Neutral and cationic palladium(II) complexes of a diazapyridinophane. Structure, fluxionality, and reactivity toward ethylene

Article abstract of DOI:10.1021/om010475e

The palladium complexes (t-Bu-N₄)PdCl₂ (1), (t-Bu-N₄)PdMeCl (2), (t-Bu-N₄)PdMe(NCMe)₊- BAr₄^- (3), and (t-Bu-N₄)PdMe(C₂ H₄)⁺BAr₄^- (4) [t-Bu-N₄ = N,N′-ditertiobutyl-2,11-diaza[3.3]-(2,6)pyridinophane, Ar = 3,5-(CF₃)₂-C₆H₃] have been synthesized and characterized by VT ¹H NMR and X-ray (for 1 and 3) analysis. The macrocyclic ligand is only bi- or tridentate, both coordination modes coexisting in solution for 1 and 3. Cationic methyl-ethylene complex 4 decomposes readily through insertion of ethylene into the Pd-Me bond, and ethylene polymerization with use of 1 (in the presence of MAO) or 3 as catalysts is therefore precluded. Complexes, 1, 3, and 4 are fluxional, the t-Bu-N₄ ligand undergoing an η²-η³ oscillatory process (ΔG? = 14.1-14.9 kcal mol^-1) as well as hindered rotation of the t-Bu subtituent of the coordinated amine function around the corresponding N-C bond (ΔG? = 8.8-10.1 kcal mol^-1).

Full text of DOI:10.1021/om010475e

5050
Organometallics 2001, 20, 5050-5055
Neu tr a l a n d Ca tion ic P a lla d iu m (II) Com p lexes of a
Dia za p yr id in op h a n e. Str u ctu r e, F lu xion a lity, a n d
Rea ctivity tow a r d Eth ylen e
Simoni Plentz Meneghetti,†,‡ Pierre J . Lutz,‡ and J acky Kress*,†
Laboratoire de Chimie des Me´taux de Transition et de Catalyse, UMR du CNRS 7513,
Institut Le Bel, 4 Rue Blaise Pascal, Universite´ Louis Pasteur, 67000 Strasbourg, France, and
Institut Charles Sadron, UPR du CNRS 22, 6 Rue Boussingault, 67000 Strasbourg, France
Received J une 5, 2001
The palladium complexes (t-Bu-N4)PdCl2 (1), (t-Bu-N4)PdMeCl (2), (t-Bu-N4)PdMe(NCMe)+-
BAr4- (3), and (t-Bu-N4)PdMe(C2H4)+BAr4- (4) [t-Bu-N4 ) N,N′-ditertiobutyl-2,11-diaza[3.3]-
(2,6)pyridinophane, Ar ) 3,5-(CF3)2-C6H3] have been synthesized and characterized by VT
1H NMR and X-ray (for 1 and 3) analysis. The macrocyclic ligand is only bi- or tridentate,
both coordination modes coexisting in solution for 1 and 3. Cationic methyl-ethylene complex
4 decomposes readily through insertion of ethylene into the Pd-Me bond, and ethylene
polymerization with use of 1 (in the presence of MAO) or 3 as catalysts is therefore precluded.
Complexes 1, 3, and 4 are fluxional, the t-Bu-N4 ligand undergoing an η2-η3 oscillatory
process (∆Gq ) 14.1-14.9 kcal mol-1) as well as hindered rotation of the t-Bu substituent of
the coordinated amine function around the corresponding N-C bond (∆Gq ) 8.8-10.1 kcal
mol-1).
Sch em e 1
In tr od u ction
Complexation studies of N,N′-dialkyl-2,11-diaza[3.3]-
(2,6)pyridinophanes (R-N4) have led to a number of
octahedral transition metal complexes in which the
tetraazamacrocyclic ligands are most often tetraden-
tate.1 Other coordination modes have been reported in
only two instances.2 Since palladium(II) is less prone
to axial interactions, it seemed likely that complexation
to this metal will generate different coordination modes
and geometries and that bidentate coordination via the
two pyridyl functions may, in particular, be expected.
Furthermore, cationic alkyl derivatives of this type could
be considered as analogues of the square-planar diimine
complexes that behave as efficient molecular catalysts
for the polymerization of olefins.3 The key characteristic
of these catalysts is steric protection of the axial
coordination sites by the ancillary diimine ligands, and
we wished to probe if cyclic ligands such as the diaza-
pyridinophanes were able to ensure a similar protection
and to give rise to comparable insertion chemistry. The
known t-Bu-N4 derivative,1c which contains bulky tert-
butyl substituents on the two amino nitrogen atoms,
was chosen to favor such steric effects and weaken yet
possible palladium-amine interactions. We describe
here the outcome of these investigations.
Resu lts a n d Discu ssion
Complexes 1, 2, and 3 were synthesized following
procedures previously described for the palladium-
diimine analogues3 (Scheme 1; 80, 65, and 67% yield,
respectively). Orange crystals of 1 and 3 were obtained
respectively from a CHCl3 or a MeCN solution and
analyzed by X-ray crystallography (Figures 1 and 2). In
the solid state, 1 consists of square-planar molecules of
(3) (a) J ohnson, L. K.; Killian, C. M.; Brookhart, M. J . Am. Chem.
Soc. 1995, 117, 6414. (b) J ohnson, L. K.; Mecking, S.; Brookhart, M.
J . Am. Chem. Soc. 1996, 118, 267. (c) Deng, L.; Woo, T. K.; Cavello,
L.; Margl, P. M.; Ziegler, T. J . Am. Chem. Soc. 1997, 119, 6177. (d)
Schleis, T.; Heinemann, J .; Spaniol, T. P.; Mulhaupt, R.; Okuda, J .
Inorg. Chem. Commun. 1998, 1, 431. (e) Musaev, D. G.; Froese, R. D.
J .; Morokuma, K. Organometallics 1998, 17, 1850. (f) Mecking, S.;
J ohnson, L. K.; Wang, L.; Brookhart, M. J . Am. Chem. Soc. 1998, 120,
888. (g) Guan, Z.; Cotts, P. M.; McCord, E. F.; McLain, S. J . Science
1999, 283, 2059. (h) Ittel, S. D.; J ohnson, L. K.; Brookhart, M. Chem.
Rev. 2000, 100, 1169. (i) Tempel, D. J .; J ohnson, L. K.; Huff, R. L.;
White, P. S.; Brookhart, M. J . Am. Chem. Soc. 2000, 122, 6686. (j)
Gottfried, A. C.; Brookhart, M. Macromolecules 2001, 34, 1140. (k)
Plentz Meneghetti, S.; Kress, J .; Lutz, P. J . Macromol. Chem. Phys.
2000, 201, 1823. (l) Held, A.; Mecking, S. Chem. Eur. J . 2000, 6, 4623.
(m) Mecking, S. Coord. Chem. Rev. 2000, 203, 325.
* E-mail: jkress@chimie.u-strasbg.fr.
† Laboratoire de Chimie des Me´taux de Transition et de Catalyse.
‡ Institut Charles Sadron.
(1) (a) Fronczek, F. R.; Mamo, A.; Pappalardo, S. Inorg. Chem. 1989,
28, 1419. (b) Sakaba, H.; Kabuto, C.; Horino, H.; Arai, M. Bull. Chem.
Soc. J pn. 1990, 63, 1822. (c) Che, C.-M.; Li, Z.-Y.; Wong, K.-Y.; Poon,
C.-K.; Mak, T. C. W.; Peng, S.-M. Polyhedron 1994, 13, 771. (d) Kru¨ger,
H.-J . Chem. Ber. 1995, 128, 531. (e) Koch, W. O.; Kru¨ger, H.-J . Angew.
Chem., Int. Ed. Engl. 1995, 34, 2671. (f) Kelm, H.; Kru¨ger, H.-J . Inorg.
Chem. 1996, 35, 3533. (g) Koch, W. O.; Schu¨nemann, V.; Gerdan, M.;
Trautwein, A. X.; Kru¨ger, H.-J . Chem. Eur. J . 1998, 4, 686 and 1255.
(h) Plentz Meneghetti, S.; Lutz, P. J .; Fischer, J .; Kress, J . Polyhedron
2001, 20, 2705.
(2) (a) Kelm, H.; Kru¨ger, H.-J . Eur. J . Inorg. Chem. 1998, 1381. (b)
Koch, W. O.; Kaiser, J . T.; Kru¨ger, H.-J . Chem. Commun. 1997, 2237.
10.1021/om010475e CCC: $20.00 © 2001 American Chemical Society
Publication on Web 10/20/2001

Neutral and Cationic Palladium(II) Complexes
Organometallics, Vol. 20, No. 24, 2001 5051
Sch em e 2
becoming thereby five-coordinate and surrounded by a
distorted square-pyramidal coordination geometry. The
tridentate macrocyclic ligand adopts the syn chair-boat
conformation. However, the palladium-amine inter-
action is weak [Pd-N(3) ) 2.67 Å], so that the macro-
cycle is much less twisted than in hexacoordinate (η4-
t-Bu-N4)NiBr2 for instance,1h and the t-Bu substituent
of the coordinated amine is directed between the two
equatorial ligands (Me and NCMe in this case). It yet
slightly displaces the Pd atom from the basal plane,
toward N(3), and pushes the NCMe framework out of
this plane, in the opposite direction. The Pd-Npy bonds
are weaker than in 1, especially the one trans to the
Me ligand, and the angle between the two pyridine rings
is reduced to ca. 48°. In contrast, the Pd-N(1) distance
between palladium and acetonitrile is remarkably short.
In solution (CD2Cl2), the two types of structures
described above, which will be designated by a (four-
coordinate, η2-ligand) and b (five-coordinate, η3-ligand),
coexist for 1 and 3 in the temperature-independent ratio
of ca. 2:3 and 3:4, respectively, whereas 2 exists as a
single isomer of type a . This can be clearly deduced from
the low-temperature 1H NMR spectra of the three
compounds, in which the half-macrocycles containing a
coordinated amine function are easily distinguished
from those containing a free amine function,5 while both
fragments constitute useful symmetry probes. For 3a ,b,
full assignment of the spectra is based on a NOESY
experiment that enabled moreover to show that coor-
dination of the amine function in 3b leads to a signifi-
cant twist of the corresponding ligand half, through
F igu r e 1. ORTEP drawing of 1. Thermal ellipsoids are
drawn at the 50% probability level. Hydrogen atoms and
solvent molecules are omitted for clarity. Selected bond
distances (Å) and angles (deg): Pd-N(1) ) 2.041(8), Pd-
N(3) ) 2.054(7), Pd-Cl(1) ) 2.314(3), Pd-Cl(2) ) 2.307-
(3), N(1)-Pd-N(3) ) 80.73(9), Cl(1)-Pd-Cl(2) ) 93.41(3).
F igu r e 2. ORTEP drawing of 3. Thermal ellipsoids are
drawn at the 50% probability level. Hydrogen atoms and
-
the BAr4 counteranion are omitted for clarity. Selected
bond distances (Å) and angles (deg): Pd-N(1) ) 2.022(4),
Pd-N(2) ) 2.200(4), Pd-N(3) ) 2.670(4), Pd-N(4) ) 2.065-
(3), Pd-C(3) ) 2.017(5), N(2)-Pd-N(4) ) 77.1(1), C(3)-
Pd-N(1) ) 88.5(2), N(2)-Pd-N(3) ) 73.3(2), N(4)-Pd-
N(3) ) 75.6(2).
7
which the t-Buc group is directed toward the NCMe
ligand and not between the Me and NCMe ligands as
in the solid state (Scheme 2). t-Buc is indeed found near
to CHc,Me,iH on one hand and CHc,NCMe,oH on the other
hand. This shows that the Pd-Nam interaction in 3b
(Nam ) amino nitrogen atom) is stronger in solution
than in the solid state and becomes closer to that
observed in (η4-t-Bu-N4)NiBr2.1h
pseudo-C2v symmetry, in which the t-Bu-N4 ligand
adopts the desired bidentate coordination mode and
retains the syn chair-chair conformation of the free
macrocycle.1c Short Pd-Npy bond distances (Npy
)
pyridyl nitrogen atom) indicate the strength of the
interaction between palladium and the two pyridine
functions. As for the tetradentate diazapyridinophane
ligands with conformation syn boat-boat,1 the Npy-M-
Npy angle is small (80.7°) and the dihedral angle that
the two pyridine rings form with each other even
smaller (ca. 56°), although still much larger than in the
free ligand.1c The two tert-butyl groups are aligned along
the N(2)-N(4) axis, providing thereby only limited steric
protection to the two axial sites of the complex.4
Complex 3 reacts smoothly with 5 equiv of ethylene
in CD2Cl2 at -30 °C to yield complex 4 (Scheme 1), as
(5) The chemical shift of the inner CHiHo protons is particularly
characteristic. If the adjacent nitrogen atom is bound to palladium,
these protons are shielded by the pyridine rings that are then in close
proximity (δ 3.62 for 1b, 3.64/3.30 for 3b). If the nitrogen atom is not
bound, they become near an apical site of palladium and the para-
magnetic anisotropy of this atom6 is shifting their resonances downfield
(δ 6.11 for 1a , 6.68 for 1b, 5.64/5.54 for 2a , 5.03/5.00 for 3a , 5.71/5.36
for 3b). This latter effect is also observed for the t-Bu substituent of
the coordinated amine functions [δ 1.64 (-26 °C) and 1.40 (-60 °C)
for 1b and 3b, respectively].
(6) Miller, R. G.; Stauffer, R. D.; Fahey, D. R.; Parnell, D. R. J . Am.
Chem. Soc. 1970, 92, 1511.
(7) Indexes i or o, f or c, and Cl, Me, or NCMe designate protons
located respectively inside or outside the macrocyclic ring, beside the
free or the coordinated amine function, and on the side of the Cl, Me,
or NCMe ligands.
The molecular structure of cationic 3 in the solid state
(Figure 2) is different insofar as the more electron-
deficient palladium center interacts furthermore api-
cally with one of the two amine functions of t-Bu-N4,
(4) The molecular structure of (Ts-N4)PdCl2 (Ts ) SO2C6H4-4-Me,
orange crystals) is similar. Pd-Npy ) 2.14(1) Å, Pd-Cl ) 2.251(6) Å.

5052 Organometallics, Vol. 20, No. 24, 2001
Meneghetti et al.
salt in high yield, is accelerated by ambient light, a
radical mechanism is probably involved.
Figure 3 shows also that the two t-Bu singlets of 4
broaden above -10 °C and coalesce at ca. 18 °C into a
single resonance at δ 1.43 at 27 °C. In the lower field
region, all other t-Bu-N4 signals, except the two triplets
due to the para-pyridyl protons, broaden similarly before
they coalesce two by two. Furthermore, the two com-
ponents of the AA′BB′ system observed for the ethylene
ligand coalesce into a singlet at 8 °C.9 The half-
macrocycle containing the coordinated amine function
is hence equilibrating with the other half, which indi-
cates the occurrence in 4 of a dynamic oscillatory process
through which the apically bound nitrogen atom is
reversibly dissociated from the palladium center, and
the conformation of the macrocyclic ligand changes from
syn chair-boat to syn chair-chair. The free activation
energy of this η2-η3 exchange process was calculated
with use of the Eyring equation:10 ∆Gq ) 14.1 ( 0.2 kcal
mol-1. A similar fluxional behavior is found for com-
pounds 1 and 3, for which it leads moreover to equili-
bration of the two isomers a and b,11 with an activation
energy of 14.9 ( 0.2 and 14.5 ( 0.2 kcal mol-1 for 1b
(in C6D5Br) and 3b (in CD2Cl2), respectively.10,12 Sur-
prisingly, the ∆Gq values seem to decrease slightly with
strengthening of the Pd-Nam bond.
F igu r e 3. Modification of the 1H NMR spectrum (500
MHz, 1.9-0.5 ppm) of 4 (+ C2H4) in CD2Cl2 on raising
progressively the temperature from -3 to 27 °C (* ) H2O).
On lowering the temperature of pentacoordinate 1b,
3b, and 4 to -90 °C in CD2Cl2, the 1H NMR singlet
7
1
assigned to t-Buc splits into two components at δ 1.72
shown by in situ H NMR analysis. Isomers 3a and 3b
(6H)/1.30 (3H), 1.59 (3H)/1.28 (6H), and 1.62 (3H)/1.23
(6H), respectively. The other resonances are not signifi-
cantly modified, except the multiplet due to the ethylene
ligand of 4, which is markedly broadened but not yet
split into a more complex pattern. As the temperature
is raised, each pair of singlets broadens and then
collapses at -65, -82, and -53 °C, respectively. This
is illustrated for 4 in Figure 4. Hence, rotation of t-Buc
around the corresponding Nam-C bond is hindered in
these compounds, probably as a result of steric inter-
actions with the ligands in the basal plane (Cl, Me,
NCMe, or C2H4). The higher rotational barrier in 4 (10.1
( 0.2 kcal mol-1),10 in comparison with 3b (8.8 ( 0.2
kcal mol-1),10 is consistent with the probably shorter
Pd-Nam bond and the stronger steric constraints cer-
tainly exerted by the ethylene ligand. Broadening of the
ethylene resonance at -90 °C (especially the high-field
component of the multiplet) probably corresponds to
slower ethylene rotation at this temperature and sug-
gests that t-Buc rotation may be concerted with hindered
ethylene rotation about the Pd-ethylene bond axis, in
a gear-wheels-type process.
are converted simultaneously and almost quantitatively
within 1 h, releasing 1 equiv of acetonitrile. The
spectrum of the single isomer detected for the cationic
ethylene complex 4 is characteristic of the square-
pyramidal geometry of type b. The apical Pd-Nam
interaction is probably favored, with respect to 3, by the
stronger electron-withdrawing nature of the C2H4 ligand.
Its strength in 4 is further confirmed by an 1H-1H
COSY experiment that reveals significant distortion of
the macrocycle around the coordinated amine function8
and allows more precise assignment. Overall, it follows
the order 4 > 3 > 1 > 2, in agreement with decreasing
electron deficiency at palladium in this series. The C2H4
ligand gives rise at -30 °C to an AA′BB′ multiplet
centered at δ 4.29 and is probably rotating quickly
around the palladium-olefin bond axis.
On raising the temperature above 0 °C, 4 decomposes
readily to yield ca. 1 equiv of propene and of the
- 1h
protonated ligand salt (t-Bu-N4)H+BAr4
,
together
with traces of ethane (Figure 3). Obviously, insertion
of ethylene into the palladium-methyl bond is fast at
these temperatures, but subsequent â-hydride elimina-
tion in the resultant palladium-n-propyl complex is even
faster, and chain growth via further insertion steps is
hence precluded. Concomitant formation of (t-Bu-N4)H+
BAr4- suggests that the migrating hydrogen is trapped
by the macrocyclic ligand, via a mechanism that has not
been investigated further. Since a deposit of metallic
palladium is formed simultaneously, and decomposition
of 3 at room temperature in CD2Cl2, which leads
similarly (although much more slowly) to the protonated
Further, the fact that only one methyl group of t-Buc
is unshielded in the limiting spectrum of 3b and 4
(Figure 4) is in agreement with the twisted conformation
(9) They do not collapse, however, with the singlet due to free
ethylene (δ 5.39), showing that chemical exchange between bound and
unbound ethylene is slow on the NMR time scale and that the
palladium-ethylene interaction is rather strong.
(10) Gu¨nther, H. La spectroscopie de RMN; Masson: Paris, France,
1993.
(11) For 3a and 3b for instance, not only the η2- and η3-t-Bu-N4
resonances coalesce, but also the two Me (at 25 °C) and the two NCMe
ones (at 13 °C). No exchange between bound and unbound acetonitrile
is yet detected at these temperatures, in agreement with the strength
of the corresponding palladium-nitrogen bond in the solid state. See
also ref 2a.
(8) The two Hm-Py protons of one of the pyridine rings (δ 6.86 and
7.13) are coupled with both Hc,i and Hc,o protons of the neighboring
CH2 group (δ 3.51 and 4.59, respectively), whereas those of the other
pyridine ring (δ 6.97 and 7.02) are coupled with the corresponding Hc,o
proton (δ 4.76), but not with the Hc,i one (δ 3.68).
(12) Shanan-Atidi, H.; Bar-Eli, K. H. J . Phys. Chem. 1970, 74, 961.

Neutral and Cationic Palladium(II) Complexes
Organometallics, Vol. 20, No. 24, 2001 5053
bidentate coordination mode is observed in some of the
complexes, while the macrocycle is tridentate in others,
and both four- and five-coordinate structures can coexist
in solution, where they interchange slowly on the NMR
time scale. In the latter, the presence of a bulky t-Bu
group on the bound amino nitrogen atom leads to more
or less distortion of the ligand frame and to hindered
rotation of this t-Bu group around the Nam-C bond. The
cationic methyl complex 3 binds ethylene and inserts it
into its Pd-C bond, but subsequent decomposition with
-
formation of (t-Bu-N4)H+BAr4 precludes its use as a
polymerization catalyst. Further studies in this field
should therefore be directed toward ligands that are less
prone to protonation.
Exp er im en ta l Section
Gen er a l P r oced u r es. Although the compounds described
herein are not significantly air-sensitive, most experiments
were performed on a vacuum line or under an argon atmo-
sphere using standard Schlenk techniques. Diethyl ether and
hexane were dried over Na/benzophenone ketyl; dichloro-
methane was dried over P2O5, and acetonitrile over calcium
hydride. The solvents were then distilled under argon. Eth-
ylene was used as received. Hex-1-ene was refluxed over
sodium and distilled trap-to-trap under vacuum. t-Bu-N4,1c
(COD)PdCl2,13 (COD)PdMeCl,14 and NaBAr4 were prepared
15
according to the procedures outlined in the literature. Methyl-
aluminoxane (MAO) was purchased as a 10% toluene solution
from Aldrich. 1H and 13C NMR spectra were recorded on a
Bruker ARX-500 spectrometer. Chemical shifts are reported
in ppm versus SiMe4 and were determined by reference to the
residual solvent peaks. Elemental analyses were performed
by the Service de Caracte´risation de l’Institut Charles Sadron
(Strasbourg).
Com p ou n d (t-Bu -N4)P d Cl2 (1). A 1.00 g sample of (COD)-
PdCl2 (3.50 mmol) and 1.23 g of t-Bu-N4 (3.50 mmol) were
dissolved in CH2Cl2 at room temperature, and the solution was
stirred for 24 h. The solvent was then evaporated under
vacuum to yield an orange powder that was recrystallized from
CHCl3 or CH2Cl2. Orange crystals of 1 were obtained in 80%
yield. 1H NMR (CD2Cl2, -26 °C):7 1a δ 7.63 (t, 2H, Hp--Py),
7.17 (d, 4H, Hm-Py), 6.11 (d, 4H, CHiHo), 4.79 (d, 4H, CHiHo),
1.34 (s, 18H, t-Bu); 1b δ 7.56 (t, 2H, Hp-Py), 7.13 (d, 2H, Hm-
Py,f), 7.02 (d, 2H, Hm-Py,c), 6.68 (d, 2H, CHf,iCHf,o), 4.85 (d, 2H,
CHf,iCHf,o), 4.81 (d, 2H, CHc,iCHc,o), 3.62 (d, 2H, CHc,iCHc,o),
F igu r e 4. Variable-temperature 1H NMR spectra (500
MHz) of 4 in CD2Cl2. Only the ethylene and the t-Bu
regions are shown. The sample is contaminated with low
amounts of 3a ,b (3b is also fluxional in this temperature
range) and water (*).
of the macrocyclic ligand in these compounds in solution
[the unshielding is assigned to paramagnetic anisotropy
of palladium,6 and it was shown in the case of (η4-t-Bu-
N4)NiBr2 that a single Me group of t-Buc is located in
proximity to palladium when t-Bu-N4 is twisted].1h For
1b, on the contrary, there are two equally unshielded
Me groups. This suggests that the η3-macrocycle is less
twisted in this compound, the Pd-Nam bond being
weaker, and that in the ground state t-Buc is probably
positioned approximately as in 3b in the solid state
(Figure 2, Scheme 2). The higher barrier to rotation in
1b (∆Gq ) 9.5 ( 0.2 kcal mol-1),10 with respect to 3b,
may also be explained in this way.
Ethylene polymerization or oligomerization attempts
with use of 1 (in the presence of MAO, rt, 6 bar, 2 h) or
3 (rt, 6 bar, 18 h) as catalysts were unsuccessful. In both
cases, pressurization with ethylene was followed by
quasi-immediate precipitation of metallic palladium.
Also hex-1-ene induces fast decomposition of 3 at room
temperature. This is slowed at -10 °C, but again no
polymer or oligomer could be detected at this temper-
ature. These results are fully consistent with the
instability of the cationic ethylene complex 4.
1.64 (s, 9H, t-Buc), 1.26 (s, 9H, t-Buf). Anal. Calcd for C22.4H32.4
-
Cl3.2N4Pd: C, 46.58; H, 5.65; N, 9.70. Found: C, 46.29; H, 5.65;
N, 9.32.
Com p ou n d (t-Bu -N4)P d MeCl (2). A 1.00 g sample of
(COD)PdMeCl (3.8 mmol) and 1.33 g of t-Bu-N4 (3.8 mmol)
were dissolved in 25 mL of diethyl ether at room temperature,
and the solution was stirred for 24 h. The solvent was then
evaporated under vacuum to yield a yellow powder that was
recrystallized by addition of hexane to a CH2Cl2 solution.
Complex 2 was obtained as a yellow solid in 65% yield. It is
rather unstable at room temperature, being slowly converted,
in dichloromethane as well as in bromobenzene, into 1 and
an unidentified unstable compound that is probably (t-Bu-N4)-
PdMe2. Decomposition of the latter yields metallic palladium
and the protonated macrocycle, as for 3 and 4. 1H NMR (CD2-
Cl2, -20 °C):7 δ 7.46 and 7.40 (t, 1H, Hp-Py,Cl and Hp-Py,Me), 7.06
and 7.00 (d, 2H, Hm-Py,Cl and Hm-Py,Me), 5.64 and 5.54, (d, 2H,
CH2, HCl,i and HMe,i), 4.63 and 4.49 (d, 2H, CH2, HCl,o and HMe,o),
1.34 (s, 18H, t-Bu), 0.60 (s, 3H, Pd-Me). Anal. Calcd for C23H35
-
ClN4Pd: C, 54.20; H, 6.90; N, 11.00. Found: C, 53.86; H, 6.90;
N, 10.64.
Con clu sion s
(13) Drew, D.; Doyle, J . R. Inorg. Synth. 1972, 13, 47.
(14) Rulke, R. E.; Ernsting, J . M.; Spek, A. L.; Elsevier, C. J .; van
Leeuwen, P. W. N. M.; Vrieze, K. Inorg. Chem. 1993, 32, 5769.
(15) Bahr, S. R.; Boudjouk, P. J . Org. Chem. 1992, 57, 5545.
This work describes the first palladium complexes of
a diazapyridinophane, as well as the first organometallic
compounds involving such macrocyclic ligands. A new

5054 Organometallics, Vol. 20, No. 24, 2001
Meneghetti et al.
Ta ble 1. X-r a y Exp er im en ta l Da ta for 1 a n d 3
1‚2CHCl3
24H34Cl8N4Pd
3
formula
C
C
C57H50BF24N5Pd
C25H38N5Pd‚C32H12BF24
22H32Cl2N4Pd‚2CHCl3
768.59
molecular wt
cryst syst
space group
a (Å)
b (Å)
c (Å)
1378.24
triclinic
P1h
monoclinic
Cc
19.7343(6)
11.0721(4)
14.6680(3)
12.0376(4)
12.5869(4)
20.0815(7)
88.554(5)
88.446(5)
81.812(5)
3009.8(3)
2
R (deg)
â (deg)
91.977(5)
γ (deg)
V (Å3)
3203.1(3)
4
Z
color
orange
yellow
crystal dimens (mm)
D
0.20 × 0.14 × 0.08
0.20 × 0.16 × 0.14
calc (g cm-3
)
1.59
1.52
F000
1552
1.269
173
0.71073
Mo KR graphite
monochromated
KappaCCD
phi scans
0,25/0,14/-19,19
2.5/27.48
3844
1388
0.424
173
0.71073
Mo KR graphite
monochromated
KappaCCD
phi scans
0,15/-15,16/-25,26
2.5/27.50
13 381
µ (mm-1
)
temperature (K)
wavelength (Å)
radiation
diffractometer
scan mode
hkl limits
θ limits (deg)
no. of data measd
no. of data with I > 3σ(I)
weighting scheme
no. of variables
R
3165
8033
4Fo2/(σ2(Fo2) + 0.0016 Fo
332
)
4Fo2/(σ2(Fo2) + 0.0064 Fo
793
)
4
4
0.027
0.054
Rw
0.036
0.079
GOF
1.212
1.425
largest peak in final
1.830
1.148
difference (e Å-3
)
-
Com p ou n d (t-Bu -N4)P d Me(NCMe)+BAr 4 (3). A 1.50 g
sample of (t-Bu-N4)PdMeCl (2) (2.9 mmol) and 2.61 g of
NaBAr4 (2.9 mmol) were dissolved in MeCN at room temper-
ature, and the solution was stirred for 24 h. The solvent was
then evaporated under vacuum to yield an orange powder that
was recrystallized at low temperature from acetonitrile.
Orange crystals of 3 were obtained in 67% yield. 1H NMR (CD2-
Cl2, -60 °C):7,16 3a δ 7.50 (t, 1H, Hp-Py,Me), 7.45 (t, 1H,
introduced at the top of the solution during a few seconds at
ambient temperature, and the NMR tube was sealed, cooled
to -80 °C, and vigorously shaken at this temperature. 1H NMR
analysis at -60 °C revealed that most of 3 had not yet reacted
at this stage (low amounts of decomposition products were
however detectable) and that 5 equiv of ethylene was present
in solution. On raising the temperature, formation of complex
4 started above -40 °C and could be followed by 1H NMR.
Almost complete conversion was achieved after ca. 1 h at -30
°C, without further decomposition of 4. The complex could then
be analyzed by VT 1H NMR between -90 and -20 °C. On
raising the temperature above -10 °C, slow decomposition of
4 begun to occur, which was accelerated at higher temperature.
1H NMR (CD2Cl2, -30 °C):7,16 δ 7.48 and 7.41 (m, 1H, Hp-Py),
7.13 and 7.02 (d, 1H, Hm-Py,f), 6.97 and 6.86 (d, 1H, Hm-Py,c),
4.83 (d, 1H, CH2, Hf,i), 4.76 (d, 1H, CH2, Hc,o), 4.70 (d, 1H, CH2,
H
p-Py,NCMe), 7.08 (d, 2H, Hm-Py,Me), 7.02 (d, 2H, Hm-Py,NCMe), 5.03
(d, 2H, CH2, HNCMe,i), 5.00 (d, 2H, CH2, HMe,i), 4.68 (d, 2H, CH2,
Me,o), 4.54 (d, 2H, CH2, HNCMe,o), 2.26 (s, 3H, MeCN), 1.31 (s,
18H, t-Bu), 0.75 (s, 3H, Pd-Me); 3b δ 7.50 (t, 1H, Hp-Py,Me), 7.42
(t, 1H, Hp-Py,NCMe), 7.12 (d, 1H, Hm-Py,Me,f), 7.03 (d, 1H, Hm-Py,Me,c),
6.98 (d, 1H, Hm-Py,NCMe,f), 6.83 (d, 1H, Hm-Py,NCMe,c), 5.71 (d, 1H,
CH2, Hf,NCMe,i), 5.36 (d, 1H, CH2, Hf,Me,i), 4.72 (d, 1H, CH2,
H
H
f,Me,o), 4.56 (d, 1H, CH2, Hf,NCMe,o), 4.52 (d, 1H, CH2, Hc,Me,o),
4.50 (d, 1H, CH2, Hc,NCMe,o), 3.64 (d, 1H, CH2, Hc,Me,i), 3.30 (d,
1H, CH2, Hc,NCMe,i), 2.18 (s, 3H, MeCN), 1.40 (s, 9H, t-Buc), 1.24
(s, 9H, t-Buf), 0.57 (s, 3H, Pd-Me). Selected 1H-1H NOESY
correlations for 3a : δ 1.31 with δ 4.54, 4.68, 7.02, and 7.08;
for 3b: δ 1.24 with δ 4.56, 4.72, 6.98, and 7.12, δ 1.40 with δ
0.57, 3.64, and 4.50. 13C NMR (CD2Cl2, -60 °C):16 3a δ 160.38,
159.80 (Co-Py), 27.61 (C(CH3)3), 3.86 (MeCN), -5.39 (Pd-Me);
3b δ 162.66, 162.40, 159.91, 158.54 (Co-Py), 27.46 (C(CH3)3),
3.86 (MeCN), -8.05 (Pd-Me); 3a + 3b δ 139.29, 138.88, 138.85,
138.39 (Cp-Py), 124.84, 124.50, 124.37, 124.31, 122.99, 120.80
(Cm-Py), 63.35, 62.02, 60.82, 59.20, 58.00, 57.58, 57.29, 57.09,
56.79 (CH2 and C(CH3)3). Anal. Calcd for C57H50BF24N5Pd: C,
49.67; H, 3.66; N, 5.08. Found: C, 49.53; H, 3.59; N, 4.78.
H
f,o), 4.59 (d, 1H, CH2, Hc,o), 4.40 (d, 1H, CH2, Hf,i), 4.38 (d,
1H, CH2, Hf,o), 4.29 (m, 4H, C2H4), 3.68 and 3.51 (d, 1H, CH2,
c,i), 1.44 (s, 9H, t-Buc), 1.29 (s, 9H, t-Buf), 0.67 (s, 3H, Pd-
H
Me). Selected 1H-1H COSY correlations: δ 1.29 with δ 4.70
and 4.38; δ 6.86 with δ 7.48, 7.13, 4.59, and 3.51; δ 6.97 with
δ 7.41, 7.02, and 4.76. It could not be determined which protons
of the macrocycle are located on the side of Me or C2H4 ligands.
X-r a y Str u ctu r es for 1 a n d 3. The X-ray structure
determinations were carried out by the Service Commun de
Rayons X de la Faculte´ de Chimie de Strasbourg. The
structures were solved using direct methods and the Nonius
MoleN Package for all calculations and refined by full-matrix
least-squares. The experimental data are collected in Table 1.
-
Com p ou n d (t-Bu -N4)P d Me(C2H4)+BAr 4 (4). This com-
P olym er iza tion Exp er im en ts. The ethylene polymeriza-
tion attempts were performed in a 1 L Buchi reactor equipped
with a mechanical stirrer. The catalyst was first introduced
into the reactor under argon as a toluene or a dichloromethane
(for 3) solution of controlled volume and concentration. The
reactor was then filled with ethylene, and, in the case of 1,
plex was generated in situ in CD2Cl2. A 15 mg sample of 3
was dissolved in 0.4 mL of CD2Cl2, and the solution was placed
in an NMR tube and cooled to ca. -20 °C. Ethylene was then
(16) The 1H and 13C NMR data for BAr4 are identical to those
-
reported previously.3f

Neutral and Cationic Palladium(II) Complexes
Organometallics, Vol. 20, No. 24, 2001 5055
MAO was added under an ethylene flow with use of a syringe.
The reactor was then pressurized with ethylene and the
pressure maintained constant during the experiment. The
addition of MAO to 1/ethylene, and of ethylene to 3, was
followed by immediate fading of the solution and precipitation
of metallic palladium. The reactions with hex-1-ene were
performed using standard Schlenk techniques (0.05 mmol of
3, 5 mL of toluene, 2.5 mL of hex-1-ene, 2 h). After quenching
the reactions between 3 and ethylene or hex-1-ene by addition
of a 10% solution of aqueous HCl in methanol, metallic
palladium was separated by centrifugation and the solutions
were analyzed by GC before they were evaporated to dryness
(no significant residue was obtained in any case).
Graf and J .-D. Sauer for running the 2D NMR experi-
ments, and to the late Prof. J . A. Osborn for his support.
We thank the CNRS for financial support (Program
Catalyse et Catalyseurs pour l’Industrie et l’Environne-
ment). S.P.M. is indebted to the Brazilian Government
(CAPES) for a fellowship.
Su p p or tin g In for m a tion Ava ila ble: Crystallographic
data for 1, 3, and (Ts-N4)PdCl2; 2D NMR spectra for 3 and 4.
This material is available free of charge via the Internet at
http://pubs.acs.org.
Ack n ow led gm en t. We are grateful to Mrs N. Kyrit-
sakas and Dr. A. De Cian for the X-ray analyses, to R.
OM010475E