Extremely bulky amido first row transition metal(II) halide complexes: Potential precursors to low coordinate metal-metal bonded systems

Article abstract of DOI:10.1021/ic302672a

Reactions of the extremely bulky potassium amide complexes, [KL′(η⁶-toluene)] or [KL″] (L′/L″ = N(Ar*)(SiR₃), Ar* = C₆H₂{C(H) Ph₂}₂Me-2,6,4; R = Me (L′) or Ph (L″)), with a series of first row transition metal(II) halides have yielded 10 rare examples of monodentate amido first row transition metal(II) halide complexes, all of which were crystallographically characterized. They encompass the dimeric, square-planar chromium complexes, [{CrL′(THF)(μ-Cl)}₂] and [{CrL″(μ-Cl)}₂], the latter of which displays intramolecular η²-Ph···Cr interactions; the dimeric tetrahedral complexes, [{ML′(THF)(μ-Br)}₂] (M = Mn or Fe), [{ML″(THF)(μ-X)}₂] (M = Mn, Fe or Co; X = Cl or Br) and [{CoL″(μ-Cl)}₂] (which displays intramolecular η²-Ph···Co interactions); and the monomeric zinc amides, [L′ZnBr(THF)] (three-coordinate) and [L″ZnBr] (two-coordinate). Solution state magnetic moment determinations on all but one of the paramagnetic compounds show them to be high-spin systems. Throughout, comparisons are made with related bulky terphenyl transition metal(II) halide complexes, and the potential for the use of the prepared complexes as precursors to low-valent transition metal systems is discussed.

Full text of DOI:10.1021/ic302672a

Article
pubs.acs.org/IC
Extremely Bulky Amido First Row Transition Metal(II) Halide
Complexes: Potential Precursors to Low Coordinate Metal−Metal
Bonded Systems
Jamie Hicks and Cameron Jones*
School of Chemistry, Monash University, P.O. Box 23, Melbourne, Victoria, 3800, Australia
S
* Supporting Information
ABSTRACT: Reactions of the extremely bulky potassium amide complexes,
[KL′(η6-toluene)] or [KL″] (L′/L″ = N(Ar*)(SiR3), Ar* = C6H2{C(H)-
Ph2}2Me-2,6,4; R = Me (L′) or Ph (L″)), with a series of first row transition
metal(II) halides have yielded 10 rare examples of monodentate amido first
row transition metal(II) halide complexes, all of which were crystallo-
graphically characterized. They encompass the dimeric, square-planar
chromium complexes, [{CrL′(THF)(μ-Cl)}2] and [{CrL″(μ-Cl)}2], the
latter of which displays intramolecular η2-Ph···Cr interactions; the dimeric
tetrahedral complexes, [{ML′(THF)(μ-Br)}2] (M = Mn or Fe),
[{ML″(THF)(μ-X)}2] (M = Mn, Fe or Co; X = Cl or Br) and [{CoL″(μ-
Cl)}2] (which displays intramolecular η2-Ph···Co interactions); and the
monomeric zinc amides, [L′ZnBr(THF)] (three-coordinate) and [L″ZnBr]
(two-coordinate). Solution state magnetic moment determinations on all but
one of the paramagnetic compounds show them to be high-spin systems. Throughout, comparisons are made with related bulky
terphenyl transition metal(II) halide complexes, and the potential for the use of the prepared complexes as precursors to low-
valent transition metal systems is discussed.
the only monodentate ligands that has been successfully applied
to the preparation of such metal(I) dimers are the bulky
terphenyls (e.g., Ar′) developed by Power and co-workers.5 This
is partly because terphenyl transition metal(II) halide precursors
to these complexes, for example, [{Ar′M(THF)nX}2] (X =
halide, n = 0 or 1), are readily available, are stable to
redistribution reactions, and can be cleanly reduced to metal(I)
dimers.5 It is perhaps surprising that very bulky monodentate
amide ligands (-NR2), which have been utilized for decades to
stabilize low coordinate transition metal complexes,15 for
example, two-coordinate [M(NR2)2],16 have not been success-
fully employed in the preparation of related metal(I)−metal(I)
dimers, for example, [LMML] (L = monodentate amide). This
may result from the fact that reports of the most logical
precursors to such compounds, that is, the amido metal(II)
halides, [LMX], are sparse, despite the many hundreds of
structurally characterized amido-transition metal complexes that
populate the literature.15 That said, monodentate amido
metal(II) halides are not unknown, though they typically require
bulky amide ligands to be isolated, for example, as in
[{Cr(NC4H2But2-2,5)(THF)(μ-Cl)}2],17 [FeCl{N(R)(ArF)}-
(tmeda)] (R = C(CD3)2CH3, ArF = C6H3FMe-2,5)18 and
[MCl{N(SiMe3)(Xyl)}(tmeda)] (M = Fe or Co, Xyl = 2,6-
xylyl).19 What is certain is that further examples of complexes of
the type [LMX], with even bulkier amide ligands, will need to be
INTRODUCTION
■
The chemistry of metal−metal bonded complexes has rapidly
expanded in recent decades.1 Many advances have been made in
this field, with the preparation of stable dimeric complexes
containing s-2 or p-block3 metal(I)−metal(I) bonds being
landmark examples. More than just being of fundamental
interest, these highly reactive, two- or three-coordinate species
have found a variety of applications in synthesis, small molecule
activation, and so forth.4 Related low coordinate systems
containing carbonyl free, first row d-block metal(I)−metal(I)
bonds are less developed, though a number of breakthroughs
have been made since 2000. These include the bulky terphenyl
coordinated complexes, [Ar′MMAr′] (M = Cr, Fe, Co, or Zn; Ar′
= C6H3Dip2-2,6, Dip = C6H3Pri2-2,6);5−8 amidinate or
guanidinate bridged systems, [M2(μ-L#)2] (L# = bulky amidinate
or guanidinate, M = Cr, Fe, Co, Ni),9−12 which contain extremely
short M−M multiple bonds; unsupported Mn−Mn bonded
systems, [L#MnMnL#] (L# = β-diketiminate or amidinate);10,13
and a considerable number of two- or higher-coordinate zinc(I)
dimers, for example, [Cp*ZnZnCp*].14 The further chemistry of
all of these compound types has been explored to varying extents,
and it has become clear that they hold significant potential for use
in catalysis, synthesis, and so forth.
The stability of the previously reported transition metal(I)
dimers mentioned above is derived from their metal centers
being coordinated by very bulky ligands. This provides the
compounds with kinetic protection from disproportionation and
other decomposition processes. To the best of our knowledge,
Received: December 5, 2012
Published: March 12, 2013
© 2013 American Chemical Society
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a
Scheme 1. Preparation of Compounds 1−10 (L′ = N(Ar*)(SiMe3), L″ = N(Ar*)(SiPh3); Ar* = C6H2{C(H)Ph2}2Me-2,6,4)
a
All reactions were carried out in THF (by-products omitted).
accessed if monodentate amido metal(I) dimer chemistry is to
develop at any pace.
furan (THF) solutions of these amides were added to 1 equiv of
CrCl2, MnBr2, FeBr2, CoCl2, or ZnBr2, as suspensions or
solutions in THF. Workup and subsequent recrystallization of
the crude reaction mixtures from either THF or toluene afforded
the amido metal halide complexes, 1−10 (Scheme 1), in yields
ranging from 43% to 91%. It is of note that the no identifiable
product could be isolated from the reaction of [KL′(η6-toluene)]
with CoCl2, while treatment of both potassium amides with
CoBr2 in THF resulted in recovery of the potassium amides and
the reproducible generation of the new cobalt bromide contact
ion-pair complex, [(THF)4Co(μ-Br)2CoBr2] (see Supporting
Information for crystallographic details). It seems that
dissolution of CoBr2 in THF yields this complex, which has a
low reactivity toward the potassium amide starting materials.
Furthermore, all attempts to obtain amido nickel(II) or copper(I
or II) complexes via reaction of the potassium amides with either
NiBr2 or copper halides in THF were not successful. No metal
deposition was observed in any of these reactions.
Other features of the synthetic studies worth noting are that
while all of the reactions were carried out in THF, and all of the
products incorporating the L′ ligand have metal coordinated
THF molecules, two of the products containing the bulkier L″
ligand (viz. 2 and 7), instead have their coordination spheres
completed by intramolecular η2-interactions from one phenyl
group of their SiPh3 or Ar* fragments (see structural discussions
below for further details). This suggests that the η2-phenyl
interactions in 2 and 7 successfully compete with THF
coordination in these compounds. It seems that, at least in the
case of 7, this is a relatively finely balanced competition, as both it
and the THF coordinated analogue of the complex, namely, 8,
can be obtained when the vacuum-dried crude reaction product
is recrystallized from a toluene/hexane solution. If that solution is
kept at room temperature for several days before crystallization
occurs, only 7 is obtained. Moreover, solid samples of 8 appear to
slowly lose their coordinated THF at ambient temperature, while
dissolution of 7 in THF leads to the immediate and quantitative
regeneration of compound 8.
Toward this goal, we have developed an extremely bulky class
of amido ligands, for example, -N(Ar*)(SiR3) (Ar*= C6H2Me-
{C(H)Ph2}2-4,2,6; R = Me (L′) or Ph (L″)),20 which we have
shown to have similar steric profiles and stabilizing properties to
Power’s widely used substituted terphenyls. This is reflected in
the fact that these ligands have allowed us entry to a variety of
unprecedented low coordinate main group metal amide
complexes, which include monomeric chloro-tetrelenes, for
example, [L′ECl] (E = Ge or Sn),20 a singly bonded amido-
digermyne [L′Ge-GeL′],21 low coordinate metal(II) cations
[L′E:]+ (E = Ge or Sn),22 an acyclic boryl-germylene
[L′Ge{B(DAB)}] (DAB = {DipNCH}2),23 and one-coordinate
group 13 metal(I) amides, [L′M:] (M = Ga, In or Tl).24 Here, we
now report the use of these bulky amides in the facile preparation
of 10 amido first row transition metal(II) halide complexes. We
believe these complexes hold considerable potential for synthetic
chemists, not only as precursors to metal(I)−metal(I) bonded
complexes, but also to other low-coordinate/low-oxidation state
synthetic targets that might require considerable steric
protection to be isolable under normal conditions.
RESULTS AND DISCUSSION
■
At the outset of this study, salt elimination reactions between
alkali metal amides and transition metal dihalides were chosen to
prepare the target complexes. Initially, reactions were carried out
between the lithium amides, [LiL′] or [LiL″],20 and a variety of
first row transition metal dihalides. However, these reactions
typically led to complex mixtures of unidentifiable products. It is
of note that one reaction between [LiL′] and MnBr2 in a diethyl
ether/THF solvent mixture afforded a very low yield (<5%) of
the crystalline “-ate” complex, [L′Mn(THF)(μ-Br)2Li(OEt2)2].
No spectroscopic data were obtained for this compound, though
details of its X-ray crystal structure can be found in the
Supporting Information.
To circumvent the formation of “-ate” complexes, the
reactions were repeated using the corresponding potassium
amide complexes, [KL′(η6-toluene)]24 and [KL″]. Tetrahydro-
All of the compounds 1−10 were crystallographically
characterized. This revealed them to possess varying coordina-
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Figure 1. Thermal ellipsoid plots (25% probability surface) of the molecular structures of 1−4, 7, 9, and 10. Hydrogen atoms are omitted. Selected
metrical parameters are given in Table 1.
tion geometries, which depend on the metal and amide ligand
involved. Examples of the molecular structures of the
compounds exhibiting unique ligand/structural motif combina-
tions can be found in Figure 1 (see Table 1 for selected metrical
parameters of all complexes), while ORTEP diagrams of 5, 6, and
8, which are isostructural to either 3 or 4, can be found in the
Supporting Information. The amido chromium compounds, 1
and 2, differ from the other complexes in the series in that they
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both have distorted square planar metal geometries, the
coordination sites of which are occupied by the amide, two
approximately symmetrically bridging chlorides, and either a
molecule of THF (1) or an intramolecular η2-phenyl interaction
(2). These structures are very similar to those of the distorted
square planar terphenyl coordinated complexes, [{Ar′Cr(μ-
Cl)}2]25 and [{ArC F 3Cr(THF)(μ-F)}2] (ArC F3
=
C6H2Dip2(CF3)-2,6,4),26 the former of which exhibits a close
contact (2.435(3) Å) between each Cr center and one Dip ipso-C
center of its Ar′ ligand. This contact constitutes the fourth
coordination site at each Cr center (cf. 2). The Cr−N distances
in 1 and 2 are in the normal range for CrII amides,27 but are
slightly less than the sum of the covalent radii for Cr and N (2.10
Å).28 Although the Cr···η2-C-Cmidpoint distances in 2 (2.423(2)
Å) are longer than normal Cr−C covalent bonds, for example,
2.041(3) Å in [{Ar′Cr(μ-Cl)}2],25 they clearly signify relatively
strong Cr···phenyl interactions.
Compounds 3−6 and 8 are essentially isostructural, in that
their metal centers all possess distorted tetrahedral geometries
involving coordination by terminal amido and THF ligands, and
by two close to symmetrically bridging halides. There are no
equivalent structural types for terphenyl manganese or iron
halide complexes, though for both metals, preliminary reports of
the crystal structures of [{Ar†Mn(μ-I)}2] and [{Ar†Fe(μ-I)}2]
(Ar† = C6HPri2Trip2-3,5,2,6; Trip = C6H2Pri3-2,4,6), which
incorporate extremely bulky terphenyl ligands, reveal planar
three-coordinate metal geometries.5 Comparisons can, however,
be made between the cobalt complex, 8, and the terphenyl cobalt
bromide species, [{ArMesCo(THF)(μ-Br)}2] (ArMes
=
C6H3Mes2-2,6; Mes = mesityl),29 both of which have similar
distorted tetrahedral cobalt geometries. It is of note that within
the series, 3−6 and 8, there is a general decrease in the M-N and/
or M-O distances with increasing molecular weight of the metal.
This is consistent with the decreasing high spin covalent radii
reported for the metal sequence Mn (1.61 Å) > Fe (1.52 Å) > Co
(1.50 Å).28 Although the N-centers in all of 3−6 and 8 have
planar geometries, none of their M-N distances are especially
short, and therefore they do not indicate significant degrees of
N→M π-bonding in the complexes. Moreover, their M···M
separations are not indicative of any substantial metal−metal
bonding.
The crystal structure of 7 resembles those of 3−6 and 8 in that
it has a distorted tetrahedral cobalt geometry, though the metal
center is not coordinated by THF and the fourth coordination
site is instead taken up by an η2-phenyl interaction. At first glance,
this appears similar to the situation in 2. However, in that
compound the interaction derives from a phenyl group of the
SiPh3 fragment, whereas in 7 it comes from a phenyl substituent
of the Ar* ligand. This difference presumably results from the
contrasting metal geometries in the complexes.
The solid state structures of the amido zinc bromide
complexes, 9 and 10, differ from the others in that the two
compounds are monomeric. Compound 9 has a three-coordinate
zinc center, including coordination by a molecule of THF.
Although two Ar* phenyl substituents lie above and below the
zinc coordination plane, the closest Zn···Cphenyl distance (3.048
Å) is too long to imply any significant interaction. The Zn−N
distance in the compound is at the short end of the known range
(1.844−2.344 Å),27 and the SiCZnBrO fragment of the
compound is close to planar. In contrast to 9, there is no
coordinated THF molecule in 10, despite the fact that it was
prepared in that solvent. This most likely arises from the larger
steric bulk of its amide ligand, relative to that in 9. As a result, the
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compound possesses a two-coordinate zinc center, with an N−
Zn−Br angle of 160.41(9)°, and one of the shortest known Zn−
N distances (1.833(3) Å). The bending in the NZnBr fragment
might be due to an interaction between the Zn center and an Ar*
phenyl group, but as the closest Zn···Cphenyl distance is long at
2.824 Å, this interaction must be considered weak at best.
Compound 10 represents the first structurally characterized
example of a two-coordinate zinc halide complex, and it differs
from corresponding solvent free terphenyl zinc halide complexes,
for example, [{Ar′Zn(μ-I)2}2], which are three-coordinate,
halide bridged dimers.30
All of the compounds prepared in this study (except 8) are
very thermally stable solids, and are indefinitely stable in solution
at ambient temperature. Little information could be gained from
the NMR spectroscopic data of all but the zinc amides, 9 and 10,
because of the paramagnetic nature of the compounds. This gave
rise to broad signals in their 1H NMR spectra that typically were
observed over wide chemical shift ranges. The 1H NMR spectra
of 9 and 10, on the other hand, exhibit sharp resonances, and are
consistent with the compounds retaining their solid state
structures in solution.
Although it was not the intention of this study to carry out in-
depth solid state magnetochemical studies of 1−8, the room
temperature solution state effective magnetic moments of all but
2 were determined using the Evans method.31 The very low
solubility of 2 in noncoordinating deuterated solvents prevented
its magnetic moment determination. While the magnetic
moment obtained for 1 (μeff = 5.81 μB per dimer) is less than
the spin-only value for two noninteracting, high-spin Cr2+ centers
(6.93 μB), it lies in the range previously reported for related
square-planar halide bridged CrII dimers, for example, [{ArCF3Cr-
(THF)(μ-F)}2] (μeff = 6.94 μB per dimer)26 and [{Cr[{N-
(Dip)}2CNMe2](μ-Cl)}2] (μeff = 3.82 μB per dimer).9b This
suggests the compound is high-spin and exhibits a degree of
antiferromagnetic coupling over the Cr2Cl2 core. Similarly, the
magnetic moments obtained for all the tetrahedral dimers, 3−8,
indicate that they are high-spin complexes, the metal centers of
which are antiferromagnetically coupled to varying extents.
Specifically, the effective magnetic moments for the manganese
complexes, 3 (5.90 μB per dimer) and 4 (6.85 μB per dimer), are
markedly less than the spin-only value (8.36 μB). It is difficult to
draw comparisons here as we are not aware of any structurally
authenticated tetrahedral, halide bridged MnII dimers that have
been the subjects of magnetochemical studies. The only
exceptions are several dimeric, tetrahedral manganese dihalide
adducts, for example, [{Mn(NEt3)I(μ-I)}2] (μeff = 6.8 μB), for
which significant antiferromagnetic coupling between the Mn
centers was proposed.32 The magnetic moments obtained for the
FeII and CoII dimers, 5 (5.38 μB per dimer), 6 (6.61 μB per
dimer), 7 (4.86 μB per dimer), and 8 (5.20 μB per dimer), are also
somewhat less than the spin-only values (Fe: 6.93 μB, Co: 5.40
μB,). The observed magnetic moments are, however, comparable
to those for related four-coordinate complexes, for example,
[{(DipNacnac)Fe(μ-F)}2] (6.2 μB per dimer)33 and [{ArMesCo-
(THF)(μ-Br)}2] (4.7 μB per dimer).29
possess square-planar (Cr) or tetrahedral (Mn, Fe, and Co)
metal coordination geometries. The two amido zinc halides are
monomeric and display either planar three-coordinate, or
distorted linear metal geometries, depending on the steric bulk
of the amido ligand involved. Where possible, comparisons have
been made with bulky terphenyl metal(II) halide complexes,
which have proved of great synthetic value in the preparation of
low oxidation state/low coordination number transition metal
complexes in recent years. We believe that the novel complexes
reported in this study will similarly prove ideal precursors for the
preparation of related low-valent amido transition metal
complexes. We are currently exploring this possibility with
encouraging results, which we will report on in due course.
EXPERIMENTAL SECTION
■
General Methods. All manipulations were carried out using
standard Schlenk and glovebox techniques under an atmosphere of
high purity dinitrogen. THF, hexane, and toluene were distilled over
molten potassium. 1H, 13C{1H}, and 29Si{1H} NMR spectra were
recorded on either Bruker AvanceIII 400 or Varian Inova 500
spectrometers and were referenced to the resonances of the solvent
used, or external SiMe4. Mass spectra were obtained from the EPSRC
National Mass Spectrometric Service at Swansea University. IR spectra
were recorded using a Perkin-Elmer RX1 FT-IR spectrometer as Nujol
mulls between NaCl plates. Microanalyses were carried out by the
Science Centre, London Metropolitan University. A reproducible
microanalysis for 4 could not be obtained because of its highly air
sensitive nature, and because total removal of the hexane and THF of
crystallization proved difficult by vacuum drying the compound at
elevated temperature. A reproducible microanalysis for 8 could not be
obtained as it slowly loses its THF of coordination in the solid state,
yielding 7. Melting points were determined in sealed glass capillaries
under dinitrogen and are uncorrected. Solution state effective magnetic
moments were determined by the Evans method.31 The compound
[KL′(η6-toluene)] was prepared by the literature method.24 [KL″] was
prepared by reacting L″H with [KN(SiMe3)2] in toluene at 20 °C for 2
h. Volatiles were removed in vacuo and the solid residue washed with
hexane to give [KL″], which was used without further purification. All
other reagents were used as received.
Preparation of [{CrL′(THF)(μ-Cl)}2] (1). To a suspension of CrCl2
(0.096 g, 0.779 mmol) in THF (30 mL) at −80 °C was added a solution
of [KL′(η6-toluene)] (0.50 g, 0.779 mmol) in THF (10 mL) over 5 min.
The reaction mixture was warmed to room temperature and stirred for 2
h, whereupon volatiles were removed in vacuo. The residue was
extracted with warm toluene (40 mL), the extract filtered and volatiles
removed in vacuo to give 1 as a turquoise solid (0.38 g, 73%). X-ray
quality blue-green crystals of 1 were obtained by recrystallizing this solid
from warm THF. M.p.: 248−250 °C (decomp.); 1H NMR (499 MHz,
C6D6, 298 K): δ = −11.71 (br.), −4.42 (br), 10.15 (br), 10.94 (br),
16.61(br), 36.09 (br); IR υ/cm−1 (Nujol): 1597(m), 1015(m), 917(s),
857(s), 829(s), 748(m), 716(m), 702(s), 603(m), 559(m); MS/EI m/z
+
(%): 511.3 (L′H+, 87), 439.2 (Ar*NH2 , 79), 167.0 (Ph2CH+, 33), 73.0
(Me3Si+, 20); μeff (Evans, C6D6, 298 K): 5.81 μB; Anal. Calc. for
C80H88Cl2Cr2N2O2Si2: C 71.67%, H 6.62%, N 2.09%, found: C 71.82%,
H 6.51%, N 2.13%.
Preparation of [{CrL″(μ-Cl)}2] (2). To a solution of CrCl2 (0.092 g,
0.747 mmol) in THF (30 mL) at −80 °C was added a solution of [KL″]
(0.50 g, 0.679 mmol) in THF (10 mL) over 5 min. The reaction mixture
was warmed to room temperature and stirred for 2 h, whereupon
volatiles were removed in vacuo. The residue was extracted with toluene
(40 mL), the extract filtered, and volatiles removed in vacuo to give 2 as a
green solid (0.41 g, 81%). X-ray quality green crystals of 2 were obtained
by recrystallizing this solid from toluene. M.p.: 156−159 °C; 1H NMR
(499 MHz, D8-toluene, 298 K): δ = −12.88 (br.), 1.83 (br.), 3.02 (br),
7.51 (br.), 10.05 (br), 14.97 (br); IR υ/cm−1 (Nujol): 1597(m),
1029(m), 944(m), 790(m), 720(s), 700(s), 604(m), 560(m), 539(m),
CONCLUSIONS
■
In summary, two extremely bulky amide ligands have been
utilized in the preparation of rare examples of monodentate
amido first row transition metal(II) halide complexes. All
prepared complexes have been spectroscopically characterized
and their X-ray crystal structures determined. The Cr, Mn, Fe,
and Co complexes are all high-spin, halide bridged dimers which
+
507(m); MS/EI m/z (%): 697.4 (L″H+, 81), 439.2 (Ar*NH2 , 83),
259.1 (Ph3Si+, 100), 167.0 (Ph2CH+, 17); Anal. Calc. for
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C102H84Cl2Cr2N2Si2: C 78.09%, H 5.40%, N 1.79%, found: C 77.99%, H
5.49%, N 1.83%. N.B. A reliable magnetic moment determination for
this compound using the Evans method could not be carried out,
because of the low solubility of the compound in D8-toluene.
with toluene (40 mL), the extract filtered, and volatiles were removed in
vacuo. The residue was washed with hexane (20 mL) to give 7 as an
orange solid (0.23 g, 43%). X-ray quality orange crystals of 7 were
obtained by recrystallizing this solid from a minimum volume of
1
Preparation of [{MnL′(THF)(μ-Br)}2] (3). To a suspension of MnBr2
(0.184 g, 0.857 mmol) in THF (30 mL) at −80 °C was added a solution
of [KL′(η6-toluene)] (0.50 g, 0.779 mmol) in THF (10 mL) over 5 min.
The reaction mixture was warmed to room temperature and stirred for 2
h, whereupon volatiles were removed in vacuo. The residue was
extracted with warm toluene (40 mL), the extract filtered and slowly
cooled to 5 °C overnight to give 3 as pink crystals (0.42 g, 75%). M.p.:
222−224 °C (decomp. on melting); 1H NMR (499 MHz, C6D6, 298 K):
δ = −32.21 (br.), 1.36 (br), 7.54 (br), 34.45 (br), 41.06 (br); IR ν/cm−1
(Nujol): 1598(m), 1013(m), 916(s), 906(s), 856(s), 832(s), 727(s),
700(s), 674(m), 622(m), 606(m), 554(m), 531(m); MS (EI) m/z (%):
511.2 (L′H+, 100), 438.2 (Ar*NH+, 23), 167.0 (Ph2CH+, 25); μeff
(Evans, C6D6, 298 K): 5.90 μB; Anal. Calc. for C80H88Br2Mn2N2O2Si2: C
66.94%, H 6.18%, N 1.95%, found: C 66.84%, H 6.26%, N 1.98%.
Preparation of [{MnL″(THF)(μ-Br)}2] (4). To a suspension of MnBr2
(0.143 g, 0.747 mmol) in THF (30 mL) at −80 °C was added a solution
of [KL″] (0.50 g, 0.679 mmol) in THF (10 mL) over 5 min. The
reaction mixture was warmed to room temperature and stirred for 2 h,
whereupon volatiles were removed in vacuo. The residue was extracted
with toluene (40 mL), the extract filtered, and volatiles removed in
vacuo to give 4 as a pale pink solid (0.38 g, 62%). X-ray quality pale pink
crystals of 4 were obtained by crystallizing this solid from a mixture of
toluene and hexane with a trace of THF added. M.p.: 296−299 °C
(decomp. on melting); 1H NMR (499 MHz, C6D6, 298 K): δ =
−34.71(br), 1.37 (br.), 13.20 (br.), 33.04 (br), 40.81 (br); IR υ/cm−1
(Nujol): 1597(m), 903(s), 798(m), 736(m), 729(s), 702(s), 605(m),
577(m), 556(m), 540(m), 504(m); MS/EI m/z (%): 697.3 (L″H+, 54),
toluene/hexane mixture. M.p.: 241−244 °C; H NMR (499 MHz,
C6D6, 298 K): δ = −52.82 (br.), −49.44 (br.), −40.48 (br.), 7.58 (br.),
12.11 (br.), 14.29 (br.), 16.29 (br.), 25.62 (br.), 59.17 (br.), 75.70 (br.),
123.04 (br); IR υ/cm−1 (Nujol): 1598(m), 895(s), 797(m), 722(s),
708(s), 697(s), 624(m), 574(m), 557(m), 540(m), 502(m); MS/EI m/
z (%): 755.3 (L″Co+, 4), 697.3 (L″H+, 80), 438.2 (Ar*NH+, 10), 259.1
(Ph3Si+, 100), 167.0 (Ph2CH+, 10); μeff (Evans, C6D6, 298 K): 4.86 μB;
Anal. Calc. for C102H84Cl2Co2N2Si2: C 77.40%, H 5.35%, N 1.77%,
found: C 77.31%, H 5.37%, N 1.80%.
Preparation of [{L″Co(THF)(μ-Cl)}2] (8). Compound 7 (0.100 g,
0.063 mmol) was dissolved in THF (5 mL), and the mixture stirred for 5
min at room temperature to give a blue/green solution. Volatiles were
removed in vacuo to yield 8 as a green solid (0.109 g, 100%). N.B. X-ray
quality green crystals were obtained by recrystallizing this solid from a
mixture of toluene, hexane, and THF. M.p.: 118−121 °C turns orange/
1
brown, 239−243 °C melts; H NMR (499 MHz, C6D6/D8-THF, 298
K): δ = −22.13 (br.), −14.11 (br.), −0.99 (br.), 10.22 (br.), 11.88 (br.),
18.07 (br.), 49.56 (br.), 54.56 (br.); IR υ/cm−1 (Nujol): 1597(m),
896(m), 880(m), 799(s), 738(m), 697(s), 604(m), 542(m), 504(m);
μeff (Evans, C6D6/D8-THF, 298 K): 5.20 μB.
Preparation of [L′ZnBr(THF)] (9). To a suspension of ZnBr2 (0.192 g,
0.857 mmol) in THF (30 mL) at −80 °C was added a solution of
[KL′(η6-toluene)] (0.50 g, 0.779 mmol) in THF (10 mL) over 5 min.
The reaction mixture was warmed to room temperature and stirred for 2
h, whereupon volatiles were removed in vacuo. The residue was
extracted with toluene (40 mL), the extract filtered, and volatiles were
removed in vacuo to give 9 as an off white solid (0.43 g, 76%). X-ray
quality colorless crystals of 9 were obtained by recrystallizing this solid
from a mixture of THF and hexane. M.p.: 176−180 °C; 1H NMR (400
MHz, C6D6, 298 K): δ = 0.52 (s, 9H, Si(CH3)3), 0.83 (m, 4H, CH2),
1.98 (s, 3H, ArCH3), 2.66 (m, 4H, CH2O), 6.54 (s, 2H, Ph2CH), 6.91−
7.50 (m, 22H, ArH); 13C{1H} NMR (101 MHz, C6D6): δ = 4.0
(Si(CH3)3), 21.3 (ArCH3), 24.6 (CH2), 52.0 (Ph2CH), 70.1 (CH2O),
126.4, 126.8, 128.5, 129.4, 129.7, 129.8, 130.2, 130.4, 141.7, 144.7, 145.4,
150.2 (Ar-C); 29Si{1H} NMR (80 MHz, C6D6): δ = 1.0 (s); IR υ/cm−1
(Nujol): 1597(m), 931(s), 860(s), 849(s), 829(s), 767(m), 733(s),
709(s), 697(s), 604(m), 554(m); MS/+veCI m/z (%): 656.1 (M+-THF,
+
439.2 (Ar*NH2 , 18), 259.0 (Ph3Si+, 100), 167.0 (Ph2CH+, 11); μeff
(Evans, C6D6, 298 K): 6.85 μB.
Preparation of [{FeL′(THF)(μ-Br)}2] (5). To a suspension of FeBr2
(0.185 g, 0.857 mmol) in THF (30 mL) at −80 °C was added a solution
of [KL′(η6-toluene)] (0.50 g, 0.779 mmol) in THF (10 mL) over 5 min.
The reaction mixture was warmed to room temperature and stirred for 2
h, whereupon volatiles were removed in vacuo. The residue was
extracted with toluene (40 mL), the extract filtered and volatiles
removed in vacuo to give 5 as a yellow solid (0.32 g, 57%). X-ray quality
yellow crystals of 5 were obtained by crystallizing this solid from a
mixture of THF and hexane. M.p.: 88−92 °C (decomp.); 1H NMR (400
MHz, C6D6, 298 K): δ = −21.01 (br), −4.07 (br), 3.99 (br), 13.36 (br),
15.19 (br), 21.35 (br), 28.35 (br), 71.19 (br); IR υ/cm−1 (Nujol):
1598(m), 917(m), 902(s), 860(s), 836(s), 766(m), 749(m), 730(s),
703(s), 605(m), 555(m), 535(m); MS/-veCI (CH4) m/z (%): 647.0
+
+
2), 512.3 (L′H2 , 100), 440.2 (Ar*NH3 , 35), 167.0 (Ph2CH+, 19);
Anal. Calc. for C40H44BrNOSiZn: C 65.98%, H 6.09%, N 1.92%, found:
C 66.07%, H 6.13%, N 2.06%.
Preparation of [L″ZnBr] (10). To a suspension of ZnBr2 (0.168 g,
0.747 mmol) in THF (30 mL) at −80 °C was added a solution of [KL″]
(0.50 g, 0.679 mmol) in THF (10 mL) over 5 min. The reaction mixture
was warmed to room temperature and stirred for 2 h, whereupon
volatiles were removed in vacuo. The residue was extracted with toluene
(40 mL), the extract filtered, and volatiles were removed in vacuo to give
10 as an off white solid (0.45 g, 79%). X-ray quality colorless crystals of
10 were obtained by recrystallizing this solid from a mixture of toluene
and hexane. M.p.: 248−250 °C; 1H NMR (400 MHz, C6D6, 298 K): δ =
1.89 (s, 3H, ArCH3), 6.14 (s, 2H, Ph2CH), 6.45−7.66 (m, 37H, ArH);
13C{1H} NMR (101 MHz, C6D6): δ = 21.3 (ArCH3), 53.0 (Ph2CH),
126.5, 128.4, 128.5, 128.6, 129.1, 129.8, 130.2, 130.4, 130.5, 131.3, 132.5,
136.8, 137.2, 142.3, 144.6, 144.7 (Ar-C); 29Si{1H} NMR (80 MHz,
C6D6): δ = −18.9 (s); IR υ/cm−1 (Nujol): 1597(m), 924(s), 909(s),
879(m), 849(s), 763(m), 756(m), 737(s), 700(s), 602(s), 575(m),
555(s), 506(s); MS/EI m/z (%): 841.2 (M+, 7), 697.4 (L″H+, 100),
−
(L′FeBr−, 100), 435.1 (Ar*NH2 , 17); μeff (Evans, C6D6, 298 K): 5.38
μB; Anal. Calc. for C80H88Br2Fe2N2O2Si2: C 66.85%, H 6.17%, N 1.95%,
found: C 66.92%, H 6.25%, N 2.06%.
Preparation of [{FeL″(THF)(μ-Br)}2] (6). To a suspension of FeBr2
(0.161 g, 0.747 mmol) in THF (30 mL) at −80 °C was added a solution
of [KL″] (0.50 g, 0.679 mmol) in THF (10 mL) over 5 min. The
reaction mixture was warmed to room temperature and stirred for 2 h,
whereupon volatiles were removed in vacuo. The residue was extracted
with toluene (40 mL), the extract filtered and volatiles removed in vacuo
to give 6 as a yellow solid (0.43 g, 70%). X-ray quality yellow crystals of 6
were obtained by recrystallizing this solid from a mixture of toluene and
1
hexane. M.p.: 276−279 °C; H NMR (400 MHz, C6D6, 298 K): δ =
−41.70 (br), 3.50 (br), 5.57 (br), 12.64 (br), 64.17 (br), 73.59 (br); IR
υ/cm−1 (Nujol): 1596(m), 918(m), 903(s), 884(m), 852(m), 791(m),
743(m), 725(s), 696(s), 604(m), 579(m), 558(m), 548(m), 506(m);
MS/EI m/z (%): 833.3 (L″FeBr+, <1), 697.3 (L″H+, 82), 439.2
+
439.2 (Ar*NH2 , 81), 259.1 (Ph3Si+, 71), 167.0 (Ph2CH+, 16); Anal.
Calc. for C51H42BrNSiZn: C 72.73%, H 5.03%, N 1.66%, found: C
72.84%, H 5.13%, N 1.56%.
+
(Ar*NH2 , 20), 259.0 (Ph3Si+, 100), 167.0 (Ph2CH+, 10); μeff (Evans,
C6D6, 298 K): 6.61 μB; Anal. Calc. for C110H100Br2Fe2N2O2Si2: C
73.01%, H 5.57%, N 1.55%, found: C 72.96%, H 5.41%, N 1.57%.
Preparation of [{L″Co(μ-Cl)}2] (7). To a suspension of CoCl2 (0.088
g, 0.679 mmol) in THF (30 mL) at −80 °C was added a solution of
[KL″] (0.50 g, 0.679 mmol) in THF (10 mL) over 5 min. The reaction
mixture was warmed to room temperature and stirred for 12 h,
whereupon volatiles were removed in vacuo. The residue was extracted
X-ray Crystallography. Crystals of 1−10, [L′Mn(THF)(μ-Br)2Li-
(OEt2)2], and [(THF)4Co(μ-Br)2CoBr2] suitable for X-ray structural
determination were mounted in silicone oil. Crystallographic measure-
ments were carried out at 123 K with an Oxford Gemini Ultra
diffractometer using a graphite monochromator with Mo Kα radiation
(λ = 0.71073 Å). The structures were solved by direct methods and
refined on F2 by full matrix least-squares (SHELX97)34 using all unique
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Table 2. Summary of Crystallographic Data for 1−10
1·(THF)4
2·(toluene)4
3·(toluene)4
4·(hexane)2(THF)2
5
empirical formula
formula weight
crystal system
color, habit
space group
a (Å)
C96H120Cl2Cr2N2O6Si2
1629.02
C130H116Cl2Cr2N2Si2
1937.33
monoclinic
green, block
P21/c
C108H120Br2Mn2N2O2Si2
1803.94
C130H144Br2Mn2N2O4Si2
2124.35
C80H88Br2Fe2N2O2Si2
1437.22
monoclinic
yellow, block
P21/n
triclinic
triclinic
triclinic
blue-green, block
pink, block
pink, block
P1
̅
P1
̅
P1
̅
11.8071(5)
13.1447(6)
15.4536)8)
70.737(4)
71.481(4)
81.584(4)
2144.58(17)
1
15.1465(12)
20.9444(12)
17.2104(15)
90
11.7659(4)
12.7628(3)
17.1373(6)
106.413(3)
103.649(3)
97.608(2)
2343.51(13)
1
14.1515(6)
14.3059(6)
14.5230(6)
103.914(4)
95.548(4)
103.950(4)
2732.2(2)
1
16.4622(14)
12.6193(7)
18.6176(14)
90
b (Å)
c (Å)
α (deg.)
β (deg)
111.995(10)
90
114.497(10)
90
γ (deg.)
vol (Å3)
5062.4(7)
2
3519.5(4)
2
Z
ρ (calcd) (g cm−3
)
1.261
1.271
1.278
1.291
1.356
μ (mm−1
)
0.399
0.345
1.198
1.040
1.630
F(000)
868
2040
946
1118
1496
reflections collected
unique reflections
Rint
12924
18451
34600
17958
13984
7659
9051
10204
10654
6877
0.0375
0.0613
0.0279
0.0316
0.0617
R1 indices [I > 2σ(I)]
wR2 indices (all data)
CCDC No.
0.0497
0.0530
0.0299
0.0452
0.0451
0.1262
0.1262
0.0766
0.1280
0.1187
914036
914038
914039
914040
914041
10
6·(toluene)1.8(hexane)1.2
7·(toluene)1.5
8·(toluene)2
9
empirical formula
formula weight
crystal system
color, habit
space group
a (Å)
C129.8H131.2Br2Fe2N2O2Si2
2078.87
C112.5H96Cl2Co2N2Si2
1720.85
monoclinic
orange, block
P21/c
C124H116Cl2Co2N2O2Si2
1911.13
C40H44BrNOSiZn
728.13
C51H42BrNSiZn
842.23
triclinic
triclinic
monoclinic
colorless, block
C2/c
triclinic
yellow, block
green, block
colorless, block
P1
̅
P1
̅
P1
̅
14.0504(4)
14.5583(5)
15.2887(5)
64.520(3)
70.367(3)
78.910(3)
2654.80(15)
1
13.3383(7)
18.1137(8)
19.0342(11)
90
11.8902(4)
14.0389(4)
15.2789(5)
81.973(2)
79.402(3)
89.569(2)
2481.94(14)
1
15.6064(5)
15.0567(4)
30.4145(8)
90
10.6299(4)
10.7824(5)
19.9387(9)
84.799(4)
89.581(3)
63.163(4)
2029.30(15)
2
b (Å)
c (Å)
α (deg.)
β (deg)
99.164(5)
90
97.485(3)
90
γ (deg.)
vol (Å3)
4540.1(4)
2
7085.9(3)
8
Z
ρ (calcd) (g cm−3
)
1.300
1.259
1.279
1.365
1.378
μ (mm−1
F(000)
)
1.103
0.502
0.467
1.887
1.656
1090
1802
1006
3024
868
reflections collected
unique reflections
Rint
39120
30822
16246
23865
27739
10417
8912
9697
7732
7958
0.0269
0.0329
0.0297
0.0275
0.0266
R1 indices [I > 2σ(I)]
wR2 indices (all data)
CCDC No.
0.0318
0.0605
0.0537
0.0347
0.0523
0.0820
0.1802
0.1439
0.0848
0.1642
914042
914043
914044
914045
914037
data. All non-hydrogen atoms are anisotropic with hydrogen atoms
included in calculated positions (riding model). Two crystallo-
graphically independent molecules of [(THF)4Co(μ-Br)2CoBr2] were
refined in the asymmetric unit of its crystal structure. There are no
significant geometric differences between them. Crystal data, details of
data collections and refinement are given in Table 2 and the Supporting
Information.
AUTHOR INFORMATION
Corresponding Author
*E-mail: cameron.jones@monash.edu.
Notes
■
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
ASSOCIATED CONTENT
* Supporting Information
Crystallographic data as CIF files for all crystal structures;
ORTEP diagrams for 5, 6, and 8; full crystallographic details for
[L′Mn(THF)(μ-Br)2Li(OEt2)2] and [(THF)4Co(μ-
Br)2CoBr2]. This material is available free of charge via the
Internet at http://pubs.acs.org.
This research was supported by the Australian Research Council
(grant to C.J.). The EPSRC is also thanked for access to the UK
National Mass Spectrometry Facility.
■
S
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