Amidinate-carboxylate complexes of dimolybdenum and ditungsten: M 2(O2CR)2((NiPr)2CR′ )2. Preparations, molecular and electronic structures and reactions

Article abstract of DOI:10.1039/b715258b

The compounds M₂(O₂CMe)₄ and the lithium amidinates Li[(NⁱPr)₂CR] react to give the new compounds trans-M₂(O₂CMe)₂[(NⁱPr) ₂CR]₂ where

Full text of DOI:10.1039/b715258b

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Amidinate–carboxylate complexes of dimolybdenum and
ditungsten: M2(O2CR)2((NiPr)2CRꢀ)2. Preparations, molecular and
electronic structures and reactions†‡§
Douglas J. Brown, Malcolm H. Chisholm* and Judith C. Gallucci
Received 4th October 2007, Accepted 24th January 2008
First published as an Advance Article on the web 22nd February 2008
DOI: 10.1039/b715258b
The compounds M2(O2CMe)4 and the lithium amidinates Li[(NiPr)2CR] react to give the new
compounds trans-M2(O2CMe)2[(NiPr)2CR]2 where M = Mo or W and R = Me (M = Mo only),
–C≡CtBu, –C≡CPh and –C≡C–Fc where Fc = 1-ferrocenyl. The limitations of this type of reaction are
described based on steric considerations together with the preparation and characterization of the
2
compound Mo2(l-O2C-9-anthracene)2[g -(NiPr)2CMe]2. The electronic structures of the
bis-amidinate–bis-carboxylate M2 complexes are described based on model compounds employing
density functional theory and are correlated with the experimental observations of their
physicochemical properties and in particular their observed electronic absorption spectra which show
intense MLCT absorption bands. Preliminary studies of the reactions of these
bis-amidinate–bis-carboxylate complexes in the preparation of 1-D oligomers are also described along
with the preparation and molecular structures of the compounds [Li(NiPr)2CR·THF]2 where R =
2-thienyl or –C≡C–Ph. The kinetic lability of these new M2-containing compounds toward ligand
exchange is also noted.
when used in conjunction with bridging dicarboxylate ligands.
Introduction
We were interested in the notion that the chemistry of amidinate
complexes, L = IV above, where the R group is bulky might
act as trans-templating groups for (RNC(Rꢀ)NR)2M22+ containing
complexes (M = Mo or W) and further that the introduction of
certain Rꢀ groups might enter into M2(d)–Rꢀ(p) conjugation and
thus complement earlier studies in this laboratory of M2(d)–L(p)
conjugation employing L = carboxylate.4,5 These ideas formed the
platform upon which the work described herein was undertaken.
Compounds having MM quadruple bonds have been shown to
have a rich and diverse coordination chemistry.1 Bidentate ligands
that can bridge the two metal atoms to form five-membered rings
yield paddle-wheel type complexes, M2L4, of which the group
involving L = carboxylate, amidate, formamidinate and amidinate
shown in drawings I–IV, respectively, are prime examples.1
Results and discussion
Synthesis
Lithium amidinates were prepared from the reaction between a
carbodiimide and an alkyllithium reagent as shown in Scheme 1.6
The carboxylate ligands are labile toward ligand exchange and
this makes them ideal as starting materials for ligand exchange
reactions. However, this can also form problems in syntheses where
a kinetic product is desired.2 The replacement of O by NR greatly
reduces the facility of ligand scrambling and the Cotton group
have used this to great effect in preparing dimers of dimers, molec-
ular loops, triangles and squares with attendant formamidinate
ligands.3 The formation of molecular loops, triangles and squares
2+
is greatly aided by the cis-templating unit (ArNCHNAr)2Mo2
Scheme 1 Synthesis of lithium amidinate salts.
In cases where an alkyllithium reagent was not commercially
available it was prepared from the reaction between BunLi and
the alkyne or thiophene. In order to impart significant steric
influence the carbodiimide was N,Nꢀ-diisopropyl. N,Nꢀ-Di-tert-
butyl proved to be too demanding. The lithium amidinates formed
large crystals upon cooling their THF solutions and two samples
were examined crystallographically. The molecular structures
Department of Chemistry, The Ohio State University, Columbus, OH, 43210,
USA
† Dedicated to Professor Ken Wade on the occasion of his 75th birthday.
‡ CCDC reference numbers 637924–637931. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b715258b
§ Electronic supplementary information (ESI) available: Full crystallo-
graphic details; attempted synthesis of higher order oligomers. See DOI:
10.1039/b715258b
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of Li[(NiPr)2CC≡CPh]·THF and Li[(NiPr)2C-2-C4H4S]·THF are
shown in ESI,§ Fig. S1 and S2, respectively. In both instances there
is a dimeric structure having a crystallographically imposed center
of inversion. The lithium atoms are four coordinate in a pseudo-
tetrahedral geometry. The amidinate ligands act as a chelating
and bridging ligands as has been well documented and thus the
molecular structures are not exceptional.7–9 The phenyl and thienyl
rings are not contained in the amidinate NCN planes which limits
the degree of p-conjugation of the thienyl unit and it is known
that the presence of bulky R and Rꢀ in IV impede the ability of the
amidinate ligand to bridge two metal centers and favor chelation
as pictorially shown in Fig. 1. The challenge was then to select
a series of amidinate ligands that would preferentially bridge the
dimolybdenum or ditungsten units and to do this we employed
exposure to ethanol for the W2-containing species was avoided
since this resulted in decomposition.
The compounds gave molecular ions by matrix assisted laser
desorption ionization time of flight (MALDI-TOF) mass spec-
trometry. The 1H NMR spectra revealed the presence of 1 :
1 carboxylate to amidinate ligands and significantly the iso-
propylmethyl groups appeared as a single doublet due to CH
to Me proton coupling. This lack of diastereotopism implies a
mirror plane of molecular symmetry and a trans arrangement
of ligands. We propose that this geometry is favored by steric
factors and further note that the product shown in Scheme 2 is
favored even when 4 equiv. of the lithium amidinate is allowed
to react with M2(O2CMe)4. The bis-bis products are thus the
kinetically or thermodynamically favored compounds, when the
bulky isopropyl groups are employed on the amidinate. With less
bulky substituents such as the dimethylbenzylamidanate (DMBA)
in the reaction with Mo2(O2CMe)4 the tetrasubstituted homoleptic
compound Mo2(DMBA)4 was isolated.
i
R = Pr and not tBu and Rꢀ = Me and alkynyl derivatives. Other
combinations proved problematic.
The reactions involving other Mo2(O2CR)4 compounds and
Li[(NiPr2)2(CRꢀ)] compounds were also investigated (Rꢀ = Me).
t
When R = Bu the reaction proceeded but was complicated by the
fact that the LiO2CtBu product was soluble and thus led to difficult
purification of the desired bis-bis product. These reactions were
not pursued further. The reactions between the Mo2(O2CR)4 com-
pounds where R = 2-thienyl and 9-anthracenyl were also investi-
gated and resulted in the formation of Mo2(O2CR)2[(NiPr)2CMe]2.
The 2-thienyl complex had the anticipated structure but the 9-
anthracenyl derivative adopted an alternate cis-cis structure, vide
infra, wherein the isopropylmethyl groups were diastereotopic
(NMR).
Fig. 1 (a) Bridging and (b) chelating modes of amidinates as influenced
by steric factors.9
For the sake of brevity the compounds of general formula and
trans-geometry M2(O2CMe)2[(NiPr)2CR]2 are refered to either as
A or B for M = Mo or W, respectively and given the number 1, 2, 3
and 4 for R = Me, –C≡CtBu, –C≡CPh and –C≡CFc, respectively.
M2(O2CMe)2[(NiPr)2CRꢀ]2 complexes
The new compounds were prepared according to the general
reaction shown in Scheme 2, where M = Mo or W and R =
Me (M = Mo only), –C≡CtBu, –C≡CPh and –C≡CFc (Fc =
1-ferrocenyl).
Electronic structure calculations
Calculations employing density functional theory with the aid
of the Gaussian 03 suite of programs were performed on model
compounds for 1A, 2A and 3A where the isopropyl group was
substituted by a hydrogen atom (see Experimental section). This
increased the symmetry and decreased computational time to
achieve a set of self-consistent results that were verified to be
a minimum on the potential energy surface. Molecular orbital
analysis was used to verify the character of the individual
orbitals as has been routinely applied in related studies of M2
carboxylates and their derivatives.4,10 The replacement of the
carboxylate group by the amidinates is similar to that of the
substitution by a formamidinate in raising the orbital energy
of the M2d orbital. Experimentally this results in lowering the
electrochemical oxidation potential and in the gas phase the first
ionization potential of the molecule.11 However, more pertinent
to this work is the nature of the ligand based p* orbitals which
in the amidinates where the Rꢀ group is unsaturated provide for
a low energy MLCT absorption. For the compounds trans-bis
carboxylate bis amidinate there are three ligand based p* MOs
of significance in the frontier orbital region. One is strictly O2C
based, another N2C and the third is an admixture of the two. For
the model compound of 1A, where R = Me, these three p* orbitals
Scheme 2 Synthesis of trans-M2(O2CCH3)2((NiPr)2CR)2.
The sparingly soluble, yellow M2(O2CMe)4 compounds and the
lithium amidinates react with a color change and the visible forma-
tion of a white precipitate of LiO2CMe. The reactions were allowed
to proceed for several hours before the solvent was removed under
a dynamic vacuum. The dried product was then extracted with
CH2Cl2 and filtered over Celite to remove the lithium salt and the
filtrate was collected and reduced in volume. Addition of ethanol
to this filtrate induced the formation of a colored finely-divided
microcrystalline product which was collected by filtration and
dried in vacuum. The compounds were air- and moisture-sensitive
and the tungsten complexes were the more sensitive. Prolonged
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are close in energy but with increasing conjugation as in 2A (R =
–C≡CtBu) and 3A (R = –C≡CPh) the amidinate p* orbital
drops in energy. This is schematically shown in Fig. 2. The time
dependent DFT calculations on the model compounds for 1A,
2A and 3A predict two relatively high energy absorptions, 310–
340 nm, for the M2(d) to CO2(p*) and the amidinate-carboxylate p*
orbital that remain fairly constant for the series but that the M2(d)
to amidinate p* transition moves to lower energy, e.g. 509 nm, for
phenylacetylide complex.
Fig. 4 UV-vis spectra of M2(O2CCH3)2((NiPr)2CC≡CPh)2 where M =
Mo (red, 3A) and M = W (blue, 3B) in THF at room temperature.
A very weak absorption around 420 nm could be the Mo2(d→d*)
transition. The spectra of the complexes 2A and 3A show lower
energy and more intense absorptions which we assign to the MLCT
bands involving the amidinate p* orbitals as predicted by the DFT
calculations and consistent with expectations based on the frontier
MO diagram shown in Fig. 2. The asymmetric nature of this
absorption with the strong tailing effect to higher energy (shorter
wavelength) may well be a result of overlapping and unresolved
vibronic progressions. These do not, however, show significant
sharpening on cooling in 2-MeTHF solutions.
The spectral features of the tungsten complexes are complemen-
tary and are red shifted as a result of the higher energy of the W2(d)
orbital. A comparison of the absorption spectra of the complexes
3A and 3B is shown in Fig. 4. The blue color of the tungsten
complex arises for the intense MLCT (W2(d) to amidinate p*)
absorption at 600 nm.
Fig. 2 Relative molecular orbital energies of M2(d) and ligand-based p*
in model complexes.
Electronic absorption spectra
Electrochemistry
All the new compounds are colored as a result of fully allowed
metal-to-ligand charge transfer bands that occur in the visible
region of the spectrum and mask the otherwise weak M2(d→d*)
transition that is anticipated around 400 nm. A comparison of the
molybdenum complexes, 1A, 2A and 3A is shown in Fig. 3. The
high energy absorptions below 300 nm are assigned to ligand p to
p* transitions. The spectrum of 1A shows absorption in the region
300–350 nm which we assign to the three close in energy MLCT
bands predicted according to the energy diagram shown in Fig. 4.
The new compounds were studied by cyclic voltammetry, CV, and
normalized DPV curves for the complexes 1A, 2A, 2B, 3A and
3D are shown in Fig. 5. It is clear that the ease of oxidation of
the M2(d) orbital is sensitive to both the amidinate substituents,
Rꢀ, and the metal as has been seen before.1 The p-conjugation
of the amidinates with the M2(d) orbital stabilizes the d orbital
Fig. 3 UV-vis spectra of Mo2(O2CCH3)2((NiPr)2CMe)2 (1A, magenta),
Mo2(O2CCH3)2((NiPr)2CC≡CtBu)2 (2A, red), and Mo2(O2CCH3)2-
((NiPr)2CC≡CPh)2 (3A, blue) complexes in THF at room temperature.
Fig. 5 Normalized differential pulse voltammograms of synthesized
complexes and estimated voltammogram for complex 1B in THF–0.1 M
0/+
[tBu4N][PF6] and referenced to FeCp2 couple.
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such that the ease of oxidation follows the order Rꢀ = Me > –
C≡CtBu > –C≡CPh. The related tungsten complexes are easier to
oxidize by ca. 0.5 V which is typically seen for related M2(O2CR)4
compounds;12 these in turn are more difficult to oxidize than the
bis-acetate–bis-amidinate complexes reported here. For reasons
which are unknown at this time we have not been able to make the
tungsten analog of 1A. Based on the oxidation trends shown in
Fig. 5 we show the anticipated oxidation at −1.0 V vs. the Cp2Fe0/+
couple.
The ethynylferrocenyl amidinates, compounds 4A and 4B war-
rant specific attention since not only are the M2 centers redox active
but so too are the ferrocenyl units which could be electronically
coupled through M2(d)–ligand p-conjugation.
The CV and DPV for the molybdenum complex 4A are shown
in Fig. 6. The first oxidation wave at −308 mV corresponds
to oxidation of the Mo2(d) orbital and is comparable to that
observed for compounds 2A and 3A. The second oxidation at
∼ +0.1 V corresponds to a two-electron oxidation wave and
involves oxidation of the ferrocenyl units. The appearance of a
single wave indicates that the two Cp2Fe units are not significantly
coupled through the Mo2 center. A similar situation pertains
to the tungsten complex 4B, where the W2 oxidation occurs at
−778 mV. The lack of electronic coupling of the two Cp2Fe
Fig. 7 ORTEP diagram of the centrosymmetric Mo2(O2CCH3)2((NiPr)2-
CMe)2 molecule (1A) drawn with 50% probability displacement ellipsoids.
Hydrogen atoms are omitted for clarity. The starred atoms (*) are related to
the corresponding unstarred atom by the crystallographic inversion center.
The Mo–Mo, Mo–O(carboxylate), and Mo–N(amidinate) interatomic dis-
˚
tances are 2.0691(2), 2.1239(11)–2.1435(11), and 2.1371(13)–2.1419(13) A,
˚
centers at a distance of ca. 16.5 A, vide infra, is perhaps not
respectively.
surprising although we do note that Ren and co-workers13 have
seen significant coupling in related Ru2 containing systems with
axially aligned alkynyl Cp2Fe units.
crystallographically imposed center of inversion and the bulky iPr
groups are oriented away or distal to the MoMo bond.
The molecular structure of the tungsten complex 3B, is shown
in Fig. 8. There is again a similar trans disposition of ligands in the
i
centrosymmetric structure with a similar arrangement of the Pr
groups. The phenyl groups are nearly coplanar with the amidinate
N2C units.
The molecular structure of the ferrocenyl complex 4A is shown
in Fig. 9. The similarity of the fundamental structural features of
these compounds is quite striking, but otherwise not exceptional
for MM quadruply bonded paddle-wheel complexes.
In contrast, the molecular structure of the Mo2((NiPr)2CMe)2-
(O2C-9-anthracene)2 shown in Fig. 10 reveals a totally different
mode of bonding. The two carboxylate ligands are cis and the
amidinates are chelating to each metal center. As noted in Fig. 3,
the chelating nature of the amidinate ligand is favored by the
introduction of bulky groups on the central carbon atom. In the
present case, however, it is most likely that the observed structure
(Fig. 10) is a result of competing steric factors. The peri CH · · · O
interactions of 9-anthracene carboxylate ligands and esters favor
a dihedral angle of ∼56◦ between the aromatic ring and the
CO2 moiety.14,15 Indeed, earlier calculations on 9,10-anthracene
dicarboxylate bridged Mo4 containing compounds predict that
the planar structure where the dihedral angle is zero is 11 kcal
mol−1 higher in energy.16 Thus, for a trans,trans-bridged amidinate
structure of the type seen for the other new compounds described
herein we would anticipate a significant steric repulsion between
the anthracene ring and the isopropyl groups which are distal to
the MM bond. As can be seen from the view of the molecule
shown in Fig. 10 this type of steric repulsion is avoided with the
cis-chelating structure.
Fig. 6 (a) Differential pulse voltammogram and (b) cyclic voltammogram
of Mo2(O2CCH3)2((iPrN)2CC≡CFc)2 (4A) in THF–0.1 M [nBu4N][PF6].
Single-crystal and molecular structures
The new compounds were readily crystallized from routine organic
solvents and three compounds were subjected to single-crystal X-
ray determinations. The molecular structure of the compound
1A is shown in Fig. 7. The expected paddle-wheel structure is
seen with the trans disposition of ligands. The molecule has a
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Fig. 8 ORTEP diagram of the centrosymmetric W2(O2CCH3)2((NiPr)2CC≡CPh)2 molecule (3B) drawn with 50% probability displacement ellipsoids.
Hydrogen atoms are omitted for clarity. The starred atoms (*) are related to the corresponding unstarred atom by the crystallographic inversion center.
˚
The W–W, W–O(carboxylate) and W–N(amidinate) interatomic distances are 2.17294(17), 2.1004(16)–2.1056(17) and 2.100(2)–2.104(2) A, respectively.
The dihedral angle between the phenyl ring and its amidinate group is 9.0◦.
Fig. 9 ORTEP diagram of the centrosymmetric Mo2(O2CCH3)2((NiPr)2CC≡CFc)2 molecule (4A) drawn with 50% probability displacement ellipsoids.
Hydrogen atoms are omitted for clarity. The starred atoms (*) are related to the corresponding unstarred atom by the crystallographic inversion center.
˚
The Mo–Mo, Mo–O(carboxylate), and W–N(amidinate) interatomic distances are 2.0779(4), 2.126(2)–2.128(2) and 2.117(2)–2.125(2) A, respectively.
The dihedral angle between cyclopentadienyl ring and its amidinate group is 91.3◦.
Ligand scrambling reactions
acetate signals were present, most likely due to cis and trans
Mo2(◦O2CMe)2(O2CCF3)2. After 3 days the sample was heated to
As noted earlier ligand scrambling reactions are facile
for M2(O2CR)4 compounds and can be catalyzed by either the
presence of trace amounts of free carboxylic acid or the carboxy-
late anion.2 The introduction of the amidinates was expected to
impart greater kinetic persistence and in order to evaluate whether
this was indeed the case the reaction between Mo2(O2CCF3)4
and Mo2(O2CMe)2[(NiPr)2CC≡CtBu]2, 2A, was monitored. These
two compounds were selected because of their similar solubility.
An equimolar mixture of the two compounds was dissolved in
1
+70 C for 3 h and by H NMR spectroscopy at least eleven
acetate methyl signals could be seen along with a significant
loss of the signal due to 2A. The MALDI-TOF mass spectrum
of the mixture formed after heating for 3 h was also recorded.
As shown in Fig. 11, ions arising from acetate–trifluoroacetate
and amidinate–trifluoroacetate exchange were observed. We can
therefore conclude that the amidinate ligands, though relatively
less labile than the carboxylates in solution at room temperature,
are still kinetically labile to ligand scrambling, especially upon
heating in solution.
R
benzene-d6 and placed in a J. Youngꢀ NMR tube under an N2
1
atmosphere. The reaction was monitored with time by both H
NMR spectroscopy and mass spectrometry.
At room temperature the 1H signals of the acetate lig-
ands were most informative. Within 6 h the appearance of
two new acetate 1H signals was detectable and these could
be assigned to the products of acetate–trifluoroacetate lig-
and exchange, namely Mo2[(NiPr)2CMe]2(O2CMe)(O2CCF3) and
Mo2(O2CCF3)3(O2CMe). Within 3 days at room temperature
the major acetate signal was still due to 2A but additional
Higher-order oligomers
The unique trans–trans geometry of the mixed acetate amidinate
complexes led us to investigate their potential in the synthesis of
1-D polymeric chains based on the replacement of the acetate
ligands by dicarboxylate ligands.17 Schematically the reaction can
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The reactions were run in various solvents (THF, hexanes,
EtOH) for periods of 14–21 days. As a prototypical bridge we
employed the use of 1,4-terephthalate (X = C6H4). The products
in these reactions were not easy to characterize as “polymers”
but rather are formulated as a mixture of relatively short chain
oligomers having terminal O2CMe and O2CC6H4COOH groups
e.g. (MeCO2)L2Mo2O2CC6H4CO2Mo2L2(O2CMe) and (MeCO2)-
L2Mo2(O2CC6H4CO2)Mo2L2(O2CC6H4CO2)Mo2L(O2CMe) based
on MALDI-TOF mass spectrometry, where L = (NiPr)2CC≡CPh.
In an attempt to prepare 1-D polymers by
a salt
metathesis reaction involving a cationic complex Mo2[(NiPr)2-
CC≡CPh)]2(CH3CN)42+[BF4−]2 and the dicarboxylate anion [O2C-
X-CO2]2−, the reaction between 2A and Et3OBF4 (2 equiv.) in
CH3CN was investigated. However, this did not lead to the
desired bisamidinate cationic complex but rather the cation
Mo2[(NiPr)2CC≡CPh](O2CMe)(CH3CN)x by replacement of
2+
both acetate and amidinate ligands. This approach was thus not
pursued further.
These reactions aimed at preparing higher order oligomers and
described in the ESI.§
2
Fig. 10 ORTEP diagram of Mo2(cis-l-O2C-9-anthracene)2(g -
(NiPr)2CMe)2 molecule drawn with 50% probability displacement
ellipsoids. Hydrogen atoms are omitted for clarity. The Mo–Mo,
Mo–O(carboxylate), and M–N(amidinate) interatomic distances are
˚
Concluding remarks
2.1308(4), 2.096(2)–2.117(2) and 2.156(3)–2.165(3) A, respectively. The
dihedral angle between anthracene ring and its carboxylate group is
76.5–63.9◦.
This work has allowed for the synthesis and characterization of
a new series of mixed amidinate–carboxylates of dimolybdenum
and ditungsten, M≡M. Though interesting in their own right,
these complexes still suffer from kinetic lability toward ligand
exchange reactions and have not proved useful in the synthesis
of 1-D polymers, which has been a topic of some interest to this
group for some time.17,18
Experimental
Physical measurements
NMR spectra were recorded on a 400 MHz Bruker DPX
Avance400 spectrometer. All 1H NMR chemical shifts are reported
in ppm relative to the protio impurity in THF-d8 at 3.58 ppm or
benzene-d6 at 7.15 ppm from a 90% benzene–10% THF mixture
by weight. Electronic spectra at room temperature were recorded
by using a Perkin-Elmer Lambda 900 spectrometer in THF
solution. Microanalyses were carried out by Atlantic Microlab,
Inc. Cyclic voltammetric and differential pulse voltammetric data
were collected with the aid of a Princeton Applied Research (PAR)
173A potentiostat-galvanostat equipped with a PAR 176 current-
to-voltage converter with iR compensation capability. A single
compartment voltammetric cell was equipped with a platinum
working electrode, a platinum wire auxiliary electrode, and a
pseudo-reference electrode consisting of a silver wire in 0.5 M
nBu4NPF6–THF separated from the bulk solution by a Vycor tip.
Ferrocene was added as an internal reference and typically was
found at +0.75 V under these conditions.
Fig. 11 MALDI-TOF mass spectra of the ligand scrambling reaction
involving 2A and Mo2(O2CCF3)4 upon heating at approximately 70 ◦C for
3 h. The chemical formula and molecular weights of identified species are
labeled.
Synthesis
be represented by eqn (1).
All reactions were carried out under an atmosphere of oxygen-
free UHP-grade argon using standard Schlenk techniques or
under a dry and oxygen-free nitrogen atmosphere using stan-
dard glovebox techniques. All solvents were dried and degassed
trans-Mo2L2(O2CMe)2 + HO2C–X–CO2X
−−−→ 1/n trans-[L2M(O2C–X–CO2)]n + 2MeCOOH (1)
solvent
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by standard methods and distilled prior to use. Dimolybde-
num tetraacetate, Mo2(O2CMe)4,19 and ditungsten tetraacetate,
W2(O2CMe)4,20 were prepared according to the literature pro-
cedures. N,Nꢀ-Diisopropylcarbodiimide, tert-butylacetylene, n-
butyllithium (2.5 M in hexanes), methyllithium (1.6 M in diethyl
ether), lithium phenylacetylide (1.0 M in THF), terephthalic
acid, and 2,5-thiophenedicarboxylic acid were purchased from
commercial sources and used as received.
Attempted preparation of W2(O2CCH3)2((NiPr)2CMe)2 (1B)
The reaction was carried out under similar conditions outlined
for the molybdenum analogue by using 600 mg of W2(O2CCH3)4
(1.0 mmol), 0.31 mL of N,Nꢀ-diisopropylcarbodiimide (2.0 mmol)
and 1.25 mL of 1.6 M methyllithium (2.0 mmol). Within minutes,
the solution turned gray. After 2 h, the solvent was removed under
a dynamic vacuum but the mixture yielded no tractable product.
Mo2(O2CMe)2((NiPr)2CC≡CtBu)2 (2A)
Preparation of Li[(NiPr)2CC≡CPh]
3.2 mL of 2.5 M n-butyllithium (8.0 mmol) was slowly added a
mixture of 1 mL of tert-butylacetylene (8.0 mmol) in25mL ofTHF
at −78 ◦C. The solution was allowed to stir at room temperature
for 2 h. The solution appeared almost colorless. It was used in situ
for the next reaction. 1.25 mL of N,Nꢀ-diisopropylcarbodiimide
1.25 mL of N,Nꢀ-diisopropylcarbodiimide (8.0 mmol) was dis-
solved in approximately 25 mL of THF and cooled to 0 ◦C. 5 mL of
1.6 M methyllithium (8.0 mmol) in THF was added to the mixture.
The solution was allowed to warm slowly to room temperature.
After 2 h, the solvent was evaporated to dryness under a dynamic
vacuum to give a tan solid in quantitative yield.
◦
(8.0 mmol) was slowly added to the in situ mixture at 0 C. The
solution was allowed to stir at room temperature for 2 h. The
solution appeared colorless. It was used in situ for the next reaction.
A slurry containing 1.72 g of Mo2(O2CMe)4 in 25 mL of THF was
cooled to 0 ◦C. The in situ amidinate salt was cooled again to
0 ◦C and slowly added to the slurry. The solution rapidly turned
red. Within the first hour the solution was dark. After stirring
overnight, the solvent was removed under a dynamic vacuum and
the residue was redissolved in approximately 50 mL of CH2Cl2.
The solution was filtered over Celite. The volume of the solution
was reduced to a minimum by a dynamic vacuum and ethanol was
added to precipitate the product. The solid was collected by using
a glass frit and washed with 2 × 10 mL of hexanes. The yield was
810 mg. The filtrate was evaporated to dryness and redissolved in
pure ethanol. The second crop of product was collected using a
glass frit and yielded 220 mg. Overall yield: 1.030 g (35.5%).
Microanalysis: found: C 49.12; H 7.26; N 7.65%. C30H52N4-
O4Mo2 requires: C 49.72; H 7.23; N 7.73%. NMR (benzene-d6):
1H (400 MHz) 4.90 (septet, JHH = 6.5 Hz, 4H, CHMe2), 2.23 (s,
6H, O2CMe), 1.19 (s, 18H, CMe3) 1.10 (d, JHH = 6.5 Hz, 24H,
CHMe2). MALDI-MS: 724.2 (100%, M+).
Preparation of Li[(NiPr)2CC4H4S]
2.0 mL of thiophene (10.0 mmol) was dissolved in approximately
25 mL of THF and cooled to 0 ◦C. 10 mL of 1.0 M n-butyllithium
(10.0 mmol) in THF was added to the mixture. The solution
was allowed to warm slowly to room temperature. After 2 h,
the solution was again cooled to 0 C and 3.9 mL of N,Nꢀ-
diisopropylcarbodiimide was slowly added to the mixture and
allowed to warm to room temperature.
◦
Preparation of Mo2(O2CMe)2((NiPr)2CMe)2 (1A)
1.25 mL of N,Nꢀ-diisopropylcarbodiimide (8.0 mmol) was dis-
solved in approximately 25 mL of THF and cooled to 0 ◦C. 5 mL of
1.6 M methyllithium (8.0 mmol) in THF was added to the mixture.
The solution was allowed to warm slowly to room temperature.
After 2 h, it was used in situ for the next reaction. A slurry of 1.72 g
of Mo2(O2CMe)4 (4.0 mmol) in approximately 25 mL of THF was
cooled to 0 ◦C. The in situ solution was cooled again to 0 ◦C and
slowly added to the slurry. The initial color change was red but
darkened with time. After stirring at room temperature overnight,
the mixture was evaporated to dryness under a dynamic vacuum
and redissolved in approximately 50 mL of dichloromethane. The
solution was filtered over Celite. The volume of the red solution
was reduced to a minimum (∼3 mL) and ethanol (∼5 mL) was
added to precipitate the product. The yellow product was collected
on a glass frit, washed with 10 mL of ethanol, and yielded 825 mg.
The filtrate was evaporated to dryness and 10 mL of ethanol was
added. This resulted in a yellow suspension. The solid was washed
three times with approximately 10 mL of ethanol and allowed
to settle (each time the supernatant liquid was cannulated off).
The remaining solid was dried and yielded a second crop 500 mg.
Overall yield: 1.325 g (55.9%).
W2(O2CMe)2((NiPr)2CC≡CtBu)2 (2B)
The reaction was carried out under similar conditions outlined
for the molybdenum analogue using 600 mg of W2(O2CMe)4
(1.0 mmol), 0.8 mL of 2.5M n-butyllithium (2.0 mmol), 0.25 mL
of tert-butylacetylene (8.0 mmol), and 0.31 mL of N,Nꢀ-
diisopropylcarbodiimide (2.0 mmol). An orange solid (310 mg,
34.3% yield) was isolated by filtration.
NMR (benzene-d6): 1H (400 MHz) 5.16 (septet, JHH = 6.5 Hz,
4H, CHMe2), 2.44 (s, 6H, O2CMe), 1.23 (s, 18H, CMe3) 1.20 (d,
JHH = 6.5 Hz, 24H, CHMe2). MALDI-MS: 900.3 (100%, M+).
Mo2(O2CMe)2((NiPr)2CC≡CPh)2 (3A)
1.25 mL of N,Nꢀ-diisopropylcabodiimide (8.0 mmol) was dis-
solved in 25 mL of THF and cooled to 0 ◦C. 8.0 mL of 1 M
lithium phenylacetylide (8.0 mmol) was added to the mixture.
The solution was allowed to warm slowly to room temperature.
After 2 h, it was used in situ for the next reaction. A slurry of
1.72 g of Mo2(O2CMe)4 in 25 mL of THF was made and cooled
to 0 ◦C. The in situ solution was cooled again to 0 ◦C and slowly
added to the slurry. The initial color was red but darkened with
Microanalysis: found:
C
40.22;
H
6.67;
N
9.18%.
C20H40N4O4Mo2 requires: C 40.55; H 6.81; N 9.46%. NMR
(benzene-d6): 1H (400 MHz) 4.19 (septet, JHH = 6.4 Hz, 4H,
CHMe2), 2.32 (s, 6H, CMe), 2.21 (s, 6H, CMe), 0.92 (d, JHH
=
6.4 Hz, 24H, CHMe2). The methyl groups of the acetate and amid-
inate have not been assigned. MALDI-MS: 593.1 (100%, M+).
This journal is
The Royal Society of Chemistry 2008
Dalton Trans., 2008, 1615–1624 | 1621
©

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reaction time. After stirring at room temperature overnight, the
solvent was evaporated to dryness and the residue was redissolved
in approximately 50 mL of dichloromethane. The solution was
filtered over Celite. The volume of the red solution was reduced
to a minimum and ethanol was added to precipitate the product.
The product was collected on a glass frit, washed with 10 mL of
ethanol, yielding 1.85 g. The filtrate was evaporated to dryness
and 10 mL of ethanol was added. This resulted in an orange
suspension. The solid was collected by filtration and was washed
three times with approximately 10 mL of ethanol and allowed to
settle (each time the supernatant liquid was cannulated off). The
remaining solid was dried and yielded a second crop 0.5 g. Overall
yield: 2.35 g (76.8%).
Microanalysis: found: C 51.52; H 5.63; N 6.74%. C34H44N4-
O4Mo2 requires: C 53.41; H 5.80; N 7.33%. NMR (benzene-d6):
1H (400 MHz) 7.56 (m, 4H, phenyl H), 7.37 (m, 6H, phenyl H),
4.77 (septet, JHH = 6.5 Hz, 4H, CHMe2), 2.39 (s, 6H, O2CMe), 0.90
(d, JHH = 6.5 Hz, 24H, CHMe2). MALDI-MS: 765.2 (100%, M+).
Preparation of W2(O2CCH3)2((NiPr)2CC≡CFc)2 (4B)
The reaction was carried out under similar conditions outlined
for the molybdenum analogue by using 604 mg of W2(O2CMe)4
(1.0 mmol), 430 mg of ethynylferrocene (2.0 mmol), 0.8 mL
of 2.5 M n-butyllithium (2.0 mmol) and 0.31 mL of N,Nꢀ-
diisopropylcarbodiimide (2.0 mmol). 280 mg of a dark red solid
yield was isolated by filtration. The filtrate was stripped to dryness
and redissolved in 10 mL of THF. This solution was placed in
◦
the −40 C refrigerator to grow crystals. After several days, the
mother-liquor was removed and a 100 mg crop of crystals was
collected. Overall yield: 380 mg (32.9%).
Microanalysis: found:
C
43.71;
H
4.49;
N
4.65%.
C42H52N4O4Fe2W2 requires: C 43.63; H 4.53; N 4.85%. NMR
(benzene-d6): 1H (400 MHz) 5.33 (septet, JHH = 6.4 Hz, 4H,
CHMe2), 4.39 (s, 4H, Fc), 4.09 (s, 10H, Fc), 3.98 (s, 4H, Fc), 2.45 (s,
6H, O2CMe), 1.27 (d, JHH = 6.4 Hz, 24H, CHMe2). MALDI-MS:
1156.2 (100%, M+).
Preparation of Mo2(O2C-2-thiophene)2((NiPr)2CMe)2
W2(O2CMe)2((NiPr)2CC≡CPh)2 (3B)
0.31 mL of N,Nꢀ-diisopropylcarbodiimide (2.0 mmol) was dis-
◦
solved in 25 mL of THF and cooled to 0 C. 1.25 mL of 1.6 M
The reaction was carried out under similar conditions outlined
for the molybdenum analogue by using 604 mg of W2(O2CMe)4
(1.0 mmol), 0.31 mL of N,Nꢀ-diisopropylcabodiimide (2.0 mmol)
and 2.0 mL of 1.0 M lithium phenylacetylide (2.0 mmol). A single
crop of blue solid (0.340 g, 36.2% yield) was collected by filtration.
Microanalysis: found: C 42.65; H 4.70; N 5.90%. C34H44N4O4W2
requires: C 43.42; H 4.72; N 5.96%. NMR (benzene-d6): 1H (400
methyllithium (2.0 mmol) was added to the mixture. The solution
was allowed to warm slowly to room temperature. After 2 h, it was
used in situ for the next reaction. A slurry of 0.7 g of Mo2(O2C-2-
thiophene)421 in 25 mL of THF was made and cooled to 0 ◦C. The
in situ solution was cooled again to 0 ◦C and slowly added to
the slurry. The initial color change was black but changed to a
deep red. After stirring at room temperature for two days, the
solvent was removed under a dynamic vacuum and the residue
was redissolved in approximately 25 mL of CH2Cl2. The solution
was filtered over Celite. The volume of the red solution was reduced
to a minimum to precipitate an orange–red solid. The product was
collected on a glass frit and washed with 2 × 5 mL of hexanes.
Additional hexanes were added to the filtrate which caused a
second precipitation. This second batch was also collected on a
frit and washed with 2 × 5 mL hexanes. The solid was dried under
vacuum for several hours. Overall yield: 130 mg (17.9%).
MHz) 7.38 (d, JHH = 7.4 Hz, 4H, phenyl o-H), 7.05 (t, JHH
=
7.6 Hz, 4H, phenyl m-H), 6.93 (d, JHH = 7.5 Hz, 2H, phenyl p-H),
5.30 (septet, JHH = 6.5 Hz, 4H, CHMe2), 2.45 (s, 6H, O2CMe), 1.24
(d, JHH = 6.5 Hz, 24H, CHMe2). MALDI-MS: 940.2 (100%, M+).
Preparation of Mo2(O2CCH3)2((NiPr)2CC≡CFc)2 (4A)
0.8 mL of 2.5M n-butyllithium was slowly added to a mixture
of 430 mg of ethynylferrocene in approximately 50 mL of THF
at 0 ◦C. The solution was allowed to stir at room temperature
for 2 h. It was used in situ for the next reaction. 0.31 mL of N,N ꢀ-
diisopropylcarbodiimide was slowly added to the in situ mixture at
0 ◦C. The solution was allowed to stir at room temperature for 2 h.
It was used in situ for the next reaction. A slurry containing 428 mg
of Mo2(O2CCH3)4 in 25 mL of THF was cooled to 0 ◦C. The in situ
solution was cooled again to 0 ◦C and slowly added to the slurry.
The solution initially turned red. Within the first hour the solution
darkened. After stirring overnight, the mixture was evaporated
to dryness and redissolved in approximately 50 mL of CH2Cl2.
The solution was filtered over Celite. The volume of the solution
was reduced to a minimum and the desired product precipitated.
The orange solid was collected using a glass frit and washed with
hexane. Overall yield: 385 mg (39.3%).
1
NMR (benzene-d6): H (400 MHz) 7.67 (d, 2H, thiophene),
6.79 (d, 2H, thiophene), 6.63 (t, 2H, thiophene), 4.16 (septet, 4H,
CHMe2), 2.01 (s, 6H, N2CMe), 0.95 (d, 24H, CHMe2). MALDI-
MS: 728.1 (100%, M+).
Preparation of Mo2(cis-l-O2C-9-anthracene)2(g2-(NiPr)2CMe)2
0.31 mL of N,Nꢀ-diisopropylcarbodiimide (2.0 mmol) was dis-
◦
solved in 25 mL of THF and cooled to 0 C. 1.25 mL of 1.6 M
methyllithium (2.0 mmol) was added to the mixture. The solution
was allowed to warm slowly to room temperature. After 2 h, it was
used in situ for the next reaction. A slurry of 1.08 g of Mo2(O2C-9-
anthracene)414 in 25 mL of THF was made and cooled to 0 ◦C. The
in situ solution was cooled again to 0 ◦C and slowly added to the
slurry. The initial color changed to a deep red. After stirring at
room temperature for two days, the solvent was removed under a
dynamic vacuum and the residue was redissolved in approximately
25 mL of CH2Cl2. The solution was filtered over Celite. The volume
of the solution was reduced to a minimum and ethanol was added
to precipitate a purple solid. The product was collected on a glass
Microanalysis: found:
C
51.53;
H
5.29;
N
5.69%.
C42H52N4O4Fe2Mo2 requires: C 51.45; H 5.35; N 5.71%. NMR
(benzene-d6): 1H (400 MHz) 5.06 (septet, JHH = 6.4 Hz, 4H,
CHMe2), 4.43 (s, 4H, Fc), 4.10 (s, 10H, Fc), 3.97 (s, 4H, Fc), 2.28 (s,
6H, O2CMe), 1.16 (d, JHH = 6.4 Hz, 24H, CHMe2). MALDI-MS:
980.1 (100%, M+).
1622 | Dalton Trans., 2008, 1615–1624
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Table 1 Crystallographic details and data collection for Li[(NiPr)2CC≡CPh], Li[(NiPr)2CC4H4S)]. Mo2(O2CCH3)2((NiPr)2CMe)2 1A and
Mo2(O2CCH3)2((NiPr)2CC≡CPh)2·3thf 3A
Mo2(O2CCH3)2-
Li[(NiPr)2CC≡CPh]
Li[(NiPr)2CC4H4S)]
((NiPr)2CMe)2 1A
Mo2(O2CCH3)2((NiPr)2CC≡CPh)2·3thf 3A
Formula
Mr
C38H54Li2N4O2
612.73
C15H25LiN2OS
288.37
Monoclinic
P21/c
200(2)
9.173(1)
10.970(1)
17.190(2)
C20H40Mo2N4O4
592.44
C34H44Mo2N4O4·3C4H8O
980.92
Crystal system
Space group
T/K
Triclinic
Triclinic
Triclinic
¯
¯
¯
P1
P1
P1
200(2)
200(2)
200(2)
˚
a/A
9.724(1)
10.008(1)
19.713(2)
93.575(5)
91.225(5)
90.848(4)
1914.0(3)
2
1.063
664
0.71073
0.065
8.3023(10)
9.0596(10)
9.5252(10)
68.840(4)
77.080(4)
65.805(5)
607.03(12)
1
1.621
304
0.71073
1.065
9.311(1)
11.735(1)
12.973(1)
66.083(3)
74.895(3)
68.780(5)
1197.1(2)
1
1.361
512
0.71073
0.574
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
95.953(7)
3
˚
V/A
1720.5(3)
4
1.113
624
0.71073
0.185
Z
Dc/g cm−3
F(000)
˚
k(Mo-Ka)/A
l/mm−1
Crystal size/mm
Measd reflect.
Indep. reflect.
Criter. obs. refl.
Rint
R1 (I > 2r(I))
wR2 (I > 2r(I))
R1 (all)
0.27 × 0.35 × 0.38
0.15 × 0.23 × 0.31
0.19 × 0.31× 0.38
0.15 × 0.31 × 0.38
36676
27382
17872
32426
6769
I > 2r(I)
0.028
0.0518
0.1348
0.0676
0.1471
3031
I > 2r(I)
0.036
0.0472
0.1249
0.0659
0.1361
2771
I > 2r(I)
0.027
0.0169
0.0432
0.0180
0.0436
5452
I > 2r(I)
0.028
0.0300
0.0797
0.0336
0.0818
wR2 (all)
Dq max., min.
0.184, −0.248
0.189, −0.185
0.345, −0.436
0.774, −0.742
Table 2 Crystallographic details and data collection for W2(O2CCH3)2((NiPr)2CC≡CPh)2 3B, Mo2(O2CCH3)2((NiPr)2CC≡CFc)2 4A,
2
W2(O2CCH3)2((NiPr)2CC≡CFc)2 4B and Mo2(cis-l-O2C-9-anthracene)2(g -(NiPr)2CMe)2
2
W2(O2CCH3)2((NiPr)2-
CC≡CPh)2 3B
Mo2(O2CCH3)2((NiPr)2-
CC≡CFc)2 4A
W2(O2CCH3)2((NiPr)2-
CC≡CFc)2 4B
Mo2(cis-l-O2C-9-anthracene)2(g -
(NiPr)2CMe)2
Formula
Mr
C34H44N4O4W2
940.43
C42H52Fe2Mo2N4O4·4C4H8O
C20H40Mo2N4O4
592.44
C34H44Mo2N4O4·3C4H8O
980.92
1268.87
Triclinic
Crystal system
Space group
T/K
Triclinic
Triclinic
Triclinic
¯
¯
¯
¯
P1
P1
P1
P1
150(2)
200(2)
150(2)
200(2)
˚
a/A
8.279(1)
9.371(1)
12.082(1)
75.741(6)
71.498(6)
78.558(5)
854.1(2)
1
1.828
456
0.71073
6.770
11.135(1)
11.862(1)
12.321(1)
67.157(1)
78.161(1)
85.503(1)
1468.0(2)
1
1.435
660
0.71073
0.956
8.3023(10)
9.0596(10)
9.5252(10)
68.840(4)
77.080(4)
65.805(5)
607.03(12)
1
1.621
304
0.71073
1.065
9.311(1)
11.735(1)
12.973(1)
66.083(3)
74.895(3)
68.780(5)
1197.1(2)
4
1.361
512
0.71073
0.574
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
3
˚
V/A
Z
Dc/g cm−3
F(000)
˚
k(Mo-Ka)/A
l/mm−1
Crystal size/mm
Measd reflect.
Indep. reflect.
Criter. obs. refl.
Rint
R1 (I > 2r(I))
wR2 (I > 2r(I))
R1 (all)
0.12 × 0.19 × 0.27
0.12 × 0.27 × 0.27
0.19 × 0.31 × 0.38
0.15 × 0.31 × 0.38
26489
40640
17872
32426
3913
I > 2r(I)
0.042
0.0169
0.0398
0.0190
0.0404
6736
I > 2r(I)
0.033
0.0422
0.1174
0.0540
0.1248
2771
I > 2r(I)
0.027
0.0169
0.0432
0.0180
0.0436
5452
I > 2r(I)
0.028
0.0300
0.0797
0.0336
0.0818
wR2 (all)
Dq max., min.
1.152, −1.393
1.232, −0.738
0.345, −0.436
0.774, −0.742
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Dalton Trans., 2008, 1615–1624 | 1623
©

View Article Online
frit and washed with 10 mL of ethanol. The solid was dried under
vacuum for several hours. Overall yield: 360 mg (39.2%).
References
1 Multiple Bonds between Metal Atoms, ed. F. A. Cotton, C. A. Murillo,
and R. A. Walton, Clarendon Press, Oxford, 3rd edn, 2005.
2 (a) M. H. Chisholm and A. M. Macintosh, J. Chem. Soc., Dalton Trans.,
1999, 1205; (b) H. Chen and F. A. Cotton, Polyhedron, 1995, 14, 2221.
3 F. A. Cotton, C. Lin and C. A. Murillo, Acc. Chem. Res., 2001, 34, 759.
4 M. H. Chisholm and N. J. Patmore, Acc. Chem. Res., 2007, 40, 17.
5 M. H. Chisholm, Proc. Natl. Acad. Sci. U.S.A., 2007, 104, 2563.
6 A. R. Sadique, M. J. Heeg and C. H. Winter, J. Am., Chem. Soc., 2003,
125, 7774.
Microanalysis: found:
C
63.21;
H
5.26;
N
3.77%.
C46H54Mo2N4O4 requires: C 60.13; H 5.92; N 6.10%. NMR
1
(benzene-d6): H (400 MHz) 9.25 (d, 4H, anthr.), 8.23 (s, 2H,
anthr.), 7.74 (d, 4H, anthr.), 7.09 (t, 4H, anthr.), 6.95 (t, 4H, anthr.),
3.83 (septet, 4H, CHMe2) 1.75 (s, 6H, N2CMe), 1.58 (d, 12H,
CHMe2), 1.09 (d, 12H, CHMe2). MALDI-MS: 919.2 (100%, M+).
7 B. S. Lim, A. Rahtu, J.-S. Park and R. G. Gordon, Inorg. Chem., 2003,
42, 7951.
Computational details
8 M. P. Coles, D. C. Swenson and R. F. Jordan, Organometallics, 1997,
16, 5183.
9 S. Dagorne and R. F. Jordan, Organometallics, 1999, 18, 4619.
10 B. E. Bursten, M. H. Chisholm, R. J. H. Clark, S. Firth, C. M. Hadad,
A. M. Macintosh, P. J. Wilson, P. M. Woodward and J. M. Zaleski,
J. Am. Chem. Soc., 2002, 124, 3050.
11 D. L. Lichtenberger, M. A. Lynn and M. H. Chisholm, J. Am. Chem.
Soc., 1999, 121, 12167.
12 M. H. Chisholm, J. S. D’Acchioli, B. D. Pate, N. J. Patmore, N. S. Dalal
and D. J. Zipse, Inorg. Chem., 2005, 44, 1061.
13 (a) G.-L. Xu, R. J. Crutchley, M. C. DeRosa, Q.-J. Pan, H.-X. Zhang,
X. Wang and T. Ren, J. Am. Chem. Soc., 2005, 127, 13354; (b) G.-L.
Xu, M. C. DeRosa, R. J. Crutchley and T. Ren, J. Am. Chem. Soc.,
2004, 126, 3728.
14 M. J. Byrnes, M. H. Chisholm, J. C. Gallucci, Y. Liu, R. Ramnauth and
C. Turro, J. Am. Chem. Soc., 2005, 127, 17343.
15 S. Jones, J. C. C. Atherton, M. R. J. Elsegood and W. Clegg, Acta
Crystallogr., Sect. C, 2000, 56, 881.
16 M. J. Byrnes, M. H. Chisholm, D. F. Dye, C. M. Hadad, P. D. Pate, P. J.
Wilson and J. M. Zaleski, Dalton Trans., 2004, 523.
Density functional theory (DFT) calculations were performed
with the hybrid Becke-3 parameter exchange functional and
the Lee–Yang–Parr nonlocal correlation functional (B3LYP)22
implemented in the Gaussian03 (Revision B.04) program suite23 in
conjunction with the 6-31G* basis set for all non-metal atoms and
the SDD basis set with effective core potential (ECP) for all metal
atoms.24 The calculations were carried out on simplified models
in which each isopropyl substituent was replaced with a hydrogen
atom. All geometries were fully optimized at the above levels using
the default optimization criteria of the program. All calculations
yielded a self-consistent set of results that were verified to be a
minimum on the potential energy surface (PES) by frequency
analysis. Orbital analyses were completed with GaussView.25 To
gain insight into the electronic transitions responsible for the
observed UV-vis spectrum of all compounds, time-dependent
density functional theory (TD-DFT) calculations were performed
using the Gaussian program suite. All calculations were run on
an Itanium 2 Cluster running Linux version 2.4.18 located at the
Ohio Supercomputer Center.
17 For a related reaction, see: M. H. Chisholm, A. J. Epstein, J. C. Gallucci,
F. Fiel and W. Pirkle, Angew. Chem., Int. Ed., 2005, 44, 6537.
18 R. H. Cayton, M. H. Chisholm, J. C. Huffman and E. B. Labkovsky,
J. Am. Chem. Soc., 1991, 113, 8709.
19 T. A. Stephenson, E. Banister and G. Wilkinson, J. Chem. Soc., 1964,
2538.
X-Ray crystal structure determinations
20 D. J. Santure, J. C. Huffman and A. P. Sattelberger, Inorg. Chem., 1985,
24, 371.
21 M. J. Byrnes, M. H. Chisholm, R. J. H. Clark, J. C. Gallucci, C. M.
Hadad and N. J. Patmore, Inorg. Chem., 2004, 43, 6334.
22 A. D. J. Becke, Chem. Phys., 1993, 98, 5648.
All crystals were coated with Paratone oil and mounted on a
quartz fiber or a nylon cryoloop affixed to a goniometer head.
All diffraction data were collected using a Nonius Kappa CCD
diffractometer. All work was done at between 150 and 200 K using
an Oxford Cryosystem Cryostream Cooler. Data integration was
done with Denzo. Scaling and merging of data was done with
Scalepack. The structures were solved by the direct or Patterson
method in SHELXS-86 or SHELXS-97. A summary of crystal
data is given in Tables 1 and 2 while full crystallographic details
are provided in Tables S1 and S2 of the ESI.§
23 M. J. Frisch, G.W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb,
J. R. Cheeseman, J. A. Montgomery, Jr., T. Vreven, K. N. Kudin, J. C.
Burant, J. M. Millam, S. S. Iyengar, J. Tomasi, V. Barone, B. Mennucci,
M. Cossi, G. Scalmani, N. Rega, G. A. Petersson, H. Nakatsuji, M.
Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T.
Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J. E.
Knox, H. P. Hratchian, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo,
R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi,
C. Pomelli, J. Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth, P.
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Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul, S.
Clifford, J. Cioslowski, B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz,
I. Komaromi, R. L. Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y.
Peng, A. Nanayakkara, M. Challacombe, P. M. W. Gill, B. G. Johnson,
W. Chen, M. W. Wong, C. Gonzalez and J. A. Pople, GAUSSIAN 03
(Revision B.04), Gaussian, Inc., Wallingfored, CT, 2003.
24 Æ. Frisch, M. J. Frisch and G. W. Trucks, Gaussian 03 User’s Reference,
Gaussian, Inc., Wallingford, CT, 2003.
CCDC reference numbers 637924–637931.
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b715258b
Acknowledgements
We thank the National Science Foundation for support of this
work, and the Ohio Supercomputer Center for the computational
resources with which the DFT calculations were performed.
25 Æ. Frisch, R. D. Dennington and T. A. Keith, GaussView Reference,
Gaussian, Inc., Wallingford, CT, 2003.
1624 | Dalton Trans., 2008, 1615–1624
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The Royal Society of Chemistry 2008
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