Different coordination behavior of a catechol phosphine and its sulfide: Formation of an unprecedented dinuclear rhodium complex with a non-coordinated PS unit

Article abstract of DOI:10.1016/j.ica.2011.02.076

Sulfurization of 3-[(diphenylphosphinyl)methyl]benzene-1,2-diol 1 produced phosphine sulfide 3. Both ligands reacted easily to form gold(I) and rhodium(I) complexes which were characterized by analytical and spectroscopic data, and single-crystal X-ray diffraction studies. Whereas the phosphine prefers to form complexes with a metal-to-ligand ratio of 1:2 with both metals, the phosphine sulfide exhibits a reduced donor power and yields only a 1:1 complex with AuCl. With rhodium(I), formation of a homobimetallic complex with a metal-to-ligand ratio of 2:1 was found. This complex displays an unusual coordination of both metal atoms to the catechol moiety whereas the phosphine sulfide moiety remains inactive.

Full text of DOI:10.1016/j.ica.2011.02.076

Inorganica Chimica Acta 374 (2011) 240–246
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Different coordination behavior of a catechol phosphine and its sulfide: Formation
of an unprecedented dinuclear rhodium complex with a non-coordinated P@S unit
Gernot Bauer a, Cornelia Englert a, Martin Nieger b, Dietrich Gudat a,
⇑
a Institute of Inorganic Chemistry, University of Stuttgart, 70569 Stuttgart, Germany
b Laboratory of Inorganic Chemistry, University of Helsinki, 00014 University of Helsinki, Finland
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 6 March 2011
Sulfurization of 3-[(diphenylphosphinyl)methyl]benzene-1,2-diol 1 produced phosphine sulfide 3. Both
ligands reacted easily to form gold(I) and rhodium(I) complexes which were characterized by analytical
and spectroscopic data, and single-crystal X-ray diffraction studies. Whereas the phosphine prefers to
form complexes with a metal-to-ligand ratio of 1:2 with both metals, the phosphine sulfide exhibits a
reduced donor power and yields only a 1:1 complex with AuCl. With rhodium(I), formation of a homo-
bimetallic complex with a metal-to-ligand ratio of 2:1 was found. This complex displays an unusual coor-
dination of both metal atoms to the catechol moiety whereas the phosphine sulfide moiety remains
inactive.
Dedicated to Professor Wolfgang Kaim on
the occasion of his 60th birthday.
Keywords:
Phosphine sulfides
Phosphines
Catechols
Ó 2011 Elsevier B.V. All rights reserved.
Rhodium
Gold
103Rh NMR
1. Introduction
process, and it has been shown that variation of the template gives
rise to a series of compounds featuring controlled variation of P–
During the last three decades, bidentate phosphine ligands have
become a powerful instrument for applications in coordination
chemistry and catalysis [1]. In spite of the tremendous evolution
of the field, the design and synthesis of tailored bisphosphine li-
gands still remains a time consuming and complex task. Recent
developments have focused in particular on modular syntheses
which permit to assemble bidentate ligands from smaller building
blocks. This task can either be achieved by employing conventional
coupling reactions allowing the introduction of two phosphine
units into an organic substrate [2], or by connecting two building
blocks by non-covalent interactions such as hydrogen bonds, elec-
trostatic attraction, or Lewis-donor–acceptor interactions [3], fol-
lowing a supramolecular ‘‘aufbau principle’’ [3].
The challenge in this approach is to control geometrical con-
straints of the ligand, which are often categorized in terms of
descriptors like the cone angle or the ‘‘natural bite angle’’ [4]. We
have recently established a method for template-controlled synthe-
sis of heterobimetallic chelate complexes 2 [5] from the flexible,
ditopic phosphine ligand 1 which exhibits binding sites at the phos-
phorus atom and the catechol unit (Scheme 1). Complexes 2 can be
put together either in a stepwise manner, introducing each metal in
a separate reaction [6], or in a single step via a self-assembly
Pd–P bite angles [5].
As an alternative to controlling the geometrical constraints by
using different templates, one can also conceive to modify the li-
gand backbone. Converting the phosphine into the corresponding
sulfide (Scheme 1) is easy to implement and would seem an obvi-
ous choice since the P@S-moiety exhibits a similar preference to
coordinate to ‘‘soft’’ lewis acids as the phosphine functionality of
2, and is known to form stable complexes with late transition met-
als [7]. In the following, we report the synthesis of phosphine sul-
fide 3, and compare the reactivity of phosphine 1 and phosphine
sulfide 3 toward some gold(I) and rhodium(I) compounds.
2. Experimental
2.1. General information
All manipulations were carried out under dry argon using stan-
dard Schlenk techniques. Solvents and triethylamine were dried by
standard procedures [8] unless otherwise mentioned. Catechol
phosphine 1 was prepared as reported earlier [9]. (Tetrahydrothio-
phene)–gold(I) chloride was prepared as described in the literature
[10], [Rh(CO)2(acac)] is commercially available and was used with-
out further purification. Solution NMR spectra were recorded on
Bruker Avance 400 (1H: 400.1 MHz, 13C: 100.5 MHz, 31P:
161.9 MHz, 103Rh: 12.74 MHz), Avance 250 (1H: 250 MHz, 13C:
⇑
Corresponding author.
E-mail address: gudat@iac.uni-stuttgart.de (D. Gudat).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.02.076

G. Bauer et al. / Inorganica Chimica Acta 374 (2011) 240–246
241
Ph2
P
Ph2
P
M
S
PPh2
P
O
O
S8, THF
Ph2
XnE
OH
OH
O
O
OH
OH
2
1
3
Scheme 1. Synthesis of phosphine 1, heterobimetallic complexes 2, and phosphine sulfide 3 (M = Pd, Pt, Cu, Ag, Au; EXn = B, SnCl2, SnMe2, GaCl, BiCl).
62.8 MHz, 31P: 101.2 MHz) or Avance 600 spectrometers (1H:
600.1 MHz, 103Rh: 18.97 MHz) at 303 K unless mentioned other-
wise; 103Rh NMR data were collected from 1H-detected 1H,103Rh
gs-HMQC experiments. Chemical shifts are referenced to external
2JHH = 12.9 Hz, 4H, o-Ph); 7.58–7.41 (m, 6H, p-, m-Ph); 6.75 (td,
3
4
4JHH = 1.9 Hz, JHH = 8.1 Hz, 1H, p-cat.); 6.51 (dt, JHH = 0.9 Hz,
4
3
3JHH = 3.9 Hz, 1H, m-cat.); 5.97 (td, JHH = 2 Hz, JHH = 7.7 Hz, 1H,
2
o-cat.); 5.94 (s broad, 1H, OH); 3.97 (d, JHH = 12.9 Hz, 2H, CH2).
TMS (1H, 13C), 85% H3PO4
(N
= 40.480747 MHz, 31P), or a virtual
31P{1H} NMR (CD2Cl2): d = 48.5 (s, broad); 30.5 (s, broad). 31P{1H}
2
1
reference frequency of
N
= 3.160000 MHz (103Rh). Coupling con-
NMR (CD2Cl2, ꢀ20 °C): d = 53.1 (dd, JPP = 315 Hz, JRhP = 142 Hz);
2 1
stants are given as absolute values; prefixes i, o, m, p-Ph denote
atoms of P–C6H5 substituents, i, o, m, p-cat represents atoms in
the catechol rings. EI-MS: Varian MAT 711, 70 eV. ESI-MS: Bruker
Daltonics-micrOTOF-Q. Given m/e-numbers refer to the mass of
the most abundant isotopomer. The suggested elemental composi-
tion was in all cases confirmed by comparison of observed and
simulated isotope patterns. IR: Nicolet 6700 FT-IR with ATR unit,
spectral range 4000–600 cmꢀ1; Elemental analyses: Perkin–Elmer
2400CHSN/O Analyser. Deviations from calculated values are in
the case of solvates attributable to nonstoichiometric amounts of
solvent; complex 6 is light sensitive and presumably underwent
some decomposition during sample preparation.
27.2 (dd, JPP = 315 Hz, JRhP = 135 Hz). IR: 3470, 3388 cmꢀ1 (OH),
1968 cmꢀ1 (CO).
2.3. Complex 5
Solid [Au(tetrahydrothiophene)Cl] (103 mg, 0.32 mmol) was
added to a solution of 1 (200 mg, 0.64 mmol) in anhydrous THF
(20 mL). The resulting mixture was stirred for 1 h at room temper-
ature. A few drops of DMF were added until the formed precipitate
had dissolved, and the clear solution was stored overnight at 4 °C
to give colorless crystals suitable for X-ray diffraction analysis
(260 mg, 84%, m.p. 190 °C). Anal. Calc. for C38H34AuO4P2Clꢁ ꢁ ꢁ
DMFꢁ ꢁ ꢁTHF: C, 53.61; H, 4.90; N, 2.78. Found: C, 53.07; H, 4.82;
N, 2.59%. (+)-ESI-MS: m/e: 813.16 [M+]. 1H NMR (250 MHZ,
DMSO-d6): d = 9.43 (s, 1H, o-OH), 8.96 (s, 1H, m-OH), 7.80–7.65
2.1.1. 3-[(Diphenylphosphorothioyl)-methyl]-benzene-1,2-diole (3)
Sulfur (255 mg, 7.95 mmol) was added to a solution of 3-
4
(m, 8H, Ph), 7.60–7.45 (m, 12H, Ph), 6.67 (dd, JHH = 2.5 Hz,
[(diphenylphosphanyl)-methyl]-benzene-1,2-diole
1
(2.24 g,
3
3JHH = 6.8 Hz, 2H, C6H3), 6.37 (t, JHH = 7.3 Hz, 2H, C6H3), 6.34 (d,
7.27 mmol) in 100 ml anhydrous THF. The mixture was stirred
for 6 h at room temperature. The solvent was then evaporated
and the residue recrystallized from MeOH to give colorless crystals,
suitable for X-ray analysis (2.14 g, yield 86%, m.p. 137 °C). Anal.
Calc. for C19H17O2PS: C, 67.05; H, 5.03. Found: C, 66.58; H, 4.97%.
EI-MS: m/e = 340.0 [M+], 324, 308 [M+ꢀS], 217 [SPPh2þ], 139
[SPPh+], 123 [C7H7O2+], 107 [C6H3O2+]. 1H NMR (DMSO-d6):
3JHH = 7.4 Hz, 2H, C6H3), 4.15 (s broad, 4H, CH2). 31P{1H} NMR
(DMSO-d6): d = 40.2 (s broad).
2.4. Complex 6
Solid [Au(tetrahydrothiophene)Cl] (112 mg, 0.35 mmol) was
added to a solution of 3 (236 mg, 0.70 mmol) in anhydrous dichlo-
romethane (20 mL). The mixture was stirred for 30 min at room
temperature. The resulting precipitate was filtered off, washed
with dichloromethane, and dried in vacuum. Recrystallization from
acetone gave colorless crystals, suitable for X-ray diffraction anal-
ysis (152 mg, 76%, m.p. 123 °C). Anal. Calc. for C19H17AuClO2PS: C,
39.84; H, 2.99. Found: C, 39.15; H, 2.97%. (ꢀ)-ESI-MS: m/e:
571.00 [M+]. 1H NMR (250 MHz, DMSO-d6): d = 9.1 (s broad, OH);
4
d = 9.11 (s, 1H, OH); 8.24 (s, 1H, OH); 7.87 (ddd, JHH = 1.7 Hz,
2
3JHH = 7.8 Hz, JHH = 12.7 Hz, 4H, o-Ph); 7.51–7.46 (m, 6H, p-, m-
4
3
Ph); 6.56 (td, JHH = 1.8 Hz, JHH = 7.7 Hz, 1H, p-cat.); 6.48 (td,
4JHH = 1.9 Hz, JHH = 7.7 Hz, 1H, m-cat.); 6.37 (t, JHH = 7.7 Hz, 1H,
3
3
o-cat.); 4.03 (d, JHH = 13.7 Hz, 2H, CH2). 31P{1H} NMR (CDCl3):
2
d = 42.8; (DMSO-d6): d = 42.1. 13C{1H} NMR (CDCl3): d = 148.8 (d,
4JCP = 3.4 Hz, C–OH); 142.2 (d, JCP = 4.8 Hz, C–OH); 132.0 (d,
3
4JCP = 3.0 Hz, p-Ph); 131.4 (d, JCP = 10 Hz, o-Ph); 130.0 (s, i-cat.);
2
3
3
4
3
129.7 (d, JCP = 12.2 Hz, m-Ph); 122.3 (d, JCP = 5.5 Hz, o-cat.);
122.8 (d, JCP = 3.1 Hz, m-cat.); 120.2 (d, JCP = 8.5 Hz, i-Ph); 114.2
(d, JCP = 3.7 Hz, p-cat.); 38.6 (d, JCP = 52.9 Hz, CH2). IR: 3476,
8.1 (s broad, OH); 7.86 (ddd, JHH = 1.4 Hz, JHH = 8.0 Hz,
4
2
2JPH = 12.8 Hz, 4H, o-Ph); 7.57–7.44 (m, 6H, p-, m-Ph); 6.57 (dt,
5
1
4JHH = 2.0 Hz, JHH = 7.5 Hz, 1H, o-cat.); 6.48–6.33 (m, 2H, p-, m-
3
cat.); 4.09 (d, JPH = 13.8 Hz, 2H, CH2). 31P{1H} NMR (DMSO-d6):
2
3389, 3273, 3170 (OH).
d = 42.6. IR: 3442, 3371 cmꢀ1 (OH).
2.2. Complex 4
2.5. Complex 7
Solid [Rh(CO)2(acac)] (82 mg, 0.32 mmol) was added to a solu-
tion of 1 (200 mg, 0.64 mmol) in anhydrous EtOH (20 mL). The
resulting mixture was stirred for 1 h at room temperature. The
formed precipitate was filtered off and dried in vacuum. Recrystal-
lisation from acetone afforded pale yellow cubic crystals, suitable
for X-ray diffraction analysis (172 mg, 72%, m.p. 227 °C). Anal. Calc.
for C39H33RhO5P2ꢁ ꢁ ꢁ2 acetone: C, 62.65; H, 5.26. Found: C, 62.67; H,
5.25%. (+)-ESI-MS: m/e: 747.09 [MH+]. 1H NMR (250 MHz, CD2Cl2):
Solid [Rh(cyclooctadiene)Cl]2 (83 mg, 0.168 mmol) was added
to a solution of 3 (120 mg, 0.35 mmol) in dry EtOH (5 mL). Trieth-
ylamine (0.06 mL, 0.9 mmol) was added and the mixture was stir-
red for 1 h at room temperature. The formed precipitate was
filtered off and dried in vacuum. Recrystallisation from acetone
gave yellow crystals, suitable for X-ray diffraction analysis
(129 mg, 76%, m.p. 139 °C). Anal. Calc. for C35H39Rh2O2PSꢁ ꢁ ꢁ1 ace-
tone: C, 55.75; H, 5.54. Found: C, 56.26; H, 5.61%. (+)-ESI-MS:
4
3
d = 8.07 (s broad, 1H, OH); 7.78 (ddd, JHH = 1.6 Hz, JHH = 8.1 Hz,

242
G. Bauer et al. / Inorganica Chimica Acta 374 (2011) 240–246
m/e: 761.06 [MH+]. 1H NMR (250 MHz, CD2Cl2): d = 7.87 (dd,
crystals, C19H17O2PSAuCl, M = 572.77 g molꢀ1, crystal size 0.20 ꢂ
2
3
3JHH = 7.7 Hz, JHH = 12.9 Hz, 2H, o-Ph); 7.81 (dd, JHH = 7.7 Hz,
0.15 ꢂ 0.10 mm, triclinic, space group P1 (No. 2), a = 9.4738(3) Å,
ꢀ
2JHH = 13.2 Hz, 2H, o-Ph); 7.49–7.33 (m, 6H, p-, m-Ph); 6.01 (d,
b = 10.0651(3) Å,
c = 10.8564(3) Å,
a
= 108.527(2)°,
b =
=
3
3JHH = 6.7 Hz, 1H, p-cat.); 5.64 (d, JHH = 5.5 Hz, 1H, m-cat.); 5.01
105.608(2)°,
c
= 98.982(2)°, V = 911.67(5) Å3, Z = 2, qcalcd
3
2
2
(t, JHH = 6.1 Hz, 1H, o-cat.); 4.68 (dd, JHH = 11.1 Hz, JPH = 13.9 Hz,
2.087 Mg mꢀ3
,
F(0 0 0) = 548, semi-empirical
l
= 8.427 mmꢀ1
,
2
1H, CH2); 3.91–3.69 (m, 8H, cod); 3.21 (t, JPH = 15.0 Hz, 1H, CH2);
absorption correction from equivalents, min/max. transm.
0.2870/0.4853, 16 429 reflections (2hmax = 55°), 4131 unique
[Rint = 0.061], 242 parameters, 5 restraints, goodness-of-fit on F2:
2.41–2.09 (m, 8H, cod); 1.99–1.88 (m, 4H, cod); 1.75–1.55 (m, 4H,
3
cod). 1H NMR (600 MHz, CD2Cl2): d = 8.00 (ddd, JHH = 8.2 Hz,
2
3
4JHH = 1.3 Hz, JPH = 12.7 Hz, 2H, o-Ph); 7.81 (dd, JHH = 8.4 Hz,
1.06, R1 (I > 2r(I)) = 0.038, wR2 (all data) = 0.098, largest diff. peak
2
4JHH = 1.2 Hz, JPH = 13.2 Hz, 2H, o-Ph); 7.61–7.57 (m, 2H, p-Ph);
and hole 3.905 (near Au1) and ꢀ3.174 e Aꢀ3. The AuCl group is dis-
ordered (ration 0.954(1):0.046(1)). Complex 7. Orange plates,
7.56–7.53 (m, 2H, m-Ph); 7.52–7.48 (m, 2H, m-Ph); 6.14 (dt,
4
3
3JHH = 6.5 Hz, JHH = 0.6 Hz, 1H, o-cat.); 5.77 (d, JHH = 5.0 Hz, 1H,
C
35H39O2PSRh2, M = 760.51 g molꢀ1
,
crystal size 0.40 ꢂ 0.30 ꢂ
3
2
ꢀ
p-cat.); 5.14 (t, JHH = 6.2 Hz, 1H, m-cat.); 4.80 (dd, JHH = 11.0 Hz,
0.25 mm, triclinic, space group P1 (No. 2), a = 10.482(1) Å,
b = 12.689(1) Å, c = 13.314(1) Å, = 110.91(1)°, b = 111.70(1)°,
= 90.77(1)°, V = 1515.3(2) Å3, Z = 2, calcd = 1.667 Mg mꢀ3
= 1.243 mmꢀ1, semi-empirical absorption correc-
2JPH = 14.1 Hz, 1H, CH2); 4.03–3.97 (m, 2H, cod); 3.94–3.89 (m,
a
2
3H, cod); 3.87–3.83 (m, 3H, cod); 3.34 (t, JPH = 14.6 Hz, 1H, CH2);
c
q
,
2.43–2.27 (m, 8H, cod); 2.10–2.04 (m, 4H, cod); 1.86–1.78 (m, 2H,
cod); 1.77–1.70 (m, 2H, cod). 31P{1H} NMR (CD2Cl2): d = 43.7 (d,
J = 3 Hz). 103Rh NMR (CD2Cl2): d = 1118, ꢀ422.
F(0 0 0) = 772, l
tion from equivalents, min/max. transm. 0.6403/0.7456, 22,746
reflections (2hmax = 55°), 6923 unique [Rint = 0.031], 370 parame-
ters, goodness-of-fit on F2: 1.08, R1 (I > 2
r(I)) = 0.031, wR2 (all
2.6. Crystal structure determinations
data) = 0.078, largest diff. peak and hole 0.890 and ꢀ0.680 e Aꢀ3
.
Complex 7-acetone. Orange crystals,
C
35H39O2PSRh2ꢂC3H6O,
Crystallographic data were collected on a Bruker Nonius Kappa
CCD diffractometer at 123(2) K (3–5, 7) or on a Nonius Kappa CCD
M = 818.59 g molꢀ1, crystal size 0.40 ꢂ 0.16 ꢂ 0.08 mm, triclinic,
ꢀ
space group P1 (No. 2), a = 11.383(1) Å, b = 12.220(1) Å, c =
diffractometer at 100(2) K (6) using Mo K
a
radiation (k = 0.71073).
13.029(1) Å,
a
= 72.45(1)°,
b = 89.12(1)°,
c = 82.82(1)°,
Direct methods (SHELXS-97 [11]) were used for structure solution
and refinement (SHELXL-97, [12] full-matrix, least-squares on F2).
Hydrogen atoms were refined using a riding model (H(O) free).
V = 1714.0(2) Å3, Z = 2,
q
calcd = 1.586 Mg mꢀ3, F(0 0 0) = 836,
l =
1.107 mmꢀ1, semi-empirical absorption correction from equiva-
lents, min/max. transm. 0.7262/0.9144, 41,778 reflections
(2hmax = 55°), 7843 unique [Rint = 0.028], 408 parameters, good-
Complex 3. Colorless crystals,
C
19H17O2PS, M = 340.36 g molꢀ1
,
crystal size 0.35 ꢂ 0.30 ꢂ 0.25 mm, triclinic, space group P1 (No.
ness-of-fit on F2: 1.05, R1 (I > 2
r(I)) = 0.0207, wR2 (all data) = 0.050,
ꢀ
2), a = 9.493(2) Å, b = 13.293(3) Å, c = 13.863(3) Å,
b = 72.32(2)°,
= 81.28(2)°, V = 1646.1(6) Å3, Z = 4, qcalcd
1.373 Mg mꢀ3, F(0 0 0) = 712, = 0.300 mmꢀ1, absorption correc-
a
= 89.55(2)°,
largest diff. peak and hole 0.516 and ꢀ0.529 e Aꢀ3
.
c
=
l
3. Results and discussion
tion: none, 16 589 reflections (2hmax = 55°), 7394 unique
[Rint = 0.040], 427 parameters, 4 restraints, goodness-of-fit on F2:
Phosphine 1 was synthesized as previously described [9]. Reac-
tion with [Rh(CO)2(acac)] in anhydrous ethanol or with [Au(tetra-
hydrothiophene)Cl] in THF produced the complexes 4 and 5
(Scheme 2), respectively. Reaction of 1 with [Rh(cyclooctadi-
ene)Cl]2 was messy and produced according to a 31P NMR assay
a mixture of several products none of which was unambiguously
identified or isolated. Crystals of 4 and 5 suitable for a single-
crystal X-ray diffraction study were obtained as pale yellow cubes
by recrystallisation of the crude samples from acetone or THF/DMF,
respectively. Crystals of 5 withered and crumbled within a few
days under loss of solvent.
The rhodium complex 4 crystallizes as solvate in the monoclinic
space group P21/c with four molecules per unit cell and two mole-
cules of acetone per complex. The molecular structure of 4 is
shown in Fig. 1 together with the most important distances and an-
gles. One solvent molecule connects via a hydrogen bond to one of
the phenolic OH-groups. In addition, there are intramolecular O–
Hꢁ ꢁ ꢁO hydrogen bonds connecting the two hydroxyl groups in
the same catechol ring, and a further one connecting the metal
bound oxygen of the chelate ligand with the closest OH-group of
the other phosphine moiety (O(1)ꢁ ꢁ ꢁO(21) 2.614(2) Å). In contrast
to other monometallic complexes derived from 1 [6,13], the two
catechol phosphine units exhibit different coordination modes.
One ligand unit is deprotonated and features a P,O-chelating coor-
dination, whereas the other one remains neutral and acts as a
monodentate, P-coordinated ligand. Both Phosphorus atoms occu-
py trans-positions at the square-planar coordinated metal. The two
distances between rhodium and phosphorus are different; The
Rh(1)–P(1) distance to the chelating ligand is noticeably shorter
(2.285(1) Å) than the opposite one (Rh(1)–P(2) 2.3320(7) Å). The
other distances in both ligands do not vary significantly from each
other or the free ligand 1 [9] and fall into known ranges of similar
compounds.
1.20, R1 (I > 2r(I)) = 0.054, wR2 (all data) = 0.130, largest diff. peak
and hole 0.571 and ꢀ0.383 e Aꢀ3. Complex 4-acetone. Pale yellow
cubic crystals, C39H33O5P2Rh ꢂ 2C3H6O, M = 862.66 g molꢀ1, crystal
size 0.30 ꢂ 0.15 ꢂ 0.10 mm, monoclinic, space group P21/c (No.
14), a = 10.593(1) Å, b = 16.620(2) Å, c = 23.179(3), b = 93.03(1)°,
V = 4075.1(8) Å3, Z = 4,
l
q
calcd = 1.406 Mg mꢀ3
,
F(0 0 0) = 1784,
= 0.548 mmꢀ1, semi-empirical absorption correction from equiv-
alents, min/max. transm. 0.7068/0.9472, 61 872 reflections
(2hmax = 55°), 9325 unique [Rint = 0.068], 509 parameters, 9 re-
straints, goodness-of-fit on F2: 1.05, R1 (I > 2
r(I)) = 0.040, wR2 (all
data) = 0.081, largest diff. peak and hole 0.607 and ꢀ0.418 e Aꢀ3
.
Complex 4-acetonitrile. Orange crystals, C39H33O5P2Rh ꢂ 2CH3CN,
M = 828.61 g molꢀ1
clinic, space group P21/c (No. 14), a = 10.624(1) Å, b = 15.477(2) Å,
c = 23.849(4) Å, b = 95.53(1)°, V = 3903.2(9) Å3, Z = 4, qcalcd
1.410 Mg mꢀ3 = 0.567 mmꢀ1
F(0 0 0) = 1704, semi-empirical
,
crystal size 0.24 ꢂ 0.08 ꢂ 0.04 mm, mono-
=
,
l
,
absorption correction from equivalents, min/max. transm.
0.7118/0.9703, 58 886 reflections (2hmax = 55°), 8934 unique
[Rint = 0.099], 489 parameters, 3 restraints, goodness-of-fit on F2:
1.07, R1 (I > 2r(I)) = 0.064, wR2 (all data) = 0.164, largest diff. peak
and hole 2.563 (near Rh1) and ꢀ1.051 e Aꢀ3
.
Complex
5ꢂ2DMFꢂTHF.
Colorless
crystals,
C
38H34O4P2AuClꢂ2C3H7-
NOꢂC4H8O, M = 1067.30 g molꢀ1
,
crystal size 0.25 ꢂ 0.20 ꢂ
ꢀ
0.15 mm, triclinic, space group P1 (No. 2), a = 9.2132(1) Å,
b = 13.2035(2) Å, c = 20.6659(3) Å,
a
= 92.041(1)°, b = 99.654(1)°,
c
= 109.079(1)°, V = 2331.13(6) Å3, Z = 2 (4 ꢂ 0.5), qcalcd
=
1.521 Mg mꢀ3
,
F(0 0 0) = 1080,
l
= 3.333 mmꢀ1
,
semi-empirical
absorption correction from equivalents, min/max. transm.
0.5059/0.6143, 46 657 reflections (2hmax = 55°), 10 666 unique
[Rint = 0.042], 564 parameters, 74 restraints, goodness-of-fit on
F2: 1.09, R1 (I > 2
r(I)) = 0.031, wR2 (all data) = 0.075, largest diff.
peak and hole 1.180 and ꢀ0.986 e Aꢀ3. Complex 6. Colorless

G. Bauer et al. / Inorganica Chimica Acta 374 (2011) 240–246
243
PPh2
OH
Cl
PPh2 CO
Rh
PPh2
Au
H
O
OH
ii)
i)
O
H
O
Ph2P
Ph2P
OH
OH
HO
OH
5
1
4
HO
Scheme 2. Synthesis of the phosphine complexes 4 and 5. (i) Rh(CO)2(acac), NEt3, EtOH; (ii) (tht)AuCl, THF.
Fig. 2. Molecular structure of one of the two crystallographically independent
complex cations of 5 (H-atoms, except those of OH-groups, omitted for clarity; 50%
probability thermal ellipsoids; dashed lines denote intramolecular hydrogen
bonds); selected bond lengths (Å) and angles (°) (values in brackets denote data
for the second crystallographically independent complex): Au(1)–P(1) 2.3092(8)
[2.3085(8)], Au(1)–O(1) 3.420(3) [3.269(2)], O(20)-Cl(1) 2.988(2), O(20)–H(2’)–Cl(1)
173(4).
Fig. 1. Molecular structure of 4 (H-atoms omitted for clarity, except H on O20; 50%
probability thermal ellipsoids); selected bond lengths (Å) and angles (°): Rh(1)–P(1)
2.285(1), Rh(1)–P(2) 2.332(1), Rh(1)–C(1C) 1.802(3), Rh(1)–O(1) 2.082(2), C(1C)–
O(1C) 1.149(3), C(1)–O(1) 1.363(3), C(20)–O(20) 1.365(3), P(1)–C(7) 1.824(2), P(2)–
C(26) 1.850(2), P(2)–Rh(1)–P(1) 172.62(2), C(1C)–Rh(1)–O(1) 174.61(9), Rh(1)–
C(1C)–O(1C) 174.7(2).
The solution NMR spectra of 4 show a marked temperature
dependence. The 31P{1H} NMR spectrum displays at ꢀ20 °C two
sharp multiplets which form the AB-part of an ABX (X = 103Rh) spin
system and broaden into two unstructured singlets at 48.5 ppm
and 30.5 ppm at ambient temperature. The 1H NMR spectrum con-
tains at ꢀ20 °C broad signals which could not be interpreted in de-
tail, and displays at ambient temperature a single set of resonances
for both catechol phosphine units. All changes are fully reversible.
We interpret these findings by assuming that the molecular struc-
ture is fluxional and the chelating and non-chelating ligands un-
The remaining OH-groups feature hydrogen bonds to solvent mol-
ecules (DMF and THF). The gold atom displays a linear coordination
by the two phosphorus atoms and features additional secondary
interactions to the oxygen atoms of the ‘‘inner’’ OH-groups (Au1–
O1 3.420(3) Å, Au10–O10 3.269(2) Å). The Au–P distances (Au1–
P1/Au10–P10 2.309(1) Å) compare well to the average Au–P
distance of 2.303 0.0043 Å in gold complexes of PPh3 [14].
Once isolated, crystalline 5 is only soluble in polar solvents like
DMSO or acetonitrile. The 31P{1H} NMR spectra of these solutions
show slightly broadened signals (d = 40.2 in DMSO-d6). A posi-
tive-mode electrospray ionization mass spectrum (ESI-MS) of an
acetonitrile solution of 5 displays a peak attributable to the cation
[(1)2Au]+ (m/z: 813.16) as the only detectable species, and corrob-
orates thus that the cationic bis-phosphine complex persists in
solution.
2
dergo mutual dynamic exchange. The magnitude of JPP of 315 Hz
suggests that the trans-alignment of the phosphine units persists
in solution.
ꢀ
The triclinic crystals (space group P1) of the gold complex 5 are
composed of an array of chloride anions and complex cations
[Au(1)2] which are evenly distributed between two crystallograph-
ically independent sites, and contain further three solvent mole-
cules (two DMF and one THF) per formula unit. The gold atoms
of both types of cations are situated on inversion centers, so that
the whole cationic complexes display thus crystallographic Ci-
symmetry. Fig. 2 shows one of the two crystallographically inde-
pendent cations together with the most important distances and
angles. The chloride anions exhibit a O–Hꢁ ꢁ ꢁCl hydrogen bond to
one of the ‘‘outer’’ OH-groups in one complex (O(20)–Hꢁ ꢁ ꢁCl(1)
2.988(2) Å), and additional weak C–Hꢁ ꢁ ꢁCl hydrogen bridging inter-
actions to carbon-bound hydrogens of further adjacent molecules.
Sulfurization of 1 was accomplished by stirring a mixture of the
free phosphine with elemental sulfur in anhydrous THF. Recrystal-
lisation from dry methanol gave the desired product 3 (Scheme 1)
as analytical pure, colorless crystals, that were soluble in most or-
ganic solvents except hydrocarbons. The 31P{1H} NMR spectrum
shows a singlet at 42.8 ppm in CDCl3, and 42.1 ppm in DMSO-d6,
respectively, which matches reported values for similar com-
pounds [15]. The compound crystallizes in the triclinic space group
ꢀ
P1 with two crystallographically independent molecules in the
unit cell, one of which is displayed together with a listing of the
most important distances and angles in Fig. 3. The P–S-distances

244
G. Bauer et al. / Inorganica Chimica Acta 374 (2011) 240–246
of 1.960(1)/1.963(1) Å correspond to the standard bond length of
1.954 0.005 Å in tertiary phosphine sulfides [16]; other distances
and angles are unpeculiar and similar to those in 1. The crystallo-
graphically independent molecules are distinguished by different
hydrogen bond patterns. Two molecules of one type form a centro-
symmetric dimer via intermolecular O–Hꢁ ꢁ ꢁS hydrogen bonds
(O(2)ꢁ ꢁ ꢁS(1)#2 3.174(2) Å). The remaining OH-group in each mole-
cule binds via a further intermolecular O–Hꢁ ꢁ ꢁO hydrogen bond
(O(1)ꢁ ꢁ ꢁO(20) 2.838(3) Å) to one OH-group of one molecule of the
second type, whereas the second OH-group of this molecule is sat-
urated by an intramolecular O–Hꢁ ꢁ ꢁS hydrogen bond (O(10)ꢁ ꢁ ꢁS(10)
3.163(3) Å). The hydrogen bond network is completed by intramo-
lecular O–Hꢁ ꢁ ꢁO hydrogen bonds connecting the adjacent OH-
groups in all catechol rings. On the whole, the hydrogen bonding
interactions lead thus to the formation of centrosymmetric supra-
molecular tetramers which display an overall rod-like shape and
contain one pair of each type of crystallographically independent
molecules.
In order to survey the coordination ability of the phosphine sul-
fide 3 we studied its reactivity, as in the case of phosphine 1 [6],
towards soft Lewis acids like gold(I), rhodium(I), silver(I), and pal-
ladium(II), respectively. Attempts to synthesize silver and palla-
dium complexes remained yet unsuccessful and produced only
black or brown, intractable materials. In contrast, reaction with
[Au(tetrahydrothiophene)Cl] under similar conditions as had been
employed for 1 gave good yields of neutral complex 6 (Scheme 3).
It should be noted that despite the presence of an excess of ligand
3, no evidence for the formation of a 2:1 complex with similar
structure as 5 was obtained. The 31P{1H} NMR spectrum of 6 shows
a broad singlet at 42.6 ppm in DMSO-d6, which does not differ
much from the free ligand, as expected.
ꢀ
Complex 6 crystallizes in the triclinic space group P1 with two
molecules per unit cell which show a pairwise arrangement with a
parallel alignment of S–Au–Cl units. Molecules in different pairs
are connected by weak intermolecular O–Hꢁ ꢁ ꢁCl hydrogen bonds
(Oꢁ ꢁ ꢁCl 3.15–3.42 Å). The molecular structure is shown in Fig. 4 to-
gether with significant distances and angles. The AuCl-group is dis-
ordered between two positions with relative site occupancies of
95:5. The distances and angles in the two disordered instances of
the S–Au–Cl-units differ to some extent, which is presumably ex-
plained by different patterns of close contacts to hydrogen atoms
in phenyl or methylene groups. The gold atom exhibits a quasilin-
ear coordination geometry and the Au–Cl is similar and the Au–S-
distance somewhat shorter than a standard bond length (Au–Cl
2.301 0.094 Å, Au–S 2.324 Å [14]). The size of the Au–Au distance
between two paired molecules (Au(1)–Au(1)#2 4.16 [4.36] Å) ex-
cludes the presence of aurophilic interactions. The PS-distance is
by some 5 pm longer than in the free ligand and matches normal
bond distances of 2.000 0.021 Å in coordinated phosphine sul-
fides [14].
Following the same procedure as in the preparation of rhodium
phosphine complex 4, we expected that reaction of 3 with
[Rh(CO)2(acac)] should yield a similar chelate complex. Surpris-
ingly, no reaction at all occurred in this case, and only starting
materials were recovered. Successful formation of a rhodium com-
plex was, however, accomplished by reacting 3 with [Rh(cycloocta-
diene)Cl]2 in ethanol in the presence of triethyl amine as proton
scavenger. The product precipitated from the reaction mixture
and was isolated in pure form after recrystallization from acetone.
The excess ligand present in the reaction mixture did not undergo
any reaction and remained unchanged after separation of the com-
plex. Characterization by analytical, spectroscopic, and X-ray dif-
fraction studies allowed us to identify the product as complex 7
whose molecular structure differs significantly from that of an
anticipated S-coordinated phosphine–sulfide complex.
The 31P {1H} NMR spectrum in CD2Cl2 shows a sharp doublet at
43.8 ppm with a coupling constant of JRh,P = 3 Hz. The data give no
clue to the coordination mode since coordinated phosphine sul-
fides show only small coordination shifts and are thus hard to dis-
tinguish from the free ligands. Crucial structural information was
derived from the 1H NMR spectrum where the signal of the ben-
zylic protons does not show up as a simple doublet as in the spec-
tra of free 3 and complex 6 but forms the AB part of an ABX spin
system (X = 31P), thus indicating that both geminal protons are
anisochronic. The signals associated with the three protons in the
catechol ring are shifted to notably higher field, which is character-
istic for protons in an aromatic ring that is p-bound to a metal. The
signals of cyclooctadiene protons appear as a highly complex pat-
tern which could not be analyzed in detail; however, evaluation of
the number of individual signals and their relative integrals per-
mits to derive the presence of two cyclooctadiene ligands with dif-
ferent chemical environment. This assignment was further
Fig. 3. Molecular structure of one of the crystallographically independent mole-
cules of 3 (H-atoms omitted for clarity; 50% probability thermal ellipsoids; dashed
lines denote intramolecular hydrogen bonds); selected bond length (Å): P(1)–S(1)
1.960(1).
S
PPh2
S
S
AuCl
(cod)Rh
ii)
i)
P
P
Ph2
Ph2
O
Rh(cod)
O
OH
OH
OH
OH
7
3
6
Scheme 3. Synthesis of complexes 6 and 7. (i) (tht)AuCl, CH2Cl2; (ii) [(cod)RhCl]2, NEt3, EtOH.

G. Bauer et al. / Inorganica Chimica Acta 374 (2011) 240–246
245
Fig. 4. Molecular structure of complex 6 in the crystal (left) and reduced plot showing the disorder scheme in the AuCl-units of a centrosymmetric supramolecular pair
(right); 50% probability thermal ellipsoids; H-atoms except those on O1 and O2 omitted for clarity; Au(1)/Au(10) and Cl(1)/Cl(10) denote disordered atomic positions with site
occupancy factors of 0.954(1) and 0.046(1); atoms labeled #2 belong to the second molecule in a supramolecular pair). Selected bond distances (Å) and angles (°): Au(1)–S(1)
2.266(1), Au(10)–S(1) 2.221(4), Au(1)–Cl(1) 2.300(1), Au(10)–Cl(10) 2.327(9), P(1)–S(1)–Au(1) 105.2(1), P(1)–S(1)–Au(10) 99.5(1), S(1)–Au(1)–Cl(1) 173.71(4), S(1)–Au(10)–
Cl(10) 176.1(8), S(1)–P(1) 2.023(2).
substantiated by measurement of a 1H, 103Rh HMQC spectrum
which revealed the presence of two 103Rh signals with chemical
shifts of 1118 and ꢀ422 ppm, respectively. Comparison with liter-
ature data suggests that the two 103Rh signals are located in the
ranges characteristic for (cyclooctadiene)rhodium(I)diketonates
and (cyclooctadiene)rhodium(p-arene) complexes, respectively
[17]. Putting all information together led us to formulate the prod-
uct as a dinuclear complex 7 featuring binding of one metal to the
oxygen atoms and the second one to the electron rich p-system of
the catecholate moiety. This hypothesis was further backed by a
positive-mode ESI-MS which displayed signals of pseudomolecular
ions of the composition [Rh2(cyclooctadiene)2(3)Na]+ (m/e: 783.0,
20%) and [Rh2(cyclooctadiene)2(3)H]+ (m/e: 761.0, 100%) beside
additional signals arising from loss or addition of a (cyclooctadi-
ene)Rh-fragment (m/e 551.0, 50%, [Rh(cyclooctadiene) (3)H2]+;
m/e: 971.0, 50%, [Rh3(cyclooctadiene)3(3)]+).
The final confirmation for the proposed structure came from the
results of a single-crystal X-ray diffraction study of crystalline sam-
ples obtained by repeated recrystallization from acetone. The
resulting crystals were either isolated as solvates with one co-
crystallized acetone molecule per complex, or without solvent.
Both pseudo-polymorphs crystallize in the triclinic space group
Fig. 5. Molecular structure of 7 (H-atoms omitted for clarity; 50% probability
thermal ellipsoids); selected bond lengths (Å) and angles (°) (values in brackets
denote data for the acetone solvate; Ar(1) denotes the centroid of the catechol ring):
Rh(1)–Ar(1) 1.837(3) [1.836(1)], Rh(2)–O(1) 2.068(2) [2.052(1)], Rh(2)–O(2)
2.048(2) [2.047(1)], C(1)–O(1) 1.308(3) [1.303(2)], C(2)–O(2) 1.308(4) [1.308(2)],
P(1)–S(1) 1.953(1) [1.957(1)], O(2)–Rh(2)–O(1) 81.6(1) [81.9(1)], O(1)–C(1)–C(2)–
O(2) ꢀ0.9(4) [ꢀ0.9(2)].
ꢀ
P1, and incorporation of solvent into the crystal induces no signif-
icant structural changes. Fig. 5 shows the molecular structure of 7
as determined from the solvent free crystal, together with the most
important distances and angles.
Each complex consists of one ligand 3 and two (cyclooctadi-
ene)Rh-units one of which binds, as expected, in a doubly O,O-che-
lating fashion to form a planar five-membered chelate ring,
oxidation state of the catechol unit [19], are remarkably short
(mean distance 1.308(2) [1.305(2)] Å; cf. distances between 1.369
and 1.375 Å for 3 and 6) and correspond more closely to a semiqui-
whereas the other one is
catecholate moiety. A similar asymmetrically
g
6-attached to the aromatic ring of the
none than
a catecholate moiety. Nevertheless, a molecular
l-bridging coordina-
structure containing a semiquinone radical would hardly be com-
patible with the diamagnetic nature of complex 7, and we prefer
to explain the bond shortening as a consequence of increased con-
tion mode for a catecholate group is known for a few Ru(II)-com-
plexes [18] but to the best of our knowledge unprecedented for
rhodium. As a result of the special coordination in 7, the two rho-
dium atoms have different electronic environments with formal
jugation between the oxygen lone-pairs and the aromatic
p-elec-
tron system which is triggered by the net -electron withdrawal
p
electron counts of 16 (O,O-chelating metal) and 18 (
p-arene coor-
associated with the metal coordination. The P(1)–S(1) bond
(1.953(1) [1.957(1)] Å) is slightly shorter than in 3 (1.960(1) Å).
dinated metal) valence electrons. The
g
6-bound metal atom sits
nearly above the center of the aromatic ring (the angle between
a line connecting the Rh1 atom and the center of the six-
membered ring (Ar1) with the normal of the ring is 3.3 [3.0]°). As
4. Conclusion
a consequence of the p-coordination, the mean aromatic CC-bond
length is much larger (1.423(1) [1.412(1)] Å) than in the free ligand
(1.390(1) Å). On the other hand, the C–O-bond lengths, which have
been established as an indicator for the evaluation of a formal
In summary, we have demonstrated that the catechol phos-
phine sulfide 3 can act in a similar way as the catechol phosphine
1 as multifunctional ligand toward soft Lewis acids like Rh(I) or

246
G. Bauer et al. / Inorganica Chimica Acta 374 (2011) 240–246
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power that impedes the coordination of two ligands to the same
metal center. Furthermore, the structural modification of the li-
gand backbone seems to reduce the tendency to form P@S,O-che-
late complexes at the expense of O,O-chelates. This behavior
became evident in the syntheses of a dinuclear rhodium complex
7 featuring an unusual coordination with O,O-attachment to one
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Acknowledgements
(j) R. Broussier, M. Laly, P. Perron, B. Gautheron, I.E. Nifant’ev, J.A.K. Howard,
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We thank Dr. J. Opitz, J. Trinkner, and K. Wohlbold (Institut für
Organische Chemie, Universität Stuttgart) for recording the mass
spectra, T. Scherer (Institut für Anorganische Chemie) for recording
IR spectra, and Dr. W. Bermel and Bruker-Biospin GmbH for record-
ing 103Rh NMR spectra. The Deutsche Forschungsgemeinschaft
(Grant Gu415/12-1) is acknowledged for financial support. M.N.
thanks the Academy of Finland for financial support (Proj.-No.
128800).
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Appendix A. Supplementary material
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Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
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