Comparison of nucleophilic- and radical-based routes to the formation of manganese-main group element single bonds

Article abstract of DOI:10.1039/c7dt01102d

Using the stable metalloradical Mn(CO)₃(CNAr^Dipp2)₂, we report the formation of manganese-main group complexes via the single-electron functionalization of main group halides. The reactions occur in a simple 1:1 stoichiometry, and demonstrate the utility of using stable open-shelled organometallics as precursors for metal-main group compounds. This has enabled the preparation of manganese complexes bearing terminal -EX_n substituents, as shown through the isolation of Mn(SnCl)(CO)₃(CNAr^Dipp2)₂ and Mn(BiCl₂)(CO)₃(CNAr^Dipp2)₂ from SnCl₂ and BiCl₃, respectively. Through this approach, we have also isolated Mn(SbF₂)(CO)₃(CNAr^Dipp2)₂ from SbF₃, which serves as a unique example of a terminal -SbF₂ complex. Although the metalloradical functionalization of binary main group halides provides the desired main group adduct in yields comparable to nucleophilic activation using the manganate Na[Mn(CO)₃(CNAr^Dipp2)₂], the former approach is shown to be far more atom-economical with respect to Mn. Additionally, we have found that Mn(CO)₃(CNAr^Dipp2)₂ also serves as a convenient precursor to MnF(CO)₃(CNAr^Dipp2). The latter is an analogue to the elusive monofluoride FMn(CO)₅.

Full text of DOI:10.1039/c7dt01102d

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Comparison of nucleophilic- and radical-based
routes to the formation of manganese-main group
element single bonds†
Cite this: DOI: 10.1039/c7dt01102d
Douglas W. Agnew, Curtis E. Moore, Arnold L. Rheingold and Joshua S. Figueroa
*
Using the stable metalloradical Mn(CO)3(CNArDipp2)2, we report the formation of manganese-main group
complexes via the single-electron functionalization of main group halides. The reactions occur in a
simple 1 : 1 stoichiometry, and demonstrate the utility of using stable open-shelled organometallics as
precursors for metal-main group compounds. This has enabled the preparation of manganese complexes
bearing terminal –EXn substituents, as shown through the isolation of Mn(SnCl)(CO)3(CNArDipp2
) and
2
Mn(BiCl2)(CO)3(CNArDipp2
) from SnCl2 and BiCl3, respectively. Through this approach, we have also iso-
2
lated Mn(SbF2)(CO)3(CNArDipp2
) from SbF3, which serves as a unique example of a terminal –SbF2
2
complex. Although the metalloradical functionalization of binary main group halides provides the
desired main group adduct in yields comparable to nucleophilic activation using the manganate
Na[Mn(CO)3(CNArDipp2)2], the former approach is shown to be far more atom-economical with respect to
Received 27th March 2017,
Accepted 17th April 2017
Mn. Additionally, we have found that Mn(CO)3(CNArDipp2
) also serves as a convenient precursor to
2
DOI: 10.1039/c7dt01102d
rsc.li/dalton
MnF(CO)3(CNArDipp2). The latter is an analogue to the elusive monofluoride FMn(CO)5.
systems,15,16 as well as the tendency of main-group halides to
function as oxidants17 towards reduced metal species. This
Introduction
Bifunctional catalysis mediated by transition metal-main often results in irreversible dimerization of the transition
group compounds is becoming an increasingly effective means metal complex as a consequence of metalloradical formation.
towards facilitating difficult bond cleavage steps in catalytic However, in limited cases some dinuclear metal complexes are
cycles.1 While this concept has found wide applicability with capable of homo-fragmentation to produce short-lived metal-
ancillary boryl ligands,2–5 it has recently been shown that loradicals, which can subsequently react with a main group
other Group 13 element fragments,6,7 as well as fragments fragment.18–20 This strategy has proven to be particularly
featuring heavier pnictogen atoms,8,9 can fill the role as an powerful in generating unique transition metal-main group
effective Lewis acid. However, the generation of these com- species.20 To examine this pathway in more detail, we have
plexes remains a particular challenge due to the difficulty in investigated the activation of binary main group halides with
preparing stable main-group nucleophiles to functionalize the stable manganese metalloradical Mn(CO)3(CNArDipp2)2,21
various metal species.10,11 Additionally, the development of with comparison to nucleophilic reaction pathways accom-
synthetic routes using binary main group halides remains plished
largely limited to either oxidative addition with late-row tran- (CO)3(CNArDipp2)2] (ArDipp2
sition metals4,5,12,13 or nucleophilic reactions with classical Importantly, we have found that the use of sterically encum-
carbonyl metallates.14 bering m-terphenyl isocyanides23–41 facilitates the formation of
by
the
corresponding
manganate
Na[Mn
=
2,6-(2,6-(i-Pr)2C6H3)2C6H3).22
For nucleophilic derivatization reactions, complications can unique, terminal main group substituents without the occur-
arise as a result of multiple additions in sterically uncongested rence of dimerization.
We recently reported the preparation of Mn(CO)3(CNArDipp2)2,
a zerovalent, square-pyramidal complex that serves as an
analogue to the unstable metalloradical Mn(CO)5.21 Consistent
Department of Chemistry and Biochemistry, University of California, San Diego,
with its low-spin, d7 ground state, Mn(CO)3(CNArDipp2
) acts
2
9500 Gilman Drive, Mail Code 0358, La Jolla, CA 92093, USA.
E-mail: jsfig@ucsd.edu
as a potent atom abstraction reagent and competent radical
scavenger in solution. For example, addition of 1 equiv. CHCl3
†Electronic supplementary information (ESI) available: Spectroscopic character-
ization and crystallographic structure determinations (PDF and CIF). CCDC
1538895–1538898. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/c7dt01102d
to Mn(CO)3(CNArDipp2
)
resulted in the generation of
2
MnCl(CO)3(CNArDipp2
)
and Mn(CHCl2)(CO)3(CNArDipp2
)
2
in a
2
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1 : 1 ratio. Interestingly, this reactivity was found to carry over
to Sn(IV) species as well. For example, reaction of 1 equiv. of
HSn(n-Bu)3 with Mn(CO)3(CNArDipp2
) was found to produce
2
an equimolar mixture of MnH(CO)3(CNArDipp2
)
as well
2
as the stannyl complex Mn(Sn(n-Bu)3)(CO)3(CNArDipp2)2. This
suggested that the intrinsic reactivity of Mn(CO)3(CNArDipp2
)
2
could be used to facilitate the formation of unique, low-valent
manganese adducts with substrates containing homolytically
cleavable E–X bonds. This mode of reactivity should
thus be complementary to the manganate complex
Na[Mn(CO)3(CNArDipp2)2], which has been established to react
with tin(II) dichloride to form the unique chloro-
substituted metallostannylene, Mn(SnCl)(CO)3(CNArDipp2)2.
Accordingly, herein we show that complexes possessing
manganese/main group element bonds can be readily accessed
by a radical-type approach using the neutral metalloradical
Mn(CO)3(CNArDipp2)2. These reactions proceed with high atom-
economy and can succeed in some cases where nucleophilic-
derivitization/salt elimination routes fail to easily provide the
desired product. In addition, in the course of this study we
have prepared the monofluoro complex MnF(CO)3(CNArDipp2)2,
which serves as an analogue to the unknown organometallic
fluoride FMn(CO)5.42
Scheme 1 Reactivity of Mn(CO)3(CNArDipp2
SbF3.
)
with BiCl3, SnCl2 and
2
readily available main group halides (Scheme 1). It was discov-
ered that the character of the halide played an important role
in facilitating a favorable transformation. Indeed, while SbCl3
Results and discussion
Based upon the observed reactivity of Mn(CO)3(CNArDipp2
and SbI3 led solely to MnCl(CO)3(CNArDipp2
)
and MnI
2
)
(CO)3(CNArDipp2)2,39 respectively, it was found that SbF3 reacts
2
with CHCl3 and HSn(n-Bu)3, we anticipated that a simple 1 : 1 with Mn(CO)3(CNArDipp2)2 over several days in DME solution to
stoichiometry between Mn(CO)3(CNArDipp2)2 and a main group form Mn(SbF2)(CO)3(CNArDipp2)2 and MnF(CO)3(CNArDipp2)2 in
halide should result in a product mixture containing the Mn- approximately a 1 : 1 ratio. Analysis of the product mixture by
main group adduct and the corresponding halide complex 19F NMR spectroscopy reveals two singlets at −59.7 ppm and
MnX(CO)3(CNArDipp2)2. Indeed, addition of SnCl2 to a stirring −166.0 ppm, and solution infrared spectroscopy supports the
diethyl ether solution of Mn(CO)3(CNArDipp2
)
provides presence of two C2v-symmetric complexes with isocyanide
2
MnCl(CO)3(CNArDipp2
)
and the previously reported stretches at 2118 cm−1 and 2086 cm−1. Indeed, crystallization
21
2
metallostannylene complex, Mn(SnCl)(CO)3(CNArDipp2)2,22 in of the product mixture in THF produces a combination of
approximately a 1.3 : 1 ratio, as assayed by 1H NMR spec- bright yellow and orange crystals. Extraction of this mixture
troscopy. Isolation of Mn(SnCl)(CO)3(CNArDipp2
)
is readily with n-pentane followed by recrystallization in pyridine was
2
accomplished via n-pentane extraction of the product mixture, found to provide Mn(SbF2)(CO)3(CNArDipp2
)
in 43% yield,
2
as MnCl(CO)3(CNArDipp2)2 is insoluble in n-pentane, providing which gives rise to the 19F NMR signal at −166.0 ppm.
green microcrystals in 32% yield upon removal of volatiles. Crystallographic analysis of Mn(SbF2)(CO)3(CNArDipp2
)
2
While this yield falls below that previously reported for revealed an octahedral geometry about manganese in the solid
the corresponding salt metathesis route using Na[Mn state with a Mn–Sb distance of 2.6111(6) Å (Fig. 1). The three-
(CO)3(CNArDipp2)2], it is notable that the metalloradical coordinate Sb center adopts a distorted pyramidal geometry
pathway allows for nearly quantitative recovery of Mn (average of two positionally disordered –SbF2 fragments:
metal centers (as Mn(SnCl)(CO)3(CNArDipp2
)
and MnCl ∠(Mn–Sb–F) = 100.3(4)°; ∠(F–Sb–F) = 92.0(5)°. While three-
2
(CO)3(CNArDipp2)2) by mass balance. As shown previously, the coordinate, terminal transition metal stibyl halides (e.g.
chloride complex can be easily reduced by one or two electrons LnMSbX2) are known for chloro-derivatives,13,15,43 Mn(SbF2)
to regenerate Mn(CO)3(CNArDipp2)2 or [Mn(CO)3(CNArDipp2)2]−, (CO)3(CNArDipp2
) represents a unique example of a mono-
2
respectively, which can then be reused in further reactions.39 meric difluorostibyl complex without intermolecular catena-
Importantly, this result supports a metalloradical approach tion between –SbF2 centers.44 Notably, it was found that Mn
towards Sn(II) derivatization, similar to that previously (SbF2)(CO)3(CNArDipp2
) could also be synthesized via a salt
2
observed for the related reactivity with Sn(IV) substrates.
elimination route from Na[Mn(CO)3(CNArDipp2)2] and SbF3 in
To further explore the generality of this metalloradical 54% yield, thus revealing a complementarity between the
approach and its comparison to salt elimination using Na[Mn nucleophilic displacement and atom abstraction approaches.
(CO)3(CNArDipp2)2], we examined the reactivity with several However, as observed for the reactivity with SnCl2, the atom
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abstraction route allows nearly quantitative recovery of ture for 3 h, or exposing −40 °C solutions to ambient light for
Mn centers (as Mn(SbF2)(CO)3(CNArDipp2
)
and MnF 20 minutes, resulted in the formation of MnCl
2
(CO)3(CNArDipp2)2), whereas 46% of the molar equivalents of (CO)3(CNArDipp2
Mn are lost to intractable products in the salt elimination route. to be solid Bi0.
) and a black precipitate, which we presume
2
Radical-type formation of Mn-bound heavier pnictogen
dihalides is not limited to antimony. While attempts to gene- two-component mixture resulting from reaction of Mn
rate the corresponding –BiF2 adduct using BiF3 under similar (CO)3(CNArDipp2
and SbF3. An alternate synthesis, involving
As mentioned above, MnF(CO)3(CNArDipp2
) is among the
2
)
2
conditions did not lead to a productive reaction, addition of the addition of solid XeF2 to
1 equiv. of solid BiCl3 to a stirring diethyl ether solution of solution of Mn(CO)3(CNArDipp2)2, was found to provide
Mn(CO)3(CNArDipp2 provided MnCl(CO)3(CNArDipp2 and MnF(CO)3(CNArDipp2)2 in 41% yield. Notably, we have not identi-
a stirring fluorobenzene
)
)
2
2
Mn(BiCl2)(CO)3(CNArDipp2
)
2
in a 2.5 : 1 ratio, as assayed by fied conditions where the use of Na[Mn(CO)3(CNArDipp2)2] as a
1H NMR spectroscopy. We contend this low ratio is the result starting material has been found to provide MnF
of the thermal- and photo-sensitivity of Mn(BiCl2) (CO)3(CNArDipp2)2, which highlights the utility of an open-shell
(CO)3(CNArDipp2
) (vide infra). Recrystallization of the product starting material for the formation of this transition
2
mixture affords red and yellow crystals of Mn(BiCl2) metal monofluoride. The infrared spectrum of MnF
(CO)3(CNArDipp2 and MnCl(CO)3(CNArDipp2)2, respectively, (CO)3(CNArDipp2
in C6D6 possesses an isocyanide band at
)
)
2
2
which can be manually separated. Following separation, 2118 cm−1 that is identical to those of the C2v-symmetric
1H NMR spectroscopic analysis of the red crystals indicated halide
complexes
MnCl(CO)3(CNArDipp2)2,
MnBr
the isocyanide ligands are in identical chemical environments, (CO)3(CNArDipp2)2, and MnI(CO)3(CNArDipp2)2.39 This obser-
supporting a trans-stereochemical orientation. Indeed, Mn vation strongly suggests that the identity of the halide ligand
(BiCl2)(CO)3(CNArDipp2
)
adopts an octahedral coordination does not effect the degree of π-backbonding by Mn to the iso-
2
geometry about Mn in the solid state, with a Mn–Bi distance of cyanide ligands. The 19F NMR spectrum of MnF
2.6809(10) Å, which is similar to other isolated transition (CO)3(CNArDipp2
) in C6D6 displays a singlet at −59.7 ppm,
2
metal halobismuth complexes.12,15,45 While most transition with no other signals observed between 200 to −500 ppm.
metal halobismuth complexes form bridging interactions in However, the three downfield peaks in the 13C{1H} NMR spec-
the solid state,46–48 Mn(BiCl2)(CO)3(CNArDipp2
)
does not trum corresponding to CNArDipp2
, COtrans, and COcis at
2
exhibit intermolecular contacts due to the encumbering nature 172.5 ppm, 210.0 ppm, and 218.0 ppm, respectively, display
of the CNArDipp2 ligands. However, despite the increased carbon–fluorine coupling (JCF = 11 Hz (COtrans), 150 Hz
kinetic stabilization afforded by CNArDipp2
,
Mn(BiCl2) (CNArDipp2), 172 Hz (COcis)) with JCF constants consistent with
(CO)3(CNArDipp2
) is thermally unstable above −40 °C and a mer,trans-stereochemical arrangement. Notably, this complex
2
shows significant sensitivity to light. Indeed, allowing Mn serves as a mixed isocyanide/carbonyl analogue of MnF(CO)5,
(BiCl2)(CO)3(CNArDipp2 to stir in the dark at room tempera- which to date has not been observed.42,49–52
)
2
In an attempt to gain further insight into the structure of
MnF(CO)3(CNArDipp2)2, single crystals were grown from a con-
centrated diethyl ether solution at −35 °C and subjected to
X-ray crystallographic analysis. The resultant structure solution
indicated the expected mer,trans-stereochemical arrangement
of the CO and CNArDipp2 ligands, respectively, and the fluoride
ligand was located in the apical position from the electron
density map. However, additional electron density corres-
ponding to another HF unit was observed in close proximity to
the Mn-bound fluoride atom, such that the structure from
these crystals is more appropriately assigned as the bifluoride
adduct Mn(FHF)(CO)3(CNArDipp2
) (Fig. 2), with a F⋯F dis-
2
tance of 2.276(2) Å. This is, to our knowledge, the first structu-
rally characterized low-valent manganese biflouride complex.53
Indeed, 1H NMR analysis of these crystals revealed the pres-
ence of a new product (Fig. S1.8 and S1.9†), which displayed a
doublet (JHF
= 411 Hz) at 10.91 ppm (C6D6, 20 °C).
Additionally, a doublet (JHF = 400 Hz) at −187.85 ppm as well
as a broadened singlet at −482.20 ppm was observed in the
19F NMR spectrum. These data are consistent with previously
reported transition metal fluorides in which an HF molecule is
strongly H-bonded to the terminal fluoride ligand.53,54 We
contend this HF molecule likely originates from the reaction of
XeF2 with adventitious water in the system.55,56 Despite
Fig. 1 Solid state structures of Mn(BiCl2)(CO)3(CNArDipp2
)
2
(top) and
Mn(SbF2)(CO)3(CNArDipp2
)
2
(bottom), with selected Dipp rings and
H atoms omitted for clarity.
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Fig. 2 (Left) Addition of XeF2 in C6H5F results in the formation of MnF(CO)3(CNArDipp2)2. Decomposition via an adventitious proton source results in
the formation of the bifluoride complex. (Right) Solid state structure of Mn(FHF)(CO)3(CNArDipp2
2 with H atoms omitted for clarity.
)
multiple attempts, we have thus far been unable to structurally complex in which the Mn-bound AlCl2 group also binds a THF
characterize MnF(CO)3(CNArDipp2
) in isolation; we nonethe- molecule. Importantly, both the diamagnetic NMR spectrum as
2
less note that the formation of MnF(CO)3(CNArDipp2)2 in solu- well as the isocyanide IR band (νCN = 2057 cm−1) are consistent
tion completes the halide series for mixed carbonyl/CNArDipp2 with a Mn(I) oxidation state, indicating the –AlCl2(THF) group to
manganese complexes, and provides a stable analogue to the be behaving as an X-type ligand.57 Attempts at thermal desolva-
unobserved metal carbonyl fluoride FMn(CO)5.
tion under vacuum led to intractable mixtures and, notably,
While metalloradical Mn(CO)3(CNArDipp2)2 can be employed preparations involving the use of non-coordinating solvents,
to generate metal bound main-group fragments, limitations such as benzene or toluene, led directly to the formation of
were observed in several cases when attempting to more broadly MnCl(CO)3(CNArDipp2)2, potentially suggesting the necessity of
extend this chemistry. For example, it was found that PCl3, PCl5, an Al-solvento adduct in facilitating salt elimination.
S2Cl2, and AlCl3 generate MnCl(CO)3(CNArDipp2
) as the exclu- Interestingly, examples of transition metal-bound AlX2 (X =
2
sive product, and is invariant of the reaction stoichiometry. halide) species are quite rare,58,59 with only one reported metal-
These reagents similarly produce MnCl(CO)3(CNArDipp2)2 when AlX2 complex occurring with diamino substituents.60 The
combined with Na[Mn(CO)3(CNArDipp2)2], with the lone excep- pendant Al(NR2)2 groups in these latter complexes have been
tion of AlCl3, which generates Mn(AlCl2·THF)(CO)3(CNArDipp2
)
2
shown in some instances to behave as Lewis acidic sites and
(Fig. 3) in 74% yield with loss of NaCl. The molecular structure participate in cooperative reactivity with the transition metal
determined from X-ray crystallography reveals an octahedral center. Accordingly, we are currently developing an understand-
ing of the pendant Lewis acidity in Mn(AlCl2·THF)
(CO)3(CNArDipp2)2 towards Lewis-basic substrates.
The above results demonstrate that, under appropriate con-
ditions, a diverse series of manganese-main group complexes
are available by both metalloradical and traditional salt elim-
ination routes. Notably, the product distribution in the cases
of BiCl3 and SbF3 are significantly dependent on the starting
metal complex, indicating different reaction pathways are
being accessed. While this breadth of reactivity was not
observed in all cases – AlCl3 being the notable example – this
indicates that bimodal, complementary reactivity available to
the starting metal complex should allow for facile exploration
of routes towards functionalized transition metal-main group
adducts. We are currently working to expand the reaction
chemistry surveyed here to understand more fully its advan-
tages and limitations.
Experimental section
General considerations
All manipulations were performed under an atmosphere of dry
dinitrogen using standard Schlenk and glovebox techniques,
unless otherwise stated. Solvents were dried and degassed
Fig. 3 (Top) Formation of Mn(AlCl2·THF)(CO)3(CNArDipp2
) via addition
2
of AlCl3 to Na[Mn(CO)3(CNArDipp2)2]. (Bottom) Solid state structure of
Mn(AlCl2·THF)(CO)3(CNArDipp2)2, with H atoms omitted for clarity.
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according to standard procedures. Reagent grade starting protons. Extraction of this mixture with n-pentane (5 × 10 ml),
materials were purchased from commercial sources and used followed by cooling of the extracts to −40 °C caused Mn(SbF2)
without further purification, unless otherwise stated. SnCl2 (CO)3(CNArDipp2
was recrystallized from THF twice and thoroughly desolvated 0.008 g, 43%.
prior to use. The isocyanide ligand CNArDipp2 was prepared
)
to precipitate as an orange solid. Yield:
2
Synthesis of Mn(SbF2)(CO)3(CNArDipp2)2 using Na[Mn
(CO)3(CNArDipp2
according to literature procedures.25 The compounds
Na[Mn(CO)3(CNArDipp2)2] and Mn(CO)3(CNArDipp2
have been
)
2
)
2
previously reported.21,22 Benzene-d6 (Cambridge Isotope To
Laboratories) was stirred over NaK for two days, distilled, (0.108 g, 0.108 mmol, 8 ml) was added SbF3 (0.029 g,
degassed, and stored over 4 Å molecular sieves. 0.162 mmol, 1.5 eq.) as a solid, which turned the solution
a
stirring THF solution of Na[Mn(CO)3(CNArDipp2)2]
Solution 1H and 13C NMR were recorded on a Bruker 300 from deep purple to orange, with concurrent formation of a
spectrometer, a Varian 400 spectrometer, a Varian X-Sens 500 black precipitate. The mixture was filtered through a Celite
spectrometer, or a JEOL ECA-500 spectrometer. 1H and plug and the volatiles removed under reduced pressure. The
13C NMR chemical shifts are reported in ppm relative to SiMe4 resulting orange solid was washed with pentane (4 × 5 ml) and
(1H and 13C δ = 0.0 ppm) with reference to residual proton res- then dissolved in benzene and filtered though a fiberglass
onances of 7.16 ppm (1H) and 128.06 ppm (13C) for benzene- plug. All volatiles were removed under reduced pressure, pro-
d6.61 19F NMR spectra are reported relative to the external stan- viding a light yellow solid. Yield: 0.067 g, 0.058 mmol, 54%.
dard BF3·(Et2O) (δ = 0.0 ppm). Room temperature FTIR spectra Diffraction quality crystals can be grown from a pyridine solu-
were recorded on a Thermo-Nicolet iS10 FTIR spectrometer. tion at −40 °C. 1H NMR (500.2 MHz, C6D6, 20 °C) δ = 7.32
Samples were prepared as benzene-d6 solutions injected into a (t, 2H, J = 8 Hz, p-Ar), 7.18 (d, 4H, J = 8 Hz, m-Ar), 6.93 (m, 8H,
ThermoFisher solution cell equipped with KBr windows. m-Dipp), 6.83 (dd, 4H, J = 8.5, 6.5 Hz, p-Dipp), 2.68 (sept, 8H,
Solvent peaks were digitally subtracted from all solution FTIR J = 7 Hz, CH(CH3)2), 1.38 (d, 24H, J = 7 Hz, CH(CH3)2), 1.01 (d,
spectra using a previously recorded spectrum of the solvent. 24H, J = 7 Hz, CH(CH3)2) ppm. 13C NMR (125 MHz, C6D6,
Combustion analyses were performed by Robertson Microlit 20 °C) = 211.6 (CO), 172.5 (CNR), 146.5, 139.2, 134.7, 130.1,
Laboratories of Madison, New Jersey (USA) and Midwest 129.7, 123.6, 31.3 (C(CH3)2), 24.9 (C(CH3)2), 24.0 (C(CH3)2)
Microlabs of Indianapolis, Indiana. HR-MS was recorded at ppm. Prolonged scanning did not uncover the second carbonyl
the UCSD Molecular Mass Spectrometry Facility using an resonance. 19F NMR (470.6 Hz, C6D6, 20 °C) δ = −166.0 ppm.
Agilent 6230 Accurate-Mass TOFMS with acetonitrile as the FTIR (C6D6, KBr windows): νCN = 2087 cm−1 (vs), νCO
eluent.
=
1979 cm−1 (s), νCO = 1964 cm−1 (s), also 2854, 1593, 1457,
1385, 1363, 1058, 758, 645 cm−1. HR-MS (ESI-TOFMS): pre-
dicted for [M + H3O]+ = C65H77F2MnN2SbO4, 1163.4270; found
m/z = 1163.4068. Repeated samples failed to provide a satisfac-
tory elemental analysis.
Synthesis of Mn(SnCl)(CO)3(CNArDipp2)2 and MnCl
(CO)3(CNArDipp2
)
2
To a stirring diethyl ether solution of Mn(CO)3(CNArDipp2
)
2
(0.046 g, 0.046 mmol, 5 ml) was added solid SnCl2 (0.009 g,
0.046 mmol, 1 eq.). The color of the solution turned from
Synthesis of MnF(CO)3(CNArDipp2
)
2
orange to light yellow over the course of 5 minutes, and the Caution: XeF2 is a highly reactive compound. Care must be
mixture was stirred a further 15 minutes before all volatiles taken to ensure limited contact with borosilicate glass contain-
were removed in vacuo. A 1H NMR of the product mixture indi- ers for prolonged periods. In a darkened glovebox, a fluoro-
cated a 1 : 1.3 distribution between Mn(SnCl)(CO)3(CNArDipp2
)
benzene solution of Mn(CO)3(CNArDipp2)2 (0.037 g, 0.0375 mmol,
2
and MnCl(CO)3(CNArDipp2
)
2
based upon integration of the 5 ml) was set stirring at room temperature in a glass scintil-
respective (CH(CH3)) protons. Extraction of the product lation vial. In a separate plastic vial, a weighed sample of XeF2
mixture with pentane (2 ml) provides Mn(SnCl) (0.010 g, 0.056 mmol, 1.5 eq.) was added in one portion to the
×
5
(CO)3(CNArDipp2
)
as a green solid. Yield: 0.032 g, 32%. stirring solution. The color of the solution gradually changed
2
Characterization data has been previously published.22
from orange to yellow over 5 minutes. With continued stirring,
all volatiles were removed under reduced pressure to yield a
yellow solid. The solid was washed with pentane (3 × 5 ml) and
extracted with diethyl ether to provide a light yellow powder.
Synthesis of Mn(SbF2)(CO)3(CNArDipp2)2 and MnF
(CO)3(CNArDipp2
)
2
A DME solution of Mn(CO)3(CNArDipp2)2 (0.016 g, 0.016 mmol, The powder was dissolved into a minimal amount of THF, fil-
4 mL) was treated with SbF3 (0.029 g, 10 eq.) in one portion at tered through a fiberglass plug, and stored at −40 °C for
room temperature. The mixture was stirred for 12 hours, after 2 days. The resulting crystals were washed with n-pentane to
1
which the DME was removed en vacuo. The solid was taken up providing a crystalline material. Yield: 0.015 g, 41%. H NMR
in C6H6 and filtered, and all volatiles were removed under (500.1 MHz, C6D6, 20 °C) δ 7.41 (t, 4H, J = 8 Hz, p-Dipp), 7.19
reduced pressure to provide a dull yellow solid. Integration (d, 8H, J = 8 Hz, m-Dipp), 6.89 (d, 4H, J = 8 Hz, m-Ar), 6.82 (dd,
from a 1H NMR spectrum reveals formation of Mn(SbF2) 2H, J = 8, 7 Hz, p-Ar), 2.64 (sept, 8H, J = 7 Hz, CH(CH3)2), 1.38
(CO)3(CNArDipp2)2 and MnF(CO)3(CNArDipp2)2 in a 1 : 1.1 ratio, (d, 24H, J = 7 Hz, CH(CH3)2), 1.02 (d, 24H, J = 7 Hz, CH(CH3)2)
respectively, based upon integration of the respective (p-Ar) ppm. 13C{1H} NMR (125.7 MHz, C6D6, 20 °C) δ = 218.0 (cis-CO,
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d, J = 172 Hz), 210.0 (trans-CO, d, J = 11 Hz), 172.5 (CN, d, J = tals of Mn(BiCl2)(CO)3(CNArDipp2)2 are obtained from a concen-
150 Hz), 146.4, 139.7, 134.3, 139.7, 128.6, 123.6, 31.5 trated THF solution at −40 °C overnight.
(CH(CH3)), 24.6 (CH(CH3)2), 24.3 (CH(CH3)2), ppm (two
Synthesis of Mn(AlCl2·THF)(CO)3(CNArDipp2
)
2
CNArDipp2 aromatic resonances are obscured by the C6D6
signal). 19F NMR (470.6 MHz, C6D6, 20 °C, TFA standard) δ =
−59.7 ppm. FTIR (C6D6, KBr windows): νCN = 2117 cm−1 (vs),
νCO = 2014 cm−1 (vs), 2008 cm−1 (sh), 1942 (s), also 2961, 2926,
2868, 1568, 1480, 1437, 1133, 758, 677, 647 cm−1. Repeated
combustion analyses routinely provided C and H values that
indicated some incorporation of HF.
A stirring THF solution of Na[Mn(CO)3(CNArDipp2)2] (0.063 g,
0.063 mmol, 5 ml) is slowly treated with a THF solution of
AlCl3 (0.009 g, 0.065 mmol, 1.05 eq., 2 ml) at room tempera-
ture over 5 minutes. After approximately 30 minutes stirring,
the deep purple color lightens to yellow. Thereafter, the
solvent is removed en vacuo to provide a yellow solid. This
solid is then subject to two cycles of n-pentane addition and
removal under vacuum to desolvate remaining salts. Extraction
of the yellow solid with Et2O (3 × 2 ml), followed by evapor-
ation of the combined extracts under vacuum, provides analyti-
Synthesis of Mn(BiCl2)(CO)3(CNArDipp2)2 and MnCl
(CO)3(CNArDipp2
)
2
To a stirring diethyl ether solution of Mn(CO)3(CNArDipp2
)
2
cally pure Mn(AlCl2·THF)(CO)3(CNArDipp2
) as a yellow solid.
2
(28 mg, 0.0284 mmol, 5 mL) was added a solution of BiCl3 in
diethyl ether (9 mg, 1 mL, 1 eq.). The orange solution became
dark orange with concomitant precipitation of a black powder,
and stirring was discontinued after 5 minutes. The solution
was filtered and the solvent was removed under reduced
pressure. Integration from 1H NMR spectra reveals a conver-
1
Yield: 0.053 g, 74%. H NMR (500.1 MHz, C6D6, 20 °C) δ 7.32
(t, 4H, J = 8 Hz, p-Dipp), 7.23 (d, 8H, J = 8 Hz, m-Dipp), 7.06 (d,
4H, J = 8 Hz, m-Ar), 6.91 (dd, 2H, J = 8, 7 Hz, p-Ar), 3.44 (m,
THF), 2.82 (sept, 8H, J = 7 Hz, CH(CH3)2), 1.48 (d, 24H, J =
7 Hz, CH(CH3)2), 1.27 (m, THF), 1.05 (d, 24H, J = 7 Hz, CH
(CH3)2) ppm. 13C{1H} NMR (125.7 MHz, C6D6, 20 °C) δ = 219.1
(trans-CO), 210.0 (cis-CO), 182.4 (CN), 146.8, 137.8, 135.7,
130.9, 129.0, 126.1, 123.4, 72.5 (THF), 31.2 (CH(CH3)2), 25.7
(CH(CH3)2), 25.0 (THF), 23.5 (CH(CH3)2), ppm. FTIR (C6D6,
KBr windows): νCN = 2057 cm−1 (vs), νCO = 1951 cm−1 (s),
1918 cm−1 (vs), also 3065, 2961, 2925, 2865, 1578, 1458, 1411,
1385, 1363, 1331, 1056, 1004, 757, 657 cm−1. Anal. calcd for
C69H82AlCl2MnN2O4: C, 71.66; H, 7.15; N, 2.42. Found: C,
71.93; H, 6.75; N, 1.99.
sion of Mn(CO)3(CNArDipp2
)
to Mn(BiCl2)(CO)3(CNArDipp2
)
2
2
and MnCl(CO)3(CNArDipp2
)
in a 0.4 : 1 ratio, respectively,
2
based upon integration of the respective (p-Ar) protons. Light
red single crystals of Mn(BiCl2)(CO)3(CNArDipp2)2 are obtained
from a concentrated THF solution at −40 °C overnight. The
compound is light sensitive and slowly decomposes above
−40 °C; decomposition provides Bi0 (as a black solid) and
MnCl(CO)3(CNArDipp2)2. Spectroscopic data for Mn(BiCl2)
1
(CO)3(CNArDipp2)2: H NMR (300.1 MHz, C6D6, 20 °C) δ = 7.34
(t, 2H, J = 8 Hz, p-Ar), 7.19 (d, 4H, J = 8 Hz, m-Ar), 6.92 (m, 8H,
m-Dipp), 6.80 (dd, 4H, J = 8.5, 6.5 Hz, p-Dipp), 2.67 (sept, 8H,
J = 7 Hz, CH(CH3)2), 1.35 (d, 24H, J = 7 Hz, CH(CH3)2), 0.99 (d,
24H, J = 7 Hz, CH(CH3)2) ppm. 13C{1H} NMR (125.7 MHz,
C6D6, 20 °C) δ = 209.4 (trans-CO), 203.8 (cis-CO), 164.7 (CN),
146.7, 139.8, 134.7, 130.4, 130.0, 123.9, 31.3 (CH(CH3)), 25.0
(CH(CH3)2), 24.3 (CH(CH3)2), ppm (two CNArDipp2 aromatic
resonances are obscured by the protio-benzene impurity peak).
Acknowledgements
We are grateful to the US Department of Energy, Office of
Science, Basic Energy Sciences for support of this research,
(DE-SC0008058) and the US Department of Education for a
GAANN fellowship to D. W. A. J. S. F is a Camille Dreyfus
Teacher-Scholar (2012–2017).
FTIR (C6D6, KBr windows): νCN = 2093 cm−1 (vs), νCO
=
1981 cm−1 (s), also 2964, 2926, 2869, 1458, 1030, 759, 645,
633 cm−1. Attempts to collect combustion analysis of the puri-
fied material prepared in this synthesis or in the salt elimin-
ation reaction failed to provide satisfactory results. We believe
this is due to the observed thermal instability which routinely
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