Isolation, dynamic NMR study and X-ray characterisation of a bis sulfonium zirconocene-ate dimer

Article abstract of DOI:10.1039/b312954c

The novel dimer [Cp₂ZrS⊕CH(Ph)CH=CPPh ₂]₂, the first example of a structurally characterised sulfur-bridged binuclear zirconathiolane complex, was prepared, characterised by NMR spectroscopy and X-ray crystallography, and

Full text of DOI:10.1039/b312954c

Isolation, dynamic NMR study and X-ray characterisation of a bis
sulfonium zirconocene-ate dimer†
Esteban Ortega,a Nadine Pirio,a Philippe Meunier*a and Bruno Donnadieub
a Laboratoire de Synthèse et Electrosynthèse Organométalliques associé au CNRS (UMR 5188), Université
de Bourgogne, Faculté des Sciences Gabriel, 6 boulevard Gabriel, 21000 Dijon, France.
E-mail: Philippe.Meunier@u-bourgogne.fr; Fax: +33(0)380396100; Tel: +33(0)380396105
b Laboratoire de Chimie de coordination du CNRS (UPR 8241), 205 route de Narbonne, 31077 Toulouse
cedex 4, France
Received (in Cambridge, UK) 15th October 2003, Accepted 9th January 2004
First published as an Advance Article on the web 11th February 2004
≤
∂
“––––––‘
The novel dimer [Cp2Zr S CH(Ph)CHNCPPh2]2, the first
summarized. The solid state structure corroborates that the five-
membered zirconacycle arising from the reductive coupling
reaction of Ph2PC·CH with the transient Cp2Zr(h2-SNCHPh) is an
a-PPh2-substituted zirconathiolane which is additionally stabilised
by the formation of a coordination dimer. To our knowledge this is
the first structural characterisation of an insertion complex starting
from a thioaldehydezirconocene. In addition, X-ray data clearly
confirmed the pentacoordinated character of 1a: the two zirco-
nium–sulfur distances Zr(1)–S(1) and Zr(1)–S(1a) and the large
angle value C(1)–Zr(1)–S(1a) are typical for five-coordinated Cp2–
Zr(IV) complexes.7,8 The Zr(1)–S(1a) distance (2.752(1) Å) is
slightly shorter than the Zr–S bond length found in the complex
example of a structurally characterised sulfur-bridged binuclear
zirconathiolane complex, was prepared, characterised by NMR
spectroscopy and X-ray crystallography, and some aspects of its
solution behaviour were studied.
The very high reactivity of thio-, seleno- and tellurocarbonyl
derivatives, formal analogs of carbonyl compounds, considerably
restricts their use in organic chemistry.1 Although some synthetical
strategies of stabilisation (electronic or steric) have been proposed.
The best way to circumvent these problems was certainly to use
transition metal complexes. As in our group a primary objective
concerns the development and the extension of zirconocene-based
methodology for the elaboration of main group heterocycles, we
developed for some years different coupling reactions of un-
saturated heteroatom-containing molecules in the coordination
sphere of zirconium.2,3 More recently we have focused our efforts
on zirconocene complexes of thioaldehydes and thioketones and
related selenium and tellurium chemistry in order to prepare new
chalcogenated heterocycles which have been regarded hard to
prepare by classical methods. The present report deals with the
synthesis and the full characterisation of a zirconacyclic precursor
of unprecedented a-phosphino-substituted thiaheterocycles, poten-
tially useful ligands in coordination chemistry.
A toluene solution of diphenylphosphinoacetylene and a zirco-
nocene thioaldehyde equivalent Cp2Zr(Me)SCH2Ph, prepared from
dimethylzirconocene and phenyl-methanethiol,4 led to the precip-
itation of 1a after 10 h of stirring at 90 °C (Scheme 1). This beige
complex was isolated with variable yields (45% to 61%) depending
on the contamination of the reaction mixture with some dithiolate
Cp2Zr(SCH2Ph)2.5 Spectroscopic data were consistent with a
dimeric formulation for 1a.6 The presence of a 1:1 ratio of two
diastereomers was readily discernable in 31P (two close singlets)
and 1H (for instance two sets of two Cp resonances: the four C5H5
ligands are equivalent by pairs in each diastereomer) NMR
spectra.‡ Suitable crystals for X-ray diffraction study‡ were
prepared by slow liquid-phase diffusion of pentane into a
dichloromethane solution of 1a. Fig. 1 shows the ORTEP view of
the meso form of 1a and important bond lengths and angles are
≤
∂
Cp Zr“–C(–Ph–P–S–)NC–P–h–(o–-‘C H ) (2.797(1)Å).2 Moreover the an-
”————’
2
2
6 4
ionic character of zirconium atom for 1a is consistent with the very
large coupling constant JCP (92.2 Hz) found in 13C NMR spectrum
for the sp2 carbon PCN directly linked to the metal. This value
compares well with the one found in the phosphonium zirconocene-
≤
∂
ate complex Cp Zr“–C(–Ph–P–C–H–NC–PP–h –)N–CH–(o–-‘C H ) (97.6
”——————’
2
2
2
6
4
Hz).9 The long bridging Zr–S bonds can let us suppose of a weak
interaction between each monomer. Therefore the variable-
temperature NMR study of 1a was anticipated. In the dynamic 1H
NMR spectra, broadening of the cyclopentadienyl resonances
occurred on warming around 340 K (Fig. 2). Increasing the
temperature also caused broadening of the resonances of –CHPh
and NCH protons at lower temperatures. The same phenomenon
was observable in variable-temperature 31P NMR spectroscopy.
The solution behaviour exhibited by 1a was attributed to the rapid
monomer–dimer equilibrium outlined in Scheme 2. From the
1
temperature-dependent H NMR spectra an activation energy of
DG* (343 K) = 69.9 ± 2 kJ.mol21 at the coalescence temperature
of the C5H5 resonances was estimated for the intermolecular
equilibration of the 1a dimers. This is in accord with the data found
in catecholato-zirconocene dimers where the activation energy was
above 90 kJ.mol21 for a stronger zirconium–oxygen associa-
tion.10
Under the same experimental conditions, dimeric complexes 1b
were formed after treatment of Cp2ZrMe2 with (4-methox-
Scheme 1
† Electronic supplementary information (ESI) available: typical experi-
mental procedure, physical and spectroscopic data of all new compounds
and VT NMR studies of 1a–c. See http://www.rsc.org/suppdata/cc/b3/
b312954c/
Fig. 1 Molecular structure of 1a. Selected bond lengths (Å) and angles(°):
Zr(1)–C(1) 2.399(3), Zr(1)–S(1) 2.574(1), Zr(1)–S(1a) 2.752(1); C(1)–
Zr(1)–S(1a) 131.49(6), S(1)–Zr(1)–S(1a) 60.51(6), Zr(1)–S(1)–Zr(1a)
119.49(6), Zr(1)–S(1)–C(3) 110.64(6), Zr(1a)–S(1)–C(3) 127.24(6).
678
C h e m . C o m m u n . , 2 0 0 4 , 6 7 8 – 6 7 9
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4

yphenyl)methanethiol and diphenylphosphinoacetylene (Scheme
1). 31P, 1H and 13C NMR data of 1a exhibited the same
characteristic features as for the sulfur-bridged binuclear 2-phos-
phinozirconathiolane complex 1a (d 31P (PPh2) 20.4, 20.3 ppm; d
1H (Cp) 5.70, 5.79, 6.00, 6.16 (OMe) 3.28, 3.34 ppm; d 13C (Cp)
110.2, 110.5, 110.9, 111.3 (OMe) 55.6, 55.7 ppm).† Despite a
lower solubility, the diastereoisomeric dimers 1a showed very
similar dynamic NMR spectra and the activation barrier for the
fluxional process was found to be the same as for 1a at the
coalescence temperature of the C5H5 resonances.
Scheme 3
In order to afford more information about the equilibrium
mentioned in Scheme 2, and to verify our hypothesis of a
monomeric intermediate, we heated at 90 °C a mixture of 1a and 1b
for one hour.11 Same experiment was also conducted at room
temperature for a more long time (the mixed dimers became
monomeric thiazirconacyclic complexes 2a,b were typical of the
phosphinozirconathiolane framework.† Their structural features
would be interesting to compare with those of corresponding
dimeric products, in particular for the geometry of the sulfur atom;
but obtaining suitable crystals for X-ray structure analysis has
failed to date.
1
observable in the H NMR spectrum after half a day). The new
complexes 1a were obtained along with the two known complexes
1a,b (Scheme 3). Same result was obtained after heating
Cp2ZrMe2, Ph2PC·CH and a half-equivalent of the two thiols
PhCH2SH and p-MeOPhCH2SH. Spectroscopic NMR data were
found to be quite simple. The 31P NMR spectrum displayed beside
the four singlets for 1a,b four singlets for 1c. The 1H NMR
spectrum exhibited as expected the four sets of two Cp resonances
for 1a,b and two sets of four Cp resonances for 1c (the four
cyclopentadienyl ligands are non equivalent in each diastereomer).
The same type of fluxional process was indicated by the appearance
of the 1H NMR spectra at increasing monitoring temperature.§
Moreover, the cleavage of binuclear thiazirconacycles 1a,b
resulting from borane addition corroborated the weak association
through bridging sulfur atoms. The BH3 protected complexes 2a,b
were prepared quantitatively by addition of borane methylsulfide
complex to the corresponding suspension in THF of dimers 1a,b
(Scheme 1). The NMR spectroscopic data for the obtained
In conclusion, we have shown that a new organometallic
precursor of a-phosphino-substituted thiaheterocycles can be easily
prepared from a zirconocene complex of thiobenzaldehyde and
diphenylphosphinoacetylene. The promising reactivity of these
new dimeric complexes is currently under active investigation as is
the unknown related chemistry with heavier congeners.
The award of a thesis grant (E. O.) from the Ministère de
l’Education Nationale, de la Recherche et la Technologie
(MENRT) is gratefully acknowledged. The authors thank S. Royer
for her helpful technical assistance.
Notes and references
‡ Most characteristic NMR data for 1a (both diastereomers) and 2a (300 K,
Bruker DRX500). 1a: 31P{1H} (toluene-d8) d 21.4, 21.1 (s); 1H (toluene-
d8) d 4.47, 4.56 (broad s, 2H, CHPh), 5.56, 5.71, 5.94, 6.08 (s, 10H, HCp),
6.78, 6.85 (dd, JHP = 15.6 Hz, JHH = 2.3 Hz, 2H, NCH) ; 13C{1H} (CD2Cl2)
d 66.2, 67.8 (d, JCP = 11.0 Hz, CHPh), 110.2, 110.5, 110.9, 111.3 (d, JCP
= 3.6 Hz, CHCp), 154.2, 155.1 (d, JCP = 9.2 Hz, NCH), 180.8, 181.8 (d, JCP
1
= 92.2 Hz, Ph2PCN). 2a: 31P{1H} (C6D6) d 27.0 (broad m); H (C6D6) d
0.10 (broad s, BH3), 2.10 (broad d, JHP = 105.7 Hz, BH3), 4.12 (dd, JHP
5.5 Hz, JHH = 1.9 Hz, 1H, CHPh), 5.45, 6.00 (s, 5H, HCp), 6.78 (dd, JHP
=
=
27.0 Hz, JHH = 1.9 Hz, 1H, NCH); 13C{1H} (C6D6) d 64.3 (d, JCP = 27.6
Hz, CHPh), 108.5, 110.8 (s, CHCp), 159.4 (d, JCP = 6.3 Hz, NCH), 172.4 (d,
JCP = 21.8 Hz, Ph2PCN).
§ Crystal data for 1a: C62H54P2S2Zr2, M = 1105.66, monoclinic, a =
15.724(5), b = 10.205(5), c = 15.825(5) Å, b = 98.201(5)°, V =
2538.0(17) Å3, T = 293(2) K, space group P 21/c, Z = 4, m(MoKa) =
0.597 mm21, 19651 reflections measured, 4985 unique (Rint = 0.0484)
which were used in all calculations. The final wR(F2) was 0.0875 (all data).
CCDC reference number 215636. See http://www.rsc.org/suppdata/cc/b3/
b312954c/ for crystallographic data in .cif or other electronic format.
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Scheme 2
C h e m . C o m m u n . , 2 0 0 4 , 6 7 8 – 6 7 9
679