Chemistry of Bis(aryloxo)palladium(II) Complexes with N-Donor Ligands: Structural Features of the Palladium-to-Oxygen Bond and Formation of O-H?O Bonds

Article abstract of DOI:10.1021/ic950563p

Reaction of palladium acetate with 2 equiv of sodium phenoxide in the presence of a chelate diamine ligand affords the complexes [Pd(OPh)₂(N～N)] (N～N = bpy (1), tmeda (2), teeda (3), dpe (4), dmap (5)). These yellow to orange bis(phenoxo)pallad

Full text of DOI:10.1021/ic950563p

526
Inorg. Chem. 1996, 35, 526-533
Chemistry of Bis(aryloxo)palladium(II) Complexes with N-Donor Ligands: Structural
Features of the Palladium-to-Oxygen Bond and Formation of O-H‚‚‚O Bonds
Gerardus M. Kapteijn,† David M. Grove,† Huub Kooijman,‡ Wilberth J. J. Smeets,‡
Anthony L. Spek,‡,§ and Gerard van Koten*,†
Department of Metal-Mediated Synthesis, Debye Institute, and Crystal and Structural Chemistry, Bijvoet
Center for Biomolecular Research, Utrecht University, Padualaan 8, 3584 CH, Utrecht, The Netherlands
ReceiVed May 11, 1995X
Reaction of palladium acetate with 2 equiv of sodium phenoxide in the presence of a chelate diamine ligand
affords the complexes [Pd(OPh)2(N∼N)] (N∼N ) bpy (1), tmeda (2), teeda (3), dpe (4), dmap (5)). These
yellow to orange bis(phenoxo)palladium(II) complexes are thermally stable at room temperature in the solid state
as well as in solution. Addition of an excess of pentafluorophenol to 1, 2, 4, and 5 affords crystalline complexes
[Pd(OC6F5)2(N∼N)] (N∼N ) bpy (6), tmeda (7), dpe (8), dmap (9)). Crystals of 1 and 6 have been subjected
to X-ray diffraction studies. Crystals of 1 are orthorhombic, space group P212121 (no. 19), with a ) 6.7655(6)
Å, b ) 16.0585(10) Å, c ) 16.7275(13) Å, and Z ) 4. Crystals of 6 are triclinic, space group P1h (no. 2), with
a ) 7.567(4) Å, b ) 12.708(3) Å, c ) 12.912(5) Å, R ) 61.51(3)°, â ) 74.74(4)°, γ ) 88.78(4)°, and Z ) 2.
The molecular structures of 1 and 6 show them to be square-planar complexes, and the main structural difference
between these complexes is the orientation of the aromatic rings. In 6 the OC6F5 ligands are almost parallel in
a face-to-face orientation (π-π stacking interactions), whereas in 1 the OC6H5 units are skewed away from each
other. An unexpected "mixed" alkoxo(aryloxo) complex [Pd(OCH(CF3)2)(OPh)(bpy)]‚HOPh (10) is formed when
1 is reacted with 1,1,1,3,3,3-hexafluoro-2-propanol. The molecular structure of 10 shows O-H‚‚‚O hydrogen
bonding (O‚‚‚O ) 2.642(8) Å) between the hydroxyl hydrogen of phenol and the oxygen atom of the phenoxide
ligand as well as an additional C-H‚‚‚O contact (C‚‚‚O) ) 2.95(1) Å), which can be regarded as the initial stage
of a base-assisted â-hydrogen elimination. Crystals of 10 are monoclinic, space group P21/c, with a ) 8.3241-
(14) Å, b ) 11.0316(17) Å, c ) 26.376(3) Å, R ) 93.01(1)°, Z ) 4. Spectroscopic data of complexes 1-10
indicate that the oxygen atom of the aryloxide or alkoxide ligand is extremely electron-rich, leading to high
polarization of the palladium-to-oxygen bond. The bis(phenoxide) complexes 1, 2, and 4 associate with two
molecules of phenol through O-H‚‚‚O hydrogen bonds to form adducts [Pd(OPh)2(N∼N)]‚2HOPh (N∼N ) bpy
(11), tmeda (12), dpe (13)). The palladium complexes 6-9 with OC6F5 groups show no tendency to form adducts
with alcohols.
Introduction
of late transition metal alkoxides and aryloxides have been
relatively less explored, probably because it was thought that
the metal-to-oxygen bond would be weak (due to a mismatch
of the hard, basic OR ligands with a “soft” group 7-10
(“platinum group”) metal center and therefore difficult to study.6
However, Ba¨ckvall et al. have shown using theoretical calcula-
tions that the metal-to-oxygen bond is of comparable strength
or stronger than the metal-to-carbon (sp3) bond.7 One dif-
ficulty in isolating metal alkoxide complexes is the ease with
The chemistry of late transition metal alkoxides and arylox-
ides has recently attracted attention,1 because it has been
discovered that they have unique chemical reactivities which
include insertion of small molecules into the metal-to-oxygen
bond,2 formation of C-O bonds,3 and association with alcohols
through O-H‚‚‚O hydrogen bonding.4 Extensive work has been
published on alkoxo and aryloxo derivatives of group 3-6
transition metals.5 Unfortunately, the synthesis and reactivity
(4) (a) Kim, Y.-J.; Osakada, K.; Takenaka, A.; Yamamoto, A. J. Am.
Chem. Soc. 1990, 112, 1096. (b) Kegley, S. E.; Schaverien, C. J.;
Freudenberger, J. H.; Bergman, R. G.; Nolan, S. P.; Hoff, C. D. J.
Am. Chem. Soc. 1987, 109, 6563. (c) Koelle, U.; Wang, M. H.; Raabe,
G. Organometallics 1991, 10, 2573. (d) Osakada, K.; Oshiro, K.;
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M.; Kasuga, N.; Komiya, S. Chem. Lett. 1991, 1949. (f) Osakada,
K.; Kim, K.-Y.; Yamamoto, A. J. Organomet. Chem. 1990, 382, 303.
(g) Seligson, A. L.; Cowan, R. L.; Trogler, W. C. Inorg. Chem. 1991,
30, 3371. (h) Simpson, R. D.; Bergman, R. G. Organometallics 1993,
12, 781. (i) Ozawa, F.; Yamagami, I.; Yamamoto, A. J. Organomet.
Chem. 1994, 473, 265.
(5) (a) Bradley, D. C.; Mehrotra, R. C.; Gauer, D. P. Prog. Inorg. Chem.
1960, 2, 203. (b) Bradley, D. C. Metal Alkoxides; Academic: London,
1978. (c) Mehrotra, R. C.; Agarwal, S. K.; Singh, Y. P. Coord. Chem.
ReV. 1985, 68, 101. (d) Mehrotra, R. C. Inorg. Chim. Acta, ReV. 1967,
1, 99.
* To whom correspondence should be addressed.
† Debye Institute.
‡ Bijvoet Center for Biomolecular Research.
§ Address correspondence regarding the crystallography to this author.
X Abstract published in AdVance ACS Abstracts, December 1, 1995.
(1) Bryndza, H. E.; Tam, W. Chem. ReV. 1988, 88, 1163.
(2) For insertion of CX (X ) O, O2, or S2) into the metal-to-oxygen bond,
see: (a) Kim, Y.-J.; Osakada, K.; Sugita, K.; Yamamoto, T.;
Yamamoto, A. Organometallics 1988, 7, 2182. (b) Hartwig, J. F.;
Bergman, R. G.; Andersen, R. A. J. Am. Chem. Soc. 1991, 113, 6499.
(c) Mandal, S. K.; Ho, D. M.; Orchin, M. Organometallics 1993, 12,
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(e) Smith, J. D.; Hansson, B. E.; Merola, J. S.; Waller, F. J.
Organometallics 1993, 12, 568. (f) To´th, I.; Elsevier, C. J. J. Chem.
Soc., Chem. Commun. 1993, 529.
(3) (a) Glueck, D. S.; Newman Winslow, L. J.; Bergman, R. G.
Organometallics 1991, 10, 1462. (b) Thompson, J. S.; Randall, S.
L.; Atwood, J. D. Organometallics 1991, 10, 3906. (c) Alsters, P.
L.; Boersma, J.; van Koten, G. Tetrahedron Lett. 1991, 32, 675. (d)
Thompson, J. S.; Bernard, K. A.; Rappoli, B. J.; Atwood, J. D.
Organometallics 1990, 9, 2727. (e) Alsters, P. L.; Boersma, J.; Smeets,
W. J. J.; Spek, A. L.; van Koten, G. Organometallics 1993, 12, 1639.
(6) (a) Pearson, R. G. J. Am. Chem. Soc. 1963, 85, 3533; (b) Hartley, F.
R. The Chemistry of Platinum and Palladium, Wiley: New York,
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Coordination Chemistry; Wilkinson, G., Ed.; Pergamon Press: Oxford,
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Inorganic Chemistry, 5th ed.; Wiley: New York, 1988; p 924.
0020-1669/96/1335-0526$12.00/0 © 1996 American Chemical Society

Bis(aryloxo)palladium(II) Complexes
Inorganic Chemistry, Vol. 35, No. 2, 1996 527
which they decompose to metal hydrides, presumably by a
â-hydrogen elimination, and this characteristic is the basis of a
classical route for the preparation of metal hydrides.8 A weak
metal-to-oxygen bond should lower the intrinsic barrier to a
â-hydrogen elimination reaction by raising the ground-state
free energy of the metal alkoxide relative to the corresponding
metal alkyl. For example, whereas the dimethoxide com-
plexes [Pt(OMe)2(dppe)] and [Pd(OMe)2(bpy)]9 decompose
readily at room temperature, the analogous dialkyl complex
[Pt(Et)2(dppe)] requires temperatures in excess of 150 °C for
slow decomposition.8b Mayer proposed that this reactivity arises
from antibonding π-interactions between lone pairs on the
oxygen atom and the filled metal d-orbitals and the consequent
formation of quite polar metal-to-oxygen bonds.10
Chart 1
An important reason for recent interest in late transition metal
alkoxides is that they have been postulated as key intermediates
in various metal-catalyzed synthetic organic reactions.11 Recent
examples include the methoxycarbonylation of alkynes12 and
the perfectly alternating copolymerization of CO and olefins.13
Results so far obtained with late transition metal alkoxides
suggest a rich and varied catalytic chemistry for such complexes,
and there is a great demand for structural and mechanistic
information to supplement the limited data available. In a
continuation of our study of N-donor-ligated alkoxopalladium-
(II) complexes,14 we now report the synthesis, properties, and
reactivity of a new class of palladium(II) complexes which
contain bidentate N-donor ligands with either two aryloxide
groups or one alkoxide in combination with one aryloxide. These
complexes readily form adducts with various alcohols, and
emphasis is placed on the nature of the O-H‚‚‚O hydrogen
bonding in these species.
Results and Discussion
Preparation of Bis(aryloxo)palladium(II) Complexes. The
1:2 molar reaction of palladium acetate with sodium phenoxide
in the presence of diamine ligands bpy (2,2′-bipyridine), tmeda
(N,N,N′,N′-tetramethylethylenediamine), teeda (N,N,N′,N′-tet-
raethylethylenediamine), dpe (1,2-dipiperidinoethane) or dmap
Figure 1. Reaction of bis(phenoxo)palladium complexes with pen-
tafluorophenol or HOCH(CF3)2.
(2-((dimethylamino)methyl)pyridine) at room temperature af-
fords yellow to orange, crystalline complexes [Pd(OPh)2(N∼N)]
(N∼N ) bpy (1), tmeda (2), teeda (3), dpe (4), dmap (5)) (see
Chart 1).
(7) (a) Ba¨ckvall, J. E.; Bjorkman, E. E.; Petterson, L.; Siegbahn, R. J. J.
Am. Chem. Soc. 1984, 106, 4369. (b) Ba¨ckvall, J. E.; Bjorkman, E.
E.; Petterson, L.; Siegbahn, R. J. J. Am. Chem. Soc. 1985, 107, 7265.
(8) (a) Schunn, R. A. In Transition Metal Hydrides; Muetterties, E. L.,
Ed.; Marcel Dekker: New York, 1971; pp 203-269. (b) Bryndza,
H. E.; Calabrese, J. C.; Marsi, M.; Roe, D. C.; Tam, W.; Bercaw, J.
E. J. Am. Chem. Soc. 1986, 108, 4805. (c) Bernard, K. A.; Rees, W.
M.; Atwood, J. D. Organometallics 1986, 5, 390. (d) Goldman, A.
S.; Halpern, J. J. Am. Chem. Soc. 1987, 109, 7537. (e) Hoffman, D.
M.; Lappas, D.; Wierda, D. A. J. Am. Chem. Soc. 1993, 115, 10538.
(9) Smith, G. D.; Hanson, B. E.; Merola, J. S.; Waller, F. J. Organome-
tallics 1993, 12, 568.
The new bis(phenoxo)palladium(II) complexes 1-5 have
been isolated in high yields (>85%) and are thermally stable
at room temperature in the solid state as well as in solution.
The decomposition temperature in the solid state for these
complexes is >170 °C without a melting point. In reactions
with pentafluorophenol (pKa ) 5.5), being more acidic than
phenol (pKa ) 9.9), complexes 1, 2, 4, and 5 undergo
quantitative substitution of the phenoxide anions for C6F5O-
to afford the corresponding fluorinated bis(aryloxo)palladium
complexes [Pd(OC6F5)2(N∼N)] (N∼N ) bpy (6), tmeda (7),
dpe (8), dmap (9)) (see Figure 1).
These complexes have been isolated in high yields (>90%)
as yellow, crystalline solids, and they are stable at room
temperature in the solid state as well as in solution. The melting
points (decomposition) for 6-9 are significantly higher by about
30 °C than those of the corresponding nonfluorinated complexes,
and this result indicates the stabilizing effect of electronegative
substituents on the aromatic ring (Vide infra). The synthesis of
the fluorinated bis(aryloxo)palladium complexes 6-9 from bis-
(phenoxo)palladium complexes is remarkable in that the liber-
ated phenol does not associate to 6-9 to form adducts through
intramolecular O-H‚‚‚O hydrogen bonding with the oxygen
atom of the pentafluorophenoxide ligands. However, the
phenoxide complexes 1-5 do form O-H‚‚‚O hydrogen-bonded
(10) Mayer, J. M. Comments Inorg. Chem. 1988, 8, 125.
(11) (a) Heil, B.; Marko, L.; Toros, S. Homogeneous Catalysis with Metal
Phosphine Complexes; Pignolet Ed.: New York, 1983; p 329. (b)
Yamamoto, A. Organotransition Metal Chemistry; Wiley Inter-
science: New York, 1986; p 36. (c) Davies, S. G. Organotransition
Metal Chemistry: Applications to Organic Syntheses; Pergamon
Press: Oxford, 1982; p 348. (d) Paonessa, R. S.; Trogler, W. C. Inorg.
Chem. 1983, 22, 1038. (e) Ali, B. E.; Alper, H. J. Org. Chem. 1991,
56, 5357. (f) Ott, J.; Schmid, B.; Venanzi, L. M.; Wang, G.; Ward,
T. R. New J. Chem. 1990, 14, 495. (g) Hirose, K.; Keim, W. J. Mol.
Catal. 1992, 73, 271. (h) Barbaro, P.; Bianchini, C.; Frediani, P.;
Meli, A.; Vizza, F. Inorg. Chem. 1992, 31, 1523.
(12) Drent, E.; Arnoldy, P.; Budzelaar, P. H. M. J. Organomet. Chem. 1993,
455, 247.
(13) Drent, E.; van Broekhoven, J. A. M.; Doyle, M. J. J. Organomet. Chem.
1990, 417, 235.
(14) (a) Alsters, P. L.; Baesjou, P. J.; Janssen, M. D.; Kooijman, H.;
Sicherer-Roetman, A.; Spek, A. L.; van Koten, G. Organometallics
1992, 11, 4124. (b) Kapteijn, G. M.; Smeets, W. J. J.; Spek, A. L.;
Grove, D. M.; van Koten, G. Inorg. Chim. Acta 1993, 207, 131. (c)
Kapteijn, G. M.; Dervisi, A.; Grove, D. M.; Lakin, M. T.; Kooijman,
H.; Spek, A. L.; van Koten, G. J. Am. Chem. Soc. 1995, 117, 10939.

528 Inorganic Chemistry, Vol. 35, No. 2, 1996
Kapteijn et al.
adducts with phenol molecules (Vide infra). Adduct formation
with alcohols is considered to be a general property of late
transition metal alkoxide complexes,4 and in earlier studies we
found that in the molecular structures of the N-donor-ligated
phenoxopalladium(II) complexes trans-[Pd(OPh)2(pyrrolidine)2]‚-
2HOPh14a and [Pd(Me)(OPh)(tmeda)]‚HOPh14c the phenol
molecules are indeed associated through O-H‚‚‚O hydrogen
bonds.
The complex [Pd(OPh)2(bpy)] (1) shows an interesting
reactivity toward an excess of 1,1,1,3,3,3-hexafluoro-2-propanol
(pKa ) 9.3), with which it reacts to afford an unusual “mixed”
alkoxo(aryloxo)palladium(II) complex, [Pd(OCH(CF3)2)(OPh)-
(bpy)]‚HOPh (10).14b This complex is the first example of a
late transition metal complex with both an alkoxide and an
aryloxide ligand. We believe that the reason that the remaining
OC6H5 unit in 10 is not substituted for OCH(CF3)2 under the
reaction conditions employed is due to the combined stabilizing
effect of the O-H‚‚‚O and C-H‚‚‚O hydrogen bonds.
In this area of chemistry, it is clear that alkoxide and aryloxide
complexes can be formed with very different characteristics,
and it is therefore worth summarizing at this point the bonding
description of alkoxide and aryloxide palladium(II) complexes.
In square-planar PdII species containing monoanionic RO-
ligands, the metal center has a total of 16 valency electrons.
The RO- ligand forms a σ-bond from the oxygen to the metal,
and this bond will be strongly influenced by the nature of the
trans ligand. In general one can expect a ligand with a high
trans influence to lengthen the M-O bond, whereas one with a
low trans influence should shorten this bond. This M-O bond
could in principle be strengthened (i.e. gain double bond
character) if π-donation from the lone pairs on oxygen to the
metal is promoted. This situation could arise, for example, if
the metal center has a low number of d-electrons; however, for
late transition metals π-back-donation is expected to be of little
importance and repulsion between the lone pairs on oxygen and
filled metal d-orbitals is likely to destabilize the M-OR
bonding. The nature of the R substituent (either alkyl or aryl)
will effect the electron density of the oxygen atom and hence
the stability of the M-O bond. With alkyl substituents the
density at oxygen will remain high and the M-O σ-bond will
be enhanced, as will competitive repulsive effects. In contrast,
aryl groups are able to delocalize some of the electron density
at oxygen into the ring systems, and although this will not effect
the M-O σ-bond too much, it will decrease destabilizing effects
of the oxygen lone pairs. If the rings bear electronegative
substituents (e.g. fluorine atoms), there appears to be a contrac-
tion of the oxygen atomic orbitals that not only yields systemati-
cally shorter C-O σ-bonds (i.e. there is increased π-donation
from oxygen to the fluorinated aromatic ring) but also lowers
the donating ability of the oxygen atom toward the metal center.
This increased π-donation from the oxygen atom to the
fluorinated aromatic ring will increase the double bond character
of the C-O bond (see Figure 2) and thereby produce larger
In the bis(aryloxo)palladium(II) complexes 1 and 6, the
environments at the metal centers are similar, and the structures
offer a unique opportunity for studying the effects related to
the nature of the aryloxide ligands. Both complexes possess
an approximate square-planar coordination geometry with
adjacent interligand angles around the palladium centers falling
in the range 80.6(2)-97.8(2)°. In complex 1 in which the
aryloxide ligands are trans to the N-donors, the Pd-O distances
are 1.996(7) and 1.983(6) Å. In related phenoxopalladium(II)
complexes having either P or O ligands trans to the aryloxide
unit, the corresponding distances are shorter by ∼0.10 Å.1,4a,d
The main structural difference between 1 and 6 concerns the
orientation of the aryloxide ligands: in 6 the fluorinated
aryloxide ligands are almost parallel (7.0(2)°) to each other,
whereas in 1 the phenoxide ligands are skewed away from each
other (72.5(5)°). An explanation, using a variety of empirical
models, for the nonbonded intramolecular contacts between the
aryloxide rings (π-π stacking) in 6 is presented in detail in
another paper.15 From this latter study it was concluded that
the origin for the difference between the two bis(aryloxide)
systems 1 and 6 lies in the electrostatic interactions between
the aromatic rings. Stacking interactions are unfavorable for
two phenyl groups (as in 1) owing to repulsive electrostatic
interactions between the π-electron densities. Fluorine substit-
uents (as in 6) reduce the effective electron density on the rings,
which lowers the π-electron repulsion to allow attractive
dipole-dipole interactions.
A single crystal X-ray diffraction study of the adduct complex
[Pd(OCH(CF3)2)(OPh)(bpy)]‚HOPh (10) (see Figure 4) shows
it to have a square-planar coordination geometry similar to those
found in the crystal structures of the bis(aryloxo)palladium
complexes 1 and 6. Complex 10 contains two different anionic
ligands, namely C6H5O- and (CF3)2CHO-, and this is, therefore,
the first structurally characterized mixed alkoxo(aryloxo)-
palladium(II) complex. We reported the molecular structure
and X-ray experimental data of 10 earlier as a communication.14b
The C-O distance of the phenoxide unit in 10 (1.359(10) Å)
is similar to the C-O distances found in 1 and 6. This is
remarkable as the oxygen atom of the phenoxide ligand in 10
is associated with a phenol molecule through O-H‚‚‚O hydro-
gen bonding (O‚‚‚O ) 2.642(8) Å), which should reduce the
donating ability of the oxygen toward the metal center. It is
known that association of phenol to the palladium aryloxide
complexes [Pd(Me)(OPh)(PMe3)2]4a or [Pd(Me)(OPh)(tmeda)]14c
can result in lengthening of the C-O bond in the aryloxide
unit. Another factor that can contribute to a lengthening of the
phenoxide C-O bond in 10 is the position of the acidic proton
of the OCH(CF3)2 group close to the oxygen atom of the
phenoxide in what can be seen as a C-H‚‚‚O interaction (C‚‚‚O
) 2.95(1) Å). It is known that a polarized C-H bond can form
an electrostatic interaction with the oxygen atom of a phenoxide
group and so stabilize the structure as a whole.14b,c This may
be termed a steering interaction which, though small in energy
(1-2 kcal mol-1), is sufficient to select a preferred molecular
conformation.16 In our case this nonbonded C-H‚‚‚O interac-
tion may be regarded as representing the incipient stage of a
base-assisted â-hydrogen elimination,17 involving transfer of the
proton from OCH(CF3)2 to the oxygen atom of the phenoxide
anion that would result in a ketone and a phenol coordinated to
the palladium center (see Figure 5). In this context it is worth
Figure 2. π-Donation from oxygen to the aromatic ring.
M-O-C angles. One anticipates different structural and
spectroscopic characteristics for C6H5O- and C6F5O-, and that
is indeed what we find.
Molecular Structures of 1, 6, and 10. Figures 3 and 4 show
the molecular structures of the bis(aryloxide) complexes [Pd-
(OPh)2(bpy)] (1) and [Pd(OC6F5)2(bpy)] (6) and the aryloxo-
(alkoxo) complex [Pd(OCH(CF3)2)(OPh)(bpy)]‚HOPh (10),
respectively. Selected bond lengths and angles for 1 and 6 are
summarized in Table 1.
(15) Hunter, C. A.; Lu, X.-J.; Kapteijn, G. M.; van Koten, G. J. Chem.
Soc., Faraday Trans. 1995, 91, 2009.
(16) Desiraju, G. R. Acc. Chem. Res. 1991, 24, 290.
(17) (a) Bu¨rgi, H. B.; Dunitz, J. D.; Shefter, E. Acta Crystallogr. 1974,
B30, 1517. (b) Bu¨rgi, H. B. Angew. Chem., Int. Ed. Engl. 1975, 14,
460. (c) Dunitz, J. D. Phil. Trans. R. Soc. London 1975, B272, 99.

Bis(aryloxo)palladium(II) Complexes
Inorganic Chemistry, Vol. 35, No. 2, 1996 529
Figure 3. Thermal motion ellipsoid plot (ORTEP, 50% probability) of the molecular structures of [Pd(OPh)2(bpy)] (1) (left) and [Pd(OC6F5)2-
(bpy)] (6) (right) together with the adopted numbering scheme.
Figure 4. Thermal motion ellipsoid plot (ORTEP, 50% probability) of the molecular structure of [Pd(OCH(CF3)2(OPh)(bpy)]‚HOPh (10) together
with the adopted numbering scheme.
Table 1. Relevant Bond Lengths (Å) and Bond Angles (deg) for
the Aryloxide Complexes 1 and 6a
1
6
1
6
Bond Lengths
Pd-O(1) 1.996(7) 2.013(3) Pd-N(2)
Figure 5. â-Hydrogen elimination from a fluorinated alkoxide
complex.
2.013(7)
1.998(5)
Pd-O(2) 1.983(6) 2.013(4) C(1)-O(1) 1.332(13) 1.309(7)
Pd-N(1) 2.005(8) 1.989(6) C(7)-O(2) 1.331(13) 1.310(7)
Literature data shows that the O-H‚‚‚O bonds between phenols
and palladium or platinum alkoxide complexes have O‚‚‚O
distances in the range 2.59-2.65 Å, and measured enthalpy
values for phenol association are typically -4.1 to -5.9 kcal
Bond Angles
O(1)-Pd-O(2) 93.7(3) 97.78(16) O(2)-Pd-N(2) 93.0(3) 90.59(18)
O(1)-Pd-N(1) 92.1(3) 90.56(18) N(1)-Pd-N(2) 81.7(3) 80.6(2)
O(1)-Pd-N(2) 171.2(3) 170.1(2) Pd-O(1)-C(1) 121.0(7) 123.3(3)
O(2)-Pd-N(1) 172.9(3) 169.93(17) Pd-O(2)-C(7) 119.6(6) 124.8(3)
mol-1 4b,d,f,14a-c
Since the phenol molecule in 10 is O-H‚‚‚O
.
a Estimated standard deviations in the least significant digits are given
in parentheses.
hydrogen bonded with the more basic phenoxide (pKa ) 9.9)
ligand and not to the less basic hexafluoroisopropoxide unit (pKa
) 9.3), one can deduce that the reactivity of anionic RO- ligands
coordinated to a metal center still follow the concepts of organic
acids and bases.
Solid State IR Spectra. The IR spectra of the bis(aryloxo)-
palladium complexes [Pd(OAr)2(N∼N)] (1-9) show a strong
absorption in the region 1275-1310 cm-1, which is ascribed
noting that complexes with coordinated ketones have recently
been proposed as intermediates in palladium-catalyzed acetal-
ization reactions.11f
The O‚‚‚O distance of 2.642(8) Å in 10 can be used as a
measure of the strength of the O-H‚‚‚O hydrogen bond.

530 Inorganic Chemistry, Vol. 35, No. 2, 1996
Kapteijn et al.
Table 2. C-O Stretching Frequencies for Bis(aryloxo)palladium
Complexes [Pd(OR)2(N∼N)]a
ν(C-O)
N∼N
R ) C6H5
R ) C6F5
bpy
1280 (1)
1280 (2)
1275 (4)
1280 (5)
1310 (6)
1310 (7)
1305 (8)
1305 (9)
tmeda
dpe
dmap
a Stretching frequencies are reported in cm-1
.
IR spectra were
recorded in the solid state as KBr pellets. For comparison: ν(C-O)
PhOH 1240 cm-1; NaOPh 1320 cm-1
.
to the (M)O-C(Ar) stretching vibration (ν(C-O)) of the
aryloxide unit (see Table 2).14a These data contrast with ν(C-
O) values for main group and early transition metal phenoxides,
Figure 6. Formation of bis(phenol) adducts and phenoxide-phenol
exchange.
which lie considerably lower in the range 1100-1200 cm-1 18
.
It is known that the C-O bond order in transition metal
phenoxides varies with the degree of metal-to-oxygen dπ-pπ
bonding, and Auerbach et al. found an increasing frequency
(from 1249 to 1298 cm-1) with decreasing dπ-pπ M-O
bonding, i.e. with increasing number of d-electrons.19 The low
ν(C-O) values of our new bis(aryloxo)palladium(II) complexes
1-9 are therefore, by analogy, evidence for the absence of dπ-
pπ bonding. One also sees that ν(C-O) values of the bis-
(pentafluorophenoxo)palladium complexes 6-9 are higher than
those of the bis(phenoxo)palladium complexes 1-5, and this
would be consistent with a C-O bond length in the fluorinated
aryloxide complexes that is shorter than in the phenoxide
complexes.
cally inequivalent, and this fact is reflected in the presence of
two sets of phenoxide carbon resonances in its 13C NMR
spectrum (CDCl3); i.e. the phenoxide ligand is significantly
influenced by the electronic properties of the trans-positioned
donor atoms. However, this ligand inequivalence is not seen
1
in the H NMR spectrum (300 MHz) of 5, where the protons
on the two aromatic rings afford one set of resonances.
Solution Behavior of Phenol Adducts (10-13). Addition
of 2 equiv of phenol to the bis(phenoxo)palladium complexes
1, 2, and 4 leads to the in situ formation of the bis(phenol)
adducts [Pd(OPh)2(bpy)]‚2HOPh (11), [Pd(OPh)2(tmeda)]‚-
2HOPh (12), and [Pd(OPh)2(dpe)]‚2HOPh (13), respectively (see
Figure 6), which have been characterized by 1H and 13C NMR.
It has not proved possible to isolate 11-13 as solids, since
attempted isolation by precipitation or crystallization regenerated
1
NMR of (Aryloxo)palladium Complexes. The H NMR
data of the complexes [Pd(OAr)2(N∼N)] (1-9) are summarized
in Table 3. For the bis(phenoxo)complexes 1-5 at room
temperature (CDCl3), the ortho, meta, and para protons of the
phenoxide ligands afford well-resolved separate resonances with
all the ortho protons and all the meta protons being equivalent
on the NMR time scale, a situation consistent with rapid rotation
of the phenyl group about the C-O axis. The ortho protons
for these complexes are significantly shifted downfield compared
to both free phenol and sodium phenolate, and this characteristic
low-field resonance position can be attributed to the bent
structure of the M-O-Ph unit ( M-O-Ar 121-124° in the
crystal structures of 1, 6, and 10). As a result of this, each
ortho proton spends a considerable amount of time in a position
above the coordination plane of the metal where it is influenced
by the magnetic anisotropy of the metal center.20 The 13C NMR
data of 2-5 are summarized in Table 4. The phenoxide 13C
NMR chemical shifts of the bis(aryloxo)palladium complexes
1
the starting materials. In the H NMR spectra of these latter
species and the mono(phenol) adduct 10, the presence of
O-H‚‚‚O hydrogen bonds between the oxygen atom of the
phenoxide ligand and the OH hydrogen of the associated phenol
in solution is clearly indicated (Vide infra).
1
In the H NMR spectra of 12 a broad resonance due to the
O-H hydrogen of the phenol molecules associated to the
oxygen atoms of [Pd(OPh)2(tmeda)] appears at ca. 7.5 ppm,
i.e. at significantly lower field than the OH hydrogen of
noncomplexed phenol at ca. 5.5 ppm in dry CDCl3. A similar
low-field shift of the O-H hydrogen has also been observed
for related late transition metal alkoxide or phenoxide complexes
in which an alcohol molecule is associated through strong
O-H‚‚‚O hydrogen bonding with the oxygen atom of an
alkoxide or aryloxide ligand.4a,b,f,14a-c However, the resonance
position of the OH hydrogen in 11-13 is less shifted to low
field than in closely related palladium phenoxide adducts (δ )
9.5-11.0 ppm), and this, together with the fact that it was not
possible to isolate these adducts, is an indication of a weak
O-H‚‚‚O hydrogen bond in 11-13. 1H NMR spectra of the
mixed alkoxide aryloxide palladium complex 10 also reveal the
presence of an OH resonance at low field (ca. 8.5 ppm), which
indicates the presence of O-H‚‚‚O hydrogen bonding in
solution.
When a CDCl3 solution of 11-13 is heated, the OH signal
shifts to higher field, consistent with a shift of the association
equilibrium toward uncomplexed 1, 2, or 4 and free phenol.
We made several attempts to determine the equilibrium constants
for O-H‚‚‚O hydrogen bond formation between the cis-bis-
(phenoxo)palladium complexes 1-5 and phenol using the
Scatchard method,23 but due to the low solubility of these com-
plexes in common organic solvents it was not possible to obtain
2-5 are similar to both those of typical anionic phenoxides like
+ 21
C6H5O-Na+ or C6H5O-NBu4
and those of analogous
palladium and platinum phenoxide complexes.14a-c In these
complexes the large ∼13 ppm low-field shift of the ipso carbon
atom (δ ≈ 167 ppm) and the significant high-field shift of ∼7
ppm of the para carbon atom (δ ≈ 114 ppm) compared to the
shift values for phenol22 indicate a strongly polarized M-O
bond. Due to the presence of a nonsymmetrical nitrogen donor
ligand in 5, the phenoxide ligands are chemically and magneti-
(18) Malhotra, K. C.; Martin, R. L. J. Organomet. Chem. 1982, 239, 159.
(19) Auerbach, U.; Weyhermu¨ller, T.; Wieghardt, K.; Nuber, B.; Bill, E.;
Butzlaff, C.; Trautwein, A. X. Inorg. Chem. 1993, 12, 508.
(20) (a) Miller, R. G.; Stauffer, R. D.; Fahey, D. R.; Farnell, D. R. J. Am.
Chem. Soc. 1970, 92, 1511. (b) Albinati, A.; Pregosin, P. S.;
Wombacher, F. Inorg. Chem. 1990, 29, 1812.
(21) (a) Kraft, T. E.; Hejna, C. I.; Smith, J. S. Inorg. Chem. 1990, 29,
2682. (b) Noyori, R.; Nishida, I.; Sakata, J. Tetrahedron Lett. 1981,
22, 3993.
(22) Johnson, L. F.; Jankowski, W. C. Carbon-13 NMR Spectra; Wiley:
New York, 1972.
(23) Joesten, M. D.; Schaad, L. J. Hydrogen Bonding; Marcel Dekker: New
York, 1974; p 173.

Bis(aryloxo)palladium(II) Complexes
Inorganic Chemistry, Vol. 35, No. 2, 1996 531
N∼N and HOCH(CF3)2
Table 3. 1H NMR Data of Palladium Aryloxide Complexesa
compound
phenoxide/phenol
1b
2
3
7.21 (d, o-H), 6.99 (t, m-H), 6.49 (t, p-H)
7.17 (d, o-H), 6.98 (t, m-H), 6.46 (t, p-H)
7.08 (d, o-H), 6.94 (t, m-H), 6.42 (t, p-H)
bpy; 8.72 (dd, H6), 8.11 (t, H4), 8.01 (d, H3), 7.58 (td, H5)
tmeda; 2.61 (s, NCH3), 2.56 (s, NCH2)
teeda; 3.02 (m, CH2CH3), 2.61 (m, CH2CH3), 2.45 (s, NCH2),
1.46 (t, CH2CH3)
4
7.15 (d, o-H), 7.00 (t, m-H), 6.45 (t, p-H)
7.16 (d, o-H), 6.85 (t, m-H), 6.31 (t, p-H)
dpe; 3.57-3.19 (m, NCH2), 2.87 (s, NCH2-CH2N),
1.72-1.32 (m, CH2)
5b
dmap; 8.40 (d, H6), 8.09 (td, H4), 7.66 (d, H3), 7.52 (t, H5),
4.30 (s, CH2), 2.70 (s, CH3)
bpy; 8.65 (dd, H6), 8.18 (t, H4), 8.04 (d, H3), 7.62 (td, H5)
tmeda; 2.60 (s, NCH2), 2.58 (s, NCH3)
6b
7
8
dpe; 3.58-3.30 (m, NCH2), 2.97 (s, NCH2-CH2N),
1.81-1.28 (m, CH2)
9b,c
dmap; 8.31 (d, H6), 8.19 (td, H4), 7.76 (d, H3), 7.60 (t, H5),
4.48 (s, CH2), 2.81 (s, CH3)
bpy; 8.83 (dd, H6), 8.47 (dd, H6′), 8.15-8.03 (m, H4, H4′),
7.98 (d, H3, H3′), 7.65 (td, H5′), 7.46 (td, H5).
HOCH(CF3)2; 4.26 (sep, OCH)
10b,d
8.5 (br s, OH), 7.32 (d, o-H), 7.07 (t, m-H),
6.57 (t, p-H)
11b
12
7.0 (s, OH), 7.25-7.10 (m, o-H PdOPh, m-H HOPh),
7.03 (t, m-H PdOPh), 6.93 (t, p-H HOPh)
6.84 (d, o-H HOPh), 6.57 (t, p-H PdOPh)
7.5 (s, OH), 7.28 (d, o-H PdOPh), 7.20 (t, m-H HOPh),
6.96 (t, m-H PdOPh), 6.89 (t, p-H HOPh)
bpy; 8.87 (dd, H6), 8.08 (t, H4), 7.97 (d, H3), 7.56 (td, H5)
tmeda; 2.51 (s, NCH3), 2.36 (s, NCH2)
6.84 (d, o-H HOPh), 6.54 (t, p-H PdOPh)
7.3 (s, OH), 7.25 (d, o-H PdOPh), 7.17 (t, m-H HOPh),
6.98 (t, p-H HOPh), 6.87 (d, o-H HOPh)
13
dpe; 3.45-3.21 (m, NCH2), 2.77 (s, NCH2-CH2N),
1.60-1.25 (m, CH2)
6.82 (d, m-H PdOPh), 6.53 (t, p-H PdOPh).
a Measurements at 300 MHz in CDCl3 at room temperature unless denoted otherwise. Abbreviations: br, broad; s, singlet; d, doublet; t, triplet;
m, multiplet. Coupling constants within the phenoxide/phenol units: 3J ) 7-8 Hz; 4J ) 1.5 Hz. b For bpy or dmap: H6, 3J ) 6-7 Hz; 4J ) 1 Hz.
3
4
3
3
H5, J ) 6-7 Hz, J ) 1 Hz. H4, J ) 7-8 Hz. H3, J ) 7-8 Hz. c Measured in acetone-d6. d For OCH(CF3)2: 2J(F, H) ) 7 Hz.
Table 4. 13C NMR Data of Palladium Aryloxidesa
compound
phenoxide/phenol
N∼N and HOCH(CF3)2
2
3
4
168.24 (ipso-C), 128.00 (m-C), 119.58 (o-C), 114.21 (p-C)
167.92 (ipso-C), 128.47 (m-C), 119.40 (o-C), 113.85 (p-C)
167.30 (ipso-C), 128.53 (m-C), 119.65 (o-C), 114.20 (pC)
tmeda; 61.88 (NCH2), 49.91 (NCH3)
teeda; 52.16 (CH2CH3), 51.34 (NCH2), 10.67 (CH2CH3)
dpe; 55.74 (NCH2), 53.26 (N(CH2)2N), 23.36 (N(CH2)2CH2),
19.59 (NCH2CH2)
5
167.21 (ipso-C), 166.97 (ipso-C), 128.78 (m-C), 128.70 (m-C)
119.90 (o-C), 119.62 (o-C), 115.03 (p-C), 114.78 (p-C)
dmap; 158.65 (C2), 149.40 (C6), 139.32, 124.14, 121.74
(C3, C4, C5), 69.97 (NCH2), 50.77 (NCH3)
12
164.76 (ipso-C PdOPh), 156.19 (ipso-C HOPh), 129.57 (m-C HOPh) tmeda; 55.74 (NCH2), 53.26 (N(CH2)2N),
129.01 (m-C PdOPh), 120.08 (o-C HOPh), 119.92 (o-C PdOPh),
116.27 (p-C PdOPh), 115.70 (p-C HOPh)
165.36 (ipso-C PdOPh), 156.73 (ipso-C HOPh), 129.44 (m-C HOPh) dpe; 56.00 (NCH2), 53.27 (N(CH2)2N)
13
128.73 (m-C PdOPh), 119.96 (o-C PdOPh), 119.64 (o-C HOPh),
115.80 (p-C HOPh), 115.59 (p-C PdOPh)
23.06 (N(CH2)2CH2), 19.57 (NCH2CH2)
a All measurements at 75 MHz in CDCl3 at room temperature (unless denoted otherwise). No 13C NMR data were obtained for 1 and 6-11
because of low solubility in organic solvents. b Measured in CD2Cl2. c For OCH(CF3)2 2J(C, F) ) 30.0 Hz; CF3 carbon atom not observed.
thermodynamic parameters using this method. Alsters et al.
have shown that it is possible to obtain thermodynamic para-
meters (Scatchard method) for association of phenol to the trans-
bis(phenoxo)palladium(II) complex [Pd(OPh)2(pyrrolidine)2].14a
show no evidence for O-H‚‚‚O hydrogen bonding, with the
O-H hydrogen of the added alcohol remaining at the resonance
position of the free nonassociated alcohol. This result is
consistent with the bonding description that fluorine atoms lower
the anionic character of the aryloxide ligand (Vide supra).
Concluding Remarks. N-donor-ligated palladium(II) com-
plexes containing two aryloxide ligands are easily prepared and
prove to be stable in the solid state as well as in solution. They
have a tendency to form O-H‚‚‚O hydrogen bonds in solution,
and this indirectly shows that the Pd-O bond in these complexes
has quite a polar character. In the C6F5O- complexes the
presence of fluorine atoms results in the formation of π-π
stacked orientation of the aryloxide rings and also lowers the
tendency for adduct formation. These new palladium complexes
have potential use as models in various palladium-catalyzed
synthetic reactions which involve metal-to-oxygen bonds, and
they offer interesting possibilities in the exploration of new
stoichiometric and catalytic reactions.
1
In the H and 13C NMR spectra of the bis(phenol) adducts
11-13, there are separate sets of resonances for the phenoxide
ligands and for associated phenol. Compared to 1, 2, and 4,
the resonances of the phenoxide in 11-13 are slightly shifted
toward those of phenol, and the resonances of the associated
phenol are shifted toward those of a phenoxide anion. The 1H
NMR data (CDCl3) in the temperature range 243-333 K provide
no evidence for exchange between the phenoxide unit and
(associated) phenol for these cis-bis(phenoxo)palladium com-
plexes. This means that when exchange is occurring it must
be slow on the NMR time scale (see Figure 6). However,
phenoxide/phenol exchange is fast on the laboratory time scale;
after addition of 2 equiv of pentadeuterophenol to a solution of
1, 2, or 4 in CDCl3, the 1H NMR spectrum shows new signals
for (associated) phenol and the phenoxide ligand signals are
reduced to half their original intensity.
Experimental Procedures
The fluorinated bis(aryloxo)palladium complexes (6-9) when
treated with either 1,1,1,3,3,3-hexafluoro-2-propanol or phenol
General Methods. Reactions were performed in an atmosphere of
nitrogen using standard Schlenk techniques. Benzene, diethyl ether,

532 Inorganic Chemistry, Vol. 35, No. 2, 1996
Kapteijn et al.
Table 6. Final Coordinates and Equivalent Isotropic Thermal
Table 5. Crystallographic Data for 1 and 6a
Parameters of the Non-Hydrogen Atoms for 1
1
6
atom
x
y
z
Ueq (Å2)a
empirical formula
formula weight
space group
cryst system
Z
a, Å
b, Å
C22H18N2O2Pd
448.82
P212121 (No. 19) P1h (No. 2)
orthorhombic
4
6.7655(6)
16.0585(10)
16.7275(13)
C22F10H8N2O2Pd
628.72
Pd
0.02855(11)
0.0747(11)
0.0078(11)
0.0238(13)
0.0135(11)
-0.0637(17)
-0.015(2)
-0.153(2)
-0.340(2)
-0.392(2)
-0.2522(18)
0.1713(17)
0.1650(19)
0.327(2)
0.18551(5)
0.2061(5)
0.0631(4)
0.3078(5)
0.1783(5)
0.1882(8)
0.1980(7)
0.1842(7)
0.1576(7)
0.1498(7)
0.1641(6)
0.0170(6)
-0.0649(7)
-0.1142(7)
-0.0868(7)
-0.0079(7)
0.0439(7)
0.3681(6)
0.4506(7)
0.4706(6)
0.4087(7)
0.3268(6)
0.2534(7)
0.2577(7)
0.1874(8)
0.1101(8)
0.1078(7)
0.14770(5) 0.0384(2)
O(1)
O(2)
N(1)
N(2)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
0.2639(4)
0.1611(4)
0.1236(4)
0.0277(4)
0.3179(6)
0.3981(6)
0.4575(6)
0.4390(7)
0.3598(7)
0.3002(6)
0.1621(6)
0.1305(6)
0.1309(7)
0.1605(6)
0.1907(6)
0.1928(6)
0.1771(6)
0.1557(7)
0.0755(7)
0.0183(6)
0.0437(6)
-0.0090(6)
-0.0920(6)
-0.1359(6)
-0.0997(6)
-0.0167(6)
0.051(3)
0.051(3)
0.043(3)
0.040(3)
0.047(3)
0.055(4)
0.066(5)
0.069(6)
0.067(5)
0.050(4)
0.042(4)
0.056(4)
0.064(5)
0.060(4)
0.059(4)
0.046(4)
0.047(3)
0.066(4)
0.058(4)
0.050(4)
0.040(3)
0.043(3)
0.050(4)
0.058(4)
0.060(5)
0.053(4)
triclinic
2
7.567(4)
12.708(3)
12.912(5)
61.51(3)
74.74(4)
88.76(4)
1044.8(9)
1.998
c, Å
R, deg
â, deg
γ, deg
V, Å3
1817.3(2)
1.640
10.3
D
µ
calcd, g cm-3
calcd, cm-1
9.9
C(8)
C(9)
radiation (Mo KR), Å 0.71073
(Zr-filtered)
25
0.71073
(graphite monochromator)
-123
0.046
0.062
C(10)
C(11)
C(12)
C(13)
C(14)
C(15)
C(16)
C(17)
C(18)
C(19)
C(20)
C(21)
C(22)
0.503(2)
0.517(2)
T, °C
RF
RwF
0.048
0.046
0.3507(17)
0.0258(16)
0.0170(19)
0.0117(18)
0.0107(16)
0.0183(14)
0.0138(18)
0.0185(19)
0.0203(15)
0.014(2)
2
a RF ) ∑||Fo| - |Fc||/∑|Fo| and RwF ) [∑w(||Fo| - |Fc||)2/∑wFo ]1/2
.
and pentane were freshly distilled from sodium benzophenone ketyl.
CH2Cl2 was distilled from CaH2. All other solvents were used as
received. The solvents acetone (p.a) and methanol (p.a) and the
materials 1,1,1,3,3,3-hexafluoro-2-propanol, 2,2′-bipyridyl, phenol,
pentafluorophenol, and Celite (filter aid) were purchased from Janssen
Chimica. 1H (300.13 MHz) and 13C NMR (75.03 MHz) spectra were
recorded on a Bruker AC 300 spectrometer at ambient temperature in
NMR solvents (CDCl3, CD2Cl2, and C6D6) obtained from ISOTEC Inc.
1H and 13C NMR data of the new complexes 1-13 are summarized in
Tables 3 and 4, respectively. Infrared spectra (KBr disks) were recorded
on a Perkin-Elmer 283 spectrometer. Elemental analyses were carried
out by Dornis und Kolbe, Mikroanalytisches Laboratorium, Mu¨lheim
a.d. Ruhr, Germany.
0.0100(19)
a Ueq ) /3 of the trace of the orthogonalized U tensor.
1
as described for 6, but starting from 2, 4, or 5 in place of 1. Mp for
7: 210 °C dec. Mp for 8: 184 °C dec. Mp for 9: 152 °C dec. Anal.
Calcd for C18H16F10N2O2Pd (7): C, 36.72; H, 2.74; N, 4.76. Found:
C, 36.70; H, 2.77; N, 4.72. Anal. Calcd for C20H12N2F10O2Pd (9): C,
39.46; H, 1.99; N, 4.60. Found: C, 39.62; H, 1.91; N, 4.71.
[Pd(OPh)2(bpy)] (1). To a solution of Pd(OAc)2 (0.50 g, 2.23
mmol) and bpy (0.36 g, 2.30 mmol) in CH2Cl2 (50 mL) was added a
solution of NaOPh (0.52 g, 4.50 mmol) in a minimum of MeOH (ca.
5 mL). The resulting dark-red mixture was stirred for 1 h, after which
the solution was evaporated to dryness under reduced pressure. The
residue was extracted with CH2Cl2 (8 × 50 mL), and the extracts were
filtered over Celite. The orange filtrate was evaporated to dryness,
and the solid product was washed with pentane and dried in Vacuo.
The solid can be crystallized by diffusion of Et2O into a CH2Cl2
solution. The resulting reddish-brown, needle-shaped crystals are
suitable for X-ray diffraction. Yield: 0.82 g (82%). Mp: 202 °C dec.
Anal. Calcd for C22H18N2O2Pd: C, 58.87; H, 4.04; N, 6.24. Found:
C, 59.56; H, 4.28; N, 6.23.
[Pd(OPh)2(N∼N)] (N∼N ) tmeda (2); teeda (3), dpe (4), dmap
(5)). Complexes 2-5 were prepared in 85-95 % yield as an orange
material as described for synthesis of 1, but using tmeda, dmap, or
dpe as the ligand. The complexes 2-5 have a better solubility in CH2-
Cl2 than 1. Mp for 2: 172 °C dec. Mp for 3: 170 °C dec. Mp for 4:
171 °C dec. Mp for 5: 139 °C dec. Anal. Calcd for C18H26N2O2Pd
(2): C, 52.87; H, 6.24; N, 6.85. Found: C, 52.69; H, 6.47; N, 6.94.
Anal. Calcd for C22H34N2O2Pd (3): C, 56.88; H, 7.40; N, 6.23.
Found: C, 56.83; H, 7.37; N, 6.03. Anal. Calcd for C24H34N2O2Pd
(4): C, 58.95; H, 7.01; N, 5.73. Found: C, 59.09; H, 7.11; N, 5.79.
Anal. Calcd for C20H22N2O2Pd (5): C, 55.18; H, 5.16; N, 6.40.
Found: C, 54.92; H, 5.42; N, 6.29.
[Pd(OC6F5)2(bpy)] (6). To a stirred suspension of 1 (0.20 g, 0.45
mmol) in CH2Cl2 (15 mL) was added pentafluorophenol (0.41 g, 2.25
mmol). After 1 h the yellow solution was filtered over Celite, and the
filtrate was evaporated to a small volume (ca. 3 mL). The pure product
was obtained by diffusion of pentane into this solution. The resulting
long, needle-shaped dark-yellow crystals (suitable for X-ray diffraction)
were washed with pentane (3 × 10 mL) and dried in Vacuo. Yield:
0.27 g (95%). Mp: 224 °C dec. Anal. Calcd for C22H8F10N2O2Pd:
C, 42.03; H, 1.28; N, 4.46. Found: C, 41.94; H, 1.35; N, 4.52.
[Pd(OC6F5)2(N∼N)] (N∼N ) tmeda (7), dpe (8), dmap (9)).
Complexes 7-9 were prepared in 85-95% yield as a yellow material
[Pd(OCH(CF3)2)(OPh)(bpy)]‚HOPh (10). To a stirred suspension
of 1 (0.20 g, 0.45 mmol) in CH2Cl2 (15 mL) was added 1,1,1,3,3,3-
hexafluoro-2-propanol (0.38 g, 2.25 mmol). After 1 h the yellow
solution was filtered off over Celite and evaporated to a small volume
(ca. 5 mL). The pure product was obtained by diffusion of pentane
into this solution. The resulting long, needle-shaped yellow crystals
(suitable for X-ray diffraction; see ref 14b) were washed with pentane
(3 × 10 mL) and dried in Vacuo. Yield: 0.22 g (81%). Mp: 192 °C
dec. Anal. Calcd for C19H14F6N2O2Pd: C, 43.66; H, 2.70; N, 5.36.
Found: C, 42.92; H, 2.74; N, 5.62.
Reactions of 1, 2, and 4 with Phenol (in Situ Preparation of the
Adducts [Pd(OPh)2(N∼N)]‚2HOPh (N∼N ) bpy (11), tmeda (12),
dpe (13)). A solution of 1, 2, or 4 in CDCl3 (0.5 mL, dried over calcium
chloride) was transferred to an NMR tube containing 2 equiv of phenol.
1H and 13C NMR data indicate the quantitative formation of the bis-
(phenol) adducts 11, 12, and 13, respectively. Due to the low solubility
of 11 in CDCl3, no 13C NMR data was obtained for this adduct. All
attempts to isolate these O-H‚‚‚O hydrogen-bonded species failed, and
during crystallization the starting materials were regenerated.
Crystal Structure Determination of [Pd(OPh)2(bpy)] (1).
A
reddish-brown, block-shaped crystal (0.12 × 0.18 × 0.50 mm) was
glued to the tip of a glass fiber and transferred to an Enraf-Nonius
CAD4-F diffractometer. Accurate unit cell parameters and an orienta-
tion matrix were determined by least-squares refinement of 25 well-
centered reflections (SET4) in the range 8.0° < θ < 13.0°. Reduced-
cell calculations did not indicate higher lattice symmetry.24 Crystal
data and details on data collection and refinement are presented in Table
5. Data were collected at ambient temperature in ω/2θ mode with
scan angle ∆ω ) 0.81 + 0.35 tan θ°. Intensity data of 3107 reflections
were collected in the range 1.21° < θ < 27.50°; of these 2938 are
independent. Data were corrected for Lorentz-polarization effects.
Three periodically measured reference reflections (2h11, 220, 172)
showed no significant decay (<1%) during 45 h of X-ray exposure
(24) Spek, A. L. J. Appl. Crystallogr. 1988, 21, 578.

Bis(aryloxo)palladium(II) Complexes
Inorganic Chemistry, Vol. 35, No. 2, 1996 533
time. Standard deviations of the intensities as obtained by counting
statistics were increased according to an analysis of the excess variance
of the reference reflections: σ2(I) ) σ2cs(I) + (0.008I)2.25 An empirical
absorption extinction correction was applied (DIFABS,26 correction
range 0.762-1.115). The structure was solved by automated direct
methods (SHELXS86).27 Refinement of F was carried out by full-
matrix least-squares techniques (SHELX76).28 Hydrogen atoms were
included in the refinement on calculated positions (C-H ) 0.98 Å)
riding on their carrier atoms. All non-hydrogen atoms were refined
with anisotropic thermal parameters; the hydrogen atoms were refined
with one overall isotropic thermal parameter of 0.065(8) Å2. Weights
were introduced in the final refinement cycles. Convergence was
reached at R ) 0.048, Rw ) 0.046, w ) 1/[σ2(F) + 0.00046F2], S )
Table 7. Final Coordinates and Equivalent Isotropic Thermal
Parameters of the Non-Hydrogen Atoms for 6
atom
x
y
z
Ueq (Å2)a
Pd(1)
F(1)
F(2)
F(3)
F(4)
F(5)
F(6)
F(7)
F(8)
F(9)
F(10)
O(1)
O(2)
N(1)
N(2)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
C(9)
C(10)
C(11)
0.21568(5)
0.6537(4)
0.7803(4)
0.5651(5)
0.2234(5)
0.0937(4)
0.3974(4)
0.4902(4)
0.2451(4)
-0.0998(4)
-0.1912(4)
0.3066(6)
0.0527(5)
0.3436(6)
0.1294(6)
0.3687(7)
0.5449(7)
0.6125(7)
0.5027(7)
0.3295(7)
0.2641(7)
0.1014(7)
0.2714(7)
0.3206(7)
0.1960(7)
0.0243(7)
0.41384(3) 0.39831(3) 0.0156(1)
0.4104(3)
0.2724(3)
0.1994(3)
0.2677(3)
0.4049(3)
0.1853(3)
0.0338(3)
-0.0471(3)
0.0220(3)
0.1798(3)
0.4779(3)
0.2670(3)
0.5597(4)
0.3801(4)
0.4105(4)
0.3747(5)
0.3046(5)
0.2699(4)
0.3037(5)
0.3730(5)
0.1906(4)
0.1475(4)
0.0685(4)
0.0270(4)
0.0644(4)
0.1442(4)
0.2060(3)
0.1007(3)
0.0032(3)
0.0081(3)
0.1133(3)
0.4297(3)
0.3393(3)
0.2635(3)
0.2863(3)
0.3704(3)
0.2153(3)
0.4417(3)
0.3796(4)
0.5726(4)
0.1656(4)
0.1578(4)
0.1053(4)
0.0538(4)
0.0578(4)
0.1105(4)
0.4013(4)
0.3937(4)
0.3491(4)
0.3109(5)
0.3208(4)
0.3630(4)
0.0313(10)
0.0329(10)
0.0329(10)
0.0332(11)
0.0312(10)
0.0259(9)
0.0284(9)
0.0304(10)
0.0312(10)
0.0267(9)
1.79, for 245 parameters and 1536 reflections with I > 2.5σ(I).
final difference Fourier map showed no residual density outside -0.72
and 0.58 e Å-3
Refinement of the alternative chirality resulted in
A
0.0282(11)
0.0241(11)
0.0206(12)
0.0192(12)
0.0195(14)
0.0219(16)
0.0211(14)
0.0219(14)
0.0216(16)
0.0209(16)
0.0189(12)
0.0203(14)
0.0209(14)
0.0216(14)
0.0200(14)
0.0188(14)
.
slightly higher values of R and Rw (0.055 and 0.051, respectively).
Positional parameters are listed in Table 6.
Crystal Structure Determination of [Pd(OC6F5)2(bpy)] (6).
A
dark-yellow, needle-shaped crystal (0.1 × 0.1 × 1.2 mm) was glued
to the tip of a glass fiber and transferred into the cold nitrogen stream
of an Enraf-Nonius CAD4-Turbo diffractometer with rotating anode.
Final lattice parameters were determined by least-squares treatment,
using the setting angles (SET4) of 25 well-centered reflections in the
range 10.0° < θ < 13.9°. The unit cell parameters were checked for
the presence of higher lattice symmetry.24 Crystal data and details on
data collection and refinement are collected in Table 5. Data were
collected at 150 K in ω/2θ mode with scan angle ∆ω ) 1.57 + 0.35
tan θ°. From a total of 3869 reflections in the range 1.83° < θ <
25.38° (3569 unique), 3161 satisfied the I > 2.5σ(I) criterion of
observability. Data were corrected for Lorentz-polarization effects and
for a decay of 3% of the three periodically measured reference
reflections (2h05h, 123h, 342) during 25 h of X-ray exposure time. An
empirical absorption extinction correction was applied (DIFABS,26
correction range 0.800-1.218). The structure was solved by automated
direct methods (SHELXS86).27 Refinement on F was carried out by
full-matrix least-squares techniques (SHELX76).28 Hydrogen atoms
were included in the refinement on calculated positions (C-H ) 0.98
Å) riding on their carrier atoms. All non-hydrogen atoms were refined
with anisotropic thermal parameters; the hydrogen atoms were refined
with one overall isotropic thermal parameter of 0.030(6) Å2. Weights
were introduced in the final refinement cycles. Convergence was
reached at R ) 0.046, Rw ) 0.062, w ) 1/[σ2(F) + 0.0001365F2], S )
1.48, for 335 parameters. A final difference Fourier map showed no
residual density outside -1.44 and 1.38 e Å-3 (near Pd), probably
absorption artifacts. Final positional parameters are listed in Table 7.
C(12) -0.0214(7)
1
a Ueq ) /3 of the trace of the orthogonalized U tensor.
Neutral atom scattering factors were taken from Cromer and Mann,29
and anomalous dispersion corrections were taken from Cromer and
Liberman.30 Geometrical calculations and illustrations were performed
with PLATON.31 All calculations were performed on a DECstation
5000/125.
Crystal Structure Determination of 10. See ref 14b.
Acknowledgment. Shell Research B.V. is gratefully thanked
(G.M.K.) for financial support. The investigations were sup-
ported in part (A.L.S., W.J.J.S.) by the Netherlands Foundation
for Scientific Research (SON) with financial aid from the
Netherlands Organization for Scientific Research (NWO).
Supporting Information Available: Further details of the structure
determinations, including listings of atomic coordinates, bond lengths
and angles, and thermal parameters for 1 and 6 (12 pages). Ordering
information is given on any current masthead page.
(25) McCandish, L. E.; Stout, G. H.; Andrews, L. C. Acta Crystallogr.
1975, A31, 245.
(26) Walker, N.; Stuart, D. Acta Crystallogr. 1983, A39, 158.
(27) Sheldrick, G. M. SHELXS86. Program for crystal structure deter-
mination. University of Go¨ttingen, Germany, 1986.
(28) Sheldrick, G. M. SHELX76. Program for crystal structure determi-
nation. University of Cambridge, Cambridge, 1976.
IC950563P
(29) Cromer, D. T.; Mann, J. B. Acta Crystallogr. 1968, A24, 321.
(30) Cromer, D. T.; Liberman, D. J. Chem. Phys. 1970, 53, 1891.
(31) Spek, A. L. Acta Crystallogr. 1990, A46, C34.