Formation of a vinyliminium palladium. Complex by C-C coupling in vinylcarbene palladium aryl complexes

Article abstract of DOI:10.1021/om051028s

Pentafluorophenyl palladium complexes 3 and 5 bearing a vinylcarbene ligand slowly decompose on heating by migratory insertion to give Pd(0) and the vinyliminium salts (Et₂N=C(C₆F₅)CH=CHPh)X(X = Br, BF₄). However, the presence of triphenylphosphine in complex 4 stabilizes 7, a compound with a C=C Pd-bound vinyliminium moiety, where there is a strong preference for the C=C versus the C=N coordination.

Full text of DOI:10.1021/om051028s

Organometallics 2006, 25, 1293-1297
1293
Formation of a Vinyliminium Palladium Complex by C-C Coupling
in Vinylcarbene Palladium Aryl Complexes
Ana C. Albe´niz,*,‡ Pablo Espinet,*,‡ Alberto Pe´rez-Mateo,‡ Ainara Nova,§ and
Gregori Ujaque§
Qu´ımica Inorga´nica, Facultad de Ciencias, UniVersidad de Valladolid, Prado de la Magdalena s/n,
47005 Valladolid, Spain, and Unitat de Qu´ımica F´ısica, Edifici C.n. UniVersitat Auto`noma de Barcelona,
08193 Bellaterra, Catalonia, Spain
ReceiVed December 1, 2005
Pentafluorophenyl palladium complexes 3 and 5 bearing a vinylcarbene ligand slowly decompose on
heating by migratory insertion to give Pd(0) and the vinyliminium salts (Et2NdC(C6F5)CHdCHPh)X
(X ) Br, BF4). However, the presence of triphenylphosphine in complex 4 stabilizes 7, a compound
with a CdC Pd-bound vinyliminium moiety, where there is a strong preference for the CdC versus the
CdN coordination.
Scheme 1. C-C Coupling in Aryl Palladium Carbene
Introduction
Complexes
Many organic transformations of unsaturated amines and
imines involve the formation of iminium cations as intermedi-
ates.1 The hydrolysis of vinylic amines and the acid-catalyzed
Manich reaction are common examples.2 Iminium salts, either
previously prepared or synthesized “in situ”, are used as
powerful electrophiles in a variety of transformations.2,3 Metal-
catalyzed reactions, such as the enantioselective isomerization
of allylamines to enamines developed by Noyori et al., are also
believed to occur via an intermediate complex with a metal-
coordinated iminium fragment.4,5 Several examples of formation
of iminium salts by C-C coupling of an N-substituted carbene
and an organometallic group on palladium have been reported
in the past few years. Most of the examples reported so far
involve N-heterocyclic carbenes, and the products are imida-
zolium salts.6-8 We have reported the formation of iminium
salts by coupling of monoaminocarbenes and a pentafluorophen-
yl group bound to palladium.9 These iminium salts are formally
the product of a reductive elimination reaction in the complex,
although a migratory insertion route can be envisioned based
on the reactions of related alkoxycarbenes, where alkyl pal-
ladium derivatives (stabilized as η3-allylic or η3-benzylic
moieties) are formed as a result of a migratory insertion process
(Scheme 1).9
We report here the formation of a vinyliminium cation by
coupling of a vinylcarbene ligand and a pentafluorophenyl group
in a palladium complex. The iminium compound remains
CdC coordinated to palladium when a suitable auxiliary ligand
is used. The coordination preferences and behavior of the
vinyliminium ligand are analyzed in detail.
‡ Universidad de Valladolid.
§ Universitat Auto`noma de Barcelona.
(1) March, J. AdVanced Organic Chemistry, 4th ed.; Wiley: New York,
1992.
(2) Arend, M.; Westermann, B.; Risch, N. Angew. Chem., Int. Ed. 1998,
37, 1044-1070.
(3) Iminium Salts in Organic Chemistry. Part 1, Advances in Organic
Chemistry Methods and Results, Vol. 9; Bo¨hme, H., Viehe, H. G., Eds.;
Wiley: New York, 1976.
Results
(4) (a) Tani, K.; Yamagata, T.; Otsuka, S.; Akutagawa, S.; Kumobayashi,
H.; Taketomi, T.; Takaya, H.; Miyashita, A.; Noyori, R. J. Chem. Soc.,
Chem. Commun. 1982, 600-601. (b) Inoue, S.-I.; Takaya, H.; Tani, K.;
Otsuka, S.; Sato, T.; Noyori, R. J. Am. Chem. Soc. 1990, 112, 4897-4905.
(c) Yamakawa, M.; Noyori, R. Organometallics 1992, 11, 3167-3169.
(5) Murahashi, S.-I. Angew. Chem., Int. Ed. Engl. 1995, 34, 2443-2465.
(6) (a) McGuinness, D. S.; Saendig, N.; Yates, B. F.; Cavell, K. J. J.
Am. Chem. Soc. 2001, 123, 4029-4040. (b) McGuinness, D. S.; Cavell, K.
J. Organometallics 2000, 19, 4918-4920. (c) McGuinness, D. S.; Green,
M. J.; Cavell, K. J.; Skelton, B. W.; White, A. H. J. Organomet. Chem.
1998, 565, 165-178. (d) Nielsen, D. J.; Magill, A. M.; Yates, B. F.; Cavell,
K. J.; Skelton, B. W.; White, A. H. Chem. Commun. 2002, 2500-2501.
(7) (a) Marshall, W. J.; Grushin, V. V. Organometallics 2003, 22, 1591-
1593. (b) Caddick, S.; Cloke, F. G. N.; Hitchcock, P. B.; Leonard, J.; Lewis,
A. K. K.; McKerrecher, D.; Titcomb, L. R. Organometallics 2002, 21,
4318-4319. (c) McGuinness, D. S.; Cavell, K. J.; Skelton, B. W.; White,
A. H. Organometallics 1999, 18, 1596-1605.
The syntheses of palladium vinylic carbene complexes are
depicted in Scheme 2. Complex 3 was prepared from complex
2 by transmetalation with the corresponding tungsten carbene
1, as previously reported by us for the preparation of other
monoamino carbene palladium complexes.9,10 The transfer of
carbene fragments from group 6 metal complexes has been also
used in the synthesis of other transition metal carbene com-
plexes.11 Addition of triphenylphosphine to 3 gave complex 4.
Both compounds were isolated as yellow (3) or orange (4) solids.
(10) Albe´niz, A. C.; Espinet, P.; Manrique, R.; Pe´rez-Mateo, A. Angew.
Chem., Int. Ed. 2002, 41, 2363-2366.
(11) (a) Go´mez-Gallego, M.; Manchen˜o, M. J.; Sierra, M. A. Acc. Chem.
Res. 2005, 38, 44-53. (b) Go¨tter-Schnetmann, I.; Aumann, R.; Bergander,
K. Organometallics 2001, 20, 3574-3581. (c) Barluenga, J.; Lo´pez, L. A.;
Lo¨ber, O.; Toma´s, M.; Garc´ıa-Granda, S.; AÄ lvarez-Ru´a, C.; Borge, J. Angew.
Chem., Int. Ed. 2001, 40, 3392-3394. (d) Liu, S. T.; Reddy, K. R. Chem.
Soc. ReV. 1999, 28, 315-322.
(8) Danopoulos, A. A.; Tsoureas, N.; Green, J. C.; Hursthouse, M. B.
Chem. Commun. 2003, 756-757.
(9) Albe´niz, A. C.; Espinet, P.; Manrique, R.; Pe´rez-Mateo, A. Chem.
Eur. J. 2005, 11, 1565-1573.
10.1021/om051028s CCC: $33.50 © 2006 American Chemical Society
Publication on Web 02/02/2006

1294 Organometallics, Vol. 25, No. 5, 2006
Scheme 2. Synthesis of Complexes 3-5
Albe´niz et al.
Figure 1. X-ray structure of complex 4. Selected bond lengths
(Å): Pd1-C1, 2.025(6); Pd1-C21, 2.031(6); Pd1-Br1, 2.4844-
(16); Pd1-P1, 2.324(2); C1-C2, 1.467(9); C1-N1, 1.300(8); C2-
C3, 1.330(10).
Removal of the bromo ligand of 3 using AgBF4 in acetonitrile
gave 5, which was characterized and used in solution. The three
complexes show a 13C NMR resonance in the range typical for
a carbene carbon bound to the metal (215-228 ppm).
Complex 4 was further characterized by single-crystal X-ray
diffraction (Figure 1). The carbene ligand lies almost perpen-
dicular to the Pd coordination plane (the dihedral angle between
the N1-C1-C2 and Pd1-Br1-P1-C1-C21 planes is 82.6°)
and shows a trans configuration of the conjugated double bond.
The pentafluorophenyl group is slightly tilted, this ring and the
Pd coordination plane making a 75.5° dihedral angle. The
phosphine ligand is trans to the carbene moiety. The C-N
distance corresponds to a double bond, whereas the Pd-
C(carbene) distance suggests a single one, as expected for a
Fischer type late transition metal carbene, and as depicted
throughout this paper for complexes 3-5. NMR spectra show
that the same structure is kept in solution. The large value of
3JC-P for the carbene carbon (147.3 Hz) confirms a trans
arrangement of the carbene and phosphine ligands. Restricted
rotation of the C6F5 group is revealed by the nonequivalence
of both Fortho (and both Fmeta) atoms.
Scheme 3. C-C Coupling in Complexes 3-5
In solution, 3 is a mixture of two isomers, out of four possible
coordination arrangements.12 Complex 5 shows a cis stereo-
chemistry with two separate 1H NMR signals for the two
nonequivalent acetonitrile ligands.
the CdC bond (Figure 2). Br and PPh3 ligands complete the
coordination sphere of the metal. The Br-Pd-P angle is very
Complexes 3-5 undergo very slow decomposition in solution
as a result of carbene-pentafluorophenyl coupling. Weeks are
needed for complete decomposition at room temperature in
CDCl3, so experiments were also carried out at 50 °C in the
same solvent. Complexes 3 and 5 give Pd(0) and the iminium
salt 6,13 but for complex 4 the formation of a Pd(0) complex 7
is observed (Scheme 3). A minor decomposition route for 4
produces some [PdBr(C6F5)(PPh3)2]. Complex 7 can be kept in
the air at room temperature for long periods, both as a solid
and in solution.
The X-ray crystal structure of 7 reveals a three-coordinated
Pd complex with a vinyliminium ligand bound to Pd through
(12) The four possible isomers arise from the combination of trans-
carbene or cis-carbene arrangements in the dimer and syn (both NEt2 groups
of the carbenes on the same side of the coordination plane) or anti (both
NEt2 groups on opposite sides) alignments. The observed isomers are
tentatively assigned the trans-syn and trans-anti configurations. This type
of isomerism has been reported and discussed before in refs 9 and 10.
(13) The decomposition of 5 is clean, giving only product 6. However
3 undergoes, along with the C-C coupling process, isomerization to a new
organometallic complex, which we believe is the cis isomer (probably a
mixture of anti and syn isomers; see ref 9). cis-3 eventually decomposes to
6 as well. Variable amounts of pentafluorobenzene are also obtained in the
decomposition of 3.
Figure 2. X-ray structure of complex 7. Selected bond lengths
(Å): Pd1-C2, 2.167(13); Pd1-C3, 2.095(12); Pd1-Br1, 2.5456-
(16); Pd1-P1, 2.278(3); C1-N1, 1.335(13); C1-C2, 1.413(15);
C2-C3, 1.416(15).

Formation of a Vinyliminium Palladium Complex
Organometallics, Vol. 25, No. 5, 2006 1295
1
Table 1. Selected H and 13C NMR Data (δ) for Compounds
Scheme 4. Reactivity of Vinyl- versus Other
R-Aminocarbene Palladium Complexes
6b, 7, and 8a
compound
H2
H3
C1
C2
C3
7
5.11
5.75
7.76
2.81
4.20
7.25
148
71.7
83.4
117.6
58.7
70.9
160.3
8b
6b
164.2
a CDCl3 as solvent; δ referenced to TMS. b See text and ref 9.
open (109.1°), to compensate the small C-Pd-C angle. This
is a feature found in many reported [Pd0(olefin)L2] complexes.14a,d
The triphenylphosphine ligand is trans to C2, and the Pd-C1
nonbonding distance is 2.692 Å (cf. 2.167 and 2.095 Å for Pd-
C2 and Pd-C3 bonds). The C1-N1 distance (1.335 Å) is short,
consistent with a double bond. The C1-C2 and C2-C3
distances are equal (1.413(15) and 1.416(15) Å) and intermediate
between a single and a double bond, a feature also observed in
complexes of iron and tungsten with vinyliminium groups
coordinated through the CdC bond and also for palladium(0)
complexes with coordinated conjugated olefins.14,15 Similar
C-C distances are also found in analogous zwitterionic pal-
ladium(0) complexes with alkenylphosphonium ligands.16 In
contrast, the iminium salt 6b shows the expected short C2-C3
(1.343(7) Å) and long C1-C2 (1.425(7) Å) bond lengths as
determined by X-ray crystal structure determination (Supporting
Information).
nocarbene complexes and from the analogous alkoxycarbene
complexes. For Fischer type vinylaminocarbene complexes, the
existence of a CdC bond conjugated to the C-N bond reduces
the electrophilicity of the carbene carbon. In fact the chemical
shifts for the 13C resonances of C(carbene) in complexes 3-5
are consistently lower (ca. 14 ppm) than the values found for
the analogous Ph and Me derivatives. Accordingly, 3-5 are
noticeably more stable and resistant to insertion than similar
complexes reported before for R ) Ph, Me.9 The evolution
following carbene insertion is also strongly influenced by the
vinylic fragment and by the ancillary ligands (Scheme 4). A
difference was already reported for methoxycarbene palladium
complexes,9 which undergo C-C coupling, leading to different
types of products depending on the R group of the carbene
moiety (Scheme 1). For aminocarbenes the insertion leads to
an iminium salt and Pd-black, whereas a remarkably stable
complex containing the coordinated iminium salt (7) is obtained
when a vinylic-substituted carbene, in addition to a good
ancillary ligand (PPh3), is used (4, Scheme 3). The decomposi-
tions of 3 or 5 should lead initially to similar palladium
complexes, but, at the temperature used and in the absence of
a good stabilizing ligand, these presumed intermediates decom-
pose to the free iminium salt and Pd(0).
NMR data for 7 reveal that the nature of the vinyliminium
moiety is strongly altered upon coordination (Table 1). Complex
7 shows a very large difference in chemical shifts for H2 and
H3. The chemical shifts for H2, H3, and C1-C3 are significantly
lower than those for the free iminium salt 6b. These data are
closer to the chemical shift differences and ranges obtained for
the palladium allylic complex [Pd(µ-Br)(η3-MeO-C(C6F5)+
CH+CHPh)]2 (8) (see Scheme 1 and Table 1).9 As it was
observed in the latter allylic complex, slow rotation about the
C1-pentafluorophenyl ring occurs for 7. Hindered rotation about
the C1-N bond is also observed. Line shape analysis afforded
∆Gq ) 66.7 ( 1.6 kJ mol-1 17
,
a lower value than the one
or for conjugated
303
found for 6b (∆Gq396 ) 78.1 ( 0.4 kJ mol-1 18
)
iminium salts.19 This easier than expected rotation is noteworthy
and is discussed below.
Discussion
An examination of complex 7 reveals how much its formula-
tion as a Pd(0) or as a Pd(II) complex is a formalism. In addition
to the olefin-palladium (B) and the palladacyclopropane (C)
resonant forms, a further aminoallylpalladium representation (A)
needs to be considered (Scheme 4). While forms B and C
explain the solid-state structure (including the long C2-C3 bond
length), they cannot explain the 1H NMR behavior in solution,
where the Et groups bound to N become equivalent at moderate
temperatures. This easy rotation is better understood in the allylic
form A. Coordination mode A, along with the contribution of
C to the “Pd(II)” form, also accounts for the reluctance of 7 to
oxidize and its high stability in the air. Looking at the low-
energy separation between the aminoallyl-palladium and the κ2-
C,C-vinyliminium-palladium isomers, it is obvious that small
changes in this kind of structure can produce a reversal of
stability. Thus, for alkoxycarbenes the lesser stability of an
oxonium moiety as compared to an iminium moiety results in
the stabilization of the alkoxyallylpalladium structure [Pd(µ-
Br){(η3-C(C6F5)(OMe)CHCHPh}]2 (Scheme 1). An interesting
related case was reported by Kurosawa et al. for a family of
derivatives prepared by reaction of a Lewis acid with η2-enone
palladium(0) complexes.20 They found a continuous structure
The reactivity of vinylaminocarbene palladium complexes
shows some features distinct from those of alkyl- or arylami-
(14) (a) Kim, H.-J.; Choi, N.-S.; Lee, S. W. J. Organomet. Chem. 2000,
616, 67-73. (b) Rabin, O. Vigalok, A.; Milstein, D. J. Am. Chem. Soc.
1998, 120, 7119-7120. (c) Benn, R.; Betz, P.; Goddard, R.; Jolly, P. W.;
Kokel, N.; Kruger, C.; Topalovic, I. Z. Naturforsch. B: Chem. Sci. 1991,
46, 1395-1405. (d) Werner, H.; Crisp, G. T.; Jolly, P. W.; Kraus, H.-J.;
Kruger, C. Organometallics 1983, 2, 1369-1377.
(15) (a) Zhang, S.; Xu, Q.; Sun, J.; Chen, J. Organometallics 2001, 20,
2387-2399. (b) Lee, L.; Chen, D.-J.; Lin, Y.-C.; Lo, Y.-H.; Lin, C.-H.;
Lee, G.-H.; Wang, Y. Organometallics 1997, 16, 4636-4644. (c) Nesm-
eyanov, A. N.; Salnikova, T. N.; Struchkov, Y. T.; Andrianov, V. G.;
Pogrebnyak, A. A.; Rybin, L. V.; Rybinskaya, M. I. J. Organomet. Chem.
1976, 117, C16-C20.
(16) (a) Huang, C.-C.; Duan, J.-P.; Wu, M.-Y.; Liao, F.-L.; Wang, S.-
L.; Cheng, C.-H. Organometallics 1998, 17, 676-682. (b) Duan, J.-P.; Wu,
M.-Y.; Liao, F.-L.; Wang, S.-L.; Cheng, C.-H. Organometallics 1997, 16,
3934-3940.
(17) Fast rotation and inversion of nitrogen brings about the equivalence
of the three methylene signals (1:1:2 ratio) in one multiplet and the
appearance of just one triplet for the methyl groups. Line shape analysis
was carried out using gNMR v3.6.5, IvorySoft; Cherwell Scientific
Publishing Ltd., Oxford.
(18) This difference in ∆Gq led to a coalescence temperature difference
of 60 °C for the methyl groups of the NEt2 moiety in 6b and 7.
(19) Mere´nyi, R. in ref 3, p 83.

1296 Organometallics, Vol. 25, No. 5, 2006
Albe´niz et al.
Figure 3. Geometries of structures 9CC and 9CN
.
variation from η2-olefin to η3-allyl type depending on the enone
and acid used (eq 1). The Pd-C1 distances found ranged from
2.41 to 2.96 Å (cf. 2.692 Å for 7).21
by the iminium CdN bond rather than by the CdC bond is
proposed as an intermediate in Noyori’s Rh-catalyzed isomer-
ization of allylamines to enamines.4 We are currently examining
the viability of CdC bound vinyliminium intermediates in the
Rh system.
In conclusion, both κ2-C,C-vinyliminium and aminoallyl
forms are close in energy and contribute to an accurate
description of the structure and properties observed for the
palladium complex 7. A nonobserved κ2-C,N-vinyliminium
coordination is higher in energy than the observed κ2-C,C form.
The structure and behavior found for complex 7 shows that
coordination to a CdC(olefin) bond is preferred over coordina-
tion to a CdN(iminium) bond. Both coordination isomers,
modeling NEt2 by NMe2, were studied using DFT calculations.
The optimized geometry for the CdC bound isomer (9CC, Figure
3) matches the solid-state structure of 7, with calculated
distances Pd1-C1 2.739 Å; Pd1-C2, 2.215 Å; and Pd1-C3,
2.139 Å. The CdN bound isomer (9CN, Figure 3), not detected
experimentally, shows a longer C-N bond length (1.438 Å)
than 9CC (1.350 Å) or complex 7 (1.335(13) Å). Stronger
π-back-donation from Pd to the π-antibonding orbitals of the
iminium CdN bond accounts for this lengthening and gives
9CN a higher Pd(II) palladacycle character. The structure 9CC is
7.3 kcal/mol more stable than the CdN bound isomer 9CN
(Figure 3). Taking this energy difference and assuming that the
entropy variation in the interconversion between both structures
should be small (in nonpolar media), a simple calculation for
the equilibrium 9CN h 9CC affords K298 ) 2.2 × 105. This leaves
the CdC bound iminium Pd complex as the only detectable
structure by NMR spectroscopy.
Experimental Section
General Procedures. All manipulations were carried out using
Schlenk techniques. Solvents were dried and distilled under nitrogen
prior to use. Compounds 123 and 224 were prepared using literature
methods. Percentages of products in the reactions mixtures were
determined by integration of 19F NMR signals. Full spectroscopic
and analytical data for the compounds can be found in the
Supporting Information.
trans-[Pd(µ-Br)(C6F5){C(NEt2)CHdCHPh}]2 (3).12 To a solu-
tion of 1 (0.2500 g, 0.489 mmol) in CH2Cl2 (20 mL) was added 2
(0.2130 g, 0.489 mmol). The mixture was stirred for 30 min. The
dark solution was then filtered through activated carbon and Celite
and evaporated to dryness. Et2O (10 mL) was added to the residue,
and the solution was kept at -20 °C for 12 h. A yellow solid
crystallized, which was filtered, washed with pentane (10 × 5 mL),
and vacuum-dried (yield 0.1623 g; 61%). trans-3 is a mixture of
syn and anti isomers (3, 3′) in solution in a 1 (3):1.6 (3′) ratio.12
[PdBr(C6F5){C(NEt2)CHdCHPh}(PPh3)] (4). PPh3 (0.0728 g,
0.278 mmol) was added to a solution of 3 (0.150 g, 0.139 mmol)
in CH2Cl2 (15 mL). The orange solution was stirred for 35 min
and evaporated to dryness. n-Hexane (10 mL) was added to the
residue, and 4 was obtained as a light orange solid, which was
filtered, washed with n-hexane (3 × 5 mL), and air-dried (yield
0.1607 g, 72%).
Although examples of simple iminium complexes coordinated
by the CdN bond have been reported for other transition
metals,22 Fe and W vinyliminium complexes also coordinate
through the CdC bond,15 suggesting that this coordination mode
is preferred. In contrast, a vinyliminium complex coordinated
[Pd(C6F5){C(NEt2)CHdCHPh}(NCMe)2]BF4 (5). Complex 3
(0.0106 g, 0.010 mmol) was added to a solution of AgBF4 (0.0038
(20) (a) Ogoshi, S.; Morita, M.; Kurosawa, H. J. Am. Chem. Soc. 2003,
125, 9020-9021. (b) Ogoshi, S.; Yoshida, Y.; Nishida, T.; Morita, M.;
Kurosawa, H. J. Am. Chem. Soc. 2001, 123, 1944-1950.
(21) A similar type of behavior has been described for rhodium
semiquinoid systems (Rh(I) and Rh(III) forms), and the authors have named
it “redox exchange”: Nikanorov, V. A.; Bakhmutov, V. I.; Galakhov, M.
V.; Sergeev, S. V.; Stepanova, E. V.; Yanovsky, A. I.; Struchkov, Y. T.;
Rozenberg, V. I.; Reutov, O. A. J. Organomet. Chem. 1988, 358, 463-
494.
(22) (a) Sepelak, D. J.; Pierpont, C. G.; Barefield, E. K.; Budz, J. T.;
Poffenberger, C. A. J. Am. Chem. Soc. 1976, 98, 6178-6185. (b) Fong, C.
W.; Wilkinson, G. J. Chem. Soc., Dalton Trans. 1975, 1100-1104.
(23) Albe´niz, A. C.; Espinet, P.; Foces-Foces, C.; Cano, F. H. Organo-
metallics 1990, 9, 1079-1085.
(24) Macomber, D. W.; Madhukar. P. Organometallics 1989, 8, 1275-
1282.

Formation of a Vinyliminium Palladium Complex
Organometallics, Vol. 25, No. 5, 2006 1297
g, 0.020 mmol) in NCMe (5 mL). The mixture was stirred for 30
min protected from light. The resulting suspension was filtered
through Celite and evaporated to dryness. Complex 5 was obtained
as a yellowish oil and characterized spectroscopically.
Decomposition of the Palladium Carbene Complexes 3 and
5. An NMR tube was charged with trans-3 (0.0080 g, 0.113 mmol)
where the NEt2 has been substituted by NMe2. The calculations
were performed using JAGUAR 5.5.27 The LACVP* basis set
describes the Pd, P, and Br atoms with an effective core potential
and a double-ú valence basis set with polarization functions.27,28
The C, N, and F atoms of the iminium group were described by
the 6-31G* basis set, and the rest of the C and H atoms were
described by the 6-31G basis set.
and CDCl3 (0.6 mL). The solution was kept at 50 °C for 12 h. 19
F
1
and H NMR spectra showed the formation of 6a (41%), C6F5H
(11%), cis-3 (19%), and unreacted trans-3 (14%) as main products.
Decomposition of 5 was carried out in the same way, and 6b
was obtained (75% after 6 days at 50 °C).
Acknowledgment. This work was supported by the Direc-
cio´n General de Investigacio´n (MEC, Grant Nos. CTQ2004-
07667 and CTQ2005-09000-C02-01) and the Junta de Castilla
y Leo´n (Projects VA057/03 and VA058/03). Fellowships to
A.P.-M. (funded by the JCyL) and A.N. (by MEC) are
acknowledged. G.U. is indebted to MEC for funding through
the “Ramo´n y Cajal” program.
[PdBr{Et2NdC(C6F5)(CHdCHPh)}(PPh3)] (7). A solution of
4 (0.0700 g, 0.065 mmol) in CHCl3 was kept at 50 °C for 24 h.
After this time the solution was a mixture of unreacted 4 (52%), 7
(36%), and [PdBr(C6F5)(PPh3)2] (10%),25 as major products. The
orange solution was evaporated to dryness, and the residue was
chromatographed in a silica column using Et2O as eluent. 7 was
separated as an orange band. The solution was evaporated to ca.
0.5 mL, and 7 crystallized by addition of n-hexane (isolated yield
0.0168 g, 24%).
X-Ray Crystal Structure Determinations. Crystals for X-ray
analysis were obtained by slow evaporation of a solution of 4
(or 7) in a mixture of CH2Cl2/n-hexane at room temperature or by
cooling a CHCl3 solution of 6b at -20 °C. X-ray measure-
ments were made using a Bruker SMART CCD area-detector
diffractometer. Reflections were collected, intensities were inte-
grated, and the structure was solved by direct methods proce-
dure.26
Supporting Information Available: Full spectroscopic and
analytical data for compounds, and details for the determination of
X-ray crystal structures and C-N rotation barriers for 7 and 6b.
CIF files for X-ray crystal structures of 4, 6b, and 7. Coordinates
for the optimized calculated geometries of 9CC and 9CN. This
material is available free of charge via the Internet at http://
pubs.acs.org.
OM051028S
(25) Elia, C.; Elyashiv-Barad, Sen, A.; Lo´pez-Ferna´ndez, R.; Albe´niz,
A. C.; Espinet, P. Organometallics 2001, 21, 4249-4256.
(26) Data analysis and drawing were performed with the following
programs: SMART V5.051, 1998; SAINT V6.02, 1999; Sheldrick, G. M.
SHELXTL V5.1, 1998: Bruker AXS, Inc.: Madison, WI.
(27) Jaguar 5.5; Schro¨dinger, LLC: Portland, OR, 2003.
(28) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 299-310.
Computational Methods. Complexes 9CC and 9CN with CdC
and CdN iminium coordination have been calculated using a model