Rhodium (thiophosphinoyl)(trimethylsilyl)methanide and bis(thiophosphinoyl) methanide complexes: S～S vs. C～S coordination

Article abstract of DOI:10.1002/ejic.201101073

A comparative study of the coordination modes of a (thiophosphinoyl) (trimethylsilyl)methanide (1^-·Li⁺) and bis(thiophosphinoyl)methanide (2^-·Li⁺) ligand with Rh^I was carried out. Several complexes we

Full text of DOI:10.1002/ejic.201101073

FULL PAPER
DOI: 10.1002/ejic.201101073
Rhodium (Thiophosphinoyl)(trimethylsilyl)methanide and Bis(thiophosphinoyl)-
methanide Complexes: S~S vs. C~S Coordination
Hadrien Heuclin,[a] Sophie Carenco,[a] Xavier-Frédéric Le Goff,[a] and Nicolas Mézailles*[a]
Dedicated to the memory of our friend and colleague Pascal Le Floch
Keywords: Rhodium / S ligands / Bidentate ligand / Anions / Density functional calculations / NBO analysis
A comparative study of the coordination modes of a (thio-
phosphinoyl)(trimethylsilyl)methanide (1–·Li+) and bis(thio-
phosphinoyl)methanide (2–·Li+) ligand with RhI was carried
out. Several complexes were synthesized and characterized.
For 1–·Li+, C~S coordination is forced, whereas for 2–·Li+, S~S
and C~S coordination can be achieved. In one case, a dy-
namic equilibrium between these two modes of coordination
was observed. DFT calculations were carried out to rational-
ize this phenomenon and the stability of the methanide com-
pounds.
Introduction
Anionic X~C~X (X = heteroatom) ligands play a signifi-
cant role in coordination chemistry and catalysis. They are
typically designed to be tridentate pincer ligands, to provide
both a strong electronic donation to the metal center and a
controlled steric environment. After a seminal report by
Shaw in the 70s, the chemistry of pincer ligands has evolved
to maturity.[1] The structures that were studied early on,
[2,6-(LCH2)2C6H3]– (L~C~L) where L is a two-electron do-
nor and C is an anionic aryl carbon atom, have allowed
researchers to uncover the peculiarities of these tridentate
ligands. Of the L~C~L ligands, the P~C~P pincers have
found the most fruitful uses.[2] Pincer ligand complexes with
an alkane backbone have attracted much less attention,
probably because of the high flexibility of the alkane rings
as well as the higher electron-donating ability of the ipso sp3
carbon atom. This increased donation results in enhanced
reactivity, which makes the complexes more difficult to ma-
nipulate. Most interestingly, the presence of the CH–M
moiety in the latter complexes can be used to generate a
C=M carbene fragment. Regardless of the nature of the
central carbon atom, sp2 or sp3, the tridentate pincer coor-
dination is observed. However, the [CH(PPh2X)2]– (X = S,
NR) anionic species may be found as tridentate,[3] bidentate
by the coordination of the two X moieties,[4] or by X and
C (Scheme 1).[5]
Scheme 1.
The parameters that govern the various coordination
modes have not been rationalized, yet this versatility might
provide controlled hemilability in catalytic processes.
Hemilability has not been observed so far with these sys-
tems but, in relation to this topic, Milstein et al. have
proved the hemilability of the N moiety in anionic N~C~P
pincer complexes of Ru, Rh, and Pt.[6] In this contribution,
we wish to address the rationalization of the coordination
in X~C~XЈ by comparing two ligand systems as well as dif-
ferent coligands on RhI centers. We have chosen two an-
ionic ligand systems, 1–·Li+ and 2–·Li+ (Scheme 2), which
are believed to bear some electronic resemblance. For
[a] Laboratoire “Hétéroéléments et Coordination”, Ecole
Polytechnique, CNRS,
91128 Palaiseau Cedex, France
E-mail: nicolas.mezailles@polytechnique.edu
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201101073.
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H. Heuclin, S. Carenco, X.-F. Le Goff, N. Mézailles
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1–·Li+, the S~C bidentate coordination is forced, whereas slow evaporation of a concentrated solution in CH2Cl2. The
for 2–·Li+, the three coordination modes can be envisaged. X-ray crystal structure of 1 is presented in Figure 1. Bond
In fact, in 2–·Li+, only very few examples of tridentate coor- lengths and angles are all standard.
dination are found.[3f] Among them, most are reported with
Y ϶ H.[3b,7] With group 9 metal fragments, only bidentate
S~S coordination has been observed,[4c] and tridentate co-
ordination was only proposed in a highly reactive IrI frag-
ment, which resulted in CH activation of the phenyl ring of
the ligand.[8]
Figure 1. ORTEP plot (50% thermal ellipsoids) of 1. Hydrogen
atoms on the phenyl and trimethylsilyl substituents and solvent
molecules are omitted for clarity. Selected bond lengths [Å] and
angles [°]: C(1)–P(1) 1.795(3), C(1)–Si(1) 1.897(3), P(1)–S(1)
1.962(1), Si(1)–C(15) 1.867(3), S(1)–P(1)–C(1) 114.9(1), P(1)–C(1)–
Si(1) 119.8(1).
Deprotonation of 1 with one equivalent of methyllithium
in tetrahydrofuran (THF), Et2O, or toluene yielded 1–·Li+
as reported by Gessner (Scheme 3).[11] Compound 1–·Li+ is
characterized by a singlet at 44.5 ppm in the 31P NMR
spectrum in C6D6. Single crystals of 1–·Li+ suitable for X-
ray diffraction were obtained by slow diffusion of hexanes
into a concentrated solution of the compound in diethyl
ether. A view of the structure of 1–·Li+ is presented in Fig-
ure 2.
Scheme 2. Possible coordination modes for 1–·Li+ and 2–·Li+.
In the first part, we present an experimental and theoreti-
cal comparison of the two anions, with the aim to quantify
the stabilization of the charge at the carbon atom by the
two substituents. In the second part, coordination with sev-
eral RhI centers was studied, which revealed that switching
between S~S and S~C is indeed possible. A dynamic ex-
change between two S moieties was observed by NMR and
rationalized by DFT calculations.
Compound 1–·Li+ crystallizes as a dimer in the solid
state. The two units are connected by an S–Li–C bridge.
Compared to neutral 1, the anion 1–·Li+ features a signifi-
cantly elongated P–S distance [2.0263(4) vs. 1.962(1) Å].
Shortened P–C(1) and C(1)–Si bonds [1.701(1) vs.
1.795(3) Å and 1.827(1) vs. 1.897(3) Å, respectively] corre-
late with the elongation. The monoanion of 2 was also syn-
thesized and studied. The structures of 2 and 2–·Li+ are
Results and Discussion
Synthesis of the Anions and DFT Calculations
The synthesis of 1 was achieved following a reported pro- known and present the related bond shortening (P–Cbridge
)
cedure by Holmes-Smith et al.[9,10] to yield 1 as a white and elongation (P–S).[12,13] These geometric changes were
crystalline solid after purification in good yield (84%, investigated by DFT using B3LYP at the 6-31+G* level of
Scheme 3).
theory on all atoms to compare the two anions. It was of
Compound 1 exhibits a sharp singlet at 37.7 ppm in the interest to quantify the stabilization of the lone pair at C by
31P NMR spectrum. Single crystals of 1 were obtained by the PPh2S and SiMe3 substituents. Our group has already
Scheme 3. Synthesis of 1–·Li+ and 2–·Li+.
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Rhodium Methanide Complexes: S~S vs. C~S Coordination
into the two antibonding σ*(P–H) and the σ*(P–S) orbitals
in I–·Li+ and into the two antibonding σ*(P–H), the σ*(P–
S), and the σ*(Si–C) orbitals in II–·Li+. The results of the
stabilization are given in Tables 2 (for I–·Li+) and 3 (for
II–·Li+). The resulting interaction energy can be estimated
by either deletion of the appropriate off-diagonal elements
of the Fock matrix in the NBO basis (Edel energy) or the
standard second-order perturbation approach [which af-
fords an E(2) energy]. The magnitude of the donor–
acceptor interaction is mainly controlled by i) the energy
gap (ΔEij) between the donor and acceptor orbitals, ii) the
corresponding Fock matrix element (Fij) and iii) the occu-
pation of the donor orbital (ni). As expected, the NBO
analysis indicates that the S–Li and C–Li interactions are
essentially electrostatic in nature (nWiberg ≈ 0.1, qLi Ͼ 0.85).
Figure 2. ORTEP plot (50% thermal ellipsoids) of 1–·Li+. Hydro-
gen atoms on the phenyl and trimethylsilyl substituents are omitted
for clarity. Selected bond lengths [Å] and angles [°]: C(1)–P(1)
1.701(1), C(1)–Si(1) 1.827(1), P(1)–S(1) 2.0263(4), S(1)–Li(1)
2.542(2), C(1)–H(1) 0.95(2), P(1)–C(1)–Si(1) 129.56(7), S(1)–P(1)–
C(1) 113.72(4).
Table 2. Main stabilization of the lone pair at the central carbon
atom in I–·Li+ [only E(2) Ͼ 0.5 kcal/mol are considered].
Donating Accepting orbital
Σ[E(2)]
orbital
type
E(2)
kcal/mol
ΔEij
(u.a.)
Fij (u.a.) kcal/mol
reported the synthesis of the dianion derived from bis(di-
phenylthiophosphanyl)methane 2 (22–·Li+2),[14] and it was
shown that the stability of this compound relies on the sta-
bilization of the negative charges at the central carbon atom
by donation into empty vicinal orbitals. Calculations have
LP1(C)
LP1(C)
LP1(C)
LP1(C)
σ*(P–S)
σ*(P–H)
σ*(P–H)
σ*(Si–C) 1.72
σ*(Si–C) 9.96
σ*(Si–C) 0.90
8.30
10.27
0.63
0.32
0.41
0.41
0.47
0.47
0.47
0.048
0.060
0.015
0.027
0.064
0.019
19.20 total
31.78
12.58
been made on model compounds derived from the crystal LP1(C)
structures of 1–·Li+ and 2–·Li+ in which the phenyl rings
LP1(C)
have been replaced by hydrogen atoms (I–·Li+ and II–·Li+,
Scheme 4). We have verified that solvent coordination at
Li+ does not significantly change the results, and only the
Table 3. Main stabilization of the lone pair at the central carbon
atom in II–·Li+ [only E(2) Ͼ 0.5 kcal/mol are considered].
simplified model is presented here. Full details of these cal-
culations are given in the Supporting Information.
Donating Accepting orbital
Σ[E(2)]
orbital
type
E(2)
ΔEij
Fij (u.a.)
kcal/mol
kcal/mol (u.a.)
LP1(C)
LP1(C)
LP1(C)
LP1(C)
σ*(P–S)
σ*(P–H)
σ*(P–S)
σ*(P–H)
10.86
9.67
10.86
9.66
0.31
0.39
0.31
0.39
0.055
0.057
0.055
0.057
20.53 total
41.05
20.52
Scheme 4. Model compounds used for theoretical calculations.
It is obvious that the stabilization brought by the PPh2S
groups in the two compounds is very similar (19.0 kcal/mol
in I–·Li+ and 20.0 kcal/mol in II–·Li+). The stabilization by
the SiMe3 substituent is 12.0 kcal/mol, which results in a
weaker overall stabilization of the lone pair in I–·Li+. The
geometric changes observed upon deprotonation are there-
fore readily rationalized. Indeed, the electron donation from
C into the antibonding orbitals results in the elongation of
the P–S bond and the shortening of the P–C bond in
II–·Li+ and a shortening of the C–Si bond in I–·Li+. As a
consequence, the stabilization of the lone pair at C in 1–·Li+
appears less efficient, which could in turn result in a better
electron transfer to a metal center.
The structural parameters for the optimized geometries
are in excellent agreement with the X-ray data. The elong-
ation of the P–S bond and the shortening of the P–C bond
are particularly well reproduced (Table 1).
Table 1. Comparison of the calculated and experimental bond
lengths [Å] in 1–·Li+ and 2–·Li+.
Distance 1–·Li+
2–·Li+
RX
RX
DFT
Δ
DFT
Δ
P1–C
P2–C
C–Si
P1–S1
P2–S2
1.70
–
1.83
2.03
–
1.75
–
1.86
2.05
–
0.05
–
0.03
0.02
–
1.71
1.71
–
1.99
1.99
1.74
1.74
–
2.02
2.02
0.03
0.03
–
0.03
0.03
Natural bond orbital (NBO) analysis was performed on
I–·Li+ and II–·Li+ with focus on the stabilization of the lone
pair at the central carbon atom. This lone pair is almost a
Coordination Chemistry
We then focused our study on the use of the two anions
pure p orbital in both species (91.3% p in I–·Li+ and 99.1% as ligands for RhI metal fragments. The addition of two
p in II–·Li+). It is stabilized by negative hyperconjugation equivalents of 1–·Li+ to a solution of one equivalent of
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H. Heuclin, S. Carenco, X.-F. Le Goff, N. Mézailles
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Scheme 5. Synthesis of 3, 4, and 5.
[Rh(COD)Cl]2 (COD = 1,5-cyclooctadiene) in toluene in- distance is longer than that in 1–·Li+ [1.739(6) vs.
stantaneously led to a dark solution. The reaction was con- 1.701(1) Å] as well as the C–Si bond [1.880(5) vs.
veniently followed by 31P NMR spectroscopy, and comple- 1.827(1) Å]. These increases in bond lengths are consistent
tion was reached within 15 min. After elimination of LiCl with the high-field chemical shift of the CH moiety in the
and evaporation of the solvent, 3 was isolated as a dark 13C NMR spectrum because they point a higher electron
orange powder (Scheme 5). Evidence of the coordination of density at C than in the anion itself. These types of com-
1–·Li+ to the rhodium center was seen by 31P NMR spec- plexes are typically used as starting materials for further
troscopy, where 3 exhibited a doublet at 37.8 ppm (2JPRh
=
transformations as the COD ligand can easily be displaced.
15.5 Hz).
Thus, the reaction of 3 with carbon monoxide or stoichio-
Complex 3 was characterized by multinuclear NMR metric amounts of 2,6-dimethylphenyl isocyanide was inves-
spectroscopy. The alkenic protons of the COD ligand were tigated (Scheme 5). Complexes 4 and 5 both exhibit a doub-
found as two well separated sets of peaks at δH = 4.68 (2 let in the 31P NMR spectra, shifted downfield compared to
2
H) and 4.22 (1 H)–3.99 ppm (1 H), which highlights the 3 (62.1 ppm with JRhP = 16.6 Hz for 4, and 51.4 ppm with
very different trans effect of the sulfur and CH moieties. 2JRhP = 12.3 Hz for 5, vs. 37.8 ppm in 3). The 13C NMR
The signal that corresponds to the central CH proton is spectrum of 4 (and 5) shows that two inequivalent CO (iso-
unfortunately masked by the COD ligand. In the 13C NMR cyanide) ligands are present as expected. Most interestingly,
spectrum, the corresponding signal is found at a high field the chemical shifts of the CH moieties in 4 and 5 are again
1
1
1
(–2.7 ppm as a doublet of doublets, JRhC = 15.5 and JPC found at higher field than in 3: –7.4 ppm (1JRhC = 12, JPC
= 26 Hz). This chemical shift is high-field shifted compared = 21 Hz) for 4 and –5.0 ppm (1JRhC = 11.5, 1JPC = 24.7 Hz)
to the starting anion (11.7 ppm). Slow evaporation of a for 5. The bidentate S~C coordination in both complexes
concentrated solution of 3 in CH2Cl2 led to the formation was proven by X-ray diffraction analysis. Quite surprisingly,
of single crystals suitable for X-ray diffraction. An ORTEP single crystals of 4 were obtained by diffusion of water into
plot of 3 is presented in Figure 3.
a concentrated solution of 4 in acetone, and crystals of 5
were obtained by diffusion of pentane into concentrated
solutions of 5 in toluene at –40 °C. Views of 4 and 5 are
given in Figures 4 and 5, respectively.
Figure 3. ORTEP plot (50% thermal ellipsoids) of 3. Hydrogen
atoms [except H(1)] are omitted for clarity. Selected bond lengths
[Å] and angles [°]: C(1)–P(1) 1.739(6), P(1)–S(1) 2.019(2), C(1)–
Si(1) 1.880(5), C(1)–Rh(1) 2.171(6), S(1)–Rh(1) 2.415(2), Rh(1)–
C(17) 2.102(5), Rh(1)–C(18) 2.160(6), Rh(1)–C(21) 2.146(6),
Rh(1)–C(22) 2.201(6), C(17)–C(18) 1.402(8), C(21)–C(22) 1.38(1),
P(1)–C(1)–Si(1) 119.6(3), S(1)–P(1)–C(1) 103.1(2), C(1)–Rh(1)–S(1)
79.8(2), P(1)–C(1)–Rh(1) 89.2(2), S(1)–P(1)–C(1)–Rh(1) 35.1.
Figure 4. ORTEP plot (50% thermal ellipsoids) of 4. Hydrogen
atoms [except H(1)] are omitted for clarity. Selected bond lengths
[Å] and angles [°]: C(1)–P(1) 1.752(3), P(1)–S(1) 2.023(1), C(1)–
Si(1) 1.883(3), Rh(1)–C(1) 2.149(3), Rh(1)–C(17) 1.888(4), Rh(1)–
C(18) 1.847(4), C(17)–O(1) 1.131(5), C(18)–O(2) 1.138(5), Rh(1)–
S(1) 2.398(1), P(1)–S(1) 2.023(1), P(1)–C(1)–Si(1) 119.7(2), O(1)–
C(17)–Rh(1) 177.4(4), O(2)–C(18)–Rh(1) 177.3(4), C(17)–C(18)–
Complex 3 features a slightly distorted square-planar ge-
ometry at the rhodium center. This geometry is usual for
ML4 complexes with 16 electrons and a d8 metal center.
The Rh–C(H) bond length falls in the range of other re-
ported pincer complexes of rhodium.[15] In 3, the P–C(1) C(1)–S(1) 3.77.
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Rhodium Methanide Complexes: S~S vs. C~S Coordination
A slightly different set of data was obtained for the X-
ray structure of 6 (Supporting Information). These data
confirmed that 2–·Li+ acts as a S~S bidentate ligand. COD
was successfully displaced from 6 using 2,6-diphenyl isocy-
anide. In a first attempt to favor S~C~S tridentate coordi-
nation of the Rh center, the reaction of 6 with one equiva-
lent of isocyanide was carried out, which resulted in the
conversion of half of 6 into a new complex characterized
by a broad singlet at 54.1 ppm in the 31P NMR spectrum
(7), leaving half of 6 unreacted. The addition of a second
equivalent of isocyanide to the crude mixture led to the
total conversion of 6 into 7 (Scheme 6). This new complex
was fully characterized by NMR spectroscopy. The signal
for the central CH proton is seen as a triplet of doublets at
Figure 5. ORTEP plot (50% thermal ellipsoids) of 5. Hydrogen
atoms [except H(1)] are omitted for clarity. Selected bond lengths
[Å] and angles [°]: C(1)–P(1) 1.749(1), P(1)–S(1) 2.0131(6), C(1)–
Si(1) 1.871(2), C(1)–Rh(1) 2.174(1), S(1)–Rh(1) 2.4097(4), C(17)–
N(1) 1.167(2), C(26)–N(2) 1.163(2), P(1)–C(1)–Si(1) 118.76(8),
S(1)–P(1)–C(1) 103.23(5), C(1)–Rh(1)–S(1) 80.06(4), P(1)–C(1)–
Rh(1) 89.21(6), S(1)–C(1)–C(26)–C(17) 2.35.
2
δH = 2.58 ppm (2JRhH = 1.5 and JPH = 8 Hz). Similarly,
the reaction of 6 with carbon monoxide led to the full con-
version of 6 into a new complex, 8, characterized by a
doublet at 62 ppm (2JRhP = 10 Hz) in the 31P NMR spec-
trum. In 8, the signal for the central CH proton is seen at
2
2
δH = 2.68 ppm (doublet of triplets, JRhH = 1.8 and JPH
=
Both complexes feature expected square planar geome-
tries. The CO bond lengths in 4 [1.131(5) and 1.138(5) Å]
are in the range for CO bonds usually reported for carbonyl
pincer complexes of RhI.[16] The same applies for the CN
bonds in 5.[17] Infrared stretches of the carbonyl groups in
4 were found at 2145 and 2078 cm–1, which indicate weak
backbonding of the rhodium center. The CN bands in 5
were found at 2117 and 2046 cm–1. Interestingly, the coordi-
nation of two strongly accepting ligands, such as CO or
CNR, did not result in a significant change of the C(H)–
Rh bond length in 4 or 5 compared to 3 [2.171(6) in 3,
2.149(3) in 4, 2.174(1) Å in 5]. The same holds for the C–P,
P–S, and C–Si bond lengths of 1–. Overall, it appears that
the coligands (COD, CNR, or CO) exert a similar influence
on 1– coordinated to the Rh center.
8 Hz). Surprisingly, in the 13C NMR spectra of 7 and 8
only one signal can be seen for the isocyanide ligands at
160.0 ppm (1JRhC = 69 Hz) for CN in 7 and 185.6 ppm
(1JRhC = 70 Hz) for CNR in 8. The signal for the PCHP
carbon atom in 7 is found at 6.2 ppm as an unresolved mul-
tiplet and at 0 ppm in 8. In this case, these chemical shifts
are at much higher field than in 2–·Li+ (20 ppm).[14] At this
point, because of the apparent equivalence of the two isocy-
anide (or carbonyl) ligands and the two phosphorus moie-
ties by NMR, three cases can be envisaged for the geometry
of 7 and 8: a) a pentacoordinate Rh center with tridentate
S~C~S coordination, b) a static S~S bidentate coordination
as in 6, or c) a fast equilibrium between two ML4 complexes
that feature S~C coordination. An initial answer was pro-
vided by the X-ray analysis of single crystals of 7 grown by
the slow diffusion of pentane into a concentrated solution
of the complex in toluene. A view of 7 is given Figure 6.
In this structure of 7, the central carbon atom is coordi-
nated to the RhI center and one pendant sulfur atom has
been decoordinated. This is confirmed by the short Rh–
Cbridge distance in 7 compared to that in 6 [2.198(3) vs.
We compared the reactivity of 1–·Li+ with 2–·Li+ with the
same rhodium precursor. The reaction of two equivalents of
2–·Li+ with one equivalent of [Rh(COD)Cl]2 led to a doub-
let at 36.1 ppm (2JRhP = 5 Hz, 6) in the 31P NMR spectrum,
which indicated coordination to the rhodium center (2–·Li+
exhibits a singlet at 37.5 ppm) as reported by Dixon et al.
(Scheme 6).[4c]
Scheme 6. Synthesis of 6, 7, and 8.
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in the sulfur exchange process, and VII-spa was found to be
a minimum on the potential energy surface. Interestingly,
when trying to optimize VII-bpt and VII-tp, both structures
evolved towards VII-spc, which features a square-planar
rhodium center in which the uncoordinated sulfur atom is
brought nearer to the metal than in VII-spa (Scheme 7). In
fact, it results from a rotation of the PPh2PS arm. Energeti-
cally, VII-spc is 6.4 kcal/mol above VII-spa. A transition
state (TS) that connects VII-spc and its mirror image was
sought but could not be found. VII-spb was also optimized
and its energy is 7.2 kcal/mol above VII-spa. This difference
in energy corroborates the fact that 7 is only found as C~S
bidentate.
These data allow us to propose the following mechanism
for the fast dynamic process observed by NMR spec-
troscopy that renders the two thiophosphinoyl moieties
equivalent (Scheme 8). From the most stable complex, VII-
spa, rotation of the arm results in an increase of the energy
to form VII-spc. In this complex, the S–Rh and C–Rh dis-
tances are 4.73 and 2.24 Å, respectively. We then propose
the reaction to go to VII-spb (the S–Rh and C–Rh distances
are 2.51 and 4.20 Å, respectively). The S atom becomes
bonded while the C atom decoordinates from the metal cen-
ter. We have not found a TS that connects these two min-
ima, which can be explained by the apparent very flat po-
tential energy surface. Indeed, experimentally, the overall
exchange was measured at 8.4 kcal/mol, which points a TS
within 2–3 kcal/mol from VII-spc.
Figure 6. ORTEP plot (50% thermal ellipsoids) of 7. Hydrogen
atoms [except H(1)] are omitted for clarity. Selected bond lengths
[Å] and angles [°]: C(1)–P(1) 1.768(3), C(1)–P(2) 1.792(3), Rh(1)–
C(1) 2.198(3), Rh(1)–S(1) 2.390(1), P(1)–S(1) 2.014(1), P(2)–S(2)
1.972(1), Rh(1)–C(27) 1.908(4), Rh(1)–C(26) 1.887(4), N(1)–C(26)
1.167(5), N(2)–C(27) 1.160(4), P(1)–C(1)–P(2) 118.7(2), N(2)–
C(27)–Rh(1) 177.0(3), N(1)–C(26)–Rh(1) 176.2(3), C(27)–C(26)–
C(1)–S(1) 2.27.
3.99 Å]. The coordination of the isocyanide ligand results
in a drastic change in the coordination mode of 2– from
S~S to S~C. In the solid state, 7 features two nonequivalent
phosphorus atoms, which rules out two of our three
hypotheses. A variable-temperature (VT) 31P NMR experi-
ment was carried out to confirm a dynamic exchange be-
tween the two S atoms. On cooling the solution from 25 °C,
a coalescence of the broad singlet at 54 ppm was observed
at ca. –65 °C. At –80 °C, the 31P NMR spectrum presents
a broadened AB system at 76.5 and 56.7 ppm. This process
is fully reversible, and increasing the temperature back to
25 °C resulted in the reappearance of the singlet at 54 ppm.
From this data, the energy associated with this dynamic
phenomenon can be calculated as 8.4 kcal/mol.[18] DFT cal-
culations were conducted to give an insight into the mecha-
nism that renders the two phosphane sulfides equivalent at
room temperature. Several complexes with different struc-
tures (VII-spa, VII-bpt, VII-tp, VII-spb) were envisaged
(Scheme 7). The starting geometry of VII-sp was taken di-
Scheme 8. Proposed mechanism for the equilibrium.
Conclusions
We compared two anionic ligand systems that have a
rectly from the X-ray structure prior to optimization, VII- “CH–PPh2S” fragment in common. These ligands differ
bpt features a five-coordinate rhodium center with a trigo- only in the remaining substituent at the carbon atom. DFT
nal bipyramid geometry, and VII-tp features a three-coordi- calculations showed that the stabilization of the lone pair
nate rhodium center with a trigonal planar geometry. VII- provided by two thiophosphinoyl fragments is more ef-
bpt and VII-tp were suspected to be possible intermediates ficient than the stabilization by one thiophosphinoyl and a
Scheme 7. Starting structures for the theoretical calculations.
1458
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© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2012, 1453–1461

Rhodium Methanide Complexes: S~S vs. C~S Coordination
Synthesis of 3: To a solution of 1–·Li+ (0.1 mmol/mL in toluene,
5 mL, 0.5 mmol) in toluene (1 mL) was added a solution of
[Rh(COD)Cl]2 (123.3 mg, 0.25 mmol) in toluene (1 mL). The solu-
tion immediately turned orange and was left to stir for 15 min.
After centrifugation and evaporation of the solvent, 3 was isolated
as a dark orange powder (231.5 mg, 90%). 31P NMR (C6D6): δ =
SiMe3 fragment. The coordination of 1–·Li+ to RhI resulted
in the expected bidentate C~S coordination with little influ-
ence of the coligands on the geometric parameters of the
complex. The coordination of 2–·Li+ to RhI resulted in both
C~S and S~S coordination, which shows that the coordina-
tion mode can be tuned by the coligands. In the C~S
bonded structure, VT NMR experiments proved a low-en-
ergy pathway that equilibrated the two PPh2S moieties.
DFT calculations showed the energies of the associated
1
37.8 (d, JRhP = 15.5 Hz) ppm. H NMR (C6D6): δ = 7.90 (m, 2 H,
2CH-ortho PPh2), 7.70 (m, 2 H, 2CH-ortho PPh2), 7.06 (m, 3 H,
2CH-meta + CH-para PPh2), 6.98 (m, 3 H, 2CH-meta + CH-para
PPh2), 4.68 (m, 2 H, 2CH COD), 4.22 (m, 1 H, CH COD), 3.99
complexes to be very similar and the S~S coordinated com- (m, 1 H, CH COD), 1.37–2.44 (m, 9 H, 4CH2 COD + PCHSiMe3),
0.26 [s, 9 H, Si(CH3)3 ppm.] 13C NMR (C6D6): δ = 140.7 (dd, J =
1.2, J = 46.5 Hz, C of phenyl); 139.3 (d, J = 81 Hz, C of phenyl);
84.6 (d, J = 8.8 Hz, CH of COD), 83.2 (d, J = 8.8 Hz, CH of
COD), 77.4 (d, J = 14 Hz, CH of COD), 70.9 (d, J = 14 Hz, CH
of COD), 32.3 (s, CH2 of COD), 30.2 (s, CH2 of COD), 29.1 (s,
CH2 of COD), 27.8 (s, CH2 of COD), 2.9 [d, JPC = 4.8 Hz,
plex was within 7.2 kcal/mol. This switch in coordination
could provide “inside tuning” of the electronic properties
of a metal center during a catalytic process.
PCHSi(CH3)3], –2.7 (dd, JRhC = 15.5, JPC = 26 Hz, PCSi) ppm.
C24H32PRhSSi (514.54): calcd. C 56.02, H 6.27; found C 55.84, H
6.23.
Experimental Section
General Procedures: All reactions were performed under an inert
atmosphere of argon or nitrogen by using Schlenk and glovebox
Synthesis of 4: To a solution of 3 (41.2 mg, 0.08 mmol) in toluene
(3 mL) was added carbon monoxide with a balloon for 5 min. The
solution turned immediately orange then brown. The solvents were
evaporated under vacuum to yield 4 as a brown powder (30 mg,
81%). 31P{1H} NMR (CD2Cl2): δ = 62.1 (d, JRhP = 16.6 Hz) ppm.
1H NMR (CD2Cl2): δ = 7.92–7.82 (m, 2 H), 7.74–7.66 (m, 2 H),
7.61–7.46 (m, 6 H), 0.76 (dd, JRhH = 1.3, JPH = 7.5 Hz, 1 H,
PCHSi), 0.00 [s, 9 H, Si(CH3)3] ppm. 13C NMR (CD2Cl2): δ =
187.3 (d, JRhC = 78 Hz, CO), 186.1 (d, JRhC = 61 Hz, CO), 137.9
(d, JPC = 55 Hz, Cipso), 136.6 (d, JPC = 78 Hz, Cipso), 131.9 (d, JPC
techniques and dry, deoxygenated solvents. Solvents were dried
using a MBRAUN SPS-800 system. NMR spectra were recorded
with a Bruker AC-300 SY spectrometer operating at 300.0 MHz
for 1H, 75.5 MHz for 13C, and 121.5 MHz for 31P. Solvent peaks
are used as internal references relative to Me4Si for 1H and 13C
chemical shifts; 31P chemical shifts are relative to a 85% H3PO4
external reference. The following abbreviations are used: s singlet,
br. s broad singlet, d doublet, dd doublet of doublets, t triplet, td
triplet of doublets, m multiplet. [Rh(COD)Cl]2 was prepared ac-
cording to a literature procedure.[19] All other reagents and chemi-
cals were obtained commercially and used as received.
= 2.9 Hz, Cpara), 131.5 (d, JPC = 2.2 Hz, Cpara), 130.8 (d, JPC
=
11.8 Hz, C), 130.0 (d, JPC = 12.2 Hz, C), 128.6 (d, JPC = 12.6 Hz,
C), 128.5 (d, JPC = 12.0 Hz, C), 3.0 [br. s, Si(CH3)3], –7.4 (dd, JRhC
= 12, JPC = 21 Hz, PCHSi) ppm. HRMS (EI): calcd. for
C18H20O2PRhSSi [M]+ 461.9746; found 461.9753.
Synthesis of 1: Compound 1 was prepared according to a slight
modification of ref.[7] To
a solution of diphenylphosphane
(2.22 mL, 12.8 mmol) in THF (30 mL) was added butyllithium
(1.6 m in hexanes, 8 mL, 12.8 mmol) at –78 °C. The solution turned
instantly red and was left to warm to room temperature. Chloro-
methyltrimethylsilane (1.8 mL, 12.8 mmol) was added at 0 °C, and
the solution was warmed to room temperature and stirred for 1 h.
The 31P NMR spectrum showed the formation of the desired phos-
phane. S8 (410.5 mg, 1.6 mmol) was then added, and the solution
was left to stir at 60 °C for 4 h. Solvents were evaporated and hex-
anes (20 mL) were added. After heating at reflux for 15 min and
filtration followed by evaporation of the solvent, 1 was isolated as
a white crystalline solid (3.3 g, 10.8 mmol, 84%). 31P{1H} NMR
(C6D6): δ = 37.7 (s) ppm. 1H NMR (C6D6): δ = 7.78–7.88 (m, 4
Synthesis of 5: To a solution of 3 (123.6 mg, 0.24 mmol) in toluene
(3 mL) was added 2,6-dimethylphenyl isocyanide (63 mg,
0.48 mmol) under nitrogen. The solution turned instantly red. After
stirring for 15 min, the solvent was evaporated under vacuum. Pe-
troleum ether (5 mL) was added under nitrogen, which caused the
precipitation of a yellow solid. The solid was isolated by centrifuga-
tion and washed twice with petroleum ether (3 mL) to yield 5
(149 mg, 93%). 31P{1H} NMR (C6D6): δ = 51.4 (d, JPRh = 12.3 Hz)
ppm. 1H NMR (C6D6): δ = 8.36–8.27 (m, 2 H), 7.82–7.73 (m, 2
H), 2.32 (s, 6 H, CH3 isocyanide), 2.09 (s, 6 H, CH3 isocyanide),
0.75 (dd, JRhH = 1.1, JPH = 7.3 Hz 1 H, PCHSi), 0.38 [s, 9 H,
Si(CH3)3] ppm. 13C NMR (C6D6): δ = 161.7 (d, JRhC = 78 Hz, CN),
161.3 (d, JRhC = 60 Hz, CN), 143.5 (d, JRhC = 48 Hz, CqatP), 142.3
(d, JRhC = 79.8 Hz, CqatP), 134.1 (s, CphenylN), 133.8 (s, CphenylN),
H, phenyl), 7.0 (m, 6 H, phenyl), 1.70 (d, 2JPH = 16 Hz, CH2), 0.06
1
[s, 9 H, Si(CH3)3] ppm. 13C NMR (C6D6): δ = 136.6 (d, JPC
=
2
80 Hz, C phenyl), 130.5 (d, JPC = 10.7 Hz, CH phenyl), 130.1 (d,
2JPC = 3.6 Hz, CH phenyl), 127.8 (d, JPC = 12.3 Hz, CH phenyl),
2
21 (d, 1JPC = 47.6 Hz, CH2), 0.02 [d, 2JPC = 3.3 Hz, Si(CH3)3] ppm.
21.4 (s, CH3 isocyanide), 21.1 (s, CH3 isocyanide), 6.7 [d, JRhC
=
4.5 Hz, Si(CH3)3], –5.0 (dd, JRhC = 11.5, JPC = 24.7, PCHSi) ppm.
HRMS (EI): calcd. for C34H38N2PRhSSi [M]+ 668.1318; found
668.1315.
Synthesis of 1–·Li+: To a solution of 1 (121.8 mg, 0.04 mmol) in
toluene at –78 °C was added methyllithium (1.6 m in Et2O,
0.25 mL, 0.04 mmol). The solution was left to warm to room tem-
perature and rapidly turned yellow. The reaction was complete after
1 h of stirring. Compound 1–·Li+ was typically not isolated but
used directly as prepared. 31P{1H} NMR (C6D6): δ = 44.5 (s) ppm.
Synthesis of 6: To a solution of dppmS2 (143.4 mg, 0.32 mmol) in
toluene (4 mL) was added methyllithium (1.6 m in Et2O, 0.2 mL,
0.32 mmol) at –78 °C. The solution was warmed to room tempera-
1H NMR (C6D6): δ = 8.12 (m, 4 H, o-phenyl), 7.08–7.19 (m, 6 H, ture and stirred for 1.5 h. The solution changed from colorless to
2
m-phenyl + p-phenyl), 0.50 [d, JPH = 9 Hz, 1 H, PCHSi(CH3)3],
yellow. [Rh(COD)Cl]2 (78.9 mg, 0.16 mmol) was added at room
temperature. The solution was left to stir for 1 h. The solution was
concentrated to ca. 0.5 mL and petroleum ether (5 mL) was added
to allow the precipitation of LiCl and a yellow solid. The solid
mixture was collected by filtration, washed twice with petroleum
0.00 [s, 9 H, Si(CH3)3] ppm. 13C NMR (C6D6): δ = 138.6 (br. s, C-
2
ipso), 131.9 (d, JPC = 11.6 Hz, o-phenyl), 130.1 (br. s, p-phenyl),
3
1
127.6 (d, JPC = 12.4 Hz, m-phenyl), 11.7 [d, JPC = 60 Hz,
3
PCHSi(CH3)3], 2.2 [d, JPC = 2 Hz, Si(CH3)3] ppm.
Eur. J. Inorg. Chem. 2012, 1453–1461
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1459

H. Heuclin, S. Carenco, X.-F. Le Goff, N. Mézailles
FULL PAPER
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2 Hz, 1 H, PCHP), 1.35–1.27 (m, 4 H, CH2 of COD) ppm. 13C
NMR (C6D6): δ = 137.7 (d, JPC = 90 Hz, Cquat), 131.0 (pseudo-t,
CHarom), 129.5 (s, CHarom), 127.2 (pseudo-t, CHarom), 80.3 (JRhC
= 12 Hz, CH of COD), 30 (s, CH2 of COD), 12.3 (td, JPC = 93,
JRhC = 4 Hz, PCHP) ppm.
Synthesis of 7: To a solution of 6 (100 mg, 0.15 mmol) in THF was
added 2,6-dimethylphenyl isocyanide (39.8 mg, 0.30 mmol). The
solution immediately went from orange to red. It was left to stir
for 15 min at room temperature and concentrated to ca. 0.5 mL.
Petroleum ether (5 mL) was added, which allowed the precipitation
of a yellow solid that was extracted by centrifugation and washed
twice with petroleum ether (117 mg, 96%). 31P{1H} NMR ([D8]-
1
toluene): δ = 54 (br. s) ppm. H NMR ([D8]toluene): δ = 7.83 (br.
s, 8 H, Harom), 7.12 (br. s, 12 H, Harom), 7.02–6.90 (singlets, Harom
isocyanides), 2.58 (td, JRhH = 1.5, JPH = 8 Hz, PCHP), 2.14 (s, 12
H, CH3 isocyanides) ppm. 13C NMR ([D8]toluene): δ = 160 (d,
JRhC = 69 Hz, CN), 137.1 (dd, JPC = 4, JPC = 75 Hz, Cipso), 134.8
[s, C(CH3) isocyanide], 132.9 (d, JPC = 11 Hz, Cortho), 130.8 (d, JPC
= 4 Hz, Cpara), 128.4 (s, Cmeta isocyanide), 128.0 (d, JPC = 12 Hz,
Cmeta), 127.5 (s, Cpara isocyanide), 19.5 (s, CH3 isocyanide), 6.2 (m,
PCHP) ppm. C43H39N2P2RhS2 (812.77): calcd. C 63.54, H 4.84;
found C 63.25, H 4.92.
[4]
Synthesis of 8: To a solution of 6 (100 mg, 0.15 mmol) in THF was
added CO with a balloon for 5 min. The solution immediately went
from orange to brown. It was left to stir for 15 min at room tem-
perature and dried under vacuum to isolate a brown solid (77 mg,
85%). 31P{1H} NMR ([D8]toluene): δ = 62 (d, JRhP = 10 Hz) ppm.
1H NMR ([D8]toluene): δ = 7.74–7.62 (m, 8 H, Harom), 7.18–6.87
(m, 12 H, Harom), 2.68 (td, JRhH = 1.8, JPH = 8 Hz, PCHP) ppm.
13C NMR ([D8]toluene): δ = 185.6 (d, JRhC = 70 Hz, CO), 135.2
(dd, JPC = 4, JPC = 76 Hz, Cipso), 132.2 (d, JPC = 11 Hz, Cmeta),
131.8 (d, JPC = 3 Hz, Cpara), 128.5 (d, JPC = 13 Hz, Cortho), 0.0 (m,
PCHP) ppm. C27H21O2P2RhS2 (606.43): calcd. C 53.47, H 3.49;
found C 53.40, H 3.67.
[5]
CCDC-847285 (for 1), -847286 (for 1–·Li+), -847287 (for 3),
-847288 (for 4), -847289 (for 5), -847290 (for 6), and -847291 (for
7) contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_requ-
est/cif.
Supporting Information (see footnote on the first page of this arti-
cle): Crystallographic details, computational details for calcula-
tions, view of computed structures, Cartesian coordinates and the
three lowest frequencies for each optimized structure.
Acknowledgments
[6]
[7]
The authors thank the Centre National de la Recherche Sci-
entifique (CNRS) and the Ecole Polytechnique for the financial
support of this work. H. H. is thankful to the Ecole Polytechnique
for a graduate fellowship. S. C. is thankful to the Direction
Générale de l’Armement (DGA) for graduate fellowship.
T. Cantat, N. Mezailles, L. Ricard, Y. Jean, P. Le Floch, Angew.
Chem. 2004, 116, 6542; Angew. Chem. Int. Ed. 2004, 43, 6382–
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Received: October 7, 2011
Published Online: January 27, 2012
Eur. J. Inorg. Chem. 2012, 1453–1461
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1461