Activation of SF6 at a Xantphos-Type Rhodium Complex

Article abstract of DOI:10.1021/acs.organomet.7b00858

As a rather inert gas, sulfur hexafluoride is still used as a dielectric in high-voltage power applications despite its high global warming potential. Its activation at transition metal complexes has been reported, but the fate of the sulfur-containing products is often unknown. The activation of SF₆ at [Rh(H){^tBuxanPOP}] (^tBuxanPOP = 9,9-dimethyl-4,5-bis(ditert-butylphosphino)xanthene) at room temperature leads to the generation of the bifluorido complex [Rh(FHF){^tBuxanPOP}]. A subsequent regeneration of [Rh(H){^tBuxanPOP}] completes a cyclic process for the degradation of SF₆. Furthermore, the SF₆ activation at [Rh(H){^tBuxanPOP}] in the presence of triethylsilane as a hydrogen source is described, which leads to the formation of the fluorido complex [Rh(F)₂(H){^tBuxanPOP}] as well as [Rh(SH){^tBuxanPOP}] and S(SiEt₃)₂ as sulfur-containing products.

Full text of DOI:10.1021/acs.organomet.7b00858

Article
Cite This: Organometallics XXXX, XXX, XXX−XXX
Activation of SF6 at a Xantphos-Type Rhodium Complex
Martin Wozniak, Thomas Braun,* Mike Ahrens, Beatrice Braun-Cula, Philipp Wittwer, Roy Herrmann,
and Reik Laubenstein
Department of Chemistry, Humboldt-Universitat zu Berlin, Brook-Taylor-Straße 2, 12489 Berlin, Germany
̈
S
* Supporting Information
ABSTRACT: As a rather inert gas, sulfur hexafluoride is still used as a
dielectric in high-voltage power applications despite its high global warming
potential. Its activation at transition metal complexes has been reported, but the
fate of the sulfur-containing products is often unknown. The activation of SF6
at [Rh(H){tBuxanPOP}] (tBuxanPOP = 9,9-dimethyl-4,5-bis(ditert-
butylphosphino)xanthene) at room temperature leads to the generation of
the bifluorido complex [Rh(FHF){tBuxanPOP}]. A subsequent regeneration of
[Rh(H){tBuxanPOP}] completes a cyclic process for the degradation of SF6.
Furthermore, the SF6 activation at [Rh(H){tBuxanPOP}] in the presence of
triethylsilane as a hydrogen source is described, which leads to the formation of
the fluorido complex [Rh(F)2(H){tBuxanPOP}] as well as [Rh(SH)-
{
tBuxanPOP}] and S(SiEt3)2 as sulfur-containing products.
and fluorosilanes with [Rh(H)(PEt3)4] in the presence of PEt3
and silane.5f−i Furthermore, it was demonstrated that SF6 can
be activated at [Pt(PR3)2] (R = Cy, iPr) complexes generating
the SF3 complex trans-[Pt(F)(SF3)(PR3)].5m,n In addition, SF6
was recently applied as a fluorinating agent, e.g., in a
photoredox process for deoxyfluorination reactions using an
iridium-based photocatalyst and diisopropylethyl amine as
reductant to induce a fluorination of allylic alcohols.5j,k,m,n,6
Herein, we describe the reactivity of the pincer complex
[Rh(H){tBuxanPOP}] (1; tBuxanPOP = 9,9-dimethyl-4,5-bis-
(ditert-butylphosphino)-xanthene) toward SF6. Hexaethyl di-
silathiane S(SiEt3)2 was obtained upon treatment of 1 with SF6
in the presence of triethyl silane as hydrogen source.
INTRODUCTION
■
SF6 is widely considered to be an extremely unreactive gas.1
Due to its outstanding properties, such as chemical stability,
low toxicity, and a high dielectric strength, SF6 persists in being
used as gaseous dielectric in high-voltage-power applications.1,2
SF6 is a highly dense, nonflammable gas, but also has been
recognized as the most potent greenhouse gas with an
atmospheric lifetime of about 3200 years and a global warming
potential which is 23 500 times higher than that of CO2.3
Before SF6 was used for various applications, its concentration
in the atmosphere was below the detection limit, suggesting
that its presence today is entirely anthropogenic. The global
SF6 concentration rose from 1 ppt in 1975 to more than 8 ppt
in 2008.3c Considering that there are often no alternative
compounds eligible for replacing SF6, increasing attention has
been paid to control or even avoid its emission. Within this
context, an efficient and controlled depletion of SF6 under mild
conditions is of current interest.1f,3c,f,4 An interesting approach
consists of SF6 degradation reactions at transition metal
complexes. While SF6 was degraded or recycled in the past
decade mainly by adsorption, separation, and decomposition
methods usually under harsh conditions, reports on the
activation of SF6 at transition metal complexes are still
scarce.3f,4c−e,5 Degradation reactions of SF6 are described at
low-valent Ti, V, Cr, and Zr as well as at Fe and reduced Ni
complexes.5a,b,d,e Sulfur-containing products were only identi-
fied in the reactions of SF6 with [Cr(C5Me5)2] and [Ti-
(1,3-tBu2C5H3)(6,6-dmch)(PMe3)] (6,6-dmch = 6,6-dimethyl-
cyclohexadienyl) as well as with K2[(LtBuNiI)2(μ−η1:η1-N22−)]
(LtBu = [(HC(CtBuNC6H3(iPr)2)2]−), which yielded, among
other compounds, [{Cr(C5Me5)(μ2-F)}3(μ3-S)]+[Cr(C5Me5)-
(F)3]−, SPMe3 or [(LtBuNiII)2(μ-S)]. We previously reported
on the activation of SF6 at a binuclear rhodium complex as well
as on the catalytic degradation of SF6 to give phosphinesulfides
RESULTS AND DISCUSSION
■
The reduction of SF6 (1 atm) with 1 at room temperature in
toluene gave the bifluorido complex [Rh(FHF){tBuxanPOP}]
(2) as the only rhodium complex after 4 days according to the
NMR spectroscopic and mass spectrometric (liquid injection
field desorption ionization mass spectrometry LIFDI-MS) data
(Scheme 1). At 50 °C the reaction was completed within 16 h.
Monitoring the reaction of 1 with SF6 by NMR spectroscopy
at room temperature revealed a full conversion of 1 already
after 16 h as well as the formation of 2, [Rh(F)2(H)-
{
tBuxanPOP}] (3), [Rh(SH){tBuxanPOP}] (4), and an
unknown Rh(III) complex as intermediates (ratio: 10:3:2:1
according to the 31P{1H} NMR spectrum). Although the fate of
the sulfur is not known in the conversion of 1 into 2, we
tentatively presume mechanistically an initial precoordination
Special Issue: Organometallic Chemistry in Europe
Received: November 29, 2017
© XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.7b00858
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1
Scheme 1. Activation of SF6 at [Rh(H){tBuxanPOP}] (1)
to a doublet splitting pattern upon H decoupling, and the
signal can be assigned to the distal fluorine atom of the
bifluorido ligand. The extraordinarily high-field shifted
resonance at δ = −498.0 ppm is attributed to the metal-
bound fluorine atom.9 In the 19F{1H} NMR spectrum recorded
at 243 K, the splitting pattern of the resonance features doublet
couplings to rhodium and to the distal fluorine atom of 184 and
111 Hz, respectively (Figure 2b).
1
The H NMR spectrum of 2 at room temperature reveals a
broad signal for the proton of the bifluorido ligand at δ = 12.46
ppm, as depicted in Figure 3a. This resonance splits into a
of the SF6 molecule via one or more fluorine atoms at the
rhodium center, followed by electron transfer steps possibly via
−
an inner-sphere mechanism to generate SF5 and a fluoride
ion.1a,5a,b,d−h,m,7 SF5 can then produce another fluoride ion
−
and other sulfur fluorides which are further defluorinated.
The 31P{1H} NMR spectrum of 2 at 298 K exhibits a signal
at δ = 47.4 ppm for the phosphine atoms of the tBuxanPOP
ligand. The resonance features a characteristic coupling for a
rhodium(I) compound, with a doublet coupling to rhodium of
148 Hz.8 The 19F NMR spectrum of complex 2 at 298 K shows
two resonances at δ = −176.6 ppm (see Figure 1a) and at δ =
Figure 3. Part of the 1H NMR spectrum of 2 at 298 K (a) and at 243
K (b).
broad signal of higher order at 243 K, which is reminiscent of a
doublet of doublets with apparent coupling constants of 1JH,F
402 Hz to the rhodium-bound distal fluorine atom and JH,F
=
=
37 Hz to the proximal one (Figure 3b). The coupling constants
are comparable to those found in other bifluorido complexes of
rhodium such as [Rh(FHF)(PEt3)3] (J = 382 Hz, 42 Hz), cis-
[Rh(FHF)(6-iPr)(PPh3)2] (J = 370 Hz, 42 Hz; 6-iPr = 1,3-
bis(2-propyl)-3,4,5,6-tetrahydropyrimidin-2-ylidine), and [Rh-
(FHF)(COD)(PiPr3)] (J = 366 Hz, 32 Hz).9g,h,j The ATR IR
spectrum of 2 shows two broad absorption bands for the
asymmetric stretching and bending modes of the bifluorido
ligand at ν
̃
= 2549 and 1871 cm−1.9l−n,10 Both bands appear at
Figure 1. Part of the 19F NMR spectrum of the bifluorido ligand of 2
at 298 K (a) and at 243 K (b).
higher energy than those found for symmetric HF2 salts such as
Na+, Cs+, and K+ HF2 (1284−1372 cm−1), indicating an
−
asymmetric hydrogen bond within the Rh(FHF) fragment.11
The energy values found for the two H−F stretching modes of
2 are also consistent to the corresponding data for literature
known phosphine-based transition metal bifluorido complexes,
e.g., [Ru(F)(FHF)(dmpe)2] (2452 and 1915 cm−1; dmpe =
1,2-bis(dimethylphosphino)ethane) and trans-[Pd(FHF)(Me)-
(PPh3)2] (2493 and 1904 cm−1).12
−498.0 ppm (see Figure 2a). The signal at lower field is split
into a doublet of doublets (1JF,H = 401 Hz, JF,F = 112 Hz) when
the spectrum is recorded at 243 K (Figure 1b). It is simplified
Gas-phase diffusion of n-hexane into the reaction solution at
273 K produced dark red crystals suitable for X-ray diffraction
(Figure 4). The crystal structure displayed a substitutional
disorder of the bifluorido ligand and a chloride ligand, which
occupies 21% of the sites. The complexes cocrystallized in the
monoclinic space group P21/c. Because 1 was synthesized from
[Rh(Cl){tBuxanPOP}], chlorine containing impurities could be
the source of the chlorido complex.13 The Rh1−F1−F2 angle
in 2 of 133.2(2)° is in the range found for bifluorido complexes
of rhodium in the oxidation state + I (121.4−147.2°).9n The
F1−F2 distance (2.339(5) Å) is comparable to those in
literature-known structures such as in [Rh(FHF)(COD)-
(PPh3)] (Rh−F 2.083(2) Å; F−F 2.3310(34) Å), trans-
Figure 2. Part of the 19F NMR spectrum of the bifluorido ligand of 2
at 243 K: (a) fully coupled; (b) H decoupled.
1
B
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Scheme 2. Activation of SF6 at [Rh(H){tBuxanPOP}] in the
Presence of HSiEt3
fluorine atoms at high field of δ = −526.9 ppm (1JF,Rh = 189
Hz) indicating the chemical equivalency of the fluorido
ligands.5f,g,9a−k,m,14a,17 The H NMR spectrum shows for the
1
hydrido ligand a doublet of triplets of triplets at δ = −19.31
ppm due to the coupling to the rhodium atom and two
equivalent fluorine and phosphorus atoms (1JH,Rh = 26.9 Hz,
Figure 4. Molecular structure of 2. (ORTEP, ellipsoids are set at 50%
probability. The chlorido ligand and all hydrogen atoms are omitted
for clarity except for H2, which was located in the difference Fourier
map and freely refined.) Selected distances [Å] and bond angles [°]:
Rh1−P1 2.2700(6), Rh1−P2 2.2662(6), Rh1−O1 2.1344(14), Rh1−
F1 2.021(3), F2−H2 0.84(8), F1−F2 2.339(5); Rh1−F1−F2
133.2(2), P1−Rh1−P2 166.31(2), F1−Rh1−O1 176.67(11), F1−
Rh1−P1 99.04(8), F1−Rh1−P2 93.28(8), P1−Rh1−O1 83.42(4),
P2−Rh1−O1 84.05(4).
2
2JH,P = 8.2 Hz, JH,F = 4.8 Hz). The coupling constants were
1
assigned based on the corresponding H{31P} NMR spectrum.
The molecular structure of 3 in the solid state was
determined by X-ray crystallography (Figure 5). Red crystals
[Rh(FHF)(Ph2PF)(Ph3P)2] (Rh−F 2.082(1) Å; F−F 2.329(2)
Å), and in Rh(FHF)(6-Me)(PPh3)2 (6-Me = 1,3-bis(methyl)-
3,4,5,6-tetrahydropyrimidin-2-ylidine; Rh−F 2.1460(12) Å; F−
F 2.343(2) Å). The Rh1−F1 bond (2.021(3) Å) in 2 is rather
short and is in the range found in Rh(I) fluorido complexes
(2.018−2.060 Å).9b,h,i,k,l
Treatment of the bifluorido complex 2 with cesium fluoride
led to the abstraction of the coordinated HF to give
[Rh(F){tBuxanPOP}] (5) according to the NMR spectroscopic
and LIFDI-MS data (Scheme 1). The 31P{1H} NMR spectrum
of 5 at 263 K reveals a doublet for the tBuxanPOP ligand at δ =
1
45.9 ppm with a coupling constant of JP,Rh = 157 Hz. The 19F
NMR spectrum (263 K) shows a resonance signal for the
fluorido ligand at δ = −530.6 ppm with a doublet coupling to
rhodium of 208 Hz. A reaction of 5 with HSiEt3 at 50 °C led to
its full conversion into the hydrido complex 1 along with the
formation of FSiEt3 after 2 h, which completes a cyclic process
for the degradation of SF6 (Scheme 1).
Figure 5. Molecular structure of 3. (ORTEP, ellipsoids are set at 50%
probability. All hydrogen atoms are omitted for clarity, except for H1,
which was located in the difference Fourier map and freely refined.)
Selected distances [Å] and bond angles [°]: Rh1−P1 2.3075(8), Rh1−
P2 2.3054(8), Rh1−O1 2.291(2), Rh1−F1 2.006(2), Rh1−F2
2.0120(19), Rh1−H1 1.54(3), F1−H1 2.00(3), F2−H1 2.90(3);
P1−Rh1−P2 163.87(3), F1−Rh1−P1 92.29(6), F1−Rh1−P2
94.23(6), F1−Rh1−H1 67.2(12), F2−Rh1−H1 109.1(12), F1−
Rh1−O1 104.60(8), F2−Rh1−O1 79.11(8).
Late transition metal fluorido complexes can be highly
reactive. Treatment with hydrogen sources, such as silanes,
often lead to the formation of the hydrido compounds,5h,i,14 yet
the reduction of SF6 (1 atm) with 1 (30.0 mg, 0.05 mmol) in
the presence of HSiEt3 (15 equiv) at ambient temperature led
to the formation of [Rh(F)2(H){tBuxanPOP}] (3) as the main
product as well as [Rh(SH){tBuxanPOP}] (4) and two
additional rhodium complexes, which could not be identified
(10:4:3:1 ratio after 2 days according to 31P{1H} NMR
spectrum). Additionally, the compounds S(SiEt3)2 (6), FSiEt3
and H2 were formed (Scheme 2).15 Surprisingly, complex 1
shows no reactivity toward HSiEt3 as it has been observed for
the iPrxanPOP complex to give [Rh(SiEt3){iPrxanPOP}].5h,i,16
However, the formation of 1 and 6 together with unknown
minor products was observed on treatment of 4 with HSiEt3 at
50 °C, whereas 4 is not reactive toward H2. The 31P{1H} NMR
spectrum of rhodium(III) complex 3 reveals a resonance for the
chelating tBuxanPOP ligand at δ = 63.2 ppm (1JP,Rh = 111 Hz)
with a doublet of triplets splitting pattern. The 19F NMR
spectrum displays one broad doublet for the metal bound
of 3 were obtained by n-hexane gas-phase diffusion into the
reaction solution at 293 K. The structure of 3 reveals a
distorted octahedral coordination geometry at the metal center
in which both phosphorus atoms of the tBuxanPOP ligand
occupy the axial positions. The fluorido ligands are located in a
mutually trans-position. The metal bound hydrogen atom was
located in the difference Fourier map and refined freely. To the
best of our knowledge, there is so far only one Rh(III) complex
bearing fluorido ligands structurally described.9m
The Rh1−O1 bond length (2.291(2) Å) is larger than the
corresponding bond lengths in [Rh(Cl)(H)2{tBuxanPOP}]
(2.254(3) Å)8a or [Rh(Cl)(η2-O2){tBuxanPOP}] (2.193(2)
Å)8d and represents, to the best of our knowledge, the longest
Rh−O distance found in tBuxanPOP complexes of Rh(III). The
C
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F1−Rh1−O1 angle (104.60(8)°) differs significantly from the
F2−Rh1−O1 angle (79.11(8)°) and the F1−H1 distance is
2.001 Å, which would be shorter than the sum of the van der
Waals radii.18 Therefore, DFT calculations were performed to
get a closer insight into the minimum structure of 3 (Figure 6).
̃
the bands of the complex [Rh(H)(SH)(pp3)]CF3SO3 (ν =
2560 cm−1, pp = tris(2-(diphenylphosphino)ethyl)-
phosphine).19c
Suitable crystals for X-ray diffraction analysis of compound 4
were obtained from a toluene solution at 193 K. The molecular
structure in the solid state is shown in Figure 7.
Figure 6. DFT-optimized structure of 3; all hydrogen atoms have been
omitted for clarity, except of the metal-bound one.
In the calculated structure the F−H distances are 2.631 and
2.426 Å. This small difference might be due to the strain
induced by the metal-bound pincer ligand. The calculated
structure is, therefore, consistent with the NMR data which
show no large F,H coupling and suggests an equivalence of the
fluorido ligands on the NMR time-scale. Hence, the distortion
in the structure of 3 in the solid state might be attributed to
packing effects. In order to clarify this further, a relaxed scan
calculation has been performed using a stepwise decrease of the
shorter F−H distance starting from the calculated gas-phase
structure toward the determined structure in the solid state.
This analysis delivers an energy difference of only 19.9 kJ/mol,
thus supporting the assumption that the short F−H distance in
the solid state is most probably due to packing effects.
Figure 7. Molecular structure of 4. (ORTEP, ellipsoids are set at 50%
probability. C−H hydrogen atoms were omitted for clarity. The sulfur-
bound hydrogen atom H1 was located in the difference Fourier map
and freely refined.) Selected distances [Å] and bond angles [°]: Rh1−
P1 2.2836(4), Rh1−P2 2.2594(4), Rh1−O1 2.1828(11), Rh1−S1
2.2865(4); P1−Rh1−P2 162.655(16), S1−Rh1−O1 171.74(12),
Rh1−S1−H1 106.9(11), S1−Rh1−P1 95.209(16), S1−Rh1−P2
100.103(17), O1−Rh1−P1 83.24(3), O1−Rh1−P2 82.73(3).
Furthermore, the formation of the sulfur-containing
disilathiane S(SiEt3)2 (6) during the conversion of SF6 with 1
in the presence of HSiEt3 was ascertained by GC-MS
measurement and NMR experiments. The 1H,29Si HMBC
NMR spectrum of a sample taken from the crude reaction
mixture shows the cross peaks for HSiEt3, FSiEt3, and 6 as the
Further evidence for the identity of the hydrosulfido complex
4 is provided by its independent synthesis by treatment of 1
with H2S (Scheme 3). Complex 4 was characterized by NMR
Scheme 3. Synthesis of [Rh(SH){tBuxanPOP}] (4) by
Reaction of 1 with H2S
only silicon containing compounds (Figure 8).20 The H,29Si
1
HMBC spectrum of 6 reveals two cross-peaks at δ = 1.1/22.0
spectroscopy, LIFDI-MS, elemental analysis, and IR spectros-
copy as well as by X-ray crystallography. The 31P{1H} NMR
spectrum of 4 shows a resonance signal for the tBuxanPOP
ligand at δ = 54.8 ppm (1JP,Rh = 149 Hz) with the expected
1
doublet splitting pattern. The H NMR spectrum shows a
signal with a splitting pattern of a triplet of doublets at δ =
2
−1.70 ppm (3JH,P = 13.8 Hz, JH,Rh = 2.5 Hz) for the thiolate
proton. The chemical shift is in the range for transition metal
SH ligands.19 In a 31P decoupling experiment, the signal
2
simplifies to a doublet which confirms the JH,Rh coupling
Figure 8. 1H,29Si HMBC NMR spectrum of HSiEt3, FSiEt3 and
S(SiEt3)2 (6). The measured sample was taken after 5 days from the
reaction mixture of the reaction of SF6 (1 atm) with 1 in the presence
of triethylsilane.
constant that is comparable to the corresponding coupling in
[Rh(SH)(CO)(PPh3)2] of JH,Rh = 1.6 Hz.19a The ATR IR
2
spectrum of 4 shows one weak absorption band for the S−H
stretching mode at ν
̃
= 2547 cm−1 which is in the same range as
D
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DFT-calculations were performed using the Gaussian 09 (revision
D.01) program package25 and the BP86 functional. Def2-svp basis sets
were employed for all atoms except rhodium, which was described on
using a RECP with the associated def2-svp basis set.26 Dispersion
effects were taken into account using the Grimme D3 dispersion
correction with Becke−Jones damping.27 Frequency calculations were
run for all stationary points to identify them as minima (no negative
eigenvalues). Energies were corrected for zero-point energy. The xyz-
coordinates for the calculated structure of 3 are given in the
Supporting Information.
ppm and δ = 0.7/22.0 ppm. 6 was also synthesized
independently by a reaction of ClSiEt3 with Li2S at room
temperature. Disilathianes have a range of application as
reactants in organic chemistry for instance in the synthesis of
thiols, in conversion of acetals and aldehydes into thioxo
derivatives and in reduction processes of aromatic azides to
form amines. Disilathianes are also used for the production of
metal sulfides and discussed as precursors for the synthesis of
transition metal sulfide monolayers by atomic layer deposi-
tion.21
Treatment of [Rh(H){tBuxanPOP}] with SF6 at Room Temper-
ature. In a PFA tube [Rh(H){tBuxanPOP}] (1) (38 mg, 0.06 mmol)
was dissolved in toluene-d8 (0.3 mL). The PFA tube was inserted into
a Young NMR tube. The sample was degassed in vacuo at −196 °C,
pressurized with gaseous SF6 to 1 atm and allowed to warm up to
room temperature. By monitoring the reaction by NMR spectroscopy,
the 31P{1H}, 1H and 19F spectroscopic data revealed a complete
conversion of 1 after 16 h into [Rh(FHF){tBuxanPOP}] (2),
[Rh(F)2(H){tBuxanPOP}] (3), [Rh(SH){tBuxanPOP}] (4) and an
unknown Rh(III) complex (1H NMR (300 MHz, C6D6, 298 K) δ =
SUMMARY AND CONCLUSIONS
■
Despite its chemical inertness, SF6 was successfully converted
by treatment of [Rh(H){tBuxanPOP}] (1) at room temperature
into the bifluorido complex [Rh(FHF){tBuxanPOP}] (2).
Complex 1 was regenerated by conversion of 2 into the
fluorido complex [Rh(F){tBuxanPOP}] (3) and subsequent
treatment of the latter with HSiEt3. Furthermore, SF6 reacted
with 1 in the presence of an excess of HSiEt3 to afford the
difluorido complex [Rh(F)2(H){tBuxanPOP}] (3), which is
stable toward HSiEt3. Moreover, the sulfur-containing products
were identified to be the hydrosulfido complex [Rh(SH)-
1
−16.22 (d, JH,Rh = 42 Hz, RhH) ppm. 31P{1H} NMR (121.5 MHz,
1
C6D6, 298 K) δ = 78.8 (d, JP,Rh = 118 Hz) ppm (ratio: 10:3:2:1
according to the 31P{1H} NMR spectrum). After 4 days the
spectroscopic data as well as mass spectrometric analysis (LIFDI-
TOF) showed only the presence of complex 2. The reaction mixture
was filtered. All volatile compounds of the filtrate were removed under
reduced pressure to obtain 2 (35 mg, 0.05 mmol, 83%) as a dark red
powder. Analytical data for 2: 1H NMR (300 MHz, toluene-d8, 298 K)
δ = 12.39 (s, br, 1H FHF); 7.62 (s, br, 2H, ArH); 6.95 (d, J = 7.5 Hz,
2H, ArH); 6.77(t, J = 7.5 Hz, 2H, ArH); 1.56 (vt, N = 13.6 Hz, 36H,
{
tBuxanPOP}] (4) and S(SiEt3)2 (6). No generation of
phosphanesulfides was observed as in the reaction of SF6
with [Rh(H)(PEt3)].5h,i However, in the SF6 activation
reactions at [{Rh(μ-H)(dippp)}2] (dippp = 1,3-bis-
(diisopropylphosphanyl)propane) in the presence of HSiEt3
the thiolato-bridged complex [Rh2(μ-H)(μ-SSiEt3)(dippp)2]
was obtained.5f,g In contrast, hydrosulfido complex 4 is
mononuclear and features a SH ligand. This might be due to
the sterical demand of the tBuxanPOP ligand.
1
C(CH3)3); 1.06 (s, 6H, C(CH3)2). H NMR (300 MHz, toluene-d8,
243 K) δ = 12.20 (dd, s in 1H{19F} NMR, 1JH,F = 402 Hz, JH,F = 37 Hz,
1H, FHF); 1.61 (vt, N = 12.5 Hz, s in 1H{31P} NMR, 36H, C(CH3)3);
1.01 (s, 6H, C(CH3)2) ppm. 19F NMR (282.4 MHz, toluene-d8, 243
K) δ = −178.2 (dd, d in 19F{1H} NMR, 1JF,H = 401 Hz, JF,F = 112 Hz,
1F, HF); −498.0 (m, dd in 19F{1H} NMR, 1JF,Rh = 184 Hz, JF,F = 111
Hz, 1F, RhF) ppm. 31P{1H} NMR (121.5 MHz, toluene-d8, 243 K) δ
EXPERIMENTAL SECTION
■
= 47.4 (d, 1JP,Rh = 148 Hz) ppm. IR (ATR, diamond): ν
FHF), 1871 (br. m, FHF) cm−1.
̃
= 2549 (br. m,
All experiments were performed on a Schlenk line under an
atmosphere of argon or in an argon-filled drybox with dioxygen levels
below 10 ppm. All solvents were purified, dried and degassed by
conventional methods and distilled under an atmosphere of argon
prior to use. [Rh(H){tBuxanPOP}] (1; tBuxanPOP = 9,9-dimethyl-4,5-
bis(ditert-butylphosphino)xanthene) and S(SiEt3)2 were prepared
according to literature procedures.8a,21d HSiEt3 was purchased from
Sigma-Aldrich. SF6 was a gift of Solvay Fluor GmbH. Microanalyses
were performed with a HEKAtech Euro EA Elemental Analyzer. The
NMR spectra were recorded at 298 K (if not stated otherwise) on a
Formation of [Rh(F){tBuxanPOP}] (5). A toluene-d8 solution of 2
(35 mg, 0.05 mmol) was treated with CsF (10 equiv). By monitoring
the reaction by NMR spectroscopy, the 31P{1H} and 19F spectroscopic
data revealed the formation of [Rh(F){tBuxanPOP}] (5). The reaction
mixture was filtered. All volatile compounds of the filtrate were
removed under reduced pressure to obtain 5 (25 mg, 0.04 mmol, 80%)
1
as a dark red powder. H NMR (300 MHz, toluene-d8) δ = 7.77 (m,
2H, ArH); 6.97 (m, 2H, ArH); 6.82 (t, J = 7.6 Hz, 2H, ArH); 1.62 (vt,
1
N = 13.5 Hz, 36H, C(CH3)3); 1.13 (s, 6H, C(CH3)2) ppm. 19F NMR
Bruker DPX 300 or a Bruker Avance III 300 spectrometer. The H
1
(282.4 MHz, toluene-d8) δ = −530.6 (d, d in 19F{1H} NMR, JF,Rh
=
NMR chemical shifts were referenced to residual toluene-d7 at δ = 7.09
ppm and δ = 2.09 ppm or to residual benzene-d5 at δ = 7.16 ppm. The
19F NMR and 31P{1H} spectra were referenced to external CFCl3 at δ
= 0.0 ppm and 85% H3PO4 at δ = 0.0 ppm. Abbreviation for virtual
coupling constants: N = 3JH,P + 5JH,P. Mass spectra were recorded on a
Micromass Q-Tof-2 instrument equipped with a Linden LIFDI source
(Linden CMS GmbH). GC-MS spectra were measured on an Agilent
6890N gas-phase chromatograph (Agilent 19091S-433 Hewlett-
Packard) equipped with an Agilent 5973 Network mass selective
detector at 70 eV. IR spectra were recorded with a Bruker Vertex 70
spectrometer equipped with an ATR unit (diamond). The crystallo-
graphic data were collected at a BRUKER D8 VENTURE area
detector, Mo Kα radiation (λ = 0.71073 Å). All measurements were
performed at 100.00(2) K. Multiscan absorption corrections
implemented in SADABS22 were applied to the data. The structures
were solved by intrinsic phasing method (SHELXT-2013)23 and
refined by full-matrix least-squares procedures based on F2 with all
measured reflections (SHELXL-2013)24 with anisotropic temperature
factors for all non-hydrogen atoms. All hydrogen atoms were added
geometrically and refined by using a riding model except for H2 in
complex 1, H1 in complex 3, and H1 in complex 4 which were found
in the difference Fourier map and freely refined.
207 Hz, RhF) ppm. 31P{1H} NMR (121.5 MHz, toluene-d8) δ = 45.9
1
2
(d, JP,Rh = 157 Hz, JP,F = 2 Hz) ppm.
Treatment of [Rh(F){tBuxanPOP}] (5) with HSiEt3. A toluene-d8
solution of 5 was treated with HSiEt3 (10 equiv) at 50 °C. By
monitoring the reaction by NMR spectroscopy, the 31P{1H} and H
1
spectroscopic data revealed a full conversion of 5 into [Rh(H)-
{
tBuxanPOP}] (1) after 2 h as well as the formation of FSiEt3.
Treatment of [Rh(H){tBuxanPOP}] with SF6 in the Presence of
HSiEt3 at Room Temperature. In a PFA tube [Rh(H){tBuxanPOP}]
(1) (30.0 mg, 0.05 mmol) and HSiEt3 (120 μL, 0.77 mmol) were
dissolved in toluene-d8 (0.2 mL). The PFA tube was inserted into a
Young NMR tube. The sample was degassed in vacuo at −196 °C,
pressurized with gaseous SF6 to 1 atm, and allowed to warm up to
room temperature. After 4 days the 31P{1H}, 1H, and 19F spectroscopic
data revealed a complete conversion of 1 into [Rh(F)2(H)-
{
tBuxanPOP}] (3) as the main product, [Rh(SH){tBuxanPOP}] (4),
and two unknown rhodium complexes (1H NMR (300 MHz, C6D6,
298 K) δ = −14.94 (m, dd in 1H{31P} NMR, 1JH,Rh = 20.2 Hz, 2JH,H
=
8.2 Hz, RhH); −21.20 (m, dd in 1H{31P} NMR, 1JH,Rh = 26.1 Hz, 2JH,H
= 8.3 Hz, RhH) ppm. 31P{1H} NMR (121.5 MHz, C6D6, 298 K) δ =
1
1
78.0 (d, JP,Rh = 117 Hz); 37.4 (d, JP,Rh = 110 Hz) ppm.) together
E
DOI: 10.1021/acs.organomet.7b00858
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
with the formation of H2 and FSiEt3. Mass spectrometric analysis as
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* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.7b00858.
Crystallographic data of the compounds 2−4 and
[Rh(I){tBuxanPOP}], computational details of the DFT
calculations, crystallographic data as well as additional
experimental data and spectra (PDF)
Optimized structure of [Rh(F)2(H){tBuxanPOP}] (3)
(XYZ)
Accession Codes
CCDC 1584179−1584182 contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/data_request/cif, or by email-
ing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
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AUTHOR INFORMATION
■
Corresponding Author
*E-mail: thomas.braun@chemie.hu-berlin.de.
ORCID
Thomas Braun: 0000-0003-1629-5352
Notes
The authors declare no competing financial interest.
(f) Zam
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Int. Ed. 2016, 55, 15072−15075. (k) McTeague, T. A.; Jamison, T. F.
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This work was financially supported by the DFG (Deutsche
Forschungsgemeinschaft). We thank Patrick McHugh for his
experimental support and the Solvay Fluor GmbH for a gift of
SF6. M. W. is a fellow of the graduate school “Fluorine as a Key
Element” financed by the DFG.
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F
DOI: 10.1021/acs.organomet.7b00858
Organometallics XXXX, XXX, XXX−XXX

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Organometallics XXXX, XXX, XXX−XXX