Synthesis and protonation of an encumbered iron tetraisocyanide dianion

Article abstract of DOI:10.1021/acs.inorgchem.5b00730

Reported here are synthetic studies probing highly reduced iron centers in an encumbering tetraisocyano ligand environment. Treatment of FeCl₂ with sodium amalgam in the presence of 2 equiv of the m-terphenyl isocyanide CNAr^Mes2 (Ar^Mes2 = 2,6-(2,4,6-Me₃C₆H₂)₂C₆H₃) produces the disodium tetraisocyanoferrate Na₂[Fe(CNAr^Mes2)₄]. Structural characterization of Na₂[Fe(CNAr^Mes2)₄] revealed a tight ion pair, with the Fe center adopting a tetrahedral coordination geometry consistent with a d¹⁰ metal center. Attempts to disrupt the cation-anion contacts in Na₂[Fe(CNAr^Mes2)₄] with cation-sequestration reagents lead to decomposition, except for the case of 18-crown-6, where a mononuclear complex featuring a dianionic 1-azabenz[b]azulene ligand was isolated in low yield. Formation of this 1-azabenz[b]azulene is rationalized to proceed by an aza-Büchner ring expansion of a CNAr^Mes2 ligand mediated by a coordinatively unsaturated Fe center. Disodium tetraisocyanoferrate Na₂[Fe(CNAr^Mes2)₄] is readily protonated by trimethylsilanol (HOSiMe₃) to produce the monohydride ferrate salt, Na[HFe(CNAr^Mes2)₄], the anionic portion of which serves as an isocyano analogue of the hydrido-tetracarbonyl metalate [HFe(CO)₄]^-. Treatment of Na[HFe(CNAr^Mes2)₄] with methyl triflate (MeOTf; OTf = [O₃SCF₃]^-) at low temperature in the presence of dinitrogen yields the five-coordinate Fe(0) complex Fe(N₂)(CNAr^Mes2)₄. The formation of Fe(N₂)(CNAr^Mes2)₄ in this reaction is consistent with the intermediacy of the neutral tetraisocyanide Fe(CNAr^Mes2)₄. The decomposition of Fe(N₂)(CNAr^Mes2)₄ to the dimeric complex [Fe(?⁶-(Mes)- 14;²-C-CNAr^Mes)]₂ and a seven-membered cyclic imine derived from a CNAr^Mes2 ligand is presented and provides insight into the ability of CNAr^Mes2 and related m-terphenyl isocyanides to stabilize zerovalent four-coordinate iron complexes in a strongly π-acidic ligand field.

Full text of DOI:10.1021/acs.inorgchem.5b00730

Article
pubs.acs.org/IC
Synthesis and Protonation of an Encumbered Iron Tetraisocyanide
Dianion
Charles C. Mokhtarzadeh, Grant W. Margulieux, Alex E. Carpenter, Nils Weidemann, Curtis E. Moore,
Arnold L. Rheingold, and Joshua S. Figueroa*
Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Drive Mail Code 0358, La Jolla
California 92093-0358, United States
S
* Supporting Information
ABSTRACT: Reported here are synthetic studies probing highly reduced
iron centers in an encumbering tetraisocyano ligand environment.
Treatment of FeCl2 with sodium amalgam in the presence of 2 equiv of
the m-terphenyl isocyanide CNArMes2 (ArMes2 = 2,6-(2,4,6-
Me3C6H2)2C6H3) produces the disodium tetraisocyanoferrate Na2[Fe-
(CNArMes2)4]. Structural characterization of Na2[Fe(CNArMes2)4] revealed
a tight ion pair, with the Fe center adopting a tetrahedral coordination
geometry consistent with a d10 metal center. Attempts to disrupt the
cation−anion contacts in Na2[Fe(CNArMes2)4] with cation-sequestration
reagents lead to decomposition, except for the case of 18-crown-6, where a
mononuclear complex featuring a dianionic 1-azabenz[b]azulene ligand
was isolated in low yield. Formation of this 1-azabenz[b]azulene is
rationalized to proceed by an aza-Buchner ring expansion of a CNArMes2
̈
ligand mediated by a coordinatively unsaturated Fe center. Disodium
tetraisocyanoferrate Na2[Fe(CNArMes2)4] is readily protonated by trimethylsilanol (HOSiMe3) to produce the monohydride
ferrate salt, Na[HFe(CNArMes2)4], the anionic portion of which serves as an isocyano analogue of the hydrido-tetracarbonyl
metalate [HFe(CO)4]−. Treatment of Na[HFe(CNArMes2)4] with methyl triflate (MeOTf; OTf = [O3SCF3]−) at low
temperature in the presence of dinitrogen yields the five-coordinate Fe(0) complex Fe(N2)(CNArMes2)4. The formation of
Fe(N2)(CNArMes2)4 in this reaction is consistent with the intermediacy of the neutral tetraisocyanide Fe(CNArMes2)4. The
decomposition of Fe(N2)(CNArMes2)4 to the dimeric complex [Fe(η6-(Mes)-μ2-C-CNArMes)]2 and a seven-membered cyclic
imine derived from a CNArMes2 ligand is presented and provides insight into the ability of CNArMes2 and related m-terphenyl
isocyanides to stabilize zerovalent four-coordinate iron complexes in a strongly π-acidic ligand field.
The impetus for generating and studying isocyanide analogues
of the carbonyl metalates stems from the fact that isocyanides
are excellent π-acids, but are far stronger σ-donors than carbon
monoxide.19−24 Accordingly, efforts have been made to exploit
this difference in σ-donor-strength to provide a class of highly
reduced organometallics that display nucleophilic character
exceeding that of the homoleptic carbonyl metalates. In recent
years, our group has extended the chemistry of isocyano
metalates through the use of sterically encumbering m-
terphenyl isocyanide ligands.25−35 The goal of these inves-
tigations has been to couple the potentially increased
nucleophilicity of isocyano metalates with a kinetically
stabilizing steric environment. This approach has resulted in
the successful synthesis of the tetraisocyano cobalt monoanion,
[Co(CNArMes2)4]− (ArMes2 = 2,6-(2,4,6-Me3C6H2)2C6H3),36
which retains a mononuclear formulation upon oxidation, and
a highly reactive synthon for the coordinatively unsaturated
trisisocyano cobalt monoanion, [Co(CNArMes2)3]−.37
INTRODUCTION
■
Tetracarbonylferrate(2−) ([Fe(CO)4]2−) is one of the most
well-known and well-studied organometallic complexes.1−5 It
has been shown to mediate a host of important transformations
in organic synthesis including carbonylation, reductive
coupling, reduction, and nucleophilic displacement.2,5 This
inherent reactivity of [Fe(CO)4]2− originates from a high-
energy, closed-shell, d10 orbital manifold that manifests from a
doubly reduced, formally Fe(2−) center. It is well-understood
that π-backbonding interactions to the carbonyl ligands stabilize
the excess charge equivalents on the Fe center of this dianion.4,6
However, the degree of π-backbonding, while significant, does
not preclude the Fe center from functioning readily as a
nucleophile toward a wide range of electrophilic substrates.2
In 2007, Ellis reported the first tetraisocyano analogue of
[Fe(CO)4]2−, namely, [Fe(CNXyl)4]2− (Xyl = 2,6-Me2C6H3),7
and showed that it exhibits structural features and a reactivity
profile toward ClSnPh3 similar to that of [Fe(CO)4]2−.8 This
work advanced the long-standing interest in isocyanide variants
of the carbonyl metalates,9−18 which began with Cooper’s
synthesis of [Co(CNXyl)4]− as an analogue of [Co(CO)4]−.9
Received: March 31, 2015
© XXXX American Chemical Society
A
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In this article, we expand our work on m-terphenyl
isocyanide-supported metalates and present the synthesis and
characterization of [Fe(CNArMes2)4]2−, which is a sterically
encumbered variant of Ellis’ dianion, [Fe(CNXyl)4]2−. We also
demonstrate that [Fe(CNArMes2)4]2− is protonated readily,
leading to the reactive monohydride isocyanometalate [HFe-
(CNArMes2)4]−. Both [Fe(CNArMes2)4]2− and [HFe-
(CNArMes2)4]− display properties that parallel their well-
known carbonyl analogues (i.e., [Fe(CO)4]2− and [HFe-
(CO)4]−),38 but also display distinct reactivity and decom-
position profiles that are emblematic of a sterically encumbered
isocyano environment.
Single crystals of Na2[Fe(CNArMes2)4] (Na2[1]) can be
grown from a saturated Et2O solution stored at −35 °C. In the
solid state, Na2[Fe(CNArMes2)4] (Na2[1]) is found as an
unsolvated contact-ion pair41 with significant interactions
between the Na cations and isocyano CN units, as well as
between the Na cations and the π-faces of the CNArMes2 mesityl
rings (Figure 1). In this regard, the solid-state structure of
RESULTS AND DISCUSSION
■
Treatment of 2 equiv of CNArMes2 with FeCl2 followed by the
addition of sodium amalgam provides the disodium tetraiso-
cyanoferrate salt, Na2[Fe(CNArMes2)4] (Na2[1]), as a brick red
crystalline solid in 23% isolated yield (Scheme 1). While the
Scheme 1
Figure 1. Molecular structure of Na2[Fe(CNArMes2)4] (Na2[1]).
Na2[Fe(CNArMes2)4] (Na2[1]) resembles that of the cobalt
isocyanometalate, Na[Co(CNArMes2)4], which likewise ex-
hibited Na/isocyano and Na/π-arene interactions.36 Despite
this ion pairing, however, the Fe center in Na2[Fe(CNArMes2)4]
(Na2[1]) adopts a tetrahedral coordination geometry (Houser
τ4 geometry index42 = 0.97) as expected for a d10, four-
coordinate metal center.
The metrical parameters associated with Na2[Fe-
(CNArMes2)4] (Na2[1]) are also consistent with a substantial
degree of Fe-to-isocyanide π-back-donation. As shown in Table
1, Na2[1] exhibits very short average Fe−Ciso bond lengths and
yield of Na2[Fe(CNArMes2)4] (Na2[1]) by this protocol is
modest, the reaction can be carried out at room temperature
and does not require a slow addition of reducing agent.7
Notably, use of a higher equivalency of CNArMes2 in this
reaction does not lead to improved yields. Tetraisocyanoferrate
Na2[Fe(CNArMes2)4] (Na2[1]) gives rise to a single, sharp set
Table 1. Average Fe−Ciso and Ciso−Niso Bond Distances for
Tetraisocyano and Related Iron Complexes
d(Fe−Ciso
)
d(Ciso−Niso)
av
av
1
of ArMes2 resonances in its H NMR spectrum (C6D6). The
compd
(Å)
(Å)
13C{1H} NMR spectrum of Na2[Fe(CNArMes2)4] (Na2[1])
likewise displays a single ArMes2 environment and additionally
features a significantly deshielded resonance at +219.2 ppm
assigned to the Fe-bound isocyano carbon atoms. Notably, the
large downfield 13C{1H} NMR resonance for the Fe-bound
carbon atoms in Na2[Fe(CNArMes2)4] (Na2[1]) is consistent
with those observed for both K2[Fe(CNXyl)4] and K2[Fe-
(CO)4] (238.7 and 234.6 ppm,7 respectively) and can be
considered an NMR spectroscopic marker for significant Fe-to-
ligand π-back-donation.15,39,40 The solution IR spectrum
(C6D6) of Na2[Fe(CNArMes2)4] (Na2[1]) is also in line with
this interpretation and features a broad, prominent band
centered at 1682 cm−1 assignable to a low-energy isocyanide
ν(CN) stretch. In comparison, K2[Fe(CNXyl)4] also gives rise
to a broad, low-energy ν(CN) band centered at 1670 cm−1
(THF).7
a
Na2[Fe(CNArMes2)4] (Na2[1])
1.789(18)
1.765(3)
1.869(3)
1.845(6)
1.877(2)
1.801(17)
1.843(20)
1.219(17)
1.237(7)
1.157(3)
1.160(5)
1.152(2)
1.208(20)
b
[K(crypt-[2.2.2])]2[Fe(CNXyl)4]
Fe(CO)4(CNArMes2) (2)
a
Fe(CO)3(CNArMes2)2 (3)
cis,cis,trans-FeI2(CO)2(CNArMes2)2 (4)
Na[HFe(CNArMes2)4] (Na[6])
Fe(N2)(CNArMes2)4 (7)
1.186(8)
a
b
Average of two crystallographically independent molecules. Ref 7.
significantly elongated average Ciso−N bond lengths relative to
the formally Fe(0) complexes Fe(CO)4(CNArMes2) (2) and
Fe(CO)3(CNArMes2)2 (3), and the formally Fe(II) complex
cis,cis,trans-FeI2(CO)2(CNArMes2)2 (4) (Figure 2). However,
the average Fe−Ciso and Ciso−N bond lengths in Na2[1] are
slightly longer and slightly shorter, respectively, than the
B
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Figure 2. Molecular structures of Fe(CO)4(CNArMes2) (2, left), Fe(CO)3(CNArMes2)2 (3, center), and cis,cis,trans-FeI2(CO)2(CNArMes2)2 (4, right).
corresponding parameters found in Ellis’ discrete dianion
[Fe(CNXyl)4]2−, isolated as its di-[K-[2.2.2]cryptand)]+ salt
(Table 1).7 We believe these small differences arise from the
steric constraints placed on the [Fe(CNR)4]2− core by both the
m-terphenyl groups and the tightly bound sodium cations,
rather than an electronic difference between the aryl
isocyanides CNArMes2 and CNXyl. Indeed, we have recently
shown that CNArMes2 and CNXyl exert a nearly identical
electronic influence on metal centers, despite the presence of
encumbering ortho-mesityl substituents in the former.24
In contrast to K2[Fe(CNXyl)4],7 disruption of the cation−
anion interactions in Na2[1] with cryptands or crown ethers
does not provide a discrete example of [Fe(CNArMes2)4]2−.
Several attempts to encapsulate the Na cations in Na2[1] with
15-crown-5 or dibenzo-18-crown-6 in THF or Et2O solution
led to intractable mixtures, with free CNArMes2 being the
dominant product. These observations mirror those made for
the cobaltate salt Na[Co(CNArMes2)4], for which Na−anion
interactions can only be disrupted when “coordinating” cations
are employed.36,37 In addition, other highly reduced carbonyl
Figure 3. Molecular structure of [Na(18-crown-6)][(η5-Me6-1-
metalates are known to decompose upon attempts to separate
azabenz[b]azulene)Fe(CNArMes2)2] (5).
contact alkali-metal cation/anion pairs.4 However, when
Na2[1] was treated with 2.0 equiv of 18-crown-6 (18-c-6),
the bis-isocyanide cycloheptatrienyl product 5 (Figure 3) was
CNArMes2 dissociation when its cation/anion contacts are
isolated in very low yield (ca. 2%) as red-brown single crystals.
disrupted.36,37
The remainder of the reaction mixture contained free CNArMes2
and several other decomposition products as assayed by H
While Na2[1] is not well behaved in cation-encapsulation
reactions, it does react with certain protic sources to yield an
1
NMR spectroscopy. Whereas the low isolated yield prevented
isocyano analogue of Na[HFe(CO)4]. As shown in Scheme 1,
full characterization by spectroscopic techniques, it is notable
treatment of Na2[1] with trimethylsilanol (HOSiMe3; pKa ≈
11.5 (DMSO)48−50) generates the anionic monohydride
that complex 5 is formally an Fe(I) species reminiscent of the
unstable metalloradical CpFe(CO)2.43 In addition, it is
complex Na[HFe(CNArMes2)4] (Na[6]) as a red-orange
important to note that the η5-cycloheptatrienyl unit in 5 is
crystalline solid. Notably, treatment of cold (∼ −100 °C)
part of a formally dianionic 1-azabenz[b]azulene formed from
Et2O solutions of Na2[1] with 1.0 equiv of stronger Brønsted
an apparent aza-Buchner ring expansion of a CNArMes2
̈
acids, such as 3,5-dimethylbenzoic acid, pivalic acid, pyridinium
chloride ([Hpy]Cl), and ethylammonium chloride ([EtNH3]-
Cl),51 led to complex mixtures containing unreacted starting
material, free ligand, and several unidentified products.
Although not conclusively observed, we presume these
reactions produce the neutral dihydride complex H2Fe-
(CNArMes2)4, which rapidly decomposes under the conditions
surveyed. In contrast however, monohydride Na[6] does not
react with additional equivalents of HOSiMe3 in Et2O solution.
Accordingly, as has been established for the tetracarbonyl
monoanion [HFe(CO)4]−,38,52 this observation indicates that
tetraisocyanide Na[6] exhibits only moderate Brønsted basicity
in nonpolar media.
ligand.44−46 While the mechanistic sequence leading to the
formation of complex 5 is presently unknown, Arnold has
reported a similar aza-Buchner ring expansion for CNArMes2 in
̈
the presence of a highly reduced, low-coordinate zirconium
center.47 On the basis of this precedent, we presume that
removal of a Na cation from Na2[1] by 18-c-6 may allow for
CNArMes2 dissociation and formation of a low-coordinate
ferrate that is capable of inducing an aza-Buchner expansion by
̈
initial coordination of a flanking mesityl ring. In this respect,
the chemistry of Na2[1] may mirror that of the tetra-isocyano
cobaltate salt Na[Co(CNArMes2)4]−, which has been shown to
yield an equivalent of three-coordinate [Co(CNArMes2)3]− via
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Crystallographic characterization of Na[HFe(CNArMes2)4]
(Na[6]) revealed an unsolvated contact-ion pair with
interactions between the Na cation and both the mesityl (i.e.,
π-arene) and CN units of the CNArMes2 ligands (Figure 4).
Scheme 2
Figure 4. Molecular structure of Na[HFe(CNArMes2)4] (Na[6]).
These contacts result in an Fe coordination geometry in the
solid state that is intermediate between trigonal bipyramidal
and square pyramidal on the basis of the Addison−Reedijk τ5
geometry index (τ5 for Na[6] = 0.53).53 Nevertheless, Na[6]
1
gives rise to a single set of ArMes2 resonances in its H NMR
spectrum (C6D6) at room temperature, thereby indicating that
the [Na]+/CNArMes2 contacts do not prevent a high degree of
fluxionality for the five-coordinate Fe center in solution. The IR
spectrum of Na[HFe(CNArMes2)4] (Na[6]) in C6D6 solution
displays several broad and unresolved bands in the ν(CN)
stretching region, which is consistent with a lowering of the
local site symmetry of either an idealized trigonal bipyramidal
Figure 5. Molecular structure of Fe(N2)(CNArMes2)4 (7).
(C3v) or square pyramidal (Cs) center by the Na cation.54
A
similar lowering of idealized site symmetry was observed in the
solution IR spectrum of the related cobaltate salt Na[Co-
(CNArMes2)4]36 and is also well-known to occur for alkali-metal
salts of [HFe(CO)4]− and its monophosphine derivatives (i.e.,
[HFe(CO)3(PR3)]−).54−56 However, the ν(CN) bands for
Na[6] fall within the range 1994−1828 cm−1 and are markedly
higher in energy that found for the dianion Na2[Fe-
(CNArMes2)4] (Na2[1]). In addition, the Fe−Ciso bond lengths
in the solid-state structure of Na[6] are elongated relative to
Na2[1] (Table 1), but are significantly shorter than those found
in the formally Fe(0) complexes Fe(CO)4(CNArMes2) (2) and
trigonal bipyramidal coordination geometry (τ5 = 0.86),53 with
the N2 ligand located in an equatorial position. The solution IR
spectrum of Fe(N2)(CNArMes2)4 (7) features a ν(NN) band
centered at 2067 cm−1, which is reflective of weak NN bond
activation in the context of mononuclear Fe(0) dinitrogen
complexes.57 Most importantly however, this product outcome
from the reaction between Na[6] and MeOTf mirrors those
established by Whitmire for the reactivity of alkyl iodides with
[HFe(CO)4]−.58 Furthermore, in these latter studies, the
unstable paramagnetic (S = 1) tetracarbonyl complex, Fe-
(CO)4,59−61 has been proposed as an unobservable inter-
mediate, which then rapidly undergoes ligand redistribution
and aggregation reactions. For the reaction between Na[6] and
MeOTf, the steric encumbrance provided by the CNArMes2
ligands presumably imparts the analogous tetraisocyanide
complex Fe(CNArMes2)4 with a lifetime sufficient to be trapped
by dinitrogen present within the reaction mixture. Notably,
several isolable zerovalent FeL4 complexes have now been
reported.62−64 However, none to date feature L-type ligands
with two orthogonal π* orbitals akin to CO, which would
render such complexes as precise electronic analogues to the
high-spin, binary carbonyl Fe(CO)4. In this respect, complex 7
potentially points to a molecular-design strategy for the
Fe(CO)3(CNArMes2
)
(3). These data and comparisons
2
indicate that the Fe center in Na[HFe(CNArMes2)4] (Na[6])
remains highly reduced and, as is the case for [HFe(CO)4]−,38
may likewise be reactive toward strong electrophiles despite
exhibiting only moderate Brønsted basicity.
To test this hypothesis, Na[HFe(CNArMes2)4] (Na[6]) was
treated with methyl triflate (MeOTf; [OTf]− = [O3SCF3]−) at
−40 °C in Et2O solution. This reaction proceeds readily
without the buildup of detectable intermediates to yield
methane (CH4) and the zerovalent dinitrogen complex,
Fe(N2)(CNArMes2
)
(7), as determined by both 1H NMR
4
spectroscopy and single-crystal X-ray diffraction (Scheme 2,
Figure 5). In the solid state, dinitrogen complex 7 adopts a near
D
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isolation of kinetically stabilized FeL4 complexes that more
appropriately mimic the electronic features of Fe(CO)4.
tion, we speculate that the driving force for the production of
dimer 8 in this reaction stems from the formation of a strong
η6-arene interaction as a means to provide a coordinatively
saturated Fe center. Formation of flanking-ring η6-arene
interactions from m-terphenyl isocyanides in this fashion is
reminiscent of our previous studies on the in-situ-generation of
three-coordinate Co and Mo isocyanide complexes.35,37 Most
importantly however, this reaction indicates that the CNArMes2
framework, although seemingly able to extend the lifetime of
putative Fe(CNArMes2)4, is not resistant to degradation
processes and secondary binding interactions by a low-
coordinate Fe(0) center. Therefore, an alternative isocyanide
architecture that is not susceptible to C−H activation or the
formation of a strong η6-arene interaction is required,24,35 at
minimum, to generate an isolable Fe(CNR)4 complex and
complete the series of isocyano analogues to the classic
mononuclear iron carbonyls Fe(CO)5,71 [Fe(CO)4]2−,7 [HFe-
(CO)4]−, and Fe(CO)4.
Thus, while the dinitrogen complex Fe(N2)(CNArMes2)4 (7)
can be viewed as a trapped form of Fe(CNArMes2)4, it is critical
to note that the dissociation of N2 from the Fe center results in
a multistep decomposition process. Furthermore, this decom-
position sequence highlights the points of incompatibility of the
CNArMes2 ligand for the goal of isolating a kinetically persistent
FeL4 species. Accordingly, when crystals of 7 are dissolved in
either C6D6 or Et2O at room temperature, complete conversion
to the diamagnetic, symmetric dimer [Fe(η6-(Mes)-μ2-C-
CNArMes)]2 (8) is observed over the course of ca. 4 h. Dimer
8 has been crystallographically characterized (Figure 6), and its
CONCLUSIONS
■
Isocyano analogues of the classic carbonyl metalates remain
intriguing synthetic targets to explore the effect of enhanced
metal-based nucleophilicity within a strongly π-acidic ligand
field. Coupling this electronic environment with a sterically
encumbering ligand topology potentially offers the ability to
further control or augment the reactivity of highly reduced
metal centers toward substrate molecules in both stoichiometric
and catalytic transformations. Here, we show that an
encumbering m-terphenyl isocyanide variant of [Fe(CO)4]2−,
namely [Fe(CNArMes2)4]2−, can be readily prepared and
isolated as a disodium contact-ion pair. The nucleophilic
character of Na2[Fe(CNArMes2)4] has been demonstrated by its
reaction with HOSiMe3 to produce the monohydride
monoanion [HFe(CNArMes2)4]−, which serves as a unique
isocyanide analogue of [HFe(CO)4]−. The latter is also shown
to react readily with MeOTf at low temperatures to produce
methane and the dinitrogen complex Fe(N2)(CNArMes2)4,
likely via the intermediacy of the four-coordinate Fe(0) species,
[Fe(CNArMes2)4]. Accordingly, this synthetic sequence illus-
trates a reaction chemistry for these isocyanometalates
paralleling that of the classic iron carbonylmetalates. We
believe the synthetic results presented here will enable further
development of small-molecule activation processes at a
sterically protected but nucleophilic Fe center. In addition,
this work has suggested the minimum requirements necessary
for an isocyanide ligand framework capable of stabilizing highly
reduced Fe centers with low coordination numbers.
Figure 6. Molecular structure of [Fe(η6-(Mes)-μ2-C-CNArMes)]2 (8).
solid-state structure shows that CNArMes2 ligands adopt a μ2-
bridging mode, and also provide an η6-arene interaction to the
Fe centers. In this respect, dimer 8 serves as a valence-
isoelectronic analogue to the neutral, bridging carbonyl dimer
[CpCo(μ2-CO)]2, which has been subject to both extensive
experimental and computational studies.65−69 However, along
with dimer 8, the decomposition of Fe(N2)(CNArMes2)4 (7)
also produces 2 equiv of free CNArMes2 and the 7-membered
cyclic imine 9 (Scheme 2), which was isolated from the reaction
mixture and structurally characterized by X-ray diffraction
(Figure 7).
EXPERIMENTAL SECTION
■
General Considerations. All manipulations were carried out
under an atmosphere of dry dinitrogen or argon using standard
Schlenk and glovebox techniques. Solvents were dried and degassed
according to standard procedures.72 The isocyanide ligand CNArMes2
was prepared as previously reported.25 Unless otherwise stated, all
other materials were obtained from commercial vendors and used as
received. Benzene-d6 was dried with Na/K/benzophenone followed by
distillation and storage over 4 Å molecular sieves for 3 days prior to
use. Celite 405 (Fischer Scientific) was dried under vacuum for 24 h at
a temperature greater than 250 °C and stored in a glovebox prior to
use.
Figure 7. Molecular structure of cyclic imine (9).
The formation of imine 9 can be rationalized by the
mechanistic sequence shown in Scheme 3, which proceeds by
methyl-group C−H activation by four-coordinate Fe-
(CNArMes2)4, followed by alkyl migration to a “tethered”
isocyano unit and subsequent C−H bond reductive elimination.
Notably, Jones has proposed a similar mechanism for the
production of C-phenyl aldimines from isocyanides and
benzene mediated by the related, and likewise unobservable,
four-coordinate Fe species [Fe(PMe3)2(CNXyl)2].70 In addi-
1
Solution H, 13C{1H} NMR spectra were recorded on a Varian
Mercury 400 spectrometer and a Varian XSENS-500 spectrometer. 1H
and 13C{1H} chemical shifts are reported in ppm relative to SiMe4 (1H
and 13C δ = 0.0 ppm) with reference to residual C6D5H solvent
E
DOI: 10.1021/acs.inorgchem.5b00730
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Inorganic Chemistry
Article
Scheme 3
references of 7.16 ppm (1H) and 128.06 ppm (13C) for benzene-d6.73
FTIR spectra were recorded on a Thermo-Nicolet iS10 FTIR
spectrometer. Samples were prepared either as KBr pellets or as
C6D6 solutions injected into a Thermo-Fisher solution cell equipped
with KBr windows. For solution FTIR spectra, solvent peaks were
digitally subtracted from all spectra by comparison with an authentic
spectrum obtained immediately prior to that of the sample. The
following abbreviations were used for the intensities and characteristics
of important IR absorption bands: vs = very strong, s = strong, m =
medium, w = weak, vw = very weak, b = broad, vb = very broad, sh =
shoulder. High-resolution mass spectrometry (HRMS) was performed
using an Agilent 6230 ESI-TOFMS running in positive or negative ion
mode as necessary. Photolysis experiments were performed with a 254
nm model UVGL-25 Hg lamp (UVP, Inc., Upland, CA). Combustion
analyses were performed by Midwest Microlab LLC, Indianapolis, IN.
Synthesis of Na2[Fe(CNArMes2)4] (Na2[1]). To a suspension of
anhydrous FeCl2 (0.607 g, 4.79 mmol, 1 equiv) in a 70:30 Et2O/THF
mixture (100 mL) was added CNArMes2 (3.08 g, 9.1 mmol, 1.9 equiv).
The resultant suspension was allowed to stir for 5 min whereupon
0.9% sodium amalgam (Na/Hg) was added (Na 1.10 g, 47.9 mmol, 10
equiv; Hg 122 g). The reaction mixture was then shaken vigorously for
20 min resulting in a color change from pale yellow to deep red. After
shaking, the reaction mixture was allowed to stir for an additional 1 h.
The supernatant was then decanted from the Na/Hg, filtered over
Celite, and evaporated to dryness. The resultant red solid was slurried
in n-pentane (30 mL) followed by evaporation to dryness. This was
repeated two additional times to desolvate the NaCl byproduct. The
red solid then obtained was then extracted with C6H6 (40 mL), filtered
over Celite, and then lyophilized under reduced pressure (∼100
mTorr). This process was repeated an additional time to ensure
removal of NaCl and Fe(0) byproducts. The resultant dark red solid
was then crystallized at −40 °C from a layered THF/n-pentane (1:6)
solution over the course of 2 days. The dark red crystals thereby
obtained were washed with n-pentane (4 mL) and then dried in vacuo.
Yield: 1.60 g, 1.1 mmol, 23%. Analytically pure crystals were obtained
from storage of a layered toluene/n-hexane solution (10:1 v/v) at −40
°C for 3 days. 1H NMR (499.8 MHz, C6D6, 20 °C): δ = 6.83 (t, 4H, J
= 8 Hz, p-Ph), 6.78 (d, 8H, J = 8 Hz, m-Ph), 6.74 (s, 16H, m-Mes),
6.24 (s, 24H, p-CH3 Mes), 2.24 (s, 24H, p-CH3 Mes), 2.09 (s, 48H, o-
CH3 Mes) ppm. 13C{1H} NMR (125.7 MHz, C6D6, 20 °C) δ = 219.2
(CNR), 140.1, 137.9, 136.8, 135.3, 134.8, 130.3, 128.4, 120.7, 21.6 (o-
CH3 Mes), 21.4 (p-CH3 Mes) ppm. FTIR (C6D6, KBr windows, 25
°C): vCN = 1682 (s), 1607 (sh) cm−1 also 2956 (m), 2920 (m), 2872
(m), 2856 (m), 2038 (m), 2009 (m), 1567 (s), 1484 (w), 1439 (w),
1406 (s) 1377 (m), 1284 (w), 1271 (w), 1252 (w), 1223 (w), 1205
(w), 1095 (w), 1068 (w), 1034 (m), 852 (m), 754 (m), 636 (w), 571
(w) cm−1. Anal. Calcd for C100H100N4Na2Fe: C, 82.28; H, 6.91; N,
3.84. Found C, 81.89; H, 6.87; N, 3.79.
Synthesis of Fe(CO)4(CNArMes2) (2). A 100 mL resealable
ampoule was charged with C6H6 (5 mL) and Fe2(CO)9 (0.537 g,
1.47 mmol) and then stirred for 5 min. Solid CNArMes2 (1.00 g, 2.95
mmol, 2 equiv) was then added over the course of 5 min. The
resulting mixture was refluxed for 5 days and then concentrated to a
solid under reduced pressure. The solid was then extracted with n-
pentane (40 mL) and filtered through Celite. The filtrate was then
evaporated to dryness under reduced pressure. The resulting residue
was dissolved in n-pentane (15 mL), filtered, and stored at −40 °C to
afford pale yellow crystals, which were collected and dried in vacuo.
1
Yield: 0.746 g, 1.47 mmol, 49.8%. H NMR (499.8 MHz, C6D6, 20
°C): δ = 6.94 (t, 1H, J = 8 Hz, p-Ph), 6.91 (s, 4H, m-Mes), 6.82 (d,
2H, J = 8 Hz, o-Ph), 2.21 (s, 6H, p-CH3 Mes), 2.02 (s, 12H, o-CH3
Mes) ppm. 13C{1H} NMR (100.6 MHz, C6D6, 20 °C): δ = 212.5
(CO), 170.6 (CNR), 139.1, 138.4, 135.5 (two peaks), 133.8, 129.5,
129.3, 129.0, 21.2 (p-CH3 Mes), 20.1 (o-CH3 Mes) ppm. FTIR (C6D6,
KBr window, 25 °C): νCN = 2164 (s) cm−1, νCO = 2051 (s), 1994 (vs),
1968 (vs) cm−1 also, 3055 (w, sh), 2975 (w), 2948 (w), 2920 (m),
2869 (w), 1614 (m), 1467 (sh), 1454 (m), 1416 (w), 1349 (w), 1330
(w), 1273 (vw), 1029 (vw), 851 (m), 813 (s), 787 (w), 757 (m), 735
(vw), 636 (s) 614 (s) cm−1. Anal. Calcd For C29H25NO4Fe: C, 68.65;
H, 4.97; N, 2.76. Found: C, 68.80, H, 4.75; N, 2.77.
Synthesis of Fe(CO)3(CNArMes2
) (3). To a 100 mL ampule
2
equipped with a side arm gas inlet was added a THF solution of
CNArMes2 (0.801 g, 2.36 mmol, 2 equiv, 40 mL) followed by Fe(CO)5
(0.231 g, 1.18 mmol, 1 equiv). The ampule was sealed and irradiated
(254 nm; Hg lamp) for 30 min, followed by a freeze−pump−thaw
cycle (40 mTorr) to degas the headspace of the reaction mixture. This
process was repeated 3 times, followed by continuous irradiation for
12 h. Analysis of an aliquot of the reaction mixture by 1H NMR at this
point revealed complete consumption of free CNArMes2. The reaction
mixture was then concentrated to a solid under reduced pressure and
washed with n-pentane (3 × 10 mL), followed by subsequent
evaporation to dryness. The resulting solid was then extracted with
Et2O (30 mL), filtered and the resulting solution evaporated to
dryness to afford Fe(CO)3(CNArMes2)2 as a yellow solid. Yield: 0.332
g, 0.405 mmol, 34.3%. X-ray diffraction quality crystals were obtained
from storage of a layered solution of THF/n-hexane (1:10) at room
F
DOI: 10.1021/acs.inorgchem.5b00730
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
1
temperature over the course of 1 week. H NMR (399.9 MHz, C6D6,
20 °C): δ = 6.91 (t, 2H, J = 8 Hz, p-Ph), 6.87 (s, 8H, m-Mes), 6.80 (d,
4H, J = 8 Hz, m-Ph), 2.22 (s, 12H, p-CH3 Mes), 2.00 (s, 24H, o-CH3
Mes) ppm. 13C{1H} NMR (125.7 MHz, C6D6, 20 °C): δ = 212.6
(CO), 178.5 (CNR), 138.6, 137.8, 135.5, 134.3, 129.2, 128.9, 128.3,
128.2, 21.2 (p-CH3 Mes), 20.2 (o-CH3 Mes) ppm. FTIR (C6D6, KBr
windows, 25 °C): vCN = 2097 (s) cm−1; vCO = 1936 (s) cm−1 also,
3030 (w), 2958 (w), 2920 (w), 2869 (w), 1416 (w), 1356 (w), 851
(w), 755 (w), 640 (w), 606 (m), 596 (w) cm−1. Anal. Calcd For
C53H50FeN2O3: C, 77.74; H, 6.16; N, 3.42. Found: C, 77.51; H, 5.88;
N, 3.51.
cm−1. Anal. Calcd for C102H104N5NaFe (Na[6]·(NCMe)): C, 82.84;
H, 7.09; N, 4.74. Found: C, 83.95; H, 6.83; N, 4.80.
Synthesis of Fe(N2)(CNArMes2)4 (7). To a thawing Et2O solution
of Na[HFe(CNArMes2)4] (Na[6], 0.043 g, 0.0302 mmol, 1 equiv, 10
mL) was added an equally cold Et2O solution of MeOTf (0.0052 g,
0.0317 mmol, 1.05 equiv, 2 mL) over the course of 1 min. Upon
completion of the addition, the reaction mixture was refrozen in a cold
well and then placed in a −40 °C freezer to thaw and stir for 45 min.
Over this time, a deep red precipitate was formed in the reaction
mixture. The suspension was then filtered and the resulting solid
extracted with thawing toluene (3 mL) and concentrated to a solid
under reduced pressure. The resulting solid was dissolved in a 1:1
Et2O/toluene mixture (2 mL), filtered, and stored at −40 °C for 1 day
Synthesis of cis,cis,trans-FeI2(CO)2(CNArMes2
)
(4). To a
2
thawing THF solution of Fe(CO)3(CNArMes2)2 (4, 0.243 g, 0.3081
mmol, 1 equiv, 13 mL) was added an equally cold THF solution of I2
(0.0782 g, 0.0308 mmol, 1 equiv, 2 mL). The resulting mixture was
allowed to slowly warm to room temperature over the course of 45
min, whereupon it was concentrated to a solid in vacuo. The red/
brown solid was then washed with n-pentane (3 × 5 mL) and filtered.
The resulting solid was then crystallized from a layered solution of
THF/n-hexane (1:10) over the course of 5 days at room temperature
to yield cis,cis,trans-FeI2(CO)2(CNArMes2)2 as large red/brown crystals.
1
to yield deep-red crystals of 7. Yield: 0.010 g, 0.007 mmol, 23.0%. H
NMR analysis of these crystals was sufficient to provide character-
ization data of the pure material. However, due to the thermal
1
instability of the complex even at −40 °C, H NMR analysis of the
supernatant revealed that 7 was present as a mixture with complex 8
and the cyclic-imine 9. A separate experiment performed in a sealed J-
Young tube in thawing C6D6 indicated the formation of methane
73
1
(CH4; δ = 0.17 ppm ) when analyzed by H NMR spectroscopy.
1
1
Characterization data for 7 follow. H NMR (499.8 MHz, C6D6, 20
Yield: 0.109 g, 0.104 mmol, 34%. H NMR (399.9 MHz, C6D6, 20
°C): δ = 6.91 (m, 16H, o-Ph + m-Ph + m-Mes), 2.30 (s, 24H, p-CH3
Mes), 2.05 (s, 48H, o-CH3 Mes) ppm. 13C{1H} NMR (125.7 MHz,
C6D6, 20 °C) δ = 139.2, 137.7, 136.9, 136,3, 131.7, 130.6, 128.8, 125.1,
21.5 (p-CH3 Mes), 20.8 (o-CH3 Mes) ppm; prolonged scanning did
not reveal the isocyanide carbon resonance. FTIR (C6D6, KBr
windows, 25 °C): vNN = 2067 (m) cm−1; vCN = 1967 (s), 1951 (s),
2017 (m, sh) cm−1 also 2970 (w), 2945 (w), 2920 (w), 2848 (w),
1542 (w), 1453 (m), 1416 (w), 1377 (w), 1324 (w), 851 (w), 804
(w), 756 (w), 668 (w), 631 (w) cm−1. Due to the thermal instability of
7, satisfactory combustion analysis could not be obtained.
°C): δ = 6.90 (m, 10H, p-Ph/m-Mes), 6.75 (d, 4H, J = 8 Hz, m-Ph),
2.24 (s, 12H, p-CH3 Mes), 2.09 (s, 24H, p-CH3 Mes) ppm. 13C{1H}
NMR (125.7 MHz, C6D6, 20 °C): δ = 211.4 (CO), 157.1 (CNR),
140.6, 138.2, 135.6, 134.8, 133.7, 130.2, 129.3, 129.2 (2 peaks), 21.3
(p-CH3 Mes), 20.5 (o-CH3 Mes) ppm. FTIR (C6D6, KBr windows, 25
°C): vCN = 2168 (s), 2140 (w, sh) cm−1; vCO = 2058 (s), 2020 (m)
cm−1 also 3005 (w), 2974 (w), 2940 (w), 2919 (w), 2868 (w), 2854
(w), 1466 (w), 1416 (w), 1378 (w), 850 (w), 756 (w), 605 (w), 591
(w) cm−1. Anal. Calcd for C52H50FeI2N2O2: C, 59.79; H, 4.82; N, 2.68.
Found: C, 59.62; H, 4.91; N, 2.67.
Isolation of [Fe(η6-(Mes)-μ2-C-CNArMes)]2 (8) from the
Isolation of [Na(18-crown-6)][(η5-Me6-1-azabenz[b]azulene)-
Fe(CNArMes2)2] (5). To a thawing Et2O solution of Na2[1] (0.078 g,
0.054 mmol, 1 equiv, 15 mL) was slowly added an equally cold
solution of 18-crown-6 (0.028 g, 0.108 mmol, 2.0 equiv, 2 mL) over
the course of 2 min. The reaction mixture was allowed to stir and
warm to room temperature over the course of 1 h resulting in a color
change from deep red to purple. All volatile materials were then
removed under reduced pressure, and the resulting purple-brown
residue was washed with n-pentane (3 × 5 mL) and dried in vacuo.
Crystallization of the residue from a layered toluene/n-hexane mixture
(7:1) at −40 °C over the course of 10 days produced a small quantity
of complex 5 as red-brown X-ray diffraction quality crystals. Analysis of
Decomposition of Fe(N2)(CNArMes2
) (7). Dinitrogen complex 7
4
was prepared as described above employing Na[HFe(CNArMes2)4]
(Na[6]; 0.025 g, 0.018 mmol, 1 equiv) and MeOTf (0.003 g, 0.020
mmol, 1.1 equiv). The deep-red precipitate obtained was dissolved in
Et2O (5 mL) and allowed to stir for 2.5 h, resulting in the complete
decomposition of 7 to a mixture of [Fe(η6-(Mes)-μ2-C-CNArMes)]2
(8) and the cyclic-imine 9. Filtration of the reaction mixture through a
fiberglass plug afforded a dark-gray solid. Extraction of this solid with
C6H6 followed by filtration through Celite and evaporation to dryness
in vacuo provided dimer 8 as a blue-green powder. Crystallization from
an Et2O solution stored at −40 °C provided single crystals suitable for
X-ray diffraction. Yield: 0.004 g, 0.005 mmol, 28% (based on Na[6]).
1H NMR (499.8 MHz, C6D6, 20 °C): δ = 7.40 (m, 4H, m-Ph), 7.26 (s,
4H, m-Mes), 7.21 (m, 2H, p-Ph), 4.04 (s, 4H, meta-(η6-Mes), 2.59 (s,
12H, o-CH3 Mes), 2.50 (s, 6H, p-CH3 Mes), 2.47 (s, 6H, p-CH3 η6-
Mes), 1.13 (s, 12H, o-CH3 η6-Mes) ppm. 13C{1H} NMR (125.7 MHz,
C6D6, 20 °C): δ = 153.5 (CNR), 140.3, 136.9, 136.8, 136.1, 135.7,
130.9, 126.8, 124.7, 124.0, 114.5, 108.3, 88.5, 87.7, 30.3, 21.6, 20.0,
17.7 ppm. FTIR (C6D6, KBr windows, 25 °C): vCN = 1707 (s) cm−1
also 2919 (w), 1542 (s), 1003 (m) cm−1. Multiple attempts to obtain a
satisfactory combustion analysis were unsuccessful. We attribute this
observation to the presence of trace amounts of cyclic-imine 9 present
in bulk samples of 8.
1
an aliquot of the crystallization mixture by H NMR spectroscopy
indicated the presence of several unidentifiable products. Several
attempts to reproduce the synthesis and isolation of 5 were
unsuccessful.
Synthesis of Na[HFe(CNArMes2)4] (Na[6]). To a thawing Et2O
solution of Na2[Fe(CNArMes2)4] (Na2[1]; 0.213 g, 0.146 mmol, 1
equiv, 15 mL) was added HOSiMe3 (0.013 g, 0.146 mmol, 1.0 equiv)
via microsyringe. The reaction mixture was allowed to slowly warm to
room temperature over the course of 3 h, whereupon it was
evaporated to dryness. The resulting red-orange solid was then
washed with n-pentane (3 × 5 mL) and then thoroughly dried in
vacuo. The resulting red solid was then extracted with C6H6 (10 mL),
filtered, and then lyophilized to yield a red-orange powder. Yield:
0.114 g, 0.079 mmol, 54.1%. X-ray diffraction quality crystals were
obtained by storage of a saturated n-pentane solution at −40 °C for 1
week. Analytically pure crystals of Na[6]·(NCMe) were obtained
crystallization from a 3:1 NCMe/Et2O mixture at −40 °C over the
Isolation of Cyclic-imine 9 from the Decomposition of
Fe(N2)(CNArMes2
)
(7). Dinitrogen complex 7 was prepared as
4
described above employing Na[HFe(CNArMes2)4] (Na[6]; 0.046 g,
0.032 mmol, 1 equiv) and MeOTf (0.006 g, 0.034 mmol, 1.05 equiv).
The deep-red precipitate obtained was dissolved in Et2O (5 mL) and
allowed to stir for 2.5 h, resulting in the complete decomposition of 7
to a mixture of [Fe(η6-(Mes)-μ2-C-CNArMes)]2 (8) and the cyclic-
imine 9. Filtration of the reaction mixture through a fiberglass plug
afforded a dark-gray solid and a brown filtrate. All volatile materials
were then removed from the filtrate in vacuo, and the resulting residue
was extracted with NCMe (3 × 5 mL). The extract was then
evaporated to dryness under reduced pressure to afford 9 as an off-
white solid. Note: Dimer 8 and free CNArMes2 show limited solubility
in NCMe. Yield: 0.002 g, 0.006 mmol, 75.0% (based on 0.25 equiv
1
course of 2 days. H NMR (499.8 MHz, C6D6, 20 °C): δ = 6.85 (m,
28H, o-Ph + p-Ph + m-Mes), 2.25 (s, 24H, p-CH3 Mes), 2.04 (s, 48H,
o-CH3 Mes), −10.9 (s, 1H, Fe−H) ppm. 13C{1H} NMR (125.7 MHz,
C6D6, 20 °C): δ = 206.1 (CNR), 137.8, 137.6, 136.2, 135.7, 134.4,
130.6, 128.8, 123.0, 21.5 (p-CH3 Mes), 21.3 (o-CH3 Mes) ppm. FTIR
(C6D6, KBr windows, 25 °C): vCN = 1994 (m), 1898 (s), 1846 (s),
1828 (s) cm−1 also 3036 (w), 2951 (w), 2918 (m), 2854 (w), 1575
(m), 1487 (w), 1407 (m), 1271 (w), 1031 (w), 852 (m), 755 (m)
G
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Inorganic Chemistry
Article
CNArMes2 per 7). 1H NMR (499.8 MHz, C6D6, 20 °C): δ = 7.46 (dd,
1H, J = 7 Hz, m-Ph), 7.41 (t, 1H, J = 5 Hz, NC(H)), 7.12 (dd, 1H, J
= 7 Hz, m-Ph), 7.05 (t, 1H, J 7 Hz, p-Ph), 6.96 (s, He, m-Mes), 6.95 (s,
1H, m-Mes), 6.85 (s, 1H, m-Mes), 6.52 (s, 1H, m-Mes), 2.71 (qd, 2H,
J = 5 Hz, J = 12 Hz, CH2), 2.36 (s, 3H, CH3 Mes), 2.30 (s, 3H, CH3
Mes), 2.25 (s, 3H, CH3 Mes), 2.14 (s, 3H, CH3 Mes), 2.00 (s, 3H,
CH3 Mes) ppm. 13C{1H} NMR (125.7 MHz, C6D6, 20 °C): δ = 159.0
(CN), 145.8, 139.2, 138.0, 137.1, 136.6, 136.5, 136.4, 136.3, 135.9,
133.5, 131.1, 130.7, 130.4, 129.1, 128.6, 127.5, 125.7, 123.0, 37.4, 22.1,
(12) L. Utz, T.; A. Leach, P.; J. Geib, S.; Cooper, N. J. Chem.
Commun. 1997, 847.
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1997, 16, 4109.
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(15) Barybin, M. V.; Brennessel, W. W.; Kucera, B. E.; Minyaev, M.
E.; Sussman, V. J.; Young, V. G.; Ellis, J. E. J. Am. Chem. Soc. 2007, 129,
1141.
(16) Barybin, M. V.; Young, V. G.; Ellis, J. E. J. Am. Chem. Soc. 1998,
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122, 4678.
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21.2, 21.1, 20.9, 20.6 ppm. FTIR (C6D6, KBr windows, 25 °C): vCN
=
1613 (m) cm−1 also 2022 (w), 2957 (w), 2919 (w) cm−1. HRMS
(ESI-TOF, pos. ion; NCMe) m/z calcd for C25H25N: 340.2065.
Found: 340.2054 [M + H]+.
Crystallographic Structure Determinations. Single-crystal X-
ray structure determinations were carried out using Bruker Platform or
Kappa X-ray diffractometers equipped with Mo or Cu radiation
sources (sealed tube or rotating anode), low-temperature cryostats,
and CCD detectors (Bruker APEX or Bruker APEX II). All structures
were solved by direct methods using SHELXS74 and refined by full
matrix least-squares procedures utilizing SHELXL74 within the Olex2
small-molecule solution, refinement, and analysis software package.75
Crystallographic data collection and refinement information are listed
in Table S1.1 (Supporting Information). Full details of disorder
modeling and structure refinement are also provided in the Supporting
Information.
121, 9237.
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(24) Carpenter, A. E.; Mokhtarzadeh, C. C.; Ripatti, D. S.; Havrylyuk,
I.; Kamezawa, R.; Moore, C. E.; Rheingold, A. L.; Figueroa, J. S. Inorg.
Chem. 2015, 54, 2936.
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A. L.; Figueroa, J. S. Inorg. Chem. 2008, 47, 9010.
(26) Ditri, T. B.; Fox, B. J.; Moore, C. E.; Rheingold, A. L.; Figueroa,
J. S. Inorg. Chem. 2009, 48, 8362.
(27) Fox, B. J.; Millard, M. D.; DiPasquale, A. G.; Rheingold, A. L.;
Figueroa, J. S. Angew. Chem., Int. Ed. 2009, 48, 3473.
(28) Labios, L. A.; Millard, M. D.; Rheingold, A. L.; Figueroa, J. S. J.
Am. Chem. Soc. 2009, 131, 11318.
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(30) Ditri, T. B.; Moore, C. E.; Rheingold, A. L.; Figueroa, J. S. Inorg.
Chem. 2011, 50, 10448.
ASSOCIATED CONTENT
* Supporting Information
■
S
Details on crystallographic structure determinations (pdf and
cif). The Supporting Information is available free of charge on
the ACS Publications website at DOI: 10.1021/acs.inorg-
chem.5b00730.
AUTHOR INFORMATION
Corresponding Author
*E-mail: jsfig@ucsd.edu.
■
(31) Emerich, B. M.; Moore, C. E.; Fox, B. J.; Rheingold, A. L.;
Figueroa, J. S. Organometallics 2011, 30, 2598.
(32) Stewart, M. A.; Moore, C. E.; Ditri, T. B.; Labios, L. A.;
Rheingold, A. L.; Figueroa, J. S. Chem. Commun. 2011, 47, 406.
(33) Tomson, N. C.; Labios, L. A.; Weyhermuller, T.; Figueroa, J. S.;
Wieghardt, K. Inorg. Chem. 2011, 50, 5763.
Notes
The authors declare no competing financial interest.
(34) Carpenter, A. E.; Wen, I.; Moore, C. E.; Rheingold, A. L.;
ACKNOWLEDGMENTS
■
Figueroa, J. S. Chem.Eur. J. 2013, 19, 10452.
We are grateful to the U.S. National Science Foundation for
support of this research (CHE-0954710) and Graduate
Research Fellowships to C.C.M. and A.E.C. J.S.F is a Camille
Dreyfus Teacher−Scholar (2012−2017).
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