Platinum complexes of rigid bidentate phosphine ligands in the hydroformylation of 1-octene

Article abstract of DOI:10.1021/om050575a

The synthesis of the two novel diphosphine compounds 1,2-bis(3- (diphenylphosphino)-4-methoxyphenyl)benzene (1; Terphos), and 1,2-bis(2-diphenylphosphino)benzene (2), both derived from a terphenyl backbone structure, are described. Straightforward synthetic routes have been employed to obtain these ligands in good yields from cheap starting materials. The coordination of ligands 1 and 2 with PtCl₂(cod) has been studied by NMR spectroscopy, and the X-ray crystal structures of the resulting complexes 4 and 5 were determined. The ³¹P NMR spectra of the mononuclear products demonstrate solely cis coordination for both bidentate ligands, with corresponding coupling constants J_Pt-p of 3810 Hz (cis-[PtCl ₂(1)], complex 4) and 3712 Hz (cis-[PtCl₂(2)], 5). The bite angles P₁-Pt-P₂ were 98.74 and 105.89°, respectively, in the distorted square-planar complexes. The new diphosphines have been applied in the platinum/tin-catalyzed hydroformylation of 1-octene, and both ligands give active and selective platinum catalysts.

Full text of DOI:10.1021/om050575a

Organometallics 2005, 24, 5377-5382
5377
Platinum Complexes of Rigid Bidentate Phosphine
Ligands in the Hydroformylation of 1-Octene
Jarl Ivar van der Vlugt,† Ruben van Duren,† Guido D. Batema,‡
Rene´ den Heeten,‡ Auke Meetsma,§ Jan Fraanje,| Kees Goubitz,|
Paul C. J. Kamer,‡, Piet W. N. M. van Leeuwen,†,‡ and Dieter Vogt*,†
Schuit Institute of Catalysis, Laboratory of Homogeneous Catalysis, Eindhoven University of
Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands, Institute of Molecular
Chemistry, University of Amsterdam, Nieuwe Achtergracht 166, Amsterdam, The Netherlands,
Crystal Structure Center, Chemical Physics, Materials Science Center, University of
Groningen, Nijenborgh 4, Groningen, The Netherlands, and Department of Crystallography,
University of Amsterdam, Nieuwe Achtergracht 166, Amsterdam, The Netherlands
Received July 8, 2005
The synthesis of the two novel diphosphine compounds 1,2-bis(3-(diphenylphosphino)-4-
methoxyphenyl)benzene (1; Terphos), and 1,2-bis(2-diphenylphosphino)benzene (2), both
derived from a terphenyl backbone structure, are described. Straightforward synthetic routes
have been employed to obtain these ligands in good yields from cheap starting materials.
The coordination of ligands 1 and 2 with PtCl2(cod) has been studied by NMR spectroscopy,
and the X-ray crystal structures of the resulting complexes 4 and 5 were determined. The
31P NMR spectra of the mononuclear products demonstrate solely cis coordination for both
bidentate ligands, with corresponding coupling constants JPt-P of 3810 Hz (cis-[PtCl2(1)],
complex 4) and 3712 Hz (cis-[PtCl2(2)], 5). The bite angles P1-Pt-P2 were 98.74 and 105.89°,
respectively, in the distorted square-planar complexes. The new diphosphines have been
applied in the platinum/tin-catalyzed hydroformylation of 1-octene, and both ligands give
active and selective platinum catalysts.
Introduction
tivities but with lower chemo- and regioselectivities
compared to those for the rhodium-based systems. For
the platinum-catalyzed hydroformylation of (terminal)
alkenes, most often (di)phosphine ligands are em-
ployed.7 Rigid xanthene-based diphosphines (Figure 1)
have been shown to give active and selective platinum
catalysts for the hydroformylation of 1-octene.8 We
previously also reported the highly selective platinum-
catalyzed hydroformylation of the industrially relevant
internal alkene methyl trans-3-pentenoate.9
Homogeneous catalysis has proven to be a very
powerful tool for the synthesis of intermediates and fine
chemicals.1 One especially significant application on an
industrial scale is the hydroformylation of alkenes.2
Most often cobalt and rhodium catalysts are applied,
but also Pt-Sn systems with phosphorus ligands have
been known since the pioneering work of Orchin.3 In
this system, the role of the SnCl2 “cocatalyst” actually
remains unclear,4 and even tin-free systems have been
reported.5 Especially in the asymmetric hydroformyla-
tion of styrene, platinum-based catalysts have been
extensively studied,6 with generally high enantioselec-
(5) (a) Tang, S. C.; Kim, L. J. Mol. Catal. 1982, 14, 231. (b) van
Leeuwen, P. W. N. M.; Roobeek, C. F.; Wife, R. L.; Frijns, J. H. G. J.
Chem. Soc., Chem. Commun. 1986, 31. (c) van Leeuwen, P. W. N. M.;
Roobeek, C. F. New J. Chem. 1990, 14, 487. (d) Botteghi, C.; Paganelli,
S.; Matteoli, U.; Scrivanti, A.; Ciociaro, R.; Venanzi, L. M. Helv. Chim.
Acta 1990, 73, 284. (e) van Leeuwen, P. W. N. M.; Roobeek, C. F.;
Frijns, J. H. G.; Orpen, A. G. Organometallics 1990, 9, 1211.
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Huijbers, J. P. J.; Mills, A. M.; Spek, A. L.; Vogt, D. Submitted for
publication in Helv. Chim. Acta. (b) Peto¨cz, G.; Berente, Z.; Ke´gl, T.;
Kolla´r, L. J. Organomet. Chem. 2004, 689, 1188. (c) Csere´pi-Szu¨cs, C.;
Bakos, J. J. Chem. Soc., Chem. Commun. 1997, 635. (d) To´th, I.; Guo,
I.; Hanson, B. E. Organometallics 1993, 12, 848. (e) Stille, J. K.; Su,
H.; Brechot, P.; Parinello, G.; Hegedus, L. S. Organometallics 1991,
10, 1183. (f) Consiglio, G.; Nefkens, S. C A.; Borer, A. Organometallics
1991, 10, 2046. (g) Parinello, G.; Stille, J. K. J. Am. Chem. Soc. 1987,
109, 7122. (h) Haelg, P.; Consiglio, G.; Pino, P. J. Organomet. Chem.
1985, 296, 281.
* To whom correspondence should be addressed. E-mail:
d.vogt@tue.nl. Tel: +31 40 2472483. Fax: +31 40 2455054.
† Eindhoven University of Technology.
‡ Institute of Molecular Chemistry, University of Amsterdam.
§ University of Groningen.
| Department of Crystallography, University of Amsterdam.
Current address: Department of Chemistry, University of St.
Andrews, St. Andrews, Fife KY16 9AJ, Scotland.
(1) Frohning, C. D.; Kohlpainter, C. W.; Bohnen, H. W. In Applied
Homogeneous Catalysis with Organometallic Compounds, 2nd ed.;
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Vol. 1, p 31.
(2) (a) Bohnen, H. W.; Cornils, B. Adv. Catal. 2002, 47, 1. (b)
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10.1021/om050575a CCC: $30.25 © 2005 American Chemical Society
Publication on Web 09/21/2005

5378 Organometallics, Vol. 24, No. 22, 2005
van der Vlugt et al.
Figure 1.
Scheme 1. Synthetic Routes to Compounds 1 and 2
An early study by Hayashi et al., aimed at quantifying
the effect of the diphosphine chelate ring size on
catalytic performance, described that in the case of
diphosphine ligands steric rather than electronic factors
govern the reaction rate and regioselectivity.10 In com-
parison to the benchmark system PtCl2(PPh3)2/SnCl2,
the addition of 1,2-bis(diphenylphosphino)ethane (dppe)
led to a considerably slower reaction rate.11 The catalytic
activity increased dramatically when a four-carbon-
bridged diphosphine such as dppb was employed (Figure
1). The trans-substituted norbornane-derived ligand
dppm-nor gave the fastest catalyst, but also with various
other ligands containing a cyclic four-carbon bridge (e.g.
dppm-cyb) increased rates were observed. The calcu-
lated natural bite angles of these particular ligands are
all around 98°.12
phine ligand in homogeneous catalysis, the Pt/Sn-
catalyzed hydroformylation of 1-octene was chosen as
a model reaction.
Results and Discussion
Synthesis of Diphosphines 1 and 2 and Selenide
3. The diphosphine compound 1 (named Terphos) was
successfully synthesized in good yield from commercially
available starting materials (Scheme 1). The palladium-
catalyzed Suzuki coupling of 1,2-dibromobenzene with
4-methoxyphenylboronic acid, in the presence of Na2-
CO3 as a base, gave compound A in 73% yield. This is
a significant improvement of the procedure reported by
Blake et al., who used Ba(OH)2 as a base in order to
obtain the same compound.13 Subsequent ortho lithia-
tion and reaction with ClPPh2, a strategy recently
applied to obtain Bisphenol A derived diphosphine
ligands,14 yielded the desired diphosphine compound 1,
which was fully characterized by 1H, 13C, and 31P NMR
spectroscopy as well as by elemental analysis. The
structurally related compound 2 was obtained by reac-
tion of the bis-nonaflate B15 with HPPh2 to yield
We herein report the synthesis of the novel diphos-
phines 1 and 2 and their Pt complexes. To obtain
information on the applicability of this type of diphos-
(9) Meessen, P.; Vogt, D.; Keim, W. J. Organomet. Chem. 1998, 551,
165.
(10) (a) Hayashi, T.; Kawabata, Y.; Isoyama, T.; Ogata, I. Bull.
Chem. Soc. Jpn. 1981, 54, 3438. (b) Kawabata, Y.; Hayashi, T.; Ogata,
I. J. Chem. Soc., Chem. Commun. 1979, 462.
(11) Schwager, I.; Knifton, J. F. J. Catal. 1976, 45, 256.
(12) van Leeuwen, P. W. N. M.; Kamer, P. C. J.; Reek, J. N. H.;
Dierkes, P. Chem. Rev. 2000, 100, 2741.
(13) Blake, A. J.; Cooke, P. A.; Doyle, K. J.; Gair, S.; Simpkins, N.
S. Tetrahedron Lett. 1998, 39, 9093.

Pt Complexes of Rigid Bidentate Phosphine Ligands
Organometallics, Vol. 24, No. 22, 2005 5379
1
compound 2, which was fully characterized by H, 13C,
and 31P NMR spectroscopy as well as by FAB-MS
spectrometry.
The σ-donor ability and hence the basicity of a
phosphine moiety is related to the coupling constant
1JSe-P in the 31P NMR spectrum of the 77Se isotopomer
of the corresponding diphenylphosphine selenide.16 We
synthesized the corresponding chalcogen compound 3
by reaction of 1 with elemental selenium. The reaction
proceeded smoothly at 60 °C in toluene within 15 min.
The 31P NMR spectrum showed a singlet at δ 32.1 ppm
with concomitant 77Se satellites. The coupling constant
1JSe-P of 724 Hz was in the range expected for diphen-
ylphosphine-derived selenides.16 For the selenide of
1
PPh3 a JSe-P value of 732 Hz is reported,17 while the
more electron-donating tris(4-methoxyphenyl)phosphine
1
selenide gives a JSe-P value of 708 Hz.18
Preparation of Dichloroplatinum(II) Complexes
4 and 5. The reaction of PtCl2(cod) with either ligand 1
or 2 led to the quantitative formation of the correspond-
ing cis complexes, as indicated by the observed coupling
constants JPt-P from 31P NMR spectroscopy.19 For
complex 4, cis-[PtCl2(1)], the 31P{1H} NMR spectrum
showed a singlet at δ 9.9 ppm, flanked by 195Pt satellites
with a JPt-P value of 3810 Hz, while the related complex
5, cis-[PtCl2(2)], appeared as a singlet at δ 8.2 ppm
together with its 195Pt satellites (JPt-P ) 3712 Hz). The
molecular structures were unequivocally determined by
X-ray crystallography and were in full agreement with
the spectroscopic data. Figure 2 depicts the molecular
structure with values for important bond lengths and
bond angles for complex 4, which crystallized in the
monoclinic space group P21/n as the CDCl3 adduct.
The geometry around the platinum atom is clearly
distorted square planar, as evident from the observed
bite angle P1-Pt-P2 of 98.74(2)°. The angles P1-Pt-
Cl2 and P2-Pt-Cl1 are 170.90 and 172.80°, respectively.
Consequently, the Cl1-Pt-Cl2 angle is small at only
84.93°. The Pt-P and Pt-Cl bond lengths are in their
expected ranges, at 2.26-2.28 and 2.34-2.36 Å, respec-
tively.20 The aromatic rings of the terphenyl backbone
Figure 2. Ortep representation of complex 4, cis-[PtCl2-
(1)]. Displacement ellipsoids are drawn at the 50% prob-
ability level. Hydrogen atoms and solvent molecules are
omitted for clarity. Selected bond lengths (Å) and bond
angles (deg): Pt-P1, 2.2847(7); Pt-P2, 2.2635(7); Pt-Cl1,
2.3565(6); Pt-Cl2, 2.3358(7); O1-C26, 1.352(3); O2-C40,
1.356(3); P1-C25, 1.832(3); P2-C41, 1.818(3); P1-P2, 3.4517(9);
P1-Pt-P2, 98.74(2); Cl1-Pt-Cl2, 84.93(2); P1-Pt-Cl1,
86.34(2); P1-Pt-Cl2, 170.90(2); P2-Pt-Cl1, 172.80(3); P2-
Pt-Cl2,89.73(2);Pt-P1-C25,122.03(9);Pt-P2-C41,110.75(9).
have torsion angles C28-C29-C31-C36 of -135.7° and
C31-C36-C37-C38 of -128.2°, showing that there is
slight distortion from the local C2 symmetry of the
backbone. The intramolecular P1-P2 distance is only
3.4517 Å, whereas the corresponding Pt complex of the
ligand Sixantphos showed a P1-P2 distance of 3.4295
Å.21 Interestingly, the latter value is significantly
smaller than reported for various other non-platinum
complexes of the strongly related Xantphos.22,23 The
molecular structure obtained for the related complex 5,
cis-[PtCl2(2)], is depicted in Figure 3, together with data
for selected bond lengths and bond angles.
Again, the geometry around the platinum atom is
distorted square planar. The observed bite angle P1-
Pt-P2 is 105.83°. The angles P1-Pt-Cl1 and P2-Pt-
Cl1 are 169.17 and 83.33°, respectively. The intramo-
lecular P1-P2 distance is found to be 3.604 Å, somewhat
longer than in complex 4. The most notable structural
difference between the two Pt compounds is the orienta-
tion of the middle phenyl ring in the backbone of the
ligands. In complex 4, this phenyl is directed away from
the metal center, while in complex 5 the central phenyl
ring of the backbone shields one face of the platinum
center, acting as a “roof”.
(14) (a) Ahlers, W.; Paciello, R.; Vogt, D.; van der Vlugt, J. I. (to
BASF AG) U.S. Patent 6,639,114, 2002; Chem. Abstr. 2002, 169060.
(b) van der Vlugt, J. I.; Grutters, M. M. P.; Mills, A. M.; Spek, A. L.;
Vogt, D. Eur. J. Inorg. Chem. 2003, 4361. (c) van der Vlugt, J. I.; Bonet,
J. M.; Mills, A. M.; Spek, A. L.; Vogt, D. Tetrahedron Lett. 2003, 44,
4389.
(15) B was kindly donated by Prof. H. J. Hiemstra, University of
Amsterdam. The general route to B starts from 1,2-dibromobenzene,
which is converted to 1,2-bis(2-anisyl)benzene via Suzuki coupling,
using (2-methoxyphenyl)boronic acid. Generation of the corresponding
biphenol with 48% HBr, followed by reaction with KSO3(CF2)3CF3 in
CH3CN in the presence of diisopropylethylamine, yielded B. A full
account of the synthesis of this ligand will be reported elsewhere:
Batema, G.; den Heeten, R.; Kamer, P. C. J.; Hiemstra, H. J.; van
Leeuwen, P. W. N. M. Unpublished work.
(16) (a) Jeulin, S.; Duprat de Paule, S.; Ratovelomanana-Vidal, V.;
Geneˆt, J. P.; Champion, N.; Dellis, P. Angew. Chem., Int. Ed. 2004,
43, 320. (b) Sua´rez, A.; Me´ndez-Rojas, M. A.; Pizzano, A. Organome-
tallics 2002, 21, 4611. (c) Andersen, N. G.; Parvez, M.; Keay, B. A.
Org. Lett. 2000, 2, 2817. (d) Zijp, E. J.; van der Vlugt, J. I.; Tooke, D.
M.; Spek, A. L.; Vogt, D. Dalton Trans. 2005, 512.
(17) Allen, D. W.; Taylor, B. F. J. Chem. Soc., Dalton Trans. 1982,
51.
(18) Pinnell, R. P.; Megerle, C. A.; Manatt, S. L.; Kroon, P. A. J.
Am. Chem. Soc. 1973, 95, 977.
(19) Cobley, C. J.; Pringle, P. G. Inorg. Chim. Acta 1997, 265, 107.
(20) (a) Johansson, M. H.; Otto, S. Acta Crystallogr. 2000, C56, e12.
(b) Maienza, F.; Wo¨rle, M.; Steffanut, P.; Mezzetti, A.; Spindler, F.
Organometallics 1999, 18, 1041. (c) van den Beuken, E. K.; Meetsma,
A.; Kooijman, H.; Spek, A. L.; Feringa, B. L. Inorg. Chim. Acta 1997,
264, 171.
Platinum-Catalyzed Hydroformylation of 1-Oc-
tene. In the original work by Hayashi, the remarkable
catalytic rate enhancement observed with diphosphines
(21) van Duren, R.; van der Vlugt, J. I.; Meeuwissen, J.; Kooijman,
H.; Spek, A. L.; Vogt, D. Unpublished work.
(22) Kamer, P. C. J., Reek, J. N. H.; van Leeuwen, P. W. N. M. Acc.
Chem. Res. 2001, 34, 895.
(23) Kranenburg, M.; Delis, J. G. P.; Kamer, P. C. J.; van Leeuwen,
P. W. N. M.; Vrieze, K.; Veldman, N.; Spek, A. L.; Goubitz, K.; Fraanje,
J. J. Chem. Soc., Dalton Trans. 1997, 1839.

5380 Organometallics, Vol. 24, No. 22, 2005
van der Vlugt et al.
Table 1. Hydroformylation of 1-Octene Catalyzed
by PtCl2/SnCl2/1 or 2a
time
T
p
conversn selald isom
TOFe
entry ligand (h) (°C) (bar)
(%)b
(%)b,c (%)b,d l:bb (h-1
)
1
2
3
4
5
6
7
1
1
1
2
2
2
2
18
60 40
20.9
42.1
77.6
51.3
13.4
48.1
39.4
96.1 6.9 34.0 12
94.9 11.3 32.2 27
93.3 75.3 18.1 39
16.5 60 80
21
64
18
18
60 80f
60 40
60 80
60 80f
98.6
>99
98.9
94.5 26.7
5.0
8.5
8
7
29.5
1.6 45.3 25
5.5 100 40
2.1 70
a Reaction conditions: 1-octene (31.0 mmol), [PtCl2(P∩P)/SnCl2]
) 0.39 mM, decane (12.5 mmol), CH2Cl2, 1-octene:Pt ) 1050:1.
b Determined by GC. c The only side product is hydrogenation.
d Defined as fraction of remaining 1-octene. e Turnover frequency,
defined as (mol of substrate converted) (mol of platinum)-1 h-1
,
determined at the end of the run. f 40 bar of CO/H2 and 40 bar of
H2.
isomerization of 1-octene to internal isomers is ex-
pressed relative to non-converted 1-octene. Both ligands
1 and 2 gave active platinum catalysts, as can be seen
from the results listed in Table 1. Activities were slightly
lower than those obtained with the ligand Xantphos (tof
of 240 at 80 °C), which has a natural bite angle ân of
112°, but comparable to those found with Homoxantphos
(natural bite angle ân of 102°).8 The chemoselectivity
to aldehydes as well as the regioselectivity are high with
ligand 1. A direct comparison with the ligands applied
by Hayashi is less straightforward, due to the varying
reaction conditions, but the chemoselectivity is better
than found with the ligand dppb, although the dppm-
cyb-based system appears to be superior.10 Increasing
the total syngas pressure to 80 bar had no effect on these
high levels with this catalyst system. When the ratio of
H2 to CO was altered to 3:1 at an overall pressure of 80
bar, i.e. 40 bar of H2 and 40 bar of syngas, the catalytic
activity was raised by about 50% (entry 3). There was
significant isomerization of 1-octene, however, a known
drawback of Pt/Sn catalysts.
On application of ligand 2, which is expected to induce
more steric hindrance around the metal center, lower
activities and regioselectivities (l:b ratio of 8.5) were
observed, compared to ligand 1, at the standard reaction
conditions of 60 °C and 40 bar of synthesis gas (entry
4). Increasing the total syngas pressure had a positive
effect on the regioselectivity (l:b ratio of 29.5), while
isomerization of 1-octene was virtually absent. As the
hydrogenolysis of an acyl-complex intermediate, to form
the aldehyde product, is usually rate limiting for Pt/Sn
systems,25 a higher hydrogen partial pressure proved
advantageous for the overall performance of the catalyst
system (entry 6). At a reaction temperature of 100 °C,
the regioselectivity dropped dramatically (l:b ratio of
2.1), with over 20% isomerized product (entry 7).
Although the bite angle difference between either ligand
1 or 2 and Homoxantphos appears relatively small, a
marked effect is noted on the catalytic results, which
implies that other factors in addition to the sterics of
the ligand and its bite angle effect the activity and
regioselectivity of Pt-Sn catalysts. Similar findings
have been reported for the Rh-catalyzed hydroformyla-
tion.26
Figure 3. Ortep representation of complex 5, cis-[PtCl2-
(2)]. Displacement ellipsoids are drawn at the 50% prob-
ability level. Hydrogen atoms and solvent molecules are
omitted for clarity. Selected bond lengths (Å) and bond
angles (deg): Pt-P1, 2.2525; Pt-P2, 2.2631; Pt-Cl1, 2.3581;
Pt-Cl2, 2.3556; P1-C11, 1.830(4); P2-C31, 1.843(4); P1-P2,
3.604(2); P1-Pt-P2, 105.89; Cl1-Pt-Cl2, 86.07; P1-Pt-
Cl1, 169.17; P1-Pt-Cl2, 83.33; P2-Pt-Cl1, 84.70; P2-Pt-
Cl2, 170.76; Pt-P1-C11, 128.03; Pt-P2-C31, 125.54.
that form large chelate rings upon complexation was
explained by the existence of a catalytic species wherein
these ligands acted as monodentates instead of biden-
tates. Although strained cyclic phosphines can undergo
dissociation of one phosphine arm, leading to more ac-
tive catalysts, this is more likely to occur in Pt com-
plexes with true monodentate ligands such as PPh3.
Therefore, the lower reaction rate of PPh3 in comparison
to these bidentate “large bite angle” ligands is not ex-
plained by this theory. It is well-known that the bite
angle has a considerable influence on the rate in the
platinum-catalyzed hydroformylation.10,21 To get insight
into the catalytic behavior of the structurally related
platinum complexes 4 and 5, the Pt-Sn-catalyzed hy-
droformylation of 1-octene was chosen as a test reaction.
By using an equimolar amount of the cocatalyst SnCl2,
high chemo- and regioselectivity to the desired linear
aldehyde have been reported.24 We therefore carried out
an initial preformation ex situ to form the [PtCl2(P∩P)-
SnCl3] adduct (eq 1), which was then in situ activated
with synthesis gas to obtain the precatalyst used in the
hydroformylation of 1-octene (eq 2).
We have performed several catalytic runs under
various reaction conditions, to examine the influences
on both activity and selectivity. The formation of the
desired linear product 1-nonanal, the unwanted branched
aldehyde 2-methyloctanal, and the hydrogenated prod-
uct octane was monitored by gas chromatography. The
(24) (a) Ferna´ndez, C. D.; Garc´ıa-Seijo, M. I.; Ke´gl, T.; Peto¨cz, G.;
Kolla´r, L.; Garc´ıa-Ferna´ndez, M. E. Inorg. Chem. 2002, 41, 4435. (b)
Foca, M.; dos Santos, E. N.; Gusevskaya, E. V. J. Mol. Chem. A 2002,
185, 17-23.
(25) As reported for several systems.9-11

Pt Complexes of Rigid Bidentate Phosphine Ligands
Organometallics, Vol. 24, No. 22, 2005 5381
1
1H NMR (400 MHz, CDCl3, ppm): δ 7.38 (d, 4H, J ) 2.4
Conclusions
Hz), 7.07 (dt, 4H, 1J ) 8.3 Hz, 2J ) 1.2 Hz), 6.77 (dt, 4H, 1J )
8.4 Hz, J ) 1.2 Hz) 3.79 (s, 6H, OCH3). 13C{1H} NMR (100
2
The novel diphosphine compounds 1 and 2 could be
synthesized via straightforward procedures in good
yields. Both ligands coordinated to platinum in a strictly
chelating cis fashion, as demonstrated by NMR spec-
troscopy. The molecular structures for the complexes cis-
[PtCl2(1)] (4) and cis-[PtCl2(2)] (5) were determined by
X-ray crystallography. The bite angles P1-Pt-P2 were
comparable for both complexes at around 100°, but
subtle conformational differences could be noted, which
led to varying steric constraints on the metal center.
The ligands have been applied in the platinum/tin-
catalyzed hydroformylation of 1-octene. Moderate activi-
ties and fairly high regioselectivities were found for both
catalytic systems under appropriate but nonoptimized
reaction conditions.
MHz, CDCl3, ppm): δ 158.2, 140.0, 134.1, 130.9, 130.5, 127.1,
113.5, 55.2 (-OCH3).
1,2-Bis(3-(diphenylphosphino)-4-methoxyphenyl)ben-
zene (1; Terphos). To a solution of A (2.20 g, 7.57 mmol) and
TMEDA (2.5 mL, 16.7 mmol) in 75 mL of ether, cooled to -40
°C, was added n-BuLi (6.7 mL, 16.7 mmol) as a 2.5 M solution
in hexanes in a dropwise fashion. The reaction mixture was
stirred overnight at room temperature. ClPPh2 (3.68 g, 16.7
mmol) in 15 mL of hexanes was added dropwise at 0 °C, after
which the solution was stirred overnight at room temperature.
Volatiles were then removed in vacuo, 50 mL of THF and 75
mL of a 25% brine solution were added, and the organic phase
was washed twice with 30 mL of water. After drying with
MgSO4, the solvent was removed and the precipitate washed
with three 25 mL portions of methanol to give a white powder.
Yield: 60% (2.11 g, 4.54 mmol).
1H NMR (400 MHz, CDCl3, ppm): δ 7.32 (m, 16H, PPh2),
7.27 (dd, 2H, 1J ) 5.6 Hz, 2J ) 3.2 Hz), 7.19 (dd, 2H, 1J ) 5.6
Hz, 2J ) 3.2 Hz), 7.16 (m, 4H), 7.06 (dd, 2H, 1J ) 8.4 Hz, 2J )
2.0 Hz), 6.82 (dd, 2H, 1J ) 8.4 Hz, 2J ) 4.8 Hz), 6.41 (dd, 2H,
Experimental Section
Chemicals were purchased from Aldrich, Acros, or Merck
and used as received. All preparations were carried out under
an argon atmosphere using standard Schlenk techniques.
Solvents were distilled from sodium/benzophenone (THF,
diethyl ether, toluene, and hexanes) or calcium hydride (CH2-
Cl2 and CDCl3) prior to use. All glassware was dried by heating
under vacuum. PtCl2(cod)27 was synthesized according to a
literature procedure. NMR spectra were recorded on Inova 500,
Varian Mercury 300, and Varian Mercury 400 spectrometers,
and chemical shifts are given in ppm referenced to solvent.
GC analyses were performed on a Shimadzu 17A chromato-
graph equipped with a 50 m PONA column. Elemental
analysis was performed by Kolbe Mikroanalytisches Labora-
torium, Mulheim an der Ruhr, Germany.
Autoclaves were manufactured in-house from stainless steel
1.4571. For good heating capacity the autoclaves were fitted
with a shrunk copper mantle. The autoclaves with a volume
of 75 mL closed on a stainless steel ring in order to have line
closure. To add substrates at elevated temperature and
pressure, the autoclave was equipped with a dripping funnel,
which could be cooled or heated. The autoclave was fitted with
a tube manometer with a pressure range from 0 to 160 bar
(Econosto), ball valves for the dripping funnel (VSM GmbH,
KH 4M 4F HT X), needle valves (Swagelock, SS-4PDF4), a
relief valve set at a pressure of 105 bar (Swagelock, SS-4R3A5-
C), various high-pressure connections (Swagelock), and high-
pressure tubing (Dockweiler, Finetron). The autoclave was
heated with an electric heating mantle, and the temperature
was measured internally with a PT-100 thermocouple. The
autoclave was also safeguarded to overheating. The contents
were stirred with an X-type stirring bar.
1,2-Bis(4-methoxyphenyl)benzene (A). This is a modi-
fication of a literature procedure:13 4-methoxyphenylboronic
acid (1.60 g, 10.53 mmol) and 1,2-dibromobenzene (0.83 g, 5.26
mmol) were added to 30 mL of a degassed 2 M solution of Na2-
CO3 and 90 mL of dimethoxyethane, together with a catalytic
amount (∼10 mol %) of Pd(PPh3)4. The reaction mixture was
refluxed overnight. The mixture was brought to pH 7 by
addition of a 4 M HCl solution. The solution was concentrated
to approximately 40 mL and the product extracted with CH2-
Cl2 (3 × 25 mL). The combined organic phases were dried over
MgSO4 and filtered by cannula, and the solvent was removed
in vacuo to leave a yellow oil. Upon addition of 10 mL of MeOH
a white precipitate was obtained that was separated, washed
twice with 10 mL of acetonitrile, and dried to give 0.72 g (73%)
of a white crystalline powder.
2
1J ) 4.8 Hz, J ) 2.0 Hz), 3.72 (s, 6H, OCH3). 13C{1H} NMR
(100 MHz, CDCl3, ppm) δ 159.6, 145.5, 140.2, 136.5 (d JP-C
)
9.8 Hz), 135.1, 134.3, 134.0 (d, JP-C ) 20.4 Hz), 131.4, 130.4,
128.5, 128.4 (d, JP-C ) 6.8 Hz), 128.4, 126.9, 110.0, 55.8
(-OCH3). 31P{1H} NMR (162 MHz, CDCl3, ppm) δ -16.5 (s).
Anal. Calcd for C44H36O2P2: C, 80.23; H, 5.51; P, 9.40. Found:
C, 80.16; H, 5.43: P, 9.55.
1,2-Bis(2-(diphenylphosphino)phenyl)benzene (2). Com-
pound B15 (2.0 g, 2.42 mmol), dppe (21.2 mg, 53.2 µmol), Pd-
(OAc)2 (10.87 mg, 48.4 µmol), and DABCO (1.1 g, 9.68 mmol)
were dissolved in 35 mL of DMF (35 mL), and the mixture
was stirred for 1 h at room temperature. HPPh2 (0.93 mL, 5.32
mmol) was then added dropwise and the reaction mixture was
heated to reflux. After 3 days the reaction was complete, as
indicated by TLC (eluent 1/1 CH2Cl2/petroleum ether). Solvent
was evaporated in vacuo, and the residue was dissolved in 75
mL of Et2O and washed with 50 mL of degassed water. The
organic layer was dried with MgSO4 and filtered over neutral
alumina. The light yellow filtrate was evaporated to dryness
in vacuo to yield 1.25 g of crude residue. This was dissolved
in a small amount of CH2Cl2 and recrystallized by slow
diffusion of hexanes, to yield 2 (0.95 g, 65%). In the 31P NMR
spectrum a small amount of byproduct was observed, which
could not be removed by silica gel column chromatography.
1H NMR (500 MHz, CDCl3, ppm): δ 7.35 (m, 16H), 7.16 (m,
8H), 7.08 (m, 6H), 6.91 (m, 2H). 13C{1H} NMR (125 MHz,
CDCl3, ppm): 140.1 (d, JC-P ) 7.2 Hz), 138.8 (d, JC-P ) 12.2
Hz), 137.7 (d, JC-P ) 11.4 Hz.), 136.3 (d JC-P ) 11.0 Hz), 134.3
(d, JC-P ) 19.8 Hz), 133.5 (d, JC-P ) 18.6 Hz), 131.4 (d, CH,
JC-P ) 4.2 Hz), 131.0 (t, JC-P ) 6.1 Hz), 128.9, 128.7 (d, JC-P
) 6.8 Hz), 128.5 (d, JC-P ) 5.9 Hz), 128.3 (d, JC-P ) 11.0 Hz)
127.4, 126.7. 31P{1H} NMR (202 MHz, CDCl3, ppm): δ -12.7
(s, ∼5%, monophosphine), -14.3 (s). MS (FAB+) (m/z) for
C42H33P2: calcd 599.2057, found 599.2044 [M + H].
1,2-Bis(3-(diphenylphosphino)-4-methoxyphenyl)ben-
zene Diselenide (3). Compound 1 (57.8 mg, 8.75 mmol) and
an excess of selenium black were suspended in 5 mL of toluene
and stirred for 15 min at room temperature. Subsequently,
the solution was filtered off to remove insolubles and the
solvent was evaporated in vacuo to leave a yellow oil. Upon
addition of 5 mL of hexanes, a white precipitate was formed
that was isolated by filtration and then redissolved in 5 mL
of dichloromethane. Removal of the solvent left 3 as a pure
white solid. Yield: 93% (66.8 mg, 8.16 mmol).
1H NMR (400 MHz, CDCl3, ppm): δ 7.81 (ddd, 8H, 1J )
2
3
1
14.4 Hz, J ) 7.2 Hz, J ) 2.0 Hz), 7.78 (d, 2H, J ) 2.8 Hz),
7.74 (d, 2H, 1J ) 2.8 Hz), 7.39 (m, 12H), 7.21 (dd, 4H, 1J ) 8.0
Hz, 2J ) 2.4 Hz), 6.81 (dd, 2H, 1J ) 8.4 Hz, 2J ) 1.6 Hz), 3.51
(26) Freixa, Z.; van Leeuwen, P. W. N. M. Dalton Trans. 2003, 1890.
(27) Clark, H. C., Manzer, L. E. J. Organomet. Chem. 1973, 59, 411.

5382 Organometallics, Vol. 24, No. 22, 2005
van der Vlugt et al.
(s, 6H, OCH3). 13C{1H} NMR (100 MHz, CDCl3, ppm): δ 159.2,
139.2, 138.0 (d, JP-C ) 11.4 Hz), 135.6 (d, JP-C ) 2.2 Hz), 132.3
(d, JP-C ) 11.3 Hz), 130.9 (d, JP-C ) 3.1 Hz), 130.6, 129.1, 128.1
(d, JP-C ) 12.9 Hz), 127.7, 111.8, 55.4 (-OCH3). 31P{1H} NMR
(162 MHz, CDCl3, ppm) δ 32.1 (s, JSe-P ) 724 Hz). Anal. Calcd
for C44H36O2P2Se2: C, 64.71; H, 4.44. Found: C, 64.75; H, 4.70.
cis-[PtCl2(1)] (4). PtCl2(cod) (35.9 mg, 95.9 µmol) was
dissolved in 15 mL of CH2Cl2, and to this solution was slowly
added ligand 1 (65.1 mg, 95.5 µmol), dissolved in 15 mL of
CH2Cl2. The solution was stirred overnight. After evaporation
of the solvent in vacuo, 4 was obtained as a white powder.
Single crystals, suitable for X-ray analysis, could be obtained
by slow evaporation of CDCl3 from an NMR tube.
and polarization effects. The structure was solved by Patterson
methods, and extension of the model was accomplished by
direct methods applied to difference structure factors using
the program DIRDIF.28 The positional and anisotropic dis-
placement parameters for the non-hydrogen atoms were
refined. The unit cell contains one molecule of CDCl3, which
is disordered over two positions. Final refinement on F2 carried
out by full-matrix least-squares techniques converged at Rw(F2)
) 0.0673 for 10 560 reflections and R(F) ) 0.0275 for 9320
reflections with Fo g 4.0 σ(Fo) and 677 parameters.
For 5, a crystal with approximate dimensions 0.30 × 0.40
× 0.50 mm was used for data collection on an Enraf-Nonius
CAD-4 diffractometer with graphite-monochromated Mo KR
radiation and ω-2θ scan. Corrections for Lorentz and polar-
ization effects were applied. Absorption correction was per-
formed with the program PLATON,29 following the method of
North et al.30 The structure was solved by the PATTY option
of the DIRDIF99 program system.28 The hydrogen atoms were
calculated, and a riding model was used during refinement.
Full-matrix least-squares refinement on F, anisotropic for the
non-hydrogen atoms and isotropic for the hydrogen atoms, was
used. A final difference Fourier map revealed a residual
electron density between -1.56 and 2.04 e Å-3 in the vicinity
of the Pt. Scattering factors were taken from Cromer and
Mann and from the International Tables of Crystallography.31
The anomalous scattering of Pt, P, and Cl was taken into
account.32 All calculations were performed with XTAL3.7,33
unless stated otherwise.
1H NMR (400 MHz, CDCl3, ppm): δ 7.83 (br s, 8H, PPh2),
7.51 (dd, 2H, 1J ) 5.2 Hz, 2J ) 2.8 Hz), 7.44 (dd, 2H, 1J ) 5.2
2
1
1
Hz, J ) 2.8 Hz), 7.23 (dd, 12H, PPh2, J ) 8.8 Hz, J ) 2.4
1
2
Hz), 6.57 (dd, 2H, Ph, J ) 8.4 Hz, J ) 4.8 Hz), 6.35 (d, 2H,
Ph, 1J ) 9.2 Hz), 5.64 (d, 2H, Ph), 3.61 (s, 6H, OCH3). 31P{1H}
NMR (162 MHz, CDCl3, ppm) δ 9.9 (s, JPt-P ) 3810 Hz). Anal.
Calcd for C44H36Cl2O2PtP2: C, 57.15; H, 3.92. Found: C, 57.25;
H, 4.06.
cis-[PtCl2(2)] (5). PtCl2(cod) (5.0 mg, 13.5 µmol) together
with ligand 2 (8.5 mg, 13.5 µmol) were dissolved in 1 mL of
CH2Cl2, and the solution was stirred for 1 h at room temper-
ature. After evaporation of the solvent in vacuo, 5 was obtained
as a white powder. Single crystals, suitable for X-ray analysis,
could be obtained by slow diffusion of Et2O into a CDCl3
solution in an NMR tube.
2
1H NMR (500 MHz, CDCl3, ppm): δ 7.59 (tq, 4H, J ) 7.5
The CCDC files 270182 and 275889 contain the supplemen-
tary crystallographic data for this paper. These data can be
obtained free of charge via www.ccdc.cam.ac.uk/conts/retriev-
ing.html (or from the Cambridge Crystallographic Data Cen-
tre, 12 Union Road, Cambridge CB2 1EZ, U.K.; fax (+44) 1223-
336-033 and email deposit@ccdc.cam.uk).
Hz, 3J ) 1.5 Hz), 7.44 (tq, 4H, 2J ) 7.5 Hz, 3J ) 1.5 Hz), 7.38
2
3
2
(dt, 4H, J ) 7.5 Hz, J ) 2.5 Hz), 7.28 (dd, 2H, J ) 5.5 Hz,
3J ) 3.5 Hz), 7.21 (m, 12H), 7.08 (dt, 4H, 2J ) 7.5 Hz, 3J ) 1.5
Hz), 6.87 (dd, 2H, 2J ) 5.5 Hz, 3J ) 3.5 Hz). 31P{1H} NMR
(121 MHz, CDCl3, ppm) δ 8.2 (s, JPt-P ) 3712 Hz). Anal. Calcd
for C42H32Cl2PtP2: C, 58.34; H, 3.73. Found: C, 58.37; H, 3.64.
Hydroformylation of 1-Octene. The appropriate cis-
[PtCl2L] complex (13.7 µmol) was dissolved in 10 mL of
dichloromethane and then added to an equimolar amount of
SnCl2 (2.6 mg, 13.7 µmol). After 2 h a yellow solution
containing the platinum/tin complex was obtained. The auto-
clave was pretreated with three consecutive vacuum-argon
cycles prior to use. The CH2Cl2 solution containing the
preformed platinum/tin complex was transferred to the auto-
clave by syringe. An additional 10 mL of dichloromethane was
added to the autoclave to get a total volume of 20 mL. The
autoclave was pressurized to 40 bar and heated to 60 °C. After
1 h of preformation a mixture of the octene (3.0 mL, 19.0 mmol)
and n-decane (1.0 mL, 5.1 mmol), dissolved in 6.0 mL of
dichloromethane, was added at the desired pressure and
temperature. The pressure was kept constant by using a gas
line with a pressure regulator. After the reaction the autoclave
was cooled to room temperature with an ice bath. After the
autoclave was vented, a sample was taken from it and
analyzed by GC to determine conversion, chemoselectivity, and
regioselectivity.
Acknowledgment. Financial support by the Na-
tional Research School Combination for Catalysis (NRSC-
C) and The Netherlands Organization for Scientific
Research (NWO) is gratefully acknowledged. Umicor AG
& Co. KG is thanked for a generous gift of PtCl2. Prof.
Hiemstra is thanked for donation of dinonaflate B.
Supporting Information Available: X-ray crystallo-
graphic files (in CIF format) for Pt complexes 4 and 5. This
material is available free of charge via the Internet at
http://pubs.acs.org.
OM050575A
(28) Beurskens, P. T.; Beurskens, G.; de Gelder, R.; Garc´ıa-Granda,
S.; Gould, R. O.; Israe¨l, R.; Smits, J. M. M. The DIRDIF-99 Program
System; University of Nijmegen, Nijmegen, The Netherlands, 1999.
(29) Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7.
(30) North, A. C. T., Phillips, D. C.; Mathews, S. F. Acta Crystallogr.
1968, A26, 351-359.
(31) Cromer, D. T.; Mann, J. B. Acta Crystallogr. 1968, A24, 321-
324. International Tables for X-ray Crystallography; Kynoch Press:
Birmingham, U.K., 1974; Vol. IV, p 55.
Crystal Structure Determination. The data for 4 were
collected on a Bruker SMART APEX CCD instrument. Data
integration and global cell refinement were performed with
the program SAINT. Intensity data were corrected for Lorentz
(32) Cromer, D. T.; Liberman, D. J. Chem. Phys. 1970, 53, 1891.
(33) Hall, S. R., du Boulay, D. J.; Olthof-Hazekamp, R. XTAL3.7
System; University of Western Australia, Australia, 2000.