen that the vibrational amplitudes in 8
i
6
i
i
4
i
(13) Pb(SArPr
427 (1800)
365 (1600)
316 (2200)
)
(14) Pb(SAr Pr
446 (4200)
372 (2500)
292 (6600)
)
(15) Ge(SeArPr
435 (7700)
358 (9000)
303 (8900)
)
2
(16) Sn(SeArPr
434 (5800)
)
4
2
2
2
368 (6900)
305 (9500)
296 (12 900)
i
(20) Pb(OArPr
370 (860)
)
2
4
300 (3000)
293 (3200)
a
Transition energy and intensities (in parentheses) given in nm and
M−1 cm−1.
the first low-energy transition at 382 nm to be a tetrylene n
(HOMO) → tetrylene p (LUMO). However, as the orbital
analysis in Figure 9 demonstrates, the exact bonding character-
istics of the frontier orbitals in divalent chalcogenolates depend
on the Ch−M−Ch bond angle, and no statements on the type
of transitions observed in the electronic spectra of 2−16 can
therefore be made based on the data available for 1. The exact
assignment of each experimental spectrum would require explicit
TD-DFT calculations to be carried out for the specific molecule
in question, which would be a very time-consuming undertaking.
However, some general comments of trends in the experimental
spectra can still be given.
As shown in Table 7, the lowest energy transition in 1−16
moves to longer wavelengths on descending group 14. Also,
more electronegative group 16 substituents more effectively
stabilize the tetrylene lone pair via an electron-withdrawing effect
and increase the energy difference between the lone pair and
the empty p orbital.2 The energy of the transition also decreases
with increasing ligand bulk. As the lowest energy transition is
presumably of HOMO → LUMO type (however, it is not known
if the structures in solution are the same as those in the crystal
phase) in all systems studied, the above trends can be correlated
to accompanying changes in the key structural parameters, that
is, the Ch−M−Ch and M−Ch−C bond angles, which directly
affect the energy of the HOMO (see Figure 9) and therefore the
electronic spectrum.
Figure 8. The rmsav of the Sn atoms in two of the compounds discussed
in the text, calculated from the temperature-dependent 119Sn Mossbauer
̈
data.
are somewhat larger than in 11. Finally, it is worth noting that
the temperature dependence of the recoil-free fraction in 9 and
16 are essentially identical, implying that replacing S (in 9) by Se
(in 16) has little effect on the metal atom dynamics in the two
compounds.
The X-ray crystal data for 10 suggest that the main difference
in the two sites is the change of the S−Sn bond lengths. For
the higher occupancy tin site, the two S−Sn bond lengths differ
slightly at 2.4919(6) and 2.4114(6) Å, whereas in the low-
occupancy site the lengths are 2.3530(12) and 2.5235(12) Å.
The QS of 2.665 mm sec−1 appears to correlate with the more
symmetric tin site with the smaller QS of 1.395 mm sec−1
corresponding with the asymmetric tin site.
Electronic Spectra. The electronic spectra of the divalent
chalcogenolates (wavelengths and intensities are given in
Table 7) are all characterized by transitions in the UV−vis and
near-UV regions for the thiolates and selenolates and in the near
UV for most of the aryloxo complexes.12,33 We have reported
recently that the experimental UV−vis spectrum of 1 can be
interpreted with the help of TD-DFT calculations which showed
The data from electronic spectra indicate that the heavier
tetrylenes have a smaller HOMO−LUMO energy separation
than their lighter congeners. Although similar trends have been
observed previously,6,10 this result is opposite of what is expected
on the basis of a comparison with transient dialkyl or diaryl
J
dx.doi.org/10.1021/ja403802a | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Article
Figure 9. Valence Kohn−Sham MOs of H−S−Ge−S−H and their energies [eV].
species6,53−56 or stable diaryl tetrylene complexes, such as
involves a combination of repulsive steric interactions and
attractive dispersion forces between the bulky substituents across
the axis that bisects the MCh2 angle. For the terphenyls, the
greatest repulsion comes from the ortho-substituents of the
flanking arene rings on the lone pair side of the group 14 atom.
The dispersion interactions occur both on the group 14 element
lone pair side and the side of chalcogenolate ligands and may be
visualized to best advantage in the illustration of the structure
of 11 (Figure 2), where these ortho-isopropyl groups (and also
the para-isopropyl groups) are brought into close approach.
The interligand interactions cause the C−Ch−M bond angles to
widen in order to relieve strain, which also cause the Ch−M−Ch
angles to contract to sub-90° angles. There appears to be little
direct interaction of the flanking arene rings with the metal based
Pri4
6,57
M(ArMe )2 and M(Ar )2 (M = Ge−Pb).
These predict the
6
transition energy should become greater descending the group
based on the inert pair effect, where s electrons become
progressively lower in energy upon descending the group.58 The
tetrylene lone pair orbital does in fact decrease in energy on
descending group 14, but energy separation between energy levels
may also decrease, due to the weakening of the bonds with
increasing atomic number. Because of the acute bond angles, there
are other orbitals that approach each other in energy in these
systems (see Figure 9). Consequently, the low energy transitions
observed in the experimental spectra of tin and lead derivatives may
also originate from the π-type lone pairs on the chalcogen atoms
and not from the tetrylene lone pair. Our recent analysis of the
electronic spectrum of the silicon derivative 1 showed these
transitions to reside only slightly higher in energy (around 60 nm in
the experimental spectrum) compared to the transition with
silylene n → p character.12
on heteronuclear NMR and 119Sn Mossbauer spectroscopy and
̈
no significant distortions within the crystal structures.
To further investigate the structural trends in dichalocogenolate
tetrylenes, a series of calculations was carried out using density
functional theory (DFT). In particular, the role of electronic and
steric effects in determining the Ch−M−Ch angle was analyzed by
Orbital Analysis. The major factor producing the acute bond
angles in tetrylenes 2−16, as well as in other similar compounds,
K
dx.doi.org/10.1021/ja403802a | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Article
carrying out geometry optimizations for R−Ch−M−Ch−R,
1° decrease in the bond angle. This is in good agreement with the
range of R−Ch−M−Ch−R systems that can be synthesized
experimentally and the straightforward nature of the synthetic
procedure used to obtain even the bulkiest derivatives (metathesis).
Optimized Structures. The results from geometry optimiza-
tions of R−Ch−M−Ch−R with different R groups (SI) show
that electronic effects of the organic substituent have very little
impact on the key geometrical parameters of the system. For
example, the Ch−M−Ch angle hardly changes at all when
comparing data for R = H systems to that of the corresponding
R = Ph species. Accordingly, there is very little substituent
induced change in the calculated atomic charge for the group 14
element. What is also notable from the calculated structures is
that the Bent’s rule is in general obeyed in both R = H and Ph
series,7,59 and the smallest Ch−M−Ch angles are found in
bisphenoxides. This strongly suggests that the counterintuitive
results obtained experimentally do not arise from electronic
effects but instead predominantly from steric and dispersion
factors. Furthermore, in all systems studied the Ch−M−Ch angle
spans a relatively modest range from 89.6° to 96.9° with the
largest values obtained when M = Si (most s−p hybridization)
and the smallest when M = Sn and Pb (least s−p hybridization).
The bonding in dichalocogenolate tetrylenes does not change
markedly from that described above even when using the parent
terphenyl ligand (Tph = C6H3-2,6-Ph2) as a substituent. The
calculated Ch−M bond lengths change somewhat only in the
case of the most crowded Ch = O derivatives but the differences
are at most 0.05 Å. Also, the range of optimized Ch−M−Ch
bond angles is only slightly narrower than that calculated for
R = Ph species, from 87.4° to 93.5°, indicating very little changes
in the electronic structure of the Ch−M−Ch moiety. Clearly the
parent terphenyl ligand (Tph) is not sterically encumbering
enough to alter the key bonding characteristics of these systems
to any significant degree. This is also apparent from the cal-
culated C−Ch−M bond angles which are between 95° and 100° for
all sulfur and selenium derivatives and are significantly less than
those observed experimentally. We therefore turned our attention to
the analysis of the more crowded structures for which X-ray data
where M = Si, Ge, Sn, Pb; Ch = O, S, Se; and R = H, Ph, Tph,
Pri8
Ar (Tph = C6H3-2,6-Ph2). However, before discussing the
results of these calculations, we begin by concentrating on an
orbital-type analysis of bonding in dichalocogenolate tetrylenes
and inspect the Kohn−Sham MOs of the parent molecular framework.
The valence MOs of the model species H−Ch−M−Ch−H
have C2v symmetry, and their relative energy levels are shown
in Figure 9 (center) for Ch = S and M = Ge combination.
The HOMO (a1) corresponds to the tetrylene lone pair and
the HOMO-1 (a2) and HOMO-2 (b1) are π-type bonding
and nonbonding combinations of the pz AOs at Ch and M;
the LUMO (b1) is the third π-type combination which is
antibonding. By visual inspection of the orbitals, it becomes
immediately evident that there is a net bonding contribution
from two σ-type orbitals within the Ch−M−Ch moiety, which
correspond to two single bonds. Furthermore, there is also a
π-type bonding orbital, HOMO-2, but its contribution to Ch−M
bonding is likely to be of less importance for systems with
nonplanar R−Ch−M−Ch moieties (i.e., 1−14) and, con-
sequently, a lower symmetry C2 point group.
Figure 9 also shows the changes in the valence MOs due to a
20° decrease in the Ch−M−Ch angle (left) or a 20° increase in
the R−Ch−M angle (right) from the calculated lowest energy
value near 94.2° and 93.3° respectively. What is most notable is
that both perturbations induce major changes in the energies and
shapes of only a few orbitals. Specifically, when the Ch−M−Ch
angle decreases, the energy of the lone pair a1 HOMO decreases
as the orbital attains more Ch···Ch bonding character. This is
supported by the 119Sn Mossbauer spectra of stannylenes, 8−11,
̈
where the isomer shift becomes more positive from 8 (3.08 mm
sec−1) to 12 (3.34 mm sec−1) indicating an increase of electron
density at the tin nucleus. At the same time, the energy of the
π-type nonbonding orbital (a2) increases as it gradually becomes
more and more Ch···Ch antibonding. Consequently, at some
point, these MOs will cross, and the nature of the HOMO will
change. We note that with realistic substituents, the molecular
point group is lowered to C2 in which both HOMO and HOMO-1
transform according to the same irreducible representation,
with the result that there will be an avoided crossing. In contrast
to the above, widening the R−Ch−M angle in R−Ch−M−Ch−R
increases the energy of the HOMO as it loses its Ch···Ch
bonding character and becomes more M−Ch antibonding.
Again, this change is counterbalanced by a decrease in the
energy of one of the orbitals which attains more M−Ch bonding
character upon increasing the R−Ch−M angle. However, in this
case there is no associated change in the relative ordering of the
orbitals as the two MOs are well separated in energy.
allows direct comparison between theory and experiment.
The calculated key metrical parameters for the R = ArPr series
i
8
are summarized in Table 8. A comparison with the available
experimental data (Table 1) shows the two sets of numbers to be
in reasonable agreement with each other: the calculated Ch-M
bond lengths are accurate to less than 0.05 Å and the optimized
Ch−M−Ch are only around 5° wider than those found
experimentally. However, what is most notable is that the
calculated structures reproduce the “inverse” of Bent’s rule that
has been observed experimentallythe widest Ch−M−Ch
angles are found for Ch = O, around 100°, and the narrowest
for Ch = Se, in which case angles close to 75° are seen.
Consequently, for the bisphenoxide tetrylenes, there is too much
steric repulsion, as well as interelectronic repulsion between the
O-M bonding pairs, to permit acute interligand bond angles
to occur. This is mainly due to their short C−O distances as
compared to C−S and C−Se bonds in corresponding thiolato and
selenolato derivatives. The calculations also accurately reproduce
the increase in the R-Ch-M bond angle upon increasing the steric
bulk of the substituent employed.
Figure 9 raises two important points. First, the relative
ordering of the frontier MOs in dichalocogenolate tetrylenes is
dependent on the key geometrical parameters which in turn
depend heavily on the identity of the M and Ch atoms and the
steric bulk of the aromatic substituent employed. Consequently,
trends in, for example, the electronic spectra, are not expected to
correlate with X-ray structural parameters in any straightforward
manner (see above). Second, the potential energy surface of
dichalocogenolate tetrylenes can, at least to some extent, adapt to
changes in the geometrical parameters through changes in the
nature of key orbital interactions. For example, the potential
energy surface for the bonding of the Ch−M−Ch angle in parent
dichalocogenolate tetrylenes is calculated to be particularly
shallow, with energy increasing only a few kJ mol−1 per successive
It would be reasonable to assume that the remaining dis-
crepancies between the data in Tables 1 and 8 are attributable to
packing effects generated by the large terphenyl substituents
as these are not modeled in calculations. However, as has
L
dx.doi.org/10.1021/ja403802a | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Article
i
Pri8
Table 8. Selected Bond Lengths [Å] and Angles [°] for Calculated Structures of Formulae ArPr −Ch−M−Ch−Ar , where
M = Si−Pb and Ch = O−Se
8
PBE0/TZVP
disp. corr. PBE0/TZVP
Ch\M
Si
Ge
Sn
Pb
Si
Ge
Sn
Pb
r(ChM)
∠MChM
∠CChM
O
S
1.772
2.210
2.354
99.1
1.874
2.322
2.442
96.2
2.123
2.553
2.663
96.0
2.248
2.647
2.751
97.3
1.759
2.203
2.348
96.4
1.869
2.315
2.435
93.0
2.109
2.539
2.649
92.3
2.228
2.631
2.736
93.0
Se
O
S
84.4
81.8
78.3
79.0
82.2
77.8
74.1
73.6
Se
O
S
81.5
80.3
76.7
77.4
79.4
78.1
72.1
72.3
136.6
117.2
115.5
136.7
117.6
115.2
136.1
117.9
115.2
136.2
118.1
115.5
136.7
116.4
114.6
133.4
117.6
114.0
134.6
119.0
117.8
134.6
119.8
117.5
Se
recently been shown60 for the quintuple bonded complex,
withdispersionforcesasevidenced bya comparison of the two sets
i
i
Pri4
ArPr CrCrAr
,
61 dispersion forces can play an important role as
of theoretical results for the R = ArPr series.
4
8
It is interesting to note that the build-up of electron density in
between the chalcogen atoms can be seen from the experi-
mentally determined difference electron density maps. For
secondary bonding interactions capable of stabilizing com-
pounds with exotic bonding environments62 and bulky sub-
stituents. To this end, we tested the effect of empirical dispersion
correction (Grimme’s DFT-D3)27 on the geometry optimization
Pri8
example, examination of the electron density map for Pb(SAr )2
i
8
of the studied R = ArPr series (see Table 8). The results show
shows electron density centralized within the plane of the
S−Pb−S angle (Figure 10). Additionally, the map of Sn(SArMe
)
2
6
that dispersion has the largest impact on the Ch−M−Ch bond
angle which decreases by 2−5° throughout the series, therefore
improving the agreement between theoretical and experimental
i
8
structures. The Pb−S derivative, Pb(SArPr )2 (14), makes an
interesting exception to the above: calculations predict it to have
a similar geometry to its lighter group 14 congeners, that is also
i
seen with the less sterically crowded plumbylenes, Pb(SArPr
)
2
4
i
(12) and Pb(SArPr )2 (13), whereas the experimental structure
of Pb(SArPr )2 (14) shows a surprisingly wide S−Pb−S angle
6
i
8
(80.07(2)°) accompanied by a significant twist in the relative
orientation of the two terphenyl groups. However, the two S−Pb
bond lengths are essentially equivalent in the experimental
structure and comparable to the calculated values, indicating that
the discrepancy in the bond angles could simply be a packing
effect since there are four solvent molecules in the crystal
i
Figure 10. Difference electron density map of (a) Sn(SArPr )2 (11)
8
shows contours of electron density bisecting the two M−S bonds. (b)
Pb(SArPr )2 (14) shows a buildup of electron density within the S−Pb−S
i
8
plane. Lines are shown connecting the sulfur and lead nuclei.
structure of 14, while there are none in those of 7, 11, or in the
i
reveals no appreciable electron density in a centralized point
theoretically calculated Si(SArPr )2.
8
within the S−Sn−S system. The difference map of the highly
The acute Ch−M−Ch bond angles in dichalocogenolate
tetrylenes are in many cases accompanied by short intra-
molecular Ch···Ch distances63 that are well below the sum of van
der Waals radii for the respective elements (see Tables 1−3).
This raises the important question of the chalcogen atoms
sharing an orbital-type (covalent) bonding interaction between
them. A visual inspection of the valence Kohn−Sham orbitals for
H−S−Ge−S−H (Figure 9) shows that there is a net Ch···Ch
bonding contribution from one MO which is that of the tetrylene
lone pair.64,65 As the Ch−M−Ch angle becomes more acute, the
energy of this MO is lowered and the Ch···Ch interaction
strengthened. However, as previously discussed, the change is
accompanied with an increase in the energy of the π-type
HOMO-1 which simultaneously acquires more Ch···Ch anti-
bonding character. It is therefore not entirely surprising that an
analysis of the theoretically determined total electron densities
of dichalocogenolate tetrylenes with Bader’s quantum theory of
atoms in molecules (QTAIM)66 failed to locate a bond critical
point connecting the chalcogen centers in any of the model
systems studied. Consequently, the short intramolecular Ch···Ch
distances are mostly a result of geometrical constrains, augmented
Pri8
bent stannylene, Sn(SAr )2, reveals yet a different picture where
one sees a large buildup of electron density bisecting the Sn−S
bonds.
Finally, we note that an analysis35b of the structural distortions
of tetravalent chalcogenolato group 14 element derivatives of
formula M(ChR)4 (M = C−Pb; Ch = O, S) has shown that the
changes in the Ch−M−Ch angles can be rationalized in terms
of the C−Ch−M−Ch−C conformations. The Ch−M−Ch angle
increases as the number of eclipsed chalcogen lone pairs
decreases (as indicated by the C−Ch−M−Ch angle). However,
there is no analogous pattern in compounds 1−14, where the
number of eclipsed chalcogen lone-pairs (cf. C−S−M−S angles
in Table 1) do not correlate well with substituent size.
CONCLUSIONS
■
(1) The principal forces leading to the sub-90° bond angles
observed in the chalcogenolato tetrylenes are those of
intramolecular steric repulsion and dispersion between the
bulky substituents across the molecules.
(2) Dispersion forces stabilize the acute interligand angles.
M
dx.doi.org/10.1021/ja403802a | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Article
(3) For an example of large geometrical distortions due to steric effects,
see: Yoshifuji, M.; Shima, M.; Inamoto, N.; Hirotsu, K.; Higuchi, T.
Angew. Chem., Int. Ed. 1980, 19, 399−400.
(3) Decreases in the bending angle below 90° for the heavier
chalcogenolate derivatives require relatively small changes
(ca. 1 kJ mol−1 deg−1) down to Ch−M−Ch angles of ca. 70°.
(4) The size of the chalcogen has a large effect on the
geometry of the tetrylenes. Because of the small radius of
oxygen, there is significantly greater interligand and bond
pair−bond pair repulsion that prevents closure of the
interligand angle much below 90°. The size increase
between oxygen (radius = 0.63 Å) and sulfur (1.03 Å) or
selenium (1.16 Å) is large, so that bond pair−bond pair
repulsion is diminished. This greatly reduces the amount
of energy required to close the S(Se)−M−S(Se) angle
below 90°. The wider M−O−C angles (ca. 10−20° wider
than M−S−C angles) also reduce steric repulsion across
the molecular axis on the tetrel lone pair side of the
molecule which reduces the steric pressure to close the
O−M−O angle. Additionally, electronegativity plays a minor
role in determining the angles. The high electronegativity of
oxygen promotes greater p character in its bonds relative to
the more electropositive sulfur and selenium (which are still
significantly more electronegative than the central metals)
which favors an interligand angle closer to 90°.
(4) Hinchley, S. L.; Morrison, C. A.; Rankin, D. W. H.; Macdonald, C. L.
B.; Wiacek, R. J.; Voigt, A.; Cowley, A. H.; Lappert, M. F.; Gundersen, G.;
Clyburne, J. A. C.; Power, P. P. J. Am. Chem. Soc. 2001, 123, 9045−9053.
(5) Weidenbruch, W.; Schlaefke, J.; Schafer, A.; Peters, K.; von Schering,
H.-G.; Marsmann, H. Angew. Chem., Int. Ed. 1994, 33, 1846−1848.
(6) (a) Lee, V. Y.; Sekiguchi, A. Organometallic Compounds of Low-
Coordinate Si, Ge, Sn and Pb: From Phantom Species to Stable Compounds;
John Wiley & Sons Ltd: Chichester, UK, 2010; 139−188., (b) Mizuhata,
Y.; Sasamori, S.; Tokitoh, N. Chem. Rev. 2009, 109, 3479−3511.
(c) Tokitoh, N.; Ando, W. Reactive Intermediate Chemistry; Moss, R. A.;
Platz, M. S.; Jones, M., Jr., Eds.; Wiley: Hoboken, 2004, Chapter 14.
(d) Asay, M.; Jones, C.; Driess, M. Chem. Rev. 2011, 111, 354−396.
(7) (a) Bent, H. J. Chem. Educ. 1960, 37, 616−624. (b) Bent, H. Chem.
Rev. 1961, 61, 275−311.
(8) (a) Cetinkaya, B.; Gumrukcu, I.; Lappert, M. F.; Atwood, J. L.;
̈
̈
̈
Rogers, R. D.; Zaworotko, M. J. J. Am. Chem. Soc. 1980, 102, 2088−
2089. (b) The lead analog was shown to be a monomer in the solid-state
based on weak X-ray data, see: Lappert, M. F. Main Group Metal. Chem.
1994, 17, 183−207. (c) Weinert, C. S.; Fenwick, A. E.; Fanwick, P. E.;
Rothwell, I. P. Dalton Trans. 2003, 532−539.
(9) Hitchcock, P. B.; Lappert, M. F.; Samways, B. J.; Weinberg, E. L. J.
Chem. Soc., Chem. Commun. 1983, 1492−1494.
(10) Merrill, W. A.; Wright, R. J.; Stanciu, C. S.; Olmstead, M. M.;
Power, P. P. Inorg. Chem. 2010, 49, 7097−7105.
ASSOCIATED CONTENT
* Supporting Information
■
S
(11) Rekken, B. D.; Brown, T. M.; Olmstead, M. M.; Fettinger, J. C.;
Power, P. P. Inorg. Chem. 2013, 52, 3054−3062.
Experimental details for compounds 4, 7, 9−11, 13, 16, 27, 28,
and 30−35; crystallographic information files, thermal ellipsoid
plots, and tables of crystallographic data for 2, 4, 5, 7−11, 13−16,
27, 28, and 30−35; crystallographic data and files for the high
residual value structures of 3 and 6. 29Si NMR spectra for
silylenes 2 and 3; 77Se NMR spectra for 15 and 16; 119Sn NMR
spectra for 8−11 and 16; 207Pb NMR spectra for 13 and 14; 119Sn
(12) Rekken, B. D.; Brown, T. M.; Fettinger, J. C.; Tuononen, H. M.;
Power, P. P. J. Am. Chem. Soc. 2012, 134, 6504−6507.
(13) Protchenko, A. V.; Birjkumar, K. H.; Dange, D.; Schwarz, A. D.;
Vidovic, D.; Jones, C.; Kaltsoyannis, N.; Mountford, P.; Aldridge, S. J.
Am. Chem. Soc. 2012, 134, 6500−6503.
(14) (a) Gehrhus, B.; Lappert, M. F.; Heinicke, J.; Boese, R.; Blaser, D.
Chem. Commun. 1995, 1931−1932. (b) Ghadwal, R. S.; Roesky, H. W.;
Propper, K.; Dittrich, B.; Klein, S.; Frenking, G. Angew. Chemie. Int. Ed.
2011, 50, 5374−5378. (c) Moser, D. F.; Guzei, I. A.; West, R. Main
Mossbauer spectrum for 19; Plot of k2 < x 2 > as a function of
̈
ave
temperature for 19; further discussion regarding the effect of
ligand bulk on the synthesis of silylenes 1-3; key structural
parameters of calculated model systems and optimized structures
Group Met. Chem. 2001, 24, 811−812. (d) Zark, P.; Schafer, A.; Mitra,
̈
A.; Hasse, D.; Saak, W.; West, R.; Muller, T. J. Organomet. Chem. 2010,
̈
i
Pri8
(xyz data) of ArPr −Ch−M−Ch−Ar (M = Si−Pb; Ch =
8
695, 398−408. (e) Becker, J. S.; Staples, R. J.; Gordon, R. G. Cryst. Res.
Technol. 2004, 39, 85−88. (f) Gehrhus, B.; Hitchcock, P. B.; Lappert, M.
F. Z. Anorg. Allg. Chem. 2005, 631, 1383−1386. (g) Kong, L.; Zhang, J.;
Song, H.; Cui, C. Dalton Trans. 2009, 5444−5446. (h) Mitra, A.;
Brodovitch, J. −C.; Krempner, C.; Percival, P. W.; Vyas, P.; West, R.
Angew. Chem., Int. Ed. 2010, 49, 2893−2895.
O−Se). This material is available free of charge via the Internet at
http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Authors
■
(15) (a) Rieke, R. D.; Hudnall, P. M. J. Am. Chem. Soc. 1972, 94, 7178−
7179. (b) Rachonz, J.; Walborsky, H. M. Tetrahedron Lett. 1989, 30,
7345−7348.
pppower@ucdavis.edu; rolfe.herber@mail.huji.ac.il; heikki.
tuononen@jyu.fi
(16) (a) Freeman, P. K.; Hutchinson, L. L. J. Org. Chem. 1983, 48,
879−881. (b) Bogdanovic, B. Acc. Chem. Res. 1988, 21, 261−267.
(17) (a) Ellison, J. J.; Ruhlandt-Senge, K.; Power, P. P. Angew. Chem.,
Int. Ed. Engl. 1994, 33, 1178−1180. (b) Sutton, A. D.; Fettinger, J. C.;
Rekken, B. D.; Power, P. P. Polyhedron 2008, 27, 2337−2340.
(c) Niemeyer, M.; Power, P. P. Inorg. Chem. 1996, 35, 7264−7272.
(18) Zhu, Z.; Fischer, R. C.; Ellis, B. D.; Rivard, E.; Merrill, W. A.;
Olmstead, M. M.; Power, P. P.; Guo, J.-D.; Nagase, S.; Pu, L. Chem.
Eur. J. 2009, 15, 5263−5272.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We are grateful to the U.S. National Science Foundation for
funding this research (Grant CHE-09848417) and for the dual
source X-ray diffractometer (Grant 0840444). We would also
like to thank the Academy of Finland, the University of Jyvaskyla,
̈
̈
(19) Ellison, J. J.; Ruhlandt-Senge, K.; Hope, H.; Power, P. P. Inorg.
Chem. 1995, 34, 49−54.
the Technology Industries of Finland Centennial Foundation for
generous financial support. The authors are indebted to Prof.
I. Nowik for fruitful discussions relating to the ME data reported
here and Prof. K. C. Molloy for useful discussions regarding the
conformations of 1−14.
(20) Sheldrick, G. M. SHELXTL, version 6.1; Siemens Analytical X-ray
Instruments, Inc.; Madison, WI, 2002.
(21) Sheldrick, G. M. SHELXS-97 and SHELXL-97; Universitat
̈
Gottingen; Gottingen, Germany, 1997.
̈
̈
(22) (a) Dolomanov, O. V.; Bourhis, L. J.; Gildea, R. J.; Howard, J. A.
K.; Puschmann, H. J. Appl. Crystallogr. 2009, 42, 339−341. (b) Hardman,
N. J.; Wright, R. J.; Phillips, A. D.; Power, P. P. J. Am. Chem. Soc. 2003,
125, 2667−2679.
REFERENCES
(1) Power, P. P. J. Organomet. Chem. 2004, 689, 3904−3919.
(2) Fischer, R. C.; Power, P. P. Chem. Rev. 2010, 110, 3877−3923.
■
N
dx.doi.org/10.1021/ja403802a | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Article
(23) (a) Mansell, S. M.; Herber, R. H.; Nowik, I.; Ross, D. H.; Russell,
C. A.; Wass, D. F. Inorg. Chem. 2011, 50, 2252−2263. (b) Glaberson, W.
http://www.megadaq.com.
(24) (a) TURBOMOLE V6.3 2011; a development of the University of
Karlsruhe and Forschungszentrum Karlsruhe GmbH (1989−2007);
TURBOMOLE GmbH (since 2007): available from http://www.
turbomole.com. (b) Laaksonen, L. J. Mol. Graph. 1992, 10, 33−34.
(c) Bergman, D. L.; Laaksonen, L.; Laaksonen, A. J. Mol. Graphics 1997,
15, 301−306.
(48) (a) Christiaens, I.; Piette, J. L.; Laitem, L.; Baiwir, M.; Denoel, J.;
Llabres, G. Org. Magn. Reson. 1976, 8, 354−356. (b) Tan, K. S.; Arnold,
A. P.; Rabenstein, D. L. Can. J. Chem. 1988, 66, 54−60.
(49) Arsenault, J. J. I.; Dean, P. A. W. Can. J. Chem. 1983, 61, 1516−
1523.
(50) (a) Flynn, P. A. In Mossbauer Isomer Shifts; Shenoy, G. K., Wagner,
̈
F.E., Eds.; North Holland Pub. Co.: Amsterdam, 1978, pp 595 ff; (b)
see also the discussion in Mossbauer Spectroscopy: , Greenwood, N. N.
̈
Gibb, T. C., Chapman Hall Ltd: London, 1972, pp 375 ff.
(c) Zuckerman, J. J. In Chemical Mossbauer Spectroscopy; Herber, R.
̈
(25) (a) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. Rev. Lett. 1996, 77,
3865−3868. (b) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. Rev. Lett.
1997, 78, 1396−1401. (c) Perdew, J. P.; Ernzerhof, M.; Burke, K. J. Chem.
Phys. 1996, 105, 9982−9985. (d) Adamo, C.; Barone, V. J. Chem. Phys.
1999, 110, 6158−6170.
H., Ed.; Plenum Press: New York, 1984, pp 271 ff.
(51) Guo, J.-Y.; Xi, H. -W.; Nowik, I.; Herber, R. H.; Li, Y.; Lim, K. H.;
So, C.-W. Inorg. Chem. 2012, 51, 3996−4001 and references therein.
(52) (a) Herber, R. H.; Nowik, I. Phosphorus, Sulfur and Silicon 2011,
186, 1336−40. (b) Herber, R. H. J. Orgonomet. Chem. 2012, 717, 41−44.
(53) (a) Magnusson, E. J. Am. Chem. Soc. 1984, 106, 1177−1185.
(b) Magnusson, E. J. Am. Chem. Soc. 1984, 106, 1185−1191.
(54) Vancik, H.; Raabe, G.; Michalczyk, M. J.; West, R.; Michl, J. J. Am.
Chem. Soc. 1985, 107, 4097−4098.
(26) Schafer, A.; Huber, C.; Ahlrichs, R. J. Chem. Phys. 1994, 100,
̈
5829−5835.
(27) Grimme, S.; Ehrlich, S.; Goerigk, L. J. Comput. Chem. 2011, 32,
1456−1465.
(28) Baceiredo and coworkers had earlier used Mg powder to
synthesize low-valent silicon species, see: Gau, D.; Kato, T.; Saffon-
Merceron, N.; Cossio, F. P.; Baceiredo, A. J. Am. Chem. Soc. 2009, 131,
8762−8763.
(55) Sakurai, H.; Sakamoto, K.; Kira, M. Chem. Lett. 1984, 1379−1382.
(56) (a) Becerra, R.; Gaspar, P. P.; Harrington, C. R.; Leigh, W. J.;
Vargas-Baca, I.; Walsh, R.; Zhou, D. J. Am. Chem. Soc. 2005, 127,
17469−17478. (b) Moriseev, A. G.; Leigh, W. J. J. Am. Chem. Soc. 2006,
128, 14442−14443. (c) Moiseev, A. G.; Leigh, W. J. Organometallics.
2007, 26, 6268−6276.
(29) Jones and Aldridge proposed a lithium bromo silylenenoid
intermediate in the synthesis of their acyclic silylene, see: Ref 13 and
Han, J. S.; Sasamori, T.; Mizuhata, Y.; Tokitoh, N. Chem.−Asian J. 2012,
7, 298−300.
(30) Lim, Y. M.; Cho, H. M.; Lee, M. E.; Baick, K. K. Organometallics
2006, 25, 4960−4964.
(31) Dickie, D. A.; MacIntosh, I. S.; Ino, D. D.; He, Q.; Labeodan, O.
A.; Jennings, M. C.; Schatte, G.; Walsby, C. J.; Clyburne, J. A. C. Can. J.
Chem. 2008, 86, 20−31.
(57) Spikes, G. H.; Peng, Y.; Fettinger, J. C.; Power, P. P. Z. Anorg. Allg.
Chem. 2006, 632, 1005−1010.
(58) (a) Drago, R. S. J. Phys. Chem. 1958, 62, 353−357. (b) Pyykko, P.
̈
Chem. Rev. 1988, 88, 563−594.
(59) (a) Reed, A. E.; Schleyer, P. v. R. J. Am. Chem. Soc. 1987, 109,
7362−7371. (b) Reed, A. E.; Schleyer, P.v.R. J. Am. Chem. Soc. 1990,
112, 1434−1445.
(32) Shaw, R. A.; Woods, M. J. Chem. Soc. A 1971, 1569−1571.
(33) (a) Apeloig, Y.; Karni, M.; West, R.; Welsh, K. J. Am. Chem. Soc.
1994, 116, 9719−9729. (b) Apeloig, Y.; Karni, M. J. Chem. Soc., Chem.
Commun. 1985, 1048−1049. (c) Michalczyk, M. J.; Fink, M. J.;
DeYoung, D. J.; Carlson, C. W.; Welsh, K. M.; West, R.; Michl, J. Silicon,
Germanium, Tin Lead Compd. 1986, 9, 75−83.
(60) Ndambuki, S.; Ziegler, T. Inorg. Chem. 2012, 51, 7794−7800.
(61) Nguyen, T.; Sutton, A. D.; Brynda, M.; Fettinger, J. C.; Long, G. J.;
Power, P. P. Science 2005, 310, 844−847.
(62) Schreiner, P. R.; Chernish, L. V.; Gunchenko, P. A.; Tikonchuk,
E. Y.; Haussman, H.; Serafin, M.; Schlecht, S.; Dahl, J. E. P.; Carlson,
R. M. K.; Fokin, A. A. Nature. 2011, 477, 308−311.
(34) (a) Grumbine, S. D.; Tilley, T. D.; Arnold, F. P.; Rheingold, A. L. J.
(63) Bleiholder, C.; Werz, D. B.; Koppel, H.; Gleiter, R. J. Am. Chem.
̈
Am. Chem. Soc. 1993, 115, 7884−7885. (b) Jutzi, P.; Steiner, W.; Konig,
Soc. 2006, 128, 2666−2674.
̈
(64) (a) Naruse, Y.; Inagaki, S. Top. Curr. Chem. 2009, 289, 265−291.
(b) Inagaki, S.; Goto, N.; Yoshikawa, K. J. Am. Chem. Soc. 1991, 113,
7144−7146. (c) Inagaki, S.; Yoshikawa, K.; Hayano, Y. J. Am. Chem. Soc.
1993, 115, 3706−3709. (d) Dewar, M. J. S. J. Am. Chem. Soc. 1984, 106,
669−682. (e) Sakai, S.; Inagaki, S. J. Am. Chem. Soc. 1990, 112, 7961−
7964.
E.; Huttner, G.; Frank, A.; Schubert, U. Chem. Ber. 1978, 111, 606−614.
(35) (a) Kersting, B.; Krebs, B. Inorg. Chem. 1994, 33, 3886−3892.
(b) Barone, G.; Hibbert, T. G.; Mahon, M. F.; Molloy, K. C.; Parkin, I.
P.; Price, L. S.; Silaghi-Dumitrescu, I. Dalton Trans. 2001, 3435−3445.
(36) (a) Kano, N.; Tokitoh, N.; Okazaki, R. Organometallics 1997, 16,
4237−4239. (b) Tokitoh, N.; Kano, N.; Okazaki, R. Phosphorus, Sulfur
and Silicon. 1999, 153, 333−334.
(65) Recently, the S23− radical, with a weak S···S interactions ascribing
to ca. 0.5 bond order, was proposed for the S2 moiety in the [Cu3S2]3+
ion, see: (a) Berry, J. F. Chem. −Eur. J. 2010, 16, 2719−2724.
(b) Sarangi, R.; Yang, L.; Winikoff, S. G.; Gagliardi, L.; Cramer, C. J.;
Tolman, W. B.; Solomon, E. I. J. Am. Chem. Soc. 2011, 133, 17180−
17191.
(37) Pyykko, P.; Matsumi, S. Chem. -Eur. J. 2009, 15, 186−197.
̈
(38) (a) Seligson, A. L.; Arnold, J. J. Am. Chem. Soc. 1993, 115, 8214−
8220. (b) Driess, M.; Janoschek, R.; Pritzkow, H.; Rell, S.; Winkler, U.
Angew. Chem., Int. Ed. Engl. 1995, 34, 1614−1616.
(39) (a) Vedeneyev, V. I.; Gurvich, L. V.; Kondrat’yev, V. N.;
Medvedev, V. A.; Frankevich, Y. L. Bond Energies, Ionization Potentials,
and Electron Affinities; St. Martin’s Press: New York, 1962. (b) Weinert,
C. S. Main Group Met. Chem 2007, 30, 93−100.
(66) (a) Bader, R. F. W. Acc. Chem. Res. 1985, 18, 9−15. (b) Bader, R.
F. W.; Slee, T. S.; Cremer, D.; Kraka, E. J. Am. Chem. Soc. 1983, 105,
5061−5068.
(40) Stanciu, C.; Richards, A. F.; Stender, M.; Olmstead, M. M.; Power,
P. P. Polyhedron 2006, 25, 477−483.
(41) Parkin, G. Acc. Chem. Res. 1992, 25, 455−460.
(42) Kennedy, J. D.; McFarlane, W.; Pyne, G. S. Bull. Soc. Chim. Belg.
1975, 84, 289−298.
(43) Paramagnetic contribution to NMR shift, see: (a) Ramsey, N. F.
Phys. Rev. 1950, 78, 699−703. (b) Muller, T. J. Organomet. Chem. 2003,
̈
686, 251−256.
(44) Wrackmeyer, B. Annu. Rep. NMR. Spectrosc. 1985, 16, 73−186.
(45) Zilm, K. W.; Lawless, G. A.; Merrill, R. M.; Millar, J. M.; Webb, G.
G. J. Am. Chem. Soc. 1987, 109, 7236−7237.
(46) Simons, R. S.; Pu, L.; Olmstead, M. M.; Power, P. P.
Organometallics 1997, 16, 1920−1925.
(47) Wrackmeyer, B. Annu. Rep. NMR Spectrosc. 2002, 47, 1−37.
O
dx.doi.org/10.1021/ja403802a | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX