Regioselective Nucleophilic Additions to Diiron Carbonyl Complexes Containing a Bridging Aminocarbyne Ligand: A Synthetic, Crystallographic and DFT Study

Article abstract of DOI:10.1002/ejic.201701115

Diiron μ-aminocarbyne compounds, 1a–e, are prepared in two steps from Fe₂Cp₂(CO)₄, negating the need for difficult purification procedures of intermediate species; they are efficiently isolated by alumina chromatography. Minor amounts of μ-aminocarbyne aryl isocyanide compounds, 2a–c, are obtained as side products. The structures of the cations in 1a,c,e are calculated using DFT; the carbyne carbon is generally predicted to be the thermodynamic site of hydride addition, in agreement with a previous experimental finding concerning 1a. Accordingly, the reaction of 1e with NaBH₄ affords a bridging aminocarbene complex, 4, in 85 % yield. Otherwise, the reaction of 1c with NaBH₄ yields the aminocarbyne–cyclopentadiene derivative 3 (70 %), presumably as a consequence of the steric protection exerted by the xylyl–methyl groups towards the carbyne moiety. The sequential treatment of 1a,c with Li₂CuCNMe₂ and MeSO₃CF₃ affords 5a,b, comprising both aminocarbyne and alkoxycarbene ligands. In accordance with DFT calculations, the alkoxycarbene moiety in 5a is the most favourable site for nucleophilic attack. Thus, the reactions of 5a with NH₂R (R = Et, iPr) and NBu₄CN, respectively, give the aminocarbyne/aminocarbene complexes, 6a,b, and the aminocarbyne-α-cyanoalkyl 7. All the products are fully characterized by spectroscopic and analytical methods; moreover, the structures of 1a, 1d, 6a and 7 are elucidated by single-crystal X-ray diffraction studies.

Full text of DOI:10.1002/ejic.201701115

DOI: 10.1002/ejic.201701115
Full Paper
Iron Aminocarbyne Complexes
Regioselective Nucleophilic Additions to Diiron Carbonyl
Complexes Containing a Bridging Aminocarbyne Ligand: A
Synthetic, Crystallographic and DFT Study
Gabriele Agonigi,[a] Marco Bortoluzzi,[b] Fabio Marchetti,*[a] Guido Pampaloni,[a]
Stefano Zacchini,[c] and Valerio Zanotti[c]
Abstract: Diiron μ-aminocarbyne compounds, 1a–e, are pre- steric protection exerted by the xylyl–methyl groups towards
pared in two steps from Fe2Cp2(CO)4, negating the need for the carbyne moiety. The sequential treatment of 1a,c with
difficult purification procedures of intermediate species; they Li2CuCNMe2 and MeSO3CF3 affords 5a,b, comprising both
are efficiently isolated by alumina chromatography. Minor aminocarbyne and alkoxycarbene ligands. In accordance with
amounts of μ-aminocarbyne aryl isocyanide compounds, 2a–c, DFT calculations, the alkoxycarbene moiety in 5a is the most
are obtained as side products. The structures of the cations in favourable site for nucleophilic attack. Thus, the reactions of
1a,c,e are calculated using DFT; the carbyne carbon is generally 5a with NH2R (R = Et, iPr) and NBu4CN, respectively, give the
predicted to be the thermodynamic site of hydride addition, in aminocarbyne/aminocarbene complexes, 6a,b, and the amino-
agreement with a previous experimental finding concerning 1a. carbyne-α-cyanoalkyl 7. All the products are fully characterized
Accordingly, the reaction of 1e with NaBH4 affords a bridging by spectroscopic and analytical methods; moreover, the struc-
aminocarbene complex, 4, in 85 % yield. Otherwise, the reac- tures of 1a, 1d, 6a and 7 are elucidated by single-crystal X-ray
tion of 1c with NaBH4 yields the aminocarbyne–cyclopentadi- diffraction studies.
ene derivative 3 (70 %), presumably as a consequence of the
Introduction
[Fe2Cp2(CO)3(CNR)] (R = alkyl or aryl group), is therefore a diffi-
cult task, and their clear spectroscopic identification is further
complicated by the fact that they exist as mixtures of isomers.[9]
The preparation of some of the compounds [Fe2Cp2(CO)3(CNR)]
has been better accomplished by alternative and more elabo-
rate routes.[7b,10] The selective formation of [Fe2Cp2(CO)3(CNR)]
is desired in that it represents the first, crucial step to the syn-
thesis of versatile monoaminocarbyne complexes, [Fe2Cp2(CO)3-
(μ-CNRR′)]+,[11] obtained from isocyanide precursors by the ad-
dition of strong alkylating agents.[12] Some reactivity of N-alkyl
aminocarbyne complexes, and in particular, [Fe2Cp2(CO)3(μ-
CNMe2)][SO3CF3], 1a, with anionic nucleophiles have been elu-
cidated in the past. Addition reactions usually occur in a select-
ive manner, depending on the nature of the reactant and are
directed to the carbyne carbon,[13] a terminal carbonyl ligand[14]
or a Cp moiety (Scheme 1).[14] Conversely, the parallel chemistry
Since its early preparation by Cotton and Wilkinson in the
1950s,[1] the easily available and rugged compound
[Fe2Cp2(CO)4] has become a “battle horse” of organometallic
chemistry.[2] It has been employed in homogeneous catalytic
processes,[3] as a convenient precursor to iron nanoparticles,[4]
and as a starting material to access a huge variety of mono-[5]
and dinuclear[6] derivatives. As a preliminary step, both ther-
mal[7] and photochemical methods[8] have been proposed for
carbon monoxide/isocyanide substitution; however, these reac-
tions generally afford mixtures of polysubstituted products. This
is true especially when aryl isocyanides are involved, in view of
their greater ability to replace CO ligands, with respect to alkyl
isocyanides.[7b] The isolation of monoisocyanide species,
of [Fe2Cp2(CO)3{μ-CN(Me)(Xyl)}][SO3CF3] (1c, Xyl
=
2,6-
C6H3Me2)[8] has been barely explored, despite the fact that the
aryl substituent is expected to provide important steric and
electronic effects.[15]
[a] Università di Pisa, Dipartimento di Chimica e Chimica Industriale,
Via Moruzzi 13, 56124 Pisa, Italy
E-mail: fabio.marchetti1974@unipi.it
www.dcci.unipi.it/~fabmar/
[b] Università Ca' Foscari Venezia, Dipartimento di Scienze Molecolari e
Nanosistemi,
Via Torino 155, 30170 Mestre (VE), Italy
[c] Università di Bologna, Dipartimento di Chimica Industriale
“Toso Montanari”,
Herein, we describe an optimized procedure to obtain diiron
aminocarbyne compounds of the general formula
[Fe2Cp2(CO)3(μ-CNMeR)][SO3CF3] from [Fe2Cp2(CO)4] and iso-
cyanides. The reactions of some of the products with a series
of nucleophiles will be discussed, with the assistance of DFT
calculations, giving insight into their thermodynamic and struc-
tural features.
Viale Risorgimento 4, 40136 Bologna, Italy
Supporting information and ORCID(s) from the author(s) for this article are
available on the WWW under https://doi.org/10.1002/ejic.201701115.
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Scheme 1. Regioselective additions of nucleophiles to the diiron aminocarbyne complex 1a.
Results and Discussion
obtained by a different route.[11c] The chromatography allowed
the recovery of the unreacted [Fe2Cp2(CO)4], too.
The commercial compound [Fe2Cp2(CO)4] was reacted with the
appropriate isocyanide, in a ca. 3:2 molar ratio, in acetonitrile
solution.[16] The reactions with alkyl isocyanides were con-
ducted under reflux conditions, whereas the reactions with aryl
isocyanides proceeded at room temperature. The resulting mix-
tures were dried under vacuum and the residues were dissolved
in dichloromethane and then treated with methyl triflate, thus
affording the μ-aminocarbyne complexes 1a–e (Scheme 2). The
difficult isolation of the monoisocyanide intermediates (see the
Introduction) was unnecessary. The final products 1a–e were
efficiently purified by alumina chromatography and were then
isolated as microcrystalline, air-stable compounds in 65–92 %
yields. The synthesis of 1c–e was accompanied by the side for-
mation of minor products derived from di-isocyanide species,
2a–c. Compounds 2a–c were recovered by the chromatography
in 3–12 % yields, although 2a was formerly reported as being
The new products 1d,e and 2b,c were characterized by ele-
mental analysis, IR spectroscopy and NMR spectroscopy. The
full NMR spectroscopic characterization of the already known
1a–c is supplied here for the first time. The carbyne nature of
the bridging [CN] moiety in 1a–e is manifested by a strongly
deshielded 13C NMR spectroscopic resonance (e.g., at δ =
327.8 ppm in the case of 1c in CDCl3 solution).[11,17] Compound
1d exists in solution as two isomeric forms in a comparable
ratio, the two isomers presumably differing in the orientation
of the aryl-substituents (i.e., Me and Cl) with respect to the
Fe–Fe axis. No change in the isomer composition was detected
by heating 1d in 2-propanol solution at reflux temperature for
24 h. Crystals of 1a and 1d suitable for X-ray diffraction analysis
were obtained. A view of the respective cations is given in Fig-
ures 1 and 2, whereas relevant bonding parameters are listed
Scheme 2. Synthesis of diiron μ-aminocarbyne complexes.
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in Tables 1 and 2. The structures of 1a and 1d closely resemble
those previously reported for analogous diiron μ-aminocarbyne
compounds, as far as the geometry and the bonding parame-
ters are concerned.[12,18] Thus, they consist of an Fe2(CO)2Cp2
unit in cis configuration and two bridging ligands; that is, a
carbon monoxide and the aminocarbyne group. The latter can
be alternatively described as an iminium: in fact, the C–N dis-
tance [1.297(4) in 1a and 1.295(5) Å in 1d] falls within the dou-
ble-bond range.[19] The structure of 1d exhibits the chlorine
atom pointing to the opposite side, with respect to the Cp
rings.
Table 1. Selected bond lengths [Å] and angles [°] for the cation within 1a.
Fe(1)–Fe(1)
Fe(1)–C(1)
C(1)–O(1)
C(3)–N(1)
Fe(1)–Cpaverage
Fe(1)–C(1)–Fe(1)
Fe(1)–C(2)–O(2)
2.5218(7)
1.933(3)
1.177(4)
1.297(4)
2.113(4)
81.41(13)
179.4(2)
Fe(1)–C(2)
Fe(1)–C(3)
C(2)–O(2)
C(4)–N(1)
1.775(2)
1.875(2)
1.138(3)
1.471(3)
Fe(1)–C(3)–Fe(1)
Sum at N(1)
84.53(13)
360.0(2)
Table 2. Selected bond lengths [Å] and angles [°] for the cation within 1d.
Fe(1)–Fe(2)
Fe(1)–C(3)
Fe(1)–C(4)
Fe(2)–C(2)
C(1)–O(1)
C(4)–N(1)
C(6)–N(1)
Fe(1)–Cpaverage
Fe(1)–C(3)–Fe(2)
Fe(1)–C(1)–O(1)
Sum at N(1)
2.504(2)
1.933(5)
1.871(4)
1.760(5)
1.143(7)
1.295(5)
1.450(5)
2.12(2)
Fe(1)–C(1)
Fe(2)–C(3)
Fe(2)–C(4)
C(3)–O(3)
C(2)–O(2)
C(5)–N(1)
C(7)–Cl(1)
Fe(2)–Cpaverage
Fe(1)–C(4)–Fe(3)
Fe(2)–C(2)–O(2)
1.754(6)
1.939(4)
1.875(4)
1.154(5)
1.134(6)
1.486(5)
1.749(6)
2.104(9)
83.92(15)
176.3(5)
80.61(17)
176.8(5)
360.0(5)
other hand, the hydride attack on 1c selectively occurs at the
Cp ligand, resulting in the formation of a cyclopentadiene
(Scheme 3, compound 3). The new complexes 3 and 4 were
purified by alumina chromatography and were characterized by
elemental analysis, IR spectroscopy and NMR spectroscopy. The
IR spectrum of 3 (in CH2Cl2) shows three absorptions related to
one bridging (1771 cm–1) and two terminal (1960, 1925 cm–1)
carbonyl ligands. A 13C NMR spectroscopic resonance at 333.6
(CDCl3 solution) represents clear evidence that the amino-
carbyne group is not involved in the reaction. Two isomers were
detected for 3 by using NMR spectroscopy (with an approxi-
mate ratio of 1.5), probably originating from the different orien-
Figure 1. View of the structure of the cation within 1a. Displacement ellip-
soids are at the 30 % probability level.
Figure 2. View of the structure of the cation within 1d. Displacement ellip-
soids are at the 30 % probability level.
To compare the electrophilic behaviour of 1a (see the Intro-
duction and Scheme 1) with that of the aryl-substituted homo-
logues, we studied the reactions of 1c and 1e with NaBH4. The
reaction involving the naphthyl derivative 1e affords a bridging
aminocarbene group (Scheme 3, compound 4), thus resembling
the previous result obtained with 1a (Scheme 1).[13] On the
Scheme 3. Regioselective hydride additions to aryl-substituted μ-amino-
carbyne complexes.
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tations that the N-substituents can assume with respect to the
The charge distribution on the aminocarbyne moiety was
nonequivalent Fe atoms, as a consequence of the double-bond calculated for compounds 1a,c,e (Figure 4), and it seems to be
character of the μ-C–N interaction (E/Z isomers). Complexes of in alignment with thermodynamic considerations: it is negligi-
the type [Fe2{μ-CN(R)(R′)}(μ-CO)(CO)(L)Cp2] (R ≠ R′, L = halide, bly affected by the nature of the N-substituents, thus suggest-
CN, Ph), in chlorinated solvents, preferentially adopt the E con- ing the absence of conjugation between the [CN] unit and the
figuration, with the Cp ligands in mutual cis position.[11c,11e,20]
The most salient spectroscopic features of 4 are the NMR
spectroscopic resonances relating to the newly formed carbene
centre, at 13.11 ppm (1H NMR) and 182.4 ppm (13C NMR). The
bridging coordination of the carbene is indicated by the IR
spectrum, consisting of one absorption ascribable to a bridging
CO (1765 cm–1) and two other absorptions due to terminal
carbonyls (1955, 1925 cm–1).
The DFT-optimized geometries of 3 and 4 are shown in Fig-
ure 3. Concerning 3, the structure displaying the xylyl on the
same side with respect to the cyclopentadiene ligand is only
slightly more stable than the alternative form with the opposite
configuration of the N-substituents (Figure S2), in agreement
with the NMR spectroscopic data of a solution of the two iso-
mers in comparable amounts (see above).
aromatic ring in 1c,e. Based on these observations, it is presum-
able that the favourable hydride attack on the aminocarbyne
carbon of 1c (see above) is inhibited due to steric protection
exerted towards that carbon centre by the methyl substituents
situated on the aryl ring, and not for electronic reasons.[15]
A
view of the electron-density surface of 1c is given in Figure S5.
We tested the thermal stability of 3 in various solvents, with
the aim of promoting intramolecular H migration from the
cyclopentadiene ligand to the carbyne carbon, as suggested by
the theoretical considerations. Unfortunately, these experi-
ments resulted in the formation of complicated mixtures of
products.
The inertness of the xylyl–aminocarbyne moiety of 1c with
respect to nucleophilic addition is also manifested in the reac-
tion with NBu4CN, proceeding with direct carbon monoxide/
To gain insight into the different outcomes of the reactions cyanide substitution to give the complex [Fe2{μ-CN(Me)(Xyl)}-
of 1a,c,e with NaBH4, we considered all the potential products (μ-CO)(CO)(CN)(Cp)2] (Scheme 4) in 84 % yield. This complex
and compared their energies in the distinct cases (see Fig- was previously prepared by replacement of the labile aceto-
ures S1–S3 in the Supporting Information). In general, the at- nitrile ligand from [Fe2{μ-CNMe(R)}(μ-CO)(CO)(NCMe)Cp2]-
tack on the aminocarbyne carbon appears to be largely favour- [SO3CF3] (R = Me, Xyl; Scheme 4).[22] Notably, the reaction of 1a
able from a thermodynamic point of view;[21] the resulting with NBu4CN at room temperature selectively results in
aminocarbene ligand may occupy either a bridging or a termi- carbyne–cyanide coupling to give the aminocarbene [Fe2
nal site, with the two sites bearing comparable energies.[13] The {μ-CN(Me)2(CN)}(μ-CO)(CO)2(Cp)2] (also see Scheme 1). On the
aminocarbene frame in 4 adopts a bridging coordination mode, other hand, the reaction of [Fe2{μ-CNMe2}(μ-CO)(CO)2Cp2][I]
possibly also due to the lack of a convenient activation barrier with KCN in solution of ethanol at reflux conditions was previ-
pathway needed to allow the exchange between the bridging, ously reported to give [Fe2{μ-CN(Me)2}(μ-CO)(CO)(CN)(Cp)2].[23]
hindered aminocarbene and a terminal carbon monoxide.
Moreover, we observed that [Fe2{μ-CN(Me)2(CN)}(μ-CO)-
Figure 3. DFT-optimized structures of: (left) 3; and (right) 4 (ωB97X functional). Selected computed bond lengths [Å] for 3: Fe1–C(cyclopentadiene) 2.028,
2.039, 2.083, 2.111, 2.657; Fe1–C(aminocarbyne) 1.840; Fe1–C(μ-CO) 1.833; Fe1–C(CO) 1.762; Fe2–C(Cp) 2.075, 2.093, 2.105, 2.111, 2.112; Fe2–C(aminocarbyne)
1.874; Fe2–C(μ-CO) 2.055; Fe2–C(CO) 1.764; Fe–Fe 2.530; C–N 1.319. Selected computed bond lengths [Å] for 4: Fe1–C(Cp) 2.079, 2.091, 2.115, 2.120, 2.128;
Fe1–C(aminocarbene) 1.964; Fe1–C(μ-CO) 1.918; Fe1–C(CO) 1.764; Fe2–C(Cp) 2.083, 2.089, 2.117, 2.129, 2.129; Fe2–C(aminocarbene) 2.012; Fe2–C(μ-CO) 1.877;
Fe2–C(CO) 1.759; Fe–Fe 2.537; C–N 1.390.
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Figure 4. DFT-optimized geometries of selected cations within aminocarbyne complexes (ωB97X functional), with Mulliken partial charges (a.u.) on the μ-
aminocarbyne moiety. Data from Hirshfeld population analyses are in parenthesis. Selected computed bond lengths and angles are compared in Table S1,
while Cartesian coordinates are collected in a separate .xyz file.
(CO)2(Cp)2], upon contact with water for a prolonged time, in
an attempt to test air/water stability, converted into [Fe2
{μ-CN(Me)2}(μ-CO)(CO)(CN)(Cp)2] (Scheme 4). These observa-
tions suggest that the replacement of a CO ligand by cyanide
is a favourable process, which may proceed through the inter-
mediate attack on the aminocarbyne carbon. The steric hin-
drance around this forces the direct formation of the thermo-
dynamic product.
To introduce further carbene functionality in 1a,c, the com-
pounds [Fe2{μ-CN(Me)(R)}(μ-CO)(CO){(C=O)Me}Cp2] (R = Me,[14]
Xyl[20]) were preliminarily prepared. These were reacted with
methyl triflate in dichloromethane, thus affording [Fe2
{μ-CN(Me)(R)}(μ-CO)(CO){C(OMe)Me}Cp2][SO3CF3] (R = Me, 5a;
R = Xyl, 5b) in 80–85 % yields, Scheme 5.
Scheme 4. Overview of the reactivity of diiron μ-aminocarbyne complexes
with the cyanide ion ([a] ref.[22]; [b] ref.[13]; [c] ref.[23]; [d] present work).
Scheme 5. Synthesis of diiron complexes with μ-aminocarbyne and alkoxy-
carbene ligands.
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The new aminocarbyne–alkoxycarbene[24] complexes 5a,b
were purified by filtration through celite and were then charac-
terized by elemental analysis, IR spectroscopy and NMR spectro-
scopy. The NMR spectra exhibit the expected resonances due
to the aminocarbyne centres (e.g., at δ = 325.4 ppm in the case
of 5a). In accord with the significant accumulation of positive
charge on the alkoxycarbene moiety (see below), even the carb-
ene carbon resonates at unusually low fields (e.g., at δ =
330.7 ppm in the case of 5a). The structure of 5a was calculated
by using DFT and its electronic features were investigated (Fig-
ure 5). Population analyses, the Hirshfeld one in particular, evi-
dence the greater electrophilicity of the alkoxycarbene function
with respect to the aminocarbyne. Accordingly, the plot of the
squared LUMO suggests that such an empty orbital is mainly
localized on the carbene, thus rendering this site accessible to
nucleophiles.
The reactivity of 5a with a small selection of nucleophiles
was studied (Scheme 6).
Figure 5. DFT-optimized geometry of 5a (ωB97X functional) with squared
LUMO surface (isovalue = 0.005 a.u.). Mulliken partial charges (a.u.) on the
C=N and C–O moieties of the bridging μ-aminocarbyne and the terminal
alkoxycarbene ligands are reported. Data from Hirshfeld population analyses
are in parenthesis. Cartesian coordinates are collected in a separate .xyz file.
The reactions of 5a with primary amines result in selective
aminolysis, to afford the new aminocarbyne/aminocarbene
complexes [Fe2(μ-CNMe2)(μ-CO)(CO){C(Me)NH(R)}(Cp)2][SO3CF3]
(R = iPr, 6a; R = Et, 6b) in good to high yields.[11a,25] Instead,
NHEt2 acts as a base towards 5a, and demethylation effectively
occurs to regenerate the parent compound [Fe2{μ-CN(Me)2}-
Compounds 6a,b were purified by alumina chromatography
(μ-CO)(CO){(C=O)Me}Cp2] (Scheme 5). When 6b is treated with and were then fully spectroscopically characterized. In 6a, the
NaBH4, the aminocarbene unit dissociates and the bridging resonances relating to the aminocarbyne and aminocarbene
hydride complex [Fe2(μ-CNMe2)(μ-H)(CO)2(Cp)2] is obtained as carbons are detected at δ = 330.4 and 261.2 ppm, respectively.
the prevalent product.[22]
The structure of 6a was ascertained by X-ray diffraction (Fig-
Scheme 6. Addition of nucleophiles to the alkoxycarbene moiety in diiron complexes containing the additional μ-aminocarbyne ligand.
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ure 6, Table 3): its geometry and bonding parameters closely
resemble those previously reported for analogous cationic di-
iron aminocarbyne/aminocarbene species with miscellaneous
substituents.[11] In particular, the Fe(2)–C(16) interaction
[1.927(4) Å] shows considerable π character and the C(16)–N(2)
distance [1.291(5) Å] also indicates some π bonding between
the carbene carbon and N(2). An intramolecular H bond involv-
ing the N(2)–H(2n) group and N(1) is present [N(2)–H(2n)
0.869(19) Å, H(2n)···N(1) 2.55(3) Å, N(2)···N(1) 3.252(4) Å,
∠N(2)H(2n)N(1) 138(4)°].
Figure 7. View of the structure of 7. Displacement ellipsoids are at the 30 %
probability level.
Table 4. Selected bond lengths [Å] and angles [°] for 7.
Fe(1)–Fe(2)
Fe(1)–C(1)
Fe(1)–C(6)
Fe(1)–C(3)
C(1)–O(1)
C(3)–N(1)
C(5)–N(1)
C(6)–C(8)
C(6)–O(3)
Fe(1)-Cpaverage
Fe(1)–C(1)–Fe(2)
Fe(1)–C(2)–O(2)
C(6)–O(3)–C(9)
2.5012(7)
1.866(4)
2.075(4)
1.845(4)
1.166(5)
1.294(5)
1.469(5)
1.470(6)
1.440(5)
2.121(9)
80.75(15)
171.7(3)
116.5(3)
Fe(2)–C(1)
Fe(2)–C(2)
Fe(2)–C(3)
C(2)–O(2)
C(4)–N(1)
C(6)–C(7)
N(2)–C(8)
O(3)–C(9)
Fe(2)-Cpaverage
Fe(1)–C(3)–Fe(2)
Sum at N(1)
C(6)–C(8)–C(2)
1.992(4)
1.756(4)
1.887(4)
1.142(5)
1.462(5)
1.532(5)
1.148(5)
1.417(5)
2.115(9)
84.14(16)
360.0(5)
178.7(4)
Figure 6. View of the structure of 6a. Displacement ellipsoids are at the 30 %
probability level.
Table 3. Selected bond lengths [Å] and angles [°] for 6a.
absorption accounting for the cyanide group at 2180 cm–1,
while the 13C NMR spectroscopic resonance due to the Fe-
bound alkyl carbon is found at δ = 57.0 ppm. We also extended
the reactivity of 5a to a reaction with NaBH4, but this was non-
selective and a complicated mixture of products was obtained.
Fe(1)–Fe(2)
Fe(1)–C(11)
Fe(1)–C(12)
Fe(1)–C(13)
C(11)–O(11)
C(13)–N(1)
C(15)–N(1)
C(16)–N(2)
Fe(1)–Cpaverage
Fe(1)–C(12)–Fe(2)
Fe(1)–C(11)–O(11)
Fe(2)–C(16)–N(2)
N(2)–C(16)–C(17)
2.5017(9)
1.750(4)
1.974(3)
1.909(3)
1.143(5)
1.284(4)
1.477(5)
1.292(5)
2.111(11)
80.95(14)
177.2(4)
125.5(3)
115.4(4)
Fe(2)–C(16)
Fe(2)–C(12)
Fe(2)–C(13)
C(12)–O(12)
C(14)–N(1)
C(16)–C(17)
N(2)–C(18)
Fe(2)–Cpaverage
Fe(1)–C(13)–Fe(2)
Sum at N(1)
Fe(2)–C(16)–C(17)
C(16)–N(2)–C(18)
1.927(4)
1.879(4)
1.843(3)
1.169(4)
1.472(5)
1.499(5)
1.499(9)
2.122(11)
83.62(14)
359.9(5)
119.1(3)
133.5(5)
Conclusion
The synthetic procedure to access cationic diiron aminocarbyne
compounds starting from the easily available [Fe2Cp2(CO)4] has
been optimized, negating the need for difficult purification pro-
cedures of intermediate species. The electrophilic behaviour of
aminocarbyne complexes has been investigated, and according
to DFT results, the aminocarbyne function is the privileged site
of hydride addition, irrespective of the nature of the N-substitu-
ents. Nevertheless, the steric protection exerted by a N-bound
xylyl group on the adjacent carbyne centre is responsible for
deviating the hydride attack on one Cp ligand and also for
avoiding carbyne–cyanide coupling. The introduction of a ter-
minal alkoxycarbene ligand beside the bridging aminocarbyne
allowed us to ascertain the higher electrophilicity of the former
function with respect to the latter, in accordance with the com-
The reaction of 5a with NBu4CN, performed in dichloro-
methane, affords the α-cyano-methoxyalkyl complex [Fe2-
{μ-CN(Me)2}(μ-CO)(CO){C(CN)(OMe)Me}Cp2], 7, in 90 % yield. The
X-ray diffraction structure of 7 (Figure 7 and Table 4) resembles
that of [Fe2{μ-CN(Me)(Xyl)}(μ-CO)(CO){C(CN)(OMe)(C≡ CPh)}Cp2],
as far as the bonding parameters and overall geometry are con-
cerned.[24a] In particular, the Fe(1)–C(6) distance [2.075(4) Å] is
that of a pure Fe–C(sp3) σ bond and is similar to that found in
the cyano–methyl complex [Fe2{μ-CN(Me)2}(μ-CO)(CO)(CH2CN)-
Cp2].[26]
Complex 7 is a racemate, due to the presence of a stereo- putational outcomes. Diiron aminocarbyne complexes are ver-
genic carbon centre. The IR spectrum (in CH2Cl2) shows the satile starting materials for obtaining a large variety of highly
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45.50, H 3.32, N 2.31; found C 45.70, H 3.25, N 2.36. IR (CH2Cl2):
functionalized hydrocarbyl ligands that are not accessible by
conventional organic chemistry;[15,27] the present results indi-
cate that fine control of the regiochemistry is viable by an accu-
rate choice of nitrogen substituents and coligands.
νCO = 2021 (vs), 1990 (w–m), 1836 (s), νCN = 1605 (m–s), νCC = 1591
˜
˜
˜
(m), 1578 (m) cm–1. 1H NMR ([D6]DMSO): δ = 7.53, 7.46 (m, 5 H, Ph),
5.77, 5.76 (m, 2 H, CH2), 5.57, 5.48 (s, 10 H, Cp), 3.98 (s, 3 H, NMe)
ppm. 13C{1H} NMR ([D6]DMSO): δ = 320.0 (μ-CN), 256.8 (μ-CO), 209.2
(CO), 134.7 (ipso-Ph), 129.7, 129.0, 127.9 (Ph), 91.1, 91.0 (Cp), 71.2
(CH2), 51.8 (NMe) ppm.
Experimental Section
[Fe2{μ-CNMe(Xyl)}(μ-CO)(CO)2Cp2][SO3CF3] (1c):[8] A solution of
2,6-dimethylphenyl isocyanide (1.00 g, 7.62 mmol) in acetonitrile
(15 mL) was added dropwise over 20 min into a solution of
[Fe2Cp2(CO)4] (4.05 g, 11.4 mmol) in acetonitrile (50 mL). The mix-
ture was left stirring at room temperature for 18 h, then the volatiles
were removed under reduced pressure. The red–brown residue was
dissolved in dichloromethane (70 mL), and CH3SO3CF3 (0.95 mL,
8.4 mmol) was added dropwise to the stirred solution. The mixture
was stirred at room temperature for further 6 h and was finally
charged on an alumina column. Elution with CH2Cl2 allowed the
recovery of the unreacted [Fe2(Cp)2(CO)4], then 2a was separated
using THF (vide infra), and 1c was finally eluted with neat methanol.
The solvent was removed under reduced pressure, then CH2Cl2
(10 mL) and petroleum ether (70 mL) were added to the residue in
the order given. The mixture was dried under vacuum; thus, 1c was
afforded as an air-stable red powder. Yield: 4.35 g, 92 % (with re-
spect to isocyanide). C24H22F3Fe2NO6S (621.19): calcd. C 46.40, H
General Experimental Details: All the reactions were routinely car-
ried out under a nitrogen atmosphere, using standard Schlenk tech-
niques. Solvents were purchased from Sigma Aldrich and were
distilled before use, under nitrogen, with appropriate drying agents.
Deuterated solvents and organic reactants were commercial prod-
ucts (Sigma Aldrich) of the highest purity available and were used
as received. [Fe2(CO)4Cp2] was purchased from Strem and was used
as received. The compounds CNMe,[28] Li2Cu(CN)Me2,[29] [Fe2-
{μ-C(CN)NMe2}(μ-CO)(CO)2Cp2][13] and [Fe2{μ-CN(Me)(R)}(μ-CO)(CO)-
{(C=O)Me}Cp2] (R = Me,[22] Xyl[20]) were prepared according to pub-
lished procedures. Once isolated, the metal products were con-
served under nitrogen. Chromatography separations were carried
out on columns of deactivated alumina (4 % w/w water) or celite.
The reaction vessels were oven-dried at 140 °C prior to use, evacu-
ated (10–2 Torr) and then filled with nitrogen. NMR spectra were
recorded at 298 K with either a Mercury Plus 400 instrument or a
Bruker Avance II DRX400 instrument equipped with a BBFO broad-
band probe. The chemical shifts for the 1H NMR and 13C NMR spec-
tra were referenced to the nondeuterated aliquot of the solvent.
NMR signals related to a secondary isomeric form (where it has
been possible to detect/resolve it) are italicized. The 1H NMR and
3.57, N 2.25; found C 46.26, H 3.68, N 2.37. IR (CH2Cl2): νCO = 2024
˜
(vs), 1992 (m), 1840 (s), νCN = 1606 (w), νCC = 1547 (w), 1530 (m)
˜
˜
cm–1. H NMR (CDCl3): δ = 7.34–7.28 (m, 3 H, C6H3Me2), 5.44, 4.78
(s, 10 H, Cp), 4.42 (s, 3 H, NMe), 2.66, 2.10 (s, 6 H, C6H3Me2) ppm.
13C{1H} NMR (CDCl3): δ = 327.8 (μ-CN), 253.9 (μ-CO), 208.6 (CO),
133.7–129.8 (C6H3Me2), 91.1, 91.3 (Cp), 56.3 (NMe), 19.3, 18.1
(C6H3Me2) ppm.
1
1
13C NMR spectra were assigned with the assistance of H,13C corre-
lation measured through gs-HSQC and gs-HMBC experiments.[30] In-
frared spectra were recorded with a Perkin–Elmer Spectrum 2000
FTIR spectrophotometer. Elemental analyses were performed with
a ThermoQuest Flash 1112 Series EA Instrument.
[Fe2{μ-CNMe(2,6-C6H3MeCl)}(μ-CO)(CO)2Cp2][SO3CF3] (1d): This
compound was obtained as an air-stable red solid by a procedure
similar to that described for the synthesis of 1c, from [Fe2Cp2(CO)4]
(3.75 g, 10.6 mmol), 2-chloro-6-methylphenyl isocyanide (1.00 g,
6.60 mmol) and methyl trifluoromethanesulfonate (0.90 mL,
8.0 mmol). Yield: 3.30 g, 78 % (with respect to isocyanide). Crystals
suitable for X-ray diffraction analysis were collected by slow diffu-
sion of diethyl ether into a dichloromethane solution of 1d at
–30 °C. C23H19ClF3Fe2NO6S (641.61): calcd. C 43.06, H 2.98, N 2.18;
Synthesis and Characterization of [Fe2{μ-CNMe(R)}(μ-CO)-
(CO)2Cp2][SO3CF3] [R = Me, 1a; R = CH2Ph, 1b; R = 2,6-C6H3Me2
(Xyl), 1c; R = 2,6-C6H3(Me)(Cl), 1d; R = C10H7, 1e]
[Fe2{μ-CNMe2}(μ-CO)(CO)2Cp2][SO3CF3] (1a):[12c] A solution of
[Fe2Cp2(CO)4] (38.0 g, 0.107 mol) in acetonitrile (ca. 80 mL) was
treated with freshly synthesized methyl isocyanide (2.94 g,
0.0716 mol), and the resulting solution was heated at reflux temper-
ature for 6 h. The volatiles were then removed under reduced pres-
sure. The dark-brown residue was dissolved in dichloromethane (ca.
100 mL), and CH3SO3CF3 (8.9 mL, 0.0786 mol) was added dropwise
to the stirred solution. The mixture was stirred at room temperature
for further 6 h and was finally charged on an alumina column. Elu-
tion with CH2Cl2 allowed the recovery of the unreacted
[Fe2(Cp)2(CO)4], then 1a was eluted by using neat methanol. Slow
evaporation of the solvent afforded air-stable, dark-red crystals of
1a suitable for X-ray diffraction analysis. Yield: 26.4 g, 69 % (with
respect to isocyanide). C17H16F3Fe2NO6S (531.06): calcd. C 38.45, H
found C 42.70, H 3.06, N 2.21. IR (CH2Cl2): νCO = 2030 (vs), 1998 (m),
˜
1841 (m), νCN = 1606 (w), νCC = 1544 (w), 1522 (w) cm–1
.
1H NMR
˜
˜
(CDCl3): δ = 7.58–7.43 (3 H, C6H3MeCl), 5.47, 5.46, 4.87, 4.81 (s, 10
H, Cp), 4.46, 4.45 (s, 3 H, NMe), 2.77, 2.17 (s, 3 H, C6H3MeCl) ppm.
Isomer ratio 3:2. 13C{1H} NMR (CDCl3): δ = 331.5 (μ-CN), 253.2, 251.0
(μ-CO), 208.1, 207.2 (CO), 145.6, 136.1, 134.8, 132.9, 131.6, 130.9,
130.7, 130.4, 129.4, 129.1, 128.5 (C6H3MeCl), 90.7, 89.9, 89.6 (Cp),
55.7, 55.4 (NMe), 19.0, 17.7 (C6H3MeCl) ppm.
[Fe2{μ-CNMe(C10H7)}(μ-CO)(CO)2Cp2][SO3CF3] (1e): This com-
pound was obtained as an air-stable red solid by a procedure similar
to that described for the synthesis of 1c, from [Fe2Cp2(CO)4] (3.70 g,
10.5 mmol), 2-naphthyl isocyanide (1.00 g, 6.53 mmol) and methyl
trifluoromethanesulfonate (0.88 mL, 7.8 mmol). Yield: 2.73 g, 65 %
(with respect to isocyanide). C26H20F3Fe2NO6S (643.20): calcd. C
48.55, H 3.13, N 2.18; found C 48.40, H 3.11, N 2.25. IR (CH2Cl2):
νCO = 2021 (vs), 1989 (w–m), 1836 (m), νCN = 1605 (w), νCC = 1565
3.04, N 2.64; found C 38.12, H 3.07, N 2.59. IR (CH2Cl2): νCO = 2022
˜
1
(vs), 1990 (w), 1835 (m), νCN = 1604 (m) cm–1. H NMR ([D6]DMSO):
˜
δ = 5.49 (s, 10 H, Cp), 4.17 (s, 3 H, NMe) ppm. 13C{1H} NMR
([D6]DMSO): δ = 315.5 (μ-CN), 257.6 (μ-CO), 209.3 (CO), 90.8 (Cp),
54.6 (NMe) ppm.
[Fe2{μ-CNMe(CH2Ph)}(μ-CO)(CO)2Cp2][SO3CF3] (1b):[12c] This com-
pound was obtained as an air-stable red solid by a procedure similar
to that described for the synthesis of 1a, from [Fe2Cp2(CO)4] (4.53 g,
12.8 mmol), benzyl isocyanide (1.00 g, 8.54 mmol) and methyl
trifluoromethanesulfonate (1.06 mL, 9.4 mmol). Yield: 4.51 g, 87 %
(with respect to isocyanide). C23H20F3Fe2NO6S (607.16): calcd. C
˜
˜
˜
(w–m), 1548 (w), 1539 (w) cm–1. 1H NMR (CDCl3): δ = 8.11, 7.98, 7.65
(m, 7 H, C10H7), 5.50, 4.71 (s, 10 H, Cp), 4.67 (s, 3 H, NMe) ppm.
13C{1H} NMR (CDCl3): δ = 324.5 (μ-CN), 254.4 (μ-CO), 208.8, 207.7
(CO), 147.5 (ipso-C10H7), 133.4, 132.8, 130.8, 129.0, 127.9, 127.8,
124.2, 122.6 (C10H7), 90.4, 90.1 (Cp), 57.4 (NMe) ppm.
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Isolation and Characterization of [Fe2{μ-CNMe(R)}(μ-CO)(CO)-
(CNR)Cp2][SO3CF3], [R = 2,6-C6H3Me2 (Xyl), 2a;[11c] R = 2,6-
C6H3(Me)(Cl), 2b; R = C10H7, 2c]: These compounds were obtained
as side products of the reactions leading to 1c–e and were sepa-
rated by chromatography using tetrahydrofuran as the eluent. The
solvent was removed under reduced pressure, then CH2Cl2 (5–
10 mL) and petroleum ether (40–60 mL) were added to the residue
in the order given. The mixture was dried under vacuum, thus 2a–
c were afforded as air-stable powders.
277.1 (μ-CO), 213.8 (CO), 182.4 (μ-CN), 148.2 (ipso-Ph), 134.5, 129.2,
128.9, 127.6, 127.3, 126.8, 124.0, 118.8, 112.0 (C10H7), 88.5, 87.3 (Cp),
40.4 (NMe) ppm.
Reactions of 1a,c with NBu4CN
(A) Synthesis of [Fe2{μ-CN(Me)(Xyl)}(μ-CO)(CO)(CN)(Cp)2]:[22]
NBu4CN (43 mg, 0.16 mmol) was added to a solution of 1c (90 mg,
0.15 mmol) in CH2Cl2 (12 mL). The mixture was stirred at room
temperature for 6 h, then it was filtered through an alumina column
with neat dichloromethane as the eluent. The product was isolated
as an air-stable green powder upon removal of the solvent under
vacuum. Yield: 59 g, 84 %. C23H22Fe2N2O2 (470.13): calcd. C 58.76,
[Fe2{μ-CNMe(Xyl)}(μ-CO)(CO){CN(Xyl)}Cp2][SO3CF3]
(2a):[11c]
Dark-brown solid. Yield: 166 mg, 3 % (with respect to xylyl isocyan-
ide). C32H31F3Fe2N2O5S (724.36): calcd. C 53.06, H 4.31, N 3.87; found
H 4.72, N 5.96; found C 58.58, H 4.82, N 5.90. IR (CH2Cl2): νCO = 1981
˜
C 53.23, H 4.30, N 3.78. IR (CH2Cl2): νCO = 1991 (vs), 1824 (s), νCN
=
˜
˜
1
(vs), 1804 (s), νC≡ N = 2091 (w) cm–1. H NMR (CDCl3): δ = 7.3 (3 H,
2120 (vs) cm–1
.
˜
C6H3Me2), 5.07, 4.22 (s, 10 H, Cp), 4.46 (s, 3 H, NMe), 2.65, 2.45 (s, 6
[Fe2{μ-CNMe(2,6-C6H3MeCl)}(μ-CO)(CO){CN(2,6-C6H3MeCl)}Cp2]-
[SO3CF3] (2b): Black solid. Yield: 505 mg, 10 % (with respect to
2-chloro-6-methylphenyl isocyanide). C30H25Cl2F3Fe2N2O5S (765.19):
calcd. C 47.09, H 3.29, N 3.66; found C 46.80, H 3.16, N 3.81. IR
H, C6H3Me2) ppm.[22]
(B) Study of the Stability of [Fe2{μ-C(CN)NMe2}(μ-CO)(CO)2-
Cp2]:[13] The air and water stability of the title compound was moni-
tored with IR spectroscopy. The compound appeared almost stable
after ten days in contact with air. A portion of the compound
(0.50 mmol) was dissolved in CH2Cl2 (2 mL), and the solution was
diluted with H2O (5 mL). After 10 d, CH2Cl2 (10 mL) was added, then
the organic phase was charged on an alumina column. Elution with
neat dichloromethane allowed the collection of a green band corre-
sponding to [Fe2{μ-CN(Me)2}(μ-CO)(CO)(CN)Cp2],[22,23] which was
isolated upon removal of the volatiles under vacuum. Yield: 137 mg,
72 %. C16H16Fe2N2O2 (380.01): calcd. C 50.57, H 4.24, N 7.37; found
(CH2Cl2): νCO = 1997 (s), 1829 (m), νCN = 2117 (vs) cm–1 1H NMR
.
˜
˜
(CDCl3): δ = 7.56–7.04 (C6H3MeCl), 5.46, 5.41, 5.34, 5.32, 4.86, 4.82,
4.79, 4.73 (s, Cp), 4.54, 4.46 (s, NMe), 2.35, 2.28, 2.22, 2.17 (s,
C6H3MeCl) ppm. Isomer ratio 2:1.5:2:1.
[Fe2{μ-CNMe(C10H7)}(μ-CO)(CO){CN(C10H7)}Cp2][SO3CF3] (2c):
Dark-brown solid. Yield: 200 mg, 12 % (with respect to 2-naphthyl
isocyanide). C36H27F3Fe2N2O5S (768.37): calcd. C 56.27, H 3.54, N
3.65; found C 56.48, H 3.48, N 3.70. IR (CH2Cl2): νCO = 1987 (s), 1826
˜
1
(m), ν = 2115 (s), 1507 (w) cm–1. H NMR (CDCl3): δ = 8.11–7.08
˜
CN
C 50.46, H 4.15, N 7.46. IR (CH Cl ): ν = 1981 (vs), 1804 (s), ν =
˜
˜
2
2
CO
CN
(C10H7), 5.48, 5.39, 5.38, 4.70, 4.66 (s, Cp), 4.64, 4.62, 4.52 (s, NMe)
ppm. Isomer ratio ca. 1:1:1.
2091 (w), 1578 (w) cm–1 1H NMR (CDCl3): δ = 4.83, 4.79 (s, 10 H,
.
Cp), 4.28, 4.14 (s, 6 H, NMe) ppm.[23]
Reactions of 1b,c with NaBH4. Synthesis and Characterization
of [Fe2{μ-CNMe(Xyl)}(μ-CO)(CO)2Cp(η4-C5H6)], 3, and [Fe2
{μ-CHNMe(C10H7)}(μ-CO)(CO)2Cp2], 4.
Synthesis and Characterization of [Fe2{μ-CN(Me)(R)}(μ-CO)(CO)-
{C(OMe)Me}Cp2][SO3CF3] (R = Me, 5a; R = Xyl, 5b)
[Fe2{μ-CNMe(Xyl)}(μ-CO)(CO)2Cp(η4-C5H6)] (3): A solution of 1c
(200 mg, 0.322 mmol) in tetrahydrofuran (10 mL) was treated with
NaBH4 (65 mg, 1.7 mmol), and the resulting mixture was stirred at
room temperature for 20 min. Then the liquid was filtered through
an alumina column using tetrahydrofuran as the eluent. The vola-
tiles were removed from the filtered solution under reduced pres-
sure. The residue was dissolved in diethyl ether and charged on an
alumina column. A red band corresponding to 3 was collected by
using neat diethyl ether as the eluent. The product was obtained
as a red powder upon removal of the solvent under vacuum. Yield:
107 mg, 70 %. C23H23Fe2NO3 (473.13): calcd. C 58.39, H 4.90, N 2.96;
[Fe2{μ-CN(Me)2}(μ-CO)(CO){C(OMe)Me}Cp2][SO3CF3] (5a): A solu-
tion of [Fe2{μ-CN(Me)2}(μ-CO)(CO){(C=O)Me}Cp2] (150 mg,
0.378 mmol) in tetrahydrofuran (15 mL) was treated with methyl
trifluoromethanesulfonate (0.047 mL, 0.42 mmol). The mixture was
stirred at room temperature for one hour, then it was filtered on a
celite pad. Addition of diethyl ether (50 mL) to the filtered solution
resulted in precipitation of an air-stable red powder. Yield: 178 mg,
84 %. Crystals suitable for X-ray diffraction analysis were obtained
from a CH2 Cl2 /diethyl ether mixture, stored at –20 °C.
C19H22F3Fe2NO6S (561.13): calcd. C 40.67, H 3.95, N 2.50; found C
40.82, H 3.87, N 2.59. IR (CH2Cl2): νCO = 1986 (vs), 1808 (s), νCN
=
˜
˜
1586 (m) cm–1. H NMR (CD2Cl2): δ = 5.04, 5.02 (s, 10 H, Cp), 4.10,
4.04 (s, 6 H, NMe), 3.74 (s, 3 H, OMe), 2.65 (s, 3 H, Fe=CMe) ppm.
13C{1H} NMR (CD2Cl2): δ = 330.7 (Fe=C), 325.4 (μ-C), 262.2 (μ-CO),
211.8 (CO), 91.1, 88.4 (Cp), 62.2 (OMe), 52.9, 52.6 (NMe), 42.2 (Fe=
CMe) ppm.
1
found C 58.50, H 4.97, N 3.02. IR (CH2Cl2): νCO = 1960 (vs), 1925 (m),
˜
1
1771 (m), νCN = 1551 (w) cm–1. H NMR (CDCl3): δ = 7.15–7.01 (m,
˜
3 H, C6H3Me2), 4.80, 4.70 (s, 5 H, Cp), 4.56, 4.49, 4.11, 3.20 (m, 4 H,
C5H4), 4.32, 4.14 (s, 3 H, NMe), 3.05, 2.79 (d, 2JH,H = 12 Hz, 2 H, CH2),
2.44, 2.37, 2.33, 2.28 (s, 6 H, C6H3Me2) ppm. Isomer ratio 3:2. 13C{1H}
NMR (CDCl3): δ = 333.6 (μ-CN), 276.4 (μ-CO), 223.1, 218.4, 213.6 (CO),
148.0 (ipso-C6H3Me2), 134.6, 133.8, 132.8, 132.7, 129.9, 129.2, 128.3,
127.9, 127.8, 127.5, 125.6 (C6H3Me2), 85.0, 82.3 (Cp), 90.0, 87.5, 85.0,
81.7, 64.5, 62.0 (C5H4), 52.7, 52.6 (NMe), 45.4 (CH2), 18.2, 18.1, 17.8,
17.7 (C6H3Me2) ppm.
[Fe2{μ-CN(Me)(Xyl)}(μ-CO)(CO){C(OMe)Me}Cp2][SO3CF3] (5b):
This product was obtained by the same procedure as that described
for the synthesis of 5a, from [Fe2{μ-CN(Me)(Xyl)}(μ-CO)(CO)-
{(C=O)Me}Cp2] (170 mg, 0.349 mmol) and methyl trifluorometh-
anesulfonate (0.043 mL, 0.38 mmol). Red solid. Yield: 186 mg, 82 %.
C26H28F3Fe2NO6S (651.26): calcd. C 47.95, H 4.33, N 2.15; found C
[Fe2{μ-CHNMe(C10H7)}(μ-CO)(CO)2Cp2] (4): This product was ob-
tained by using a procedure closely resembling that described for
48.08, H 4.20, N 2.28. IR (CH Cl ): ν = 1987 (vs), 1809 (s), ν
=
˜
˜
2
2
CO
CN
1
3, from 1e (200 mg, 0.311 mmol) and NaBH4 (60 mg, 1.6 mmol). 1522 (m) cm–1. H NMR (CD2Cl2): δ = 7.5–7.2 (3 H, C6H3Me2), 5.19,
Dark-green solid. Yield: 131 mg, 85 %. C25H21Fe2NO3 (495.14): calcd.
4.43 (s, 10 H, Cp), 4.35 (s, 3 H, NMe), 3.94 (s, 3 H, OMe), 2.90, 2.54,
C 60.64, H 4.28, N 2.83; found C 60.38, H 4.16, N 2.90. IR (CH2Cl2): 2.35 (s, 9 H, Fe=CMe, C6H3Me2) ppm. 13C{1H} NMR (CD2Cl2): δ =
νCO = 1955 (vs), 1925 (m), 1765 (m), 1625 (w), 1597 (w), 1508 (w)
333.3, 333.0 (μ-C, Fe=C), 262.0 (μ-CO), 212.1 (CO), 147.4 (ipso-
C6H3Me2), 132.9, 132.8, 130.2, 128.9, 128.9 (C6H3Me2), 91.8, 88.0 (Cp),
63.3 (OMe), 55.0 (NMe), 43.6 (Fe=CMe), 18.6, 17.2 (C6H3Me2) ppm.
˜
cm–1. 1H NMR (CDCl3): δ = 13.11 (μ-CH), 7.94–7.02 (7 H, C10H7), 4.79,
4.72 (s, 10 H, Cp), 3.18 (s, 3 H, NMe) ppm. 13C{1H} NMR (CDCl3): δ =
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Reactions of 5a with Amines
Compound [Fe2{μ-CN(Me)2}(μ-CO)(CO){(C=O)Me}Cp2][14] was finally
recovered in ca. 70 % yield after alumina chromatography.
Synthesis and characterization of [Fe2(μ-CNMe2)(μ-CO)(CO)-
{C(Me)NH(R)}(Cp)2][SO3CF3] (R = iPr, 6a; R = Et, 6b): A solution of
5a (88 mg, 0.157 mmol) in tetrahydrofuran (12 mL) was treated with
NH2iPr (0.10 mL, 1.16 mmol). The mixture was stirred for 2 h, then
the volatile materials were removed under vacuum. The resulting
residue was dissolved in CH2Cl2 (5 mL) and was charged on an
alumina column. A red band corresponding to 6a was collected by
using methanol as the eluent, then the product was isolated as a
red solid after removal of the solvent under vacuum. Yield: 78 mg,
84 %. C21H27F3Fe2N2O5S (588.20): calcd. C 42.88, H 4.63, N 4.76;
Reaction of 5a with NBu4CN: Synthesis and Characterization of
[Fe2{μ-CN(Me)2}(μ-CO)(CO){C(CN)(OMe)Me}Cp2] (7): A solution of
5a (120 mg, 0.214 mmol) in dichloromethane (15 mL) was treated
with NBu4CN (69 mg, 0.26 mmol). The mixture was stirred for 1 h,
then the resulting solution was charged on an alumina column. The
band corresponding to 7 was collected by using neat dichloro-
methane as the eluent, then the product was isolated as a dark-red
solid upon removal of the solvent under vacuum. Yield: 84 mg,
90 %. Crystals suitable for X ray analysis were collected by a CH2Cl2
solution layered with petroleum ether and stored at –30 °C.
found C 43.06, H 4.66, N 4.67. IR (CH2Cl2): νCO = 1973 (vs), 1795 (s),
˜
1
ν
˜
= 1570 (m) cm–1. H NMR (CDCl3): δ = 4.82, 4.61 (s, 10 H, Cp),
CN
C
19H22Fe2N2O3 (438.09): calcd. C 52.09, H 5.06, N 6.39; found C
3
4.24, 4.04 (s, 6 H, NMe2), 3.66 (septet, JH,H = 6.4 Hz, 1 H, CHMe2),
1.95 (s, 3 H, Fe=CMe), 0.94, 0.90 (d, 3JH,H = 6.4 Hz, 6 H, CHMe2) ppm.
13C{1H} NMR (CDCl3): δ = 330.4 (μ-CN), 271.6 (μ-CO), 261.2 (Fe=C),
211.7 (CO), 88.6, 88.3 (Cp), 53.9, 52.1 (NMe2), 50.8 (CHMe2), 32.8 (Fe=
CMe), 21.6, 21.4 (CHMe2) ppm.
52.20, H 4.99, N 6.44. IR (CH2Cl2): νC≡ N = 2180 (w), νCO = 1965 (vs),
˜
˜
1774 (s), νCN = 1561 (m) cm–1. 1H NMR (CDCl3): δ = 4.74, 4.54 (s, 10
˜
H, Cp), 4.44, 4.06 (s, 6 H, NMe2), 2.71 (s, 3 H, OMe), 1.43 (s, 3 H,
FeCMe) ppm. 13C{1H} NMR (CDCl3): δ = 332.8 (μ-CN), 270.7 (μ-CO),
215.4 (CO), 130.2 (C≡ N), 89.2, 86.6 (Cp), 57.0 (FeCMe), 53.0, 50.0
(NMe2), 50.3 (OMe), 27.1 (FeCMe) ppm.
To obtain 6b, a large excess of NH2Et was bubbled into a solution
of 5a (130 mg, 0.232 mmol) in CH2Cl2 (20 mL), then the mixture
was stirred at room temperature for 45 min. The final solution was
charged on an alumina column and a red band corresponding to
6b was eluted using neat CH2Cl2 as the eluent. The product was
isolated as a red powder upon removal of the solvent under vac-
uum. Yield: 93 mg, 70 %. C20H25F3Fe2N2O5S (574.18): calcd. C 41.84,
X-ray Diffraction Crystallography: Crystal data and collection de-
tails for 1a, 1d·CHCl3, 6a and 7 are reported in Table 5. The diffrac-
tion experiments were carried out with a Bruker SMART 2000 (6a)
and Bruker APEX II (1a, 1d·CHCl3 and 7) diffractometer, equipped
with a CCD (6a) or CMOS (1a, 1d, 7) detector using Mo-Kα radiation.
Data were corrected for Lorentz polarization and absorption effects
(empirical absorption correction SADABS).[31] Structures were
solved by direct methods and refined by full-matrix least-squares
based on all data using F2.[32] Hydrogen atoms were fixed at calcu-
lated positions and refined by a riding model, except N-bonded
hydrogens of 6a, which were located in the Fourier map. All non-
hydrogen atoms were refined with anisotropic displacement param-
eters, unless otherwise stated. Crystals of 1a contain half of the
cations and half of the anions located on m. Crystals of 6a contain
two independent molecules, with similar structures and bonding
H 4.39, N 4.88; found C 41.65, H 4.47, N 4.95. IR (CH2Cl2): νCO = 1975
˜
(vs), 1796 (s), νCN = 1566 (m) cm–1
.
1H NMR (CDCl3): δ = 8.46 (s, 1
˜
H, NH), 4.98, 4.84 (s, 10 H, Cp), 4.46, 4.28 (s, 6 H, NMe2), 3.34, 3.26
(m, 2 H, CH2CH3), 2.23 (s, 3 H, Fe=CMe), 1.01 (t, 3JH,H = 7.34, 6.60 Hz,
3 H, CH2CH3) ppm. 13C{1H} NMR (CDCl3): δ = 329.1 (μ-CN), 269.1 (μ-
CO), 261.7 (Fe=C), 211.9 (CO), 89.0, 88.2 (Cp), 54.3, 52.9 (NMe2), 44.0
(CH2), 33.5 (Fe=CMe), 13.8 (CH3) ppm.
The reaction of 5a (0.80 mmol) with NHEt2 (0.80 mmol) was carried
out by a procedure similar to that described for the synthesis of 6a.
Table 5. Crystal data and measurement details for 1a, 1d·CHCl3, 6a and 7.
1a
1d·CHCl3
6a
7
Empirical formula
Formula mass [g/mol]
C17H16F3Fe2NO6S
531.07
C24H20Cl4F3Fe2NO6S
760.97
C21H27F3Fe2N2O5S
588.20
C19H22Fe2N2O3
438.08
T [K]
100(2)
295(2)
293(2)
100(2)
λ [Å]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
ꢀ [°]
0.71073
orthorhombic
Pnma
15.0150(14)
10.0255(9)
13.0438(12)
90
90
90
1963.5(3)
4
1.796
0.71073
triclinic
0.71073
triclinic
0.71073
orthorhombic
P212121
8.3837(7)
13.0412(10)
16.6589(13)
90
90
90
1821.4(3)
4
1.598
P1
P1
¯
¯
8.6653(7)
13.3677(13)
14.6970(12)
70.288(3)
73.740(2)
71.215(2)
1489.0(2)
2
13.562(3)
13.585(3)
15.886(3)
102.20(3)
109.69(3)
107.32(3)
2467.6(11)
4
γ [°]
Cell volume [Å3]
Z
Dcalcd. (g cm–3
)
1.697
1.462
764
1.583
1.317
1208
μ [mm–1
F(000)
]
1.647
1072
1.614
904
Crystal size [mm]
θ limits [°]
0.19 × 0.16 × 0.12
2.068–26.999
25914
2264 [Rint = 0.0609]
2264/0/149
1.139
0.19 × 0.16 × 0.12
1.672–25.499
18616
5539 [Rint = 0.0279]
5539/470/474
1.051
0.22 × 0.19 × 0.14
1.451–27.485
27089
11334 [Rint = 0.0431]
11334/241/629
1.027
0.19 × 0.13 × 0.12
1.983–25.875
13635
3494 [Rint = 0.0569]
3494/42/240
1.085
Reflections collected
Independent reflections
Data/restraints/parameters
Goodness of fit on F2
R1 [I > 2σ(I)]
0.0356
0.0567
0.0493
0.0304
wR2 (all data)
0.0691
0.501, –0.475
0.1621
1.409, –0.921
0.1407
0.845, –0.365
0.0583
0.293, –0.316
Largest diff. peak and hole [e Å–3
]
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Acknowledgments
The University of Pisa and the University of Bologna are grate-
fully acknowledged for financial support.
Keywords: Iron · Ligand effects · Organometallic
synthesis · Carbonyl ligands · Carbenes
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Iron Aminocarbyne Complexes
G. Agonigi, M. Bortoluzzi,
F. Marchetti,* G. Pampaloni,
S. Zacchini, V. Zanotti .................... 1–13
Regioselective Nucleophilic Addi-
tions to Diiron Carbonyl Complexes
Containing a Bridging Aminocarb-
yne Ligand: A Synthetic, Crystallo-
graphic and DFT Study
A convenient procedure to access and alkoxycarbene coligands on the
cationic diiron μ-aminocarbyne com- electrophilic behaviour of the cationic
pounds, starting from [Fe2Cp2(CO)4], is complexes is investigated experimen-
described; the effect of N-substituents tally and by using DFT calculations.
DOI: 10.1002/ejic.201701115
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