Cyclopalladation of 6-substituted-2,2′-bipyridines. Metalation of unactivated methyl groups vs aromatic C-H activation

Article abstract of DOI:10.1021/om000239o

6-Alkyl-2,2′-bipyridines, HL, (N₂C₁₀H₇R;R = CH₂Me, HL^et.; CHMe₂, HL^ip.; CMe₃, HL^tb, CH₂CMe₃, HL^np, CMe₂Ph, HL^dm) react with Na₂[PdCl₄] to give either 1:1 adducts [Pd(HL)Cl₂] (HL^et, HL^ip, HL^np) or cyclometalated complexes [Pd(L)Cl] (HL^tb, HL^dm). Reaction of palladium(II) acetate, followed by exchange with LiCl, affords a series of cyclopalladated species [Pd(L)Cl] where L is a terdentate anionic N-N-C ligand which originates from HL through direct activation of a C(sp³)-H or a C(sp²)-H bond. The structures of [Pd(L^tb)Cl] and [Pd(L^np)Cl], which contain a [5,5] or a [5,6] fused ring system, respectively, have been determined by X-ray diffraction and are compared. In the case of the ligand HL^ip, three different cyclometalated species have been isolated, [Pd(L)Cl], [Pd(L)Cl]₂, and [Pd{N₂C₁₀H₇[CH(CH₂OC(O)CH₃) (CH₂)]}Cl], the latter one arising from activation of both methyl groups of the substituent. The isolation of two [Pd(L^dm)Cl] species (compounds 8 and 9), having an aromatic or an aliphatic carbon-metal bond, respectively, is an example of isomerism, still rare in organometallic chemistry.

Full text of DOI:10.1021/om000239o

Organometallics 2000, 19, 4295-4304
4295
Cyclop a lla d a tion of 6-Su bstitu ted -2,2′-bip yr id in es.
Meta la tion of Un a ctiva ted Meth yl Gr ou p s vs Ar om a tic
C-H Activa tion
Antonio Zucca, Maria Agostina Cinellu, Maria Vittoria Pinna,
Sergio Stoccoro, and Giovanni Minghetti*,†
Dipartimento di Chimica, Universita` di Sassari, Via Vienna 2, I-07100 Sassari, Italy
Mario Manassero*,‡ and Mirella Sansoni
Dipartimento di Chimica Strutturale e Stereochimica Inorganica, Universita` di Milano,
Centro CNR, Via Venezian 21, I-20133 Milano, Italy
Received March 17, 2000
6-Alkyl-2,2′-bipyridines, HL, (N2C10H7R; R ) CH2Me, HLet; CHMe2, HLip; CMe3, HLtb, CH2-
CMe3, HLnp, CMe2Ph, HLdm) react with Na2[PdCl4] to give either 1:1 adducts [Pd(HL)Cl2]
(HLet, HLip, HLnp) or cyclometalated complexes [Pd(L)Cl] (HLtb, HLdm). Reaction of palladium-
(II) acetate, followed by exchange with LiCl, affords a series of cyclopalladated species [Pd-
(L)Cl] where L is a terdentate anionic N-N-C ligand which originates from HL through
direct activation of a C(sp3)-H or a C(sp2)-H bond. The structures of [Pd(Ltb)Cl] and [Pd-
(Lnp)Cl], which contain a [5,5] or a [5,6] fused ring system, respectively, have been determined
by X-ray diffraction and are compared. In the case of the ligand HLip, three different
cyclometalated species have been isolated, [Pd(L)Cl], [Pd(L)Cl]2, and [Pd{N2C10H7[CH(CH2-
OC(O)CH3)(CH2)]}Cl], the latter one arising from activation of both methyl groups of the
substituent. The isolation of two [Pd(Ldm)Cl] species (compounds 8 and 9), having an aromatic
or an aliphatic carbon-metal bond, respectively, is an example of isomerism, still rare in
organometallic chemistry.
In tr od u ction
In this paper we report the synthesis of new adducts
and metalated species of palladium, the latter having
both M-CH2 and M-Ar bonds, and show that the
nature of the substituent on the 2,2′-bipyridine is crucial
in driving the reactivity of the ligand, often in unpre-
Cyclopalladation of N donor ligands has been studied
for many years:1 it is a common belief that five-
membered rings and activation of C(sp2)-H bonds are
preferred.1,2 Accordingly, very many species having
Caromatic-metal bonds and five-membered rings can be
found in the literature. Although a number of deriva-
tives containing nitrogen ligands and C(sp3)-Pd bonds
are known, those derived from activation of simple
alkyls to give Pd-CH2 bonds are still a minority.2b,3
Recently there has been an increasing interest in
species containing terdentate anionic ligands, the se-
quence of donor atoms being either N-N-C4 or N-C-
N,5 owing to their potential in several fields. Their
properties have often been compared with those of the
classical N,N,N coordination species.
(3) (a) Vicente, J .; Chicote, M. T.; Rubio, C.; Ramirez de Arellano,
M. C.; J ones, P. G. Organometallics 1999, 18, 2750. (b) Sokolov, V. I.;
Sorokina, T. A.; Troitskaya, L. L.; Solovieva, L. I.; Reutov, O. A. J .
Organomet. Chem. 1972, 36, 389. (c) Constable, A. G.; McDonald, W.
S.; Sawkins, L. C.; Shaw, B. L. J . Chem. Soc., Dalton Trans. 1980,
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J . Organomet. Chem. 1981, 205, 117. (f) Fuchita, Y.; Hiraki, K.;
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Hiraki, K.; Matsumoto, Y. J . Organomet. Chem. 1985, 280, C51. (h)
Baldwin, J . E.; J ones, R. H.; Najera, C.; Yus, M. Tetrahedron 1985, 41
(4), 699. (i) Fuchita, Y.; Nakashima, M.; Hiraki, K.; Kawatani, M. J .
Chem. Soc., Dalton Trans. 1988, 785. 1988, 785. (j) Hiraki, K.;
Nakashima, M.; Uchiyama, T.; Fuchita, Y. J . Organomet. Chem. 1992,
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Chem. 1993, 32, 3675. (l) Nojima, Y.; Nonoyama, M.; Nakajima, K.
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(4) For example: (a) Vila, J . M.; Gayoso, M.; Pereira, M. T.; Lopez
Torres, M.; Fernandez, J . J .; Fernandez, A.; Ortigueira, J . M. J .
Organomet. Chem. 1997, 532, 171. (b) Lai, S. W.; Chan, M. C. W.;
Cheung, K. K.; Che, C. M. Organometallics 1999, 18, 3327. (c) Neve,
F.; Crispini, A.; Campagna, S.; Serroni, S. Inorg. Chem. 1999, 38, 2250.
(5) For example: (a) Cardenas, D. J .; Echavarren, A. M.; Ramirez
de Arellano, M. C. Organometallics 1999, 18, 3337. (b) Kleij, A. W.;
Kleijn, H.; J astrzebski, J . T. B. H.; Spek, A. L.; van Koten, G.
Organometallics 1999, 18, 277. (c) Steenwinkel, P.; Gossage, R. A.; van
Koten, G. Chem. Eur. J . 1998, 4(5), 759. (d) Steenwinkel, P.; Gossage,
R. A.; Maunula, T.; Grove, D. M.; van Koten, G. Chem. Eur. J . 1998,
4 (5), 763. (e) Canty, A. J .; Minchin, N. J .; Skelton, B. W.; White, A. H.
J . Chem. Soc., Dalton Trans. 1987, 1477.
In the last years we have studied the behavior of a
series of 6-substituted 2,2′-bipyridines with Pd(II),6 Pt-
(II),7 Au(III),8 and Rh(III)9 ions and characterized cy-
clometalated species with terdentate N,N,C anions.
† E-mail: mingh@ssmain.uniss.it.
‡ E-mail: m.manassero@csmtbo.mi.cnr.it.
(1) For example: (a) Omae, I. Organometallic Intramolecular-
Coordination Compounds; Elsevier Science Publishers: Amsterdam,
New York, 1986. (b) Dunina, V. V.; Zalevskaya, O. A.; Potapov, V. M.
Russ. Chem. Rev. 1988, 57 (3), 250. (c) Ryabov, A. D. Chem. Rev. 1990,
90, 403.
(2) (a) Crabtree, R. H. Chem. Rev. 1985, 85, 245. (b) Alsters, P. L.;
Engel, P. F.; Hogerheide, M. P.; Copijn, M.; Speck, A. L.; van Koten,
G. Organometallics 1993, 12, 1831.
10.1021/om000239o CCC: $19.00 © 2000 American Chemical Society
Publication on Web 09/09/2000

4296 Organometallics, Vol. 19, No. 21, 2000
Zucca et al.
Ch a r t 1
dictable ways: even subtle differences can play a role
in the outcome of the reaction.
HLet, HLip, and HLtb, should be able to give five-
membered cyclometalated species, and HLnp a less
common six-membered ring. In principle, activation of
a methyl or a phenyl group to give a five- or a
six-membered ring, respectively, should be possible for
Noteworthy is the behavior of HLdm, able to give both
aromatic and aliphatic C-H activation under the same
experimental conditions. In two cases (HLip and HLdm
)
a stereogenic carbon atom, â to the metal atom, is
directly generated by metalation.
The structures of compounds 6 and 7 in the solid state
were solved by X-ray diffraction to compare the five- vs
the six-membered C,N ring. A brief report of part of this
work has been previously given.10
HLdm
.
The behavior of the various ligands toward Pd(II)
salts is summarized in Scheme 1. Striking differences
are observed in their reactivity so that almost each of
them has a peculiar behavior.
The reaction of Na2[PdCl4] with HL in aqueous HCl
(Scheme 1, eq 1) affords adducts or cyclometalated deriv-
atives depending on the ligand. Pure 1:1 adducts [Pd-
(HLet)Cl2] (1), [Pd(HLip)Cl2] (2), and [Pd(HLnp)Cl2] (3)
were obtained in good yields (>85%) both at room temp-
erature and in refluxing conditions. The behavior of
HLtb is different: in this case we were unable to isolate
the adduct. The metalated complex [Pd(Ltb)Cl] (6) was
obtained even at room temperature. The easy C-H
activation of the tert-butyl group has been previously
reported and commented on.9 With the other alkyl-
substituted ligands, HLet, HLip, and HLnp, even at reflux
temperature no cyclometalated complex was obtained.
Compounds 1-3 are characterized by correct elemental
analyses and FAB mass spectra which show the M -
Cl and M - 2Cl peaks. In the 1H NMR spectra the
resonances of the protons on the substituents at C(6),
as well as of H(6′), are strongly deshielded, as usually
observed when a chlorine atom is in proximity of a
proton.12
Different routes were envisaged for the synthesis of
the metalated species [Pd(Let)Cl] (4), [Pd(Lip)Cl] (5), [Pd-
(Ltb)Cl] (6), and [Pd(Lnp)Cl] (7), as shown in Scheme 1.
Apart from compound 6, which can be obtained also
from Na2[PdCl4], the other complexes were achieved
only by reaction of Pd(II)acetate, in refluxing benzene
(4 and 5) or acetic acid (7), followed by treatment with
LiCl in H2O/acetone. Owing to the rather vigorous
conditions, these reactions are quite complex, giving
often a mixture of metalated species, some of which were
identified and will be described below. In the case of
HLet, complex 4 was isolated in very low yield (ca. 2%).
The reaction afforded a mixture of products that have
proved difficult to separate. The amount of 4 that we
isolated in pure form upon a very slow crystallization
was considerably less than the amounts actually formed
during the reaction (ca. 30%). Several attempts to
improve the yield have been carried out, but even
Resu lts a n d Discu ssion
The ligands HL (see Chart 1) were obtained as
previously described.11
Our purpose in this study was to evaluate the influ-
ence of the substituents on the behavior of the ligands:
(6) (a) Minghetti, G.; Cinellu, M. A.; Chelucci, G.; Gladiali, S.;
Demartin, F.; Manassero, M. J . Organomet. Chem. 1986, 307, 107. (b)
Minghetti, G.; Cinellu, M. A.; Stoccoro, S.; Zucca, A. Gazz. Chim. Ital.
1992, 122, 455.
(7) (a) Minghetti, G.; Zucca, A.; Stoccoro, S.; Cinellu, M. A.; Manas-
sero, M.; Sansoni, M. J . Organomet. Chem. 1994, 481, 195. (b)
Minghetti, G.; Cinellu, M. A.; Stoccoro, S.; Zucca A.; Manassero, M. J .
Chem. Soc., Dalton Trans. 1995, 777.
(8) (a) Cinellu, M. A.; Zucca, A.; Stoccoro, S.; Minghetti, G.; Manas-
sero, M.; Sansoni, M. J . Chem. Soc., Dalton Trans. 1995, 2865. (b)
Cinellu, M. A.; Zucca, A.; Stoccoro, S.; Minghetti, G.; Manassero, M.;
Sansoni, M. J . Chem. Soc., Dalton Trans. 1996, 4217.
(9) Zucca, A.; Stoccoro, S.; Cinellu, M. A.; Minghetti, G.; Manassero,
M. J . Chem. Soc., Dalton Trans. 1999, 3431.
(11) (a) Azzena, U.; Chelucci, G.; Delogu, G.; Gladiali, S.; Marchetti,
M.; Soccolini, F.; Botteghi, C. Gazz. Chim. Ital. 1986, 116, 307. (b)
Botteghi, C.; Chelucci, G.; Chessa, G.; Delogu, G.; Gladiali, S.; Soccolini,
F. J . Organomet. Chem. 1986, 304, 217.
(10) Stoccoro, S.; Chelucci, G.; Cinellu, M. A.; Zucca, A.; Minghetti,
G. J . Organomet. Chem. 1993, 450, C15.
(12) Byers, P. K.; Canty, A. J . Organometallics 1990, 9, 210.

Cyclopalladation of 6-Substituted-2,2′-bipyridines
Organometallics, Vol. 19, No. 21, 2000 4297
Sch em e 1a
a
(i) H2O/HCl, rt or ∆, see text; (ii) (a) benzene, ∆; (b) H2O/acetone, LiCl; (iii) (a) CH3COOH, rt; (b) H2O/acetone, LiCl.
reaction of the adduct 1 with sodium acetate in refluxing
methanol was unsuccessful, despite the easy conversion
of 2 into the metalated compound 5 under the same
conditions.
which are, on the contrary, strongly shielded (∆δ ) ca.
0.4-0.5 ppm). Complexes having a stereogenic carbon
atom arising from metalation are not unprecedented but
are still rare.3a,b,9,13
In this context it is worth noting that in some cases
the reaction can be reversed, as shown by the conversion
of the metalated compound 7 into the adduct 3 in
aqueous HCl (see Experimental Section). This can
account for the unsuccessful isolation of 7 under condi-
tions i in Scheme 1.
Two of these complexes, 6 and 7, have been studied
in depth and fully characterized both in solution, by 1H,
1
13C, 2D COSY, and H-13C HETCOR NMR experiments
(Table 2), and in the solid state by an X-ray diffraction
study, to compare in detail a five-membered with a six-
membered cyclometalated ring.
The metalation in compounds 5-7 is easily confirmed
The structure of 6 consists of the packing of three
crystallographically independent [Pd(Ltb)Cl] molecules
(labeled molecules A, B, and C, respectively) in the
asymmetric unit of space group P1h. Principal bond
lengths and angles for the three molecules are reported
in Table 3. An ORTEP14 view of molecule A is shown in
1
by the H and 13C NMR spectra, which give unambigu-
ous evidence for the presence of a metalated CH2 group
(see Table 1). The H(6′) proton is strongly deshielded
only in compound 7 (∆δ ca. 0.5 ppm), having a [5,6]
fused ring system: in compounds 4-6, the resonances
are slightly deshielded (∆δ ca. 0.1-0.2 ppm). In complex
5, because of the stereogenic carbon the hydrogen atoms
of the M-CH2 group are diastereotopic (δ 2.43 dd, 2.90
dd). In the aromatic region all the signals are deshielded
with respect to the free ligands except for H(3) and H(3′),
(13) (a) Sokolov, V. I.; Troitskaya, L. L.; Reutov, O. A. J . Organomet.
Chem. 1979, 182, 537. (b) Spencer, J .; Maassarani, F.; Pfeffer, M.;
DeCian, A.; Fisher, J . Tetrahedron: Asymmetry 1994, 353. (c) Pfeffer,
M. Inorg. Synth. 1989, 26, 213. (d) Sokolov, V. I. J . Organomet. Chem.
1995, 500, 299.

4298 Organometallics, Vol. 19, No. 21, 2000
Ta ble 1. P r oton a n d 31P NMR Da ta a
Zucca et al.
compound
CH3
CH2
CH
H(6′)
other aromatics
7.37-8.12 [m, 6H]
31P
[Pd(HLet)Cl2]
1
2
3
4
1.42 [t, 3H] (7.6)
1.32 [d, 6H] (6.9)
1.07 [s, 9H]
3.66 [q, 2H] (7.6)
9.28 [dd, 1H]
[Pd(HLip)Cl2]
[Pd(HLnp)Cl2]
[Pd(Let)Cl]
4.63 [m, 1H] (6.9) 9.19 [ddd, 1H] 7.37-8.21 [m, 6H]
9.22 [dd, 1H] 7.35-8.15 [m, 6H]
3.84 [s, 2H]
2.79 [t, 2H] (6.6)
3.25 [t, 2H] (6.6)
8.80 [ddd, 1H] 7.42-8.02 [m, 6H]
[Pd(Lip)Cl]
5
1.41 [d, 3H] (7.1) 2.43 [dd, 1H] (6.1, 9.8) 3.43 [m, 1H]
2.90 [dd, 1H] (6.9, 9.8)
1.43 [s, 6H]
1.06 [s, 6H]
8.78 [ddd, 1H] 7.35-8.05 [m, 6H]
[Pd(Ltb)Cl]
[Pd(Lnp)Cl]
6
7
2.53 [s, 2H]
2.22 [s, 2H]
2.94 [s, 2H]
8.75 [dm, 1H]
9.22 [d, 1H]
7.25-8.01 [m, 6H]
7.35-8.05 [m, 6H]
[Pd(Ldm)Cl] (Csp -Pd)
8
9
2.15 [s, 6H]
1.89 [s, 3H]
9.27 [ddd, 1H] 6.84-8.05 [m, 6H]
8.90 [dt, 1H] 6.96-8.02 [m, 6H]
2
[Pd(Ldm)Cl] (Csp -Pd)
2.86 [1H] (9.8)
3.12 [1H] (9.8)
3
[Pd{C10H7N2CH-
12
2.06 [s, 3H]
2.47 [1H] (4.6, 10.3)
2.77 [1H] (7.1, 10.3)
4.33 [1H] (7.7, 11.1)
4.38 [1H] (5.9, 11.1)
2.16 [d, 2H] {4.4}
2.06, 2.64
3.55 m [1H]
8.80 [ddd, 1H] 7.46-8.05 [m, 6H]
[CH2OC(O)CH3]CH2}Cl]
[Pd(Ltb)(PPh3)][BF4]
14
15
1.38 [s, 6H]
1.32 [s, 12H]
7.11-8.66 [m, 22H] 34.00
7.18-8.35 [m, 34H] 28.77
[Pd2(Ltb)2(µ-dppe)][BF4]2
a
Spectra recorded at room temperature in CDCl3, chemical shifts in ppm from internal TMS (1H) and external 85% H3PO4 31P);
(
coupling constants are given in hertz: J (H-H) in parentheses, J (P-H) in curly brackets; s ) singlet, d ) doublet, br ) broad, m )
multiplet, dd ) double doublet, t ) triplet.
Ta ble 2. P r oton a n d 13C NMR Da ta for HLtb, HLn p
6, a n d 7a
,
Ta ble 3. P r in cip a l Bon d Dista n ces (Å) a n d An gles
(d eg) w ith Esd ’s in P a r en th eses for th e Th r ee
In d ep en d en t Molecu les of Com p ou n d 6, [P d (Ltb)Cl]
HLtb
Pd(Ltb)Cl, 6
HLnp
Pd(Lnp)Cl, 7
molecule A
molecule B
molecule C
1H CH3
CH2-Pd
1.43 s
1.43 s
2.53 s
1.01 s
1.06 s
2.25 s
2.94 s
9.22 ddd
7.53 m
7.95 overlap
8.03 dd
7.95 dd
7.93 t
7.39 dd
28.9
Pd-Cl
2.321(1)
2.155(2)
1.962(2)
2.003(3)
2.306(1)
2.147(2)
1.967(2)
2.012(3)
2.308(1)
2.135(2)
1.968(2)
2.021(3)
CH2
H(6′)
H(5′)
H(4′)
H(3′)
2.76 s
8.66 ddd
7.27 m
7.79 td
8.44 dt
8.22 dd
7.69 t
Pd-N(1)
Pd-N(2)
Pd-C(12)
8.66 ddd
7.28 m
7.81 td
8.54 dt
8.21 dd
7.74 t
8.75 ddd
7.58 m
8.08 td
8.02 dt
7.86 dd
7.95 t
7.28 dd
31.1,
34.9
Cl-Pd-N(1)
Cl-Pd-N(2)
Cl-Pd-C(12)
N(1)-Pd-N(2)
N(1)-Pd-C(12)
N(2)-Pd-C(12)
100.2(1)
176.2(1)
97.6(1)
79.3(1)
161.9(1)
82.8(8)
101.1(1)
178.5(1)
97.2(1)
78.9(1)
161.1(1)
82.7(1)
99.5(1)
176.9(1)
98.6(1)
78.9(1)
161.6(1)
82.9(1)
H(3)
H(4)
H(5)
7.36 dd
30.2
7.11 dd
29.65
13C CH3
CH2-Pd
CH2
32.8
54.9
32.9
51.9
32.0
C(CH3)3
C(6′)
C(5′)
C(4′)
C(3′)
C(3)
C(4)
C(5)
C(6)
148.8
123.3
136.6
121.0
117.5
136.9
118.9
168.3
149.1
127.0
138.9
121.6
119.5
138.1
123.2
177.5
149.0
123.4
136.8
121.2
118.0
136.4
124.6
159.7
149.3
126.1
138.3
121.1
119.6
138.0
127.8
161.5
C(2), C(2′) 154.3, 156.7 154.7, 153.3 155.0, 156.8 153.2, 156.5
a
Assignments based on 1H-1H COSY and 1H-13C HETCOR
experiments, room temperature, solvent CDCl3, chemical shifts
in ppm from internal TMS.
Figure 1. As can be seen in Table 3, bond parameters
for molecules A, B, and C are all very similar, although
not always statistically equal. This fact is principally
due to the very low values of single esd’s. The same
similarity is present in conformational parameters of
the three molecules and in particular in corresponding
least-squares planes. Thus, in all three molecules the
palladium atom displays a square-planar coordination
with a very slight square-pyramidal distortion, maxi-
mum distances from the corresponding best planes
F igu r e 1. ORTEP view of molecule A in compound 6.
Thermal ellipsoids are drawn at the 30% probability level.
being +0.047(1) Å for Pd and -0.025(2) Å for N(2) in
molecule A, +0.044(1) Å for Pd and -0.038(3) Å for
C(12) in molecule B, and +0.040(1) Å for Pd and
-0.0108 Å for C(12) in molecule C. The Pd-N(1)-C(5)-
C(6)-N(2) pentaatomic ring is quasi planar in all three
molecules, with largest displacements from the corre-
(14) J ohnson, C. K. ORTEP, Report ORNL-5138; Oak Ridge Na-
tional Laboratory: Oak Ridge, TN, 1976.

Cyclopalladation of 6-Substituted-2,2′-bipyridines
Organometallics, Vol. 19, No. 21, 2000 4299
Ta ble 4. Aver a ge Bon d Dista n ces (Å) a n d An gles
Ta ble 5. P r in cip a l Bon d Dista n ces (Å) a n d An gles
(d eg) w ith Esd ’s in P a r en th eses for Com p ou n d 7,
[P d (Ln p )Cl]
(d eg) for Com p lexes [M(Ltb)Cl] (M ) P d , P t)
M ) Pda
M ) Ptb
Pd-Cl
2.314(1)
2.046(2)
Pd-N(1)
2.138(2)
2.022(3)
M-Cl
2.312
2.146
1.966
2.012
2.300
2.114
1.948
2.003
Pd-N(2)
Pd-C(13)
M-N(1)
M-N(2)
M-C(12)
Cl-Pd-N(1)
Cl-Pd-C(13)
N(1)-Pd-C(13)
96.3(1)
88.1(1)
175.6(1)
Cl-Pd-N(2)
N(1)-Pd-N(2)
N(2)-Pd-C(13)
174.4(1)
79.1(1)
96.5(1)
C1-M-N(1)
C1-M-N(2)
C1-M-C(12)
N(1)-M-N(2)
N(1)-M-C(12)
N(2)-M-C(12)
100.3
177.2
97.8
79.0
161.5
82.8
98.6
178.3
97.8
79.9
163.4
83.6
a
b
This work, average of three. Reference 7b, average of two.
sponding best plane of +0.059(2) Å for N(2) and -0.053
Å for C(6) in molecule A, +0.052(2) Å for N(2) and
-0.039(1) Å for Pd in molecule B, and +0.041(2) Å for
N(2) and -0.041(3) Å for C(6) in molecule C. In the Pd-
N(2)-C(10)-C(11)-C(12) pentaatomic ring the quasi
planarity is limited to atoms Pd, N(2), C(10), and C(12),
with atom C(11) displaced from their best plane of
+0.374(3), +0.421(3), and +0.352(3) Å in molecules A,
B, and C, respectively. The two pyridinic rings are
planar and are twisted with respect to each other by
8.8(4)° 3.4(1.1)°, and 7.4(5)° in molecules A, B, and C,
respectively. Since direct comparison of analogous Pt-
(II) and Pd(II) organometallic complexes is still rare,15
Table 4 lists the average bond parameters for the
present complex and for the analogous Pt(II) derivative,
[Pt(Ltb)Cl].7b It is to be noted that the two complexes
are not isomorphous since the Pt(II) derivative crystal-
lizes in monoclinic space group P21/c with two crystal-
lographically independent molecules in the asymmetric
unit. An inspection of Table 4 shows that bond lengths
involving platinum are always shorter than correspond-
ing bond lengths involving palladium, thus suggesting
that the covalent radius of Pt(II) is slightly shorter than
that of Pd(II). The amount of the shortening, averaged
on the M-Cl, M-N, and M-C distances reported in
Table 4, is 0.018 Å. It must be observed that no similar
regularity had been found in previous reports.15,16 The
slight differences between corresponding angles in the
Pd and Pt derivatives (see Table 4) may be due both to
the different corresponding bond lengths and to packing
forces. In the present palladium derivative there are five
rather short Cl‚‚‚‚H contacts, in the range 2.69-2.80
Å, that suggest the possibility of weak intermolecular
hydrogen bonds.
F igu r e 2. ORTEP view of compound 7. Thermal ellipsoids
as in Figure 1.
with a very slight square-pyramidal distortion, maxi-
mum distances from the best plane being +0.034(2) Å
for N(2) and -0.0289(1) Å for Pd. The Pd-N(1)-C(5)-
C(6)-N(2) pentaatomic ring is quasi planar, with maxi-
mum distances from the best plane of +0.053(3) Å for
C(6) and -0.066(2) Å for N(2). The Pd-N(2)-C(10)-
C(11)-C(12)-C(13) six-membered ring is in an irregular
conformation, which does not approach any of the
common ones (chair, boat, or twisted boat). Actually, the
Pd, N(2), C(10), and C(13) atoms are essentially copla-
nar, maximum deviations from their best plane being
+0.018(2) and -0.012(3) Å for N(2) and C(10), respec-
tively, with atoms C(11) and C(12) lying -0.345(3) and
+0.443(3) Å below and above the best plane, respec-
tively. The two pyridinic rings are planar and are
twisted 6.0(6)° with respect to each other. Bond lengths
and angles involving the palladium atom can be com-
pared with the corresponding parameters observed in
compound 6, [Pd(Ltb)Cl]. Thus, the Pd-Cl, Pd-N(1),
and Pd-C bond lengths in the two compounds are very
similar: the three values observed in 7, 2.314(1), 2.138-
(2), and 2.022(3) Å, respectively, are very close to the
average values found in 6, 2.312, 2.146, and 2.012 Å,
respectively. Instead, the Pd-N(2) distance found in 7,
2.046(2) Å, is markedly longer than the average Pd-
N(2) bond length found in 6, 1.966. We can consider the
2.046(2) value found in 7 as the normal one, and the
1.966 Å value found in 6 as imposed by the presence of
the two 5,5 fused rings, which usually display a rather
short “central” metal-ligand distance: compare for
instance 1.948 Å in [Pt(Ltb)Cl],7b 1.976(5) Å in cation
[Au(Ltb)Cl]+,8b and 1.960(4) in [Pd(L)Cl] (HL ) 6 phenyl-
The structure of 7 consists of the packing of [Pd(Lnp)-
Cl] molecules with normal van der Waals contacts (but
see later for a possible weak hydrogen bond). Principal
bond lengths and angles are reported in Table 5. An
ORTEP view of the molecule is shown in Figure 2. The
palladium atom displays a square-planar coordination
(15) (a) McCrindle, R.; Ferguson, G.; McAlees, A.; Arsenault, G. J .;
Gupta, A.; J ennings, M. C. Organometallics 1995, 14, 2741. (b)
McGrindle, R.; Ferguson, G.; Arsenault, G. J .; McAlees, A. J .; Ruhl,
B. L.; Sneddon, D. W. Organometallics 1986, 5, 1171. (c) Ferguson,
G.; Ruhl, B. Acta Crystallogr. C 1984, 40, 2020. (d) McGrindle, R.;
Ferguson, G.; McAlees, A. J .; Parvez, M.; Roberts, P. J . J . Chem. Soc.,
Dalton Trans. 1982, 1699. (e) Del Pra, A.; Zanotti, G.; Bombieri, G.;
Ros, R. Inorg. Chim. Acta 1979, 36, 121.
(16) (a) Wisner, J . M.; Bartczak, T. J .; Ibers, J . A. Organometallics
1986, 5, 2044. (b) Wisner, J . M.; Bartczak, T. J .; Ibers, J . A.; Low, J .
J .; Goddard, W. A. J . Am. Chem. Soc. 1986, 108, 347. (c) Cavell, K. J .;
J in, H.; Skelton, B. W.; White, A. H. J . Chem. Soc., Dalton Trans. 1993,
1973.

4300 Organometallics, Vol. 19, No. 21, 2000
Zucca et al.
Sch em e 2a
a
(i) Na2[PdCl4], H2O/HCl, ∆; (ii) (a) Pd(CH3COO)2, CH3COOH, ∆, (b) acetone/H2O, LiCl; (iii) CH3COOH, reflux temperature.
2,2′-bipyridine).17 With the obvious exception of the
N(1)-Pd-N(2) angle (79.1(1)° in 7 and 79.0° in 6),
angles at the metal atom are different in the two
complexes (see Tables 3 and 5). This is due to the
different bites of the Ltb and Lnp ligands: the former,
which forms a five-membered ring, imposes a N(2)-
Pd-C angle of 82.8°, whereas the latter, which forms a
six-membered ring, imposes a N(2)-Pd-C angle of 96.5-
(1)°. The deviation from the ideal value of 90° is
approximately the same in the two rings, but in differ-
ent directions. As already discussed, this difference in
bond angles does not induce marked differences in the
planarity of the two metal coordination planes. Also in
compound 7 there is the possibility of a weak intermo-
lecular hydrogen bond, suggested by a rather short Cl‚
‚‚H contact of 2.79 Å.
likely to be the different behavior of the two metalated
species toward acetolysis.
In solution complexes 8 and 9 have been studied
1
mainly by means of H NMR spectroscopy. In complex
8, which is likely to adopt a boatlike conformation,6a the
six-membered ring is fluxional, on the NMR time scale,
as shown by the equivalence of the CH3 groups (δ 2.15,
1
s, 6H). The H NMR spectrum of 9, which contains a
stereogenic carbon, shows only one methyl group (δ 1.89
s, 3H), an AB system (CH2) (δA 2.86, δB 3.12, J AB ) 9.8
Hz), and 12 aromatic protons. In the IR spectrum an
absorption at ca. 700 cm-1, not observed in the spectrum
of 8, confirms the presence of a monosubstituted phenyl
ring.
Examples of aliphatic C-H activation preferred to an
aromatic one are extremely rare.2b,18,19 In our case the
two processes also imply five- vs six-member ring
formation, to give [5,5] or [5,6] fused rings, so that
different factors should be taken into account.
“Roll Over ” Meta la tion . As previously mentioned,
the reaction of the alkyl-substituted ligands with pal-
ladium(II) acetate often gives more metalated species
(Scheme 3). Thus the reaction of HLip and HLnp in re-
fluxing benzene, followed by exchange with LiCl, besides
the terdentate-bound species 5 and 7 gives the uncom-
mon metalated compounds [Pd(L)Cl]2 10 and 11, re-
spectively. The compounds arising from activation of the
C(3)-H bond of the substituted pyridine are an example
of “roll over” metalation. As far as we know, only two
complexes of this type, namely, an iridium20 and a
platinum21 derivative, have been previously reported.
The structure of compound 10, solved by X-ray de-
termination, has been recently reported by us.22 The
Alip h a tic vs Ar om a tic Activa tion . Among the
ligands employed, HLdm is peculiar, as both aromatic
and aliphatic C-H activation are possible. Recently we
have reported that aliphatic C-H activation can be
achieved by reaction with RhCl3 to give the octahedral
species [Rh(Ldm)Cl2(CH3CN)].9 In the case of palladium-
2
3
(II) two isomers [Pd(L)Cl] (Csp -Pd), 8, and (Csp -Pd),
9, have been obtained. Compounds 8 and 9 as obtained
from palladium(II) acetate under the same experimental
conditions (see Scheme 2) can be separated taking
advantage of the different solubility in chlorinated
solvents. In our experience species with aromatic C-M
bonds are usually much less soluble in common organic
solvents than those with aliphatic C-M bonds. Com-
pound 8 is converted almost quantitatively into 9 in
refluxing acetic acid. This behavior is reminiscent of the
isomerization of cyclopalladated derivatives of N-mesi-
tylbenzylideneamines described by Sales and co-work-
ers18 as an example of intramolecular exchange reaction.
In acid media the driving force of the isomerization is
(18) Albert, J .; Ceder, R. M.; Gomez, M.; Granell, J .; Sales, J .
Organometallics 1992, 11, 1536.
(19) (a) Cardenas, D. J .; Echavarren, A.; Vegas, A. Organometallics
1994, 13, 882. (b) Albert, J .; Granell, J .; Sales, J .; Solans, X.; Font-
Altaba, M. Organometallics 1986, 5, 2567. (c) Ceder, R. M.; Granell,
J .; Sales, J . J . Organomet. Chem. 1986, 307, C44. (d) De Munno, G.;
Ghedini, M.; Neve, F. Inorg. Chim. Acta 1995, 239, 155.
(17) D. Constable, E. C.; Henney, R. P. G.; Leese, T. A.; Tocher, D.
A. J . Chem. Soc., Chem. Commun. 1990, 513.

Cyclopalladation of 6-Substituted-2,2′-bipyridines
Organometallics, Vol. 19, No. 21, 2000 4301
Sch em e 3a
a
(i) (a) benzene, reflux, (b) H2O/acetone, LiCl; (ii) (a) CH3COOH rt; (b) H2O/acetone, LiCl.
Reaction of 10a and 11a with (18-crown-6)‚HBF4‚H2O
23or HBF4‚Et2O, respectively, gives the cationic species
[Pd(L)(PPh3)Cl]‚HBF4 (L ) HLip, 10b ; HLnp, 11b )
characterized on the basis of spectroscopic (IR and
NMR) and analytical data. The 1H NMR spectra, in
particular, show the presence of a strongly deshielded
NH proton (δ 13.18, 10b broad; 13.06, 11b broad).
Rea ctivity of HLip . In this series of ligands the
behavior of HLip is much more complicated than that
of the other ligands. Indeed by reaction with Pd(II)
acetate three different species were obtained, as re-
ported in Scheme 3, originating from different C-H
activations.
The cyclometalated species 12 was obtained from
palladium acetate, in acetic acid, followed by treatment
with LiCl in H2O/acetone. 1H and 13C NMR spectra show
in the aliphatic region the disappearance of the signals
of the two methyl groups of the isopropylic substituent.
1
The H NMR spectrum shows a complicated situation
consistent with a -CH(CH2X)CH2-Pd system, origi-
nated by a double Caliphatic-H activation. In agreement,
the 13C NMR spectrum shows the presence of one CH,
two CH2, and one CH3 carbon atom (APT experiments).
On the whole, analytical and spectroscopic data are
consistent with the formula [Pd{C10H7N2-[CH(CH2)(CH2-
OC(O)CH3)]}Cl], where a hydrogen atom of a methyl
group has been substituted by an acetato group.24
dimeric compounds 10 and 11 can be split by PPh3 to
give mononuclear species [Pd(L)(PPh3)Cl] (P trans to N),
10a and 11a .
In the attempt to gain insight into the reaction
pathway, we reacted either the adduct or the N,N,C
cyclometalated species with acetic acid or sodium ac-
In the case of HLet a mixture of 4 and [Pd(Let)Cl]2 was
obtained in solution. [Pd(Let)Cl]2 was not isolated, but
in the aromatic region of the 1H NMR spectrum, a
typical AB system indicates roll over metalation.
In the case of HLtb only complex 6 was detected in
solution: this can be due to the strong tendency of HLtb
to give the terdentate-bound cyclometalated species and
to the difficulty of obtaining an adduct likely due to the
presence of the bulky substituent.
1
etate. In both cases the H NMR spectra provided no
evidence of the formation of complex 12. Although
several pathways may be envisaged, the mechanism
likely involves an equilibrium between a cyclometalated
and a hydrido-olefinic species (â-hydrogen transfer), a
nucleophilic attack of an acetato on the olefin, followed
by a second metalation of a methyl group.
R ea ct ivit y of Com p lex 6 w it h CO, P P h 3, a n d
d p p e. The reactivity of complex 6 with CO has been
studied in ethanol solution. Up to 70 °C and 70 atm no
reaction occurs. Only under more severe conditions (100
(20) (a) Nord, G.; Hazell, A. C.; Hazell, R. G.; Farver, O. Inorg. Chem.
1983, 22, 3429. (b) Spellane, P. J .; Watts, R. J .; Curtis, C. J . Inorg.
Chem. 1983, 22, 4060. (c) Braterman, P. S.; Heat, G. H.; Mackenzie,
A. J .; Noble, B. C.; Peacock, R. D.; Yellowlees, L. J . Inorg. Chem. 1984,
23, 3425.
(21) Skapski, A. C.; Sutcliffe, V. F.; Young, G. B. J . Chem. Soc.,
Chem. Commun. 1985, 609.
(22) Minghetti, G.; Doppiu, A.; Zucca, A.; Stoccoro, S.; Cinellu, M.
A.; Manassero, M.; Sansoni, M. Chem. Het. Comput. (Russ. Ed.) 1999,
8, 1127.
(23) Chenevert, R.; Rodrigue, A.; Pigeon-Gosselin, M.; Savoie, R.
Can. J . Chem. 1982, 60, 853.
1
(24) 2D 13C-1H inverse correlation spectra (HMQC for J CH spin
couplings, and HMBC, for long-range C-H correlations): Lucchini,
V. Personal communication.

4302 Organometallics, Vol. 19, No. 21, 2000
Zucca et al.
and 3 mL of 2 M HCl. The mixture was stirred for 16, 1, or 5
h, respectively. The precipitate formed was filtered off and
washed with water, ethanol, and diethyl ether. The crude
obtained was recrystallized from CH2Cl2/Et2O to give the
analytical sample.
atm, 100 °C) is the extrusion of palladium and formation
of two organic species identified via GCMS as the ligand
HLtb (80%) and 3-methyl-3-[6-(2,2′-dipiridyl)]ethylbu-
tanoate, 13 (20%), observed. Compound 13 is an ex-
1: orange, yield 93%, mp 227 °C. Found: C, 40.10; H, 3.54;
N, 7.48 (calcd for C12H12Cl2N2Pd: C, 39.87; H, 3.35; N, 7.75).
FAB mass spectrum: m/z 325 [M - Cl], 290 [M - 2Cl]. IR
(Nujol) νmax/cm-1: 1596 s, 1564 m, 342 s.
2: orange, yield 82%, mp 250 °C. Found: C, 41.38; H, 3.72;
N, 7.18 (calcd for C13H14Cl2N2Pd: C, 41.57; H, 3.76; N, 7.46).
FAB mass spectrum: m/z 339 [M - Cl], 304 [M - 2Cl], 713
[M2 - Cl]. IR (Nujol) νmax /cm-1: 1597 s, 1563 m, 337 s, 303
m.
3: orange-yellow, yield 98%, mp 248 °C (dec). Found: C,
44.65; H, 4.65; N, 7.38 (calcd for C15H18Cl2N2Pd: C, 44.64; H,
4.50; N, 6.94). FAB mass spectrum: m/z 367 [M - Cl], 332 [M
- 2Cl]. IR (Nujol) νmax/cm-1: 1600 s, 1560 w, 340 s.
[P d (Let)Cl], 4. A mixture containing HLet (377.7 mg, 2.05
mmol) and Pd(CH3COO)2 (460.2 mg, 2.05 mmol) in benzene
(50 mL) was refluxed under stirring for 15 h, then filtered and
evaporated to dryness. The crude obtained was treated with
1/3 water/acetone (40 mL) containing an excess of LiCl and
stirred for 4 days, then evaporated to dryness and crystallized
from CH2Cl2. Yield: ca. 2%, mp 223-224 °C (dec). Found: C,
44.02; H, 3.38; N, 8.60 (calcd for C12H11ClN2Pd: C, 44.33; H,
3.41; N, 8.62). FAB mass spectrum: m/z 324 [M+], 289 [M -
Cl].
[P d (Lip )Cl], 5. (a) A mixture containing 2 (50.0 mg, 0.133
mmol) and sodium acetate (12.8 mg) in MeOH (15 mL) was
refluxed for 15 min, then filtered and evaporated to dryness.
The crude obtained was recrystallized from CH2Cl2/Et2O to
give the analytical sample in almost quantitative yield.
(b) [Pd(Lip)Cl] 5 and [Pd(Lip)Cl]2 10: A solution of HLip (297.4
mg, 1.50 mmol) and Pd(CH3COO)2 (336.7, 1.50 mmol) in
benzene (40 mL) was refluxed for 7 h, then filtered, evaporated
to dryness, and treated with 1/3 water/acetone (40 mL)
containing an excess of LiCl. The mixture was stirred for 6
days. The precipitate formed was filtered and crystallized from
CH2Cl2 to give [Pd(Lip)Cl]2, 10, as a yellow solid (yield ca. 25%).
The filtrate consisted of a mixture of compounds 5 and 10 in
a 2/1 ratio (NMR criterion). Pure 5 was obtained by chroma-
tography on a column of silica gel (60 mesh) using a benzene/
acetone mixture (3/2) as eluent.
pected reaction product, likely generated by nucleophilic
attack of an ethylate to an acylic intermediate formed
by insertion of CO into the Pd-C bond. The formation
of the ligand, HLtb, is not unprecedented.25
Reaction of 6 with PPh3 does not require displacement
of the chloride by silver salts, in contrast with the
behavior observed for the cyclometalated species derived
from 6-benzyl-substituted 2,2′-bipyridines but in line
with what is observed for the analogous platinum(II)
derivatives.7b In the presence of BF4-, the cationic
species [Pd(Ltb)(PPh3)]+, 14, was isolated in fairly good
1
yield. In the H NMR spectrum the signals of the H(6)
(hidden by other aromatic signals) and of the CH2-Pd
3
(δ 2.21, J P-H) 29.2 Hz) protons are shielded, as
expected owing to the PPh3 ligand in their proximity.
The reaction of 6 with the potentially bidentate ligand
Ph2P(CH2)2PPh2, dppe, has been investigated in order
to study the robustness of the terdentate ligand. With
a 1/1 Pd/dppe molar ratio an unstable crude product is
formed which turns into complex 15 upon recrystalli-
zation. With the appropriate Pd/dppe ratio (2/1) the
reaction to give complex 15, i.e., a species with bridging
dppe, is straightforward.
Exp er im en ta l Section
5: yield 10%; mp 205 °C (dec). Found: C, 45.71; H, 3.64; N,
8.09 (calcd for C13H13N2ClPd: C, 46.04; H, 3.86; N, 8.26). IR
(Nujol) νmax/cm-1: 1591 s, 1558 m.
The bipyridines HL were prepared according to literature
methods.11 Na2[PdCl4] (29.15% Pd) and Pd(CH3COO)2 (47.4%
Pd) were obtained from J ohnson Matthey and Engelhard,
respectively. All the solvents were purified before use according
to standard methods. Elemental analyses were performed with
a Perkin-Elmer elemental analyzer 240B by Mr. A. Canu
(Dipartimento di Chimica, Universita` di Sassari). Conductivi-
ties were measured with a Philips PW 9505 conductimeter.
The neutral complexes 1-9 and 12 are nonconducting in
acetone. Infrared spectra were recorded with a Perkin-Elmer
983 using Nujol mulls. 1H, 13C{1H}, and 31P{1H} NMR spectra
were recorded with a Varian VXR 300 spectrometer operating
at 299.9, 75.4, and 121.4 MHz, respectively, and are collected
in Tables 1 and 2. Chemical shifts are given in ppm relative
to internal TMS (1H, 13C) and external 85% H3PO4 (31P). The
2D experiments were performed by means of standard pulse
sequences. The mass spectrometric measurements were per-
formed on a VG 7070EQ instrument, equipped with a PDP
11-250J data system and operating under positive ion fast
atom bombardment (FAB) conditions with 3-nitrobenzyl alco-
hol as supporting matrix.
[P d (Ltb)Cl], 6. To a solution of Na2[PdCl4] (365.0 mg, 1.00
mmol) in water (50 mL) were added HLtb (212.3 mg, l.00 mmol)
and 5 mL of 2 M HCl. The mixture was stirred at room
temperature for 3 h. The precipitate formed was filtered off,
washed with water, ethanol, and diethyl ether, and recrystal-
lized from CH2Cl2/Et2O to give the analytical sample as a
yellow solid. Yield: 92%, mp 181 °C. Found: C, 48.08; H, 4.24;
N, 7.55 (calcd for C14H15ClN2Pd: C, 47.62; H, 4.28; N, 7.93).
IR (Nujol) νmax /cm-1: 1600 s, 1560 m.
[P d (Ln p )Cl], 7. To a solution of [Pd(CH3COO)2] (224.5 mg,
1.00 mmol) in acetic acid (25 mL) was added 226.3 mg of HLnp
(1.00 mmol). The solution was stirred at room temperature
for 1 day, then evaporated to dryness and treated with 1/2
water/acetone (30 mL) containing an excess of LiCl. The
suspension was stirred for 3 days. The yellow precipitate
formed was filtered off, washed with diethyl ether, and
recrystallized from CH2Cl2/Et2O to give the analytical sample
as a yellow solid. Yield: 33%, mp 254 °C (dec). Found: C,
48.84; H, 4.51; N, 7.39 (calcd for C15H17ClN2Pd: C, 49.07, H,
4.67, N, 7.63). FAB mass spectrum, m/z: 366 [M+], 331 [M -
Cl]. IR (Nujol) νmax /cm-1: 1600 s, 1560 w, 780 s, 320 s.
Rea ction of 7 w ith HCl. To a suspension of 7 (100.0 mg,
0.272 mmol) in water (10 mL) was added 2 mL of 2 N HCl.
The mixture was refluxed for 5 h, then evaporated to dryness.
P r ep a r a tion s. [P d (HL)Cl2] [HL ) HLet (1), HLip (2),
HLn p (3)]. (a) To a solution of Na2[PdCl4] (365.0 mg, 1.00
mmol) in water (40 mL) were added 1.00 mmol of HL (184.2,
198.3, and 226.3 mg for HLet, HLip, and HLnp, respectively)
(25) Nielson, A. J . J . Chem. Soc., Dalton Trans. 1981, 205.

Cyclopalladation of 6-Substituted-2,2′-bipyridines
Organometallics, Vol. 19, No. 21, 2000 4303
Ta ble 6. Cr ysta llogr a p h ic Da ta
The crude obtained was crystallized from CH2Cl2/Et2O to give
complex 3 in almost quantitative yield (NMR criterion).
6
7
[P d (Ldm )Cl] (Csp -P d ), 8. To a solution of Na2[PdCl4] (1.095
2
formula
M
color
cryst syst
space group
a/Å
b/Å
c/Å
C
353.1
yellow
14H15ClN2Pd
C15H17ClN2Pd
367.2
g, 3.00 mmol) in water (30 mL) were added HLdm (0.823 g,
3.00 mmol) and 10 mL of 2 M HCl. The mixture was heated
in a water bath until the solution was colorless. The yellow
precipitate formed was filtered off, washed with water, ethanol,
and diethyl ether, and recrystallized from CH2Cl2/Et2O to give
the analytical sample as a yellow solid. Yield: 80%, mp 244
°C. Found: C, 55.41; H, 4.54; N, 6.51 (calcd for C19H17ClN2Pd:
C, 54.96; H, 4.13; N, 6.75). FAB mass spectrum, m/z: 414 [M+],
379 [M - Cl]. IR (Nujol) νmax/cm-1: 1592 s, 1563 m, 1552 m,
346 s, 331 s.
yellow
triclinic
P1h (no. 2)
9.289(2)
11.404(2)
20.046(4)
83.81(2)
86.49(2)
87.14(2)
2105.2(8)
293
monoclinic
P21/c (no. 14)
9.104(2)
11.219(1)
14.709(1)
R/deg
â/deg
102.07(2)
γ/deg
U/Å3
1469.1(4)
293
[P d (Ld m )Cl] (Csp -P d ), 9. (a) A suspension of 8 (103.8 mg,
T/K
Z
F(000)
3
6
4
736
1.660
0.25 mmol) in acetic acid (20 mL) was refluxed for 1 h. The
solution obtained was evaporated to dryness. The crude
obtained was crystallized from CH2Cl2/Et2O to give 9 in almost
quantitative yield.
1056
1.671
Dc/g cm-3
crystal dimens/mm
µ(Mo KR)/cm-1
min., max. transmsn
factors
0.34 × 0.39 × 0.45 0.17 × 0.23 × 0.51
14.8
14.2
0.92-1.00
0.89-1.00
(b) To a solution of Pd(CH3COO)2 (112.2 mg, 0.50 mmol) in
acetic acid (10 mL) was added 137.2 mg of HLdm (0.50 mmol)
in the same solvent (3 mL).The mixture was stirred for 20 h.
After addition of water the organometallic compounds were
extracted with CH2Cl2, dried with Na2SO4, neutralized with
K2CO3, filtered, and evaporated to dryness. The crude obtained
was treated with a water/acetone mixture (1/2, 15 mL) and
an excess of LiCl, stirred for 2 day, then evaporated to dryness
and crystallized from CH2Cl2/Et2O. The product obtained was
a mixture of compounds 8 and 9 (ca. 1/1, NMR criterion). Pure
9 (yield 20%) was obtained by extraction with a mixture Et2O/
CH2Cl2 (2/1) and precipitation with Et2O. Mp: 187-189 °C.
Found: C, 53.35 H, 4.11 N, 6.67 (calcd for C19H17ClN2Pd‚0.25
CH2Cl2: C, 52.98; H, 4.04; N, 6.42). FAB mass spectrum, m/z:
scan mode
ω-scan width
θ-range
ω
ω
1.1 + 0.35 tan θ
3-27
reciprocal space explored +h, (k, (l
1.4 + 0.35 tan θ
3-27
+h, +k, (l
3187
no. of measd reflns
no. of unique obsd rflns
with I>3σ(I)
9139
7393
2518
final R and R′ indicesa
no. of variables
0.021, 0.034
487
0.023, 0.030
172
goodness of fitb
1.35
1.45
a
2 1/2
] .
b GOF
R ) [∑(|Fo - k|Fc||)/∑Fo], R′ ) [∑w(Fo - k|Fc|)2/∑wFo
) [∑w(Fo - k|Fc|)2/(No - Nv)]1/2, where w ) 4Fo2/[σ(Fo2)]2. σ(Fo2) )
[σ2(Fo2) + (PFo2)2]1/2, No is the number of observations, Nv is the
number of variables, and P, the ignorance factor, ) 0.04 for 6 and
0.03 for 7.
793 [M2 - Cl], 414 [M+], 379 [M - Cl]. IR (Nujol) νmax/cm-1
1593 s, 1556 m, 702 s, 336 m.
:
[P d (L)(P P h 3)Cl]‚HBF 4 (L ) Lip (10b), Ln p (11b)). To a
solution of the relevant [Pd(L)(PPh3)Cl] (10a , 23.5 mg, 0.039
mmol; 11a , 25.2 mg, 0.04 mmol) in CH2Cl2 (10 mL) was added
under vigorous stirring a 5% excess of 18-crown-6‚HBF4‚H2O.
The solution was stirred for 6 h, then filtered and evaporated
to small volume. The precipitate formed after addition of
diethyl ether was filtered and washed with diethyl ether to
give the analytical sample as a cream solid in almost quantita-
tive yield.
[2M - Cl], 302 [M - Cl-CH3COO]. 13C NMR (CDCl3): δ 19.14
(CH2-Pd), 20.88 (CH3), 54.04 (CH), 66.92 (CH2-O), 119.35,
121.24, 123.81, 126.78, 137.30, 138.57 (aromatic CH), 149.24
(C6′), 153.25, 154.25 (C2, C2′), 170.39, 170.66 (C(2), CO). IR
(Nujol) νmax/cm-1: 1725 s, 1592 s, 1557 w, 328 m.
Rea ction betw een 6 a n d CO. A solution of complex 6 (50.1
mg, 0.142 mmol) in EtOH (30 mL) was placed in a stainless
steel autoclave, pressurized with CO (100 atm), heated at 100
°C, and stirred for 6 h. Metallic palladium was formed. After
filtration, the solution was evaporated to dryness, solubilized
with CH2Cl2, treated with K2CO3, then filtered and evaporated
to dryness. The oil obtained was analyzed by GCMS. Two
products were identificated: HLtb (80%) and 3-methyl-3-[6-
(2,2′-dipiridyl)]ethylbutanoate, 13 (20%). GCMS: HLtb , m/z:
212 (25%, M+), 197 (100%, M - CH3), 155 (40%, M - C(CH3)3).
13, m/z: 284 (10%, M+), 211 (100%, M - CH3CH2OC(O)), 197,
155.
Compounds 11b can be obtained also by reaction of 11a with
HBF4‚Et2O.
10b: mp158-160 °C (dec). Found: C, 52.10 H, 4.13 N, 3.79
(calcd for C31H29BClF4N2PPd‚H2O: C, 52.64; H, 4.39; N, 3.96).
IR (Nujol) νmax/cm-1: 3520 br, 1626 s, 1604 m, 1558 m, 1060
vs br, 331w, 302w. ΛM (5 × 10-4 M, acetone): 122 Ω-1 cm2
mol-1 1H NMR (CDCl3): δ 1.32 (CH3), 3.66 CH-CH3, 6.84
.
(H5), 7.33 (H4), 7.66 (H5′), 8.28 (H4′), 8.82 (H3′), 9.76 (H6′),
7.76 (Hortho), 7.45 (Hmeta), 7.55 (Hpara), 13.18, broad (NH). 31P
NMR (CDCl3): δ 42.03.
[P d (Ltb)(P P h 3) ][BF 4], 14. To a solution of 6 (50.2 mg, 0.142
mmol) in acetone (15 mL) was added under vigorous stirring
42.0 mg of PPh3 (0.16 mmol). To the resulting colorless solution
was added 100 mg of NaBF4, and the mixture was stirred for
1 h, then evaporated to dryness and the residue crystallized
from CH2Cl2/Et2O to give the analytical sample as a white
solid. Yield: 82%, mp 254-257 °C. Found: C, 57.30; H, 4.67;
N, 4.28 (calcd for C32H30BF4N2PPd: C, 57.64; H, 4.53; N, 4.20).
FAB mass spectrum, m/z: 579 [M+], 317 [M - PPh3]. IR (Nujol)
11b: mp155-160 °C (dec). Found: C, 53.45 H, 4.88 N, 3.68
(calcd for C33H33BClF4N2PPd‚H2O: C, 53.90; H, 4.76; N, 3.68).
IR (Nujol) νmax/cm-1: 3540 s vbr, 1626 s, 1603 m, 1556 m, 1050
s br, 706.s, 693 s, 355 w, 286 w. ΛM (5 × 10-4 M, acetone):
1
116 Ω-1 cm2 mol-1. H NMR (CDCl3): δ 0.96 (CH3), 2.96 CH2,
6.73 (H5), 7.29 (H4), 7.66 (H5′), 8.27 (H4′), 8.78 (H3′), 9.75
(H6′), 7.76 (Hortho), 7.45 (Hmeta), 7.55 (Hpara), 13.06, broad (NH).
31P NMR (CDCl3): δ 41.61.
[P d {C10H7N2CH(CH2OC(O)CH3)CH2}Cl], 12. A solution
of HLip (198.3 mg, 1.00 mmol) and Pd(CH3COO)2 (224.5 mg,
1.00 mmol) in acetic acid (30 mL) was stirred for 4 days at
room temperature, then evaporated to dryness. The crude
obtained was treated with 1/2 water/acetone (30 mL) contain-
ing an excess of LiCl and stirred for 3 days, then evaporated
to dryness and crystallized from CH2Cl2/Et2O to give the
analytical product. Yield: 45%, mp 174 °C (dec). Found: C,
44.98; H, 3.65; N, 6.93 (calcd for C15H15ClN2O2Pd: C, 45.36;
H, 3.81; N, 7.05). FAB mass spectrum m/z: 361 [M - Cl] 757
ν
max/cm-1: 1594 s, 1561 m, 1060 vs (br), 697 s. ΛM (5 × 10-4
M, acetone): 156 Ω-1 cm2 mol-1
.
[P d 2(Ltb)2(µ-d p p e)][BF 4]2, 15. To a solution of 6 (176.6 mg,
0.50 mmol) in acetone (20 mL) were added under vigorous
stirring 99.6 mg of dppe (0.25 mmol) and 200 mg of NaBF4.
The mixture was stirred for 1 h, then evaporated to dryness
and the residue recrystallized from CH2Cl2/Et2O to give the
analytical sample as a white solid. Yield: 80%, mp > 280 °C.
Found: C, 54.16; H, 4.85; N, 4.51 (calcd for C54H54B2F8N4P2-

4304 Organometallics, Vol. 19, No. 21, 2000
Zucca et al.
Pd2: C, 53.72; H, 4.51; N, 4.64). IR (Nujol) νmax/cm-1: 1594 s,
1565 m, 1060 vs (br), 699 s. ΛM (5 × 10-4 M, acetone): 280
The structures were solved by Patterson and Fourier
methods and refined by full-matrix least-squares, minimizing
the function ∑w(Fo - k|Fc|)2. Anisotropic thermal factors were
refined for all the non-hydrogen atoms of both 6 and 7. All
the hydrogen atoms were placed in their ideal positions (C-H
) 0.97 Å, B 1.15 times that of the carbon atom to which they
are attached) and not refined. The final Fourier maps showed
maximum residuals of 0.33(5) e Å-3 at 0.90 Å from PdA in 6
and 0.78(6) e Å-3 at 1.41 Å from Cl in 7. The atomic coordinates
of the structure models have been deposited with the CCDC.
Ω-1 cm2 mol-1
.
X-r a y Da ta Collection s a n d Str u ctu r e Deter m in a tion s.
Crystal data and other experimental details are summarized
in Table 6. Crystals of 6 and 7 were mounted on an Enraf-
Nonius CAD-4 diffractometer at room temperature using Mo
KR radiation (λ ) 0.71073 Å) with a graphite crystal mono-
chromator in the incident beam. Cell parameters and orienta-
tion matrixes were obtained from the least-squares refinement
of 25 reflections in the range 2° < θ < 23°. A periodic
monitoring of the three standard reflections did not reveal any
crystal decay for either 6 or 7. The diffracted intensities were
corrected for Lorentz, polarization, and absorption effects
(empirical correction).26 The calculations were performed on
an AST Power Premium 486/33 computer using the Personal
Structure Determination Package27 and the physical constants
tabulated therein. Scattering factors and anomalous dispersion
corrections were taken from ref 28.
Ack n ow led gm en t. Financial support from Minis-
tero dell’Universita` e della Ricerca Scientifica e Tecno-
logica (MURST, 40% and 60%) and Consiglio Nazionale
delle Ricerche (CNR) is gratefully acknowledged. We
thank Prof. Vittorio Lucchini (University of Venezia) for
assistance and discussion of some NMR experiments.24
Su p p or tin g In for m a tion Ava ila ble: X-ray structural
information on compounds 6 and 7. This material is available
free of charge via the Internet at http://pubs.acs.org.
(26) North, A. C. T.; Phillips, D. C.; Mathews, F. S. Acta Crystallogr.
Sect. A 1968, 24, 351.
(27) Frenz, B. A. Comput. Phys. 1988, 2, 42. (b) Frenz, B. A.
Crystallographic Computing 5; Oxford University Press: Oxford, U.K.,
1991; Chapter 11, p 126.
OM000239O
(28) International Tables for X-ray Crystallography; Kynoch Press:
Birmingham, 1974; Vol. 4.