Stable Organopalladium(II) and Organoruthenium(II) Complexes with Spin-Labeled Phosphine Ligands

Article abstract of DOI:10.1021/om9905862

Palladium(II) and ruthenium(II) complexes containing aminoxyl radical-substituted triphenylphosphine ligands are reported. The novel spin-labeled phosphine ligands [(p-(4,4,5,5,-tetramethylimidazolinyl-1-oxyl-3-oxide)phenyl)diphenylphosphine] (1) and [(p-(N-oxyl-tert-butylamino-2-)phenyl)diphenylphosphine] (2) react with PdCl₂ to yield trans-Pd[1]₂Cl₂ and trans-Pd[2]₂Cl₂ (complexes 3 and 4, respectively), which show exchange-coupled EPR spectra. This through-space, intramolecular coupling provides a method of determining the number of radical phosphines coordinated to the Pd(II) center. Systems with only one coordinated phosphine show EPR spectra typical of the ligand. Phosphine 2 reacts with [(η³-C₃H₅)PdCl]₂ and [(η⁶-p-cymene)RuCl₂]₂ to form the mononuclear metal phosphine adducts (η³-C₃H₅)Pd[2]Cl (5) and (η⁶-p-cymene)Ru[2]Cl₂ (6). All complexes show broad, shifted ¹H NMR spectra, and magnetic susceptibility measurements confirm the presence of one (complexes 5, 6) or two (complexes 3, 4) radicals per complex accordingly. The X-ray crystal structures of Pd[2]₂Cl₂ and (η³-C₃H₅)Pd[2]Cl are also reported. Complexes 5 and 6 are unusual examples of stable organometallic systems with peripheral free radicals, i.e., spin-labeled organometallics.

Full text of DOI:10.1021/om9905862

Organometallics 1999, 18, 5097-5102
5097
Sta ble Or ga n op a lla d iu m (II) a n d Or ga n or u th en iu m (II)
Com p lexes w ith Sp in -La beled P h osp h in e Liga n d s
Daniel B. Leznoff,† Corinne Rancurel,† J ean-Pascal Sutter,*,† Steven J . Rettig,‡
Maren Pink,§ and Olivier Kahn*,†
Laboratoire des Sciences Mole´culaires, Institut de Chimie de la Matie`re Condense´e de
Bordeaux, UPR CNRS No. 9048, F-33608 Pessac, France, Department of Chemistry,
University of British Columbia, 2036 Main Mall, Vancouver, B.C. V6T 1Z1, Canada, and
X-ray Crystallographic Center, Department of Chemistry, 160 Kolthoff Hall, University of
Minnesota, Minneapolis, Minnesota 55455
Received J uly 26, 1999
Palladium(II) and ruthenium(II) complexes containing aminoxyl radical-substituted
triphenylphosphine ligands are reported. The novel spin-labeled phosphine ligands [(p-
(4,4,5,5,-tetramethylimidazolinyl-1-oxyl-3-oxide)phenyl)diphenylphosphine] (1) and [(p-(N-
oxyl-tert-butylamino-2-)phenyl)diphenylphosphine] (2) react with PdCl2 to yield trans-
Pd[1]2Cl2 and trans-Pd[2]2Cl2 (complexes 3 and 4, respectively), which show exchange-coupled
EPR spectra. This through-space, intramolecular coupling provides a method of determining
the number of radical phosphines coordinated to the Pd(II) center. Systems with only one
coordinated phosphine show EPR spectra typical of the ligand. Phosphine 2 reacts with [(η3-
C3H5)PdCl]2 and [(η6-p-cymene)RuCl2]2 to form the mononuclear metal phosphine adducts
1
(η3-C3H5)Pd[2]Cl (5) and (η6-p-cymene)Ru[2]Cl2 (6). All complexes show broad, shifted H
NMR spectra, and magnetic susceptibility measurements confirm the presence of one
(complexes 5, 6) or two (complexes 3, 4) radicals per complex accordingly. The X-ray crystal
structures of Pd[2]2Cl2 and (η3-C3H5)Pd[2]Cl are also reported. Complexes 5 and 6 are unusual
examples of stable organometallic systems with peripheral free radicals, i.e., spin-labeled
organometallics.
In tr od u ction
cals are known to interact directly with metal centers
via the N-O group as a weak ligand,8-10 in these
systems the radical groups are actively involved with
the metal center and hence cannot be termed “spin-
labeled” complexes. One notable example of a simple
route for addition of a remote spin label to organome-
tallic systems is the oxidative addition of alkyl bromides
(R-Br) to (bipy)PtMe2, where the alkyl R-group contains
a pendant TEMPO radical.11 This method of integration
of a spin label into organometallics, while clearly facile,
is specific to metals that can undergo oxidative addition
reactions. On the other hand, phosphines are ubiquitous
in organometallic chemistry and especially important
in catalysis.12 The use of spin-labeled phosphines would
thus provide a particularly simple method to introduce
a spin label into a wide range of organometallic systems.
In this paper we present novel triphenylphosphine
ligands that have been spin-labeled with stable ami-
noxyl and nitronyl nitroxide radicals and illustrate their
stability when bound to catalytically important orga-
nometallic palladium(II) and ruthenium(II) complexes.
The spin-labeling technique, which involves the in-
corporation of a stable free radical into a larger, complex
system in a noninvasive fashion, has found great utility
in macromolecular and biological chemistry.1,2 Stable
N-aminoxyl and nitronyl nitroxide radicals are featured
strongly in these studies.3,4 Generally, EPR spectroscopy
is used to probe the local environment of the radical.
The high sensitivity of EPR spectroscopy allows these
investigations to proceed at very low concentrations of
complex.5 The use of spin-labeling has proven important
for unraveling such issues as cholesterol interactions
in biological membranes and peptide structures in
solution.4,6,7
In contrast, the use of spin-labeling in organometallic
chemistry is far less common. Although nitroxide radi-
† Institut de Chimie de la Matie`re Condense´e de Bordeaux.
‡ University of British Columbia.
§ University of Minnesota.
(1) Keana, J . F. W. Chem. Rev. 1978, 78, 37.
(2) Keana, J . F. W. Spin Labeling in Pharmacology; Academic
Press: New York, 1984.
(8) Eaton, S. S.; Eaton, G. R. Coord. Chem. Rev. 1988, 83, 29.
(9) Eaton, S. S.; Eaton, G. R. Coord. Chem. Rev. 1978, 26, 207.
(10) Caneschi, A.; Gatteschi, D.; Sessoli, R.; Rey, P. Acc. Chem. Res.
1989, 22, 392.
(11) Rendina, L. M.; Vittal, J . J .; Puddephatt, R. J . Organometallics
1995, 14, 2188.
(12) Collman, J . P.; Hegedus, L. S.; Norton, J . R.; Finke, R. G.
Principles and Applications of Organotransition Metal Chemistry;
University Science Books: Mill Valley, CA, 1987; Chapter 1.
(13) Rancurel, C.; Sutter, J .-P.; Le Hoerff, T.; Ouahab, L.; Kahn, O.
New J . Chem. 1998, 22, 1333.
(3) Kocherginsky, N.; Swartz, H. M. Nitroxide Spin Labels: Reac-
tions in Biology and Chemistry; CRC Press: New York, 1995.
(4) Volodarsky, L. B.; Reznikov, V. A.; Ovcharenko, V. I. Synthetic
Chemistry of Stable Nitroxides; CRC Press Inc.: Boca Raton, FL, 1994.
(5) Weil, J . A.; Bolton, R. B.; Wertz, J . E. Electron Paramagnetic
Resonance: Elementary Theory and Practical Applications; J ohn Wiley
& Sons: New York, 1994.
(6) Naik, N.; Braslau, R. Tetrahedron Lett. 1998, 54, 667.
(7) Dunham, S. U.; Dunham, S. U.; Turner, C. J .; Lippard, S. J . J .
Am. Chem. Soc. 1998, 120, 5395.
10.1021/om9905862 CCC: $18.00 © 1999 American Chemical Society
Publication on Web 11/03/1999

5098 Organometallics, Vol. 18, No. 24, 1999
Leznoff et al.
Sch em e 1
tuted phenyl group could not be observed due to delo-
calization of the unpaired electron into this fragment.
The phenyl protons of the unsubstituted rings are found
at δ ) 7.25 and 7.6 ppm in 3 and at δ ) 8.6, 7.6, and
7.4 ppm in 4. The methyl groups adjacent to the
nitroxide moiety are visible only in 4 at δ ) -1.55 ppm
as a very broad signal.
The variable-temperature magnetic susceptibility of
3 and 4 was measured on a SQUID susceptometer in
the 2-300 K range, giving room-temperature values of
øMT of 0.70 and 0.67 cm3 mol-1 K, respectively, corre-
sponding to two unpaired electrons per complex, i.e., two
nitroxyl groups. These systems show very weak anti-
ferromagnetic coupling at low temperatures, contrary
to other systems containing nitroxide radicals which
interact directly with a Pd(II) center, and as a result
show strong antiferromagnetic coupling.18,19
An X-ray crystal structure of 4 was obtained to
confirm the presence of the two radical-substituted
phosphines. Orange prism crystals were obtained by
slow evaporation of a MeCN solution. Crystallographic
data appear in Table 1. The molecular structure, shown
in Figure 1, is as expected for trans-Pd[2]2Cl2, with a
square planar Pd(II) center and two pendant nitroxide
radicals. The NO radical fragment is tilted 13.2° out of
the plane of the phenyl to which it is joined. Note that
the radical-substituted phosphine 2 cannot be isolated
in the solid state in the absence of a coordinating
metal.16 Phosphine 2 has also been stabilized by coor-
dination to a gold(I) center.20 The Pd-Cl and Pd-P bond
lengths of 2.2865(7) and 2.3298(6) Å, respectively (Table
2), are comparable to those found in the parent com-
pound PdCl2(PPh3)2, illustrating that the addition of a
remote radical group does not significantly alter the
coordination sphere of the metal. This important point
is one requirement for the application of the spin-
labeling technique: that the spin label should be non-
invasive. The N-O bond length of 1.286(3) Å is typical
of those found in other t-BuNO systems.21
The room-temperature EPR of the phosphine ligands
1 and 2 in solution are shown in Figure 2, with the EPR
spectra of 3 and 4 below them. The EPR of the free
ligands show five- and three-line patterns for 1 and 2,
respectively, as expected for coupling to two (1) and one
(2) nitrogen atoms (Figure 2). Note that fine structure
is easily observable in the case of 2, attributable to
delocalization of the unpaired electron through the
phenyl ring and its consequent coupling to the two sets
of protons and the phosphorus atom;16 this is much
weaker in nitronyl nitroxide derivatives. When compar-
ing the free radical ligands with their palladium com-
plexes, it is immediately obvious that coupling is
observed between the two remote pendant radicals on
Resu lts a n d Discu ssion
Syn th esis a n d Ch a r a cter iza tion of Sp in -La beled
tr a n s-P dCl2(P P h 3)2 Com plexes. The synthesis of phos-
phines 113,14 and 215,16 has been previously described.
Reaction of the radical precursor 1H with PdCl2(MeCN)2
and subsequent in situ oxidation of the product 3H with
NaIO4 gave the final radical-containing trans-Pd[1]2Cl2
complex 3 in good yield (Scheme 1) as a green solid. The
same product could be obtained directly by reaction of
PdCl2(MeCN)2 with phosphine 1 but in lower overall
yield.
Similarly, the reaction of phosphine 2 with PdCl2-
(MeCN)2 gave the corresponding orange complex 4 in
moderate yield (eq 1). The products are air and moisture
stable and, more important, are stable with respect to
decomposition of the radical.
(1)
(14) Rancurel, C.; Sutter, J .-P.; Kahn, O.; Guionneau, P.; Bravic,
G.; Chasseau, D. New J . Chem. 1997, 21, 275.
(15) Leznoff, D. B.; Rancurel, C.; Sutter, J .-P.; Golhen, S.; Ouahab,
L.; Rettig, S. J .; Kahn, O. Mol. Cryst. Liq. Cryst. 1999, 334, 425.
(16) Torssell, K. Tetrahedron 1977, 33, 2287.
(17) Lamar, G. N.; Horrocks, W. D.; Holm, R. H. NMR of Paramag-
netic Molecules; Academic Press: New York, 1973.
(18) Ovcharenko, V. I.; Fokin, S. V.; Reznikov, V. A.; Ikorskii, V.
N.; Romanenko, G. V.; Sagdeev, R. Z. Inorg. Chem. 1998, 37, 2104.
(19) Oshio, H.; Ohto, A.; Ito, T. J . Chem. Soc., Chem. Commun. 1996,
1541.
(20) Leznoff, D. B.; Rancurel, C.; Sutter, J .-P.; Rettig, S. J .; Pink,
M.; Paulsen, C.; Kahn, O. J . Chem. Soc., Dalton Trans. 1999, 3593.
(21) Ishida, T.; Iwamura, H. J . Am. Chem. Soc. 1991, 113, 4238.
1H NMR spectra are observable for the complexes, but
due to the presence of the unpaired electrons, the
resonances are broadened and shifted relative to their
diamagnetic counterparts and all coupling information
is lost.17 The proton resonances of the radical-substi-

Pd(II) and Ru(II) Complexes with Phosphine Ligands
Organometallics, Vol. 18, No. 24, 1999 5099
Ta ble 1. Su m m a r y of Cr ysta llogr a p h ic Da ta
Ta ble 2. Selected Bon d Len gth s a n d An gles for
tr a n s-Bis[(p-t-Bu NO-p h en yl)d ip h en ylp h osp h in e]-
d ich lor op a lla d iu m (II), P d [2]2Cl2 (4)
4a
5b
formula
fw
color, habit
crystal system
space group
a, Å
C44H46Cl2N2O2P2Pd C25H28ClNOPPd
Pd(1)-Cl(1)
P(1)-C(1)
P(1)-C(17)
N(1)-C(4)
2.2865(7)
1.808(2)
1.819(3)
1.420(3)
Pd(1)-P(1)
P(1)-C(11)
N(1)-O(1)
N(1)-C(7)
2.3298(6)
1.821(3)
1.286(3)
1.488(3)
874.11
531.30
orange, plate
orthorhombic
Pbca
orange, block
triclinic
P1h
10.1431(13)
10.7121(10)
11.540(2)
65.461(2)
73.033(2)
64.194(4)
1017.4(2)
1
18.8681(5)
12.9784(7)
19.3052(7)
90
90
90
Cl(1)-Pd(1)-Cl(1)a 180.0
Cl(1)-Pd(1)-P(1)
92.15(2)
b, Å
c, Å
Cl(1)-Pd(1)-P(1)a
Pd(1)-P(1)-C(1)
87.85(2) P(1)-Pd(1)-P(1)a 180.0
105.08(8) Pd(1)-P(1)-C(11) 117.89(8)
Pd(1)-P(1)-C(17) 117.30(9) C(1)-P(1)-C(11) 105.56(12)
R, deg
â, deg
γ, deg
V, Å3
C(1)-P(1)-C(17)
O(1)-N(1)-C(4)
C(4)-N(1)-C(7)
108.45(11) C(11)-P(1)-C(17) 101.84(12)
115.5(2)
126.0(2)
O(1)-N(1)-C(7)
N(1)-C(4)-C(3)
118.4(2)
117.3(2)
4727.4(3)
8
Z
F
a
calc, g/cm3
1.427
1.493
Symmetry operation: 1-x, 1-y, -z.
F(000)
450
2168
T (K)
180
173
radiation
Mo
7.05
Mo
9.82
µ, cm-1
crystal size, mm
transmission factors 0.8401-1.00
2θmax, deg
0.15 × 0.20 × 0.25
0.08 × 0.06 × 0.02
0.8832-1.00
50
24651
4178
0.050
3383
402
0.038, 0.071
0.056, 0.077
61.1
9378
4692
0.043
3232
241
0.034, 0.029
0.061, 0.062
total no. of reflns
no. of unique reflns
Rmerge
no. with I g xσ(I)c
no. of variables
R, wR2 (I g xσ(I))c
R, wR2 (all data)
a
Rigaku/ADSC CCD diffractometer, detector swing angle -10.0°,
aperture 94.0 × 94.0 mm at a distance of 38.86 mm from the
crystal, Mo KR radiation (λ ) 0.71073 Å), graphite monochromator,
function minimized ∑w(|Fo - Fc |)2, where w -1) σ2(Fo2), R )
2
2
2
b
∑||Fo| - |Fc||/∑|Fo|, wR2 ) (∑w(Fo - Fc2)2/∑w(Fo2)2)1/2
.
Siemens
SMART CCD diffractometer, Mo KR (λ ) 0.71073 Å), function
minimized ∑w(|Fo - Fc |)2 where w-1 ) σ2(Fo2), R ) ∑|Fo - |Fc|/
2
2
F igu r e 2. EPR spectra for phosphine ligands 1 (a) and 2
(b) and the corresponding PdCl2(phosphine)2 adducts 3 (c)
and 4 (d) recorded in CH2Cl2 solutions at 298 K (microwave
power 0.2 mW, modulation amplitude 0.5 G, ν ) 9.75 GHz).
∑|Fo|, wR2 ) ∑|(w1/2(Fo - Fc)|/∑|(w)1/2Fo|. x ) 3 (Rigaku); x ) 2
c
(Siemens)
> aN). However, the relative amplitude ratios are
different from that expected for strong exchange cou-
pling (J . aN), i.e., 1:4:10:16:19:16:10:4:1 and 1:2:3:2:1
ratios for four and two equivalent nitrogen atoms,
respectively.23 This coupling, as it is observed in dilute
solution at room temperature, is intramolecular in
origin. Coordination to the metal center of two spin-
labeled phosphines thus generates the coupling pattern
shown. Hence, using the spin-labeled phosphines, it is
possible to determine how many phosphines are coor-
dinated to a metal center (an important factor in
catalytic systems) from observing the coupling pattern
in the EPR spectrum. Furthermore, the high sensitivity
of EPR allows this determination to be accomplished
at much lower concentrations of metal complex (10-6
M) than would be possible with the more commonly used
NMR techniques.24 The observation of changes in
coupling patterns between spin labels has been used
with polyazamacrocycles,25 calixarenes,26,27 and acyclic
(22) Wautelet, P.; Bieber, A.; Turek, P.; Moigne, J . L.; Andre´, J .-J .
Mol. Cryst. Liq. Cryst. 1997, 305, 55. Ullman, E. F.; Osiecki, J . H.;
Boocock, D. G. B.; Darcy, R. J . Am. Chem. Soc. 1972, 94, 7049.
(23) Brie`re, R.; Dupeyre, R. M.; Lemaire, H.; Morat, C.; Rassat, A.;
Rey, P. Bull. Soc. Chim. Fr. 1965, 3290-97. Bencini, A.; Gatteschi, D.
EPR of Exchange Coupled Systems; Springer-Verlag: Berlin, 1990.
(24) Drago, R. S. Physical Methods for Chemists, 2nd ed.; Saunders
College Publishing: Orlando, 1992.
(25) Ulrich, G.; Turek, P.; Ziessel, R.; DeCian, A.; Fischer, J . J .
Chem. Soc., Chem. Commun. 1996, 2461.
(26) Ulrich, G.; Turek, P.; Ziessel, R. Tetrahedron Lett. 1996, 37,
8755.
F igu r e 1. Molecular structure (ORTEP, 33% ellipsoids)
and numbering scheme for Pd[2]2Cl2 (4).
the phosphines.21,22 The spectra of 3 and 4 show
respectively a nine- and five-line pattern with apparent
hyperfine coupling constants of 3.7 and 6.2 G. The
position of these absorption features as well as the
multiplicity of the spectra is characteristic of an ex-
change coupling larger than the hyperfine coupling (J

5100 Organometallics, Vol. 18, No. 24, 1999
Leznoff et al.
glycols28,29 as a sensor for the binding of metal cations
and other substrates.
A simple example of this principle in action is given
in eq 2. It is well-known that Pd-phosphine complexes
undergo ligand exchange in the presence of excess
phosphine. This reaction is often investigated by 31P
NMR spectroscopy; the spin-labeled phosphines pre-
sented here offer another method to study, in particular,
the case of ligand self-exchange.
Pd[2]2Cl2 {L} Pd[2](L)Cl2 + 2 {L
\ \} Pd(L)2Cl2 + 2 (2)
Thus, addition of an excess of PPh3 to a solution of 4
has two immediate consequences. First, within a few
seconds the color of the solution changes from orange
to red-pink, the color of free phosphine 2. More impor-
tantly, the EPR spectrum of the reaction mixture
collapses from five lines to three. This loss of coupling
indicates that at least one spin-labeled phosphine has
been displaced from the metal center. This technique
could potentially be applied to more complex systems.
(η3-Allyl)p a lla d iu m (II) a n d (η6-p-Cym en e)r u th e-
n iu m (II) Com p lexes w ith [(p-t-Bu NO-P h )P P h 2]. In
order for spin-labeled phosphines to be of use in orga-
nometallic systems, it is important to illustrate their
stability in the presence of organometallic fragments.
Two well-known families of organometallic catalysts are
(η3-allyl)Pd30 and (η6-arene)Ru31 compounds. Their use
in organic synthesis is well-documented, but the reac-
tion mechanisms they are involved in are still under
investigation.32-34 Thus the reactions of 2 with [(η3-
C3H5)PdCl]2 and [(η6-p-cymene)RuCl2]2 were examined.
Addition of the phosphine 2 to solutions of these dimers
gave bright red-orange solutions, from which the mono-
nuclear products (η3-C3H5)Pd[2]Cl (5) and (η6-p-cymene)-
Ru[2]Cl2 (6) were isolated in high yield (eqs 3 and 4).
Significantly, both complexes are stable with respect to
destruction of the pendant radical (e.g., by redox pro-
cesses).
F igu r e 3. Molecular structure (ORTEP, 33% ellipsoids)
and numbering scheme for (η3-C3H5)Pd[2](Cl) (5). The
minor occupancy fragment of the η3-allyl group has been
removed for clarity.
moieties and are essentially unchanged relative to the
EPR spectrum of the free ligand. Contrary to complexes
3 and 4, there is only one phosphine bound to the metal
center, and hence, no inter-radical coupling is observed.
(4)
1
The H NMR spectra of complexes 5 and 6 are more
informative than those of complexes 3 and 4 presented
above by virtue of the presence of organometallic
fragments. The resonances in the spectra are broadened
as expected, but still provide compound fingerprints. For
compound 5, in addition to the phenyl resonances (from
the nonsubstituted phenyl rings) at δ ) 8.5, 7.5, and
7.2 ppm and the broad feature at δ ) -2 ppm (t-Bu), a
broad resonance attributable to the terminal allyl
protons is visible at δ ) 6.2 ppm. The single central
proton of the η3-allyl group could not be unambiguously
assigned. For complex 6, the phosphine phenyl reso-
nances occur at δ ) 8.4, 7.35, and 7.0 ppm. The phenyl
protons of the η6-p-cymene fragment are at δ ) 5.0 ppm,
while the resonances assignable to the methyl and
isopropyl (CH3 and H) protons of the p-cymene are at δ
) 1.88, 1.13, and 3.0 ppm, respectively. Note that the
resonances of the organometallic fragments are broad-
ened, indicating the effect of the remote aminoxyl
radical on each proton, but only slightly shifted with
respect to the corresponding PPh3 derivative.35,36
The X-ray crystal structure of complex 5 was solved;
the result is shown in Figure 3. It confirms the presence
of both the spin-labeled phosphine and an η3-allyl
fragment in the same molecule. The aminoxyl moiety
is a mere 4.4° out of the plane of the phenyl to which it
(3)
Magnetic susceptibility measurements confirm the
stability of the complexes, with values of øMT of 0.35
and 0.37 cm3 mol-1 K for 5 and 6, respectively, corre-
sponding to one unpaired electron per complex. The EPR
spectra of both systems show the standard three-line
pattern with fine structure typical of phenyl-aminoxyl
(27) Araki, K.; Nakamura, R.; Otsuka, H.; Shinkai, S. J . Chem. Soc.,
Chem. Commun. 1995, 2121.
(28) Gagnaire, G.; J eunet, A.; Pierre, J .-L. Tetrahedron Lett. 1991,
32, 2021.
(29) Gagnaire, G.; J eunet, A.; Pierre, J .-L. Tetrahedron Lett. 1989,
30, 6507.
(30) Tsuji, J . Palladium Reagents and Catalysts; J ohn Wiley & Sons
Ltd.: West Sussex, U.K., 1995.
(31) Naota, T.; Takaya, H.; Murahashi, S.-I. Chem. Rev. 1998, 98,
2599.
(32) Kuhn, O.; Mayr, H. Angew. Chem., Int. Ed. Engl. 1999, 38, 343.
(33) Hagelin, H.; Akermark, B.; Norrby, P.-O. Chem. Eur. J . 1999,
5, 902.
(34) Picquet, M.; Touchard, D.; Burneau, C.; Dixneuf, P. H. New J .
Chem. 1999, 23, 141.
(35) Bennet, M. A.; Smith, A. K. J . Chem. Soc., Dalton Trans. 1974,
233.
(36) Faller, J . W.; Blankenship, C.; Whitmore, B.; Sena, S. Inorg.
Chem. 1985, 24, 4483.

Pd(II) and Ru(II) Complexes with Phosphine Ligands
Organometallics, Vol. 18, No. 24, 1999 5101
Ta ble 3. Selected Bon d Len gth s a n d An gles for
[(p-t-Bu NO-p h en yl)d ip h en ylp h osp h in e]-
field strength. The data were corrected for the diamagnetism
of the constituent atoms.
(η3-C3H5)ch lor op a lla d iu m (II), (η3-C3H5)P d [2](Cl) (5)
Syn th esis of Bis[(p-n itr on yl n itr oxid e-p h en yl)d ip h en -
ylph osph in e]dich lor opalladiu m (II), P d[1]2Cl2 (3). Meth od
A. Phosphine 1 (0.045 g, 0.107 mmol) was dissolved in CH2-
Cl2 (10 mL) in a round-bottomed flask. The resulting blue
solution was added dropwise to a yellow MeCN solution (10
mL) of PdCl2 (0.010 g, 0.056 mmol) to give a green solution,
which was stirred for 3 h. The solvent was then removed in
vacuo to give a green solid, which was redissolved in CH2Cl2/
hexanes. Slow evaporation of this solution gave microcrystal-
line 3 (0.030 g, 53%).
Meth od B. PdCl2 (0.021 g, 0.118 mmol) was suspended in
MeCN (15 mL) and stirred overnight to give PdCl2(MeCN)2
as a yellow solution. A solution of phosphine 1H (0.100 g, 0.238
mmol) in MeCN (10 mL) was added, with stirring, to yield a
pale yellow precipitate. After stirring for 30 min, the solvents
were removed in vacuo to give crude 3H as a pale yellow solid.
The crude solid was resuspended in CH2Cl2 (15 mL), and a
solution of NaIO4 (0.075 g, 0.352 mmol) in H2O (10 mL) was
added slowly. After 1 h of vigorous stirring, a green color had
developed in the organic layer. The mixture was stirred
overnight, during which the insoluble 3H completely reacted
to give a dark green solution in the organic layer, which was
separated and dried with MgSO4, and the solvent was removed
in vacuo. The residue was redissolved in CH2Cl2/hexanes, and
subsequent slow evaporation gave green microcrystalline 3
(0.095 g, 79%). Despite drying under vacuum, the crystals
retained CH2Cl2, as indicated by 1H NMR. Anal. Calcd for
Pd(1)-Cl(1)
Pd(1)-Callyl(av)
P(1)-C(11)
N(1)-O(1)
2.3717(10)
2.16
1.839(3)
1.278(4)
1.517(5)
1.39(2)
Pd(1)-P(1)
P(1)-C(1)
P(1)-C(17)
N(1)-C(4)
C(23)-C(24)
2.3095(9)
1.833(3)
1.830(4)
1.424(4)
1.42(2)
N(1)-C(7)
C(24)-C(25)
P(1)-Pd(1)-Cl(1) 103.82(3) Pd(1)-P(1)-C(1)
Pd(1)-P(1)-C(11) 119.93(11) Pd(1)-P(1)-C(17)
112.91(11)
112.22(11)
103.9(2)
116.3(3)
126.0(3)
C(1)-P(1)-C(11) 103.2(2)
C(11)-P(1)-C(17) 103.0(2)
C(1)-P(1)-C(17)
O(1)-N(1)-C(4)
C(4)-N(1)-C(7)
O(1)-N(1)-C(7)
N(1)-C(4)-C(3)
117.7(3)
118.0(3)
C(23)-C(24)-C(25) 120.1(14)
is bound. The Pd-Cl and Pd-P bond lengths of 2.3717-
(10) and 2.3095(9) Å, respectively (Table 3), compare
well with those found in other Pd-allyl complexes.37,38
The N-O bond length of 1.278(4) Å is very similar to
that found in complex 2 above. Again, it is clear that
the incorporation of an organic radical group remote to
the metal center does not perturb the coordination
sphere of the metal. Additionally, the structure il-
lustrates the stability of the organometallic fragment
in the presence of a pendant organic radical.
Con clu sion s
C
50H52Cl2N4O4P2Pd‚0.75CH2Cl2: C, 56.65; H, 5.01; N, 5.21.
1
Triphenylphosphine ligands substituted with nitronyl
nitroxide or N-aminoxyl moieties, persistent organic
radicals, can be considered as spin-labeled phosphines.
Their incorporation into PdCl2(phosphine)2 complexes
and the subsequent coupled EPR spectra showed their
possible utility in determining the number of phos-
phines bound to a metal center in low-concentration
solutions. The spin-labeled phosphines also formed
stable complexes with organometallic Pd(II) and Ru(II)
systems. Significantly, all compounds were stable in
solution over periods of several hours to days with
respect to the destruction of the radical moiety. The use
of these radical-substituted phosphines is perhaps the
easiest and most generally applicable method for intro-
ducing a spin label into organometallic complexes.
Found: C, 56.66; H, 5.04; N, 5.05. H NMR (CDCl3, ppm): δ
) 7.6, 7.25 (Ph). IR (KBr): 3054, 2987, 1482, 1435, 1387, 1365
(νNO), 1304, 1165, 1133, 1096, 832, 743, 703 cm-1. EPR (CH2-
Cl2, 298 K): 9-line pattern (g ) 2.006; aN ) 3.7 G).
Syn th esis of Bis[(p-t-Bu NO-ph en yl)diph en ylph osph in e]-
d ich lor op a lla d iu m (II), P d [2]2Cl2 (4). PdCl2 (0.019 g, 0.107
mmol) was suspended in MeCN (15 mL) and stirred overnight
to give PdCl2(MeCN)2 as a yellow solution. Separately, phos-
phine 2H (0.075 g, 0.214 mmol) was dissolved in CH2Cl2 (10
mL) and solid Ag2O (0.05 g, 0.214 mmol) was added, with
stirring, yielding a bright orange solution. After stirring for
15 min, the resulting solution of phosphine radical 2 was
filtered through Celite directly into the Pd-containing solution
to give an orange-yellow solution, which was stirred for an
additional hour, then filtered through Celite. The solvents were
then removed in vacuo to give an orange solid. The crude
product was triturated with CCl4 to remove an impurity of
PdCl2[2][2H] (i.e., a monoradical species) and the remaining
solid dried to give Pd[2]2Cl2 (4) (0.071 g, 76%). Recrystallization
by slow evaporation of a concentrated MeCN solution gave
orange prism crystals suitable for X-ray crystallographic
analysis. Anal. Calcd for C44H46Cl2N2O2P2Pd: C, 60.46; H, 5.30;
Exp er im en ta l Section
Gen er a l P r oced u r es. Unless otherwise stated all manipu-
lations were performed in
a nitrogen atmosphere using
standard Schlenk techniques. Hexanes and CH2Cl2 were
refluxed over CaH2 under a nitrogen atmosphere and distilled
prior to use; diethyl ether and THF were distilled from sodium
benzophenone ketyl under a nitrogen atmosphere. Phosphines
1
N, 3.20. Found: C, 60.02; H, 5.26; N, 3.12. H NMR (CDCl3,
ppm): δ ) 8.6 (4H, o-Ph), 7.6 (4H, m-Ph), 7.4 (2H, p-Ph), -1.5
(9H, t-Bu). IR (KBr): 3048, 2981, 2928, 1481, 1437, 1186
(νNO), 1098, 819, 733, 692 cm-1. EPR (CH2Cl2, 298 K): 5-line
pattern (g ) 2.005; aN ) 6.2 G).
1H, 1,13,14 and 2H15,16 and [(η6-p-cymene)RuCl2]2 were pre-
35
pared according to published procedures. PdCl2(MeCN)2 was
prepared by dissolving PdCl2 in MeCN. The resulting solution
was used directly for subsequent synthetic steps. Phosphine
2H was selectively oxidized at the N-OH group by Ag2O in
CH2Cl2 at room temperature within 15 min to give radical
phosphine 2, which was used in situ. All other reagents were
obtained from commercial sources and used as received.
Magnetic susceptibility data were collected using a SQUID
MPMS-5S magnetometer in the range 2-300 K at 1000 Oe
Syn th esis of [(p-t-Bu NO-p h en yl)d ip h en ylp h osp h in e]-
(η3-C3H5)ch lor op a lla d iu m (II), (η3-C3H5)P d [2](Cl) (5). Phos-
phine 2H (0.070 g, 0.200 mmol) was dissolved in CH2Cl2 (10
mL) in a foil-protected round-bottomed flask. To this was
added solid Ag2O (0.046 g, 0.200 mmol). Upon stirring for 5
min an orange color developed, and after 15 min the mixture
was filtered through Celite. The solution of 2 was added
dropwise to a 10 mL THF solution of [(η3-C3H5)PdCl]2 (0.037
g, 0.100 mmol) to give a brilliant red solution. The mixture
was stirred for 2 h and then filtered through Celite, after which
the solvent was removed in vacuo to give a red oil. Recrystal-
lization from minimum CH2Cl2/Et2O gave deep red crystals of
5 (0.095 g, 89%) suitable for X-ray analysis. Anal. Calcd for
(37) Ohta, T.; Hosokawa, T.; Murahashi, S.-I.; Miki, K.; Kasai, N.
Organometallics 1985, 4, 2080.
(38) Sutter, J .-P.; Pfeffer, M.; DeCian, A.; Fischer, J . Organometallics
1992, 11, 386. van der Schaaf, P. A.; Sutter, J .-P.; Grellier, M.; van
Mier, G. P. M.; Spek, A. L.; van Koten, G.; Pfeffer, M. J . Am. Chem.
Soc. 1994, 116, 5134.
C
25H28ClNOPPd: C, 56.51; H, 5.31; N, 2.64. Found: C, 56.41;

5102 Organometallics, Vol. 18, No. 24, 1999
Leznoff et al.
1
H, 5.36; N, 2.67. H NMR (CDCl3, ppm): δ ) 8.5 (4H, o-Ph),
positions (C-H ) 0.98 Å, Biso ) 1.2B(parent atom)). Neutral
atom scattering factors and anomalous dispersion corrections
were taken from the International Tables for X-ray Crystal-
lography.40 Selected bond lengths and angles are found Table
2.
7.7 (4H, m-Ph), 7.25 (2H, p-Ph), 6.2 (4H, CH2-CH-CH2), -1.5
(broad, t-Bu). IR (KBr): 3044, 2986, 1478, 1435, 1407, 1302,
1237, 1179, 1096, 1207, 827, 816 cm-1. EPR (CH2Cl2, 298 K):
3-line pattern (g ) 2.005; aN ) 12.1 G).
[(p-t-Bu NO-ph en yl)diph en ylph osph in e](η3-C3H5)ch lor o-
p a lla d iu m (II), (η3-C3H5)P d [2](Cl) (5). Da ta Collection a n d
P r ocessin g. Crystallographic data are in Table 1. A crystal
of 5 was mounted on a glass fiber and measured on a Siemens
SMART CCD system at 173(2) K. A randomly oriented region
of reciprocal space was surveyed to the extent of 1.3 hemi-
spheres and to a resolution of 0.84 Å. Three major swaths of
frames were collected with 0.30 steps in ω. The data were
processed using SAINT.41 Final cell constants were calculated
from the xyz centroids of 8192 reflections from the actual data
after integration. The data were corrected for absorption using
SADABS (Sheldrick, 1996).
Str u ctu r e An a lysis a n d Refin em en t. A direct-methods
solution located most non-hydrogen atoms. The remaining
atoms were found by conducting full-matrix least-squares and
difference Fourier cycles. All non-hydrogen atoms were refined
with anisotropic displacement parameters, and all hydrogen
atoms, except for the hydrogens of the disordered allyl group,
were located from the difference map and were refined with
isotropic displacement paramaters. For the allyl fragment
occupying the major site (77% occupancy), hydrogen atoms
were refined at a fixed distance. For the minor site the
hydrogen atoms were placed in ideal positions and refined as
riding atoms with individual or group (H25c and H25d)
isotropic displacement parameters. Selected bond lengths and
angles are found in Table 3.
Syn th esis of [(p-t-Bu NO-p h en yl)d ip h en ylp h osp h in e]-
(η6-p-cym en e)d ich lor or u th en iu m (II), (η6-p-cym en e)Ru -
[2]Cl2 (6). Phosphine 2H (0.033 g, 0.095 mmol) was dissolved
in CH2Cl2 (10 mL) in a foil-protected round-bottomed flask.
To this was added solid Ag2O (0.022 g, 0.095 mmol). Upon
stirring for 5 min an orange color developed, and after 15 min
the mixture was filtered through Celite. This solution of 2 was
added dropwise to a 15 mL CH2Cl2 solution of [(η6-p-cymene)-
RuCl2]2 (0.030 g, 0.048 mmol) to give a red-orange solution,
which was stirred for 2 h. Subsequently, the solvent was
removed in vacuo to give a red powder. Slow evaporation of a
CH2Cl2/Et2O solution of this crude product gave 6 (0.057 g,
87%) as very thin plate crystals. Anal. Calcd for C32H37Cl2-
NOPRu: C, 58.72; H, 5.70; N, 2.14. Found: C, 58.45; H, 5.86;
1
N, 2.07. H NMR (CDCl3, ppm): δ ) 8.4 (4H, o-Ph), 7.35 (4H,
m-Ph), 7.0 (2H, p-Ph), 5.0 (4H, cymene), 3.0 (1H, Me2CH), 1.88
(3H, MePh), 1.13 (6H, CH-Me2). IR (KBr): 3061, 2959, 1481,
1435, 1262, 1185, 1096, 1058, 1032, 823, 800 cm-1. EPR (CH2-
Cl2, 298 K): 3-line pattern (g ) 2.005; aN ) 12.0 G).
X-r a y Cr ysta llogr a p h ic An a lysis. Bis[(p-t-Bu NO-p h en -
yl)d ip h en ylp h osp h in e]d ich lor op a lla d iu m (II), P d [2]2Cl2
(4). Da ta Collection a n d P r ocessin g:39 Crystallographic
data appear in Table 1. A crystal of 4 was mounted on a glass
fiber and measured on a Rigaku/ADSC CCD diffractometer
at 180(1) K. Data were collected in 0.50° oscillations with 20.0
s exposures. A sweep of data was done using φ oscillations from
0.0° to 190.0° at ø ) -90°, and a second sweep was performed
using ω oscillations between -23.0° and 18.0° at ø ) -90°.
The final unit-cell parameters were obtained by conducting
least-squares calculations on 6445 strong reflections (2θ range
4.0-61.1). The data were processed and corrected for Lorentz
and polarization effects and absorption.
Ack n ow led gm en t. This paper is dedicated to the
memory of Steven J . Rettig, friend and colleague, who
passed away suddenly on October 27, 1998. The X-ray
crystal structure of 5 was obtained at the X-ray Crystal-
lography Laboratory, University of Minnesota, in con-
junction with Victor G. Young, J r. Financial support was
provided by NSERC of Canada in the form of a Post-
doctoral Fellowship (to D.B.L.) and by the TMR Re-
search Network ERBFMRXCT980181 of the European
Union, entitled “Molecular Magnetism, from Materials
toward Devices”.
Str u ctu r e An a lysis a n d Refin em en t. The structure was
solved by heavy-atom Patterson methods and expanded using
Fourier techniques. The metal atom lies on
a center of
symmetry; thus the coordination group is exactly planar. Full-
matrix least-squares refinement was conducted with all non-
hydrogen atoms anisotropic and hydrogen atoms in calculated
(39) d*TREK: Area Detector Software; Molecular Structure Corp.:
The Woodlands, TX, 1997.
Su p p or tin g In for m a tion Ava ila ble: Complete tables of
bond lengths and bond angles, atomic coordinates, anisotropic
thermal parameters, torsion angles, intermolecular contacts,
and least-squares planes. This material is available free of
charge via the Internet at http://pubs.acs.org.
(40) (a) International Tables for X-ray Crystallography; Kynoch
Press: Birmingham, U.K. (present distributor Kluwer Academic
Publishers: Boston, MA), 1974; Vol. IV, pp 99-102. (b) International
Tables for Crystallography; Kluwer Academic Publishers: Boston, MA,
1992; Vol. C, pp 200-206.
(41) SAINT; Siemens Industrial Automation, Inc.: Madison, WI.
OM9905862