Formation of (σ-alkenyl)- and (μ-vinylidene)palladium and -platinum complexes by oxidative addition of 4,4-dichloro-1,1 -diphenyl-2-azabuta-1,3-diene - The molecular structure of an unusual asymmetric (μ-vinylidene)Pd-Pd complex

Article abstract of DOI:10.1002/ejic.200390073

4,4-Dichloro-1,1-diphenyl-2-azabuta-1,3-diene (1) oxidatively adds to [Pd(PPh₃)4] and [Pt(C₂H₄)(PPh₃)2] giving rise to the σ-alkenyl complexes trans-[MCl{[C(Cl)=C(H)-N= CPh₂]}(PPh₃)₂] (2a: M = Pd; 2b: M = Pt). When 1 is treated with [Pd(PPh₃)₄] in a 1:2 ratio in refluxing toluene, the dimetallic μ-vinylidene complex [(PPh₃)ClPd{μ- [C=C(H)-N= CPh₂]}PdCl(PPh₃)₂] (3) is formed. In this fluxional compound, a PPh₃ ligands migrates in a reversible manner between the two Pd centers. Substitution of the PPh₃ ligands of 3 by 2 equiv. of Ph₂PCH₂PPh₂ affords the A-frame complex [ClPd(μ-dppm)₂{μ-[C=C(H)-N=CPh₂]}PdCl] (4). Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.

Full text of DOI:10.1002/ejic.200390073

FULL PAPER
Formation of (σ-Alkenyl)- and (µ-Vinylidene)palladium and -platinum
Complexes by Oxidative Addition of 4,4-Dichloro-1,1-diphenyl-2-azabuta-
1,3-diene ؊ The Molecular Structure of an Unusual Asymmetric
(µ-Vinylidene)Pd؊Pd Complex
[a]
[a]
[b]
[b]
´
Michael Knorr,* Gerard Schmitt,* Marek M. Kubicki, and Estelle Vigier
Keywords: Palladium / Vinylidene ligands / Platinum / Metal-metal interactions
4,4-Dichloro-1,1-diphenyl-2-azabuta-1,3-diene (1) oxidatively a PPh3 ligands migrates in a reversible manner between the
adds to [Pd(PPh3)4] and [Pt(C2H4)(PPh3)2] giving rise
to the σ-alkenyl complexes trans-[MCl{[C(Cl)=C(H)−N=
CPh2]}(PPh3)2] (2a: M = Pd; 2b: M = Pt). When 1 is treated
with [Pd(PPh3)4] in a 1:2 ratio in refluxing toluene, the dime-
tallic µ-vinylidene complex [(PPh3)ClPd{µ-[C=C(H)−N=
CPh2]}PdCl(PPh3)2] (3) is formed. In this fluxional compound,
two Pd centers. Substitution of the PPh3 ligands of 3 by 2
equiv. of Ph2PCH2PPh2 affords the A-frame complex [ClPd(µ-
dppm)2{µ-[C=C(H)−N=CPh2]}PdCl] (4).
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2003)
Introduction
dination of this compound. We present here the first ap-
plication of 1 in the organometallic chemistry of palladium
Due to the eminent role of palladium in organometallic and platinum.
synthesis and homogenous catalysis, several methods for
the formation of palladiumϪcarbon bonds have been de-
veloped.[1] Among them, the oxidative addition of alkyl and Results and Discussion
aryl halides to Pd0 complexes is common. It has been
Upon heating in toluene at 50 °C, complex 1 oxidatively
adds to [Pd(PPh3)4] to yield trans-[PdCl{[C(Cl)ϭ
C(H)ϪNϭCPh2]}(PPh3)2] (2a) (Scheme 1). The expected
shown that vinyl chlorides may also oxidatively add to
[Pd(PPh3)4] giving rise to σ-alkenyl complexes of the type
trans-[PdCl{[C(R)ϭCR2]}(PPh3)2].[2] In the course of our
earlier studies in the field of organic 1,3-dipolar cycloaddi-
tion reactions, we prepared the new dichloro vinyl-like
compound 4,4-dichloro-1,1-diphenyl-2-azabuta-1,3-diene
(1).[3,4] This compound exhibits some promising features for
coordination to inorganic and/or organometallic units as it
bears a conjugated π-system and a potentially reactive Cϭ
N double bond. Furthermore, the basic iminium nitrogen
atom may act as a potential donor for coordination of fur-
ther metal centres to assemble (hetero)dimetallic systems.
The group-10 late transition metal (Pd, Pt) complexes seem
to be particularly good candidates for activation and coor-
[‡]
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
[a]
´
´
Laboratoire de Chimie des Materiaux et Interfaces Universite
´
´
de Franche-Comte, Faculte des Sciences et des Techniques
16 Route de Gray, 25030 Besancon Cedex, France
¸
E-mail: michael.knorr@univ-fcomte.fr
[b]
`
`
d’Electrosynthese
Laboratoire
de
Synthese
et
´
´
Organometalliques (UMR, 5632) Universite de Bourgogne,
´
Faculte des Sciences et des Techniques
9 Av. A. Savary, 21000 Dijon Cedex, France
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
Scheme 1
514
 2003 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim 1434Ϫ1948/03/0203Ϫ0514 $ 20.00ϩ.50/0 Eur. J. Inorg. Chem. 2003, 514Ϫ517

Formation of (σ-Alkenyl)- and (µ-Vinylidene)palladium and -platinum Complexes
FULL PAPER
trans orientation of the two PPh3 ligands follows from the bond,[6,7] therefore Pd(1) may be described as five-coordin-
31P{1H} NMR spectrum, which displays a singlet at δ ϭ ate. In contrast, Pd(2) is ligated with Cl(2) and only one
23.6 ppm. In order to obtain an unambiguous assignment phosphane ligand. To achieve the necessary 16-electron
of the stereochemistry of 2a, the Pt analogue trans- count, the metalϪmetal interaction is best described as a
[PtCl{[C(Cl)ϭC(H)ϪNϭCPh2]}(PPh3)2] (2b) was prepared dative Pd1ǞPd2 bond.
by treating 1 in toluene with [Pt(C2H4)(PPh3)2] at 60 °C.
To the best of our knowledge, no related PdϪPd com-
The 1H NMR spectrum of 2b indicates that the regioisomer pound has been structurally characterized to date. However,
with the hydrogen atom on C-β in the cis position relative the overall core structure in 3 is quite similar to that
to the platinum atom is formed exclusively.[5] Since the found in
a
platinum derivative [(PEt3)BrPt{µ-[Cϭ
chemical shifts for the olefinic hydrogen atom of 2a (δ ϭ C(H)ϪPh]}PtBr(PEt3)2].[8] Compound 3 is fluxional in so-
3
6.21 ppm) and 2b [δ ϭ 6.19 ppm, Jcis(PtϪH) ϭ 27 Hz] are lution, since a very broad singlet resonance at δ ϭ 27.4 ppm
quite close, we suggest a (Z) configuration for these com- is observed in the 31P{1H} NMR spectrum at 293 K, which
plexes.
sharpens upon heating to 323 K. At low temperature
When 1 is treated with [Pd(PPh3)4] in a 1:2 ratio in re- (223 K), the spectrum consists of distinct triplet and doub-
fluxing toluene, a two-centre, three-fragment oxidative ad- let resonances in a 1:2 ratio at δ ϭ 34.0 and 24.8 ppm (see
dition of both vinylideneϪchloride bonds across two Pd Figure 2). Addition of 2 equiv. of PPh3 (at 293 K) to a
centers occurs affording the dimetallic µ-vinylidene complex sample of 3 has no influence on the chemical shift or shape
[(PPh3)ClPd{µ-[CϭC(H)ϪNϭCPh2]}PdCl(PPh3)2] (3) in of the resonance.
49% yield {together with small amounts of 2a and trans-
[PdCl2(PPh3)2]}. Suitable crystals of 3 for an X-ray diffrac-
tion study (Figure 1) were grown as red needles from a tolu-
ene/heptane solution. Surprisingly, this dimetallic complex
possesses two different coordination spheres around each
palladium atom; Pd(1) is ligated by P(1), P(2), and Cl(1),
and the two PdII centers are bridged by C(1) in an slightly
asymmetric manner [Pd(1)ϪC(1) 2.031(3), Pd(2)ϪC(1)
˚
1.910(3) A]. The close contact between Pd(1) and Pd(2) of
˚
2.6785(3) A is indicative of the existence of a metalϪmetal
Figure 2. 31P{1H} NMR spectrum of 3 recorded in CDCl3 at 223 K
(a) and 313 K (b)
This fluxionality may be explained by a nondissociative
intramolecular flipping[9a] of one PPh3 ligand between
Pd(1) and Pd(2) with concomitant switching of the vector
Ǟ
ǟ
of the dative bond, resulting in an averaged 3 3Ј equilib-
rium on the NMR time scale. Note that this hypothesis in-
volving the intermediacy of a µ-PPh3 ligand is supported by
Figure 1. View of the crystal structure of 3; selected bond lengths
˚
the structural characterization of a stable Rh(µ-PMe3)2Rh
complex.[9b,9c] Furthermore, a related reversible and non-
dissociative migration of a PR3 ligand has been studied in
detail very recently for the dimetallic system [{(η5-
C5Me5)Ru}2(PR3)(µ-H)2].[9d] The ligation of Pd(2) by just
one PPh3 ligand is probably due to steric reasons. To avoid
steric overcrowding by four bulky PPh3 ligands in a mutual
[A] and angles [°]: PdϪPd 2.6785(3), Pd(1)ϪP(1) 2.3375(9),
Pd(1)ϪP(2) 2.3430(9), Pd(2)ϪP(3) 2.2399(9), Pd(1)ϪC(1) 2.031(3),
Pd(2)ϪC(1) 1.910(3), Pd(1)ϪCl(1) 2.3897(9), Pd(2)ϪCl(2)
2.3887(9), C(1)ϪC(2) 1.339(4), NϪC(2) 1.407(40), NϪC(3)
1.302(4);
Cl(1)ϪPd(1)ϪC(1)
173.27(9),
P(1)ϪPd(1)ϪP(2)
174.82(3), P(1)ϪPd(1)ϪC(1) 93.74(9), P(2)ϪPd(1)ϪC(1) 91.28(9),
P(3)ϪPd(2)ϪC(1) 104.33(10), Pd(2)ϪC(1)ϪPd(1) 85.58(13),
C(1)ϪPd(1)ϪPd(2) 45.32(9), C(1)ϪPd(2)ϪPd(1) 49.10(10),
C(1)ϪPd(2)ϪCl(2) 155.54(10), C(1)ϪC(2)ϪN 121.5(3)
Eur. J. Inorg. Chem. 2003, 514Ϫ517
515

M. Knorr, G. Schmitt, M. M. Kubicki, E. Vigier
FULL PAPER
Preparation of trans-[PtCl{[C(Cl)؍C(H)؊N؍CPh2]}(PPh3)2] (2b):
A mixture of [Pt(C2H4)(PPh3)2] (750 mg, 1 mmol) and 1 (304 mg,
1.1 mmol) in toluene (20 mL) was heated to 60 °C for 14 h. The
resulting clear yellowish solution was concentrated to ca. 10 mL
and layered with heptane. After keeping at Ϫ25 °C, 2b precipitated
as an off-white, air-stable, microcrystalline solid, which was dried
in vacuo. Yield: 79% (778 mg). 1H NMR: δ ϭ 6.19 [s, 1 H, CϭCH,
3Jcis(Pt-H) ϭ 27 Hz], 6.94Ϫ7.92 (m, 23 H, phenyl) ppm. 31P{1H}
NMR: δ ϭ 24.8 (s, 1JPt,P ϭ 3015 Hz). 195Pt{1H} NMR: δ ϭ Ϫ2641
trans arrangement on each Pd center, steric repulsion is
minimized by dissociation of one of the four PPh3 ligands,
followed by an electronic quasi saturation of Pd(2) (up to
16 eϪ) by formation of a dative PdǞPd bond during forma-
tion of 3. This hypothesis is corroborated by the observa-
tion that after addition of 2 equiv. of dppm, the three PPh3
ligands are instantaneously replaced by two diphosphane
ligands giving complex 4 quantitatively (31P{1H} NMR
monitoring, Scheme 2). As expected for an unsymmetrical
1
(t, JPt,P ϭ 3015 Hz) ppm. C51H41Cl2NP2Pt (995.85.): calcd. C
dipalladium A-frame complex,[10Ϫ12] 4 displays an AAЈBBЈ 61.51, H 4.15, N 1.41; found C 61.89, H 4.02, N 1.21.
pattern in the 31P{1H} NMR spectrum centered at δ ϭ
Preparation of [(PPh3)ClPd{µ-[C؍C(H)؊N؍CPh2]}PdCl(PPh3)2]
16.3 ppm. This asymmetry may be explained by the
(3): Complex 1 (55 mg, 0.2 mmol) was added to a suspension of
coplanar orientation of the µ-azabutadiene unit with the
ClϪPdϪCµϪPdϪCl array, thus rendering the two Pd
environments nonequivalent.
[Pd(PPh3)4] (462 mg, 0.4 mmol) in toluene (10 mL) and the mixture
heated under reflux for 5 h. The solvent was then evaporated and
the residue was washed with Et2O (5 mL). The remaining solid was
redissolved in warm toluene and layered with heptane. A mixture
of red, air-stable, needle-shaped crystals of 3 and yellow crystals of
2a and of trans-[PdCl2(PPh3)2] co-crystallized; they were separated
manually. Yield: 49% (134 mg). 1H NMR: δ ϭ 6.30 (s, 1 H, Cϭ
CH), 6.32Ϫ7.98 (m, 55 H, phenyl) ppm. 31P{1H} NMR (223 K):
3
3
δ ϭ 24.8 (d, 2 P, JP,P ϭ 23 Hz), 34.0 (t, 1 P, JP,P ϭ 23 Hz) ppm.
C69H56Cl2NP3Pd2·C7H8 (1367.99): calcd. C 66.73, H 4.72, N 1.02;
found C 66.98, H 4.54, N 0.97.
Preparation of [ClPd(µ-dppm)2{µ-[C؍C(H)؊N؍CPh2]}PdCl] (4):
To a solution of 3 (14 mg, 0.01 mmol) in CH2Cl2 (2 mL) was added
dppm (8 mg, 0.021 mmol). The resulting orange solution was
stirred for a further 10 min, and then the solvent was removed un-
der reduced pressure. The residue was rinsed with Et2O (2 mL) and
than dried to afford orange, air-stable 4 in almost quantitative yield
(12 mg). 1H NMR: δ ϭ 2.55 (m, 2 H, PCHAP), 3.02 (m, 2 H,
PCHBP), 6.53 (m, 1 H, CϭCH), 6.70Ϫ7.94 (m, 50 H, phenyl) ppm.
1H{31P} NMR: δ ϭ 2.55 (d, 2 H, PCHAP), 3.02 [d, 2 H, PCHBP,
J(HA-HB) ϭ 12.9 Hz], 6.53 (s, 1 H, CϭCH), 6.70Ϫ7.94 (m, 50 H,
phenyl) ppm. 31P{1H} NMR: δ ϭ 16.3 (m, AAЈBBЈ pattern) ppm.
C65H55Cl2NP4Pd2 (1257.78): calcd. C 62.07, H 4.41, N 1.12; found
C 61.68, H 4.24, N 0.96.
Scheme 2
The potential of 1 and its derivatives as pincer ligands for
cyclometallation and carbonϪcarbon coupling reactions as
well for synthesis of other (hetero)dimetallic compounds is
currently under investigation.[13]
Experimental Section
X-ray Crystal Structure Determination of 3·Toluene: A small (0.10
ϫ 0.08 ϫ 0.05 mm) irregularly shaped solvated (toluene) single
crystal of 3 was mounted on a Nonius Kappa CCD diffractometer.
The unit cell determination and intensity data collection were car-
General: All reactions were performed in Schlenk-tube flasks under
purified nitrogen. Solvents were dried and distilled under nitrogen
before use: toluene and heptane from sodium, dichloromethane
˚
ried out with Mo-Kα radiation (λ ϭ 0.71073 A) at 120 K. The
1
from P4O10. The H, 31P{1H} NMR, and 195Pt{1H} NMR spectra
measured intensities were reduced with the DENZO program.[14]
The structure was solved by both Patterson and direct methods
using the routines incorporated in SHELXS-97.[15] The asymmetric
unit contains one dinuclear complex and one toluene molecule. The
model was further refined with SHELXL-97.[15]
were recorded with a Bruker Avance 300 MHz spectrometer
(300.13, 121.49 MHz, and 64.52 MHz for 1H, 31P, and 195Pt, re-
spectively). Phosphorus chemical shifts are referenced to 85%
H3PO4 in H2O with downfield shifts reported as positive. 195Pt
chemical shifts are referenced to external K2PtCl4 in water with
downfield chemical shifts reported as positive. All NMR spectra
were recorded in CDCl3.
Crystallographic Data: C76H64Cl2NP3Pd2 (M ϭ 1367.89): mono-
clinic, space group P21/n; a ϭ 16.2461(2), b ϭ 25.3368(3), c ϭ
3
˚
˚
16.7569(2) A, β ϭ 108.934(1)°, V ϭ 6524.34(14) A , Z ϭ 4, ρcalcd. ϭ
1.393 g·cmϪ3, F(000) ϭ 2792; 35364 measured reflections in the
scan range 5.4° Ͻ 2θ Ͻ 61.0°, of which 18823 independent and
9156 observed with I Ͼ 2σ(I) were used in the structure solution
and refinement for 757 parameters; R1 ϭ Σ|Fo Ϫ Fc|/Σ|Fo| ϭ 0.049
[I Ͼ 2σ(I)], wR2 ϭ [Σw(F2o Ϫ Fc2)2/ΣwF4o]1/2 ϭ 0.101 (all data),
S(GoF) ϭ 0.929; anisotropic refinement for non-hydrogen atoms;
Preparation of trans-[PdCl{[C(Cl)؍C(H)؊N؍CPh2]}(PPh3)2] (2a):
Complex 1 (122 mg, 0.44 mmol) was added to a suspension of
[Pd(PPh3)4] (462 mg, 0.4 mmol) in toluene (15 mL) and the mixture
warmed to 50 °C for 5 h. The resulting clear, orange solution was
then concentrated to 8 mL, and layered with heptane. After keeping
overnight in a refrigerator, 2a crystallized. The yellow microcrystal-
line compound was rinsed with hexane (4 mL) and dried in vacuo. hydrogen atoms in idealized (riding model) geometries. The highest
Yield: 66% (241 mg). 1H NMR: δ ϭ 6.21 (s, 1 H, CϭCH),
residual electron-density peak in the differential Fourier map of
6.49Ϫ7.86 (m, 40 H, phenyl) ppm. 31P{1H} NMR: δ ϭ 23.6 (s) 0.98 e·A is quasi-symmetrically located between the heavy palla-
Ϫ3
˚
˚
˚
ppm. C51H41Cl2NP2Pd (907.15): calcd. C 67.53, H 4.56, N 1.54;
found C 67.98, H 4.56, N 1.90.
dium atoms (1.38 A from Pd1 and 1.40 A from Pd2). CCDC-
185833 (3) contains the supplementary crystallographic data for
516
Eur. J. Inorg. Chem. 2003, 514Ϫ517

Formation of (σ-Alkenyl)- and (µ-Vinylidene)palladium and -platinum Complexes
FULL PAPER
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Acknowledgments
´
`
´
The Ministere de la Recherche et de la Technologie, la Region de
´
Franche-Comte and the CNRS are gratefully thanked for finan-
cial support.
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