A new homobimetallic arenediyl diplatinum(II) unit as building block for macromolecular synthesis. X-ray crystal structure of [C6H2{CH2NMe2} 2-1,5-{PtCl(PPh3)}2-2,4]

Article abstract of DOI:10.1016/S0022-328X(01)01176-7

Treatment of the diaminobenzene [C₆H₄{CH₂NMe₂}₂-1,3] (NCN-H, 1) with one or two equivalents of cis-PtCl₂(DMSO)₂ leads to exclusive formation of the doubly cycloplatinated species

Full text of DOI:10.1016/S0022-328X(01)01176-7

Journal of Organometallic Chemistry 640 (2001) 166–169
www.elsevier.com/locate/jorganchem
A new homobimetallic arenediyl diplatinum(II) unit as building
block for macromolecular synthesis. X-ray crystal structure of
[C6H2{CH2NMe2}2-1,5-{PtCl(PPh3)}2-2,4]
Michel D. Meijer a, Arjan W. Kleij a, Martin Lutz b, Anthony L. Spek b,*,
Gerard van Koten a,*
a Debye Institute, Department of Metal-Mediated Synthesis, 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 11 June 2001; accepted 28 July 2001
Abstract
Treatment of the diaminobenzene [C6H4{CH2NMe2}2-1,3] (NCN-H, 1) with one or two equivalents of cis-PtCl2(DMSO)2 leads
to exclusive formation of the doubly cycloplatinated species [C6H4{CH2NMe2}2-1,5-{PtCl(DMSO)}2-2,4] (3), which upon addition
of triphenylphosphine yields the bisphosphine adduct [C6H4{CH2NMe2}2-1,5-{PtCl(PPh3)}2-2,4] (4). The X-ray molecular
structure of 4 revealed the presence of highly distorted square planar Pt(II) centers which is caused by close proximity of the two
phosphine donor ligands. Complexes of type 3 can be regarded as suitable starting materials for the directional build-up of larger
macromolecular structures. © 2001 Published by Elsevier Science B.V.
Keywords: Arylamine ligands; Building blocks; CꢀH activation; Platinum
1. Introduction
centers onto aromatic ligands has been developed [4,6].
Herein, we report our first results on the synthesis of a
doubly cycloplatinated diaminoarene ligand by treat-
ment of C6H4{CH2NMe2}2-1,3 (1, NCN-H) with cis-
PtCl2(DMSO)2, and the subsequent exchange of the
pendant dimethylsulfoxide ligands for triphenylphos-
phine donor ligands.
Macromolecular synthesis with organometallic com-
plexes is a field of research that is increasingly investi-
gated with the ultimate goal of creating novel materials
with unprecedented properties [1]. Prerequisites for the
build up of large metal-containing structures seem to be
the synthetic availability and stability of such metalated
synthons [2]. Additionally, these organometallic com-
plexes should include weak donor ligands which upon
exchange with polydentate Lewis bases can give rise to
self-assembled structures. Recently, the preparation of
metalated (N,)C,N- [3,4] or S,C,S-chelating [5] aryl
ligands suitable as fragments of larger synthetic
supramolecules has been reported. Simultaneously, the
use of platinum(II) dimethylsulfoxides as mild and ver-
satile metalating reagents for introduction of Pt(II)
2. Results and discussion
2.1. Synthesis and characterization of diplatinated species
Direct cycloplatination of the NCN-H ligand (1) with
cis-PtCl2(DMSO)2 in a 1:1 molar ratio was initially
aimed at the activation of the 1-position (Ha, Scheme
1), which would afford known 2. To this end, equimo-
lar amounts of cis-PtCl2(DMSO)2 and 1 (Fig. 1) were
mixed in refluxing MeOH in the presence of NaOAc as
an external base. After initial dissolution of the plat-
inum salt, a white precipitate was formed, which was
isolated (48% yield) and characterized by NMR spec-
* Corresponding authors. Tel.: +31-30-2533120; fax: +31-30-
2523615 (G. van Koten).
E-mail addresses: a.l.spek@chem.uu.nl (A.L. Spek), g.vankoten@
chem.uu.nl (G. van Koten).
0022-328X/01/$ - see front matter © 2001 Published by Elsevier Science B.V.
PII: S0022-328X(01)01176-7

M.D. Meijer et al. / Journal of Organometallic Chemistry 640 (2001) 166–169
167
1
troscopy. The H-NMR spectrum displayed the pres-
Complex 3 proved to be rather insoluble in common
organic solvents. Therefore, a PPh3-for-DMSO ligand
exchange in CH2Cl2 was carried out. This procedure
afforded the bisphosphine complex 4 in almost quanti-
tative yield as white needles. Complex 4 was analyzed
using multinuclear NMR spectroscopy, elemental
analyses and also by a single crystal structure determi-
nation (see Section 2.2). Of particular note is the high
field shift of ArꢀHb positioned at 5.77 ppm (cf., 8.10
ppm in 3). It seems likely that this high field shift arises
from specific shielding caused by the y-electron density
of the phenyl rings of each of the PPh3 ligands in a
close proximity to Hb. The proposed trans-position of
both phosphine ligands (with respect to the NMe2
donor fragment) in 4 is supported by 31P-NMR spec-
troscopy, which shows a single singlet flanked by plat-
ence of a single organometallic product, which to our
surprise was identified as the doubly platinated NCN
derivative [C6H2{CH2NMe2}2-1,5-{PtCl(DMSO)}2-2,4]
1
(3). Illustrative in the H-NMR spectrum of 3 is the
presence of a low-field, singlet resonance at 8.10 ppm
with platinum couplings (3J(PtꢀH)=51.8 Hz), which
was attributed to Hb (Scheme 1). Additionally, Ha was
observed as a single resonance at 6.78 ppm.
Remarkably, no mono-metalated species were de-
tected. Earlier results in analogous palladation reac-
tions of the NCN-H ligand with Pd(OAc)2 and
Li2[PdCl4] also yielded biscyclometalated complexes
[3d], [7]. These results suggest strongly that the interme-
diate monometalated species is more susceptible to
electrophilic metalation then NCN-H itself, affording
exclusively the bismetalated product. Moreover, the
observed regioselectivity suggests that the 1-position of
the NCN ligand is more sterically hindered with respect
to the 3- and 5-position [8]. We also carried out the
analogous cycloplatination reaction of NCN-H (1) in
the presence of two equivalents of the platinum(II) salt.
As expected, 3 was formed selectively (78% isolated
yield) and no other platinum species could be detected.
1
inum satellites at 15.8 ppm, J(PtꢀP)=4377 Hz. This
coupling constant closely relates to previously reported
data on similar complexes [4].
2.2. X-ray crystal structure of 4
Compound 4 was subjected to an X-ray crystal struc-
ture determination. The molecular structure is shown in
Scheme 1. Cycloplatination of the NCN-H ligand (1). Reagents and conditions: (i) PtCl2(DMSO)2, NaOAc, MeOH, 65 °C; (ii) PPh3, CH2Cl2.
Fig. 1. Displacement ellipsoid plot (50% probability level) of the molecular structure of 4, with the adopted numbering scheme. All hydrogen
,
atoms have been omitted for clarity. Selected bond lengths (A) and angles (°): Pt(1)ꢀCl(1) 2.4007(8), Pt(1)ꢀP(1) 2.2242(7), Pt(1)ꢀN(1) 2.141(3),
Pt(1)ꢀC(1) 2.016(3), Pt(2)ꢀCl(2) 2.4007(6), Pt(2)ꢀP(2) 2.2268(7), Pt(2)ꢀN(2) 2.159(2), Pt(2)ꢀC(3) 2.009(2), C(1)ꢀPt(1)ꢀN(1) 80.02(10),
N(1)ꢀPt(1)ꢀCl(1) 90.70, Cl(1)ꢀPt(1)ꢀP(1) 90.68(3), P(1)ꢀPt(1)ꢀC(1) 98.75(8), C(1)ꢀPt(1)ꢀCl(1) 169.58(8), N(1)ꢀPt(1)ꢀP(1) 177.68(6), C(3)ꢀPt(2)ꢀP(2)
96.83(7), P(2)ꢀPt(2)ꢀCl(2) 94.38(2), Cl(2)ꢀPt(2)ꢀN(2) 90.40(6), N(2)ꢀPt(2)ꢀC(3) 79.99(9), C(3)ꢀPt(2)ꢀCl(2) 165.12(7), N(2)ꢀPt(2)ꢀP(2) 170.54(6).

168
M.D. Meijer et al. / Journal of Organometallic Chemistry 640 (2001) 166–169
Fig. 1. Relevant bond angles and distances have been
deposited as Section 5.
The two platinum centers are positioned opposite to
The starting materials cis-PtCl2(DMSO)2 [6] and NCN-
H (1) [9] were prepared according to literature. NMR
spectroscopic measurements were carried out on a
Varian Inova 300 MHz spectrometer at room tempera-
ture (r.t.). Chemicals shifts are in ppm and referenced
to residual solvent resonances. Elemental analyses were
performed by Dornis and Kolbe, Mikroanalytisch
Labor, Mu¨lheim a/d Ruhr, Germany.
,
the central arene plane, 0.221(1) A above the plane for
,
Pt1 and 0.253 A below the plane for Pt2, respectively.
They are in distorted planar environments with dihe-
dral angles of 5.15(9) and 14.06(11)° between the
NꢀPtꢀC and PꢀPtꢀCl planes for Pt1 and Pt2, respec-
tively. This distortion is caused by the strain of the two
five membered chelate rings. Interestingly, these chelate
rings have different conformations: the first ring is best
4.2. [C6H2{CH2NMe2}2-1,5-{PtCl(DMSO)}2-2,4] (3)
,
described as a twist conformation with N1 0.774(2) A
above the plane of the central arene ring; the second
ring is in an envelope conformation with N2 1.212(2) A
To a solution of C6H4(CH2NMe2)2-1,3 (0.32 g, 1.70
mmol) in MeOH (40 ml) was added solid cis-
PtCl2(DMSO)2 (1.45 g, 3.43 mmol) and NaOAc (0.29 g,
3.45 mmol). The reaction mixture was stirred at 65 °C
and within 15 min a clear yellow solution was obtained.
The solution was stirred at 65 °C for 3 h whereupon a
white solid precipitated from solution. The product was
collected by decantation, washed with MeOH (50 ml),
Et2O (2×50 ml) and dried in vacuo to yield a white
solid (1.07 g, 78%). 1H-NMR (CDCl3): l 8.10 (s,
3J(PtꢀH)=51.8 Hz, 1H, Ar-Hortho), 6.78 (s, 1H, Ar-H),
3.89 (s, 3J(PtꢀH)=40.6 Hz, 4H, CH2N), 3.54 (s,
,
below the central arene plane. The NꢀPtꢀC bite angles
of 80.03(9) and 79.98(9)° are significantly smaller than
the ideal values. The two PPh3 ligands are located trans
to the amino groups. The conformations of the PPh3
groups slightly differ: the first ligand is in a gauche
conformation with respect to the Pt1ꢀCl1 bond, while
the second ligand is in a staggered conformation to
Pt2ꢀCl2. We assume that the PPh3 ligands behave like
‘cogwheels’ and that this interaction between them de-
termines the conformation. Moreover, in this confor-
3
3J(PtꢀH)=23.4 Hz, 12H, SCH3), 2.90 (s, J(PtꢀH)=
mation,
a
close proximity between the aromatic
33.2 Hz, 12H, NCH3). 13C{1H} NMR (CDCl3): d 142.5,
139.6 (2J(PtꢀC)=65.9 Hz), 134.9, 115.2 (3J(PtꢀC)=
40.2 Hz), 74.8 (2J(PtꢀC)=54.8 Hz, CH2N), 52.0
(NCH3), 46.4 (2J(PtꢀC)=65.5 Hz, SCH3). The com-
pound proved to be insoluble for a decent 13C{1H}
NMR spectroscopic analysis. Anal. Calcd. for
C16H30Cl2N2O2Pt2S2: C, 23.79; H, 3.74; N, 3.47. Found:
C, 23.81; H, 3.72; N, 3.39%.
hydrogen H2 and the two phenyl groups of the PPh3
ligands is present, as supported by the NMR spectro-
scopic studies. The distance between H2 and C31 is
,
2.79 A, which is significantly shorter than the sum of
,
the covalent radii (C+H=2.90 A). Moreover, the
,
,
H2ꢀC30 (3.03 A) and H2ꢀC25 (2.23 A) distances are
indicative for the close proximity of H2 and the phenyl
groups.
4.3. [C6H2{CH2NMe2}2-1,5-{PtCl(PPh3)}2-2,4] (4)
3. Conclusions
To a suspension of 1 (0.18 g, 0.19 mmol) in CH2Cl2
(10 ml) was added PPh3 (0.16 g, 0.61 mmol) dissolved
in CH2Cl2 (5 ml). The suspension gradually turned into
a clear, yellow solution. After 4 h, Et2O (60 ml) was
added to the mixture whereupon white crystals sepa-
rated from the solution, which were dried in vacuo
The presented results show that bisplatinum(II)
derivatives of the diaminoarene ligand NCN-H are
easily accessible via a direct and selective cycloplatina-
tion route. Moreover, recent experiments have unam-
biguously demonstrated the chemical stability of
complexes of type 4 in subsequent synthesis [4c,d].
Future research programmes are focused on application
of the presented building blocks in macromolecular
synthesis by using suitable ligands with a predefined
directional character.
1
(0.22 g, 95%). H-NMR (CDCl3): l 7.39–7.24 (m, 20H,
PArꢀH), 7.14–7.06 (m, 10H, PArꢀH), 6.82 (s, 1H,
ArꢀH), 5.77 (s, 4J(PꢀH)=5.20 Hz, 3J(PtꢀH)=55.0
3
Hz, 1H, ArꢀHortho), 3.94 (s, 4H, J(PtꢀH)=30.0 Hz,
3
3
CH2N), 2.70 (d, J(PtꢀH)=31.4 Hz, J(PꢀH)=1.8 Hz,
12H, NCH3). 13C{1H} NMR (CDCl3):
d 146.7
(2J(PꢀC)=4.8 Hz), 140.2, 137.8 (1J(PꢀC)=7.0 Hz,
PArꢀCipso), 134.9 (2J(PꢀC)=11.8 Hz, PArꢀCortho),
131.3, 130.5, 129.8 (4J(PꢀC)=2.5 Hz, PArꢀCpara),
4. Experimental
127.4
(3J(PꢀC)=10.9
Hz,
PArꢀCmeta),
115.1
4.1. General
(3J(PtꢀC)=34.8 Hz), 73.9 (2J(PtꢀC)=50.7 Hz,
CH2N), 50.1 (NMe2). 31P{1H}-NMR (CDCl3, 81
MHz): l 15.8 (1J(PtꢀP)=4377 Hz). Anal. Calcd. for
C48H48Cl2N2P2Pt2: C, 49.03; H, 4.11; N 2.38. Found: C,
48.88; H, 4.18; N, 2.31%.
All chemicals were purchased from Acros/Aldrich
and used without further purification. Solvents were
distilled from appropriate drying agents prior to use.

M.D. Meijer et al. / Journal of Organometallic Chemistry 640 (2001) 166–169
169
4.4. Crystal structure determinaton of 4
Organization for Scientific Research (NWO) for finan-
cial contribution.
Complex 4: C48H48Cl2N2P2Pt2·C4H10O, Fw=1250.02,
colourless needle, 0.48×0.09×0.06 mm3, monoclinic,
P21/c (No. 14), a=13.2504(1), b =23.3587(2), c=
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unique reflections (Rint=0.051). Intensities were mea-
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,
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Copies of this information may be obtained free of
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Acknowledgements
The authors thank Dr P. Steenwinkel for valuable
experimental assistance and stimulating discussions and
The Council for Chemical Sciences (CW) of the Dutch