Reactivity studies of cationic palladium(II) phosphine carboxylate complexes with lewis bases: Substitution versus cyclometalation

Article abstract of DOI:10.1021/om070069g

Two classes of cationic palladium(II) phosphine carboxylate complexes were isolated and characterized. Reactions of trans-[(R₃P) ₂Pd(O₂CR′)₂] (1) with [Li(OEt ₂)_2.5][B(C₆F₅)₄] in MeCN led to carboxylate abstraction and formation of trans-[(R₃P) ₂Pd(O₂CR′)(MeCN)][B(C₆F₅) ₄] (2) in good to excellent yields. On the other hand, carboxylate abstraction reactions of 1 with [Me₂(H)NPh][B(C₆F ₅)₄] or p-toluenesulfonic acid (HOTs·H ₂O) in CH₂Cl₂ furnished the palladium cations [(R₃P)₂Pd(κ²-O,O-O₂CR′)] ⁺ (3). The reactions of 2 and 3 with Lewis bases were found to be different in some cases. For example, reactions of 2 with pyridine furnished the simple products of acetonitrile substitution, trans-[(R₃P) ₂Pd(O₂CR′)(py)][B(C₆F₅) ₄]. In contrast, the reaction of 3e (R = ⁱPr, R′ = CH₃) with CD₃CN in the presence of excess sodium carbonate yielded a material derived from cyclometalation of one of the ⁱPr arms of ⁱPr₃P ligand. New complexes were characterized by elemental analyses and NMR (¹H, ¹³C, and ³¹P) spectroscopic methods and in two cases by single-crystal X-ray structural methods.

Full text of DOI:10.1021/om070069g

Organometallics 2007, 26, 3157-3166
3157
Reactivity Studies of Cationic Palladium(II) Phosphine Carboxylate
Complexes with Lewis Bases: Substitution versus Cyclometalation
Natesan Thirupathi,†,‡ Dino Amoroso,§ Andrew Bell,§ and John D. Protasiewicz*,†
Department of Chemistry, Case Western ReserVe UniVersity, CleVeland, Ohio 44106, and Promerus,
CleVeland, Ohio 44141
ReceiVed January 23, 2007
Two classes of cationic palladium(II) phosphine carboxylate complexes were isolated and characterized.
Reactions of trans-[(R3P)2Pd(O2CR′)2] (1) with [Li(OEt2)2.5][B(C6F5)4] in MeCN led to carboxylate
abstraction and formation of trans-[(R3P)2Pd(O2CR′)(MeCN)][B(C6F5)4] (2) in good to excellent yields.
On the other hand, carboxylate abstraction reactions of 1 with [Me2(H)NPh][B(C6F5)4] or p-toluenesulfonic
acid (HOTs‚H2O) in CH2Cl2 furnished the palladium cations [(R3P)2Pd(κ2-O,O-O2CR′)]+ (3). The reactions
of 2 and 3 with Lewis bases were found to be different in some cases. For example, reactions of 2 with
pyridine furnished the simple products of acetonitrile substitution, trans-[(R3P)2Pd(O2CR′)(py)][B(C6F5)4].
In contrast, the reaction of 3e (R ) iPr, R′ ) CH3) with CD3CN in the presence of excess sodium carbonate
yielded a material derived from cyclometalation of one of the iPr arms of a iPr3P ligand. New complexes
were characterized by elemental analyses and NMR (1H, 13C, and 31P) spectroscopic methods and in two
cases by single-crystal X-ray structural methods.
and trans isomers. For example, Coles et al. have shown that
the reaction of Pd(O2CMe)2 with 2 equiv of 3,3,1-PPBN and
4,2,1-PPBN (PPBN ) 9-phenyl-9-phosphabicyclononane) gives
trans-[(R3P)2Pd(O2CMe)2] (PR3 ) 3,3,1-PPBN, 4,2,1-PPBN),
whereas the same reaction with the similar but sterically less
hindered 1-phenylphospholane gives cis-[(R3P)2Pd(O2CMe)2]
(PR3 ) 1-phenylphospholane).5
Introduction
Admixtures of palladium acetate and phosphines, as well as
discrete adducts of palladium acetate (and other palladium salts)
with phosphines, constitute the basic ingredients for implement-
ing a large number of important catalytic transformations.1,2
Early investigations of the chemistry of palladium acetate and
palladium carboxylates with phosphines date back to the 1960s.
For example, Wilkinson and co-workers reported the isolation
of the simple adducts trans-[(Ph3P)2Pd(O2CR′)2] (R′ ) Me, Et,
Ph) from reactions involving Pd(O2CR′)2 and PPh3.3 Interest-
ingly, similar reactions performed using differing Pd:PPh3 ratios
afforded a dinuclear complex, [(Ph3P)Pd(O2CMe)2]2, which
bears both terminal and bridging acetate moieties.4 These
reactions portended a chemistry for palladium phosphine
carboxylate complexes richer than that first imagined. Com-
plexes of the form [(R3P)2Pd(O2CMe)2] can also show both cis
Further studies into the catalytically active species have
revealed additional complexities. In careful studies aimed at
determining the source of palladium(0) from mixtures of Pd-
(O2CMe)2 and PPh3, anionic complexes have been identified
as key intermediates. The oxidation of PPh3 serves as the source
of electrons necessary for the reduction of Pd(II).6 Adding even
more complexity to these reactions is the propensity of the
palladium center to react with certain phosphines to yield
cyclometalated complexes. In particular, reactions of Pd(O2-
CMe)2 with phosphines bearing at least an o-tolyl, mesityl,
1-naphthyl, or tert-butyl substituent or with (R-ferrocenylalkyl)-
phosphines commonly afforded cyclopalladated acetate bridged
dinuclear palladium complexes, some of which show great utility
in catalysis.7 Even being identified as such, these cyclometalated
complexes can be also involved in dynamic equilibria with other
* To whom correspondence should be addressed. E-mail:
protasiewicz@case.edu.
† Case Western Reserve University.
‡ Current address: Department of Chemistry, University of Delhi, Delhi
110 007, India.
§ Promerus.
(1) (a) Nair, D.; Scarpello, J. T.; Vankelecom, F. J.; Freitas Dos Santos,
L. M.; White, L. S.; Kloetzing, R. J.; Welton, T.; Livingston, A. G. Green
Chem. 2002, 4, 319-324. (b) Yus, M.; Gomis, J. Eur. J. Org. Chem. 2002,
1989-1995. (c) Pawlow, J. H.; Sadow, A. D.; Sen, A. Organometallics
1997, 16, 1339-1342. (d) Zargarian, D.; Alper, H. Organometallics 1993,
12, 712-724. (e) Cacchi, S.; Lupi, A. Tetrahedron Lett. 1992, 33, 3939-
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Pietroni, B. R. J. Org. Chem. 1992, 57, 976-982. (g) Cacchi, S.; Morera,
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E. P.; Bennett, B. PCT Int. Appl. WO 0350158, 2003. (b) Nomura, K.;
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254-278.
10.1021/om070069g CCC: $37.00 © 2007 American Chemical Society
Publication on Web 05/18/2007

3158 Organometallics, Vol. 26, No. 13, 2007
Thirupathi et al.
dergoes a reversible autoionization to generate [(dppe)2Pd]2+
species. For example, the acetate-bridged dinuclear palladacycle
,
Ia was shown to equilibrate with the monomer Ib.8,9
as shown by a 31P NMR spectroscopic study.10c Subsequent
work determined that the reaction of Pd(O2CMe)2 with dppe in
CD2Cl2 produces the kinetic product [(dppe)2Pd]2+, which
eventually yields the thermodynamically more stable [(dppe)-
Pd(O2CMe)2] upon reaction with Pd(O2CMe)2.13 The reaction
of Pd(O2CMe)2 with dppp (dppp ) 1,2-bis(diphenylphosphino)-
propane) in MeOH/CF3CO2H, however, affords [(dppp)Pd(κ2-
O,O-O2CMe)]+, which upon reaction with an additional 1 equiv
of dppp gives [(dppp)2Pd]2+ 14
.
Clearly, these examples and others too numerous to detail
here serve to illustrate the diversity and complexity of the
fundamental chemistry of palladium carboxylates with phos-
phines. Recently, we communicated the syntheses and charac-
terization of examples of two types of cationic palladium
phosphine carboxylate complexes (2 and 3) that are derived by
the action of lithium salts or acids on trans-[(R3P)2Pd(O2CMe)2],
as well as the conditions under which these complexes are
susceptible to facile and reversible cyclometalation of coordi-
nated phosphine ligands.15
Studies of the reaction of Pd(O2CMe)2 with chelating
phosphines revealed other possibilities. The specific products
obtained were shown to depend on the nature of the substituents
attached to phosphorus as well as on the nature of intervening
atoms between two phosphorus donors. The reaction of Pd(O2-
CMe)2 with chelating diphosphines possessing sterically less
hindered substituents on phosphorus can furnish mononuclear
chelate complexes of the form cis-[(P-P)Pd(O2CMe)2] (P-P )
chelating diphosphine).10 In other cases, reactions with chelating
phosphines (such as 1,2-bis((di-tert-butylphosphino)methyl)-
benzene or 1,3-bis(di-tert-butylphosphino)propane) can afford
the doubly ortho-palladated complexes II or cyclotetrameric
complexes III.11 However, the reaction of Pd(O2CMe)2 with
bis(tert-butylaminomethylphosphine) was shown to furnish the
mononuclear complex IV.12
The delightful diversity of products derived from palladium
carboxylates with ligands extends to N-heterocylic carbenes
(phosphine mimics).16 Scheme 1 ([BArF24]- ) tetrakis[(3,5-
trifluoromethyl)phenyl]borate; R ) CH3, CF3) depicts some of
the unusual products (V-VII) recently reported and their
dependence on the choice of carboxylate abstraction reagent.16a
As part of our continuing interest in understanding the factors
that control the nature of products of palladium carboxylates
with phosphines, we now give a full report on the syntheses
and characterization of a wider family of complexes 2 and 3,
as well as an examination of their reactivity with Lewis bases.
The reactions of Pd(O2CMe)2 with chelating diphosphines
have also shown their propensity to yield cationic complexes
in reactions that are highly solvent dependent. Bianchini et al.
found that the reaction of Pd(O2CMe)2 with dppe (dppe ) 1,2-
bis(diphenylphosphino)ethane) in MeOH-d4 initially yields
[(dppe)Pd(O2CMe)2] and that this complex subsequently un-
Experimental Section
General Considerations. All manipulations were carried out
using standard Schlenk or drybox techniques, unless stated other-
wise. Solvents were purified by standard procedures. Pd(O2CMe)2
(Strem, Johnson Matthey), PiPr3, PCy3, P(NMe2)3 (Strem, Aldrich),
[Li(OEt2)2.5][B(C6F5)4], [Me2(H)NPh][B(C6F5)4] (Boulder Scien-
tific), HOTs‚H2O (Fischer; Ts ) tosyl), pyridine (Acros), 2,6-
dimethylphenyl isocyanide (Fluka), 4-tert-butylpyridine, and DMAP
(Aldrich) were used as received. Pd(O2CPh)217 and Pd(O2CtBu)2
were prepared by following literature procedures. Elemental
analyses were performed by Robertson Microlit Laboratories Inc.
(Madison, NJ) after drying samples in a Fisher Isotemp 282A
(7) Dunina, V, V.; Gorunova, O. N. Russ. Chem. ReV. 2004, 73, 309-
350.
18
(8) Herrmann, W. A.; Brossmer, C.; Ofele, K.; Reisinger, C.-P.;
Priermeier, T.; Beller, M.; Fischer, H. Angew. Chem., Int. Ed. 1995, 34,
1844-1847.
(9) Fiddy, S. G.; Evans, J.; Newton, M. A.; Neisius, T.; Tooze, R. P.;
Oldman, R. Chem. Commun. 2003, 2682-2683.
(10) a) Neo, Y. C.; Vittal, J. J.; Hor, T. S. A. Dalton Trans. 2002, 337-
342. (b) Neo, Y. C.; Yeo, J. S. L.; Low, P. M. N.; Chien, S. W.; Mak, T.
C. W.; Vittal, J. J.; Hor, T. S. A. J. Organomet. Chem. 2002, 658, 159-
168. (c) Bianchini, C.; Lee, H. M.; Meli, A.; Oberhauser, W.; Peruzzini,
M.; Vizza, F. Organometallics 2002, 21, 16-33. (d) Sjovall, S.; Johansson,
M. H.; Andersson, C. Eur. J. Inorg. Chem. 2001, 2907-2912. (e) Bianchini,
C.; Lee, H. M.; Meli, A.; Moneti, S.; Vizza, F.; Fontani, M.; Zanello, P.
Macromolecules 1999, 32, 4183-4193.
(13) Bianchini, C.; Meli, A.; Oberhauser, W. Organometallics 2003, 22,
4281-4285.
(14) Pivovarov, A. P.; Novikova, E. V.; Belov, G. P. Russ. J. Coord.
Chem. 2000, 26, 38-44.
(15) Thirupathi, N.; Amoroso, D.; Bell, A.; Protasiewicz, J. D. Orga-
nometallics 2005, 24, 4099-4102.
(16) (a) Slootweg, J. C.; Chen, P. Organometallics 2006, 25, 5863-
5869. (b) Viciu, M. S.; Stevens, E. D.; Petersen, J. L.; Nolan, S. P.
Organometallics 2004, 23, 3752-3755.
(11) Clegg, W.; Eastham, G. R.; Elsegood, M. R. J.; Tooze, R. P.; Wang,
X. L.; Whiston. K. Chem. Commun. 1999, 1877-1878.
(12) (a) Me´ry, D.; Heuze´, K.; Astruc, D. Chem. Commun. 2003, 1934-
1935. (b) Knight, J. G.; Doherty, S.; Harriman, A.; Robins, E. G.; Betham,
M.; Eastham, G. R.; Tooze, R. P.; Elsegood, M. R. J.; Champkin, P.; Clegg,
W. Organometallics 2000, 19, 4957-4967.
(17) Hermans, S; Wenkin, M; Devillers, M. J. Mol. Catal. A: Chem.
1998, 136, 59-68.
(18) Bancroft, D. P.; Cotton, F. A; Falvello, L. R.; Schwotzer, W.
Polyhedron 1988, 7, 615-621.

Pd(II) Phosphine Carboxylate Complexes
Organometallics, Vol. 26, No. 13, 2007 3159
Scheme 1
vacuum oven under vacuum at 35 °C for 24 h. Proton and 13C
NMR spectra were recorded on Varian 300 and Varian 600 MHz
NMR spectrometers, and the residual solvent proton signal served
as a reference signal. The 31P and 19F NMR spectra were recorded
on a Varian 300 spectrometer using 85% H3PO4 and trifluoroacetic
acid, respectively, as the external standards.
26.6, 27.9 (vt, 2JPC + 4JPC ) 5.0 Hz), 29.2, 32.0 (vt, 1JPC + 3JPC
)
8.5 Hz), 39.8, 182.4. The signal at δC 29.2 ppm arises due to the
combination of resonances corresponding to the CH3 nuclei of tBu
and one of the CH2 nuclei of C6H11, as independently confirmed
by two-dimensional HMQC experiments.
trans-[(Cy3P)2Pd(O2CCF3)2] (1d). Complex 1d was prepared
from Pd(O2CCF3)2 (1.592 g, 4.79 mmol) and PCy3 (2.859 g, 10.195
mmol) in dichloromethane (10, 16 mL) in 67% yield (2.86 g) by a
procedure analogous to that used for 1a. Anal. Calcd for
C40H66O4P2F6Pd: C, 53.78; H, 7.45. Found: C, 53.90; H, 7.24.
trans-[(Cy3P)2Pd(O2CMe)2] (1a). In a two-neck round-bottom
flask equipped with an addition funnel, a reddish brown suspension
of Pd(O2CMe)2 (5.00 g, 22.3 mmol) in dichloromethane (50 mL)
was stirred at -78 °C. The addition funnel was charged with a
dichloromethane solution (30 mL) of PCy3 (13.12 g, 46.78 mmol),
and this solution was then slowly added to the stirred suspension
over the course of 15 min, resulting in a gradual change from
reddish brown to yellow. After 1 h of stirring at -78 °C, the
suspension was warmed to room temperature, stirred for an
additional 2 h, and then diluted with hexanes (20 mL). The yellow
solid was then collected by filtration, washed with pentane (5 ×
10 mL), and dried under vacuum. A second crop was isolated by
cooling the filtrate to 0 °C and filtering, washing, and drying.
Yield: 15.42 g (88%). Anal. Calcd for C40H72O4P2Pd: C, 61.17;
H, 9.24. Found: C, 61.44; H, 9.58. 31P{1H} NMR (CD2Cl2): δ
1
31P{1H} NMR (CDCl3): δ 24.5. H NMR (CDCl3): δ 1.08-1.38
(m, 18H), 1.56-1.86 (m, 36H), 1.94 (br d, J ) 12.0 Hz, 12H).
2
4
13C{1H} NMR (CDCl3): δ 26.6, 27.8 (vt, JPC + JPC ) 5.4 Hz),
1
3
1
29.6, 32.7 (vt, JPC + JPC ) 9.1 Hz), 114.3 (q, JCF ) 289.3 Hz,
CF3), 160.9 (q, 2JCF ) 36.2 Hz, CdO). 19F NMR (CDCl3): δ 4.6.
trans-[(iPr3P)2Pd(O2CMe)2] (1e). Complex 1e was prepared
from Pd(O2CMe)2 (5.00 g, 22.3 mmol) and PiPr3 (7.14 g, 44.6
mmol) in dichloromethane (20, 30 mL) in 90% yield (10.94 g) by
a procedure analogous to that used for 1a. Anal. Calcd for
1
C22H48O4P2Pd: C, 48.49; H, 8.88. Found: C, 48.55; H, 8.85. H
NMR (CD2Cl2): δ 1.37 (m, 36H), 1.77 (s, 6H), 2.12 (br, 6H). 31P-
{1H} NMR (CD2Cl2): δ 33.0. 13C{1H} NMR (CDCl3): δ 19.6,
1
21.3. H NMR (CD2Cl2): δ 1.15-1.34 (br m, 18H), 1.64-1.71
1
3
23.7 (vt, JCP + JCP ) 9.2 Hz), 23.8, 175.9.
(br m, 18H), 1.80-1.82 (br m, 18H), 1.84 (s, 6H), 1.99 (br d, J )
14.4 Hz, 12H). 13C{1H} NMR (CDCl3): δ 23.9, 26.7, 28.2 (vt,
2JCP + 4JCP ) 5.3 Hz), 29.6, 33.2 (vt, 1JCP + 3JCP ) 8.8 Hz), 175.3.
trans-[(Cy3P)2Pd(O2CPh)2] (1b). Complex 1b was prepared
from Pd(O2CPh)2 (1.380 g, 3.954 mmol) and PCy3 (2.539 g, 9.054
mmol) in dichloromethane (10, 10 mL) in 74% yield (2.651 g) by
a procedure analogous to that used for 1a. Anal. Calcd for
C50H76O4P2Pd: C, 66.03; H, 8.42. Found: C, 65.49; H, 8.51. The
NMR (1H and 31P) spectral data of 1b were consistent with
previously reported values.19
trans-{[(Me2N)3P)]2Pd(O2CMe)2} (1f). Complex 1f was pre-
pared from Pd(O2CMe)2 (368 mg, 1.719 mmol) and P(NMe2)3 (568
mg, 3.48 mmol) in 70% yield (664 mg) by a procedure analogous
to that adopted for 1a, except that the dichloromethane (3 mL)
solution of P(NMe2)3 was added to the dichloromethane (3 mL)
solution of Pd(O2CMe)2 at -35 °C. 31P{1H} NMR (CDCl3): δ 93.3.
1H NMR (CDCl3): δ 1.85 (s, 6H, O2CCH3), 2.66 (apparent t, 5JPH
+ 3JPH ) 4.74 Hz, 36H, N(CH3)2). 13C{1H} NMR (CDCl3): δ 23.6,
38.5, 177.4.
trans-[(Cy3P)2Pd(O2CtBu)2] (1c). Complex 1c was prepared
from Pd(O2CtBu)2 (466 mg, 1.511 mmol) and PCy3 (887 mg, 3.163
mmol) in dichloromethane (10 mL) in 74% yield (978 mg) by a
procedure analogous to that used for 1a. Anal. Calcd for C46H84O4P2-
Pd‚C4H9CO2H: C, 63.04; H, 9.75. Found: C, 62.52; H, 9.71. 31P-
{1H} NMR (CDCl3): δ 17.4. 1H NMR (CDCl3): δ 1.08 (s, 18H),
1.20 (q, J ) 12.6 Hz, 12H), 1.35 (qt, J ) 12.6, 3.3 Hz, 4H), 1.68
(d, J ) 12.6 Hz, 8H), 1.72 (d, J ) 12.6 Hz, 10H), 1.78 (d, J )
13.2 Hz, 14H), 1.87-1.96 (m, 18H). 31C{1H} NMR (CDCl3): δ
trans-[(PCy3)2Pd(O2CMe)(MeCN)][B(C6F5)4] (2a). An aceto-
nitrile (5 mL) solution of [Li(Et2O)2.5][B(C6F5)4] (864 mg, 0.992
mmol) was slowly added to the acetonitrile (40 mL) solution of 1a
(764 mg, 0.972 mmol), the reaction mixture stirred for 3 h, filtered
through 0.45 µm filter and solvent removed under vacuum to furnish
1.40 g of 2a (99%). Anal. Calcd. for C64H72NO2P2BF20Pd‚1Et2O:
C, 53.71; H, 5.44; N, 0.92%. Found: C, 53.85; H, 5.18; N, 0.93.
1
31P{1H} NMR (CDCl3): δ 32.7. H NMR (CDCl3): δ 1.12-1.22
(m, 12H), 1.28 (qt, J ) 12.9 Hz, 3.2 Hz, 6H), 1.62 (q, J ) 12.45
Hz, 12H), 1.77 (d, J ) 12.6 Hz, 6H), 1.89 (d, J ) 13.8 Hz, 14H),
1.93 (d, J ) 11.4 Hz, 16H), 2.00 (s, 3H), 2.39 (s, 3H). 13C{1H}
(19) Grushin, V. V.; Alper, H. J. Am. Chem. Soc. 1995, 117, 4305-
4315.
2
NMR (CDCl3): δ 3.30, 23.4, 26.3, 27.9 (virtual t, JCP
+

3160 Organometallics, Vol. 26, No. 13, 2007
Thirupathi et al.
1
3
4JCP ) 9 Hz), 29.9, 33.7 (virtual t, JCP + JCP ) 9.45 Hz), 124.5
2.34 (s, 3H). 13C{1H} NMR (CDCl3): δ 4.2, 19.6, 23.2, 24.5 (virtual
t, 1JCP + 3JCP ) 10.1 Hz), 124.4 (br), 128.5, 136.9 (d, JCF ) 248
1
1
1
(br), 127.2, 136.4 (d, JCF ) 242 Hz), 138.4 (d, JCF ) 244 Hz),
1
1
1
148.4 (d, JCF ) 243 Hz), 175.5.
Hz), 138.8 (d, JCF ) 243 Hz), 148.7 (d, JCF ) 240 Hz), 176.0.
trans-[(Cy3P)2Pd(O2CPh)(MeCN)][B(C6F5)4] (2b). Complex 2b
was prepared from an acetonitrile (10 mL) solution of [Li(OEt2)2.5]-
[B(C6F5)4] (142 mg, 0.164 mmol) and a dichloromethane (6 mL)
solution of 1b (146 mg, 0.161 mmol) in 98% yield (242 mg) by a
procedure analogous to that used for 2a, with the reaction time
being 15 h. Anal. Calcd for C69H74NO2P2PdBF20: C, 54.94; H,
4.94; N, 0.93. Found: C, 54.75; H, 4.75; N, 0.94. 31P{1H} NMR
[(Cy3P)2Pd(κ2-O,O′-O2CMe)][B(C6F5)4] (3a). Method 1. A
dichloromethane solution (25 mL) of [Me2(H)NPh][B(C6F5)4]
(1.025 g, 1.279 mmol) was slowly added to a dichloromethane
solution (50.0 mL) of 1a (1.004 g, 1.273 mmol) at -35 °C. The
reaction mixture was slowly raised to room temperature and stirred
for 21 h. During the course of the reaction, the reaction mixture
became deep orange. The volatiles from the reaction mixture were
then removed under reduced pressure to give a paste, to which was
added diethyl ether (ca. 30 mL) to induce the formation of an orange
powder. The orange powder was collected by filtration, washed
with acetonitrile (10.0 mL), and dried under reduced pressure to
furnish 3a as an air- and moisture-stable orange solid. Yield: 1.02
g (57%).
(CDCl3): δ 32.6. 1H NMR (CDCl3): δ 0.92-1.14 (m, 11H), 1.15-
3
1.36 (m, 7H), 1.54-2.06 (m, 48H), 2.42 (s, 3H), 7.36 (t, JHH
)
3
3
7.6 Hz, 2H), 7.46 (t, JHH ) 6.6 Hz, 1H), 7.88 (d, JHH ) 8.1 Hz,
2H). 13C{1H} NMR (CDCl3): δ 3.3, 26.2, 27.8 (vt, 2JPC + 4JPC
)
1
3
5.3 Hz), 29.9, 33.6 (vt, JPC + JPC ) 9.1 Hz), 124.5 (br), 127.3,
128.4, 129.8, 131.9, 133.6, 136.4 (d, JCF ) 248 Hz), 138.4 (d,
1
1
1JCF ) 242 Hz), 148.4 (d, JCF ) 238 Hz), 170.8.
Method 2. Dichloromethane (5.0 mL) was syringed into the
mixture of 1a (333 mg, 424 µmol) and HOTs‚H2O (85.0 mg, 446
µmol). The resulting mixture was stirred for 22 h. A 31P NMR
spectrum of the reaction mixture revealed a new peak at δ 59.0. A
dichloromethane (2.0 mL) solution of [Li(OEt2)2.5][B(C6F5)4] (400
mg, 459 µmol) was then introduced into the above reaction mixture,
stirred for 5 min, and filtered through a medium-porosity frit. The
volatiles were removed under vacuum to give a foam that was
triturated with hexane (5.0 mL) and dried under reduced pressure
to give a yellow solid (577 mg). This solid was then sonicated in
the presence of acetonitrile (2 × 3 mL), filtered, and dried under
reduced pressure to give 471 mg of 3a (79%). Anal. Calcd for
C62H69O2P2BF20Pd: C, 52.99; H, 4.95. Found: C, 53.29; H, 5.05.
trans-[(Cy3P)2Pd(O2CtBu)(MeCN)][B(C6F5)4] (2c). Complex 2c
was prepared from an acetonitrile (6 mL) solution of [Li(OEt2)2.5]-
[B(C6F5)4] (87.0 mg, 0.100 mmol) and a dichloromethane (6 mL)
solution of 1c (83.6 mg, 0.096 mmol) in 99% yield (142 mg) by a
procedure analogous to that used for 2a with the following
exceptions. The reaction time was 5 h. The product was finally
purified by triturating with pentane (10 mL) followed by vacuum
drying. Anal. Calcd for C67H78NO2P2BF20Pd: C, 54.06; H, 5.28;
N, 0.94. Found: C, 53.59; H, 4.91; N, 0.77. 31P{1H} NMR (THF-
1
d8): δ 31.0. H NMR (THF-d8): δ 1.22 (s, 9H), 1.28-1.44 (m,
18H), 1.72-1.85 (m, 18H), 1.89 (br d, J ) 11.4 Hz, 12H), 2.07
(br d, J ) 12.0 Hz, 12H), 2.13 (t, J ) 11.7 Hz, 6H), 2.77 (s, 3H).
1
31P{1H} NMR (CDCl3): δ 59.3. H NMR (CDCl3): δ 1.24-1.34
2
4
31C{1H} NMR (THF-d8): δ 3.1, 27.0, 28.4 (vt, JPC + JPC ) 5.6
1
3
(m, 20H), 1.66 (q, J ) 11.4 Hz, 12H), 1.80 (br, 6H), 1.90 (br,
12H), 1.96 (d, J ) 13.8 Hz, 12H), 2.00 (d, J ) 12.0 Hz, 4H), 2.04
(s, 3H). 13C{1H} NMR (CDCl3): δ 25.1, 25.7, 27.2 (virtual t, 2JCP
+ 4JCP ) 5.5 Hz), 30.2, 34.7 (m), 124.2 (br), 136.2 (d, 1JCF ) 248
Hz), 29.6, 30.5, 34.2 (vt, JPC + JPC ) 9.1 Hz), 40.6, 124.7 (br),
129.8, 137.1 (d, JCF ) 245 Hz), 139.1 (d, JCF ) 246 Hz), 149.2
1
1
1
(d, JCF ) 234 Hz), 182.4.
trans-[(Cy3P)2Pd(O2CCF3)(MeCN)][B(C6F5)4] (2d). An aceto-
nitrile solution (3 mL) of [Li(OEt2)2.5][B(C6F5)4] (264 mg, 0.303
mmol) was slowly added to the acetonitrile (20 mL) solution of
1d (266 mg, 0.298 mmol) with stirring. The 31P NMR spectrum of
the reaction product revealed peaks at 35.3 and 43.4 ppm in a 77:
23 ratio; the former signal is attributed to 2d (see below). After it
was stirred for 12 h, the reaction mixture was filtered through a
0.45 µm filter. Evaporation of the solvent to a volume of 5 mL
produced a pale brown powder, which after drying afforded 2d in
59% yield (263 mg). Anal. Calcd for C64H69NO2P2PdBF23‚CH3-
CN: C, 51.43; H, 4.71; N, 1.82. Found: C, 51.27; H, 4.93; N,
1.94. 31P{1H} NMR (CDCl3): δ 35.0. 1H NMR (CDCl3): δ 1.08-
1.38 (m, 18H), 1.63 (q, J ) 11.7 Hz, 12H), 1.77 (br d, J ) 10.2
Hz, 8H), 1.82-1.98 (br m, 28H), 2.45 (s, 3H). 31C{1H} NMR
1
1
Hz), 138.1 (d, JCF ) 242 Hz), 148.2 (d, JCF ) 239 Hz), 194.9.
Preparation of [(Cy3P)2Pd(κ2-O,O-O2CPh)][B(C6F5)4] (3b).
Method 1. The solid [Me2(H)NPh][B(C6F5)4] (162 mg, 0.203
mmol) was added in portions to a dispersion of 1b (179 mg, 0.197
mmol) in diethyl ether (30 mL) in a 100 mL round-bottom flask,
and the mixture was stirred for 72 h. The volume of the reaction
mixture was then reduced to 10 mL and diluted with hexane (15
mL) to afford a gray solid. The gray solid was washed with
acetonitrile (3 × 6 mL) and dried under vacuum to furnish 3b as
a yellow solid in 52% yield (150 mg).
Method 2. Dichloromethane (6 mL) was syringed into a 100
mL round-bottom flask that contained a mixture of 1b (321 mg,
0.353 mmol) and HOTs‚H2O (76.5 mg, 0.402 mmol), and the
resulting mixture was stirred for 22 h. A dichloromethane (3 mL)
solution of [Li(OEt2)2.5][B(C6F5)4] (373 mg, 0.428 mmol) was then
introduced into the above reaction mixture, and the solution was
stirred for 1 h and filtered. The volatiles from the filtrate were
removed under vacuum to furnish a brown solid. The solid was
sonicated in the presence of acetonitrile (3 × 3 mL) to facilitate
precipitation of a powder. The powder was collected by filtration
through a fine porous frit, washed with acetonitrile (3 mL), and
dried under vacuum to furnish 3b as a yellow solid in 80% yield
(411 mg). Anal. Calcd for C67H71O2P2PdBF20: C, 54.84; H, 4.88.
2
4
(CDCl3): δ 3.5, 26.2, 27.7 (vt, JPC + JPC ) 5.3 Hz), 29.9, 33.6
(vt, 1JPC + 3JPC ) 9.4 Hz), 114.4 (q, 1JCF ) 287.9 Hz, CF3), 124.0
3
3
(br), 128.4, 136.4 (d, JCF ) 244.8 Hz), 138.3 (d, JCF ) 244.2
Hz), 148.3 (d, 3JCF ) 241.5 Hz), 160.8 (q, 2JCF ) 37.0 Hz, CdO).
19F NMR (CDCl3): δ -89.3 (br t, 3JFF ) 17.1 Hz), -85.4 (t, 3JFF
) 20.6 Hz), -54.9, 5.1.
trans-[(PiPr3)2Pd(O2CMe)(MeCN)][B(C6F5)4] (2e). Complex 2e
was prepared from an acetonitrile (10 mL) solution of [Li(OEt2)2.5]-
[B(C6F5)4] (960 mg, 1.102 mmol) and an acetonitrile solution (20
mL) of 1e (599 mg, 1.099 mmol) in quantitative yield (1.325 g)
by a procedure analogous to that used for 2a, with the following
exceptions. The reaction time was 4 h. The final product was
purified by triturating with pentane (10 mL) followed by vacuum
drying. Interestingly, 2e was also formed in quantitative yield from
the reaction of 1e (201 mg, 0.369 mmol) with [Me2N(H)Ph]-
[B(C6F5)4] (302 mg, 0.377 mmol) in acetonitrile (15 mL) over 90
min, as revealed by 31P NMR spectroscopy (δ 45.0 ppm). Anal.
Calcd for C46H48NO2P2BF20Pd: C, 45.81; H, 4.01; N, 1.16.
Found: C, 46.00; H, 3.92; N, 1.18. 31P{1H} NMR (CDCl3): δ 44.5.
1H NMR (CDCl3): δ 1.37 (m, 36H), 1.92 (s, 3H), 2.22 (m, 6H),
Found: C, 54.72; H, 4.71. 31P{1H} NMR (CDCl3): δ 59.6. 1H NMR
3
(CDCl3): δ 1.31 (br, 18H), 1.64-2.18 (m, 48H), 7.46 (t, JHH
)
3
3
7.8 Hz, 2H), 7.61 (t, JHH ) 7.5 Hz, 1H), 7.95 (d, JHH ) 7.2 Hz,
2H). 13C{1H} NMR (CDCl3): δ 26.0, 27.5 (vt, JCP + JCP ) 5.6
Hz), 30.5, 35.1 (m), 124.7 (br), 128.7, 128.8, 131.8, 134.2, 136.4
(d, 1JCF ) 238 Hz), 138.3 (d, 1JCF ) 245 Hz), 148.4 (d, 1JCF ) 239
Hz), 188.2.
2
4
Preparation of [(Cy3P)2Pd(κ2-O,O-O2CtBu)][B(C6F5)4] (3c).
Dichloromethane (18 mL) was syringed into a 100 mL round-
bottom flask that contained a mixture of 1c (448 mg, 0.515 mmol)

Pd(II) Phosphine Carboxylate Complexes
Organometallics, Vol. 26, No. 13, 2007 3161
and HOTs‚H2O (107 mg, 0.563 mmol), and the resulting hetero-
geneous mixture was stirred for 24 h. During the course of the
above period, the reaction mixture turned into a homogeneous
yellow solution and the 31P NMR spectrum of this solution revealed
complete consumption of 1c with the appearance of a new peak at
δ 58.6. A dichloromethane (4 mL) solution of [Li(OEt2)2.5]-
[B(C6F5)4] (512 mg, 588 mmol) was introduced into the above
reaction mixture, and the mixture was stirred for 10 min and then
filtered through filter paper. The volatiles from the filtrate were
removed under vacuum to give a foam that was dissolved in the
minimum amount of acetonitrile to give a yellow solution. The
yellow solution was sonicated (to facilitate precipitate formation)
until no more yellow solid deposited. The yellow solid was collected
by filtration and dried under vacuum to furnish 3c in 69% yield
(517 mg). Anal. Calcd for C65H75O2P2PdBF20: C, 53.94; H, 5.22.
Found: C, 53.78; H, 4.98. 31P{1H} NMR (CDCl3): δ 58.4. 1H NMR
(CDCl3): δ 1.13 (s, 9H), 1.20-1.40 (br m, 18H), 1.56-1.74 (br
m, 12H), 1.76-2.10 (br m, 36H). 31C{1H} NMR (CDCl3): δ 25.8,
26.1, 27.3 (vt, JPC + JPC ) 5.6 Hz), 30.3, 34.8 (m), 41.1, 123.9
(br), 136.2 (d, 1JCF ) 247 Hz), 138.2 (d, 1JCF ) 244 Hz), 148.2 (d,
1JCF ) 240 Hz), 202.9.
Reaction of 1d with HOTs‚H2O. A dichloromethane solution
(6 mL) of 1d (231 mg, 0.256 mmol) was added to HOTs‚H2O (52
mg, 0.273 mmol), and the resulting heterogeneous mixture was
stirred for 24 h. The 31P NMR spectrum of the reaction product
indicated the presence of 1d (24.2 ppm, major) along with other
unidentified species (27.7 (major) and 52.6, 54.8, and 56.8 ppm
(all minor)).
trans-[(Cy3P)2Pd(O2CMe)(C5H5N)][B(C6F5)4] (4a). Complex
2a (198 mg, 0.137 mmol) and pyridine (61 mg, 0.77 mmol) were
separately dissolved in toluene (4 and 1 mL, respectively) and
cooled to -35 °C. The toluene solution of pyridine was added to
the toluene solution of 2a, and the mixture was stirred at room
temperature for 100 min. The volatiles from the reaction mixture
were removed under vacuum to furnish a residue that was
subsequently triturated with hexane (3 × 10 mL) and collected by
filtration. The solid was dried under vacuum to give 4a in 99%
yield (202 mg). Anal. Calcd for C67H74NO2P2PdBF20: C, 54.21;
H, 5.02; N, 0.94. Found: C, 54.34; H, 4.92; N, 0.83. 31P{1H} NMR
1
(CDCl3): δ 22.1. H NMR (CDCl3): δ 1.04 (m, 12H), 1.22 (m,
6H), 1.50-1.70 (m, 18H), 1.71-1.90 (m, 30H), 2.00 (s, 3H), 7.54
3
3
3
(t, JHH ) 7.0 Hz, 2H), 7.98 (t, JHH ) 7.8 Hz, 1H), 8.77 (d, JHH
) 4.8 Hz, 2H). 13C{1H} NMR (CDCl3): δ 23.6, 26.7, 28.2 (vt,
2JCP + 4JCP ) 5.0 Hz), 30.2, 34.6 (vt, 1JCP + 3JCP ) 8.8 Hz), 124.5
1
1
(br), 127.8, 136.8 (d, JCF ) 253.5 Hz), 138.8 (d, JCF ) 244.3
Hz), 140.8, 148.7 (d, JCF ) 237.3 Hz), 154.3, 176.0.
1
2
4
trans-[(Cy3P)2Pd(O2CMe)(4-Me2NC5H4N)][B(C6F5)4] (4b). Com-
plex 4b was prepared from 2a (210 mg, 0.145 mmol) and DMAP
(20 mg, 0.16 mmol) in THF (6 mL) in quantitative yield (221 mg)
by a procedure analogous to that used to prepare 4a. Anal. Calcd
for C69H79N2O2P2PdBF20: C, 54.25; H, 5.21; N, 1.83. Found: C,
54.17; H, 5.03; N, 1.78. 31P{1H} NMR (CDCl3): δ 21.8. 1H NMR
(CDCl3): δ 0.95-1.36 (m, 18H), 1.48-1.95 (m, 48H), 1.97 (s,
3H), 3.03 (s, 6H), 6.55 (d, 3JHH ) 6.6 Hz, 2H), 8.01 (d, 3JHH ) 6.6
2
Hz, 2H). 13C{1H} NMR (CDCl3): δ 23.7, 26.3, 27.9 (vt, JCP
+
4JCP ) 5.4 Hz), 29.8, 34.0 (vt, 1JCP + 3JCP ) 8.8 Hz), 39.4, 108.8,
124.2 (br), 136.4 (d, 1JCF ) 242.2 Hz), 138.3 (d, 1JCF ) 243.6 Hz),
[(iPr3P)2Pd(κ2-O,O′-O2CMe)][B(C6F5)4] (3e). Method 1. A
mixture of 1e (51.0 mg, 93.6 µmol) and [Me2(H)NPh][B(C6F5)4]
(76.0 mg, 94.8 µmol) in dichloromethane (5.0 mL) was stirred at
room temperature for 24 h. Removal of the volatile materials under
reduced pressure yielded an orange gummy material. The 31P NMR
spectrum of the material revealed the presence of 3e (δ 70) and
many other unidentified products. Attempts to isolate 3e from the
reaction mixture were not successful.
1
148.4 (d, JCF ) 237.9 Hz), 151.6, 154.7, 176.0.
trans-[(Cy3P)2Pd(O2CMe)(CNC6H3Me2-2,6)][B(C6F5)4] (4d).
Complex 4d was obtained from 2a (298 mg, 0.206 mmol) and 2,6-
dimethylphenyl isocyanide (28 mg, 0.21 mmol) in THF (6 mL) in
quantitative yield (316 mg) by a procedure analogous to that used
to prepare 4a. Anal. Calcd for C71H78NO2P2PdBF20‚C4H8O: C,
55.99; H, 5.39; N, 0.87. Found: C, 56.23; H, 5.38; N, 0.78. 31P-
{1H} NMR (CDCl3): δ 40.6. 1H NMR (CDCl3): δ 1.10-1.38 (m,
18H), 1.60-1.80 (m, 18H), 1.87 (br d, J ) 12.0 Hz, 12H), 2.03
(br d, J ) 12.0 Hz, 12H), 2.06 (s, 3H), 2.16 (m, 6H), 2.47 (s, 6H),
7.24 (d, 3JHH ) 7.3 Hz, 2H), 7.37 (t, 3JHH ) 7.3 Hz, 1H). 13C{1H}
Method 2. Dichloromethane (7.0 mL) was syringed into a
mixture of 1e (378 mg, 694 µmol) and HOTs‚H2O (137 mg, 720
µmol), and the mixture was stirred for 22 h. A 31P NMR spectrum
of the reaction mixture revealed a new peak at δ 70 (major) and
smaller peaks at δ 37.1 and 54.0; no signal was observed for 1e. A
dichloromethane (4.0 mL) solution of [Li(OEt2)2.5][B(C6F5)4] (628
mg, 720 µmol) was then introduced into the reaction mixture. After
the mixture was stirred for 5 min, solvent was removed under
reduced pressure to give an orange solid. The orange solid was
sonicated twice in the presence of diethyl ether (5 mL) to induce
precipitation of a yellow powder. This powder was collected by
filtration and dried under vacuum to furnish air- and moisture-stable
3e. Yield: 645 mg (80%). Anal. Calcd. for C44H45O2P2PdBF20: C,
45.36; H, 3.89. Found: C, 45.37; H, 3.88. 31P{1H} NMR (CDCl3):
2
4
NMR (CDCl3): δ 18.9, 24.4, 26.6, 28.1 (vt, JCP + JCP ) 5.3
Hz), 30.7, 35.6 (vt, 1JCP + 3JCP ) 9.4 Hz), 36.7, 124.4 (br), 125.7,
1
1
129.8, 132.1, 135.4, 136.8 (d, JCF ) 249.9 Hz), 138.8 (d, JCF
)
1
252.4 Hz), 148.7 (d, JCF ) 243.7 Hz), 176.0.
trans-[(iPr3P)2Pd(O2CMe)(C5H5N)][B(C6F5)4] (4e). Complex 4e
was prepared from 2e (173 mg, 0.143 mmol) and pyridine (48 mg,
0.60 mmol) in dichloromethane (10 mL) in 99% yield (177 mg)
by a procedure analogous to that used to prepare 4a. Anal. Calcd
for C49H50NO2P2PdBF20‚C5H5N: C, 49.01; H, 4.19; N, 2.12.
Found: C, 48.45; H, 3.93; N, 1.81. 31P{1H} NMR (CD2Cl2): δ
33.4. 1H NMR (CD2Cl2): δ 1.27 (m, 36H), 1.91 (s, 3H), 1.98 (m,
6H), 7.57 (t, 3JHH ) 7.2 Hz, 2H), 7.96 (t, 3JHH ) 7.8 Hz, 1H), 8.78
1
δ 69.4. H NMR (CDCl3): δ 1.45 (m, 36H), 2.02 (s, 3H), 2.26-
2.39 (m, 6H).13C{1H} NMR (CDCl3): δ 20.1, 25.3, 26.3 (m), 124.4
(br), 136.9 (d, 1JCF ) 241 Hz), 138.8 (d, 1JCF ) 243 Hz), 148.8 (d,
1JCF ) 237 Hz), 196.1.
3
(d, JHH ) 4.8 Hz, 2H). 13C{1H} NMR (CD2Cl2): δ 19.6, 23.5,
24.9 (vt, 1JCP + 3JCP ) 9.7 Hz), 124.2 (br), 128.0, 136.9 (d, 1JCF
244.9 Hz), 138.8 (d, JCF ) 243.0 Hz), 141.3, 148.7 (d, JCF
236.8 Hz), 154.2, 176.7.
)
)
1
1
{[(Me2N)3P]2Pd(κ2-O,O-O2CMe)}B(C6F5)4 (3f). A diethyl ether
(5 mL) solution of [Me2(H)NPh][B(C6F5)4] (596 mg, 0.710 mmol)
was slowly added to 1f (371 mg, 0.673 mmol) that was also
dispersed in diethyl ether (5 mL). The reaction mixture was stirred
for 12 h at room temperature. The volatiles from the filtrate were
removed under vacuum to give a yellow solid. The yellow solid
was washed with the minimum amount of diethyl ether, collected
by filtration, and dried under vacuum to furnish 3f in 65% yield
(515 mg). Anal. Calcd for C38H39N6O2P2BF20Pd: C. 38.98; H, 3.36;
N, 7.18. Found: C, 39.04; H, 2.98; N, 7.16. 31P{1H} NMR
(CDCl3): δ 88.9. 1H NMR (CDCl3): δ 1.99 (s, 3H, O2CCH3), 2.70
trans-[(iPr3P)2Pd(O2CMe)(CNC6H3Me2-2,6)][B(C6F5)4] (4f).
Complex 4f was prepared from the reaction of 2,6-dimethylphenyl
isocyanide with 2e or 3e as described below.
From 2e. Complex 2e (98 mg, 84.1 µmol) and 2,6-dimethylphe-
nyl isocyanide (13 mg, 99 µmol) were separately dissolved in THF
(4 and 1 mL, respectively) and cooled to -35 °C. The THF solution
of 2,6-dimethylphenyl isocyanide was added to the THF solution
of 2e and the reaction mixture stirred at ambient temperature for 2
h. The volatiles from the reaction mixture were removed under
vacuum to furnish 4f in 99% yield (108 mg).
5
3
(apparent t, JPH + JHP ) 5.13 Hz, 36H, P(N(CH3)2)3).

3162 Organometallics, Vol. 26, No. 13, 2007
Thirupathi et al.
Table 1. Crystal Data and Structure Refinement Details for
2c and 4b
From 3e. Complex 3e (197 mg, 0.169 mmol) and 2,6-dimeth-
ylphenyl isocyanide (23 mg, 0.175 mmol) were separately dissolved
in dichloromethane (6 and 4 mL, respectively). The dichloromethane
solution of 2,6-dimethylphenyl isocyanide was added to the
dichloromethane solution of 3e at ambient temperature and stirred
at the same temperature for 3 h. The volatiles from the reaction
mixture were removed under vacuum to furnish 4f as a light brown
solid in 96% yield (210 mg). Anal. Calcd for C53H54NO2P2-
PdBF20: C, 49.10; H, 4.20; N, 1.08. Found: C, 48.94; H, 3.88; N,
1.52. 31P{1H} NMR (CD2Cl2): δ 53.8. 1H NMR (CD2Cl2): δ 1.42
2c
4b
empirical formula
formula wt
temp (K)
wavelength (Å)
cryst syst
space group
unit cell dimens
a (Å)
C67H78BF20NO2P2Pd C69H79BF20N2O2P2Pd
1488.45
293(2)
0.710 73
monoclinic
P21/n
1527.49
293(2)
0.710 73
triclinic
P1h
20.382(4)
14.910(3)
15.0468(19)
18.300(3)
69.387(10)
67.634(12)
88.773(12)
3523.5(9)
2
b (Å)
14.982(3)
(m, 36H), 1.96 (s, 3H), 2.43 (s, 6H), 2.47 (m, 6H), 7.22 (d, 3JHH
)
c (Å)
23.225(5)
90
7.5 Hz, 2H), 7.36 (t, 3JHH ) 7.5 Hz, 1H). 13C{1H} NMR (CD2Cl2):
δ 19.1, 20.1, 24.1, 26.0 (vt, 1JCP + 3JCP ) 10.6 Hz), 124 (br), 125.5,
129.7, 132.1, 135.0 (br), 135.7, 136.9 (d, 1JCF ) 243.0 Hz), 138.8
R (deg)
â (deg)
106.124(11)
γ (deg)
90
V (Å3)
6813(2)
1
1
(d, JCF ) 242.4 Hz), 148.7 (d, JCF ) 239.9 Hz), 176.6.
Z
4
calcd density (Mg/m3)
1.451
1.440
Reaction of 3e with CD3CN in the Presence of Sodium
Carbonate. Sodium carbonate (191 mg, 1.806 mmol) was added
to a CD3CN solution (3.5 mL) of 3e (162 mg, 0.139 mmol), and
the resulting heterogeneous mixture was stirred for 15 h at room
temperature. The reaction mixture was filtered, and the volatiles
from the filtrate were removed under vacuum to give a waxy
material of 5a in 97% yield (155 mg). Elemental analysis could
not be obtained for 5a because of its waxy nature and the difficulty
in obtaining an isolable solid. 31P{1H} NMR (CD3CN): δ 51.7 (d,
abs coeff (mm-1
F(000)
)
0.418
0.407
1568
3056
cryst size (mm)
0.24 × 0.20 × 0.10
0.30 × 0.30 × 0.25
yellow, irreg block
1.91-24.00
-1 e h e 17
-15 e k e 15
-19 e l e 20
12 135
cryst color, shape
yellow, irreg block
θ range data collecn (deg) 1.80-24.01
limiting indices
-23 e h e 1
-17 e k e 1
-25 e l e 26
12 707
no. of rflns collected
no. of indep rflns
10 686 (Rint
)
10751 (Rint )
0.0370)
0.0471)
nonmetalated phosphorus), 43.2 (d, metalated phosphorus), 2JPP
)
refinement method
no. of data/restraints/
params
full-matrix least squares on F2
10 686/0/845
30.2 Hz. 31P{1H} NMR (THF-d8): δ 52.4 (br, nonmetalated
phosphorus), 44.0 (br, metalated phosphorus). 1H NMR (THF-d8):
δ 1.29 (m, 18H), 1.46 (dd, J ) 17.4, 15.3 Hz, 6H and d, J ) 17.4
Hz, 6H), 1.63 (dd, J ) 12.7, 9.7 Hz, 6H), 2.21 (m, 3H), 2.65 (m,
2H). 13C{1H} NMR (THF-d8): δ 1.33 (m), 20.1, 20.4 (d, J ) 5.1
Hz), 20.5 (m), 21.9, 23.8 (br), 45.7 (br), 125.4 (br), 137.1 (d, 1JCF
10 751/0/877
goodness of fit on F2
1.013
1.032
final R indices (I > 2σ(I)) R1 ) 0.0644a
R1 ) 0.0647
wR2 ) 0.1441
R1 ) 0.1150
wR2 ) 0.1675
wR2 ) 0.1237b
R indices (all data)
R1 ) 0.1421
wR2 ) 0.1529
1
1
) 242.4 Hz), 139.1 (d, JCF ) 243.0 Hz), 149.2 (d, JCF ) 240.6
Hz). No peak was observed for CD3CN. To the CDCl3 (0.75 mL)
solution of 5a (50 mg, 43.5 µmol) was added acetic acid (3 µL),
and NMR (1H and 31P) spectra were recorded immediately that
indicated the formation of 3e as the only product.
2
2
a R1(F) ) ∑||Fo| - |Fc||/∑|Fo|. b wR2(F2) ) [∑{w(Fo - Fc )2}/
2
2
2
2
∑{w(Fo )2}]0.5; w-1 ) σ2(Fo ) + (aP)2 + bP, where P ) [Fo + 2Fc ]/3
and a and b are constants adjusted by the program.
1
1JCF ) 245.4 Hz), 138.4 (d, JCF ) 244.2 Hz), 138.8, 148.4 (d,
1JCF ) 237.3 Hz), 151.1. Anal. Calcd for C47H46NP2PdBF20: C,
47.67; H, 3.92; N, 1.18. Found: C, 47.67; H, 3.63; N, 1.17.
Preparation of cis-[(iPr3P)Pd(κ2-P,C-PiPr2CMe2)(4-tBuC5H4N)]-
[B(C6F5)4] (5c). Complex 5c was prepared from 3e (503 mg, 0.432
mmol) and 4-tert-butylpyridine (228 mg, 1.686 mmol) in dichlo-
romethane (10 mL) in 95% yield (508 mg) by a procedure
analogous to that used to prepare 5b. Anal. Calcd for C51H54NP2-
PdBF20: C, 49.38; H, 4.39; N, 1.13. Found: C, 49.54; H, 4.15; N,
1.44. 1P{1H} NMR (CDCl3): δ 49.2 (d, nonmetalated phosphorus),
1H NMR Monitoring of Cyclometalation Involving 3e and
Pyridine. Complex 3e (115 mg, 99 µmol) was dissolved in CD2-
Cl2 (0.4 mL). To the above solution was added a CD2Cl2 (0.3 mL)
solution of pyridine (44 mg, 0.56 mmol) in a 5 mm screw-cap NMR
tube; the contents of the NMR tube were shaken well and stored at
ambient temperature for 4 h. NMR (1H and 31P) data for the above
reaction products are given below. 31P{1H} NMR (CD2Cl2): δ 49.0
(d, nonmetalated phosphorus), 37.1 (d, metalated phosphorus), 2JPP
1
) 32.7 Hz. H NMR (CD2Cl2): δ 1.15-1.26 (m, 24H), 1.43 (dd,
2
36.4 (d, metalated phosphorus), JPP ) 32.9 Hz. 1H NMR
J ) 7.2 Hz, 3.9 Hz, 6H), 1.49 (dd, J ) 7.5 Hz, 3.9 Hz, 6H), 2.05
(m, 6H), 2.54 (m, 2H), 7.32 (br), 7.72 (br), 8.59 (br), 14.09 (s,
1H).
(CDCl3): δ 1.11-1.25 (m, 24H, CH(CH3)2, ring C(CH3)2), 1.33
(s, 9H, C(CH3)3), 1.40 (dd, J ) 7.1 Hz, 4.9 Hz, 6H, CH(CH3)2),
1.46 (dd, J ) 7.2, 5.1 Hz, 6H, CH(CH3)2), 1.99 (m, 3H, CH(CH3)2),
2.50 (m, 2H, CH(CH3)2), 7.48 (d, 3JHH ) 6.0 Hz, 2H, 4-tBuC5H4N),
cis-[(iPr3P)Pd(κ2-P,C-PiPr2CMe2)(C5H5N)][B(C6F5)4] (5b). Com-
plex 3e (508 mg, 0.436 mmol) was dissolved in dichloromethane
(6 mL), and the solution was stirred. To the above solution was
added a dichloromethane (6 mL) solution of pyridine (164 mg,
2.073 mmol), and the mixture was stirred for 5 h. The initial light
orange color slowly disappeared with the development of a colorless
solution. The volatiles from the reaction mixture were removed
under vacuum to furnish 5b in quantitative yield (516 mg).
3
8.36 (d, JHH ) 6.0 Hz, 2H, 4-tBuC5H4N). 13C{1H} NMR
(CDCl3): δ 20.2, 20.3 (d, 2JPC ) 3.1 Hz), 21.9 (d, 2JPC ) 2.5 Hz),
22.6 (m), 24.6 (d, 1JCP ) 13.9 Hz), 24.7 (dd, 1JCP ) 25.2 Hz, 3JCP
2
) 3.1 Hz), 30.3, 35.4, 40.5 (dd, JPC ) 46.2, 29.3 Hz, 1C, ring
C(CH3)2), 123.3, 124.0 (br), 136.4 (d, 1JCF ) 245.4 Hz), 138.4 (d,
1
1JCF ) 244.8 Hz), 148.4 (d, JCF ) 240.3 Hz), 150.6, 164.1.
Reaction of 3a with Pyridine. Complex 3a (147 mg, 0.105
mmol) was dissolved in dichloromethane (3 mL), and the solution
was stirred. To the above solution was slowly added a dichlo-
romethane (3 mL) solution of pyridine (70 mg, 2.07 mmol), and
this mixture was stirred for 18 h. No new product was formed, as
revealed by 31P NMR spectroscopy. The reaction mixture was stirred
for additional 76 h. The 31P NMR spectrum of the reaction mixture
indicated a pair of doublets (36.9 and 32.0 ppm (d, 1JPP ) 22 Hz))
in addition to a broad singlet at 22.0 ppm.
1
Assignments of the H and 13C peaks were unambiguously made
with the aid of two-dimensional COSY, HMQC, and HMBC NMR
spectroscopic measurements. 31P{1H} NMR (CDCl3): δ 49.1 (d,
2
nonmetallated phosphorus), 37.2 (d, metalated phosphorus), JPP
) 29.3 Hz. 1H NMR (CDCl3): δ 1.14-1.21 (m, 24H, CH(CH3)2,
ring C(CH3)2), 1.41-1.47 (m, 12H, CH(CH3)2), 2.00 (m, 3H,
3
CH(CH3)2), 2.52 (m, 2H, CH(CH3)2), 7.50 (t, JHH ) 6.3 Hz, 2H,
3
3
C5H5N), 7.87 (t, JHH ) 7.2 Hz, 1H, C5H5N), 8.51 (d, JHH ) 4.2
Hz, 2H, C5H5N). 13C{1H} NMR (CDCl3): δ 20.1, 20.3, 21.8, 22.5,
24.6 (d, JCP ) 13.8 Hz), 24.8 (d, JCP ) 26.8 Hz), 40.9 (dd, JPC
) 46.0, 28.3 Hz, 1C, ring C(CH3)2), 124.1 (br), 126.2, 136.4 (d,
X-ray Diffraction Studies. Details of the data collections and
structure solutions are presented in Table 1. Further details may
be found in the Supporting Information.
1
1
2

Pd(II) Phosphine Carboxylate Complexes
Organometallics, Vol. 26, No. 13, 2007 3163
resonances for the Cy moieties, two of them being singlets and
two others being virtual triplets due to the trans geometry of
these complexes in solution, as was also reported for 1b18 and
trans-[(Cy3P)2PdCl2].26 The 13C NMR spectrum of 1e displays
two resonances constituting a singlet for the methyl carbon and
Results and Discussion
(a) Synthesis and Characterization of [(R3P)2Pd(O2CR′)2].
The reactions of Pd(O2CR′)2 with various PR3 ligands in CH2-
Cl2 at -78 °C furnished air- and moisture-stable [(R3P)2Pd(O2-
CR′)2] (1a-f) as yellow crystalline solids in good yields
(Scheme 2). Although 1a2 and 1e2a have been noted, their
i
a virtual triplet for the methine carbon of Pr moieties, again
indicating a probable trans geometry. Compound 1a displays
some degree of thermal stability compared to trans-[(Ph3P)2-
Pd(O2CMe)2],22 for its 31P and 1H NMR spectra remained
unchanged even after heating in toluene-d8 solution at 63 °C
for 23 h.
Scheme 2
(b) Carboxylate Abstraction Reactions of [(R3P)2Pd-
(O2CR′)2]. Studies have revealed that the primary mode of
action of 1 equiv of [Li(OEt2)2.5][B(C6F5)4] or [Me2(H)NPh]-
[B(C6F5)4] on [(R3P)2Pd(O2CR′)2] is to abstract one of the
carboxylate groups to generate cationic complexes. The specific
products obtained vary, depending on solvent and reaction
conditions. Reactions performed in acetonitrile with these
reagents led to compounds 2a-e (Scheme 3).
R
R′
yield (%)
31P NMR (δ)
1a
1b
1c
1d
1e
1f
Cy
Cy
Cy
Me
Ph
88
74
74
67
90
70
21.3
23.7
17.4
24.5
33.0
93.3
tBu
CF3
Me
Me
Cy
iPr
NMe2
Scheme 3
characterization was partially reported. The formation of
complexes 1a-e was readily apparent from 31P NMR spectra,
which revealed a single peak shifted downfield as compared to
that for the free ligand.
Specifically, the 31P NMR signals for 1a,e resonate at lower
field as compared to those for uncoordinated PCy3 (10.9 ppm)
and PiPr3 (20.7 ppm), respectively.20 The coordination chemical
shifts ∆δ21 for 1a-e are 10.4, 12.8, 6.5, 13.6, and 12.3 ppm,
respectively. The values, however, are somewhat smaller than
that reported for trans-[(Ph3P)2Pd(O2CMe)2] (∆δ 15.0).22 In
contrast, the 31P NMR spectrum of 1f revealed a resonance at
δ 93.3 ppm which is upfield (∆δ -29.7) compared to free
P(NMe2)3 (δ 123.0 ppm).20 A positive coordination chemical
shift was observed for [Cy3PAuCl (∆δ 43.5)23 and [(iPr3P)-
AuCl] (∆δ 44.1),23 whereas a negative coordination chemical
R
R′
yield (%)
31P NMR (δ)
2a
2b
2c
2d
2e
Cy
Cy
Cy
Cy
iPr
Me
Ph
99
98
99
59
99
32.7
32.6
31.0
35.0
44.5
tBu
CF3
Me
shift (∆δ -12.3) was observed for [(Me2N)3P]AuCl.24 The 13
C
New complexes were characterized by 31P NMR resonances
that are notably shifted downfield relative to corresponding
resonances determined for compounds 1a-e. The H NMR
spectra of 2a-e confirm the incorporation of one acetonitrile
ligand per two phosphine ligands. These materials are air-stable
crystalline compounds. In solution, these materials start to
decompose above 60 °C, in contrast to the related carbene-
supported cationic palladium carboxylates Va and Vb (Scheme
1), which are stable at 80 °C for at least 24 h.16a
NMR spectra of 1a,c,e,f revealed a characteristic singlet around
180 ppm for the carbonyl carbon of the carboxylate group,
comparable to the value of 171.2 ppm previously established
for 1b,19 and also for related bis(acetato)palladium(II) bis-
(carbene) complexes.25 On the other hand, the 13C NMR
1
spectrum of 1d revealed a quartet centered at δ 160.9 (2JCF
)
32.6 Hz) due to the coupling of a carbonyl carbon to CF3 nuclei.
In addition, the 13C NMR spectrum of 1d revealed a quartet
centered at δC 114.3 (1JCF ) 289.3 Hz) assignable to coupling
of the CF3 carbon nucleus to three fluorine nuclei attached to
it. The carbon chemical shifts for carbonyl and CF3 carbons
The reactions of 1a-c,e with [Li(OEt2)2.5][B(C6F5)4] in
MeCN gave 2a-c,e in nearly quantitative yield. However, the
reaction of 1d with [Li(OEt2)2.5][B(C6F5)4] in MeCN gave, in
addition to 2d, an unidentified species (31P NMR: 43.4 ppm)
in significant quantities, and thus the yield of 59% is diminished
relative to those of the other reactions. Carboxylate abstractions
from 1a-e could also be performed using [Me2(H)NPh]-
[B(C6F5)4] in place of [Li(OEt2)2.5][B(C6F5)4], but isolation of
pure materials from the reaction mixtures proved more difficult,
despite the fact that 31P NMR spectroscopy suggested that high
yields of 2a-c are produced.
1
and the JCF value of 1d are comparable to those reported for
a bis(trifluoroacetato)palladium(II) bis(carbene) complex (car-
bonyl and CF3 chemical shifts 163.9 and 116 ppm, respectively;
1JCF ) 289.7 Hz).25c Compounds 1a,c,d all exhibit four
(20) Tebby, J. C. Handbook of Phosphorus-31 Nuclear Resonance Data;
CRC Press: Boca Raton, FL, 1991.
(21) Garrou, P. E. Chem. ReV. 2000, 203, 325-351.
(22) (a) Amatore, C.; Carre, E.; Jutand, A.; M’Barkii, M. A. Organo-
metallics 1995, 14, 1818-1826. (b) Amatore, C.; Jutand, A.; M’Barkii, M.
A. Organometallics 1992, 11, 3009-3013.
(23) Isab, A. A.; Fettouhi, M.; Ahmad, S.; Ouahab, L. Polyhedron 2003,
22, 1349-1354.
Single crystals of compound 2c were obtained by vapor
diffusion of heptane into a diethyl ether solution of 2c, and the
results of an X-ray diffraction study are presented in Figure 1.
(24) Bauer, A.; Mitzel, N. W.; Schier, A.; Rankin, D. W. H.; Schmidbaur,
H. Chem. Ber. 1997, 130, 323-328.
(25) (a) Konnick, M. M.; Guzei, I. A.; Stahl, S. S. J. Am. Chem. Soc.
2004, 126, 10212-10213. (b) Kuhn, N.; Maichle-Mossmer, C.; Niquet, E.;
Walker, I. Z. Naturforsch. 2002, 57b, 47-52. (c) Huynh, H. V.; Neo, T.
C.; Tan, G. K. Organometallics 2006, 25, 1298-1302.
(26) Grushin, V. V.; Bensimon, C.; Alper, H. Inorg. Chem. 1994, 33,
4804-4806.

3164 Organometallics, Vol. 26, No. 13, 2007
Thirupathi et al.
H2O in CH2Cl2 for 24 h showed that [(Cy3P)2Pd(κ2-O,O-O2C-
tBu)]OTs (δP 58.6) is cleanly produced. The successful synthesis
of carbene complexes Va also required an analogous two-step
process.16a Attempts to isolate the trifluoroacetato analogue 3d
were unsuccessful by either reaction of 1d with [Me2(H)NPh]-
[B(C6F5)4] or by reaction of 1d with HOTs‚H2O/[Li(OEt2)2.5]-
[B(C6F5)4]. The 31P NMR resonances of 3a-c,e are markedly
downfield compared to those of the analogous acetonitrile
adducts 2a-e. Interestingly, the magnitude of ∆δ for 3f is very
small and is opposite in sign (∆δ -4.4). The 13C NMR
resonances for the carbonyl carbons of 3a-c,e are consistently
shifted about 20 ppm downfield (161-182 ppm) relative to those
of the same atoms in 2a-c,e.
(c) Reaction of Cationic Complexes with Lewis Bases. (i)
Substitution Reactions. Our studies of the reactions of these
complexes were prompted by the observation that the κ2
complexes did not react with acetontrile to yield 2. The presence
of a labile acetonitrile ligand in complexes 2a-e, as well as
the known fluxionality of carboxylate ligands (between κ2 and
κ1 binding modes), suggested that these complexes should be
amenable to facile ligand substitution and addition reactions.
Reactions of these materials were thus examined with some
Lewis bases. During these investigations it was discovered that
cyclometalation of the phosphine ligands can occur in preference
to ligand addition. The substitution reactions are described first.
In general, reactions of 2a,b with added ligands proceeded
without difficulty to exchange the acetonitrile (Scheme 5). For
Figure 1. ORTEP representation of 2c (hydrogen atoms and anion
omitted for clarity). Selected bond distances (Å) and angles (deg):
Pd(1)-O(2), 1.994(5); Pd(1)-N(1), 1.998(6); Pd(1)-P(2), 2.376(2);
Pd(1)-P(1), 2.379(2); N(1)-C(6) 1.129(8); O(1)-C(1), 1.201(9);
O(2)-C(1), 1.300(9); O(2)-Pd(1)-N(1), 169.7(2); O(2)-Pd(1)-
P(2), 89.2(1); N(1)-Pd(1)-P(2), 91.0(2); O(2)-Pd(1)-P(1), 90.2(1);
N(1)-Pd(1)-P(1), 88.6(2); P(2)-Pd(1)-P(1), 174.03(7).
Complexes 2a and 2c have essentially identical average Pd-P
bond lengths (ca. 2.38 Å).15 Compound 2c, however, has shorter
(possibly statistically insignificant) Pd-O bond lengths (1.994-
(5) vs 2.007(4) Å) and longer Pd-N bond lengths (1.998(6) vs
1.986(5) Å). This ever so slight bias of the parameters may be
due to the fact that the pivalato group is a better donor for
palladium than the acetato group, and thus in response, the
binding of the acetonitrile is weaker in the pivalato complex.
The remainder of the two structures are in close accord with
one another and are within expectations for four-coordinate
palladium(II) complexes.
Scheme 5
Reactions of 1a-d,f with [Li(OEt2)2.5][B(C6F5)4] or [Me2-
(H)NPh][B(C6F5)4] in the noncoordinating solvent CH2Cl2,
however, take a different course and produce the cationic
complexes 3a-c,e,f (Scheme 4) lacking the coordinating solvent
R
L
yield (%)
31P NMR (δ)
Scheme 4
4a
4b
4c
4d
4e
4f
Cy
Cy
Cy
Cy
iPr
iPr
C5H5N
99
99
22.1
21.8
22.4
40.6
33.4
53.8
4-Me2NC5H4N
NC4H4N
CNC6H3Me2-2,6
C5H5N
39 (NMR)
99
99
CNC6H3Me2-2,6
99 [96]a
a Yield from 3e and CNC6H3Me2-2,6.
R
R′
yield (%)
31P NMR (δ)
example, the reaction of 2a with pyridine in toluene and with
DMAP in THF furnished 4a,b, respectively, in nearly quantita-
tive yields. Similarly, complex 2e upon treatment with pyridine
in dichloromethane gave 4e in quantitative yield. The new
palladium complexes 4 are stable to air and moisture for at least
several days, like their precursors 2 and 3.
3a
3b
3c
3d
3e
3f
Cy
Cy
Cy
Me
Ph
79
80
69
59.3
59.6
58.4
tBu
CF3
Me
Me
Cy
iPr
80
65
69.4
88.9
NMe2
The crystal structure of 4b was determined by X-ray
diffraction on a sample obtained by diffusing pentane into a
THF solution of 4b, and the results are depicted in Figure 2.
The structure shows no unusual features and is closely related
to the structures of 2a15 and 2c. The coordination geometry
around palladium in 4b is square planar, with two PCy3 ligands
occupying trans positions. The Pd-P distances in 4b of 2.40 Å
are somewhat longer than those observed in 2a and 2c (2.38
Å). This observation may reflect the higher basicity of DMAP
relative to acetonitrile. The longer Pd-O distance of 2.013(4)
Å in 4b is consistent with this proposal.
molecule. In order to satisfy the coordination needs of the
palladium centers, these complexes feature κ2-carboxylate
ligands. By necessity, the two phosphine ligands are cis in these
materials. Variations of reaction conditions led to the finding
that higher yields (∼20% better) and easier product purification
could be achieved if the reactions were performed via a two-
step process. Specifically, addition of p-toluenesulfonic acid to
[(R3P)2Pd(O2CR′)2] led to formation of [(R3P)2Pd(κ2O,O-O2-
CR′)]OTs, which upon addition of [Li(OEt2)2.5][B(C6F5)4] led
to formation of [(R3P)2Pd(κ2-O,O-O2CR′)][B(C6F5)4] (3a-c,e,f)
in good yields. These intermediary tosylate salts were not fully
characterized, but analysis of the reaction of 1c with HOTs‚
Attempts to isolate the product of reaction of 2a with pyrazine
in THF, however, were less productive. The desired pyrazine

Pd(II) Phosphine Carboxylate Complexes
Organometallics, Vol. 26, No. 13, 2007 3165
Scheme 6
R
CR′′2
CMe2
CMe2
CMe2
L
31P NMR (δ)
5a
5b
5c
5d
iPr
iPr
iPr
Cy
CD3CN
C5H5N
51.7, 43.2 (JPP ) 30 Hz)
49.1, 37.2 (JPP ) 29 Hz)
49.2, 36.4 (JPP ) 33 Hz)
36.9, 32.0 (JPP ) 22 Hz)
4-tBuC5H4N
C5H5N
-C(CH2)5-
than 2 equiv of N-donor is used, so as to consume 1 equiv as
proton scavenger of the proton from the cyclometalation process.
The properties of 5c are in full accord with those of the
previously reported analogue 5b. Specifically, the 31P NMR
spectrum of 5c displayed a pair of doublets centered at δP 49.2
and 36.4 for nonmetalated and metalated phosphorus, respec-
tively.21,27 These shifts are comparable to those reported for 5a
(δP 51.7 (nonmetalated phosphorus), 43.2 (metalated phospho-
rus)) and 5b (δP 49.1 (nonmetalated phosphorus), 37.2 (meta-
lated phosphorus)). The X-ray structure of 5b unambiguously
revealed a square-planar geometry around palladium in which
the metalated phosphorus was located trans to pyridine.15 We
thus propose that both 5a and 5c possess structures analogous
to that of 5b. The cis disposition of phosphines in 5c is also
indicated by the small phosphorus-phosphorus coupling con-
stant (2JPP ) 33 Hz), which is comparable to those values
reported for 5a (2JPP ) 30 Hz) and 5b (2JPP ) 29 Hz). These
values are also comparable to that of a related neutral platinum
complex, VIII (2JPP ) 30 Hz).28 Complexes 5b,c each exhibit
Figure 2. ORTEP representation of 4b (hydrogen atoms and anion
omitted for clarity). Selected bond distances (Å) and angles (deg):
Pd(1)-O(1), 2.013(4); Pd(1)-N(1), 2.021(5); Pd(1)-P(1), 2.400(2);
Pd(1)-P(2), 2.401(2); O(1)-Pd(1)-N(1), 172.1(2); O(1)-Pd(1)-
P(1), 88.3(1); N(1)-Pd(1)-P(1), 92.7(2); O(1)-Pd(1)-P(2), 86.9(1);
N(1)-Pd(1)-P(2), 93.7(2); P(1)-Pd(1)-P(2), 167.26(6).
adduct 4c is only produced in about 39% yield (as ascertained
by 31P NMR spectroscopy) upon addition of 1 equiv of pyrazine
to 2a. Longer reaction times (19 h) and the addition of 3 equiv
of pyrazine to the reaction mixture did not significantly increase
the amount of 4c produced. Apparently, the weaker nucleophi-
licity of pyrazine as compared to that of MeCN and pyridine
yields only an equilibrium mixture of 2a, acetonitrile, pyrazine,
and 4c. The reaction of 2a with 5 equiv of DABCO in
dichloromethane yielded no new species, as revealed by 31P
NMR spectroscopy. This result might be due to unfavorable
steric repulsion between PCy3 in 2a and the incoming DABCO.
The reactions of 2a,e with 2,6-dimethylphenyl isocyanide
afforded high yields of isocyanide complexes 4d,f. These new
adducts were identified by standard NMR spectroscopic meth-
ods, as well as elemental analysis. While complexes 4a,b,e each
revealed a 31P NMR signal at higher field than for their
respective parent complexes 2, the isocyanide complexes, in
contrast, have 31P resonances at lower field relative to those of
2a,e. The collective spectroscopic data support a trans geometry
for palladium in all of the adducts 4. Intriguingly, 4f could also
be obtained from the reaction of 3e with 2,6-dimethylphenyl
isocyanide in dichloromethane in 96% yield, whereas the
reactions with N-centered Lewis bases produced different types
of products (vide infra).
a characteristic pair of doublets centered at δP 40.9 (1JPC ) 46
2
2
Hz, JPC ) 28 Hz) and at δP 40.5 (1JPC ) 46 Hz, JPC ) 29
Hz), respectively, for the ring CMe2 carbon, due to coupling
with two nonequivalent phosphorus nuclei. These chemical shifts
are in the region expected for the ring carbon in a three-
membered palladacycle.29
Initial attempts to extend the cyclometalation reaction to
complexes bearing the cyclohexyl groups are informative but
inconclusive at this time. The reaction of 3a and pyridine in
dichloromethane was very slow, and two products appeared at
the expense of perhaps half of 3a after 4 days, as revealed by
31P NMR spectroscopy. The material present in greater quantity
(ii) Cyclometalation Reactions. While reactions of the
acetonitrile complexes 2 with pyridines gave the products of
simple substitution, the reactions of complexes 3 are more
complicated, despite the fact that these materials are effectively
“acetonitrile-free” analogues of 2. Cyclometalation of the iPr3P
ligand of 3e was discovered during attempts to convert
complexes 3e to 2e by the addition of acetonitrile.
(27) Goel, R. G.; Montemayor, R. G. Inorg. Chem. 1977, 16, 2183-
2186.
(28) Bresadola, S.; Bresciani-Pahor, N. J. Organomet. Chem. 1979, 179,
73-79.
As previously noted, the cyclometalation reaction of 3e occurs
upon dissolution of 3e in CD3CN and affords an equilibrium
mixture containing 30% of 5a (Scheme 6).15 Addition of sodium
carbonate (as a convenient base) drives the reaction to comple-
tion. We also found that solutions of 3e and pyridine provided
the related complex 5b as a crystalline solid, which was fully
characterized. The reaction of 3e can also be extended to
derivative 5c by using 4-tert-butylpyridine. Like the reaction
of 3e and pyridine, the yields of 5c are maximal (95%) if more
(29) van der Sluis, M.; Beverwijk, V.; Termaten, A.; Bickelhaupt, F.;
Kooijman, H.; Spek, A. L. Organometallics 1999, 18, 1402-1407.
(30) (a) Ingleson, M. J.; Mahon, M. F.; Weller, A. S. Chem. Commun.
2004, 2398-2399. (b) Thorn, D. L. Organometallics 1998, 17, 348-352.
(c) Esteruelas, M. A.; Lopez, A. M.; Onate, E.; Royo, E. Organometallics
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3166 Organometallics, Vol. 26, No. 13, 2007
Thirupathi et al.
was identified by a pair of doublets centered at δP 36.9 and
32.0 (2JPP ) 22 Hz), and the minor product displayed a broad
singlet at δP 22.0 ppm. The species displaying the pair of
doublets is very likely to be the cyclometalated complex 5d. A
greater resistance to cyclometalation for compound 3a compared
to that for 3e can probably be attributed to the formation of a
spirocyclic ring system in a compound such as 5d. The broad
signal at 22 ppm is identified as the product of simple
substitution, 4a. Thus, for this material, substitution can occur
competitively, albeit slowly, with cyclometalation.
Base-induced cyclometalation of alkylphosphines coordinated
to transition metals is a well-known method to generate
metallacycles. The C-H bond in PiPr3 coordinated to a transition
metal can be activated in two ways, involving methyl or methine
protons, the former process leading to either the four-membered
metallacycle IX or the three-membered metallacycle X. While
gives the only the product of substitution. Since 3a provides
both cyclometalation and substitution upon reaction with
pyridine, one can ponder what specific factors control the type
of product that is obtained. One possibility would involve
interconversion of the κ1- and κ2-carboxylate complexes prior
to ligand addition. Attempts to observe this interconversion,
however, were only partially successful. 31P NMR observation
of solutions of 2a and 2e heated to greater than 60 °C reveal a
slow decomposition of these materials to produce a mixture of
Pd metal and PdH complexes (as suggested by the presence of
1H NMR signals at around -15 ppm). Spectral signatures for
significant amounts of the corresponding κ2 complexes, however,
are seen during these reactions. Heating solutions of 3a and 3e
with acetonitrile under various conditions does not produce
evidence for formation of acetonitrile adducts 2a and 2e. More
work is required to properly explain the reasons for the product
diversity and chemistry of these palladium complexes.
Conclusions
A diverse set of bis(carboxylato)palladium(II) bis(phosphine)
complexes was isolated in high yield and characterized. Car-
boxylate abstraction reactions yielded cationic palladium car-
boxylate complexes, whose specific natures were very dependent
on the choice of solvent. Reactions of trans-[(R3P)2Pd(O2CR′)2]
(1) with [Li(OEt2)2.5][B(C6F5)4] in MeCN led to carboxylate
abstraction and formation of trans-[(R3P)2Pd(O2CR′)(MeCN)]-
[B(C6F5)4] (2), while carboxylate abstraction reactions of 1 with
[Me2(H)NPh][B(C6F5)4] or p-toluenesulfonic acid (HOTs‚H2O)
in CH2Cl2 furnished cationic complexes of the form [(R3P)2-
Pd(κ2-O,O-O2CR′)]+ (3). Reactions of these materials with
pyridine gave two different types of products, either the products
of acetonitrile substitution (4) or those of cyclometalation (5).
numerous four-membered metallacycles are known in the
literature, three-membered metallacycles are rarer. The reaction
of cis-[(Me3P)4Ru(O2CMe)Cl] or cis-[(Me3P)4Ru(O2CMe)2]
with LiN(SiMe3)2 furnishes cyclometalated cis-[(Me3P)3RuCl-
(κ2-P,C-PMe2CH2)] and spirocyclic cis-[(Me3P)2Ru(κ2-P,C-
PMe2CH2)2], respectively.31Another closely related example
reported in the literature involves activation of the ipso C-H
bond of PCy3 in [(η5-C5Me5)Re(CO)(N2)(PCy3)] upon irradia-
tion with UV light to furnish the cyclometalated XI in 66%
yield, which was unambiguously characterized by X-ray crystal-
lography.32
Acknowledgment. We thank Promerus LLC, for funding.
While addition of pyridine to 3e provide the products of
cyclometalation, addition of 2,6-dimethylphenyl isocyanide
Supporting Information Available: CIF files giving crystal-
lographic information for 2c and 4b and figures giving NMR
spectra. This material is available free of charge via the Internet at
http://pubs.acs.org.
(31) Mainz, V. V.; Andersen, R. A. Organometallics 1984, 3, 675-
678.
(32) Aramini, J. M.; Einstein, F. W. B.; Jones, R. H.; Klahn-Oliva, A.
H.; Sutton, D. J. Organomet. Chem. 1990, 385, 73-90.
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