Coordination of a diphosphine-phosphine oxide to Au, Ag and Rh: When polyfunctionality rhymes with versatility

Article abstract of DOI:10.1039/c2dt31848b

Gold, silver and rhodium complexes of the diphosphine-phosphine oxide DPPO = {[o-iPr₂P-(C₆H₄)]₂P(O)Ph} have been prepared and characterized. Thanks to its polyfunctional character, DPPO features versatile coordination properties. According to crystallographic data, only one phosphine moiety is engaged in coordination towards (AuCl) and [RhCl(nbd)]. However, NMR data indicate fluxional behavior in solution, as the result of the exchange between the free and coordinated phosphines around the metal. Chelating coordination via the two phosphine sites is observed towards (Au⁺) and (AgCl) with PMP bite angles varying from 122° to 159°. According to X-ray and theoretical analyses, the oxygen atom of the central phosphine oxide moiety points towards the metal but does not interact significantly with it. Tridentate coordination via the two phosphines as well as the oxygen atom of DPPO occurs with [Rh(CO)⁺], leading to an original PO(P)P pincer structure.

Full text of DOI:10.1039/c2dt31848b

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PAPER
Coordination of a diphosphine–phosphine oxide to Au, Ag and Rh:
when polyfunctionality rhymes with versatility†
Eric J. Derrah,‡a,b Carmen Martin,a,b Sonia Ladeira,c Karinne Miqueu,d Ghenwa Bouhadir*a,b and
Didier Bourissou*a,b
Received 13th August 2012, Accepted 12th September 2012
DOI: 10.1039/c2dt31848b
Gold, silver and rhodium complexes of the diphosphine–phosphine oxide DPPO = {[o-iPr2P–(C6H4)]2P
(O)Ph} have been prepared and characterized. Thanks to its polyfunctional character, DPPO features
versatile coordination properties. According to crystallographic data, only one phosphine moiety is
engaged in coordination towards (AuCl) and [RhCl(nbd)]. However, NMR data indicate fluxional
behavior in solution, as the result of the exchange between the free and coordinated phosphines around
the metal. Chelating coordination via the two phosphine sites is observed towards (Au+) and (AgCl) with
PMP bite angles varying from 122° to 159°. According to X-ray and theoretical analyses, the oxygen
atom of the central phosphine oxide moiety points towards the metal but does not interact significantly
with it. Tridentate coordination via the two phosphines as well as the oxygen atom of DPPO occurs with
[Rh(CO)+], leading to an original PO(P)P pincer structure.
ambiphilic ligands were shown to possess peculiar properties,
Introduction
particularly due to the ability of the Lewis acid moiety E to co-
ordinate as a σ-acceptor, Z-type ligand15 (M → E interactions).
Polyfunctional ligands play a pivotal role in coordination chem-
istry. Their properties can be broadly modulated by variation of
the stereoelectronic characteristics of the coordination sites as
well as the size and rigidity of the connecting linkers. Addition-
ally, polyfunctional systems may possess hemilabile character
and/or participate actively in chemical transformations (so-called
non-innocent character), which is most interesting for catalytic
purposes.1 Among tridentate ligands, considerable interest has
been devoted over the last two decades to PEP frameworks in
which a central p-block element E is flanked by two phosphine
groups. In particular, pincer complexes derived from PEP
ligands (E = C,2,3 Si,4 N,5 P, 6,7 O,8 S9) have been extensively
investigated. Recently, our group has contributed to this research
area by exploring original PEP ligands featuring a central Lewis
acid moiety (E = B,10,11 Al, Ga,12 Si, Sn13).14 These so-called
We have also started to investigate the behaviour of an original
diphosphine–phosphine oxide ligand referred to as DPPO 1.
Upon coordination to Pd(0), an unexpected Ph–P(O) bond clea-
vage was observed, leading to an original PP(O)P pincer
complex 2 (eqn (1)).16
ð1Þ
Hereafter, we report on the coordination of ligand 1 to Au, Ag
and Rh. In all cases, the DPPO ligand remains intact but depend-
ing on the metal fragment, it is shown to behave as a mono-, bi-
or tri-dentate ligand. The participation or not of the central
OvPPh moiety in coordination has been carefully examined by
crystallographic and theoretical means and a new type of PO(P)P
pincer complex has been authenticated.
aUniversité de Toulouse, UPS, LHFA, 118 route de Narbonne, 31062
Toulouse, France
bCNRS, LHFA, UMR 5069, 31062 Toulouse, France.
E-mail: bouhadir@chimie.ups-tlse.fr, dbouriss@chimie.ups-tlse.fr;
Fax: +33 (0) 561 55 82 04; Tel: +33 (0) 561 55 68 03
cUniversité Paul Sabatier, Institut de Chimie de Toulouse (FR 2599),
118 route de Narbonne, 31062 Toulouse cedex 9, France
dInstitut Pluridisciplinaire de Recherche sur l’Environnement et les
Matériaux UMR-CNRS 5254, Université de Pau et des Pays de l’Adour,
Hélioparc, 2 avenue du Président Angot, 64053 Pau Cedex 09, France
†Electronic supplementary information (ESI) available: NMR spectra
for 3–8; computational studies (Z matrices). CCDC 895721–895724.
For ESI and crystallographic data in CIF or other electronic format see
DOI: 10.1039/c2dt31848b
Results and discussion
Coordination of the diphosphine–phosphine oxide 1 to gold(I) is
readily achieved upon treatment with (Me2S)AuCl (1 equiv.) in
dichloromethane at room temperature. After work-up, the corres-
ponding complex 3 is obtained as a white solid in 90% yield
(Scheme 1). Crystallographic analysis (Fig. 1) revealed κ1-
coordination of the DPPO ligand via one of the lateral phosphine
‡Current address: Organic Chemistry & Catalysis, Utrecht University,
Faculty of Science, Debye Institute for Nanomaterial Science, Padualaan
8, 3584 CH Utrecht, The Netherlands.
14274 | Dalton Trans., 2012, 41, 14274–14280
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Scheme 1 Coordination of the diphosphine–phosphine oxide ligand 1
to gold(I).
Fig. 2 Optimized structure of complex 4a*. Selected bond lengths (Å)
and bond angles (°): P2–Au 2.335; P3–Au 2.324; P1–O1 1.411;
P3–Au–P2 159.49.
computational study was performed on the real complex at the
B3PW91/SDD+f(Pd),6-31G**(other atoms) level of theory.†
The global energy minimum corresponds to a dicoordinate
quasi-linear gold(I) complex 4a* (Fig. 2). The oxygen atom of
the OvPPh moiety points towards gold but remains rather far
away. The O⋯Au distance (2.613 Å) is shorter than the sum of
the van der Waals radii (3.65 Å),18 but exceeds the sum of the
covalent radii19 by about 30%, suggesting weak, if any, inter-
action. This view is corroborated by NBO analysis, where only a
weak donor–acceptor interaction is found from oxygen to gold
(ΔENBO = 3.1 kcal mol−1). Note that another minimum 4b* was
identified 22.1 kcal mol−1 higher in energy than 4a*. The two
structures differ in the orientation of the central OvPPh moiety,
with the Ph group instead of the O pointing towards gold in 4b*.
In addition, a gold(III) complex 4c* resulting from oxidative
addition of the P(O)–Ph bond was found 12.7 kcal mol−1 higher
in energy than 4a*.20
The DPPO ligand was thus found to coordinate to gold(I) via
one or the two phosphine sites, depending on the neutral vs.
cationic character of the complex. In order to explore further
its coordination properties, we then became interested in other
transition metals, starting with silver(I). Treatment of 1 with a
suspension of AgCl in dichloromethane led to the formation of
the new complex 5 within 12 h at room temperature (Scheme 2).
Colorless crystals were grown from a dichloromethane–diethyl
ether (5 : 1) solution at −30 °C and an X-ray diffraction study
was carried out. The silver center is surrounded by the two phos-
phines (PAg distances = 2.443(1) and 2.439(1) Å) and the chlor-
ide (ClAg = 2.482(1) Å) organized in a trigonal planar
arrangement (ΣαAg = 359.6°) (Fig. 3). The oxygen atom of the
central P(vO)Ph moiety points towards the silver center but
remains at a rather long distance (OAg = 2.640(2) Å, 25%
higher than the sum of the covalent radii19). The absence of sig-
nificant interaction between O and Ag was further supported by
DFT computations.† The optimized geometry of 5* fits nicely
Fig. 1 Molecular view of complex 3. Thermal ellipsoids are drawn at
50% probability. For clarity, hydrogen atoms are omitted and isopropyl/
phenyl groups at phosphorus are simplified. Selected bond lengths (Å)
and bond angles (°): P3–Au 2.253(1); Cl–Au 2.287(1); P1–O1 1.483(1);
P3–Au–Cl 175.68(4).
groups. The gold center adopts a quasi linear arrangement
(P3AuCl = 175.68(4)°) and points away from the phosphine-
oxide moiety. Neutral gold(I) complexes most commonly adopt
linear dicoordination,17 and thus the coordination mode observed
in complex 3 is in a sense nothing but expected. However, it
strikingly differs from the chelating coordination systematically
observed so far upon coordination of the related PEP ligands
(E = B, Al, Ga, Si, Sn) to gold(I), whatever the presence or not
of a central Au → E interaction.10–13 This suggests that the
central P(vO)Ph moiety influences very subtly the confor-
mational and thereby the coordination properties of ligand 1
compared with the other PEP ligands. Spectroscopic data indi-
cate fluxional behavior for complex 3 in solution.† At room
1
temperature, the 31P and H NMR spectra display two sets of
broad signals for the coordinated and free PiPr2 groups. This
suggests that the two phosphines of the DPPO ligand exchange
around gold relatively slowly at the NMR timescale. At 60 °C,
this fluxional process occurs significantly faster and a unique set
1
of H NMR signals is observed for the two PiPr2 groups while
the corresponding 31P NMR signals are further broadened.
To favor concomitant coordination of the two phosphine sites
to gold, the chloride at gold was abstracted by treating complex
3 with silver triflate (Scheme 1). The ensuing cationic complex 4
was fully characterized by multi-nuclear NMR spectroscopy.
The 31P NMR spectrum displays a doublet at δ 68.1 ppm and a
triplet at δ 45.4 ppm (JPP = 9.4 Hz) with relative integrations of
2 : 1. This indicates the symmetric coordination of the two phos-
phines but does not infer about the participation or not of the
central OvPPh moiety in coordination. Since crystals suitable
for X-ray diffraction studies could not be obtained in this case,
we referred to DFT calculations to shed light into the coordi-
nation mode of the DPPO ligand in complex 4. The
Scheme 2 Coordination of the diphosphine–phosphine oxide ligand 1
to silver(I).
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Fig. 3 Molecular view of complex 5. Thermal ellipsoids are drawn at
50% probability. For clarity, hydrogen atoms are omitted and isopropyl/
phenyl groups at phosphorus are simplified. Selected bond lengths (Å)
and bond angles (°): P2–Ag 2.443(1); P3–Ag 2.439(1); Cl–Ag 2.482(1);
P1–O1 1.481(1); P3–Ag–P2 122.75(3); P3–Ag–Cl 120.25(3); P2–Ag–
Cl 116.62(3).
Scheme 3 Coordination of the diphosphine–phosphine oxide ligand 1
to rhodium.
with that determined crystallographically and only a very weak
O → Ag interaction was found by NBO analysis (ΔENBO
=
1.3 kcal mol−1). According to the spectroscopic data, complex 5
adopts the same coordination mode in solution. In the 31P NMR
spectrum, the two phosphines are equivalent and appear at δ
18.1 ppm as a pair of doublets due to well-resolved couplings
with the two isotopes of silver (1JPAg = 376.3 Hz for 107Ag and
431.8 Hz for 109Ag). The OvPPh moiety is associated with a
signal of half intensity at δ 40.1 ppm.
In the silver complex 5, the DPPO ligand coordinates via the
two phosphines while in the corresponding gold complex 3, only
one phosphine participates in coordination. This difference is
consistent with the tendency of silver(I) to adopt higher coordi-
nation numbers than gold(I).17 Cationization of the gold center
(complex 4) favors chelating coordination of DPPO as observed
in the neutral silver complex 5. However, the dicoordinate vs.
tricoordinate nature of the metal center results in significantly
different bite angles (PAuP = 159.5° in 4 vs. PAgP =
122.7° in 5).
Fig. 4 Molecular view of complexes 6 (a) and 8 (b). Thermal ellip-
soids are drawn at 50% probability. For clarity, hydrogen atoms and
triflate counter-anion are omitted and isopropyl/phenyl groups at phos-
phorus are simplified. Selected bond lengths (Å) and bond angles (°): 6:
P2–Rh 2.335(1); Cl–Rh 2.363(1); P1–O1 1.488(2); P2–Rh–Cl
91.274(2). 8: P2–Rh 2.307(2); P3–Rh 2.308(2); C3–Rh 1.802(6): O1–
Rh 2.079(1); P1–O1 1.520(4); C3–Rh–O1 178.4(2); C3–Rh–P2
96.81(18); O1–Rh–P2 82.20(10); C3–Rh–P3 97.68(18), O1–Rh–P3
83.04(10); P2–Rh–P3 161.26(5).
The coordination properties of DPPO towards Rh(I) fragments
were then investigated. Upon reaction of 1 with half an equival-
ent of [Rh(nbd)(μ-Cl)]2 (nbd = 2,5-norbornadiene), the new
complex 6 was obtained in quantitative yield as an orange
powder (Scheme 3). According to X-ray diffraction data
(Fig. 4a), the DPPO ligand has split the chloro-bridge of the Rh
precursor and coordinates to Rh by one of the phosphine sites.
The Cl atom and the nbd fragment complete the coordination
sphere of Rh (typical square-planar environment). 31P NMR
analysis of complex 6 in CDCl3 gives an unexpectedly simple
spectrum. The OvPPh moiety appears as a triplet at δ 43.3 ppm
(JPP = 17 Hz) while the two phosphines give a unique signal at
complex 6. In this case, the two phosphines give a unique 31P
NMR signal even at −80 °C.
A significantly different result was obtained when the nbd co-
ligand at rhodium was replaced by CO. Using [Rh(CO)2Cl]2 as a
precursor (0.5 equiv.), the coordination of the DPPO ligand 1
proceeds within minutes at room temperature and the reaction is
accompanied by CO release. After work-up, complex 7 was iso-
lated as a bright yellow powder in 95% yield. Despite many
attempts, no X-ray quality crystals of 7 could be obtained. To cir-
cumvent this problem, we envisioned to exchange the chloride
for a triflate group. Treatment of 7 with Me3SiOTf gives a new
complex 8 featuring similar spectroscopic characteristics and
gratifyingly, crystals of 8 could be grown in this case from an
acetonitrile–diethyl ether solution (Fig. 4b). Accordingly,
complex 8 adopts a discrete ion pair structure with triflate as a
counter-anion. The DPPO ligand coordinates to Rh via the two
phosphine sites (PRh distances = 2.308(2) and 2.307(2) Å;
PRhP = 161.26(5)°) as well as the O atom of the central OvPPh
moiety (ORh distance = 2.079(1) Å).22 The PvO bond length is
δ 14.8 ppm (relative integration: 2, doublet of doublet, JPP
=
17 Hz, JPRh = 90.4 Hz).21 The latter 31P NMR chemical shift
and JPRh coupling constant are in between those expected for
free and Rh-coordinated PiPr2 fragments, suggesting rapid
exchange of the two phosphines around Rh at the NMR time-
scale. This fluxional process is reminiscent of that observed in
the neutral gold complex 3, but the exchange between the free
and coordinated phosphines occurs much faster in the rhodium
14276 | Dalton Trans., 2012, 41, 14274–14280
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substantially elongated upon coordination, from 1.48–1.49 Å in
complexes 3, 5 and 7 to 1.520(4) Å in complex 8. The rhodium
center adopts a slightly distorted square planar arrangement, with
a CO molecule occupying the position trans to the PvO moiety.
The concomitant and symmetric coordination of the two phos-
phine sites of DPPO is clearly apparent from the 31P NMR spec-
trum: the corresponding signal appears at δ 52.1 ppm with a
dichloromethane (2 mL) at 0 °C. The mixture was stirred during
3 h and slowly warmed to room temperature. A clear colourless
solution of (DPPO)AuCl was obtained after filtration. The
solvent and SMe2 were removed under vacuum. The resulting
white residue was extracted with diethyl ether (10 mL) and
purified by recrystallization in a mixture of dichloromethane–
pentane to give a (DPPO)AuCl complex (334.0 mg, 0.45 mmol,
90% yield) in 99% purity. 1H NMR (300.18 MHz, 60 °C,
C6D6): δ 7.98 (s br, 2H, H3), 7.56 (m, 2H, H6), 7.11–6.89 (m,
7H, H4, H5, Ho and Hp), 6.78 (m, 2H, Hm), 2.83 (s br, 4H, H7),
1.18 (dd, 3JHP = 16.2 Hz, 3JHH = 6.9 Hz, 6H, H8), 1.02 (m, 12H,
1
large JPRh coupling constant (123.6 Hz) while the OvPPh
moiety resonates as a triplet (JPP = 8.0 Hz) at δ 47.8 ppm. The
magnitude of the O to Rh coordination was assessed theoreti-
cally.† Calculations were performed on the real complex 8* and
NBO analysis revealed the presence of a relatively strong
P(O) → Rh interaction (ΔENBO = 55.6 kcal mol−1).
The DPPO ligand thus behaves very differently in the
rhodium complexes 6 on the one hand and 7/8 on the other
hand. The presence of π-acceptor CO co-ligands instead of nbd
favors the coordination of the two phosphines and additionally,
the coordination of the central OvPPh induces ionization by
displacement of the chloride.
3
3
H8), 0.42 (dd, JHP = 16.1 Hz, JHH = 6.9 Hz, 6H, H8); 31P{1H}
(121.47 MHz, C6D6): δ 90.8 (s br, 1P, PiPr2), 35.3 (s br, 1P, P(O)-
Ph), −2.6 (s br, 1P, PiPr2); 31P{1H} (121.47 MHz, 60 °C, C6D6):
3
δ 90.8 (s br, 1P, PiPr2), 35.3 (t, JPP = 10.8 Hz s, 1P, P(O)Ph),
−2.6 (s br, 1P, PiPr2); HRMS (CI, CH4): exact mass (monoisoto-
pic) calcd for C30H41OP3Au, 707.2036; found, 707.2036
(average of 3 trials); mp: 217–219 °C.
Synthesis of [(DPPO)Au]OTf complex 4. To a Schlenk flask
containing
a colourless solution of Ag(OTf) (100 mg,
Conclusion
0.40 mmol) in DCM (2 mL) was added a solution of (DPPO)
AuCl 3 (300 mg, 0.40 mmol, 1 equiv.) in DCM (2 mL) at
−60 °C. The resulting mixture was stirred for 1 h to give a col-
ourless solution with a fine white precipitate. A clear colourless
solution of [(DPPO)Au]OTf was obtained after filtration and the
solvent was removed under vacuum. The resulting white powder
was washed with pentane (3 × 5 mL) to give [(DPPO)Au]OTf
(300.0 mg, 0.34 mmol, 85% yield) in 99% purity. 1H NMR
In conclusion, gold, silver and rhodium complexes of the diphos-
phine–phosphine oxide DPPO are described. Depending on the
metal fragment, DPPO is shown to behave as a mono-, bi- or tri-
dentate ligand. Participation of the central OvPPh moiety in
coordination eventually leads to a new type of PO(P)P pincer
complex. Efforts are ongoing in our laboratory to explore further
the coordination properties of diphosphine–phosphine oxide
ligands and to investigate the reactivity of the ensuing
complexes.
3
3
(500.33 MHz, CDCl3): δ 7.92 (dd, JHP = 13.5 Hz, JHH
8.0 Hz, 2H, H3), 7.86–7.83 (m, 4H, H5 and H6), 7.70–7.67 (m,
=
3
3
2H, H4), 7.56 (t, JHH = 7.3 Hz, 1H, Hp), 7.46 (td, JHH
=
4
3
3
7.7 Hz, JHP = 2.8 Hz, 2H, Hm), 7.24 (dd, JHP = 12.4 Hz, JHH
= 7.5 Hz, 2H, Ho), 3.33–3.25 (m, 2H, H7), 2.91–2.83 (m, 2H,
H7), 1.49–1.42 (m, 18H, H8), 1.15–1.10 (m, 6H, H8); 13C{1H}
NMR (125.81 MHz, CDCl3): δ 137.3–137.1 (m, C3), 136.8 (d,
Experimental
General comments
1JCP = 107.6 Hz, C1), 136.8 (dt, JCP = 92.6 Hz, JCP = 6.7 Hz,
1
4
All reactions and manipulations were carried out under an atmos-
phere of dry argon using standard Schlenk techniques. All sol-
vents were sparged with argon and dried using an MBRAUN
Solvent Purification System (SPS). 1H, 13C and 31P NMR
spectra were recorded on Bruker Avance 500 or 300 spec-
trometers. Chemical shifts are expressed with a positive sign, in
Ci), 134.8 (dd, 1JCP = 19.4 Hz, 2JCP = 7.7 Hz, C2), 134.6 (d, JCP
4
= 10.1 Hz, C6), 132.9–132.8 (m, C5), 132.3 (d, JCP = 2.8 Hz,
2
Cp), 131.5 (d, JCP = 9.9 Hz, Co), 130.7 (d, JCP = 12.5 Hz, C4),
3
129.1 (d, JCP = 12.1 Hz, Cm), 114.6 (br, ω1/2 = 575 Hz, CF3),
29.0 (AA′X, N = 14.0 Hz, C7), 24.0 (AA′X, N = 14.0 Hz, C7),
20.7 (AA′X, N = 1.2 Hz, C8), 20.6 (AA′X, N = 2.3 Hz, C8), 19.9
(AA′X, N = 5.1 Hz, C8), 18.6 (s, C8); 31P{1H} (202.54 MHz,
CDCl3): δ 68.1 (d, JPP = 9.4 Hz, 2P, PiPr2), 45.4 (t, JPP
9.4 Hz, 1P, P(O)Ph).
parts per million, calibrated to residual H (7.24 ppm) and 13C
1
(77.16 ppm) solvent signals and 85% H3PO4 (0 ppm) respect-
ively. Unless otherwise stated, NMR was recorded at 25 °C. The
N values corresponding to 1/2[J(AX)–J(A′X)] are provided
when the second-order AA′X systems were observed in 13C
NMR.23 The same atom numbering has been used for the DPPO
ligand of all compounds.24 Mass spectra were recorded on a
Waters LCT mass spectrometer. The DPPO ligand was prepared
as previously described.16
3
3
=
Synthesis of [(DPPO)AgCl] complex 5. To a Schlenk flask
containing a suspension of AgCl (41.5 mg, 0.29 mmol, 1 equiv.)
in dichloromethane (2 mL) was added diphosphanyl–phenylpho-
sphine oxide 1 (150.0 mg, 0.29 mmol, 1 equiv.) in dichloro-
methane (2 mL) at room temperature. The mixture was stirred
during 12 h. A clear colorless solution of (DPPO)AgCl was
obtained after filtration and the solvent was removed under
vacuum. The resulting white residue was purified by recrystalli-
zation in a mixture of dichloromethane–diethyl ether (5 : 1) to
give colorless crystals at −30 °C (123.3 mg, 0.19 mmol,
65% yield) in >99% purity. 1H NMR (300.18 MHz, CDCl3):
δ 7.78–7.69 (m, 2H, H3), 7.61–7.52 (m, 3H, H4 and Hp),
Preparations
Synthesis of (DPPO)AuCl complex 3. To a Schlenk flask con-
taining a suspension of AuCl(SMe2) (147.3 mg, 0.50 mmol,
1 equiv.) in dichloromethane (4 mL) was added diphosphanyl–
phenylphosphine oxide 1 (255.3 mg, 0.5 mmol, 1 equiv.) in
This journal is © The Royal Society of Chemistry 2012
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2
7.50 −7.43 (m, 4H, Ho and Hm), 7.42–7.35 (m, 2H, H5),
7.34–7.25 (m, 2H, H6), 2.50 (m, 4H, H7), 1.42–1.17 (m, 18H,
H8), 0.87–0.73 (m, 6H, H8); 13C{1H} NMR (75.47 MHz,
= 5.4 Hz, Ci), 132.2 (d, JCP = 11.0 Hz, Co), 130.9 (d, JCP
=
=
1
3
13.3 Hz, C5), 130.4 (d, JCP = 110.2 Hz, C1), 129.6 (d, JCP
12.7 Hz, Cm), 28.3 (AA′X, N = 10.6 Hz, C7), 22.5 (AA′X, N =
12 Hz, C7), 21.5 (s, C8), 18.7 (s, C8), 22.5 (AA′X, N = 4.4 Hz,
C7), 18.0 (s, C8); 31P{1H} (202.54 MHz, CDCl3): δ 51.9
(dd, JPRh = 123.6 Hz, JPP = 8.2 Hz, 2P, PiPr2), 47.8 (t, JPP
8.1 Hz, 1P, P(O)Ph); mp: 165–167 °C.
1
4
CDCl3): δ 141.1 (m, C2), 137.7 (dt, JCP = 99.4 Hz, JCP
=
1
8.6 Hz, Ci), 135.1 (m, C6), 134.9 (d, JCP = 106.5 Hz, C1),
2
1
3
3
133.7 (d, JCP = 11.8 Hz, C3), 131.9 (m, Cp and Cm), 130.9 (s
=
2
br, C4), 128.7 (d, JCP = 11.7 Hz, Co), 128.3 (d, JCP = 12.7 Hz,
C5), 28.2 (AA′X, N = 4.6 Hz, C7), 23.1 (AA′X, N = 2.8 Hz, C7),
20.4 (AA′X, N = 5.9 Hz, C8), 19.8 (AA′X, N = 3.8 Hz, C8), 19.7
Synthesis of [(DPPO)Rh(CO)]OTf complex 8. 0.9 mmol of
(Me3Si)OTf (16 μL, 1.0 equiv.) were added to a Schlenk flask
containing a yellow solution of Rh(CO)(DPPO)Cl 7 (61.71 mg,
0.09 mmol, 1 equiv.) in dichloromethane (2 mL) at room temp-
erature. The resulting mixture was stirred for 1 h to give a yellow
solution of [Rh(CO)(DPPO)]OTf. The solvent was removed
under vacuum and the resulting yellow powder was washed with
pentane (3 × 2 mL) to give [Rh(CO)(DPPO)]OTf (64.0 mg,
0.08 mmol, 90% yield) as a bright yellow powder in >99%
purity. Crystals suitable for X-ray diffraction studies were
obtained from an acetonitrile–diethyl ether solution. 1H NMR
(300.18 MHz, CDCl3): δ 7.95–7.68 (m, 2H, H6), 7.83–7.65 (m,
6H, H3, H4 and H5), 7.60 (t br, 3JHH = 7.7 Hz, 2H, Hp), 7.42 (td,
(AA′X, N = 8.7 Hz, C7), 18.7 (AA′X, N = 2.4 Hz, C8); 31P{1H}
109
(121.49 MHz, CDCl3): δ 40.1 (s, 1P, P(O)Ph), 18.1 (dd, 1JP
Ag
107
3
= 431.8 Hz, 1JP
= 376.3 Hz, JPP = 2.7 Hz, 2P, PiPr2);
Ag
HRMS (CI, CH4): exact mass (monoisotopic) calcd for
C30H41OP3107Ag, 617.1421; found, 617.1434 (average of 3
trials); mp: 247–250 °C.
Synthesis of (DPPO)Rh(nbd)Cl complex 6. To a Schlenk flask
containing a yellow solution of [Rh(nbd)(μ-Cl)]2 (115.3 mg,
0.25 mmol, 1 equiv.) in dichloromethane (2 mL) was added
diphosphanyl–phenylphosphine oxide 1 (255.3 mg, 0.5 mmol,
2 equiv.) in dichloromethane (2 mL) at 0 °C. The mixture was
stirred during 4 h and slowly warmed to room temperature. A
clear yellow solution of (DPPO)RhCl(nbd) was obtained and the
solvent was removed under vacuum. The resulting orange solid
was washed with pentane (3 × 5 mL) to give (DPPO)Rh(nbd)Cl
(363.1 mg, 0.49 mmol, 98% yield) in >99% purity. Orange crys-
tals were obtained from a dichloromethane–diethyl ether solu-
4
3JHH = 7.7 Hz, JHP = 2.9 Hz, 2H, Hm), 7.11–7.00 (m, 2H, Ho),
2.95 (m, 2H, H7), 2.45 (m, 2H, H7), 1.41–1.20 (m, 18H, H8),
1.19–1.05 (m, 6H, H8); 31P{1H} (121.49 MHz, CDCl3): δ 52.1
1
3
3
(dd, JPRh = 123.2 Hz, JPP = 8.0 Hz, 2P, PiPr2), 48.3 (t, JPP
=
8.0 Hz, 1P, P(O)Ph); HRMS (CI, CH4): exact mass (monoisoto-
pic) calcd for C31H41O2P3Rh, 641.1374; found, 641.1365
(average of 3 trials); mp: 216–218 °C.
1
tion. H NMR (300.18 MHz, CDCl3): δ 7.86–7.55 (m, 7H, Hp,
H3, H4 and H5), 7.52–7.43 (m, 2H, H6), 7.42–7.33 (m, 2H, Hm),
7.00–6.88 (m, 2H, Ho), 4.20 (m br, 4H, CHvCHnbd), 3.80 (s br,
2H, CHnbd), 2.50 (m, 2H, H7), 2.27 (m, 2H, H7), 1.36 (s br, 2H,
Crystallographic data for complexes 3, 6 and 8
3
3
Crystallographic data were collected at 193 K on a Bruker-AXS
APEX-II QUAZAR diffractometer equipped with an air-cooled
microfocus source (5 and 8) or on Bruker-AXS SMART
APEX-II (3 and 6), using Mo Kα radiation (λ = 0.71073 Å).
Semi-empirical absorption corrections were employed.25 The
structures were solved by direct methods (SHELXS 97),26 and
all non-hydrogen atoms were refined anisotropically using the
least-squares method on F2.27 The crystallographic data for the
structures are given in Table 1.
CH2 nbd), 1.11 (dd, JHP = 13.8 Hz, JHH = 6.9 Hz, 12H, H8),
0.99 (dd, 6H, 3JHP = 14.8 Hz, 3JHH = 7.1 Hz, H8), 0.79 (dd, 6H,
3
3JHP = 15.9 Hz, JHH = 7.0 Hz, H8); 31P{1H} (121.49 MHz,
CDCl3): δ 43.3 (t, 3JPP = 17.0 Hz, 1P, P(O)Ph), 14.8 (dd, 1JPRh
90.4 Hz, JPP = 17.0 Hz, 2P, PiPr2); HRMS (CI, CH4): exact
mass (monoisotopic) calcd for C37H49OP3Rh, 705.2051; found,
705.2070 (average of 3 trials); mp: 178–180 °C.
=
3
Synthesis of [(DPPO)Rh(CO)]Cl complex 7. To a Schlenk
flask containing a light yellow solution of [Rh(CO)2Cl]2
(290 mg, 0.75 mmol) in dichloromethane (2 mL) was added
diphosphanyl–phenylphosphine oxide 1 (762 mg, 1.5 mmol,
2 equiv.) in dichloromethane (2 mL). The mixture was stirred
until the effervescence ceased (∼10 min). The solution was
filtered to remove a black precipitate and the solvent was
removed under vacuum to give a yellow oil. Trituration with
pentane (3 × 5 mL), followed by toluene (3 × 5 mL) wash, gave
[Rh(CO)(DPPO)]Cl (960 mg, 1.4 mmol, 95% yield) as a bright
yellow powder in >99% purity. 1H NMR (500.33 MHz, CDCl3):
Computational details
Calculations were carried out with the Gaussian 03 program28 at
the DFT level of theory using the hybrid functional B3PW91.29
B3PW91 is Becke’s 3 parameter functional, with the non-local
correlation provided by the Perdew 91 expression. Au, Ag and
Rh were treated with the Stuttgart–Dresden set-RECP (relativis-
tic effective core potential) in combination with its adapted basis
set.30 The latter has been augmented by a set of f polarization
functions.31 All the other atoms (C, H, O, P, Cl) have been
described with a 6-31G(d,p) double-ζ basis set.32 Geometry
optimizations were carried out without any symmetry restric-
tions, the nature of the extrema was verified with analytical
frequency calculations. Electronic structure of the different com-
plexes was studied using Natural Bond Orbital analysis (NBO-5
program).33 The Natural Localized Molecular Orbital (NLMO)
obtained from the second-order NBO analysis was plotted by
using the molecular graphic package Molekel.34
3
δ 7.94–7.85 (m, 6H, H3, H4 and H6), 7.80 (td, JHH = 7.4 Hz,
3
5
JHP = 2.3 Hz, 2H, H5), 7.63 (td, JHH = 7.7 Hz, JHP = 1.2 Hz,
3
4
2H, Hp), 7.45 (td, JHH = 7.7 Hz, JHP = 3.5 Hz, 2H, Hm),
7.12–7.05 (m, 2H, Ho), 3.04–3.00 (m, 2H, H7), 2.53–2.46 (m,
2H, H7), 1.39–1.33 (m, 12H, H8), 1.32–1.28 (m, 6H, H8),
1.17–1.12 (m, 6H, H8); 13C{1H} NMR (125.81 MHz, CDCl3):
δ 192.2 (dt, JCRh = 77.5 Hz, JCP = 12.7 Hz, CO), 135.6–135.4
(m, C2 and C3), 134.4 (d, JCP = 2.4 Hz, Cp), 134.1 (m, C4),
1
2
4
2
1
4
133.1 (d, JCP = 11.5 Hz, C6), 132.9 (dt, JCP = 102.9 Hz, JCP
14278 | Dalton Trans., 2012, 41, 14274–14280
This journal is © The Royal Society of Chemistry 2012

View Article Online
Table 1 Crystallographic data for compounds 3, 5, 6 and 8
3
5
6
8
Empirical formula
Formula weight
C30H41AuClOP3
742.96
C30H41AgClOP3
653.86
C37H49ClOP3Rh
741.03
C31H41O2P3Rh, CF3O3S
790.54
Crystal system
Space group
Orthorhombic
Pbca
Monoclinic
P21/n
Triclinic
P1
Triclinic
P1
ˉ
ˉ
a/Å
b/Å
c/Å
α/°
15.4329(3)
15.7352(3)
25.7359(5)
90
90
90
6249.7(2)
8
1.579
8.832(4)
18.830(8)
18.315(8)
90
97.935(10)
90
3017(2)
4
1.44
10.4107(2)
10.5382(2)
17.9760(3)
75.4240(10)
74.6830(10)
71.3380(10)
1771.69(6)
2
8.1191(5)
19.9268(12)
23.3037(15)
68.072(3)
85.812(3)
85.295(3)
3482.0(4)
4
β/°
γ/°
V/Å3
Z
Densitycalcd/mg m−3
1.389
0.721
1.508
0.742
μ/mm−1
4.968
0.937
Reflections collected
Independent reflection
R1 [I > 2σ(I)]
wR2
103 280
9682
0.0344
0.0929
1.549 and −0.79
193(2)
20 202
5976
0.0325
0.0766
0.357 and −0.355
193(2)
40 865
10 728
0.0255
0.0707
0.753 and −0.491
193(2)
52 047
14 095
0.0602
0.1396
1.047 and −0.887
193(2)
(Δ/r)max/e Å−3
T
6 For triphosphine pincer complexes, see: (a) G. Jia, H. M. Lee and
I. D. Williams, Organometallics, 1996, 15, 4235; (b) F. Meidine,
J. L. Pombeiro and F. Nixon, J. Chem. Soc., Dalton Trans., 1999, 3041;
(c) R. Goikhman, M. Aizenberg, Y. Ben-David, L. J. W. Shimon and
D. Milstein, Organometallics, 2002, 21, 5060; (d) L. Fadini and
A. Togni, Chem. Commun., 2003, 30; (e) U. Helmstedt, P. Lönnecke and
E. Hey-Hawkins, Inorg. Chem., 2006, 45, 10300.
This work was supported financially by the Centre National
de la Recherche Scientifique (CNRS), the Université Paul
Sabatier (UPS), and the Agence Nationale de la Recherche
Scientifique (ANR-10-BLAN-070901). Idris is acknowledged
for computer facilities. Part of the theoretical work was granted
access to HPC resources of Idris under allocation 2011
(i2010080045) made by GENCI (Grand Equipement National de
Calcul Intensif). COST action CM0802 (PhoSciNet) is also
acknowledged.
7 For PP−P, P P +P, P P +(O)P pincer complexes, see: (a) N. P. Mankad,
E. Rivard, S. B. Harkins and J. C. Peters, J. Am. Chem. Soc., 2005, 127,
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and J. C. Peters, Organometallics, 2008, 27, 5741; (c) R. C. Bauer,
Y. Gloaguen, M. Lutz, J. N. H. Reek, B. de Bruin and J. I. van der Vlugt,
Dalton Trans., 2011, 40, 8822; (d) B. Pan, M. W. Bezpalko,
B. M. Foxman and C. M. Thomas, Organometallics, 2011, 30, 5560;
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a
downfield shift of the 31P NMR resonance signal (from 10.7
1
to 46.5 ppm). The corresponding JPRh coupling constant amounts to
167.5 Hz.
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14280 | Dalton Trans., 2012, 41, 14274–14280
This journal is © The Royal Society of Chemistry 2012