Synthesis and crystal structure of [K{O(Ph SiO) SiPh OH}] ؒC H ;
2
2
2
2
6
6
the first structurally characterised example of a monometallated
derivative of an á,ù-siloxane diol. Solution chemistry in relation to
KOH-promoted ring-opening polymerisation of (Ph SiO)3
2
Barbara Laermann, Michael Lazell, Majid Motevalli and Alice C. Sullivan*
Department of Chemistry, Queen Mary and Westfield College, Mile End Road, London E1 4NS, UK
t
4
have been characterised, e.g. [Li{OSi(OH)Bu }] and [Na-
2
4
t
5
The first structurally characterised example of a
{OSi(OH)Bu }ؒthf] , compound 1 is the first example of a
2 6
monometallated derivative of an α,ω-siloxane diol compound
structurally characterised monometallated α,ω-siloxane diol.
One of the standard routes to silicone polymers involves
KOH in anionic ring-opening polymerisation of cyclic silox-
[
[
K{O(Ph SiO) SiPh OH}] ؒC H has been isolated {from
2
2
2
2
t
6
6
(Ph SiOH) O] and KOBu , 1:1 molar ratio} and structurally
2
2
6
characterised by X-ray crystallography, proton NMR, IR and
anes and it is generally accepted that catalytic activity depends
2
9
variable-temperature Si NMR and its chemistry in relation to
KOH-promoted ring-opening polymerisation of (Ph SiO) is
on the presence of free ion pairs which are in equilibrium with
6
,7
dormant associated ion pairs. Much of the evidence is derived
from extensive analysis of the kinetics as well as solution con-
ductivity during polymerisation. It is possible that structure 1
might represent the associated product of the first step in the
ring-opening polymerisation of (Ph SiO) . We investigated the
2
3
discussed.
The co-ordination chemistry of α,ω-siloxane diolates [(R SiO) -
2
1
n
2
3
2
Ϫ
O] represents one area of metallasiloxane chemistry which
also covers metal complexation by a range of other important
siloxanolate ligand types, for example, species with RSiO3,
R SiO and R SiO functionalities. Some of these compounds
reaction between KOH and (Ph SiO) (1:1) in dry 5% toluene
2 3
in ethanol, at room temperature. A crop of colourless crystals
deposited from a solution of the reaction products in toluene
at Ϫ25 ЊC was not compound 1 but (Ph SiO) . Ring-opening
2
2
3
2
4
are of interest both as precatalysts for olefin polymerisation and
as precursors for metal oxide–silica materials. In recent years
polymerisations of cyclic siloxanes are known to proceed ini-
tially to the linear polymer with subsequent rearrangement to
the more thermodynamically stable cyclics. However com-
1
6
we have described a number of co-ordination compounds
derived from the dilithium and disodium salts of the disil-
pound 1 itself showed no activity towards (Ph SiO) in refluxing
2
3
2
oxane diol [(Ph SiOH) O]. The direct reaction between metal
thf [1:(Ph SiO) , 1:0.01]. The cyclic trimer (Ph SiO) was
2
2
2
3
2
3
and diol was employed for the formation of the disodium com-
pound but we were unable to isolate a potassium compound
in this way. Thus we investigated alternative routes to such
reagents. In the course of this we investigated the reaction
recovered unchanged, and this suggests that 1 remains associ-
ated in thf solution and is not in equilibrium with an ion pair
which might have promoted ring-opening oligomerisation.
However compound 1, not surprisingly, does react with KOH
(molar ratio 10:1) in toluene–ethanol as evidenced by changes
in the IR spectrum of the product (products not characterised).
Thus, the isolation of (Ph SiO) , rather than compound 1, from
t
between [(Ph SiOH) O] and KOBu in toluene–tetrahydrofuran
2
2
(
thf), molar ratio 1:1, and isolated the compound [K{O(Ph Si-
2
O) SiPh OH}] ؒC H 1 in 12% yield after two recrystallisations
2
2
2
6
6
2
4
of the first crop from hot toluene–benzene.† We have previously
the reaction between KOH and (Ph SiO) suggests either that
compound 1 once formed competes with (Ph SiO) for reaction
2 3
2 3
2
Ϫ
observed chain expansion from disiloxane in [(Ph SiO) O] to
2
2
2
Ϫ
trisiloxanediolate [O(Ph SiO) SiPh O] during the transfer of
the diolate ligand from the dilithium and disodium salts to Sn
and some transition metals. The formation of the dilithium
and disodium reagents themselves however proceeded without
such chain expansion. The formation of 1 as described here
with KOH and these initial products react with (Ph SiO) , or
2
2
2
2 3
IV
that a reactive monomeric version of 1 is formed which can
promote oligomerisation of (Ph SiO) before the dimer 1 can
2
2
3
form.
The crystal structure of 1‡ shows two independent molecules
3
proceeds with chain expansion. Compound 1 is sparingly sol-
uble in aromatic hydrocarbons but dissolves readily in chloro-
form, thf, ethanol and acetone. A powdered sample of 1
appeared unchanged (by IR) after standing in air for 30 min.
While some monometallated derivatives of diorganosilanediols
‡
Crystal data for C H K O Si : cube, M = 1378.28, triclinic, space
78 68 2 8 6
¯
group P1, dimensions 0.34 × 0.45 × 0.24 mm, a = 12.119(1), b =
1
3.219(1), c = 24.460(2) Å, α = 103.44(2), β = 77.13(1), γ = 100.98(2)Њ,
3
Ϫ3
U = 3675.5(5) Å , Z = 2, D = 1.245 Mg m , F(000) = 1440, µ(Mo-Kα)
c
Ϫ1
=
0.281 mm . Data were collected at ≈293 K on a CAD4 diffracto-
t
†
Compound 1. To a suspension of KOBu (0.90 g, 8.10 mmol) in tolu-
meter using Mo-Kα radiation (λ = 0.710 69 Å) and were not corrected
3
ene (50 cm ) at 0 ЊC was added a solution of [(Ph SiOH) O] (3.34 g, 8.10
mmol) in thf (15 cm ). This mixture was stirred for 3 h, the solvent
for absorption. The structure was solved by standard heavy atom tech-
2
2
3
8
2
niques (SHELXS 86) and refined by full-matrix least-squares (on F )
(SHELXL 93) with phenyl groups treated as rigid hexagons [C᎐C
3
9
evaporated and the residue extracted with toluene (ca. 30 cm ). The
toluene extract was concentrated until turbid. A clear solution was
obtained on heating and colourless crystals of 1 were obtained on slow
cooling to room temperature. These were recrystallised from toluene–
benzene (9:1) to give 0.7 g of 1 (12% based on available potassium).
Material remaining in the mother-liquors was not further character-
ised. For compound 1 m.p. 120–122 ЊC (Found: C, 68.05; H, 5.15. Calc.
1.395 Å, C᎐C᎐C 120Њ, and with inclusion of hydrogen atoms at fixed
positions C᎐H 0.93 Å]. A total of 10 202 reflections were measured of
which 10 199 were used in the final refinement. Final R1 = 0.0697,
wR2 = 0.1636 [I > 2σ(I)] and R1 = 0.1763, wR2 = 0.1843 (all data)
2
2
2
for 705 parameters. Weighting scheme w = 1/[σ (F ) ϩ (0.0894P) ϩ
o
2
2
0.00P] where P = (Fo ϩ 2F )/3. Atomic coordinates, thermal
c
1
for C H K O Si : C, 67.9; H, 4.95%). H NMR (80 MHz, CDCl ):
parameters, and bond lengths and angles have been deposited at the
Cambridge Crystallographic Data Centre (CCDC). See Instructions for
Authors, J. Chem. Soc., Dalton Trans., 1997, Issue 1. Any request to the
CCDC for this material should quote the full literature citation and the
reference number 186/456.
7
8
68
2
8
6
3
2
9
δ 7.7 (m, m-H of Ph) and 7.2 (m, o- and p-H of Ph). Si NMR (acetone/
2
[
H ]acetone, 193 K): δ Ϫ42.1 (s) and Ϫ46.6 (s), relative intensity 2:1.
6
Ϫ1
IR (Nujol, cm ): 3500w (br), 1588m, 1429s, 1261m, 1119s, 1038s, 997s,
9
38s, 802m, 755m, 743m, 700s, 627w, 614w, 526s and 508s.
J. Chem. Soc., Dalton Trans., 1997, Pages 1263–1264
1263