Orthopalladation of iminophosphoranes: Synthesis, structure and study of stability

Article abstract of DOI:10.1039/b714485g

The reaction of Pd(OAc)₂ with polyfunctional iminophosphoranes Ph₃P=NCH₂CO₂Me (1a), Ph₃P=NCH ₂C(O)NMe₂ (1b), Ph₃P=NCH₂CH ₂SMe (1c) and Ph₃P=NCH₂-2-NC₅H ₄ (1d), gives the orthopalladated dinuclear complex [Pd(μ-Cl){C₆H₄(PPh₂=NCH₂CO ₂Me-κ-C,N)-2}]₂ (2a) and the mononuclear derivatives [PdCl{C₆H₄(PPh₂=NCH₂CONMe ₂-κ-C,N,O)-2}] (2b), [PdCl{C₆H₄(PPh ₂=NCH₂CH₂SMe-κ-C,N,S)-2}] (2c) and [PdCl{C₆H₄(PPh₂=₂-2-NC ₅H₄-κ-C,N,N)-2}] (2d). The reaction implies the activation of a C-H bond in a phenyl ring of the phosphonium group, this fact being worthy of note due to the strongly deactivating nature of the phosphonium unit. The palladacycle containing the metallated carbon atom is remarkably stable toward the coordination of incoming ligands, while that formed by the iminic N atom and another heteroatom (O, 2a and 2b; S, 2c; N, 2d) is less stable and the resulting complexes can be considered as hemilabile. The X-ray crystal structures of the cyclopalladated [Pd(μ-Cl){C₆H ₄(PPh₂=NCH₂CO₂Me-κ-C,N)-2}] ₂ (2a), [PdCl{C₆H₄(PPh₂=NCH ₂-2-NC₅H₄-κ-C,N,N)-2}] (2d), [Pd{C ₆H₄(PPh₂=₂CONMe₂-κ- C,N,O)-2}(NCMe)](ClO₄) (3b) and [Pd{C₆H ₄(PPh₂=NCH₂CONMe₂-κ-C,N,O)-2} (py)](ClO₄) (7b), and the coordination compound cis-[Pd(Cl) ₂(Ph₃P=₂CH₂SMe-κ-N,S)] (8) are also reported. The Royal Society of Chemistry.

Full text of DOI:10.1039/b714485g

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PAPER
www.rsc.org/dalton | Dalton Transactions
Orthopalladation of iminophosphoranes: synthesis, structure and study of
stability†‡
Raquel Bielsa,a Rafael Navarro,a Tatiana Solerb and Esteban P. Urriolabeitia*a
Received 19th September 2007, Accepted 3rd December 2007
First published as an Advance Article on the web 20th December 2007
DOI: 10.1039/b714485g
=
The reaction of Pd(OAc)2 with polyfunctional iminophosphoranes Ph3P NCH2CO2Me (1a),
=
=
=
Ph3P NCH2C(O)NMe2 (1b), Ph3P NCH2CH2SMe (1c) and Ph3P NCH2-2-NC5H4 (1d), gives the
=
orthopalladated dinuclear complex [Pd(l-Cl){C6H4(PPh2 NCH2CO2Me-j-C,N)-2}]2 (2a) and the
=
=
mononuclear derivatives [PdCl{C6H4(PPh2 NCH2CONMe2-j-C,N,O)-2}] (2b), [PdCl{C6H4(PPh2
=
NCH2CH2SMe-j-C,N,S)-2}] (2c) and [PdCl{C6H4(PPh2 NCH2-2-NC5H4-j-C,N,N)-2}] (2d). The
reaction implies the activation of a C–H bond in a phenyl ring of the phosphonium group, this fact
being worthy of note due to the strongly deactivating nature of the phosphonium unit. The palladacycle
containing the metallated carbon atom is remarkably stable toward the coordination of incoming
ligands, while that formed by the iminic N atom and another heteroatom (O, 2a and 2b; S, 2c; N, 2d) is
less stable and the resulting complexes can be considered as hemilabile. The X-ray crystal structures of
=
=
the cyclopalladated [Pd(l-Cl){C6H4(PPh2 NCH2CO2Me-j-C,N)-2}]2 (2a), [PdCl{C6H4(PPh2
=
NCH2–2-NC5H4-j-C,N,N)-2}] (2d), [Pd{C6H4(PPh2 NCH2CONMe2-j-C,N,O)-2}(NCMe)](ClO4)
=
(3b) and [Pd{C6H4(PPh2 NCH2CONMe2-j-C,N,O)-2}(py)](ClO4) (7b), and the coordination
=
compound cis-[Pd(Cl)2(Ph3P NCH2CH2SMe-j-N,S)] (8) are also reported.
Introduction
The iminophosphoranes are compounds of stoichiometry
ꢀ
ꢀ
=
R3P NR (R = alkyl, aryl; R = alkyl, aryl, cyano, keto, etc.),
which are easily synthesized through several preparative methods.
Amongst them, the methods reported by Staudinger,1 Kirsanov2
and Pomerantz3 are the most representative. In addition to their
interest as versatile reagents in organic synthesis,4,5 the presence of
a lone pair on the N atom allows these species to behave as good
ligands toward transition metals, and their bonding properties
have been extensively studied.6–8 The iminophosphoranes are
also able to undergo C–H bond activation processes in one or
several different parts of their molecular skeleton. The C–H bond
activation transforms the neutral molecule into an anionic (or
dianionic) ligand and the number of potential coordinating atoms
increases. Representative bonding modes of the resulting species
are shown in Fig. 1. Modes a9 and b10 arise from the single
or double deprotonation at the methylene unit of a dppm-like
skeleton R2PCH2PR2. Mode b is formally a carbene ligand and
the synthesis of complexes with this bonding mode has been the
subject of extensive research.10 Related with mode a is mode c,11
and these two bonding modes can be considered coordination
isomers.
Fig. 1 Different bonding modes of iminiphosphoranes after C–H bond
activation.
Bonding mode d12 arises from proton abstraction at the alkylic
framework of a dppe group, and it is scarcely represented.
However, the activation of CH bonds at ancillary chains of
the phosphorus substituents (mode e)13 has become an efficient
method to functionalize the iminophosphoranes. Mode e is usually
the result of the activation at a methyl or a methylene group of
a substituent of the P atom. The N-iminate ligands bonded as
shown in mode f,14 although they are not properly derived from
C–H bond activations, must be mentioned here due to their wide
use in the design of homogeneous catalysts. After considering all
these possible bonding modes of the iminophosphorane ligands,
it is quite surprising that the orthometallated complexes (bonding
aDepartamento de Compuestos Organometa´licos, Instituto de Ciencia
de Materiales de Arago´n, CSIC-Universidad de Zaragoza, Plaza San
Francisco s/n, 50009, Zaragoza, Spain. E-mail: esteban@unizar.es;
Fax: (+34)976761187
bServicios Te´cnicos de Investigacio´n, Facultad de Ciencias Fase II, 03690,
San Vicente de Raspeig, Alicante, Spain
† CCDC reference numbers 661531–661535. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b714485g
‡ Electronic supplementary information (ESI) available: Experimental
details and crystal structure data. See DOI: 10.1039/b714485g
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mode g) still remains as one of the less developed class of
compounds.8e,11c,15,16
The synthesis of the cyclometallated complexes can be achieved
through two main preparative methods, the most elegant being
the direct C–H bond activation reaction,8e,11c,15 which can involve
either reaction of the non bonded iminophosphorane with an
activating reagent, or rearrangement of a previously coordinated
ligand. The transmetallation reaction from a lithium derivative
to the corresponding transition metal,16 is also a very powerful
synthetic method.
Aiming to expand the field of orthopalladated complexes
derived from iminophosphoranes, through direct C–H bond
activation, we report here the palladation reactions of the
=
=
alkyl-substituted Ph3P NCH2CO2Me, Ph3P NCH2C(O)NMe2,
7q
=
=
Ph3P NCH2CH2SMe and Ph3P NCH2–2-NC5H4 derivatives,
as representative examples of substrates with a single arylic
metallation position (Fig. 2) at the PPh3 unit. The presence
of additional functional groups with additional bonding atoms
allows the metallated ligands to show multidentate behaviour, and
a detailed study of the resulting palladacycles has shown that they
are very stable.
Scheme 1 (i) Pd(OAc)2, CH2Cl2, D; (ii) LiCl, MeOH, r. t.; (iii) AgClO4,
NCMe, -AgCl; (iv) L, CH2Cl2; (v) AgClO4, THF, -AgCl; (vi) PPh3,
AgClO4, THF, -AgCl.
=
nuclear [PdCl{C6H4(PPh2 NCH2CONMe2-j-C,N,O)-2}] 2b
(scheme 2). However, the reaction of 1c with Pd(OAc)2, also
under the same reaction conditions (1 : 1 molar ratio, refluxing
CH2Cl2, 1 h; LiCl, MeOH), gives the coordination compound
=
[PdCl2(Ph3P NCH2CH2SMe-j-N,S)] 8 (scheme 3). Prolonged
reflux in CH2Cl2 (5 h) is needed to obtain the orthopalladated
Fig. 2 Ligands used in this work.
=
[Pd{C6H4(PPh2 NCH2CH2SMe-j-C,N,S)-2}(Cl)] 2c. In
a
similar way, stronger reaction conditions to those described for
the metallation of 1a and 1b are needed to promote a CH bond
activation in 1d. The reaction of 1d and Pd(OAc)2 (1 : 1 molar
ratio) is accomplished in toluene as solvent, and the best yields
were obtained heating the mixture at the reflux temperature for
Results and discussion
Cyclopalladation reactions
The synthesis of the starting iminophosphoranes 1a–1d7q has
been carried out through the Staudinger method1a from the
corresponding azides17 using standard procedures. The IR spectra
of 1a–1d show the mPN absorption in the range 1240–1310 cm−1,
typical for this bond in this class of compounds.18 In addition, the
IR spectrum of 1a shows the band due to the carbonyl stretch
of the ester group at 1746 cm−1, while the IR of 1b shows the
corresponding absorption of the amide group at a lower energy
(1639 cm−1), due to the carbonyl resonance delocalization.19 The
1 h giving, after usual acetate–chloride metathesis, compound
ꢀ
=
[Pd{C6H4(PPh2 NCH2–C5H4N-2 -j-C,N,N)-2}(Cl)] 2d (eqn (1)).
1
31P{ H} NMR spectra of 1a–1d shows a single peak in each case
in the range 12–17 ppm, in the same region reported for other
non stabilized iminophosphoranes.20 The 1H NMR spectra show
signals due to the presence of the expected functional groups. All
ligands thus prepared have a metallable unit (the PPh3 group) and,
at least, two additional donor atoms of different nature (N iminic,
O carbonyl, S thioether, N pyridine).
The reaction of 1a with Pd(OAc)2 (1 : 1 molar ratio) in
refluxing CH2Cl2 for 1 h, followed by treatment of the acetate
intermediate with excess of LiCl in MeOH gives [Pd(l-Cl){C6H4-
=
(PPh2 NCH2COOMe-j-C,N)-2}]2 2a (Scheme 1).
The reaction of 1b with Pd(OAc)2, under strictly the same
reaction conditions as those described for 1a, gives the mono-
Scheme 2 (i) Pd(OAc)2, CH2Cl2, D; (ii) LiCl, MeOH, r. t.; (iii) AgClO4,
NCMe, -AgCl; (iv) L, CH2Cl2.
1204 | Dalton Trans., 2008, 1203–1214
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showing that this part of the molecule is involved in a dynamic
1
process. The measurement of the H NMR spectrum at 253 K
shows that the broad resonances have split into three different
sets of peaks, suggesting that at this temperature we have three
different species in solution (molar ratios 1 : 5 : 5; see Experimental
and ESI‡). A very plausible explanation can be given taking into
account that the IR spectrum of 2a has shown a decrease in the
position of the carbonyl band with respect to the free ligand
1a, suggesting that the carbonyl could be O-bonded to the Pd
center. An equilibrium involving bonding–non bonding of the
carbonyl group, as that depicted in Scheme 1, could account for
all experimental facts: (i) in solution three species are detected,
one mononuclear and two dinuclear (cis and trans isomers); (ii)
only the fragment CH2CO2Me is involved in the equilibrium, since
the orthopalladated unit is static on the NMR time scale; (iii) the
mononuclear species contains the O–bonded ester. Similar facts
are observed in the remaining NMR spectra.
1
The 31P{ H} NMR spectra of 2a–2d show the presence of
Scheme 3 (i) Pd(OAc)2, CH2Cl2, D, 5 h; (ii) LiCl, MeOH, r. t.;
(iii) Pd(OAc)2, CH2Cl2, D, 1 h; (iv) AgClO4, NCMe, -AgCl; (v) L, CH2Cl2.
a single peak, on each case, in the 48–58 ppm region, this
fact showing that the P atom is contained in a five-membered
palladacycle.15g,i The position of this peak for 2b–2d occurs in a
narrow range of frequencies and it is not temperature dependent.
However, the NMR spectrum of 2a at low temperature (253 K)
shows that the broad room temperature signal (57.50 ppm) splits
in three peaks, two at 58.17 and 58.12 ppm (assigned to the cis
and trans isomers of the dinuclear structure) and another one at
50.54 ppm, assigned to the mononuclear structure by similarity
The IR spectra of 2a–2d show that the iminophosphorane is N–
bonded, since the position of the mPN stretch band has been shifted
to lower energies in all cases [Dm = mbonded − mfree = −41 cm−1 (2a),
−46 cm−1 (2b), −18 cm−1 (2c) and −19 cm−1 (2d)]. In addition,
the IR spectrum of 2a shows a shift to lower wavenumbers of
the carbonyl stretch [Dm = −21 cm−1], and the same feature is
observed in the IR spectrum of 2b [Dm = −33 cm−1], meaning that
the carbonyl group is probably bonded to the Pd center through
the oxygen atom.
with mononuclear 2b–2d. The 13C{ H} NMR spectra of 2a–2d
1
show similar features to those described for the 1H and 31P nuclei,
and it must be mentioned that the orthometallated carbon appears
in the 149–157 ppm range.
The NMR spectra of 2a–2d give definitive proofs of the
1
orthopalladation. The H NMR spectra of 2a–2d show, in the
aromatic region, the presence of signals due to the presence of
the PdC6H4 unit and the PPh2 moiety. In some cases the signals
are well resolved and seven different peaks (relative intensity
1/1/1/1/4/2/4) can be detected, while in other cases extensive
overlap is observed. For 2b–2d the aliphatic regions also show
sharp peaks for the NCH2, NMe2, CH2S and SCH3 protons, and
the same feature is observed for the pyridinic protons of 2d. The
deshielding of the SMe (2c) and H6 (py) protons (2d), with respect
to their position in the non bonded iminophosphoranes, strongly
suggest the S- and N-bonding, respectively, of the ancillary groups
in solution.
The mononuclear nature of 2b–2d and the existence of an
equilibrium monomer–dimer for 2a in solution can also be
characterized through NMR diffusion experiments (DOSY), since
an additional proof of the nuclearity of each complex could be
related with the molecular size. The pulsed gradient spin-echo
(PGSE) NMR diffusion methods (DOSY) have proved to be a
valuable tool for the determination of relative molecular sizes
in solution,21 and we have recently applied this technique to
determine the nuclearity of phosphorus ylide mono- and dinuclear
derivatives.21f The diffusion coefficients D (m2 sg−1) of complexes
2a, 2c and 2d have been measured under the same experimental
conditions (CD2Cl2, T = 303 K, d = 1.50 ms, D = 100 ms,
concentrations ranging 1–1.5 mM), and spinning the samples to
minimize the convection currents.22 While the values found for
complexes 2c and 2d were nearly identical, 12.0 × 10−10 m2 sg−1
and 11.6 × 10−10 m2 sg−1 respectively, strongly suggesting a very
similar molecular size (2b was only adequately soluble in dmso-
d6 and could not be compared), the value found for 2a is smaller
(9.65 × 10−10 m2 sg−1), suggesting a larger size of 2a when compared
with 2c and 2d, and accounting for the presence of an equilibrium
between mono- and dinuclear forms.
These facts, and the IR observations, suggest that 2b–2d
are mononuclear complexes containing the iminophosphorane
bonded through the iminic N atom, the donor atom of the ancillary
group (O, S, N), and the orthopalladated aryl ring, as shown in
schemes 2 and 3 and eqn (1). The X-ray structure determination
1
of 2d gives additional proof. The H NMR spectra of 2b–2d are
not temperature dependent in the range 313–183 K.
(1)
In summary, the orthometallation of iminophosphoranes 1a–
1d, through a C–H bond activation promoted by Pd(OAc)2,
gives cyclopalladated complexes of different nuclearity 2a–2d in
a very efficient way. This easy palladation is quite noteworthy.
It is generally accepted that the cyclopalladation reaction in
solvents such as CH2Cl2 or toluene occurs through electrophilic
substitution on an aromatic ring.15q,r,23a Considering substrates
(i) Pd(OAc)2, toluene, D; (ii) LiCl, MeOH, r. t.
However, the H NMR spectrum of 2a shows, in addition to
sharp peaks on the aromatic zone, very broad signals at 293 K
assigned to the NCH2 and CO2Me protons (3.44–3.67 region),
1
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1a–1d, the C–H bond to be activated is located in a phenyl ring
bonded to a phosphorus atom which support a high degree of
formal positive charge,13c this fact reducing the susceptibility of
such Ph ring to undergo an electrophilic attack. However, even in
the presence of this deactivating substituents, the orthopalladation
takes place. Other factors which can also help to the promotion of
the orthometallation are the relief of steric crowding23b,c and the
assistance of ancillary functional groups. It seems that both facts
could be present in the orthopalladation of 1a–1d, although we
have shown that the orthopalladation of iminophosphoranes can
be produced at the less strained side of the molecule15q,r and that
the presence of additional coordinating functional groups is not a
mandatory prerequisite.15g Therefore, these factors must be taken
into account altogether.
ability, since it is easily displaced by a weak coordinating ligand as
NCMe. However, the carbonyl oxygen of 2b and the sulfur atom of
2c form strong bonds with the Pd atom, and they are not displaced
by NCMe, showing the stability of the two fused metallacycles on
2b and 2c toward coordinating solvents.
The reaction of 2a with neutral ligands L (PPh3, py) promotes
the cleavage of the bridging system and the formation of the
mononuclear species 4a (PPh3) and 5a (py). Further treatment
of these complexes with AgClO4 (1 : 1 molar ratio) results in
the synthesis of the O-bonded derivatives 6a (PPh3) and 7a (py)
(Scheme 1). Complexes 6a and 7a can also be obtained by direct
reaction of 2a with AgClO4 (1 : 2 molar ratio) in THF and
treatment of the solvate intermediate with the stoichiometric
amount of ligand L (1 : 1 molar ratio).
The X-ray crystal structure determinations of 2a and 2d
showed dinuclear and mononuclear arrangements on the crystal,
respectively (see below). While the tridentate coordination modes
of 2c and 2d can not be considered unusual, due to the known
affinity of the Pd center for S and N-donor ligands, the different
reactivity of 2a and 2b (two O-donor systems) is remarkable.
A sensible explanation can be given taking into account that
in the most representative resonance form of the amide group
the oxygen atom shows a high degree of negative formal charge
and could behave as a better donor atom than the oxygen of the
ester group. The different nature of the donor atoms should result
in metallacycles of different stability, and this stability has been
examined.
The structures shown in Scheme 1 for 4a–7a agree with the
known reluctance of PR3 ligands to bind trans to an arylic carbon
atom (or transphobia),24 and with the usual reactivity of the
halogen bridging systems towards neutral ligands,25 which gives
cis-to-C bonding of the incoming ligands L. The presence in the
IR spectra of absorptions at 1762 cm−1 (4a) and 1751 cm−1 (5a)
shows that the carbonyl group is not bonded in these complexes
to the metal center. On the other hand, the presence of two peaks
1
in the 31P{ H} NMR spectrum of 4a at 38.82 and 46.76 ppm
are assigned to the PPh3 ligand and the metallated C6H4-2-PPh2
groups, respectively, while the observation of a strongly shielded H6
resonance in 5a with respect to the starting compound 2a accounts
for the cis coordination of the pyridine ligand with respect to the
palladated unit due to the anisotropic shielding26 of the pyridine
ring.25b The abstraction of a chlorine ligand in 4a and 5a generates
a coordination vacancy, which is occupied by the carbonyl oxygen
in 6a and 7a. This fact is reflected in their IR spectra, through
the observation of the carbonyl stretch at 1644 cm−1 (6a) and
1652 cm−1 (7a), that is, shifted by more than 100 cm−1 to lower
energies with respect to the starting compounds 4a and 5a. The
Reactivity of the cyclopalladated complexes
The palladated iminophosphorane in complex 2a behaves as a
j2-C,N-chelate, while the corresponding metallated ligands in 2b,
2c and 2d behave as j3-C,N,O, j3-C,N,S and j3-C,N,N tridentate,
respectively. Two types of palladacycles are thus formed, a five
membered ring including the metallated carbon atom and another
five membered ring including the ancillary functional group, both
sharing the Pd–N bond. The stability of these two palladacycles
towards the addition of ligands has been examined.
1
effect of the O-coordination is also observed in the 13C{ H} NMR
spectra through the shift of the carbonyl carbon, which appears
at 186.12 ppm (6a) and 184.59 ppm (7a), clearly downfield shifted
with respect to the position in the respective starting material 4a
(173.98 ppm) and 5a (173.45 ppm). The change on the nature of
the atom trans to the palladated carbon atom (Cl versus O) is also
observed in the chemical shift of the orthopalladated carbon on
The reaction of 2a–2c with AgClO4 (molar ratio Pd : Ag 1 : 1) in
a coordinating solvent as NCMe results in the synthesis of the bis-
solvate 3a (Scheme 1) or the mono-solvate 3b and 3c derivatives
(Schemes 2 and 3). The incorporation of two solvent molecules
in 3a is clearly inferred from its spectroscopic data since two
peaks, assigned to the methyl groups of the two different NCMe
1
the 13C{ H} NMR spectrum, which is shifted to high field: these
peaks appear at 159.34 ppm (4a) and 155.50 ppm (5a) and are
shifted to 147.32 ppm (6a) and 146.77 ppm (7a).
1
1
ligands, were observed in the H and 13C{ H} NMR spectra of
3a. This fact implies the non bonding of the carbonyl group, and
this is reflected in the IR of 3a, which shows the carbonyl band
at 1741 cm−1. This band has been shifted to higher energies with
respect to 2a (1725 cm−1) in agreement with the disappearance of
the equilibrium between the coordinated and the uncoordinated
forms of the carbonyl group.
When the cleavage of the bridging system of 2a is performed
with a large excess of phosphine (1 : 4 molar ratio), complex
4a is the unique species detected in solution, together with free
phosphine. The chemical shift of the free PPh3 in this mixture
appears slightly shifted to low field, while the chemical shift of
the bonded PPh3 moves also slightly to high field, both signals
showing a very broad lineshape and suggesting that they are
involved in a dynamic equilibrium. The chemical shift of the P
nucleus at the metallacycle appears to be invariable with respect
to the PPh3 addition and keeps a sharp lineshape, showing that
the C,N-metallacycle is not involved in such dynamic equilibrium
and remains stable towards the phosphine addition. A further
increase of the amount of phosphine added does not produce
additional effects, and no other species—such as an hypothetical
bis(phosphine) derivative—were observed. A similar test has been
However, the NMR spectra of 3b and 3c show only one signal
due to the methyl group of the NCMe ligand, and thus only one
NCMe molecule is bonded on each complex. The O-bonding of
the carbonyl fragment can be deduced from the observation of
an absorption at 1609 cm−1 in the IR spectrum, similar to that
found in the starting compound 2b (1607 cm−1). In addition, the
X-ray structure of 3b has been determined. This means that the
oxygen of the carbonyl group in 2a displays a low coordinating
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performed using the cationic complex 6a. The reaction of 6a with
PPh3 (1 : 1 molar ratio) shows NMR features similar to those
described for 4a—the peaks assigned to free and bonded PPh3
move slightly and change dramatically their lineshape, while those
assigned to the C,N-metallacycle remain unaffected. These facts
mean that not only the orthometallated ring is stable towards the
moderate addition of PPh3, but also that the N,O-five membered
ring is equally stable, since we have not observed the cleavage
of the Pd–O bond and the incorporation of a second phosphine
ligand. The IR spectrum of this solution provides additional
evidences for the persistence of the Pd–O bond in solution, since
the carbonyl stretch appears at 1650 cm−1, a position closely
related with that observed in the pure product 6a in solid state
(1644 cm−1). However, the stability of 6a towards the addition of
large amounts of phosphine is more limited than that observed for
4a. The reaction of 6a with PPh3 (molar ratio > 1 : 4) promotes
the complete decomposition of the two metallacycles, amongst
other unidentified processes. In this respect, it is known that PPh3
promotes reductive couplings in palladium chemistry.27
Fig. 3 Molecular structure of 2a with ellipsoids drawn at the 50%
◦
˚
probability level. Selected bond distances [A] and angles [ ]: Pd(1)–C(1)
1.976(4); Pd(1)–N(1) 2.028(3); Pd(1)–Cl(1) 2.3439(1); P(1)–N(1) 1.590(3);
N(1)–C(19) 1.493(5); C(20)–O(1) 1.193(5); C(1)–Pd(1)–N(1) 85.36(14);
N(1)–Pd(1)–Cl(1A) 93.87(9); Cl(1A)–Pd(1)–Cl(1) 86.44(4); C(1)–Pd(1)–
Cl(1) 94.23(11); P(1)–N(1)–Pd(1) 111.33(18); P(1)–N(1)–C(19) 124.3(3);
Pd(1)–N(1)–C(19) 122.5(2).
The reactivity of complexes 3b and 3c towards monodentate
ligands has also been examined. The reaction of 3b with L in
CH2Cl2 (1 : 1 molar ratio) affords complexes 6b (L = PPh3) or
7b (L = py) by displacement of the weakly bonded NCMe by the
incoming L ligand (scheme 2). In the same way, the reaction of
3c with py (1 : 1 molar ratio) gives complex 7c (scheme 3). The
characterization of 6b, 7b and 7c show clearly the presence of
C,N,O and C,N,S metallacycles. The O-bonding in 6b and 7b is
easily inferred from the IR spectra of these complexes, since the mCO
absorption appears at 1602 (6b) and 1607 (7b) cm−1, very near to
the position found in 3b (1609 cm−1). The observation of signals
The molecular structure of 2a·2CHCl3 shows a dinuclear
compound in which each Pd atom is located in a slightly distorted
square planar environment, surrounded by two chlorine atoms
Cl(1) and Cl(1A), the iminic N atom N(1) and the metallated C
atom C(1).
The two square planes share an edge, at whose extremes
are located two bridging Cl atoms. The two Pd centers and
all the donor atoms are rigorously coplanar, as imposed by a
crystallographic inversion center located in the middle of the
Pd(1)–Pd(1A)–Cl(1)–Cl(1A) square. The relative arrangement of
the two cyclopalladated units is trans. Complexes 2d, 3b, 7b and 8
are mononuclear. In all cases, the Pd atom is located in a square
planar environment, very slightly distorted in spite of the presence
of different ligands. In 2d the Pd center is bonded to the chlorine
atom Cl(1) and to the carbon C(1) and nitrogen atoms [N(1),
N(2)] of the metallated group, which acts as an anionic C,N,N-
tridentate ligand. In 3b and 7b the cyclometallated group also acts
as an anionic C,N,O-tridentate ligand through the arylic carbon
C(1), the iminic N(1) and the amidic O(1) atoms, while in 8 the
iminophosphorane behaves as a neutral ligand and bonds to the
Pd atom through the sulfur S(1) and the iminic nitrogen N(1).
All these results are in good agreement with the spectroscopic
conclusions.
1
at 46.31 (6b) and 51.41 (7b) ppm in the 31P{ H} NMR spectra
suggest that the C,N-palladacycle is present in these molecules.
1
The presence of an additional peak at 38.91 ppm in the 31P{ H}
NMR spectrum of 6b, due to the PPh3 ligand, or the anisotropic
shielding of the H6 proton in the 1H NMR spectrum of 7b,
due to the pyridine ligand, gives proof of the presence of the
added L ligands. Complex 7c was characterized following similar
spectroscopic parameters.
The stability of the metallacycles in 6b towards the addition of
monodentate L ligands has been attempted in a similar way to that
described previously. The obtained results show that the response
of the systems to the addition of different amounts of PPh3 is
also similar to that observed with 6a. In low 6b/PPh3 molar ratios
(up to 1 : 2) only the exchange of the free and bonded phosphine
ligands is observed, while in larger molar ratios (more than 1 : 4)
the complete decomposition of the complex is produced. Finally,
the reactivity of 3c or 7c toward phosphines PR3 is not so clear
as that described previously and complex mixtures of unidentified
products were obtained.
The Pd(1)–C(1) bond distances in 2a–7b cover a narrow range of
˚
values [1.948(6)–1.978(2) A], in spite of the presence of different
donor atoms in their trans positions (Cl, N, O) and the neutral
(2a, 2d) or cationic (3b, 7b) character of the organometallic part
of these complexes. These distances also fall in the usual range of
distances found in the literature for this type of bond [1.959(3)–
15i,16d
˚
2.019(3) A].
However, the Pd(1)–N(1) bond distances in 2d–7b [range
X-Ray determinations
˚
1.972(5)–1.9942(17) A] are shorter than that found in 2a
˚
The X-ray crystal structures of 2a, 2d, 3b, 7b and 8 have been
determined by diffraction methods. Molecular drawings are shown
in Fig. 3 (2a), 4 (2d), 5 (3b), 6 (7b) and 7 (8), together with selected
bond distances and angles. Table 1 summarises the most important
parameters concerning data collection and structure solution and
refinement.
[2.028(3) A] and are also shorter than other reported values [range
˚
2.047(2)–2.172(3) A] for similar orthopalladated iminophospho-
˚
ranes. The P(1)–N(1) bond distances [range 1.590(3)–1.599(3) A]
are also identical, within experimental error, in all complexes. Fi-
nally, other Pd–N (py or NCMe), Pd–O (amide), Pd–S (thioether)
or Pd–Cl bond distances fall in the expected ranges.28 Internal
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Table 1 Crystal data and structure refinement for compounds 2a·2CHCl3, 2d, 3b·CH2Cl2, 7b and 8
2a·2CHCl3
2d
3b·CH2Cl2
7b
8
Empirical formula
FW
C44H40Cl8N2O4P2Pd2
1219.12
Monoclinic
P21/n
11.9958(2)
13.5663(3)
14.8552(2)
99.8661(14)
2381.76(7)
2
C24H20ClN2PPd
509.24
Monoclinic
P21/n
11.2481(3)
15.4741(4)
12.6043(4)
104.696(3)
2122.06(10)
4
C25H27Cl3N3O5PPd
693.22
Monoclinic
P21/n
8.0096(12)
22.592(3)
15.594(2)
92.464(3)
2819.2(7)
4
C27H27ClN3O5PPd
646.34
Monoclinic
P21/c
13.1099(11)
13.2935(11)
16.0085(13)
106.620(1)
2673.3(4)
4
C21H22Cl2NPPdS
528.73
Monoclinic
P21/n
7.9372(5)
16.4538(11)
16.6017(11)
90.214(1)
2168.1(2)
4
Cryst syst.
Space group
˚
a/A
˚
b/A
˚
c/A
b/◦
V/A
3
˚
Z
D
calc/Mg m−3
1.700
1.315
1.594
1.089
1.633
1.040
1.606
0.897
1.620
1.279
l/mm−1
Cryst. size
0.24 × 0.23 × 0.11
0.60 × 0.33 × 0.22
0.18 × 0.08 × 0.07
0.13 × 0.10 × 0.09
0.16 × 0.06 × 0.05
Reflns. collected
Reflns. independent
Data/restr./param
R1 [I > 2r(I)]
wR2 [I > 2r(I)]
R1 [all data]
wR2 [all data]
Gof
Largest diff peak, hole/e A
Temp./K
29116
21998
20461
17019
18890
5463, Rint = 0.0337
5463/42/309
0.0456
0.0912
0.0576
0.0950
1.139
6652, Rint = 0.0268
6652/0/262
0.0303
0.0781
0.0499
0.0817
0.963
4972, Rint = 0.1116
4972/31/383
0.0586
0.1245
0.0942
0.1408
0.993
6119, Rint = 0.0497
6119/0/345
0.0418
0.0888
0.0625
0.0971
1.010
4967, Rint = 0.0577
4967/0/245
0.0454
0.0915
0.0661
0.0999
1.019
−3
˚
1.296, −0.876
1.907, −0.527
0.639, −1.136
0.758, −0.429
0.633, −0.851
123(1)
150(1)
100(1)
100(1)
100(1)
˚
Radiation, k/A
0.71073
0.71073
0.71073
0.71073
0.71073
Fig. 5 Molecular structure of 3b with ellipsoids drawn at the 50%
probability level. Pd(1)–O(1) 2.122(4); Pd(1)–N(3) 2.004(6); Pd(1)–C(1)
1.948(6); Pd(1)–N(1) 1.972(5); N(1)–P(1) 1.598(5); N(1)–C(19) 1.471(8);
C(19)–C(20) 1.502(9); C(20)–O(1) 1.268(3); C(20)–N(2) 1.302(8); N(3)–
Pd(1)–C(1) 93.6(2); C(1)–Pd(1)–N(1) 87.6(2); N(1)–Pd(1)–O(1) 80.20(19);
O(1)–Pd(1)–N(3) 98.6(2); C(19)–C(20)–N(2) 118.3(6); O(1)–C(20)–N(2)
121.6(6); C(19)–C(20)–O(1) 120.2(6); Pd(1)–N(1)–C(19) 116.8(4).
Fig.
4
Molecular structure of 2d with ellipsoids drawn at the
50% probability level. Pd(1)–C(1) 1.978(2); Pd(1)–N(1) 1.9942(17);
Pd(1)–N(2) 2.1180(19); Pd(1)–Cl(1) 2.3108(6); P(1)–N(1) 1.5985(18);
N(1)–C(19) 1.461(3); C(19)–C(20) 1.495(3); C(1)–Pd(1)–N(1) 87.64(8);
N(1)–Pd(1)–N(2) 79.96(7); N(2)–Pd(1)–Cl(1) 96.64(5); C(1)–Pd(1)–Cl(1)
95.75(6); P(1)–N(1)–Pd(1) 116.76(10); P(1)–N(1)–C(19) 123.41(14);
Pd(1)–N(1)–C(19) 116.60(14).
but in most cases a tridentate coordination (C,N,O-, C,N,S- or
C,N,N-) is observed. The resulting palladacycles are remarkably
stable towards the addition of phosphine ligands.
parameters of the metallated aryl rings as well as those of the
ancillary ligands do not show unusual facts.
Conclusions
Experimental
=
The palladation of non-stabilized iminophosphoranes Ph3P N–
CH2–R (R = CO2Me, CONMe2, CH2SMe, NC5H4-2) is easily
accomplished by their treatment with Pd(OAc)2. The reaction
occurs through a C–H bond activation process in a strongly
deactivated Ph ring, this fact being noteworthy. In some cases, the
resulting anionic ligand bonds as a C,N-chelate to the Pd center,
Safety note
Caution! Perchlorate salts of metal complexes with organic ligands
are potentially explosive. Only small amounts of these materials
should be prepared and they should be handled with great caution.
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1
1
1
The H, 13C{ H} and 31P{ H} NMR spectra were recorded in
CDCl3, CD2Cl2 or dmso-d6 solutions at 25 ◦C (other temperatures
were specified) on Bruker ARX-300, AvanceII-300, Avance-
400 and Avance-500 spectrometers (d, ppm; J, Hz); 1H and
1
13C{ H} were referenced using the solvent signal as internal
1
standard while 31P{ H} was externally referenced to H3PO4 (85%).
The 1H SELNO-1D and SELRO-1D NMR experiments were
performed with optimized mixing times (D8/P15), depending on
the irradiated signal. ESI/APCI mass spectra were recorded using
an Esquire 3000 ion-trap mass spectrometer (Bruker Daltonic
GmbH, Bremen, Germany) equipped with a standard ESI/APCI
source. Samples were introduced by direct infusion with a syringe
pump. Nitrogen served both as the nebulizer gas and the dry gas.
Helium served as a cooling gas for the ion trap and collision
gas for MSn experiments. Other mass spectra (positive ion FAB)
were recorded from CH2Cl2 solutions on a V. G. Autospec spec-
trometer. The starting azides N3CH2CO2Me, N3CH2CONMe2,
N3CH2CH2SMe and N3CH2-2-NC5H4 were prepared according
to published procedures.17
Fig. 6 Molecular structure of 7b with ellipsoids drawn at the 50% proba-
bility level. Pd(1)–C(1) 1.974(3); Pd(1)–N(1) 1.988(3); Pd(1)–N(3) 2.037(3);
Pd(1)–O(1) 2.118(2); P(1)–N(1) 1.599(3); N(1)–C(19) 1.4541(4); C(19)–
C(20) 1.530(5); O(1)–C(20) 1.253(4); C(20)–N(2) 1.316(4); C(1)–Pd(1)–
N(1) 88.33(13); N(1)–Pd(1)–O(1) 80.22(10); O(1)–Pd(1)–N(3) 94.91(10);
N(3)–Pd(1)–C(1) 96.59(13); P(1)–N(1)–Pd(1) 117.20(16); Pd(1)–N(1)–
C(19) 116.6(2); C(19)–C(20)–O(1) 120.21(3); C(20)–O(1)–Pd(1) 113.8(2).
=
Synthesis of [Ph3P NCH2COOMe] (1a). Staudinger
method1a. To a solution of N3CH2CO2Me (0.795 g, 6.90 mmol) in
freshly distilled CH2Cl2 (10 mL) under Ar atmosphere, a solution
of PPh3 (1.80 g, 6.90 mmol) in dry CH2Cl2 (10 mL) was added
dropwise. The addition was completed in 20 min, and during this
time the evolution of N2 was evident. The resulting solution was
stirred at room temperature for 12 h, until the evolution of N2
ceased. Then, the solvent was evaporated to dryness, giving 1a
as a slightly pink oil. The compound can be used in subsequent
reactions without further purification. Yield: 1.952 g (81.0%).
Anal. Calc. for C21H20NO2P (349.36): C, 72.20; H, 5.77; N, 4.01.
Found: C, 71.70; H, 5.69; N, 3.85. IR (m, cm−1): 1746 (mCO),
1
1295 (mPN). MS (MALDI) [m/z, (%)]: 350 (100) [M + H]+. H
NMR (CDCl3): d = 3.48 (s, 3H, OMe), 3.82 (d, 2H, 3JPH = 21.8,
CH2), 7-33-7.35 (m, 6H, Hm, PPh3), 7.36–7.42 (m, 3H, Hp, PPh3),
1
7.56–7.61 (m, 6H, Ho, PPh3). 13C{ H} NMR (CDCl3): d = 48.21
2
3
(d, JPC = 3.4, CH2), 51.43 (OMe), 128.41 (d, JPC = 11.6, Cm,
PPh3), 130.83 (d, 1JPC = 97.1, Ci, PPh3), 131.44 (d, 4JPC = 2.7, Cp,
2
3
Fig. 7 Molecular structure of 8 with ellipsoids drawn at the 50% prob-
ability level. Pd(1)–Cl(1) 2.3068(10); Pd(1)–Cl(2) 2.3144(10); Pd(1)–N(1)
2.042(3); Pd(1)–S(1) 2.2590(10); P(1)–N(1) 1.609(3); N(1)–C(19) 1.478(5);
C(19)–C(20) 1.517(5); C(20)–S(1) 1.816(4); S(1)–C(21) 1.804(4); N(1)–
Pd(1)–S(1) 85.29(9); N(1)–Pd(1)–Cl(1) 94.45(9); Cl(1)–Pd(1)–Cl(2)
92.83(4); S(1)–Pd(1)–Cl(2) 87.39(4); P(1)–N(1)–Pd(1) 129.91(18); Pd(1)–
N(1)–C(19) 110.1(2); C(20)–S(1)–Pd(1) 99.86(13); C(20)–S(1)–C(21)
100.5(2); C(21)–S(1)–Pd(1) 103.21(14).
PPh3), 132.62 (d, JPC = 9.1, Co, PPh3), 175.44 (d, JPC = 17.5,
CO). 31P{ H} NMR (CDCl3): d = 15.58.
1
=
Synthesis of [Pd(l-Cl){C6H4(PPh2 NCH2CO2Me-j-C,N)-2}]2
(2a). To a solution of 1a (1.950 g, 5.58 mmol) in CH2Cl2
(20 mL), Pd(OAc)2 (1.250 g, 5.58 mmol) was added, and the
resulting mixture was refluxed for 1 h. After the reaction time,
decomposition is evident. The cooled black suspension was treated
with charcoal for 15 min, and then filtered over Celite giving a deep
orange solution. This solution, which contains the acetate bridge
intermediate, was evaporated to dryness. The oily brown residue
was redissolved in MeOH and treated with an excess of anhydrous
LiCl (0.946 g, 22.3 mmol). After a few seconds, an orange solid
precipitated, but the stirring was maintained for additional 3 h at
25 ◦C. The resulting suspension was filtered, and the orange solid
was washed with MeOH (20 mL) and Et2O (50 mL), dried by
suction and identified as the equilibrium mixture 2a. Yield: 1.340 g
(49%). Compound 2a crystallized as 2a·2CHCl3 from slow vapour
diffusion of Et2O into a CHCl3 solution of the crude compound.
Crystals were used for spectroscopic and analytic measurements.
Anal. Calc. for [C42H38Cl2N2O4P2Pd2]·2CHCl3 (1219.12): C, 43.35;
See W. C. Wolsey, J. Chem. Educ. 1973, 50, A335–A337. The
organic azides are highly hazardous materials which can explode,
and whose preparation and manipulation must be carried out with
maximum caution. They must be stored at low temperature (T ≈
0 ◦C) and dissolved in an inert solvent.17
General methods
Solvents were dried and distilled under argon using standard
procedures before use. Elemental analyses were carried out on
a Perkin-Elmer 2400-B microanalyser. Infrared spectra (4000–
200 cm−1) were recorded on a Perkin-Elmer 883 infrared spec-
trophotometer from Nujol mulls between polyethylene sheets.
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H, 3.31; N, 2.30. Found: C, 43.32; H, 3.52; N, 2.29. IR (m, cm−1):
1725 (mCO), 1254 (mPN). MS (FAB+) [m/z, (%)]: 943 (100) [M2 − Cl]+.
1H NMR (CDCl3): d = 3.44–3.67 (very broad, 5H, CH2 + OMe),
=
Synthesis of [PdCl{C6H4(PPh2 NCH2–2-NC5H4-j-C,N,N)-2}]
(2d). Complex 2d was prepared following the same preparative
method as that described for 2a, except that the reaction solvent
was toluene. Thus, 1d (0.300 g, 0.81 mmol) was reacted with
Pd(OAc)2 (0.18 g, 0.81 mmol) in refluxing toluene (20 mL), and
with excess LiCl (0.210 g, 5.00 mmol) in MeOH (20 mL) to give
2d as a deep orange solid. Yield: 0.315 g (76%). Anal. Calc. for
C24H20ClN2PPd (509.2): C, 56.55; H, 3.95; N, 5.50. Found: C,
56.10; H, 3.47; N, 5.16. IR (m, cm−1): 1287 (mPN). MS (FAB+) [m/z,
4
3
6.72–6.76 (m, 1H, H3, C6H4), 6.87 (dd, 1H, JHH = 5.4, JHH
=
9.3, H4, C6H4), 7.00 (t, 1H, 3JHH = 5.4, H5, C6H4), 7.42–7.46 (m,
4H, Hm, PPh2), 7.53–7.56 (m, 3H, 2 Hp (PPh2) + H6 (C6H4)), 7.67–
1
7.71 (m, 4H, Ho, PPh2). 13C{ H} NMR (CDCl3): d = 48.69 (CH2),
51.76 (OMe), 124.13 (d, 3JPC = 14.4, C4, C6H4), 128.24 (d, 2JPC
=
3
12.3, C3, C6H4), 129.05 (d, JPC = 11.3, Cm, PPh2), 131.91 (Cp,
PPh2), 132.10 (d, 4JPC = 9.2, C5, C6H4), 132.98 (d, 2JPC = 9.3, Co,
PPh2), 134.89 (d, 3JPC = 10.3, C6, C6H4), 174.75 (CO). Signals to be
assigned to the carbon atoms Ci (PPh2) and C1, C2 (C6H4) were not
(%)]: 507 (20) [M − 2H]+. H NMR (CDCl3): d = 4.41 (d, 2H,
1
3JPH = 7.0, CH2), 6.80 (ddd, 1H, 4JHH = 1.4, 3JHH = 7.6, JPH = 11.2,
C6H4), 6.95 (m, 1H, C6H4), 7.10 (d, 1H, JHH = 7.8, C6H4), 7.15–
7.19 (m, 2H, H4, H5, py), 7.52–7.57 (m, 4H, Hm, PPh2), 7.61–7.66
(m, 3H, 2Hp (PPh2) + 1H (C6H4)), 7.74–7.79 (m, 4H, Ho, PPh2),
1
observed. 31P{ H} NMR (CDCl3): d = 57.50. 1H NMR (CDCl3,
253 K): d = 3.53 (OMe), 3.55 (OMe), 3.61 (d, 3JPH = 18.6, CH2),
3.72 (d, 3JPH = 18.9, CH2), 3.82 (OMe), 3.88 (d, 3JPH = 7.6, CH2),
6.84–6.88 (m, H3, C6H4), 6.98–7.01 (m, H4, C6H4), 7.07–7.15 (m,
H5, C6H4), 7.52–7.55 (m, Hm, PPh3), 7.63–7.66 (m, Hp (PPh3) +
5
4
3
8.12 (ddd, 1H, JHH = 0.7, JHH = 2.3, JHH = 7.8, H3, py), 8.98
(dd, 1H, 5JHH = 0.7, 3JHH = 5.3, H6, py). 13C{ H} NMR (CDCl3):
1
d = 51.43 (CH2), 119.51 (C6H4), 121.33 (py), 123.00 (d, JPC
=
=
1
H6 (C6H4)), 7.75–7.79 (m, Ho, PPh3). 31P{ H} NMR (CDCl3, 253
1
15.1, C6H4), 126.05 (d, JPC = 83.7, Ci, PPh2), 127.99 (d, JPC
22.0, C6H4), 128.25 (d, 3JPC = 11.5, Cm, PPh2), 130.0 (d, JPC = 3.2,
K): d = 50.55 (mononuclear), 58.12, 58.17 (cis + trans dinuclear);
molar ratio = 1 : 5.
2
4
py), 131.76 (d, JPC = 9.8, Co, PPh2), 132.09 (d, JPC = 2.7, Cp,
4
PPh2), 136.18 (C6H4), 137.58 (d, JPC = 14.7, C3, py), 141.05 (d,
1JPC = 142.4, C2, C6H4), 148.22 (C6, py), 153.97 (d, JPC = 19.0,
2
=
Synthesis of [PdCl{C6H4(PPh2 NCH2CONMe2-j-C,N,O)-2}]
C1, C6H4), 165.40 (d, 3JPC = 17.5, C2, py). 31P{ H} NMR (CDCl3):
1
(2b). Complex 2b was prepared following the same preparative
method as that described for 2a. Thus, 1b (0.570 g, 1.53 mmol) was
reacted with Pd(OAc)2 (0.343 g, 1.53 mmol) in refluxing CH2Cl2
(20 mL), and with excess LiCl (0.946 g, 22.3 mmol) in MeOH (20
mL) to give 2b as a yellow solid. Yield: 0.215 g (27.4%). Anal. Calc.
for C22H22ClN2OPPd (503.3): C, 52.45; H, 4.40; N, 5.56. Found:
C, 51.90; H, 4.85; N, 5.46. IR (m, cm−1): 1607 (mCO), 1258 (mPN). MS
d = 48.53.
=
[Pd{C6H4(PPh2 NCH2CO2Me-j-C,N)-2}-
Synthesis
of
(NCMe)2](ClO4) (3a). A suspension of 2a (0.200 g, 2.03 mmol)
in dry NCMe (15 mL) was treated with AgClO4 (0.084 g,
4.07 mmol), and the resulting suspension was stirred at 25 ◦C for
1 h with exclusion of light. After the reaction time, the insoluble
AgCl was filtered, and the resulting solution was evaporated to
small volume (≈2 mL). By Et2O (20 mL) addition and further
stirring, 3a was obtained as a white solid. Yield: 0.187 g (72.5%).
Anal. Calc. for C25H25ClN3O6PPd (636.3): C, 47.19; H, 3.96;
N, 6.60. Found: C, 47.31; H, 3.64; N, 6.82. IR (m, cm−1): 2291
(mCN), 1741 (mCO), 1216 (mPN). MS (FAB+) [m/z, (%)]: 455 (100)
[M-2NCMe-ClO4]+. 1H NMR (CDCl3): d = 2.00 (s, 3H, NCMe),
1
(FAB+) [m/z, (%)]: 467 (100) [M − Cl]+. H NMR (DMSO-d6):
d = 2.81 (s, 3H, NMe), 2.85 (s, 3H, NMe), 3.96 (d, 2H, 3JPH = 6.8,
CH2), 6.84–6.89 (m, 1H, C6H4), 6.96–7.00 (m, 1H, C6H4), 7.05–
7.08 (m, 1H, C6H4), 7.65–7.78 (m, 11H, 1H (C6H4) + 10H (PPh2)).
1
31P{ H} NMR (DMSO-d6): d = 48.13.
=
Synthesis of [PdCl{C6H4(PPh2 NCH2CH2SMe-j-C,N,S)-2}]
3
2.51 (s, 3H, NCMe), 3.83 (s, 3H, OMe), 3.88 (d, 2H, JPH = 8.1,
(2c). Complex 2c was prepared following the same preparative
method as that described for 2a, except that the reaction time was
5 h. Thus, 1c (0.675 g, 1.72 mmol) was reacted with Pd(OAc)2
(0.386 g, 1.72 mmol) in CH2Cl2 (20 mL), and with excess LiCl
(0.291 g, 6.80 mmol) in MeOH (20 mL) to give 2c as a deep yellow
solid. Yield: 0.426 g (57.2%). Anal. Calc. for C21H21ClNPPdS
(492.0): C, 51.22; H, 4.29; N, 2.84. Found: C, 51.11; H, 4.24;
N, 2.92. IR (m, cm−1): 1228 (mPN). MS (FAB+) [m/z, (%)]: 492 (27)
[M]+. 1H NMR (CD2Cl2): d = 2.32 (s, 3H, SMe), 2.79 (s, br, 2H,
SCH2), 2.91 (dd, 2H, 3JHH = 5.8, 2JPH = 12.6, NCH2), 6.82 (ddd,
1H, 3JHH = 7.5, 4JHH = 1.5, 3JPH = 9.1, H3, C6H4), 6.98 (tdd, 1H,
CH2), 6.90 (ddd, 1H, JHH = 0.6, JHH = 2.8, JHH = 7.2, C6H4),
7.11–7.18 (m, 1H, C6H4), 7.21–7.29 (m, 2H, C6H4), 7.60–7.77
(m, 10H, PPh2). 13C{ H} NMR (CDCl3): d = 2.16 (NCMe), 3.79
1
1
(NCMe), 49.12 (CH2), 54.87 (OMe), 124.25 (d, JPC = 50.1, Ci,
3
PPh2), 125.97 (d, JPC = 14.5, C6H4), 129.86 (d, JPC = 11.9, Cm,
2
PPh2), 130.16 (C6H4), 131.90 (C6H4), 132.16 (d, JPC = 10.2, Co,
4
PPh2), 134.22 (d, JPC = 1.0, Cp, PPh2), 136.20 (d, JPC = 13.3,
3
C6H4), 178.4 (d, JPC = 2.2, CO). Signals to assign to C1, C2
(C6H4) and CN carbon atoms were not observed. 31P{ H} NMR
1
(CDCl3): d = 57.64.
3JHH = 7.4, 4JHH = 1.1, 4JPH = 5.0, H4, C6H4), 7.17 (tt, 1H, 4JHH
=
Synthesis of [PdCl{C6H4(PPh2 NCH2CO2Me-j-C,N)-2}-
=
1.6, 3JPH = 7.7, H5, C6H4), 7.50–7.54 (m, 4H, Hm, PPh2), 7.61–7.68
(m, 6H, 4Ho + 2Hp, PPh2), 7.92 (ddd, 1H, 4JHH = 1.0, 3JHH = 9.4,
(PPh3)] (4a). To a suspension of 2a (0.150 g, 1.52 mmol) in
15 mL of CH2Cl2, PPh3 (0.080 g, 3.05 mmol) was added. The
initial suspension gradually dissolved and, after the reaction
time (1 h), a clear yellow solution was obtained. Any insoluble
impurity was filtered at this point and discarded. The resulting
clear solution was evaporated to dryness and Et2O (20 mL) was
added to the oily residue. Further stirring allowed the isolation
of 4a as a yellow solid. Yield: 0.176 g (77.2%). Anal. Calc. for
C39H34ClNO2P2Pd (751.9): C, 62.00; H, 4.50; N, 1.80. Found:
C, 61.97; H, 3.92; N, 1.63. IR (m, cm−1): 1762 (mCO), 1262 (mPN).
1
4JPH = 1.9, H6, C6H4). 13C{ H} NMR (CD2Cl2): d = 17.77 (SMe),
42.41 (d, 3JPC = 18.4, SCH2), 45.40 (NCH2), 124.40 (d, 3JPC = 14.6,
C4, C6H4), 127.01 (d, 1JPC = 83.6, Ci, PPh2), 128.51 (d, 2JPC = 12.1,
C3, C6H4), 129.15 (d, 3JPC = 11.5, Cm, PPh2), 131.07 (d, 4JPC = 3.2,
C5, C6H4), 132.57 (d, 3JPC = 9.7, Co, PPh2), 133.02 (d, 4JPC = 2.5,
3
2
Cp, PPh2), 136.43 (d, JPC = 14.8, C6, C6H4), 140.67 (d, JPC
=
141, C2, C6H4 , 157.21 (d, 2JPC = 20.2, C1, C6H4). 31P{ H} NMR
)
1
(CD2Cl2): d = 50.37.
1210 | Dalton Trans., 2008, 1203–1214
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MS (FAB+) [m/z, (%)]: 717 (100) [M − Cl]+. 1H NMR (CDCl3):
6.91. Found: C, 47.27; H, 4.50; N, 6.53. IR (m, cm−1): 2326, 2293
(mCN), 1610 (mC=O), 1259 (mP=N). MS (FAB+) [m/z, (%)]: 467 (100)
4
3
d = 3.43 (s, 3H, OMe), 4.12 (dd, 2H, JPH = 19.7, JPH = 5.3,
3
3
1
CH2), 6.39 (t, 1H, JHH = 7.5, H5, C6H4), 6.54 (dt, 1H, JHH
=
[M − NCMe − ClO4]+. H NMR (CD2Cl2): d = 2.51 (s, 3H,
7.3, 4JHH = 1.5, H6, C6H4), 6.65 (dd, 1H, 3JHH = 7.3, 4JPH = 12.1,
H4, C6H4), 6.82 (ddd, 1H, 3JHH = 7.5, 4JHH = 1.5, 3JPH = 9.0, H3,
C6H4), 7.16–7.20 (m, 6H, Hm, PPh3), 7.25–7.30 (m, 3H, Hp, PPh3),
NCMe), 2.93 (s, 3H, NMe), 3.00 (s, 3H, NMe), 3.95 (d, 2H, 3JPH
=
6.8, CH2), 6.92 (ddd, 1H, 3JHH = 7.2, 4JHH = 1.2, 4JPH = 11.2, H6,
C6H4), 7.13–7.18 (m, 1H, H5, C6H4), 7.24–7.31 (m, 2H, H3, H4,
C6H4), 7.66–7.71 (m, 4H, Hm, PPh2), 7.74–7.80 (m, 6H, 4Ho + 2Hp,
3
4
7.44–7.49 (td, 4H, JHH = 7.3, JHH = 2.5, Hm, PPh2), 7.54–7–58
(m, 8H, 6Ho (PPh3) + 2Hp (PPh2)) 7.80 (dd, 4H, 3JHH = 7.0, 3JPH
=
PPh2). 13C{ H} NMR (CD2Cl2): d = 3.59 (NCMe), 36.04 (NMe),
1
11.3, Ho, PPh2). 13C{ H} NMR (CDCl3): d = 47.83 (d, 3JPC = 2.3,
CH2), 51.46 (s, OMe), 122.87 (d, JPC = 14.1, C6H4), 127.78 (d,
3JPC = 10.7, Cm, PPh3), 128.09 (d, JPC = 10.9, C6H4), 128.76 (d,
3JPC = 11.4, Cm, PPh2), 129.19 (C6H4), 130.08 (d, 4JPC = 1.9, Cp,
38.22 (NMe), 49.55 (NCH2), 119.25 (NC), 125.18 (d, 1JPC = 89.6,
Ci, PPh2), 125.49 (d, 4JPC = 5.1, C5, C6H4), 129.76 (d, 3JPC = 12.3,
1
3
3
Cm, PPh2), 130.31 (d, JPC = 20.6, C6, C6H4), 132.05 (d, JPC
=
=
=
2.1, C4, C6H4), 132.63 (d, 2JPC = 10.3, Co, PPh2), 134.05 (d, 3JPC
1
1
PPh3), 130.39 (d, JPC = 65.8, Ci, PPh2), 131.94 (d, JPC = 48.8,
2.1, Cp, PPh2), 135.67 (d, 2JPC = 13.3, C3, C6H4), 141.12 (d, 1JPC
Ci, PPh3), 132.50 (d, 4JPC = 2.1, Cp, PPh2), 133.37 (d, 2JPC = 9.7,
144.2, C2, C6H4), 147.24 (d, JPC = 16.4, C1, C6H4), 180.51 (d,
2
2
1
Co, PPh2), 135.25 (d, JPC = 11.7, Co, PPh3), 139.75 (dd, JPC
=
3JPC = 18.5, CO). 31P{ H} NMR (CD2Cl2): d = 55.23.
13.2, JPC = 14.8, C6H4), 141.16 (d, 1JPC = 136.6, C2, C6H4), 159.34
(d, JPC = 18.8, C1, C6H4), 173.98 (d, JPC = 10.8, CO). 31P{ H}
2
3
1
=
Synthesis of [Pd{C6H4(PPh2 NCH2CONMe2-j-C,N,O)-2}-
3
3
NMR (CDCl3): d = 38.82 (d, JPP = 2.5, PPh3), 46.76 (d, JPP
=
(PPh3)](ClO4) (6b). To a solution of 3b (0.040 g, 0.061 mmol)
in CH2Cl2 (15 mL), PPh3 (0.020 g, 0.061 mmol) was added. The
resulting solution was stirred for 40 min at 25 ◦C, then evaporated
to dryness. By Et2O (25 mL) addition to the oily residue and
further stirring, 6b was obtained as a yellow solid. The yield was
quantitative (0.044 g). Anal. Calc. for C40H37ClN2O5P2Pd (829.5):
C, 57.92; H, 4.50; N, 3.38. Found: C, 57.81; H, 4.78; N, 3.70. IR
(m, cm−1): 1602 (mC=O), 1257 (mP=N). MS (FAB+) [m/z, (%)]: 729
2.9, C6H4PPh2).
=
Synthesis of [Pd{C6H4(PPh2 NCH2CO2Me-j-C,N,O)-2}-
(PPh3)](ClO4) (6a). Method A. A solution of 4a (0.130 g,
1.77 mmol) in dry THF (20 mL) was treated with AgClO4
(0.036 g, 1.77 mmol), and the resulting suspension was stirred
with exclusion of light for 1 h. After the reaction time the insoluble
AgCl was filtered over Celite, and the resulting yellow solution
was evaporated to dryness. By Et2O addition (25 mL) and further
stirring, complex 6a was obtained as a yellow solid. Yield: 0.112 g
(77.5%). Method B. To a solution of 2a (0.150 g, 0.15 mmol) in
THF (20 mL), AgClO4 (0.063 g, 0.30 mmol) was added, and the
resulting solution was stirred for 30 min at room temperature
with exclusion of light. The obtained suspension was filtered, and
the resulting solution was treated with PPh3 (0.08 g, 0.3 mmol)
and stirring at 25 ◦C for 5 h. At the end of the reaction time,
the solution was evaporated to dryness and the residue treated
with Et2O (15 mL). Further stirring gives 6a as a yellow solid.
Yield: 0.188 g (77%). Anal. Calc. for C39H34ClNO6P2Pd (816.5):
C, 57.36; H, 4.19; N, 1.71. Found: C, 57.33; H, 4.12; N, 1.69. IR
(m, cm−1): 1644 (mCO), 1272 (mPN). MS (FAB+) [m/z, (%)]: 716 (100)
[M − ClO4]+. 1H NMR (CD2Cl2): d = 3.76 (s, 3H, OMe), 4.14 (dd,
2H, 4JPH = 7.2, 3JPH = 2.4, CH2), 6.67 (m, 1H, H6, C6H4), 6.78 (m,
1H, H5, C6H4), 6.92–7.03 (m, 2H, H4, H3, C6H4), 7.44–7.61 (m,
1
(100) [M − ClO4]+. H NMR (CD2Cl2): d = 2.36 (s, 3H, NMe),
2.75 (s, 3H, NMe), 4.04 (dd, 2H, 4JPH = 1.3, 3JPH = 7.4, CH2), 6.56
(m, 1H, H6, C6H4), 6.66 (m, 1H, C6H4), 6.81–6.88 (m, 2H, C6H4),
7.37 (m, 6H, Hm, PPh3), 7.45 (m, 3H, Hp, PPh3), 7.60 (m, 6H, Ho,
1
PPh3), 7.64–7.72 (m, 10H, PPh2). 13C{ H} NMR (CDCl3): d =
2
36.38 (NMe), 38.45 (NMe), 49.67 (d, JPC = 1.4, NCH2), 124.69
(d, JPC = 14.7, C6H4), 126.32 (d, 1JPC = 86.2, Ci, PPh2), 128.70 (d,
1
3JPC = 10.8, Cm, PPh3), 129.41 (d, JPC = 49.1, Ci, PPh3), 129.80
2
(d, JPC = 11.8, Co, PPh3), 130.94 (d, JPC = 20.8, C6H4), 131.37
4
(d, JPC = 2.3, Cp, PPh3), 131.48 (d, JPC = 5.1, C6H4), 132.78 (d,
3JPC = 10.1, Cm, PPh2), 133.81 (d, 4JPC = 2.7, Cp, PPh2), 134.93 (d,
2JPC = 12.2, Co, PPh2), 140.54 (t, JPC = 26.7, C6H4), 143.25 (dd,
3JPC = 10.4, 1JPC = 131.0, C2, C6H4), 150.26 (dd, 2JPC = 5.0, 2JPC
=
1
16.3, C1, C6H4), 181.85 (dd, 3JPC = 5.5, 3JPC = 19.8, CO). 31P{ H}
NMR (CD2Cl2): d = 38.91 (d, 3JPP = 5.2, PPh3), 46.31 (d, PPh2N).
1
10H, PPh2), 7.64–7.82 (m, 15H, PPh3). 13C{ H} NMR (CDCl3):
=
Synthesis of [Pd{C6H4(PPh2 NCH2CH2SMe-j-C,N,S)-2}-
3
d = 49.27 (CH2), 55.09 (s, OMe), 125.31 (d, JPC = 14.7, C4,
(NCMe)](ClO4) (3c). Complex 3c was prepared following a
synthetic method similar to that reported for 3a. Thus, 2c (0.200 g,
2.30 mmol) was reacted with AgClO4 (0.046 g, 2.30 mmol) in
NCMe (10 mL) to give 3c as a yellow solid. Yield: 0.166 g (67.1%).
Anal. Calc. for C23H24ClO4N2PPdS (597.4): C, 46.20; H, 4.04;
N, 4.68; S, 5.30. Found: C, 46.00; H, 3.91; N, 4.61; S, 6.00. IR
(m, cm−1): 2324, 2293 (mCN), 1230 (mP=N). MS (FAB+) [m/z, (%)]:
C6H4), 125.85 (d, 1JPC = 86.9, Ci, PPh2), 127.67 (d, 1JPC = 87.4, Ci,
2
2
PPh3), 128.87 (d, JPC = 11.0, Cm, PPh3), 129.87 (d, JPC = 11.9,
Cm, PPh2), 131.23 (d, 2JPC = 20.4, C3, C6H4), 131.68 (d, 4JPC = 2.1,
Cp, PPh3), 131.97 (dd, 4JPC = 3.1, 4JPC = 5.3, C5, C6H4), 132.57 (d,
3JPC = 10.2, Co, PPh2), 134.08 (d, 4JPC = 2.4, Cp, PPh2), 134.80 (d,
3
3JPC = 12.3, Co, PPh3), 140.39 (t, JPC = 13.6, C6, C6H4), 141.93
(dd, 1JPC = 139.6, 4JPC = 1.6, C2, C6H4), 147.32 (dd, 2JPC = 15.1,
1
497 (100) [M − ClO4]+. H NMR (DMSO-d6): d = 2.07 (s, 3H,
3
3
2JPC = 3.2, C1, C6H4), 186.12 (dd, JPC = 23.1, JPC = 5.5, CO).
3
NCMe), 2.46 (s, 3H, SMe), 3.04 (t, 2H, JHH = 5.2, SCH2), 3.26
31P{ H} NMR (CD2Cl2): d = 39.29 (PPh3), 47.55 (C6H4PPh2).
1
(m, 2H, NCH2), 7.17–7.28 (m, 2H, H3, H4, C6H4), 7.42 (t, 1H,
Synthesis of [Pd{C6H4(PPh2 NCH2CONMe2-j-C,N,O)-2}-
3JHH = 8.0, H5, C6H4), 7.67–7.82 (m, 10H, PPh2), 7.94 (dd, 1H,
=
1
(NCMe)](ClO4) (3b). Complex 3b was prepared following a
synthetic method similar to that reported for 3a. Thus, 2b (0.100 g,
0.97 mmol) was reacted with AgClO4 (0.040 g, 1.94 mmol) in
NCMe (10 mL) to give 3b as a white solid. Yield: 0.102 g (79.4%).
Anal. Calc. for C24H25ClN3O5PPd (608.1): C, 47.36; H, 4.14; N,
3JHH = 8.0, 4JHH = 1.6, H6, C6H4). 13C{ H} NMR (DMSO-d6): d =
2
0.02 (NCMe), 14.38 (SMe), 39.56 (d, JPC = 15.2, CH2S), 44.08
1
(CH2N), 116.99 (NC), 124.84 (d, JPC = 86.0, Ci, PPh2), 125.29
3
(d, JPC = 13.5, C6H4), 128.60 (d, JPC = 11.7, Cm, PPh2), 129.58
2
(d, JPC = 21.0, C6H4), 131.34 (d, JPC = 10.2, Co, PPh2), 132.71
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Dalton Trans., 2008, 1203–1214 | 1211
©

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(d, 4JPC = 1.7, Cp, PPh2), 133.51 (d, JPC = 14.7, C6H4), 140.81 (d,
Sundermeyer, B. Kovacevic and Z. B. Maksic, J. Am. Chem. Soc., 2005,
¨
1
1JPC = 135.6, C2, C6H4), 156.04 (d, 2JPC = 20.8, C1, C6H4). 31P{ H}
127, 15738; (h) M. P. Cassidy, A. D. Ozdemir and A. Padwa, Org. Lett.,
2005, 7, 1339; (i) B. Alcaide, P. Almendros and J. M. Alonso, J. Org.
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NMR (DMSO-d6): d = 54.27.
Crystal structure determination of complexes 2a·2CHCl3, 2d,
3b·CH2Cl2, 7b and 8. Crystals of adequate quality for X-ray
measurements were grown by vapour diffusion of Et2O into
CH2Cl2 (2d, 3b, 7b) or CHCl3 solutions (2a, 8) of the corresponding
crude products at room temperature. A single crystal of each
compound (dimensions specified in Table 1) was mounted at the
end of a quartz fiber in a random orientation, covered with magic
oil and placed under a cold stream of nitrogen. Data collection was
performed at 100 K or 123 K (see Table 1) on Bruker Smart CCD
or Oxford Diffraction Xcalibur2 diffractometers using graphite-
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monocromated Mo-Ka radiation (k = 0.71073 A). In all cases
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an hemisphere of data was collected based on three x-scan
and φ-scan runs. The diffraction frames were integrated using
the programs SAINT29 or CrysAlis RED30 and the integrated
intensities were corrected for absorption with SADABS.31 The
structures were solved and developed by direct or Patterson
methods.32 All non-hydrogen atoms were refined with anisotropic
displacement parameters. The hydrogen atoms were placed at
idealized positions and treated as riding atoms. Each hydrogen
atom was assigned an isotropic displacement parameter equal to
1.2 times the equivalent isotropic displacement parameter of its
parent atom. The structures were refined to Fo2, and all reflections
were used in the least-squares calculations.33
CCDC reference numbers 661531–661535.
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b714485g
Acknowledgements
Funding by the Ministerio de Educacio´n y Ciencia (MEC) (Spain,
Project CTQ2005–01037) is gratefully acknowledged. R. B. thanks
the MEC(BES2003–0296) for a PhD research grant.
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