Palladium iminoacyl imine complexes: Strategies toward imine n insertion

Article abstract of DOI:10.1021/om900574b

The syntheses and characterization of a number of palladium complexes containing imine and/or iminoacyl groups are reported. Our strategies toward the insertion of imines into palladium iminoacyl complexes are outlined. The imine complexes [Pd(Me)(L₂){ N(R^')=C(H)Ph}]X (where L ₂ = dppe, dppp, dppf; R^' = Ph, Me, Bz; and X = BF ₄ or OTf) were prepared and fully characterized. [Pd(Me)(dppe){N(Ph)= C(H)Ph}]BF₄ (1) and [Pd(Me)(dppp){N(Ph)=C(H)Ph}]OTf (4) were structurally characterized by X-ray crystallography. The iminoacyl-imine complexes [Pd{C(Me)=NXyl} (L₂){N=C(Me)OCH₂CH ₂}]BF₄ (L₂ = dppe, 12; dppp, 13) were prepared. The bis-imine complex [Pd(dppe){N=C(Me)OCH₂CH₂} ₂][BF₄]₂ (14) resulting from disproportionation of 12 was also prepared and structurally characterized. Protonation of the iminoacyl fragment provided iminoacyl imine complex [Pd{C(CH₃)=N(H) Xyl}(dppe){N(Bz)=CPhH}][BF₄]₂ (17), which was sufficiently stable to be structurally characterized, providing some insight into the coordination of these fragments to palladium.

Full text of DOI:10.1021/om900574b

Organometallics 2009, 28, 5783–5793 5783
DOI: 10.1021/om900574b
Palladium Iminoacyl Imine Complexes: Strategies toward Imine
Insertion§
Gareth R. Owen,*,† Andrew J. P. White,‡ and Ramon Vilar*,‡
‡
†The School of Chemistry, University of Bristol, Bristol, BS8 1TS, U.K., and Department of Chemistry,
Imperial College, London, South Kensington, SW7 2AY, U.K.
Received July 3, 2009
The syntheses and characterization of a number of palladium complexes containing imine and/or
iminoacyl groups are reported. Our strategies toward the insertion of imines into palladium iminoacyl
complexes are outlined. The imine complexes [Pd(Me)(L2){N(R0)dC(H)Ph}]X(whereL2 = dppe, dppp,
dppf; R0 = Ph, Me, Bz; and X = BF4 or OTf) were prepared and fully characterized.
[Pd(Me)(dppe){N(Ph)dC(H)Ph}]BF4 (1) and [Pd(Me)(dppp){N(Ph)dC(H)Ph}]OTf (4) were structu-
rally characterized by X-ray crystallography. The iminoacyl-imine complexes [Pd{C(Me)dNXyl}
(L2){NdC(Me)OCH2CH2}]BF4 (L2 = dppe, 12; dppp, 13) were prepared. The bis-imine complex
[Pd(dppe){NdC(Me)OCH2CH2}2][BF4]2 (14) resulting from disproportionation of 12 was also prepared
and structurally characterized. Protonation of the iminoacyl fragment provided iminoacyl imine complex
[Pd{C(CH3)dN(H)Xyl}(dppe){N(Bz)dCPhH}][BF4]2 (17), which was sufficiently stable to be structu-
rally characterized, providing some insight into the coordination of these fragments to palladium.
Introduction
other biologically important species. In the search for new
routes to these targets, and by analogy to the copolymeri-
zation of olefins and carbon monoxide,5 there have been
some studies on the insertion of imines (R0R00CdNR) into
metal-acyl bonds.6 In 1998, Sen and Arndtsen indepen-
dently showed the insertion of an imine into palladium-acyl
bonds.7,8 The resulting complexes, however, were unreactive
Palladium-catalyzed carbon-carbon bond formation is a
well-established methodology for the synthesis of new and
valuable organic compounds.1 More recently efficient meth-
odologies for the coupling of nitrogen, sulfur, and oxygen
fragments to carbon have also been established.2-4 The
synthesis of new C-N, C-S, and C-O bonds has great
potential for the preparation of new pharmaceuticals and
(3) Selected examples of C-S bond formation: (a) Kuniyasu, H.;
Kurosawa, H. Chem.;Eur. J. 2002, 8, 2660. (b) Li, G. Y. J. Org. Chem.
2002, 67, 3643. (c) Kondo, T.; Mitsudo, T.-A. Chem. Rev. 2000, 100, 3205.
(c) Mann, G.; Baranano, D.; Hartwig, J. F.; Rheingold, A. L.; Guzei, I. A.
J. Am. Chem. Soc. 1998, 120, 9205. (d) Eichman, C. C.; Stambuli, J. P.
J. Org. Chem. 2009, 74, 4005. (e) Fernandez-Rodriguez, M. A.; Hartwig,
J. F. J. Org. Chem. 2009, 74, 1663. (f) Correa, A.; Carril, M.; Bolm, C. Angew.
Chem., Int. Ed. 2008, 47, 2880. (g) Zhang, Y.; Ngeow, K. C.; Ying, J. Y. Org.
Lett. 2007, 9, 3495. (h) Hartwig, J. F. Acc. Chem. Res. 2008, 41, 1534.
(4) Selected examples of C-O bond formation see: (a) Krug, C.;
Hartwig, J. F. J. Am. Chem. Soc. 2002, 124, 1674. (b) Mann, G.; Hartwig,
J. F. J. Am. Chem. Soc. 1996, 118, 13109. (c) Widenhoefer, R. A.;
Buchwald, S. L. J. Am. Chem. Soc. 1998, 120, 6504. (d) Widenhoefer,
R. A.; Zhong, H. A.; Buchwald, S. L. J. Am. Chem. Soc. 1997, 119, 6787.
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(f) Schlummer, B.; Scholz, U. Adv. Synth. Catal. 2004, 346, 1599.
(5) (a) Drent, E. Eur. Pat. Appl. 1986, 229, 408. ; Chem. Abstr. 1988,
108, 6617. (b) Drent, E.; van Broekhoven, J. A. M.; Doyle, M. J.
J. Organomet. Chem. 1991, 417, 235. (c) Drent, E.; Budzelaar, P. H. M.
Chem. Rev. 1996, 96, 663.
*Corresponding authors. (R.V.) Tel: þ44 (0)207 594 1967. E-mail:
r.vilar@imperial.ac.uk. (G.R.O.) Tel: þ44 (0)117 928 7652. E-mail:
gareth.owen@bristol.ac.uk.
§ This article is dedicated to the memory of Dr. Daniela Rais.
(1) Reviews on C-C bond formation: (a) Collman, J. P.; Hedgus, L. S.;
Norton, J. R.; Finke, R. G. Principles and Applications of Organotransition
Metal Chemistry; University Science Books: Mill Valley, CA, 1987. (b) Tsuji, J.
Palladium Reagents: Innovations in Organic Synthesis; Wiley: Chichester,
1995. (c) Crabtree, R. H. The Organometallic Chemistry of the Transition
Metals; Wiley Interscience, New York, 1994. (d) Yamamoto, A. Organotransi-
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Adv. Synth. Catal. 2004, 346, 1583.
(2) Selected examples of C-N bond formation: (a) Deubel, D. V.,
Ziegler, T. Organometallics, 2002, 21, 1603, and reference therein.
(b) Klapars, A.; Huang, X.; Buchwald, S. L. J. Am. Chem. Soc. 2002,
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13848. (j) Shen, Q.; Hartwig, J. F. Org. Lett. 2008, 10, 4109. (k) Christmann,
U.; Vilar, R. Angew. Chem., Int. Ed. 2005, 44, 366. (l) Monnier, F.; Taillefer,
M. Angew. Chem., Int. Ed. 2008, 47, 3096. (m) Ley, S. V.; Thomas, A. W.
Angew. Chem., Int. Ed. 2003, 42, 5400.
(6) For further routes to similar compounds see: (a) Krueger, C. A.;
Kuntz, K. W.; Dzierba, C. D.; Wirschun, W. G.; Gleason, J. D.;
Snapper, M. L.; Hoveyda, A. H. J. Am. Chem. Soc. 1999, 121, 4284.
(b) Jia, L.; Ding, E.; Anderson, W. R. J. Chem. Soc., Chem. Commun. 2001,
1436. (c) Beller, M.; Eckert, M. Angew. Chem., Int. Ed. 2000, 39, 1010.
(d) Kim, J. S.; Sen, A. J. Mol. Catal. A 1999, 143, 197.
(7) (a) Kacker, S.; Kim, J. S.; Sen, A. Angew. Chem., Int., Ed. 1998, 37,
1251. (b) Kang, M.; Sen, A. Organometallics 2005, 24, 3508.
(8) (a) Arndtsen, B. A.; Dghaym, R. D.; Yaccato, K. J. Organome-
tallics 1998, 17, 4. (b) Davies, J. L.; Arndtsen, B. A. Organometallics 2000,
19, 4657. (c) Lafrance, D.; Davis, J. L.; Dhawan, R.; Arndtsen, B. A.
Organometallics 2001, 20, 1128. (d) Dghaym, R. D.; Dhawan, R.; Arndsten,
B. A. Angew. Chem., Int. Ed. 2001, 40, 3228. (e) Dghaym, R. D.; Dhawan,
R.; Arndsten, B. A. J. Am. Chem. Soc. 2003, 125, 1474.
r
2009 American Chemical Society
Published on Web 09/08/2009
pubs.acs.org/Organometallics

5784 Organometallics, Vol. 28, No. 19, 2009
Owen et al.
Scheme 1. Two Methodologies for Imine Insertion into the Palladium-Iminoacyl Bond
Scheme 2. General Synthesis of the Imine Complexes 1-9
to further insertion due to the strong chelation of the amide
functionality to the metal center. More recently, Arndsten
has reviewed this area, showing the wide range of potential
reactions that can be performed with this organometallic
fragment.9 On the other hand, Sun reported the first exam-
ples of copolymerization of carbon monoxide and imines,
providing a novel method for the formation of polypeptides
with molecular weights of about 2000 Da.10 Sun employed
[Co(CH2Ph)(CO)4] as a precursor, which is initiated by
the loss of one molecule of carbon monoxide. The active
species subsequently undergoes alternating insertion of
imine and carbon monoxide, which is eventually terminated
via β-hydride elimination.
We have previously reported the insertion of olefins into
iminoacyl-palladium complexes containing bidentate phos-
phine ligands.11 Insertion of imines into the iminoacyl group
could provide an alternative route to precursors for the
formation of heterocyclic products. Moreover, the products
resulting from potential insertion of the imine into the
iminoacyl moiety, i.e., amidines, are molecules of great
biological interest.12 We were therefore interested in in-
vestigating the potential of imine insertion into palla-
dium-iminoacyl bonds. Herein, we outline our strategies
toward imine insertion into palladium-iminoacyl bonds.
palladium-acyl bonds, where the palladium is coordinated
to chelating phosphines rather than to related nitrogen-
based ligands. Furthermore, following the publication by
Sen and Arndtsen, reporting the insertion of imine into a
palladium-acyl bond, a theoretical study by Cavallo was
reported.13 This study confirmed that imine insertion into
Pd-acyl bonds is energetically favorable and proceeds via a
lower energy barrier when the co-ligands are bis-phosphines
in comparison to bis-nitrogen ligands. Cavallo explained
that a larger trans influence of the phosphines made the bond
lengths of both the acyl and imine ligands closer to that of the
calculated transition state of the insertion process. This effect
reduces the strain on going through the transition state and
makes the barrier to insertion lower. This would explain why
complexes with bis-nitrogen ligands reported by Arndtsen
required elevated temperatures for insertion to take place.
The larger driving force for Pd-acyl insertion comes mainly
from formation of a strong amido bond. Cavallo confirmed
the stability of the σ-bonded coordination mode of the imine
over the π-bonded form (π-coordination ca. 20 kcal mol-1
higher in energy relative to the σ-coordination mode). Never-
theless, Cavallo further calculated that some π-bonded
character is necessary during the final stages of the transition
state for insertion. π-Bonding reduces the bond order of the
imine, and therefore the complex is closer in energy to the
transition state needed for insertion.
Results and Discussion
Two different methodologies were initially envisaged to
achieve the iminoacyl-imine species A, which could in prin-
ciple undergo imine insertion into the palladium-iminoacyl
bond, forming product B (Scheme 1). First, by analogy to the
chemistry developed by Sen and Arndtsen,7,8 a palladium
methyl-imine complex was prepared and 1 equiv of isocya-
nide was subsequently added to the complex. A second
method involved initial formation of the iminoacyl complex
followed by halide abstraction in the presence of imine.
Method 1: Addition of Isocyanide to Imine Complexes. The
first step in our studies toward imine insertion was to
synthesize and fully characterize a series of palladium-imine
complexes for further reactivity (Scheme 2). The bis-phos-
phine complexes were targeted since Sen had previously
established a greater propensity for imine insertion into
A small number of palladium complexes containing imines
and chelating phosphines had been previously described by
Sen.7 However their full characterization was not reported.
A general method of preparation of the imine complexes is
described herein. [PdCl(Me)L2] (L2 = dppp, dppe, dppf) was
dissolved in CH2Cl2. Chloride was then removed by addition
of 1 equiv of AgBF4 or AgOTf, in the presence of a slight
excess (1.1 equiv) of imine. The resulting AgCl precipitate was
removed by filtration, and the product was isolated by addi-
tion of hexane and slowly evaporating CH2Cl2 under reduced
(9) Arndtsen, B. A. Chem.;Eur. J. 2009, 15, 302.
(10) Sun, H.; Zhang, J.; Liu, Q.; Yu, L.; Zhao, J. Angew. Chem., Int.
Ed. 2007, 46, 6068.
(11) Owen, G. R.; Vilar, R.; White, A. J. P.; Williams, D. J.
Organometallics 2002, 21, 4799.
(12) (a) Greenhill, J. V.; Lue, P. Prog. Med. Chem. 1993, 30, 203.
(b) Echevarriaa, A.; Santosa, L. H.; Miller, J.; Mahmood, N. Biol. Med.
Chem. Lett. 1996, 6, 1901.
(13) Cavallo, L. J. Am. Chem. Soc. 1999, 121, 4238.

Article
Table 1. Isolated Yields of [L2M(Me)(imine)]X (1-9)
Organometallics, Vol. 28, No. 19, 2009 5785
Table 2. 31P{1H} NMR Spectroscopic Data for Complexes 1-9
31P{1H} NMR δ (ppm)
complexa
L2
imine
yield (%)
complexa
trans to methylb
trans to imineb
JPP (Hz)
1
2
3
4
5
6
7
8
9
dppe
dppe
dppe
dppp
dppp
dppp
dppp
dppf
dppf
N(Ph)dCPhH
N(Me)dCPhH
N(Bz)dCPhH
N(Ph)dCPhH
N(Ph)dCPhH
N(Me)dCPhH
N(Bz)dCPhH
N(Ph)dCPhH
N(Bz)dCPhH
79
78
76
62
73
71
68
79
78
1
2
3
57.6
57.7
57.0
23.8
23.1
22.7
21.9
38.1
36.8
39.1
39.9
39.7
-2.1
-2.3
0.2
0.3
19.6
19.2
23
23
23
51
52
50
50
29
29
4
5c
6
7c
8
a Noncoordinating anion is BF4 except for complex 4, which is OTf.
9
a Recorded in CDCl3. b This assignment was made by comparison
with similar complexes such as [L2Pd(Me)(NCMe)]X; see ref 24b.
c Recorded in THF.
pressure. The resulting solid was washed with diethyl ether to
remove excess imine. The dppp and dppe products were
isolated as white solids, and the dppf products were isolated
as analytically pure yellow to orange solids in high yields. The
numbering scheme of the prepared complexes is shown in
Table 1 together with their isolated yields.
Table 3. Comparison of 1H NMR Spectroscopic Data and IR
Spectroscopic Data for Imine Complexesa
The products (1-9) were fully characterized by 31P{1H}
NMR (Table 2), 1H NMR (Table 3), and IR spectroscopies
(Table 3), FABþ mass spectrometry, and elemental analysis.
Crystallographic studies were carried out on two of the
complexes, 1 and 4 (see below).
NdCPh
ortho-H’s
(ppm)
NdCH
(ppm)
M-CH3
(ppm)
CdN
compounda
(cm-1
)
N(Ph)dCPhH
1
1624
1606
1608
1624
1607
1652
1637
1645
1643
1617
1626
1626
8.48
8.05
8.04
8.35
8.07
8.37
8.37
8.46
0.54
0.37
0.36
0.41
The 31P{1H} NMRspectra ofthese complexes comprised of
a pair of doublets as expected from a cis chelating phosphine
with two different ligands in the trans positions (methyl and
imine). The dppe-based complexes are found at lower field
chemical shifts with smaller coupling constants compared
to the dppp complexes. This is consistent with previously
reported data comparing these two chelating phosphines.14
The chemical shifts and coupling constants for each product
are shown in Table 2. The 1H NMR spectra of compounds
1-9 revealed a doublet of doublet signal integrating for three
protons, representing the methyl group bound to the palla-
dium (between 0.08 and 0.37 ppm). The proton of the imines,
N(R)dC(H)Ph was found between 7.84 and 8.52 ppm
as a doublet of doublets (with approximate 4JPH = 9.5 and
2.0 Hz, trans and cis coupling, respectively, to the diphos-
phine). An additional signal, found between 7.68 and 8.46
ppm (integrating for two protons) in the 1H NMR spectra of
the nine complexes, was observed at lower field chemical shifts
than the other aromatic signals. These resonances were as-
signed to the two ortho-protons on the phenyl group of
N(R)dCPhH. This assignment was made on the basis of an
agostic interaction that is maintained in solution (see below
for structural information) and is in accordance with pre-
viously reported agostic interactions involving imines’ aryl
groups.15-17 An important feature of the reported complexes
was the characteristic downfield chemical shift (approxi-
mately 1.0-1.5 ppm), in the 1H NMR spectra, from the
corresponding signals for the free imine. The extreme of this
4
5
8
N(Me)dCPhH
2
8.52
8.10
7.94
7.68
0.48
0.35
6
N(Bz)dCPhH
3
7
9
8.62
7.84
8.15
8.03
8.15
8.45
0.18
0.01
0.08
a NMR spectroscopy carried out in CDCl3.
interaction leads to cyclometalation, of which there are many
more examples.18 The IR spectra of these complexes display
the characteristic CdN stretching frequency of imines, with
reduced frequency relative to the free imine. This is with the
exception of complex 5, which showed no shift in the imine
frequency. The IR spectra also revealed characteristic
stretches for either the tetrafluoroborate (1057-1069 cm-1
)
or triflate (1262, 1152, and 1031 cm-1) anions present as
counterions in the different complexes. The FABþ mass
spectra of 1-9 showed molecular ion peaks for the expected
complexes and fragments corresponding to loss of imine. The
molecular composition of the complexes was further con-
firmed by elemental analysis.
X-ray Crystal Structures of Complexes 1 and 4. Crystals
of complexes 1 and 4 suitable for X-ray crystallography
were obtained by careful addition of a layer of hexane to a
concentrated THF solution of the corresponding complex.
The solid state structures of these complexes showed them
to be the expected products in each case (Figures 1 and 2,
respectively). In both structures the palladium adopts a dis-
torted square-planar geometry with cis angles in the ranges
85.83(4)-91.91(9)° and 86.2(4)-94.20(12)° for 1 and 4, respec-
tively. However, whereas in 4 the metal and the four donor
(14) (a) Lindner, E.; Fawzi, R.; Mayer, H. A.; Eichele, K.; Hiller, W.
Organometallics 1992, 11, 1033. (b) Garrou, P. E. Chem. Rev. 1981, 81, 229.
(c) Palenik, G. J.; Mathew, M.; Steffen, W. L.; Beran, G. J. Am. Chem. Soc.
1975, 97, 1059. (d) Pavigianiti, A. J.; Minn, D. J.; Fultz, W. C.; Burmeister,
M. J. L. Inorg. Chim. Acta 1989, 159, 65. (e) Appleton, T. G.; Bennett,
M. A.; Tomkins, I. B. J. Chem. Soc., Dalton Trans. 1976, 439.
(15) Brookhart, M.; Green, M. L. H.; Wong, L. L. Prog. Inorg. Chem.
1988, 36, 1.
(16) (a) Kuzmina, L. G.; Struchkov, Y. T. Cryst. Struct. Commun.
1979, 8, 715. (b) Clark, P. W.; Dyke, S. F.; Smith, G.; Kennard, C. H. L.
J. Organomet. Chem. 1987, 330, 447. (c) Lee, M.; Yoo, Y.-S.; Choi, M. H.;
Chang, H.-Y. J. Mater. Chem. 1998, 8, 277.
˚
atoms are all coplanar to better than 0.01 A, in 1 the P(1)
˚
phosphorus atom lies ca. 0.26 A out of the {Pd,P(2),N(1),C(2)}
˚
plane (which is coplanar to within ca. 0.01 A). This is pos-
sibly associated with the decreased bite angle of the dppe
(18) (a) Pfeffer, M. Pure Appl. Chem. 1992, 64, 335. (b) Bruce, M. I.
Angew. Chem., Int. Ed. Engl. 1977, 16, 73. (c) Constable, E. C. Polyhedron
1984, 3, 1037. (d) Omae, I. Chem. Rev. 1979, 79, 287.
(17) van Baar, J. F.; Vrieze, K.; Stufkens, D. J. J. Organomet. Chem.
1974, 81, 247.

5786 Organometallics, Vol. 28, No. 19, 2009
Owen et al.
Table 4. Selected Bond Lengths (A) and Angles (deg) for 1
˚
Pd-P(1)
2.2221(10)
2.140(3)
1.286(6)
Pd-P(2)
Pd-C(2)
2.3381(10)
2.128(4)
Pd-N(1)
N(1)-C(1)
P(1)-Pd-P(2)
P(1)-Pd-C(2)
P(2)-Pd-C(2)
85.83(4)
90.59(12)
176.11(13)
P(1)-Pd-N(1)
P(2)-Pd-N(1)
N(1)-Pd-C(2)
173.54(11)
91.91(9)
91.82(15)
˚
Table 5. Selected Bond Lengths (A) and Angles (deg) for 4
Pd-P(1)
2.240(3)
2.133(9)
1.259(15)
94.20(12)
86.2(4)
Pd-P(2)
Pd-C(2)
2.383(3)
2.105(13)
Pd-N(1)
N(1)-C(1)
P(1)-Pd-P(2)
P(1)-Pd-C(2)
P(2)-Pd-C(2)
P(1)-Pd-N(1)
P(2)-Pd-N(1)
N(1)-Pd-C(2)
174.0(3)
91.8(3)
87.8(4)
179.5(4)
Scheme 3. Schematic Representation of the Observed Reactivity
of 1-3 with Isocyanide
Figure 1. Molecular structure of the cation in 1. The agostic
˚
interaction “a” has an H Pd distance of ca. 2.42 A.
3 3 3
protons of the C-bound phenyl ring of the imine ligand
approaches the metal center in an agostic interaction with
˚
H
Pd separations of ca. 2.42 and 2.38 A in 1 and 4,
3 3 3
respectively,20 with the H Pd vectors being inclined in each
3 3 3
case by ca. 75° to the respective palladium coordination plane.
Isocyanide Insertion Reactions. The reactions of complexes
1-9 with 2,6-dimethylphenyl isocyanides was subsequently
investigated. We hypothesized that the addition of isocya-
nide should result in the temporary replacement of the imine
ligand followed by insertion into the palladium-methyl
bond. Once the iminoacyl moiety was formed, the imine
would then re-coordinate to the vacant coordination site on
the palladium center. Insertion of the imine into the
Pd-iminoacyl bond could then occur as shown in Scheme 1.
Complexes containing the dppe ligand are known to
exhibit slower (and sometimes differing) reactivity than their
dppp analogues.19 It was therefore decided to carry out the
reactions with the dppe complexes first. The slower reactivity
perhaps would allow the isolation of the iminoacyl-imine
product A before reaction to the imine insertion product B
(Scheme 1). However, instead of either of the expected
products, addition of 1 equiv of CNXyl to THF solutions
of [Pd(Me)(dppe){N(R)dCPhH}]BF4 (1, 2, and 3) led to the
formation of [Pd(Me){CNXyl}(dppe)]BF4 (10), where the
isocyanide is terminally coordinated (see Scheme 3). The
experimental evidence for the formation of this product
came from spectroscopic studies. 31P{1H} NMR spectrosco-
py gave the same set of resonances (δ = 59.4(d) and 46.5(d)
ppm) for the three reactions, suggesting that the imine was
being displaced. The 1H NMR spectra of the solids isolated
from these three reactions (upon addition of hexane to the
corresponding reaction mixture) confirmed the absence
of resonances associated with the corresponding imine.
Figure 2. Molecular structure of the cation in 4. The agostic
˚
interaction “a” has an H Pd distance of ca. 2.38 A.
3 3 3
diphosphine ligand [85.83(4)° with an ethyl linkage] compared
to the dppp ligand [94.20(12)° with a propyl linkage].19 In each
structure the Pd-P bond to the phosphorus atom trans to the
˚
neutral imine donor [Pd-P(1) 2.2221(10) and 2.240(3) A in 1
and 4, respectively] is significantly shorter than that trans to
˚
methyl [Pd-P(2) 2.3381(10) and 2.383(3) A], reflecting the
greater trans influence of methyl compared with the imine. The
Pd-N bonds to the imine ligands in the two complexes,
however, are the same [2.140(3) and 2.133(9) A in 1 and 4,
respectively]. Interestingly, in both structures one of the ortho
˚
(19) van Leeuwen, P. W. N. M.; Kamer, P. C. J.; Reek, J. N. H.;
Dierkes, P. Chem. Rev. 2000, 100, 2741.
(20) The hydrogen atoms involved in these interactions were placed in
calculated positions, and for the purpose of calculating the geometries of
˚
the interactions their parent C-H distances were normalized to 0.96 A.

Article
Organometallics, Vol. 28, No. 19, 2009 5787
Scheme 4. Reaction of Complexes 5, 6, and 7 with 2,6-Dimethylphenyl Isocyanide
Scheme 5. Diagram Showing the Attack of Water upon the Iminoacyl Group
In addition, a doublet of doublets at 0.77 pm [3JPHtrans = 6.5
Hz, 3JPHcis = 4.5 Hz] corresponding to the palladium-bound
methyl group and a singlet (6 H) at 2.16 ppm, corresponding
to the ortho-methyl groups of the bound 2,6-dimethylphenyl
isocyanide [C6H3(CH3)2], were observed. The IR spectra of
Various attempts were made to isolate products 5A, 6A,
and 7A from these reactions, without any contamination of
11. In most cases the precipitates contained only minor
amounts of the desired species. FABþ mass spectrometry
was unable to provide evidence for the formation of 5A or
6A. However, the solid isolated from the methyl imine
reaction (7A) showed a peak of high intensity at 783 amu
corresponding to [Pd{C(CH3)dNXyl}(dppp){N(Me)d
CPhH}]þ. Furthermore, although it was not possible to fully
the three solids gave a sharp and strong band at 2180 cm-1
,
which is consistent with a terminally coordinated isocyanide.
The FABþ mass spectra of the three solids showed a peak at
651 amu corresponding to [Pd(Me)(CNXyl)(dppe)]þ.
Complex 10 was also prepared by addition of 1 equiv of
AgBF4 to [Pd{C(CH3)dNXyl}Cl(dppe)].11 This resulted in
the deinsertion of the isocyanide from the iminoacyl frag-
ment, yielding 10. It was clear that the products resulting
from addition of 2,6-dimethylphenyl isocyanide to com-
plexes 1-3 were the substitution products and not the
desired products A and B (Scheme 1). Unfortunately, all of
our attempts to drive the reaction by heating or addition of
excess equivalents of imine proved unsuccessful.
Considering the results obtained with the dppe complexes,
it was decided to investigate whether analogous reactions
would take place with the corresponding dppp complexes.
It is well documented that complexes with dppp are generally
more reactive toward insertion than the corresponding dppe
analogues.19 Addition of 1 equiv of CNXyl to THF solutions
of the complexes [Pd(Me)(dppp){N(R)dCPhH}]BF4 (5, 6,
and 7) led to the formation of a new species (within 5 min) in
each case. The corresponding new products showed two
doublets in the 31P{1H} NMR spectra (one of the doublets
appeared between 18.5 and 14.2 and the second doublet
between 5.8 and 5.5 ppm). In spite of the clean transforma-
tion of complexes 5-7 into the corresponding new species
(tentatively assigned to species 5A-7A; see Scheme 4), the
later decomposed over time to the known hydroxo-bridged
dimer [Pd(μ-OH)2(dppp)](BF4)2 (11).21 This was evident
from the singlet resonance at 15.4 ppm in the 31P{1H}
NMR spectra of the three reactions in addition to a reso-
nance at -2.4 ppm in the 1H NMR spectra (assigned to the
bridging OH groups).
1
determine the identity of these compounds, the H NMR
spectra of 5A-7A showed that further reactivity of the
corresponding imine with the complex had occurred. Since
the metal complex isolated from the above reactions did not
contain either the iminoacyl or imine species, it was of
interest to identify any organic moieties being eliminated
from the complex. With this aim, the reaction solvent was
removed from the reaction involving 6, and the organic
material was extracted with diethyl ether and analyzed by
GC-MS, which revealed the presence of two major species.
The first species corresponded to unreacted imine, confirm-
ing that insertion into the corresponding iminoacyl fragment
either had not occurred or that the insertion product frag-
mented, re-forming the starting imine. The second product
detected by GC-MS was N-(2,6-dimethylphenyl)acetamide
(Scheme 5), which formed from the reaction between water
and the iminoacyl fragment of the complex. The formation
of this product appears to be the driving force for the
decomposition of complexes 5A-7A.
Our observations correlate somehow with those of Sen,
who had shown that imine insertion into a palladium-acyl
bond was efficient only in the case of dppp complexes.7a It is
also noteworthy that Sen had previously noted significant
decomposition in a number of reactions involving insertion
of imine into a palladium-acyl bond. From the results
discussed above it is clear that the nature of the chelating
phosphine has an important influence on the outcome of the
reactions under study. These differences are summarized in
Scheme 6.
In the case of complexes 1-3 (with dppe) substitution of
the imine with isocyanide takes place yielding complex 10,
which contains a terminal isocyanide. This can be attributed
to two main factors: (a) isocyanide insertions are generally
(21) Pisano, C.; Consiglio, G.; Sironi, A.; Moret, M. J. Chem. Soc.,
Chem. Commun. 1991, 421.

5788 Organometallics, Vol. 28, No. 19, 2009
Scheme 6. Schematic Representation of the Attempted Imine Insertion Reactions: Method 1
Owen et al.
less favored in complexes containing dppe (as compared to
other chelating phosphines such as dppp),11 which has been
attributed to differences in bite angles;19 (b) coordination of
imine to the Pd-dppe complex is not as strong as in Pd-dppp
complexes.
Scheme 7. Synthesis of Iminoacyl-imine Complexes 12 and 13
In contrast, with the dppp complexes, insertion of isocya-
nide is much more facile, yielding the iminoacyl-imine com-
plexes 5A, 6A, and 7A (detected only in solution). However,
these complexes proved to be unstable and readily react with
traces of water to yield the hydroxo-bridged dimer 11.
Method 2: Imine Addition to Iminoacyl Complexes. Despite
our efforts, it was evident that method 1 would not yield
the desired insertion products. Therefore, a second method
involving preparation of the iminoacyl complex prior to
addition of imine was investigated (Scheme 1). This sequence
of reactivity was perhaps a better method since the iminoacyl
fragment was already in place and it would be less likely for
the isocyanide fragment to deinsert. This is particularly
important with the dppe complexes, which require a strong
driving force for insertion of isocyanide into the palla-
dium-methyl bond. We have previously shown that this
approach could be utilized to synthesize palladium iminoa-
cyl/imine complexes (complex type A in Scheme 1) with
Pd{C(Me)dNXyl}(NdC(Me)OCH2CH2)]BF4 (where P-P =
dppe (12) and dppp (13), respectively) (Scheme 7).
Samples of 12 and 13 were obtained, in good yields, by
removing the precipitated AgCl via filtration of the reaction
mixture followed by reduction of solvent volume. Addition
of hexane to the remaining solution yielded 12 and 13 as pale
yellow and white solids, respectively. These complexes were
fully characterized by NMR and infrared spectroscopy
and by elemental analysis. The 1H NMR spectra of 12
and 13 were consistent with the formation of the expected
iminoacyl/imine complexes. The IR spectra of both products
showed a reduction in the frequency of the imine CdN
stretch as compared to the corresponding free imine.
Elemental analyses of these products, were consistent
with the expected formulation [Pd{C(CH3)dNXyl}(dppe)-
t
dinitrogen ligands such as bipy and Bu2bipy,22 although
we were unable to provide evidence of insertion of the imine
fragment into the palladium-iminoacyl bond in that case.
Some of our preliminary tests using method 2 with the
aldimines N(R)dCPhH (where R = Ph, Me, Bz) also gave
similar results to those found with method 1 (namely, no
insertion was detected, decomposition of the iminoa-
cyl-imine products, etc.). Therefore, our attention moved
toward investigating a more strongly coordinating imine to
increase the stability of the intermediate species (complexes
type A in Scheme 1). The reactions of cyclic imine methylox-
azaline with [Pd{C(CH3)dNXyl}Cl(dppe)] and [Pd{C-
(CH3)dNXyl}Cl(dppp)] were therefore investigated. In
this particular imine, the relative ring strain renders the lone
pair of the nitrogen more available for coordinating to the
metal, and the release in strain would additionally provide a
stronger driving force for insertion. One equivalent of
AgBF4 was added to solutions of the iminoacyl complexes
[Pd{C(CH3)dNXyl}Cl(dppe)] and [Pd{C(CH3)dNXyl}Cl-
(dppp)]11 in THF in the presence of excess methyloxazaline.
The 31P{1H} NMR spectra indicated quantitative conver-
sion of the starting material into the twonew products[(P-P)-
{NdC(Me)OCH2CH2}]BF4 (12) and [Pd{C(CH3)dNXyl}-
(dppp){NdC(Me)OCH2CH2}]BF4 (13), respectively. Full
characterization of these two compounds was encouraging
because it provided evidence of imines coordination to
iminoacyl complexes.
Since insertion of imine into the palladium-iminoacyl
bond was the ultimate goal of these reactions, we were
interested in the further reactivity of these complexes. Solu-
tions of 12 and 13 were monitored by 31P{1H} NMR
spectroscopy over time to see if any new products would
form. After leaving a solution of 12 for 1 h, a small amount of
a new product identified by a singlet at 66.4 ppm was
detected in the 31P{1H} NMR spectrum. When the solution
was left for a further 24 h, colorless crystals appeared. An
X-ray crystal structure determination performed on these
crystals revealed the product to be the disproportionated
bis-imine complex, [Pd{NdC(Me)OCH2CH2}2(dppe)][BF4]2
(14), where the iminoacyl fragment has disappeared
(Figure 3). The geometry at the palladium center is distorted
square planar with cis angles in the range 83.63(3)-96.08(9)°,
with the metal and the four donor atoms coplanar to within
(22) Owen, G. R.; Vilar, R.; White, A. J. P.; Williams, D. J.
Organometallics 2003, 22, 3025.
˚
ca. 0.02 A. Interestingly, the bite angle of the chelating dppe

Article
Organometallics, Vol. 28, No. 19, 2009 5789
Scheme 8. Proposed Method for the Formation of 14
Scheme 9. Formation of the Protonated Iminoacyl/Imine Com-
plex 17
signals. Further analysis of the organic material, by GC-MS,
confirmed the formation of significant quantities of N-(2,6-
dimethylphenyl)acetamide, confirming that disproportiona-
tion followed by decomposition of complex 12 had occurred
in this case. Unfortunately, all of our attempts to drive the
insertion of the imine into the palladium-iminoacyl bond in
complexes 12 and 13 were unsuccessful.
Protonated Iminoacyl Complexes. A difficultly found with
iminoacyl complexes containing phosphine co-ligands is the
propensity to undergo deinsertion of isocyanide when there
is a weakly coordinated ligand in the fourth coordination
site. A method to prevent this from occurring is by proto-
nating the iminoacyl functionality. We have previously
reported the synthesis of the protonated compounds
[Pd{C(CH3)dNHXyl}Cl(dppe)]OTf (15) and [Pd{C(CH3)d
NHXyl}Cl(dppe)]BF4 (16)23 and have shown that removal
of the halide does not lead to the deinsertion. Furthermore,
protonation of the iminoacyl fragment should in principle
make the sp2 carbon more electrophilic and might favor the
insertion of the nucleophilic nitrogen atom of the imine into
the palladium-iminoacyl bond. Thus, the reaction of one of
these protonated complexes (16) with an imine was investi-
gated. Addition of 1 equiv of AgBF4 to a solution of 16 in
CH2Cl2 in the presence of 1 equiv of N(Bz)dCPhH resulted
in the formation of one main new product (ca. 90% of
the phosphine-containing compounds) associated to a
pair of doublets at 54.4 and 52.2 ppm. A white solid with
the formulation [Pd{C(CH3)dN(H)Xyl}(dppe){N(Bz)d
CPhH}](BF4)2 (17) was isolated from the reaction mixture
by reduction of the volume followed by addition of hexane
(Scheme 9).
Figure 3. Molecular structure of the dication in 14.
˚
Table 6. Selected Bond Lengths (A) and Angles (deg) for 14
Pd-P(1)
2.2723(10)
2.112(3)
83.63(3)
173.96(9)
90.35(9)
Pd-P(2)
2.2492(10)
2.090(3)
96.08(9)
178.42(9)
89.95(12)
Pd-N(1)
Pd-N(6)
P(1)-Pd-P(2)
P(1)-Pd-N(6)
P(2)-Pd-N(6)
P(1)-Pd-N(1)
P(2)-Pd-N(1)
N(1)-Pd-N(6)
diphosphine ligand here in 14 [83.63(3)°] is ca. 2° smaller than
seen in 1 [85.83(4)°], though there is no obvious reason for this
difference. There is evidence for an intramolecular π-π
stacking interaction between the N(6) C3NO ring and the
adjacent phenyl ring bound to P(2) [centroid centroid and
3 3 3
˚
mean interplanar separations ca. 3.83 and 3.60 A, planes
inclined by ca. 21°], but if this is having an effect, it would
be to make the bite angle larger. This interaction, however,
˚
may explain why the Pd-P(2) [2.2492(1) A] bond is signifi-
cantly shorter than that to P(1) [2.2723(10) A] when the trans
˚
ligands are otherwise identical. The Pd-N bonds also differ,
with that to N(6) [2.090(3) A] shorter than that to N(1)
˚
The formulation of this white solid was established by
spectroscopic, analytic, and structural techniques. The
FABþ mass spectrum of the solid showed a peak at 932
amu, which corresponds to the molecular mass of complex
17 minus one of the BF4 counterions. The IR spectrum shows
stretches at 3198, 1075, and 1560 cm-1, corresponding to
N-H, BF4, and protonated iminoacyl (CdNH) moieties,
respectively. The CdN stretching region of the spectrum
˚
[2.112(3) A] so that the shorter Pd-N bond is trans to the
longer Pd-P bond, and vice versa.
The 31P{1H} NMR spectrum of the crystalline material
gave a singlet at 66.4 ppm, which is the same chemical shift as
that previously observed in the reaction mixture. The pro-
duct presumably precipitated driving the equilibrium of the
mixture toward the bis-imine product. The formation of 14
implies that there should be a bis-iminoacyl complex being
formed in the mixture (Scheme 8). The 31P{1H} NMR
spectrum of the resulting mixture revealed many phosphorus
(23) Owen, G. R.; Vilar, R.; White, A. J. P.; Williams, D. J.
Organometallics 2003, 22, 4511.

5790 Organometallics, Vol. 28, No. 19, 2009
Owen et al.
P(2) [centroid centroid and mean interplanar separations
3 3 3
˚
ca. 3.74 and 3.41 A, planes inclined by ca. 3°]. Despite a
number of attempts, we found no evidence to indicate that
insertion of the imine into the palladium-carbon bond had
occurred even after prolonged periods of time.
Conclusions
There may be a number of reasons why insertion of imine
into the Pd-iminoacyl bond was not observed during the
course of our investigations. The amidine product may
provide a lower driving force for insertion product in com-
parison to the corresponding amide.24 Irrespective of this,
the chelation of the amidine functional group to the fourth
coordination site on palladium should provide a strong
driving force for insertion (Figure 5). A further reason why
imine insertion is not observed in the above reactions could
originate from lower electrophilicity of the iminoacyl group
in comparison to the analogous acyl complexes. This would
hinder the attack of the imine at the iminoacyl carbon. Suggs
has previously shown that the electrophilicity of iminoacyl
groups can be significantly altered by a change in the
oxidation state of the transition metal center.25 This suggests
that a subtle change in the electronic environment of the
metal center can dramatically alter its reactivity. The proto-
nated iminoacyl complex 17 is certainly more electrophilic at
the carbon center and should, in principle, increase its
reactivity with the imine; however in this case the driving
force to the five-membered chelate (Figure 5) is lost. Addi-
tional equivalents of imine were added to the reaction
mixtures in an attempt to drive the reactions to the insertion
product. Unfortunately this did not lead to any success. The
more strongly binding coordination of the cyclic imines
showed that stable iminoacyl/imine complexes can be
prepared.
Figure 4. Molecular structure of the dication in 17. The agostic
˚
interaction “a” has an H Pd distance of ca. 2.51 A.
3 3 3
˚
Table 7. Selected Bond Lengths (A) and Angles (deg) for 17
Pd-P(1)
2.2723(15)
2.102(5)
1.283(8)
84.43(6)
92.34(16)
175.78(17)
Pd-P(2)
2.3455(15)
2.062(6)
1.298(8)
173.76(14)
95.09(14)
87.8(2)
Pd-N(1)
Pd-C(16)
N(1)-C(1)
N(16)-C(16)
P(1)-Pd-N(1)
P(2)-Pd-N(1)
N(1)-Pd-C(16)
P(1)-Pd-P(2)
P(1)-Pd-C(16)
P(2)-Pd-C(16)
In spite of the unsuccessful insertion reactions initially
targeted, several interesting results were obtained in the
course of these investigations. A series of imine complexes
were prepared and fully characterized. The X-ray crystal
structures of some of these complexes have revealed strong
agostic interactions between the aryl group of the imine
and the palladium metal center. These interactions are
retained in solution as shown by 1H NMR spectro-
scopy. The reaction of these imine complexes with isocyanide
has been studied and found to have differing reactivity
depending on the nature of the co-ligands. From the analysis
of all the attempted reactions it can be concluded that
the acyclic aldimine coordination is weak and that attempts
to insert the imine via these systems are unlikely to be
successful.
Figure 5. Chelation of the amidine functionality to the fourth
coordination site on palladium.
shows a band at 1618 cm-1 (cf. 1643 cm-1 for the noncoor-
dianted imine). Crystals suitable for X-ray crystallography
were obtained by addition of diethyl ether to a concentrated
CH2Cl2 solution of 17 in the presence of 5 equiv of imine. The
palladium coordination geometry in the structure of 17
(Figure 4) is distorted square planar, with the cis angles
ranging between 84.43(6)° and 95.09(14)° and with the P(1)
˚
phosphorus atom lying ca. 0.17 A out of the {Pd,P(2),N(1),
˚
C(16)} plane, which is coplanar to within ca. 0.04 A. The bite
A handful of iminoacyl/imine complexes have been pre-
pared and characterized. Our studies have shown that
the iminoacyl fragments are susceptible to reaction with
water due to the strong driving force of formation of the
organic amide product N-(2,6-dimethylphenyl)acetamide.
Our strategies to hinder the deinsertion of the isocyanide
have involved the protonation of the iminoacyl fragment.
The protonation reactions have led to the isolation of an
iminoacyl/imine complex, which has been confirmed by
angle of the chelating dppe diphosphine ligand [84.83(6)°] is
intermediate between those seen in 1 [85.83(4)°] and 14
[83.63(3)°]. The Pd-P bond trans to the iminoacyl ligand
˚
[Pd-P(2) 2.3455(15) A] is significantly longer than that trans
˚
to the imine [Pd-P(1) 2.2723(15) A], reflecting the stronger
˚
binding of the iminoacyl moiety [Pd-C(16) 2.062(6) A]
˚
compared to the imine unit [Pd-N(1) 2.102(5) A]. As was
seen in the structures of 1 and 4, one of the ortho protons of
the C-bound phenyl ring of the imine ligand approaches the
metal center in an agostic interaction with an H Pd
3 3 3
20
separation of ca. 2.51 A and with the H Pd vector
˚
3 3 3
(24) Gautier, J. A.; Miocque, M.; Farnoux, C. C. In The Chemistry of
Amidines and Imidates; Patai, S., Ed.; John Wiley & Sons: London, 1975;
p 283.
inclined by ca. 80° to the palladium coordination plane.
The same phenyl ring is involved in an intramolecular π-π
stacking interaction with the proximal phenyl ring bound to
(25) Suggs, J. W.; Cox, S. D. Organometallics 1982, 1, 402.

Article
Organometallics, Vol. 28, No. 19, 2009 5791
structural characterization. Furthermore, the utilization of
more strongly coordinating imines can also allow access to
complexes containing both iminoacyl and imine fragments.
Although our efforts have not provided an example of an
insertion reaction with an imine, a number of possible routes
have been explored.
(PCH2CH2P)], 4.75 (d, 1H, NCHAHBPh, 2JHH = 5 Hz), 4.90 (d,
1H, NCHAHBPh, 2JHH = 5 Hz), 7.11-7.70 (m, 28H, 4(PC6H5)
þ 3,4,5-H {NdC(H)C6H5} þ {N(CH2C6H5)dC(Ph)H}], 8.03
3
(d, 2H, 2,6-H {NdC(H)C6H5}, JHH = 7 Hz), 8.62 (dd, 1H,
4
4
{NdC(C6H5)H}, JPH = 10 Hz, JPH = unresolved). MS-
FABþ m/z (rel intensity): 714 (63) [M - Cl]þ, 699 (6) [M -
Me]þ, 519 (100) [M - imine]þ, 504 (33) [dppePd]þ.
[Pd(Me)(dppp)(N(Ph)dCPhH)]OTf (4). A degassed solution
of N(Ph)dCPhH (0.08 g, 0.44 mmol) in DCM (5 mL) was added
to a solution of [PdCl(Me)(dppp)] (0.21 g, 0.37 mmol) in DCM
(20 mL). AgOTf (0.11 g, 0.37 mmol) was quickly added. The
resulting solution was stirred for about 15 min, the precipitated
AgCl was removed by filtration, and the resulting complex was
isolated by addition of hexane and evaporation of the DCM,
resulting in precipitation of a white solid. This was then washed
twice with ether to remove any free imine.
Experimental Section
Materials and Apparatus. All manipulations were carried out
in an atmosphere of purified and dry nitrogen using standard
Schlenk line techniques unless otherwise stated. Solvents were
dried from the appropriate drying agent, degassed, and stored
under nitrogen. 1H, 31P, and 13C NMR spectra were recorded on
a JEOL-EX270 spectrometer (270.17, 109.38, 67.94 MHz, re-
spectively) with TMS, H3PO4, and TMS, respectively, as inter-
nal references. IR spectra were recorded on a Research Series
FT-IR using KBr disks in the range 4000-500 cm-1. Mass
spectrometry and X-ray crystallography were carried out at
Imperial College. Elemental analysis was carried out at the
University of North London. The complexes [Pd(Me)Cl(L2)]
(L2 = dppp, dppe, dppf) were synthesized according to pre-
viously reported procedures.26 The complex [Pd{C(Me)d
NXyl}Cl(dppe)] was synthesized using a methodology we re-
cently reported.11
[Pd(Me)(dppe)(imine)]BF4 (1, 2, 3). A degassed solution of
imine, RNdCHPh [R = Ph, 0.036 g; R = CH2Ph, 37.6 μL; R =
Me, 24.6 μL (0.20 mmol), in DCM (5 mL)], was added to a
solution of [PdCl(Me)(dppe)] (0.100 g, 0.18 mmol) in DCM
(15 mL). AgBF4 (0.035 g, 0.18 mmol) was quickly added. The
resulting solution was stirred for about 15 min, the precipitated
AgCl was removed by filtration, and the resulting complex was
isolated by addition of hexane and evaporation of the DCM,
resulting in precipitation of a white solid. This was then washed
twice with ether to remove any free imine.
Yield = 62%. Anal. Found: C, 57.04; H, 4.35; N, 1.99
(C42H40NPdP2SO3F3 0.3CH2Cl2 requires C, 57.11; H, 4.60,
3
N, 1.57). IR (νmax/cm-1) (KBr): 1608m, 1586m, 1569w
(NdC), 1486m, 1436m (dppp), 1262s, 1152s, 1031s (OTf). 31P-
{1H} NMR: (CDCl3): δ 23.8 (d, 1P, 2JPP = 51 Hz), -2.1 (d, 1P,
2JPP = 51 Hz). 1H NMR (CDCl3): δ 0.37 [dd, 3H, PdCH3,
3
3JPH = 6.5 Hz, JPH = 3.5 Hz], 2.77 [m br, 6H, (PCH2CH2C
H2P)], 6.90-7.81 [m, 28H, 4(PC6H5) þ 3,4,5-H {NdC(H)C
6H5} þ {N(C6H5 )dC(Ph)H}], 8.05 (dd, 1H, { NdC H}, 4JPH
=
9.5 Hz, 4JPH = 2.0 Hz), 8.37 [dd, 2H, 2,6-H {NdC(H)C 6H5},
HH
3
3J
= 6.0 Hz, JHH = unresolved]. MS-FABþ m/z (rel
intensity): 714 (2) [M - Cl]þ, 533 (18) [dpppPdMe]þ, 518 (3)
[(dppp)Pd].
[Pd(Me)(dppp)(imine)]BF4 (5, 6, 7). A degassed solution of
imine RNdCHPh [R = Ph, 0.036 g; R = CH2Ph, 37.6 μL; R =
Me, 24.6 μL; (0.20 mmol), in DCM (5 mL)] was added to a
solution of [PdCl(Me)(dppp)] (0.102 g, 0.18 mmol) in DCM
(15 mL). AgBF4 (0.035 g, 0.18 mmol) was quickly added. The
resulting solution was stirred for about 15 min, the precipitated
AgCl was removed by filtration, and the resulting complex was
isolated by addition of hexane and evaporation of the DCM,
resulting in precipitation of a white solid. This was then washed
twice with ether to remove any free imine.
1: R = Ph, yield 79%. Anal. Found: C, 61.05; H, 4.76; N, 1.69
(C40H38NP2PdBF4 requires: C, 60.98; H, 4.86; N, 1.78). IR
(νmax/cm-1) (KBr): 1606s, 1589w, 1569w (NdC), 1060vs br
(BF4). 31P{1H} NMR: (CDCl3): δ 57.6 (d, 1P, JPP = 23 Hz),
2
39.1 (d, 1P, 2JPP = 23 Hz). 1H NMR (CDCl3): δ 0.54 (dd, 3H,
PdCH3, 3JPH = 7 Hz, 3JPH = 3 Hz), 2.39 [m, 3H, (PCH2CH2P)],
2.97 [m, 1H, (PCH2CH2P)], 7.08-7.74 (m, 28H, 4(PC6H5) þ
5: R = Ph; yield = 73%. Anal. Found: C, 61.29; H, 4.92; N,
1.68 (C41H40NPdP2BF4 requires C, 61.41; H, 5.03; N, 1.75). IR
(νmaz/cm-1) (KBr): 1624m, 1588w, 1577w (NdC), 1069vs (BF4).
31P{1H} NMR (THF): δ 23.1 (d, 1P, 2JPP = 52 Hz), -2.3 (d, 1P,
3,4,5-H {NdC(H)C6H5} þ {N(C6H5)dC(Ph)H}], 8.07 (d, 2H,
1
2JPP = 53 Hz). H NMR (CDCl3): δ 0.36 (dd, 3H, PdCH3,
3
2,6-H {NdC(H)C6H5}, JHH
= 7 Hz), 8.48 (dd, 1H,
3
3JPH = 7.0 Hz, JPH = 4.0 Hz), 2.86 [m br, 6H, (PCH2CH2-
{NdC(C6H5)H}, JPH = 10 Hz, JPH = 2 Hz). MS-FABþ
m/z (rel intensity): 700 (1) [M]þ, 519 (13) [M - imine]þ, 504 (9)
[dppePd]þ, 399 (2) [dppe]þ.
4
4
CH2P)], 6.91-7.83 (m, 28H, 4(PC6H5) þ 3,4,5-H {NdC(H)-
C6H5} þ {N(C6H5)dC(Ph)H}], 8.04 (dd, 1H, {NdC(C6H5)H},
4
4JPH = 9.5 Hz, JPH = 2.5 Hz), 8.37 [dd, 2H, 2,6-H
2; R = Me; yield 78%. Anal. Found: C, 58.05; H, 5.38; N,
1.88 (C35H36NP2PdNBF4.0.2C4H10O requires: C, 58.05; H,
5.17; N, 1.89). IR (νmax/cm-1) (KBr): 1637s, 1571w (NdC),
3
3
{NdC(H)C6H5} JHH = 7.0 Hz, JHH = unresolved]. MS-
FABþ m/z (rel intensity): 714 (20) [M]þ, 698 (4) [M - CH3]þ, 533
(65) [M - imine]þ, 518 (24) [(dppp)Pd]þ.
1052vs br (BF4). 31P{1H} NMR (CDCl3): δ 57.7 (d, 1P, 2JPP
=
2
1
6: R = Me; yield 71%. Anal. Found: C, 58.39; H, 4.94; N,
1.95 (C36H38NP2PdBF4 requires: C, 58.44; H, 5.17; N, 1.89). IR
(νmax/cm-1) (KBr): 1645s, 1599w, 1578w (NdC), 1482w, 1436m
(dppp), 1057s (BF4). 31P{1H} NMR (CDCl3): δ 22.7 (d, 1P,
2JPP = 50 Hz), 0.2 (d, 1P, 2JPP = 50 Hz). 1H NMR (CDCl3): δ
0.35 (dd, 3H, PdCH3, 3JPH = 7.0 Hz, 3JPH = 3.5 Hz), 1.84 [m,
2H, (PCH2CH2CH2P)], 2.77 [m, 4H, (PCH2CH2CH2P)], 3.44 [s
br, 3H, NCH3], 6.91-7.55 (m, 20 H, 4(PC6H5) þ 3H
{NdC(H)C6H5}], 7.68 [m, 2H, {NdC(H)C6H5}], 8.10 (dd,
23 Hz), 39.9 (d, 1P, JPP = 23 Hz). H NMR (CDCl3): δ 0.48
3
3
(dd, 3H PdCH3, JPH = 7 Hz, JPH = 3 Hz), 2.35 [m, 3H,
(PCH2CH2P)], 2.85 [m, 1H, (PCH2CH2P)], 3.70 (s, 3H, NCH3),
7.10-7.60 (m, 23H, 4(PC6H5) þ 3,4,5-H {NdC(H)C6H5}], 7.94
3
[d, 2H, 2,6-H {NdC(H)C6H5}, JHH = 7 Hz], 8.52 (dd, 1H,
4
4
{NdC(C6H5)H}, JPH = 11 Hz, JPH = unresolved]. MS-
FABþ m/z (rel intensity): 638 (65) [M]þ, 623 (4) [M - Me]þ,
519 (90) [M - imine]þ, 504 (33) [dppePd]þ.
3; R = CH2Ph; yield 76%. Anal. Found: C, 61.93; H, 5.40; N,
4
4
1H, {NdC(C6H5)H}, JPH = 5.0 Hz, JPH = 3.0 Hz). MS-
FABþ m/z (rel intensity): 652 (40) [M - Cl]þ, 636 (4) [M - Cl -
Me]þ, 533 (58) [dpppPdMe]þ, 518 (17) [dpppPd]þ.
1.90 (C41H40NP2PdNBF4 0.1(C14H13N) requires: C, 61.95; H,
3
5.06; N, 1.87). IR (νmax/cm-1) (KBr): 1617m, 1575w (NdC),
=
1052vs br (BF4). 31P{1H} NMR: (CDCl3): δ 57.0 (d, 1P, 2JPP
2
1
7: R = CH2Ph; yield 68%. Anal. Found: C, 61.05; H, 4.88; N,
1.54 (C42H42NP2PdBF4 1/4CH2Cl2 requires: C, 60.61; H, 5.11;
23 Hz), 39.7 (d, 1P, JPP = 23 Hz). H NMR (CDCl3): δ 0.18
(dd, 3H, PdCH3, JPH = 7 Hz, JPH = 4 Hz), 2.52 [m, 4H,
3
3
3
N, 1.67). IR (νmax/cm-1) (KBr): 1626, 1574 (NdC), 1057 (BF4).
31P{1H} NMR (THF): δ 21.9 (d, 1P, 2JPP = 50 Hz), 0.3 (d, 1P,
1
2JPP = 50 Hz). H NMR (CDCl3): δ 0.01 (dd, 3H, PdCH3,
(26) (a) Appleton, T. G.; Bennett, M. A.; Tomkins, I. B. J. Chem.
Soc., Dalton Trans. 1976, 439. (b) Dekker, G. P. C. M.; Elsevier, C. J.;
Vrieze, K. Organometallics 1992, 11, 1589.
3
3JPH = 6.5 Hz, JPH = 3.5 Hz), 1.85 [m br, 2H, (PCH2-
CH2CH2P)], 2.85 [m br, 4H, (PCH2CH2CH2P)], 4.36 (d, 1H,

5792 Organometallics, Vol. 28, No. 19, 2009
Table 8. Crystal Data, Data Collection, and Refinement Parameters for Compounds 1, 4, 14, and 17a
Owen et al.
data
1
4
14
17
formula
solvent
fw
[C40H38NP2Pd](BF4)
[C41H40NP2Pd](CF3SO3)
CH2Cl2
949.08
[C34H38N2O2P2Pd](BF4)2
C4H8O 1/3H2O
926.68
[C50H50N2P2Pd](BF4)2
0.75CH2Cl2
1084.57
3
787.86
color, habit
cryst size/mm
temp/K
pale yellow prisms
0.77 ꢁ 0.73 ꢁ 0.20
293
colorless platy needles
0.80 ꢁ 0.45 ꢁ 0.23
293
yellow prisms
0.20 ꢁ 0.17 ꢁ 0.13
203
colorless blocky needles
0.60 ꢁ 0.30 ꢁ 0.20
293
cryst syst
space group
monoclinic
P21/n (no. 14)
12.6377(13)
16.066(3)
orthorhombic
Pna21 (no. 33)
12.968(5)
32.330(3)
10.5365(12)
triclinic
P1 (no. 2)
12.0486(7)
13.0469(4)
13.2701(5)
91.799(3)
95.704(6)
96.529(3)
2060.30(16)
2
1.494
Cu KR
5.032
120
6113
monoclinic
P21/c (no. 14)
20.2999(10)
24.3276(11)
˚
a/A
˚
b/A
˚
c/A
18.390(2)
10.5517(7)
R/deg
β/deg
γ/deg
92.298(12)
104.639(7)
3
˚
V/A
Z
3730.9(9)
4
1.403
Mo KR
0.632
50
6061
4646
443
0.042, 0.099
4417.5(18)
4
1.427
Mo KR
0.712
50
4084
2634
506
0.059, 0.118
5041.8(5)
4
1.429
Cu KR
4.866
120
7436
5046
654
0.059, 0.160
Dc/g cm-3
radiation used
μ/mm-1
2θmax/deg
no. of unique reflns measd
obs, |Fo| > 4σ(|Fo|)
no. of variables
R1(obs), wR2(all) b
5457
555
0.036, 0.087
a Details in common: graphite-monochromated radiation, refinement based on F2. b R1 = Fo| - |Fc /|Fo|; wR2 = {[w(Fo2 - Fc2)2]/[w(Fo2)2]}1/2
;
w
-1 = σ2(Fo2) þ (aP)2 þ bP.
2
NCHAHBPh, JHH = 14.5 Hz), 4.78 (d, 1H, NCHAHBPh,
2JHH = 14.5 Hz), 6.94-7.63 (m, 28H, 4(PC6H5) þ 3,4,5-H
{NdC(H)C6H5} þ {N(CH2C6H5)dC(Ph)H}],), 7.84 [dd, 1H,
{NdC(C6H5)H}, 4JPH = 9 Hz, 4JPH = 2 Hz], 8.15 [dd, 2H, 2,6-
H {NdC(H)C6H5}, 3JHH = 11 Hz, 3JHH = 2 Hz]. MS-FABþ m/z
(rel intensity): 728 (67) [M]þ, 713 (10) [M - CH3]þ, 533 (100)
[(dppp)PdMe]þ, 518 (43) [(dppp)Pd]þ.
Synthesis of [Pd(Me)(CNXyl)(dppe)]BF4 (10). Method 1. To
a solution of [PdCl(Me)(dppe)] (0.2 g, 0.36 mmol) in THF (10
mL) was added AgBF4 (0.075 g, 0.38 mmol), followed by CNXyl
(0.05 g, 0.38 mmol). The resulting mixture was stirred for 15 min,
and then the precipitated AgCl was removed by filtration. The
31P{1H} NMR of the filtrate was recorded. 31P{1H} NMR
(THF): δ 59.0 (d), 46.9 (d).
[Pd(Me)(dppf)(imine)]BF4 (8, 9). A degassed solution of imine
RNdCHPh [R = Ph, 0.11 g; R = CH2Ph, 116 μL (0.61 mmol),
in DCM (10 mL)] was added to a solution of [PdCl(Me)(dppf)]
(0.400 g, 0.56 mmol) in DCM (25 mL). AgBF4 (0.120 g,
0.61 mmol) was added in one portion. The resulting solution
was stirred for about 15 min, the precipitated AgCl was removed
by filtration, and the resulting complex was isolated by addition
of hexane and evaporation of the DCM, resulting in precipita-
tion of a white solid. This was then washed twice with ether to
remove any free imine.
Method 2. To
a solution of [Pd(Me)(dppe){N(Bz)d
CPhH}]BF4 (0.10 g, 0.12 mmol) in THF (10 mL) was added
CNXyl (0.017 g, 0.13 mmol). The colorless solution turned
yellow over 15 min, after which time the solvent level was
reduced to ca. 5 mL under reduced pressure. Hexane (10 mL)
was then added to precipitate a yellow solid.
Yield = 0.05 g, 0.06 mmol, 57%. Anal. Found: C, 55.68; H,
4.56; N, 1.83 (calcd for C36H36NP2PdBF4 0.25AgCl: C, 55.88;
3
H, 4.69; N, 1.81). IR (νmax/cm-1) (KBr): 2181s (CtN), 1057br
(BF4). 31P{1H} NMR (CDCl3): δ 58.5 (d, 1P, JPP = 29 Hz),
2
8: R = Ph; yield 0.42 g, 79%. IR (νmax/cm-1) (KBr): 1607s,
1598w, 1569w (NdC), 1095, 1058vs br (BF4). 31P{1H} NMR
44.8 (d, 1P, 2JPP = 29 Hz). 1H NMR (CDCl3): δ 0.77 [dd, 3H,
(PdCH3), JPH = 6.5 Hz, JPH = 4.5 Hz), 2.16 [s, 6H,
{C6H3(CH3)2}], 2.66 [m, 4H, (PCH2CH2P)], 7.10 [d, 2H,
3
3
2
2
(CDCl3): δ 38.1 (d, 1P, JPP = 29 Hz), 19.6 (d, 1P, JPP = 29
Hz). 1H NMR (CDCl3): δ 0.41 (dd, 3H, PdCH3, JPH = 6 Hz,
3
3
3,5-H {C6H3(CH3)2}, JHH = 7.5 Hz], 7.28 [m, 1H, 4-H
3JPH = 4 Hz), 3.81 [m, 2H, (PC5H4)], 4.22 [s, 2H, (PC5H4)], 4.48
[d, 2H, (PC5H4], 4.67 [s, 2H, (PC5H4)], 6.98-7.88 (m, 28H,
4(PC6H5) þ 3,4,5-H {NdC(H)C6H5} þ {N(C6H5)dC(Ph)H}],
8.35 [dd, 1H, {NdC(C6H5)H}, 4JPH = 10.5 Hz, 4JPH = 2.5 Hz],
8.46 [d, 2H, 2,6-H {NdC(H)C6H5}], 3JHH = 7.5 Hz]. MS-FABþ
m/z (rel intensity): 858 (15) [M]þ, 675 (100) [M - imine]þ, 662
(20) [dppePd]þ.
{C6H3(CH3)2}], 7.58 [m, 20H, 4(PC6H5)]. MS (FABþ) m/z (rel
intensity): 652 (2) [M]þ, 519 (3) [(dppe)Pd(Me)]þ, 504 (12)
[(dppe)Pd]þ.
[Pd{C(Me)dNXyl}(dppe)(NdC(Me)OCH2CH2)]BF4 (12). To
solution of [Pd{C(CH3)dNXyl}Cl(dppe)] (1) (0.15 g,
a
0.22 mmol) in THF (20 mL) was added methyloxazaline
(18.6 μL, 0.22 mmol). AgBF4 (0.043 g, 0.22 mmol) was then added
to the stirring mixture, which resulted in the precipitation of AgCl
from the mixture. This precipitate was removed by filtration
after 15 min. The solvent level of the filtrate was then reduced to
ca. 10 mL, and hexane was added, which resulted in the precipi-
tation of a yellow solid. The solid was then washed with diethyl
ether.
9: R = Bz; yield 0.42 g, 78%. Found: C, 61.33; H, 4.58; N,
1.58 (C49H44NP2PdFeBF4 requires: C, 61.44; H, 4.63; N, 1.46).
IR (νmax/cm-1) (KBr): 1626s, 1598w, 1571w (NdC), 1083,
1055vs br (BF4). 31P{1H} NMR (CDCl3): δ 36.8 (d, 1P,
2JPP = 29 Hz), 19.2 (d, 1P, 2JPP = 29 Hz). 1H NMR (CDCl3):
δ 0.08 (dd, 3H, PdCH3, 3JPH = 6 Hz, 3JPH = 2 Hz), 3.81 [s, 1H,
(PC5H4)], 3.75 [s, 1H, (PC5H4)], 4.21 [s, 2H, (PC5H4)], 4.48 [m,
3H, (2H, {PC5H4}) þ (1H, NCHaHbPh) overlapping], 4.81 [m,
3H, (2H, {PC5H4}) þ (1H, NHaHbPh) overlapping)], 7.10-
Yield = 0.12 g, 0.15 mmol, 66%. Anal. Found: C, 58.28; H,
5.23; N, 3.34 (calcd for C40H43N2P2OBF4Pd requires C, 58.38;
H, 5.27; N, 3.40). IR (νmax/cm-1) (KBr): 1662, 1615, 1583
(CdN), 1259 (C-O), 1085, 1057 (BF4). 31P{1H} NMR (THF-
7.76 (m, 28H, 4(PC6H5)
þ
3,4,5-H {NdC(H)C6H5}
þ
{N(CH2C6H5)dC(Ph)H}], 8.15 (dd, 1H, {NdC(C6H5)H},
4
4JPH = 10.5 Hz, JPH = 1.5 Hz), 8.45 (d, 2H, 2,6-H
d8): δ 39.5 (d, 1P, 2JPP = 33 Hz), 41.4 (d, 1P, 2JPP = 30 Hz). 1H
{NdC(H)C6H5}, 3JHH = 7.5 Hz). MS-FABþ m/z (rel intensity):
675 (6) [M - imine]þ, 660 (5) [dppePd]þ.
NMR (THF-d8): δ 1.51 [br, dd, Pd{C(CH3)dNXyl}, JPH
=
4
unresolved, 4JPH = unresolved], 1.62 [s, 6H, C6H3(CH3)2], 2.04

Article
Organometallics, Vol. 28, No. 19, 2009 5793
[s, 3H, NdC(CH3)], 2.37 [br, m, 4H (PCH2CH2P)], 4.00 [m, 2H,
NCH2CH2O], 4.38 [m, 2H, OCH2CH2N], 6.61 [m, 1H, C6H3-
(CH3)2], 6.75 [m, 2H, C6H3(CH3)2], 7.45-8.18 [m, 20H,
4(PC6H5)]. MS-FABþ m/z (rel intensity): 650 (10) [M - imine]þ,
519 (4) [(dppe)PdMe],, 504 (5) [(dppe)Pd]þ.
mmol) in DCM (20 mL) was added N(Bz)dCPhH (0.19 mL, 1.0
mmol). AgBF4 (0.045 g, 0.21 mmol) was then added to the stirring
mixture, which resulted in the precipitation of AgCl from the
mixture. This precipitate was removed by filtration after 15 min.
The solvent level of the filtrate was then reduced to ca. 10 mL, and a
layer of diethyl ether was carefully added to the reaction mixture. A
colorless crystalline solid then precipitated over 2 days.
[Pd{C(Me)dNXyl}(dppp)(NdC(Me)OCH2CH2)]BF4 (13).
To a solution of [Pd{C(CH3)dNXyl}Cl(dppp)] (2) (0.09 g,
0.13 mmol) in THF (10 mL) was added methyloxazaline
(21 μL, 0.26 mmol). AgBF4 (0.03 g, 0.13 mmol) was then added
to the stirring mixture, which resulted in the precipitation of
AgCl from the mixture. This precipitate was removed by filtra-
tion after 15 min. The solvent level of the filtrate was then
reduced to ca. 10 mL, and hexane was added, which resulted in
the precipitation of an off-white solid. The solid was then
washed with diethyl ether.
Yield=0.18 g, 0.17 mmol, 88%. IR (νmax/cm-1) (KBr): 3198
(N-H), 1616, 1596 (CdN), 1560 (CdNH), 1075 (BF4). 31P{1H}
NMR (DCM): δ 54.4 (d, 1P, 2JPP = 20 Hz), 52.2 (d, 1P, 2JPP=20
Hz). MS-FABþ m/z (rel intensity): 932 (2) [M]þ, 845 (7) [M -
BF4]þ, 650 (96) [M - (BF4)2]þ, 519 (20) [(dppe)PdMe]þ, 504 (38)
[(dppe)Pd]þ.
X-ray Crystallography. Table 8 provides a summary of
the crystallographic data for compounds 1, 4, 14, and 17.
Data were collected using Siemens P4 (1 and 4) P4/RA (14)
and Bruker P4 (17) diffractometers, and the structures were
refined based on F2 using the SHELXTL and SHELX-97
Yield = 0.06 g, 0.07 mmol, 55%. Anal. Found: C, 58.72; H,
5.34; N, 3.23 (calcd for C41H45N2OP2BF4Pd requires C, 58.84;
H, 5.41; N, 3.35). IR (νmax/cm-1) (KBr): 1664, 1609, 1579
(CdN), 1255 (C-O), 1102, 1057 (BF4). 31P{1H} NMR (THF-
d8): δ 5.4 (br, d, 1P, 2JPP = unresolved), 1.8 (d, 1P, 2JPP = 67
Hz). 1H NMR (THF-d8): δ 1.47 [dd, Pd{C(CH3)dNXy},
program systems.27 The absolute structure of 4 could not be
þ
unambiguously determined by either R-factor tests [R1
=
0.0586, R1-=0.0587] or the use of the Flack parameter [xþ=
þ0.37(17), x-=þ0.63(17)]. CCDC 736713 to 736716.
4
4JPH = 5 Hz, JPH = unresolved], 1.63 [s, 6H, C6H3(CH3)2],
Acknowledgment. We are grateful to the EPSRC and
Royal Society for funding (G.R.O.) and to Johnson
Matthey for loan of palladium salts.
2.06 [s, 3H, NdC(CH3)], 1.90 [br, m, 2H (PCH2CH2CH2P)],
2.89 [m, 4H (PCH2CH2CH2P)], 3.41 [m, 2H, NCH2CH2O], 4.02
[m, 2H, OCH2CH2N], 6.62 [m, 1H, 4-H {C6H3(CH3)2}], 6.74 [m,
2H, 3,5-H {C6H3(CH3)2}], 7.35 [m, 12H, 3,4,5-H 4(PC6H5)],
7.73 [m, 4H, 2,6-H 2(PC6H5)], 8.08 [m, 4H, 2,6-H 2(PC6H5)].
MS-FABþ m/z (rel intensity): 664 (18) [M - imine]þ, 533 (5)
[(dppp)PdMe]þ, 518 (9) [(dppp)Pd]þ.
Supporting Information Available: This material is available
free of charge via the Internet at http://pubs.acs.org.
(27) SHELXTL PC version 5.1, Bruker AXS: Madison, WI, 1997.
Sheldrick, G. SHELX-97; Institut Anorg. Chemie: Gottingen, Germany, 1998.
[Pd{C(CH3)dN(H)Xyl}(dppe){N(Bz)dCPhH}][BF4]2 (17). To
a solution of [Pd{C(CH3)dNHXyl}Cl(dppe)]BF4 (0.15 g, 0.20
€