Allyl amination of phosphinoquinoline allyl complexes of palladium. Influence of the allyl hapticity on the reaction rate and regiochemistry

Article abstract of DOI:10.1021/om100315d

The ligands 8-diphenylphosphanylquinoline (DPPQ) and 8-diphenylphosphanyl- 2-methylquinoline (DPPQ-Me) react in chlorinated solvents with the allyl dimers [Pd(μ-Cl)(η³-C₃H₅)]₂ and [Pd(μ-Cl)(η³-C₃H₃Me₂)] ₂, yielding palladium allyl phosphanylquinoline complexes whose structure is strongly influenced by the ancillary ligand and the presence or the absence of chloride ion in solution. Thus, the allyl fragments in the DPPQ derivatives assume η³-hapticity in the absence of chloride and display monohapto coordination when the chloride is not removed from the reaction mixture. In the DPPQ-Me allyl derivatives the allyl fragment is always η³-coordinated, while the ancillary ligand may act as bis-or monochelating in the absence or in the presence of chloride, respectively. The reactivity of the allyl complexes was tested by means of the allyl-amination reaction carried out by either NMR or UV-vis techniques. It was noticed that the η³-derivatives generally display a higher reactivity than their η¹-allyl analogues, under the same experimental conditions. It is apparent that chloride in chlorinated solvents is a quite good nucleophile, and therefore it may force the allyl moiety to assume the monohapto coordination or partially displace the hemilabile bis-chelate DPPQ-Me ligand. This experimental finding was also theoretically confirmed by means of an ab initio DFT computation. The crystal structures of the complexes [Pd(η³- C₃H₅)-(DPPQ)]ClO₄ and [Pd(η¹- C₃H₅)(DPPQ)Cl] were resolved. The latter represents the seventh structure of a palladium complex with a σ-coordinated allyl fragment described in the literature.

Full text of DOI:10.1021/om100315d

Organometallics 2010, 29, 3027–3038 3027
DOI: 10.1021/om100315d
Allyl Amination of Phosphinoquinoline Allyl Complexes of Palladium.
Influence of the Allyl Hapticity on the Reaction Rate and Regiochemistry
L. Canovese,*,† F. Visentin,† C. Santo,† G. Chessa,† and V. Bertolasi‡
†
‡
Dipartimento di Chimica, Universita Ca’ Foscari, Venice, Italy, and Dipartimento di Chimica and Centro di
ꢀ
Strutturistica Diffrattometrica Universita di Ferrara, Ferrara, Italy
ꢀ
Received April 19, 2010
The ligands 8-diphenylphosphanylquinoline (DPPQ) and 8-diphenylphosphanyl-2-methylquinoline
(DPPQ-Me) react in chlorinated solvents with the allyl dimers [Pd( μ-Cl)(η3-C3H5)]2 and [Pd( μ-Cl)(η3-
C3H3Me2)]2, yielding palladium allyl phosphanylquinoline complexes whose structure is strongly influ-
enced by the ancillary ligand and the presence or the absence of chloride ion in solution. Thus, the allyl
fragments in the DPPQ derivatives assume η3-hapticity in the absence of chloride and display monohapto
coordination when the chloride is not removed from the reaction mixture. In the DPPQ-Me allyl derivatives
the allyl fragment is always η3-coordinated, while the ancillary ligand may act as bis- or monochelating in
the absence or in the presence of chloride, respectively. The reactivity of the allyl complexes was tested by
means of the allyl-amination reaction carried out by either NMR or UV-vis techniques. It was noticed that
the η3-derivatives generally display a higher reactivity than their η1-allyl analogues, under the same
experimental conditions. It is apparent that chloride in chlorinated solvents is a quite good nucleophile, and
therefore it may force the allyl moiety to assume the monohapto coordination or partially displace the
hemilabile bis-chelate DPPQ-Me ligand. This experimental finding was also theoretically confirmed by
means of an ab initio DFT computation. The crystal structures of the complexes [Pd(η3-C3H5)-
(DPPQ)]ClO4 and [Pd(η1-C3H5)(DPPQ)Cl] were resolved. The latter represents the seventh structure of
a palladium complex with a σ-coordinated allyl fragment described in the literature.
Introduction
fragment may induce alternative and interesting mechanisms.4
The allyl fragment may be forced to assume the monohapto
configuration by potentially terdentate ligands or under the
action of strong nucleophiles.5 In particular, in the cases of
terdentate ligands such as terpyridine and 2,6-(diphenylphos-
phonylmethyl)pyridine the synthesis of stable complexes al-
lowed X-ray structural determination.5i,j It is however note-
worthy that the synthesis of remarkably stable species and their
consequent X-ray structural determinations were possible also
for complexes bearing phospho- or phosphonite(oxazoline)
(P-N) bidentate or potentially terdentate bis(oxazoline)phenyl-
phosphonite (NOPON) ligands5d-h (in the latter case the
NOPON acts as a bidentate ligand with an uncoordinated
wing). Notably, all the η1-allyl complexes bearing bidentate
PN or potentially terdentate NOPON were always asso-
ciated with a chloride moiety, which, while occupying the
third coordinative position, stabilizes such unusual allyl
hapticity. The recent papers by Jutand and Amatore dealing
The nucleophilic attack by “soft” nucleophiles, which usually
occurs at the terminal carbon of the η3-coordinated allyl frag-
ment in palladium complexes, has been extensively studied and
reviewed, since this reaction represents an important methodol-
ogy in the vast field of palladium-catalyzed organic synthesis.1
In some cases different reaction products due to nucleophilic
attacks governed by different stereo-2 and regioselectivity3 were
proposed. Moreover, the allyl hapticity can be somehow influ-
enced, and it is well known that the monohapticity of the allyl
*To whom correspondence should be addressed. E-mail: cano@unive.it.
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p 585. (c) Tsuji, J. In Palladium and Catalysts Innovation in Organic
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palladium Chemistry for Organic Synthesis; Negishi, E., Ed.; Wiley: New
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2010 American Chemical Society
Published on Web 06/10/2010
pubs.acs.org/Organometallics

3028 Organometallics, Vol. 29, No. 13, 2010
Canovese et al.
Scheme 1
Scheme 2
with the role of the “not-innocent” chloride when the palla-
dium-catalyzed reactions are taken into consideration,5c,6 the
original work of Akermark pointing out the possibility of the
alternative nucleophilic attack at a η1-coordinate allyl group
(SN20, SN2),7 and finally our recent study on the thermodynamic
aspects of the migratory insertion of the allyl group in palladium
isocyanide complexes5a drove us to plan an exhaustive investiga-
tiononthenatureandthefeaturesofsomeη1-allyl complexes. We
have thus undertaken the present study with the aim of contribut-
ing to the comprehension of the factors that might determine the
allyl hapticity and of the overall reactivity and regioselectivity of
such complexes when involved in reactions of allyl amination. We
have chosen the allyl amination as reference reaction owing to its
appropriate rate and the easy monitoring of the reaction
progress.3,8 The complexes studied are summarized in Scheme 1.
Chart 1
Result and Discussion
General Remarks. When the dimers [Pd( μ-Cl)(η3-C3H3-
R2)]2 (R=H, Me) react in chlorinated solvents with two equi-
valents of the ligands DPPQ (1) and DPPQ-Me (2), we can
anticipate that two different compounds were obtained
according to the reactions reported in Scheme 2.
Irrespectively of the allyl substituents R0, both pro-
ducts are neutral with chloride coordinated to the palladium
center. However, the allyl fragment in the DPPQ derivative is
η1-coordinated, while in the DPPQ-Me complex it adopts
η3-hapticity with the consequent decoordination of the quino-
line nitrogen.
The reactions in Scheme 2 can also be carried out in mixed
solvent (CH2Cl2/MeOH) in the presence of the dechlorinat-
ing agent NaClO4. In these cases upon separation of NaCl
and irrespectively of the nature of R and R0, the reactions
always yield the catioþnic species 1A, 1B, 2A, and 2B ([Pd(η3-
C3H3R2)(DPPQ-R0)] ; R=H, Me; R0 = H, Me).
Characterization and Properties of the Allyl Complexes.
For the sake of clarity, it is convenient to describe the char-
acterization and the solution behavior of all the studied com-
plexes when they bear the same ancillary ligand and allyl frag-
ment in the absence and in the presence of the chloride ion.
(i) We have already stated that the reaction between the
dimer [Pd( μ-Cl)(η3-C3H5)]2 and the ligand DPPQ (1) carried
out in the presence of NaClO4 yields the cationic complex
1A, topologically represented together with its numbering
scheme in Chart 1.
(6) (a) Cantat, T.; Agenet, N.; Jutand, A.; Pleixats, R.; Moreno-
~
ꢁ
Manas, M. Eur. J. Org. Chem. 2005, 4277–4286. (b) Cantat, T.; Genin, E.;
Giroud, C.; Meyer, G.; Jutand, A. J. Organomet. Chem. 2003, 687, 365–376.
(c) Amatore, C.; Jutand, A.; M'Barki, M. A.; Meyer, G.; Mottier, L. Eur. J.
Inorg. Chem. 2001, 873–880.
˚
˚
(7) Akermark, B.; Akermark, G.; Hegedus, L. S.; Zetterberg, K.
J. Am. Chem. Soc. 1981, 103, 3037–3040.
(8) (a) Crociani, B.; Antonaroli, S.; Canovese, L.; Visentin, F.; Uguagliati,
P. Inorg. Chim. Acta 2001, 315, 172–182. (b) Crociani, B.; Antonaroli, S.;
Bandoli, G.; Canovese, L.; Visentin, F.; Uguagliati, P. Organometallics 1999, 18,
1137–1147, and references therein. (c) Canovese, L.; Visentin, F; Uguagliati, P.;
Chessa, G.; Lucchini, V.; Bandoli, G. Inorg. Chim. Acta 1998, 275-276, 385–
394. (d) Canovese, L.; Visentin, F; Uguagliati, P.; Chessa, G.; Pesce, A.
J. Organomet. Chem. 1998, 566, 61–71. (e) Canovese, L.; Visentin, F; Uguagliati,
P.;Chessa, G.;Crociani, B.;DiBianca, F.Inorg. Chim. Acta 1995, 235, 45–50. (f )
Canovese, L.; Visentin, F.; Uguagliati, P.; Di Bianca, F.; Antonaroli, S.; Crociani, B.
J. Chem. Soc., Dalton Trans. 1994, 3113–3118.

Article
The low-temperature (213 K) 1H NMR spectrum of
Organometallics, Vol. 29, No. 13, 2010 3029
Chart 2
complex 1A in CD2Cl2 displays five groups of signals ascrib-
able to allyl protons at 2.97, 4.08, 4.29, 5.04, and 6.03 ppm.
The doublets at 2.97 and 4.04 ppm are due to the Hcanti and
Hcsyn coupling (protons in trans position with respect to the
quinoline nitrogen atom), the doublets of doublets at 4.29
and 5.05 ppm are ascribable to the Haanti and Hasyn coupling
with the phosphorus atom in trans position, while the multi-
plet at 6.03 ppm is due to the central allyl proton Hb
cen
coupling with four inequivalent protons.
On increasing the temperature (298 K), the massive broad-
ening of the signals of the protons Hc is observed. This
phenomenon is due to the well-known selective syn-anti iso-
merism that is traceable back to a η3-η1-η3 fluxionality.5i,9
Notably, such a phenomenon is triggered by the remarkable
trans-labilizing influence of phosphorus.
The RT 13C{1H} NMR confirms the labilization of the allyl
carbon (Ca) in trans position to phosphorus, which resonates
as a doublet at 83.2 ppm, while the Cc resonates at higher field
(51.9 ppm). The position of the signal ascribable to the central
carbon atom (Cb) is about 120 ppm, which represents a
predictable frequency for this type of allyl derivative.
(ii) The CD2Cl2 1H NMR spectrum at 213 K of the
derivative 1C obtained by adding the ligand DPPQ (1) to a
CH2Cl2 solution of [Pd( μ-Cl)(η3-C3H5)]2 without subsequent
dechlorination of the solution (no NaClO4 addition) displays a
quite different behavior. In this case only four groups of signals
ascribable to the allylic protons can be noticed, at 2.61, 4.04, 4.32,
Chart 3
and 6.09 ppm. The high-field signal (doublet of doublets; JHH
=
8.2, JHP=4.1 Hz) is ascribable to two equivalent protons of the
carbon directly coordinated to the palladium belonging to a η1-
coordinated allyl fragment in cis position to a phosphorus atom.
The corresponding carbon (Cc) resonates at about 20 ppm in the
13C{1H} NMR spectrum, thereby indicating the alkylic nature of
the carbon directly coordinated to the metal.5e,f The couple of
doublets at 4.04 and 4.32 ppm are traceable back to the protons
trans (JHH=17.1 Hz) and cis (JHH=9.9 Hz) to the central proton
Hb, which resonates as a multiplet at 6.09 ppm. Moreover, the
position of the signals due to the central and terminal carbon in
the η1 complex differs substantially from those of the η3-species
(see Experimental Section). The fourth coordinative position is
occupied by a chloride, which induces a remarkable deshielding
of the quinoline H2 proton that resonate at a quite low field (9.89
ppm). This phenomenon, which has been already observed,10 is
probably due to an anisotropic effect. Notably, a similar out-
come is observed also in complexes bearing halogen atoms
coordinated to pyridylthioether methyl palladium species in
which the deshielding extent is influenced by the nature of the
halide (I->Br->Cl-).10b Coordination of the chloride is also
supported by the IR spectrum, which, at variance with complex
1A, displays a Pd-Cl stretching at 272 cm-1, but mainly by the
structural characterization of the complex 1C (vide post).
Interestingly, complex 1C displays a η1-η3-η1 fluxional
rearrangement as a consequence of the increasing tempera-
ture. Such a phenomenon is not so frequent and to the best of
our knowledge was observed in one more case.5i As a matter
collapse at 353 K (C2D2Cl4). At this temperature the signal of
the four terminal allyl protons becomes a broad singlet at
3.75 ppm, while the central allyl proton resonates as a sharp
quintet (see Supporting Information: Figure 2 SI).
(iii) The reaction of the ligand DPPQ (1) with the dimer
[Pd(μ-Cl)(η3-C3H3Me2)]2 in chlorinated solvents in the pre-
sence of NaClO4 yields the complex 1B, which can be isolated as
a couple of diastereoisomers (1B(a)/1B(b)=1.4:1) (Chart 3)
The isomeric ratio can be easily inferred from the 1H NMR
spectra in CD2Cl2 at 253 K of the isomeric mixture in which
only the syn and anti protons trans to phosphorus give rise to
two doublets of doublets at 4.74 and 4.22 ppm, respectively
(see Experimental Section).
(iv) The reaction between the dimer [Pd(μ-Cl)(η3-C3H3-
Me2)]2 and the ligand DPPQ (1) carried out without dechlo-
rinating agents yields the complex 1D. As expected, in ana-
logy with the previous results, the complex 1D displays the
allyl fragment σ coordinated to palladium via the less sub-
stituted carbon (η1 hapticity) (Chart 4)
As in the previously described complex 1C, the 1H and 13
C
NMR spectra of complex 1D suggest the allyl monohapticity. In
particular the doublet of doublets at 2.89 ppm is traceable back
to the protons bonded to the Cc carbon of the allyl fragment
coupling with the allyl central proton and with the phosphorus
in cis position (JHP ≈ 3 Hz). The high-field resonance of the allyl
carbon Cc (δ=15.6 ppm), the proximity of the Ca-coordinated
methyl protons signals (Δδ = 0.21 ppm), which is not unprece-
dented5a and not consistent with that of geminal methyl groups
of a η3-coordinated 1,1-dimethylallyl, and the low-field reso-
nance of the H2 quinoline proton (10.03 ppm) strongly suggest
the structure depicted in Chart 4 for the complex 1D.
1
of fact, the H NMR spectrum at 298 K shows the partial
coalescence of the terminal allyl protons, which completely
(9) Canovese, L.; Visentin, F; Uguagliati, P.; Lucchini, V.; Bandoli,
G. Inorg. Chim. Acta 1998, 277, 247–252.
(10) (a) Canovese, L.; Visentin, F.; Chessa, G.; Uguagliati, P.;
Bandoli, G. Organometallics 2000, 19, 1461–1463. (b) Canovese, L.;
Chessa, G.; Santo, C.; Visentin, F; Uguagliati, P. Inorg. Chim. Acta 2003,
346, 158–168.

3030 Organometallics, Vol. 29, No. 13, 2010
Canovese et al.
Chart 4
Scheme 3
Chart 6
Chart 5
rearrangements) usually induced by the presence of adventitious
nucleophiles.8b Apparently, in this case the role of the nucleophile
is fulfilled by the quinoline nitrogen of the uncoordinated wing.
Further evidence on the structure of complex 2C is given by
the resonance of the methyl protons in position 2 of the quinoline
ring. These protons resonate at 2.71 ppm, which is very near the
resonance of the same protons of the uncoordinated DPPQ-Me
(2.60 ppm) and at a quite different field if compared with the
resonance of the bis-coordinate ligand (i.e., the methyl protons in
the case of the dechlorinated complex [Pd(η3-C3H5)(DPPQ-Me)]
(2A) resonate at 3.11 ppm; see Experimental Section). From the
NMR spectra at low temperature (178 K) it is possible to deduce
that a further process takes place. On decreasing the tempera-
ture, the 31P signal significantly shifts from 22.7 to 32.0 ppm.
Moreover, the 1H NMR at the same temperature can be inter-
preted on the basis of the formation of the complex [Pd(η3-C3H5)
(DPPQ-Me)]+Cl-, in which the DPPQ-Me moiety acts again as
a bidentate ligand (see Supporting Information: Figure 7 SI).
Apparently, the equilibrium reported in Scheme 3 between
the neutral and the cationic allyl complexes takes place.
(vii) The reaction between the dimer [Pd(μ-Cl)(η3-C3H3-
Me2)]2 and the ligand DPPQ-Me (2) in the presence of NaClO4
at 298 K yields the diastereoisomers depicted in Chart 6.
At variance with the case related to complex 1B, theisomer2B
(b) represents the most abundant species (2B(b)/2B(a)=2.3:1)
probably due to the mutual steric interference exerted by the
methyl groups of the allyl fragment and of the quinoline ring.
Notably, the equilibrium between isomers is influenced by tem-
perature, and at 198 K the ratio becomes 2B(b)/2B(a)=6.3:1.
(viii) The same reaction carried out in the presence of
chloride yields complex 2D, which is present in solution only
as the isomer bearing the allylic methyl groups in trans
position to the phosphorus atom (see Chart 7).
(v) The reaction between the ligand DPPQ-Me (2) and the
allyl dimer [Pd(μ-Cl)(η3-C3H5)]2 in the absence of chloride
yields the 3-hapto derivative [Pd(η3-C3H5)(DPPQ-Me)] (2A),
which behaves similarly to its DPPQ analogue. As a matter of
fact, the NMR spectra of the two derivatives look very similar,
and the selective syn-anti isomerization (η3-η1-η3) is opera-
tive in this case also.
(vi) The same reaction carried out in the presence of
chloride gives the species [Pd(η3-C3H5)(κ1-DPPQ-Me)Cl]
(2C), which is topologically represented in Chart 5
The structure in Chart 5 clearly emerges from analysis of
the 298 K 1H and 13C NMR spectra of complex 2C and might
be somehow referred to that of the complex [Pd(η3-C3H3-
Me2)(dmphen)], which displays a marked asymmetry be-
tween the two Pd-N bonds.11
The terminal allyl protons resonate at 3.65 ppm as a doublet of
doublets with JHH =10 and JHP = 3.9 Hz, which represent a
reasonable average of the coupling constants among the anti and
the syn protons with the central allyl protons and the phosphorus
atom, respectively, while the central allyl proton resonates as a
well-resolved quintet at 5.67 ppm (JHH=10 Hz). Accordingly,
the 13C NMR spectrum at the same temperature (298 K) displays
a unique signal for the terminal carbons at 68 ppm (reasonable
average between the signals of one carbon trans to phosphorus
and another trans to chloride), while the central carbon assumes
the typical position of a η3-allyl system at about 118 ppm (JCP
=
5.8 Hz).12
The observed behavior is traceable back to the extensive
As a matter of fact, the 1Hand13CNMRspectrainCD2Cl2 at
298 K strongly suggest this conclusion. The central allyl proton,
which resonates as a triplet at 5.19 ppm, is coupled with the allyl
terminal protons resonating as a doublet at 2.75 ppm The
coupling constant JHH=9.8 Hz represents the average between
one syn and one anti proton trans to chloride. This observation
suggests that the syn-anti selective isomerism rules out the
formation of an allyl group η1-coordinated to the palladium
via the most substituted terminal carbon. The allyl methyl
fluxional phenomena (typically syn-anti and syn-syn anti-anti
˚
€
(11) Hansson, S.; Norrby, P.-O.; Sjogren, M. P. T.; Akermark, B.;
Cucciolito, M. E.; Giordano, F.; Vitagliano, A. Organometallics 1993,
12, 4940–4948.
˚
(12) Akermark, B.; Krakenberg, B.; Hansson, S.; Vitagliano, A.
Organometallics 1987, 6, 620–628.

Article
Organometallics, Vol. 29, No. 13, 2010 3031
Figure 1. 1H NMR spectra in CD2Cl2 of complex 2D at different temperatures.
Chart 7
Scheme 4
based on an ab initio DFT method in order to better under-
stand this peculiar difference in the ligand behavior.13,14 The
computational response is depicted in Figure 2.
groups resonate as two doublets at 1.37 and 1.80 ppm since they
are coupled with the phosphorus in trans position. The 13C
NMR spectrum is in accord with these conclusions. In particu-
lar, the less substituted terminal carbon resonates at 48.9 ppm,
which represents a reasonable frequency for a carbon trans to
chloride, while the signal of the most substituted quaternary
carbon is found as a doublet (JCP = 25 Hz) at 114 ppm.
As can be deduced from Figure 1, a decreasing tempera-
ture favors the establishment of the equilibrium in Scheme 5.
However, probably due to the inadequate instrumental
sensitivity of the two possible isomers of the cationic com-
plex [Pd(η3-C3H3Me2)(DPPQ-Me]+Cl-, only the derivative
bearing the substituted allyl terminus cis to phosphorus was
identified in solution at 193 K (see Scheme 4).
Computational Investigation. It has been observed that the
ligands DPPQ and DPPQ-Me when reacting with the dimer
[Pd(μ-Cl)(η3-C3H5)]2 in the presence of chloride quite surpris-
ingly promote the formation of the complex [Pd(η1-C3H5)(DP-
PQ)Cl] (1A) or [Pd(η3-C3H5)(κ1-DPPQ-Me)Cl] (2C). We have
therefore resorted to a theoretical computational approach
It is apparent that the theoretical evidence is in accord with
the experimental results. Thus, the formation of the complex
[Pd(η1-C3H5)(DPPQ)Cl] (1C) is energetically favored if com-
pared with that of the hypothetical complex [Pd(η3-C3H5)
(DPPQ)Cl], while the corresponding complexes bearing the
ligand DPPQ-Me display an inversion in the energy levels.
As a matter of fact, the distortion induced by the methyl
substituent in the quinoline ring favors breaking of
the N-Pd bond instead of reduction of the allyl hapticity
(η3 f η1). This destabilizing effect is well known and was
previously observed in other palladium derivatives.10,15
Crystal Structure Determinations. ORTEP16 views of the
complexes 1C and 1A are shown in Figures 5 and 6. The Pd(II)
complex 1C exhibits square-planar coordination with the η1-
allyl ligand trans to the nitrogen N1 of quinoline moiety. The
˚
Pd1-N1 bond length of 2.161(2) A is in agreement with Pd-N
2
˚
(sp ) distances in the range 2.13-2.18 A of complexes having
similar coordination geometries.5d-h These bonds display a
˚
lengthening with respect to distances [2.06(2) A, on average] in
[Pd(P-N)Cl2] complexes where the nitrogen is trans to a Cl,5e,17
(13) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson,
G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.;
Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.;
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Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.;
Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.;
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Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.;
Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.;
Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth,
G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas,
O.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; , Fox, D. J. Gaussian 09,
Revision A.1; Gaussian, Inc.: Wallingford, CT, 2009.
(14) (a) Zhao, Y.; Truhlar, D. G. Theor. Chem. Acc. 2008, 120, 215–241.
(b) Weigend, F.; Ahlrichs, R. Phys. Chem. Chem. Phys. 2005, 7, 3297–3305.
(15) Canovese, L.; Visentin, F.; Chessa, G.; Santo, C.; Dolmella, A.
Dalton Trans. 2009, 9475–9485.
(16) Burnett, M. N.; Johnson, C. K. ORTEP III, Report ORNL-6895;
Oak Ridge National Laboratory: Oak Ridge, TN, 1996.
(17) (a) Shaffer, A. R.; Schmidt, J. A. R. Organometallics 2008, 27,
1259–1266. (b) Agostinho, M.; Banu, A.; Braunstein, P.; Welter, R.; Morise,
X. Acta Crystallogr. Sect. C 2006, 62, m81–m86. (c) Ankersmit, H. A.;
Løken, B. H.; Kooijman, H.; Spek, A. L.; Vrieze, K.; van Koten, G. Inorg.
Chim. Acta 1996, 252, 141–155. (d) Apfelbacher, A.; Braunstein, P.;
Brissieux, L.; Welter, R. Dalton Trans. 2003, 1669–1674.

3032 Organometallics, Vol. 29, No. 13, 2010
Canovese et al.
Figure 2. Calculated ΔG0 of formation for the complexes [Pd(η3-C3H5)(κ1-DPPQ)Cl] and [Pd(η3-C3H5)(κ1-DPPQ-Me)Cl] (2C).
Scheme 5
showing that the η1-allyl group exerts on N a trans influence
greater than Cl. The conformation of the coordinated η1-allyl
group can be described by the torsion angles Pd-C1-C2-
C3 = 110.6(4)ꢀ and P-Pd-C1-C2=-109.1(2)ꢀ. The plane of
the allyl group makes a dihedral angle of 69.6(3)ꢀ with the mean
coordination plane. The C1-C2 and C2-C3 bond distances of
η3-allyl carbon distances, which are longer trans to the P
˚
˚
(2.214(4) A) than trans to the N atom (2.107(4) A). The same
effect can be observed in other [Pd(η3-C3H5)(P-N)]þ com-
plexes,5e,f,17a,18 where Pd-C(trans to P) and Pd-C(trans to N)
˚
bond lengths display average values of 2.22(2) and 2.11(1) A,
respectively. The η3-coordinated allyl moiety, forming a dihedral
angle of 56.6(7)ꢀ, is obliquely placed with respect to the metal
square plane. The central C2 atom of the η3-allyl group is located
˚
1.454(4) and 1.319(5) A clearly show a differentiation between
single and double bonds and are within the ranges of distances
˚
˚
of 1.45-1.47 and 1.30-1.37 A, respectively, observed in allyl
above the mean coordination plane by 0.326(6) A (Figure 5).
groups of [Pd(η1-C3H5)(P-N)Cl] complexes.5d-h
In cationic complex 1A the palladium atom bonded to one
nitrogen, one phosphorus, and two terminal η3-allylic carbon
atoms shows a distorted-square-planar coordination. The great-
er trans influence exerted by the phosphine moiety as compared
to the N(quinoline) group is evidenced by the Pd-terminal
(18) (a) Mandal, S. K.;Gowda, G. A. N.;Krishnamurthy, S. S.;Nethaji,
M. Dalton Trans. 2003, 1016–1027. (b) Franco, D.; Gomez, M.; Jimenez, F.;
Muller, G.; Rocamora, M.; Maestro, M. A.; Mahia, J. Organometallics 2004, 23,
3197–3209. (c) Pascu, S. I.; Coleman, K. S.; Cowley, A. R.; Green, M. L. H.;
Rees, N. H. J. Organomet. Chem. 2005, 690, 1645–1658. (d) Faller, J. W.;
Sarantopoulos, N. Organometallics 2004, 23, 2008–2014.

Article
Organometallics, Vol. 29, No. 13, 2010 3033
was over in about 4 min, while that of complex 1C took more
than 45 minto be complete. Evidently, the attack at the η1-
allyl is disfavored with respect to that at the η3-coordinated
allyl moiety. In both cases the reaction products were the
palladium(0) derivative [Pd(η2-dmfu)(DPPQ)] (P), the 1-
allylpiperidine (3), and the protonated piperidine. However,
owing to the symmetry of the allyl fragment, no information
on the site of attack and on the related rates could be
gathered, although it may be suggested that attack of the
piperidine takes place principally at the most electropositive
terminal allyl carbon, which is trans to phosphorus12 and at
the allyl face opposite the palladium center.3 We have there-
fore resorted to the complexes 1B and 1D in an attempt to
obtain deeper insight into the mechanism. The most evident
piece of information we have obtained in these cases is given
by the remarkable increase of reaction time. Under the same
experimental conditions of concentration and temperature,
the reaction of 1B and 1D with piperidine takes about 20 and
420 min, respectively. The ratio of rates is roughly main-
tained (4:45 to 20:420 min), but steric hindrance clearly plays
an important role in determining the reaction rates in the
case of associative mechanisms. Moreover, upon piperidine
and dmfu addition, complex 1B yields the usual derivative
P and a 1:4 mixture of the compounds 1-(1,1-dimethylal-
lyl)piperidine (3a) and 1-(3-methylbut-2-enyl)piperidine (3b)
(3a/3b = 1:4). When the amination of the chlorinated
η1-allyl complex 1D is taken into consideration, an inversion
in the regioselectivity is observed since the ratio between the
allyl-amines becomes 3a/3b = 2:1. It is well known that the
presence of nucleophiles in solution causes an extensive flux-
ionality in palladium η3-allyl complexes.8b Therefore the addi-
tion of piperidine to a solution of the complex 1B might induce
a fast isomerization process between the two possible isomers
1B(a) and 1B(b), thereby enforcing the Curtin-Hammet
regime.19 The kinetic solution of the system under study is
however not possible, although the reasonable hypothesis that
the most reactive species could be the 1B(b) isomer might be
advanced since this isomer has the less hindered allyl carbon
trans to phosphorus. On the contrary, complex 1D undergoes
no isomeric rearrangements even under the action of piper-
idine. Consequently, it is evident that attack to both terminal
carbons of the η1-allyl fragment is possible (SN20 and SN2).
Moreover, on the basis of the observed ratio of the concentra-
tions of the allyl-amines 3a and 3b it may be deduced that the
SN20 path represents the less energy demanding route to the
products (Chart 8).
Figure 3. ORTEP view of complex 1C showing the thermal
ellipsoids at the 30% probability level.
Figure 4. ORTEP view of the cationic complex 1A showing the
thermal ellipsoids at the 30% probability level.
We have also monitored by the NMR technique the
reaction of the complexes 2A and 2C with piperidine . The
two complexes display a similar reactivity trend (vide infra)
since the unsubstituted allyl fragment remains η3- coordi-
nated in both derivatives.
Solvent Effect. The nucleophilic capability of halide ions
toward palladium(II) in chlorinated solvents is well known
and established,20 and therefore the behavior of palladium
allyl complexes in the presence of chloride is remarkably
influenced by the nature of the solvent. Thus, solutions of the
complexes 1A and 1C in CD3OD display the same NMR
spectra and exactly the same reaction rate when reacted with
piperidine. Solvolysis depresses the nucleophic capability of
chloride and favors the re-establishment of the η3-hapticity
Figure 5. Orientation of the η3-allyl group with respect to the
Pd coordination plane in 1A.
Allyl Amination. Preliminary NMR Studies. Since com-
plexes with different ligand organization might display dif-
ferent reactivity, we have decided to compare some of the
complexes described by means of the allyl-amination reac-
tion using piperidine as reference nucleophile in the presence
of dimethylfumarate (dmfu), which stabilizes the palladium-
(0) residue (Scheme 5).
We have first monitored the reaction progress by 1H and
31P NMR techniques by adding an adequate quantity of
piperidine and dmfu to a CD2Cl2 solution of the complexes
under study at RT. In the case of complex 1A the reaction
(19) Seeman, J. I. Chem. Rev. 1983, 83, 83–134.
(20) Canovese, L.; Chessa, G.; Santo, C.; Visentin, F.; Uguagliati, P.
Inorg. Chim. Acta 2003, 346, 158–168.

3034 Organometallics, Vol. 29, No. 13, 2010
Canovese et al.
Figure 6. (a) Linear regression analysis for the reaction between complex 1A and piperidine. (b) Linear regression analysis for the
reaction between complex 1C and piperidine.
Chart 8
reasonable conclusion when the overall approach is adopted.
We have therefore determined the equilibrium constant be-
tween the complexes 1A and 1C and between the complexes 2A
and 2C by spectrophotometric titration of the complex 1A or
2A with a CH2Cl2 solution of TEBACl (triethylbenzylammo-
nium chloride).
Determination of Equilibrium Constants. The Equilibrium
Constants.
KE ¼ ½1Cꢀ=½1Aꢀ½Cl- ꢀ
0
and
of the allyl group. Thus, the two complexes are better
described as the same species bearing different counterions
([Pd(η3-C3H5)(DPPQ)]þX-; X- = Cl-, ClO4-).
KE ¼ ½2Cꢀ=½2Aꢀ½Cl- ꢀ
00
corresponding to the general equation KE = [C]/[A][Cl-]22
were determined by means of nonlinear regression analysis
of the total absorbance of the system upon addition of
chloride, calculated on the basis of the following equations
in the SCIENTIST environment:
As expected, the reactivity of piperidine as a consequence
of solvolysis is also lowered in methanol since its nucleophilic
ability and the consequent reaction rate are depressed.
Spectrophotometric Studies. The spectrophotometric ap-
proach to the kinetic problems is often convenient since it com-
bines a reduced experimental difficulty and a prompt response
with a clear-cut determination. Moreover, the NMR outputs
are not always superimposable to the UV-vis interpretations
particularly when equilibrium reactions are involved. As a
matter of fact, the different concentrations of the sample im-
posed by the two different techniques might severely affect the
equilibrium position, and consequently the reproducibility of
independent observations is not warranted.
In the case of spectrophotometric determinations, the ac-
companying high dilution of the starting chlorinated complexes
(1C, 2C) renders chloride dissociation and consequently the
concentration of the cationic 1A and 2A significant.21 Thus, the
complete mechanistic scheme related to piperidine attack to
the allyl derivative in the case of an established equilibrium
mixture between dechlorinated and chlorinated allyl complexes
is more appropriately described by Scheme 6.8
½Cꢀ ¼ KEð½Aꢀ0 - ½CꢀÞð½Cl- ꢀ0 - ½CꢀÞ
ð1Þ
Di ¼ εC½Cꢀ þ εAð½Aꢀ0 - ½CꢀÞ
ð2Þ
where [C] represents the actual concentration of 1C (or 2C), [A]0
the initial concentration of 1A (or 2A), and [Cl-]0 the concen-
tration of TEBACl after each addition. Di represents the optical
density of the system at any chloride addition, while εA and εC
are the molar extinction coefficients of the complexes involved
in the titration. The ensuing KE values determined as refined
5
0
parameters together with εC were KE =(6.7 ( 0.9) ꢁ 10 and
KE00=(8.1 ( 0.5) ꢁ 103, respectively, while the extinction coeffi-
cients εC were coincident with those experimentally determined
from solutions of authentic 1C or 2C samples.
In these cases, the most convenient solution of the problem
consists in the separation of the different branches followed by
appropriate investigation of the simplified network. The high
correlation among parameters would otherwise invalidate any
Determination of Rate Constants. Reactivity of 1A and
1C. As already stated, the network in Scheme 6 can be
kinetically resolved by studying each step individually. Thus,
the perchlorate salts of complex 1A in the absence of chloride
(21) When the equilibrium between the complexes 2A and 2C in the
presence of an equimolecular amount of chloride is taken into consid-
eration (KE00 = 8100), the degree of advancement of the reaction is ξ =
0.93 at NMR concentration ([2A] = 2 ꢁ 10-2 mol dm-3) and ξ = 0.35 at
UV-vis concentration ([2A] = 1 ꢁ 10-4 mol dm-3).
(22) The formulation of the equilibrium constant should require the
knowledge of the concentrations of all the species in solution. Although
such knowledge is not warranted in apolar solvents, we have somehow
resorted to the classical and widely accepted semiquantitative expres-
sion.

Article
Organometallics, Vol. 29, No. 13, 2010 3035
Figure 7. (a) Linear regression analysis for the reaction between complex 2C and piperidine. (b) Parabolic regression analysis for the
reaction between complex 2A and piperidine.
and complex 1C in the presence of TEBACl ([TEBACl] =
10[1C]0) were reacted under spectrophotometric conditions
(see Experimental Section) with solutions of piperidine
under pseudo-first-order conditions ([piperidine] g 10[A]0;
[piperidine] g 10[C]0). In the case of the determination of0the
Scheme 6
0
reactivity of complex 1C (k2 ), although the KE0 value (KE
=
6.7 ꢁ 105) under the described conditions ensures the com-
plete displacement of the equilibrium position to the right
with the consequent total transformation of 1A into 1C (ξ =
1.00), two kinetic measurements were repeated with in-
creased TEBACl concentration ([TEBACl] = 15 ꢁ, 20 ꢁ
[1C]0) at the same piperidine concentration ([piperidine] =
10 ꢁ [1C]0). No significant differences among the kobs were
noticed, the ensuing values being comparable within 5%.
All the reactions went smoothly to completion and were
fitted by the monoexponential equation
ðDt - D¥Þ ¼ ðD0 - D¥Þ expð - kobstÞ
where D0, D¥, and Dt are the optical density at t = 0, at the
end of reaction (t = ¥), and at time t. The ensuing kobs values
were fitted versus piperidine concentration, and the linear
dependence shown in Figure 6a,b was observed for the
complexes under study.
The linear regression in both cases is conveniently described
by the equations kobs=k2[piperidine] (k2=(00.25 ( 0.01) mol-1
dm3 s-1; 1A) and kobs = k2 [piperidine] (k2 =(1.44 ( 0.07) ꢁ
0
10-2 mol-1 dm3 s-1; 1C). Complex 1C, with the allyl fragment
forced to η1-hapticity, displays a reaction rate about 20 times
smaller than that of the “classical” η3-allyl complex 1A.
Reactivity of 2A and 2C. The reaction of complex 2C in the
presence of TEBACl ([TEBACl]=10 ꢁ [2C]) with piperidine
also obeys a simple monoexponential law. Again, the ensuing
kobs displays a linear dependence on piperidine concentration
that is well described by the usual equation kobs = k2-
[piperidine] (k2 = (0.74 ( 0.04) mol-1 dm3 s-1; 2C) (see Figure
7a). Apparently, complex 2C reacts similarly to complex 1A
owing to the same η3-hapticity of the allyl moiety and almost
irrespectively of the nature of the ancillary ligand, the differ-
ences between rate constants being insignificant.
Notably, complex 2A reacts differently. In Figure 7b the
parabolic dependence of kobs on the piperidine concentration is
clearly noticed. In keeping with the previously discussed beha-
vior ascribable to the weakness of the bond between palladium
and nitrogen of the DPPQ-Me molecule, we propose in this
case the alternative mechanism depicted in Scheme 7.
The overall reaction rate for the mechanism depicted in
Scheme 7 is
2
0
kobs ¼ ðk2½piperidineꢀ þ k2 KE½piperidineꢀ Þ=
ð1 þ KE½piperidineꢀÞ
ð1Þ
0
which reduces to the equation kobs = k2[piperidine] þ k2 KE-
[piperidine]2 when the term KE[piperidine] is0 negligible with
respect to 1.23 The ensuing values for k2 and k2 KE are 0.6 ( 02
and 70 ( 15 mol-1 dm3 s-1, respectively. This finding is not
unprecedented and was already observed in reactions between
palladium iminophosphine allyl derivatives and secondary
(23) In the case in which one could be ignored (1, KE) with respect to
the term KE[piperidine], eq 1 would became a straight line.

3036 Organometallics, Vol. 29, No. 13, 2010
Canovese et al.
Scheme 7
chloride tends to give monocoordination, and consequently
derivatives bearing the allyl fragment are η3-coordinated.
A diffractometric study of the complexes 1A and 1C was
also carried out. The resolved structure of 1C represents one
of the few examples of η1- coordinated allyl fragments in the
literature.
The reactivity of the allyl derivatives toward allyl amina-
tion was also investigated and in some cases studied in detail
by NMR and UV-vis techniques. It was shown that the η1-
allyl derivatives react slowly with respect to their η3-counter-
parts. From NMR experiments it was also shown that the η1-
C3H3Me2 derivative, besides the reduced reactivity, displays
a significant inversion in the regioselectivity dictated by the
preferential attack of piperidine to the most substituted allyl
termini (SN20), although the SN2 path is also operative.
Experimental Section
Computational Details. Theoretical calculations were per-
formed with the Gaussian 0913 package using the functional
hybrid meta-GGA M0614a and the Def2-TZVP basis set.14b The
geometry optimization was performed without any symmetry
constraint, followed by analytical frequency calculation to
confirm that a minimum or a transition state had been reached.
Nonlinear and linear analysis of the data related to equilib-
rium and kinetics measurements were performed by locally
adapted routines written in ORIGIN 7.5 or SCIENTIST en-
vironments.
Crystal Structure Determination. The crystal data of com-
pounds 1C and 1A were collected at room temperature using a
Nonius Kappa CCD diffractometer with graphite-monochro-
mated Mo KR radiation. The data sets were integrated with the
Denzo-SMN package24 and corrected for Lorentz, polarization,
and absorption effects (SORTAV).25 The structures were solved
by direct methods using the SIR9726 system of programs and
refined using full-matrix least-squares with all non-hydrogen
atoms anisotropically refined and hydrogens included on calcu-
lated positions, riding on their carrier atoms, except for the
hydrogens of the allyl moiety in compound 1C, which were
refined isotropically. In compound 1A the O2, O3, and O4
aliphatic amines.8b The small KE value is confirmed by the
impossibility of detecting any appreciable formation of the
complex [Pd(η3-C3H5)(κ1-DPPQ-Me)(piperidine)] by NMR
technique when piperidine is added to the complex [Pd(η3-
C3H5)(DPPQ-Me)]ClO4. Moreover, similar values between the
reaction constants of the complexes 2A and 2C (0.6 vs 0.74)
suggest that substitution of a chloride ion in a neutral substrate
by piperidine with the consequent formation of a cationic
species hardly affects the reactivity of the derivatives, which
probably depends on the allyl hapticity.
-
oxygens of ClO4 anion are disordered and refined over two
positions with occupancies of 0.5 each.
All calculations were performed using SHELXL-9727 and
PARST28 implemented in the WINGX29 system of programs.
The crystal data and selected bond distances and angles are
reported as Table 1 SI and Table 2 SI, respectively, in the
Supporting Information.
Conclusions
We have prepared some new allyl complexes of palladium
with two phosphoquinoline ligands. Taking advantage of the
nature of the two different ligands, we have synthesized six
derivatives bearing the allyl fragment with its typical η3-
hapticity and two with the allyl η1-coordinated.
Kinetic Measurements (NMR). The kinetics of attack of piper-
idine on allyl palladium complexes were carried out by means of 1H
or 31P NMR techniques under the following experimental condi-
tions: [complex]=2 ꢁ 10-2, [piperidine]=1 ꢁ 10-1, and [dmfu] =
We have found that formation of η1-allyl derivatives
of palladium with potentially bidentate ligands is promoted
by (i) the enhancement of the halide coordinative capa-
bility promoted by the use of an aprotic solvent (CH2Cl2,
CHCl3); (ii) the presence of the strong trans-labilizing phos-
phorus atom weakening the Pd-C bond trans to it; and (iii)
the weak tendency of the bidentate ligand to act as mono-
dentate.
2.4 ꢁ 10-2 mol dm-3
.
The reactions were monitored by recording 1H or 31P NMR
spectra as a function of time (time=0 at piperidine addition).
Equilibrium Measurements. The equilibrium constants KE were
obtained by spectrophotometric titration of 50 mL of a solution of
the complex [Pd(η3-C3H5)(DPPQ)] ([1A]=1 ꢁ 10-4 mol dm-3) or
[Pd(η3-C3H5)(DPPQ-Me)] ([2A] = 9.53ꢁ 10-5 mol dm-3) with
Point (i) arises from the observation that in MeOH the
solvated chloride does not coordinate at palladium and acts
only as a counterion. Point (ii) represents experimental
evidence that confirms the literature findings.5d-h As for
point (iii), it was noticed that in the presence of chloride the
DPPQ ligand, which has no tendency for monocoordination,
forces the allyl group to η1-hapticity. On the contrary,
the ligand DPPQ-Me, owing to the distortion induced by
the methyl group in the complex frame, in the presence of
(24) Otwinowski, Z.; Minor, W. In Methods in Enzymology; Carter,
C. W.; Sweet, R. M. Eds.; Academic Press: London, 1997; Vol. 276, Part A,
pp 307-326.
(25) Blessing, R. H. Acta Crystallogr., Sect. A 1995, 51, 33–38.
(26) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.;
Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G.; Polidori, G.; Spagna,
R. J. Appl. Crystallogr. 1999, 32, 115–119.
(27) Sheldrick, G. M. SHELX-97, Program for Crystal Structure
Refinement; University of Gottingen: Germany, 1997.
(28) Nardelli, M. J. Appl. Crystallogr. 1995, 28, 659–659.
(29) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837–838.

Article
Organometallics, Vol. 29, No. 13, 2010 3037
microaliquots of a concentrated CH2Cl2 solution of TEBACl . The
ensuing spectra were recorded in the 300-450 nm wavelength range.
Kinetic Measurements (UV-Vis). The kinetic measurements
were performed by adding microaliquots of a concentrated CH2Cl2
solution of piperidine to 3 mL of the complex under study ([com-
plex]=1 ꢁ 10-4 mol dm-3) in the presence of dmfu ([dmfu] = 3 ꢁ
10-4 mol dm-3) and in the presence of TEBACl ([TEBACl] = 1 ꢁ
absence of TEBACl ([TEBACl] = 0 mol dm-3; determination of
k2). The reactions were monitored by recording the UV-vis spectra
as a function of time at the wavelength of the largest absorbance
change (327 nm).
(300 MHz, CD2Cl2, T=298 K, ppm): δ 33.97.Isomer 1B(b). 1H
NMR (300 MHz, CD2Cl2, T = 253 K, ppm): δ 1.14 (d, 3H,
JPH = 6.3 Hz, allyl -CH3anti), 1.69 (d, 3H, JPH = 9.0, allyl
-CH3syn), 4.22 (dd, 1H, J = 14.4 Hz, JPH = 10.2 Hz, allyl Hanti
trans-P), 4.74 (dd, 1H, J = 7.5 Hz, JPH = 7.5 Hz, allyl
Hsyn trans-P), 5.87 (m, 1H, Hcentral), 9.53 (d, 1H, J = 4.8
Hz, H2). 31P{1H} NMR (300 MHz, CD2Cl2, T = 298 K, ppm):
δ 27.56. IR (KBr pellet): νCN 1607, 1583, 1573 cm-1; νClO 1093
10-3, 1.5ꢁ 10-3, 2ꢁ 10-3 mol dm-3; determination of k2 ) orinthe
0
cm-1, δClO = 622 cm-1
.
[Pd(η3-C3H5)(DPPQ-Me)]þClO4- (2A): yellow ochre micro-
crystals (yield = 92%). 1H NMR (300 MHz, CD2Cl2, T = 213
K, ppm): δ 2.95 (d, 1H, J = 12.3 Hz, allyl Hanti trans-N), 3.04 (s,
3H, CH3), 3.93 (d, 1H, J = 7.2 Hz, allyl Hsyn trans-N), 4.09 (dd,
1H, J = 15.0 Hz, JPH = 9.6 Hz, allyl Hanti trans-P), 5.33 (dd, 1H,
J = 7.2 Hz, JPH = 7.0 Hz, allyl Hsyn trans-P), 5.85 (m, 1H, allyl
Materials. All solvents were purified by standard procedures and
distilled under argon immediately prior to use. 1D- and 2D-NMR
spectra were recorded using a Bruker 300 Avance spectrometer.
Chemical shifts (ppm) are given relative to TMS (1Hand13CNMR)
and 85% H3PO4 (31P NMR). Peaks are labeled as singlet (s), doub-
let (d), triplet (t), quartet (q), multiplet (m), and broad (br). The
Hcentral), 7.43-7.62 (m, 10H, 10 PPh2), 7.79 (m, 2H, H7
,
qui
H3qui), 7.87 (m, 1H, H6qui), 8.22 (d, 1H, JHH = 7.8 Hz, H5),
8.54 (dd, 1H, JHH = 8.4 Hz, JHH = 1.8 Hz, H4). 13C{1H} NMR
(CD2Cl2, T = 298 K, ppm): δ 33.0 (CH3), 52.8 (CH2, allyl trans-
N), 84.2 (d, CH2, JCP = 30.8 Hz, allyl trans-P), 119.9 (d, CH,
JCP = 6.5 Hz, allyl Ccentral,), 124.5 (CH, C3), 127.6 (d, CH,
JCP = 6.8 Hz, C6), 130.5 (d, C, JCP = 42.0 Hz, C8), 132 (CH, C5),
138.0 (CH, C7), 140.6 (CH, C4), 151.7 (C, C10), 151.9 (C, C9),
164.9 (C, C2). 31P{1H} NMR (300 MHz, CD2Cl2, T = 298 K,
1
proton and carbon assignment was performed by H-2D COSY,
1H-2D NOESY, 1H-13C HMQC, and HMBC experiments. UV-
vis spectra were recorded on a Perkin-Elmer Lamda 40 spectro-
photometer equipped with a Perkin-Elmer PTP 6 (Peltier tempera-
ture programmer) apparatus. IR spectra were recorded on a Perkin-
Elmer Spectrum One spectrophotometer. DPPQ,30 DPPQ-Me,31
[Pd( μ-Cl)(η3-C3H5)]232, and [Pd( μ-Cl)(η3-C3H3Me2)]233 were pre-
pared following literature procedures. All other chemicals were
commercial grade and were used without further purification.
ppm): δ 34.05. IR (KBr pellet): νCN 1605 cm-1; νClO 1088 cm-1
;
δ
ClO = 624 cm-1
.
[Pd(η3-C3H3Me2)(DPPQ-Me)]þClO4 (2B): yellow ochre
-
-
Synthesis of the Complexes. [Pd(η3-C3H5)(DPPQ)]þClO4
1
microcrystals (yield=89%).Isomer 2B(a). H NMR (300 MHz,
CD2Cl2, T = 298 K, ppm): δ 1.68 (d, 3H, JPH = 7.2 Hz, allyl
-CH3anti), 2.19 (d, 3H, JPH = 12.0 Hz, allyl -CH3syn), 2.8 bs (2H,
(1A). To 0.0518 g (0.1416 mmol) of [Pd( μ-Cl)(η3-C3H5)]2 dissolved
in 5.5 mL of CH2Cl2 were added 0.090 g (0.2872 mmol) of DPPQ in
3 mL of CH2Cl2 and 0.0785 g (0.5589 mmol) of NaClO4 in 3 mL of
MeOH. The resulting solution was stirred for 30 min and taken to
dryness under vacuum. The residue was dissolved in CH2Cl2 and
the undissolved NaCl filtered off. The resulting clear solution was
treated with activated charcoal, filtered on a Celite filter, and
concentrated to a small volume. Addition of diethyl ether induced
the precipitation of 0.1468 g of yellow microcrystals, which were
filtered into a Gooch and washed with diethyl ether and n-pentane
(yield = 93%). 1H NMR (300 MHz, CD2Cl2, T = 213 K, ppm): δ
2.97 (d, 1H, J=12.6 Hz, allyl Hanti trans-N), 4.08(d, 1H, J=6.0Hz,
allyl Hsyn trans-N), 4.29 (dd, 1H, J = 12.0 Hz, JPH = 9.3 Hz, allyl
H
syn, Hanti trans N) 3.09 (s, 3H, CH3qui), 5.49 (t, 1H, J = 9.9 Hz,
allyl Hcentral), 7.92 (m, 1H, H7), 8.22 (d, 1H, J = 7.91 Hz, H5), 8.52
(d, 1H, J = 8.6 Hz, H4). 31P{1H} NMR (300 MHz, CD2Cl2, T=
298 K, ppm): δ 36.32.Isomer 2B(b). 1H NMR (300 MHz, CD2Cl2,
T = 298 K, ppm): δ 1.13 (d, 3H, JPH=6.9 Hz, allyl -CH3anti), 1.46
(d, 3H, JPH=10.2 Hz, allyl -CH3syn), 3.09(s, 3H, CH3qui), 4.02 (dd,
1H, J = 14.5 Hz, JPH=10.5 Hz, allyl Hanti trans-P), 4.97 (dd, 1H,
J = 8.1 Hz, JPH = 8.1 Hz, allyl Hsyn trans-P), 5.66 (m, 1H, allyl
H
central), 8.01 (m, 1H, H7), 8.20 (d, 1H, J=8.1 Hz, H5), 8.49 (d, 1H,
J = 8.6 Hz, H4). 31P{1H} NMR (300 MHz, CD2Cl2, T = 298 K,
ppm): δ 31.02. IR (KBr pellet): νCN 1605 cm-1; νClO 1095 cm-1
ClO = 623 cm-1
[Pd(η1-C3H5)(DPPQ)Cl] (1C). To 0.0495 g (0.1353 mmol) of
;
Hanti trans-P), 5.04 (dd, 1H, J = 7.0 Hz, JPH = 7.0 Hz, allyl Hsyn
δ
.
trans-P), 6.03 (m, 1H, allyl Hcentral), 7.49-7.57 (m, 10 H, PPh2),
7.83-7.90 (m, 2H, H3, H6), 8.11 (m, 1H, H7), 8.28 (d, 1H, J = 8.10
Hz, H5), 8.71 (dd, 1H, J = 9.0 Hz, JPH = 1.2 Hz, H4), 9.51 (d, 1H,
J = 4.8 Hz, H2). 13C{1H} NMR (CD2Cl2, T = 298 K, ppm): δ 51.9
(CH2, allyl trans-N), 83.2 (d, CH2, JCP = 29.2 Hz, allyl trans-P),
123.0 (d, CH, JCP = 6.5 Hz, allyl Ccentral), 123.9 (CH, C3), 128.6 (d,
CH, JCP = 6.6 Hz, C6), 131.9 (d, C, JCP= 42.8 Hz, C8), 133.1 (CH,
C5), 138.9 (CH, C7), 140.8 (CH, C4), 151.0 (C, C10), 151.3 (C, C9),
160.0 (C, C2). 31P{1H} NMR (300 MHz, CD2Cl2, T = 298 K,
ppm): δ 32.45. IR (KBr pellet): νCN 1606, 1582, 1572 cm-1; νClO
[Pd( μ-Cl)(η3-C3H5)]2 dissolved in 20 mL of anhydrous CH2Cl2
was added 0.0864 g (0.2757 mmol) of DPPQ under inert atmo-
sphere and in an ice bath. The solution was stirred for 15 min and
evaporated under vacuum to small volume. Addition of diethyl
ether induced the precipitation of 0.1222 g of the title complex as
dark yellow microcrystals, which were filtered into a Gooch and
dried under vacuum (yield = 91%). 1H NMR (300 MHz, CD2Cl2,
T = 223 K, ppm): δ 2.61 (dd, 2H, JHH = 12.0 Hz, JPH = 3.9 Hz,
Pd-CH2), 4.04 (d, 1H, J = 16.8 Hz, dCH2trans), 4.32 (d, 1H, J =
9.9, dCH2cis), 6.09 (m, 1H, dCH), 7.46-7.49 (m, 6H, 6 PPh2),
7.67-7.78 (m, 6 H, 4 PPh2, H6, H3), 8.11-8.14 (m, 2H, H7, H5),
8.47 (d, 1H, J = 8.4 Hz, H4), 9.89 (d, 1H, J = 6.6 Hz, H2). 13C{1H}
NMR (CD2Cl2, T = 298 K, ppm): δ 19.7 (CH2, Pd-CH2), 107.3
(CH2, dCH2), 123.1 (CH, C3), 127,8 (d, CH, JCP = 6.9 Hz, C6),
132.1 (CH, C5), 133.9 (C, JCP =44.9 Hz, C8), 136.7 (CH, C7), 138.7
(CH, C4), 141.6 (CH, dCH), 149.9 (C, C10), 150.2 (C, C9), 153.6
(CH, C2). 31P{1H} NMR (300 MHz, CD2Cl2, T = 298 K, ppm): δ
1088 cm-1, δClO = 624 cm-1
.
The following complexes were synthesized following a similar
procedure using the appropriate starting complexes and ancil-
lary ligands.
[Pd(η3-C3H3Me2)(DPPQ)]þClO4- (1B): yellow ochre micro-
crystals (yield = 89%).Isomer 1B(a). 1H NMR (300 MHz,
CD2Cl2, T=253 K, ppm): δ 1.67 (d, 3H, JPH =6.0 Hz, allyl
-CH3anti), 2.19 (d, 3H, JPH = 9.9 Hz, allyl -CH3syn), 3.08 (s,
1H, allyl Hanti trans-N), 3.77 (s, 1H, allyl Hsyn trans-N), 5.51 (m,
1H, Hcentral), 9.08 (d, 1H, JHH = 4.8 Hz, H2). 31P{1H} NMR
38.54. IR (KBr pellet): νCN 1603, 1589, 1570 cm-1
.
The following complexes were synthesized following a similar
procedure using the appropriate starting complexes and ancil-
lary ligands.
(30) Wehman, P.; van Donge, H. M. A.; Hagos, A.; Kamer, P. C.
J. Organomet. Chem. 1997, 535, 183–193.
(31) Canovese, L.; Visentin, F.; Chessa, G.; Uguagliati, P.; Santo, C.;
Dolmella, A. Organometallics 2005, 24, 3297–3308.
(32) Hartley, F. R.; Jones, S. R. J. Organomet. Chem. 1974, 66, 465–
473.
[Pd(η1-C3H3Me2)(DPPQ)Cl] (1D): dark yellow microcrystals
(yield = 87%). 1H NMR (300 MHz, CDCl3, T = 298 K, ppm): δ
1.19 (s, 3H, dCCH3trans), 1.40 (d, 3H, J = 2.4 Hz, dCCH3cis), 2.89
(d, 2H, J = 6.9 Hz, Pd-CH2), 5.47 (t, 1H, J = 6.9 Hz, Hcentral),
7.41-7.54 (m, 6H, 6 PPh2), 7.61-7.68 (m, 2H, H3, H6), 7.70-7.79
(m, 4H, 4 PPh2), 7.94 (m, 1H, H7), 8.02 (d, 1H, J = 8.1 Hz, H5),
(33) Auburn, P. R.; Mackenzie, P. B.; Bosnich, B. J. Am. Chem. Soc.
1985, 107, 2033–2046.

3038 Organometallics, Vol. 29, No. 13, 2010
Canovese et al.
8.34 (d, 1H, J = 8.1 Hz, H4), 10.03 (d, 1H, J = 4.8 Hz, H2).
13C{1H} NMR (CD2Cl2, T = 298 K, ppm): δ 15.6 (CH2, dCH2),
18.4 (CH3, dC-CH3 trans), 26.6 (CH3, dC-CH3 cis), 122.9 (CH,
C3), 127.4 (d, CH, JCP = 6.7 Hz, C6), 129.0 (s, CH, dCH), 131.5
(CH, C5), 135.3 (d, CH, JCP = 43.8 Hz, C8), 136.0 (CH, C7), 138.0
(CH, C4), 149.6 (C, C10), 149.9 (C, C9), 153.7 (CH, C2). 31P{1H}
NMR (300 MHz, CD2Cl2, T = 298 K, ppm): δ 35.45. IR (KBr
CH3), 2,75 (d, 2H, J = 9.9 Hz, allyl H trans-Cl, allyl H trans-Cl),
5.19 (t, 1H, J = 9.6 Hz, J = 9.9 Hz, Hcentral), 7.23-7.30 (m, 1 H,
H7), 7.34-7.49 (m, 8H, H6, H3, 6 PPh2), 7.64-7.73 (m, 4 H, 4
PPh2), 7.95 (d, 1H, J = 8.1 Hz, H5), 8.16 (d, 1H, J = 9.3 Hz, H4).
13C{1H} NMR (CD2Cl2, T = 298 K, ppm): δ 20.3 (CH3,
-CH3syn), 25.1 (CH3, -CH3qui), 26.0 (CH3, -CH3anti), 48.9
(CH2, allyl -CH2), 111.4 (CH, Ccentral), 114.3 (C, -C(CH3)2),
122.6 (CH, C3), 125.2 (d, CH, JCP = 8.3 Hz, C6), 130.3 (CH, C5),
133.3 (d, C, JCP = 44.7 Hz, C8), 133.9 (s, CH, C7), 136.0 (CH,
C4), 147.7 (C, C10), 147.8 (C, C9), 158.9 (CH, C2). 31P{1H} NMR
(300 MHz, CD2Cl2, T = 298 K, ppm): δ 23.34. IR (KBr pellet):
pellet): νCN 1634, 1592, 1570 cm-1
.
[Pd(η3-C3H5)(K1-DPPQ-Me)Cl] (2C): yellow ochre micro-
crystals (yield = 88%). H NMR (300 MHz, CD2Cl2, T = 298
1
K, ppm): δ 2.72 (s, 3H, CH3), 3.65 (dd, 4H, J = 12.0 Hz, JPH = 3.9
Hz, allyl Hanti trans-N, allyl Hsyn trans-N, allyl Hanti trans-P, allyl
Hsyn trans-P), 5.67 (m, 1H, allyl Ccentral), 7.68-7.39 (m, 13H, 10
PPh2, H7, H3, H6), 8.02 (d, 1H,, JHH = 7.8 Hz, H5), 8.25 (dd, 1H,
J = 9.0 Hz, J = 1.5 Hz, H4). 13C{1H} NMR (CD2Cl2, T = 298 K,
ppm): δ 28.2 (CH3, -CH3qui), 68.6 bs (2 CH2, allyl trans-P, allyl
trans-N), 118.9 (d, CH, JCP = 5.8 Hz, allyl Ccentral), 123.5 (CH, C3),
128.6 (d, CH, JCP = 4.3 Hz, C6), 131.3 (C, C5), 135.5 (CH, C7),
136.2 (CH, JCP = 2.8 Hz, C8), 137.7 (CH, C4), 149.4 (C, C10), 152.6
(C, C9), 161.2 (C, C2). 31P{1H} NMR (300 MHz, CD2Cl2, T = 298
ν
CN 1600 cm-1
.
Supporting Information Available: Crystallographic data
(excluding structure factors) have been deposited at the Cam-
bridge Crystallographic Data Centre and allocated the deposi-
tion numbers CCDC 771053-771054. These data can be ob-
tained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.
html or on application to CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK [fax: (þ44)1223-336033, e-mail: deposit@ccdc.
cam.ac.uk]. Tables of crystallographic data (Table 1SI) and of
the selected bond distances and angles (Table 2SI), NMR and
IR spectra, and the nonlinear regression equilibrium fits are also
reported. This material is available free of charge via the Internet
at http://pubs.acs.org.
K, ppm): δ 22.69. IR (KBr pellet): νCN 1602 cm-1
.
[Pd(η3-C3H3Me2)(K1-DPPQ-Me)Cl] (2D). light yellow mi-
crocrystals (yield = 78%). H NMR (300 MHz, CD2Cl2, T=
1
298 K, ppm): δ 1.37 (d, 3H, JPH = 5.7 Hz, allyl CH3anti trans-P),
1.80 (d, 3H, JPH = 8.7 Hz, allyl CH3syn trans-P), 2,60 (s, 3H,