N-Cobaltocenium Amide as Reactive Nucleophilic Reagent for Donor-Acceptor Bimetallocenes

Article abstract of DOI:10.1021/acs.organomet.7b00790

Deprotonation of the aminocobaltocenium ion [Cc-NH₂]⁺ ([H-1]⁺) generates the nucleophilic imine CcNH (1). Reaction of 1 with acid chlorides R-COCl (R = Ph, Fc, and Cc⁺) yields the reference amide [Ph-CO-NH-Cc]⁺ (2⁺) and the amide-linked hetero- and homobimetallocenes [Fc-CO-NH-Cc]⁺ (3⁺) and [Cc-CO-NH-Cc]²⁺ (4²⁺), respectively. Cation-anion interactions of charged amides 2⁺-4²⁺ in the solid state and in solution are probed by single crystal X-ray diffraction and NMR and IR spectroscopy. Intramolecular metal-metal interactions in donor-acceptor heterobimetallocene 3⁺ and in mixed-valent homobimetallocene 4⁺ (prepared electrochemically) are discussed within the Marcus-Hush framework aided by spectroelectrochemical experiments and time-dependent density functional theory calculations.

Full text of DOI:10.1021/acs.organomet.7b00790

Article
Cite This: Organometallics XXXX, XXX, XXX−XXX
N‑Cobaltocenium Amide as Reactive Nucleophilic Reagent for
Donor−Acceptor Bimetallocenes
Maximilian Lauck, Christoph Forster, and Katja Heinze*
̈
Institute of Inorganic Chemistry and Analytical Chemistry, Johannes Gutenberg University of Mainz, Duesbergweg 10-14, D-55128
Mainz, Germany
S
* Supporting Information
ABSTRACT: Deprotonation of the aminocobaltocenium ion
[Cc-NH2]+ ([H-1]+) generates the nucleophilic imine CcNH
(1). Reaction of 1 with acid chlorides R−COCl (R = Ph, Fc,
and Cc+) yields the reference amide [Ph-CO-NH-Cc]+ (2+) and
the amide-linked hetero- and homobimetallocenes [Fc-CO-NH-
Cc]+ (3+) and [Cc-CO-NH-Cc]2+ (42+), respectively. Cation−
anion interactions of charged amides 2+−42+ in the solid state
and in solution are probed by single crystal X-ray diffraction and
NMR and IR spectroscopy. Intramolecular metal−metal
interactions in donor−acceptor heterobimetallocene 3+ and in
mixed-valent homobimetallocene 4+ (prepared electrochemi-
cally) are discussed within the Marcus−Hush framework aided
by spectroelectrochemical experiments and time-dependent
density functional theory calculations.
strongly interested in the employment of charged cobaltoce-
nium Cc+ building blocks in analogous isosteric systems. The
positive charges in the parent systems and the expanded redox
potential range toward more negative values are attractive assets
INTRODUCTION
■
The ferrocene/ferrocenium couple (Fc/Fc+) occupies an
outstanding position in the metallocene series.1 This central
role in organometallic chemistry is based on its reversible redox
behavior and its highly versatile substitution chemistry allowing
for strongly electron-withdrawing and -donating substituents.
The accessible potential range for the Fc/Fc+ redox process
spans approximately 1.7 V based on substituent effects.2
Furthermore, ferrocene can be conjugated to nearly every
conceivable building block, including biomolecules, dyes or
electrode surfaces for sensing applications.1,3−5 Typically, Fc is
introduced in the neutral form, thus acting as an electron-
donating unit in photoinduced electron transfer (PET)
systems4,5 and in charge transfer (CT) complexes.6,7
in these applications.2a,12,13b The now good availability of [Cc-
13a
COOH]+
already allowed us to devise a porphyrin-
cobaltocenium dyad [P-NHCO-Cc+]. This chromophore−
acceptor system displays photoinduced charge separation after
irradiation into the chromophore bands delivering a charge-
shifted state with porphyrin radical cation−cobaltocene
character [P+-NHCO-Cc].10
In contrast to Fc-NH2 derivatives,4i,j,5b,7,14,15d,e,18 N-sub-
stituted Cc+ complexes which would constitute more electron-
rich Cc+ building blocks are rare. In fact, only few reactions
toward N-substituted Cc+ units are known so far. Starting from
N-substituted lithium or sodium cyclopentadienides and CoCl2
only 1,1′-disubstituted cobaltocenium ions are accessible after
oxidation.11a,b,e A unique isonitrile insertion into a cyclo-
pentadienyl pentadienyl cobalt(III) complex gives the amino
substituted sterically demanding [CpCo(η5-C5Me4NHtBu)]+
complex.11f Nucleophilic substitution of the nitro group of
[Cc-NO2]+ by n-butyl amine gives [Cc-NHnBu]+.12b Heck
reported the formation of the Boc-protected [Cp*Co(η5-
C5H4NHC(O)OtBu)]+ ion with one Cp* ligand starting from
[Cp*Co(η5-C5H4COCl)]+ and sodium azide, followed by a
8
Electron-poor metallocenes such as Cp2Ti(CCR)2 or
[Cp2Co]+ (Cc+)6,9 were successfully incorporated as electron
acceptors in CT systems. Compared to the ubiquitous Fc/Fc+
couple, the Cc/Cc+ couple has been less often employed in CT
and PET schemes.6,9,10 This underdeveloped attention is
certainly due to the more difficult and less established
substitution chemistry of Cc+.11 Only in the last years have
the groups of Bildstein and Heck put forward reliable routes
toward important Cc+ key building blocks, such as [Cc-Br]+,
[Cc-NO2]+, [Cc-N3]+, [Cc-COOH]+, or [Cc-NH2]+.12,13
As our group and others have a strong interest in the
development of redox-active oligoferrocene amide foldamers,14
ferrocene-based redox switches involving classical NH···X and
nonclassical NH···Fe hydrogen bonds,15 ferrocene amide ion
sensors,16 amide-linked ferrocene-chromophore conju-
gates,4i,j,5b,6 and redox-appended enzyme models,17 we became
12a
t
Curtius reaction in BuOH.
Versatile key building block
[CcNH2]+ is obtained from [Cc-COCl]+ and NaN3 in an
Received: October 26, 2017
© XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.7b00790
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
optimized procedure reported by Bildstein.13b Thanks to the
good availability of [Cc-NH2]+ we are now in the position to
construct bimetallocene amides with [Cc-NHCO-R]+ units.
Here we report a strategy to activate [Cc-NH2]+ toward
acylation. After activation of [Cc-NH2]+, acid chlorides R-
COCl were employed as acylating agents with R = Ph, Fc, and
Cc+. This gives access to Cc-[NHCO-R]+ amides with the
charged cobaltocenium ion connected to the N-side of the
amide unit. The metal−metal interaction in the two novel
homo- and heterometallic bimetallocenes [Cc-CONH-Cc]2+/+
and [Fc-CONH-Cc]+ via the amide unit is probed by optical
spectroscopy and UV/vis/NIR spectroelectrochemistry
(Scheme 1). The CT properties of the novel heterobimetallo-
according to the Bildstein procedure13b was deprotonated by
a slight excess of sodium hydride in THF (Scheme 2). After the
Scheme 2. Deprotonation of [H-1]+ and Resonance
a
Structures of 1
a
Atom numbering for NMR assignment.
Scheme 1. Reported and Unknown Amide Bridged
Bimetallocenes with Fc and Cc+ Building Blocks.6,14d,e,i
color change from yellow to red within a few minutes (Figure
1), the solution was separated from the excess NaH by
filtration. Prolonged reaction with NaH leads to decomposition
according to the formation of a black insoluble precipitate (see
the Experimental Section). All attempts to crystallize neutral
complex 1 were unsuccessful. Consequently, red cobalt
complex 1 was investigated spectroscopically in solution and
by density functional theory (DFT) calculations (B3LYP/def2-
TZVP/PCM THF).
Cobaltocenium hexafluoridophosphate exhibits absorption
bands at 262, 301, and 404 nm in CH3CN characteristic for
many Cc+ complexes (Figure S1).20 The latter two bands are
clearly identified as spin-allowed ligand field transitions based
on their weak intensity, while the high energy intense band has
been assigned ligand-to-metal charge transfer (LMCT)
character.20a In THF, the amino substituent in [H-1]+ shifts
all bands to lower energy, namely, 278, 358, and 414 nm.
Deprotonation of [H-1]+ to 1 augments the shift to 280, 371,
and 440 nm, respectively, and gives a new shoulder around 550
nm (Figure 1). The 440/550 nm bands of 1 account for its red
color.
Time-dependent DFT (TD-DFT) calculations find com-
posed bands at 317, 421, and 490 nm for [H-1]+ (Figure S2).
The energies are calculated as roughly 0.5 eV too low probably
due to the failure of TD-DFT to describe these transitions
properly in a quantitative sense. A very weak ligand field
transition is calculated at 501 nm. All calculated bands for [H-
1]+ display essentially ligand field character with the high-
energy band at 317 nm featuring some LMCT contribution,
originating from the nitrogen lone pair. Bands at 330, 426, 488,
and 554 nm are calculated by TD-DFT for 1 (Figure S2).
Again, all bands are composed of ligand field transitions but
with additional nitrogen lone pair → cobalt LMCT character
(Figure 1). Although the numerical agreement is far from
perfect, the batho- and hyperchromic effects experienced by the
first three spin-allowed ligand field bands due to the increased
LMCT character in 1 are reproduced well by the calculations
(Figures 1 and S2).
The electronic structure of the aminocobaltocenium
derivatives is best described with significant iminium ion
character showing bond length alternation within the
substituted C5H5NH2 ring, short exocyclic C−N bond lengths
of 1.340(4)−1.372(4) Å, and a tilted substituted ring with the
ipso carbon atom being at a larger distance from the cobalt
center (tilt angles 173.8(3)−175.7(4)°).12a,13b,21 DFT calcu-
lations on [H-1]+ reproduce these numbers reasonably well
with a C−N bond length of 1.35 Å and a tilt angle of 173°
(Figure S3).
cene [Fc-CONH-Cc]+ are compared to those of its [Cc-
CONH-Fc]+ isomer which shows strongly solvatochromic CT
bands (Scheme 1).6 The electronic interaction in novel d6-/d7-
mixed-valent cation [Cc-CONH-Cc]+ are contrasted to those
of the d5-/d6-mixed-valent cation [Fc-CONH-Fc]+.14d,e
RESULTS AND DISCUSSION
■
The major challenge toward the introduction of [Cc-NH]+
units into amides is the very low basicity and nucleophilicity of
the [Cc-NH2]+ cation with a pKb value of 15.6.11c In fact, all
conventional amide coupling formation reactions with [Cc-
NH2]+ and strong electrophiles or potent coupling reagents
failed in our hands. Reduction of positively charged poor
nucleophile [CcNH2]+ to corresponding neutral amino
cobaltocene Cc-NH2 by KC8 and subsequent acylation by R−
COCl was unsuccessful as well due to competing decom-
position side reactions. Deprotonation of [Cc-NH2]+ to CcNH
by methyl lithium, potassium bis(trimethylsilyl)amide or tert-
butylimino-tris(dimethylamino)phosphorane and subsequent
acylation with R−COCl failed to give the desired pure products
in isolable form due to the formation of side products. Finally,
sodium hydride proved to be the ideal base for this propose.19
Preparation and Properties of CcNH (1). Amino-
cobaltocenium hexafluoridophosphate [H-1][PF6] prepared
B
DOI: 10.1021/acs.organomet.7b00790
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
1
Figure 2. H NMR spectra of [H-1][PF6] (black) and 1 (red) in d8-
THF.
(C4) dramatically shifts by 26.5 ppm to lower field from 132.1
to 158.6 ppm. The latter value indicates R2CNR′ imine
character.22
The change in electron density upon deprotonation should
also affect the 59Co NMR shift. Hence, attempts to observe
59Co NMR resonances of [H-1]+ and 1 in THF were
undertaken. The 59Co NMR resonance of [CcH]+ has been
reported at −2140 ppm,23a while typical (cyclopentadienyl)-
bis(olefine) cobalt(I) complexes display 59Co NMR resonances
in the range from −1100 to −1640 ppm (all referenced against
K3Co(CN)6 in D2O).23b For [H-1]+, a resonance at −2035
ppm could be found consistent with a cobaltocenium ion
(Figure S7). Unfortunately, no 59Co NMR resonance could be
detected for 1 under our conditions in the chemical shift range
from −12 000 to +27 000 ppm.
Deprotonation of iminium ion [H-1]+ to imine 1 is fully
reversible as addition of triflic acid restores the yellow color, the
optical spectrum and the 1H NMR spectrum of [H-1]+
(Figures 1 and S8−S10).
The symmetric and antisymmetric NH stretching vibrations
of [H-1]+ and the NH2 deformation appear at 3444, 3334, and
1639 cm−1, respectively, in the infrared spectrum in THF
solution (Figures S11 and S12). Expectedly, a single band for
the NH stretching vibration is observed for 1 at 3283 cm−1,
while the NH2 deformation band has vanished in THF.
Numerical frequency calculations on the DFT level (B3LYP/
def2-TZVP/PCM THF; scaled by 0.945) calculate these
vibrational energies at 3476 and 3374 cm−1 ([H-1]+) and at
3246 cm−1 (1) in reasonable agreement with the experiment
lending credence to the imine description of 1 with minor
contribution of the zwitterionic resonance structure (Scheme
2). We hypothesized that imine 1 should be nucleophilic
enough for acylation reactions.
Figure 1. UV/vis spectra of [H-1][PF6] (black), 1 (red), and 1 with
CF3SO3H added (blue) in THF. TD-DFT calculated difference
electron densities for relevant transitions of [H-1]+ and 1 with contour
values of 0.01 a.u.; purple = electron density depletion, orange =
electron density gain. CH hydrogen atoms omitted for clarity.
According to DFT calculations on 1, the C−N distance
shortens to 1.30 Å and the tilt angle reduces to 163°.
Consequently, a description of the N-substituted C5 ligand as
2,4-cyclopentadiene-1-imine coordinated to cobalt(I) is appro-
priate for 1 with only minor zwitterionic character (Scheme 2;
Figure S3).
Proton and carbon NMR shifts are substantially affected by
deprotonation of [H-1]+ to 1 (Figures S4−S6). The proton
resonances shift to higher field (Figure 2) by 0.88, 0.16, and
0.54 ppm (H3, H2, and NH). Even the proton resonances of the
unsubstituted Cp ring (H1) experience a strong shift by 0.51
ppm suggesting significant reorganization of the entire
electronic structure. Similarly, the 13C resonances for C1, C2,
and C3 shift to higher field, while the ipso carbon resonance
Preparation and Properties of [R-CONH-Cc]n+ (2+, 3+,
and 42+). Treatment of imine 1 with acid chlorides R−COCl
(R = Ph, Fc, and Cc+) yields corresponding amides 2[PF6],
3[PF6], and 4[PF6]2 in good yields of 62, 89, and 73%,
respectively (Scheme 3). In the reaction mixture of 1 with Ph-
COCl, the doubly acylated amine [Cc-N(COPh)2]+ was
detected by ESI+ mass spectrometry, suggesting that smaller
electrophiles can attack the nitrogen atom even twice. No
double substitution was observed for the larger metallocenyl
acid chlorides. All amides were fully characterized by elemental
analysis, ESI+ and HR-ESI+ mass spectrometry, and NMR and
IR spectroscopy (Figures S13−S34). Optical and electro-
chemical properties of bimetallocences 3+ and 42+ and reference
cobaltocenium amide 2+ were probed by UV/vis/NIR
C
DOI: 10.1021/acs.organomet.7b00790
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Scheme 3. Synthesis of [CcNH]+ Amides 2[PF6], 3[PF6],
and 4[PF6]2
counterions and is thus a poor reference compound for charged
amides 2+−42+.25
Single crystals of 2[PF6] and 3[PF6] suitable for X-ray
diffraction analysis were obtained (Figure 3a,b; Table 1).
a
a
Atom numbering for NMR assignment.
spectroscopy, electrochemistry, and UV/vis/NIR spectroelec-
trochemistry. The solid state structures of 2[PF6] and 3[PF6]
were ascertained by X-ray crystallography.
The ESI+ and HR-ESI+ mass spectra display peaks at mass-
to-charge ratios appropriate for the cations 2+, 3+, and [4-H]+
(see the Experimental Section and Figures S13−S15).
In the multinuclear NMR spectra of 2[PF6], 3[PF6], and
4[PF6]2 (1H, 13C, 19F, and 31P; Figures S16−S33) all
resonances have been assigned to corresponding nuclei. The
1H (H1, H2, and H3) and 13C resonances (C1, C2, and C3) of
the Cc+ units of 2+, 3+, and 42+ are negligibly affected by the R
substituents. The resonance of the C4 nuclei shifts to higher
field from 114.4 and 113.8 to 111.0 ppm for R = Fc, Ph, and
Cc+ with increasing electron-withdrawing nature of R. The
same trend holds for the carbonyl resonances C5 with δ =
170.8, 167.2, and 162.0 ppm for R = Fc, Ph, and Cc+,
respectively. The NH proton resonance does not follow this
trend with δ = 8.41, 9.17, and 8.96 ppm for R = Fc, Ph, and
Cc+, suggesting other determining factors such as hydrogen
bonding. In fact, small variations in the 19F chemical shifts of
the hexafluoridophosphate counterions display a similar trend
with δ = −72.9, −73.2, and −73.1 ppm for R = Fc, Ph, and Cc+
which might be indicative of ion-pair formation via NH···F
hydrogen bonds in acetonitrile solution. Such ion-pair
formation has been previously observed in positively charged
ferrocenium and cobaltocenium amides, thioamides, ureas and
thioureas.6,10,14f,15e,24
Figure 3. Molecular structures of (a) 2[PF6] and (b) 3[PF6] ×
1/2C6H6 in the solid state including a nearest neighbor molecule and
counterions (Thermal ellipsoids at 50% probability. CH hydrogen
atoms and solvent omitted; atom numbering modified with respect to
the deposited data for clarity).
Table 1. Selected Bond Distances (Å) and Angles (deg) of
a
2[PF6] and 3[PF6]
2[PF6]
3[PF6]
Cp−Cp (Cc+)
Cp−Cp (Fc)
C1−N1
N1−C2
C2−O1
C2−C3
N1···F6
F6···H1
3.275(2)
3.281(3)
3.303(3)
1.386(4)
1.374(4)
1.223(4)
1.474(5)
2.920(19)
2.19
1.389(3)
1.371(3)
1.220(3)
1.499(3)
3.070(2)
2.23
N1−H1···F6
Co1−Fe1
160.3
140.0
NH hydrogen bonding was further probed by IR spectros-
copy (Figure S34). In fact, absorption bands for NH stretching
6.069(2)
3.555(3)
Cp(Cc)−Cp(Fc) (intermolec.)
Ph−Ph (intermolec.)
Cp−Co1−Cp
Cp−Fe1−Cp
C1−N1−C2
N1−C2−C3
N1−C2−O1
and amide I vibrations appear at νNH
̃
= 3264, 3394, and 3305
4.041(2)
cm−1 and νamideI
̃
= 1654, 1678, and 1664 cm−1 for R = Fc, Ph,
179.16(6)
178.95(10)
177.66(10)
125.5(3)
and Cc+, respectively. These data suggest the strongest NH
hydrogen bond for 3+ (R = Fc) and the weakest one for 2+ (R =
Ph). Charging of the CO substituted metallocene in a formal Fc
to Cc+ isosteric replacement (3+ → 42+) diminishes the NH
hydrogen bond strength. Neutral diphenylamide Ph−CONH−
124.13(17)
116.55(18)
121.86(19)
115.0(3)
122.7(3)
̃
= 3345 cm−1 and νamideI = 1654 cm−1 only forms
a
Ph with νNH
intermolecular NH···OC hydrogen bonds due to the absence of
̃
Cp denotes center of cyclopentadienyl rings; Ph denotes center of
phenyl rings.
D
DOI: 10.1021/acs.organomet.7b00790
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
However, 4[PF6]2 crystallized under many attempted con-
ditions only as heavily intergrown, sometimes very large
crystallites which were unsuitable for single crystal diffraction
(Figure S34). The cation of 2+ forms a NH···F hydrogen bond
−
to a PF6 counterion with a N···F distance of 3.070(2) Å
(Figure 3a, Table 1). 3+ forms a closer contact to its counterion
with a shorter N···F distance of 2.920(19) Å (Figure 3b, Table
1). Although not very pronounced, this difference fits to the
results from the NMR and IR data with 3+ (R = Fc) forming
stronger hydrogen bonds than 2+ (R = Ph). The contact ion
pairs 2[PF6] and 3[PF6] pack via π stacking of the Ph
substituents (center-to-center distance 4.041(2) Å; Figure 3a)
or via Cp···Cp contacts (center-to-center distance 3.555(3) Å;
Figure 3b), respectively.
Similar to the well-explored Fc/Fc+ redox chemistry, the Cc/
Cc+ redox potential can be tuned over a wide range, currently
from −0.97 V to −2.37 V vs FcH/FcH+. Linear correlations
with substituent properties apply as well.2a,6,12b,13b The phenyl
substituted reference amide 2+ is reversibly reduced to the
cobaltocene 2 at −1.360 V in the cyclic voltammogram (Figure
4a, Table 2). At Ep = −2.265 V an irreversible CoII/CoI
reduction wave12b (likely associated with reductive deprotona-
tion of the amide proton) appears, which gives rise to a follow-
up product that is reoxidized at −1.825 V (Figure 4a).
Spectroelectrochemical reduction of 2+ to 2 and reoxidation to
2+ is reversible as well, provided that the second irreversible
reduction is not addressed (Figure S35).
Replacing the Ph substituent in 2+ by the Fc substituent in 3+
barely affects the reversible Cc/Cc+ redox process (E1/2
=
−1.355 V) and the irreversible CoII/CoI reduction/follow-up
reaction (Ep = −2.290 and −1.840 V), respectively (Figure 4b;
Table 2). The reversible Fc/Fc+ oxidation of 3+ is observed in
the expected range for CO substituted ferrocenes at 0.305 V.2a
Compared to the [Cc-CONH-Fc]+ isomer (Scheme 1) with an
easy-to-reduce Cc+ unit (E1/2 = −1.150 V) and an easy-to-
oxidize Fc unit (E1/2 = −0.015 V), the potential difference
between the respective redox processes has increased by more
than 0.5 V from 1.135 V in [Cc-CONH-Fc]+ to 1.660 V in 3+.6
Expectedly, the bicobaltocenium complex 42+ is reduced
reversibly two times (Table 2, Figure 4c) and irreversibly at
lower potential (Ep = −2.100 V) with an oxidation wave of the
follow-up product at Ep = −1.570 V (Figure 4c, Table 2). The
assignment of the Cc+ reduction waves to individual Cc+ units
in 42+ is straightforward according to expected substituent
effects, reference compounds (2+ and reported [CcCOR]+
derivatives), and DFT calculations (Figure 4c).2a,6,10,13b
For the prototypical symmetric [Cc-Cc]2+ bimetallocenium,
the potential difference between the reductions has been
reported by Weaver as 0.395 V.26 The potential difference of
42+ is with 0.400 V accidentally similar due to compensating
Co···Co distance and substituent effects.
The electronic spectrum of 2[PF6] in CH3CN (Figure 5a)
shows a prominent LMCT maximum at 280 nm, a less intense
band at 347 nm, and a shoulder at 406 nm. This pattern is
characteristic for cobaltocenium ions (see above).20 The
bicobaltocenium ion 42+ displays essentially the same pattern
(λ = 271, 346, 406 nm), yet with higher intensity (Figure 5a,
Experimental Section).
In the heterobimetallic complex 3+ the ferrocene can act as
donor moiety, similar to its [Cc-CONH-Fc]+ isomer (Scheme
1).6 The latter isomer with the smaller redox potential gap (and
consequently a smaller HOMO−LUMO gap), features a
solvatochromic absorption band with MM’CT character at
Figure 4. Cyclic voltammograms of (a) 2[PF6], (b) 3[PF6], and (c)
4[PF6]2 in CH3CN/[nBu4N][PF6] (scan rate 100 mV s−1). DFT
calculated spin densities of 4+ and 4 with contour values of 0.01 a.u.;
CH hydrogen atoms omitted for clarity.
E
DOI: 10.1021/acs.organomet.7b00790
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
transition in 3+ at 471 nm. This MM’CT occurs at considerably
higher energy in 3+ (by 2500 cm−1) as compared to the
MM’CT of the [Cc-CONH-Fc]+ isomer which fits well to the
electrochemical data (see above).6 Hush analysis with the
modified Hush formula for closed-shell donor−acceptor
Table 2. Redox Potentials (V) in Acetonitrile/[NBu4][PF6]
vs FcH/FcH+
2[PF6]
3[PF6]
4[PF6]2
E1/2 (Fc/Fc+)
0.305
E1/2 (C−Cc/C−Cc+)
E1/2 (N−Cc/N−Cc+)
Ep (ox; follow-up)
Ep (CoII/CoI)
−1.020
−1.420
−1.570
−2.100
̃ ̃
systems9g HAB = 2.05 × 10−2 (0.5εmax 1/2/r gives
Δ1/2ννmax)
−1.360
−1.825
−2.265
−1.355
−1.840
−2.290
the electronic coupling matrix element HAB = 584 cm−1 for the
closed-shell mixed-metal system 3+ (Table 3).
Further proof that the MM’CT assignment of 3+ is correct
comes from spectroelectrochemistry. Oxidation of 3+ to the
cobaltocenium−ferrocenium complex 32+ bleaches the MM’CT
band around 471 nm, while the characteristic ferrocenium
absorption of [Fc−C(O)R]+ units at 632 nm grows (Figures 5b
and S37).20a,27 Likewise, reduction of 3+ to 3 bleaches the
MM’CT band as the Cc+ electron acceptor is reduced to
cobaltocene (Figure S37). No distinct new bands grow in
similar to the reduction of 2+ to 2 (Figure S35). The overall
reduction of 3+ to 3 is spectroscopically more complicated
534 nm in CH3CN.6 For 3+, the cobaltocenium ligand field
band around 406 nm is indeed considerably broadened on the
lower energy side. According to TD-DFT calculations on 3+,
these absorptions represent MM’CT transitions from iron to
cobalt (Figure 5a). To distinguish the MM’CT from the normal
Cc+ and Fc absorption pattern, the Cc+ pattern of the spectrum
of 2+ and the spectrum of Fc-COOMe were subtracted from
the composed spectrum of 3+ (Figure S36). This procedure
yields an approximate absorption band for the MM’CT
Figure 5. (a) UV/vis spectra of 2[PF6], 3[PF6], and 4[PF6]2 in CH3CN. Changes in the UV/vis/NIR spectra in the course of redox events in
CH3CN/[nBu4N][PF6] during OTTLE spectroelectrochemistry: (b) oxidation of 3+ → 32+, (c) reduction of 42+ → 4+, and (d) reduction of 4+ → 4.
TD-DFT calculated difference electron densities with contour values of 0.01 a.u.: purple = electron density depletion, orange = electron density gain.
CH hydrogen atoms omitted for clarity.
F
DOI: 10.1021/acs.organomet.7b00790
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Table 3. Results of the Hush Analysis of the MM’CT (IVCT) Bands of Several Bimetallocenes Composed of Fc, Fc+, Cc, and
a
Cc+ Moieties
a
ν
̃
(cm−1) (ε (M−1 cm−1))
Δν1/2
̃
(cm−1
)
ΔG0 (cm−1
)
r (Å)
HAB (cm−1
)
α
λ (cm−1
)
b
[Fc-Fc]+ (ref 26a)
5680 (750)
18115 (2480)
6580 (3500)
4910 (1340)
9556 (95)
3620
2541
12752
3186
5.0
5.0
5.0
6.9
6.9
6.9
6.9
6.9
509
1256
1229
503
0.090
0.069
0.187
0.102
0.015
0.021
0.028
0.044
3139
5363
3394
3539
6168
9582
7851
9249
b
[Cc-Fc]+ (refs 9a and 9g)
4176
3900
4360
2443
5584
4113
5436
b
[Cc-Cc]+ (ref 26a)
c
[Fc-CHCH-Fc]+ (ref 26b)
1371
d
[Fc-CONH-Fc]+ (refs 14d and 14e)
3388
140
b
[Cc-CONH-Fc]+ (ref 6)
18736 (347)
21240 (886)
12475 (505)
9154
400
b
[Fc-CONH-Cc]+ 3+
13389
584
b
[Cc-CONH-Cc]+ 4+
3226
550
a
b
c
d
Average distances of the two metal centers as estimated by DFT calculations. In CH3CN. In CH2Cl2. In THF.
involving three individual steps with distinct isosbestic points
(Figure S37). We also note some precipitation during
electrolysis. However, the overall process 3+ → 3 → 3+ is
reversible (Figure S37).
All amide-bridged bimetallocenes [Mc-NHCO-Mc]+ (Mc =
Fc and Cc) display MM’CT or IVCT transitions albeit with
different intensities due to the different orbital symmetry and all
belong clearly to class II of the Robin/Day system. They all
exhibit similar nuclear reorganization energies λ = νmax
− ΔG0
̃
Reduction of 42+ to 4+ yields the redox-asymmetric d7-CoII/
d6-CoIII mixed-valence system with the [CcCO]+ unit reduced
to the cobaltocene moiety (Figure 4c). Spectroelectrochemical
reduction delivers a new prominent band at 524 nm and a very
broad band at 803 nm (Figure 5c). Both bands bleach upon
reoxidation to 42+ and upon further reduction of 4+ to the
CoIICoII complex 4 (Figures S38 and 5d). These findings
suggest that these bands are associated with the uncharged [Cc-
CO] cobaltocene moiety. Indeed, TD-DFT calculations on 4+
assign the band at 524 nm to a metal-to-ligand charge transfer
(MLCT) from the electron-rich [Cc-CO] cobaltocene moiety
to the carbonyl group of the bridge and importantly describe
the band at 803 nm as an intervalence charge transfer (IVCT)
transition from the electron-rich [Cc-CO] cobaltocene to the
electron-deficient [Cc-NH]+ cobaltocenium unit.
(Table 3) which has been discussed before for other linked
bimetallocenes based on the similar bond length and vibrational
data of the involved metallocenes.26a However, the reorganiza-
tion energy λ of the amide-bridged bimetallocenes [Mc-
NHCO-Mc]+ is significantly larger than the reorganization
energy of [Fc-Fc]+, [Fc-Cc]+, and [Cc-Cc]+ with a direct link
(Table 3). It is also larger than estimated for the vinylene
bridged biferrocene [Fc-CHCH-Fc]+ with a similar metal−
metal distance.26b It is tempting to attribute this extra effect to
the connecting amide unit and especially the hydrogen bonds
of counterions to the NH group. Charge transfer across the
amide unit and the hydrogen-bonded counterion certainly
affects the NH···X bonding situation and contributes to the
inner-sphere reorganization energy (if one ascribes the
hydrogen-bonded counterion to the inner sphere). More
systematic studies on solvent and counterion effects in amide-
linked metallocenes are clearly warranted and will be conducted
in the future.
Gaussian deconvolution of the absorption spectrum of 4+
yields the IVCT absorption band data (Table 3; Figure S39).
With an (averaged) Co···Co distance of r = 6.9 Å, Hush’s
formula28 delivers the electronic coupling matrix element HAB
=
̃ ̃
2.05 × 10−2 (εmax 1/2/r = 550 cm−1 for the open-shell
Δ1/2ννmax)
system 4+. This is less than half of HAB obtained for the redox-
symmetric bimetallocene [Cc-Cc]+ lacking the amide unit
(Table 3). This decrease is likely due to the redox asymmetry,
the larger metal−metal distance, and the less conjugated amide
bridge in 4+ dramatically decreasing the transition dipole
moment for the IVCT transition.
CONCLUSIONS
■
The poor nucleophile [Cc-NH2]+ [H-1]+ has been successfully
activated by deprotonation to the imine CcNH 1 by NaH.
Acylation of 1 by R−COCl gave the cobaltocenium amides [R-
CONH-Cc]+ 2+, 3+, and 42+ (R = Ph, Fc, and Cc+). They form
contact ion pairs with hexafluoridophosphate counterions in
solution (2+, 3+, and 42+) and in the solid state (2+, 3+, and
likely 42+) via NH···F hydrogen bonds. Both the donor−
acceptor heterobimetallocene 3+ and the mixed-valent CoIII/
CoII complex 4+ (prepared by spectroelectrochemistry) are
Robin/Day class II systems with similar nuclear reorganization
energies but different electronic mixing coefficients α. The
electronic coupling in the mixed-valent CoIII/CoII complex 4+ is
4-fold higher than that of the mixed-valent FeIII/FeII complex
[Fc-CONH-Fc]+ due to the more favorable π symmetry of the
redox orbitals in 4+. The reorganization energies λ of the amide-
bridged bimetallocences are increased by the hydrogen-bonded
counterions relative to those of bimetallocenes with a direct
link.
Compared to the d6-FeII/d5-FeIII mixed-valent system [Fc-
CONH-Fc]+, HAB of 4+ is approximately four times larger.14e
The same trend holds for the electronic mixing coefficients α =
HAB/νmax (Table 3). Clearly, orbital symmetry plays a major
̃
role with the mainly iron-centered e orbitals with local δ
symmetry interacting only weakly. However, the redox orbitals
in the d7-CoII/d6-CoIII system both feature π* character with
both ipso carbon atoms involved. Such a symmetry of the redox
orbitals enables electronic interaction via the amide bridge (see
Figure 5c).
In the heterometallic isomeric bimetallocenes [Cc-CONH-
Fc]+ and [Fc-CONH-Cc]+ (3+), the electronic mixing
coefficient α is larger than that in [Fc-CONH-Fc]+ due to
the extended Cc+ acceptor π system (Figure 5a) but smaller
than that in [Cc-CONH-Cc]+ (4+) due to the very localized Fc
donor system in the heterometallics (Figure 5a). The electronic
mixing coefficient α increases in the series [Fc-CONH-Fc]+,
[Cc-CONH-Fc]+, [Fc-CONH-Cc]+, and [Cc-CONH-Cc]+
(Table 3).
On the basis of the availability of suitably substituted
aminocobaltocenium complexes and the here developed amide-
coupling chemistry, conducting peptidic molecular wires with
cobaltocene/cobaltocenium units in the main chain are now
within reach. The development of molecular wires, as well as
sensing and charge-separating systems with amino-substituted
G
DOI: 10.1021/acs.organomet.7b00790
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
= 1212; crystal size 0.460 × 0.287 × 0.120 mm3; θ = 2.091−28.337°;
−10 ≤ h ≤ 10, −25 ≤ k ≤ 25, −19 ≤ l ≤ 20; rfln collected = 13 537;
rfln unique = 5541 [R(int) = 0.0466]; completeness to θ = 25.242° =
99.4%; semiempirical absorption correction from equivalents; max and
min transmission 1.31360 and 0.81612; data 5541; restraints 126;
parameters 379; goodness-of-fit on F2 = 1.052; final indices [I > 2σ(I)]
R1 = 0.0472. wR2 = 0.1121; R indices (all data) R1 = 0.0719, wR2 =
0.1323; largest diff. peak and hole 0.636 and −0.393 e Å−3. The
hexafluoridophosphate counterion is disordered over two positions.
CCDC 1581720 and 1581721 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of charge
from Cambridge Crystallographic Data Center via www.ccdc.cam.ac.
uk/data_request/cif.
Materials. Unless otherwise noted, all chemical reagents were used
without any further purification as received from suppliers (Sigma-
Aldrich, Acros, Alfa Aesar). Tetrahydrofuran was freshly distilled from
potassium, CH3CN from calcium hydride. For the characterization
experiments of 1, the sodium hydride was freed from mineral oil prior
the reaction by washing with absolute THF. Cc[PF6],13a [H-
1][PF6],13b [Cc-COOH][PF6],13a and Fc-COOH45 were prepared
according to literature procedures.
cobaltocenium electron acceptor units as building blocks is now
actively pursued.
EXPERIMENTAL SECTION
■
Instrumentation. NMR spectra were recorded on a Bruker
Avance DRX 400 spectrometer at 400.31 MHz (1H), 100.05 MHz
(13C{1H}), 376.67 MHz (19F), and 162.05 MHz (31P) and on a Bruker
Avance DSX 400 spectrometer at 94.88 MHz (59Co). Chemical shifts
are reported on the δ scale in ppm relative to the solvent signal as an
internal standard (CD3CN (1H: δ = 1.94 ppm; 13C: δ = 118.26 ppm),
d8-THF (1H: δ = 3.58 ppm; 13C: δ = 67.57 ppm))29 or relative to an
external standard (19F: CFCl3, 31P: H3PO4, 59Co: 1.0 M K3[Co(CN)6]
in H2O); s = singlet, d = doublet, and t = triplet. IR spectra were
recorded with a Thermo Nicolet 5700 FT-IR as ATR and with a
Bruker ALPHA FT-IR spectrometer as KBr disk, and in THF, with
signal intensities: s = strong, m = medium, w = weak. ESI and HR ESI
mass spectra were recorded on a Micromass Q-TOF-Ultima
spectrometer and a Waters Q-Tof Ultima 3 spectrometer, respectively.
Cyclic voltammetric measurements were carried out with a BioLogic
SP-50 voltammetric analyzer in CH3CN containing 0.1 M [nBu4N]-
[PF6] as supporting electrolyte at a platinum working electrode, a
platinum wire as counter electrode, and a 0.01 M Ag/AgNO3 electrode
as the reference electrode. All cyclic voltammetric measurements were
recorded at 100 mV s−1 scan rate. Ferrocene or decamethylferrocene
were employed as an internal reference redox system. (rev.) =
reversible, (irrev.) = irreversible redox process. Spectroelectrochemical
experiments were performed using a Specac omni-cell liquid
transmission cell with CaF2 windows equipped with a Pt gauze
working electrode, a Pt counter electrode, and a Ag pseudoreference
electrode, melt-sealed in a polyethylene spacer (path length 0.7
mm).30 UV/vis/NIR absorption spectra were measured on a Varian
Cary 5000 spectrometer in 1.0 cm cells (Hellma, Suprasil); sh =
shoulder.
General Procedures. All preparations (until quenching with
water) were performed under an inert atmosphere of argon, using an
M. Braun glovebox and absolute solvents.
Cc[PF6]. UV/vis (CH3CN): λ [nm] (ε [M−1 cm−1]) = 262
(36 140), 301 (1140), 404 (230) consistent with Cc[ClO4]: UV/vis
(H2O): λ [nm] (ε [M−1 cm−1]) = 263 (38 000), 300 (1200), 407
(220).20a
[H-1][PF6]. 1H NMR (d8-THF): δ [ppm] = 5.24 (t, 2H, 3JHH = 1.9
Hz, H3), 5.40 (t, 2H, 3JHH = 1.9 Hz, H2), 5.45 (s, 5H, H1), 5.61 (s, 2H,
H
NH). 13C {1H} NMR (d8-THF): δ [ppm] = 66.4 (C3), 79.1 (C2),
84.9 (C1), 132.1 (C4). 59Co NMR (THF): δ [ppm] = −2035. UV/vis
(THF): λ [nm] (ε [m−1 cm−1]) = 278 (20 180), 358 (4480), 414 (sh,
1220). IR (KBr): ν
(s, CH), 3124 (s, CH), 1633 (s, CN), 1538 (s, CN), 1414 (m, C = C),
831 (m, PF), 638, 557 (m, FPFdef), 452. IR (KBr): ν
[cm−1] = 3503 (s,
NHasym), 3402 (s, NHsym), 1633 (s, NH2,def), 1538 (s, CN), 831 s, PF),
557 (s, PF2,def). IR (THF): ν
[cm−1] = 3444 (s, NHasym), 3334 (s,
̃
[cm−1] = 3503 (s, NHasym), 3402 (s, NHsym), 3244
Density Functional Calculations. Calculations were carried out
with the ORCA 4.0.1/DFT series of programs.31 The B3LYP
formulation of density functional theory was used for geometry
optimizations and numerical frequency calculations employing the
ZORA-Def2-tzvp basis set,32,33 the RIJCOSX approximation,34,35 the
zeroth order regular approximation (ZORA),36,37 and the KDIIS
algorithm38 at GRID5. No symmetry constraints were imposed on the
molecules. Solvent modeling was done employing the conductor-like
continuum polarization model (CPCM CH3CN, and THF).39
Crystal Structure Determinations. Intensity data were collected
with a STOE IPDS-2T diffractometer using Mo Kα radiation (λ =
0.71073 Å). The diffraction frames were integrated using the STOE X-
RED package and most were corrected for absorption with MULABS
of the PLATON software package.40−42 The structure was solved by
direct methods and refined by the full-matrix method based on F2
using the SHELX software package.43,44 All non-hydrogen atoms were
refined anisotropically, while the positions of all hydrogen atoms were
generated with appropriate geometric constraints and allowed to ride
on their respective parent carbon atoms with fixed isotropic thermal
parameters.
̃
̃
NHsym), 1639 (s, NH2,def), 1542 (s, CN), 559 (s, PF2,def).
Synthesis of 1. Aminocobaltocenium hexafluoridophosphate [H-
1]PF6 (10 mg, 29 μmol, 1 equiv) was dissolved in THF (5 mL) and
NaH (1.4 mg, 58 μmol, 2 equiv) was added. The solution was stirred
and the color changed from orange to red. After 5 min, the solution
was filtered through a 0.2 μm PTFE syringe filter. Prolonged reactions
times (ca. 20 min) lead to the formation of a black precipitate,
decreasing the yield of 1.
1H NMR (d8-THF): δ [ppm] = 4.19 (s, 2H, H3), 4.94 (s, 5H, H1),
5.07 (s, 1H, HNH), 5.17 (s, 2H, H2). 13C {1H} NMR (d8-THF): δ
[ppm] = 60.2 (C3), 76.6 (C2), 81.7 (C1), 158.6 (C4). UV/vis (THF):
λ [nm] (ε [M−1 cm−1]) = 280 (17 515), 371 (5660), 440 (2565). IR
(THF): ν
̃
[cm−1] = 3283 (m, NH), 1565 (s, CN).
Synthesis of 2[PF6]. Aminocobaltocenium hexafluoridophosphate
[H-1][PF6] (187.6 mg, 537 μmol, 1.0 equiv) was dissolved in THF
(25 mL) and NaH (150 mg, 3.75 mmol, 7.0 equiv, 60% dispersion in
mineral oil) was added. The solution was stirred and the color shifted
from orange to red. After 10 min, CcNH the solution was filtered
through a 0.2 μm PTFE syringe filter.
Crystallographic Data of 2[PF6]. C17H15CoF6NOP (453.20);
triclinic, P1; a = 7.6178(15) Å, b = 9.4454(19) Å, c = 12.203(2) Å,
̅
α = 73.80(3)°, β = 85.77(3)°, γ = 81.08(3)°, V = 832.6(3) Å3, Z = 2;
density, calcd. = 1.808 g cm−3, T = 100 K, μ = 1.198 mm−1; F(000) =
456; crystal size 0.140 × 0.117 × 0.090 mm3; θ = 2.268−28.127°; −10
≤ h ≤ 10, −10 ≤ k ≤ 12, −16 ≤ l ≤ 16; rfln collected = 8491; rfln
unique = 4049 [R(int) = 0.0383]; completeness to θ = 25.242° =
99.7%; semiempirical absorption correction from equivalents; max.
and min transmission 1.19124 and 0.90255; data 4049; restraints 0;
parameters 244; goodness-of-fit on F2 = 1.053; final indices [I > 2σ(I)]
R1 = 0.0323. wR2 = 0.0736; R indices (all data) R1 = 0.0411, wR2 =
0.0791; largest diff. peak and hole 0.478 and −0.429 e Å−3.
Benzoyl chloride (80 μL, 694 μmol, 1.3 equiv) was dissolved in
THF (15 mL) and added dropwise to the CcNH solution over 5 min.
The solution was stirred for 3 h at room temperature. Water (80 mL),
acetic acid (0.5 mL), and potassium hexafluoridophosphate (500 mg,
2.71 mmol, 5.1 equiv) were added. After 12 h of stirring, the THF was
removed under reduced pressure and the solution was extracted with
dichloromethane (3 × 50 mL). The solvent was removed under
reduced pressure. The solid was washed on a short alumina column
with hexane/acetic acid (100:5) and with ethanol. On a second
alumina column, the product was washed with THF:H2O (85:15) and
eluted with THF. The solvent was removed under reduced pressure.
The solid and potassium hexafluoridophosphate (500 mg, 2.71 mmol,
5.1 equiv) were dissolved in acetone (50 mL) and stirred for 5 h.
Cyrstallographic Data of 3[PF6] × 1/2C6H6. C24H22CoF6FeNOP
(600.17); monoclinic, P21/c; a = 7.5786(15) Å, b = 19.480(4) Å, c =
15.757(3) Å, α = 90°, β = 102.42(3)°, γ = 90°, V = 2271.8(8) Å3, Z =
4; density, calcd. = 1.755 g cm−3, T = 193 K, μ = 1.507 mm−1; F(000)
H
DOI: 10.1021/acs.organomet.7b00790
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Water (250 mL) was added, and the solution was extracted with
dichloromethane (5 × 30 mL). The organic phase was dried over
sodium sulfate. The solvent was removed under reduced pressure
yielding a yellow glassy solid. Yield 151 mg (0.333 μmol, 62%). For
further purification, the solid was recrystallized from a benzene
solution at 6 °C. These crystals were suitable for X-ray diffraction
analysis.
Found: C, 44.45; H, 3.88; N, 2.51. The water content was confirmed
by H NMR spectroscopy.
1
Synthesis of 4[PF6]2. Amino cobaltocenium hexafluoridophos-
phate [H-1][PF6] (106 mg, 304 μmol, 1.0 equiv) was dissolved in
THF (15 mL) and NaH (100 mg, 2.50 mmol, 8.2 equiv, 60%
dispersion in mineral oil) was added. The solution was stirred, and the
color shifted from orange to red. After 30 min, the CcNH solution was
filtered through a 0.2 μm PTFE syringe filter. Carboxycobaltocenium
hexafluoridophosphate (116 mg, 307 μmol, 1.0 equiv) and Ghosez’s
reagent (0.2 μL, 1.51 mmol; 4.97 equiv) were dissolved in
dichloromethane (50 mL), and the solution was refluxed for 18 h.
The solvent was removed under reduced pressure, the solid was
washed with dichloromethane (30 mL). The solvent was removed
under reduced pressure. The solid was suspended in acetonitrile (25
mL), and the CcNH solution was added dropwise over 2 min. The
mixture was stirred for 6 h at room temperature. Ammonium
hexafluoridophosphate (330 mg, 2.02 mmol; 6.6 equiv) was added,
and the solution was stirred for 14 h. The solvent was removed under
reduced pressure, and the solid was washed on a short alumina column
with ethyl acetate, ethyl acetate/ethanol (1:2), and acetone. The
product was dissolved in acetonitrile (50 mL) and filtered through a
0.2 μm PTFE filter. The solvent was removed under reduced pressure
yielding a yellow powder. Yield 158 mg (223 μmol, 73%). For further
purification, the product was recrystallized by diffusing diethyl ether in
an acetonitrile solution.
MS (ESI+, CH3CN): m/z (%) = 308.05 (100) [M − PF6]+. HR-MS
(ESI+, CH3CN): obs. m/z = 308.0477; calcd. for [M − PF6]+
=
308.0486. 1H NMR (CD3CN): δ [ppm] = 5.54 (t, 2H, 3JHH = 2.0 Hz,
3
H2), 5.62 (s, 5H, H1), 6.16 (t, 2H, JHH = 2.0 Hz, H3), 7.59 (t, 2H,
3JHH = 7.6 Hz, H8), 7.69 (t, 1H, 3JHH = 7.4 Hz, H9), 7.98 (d, 2H, 3JHH
= 7.3 Hz, H7), 9.17 (s, 1H, HNH). 13C {1H} NMR (CD3CN): δ [ppm]
= 74.4 (C3), 80.8 (C2), 85.8 (C1), 113.8 (C4), 128.7 (C7), 129.7 (C8),
133.9 (C9), 133.8 (C6), 167.2 (C5). 19F NMR (CD3CN): δ [ppm] =
1
−73.2 (d, 6F, JPF = 706 Hz, FPF ). 31P NMR (CD3CN): δ [ppm] =
6
−143.5 (sept, 1P, 1JPF = 706 Hz, PPF ). IR (ATR): ν
̃
[cm−1] = 3394 (s,
6
NH), 3122 (s, CH), 3100 (s, CH), 1678 (s, CO), 1530 (s, NC), 1498,
1485, 1413, 1393, 1361, 1336, 1259 (s), 1099, 820 (m, PF), 704, 651,
553 (m, FPFdef), 459. UV/vis (CH3CN): λ [nm] (ε [M−1 cm−1]) =
244 (13 90), 280 (25 000), 347 (4720), 406 (sh, 970). CV (FcH/
FcH+, 100 mV−1, CH3CN, 0.1 M [nBu4N][PF6]): E1/2 [V] = −1.360
(rev.), −1.825 (irrev. ox.), −2.265 (irrev.). Elemental analysis: Anal.
Calcd for C17H15NOCoPF6 (453.23): C, 45.05; H, 3.34; N, 3.09.
Found: C, 44.81; H, 3.65; N, 3.31.
MS (ESI+, CH3CN): m/z (%) = 209.52 (97) [M − 2PF6]2+, 418.04
(100) [M − H − 2PF6]+, 564.01 (34) [M − PF6]+, 1273.03 (16) [2M
− PF6]+. HR-MS (ESI+, CH3CN): obs. m/z = 418.0054; calcd. for [M
Synthesis of 3[PF6]. Aminocobaltocenium hexafluoridophosphate
[H-1][PF6] (564 mg, 1.62 mmol, 1.1 equiv) was dissolved in THF
(100 mL) and NaH (250 mg, 6.25 mmol, 4.1 equiv, 60% dispersion in
mineral oil) was added. The solution was stirred, and the color shifted
orange to red. After 90 min, the CcNH solution was filtered through a
0.2 μm PTFE syringe filter. Carboxyferrocene (344 mg, 1.50 mmol,
1.0 equiv) and Ghosez’s reagent (0.7 mL, 5.29 mmol, 3.5 equiv) were
dissolved in dichloromethane (100 mL), and the solution was refluxed
for 18 h. The solvent was removed under reduced pressure, the solid
was washed with dichloromethane (50 mL), and the solvent was
removed under reduced pressure. The solid was suspended in THF
(50 mL), and the CcNH solution was added dropwise over 10 min to
the FcCOCl solution. The mixture was stirred for 24 h at room
temperature and terminated by adding water (1 mL). The solvent was
removed under reduced pressure, and the resulting oil was washed on
an alumina column with ethyl acetate and with ethanol. The solution
was filtered through a 0.2 μm PTFE filter, and the solvent was
removed under reduced pressure. The solid was dissolved in acetone
(30 mL), and potassium hexafluoridophosphate (1.00 g, 5.42 mmol,
3.4 equiv) was added. The solution was stirred for 3 h. Water (250
mL) was added, the solution extracted with dichloromethane (5 × 50
mL), and the organic phase washed with water (3 × 50 mL). The
organic phase was dried over sodium sulfate. The solvent was removed
under reduced pressure yielding a red powder. Yield 751 mg (1.33
mmol, 89%). For further purification, the product was recrystallized by
diffusing diethyl ether in an acetonitrile solution. Crystals suitable for
X-ray diffraction analysis were obtained by recrystallization from a
benzene solution at 6 °C.
1
− H − 2xPF6]+ = 418.0052. H NMR (CD3CN): δ [ppm] = 5.55 (t,
2H, 3JHH = 2.1 Hz, H2), 5.63 (s, 5H, H1), 5.76 (s, 5H, H9), 5.86 (t, 2H,
3JHH = 2.0 Hz, H8), 6.09 (t, 2H, 3JHH = 2.1 Hz, H3), 6.19 (t, 2H, 3JHH
=
2.0 Hz, H7), 8.96 (s, 1H, HNH). 13C {1H} NMR (CD3CN): δ [ppm] =
74.7 (C3), 80.8 (C2), 84.8 (C7), 85.7 (C1), 87.0 (C9), 87.1 (C8), 92.7
(C6), 111.0 (C4), 162.0 (C5). 19F NMR (CD3CN): δ [ppm] = −73.1
1
(d, 6F, JPF1 = 706 Hz, FPF ). 31P NMR (CD3CN): δ [ppm] = −143.5
6
(sept, 1P, JPF = 706 Hz, PPF ). IR (ATR): ν
̃
[cm−1] = 3305 (s, NH),
6
3220 (s, CHCc(C)), 3129 (s, CH), 3104 (s, CH), 1664 (s, amide I),
1557 (s, NC), 1494, 1464, 1421, 1384, 1384, 1286 (s), 1160, 816 (m,
PF), 640, 554 (m, FPFdef), 456. UV/vis (CH3CN): λ [nm] (ε [M−1
cm−1]) = 221 (12980), 271 (39570), 346 (6590), 406 (sh, 1900). CV
(FcH/FcH+, 100 mV−1, CH3CN, 0.1 M [nBu4N][PF6]): E1/2 [V] =
−1.020 (rev.), −1.420 (rev.), −1.570 (irrev. ox.), −1.900 (irrev. ox.),
−2.100 (irrev.). Elemental analysis: Anal. Calcd for
C21H19NOCo2P2F12 (709.21) × 1/4CH3CN: C, 35.89; H, 2.77; N,
2.43. Found: C, 35.89; H, 2.77; N, 2.46. The CH3CN content was
1
confirmed by H NMR spectroscopy.
ASSOCIATED CONTENT
■
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.7b00790.
MS (ESI+, CH3CN): m/z (%) = 416.03 (100) [M − PF6]+, 977.04
(7) [2xM − PF6]+. HR-MS (ESI+, CH3CN): obs. m/z = 416.0139;
Cartesian coordinates of DFT optimized geometries
(XYZ)
1
calcd for [M − PF6]+ = 416.0148. H NMR (CD3CN): δ [ppm] =
1
3
3
4.25 (s, 5H, H9), 4.54 (t, 2H, JHH = 1.6 Hz, H8), 4.86 (t, 2H, JHH
=
Figures and spectroscopic data (UV/vis, IR, H NMR,
1.6 Hz, H7), 5.49 (t, 2H, 3JHH = 1.9 Hz, H2), 5.55 (s, 5H, H1), 6.08 (t,
2H, 3JHH = 1.9 Hz, H3), 8.41 (s, 1H, HNH). 13C {1H} NMR (CD3CN):
δ [ppm] = 69.7 (C7), 70.9 (C9), 72.8 (C8), 73.6 (C3), 74.8 (C6), 80.5
(C2), 85.6 (C1), 114.4 (C4), 170.8 (C5). 19F NMR (CD3CN): δ [ppm]
13C NMR, 31P NMR, 19F NMR, 59Co NMR, 1H1H
COSY, 1H13C HMBC, UV/vis/NIR spectra during
OTTLE spectroelectrochemistry, Gaussian deconvolu-
tion of CT bands (PDF)
= −72.8 (d, 6F, 1JPF = 707 Hz, FPF ). 31P NMR (CD3CN): δ [ppm] =
6
−143.4 (sept, 1P, 1JPF = 707 Hz, PPF ). IR (ATR): ν
̃
[cm−1] = 3364 (s,
6
Accession Codes
NH), 3188 (s, CHFc), 3121 (s, CH), 3100 (s, CH), 1654 (s, amide I),
1533 (s, NC), 1498, 1449, 1418, 1379, 1283 (s), 1139, 823 (m, PF),
644, 555 (m, FPFdef), 468. UV/vis (CH3CN): λ [nm] (ε [M−1 cm−1])
= 281 (21370), 347 (4160), 419 (1600). CV (FcH/FcH+, 100 mV−1,
CH3CN, 0.1 M [nBu4N][PF6]): E1/2 [V] = 0.305 (rev.), −1.355 (rev.),
−1.840 (irrev. ox.), −2.290 (irrev.). Elemental analysis: Anal. Calcd for
C21H19NOFeCoPF6 (561.13) × 1/2H2O: C, 44.24; H, 3.54; N, 2.46.
CCDC 1581720−1581721 contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/data_request/cif, or by email-
ing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
I
DOI: 10.1021/acs.organomet.7b00790
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(5) (a) Siemeling, U.; Vor der Bruggen, J.; Vorfeld, U.; Neumann, B.;
̈
AUTHOR INFORMATION
Corresponding Author
*E-mail: katja.heinze@uni-mainz.de.
ORCID
Katja Heinze: 0000-0003-1483-4156
Notes
The authors declare no competing financial interest.
■
Stammler, A.; Stammler, H.-G.; Brockhinke, A.; Plessow, R.; Zanello,
P.; Laschi, F.; Fabrizi de Biani, F.; Fontani, M.; Steenken, S.; Stapper,
M.; Gurzadyan, G. Chem. - Eur. J. 2003, 9, 2819−2833. (b) Heinze, K.;
Hempel, K.; Beckmann, M. Eur. J. Inorg. Chem. 2006, 2006, 2040−
2050.
(6) Huesmann, H.; Forster, C.; Siebler, D.; Gasi, T.; Heinze, K.
̈
Organometallics 2012, 31, 413−427.
(7) (a) Neidlinger, A.; Ksenofontov, V.; Heinze, K. Organometallics
2013, 32, 5955−5965. (b) Neidlinger, A.; Forster, C.; Heinze, K. Eur.
̈
ACKNOWLEDGMENTS
J. Inorg. Chem. 2016, 2016, 1274−1286. (c) Neidlinger, A.; Forster, C.;
̈
■
Heinze, K. Eur. J. Org. Chem. 2016, 2016, 4852−4864.
Parts of this research were conducted using the supercomputer
Mogon and advisory services offered by Johannes Gutenberg
University Mainz (www.hpc.uni-mainz.de), which is a member
of the AHRP and the Gauss Alliance e.V. We thank Dr. Dieter
Schollmeyer for collection of the diffraction data and Dr. Mihail
Mondeshki for assistance in the NMR spectroscopy facility,
especially for recording the 59Co NMR spectrum. We thank
Min Thu Pham for preparative assistance.
(8) Turlington, M. D.; Pienkos, J. A.; Carlton, E. S.; Wroblewski, K.
N.; Myers, A. R.; Trindle, C. O.; Altun, Z.; Rack, J. J.; Wagenknecht, P.
S. Inorg. Chem. 2016, 55, 2200−2211.
(9) (a) Schwarzhans, K.-E.; Stolz, W. Monatsh. Chem. 1987, 118,
875−878. (b) Beer, P. D.; Chen, Z.; Goulden, A. J.; Graydon, A.;
Stokes, S. E.; Wear, T. J. Chem. Soc., Chem. Commun. 1993, 1834−
1836. (c) Casado, C. M.; Gonzal
Moran, M.; Losada, J. Angew. Chem. 2000, 112, 2219−2222.
́
(d) Casado, C. M.; Gonzalez, B.; Cuadrado, I.; Alonso, B.; Moran,
́
ez, B.; Cuadrado, I.; Alonso, B.;
́
́
REFERENCES
M.; Losada, J. Angew. Chem., Int. Ed. 2000, 39, 2135−2138. (e) Barlow,
S. Inorg. Chem. 2001, 40, 7047−7053. (f) Laus, G.; Strasser, C. E.;
Holzer, M.; Wurst, K.; Purstinger, G.; Ongania, K.-H.; Rauch, M.;
■
̌
(1) (a) Step
̌
nick
̌
a, P. The Multifaceted Chemistry of Ferrocene. Eur.
̈
J. Inorg. Chem. 2016, 215−216. (b) Heinze, K.; Lang, H. Thematic
issue “Ferrocene−Beauty and Function. Organometallics 2013, 32,
5623−5625. (c) Ferrocenes: Ligands, Materials and Biomolecules;
Stepnicka, P., Ed.; Wiley: Chichester, U.K., 2008. (d) Ferrocenes:
Homogeneous Catalysis, Organic Synthesis, Materials Science; Togni, A.,
Hayashi, T., Eds.; VCH: Weinheim, Germany, 1995. (e) Hailes, R. L.
N.; Oliver, A. M.; Gwyther, J.; Whittell, G. R.; Manners, I. Chem. Soc.
Rev. 2016, 45, 5358−5407. (f) Astruc, D. Eur. J. Inorg. Chem. 2017,
Bonn, G.; Schottenberger, H. Organometallics 2005, 24, 6085−6093.
(g) Warratz, R.; Peters, G.; Studt, F.; Romer, R.-H.; Tuczek, F. Inorg.
̈
Chem. 2006, 45, 2531−2542. (g) Ornelas, C.; Ruiz, J.; Astruc, D.
Organometallics 2009, 28, 2716−2723. (i) Astruc, D.; Ornelas, C.;
Ruiz, J. Chem. - Eur. J. 2009, 15, 8936−8944. (j) Gilroy, J. B.; Patra, S.
K.; Mitchels, J. M.; Winnik, M. A.; Manners, I. Angew. Chem. 2011,
123, 5973−5977. (k) Gilroy, J. B.; Patra, S. K.; Mitchels, J. M.; Winnik,
M. A.; Manners, I. Angew. Chem., Int. Ed. 2011, 50, 5851−5855.
́
2017, 6−29. (g) Molina, P.; Tarraga, A.; Alfonso, M. Dalton Trans.
2014, 43, 18−29.
(10) Lauck, M.; Forster, C.; Gehrig, D.; Heinze, K. J. Organomet.
̈
(2) (a) Lu, S.; Strelets, V. V.; Ryan, M. F.; Pietro, W. J.; Lever, A. B.
Chem. 2017, 847, 33−40.
P. Inorg. Chem. 1996, 35, 1013−1023. (b) Khobragade, D. A.;
(11) (a) Knox, G. R.; Munro, J. D.; Pauson, P. L.; Smith, G. H.;
Watts, W. E. J. Chem. Soc. 1961, 4619−4624. (b) Pauson, P. L.; Knox,
G. R. U.S. Patent 3278514, 1966. (c) Sheats, J. E.; Rausch, M. D. J.
Org. Chem. 1970, 35, 3245−3249. (d) Yamazaki, H.; Wakatsuki, Y.
Bull. Chem. Soc. Jpn. 1979, 52, 1239−1240. (e) Stahl, K.; Boche, G.;
Massa, W. J. Organomet. Chem. 1984, 277, 113−125. (f) Butovskii, M.
V.; Englert, U.; Herberich, G. E.; Koelle, U. Eur. J. Inorg. Chem. 2005,
2005, 971−980.
̌ ̌ ̌
Mahamulkar, S. G.; Pospísil, L.; Císarova, I.; Rulísek, L.; Jahn, U.
Chem. - Eur. J. 2012, 18, 12267−12277. (c) Shafir, A.; Power, M. P.;
Whitener, G. D.; Arnold, J. Organometallics 2000, 19, 3978−3982.
(3) (a) Kraatz, H.-B.; Lusztyk, J.; Enright, G. D. Inorg. Chem. 1997,
36, 2400−2405. (b) Brosch, O.; Weyhermuller, T.; Metzler-Nolte, N.
̈
Inorg. Chem. 1999, 38, 5308−5313. (c) van Staveren, D. R.; Metzler-
Nolte, N. Chem. Rev. 2004, 104, 5931−5985. (d) Moriuchi, T.; Hirao,
T. Chem. Soc. Rev. 2004, 33, 294−301. (e) Heinze, K.; Beckmann, M.
Eur. J. Inorg. Chem. 2005, 2005, 3450−3457. (f) Heinze, K.; Wild, U.;
(12) (a) Wolter-Steingrube, A.; Bugenhagen, B. E. C.; Herrmann, C.;
Heck, J. Eur. J. Inorg. Chem. 2014, 2014, 4115−4122. (b) Wolter-
Steingrube, A.; Cordsen, K.; Heck, J. Eur. J. Inorg. Chem. 2017, 2017,
1314−1319.
Beckmann, M. Eur. J. Inorg. Chem. 2007, 2007, 617−623. (g) Djakovic,
S.; Siebler, D.; Semencic, M. C.; Heinze, K.; Rapic, V. Organometallics
2008, 27, 1447−1453. (h) Lataifeh, A.; Beheshti, S.; Kraatz, H.-B. Eur.
J. Inorg. Chem. 2009, 2009, 3205−3218. (i) Semencic, M. C.; Siebler,
D.; Heinze, K.; Rapic, V. Organometallics 2009, 28, 2028−2037.
(j) Forster, C.; Kovacevic, M.; Barisic, L.; Rapic, V.; Heinze, K.
Organometallics 2012, 31, 3683−3694.
́
̌
́
́
(13) (a) Vanicek, S.; Kopacka, H.; Wurst, K.; Muller, T.;
̈
̌
́
Schottenberger, H.; Bildstein, B. Organometallics 2014, 33, 1152−
́
̌
1156. (b) Vanicek, S.; Kopacka, H.; Wurst, K.; Muller, T.; Hassenruck,
̈
̈
́
̌
́
́
̈
C.; Winter, R.; Bildstein, B. Organometallics 2016, 35, 2101−2109.
(14) (a) Heinze, K.; Schlenker, M. Eur. J. Inorg. Chem. 2004, 2004,
2974−2988. (b) Chowdhury, S.; Schatte, G.; Kraatz, H.-B. Angew.
Chem. 2006, 118, 7036−7038. (c) Chowdhury, S.; Schatte, G.; Kraatz,
H. B. Angew. Chem., Int. Ed. 2006, 45, 6882−6884. (d) Heinze, K.;
Siebler, D. Z. Z. Anorg. Allg. Chem. 2007, 633, 2223−2233. (e) Siebler,
(4) (a) Mansour, H.; El-Khouly, M. E.; Shaban, S. Y.; Ito, O.; Jux, N.
J. Porphyrins Phthalocyanines 2007, 11, 719−728. (b) Poddutoori, P.
K.; Sandanayaka, A. S. D.; Hasobe, T.; Ito, O.; van der Est, A. J. Phys.
Chem. B 2010, 114, 14348−14357. (c) Bakar, M. A.; Sergeeva, N. N.;
Juillard, T.; Senge, M. O. Organometallics 2011, 30, 3225−3228.
(d) Suijkerbuijk, B. M. J. M.; Klein Gebbink, R. J. M. Angew. Chem.
2008, 120, 7506−7532. (e) Suijkerbuijk, B. M. J. M.; Klein Gebbink,
R. J. M. Angew. Chem., Int. Ed. 2008, 47, 7396−7421. (f) Dammer, S.
J.; Solntsev, P. V.; Sabin, J. R.; Nemykin, V. N. Inorg. Chem. 2013, 52,
9496−9510. (g) Vecchi, A.; Gatto, E.; Floris, B.; Conte, V.; Venanzi,
M.; Nemykin, V. N.; Galloni, P. Chem. Commun. 2012, 48, 5145−
5147. (h) Nemykin, V. N.; Rohde, G. T.; Barrett, C. D.; Hadt, R. G.;
Bizzarri, C.; Galloni, P.; Floris, B.; Nowik, I.; Herber, R. H.; Marrani,
A. G.; Zanoni, R.; Loim, N. M. J. Am. Chem. Soc. 2009, 131, 14969−
14978. (i) Melomedov, J.; Ochsmann, J. R.; Meister, M.; Laquai, F.;
Heinze, K. Eur. J. Inorg. Chem. 2014, 2014, 1984−2001.
(j) Melomedov, J.; Ochsmann, J. R.; Meister, M.; Laquai, F.;
Heinze, K. Eur. J. Inorg. Chem. 2014, 2014, 2902−2915.
D.; Linseis, M.; Gasi, T.; Carrella, L. M.; Winter, R. F.; Forster, C.;
̈
Heinze, K. Chem. - Eur. J. 2011, 17, 4540−4551. (f) Siebler, D.;
Forster, C.; Heinze, K. Dalton Trans. 2011, 40, 3558−3575. (g) Siebler,
̈
D.; Forster, C.; Gasi, T.; Heinze, K. Organometallics 2011, 30, 313−
̈
327. (h) Siebler, D.; Heinze, K. J. Organomet. Chem. 2016, 821, 19−24.
(i) Acton, E. M.; Silverstein, R. M. J. Org. Chem. 1959, 24, 1487−1490.
(15) (a) Forster, C.; Veit, P.; Ksenofontov, V.; Heinze, K. Chem.
̈
Commun. 2015, 51, 1514−1516. (b) Veit, P.; Forster, C.; Seibert, S.;
̈
Heinze, K. Z. Anorg. Allg. Chem. 2015, 641, 2083−2092. (c) Veit, P.;
Prantl, E.; Forster, C.; Heinze, K. Organometallics 2016, 35, 249−257.
̈
(d) Kienz, T.; Forster, C.; Heinze, K. Organometallics 2016, 35, 3681−
̈
3691. (e) Hanauer, K.; Pham, M. T.; Forster, C.; Heinze, K. Eur. J.
̈
Inorg. Chem. 2017, 2017, 433−445.
J
DOI: 10.1021/acs.organomet.7b00790
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(16) (a) Heinze, K.; Schlenker, M. Eur. J. Inorg. Chem. 2005, 2005,
66−71. (b) Molina, P.; Tar
́
raga, A.; Caballero, A. Eur. J. Inorg. Chem.
2008, 2008, 3401−3417. (c) Siebler, D.; Forster, C.; Heinze, K. Eur. J.
̈
Inorg. Chem. 2010, 2010, 523−527.
(17) (a) Camara, J. M.; Rauchfuss, T. B. Nat. Chem. 2011, 4, 26−30.
(b) Huttinger, K.; Forster, C.; Heinze, K. Chem. Commun. 2014, 50,
̈
̈
4285−4288.
(18) Sethi, S.; Das, P. K.; Behera, N. J. Organomet. Chem. 2016, 824,
140−165.
(19) Enk, B.; Kopacka, H.; Wurst, K.; Muller, T.; Bildstein, B.
̈
Organometallics 2009, 28, 5575−5586.
(20) (a) Gray, H. B.; Sohn, Y. S.; Hendrickson, N. J. Am. Chem. Soc.
1971, 93, 3603−3612. (b) el Murr, N. E. J. Organomet. Chem. 1976,
112, 189−199.
(21) Inyushin, S.; Shafir, A.; Sheats, J. E.; Minihane, M.; Whitten, C.
E., Jr.; Arnold, J. Polyhedron 2004, 23, 2937−2942.
(22) (a) Lee, J. H.; Gupta, S.; Jeong, W.; Rhee, Y. H.; Park, J. Angew.
Chem. 2012, 124, 11009−11013. (b) Lee, J. H.; Gupta, S.; Jeong, W.;
Rhee, Y. H.; Park, J. Angew. Chem., Int. Ed. 2012, 51, 10851−10855.
(23) (a) Lucken, E. A. C.; Noack, K.; Williams, D. F. J. Chem. Soc. A
1967, 148−154. (b) Benn, R.; Cibura, K.; Hofmann, P.; Jonas, K.;
Rufinska, A. Organometallics 1985, 4, 2214−2221.
(24) Kienz, T.; Forster, C.; Heinze, K. Organometallics 2014, 33,
̈
4803−4812.
(25) Gockel, S. N.; Hull, K. L. Org. Lett. 2015, 17, 3236−3239.
(26) (a) McManis, G. E.; Nielson, R. M.; Weaver, M. J. Inorg. Chem.
1988, 27, 1827−1829. (b) Ribou, A.-C.; Launay, J.-P.; Sachtleben, M.
L.; Li, H.; Spangler, C. W. Inorg. Chem. 1996, 35, 3735−3740.
(27) Siebler, D.; Forster, C.; Heinze, K. Eur. J. Inorg. Chem. 2010,
̈
2010, 3986−3992.
(28) Hush, N. S. In Prog. Inorg. Chem.; Cotton, F. A., Ed.; John Wiley
& Sons, Inc.: Hoboken, NJ, 1967; pp 391−444.
(29) Fulmer, G. R.; Miller, A. J. M.; Sherden, N. H.; Gottlieb, H. E.;
Nudelman, A.; Stoltz, B. M.; Bercaw, J. E.; Goldberg, K. I.
Organometallics 2010, 29, 2176−2179.
(30) Krejcik, M.; Danek, M.; Hartl, F. J. Electroanal. Chem. Interfacial
Electrochem. 1991, 317, 179−187.
(31) Neese, F. WIREs Comput. Mol. Sci. 2012, 2, 73−78.
(32) Weigend, F.; Ahlrichs, R. Phys. Chem. Chem. Phys. 2005, 7,
3297−3305.
(33) Weigend, F. Phys. Chem. Chem. Phys. 2006, 8, 1057−1065.
(34) Neese, F.; Wennmohs, F.; Hansen, A.; Becker, U. Chem. Phys.
2009, 356, 98−109.
́
(35) Izsak, R.; Neese, F. J. Chem. Phys. 2011, 135, 144105.
(36) van Lenthe, E.; Baerends, E. J.; Snijders, J. G. J. Chem. Phys.
1993, 99, 4597−4610.
(37) van Wullen, C. J. J. Chem. Phys. 1998, 109, 392−399.
̈
(38) Kollmar, C. J. Chem. Phys. 1996, 105, 8204−8212.
(39) Barone, V.; Cossi, M. J. Phys. Chem. A 1998, 102, 1995−2001.
(40) X-red; Stoe & Cie: Darmstadt, Germany, 2002.
(41) Blessing, R. H. Acta Crystallogr., Sect. A: Found. Crystallogr. 1995,
51, 33−38.
(42) Spek, A. L. Acta Crystallogr., Sect. D: Biol. Crystallogr. 2009, 65,
148−155.
(43) Sheldrick, G. M. Acta Crystallogr., Sect. C: Struct. Chem. 2015, 71,
3−8.
(44) Sheldrick, G. M. SHELXL-2014/7; University of Gottingen,
̈
Gottingen, Germany, 2014.
̈
(45) Rausch, M. D.; Ciappenelli, D. J. J. Organomet. Chem. 1967, 10,
127−136.
K
DOI: 10.1021/acs.organomet.7b00790
Organometallics XXXX, XXX, XXX−XXX