Metallo-phosphorylation of olefins: reaction of diethyl
chlorophosphate with zirconocene–ethylene complex†
Chanjuan Xi,* Mingming Ma and Xiaodong Li
Key Laboratory for Bioorganic Phosphorus Chemistry of Ministry of Education, Department of
Chemistry, Tsinghua University, Beijing 100084, China. E-mail: cjxi@tsinghua.edu.cn;
Fax: +86-10-62566383; Tel: +86-10-62782695
Received (in Cambridge, UK) 29th August 2001, Accepted 23rd October 2001
First published as an Advance Article on the web 9th November 2001
Zirconocene–ethylene complex Cp
2
Zr (CH
2
= CH
2
) reacted
chloride did not proceed. The zircono-ethylphosphonate re-
quires initial reaction with CuCl to give the alkylcopper
reagent,4 which then undergoes smooth reaction with acyl
chloride to give (2e). This is due to the different reactivity of the
carbon attached to zirconium in the zircono-ethylphospho-
nate.
with chlorophosphate to form zircono-ethylphosphonate,
which could be converted into various functionalized
ethylphosphonates.
Introduction of a heteroatom to multiple carbon–carbon bonds
is attractive from the synthetic viewpoint. In this regard, a
1
The reaction of zirconocene–ethylene complex Cp
2
Zr
particularly attractive and interesting subject is the simultane-
ous introduction of a metal and another heteroatom to multiple
carbon–carbon bonds, since it is a more versatile and elegant
synthetic elaboration. While the related carbometallation of
multiple carbon–carbon bonds has been extensively studied,2
only a few reactions for the preparation of such a complex,
which contains a metal and a heteroatom to a carbon–carbon
bond, have been studied. In this paper, we would like to report
(CH = CH ) with various unsaturated compounds such as
2
2
5
3
6
alkynes, alkenes, ketone, and nitriles, in which the reactions
afforded five-membered zirconacycles was investigated. To
elucidate the intermediate of this reaction, the reaction of
31
Cp
2
Zr(CH
2
= CH
2
) with chlorophosphate was followed by
P
NMR spectroscopy. Immediately following the addition of
chlorophosphate at 278 °C, the reaction mixture was analysed
31
31
by P NMR. The P NMR spectrum showed only one peak at
3.2 ppm, which was confirmed to be due to the phosphorus of
the chlorophosphate. Then, the reaction mixture was stirred for
10 minutes from 278 °C to room temperature. Three peaks
appeared in the 31P NMR spectrum. One appeared at 3.2 ppm
and another at 23.8 ppm. The latter signal is consistent with
a
novel reaction of zirconocene–ethylene complex
Cp
2
Zr(CH
2
= CH
2
) with chlorophosphate to form zircono-
ethylphosphonate (1) (Scheme 1), which can be converted into
various functionalized ethylphosphonates.
A typical experiment was carried out as follows. To a solution
3
7
of zirconocene–ethylene complex Cp
erated by the reaction of Cp ZrCl
2
Zr(CH
2
= CH
2
), gen-
phosphorus of coordination number five. The third signal was
2
2
with 2 equiv. of EtMgBr in
at 33.7 ppm and was assigned to the phosphorus of zircono-
ethylphosphonate (1). Following continuous stirring of the
reaction mixture for 30 minutes at room temperature, the peak
at 3.2 ppm completely disappeared and the peak at 33.7 ppm
increased. Finally, the peak at 23.8 ppm disappeared after the
reaction mixture was stirred for 24 hours at room tem-
perature.
THF, was added one equiv. of diethyl chlorophosphate. The
reaction mixture was kept at room temperature for 24 hours, and
then it was quenched with 2M HCl. Purification of crude
product was carried out by column chromatography on silica gel
(
ethyl acetate–petroleum ether = 2+1). Ethylphosphonate (2a)
was obtained in 87% yield.
The product ethylphosphonate did not come from the reaction
of EtMgBr with chlorophosphate: hydrolysis was replaced by
iodination of the reaction mixture and 2-iodoethylphosphonate
Based on the above results, a proposed reaction mechanism is
shown in Scheme 2. The reaction of Cp
EtMgBr gives Cp ZrEt
give resonance hybrids Cp
pane (3). The Zr–C bond of zirconacyclopropane (3) reacts
with chlorophosphate to form five-membered zirconacycle (4).
Then, elimination of chloride from zirconacycle (4) takes place
to form zircono-ethylphosphonate.
2
ZrCl
, which smoothly decomposes at 0 °C to
Zr-ethylene and zirconacyclopro-
2
with 2 equiv. of
2
2
(
2b) was obtained in 85% yield, which suggested that the
2
3
intermediate of the reaction of zirconocene–ethylene complex
with chlorophosphate contains a Zr–C bond before hydroly-
sis.
Zircono-ethylphosphonate could be converted into function-
alized ethylphosphonate by coupling with various electrophiles
such as I
reactions are summarized in Table 1. The reaction of zircono-
ethylphosphonate with I or NBS gave 2-iodoethylphosphonate
2
, NBS, acyl chloride and allyl bromide. The various
Table 1 Reaction of a mixture of Cp
2
ZrEt
2
and chlorophosphate with
electrophiles
2
Entry Electrophile T/°C Time/h Product
Yield (%)a
87 (63)
or 2-bromoethylphosphonate (2c) in 85% and 73% yields,
respectively. Moreover, treatment of zircono-ethylphosphonate
with allyl bromide obtained (2d) in 77% yield, in which the new
carbon–carbon bond was formed. It is noteworthy that without
CuCl the reaction of zircono-ethylphosphonate with acyl
1
2
3
4
5b
a
HCl
rt
1
3
3
6
6
I
2
rt
85 (60)
73 (49)
77 (56)
64 (45)
b
NBS
rt
rt
MeCOCl
50
Scheme 1
GC yields. Isolated yields are given in parentheses; CuCl (1 equiv.) was
added.
†
Electronic supplementary data available: experimental procedure and
NMR data. See http://www.rsc.org/suppdata/cc/b1/b107755d/
2554
Chem. Commun., 2001, 2554–2555
This journal is © The Royal Society of Chemistry 2001
DOI: 10.1039/b107755d