The iminophosphorane-phosphane Ph2PC6H 4OC6H4PPh2=NP(O)(OPh)2: Synthesis, reactivity, and catalytic activity in Suzuki cross-coupling and the homogeneous hydrogenation of olefins

Article abstract of DOI:10.1002/ejic.200601126

The iminophosphorane-phosphane ligand Ph₂PC₆H ₄OC₆H₄-PPh₂=NP(O)(OPh)₂ (1) has been synthesized by partial imination of bis[2-(diphenylphosphanyl) phenyl] ether (DPEphos) with phosphoryl azide (PhO)₂P(O)N ₃. A similar reaction in a 1:2 stoichiometry affords the bis(iminophosphorane) O-{C₆H₄PPh₂=NP(O)(OPh) ₂}₂ (2). The chalcogen derivatives O{C₆H ₄P(E)Ph₂}₂ [E = S (3) and Se (4)] and Ph ₂P(E)-C₆H₄OC₆H₄PPh ₂=NP(O)(OPh)₂ [E = S (5) and Se (6)] are also synthesized by treating DPEphos and 1 with elemental sulfur and selenium, respectively. The mononuclear complexes trans-[MCl₂{κ¹-P-Ph ₂PC₆H₄OC₆H₄PPh ₂=NP(O)(OPh)₂}₂] [M = Pt (7) Pd (8)] and trans-[Rh(CO)Cl{κ¹-P-Ph₂PC₆-H ₄OC₆H₄PPh₂=NP(O)(OPh) ₂}₂] (12) are prepared by the reaction of 1 with [Pt(COD)Cl₂], [Pd(COD)Cl₂], and [{Rh(CO) ₂-Cl}₂], respectively. Treatment of 1 with [Pd ₂(dba₃)] (dba = dibenzylideneacetone) affords the mononuclear complex [Pd⁰{κ²-P,O-Ph ₂PC₆H₄OC₆H₄PPh ₂=NP(O)(OPh)₂}₂] (9) in which ligand 1 coordinates through its P and O centers in a κ²-P,O chelating fashion. The monocoordinated Au^I complex [AuCl{κ¹-P- Ph₂PC₆H₄OC₆H₄PPh ₂=NP(O)(OPh)₂}] (10) has been prepared by the reaction of 1 and [AuCl(SMe₂)] and its structure has been confirmed by X-ray crystallography. The reaction of 1 with [{Rh(COD)Cl}₂] in the presence of AgOTf affords the cationic Rh^I complex cis-[Rh(COD){κ²-P,O-Ph₂PC₆H ₄OC₆H₄PPh₂=NP(O)(OPh) ₂}][OTf] (11). The catalytic activity of the Pd⁰ complex 9 has been investigated in Suzuki cross-coupling reactions. Homogeneous catalytic hydrogenation of olefins has also been studied using the cationic Rh ^I complex 11. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.

Full text of DOI:10.1002/ejic.200601126

FULL PAPER
DOI: 10.1002/ejic.200601126
The Iminophosphorane-Phosphane Ph2PC6H4OC6H4PPh2=NP(O)(OPh)2:
Synthesis, Reactivity, and Catalytic Activity in Suzuki Cross-Coupling and the
Homogeneous Hydrogenation of Olefins
Ramalingam Venkateswaran,[a] Maravanji S. Balakrishna,*[a] and Shaikh M. Mobin[b]
Keywords: Monoimination / Monophosphane / Iminophosphorane-phosphane / Staudinger reaction / Suzuki cross-
coupling
The iminophosphorane-phosphane ligand Ph2PC6H4OC6H4-
PPh2=NP(O)(OPh)2 (1) has been synthesized by partial imin-
ation of bis[2-(diphenylphosphanyl)phenyl] ether (DPEphos)
with phosphoryl azide (PhO)2P(O)N3. A similar reaction in a
1:2 stoichiometry affords the bis(iminophosphorane) O-
{C6H4PPh2=NP(O)(OPh)2}2 (2). The chalcogen derivatives
[Pd0{κ2-P,O-Ph2PC6H4OC6H4PPh2=NP(O)(OPh)2}2] (9) in
which ligand 1 coordinates through its P and O centers in a
κ2-P,O chelating fashion. The monocoordinated AuI complex
[AuCl{κ1-P-Ph2PC6H4OC6H4PPh2=NP(O)(OPh)2}] (10) has
been prepared by the reaction of 1 and [AuCl(SMe2)] and its
structure has been confirmed by X-ray crystallography. The
reaction of 1 with [{Rh(COD)Cl}2] in the presence of AgOTf
affords the cationic RhI complex cis-[Rh(COD){κ2-P,O-
Ph2PC6H4OC6H4PPh2=NP(O)(OPh)2}][OTf] (11). The cata-
lytic activity of the Pd0 complex 9 has been investigated in
Suzuki cross-coupling reactions. Homogeneous catalytic hy-
drogenation of olefins has also been studied using the cat-
ionic RhI complex 11.
O{C6H4P(E)Ph2}2 [E
= S (3) and Se (4)] and Ph2P(E)-
C6H4OC6H4PPh2=NP(O)(OPh)2 [E = S (5) and Se (6)] are also
synthesized by treating DPEphos and 1 with elemental sulfur
and selenium, respectively. The mononuclear complexes
trans-[MCl2{κ1-P-Ph2PC6H4OC6H4PPh2=NP(O)(OPh)2}2]
[M
=
Pt (7) Pd (8)] and trans-[Rh(CO)Cl{κ1-P-Ph2PC6-
H4OC6H4PPh2=NP(O)(OPh)2}2] (12) are prepared by the re-
action of 1 with [Pt(COD)Cl2], [Pd(COD)Cl2], and [{Rh(CO)2-
Cl}2], respectively. Treatment of 1 with [Pd2(dba3)] (dba = di-
benzylideneacetone) affords the mononuclear complex
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
olefins,[12] olefin oligomerization,[13] transfer hydrogenation
of ketones,[14,15] and cross-coupling of secondary amines
with aryl halides.[16] Surprisingly, their involvement in Su-
zuki cross-coupling reaction still remains unexplored.
van Leeuwen and co-workers[17] and others[18] have ex-
tensively studied the coordination chemistry and the cata-
lytic utility of the bis[2-(diphenylphosphanyl)phenyl] ether
Ph2PC6H4OC6H4PPh2. The complexes of this large-bite bis-
(phosphane) are found to be very effective in catalyzing a
variety of organic transformations.[19–21]As a continuation
of our work in designing new phosphorus-based ligands in
order to explore their coordination chemistry[22–29] and
catalytic activity,[30–33] we report herein the synthesis, coor-
dination chemistry, and catalytic activity of the iminophos-
phorane-phosphane Ph2PC6H4OC6H4PPh2=NP(O)(OPh)2
(1) derived from Ph2PC6H4OC6H4PPh2.
Introduction
There has been considerable interest in recent years in
the chemistry of iminophosphorane-phosphane ligands due
to their interesting coordination chemistry and applications
in organic syntheses such as aza-Wittig reactions.[1] These
iminophosphorane-phosphane ligands have been synthe-
sized by selective imination of bis(phosphanes) in a Staud-
inger reaction.[2–4] Various types of organic azides have
been employed for the synthesis of such ligands, including
RЈ3SiN3 and RЈ2P(O)N3.[5–11] The monoimination of bi-
s(phosphanes) with phosphoryl azide RЈ2P(O)N3 leads to
the formation of the hemilabile iminophosphorane-phos-
phane ligands R2P-X-P{=NP(O)RЈ2}R2 (X = divalent
bridging group). These ligands have the ability to offer dif-
ferent coordination modes such as κ1-P, κ2-P,N, κ2-P,O, and
κ3-P,N,O, and its hemilabile behavior has been successfully
utilized in homogeneous catalysis such as hydrogenation of
Results and Discussion
[a] Phosphorus Laboratory, Department of Chemistry, Indian In-
stitute of Technology Bombay,
Powai, Mumbai 400076, India
Synthesis of the Ligand and Chalcogen Derivatives
Fax: +91-22-2576-7152, -2572-3480
E-mail: krishna@chem.iitb.ac.in
Reaction of the phosphoryl azide (PhO)2P(O)N3 with
bis[2-(diphenylphosphanyl)phenyl]
(1:1 molar ratio) in thf at –78 °C affords the iminophos-
[b] National Single Crystal X-ray Diffraction facility, Indian Insti-
tute of Technology Bombay,
ether
(DPEphos)
Mumbai 400076, India
1930
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Iminophosphorane-Phosphanes and Their Catalytic Activity
FULL PAPER
Scheme 1.
phorane-phosphane Ph2PC6H4OC6H4PPh2=NP(O)(OPh)2 Synthesis of Metal Complexes
(1) in good yield. A similar reaction in a 2:1 molar
ratio at 0 °C affords the bis(iminophosphorane)
O{C6H4PPh2=NP(O)(OPh)2}2 (2). Compounds 1 and 2 are spective of the stoichiometry, afford the mononuclear com-
moderately air stable and highly soluble in dichlorometh- plexes
trans-[MCl2{κ1-P-Ph2PC6H4OC6H4PPh2=NP(O)-
The reactions of 1 with [M(COD)Cl2] (M = Pt, Pd), irre-
ane, diethyl ether, acetonitrile, and toluene.
(OPh)2}2] [M = Pt (7) and Pd (8)]. These complexes were
The 31P{1H} NMR spectrum of ligand 1 shows three well- therefore prepared in good yield from the reagents in
separated phosphorus signals with equal relative intensities. 2:1 molar ratio. The 31P{1H} NMR spectroscopic data are
The terminal phosphoryl PV (δ = –10.5 ppm) and imino- very diagnostic for characterizing the complexes. The 31P
[O]
phosphorane PV (δ = 10.4 ppm) signals appear as simple chemical shift due to the coordinated PPh2 group is shifted
[N]
doublets with a 2JP,P value of 37.7 Hz. The trivalent phospho- considerably downfield as a result of coordination whereas
rus appears as a singlet at δ = –20.1 ppm. The EI mass spec- the resonances due to the PV and PV groups do not
[N]
[O]
2
trum supports the structure as it shows the molecular ion exhibit such a large change in their chemical shift and JP,P
peak at m/z 786.47 [M + H]+. The 31P{1H} NMR spectrum values, thereby indicating their non-involvement in the com-
of 2 shows two doublets of equal intensity [δ = 10.9 (PV
)
[N]
plex formation. The 31P{1H} NMR spectrum of complex 7
2
and –10.6 ppm (PV[O]); JP,P = 40.4 Hz] with chemical shift shows a singlet at δ = 10.3 ppm corresponding to the coor-
1
values comparable to those described for analogous com- dinated phosphorus with a JPt,P value of 2642 Hz and two
pounds of the type [RNPPh2NP(O)(OPh)2]2.[8,10,11] The EI doublets at δ = 11.4 (P=N) and –10.6 ppm (P=O) with a
mass spectrum of compound 2 shows the molecular ion peak 2JP,P value of 37.9 Hz. The low JPt,P value suggests a trans
1
at m/z 1033.57 [M + H]+. Treatment of DPEphos and 1 with geometry for complex 7.[34] The EI mass spectrum of com-
elemental sulfur and selenium results in the isolation of plex 7 shows the molecular ion peak at m/z 1838.01 [M +
the bis-chalcogenides O{C6H4P(E)Ph2}2 [E = S (3) and Se H]+. The 31P{1H} NMR spectrum of complex 8 shows one
(4)] and the thio- and selenoyl derivatives Ph2P(E)- singlet at δ = 14.2 ppm for the coordinated phosphorus and
C6H4OC6H4PPh2=NP(O)(OPh)2 [E = S (5) and Se (6)], two doublets at δ = 11.7 and –10.6 ppm (2JP,P = 38.1 Hz)
respectively, in good yield. The 31P{1H} NMR spectra of for the other two phosphorus centers.
compounds 3 and 4 show single resonances at δ = 39.1 and
The reaction of 1 with [Pd2(dba)3] in a 2:1 molar ratio in
29.4 ppm (1JSe,P = 734.1 Hz), respectively. The EI mass toluene affords the Pd0 complex 9 in good yield (Scheme 2).
spectrum of 4 shows the molecular ion peak at m/z 699.04 The
31P{1H} [Pd{κ2-P,O-
NMR
spectrum
of
[M + H]+. The 31P{1H} NMR spectra of 5 and 6 show Ph2PC6H4OC6H4PPh2=NP(O)(OPh)2}2] (9) shows three
three resonances, similar to the parent compound 1. The resonances at δ = 23.6, 11.7, and –7.8 ppm for the PPh2,
31P resonances due to the chalcogenide phosphorus centers PV[N], and PV
centers, respectively. The reaction of 1
[O]
in 5 and 6 show a considerable downfield shift and appear with [AuCl(SMe2)] in CH2Cl2 affords [AuCl{κ1-P-
at δ = 37.7 and 27.6 ppm, respectively, whereas the chemical Ph2PC6H4OC6H4PPh2=NP(O)(OPh)2}] (10) in quantitative
shift values of the other two phosphorus centers are almost yield as a colorless crystalline solid. The 31P{1H} NMR
the same as those of compound 1. The selenoyl derivative spectrum of complex 10 shows three well-separated signals
1
6 shows a JSe,P coupling of 744 Hz. The mass spectra of with equal intensities. The coordinated phosphorus center
compounds 5 and 6 support their structure, with molecular exhibits a singlet at δ = 19.0 ppm; there is no major change
ion peaks at m/z 818.15 [M + H]+ and 866.13 [M + H]+, in the chemical shift values for the other two phosphorus
respectively (Scheme 1).
centers with respect to ligand 1. The elemental analysis and
Eur. J. Inorg. Chem. 2007, 1930–1938
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1931

R. Venkateswaran, M. S. Balakrishna, S. M. Mobin
FULL PAPER
Scheme 2.
mass spectrum of complex 10 are in accordance with the atoms of the phosphoryl group was confirmed by its 31P
proposed structure, which was further confirmed by single- NMR spectroscopic data. The 31P{1H} NMR spectrum of
crystal X-ray diffraction studies.
11 consists of three resonances with equal intensities. The
The mononuclear rhodium complex cis-[Rh(COD){κ2- coordinated phosphorus appears as a doublet at δ =
1
P,O-Ph2PC6H4OC6H4PPh2=NP(O)(OPh)2}][OTf] (11) was 12.9 ppm with a JRh,P value of 149.3 Hz while the imino-
prepared by the reaction of 1 with [{Rh(COD)Cl}2] fol- phosphorane and phosphoryl groups show mutually cou-
lowed by the addition of AgOTf in an equimolar ratio. The pled doublets centered at δ = 8.8 and –11.1 ppm, respec-
2
1H NMR spectrum of 11 confirmed the presence of a cyclo- tively, with a JP,P value of 39 Hz. The doublet due to the
2
octadiene group, which exhibits broad signals at around δ phosphoryl group shows an additional JRh,P coupling of
= 1.27–2.37 ppm for the four CH2 groups and two doublets 6.6 Hz, thus indicating the coordination of the phosphoryl
2
at δ = 2.90 and 5.13 ppm for the olefin protons with JRh,H oxygen to the rhodium center, similar to an analogous com-
values of 119.2 and 115.6 Hz, respectively. The formation pound reported in the literature.[5b] The EI mass spectrum
of an 11-membered chelate ring by binding of the P and O of cationic complex 11 shows the molecular ion peak at m/z
Table 1. Summary of 31P{1H} NMR data for compounds 1–12 [δ in ppm and J in Hz].
Compound
δPPh
δPh P=N
δ(PhO) P=O
2JP,P
2
2
2
1
–20.1 (s)
10.4 (d)
10.9 (d)
–10.5 (d)
–10.6 (d)
37.7
40.4
2
3
39.1 (s)
29.4 (s), JSe,P = 734.1
37.7 (s)
27.6 (s), JSe,P = 744.0
1
4
5
10.8 (d)
10.8 (d)
11.4 (d)
11.7 (d)
11.7 (d)
10.4 (d)
8.8 (d)
–10.5 (d)
–10.5 (d)
–10.6 (d)
–10.6 (d)
–7.8 (d)
–10.5 (d)
–11.1 (dd), JRh,P = 6.6
–10.6 (d)
38.9
39.0
37.9
38.1
39.5
37.9
39.0
37.9
1
6
1
7
10.3 (s), JPt,P = 2642
8
14.2 (s)
23.6 (s)
19.0 (s)
12.9 (d), JRh,P = 149.3
22.5 (d), JRh,P = 140.3
9
10
11
12
1
2
1
11.3 (d)
Scheme 3.
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Iminophosphorane-Phosphanes and Their Catalytic Activity
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996.2 [M – OTf]+. The reaction of [{Rh(CO)2Cl}2] with 1 Catalytic Studies
in
a
1:2 molar ratio affords trans-[Rh(CO)Cl{κ1-P-
Suzuki Cross-Coupling Reactions
Ph2PC6H4OC6H4PPh2=NP(O)(OPh)2}2] (12), as is evident
from the 31P{1H} NMR, mass, and elemental analysis data.
The 31P{1H} NMR spectrum of complex 12 consists of
Although iminophosphorane-phosphane ligands have
been employed in homogeneous catalysis, there are no re-
1
three doublets. The doublet at δ = 22.5 ppm with a JRh,P
coupling of 140 Hz is due to the coordinated phosphorus
whereas the remaining two doublets at δ = 11.3 and
–10.6 ppm are assigned to PV[N] and PV[O], respectively, with
a 2JP,P coupling of 37.9 Hz. The mass spectrum of 12 exhib-
its the molecular ion peak at m/z 1701.1 [M – Cl]+. The
IR spectrum of 12 shows νCO at 1958 cm–1 (Table 1 and
Scheme 3).
Crystal Structure of Complex 10
A perspective view of the molecular structure of complex
10 with the atom numbering scheme is shown in Figure 1.
Crystal data and details of crystal structure determination
are given in the Experimental Section, while the selected
bond lengths [Å] and bond angles [°] are displayed in
Table 2. The P(1)–Au(1)–Cl(1) bond angle of 177.81(7)° in-
dicates that the gold is in a slightly distorted linear geome-
try. The Au(1)–Cl(1) and Au(1)–P(1) bond lengths are
2.284(1) and 2.230(1) Å, respectively, and are close to the
reported values for [O(C6H4PPh2AuCl)2].[18b] There is an
intermolecular interaction between O(2_j) and H(34), as is
evident from the bond length of 2.402 Å (less than the sum
of the van der Waal’s radii)[35] and the C(34)–H(34)–O(2_j)
bond angle of 172°.
Figure 2. Influence of catalyst concentration on the coupling of 4-
bromobenzaldehyde (1.0 mmol) and phenylboronic acid
(1.5 mmol). Conditions: K3PO4 (2.0 mmol), toluene/thf (10 mL), t
= 15 min, T = 70 °C.
Table 3. Effect of solvent on the coupling of 4-bromobenzaldehyde
with phenylboronic acid.
Entry Solvent
Base
Time [h] Conversion [%][a]
1
2
3
4
5
6
tetrahydrofuran
dioxane
dimethylformamide
toluene
acetonitrile
methanol
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
2
2
2
2
2
2
84.6
63.2
100
100
63.7
69.8
[a] Conversion to coupled product determined by GC, based on
aryl halides; average of two runs.
Table 4. Effect of base on the coupling of 4-bromobenzaldehyde
with phenylboronic acid.
Figure 1.
Molecular
structure
of
[AuCl{κ1-P-
Ph2PC6H4OC6H4PPh2=NP(O)(OPh)2}] (10). All hydrogen atoms
have been omitted for clarity. Thermal ellipsoids are drawn at the
50% probability level.
Table 2. Selected bond lengths [Å] and bond angles [°] for 10.
Bond lengths
Bond angles
Entry
Base
Solvent
Time [h]
Conversion [%][a]
Au(1)–Cl(1)
Au(1)–P(1)
P(2)–N(1)
P(3)–N(1)
P(3)–O(2)
P(3)–O(3)
P(3)–O(4)
H(34)–O(2_j)
C(34)–O(2_j)
2.284(1)
2.230(1)
1.586(5)
1.570(5)
1.463(4)
1.605(4)
1.623(5)
2.402
Au(1)–P(1)–C(1)
P(1)–Au(1)–Cl(1)
N(1)–P(3)–O(2)
N(1)–P(3)–O(3)
P(2)–N(1)–P(3)
C(18)–O(1)–C(19)
112.90(2)
177.81(7)
122.40(3)
103.20(2)
135.40(3)
118.10(4)
1
2
3
4
5
6
Cs2CO3
K3PO4
K2CO3
NaOH
TMEDA
none
toluene
toluene
toluene
toluene
toluene
toluene
2
2
2
2
2
2
100
100
97.1
73.5
15.6
1.6
C(34)–H(34)–O(2_j) 172.00
[a] Conversion to coupled product determined by GC, based on
aryl halides; average of two runs.
3.325(7)
Eur. J. Inorg. Chem. 2007, 1930–1938
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R. Venkateswaran, M. S. Balakrishna, S. M. Mobin
FULL PAPER
ports of their application in Suzuki cross-coupling reac- in good yield. It is important to achieve good yields using
tions. Interestingly, the iminophosphorane-phosphane li- minimum amounts of catalyst, therefore we examined the
gand 1 shows excellent activity for Suzuki cross-coupling effect of catalyst loading on the coupling between 4-bro-
reactions with high turnover numbers at very low catalyst mobenzaldehyde and phenylboronic acid (Figure 2 and
concentrations. The Pd0 complex 9 effectively catalyzes the Tables 3, 4, and 5). Complete conversion of the starting ma-
Suzuki cross-coupling reactions of a variety of aryl bro- terials into 4-phenylbenzaldehyde was achieved with
mides and phenylboronic acids to afford the desired biaryls 0.5 mol-% of catalyst in 1 h or 0.05 mol-% in 2 h, therefore
in remarkably high yields. These reactions were studied sys- a concentration of 0.05 mol-% was selected as the optimal
tematically to find the optimal conditions to afford biaryls concentration for catalytic loading.
Table 5. Suzuki cross-coupling of aryl halides (1 mmol) with phenylboronic acid (1.5 mmol) catalyzed by 9 in the presence of K3PO4
(2 mmol) in toluene (10 mL).
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Iminophosphorane-Phosphanes and Their Catalytic Activity
FULL PAPER
1
The above investigations showed that the reaction rate formation was confirmed by H NMR spectroscopy. The
and the catalyst activity are significantly influenced by the results are displayed in Figure 3.
base and the solvent employed. Various solvents were tested
The turnover number (TON) for the conversion of sty-
in the coupling reaction with K3PO4 as base. Toluene and rene to ethylbenzene was 200,000 and the turnover fre-
dmf allowed complete conversion of 4-bromobenzaldehyde quency (TOF) at 50% conversion was 300,000 h–1. The
into 4-phenylbenzaldehyde. Considering the ease of separa- TOF improved to 600,000 h–1 when the pressure of H2 was
tion of the product, toluene was chosen as the best increased to 10 atm and the temperature to 70 °C. The cata-
solvent.
lytic activity was tested on other substrates such as α-meth-
Inorganic bases such as Cs2CO3, K3PO4, K2CO3, and ylstyrene, 4-methylstyrene, and phenylacetylene with a cata-
NaOH gave excellent yields whereas the reaction proceeded lyst loading of 0.005 mol-%. The results are displayed in
very slowly with TMEDA. Considering the high activity Table 6. Complex 11 was found to be more effective in
and cost effectiveness, K3PO4 was chosen as the base.
homogeneous hydrogenation under mild conditions than
Under these optimized reaction conditions, a wide array [RhCl(PPh3)3], for which complete conversion was observed
of aryl bromides react with phenylboronic acid to provide under the following conditions: [styrene]/[catalyst] = 1200,
the cross-coupling products in excellent yields (Table 5). T = 80 °C, t = 2 h, H2 pressure: 28 atm.[37]
The palladium(0) catalyst 9 is very effective in Suzuki cross-
coupling reactions and exhibits remarkable tolerance
towards both “deactivating” electron-donating substituents
Table 6. Hydrogenation of olefins using complex 11.[a]
Entry
Substrate
Time
[min]
Conversion
[%]
TOF
[h–1
(Table 5, entries 7, 9 and 10) and sterically encumbering or-
tho substituents (Table 5, entry 5) on aryl bromides. The
catalytic activity of 9 is found to be better than that of the
catalyst [Pd2(dba)3] + [1,1Ј-bis(diphenylphosphanyl)ferro-
cene (dppf)], which catalyzes the coupling of 4-bromoace-
tophenone and phenylboronic acid in toluene at 70 °C (2 h) 5[b]
in 86.5% yield,[36a] whereas it is similar to that of the parent
compound DPEphos. However, DPEphos shows better ac-
tivity only at higher temperature and higher catalytic load-
ing.[36b]
]
1
2
3
4
styrene
30
40
30
70
20
100
100
100
100
100
40,000
30,000
40,000
17,143
600,000
α-methylstyrene
4-methylstyrene
phenylacetylene
styrene
[a] Conditions: olefin (1.0 mmol), Et3N (0.1 mmol), 11 (0.005 mol-
%), thf (20 mL); H2 pressure: 4 atm; room temp.; stirring speed:
400 rpm. [b] 11 (0.0005 mol-%), H2 pressure: 10 atm; T: 70 °C.
Summary
Catalytic Hydrogenation of Styrene
The hemilabile iminophosphorane-phosphane ligand 1
has been synthesized by monoimination of bis[2-(diphenyl-
phosphanyl)phenyl] ether by a Staudinger reaction and its
chalcogen derivatives 3–6 have been prepared and charac-
terized. The imino-phosphorane shows both a monodentate
and bidentate (κ2-P,O) chelating coordination mode. The
platinum(II), palladium(II), and rhodium(I) complexes 7, 8,
and 12, respectively, are obtained as trans isomers with sim-
ple monodentate coordination modes. The Pd0 complex 9,
in which ligand 1 binds in a chelating (κ2-P,O) fashion, has
been synthesized by the reaction of 1 with [Pd2(dba)3]. The
reaction of 1 with [{Rh(COD)Cl}2] and AgOTf affords the
11-membered macrocyclic square-planar complex 11 with
the imino-phosphorane ligand showing a chelating biden-
tate mode of coordination. The cationic rhodium(I) com-
plex 11 is catalytically active for the hydrogenation of ole-
fins with a TON of 2ϫ105 and a TOF of 6ϫ105 h–1. The
Pd0 complex 9 is catalytically active for Suzuki cross-coup-
ling reactions of various aryl bromides and phenylboronic
acid. A lower catalytic loading of 0.05 mol-% of 9 allows
complete conversion of several aryl bromides into biaryls.
The cationic RhI complex 11 was tested as a catalyst for
the hydrogenation of styrene. The catalyst (0.0005 mol-%)
shows effective conversions under mild conditions (4 atm of
H2 at room temperature). The conversion rate was moni-
tored periodically by gas chromatography and the product
Experimental Section
Figure 3. Hydrogenation of styrene. Conditions: styrene
(1.0 mmol), Et3N (0.1 mmol), 11 (0.0005 mol-%), thf (20 mL); H2
pressure: 4 atm; room temperature; stirring speed: 400 rpm.
Reagents and Techniques: All manipulations were performed under
an atmosphere of dry nitrogen using standard Schlenk techniques.
Eur. J. Inorg. Chem. 2007, 1930–1938
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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1935

R. Venkateswaran, M. S. Balakrishna, S. M. Mobin
FULL PAPER
All the solvents were purified by conventional procedures and dis-
tilled under nitrogen prior to use. The compounds DPEphos,[17a]
Synthesis of Ph2P(S)C6H4OC6H4PPh2=NP(O)(OPh)2 (5): A mix-
ture of 1 (0.100 g, 0.127 mmol) and sulfur (0.003 g, 0.016 mmol)
[M(COD)Cl2] (M = Pd, Pt),[38] [{Rh(COD)(µ-Cl)}2],[39] [{Rh(CO)2- was refluxed in toluene (5 mL) for 24 h with constant stirring. The
(µ-Cl)}2],[40] [Pd2(dba)3],[41] and [AuCl(SMe2)][42] were prepared ac-
solution was then cooled to room temperature and petroleum ether
(5 mL) was added to give white precipitate 5. Yield: 93% (0.096 g);
m.p. 98–100 °C. C48H38P3O4NS (817.8): calcd. C 70.49, H 4.68, N
1.71, S 3.92; found C 70.52, H 4.44, N 1.82, S 4.09. 1H NMR
cording to published procedures. (PhO)2P(O)N3 was purchased
1
from Lancaster and used as received. The H and 31P{1H} NMR
spectra (δ in ppm) were recorded with Varian 300 or 400 mercury
plus spectrometers operating at the appropriate frequencies using
TMS and 85% H3PO4 as internal and external references, respec-
tively. Microanalyses were performed with a Carlo–Erba Model
1112 elemental analyzer. The IR spectra were recorded with a Nic-
olet Impact 400 FT-IR instrument as KBr disc. Electrospray ion-
ization (EI) mass spectrometry experiments were carried out with
a Waters Q-Tof micro-YA-105 spectrometer. Melting points were
recorded in capillary tubes and are uncorrected. GC analyses were
performed with a Perkin–Elmer Clarus 500 GC fitted with a
packed column.
(400 MHz, CDCl3): δ = 5.87–7.97 (m, 38 H, Ph) ppm. 31P{1H}
2
NMR (162 MHz, CDCl3): δ = 37.7 (s, PV[S]), 10.8 (d, JP,P
=
38.9 Hz, PV[N]), –10.5 (d, 2JP,P = 38.9 Hz, PV[O]) ppm. MS (EI): m/z
818.15 [M + H]+.
Synthesis of Ph2P(Se)C6H4OC6H4PPh2=NP(O)(OPh)2 (6): A mix-
ture of 1 (0.100 g, 0.127 mmol) and Se (0.010 g, 0.127 mmol) was
refluxed in toluene (5 mL) for 24 h with constant stirring. The solu-
tion was then cooled to room temperature and petroleum ether
(5 mL) was added to give a white microcrystalline solid of 6. Yield:
98% (0.108 g); m.p. 120–122 °C. C48H38NO4P3Se (864.7): calcd. C
66.67, H 4.42, N 1.61; found C 66.97, H 4.21, N 1.73. 1H NMR
(400 MHz, CDCl3): δ = 5.89–7.92 (m, 38 H, Ph) ppm. 31P{1H}
Synthesis of Ph2PC6H4OC6H4PPh2=NP(O)(OPh)2 (1): A thf solu-
tion (20 mL) of (PhO)2P(O)N3 (0.153 g, 0.557 mmol) was added
dropwise to a solution of DPEphos (0.300 g, 0.557 mmol) in thf
(20 mL) at –78 °C. After stirring the mixture for 8 h at room tem-
perature, all the solvents were removed under vacuum and the resi-
due washed with petroleum ether (b.p. 60–80 °C), then extracted
with Et2O (15 mL) and dried to give an analytically pure white
solid. Yield: 85% (0.372 g); m.p. 76–78 °C. C48H38NO4P3 (785.7):
1
NMR (162 MHz, CDCl3): δ = 27.6 (s, JSe,P = 744.0 Hz, PV[Se]),
2
2
10.8 (d, JP,P = 39.0 Hz, PV[N]), –10.5 (d, JP,P = 39.0 Hz, PV
)
[O]
ppm. MS (EI): m/z 866.13 [M + H]+.
Synthesis of trans-[PtCl2{κ1-P-Ph2PC6H4OC6H4PPh2=NP(O)-
(OPh)2}2] (7): A solution of [Pt(COD)Cl2] (0.034 g, 0.091 mmol) in
CH2Cl2 (5 mL) was added dropwise to a solution of 1 (0.144 g,
0.183 mmol) in CH2Cl2 (10 mL) at room temperature. The reaction
mixture was stirred for 8 h to give a pale-yellow solution, which
was concentrated to 5 mL. Et2O (10 mL) was added to give a pale-
yellow precipitate of 7, which was then filtered, washed, and dried.
Yield: 87% (0.145 g); m.p. Ͼ 250 °C. C96H76Cl2N2O8P6Pt (1837.5):
1
calcd. C 73.37, H 4.87, N 1.78; found C 72.81, H 4.43, N 1.93. H
NMR (400 MHz, CDCl3): δ = 5.93–8.18 (m, 38 H, Ph) ppm.
31P{1H} NMR (162 MHz, CDCl3): δ = –20.1 (s, PIII), 10.4 (d, 2JP,P
2
= 37.7 Hz, PV[N]), –10.5 (d, JP,P = 37.7 Hz, PV[O]) ppm. MS (EI):
m/z 786.47 [M + H]+.
1
calcd. C 62.75, H 4.16, N 1.52; found C 62.58, H 4.15, N 1.58. H
Synthesis of O{C6H4PPh2=NP(O)(OPh)2}2 (2): A solution of
DPEphos (0.2 g, 0.371 mmol) in thf (10 mL) was added dropwise
to a solution of (PhO)2P(O)N3 (0.204 g, 0.742 mmol) in thf (10 mL)
at 0 °C. After stirring the mixture for 8 h at room temperature, all
the solvents were removed under vacuum and the residue washed
with petroleum ether, then extracted with Et2O (10 mL) and dried
to give 2 as a white solid. Yield: 90% (0.350 g); m.p. 72–74 °C.
C60H48N2O7P4 (1032.9): calcd. C 69.77, H 4.68, N 2.71; found C
70.26, H 4.51, N 2.84. 1H NMR (400 MHz, CDCl3): δ = 6.12–7.65
(m, 48 H, Ph) ppm. 31P{1H} NMR (162 MHz, CDCl3): δ = 10.9
NMR (400 MHz, CDCl3): δ = 5.87–8.21 (m, 76 H, Ph) ppm.
1
31P{1H} NMR (162 MHz, CDCl3): δ = 10.3 (s, JPt,P = 2642 Hz,
2
2
P[Pt]), 11.4 (d, JP,P = 37.9 Hz, PV[N]), –10.6 (d, JP,P = 37.9 Hz,
PV[O]) ppm. MS (EI): m/z 1838.01 [M + H]+.
Synthesis of trans-[PdCl2{κ1-P-Ph2PC6H4OC6H4PPh2=NP(O)-
(OPh)2}2] (8): A solution of [Pd(COD)Cl2] (0.031 g, 0.109 mmol)
in CH2Cl2 (10 mL) was added dropwise to a solution of 1 (0.170 g,
0.217 mmol) in CH2Cl2 (10 mL) at room temperature. The bright
yellow solution was stirred for 8 h then concentrated to 5 mL. Ad-
dition of Et2O (10 mL) gave the mononuclear trans complex 8
2
2
(d, JP,P = 40.4 Hz, PV[N]), –10.6 (d, JP,P = 40.4 Hz, PV[O]) ppm.
as
a yellow solid. Yield: 83% (0.158); m.p. 210–212 °C.
MS (EI): m/z 1033.57 [M + H]+.
C96H76Cl2N2O8P6Pd (1748.8): calcd. C 65.93, H 4.38, N 1.60;
1
found C 65.24, H 3.99, N, 1.75. H NMR (300 MHz, CDCl3): δ =
Synthesis of O{C6H4P(S)Ph2}2 (3):
A mixture of DPEphos
5.85–8.20 (m, 76 H, Ph) ppm. 31P{1H} NMR (121 MHz, CDCl3):
(0.200 g, 0.371 mmol) and sulfur (0.024 g, 0.093 mmol) was re-
fluxed in toluene (10 mL) for 24 h with constant stirring to give
a white precipitate of 3. The solution was then cooled to room
temperature, filtered, and recrystallized from hot CHCl3. Yield:
92% (0.206 g); m.p. Ͼ 250 °C. C36H28OP2S2 (602.7): calcd. C 71.74,
H 4.68, S 10.64; found C 71.62, H 4.81, S 10.88. 1H NMR
(400 MHz, CDCl3): δ = 6.20–7.68 (m, 28 H, Ph) ppm. 31P{1H}
NMR (162 MHz, CDCl3): δ = 39.1 (s) ppm.
2
2
δ = 14.2 (s, P[Pd]), 11.7 (d, JP,P = 38.1 Hz, PV[N]), –10.6 (d, JP,P
=
38.1 Hz, PV[O]) ppm.
Synthesis of [Pd{κ2-P,O-Ph2PC6H4OC6H4PPh2=NP(O)(OPh)2}2]
(9): A solution of [Pd2(dba)3] (0.05 g, 0.048 mmol) in toluene
(20 mL) was added dropwise to a stirring solution of 1 (0.152 g,
0.193 mmol) in toluene (10 mL) at room temperature. After 4 h the
solution had turned yellow and all the solvents were removed in
vacuo. The residual solid was washed several times with petroleum
ether to remove dba and dried. Yield: 78% (0.126 g); m.p. 112 °C
(dec). C96H76N2O8P6Pd (1677.9): calcd. C 68.72, H 4.57, N 1.67;
Synthesis of O{C6H4P(Se)Ph2}2 (4): A mixture of DPEphos
(0.200 g, 0.371 mmol) and selenium (0.059 g, 0.742 mmol) was re-
fluxed in toluene (10 mL) for 24 h with constant stirring to give
a white precipitate of 4. The solution was then cooled to room
temperature, filtered, and recrystallized from hot CHCl3. Yield:
90% (0.233 g); m.p. Ͼ 250 °C. C36H28OP2S2 (696.5): calcd. C 62.08,
1
found C 68.48, H 4.76, N 1.80. H NMR (400 MHz, CDCl3): δ =
5.93–8.30 (m, 38 H, Ph) ppm. 31P{1H} NMR (162 MHz, CDCl3):
2
2
δ = 23.6 (s, P[Pd]), 11.7 (d, JP,P = 39.5 Hz, PV[N]), –7.8 (d, JP,P
=
39.5 Hz, PV[O]) ppm.
1
H 4.05; found C 62.45, H 4.26. H NMR (400 MHz, CDCl3): δ =
6.30–7.67 (m, 28 H, Ph) ppm. 31P{1H} NMR (162 MHz, CDCl3):
Synthesis of [AuCl{κ1-P-Ph2PC6H4OC6H4PPh2=NP(O)(OPh)2}]
(10): A solution of [AuCl(SMe2)] (0.03 g, 0.102 mmol) in CH2Cl2
(5 mL) was added dropwise to a solution of 1 (0.08 g, 0.102 mmol)
1
δ = 29.4 (s, JSe,P = 734.1 Hz) ppm. MS (EI): m/z 699.04
[M + H]+.
1936
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2007, 1930–1938

Iminophosphorane-Phosphanes and Their Catalytic Activity
FULL PAPER
in CH2Cl2 (10 mL) at room temperature. The reaction mixture was
stirred for 12 h, then concentrated to 2 mL and layered with Et2O
(5 mL) to give colorless crystals of analytical purity. Yield: 92%
(0.095 g); m.p. 216–218 °C. C48H38AuClNO4P3 (1018.2): calcd. C
56.62, H 3.76, N 1.38; found C 56.64, H 3.79, N 1.38. 1H NMR
Table 7. Crystallographic data for complex 10.
Formula
Molecular weight
C48H38AuClNO4P3
1018.12
Crystal system
Space group
monoclinic
P21/c
(400 MHz, CDCl3): δ = 6.15–7.88 (m, 38 H, Ph) ppm. 31P{1H}
a [Å]
b [Å]
c [Å]
α [°]
15.9417(14)
10.9513(16)
25.3394(18)
90
2
NMR (162 MHz, CDCl3): δ = 19.0 (s, P[Au]), 10.4 (d, JP,P
=
37.9 Hz, PV[N]), –10.5 (d, 2JP,P = 37.9 Hz, PV[O]) ppm. MS (EI): m/z
982.49 [M – Cl]+.
β [°]
101.717(7)
90
4331.6(8)
4
1.561
3.614
2024
0.26ϫ0.21ϫ0.18
150(2)
Synthesis of cis-[Rh(COD){κ2-P,O-Ph2PC6H4OC6H4PPh2=NP(O)-
γ [°]
V [Å3]
(OPh)2}][OTf] (11):
A mixture of 1 (0.066 g, 0.083 mmol),
[{Rh(COD)Cl}2] (0.021 g, 0.042 mmol), and AgOTf (0.021,
0.083 mmol) in CH2Cl2 (10 mL) was stirred for 8 h at room tem-
perature. The yellow solution was concentrated to 2 mL and Et2O
(10 mL) added to give a yellow oily substance. The supernatant
liquid was discarded and dried to give a yellow foamy substance
11, which was washed with Et2O and dried. Yield: 78% (0.044 g,
0.025 mmol); m.p. 144–146 °C. C57H50F3NO7P3RhS (1145.9):
calcd. C 59.74, H 4.39, N 1.22, S 2.80; found C 60.11, H 4.08, N
Z
ρcalc [gcm–3]
µ (Mo-Ka) [mm–1]
F(000)
Crystal size [mm3]
T [K]
2θ range [°]
Total number of reflections
GOF [F2]
2.95–25.00
21719 [Rint = 0.0702]
0.778
0.0349
0.0563
1
[a]
1.30, S 2.85. H NMR (400 MHz, CDCl3): δ = 1.27–2.37 (br. m, 8
R1
2
[b]
H, CH2), 2.90 (br. d, JRh,H = 119.2 Hz, 2 H, CH), 5.13 (br. d,
wR2
2JRh,H = 115.6 Hz, 2 H, CH), 6.26–7.99 (m, 38 H, Ph) ppm.
2
2
[a] R = Σ||Fo| – |Fc||/Σ|Fo|. [b] Rw = {[Σw(Fo – Fc )/Σw(Fo2)2]}1/2; w
1
31P{1H} NMR (162 MHz, CDCl3): δ = 12.9 (d, JRh,P = 149.3 Hz,
2
2
= 1/[σ2(Fo2) + (xP)2], where P = (Fo + 2Fc )/3.
2
2
P
[Rh]), 8.8 (d, JP,P = 39.0 Hz, PV[N]), –11.1 (dd, 2JP,P = 39.0, JRh,P
= 6.6 Hz, PV[O]) ppm. MS (EI): m/z 996.29 [M – OTf]+.
Synthesis of trans-[Rh(CO)Cl{κ1-P-Ph2PC6H4OC6H4PPh2=NP-
(O)(OPh)2}2] (12): A CH3CN (8 mL) solution of [{Rh(CO)2Cl}2]
(0.015 g, 0.039 mmol) was added dropwise to a solution of 1
(0.121 g, 0.154 mmol) in CH3CN (10 mL) at room temperature.
The reaction mixture was stirred for 4 h to give the trans complex
12 as a yellow precipitate, which was then filtered, washed with
CH3CN (2 mL), and dried. Yield: 88% (0.118 g, 0.068 mmol); m.p.
242–244 °C. C97H76ClN2O9P6Rh (1737.9): calcd. C 67.04, H 4.41,
N 1.61; found C 66.37, H 4.80, N 1.82. 1H NMR (400 MHz,
CDCl3): δ = 6.77–8.12 (m, 76 H, Ph) ppm. 31P{1H} NMR
atmosphere of nitrogen until the conversion stopped (the course of
the reaction was monitored by GC analysis). The solvent was then
removed under reduced pressure. The resultant residual mixture
was quenched with H2O (10 mL) and extracted twice with Et2O
(2ϫ10 mL). The combined organic fraction was dried (MgSO4),
the solvent removed under vacuum, and the residue dissolved in
CH2Cl2 (5 mL). An aliquot of the solution was subjected to GC
analysis. Yields were calculated with respect to aryl halides or do-
decane as an internal standard.
1
Catalytic Hydrogenation of Olefins: A mixture of RhI complex 11
(0.0005 or 0.005 mol-%), olefin (1.0 mmol), and triethylamine
(0.1 mmol) was dissolved in 20 mL of thf and was introduced into
a 50-mL glass vessel, which was placed into a steel autoclave and
the reactor sealed. The vessel was purged three times with hydrogen
and then the autoclave was pressurized with 4 atm of hydrogen.
The reaction mixture was stirred at a room temperature for the
required time. The extent of conversion was determined by periodic
GC analysis until complete conversion was observed.
(162 MHz, CDCl3): δ = 22.5 (d, JRh,P = 140.3 Hz, P[Rh]), 11.3 (d,
2
2JP,P = 37.9 Hz, PV[N]), –10.6 (d, JP,P = 37.9 Hz, PV[O]) ppm. FT-
IR (KBr disc): ν = 1958 cm–1 [νCO]. MS (EI): m/z 1701.70
˜
[M – Cl]+.
Crystal Structure Determination: Single crystals of 8 suitable for X-
ray diffraction were grown by slow diffusion of diethyl ether into a
dichloromethane solution and mounted on a glass fiber with epoxy
resin. Unit cell determination and data collection of 8 were per-
formed with an Oxford Diffraction XCALIBUR-S CCD system
using Mo-Kα radiation (λ = 0.71073 Å). The structure was solved
and refined by full-matrix least-squares techniques on F2 using the
SHELX-97 (SHELXL program package).[43] The absorption cor-
rections were done by multi-scan and all the data were corrected
for Lorentz and polarization effects. The non-hydrogen atoms were
refined with anisotropic thermal parameters. All the hydrogen
atoms were geometrically fixed and allowed to refine using a riding
model (Table 7).
Acknowledgments
We are grateful to The Department of Science and Technology
(DST) for financial support of this work through grant SR/S1/IC-
05/2003. We would also like to thank the Sophisticated Analytical
Instrument Facility (SAIF) IIT Bombay, Department of Chemistry
IIT Bombay and National Single Crystal X-ray Diffraction Facility
IIT Bombay for instrument facilities. R. V. is grateful to IIT Bom-
bay for JRF and SRF Fellowships.
CCDC-616229 (for 9) contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
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Eur. J. Inorg. Chem. 2007, 1930–1938
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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1937

R. Venkateswaran, M. S. Balakrishna, S. M. Mobin
FULL PAPER
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