Synthesis, characterization, and reactivity of 1,1′-bis(diphenylphosphino)osmocene: Palladium(II) complexes and their use as catalysts in the methoxycarbonylation of olefins

Article abstract of DOI:10.1021/om0208366

The synthesis, characterization, and reactivity of 1,1′-bis(diphenylphosphino)osmocene (dppo) were discussed. It was found that dppo was prepared using lithiation of osmocene on n-hexane/diethyl ether, followed by reaction with chlorodiphenylphosphine. It forms a variety palladium(II) complexes showing either the κ²P,P or κ³Os,P,P bonding mode. The complex [Pd(OTs)(dppo)OTs (OTs = p-toluenesulfonate) was found to an effective precursor for the selective methoxycarbonylation of ethylene to methyl propanoate and of styrene to a mixture of methyl 3-phenylpropanoate and methyl 2-phenylpropanoate.

Full text of DOI:10.1021/om0208366

Organometallics 2003, 22, 913-915
913
Syn th esis, Ch a r a cter iza tion , a n d Rea ctivity of
1,1′-Bis(d ip h en ylp h osp h in o)osm ocen e: P a lla d iu m (II)
Com p lexes a n d Th eir Use a s Ca ta lysts in th e
Meth oxyca r bon yla tion of Olefin s
Oleg V. Gusev,* Alexander M. Kalsin, Pavel V. Petrovskii, and
Konstantin A. Lyssenko
N. Nesmeyanov Institute of Organoelement Compounds of the Russian Academy of Sciences,
Vavilov St. 28, 119991 Moscow, Russian Federation
Yuri F. Oprunenko
Department of Chemistry, M. V. Lomonosov Moscow State University,
Leninskie Gory, 119899 Moscow, Russian Federation
Claudio Bianchini,* Andrea Meli, and Werner Oberhauser
Istituto di Chimica dei Composti Organometallici (ICCOM-CNR),
Via J . Nardi 39, 50132 Firenze, Italy
Received October 7, 2002
Summary: The new ligand 1,1′-bis(diphenylphosphino)-
osmocene (dppo) forms a variety of palladium(II) com-
plexes showing either the κ2P,P or κ3Os,P,P bonding
dppr2b using comparable procedures, which reflects the
lower propensity to metalation of osmocene as compared
to ferrocene and ruthenocene.3,4
mode. The complex [Pd(OTs)(dppo)]OTs (OTs
)
The plain reactions of dppo with PdCl2(PhCN)2 and
PdCl(Me)(cod) gave PdCl2(dppo) (1) and PdCl(Me)(dppo)
(2), respectively (Scheme 1). Complexes 1 and 2 are key
compounds to enter the organometallic chemistry of the
Pd-dppo system by treatment with halide scavengers.
Silver tosylate rapidly and quantitatively transformed
1 in CH2Cl2 into the tosylate adduct [Pd(OTs)(dppo)]-
OTs (3), while silver triflate gave [Pd(NCMe)(dppo)]-
(OTf)2 (4) upon reaction in CH2Cl2/MeCN. Both com-
pounds contain a tridentate (κ3Os,P,P) dppo ligand as
a result of the replacement of the strong chloride donors
by relatively weak ligands such as H2O and MeCN. The
osmium-centered e2g electron density apparently com-
petes for coordination with a second molecule of either
water or acetonitrile. The removal of the chloride ligand
with NaBAr′4 from 2 in CH2Cl2 generated the κ3-dppo
complex [Pd(Me)(dppo)]BAr′4 (5), which was converted
into the acyl derivative [Pd(COMe)(dppo)]BAr′4 (6) by
reaction with CO.
Both dppo and its Pd(II) complexes were unambigu-
ously identified by multinuclear NMR spectroscopy that,
inter alia, provided a simple diagnostic tool for distin-
guishing the κ2P,P and κ3Os,P,P coordination modes of
dppo. Indeed, as previously observed for Pd(II) com-
plexes with dppf and dppf-related ligands,5-7 the in-
tramolecular formation of MfPd bonds causes a re-
markable high-field shift of the phosphorus resonance
as compared to κ2P,P derivatives. As an example, the
p-toluenesulfonate) is an effective catalyst precursor for
the selective methoxycarbonylation of ethylene to methyl
propanoate and of styrene to a mixture of methyl
3-phenylpropanoate and methyl 2-phenylpropanoate.
1,1′-Bis(diphenylphosphino)ferrocene1 (dppf) and 1,1′-
bis(diphenylphosphino)ruthenocene2 (dppr) form stable
complexes with a large variety of late transition metals
and, as such, have manifold applications in organome-
tallic chemistry and homogeneous catalysis. Since a
relevant role in determining the chemistry and stere-
ochemistry of the resultant metal complexes is played
by the sandwiched metal, we decided to study the
synthetic feasibility of the missing compound along the
iron triad, i.e., 1,1′-bis(diphenylphosphino)osmocene
(dppo), to complete the series and possibly establish a
reactivity trend. In this communication, we present a
brief account of our successful attempt to prepare dppo
and outline the great potential of this potentially
tridentate ligand in homogeneous catalysis.
dppo was prepared via lithiation of osmocene in
n-hexane/diethyl ether, followed by reaction with chlo-
rodiphenylphosphine. The yields were acceptable (25-
30%), yet lower than those reported for both dppf3 and
(1) (a) Gan, K.-S.; Hor, T. S. A. In Ferrocenes: Homogeneous
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10.1021/om0208366 CCC: $25.00 © 2003 American Chemical Society
Publication on Web 01/31/2003

914 Organometallics, Vol. 22, No. 5, 2003
Sch em e 1. Syn th esis of d p p o a n d P a lla d iu m (II) Com p lexesa
Communications
a
Legend: (i) nBuLi/TMEDA; (ii) PPh2Cl. Abbreviations: Ar′ ) 3,5-(CF3)2C6H3; OTf ) trifluoromethanesulfonate; OTs )
p-toluenesulfonate.
31P{1H} NMR spectrum of 4 shows a singlet at -18.3
ppm for the two magnetically equivalent P nuclei that
resonate at 37.9 ppm in the dichloride precursor 1. The
presence of Os-Pd bonds in 3-6 can also be inferred
by the large chemical shift difference between the R-
and â-hydrogen/carbon atoms of the cyclopentadienyl
rings as compared to κ2P,P complexes.5-7 A single-
crystal X-ray analysis removed any residual doubt, if
any, regarding the presence of a Os-Pd bond in 4‚2CH2-
Cl2. An ORTEP drawing of the complex cation is
provided in Figure 1.8 The coordination geometry around
palladium can be described as slightly distorted square
planar with trans phosphorus atoms (P(1)-Pd(1)-P(2)
) 164.9(1)°). Similar angles have been reported for [Pd-
(PPh3)(dppf)](BF4)2 and [Pd(Me)(dtpf)]OTf7b (dtpf )
5
1,1′-bis(di-tert-butylphosphino)ferrocene). The coordina-
tion polyhedron of the palladium center is completed
by osmium and an η1-N MeCN ligand. The Os-Pd
distance (2.840(1) Å) is consistent with a strong bonding
interaction and is apparently responsible for the tilting
of the Cp rings outward from the palladium atom by
28.2°. The Cp rings are eclipsed, which is unusual for
palladium complexes with either dppf or dppr.1-3
The formation of stable Pd-methyl and Pd-acyl
compounds anticipated the potential of dppo-Pd(II)
complexes as catalyst precursors for the carbonylation
of olefins.6,9 Indeed, a study of the methoxycarbonylation
of ethene has revealed that the tosylate complex 3 is
an effective catalyst for the selective production of
methyl propanoate (Scheme 2a).10 The remarkable
selectivity exhibited by 3 contrasts dramatically with
that of the dppf precursor [Pd(H2O)2(dppf)](OTs)2, which,
under comparable reaction conditions, produces various
low-molecular-weight oxygenates spanning from methyl
propanoate to alternating polyketones.6 Preliminary
studies of ethene methoxycarbonylation by palladium-
F igu r e 1. ORTEP drawing of 4‚2CH2Cl2. Thermal el-
lipsoids are drawn at the 50% probability level. The OTf
anion is omitted for clarity. Select bond lengths (a) and
angles (deg): Pd-P1 ) 2.259(3); Pd-P2 ) 2.272(3); Pd-
Os ) 2.840(1); Pd-N ) 1.885(11); P1-Pd-P2 ) 164.87-
(14); Os-Pd-N ) 179.1(3).
Sch em e 2. Meth oxyca r bon yla tion of Eth en e (a )
a n d Styr en e (b) w ith 3 a s P r eca ta lysta
(7) (a) Zuideveld, M. A.; Swennenhuis, B. H. G.; Kamer, P. C. J .;
van Leeuwen, P. W. N. M. J . Organomet. Chem. 2001, 637, 805. (b)
Zuideveld, M. A.; Swennenhuis, B. H. G.; Boele, M. D. K.; Guari, Y.;
van Strijdonck, G. P. F.; Reek, J . N. H.; Kamer, P. C. J .; Goubitz, K.;
Fraanje, J .; Lutz, M.; Spek, A. L.; van Leeuwen, P. W. N. M. J . Chem.
Soc., Dalton Trans. 2002, 2308.
(8) Crystal data: C40H35Cl4F6NO6S2OsP2Pd, T ) 110(2) K, orthor-
hombic, space group Pca21, a ) 26.438(5) Å, b ) 16.967(3) Å, c )
10.272(2) Å, V ) 4608(1) Å3, Z ) 4, Dcalcd ) 1.880 g cm-3, µ ) 3.608
mm-1, F(000) ) 2544, 13 121 reflections, GOF ) 0.854, R indices (I >
2σ(I)) R1 ) 0.0490 and wR2 ) 0.0713.
(9) Beller, M.; Tafesh, A. M. In Applied Homogeneous Catalysis with
Organometallic Compounds; Cornils, B., Hermann, W. A., Eds.; Wiley-
VCH: Weinheim, Germany, 1996; p 187.
a
Conditions: (a) catalyst 0.01 mmol, 1:1 CO/C2H4, 600 psi
(constant pressure), TsOH 0.4 mmol, solvent 100 mL, 85 °C,
1 h; (b) catalyst 0.01 mmol, styrene 2 mmol, CO, 800 psi, TsOH
0.4 mmol, solvent 20 mL, 80 °C, 3 h. TOF is given in units of
mol of product ((mol of cat) h)-1
.
(II) catalysts modified with dppf, dppr, or dppo have
shown that the formation of dative M-Pd bonds (hence
of complexes with a trans arrangement of the phospho-
rus atoms) favors the selective production of methyl
(10) Robertson, R. A. M.; Cole-Hamilton, D. J . Coord. Chem. Rev.
2002, 225, 67.

Communications
Organometallics, Vol. 22, No. 5, 2003 915
propanoate, while the propensity to form M-P bonds
increases in the order Fe < Ru < Os.11
COOMe and protonolysis.13 Starting from Pd-H, both
A and B may form, depending on the insertion mech-
anism of styrene (both 1,2- and 2,1-modes are possible,
in fact), followed by CO insertion into a Pd-styryl bond
and termination by methanolysis.14b,16
Good selectivity was also exhibited in the carbonyla-
tion of styrene, which gave exclusively the saturated
esters methyl 3-phenylpropanoate (A) and methyl 2-phe-
nylpropanoate (B) (Scheme 2b).9,12-14 No comparison
with either dppf or dppr palladium complexes can be
made for the absence of appropriate reports in the
literature. Under the present experimental conditions,
both Pd-OMe and Pd-H catalysis initiators may
form.15 The former species will generate A via CO
insertion, followed by 2,1-insertion of styrene into Pd-
Ack n ow led gm en t. Thanks are due to the EC for
support under Contract No. HPRN-CT-2002-00196, to
a CNR-RAS bilateral agreement, to the Russian Foun-
dation for Basic Research (Grant Nos. 00-03-32855 and
01-03-06145), and to the Haldor Topsøe A/S.
Su p p or tin g In for m a tion Ava ila ble: Text giving syn-
thetic procedures for ligand and palladium complexes with full
spectroscopic and elemental characterization data and tables
of bond lengths and angles and positional and thermal
parameters for the complex 4‚2CH2Cl2. This material is
available free of charge via the Internet at http://pubs.acs.org.
(11) Bianchini, C.; Meli, A.; Oberhauser, W. Manuscript in prepara-
tion.
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Bru¨ggeller, P.; Stampfl, T. J . Chem. Soc., Dalton Trans. 2001, 690.
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OM0208366
(15) Milstein, D. Acc. Chem. Res. 1988, 212, 428.
(16) Tooze, R. P.; Whiston, K.; Molyan, V.; Taylor, M. J .; Wilson, N.
W. J . Chem. Soc., Dalton Trans. 2000, 3441.