High oxidation state chromium, molybdenum and tungsten imido metallasiloxanes

Article abstract of DOI:10.1039/a904429i

Reactions between the bis-imido compounds [M(NBu^t)₂X₂] (M = Cr or Mo, X = Cl, M = W, X = NHBu^t) and tetraphenyldisiloxanediol (1:1) in the presence of two equivalents of added py where X = Cl gave the products [{CrO(NBu^t)(O(Ph₂SiO)₂)}²] 1, [Mo(NBu^t)(py)(O(Ph₂SiO)₂)₂] 2 and [W(NBu^t)(NH₂Bu^t)(O(Ph₂SiO) ₂)₂] 3 showing a marked variation from Cr to Mo and W. Single crystal X-ray studies of 1·C₆H₅Me, 2·py and 3·C₆H₅Me were made. Compound 1 is the first chromium(VI) oxo-imido compound to be structurally characterised and the first example of a chromium(VI) monocyclic metallasiloxane. Compounds 2 and 3 incorporate the first examples of six-membered metallasiloxane rings for compounds of Mo or W. The compounds were also characterised by multinuclear NMR and mass spectroscopy. The Royal Society of Chemistry 1999.

Full text of DOI:10.1039/a904429i

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High oxidation state chromium, molybdenum and tungsten imido
metallasiloxanes
Lawrence King, Majid Motevalli and Alice C. Sullivan*
Department of Chemistry, Queen Mary and Westfield College, Mile End Road, London,
UK E1 4NS. E-mail:a.c.sullivan@qmw.ac.uk
Received 3rd June 1999, Accepted 30th July 1999
Reactions between the bis-imido compounds [M(NBut)2X2] (M = Cr or Mo, X = Cl, M = W, X = NHBut) and
tetraphenyldisiloxanediol (1:1) in the presence of two equivalents of added py where X = Cl gave the products
[{CrO(NBut)(O(Ph2SiO)2)}2] 1, [Mo(NBut)(py)(O(Ph2SiO)2)2] 2 and [W(NBut)(NH2But)(O(Ph2SiO)2)2] 3 showing
a marked variation from Cr to Mo and W. Single crystal X-ray studies of 1ؒC6H5Me, 2ؒpy and 3ؒC6H5Me were made.
Compound 1 is the first chromium() oxo-imido compound to be structurally characterised and the first example
of a chromium() monocyclic metallasiloxane. Compounds 2 and 3 incorporate the first examples of six-membered
metallasiloxane rings for compounds of Mo or W. The compounds were also characterised by multinuclear NMR
and mass spectroscopy.
Homoleptic compounds having ligands of the type [(OSiR2)n-
O]2Ϫ are comparatively abundant with many examples of main-
group, transition metal and recently lanthanide compounds
known.1,2 In contrast, very few heteroleptic systems incorpor-
ating the same class of ligand are known. Notable heteroleptic
systems are the Group 4 cyclopentadienyl (η5-C5H5, Cp)
metallasiloxanes: [{ZrCp2(OSiPh2O)}2] and [{ZrCp2(OSiPh2-
OSiPh2O)}2].3 We were interested in developing routes to the
isoelectronic Group 6 compounds containing imido [NR]2Ϫ
ligands. In recent years numerous synthetic entries into Group
6 imido chemistry have been described some of which have
been used in this work. We report here on interesting results
from reactions between [M(NBut)2X2] (M = Cr or Mo, X = Cl;
M = W, X = NHBut) and tetraphenyldisiloxanediol (1:1) in the
presence of two equivalents of added py where X = Cl.4–7
transfer of oxygen and elimination of (Ph2SiO)n and ButNH2
and formation of [Cr(O)(NBut)Cl2] from which compound 1
may be derived, e.g. eqn. (4). The recrystallised yield of
[Cr(NBut)2Cl2] ϩ O(Ph2SiOH)2 →
“Cr(NHBut)(NBut)Cl2(OSiPh2OSiPh2OH)” →
[Cr(O)(NBut)Cl2] ϩ (Ph2SiO)n ϩ ButNH2 (4)
1ؒC6H5Me increased from 14 to 25% when a 1:2 molar ratio of
reagents [Cr(NBut)2Cl2]:O(Ph2SiOH)2 was employed. Oxo–
imido exchange in the compounds [Cr(NBut)2Cl2]9 and [Cr-
(NBut)2(OSiMe3)2]10 has been reported to occur on addition of
stoichiometric quantities of aqueous HCl and a red oil believed
to be [Cr(O)(NBut)Cl2] has been reported. To our knowledge 1
is the first example of a chromium() monocyclicmetalla-
siloxane (the cage compound [(c-C5H11)7Si7O11(OSiMe3)-
CrO2]11 and the mononuclear compound [CrO2(Ph3SiO)2]12
are known). There are no other structurally characterised
chromium() oxo-imido or monoimido compounds although
an oxo-imido chromium() species is known.13
Results and discussion
Synthesis
The air and moisture sensitive metallasiloxane compounds 1, 2
and 3 were isolated from reactions (1)–(3) between the Group 6
bis-imido metal compounds and tetraphenyldisiloxane diol in
1:1 molar ratio in toluene at room temperature. In the reactions
involving [Cr(NBut)2Cl2] and [Mo(NBut)2Cl2] two molar
equivalents of pyridine were added to effect [Hpy]Cl formation
which is subsequently separated from the products by filtration.
However the expected bis-imidometallasiloxanes are not
formed. The reaction with the chromium compound proceeds
to a disiloxanediolato bridged dimer but with replacement of
one of the imido groups at each chromium by an oxo group. In
addition to the isolated red crystalline 1ؒC6H5Me some toluene
soluble colourless crystalline product (infrared features consist-
ent with polysiloxane (Ph2SiO)n) is also formed. We have iso-
lated similar polysiloxane type by-products in several other
cases where the siloxanediolate has functioned as an oxo-
transfer reagent.8 Thus the reaction with the silanol may pro-
ceed by initial protonation of an imide group with subsequent
Treatment of the molybdenum compound [Mo(NBut)2Cl2]
with a solution of O(Ph2SiOH)2 and 2 equivalents of pyridine
in toluene gives the mononuclear monoimido bis-chelate
product 2ؒpy. This indicates a 1:2 rather than 1:1 stoichiometric
reaction between [Mo(NBut)2Cl2] and O(Ph2SiOH)2. When the
stoichiometric ratio was changed to 1:2 the yield of 2ؒpy
increased from 28 to 40%. In the reaction leading to compound
2 there is elimination of both HCl and the amine ButNH2, but
no oxo–imido exchange as found for 1. Instead the relatively
large co-ordination sphere of the metal accommodates two
mutually trans-disiloxanediolato ligands in chelate co-
ordination mode with tert-butylimido, ButN, and pyridine
occupying the fifth and sixth co-ordination sites so that the
metal centre is both electronically and sterically saturated. We
observed a similar result in the product from reaction of
O(Ph2SiOH)2 with the tungsten compound [W(NBut)2(NH-
But)2]. Once again there is a 1:2 stoichiometric reaction
[{CrO(NBut)(O(Ph2SiO)2)}2] 1 14%.
ϩ O(Ph2SiOH)2 ϩ 2py (r.t.) →
[Cr(NBut)2Cl2]
[Mo(NBut)2Cl2]
Red crystals 1ؒC6H5Me from toluene at Ϫ20 ЊC, mp 169–171 ЊC
ϩ O(Ph2SiOH)2 ϩ 2py (r.t.) → [Mo(NBut)(py)(O(Ph2SiO)2)2] 2 31%.
Yellow crystals 2ؒpy from toluene at Ϫ20 ЊC, mp 165–167 ЊC
[W(NBut)(NH2But)(O(Ph2SiO)2)2] 3 49%.
(1)
(2)
(3)
[W(NBut)2(NHBut)2] ϩ O(Ph2SiOH)2 (r.t.) →
Cream crystals 3ؒC6H5Me from CH2Cl2 at Ϫ20 ЊC; mp 186–188 ЊC
J. Chem. Soc., Dalton Trans., 1999, 3225–3228
3225
This journal is © The Royal Society of Chemistry 1999

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Table 1 Bond lengths [Å] and angles [Њ] for compound 1ؒC6H5Me
Cr(1)–O(1)
Cr(1)–N(1)
Cr(1)–O(2)
Cr(1)–O(3)
Cr(2)–O(5)
Cr(2)–N(2)
Cr(2)–O(6)
Cr(2)–O(7)
Si(1)–O(4)1
1.573(5)
1.624(7)
1.767(5)
1.769(5)
1.574(5)
1.621(7)
1.769(5)
1.772(5)
1.621(6)
Si(1)–O(3)
Si(2)–O(4)
Si(2)–O(2)
Si(3)–O(8)
Si(3)–O(7)
Si(4)–O(8)
Si(4)–O(6)2
O(4)–Si(1)1
O(6)–Si(4)2
1.630(6)
1.611(6)
1.625(5)
1.617(5)
1.629(5)
1.623(5)
1.625(5)
1.621(6)
1.625(5)
O(1)–Cr(1)–N(1)
O(1)–Cr(1)–O(2)
N(1)–Cr(1)–O(2)
O(1)–Cr(1)–O(3)
N(1)–Cr(1)–O(3)
N(2)–Cr(1)–O(3)
O(5)–Cr(2)–N(2)
O(5)–Cr(2)–O(6)
N(2)–Cr(2)–O(6)
O(5)–Cr(2)–O(7)
N(2)–Cr(2)–O(7)
O(6)–Cr(2)–O(7)
107.0(3)
110.6(3)
107.2(3)
109.6(3)
109.9(3)
112.4(3)
107.1(3)
110.4(3)
107.0(3)
109.8(3)
110.0(3)
112.5(2)
O(4)1–Si(1)–O(3)
O(4)–Si(2)–O(2)
O(8)–Si(3)–O(7)
O(8)–Si(4)–O(6)2
Si(2)–O(2)–Cr(1)
Si(1)–O(3)–Cr(1)
Si(2)–O(4)–Si(1)1
Si(4)2–O(6)–Cr(2)
Si(3)–O(7)–Cr(2)
Si(3)–O(8)–Si(4)
C(25)–N(1)–Cr(1)
C(53)2–N(2)–Cr(2)
108.1(3)
106.7(3)
108.5(3)
106.4(3)
140.3(3)
141.0(3)
154.2(4)
140.0(3)
139.2(3)
151.8(4)
145.6(6)
146.4(6)
Fig.
1
Molecular structure of compound 1ؒC6H5Me (thermal
ellipsoids at the 50% probability level).
Symmetry transformations used to generate equivalent atoms: 1
Ϫx ϩ 1, Ϫy, Ϫz ϩ 1; 2 Ϫx, Ϫy Ϫ 1, z ϩ 1.
Table 2 Bond lengths [Å] and angles [Њ] for compound 2ؒpy
Mo(1)–N(1)
Mo(1)–O(1)
Mo(1)–O(6)
Mo(1)–O(3)
Mo(1)–O(4)
Mo(1)–N(2)
Si(1)–O(2)
1.804(5)
1.912(5)
1.928(5)
1.939(5)
1.942(5)
2.270(5)
1.631(5)
1.639(5)
Si(2)–O(3)
Si(2)–O(2)
Si(3)–O(4)
Si(3)–O(5)
Si(4)–O(6)
Si(4)–O(5)
N(1)–C(54)
1.619(5)
1.632(5)
1.626(5)
1.641(5)
1.621(5)
1.624(5)
1.401(11)
Si(1)–O(1)
N(1)–Mo(1)–O(1)
N(1)–Mo(1)–O(6)
O(1)–Mo(1)–O(6)
N(1)–Mo(1)–O(3)
O(1)–Mo(1)–O(3)
O(6)–Mo(1)–O(3)
N(1)–Mo(1)–O(4)
O(1)–Mo(1)–O(4)
O(6)–Mo(1)–O(4)
O(3)–Mo(1)–O(4)
N(1)–Mo(1)–N(2)
O(1)–Mo(1)–N(2)
O(6)–Mo(1)–N(2)
O(3)–Mo(1)–N(2)
94.4(2)
95.1(2)
90.0(2)
99.6(2)
90.1(2)
165.2(2)
99.9(2)
165.7(2)
88.61(19)
87.6(2)
174.9(2)
82.04(18)
81.37(19)
83.99(19)
O(4)–Mo(1)–N(2)
O(2)–Si(1)–O(1)
O(3)–Si(2)–O(2)
O(4)–Si(3)–O(5)
O(6)–Si(4)–O(5)
C(54)–N(1)–Mo(1)
Si(1)–O(1)–Mo(1)
Si(2)–O(2)–Si(1)
Si(2)–O(3)–Mo(1)
Si(3)–O(4)–Mo(1)
Si(4)–O(5)–Si(3)
Si(4)–O(6)–Mo(1)
C(49)–N(2)–Mo(1)
C(53)–N(2)–Mo(1)
83.70(19)
108.4(3)
109.0(3)
107.9(3)
108.3(3)
170.3(5)
139.2(3)
132.1(3)
136.8(3)
136.5(3)
132.4(3)
140.4(3)
120.7(2)
119.3(2)
Fig. 2 Molecular structure of compound 2ؒpy, as in Fig. 1.
(although a 1:1 molar ratio was employed). The reaction is
virtually quantitative in terms of available silicon reagent. As
with the molybdenum compound 2ؒpy, elimination of both HCl
and the amine ButNH2 occurs without oxo–imido exchange and
the product [W(NBut)(NH2But)(O(Ph2SiO)2)2]ؒC6H5Me, 3ؒtolu-
ene, is formed. Roesky and co-workers14 have previously
reported on formation of the bis-imido tungsten dimer com-
pound [(NBut)2W(OBut2SiO)]2 from the reaction between
[W(NBut)2(NHBut)2] and the silanediol But2Si(OH)2, so it may
be inferred that the acidity of the silanol proton is an important
factor in determining whether or not protonation of the imido
group occurs. Silanol acidity is discussed extensively in a recent
review by Lickiss.15
The pattern of reactivity which resulted in the present series
of compounds is largely consequent upon the fact that the
imido groups are readily protonated by an acidic disiloxanediol
even in the presence of pyridine. Also the ligand (O(Ph2SiO)2)2Ϫ
can function as an oxo-transfer reagent particularly when
associated with oxophilic metal centres.
[(c-C5H11)7Si7O11(OSiMe3)CrO2] 1.557(5),1.574(5) Å.11 The
Cr᎐N distance in 1 1.624(7) Å is slightly longer and the Cr–
N–C angle 145.6(6)Њ bent compared to Cr–N 1.548(15) Å and
Cr–N–C 160.7(13) and 174.3(13)Њ in [Cr(NBut)2(OSiPh3)2].16
The molybdenum compound 2 crystallises with one pyridine
solvent molecule per unit cell and adopts the classic py solvated
vanadyl acetate type structure. The six-coordinated Mo atom
sits slightly below the equatorial plane described by the chelat-
ing disiloxanolate ligands. The structural parameters of the
planar molybdadisiloxane rings are within the ranges seen for
other six-membered metallasiloxane rings. The imido function
displays the linear co-ordination of the 6e-donor ligand. The
Mo–N(1) distance is 1.804(5)Å (there are no structures with
comparable geometry having the NBut group but values
between 1.704(8) and 1.733(7) Å are reported for other linear
Mo–NBut fragments in d0 complexes).
Crystal structures
The structures of one of two crystallographically distinct mole-
cules of compound 1ؒC6H5Me and 2 are shown in Figs. 1 and 2.
Selected bond distances and angles are given in Tables 1 and 2.
There is a slightly puckered 12-membered dichromiahexa-
siloxane ring in 1 (deviations from the plane described by the
ligating oxygens O(2) and O(3) are Cr(1) Ϫ0.4575, Si(1)
Ϫ0.4806, Si(2) Ϫ0.6270, O(4) 0.2423 Å). The distances and
angles associated with the disiloxanediolate ligand are within
the normal ranges while the geometry at chromium is tetra-
X-Ray data collected on a crystal of compound 3ؒC6H5Me at
180 K failed to distinguish clearly between a centrosymmetric
¯
P1 and non-centrosymmetric P1 structure. The solution in P1
started off with two different tungsten-nitrogen distances with-
in the trans-ButN–W–NButH2 unit. With further refinement
cycles the nitrogen positions became non-positive definite and
hedral. The Cr᎐O distance in 1 1.573(5) Å is close to those in
᎐
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J. Chem. Soc., Dalton Trans., 1999, 3225–3228

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Table 3 Bond lengths [Å] and angles [Њ] for compound 3ؒC6H5Me
nitrogen filled glove-box. Solvents were refluxed over an
appropriate drying agent and degassed prior to use. Melting
points were recorded on samples sealed in capillaries under
nitrogen. The NMR spectra were recorded on Bruker WH250
(1H, 13C) and AMX600 (29Si) spectrometers, IR spectra on a PE
1720X FT instrument with a solid-state ATR attachment.
Microanalyses were obtained from the service at University
College London, and mass spectra from the EPSRC Mass
Spectroscopy Service, Wales, Pyridine was distilled over KOH
and stored over 4 Å molecular sieves.
W(1)–O(1)
W(1)–O(1)1
W(1)–O(3)1
W(1)–O(3)
W(1)–N(1)
W(1)–N(1)1
1.919(5)
1.919(5)
1.932(5)
1.932(5)
2.013(7)
2.013(7)
Si(1)–O(1)
Si(1)–O(2)
Si(2)–O(3)
Si(2)–O(2)
N(1)–C(25)
1.617(5)
1.640(5)
1.617(5)
1.636(5)
1.456(11)
O(1)–W(1)–O(1)1
O(1)–W(1)–O(3)1
O(1)1–W(1)–O(3)1
O(1)–W(1)–O(3)
O(1)1–W(1)–O(3)
O(3)1–W(1)–O(3)
O(1)–W(1)–N(1)
O(1)1–W(1)–N(1)
O(3)1–W(1)–N(1)
O(3)–W(1)–N(1)
O(1)–W(1)–N(1)1
180.0(3)
90.0(2)
90.0(2)
90.0(2)
90.0(2)
180.0(3)
90.2(2)
89.8(2)
90.3(3)
89.7(3)
89.8(2)
O(1)1–W(1)–N(1)1
O(3)1–W(1)–N(1)1
O(3)–W(1)–N(1)1
N(1)–W(1)–N(1)1
O(1)–Si(1)–O(2)
O(3)–Si(2)–O(2)
Si(1)–O(1)–W(1)
Si(2)–O(2)–Si(1)
Si(2)–O(3)–W(1)
C(25)–N(1)–W(1)
90.2(2)
89.7(3)
90.3(3)
180.0(6)
109.5(3)
108.9(3)
138.2(3)
131.2(3)
139.0(3)
161.9(7)
Syntheses
[{CrO(NBut)(OSiPh2OSiPh2O)}2] 1. To a solution of [Cr-
(NBut)2Cl2] (0.32 g, 1.2 mmol) in toluene (25 cm3) was added
dropwise, with stirring, a mixture of (Ph2SiOH)2O (0.50 g, 1.2
mmol) and pyridine (0.2 cm3, 2.4 mmol) in toluene (25 cm3).
Following the addition of the siloxanediol the dark red solution
immediately lightened and a fine precipitate was deposited.
After 4 h at room temperature the solution was filtered and the
mother-liquor reduced in vacuo to yield a red oil. Dissolution of
the oil in the minimum quantity of toluene (ca. 15 cm3), fol-
lowed by the addition of an excess of hexane (ca. 50 cm3),
precipitated halide salts and siloxane (Ph2SiO)n. Filtration of
the solution followed by reduction in vacuo afforded the crude
product as a red oil. X-Ray quality crystals of [{CrO(NBut)-
(OSiPh2OSiPh2O)}2] were grown in low yield (0.20 g, 14%) from
a concentrated toluene solution at Ϫ20 ЊC, mp 169–171 ЊC. IR
(cmϪ1): 3045w, 2978w, 1591w, 1568w, 1429m, 1116s, 1062s,
1026s, 998s, 966s, 911vs, 742s, 718vs, 697vs, 496s and 481s.
Symmetry transformations used to generate equivalent atoms: 1 Ϫx,
Ϫy, Ϫz; 2 Ϫx Ϫ 1, Ϫy Ϫ 1, Ϫz Ϫ 1.
1
NMR: H (CDCl3, 250 MHz, 298 K), δ 1.0 (s, 18 H, NBut),
7.15–7.4 (m, m-, p-H of Ph, CDCl3 solvent) and 7.55–7.7 (m, 16
H, o-H of Ph); 13C (C6D6, 62.9 MHz, 298 K), δ 28.5 (C(CH3)3),
69.0 (C(CH3)3), 127.6 (m-C of Ph), 129.8 (p-C of Ph), 134.9,
135.0 (o-C of Ph) and 135.5(ipso-C of Ph); 29Si (CDCl3,
119.2 MHz, 300 K ), δ Ϫ35.97 (s). Accurate mass FAB (liquid
secondary ion mass spectroscopy) (polyethylene glycol)–3-
nitrobenzyl alcohol matrix): found m/z 1103.2088, calculated
for C56H59Cr2N2O8Si4(MHϩ) 1103.215875.
Fig. 3 Molecular structure of compound 3ؒC6H5Me, as in Fig. 1.
the refinement became unstable. The presence of trans imido–
When the reaction was repeated using a 1:2 molar ratio of
[Cr(NBut)2Cl2] and (Ph2SiOH)2O the yield of compound
1ؒC6H5Me increased to 25%.
amine ligation, trans-ButN–W–NButH2, is confirmed by 1H and
13
¯
C NMR spectra of 3. The refinement in P1 on the other hand
[Mo(NBut)(py)(OSiPh2OSiPh2O)2] 2. To
a solution of
was stable and the residual electron density in the difference
map relatively low. In this solution the bond distances and
angles in the trans-ButN–W–NButH2 unit given in Table 3 are
an average of those expected for the isomeric bis-amide and
imide–amine systems, e.g. compare values for compound 3
W–N,W–N–C [W(NHBut)2] 2.013(7) Å,161.9(7)Њ with those in
[Mo(NBut)2Cl2] (0.52 g, 1.7 mmol) in toluene (25 cm3) was
added dropwise, with stirring, a mixture of (Ph2SiOH)2O (0.69
g, 1.7 mmol) and pyridine (0.27 cm3, 3.3 mmol) in toluene (50
cm3). Upon addition of the siloxanediol the solution turned
orange, and a fine precipitate was deposited. After 4 h at room
temperature the solution was filtered and the mother-liquor
reduced in vacuo to yield a yellow oil. Dissolution of the oil
in toluene (ca. 20 cm3), followed by filtration and reduction
in vacuo then cooling to Ϫ20 ЊC afforded yellow crystals of
[Mo(NBut)(py)(OSiPh2OSiPh2O)2]ؒpy (0.55 g, 28%), mp 165–
167 ЊC. IR (cmϪ1): 3048w, 2973w, 1603w, 1591w, 1486w, 1446w,
1429m, 1216w, 1115s, 1070s, 1033s, 1006s, 990s, 879vs, 743s,
715s, 695vs, 513s, 503s, and 473s. NMR: 1H (CDCl3, 250 MHz,
298 K), δ 0.7 (s, 9 H, NBut), 6.25 (t, 2 H, py), 7.0–7.35 (m, m-,
p-H of Ph, CDCl3 solvent), 7.55–7.61 (m, 8 H), 7.9–8.0 (s, 1 H,
py), 8.1–8.2 (m, 8 H) and 8.7–8.8 (m, 2 H, py); 13C (CDCl3, 62.9
MHz, 298 K), δ 28.7 (C(CH3)3), 75.0 (C(CH3)3), 122.4(py),
127.3, 127.5 (m-C of Ph), 129.1(py) 129.3, 129.7 (p-C of Ph),
134.5, 134.9 (o-C of Ph), 136.5, 137.0 (ipso-C of Ph) and
149.5(py); 29Si (CDCl3, 119.2 MHz, 300 K), δ Ϫ38.73 (s).
Found: C, 63.3; H, 5.4; N, 2.8. Calc. for C57H54MoN2O6Si4: C,
63.8; H, 5.1; N, 2.6%.
17
BzpW(NBut)(NHBut)2 W–N, W–N–C[W(NHBut)2] 1.924(5)
Å, 139.5(4) and 1.931(4) Å, 140.6(4)Њ and W–N,W–N–C-
[W(NBut)] 1.753(4) Å, 161.0(4)Њ or those in [W(NBut)(OBut)3-
Cl(NH2But)]18 W–N,W–N–C [W(NBut)]1.740(9) Å, 171.9(5)Њ,
W–N,W–N–C[W(NH2But)] 2.429(5) Å, 130.8(4)Њ. Despite the
averaging within the trans-ButN–W–NButH2 unit the structure
does provide confirmation that the gross structural features of
the molecule, shown in Fig. 3, are similar to those of the
molybdenum compound 2ؒpy. The latter and 3 are examples of
the class of compounds [M(NR)X4Ln],4 e.g. [W(NBut)(OBut)3-
Cl(NH2But)]18 and [Mo(NC6H4Me)Cl4]thf.19 However there are
no other examples of compounds of Mo or W having six-
membered metallasiloxane rings ([WO(O(Ph2SiO)3)2] with
eight-membered tungstasiloxane rings was recently reported).20
Further investigations of the chemistry of the compounds
1–3 and modifications to the sequence of reactions in which
they were formed are in progress.
When the reaction was repeated using a 1:2 molar ratio of
[Mo(NBut)2Cl2] and (Ph2SiOH)2O the yield of compound 2ؒpy
increased to 40%.
Experimental
All manipulations were carried out under an atmosphere of dry
nitrogen using standard Schlenk techniques and a conventional
[W(NBut)2(NH2But)(OSiPh2OSiPh2O)2] 3. To a solution of
J. Chem. Soc., Dalton Trans., 1999, 3225–3228
3227

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Table 4 X-Ray data for compounds 1ؒC6H5Me, 2ؒpy and 3ؒC6H5Me
1ؒC6H5Me
2ؒpy
3ؒC6H5Me
Empirical formula
Formula weight
C63H66Cr2N2O8Si4
1195.54
C62H59MoN3O6Si4
1150.42
C63H66N2O6Si4W
1243.39
T/K
Crystal system
Space group
220(2)
293(2)
180(2)
Triclinic
Triclinic
Triclinic
¯
¯
¯
P1
P1
P1
a/Å
b/Å
c/Å
α/Њ
13.931(7)
15.948(9)
16.469(8)
68.08(6)
111.08(5)
89.96(7)
3129(3)
2
0.477
13.655(9)
14.524(10)
16.072(12)
102.67(8)
87.75(6)
107.62(6)
2963(4)
10.333(4)
10.733(8)
14.149(7)
110.88(6)
90.08(4)
99.91(4)
1440.9(14)
2
β/Њ
γ/Њ
V/Å3
Z
2
µ/mmϪ1
0.354
2.140
Reflections collected
Independent reflections
Final R1, wR2 [I > 2σ(I)]
(all data)
9964
10403
5351
9614 [R(int) = 0.3003]
0.0716, 0.1543
0.2487, 0.2077
10401 [R(int) = 0.0000]
0.1150, 0.2584
0.2366, 0.3001
5054 [R(int) = 0.0173]
0.0638, 0.1566
0.0696, 0.1619
[W(NBut)2(NHBut)2] (0.50 g, 1.1 mmol) in toluene (25 cm3) was
added dropwise, with stirring, a solution of (Ph2SiOH)2O (0.44
g, 1.1 mmol) in toluene (25 cm3). No visible changes were
observed following the diol addition. After 18 h at room tem-
perature the solution was reduced in vacuo to yield a yellow oil.
Recrystallisation from a concentrated CH2Cl2 solution at
Ϫ20 ЊC, afforded compound 3 (0.62 g, 49%) as colourless cubes,
mp 186–188 ЊC. IR (cmϪ1): 3314w, 3047w, 2974w, 1591w,
1429m, 1274m, 1215w, 1114s, 1032m, 1005s, 989s, 883vs, 744s,
for NMR and the EPSRC National Mass Spectrometry Service
for mass spectra.
References
1 R. Murugavel, A. Voigt, M. G. Walawalkar and H. W. Roesky,
Chem. Rev., 1996, 96, 2205; L. King and A. C. Sullivan, Coord.
Chem. Rev., 1999, in the press.
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and F. T. Edelmann, Chem. Commun., 1998, 2217.
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Robert, Inorg. Chem., 1994, 33, 1292; A. M. Piotrowski and E. I.
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4 D. E. Wigley, Prog. Inorg. Chem., 1994, 42, 239.
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Bates and M. B. Hursthouse, Polyhedron, 1990, 9, 2625.
6 G. Schoettel, J. Kress and J. A. Osborn, J. Chem. Soc., Chem.
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7 W. A. Nugent, Inorg. Chem., 1983, 22, 965; W. A. Nugent, R. L.
Harlow, Inorg. Chem., 1980, 19, 777.
8 M. Motevalli, D. Shah, S. A. A. Shah and A. C. Sullivan,
Polyhedron, 1996, 15, 2387.
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1990, 9, 774.
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12 L. M. Baker and W. L. Carrick, J. Org. Chem., 1970, 35, 774.
13 W.-H. Leung, A. A. Danopoulos, G. Wilkinson, B. Hussain-Bates
and M. B. Hursthouse, J. Chem. Soc., Dalton Trans., 1991, 2051;
H.-W. Lam, G. Wilkinson, B. Hussain-Bates and M. B. Hursthouse,
J. Chem. Soc., Dalton Trans., 1993, 1477.
14 H.-J. Gosink, H. W. Roesky, H.-G. Schmidt, M. Noltemeyer,
E. Irmer and R. Herbst-Irmer, Organometallics, 1994, 13, 3420.
15 P. D. Lickiss, Adv. Inorg. Chem. Radiochem., 1995, 42, 147.
16 W. A. Nugent, R. J. McKinney, R. V. Dasowski and F. A.
Van-Catledge, Inorg. Chim. Acta, 1982, 65, L91.
17 M.-T. Chan, W. C. Fultz, W. A. Nugent, D. C. Roe and T. H. Tulip,
J. Am. Chem. Soc., 1985, 107, 251.
18 D. C. Bradley, A. J. Howes, M. B. Hursthouse and J. D. Runnacles,
Polyhedron, 1991, 10, 477.
19 H. W. Roesky, H. Plenio, K. Keller, M. Noltemeyer and G. M.
Sheldrick, Chem. Ber., 1986, 119, 3150.
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Dalton Trans., 1998, 19, 32.
1
715s, 696vs, 517s, 505s, and 472vs. NMR: H (toluene-d8, 250
MHz, 298 K), δ 0.4 (s, 9 H, NButH2), 0.6 (s, 9 H, NBut), 2.05 (s,
2 H, NButH2), 7.0–7.3 (m, m-, p-H of Ph, C7D8 solvent), 7.92
(dd, 8 H, o-H of Ph) and 8.1 (dd, 8 H, o-H of Ph); 13C (CDCl3,
62.9 MHz, 298 K), δ 30.8 (C(CH3)3 of NH2But), 31.5
(C(CH3)3 of NBut), 49.0 (C(CH3)3 of NH2But), 70.1 (C(CH3)3
of NBut), 127.7 (m-C of Ph), 129.9, 130.0 (p-C of Ph), 134.4,
134.7 (o-C of Ph), 135.8, 136.3 (ipso-C of Ph); 29Si (CDCl3, 119.2
MHz, 300 K), δ Ϫ36.9.
X-Ray crystallography
Data were collected on a CAD4 diffractometer using Mo-Kα
(λ = 0.71069 Å) radiation and corrected for absorption using
ψ scans and DIFABS21 for compound 3ؒC6H5Me (see Table 4
for details of data collection and refinement). The structures
were solved by standard heavy atom techniques (SHELXS 86)22
and refined by full-matrix least squares (on F 2, SHELXL 97).23
The phenyl groups were treated as rigid hexagons [C–C 1.395
Å, C–C–C 120Њ, with inclusion of hydrogen atoms at fixed posi-
tions C–H 0.93 Å ]. The lattice held pyridine in compound 2ؒpy
showed positional disorder which was modelled (as a rigid
hexagon) using a 60/40 two site occupation. Hydrogens were
included at fixed positions. The high residual factor for it may in
part be due to this disorder. Solutions for 3ؒC6H5Me in P1 and
¯
¯
P1 were discussed above. For the toluene molecule in the P1
four of the carbon sites including the methyl group and its 3
nearest neighbours were modelled for 2-site occupancy about
the centre of symmetry.
CCDC reference number 186/1600.
See http://www.rsc.org/suppdata/dt/1999/3225/ for crystallo-
graphic files in .cif format.
21 N. Walker and D. Stuart, DIFABS, Acta Crystallogr., Sect. A, 1983,
39, 158.
22 G. M. Sheldrick, Acta Crystallogr. Sect. A, 1990, 46, 467.
23 G. M. Sheldrick, SHELXL 97, Program for the Refinement of
Crystal Structures, University of Göttingen, 1997.
Acknowledgements
We thank EPSRC for support ROPA GR/K90425, G. Coum-
barides (Queen Mary and Westfield College) and Peter Haycock
from University of London Interdisciplinary Research Service
Paper 9/04429I
3228
J. Chem. Soc., Dalton Trans., 1999, 3225–3228