Synthesis of the diphenylacetylene-based, tetra-amine ligand 1,2-bis(3,5-bis[(dimethylamino)methyl]phenyl)acetylene by palladium-catalysed cross-coupling: Isolation and crystal structure of the catalyst trans-(3,5-bis[(dimethylamino)methyl]phenyl)bis(trip

Article abstract of DOI:10.1016/S0022-328X(99)00665-8

Reaction of 3,5-bis[(dimethylamino)methyl]phenyl iodide with 3,5-bis[(dimethylamino)methyl]phenylacetylene in diethylamine in the presence of bis(triphenylphosphine)palladium(II) dichloride (3.6 mol%) and copper(I) iodide (3.0 mol%) gave 1,2-(bis(3,5-bis[

Full text of DOI:10.1016/S0022-328X(99)00665-8

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 598 (2000) 24–27
Synthesis of the diphenylacetylene-based, tetra-amine ligand
1,2-bis(3,5-bis[(dimethylamino)methyl]phenyl)acetylene by
palladium-catalysed cross-coupling: isolation and crystal structure
of the catalyst trans-(3,5-bis[(dimethylamino)methyl]-
phenyl)bis(triphenylphosphine)palladium(II) iodide
Marieke P.R. Spee a, Bart Ader a, Pablo Steenwinkel a, Huub Kooijman b,
Anthony L. Spek b,1, Gerard van Koten a,*
a Department of Metal-Mediated Synthesis, Debye Institute, Utrecht Uni6ersity, Padualaan 8, 3584 CH Utrecht, The Netherlands
b Department of Crystal and Structural Chemistry, Bij6oet Center for Biomolecular Research, Utrecht Uni6ersity, Padualaan 8,
3584 CH Utrecht, The Netherlands
Received 17 September 1999; received in revised form 25 October 1999
Abstract
Reaction of 3,5-bis[(dimethylamino)methyl]phenyl iodide with 3,5-bis[(dimethylamino)methyl]phenylacetylene in diethylamine
in the presence of bis(triphenylphosphine)palladium(II) dichloride (3.6 mol%) and copper(I) iodide (3.0 mol%) gave 1,2-(bis(3,5-
bis[(dimethylamino)methyl]phenyl)acetylene (1) in 82% yield. The palladium catalyst was recovered in 93% yield as trans-(3,5-bis-
[(dimethylamino)methyl]phenyl)bis(triphenylphosphine)palladium(II) iodide (2). The crystal structure of 2 shows that the coordi-
nation geometry of the palladium is distorted square-planar. No inter- or intramolecular interactions between the N-donor atoms
and the Pd are observed. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Palladium; Catalysis; Sonogashira coupling; Tetraamine ligand; X-ray
1. Introduction
2. Results and discussion
The compound 1,2-(bis(3,5-bis[(dimethylamino)-
methyl]phenyl)acetylene (1) (see Scheme 1), is a repre-
sentative of a new class of ligand structures from which
bimetallic compounds might be obtained in which the
metal centres are connected by p-conjugation through a
dianionic organic bridge [1]. We describe here its prepa-
ration via the palladium-catalysed cross-coupling of a
terminal alkyne with the appropriate aryl halide, usu-
ally referred to as the Sonogashira coupling [2].
3,5-Bis[(dimethylamino)methyl]phenylacetylene was
reacted with 3,5-bis[(dimethylamino)methyl]phenyl io-
dide in a 1:1 molar ratio in diethylamine in the presence
of catalytic amounts of bis(triphenylphosphine)pal-
ladium(II) dichloride and copper(I) iodide (Scheme 1).
The cross-coupling product 1,2-(bis(3,5-bis[(dimethyl-
amino)methyl]phenyl)acetylene (1) was isolated as a
solid in 82% yield.
Interestingly, the palladium catalyst was recovered as
trans - (3,5 - bis[(dimethylamino)methyl]phenyl)bis(tri-
phenylphosphine)palladium(II) iodide (2), (see Scheme
1). The isolated yield of 2 was 93% based on the
starting amount of PdCl2(PPh3)2 catalyst. This points to
a quantitative conversion of PdCl2(PPh3)2. Although
several trans-Pd(X)(Ar)(PPh3)2 complexes have been
reported, mainly with X=Cl, or Br, and with
* Corresponding author. Fax: +31-30-2523615.
E-mail address: g.vankoten@chem.uu.nl (G. van Koten)
1 Crystallographic correspondence to this author.
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00665-8

M.P.R. Spee et al. / Journal of Organometallic Chemistry 598 (2000) 24–27
25
phenyl groups bearing substituents mainly at the ortho-
position [3], little is known of such palladium com-
plexes with X=I and meta-substituted phenyl groups.
So far, only one complex is known, (cis-[Pt(PEt3)2-
{C6H3(CH2NMe2)2-3,5}2] (3), in which the (dimethyl-
amino)methyl-substituents of the 3,5-bis[(dimethyl-
amino)methyl]phenyl anion are in a meta position to
the metalꢀcarbon bond [4]. Since the formation of 2
potentially opens pathways to multimetallic species via
a 4-lithiation/transmetallation sequence, as has been
demonstrated for 3, its crystal structure has been eluci-
dated.
Complex 2 was obtained as a deep-red crystalline
material from a pentane solution. The crystals could be
kept in air for several months without any observable
degradation. The crystal structure of 2 shows that the
coordination geometry of the palladium is distorted
square-planar (see Fig. 1) with P(1)ꢀPdꢀP(2) and
C(1)ꢀPdꢀI bond angles of 174.93(2) and 173.40(7)°,
respectively. The PdꢀP(1) and PdꢀP(2) distances
Fig. 1. ORTEP drawing (50% probability atomic displacement ellip-
soids) of 2. Hydrogen atoms have been omitted for clarity.
,
(2.3262(7) and 2.3238(7) A, respectively) are in the
range expected for trans-positioned triphenylphosphine
,
ligands (2.319–2.342 A) [5]. Both the PdꢀI distance
(2.6968(4) A) and the PdꢀC(1) distance (2.025(2) A)
agree well with those reported for trans-iodo(methyl-
,
,
thiomethylphenyl)bis(triphenylphosphine)palladium(II)
,
[3e] (PdꢀI (2.692(1), PdꢀC 2.029(6) A) in which likewise
the PdꢀI bond is trans to a C sp2 donor atom of high
trans influence. No inter- or intramolecular interactions
between the N-donor atoms and Pd were observed.
Compound 2 is probably formed by oxidative addi-
tion of 3,5-bis[(dimethylamino)methyl]phenyl iodide to
a catalytically active 14-electron complex Pd(PPh3)2.
In a separate experiment, 2 was obtained quantitative-
ly from the reaction of 3,5-bis[(dimethylamino)-
methyl]phenyl iodide with Pd(PPh3)4 in toluene. It is
known that Pd(PPh3)2 can be formed from PdCl2-
(PPh3)2 by reduction with in situ generated copper(I)
acetylide [2a,6]. In the present catalytic cycle Pd(PPh3)2
will be regenerated by reductive elimination of 1 from
an aryl-alkynyl palladium(II) derivative. The stability
of the reaction mixture with respect to separation of
zerovalent palladium metal may arise from the presence
of alkynyl groupings in both starting and product
compounds. This stability then allows the recovery of
the palladium as the iodide salt 2 from the reaction
medium.
3. Experimental
3.1. General
All reactions and handling were performed under an
inert atmosphere of dinitrogen. Melting points were
determined in sealed capillaries. NMR spectra were
recorded on Varian Inova 200 and 300 spectrometers.
Elemental analyses were performed by Dornis und
Scheme 1.

26
M.P.R. Spee et al. / Journal of Organometallic Chemistry 598 (2000) 24–27
Kolbe, Mikroanalytisches Laboratorium (Mu¨hlheim,
Germany). All chemicals were purchased from Acros.
Kieselgel 60 was purchased from Merck. CuI and
PdCl2(PPh3)2 were prepared according to literature pro-
cedures [4,5]. Dry solvents were freshly distilled from
sodium sand under a dinitrogen atmosphere.
ArCH2), 2.27, (s, 12H, NMe2). 13C-NMR (CDCl3, 75
MHz): 139.2, 130.9, 129.6, 123.0 (Ar), 89.3
(ArCꢁCAr), 63.9 (ArCH2), 45.4 (NMe2).
l
3.3. Crystal structure determination of 2
Crystallographic data: C48H49IN2P2Pd, space group
P1, a=11.9594(12), b=13.9118(18), c=14.2892(18)
(
3.2. Synthesis of 1,2-(bis(3,5-bis[(dimethylamino)-
methyl]phenyl)acetylene (1) and isolation of
trans-(3,5-bis[(dimethylamino)methyl]phenyl)bis-
(triphenyl-phosphine)palladium(II) iodide (2)
,
A, h=90.511(5), i=96.737(8), k=96.951(7)°, V=
3
2343.0(5) A , Z=2, Dcalc. =1.345 g cm−3, Mw=
,
949.20, v (Mo–Ka)=1.16 mm−1, T=150 K, deep-red
crystal, 0.2×0.2×0.3 mm. X-ray data were collected
on a Nonius Kappa CCD [Mo–Ka, Rotating anode,
3,5-Bis[(dimethylamino)methyl]phenyl iodide (4.99 g,
15.7 mmol) and 3,5-bis[(dimethylamino)methyl]phenyl-
acetylene (3.40 g, 15.7 mmol) were dissolved in diethyl-
amine (100 ml). CuI (0.08 g, 0.44 mmol) and
PdCl2(PPh3)2 (0.40 g, 0.57 mmol) were added to this
solution. After 6 days of stirring at room temperature,
the solvent was evaporated in vacuo. The residue was
dissolved in a diethyl ether–diethylamine (v/v=95/5)
mixture and then filtered over a short column of
Kieselgel 60. After evaporation of the solvent from the
filtrate in vacuo the resulting residue was dissolved in
pentane (100 ml). Immediately a small amount of black
precipitate was formed. This mixture was allowed to
stand for 3 days at room temperature, after which red
crystals of 2 had formed from the deep-red solution.
Umax=27.5°]. The structure was solved using SHELXS-
86/PATT and refined on F2 with SHELXL-97-2. Hydro-
gen atoms were taken into account at calculated
positions and refined riding on their carrier atoms. The
structure was found to contain a void at an inversion
centre with poorly defined electron density. The contri-
bution of this density was taken into account using the
PLATON/SQUEEZE procedure. The integrated den-
sity in the solvent area amounts to 45 electrons, proba-
bly due to the presence of one disordered pentane
molecule of crystallisation per unit cell. Convergence
was reached at R=0.0330 (9082 reflections with I\
2|(I)), wR2=0.0721 (10363 unique reflections), 491
parameters, S=1.073, −0.71BDzB0.54 electron
−3
,
A
.
1
Yield of 2: 0.5 g (0.53 mmol, 93% of Pd). H-NMR
(CD2Cl2, 300 MHz): l 7.57–7.50 (m, 12H, ortho-H
PPh3), 7.40–7.27 (m, 18H, meta/para-H PPh3), 6.55 (s,
2H, ortho-ArH), 6.24 (s, 1H, para-ArH), 2.72 (s, 4H,
ArCH2), 1.95, (s, 12H, NMe2). 31P-NMR (CDCl3, 80
MHz), 200 MHz): l 24.0 (PPh3). 13C-NMR (CD2Cl2,
75 MHz): l 135.2–134.8 (m, PPh3), 130.0–130.2
(d, PPh3), 128.2–127.6 (m, PPh3), 134.7, 130.4, 123.8
(Ar), 64.5 (ArCH2), 45.2 (NMe2). Anal. Calc. for
C48H49N2P2PdI: C, 60.74; H, 5.20; N, 2.95. Found: C,
60.86; H, 5.28; N, 2.88%.
4. Supplementary material
Crystallographic data for the structural analysis of 2
have been deposited with the Cambridge Crystallo-
graphical Data Centre, CCDC no. 133325.
Acknowledgements
The remaining solution was decanted and filtered
over a short alumina column. The solvent was evapo-
rated in vacuo after which methanol (50 ml) was added.
To this solution a solution of HBF4 in water (25 ml,
35%) was added. The mixture was stored at −30°C for
a day, after which a yellow–white solid had precipi-
tated. The solid was isolated and washed first with cold
methanol (25 ml) and then with diethyl ether (15 ml).
The resulting white solid was dissolved in aqueous
This work has been performed under the auspices of
NIOK, the Netherlands Institute for Catalysis Re-
search, Lab Report No. UU 94-AH.
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