Catalytic hydroarylation of olefins promoted by dicationic platinum(II) and palladium(II) complexes. the interplay of C-C bond formation and M-C bond cleavage

Article abstract of DOI:10.1021/om700692s

The coordinated olefin in dicationic platinum(II) and palladium(II) complexes [M(PNP)(olefin)](SbF₆)₂ (M = Pt, Pd; PNP = 2,6-bis(diphenylphosphinomethyl)pyridine; olefin = ethene, propene) is electrophilic enough to react with benzene rings activated by methoxy substituents. If the proton released by the aromatic ring is trapped by a base, stable a-alkyl derivatives of the type [M(PNP)CH₂CH(R)Ar](SbF ₆) or [M(PNP)CH(R)CH₂Ar](SbF₆) (R = H, Me) are formed; otherwise the M-C σ-bond can be cleaved by the proton, setting up a catalytic cycle that leads to the alkylated aromatic compound. The molecular structure of the σ-alkyl derivative [(PNP)PtCH₂CH ₂-C₆H₂(OMe)₃](BF₄) has been determined by X-ray diffraction analysis, and the factors affecting the mechanism and the rates of the catalytic reaction have been qualitatively investigated and rationalized, showing that the rates of C-C bond formation and M-C bond cleavage are inversely correlated.

Full text of DOI:10.1021/om700692s

5216
Organometallics 2007, 26, 5216-5223
Catalytic Hydroarylation of Olefins Promoted by Dicationic
Platinum(II) and Palladium(II) Complexes. The Interplay of C-C
Bond Formation and M-C Bond Cleavage
Maria Elena Cucciolito, Angela D’Amora, Angela Tuzi, and Aldo Vitagliano*
Dipartimento di Chimica “Paolo Corradini”, UniVersita` di Napoli “Federico II”,
Complesso UniVersitario di Monte S. Angelo, Via Cintia, I 80126 Napoli, Italy
ReceiVed July 11, 2007
The coordinated olefin in dicationic platinum(II) and palladium(II) complexes [M(PNP)(olefin)](SbF6)2
(M ) Pt, Pd; PNP ) 2,6-bis(diphenylphosphinomethyl)pyridine; olefin ) ethene, propene) is electrophilic
enough to react with benzene rings activated by methoxy substituents. If the proton released by the
aromatic ring is trapped by a base, stable σ-alkyl derivatives of the type [M(PNP)CH2CH(R)Ar](SbF6)
or [M(PNP)CH(R)CH2Ar](SbF6) (R ) H, Me) are formed; otherwise the M-C σ-bond can be cleaved
by the proton, setting up a catalytic cycle that leads to the alkylated aromatic compound. The molecular
structure of the σ-alkyl derivative [(PNP)PtCH2CH2-C6H2(OMe)3](BF4) has been determined by X-ray
diffraction analysis, and the factors affecting the mechanism and the rates of the catalytic reaction have
been qualitatively investigated and rationalized, showing that the rates of C-C bond formation and M-C
bond cleavage are inversely correlated.
rearrangement of the carbocation can result in the cleavage of
the metal-carbon σ-bond, thus making a coordination site
available to a further olefin molecule and opening the way to a
catalytic process (Scheme 1). More usually, the attack can be
carried out by a nonbonding lone pair on a heteroatom such as
nitrogen. In this case no electron vacancy is produced, and the
positive charge rests on the heteroatom. If the heteroatom brings
a proton, this becomes acidic and could in principle cleave the
M-C σ-bond, thus starting a catalytic cycle. The problem is
that the same factors that favor the nucleophilic attack, i.e., the
positive charge on the metal ion and the resulting higher stability
of the σ-bonded derivative, also disfavor the protolytic cleavage
of the M-C σ-bond.8-10 In practice, catalytic processes involv-
ing nitrogen nucleophiles have recently been achieved using
amides rather than amines,11 so that the poorly coordinating and
poorly basic nucleophile does not compete with the olefin for
coordination to the metal and at the same time produces a very
acidic proton after the nucleophilic attack. Less well-balanced
conditions would either produce no reaction at all or give a
stable σ-bonded alkyl derivative that would not evolve further.4,5
Another class of nucleophiles that could in principle react
via a π-bonding pair are the aromatic rings, in a reaction quite
similar to Friedel-Crafts alkylations. In this case, the recon-
stitution of the aromaticity from the primary intermediate would
Introduction
The electrophilic activation of unsaturated substrates by
coordination to a transition metal ion is a very remarkable
phenomenon, which is found at the core of most relevant metal-
catalyzed processes.1 As could be intuitively anticipated, there
is also wide experimental2 and theoretical3 evidence that the
electrophilicity of the coordinated alkene can be enhanced by
increasing the positive charge on the metal ion. For example,
dicationic Pt(II) and Pd(II) olefin complexes easily undergo the
nucleophilick attack of aromatic amines such as chloroanilines,4,5
while the neutral species need the more basic aliphatic amines
to react.6
The primary product of a nucleophilic attack is a M-C
σ-bonded species, whose successive fate depends on the kind
of nucleophile carrying on the attack. We recently found that
when the coordinated olefin is strongly activated, as in dicationic
complexes of the tridentate pincer ligand 2,6-bis(diphenylphos-
phinomethyl)pyridine (PNP), the attack can be carried out by a
bonding π-electron pair of an electron-rich olefin.7 In this case
an electron vacancy is left on the adjacent carbon atom and a
carbocation is formed as an intermediate. The successive
* Corresponding author. E-mail: alvitagl@unina.it.
(1) Crabtree, R. H. The Organometallic Chemistry of Transition Metals,
4th ed.; John Wiley & Sons: New York, 2005.
(2) (a) Maresca, L.; Natile, G.; Rizzardi, G. Inorg. Chim. Acta 1980,
38, 53. (b) Maresca, L.; Natile, G. J. Chem. Soc., Chem. Commun. 1983,
40. (c) Maresca, L.; Natile, G. Comments Inorg. Chem. 1994, 16, 95, and
references therein.
(3) (a) Sasaki, S.; Maruta, K.; Ohkubo, K. Inorg. Chem. 1987, 26, 2499.
(b) Stro¨mberg, S.; Svensson, M.; Zetterberg, K. Organometallics 1997, 16,
3165.
(4) Hahn, C.; Morvillo, P.; Vitagliano, A. Eur. J. Inorg. Chem. 2001,
419.
(5) Hahn, C.; Morvillo, P.; Herdtweck, E.; Vitagliano, A. Organometallics
2002, 21, 1807.
(8) Whether the protonolysis takes place via a concerted three-center
mechanism or via a prior oxidative addition to the metal,9 an interaction of
the proton with the metal is involved, which is expected to be disfavored
by the positive charge on the metal when the complex is cationic. Indeed,
while in zwitterionic or neutral alkyl derivatives derived from the nucleo-
philic attack of amines on platinum-olefin complexes the M-C bond is
easily cleaved by HCl,10 reversal of the attack was observed in cationic
derivatives.5
(9) Romeo, R.; D’Amico, G. Organometallics 2006, 25, 3435.
(10) Panunzi, A.; De Renzi, A.; Palumbo, R.; Paiaro, G. J. Am. Chem.
Soc. 1969, 91, 3879.
(6) Haszeldine, R. N.; Parish, R. V.; Robbins, D. W. J. Chem. Soc.,
Dalton Trans. 1976, 2355.
(7) (a) Hahn, C.; Cucciolito, M. E.; Vitagliano, A. J. Am. Chem. Soc.
2002, 124, 9038. (b) Cucciolito, M. E.; D’Amora, A.; Vitagliano, A.
Organometallics 2005, 24, 3359.
(11) (a) Karshtedt, D.; Bell, A. T.; Tilley, T. D. J. Am. Chem. Soc. 2005,
127, 12640. (b) Wang, X; Widenhoefer, R. A. Organometallics 2004, 23,
1649. (c) Bender, C. F.; Widenhoefer, R. A. J. Am. Chem. Soc. 2005, 127,
1070. (d) Michael, F. E.; Cochran, B. M. J. Am. Chem. Soc. 2006, 128,
4246.
10.1021/om700692s CCC: $37.00 © 2007 American Chemical Society
Publication on Web 08/29/2007

Catalytic Hydroarylation of Olefins
Organometallics, Vol. 26, No. 21, 2007 5217
Scheme 1
Scheme 2
release a proton, acidic enough to cleave the M-C σ-bond,
thereby starting a catalytic cycle. Indeed, a Friedel-Crafts
coupling of olefins with aromatic rings has been recently
obtained in moderate yields using the combination of Zeise’s
dimer and silver fluoroborate as catalyst,12 but neither the truly
active species nor any intermediate has been isolated. Following
our previous studies7 on catalytic cross-coupling reactions
promoted by highly electrophilic Pt2+ and Pd2+ species, we
report in this paper an investigation of the stoichiometric and
catalytic coupling of ethene and propene with arenes activated
by methoxy substituents, including the X-ray characterization
of a σ-bonded intermediate. The choice of methoxy substituents
was suggested by the need to avoid activating substituents, such
as hydroxy or amino groups, which could themselves be good
nucleophiles for the coordinated olefin.
Results and Discussion
Reactions of the Ethene Complex [Pt(PNP)(C2H4)](SbF6)2
(1a) with 1,3,5-Trimethoxybenzene. In a preliminary test, the
complex was reacted with a slight excess of 1,3,5-trimethoxy-
benzene in 9:1 CD2Cl2/CD3NO2 solution, and the reaction was
1
monitored by H NMR. Immediately after dissolution of the
reactants, multiplets of very small intensity (accounting for less
than 1% of the reactants) appeared at δ ) 2.0 and δ ) 2.45,
indicating the presence of a Pt-CH2-CH2-Ar fragment. These
signals did not grow further with time, but other signals appeared
and slowly increased, which could be ascribed to the alkylation
(12) Karshtedt, D.; Bell, A. T.; Tilley, T. D. Organometallics 2004, 23,
4169.

5218 Organometallics, Vol. 26, No. 21, 2007
Cucciolito et al.
product 2-ethyl-1,3,5-trimethoxybenzene (2). After 4 h, 20%
conversion of the substrate to the alkylation product was
observed.
The spontaneous cleavage of the Pt-C σ-bond by the proton
released from the aromatic ring indicated that the reaction can
in principle be catalytic. Accordingly, we ran it in the presence
of 30 equiv of 1,3,5-trimethoxybenzene under 1 bar pressure
of ethene, and a very modest catalytic activity was in fact
revealed, 2 equiv (with respect to the catalyst) of the alkylation
product being obtained after 72 h at room temperature. The
activity increased by switching to pure nitromethane as solvent
(4 equiv after 72 h) and by raising the temperature (7 equiv
being obtained in MeNO2 after 24 h at 70 °C and 7 bar).
In another experiment, the addition of 20 µL of water to the
sample after the dissolution of the reactants caused the immedi-
ate formation of the σ-alkyl derivative [(PNP)PtCH2CH2-C6H2-
(OMe)3]SbF6 (2a), which in a larger scale experiment was
isolated as fluoroborate salt and characterized by X-ray structural
analysis (see later). In two different attempts to cleave the Pt-C
σ-bond by addition of a strong acid, complex 2a was treated
with gaseous HCl and with HBF4‚Et2O in dichloromethane
solution. Somehow unexpectedly, in both cases no cleavage of
the Pt-C σ-bond was observed, but the coupling reaction was
reversed (eq 1), giving trimethoxybenzene and the complexes
[Pt(PNP)Cl]Cl and [Pt(PNP)(C2H4)](BF4)2, respectively, in the
former and latter case.
Figure 1. ORTEP drawing of the cation of complex 2a. H atoms
are not shown, and thermal ellipsoids are drawn at the 30%
probability level.
Table 1. Selected Bond Lengths (Å), Bond Angles (deg), and
Torsion Angles (deg) for 2a-BF4 with esd’s in Parentheses
Pt1-P1
Pt1-P2
Pt1-N1
Pt1-C1
P1-C12
P2-C13
C1-C2
C2-C3
2.263(3)
2.282(3)
2.098(9)
2.157(9)
1.798(9)
1.844(11)
1.421(16)
1.520(17)
The above experiments indicate that the whole catalytic
process proceeds through the mechanism depicted in Scheme
2. In a first rapid equilibrium step (i), the electrophilic-
coordinated ethene molecule attacks the activated aromatic ring,
forming a transient arenium ion as usual for Friedel-Crafts
alkylations. Although fast (as proven by the immediate formation
of the σ-alkyl species 2a), this equilibrium is largely shifted
toward the reactants, and only an extremely small amount of
the arenium ion is probably present in solution. Indeed, the
signals of the σ-bonded species revealed after mixing of the
reagents coincide with those of the isolated complex 2a and,
therefore, most likely belong not to a true arenium ion but to
its deprotonation product by traces of water present in the
solvent mixture. The fast “side step” ii must also be reversible,
as proven by the reversal of the coupling reaction after addition
of a strong acid, while the “productive” step iii, involving the
protolytic cleavage of the Pt-C σ-bond, is irreversible but very
slow. The protonolysis of the Pt-C σ-bond leaves a coordination
site available to a new ethene molecule, and the catalytic cycle
is thus closed in step iV. The slowness of step iii is not surprising,
since the protonolysis of the Pt-C σ-bond is expected to have
a barrier increasing with the positive charge on the metal,8 but
an open question is whether it is effected intramolecularly by
the proton released by the arenium ion or intermolecularly by
a proton first transferred to a water molecule present in the
solvent or to the solvent itself. It is worth noting that isotope
labeling experiments do not help in answering this question,
because in the reaction mixture the protons on the activated
aromatic ring are exchanging anyhow with protic species (e.g.,
water) present in the acidic medium. Nevertheless we tend to
favor the hypothesis of the intramolecular cleavage, on the
grounds that the addition of a strong acid failed to cleave the
Pt-C σ-bond, causing instead the reversal of the ethene attack
on the aromatic ring (eq 1).
P1-Pt1-P2
P1-Pt1-P2
P1-Pt1-C1
P2-Pt1-N1
P2-Pt1-C1
N1-Pt1-C1
Pt1-C1-C2
C1-C2-C3
164.9(1)
82.2(3)
95.5(3)
83.9(3)
98.7(3)
176.6(4)
116.3(7)
109.7(9)
Pt1-C1-C2-C3
P1-C12-C18-N1
P2-C13-C14-N1
C1-C2-C3-C4
179.2(8)
25.7(13)
24.7(15)
94.2(15)
Molecular Structure of [(PNP)PtCH2CH2-C6H2(OMe)3]-
BF4 (2a-BF4). Single crystals of the compound suitable for
X-ray analysis were obtained from a methylene chloride/diethyl
ether solution. The molecular structure of the cation is shown
in Figure 1, and selected bond lenghts and angles are given in
Table 1. The compound (monoclinic, space group P21/c)
crystallizes with one square-planar cationic Pt complex and one
-
separate BF4 anion in the asymmetric unit. The PNP ligand
acts as tridentate, exhibiting a local C2 symmetry around the
axis passing through the Pt-N bond, and the trimethoxyphe-
nylethyl group is σ-bonded to the metal. The expected square-
planar coordination geometry around the Pt atom is slightly
distorted, owing to the constraints of the PNP chelate (bite angles
N-Pt-P are 82.2(3)° and 83.9(3)°, P-N-P angle is 164.9-
(1)°). The Pt-C1 bond distance (2.157(9) Å) is slightly longer

Catalytic Hydroarylation of Olefins
Organometallics, Vol. 26, No. 21, 2007 5219
Table 2. Yield and Product Distribution in the Reaction of
Ethene with 1,3-Dimethoxybenzene under Various
Conditionsa
Chart 1. Alkylated Arenes Resulting from the
Cross-Coupling Reactions
product distribution
(mol %)b
no. equiv
% reacted
entry substrate T (°C) p (bar) substrate
3
4
5
1c
2
3
4
5
30
30
30
30
50
75
24
24
24
70
70
70
1
1
7
7
7
7
16
50
83
100
100
80
86
57
40
35
31
68
14
15
21
0
8
13
0d
28
39
65
61
19
6
a Concentration of the catalyst (1a) before addition of the substrate: 0.10
b
M in nitromethane. The given abundances are relative to the major products.
c
Other minor products cumulatively did not exceed 5% of the total. Solvent:
d
CH2Cl2 containing 10% MeNO2. Detectable in traces (<0.4%).
than expected for a Pt-C bond trans to nitrogen,13 and
conversely, the Pt-N bond distance (2.098(9) Å) is slightly
shorter than expected for a Pt-N bond trans to carbon.13 This
may be due to the rigidity of the coordinated PNP and to its
rather invariable structural features when changing the metal
or the other ligand.5,14 The CH2-CH2 chain derived from the
attack to the coordinated ethene molecule is in a trans
conformation, as apparent from the value of the torsion angle
Pt-C1-C2-C3 ) 179.2(8)°. The trimethoxyphenyl group is
all planar and roughly parallel to the coordination plane (angle
between mean planes is 17.1(1)°), being stabilized in this
conformation by a face-to-face van der Waals interaction with
the pyridine ring of an adjacent molecule (distance between
centroids is 3.825(3) Å).
Reactions of [Pt(PNP)(C2H4)](SbF6)2 (1a) with 1,3-
Dimethoxybenzene. Although the disubstituted benzene ring
of 1,3-dimethoxybenzene is in principle less activated than that
of 1,3,5-trimethoxybenzene, the former proved to be more
reactive in the coupling reaction. We tested the reaction under
various catalytic conditions, and the results are reported in Table
2, the alkylation products being listed in Chart 1.
cleavage to be the rate-determining step of the catalytic reaction
as in the case of 1,3,5-trimethoxybenzene reported above.
However, the reaction of the σ-alkyl derivatives 3a-5a with
gaseous HCl in CH2Cl2 solution gave the corresponding
alkylated arenes 3-5, while in the case of 2a only the reversal
of the coupling reaction (eq 1) was observed. The different
behavior may be explained by the higher stability of the transient
arenium ion for 2a compared to 3a-5a, which directs the proton
attack on the aromatic ring rather than on the Pt-C σ-bond.
This also explains the lower reactivity of 1,3,5-trimethoxyben-
zene in the catalytic reaction, since the higher stability of the
arenium ion is expected to slow down the rate-determining Pt-C
σ-bond cleavage.
Reactivity of [Pt(PNP)(C2H4)](SbF6)2 (1a) with Other
Substrates. Moving to a less activated aromatic ring, we treated
1a in MeNO2 solution with a 10-fold molar excess of 3-
methylanisole under 1 atm pressure of ethene at room temper-
ature. A sluggish reaction was observed, and 2 equiv of a
mixture of the alkylation products 6 and 7 was formed after 96
h at room temperature. However by performing the reaction at
70 °C with 30 and 50 equiv of 3-methylanisole under a 7 bar
pressure of ethene, a complete conversion of the substrate to
the dialkylated product 8 was surprisingly obtained (Table 3,
entries 1 and 2), with only tiny amounts of the monoalkylated
products 6 and 7. However, when we performed the base-
assisted stoichiometric reaction by adding 20 µL of water to a
NMR sample of 1a and 3-methylanisole (2 equiv) in CD3NO2,
the corresponding σ-alkyl derivatives 6a and 7a were not formed
immediately, but with an approximate half-life of the starting
complex of 50 min, a complete conversion being observed in
ca. 3 h. As expected, treating the mixture of the σ-alkyl
derivatives 6a and 7a with gaseous HCl in CH2Cl2 caused the
immediate cleavage of the Pt-C σ-bond, giving the correspond-
ing alkylated arenes 6 and 7.
As in the case of 1,3,5-trimethoxybenzene, the addition of
20 µL of water to a NMR sample of 1a and 1,3-dimethoxy-
benzene in 9:1 CD2Cl2/CD3NO2 caused the immediate conver-
sion of the complex to a mixture of the σ-alkyl derivatives 3a-
5a (Chart 2).15 The slow formation of the cleavage products
3-5 under catalytic conditions, compared to the rapid formation
of 3a-5a under the assistance of a base (H2O), suggested the
addition step to be fast and reversible16 and the Pt-C bond
(13) (a) Zhao, S-B.; Wu, G.; Wang, S. Organometallics 2006, 25, 5979.
(b) Wile, B. M.; Burford, R. J.; McDonald, R.; Ferguson, M. J.; Stradiotto,
M. Organometallics 2006, 25, 1028. (c) Ganis, P.; Orabona, I.; Ruffo, F.;
Vitagliano, A. Organometallics 1998, 17, 2646.
(14) (a) Hahn, C.; Vitagliano, A.; Giordano, F.; Taube, R. Organome-
tallics 1998, 17, 2060. (b) Steffey, B. D.; Miedaner, A.; Maciejewski-Farmer,
M. L.; Bernatis, P. R.; Herring, A. M.; Allured, V. S.; Carperos, V.; DuBois,
D. L. Organometallics 1994, 13, 4844. (c) Barloy, L.; Ramdeehul, S.;
Osborn, J. A.; Carlotti, C.; Taulelle, F.; De Cian, A.; Fischer, J. Eur. J.
Inorg. Chem. 2000, 2523. (d) Hahn, C.; Sieler, J.; Taube, R. Chem. Ber.
1997, 130, 393.
(15) To help their identification by 1H and 13C NMR, 3a-5a were
isolated (without separation) from two larger scale reactions, run in the
presence of different amounts of the aromatic substrate. Using a slight excess
of 1,3-dimethoxybenzene 3a, 4a, and 5a were obtained in 47%, 15%, and
38% molar abundances, respectively. A 10-fold excess of the aromatic
substrate favored the monosubstituted products, yielding 3a, 4a, and 5a in
85%, 10%, and 5% molar abundances, respectively.
(16) The reversibility of the addition step was proven by dissolving a
mixture of 3a, 4a, and 5a (47%, 15%, and 38%, respectively) in CD2Cl2,
in the presence of 4 equiv of 1,3-dimethoxybenzene and 0.5 equiv of
etherated HBF4. The solution equilibrated within a few minutes, giving a
mixture of 90% 3a, 10% 4a, and only traces of 5a.
The effect of further decreasing the aromatic ring activation
was probed by using anisole. In this case no reaction was
obtained at room temperature, and even the base-assisted
addition was sluggish and did not produce clean σ-alkyl

5220 Organometallics, Vol. 26, No. 21, 2007
Chart 2. Alkyl Derivatives Resulting from the Base-Assisted Stoichiometric Reactions
Cucciolito et al.
Table 3. Yield and Product Distribution in the Reactions of
Ethene and Propene with Different Substratesa
At 70 °C and using a larger excess (30 equiv) of 1,3-
dimethoxybenzene under a 2 bar pressure of propene, a 40%
conversion of the substrate to a mixture of the alkylated products
11, 12, and 13 (in 70%, 15% and 15% molar abundances, see
Table 3, entry 5) was observed. Quite interesting was the result
of the base-assisted reactions with 1,3,5-trimethoxybenzene and
1,3-dimethoxybenzene, which were performed by adding 2.5
equiv of the aromatic substrate, 5 equiv of propene, and 10 µL
of water to a solution of 10a in CD3NO2 and monitored by 1H
NMR. In contrast to the case of the ethene complex 1a, the
reactions were not immediate. The reaction with 1,3,5-tri-
methoxybenzene took place with an approximate half-life of
10 min, but reached an equilibrium within 30 min, giving a
mixture of 40% starting complex 10a, 35% 14a (anti-Mark-
ovnikov addition product), and 25% 15a (Markovnikov addition
product). The equilibrium was completely shifted to the σ-alkyl
products by further addition of water. The reaction with 1,3-
dimethoxybenzene took place much more slowly, with an
approximate half-life of 3 h, but finally producing a 90:10
mixture of the Markovnikov products 11a and 13a, with a tiny
amount of the anti-Markovnikov monoalkylated product and
no detectable amount of the starting complex left at equilibrium.
catalyst,
olefin
substrate,b % reacted
no. equiv substrate
relative products
entry
distributionc (mol %)
1
2
3
4
5
6
1a, ethene
1a, ethene
1a, ethene
1a, ethene
man, 30
man, 50
an, 30
100
100
100
100
40
8, 100
8, 100
9, 100
an, 50
9, 100
10a, propened dmb, 30
11, 70 12, 15 13, 15
1b, ethene
dmb, 30
35
3, 85
4, 10
5, 5
b
a Solvent: nitromethane; T ) 70 °C; p ) 7 bar. dmb ) 1,3-
c
dimethoxybenzene; man ) 3-methylanisole; an ) anisole. The given
abundances are relative to the three major products. Other minor products
cumulatively did not exceed 5% of the total. d p ) 2 bar.
derivatives. By contrast, running the reaction at 70 °C under a
7 bar pressure of ethene, a complete conversion of the substrate
was observed, leading almost exclusively to the dialkylated
product 9 (Table 3, entries 3 and 4).
The above results show that, by reducing the activation of
the aromatic ring, the rate of the addition step is correspondingly
reduced (and so is the equilibrium constant for the formation
of the arenium ion), while the rate of the Pt-C σ-bond cleavage
is increased due to the increased acidity of the arenium ion. In
the case of 3-methylanisole and anisole the rates of the two
steps are probably comparable and a productivity even larger
than in the case of 1,3-dimethoxybenzene was observed when
running the catalytic reaction at 70 °C, as shown by the complete
conversion of the substrate to the dialkylated product (entries 2
and 4 in Table 3 versus entry 5 in Table 2).
Reactivity of [Pt(PNP)(CH2dCHMe)](SbF6)2 (10a). Pro-
pene proved to be less reactive than ethene in the catalytic
coupling reactions. At room temperature and using a moderate
excess of substrate, no reaction was observed with 1,3,5-
trimethoxybenzene and a very sluggish reaction took place with
1,3-dimethoxybenzene (less than 1 equiv reacted after 4 days).
The above results clarify some further details of the general
picture given in Scheme 2. If we just consider the stoichiometric
addition to give the σ-alkyl complex, this consists of the rate-
determining formation of an arenium ion (step i in Scheme 2),
followed by a fast proton transfer (step ii in Scheme 2) from
the arenium ion to an external base (H2O in our case). Both are
equilibrium reactions, and the overall equilibrium constant K
is given by K ) KiKii, while the overall reaction rate is
determined by the forward kinetic constant ki of the first step.
The rate of the first step appears to be controlled by the stability
of the arenium ion, with the rate constant ki and the equilibrium
constant Ki increasing with the number of electron-releasing
methoxy substituents. The equilibrium constant Kii of the proton-

Catalytic Hydroarylation of Olefins
Organometallics, Vol. 26, No. 21, 2007 5221
transfer step is also controlled by the stability of the arenium
ion, but in the reverse way, an increasing number of electron-
releasing methoxy substituents decreasing the acidity of the
arenium ion and thus disfavoring the proton transfer. The above
experiments show that upon going from 1,3-dimethoxybenzene
to 1,3,5-trimethoxybenzene, while the kinetic constant increases,
the overall equilibrium constant K decreases, which can quite
reasonably be ascribed to the steric hindrance of the carbon chain
placed between two ortho substituents in 14a and 15a. This
steric hindrance also accounts for the 60% anti-Markovnikov
addition in the case of 1,3,5-trimethoxybenzene versus more
than 95% Markovnikov addition in the case of 1,3-dimethoxy-
benzene (11a and 13a).
the relative abundances of the four species at equilibrium (1a,
1b, 2a, 2b) were determined by integration of appropriate signals
in the equilibrium mixture, leading to an estimate for the ratio
of the addition constants Ki(Pt)/Ki(Pd) of about 8. Since this value
appears to be not large enough to be the only source of the
markedly larger reactivity of the platinum species in the catalytic
reactions, it can be inferred that also the rate constant of the
protolytic cleavage is higher for the platinum σ-alkyl complexes
than for the corresponding palladium species. This is not
surprising, if a protonolysis mechanism is considered in which
the proton either oxidatively adds to the metal or simultaneously
interacts with the metal and the carbon atoms in a three-center
transition state.8 In both cases either a full or a partial oxidative
addition to the metal is involved, which is expected to be easier
for platinum than for palladium.
About the catalytic coupling reaction, it is interesting to note
that the amount of the anti-Markovnikov product 12 produced
was substantially larger than that observed in the stoichiometric
addition. Most likely, the σ-alkylarenium ion containing a
branched alkyl chain bound to the metal is less stable and so it
does give a small amount of product in the stoichiometric
reaction, but for the very same reason it is more reactive to the
protolytic cleavage, resulting in the observed product distribution
(Table 3, entry 5). The lower reactivity of propene compared
to ethene can be ascribed to a lower concentration of the arenium
ion (under similar conditions), due to a lower value of the
addition equilibrium constant Ki. This is consistent with the
results obtained in the case of the nucleophilic attack of amines,
where the addition constant was found to be 1-2 orders of
magnitude smaller for propene than for ethene.4,5 To directly
confirm this hypothesis, we did a competitive experiment, in
which a NMR sample containing equimolar amounts (10 µmol)
of the ethene complex 1a and of the propene complex 10a in
the presence of a slight excess of 1,3,5-trimethoxybenzene in
CD3NO2 was treated with 3 µL of water. Under these conditions
75% of the ethene complex was converted to the σ-alkyl
derivative 2a, while less than 1% of the propene complex gave
the corresponding species 14a and 15a, indicating that the
addition to the propene complex is indeed thermodynamically
less favored by at least 2 orders of magnitude of Ki.
Conclusions
The results reported in this paper show that the coordination
to dicationic Pt2+ and Pd2+ species enhances the electrophilicity
of an olefin to the point of promoting the attack to aromatic
rings activated by electron-donating substituents such as meth-
oxy groups. The reaction can take place catalytically, since the
proton released by the intermediate arenium ion is able to cleave
the M-C σ-bond. The consistent qualitative picture emerging
from the results shows the influence of the ring substituents on
the rates of the two crucial steps of the catalytic reaction, i.e.,
the attack of the coordinated olefin to the aromatic ring (step i
in Scheme 2) and the successive (most likely intramolecular)
protolytic cleavage of the M-C σ-bond (step iii in Scheme 2).
Decreasing the activation of the aromatic ring decreases the rate
of the attack but increases the rate of the protolytic cleavage,
so that in the delicate interplay between the two effects an
aromatic ring that is less activated to the stoichiometric coupling
can become more reactive in the catalytic reaction, as is the
case of anisole and 3-methylanisole versus 1,3-dimethoxyben-
zene and 1,3,5-trimethoxybenzene. Looking at the influence of
the olefin and the metal, it also appears that changing the olefin
from ethene to propene considerably disfavors the attack,
without having much effect on the rate of the protolytic cleavage,
while switching from Pt2+ to Pd2+ disfavors the attack, but also
slows the rate of the protolytic cleavage.
Reactivity of [Pd(PNP)(C2H4)](SbF6)2 (1b). The palladium
complex proved to be less reactive in the catalytic reaction
compared to its platinum analogue 1a. At room temperature,
no reaction at all was observed with 1,3,5-trimethoxybenzene
and only traces of the coupling product 3 were observed with
1,3-dimethoxybenzene after 48 h. A modest activity was
observed at 70 °C, where a 35% conversion to a mixture of 3,
4, and 5 (85%, 10%, and 5% molar abundances, respectively)
was observed in 24 h using 30 equiv of 1,3-dimethoxybenzene
under a 7 bar pressure of ethene (Table 3, entry 6). These results
suggest that also in the palladium case the protolytic cleavage
of the M-C σ-bond is the rate-determining step of the catalytic
reaction, as discussed in the case of the platinum complex.
Indeed, the base-assisted addition of both 1,3,5-trimethoxyben-
zene and 1,3-dimethoxybenzene, performed as described for the
platinum complex 1a, within a couple of minutes gave the
σ-alkyl derivatives 2b and 3b-4b, respectively. To assess
whether the lower catalytic activity of the palladium complex
compared to the platinum complex is due to a lower value of
the addition equilibrium constant Ki or to a higher barrier to
the protolytic cleavage, we did a competitive experiment similar
to the one described above. A NMR sample containing
equimolar amounts (10 µmol) of the platinum complex 1a and
of the palladium complex 1b in the presence of a slight excess
of 1,3,5-trimethoxybenzene in CD3NO2 was treated with 4 µL
of water. The solution equilibrated within a few minutes, and
As a final remark, we note that apart from the potential
synthetic uses of the reaction, a major conceptual interest lies
in a catalytic process in which the single steps can be performed
at a stoichiometric level and the trends controlling them can be
satisfactorily rationalized.
Experimental Section
General Procedures. CD2Cl2, CD3NO2, and MeNO2 (free from
nitriles) were dried with 4 Å molecular sieves. The aryl substrates
were obtained by Aldrich and were used without further purification.
The NMR spectra were recorded on Varian VXR 200, Varian
Gemini 300, and Bruker WH 400 instruments. The 1H NMR shifts
were referenced to the resonance of the residual protons of the
solvents; the 13C NMR shifts, to the solvent resonance (δ ) 53.8,
CD2Cl2; δ ) 62.8, CD3NO2). Abbreviations used in NMR data: s,
singlet; d, doublet; t, triplet; ps t, pseudo triplet; m, multiplet; br,
broad.
Syntheses. The complexes [Pt(PNP)(CH2dCHR)](SbF6)2 and
[Pd(PNP)(CH2dCH2)](SbF6)2 were prepared according to the
procedures described in the literature.4,5
Preparation of σ-Derivatives. General Procedure. To a
solution of the alkene complex (0.04 mmol) in 2 mL of CH2Cl2
were added 1.5 equiv of aryl compound and 20 µL of H2O. The

5222 Organometallics, Vol. 26, No. 21, 2007
Cucciolito et al.
mixture was stirred for 15 min (2 h in the case of 3-methylanisole
and 4 h in the case of the propene complex with all the aryl
derivatives). The solution was dried over Na2SO4, filtered, and
concentrated in Vacuo. The product was precipitated by dropwise
addition of diethyl ether, filtered off, and dried under vacuum.
Except for the case of 1,3,5-trimethoxybenzene a mixture of alkyl
derivatives was obtained. Since initial separation attempts were
unsuccessful, the complexes were characterized directly in their
6a (in a mixture with 7a). Yield: 95%; white solid. Anal. Calcd
for C41H40F6NOP2PtSb: C, 46.66; H, 3.82; N, 1.33. Found: C,
1
47.00; H, 3.67; N, 1.32. H NMR (300 MHz, CD2Cl2): δ 1.54
(s, 3 H, Me-Ar), 1.90 (m, 2 H, PtCH2), 2.34 (m, CH2Ar), 3.62
(s, 3 H, OMe), 4.42 (ps t, 4 H, PCH2), 6.26 (d, 1 H, Ar), 6.39 (dd,
1 H, Ar), 6.41 (d, 1 H, Ar), 7.50-7.90 (m, PPh, py), 8.00 (t, 1 H,
py). 13C NMR (75 MHz, CD2Cl2): δ 2.70 (PtCH2, JPt ) 637 Hz),
1
19.0 (MeAr), 38.0 (CH2Ar), 46.6 (ps t, JP ) 31 Hz, PCH2), 55.4
1
mixture by H and 13C NMR. In addition, the assigned structures
(OMe), 111.1 (C-3, Ar), 115.6 (C-5, Ar), 123.1 (py-3,5), 127.3 (ps
1
were confirmed by reductive and/or protolytic degradation of the
complex mixture and successive identification of the resulting
organic products.
t, JP ) 50 Hz, PPhj), 128.9 (C-1, Ar), 129.3 (C-6, Ar), 130.0
(PPhm), 132.7 (PPhp), 133.6 (PPho), 136.4 (C-2, Ar), 140.2 (py-4),
2
157.6 (C-4, Ar), 159.6 (ps t, JPt ) 33 Hz, py-2,6).
7a (in a mixture with 6a). 1H NMR (300 MHz, CD2Cl2): δ 1.98
(m, 2 H, PtCH2), 2.18 (s, 3 H, Me-Ar), 2.34 (m, CH2Ar overlapped
by signals from 6a), 3.42 (s, 3 H, OMe), 4.40 (ps t, 4 H, PCH2),
6.22 (d, 1 H, Ar), 6.44 (d, 1 H, Ar), 6.47 (s, 1 H, Ar), 7.50-7.90
(m, PPh, py), 8.02 (t, 1 H, py). 13C NMR (75 MHz, CD2Cl2): δ
2.3 (PtCH2), 21.4 (MeAr), 35.2 (CH2Ar), 46.4 (ps t, 1JP ) 35 Hz,
PCH2), 55.2 (OMe), 111.6 (C-3, Ar), 121.0 (C-5, Ar), 123.1 (py-
2a. Yield: 97%; whitish solid. Anal. Calcd for C42H42F6NO3P2-
PtSb: C, 45.80; H, 3.84; N, 1.27. Found: C, 45.73; H 3.89; N,
1.26. 1H NMR (300 MHz, CD2Cl2): δ 2.02 (m, 2 H, PtCH2, JPt
)
78 Hz), 2.45 (m, 2 H, CH2Ar), 3.36 (s, 6 H, OMe), 3.67 (s, 3 H,
OMe), 4.37 (ps t, 4 H, PCH2), 5.93 (s, 2 H, Ar), 7.50-7.90 (m, 22
H, PPh, py), 8.02 (t, 1 H, py). 13C NMR (75 MHz, CD2Cl2): δ 1.1
1
(1JPt ) 585 Hz, PtCH2), 27.9 (CH2Ar), 46.9 (ps t, JP ) 30 Hz,
1
PCH2), 55.5 (OMe), 90.7 (C-3 and C-5, Ar), 114.7 (C-1, Ar), 123.0
3,5), 127.7 (ps t, JP ) 50 Hz, PPhj), 130.0 (PPhm), 131.3 (C-6,
Ar), 132.7 (PPhp), 133.6 (PPho), 140.2 (py-4), 156.9 (C-2, Ar), 159.6
1
(py-3,5), 128.0 (ps t, JP ) 54 Hz, PPhj), 130.0 (PPhm), 132.5
(PPhp), 133.5 (PPho), 140.2 (py-4), 158.3 (C-2 and C-6, Ar), 159.2
(py-2,6 overlapped by signals from 6a).
2
1
(C-4, Ar), 159.7 (ps t, JPt ) 35 Hz, py-2,6).
11a (in a mixture with 13a). H NMR (300 MHz, CD2Cl2): δ
2b. Yield: 94%; white solid. Anal. Calcd for C42H42F6NO3P2-
PdSb: C, 49.81; H, 4.18; N, 1.38. Found: C, 49.75; H, 4.27; N,
1.36. 1H NMR (300 MHz, CD2Cl2): δ 2.14 (m, 2 H, PdCH2), 2.64
(m, 2 H, CH2Ar), 3.40 (s, 6 H, OMe), 3.70 (s, 3 H, OMe), 4.36 (ps
t, 4 H, PCH2), 5.96 (s, 2 H, Ar), 7.40-7.80 (m, 22 H, PPh, py),
7.93 (ps t, 1 H, py). 13C NMR (75 MHz, CD2Cl2): δ 17.2 (PdCH2),
0.60 (d, 3 H, Me), 1.85 (m, 1 H, Pt-CHH, JPt ) 72 Hz), 2.46 (m,
1 H, Pt-CHH, JPt ) 78 Hz), 3.02 (m, 1 H, CH-Ar), 3.30 (s, 3 H,
OMe), 3.68 (s, 3 H, OMe), 4.45 (m, 4 H, PCH2), 6.19 (d, 1 H, Ar),
6.22 (s, 1 H, Ar), 6.53(d, 1 H, Ar), 7.45-7.90 (m, PPh, py), 8.02
(t, 1 H, py). 13C NMR (75 MHz, CD2Cl2): δ 11.6 (JPt ) 646 Hz,
PtCH2), 24.7 (MeCH), 37.8 (CHMe), 46.8 (ps t, 1JP ) 34 Hz,
PCH2), 55.0 (OMe), 55.5 (OMe), 98.3 (C-3, Ar), 104.2 (C-5, Ar),
1
26.9 (CH2Ar), 45.5 (ps t, JP ) 26 Hz, PCH2), 55.6 (OMe), 90.7
(C-3 and C-5, Ar), 112.8 (C-1, Ar), 123.0 (py-3,5), 128.9 (ps t, 1JP
) 45 Hz, PPhj), 130.0 (PPhm), 132.1 (PPhp), 133.3 (ps t, PPho),
140.8 (py-4), 158.3 (C-2, C-4, and C-6, Ar), 159.4 (py-2,6).
1
123.1 (py-3,5), 126.2 (C-6, Ar), 127.5 (ps t, JP ) 57 Hz, PPhj),
1
128.5 (ps t, JP ) 55 Hz, PPhj), 129.7 (PPhm), 131.5 (C-1, Ar),
132.3 (PPhp), 132.5 (PPhp), 133.2 (PPho), 133.6 (PPho), 140.2 (py-
2
3a (in a mixture with 4a and 5a). 1H NMR (300 MHz, CD2Cl2):
δ 1.98 (m, 2 H, PtCH2), 2.34 (m, 2 H, CH2Ar), 3.41 (s, 3 H, OMe),
3.73 (s, 3 H, OMe), 4.40 (m, PCH2), 6.16 (dd, 1 H, Ar), 6.22 (s, 1
H, Ar), 6.24 (d, 1 H, Ar), 7.44-8.06 (m, PPh, py). 13C NMR (50
MHz, CD2Cl2): δ 2.4 (PtCH2), 35.0 (CH2Ar), 46.4 (ps t, 1JP ) 35
Hz, PCH2), 55.5 (OMe), 98.3 (C-3, Ar), 104.2 (C-5, Ar), 123.0
4), 157.1 (C-2, Ar), 158.7 (C-4, Ar), 159.6 (ps t, JPt ) 35 Hz,
py-2,6).
13a (two diastereomers in equal abundance (in a mixture with
11a)). 1H NMR (300 MHz, CD2Cl2): δ 0.42 (d, Me), 0.48 (d, Me),
2.85 (m, CH), 3.21 (s, OMe), 3.34 (s, OMe), 5.99 (s, Ar), 6.01 (s,
Ar), 6.02 (s, Ar), 6.03 (s, Ar), 7.45-7.90 (m, PPh, py).
1
(py-3,5), 127.0 (C-1, Ar), 127.8 (ps t, JP ) 54 Hz, PPhj), 129.5
14a (in a mixture with 15a). Yield: 92%; white solid. Anal.
Calcd for C43H44F6NO3P2PtSb: C, 46.30; H, 3.98; N, 1.26.
Found: C, 46.26; H, 4.05; N, 1.25. 1H NMR (300 MHz, CD2Cl2):
δ 0.87 (d, 3 H, Me, JPt ) 53 Hz), 2.27 (t, 1 H, CHH-Ar), 2.40
(m, 1 H, Pt-CH), 2.82 (dd, 1H, CHH-Ar), 3.30 (s, 6 H, OMe),
3.66 (s, 3 H, OMe), 4.20-4.55 (m, PCH2), 5.88 (s, 2H, Ar), 7.45-
8.05 (m, PPh, py). 13C (50 MHz, CD2Cl2): δ 22.3 (PtCH), 24.5
(Me), 33.6 (CH2Ar), 46.6 (ps t, 1JP ) 36 Hz, PCH2), 55.3 (OMe),
90.4 (C-3 and C-5, Ar), 111.5 (C-1, Ar), 123.2 (py-3,5), 128.1 (ps
(C-6, Ar), 130.0 (PPhm), 132.5 (PPhp), 133.5 (PPho), 140.3 (py-4),
2
158.0 (C-2, Ar), 159.0 (C-4, Ar), 159.5 (ps t, JPt ) 38 Hz, py-
2,6).
4a (in a mixture with 3a and 5a). 1H NMR (300 MHz, CD2Cl2):
δ 2.18 (m, PtCH2 overlapped by signals from 5a), 2.52 (m, 2 H,
CH2Ar), 3.38 (s, 6 H, OMe), 4.40 (m, PCH2), 6.34 (d, 2 H, Ar),
6.96 (t, 1 H, Ar), 7.44-8.06 (m, PPh, py).
5a (in a mixture with 3a and 4a). 1H NMR (300 MHz, CD2Cl2):
δ 1.86 (m, 4 H, PtCH2), 2.18 (m, CH2Ar), 3.36 (s, 6 H, OMe),
4.40 (m, PCH2), 5.64 (s, 1 H, Ar), 6.06 (s, 1 H, Ar), 7.44-8.06
(m, PPh, py).
1
t, JP ) 53 Hz, PPhj), 129.7 (PPhm), 132.6 (PPhp), 133.2 (PPho),
2
140.3 (py-4), 158.8 (ps t, JPt ) 35 Hz, py-2,6), 159.0 (C-2 and
C-4, Ar), 159.7 (C-6, Ar).
15a (in mixture with 14a). H NMR (300 MHz, CD2Cl2): δ
1
3b (in a mixture with 4b) Yield: 94%; white solid. Anal. Calcd
0.72 (d, 3 H, Me), 2.42 (m, 1 H, Pt-CHH), 2.55 (m, 1 H, Pt-
CHH), 3.17 (s, 6 H, OMe), 3.40 (m, 1 H, CH-Ar), 3.68 (s, 3 H,
OMe), 4.20-4.55 (m, PCH2), 5.89 (s, 2 H, Ar), 7.45-8.05 (m,
PPh, py). 13C NMR (50 MHz, CD2Cl2): δ 1.1 PtCH2), 13.4 (Me),
for C41H40F6NO2P2PdSb: C, 50.11; H 4.10; N, 1.43. Found: C,
49.89; H, 4.22; N, 1.41. H NMR (300 MHz, CD2Cl2): δ 2.10
1
(m, 2 H, PdCH2), 2.50 (m, 2 H, CH2Ar), 3.45 (s, 3 H, OMe), 3.69
(s, 3 H, OMe), 4.41 (ps t, 4 H, PCH2), 6.20 (dd, 1 H, Ar), 6.26
(d, 1 H, Ar), 6.33 (d, 1 H, Ar), 7.50-7.80 (m, PPh, py), 7.91 (t, 1
H, py). 13C (75 MHz, CD2Cl2): δ 17.7 (PdCH2), 33.5 (CH2Ar),
45.0 (ps t, 1JP ) 28 Hz, PCH2), 55.5 (OMe), 98.7 (C-3, Ar), 104.3
(C-5, Ar), 123.3 (py-3,5 PPhj), 125.1 (C-1, Ar), 128.7 (ps t, 1JP )
43 Hz, PPhj), 129.4 (C-6, Ar), 130.0 (PPhm), 132.0 (PPhp), 133.4
(PPho), 140.9 (py-4), 158.0 (C-2, Ar), 158.3 (py-2,6), 159.4
(C-4, Ar).
4b (in a mixture with 3b). 1H NMR (300 MHz, CD2Cl2): δ 2.36
(m, 2 H, PdCH2), 2.71 (m, 2 H, CH2Ar), 3.41 (s, 6 H, OMe), 4.38
(ps t, 4 H, PCH2), 6.37 (d, 2 H, Ar), 6.99 (t, 1 H, Ar), 7.50-8.00
(m, PPh, py).
1
37.2 (CHAr), 47.0 (ps t, JP ) 36 Hz, PCH2), 55.5 (OMe), 90.4
(C-3 and C-5, Ar), 111.5 (C-1, Ar), 123.2 (py-3,5), 127.6 (ps t, 1JP
) 57 Hz, PPhj), 130.0 (PPhm), 132.2 (PPhp), 134.4 (PPho), 140.3
(py-4), 158.8 (ps t, 2JPt ) 35 Hz, py-2,6), 159.0 (C-2 and C-4, Ar),
159.7 (C-6, Ar).
Catalytic Reactions. The catalytic reactions were run in a small
glass autoclave under the conditions reported in Tables 2 and 3.
The appropriate metal complex (0.03 mmol) was dissolved in 0.3
mL of anhydrous MeNO2 (free from nitriles), and 20-75 equiv of
the appropriate aryl compound was added (see Tables 2 and 3).
The solution was stirred under ethene or propene for 24 h and then

Catalytic Hydroarylation of Olefins
Organometallics, Vol. 26, No. 21, 2007 5223
evaporated to dryness, and the residue was extracted with diethyl
ether. The solution was separated and evaporated to dryness, and
the residue was analyzed by H NMR.
idealized positions and refined by a riding model with thermal
parameters Uiso set to the Ueq of the carrier atoms. The light atoms
in the molecule are affected by rather large thermal motion since
it was not possible to collect data at low temperature. This accounts
for low bond precision on some C-C bonds and for an average
C-C ring (1.37 Å) distance smaller than standard. The high value
of Rint, greater than 0.10, may be ascribed to the not very high
quality of crystals that were obtained only with great difficulty.
One peak of residual electronic density larger than 1.0 e Å-3 was
found near the heavy atom, so it makes no chemical sense. For the
graphical representation, ORTEP-III for Windows was used as
implemented in the program system WinGX.20
All crystallographic data have been deposited with the Cambridge
Crystallographic Data Center (CCDC). The deposition number is
CCDC 653493. These data can be obtained free of charge at
www.ccdc.cam.ac.uk/conts/retrieving.html or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2
1EZ,UK[fax: (internat.)+44-1223/336-033;e-mail: deposit@ccdc.cam.ac.uk].
1
Reductive Degradation with NaBH4. The reduction was
performed on all the σ-alkyl derivatives. The mixture of complexes
resulting from the base-assisted addition reaction (30-50 mg) was
dissolved in 1.5 mL of CH2Cl2/MeOH (5:2), and an excess of solid
NaBH4 was added. The mixture was stirred for 12 h and then treated
with 1.0 mL of a NH4Cl-saturated aqueous solution. The organic
phase was separated and evaporated to dryness. The residue was
extracted with diethyl ether, the ether extract was evaporated to
dryness, and the residue was analyzed by 1H NMR for identifying
the organic products.
Reaction with HCl. Protolytic degradation was performed on
all the σ-alkyl derivatives. The complexes (10 mg) were dissolved
in 0.6 mL of CD2Cl2, and gaseous HCl was bubbled through. The
solution containing M(PNP)Cl2 and organic products was character-
1
ized by H NMR spectroscopy.
X-ray Analysis. Crystal data and collection details for 2a-BF4
are given in the Supporting Information. The most relevant bond
distances and angles are reported in Table 1. Data collection was
performed at 298 K on a Bruker-Nonius KappaCCD single-crystal
diffractometer with monochromated Mo KR (λ ) 0.71073 Å)
radiation. Data were collected and integrated using the Bruker
Nonius COLLECT software package,17 and a semiempirical absorp-
tion correction was applied (multiscan SADABS18). The structure
was solved by direct methods and refined by the full matrix least-
squares method on F2 against all independent measured reflections
(SHELX-97 package19). All non-hydrogen atoms were refined with
anisotropic displacement parameters. H atoms were placed in
Acknowledgment. This work was supported in part by
MIUR (PRIN Grant No. 2004-030719). We thank the CIMCF,
University of Napoli, for access to the NMR facilities and Miss
Cinzia Barbato for experimental assistance.
Supporting Information Available: Crystallographic informa-
tion file (CIF) for compound 2a-BF4. This material is available
free of charge via the Internet at http://pubs.acs.org.
OM700692S
(19) Sheldrick, G. M. SHELX97 [Includes SHELXS97, SHELXL97],
Programs for Crystal Structure Analysis (Release 97-2); Institu¨t fu¨r
Anorganische Chemie der Universita¨t: Go¨ttingen, Germany, 1998.
(20) Farrugia, L. J. WinGX, Version 1.70.00, An Integrated System of
Windows Programs for the Solution, Refinement and Analysis of Single-
crystal X-Ray Diffraction Data. J. Appl. Crystallogr. 1999, 32, 837-838.
(17) Collect, Data collection software; Nonius BV: Amsterdam, 1997-
2000.
(18) SADABS, area detector scaling and absorbption correction; Bruker
AXS, 2002