Structure and magnetic behaviour of mono- and bimetallic chromium(III) complexes of amine-bis(phenolate) ligands

Article abstract of DOI:10.1039/b910254j

Two lithium amine-bis(phenolate) and four chromium(iii) amine-bis(phenolate) complexes have been prepared. The diprotonated tripodal tetradentate ligand precursors 2-tetrahydrofurfuryl-N,N-bis(2-methylene-4- methyl-6-tert-butylphenol), H₂[O

Full text of DOI:10.1039/b910254j

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www.rsc.org/dalton | Dalton Transactions
Structure and magnetic behaviour of mono- and bimetallic chromium(III)
complexes of amine-bis(phenolate) ligands†
a
a
b
c
a
Rebecca K. Dean, Stephanie L. Granville, Louise N. Dawe, Andreas Decken, Karen M. Hattenhauer and
a
Christopher M. Kozak*
Received 26th May 2009, Accepted 11th September 2009
First published as an Advance Article on the web 6th October 2009
DOI: 10.1039/b910254j
Two lithium amine-bis(phenolate) and four chromium(III) amine-bis(phenolate) complexes have been
prepared. The diprotonated tripodal tetradentate ligand precursors 2-tetrahydrofurfuryl-N,N-
BuMe
bis(2-methylene-4-methyl-6-tert-butylphenol), H
2
[O
2
NO]
; 2-tetrahydrofurfuryl-N,N-bis(2-
BuBu
methylene-4,6-tert-butylphenol), H
2
[O NO] ; 2-pyridylamino-N,N-bis(2-methylene-4,6-
; and 2-pyridylamino-N,N-bis(2-methylene-4,6-tert-butylphenol),
NN¢] ; can be lithiated using n-butyllithium. Isolation of the Li
2
MeMe
methylphenol), H
2
[O
2
NN¢]
BuBu
RR¢
H
2
[O
2
2
[O NO] compounds
2
RR¢
generates dimeric {Li
2
[O
2
NO]
} (R = t-Bu, R¢ = Me in 1 and R = R¢ = t-Bu in 2) in the solid state as
2
shown by single-crystal X-ray diffraction. The lithiated ligands were used to prepare a series of Cr(III)
complexes. Monometallic complexes are obtained when prepared and purified under strictly anhydrous
RR¢
conditions, giving CrCl(THF)[O
2
NO] (R = t-Bu, R¢ = Me in 3 and R = R¢ = t-Bu in 4). However,
bimetallic Cr complexes are obtained upon recrystallization in air, where adventitious water reacts with
the complex resulting in protonation of one of the phenolate groups of the ligand and generating
hydroxide, which bridges two Cr(III) centres. Solid-state single-crystal X-ray diffraction studies of
MeMe
MeMe
BuBu
{
CrCl[O
2
NN¢]
}(m-HO){CrCl[HO
2
NN¢]
}, 5, and {CrCl[O
2
NN¢] }(m-HO){CrCl-
BuBu
[
HO
2
NN¢] }, 6, were performed. The paramagnetic Cr(III) complexes were also characterized by
UV-vis spectroscopy, mass spectrometry and magnetic measurements.
Introduction
ligands, which effectively catalyze the cross-coupling of aromatic
Grignard reagents with alkyl halides possessing b-hydrogens.
7,8
The use of chelating tetradentate amine-bis(phenolate) ligands is
playing an increasingly important role in transition-metal catalyst
design. They have been predominantly used with high oxidation-
state early transition-metals where they have been employed
as alternative auxiliary ligands to cyclopentadienyl-based sys-
tems. In combination with group 4 and 5 metals, they display
While there are plentiful examples of chromium complexes of
diimine-bis(phenolate) (the so-called salen) ligands, particularly
9,10
from the group of Darensbourg,
related complexes bearing
11,12
diamine-bis(phenolate) ligands are limited.
When considering
the “branched” or “tripodal” tetradentate amine-bis(phenolate)
ligands related to those shown in Chart 1, the only Group 6
complexes reported are dioxomolybdenum(VI) and -tungsten(VI)
1,2
high activities towards olefin or cyclic ester polymerization.
Also, group 3 and lanthanide metal complexes of these ligands
have been effective as catalysts or initiators for ring-opening-
13
compounds, while only one chromium(III) complex of a triden-
6
tate amine-bis(phenolate) ligand has been reported.
3
polymerization of lactide and e-caprolactone. By comparison,
there has been limited use of amine-bis(phenolate) ligands with the
4
mid-to-late first row transition-metals. Some Fe(III) complexes
5,6
of this class of ligand have been investigated as a result of
their close relationship to phenol-containing ligands found in
non-heme iron containing metalloenzymes. We have recently
reported novel iron(III) compounds bearing amine-bis(phenolate)
a
Department of Chemistry, Memorial University of Newfoundland,
St. John’s, Newfoundland, Canada A1B 3X7. E-mail: ckozak@mun.ca;
Tel: +1-709-737-8082
C-CART X-Ray Diffraction Laboratory, Department of Chemistry, Memo-
rial University of Newfoundland, St. John’s, Newfoundland, Canada A1B
Chart 1
b
3
X7
There is considerable interest in chromium complexes as ho-
mogeneous models for commercially used heterogeneous catalysts
for the polymerization of ethylene and a-olefins. Additionally, Cr
complexes have been used as catalysts for the co-polymerization
As a result of our own interest in
polymerization catalysis, we sought to investigate the coordination
c
Department of Chemistry, University of New Brunswick, Fredericton,
New Brunswick, Canada E3B 5A3
14
†
Electronic supplementary information (ESI) available: Cyclic voltammo-
BuBu
2 2
grams of 4 and H [O NO] . CCDC reference numbers 733954–733959.
9,15
of CO
2
with epoxides.
For ESI and crystallographic data in CIF or other electronic format see
DOI: 10.1039/b910254j
5
48 | Dalton Trans., 2010, 39, 548–559
This journal is © The Royal Society of Chemistry 2010

chemistry of Cr(III) with these tetradentate mixed-donor ligands.
Herein we describe the preparation of chromium complexes
possessing amine-bis(phenolate)-ether and amine-bis(phenolate)-
pyridyl ligands, and the structural and magnetic behaviour of
monomeric and bimetallic chromium(III) complexes supported by
diamine-bis(phenolate)s.
Results and discussion
Synthesis and characterization of lithium amine-bis(phenolate)
complexes
The substituted amine-bis(phenol) compounds in Chart 1 were
prepared by modified literature procedures employing Mannich
condensation of the corresponding phenol, amine and formalde-
hyde. Previously, these compounds have been prepared in refluxing
2,16
methanol. The use of water as a reaction medium proves to
be much more effective at generating the desired compounds in
17,18
higher yield and requires shorter heating time.
The synthesis
of both lithium salts was achieved by reacting 2 equiv. of n-BuLi
BuMe
with the appropriate ligand in THF to give {Li
2
[O
2
NO]
}
2
, 1,
BuBu
and {Li
2
[O
2
NO]
}
2
, 2, (Scheme 1). Colourless single crystals
suitable for X-ray diffraction studies were successfully obtained
from a 1 : 1 toluene–hexane mixture for 1, and benzene for 2.
X-Ray structures of 1 and 2 are shown in Fig. 1 and selected bond
lengths and angles for 1 are given in Table 1. Crystallographic data
are given in Table 3. Bond lengths and angles for 2 are given in
the ESI.†
Fig. 1 Molecular structure (ORTEP) and partial numbering scheme of
BuMe
BuBu
{
Li
2
[O
2
NO]
}
2
1 (top) and {Li
2
[O
2
NO]
}
2
2 (bottom). Ellipsoids are
shown at 50% probability. Hydrogen atoms omitted for clarity.
˚
Li–O bond lengths in 1 range from 1.783(6) A for Li(3)–O(4)
˚
to 1.954(6) A for Li(1)–O(5), whereas the Li(1)–N(1) and Li(4)–
˚
˚
N(2) bond lengths are 2.035(6) A and 2.031(6) A, respectively. As
anticipated, the longest Li–O bond distances are those involving
NO]RR¢
2
complexes.
Scheme 1 Synthetic route to {Li
2
[O
2
}
the m -O atoms, O(2) and O(3), and for the neutral O donors
of the pendant tetrahydrofurfuryl group. The structure of 2
3
The molecular structures of complexes 1 and 2 exhibit mildly
curved “ladder” motifs similar to those observed in related
contains an internal rotation axis resulting in two unique Li
19
˚
lithium diamine-bis(phenolate) complexes reported by O’Hara
environments. The Li–O bond lengths in 2 range from 1.791(5) A
20
˚
and Chen. Four alternating Li–O interactions are capped by
two amine-bis(phenolate)-ether ligands. Two lithium ions (Li(1)
and Li(4) in 1 and Li(1)/Li(1)* in 2) show distorted tetrahedral
geometries whereas Li(2) and Li(3) in 1 and Li(2)/Li(2)* in 2
adopt distorted trigonal planar geometries. Unlike the complex
reported by O’Hara, complexes 1 and 2 do not show close-
contacts between the four-coordinate Li centres and the ipso-
carbon of the phenolate group. In the structure of the base-free
for Li(2)–O(1) to 1.955(4) A for Li(2)–O(3) and are consistent
with those observed in 1 and other related Li amine-bis(phenolate)
1
9–21
complexes.
with the m
Again, the shortest Li–O bond lengths are observed
˚
-O atom, O(1). The Li(1)–N(1) distance of 2.025(5) A
2
is experimentally identical to the Li–N distances observed in 1
and other related complexes. In 1, the sum of the O–Li(1)–O
◦
◦
angles is 347.5 and the sum of the O–Li(4)–O angles is 358.5 .
The N-donor of each ligand occupies the apical position of the
trigonal pyramid with average O–Li(1)–N(1) and O–Li(4)–N(2)
˚
dimeric complex of O’Hara, a Li ◊ ◊ ◊ C distance of 2.437(5) A was
◦
◦
observed. Both complexes 1 and 2 exhibit interatomic distances
bond angles of 94.6 and 94.8 , respectively. In 2 the sum of the
basal angles is 357.8 and the average O–Li(1)–N(1) angle is 95.4 .
The cores of 1 and 2 are composed of three essentially planar Li
◦
◦
˚
greater than 2.5 A, which are similar to the interatomic distances
observed in the tetralithium complexes reported by Chen. The
2
O
2
This journal is © The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 548–559 | 549

◦
Table 1 Bond lengths ( A˚ ) and angles ( ) for 1
structure is maintained in solution. Surprisingly, two phenolate
environments are indeed observed in d -pyridine solution, that
is, four aromatic H resonances are visible in the spectra of 1
and 2, as well as two t-butyl and two CH resonances in the
case of 1 and four t-butyl resonances in the spectrum of 2.
This suggests that either the dimeric structure remains intact in
solution even in pyridine, or the pyridine adduct itself possesses
5
O(1)–C(3)
O(1)–Li(2)
O(1)–Li(1)
O(2)–C(19)
O(2)–Li(3)
O(2)–Li(2)
O(2)–Li(1)
O(3)–C(25)
O(3)–Li(2)
O(3)–Li(3)
O(3)–Li(4)
O(4)–C(39)
O(4)–Li(3)
O(4)–Li(4)
O(5)–Li(1)
O(6)–Li(4)
N(1)–Li(1)
N(2)–Li(4)
Li(1) ◊ ◊ ◊ Li(2)
Li(2) ◊ ◊ ◊ Li(3)
Li(3) ◊ ◊ ◊ Li(4)
O(1)–Li(1)–O(5)
O(1)–Li(1)–O(2)
O(5)–Li(1)–O(2)
O(1)–Li(1)–N(1)
O(5)–Li(1)–N(1)
O(2)–Li(1)–N(1)
O(1)–Li(2)–O(3)
1.334(4)
1.792(6)
1.887(6)
1.355(4)
1.905(6)
1.942(6)
1.983(5)
1.361(4)
1.878(6)
1.889(6)
1.979(6)
1.336(4)
1.783(6)
1.868(6)
1.954(6)
1.944(6)
2.035(6)
2.031(6)
2.406(8)
2.446(8)
2.426(8)
126.6(3)
98.8(2)
O(1)–Li(2)–O(2)
O(3)–Li(2)–O(2)
O(4)–Li(3)–O(3)
O(4)–Li(3)–O(2)
O(3)–Li(3)–O(2)
O(4)–Li(4)–O(6)
O(4)–Li(4)–O(3)
O(6)–Li(4)–O(3)
O(4)–Li(4)–N(2)
O(6)–Li(4)–N(2)
O(3)–Li(4)–N(2)
C(3)–O(1)–Li(2)
C(3)–O(1)–Li(1)
Li(2)–O(1)–Li(1)
C(19)–O(2)–Li(3)
C(19)–O(2)–Li(2)
Li(3)–O(2)–Li(2)
C(19)–O(2)–Li(1)
Li(3)–O(2)–Li(1)
Li(2)–O(2)–Li(1)
C(25)–O(3)–Li(2)
C(25)–O(3)–Li(3)
Li(2)–O(3)–Li(3)
C(25)–O(3)–Li(4)
Li(2)–O(3)–Li(4)
Li(3)–O(3)–Li(4)
C(39)–O(4)–Li(3)
C(39)–O(4)–Li(4)
Li(3)–O(4)–Li(4)
103.8(3)
98.7(3)
102.6(3)
155.5(4)
99.6(3)
124.3(3)
96.3(3)
137.9(3)
100.2(3)
87.4(2)
96.9(3)
154.2(3)
108.5(2)
81.7(2)
104.9(2)
169.0(2)
78.9(2)
96.5(2)
145.5(3)
75.6(2)
104.5(2)
170.7(3)
81.0(3)
94.8(2)
152.7(3)
77.6(2)
154.1(3)
109.3(2)
83.2(3)
3
low symmetry, thus generating inequivalent phenolate groups. It
RR¢
should be noted that the [O
2
NO]
ligands do possess chiral
centres in the tetrahydrofurfuryl pendant, thereby generating
the observed asymmetry between the phenolate fragments. The
RR¢
protonated compounds, H
2
[O NO] , however, are reported to
2
exhibit equivalent phenolate groups in solution as shown by
8,22
NMR spectroscopy in CDCl
3
.
This suggests free rotation of
the tetrahydrofurfuryl fragment in the protonated ligands. In Li
complexes 1 and 2, this fragment is held in place by coordination to
the metal ion, therefore causing the inequivalence of the phenolate
environments.
Synthesis of chromium(III) complexes
133.1(3)
99.8(3)
87.3(2)
96.6(2)
152.4(4)
The Li-salts were used in the synthesis of two chromium complexes
shown in Scheme 2. Both Cr(III) complexes 3 and 4 were
synthesized by reaction of the appropriate Li-salt (1 and 2,
◦
respectively) with CrCl
3
(THF)
3
in THF at -78 C. Complexes
3
and 4 were isolated as purple powders. MALDI-TOF mass
spectrometry of 3 and 4 using anthracene as matrix was performed
and both complexes show molecular ion peaks and characteristic
fragment ions. The chloride ligand is observed to be lost from the
parent ion in both of these compounds, that is, intense [M - Cl]
peaks were observed in both spectra.
rhombic units. Complex 1 possesses three crystallographically
distinct rhombic units, namely Li(1)–O(1)–Li(2)–O(2), Li(2)–
O(2)–Li(3)–O(3), and Li(3)–O(3)–Li(4)–O(4), which exhibit sums
+
◦
◦
◦
of angles of 359.9 , 358.2 and 359.8 , respectively. Complex 2
possesses two crystallographically distinct units having sums of
angles for Li(1)–O(1)–Li(2)–O(3) and Li(2)–O(3)–Li(2)*–O(3)* of
◦
◦
3
59.5 and 357.8 , respectively.
1
Solution H NMR experiments were carried out in d
8
-toluene
and d
5
-pyridine on both compounds 1 and 2 One equivalent
.
1
of coordinated THF is observed in the H NMR spectra of the
amorphous powders of each of the lithium salts of the [O NO]
RR¢
2
ligands, however, upon recrystallization this coordinated solvent
◦
molecule is lost. In toluene at 25 C complexes 1 and 2 exhibit
NO]RR¢ complexes.
Scheme 2 Synthesis of CrCl(THF)[O
2
broad resonances making assignment of peaks difficult. Variable-
1
temperature H NMR studies were therefore carried out on
Following work using the tetrahydrofurfuryl-containing lig-
both compounds; unfortunately peaks became broader with both
decreasing and increasing temperature in this solvent. This differs
from the NMR data obtained for a linear diamine-bis(phenolate)
ands, H [L1], the related pyridyl-containing compounds, H [L2],
were examined. Two methods were used to prepare Cr(III)
complexes of these ligands (Scheme 3). In the first method, reaction
2
2
19
recently reported, where room temperature spectra give sharp
lines and coupling constants can be determined. The pendant
nature of the tetrahydrofurfuryl donors in 1 and 2 may allow
very rapid exchange processes in complexes 1 and 2 in toluene
solutions. Reports of lithium salts of more closely related branched
amine-bis(phenolate) ligands possessing methoxyethyl pendants
1
also display a reasonably sharp H NMR spectrum at room
20
temperature for CDCl
for 1 and 2 upon using d
3
solutions. Sharper peaks can be obtained
-pyridine, however, it is anticipated
5
that the coordinating pyridine may lead to fragmentation of
the tetralithium dimer to give adducts similar to the dioxane
21
adducts previously reported by our group. From the crystal
structures of 1 and 2, two chemically distinct phenolate groups
RR¢
corresponding to m
2
-O and m
3
-O bonding modes should be
Scheme 3 Synthetic routes to CrCl[O NN¢] complexes and reaction
2
1
observed in the H NMR spectrum if indeed the solid state
with water to give the proposed hydroxide-bridged species, 5 and 6.
5
50 | Dalton Trans., 2010, 39, 548–559
This journal is © The Royal Society of Chemistry 2010

RR¢
of the protonated diamine-bis(phenol) compounds, H
(
2
[O
2
NN¢]
t
◦
R = R¢ = Me or R = R¢ = Bu), at -78 C in THF
with n-butyllithium produced the appropriate dilithio diamine-
RR¢ 20
RR¢
bis(phenolate) ligands, Li
with CrCl (THF)
2
[O
2
NN¢] . Reaction of Li
2
[O NN¢]
2
◦
3
3
in THF at -78 C resulted in an immedi-
ate colour change from purple to brown. Purification of the
crude product by recrystallization produced green, paramagnetic
RR¢
CrCl[O
2
NN¢] complexes, which were obtained in good yield.
RR¢
Alternatively, stirring a mixture of H
CrCl
2
[O NN¢] and anhydrous
2
2
under nitrogen for 12 h followed by stirring in air for 4 h
caused a colour change from grey-green to brown. By this method,
RR¢
CrCl[O NN¢] was also obtained in good yield. MALDI-TOF
2
MeMe BuBu
mass spectrometry of CrCl[O
2
NN¢]
and CrCl[O
2
NN¢]
us-
ing anthracene as matrix was performed and both complexes show
molecular ion peaks and characteristic fragment ions. Similarly to
compounds 3 and 4, the chloride ligand is shown to be easily lost
from the parent ion in 5 and 6 and intense [M - Cl] peaks were
observed in both spectra.
Fig. 3 Molecular structure (ORTEP) and partially labelled numbering
BuBu
scheme of CrCl(THF)[O NO]
2
4. Ellipsoids are shown at 50%
probability and hydrogen atoms omitted for clarity. Selected bond
+
distances (A) and angles ( ): Cr(1)–O(3), 1.937(2); Cr(1)–O(1),
˚
◦
1
2
1
.911(2); Cr(1)–O(2), 2.020(2); Cr(1)–O(4), 2.048(2); Cr(1)–N(1),
.124(3); Cr(1)–Cl(1), 2.3394(9); O(1)–C(1), 1.334(3); O(3)–C(27),
.335(3); O(1)–Cr(1)–O(3), 176.39(10); O(1)–Cr(1)–O(2), 92.19(11);
Structural characterization
O(3)–Cr(1)–O(2), 90.99(10); O(1)–Cr(1)–O(4), 89.90(9); O(3)–Cr(1)–O(4),
6.81(9); O(2)–Cr(1)–O(4), 175.51(9); O(1)–Cr(1)–N(1), 88.14(9);
O(3)–Cr(1)–N(1), 90.70(9); O(2)–Cr(1)–N(1), 80.33(9); O(4)–Cr(1)–N(1),
5.78(9); O(1)–Cr(1)–Cl(1), 88.88(7); O(3)–Cr(1)–Cl(1), 92.65(7);
8
Slow evaporation of toluene solutions of 3 and 4 under a N at-
2
mosphere in a glove box provided single crystals suitable for X-ray
diffraction analysis. The structures of 3 and 4 are shown in Fig. 2
and 3, respectively. The structures of both complexes show the
ligands adopt tetradentate bonding with the two phenolate groups
coordinating in a mutually trans orientation at the chromium
centre. The coordination geometry is distorted octahedral with
the chloride ligand residing trans to the amino donor. The six-
coordinate geometry is completed by a THF ligand trans to the
9
O(2)–Cr(1)–Cl(1), 93.22(7); O(4)–Cr(1)–Cl(1), 90.79(7); N(1)–
Cr(1)–Cl(1), 172.78(7); C(1)–O(1)–Cr(1), 135.19(18); C(27)–O(3)–Cr(1),
1
25.33(18).
The bond distances lie within the typical ranges for chromium
complexes possessing chelating ligands with amine-nitrogen and
6,11,12,23
phenolate-oxygen donors.
pendant tetrahydrofurfuryl group of the [O
2
NO] ligand. The cis
These amine-bis(phenolate) chromium complexes are mildly hy-
◦
angles of complex 3 range from 81.0(4) to 94.32(14) , and from
groscopic and proceed to react with adventitious moisture present
◦
8
0.33(9) to 95.78(9) in 4, with the most acute angles being
RR¢
in air or solvent. When recrystallization of the CrCl[O NN¢]
2
the O(2)–Cr(1)–N(1) angles of the five-membered chelate ring.
compounds was performed in air, single crystals of 5 and 6
were each obtained by slow evaporation of toluene solutions.
X-Ray structures of 5 and 6 with selected bond lengths and
angles are shown in Fig. 4 and 5, respectively. The structures of
both complexes are bimetallic and possess a bridging oxygen-
containing ligand. Identical structures were obtained regardless
of whether the complexes were prepared via salt metathesis or by
the protonolysis/oxidation route. The exact nature of the oxygen-
containing bridging ligand is not obvious from first inspection.
2
-
If it is considered a bridging oxide, O , ligand, this would imply
the existence of two Cr(IV) metal centres, since the tetradentate
ligand is formally dianionic with the chloride ligand completing
the coordination sphere. Alternatively, the bridging ligand could
be a water molecule, thereby supporting the existence of two
Cr(III) ions in the complex. Lastly, the ligand may be considered
Fig.
CrCl(THF)[O
2
Molecular structure (ORTEP) and numbering scheme of
BuMe
-
2
NO]
3. Ellipsoids are shown at 30% probability
a bridging hydroxide, HO . This last possibility implies either a
and hydrogen atoms omitted for clarity. Selected bond distances ( A˚ )
and angles ( ): Cr(1)–O(3), 1.899(4); Cr(1)–O(1), 1.916(4); Cr(1)–O(2),
mixed valence Cr(III)/Cr(IV) system, or requires the presence of a
cationic counterion. Careful examination of the crystallographic
data, comparison with previously reported complexes possessing
single oxide, hydroxide or aquo ligands, as well as magnetic,
spectroscopic and electrochemical data will be used to propose
the identity of these bimetallic compounds.
Compounds 5 and 6 adopt “butterfly-like” geometries where
one side of each amine-bis(phenolate) ligand is pushed towards the
ligand on the other Cr centre. The Cr(III) ions themselves reside in
distorted octahedral geometries. In each metal–ligand unit of the
◦
2
2
.009(13); Cr(1)–O(4), 2.043(3); Cr(1)–N(1), 2.109(4); Cr(1)–Cl(1),
.3329(14); O(1)–C(1), 1.337(6); O(3)–C(29), 1.332(6); O(3)–Cr(1)–
O(1), 177.29(17); O(3)–Cr(1)–O(2), 99.4(3); O(1)–Cr(1)–O(2), 83.3(3);
O(3)–Cr(1)–O(4), 90.24(15); O(1)–Cr(1)–O(4), 87.06(15); O(2)–Cr(1)–
O(4), 169.2(3); O(3)–Cr(1)–N(1), 89.03(14); O(1)–Cr(1)–N(1), 91.32(14);
O(2)–Cr(1)–N(1), 81.0(4); O(4)–Cr(1)–N(1), 94.32(14); O(3)–Cr(1)–Cl(1),
8
8.95(11); O(1)–Cr(1)–Cl(1), 91.00(11); O(2)–Cr(1)–Cl(1), 93.1(3);
O(4)–Cr(1)–Cl(1), 92.09(10), N(1)–Cr(1)–Cl(1), 173.29(11); C(1)–O(1)–
Cr(1), 130.4(3).
This journal is © The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 548–559 | 551

Fig.
4
Molecular structure (ORTEP) and numbering scheme of
Fig.
5 Molecular structure (ORTEP) and numbering scheme of
MeMe
MeMe
{
CrCl[O
2
NN¢]
}(m-HO){CrCl[HO
2
NN¢]
}
5. Ellipsoids are
BuBu
BuBu
{
CrCl[O
2
NN¢] }(m-HO){CrCl[HO
2
NN¢] } 6. Ellipsoids are shown
shown at 50% probability and hydrogen atoms omitted for clarity.
at 50% probability and hydrogen atoms other than H(117) and H(118)
◦
Selected bond distances ( A˚ ) and angles ( ): Cr(1)–O(1), 1.905(3);
◦
are omitted for clarity. Selected bond distances (A) and angles ( ):
Cr(1)–O(1), 1.8930(18); Cr(1)–O(5), 1.9737(17); Cr(1)–O(2), 2.0360(18);
Cr(1)–N(2), 2.096(2); Cr(1)–N(1), 2.115(2); Cr(1)–Cl(1), 2.3457(7);
Cr(2)–O(4), 1.8875(17); Cr(2)–O(5), 1.9730(17); Cr(2)–O(3), 2.0484(17),
Cr(2)–N(4), 2.099(2); Cr(2)–N(3), 2.117(2); Cr(2)–Cl(2), 2.3356(7);
O(1)–C(1), 1.338(3); O(2)–C(36), 1.380(3); O(3)–C(37), 1.384(3);
O(4)–C(72), 1.332(3); O(3)–H(117), 0.9470; O(5)–H(118), 0.8910;
O(1)–Cr(1)–O(5), 89.36(7); O(1)–Cr(1)–O(2), 175.37(7); O(5)–Cr(1)–O(2),
˚
Cr(1)–O(3), 1.9745(16); Cr(1)–O(2), 2.004(4); Cr(1)–N(2), 2.080(4);
Cr(1)–N(1), 2.098(4); Cr(1)–Cl(1), 2.3526(14); O(1)–C(9), 1.337(5);
O(2)–C(1), 1.383(6); O(1)–Cr(1)–O(3), 89.77(16); O(1)–Cr(1)–O(2),
1
76.38(13); O(3)–Cr(1)–O(2), 88.00(17); O(1)–Cr(1)–N(2), 91.14(16);
O(3)–Cr(1)–N(2), 172.72(11); O(2)–Cr(1)–N(2), 90.71(16); O(1)–
Cr(1)–N(1), 86.27(15); O(3)–Cr(1)–N(1), 93.00(11); O(2)–Cr(1)–
N(1), 91.00(15); N(2)–Cr(1)–N(1), 79.85(15); O(1)–Cr(1)–Cl(1),
9
1.67(10); O(3)–Cr(1)–Cl(1), 96.11(5); O(2)–Cr(1)–Cl(1), 91.40(10);
8
6.71(7); O(1)–Cr(1)–N(2), 94.59(8); O(5)–Cr(1)–N(2), 172.13(8);
O(2)–Cr(1)–N(2), 89.03(8); O(1)–Cr(1)–N(1), 87.44(8); O(5)–Cr(1)–N(1),
3.09(8); O(2)–Cr(1)–N(1), 90.33(7); N(2)–Cr(1)–N(1), 80.31(8);
O(1)–Cr(1)–Cl(1), 90.08(6); O(5)–Cr(1)–Cl(1), 96.14(5); O(2)–Cr(1)–Cl(1),
2.76(5); N(2)–Cr(1)–Cl(1), 90.66(6); N(1)–Cr(1)–Cl(1), 170.41(6);
N(2)–Cr(1)–Cl(1), 91.08(12); N(1)–Cr(1)–Cl(1), 170.65(12); C(9)–O(1)–
Cr(1), 126.2(3); C(1)–O(2)-–Cr(1), 120.5(3); Cr(1)*–O(3)–Cr(1), 143.5(3).
Symmetry transformation used to generate equivalent atoms: 1/2 - x, y,
9
1
/2 - z.
9
O(4)–Cr(2)–O(5), 90.67(7); O(4)–Cr(2)–O(3), 177.21(7); O(5)–Cr(2)–O(3),
87.11(7); O(4)–Cr(2)–N(4), 90.95(8); O(5)–Cr(2)–N(4), 172.00(8);
O(3)–Cr(2)–N(4), 91.02(8); O(4)–Cr(2)–N(3), 87.12(8); O(5)–Cr(2)–N(3),
91.92(7); O(3)–Cr(2)–N(3), 91.26(7); N(4)–Cr(2)–N(3), 80.34(8);
O(4)–Cr(2)–Cl(2), 91.36(6); O(5)–Cr(2)–Cl(2), 94.97(5); O(3)–Cr(2)–Cl(2),
bimetallic complex, the phenolate oxygen atoms are trans to one
another, as are the chloride atoms to the central nitrogen donor of
tetradentate ligands. The bridging O-containing ligand is therefore
trans orientated to the nitrogen donor of the pyridyl group.
The angle subtended at this ligand itself, Cr(1)*–O(3)–Cr(1), is
9
0.52(5); N(4)–Cr(2)–Cl(2), 92.82(6); N(3)–Cr(2)–Cl(2), 172.97(6);
◦
◦
C(1)–O(1)–Cr(1), 132.81(16); C(36)–O(2)–Cr(1), 119.64(14); C(37)–O(3)–
Cr(2), 118.66(14); C(72)–O(4)–Cr(2), 132.65(16); Cr(2)–O(5)–Cr(1),
1
43.5(3) in 5 while in 6 the Cr(2)–O(5)–Cr(1) angle is 147.70(9) .
These angles are typical of Cr complexes possessing bridging
1
47.70(9); C(37)–O(3)–H(117), 114.2; Cr(2)–O(3)–H(117), 103.4.
24-27
oxygen-containing ligands (water or hydroxide).
The Cr(III)–
O–Cr(III) bond angles in oxide-bridged compounds containing a
single bridging ligand are often approximately, or equal to, 180 .
The metal–oxygen ligand distances suggest some ionic interaction
◦
27
˚
in these compounds lie between 1.918 and 1.981 A and thus are
consistent with those found in 5 and 6.
˚
exists. That is, the Cr(1)–O(3) distance is 1.9745(16) A in 5, and
The bond distances between the Cr(III) centres and the oxygen
donors of the phenolate groups in 5 and 6 are not symmetrical. In
complex 5, Cr(1)–O(1) is 1.905(3) A and Cr(1)–O(2) is 2.004(4) A.
In the bulkier, t-butyl substituted complex 6, Cr(1)–O(1) is
˚
in 6 the Cr(1)–O(5) and Cr(2)–O(5) lengths are 1.9737(17) A
˚
˚
˚
and 1.9713(17) A, respectively. Structurally characterized dimeric
complexes of Cr(III) bearing only one bridging oxygen-containing
-
2-
24–27
˚ ˚
ligand (H
2
O, OH or O ) are rare.
The Cr–O bond lengths
1.8930(18) A and Cr(1)–O(2) is 2.0360(18) A while Cr(2)–O(4)
-
˚
˚
observed in OH bridged Cr(III) compounds are between 1.941
is 1.8875(17) A and Cr(2)–O(3) is 2.0484(17) A. The longer
interactions occur on the sides of the ligand that are forced
into the space occupied by the ligand on the other Cr centre
within the bimetallic unit. Cr–O bond distances of greater than
˚
and 1.989 A, similar to the bond distances found in 5 and 6. The
2
-
bond distances exhibited by O bridged compounds of Cr(III)
˚
are much shorter, between 1.767 and 1.82 A. The vast majority
-
˚
of bimetallic, OH bridged Cr(III) compounds contain more than
2.0 A typically indicate coordinate-covalent interactions such as
one bridging group, hence direct comparison of bond angles to
with neutral ether, alcohol or water ligands rather than anionic
alkoxide or aryloxide ligands. If one of the phenolate oxygen
28,29
30
these systems is unreliable.
However, the Cr–O bond distances
5
52 | Dalton Trans., 2010, 39, 548–559
This journal is © The Royal Society of Chemistry 2010

atoms are protonated, a hydrogen-bonding interaction involving
the phenolate oxygen of the other ligand could be involved. This
would potentially explain the lengthened Cr–O bond lengths and
the “pinching-in” of the two amine-bis(phenolate) ligands on one
side of the bimetallic complex. Of course, bridging aryloxides
12,31
˚
may also exhibit Cr–O bond lengths longer than 2.0 A.
This prompted a re-examination of the crystallographic data.
Careful examination of the residual electron density (Q-peaks)
in the final difference map supported this proposal, and so the
structure was refined according to this model. Hydrogens H(117)
bonded to O(3) and H(118) bonded to O(5) were introduced in
difference map positions and initially refined positionally (on x,
y, z) with fixed thermal parameters, and finally on the riding
model, with isotropic thermal parameters set twenty percent
greater than those of their bonding partners. This refinement
generated an improved solution, resulting in an R-factor of 6.82%
(
compared to 6.87% for the initial solution where these H-atoms
were not included in the model). Infrared data on the solid
-
1
samples showed a broad O–H band at 3200 cm , but does not
-
confirm whether the bridging ligand is H
2
O or OH . Elemental
analysis for each of 5 and 6 favourably supports the presence of
between one and two formula units of “H O” per two molecules
2
RR¢
of CrCl[O NN¢] . MALDI-TOF mass spectrometry of 5 shows
2
fragments of a bimetallic unit (namely m/z of 887.1 corresponding
Fig. 6 Magnetic susceptibility (per mole of bimetallic complex) versus
temperature plot (top) and magnetic moment versus temperature plot
MeMe
+
to [{Cr[O
2
NN¢]
}
2
Cl] ), but no peak corresponding to the
(
bottom) for 6. The solid line (—) was generated using the Heisenberg
molecular ion predicted from the crystallographically verified
-1
dimer model with J = -16.5 cm , g = 1.92 and P = 0.0079. Experimental
structure. The mass spectra of both 5 and 6 do show peaks
-4
3
-1
data were corrected for TIP = 23.0 ¥ 10 cm mol . The dashed line
+
corresponding to [CrCl[L]] (m/z = 461.1 for 5 and m/z =
-1
(
-
---) was generated using a biquadratic function with J = -18.2 cm , j =
6
29.1 for 6). In light of the analytical data, the most reasonable
-1
0.69 cm , g = 2.10 and P = 0.011.
interpretation of the structures of complexes 5 and 6 is that each
contains a bridging hydroxide ligand and a protonated phenol
group on one of the two tetradentate ligands present in each
bimetallic complex. This would imply the oxidation states of the
metal centres are both Cr(III). Indeed, the magnetic measurements
and electronic spectroscopy data discussed below support this
assignment.
To account for the presence of a small amount of paramagnetic
impurity the expression was combined with the Curie law term,
para = C/T, according to c = [1 - P]c + Pcpara, where P
represents the fraction of paramagnetic S = 3/2 impurity, likely
CrCl (H O)
. The resulting analysis of the data yielded J =
16.5 cm , g = 1.92 and P = 0.0079. The presence of temperature
independent paramagnetism (TIP) was also included in the model,
c
m
3
2
x
-
1
-
Magnetic data
-
4
3
-1
where TIP = 23.0 ¥ 10 cm mol . While the calculated g is
Solution magnetic moments for 3 and 4 were obtained by Evans’
slightly lower than typically predicted for Cr(III) (where values
33
method. Both complexes exhibited moments of 3.8m
B
, consistent
with S = 3/2 spin states of Cr(III) d centres. The room temperature
per
nearer to 1.98 are commonly observed), and the TIP can be
considered high for this ion, these values are in agreement with
3
5
+
magnetic moments of 5 and 6 are identical with meff = 5.3m
B
those reported for [(MeCN)
5
Cr(OH)Cr(MeCN)
5
] , where g =
-
4
3 25
bimetallic unit. These values are only slightly lower than expected
1.966(4) and TIP = 89(3) ¥ 10 cm . In addition, the Cr–O–Cr¢
◦
◦
for two isolated Cr(III) ions (the spin-only moment for two S =
bond angle of 147.5(2) in this compound is very similar to the
◦
3
/2 ions exhibiting no magnetic exchange would be ª 5.48m
B
).
bond angles of 143.5(3) and 147.40(10) observed in complexes
5 and 6, respectively.
The temperature (T) dependence of the magnetic susceptibility
(
c
m
) of 6 was measured from 2–300 K. The plots of c vs. T
m
An alternate model was examined where the paramagnetic
and meff vs. T per chromium dimer are shown in Fig. 6. Complex 6
shows a significant decrease in meff as T decreases as well as a broad
impurity was considered to obey the Curie–Weiss law, hence cpara
=
C/(T - q) was included in the calculation of c . This model gave
m
-
1
maximum in the plot of c
coupling between the metal atoms. Data were first modelled
, considering a pair
m
vs. T indicative of antiferromagnetic
similar values of J = -16.6 cm and g = 1.95 compared to the
model employed above. Other terms obtained were q = -0.4, P =
-
4
3
using the spin Hamiltonian H = -2JS
1
·S
2
0.0095 and TIP = 20.0 ¥ 10 cm . The calculated Curie–Weiss
33
of exchange coupled centres where S
1
= S
2
= 3/2 according to the
term q is slightly larger than expected for Cr(III), but only
32
Heisenberg dimer model:
moderately decreases the amount of TIP. Fixing the TIP to
-
4
3
values of 6.0 ¥ 10 cm or lower only raises the percentage of
paramagnetic impurity and gives unrealistic g values.
2
2
2J / kT
6J / kT
12J / kT
⎧
⎪
⎨
⎫⎪
⎪
⎬
⎪
⎭⎪
2
Ng m
e
+ 5e
+14e
B
25,26,29
c =
The magnetic properties of some Cr(III) dimers
have
2
J / kT
6J / kT
12J / kT
kT
⎪1+ 3e
+ 5e
+ 7e
been modelled by including biquadratic exchange interactions
This journal is © The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 548–559 | 553

according to the general exchange Hamiltonian H = -2JS
j(S ) , where j is the biquadratic exchange constant. This leads
·S
to the following expression:
1
·S
2
-
same spin multiplicity is expressed by the formula g = 2.0023 -
2
33
~
-1
1
2
(8l/10Dq) where l is the spin–orbit coupling constant (l = 92 cm
4
for Cr(III)) and 10Dq is the energy of the lowest excited state ( T
2
).
-
1
For 3 and 4, 10Dq is 19 417 cm , giving g = 1.96.
2
2
The UV-vis spectrum of complexes 5 and 6 also show changes
2
Ng m
B
c =
×
to the energies of their d–d transitions in different solvents.
kT
4
4
-1
Compound 5 shows the T
2
← A
2
band at 523 nm (19 120 cm )
(
2J - 6.5j ) / kT
(6J - 13.5j ) / kT
(12J - 9j ) / kT
(12J - 9j ) / kT
⎧
⎪
⎫⎪
⎪
⎬
⎪
⎭⎪
e
+ 5e
+14e
-1
⎪
⎨
⎪
and shoulders at approximately 416 nm (24 038 cm ) for the
band in acetonitrile. In THF, the T
appears at 500 nm (20 000 cm ) and T
(25 000 cm ). Compound 6 shows the T
18 868 cm ) in acetonitrile and T
23 810 cm ). In THF these bands appear at 500 nm (20 000 cm )
and 398 nm (25 126 cm ). The resulting ligand field strength
of the amine-bis(phenolate)-pyridyl ligands gives 10Dq (D ) of
0 000 cm , which is larger than that of the tetrahydrofurfuryl-
(
2J - 6.5j ) / kT
(6J - 13.5j ) / kT
1+ 3e
+ 5e
+ 7e
4
4
4
4
⎩
⎪
T
← A
← A
band
appears at 400 nm
band at 530 nm
1
2
2
2
-
1
4
4
1
4
← A
2
4
-
1
-
1
-1
2
← A
2
Using this model, J = -18.2 cm , j = -0.69 cm , g = 2.10 and
P = 0.011. The exchange coupling constants, J for both models
are similar in magnitude and suggest antiferromagnetic coupling
between two Cr(III) centres. The biquadratic exchange constant j
-
1
4
4
(
(
1
← A
2
appears at 420 nm
-
1
-1
-
1
33
o
is of much lower amplitude with a j/2J ratio equal to 0.02. This
model, however, employs a larger g value, which is unreasonable
-
1
2
3
containing ligand. This is consistent with the stronger ligand field
strength of pyridine compared to THF. Estimates of the Racah
for a d ion. A larger paramagnetic impurity contribution is also
required, but as shown in Fig. 6, the model provides a good fit
of the experimental data, particularly at lower temperature. The
magnetic properties of 6 are similar to other hydroxide-bridged
compounds, particularly when compared to systems possessing
-
1
parameter give B = 454 cm . These values yield an estimate for
g = 1.97, which is close to the value obtained from magnetic data
of 6 when the Heisenberg dimer model is employed and using a
Curie–Weiss term for the paramagnetic impurity.
25
similar Cr–O–Cr bond angles.
Cyclic voltammetry
Electronic absorption data
Electrochemistry experiments were carried out using a three-
compartment electrochemical cell, consisting of a platinum
counter electrode, saturated calomel reference electrode (SCE)
Electronic absorption spectra of complexes 3 to 6 show multiple
intense bands in the UV and visible regions. The absorption
maxima observed in the UV region (below 300 nm) are caused
by p → p* transitions involving the phenolate units—absorptions
in this region are observed in the spectra of the unmetallated ligand
precursors. Intense bands are also observed in the region between
and a glassy carbon working electrode. Compounds 3, 4 and 6
BuBu
along with the metal-free ligand precursor, H
investigated by cyclic voltammetry (CV) in CH
taining 0.1 M [(n-Bu) N]PF as electrolyte. Results are summarized
in Table 2 and representative cyclic voltammograms are shown
2
[O
2
NO] , were
2
Cl
2
solutions con-
3
00 and 450 nm, which are assigned to charge transfer transitions
from the p orbital (HOMO) of the phenolate oxygen to the empty
x2-y2 /dz2 and the half-filled dp* orbital of Cr(III). A shift of these
LMCT bands is observed on changing the solvent used. Weaker,
4
6
p
BuBu
in Fig. 7. Voltammograms of 4 and H
2
[O
2
NO]
are given in
d
the ESI.† All experiments were performed at a scan rate of 200
-
1
-
1
-1
mV s . The CVs of the Cr(III) complexes are virtually identical
and display two reversible oxidations. Related Cr(III) complexes
very broad bands (e ª 200 L mol cm ) are observed between 450
and 700 nm, which can be assigned to d–d transitions. The intense
LMCT bands obscure the high frequency visible region making
definitive assignment of the metal-centred transitions difficult. The
34
6
bearing three aminophenolato and two amine-bis(phenolate)
ligands, each display three and four oxidation waves, respectively.
These oxidations were assigned as ligand centred since Cr(III) is
4
4
-1
T
2
← A
2
(O ) band is observed at 515 nm (19 417 cm ) in THF
h
34
-
1
expected to be redox-inert. These ligand oxidations are attributed
to the oxidation of the phenolate form of the ligand to the radical
anion, hence the presence of two phenolate groups per metal
in complexes 3 and 4 results in the two observed potentials.
No reversible redox activity was observed at negative potential.
Perhaps surprisingly, complex 6 also exhibits two reversible oxi-
dation waves despite being bimetallic and possessing two amine-
bis(phenolate) ligands per unit. This suggests that in solution the
bimetallic species may undergo dissociation to monomeric units,
at least under the conditions employed during the electrochemical
solutions of both 3 and 4, and at 560 nm (17 857 cm ) and 573 nm
-
1
(17 452 cm ) in acetonitrile solutions of 3 and 4, respectively.
This solvent dependence suggests the THF ligand present in the
solid state structure is sufficiently labile and undergoes exchange
with other donor solvents. Thus, acetonitrile adducts are likely
formed in this solvent and the shift to lower energy of this
transition is consistent with the decrease in ligand field strength
4
4
on going from THF to acetonitrile. The T
1
← A
2
(O ) band is
h
obscured by the CT bands and exist as poorly-resolved shoulders.
Estimates place this transition at 410 nm (24 390 cm ) and 416 nm
24 038 cm ) in THF for complexes 3 and 4, respectively. This
band appears at 429 nm (23 310 cm ) and 440 nm (22 727 cm )
-
1
-
1
study. The redox behaviour of the unmetallated ligand precursor,
(
BuBu
-
1
-1
H [O NO] , was also examined. The cyclic voltammogram (see
2
2
ESI†) exhibits only a quasi-reversible oxidation suggesting sample
decomposition.
for 3 and 4, respectively, in acetonitrile. These data provide ligand-
field strengths, 10Dq (D ), of the two amine-bis(phenolate)-THF
o
-
1
ligands of 19 417 cm , or slightly lower than that of the ammonia
4
4
ligand in the spectrochemical series. Since the T
1
← A
2
band
Conclusions
is obscured by the LMCT bands, only an approximate value for
the Racah parameter, B, of 450 cm can be calculated. For the
ground term for the Cr(III) ion, the mixing of terms with the
-
1
A series of lithium and chromium complexes stabilized by
a family of dianionic amine-bis(phenolate) ligands has been
A
2
5
54 | Dalton Trans., 2010, 39, 548–559
This journal is © The Royal Society of Chemistry 2010

Table 2 Half wave potentials for oxidation of complexes 3, 4, 6 and ligand
of complex 4
exploring the potential of the water-free complexes as catalysts for
small molecule activation and catalysis.
ox
ox
E
2
/V
E
1
/V
Experimental
a
a
3
1.14
1.14
1.16
—
0.75
0.69
0.68
0.86
a
a
a,c
a
4
General experimental conditions
6
H
BuBu
b
2 2
[O NO]
Unless otherwise stated, all manipulations were performed
under an atmosphere of dry oxygen-free nitrogen by means of
standard Schlenk techniques or using an MBraun Labmaster
glove box. Anhydrous THF was stored over sieves and distilled
from sodium benzophenone ketyl under nitrogen. Reagents were
purchased either from Aldrich or Alfa Aesar and used without
a
c
b
Reversible reaction. Irreversible reaction,
E1/2 value estimated.
Oxidation and reduction waves possess a slight shoulder.
further purification. CrCl
3
(THF) was prepared by the standard
3
35
BuBu
MeMe
BuMe
method, whereas H
2
[O
2
NN¢] , H
2
[O
2
NN¢]
, H
2
2
[O NO]
BuBu
and H
2
[O
2
NO]
were prepared by modification of the liter-
16,22,36
ature methods
by using water instead of methanol as the
7,17
reaction medium. MALDI-TOF MS was performed using an
Applied Biosystems Voyager DE-PRO equipped with a reflectron,
delayed ion extraction and high performance nitrogen laser (337
nm). Anthracene was used as the matrix. NMR spectra were
recorded on a Bruker AVANCE 500 MHz spectrometer. Variable-
temperature magnetic moments were measured on powdered
samples at 1000 G using a Quantum Design MPMS-5S SQUID
magnetometer. The data were corrected for background and for
the diamagnetism of all atoms. UV-vis spectra were recorded on
an Ocean Optics USB4000+ fiber optic spectrophotometer. Cyclic
voltammetry measurements were performed on a Model HA
3
01 Hokuto Deuko Potentiostat/Galvanostat. Elemental analyses
were performed at Canadian Microanalytical Service, Ltd. Delta,
BC, Canada or Guelph Chemical Laboratories, Guelph, ON,
Canada.
Synthesis of compounds
BuMe
BuMe
{Li
2
[O
2
NO]
}
2
(1).
H
2
[O
2
NO]
(5.01 g, 11.04 mmol) was
◦
dissolved in THF (100 mL) and cooled to -78 C. n-Butyllithium
(1.6 M, 14 mL, 22.40 mmol) was slowly added resulting in a clear,
yellow solution, which was warmed to room temperature and
stirred for 2 h. Solvent was removed under vacuum and the product
was washed with pentane. Removal of volatiles under vacuum
yielded 6.08 g of beige product, which upon combustion analysis
was shown to contain two equivalents of THF per dilithium salt
2 2
Fig. 7 Cyclic voltammograms of 3 (top) and 6 (bottom) in CH Cl (0.1 M
◦
-1
4 6
[(n-Bu) N]PF ) at 20 C and a scan rate of 200 mV s .
(
7
percent yield of 90%). Anal. calcd for C29
2.88, H 9.42, N 2.30. Found: C 73.13, H 9.02, N 2.62%. H NMR
H
41Li
2
NO
3
·(C
4
1
H
8
O)
2
: C
synthesized and characterized. In the solid state, the base-free
lithium complexes are dimeric possessing a tetrametallic ladder-
4
(500 MHz, 295K, d
5
-pyridine, d): 7.25 (d, JH1-H2 =2.5 Hz, ArH, 1
like core. In d
only broad resonances in the H NMR spectrum. Sharp, assignable
resonances are visible when d -pyridine is used, likely due to
8
-toluene solution, the complexes are fluxional giving
4
4
H); 7.24 (d, JH1-H2 = 2.5 Hz, ArH, 1 H); 7.00 (d, JH1-H2 = 2.5 Hz,
1
4
2
ArH, 1 H); 6.88 (d, JH1-H2 = 2.5 Hz, ArH, 1 H); 4.34 (d, JH1-H2
=
5
2
1
1
(
(
(
2.0 Hz, ArCHHN, 1 H); 4.18 (d, JH1- H2 = 12.0 Hz, ArCHHN,
solvent coordination and reduced fluxionality. The chromium
complexes made using these lithium salts generate monometal-
lic, THF coordinated compounds when handled under strictly
anhydrous conditions. Interestingly, related chromium complexes
form bimetallic dichromium complexes when handled in air. The
H); 3.74 (m, CH
2
CH(O)CH , 1 H); 3.67 (m, CHH, 1 H); 3.33
2
2
d, JH1-H2 = 12.0 Hz, ArCHHN, 1 H); 3.31 (m, CHH, 1 H); 3.20
2
d, JH1-H2 = 12.0 Hz, ArCHHN, 1 H); 3.14 (m, CHH, 1 H); 2.70
m, CH
2
, 2 H); 2.38 1.62 (s, C(CH
3
)
3
, 9 H).
BuBu
BuBu
chromium complexes are hygroscopic and react with water to
{Li [O
2
2
NO]
}
2
(2).
H
2
[O
2
NO]
(5.01 g, 9.31 mmol) was
-
◦
generate either a H
2
O or HO bridging group. Close investigation
dissolved in THF (100 mL) and cooled to -78 C. n-Butyllithium
(1.6 M, 12 mL, 19.20 mmol) was slowly added resulting in a
clear, yellow solution, which was warmed to room temperature
and stirred for 2 h. Solvent was removed under vacuum; the
product was then washed with pentane. Removal of volatiles
of crystallographic and magnetic data suggests the latter, whereby
cleavage of a water H–O bond results in protonation of one of
the ligand phenolate groups and incorporation of the resulting
hydroxide bridge into the molecule. Current work is focused on
This journal is © The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 548–559 | 555

MeMe
under vacuum yielded 6.11 g of beige product 2. Anal. calcd for
of H
2
[O
2
NN¢]
(2.00 g, 4.44 mmol) in THF (50 mL) at
◦
C
35
H
53Li
2
NO
3
·(C
4
H
8
O)1.8: C 74.59, H 10.00, N 2.06. Found: C
-78 C. The reaction mixture was warmed to room temperature
and stirred for 2 h to give a clear pale yellow solution. This
mixture was transferred via cannula to a solution of CrCl
(1.65 g, 4.44 mmol) in THF (25 mL) at -78 C to give a cloudy
orange/brown solution. Upon warming to room temperature and
stirring overnight the mixture darkened. The solvent was removed
in vacuo and the product was extracted into dichloromethane. The
mixture was filtered through Celite and the solvent was removed
under vacuum. The product was then washed with pentane and
dried to yield 1.64 g of a dark olive green powder.
1
74.13, H 9.82, N 1.74%. H NMR (500 MHz, 295K, d
5
-pyridine,
4
4
d): 7.52 (d, JH1-H2 = 2.5 Hz, ArH, 1 H); 7.49 (d, JH1-H2 = 2.5 Hz,
3
(THF)
3
4
4
◦
ArH, 1 H); 7.28 (d, JH1-H2 = 2.5 Hz, ArH, 1 H); 7.10 ( JH1-H2
=
2
2
.5 Hz, ArH, 1 H); 4.41 (d, JH1-H2 = 12.0 Hz, ArCHHN, 1 H); 4.26
2
(
d JH1-H2 = 12.0 Hz, ArCHHN, 1 H); 3.78 (m, CH
2
CH(O)CH , 1
2
2
H); 3.47 (d, JH1-H2 = 12.0 Hz, ArCHHN, 1 H); 3.32 (m, CHH, 1
2
H); 3.27 (d, JH1-H2 = 12.0 Hz, ArCHHN, 1 H); 3.05 (m, CHH, 1
H); 2.73 (m, CHH, 1 H); 2.43 (m, CHH, 1 H); 1.67 (s, C(CH
3
)
3
, 9
H); 1.66 (s, C(CH
3
)
3
, 9 H); 1.43 (s, C(CH
3
)
3
, 9 H); 1.40 (s, C(CH
3
3
) ,
9
H).
Method B. Anhydrous CrCl
2
(0.33 g, 2.66 mmol) and
(1.0 g, 2.66 mmol) in THF (50 mL) was stirred for
2 h to give a cloudy teal blue solution with a teal blue solid residue.
BuMe
BuMe
CrCl(THF)[O
2
NO]
(3).
H
2
[O
2
NO]
(2.00 g, 4.41 mmol)
MeMe
H
1
2
2
[O NN¢]
◦
was dissolved in THF (50 mL) and cooled to -78 C.
n-Butyllithium (4.7 mL, 7.52 mmol) was slowly added to give
a clear, yellow solution of Li
room temperature and further stirred for 2 h. This mixture was
The reaction flask was opened to air and the reaction mixture was
stirred for 4 h to give a dark green/black solution with a green
precipitate. Removing the solvent under vacuum yielded an olive
green powder.
The crude product was recrystallized from toluene in air to give
analytically pure 5 (65% yield). Anal. calcd for C48
BuMe
2
[O
2
NO]
, which was warmed to
transferred via cannula to a solution of CrCl
3
(THF) (1.64 g,
3
◦
4
.41 mmol) in THF (50 mL) cooled to -78 C to give a bright
purple suspension. Warming to room temperature and stirring for
6 h produced a dark purple solution. The solvent was removed
H
54Cl
2
Cr
2
N
4
5
O :
1
C 61.21, H 5.78, N 5.95. Found: C 60.27, H 5.74, N 5.90%. MS
in vacuo and the residue was extracted into toluene. The mixture
was filtered through Celite and the solvent was removed under
vacuum. The product was washed with pentane and dried to
yield 2.45 g of purple-brown powder. Crystals suitable for X-ray
diffraction were obtained by slow evaporation of a solution of
+
(
[
4
(
MALDI-TOF) m/z (%, ion): 887.1 (100, [(Cr[L])
2
Cl] ), 461.1 (40,
+
CrCl[L]] ). UV-vis (THF) lmax, nm (e): 500 (200), 400 (250), 300–
50 (1257); (MeCN) lmax, nm (e): 523 (212), 416 sh (308), 300–500
-1
1215). IR (cm ): 3407 (OH); 2917 (C–H); 1611 (C=C, phenyl
◦
ring); 1477 (s); 1261 (m); 856 (w); 809 (w). meff (solid, 25 C) 5.3m
B
.
3
in toluene at room temperature under inert atmosphere. Anal.
calcd for C33
H
49ClCrNO
4
: C 64.85, H 8.08, N 2.29. Found: C
BuBu
BuBu
{
CrCl[O
2
NN¢] }(l-HO){CrCl[HO
2
NN¢] } (6).
6
4.35, H 7.95, N 2.16%. MS (MALDI-TOF) m/z (%, ion): 538.2
+
+
(
100, [CrCl[L] ]), 503.2 (45, [Cr[L] ]). UV-vis (THF) lmax, nm (e):
Method A. A 1.6 M hexanes solution of n-butyllithium (6.0 mL,
.1 mmol) was added via syringe to a stirring solution of
(2.00 g, 3.67 mmol) in THF (50 mL) at -78 C. The
reaction mixture was warmed to room temperature and stirred
for 2 h to give a clear pale yellow solution. This mixture was
transferred via cannula to a solution of CrCl
3.67 mmol) in THF (25 mL) at -78 C to give a cloudy
orange/brown solution. Upon warming to room temperature and
stirring overnight the mixture darkened. The solvent was removed
in vacuo and the residue was extracted into toluene. The mixture
was filtered through Celite and the solvent was removed under
vacuum. The product was washed with pentane and dried to yield
2.47 g of a dark olive green powder.
5
5
2
15 (200), 410 sh (525), 200–400 (1270); (MeCN) lmax, nm (e):
8
H
60 (200), 429 sh (300), 200–400 (1200). meff (solution in benzene,
BuBu
◦
2
[O
2
NN¢]
◦
5 C) 3.8m
B
.
BuBu
BuBu
CrCl(THF)[O
2
NO]
(4).
H
2
[O
2
NO]
(2.00 g, 3.72 mmol)
◦
was dissolved in THF (50 mL) and cooled to -78 C.
n-Butyllithium (4.7 mL, 7.52 mmol) was slowly added to give
a clear, yellow solution of Li
room temperature and further stirred for 2 h. This mixture was
3
(THF) (1.36 g,
3
◦
BuBu
2
[O NO] , which was warmed to
2
transferred via cannula to a solution of CrCl
3
(THF) (1.38 g,
3
◦
3
.72 mmol) in THF (20 mL) cooled to -78 C to give a bright
purple suspension. Warming to room temperature and stirring for
6 h produced a dark purple solution. The solvent was removed
1
in vacuo and the residue was extracted into toluene. The mixture
was filtered through Celite and the solvent was removed under
vacuum. The product was washed with pentane and dried to
yield 2.17 g of dark purple powder. Crystals suitable for X-ray
diffraction were obtained by slow evaporation of a solution of
Method B. Anhydrous CrCl
2
(0.23 g, 1.91 mmol) and
BuBu
H
2
2
[O NN¢]
(1.0 g, 1.91 mmol) in THF (50 mL) was stirred
for 12 h under nitrogen to give a cloudy dark brown solution. The
reaction flask was opened to the air and the reaction mixture was
stirred for 4 h. Removing the solvent in vacuo yielded 1.20 g of a
dark brown powder.
The crude product was recrystallized from toluene in air to give
analytically pure 6 (70% yield). Anal. calcd for C H Cl Cr N O :
4
in toluene at room temperature under inert atmosphere. Anal.
calcd for C39 61ClCrNO : C 67.36, H 8.84, N 2.01. Found: C
6.59, H 8.80, N 1.89%. MS (MALDI-TOF) m/z (%, ion): 622.2
H
4
6
+
+
(
60, [CrCl[L] ]), 587.2 (100, [Cr[L] ]). UV-vis (THF) lmax, nm (e):
72
102
2
2
4
5
C 67.64, H 8.04, N 4.38. Found: C 66.53, H 8.05, N 4.11%. MS
5
5
2
15 (200), 440 sh (750), 200–350 (1267); (MeCN) lmax, nm (e):
+
(
MALDI-TOF) m/z (%, ion): 1258.6 (10, [(CrCl[L])
2
] ) 629.1 (60,
73 (253), 416 sh (450), 200–340 (1270). meff (solution in benzene,
+
+
◦
[CrCl[L]] ), 594.2 (100, [Cr[L]] ). UV-vis (THF) lmax, nm (e): 500
5 C) 3.8m
B
.
(
(
200), 398 sh (800), 280–380 (1287); (MeCN) lmax, nm (e): 530
253), 420 sh (450), 280–340 (1270). IR (cm ): 3422 (OH); 2955
MeMe
MeMe
{
CrCl[O
Method A. A 1.6 M hexanes solution of n-butyllithium
5.63 mL, 9.00 mmol) was added via syringe to a stirring solution
2
NN¢]
}(l-HO){CrCl[HO
2
NN¢]
} (5).
-1
(C–H); 1612 (C=C, phenyl ring); 1500 (m); 1240 (m); 850 (w). meff
◦
(
(solid, 25 C) 5.3m
B
.
5
56 | Dalton Trans., 2010, 39, 548–559
This journal is © The Royal Society of Chemistry 2010

Table 3 Crystallographic and structure refinement data for compounds 1 to 6
Compound
1
2
3
4
5
6
Chemical formula
C
58
6
H
H
84Li
4
N
2
O
6
-
C
70
H
106Li
4
N
2
O
6
C
(C
33
H
H
50NO
4
CrCl
C
(C
39
H
H
61NO
4
CrCl- [(C24
H
26
N
2
O
2
)CrCl]
2
-
50 2 2 2
[(C36H O N )CrCl] -
(
C
6
)
0.75
7
8
)
0.6
7
8
)
0.5
(HO)(H)(C
1033.99
198
7
H
8
)
(HO)(H)(C
1462.80
118
7 8 2
H )
Formula weight
T/K
Colour, habit
Crystal
dimensions/mm
Crystal system
991.66
123
Colorless, block
1099.38
123
Colorless, prism
667.50
118
Pink, irregular
741.43
123
Pink, prism
Green, plate
Green, prism
0.31 ¥ 0.26 ¥ 0.25
0.52 ¥ 0.23 ¥ 0.12 0.14 ¥ 0.13 ¥ 0.07 0.12 ¥ 0.12 ¥ 0.06 0.32 ¥ 0.06 ¥ 0.05 0.40 0.20 ¥ 0.05
Triclinic
P1 (#2)
Monoclinic
C2/c (#15)
16.331(4)
14.455(4)
28.696(7)
90
92.989(5)
90
6765(3)
4
Monoclinic
P2 /c (#14)
16.182(4)
16.300(3)
16.266(4)
90
118.046(4)
90
3786.7(15)
4
Monoclinic
P2 /c (#14)
12.816(2)
20.060(4)
16.455(3)
90
94.055(4)
90
4219.6(13)
4
Monoclinic
P2/n (#13)
14.222(3)
13.867(3)
14.612(3)
90
108.533(3)
90
2732.2(9)
2
Triclinic
¯
¯
Space group
1
1
P1 (#2)
a/A˚
b/A˚
c/A˚
10.600(4)
14.427(7)
20.499(9)
106.425(13)
93.594(7)
91.928(8)
2997(2)
2
15.8636(18)
16.1865(16)
18.334(2)
71.836(7)
78.206(9)
67.999(7)
4126.9(8)
2
1.177
3.79
1568.00
2.56 to 26.50
◦
a/
◦
b/
◦
g /
V/A˚
3
Z
D
c
/g cm-
3
1.099
0.68
1.079
0.66
2400
1.171
4.09
1432
1.167
3.73
1600
1.257
5.44
1084.00
-1
m(MoKa)/cm
F(000)
1075.00
2.3643 to 30.9845 2.8 to 30.6
q range for
2.4391 to 30.6011 2.1975 to 30.8114 1.47 to 27.50
◦
collection/
Reflections collected
Independent
24 396
12 170
44 372
6994
25 913
7833
37 202
8726
18 165
6028
71 780
17081
reflections
Parameters/restraints 731/0
389/0
461/0
479/0
335/6
893/0
R
R, wR
R, wR
int
0.0259
0.0711
0.0609
0.0532
0.0573
0.0281
2
2
(all)
0.1037, 0.2800
0.0935, 0.2678
1.072
0.0992, 0.1952
0.0905, 0.1894
1.217
0.1246, 0.2911
0.1049, 0.2758
1.148
0.0807, 0.1964
0.0744, 0.1906
1.101
0.1339, 0.2609
0.0701, 0.2174
1.046
0.0699, 0.1924
0.0682, 0.1905
1.080
[I > 2s(I)]
2
GOF on F
Crystallography
C(17A and 19A) and H(25A, 27A and 28A) at 40% occupancy. For
, one 3/5-occupancy toluene molecule is present as lattice solvent.
A pendant ligand tetrahydrofuran group is disordered over two
3
Crystallographic data are given in Table 3. Single crystals of
, 2, 3, 4 and 6 were mounted on glass fibers using Paratone-
1
positions, each with 50% occupancy. For 4, one disordered
N oil. All measurements were made on a Rigaku Saturn CCD
area detector with graphite monochromated Mo-Ka radiation
solved on an AFC8-Saturn 70 single-crystal X-ray diffractome-
ter from Rigaku/MSC, equipped with an X-stream 2000 low
temperature system. The data were processed and corrected for
Lorentz and polarization effects and absorption. Neutral atom
scattering factors for all non-hydrogen atoms were taken from the
1
/2-occupancy toluene molecule is present as lattice solvent. A
pendant ligand tetrahydrofurfuryl group is disordered over two
positions (65/35%).
Single crystals of 5 were coated with Paratone-N oil, mounted
using a polyimide MicroMount and frozen in the cold nitrogen
stream of the goniometer. A hemisphere of data was collected
on a Bruker AXS P4/SMART 1000 diffractometer using w and
37
3
8
39
International Tables for X-Ray Crystallography. All structures
were solved by direct methods using SIR92 and expanded using
◦
q scans with a scan width of 0.3 and 40 s exposure times. The
40
47
detector distance was 5 cm. The data were reduced (SAINT) and
41
Fourier techniques (DIRDIF99). All non-hydrogen atoms were
refined anisotropically. Hydrogen atoms were refined using the
riding model. Anomalous dispersion effects were included in
48
corrected for absorption (SADABS). The structure was solved
by direct methods and refined by full-matrix least squares on
2
46
F (SHELXTL). A toluene molecule was disordered over two
4
2
F
calcd
;
the values for Df ¢ and Df ¢¢ were those of Creagh and
sites and refined with equal site occupancy factors. Structural
43
McAuley. The values for the mass attenuation coefficients are
49
illustrations were created using ORTEP-III for Windows.
44
those of Creagh and Hubbell. All calculations were performed
45
using the CrystalStructure crystallographic software package
except for refinement, which was performed using SHELXL-
Acknowledgements
46
9
7. For 1, the asymmetric unit contains one toluene solvent
molecule modelled at 60% occupancy. Two disordered pendant
tetrahydrofuryl groups were modelled using partial occupancy
carbons. One tetrahydrofuranyl ring was modelled over two sites
with 75/25% occupancy, the other is modelled similarly but with
Financial support was provided by Memorial University, Canada
Foundation for Innovation (CFI) Leaders Opportunity Fund,
the Newfoundland Industrial Research and Innovation Fund
(IRIF) and NSERC of Canada Research Tools and Instruments
Grant to C. M. K, NSERC Discovery Grants to C. M. K.
and K. H., a postgraduate scholarship to R. K. D. and an
undergraduate student research award to S. G. We also thank
Prof. Laurence K. Thompson for the collection of the magnetic
6
0/40% occupancy. All but two hydrogen atoms on the two
disordered groups were omitted and three carbon atoms were
refined isotropically. For 2, the pendant THF group is disordered,
with C(17 and 19) and H(25, 27 and 28) at 60% occupancy and
This journal is © The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 548–559 | 557

data and helpful discussions, and Prof. Peter Pickup for the use of
his electrochemistry equipment.
K. H. Theopold and L. A. MacAdams, Organometallics, 2002, 21, 952;
W. K. Kim, M. J. Fevola, L. M. Liable-Sands, A. L. Rheingold and
K. H. Theopold, Organometallics, 1998, 17, 4541; K. H. Theopold,
Eur. J. Inorg. Chem., 1998, 15; K. Albahily, E. Koc, D. Al-Baldawi,
D. Savard, S. Gambarotta, T. J. Burchell and R. Duchateau, Angew.
Chem., Int. Ed., 2008, 47, 5816; Y. J. Chen, W. W. Zuo, P. Hao, S. Zhang,
K. Gao and W. H. Sun, J. Organomet. Chem., 2008, 693, 750; S. Zhang,
S. Y. Jie, Q. S. Shi and W. H. Sun, J. Mol. Catal. A: Chem., 2007, 276,
174; T. Q. Xu, Y. Mu, W. Gao, J. G. Ni, L. Ye and Y. C. Tao, J. Am.
Chem. Soc., 2007, 129, 2236; K. M. Smith, Curr. Org. Chem., 2006, 10,
955.
References
1
A. Yeori, I. Goldberg and M. Kol, Macromolecules, 2007, 40, 8521; A.
Yeori, I. Goldberg, M. Shuster and M. Kol, J. Am. Chem. Soc., 2006,
1
28, 13062; S. Gendler, S. Segal, I. Goldberg, Z. Goldschmidt and M.
Kol, Inorg. Chem., 2006, 45, 4783.
E. Y. Tshuva, I. Goldberg and M. Kol, J. Am. Chem. Soc., 2000, 122,
2
3
1
0706; Y. Sarazin, R. H. Howard, D. L. Hughes, S. M. Humphrey and
15 D. J. Darensbourg, A. I. Moncada, W. Choi and J. H. Reibenspies,
J. Am. Chem. Soc., 2008, 130, 6523; D. J. Darensbourg, P. Bottarelli
and J. R. Andreatta, Macromolecules, 2007, 40, 7727; D. J. Darensbourg
and S. B. Fitch, Inorg. Chem., 2007, 46, 5474; D. J. Darensbourg and
R. M. Mackiewicz, J. Am. Chem. Soc., 2005, 127, 14026; D.-Y. Rao, B.
Li, R. Zhang, H. Wang and X.-B. Lu, Inorg. Chem., 2009, 48, 2830.
16 T. Toupance, S. R. Dubberley, N. H. Rees, B. R. Tyrrell and P.
Mountford, Organometallics, 2002, 21, 1367.
17 F. M. Kerton, S. Holloway, A. Power, R. G. Soper, K. Sheridan, J. M.
Lynam, A. C. Whitwood and C. E. Willans, Can. J. Chem., 2008, 86,
435.
18 K. L. Collins, L. J. Corbett, S. M. Butt, G. Madhurambal and F. M.
Kerton, Green Chemistry Letters and Reviews, 2007, 1, 31.
19 W. Clegg, M. G. Davidson, D. V. Graham, G. Griffen, M. D. Jones,
A. R. Kennedy, C. T. O’Hara, L. Russo and C. M. Thomson, Dalton
Trans., 2008, 1295.
20 C. A. Huang and C. T. Chen, Dalton Trans., 2007, 5561.
21 F. M. Kerton, C. M. Kozak, K. Luttgen, C. E. Willans, R. J. Webster
and A. C. Whitwood, Inorg. Chim. Acta, 2006, 359, 2819.
22 S. Groysman, I. Goldberg, M. Kol, E. Genizi and Z. Goldschmidt,
Inorg. Chim. Acta, 2003, 345, 137.
23 A. R. F. Cox, V. C. Gibson, E. L. Marshall, A. J. P. White and D.
Yeldon, Dalton Trans., 2006, 5014.
24 A. G. Dossetter, T. F. Jamison and E. N. Jacobsen, Angew. Chem., Int.
Ed., 1999, 38, 2398.
25 N. H. Andersen, A. Dossing and A. Molgaard, Inorg. Chem., 2003, 42,
6050.
26 S. J. Cline, J. Glerup, D. J. Hodgson, G. S. Jensen and E. Pedersen, Inorg.
Chem., 1981, 20, 2229; D. J. Hodgson and E. Pedersen, Inorg. Chem.,
1980, 19, 3116; J. T. Veal, D. Y. Jeter, J. C. Hempel, R. P. Eckberg, W. E.
Hatfield and D. J. Hodgson, Inorg. Chem., 1973, 12, 2928.
27 K. B. P. Ruppa, K. Feghali, I. Kovacs, K. Aparna, S. Gambarotta,
G. P. A. Yap and C. Bensimon, J. Chem. Soc., Dalton Trans., 1998,
1595; B. G. Gafford, R. A. Holwerda, H. J. Schugar and J. A. Potenza,
Inorg. Chem., 1988, 27, 1126; M. Di Vaira and F. Mani, Inorg. Chem.,
1984, 23, 409.
28 L. Z. Zhang, Y. H. Wang, W. Gu, X. Liu and D. Z. Liao, Inorg. Chem.
Commun., 2006, 9, 46; L. Spiccia, G. D. Fallon, A. Markiewicz, K. S.
Murray and H. Riesen, Inorg. Chem., 1992, 31, 1066; K. Wieghardt, W.
Schmidt, R. Vaneldik, B. Nuber and J. Weiss, Inorg. Chem., 1980, 19,
2922.
29 M. A. Heinrichs, D. J. Hodgson, K. Michelsen and E. Pedersen, Inorg.
Chem., 1984, 23, 3174; S. J. Cline, S. Kallesoe, E. Pedersen and D. J.
Hodgson, Inorg. Chem., 1979, 18, 796; R. P. Scaringe, P. Singh, R. P.
Eckberg, W. E. Hatfield and D. J. Hodgson, Inorg. Chem., 1975, 14,
1127; J. P. Costes, V. Ciornea, S. Shova, I. Filippova, Y. A. Simonov,
A. Gulea and G. Novitchi, Eur. J. Inorg. Chem., 2005, 5, 929; J. T. Veal,
W. E. Hatfield, D. Y. Jeter, J. C. Hempel and D. J. Hodgson, Inorg.
Chem., 1973, 12, 342; X. Y. Chen, J. Xia, B. Zhao, P. Cheng, S. P. Yan,
D. Z. Liao, Z. H. Jiang, H. B. Song and H. G. Wang, J. Coord. Chem.,
2004, 57, 231.
M. Bochmann, Dalton Trans., 2006, 340.
F. M. Kerton, A. C. Whitwood and C. E. Willans, Dalton Trans., 2004,
2
237; C. E. Willans, M. A. Sinenkov, G. K. Fukin, K. Sheridan, J. M.
Lynam, A. A. Trifonov and F. M. Kerton, Dalton Trans., 2008, 3592; F.
Bonnet, A. R. Cowley and P. Mountford, Inorg. Chem., 2005, 44, 9046;
H. E. Dyer, S. Huijser, A. D. Schwarz, C. Wang, R. Duchateau and
P. Mountford, Dalton Trans., 2008, 32; A. Amgoune, C. M. Thomas
and J. F. Carpentier, Pure Appl. Chem., 2007, 79, 2013; A. Amgoune,
C. M. Thomas, T. Roisnel and J. F. Carpentier, Chem.–Eur. J., 2006,
1
2, 169; Y. Yao, M. Ma, X. Xu, Y. Zhang, Q. Shen and W. T. Wong,
Organometallics, 2005, 24, 4014.
4
5
T. Nagataki and S. Itoh, Chem. Lett., 2007, 36, 748; L. Rodriguez,
E. Labisbal, A. Sousa-Pedrares, J. A. Garcia-Vazquez, J. Romero, M.
Luz Duran, J. A. Real and A. Sousa, Inorg. Chem., 2006, 45, 7903;
A. Philibert, F. Thomas, C. Philouze, S. Hamman, E. Saint-Aman and
J.-L. Pierre, Chem.–Eur. J., 2003, 9, 3803; O. Rotthaus, F. Thomas, O.
Jarjayes, C. Philouze, E. Saint-Aman and J.-L. Pierre, Chem.–Eur. J.,
2
006, 12, 6953.
E. Safaei, T. Weyhermuller, E. Bothe, K. Wieghardt and P. Chaudhuri,
Eur. J. Inorg. Chem., 2007, 2334; M. Velusamy, M. Palaniandavar,
R. S. Gopalan and G. U. Kulkarni, Inorg. Chem., 2003, 42, 8283;
M. Velusamy, R. Mayilmurugan and M. Palaniandavar, Inorg. Chem.,
2
004, 43, 6284; R. Viswanathan, M. Palaniandavar, T. Balasubrama-
nian and T. P. Muthiah, Inorg. Chem., 1998, 37, 2943; M. Merkel, F. K.
Muller and B. Krebs, Inorg. Chim. Acta, 2002, 337, 308; P. Mialane,
E. Anxolabehere-Mallart, G. Blondin, A. Nivorojkine, J. Guilhem, L.
Tchertanova, M. Cesario, N. Ravi, E. Bominaar, J. J. Girerd and E.
Munck, Inorg. Chim. Acta, 1997, 263, 367; J. Hwang, K. Govindaswamy
and S. A. Koch, Chem. Commun., 1998, 1667; M. S. Shongwe, C. H.
Kaschula, M. S. Adsetts, E. W. Ainscough, A. M. Brodie and M. J.
Morris, Inorg. Chem., 2005, 44, 3070; T. Kurahashi, K. Oda, M.
Sugimoto, T. Ogura and H. Fujii, Inorg. Chem., 2006, 45, 7709.
T. Weyhermuller, T. K. Paine, E. Bothe, E. Bill and P. Chaudhuri, Inorg.
Chim. Acta, 2002, 337, 344.
K. Hasan, C. Fowler, P. Kwong, A. K. Crane, J. L. Collins and C. M.
Kozak, Dalton Trans., 2008, 2991–2998.
R. R. Chowdhury, A. K. Crane, C. Fowler, P. Kwong and C. M. Kozak,
Chem. Commun., 2008, 94.
D. J. Darensbourg, E. B. Frantz and J. R. Andreatta, Inorg. Chim.
Acta, 2007, 360, 523; D. J. Darensbourg, R. M. Mackiewicz and D. R.
Billodeaux, Organometallics, 2005, 24, 144.
6
7
8
9
1
0 D. J. Darensbourg, R. M. Mackiewicz, J. L. Rodgers, C. C. Fang,
D. R. Billodeaux and J. H. Reibenspies, Inorg. Chem., 2004, 43, 6024;
D. J. Darensbourg and J. C. Yarbrough, J. Am. Chem. Soc., 2002,
1
24, 6335; M. Tsuchimoto, N. Yoshioka and S. Ohba, Eur. J. Inorg.
Chem., 2001, 1045; T. L. Siddall, N. Miyaura, J. C. Huffman and J. K.
Kochi, J. Chem. Soc., Chem. Commun., 1983, 1185; S. Wang, P. Day,
J. D. Wallis, P. N. Horton and M. B. Hursthouse, Polyhedron, 2006,
2
5, 2583; J. W. Kramer, E. B. Lobkovsky and G. W. Coates, Org. Lett.,
006, 8, 3709; K. B. Hansen, J. L. Leighton and E. N. Jacobsen, J. Am.
2
Chem. Soc., 1996, 118, 10924.
30 J. Hesschenbrouck, E. Solari, C. Floriani, N. Re, C. Rizzoli and A.
Chiesi-Villa, J. Chem. Soc., Dalton Trans., 2000, 191; T. Agapie, S. J.
Schofer, J. A. Labinger and J. E. Bercaw, J. Am. Chem. Soc., 2004, 126,
1304.
31 J. J. H. Edema, A. Meetsma, S. Gambarotta, S. I. Khan, W. J. J. Smeets
and A. L. Spek, Inorg. Chem., 1991, 30, 3639.
32 C. J. O’Connor, Prog. Inorg. Chem., 1982, 29, 203.
33 R. L. Carlin, ‘Magnetochemistry’, Springer-Verlag, Heidelberg, 1986.
34 H. Chun, C. N. Verani, P. Chaudhuri, E. Bothe, E. Bill, T. Weyhermuller
and K. Wieghardt, Inorg. Chem., 2001, 40, 4157.
35 J.-H. So and P. Boudjouk, Inorg. Chem., 1990, 29, 1592.
36 Y. Shimazaki, S. Huth, A. Odani and O. Yamauchi, Angew. Chem., Int.
Ed., 2000, 39, 1666.
1
1
1 R. Sanzenbacher, A. Bottcher, H. Elias, M. Huber, W. Haase, J. Glerup,
T. B. Jensen, M. Neuburger, M. Zehnder, J. Springborg and C. E. Olsen,
Inorg. Chem., 1996, 35, 7493.
2 A. Bottcher, H. Elias, J. Glerup, M. Neuburger, C. E. Olsen, H. Paulus,
J. Springborg and M. Zehnder, Acta Chem. Scand., 1994, 48, 967; A.
Bottcher, H. Elias, J. Glerup, M. Neuburger, C. E. Olsen, J. Springborg,
H. Weihe and M. Zehnder, Acta Chem. Scand., 1994, 48, 981.
3 A. Lehtonen, M. Wasberg and R. Sillanp a¨ a¨ , Polyhedron, 2006, 25, 767.
4 K. A. Kreisel, G. P. A. Yap and K. H. Theopold, Inorg. Chem.,
1
1
2
008, 47, 5293; L. A. MacAdams, G. P. Buffone, C. D. Incarvito,
A. L. Rheingold and K. H. Theopold, J. Am. Chem. Soc., 2005, 127,
082; W. K. Kim, L. M. Liable-Sands, I. A. Guzei, A. L. Rheingold,
1
5
58 | Dalton Trans., 2010, 39, 548–559
This journal is © The Royal Society of Chemistry 2010

3
3
3
4
4
7 J. W. Pflugrath, Acta Crystallogr., Sect. D: Biol. Crystallogr., 1999, 55,
718.
8 A. C. Larson, ‘Crystallographic Computing’, ed. F. R. Ahmed, Munks-
gaard, Copenhagen, 1970, p. 291.
9 D. T. Cromer and J. T. Waber, ‘International Tables for X-ray
Crystallography’, The Kynoch Press, Birmingham, UK, 1974.
0 A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, M. Burla,
G. Polidori and M. Camalli, J. Appl. Crystallogr., 1994, 27, 435.
1 P. T. Beurskens, G. Admiraal, G. Beurskens, W. P. Bosman, R. de
Gelder, R. Israel and J. M. M. Smits, ‘DIRDIF99¢, University of
Nijmegen, Netherlands, 1999.
44 D. C. Creagh and J. H. Hubbell, ‘International Tables for Crystallogra-
phy’, ed. A. J. C. Wilson, Kluwer Academic Publishers, Boston, 1992,
vol. C, Table 4.2.4.3, pp. 200–206.
45 D. J. Watkin, C. K. Prout, J. R. Carruthers and P. W. Betteridge,
CRYSTALS Issue 10, Chemical Crystallography Laboratory, Oxford,
UK, 1996; CrystalStructure 3.7.0: Crystal Structure Analysis Package,
Rigaku and Rigaku/MSC, The Woodlands, Texas, 2000–2005.
46 G. M. Sheldrick, SHELXL-97, Program for refinement of crystal
structures, University of G o¨ ttingen, Germany, 1997.
1
47 SAINT 7.23A, Bruker AXS Inc., Madison, Wisconsin,
2006.
4
4
2 J. A. Ibers and W. C. Hamilton, Acta Crystallogr., 1964, 17, 781.
3 D. C. Creagh and W. J. McAuley, ‘International Tables for Crystallog-
raphy’, ed. A. J. C. Wilson, Kluwer Academic Publishers, Boston, 1992,
vol. C, Table 4.2.6.8, pp. 219–222.
48 G. M. Sheldrick, SADABS, Program for area detector adsorption
correction, Institute for Inorganic Chemistry, University of G o¨ ttingen,
Germany, 1996.
49 L. J. Farrugia, J. Appl. Crystallogr., 1997, 30, 565.
This journal is © The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 548–559 | 559