Unusual hydrogenation of fumarate anion followed by metal-carbon bond formation: Synthesis and characterization of two metallochelates

Article abstract of DOI:10.1021/om800341p

The treatment of [M(dppf)(H₂O)₂](OTf)₂ (dppf =1,1′-bis(diphenylphosphino)ferrocene; M = Pd, Pt) with 1 equiv of disodium fumarate in methanol medium showed an unusual hydrogenation of the ethylenic bond followed by the formation of metallochelates linking M through one of the carboxylates and the β-carbon with respect to COO^-. Despite the possibility of formation of a [2 + 2] or [4 + 4] self-assembled macrocycle, the reduction of fumarate to succinate, and in particular the linking through the β-carbon, is unique since a similar treatment using disodium succinate instead of disodium fumarate yielded an expected metallochelate where both the carboxylates were coordinated to the square-planar metal.

Full text of DOI:10.1021/om800341p

3806
Organometallics 2008, 27, 3806–3810
Unusual Hydrogenation of Fumarate Anion Followed by
Metal-Carbon Bond Formation: Synthesis and Characterization of
Two Metallochelates
Arun Kumar Bar, Rajesh Chakrabarty, and Partha Sarathi Mukherjee*
Inorganic and Physical Chemistry Department, Indian Institute of Science, Bangalore-560012, India
ReceiVed April 16, 2008
The treatment of [M(dppf)(H2O)2](OTf)2 (dppf )1,1′-bis(diphenylphosphino)ferrocene; M ) Pd, Pt)
with 1 equiv of disodium fumarate in methanol medium showed an unusual hydrogenation of the ethylenic
bond followed by the formation of metallochelates linking M through one of the carboxylates and the
ꢀ-carbon with respect to COO-. Despite the possibility of formation of a [2 + 2] or [4 + 4] self-
assembled macrocycle, the reduction of fumarate to succinate, and in particular the linking through the
ꢀ-carbon, is unique since a similar treatment using disodium succinate instead of disodium fumarate
yielded an expected metallochelate where both the carboxylates were coordinated to the square-planar
metal.
The coordination-driven self-assembly of appropriate building
Because of the hard basic nature of the carboxylate oxygen, a
Pt- or Pd-O bonding interaction is not the right choice for
constructing supramolecules of these metal ions, due to an
unfavorable hard-soft combination. However, Pt-O bond
driven finite metallamacrocycles are rare, and only a few
examples3 are known where oxygen donor linkers have been
introduced to form neutral Pt ensembles. We have also recently
utilized a Pd-O bonding interaction as a driving force for
designing a discrete assembly of finite shape and size.4
Surprisingly, no example is known where an R,ꢀ-unsaturated
dicarboxylate has been used in combination with a cis-blocked
90° Pd/Pt acceptor, though such acids have been used in
conjunction other Pt(II) acceptors.3c,d This prompted us to see
whether the use of an R,ꢀ-unsaturated dicarboxylate in conjunc-
tion with a cis-blocked 90° Pd/Pt acceptor could lead to
dicarboxylate-bridged neutral assemblies. As demanded by their
geometry, interaction of a cis-blocked 90° Pd/Pt acceptor with
fumarate, an R,ꢀ-unsaturated dicarboxylate, should provide
either a [4 + 4] molecular square or a [2 + 2] dimer (Scheme
1). Much to our surprise, the above reaction led to an unusual
reduction of the C-C double bond followed by coordination
of the ꢀ-carbon (with respect to the carboxylate) to Pd and Pt.
We herein report the isolation of two new palladium and
platinum chelates (2a,b) of the general formula [M(dppf)-
(C4H4O4)] (where M ) Pd for 2a and M ) Pt for 2b).
units to form discrete supramolecular entities has grown
immensely in the past few years.1 Wide arrays of molecular
architectures with various aesthetically pleasing shapes, sizes,
and symmetries have been reported. Many of these discrete
supramolecular entities are increasingly finding application in
various ways, such as guest encapsulation, photo- and electro-
chemical sensing, and cavity-driven catalysis.2 Pt(II)- and Pd(II)-
based molecular units with pyridyl or nitrogen donor linkers
are most extensively used for the design of such nanostructures,
because of their rigid square-planar coordination environments.
* To whom correspondence should be addressed. Tel: 91-80-2293-3352.
Fax: 91-80-2360-1552. E-mail: psm@ipc.iisc.ernet.in.
(1) (a) Leininger, S.; Olenyuk, B.; Stang, P. J. Chem. ReV. 2000, 100,
853. (b) Seidel, S. R.; Stang, P. J. Acc. Chem. Res. 2002, 35, 972. (c)
Swiegers, G. F.; Malefetse, T. J. Coord. Chem. ReV. 2002, 225, 91. (d)
Fujita, M. Chem. Soc. ReV. 1998, 27, 417. (e) Vickers, M. S.; Beer, P. D.
Chem. Soc. ReV. 2007, 2, 211. (f) Nehete, U. N.; Anantharaman, G.;
Chandrasekhar, V.; Murugavel, R.; Roesky, H. W.; Vidovic, D.; Magull,
J.; Samwer, K.; Sass, B. J. Angew. Chem., Int. Ed. 2004, 43, 3832. (g)
Maurizot, V.; Yoshizawa, M.; Kawano, M.; Fujita, M. Dalton Trans. 2006,
2750. (h) Pathak, B.; Pandian, S.; Hosmane, N. S.; Jemmis, E. D. J. Am.
Chem. Soc. 2006, 128, 10915. (i) Fiedler, D.; Leung, D. H.; Bergman, R. G.;
Raymond, K. N. Acc. Chem. Res. 2005, 38, 351. (j) Chai, J.; Jancik, V.;
Singh, S.; Zhu, H.; He, C.; Roesky, H. W.; Schmidt, H.-G.; Noltemeyer,
M.; Hosmane, N. S. J. Am. Chem. Soc. 2005, 127, 7521. (k) Ghosh, S.;
Mukherjee, P. S. Organometallics 2008, 27, 316. (l) Leung, D. H.; Bergman,
R. G.; Raymond, K. N. J. Am. Chem. Soc. 2008, 130, 2798. (m) Davis,
A. V.; Fiedler, D.; Ziegler, M.; Terpin, A.; Raymond, K. N. J. Am. Chem.
Soc. 2007, 129, 15354.
(2) (a) Kryschenko, Y. K.; Seidel, S. R.; Arif, A. M.; Stang, P. J. J. Am.
Chem. Soc. 2003, 125, 5193. (b) Fujita, M.; Tominaga, M.; Hori, A.;
Therrien, B. Acc. Chem. Res. 2005, 38, 371. (c) Oin, Z.; Jennings, M. C.;
Puddephatt, R. J. Chem. Commun. 2001, 2676. (d) Leininger, S.; Fan, J.;
Schmitz, M.; Stang, P. J. Proc. Nalt. Acad. Sci. U.S.A. 2000, 97, 1380. (e)
Stang, P. J.; Olenyuk, B. Acc. Chem. Res. 1997, 30, 502. (f) Amijs, C. H. M.;
van Klink, G. P. M.; Koten, G. Dalton Trans. 2006, 308. (g) Yamaguchi,
T.; Tashiro, S.; Tominaga, M.; Kawano, M.; Ozeki, T.; Fujita, M. Chem.
Asian J. 2007, 2, 468. (h) Tashiro, S.; Tominaga, M.; Yamaguchi, Y.; Kato,
K.; Fujita, M. Angew. Chem., Int. Ed. 2006, 45, 241. (i) Goshe, A. J.; Steele,
I. M.; Ceccarelli, C.; Rheingold, A. L.; Bosnich, B. Proc. Natl. Acad. Sci.
U.S.A. 2002, 99, 4823. (j) Fiedler, D.; van Halbeek, H.; Bergman, R. G.;
Raymond, K. N. J. Am. Chem. Soc. 2006, 128, 10240. (k) Shin, R. Y. C.;
Tan, G. K.; Koh, L. L.; Vittal, J. J.; Goh, L. Y.; Webster, R. D.
Organometallics 2005, 24, 539. (l) Mondal, K. C.; Song, Y.; Mukherjee,
P. S. Inorg. Chem. 2007, 46, 9736. (m) Ghosh, S.; Mukherjee, P. S. Dalton
Trans. 2007, 2542. (n) Yoshizawa, M.; Tamura, M.; Fujita, M. Science
2006, 312, 251.
Results and Discussion
The 1:1 molar reaction of a methanolic solution of [Pd-
(dppf)(H2O)2](OTf)2 (1a; dppf ) 1,1′-bis(diphenylphosphino)-
ferrocene) with disodium fumarate afforded an orange complex
(3) (a) Das, N.; Ghosh, A.; Singh, O. M.; Stang, P. J. Org. Lett. 2006,
8, 1701. (b) Das, N.; Ghosh, A.; Arif, A. M.; Stang, P. J. Inorg. Chem.
2005, 44, 7130. (c) Mukherjee, P. S.; Das, N.; Kryschenko, Y. K.; Arif,
A. M.; Stang, P. J. J. Am. Chem. Soc. 2004, 126, 2464. (d) Das, N.;
Mukherjee, P. S.; Arif, A. M.; Stang, P. J. J. Am. Chem. Soc. 2003, 125,
13950. (e) Bianchini, C.; Laschi, F.; Meli, A.; Peruzzini, M.; Zanello, P.;
Frediani, P. Organometallics 1988, 7, 2575.
(4) (a) Ghosh, S.; Turner, D.; Batten, S. R.; Mukherjee, P. S. Dalton
Trans. 2007, 1869. (b) Al-Allaf, T. A. K.; Schmidt, H.; Merzwiler, K.;
Wanger, C.; Steinborn, D. J. Organomet. Chem. 2003, 678, 48.
10.1021/om800341p CCC: $40.75
2008 American Chemical Society
Publication on Web 07/09/2008

Hydrogenation of Fumarate Anion
Organometallics, Vol. 27, No. 15, 2008 3807
Scheme 1. Formation of complexes 2a & 2b and other possible macrocycles
(2a) (Scheme 1). The expected geometry of the product of a
1:1 molar reaction of a 90° acceptor and a rigid dicarboxylate
with an sp3-hybridized donor atom is a [2 + 2]-assembled
rhomboid or a [4 + 4]-assembled molecular square (Scheme
1). Surprisingly, in the presently described system, the treatment
of a cis-protected 90° Pd(II) center with a fumarate linker
resulted in the reduction of the ethylenic moiety of fumarate
followed by coordination to the Pd(II) center through one
carboxylate oxygen and the ꢀ-carbon with respect to the
carboxylate to yield the unique neutral mononuclear assembly
2a. In an earlier report, reduction of the C-C double bond in
maleate was found and, in that case, such conversion was
triggered by a change of the oxidation state of the metal center
(Rh(I)/Rh(III)) in a rhodium-tripodal phosphine complex.3e
Earlier reactions of cis-protected [M(dppf)Cl2] (M ) Pt, Pd)
with potassium salts of dicarboxylic acids such as oxalic acid,
malonic acid, and 1,1-cyclobutanedicarboxylic acid in H2O have
led to the binding of the carboxylate oxygens to the metal
center.4 However, in the present case, despite the possibility of
binding through both the carboxylate oxygens in a κ2O,O
fashion, the formation of a five-membered chelate ring through
Single crystals suitable for structure determination were
obtained by slow diffusion of ether into the nitromethane
solution of the complex. An X-ray structural analysis of the
crystal of 2a (Figure 1) revealed that the C-C double bond in
the fumarate ligand has indeed undergone an unexpected
reduction followed by Pd-C bond formation. The crystal-
lographic parameters of 2a are presented in Table 1, while the
selected bond distances and angles are given in Table 2. The
carboxylate oxygen on one end of the fumarate ion has
coordinated through the carboxylate oxygen as expected, while
the other end has, to our surprise, coordinated through the carbon
-
atom ꢀ to the CO2 group, forming a five-membered chelate
ring with the concomitant reduction of the olefinic double bond.
Within each molecule of the complex 2a, the Pd(II) atom is
coordinated to two phosphorus atoms from dppf, an oxygen
atom from the carboxylate group on one end of the fumarate,
and the carbon atom adjacent to the free -COOH group at the
other end, completing the distorted-square-planar geometry
around Pd(II). The bond distances around the Pd(II) ion are
typical, with Pd-P distances in the range 2.380-2.242,Å while
the Pd-O and Pd-C bond distances are 2.059 and 2.098 Å,
respectively. The C(36)-C(37) distance of 1.513 Å is typical
of a single bond, indicating that it has indeed been reduced to
a C-C single bond. The angle around the “CP2O” coordination
sphere of palladium reflects the considerably distorted nature
of the square-planar geometry. An inspection of the packing
diagram of complex 2a (Supporting Information) shows that
the complexes are hydrogen-bonded (O(4)-H(38) · · · O(3)i )
2.635(4) Å; (i) -x + 1, -y + 1, -z + 2) through the free
carboxylate group to form a dimer.
-
the oxygen of the CO2 group and the carbon atom ꢀ to the
-
CO2 group is intriguing.
The complex 2a is air-stable and soluble in polar organic
solvents such as nitromethane, chloroform, etc. The 31P{1H}
NMR spectrum of 2a recorded in CDCl3 displays two sharp
singlets of equal intensities at 35.79 and 18.57 ppm. The
appearance of two 31P signals is indicative of the presence of
two nonequivalent phosphorus nuclei. The upfield shift of the
signals relative to the precursor 1a is an indication of ligand to
1
metal coordination. Moreover, the H NMR spectrum of 2a
As the hydrogenated form of fumaric acid is succinic acid, it
was of our interest to see whether disodium succinate also binds
in a similar fashion or acts as a chelating dicarboxylate like
oxalate, malonate, etc. Interestingly, the treatment of disodium
showed the disappearance of the ethylenic protons of fumarate
and the appearance of new proton signals in the alkyl region
(Supporting Information).
Figure 1. ORTEP representations (30% probability ellipsoids) for the complexes [Pd(dppf)(C4H4O3)] (2a) and [Pt(dppf)(C4H4O3)] (2b).
Carbon atoms of the phenyl and cp rings were not labeled, for the sake of clarity.

3808 Organometallics, Vol. 27, No. 15, 2008
Bar et al.
Table 1. Crystallographic Data and Refinement Parameters of 2a,b
2a
2b
formula
Mr
C38H32FeO4P2Pd
776.83
C38H32FeO4P2Pt
865.52
cryst syst
space group
Τ, Κ
triclinic
P1
293
triclinic
P1
293
j
j
λ(Mo KR), Å
0.710 73
10.647(3)
10.747(3)
15.536(5)
85.044(5)
72.925(5)
72.852(5)
1623.8(8)
2
0.710 73
10.562(3)
10.742(3)
15.340(4)
84.819(6)
72.969(6)
73.107(5)
1592.3(7)
2
1.805
4.986
9044
5528
a, Å
b, Å
c, Å
R, deg
ꢀ, deg
γ, deg
V, Å3
Z
Fcalcd, g cm-3
µ(Mo KR), mm-1
no. of collected rflns
no. of unique rflns
Rint
1.589
1.140
15 720
5706
0.0342
0.0354
0.0679
1.071
0.0719
0.1491
0.3901
1.118
R1a
wR2a
GOF on F2
2
2 2
a R1 ) ∑||Fo| - |Fc||/∑|Fo|. wR2 ) {∑[w(Fo - Fc ) ]/∑[w(Fo2)2]}1/2
,
where w ) 1/[σ2(Fo2) + (aP)2 + bP] and P ) [2Fc + Max(Fo2,0)]/3.
2
Figure 2. 31P NMR of the dicarboxylate-bound mononuclear
complex [Pt(dppf)(OOCCH2CH2COO)] (2c).
Table 2. Selected Bond Distances (Å) and Angles (deg) for 2a,b
Compound 2a
Pd(1)-O(1) 2.059(2) Pd(1)-P(1) 2.242(1) Pd(1)-P(2) 2.380(2)
triplet at 3.38 and 3.56 ppm due to -CH and -CH2 fragments,
respectively, indicates the reduction of the carbon-carbon
double bond of the fumarate moiety (Figure 3).
Pd(1)-C(37) 2.098(4) C(36)-C(37) 1.513(5)
O(1)-Pd(1)-C(37)
C(37)-Pd(1)-P(1)
C(37)-Pd(1)-P(2)
82.02(13)
93.48(11)
165.60(11)
O(1)-Pd(1)-P(1)
O(1)-Pd(1)-P(2)
P(1)-Pd(1)-P(2)
169.53(8)
89.26(8)
96.92(4)
It is interesting to note here that the reaction of [Pd(dppf)-
(H2O)2](OTf)2 (1a) with fumaric acid in the presence of
triethylamine as base resulted in the isolation of the orange
complex 3. The characterizations5 (1H NMR, 31P NMR, and
X-ray crystallography) of complex 3 show it to be Ph2P(O)-
C5H4FeC5H4P(O)PPh2 (dppfO2). A similar oxidation of dppf
to dppfO2 catalyzed by palladium has been reported earlier.6
Compound 2b
Pt(1)-C(35) 2.11(3) Pt(1)-P(1) 2.232(8)
Pt(1)-O(1) 2.04(3)
Pt(1)-P(2) 2.336(8) C(37)-C(38) 1.42(5)
O(1)-Pt(1)-C(35)
C(35)-Pt(1)-P(1)
C(35)-Pt(1)-P(2)
82.3(9)
93.6(4)
166.3(6)
O(1)-Pt(1)-P(1)
O(1)-Pt(1)-P(2)
P(1)-Pt(1)-P(2)
170.1(8)
88.7(8)
96.8(3)
Although the mechanistic pathway for the observed trans-
formation is not clear to us, the speculative sequences given in
Scheme 3 seem to be probable. The initial step involves the
coordination of the fumarate (A) to the complex 1, followed
by an intermediate where the olefinic double bond binds to the
metal center in an η2 fashion (B). In the next step a hydride ion
from methanol is shifted to the ꢀ-carbon (C) with in situ
generation of formaldehyde, formation of which was qualita-
tively confirmed by the appearance of an orange-yellow
precipitate upon addition of 2,4-dinitrophenylhydrazine (DNP)
solution to the reaction mixture. This indicates that the methanol
is the most probable source of hydride. Although such a
transformation is unprecedented, to the best of our knowledge,
platinum-mediated oxidation of methanol is documented in the
literaure.7
succinate with [Pt(dppf)(H2O)2](OTf)2 (1b) under identical
reaction conditions yielded a light brown product, which showed
a single peak in the 31P NMR spectrum (Figure 2).
Finally, mass spectrometric analysis confirmed the mono-
nuclear composition [Pt(dppf)(OOCCH2CH2COO)] (2c). NMR
and mass spectrometric analyses confirm the formation of a
mononuclear complex where Pt(II) is coordinated through both
of the carboxylates (Scheme 2). Hence, the coordination of the
ꢀ carbon to Pd was mediated by in situ hydrogenation.
To test the generality of such a transformation, we also reacted
[Pt(dppf)(H2O)2](OTf)2 (1b) with disodium fumarate under
similar conditions in methanol (Scheme 1). The reaction afforded
a yellowish orange complex (2b). The X-ray crystallographic
determination (Table 1) of the structure revealed a similar
reduction of the ethylenic moiety of fumarate, followed by the
linking of Pt(II) through one carboxylate and the ꢀ-carbon with
respect to this carboxylate (Figure 1). Platinum adopts a
distorted-square-planar geometry with Pt-P(av), Pt-O, and
Pt-C distances of 2.284, 2.04, and 2.11 Å, respectively. The
observed C-C bond distances are in good agreement with its
bond description. As demanded by the geometry of the complex
2b, two sharp singlets at 22.44 and 11.02 ppm for the
nonequivalent phosphorus atoms along with appropriate Pt
satellites were observed in the 31P NMR spectrum of 2b. In the
1H NMR spectrum of 2b, the appearance of a doublet and a
(5) Complex 3, Ph2P(O)C5H4FeC5H4P(O)PPh2 (dppfO2): to a acetone
solution of [Pd(dppf)(H2O)2](OTf)2 (1; 20.0 mg; 0.02 mmol) was added
fumaric acid (3.2 mg; 0.02 mmol). To this reaction mixture was added excess
Et3N, and this mixture was stirred for 4 h to give a brown precipitate. The
orange filtrate upon slow evaporation gave crystals of 3. Anal. Calcd: C,
69.64; H, 4.81. Found: C, 68.95; H, 4.21. 1H NMR (400 MHz, CDCl3,
ppm): 7.64-7.26 (m, 20H, Ph), 4.71-4.25 (m, 10H, cp). 31P{1H} NMR
(CDCl3, 121 MHz, ppm): 28.77 (s). Crystal data for compound 3:
C34H28FeO2P2.H2O, Mr ) 604.37, monoclinic, space group P21/c, a )
22.552(6) Å, b ) 10.590(3) Å, c ) 12.220(3) Å, ꢀ ) 95.930(5)°, V )
2902.7(13) Å3, Z ) 4, Fcalcd ) 1.383 Mg m-3, 24 852 reflections collected,
6856 unique reflections, Rint ) 0.0790, R1 ) 0.0735 and wR2 ) 0.1319.
(6) Grushin, V. V. Organometallics 2001, 20, 3950.
(7) Halder, S.; Drew, M. G. B.; Bhattacharya, S. Organometallics 2006,
25, 5969.

Hydrogenation of Fumarate Anion
Organometallics, Vol. 27, No. 15, 2008 3809
Scheme 2. Formation of 2b,c from the Starting Precursor 1a
removal of the solvent using a vacuum pump. The complexes
[M(dppf)(H2O)2](OTf)2 (M ) Pd (1a), Pt (1b)) were prepared by
following the reported procedures.8 1H and 31P NMR spectra were
recorded using a Bruker 400 MHz spectrometer. C, H, N analyses
were done using a Perkin-Elmer 2400 Series II CHNS/O analyzer.
1H NMR chemical shifts reported are referenced to TMS. 31P{1H}
chemical shifts are reported relative to an external, unlocked sample
of H3PO4 (δ 0.0 ppm).
X-ray Crystallographic Studies. The crystal data for 2a,b were
collected on a Bruker SMART APEX CCD diffractometer using
the SMART/SAINT software.9 X-ray-quality crystals were mounted
on a glass fiber with traces of viscous oil. Intensity data were
collected using graphite-monochromatized Mo KR radiation (0.7107
Å) at 293 K. The structures were solved by direct methods using
the SHELX-97 program10 incorporated in WinGX.11 Empirical
absorption corrections were applied with SADABS.12 All non-
hydrogen atoms were refined with anisotropic displacement coef-
ficients. Hydrogen atoms were assigned isotropic displacement
coefficients, U(H) ) 1.2[U(C)] or 1.5[U(C-methyl)], and their
In conclusion, our attempt to prepare a supramolecular
ensemble using a 90° ditopic acceptor and fumarate, an R,ꢀ-
unsaturated dicarboxylic acid, as linker led to the observation
of an unusual transformation of the fumarate ion, where it
chelates to the metal center with concomitant reduction of the
double bond. A similar treatment using the saturated form
(succinate) of fumarate yielded a metallacycle where the metal
is coordinated to both of the carboxylates in the usual fashion.
The present results represent the first report on the treatment of
a cis-blocked Pd/Pt-based 90° acceptor with an R,ꢀ-unsaturated
dicarboxylate and unusual reduction of the CdC bond followed
by the coordination of the metal through the ꢀ-carbon.
Experimental Section
Materials and Methods. All the materials used in this work
were obtained from commercial sources and used as supplied.
Disodium fumarate was prepared by neutralizing a methanolic
solution of fumaric acid with 2 equiv of NaOMe followed by
1
Figure 3. 31P (left) and H NMR (right) spectra of complex 2b in CDCl3.
Scheme 3. Probable Mechanism for the Transformation from 1 to 2

3810 Organometallics, Vol. 27, No. 15, 2008
Bar et al.
coordinates were allowed to ride on their respective carbons.
Structures were drawn using either ORTEP-3 for Windows13 or
PLUTON.14
Acknowledgment. We are grateful to the Department of
Science and Technology, New Delhi (Under Fast Track
Scheme for Young Scientists), and the Council of Scientific
and Industrial Research (CSIR), New Delhi, for financial
support. R.C. thanks the CSIR, New Delhi, for a research
fellowship.
[Pd(dppf)(C4H4O4)] (2a). To a methanolic solution of disodium
fumarate (3.2 mg; 0.02 mmol) was added a 1 mL solution of
[Pd(dppf)(H2O)2](OTf)2 (1a; 20.0 mg; 0.02 mmol) in methanol, and
this mixture was stirred at room temperature for 4 h. The solvent
was then evaporated under reduced pressure to yield a yellowish
solid. X-ray-quality crystals were obtained by slow diffusion of
diethyl ether into a nitromethane solution of the solid. Yield: 93%.
Anal. Calcd: C, 58.75; H, 4.15. Found: C, 58.42; H, 4.31. 31P{1H}
NMR (CDCl3, 121 MHz, ppm): 35.98 (s), 18.57 (s). 1H NMR (400
MHz, CDCl3, ppm): 7.81-7.25 (m, 20H, Ph), 4.66-3.32 (m, 10H,
cp), 3.42 (s, 2H, HR), 3.25 (t, 1H, Hꢀ).
Supporting Information Available: CIF files giving crystal-
lographic data for 2a,b and 3 and figures giving a packing
diagram of complex 2b and 31P and 1H NMR spectra of complex
2a. This material is available free of charge via the Internet at
http://pubs.acs.org.
OM800341P
[Pt(dppf)(C4H4O4)] (2b). Complex 2b was prepared in a manner
analogous to that for complex 2a, replacing [Pd(dppf)(H2O)2](OTf)2
with [Pt(dppf)(H2O)2](OTf)2. Yield: 89%. Anal. Calcd: C, 52.73;
H, 3.73. Found: C, 52.02; H, 4.01. 31P{1H} NMR (CDCl3, 121
MHz, ppm): 22.44 (s), 11.02 (s). 1H NMR (400 MHz, CDCl3, ppm):
7.85-7.38 (m, 20H, Ph), 4.88-4.52 (m, 10H, cp), 3.56 (s, 2H,
HR), 3.38 (s, 1H, Hꢀ).
(10) Sheldrick, G. M. SHELX-97, Program for the Solution and
Refinement of Crystal Structures; University of Go¨ttingen, Go¨ttingen,
Germany, 1998.
(11) Farrugia, L. J. WinGX: An Integrated System of Windows Programs
for the Solution, Refinement and Analysis for Single Crystal X-ray
Diffraction Data, version 1.65.04; Department of Chemistry, University of
Glasgow, Glasgow, U.K., 2003. Farrugia, L. J. J. Appl. Crystallogr. 1999,
32, 837.
(12) Sheldrick, G. M. SADABS, Bruker Nonius Area Detector Scaling
and Absorption Correction, version 2.05; University of Go¨ttingen, Go¨ttingen,
Germany, 1999.
(8) Stang, P. J.; Olenyuk, B.; Fan, J.; Arif, A. M. Organometallics 1996,
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