Formation of ArPdXL(amine) complexes by substitution of one phosphane ligand by an amine in trans-ArPdX(PPh3)2 complexes

Article abstract of DOI:10.1002/ejic.200400413

Amines (piperidine, morpholine, diisopropylamine, terbutylamine), which may be used as bases in copper-free palladium-catalyzed Sonogashira reactions, substitute one phosphane PPh₃ in trans-ArPdX(PPh₃) ₂ complexes (Ar = Ph, 4-NC-C₆H₄, 4-MeOC-C ₆H₄, 2-thienyl; X = I, Br, Cl) to generate ArPdX(PPh ₃)(amine) complexes in a reversible reaction whose equilibrium constant is determined in chloroform, THF, and DMF. The equilibrium constant depends on Ar, X, the basicity, and the steric hindrance of the amine. Wiley-VCH Verlag GmbH & Co. KGaA, 2005.

Full text of DOI:10.1002/ejic.200400413

SHORT COMMUNICATION
Formation of ArPdXL(amine) Complexes by Substitution of One Phosphane
Ligand by an Amine in trans-ArPdX(PPh3)2 Complexes
Anny Jutand,*[a] Serge Négri,[a] and Anna Principaud[a]
Keywords: Amines / Phosphanes / Palladium / Ligand substitution
Amines (piperidine, morpholine, diisopropylamine, terbutyl-
amine), which may be used as bases in copper-free palla-
dium-catalyzed Sonogashira reactions, substitute one phos-
phane PPh3 in trans-ArPdX(PPh3)2 complexes (Ar = Ph, 4-
NC–C6H4, 4-MeOC–C6H4, 2-thienyl; X = I, Br, Cl) to gener-
ate ArPdX(PPh3)(amine) complexes in a reversible reaction
whose equilibrium constant is determined in chloroform,
THF, and DMF. The equilibrium constant depends on Ar, X,
the basicity, and the steric hindrance of the amine.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2005)
Palladium-catalyzed Sonogashira reactions (Scheme 1) proceed first with displacement of one ligand to give inter-
require the presence of a base, which is very often an am- mediate complexes: ArPdXL(η2-HCϵCR).[10] The ligated
ine.[1,2]
alkyne would then be more easily deprotonated by the amine,
and a new complex would be formed ArPd(–CϵCR)Ln
(n = 1 or 2), which gives the coupling product ArCϵCR
by reductive elimination. In the absence of any amine, a
carbopalladation step[11,12] takes place, which leads to R–
C(PdXL2)=CH–Ar complexes,[12] presumably by formation
of ArPdXL(η2-HCϵCR) complexes.[11]
Herein we report that amines react with trans-
ArPdX(PPh3)2 (1) complexes by substitution of one PPh3
to generate ArPdX(PPh3)(amine) (2) complexes (Scheme 3).
In other words, competition between the amine and the al-
kyne for the substitution of one phosphane group in
ArPdX(PPh3)2 complexes may occur in palladium-cata-
lyzed copper-free Sonogashira reactions.
Scheme 1.
In copper-free Sonogashira reactions (Scheme 2), the role
of the base is crucial, and specific amines are required.[3–10]
Among them, secondary amines such as piperidine,[3,6,8–10]
morpholine,[10] and diisopropylamine[8,10] proved to be very
efficient. The amines are usually used in excess,[5,6,8,9] even
as the solvent.[3,6,7] PPh3 is often a ligand of the palladium
catalyst when aryl iodides, bromides or triflates are
used.[3,4,7–9]
Scheme 2.
The mechanism of the copper-free reaction is not well
known. The first step of the reaction is an oxidative ad-
dition of ArX to a Pd0 complex, which generates ArPdXL2
complexes (e.g. L = PPh3). However, the second step of the
reaction is under debate. The amines employed in such reac-
tions (e.g. piperidine, morpholine, etc.) are usually not able
to deprotonate the alkyne to generate the anionic nucleo-
phile RCϵC– that is able to react with ArPdXL2 in a trans-
metallation step. It is for this reason that complexation of
the alkyne to the trans-ArPdXL2 complexes is supposed to
Scheme 3.
The reactions of the secondary (piperidine, morpholine,
and diisopropylamine) and primary amines (terbutylamine)
with 1 were monitored by H and 31P NMR spectroscopy
1
in DMF, THF, acetone, and chloroform, after successive
additions of known amounts of amine. Besides the set of
1
the H NMR signals for the protons of the Ar group in 1,
a new set of signals appears at lower field, suggesting that
a new complex 2 is formed. The magnitude of the 1H NMR
signals of 2 increases at the expense of those of complexes
[a]
Ecole Normale Supérieure, Département de Chimie, UMR
CNRS-ENS-UPMC 8640,
1 as the amine concentration is increased. Concomitant 31
P
24 Rue Lhomond, 75231 Paris Cedex 5, France
Fax: +33-1-4432-3325
E-mail: Anny.Jutand@ens.fr
NMR spectroscopy performed on the same solutions shows
that signals for free PPh3
spectra, together with a new singlet (δ2 in Table 1) located
[13]
are detected in the 31P NMR
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
Eur. J. Inorg. Chem. 2005, 631–635
DOI: 10.1002/ejic.200400413
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
631

A. Jutand, S. Négri, A. Principaud
SHORT COMMUNICATION
Table 1. Equilibrium constants K and 31P NMR shifts (101 MHz, H3PO4) of trans-ArPdX(PPh3)2 (δ1)and ArPdX(PPh3)(amine) (δ2)
generated by the reversible substitution of one PPh3 group by the amine group (Scheme 3)
Entry
trans-ArPdX(PPh3)2
δ1 [ppm]
ArPdX(PPh3)(amine)
δ2 [ppm][a]
K
Solvent
1
Solvent
2
Solvent
3
Solvent
4
5
6
7
8
[D7]DMF
23.14
[D8]THF
23.22
[D6]acetone
23.04
CDCl3
23.03
[D7]DMF
32.56[b]
[D7]DMF
0.095
[D8]THF
0.14
PhPdI(PPh3)2
PhPdI(PPh3)2
PhPdI(PPh3)2
PhPdI(PPh3)2
PhPdI(PPh3)(piperidine)
PhPdI(PPh3)(piperidine)
PhPdI(PPh3)(piperidine)
[D8]THF
[c]
33.18
[D6]acetone
32.83
CDCl3
32.45
[D6]acetone
n.d.[j]
CDCl3
0.11
0.026
PhPdI(PPh3)(piperidine)
PhPdI(PPh3)(morpholine)
PhPdI(PPh3)(tBuNH2)
32.73
32.09[d]
31.72[e]
32.08
0.002
PhPdI(PPh3)(iPr2NH)
7 × 10–5
0.28
PhPdBr(PPh3)2
PhPdCl(PPh3)2
23.72
23.73
22.97
23.75
23.69
21.97
PhPdBr(PPh3)(piperidine)
PhPdBr(PPh3)(morpholine)
PhPdCl(PPh3)(piperidine)
PhPdCl(PPh3)(morpholine)
(4-NC–C6H4)PdI(PPh3)(piperidine)
(4-NC–C6H4)PdI(PPh3)(morpholine)
(4-NC–C6H4)PdBr(PPh3)(piperidine)
(4-NC–C6H4)PdBr(PPh3)(morpholine)
(4-MeOC–C6H4)PdBr(PPh3)-(piperi-
dine)
9
32.37
0.014
0.21
0.013
0.023
0.0038
0.038
10
11
12
13
14
15
16
31.76[f]
31.98
(4-NC–C6H4)PdI(PPh3)2
(4-NC–C6H4)PdBr(PPh3)2
31.83[g]
32.25[h]
31.48
31.97
0.0033
(4-MeOC–C6H4)
PdBr(PPh3)2
(2-Th)PdI(PPh3)2
31.71[i]
n.d.[k]
[l]
17
(2-Th)PdI(PPh3)(piperidine)
30.72
0.1
[a] δ2 is the shift of the major isomer. [b] A minor isomer (16%) was observed at δ = 30.52 ppm. [c] A minor isomer (6%) was observed
at δ = 32.22 ppm. [d] A minor isomer (11%) was observed at δ = 27.62 ppm. [e] Two other isomers (11%) were observed at δ = 28.20 and
30.10 ppm. [f] A minor isomer (13%) was observed at δ = 33.82 ppm.[g] A minor isomer (27%) was observed at δ = 31.31 ppm. [h] A
minor isomer (40%) was observed at δ = 31.62 ppm. [i] A minor isomer (39%) was observed at δ = 31.42 ppm. [j] None determined
because of the very low solubility of trans-PhPdI(PPh3)2 in acetone. [k] None determined because of the presence of some triphenylphos-
phane oxide. [l] Th means thienyl.
at lower field than those of the initial complexes 1 (δ1 in ture, given in Scheme 3, was deduced from its 13C NMR
Table 1). The magnitude of the singlet for free PPh3 is sim- spectrum, in agreement with the value of the JCP coupling,
ilar to those of the new complexes 2 and both increase con- characteristic of a phosphane cis to the aryl group. In some
comitantly at the expense of those of 1 as the amine concen- cases, a second minor singlet near that observed at δ2 is
tration is increased. These experiments establish that one detected (Table 1), which suggests isomerisation of the li-
PPh3 group is substituted by one amine group gands of 2 around the PdII centre, as observed for the P(o-
(Scheme 3).[14–18] The coordinated amine was characterized Tol)3 (o-Tol: ortho-tolyl) ligand.[20] Indeed, related com-
1
by its H and 13C NMR signals in isolated complexes 2.
plexes ArPdBr(amine)(P[o-Tol]3) have been synthesized by
The reversibility of the substitution is proved by the fact a quite different reaction, not by ligand substitution but by
that the amount of 2 increases at the expense of 1 when the cleavage of the bromide bridges by the amine in dimeric
amine concentration is increased, and addition of PPh3 to [ArPdBr(P[o-Tol]3)]2 complexes (Scheme 4).[20,21] The major
solutions containing both complexes 1 and 2 results in an isomer ArPd(amine)(P[o-Tol]3) has the same structure as
increase in the amount of 1 to the detriment of 2. Addition complexes 2 with the phosphane trans to the amine
of PPh3 to the isolated complex 2-ThPdI(PPh3)(piperidine) group.[20] Two other minor isomers only characterized by
(Th = thienyl) results in the formation of trans-2- 31P NMR singlets are also observed.[20]
ThPdI(PPh3)2, and the release of the free piperidine is
clearly detected by the 1H NMR spectroscopy – further evi-
dence of the equilibrium in Scheme 3. Complexes 1 and 2
are involved in equilibria that are slow relative to the time
scale of NMR spectroscopy.
The substitution of the two PPh3 was never observed,[19]
Scheme 4.
even in the presence of a large amount of amine. Indeed,
the integration of the 31P NMR signal for the free phos-
The complexes ArPdX(PPh3)(amine) 2 generated in situ
phane never exceeded that of the monosubstituted complex were rather stable with time in chloroform. After some days,
ArPdX(PPh3)(amine). phosphane oxide was detected as a by-product, with the
The substitution of PPh3 in trans-ArPdX(PPh3)2 (1) by effect that the amount of complexes 2 had increased relative
the amine occurs irrespective of the identity of X (= I, Br, to that of complexes 1, by the shift of the equilibrium in
Cl) and the aryl groups (Ar = Ph, 2-thienyl, 4-NC–C6H4, Scheme 3 to the right as a result of the oxidation of PPh3.
4-MeOC–C6H4) investigated here (Table 1). One major As an isolated complex, PhPdI(PPh3)(piperidine) was stable
complex of type 2 is generally generated (Table 1). Its struc- for at least four days in chloroform.
632
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Eur. J. Inorg. Chem. 2005, 631–635

Formation of ArPdXL(amine) Complexes by Substitution of a Phosphane Ligand
SHORT COMMUNICATION
The value of the equilibrium constant in Scheme 3, K = place the phosphane. The equilibrium constant is not signif-
[2][PPh3]/[1][amine] was determined by 31P NMR spec- icantly affected by the solvent (entries 1,2,4).
troscopy by using the respective integration of the singlets
For a given X, amine and solvent, K decreases when the
of complexes 1 and 2;[22] K = x2/(1 – x)(n – x), where x is para substituent on the aryl group is an electron acceptor
the molar fraction of 2 in the equilibrium: x = 2S2/ (entries 4 and 12, 5 and 13, 8 and 14, and 9 and 15).[24,25]
(S1 + 2S2) [S1 and S2: magnitude of the singlet of 1 and 2, The reaction was not tested with an electron-donor substit-
respectively], n is the equiv. of amine added to 1. The plot uent because of the instability of the related trans-
of x2 versus (1 – x)(n – x) is linear, and K is determined ArPdX(PPh3)2 due to scrambling between the Ph group of
from the slope of the straight line (Figure 1,Table 1).
the ligand and the Ar group.[26,27]
The influence of X (X = I, Br, Cl) on the substitution was
tested for a given Ar group, amine and solvent. Whereas for
the substitution of PPh3 by the piperidine K follows the
order: Br Ͼ Cl Ͼ I (entries 4, 8,10; entries 12, 14), a reverse
order: I Ͼ Br Ϸ Cl (entries 5, 9, 11; entries 13,15) is found
for the substitution by morpholine. The effect of the halides
is hard to rationalize, since they cannot have a trans influ-
ence on the substitution of the phosphane due to the struc-
ture of the initial complexes 1.[24,25]
In conclusion, ArPdX(PPh3)(amine) complexes were
generated by the reaction of amines with trans-
ArPdX(PPh3)2 complexes. The reversible substitution of
one PPh3 group by one amine was characterized by the de-
termination of the equilibrium constant between the two
Figure 1.Determination of the equilibrium constant K between
trans-ArPdX(PPh3)21 and ArPdX(PPh3)(amine) 2 (Scheme 3) as
monitored by 31P NMR spectroscopy; plot of x2 versus (1 – x)(n –
x) [x is the molar fraction of 2 in the equilibrium; n is the equiv.
of amine added to 1]; K is determined from the slope; a) equilib- complexes. These results establish that in copper-free Sono-
rium between trans-(4-NC–C6H4)PdBr(PPh3)2 (initially 30 mm) and
gashira reactions, the formation of ArPdX(PPh3)(amine)
(4-NC–C6H4)PdBr(PPh3)(morpholine) in CDCl3 (n = 10, 20, 40,
complexes has to be taken into account. There will be an
80); b) equilibrium between trans-PhPdI(PPh3)2 (initially 20 mm)
evident competition between the alkyne and the amine for
and PhPdI(PPh3)(piperidine) in [D8]THF (n = 2, 4, 10, 20)
the substitution of one PPh3 group in ArPdX(PPh3)2 com-
The value of K is less than 1 (Table 1), which means that, plexes. The fact that the amine is often used in large ex-
under identical concentrations of ArPdX(PPh3)2 and am- cess[5,6,8,9] or as the solvent[3,6,7] encourages the substitution
ine, the equilibrium lies in favor of ArPdX(PPh3)2. How- of the phosphane by the amine group. Work is in progress
ever, in catalytic reactions where the concentration of the to better define the contribution of such new amine com-
amine is always considerably higher than that of the cata- plexes in the mechanism of palladium-catalyzed reactions
lytic palladium species, the equilibrium will be shifted to- involving amines in copper-free Sonogashira reactions.
ward the formation of ArPdX(PPh3)(amine). As an exam-
ple, if the concentration of the piperidine is 50 times higher
Experimental Section
than that of trans-PhPdI(PPh3)2 in DMF (corresponding to
a catalytic reaction run with 2% of catalyst), then, with K
= 0.095 (Table 1), one calculates that the concentration of
PhPdI(PPh3)(piperidine) will be 5.5 times higher than that
of trans-PhPdI(PPh3)2.
The ligand substitution was studied under reversible con-
ditions. We only have the thermodynamic data for the for-
mation of complexes 2. From the values of the equilibrium
constant K collected in Table 1, it can be seen that for a
given Ar group and X, K increases, and consequently the
substitution is favored as the amine basicity[23] increases
within the cyclic series (piperidine and morpholine: com-
pare entries 4 and 5, 8 and 9, 10 and 11, 12 and 13, and 14
and 15). However, the magnitude of K follows the order
(compare entries 4–7): piperidine Ͼ morpholine Ͼ tBuNH2
ϾϾ iPr2NH.
General: All experiments were conducted under argon. The deuter-
ated solvents DMF, THF, acetone and chloroform were obtained
commercially and degassed just before use. The amines (piperidine;
morpholine, diisopropylamine, terbutylamine), phenyl halides (X
= I, Br, Cl), 4-NC–C6H4–X (X = Br, Cl), 4-MeOC–C6H4–Br, 2-
iodothiophene were obtained commercially. The complexes trans-
ArPdX(PPh3)2 were synthesized by reacting aryl halides with
Pd0(PPh3)4.[28–30]
General Procedure for the Ligand Exchange as Monitored by 1H and
31P NMR Spectroscopy: trans-PhPdI(PPh3)2 (8.3 mg, 0.01 mmol)
was introduced in CDCl3 (0.5 mL). The H and 31P NMR spectra
1
were recorded at room temperature. Piperidine (2 µL, 0.02 mmol)
was first added, followed by further additions of piperidine (0.02,
0.06 and 0.10 mmol, respectively). H and 31P NMR spectra were
1
recorded after each addition of piperidine.
General Procedure for the Synthesis of ArPdX(PPh3)(amine): Piperi-
dine (500 µL, 5 mmol) was added to trans-PhPdI(PPh3)2 (83 mg,
0.1 mmol) in chloroform (5 mL). After 30 min, the solution was
concentrated under vacuum. Precipitation in pentane gave 48 mg
of PhPdI(PPh3)(piperidine), as a gray-white solid (72 % yield). The
isolated complex exhibits the same 1H and 31P NMR spectra as
This does not reflect the amine basicity order since on
one hand morpholine is less basic than tBuNH2 and
iPr2NH, and on the other hand iPr2NH is slightly more
basic than tBuNH2.[23] The steric hindrance of the amine
may also affect the substitution. Indeed, N-methylmorph-
oline, even when used at high concentrations, could not dis- those recorded during ligand exchange in the NMR tube, but the
Eur. J. Inorg. Chem. 2005, 631–635
www.eurjic.org © 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 633

A. Jutand, S. Négri, A. Principaud
SHORT COMMUNICATION
protons of the ligated piperidine are more clearly detected because
of the absence of excess piperidine. A 13C NMR spectrum was also
recorded on the isolated complex to elucidate its structure.
Acknowledgments
This work has been supported in part by the Centre National de
la Recherche Scientifique (UMR CNRS-ENS-UPMC 8640) and
the Ministère de la Recherche (Ecole Normale Supérieure). We
thank Johnson Matthey for the loan of sodium tetrachloropallad-
ate.
The complexes with morpholine, ArPdX(PPh3)(morpholine), could
not be isolated as pure compounds because the equilibrium lies less
in favor of their formation than for the formation of
ArPdX(PPh3)(piperidine). The reversibility explains the difficulty
in their isolation. Consequently, most of them were characterized
in situ in solution.
[1] K. Sonogashira, N. Hagihara, Tetrahadron Lett. 1975, 4467–
4470.
[2] K. Sonogashira, “Sonogashira Alkynes Synthesis”, in The
Handbook of Organopalladium Chemistry for Organic Synthesis
(Ed.: E. Negishi), Wiley-Interscience, New York, 2002, vol. 1,
pp. 493–529.
trans-PhPdI(PPh3)2:[28] 1H NMR (250 MHz, CDCl3, TMS): δ =
6.21 (t, J = 7 Hz, 2 H, m-H of Ph), 6.33 (t, J = 7 Hz, 1 H, p-H of
Ph), 6.60 (d, J = 7 Hz, 2 H, o-H of Ph), 7.23 (t, J = 7 Hz, 12 H,
m-H in PPh3), 7.32 (t, J = 7 Hz, 6 H, p-H in PPh3), 7.50 (dd, J =
7, J = 6 Hz, 12 H, o-H in PPh3) ppm. 13C NMR (62.89 MHz,
CDCl3, TMS): δ = 127.76 (t, JC3P = 5 Hz, C3 of Ph in PPh3), 127.90
(t, JC3P = 4 Hz, C3 of Ph–Pd), 129.69 (s, C4 of Ph in PPh3), 131.31
(s, C4 of Ph–Pd), 132.21 (t, JC1P = 23 Hz, C1 of Ph in PPh3), 134.65
(t, JC2P = 6 Hz, C2 of Ph–Pd), 134.89 (t, JC2P = 6 Hz, C2 of Ph in
PPh3), 136.03 (t, JC1P = 5 Hz, C1 of Ph–Pd) ppm. 31P NMR
(101 MHz, CDCl3, H3PO4): δ = 23.03 (s) ppm.
[3] M. Alami, F. Ferri, G. Linstrumelle, Tetrahedron Lett. 1993,
34, 6403–6406.
[4] J. F. Nguefack, V. Bolitt, D. Sinou, Tetrahedron Lett. 1996, 37,
5527–5530.
[5] V. P. W. Böhm, W. A. Herrmann, Eur. J. Org. Chem. 2000,
3679–3681.
[6] R. G. Heidenreich, K. Kölher, J. G. E. Krauter, J. Pietsch, Syn-
lett 2002, 1118–1122.
[7] M. Pal, K. Parasuraman, S. Gupta, K. R. Yeleswarapu, Synlett
2002, 1976–1982.
trans-(4-NC–C6H4)PdBr(PPh3)2:[30] 1H NMR (CDCl3, TMS): δ =
6.41 (d, J = 8 Hz, 2 H, m-H), 6.80 (d, J = 8 Hz, 2 H, o-H), 7.30
(m, 18 H, m-H and p-H in PPh3), 7.52 (dd, J = 7, J = 6 Hz, 12 H,
o-H in PPh3) ppm. 31P NMR (CDCl3, H3PO4): δ = 23.75 (s) ppm.
[8] T. Fukuyama, M. Shinmen, S. Nishitani, M. Sato, I. Ryu, Org.
Lett. 2002, 4, 1691–1694.
[9] N. E. Leadbeater, B. J. Tominack, Tetrahedron Lett. 2003, 44,
1
trans-(2-Th)PdI(PPh3)2: H NMR (CDCl3, TMS): δ = 5.89 (d, J =
8653–8656.
3.3 Hz, 1 H, 5-H in Th), 6.34 (dd, J = 5, J = 3.3 Hz, 1 H, 4-H in
Th), 6.82 (d, J = 5 Hz, 1 H, 3-H in Th), 7.29 (m, 18 H, m-H and
p-H in PPh3), 7.53 (dd, J = 6, J = 5.5 Hz, 12 H, o-H in PPh3) ppm.
31P NMR (CDCl3, H3PO4): δ = 30.72 (s) ppm.
[10] A. Soheili, J. Albaneze-Walker, J. A. Murry, P. G. Dormer,
D. L. Hughes, Org. Lett. 2003, 5, 4191–4194.
[11] S. Cacchi, G. Fabrizi, “Carbopalladation of Alkynes Followed
by Trapping with Nucleophilic Reagents”, in The Handbook
of Organopalladium Chemistry for Organic Synthesis (Ed.: E.
Negishi), Wiley-Interscience, New York, 2002, vol. 1, pp. 1335–
1367.
PhPdI(PPh3)(piperidine): Isolated complex, yield 72%. 1H NMR
(250 MHz, CDCl3, TMS): δ = 1.25 (m, 2 H, γCH2), 1.38 (m, 2 H,
βCH2), 1.55 (m, 2 H, βCH2), 2.39 (ddd, J = 13 Hz, 2 H, HC–N–
CH), 3.29 (d, J = 13 Hz, 2 H, HC–N–CH), 3.43 (br. s, 1H, NH),
6.67 (m, 3 H, m-H and p-H of Ph), 6.95 (br. d, J = 4.5 Hz, 2 H, o-
H of Ph), 7.22 (t, J = 6 Hz, 6 H, m-H in PPh3), 7.25 (m, 3 H, p-H
in PPh3), 7.46 (t, 6 H, o-H in PPh3) ppm. 13C NMR (62.89 MHz,
CDCl3, TMS): δ = 23.83 (CH2–CH2–CH2 of piperidine), 24.75 (N–
CH2–CH2 of piperidine), 49.34 (NCH2 of piperidine), 127.53 (d,
JC3P = 1.5 Hz, C3 of Ph–Pd), 127.76 (d, JC3P = 10.5 Hz, C3 of Ph
in PPh3), 127.99 (s, C4 of Ph–Pd), 129.99 (s, C4 of Ph in PPh3),
132.1 (d, JC1P = 50 Hz, C1 of Ph in PPh3), 134.28 (d, JC2P = 4.6 Hz,
C2 of Ph–Pd), 134.78 (d, JC2P = 11 Hz, C2 of Ph in PPh3), 160.58
(d, JC1P = 2.3 Hz, C1 of Ph–Pd) ppm. 31P NMR (101 MHz, CDCl3,
H3PO4): δ = 32.45 (s) ppm. C29H31INPPd (657.8): calcd. C 52.9,
H 4.7, N 2.1; found C 51.9, H 4.2, N 1.8.
[12] C. Amatore, S. Bensalem, S. Ghalem, A. Jutand, J. Organomet.
Chem. 2004, 689, 4642–4646.
[13] The 31P NMR singlet of the free PPh3 was located at –5.24 in
[D8]THF, –5.62 in [D9]DMF, –5.46 in [D6]acetone and –
5.18 ppm in CDCl3.
[14] The substitution of one phosphane group by one amine group
in square-planar d8 complexes trans-RMXL2 (M = Pt, Pd; R
= organic group; X = halide andL = PRЈ3) is quite un-
usual.[15,16] What is often observed is the substitution of one
halide ligand in trans-RMXL2 (M = Pt, Pd; X = Br, Cl) com-
plexes by an amine to generate cationic complexes [RM(amine)
L2]+X–, as in the reaction of pyridine (py) with trans-
ArPtCl(PEt3)2 complexes that forms trans-[ArPt(PEt3)2(py)]
+Cl–.[17,18]
[15] For substitutions reactions in square-planar d8 complexes
trans-RMXL2 see: M. L. Tobe, “Reactions Mechanisms”, in
Comprehensive Coordination Chemistry (Eds.: G. Wilkinson,
R. D. Gillard, J. A. McCleverty), Pergamon Press, 1987, vol.
1., pp. 281–329.
[16] See also: R. B. Jordan, “Ligand Substitution Reactions,” in Re-
action Mechanisms of Inorganic and Organometallic system, 2nd
ed., Oxford University Press, 1998, pp. 35–101.
[17] F. Basolo, J. Chatt, H. B. Gray, R. G. Pearson, B. L. Shaw, J.
Chem. Soc. 1961, 2207–2215.
(4-NC–C6H4)PdBr(PPh3)(morpholine): Isolated complex. 1H NMR
(250 MHz, CDCl3, TMS): δ = 2.57 (ddd, J = 12 Hz, 2 H,
HCNCH), 3.10 (d, J = 12 Hz, 2 H, HCNCH), 3.49 (dd, J = 12 Hz,
2 H, HCOCH), 3.73 (m, 2 H, HCOCH), 6.92 (d, J = 8 Hz, 2 H,
m-H), 7.17 (d, J = 8 Hz, 2 H, o-H), 7.30 (m, 9 H, m-H and p-H in
PPh3), 7.52 (m, 6 H, o-H in PPh3) ppm. 31P NMR (101 MHz,
CDCl3, H3PO4): δ = 32.38 (s) ppm.
(2-Th)PdI(PPh3)(piperidine): Isolated complex. 1H NMR
(250 MHz, CDCl3, TMS): δ = 1.32 (m, 2 H, γCH2), 1.65 (br. t, 4
H, βCH2), 2.70 (ddd, J = 12 Hz, 2 H, HCNCH), 3.09 (s, 1 H, NH),
3.25 (d, J = 13.5 Hz, 2 H, HCNCH), 6.35 (d, J = 3.3 Hz, 1 H, 5-
H in Th), 6.72 (dd, J = 5, J = 3.3 Hz, 1 H, 4-H in Th), 7.10 (d, J
= 5 Hz, 1 H, 3-H in Th), 7.32 (m, 9 H, m-H and p-H in PPh3),
7.52 (m, 6 H, o-H in PPh3) ppm. 31P NMR (101 MHz, CDCl3,
H3PO4): δ = 30.72 (s) ppm.
[18] G. Faraone, V. Ricevuto, R. Romeo, M. Trozzi, J. Chem. Soc.
Dalton Trans. 1974, 1377–1380.
[19] This is in contrast to monobenzylamines [e.g. Me(PhCH2)NH]
which, when used in large excess, can displace the P(o-Tol)3
ligand in the dimers [ArPdX(P[o-Tol]3)]2 (X = I, Br, Cl) to gen-
erate bis(amine) ArPdX(Me[PhCH2]NH)2 complexes via the
intermediate mono(amine) complex ArPdX(Me[PhCH2]-
NH)(P[o-Tol]3). See: R. A. Widenhoefer, S. L. Buchwald, Or-
ganometallics 1996, 15, 3534–3542.
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Formation of ArPdXL(amine) Complexes by Substitution of a Phosphane Ligand
SHORT COMMUNICATION
[20] F. Paul, J. Patt, J. F. Hartwig, Organometallics 1995, 14, 3030–
3039.
[21] The reaction in Scheme 4 is reversible for benzylamines. The
geometry of the resulting complexes is not established. The am-
ine is supposed to be trans to the phosphane. R. A. Widenho-
efer, A. H. Zhong, S. L. Buchwald, Organometallics 1996, 15,
2745–2754.
[22] When a second isomer was formed and detected by its singlet
(Table 1), its integration was taken into account to determine
the equilibrium constant.
[23] The basicity scale is given in aqueous solution (pKa): piperidine
(11.12), iPr2NH (10.96), tBuNH2 (10.83), morpholine (8.21);
R. C. Weast (Ed.), Handbook of Chemistry and Physics, 52nd
ed., The Chemical Rubber Co., Ohio, USA, 1971/1972, p. D-
117.
trans to the leaving group can weaken the bond of the leaving
group in the ground state of the reactant. In complexes 1, the
aryl group and the halide are in a cis position to the leaving
group and would have a cis influence on the substitution. In
general, the cis influence is less effective than the trans influ-
ence.[25]
[25] T. G. Appleton, H. C. Clark, L. E. Manzer, Coord. Chem. Rev.
1973, 10, 335–422.
[26] For scrambling reactions, see: F. E. Goodson, T. I. Wallow,
B. M. Novak, J. Am. Chem. Soc. 1997, 119, 12441–12453.
[27] A scrambling reaction was also observed with trans-(4-NC–
C6H4)PdCl(PPh3)2, which suggests that the scrambling also de-
pends on the halide ligated to the PdII centre.
[28] P. Fitton, M. P. Johnson, J. E. McKeon, Chem. Commun. 1968,
6–7.
[24] It has been established that the ligand in a trans position to
the leaving group has a significant effect on the rate of the
substitution reactions (trans effect). Here we are discussing
thermodynamic factors (trans influence),[25] i.e. how the ligand
[29] D. R. Coulson, Chem. Commun. 1968, 1530–1532.
[30] P. Fitton, E. A. Rick, J. Organomet. Chem.1971, 28, 287–791.
Received May 19, 2004
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