Synthesis and Reactivity of Manganese(II) Complexes Containing N-Heterocyclic Carbene Ligands

Article abstract of DOI:10.1021/acs.organomet.5b00684

A series of manganese(II) complexes containing aryl-substituted N-heterocyclic carbene (NHC) ligands have been synthesized and characterized. Chloride complexes of Mn(II) containing the NHC ligands 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) and 1,3-dimesitylimidazol-2-ylidene (IMes) were prepared in straightforward fashion by direct carbene addition to MnCl₂(THF)_1.6. These complexes exist as chloride-bridged dimers in solution of formula [Mn₂Cl₂(μ-Cl)₂(NHC)₂]. The monomeric complex [MnCl₂(IMes)₂] has also been prepared and structurally characterized, although NMR studies are consistent with facile dissociation of one of the IMes ligands in solution. [Mn₂Cl₂(μ-Cl)₂(IPr)₂] serves as a precursor to dimeric alkyl and aryl compounds of Mn(II) including [Mn₂R₂(μ-Cl)₂(NHC)₂] (R = Bn, o-tolyl, and Ph) and the bridging methyl complex [Mn₂Me₂(μ-Me)₂(IPr)₂]. Stoichiometric reactions of these hydrocarbyl species with bromocyclohexane demonstrate that they are not chemically competent in C-C coupling reactions involving alkyl electrophiles.

Full text of DOI:10.1021/acs.organomet.5b00684

Article
pubs.acs.org/Organometallics
Synthesis and Reactivity of Manganese(II) Complexes Containing
N‑Heterocyclic Carbene Ligands
Malik H. Al-Afyouni,†,‡,§ V. Mahesh Krishnan, Hadi D. Arman, and Zachary J. Tonzetich*
†,§
†
,†
†Department of Chemistry, University of Texas at San Antonio, San Antonio, Texas 78249, United States
‡Department of Chemistry, University of Rochester, Rochester, New York 14627, United States
*
S Supporting Information
ABSTRACT: A series of manganese(II) complexes containing aryl-
substituted N-heterocyclic carbene (NHC) ligands have been synthesized
and characterized. Chloride complexes of Mn(II) containing the NHC
ligands 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) and 1,3-
dimesitylimidazol-2-ylidene (IMes) were prepared in straightforward
fashion by direct carbene addition to MnCl (THF) . These complexes
2
1.6
exist as chloride-bridged dimers in solution of formula [Mn Cl (μ-
2
2
Cl) (NHC) ]. The monomeric complex [MnCl (IMes) ] has also been
2
2
2
2
prepared and structurally characterized, although NMR studies are
consistent with facile dissociation of one of the IMes ligands in solution.
[
(
Mn Cl (μ-Cl) (IPr) ] serves as a precursor to dimeric alkyl and aryl compounds of Mn(II) including [Mn R (μ-Cl) (NHC) ]
2 2 2 2 2 2 2 2
R = Bn, o-tolyl, and Ph) and the bridging methyl complex [Mn Me (μ-Me) (IPr) ]. Stoichiometric reactions of these
2
2
2
2
hydrocarbyl species with bromocyclohexane demonstrate that they are not chemically competent in C−C coupling reactions
involving alkyl electrophiles.
INTRODUCTION
However, these complexes have been shown to take part in
reactions unique from those observed for other 3d organo-
metallics.
■
The fundamental organometallic chemistry of the 3d transition
metals continues to enjoy an upsurge in activity as new catalytic
methodologies utilizing earth-abundant metals proliferate. Yet
among the base metals examined for catalytic organic
transformations, especially those involving C−C bond for-
mation, manganese finds much less use than other mid 3d
39,40
As part of our interest in exploring the organometallic
chemistry of first-row transition metals containing aryl-
substituted N-heterocyclic carbene ligands (NHCs), we have
4
1
turned our focus to manganese NHC complexes. We
envisioned that such complexes might display parallels to the
chemistry of Fe and Co, both of which demonstrate activity in
1
−6
metals. Despite this scarcity, manganese remains popular for
use in oxidation catalysis and select C−X bond forming
4
2−53
7
−10
C−C cross-coupling reactions.
Scattered examples of
reactions.
Many of the difficulties surrounding the use of
Mn(II) NHC compounds are present in the literature dating
manganese in classical organometallic reactions stem from the
lack of well-characterized examples of organomanganese
complexes in oxidation states other than +1. Although
manganese is most frequently encountered in the +2 oxidation
state, the majority of its organometallic chemistry concerns the
back to Cowley and Jones’ isolation of a manganocene NHC
54
complex in 2001. Subsequent work by Roesky reported a
variety of NHC adducts to Mn(II) salts and Mn(II) β-
55−57
diketiminate species.
More recently, both Mulvey and
1
1,12
Goicoechea have reported examples of three-coordinate
Mn(II)-alkyl species by treatment of manganese hydrocarbyl
aggregates, [MnR ] (R = CH SiMe , CH(SiMe ) , or mesityl),
univalent state.
Such Mn(I) compounds exhibit almost
6
exclusively low-spin d configurations and typically feature very
strong-field ligands such as carbonyl. Complexes of divalent
manganese containing metal−carbon bonds are known, albeit
2
n
2
3
3 2
58,59
with IPr.
A variant of the NHC ligand, the cyclic alkyl
13−35
amino carbene, has also been used to generate low-coordinate
much less common.
The bonding in these high-spin
60
Mn species. In addition to these examples that feature
monodentate carbenes, chelating variants of NHC ligands have
been employed to stabilize manganese complexes in the +2
Mn(II) complexes is believed to be much more ionic than that
in Mn(I) compounds, invoking parallels with Grignard
3
4,36
reagents.
Even in those Mn(II) complexes containing
61−65
through +5 oxidation states.
Despite this precedent, no
strong-field ligands such as cyclopentadienyl, the ionic nature of
metal−carbon bonding persists due to the large spin-pairing
energy of manganese. Thus, high-spin configurations are
comprehensive study has examined the preparation and
reactivity of simple manganese carbene complexes of the type
likely to be encountered in binary mixtures of Mn(II) salts and
37,38
observed for most Mn(II) organometallics.
These species
exhibit no spin-allowed ligand field transitions and broadened
or nearly featureless NMR spectra, resulting in few reported
studies featuring their detailed solution characterization.
Received: August 7, 2015
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.5b00684
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Article
the commercially available IPr and IMes NHC coligands. In
this paper we describe the synthesis of well-defined Mn(II)
halide and alkyl complexes containing aryl-substituted NHC
ligands. The structure and reactivity of these compounds are
discussed in the context of potential catalytic C−C bond
forming reactions with Mn(II).
RESULTS AND DISCUSSION
■
Addition of 2 equiv of IMes to MnCl (THF) produced the
2
1.6
Reaction of MnCl (THF) with 1 equiv of IPr in THF
2
1.6
monomeric bis-NHC complex [MnCl (IMes) ] (3, eq 3). The
2
2
afforded the chloride-bridged dimer [Mn Cl (μ-Cl) (IPr) ]
2
2
2
2
(
1
1), in analogous fashion to that observed for Fe and Co (eq
47,50
).
The equivalent reaction with IMes yielded the
corresponding [Mn Cl (μ-Cl) (IMes) ] (2). Both complexes
2
2
2
2
are soluble in arene solvents, albeit sparingly in the case of 2.
1
H NMR spectra of 1 and 2 in benzene-d6 are nearly
featureless, displaying only a few very broadened peaks between
0
and 10 ppm (see Supporting Information). Magnetic
solid-state structure of 3 depicted in Figure 1 compares well to
susceptibility measurements of 1 in benzene-d gave an effective
the previously reported [MnCl ([C(Me)N(iPr)] C) ] complex
6
2
2
2
magnetic moment of 6.7(2) μ , which is consistent with weakly
in both Mn−C
(Δ M−C = 0.021 Å) and Mn−Cl (Δ M−
B
NHC
av
av
56
antiferromagnetically coupled high-spin Mn(II) centers. Such a
description is further corroborated by the solid-state structure
of 1 (Figure 1), which displays a Mn−Mn separation of
Cl = 0.011 Å) bond distance. However, the tetrahedral
geometry about the Mn center in 3 is substantially more
distorted, with a CNHC−Mn−C
angle of 127.41(7)°, very
NHC
6
6
47,50
3
.355(1) Å. No evidence for the formation of the manganate
similar to that observed in the Fe and Co analogues.
In
salt (IPrH)[MnCl (IPr)] was observed during the synthesis of
contrast to the analogous Fe and Co complexes, however,
observation of 3 by H NMR spectroscopy demonstrated that
carbene dissociation occurs readily in solution. Spectra of 3 in
3
1
1
and 2, although this species has been reported to be formed
in reactions of IPr with Mn(II) halides.
67
Halide-bridged dimers analogous to 1 and 2 containing Fe
benzene-d are analogous to those of 2, but show additional
6
and Co are known to cleave readily in the presence of Lewis
peaks consistent with free IMes. Titration of 2 with IMes
resulted in a spectrum identical to that of 3 with no change to
the broadened, paramagnetically shifted peaks of the Mn-bound
carbene ligand (see Supporting Information). We therefore
propose that the equilibrium depicted in eq 4 is established
upon dissolution of 3 and that it lies predominantly toward 2
and free IMes. We note that the ability of NHCs to dissociate
from mid 3d metals was also recently observed in studies with
4
7,48,51
bases.
In a similar fashion, treatment of 1 with 4-
cyanopyridine resulted in cleavage of the dimer and formation
of the monomeric pyridine adduct [MnCl (4-CNpy)(IPr)]
2
(
1py, eq 2). The solid-state structure of 1py was determined
crystallographically and can be found in the Supporting
Information. Magnetic susceptibility measurements of 1py in
benzene were consistent with a monomeric high-spin Mn(II)
complex, giving an effective magnetic moment of 5.7(2) μB.
68,69
iron.
Figure 1. Thermal ellipsoid renderings (50%) of the solid-state structures of 1 (left) and 3 (right). Hydrogen atoms and cocrystallized solvent
molecules are omitted for clarity. Bond distances and angles can be found in the Supporting Information.
B
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Article
Figure 2. Thermal ellipsoid renderings (50%) of the solid-state structures of 4 (left) and 6 (right). Hydrogen atoms and crystallographically
independent molecules (4) are omitted for clarity. Bond distances and angles can be found in the Supporting Information.
Given the observation that carbene dissociation occurs
readily for 3, we chose to focus on compound 1 as a precursor
to alkylated species. This species is more soluble than 2, and we
reasoned that any hydrocarbyl complex containing the bulkier
IPr ligand might prove more stable than the corresponding
analogue with IMes. Accordingly, treatment of 1 with 2 equiv of
RMgCl (R = Ph, o-tolyl, or Bn) led to formation of chloride-
bridged monoalkyl species of formula [Mn R (μ-Cl) (IPr) ]
elongated Mn−Mn contact of 3.421(1) Å (see Supporting
Information).
Similar reactions to those displayed in eq 5 were also
examined for MeMgCl. Surprisingly, however, no halide-
bridged species was formed from this reaction. Instead, the
methyl-bridged complex [MnMe (μ-Me) (IPr) ] (8) was
2
2
2
isolated as a pale orange solid (eq 6). Solution magnetic
2
2
2
2
1
(4−6, eq 5). The H NMR spectra of 4−6 are essentially
susceptibility measurements on 8 yielded a value of 2.4(2) μB.
This value is indicative of substantial antiferromagnetic
coupling between the Mn centers and is in line with values
reported previously for other methyl-bridged complexes of
featureless, similar to what is observed for 1 and 2 (see
Supporting Information). In no instance were dialkyl
complexes isolated from these reactions even when 4 equiv
of the corresponding Grignard reagent was employed. The
isolation of monoalkyl-monochloride species for Mn(II)
contrasts findings with Fe and Co IPr species, where only
monometallic dialkyl complexes (Fe) or decomposition
products (Co) were obtained upon treatment with these
71,72
Mn(II).
The solid-state structure of 8 is depicted in Figure
3. In like fashion to compounds 4 and 6, 8 crystallizes on an
inversion center. The complex displays a Mn−Mn distance of
2.680(2) Å, which is shorter than that observed in select
systems featuring metal−metal bonding between two low-spin
66,73,74
Mn(II) centers.
It is therefore likely that a Mn−Mn
interaction in 8 arising from the spatial overlap of d orbitals
results in stronger antiferromagnetic coupling as compared with
the chloride-bridged species, consistent with solution phase
magnetic susceptibility measurements. The Mn(1)−C(1)
distance of 2.219(4) Å is comparable to that observed in
compounds 1, 4, and 6, and the Mn(1)−C(30) distance of
45,47,50,70
Grignard reagents.
Moreover, no high-spin phenyl
complex of either Fe or Co has been isolated to date with the
IPr ligand. Compounds 4−6 all proved very sensitive to
ambient conditions, decomposing in a matter of seconds when
exposed to air. The compounds are also thermally sensitive,
especially 4 and 6, which were found to decompose in the solid
state to an intractable black solid when stored at ambient
temperature for several days.
2.136(4) Å is consistent with the terminal Mn−C
distance
benzyl
of 2.142(3) Å in 4. The planar diamond-shaped Mn C core
2
2
features nearly symmetric Mn−C bonds at 2.254(5) and
2.262(5) Å with internal angles of 72.79(14)° and 107.21(14)°
for Mn(1)−C(29)−Mn(1A) and C(29)−Mn(1)−C(29A),
respectively. Similar metric parameters were reported for the
diamond Mn C motifs of other methyl-bridged Mn(II)
The solid-state structures of complexes 4 and 6 are depicted
in Figure 2. The Mn−Mn distances for both compounds are
similar (cf. 3.393(1) Å for 6) and close to that observed for
complex 1 (3.355(1) Å). In line with the Mn−Mn separation
for 4 and 6 is the solution magnetic moment value of 7.0(2) μB
measured for 6, which is consistent with weakly antiferromag-
netically coupled Mn(II) centers. Synthesis of the IMes
analogue of 6, [Mn Ph (u-Cl) (IMes) ] (7), was also
2
2
3
0,71,72
complexes.
To the best of our knowledge, 8 represents
the only example of a bridging-methyl complex of any first-row
75
transition metal containing NHC ligands.
In order to establish the versatility of 1 as a general starting
material for alkylated Mn NHC complexes, we also examined
its ability to serve as precursor to the previously reported three-
2
2
2
2
accomplished by the treatment of 2 with PhMgCl. The solid-
state structure of 7 is very similar to that of 6 with a slightly
C
DOI: 10.1021/acs.organomet.5b00684
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Article
bromocyclohexane and 4-bromotoluene with phenyl Grignard
(
Scheme 2). Complex 1 demonstrated no activity for the
Scheme 2. Attempted Catalytic Reactions of Complex 1
coupling of PhMgCl with 4-bromotoluene. To our surprise,
however, the reaction of PhMgCl with bromocyclohexane in
the presence of 5 mol % of 1 was found to lead to small
amounts (∼25%) of cross-coupled product. This result suggests
that in the presence of excess Grignard, species other than 6
may form that are active for C−C cross-coupling with alkyl
electrophiles. The identity of such species, although unknown
Figure 3. Thermal ellipsoid renderings (50%) of the solid-state
structures of 8. Hydrogen atoms are omitted for clarity. Bond distances
and angles can be found in the Supporting Information.
58
coordinate Mn(II) species [Mn(CH SiMe ) (IPr)]. Treat-
2
3 2
ment of 1 with 4 equiv of Me SiCH MgCl produced, after
3
2
at this time, may likely be per-alkylated Mn(II) complexes given
workup, a mixture of two crystalline species. Mechanical
separation of the mixture afforded a set of white crystals and a
set of pale yellow crystals (Scheme 1). Examination of the
2,25,78,79
the precedent for such compounds
and the propensity
for NHC dissociation observed in the present study.
CONCLUSIONS
■
Scheme 1. Alkylation of Complex 1 with TMSCH MgCl
2
We have demonstrated that simple aryl-substituted NHC
complexes of Mn(II) can be prepared in straightforward fashion
by direct carbene addition to MnCl (THF) . The solid-state
2
1.6
structures and aggregation behavior of manganese chloride
complexes containing IPr and IMes ligands are akin to those of
the corresponding Fe and Co compounds. Despite this
similarity, carbene dissociation from [MnCl (IMes) ] appears
2
2
to occur much more readily in solution. Treatment of
Mn Cl (μ-Cl) (IPr) ] with a series of Grignard reagents
[
2
2
2
2
leads to new hydrocarbyl complexes, nearly all of which are
unprecedented in Fe and Co NHC chemistry. The diversity of
hydrocarbyl complexes isolable with the IPr-Mn(II) system is
greater than that of either Fe or Co and suggests that such
species are more stable. In agreement with this apparent
stability is the lack of reactivity with the prototypical
electrophile, bromocyclohexane. Therefore, the prospect of
catalytic cross-coupling by well-defined Mn(II) NHC com-
plexes appears uncertain. Nonetheless, these new complexes
may in fact offer clues as to the structures of intermediate
species in Fe- and Co-catalyzed reactions.
yellow crystals by X-ray crystallography demonstrated that they
were in fact the desired [Mn(CH SiMe ) (IPr)] complex.
2
3 2
However, X-ray analysis of the white crystals revealed that they
corresponded to the magnesium complex [Mg-
58
(
CH SiMe ) (IPr)], also reported previously by Mulvey.
2 3 2
These results are consistent with less robust IPr coordination to
Mn(II) than in analogous Fe and Co complexes, further
consistent with our observation of carbene dissociation from
4
5,50
3.
As a final set of experiments, we investigated the activity of
EXPERIMENTAL SECTION
■
several of the Mn NHC complexes in C−C bond forming
reactions. Several paramagnetic iron(II) alkyl complexes have
been reported to react rapidly and cleanly with alkyl bromides
General Comments. All manipulations were performed under an
atmosphere of purified nitrogen gas in a Vacuum Atmospheres
glovebox. Tetrahydrofuran, diethyl ether, pentane, and toluene were
purified by sparging with argon gas and passage through two columns
packed with 4 Å molecular sieves. Benzene-d was dried over sodium
ketyl and vacuum-distilled prior to use. H NMR spectra were
53,76,77
to generate the products of C−C coupling.
In contrast,
treatment of complexes 6 and 8 with bromocyclohexane in
THF at room temperature was found to result in no
consumption of the electrophile, as judged by GC-MS.
Therefore, the Mn(II) NHC alkyl complexes examined here
do not appear to be chemically competent in C−C bond
forming reactions. To determine if this lack of reactivity shuts
down any possible catalytic activity, we also investigated the
efficacy of 1 as a pre-catalyst for the cross-coupling of
6
1
recorded in benzene-d on a Varian spectrometer operating at 500
6
1
MHz ( H) and referenced to the residual proton resonance of the
solvent (δ 7.16 ppm). FT-IR spectra were recorded with a
ThermoNicolet iS 10 spectrophotometer running the OMNIC
software; solid samples were pressed into KBr disks. Solution
magnetic susceptibility measurements were determined by the Evans
method without a solvent correction using reported diamagnetic
D
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8
0
corrections. Combustion analyses were obtained from the CENTC
Elemental Analysis Facility at the University of Rochester.
[MnCl (IMes) ], 3. A solution of IMes (36 mg, 0.118 mmol) in
2
2
THF (7 mL) was added to a vial containing 2 (50 mg, 0.058 mmol) to
form a colorless solution. The solution was stirred at room
temperature for 4 h. The volatile components were removed under
reduced pressure, and the residue was rinsed with pentane (5 mL) to
give an off-white solid. The solid was extracted into 5 mL of 2-
MeTHF, filtered, and then concentrated to ∼2 mL. The solution was
set aside at −30 °C for 20 h, during which time colorless crystals
formed. The crystals were isolated by decanting the mother liquor and
washed with pentane to give 43 mg (50%). Crystals suitable for X-ray
diffraction were grown by vapor diffusion of pentane into a saturated
benzene solution of the complex. Due to the observed dissociation of
IMes from the complex in solution, no magnetic susceptibility was
recorded. As with 2, repeated elemental analyses gave low values for
carbon and nitrogen. Anal. Calcd for C H Cl MnN : C, 68.66; H,
Materials. IMes, IPr, and MnCl (THF) were prepared according
to published procedures or slight modification thereof.
2
1.6
8
1−84
4-
Cyanopyridine was purchased from Acros Organics and used as
received. All Grignard reagents were obtained from commercial
suppliers and titrated prior to use with 1-octanol employing 1,10-
phenanthroline as an indicator.
X-ray Data Collection and Structure Solution Refinement.
Crystals suitable for X-ray diffraction were mounted in Paratone oil
onto a glass fiber and frozen under a nitrogen cold stream maintained
by an X-Stream low-temperature apparatus. The data were collected at
9
8(2) K using a Rigaku AFC12/Saturn 724 CCD fitted with Mo Kα
radiation (λ = 0.710 73 Å). Data collection and unit cell refinement
were performed using Crystal Clear software. Data processing and
absorption correction, giving minimum and maximum transmission
factors, were accomplished with Crystal Clear and ABSCOR,
42
48
2
4
6
.59; N, 7.63. Found: C, 63.49; H, 6.46; N, 6.60.
Mn (CH C H ) (μ-Cl) (IPr) ], 4. A solution of C H CH MgCl (90
[
2
2
6
5 2
2
2
6
5
2
8
5,86
respectively.2
All structures were solved by direct methods and
μL, 1.0 M, 0.090 mmol) in THF was added dropwise to a solution of 1
50 mg, 0.049 mmol) in THF (7 mL). The resulting solution
immediately became yellow. The reaction mixture was stirred at room
temperature for 1 h. All volatile materials were removed under reduced
pressure, and the resulting residue was extracted into 5 mL of toluene.
The solution was filtered through Celite, and the toluene was removed
refined on F using full-matrix, least-squares techniques with SHELXL-
(
8
7,88
9
7.
All non-hydrogen atoms were refined with anisotropic
displacement parameters. All carbon-bound hydrogen atom positions
were determined by geometry and refined by a riding model.
Crystallographic data and refinement parameters for each structure
can be found in the Supporting Information.
under reduced pressure. The residue was dissolved in 2 mL of Et O
2
[
Mn Cl (μ-Cl) (IPr) ], 1. A solution of IPr (500 mg, 1.28 mmol) in
2 2 2 2
and set aside at −30 °C for 20 h, during which time yellow crystals
formed. The yellow crystals were isolated by decanting the mother
liquor and washed with pentane to give 25 mg (45%). Crystals suitable
for X-ray diffraction were grown by slow cooling of a saturated toluene
solution at −30 °C. μ (Evans, C D , 25 °C): 6.6(2) μ . Combustion
THF (10 mL) was combined with MnCl (THF) (331 mg, 1.37
2
1.6
mmol) and stirred at room temperature for 12 h. The beige
suspension was then filtered through Celite, and all volatiles were
removed under reduced pressure. The resulting white residue was
extracted into 10 mL of toluene and filtered through Celite. The
volatile components were again removed under reduced pressure to
ensure removal of THF. The white solid was then redissolved in 6 mL
of toluene and set aside at −30 °C for 20 h, during which time
colorless crystals formed. The crystals were isolated by decanting the
mother liquor and washed with pentane to give 498 mg (75%).
Crystals suitable for X-ray diffraction were grown by vapor diffusion of
pentane into a saturated benzene solution of the complex. μeff (Evans,
C D , 25 °C): 6.7(2) μ . Anal. Calcd for C H N Cl Mn : C, 63.04;
eff
6
6
B
analyses of the compound were attempted, but satisfactory values
could not be obtained due its sensitivity. Anal. Calcd for
C H Cl Mn N : C, 71.63; H, 7.60; N, 4.91. Found: C, 66.55; H,
6
8
86
2
2
4
7
.42; N, 3.80.
Mn (2-MeC H ) (μ-Cl) (IPr) ], 5. A solution of 2-MeC H MgCl
[
2
6
4 2
2
2
6
4
(
90 μL, 1.0 M, 0.090 mmol) was added dropwise to a solution of 1 (50
mg, 0.049 mmol) in THF (7 mL) to give a light brown solution. The
solution was stirred for 4 h at room temperature. All volatiles were
removed under reduced pressure. The brown residue was extracted
with toluene (∼7 mL) and filtered through Celite. The filtrate was
dried under reduced pressure. The residue was redissolved in 2 mL of
toluene, filtered, and set aside at −30 °C for 20 h, during which time
brown crystals formed. The crystals were isolated by decanting the
mother liquor and washed with pentane to give 36 mg (65%). μeff
6
6
B
54 72
4
4
2
H, 7.05; N, 5.45. Found: C, 62.81; H, 7.10; N, 5.81.
MnCl (4-CNpy) (IPr)], 1py. A solution of 4-CNpy (15 mg, 0.14
[
2
mmol) in THF (5 mL) was added to a solution of 1 (75 mg, 0.073
mmol) in THF (5 mL) at room temperature. This colorless solution
was stirred at room temperature for 4 h. All volatiles were removed
under reduced pressure. The residue was extracted into 7 mL of
toluene and filtered through Celite. The resulting solution was dried
under reduced pressure, and the remaining colorless solid was rinsed
with pentane (5 mL). The crude product was redissolved in 3 mL of
toluene and set aside at −30 °C for 20 h, during which time colorless
crystals formed. The crystals were decanted and washed with pentane
to give 56 mg (62%). Crystals suitable for X-ray diffraction were grown
by vapor diffusion of pentane into a saturated benzene solution of the
complex. μ (Evans, C D , 25 °C): 5.7(2) μ . IR (νCN, KBr): 2242
(
Evans, C D , 25 °C): 7.6(2) μ . As with 4, the sensitivity of the
6 6 B
compound hampered combustion analysis. Anal. Calcd for
C H N Cl Mn : C, 71.63; H, 7.60; N, 4.91. Found: C, 70.40; H,
68 86
4
2
2
7
.62; N, 4.83.
Mn (C H ) (μ-Cl) (IPr) ], 6. A solution of C H MgCl (70 μL, 2.78
[
2
6
5 2
2
2
6
5
M, 0.19 mmol) in THF was added dropwise to a solution of 1 (100
mg, 0.097 mmol) in THF (7 mL) to give a light yellow solution. The
solution was stirred at room temperature for 4 h. The volatile
components were removed under reduced pressure, and the resulting
residue was extracted into 7 mL of toluene. After filtration, the toluene
solution was evaporated under reduced pressure. The residue was
eff
6
6
B
−1
cm . Anal. Calcd for C H N Cl Mn: C, 64.08; H, 6.52; N, 9.06.
Found: C, 64.74; H, 6.40; N, 9.03.
Mn Cl (μ-Cl) (IMes) ], 2. A solution of IMes (139 mg, 0.455
mmol) in THF (7 mL) was combined with MnCl (THF) (118 mg,
.489 mmol) to give a beige mixture. The mixture was stirred at room
temperature for 12 h. The volatile components were removed under
reduced pressure to give an off-white solid, which was washed with 5
mL of toluene. The yield of the crude product is essentially
quantitative. The crude material was extracted into 10 mL of hot 2-
MeTHF and filtered through Celite. The resulting solution was
concentrated (∼4 mL) and set aside at −30 °C for 20 h, during which
time colorless crystals formed. The crystals were isolated by decanting
the mother liquor and washed with pentane to give 50 mg (13%). The
poor solubility of this complex in most organic solvents resulted in low
yields of recrystallized material. Repeated combustion analyses of the
compound consistently gave low values for carbon and nitrogen. Anal.
Calcd for C H Cl Mn N : C, 58.62; H, 5.62; N, 6.51. Found: C,
3
3
40
4
2
[
2
2
2
2
dissolved in 2 mL of Et O, filtered, and set aside at −30 °C for 20 h,
2
2
1.6
during which time pale yellow-brown crystals formed. The crystals
were isolated by decanting the mother liquor and washed with pentane
0
to give 71 mg (66%). μeff (Evans, C D , 25 °C): 7.0(2) μ . As with 4,
6
6
B
the sensitivity of the compound hampered combustion analysis. Anal.
Calcd for C66 Mn : C, 71.28; H, 7.43; N, 5.04. Found: C,
66.22; H, 9.02; N, 4.53.
[Mn (C (μ-Cl) (IMes)
mL, 2.0 M, 0.27 mmol) in THF was added dropwise to a suspension
of 2 (100 mg, 0.136 mmol) in Et O cooled to −30 °C. The solution
H
82Cl
N
2 4
2
H
6
)
2
], 7. A solution of C H MgCl (0.136
2 6 5
2
5
2
2
was then stirred at room temperature for 1 h. The volatile materials
were removed under reduced pressure. The residue was extracted into
8 mL of toluene and filtered through Celite. Concentration of the
toluene solution and storage at −30 °C produced crystals of 7 suitable
for X-ray diffraction.
42
48
4
2
4
5
6.63; H, 5.58; N, 5.73.
E
DOI: 10.1021/acs.organomet.5b00684
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
[
Mn (CH ) (μ-CH ) (IPr) ], 8. A solution of MeMgCl (110 mL, 3.0
2 3 2 3 2 2
ACKNOWLEDGMENTS
■
M, 0.33 mmol) in THF was added dropwise to a solution of 1 (83 mg,
.081 mmol) in THF (7 mL) to give an orange solution. The solution
The authors acknowledge UTSA and the Welch Foundation
AX-1772 to Z.J.T.) for financial support of this work. The
CENTC Elemental Analysis Facility is supported by NSF
(CHE-0650456).
0
(
was allowed to stir at room temperature for 1 h. The volatile
components were removed under reduced pressure. The residue was
extracted into 7 mL of toluene and filtered through Celite. The filtrate
was concentrated to ∼2 mL and stored at −30 °C for 20 h, during
which time pale orange crystals formed. The crystalline solid was
isolated by decanting the mother liquor and washed with pentane to
give 58 mg (76%). Crystals suitable for X-ray diffraction were grown
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6 6 B 58 84 4 2
7
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ASSOCIATED CONTENT
■
*
S
Supporting Information
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AUTHOR INFORMATION
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*
Corresponding Author
E-mail: zachary.tonzetich@utsa.edu.
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F
DOI: 10.1021/acs.organomet.5b00684
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G
DOI: 10.1021/acs.organomet.5b00684
Organometallics XXXX, XXX, XXX−XXX