Synthesis of a h2-2,3-diphosphabutadiene complex of zerovalent platinum
from the corresponding h2-phosphaalkyne complex
Maria Helena Araujo,a Peter B. Hitchcock,a John F. Nixon,*a Uwe Kuehnerb and Othmar Stelzer†b
a School of Chemistry, Physics and Environmental Science, University of Sussex, Brighton, Sussex,
UK BN1 9QJ
b Fachbereich 9, Anorganische Chemie, Bergische Universitat -GH, Wuppertal D-42097, Germany
Received (in Cambridge, UK) 3rd February 2003, Accepted 14th March 2003
First published as an Advance Article on the web 2nd April 2003
Hydrozirconation of the h2-phosphaalkyne complex
[Pt(dppe)(h2-tBuCP)] with [ZrHCl(h5-C5H5)2], followed by
treatment with the chlorophosphaalkene ClPNC(SiMe3)2
affords
the
h2-2,3-diphosphabutadiene
complex
[Pt(dppe)(h2-tBuC(H)NPPNC(SiMe3)2]. In the presence of
[Pt(PPh3)2] the latter undergoes an addition reaction with
water to afford the structurally characterised Pt(II) complex
[Pt(dppe)(tBuCH2P(O)HPC(SiMe3)2]
In spite of the considerable activity over the past few years in
the area of unsaturated organophosphorus compounds, there are
relatively few reports of 2,3-diphosphabutadienes of the type
R1R2CNPPNCR3R4 and to date mainly symmetric compounds
(R1R2 = R3R4) have been described.1–6 Two different methods
t
affording the symmetrical 2,3-diphosphabutadiene Bu(OSi-
Me3)CNPPNCtBu(OSiMe3) 1 are known (i) by treatment of
tBu(OSiMe3)CNPSiMe3 with C2Cl6 and (ii) reacting Me3SiPN
PSiMe3 with tBuCOCl. The unsymmetrical 2,3-diphosphabuta-
t
diene, Bu(OSiMe3)CNPPNCPh(SiMe3), rearranges on heating
in acetonitrile to give 1 together with the unstable 2,3-diph-
osphabutadiene Ph(SiMe3)CNPPNCPh(SiMe3), which then
polymerises. The latter compound, as well as the diphosphane
Ph2PPPh2, also resulted from thermolysis of Ph(Si-
Me3)CNPPh2
Since it is well known that ligation of unstable multiply
bonded species to transition metal complexes can enhance their
2
stability, we now describe a totally new synthetic route to an h -
ligated unsymmetrical 2,3-diphosphabutadiene using this strat-
egy. Previously,7 we described the synthesis of the zerovalent
2
platinum complex 4 containing the h -ligated unstable phos-
2
phaalkene tBuC(H)NPH , via hydrozirconation of the h -
2 t
phosphaalkyne complex [Pt(dppe)(h - BuCP)]
2
with
5
2
[ZrHCl(h -C5H5)2], followed by protolysis of the resulting h
2
-metallaphosphaalkene
complex
[Pt(dppe)(h -
tBuC(H)NPZrCl(h -C5H5)2] 3. Subsequently Heydt, Regitz and
5
Schroder8 have synthesised the corresponding phosphaalkene
tBuC(H)NPPNC(SiMe3)2Pt(PPh3)2] 7. Although the product
could not be isolated, support for its formulation came from the
observation that whereas 6 is unreactive towards water,
complex 7 on work-up readily lost the [Pt(PPh3)2] fragment in
the adventitious presence of water readily to afford the platinum
complex [Pt(PPh3)2(h - BuC(H)NPtBu] 5 by direct reaction of
2 t
the
stable
phosphaalkene
tBuC(H)NPtBu
with
[Pt(PPh3)2(C2H4)].
We now find that treatment of 3 with the chlorophosphaalk-
ene ClPNC(SiMe3)2 readily affords the unsymmetrical 2,3-diph-
osphabutadiene
(SiMe3)2] 6, whose identity was unambiguously established by
its characteristic 31P1{H} NMR spectrum‡ which exhibited (i)
the expected four different types of phosphorus nuclei, with a
II) complex [Pt(dppe)(tBuCH2P(O)HPC(SiMe3)2] 8. The latter
2 t
(
complex
[Pt(dppe)(h - BuC(H)NPPNC-
which was fully structurally characterised by a single crystal X-
1
ray diffraction study,§(See Figure 1), showed the expected H
and 31P NMR spectra,‡ is presumably formed by insertion of the
large one bond coupling constant (1JP P = 260.5 Hz) for the
two adjacent P atoms of the diphosphabutadiene and (ii) the
characteristic 195Pt satellites of the appropriate magnitude
around each of the the resonances of PA (368.4 Hz), PB (68.2
Hz), PC (3390 Hz) and PD (3166 Hz). The 195Pt {1H} NMR
spectrum of 4 was totally consistent with the proposed structure,
showing the required 16-line pattern from coupling to the four
non-equivalent phosphorus centres.‡
A
B
retained [Pt(dppe)] fragment into the intermediate diphosphir-
t
ane ring system BuCH2PP(OH)C(SiMe3)2, which arises from
H2O addition to the unsaturated –CNP–PNC system, followed by
an Arbusov-type rearrangement of the resulting –P(OH) bond to
afford the pentavalent –P(O)H unit. The molecular structure of
8 also confirms the formation of the P–P bond, as proposed in
the synthesis of 6 from 3.
We showed previously9,10 the quantitative nature of insertion
reactions of the zerovalent d10 transition metal-ligand fragments
[M(PR3)2], (M = Ni, Pd, Pt), into both phosphirene and
phosphirane rings, to afford the corresponding four-membered
metalla-phospha-cyclobutene and metalla-phospha-cyclobu-
tane ring systems respectively. Interestingly the structurally
The further ligating potential of the 2,3-diphosphabutadiene
unit in 6 as a 4e donor, was explored in its reaction with
[Pt(PPh3)2(C2H4)] in an attempt to form [Pt(dppe)(h -h -
2
2
† (Deceased)
1092
CHEM. COMMUN., 2003, 1092–1093
This journal is © The Royal Society of Chemistry 2003
Araujo, Maria Helena
