Tetrahedral versus planar four-coordinate carbon: A sulfonyl-substituted methandiide

Article abstract of DOI:10.1002/chem.201201369

Flattened. The mono- and dilithiation of a sulfonyl-substituted phosphane sulfide is reported. The new dilithio methandiide features a distorted carbon environment between the typical tetrahedral and planar arrangement (see figure). This geometry results from geometrical restrictions of the donor functions and can be described by two unusual bonding modes of the lithium atoms with the sp²-hybridized methanide carbon. Copyright

Full text of DOI:10.1002/chem.201201369

COMMUNICATION
DOI: 10.1002/chem.201201369
Tetrahedral versus Planar Four-Coordinate Carbon: A Sulfonyl-Substituted
Methandiide
Peter Schrçter and Viktoria H. Gessner*[a]
The electronic structure of compounds with main-group
elements in unusual oxidation states or coordination envi-
ronments has inspired research during recent decades. Dif-
ferences between the second-row elements and their heavier
congeners have been illustrated with many examples, such
as the intensively studied differences between alkenes and
alkynes compared with their heavier trans-bent analogues.[1]
Although the chemistry of carbon belongs to the oldest and
most studied fields in chemistry, new bonding modes and
concepts are still being established. Some recent examples
whether planarization is solely the result of geometric re-
strictions caused by the coordinating side arms or whether it
results from an unknown bonding motif of carbon. To ad-
dress this question, we set out to prepare new dilithio meth-
andiides. Due to their extremely limited accessibility, inves-
tigations have so far concentrated on, but are not limited to,
the readily available bis(phosphonium)-substituted com-
pounds.[12] To clarify the influence of the Li coordination by
intramolecular donor functions, further substituents at the
dimetallated carbon have to be examined.[13] Herein, we de-
scribe the synthesis and structure of a sulfonyl-substituted
geminal dianion and discuss its electronic structure with re-
spect to the planarization of the four-coordinate carbon
atom.
[2]
are the introduction of quadruple bonding in diatomic C2
or divalent carbon(0) in carbodi-
phosphoranes (carbones).[3] This
research is often driven by the
unique reactivity of these com-
pounds, which is based on the
unusual electronic structure. As
such, bond activation reactions,
The starting a-thiophosphinoyl-substituted sulfone 1 was
synthesized from methyl phenyl sulfone by a sequence of
lithiation followed by trapping with Ph2PCl and oxidation
with elemental sulfur (Scheme 1). Due to competing forma-
a research field long limited to
transition-metal complexes, has
started to evolve.[4]
One of the long indisputable
concepts in the chemistry of
carbon compounds is that of the
tetrahedral arrangement of four-
coordinate carbon, as manifested
in vanꢀt Hoffꢀs proposal.[5] How-
ever, this rule has been chal-
lenged, firstly, by computation
by Schleyer and co-workers predicting the stabilization of
planar tetracoordinate carbon by electropositive substitu-
ents.[6] Finally, this prediction was verified experimentally in
2010 by Liddle and co-workers, who succeeded in the isola-
tion of a compound with such a planar four-coordinate
carbon in the bis(phosphonium)-stabilized methandiide I.[7,8]
However, no other known methandiide, such as II, although
limited in number, has been shown to feature this planar
carbon conformation.[9,10,11] This provokes the question, of
Scheme 1. Synthesis and lithiation of a-thiophosphinoyl-substituted sul-
fone 1.
tion of the disubstituted compound, 1 could only be ob-
tained in moderate yields of up to 49% as a colorless crys-
talline solid. To evaluate the deprotonation behavior of 1,
lithiation was first accomplished with one equivalent of
methyllithium in THF solution. Storage at 08C gave crystals
of the lithium salt 1-Li in 81% yield. Compounds 1 and 1-Li
were characterized by multinuclear NMR spectroscopy,
single-crystal X-ray diffraction analysis (see the Supporting
Information), and elemental analysis.
The molecular structure of 1-Li is illustrated in Figure 1.
The asymmetric unit contains half a molecule, which is as-
sembled to the dimer through inversion. The lithium atom is
neither coordinated to the methanide carbon nor to the
[a] Dipl.-Chem. P. Schrçter, Dr. V. H. Gessner
Institut fꢁr Anorganische Chemie
Julius-Maximilians-Universitꢂt Wꢁrzburg
Am Hubland, 97074 Wꢁrzburg (Germany)
E-mail: vgessner@uni-wuerzburg.de
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201201369.
Chem. Eur. J. 2012, 00, 0 – 0
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
1
&
ÞÞ
These are not the final page numbers!

plete consumption of 1 and the formation of a single species
at d=26.4 ppm. Trapping of the reaction mixture with iodo-
methane gave the dimethylated compound 2 nearly quanti-
tatively (Scheme 1 and the Supporting Information). After
work-up, 2 could be isolated in 88% yield.[17] For isolation
of the intermediate dilithio species, a THF solution of sul-
fone 1 was treated with two equivalents MeLi at À308C.
Storage at room temperature gave the dilithiated species as
a crystalline solid in 73% isolated yield.
X-ray diffraction analysis confirmed the double lithiation
and revealed an unusual dimeric structure (Figure 2a and
the Supporting Information). The asymmetric unit contains
half a molecule, which is assembled to the dimer through in-
version. The structure consists of four methandiides and six
coordinating THF molecules. In contrast to many oligomeric
Figure 1. Molecular structure of 1-Li. Hydrogen atoms (except for the
methanide hydrogen) are omitted for clarity. Thermal ellipsoids are at
50% probability.
thioACHTUNGTRENNUNG
phosphinoyl moiety.[10c] Completion of the Li coordina-
tion sphere is solely achieved by the coordination of the two
sulfone oxygen atoms and two additional THF molecules.
The central structural motif is an (O-S-O-Li)2 eight-mem-
bered ring featuring a chair-like conformation. Compared
with the neutral compound 1, the most remarkable change
in the structural parameters concerns the P-C-S backbone.
À
À
The C P and the C S (1.740(3) and 1.651(2) ꢄ, respective-
ly) bond lengths are significantly shorter than those for
1 (1.839(4) and 1.801(4) ꢄ). The carbon atom possesses
a planar arrangement (sum of angles=359.6(2)) with a wid-
ening of the P-C-S bond angle from 113.8(2) to 124.6(2)8.[14]
The latter indicates a considerable change in the electronic
structure and an increased s-character in the bonds to the
methanide carbon (see below).
7
The 31P{1H} and the Li NMR spectra exhibited singlets at
d=32.6 and 0.0 ppm, respectively, indicating no interaction
between the methanide carbon and lithium in solution. The
methanide signals appear as doublets at d=2.73 ppm (2JHP
=
12.1 Hz) in the 1H NMR and at d=44.0 ppm in the
13C{1H} NMR spectrum, with a large coupling constant of
1JCP =109.8 Hz compared with the 1 (59.7, 1JCP =41.6 Hz).
This is in line with the increased bond angle around carbon
and the assumed increased s-character. The 1H and
13C NMR signals were shifted upfield compared with those
of 1. It is noteworthy that 1-Li features exclusively sharp sig-
nals indicating a rigid structure in solution or fast exchange
processes. DFT calculations of dimeric 1-Li and possible
monomeric structures showed only small energetic differen-
ces, so that both species are possible in particular in coordi-
nating solvents.[15,16]
Figure 2. a) Molecular structure of 1-Li2. Hydrogen atoms and noncoordi-
nating THF molecules in the unit cell are omitted for clarity. Thermal el-
lipsoids are at 50% probability. Selected bond lengths [ꢄ] and angles [8]:
À
À
À
À
C1 P1 1.831(3), C7 P1 1.836(2), C13 S2 1.620(3), C13 P1 1.720(3),
À
À
À
À
C13 Li3 2.138(7), C13 Li2 2.332(7), C14 S2 1.801(4), P1 S1 2.008(2),
À
À
À
À
O1 S2 1.498(2), O2 S2 1.500(2), C1B P1B 1.833(4), C7B P1B 1.837(4),
À
À
À
À
C13B S2B 1.605(4), C13B P1B 1.700(4), C13B Li4 2.202(8), C13B Li3
With the monoanion 1-Li in hand, a second deprotonation
was attempted. For this purpose, compound 1 was treated
with two equivalents of MeLi at room temperature. After
4 h, the 31P{1H} NMR spectrum in C6D6 showed the com-
À
À
À
3.227(7), C14B S2B 1.804(4), P1B S1B 2.028(2), O1B S2B 1.505(3),
O2B S2B 1.501(3); S2-C13-P1 120.9(2), S2B-C13B-P1B 121.9(2), Li3-
À
C13-Li2 74.1(2), Li3-C13B-Li4 97.8(2). b),c) Coordination environments
of the methandiide carbon atoms.
&
2
&
www.chemeurj.org
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!

Tetrahedral versus Planar Four-Coordinate Carbon
COMMUNICATION
organolithium compounds and previously reported dialkali
metal methandiides, no regular Li polyhedron is formed,
rather a peculiar structure, in which the Li atoms form four-,
six-, or eight-membered rings with the donor atoms, which
are connected with each other by one common side.[11,18] In
contrast to 1-Li, the Li atoms in 1-Li2 show contacts to the
methandiide carbon atom and the thiophosphinoyl moiety.
In comparison with the neutral compound 1 and anion 1-Li,
the double deprotonation resulted in a further contraction
porting Information). Because the structure of 1-Li2 has four
different Li and two different phosphorous environments,
these NMR data indicate either a breaking of the aggregate
in solution to a monomeric species or further exchange pro-
cesses, which could not be resolved by cooling to À808C.
Due to these processes and 7Li–13C coupling, the
13C{1H} NMR signal of the methanide carbon (d=50.6 ppm)
is broad. This signal is downfield by Dd=14.6 ppm com-
pared with 1-Li, which is in line with studies on related sul-
fonyl-substituted methandiides by Gais and co-workers.[12]
The observed changes in the bond lengths and angles to-
gether with the NMR data suggested a rehybridization by
deprotonation of 1 to 1-Li and 1-Li2 from sp3 to sp2. To fully
rationalize the electronic structure of dianion 1-Li2 and to
evaluate the differences between the planar and distorted
tetrahedral coordination, DFT calculations were per-
formed.[15] At first, a monomeric model system A was
chosen, featuring the environment around C13B (Figure 2a)
with THF and the contacts to the second methandiide re-
placed by the coordination of dimethyl ether. The energy-
optimized structure of model system A is in good agreement
with the molecular structure (see the Supporting Informa-
tion). The calculated atomic charges and the Wiberg bond
indices (Figure 3b) suggest a highly ionic resonance struc-
ture for methandiide A with a highly negatively charged
À
of the P-C-S backbone. In comparison to 1, the C P bond
lengths are shortened by 7% (1: 1.839(4) ꢄ; 1-Li2: 1.700(4)
À
and 1.720(3) ꢄ) and the C S bond lengths by 10% (1:
À
À
1.801(4) ꢄ; 1-Li2: 1.620(3) and 1.605(3) ꢄ). The P S and S
O bond lengths exhibited a lengthening of 4%. These bond
length changes continue the tendencies observed for 1-Li
(Table 1).
Table 1. Comparison of the structural parameters (average values for 1-
À
Li2 and the P CPh bond lengths) and NMR data ([D8]THF (1 and 1-Li),
[D8]toluene (1-Li2)) for the P-C-S moiety in 1, 1-Li, and 1-Li2.
1
1-Li
1-Li2
À
C S [ꢄ]
1.801(4)
1.839(4)
1.949(1)
1.439(3)
1.771(4)
1.844(4)
113.8(2)
4.80, 10.5
58.4, 44.1
1.651(2)
1.740(3)
1.982(1)
1.459(2)
1.792(3)
1.835(2)
124.6(2)
2.73, 12.1
44.0, 109.8
1.613(3)
1.710(3)
2.018(2)
1.501(2)
1.803(4)
1.834(3)
121.4(2)
–
À
C P [ꢄ]
À
P S [ꢄ]
À
S O [ꢄ]
À
S CPh [ꢄ]
À
P CPh [ꢄ]
P-C-S [8]
dH, 2JHP [ppm,Hz]
dC, 1JCP [ppm,Hz]
50.6 (br)
Concerning the question of planarization, the coordina-
tion sphere of the two different methandiide carbon atoms
has to be discussed in more detail. Both coordination
spheres strongly deviate from the ideal tetrahedral environ-
ment. Atom C13B (Figure 2b) exhibits a strangely distorted
fourfold coordination with an approximately planar C-P-S-
Li4 unit (least square plane, deviation: 0.17 ꢄ). Atom Li3
coordinates almost perpendicularly to this plane with an tor-
sion angle (Li4-C-P-Li3) of 97.6(2)8. The coordination
sphere around C13 (Figure 2c) contains a third Li atom and
is best described by a plane consisting of Li3-C13-P-S-Li1,
on top of which Li2 is coordinated. This bonding motif of
C13 resembles that of the planar four-coordinate carbon
atom in I. Neglecting the contact to Li2, C13 exhibits
a quasi-planar arrangement with a short contact to Li3
(2.138(7) ꢄ) and rather long contact to Li1 (3.309(6) ꢄ).
Nevertheless, no planar four-coordinate carbon as in com-
pound I was detected in 1-Li2, but rather an intermediate
coordination form.
Figure 3. a) Model system A; b) natural atomic charges and Wiberg bond
indices; c) orbital representations of the HOMO and HOMO-1 (isosur-
face contour value: 0.05 eꢄ3).
carbon atom (qC =À1.51). This suggests little p-type elec-
tron delocalization in the P-C-S backbone, and that two
lone pairs are essentially localized on the central carbon
À
À
atom. Thus, the contracted C P and C S bond lengths ob-
Multinuclear NMR studies of 1-Li2 at room temperature
revealed broadened signals, especially in the 1H and
7Li NMR, in nonpolar (C6D6, [D8]toluene) and coordinating
solvents ([D8]THF). Variable temperature studies from
room temperature to À808C showed no significant change
in the 31P{1H} NMR, but a clear splitting to two sharp sin-
served in the crystal structure result from electrostatic at-
[19]
tractions in P+-C2À-S2+
.
It is noteworthy that the shorten-
À
ing of the C P bond length is more pronounced in the bis-
(phosphonium) substituted dianions, such as I and II.[11] This
is the result of stronger interactions of the lone pairs at
carbon with the sulfonyl moiety compared with the thio-
phosphinoyl unit. This high anion-stabilizing ability of the
7
glets in the Li NMR spectrum at around 08C (see the Sup-
Chem. Eur. J. 2012, 00, 0 – 0
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
&
3
&
ÞÞ
These are not the final page numbers!

V. H. Gessner and P. Schrçter
sulfonyl unit was also confirmed by the lower charge con-
centration at the methanide carbon (qC =À1.51) compared
with the bis(thiophosphinoyl) system (qC =À1.77)[11b] and by
the viability of the dilithiation, which is reflected by a re-
markably low reaction barrier of only 26.2 kJmolÀ1.
Concerning the planarization of the carbon atom, the or-
bital properties are of particular interest. The HOMO and
HOMO-1 of A (Figure 3c) represent the two lone pairs at
the methandiide carbon atom. The HOMO is essentially
nonbonding, whereas the HOMO-1 points towards one of
the lithium atoms. Natural bond orbital (NBO) analyses sug-
gests an approximately sp2 hybridized methanide carbon
with two nonequivalent lone pairs differing in their energy
and hybridization (LP(1)/HOMO-1: sp2-hybrid orbital
(sp1.99); LP(2)/HOMO: p-orbital (sp99.9)].[20,21] This orbital
representation is close to that of the planar bis(phosphoni-
um) system I. The energy-optimized structure of I also ex-
hibits two different NBOs for the lone pairs, however, with
a slightly higher p-character for LP(1) and thus a higher s-
Figure 4. Bonding modes of two lithium atoms with a sp2-hybridized
carbon atom and NBOs of LP(1) and LP(2) in a) planar arrangement
(Aꢀ) and b) distorted arrangement (B).
character in the C P bonds (sp1.45, sp2.10 for A). This is in
À
line with the observed broadened P-C-P angle (132.18) com-
pared with the P-C-S angle (121.48) in 1-Li2. To evaluate if
a higher p-character of the two lone pairs may also favor
a planar arrangement in 1-Li2, variations of model system A
were calculated: Aꢀ with a constrained planar Li-P-C-S-Li
moiety and A-131 and A-135 with P-C-S bond angles fixed
at 131 and 1358, respectively. Energy optimization revealed
À
À
(e.g., Wiberg bond indices for Li O and Li C: nWiberg <0.1),
which means that structure formation is dominated by the
interaction of charges and less by the overlap of orbitals.
This suggests that the isolation of further methandiides with
a planar four-coordinate carbon should be possible by care-
ful selection of the coordinating side arms and the reaction
conditions (additives). It will be interesting to see, if these
new bonding modes of carbon are maintained in complexes
with transition metals with carbon–metal bonds of more co-
valent character, and if this influences the reactivity of these
compounds.
an energetic preference of the model system
A by
21.6 kJmolÀ1 over its planar analogue and most importantly
a preference of a nonplanar arrangement in A-131 and A-
135. Interestingly, NBO analyses of these derivatives, includ-
ing the planar system Aꢀ, showed no significant changes in
the orbital interactions, so that in general all structures can
be described by a sp2-hybridized methanide carbon atom.
However, this orbital setting has been used to explain the
planar geometry at the methanide carbon in compound I.
Next question is: how is this then in line with the structure
of 1-Li2, especially given the nonplanar coordination and the
strongly distorted arrangement around C13 (Figure 2c).
Overall, the calculations indicate two borderline cases for
the bonding in methandiides shown in Figure 4: a) The four
substituents are exclusively bound to the sp2-hybrid orbitals
In conclusion, the synthesis and characterization of mono-
and dilithiated sulfonyl-substituted phosphine sulfide 1 was
presented. Upon metalation, dramatic changes in bond
lengths and angles of the methanide carbon were observed,
which resulted from rehybridization and electrostatic inter-
actions in the P-C-S backbone. The dilithio methandiide fea-
tures a distorted carbon environment, which crucially differs
from the tetrahedral arrangement. This geometry is caused
mainly by geometrical restriction of the donor functions and
can be described by two different bonding modes of the lith-
ium atoms with the sp2 hybridized carbon atom.
À
through two 2e,2c bonds (C X bonds) and one 2e,3c bond
(Li-C-Li) giving way to a planar four-coordinate carbon
atom (compound I). b) All substituents form 2e,2c bonds,
whereas one of the lithium atoms is bound to the p-orbital
at the carbon. This results in a strongly distorted tetrahedral
arrangement with a small Li-C-Li angle (Li3-C13B-Li4
97.8(2)8 in 1-Li2). Although the planar system I is described
by bonding mode a), for the description of the structure of
1-Li2 both bonding modes have to be applied. This can
easily be seen from the environments of C13 and C13B in
Figure 2 and was confirmed by NBO analysis of model
system B for the environment around C13 (Figure 4b and
the Supporting Information).
Acknowledgements
We thank the Deutsche Forschungsgemeinschaft, the Alexander von
Humboldt Foundation and the Fonds der Chemischen Industrie for finan-
cial support. We also thank Prof. Dr. H. Braunschweig for generous sup-
port and helpful advices.
One always has to keep in mind that the interactions in
dilithio methandiides are essentially electrostatic in nature
Keywords: alkali metals · carbanions · lithium · planar four-
coordinate carbon · structure elucidation
&
4
&
www.chemeurj.org
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!

Tetrahedral versus Planar Four-Coordinate Carbon
COMMUNICATION
[12] For examples of other geminal dianions, see: a) J. Vollhardt, H.-J.
Gais, K. L. Lukas, Angew. Chem. 1985, 97, 607–609; Angew. Chem.
Int. Ed. Engl. 1985, 24, 610–611; b) J. Vollhardt, H.-J. Gais, K. L.
Lukas, Angew. Chem. 1985, 97, 695–697; Angew. Chem. Int. Ed.
Engl. 1985, 24, 696–697; c) H.-J. Gais, J. Vollhardt, J. Am. Chem.
Soc. 1988, 110, 978–980; d) J. F. K. Mꢁller, M. Neuburger, M.
Zehnder, Helv. Chim. Acta 1997, 80, 2182–2190; e) G. Linti, A.
Rodig, H. Pritzkow, Angew. Chem. 2002, 114, 4685–4687; Angew.
Chem. Int. Ed. 2002, 41, 4503–4506.
[1] a) P. P. Power, Organometallics 2007, 26, 4362–4372; b) A. Sekigu-
chi, Pure Appl. Chem. 2008, 80, 447–457; c) Y. Jung, M. Brynda,
P. P. Power, M. Head-Gordon, J. Am. Chem. Soc. 2006, 128, 7185–
7192.
[2] S. Shaik, D. Danovich, W. Wu, P. Su, H. S. Rzepa, P. C. Hiberty, Nat.
Chem. 2012, 4, 195–200.
[3] a) R. Tonner, F. ꢅxler, B. Neumꢁller, W. Petz, G. Frenking, Angew.
Chem. 2006, 118, 8206–8211; Angew. Chem. Int. Ed. 2006, 45, 8038–
8042; b) G. Frenking, R. Toner, Pure Appl. Chem. 2009, 81, 597–
601.
[13] V. H. Gessner, Organometallics 2011, 30, 4228–4231.
[14] The methanide hydrogen has been found in the difference Fourier
map and refined independently.
[4] P. P. Power, Nature 2010, 463, 171–177.
[5] J. H. vanꢀt Hoff, Arch. Neerl. Sci. Exactes Nat. 1874, 445–454.
[6] J. B. Collins, J. D. Dill, E. D. Jemmis, Y. Apeloig, P. v. R. Schleyer, R.
Seeger, J. A. Pople, J. Am. Chem. Soc. 1976, 98, 5419–5427.
[7] O. J. Cooper, A. J. Wooles, J. McMaster, W. Lewis, A. J. Blake, S. T.
Liddle, Angew. Chem. 2010, 122, 5702–5705; Angew. Chem. Int. Ed.
2010, 49, 5570–5573.
[8] For transition metal complexes with a planar tetracoordinate main
group element, see: a) T. Beringhelli, G. Ciani, G. D. Alfonso, A.
Sironi, M. Freni, J. Chem. Soc. Chem. Commun. 1985, 978–979;
b) D. Rçttger, G. Erker, Angew. Chem. 1997, 109, 840–856; Angew.
Chem. Int. Ed. Engl. 1997, 36, 812–827; c) H. Braunschweig, R. D.
Dewhurst, K. Kraft, S. ꢅstreicher, K. Radacki, Angew. Chem. 2012,
124, 2225–2228; Angew. Chem. Int. Ed. Engl. 2012, 51, 2183–2186.
[9] Dilithiomethane [(H2CLi2)2] can be described as a dimer of two
planar [H2CLi2] molecules.
[10] For reviews, see: a) N. D. Jones, R. G. Cavell, J. Organomet. Chem.
2005, 690, 5485–5496; b) T. Cantat, N. Mꢆzailles, A. Auffrant, P. Le
Floch, Dalton Trans. 2008, 1957–1972; c) S. T. Liddle, D. P. Mills,
A. J. Wooles, Organomet. Chem. 2010, 36, 29; d) S. Harder, Coord.
Chem. Rev. 2011, 255, 1252–1267.
[11] For examples of isolated bis(phosphonium)substituted methandiides,
see: a) A. Kasani, R. P. K. Babu, R. McDonald, R. G. Cavell,
Angew. Chem. 1999, 111, 1580–1581; Angew. Chem. Int. Ed. 1999,
38, 1483–1484; b) T. Cantat, L. Ricard, P. Le Floch, N. Mꢆzailles,
Organometallics 2006, 25, 4965–4976; c) L. Orzechowski, G. Jansen,
S. Harder, Angew. Chem. 2009, 121, 3883–3887; Angew. Chem. Int.
Ed. 2009, 48, 3825–3829; d) M. Demange, L. Boubekeur, A. Auf-
frant, N. Mꢆzailles, L. Ricard, X. Le Goff, P. Le Floch, New J. Chem.
2006, 30, 1745–1754.
[15] All calculations were performed with the Gaussian 03 (Revi-
sion E.01) set of programs and the B3PW91 functional. The 6-31+
G* basis set was used for hydrogen and lithium, 6–311+G** for all
other atoms. NBO analyses were carried out on the optimized sys-
tems using the NBO 5.G program implemented in the Gaussian 03
package.
[16] Dimeric 1-Li is enthalpically favoured by 44.8 kJmolÀ1, but entropi-
cally disvafoured (DG=12.8 kJmolÀ1) compared with a monomeric
derivative (see the Supporting Information).
[17] Although the dilithiation proceeds quantitatively, trapping with
other, more sterically demanding electrophiles (e.g., Me3SiCl and
BnCl) resulted in the monosubstituted compound due to the high
stability of the resulting monoanionic intermediate.
[18] For reviews, see: a) T. Stey, D. Stalke in The Chemistry of Organo-
lithium Compounds (Eds.: Z. Rappoport, I. Marek),Wiley, Chiches-
ter, 2004, pp. 47–120; b) V. H. Gessner, C. Dꢂschlein, C. Strohmann,
Chem. Eur. J. 2009, 15, 3320–3334.
[19] L. Orzechowski, G. Jansen, S. Harder, J. Am. Chem. Soc. 2006, 128,
14676–14684.
[20] A. E. Reed, F. Weinhold, J. Chem. Phys. 1985, 83, 1736–1740.
[21] Both LPs are involved in negative hyperconjugation mainly into the
À
À
À
antibonding s*
G
G
ACHTUNGTRENNUNG(P
À
CPh) and s*ACTHUNGTRENNUNG
tions resulted in significant stabilization and in the observed length-
ening of the respective bonds.
Received: April 21, 2012
Published online: && &&, 0000
Chem. Eur. J. 2012, 00, 0 – 0
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
&
5
&
ÞÞ
These are not the final page numbers!

V. H. Gessner and P. Schrçter
Flattened! The mono- and dilithiation
of a sulfonyl-substituted phosphane
sulfide is reported. The new dilithio
methandiide features a distorted
carbon environment between the typi-
cal tetrahedral and planar arrangement
(see figure). This geometry results
from geometrical restrictions of the
donor functions and can be described
by two unusual bonding modes of the
lithium atoms with the sp2-hybridized
methanide carbon.
Alkali-Metal Complexes
P. Schrçter, V. H. Gessner* . &&&& — &&&&
Tetrahedral versus Planar Four-Coor-
dinate Carbon: A Sulfonyl-Substituted
Methandiide
&
6
&
www.chemeurj.org
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!