Reactions of [W2(OCH2tBu)8] (M=M) with diazobenzene and trimethylsilyldiazomethane. Preparation and structures of W2(OCH2tBu)8(NPh) and W2(OCH2tBu)8(N2C(H) SiMe3)

Article abstract of DOI:10.1039/b304587k

Hydrocarbon solutions of W₂(OCH₂^tBu)₈ (M=M) react with azobenzene at room temperature to give the phenylimido-bridged compound W₂(μ-NPh)(μ-OCH₂^tBu)₂(OCH ₂^tBu)₆ which has a confacial biooctahedral geometry with a W-W single bond length of 2.5613(2) A and W-N = 1.987(3) A (ave). Similarly, W₂(OCH₂^tBu)₈ (M=M) and trimethylsilyldiazomethane react to give the 1 : 1 adduct W₂ (μ-N₂C(H)SiMe₃)(μ-OCH₂^tBu) ₂(OCH₂^tBu)₆ which has a W-W distance of 2.5626(2) A and W-N = 1.985(1) A (ave). The μ- N₂CHSiMe₃ ligand can be described as a hydrazonido(2-) ligand. The N-N distance is 1.366(4) A and the N-N-C angle is 120.1(3)°. The NNC plane of the bridging ligand is perpendicular to the W-W bond axis. The bonding in these molecules is discussed in the light of electronic structure calculations employing density functional theory. The present findings are contrasted with related reactions involving MM multiply bonded compounds and with low valent early transition metal complexes that are similarly known to activate N-N bonds.

Full text of DOI:10.1039/b304587k

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Reactions of [W (OCH tBu) ] (M᎐M) with diazobenzene and
᎐
2
2
8
trimethylsilyldiazomethane. Preparation and structures of
t
W2(OCH2tBu)8(NPh) and W2(OCH2 Bu)8(N2C(H)SiMe3)
Malcolm H. Chisholm,* Damon R. Click, Judith C. Gallucci and Christopher M. Hadad
Department of Chemistry, The Ohio State University, 100 W. 18th Avenue, Columbus,
Ohio 43210, USA. E-mail: chisholm@chemistry.ohio-state.edu
Received 25th April 2003, Accepted 6th June 2003
First published as an Advance Article on the web 15th July 2003
t
Hydrocarbon solutions of W (OCH Bu) (M᎐M) react with azobenzene at room temperature to give the
᎐
2
2
8
t
t
phenylimido-bridged compound W2(µ-NPh)(µ-OCH2 Bu)2(OCH2 Bu)6 which has a confacial biooctahedral geometry
with a W–W single bond length of 2.5613(2) Å and W–N = 1.987(3) Å (ave). Similarly, W (OCH Bu) (M᎐M) and
t
᎐
2
2
8
t
t
trimethylsilyldiazomethane react to give the 1 : 1 adduct W2(µ-N2C(H)SiMe3)(µ-OCH2 Bu)2(OCH2 Bu)6 which
has a W–W distance of 2.5626(2) Å and W–N = 1.985(1) Å (ave). The µ-N2CHSiMe3 ligand can be described as a
hydrazonido(2Ϫ) ligand. The N–N distance is 1.366(4) Å and the N–N–C angle is 120.1(3)Њ. The NNC plane of the
bridging ligand is perpendicular to the W–W bond axis. The bonding in these molecules is discussed in the light of
electronic structure calculations employing density functional theory. The present findings are contrasted with related
reactions involving MM multiply bonded compounds and with low valent early transition metal complexes that are
similarly known to activate N–N bonds.
In contrast to the extensive reaction chemistry of the MM triple
bond complexes, those having MM double bonds have been
little studied.1 In part, this may reflect upon two factors. 1)
There are relatively few complexes having MM double bonds
and 2) of those that are known, many are coordinatively satur-
ated involving face or edge sharing biooctahedra as seen in the
solid state structure of MoO2.2 Although the compound
reactions, a trace of a colorless crystalline compound was
formed. We were not able to collect sufficient of this to charac-
t
terize it, but we consider it is quite probably PhNW(OCH2 Bu)4
which is akin to the known ArNW(OR)4 compounds6 and, in
this reaction, may be formed by a competitive kinetic pathway.
t
b
[W2(ꢀ-N2CHSiMe3)(ꢀ-OCH2 Bu)2(OCH2tBu)6.
t
t
[W2(OCH2 Bu)8] and trimethylsilyldiazomethane (1 equiv.)
react in hydrocarbon solvents at 25 ЊC to yield the 1 : 1 adduct
as a red crystalline solid upon crystallization from cold hexanes
solutions. This compound is inert with respect to further
reaction with Me3SiCHN2 at this temperature.
[W2(OCH2 Bu)8] is believed to adopt a similar structure in the
solid state,3 it reacts as though it were coordinatively unsatur-
ated and can ligate such molecules as carbon monoxide, ethyne,
ethylene, allene and acetone.4 It is also reactive to the Group 16
t
t
elements forming the series W2(µ-E)(µ-OCH2 Bu)2(OCH2 Bu)6
where E = O, S, Se and Te.5 This reaction represents the formal
conversion of a MM double bond to a MM single bond by a
two-electron redox process. We thus became interested in the
Spectroscopic characterization data
1
Both compounds are diamagnetic and yield H NMR spectra
t
reactions between [W2(OCH2 Bu)8] and azobenzene which
consistent with their solid-state structures (vide infra) in which
there are confacial biooctahedra with two bridging alkoxides
and one nitrogen-containing bridging ligand. In solution, these
approximate C2v symmetry and the RO groups give rise to three
might, by a double bond metathesis reaction, lead to PhNW-
t
(OCH2 Bu)4 or some other product of addition. Compounds of
the type ArNW(OR)4 are well known,6 and earlier work by
Cotton had shown a similar metathesis reaction involving a
NbNb double bond.7 Also, the direct addition of molecular O2
t
singlets arising from the Bu groups in the ratio 4 : 2 : 2. The
methylene protons appear as two singlets of relative intensity
4 : 4 and an AB quartet of intensity 8. The singlets arise from
the methylene protons associated with the bridging neopentox-
ide groups and those that are trans to the bridging nitrogen
atom. These all lie on a mirror plane. The methylene protons
on the other four alkoxide ligands are diastereotopic. The
phenylimido ligand shows the expected signals for a C6H5
moiety while the diazoalkane group has a methine proton sig-
nal at δ 8.54 and a methine carbon signal at 166.5 ppm consist-
ent with an “sp2-like” carbon atom.
The electronic absorption spectra of the diazoalkane and
phenylimido compound show intense absorption in the UV
region of the spectrum which tails into the visible. This low
energy shoulder at λmax ≈ 500 nm is relatively weak (ε ≈ 300 MϪ1
cmϪ1) and is assignable to a MM based electronic transition
while, for the diazoalkane complex, the absorption centered at
260 nm, which shows a vibronic progression (v ≈ 1000 cmϪ1), is
associated with a N lp to π* transition of the bridging ligand.
See Fig. 1.
t
t
to [W2(OCH2 Bu)8] gives OW(OCH2 Bu)4.4 Similarly diazo-
alkanes are known to add to some MM bonded complexes,8
and, in other cases, eliminate N2 and yield carbenes. We have
t
t
previously shown that [W2(µ-CH2)(µ-OCH2 Bu)2(OCH2 Bu)6] is
t
formed in the reaction between [W (OCH Bu) ] and Ph P᎐
᎐
3
2
2
8
CH ,4 while M (OR) (M᎐M) compounds (M = Mo or W) react
᎐
2
2
6
with diazoalkanes to give products of oxidative-addition and
reduction of the diazo ligand.8d This prompted us to investigate
t
the reaction between [W2(OCH2 Bu)8] and Me3SiCHN2. We
describe herein the results of our studies of these two reactions.
Results and discussion
Syntheses
t
a
W2(ꢀ-NPh)(ꢀ-OCH2tBu)2(OCH2tBu)6. [W2(OCH2 Bu)8]
reacts with azobenzene in hydrocarbon solvents at 50 ЊC over
24 hours to give the red phenylimido compound W2(NPh)-
t
(OCH2 Bu)8 which can be crystallized at low temperatures from
concentrated hydrocarbon solution. This phenylimido com-
pound is formed when [W2(OCH2 Bu)8] was allowed to react
with 0.5, 1.0 and 5.0 equiv. of azobenzene. It is inert to the
Solid state and molecular structures
W2(NPh)(OCH2tBu)8. An ORTEP drawing of the phenyl-
t
presence of excess azobenzene at 50 ЊC. However, in all
imido complex is shown in Fig. 2. There is a central confacial
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
D a l t o n T r a n s . , 2 0 0 3 , 3 2 0 5 – 3 2 1 0
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t
Fig. 3 ORTEP drawing for the W2(µ-N2C(H)SiMe3)(µ-OCH2 Bu)2-
t
(OCH2 Bu)6 molecule. Thermal ellipsoids are drawn at the 50%
probability level.
Fig.
1
Electronic absorption spectrum of W2(µ-N2C(H)SiMe3)-
t t
(µ-OCH2 Bu)2(OCH2 Bu)6 in the 350–210 nm range (bottom), and
400–700 nm (top), recorded as a THF solution at 25 ЊC.
has been oxidized and now has a W–W single bond. The W–N
distances are similar to those in the phenylimido complex
and the nitrogen bonded to each tungsten is essentially planar,
with 358.7Њ as the sum of the angles about N1. The W–O
distances follow a similar pattern implying again that the
bridging nitrogen ligands have a higher trans-influence than the
alkoxides.
A view of the diazoalkane complex looking down the WW
bond axis is given in Fig. 4. This view shows that the bridging
diazoalkane ligand is distinctly angular with NNC and NCSi
angles of 120.1(3) and 121.2(3)Њ, respectively. This, together
with the N–N distance, 1.366(4) Å, and N–C = 1.266(5) Å
indicate that the bridging ligand is best considered as a
hydrazonido(2Ϫ) ligand.
t
t
Fig. 2 ORTEP24 drawing of the W2(µ-NPh)(µ-OCH2 Bu)2(OCH2 Bu)6
molecule. Thermal ellipsoids are drawn at the 50% probability level.
biooctahedral O3WO2NWO3 unit with a W–W separation of
2.5613(2) Å, consistent with a MM single bond. The sum of the
angles at nitrogen are 360Њ consistent with sp2 hybridization.
The W–O distances of the bridging ligands are notably longer
than those of the terminal alkoxides as would be expected:
2.087–2.091(2) vs. 1.878–1.952(2) Å. The short W–N distances,
together with the trigonal nitrogen atom, implies that the nitro-
gen p orbital that is perpendicular to the W2N plane is intim-
ately involved in π-bonding. Selected bond distances and bond
angles are given in Table 1.
W2(N2CHSiMe3)(OCH2tBu)8. An ORTEP drawing of the
diazoalkane adduct is given in Fig. 3. This drawing gives the
atom number scheme and emphasizes the similarity of the con-
facial biooctahedral O3WNO2WO3 moiety. Selected bond dis-
tances and angles are given in Table 2. The metric parameters
of this central unit are remarkably similar to those of the imido
complex leading to the view that the diazoalkane ligand can be
considered as a dianionic ligand and that the ditungsten center
Fig.
4
ORTEP drawing for the molecule W2(µ-N2C(H)SiMe3)-
t t
(µ-OCH2 Bu)2(OCH2 Bu)6 looking down the W–W axis. This view of
the molecule clearly emphasizes the confacial central O3WO2NWO3
skeleton and the angular geometry of the NNC group of the bridg-
ing diazoalkane ligand. Thermal ellipsoids are drawn at the 50%
probability level.
D a l t o n T r a n s . , 2 0 0 3 , 3 2 0 5 – 3 2 1 0
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t
t
Table 1 Selected experimental and calculated bond distances (Å) and angles (Њ) for W2(µ-NPh)(µ-OCH2 Bu)2(OCH2 Bu)6 and W2(µ-NPh)-
(µ-OCH3)2(OCH3)6 molecules, respectively
W(1)–W(2)
W(1)–N
Exp.
Calc.
Exp.
Calc.
Exp.
Calc.
Exp.
Calc.
Exp.
Calc.
Exp.
Calc.
Exp.
Calc.
2.5613(2)
2.61
1.987(3)
2.03
1.878(2)
1.92
1.887(2)
1.92
1.946(2)
1.97
2.087(2)
2.12
2.091(2)
2.12
W(2)–N
Exp.
Calc.
Exp.
Calc.
Exp.
Calc.
Exp.
Calc.
Exp.
Calc.
Exp.
Calc.
Exp.
Calc.
1.987(3)
2.03
2.088(2)
2.12
2.090(2)
2.12
1.889(3)
1.92
1.883(3)
1.92
1.952(2)
1.97
1.418(5)
1.39
W(2)–O(4)
W(2)–O(5)
W(2)–O(6)
W(2)–O(7)
W(2)–O(8)
N–C(1)
W(1)–O(1)
W(1)–O(2)
W(1)–O(3)
W(1)–O(4)
W(1)–O(5)
W(1)–N–W(2)
W(1)–N–C(1)
W(2)–N–C(1)
N–W(1)–O(3)
Exp.
Calc.
Exp.
Calc.
Exp.
Calc.
Exp.
Calc.
80.3(1)
79.9
139.3(3)
140.2
140.5(3)
139.9
176.7(1)
174.7
N–W(2)–O(8)
Exp.
Calc.
Exp.
Calc.
Exp.
Calc.
176.4(1)
174.6
75.7(1)
76.1
75.6(1)
76.1
W(1)–O(4)–W(2)
W(2)–O(5)–W(1)
t
t
Table 2 Selected experimental and calculated bond distances (Å) and angles (Њ) for W2(µ-N2C(H)SiMe3)(µ-OCH2 Bu)2(OCH2 Bu)6. The calculations
were performed on the model complex W2(µ-N2C(H)SiMe3)(µ-OCH3)2(OCH3)6
W(1)–W(2)
W(1)–N(1)
W(1)–O(1)
W(1)–O(2)
W(1)–O(3)
W(1)–O(4)
W(1)–O(5)
N(1)–N(2)
Exp.
Calc.
Exp.
Calc.
Exp.
Calc.
Exp.
Calc.
Exp.
Calc.
Exp.
Calc.
Exp.
Calc.
Exp.
Calc.
2.5626(2)
2.62
1.984(2)
2.03
2.082(2)
2.12
2.100(2)
2.12
1.889(2)
1.91
1.941(2)
1.97
1.889(2)
1.92
1.366(4)
1.35
W(2)–N(1)
W(2)–O(1)
W(2)–O(2)
W(2)–O(6)
W(2)–O(7)
W(2)–O(8)
N(2)–C(1)
Exp.
Calc.
Exp.
Calc.
Exp.
Calc.
Exp.
Calc.
Exp.
Calc.
Exp.
Calc.
Exp.
Calc.
1.986(3)
2.03
2.099(2)
2.12
2.094(2)
2.12
1.884(2)
1.91
1.939(2)
1.97
1.882(2)
1.92
1.266(5)
1.29
W1)–N(1)–W(2)
N(1)–W(1)–O(4)
N(1)–N(2)–C(1)
N(1)–W(2)–O(7)
Exp.
Calc.
Exp.
Calc.
Exp.
Calc.
Exp.
Calc.
80.4(1)
80.3
176.9(1)
172.2
120.1(3)
121.3
174.8(1)
172.3
N(2)–C(1)–Si
Exp.
Calc.
Exp.
Calc.
Exp.
Calc.
121.2(3)
119.8
137.5(2)
138.5
140.8(2)
138.7
W(1)–N(1)–N(2)
W(2)–N(1)–N(2)
(OCH2 Bu)8, where E = O, S, Se and Te.5 It is, however, fair to
state that the calculations are consistent with the existence
of a M–M single bond and either a bridging phenylimido or
hydrazonido(2Ϫ) ligand.
t
Electronic structure and bonding
In order to examine the bonding in the imido and diazoalkane
complexes, we have undertaken electronic structure calcu-
lations employing density functional theory with the aid of
the Gaussian 98 suite of programs (See Experimental section).
In both cases, the neopentoxide ligands were modeled with
methoxide and the starting geometry of W2(OCH3)8(µ-bridge)
was taken from the crystal structure and allowed to optimize in
C1 symmetry. A comparison of the calculated and observed
bond distances for the central core of the two molecules is
given in Tables 1 and 2. The calculation consistently over-
estimates the W–W, W–N and W–O bond distances though
the trends are consistent with those observed. A similar
finding was observed for the calculations performed on the
series W2(µ-E)(OCH3)8 in relation to the experimental W2(µ-E)-
The frontier orbitals for the phenylimido compound are
shown in Fig. 5. The HOMO is the M–M σ orbital comprised
2
mostly of W dz atomic orbitals. The HOMO Ϫ 1 is mostly
bridge centered having some Np to Wd character (a metal π/d
combination), and considerable phenyl π character. The orien-
tation of the C5 ring allows for maximum overlap with the Npπ
orbital and, in the HOMO, this interaction is antibonding. The
LUMO is comprised of an in-phase combination of two
metal hybrid π/δ type orbitals that are out-of-phase in regards
to the in-phase π-combination of the N and C(ipso) carbon pπ
orbitals. The LUMO ϩ 1 is mainly an out-of-phase combin-
ation of two metal π/δ hybrids.
D a l t o n T r a n s . , 2 0 0 3 , 3 2 0 5 – 3 2 1 0
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Fig.
5
Plots of the frontier molecular orbitals of W2(µ-NPh)-
(µ-OCH3)2(OCH3)6.
The frontier molecular orbitals for the diazoalkane adduct
are shown in Fig. 6. The HOMO is predominantly M–M
2
σ bonding which is comprised of overlap of the tungsten dz
orbitals. The HOMO Ϫ 1 orbital is pπ lone-pair based that is
essentially non-bonding with respect to the dinuclear center.
The HOMO Ϫ 2 orbital is comprised of an N lone-pair orbital
that is parallel with respect to the metal–metal bond and this
Fig. 6 GaussView plots of the frontier molecular orbitals of W2(µ-N2-
C(H)SiMe3)(OCH3)8.
MO is also C᎐N π bonding. The LUMO is comprised of an
᎐
out-of-phase combination of two metal hybrid π/δ type orbitals
that are out-of-phase in regard to the terminal oxygen pπ
orbitals. The LUMO ϩ 1 is an in-phase combination of two
metal hybrid π/δ type orbitals which are out-of-phase with
respect to terminal oxygen pπ orbitals. The LUMO ϩ 2 orbital
is an in-phase combination of two metal hybrid π/δ type orb-
tials that are out-of-phase with respect to four terminal oxygen
pπ orbitals and the two bridging oxygen pπ orbitals. In com-
contrast, the reactions of M–M double bonded complexes
[(η5-C5R5)M(CO)2]2, where M = Co, Rh, Ir and R = H, Me, gave
bridging alkylidene complexes with elimination of dinitrogen.9
In the chemistry of diazobenzene, Cotton and co-workers
were the first to report the cleavage of the N–N double bond in
a reaction with a Nb–Nb double bonded complex: [NbCl2-
(SMe2)]2(µ-Cl)2(µ-SMe) ϩ PhNNPh
[NbCl2(SMe2)(NPh)]2-
t
parison, for the related complex W2(µ-NPh)(µ-OCH2 Bu)2-
(µ-Cl)2.7 Reactions of the MM triply-bonded complexes
M2(OR)6 (M = Mo, W) were also found to reductively cleave
azobenzene and, more recently, Floriani working with M–M
double bonded complexes of niobium and molybdenum sup-
ported by calixarene ligands reported four electron reductions
of diazobenzene to phenylimido-niobium() and -molyb-
denum() complexes.10 With mononuclear tungsten() arly-
oxides, Rothwell has also seen the four-electron reduction to
give (ArO)2W(NPh)2 compounds.11 In main group element
chemistry, addition is often seen across an element–element
t
(OCH2 Bu)6, the HOMO is predominantly M–M σ bonding
2
which is comprised of the tungsten’s dz orbitals. The HOMO
Ϫ 1 orbital is comprised of an out-of-plane N pπ orbital that is
bonding in a π-type fashion with the in-phase combination of
two metal hybrid π/δ type orbitals. Furthermore, the phenyl
ring has a bonding and anti-bonding combination with one
node and the out-of-plane N pπ orbital is anti-bonding with
regard to this combination. The LUMO is comprised of an
in-phase combination of two metal hybrid π/δ type orbitals that
are out-of-phase in regard to an in-phase π combination of the
N and C(ipso) orbitals. The LUMO ϩ 1 is mainly an out-of-
phase combination of two metal hybrid π/δ type orbitals.
double bond as in the addition of Me SiCHN to [Ge᎐Ge].12
᎐
3
2
Given these findings of others, our results are interesting but
not exceptional. It is, however, noteworthy that in the reactions
t
of [W2(OCH2 Bu)8], the reaction stops at the 2-electron redox
Comparisons with related chemistry
stage. The reactions proceed to convert d2–d2 M–M double
bonded compounds to d1–d1 M–M single bonded ones, and the
latter are inert to further oxidation to give (RO)4W()-imido or
-hydrazonido compounds, despite the fact that the latter are
known and may be prepared by alternate routes. It seems likely
that the tungsten() complexes are indeed the thermodynamic
products and, in this instance, the d1–d1 dinuclear compounds
Given the propensity of the elements molybdenum and tung-
sten to bind nitrogen and to form M–N multiple bonds, it is not
surprising to find that earlier studies of the reactions between
diazoalkanes and dinuclear compounds with M–M triple
bonds, specifically Cp2Mo2(CO)4 and M2(OR)6 were also found
to give diazoalkane adducts, both bridging and terminal.8 In
D a l t o n T r a n s . , 2 0 0 3 , 3 2 0 5 – 3 2 1 0
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are the kinetic products. It also seems likely that the first step in
the reaction is adduct formation to give a compound of the type
(RO)3W(µ-OR)3W(OR)2L where L = η1-PhNNPh or N2CH-
SiMe3. Then a redox reaction and terminal bridge exchange
leads to the observed bridged imido or hydrazonido complexes.
Further speculation at this time is not warranted.
Electronic structure calculations
Density functional theory (DFT) calculations with the
Gaussian 98 suite of programs13 utilized the B3LYP14–16
method and standard basis sets. C, H, O, and N were described
with the 6-31G* basis set (and 5 “pure” d functions), while W17
was represented by an SDD effective core potential. The geom-
etries were optimized under C1 symmetry starting from the
solid-state structure coordinates using the default optimization
criteria. Methoxide ligands were substituted for neopentoxides.
Stationary points were characterized as minima by vibrational
frequency calculations.
Experimental
All manipulations were carried out under an inert atmos-
phere of oxygen-free UHP-grade argon using standard Schlenk
techniques or under a dry and oxygen-free atmosphere of nitro-
gen in a Vacuum Atmospheres Co. Dry Lab System. Hexane
was degassed and distilled from potassium under nitrogen.
Toluene-d8 was degassed, stirred over sodium for 24 h and
vacuum transferred to an ampoule. Azobenzene and trimethyl-
silyldiazomethane were purchased form Aldrich and used as
received. NMR spectra were recorded on a 400 MHz Bruker
Crystallographic studies
t
t
W2(ꢀ-N2C(H)SiMe3)(ꢀ-OCH2 Bu)2(OCH2 Bu)6. The data
collection crystal was an amber colored, triangular plate.
Examination of the diffraction pattern on a Nonius Kappa
CCD diffractometer indicated
a triclinic crystal system.
1
DPX Avance400 spectrometer. All H NMR chemical shifts are
All work was done at 200 K using an Oxford Cryosystems
Cryostream Cooler. The data collection strategy was set up to
measure a hemisphere of reciprocal space with a redundancy
factor of 3, which means that 90% of the reflections were meas-
ured at least 3 times. A combination of ꢀ and ω scans with a
frame width of 1.0Њ was used. Data integration was done with
Denzo.18 Scaling and merging of the data were done with
Scalepack;18 application of an absorption correction is inherent
in this treatment and is reflected in the scale factor range of
9.14 to 12.56. Merging the data and averaging the symmetry
equivalent reflections results in an R(int) value of 0.051. The
1
reported in ppm relative to the H impurity in toluene-d8 at
t
δ 2.09. [W2(OCH2 Bu)8]n was prepared according to literature
procedures.3
t
Preparation of W2(ꢀ-NPh)(ꢀ-OCH2tBu)2(OCH2 Bu)6
t
To a 25 mL round-bottomed flask was added [W2(OCH2 Bu)8]n
(0.100 g, 0.094 mmol) and PhNNPh (9.5 mg, 0.094 mmol).
Hexanes (10 mL) were added to give a purple slurry and the
reaction was heated to 50 ЊC. After stirring for 24 h, the solu-
tion was filtered through a medium glass frit with a Celite pad.
Stripping the solvent gave a red solid identified as W2(µ-NPh)-
teXsan19 package indicated the space group to be P1 based on
the intensity statistics.
¯
t
t
(µ-OCH2 Bu)2(OCH2 Bu)6 in 95% crude yield. X-Ray quality
crystals were obtained upon crystallization from hexanes at
The positions of the two W atoms were determined by the
Patterson method in SHELXS-86.20 The rest of the non-hydro-
gen atoms were located by a combination of DIRDIF21 and
standard Fourier methods. Full-matrix least-squares refine-
ments based on F 2 were performed in SHELXL-93.22
For both structures, the methyl group hydrogen atoms were
added at calculated positions using a riding model with U(H) =
1.5 × Ueq(bonded C atom). For each methyl group, the torsion
angle which defines its orientation about the Si–C or C–C bond
was refined. The other hydrogen atoms were included in the
model at calculated positions using a riding model with U(H) =
1.2 × Ueq(bonded C atom). Neutral atom scattering factors
were used and include terms for anomalous dispersion.23
Crystallographic details of both structures are in Table 3.
1
Ϫ20 ЊC. H NMR (400 MHz, toluene-d8, 27 ЊC): δ 0.98 (s,
36 H), 1.02 (s, 18 H), 1.24 (s, 18 H), 4.22 (d, 4 H, JH–H = 10 Hz),
4.36 (d, 4 H, JH–H = 10 Hz), 4.63 (s, 4 H), 4.83 (s, 4 H), 7–8 (m,
Ph). 13C{1H} NMR (100 MHz, toluene-d8, 27 ЊC): δ 26.72 (s,
C(CH3)3), 27.70 (s, C(CH3)3), 28.00 (s, C(CH3)3), 33.85 (s,
CH2), 34.26 (s, CH2), 34.90 (s, CH2), 81.30 (s, C(CH3)3, 83.12
(s, C(CH3)3, 85.09 (s, C(CH3)3, 120–140 (Ph). Anal. Calc. for
W2O8NC46H93: C, 47.77; H, 8.10; N, 1.27 Found: C, 47.25; H,
8.01; N, 1.25%.
Preparation of W2(ꢀ-NNC(H)SiMe3)(ꢀ-OCH2tBu)2(OCH2tBu)6
t
To a 25 mL round-bottomed flask was added [W2(OCH2 Bu)8]n
(0.100 g, 0.094 mmol). Hexanes (10 mL) were added to give a
purple slurry and the solution was cooled to Ϫ30 ЊC. NNC(H)-
SiMe3 (37.5 µL, 0.094 mmol).was added by syringe and the reac-
tion was allowed to warm to room temperature. After stirring for
24 h the solution was filtered through a medium glass frit with a
Celite pad. Stripping the solvent gave a red solid identified as
W2(µ-NNC(H)SiMe3)(µ-OCH2 Bu)2(OCH2 Bu)6 in 95% crude
yield. X-Ray quality crystals were obtained upon crystallization
from hexanes at Ϫ20 ЊC. 1H NMR (400 MHz, toluene-d8, 27 ЊC):
δ 0.33 (s, 9 H), 0.99 (s, 36 H), 1.02 (s, 18 H), 1.21 (s, 18 H), 4.38 (d,
t
W2(ꢀ-NPh)(ꢀ-OCH2tBu)2(OCH2 Bu)6ؒ½hexane. The data
collection crystal was an orange-red rectangular rod. Examin-
ation of the diffraction pattern on a Nonius Kappa CCD dif-
fractometer indicated a triclinic crystal system. All work was
done at 200 K using an Oxford Cryosystems Cryostream Co-
oler. The data collection strategy was set up to measure a hemi-
sphere of reciprocal space with a redundancy factor of 2.7,
which means that 90% of the reflections were measured at least
2.7 times. A combination of ꢀ and ω scans with a frame width
of 1.0Њ was used. Data integration was done with Denzo.18 Scal-
ing and merging of the data were done with Scalepack;18 appli-
cation of an absorption correction is inherent in this treatment
and is reflected in the scale factor range of 9.41–12.39. Merging
the data and averaging the symmetry equivalent reflections
resulted in an R(int) value of 0.046. The teXsan19 package indi-
t
t
4 H, JH–H = 11 Hz), 4.52 (s, 4 H), 4.71 (s, 4 H), 4.82 (d, 4 H, JH–H
=
11 Hz), 8.54 (s, 1 H). 13C{1H} NMR (100 MHz, toluene-d8,
27 ЊC): δ 0.00 (s, SiMe3), 28.69 (s, C(CH3)3), 29.47 (s, C(CH3)3),
29.72 (s, C(CH3)3), 35.67 (s, CH2), 36.14 (s, CH2), 36.50 (s, CH2),
81.05 (s, C(CH3)3, 85.38 (s, C(CH3)3, 88.56 (s, C(CH3)3, 166.50 (s,
NNC(H)SiMe3). IR (νmax/cmϪ1): 1477 (s), 1463 (vs), 1419(vw),
1392 (s), 1377 (s), 1363 (s), 1372 (s), 1301 (vw), 1289 (vw), 1260
(w), 1250 (m), 1217 (w), 1058 (vs), 1031 (s), 1022 (vs), 1005 (vs),
994 (s), 932 (m), 905 (w), 864 (m), 845 (m), 805 (w), 754 (m), 721
(w), 690 (s), 680 (s), 658 (s), 639 (m), 600 (m), 577 (w), 492 (vw),
458 (m), 436 (vw), 403 (m), 375 (s). UV-vis (THF, λmax/nm): 475
(ε/dm3 molϪ1 cmϪ1 = 300), 268 (37,000), 255 (74,000), 249 (64,000)
244 (52,000), 239 (40,000), 234 (30,000). Anal. Calc. for W2N2O8-
C44H98: C, 44.82; H, 8.39; N, 2.38. Found: C, 44.72; H, 8.39; N,
2.32%.
¯
cated the space group to be P1 based on the intensity statistics.
The structure was solved by the Patterson method in
SHELXS-86.20 Besides the W complex, the asymmetric unit
contains a hexane molecule positioned on an inversion
center. Full-matrix least-squares refinements based on F 2 were
performed in SHELXL-93.22 The hexane molecule was refined
isotropically, and only the hydrogen atoms bonded to the CH2
groups were included in the model.
CCDC reference numbers 192252 and 192253.
D a l t o n T r a n s . , 2 0 0 3 , 3 2 0 5 – 3 2 1 0
3209

View Article Online
Table 3 Crystallographic details
t
t
t
t
W2(µ-N2C(H)SiMe3)(µ-OCH2 Bu)2(OCH2 Bu)6
W2(µ-NPh)(µ-OCH2 Bu)2(OCH2 Bu)6ؒ½hexane
Empirical formula
Formula weight
Temperature/K
C44H98N2O8SiW2
1179.03
200
C46H93NO8W2 ϩ ½ hexane
1199.00
200(2)
Wavelength/Å
Crystal system
Space group
0.71073
0.71073
Triclinic
P1
Triclinic
¯
¯
P1
a/Å
b/Å
11.921(1)
11.954(1)
12.030(1)
12.048(1)
c/Å
α/Њ
21.526(2)
88.91(1)
20.567(2)
92.84(1)
β/Њ
85.00(1)
74.92(1)
2950.6(5)
99.67(1)
102.96(1)
2851.9(5)
γ/Њ
Volume/Å3
Z
2
2
Dc/Mg mϪ3
1.327
3.957
1204
1.396
4.075
1226
Absorption coefficient/mmϪ1
F(000)
Crystal size/mm
Reflections collected
Independent reflections
Goodness-of-fit on F 2
Final R indices [I>2σ(I )]a
R indices (all data)
Largest diff. peak and hole/e ÅϪ3
0.15 × 0.31 × 0.42
79939
13454 [R(int) = 0.051]
1.034
R1 = 0.0263, wR2 = 0.0578
R1 = 0.0421, wR2 = 0.0621
1.46 and Ϫ0.84
0.08 × 0.15 × 0.31
63505
13080 [R(int) = 0.046]
1.092
R1 = 0.0295, wR2 = 0.0569
R1 = 0.0481, wR2 = 0.0613
1.43 and Ϫ1.01
a R1 = Σ||Fo| Ϫ |Fc||/Σ|Fo| and wR2 = [Σw(Fo2 Ϫ Fc2)2/Σw(Fo )2]1/2
.
2
10 (a) A. Zanotti-Gerosa, E. Solari, L. Giannisi, C. Floriani,
A. Chiesi-Villa and C. Rizzoh, J. Am. Chem. Soc., 1998, 120, 437;
(b) G. Guillemot, E. Solari, R. Scopelliti and C. Floriani,
Organometallics, 2001, 20, 2446.
See http://www.rsc.org/suppdata/dt/b3/b304587k/ for crystal-
lographic data in CIF or other electronic format.
11 F. Maseras, M. A. Lockwood, O. Eisenstein and I. P. Rothwell,
J. Am. Chem. Soc., 1998, 120, 6598.
12 H. Schaefer, W. Saak and M. Weidenbruch, Organometallics, 1999,
18, 3159.
Acknowledgements
We thank the National Science Foundation for financial sup-
port and The Ohio Supercomputing Center for computational
resources.
13 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A.
Robb, J. R. Cheeseman, V. G. Zakrzewski, J. A. J. Montgomery,
R. E. Stratmann, J. C. Burant, S. Dapprich, J. M. Millam, A. D.
Daniels, K. N. Kudin, M. C. Strain, O. Farkas, J. Tomasi, V. Barone,
M. Cossi, R. Cammi, B. Menuucci, C. Pomelli, C. Adamo,
S. Clifford, J. Ochterski, G. A. Pertersson, P. Y. Ayala, Q. Cui,
K. Morokuma, D. K. Malick, A. D. Rabuck, K. Raghavachari,
J. B. Foresman, J. Cioslowski, J. V. Ortiz, A. G. Baboul, B. B.
Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. J.
Gomperts, R. L. Martin, D. J. Fox, T. Keith, M. A. Al-Lahman,
C. Y. Peng, A. Nanayakkara, M. Challacombe, P. M. W. Gill,
B. Johnson, W. Chen, M. W. Wong, J. L. Andres, C. Gonzalez,
M. Head-Gordon, E. S. Replogle and J. A. Pople, Gaussian 98
Version A9, Gaussian Inc., Pittsburgh, PA, 1998.
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D a l t o n T r a n s . , 2 0 0 3 , 3 2 0 5 – 3 2 1 0
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