Dimeric diphenylzinc adducts with cyclic thioethers

Article abstract of DOI:10.1039/b003985n

The 1:1 adducts formed between diphenylzinc and the cyclic thioethers S(CH₂)_n with n = 3 or 4 have dimeric structures with bridging phenyl groups. The Royal Society of Chemistry 2000.

Full text of DOI:10.1039/b003985n

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Dimeric diphenylzinc adducts with cyclic thioethers
Ron S. Dickson,* Gary D. Fallon and Qian-Qian Zhang†
Department of Chemistry, Monash University, PO Box 23, Victoria 3800, Australia.
E-mail: ron.dickson@sci.monash.edu.au
Received 18th May 2000, Accepted 23rd May 2000
Published on the Web 31st May 2000
The 1:1 adducts formed between diphenylzinc and the
cyclic thioethers S(CH2)n with n ؍ 3 or 4 have dimeric
structures with bridging phenyl groups.
Organo–zinc compounds that incorporate direct zinc–sulfur as
well as zinc–carbon bonds are not common. In this communi-
cation, we report the first examples of complexes of the type
R2ZnL where L is a sulfur-donor ligand, and we describe the
unexpected dimeric structure of these compounds which
incorporate bridging phenyl groups.
The known organo–zinc–sulfur compounds include a few
cyclic oligomers1 and polymers2 of the type [RZn(SRЈ)]n. The
pyridine adduct of one of these compounds, [MeZn{S(tBu)}],
has been isolated and characterised.3 Several dithiocarbamate
compounds of formula [RZn(S2CNEt2)]2 have also been char-
acterised.4,5 Interest in the latter was stimulated by problems
encountered in the chemical vapour deposition of the import-
ant wide band gap semiconductor ZnS using conventional
source compounds such as R2Zn (R = Me, Et) and H2S.6,7 The
dithiocarbamate compounds can be used as single source pre-
cursors for the growth of ZnS.4,5 Common structural features
of the two classes of compounds described above are: (i) each
zinc atom forms a single Zn–C bond; and (ii) in associated
species, the bridging groups are bound through sulfur donor
atoms. The unique features of the new compounds we have
prepared are that they are adducts of R2Zn compounds, and
that the bridging groups in the dimeric stuctures have carbon
rather than sulfur donor atoms.
Diphenylzinc was chosen for the initial study because it
is expected to bind more strongly than would dialkylzinc
compounds with Lewis bases. Under nitrogen, a solution of
diphenylzinc in hexane was treated with one equivalent of tri-
methylene sulfide, and the reaction mixture was stirred at room
temperature for several hours. A small amount of solid material
was removed by filtration, and the filtrate was cooled to Ϫ78 ЊC.
The white crystalline solid that deposited was isolated by fil-
tration, washed with cold pentane, and dried in a nitrogen flow.
The product was isolated in 55% yield based on the 1:1 adduct
[Ph2Zn{S(CH2)3}].‡ The 1H NMR spectrum confirmed the 1:1
ratio of Ph2Zn to S(CH2)3 in the product. The MS did not show
a molecular ion, but peaks corresponding to the individual
components Ph2Zn and S(CH2)3 were clearly present. The smell
of the sulfur ligand was immediately evident if the compound
was exposed to the atmosphere.
Repetition of the reaction with tetramethylene sulfide gave a
similar result. Well formed crystals of [Ph2Zn{S(CH2)4}] were
isolated after cooling the reaction solution.‡ An X-ray diffrac-
tion study revealed a dimeric structure with bridging phenyl
groups (Fig. 1).§ Surprising aspects of the structure are its
dimeric nature and the presence of bridging phenyl groups. In
contrast to the dimeric or polymeric structures found for R2Be8
and R2Mg9 compounds, R2Zn compounds are generally
monomeric and the molecules are linear. Prior to this structure,
alkynyl groups were the only organic groups able to form stable
Fig. 1 Molecular structure and atom numbering scheme for [Ph2Zn-
{S(CH2)4}]2. Selected bond lengths (Å) and angles (Њ): Zn(1)–Zn(1)
2.4892(2), Zn(1)–S(1) 2.5025(5), Zn(1)–C(5) 1.983(2), Zn(1)–C(11)
2.114/2.261(2);
Zn(1)–C(11)–Zn(1)
69.27(5),
S(1)–Zn(1)–C(5)
111.59(5), S(1)–Zn(1)–C(11) 100.40(5), C(5)–Zn(1)–C(11) 121.98(7),
C(11)–Zn(1)–C(11) 110.73(5).
carbon-bridges between zinc atoms.10 Adducts of R2Zn
compounds with O-donors such as dimethyl ether, 1,4-dioxane
and 1,2-dimethoxyethane are also monomeric and contain
3-coordinate zinc.11 A coordination of four is achieved in
adducts such as [R2Zn(TMEN)], but again the molecular struc-
ture is monomeric with a bidentate attachment of the N-donor
ligand.12 In the oligomeric and polymeric [RZn(SRЈ)]n com-
pounds, it is the sulfur atoms that occupy the bridging posi-
tions.1,2 The structure of [Ph2Zn{S(CH2)4}] does resemble that
proposed for [Et2Mg(Et2O)]2 based on IR and Raman results.13
Selected bond distances and angles for [Ph2Zn{S(CH2)4}]2
14
are included in Fig. 1. As in the structures of [Ph3Al]2 and
[(o-Tol)3Al]2,15 the bridge angles are acute (69.3Њ) and the bridg-
ing phenyl ring planes are perpendicular to the metal–metal
axis. The Zn–C distances for terminal (1.983 Å) and bridging
(2.114 Å) phenyl groups vary in the expected way. The Zn–S
distances are 2.5025 Å; this is slightly longer than the sum of
the covalent radii (2.35 Å) reflecting weak coordination of the
ligand. There is a short Zn–Zn separation of 2.4892 Å which is
within the sum of covalent radii for two zinc atoms. This close
approach of the zinc atoms can be attributed to the need for
good overlap between the Zn(sp3) and C(sp2) orbitals needed to
generate the 3-centre, 2-electron bridge bonds.
Although these compounds are not sufficiently stable for
CVD applications, they are inherently interesting because of
their unique structure and as the first examples of diorgano-
zinc–sulfur compounds.
Acknowledgements
We thank the China Scholarship Council for a scholarship
(Q.-Q. Z.) and the Australian Research Council for financial
support.
† Present address: Chemistry Department, Ocean University of
Qingdao, Qingdao 266003, P. R. China.
DOI: 10.1039/b003985n
J. Chem. Soc., Dalton Trans., 2000, 1973–1974
This journal is © The Royal Society of Chemistry 2000
1973

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Notes and references
‡ The new compounds were characterised by recording their IR and
NMR spectra. The compounds were unstable in air at ambient tem-
perature and we were unable to obtain satisfactory microanalytical
results for C,H and S. 1H NMR data (C6D6, 298 K) for [Ph2Zn-
{S(CH2)4}]: δ 7.66 (dd, 7.4 and 1.7 Hz, 4H, o-H of phenyl), 7.20–7.45
(m, 6H, m- and p-H of phenyl), 2.38–2.51 (m, 4H, SCH2), 1.15–1.38 (m,
4H, CH2).
4 M. A. Malik, M. Motevalli, J. R. Walsh and P. O’Brien, Organo-
metallics, 1992, 11, 3136.
5 P. O’Brien, J. R. Welsh, I. M. Watson. M. Motevalli and L.
Henriksen, J. Chem. Soc., Dalton Trans., 1996, 2491.
6 P. J. Wright and B. Cockayne, J. Crystal Growth, 1982, 59, 148.
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§ Crystal data for [Ph2Zn{S(CH2)4}]2: C32H36S2Zn2, M = 615.52, mono-
clinic, space group P21/n (no. 14), a = 8.1004(2), b = 17.0908,
c = 11.0200(2) Å, β = 108.825(1)Њ, V = 1441.67(5) Å3, T = Ϫ150 ЊC,
Z = 2, µ(Mo-Kα) = 18.28 cmϪ1
,
N = 23610, N(unique) = 4212
(Rint = 0.051), Nobs = 2821 [I > 2.50σ(I)]. Data collected from a colorless
tabular crystal (0.32 × 0.25 × 0.07 mm). All measurements made on a
Nonius KappaCCD area detector. Hydrogen atoms were included
but not refined. Final R(F) = 0.035, Rw(F) = 0.039. CCDC reference
number 186/1996. See http://www.rsc.org/suppdata/dt/b0/b003985n/ for
crystallographic files in .cif format.
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J. Chem. Soc., Dalton Trans., 2000, 1973–1974