Influence of pyridine-imidazoline ligands on the reactivity of palladium-methyl complexes with carbon monoxide

Article abstract of DOI:10.1021/om020568b

The influence of pyridine-imidazoline ligands on the reactivity of palladium-methyl complexes with carbon monoxide was discussed. For the complexes with electron-donating substituents, the intermediates of the insertion reaction were found to be detected,

Full text of DOI:10.1021/om020568b

5820
Organometallics 2002, 21, 5820-5829
In flu en ce of P yr id in e-Im id a zolin e Liga n d s on th e
Rea ctivity of P a lla d iu m -Meth yl Com p lexes w ith Ca r bon
Mon oxid e
Amaia Bastero, Aurora Ruiz, and Carmen Claver*,†
Departament de Quı´mica Fı´sica i Inorga`nica, Universitat Rovira i Virgili, Pl. Imperial
Ta`rraco I, 43005 Tarragona, Spain
Barbara Milani* and Ennio Zangrando
Dipartimento di Scienze Chimiche, Universita` degli Studi di Trieste, Via Licio Giorgieri 1,
34127 Trieste, Italy
Received J uly 16, 2002
-
Two series of monocationic Pd-methyl complexes [Pd(Me)(NCMe)(N-N′)][X] (X ) PF6
,
BAr′4-) were synthesized, where N-N′ are pyridine-imidazoline ligands of C1 symmetry,
electronically modified with various R substituents at the aminic N atom of the imidazoline
ring. These substituents make it possible to vary the electronic properties of the nitrogen-
donor atoms. The crystal structures of two neutral palladium precursors [Pd(Me)2-nCln(N-N′)]
(n ) 1, 2) with different R substituents show different Pd-N coordination distances and
geometrical distortions in the imidazoline ring. The characterization in solution of the neutral
derivatives evidences the presence of the complex with the Pd-Me group cis to the imidazoline
ring (cis isomer). For the cationic complexes, the number and the kind of stereoisomers
present in solution depend on the nature of both the ligand and the anion. One isomer is
always observed when the anion is BAr′4-: the cis when electron-donating substituents are
present on the imidazoline ring and the trans when electron-withdrawing groups are present.
-
Both cis and trans isomers were found for the latter kind of ligands, when PF6 was the
anion. The reactivity of the cationic complexes with carbon monoxide was studied in solution
by multinuclear NMR spectroscopy, and it was shown that the Pd-acyl-carbonyl species was
formed as the final product. For the complexes with electron-donating substituents, the
intermediates of the insertion reaction were detected, namely, Pd-methyl-carbonyl and Pd-
acyl-acetonitrile species. Moreover, only one stereoisomer was seen to form: the one with
the Pd-acyl group trans to the imidazoline ring. For the other ligands, the final product is
a mixture of cis and trans stereoisomers for both anions, and their distribution depends on
the type of ligand. The cationic complexes with BAr′4- behave as catalysts in the CO/4-tert-
butylstyrene copolymerization and yield polyketones whose stereoregularity depends on the
nature of the ligand. The stereocontrol in the copolymerization process is tentatively explained
on the basis of the results of this mechanistic investigation.
In tr od u ction
Pd-alkyl to CO and of Pd-acyl to olefin.3 While the
reactions responsible for the growth of the polymeric
chain are common to all catalytic systems, the initiation
and termination steps depend on the nature of both the
olefin and the palladium catalyst precursor. Most
mechanistic investigations have been carried out in
solution. Recently, however, there has been a study in
the solid state.4
The insertion of unsaturated molecules into metal-
carbon bonds is a fundamental step for C-C bond
formation reactions catalyzed by organometallic com-
pounds.1 In the last fifteen years, the carbon monoxide/
olefin copolymerization reaction has attracted much
interest from both the academic and industrial scientific
community. This reaction is homogeneously catalyzed
by palladium(II) salts modified with P- or N-donor
ligands, and its products are perfectly alternating
polyketones.2 The study of the intimate mechanism of
the copolymerization reaction started with the demon-
stration that the propagation step consists of two
successive alternate migratory insertion reactions of
The various reactions involved in the initiation step
are (i) insertion of CO into the Pd-Me bond; (ii)
(2) (a) Sen, A.; Lai, T. W. J . Am. Chem. Soc. 1982, 104, 3520. (b)
Drent, E.; Budzelaar, P. H. M. Chem. Rev. 1996, 96, 613. (c) Nozaki,
K.; Hiyama, T. J . Organomet. Chem. 1999, 576, 248. (d) Bianchini, C.;
Meli, A. Coord. Chem. Rev. 2002, 225, 35.
(3) (a) van Asselt, R.; Gielens, E. E. C. G.; Ru¨lke, R. E.; Elsevier, C.
J . J . Chem. Soc., Chem. Commun. 1993, 1203. (b) van Asselt, R.;
Gielens, E. E. C. G.; Ru¨lke, R. E.; Vrieze, K.; Elsevier, C. J . J . Am.
Chem. Soc. 1994, 116, 977.
† E-mail: claver@correu.urv.es. Fax: 34-977-559563.
(1) Cornils, B.; Herrmann, W. A. Applied Homogeneous Catalysis
with Organometallic Compounds; VCH: Weinheim, Germany, 1996;
Vol. 2.
(4) Mul, W. P.; Oosterbeek, H.; Beitel, G. A.; Kramer, G.-J .; Drent,
E. Angew. Chem., Int. Ed. 2000, 39, 1848.
10.1021/om020568b CCC: $22.00 © 2002 American Chemical Society
Publication on Web 11/21/2002

Reactivity of Palladium-Methyl Complexes
Organometallics, Vol. 21, No. 26, 2002 5821
Sch em e 1. P yr id in e-Im id a zolin e Liga n d s Stu d ied
w ith Th eir Nu m ber in g Sch em e a n d th e
insertion of CO into the Pd-OMe group; (iii) insertion
of olefin into the Pd-H bond. Several groups have
focused on the study of these insertion reactions and
used Pd(II) systems containing bidentate nitrogen
ligands. For the phenanthroline-based system [Pd(Me)-
(L)(phen)][BAr′4] (L ) solvent molecule; Ar′ ) 3,5-
(CF3)2C6H3), a complete catalytic cycle has been con-
structed from kinetic and thermodynamic studies for the
copolymerization of ethylene and CO.5
Cor r esp on d in g P a lla d iu m Neu tr a l Com p lexes
For unsymmetrical ligands, the insertion reactions
may afford two different stereoisomers. The formation
of one or both stereoisomers could influence the products
of the copolymerization reaction. An intermediate re-
sulting from the insertion of ethylene into a Pd-acyl
bond has recently been isolated and characterized by
X-ray for the first time for a complex containing the
unsymmetrical 6-methyl-2,2′-bipyridine. A single stereo-
isomer was observed throughout the reaction sequence.6
Sch em e 2. Ca tion ic P a lla d iu m Com p lexes 3a -3d
a n d 4a -4d (M ) m a jor isom er , m ) m in or isom er ;
n .o. ) n ot obser ved )
When the copolymerization reaction involves styrene,
the ligand can also play a role in controlling the
stereoregularity of the synthesized polyketone. In the
case of bisnitrogen planar ligands of C2v or Cs symmetry
(e.g., 2,2′-bipyridine, 1,10-phenanthroline, 5-NO2-1,10-
phenanthroline, 2,2′-bipyrimidine, diazabutadiene de-
rivatives, pyridine-pyrazole) the syndiotactic polyketone
is obtained.7-12 C2-symmetry chiral bidentate ligands
(e.g., bisoxazoline, dioxazoline, diketiimines) provide
good enantioface control and give isotactic copoly-
mers.10,13,14 Interestingly the C1-symmetrical chiral
ligands (e.g., N-N′, P-N, P-OP) led to syndiotactic15
or isotactic microstructures,16 depending on the relative
influence of the chain-end or the enantiomorphic control.
It has been reported that the site-selective coordina-
tion of the olefin on the palladium complex determines
its enantioface discrimination. In the case of palladium
complexes modified with unsymmetrical N-N′ ligands,
the different trans effect of nitrogen atoms and the steric
properties of the ligand seem to be responsible for the
site-selective coordination.15 Moreover, for P-N ligands,
the isolation and characterization of some insertion
intermediates have always shown that a single stereo-
isomer is formed.17-19
We have recently reported the synthesis of C1-sym-
metrical pyridine-imidazoline ligands (N-N′ ) 1a -1d )-
(Scheme 1) and their coordination to palladium. The
modification of the R substituent on the imidazoline
moiety leads to variation of the electronic properties of
the nitrogen donors. The Pd(II) complexes of general
formula [Pd(Me)(NCMe)(N-N′)][BAr′4] (4a-4d) (Scheme
2) behave as catalyst precursors for the copolymeriza-
tion of carbon monoxide and 4-tert-butylstyrene (TBS).
By changing the electronic properties in the pyridine-
imidazoline ligands the stereochemistry of these com-
plexes, and therefore of the polyketones obtained, can
be modified.20
To learn more about the influence of our electronic
tunable ligands, we studied the stereochemistry and the
reactivity of intermediates involved in the mechanism.
The X-ray structures of two neutral complexes [Pd-
(Me)2-nCln(N-N′)] (n ) 1, 2; N-N′ ) 1d , 1b) were
determined. The reactivity of the palladium-methyl
precursors [Pd(Me)(NCMe)(N-N′)][PF6] (3a -3d ) to-
ward CO was investigated in depth by in situ 1H and
(5) (a) Rix, F. C.; Brookhart, M. J . Am. Chem. Soc. 1995, 117, 1137.
(b) Rix, F. C.; Brookhart, M.; White, P. S. J . Am. Chem. Soc. 1996,
118, 4746.
(6) Stoccoro, S.; Minghetti, G.; Cinellu, M. A.; Zucca, A.; Manassero,
M. Organometallics 2001, 20, 4111.
(7) Barsacchi, M.; Consiglio, G.; Medici, L.; Petrucci, G.; Suter, U.
W. Angew. Chem., Int. Ed. Engl. 1991, 30, 989.
(8) (a) Milani, B.; Corso, G.; Mestroni, G.; Carfagna, C.; Formica,
M.; Seraglia, R. Organometallics 2000, 19, 3435. (b) Milani, B.;
Anzilutti, A.; Vicentini, L.; Sessanta o Santi, A.; Zangrando, E.;
Geremia, S.; Mestroni, G. Organometallics 1997, 16, 5064.
(9) Sen, A.; J iang, Z. Macromolecules 1993, 26, 911.
(10) (a) Brookhart, M.; Rix, F. C.; DeSimone, J . M.; Barborak, J . C.
J . Am. Chem. Soc. 1992, 114, 5894. (b) Brookhart, M.; Wagner, M. I.;
Balavoine G. G. A.; Haddou, H. A. J . Am. Chem. Soc. 1994, 116, 3641.
(11) Carfagna, C.; Gatti, G.; Martini, D.; Pettinari, C. Organo-
metallics 2001, 20, 2175.
(12) Bastero, A.; Ruiz, A.; Reina, J . A.; Claver, C.; Guerrero, A. M.;
J alo´n, F. A.; Manzano, B. R. J . Organomet. Chem. 2001, 619, 287.
(13) Bartolini, S.; Carfagna, C.; Musco, A. Macromol. Rapid
Commun. 1995, 16, 9.
(14) Reetz, M. T.; Haderlein, G.; Angermund, K. J . Am. Chem. Soc.
2000, 122, 996.
(15) Aeby, A.; Consiglio, G. Inorg. Chim. Acta 1999, 296, 45.
(16) (a) Nozaki, K.; Komaki, H.; Kawashima, Y.; Hiyama, T.;
Matsubara, T. J . Am. Chem. Soc. 2001, 123, 534. (b) Sperrle, M.; Aeby,
A.; Consiglio, G.; Pfaltz, A. Helv. Chim. Acta 1996, 79, 1387.
(17) Brinkmann, P. H. P.; Luinstra, G. A. J . Organomet. Chem. 1998,
572, 193.
(18) Braunstein, P.; Fryzuk, M. D.; Le Dall, M.; Naud, F.; Rettig, S.
J .; Speiser, F. J . Chem. Soc., Dalton Trans. 2000, 1067.
(19) Aeby, A.; Bangerter, F.; Consiglio, G. Helv. Chim. Acta 1998,
81, 764.
(20) Bastero, A.; Castillo´n, S.; Claver, C.; Ruiz, A. Eur. J . Inorg.
Chem. 2001, 12, 3009.

5822 Organometallics, Vol. 21, No. 26, 2002
Bastero et al.
F igu r e 2. Molecular structure (ORTEP drawing, 40%
thermal ellipsoids) with atom-labeling scheme of 2b′.
F igu r e 1. Molecular structure (ORTEP drawing, 50%
thermal ellipsoids) with atom-labeling scheme of 2d .
Ta ble 1. Selected Bon d Len gth s (Å) a n d
13C NMR experiments. The complete sequence of inter-
mediates was established for complexes with ligands 1a
and 1b. The [Pd(COMe)(CO)(1a )][PF6] was isolated and
characterized. Some correlations between NMR results
and the catalytic activity of the precursors are also
discussed.
An gles (d eg) for Com p lexes 2b′ a n d 2d
2b′‚CDCl3
X ) Cl(2)a
2d
X ) C(1)
Pd-N(1)
Pd-N(2)
Pd-Cl(1)
Pd-X
N(1)-C(2)
N(1)-C(6)
N(2)-C(7)
N(2)-C(9)
N(3)-C(7)
N(3)-C(8)
N(3)-C(22)
N(3)-S
2.088(3)
2.000(3)
2.304(1)
2.194(2)
1.336(5)
1.364(5)
1.303(5)
1.481(4)
1.358(5)
1.486(5)
1.461(5)
2.149(5)
2.065(4)
2.282(2)
2.071(4)
1.325(7)
1.352(7)
1.279(6)
1.480(7)
1.423(6)
1.503(6)
Resu lts a n d Discu ssion
Syn th esis a n d Ch a r a cter iza tion of [P d (Me)(Cl)-
(N-N′)] a n d of [P d (Me)(NCMe)(N-N′)][X] Com -
p lexes 2a -2d , 3a -3d , a n d 4a -4d . We have recently
communicated the synthesis of complexes [Pd(Me)-
(NCMe)(N-N′)][BAr′4], 4a -4d , together with their
catalytic behavior in the CO/TBS copolymerization
1.631(4)
N(1)-Pd-N(2)
N(1)-Pd-Cl(1)
N(1)-Pd-X
78.6(1)
77.5(2)
97.3(1)
175.7(2)
174.7(1)
98.3(2)
86.9(1)
1
reaction.20 To simplify the H NMR spectra, the related
96.62(9)
172.6(1)
174.51(9)
94.0(1)
cationic palladium complexes with PF6- as the counter-
ion have been synthesized in a similar way, starting
from the corresponding neutral derivatives [Pd(Me)(Cl)-
(N-N′)], 2a -2d , by using AgPF6 in place of BAr′4
(Schemes 1 and 2).
N(2)-Pd-Cl(1)
N(2)-Pd-X
Cl(1)-Pd-X
90.77(6)
a
The chloride is partially disordered with a methyl ligand (see
Experimental Section).
Single crystals suitable for X-ray analysis were ob-
tained for the neutral derivative 2d with the ligand
bearing the triflate substituent (Figure 1). Efforts to
obtain single crystals of the neutral complex 2b, with
the ligand bearing an electron-donating group, resulted
in the dichloride species [PdCl2(1b)], 2b′ being isolated,
because the methyl group exchanged with the chloride
in the chlorinated solvent (Figure 2). Figures 1 and 2
show the molecular structures of 2b′ and 2d complexes
together with the atom-numbering scheme, and Table
1 shows a selection of bond lengths and angles.
The structural determination of complex 2b′ shows
a significant difference in the Pd-Cl bond lengths
(Pd-Cl(1) ) 2.304(1) Å, Pd-Cl(2) ) 2.194(2) Å). This,
together with the short Pd-N(py) bond distance trans
to Cl(2) (2.088(3) Å), is further evidence for the previ-
ously mentioned exchange reaction at the methyl and
suggests that the Pd-Cl(2) bond length actually appears
as an artifact arising from a mixed chloride/methyl
ligand (see Experimental Section). The square planar
geometry of palladium is slightly tetrahedrally dis-
torted, and the donor atoms deviate by (0.023 Å from
the coordination mean plane. Both the Pd-N bond
distances with pyridine and imidazoline, 2.088(3) and
2.000(3) Å, respectively, are significantly shorter than
those measured in 2d (see below). For purposes of
comparison, the Pd-N(py) and Pd-N(imidazoline)
bond lengths in the crystal structure of the bischelated
head-tail [Pd(1b)2]2+ complex are similar (mean value
2.017(7) and 2.021(7) Å, respectively).21
In complex 2d the square planar geometry around Pd
involves the nitrogen atoms of the chelating ligand and,
as expected, a chloride and a methyl group with donor
atoms that are coplanar within (0.017 Å. The data in
Table 1 indicate that the coordination distances for the
chelating ligand are considerably different, Pd-N(1) )
2.149(5), Pd-N(2) ) 2.065(4) Å, and longer than those
found in 2b′. In fact, the former is induced by the trans
influence of the methyl, while the latter is affected by
the strong electron-withdrawing properties of the CF3SO2
group, which provides a less basic iminic N donor. The
Pd-Cl(1) and Pd-C(1) bond distances, 2.282(2) and
2.071(4) Å, respectively, fall in the range usually
observed for Pd(II) complexes and follow the trend of
those detected, for example, in the [Pd(Me)(Cl)(2,9-dm-
phen)] derivative (2,9-dm-phen ) 2,9-dimethyl-1,10-
phenanthroline; Pd-Me ) 2.015(6) Å, Pd-Cl ) 2.312(1)
Å, Pd-N(1) ) 2.229(4) Å, Pd-N(2) ) 2.066(4) Å).22
(21) Data from these labs, unpublished result.
(22) De Felice, V.; Albano, V. G.; Castellari, C.; Cucciolito, M. E.;
De Renzi, A. J . Organomet. Chem. 1991, 403, 269.

Reactivity of Palladium-Methyl Complexes
Organometallics, Vol. 21, No. 26, 2002 5823
F igu r e 3. Crystal packing: head-to-tail arrangement of 2b′ and 2d molecules related by a center of symmetry.
In both complexes, the rings of the chelating ligand
are not coplanar, but slightly tilted, as indicated by the
N(1)-C(6)-C(7)-N(2) torsion angle of 9.0(4)° (in 2b′)
and 11.2(7)° (in 2d ). On the other hand, the dihedral
angles formed by the planes through the pyridine and
imidazoline atoms are 13.0(2)° and 18.1(1)°, respectively.
The phenyl rings at C(8) and C(9) are oriented, as
expected, on the same side of the imidazoline plane and
avoid an eclipsed conformation through a torsion angle
C(16)-C(8)-C(9)-C(10) of 20.3(5)° (2b ′) and 27.9(7)°
(2d ). This causes considerable distortions inside the five-
membered ring of both complexes and induces a certain
degree of strain. The ring atoms (principally N(3), C(8),
and C(9)) deviate by up (0.15 Å from the mean plane.
Moreover, in 2b′ the N(2)-C(7) and N(3)-C(7) bond
distances, 1.303(5) and 1.358(5) Å, are consistent with
a delocalization inside the N(2)-C(7)-N(3) fragment,
as already observed in the molecular structure of two
ruthenium derivatives where the pyridine-imidazoline
ligand has a hydrogen or a methyl bound to the aminic
nitrogen N(3).23 In addition, in 2b′ the sum of the bond
angles around N(3) is 353.9° (in 2d 349.1°), which
supports the degree of delocalization across the amidine.
On the other hand, the corresponding figures in 2d
agree with a double (N(2)-C(7) ) 1.279(6) Å) and a
single bond character (N(3)-C(7) ) 1.423(6) Å), a
feature that seems to be induced by the electronic
properties of CF3SO2. Therefore, the Pd-N(2) and the
N-C distances in the N(2)-C(7)-N(3) fragment can be
regarded as a proof of the electronic properties of the R
substituent.
The analysis of the crystal packing in 2d shows pairs
of complexes arranged head-to-tail about a symmetry
center with a short intermetallic Pd- - -Pd′ distance of
3.440 Å (Figure 3), a feature often encountered in square
planar Pd and Pt complexes.24,25 Similar packing is also
observed in the crystal structure of 2b′, but the pair of
complexes are related in such a way that Cl(2) lies
almost at the metal apical position of the symmetry-
related molecule (Cl(2)- - -Pd′ ) 3.966 Å, Pd- - -Pd′ )
4.980 Å). This arrangement prevents steric clashes
between Cl(2) and the benzyl ring of the second mol-
ecule. The stacking of this latter ring with that of a
nearby complex (shortest C- - -C distance 3.88 Å) ac-
counts for the narrow torsion angle of 19.1(5)° detected
in the N(3)-C(22)-C(23)-C(28) fragment.
Finally in 2d , it is worthwhile to point out the short
intramolecular distance (3.81 Å) between the methyl
carbon atom and the centroid of phenyl C(10-15) (see
Figure 1).
The neutral derivatives 2a -2d were characterized in
solution by 1H NMR spectroscopy. For all the complexes
2a -2d in the aromatic region of the spectra, the H6
signal (Scheme 1) is considerably downfield shifted with
respect to the one in the free ligand (∆δ ) 0.55 ppm),
indicating that the chloride is cis coordinated to the
pyridine moiety.26 This coordination is confirmed by
NOE experiments: irradiation of the Pd-Me protons
shows an NOE effect with the H5’ of the imidazoline.
The Pd-Me singlets are in the 0.50-0.25 ppm range,
upfield shifted with respect to the same resonance in
similar complexes [Pd(Me)(Cl)(pzpy)] (pzpy ) 2-(pyrazol-
1-yl)pyridine).27 This shift is related to the proximity of
the shielding cone of the phenyl ring in position 5′ on
the imidazoline ring, as indicated by the X-ray analysis
(Figure 1). For all the neutral derivatives, only the
isomer that corresponds to the one found in the solid
state is observed in solution, as found in the related
pyridine-oxazoline (pyox) complexes [Pd(Me)(Cl)(py-
ox)].28
No crystal suitable for structural determination was
obtained for the cationic complexes 3a -3d or 4a -4d
(Scheme 2). They were completely characterized in
(26) Ru¨lke, R. E.; Ernsting, J . M.; Spek, A. L.; Elsevier, C. J .; van
Leeuwen, P. W. N. M.; Vrieze, K. Inorg. Chem. 1993, 32, 5769.
(27) Elguero, J .; Guerrero, A.; Go´mez de la Torre, F.; de la Hoz, A.;
J alo´n, F. A.; Manzano, B. R.; Rodr´ıguez, A. New J . Chem. 2001, 25,
1050.
(28) Gsponer, A.; Schmid, T. M.; Consiglio, G. Helv. Chim. Acta 2001,
84, 2986.
(23) Davenport, A. J .; Davies, D. L.; Fawcett, J .; Russell, D. R. J .
Chem. Soc., Perkin Trans. 2001, 1, 1500.
(24) Milani, B.; Alessio, E.; Mestroni, G.; Zangrando, E.; Randaccio,
L.; Consiglio, G. J . Chem. Soc., Dalton Trans. 1996, 1021.
(25) Cini, R.; Fanizzi, F. P.; Intini, F. P.; Maresca, L.; Natile, G. J .
Am. Chem. Soc. 1993, 115, 5123.

5824 Organometallics, Vol. 21, No. 26, 2002
Bastero et al.
Ta ble 2. Selected 1H NMR Da ta for Com p lexes
) 1c, 1d ), which are differentiated by the trans or cis
coordination of the methyl group to the imidazoline ring
(Scheme 2). In particular, the Pd-Me fragment of the
major species is trans to the imidazoline ring. The ratio
between the trans and cis isomers is 2:1 for 3c and 3:1
for 3d . The chemical shifts for the Pd-Me protons in the
trans isomer are very close to those observed for
complexes [Pd(Me)(NCMe)(N-N′)][BAr′4], 4c-4d, which
show only the trans isomer in solution (Table 2).20
In summary, for complexes 4a -4d only one stereo-
isomer is observed in solution, regardless of the nature
of the ligand. The stereoisomer formed depends on the
R substituent on the imidazoline ring: it is the cis when
R is H or Bn (4a and 4b) and the opposite for R ) Ts,
Tf (4c and 4d ) (Scheme 2).20 When the anion changes
from BAr′4- to PF6-, there is no difference for complexes
with the ligand 1a or 1b. With 1c or 1d , however,
stereochemical control is partially lost, even though the
preferential isomer has the same stereochemistry found
in 4c and 4d . These results suggest that, in all cases,
the methyl group of the stereoisomer that is preferen-
tially formed is trans to the less basic nitrogen atom.
The effect of the anion on the stereochemistry of the
complexes might be related to its position in solution
with respect to the cation. Studies in solution on
3a -3d , 4a -4d , a n d F r ee Liga n d s 1a -1d a
H6
Pd-Me
Pd-NCMe
3
1a
3a
4a
1b
3b
4b
1c
3cb
8.63 (d, J ) 5.0)
3
8.59 (d, J ) 5.1)
0.54 (s)
0.31 (s)
2.41 (s)
2.16 (s)
3
9.37 (d, J ) 5.8)
3
8.69 (d, J ) 4.8)
3
8.99 (d, J ) 4.4)
0.47 (s)
0.56 (s)
2.47 (s)
2.27 (s)
3
8.44 (d, J ) 5.2)
3
8.64 (d, J ) 5.0)
M 8.64c
M 1.10 (s)
m 0.32 (s)
0.99 (s)
M 1.59 (s)
m 2.45 (s)
1.40 (s)
3
m 8.79 (d, J ) 4.4)
3
4c
8.52 (d, J ) 5.6)
3
1d
8.78 (d, J ) 4.8)
3d b
M 8.69 (d, J ) 5.7)
M 1.22 (s)
m 0.46 (s)
1.06 (s)
M 1.64 (s)
m 2.47 (s)
1.50 (s)
3
3
m 8.88 (d, J ) 5.1)
3
4d
8.51 (d, J ) 5.6)
a
1H NMR spectra recorded in CDCl3 at room temperature; (s)
) singlet, (d) ) doublet; δ values are in ppm, J in Hz; M ) major
isomer, m ) minor isomer. b 1H NMR spectra recorded in CD2Cl2
at room temperature. c Overlapped with H3 signals, no multiplicity
could be assigned.
1
solution by recording the H NMR spectra in CDCl3 or
in CD2Cl2 (Table 2). The most significant signals are
those related to H6 for the ligand and to the Pd-Me and
the Pd-NCMe fragments. The signals were assigned to
the protons on the basis of selective decoupling experi-
ments and on the multiplicity of the signals.
For both complexes 3a and 3b one set of signals
related to the N-N′ ligand is evident at room temper-
ature. All the signals are shifted with respect to the free
ligand. By irradiating the signal of the methyl group
bound to palladium, an NOE effect with H5′ was evident.
This indicates that only one species was present in
solution, whose Pd-Me bond was cis to the imidazoline
ring (Scheme 2). This stereochemistry is analogous to
that observed in the neutral derivatives and in the
cationic species 4a -4b with BAr′4- as anion.20 (Isomers
are cis or trans depending on the position of the methyl
group with respect to the imidazoline ring.)
In the spectra of complexes with the electron-
withdrawing substituents 3c and 3d , two sets of signals
of different intensity are clearly evident (Table 2). In
the aromatic region of the spectra the signals of each
pyridine ring can be recognized through homonuclear
COSY experiments. No signal belongs to the free N-N′
ligand. In particular, for 3d two H6 signals are clearly
evident. For 3c, however, one of them overlaps the H3
signals. In the aliphatic region of the spectra, there are
also two sets of resonances for the Pd-Me group (minor
species: 0.32 ppm for 3c and 0.46 ppm for 3d ; major
species: 1.10 ppm for 3c and 1.22 ppm for 3d ) and the
Pd-NCMe fragment (minor species: 2.45 ppm for 3c and
2.47 ppm for 3d ; major species: 1.59 ppm for 3c and
1.64 ppm for 3d ). For both complexes, in each species
the ratio between Pd-Me and Pd-NCMe is 1. When NOE
experiments were performed on 3c or 3d by irradiating
the Pd-Me singlet of the minor species, the spectrum
also shows a negative signal for the Pd-Me singlet of
the major species, thus indicating that they are in
equilibrium. This is confirmed because the signals
broaden when the temperature is increased to 313 K.
Moreover, an NOE effect is observed between the
Pd-Me and H5′ for the minor species in both the 3c and
3d complexes. On the basis of these NMR data, it is
clear that the two species present in solution are the
two stereoisomers [Pd(Me)(NCMe)(N-N′)][PF6] (N-N′
complexes [Pd(OMe-COD)(bipy)][Y] (OMe-COD ) η1,η2-
-
C8H12OMe; Y ) BPh4-, CF3SO3-, BF4-, PF6-, SbF6
,
BAr′4-) showed that the anion is preferentially located
above or below the coordination plane and shifted
toward the bipy ring trans to the Pd-C σ-bond. When
BAr′4 changes to PF6-, the strength of the interionic
-
interactions increases and favors the dissociation of one
N-arm of the bipy molecule.29 Therefore, in the case of
complexes 3c and 3d , this may be responsible for the
trans to cis isomerization process.
The presence of stereochemical isomers in Pd(II)
complexes of general formula [Pd(Me)(NCMe)(L-L′)][X],
involved in the copolymerization process, has been
observed in two other examples, where L-L′ is 2-(1-
(3,5-dimethyl)pyrazolyl)pyrimidine12 or diphosphino-
ferrocene ligands derived from J osiphos.30 In the first
case, the presence of the less favored isomer, on the
basis of electronic consideration, has been explained in
terms of the steric hindrance of the ligand. In the
diphosphine derivatives, a strict relationship was not
found between the electronic effect of the ligand and the
ratio of the stereoisomer mixture.
Rea ctivity of [P d (Me)(NCMe)(N-N′)][X] Com -
p lexes, 3a -3d a n d 4b, 4d w ith Ca r bon Mon oxid e.
All the complexes 3a -3d were reacted with carbon
monoxide, and the reaction was studied by in situ 1H
and 13C NMR spectroscopy.
When carbon monoxide is bubbled for 5 min through
a solution of [Pd(Me)(NCMe)(1a )][PF6], 3a , or of [Pd-
(Me)(NCMe)(1b)][PF6], 3b, in CD2Cl2, at 273 K, five new
singlets (e.g., for 3a +CO: 0.88, 1.52, 1.69, 2.10, 2.37
1
ppm) are present in the aliphatic region of the H NMR
spectra, recorded after 15 min, together with the
resonance due to the methyl group of the precursor
(Figure 4a,b) (Table 3). When labeled 13CO is used, in
(29) Macchioni, A.; Bellachioma, G.; Cardaci, G.; Travaglia, M.;
Zuccaccia, C.; Milani, B.; Corso, G.; Zangrando, E.; Mestroni, G.;
Carfagna, C.; Formica, M. Organometallics 1999, 18, 3061.
(30) Gambs, C.; Consiglio, G.; Togni, A. Helv. Chim. Acta 2001, 84,
3105.

Reactivity of Palladium-Methyl Complexes
Organometallics, Vol. 21, No. 26, 2002 5825
These NMR data indicate that the final product
corresponds to the palladium-acyl-carbonyl species
[Pd(COMe)(CO)(N-N′)][PF6] (N-N′ ) 1a , 1b), 7a or 7b,
which is the result of inserting CO into the Pd-Me bond
(Scheme 3). The other signals observed at lower CO
concentrations are attributed to the intermediates of the
insertion reaction. In particular, for the complex with
ligand 1a , the signal at 0.88 ppm, which is still a singlet
in the presence of 13CO, is due to the palladium-methyl-
carbonyl derivative [Pd(Me)(CO)(1a )][PF6], 5a , whose
corresponding signal in the 13C NMR spectrum is at
176.6 ppm. Finally, the resonance at 1.52 ppm, which
becomes a doublet after bubbling 13CO, and the singlet
at 2.37 ppm belong to the palladium-acyl-acetonitrile
intermediate [Pd(COMe)(NCMe)(1a )][PF6], 6a . The
corresponding signal in the 13C NMR spectrum is at
220.9 ppm.
The most significant signal in the aromatic region of
the spectra is the one related to the H6 in the pyridine
ring. For the intermediates, three signals are attributed
to H6, but they could not be clearly assigned to the
corresponding species. In the final palladium-acyl-
carbonyl species 7a , H6 gives a doublet at 8.48 ppm,
upfield shifted with respect to the precursor. Thanks
to the NOE effect between H6 and the protons in the
acyl group of 7a , it was possible to recognize this species
as the trans isomer. The same situation is observed for
7b . The 1H NMR spectra of both 7a and 7b did not
vary when the temperature was decreased by as much
as 213 K, which confirmed the presence of a single
stereoisomer. No direct experiment was performed on
the stereochemistry of the intermediates.
F igu r e 4. Reactivity of 3a with carbon monoxide. 1H NMR
spectra recorded in CD2Cl2 at 273 K, region of aliphatic
protons: (a) spectrum of 3a ; (b) spectrum of 3a + CO; (c)
spectrum of 3a + 13CO; (d) spectrum of 3a + excess of 13CO.
The palladium-acyl-carbonyl derivative 7a was also
isolated by bubbling CO in a dichloromethane solution
of [Pd(Me)(NCMe)(1a )][PF6] at 273 K. It was stored at
278 K without decomposition. Its 1H NMR spectrum
shows the same signals observed in the in-situ NMR
experiments.
Ta ble 3. Selected 1H a n d 13C NMR Da ta for
Rea ctivity of Com p lexes 3a a n d 3b w ith COa
When carbon monoxide is bubbled for 5 min through
a solution of [Pd(Me)(NCMe)(1c)][PF6], 3c, or of [Pd(Me)-
(NCMe)(1d )][PF6], 3d , in CD2Cl2, at 273 K, the 1H NMR
spectra, recorded after 15 min at 263 K, showed only
two broad signals in the aliphatic region (e.g., for
3c+CO: 1.65, 1.98 ppm) and the complete disappear-
ance of the precursor’s resonance (Table 4). When the
labeled 13CO was used, no variation was observed in
1
the H NMR spectrum. In the corresponding 13C NMR
spectrum two broad signals appeared (e.g., for 3c+CO:
172.8, 211.5 ppm) (Figure 5a and Table 4) due to
a Pd-CO and a Pd-COMe moiety, respectively. Low-
temperature NMR studies were performed by decreas-
ing the temperature from 263 to 183 K. In the case of
3c, the signal at 1.65 ppm disappeared at 233 K. Two
peaks became evident at 183 K (1.41 and 2.74 ppm),
and there was a sharp singlet at 1.99 ppm. The two
peaks were of different intensity, the resonance at 1.41
ppm being higher than that at 2.74 ppm in a ratio of
4.2:1. Moreover, the weighted sum of the two resonances
corresponds to the chemical shift (1.66 ppm) of the
signal observed at 263 K. At the same temperature in
the 13C NMR spectrum four signals appeared that can
be grouped into two pairs on the basis of their intensities
(170.7 and 217.1 ppm, 172.4 and 211 ppm) (Figure 5b).
The reaction of 3d with carbon monoxide was similar:
a
NMR spectra recorded in CD2Cl2 at 273 K; δ values are in
ppm; n.d.: not determined.
the 1H NMR spectrum two singlets (e.g., for 3a +CO:
1.52 and 1.69 ppm) become doublets, indicating that
they belong to two acyl groups (Figure 4c). In the
corresponding 13C NMR spectra there are four signals
(e.g., for 3a +CO: 174.3, 176.6, 210.8, 220.9 ppm); the
two at lower frequency are typical for Pd-CO frag-
ments, while the other two are related to Pd-COMe
species.5b When the concentration of CO in the same
solution is increased, only two signals are still present
1
in the H NMR spectra: a doublet and a singlet (e.g.,
for 3a +CO: 1.69, 2.10 ppm) (Figure 4d). The same is
true of the 13C NMR spectra (e.g., for 3a +CO: 174.3,
210.8 ppm). The signal at 2.10 ppm in the 1H NMR
spectra is due to free acetonitrile.

5826 Organometallics, Vol. 21, No. 26, 2002
Bastero et al.
Sch em e 3. Rea ctivity of Com p lexes w ith Ca r bon Mon oxid e: (a ) 3a a n d 3b; (b) 3c a n d 3d
the peak at 2.33 ppm at 263 K, which disappears at 233
K, splits into two peaks (2.76 and 1.52 ppm) at 183 K.
For this complex, the intensity of the signals was just
3d +CO), are attributed to two Pd-COMe groups. The
resonances found in the 13C NMR spectrum at the same
temperature confirm that two Pd-COMe groups and two
Pd-CO moieties are present. Therefore, these NMR data
indicate that the final product is the palladium-acyl-
carbonyl species [Pd(COMe)(CO)(N-N′)][PF6] (N-N′ )
1c, 1d ), 7c or 7d , which is present as a mixture of two
isomers in equilibrium (Scheme 3). The rate of this
equilibrium is intermediate on the NMR time scale at
263 K.
1
the reverse of what was found for 3c: in the H NMR
spectrum, the most intense peak was at the highest
frequency (2.76 ppm), with a ratio of 1.7:1 (Table 4). The
same inversion of intensity is observed in the corre-
sponding 13C NMR spectrum.
1
The signal at 1.99 ppm in the H NMR spectra is due
to free acetonitrile. At the lowest temperature reached,
the two resonances at 1.41 and 2.74 ppm, for the
reactivity of 3c with CO (or 1.52 and 2.76 ppm for
In the temperature range we investigated, the analy-
sis of the H6 signal for both complexes always reveals
broad signals, and even at the lowest temperature
reached, no assignment was possible, since decoales-
cence was not complete. Therefore, the stereochemistry
of the two isomers could not be determined.
Finally, no signals from the intermediates were
observed for either of the complexes, and the resonances
of the precursors disappeared, indicating a higher
reactivity with carbon monoxide than with 3a and 3b.
The reactivity with carbon monoxide was also inves-
-
tigated for two exponents of the series with BAr′4
,
namely, 4b and 4d . They behaved similarly to the
-
corresponding PF6 derivatives: one isomer for the
complex with ligand 1b and two isomers for the species
containing 1d . Indeed, in the spectrum at 273 K,
recorded after bubbling CO in a solution of 4b, only the
signal at 1.65 ppm is present in the aliphatic region.
This indicates that trans-[Pd(COMe)(CO)(1b)][BAr′4]
(8b) has been formed. This signal is shifted at 1.50 ppm
F igu r e 5. Reactivity of 3c with 13CO. 13C NMR spectra
recorded in CD2Cl2: (a) at T ) 263 K; (b) at T ) 183 K.

Reactivity of Palladium-Methyl Complexes
Organometallics, Vol. 21, No. 26, 2002 5827
Ta ble 4. Selected 1H a n d 13C NMR Da ta for
Rea ctivity of Com p lexes 3c a n d 3d w ith COa
complexes with carbon monoxide. Only one stereoisomer
is obtained for Pd-Me complexes with ligands 1a ,1b. It
slowly reacts with carbon monoxide and yields only one
Pd-acyl stereoisomer (Pd-acyl fragment trans to imida-
zoline). Both stereoisomers were found for Pd-Me com-
plexes with ligands 1c,1d . They react with CO faster
than the complexes with 1a and 1b, to yield the
corresponding Pd-acyl stereoisomers. The ratio between
the stereoisomers depended on the ligand. The higher
catalytic activity found for the precursor with 1d ,
together with the prevailing presence of the opposite
stereoisomer with respect to 1a (or 1b), might indicate
that the Pd-acyl fragment cis to imidazoline is more
reactive than the trans one.
It is well known that the insertion of the olefin is the
rate-determining step of the copolymerization reaction
and that the enantioface selection during the olefin
insertion is due to the chain end or to the enantio-
morphic site control. The fact that the polyketone
obtained with ligands 1a and 1b tends to isotacticity,
together with the presence of a single stereoisomer
(Pd-COMe trans to imidazoline), might indicate that
there is site-selective coordination of the olefin cis to
the chiral moiety of the ligand. The enantioface selection
of the ligand is nevertheless not efficient enough to
completely overcome the chain-end control, and the
result is, therefore, the synthesis of an atactic copoly-
mer. On the other hand, the synthesis of the syndio-
tactic copolymer, together with the presence of the
two isomers in the case of 1c and 1d ligands, might
indicate that isomerization takes place very easily by
exchanging the coordination site of the polymer growing
chain and the olefin. The greater reactivity of the
stereoisomer with the Pd-COMe fragment cis to imida-
zoline might favor the insertion of the olefin preferen-
tially under chain-end control and lead to a prevailing
syndiotactic copolymer. However, due to the similarity
of species 3a -3d , two regioisomeric intermediates
might be present for all the complexes. As a conse-
quence, the variation in the microstructure of the
produced copolymers should arise from different con-
tribution of these regioisomers.
a
NMR spectra recorded in CD2Cl2; δ values are in ppm; b )
broad.
when the spectrum is recorded at 193 K. In the reaction
of 4d with CO, only one broad signal is present at 2.11
ppm at 273 K. It is split into two signals (2.72 and 1.50
ppm) when the temperature was decreased down to 193
K. Therefore, both cis and trans [Pd(COMe)(CO)(1d )]-
[BAr′4] (8d ) isomers are present in a ratio of 1:1.
No successful direct experiment was done to unam-
biguously assign the stereochemistry of the two isomers
for complexes 7c, 7d , and 8d . However, comparing the
chemical shifts at the lowest temperature reached, in
particular for 8b and 8d , suggests that the resonance
at 1.5 ppm is due to the Pd-acyl-carbonyl species with
the acyl group trans to the imidazoline ring.
Con clu sion s
Pyridine-imidazoline ligands of C1 symmetry, elec-
tronically modified with different R substituents, pro-
vide information about the stereochemistry of the
intermediates in the copolymerization reaction.
Finally, it should be noted that the stereocontrol
observed in the BAr′4 precursors is partially lost after
the reaction with carbon monoxide.
The neutral complexes [Pd(Me)(Cl)(N-N′)] have the
same stereochemistry with all the ligands, and the
methyl group is cis to imidazoline. The behavior of the
cationic complexes in solution depends on the ligand
Our study of the insertion of 4-tert-butylstyrene in the
Pd-acyl-carbonyl species formed in situ (7a -7d ) was
unsuccessful, maybe due to the combined effect of
decomposition and slow insertion of the olefin.
-
(1a ,1b or 1c,1d ) as well as on the counterion (PF6 or
Complexes 4a -4d have been used as catalyst precur-
sors for the CO/4-tert-butylstyrene copolymerization
reaction. The nature of the ligand was found to have
an effect both on the productivity of the system and on
the tacticity of the polyketones obtained.20 Complexes
4a ,4b showed little activity and gave atactic polyketones
with a slight prevalence of the isotactic triad. On the
other hand, the syndiotactic polyketone was obtained
with 4c and 4d . Moreover, the last precursor showed
the highest catalytic activity. This catalytic behavior
might be correlated with the different reactivity of these
BAr′4-). It is straightforward to note that the Pd-Me and
the Pd-NCMe chemical shifts in the two isomers are
very different, and they can be considered as a probe
for the stereochemistry of the resulting complexes.
All the intermediates of the reaction of the Pd-Me
precursors with carbon monoxide, which yields the
Pd-acyl-carbonyl final species, were detected in solution
using 1H and 13C NMR spectroscopy. Depending on
the R substituent of the ligand, one or both [Pd(COMe)-
(CO)(N-N′)][X] stereoisomers were detected and char-

5828 Organometallics, Vol. 21, No. 26, 2002
Bastero et al.
[P d (Me)(NCMe)(N-N′)][P F 6] (3a -d ). To a solution of
[Pd(Me)(Cl)(N-N′)] (0.18 mmol) in dichloromethane (3 mL)
was added 1.2 equiv of AgPF6 (0.22 mmol) dissolved in
acetonitrile (1 mL). After stirring for 1 h in the absence of light,
the AgCl formed was filtrated, and when diethyl ether was
added, the solution was concentrated under vacuum to yield
a pale yellow solid. Average yield: 75%.
acterized. Finally, the reactivity of the cationic Pd-Me
complexes toward CO was seen to be related to the
copolymerization results. The catalytic activity of
the hexafluorophosphate derivatives as well as of the
stereochemistry of the synthesized polyketones is being
evaluated at present.
[P d (Me)(NCMe)(1a )][P F 6]‚0.3Et2O (3a ). Anal. Calcd for
Exp er im en ta l Section
C
24.3H26.3F6N4O0.3PPd: C, 42.99; H, 3.39; N, 8.88. Found: C,
Gen er a l Com m en ts. Commercial Na2[PdCl4] and [Sn-
(CH3)4] were purchased from J ohnson Matthey and Aldrich,
respectively, and used as received. Solvents for synthetic
purposes were distilled and deoxygenated prior to use unless
otherwise stated. Solvents for spectroscopy were used without
further purification. Carbon monoxide (labeled and unlabeled,
CP grade, 99%) was supplied by Aldrich. Ligands 1a -1d were
prepared according to published methods.20 The salt BAr′4 (Ar′
) 3,5-(CF3)2C6H3) was prepared according to the reported
method.31 All reactions were carried out under nitrogen
atmosphere, at room temperature, using standard Schlenk
techniques. 1H and 13C NMR spectra were recorded on a
Varian Gemini spectrometer with a 1H resonance frequency
of 300 MHz and a 13C frequency of 75.4 MHz, on a Varian
Mercury VX spectrometer with a 1H resonance frequency of
400 MHz and a 13C frequency of 100.5 MHz, and on a J EOL
EX 400 spectrometer with a 1H frequency at 400 MHz and a
13C frequency of 100.5 MHz. The resonances were referenced
to the solvent peak versus TMS (CDCl3 at 7.26 δ for 1H and
77.23 δ for 13C, CD2Cl2 at 5.32 δ for 1H and 54.0 δ for 13C).
The NOE experiments were run with a 1H pulse of 12 µs (300
MHz) and of 13.3 µs (400 MHz). Two-dimensional correlation
spectra (gCOSY) were obtained with the automatic program
of the instrument. Elemental analyses were carried out on a
Carlo Erba microanalyzer EA 1108. MS (FAB positive) were
obtained on a Fisons V6-Quattro instrument.
42.75; H, 3.35; N, 8.66. 1H NMR (400 MHz, CDCl3): δ 8.59
3
4
3
4
(dd, J ) 5.1 Hz, J ) 0.6 Hz, 1H, H6), 8.21 (td, J ) 8 Hz, J
) 0.7 Hz, 1H, H4), 8.06 (dd, J ) 8 Hz, J ) 0.7 Hz, 1H, H3),
3
4
7.83 (dd, J ) 8 Hz, J ) 5.1 Hz, 1H, H5), 5.81 (d, J ) 11.2
3
3
3
Hz, 1H, H5′), 5.48 (d, J ) 11.2 Hz, 1H, H4′), 2.41 (s, 3H, Pd-
3
NCMe), 0.54 (s, 3H, Pd-Me). MS (FAB positive) m/z: 461.2
[M]+, 404 [M - NCMe]+.
[P d (Me)(NCMe)(1b)][P F 6]‚0.3Et2O (3b). Anal. Calcd for
C
31.3H32.3F6N4O0.3PPd: C, 47.90; H, 4.20; N, 7.26. Found: C,
48.00; H, 3.98; N, 7.46. 1H NMR (400 MHz, CDCl3): δ 8.99
3
(d, J ) 4.4 Hz, 1H, H6), 8.02 (m, 3H, H3, H4 + H5), 7.35-6.80
(m, 10H, Ph), 5.50 (d, 3J ) 11.7 Hz, 1H, H5′), 5.40 (d, 3J )
11.7 Hz, 1H, H4′), 5.19 (d, 3J ) 17.6 Hz, 1H, CH2), 4.42 (d,
3J ) 17.6 Hz, 1H, CH2), 2.47 (s, 3H, Pd-NCMe), 0.47 (s, 3H,
Pd-Me).
[P d (Me)(NCMe)(1c)][P F 6] (3c). Anal. Calcd for C30H29F6-
N4O2PPdS: C, 47.35; H, 3.84; N, 7.36. Found: C, 46.99; H,
3.70; N, 7.34. Ratio of isomers in CD2Cl2 M:m ) 2:1. Major:
3
1H NMR (400 MHz, CD2Cl2): δ 8.67 (m, J ) 7.9 Hz, 1H, H3),
3
4
8.64 (m, 1H, H6), 8.35 (td, J ) 7.9 Hz, J ) 1.1 Hz, 1H, H4),
7.92 (dd, J ) 7.9 Hz, J ) 6 Hz, 1H, H5), 7.76-6.71 (m, 14H,
Ph), 5.86 (d, 3J ) 8.8 Hz, 1H, H5′), 5.44 (d, 3J ) 8.8 Hz, 1H,
H4′), 2.5 (s, 3H, Me Ts), 1.59 (s, 3H, Pd-NCMe), 1.10 (s, 3H,
Pd-Me). Minor: 8.79 (d, 3J ) 4.6 Hz, 1H, H6), 8.64 (m, 1H, H3),
3
3
8.28 (td, J ) 7.7 Hz, J ) 1.2 Hz, 1H, H4), 8.03 (dd, J ) 7.7
3
4
3
Hz, J ) 4.6 Hz, 1H, H5), 7.76-6.71 (m, 14H, Ph), 5.85 (d, J
3
3
Syn th esis. Na2[PdCl4], used as starting material, was
transformed into [PdCl2(COD)] (COD ) 1,5-cyclooctadiene)
according to the literature.32 [Pd(Me)(Cl)(COD)], obtained from
[PdCl2(COD)],26 was transformed into [Pd(Me)(Cl)(N-N′)]
(2a -2d ) following the method already reported.20 Abstraction
of the chloride to synthesize the monocationic derivatives
(3a -3d and 4a -4d ) was done both with AgPF6 (see below)
and with BAr′4.
3
) 9.6 Hz, 1H, H5′), 5.29 (d, J ) 9.6 Hz, 1H, H4′), 2.50 (s, 3H,
Me Ts), 2.45 (s, 3H, Pd-NCMe), 0.32 (s, 3H, Pd-NCMe). MS
(FAB positive) m/z: 615.1 [M]+, 558 [M - Me, NCMe]+, 403
[M - Me, NCMe, Ts]2+
.
[P d (Me)(NCMe)(1d )][P F 6] (3d ). Anal. Calcd for C24H22
-
F9N4O2PPd: C, 39.01; H, 3.00; N, 7.58. Found: C, 38.87; H,
2.94; N, 7.39. Ratio of isomers in CD2Cl2 M:m ) 3:1. Major:
1H NMR (400 MHz, CD2Cl2): 8.69 (d, 3J ) 5.7 Hz, 3H, H6),
[P d (Me)(Cl)(N-N′)] (2a -2d ). The synthesis has already
been reported.20 2a : 1H NMR (400 MHz, CDCl3, rt): δ 8.91
(ddd, 3J ) 5.1 Hz, 4J ) 1.7 Hz, 5J ) 0.6 Hz, 1H, H6), 8.05 (ddd,
8.44 (m, 1H, H3), 8.38 (td, J ) 7.8 Hz, J ) 1.5 Hz, 1H, H4),
7.97 (ddd, 3J ) 7.8 Hz, 3J ) 5.7 Hz, 4J ) 1.5 Hz, 1H, H5),
6.17 (m, 2H, H4′ + H5′), 1.64 (s, 3H, Pd-NCMe), 1.22 (s, 3H,
Pd-Me). Minor: 8.88 (d, 3J ) 5.1 Hz, 1H, H6), 8.44 (m, 1H,
3
4
4
5
3
3J ) 7.8 Hz, J ) 1.2 Hz, J ) 0.6 Hz, 1H, H3), 7.90 (td, J )
4
3
3
7.8 Hz, J ) 1.7 Hz, 1H, H4), 7.52 (ddd, J ) 7.8 Hz, J ) 5.1
3
3
3
H3), 8.30 (t, 1H, J ) 7.8 Hz, H4), 8.10 (dd, J ) 7.8 Hz, J )
Hz, J ) 1.2 Hz, 1H, H5), 6.89-6.75 (m, 10H, Ph), 5.60 (d, J
4
3
5.1 Hz, 1H, H5), 6.17 (m, 1H, H4′ or H5′), 6.03 (d, J ) 8.8 Hz,
3
3
) 11.4 Hz, 1H, H5′), 5.4 (d, J ) 11.4 Hz, 1H, H4′), 0.36 (s, 3H,
1H, H4′ or H5′), 2.47 (s, 3H, Pd-NCMe), 0.46 (s, 3H, Pd-Me).
Pd-Me). 2b: 1H NMR (400 MHz, CDCl3, rt): δ 9.22 (d, 3J )
4.8 Hz, 1H, H6), 7.86 (m, 2H, H3 + H4), 7.59 (q, 3J ) 5.2 Hz, 4J
MS (FAB positive) m/z: 593.1 [M]+, 536.0 [M - Me, NCMe]+,
403.1 [M - Me, NCMe, Tf]2+
.
) 5.2 Hz, 1H, H5), 7.25-6.76 (m, 15H, Ph), 5.46 (d, J ) 11.6
3
3
2
Hz, 1H, H4′), 5.37 (d, J ) 11.6 Hz, 1H, H5′), 5.03 (d, J ) 17.2
Hz, 1H, CH2), 4.33 (d, 2J ) 17.2 Hz, 1H, CH2), 0.49 (s, 3H,
Pd-Me). 2c: 1H NMR (400 MHz, CDCl3, rt): δ 9.20 (ddd, 3J )
X-r a y Str u ctu r e Deter m in a tion for Com p lexes 2b′ a n d
2d . For both complexes crystals suitable for X-ray analysis
were obtained. Efforts to crystallize 2b from CDCl3/Et2O gave
suitable crystals of 2b′. 2d was crystallized from a CH2Cl2/
Et2O mixture.
Crystal and experimental data are summarized in Table 5.
All the data were collected on a Nonius DIP-1030H system
with Mo KR radiation. A total of 30 frames were collected, each
with an exposure time of 15 min, over half of the reciprocal
space with a rotation of 6° about æ. The detector was at a
distance of 90 mm from the crystal. Cell refinement, indexing,
and scaling of the data sets were carried out using Mosflm33
and Scala.33 The structures were solved by Patterson and
Fourier analyses34 and refined by the full-matrix least-squares
4
5
3
5.1 Hz, J ) 2.7 Hz, J ) 1.2 Hz, 1H, H6), 8.64 (dt, J ) 7.9
Hz, 4J ) 1.3 Hz, 5J ) 1.3 Hz, 1H, H3), 8.16 (td, 3J ) 7.9 Hz, 4J
3
3
4
) 2.7 Hz, 1H, H4), 7.82 (ddd, J ) 7.9 Hz, J ) 5.1 Hz, J )
1.3 Hz, 1H, H5), 7.75 (d, 3J ) 7.5 Hz, 2H, Harom. Ts), 7.51 (d, 3J
) 7.5 Hz, 2H, Harom. Ts), 7.07- 6.71 (m, 10H, Ph), 5.67 (d, 3J )
9 Hz, 1H, H5′), 5.05 (d, 3J ) 9 Hz, 1H, H4′), 2.55 (s, 3H, Me
Ts), 0.28 (s, 3H, Pd-Me). 2d : 1H NMR (400 MHz, CDCl3, rt):
δ 9.27 (ddd, 3J ) 5.1 Hz, 4J ) 1.7 Hz, 5J ) 0.8 Hz, 1H, H6),
5
8.32 (ddd, 3J ) 7.9 Hz, 4J ) 1.2 Hz, J ) 0.8 Hz, 1H, H3), 8.15
3
4
3
(dt, J ) 7.9 Hz, J ) 1.7 Hz, 1H, H4), 7.83 (ddd, J ) 7.9 Hz,
3J ) 5.1 Hz, 4J ) 1.2 Hz, 1H, H5), 7.24-6.69 (m, 10H, Ph),
6.11 (s, 2H, H4′+ H5′), 0.45 (s, 3H, Pd-Me).
(33) Collaborative Computational Project, Number 4. Acta Crystal-
logr. Sect. D 1994, 50, 760.
(34) Sheldrick, G. M. SHELXS-86, Program for Structure Solution.
Acta Crystallogr. 1990, A46, 467.
(31) Bahr, S. R.; Boudjouk, P. J . J . Org. Chem. 1992, 57, 5545.
(32) Chatt, J .; Vallarino, L. M.; Venanzi, L. M. J . Chem. Soc. 1957,
3413.

Reactivity of Palladium-Methyl Complexes
Organometallics, Vol. 21, No. 26, 2002 5829
[P d (COMe)(CO)(1b )][P F 6] (7b ). 1H NMR (400 MHz,
Ta ble 5. Cr ysta l Da ta a n d Deta ils of Str u ctu r e
3
273 K, CD2Cl2): δ 8.63 (d, J ) 4.9 Hz, 1H, H6), 8.23 (m, 2H,
Refin em en ts for Com p ou n d s 2b′ a n d 2d
3
3
H3 + H4), 7.89 (dd, J ) 6.4 Hz, J ) 4.9 Hz, 1H, H5), 7.37-
2b′‚CDCl3
2d
6.86 (m, 15H, Ph), 5.54 (d, J ) 12.7 Hz, 1H, H5′ or H4′), 5.47
3
formula
fw
C28H23DCl5N3Pd C22H19ClF3N3O2PdS
(d, 3J ) 12.7 Hz, 1H, H4′ or H5′), 5.29 (d, 3J ) 17.1 Hz, 1H,
686.15
588.31
3
CH2), 4.50 (d, J ) 17.1 Hz, 1H, CH2), 1.67 (s, 3H, Pd-COMe).
temp, K
cryst syst
space group
a, Å
b, Å
c, Å
150(2)
298(2)
13C NMR (100.5 MHz, 273 K, CD2Cl2): δ 174.3 (s, Pd-CO),
212.5 (s, Pd-COMe).
monoclinic
P21/c (No. 14)
13.186(3)
12.405(3)
17.813(5)
105.01(2)
2814.3(12)
4
monoclinic
P21/c (No. 14)
10.698(3)
10.368(4)
21.206(5)
99.84(2)
2317.5(12)
4
[P d (COMe)(CO)(1c)][P F 6] (7c). Ratio of isomers in
CD2Cl2 M:m ) 4.2:1. 1H NMR (400 MHz, 183 K, CD2Cl2): δ
8.64 (br), 8.36 (br), 8 (br), 7.65-6.31 (br), 5.76 (d, 3J ) 9.6 Hz,
H5′ or H4′), 5.08 (d, 3J ) 9.6 Hz, H4′ or H5′), 2.74 (s, Pd-COMem),
2.48 (s, Me), 1.41 (s, Pd-COMeM). 13C NMR (100.5 MHz,
183 K, CD2Cl2): δ 170.7 (s, Pd-COm), 172.4 (s, Pd-COM), 211
(s, Pd-COMeM), 217.1 (s, Pd-COMem).
[P d (COMe)(CO)(1d )][P F 6] (7d ). Ratio of isomers in
CD2Cl2 M:m ) 1.7:1. 1H NMR (400 MHz, 183 K, CD2Cl2): δ
8.67-6.21 (br), 2.76 (s, Pd-COMeM), 1.53 (s, Pd-COMem). 13C
NMR (100.5 MHz, 183 K, CD2Cl2): δ 170.3 (s, Pd-COM), 171.7
(s, Pd-COm), 210.2 (s, Pd-C(O)Mem), 216.4 (s, Pd-COMeM).
[P d (COMe)(CO)(1b )][BAr ′4] (8b ). 1H NMR (400 MHz,
â, deg
V, Å3
Z
density (calcd), g cm-3 1.619
1.686
1.055
1176
µ(Mo KR), mm-1
F(000)
1.158
1376
ϑ range for data
collection
2.38-28.62
2.19-29.06
no. reflns collected/
unique
R(int)
refinement method
no. of reflns I > 2σ(I)
no. of params
goodness-of-fit
13441/6978
0.0565
11040/5719
0.0547
full-matrix least-squares on F2
3
3
193 K, CD2Cl2): δ 8.49 (d, J ) 5.2 Hz, 1H, H6), 8.07 (t, J )
4790
335
1.034
3296
299
1.032
7.7 Hz, 1H, H4), 7.98 (d, 3J ) 7.7 Hz, 1H, H3), 7.72 (s, 8H,
BAr′
5
HBAr′ ), 7.35 (s, 4H, H
), 7.33-6.64 (m, 16H, H + Ph), 5.59
4
4
(d, J ) 13 Hz, 1H, H5′ or H4′), 5.45 (d, J ) 13 Hz, 1H, H5′ or
H4′), 5.23 (d, 3J ) 17.6 Hz, 1H, CH2), 4.47 (d, 3J ) 17.6 Hz,
1H, CH2), 1.50 (s, 3H, Pd-COMe).
3
3
R1 (Fo)
0.0424
0.1035
0.531, -0.639
0.0509
0.1319
0.713, -0.803
2
wR2 (Fo
)
residuals, e Å-3
[P d (COMe)(CO)(1d )][BAr ′4] (8d ). Ratio of isomers in
method based on F2 with all observed reflections.35 Anisotropic
temperature factors for all non-H atoms of the two complexes
were used. In 2b′ the methyl ligand was partially exchanged
by a chlorine atom, and the site was refined with a mixed Cl/C
species (any attempt to refine two separate peaks was unsat-
isfactory). Since the relative occupancies indicate a slight
excess of the chlorine, 0.53/0.47, the compound is reported as
a dichloro species. Moreover, a CDCl3 solvent molecule was
located in the difference Fourier map. The contribution of the
hydrogen atoms (excluding those of the disordered methyl) was
included at calculated positions in the final cycles of refine-
ments. All the calculations were performed using the WinGX
System, Ver 1.64.03.36
CD2Cl2 M:m ) 1.2:1. 1H NMR (400 MHz, 193 K, CD2Cl2): δ
BAr′
8.50-7.90 (br), 7.71 (s, HBAr′ ), 7.52 (s, H
), 7.44-5.96 (br),
4
4
2.72 (s, 3H, Pd-COMem), 1.50 (s, 3H, Pd-COMeM).
Syn th esis of [P d (COMe)(CO)(1a )][P F 6] (7a ). 3a was
dissolved in the minimum amount of dichloromethane, and
the solution was cooled to 273 K. CO was bubbled through
the solution for 20 min, and the color changed from light to
bright yellow. Addition of diethyl ether at room temperature
resulted in the precipitation of the desired complex as a light
yellow solid. Yield: 70%. Anal. Calcd for C23H20F6N3O2PPd:
C, 44.43; H, 3.24; N, 6.75. Found: C, 43.56; H, 3.62; N, 6.5.
1H NMR (400 MHz, CD2Cl2, rt): δ 8.50 (d, 3J ) 5.2 Hz, 1H,
H6), 8.33 (m, 2H, H3 and H4), 7.85 (m, 1H, H5), 7.52 (s, 1H,
Rea ctivity of th e Com p lexes [P d (Me)(NCMe)(N-N′)]-
[P F 6] (3a -3d ) a n d [P d (Me)(NCMe)(N-N′)][BAr ′4] (4b, 4d )
w ith Ca r bon Mon oxid e. The reactivity of all the complexes
[Pd(Me)(NCMe)(N-N′)][PF6] (3a -3d ) and [Pd(Me)(NCMe)-
(N-N′)][BAr′4] (4b, 4d ) with carbon monoxide was studied in
situ by 1H and 13C NMR spectroscopy. CD2Cl2 (0.7 mL) was
placed in a NMR tube charged with the complex (7 × 10-3
mmol). The solution was cooled at 273 K and CO was bubbled
for 5 min. The NMR sample was placed in a precooled NMR
probe, and spectra were obtained after 15 min.
3
Ph), 7.13-6.89 (m, 9H, Ph), 5.84 (d, 1H, J ) 12.2 Hz, H5′ or
H4′), 5.49 (d, 1H, 3J ) 12.2 Hz, H4′ or H5′), 1.74 (s, 3H, Pd-
COMe).
Ack n ow led gm en t. We thank the Spanish Mini-
sterio de Ciencia y Tecnolog´ıa for financial support
(MCYT BQU2001-0656 and 2FD97-1565) and for award-
ing a research grant (to A.B.) and the COST D17 Action
for a research stay at the University of Trieste (to A.B.).
[P d (COMe)(CO)(1a )][P F 6] (7a ). 1H NMR (400 MHz,
273 K, CD2Cl2): see synthesis of the complex. 13C NMR
(100.5 MHz, CD2Cl2): δ 174.3 (s, Pd-CO), 210.8 (s, Pd-COMe).
Su p p or tin g In for m a tion Ava ila ble: This material is
available free of charge via the Internet at http://pubs.acs.org.
(35) Sheldrick, G. M. SHELXL-97, Program for crystal structure
refinement; University of Go¨ttingen: Germany, 1997.
(36) Farrugia, L. J . J . Appl. Crystallogr. 1999, 32, 837.
OM020568B