Supramolecular trans-coordinating phosphine ligands

Article abstract of DOI:10.1021/om050865r

We report a new urea-functionalized phosphorus ligand and palladium complexes thereof that self-associate by hydrogen bond formation. The solution studies of a urea-based phosphine ligand {m-[EtO-(CO)CH₂NH(CO)NH] C₆H₄PPh₂}, 1, and the palladium complex (1)₂PdMeCl, ₂, show that intermolecular and intramolecular hydrogen-bonding, respectively, is present between the urea hydrogens and the carbonyl of a second urea moiety. Introduction of NBu₄Cl to 2 results in the disruption of the self-association and the production of {[frares-(1₂Cl)PdMeCl]^-[NBu₄]⁺}, 3, with an anion-templated, bidentate phosphine ligand system. Although the ligands are hydrogen-bonding to the chloride anion, they remain in a trans configuration about the metal center. If another equivalent of 1 is added to 2, a zwitterionic palladium, methyl complex ligated by three phosphine ligands is produced and the chloride anion is abstracted from the metal center into the resulting tris-urea hydrogen-bonding pocket, generating [(1₃Cl)PdMe], 4. If at -80°C ¹³CO is introduced to 2 instead of 1, the chloride anion is once again abstracted into the bis-urea pocket and the zwitterionic CO-adduct trans-[(12Cl)Pd(¹³CO)(Me)], 5, results. However, upon warming to ambient temperature, CO migratory insertion occurs to generate the acetyl species and the chloride anion migrates back to the palladium center, regenerating a neutral complex. The analogous CO-adduct of 3 could not be produced since the urea pocket is already blocked with a chloride anion, stressing the subtle control the urea pocket exerts over the reactivity of the palladium center.

Full text of DOI:10.1021/om050865r

954
Organometallics 2006, 25, 954-960
Supramolecular trans-Coordinating Phosphine Ligands
Lisa K. Knight, Zoraida Freixa, Piet W. N. M. van Leeuwen, and Joost N. H. Reek*
Homogeneous Catalysis, Van’t Hoff Institute of Molecular Sciences, Nieuwe Achtergracht 166,
Amsterdam, 1018WV, The Netherlands
ReceiVed October 6, 2005
We report a new urea-functionalized phosphorus ligand and palladium complexes thereof that self-
associate by hydrogen bond formation. The solution studies of a urea-based phosphine ligand {m-[EtO-
(CO)CH2NH(CO)NH]C6H4PPh2}, 1, and the palladium complex (1)2PdMeCl, 2, show that intermolecular
and intramolecular hydrogen-bonding, respectively, is present between the urea hydrogens and the carbonyl
of a second urea moiety. Introduction of NBu4Cl to 2 results in the disruption of the self-association and
the production of {[trans-(12Cl)PdMeCl]-[NBu4]+}, 3, with an anion-templated, bidentate phosphine
ligand system. Although the ligands are hydrogen-bonding to the chloride anion, they remain in a trans
configuration about the metal center. If another equivalent of 1 is added to 2, a zwitterionic palladium
methyl complex ligated by three phosphine ligands is produced and the chloride anion is abstracted from
the metal center into the resulting tris-urea hydrogen-bonding pocket, generating [(13Cl)PdMe], 4. If at
-80 °C 13CO is introduced to 2 instead of 1, the chloride anion is once again abstracted into the bis-urea
pocket and the zwitterionic CO-adduct trans-[(12Cl)Pd(13CO)(Me)], 5, results. However, upon warming
to ambient temperature, CO migratory insertion occurs to generate the acetyl species and the chloride
anion migrates back to the palladium center, regenerating a neutral complex. The analogous CO-adduct
of 3 could not be produced since the urea pocket is already blocked with a chloride anion, stressing the
subtle control the urea pocket exerts over the reactivity of the palladium center.
drogenation of a trisubstituted cyclic enamide, which yielded
unprecedented selectivities.2e Breit has reported the production
of homo- and heterodimeric bidentate, cis-coordinated phosphine
ligands via hydrogen-bonding interactions, and these ligands
performed very well in the rhodium-catalyzed hydroformylation
of alkenes.4bc The number of hydrogen-bonded bidentate phos-
phine ligands is still small, and so far only cis-coordinated (up
to 120° for trigonal bipyramidal) metal complexes have been
reported. Even when traditional synthetic routes are employed,
there are still relatively few examples of trans-spanning biden-
tate phosphines that do not utilize an additional heteroatom (i.e.,
are in fact tridentate).5 These trans-spanning ligands allow for
the exploration of different coordination geometries about the
metal center to provide insight into known catalytic pathways
and the development of new catalysts with unique properties.
Herein we report the synthesis of a versatile urea-based ligand
system that provides the first examples of a hydrogen-bonded
trans-coordinating bidentate phosphine ligand system (Scheme
1).6 The bis-urea binding pocket also accommodates chloride
anions, which in turn controls the reactivity of the metal center.
Introduction
Ligand modification is the most important tool to control the
reactivity and selectivity of homogeneous transition metal
catalysts. Bidentate chelating ligands comprise an important
class of compounds employed to support these transition metal
catalysts.1 Traditionally bidentate ligands have been produced
by conventional synthetic routes, but recent results from our
group2 and others3,4 have shown that a new class of bidentate
ligands can be formed by a self-assembly process of two
monodentate species. We have used the zinc(II)porphyrin-
pyridyl interaction as an assembly motif to generate bidentate
phosphorus-based ligands and have shown that only 14 building
blocks were required to generate a library of 48 bidentate
phosphorus ligands that was successfully used in hydrofor-
mylation and asymmetric allylic alkylation.2 More recently this
approach was extended to asymmetric rhodium-catalyzed hy-
* To whom correspondence should be addressed. Tel: +31 20 525 6437.
Fax: +31 20 525 5604. E-mail: reek@science.uva.nl.
(1) (a) van Leeuwen, P. W. N. M.; Kamer, P. C.; Reek, J. N. H.; Dierkes,
P. Chem. ReV. 2000, 100, 2741. (b) Mecking, S. Coord. Chem. ReV. 2000,
203, 325. (c) Elsevier, C. J. Coord. Chem. ReV. 1999, 185-186, 809. (d)
Bo¨rner, A. Chirality 2001, 13, 625.
Results and Discussion
(2) (a) Slagt, V. F.; Ro¨der, M.; Kamer, P. C.; van Leeuwen, P. W. N.
M.; Reek, J. N. H. J. Am. Chem. Soc. 2004, 126, 4056. (b) Slagt, V. F.;
Kamer, P. C.; van Leeuwen, P. W. N. M.; Reek, J. N. H. Chem. Commun.
2003, 2474. (c) Slagt, V. F.; van Leeuwen, P. W. N. M.; Reek, J. N. H.
Angew. Chem., Int. Ed. 2003, 42, 5619. (d) Reek, J. N. H.; Ro¨der, M.;
Goudriaan, P. E.; Kamer, P. C.; van Leeuwen, P. W. N. M.; Slagt, V. F. J.
Organomet. Chem. 2005, 605, 4505-4516. (e) Jiang, X.-B.; Lefort, L.;
Goudriaan, P. E.; de Vries, A. H. M.; van Leeuwen, P. W. N. M.; de Vries,
J. G.; Reek, J. N. H. Angew. Chem., Int. Ed. 2005, 44, accepted, DOI:
10.1002/anie.200503663.
(3) For reviews see: (a) Wilkinson, M. J.; van Leeuwen, P. W. N. M.;
Reek, J. N. H. Org. Biomol. Chem. 2005, 3, 2371-2383. (b) Breit, B Angew.
Chem., Int. Ed. 2005, 44, 6816.
(4) (a) Takacs, J. M.; Reddy, D. S.; Moteki, S. A.; Wu, D.; Palencia, H.
J. Am. Chem. Soc. 2004, 126, 4494. (b) Breit, B.; Seiche, W. Angew. Chem.,
Int. Ed. 2005, 44, 1640. (c) Breit, B.; Seiche, W. J. Am. Chem. Soc. 2003,
125, 6608.
The urea-based phosphine ligand (m-Ph2PC6H4NH(CO)NH-
CH2(CO)OEt), 1, was synthesized by converting m-fluoroaniline
(5) (a) Freixa, Z.; Beentjes, M. S.; Batema, G. D.; Dieleman, C. B.; van
Strijdonck, G. P. F.; Reek, J. N. H.; Kamer, P. C.; Fraanje, J.; Goubitz, K.;
van Leeuwen, P. W. N. M. Angew. Chem., Int. Ed. 2003, 42, 1284. (b)
Bessel, C. A.; Aggarwal, P. Chem. ReV. 2001, 101, 1031, and references
therein. (c) Smith, R. C.; Bodner, C. R.; Earl, M. J.; Sears, N. C.; Hill, N.
E.; Bishop, L. M.; Sizemore, N.; Hehemann, D. T.; Bohn, J. J.; Protasiewicz,
J. D. J. Organomet. Chem. 2005, 690, 477. (d) Thomas, C. M.; Mafia, R.;
Therrien, B.; Rusanov, E.; Stœckli-Evans, H.; Su¨ss-Fink, G. Chem. Eur. J.
2002, 8, 3343.
(6) After submission of the manuscript an article appeared describing
similar ideas: Duckmanton, P. A.; Blake, A. J.; Love, J. B. Inorg. Chem.
2005, 7708.
10.1021/om050865r CCC: $33.50 © 2006 American Chemical Society
Publication on Web 01/10/2006

Supramolecular trans-Coordinating Phosphine Ligands
Organometallics, Vol. 25, No. 4, 2006 955
Scheme 1. Formation of a trans-Coordinating Phosphine
Ligand System via Self-Association, 2 (left), or
Anion-Templation, 3 (right)
Figure 1. Calculated structure of models of 2 (left) and 3 (right)
clearly showing an intramolecular hydrogen bond and the trans
configuration about Pd and the interactions between Cl and the
NH’s of the urea’s.
Scheme 2. Synthesis of Urea-Based Phosphine Ligand 1
into m-(diphenylphosphorus)aniline with potassium diphenyl
phosphide7 (KPPh2) and subsequent reaction of m-(diphen-
ylphosphorus)aniline with ethyl isocyanatoacetate to generate
the urea functionality (Scheme 2). Two equivalents of 1 were
added to CODPdMeCl to produce the metal complex 12PdMeCl,
2, which was fully characterized by 1H, 13C, and 31P{1H} NMR
and IR spectroscopy, ESI-MS, and elemental analysis. The
singlet observed in the 31P{1H} NMR spectrum at 32.7 ppm
indicates that the phosphine ligands are coordinated in a trans
configuration about the metal center. In addition, a 3J(P-H) value
of 6.0 Hz was observed for the Pd-CH3 resonance, character-
istic of palladium complexes with trans-coordinated phos-
phines.8
Figure 2. Binding of a chloride anion in the pocket of complex 2
monitored by H NMR spectroscopy: (A) solution of 2; (B) a
1
Infrared spectroscopic measurements of 2 in CDCl3 show that,
in contrast to 1, the urea functional groups are involved in
hydrogen-bonding even at relatively low concentrations (<14
mM). The hydrogen-bonding is predominantly due to intramo-
lecular interactions, since the ratio between the N-H stretches
for free and hydrogen-bonded urea groups, at 3410 and 3340
cm-1, respectively,9,10 are not concentration dependent between
the range of 4 and 42 mM (note that in structure 2 only 50% of
the NH groups are involved in hydrogen-bonding). Evidently,
the preorganization of the urea groups by coordination to the
palladium metal center promotes intramolecular hydrogen-
bonding instead of the intermolecular hydrogen-bonding ob-
served with more concentrated solutions of 1 (>20 mM).
Computational studies (DFT, B3LYP) on a model of complex
2 clearly illustrate the intramolecular hydrogen-bonding interac-
tion between the urea NH’s and the n electrons of the carbonyl
group of the urea moiety of the second ligand (Figure 1), and
the NH-O distances are 1.95 and 2.17 Å.11 The palladium
complex with the intramolecular hydrogen bonds is energetically
more favorable than the non-hydrogen-bonded system by 9 kcal/
mol.12
solution of 2 with 1.0 equiv of nBu4NCl; and (C) a solution of 2
with 10.0 equiv of nBu4NCl.
Urea groups are frequently employed to construct receptors
for anion recognition,13 so we anticipated that the bis-urea motif
in complex 2 might also bind anions. Addition of various
equivalents of tetra-n-butylammonium chloride (nBu4NCl) to
a solution of 2 in CDCl3 indeed resulted in significant downfield
shifts of the NH resonances of the urea moiety (Figure 2). In
the presence of 10 equiv of nBu4NCl, the NH adjacent to the
aryl group shifted to lower field by ∼1.7 ppm to 9.84 ppm,
whereas the NH next to the CH2 group shifted ∼1.2 ppm
downfield. These changes in chemical shifts clearly point to
the chloride binding in the bis-urea pocket at the expense of
the hydrogen bonds between the urea functionalities,13 generat-
ing a palladium complex supported by an anion-templated
bidentate chelating ligand, [(12Cl)PdMeCl]-[nBu4N]+, 3 (Scheme
1). The binding constant of the chloride in the pocket of 2,
determined from NMR titrations, is K ) (10 ( 2) × 102 M-1
,
which is much higher than the binding constant associated with
the complexation of a single urea ligand 1 to chloride (nBu4-
NCl), K ) 55 ( 5 M-1 14
Interestingly, the ligands in 3 are
.
also in a trans configuration about the metal center, as evident
(7) Hingst, M.; Tepper, M.; Stelzer, O. Eur. J. Inorg. Chem. 1998, 73.
(8) Dekker: G. P. C. M.; Elsevier, C. J.; Vrieze, K.; van Leeuwen, P.
W. N. M. Organometallics 1992, 11, 1598, and references therein.
(9) Mido, Y. Spectrochim. Acta 1973, 29A, 431.
(10) (a) Boas, U.; Sontjens, S. H. M.; Jensen, K. J.; Christensen, J. B.;
Meijer, E. W. ChemBioChem 2002, 3, 433. (b) de Loos, M.; Ligten-barg,
A. G. J.; van Esch, J.; Kooijman, H.; Spek, A. L.; Hage, R.; Kellogg, R.
M.; Feringa, B. L. Eur. J. Org. Chem. 2000, 3675.
(11) (a) Massat, A.; Guillaume, Ph.; Doucet, J. P.; Dubois, J. E. J. Mol.
Struct. 1991, 244, 69. (b) Laurence, C.; Berthelot, M.; Helbert, M.
Spectrochim. Acta 1985, 41A, 883.
(12) The structures of the complexes were generated using TITAN and
were optimized using DFT optimization (B3LYP, 6-31G**).
by the singlet that is present in the 31P{1H} NMR spectrum (at
(13) For select examples: (a) Bondy, C. R.; Gale, P. A.; Loeb, S. J. J.
Am. Chem. Soc. 2004, 126, 5030. (b) Werner, F.; Schneider, H.-J. HelV.
Chim. Acta 2000, 83, 465. (c) Hishizawa, S.; Bu¨hlmann, P.; Iwao, M.;
Umezawa, Y. Tetrahedron Lett. 1995, 36, 6483. (d) Beer, P. D.; Gale, P.
A. Angew. Chem., Int. Ed. 2001, 40, 486, and references therein. (e) Scheele,
J.; Timmerman, P.; Reinhoudt, D. N. Chem. Commun. 1998, 2613. (f)
Tovilla, J. A.; Vilar, R.; White, A. J. P. Chem. Commun. 2005, 4839.
(14) We have analyzed the titration curves with a fitting program
developed by Hunter et al.: Bisson, A. P.; Hunter, C. A.; Carlos, J.; Young,
K. Chem. Eur. J. 1998, 4, 845.

956 Organometallics, Vol. 25, No. 4, 2006
Knight et al.
Scheme 3. Migration of Chloride Anion to/from the Palladium Center to Generate Zwitterionic and Ionic Complexes and Their
1
Corresponding 31P and H NMR Spectra
-80 °C) and the triplet (3J(P-H) ) 5.5 Hz) observed for the
Indeed, when an “additional” equivalent of 1 was introduced
to a solution of 2, zwitterionic complex 4, [(13Cl)PdMe], was
formed with three phosphine ligands bound to the metal center17
and the chloride anion in the tris-urea pocket (Scheme 3).
Accordingly, the 31P{1H} NMR spectrum contains a doublet
and a triplet that integrate in a ratio of 2:1, with a coupling
constant (2JP-Pcis ) 37 Hz) that is typical of phosphorus atoms
coordinated in a cis fashion (Scheme 3, middle).18,19 Interest-
ingly, the chloride anion is hydrogen-bonding to all three of
1
Pd-CH3 resonance in the H NMR spectrum.8 Computational
studies (DFT, B3LYP) on a model of complex 3 show that the
chloride anion fits nicely in the pocket, but that it does not lie
perfectly in the plane created by the NH’s of the urea groups
(Figure 1).12 This is the first example of a trans-coordinating,
anion-templated, hydrogen-bonded phosphine ligand system.5,6,15
The formation of 3 was also monitored by IR spectroscopy.
The two stretching frequencies corresponding to the NH’s of 2
disappear upon introduction of 1 equiv of nBu4NCl, and a new
band at a lower wavenumber (3297 cm-1) is observed for the
N-H bound to Cl. It is well-known that a larger shift in
wavenumbers upon complexation, ∆ν(Ν-Η), corresponds to
a stronger hydrogen-bonding interaction.16 With ∆ν(Ν-Η)
values of 113 and 70, respectively, the hydrogen bond between
the ureas and the chloride anion of 3 is clearly stronger than
the self-association of the urea moieties in 2, likely due to the
anionic nature of the chloride. In addition to the increase in
strength, the number of hydrogen bonds involved is larger (4
vs 2) in the anion-templated system, enabling the chloride anion
to compete with the intramolecular hydrogen-bonded complex.
1
the urea groups, as there are two signals observed in the H
NMR spectrum for the NH’s adjacent to the aryl ring at 9.79
and 9.47 ppm, which also integrate with respect to one another
in a 2:1 ratio. These experiments clearly show that the exchange
of these ligands is slow on the NMR time scale. The resonance
for the methyl group of this zwitterionic species has shifted
downfield to 0.38 ppm from 0.01 ppm for the neutral complex
2, and it consists of an overlapping set of doublets of triplets
instead of the simple triplet observed for 2.20 When 2 equiv of
nBu4NCl are added to a solution of 4, the third phosphine ligand
dissociates from the metal to regenerate 3 (Scheme 3, bottom).
(17) (a) Gretz, E. F.; Sen, A. J. Am. Chem. Soc. 1986, 108, 6038. (b)
Yamashita, R.; Kikukawa, K.; Wada, F.; Matsuda, T. J. Organomet. Chem.
1980, 201, 463.
Although the bis-urea pocket binds chloride anions, it
apparently is unable to remove the chloride from the palladium
center to form a zwitterionic species. We anticipated, however,
that such an intramolecular chloride shift from the metal to the
binding site could be promoted by the presence of donors.
(18) (a) Zudin, V. N.; Chinakov, V. D.; Nekipelov, V. M.; Likholobov,
V. A.; Yermakov Y. I. J. Organomet. Chem. 1985, 289, 425. (b) Crumbliss,
A. L.; Topping, R. J. In Phosphorus-31 NMR Spectroscopy in Stereochem-
ical Analysis; Verkade, J. G., Quin, L. D., Eds.; VCH Publishers: Germany,
1987; pp 535-547.
(15) ) An example of an anion-templated cis hydrogen-bonded system
was recently reported: Lu, X.-X.; Tang, H.-S.; Ko, C.-C.; Wong, J. K.-Y.;
Zhu N.; Yam, V. W.-W. Chem. Commun. 2005, 1572.
(16) Kazarian, S. G.; Hamley, P. A.; Poliakoff, M. J. Am. Chem. Soc.
1993, 115, 9069.
(19) A small quantity of 2 and 1 is also observed in the 31P NMR
spectrum due to the equilibrium between these three species.
(20) A small amount (5-10%) of an unidentifiable species is sometimes
observed in the 1H NMR spectrum, and it is believed to be due to
decomposition of 4 that ultimately occurs in solution over several days.

Supramolecular trans-Coordinating Phosphine Ligands
Organometallics, Vol. 25, No. 4, 2006 957
Scheme 4. Thermodynamically Controlled Equilibrium between 4, 2, (1)(PPh3)PdMeCl, and (PPh3)2PdMeCl and
Variable-Temperature 31P{1H} Spectra
As expected, the addition of another equivalent of 1 to a solution
of 3 (2 in the presence of 2 equiv of Cl- to drive the equilibrium
to 3) does not result in the formation of the zwitterionic complex
4, and only the anion-templated species, 3, and the free ligand,
1, are observed in solution. This indicates that the complex
formation is under thermodynamic control. A separate experi-
ment using (Ph3P)2PdMeCl and 1 equiv of PPh3 (in CD2Cl2)
demonstrates that the urea pocket is necessary to generate the
zwitterionic palladium species with three phosphine ligands,
since only two singlets were observed (even at low temperatures)
in the 31P{1H} NMR spectrum for (Ph3P)2PdMeCl and free
PPh3.
We were interested in probing the importance of the third
urea-chloride interaction in complex 4 and if this interaction
was required to facilitate the phosphine-chloride substitution
reaction of complex 2. Therefore an additional experiment was
conducted in which PPh3 (2/3 equiv) was added to a solution
of complex 2 instead of ligand 1. If the third urea is not
important, we expected to see a similar substitution of the
chloride by PPh3. However, if the third urea-chloride interaction
is crucial for the substitution process, a mixture of complex 2
and free PPh3 should be observed, or a rearrangement of the
ligands takes place resulting in a mixture of complexes. The
typical doublet and triplet in the 31P NMR spectrum and the
two singlets for the NH’s hydrogen-bonded to the chloride anion
near 10 ppm (in a 2:1 ratio) were observed, with the corre-
sponding methyl resonance at 0.39 ppm in the 1H NMR
spectrum, indicating the formation of 4 at ambient temperature.
Signals at 33.0, 32.3, and 31.8 ppm due to 2, (1)(PPh3)-
PdMeCl,21 and (PPh3)2PdMeCl, respectively, are also apparent
at 20 °C, and the four metal complexes are present in a 1.0:
0.4:0.3:0.3 ratio (Scheme 4). This clearly indicates that the third
urea significantly stabilizes the binding of the chloride. Interest-
ingly, if the sample is cooled to -30 °C, the equilibrium shifts
in favor of 4, and the remaining 1/3 of Pd metal is ligated by
the “residual” PPh3 in solution to generate (PPh3)2PdMeCl. At
this temperature, these two complexes are present in a 2:1 ratio,
but if the solution is warmed back up to ambient temperature,
all four of the palladium complexes are observed in solution
again and in the same ratio as before. (Free phosphine, 1, and/
or PPh3 are also present in solution, but the amount of free
phosphine decreases significantly upon cooling to -30 °C and
returns after the solution is rewarmed to room temperature.)
This temperature dependence indicates a low barrier for the
exchange process between the different species. The formation
of the most stable palladium complex at -30 °C, 4, is enthalpy
driven. If the reverse experiment is performed, such that (Ph3P)2-
PdMeCl is mixed with 2 equiv of 1, comparable resonances
are observed in the 31P and 1H NMR spectra, except that due to
the rapid exchange between 2, (1)(PPh3)PdMeCl, and (PPh3)2-
PdMeCl on the NMR time scale, only a broad resonance (instead
of 3 singlets) is present at 32.5 ppm.
Since in complex 2 the chloride can be readily substituted
by a ligand to generate a zwitterionic complex, the reactivity
of 2 was examined in the presence of 13CO. At -78 °C, 13CO
was bubbled through an NMR tube solution of 2 in CD2Cl2 (or
the NMR tube was pressurized with 5 bar of CO), and at this
temperature, resonances corresponding to the four-coordinate
CO-adduct, 5,22,23 were observed at 30.8 ppm and at 179.6 ppm
in the 31P{1H} and 13C{1H} NMR spectra, respectively (Scheme
5). In the 1H NMR spectrum, the resonance for the N-H
adjacent to the aryl ring shifted downfield by 2.05 ppm to 10.20
ppm, indicating a similar substitution of the chloride anion as
observed in the presence of additional ligand. Upon warming
to room temperature, migratory insertion occurred to produce
the acetyl species, (1)2Pd(C(O)CH3)Cl, 6, and singlets at 21.0
ppm in the 31P{1H} spectrum and 233.5 ppm in the 13C{1H}
NMR spectra showed that the ligands are still bound to the metal
in a trans configuration. After the formation of the acetyl
species, the chemical shift of the NH’s indicated that the chloride
is no longer present in the pocket, but has migrated back to the
(22) Shultz, C. S.; Ledford, J.; DeSimone, J. M.; Brookhart, M. J. Am.
Chem. Soc. 2000, 122, 6351.
(23) The major species present in solution (between -80 and -40 °C)
is the four-coordinate CO-adduct, which was followed by variable-
temperature NMR spectroscopy, and it formed the acetyl complex. Below
-70 °C, an unidentifiable minor species is observed in solution, and this
complex is a potential intermediate that ultimately results in the formation
of the acetyl product.
(21) (1)(Ph3P)2PdMeCl was identified by comparison with a separate
NMR tube experiment.

958 Organometallics, Vol. 25, No. 4, 2006
Knight et al.
Scheme 5. Reactivity of 2 with 13CO
palladium center, regenerating a neutral species. In comparison,
when 13CO was introduced to a CD2Cl2 solution of (Ph3P)2-
PdMeCl at -78 °C, a four-coordinate 13CO-adduct was not
observed in the 13C{1H} NMR spectra, showing that the bis-
urea pocket is necessary to generate a cationic palladium center
with a free site available for 13CO coordination. When the
analogous experiment is performed with 3 (i.e., the pocket of 2
is blocked by an external chloride anion), the four-coordinate
13CO-adduct was also not observed in the 13C{1H} NMR
spectrum between -80 and 20 °C. On the other hand, at room
temperature and presumably via an unobserved five-coordinate
CO-adduct,24 an acetyl species, [(12Cl)Pd((CO)CH3)Cl]-[nBu4N]+,
7, was produced, as evident by the new resonances in the 31P-
{1H} and the 13C{1H} NMR spectra at 21.8 and 230.2 ppm,
respectively.25 On the basis of the 1H NMR spectrum, the trans-
coordinating, chloride-templated, phosphine ligand system also
remains intact after the formation of the acetyl complex. The
inability to observe the four-coordinate CO-adduct of 3 em-
phasizes the subtle control of the bis-urea pocket on the
reactivity of the metal center.13e
produce salts as side-products might change the ligation around
the metal center. Currently, investigations are underway to study
this and to extend this approach, such as the use of a large
variety of anions, including chiral templating anions, to induce
unique reactivities and selectivities at the metal center.
Experimental Section
General Conditions. All manipulations were performed under
argon using standard Schlenk techniques. Toluene was distilled from
sodium, and CH2Cl2, pentane, CDCl3, and CD2Cl2 were distilled
from CaH2. The metal complex CODPdMeCl was synthesized
according to a literature procedure.26 The palladium complex
(Ph3P)2PdMeCl27 was synthesized in an analogous manner to
compound 2. The 13CO was purchased from Praxair. All other
reagents were purchased from Aldrich or Acros and used as
received. The NMR spectra were recorded on a Varian Inova 500
and a Bruker DRX 300 NMR spectrometer in CDCl3 unless
otherwise specified. The IR spectra were measured on a BIO-RAD
FTS-7 in a NaCl solution cell in CDCl3. Electrospray-ionization
mass spectra (in MeOH) were recorded on a Shimadzu LCMS-
2010A via direct injection. Elemental analysis was performed by
H. Kolbe Mikroanalytisches Laboratorium.
Conclusion
Synthesis of m-(Diphenylphosphorus)aniline. A THF solution
of potassium diphenylphosphide (4.04 g, 1.80 × 10-2 mol) and
m-fluoroaniline (2.01 g, 1.81 × 10-2 mol) were combined in a
Schenk flask and refluxed for 3 days. The THF was removed in
vacuo, and the yellow solid was washed with degassed H2O (4 ×
20 mL). The m-(diphenylphosphorus)aniline was purified by column
chromatography (eluent: 100% CHCl3). Yield: 3.692 g, 74.0%.
1H NMR: δ 7.90-7.15 (m, 10H, C6H5), 7.20 (m, 1H, C6H4), 6.67
(m, 3H, C6H4), and 3.62 (br s, 2H, NH). 13C{1H}: δ 146.2 (br s,
NC-aryl), 138.1 (m, PCipso), 137.2 (m, PCipso), 133.8 (d, o-PC6H5,
2JP-C ) 19.5 Hz), 129.4 (d, m-PC6H4N, 3JP-C ) 7.3 Hz), 128.5 (d,
In summary, a new urea-based phosphine ligand has been
synthesized and the urea functional groups of the palladium
complex 2 self-associate to produce the first example of a trans-
coordinating hydrogen-bonded ligand system. The addition of
chloride anions to 2 converts it into the chloride-templated,
trans-coordinating bidentate phosphine metal species 3. The
presence of additional ligand 1 (or PPh3) leads to the formation
of a zwitterionic complex, [(13Cl)PdMe], with three phosphine
ligands bound to the metal center and the chloride anion in a
tris-urea pocket. The formation of this complex is reversible,
as the chloride moves back to the palladium upon addition of
nBu4NCl. These experiments clearly show that the complex
responds to external stimuli as a consequence of the supramo-
lecular interactions. The palladium metal center also shows
special reactivity toward CO as a result of the presence of the
bis-urea pocket. Substitution of the chloride by CO is observed,
resulting in the formation of zwitterionic complexes with the
chloride being transferred from the metal center to the bis-urea
binding site. Interestingly, after CO migratory insertion occurs
to form the palladium-acetyl species, the chloride migrates back
to the palladium center. In view of future developments of self-
assembled bidentate ligands based on hydrogen bonds the
current results are important, since it suggests that reactions that
3
m-PC6H5, JP-C ) 12.2 Hz), 128.3 (s, p-C6H5P), 124.2 (d,
2
2
6
o-PC H4N, JP-C ) 19.5 Hz), 120.0 (d, o-PC6H4N, JP-C ) 19.5
Hz), 115.6 (s, p-PC6H4N). 31P{1H}: δ -4.49 ppm.
Synthesis of 1. A Schenk flask was charged with m-(diphen-
ylphosphorus)aniline (1.414 g, 5.10 × 10-3 mol), which was
dissolved in CH2Cl2 (10 mL). Ethyl isocyanatoacetate (0.656 g,
5.08 × 10-3 mol) was added via syringe to the reaction mixture,
and it was stirred at room temperature for 4 h. The solvent was
removed in vacuo, and toluene (15 mL) was added to the white
sticky solid. Initially the white solid dissolved in the toluene, but
after approximately 20 min of stirring a white, thick opaque powder
precipitated out of the toluene solution. The solvent was removed
by filtration, and the precipitate was washed with toluene (∼5 mL)
twice more. The white solid was dried under reduced pressure.
1
3
Yield: 1.765 g, 85.2%. H NMR: δ 7.51 (d, 1H, C6H4, JH-H
)
(24) van Leeuwen, P. W. N. M.; Zuideveld, M. A.; Swennenhuis, B. H.
G.; Freixa, Z.; Kamer, P. C. J.; Goubitz, K.; Fraanje, J.; Lutz, M.; Spek, A.
J. Am. Chem. Soc. 2003, 125, 5523
(25) Since the CO and methyl groups should be arranged cis with respect
to one another for facile migratory insertion to occur and these palladium
complexes were never observed in this coordination mode, the carbonylation
must occur immediately upon rearrangement to the cis species, which is
followed by a successive rearrangement to the thermodynamic trans-acetyl
product.
8.7 Hz), 7.44-7.20 (m, 11H, C6H4 and C6H5), 7.02 (t, 2H, C6H4,
3JH-H ) 7.5 Hz), 6.49 (s, 1H, NH), 5.22 (m, 1H, NHCH2), 4.21 (q,
(26) Ru¨lke, R. E.; Ernsting, J. M.; Spek, A. L.; Elsevier, C. J.; van
Leeuwen, P. W. M. N.; Vrieze, K. Inorg. Chem. 1993, 32, 5769.
(27) Bacchi, A.; Carcelli, M.; Pelizzi, C.; Pelizzi, G.; Pelagatti, P.;
Ugolotti, S. Eur. J. Inorg. Chem. 2002, 2179.

Supramolecular trans-Coordinating Phosphine Ligands
Organometallics, Vol. 25, No. 4, 2006 959
2H, CH2CH3, 3JH-H ) 7.2 Hz), 4.00 (d, 2H, NHCH2, 3JH-H ) 5.1
N-H1b), 6.70 (m, 1H, Ar-H), 6.39 (m, 2H, Ar-H), 6.01 (t, 1H, Ar-
3
3
Hz), 1.27 (t, 3H, CH2CH3, JH-H ) 7.2 Hz). 13C{1H}: δ 171.2
H), 4.19 (q, 6H, CH2CH3, JH-H ) 7.2 Hz), 4.08 (d, 2H, CH2NH,
(CdO), 155.6 (CdO), 138.8 (d, NC-aryl, JP-C ) 8.5 Hz), 137.9
3JH-H ) 5.7 Hz), 4.02 (d, 4H, CH2NH, JH-H ) 5.7 Hz), 1.28 (t,
3
3
3
(m, PCipso), 136.7 (m, PCipso), 133.8 (d, PCCH, 2JP-C ) 19.5 Hz),
9H, CH2CH3, JH-H ) 7.2 Hz ), and 0.38 (br d × t, 3H, PdCH3).
13C{1H}: δ 171.0 (CdO), 156.3 (CdO), 140.84, 140.77, 140.0,
139.8, 135.1, 134.8, 134.7, 132.12, 132.08, 132.0, 131.8, 130.9,
130.4, 130.1, 129.9, 129.5, 128.5, 128.2, 128.1, 124.8, 124.6, 124.4,
121.3 and 121.0 (Ar-C), 61.0 (OCH2CH3), 60.9 (OCH2CH3), 42.0
(HNCH2), 41.7 (HNCH2), 14.2 (CH2CH3), 14.1 (CH2CH3), and 6.6
(PdCH3). 31P{1H}: δ 37.8 (d, 2P, P(cis to Me), 2JP-Pcis ) 37 Hz) and
3
129.3 (d, m-PC6H4N , JP-C ) 7.3 Hz), 128.8 (s, p-PC6H5), 128.5
3
(d, m-PC6H5, JP-C ) 7.3 Hz), 125.2 (m, PC6H4N), 124.9 (s,
PC6H4N), 120.8 (s, p-PC6H4N), 61.5 (s, OCH2CH3), 41.9 (s,
HNCH2), and 14.0 (s, CH2CH3). 31P{1H}: δ -4.19 ppm. IR
(νmax): 3434 (NHfree), 3317 (NHAssoc), 1744 (CdOEster), 1696 (Cd
O
Amide I), 1532 (C-NAmide II), and 1204 (C-O) cm-1. Anal. Calcd
2
22.3 (t, 1P, P(trans to Me), JP-Pcis ) 37 Hz).
for C23H23N2O3P: C, 67.98; H, 5.70; N, 6.89. Found: C, 68.08;
H, 5.79; N, 6.80.
Competition Studies between 4 and nBu4NCl and between
3 and 1. Stock solutions of 1 (0.013 g, 0.041 M), 2 (0.024 g, 0.021
M), and nBu4NCl (0.009 g, 0.041 M) were prepared in CD2Cl2.
Complex 4 was generated in situ by combining 2 (0.4 mL, 8.3 ×
10-6 mol) and 1 (0.20 mL, 8.3 × 10-6 mol); afterward, nBu4NCl
was added in 3 portions (1.5, 1.5, and 1.0 mL) and monitored by
1H and 31P NMR spectroscopy to determine the number of
equivalents of chloride anion necessary to generate 3 as well as 1
bound to a chloride anion. Summing the volumes of the three
portions, 2.0 equiv of nBu4NCl were required.
Synthesis of trans-(1)2PdMeCl (2). 1,5-Palladium methylchlo-
rocyclooctadiene (CODPdMeCl) (0.095 g, 3.58 × 10-4 mol) was
combined with 2 equiv of 1 (0.291 g, 7.16 × 10-4 mol), and CH2-
Cl2 (10 mL) was syringed into the Schlenk, yielding a clear, pale
yellow solution. The reaction mixture was stirred overnight, and
the solution becomes a deep yellow color. The solution was
concentrated to approximately 3 mL, and pentane (5 mL) was added
to the reaction mixture, generating a yellow sticky precipitate. The
solvent was removed by filtration, and the purification of the solid
was repeated twice more. Last, CH2Cl2 (5 mL) and pentane (5 mL)
were syringed onto the solid, and it was stirred at room temperature
for 30 min. The volatiles were removed in vacuo. Yield: 0.315 g,
90.7%. 1H NMR: δ 8.29 (br m, 2H, C-H aryl), 8.15 (s, 2H, N-H),
7.66 (m, 8H, C6H5), 7.40 (br s, 14H, C6H5), 7.16 (br t, 2H, C-H
Complex 3 was generated in situ by combining 2 (0.4 mL, 8.3
× 10-6 mol) and nBu4NCl (0.20 mL, 8.3 × 10-6 mol) and verified
1
by H and 31P NMR spectroscopy. The ligand 1 (0.20 mL, 8.3 ×
10-6 mol) was added to the solution, and it was determined by
NMR spectroscopy that only 1 equiv of nBu4NCl to form 3 was
not sufficient to prevent the formation of a mixture of 4 and complex
3 with free ligand 1.
3
aryl, JH-H ) 8.5 Hz), 6.98 (br s, 2H, C-H aryl), 6.26 (br s, 2H,
CH2NH), 4.11 (q, 4H, CH2CH3, 3JH-H ) 7.0 Hz), 3.72 (d, 4H, CH2-
3
3
NH, JH-H ) 5.0 Hz), 1.23 (t, 6H, CH2CH3, JH-H ) 7.0 Hz) and
In a separate experiment, complex 3 was generated in situ, but
a larger excess of nBu4NCl (0.005 g, 1.8 × 10-5 mol) was utilized
with 2 (0.008 g, 8.3 × 10-6 mol). Upon addition of 1 (0.003 g, 7.4
× 10-6), only 3 and free 1 were observed in the 1H and 31P NMR
spectra (vide supra).
3
0.01 (t, PdCH3, JP-H ) 6.0 Hz). 13C{1H}: δ 171.3 (CdO), 156.2
(CdO), 139.1 (t, NCipso, JP-C ) 7.7 Hz), 134.9 (t, C aryl, JP-C
6.2 Hz), 131.2 (t, PCipso, JP-C ) 22.9 Hz), 131.0 (t, PCipso, JP-C
)
)
21.4 Hz), 128.9 (br m, C aryl), 128.7 (s, C aryl), 128.1 (m, C aryl),
127.0 (C6H4), 122.5 (C6H4), 61.0 (OCH2CH3), 41.6 (HNCH2), 14.1
(CH2CH3), and 6.4 (PdCH3). 31P{1H}: δ 32.7 ppm. IR (νmax): 3411
(NHfree), 3329 (NHAssoc), 1738 (CdOEster), 1695 (CdOAmide I), 1553
(C-NAmide II), and 1209 (C-O) cm-1. Anal. Calcd for C47H49N4O6P2-
ClPd: C, 58.25; H, 5.09; N, 5.78. Found: C, 58.35; H, 5.15; N,
5.66.
Formation of trans-[(12Cl)Pd(13CO)(Me)] (5) by Bubbling
13CO. The palladium complex 2 (0.0135 g, 1.39 × 10-5 mol) was
dissolved in CD2Cl2 (0.7 mL), and the NMR tube was cooled to
-78 °C. At this temperature, the 13CO-adducts were generated by
bubbling 13CO through the yellow solution for 7 min. 13C NMR (T
) -80 °C): δ (CD2Cl2) 179.7 and 177.7 ppm (CdO of CO-
adducts). 31P NMR (T ) -80 °C): δ (CD2Cl2) 33.6 and 30.8 ppm
(CO-adducts). At -30 °C, only one CO-adduct that corresponds
to 5 is visible in the spectra. 13C NMR (T ) -30 °C): δ (CD2Cl2)
179.7 ppm (CdO). 31P NMR (T ) -30 °C): δ (CD2Cl2) 33.6 (CO-
adduct). The CO migratory insertion was followed by NMR
spectroscopy, and on the basis of the NMR data, the reaction
proceeds to completion (100%). The NMR data are the same as
for 4 (vide supra).
Generation of {[trans-(12Cl)PdMeCl]-[NBu4]+ } (3). The
anion-templated complex was produced in situ in an NMR tube.
The reagents 2 (0.010 g, 1.03 × 10-5) and nBu4NCl (0.003 g, 1.1
× 10-5 mol) were combined and dissolved in CDCl3 (0.5 mL). On
the basis of NMR spectroscopy, the reaction proceeds to completion.
1H NMR: δ 9.49 (s, 2H, N-H), 8.12 (br m, 4H, C-H aryl), 7.63
(m, 8H, C6H5), 7.36 (m, 12, C6H5), 7.29 (br s, 2H, CH2NH), 7.20
3
(br t, 2H, C-H aryl, JH-H ) 7.5 Hz), 6.83 (br s, 2H, C-H aryl),
4.15 (q, 4H, CH2CH3, 3JH-H ) 7.5 Hz), 3.99 (d, 4H, CH2NH, 3JH-H
) 5.5 Hz), 3.10 (m, 8H, NBu), 1.49 (m, 8H, NBu), 1.29-1.22 (m,
14H, NBu and CH2CH3), 0.86 (t, 12H, NBu, 3JH-H ) 7.0 Hz), and
Formation of trans-(1)2Pd(C(O)Me)Cl by High Pressure via
a CO-Adduct. The palladium complex 2 (14.741 mg, 1.53 × 10-5
mol) was weighed out into a Schlenk flask and dissolved in CD2-
Cl2 (2.0 mL). The yellow solution was transferred to the high-
pressure NMR tube and cooled to -78 °C for 1 h. CO gas (5.0
bar) was pressurized into the tube, and the progress of the reaction
was monitored by variable, low-temperature NMR spectroscopy.
The formation of the four-coordinate CO-adduct (5) with the
chloride anion displaced into the urea hydrogen-bonding pocket
3
0.03 (t, 3H, PdCH3, JP-H ) 6.0 Hz). 13C{1H}: δ 171.0 (CdO),
156.5 (CdO), 140.6 (t, NCipso, 3JP-C ) 7.7 Hz), 134.9 (t, o-PC6H5,
2JP-C ) 6.0 Hz), 131.8 (t, PCipso, 1JP-C ) 21.4 Hz), 130.8 (t, PC6H5,
JP-C ) 22.1 Hz), 129.7 (s, p-PC6H5), 128.5 (m, PC6H4N), 127.8
(t, m-PC6H5, 3JP-C ) 4.5 Hz), 127.0 (m, PC6H4N), 126.0 (PC6H4N),
60.6 (OCH2CH3), 58.8 (s, nBu), 41.7 (HNCH2), 23.9 (s, nBu), 19.6
(s, nBu), 14.2 (CH2CH3) 13.6 (s, nBu), and 6.6 (PdCH3). 31P{1H}:
δ 32.0 ppm. IR (νmax): 3398 (NHAssoc), 1749 (CdOester), 1692 (Cd
1
1
was apparent from the H NMR spectrum. H NMR (T ) -80
°C): δ (CD2Cl2) 10.20 (br s, 2H NH-Ar), 8.32 (br s, 2H, Ar-H),
7.95-6.80 (br m, 26H, Ar-H and CH2NH), 6.60 (br s, 2H, Ar-H),
4.40-2.95 (br m, 8H, CH2CH3 and CH2NH), 1.15 (br s, 6H,
CH2CH3), and 0.42 (br s, 3H, PdCH3). 31P{1H} NMR (T ) -80
°C): δ (CD2Cl2) 30.8 ppm (s). If the NMR tube is left in the NMR
spectrometer for 185 min at -30 °C, the reaction progresses to the
production of the acetyl compound. NMR data for 6 are listed
below.
O
Amide I), 1556 (C-NAmide II), and 1201 (C-O) cm-1
.
Formation of [(13Cl)PdMe], 4, in Situ. Both the palladium
complex 2 (0.010 g, 1.03 × 10-5mol) and 1 (0.004 g, 9.84 × 10
-6
mol) were weighed into separate vials, dissolved into CD2Cl2
(0.3 mL each), and combined in an NMR tube. On the basis of
NMR spectroscopy, the reaction proceeded to completion. 1H NMR
(CD2Cl2): δ 9.79 (s, 2H, N-H2a), 9.47 (s, 2H, N-H2b), 8.01 (d, 2H,
3
3
Ar-H, JH-H ) 8.1 Hz) 7.83 (d, 1H, Ar-H, JH-H ) 7.2 Hz), 7.74
(br t, 2H, Ar-H, 3JH-H ) 7.5 Hz), 7.62-6.85 (m, 36H, Ar-H, N-H1a,
Formation of trans-(1)2Pd(C(O)Me)Cl (6) in Situ. The pal-
ladium species 2 (0.0084 g, 8.66 × 10-6 mol) was dissolved in

960 Organometallics, Vol. 25, No. 4, 2006
Knight et al.
CDCl3 (0.7 mL), and the acetyl species was generated by bubbling
CO gas through the yellow solution for 10 min at room temperature
in an NMR tube. On the basis of NMR data, the reaction proceeds
ature to generate the acetyl complex 7. The reaction proceeds to
completion on the basis of NMR spectroscopy. H NMR: δ 9.80
1
(s, 2H, N-H), 8.45 (br m, 2H, C6H4), 8.20 (br m, 2H, C6H4), 8.02
(br s, 2H, CH2NH), 7.65-7.06 (m, 20H, C6H5) 7.19 (t, 2H, C6H4,
3JH-H ) 7.5 Hz), 6.77 (m, 2H, C6H4), 4.18 (q, 4H, CH2CH3, 3JH-H
) 7.5 Hz), 4.03 (br s, 4H, CH2NH), 2.92 (m, 8H, NBu), 1.48 (br
1
to completion (100%). H NMR: δ 8.58 (br m, 2H, PCCHN of
C6H4), 7.97 (s, 2H, N-H), 7.90-7.20 (br m, 12H, C6H5 and C6H4),
7.10 (br s, 2H, C6H4), 7.00, (br s, 2H, C6H4), 6.13 (br s, 2H,
3
CH2NH), 4.11, (q, 4H, CH2CH3, JH-H ) 7.0 Hz), 3.64 (br s, 4H,
s, 3H, PdCH3), 1.38 (m, 8H, NBu), 1.28 (t, 6H, CH2CH3, 3JH-H
)
3
3
CH2NH), 1.40 (br s, PdCH3), and 1.22 (t, 6H, CH2CH3, JH-H
)
7.5 Hz), 1.14 (m, 8H, NBu), and 0.79 (t, 12H, NBu, JH-H ) 7.5
Hz). 13C{1H}: δ 184.2 (PdCOCH3), 171.2 (CdO), 156.5 (CdO),
140.7 (s, PC6H4N), 135.7 (m, C6H5), 133.4 (m, C6H5), 132.0 (m,
C6H5), 130.2 (m, C6H5), 128. 8 (m, PC6H4N), 128.1 (s, C6H5), 127.9
(m, PC6H4N), 125.9 (s, PC6H4N), 120.9 (s, PC6H4N), 60.7 (OCH2-
CH3), 58.6 (nBu), 41.8 (HNCH2), 39.2 (PdCOCH3), 23.8 (nBu),
19.5 (nBu), 14.2 (CH2CH3), and 13.6 (NBu). 31P{1H}: δ 20.9 ppm.
IR: 3298 (NHAssoc), 1748 (CdOester), 1688 (Pd(CdO)Me), 1556
7.0 Hz). 13C{1H}: δ 184. 2 (Pd(CdO)CH3), 171.7 (CdO), 155.8
(CdO), 139.4 (m, NCipso), 134.6 (br m, C6H5), 131.4 (br m, C aryl),
130.5 (s, C aryl), 129.2 (PCCN of C6H4), 128.4 (br m, C6H5), 127.1
(s, C6H4), 122.9 (s, C6H4), 61.1 (OCH2CH3), 41.6 (HNCH2), 39.4
(Pd(CO)CH3), and 14.1 (CH2CH3). 31P{1H}: δ 20.2 ppm. IR
(νmax): 3414 (NHfree), 3341 (NHAssoc), 1746 (CdOester), 1692 (Cd
OMe), 1553 (C-NAmide II), and 1205 (C-O) cm-1
.
Synthesis of (Ph3P)2PdMeCl.27 Both CODPdMeCl (0.097 g,
3.66 × 10-4 mol) and triphenylphosphine (0.191 g, 7.28 × 10-4
mol) were combined in a Schlenk flask, and CH2Cl2 (10 mL) was
added to the contents. The reaction mixture never fully dissolved
in the solvent, but after about 10 min, considerably more white
precipitate was present in the flask. The reaction was stirred at room
temperature for 24 h. Pentane (5 mL) was syringed into the reaction
mixture, and the solvent was removed by cannula filtration. The
white solid was washed twice more with pentane (2 × 2 mL), and
the residual solvent was removed under reduced pressure. Yield:
(C-NAmide II), and 1200 (C-O) cm-1
.
Attempted Formation of the 13CO-Adduct of 3. The in situ
formation of {[trans-(12Cl)Pd(13CO)(Me)Cl]-[NBu4]+} was at-
tempted by the same procedure as for trans-(1)2Pd(13CO)(Me)Cl
except that 2 (0.0084 g, 8.66 × 10-6 mol) was combined with 15
equiv of nBu4NCl (0.030 g, 1.08 × 10-4 mol) and dissolved in
CD2Cl2 (0.7 mL) before bubbling 13CO through the solution at -78
°C for 7 min. No 13CO-adduct was observed at -80 °C (only free
13CO at 184.2 ppm; however, upon warming the NMR tube, CO
migratory insertion occurred and the reaction proceeded to comple-
tion (100%)). The NMR data are the same as for 5 (vide supra).
Competition Studies between 2 and Ph3P and between
(Ph3P)2PdMeCl and 1. The palladium complex 2 (10.006 mg, 1.03
× 10-5 mol) and 2/3 equiv of PPh3 (1.877 mg, 7.15 × 10-6 mol)
1
0.241 g, 96.6%. H NMR: δ 7.73 (m,12H, C6H5), 7.42 (m, 18H,
3
C6H5), and -0.01 (t, 3H, PdCH3, JP-H ) 6.0 Hz). 31P NMR: δ
30.7 ppm.
Attempted Formation of the 13CO-Adduct of (Ph3P)2PdMeCl
and Production of (Ph3P)2Pd(13C(O)Me)Cl in Situ. The palladium
complex (0.010 g, 1.47 × 10-5 mol) was weighed into a Schenk
flask and dissolved in CD2Cl2 (1.4 mL). The solution was
transferred to an NMR tube and cooled at -78 °C for 20 min. For
7 min, the 13CO was bubbled through the solution at this
temperature. The sample was placed in the NMR spectrometer at
-78 °C, and the progress of the reaction was monitored. At -78
°C, only free 13CO (i.e., no CO-adduct) was observed in the 13C-
{1H} NMR spectrum, and only one sharp singlet was present in
the 31P{1H} NMR spectrum. 1H NMR (T ) -80 °C): δ (CD2Cl2)
7.62 (m, 12H, C6H5), 7.43 (m, 18H, C6H5), and -0.17 (br t, 3H,
PdCH3). 13C NMR (T ) -80 °C): δ (CD2Cl2) 184.1 ppm (free
13CO). 31P NMR (T ) -80 °C): δ (CD2Cl2) 32.7 ppm. Upon
warming the sample to 20 °C, the palladium acetyl complex was
formed on the basis of NMR spectroscopy. 1H NMR (T ) 20 °C):
δ (CD2Cl2) 7.75 (m, 12H, C6H5), 7.44 (m, 18H, C6H5), and 1.38
(br s, 3H, Pd(CO)CH3). 13C NMR (T ) 20 °C): δ (CD2Cl2) 235.4
ppm (Pd(13CO)Me). 31P NMR (T ) 20 °C): δ (CD2Cl2) 20.3 ppm.
Formation of {[trans-(12Cl)Pd(C(O)Me)Cl]-[NBu4]+ } (7).
The complex 2 (0.019 g, 1.96 × 10-5 mol) was weighed into a
vial and dissolved in CDCl3 (0.6 mL). The nBu4NCl (0.2 mL) from
a 0.100 M stock solution in CDCl3 was syringed into an NMR
tube containing the palladium species. Carbon monoxide (CO) was
bubbled through the reaction mixture for 15 min at room temper-
1
were weighed together and dissolved in CD2Cl2 (0.8 mL). H and
31P{1H} NMR spectra were recorded at 20, 0, -20, -30, and -40
°C. 31P{1H}: (T ) 20 °C) δ 36.6 and 21.1 (4, 1.0 equiv), 33.0 (1,
0.4 equiv), 32.3 ((1)(PPh3)PdMeCl, 0.3 equiv), 31.8 ((Ph3P)2-
PdMeCl, 0.3 equiv), and -4.4 (br s of 1 and/or PPh3, 0.4 equiv)
ppm; (T ) -30 °C) δ 36.6 and 21.1 (4, 1 equiv), 31.8 ((Ph3P)2-
PdMeCl, 0.5 equiv), and -4.4 (br s of 1 and/or PPh3, 0.05 equiv)
ppm.
The palladium species (Ph3P)2PdMeCl (0.007 g, 1.0 × 10-5 mol)
and 2 equiv of 1 (0.008 g, 2.0 × 10-5 mol) were weighed together
1
and dissolved in CD2Cl2 (0.8 mL). H and 31P{1H} NMR spectra
were recorded only at ambient temperature. 31P{1H}: (T ) 20 °C)
δ 36.6 and 21.1 (4, 1.0 equiv), 32.5 (1, (1)(PPh3)PdMeCl and
(Ph3P)2PdMeCl 0.9 equiv), and -4.4 (br s of 1 and/or PPh3, 1.0
equiv) ppm.
Acknowledgment. The Dutch Organization for Scientific
Research (NWO) and the University of Amsterdam are kindly
acknowledged for financial support (VICI grant to J.N.H.R.).
Supporting Information Available: NMR titrations, IR studies,
and experimental details. This material is available free of charge
via the Internet at http://pubs.acs.org.
OM050865R