The role of ancillary ligands and of electron poor alkenes and alkynes in stabilizing Pd(0) derivatives: A comparative study

Article abstract of DOI:10.1016/j.jorganchem.2008.11.012

The peculiar characteristics of the ligand neocuproine (2,9-dimethylphenanthroline) allow a number of exchange equilibrium studies between the low valence complex [Pd(η²-nq)(Neocup)] (nq = naphthoquinone; Neocup = neocuproine) and several alken

Full text of DOI:10.1016/j.jorganchem.2008.11.012

Journal of Organometallic Chemistry 694 (2009) 411–419
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
The role of ancillary ligands and of electron poor alkenes and alkynes
in stabilizing Pd(0) derivatives: A comparative study
a
a
b
Luciano Canovese a, , Fabiano Visentin , Claudio Santo , Alessandro Dolmella
*
a Dipartimento di Chimica, Università Ca’ Foscari di Venezia, 30129 Venice, Italy
b Dipartimento di Scienze Farmaceutiche, Università di Padova, Padua, Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
The peculiar characteristics of the ligand neocuproine (2,9-dimethylphenanthroline) allow a number of
exchange equilibrium studies between the low valence complex [Pd(
2-nq)(Neocup)] (nq = naphthoqui-
Received 4 September 2008
Received in revised form 5 November 2008
Accepted 6 November 2008
Available online 13 November 2008
g
none; Neocup = neocuproine) and several alkenes and alkynes. A new order of stability which compares
differently unsaturated molecules was established. An overview of the factors governing the stability of
palladium(0) alkene and alkyne derivatives as a function of the steric and electronic characteristics of
both the unsaturated molecule and the ligand becomes accessible and a comparison with the previously
determined order was therefore feasible. Such a comparison enlightens the importance of the substituent
methyl groups in ortho position of the hetero-aromatic ring which represents the molecular fragment
common to all the ligands considered. Taking advantage of the steric requirements of the alkene tmetc
(tmetc = tetramethylethylenetetracarboxylate) a kinetic investigation of the reaction between the olefin
itself and the complexes [Pd(g2-dmfu)(L-L0)] (dmfu = dimethylfumarate; L–L0 = 8-diphenylphosphanyl-2-
methyl-quinoline, neocuproine, phenanthroline) was carried out. The structures of the complexes
Keywords:
Alkenes
Alkynes
Palladium(0) complexes
Exchange equilibria
[Pd(
reported in the present paper. The structure of the latter represents the first example of a palladium(0)
complex in which the N2C2 donor set around the metal centre is supported by a chelating
2-alkyne.
g g
2-dmfu)(DPPQ)] and [Pd( 2-deta)(Neocup)] (deta = but-2-ynedioc acid diethyl ester) were also
g
Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction
as stabilizing molecules in reactions producing palladium(0) sub-
strates [7] and the possibility of expanding the stability order also
to the alkynes induced us to undertake a novel investigation using
a palladium(0) species bearing the neocuproine ligand (Neocup) as
a reference. As a matter of fact, it is well known that steric hindrance
may stabilize the formation of palladium(0) alkyne species [8] which
in the presence of an excess of alkyne otherwise collapse into the
palladacyclopentadienyl derivatives [4p,4t]. Therefore, the complex
Owing to the great importance of palladium(0) olefin deriva-
tives in catalysing cross-coupling [1], allyl alkylation [2], allyl ami-
nation [3] reactions and processes involving unsaturated
molecules [4] we decided to carry out an exhaustive study with
the aim of gaining a better comprehension of the stability of such
complexes as a function of the nature of the olefin, alkyne (when
possible) and ancillary ligand. Several papers have appeared in
the literature dealing with the stability that deactivated olefins im-
part to the corresponding palladium(0) derivatives [5] and, in par-
ticular, our group determined in some cases a stability order based
on the equilibrium constant of the direct exchange between olefins
according to the following reaction [6a,6b]:
[Pd(g
2-nq)(Neocup)] (nq = naphthoquinone) would represent an
ideal substrate for a useful comparison of the stability induced by
olefins or alkynes in palladium(0) complexes. Moreover, the olefin
nq due to its spectroscopic characteristics was widely used in the
equilibrium constants measured so far. Thus, a comparative analysis
among different complexes bearing different ligands and the same
olefin becomes feasible. Moreover, the ensuing results would also
give an indication of the dependence of the stability order on the
nature of the ancillary ligands. At the best of our knowledge, this sort
of investigation represents a quite novel approach which was never
exploited before. All the complexes and the olefins (or alkynes) in-
volved in the present work are reported in the following Schemes.
In particular, Scheme 1 displays the newly prepared complexes
and those used for comparative purposes, while in Scheme 2 only
the complexes specifically synthesized for this study are reported.
½Pdðg
2-ol1ÞðL-L0Þꢀ þ ol2 ꢀ ½Pdð
g
2-ol1ÞðL-L0Þꢀ þ ol1:
ð1Þ
The previous studies, however, took into account reactions involving
complexes bearing strictly homogenous series of ligands; thus only
the mutual olefin stability order could be assessed [6]. However,
some recent findings about the reactivity of the olefins when used
* Corresponding author. Tel.: +39 041 2348571; fax: +39 041 2348517.
E-mail address: cano@unive.it (L. Canovese).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.11.012

412
L. Canovese et al. / Journal of Organometallic Chemistry 694 (2009) 411–419
Scheme 1.
Scheme 2.
pared with the signals of the free olefins are shifted upfield (2–3
2. Results and discussion
and 80–90 ppm, respectively). In the 13C NMR spectra of the al-
kyne–palladium complexes, the alkyne carbon resonances appear
at lower frequency (approximately 35 ppm) compared with those
of the free molecules. These findings testify the strong metal to al-
2.1. Synthesis and characterization of palladium(0) complexes
The palladium(0) alkene and alkyne derivatives were usually
obtained by reacting the appropriate ligand (L-L0) and olefin (ol)
with Pd2DBA3 ꢁ CHCl3 dissolved in anhydrous acetone under inert
atmosphere (Ar). The palladium(0) complexes bearing Phen, Neo-
cup and BiPy as ancillary ligand and ma or nq as stabilizing olefin
were obtained by reacting the appropriate dmfu derivatives with
the specific olefin because their low solubility makes the work-
up of standard procedure very difficult.
kene and metal to alkyne
by the lower frequency shifts of the alkenic and alkynic
in the IR spectra. The chemical shifts of the sp carbons of the three
coordinated alkynes ([Pd(
2-dma)(Neocup)], [Pd( 2-deta)(Neo-
cup)], [Pd(
2-dbua)(Neocup)]) appear not to be influenced by the
p
back donation which is also reflected
mC@O bands
g
g
g
nature of the alkynes themselves (d values span within 1 ppm).
m
Similar behaviour can be found when the chemical shifts of the
sp2 carbons in cis or trans olefins are compared ([Pd( 2-cis-
g
In the 1H and 13C NMR spectra of the olefin complexes, the res-
onances ascribable to the alkene protons and carbons when com-
sulf)(Neocup)], [Pd(g
2-trans-sulf)(Neocup)]) irrespectively of the

L. Canovese et al. / Journal of Organometallic Chemistry 694 (2009) 411–419
413
Table 1
large differences among the formation equilibrium constants. This
Selected bond lengths (Å) and angles (deg) for the complexes [Pd(
and [Pd(
g
2-dmfu)(DPPQ)]
fact also testifies the scarce influence of the nature of the alkene or
alkyne on the NMR parameters when series of homogeneous com-
pounds are taken into consideration [9]. Conversely the coordina-
tion of the ancillary ligands is shown by a general, but less
g
2-deta)(Neocup)].
[Pd(
g
2-dmfu)(DPPQ)]
[Pd(g
2-deta)(Neocup)]
Pd–N
Pd–P
Pd–C(22)
Pd–C(23)
C(22)–C(23)
N–Pd–P
N–Pd–C(22)
N–Pd–C(23)
P–Pd–C(22)
P–Pd–C(23)
C(22)–Pd–C(23)
2.156
2.266
2.066
2.112
1.426
83.2
156.8
116.9
120.0
159.9
39.9
(3)
(1)
(3)
(3)
(5)
(1)
(1)
(1)
(1)
(1)
(1)
Pd–N(1)
Pd–N(2)
Pd–C(1)
Pd–C(5)
2.153
2.149
2.006
1.996
1.280
77.8
158.1
120.9
123.8
160.7
37.3
(3)
(3)
(4)
(4)
(5)
(1)
(1)
(1)
(1)
(1)
(1)
significant downfield shift of all their signals, indicating that
donation is predominant in the palladium–ligand bond.
r
At variance with the RN-SR [6b] and PyN2 [6a] derivatives the
complexes bearing the ligands Phen, Neocup, BiPy and DPPQ do
not show fluxional rearrangements in solution at 298 K.
C(1)–C(5)
N(1)–Pd–N(2)
N(1)–Pd–C(1)
N(1)–Pd–C(5)
N(2)–Pd–C(1)
N(2)–Pd–C(5)
C(1)–Pd–C(5)
2.2. X-ray crystal structure
The crystal structures of the complexes [Pd(
and [Pd(
2-deta)(Neocup)] are shown in Fig. 1, whereas selected
g
2-dmfu)(DPPQ)]
g
bond lengths and angles of the two molecules are listed in Table 1.
It is worth noting here that despite the large number of re-
ported Pd structures there are only ten mononuclear square planar
In both complexes the polycyclic chelating ligand forms a five-
membered ring showing an envelope (Cs) conformation. The in-
volved atoms other than Pd in [Pd(
g
2-dmfu)(DPPQ)] are P, C(7),
Pd complexes showing a coordinated
g
2-alkyne. In these cases the
C(8), N, while in [Pd(
g
2-deta)(Neocup)] they are N(2), C(19), C(20),
other coordination positions are held by a chelating diphosphine
and thus the donor set is P2C2. Similarly, only five mononuclear
square planar Pd complexes show the metal chelated by a phenan-
throline-like moiety and by a chelating olefin defining the N2C2 do-
nor set [10b]. Accordingly, to the best of our knowledge, the
N(1). In the former complex the Pd atom is off plane by 0.37 Å and
torsion angles in the ring range from ꢂ11.3° to +13.8°, in the latter
the Pd atom deviates by 0.27 Å and torsion angles in the ring vary
from ꢂ9.4° to +9.1°. As for the overall geometry, in [Pd(g2
-
dmfu)(DPPQ)] the main coordination plane makes dihedral angles
complex [Pd(
the first reported example in which the N2C2 donor set around Pal-
ladium is supported by a coordinated
2-alkyne. In this neutral
g
2-deta)(Neocup)] presented here turns out to be
of 15.3° with the mean plane of the quinoline moiety and of 7.1° with
the average five-membered ring plane. In [Pd(g
2-deta)(Neocup)]
g
the corresponding angles are of 11.5° with the mean plane of neo-
cuproine and of 6.4° with the average five-membered ring plane.
complex the Pd(0) atom lies at the centre of an almost regular
square planar and its averaged Pd–C bond length displays a notice-
able shortening if compared with those determined when diphos-
phine ligands are employed (2.001 versus 2.051 Å) [10b]. The
lower trans-influence of the neocuproine nitrogen with respect to
that of phosphorus atom is apparent also when complexes of pal-
ladium(0) are considered.
2.3. Determination of the equilibrium constants
All the equilibrium constants related to reaction (1) were pre-
liminarily studied by 1H NMR technique in CDCl3 and then deter-
mined by recording the UV–Vis spectral changes in the range
300–600 nm obtained upon addition of the titrant alkene (or al-
kyne) to the complex solution in CHCl3 at 298 K. In any case, the
equilibrium was rapidly established and the ensuing absorbance
versus olefin concentration data were analyzed at suitable wave-
length by means of a non-linear least-squares program according
to the model (in some cases where KE was large an excess of free
ol1 had to be added to balance the equilibrium position):
In [Pd(
plane (N, P, C(22), C(23)) and Pd are coplanar within 0.01 Å; in
[Pd(
2-deta)(Neocup)] the atoms N(1), N(2), C(1), C(5) are coplanar
g
2-dmfu)(DPPQ)] the atoms in the main coordination
g
within 0.02 Å and Pd is off by 0.06 Å. The dihedral angle between
the planes N–Pd–P and C(22)–Pd–C(23) is 1.0°, the corresponding
one between N(1)–Pd–N(2) and C(1)–Pd–C(5) is 4.6°.
The C–C distances of the coordinated olefin/alkyne in the two
complexes fit with known data and reflect the double bond/triple
KE ¼ ½½Pdð
½Pdꢀ0 ¼ ½½Pdð
½ol1ꢀ þ ½ol2ꢀ ¼ ½ol1ꢀ0 þ ½ol2ꢀ0;
½ol1ꢀ ¼ ½ol1ꢀ0 þ ½½Pdð
Dk ¼ e1 ꢁ ½½Pdð
g
2-ol2ÞðL-L0Þꢀꢀ ꢁ ½ol1ꢀ=½½Pdð
g
2-ol1ÞðL-L0Þꢀꢀ ꢁ ½ol2ꢀ;
bond nature of the link. In [Pd(g
2-dmfu)(DPPQ)], the C(22)–C(23)
g
2-olÞ2ÞðL-L0Þꢀꢀ þ ½½Pdð
g
2-ol1ÞðL-L0Þꢀꢀ;
distance is 1.426(5) Å, very close to the average of 1.427 Å found
in 51 tetracoordinated complexes in which Pd is bound to an
acyl-substituted olefin. In [Pd(g
2-deta)(Neocup)], the C(1)–C(5)
g
2-ol2ÞðL-L0Þꢀꢀ;
bond is 1.280(5) Å, at the upper end of the range found in the liter-
ature [10b].
g
2-ol1ÞðL-L0Þꢀꢀ þ e2 ꢁ ½½Pdð
g
2-ol2ÞðL-L0Þꢀꢀ;
Fig. 1. Ortep [10a] views of the complexes [Pd(
dashed lines. Thermal ellipsoids at the 40% probability level; hydrogen atoms not shown for clarity.
g g
2-dmfu)(DPPQ)] (left) and [Pd( 2-deta)(Neocup)] (right), together with the numbering scheme. Pd–C bonds are shown as

414
L. Canovese et al. / Journal of Organometallic Chemistry 694 (2009) 411–419
Table 2
where e1 and e2 are the extinction coefficients of the complexes
[Pd(g2-ol1)(L-L0)] and [Pd(g2-ol2)(L-L0)], respectively, with KE and
Olefin exchange equilibrium constants directly determined for the reactions.
[Pd(g2-ol1)(L-L0)]
ol2
KE
0.018 0.003
310 50
630 180
0.0088 0.0022
0.20 0.04
e2 as the parameters to be optimized. The latter parameter (e2
)
turned out to be coincident with that directly determined from
the Lambert–Beer analysis carried out at the same wavelength for
the independently synthesized final product (Fig. 2).
All the KE values directly determined in this study (apart from
four values included for reasons of convenience) are reported in
Table 2.
As can be seen the alkynes dma, deta, dbua and pna are in-
cluded in Table 2 since the peculiar structure of Neocup stabilizes
the monoalkyne palladium(0) derivative which otherwise would
add a further alkyne molecule to give a palladium(II) cyclopentadi-
enyl derivative [4t and references therein].
[Pd(
[Pd(
[Pd(
[Pd(
[Pd(
[Pd(
[Pd(
[Pd(
[Pd(
[Pd(
[Pd(
[Pd(
[Pd(
[Pd(
[Pd(
[Pd(
[Pd(
[Pd(
[Pd(
[Pd(
[Pd(
g
g
g
g
g
g
g
g
g
g
g
g
g
g
g
g
g
g
g
g
g
2-nq)(Neocup)]
2-nq)(Neocup)]
2-nq)(Neocup)]
2-fn)(Neocup)]
2-fn)(Neocup)]
2-fn)(Neocup)]
2-fn)(Neocup)]
2-dmfu)(Neocup)]
2-dmfu)(Neocup)]
2-nq)(DPPQ)]
dbua
fn
ma
deta
cis-sulf
trans-sulf
dma
pna
dbua
fn
ma
fn
cis-sulf
nq
fn
15
5
0.0122 0.0006 [4t]
0.236 0.004 [7a]
57
4
1.4 0.3
4.5 0.4
4600 600 [9]
270 50 [9]
2600 800
12 3.6
38 17
3.9 0.7
10.7 0.6
2.5 0.2
5600 1600
4.8 0.5
2-nq)(DPPQ)]
2-dmfu)(DPPQ)]
2-fn)(DPPQ)]
2-dmfu)(DPPQ-Me)]
2-nq)(DPPQ-Me)]
2-nq)(DPPQ-Me)]
2-nq)(Phen)]
2.4. New neocuproine based stabilizing order
ma
fn
ma
fn
nq
ma
2-nq)(Phen)]
Taking advantage of such particular behaviour, we are now able
to propose a new and wider order in which the stabilizing charac-
ters of some olefins and alkynes are directly compared for the first
time (Table 3):
2-nq)(BiPy)]
2-dmfu)(BiPy)]
2-dma)(BiPy)]
2-ol1ÞðNeocupÞꢀ þ ol2 ꢀ ½Pdð 2-ol2ÞðNeocupÞꢀ þ ol1.
g
From these values it is possible to infer that:
½Pdð
½Pdð
g
g
2-ol1ÞðNeocupÞꢀ þ alkyne ꢀ ½Pdð
g
2-alkyneÞðNeocupÞꢀ þ ol1.
(a) In the case of the already studied alkenes the coordinating
capability order parallels those previously determined
(dmfu ꢃ nq < fn 6 ma) [6a,6b].
Table 3
Alkene or alkyne exchange equilibrium constants directly determined or calculated as
a combination of the directly measured KE values (Table 2), for the reactions.
(b) The trans-sulf, the cis-sulf and the alkynes represent quite
new entries in the molecular set establishing the stability
order of the palladium(0) derivatives (items 1, 3, 5, 6, 7, 10).
(c) The same substituent (COOMe) imparts a different stabiliz-
ing property to its alkene or alkyne derivative. The alkyne
dma is more efficient than the alkene dmfu (items 2, 6).
(d) The stability of the complex bearing trans-sulf is consider-
ably higher than that of the complex bearing cis-sulf (items
10, 7).
ol2/alkyne
KE
1
2
3
4
5
6
7
8
9
10
pna
0.000082 0.000001
0.00032 0.00002
0.018 0.003
1
dmfu
dbua
nq
deta
dma
cis-sulf
fn
2.7 0.7
3.8 0.6
62 16
310 50
630 180
4650 1700
ma
trans-sulf
(e) The stability range of the structurally similar trans olefins is
modulated by the nature of the substituents according to the
following order: SO2 > CN > COOCH3 (items 10, 8, 2).
(f) The steric hindrance of the alkynes is of paramount impor-
tance in determining the equilibrium constant values (items
3, 5, 6).
½Pdð
½Pdð
g
g
2-nqÞðNeocupÞꢀ þ ol2 ꢀ ½Pdð
g
2-ol2ÞðNeocupÞꢀ þ nq.
2-nqÞðNeocupÞꢀ þ alkyne ꢀ ½Pdð
g
2-alkyneÞðNeocupÞꢀ þ nq.
As can be deduced from Table 3, the coordinating capability of
(g) The COOMe group displays a greater capability in stabilizing
the palladium(0) derivatives than the -C6H4NO2-4 moiety
(items 1, 6).
the alkynes deta and dma is similar to that of nq which represents
our reference, while dbua and pna are about two and three orders
of magnitude less stabilizing than nq, respectively. As for point (c)
it is noteworthy that the same substituent (COOMe) imparts to the
alkyne dma a stabilizing efficiency of about four orders of magni-
tude higher than that of the alkene dmfu. Apparently, the higher
electron withdrawing character of the alkyne as compared with
that of the corresponding alkene favours a larger electron back-
donation from the palladium(0) centre. Point (d) consists of an
observation based on a unique experimental datum. Such an obser-
vation, however, probably represents a general trend due to the
fact that the intrinsic higher thermodynamic stability of the trans
olefin when compared with that of the cis one is somehow trans-
ferred to its corresponding palladium(0) derivative. For instance,
the authors were never able to obtain a palladium(0) complex
bearing dimethyl-maleate as stabilizing olefin and in one case
the reaction between the complex [Pd(g
2-dmfu)(DPPQ)] and di-
methyl-maleate seems to indicate an exchange equilibrium con-
stant of ca. 1 ꢄ 10ꢂ4 [11].
As for point (f) it is evident that the steric hindrance of the
entering alkyne plays an important role in destabilizing the corre-
sponding palladium(0) derivative. As a matter of fact, the equilib-
rium constant related to the bulky dbua is two orders of
magnitude smaller than that of dma and deta although these are
almost equivalent from the electronic point of view.
Fig. 2. Fit of absorbance versus [dbua] at 298 K and 425 nm for the
reaction:½Pdð
g
2-dmfuÞðNeocupÞꢀ þ dbua¡½Pdð
g
2-dbuaÞðNeocupÞꢀ þ dmfu.

L. Canovese et al. / Journal of Organometallic Chemistry 694 (2009) 411–419
415
Points (g), and (e) summarize the efficiency of the substituent
groups in the alkenes or alkynes in stabilizing the palladium(0)
derivatives according to the following order:
SO2 > CN > COOCH3 > C6H4NO2-4:
2.5. Comparison among equilibrium constants in complexes bearing
different ancillary ligands
On the basis of the present and the already published data
[6a,6b], we are able to propose Table 4 in which the KE values were
obtained when the same olefins are exchanged in substrates bear-
ing different ancillary ligands. Whatever the ligand considered, the
general olefin stabilization order is confirmed and the KE values are
almost always maintained within a narrow interval. The most sur-
prising result is represented by the unusually high values of KE
when fn and ma are involved as entering olefins in complexes
bearing ligands with ortho-substituted hetero-aromatic ring. It is
evident (see bold numbers in Table 4) that the ratios between KE
for reactions involving the displacement of nq by fn or ma in com-
plexes with an unsubstituted pyridine ancillary ring are usually
considerably less than twenty (9.5 average). In the case of com-
plexes with ligands bearing a substituted pyridine (or quinoline)
ring the ratio jumps to 40 or more (cases concerning DPPQ-Me
and MeN-SPh, respectively). Moreover, when Neocup is involved
a marked increase is noticed and the values soar to 311 and 630,
respectively (items 8, 9 of Table 3).
Fig. 3. Concentration profiles versus time determined by 1H NMR technique at
25 °C in CDCl3 for the reaction: ½Pdð
g
2-dmfuÞðDPPQ-MeÞꢀ þ tmetc½Pdð
g
2-tmetcÞ
ðDPPQ-MeÞꢀ þ dmfu½½Pdð
g
2-dmfuÞðDPPQ-MeÞꢀꢀ0 ¼ 9:9 ꢄ 10ꢂ3 mol dmꢂ3½tmetcꢀ0
¼
1:26 ꢄ 10ꢂ2
.
palladium(0) olefin derivatives, could induce a remarkable de-
crease in the olefin exchange reaction rates which otherwise are
very fast. We have therefore studied the following reaction by
means of 1H NMR technique:
On the other hand, the ratios become directly comparable when
the exchange between nq and dmfu is taken into account for any
complex bearing different ancillary ligands (see column 2 in Table
4). Apparently, the efficiency in stabilizing the palladium(0) olefin
complexes is markedly enhanced when olefins with reduced steric
requirements and remarkable electron withdrawing capability are
used. We surmise that the increase of the KE values when fn and
½Pdð
g
2-dmfuÞðL-L0Þꢀ þ tmetc ! ½Pdð
g
2-tmetcÞðL-L0Þꢀ þ dmfuL-L0
¼ DPPQ-Me; Neocup; Phen:
ð2Þ
The ensuing rate constants are markedly influenced by the nature of
the ancillary ligand. Thus, the less hindered phenanthroline substrate
reacts instantaneously, while the second order rate constant of its
obvious counterpart [Pd(
g
2-dmfu)(Neocup)] is about 3 ꢄ
ma react with [Pd(g g
2-nq)(Neocup)] and [Pd( 2-dmfu)(Neocup)]
10ꢂ4 molꢂ1 dm3 sꢂ1 [12]. Interestingly, the steric requirement of
the Neocup moiety does not only influence the thermodynamic
parameters (cfr. Table 4), but also the kinetics of the reaction, thereby
confirming the associative nature of the olefin exchange. Stahl and
co-workers pointed out that the rate of reactions involving olefins ex-
change would be increased by the nucleophilicity of palladium(0)
center [13]. In this case, however, the enhanced nucleophilicity in-
duced by Neocup on the metallic center appears to be overshadowed
by the steric demand involved in the transition state.
is probably due to the steric release involved in the conversion of
the crowded nq or dmfu complexes into the less hindered ma or
fn derivative, but it is also caused by the increasing electronic den-
sity of palladium induced by the more basic substituted phenan-
throline. This excess of charge is more efficiently delocalized by
the electron poorer fn and ma olefins.
2.6. Kinetic measurements
On the other hand, the reactivity of the complex [Pd(g2
-
We have also undertaken some kinetic studies taking advantage
of the bulkiness of the olefin tetramethyl-ethylene-tetracarboxyl-
ate (tmetc) which, when coupled with the steric hindrance of the
dmfu)(DPPQ-Me)] can be determined by means of a second order
kinetic study carried out under NMR conditions (Fig. 3) The corre-
sponding rate constant (k2 = 0.31 0.01 molꢂ1 dm3 sꢂ1) lies be-
tween those of the less (Phen) and the more (Neocup) hindered
derivatives and represents one of the few values determined for
olefin exchange in palladium(0) complexes [6,13].
Table 4
Comparative olefin exchange equilibrium constants for the reaction.
ol2
dmfu
nq
fn
ma
KEma/KEfn
½Pdð
½Pdð
g
g
2-dmfuÞðDPPQ-MeÞꢀ j
2-tmetcÞðDPPQ-MeÞꢀ N
L-L0
[6b] HN-SMe
[6b] HN-SEt
[6b] HN-Si-Pr
[6b] HN-St-Bu
[6b] HN-SPh
[6b] MeN-SPh
BiPy
Phen
DPPQ
DPPQ-Me
[6a] PyN2
Neocup
1
1
1
1
1
1
1
1
1
1
1
1
17
12
18
16
9
6.9
7.2
49
4.8
10.7
4.5
38
1.05
1.33
1.35
1.25
0.86
3.06
1.92
2.74
3.2
6.7
5.5
8.4
16
2.5
3.9
1.4
12.1
4.55
311
3. Conclusions
ꢅ We were able to prepare several complexes of palladium(0)
bearing different ancillary ligands and alkenes or alkynes as
stabilizing unsaturated molecules and to determine the struc-
1.8 ꢄ 10ꢂ4
*
3.0 ꢄ 10ꢂ4
3.8 ꢄ 10ꢂ4
1 ꢄ 10ꢂ3
ture of the complexes [Pd(g -
2-dmfu)(DPPQ)] and [Pd(g2
3.14
1.80
2.02
8.17
630
deta)(Neocup)]. The structure of the latter represents the first
example of an alkyne derivative of palladium(0) with a N2C2
donor set.
3.2 ꢄ 10ꢂ4
½Pdð
g
2-nqÞðL-L0Þꢀ þ ol2 ꢀ ½Pdð
g
2-ol2ÞðL ꢂ L0Þꢀ þ nq.
Cases discussed in bold.
ꢅ The exchange equilibrium constants between some complexes
*
Not determined for solubility problems.
and the entering alkene or alkyne were determined by direct

416
L. Canovese et al. / Journal of Organometallic Chemistry 694 (2009) 411–419
spectrophotometric titration and a novel order comparing the
different stabilizing character of both alkene and alkyne moie-
ties was established for the first time.
microaliquots of a concentrated CDCl3 solution of the exchanging
olefin ol2 according to reaction (1). The reaction progress was fol-
lowed by monitoring the signal for the disappearance of the start-
ing complex and the contemporary appearance of the final product
[Pd(g2-ol2)(L-L0)]. The UV–Vis preliminary study was carried out
by placing 3 ml of freshly prepared solution of the complex
[Pd(g2-ol1)(L-L0)] ([[Pd(g2-ol1)(L-L0)]]0 = 1 ꢁ 10ꢂ4 mol dmꢂ3) in the
thermostatted (298 K) cell compartment of the UV–Vis spectro-
photometer. Microaliquots of solution containing the exchanging
olefin ol2 at adequate concentrations were added and the absor-
bance changes were monitored in the 250–400 nm wavelength
interval or at fixed wavelength (320 nm); (in some cases where
KE was large an excess of free ol1 had to be added to balance the
equilibrium position).
ꢅ The coordinating capability order for the olefins was confirmed
and the new entry trans-sulfone proved to be a quite strong
coordinating moiety. Moreover, the trans olefins show an
enhanced coordinating capability when compared with their
cis counterparts. In the presence of similar electronic character-
istics the stabilizing properties of the alkynes are strongly influ-
enced by their steric demand.
ꢅ The nature of the ancillary ligands does not have a remarkable
importance in stabilizing their palladium(0) derivatives. Only
the presence of methyl groups in ortho position on the pyridine
ring seems to enhance the stability of the complexes bearing fn
and ma olefins. In this respect the neocuproine ligand proves to
be the most effective.
4.5. X-ray analyses
ꢅ A kinetic determination of the reaction rates when the bulky
tmetc was employed as entering alkene on the complex
Crystals suitable for X-ray work were obtained by slow diffu-
[Pd(g
2-dmfu)(DPPQ-Me)] was carried out by standard 1H NMR
sion of hexane in
dmfu)(DPPQ)] and of diethyl ether in a dichloromethane solution
for [Pd(
2-deta) (Neocup)]. The selected specimen of the [Pd(g2
a -
dichloromethane solution for [Pd(g2
technique.
g
-
dmfu)(DPPQ)] complex was then fastened on the top of a glass fi-
ber and transferred to a Nonius MACH3 diffractometer made
available by Colleagues at the Department of Environmental Sci-
4. Experimental
ences of SUN, Caserta, Italy. The chosen item of [Pd(g
2-deta)(Neo-
4.1. Solvents and reagents
cup)] was inserted in a glass capillary and mounted on the
goniometer head of a Philips PW1100 diffractometer at the
C.N.R.-I.C.I.S. Institute of Padua, Italy. The raw data were collected
Acetone and CH2Cl2 were distilled over CaH2 and 4 Å molecular
sieves, respectively. CHCl3 was distilled over silver foil under inert
atmosphere. All the other chemicals were commercially available
grade products and were used as purchased. Unless otherwise sta-
ted, all manipulations were carried out under an argon atmosphere
using standard Schlenk techniques.
at room temperature by using graphite-monochromated Mo K
a
radiation (k = 0.70930 Å on the MACH3 and k = 0.71073 Å on the
PW1100). Crystal stability was assessed by monitoring either a
single ([Pd(g g
2-dmfu)(DPPQ)]) or three ([Pd( 2-deta)(Neocup)])
The synthesis of the ligands 8-diphenylphosphanylquinoline
(DPPQ) [14] and 8-diphenylphosphanyl-2-methylquinoline
(DPPQ-Me) [15], the alkenes cis- and trans-1,2-bis[(4-methyl-
phenyl)sulphonyl]ethene [16] (cis-sulf, trans-sulf) and the com-
standard reflections every 200 measurements; neither of the
two crystals showed sign of deterioration. Both structures were
solved by direct methods and refined by standard full–matrix
least–squares based on F2o with the SHELXTL NT [19] and SHELXL-97
[20] programs. All non-hydrogen atoms were refined anisotropi-
cally; hydrogen atoms were included in idealized positions and
refined as ‘‘riding model”.
plexes [Pd(
[Pd(
2-ma)(DPPQ-Me)] [4p], [Pd(
dmfu)(Phen)] [17] and [Pd(
2-dmfu)(BiPy)] [18] was carried out
g
2-dmfu)(DPPQ-Me)], [Pd(
g
2-dmfu)(DPPQ)] [11],
g
g
2-dmfu)(Neocup)] [4t], [Pd(g2
-
g
according to published procedures.
4.6. Crystal data for [Pd(g
2-dmfu)(DPPQ)]
4.2. Data analysis
C27H24NO4PPd, fw = 563.8, monoclinic, space group P21/c (No.
14), a = 17.380(4) Å, b = 9.421(2) Å, c = 16.273(3) Å, b = 111.38(3)°,
Mathematical and statistical analysis of equilibrium and kinetic
data was carried out by locally adapted non linear regression algo-
rithms written under SCIENTISTTM environment.
V = 2481(1) Å3, Z = 4,
q l
= 1.509 g/cm3, = 0.85 mmꢂ1. A total of
3533 unique reflections with I > 2r(I) were observed. Final agree-
ment factors: R = 0.032, Rw = 0.078, GOF = 1.032.
4.3. IR, NMR, and UV-Vis measurements
4.7. Crystal data for [Pd(g
2-deta)(Neocup)]
The IR, 1H and 13C NMR spectra were recorded on a Perkin-
Elmer Spectrum One spectrophotometer. 1D- and 2D-NMR spectra
were recorded using a Bruker DPX300 or Bruker DPX500 spectrom-
eter. Chemical shifts (ppm) are given relative to TMS (1H and 13C
C22H22N2O4Pd, fw = 484.8, monoclinic, space group P21/n (No.
14), a = 16.280(3) Å, b = 7.889(1) Å, c = 16.988(3) Å, b = 109.16(3)°,
V = 2061(1) Å3, Z = 4,
q l
= 1.562 g/cm3, = 0.93 mmꢂ1. A total of
NMR) and 85% H3PO4 (
31P NMR). Peaks are labelled as singlet (s),
4576 unique reflections with I > 2r(I) were observed. Final agree-
doublet (d), triplet (t), quartet (q), multiplet (m) and broad (br).
The proton and carbon assignment was performed by 1H-2D COSY,
1H-2D NOESY, 1H-13C HMQC and HMBC experiments.
UV–Vis spectra were taken on a Perkin–Elmer Lambda 40 spec-
trophotometer equipped with a Perkin–Elmer PTP6 (Peltier tem-
perature programmer) apparatus.
ment factors: R = 0.043, Rw = 0.104, GOF = 1.201. Additional crys-
tallographic data (atomic coordinates, full listings of bond
lengths and angles, anisotropic thermal parameters) are available
as Supporting information (pdq.cif for [Pd(
g
2-dmfu)(DPPQ)],
can.cif for [Pd(
g
2-deta)(Neocup)]).
4.8. Synthesis of [Pd(
g
2-nq)(DPPQ)]
4.4. Preliminary studies and equilibrium measurements
To solution of nq (0.0389 g, 0.246 mmol) and DPPQ
a
All the equilibrium reactions were preliminarily studied by 1H
NMR technique by dissolving the complex under study in 0.6 ml
of CDCl3 ([[Pd(g2-ol1)(L-L0)]]0 1 ꢆ 3 ꢁ 10ꢂ2 mol dmꢂ3) and adding
(0.0763 g, 0.244 mmol) in dry acetone (15 ml) solid
Pd2DBA3 ꢁ CHCl3 [21] (0.120 g, 0.116 mmol) was added under in-
ert atmosphere (Argon). The reaction mixture was stirred for 1 h

L. Canovese et al. / Journal of Organometallic Chemistry 694 (2009) 411–419
417
at room temperature and the initial dark suspension turned to
an orange solution which was taken to dryness under reduced
pressure and the residue re-dissolved in dichloromethane. Addi-
tion of charcoal and filtration on celite removed the traces of
metallic palladium yielding a clear orange solution. Reduction
to small volume (3–4 cm3) and slow addition of diethyl ether
gave the product as microcrystalline orange solid (0.1014 g, yield
ꢇ76%).
4.11. [Pd(g
2-deta)(Neocup)]
Yield: ꢇ65% (yellow solid). Selected data: 1H NMR (300 MHz,
CDCl3, T = 298 K, ppm) d: 1.37 (t, 6H, J = 7.1 Hz, ethyl-CH3); 3.12
(s, 6H, neocuproine-CH3); 4.33 (q, 4H, J = 7.1 Hz, ethyl-CH2); 7.69
(d, 2H, J = 8.3 Hz, H3); 7.76 (s, 2H, H5); 8.24 (d, 2H, J = 8.3 Hz, H4).
13C{1H} NMR (CDCl3, T = 298 K, ppm) d: 14.4 (CH3, ethyl-CH3);
29.9 (CH3, neocuproine-CH3); 60.6 (CH3, ethyl-CH2); 110.0 (C,
C„C); 124.9 (CH, C3); 125.5 (CH, C5); 127.2 (C, C6); 136.6 (CH,
C4); 145.4 (C, C7); 161.4 (C, C2); 163.7 (CO, CO). IR(KBr pellet)
Selected data: 1H NMR (300 MHz, CDCl3, T = 298 K, ppm) d: 5.03
(dd, 1H, JPH = 9.2 Hz, CH@CH JCH@CH = 6.9 Hz, trans-P); 5.22 (d, 1H,
JCH@CH = 6.9 Hz, CH@CH trans-N); 7.18–7.70 (m, 12H, Hc, PPh2),
7.66 (t; H, J = 8.2 Hz; H6); 7.68 (dd; H, J = 8.3 Hz; J = 4.7 Hz; H3);
7.90–8.07 (m, 4H, H7, H5, Hb); 8.36 (d; 1H, J = 8.3 Hz; H4); 9.07
(d; 1H, J = 4.7 Hz; H2). 31P{1H} NMR (CDCl3, T = 298 K, ppm) d:
25.3 13C{1H} NMR (CDCl3, T = 298 K, ppm) d: 64.6 (CH, CH@CH
trans-N); 70.3 (d, CH, JCP = 17.6 Hz CH@CH trans-P); 123.5 (CH,
C3); 124.6, 125.2 (CH, Cb); 127.5 (d, CH, JCP = 4.8 Hz, C6); 131.0
(CH,C5); 130.5, 131.4 (CH, Cc); 134.6 (d,C, JCP = 35.0 Hz, C8);
136.5, (C, Ca trans-N); 137.0 (C, Ca trans-P); 137.7 (d, CH,
JCP = 2.3 Hz, C7); 138.4 (CH, C4); 150.0 (C, C9); 151.3 (C, C10);
152.2 (CH, C2); 177.1 (d, CO, JCP = 6.3 Hz CO trans-N); 183.4 (CO,
m
= 1842, 1675 cmꢂ1 (C@O). Anal. Calc. for C22H22N2O4Pd: C,
54.50; H, 4.57; N, 5.78. Found: C, 54.65; H, 4.64; N, 5.82%.
4.12. [Pd(g
2-dbua)(Neocup)]
Yield: ꢇ70% (yellow solid). Selected data: 1H NMR (300 MHz,
CDCl3, T = 298 K, ppm) d: 1.59 (s, 18H, t-Bu); 3.17 (s, 6H, neocupr-
oine-CH3); 7.68 (d, 2H, J = 8.3 Hz, H3); 7.75 (s, 2H, H5); 8.23 (d, 2H,
J = 8.3 Hz, H4). 13C{1H} NMR (CDCl3, T = 298 K, ppm) d: 28.4 (CH3, t-
Bu); 30.2 (CH3, neocuproine-CH3); 80.3 (C, t-Bu); 110.6 (C, C„C);
124.7 (CH, C3); 125.4 (CH, C5); 127.2 (C, C6); 136.5 (CH, C4);
145.4 (C, C7); 161.3(C, C2); 162.8 (CO, CO). IR(KBr pellet)
CO trans-P). IR(KBr pellet)
m
= 1636, 1622, 1588 cmꢂ1 (C@O). Anal.
Calc. for C31H22NO2PPd: C, 64.43; H, 3.84; N, 2.42. Found: C, 64.27;
H, 3.94; N, 2.50%.
m
= 1803, 1680 cmꢂ1 (C@O). Anal. Calc. for C26H30N2O4Pd: C,
57.73; H, 5.59; N, 5.18. Found: C, 57.64; H, 4.66; N, 5.25%.
The following complexes were synthesized in an analogous way
using Pd2DBA3 ꢁ CHCl3, the appropriate ligand and alkene or alkyne,
in the same molar ratios.
4.13. [Pd(g
2-trans-sulf)(Neocup)]
Yield: ꢇ80% (pale yellow solid). Selected data: 1H NMR
(300 MHz, CDCl3, T = 298 K, ppm) d: 2.39 (s, 6H, tol-CH3); 3.40 (s,
6H, neocuproine-CH3); 4.17 (s, 2H, CH@CH); 6.96 (d, 4H,
J = 8.0 Hz, Hc); 7.42 (d, 4H, J = 8.0 Hz, Hb); 7.71 (d, 2H, J = 8.3 Hz,
H3); 7.78 (s, 2H, H5); 8.27 (d, 2H, J = 8.3 Hz, H4). 13C{1H} NMR
(CDCl3, T = 298 K, ppm) d: 21.5 (Ph-CH3); 30.8 (CH3, neocuproine-
CH3); 54.3 (CH, C=C); 125.45 (CH, C3); 125.47 (CH, C5); 126.4
(CH, Cb); 127.3 (C, C6); 129.1 (CH, Cc); 137.4 (CH,C4); 139.5 (C,
Ca); 141.7 (C, Cd); 146.0 (C, C7); 162.4 (C, C2); IR(KBr pellet)
4.9. [Pd(g
2-nq)(DPPQ-Me)]
Yield: ꢇ80% (orange solid). Selected data: 1H NMR (300 MHz,
CDCl3, T = 298 K, ppm)) d: 3.14 (s, 3H, quinoline-CH3) 5.01 (m,
2H, CH@CH trans-P and trans-N); 7.06–7.13 (m, 2H, PPh2),
7.29–7.35 (m, 2H, PPh2), 7.38–7.47 (m, 6H, Hc, PPh2), 7.48–
7.62 (m, 4H, H3, H6 PPh2); 7.69 (d; H, J = 7.3 Hz; Hb); 7.86 (t,
1H, J = 7.5 Hz H7); 7.90 (d; H, J = 7.9 Hz; H5); 8.04 (d; H,
J = 7.3 Hz; Hb); 8.19 (d; 1H, J = 8.4 Hz; H4). 31P{1H} NMR (CDCl3,
T = 298 K, ppm) d: 25.4. 13C{1H} NMR (CDCl3, T = 298 K, ppm)
d: 30.2 (CH3, quinoline–CH3); 62.6 (CH, CH@CH trans-N); 66.2
(d, CH, JCP = 21.0 Hz CH@CH trans-P); 123.8 (CH, C3); 125.0,
125.4 (CH, Cb); 126.3 (d, CH, JCP = 4.8 Hz, C6); 131.0 (CH,C5);
130.1, 131.2 (CH, Cc); 134.3 (d,C, JCP = 35.1 Hz, C8); 136.0, (C, Ca
trans-N); 136.5 (C, Ca trans-P); 137.8 (d, CH, JCP = 2.3 Hz, C7);
138.3 (CH, C4); 151.2 (C, C9); 151.5 (C, C10); 165.6 (C, C2);
184.0 (d, CO, JCP = 5.6 Hz CO trans-N); 185.1 (CO, CO trans-P).
m
= 1287, 1140 cmꢂ1 (S=O). Anal. Calc. for: C28H27NO4PdS3: C,
52.21; H, 4.22; N, 2.17. Found: C, 52.14; H, 4.28; N, 2.26%.
4.14. [Pd(g
2-nq)(Neocup)]
0.0130 g (0.082 mmol) of naphthoquinone was added to a solu-
tion of 0.0360 g (0.079 mmol) of [Pd(
2-dmfu)(Neocup)] in 5 ml of
g
anhydrous CH2Cl2. Immediate precipitation of an orange solid was
observed and the reaction mixture was stirred for 30 min. The
solution was concentrated under reduced pressure and the precip-
itation was completed by addition of diethyl ether. The orange
product was filtered off (G4) and washed with small aliquots of
diethyl ether and pentane and dried under vacuum. Yield
0.0360 g, ꢇ96%. Selected data: 1H NMR (300 MHz, CDCl3,
T = 298 K, ppm) d: 3.09 (s, 6H, neocuproine-CH3); 4.86 (s, 2H,
CH@CH); 7.41 (m, 2H, Hc); 7.66 (d, 2H, J = 8.3 Hz, H3); 7.72 (s,
2H, H5); 7.97 (m, 2H, Hb); 8.21 (d, 2H, J = 8.3 Hz, H4). 13C{1H}
NMR (CDCl3, T = 298 K, ppm) d: 30.0 (CH3, neocuproine-CH3);
55.3 (CH, CH@CH); 125.2 (CH, Cb); 125.4 (CH, C3); 125.6 (CH, C5);
127.4 (C, C6); 131.2 (CH, Cc); 137.1 (CH, C4); 145.6 (C, C7); 163.0
IR(KBr pellet)
m
= 1637, 1622, 1587 cmꢂ1 (C@O). Anal. Calc. for
C32H24NO2PPd: C, 64.93; H, 4.09; N, 2.37. Found: C, 64.64; H,
4.14; N, 2.27%.
4.10. [Pd(g
2-ma)(DPPQ)]
Yield: ꢇ80% (yellow solid). Selected data: 1H NMR (300 MHz,
CDCl3, T = 298 K, ppm)) d: 4.11 (dd, 1H, JPH = 10.3 Hz, CH@CH
JCH@CH = 3.7 Hz, trans-P); 5.22 (dd, 1H, JCH@CH = 3.7 Hz, JPH = 3.1 Hz,
CH@CH trans-N); 7.35–7.61 (m, 11H, H3, PPh2), 7.71 (t; H,
J = 7.8 Hz; H6); 7.95 (t; H, J = 7.8 Hz; H7); 8.02 (d; H, J = 7.8 Hz;
H5); 8.41 (d; 1H, J = 8.3 Hz; H4); 9.40 (d; 1H, J = 4.7 Hz; H2).
31P{1H} NMR (CDCl3, T = 298 K, ppm) d: 23.3. 13C{1H} NMR (CDCl3,
T = 298 K, ppm) d: 48.0 (CH, CH@CH trans-N); 48.4 (d, CH,
JCP = 31.0.6 Hz CH@CH trans-P); 123.1 (CH, C3); 127.8 (d, CH,
JCP = 5.0 Hz, C6); 130.5 (d, C, JCP = 37.5 Hz, C8); 131.2 (CH, C5);
138.0 (d, CH, JCP = 2.1 Hz, C7); 138.6 (CH, C4); 150.7 (C, C9); 151.0
(C, C10); 156.4 (CH, C2); 171.7 (d, CO, JCP = 5.3 Hz CO trans-N);
(C, C2); 188.2 (CO, naphthoquinone-CO). IR(KBr pellet)
m = 1627,
1588 cmꢂ1 (C@O). Anal. Calc. for C24H18N2O2Pd: C, 60.96; H, 3.84;
N, 5.92. Found: C, 60.78; H, 3.78; N, 5.82%.
4.15. [Pd(g
2-ma)(Neocup)]
This complex was synthesized in an analogous way using ma as
entering alkene. Yield: ꢇ83% (pale yellow solid). Selected data: 1H
NMR (300 MHz, CDCl3, T = 298 K, ppm) d: 3.16 (s, 6H, neocuproine-
CH3); 4.15 (s, 2H, CH@CH); 7.74 (d, 2H, J = 8.3 Hz, H3); 7.82 (s, 2H,
172.7 (CO, CO trans-P). IR(KBr pellet)
m
= 1793, 1713 cmꢂ1 (C@O).
Anal. Calc. for C25H18NO3PPd: C, 57.99; H, 3.50; N, 2.70. Found: C,
57.70; H, 3.64; N, 2.78%.

418
L. Canovese et al. / Journal of Organometallic Chemistry 694 (2009) 411–419
H5); 8.27 (d, 2H, J = 8.3 Hz, H4). IR(KBr pellet)
m
= 1787, 1722 cmꢂ1
Acknowledgements
(C@O). Anal. Calc. for C18H14N2O3Pd: C, 52.38; H, 3.42; N, 6.79.
Found: C, 52.27; H, 3.36; N, 6.94%.
The authors gratefully thank Dr. R. Iacovino of the Dipartimento
di Scienze Ambientali of SUN (Caserta, Italy) and Dr. F. Benetollo of
the C.N.R.-I.C.I.S. Institute (Padua, Italy) for allowing access to the
MACH3 and PW1100 diffractometers, supervisioning the X-ray
data collection process and for help in the interpretation of the
structures.
4.16. [Pd(g
2-nq)(Phen)]
0.0154. g (0.098 mmol) of naphthoquinone was added to a solu-
tion of 0.0400 g (0.093 mmol) of [Pd(
2-dmfu)(Phen)] in 5 ml of
g
anhydrous CH2Cl2. Immediate precipitation of an orange solid
was observed and the reaction mixture was stirred for 30 min.
The solution was concentrated under reduced pressure and the
precipitation was completed by addition of diethyl ether. The or-
ange product was filtered off (G4) and washed with small aliquots
of diethyl ether and pentane and dried under vacuum. Yield
0.0385 g, ꢇ93%. Selected data: 1H NMR (300 MHz, CDCl3,
T = 298 K, ppm) d: 5.03 (s, 2H, CH@CH); 7.44 (m, 2H, Hc); 7.81
(dd, 2H, J = 8.3 Hz, J = 4.8 Hz, H3); 7.83 (s, 2H, H5); 8.08 (m, 2H,
Hb); 8.38 (dd, 2H, J = 8.2 Hz, J = 1.5 Hz, H4) 8.95 (dd, 2H,
J = 4.3 Hz, J = 1.5 Hz, H2). 13C{1H} NMR (CDCl3, T = 298 K, ppm) d:
125.0 (CH, Cb); 125.4 (CH, C3); 126.7 (CH, C5); 129.2 (C, C6);
130.9 (CH, Cc); 137.0 (C, Ca) 137.2 (CH, C4); 145.1 (C, C7); 150.4
(C, C2); 179.3 (CO, naphthoquinone-CO). CH, CH@CH not detect-
Appendix A. Supplementary material
Figure concerning the equilibrium titration curves for the deter-
mination of equilibrium exchange constants and X-ray crystallo-
graphic data. Supplementary data associated with this article can
be found, in the online version, at doi:10.1016/j.jorganchem.2008.
11.012.
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C22H14N2O2Pd: C, 59.41; H, 3.17; N, 6.30. Found: C, 59.50; H,
3.23; N, 6.89%.
m
= 1616, 1583 cmꢂ1 (C@O). Anal. Calc. for
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(f) M.J. Brown, K.K. Hii, Angew. Chem., Int. Ed. Engl. 108 (1996) 679–682;
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678;
4.17. [Pd(g
2-ma)(Phen)]
This complex was synthesized in an analogous way using ma as
entering alkene. Yield: ꢇ88% (yellow solid). Selected data: 1H NMR
(300 MHz, CDCl3, T = 298 K, ppm) d: 4.17 (s, 2H, CH@CH); 7.84 (dd,
2H, J = 8.2 Hz, J = 4.8 Hz, H3); 7.96 (s, 2H, H5); 8.49 (dd, 2H,
J = 8.2 Hz, J = 1.5 Hz, H4) 9.25 (dd, 2H, J = 4.8 Hz, J = 1.5 Hz, H2).
(h) A. de Meijere, F.E. Meyer, Angew. Chem., Int. Ed. Engl. 106 (1994) 2473–
2506;
(i) J.K. Stille, Angew. Chem., Int. Ed. Engl. 25 (1986) 508–524;
(j) V. Farina, in: E.W. Abel, F.G.A. Stone, G. Wilkinson (Eds.), Comprehensive
Organometallic Chemistry II, vol. 12, Pergamon, Oxford, 1995 (Chapter 3.4);
(k) V. Farina, G.P. Roth, Adv. Metalorg. Chem. 5 (1996) 1–53;
(l) B. Crociani, S. Antonaroli, L. Canovese, P. Uguagliati, F. Visentin, Eur. J. Inorg.
Chem. (2004) 732–742.
IR(KBr pellet)
m
= 1796, 1720 cmꢂ1 (C@O). Anal. Calc. for
C16H10N2O3Pd: C, 49.96; H, 2.62; N, 7.28. Found: C, 49.80; H,
2.70; N, 7.36%.
[2] (a) A. Pfaltz, Acta Chem. Scand. 50 (1996) 189–194;
(b) O. Reiser, Angew. Chem., Int. Ed. Engl. 105 (1993) 576–578;
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Chem. 566 (1998) 61–71;
4.18. [Pd(g
2-nq)(BiPy)]
(b) B. Crociani, S. Antonaroli, G. Bandoli, L. Canovese, F. Visentin, P. Uguagliati,
Organometallics 18 (1999) 1137–1147;
0.0163 g (0.103 mmol) of naphthoquinone was added to a
solution of 0.0400 g (0.079 mmol) of [Pd(
2-dmfu)(BiPy)] in
(c) K. Selvakumar, M. Valentini, M. Wörle, P.S. Pregosin, A. Albinati,
Organometallics 18 (1999) 1207–1215.
[4] (a) N.E. Schore, Chem. Rev. 88 (1988) 1081–1119;
(b) H. Tom Dieck, C. Munz, C. Mueller, J. Organomet. Chem. 384 (1987) 243–
255;
g
5 ml of anhydrous CH2Cl2. Immediate precipitation of an orange
solid was observed and the reaction mixture was stirred for
30 min. The solution was concentrated under reduced pressure
and the precipitation was completed by addition of diethyl ether.
The orange product was filtered off (G4) and washed with small
aliquots of diethyl ether and pentane and dried under vacuum.
Yield 0.0408 g, ꢇ94%. Selected data: 1H NMR (300 MHz, CDCl3,
T = 298 K, ppm) d: 4.92 (bs, 2H, CH@CH); 7.45 (m, 2H, Hc);
7.50 (ddd, 2H, J = 7.5 Hz, J = 5.1 Hz, J = 1.9 Hz, H3); 7.94 (m, 4H,
H5, H4); 8.08 (m, 2H, Hb); 8.65 (d, 2H, J = 5.1 Hz, H2). IR (KBr pel-
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(1997) 1743–1745;
(f) R. van Belzen, R.A. Klein, H. Kooijman, N. Veldman, A.L. Spek, C.J. Elsevier,
Organometallics 17 (1998) 1812–1825;
(g) R. van Belzen, C.J. Elsevier, A. Dedieu, N. Veldman, A.L. Spek,
Organometallics 22 (2003) 722–736;
(h) B.M. Trost, G.J. Tanoury, J. Am. Chem. Soc. 109 (1987) 4753–4755;
(i) B.M. Trost, G.J. Tanoury, J. Am. Chem. Soc. 110 (1988) 1636–1638;
(j) B.M. Trost, M.K. Trost, J. Am. Chem. Soc. 113 (1991) 1850–1852;
(k) B.M. Trost, S.K. Hashmi, J. Am. Chem. Soc. 116 (1994) 2183–2184;
(l) H. Suzuki, K. Itoh, Y. Ishii, K. Simon, I.A. Ibers, J. Am. Chem. Soc. 98 (1976)
8494–8500;
let)
m
= 1616, 1582, 1565 cmꢂ1 (C@O). Anal. Calc. for
C20H14N2O2Pd: C, 57.06; H, 3.35; N, 6.66. Found: C, 57.14; H,
3.28; N, 6.78%.
(m) C.M. Crawforth, I.J.S. Fairlamb, A.R. Kapdi, J.L. Serrano, R.J.K. Taylor, G.
Sanchez, Adv. Synth. Catal. 348 (2006) 405–412;
(n) J.L. Serrano, I.J.S. Fairlamb, G. Sanchez, L. Garcia, J. Perez, J. Vives, G. Lopez,
C.M. Crawforth, R.J.K. Taylor, Eur. J. Inorg. Chem. 13 (2004) 2706–2715;
(o) A. Holuigue, C. Sirlin, M. Pfeffer, K. Goubitz, J. Fraanje, C.J. Elsevier, Inorg.
Chim. Acta 359 (2006) 1773–1778;
(p) L. Canovese, F. Visentin, G. Chessa, P. Uguagliati, C. Levi, A. Dolmella,
Organometallics 24 (2005) 5537–5548;
(q) L. Canovese, F. Visentin, G. Chessa, C. Santo, C. Levi, P. Uguagliati, Inorg.
Chem. Commun. 9 (2006) 388–390;
(r) L. Canovese, F. Visentin, G. Chessa, P. Uguagliati, C. Levi, A. Dolmella, G.
Bandoli, Organometallics 25 (2006) 5355–5365;
4.19. [Pd(g
2-ma)(BiPy)]
This complex was synthesized in an analogous way using ma as
entering alkene. Yield: ꢇ93% (pale yellow solid). Selected data: 1H
NMR (300 MHz, CDCl3, T = 298 K, ppm) d: 4.04 (s, 2H, CH@CH));
7.53 (ddd, 2H, J = 7.5 Hz, J = 5.0 Hz, J = 1.9 Hz, H3); 8.05 (m, 4H,
H5, H4); 8.94 (d, 2H, J = 5.0 Hz, H2). IR(KBr pellet)
m = 1783,
1720 cmꢂ1 (C@O). Anal. Calc. for C14H10N2O3Pd: C, 46.62; H, 2.79;
(s) L. Canovese, F. Visentin, G. Chessa, P. Uguagliati, C. Santo, L. Maini, J.
Organomet. Chem. 692 (2007) 2342–2345;
N, 7.77. Found: C, 46.80; H, 2.70; N, 7.66%.

L. Canovese et al. / Journal of Organometallic Chemistry 694 (2009) 411–419
419
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16 (1997) 3447–3453.
carried out by NMR kinetic experiment using the relationship k2 =
ln((2B0 ꢂ A0)/B0)/(B0 ꢂ A0)/t1/2
.
A0 = 1.8 ꢄ 10ꢂ2 mol dmꢂ3 and B0 = 2.1 ꢄ 10ꢂ2
mol dmꢂ3 represent the initial concentrations of the complex [Pd(g2
-
dmfu)(Neocup)] and of the olefin tmetc, respectively, t1/2 represents the
reaction half time (42 h). It is noteworthy that even under second order
conditions the equilibrium position is completely shifted to the right when
dmfu is displaced by tmectc (cfr. Ref. [6a]). From the estimated equilibrium
constant (ca. 1000) the forward reaction is about three orders of magnitude
higher than the reverse one, therefore the latter could be ignored.
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3324–3330;
[18] B. Crociani, F. Di Bianca, P. Uguagliati, L. Canovese, A. Berton, J. Chem. Soc.,
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[9] The mC@O and mS@O frequencies of the free unsaturated molecules are:
Dalton Trans. (1991) 71–79.
}
[19] G.M. Sheldrick, SHELXTL NT, Version 5.10; Bruker AXS Inc., Madison, WI, 1999.
[20] G.M. Sheldrick, SHELXL-97, Program for the Refinement of Crystal Structures,
University of Göttingen, Germany, 1997.
m
C@O(dmfu) = 1725;
m
C@O(ma) = 1850, 1792, 1780;
mC@O(nq) = 1650; mC@O = 1718;
mS@O(dbua)(trans-sulf) = 1328, 1141;
m
S@O(cis-sulf) = 1317, 1149 cmꢂ1
.
[21] T. Hukai, H. Kawazura, Y. Ishii, J. Organomet. Chem. 65 (1974) 253–266.