Syntheses and structures of [Me2Si{As(PtBu)3}2] and [(CyP)3SiMe2] (Cy = cyclohexyl, C6H11)

Article abstract of DOI:10.1016/j.jorganchem.2009.12.011

The reaction of the anion [(^tBuP)₃As]^- (1) with Me₂SiCl₂ results in nucleophilic substitution of the Cl^- anions, giving the di- and mono-substituted products [Me₂Si{As(P^t

Full text of DOI:10.1016/j.jorganchem.2009.12.011

Journal of Organometallic Chemistry 695 (2010) 1069–1073
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Syntheses and structures of [Me2Si{As(PtBu)3}2] and [(CyP)3SiMe2]
(Cy = cyclohexyl, C6H11)
*
Wesley T.K. Chan, Felipe García, Mary McPartlin, Rebecca L. Melen, Dominic S. Wright
Chemistry Department, Lensfield Road, Cambridge CB2 1EW, UK
a r t i c l e i n f o
a b s t r a c t
The reaction of the anion [(tBuP)3As]ꢀ (1) with Me2SiCl2 results in nucleophilic substitution of the Clꢀ
anions, giving the di- and mono-substituted products [Me2Si{As(PtBu)3}2] (3a) and [Me2Si(Cl){As(PtBu)3}]
(3b). Analogous reactions of the pre-isolated [(CyP)4As]ꢀ anion (2) (Cy = cyclohexyl) with Me2SiCl2 pro-
duced mixtures of products, from which no pure materials could be isolated. However, reaction of 2 [gen-
erated in situ from CyPHLi and As(NMe2)3] gives the heterocycle [(CyP)3SiMe2] (4). The X-ray structures of
3a and 4 are reported.
Article history:
Received 26 October 2009
Received in revised form 11 December 2009
Accepted 14 December 2009
Available online 21 December 2009
Keywords:
Arsenic
Ó 2009 Elsevier B.V. All rights reserved.
Heterocycle
Silicon
X-ray
1. Introduction
coupling into the As–As bonded dimer [(tBuP)3As]2 (Scheme 3a) [8].
However, the intact [(tBuP)3As] framework is transferred in
Heterocyclic anions of the type [(RP)nE]ꢀ (where E = P, As, Sb;
n = 3 or 4) are an interesting, and at present relatively little-stud-
ied, class of potential ligands for a range of metals and non-metals
[1–3]. We have found that simple access to the As and Sb deriva-
tives is offered by the direct reactions of alkali metal primary phos-
phides [RPHM] (M = an alkali metal) with the series of reagents
[E(NMe2)3] (Scheme 1, step 1) [1–3]. These reactions are difficult
to control in the case of the Sb heterocycles [(RP)nSb]ꢀ owing to
the relative weakness of P–Sb bonds and the resulting thermal
instability (Scheme 1, step 2). For example, the five-membered,
heterocyclic anion [(CyP)4Sb]ꢀ (Cy = cyclohexyl) decomposes at
temperatures above ca. 0 °C into the Zintl ion [Sb7]3ꢀ and the cyclic
phosphane [CyP]4 [4]. This type of main group dehydrocoupling
reaction can be seen to be driven thermodynamically by the
strength of the P–P single bond, which has the highest homoatomic
bond energy between of any of the group 15 elements (ca.
201 kJ molꢀ1) [5]. The phosphorus counterparts [(tBuP)4P]ꢀ have
been obtained by the in situ reactions of tBuPCl2 and PCl3 with
Na metal in THF (Scheme 2) [6].
reactions with transition metal half-sandwich compounds.
Interestingly, while the reaction of 1 with [CpFe(CO)2Cl] gives the
expected addition to the Fe centre (Scheme 3b), addition of the
[(tBuP)3As] unit to the Cp ligand occurs for [CpM(CO)3Cl] (M = Mo,
W) (Scheme 3c) [7a,9]. The products of the latter reaction,
[C5H4{As(PtBu)3}M(CO)3Cl], probably result from a mechanism
involving initial addition to the metal (M) followed by transfer to
the Cp ligand (with formal elimination of Hꢀ). In contrast,
reactions of organic electrophiles (R–X; R = Me, X = I; R = PhCH2,
CH2 = CHCH2, X = Br) give the neutral triphosphanes [(tBuP)(tBuPR)2],
via an SN2-type mechanism involving cleavage of the As–P bonds
(Scheme 3d) [7b]. This route gives rise to a potentially broad range
of new phosphane ligand frameworks.
Given the reactivity patterns described above, there is an obvi-
ous potential for the development of a general approach to neutral
heterocycles of the type [(RP)nER0m] using reactions of [(RP)nAs]ꢀ
anions like 1 with group 13 or 14 organohalide electrophiles
[group 13 R0EX2 (E = P–Bi); group 14 R02EX2; E = C–Sn; X = halogen]
(Scheme 4). In the current work we have explored this potential for
the first time in a study of the reactions of the anions 1 and the re-
lated five-membered anion [(CyP)4As]ꢀ (2) with Me2SiCl2. We find,
however, that the reaction of 1 with Me2SiCl2 in 3:2 stoichiometric
ratio (suggested by analogy with reaction d, Scheme 3) does not
produce the heterocyclic product [(tBuP)3SiMe2] (Scheme 4, top).
Instead, intact transfer of the [(tBuP)3As] unit occurs, producing a
mixture of the di- and mono-substituted products [Me2Si{As-
(PtBu)3}2] (3a) and [Me2Si(Cl){As(PtBu)3}] (3b) (Scheme 4, bottom).
Although no solid products could be obtained from the reaction of
A particular interest in the coordination chemistry of the
[(RP)nE]ꢀ anions is their potential to deliver group 15 atoms, by
the reductive elimination of cyclic phosphanes. Our studies in this
area have focused on the coordination behaviour and reactivity of
the readily prepared [(tBuP)3As]ꢀ anion (1) [7]. Disappointingly,
reactions of 1 with a range of main group metals results in oxidative
* Corresponding author.
E-mail address: dsw1000@cam.ac.uk (D.S. Wright).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.12.011

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W.T.K. Chan et al. / Journal of Organometallic Chemistry 695 (2010) 1069–1073
LiꢁTMEDAꢁTHF] (2ꢁTMEDAꢁTHF) [TMEDA = Me2N(CH2)2] [3] were
−
E(NMe2)3
Δ
−
x
used as sources of the anions 1 and 2, respectively. The 3:2 stoichi-
ometric reaction of Me2SiCl2 (1.8 mmol) with the 1ꢁ2DABCOꢁTHF
(1.2 mmol) in THF/toluene (Scheme 4, top) gives a mixture of
two closely related products (3a and 3b; ca. 3:2), as revealed by
an in situ 31P{1H} NMR study of the reaction mixture after
filtration of the LiCl precipitate (see Table 1). Both products appear
[RP]n
RPHM
[E]m
E
+
R
P
n
heterocycles
[(RP)nE]-
cyclicphosphane
Zintlion
Scheme 1.
as
a doublet and a triplet [3a,d-62.6{d,P(1,3)},d-15.7{t,P(2)}
(1JP–P = 159 Hz);3b,d-63.4{d,P(1,3)},d-13.5{t,P(2)}(1JP–P = 156 Hz)],
consistent with presence of P3 units in both products. The similar-
ity of the chemical shifts and the coupling constants involved sug-
gests that 3a and 3b are closely related chemically. Based on this,
and the later full characterisation of the major product 3a as the
di-substituted species [Me2Si{As(PtBu)3}2], the minor isomer (3b)
is most likely to be the mono-substituted species [Me2Si(Cl){As
(PtBu)3}]. This conclusion is also roughly consistent with fact that
an excess of 1 was used in this initial reaction. Unfortunately, no
further characterisation of 3b (or 3a) by mass spectroscopy was
possible owing to air-sensitivity. However, even changing the reac-
tion stoichiometry to 1:1 resulted in the formation of a mixture of
3a and 3b. Noticeably, although the chemical shifts of the central P
atoms within the P3As ring units of 3a and 3b [P(2)] are similar to
those present in alkali metal complexes of the anion 1 (d ꢀ15.7 and
d ꢀ13.5 in 3a and 3b, respectively), the terminal P atoms [P(1,3)]
are significantly deshielded (d ꢀ62.6 and ꢀ63.4 in 3a and 3b; cf d
ꢀ73.6 to ꢀ89.9 in alkali metal complexes of 1) [2]. This increase
in chemical shift is synonymous with a reduction in the partial
charge of the [(tBuP)3As] units in 3a and 3b, resulting from the for-
mation of covalent As-Si bonds. Storage of the reaction solution at
tBu
tBu
P
P
P
THF
P
Na(THF)4
4tBuPCl2 + PCl3 + 12Na
-11NaCl
P
tBu
tBu
Scheme 2.
the pure anion 2 with Me2SiCl2, a low yield of the heterocycle [(Cy-
P)3SiMe2] (4) could be formed from the addition of Me2SiCl2 to a
3:1 mixture of CyPHLi and As(NMe2)3 (Scheme 5).
2. Results and discussion
The previously reported complexes [{(tBuP)3As]Liꢁ2DABCOꢁTHF]
(1ꢁ2DABCOꢁTHF) [DABCO = N{(CH2)2}3] [2b] and [{(CyP)4As}-
tBu
P
tBu
P
tBu
P
P
tBu
x2/-2e
As
As
a
b
P
P
tBu
tBu
a
Fe
OC
Cl
OC
Fe
b
tBu
tBu
–
OC
P
P
As
tBu
P
-Cl
OC
P
-
tBu
tBu
P
As
tBu
M
P
OC
OC
CO
Cl
tBu
P
c
tBu
As
P
M=W,Mo
c
P
tBu
1
–
M
-H
CO
Cl
OC
OC
d
tBu
P
R
3RX
-LiX/RAsX2
tBu
P
d
P
R
tBu
Meso
Scheme 3.

W.T.K. Chan et al. / Journal of Organometallic Chemistry 695 (2010) 1069–1073
1071
Scheme 4.
the fact that the starting material 2ꢁTMEDAꢁTHF, although the most
easily prepared source of the anion 2, is only isolated in relatively
low yield from the 3:1 reaction of CyPHLi with As(NMe2)3 in the
presence of TMEDA/THF and is difficult to purify (taking several
weeks to crystallize). We therefore investigated the in situ genera-
tion of the anion 2 via the 3:1 reaction of CyPHLi with As(NMe2)3 in
TMEDA/THF. An in situ 31P{1H} spectroscopic study of this reaction
mixture does indeed show the presence of significant amounts of
the [(CyP)4As]ꢀ anion, in addition to a number of other unidenti-
fied species. Reaction of this solution at ꢀ78 °C with an excess of
Me2SiCl2 gave a precipitate of LiCl. The in situ NMR spectrum of
the filtered solution clearly shows the presence of [(CyP)3SiMe2]
(4) as a principal product of the reaction (see Table 2). Crystalline
4 was isolated in 10% yield after storage of the reaction solution at
ꢀ20 °C. The room temperature 31P{1H}NMR spectrum of 4 shows
the expected triplet [d ꢀ44.8, P(2)] and doublet [d ꢀ97.6, P(1,3)]
(1JP–P = 128 Hz). These resonances are distinctly different from
those found for either 3a or 3b, providing preliminary evidence
of the presence of a very different (P3Si as opposed to P3As) ring
unit in 4. It is not certain how the four-membered P3Si ring of 4
is formed in this reaction. However, it can be noted that no inter-
mediate [(CyP)3As]ꢀanion could be observed in the in situ reaction
mixture of CyPHLi with As(NMe2)3, prior to the addition of
Me2SiCl2. Thus, it appears that the four-membered ring of 4 is
generated from the observed intermediate five-membered anion
[(CyP)4As]ꢀ (2). The observation that the reaction of Ph2SiCl2 with
CyPHLi does not generate 4 (only the Si2P2 ring compound trans-
[Ph2SiPCy]2) [8] further supports the view that As(NMe2)3 is vital
to the formation of 4, presumably because it is responsible for
the formation of P–P bonds before electrophilic ring opening
occurs with Me2SiCl2.
Scheme 5.
ꢀ20 °C gave a 23% yield of light-yellow crystals of 3a, which was
spectroscopically- and structurally-characterised. However,
repeated attempts to isolate 3b using various reaction stoichiome-
tries and conditions failed. The isolation of 3a as the product was
confirmed by 31P{1H} spectroscopy at room temperature (in
d8-THF). Interestingly, the 1H NMR spectrum of 3a (in benzene)
shows three doublets in the tBu region (ratio 1:1:1), consistent
with the adoption of a rigid molecular conformation in solution
t
in which the three Bu groups are magnetically inequivalent. This
is not altogether unexpected bearing in mind the sterically con-
gested nature of the solid-state molecular structure (Fig. 1), which
is likely to result in restricted rotation of the Si–As bonds. Table 1
summarises the 31P NMR spectroscopic data on the new com-
pounds 3a, 3b and 4.
A number of reactions of 2ꢁTMEDAꢁTHF with R2SiCl2 (R = Me,
Ph) were undertaken. Several unidentified products were observed
by in situ 31P{1H} NMR spectroscopy. However, irrespective of the
solvent or reaction conditions, no solid products could be isolated.
A further problem which limited the extent of these studies was
The low-temperature [180(2) K] X-ray structure of 3a confirms
the essential features ascertained from spectroscopic analysis. The
molecular structure consists of two [(tBuP)3As] ring units which
are bridged by a Me2Si group (Fig. 1). The structure provides final
confirmation that nucleophilic attack of the [(tBuP)3As]ꢀ anion at
the silicon centre occurs in this case, as opposed to electrophilic
ring opening. The bridging Si atom exhibits a distorted tetrahedral
geometry [range of angle at Si(1) 101.69(7)–115.9(2)°], while the
acute angles at the As centres [82.95(7)–98.53(7)°] a large degree
of p-orbital character within the bonds involved. The mean planes
Table 1
Summary of 31P{1H} NMR data for the new compounds 3a, 3b and 4.
Compound
3a
Chemical shift (d) (coupling constant, J)
ꢀ62.6 [d, P(1,3)], ꢀ15.7 [t, P(2)]
(1JP–P = 159 Hz)
3b
4
ꢀ63.4 [d, P(1,3)], ꢀ13.5 [t, P(2)]
(1JP–P = 156 Hz)
ꢀ97.6 [d, P(1,3)], -44.8, [t, P(2)]
(1JP–P = 128 Hz)

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W.T.K. Chan et al. / Journal of Organometallic Chemistry 695 (2010) 1069–1073
Fig. 1. Molecular structure of the di-substituted product 3a. H-atoms have been omitted for clarity. Key bond lengths (Å) and angle (o); P(1)–P(2) 2.215(2), P(2)–P(3) 2.223(3),
P(1)–As(1) 2.346(2), P(2)–As(1) 2.342(2), As(1)–Si(1) 2.358(2), P(4)–P(6) 2.221(3), P(5)–P(6) 2.216(2), P(4)–As(2) 2.350(2), P(5)–As(2) 2.340(2), As(2)–Si(1) 2.363(2), P(1)–
P(3)–P(2) 88.90(9), P(3)–P(1)–As(1) 86.77(8), P(3)–P(2)–As(1) 86.70(9), P(1)–As(1)–P(2) 82.95(7), P(1)–As(1)–Si(1) 97.25(7), P(2)–As(1)–Si(1) 97.52(7), P(4)–P(6)–P(5)
89.30(9), P(6)–P(5)–As(2) 86.86(8), P(6)–P(4)–As(2) 86.50(8), P(4)–As(2)–P(5) 83.40(7), P(4)–As(2)–Si(1) 98.53(7), P(5)–As(1)–Si(1) 96.33(7), As(1)–Si(1)–As(2) 101.69(7)
[range of other angles at Si 106.7(2)–115.9(2)], mean puckering of the P3As rings 140 (about the P. . .P vectors).
Table 2
Details of the data collections and structural solutions of 3a and 4.
Compound
3a
4
Chemical formula
Formula weight
Crystal system
Space group
C26H60As2P6Si
736.49
C20H39P3Si
400.51
monoclinic
P2(1)/m
triclinic
ꢀ
P1
Unit cell dimensions
a (Å)
b (Å)
c (Å)
9.4278(2)
13.5822(3)
16.7416(4)
113.4493(9)
91.6253(9)
95.4497(10)
1952.69(8)
2
5.934(2)
15.006(4)
13.576(3)
a
(°)
b (°)
100.74(3)
c
(°)
V (Å3)
1187.7(6)
2
1.120
Z
qcalc (Mg/m3)
1.253
2.002
l
(Mo K
a
) (mmꢀ1
)
0.302
Reflections collected
Independent reflections (Rint
23 800
5592
(0.080)
0.052, 0.133
0.081, 0.149
2505
1735
(0.045)
0.052, 0.120
0.091, 0.140
Fig. 2. Molecular structure of the P3Si heterocycle 4. H-atoms have been omitted for
clarity. Key bond lengths (Å) and angle (o); P(1)–P(2) 2.236(2), P(1)–Si(1) 2.274(2),
P(1)–P(2)–P(1A) 91.21(8), P(2)–P(1)–Si(1) 81.28(6), P(1)–Si(1)–P(1A) 89.28(8),
puckering of P3Si ring 134.7 (about the P(1). . .P(1A) vector).
)
R1, wR2 [I > 2
r
(I)]
R1, wR2 (all data)
Data in common; k = 0.71073 Å, T = 180(2) K.
Nonetheless, 4 is the first example of a heterocycle containing a
P3Si ring unit, although related five-membered P4Si and P4Ge sys-
tems have been reported previously [13]. As in the structure of 3a,
the P–Si [2.274(2) Å] and P–P [2.236(2) Å] bonds are as expected
for single bonds [10]. Like [(tBuP)3SntBu2] [12] and [(RP)3As]ꢀ an-
ions [2], the heterocyclic ring of 4 is puckered [dihedral angle of
134.7° at the P(1)ꢁ ꢁ ꢁP(1A) vector].
of the two P3As ring units are orientated roughly perpendicularly
to each other largely in order to minimise steric congestion be-
tween the Bu and Me groups across the bridge. A further effect
t
of this alignment of the P3As rings is the reduction of potential
repulsion between the lone-pairs on the As centres (which are
roughly perpendicular to each other). The As–Si (mean 2.36 Å),
P–As (mean 2.34 Å) and P–P (mean 2.22 Å) bonds in 3a are typical
of single bonds of these types [10]. While the puckering of the
[(tBuP)3As] ring units in 3a (dihedral angle of 140° about the
Pꢁ ꢁ ꢁP vectors of the P3As rings) is similar to that found in the
3. Conclusions
The results presented in this paper show that the reactions of
[(RP)nAs]ꢀ anions with main group electrophiles (in this case
Me2SiCl2) can provide access to a range of new heterocyclic spe-
cies. The reaction characteristics observed in this study, nucleo-
philic substitution in the case of 2 and apparent electrophilic ring
opening in the case of 4, have been seen previously in studies of
the interaction of the [(tBuP)3As]ꢀ anion with transition metal
complexes and organic electrophiles (see Scheme 3). Further
studies with main group metal complexes should be of interest,
especially where lower oxidation state metal halides are involved.
structures
a range of compounds containing neutral and
anionic [(RP)3As] units; most notably in the As–As bonded dimer
[(tBuP)3As]2 [11]. The conformation of the [(tBuP)3As] ring units
in 3a and related compounds is (not surprisingly) largely influ-
enced by steric rather than electronic factors.
The structure of 4 is that of a four-membered, P3Si heterocycle
of crystallographic Cs symmetry (Fig. 2), and is closely related to
the previously reported tin(IV) heterocycle [(tBuP)3SntBu2] [12].

W.T.K. Chan et al. / Journal of Organometallic Chemistry 695 (2010) 1069–1073
1073
tion at ꢀ25 °C afforded yellow crystals of 4. Yield 0.16 g (10%).
31P{1H} (161.98 MHz, +25 °C, d6-benzene), d = 2.0–0.8 (m, 44H,
Cy). 1H NMR (400.16 MHz,+25 °C, d6-benzene), d = ꢀ44.8 (t, 1P),
ꢀ97.6 (d, 2P) (1JP–P = 127.6 Hz). 29Si NMR (79.49 MHz, +25 °C, d6-
benzene, rel. Me4Si), d = ꢀ23.5. Calculated for 4, C, 60.0; H, 9.8; P,
23.2; cald. for 2, C, 60.1, H, 10.1, P, 24.2.
3. Experimental
3.1. General experimental procedures
All compounds described in this paper are air- and moisture
sensitive. Preparations were performed on a double-manifold
vacuum line under argon atmosphere. Products were isolated
and stored with the aid of a nitrogen-filled glove box (Saffron type
b), equipped with Cu and molecular sieve columns in order to
remove O2 and moisture (respectively) from the atmosphere.
[{(tBuP)3As]Liꢁ2DABCOꢁTHF] (1ꢁ2DABCOꢁTHF) and [{(CyP)4As}Liꢁ
TMEDAꢁTHF] (2ꢁTMEDAꢁTHF) were prepared as crystalline samples
for further reactions according to the literature procedures.
Me2SiCl2 (Aldrich) was used as supplied commercially. TMEDA
(Aldrich) was dried over Na and stored under argon. In situ 31P
NMR studies were undertaken by placing ca. 0.8 ml of the reaction
solutions within a Wilmad 528PP (thin-walled) NMR tube contain-
ing d6-acetone capillary to obtain a lock. All 1H and 31P{1H} and
fully-coupled NMR spectra were recorded using a Bruker DPX
500 MHz NMR spectrometer. 31P NMR spectra were referenced to
an external standard of 85% H3PO4/D2O, while 1H NMR spectra
were referenced internally to the solvent peaks. Elemental (C, H,
N) analyses were obtained using an Exeter CE-440 Elemental Ana-
lyser. P analysis was obtained using spectrophotometric methods.
Samples for analysis (1–2 mg) were placed in pre-weighed, air-
tight aluminium boats in the glove box prior to analysis.
3.2. X-ray crystallographic studies of synthesis of 2 and 4
Data for both complex were collected on a Nonius Kappa CCD
diffractometer and solved by direct methods and refined by full-
matrix least squares on F2 [14].
4. Supplementary material
CCDC 756885 and 756886 contain the supplementary crystallo-
graphic data for 3a and 4. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via http://
www.ccdc.cam.ac.uk/data_request/cif.
References
[1] A.D. Hopkins, J.A. Wood, D.S. Wright, Coord. Chem. Rev. 216 (2001) 155.
[2] (a) [(tBuP)3As]ꢀ anion M.A. Beswick, N. Choi, A.D. Hopkins, M. McPartlin,
M.E.G. Mosquera, P.R. Raithby, A. Rothenberger, D. Stalke, A.E.H. Wheatley, D.S.
Wright, J. Chem. Soc., Chem. Commun. (1998) 2485;
(b) A. Bashall, M.A. Beswick, N. Choi, A.D. Hopkins, S.J. Kidd, Y.G. Lawson,
M.E.G. Mosquera, P.R. Raithby, A.E.H. Wheatley, J.A. Wood, D.S. Wright, J.
Chem. Soc., Dalton Trans. (2000) 479.
Synthesis of 3a; Me2SiCl2 (0.22 ml, 1.8 mmol) was added to a
solution of 2ꢁ2DABCOꢁTHF (0.80 g, 1.2 mmol) in toluene (30 ml)
and THF (30 ml) at room temperature. The resulting solution was
allowed to stir for ca. 20 h, resulting in a yellow solution and a
white precipitate. The solution was filtered through Celite and
the solvent partially removed under vacuum to generate a satu-
rated solution (ca. 30 ml remaining). Storage of the solution at
ꢀ20 °C afforded colourless crystals of 3a. Yield 0.42 g (23%). M.p.
decomp. >185 °C. 31P{1H} (161.98 MHz, +25 °C, d8-THF), d = ꢀ62.6
(d, 2P), ꢀ15.7 (t, P) (1JP–P = 159 Hz). 1H NMR (400.16 MHz, +25 °C,
[3] [(CyP)4As]ꢀ anion A. Bashall, F. García, A.D. Hopkins, J.A. Wood, M. McPartlin,
A.D. Woods, D.S. Wright, J. Chem. Soc., Dalton Trans. (2003) 1143.
[4] M.A. Beswick, N. Choi, C.N. Harmer, A.D. Hopkins, M. McPartlin, D.S. Wright,
Science 281 (1998) 1500.
[5] R.J. Less, R.L. Melen, V. Naseri, D.S. Wright, Chem. Commun. (2009) 4929.
[6] A. Schisler, P. Lönnecke, U. Huniar, R. Ahlrichs, E. Hey-Hawkins, Angew. Chem.,
Int. Ed. Engl. 40 (2001) 4217.
[7] (a) A. Bashall, A.D. Hopkins, M.J. Mays, M. McPartlin, J.A. Wood, A.D. Woods,
D.S. Wright, Chem. Soc., Dalton Trans. (2000) 1825;
(b) A.R. Armstrong, N. Feeder, A.D. Hopkins, M.J. Mays, D. Moncrieff, J.A. Wood,
A.D. Woods, D.S. Wright, J. Chem. Soc., Chem. Commun. (2000) 2483.
[8] F. García, Ph.D. Thesis, Cambridge University, 2002.
t
3
d6-benzene), d = 1.26 (d, 18H, Bu, JP–H = 12.2 Hz), 1.24 (d, 18H,
3
t
3
tBu, JP–H = 12.8 Hz), 1.17 (d, 18H, Bu, JP–H = 13.0 Hz), 1.01 (s, 6H,
SiMe3). Calculated for 3a, C, 42.4; H 8.2; cald. for 3a, C 41.1, H, 7.1.
Synthesis of 4; nBuLi (8.0 ml, 1.5 mol dmꢀ3 in hexanes,
12.0 mmol) was added dropwise to a stirred solution of CyPH2
(1.6 ml, 12.0 mmol) in toluene (30 ml) was cooled to ꢀ78 °C. Stir-
ring at room temperature for 1 h gave a yellow precipitate of the
lithiate. The mixture was cooled to ꢀ78 °C and a solution of
As(NMe2)3 in toluene (2.0 ml, 2.0 mol dmꢀ3, 4.0 mmol). After stir-
ring for 24 h at room temperature, Me2SiCl2 (1.47 ml, 12.0 mmol,
excess) was added dropwise to the resulting orange solution at
ꢀ78 °C. After stirring for 48 h a yellow solution was produced.
Reduction of the volume of this solution under vacuum gave a pre-
cipitate which was heated back into solution. Storage of the solu-
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December, 2009).
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