Alkyne-isocyanide coupling in [Fe2(CNMe)(CO)3(Cp) 2]: A new route to diiron -vinyliminium complexes

Article abstract of DOI:10.1021/om070097z

Alkynes (RC≡CR') insert into the metal-isocyanide bond of [Fe ₂(CNMe)(CO)₃(Cp)₂] (1), under UV irradiation, affording the complexes [Fe₂{μ-η:η³-C(R)C(R')C= N(Me)}(μ-CO)(CO)(Cp)₂] (R = R'= Ph, 2a; R = R' = Me, 2b; R = R' = Et, 2c; R = Ph, R' = H, 2d; R = Tol, R' = H, 2e; R = SiMe₃, R' = H, 2f; R = Me, R' = H, 2g; R = CH₂OH, R' = H, 2h; Tol = 4-MeC ₆H₄), with displacement of one CO ligand. Compounds 2b,c exist as a mixture of cis and trans isomers (with reference to the mutual Cp position), whereas 2a,d-h exclusively have the cis geometry. The insertion of terminal alkynes is regioselective, since C-C bond formation occurs selectively between the isocyanide and the nonsubstituted carbon of HC≡CR. Compound 1 reacts with 2 equiv of HC≡CCO₂Me under UV irradiation, affording [Fe₂{μ-η²:η⁴-C(OH) C(CO₂Me}C(H)CN(Me)(CH=CHCO₂Me}(CO)(Cp)₂] (4). Complexes 2a,c undergo electrophilic addition at the N atom by treatment with HSO₃CFs, allyl iodide (ICH₂CH=CH₂), and methyl chloroformate (CICOOMe), affording the corresponding vinyuminium cations [Fe₂{u-η¹:η³-C(R)=C(R)C= N(Me)(E)}(μ-CO)(CO)(Cp)₂]⁺ (R = Ph, E = H, 5a; R = Et, E = H, 5b; R = Ph, E = CH₂CH=CH₂, 6; R = Ph, E = CO ₂Me, 7). The reactions of 6 with NaBH₄ and NBu ₄CN afford [Fe₂{μ-η:η³-C(Ph)C(Ph)= C(H)N(Me)(CH₂CH=CH₂)}(u-CO)(CO)(Cp)₂] (8) and [Fe₂{μ-η¹:η³-C(Ph)C(Ph)C(CN)N(Me)- (CH₂CH-CH₂)}(μ-CO)(CO)(Cp)₂] (9), respectively. The molecular structures of cis-2c, [Fe₂{μ- η¹:η³-C(Et)=C(Et)C=N(Me)(Xyl)}(μ-CO)(CO)(Cp) ₂][SO₃CF₃] (3), 4, and Sa have been established by X-ray diffraction studies.

Full text of DOI:10.1021/om070097z

3448
Organometallics 2007, 26, 3448-3455
Alkyne-Isocyanide Coupling in [Fe2(CNMe)(CO)3(Cp)2]: A New
Route to Diiron µ-Vinyliminium Complexes†
Vincenzo G. Albano,‡ Luigi Busetto,*,§ Fabio Marchetti,| Magda Monari,‡
Stefano Zacchini,§ and Valerio Zanotti§
Dipartimento di Chimica Fisica e Inorganica, UniVersita` di Bologna, Viale Risorgimento 4,
40136 Bologna, Italy, Dipartimento di Chimica “G. Ciamician”, UniVersita` di Bologna, Via Selmi 2,
40126 Bologna, Italy, and Dipartimento di Chimica e Chimica Industriale, UniVersita` di Pisa,
Via Risorgimento 35, I-56126 Pisa, Italy
ReceiVed February 1, 2007
Alkynes (RCtCR′) insert into the metal-isocyanide bond of [Fe2(CNMe)(CO)3(Cp)2] (1), under UV
irradiation, affording the complexes [Fe2{µ-η1:η3-C(R)C(R′)CdN(Me)}(µ-CO)(CO)(Cp)2] (R ) R′) Ph,
2a; R ) R′ ) Me, 2b; R ) R′ ) Et, 2c; R ) Ph, R′ ) H, 2d; R ) Tol, R′ ) H, 2e; R ) SiMe3, R′ )
H, 2f; R ) Me, R′ ) H, 2g; R ) CH2OH, R′ ) H, 2h; Tol ) 4-MeC6H4), with displacement of one CO
ligand. Compounds 2b,c exist as a mixture of cis and trans isomers (with reference to the mutual Cp
position), whereas 2a,d-h exclusively have the cis geometry. The insertion of terminal alkynes is
regioselective, since C-C bond formation occurs selectively between the isocyanide and the nonsubstituted
carbon of HCtCR. Compound 1 reacts with 2 equiv of HCtCCO2Me under UV irradiation, affording
[Fe2{µ-η2:η4-C(OH)C(CO2Me)C(H)CN(Me)(CHdCHCO2Me}(CO)(Cp)2] (4). Complexes 2a,c undergo
electrophilic addition at the N atom by treatment with HSO3CF3, allyl iodide (ICH2CHdCH2), and methyl
chloroformate (ClCOOMe), affording the corresponding vinyliminium cations [Fe2{µ-η1:η3-C(R)dC(R)Cd
N(Me)(E)}(µ-CO)(CO)(Cp)2]+ (R ) Ph, E ) H, 5a; R ) Et, E ) H, 5b; R ) Ph, E ) CH2CHdCH2,
6; R ) Ph, E ) CO2Me, 7). The reactions of 6 with NaBH4 and NBu4CN afford [Fe2{µ-η1:η3-
C(Ph)C(Ph)dC(H)N(Me)(CH2CHdCH2)}(µ-CO)(CO)(Cp)2] (8) and [Fe2{µ-η1:η3-C(Ph)C(Ph)C(CN)N(Me)-
(CH2CHdCH2)}(µ-CO)(CO)(Cp)2] (9), respectively. The molecular structures of cis-2c, [Fe2{µ-η1:η3-
C(Et)dC(Et)C)N(Me)(Xyl)}(µ-CO)(CO)(Cp)2][SO3CF3] (3), 4, and 5a have been established by X-ray
diffraction studies.
Scheme 1
Introduction
The transition-metal-promoted conversion of C1 ligands into
organic compounds remains a major goal in organometallic
chemistry. In this context, the insertion of alkynes into the
metal-carbon bond of bridging CO,1 µ-alkylidenes,2 and
µ-alkylidynes3 provides an efficient route to the C-C bond
formation in dinuclear complexes. These reactions, which
generally result in the formation of C3-bridged species, have
attracted great attention because of the implications with the
carbon-carbon chain growth in the Fischer-Tropsch (FT)
process.4
Our work in this area has shown that the coupling of C1
(aminocarbyne) and C2 (alkyne) units affords C3 bridging
vinyliminium species (Scheme 1).5,6
These latter species have been further modified and have
grown in complexity by introduction of new functionalities,
under regio- and stereoselective conditions. Indeed, we have
reported that the bridging vinyliminium ligands undergo a
variety of transformations upon addition of hydride,7 cyanide,8
acetylides,9 and organolithium reagents.10 Further modifications
(2) (a) Dyke, A. F.; Knox, S. A. R.; Naish, P. J.; Taylor, G. E. J. Chem.
Soc., Chem. Commun. 1980, 803. (b) Sumner, C. E.; Collier, J. A.; Pettit,
R. Organometallics 1982, 1, 1350. (c) Adams, P. Q.; Davies, D. L.; Dyke,
A. F.; Knox, S. A. R.; Mead, K. A.; Woodward, P. J. Chem. Soc., Chem.
Commun. 1983, 222. (d) Levisalles, J.; Rose-Munch, F.; Rudler, H.; Daran,
J. C.; Jeannin, Y. J. Organomet. Chem. 1985, 279, 413. (e) Akita, M.; Hua,
R.; Nakanishi, S.; Tanaka, M.; Moro-oka, Y. Organometallics 1987, 16,
5572. (f) Navarre, D.; Parlier, A.; Rudler, H.; Daran, J. C. J. Organomet.
Chem. 1987, 322, 103. (g) Colburn, R. E.; Davies, D. L.; Dyke, A. F.;
Knox, S. A. R.; Mead, K. A.; Orpen, A. G. J. Chem. Soc., Dalton Trans.
1989, 1799. (h) Knox, S. A. R. J. Organomet. Chem. 1990, 400, 255. (i)
Kaneko, Y.; Suzuki, T.; Isobe, K.; Maitlis, P. M. J. Organomet. Chem.
1998, 554. (j) Royo, E.; Royo, P.; Cuenca, T.; Galakhov, M. Organome-
tallics 2000, 19, 5559. (k) Rowsell, B. D.; McDonald, R.; Ferguson, M. J.;
Cowie, M. Organometallics 2003, 22, 2944. (l) Wigginton, J. R.; Chokshi,
A.; Graham, T. W.; McDonald, R.; Ferguson, M. J.; Cowie, M. Organo-
metallics 2005, 24, 6398.
* To whom correspondence should be addressed. E-mail: luigi.busetto@
unibo.it.
† Dedicated to Professor Robert J. Angelici on the occasion of his 70th
birthday.
‡ Dipartimento di Chimica “G. Ciamician”, Universita` di Bologna.
§ Dipartimento di Chimica Fisica e Inorganica, Universita` di Bologna.
| Universita` di Pisa.
(1) (a) Dyke, A. F.; Knox, S. A. R.; Naish, P. J.; Taylor, G. E. J. Chem.
Soc., Chem. Commun. 1980, 409. (b) Davies, D. L.; Dyke, A. F.; Knox, S.
A. R.; Morris, M. J. J. Organomet. Chem. 1981, 215, C30-C32. (c) Dyke,
A. F.; Knox, S. A. R.; Naish, P. J.; Taylor, G. E. J. Chem. Soc., Dalton
Trans. 1982, 1297. (d) Gracey, B. P.; Knox, S. A. R.; Macpherson, K. A.;
Orpen, A. G.; Stobart, S. R. J. Chem. Soc., Dalton Trans. 1985, 1935. (e)
Fontaine, X. L. R.; Jacobsen, G. B.; Shaw, B. L.; Thornton-Pett, M. J. Chem.
Soc., Dalton Trans. 1988, 741.
10.1021/om070097z CCC: $37.00 © 2007 American Chemical Society
Publication on Web 06/06/2007

Diiron µ-Vinyliminium Complexes
Scheme 2
Organometallics, Vol. 26, No. 14, 2007 3449
Figure 1. ORTEP drawing of cis-[Fe2{µ-η1:η3-C(Et)C(Et)Cd
N(Me)}(µ-CO)(CO)(Cp)2] (2c). Hydrogen atoms are omitted for
clarity; thermal ellipsoids are given at the 30% probability level.
Table 1. Selected Bond Lengths (Å) and Angles (deg) for 2c,
3, and 5a
of the bridging vinyliminium ligand have also been found, owing
to the acidic character of the Câ-H.11
2c
3
5aa
Herein we report on the extension of these studies to the
alkyne-isocyanide coupling in the diiron complex [Fe2(CNMe)-
(CO)3(Cp)2] (1). To the best of our knowledge, the reactivity
of 1 toward alkynes is still unexplored, in spite of the fact that
the chemistry of isocyanide complexes has been extensively
investigated in the past.12
Fe(1)-C(1)
Fe(2)-C(1)
Fe(1)-C(3)
Fe(2)-C(3)
Fe(1)-C(4)
Fe(1)-C(5)
C(1)-O(1)
1.866(3)
1.949(3)
2.029(2)
1.967(2)
2.056(3)
1.952(3)
1.186(3)
2.5249(7)
1.135(4)
1.427(4)
1.431(4)
1.237(4)
1.470(4)
1.949(4)
1.896(4)
2.030(4)
1.976(4)
2.073(4)
1.853(4)
1.163(5)
2.5532(8)
1.130(6)
1.410(6)
1.444(5)
1.292(5)
1.962(6) [1.981(6)]
1.867(6) [1.887(6)]
2.059(5) [2.047(5)]
1.960(5) [1.973(5)]
2.105(4) [2.103(5)]
1.832(5) [1.841(5)]
1.177(6) [1.166(6)]
2.560(1) [2.554(1)]
1.132(7) [1.138(7)]
1.430(7) [1.424(7)]
1.421(7) [1.428(7)]
1.289(6) [1.27886)]
Fe(1)-Fe(2)
C(2)-O(2)
Results and Discussion
C(3)-C(4)
Alkyne Insertion into the Metal-Isocyanide Bond. The
complex [Fe2(CNMe)(CO)3(Cp)2] (1) consists of an isomeric
mixture of terminal and bridging isocyanide, with a large
prevalence of the second form.13 The reactions of 1 with mono-
and disubstituted alkynes RCtCR′, under UV irradiation in
Et2O solution, result in the formation of [Fe2{µ-η1:η3-
C(R)C(R′)CdN(Me)}(µ-CO)(CO)(Cp)2] (2a-h) in about 60%
yield (Scheme 2).
C(4)-C(5)
C(5)-N(1)
C(10)-N(1)
C(6)-N(1)
1.484(5)
1.455(5)
2.099
1.468(7) [1.466(7)]
C(9)-N(1)
Fe(1)-C(Cp) (av)
2.094
2.115
2.096 [2.103]
2.119 [2.136]
Fe(2)-C(Cp) (av)b
2.116
C(3)-C(4)-C(5)
N(1)-C(5)-C(4)
C(5)-N(1)-C(10)
C(5)-N(1)-C(9)
C(5)-N(1)-C(6)
C(6)-N(1)-C(9)
C(5)-N(1)-H(1)
117.1(2)
137.1(2)
120.0(3)
114.9(3)
132.7(3)
114.3(4) [114.3(4)]
131.7(5) [133.4(5)]
(3) (a) Jeffery, J. C.; Mead, K. A.; Razay, H.; Stone, F. G. A.; Went, M.
J.; Woodward, P. J. Chem. Soc., Dalton Trans. 1984, 1383. (b) Chisholm,
M. H.; Heppert, J. A.; Huffman, J. C. J. Am. Chem. Soc. 1984, 106, 1151.
(c) Seyferth, D.; Ruschke, D. P.; Davis, W. M. Organometallics 1994, 13,
4695. (d) Casey, C. P.; Woo, L. K.; Fagan, P. J.;Palermo, R. E.; Adams, B.
R. Organometallics 1987, 6, 447.
121.1(3)
122.0(4)
116.8(3)
124.5(5) [124.8(5)]
116(4) [118(4)]
a Data for the second conformer of 5a are given in brackets. b Main image
(4) (a) Maitlis, P. M. J. Organomet. Chem. 2004, 689, 4366. (b) Turner,
M. L.; Marsih, N.; Mann, B. E.; Quyoum, R.; Long, H. C.; Maitlis, P. M.
J. Am. Chem. Soc. 2002, 124, 10456. (c) Overett, M. J.; Hill, R. O.; Moss,
J. R. Coord. Chem. ReV. 2000, 206-207, 581-605. (d) Roberts, M. W.
Chem. Soc. ReV. 1977, 6, 373-391. (e) Cowie, M. Can. J. Chem. 2005,
83, 1043-1055.;
of the Cp ligand.
Chart 1
(5) (a) Albano, V. G.; Busetto, L.; Marchetti, F.; Monari, M.; Zacchini,
S.; Zanotti, V. Organometallics 2003, 22, 1326. (b) Albano, V. G.; Busetto,
L.; Marchetti, F.; Monari, M.; Zacchini, S.; Zanotti, V. J. Organomet. Chem.
2004, 689, 528.
(6) Busetto, L.; Marchetti, F.; Zacchini, S.; Zanotti, V. J. Organomet.
Chem. 2006, 691, 2424.
(7) (a) Albano, V. G.; Busetto, L.; Marchetti, F.; Monari, M.; Zacchini,
S.; Zanotti, V. Organometallics 2004, 23, 3348. (b) Albano, V. G.; Busetto,
L.; Marchetti, F.; Monari, M.; Zacchini, S.; Zanotti, V. J. Organomet. Chem.
2005, 690, 837.
(8) Albano, V. G.; Busetto, L.; Marchetti, F.; Monari, M.; Zacchini, S.;
Zanotti, V. J. Organomet. Chem. 2006, 691, 4234.
(9) Busetto, L.; Marchetti, F.; Zacchini, S.; Zanotti, V. Eur. J. Inorg.
Chem. 2006, 285.
(10) Albano, V. G.; Busetto, L.; Marchetti, F.; Monari, M.; Zacchini,
S.; Zanotti, V. J. Organomet. Chem. 2005, 690, 4666.
(11) Busetto, L.; Marchetti, F.; Zacchini, S.; Zanotti, V. Organometallics
2005, 24, 2297.
(12) (a) Adams, R. D.; Cotton, F. A. Synth. React. Inorg. Met.-Org. Chem.
1974, 4, 477. (b) Adams, R. D.; Cotton, F. A. Inorg. Chem. 1974, 13, 249.
(c) Bellerby, J.; Boylan, M. J.; Ennis, M.; Manning, A. R. J. Chem. Soc.,
Dalton Trans, 1978, 1185. (d) McNally, G.; Murray, P. T.; Manning, A.
R. J. Organomet. Chem. 1983, 243, C87. (e) Fehlhammer, W. P.; Mayr,
A.; Kehr, W.; J. Organomet. Chem. 1980, 197, 327.
The synthesis of 2a-h is the result of alkyne insertion into
the metal-isocyanide bond of 1, promoted by photochemical
loss of a CO ligand. All the compounds have been purified by
column chromatography on alumina and characterized by IR
and NMR spectroscopy and elemental analysis. The structure
of 2c has been determined by X-ray diffraction. The ORTEP
molecular diagram is shown in Figure 1, and relevant bond
lengths and angles are reported in Table 1. This is the first
structural study for this family of compounds in which the
multibridging ligand bears an imine fragment. The electronic
structure of the N-CR-Câ-Cγ unit can be schematized in three
different ways: (A) allylimine, (B) enimine (azabutadienyl), and
(C) ketenimine. As a consequence, the ligand-metal bonding
interactions can be described differently, as shown in Chart 1.
An analysis of the bond parameters is necessary in order to find
out the best representation of the electronic structure of this
(13) Adams, R. D.; Cotton, F. A.; Troup, J. M. Inorg. Chem. 1974, 13,
257.

3450 Organometallics, Vol. 26, No. 14, 2007
Albano et al.
2c reveals the effects of changing the nature of the nitrogen
from imine to iminium. The bonding interactions of Cγ (C(3))
and Câ (C(4)) are substantially unaffected, while CR (C(5))
exhibits significant variations. The CR-N bond is lengthened
with respect to 2c (1.292(5) vs 1.237(4) Å). This lengthening
is accompanied by a shortening of the CR-Fe bond (C(5)-
Fe(1): 1.853(4) vs 1.952(3) Å). These figures indicate that the
pz orbital on CR is less involved in π bonding to N and more
involved in bonding to Fe(1). The result is a higher electron
donation to the metal with respect to 2c. This rationalization is
confirmed by the inversion of the asymmetry of the bridging
carbonyl, which is now farther from Fe(1) (Fe(1)-C(1) )
1.949(4) Å and Fe(2)-C(1) ) 1.896(4) Å vs 1.866(3) and
1.949(3) Å in 2c), while the other bond interactions of Fe(1)
are slightly (but not significantly) lengthened. The electronic
structure of the N-CR-Câ-Cγ grouping is not significantly
changed with respect to the neutral species 2c, and the system
can still be described as azabutadienyl with a torsion angle along
the chain N-C(5)-C(4)-C(3) (34.7(4)° in 3 vs 39.0(3)° in 2c).
The IR spectra (in CH2Cl2 solution) of 2a-h exhibit a weak
absorption in the range 1714-1740 cm-1, attributable to the
imine CR-N bond and the usual ν(CO) band pattern (e.g., for
2a at 1972 and 1788 cm-1).
Several isomeric forms are, in theory, possible for 2a-h due
to the mutual Cp position (cis and trans isomers) or to the two
possible orientations of the N-Me group in the imine moiety
(E and Z isomers). Nonetheless, NOE studies, carried out on
compounds 2a-c, indicate that these species adopt a Z config-
uration in solution, in agreement with the geometry found in
the solid state. Moreover, 2a exists only in the cis form, whereas
both cis and trans isomers are present in the case of 2b,c.
Mixtures of 2b,c as the cis and trans isomers have been
completely converted into the more stable cis-2b and cis-2c,
upon heating at reflux temperature in toluene for 2 h.
Figure 2. ORTEP drawing of the cation of (cis,Z)-[Fe2{µ-η1:η3-
C(Et)dC(Et)CdN(Me)(Xyl)}(µ-CO)(CO)(Cp)2][CF3SO3] (3). Hy-
drogen atoms are omitted for clarity; thermal ellipsoids are given
at the 30% probability level.
Table 2. Selected Bond Lengths (Å) and Angles (deg) for
[Fe(Cp){η5-Fe(Cp)(CO){µ-η2-C{N(Me)(CHdCHCO2Me)}-
CHC(CO2Me)C(OH)}] (4)
Fe(1)-Fe(2)
Fe(1)-C(1)
Fe(2)-C(1)
Fe(2)-C(3)
Fe(1)-C(3)
Fe(1)-C(4)
Fe(1)-C(5)
Fe(2)-C(2)
C(1)-O(1)
C(2)-O(2)
C(3)-N(1)
C(3)-C(4)
C(4)-C(5)
2.5561(13)
2.017(6)
1.907(7)
1.988(6)
1.986(6)
2.014(6)
2.022(7)
1.737(7)
1.379(8)
1.149(9)
1.412(8)
1.459(9)
1.430(9)
C(5)-C(1)
1.415(9)
1.469(9)
1.311(9)
1.441(8))
1.365(9)
1.35(1)
1.35(1)
1.47(1)
1.18(1)
1.441(8)
2.063
C(5)-C(6)
C(6)-O(3)
O(3)-C(7)
N(1)-C(9)
C(9)-C(10)
C(11)-O(6)
O(6)-C(12)
C(11)-O(5)
N(1)-C(8)
Fe(1)-C(Cp) (av)
Fe(2)-C(Cp) (av)
2.111
Fe(1)-C(1)-O(1)
Fe(2)-C(1)-O(1)
C(4)-C(3)-N(1)
C(1)-Fe(2)-C(3)
Fe(2)-C(3)-C(4)
C(3)-C(4)-C(5)
128.6(5)
C(3)-N(1)-C(9)
C(4)-C(5)-C(6)
C(8)-N(1)-C(9)
C(4)-C(5)-C(1)
C(5)-C(1)-Fe(2)
118.8(5)
121.8(6)
119.3(6)
113.5(6)
115.8(5)
122.8(4)
117.9(5)
82.0(3)
111.8(4)
112.6(5)
For complexes 2d-h, obtained by insertion of unsymmetric
alkynes, a third type of isomerism is possible, due to the
unconventional NC3Fe2 grouping. The C(5)-N(imine) interac-
tion (1.237(4) Å) indicates a localized double bond. (Compare
this value with the genuine single bond N-C(10)(methyl) )
1.470(4) Å.) The torsion angle in the chain Cγ-Câ-CR-N
(C(3)-C(4)-C(5)-N ) 39.0(3)°) is high for an efficient
π-bond delocalization, as required by structures A and C.
Therefore, a good approximation of the electronic structure of
the NC3 fragment is as azabutadienyl (B) and its interaction
with the Fe2 core is η1 to Fe(2) and η1:η2 to Fe(1). The degree
of nonequivalence of the iron atoms in this asymmetric molecule
is assessed by the bonding asymmetry of the bridging carbonyl
(Fe(1)-C(1) ) 1.866(3) Å, Fe(2)-C(1) ) 1.949(3) Å). The
shorter distance from Fe(1) indicates greater donation to this
atom to which CR (C(5)) acts essentially as a one-electron donor,
its pz orbital being primarily engaged in the localized π bond
to N. The quite long Fe(1)-C(5) distance (1.952(3) Å) is in
accord with this interpretation.
The bridging ligand in the neutral complex 2c is strictly
related to the analogous grouping present in the cationic [Fe2-
{µ-η1:η3-C(Et)dC(Et)CdN(Me)(Xyl)}(µ-CO)(CO)(Cp)2][SO3-
CF3] (3).5b Complex 3 is formally derived from 2c by addition
of a Xyl+ fragment at the nitrogen atom. In order to ascertain
the structural effects of a second substituent of the nitrogen atom,
we have now determined the X-ray structure of 3. The molecular
diagram is shown in Figure 2, and relevant bond lengths and
angles are given in Table 2. Expectedly, we find that the bond
parameters in 3 are comparable, within experimental error, to
those already reported for [Fe2{µ-η1:η3-C(Me)dC(Me)Cd
N(Me)(Xyl)}(µ-CO)(CO)(Cp)2][SO3CF3].5b A comparison with
1
insertion mode of the primary alkynes. Interestingly, the H
NMR spectra of 2d-h exhibit a single set of resonances,
indicating that the insertion reaction is regioselective. In
1
particular, the H NMR spectra show that the CH portion of
the inserted HCCR generates a resonance at about δH 2.85-
3.19 ppm, as expected for Câ-H. In contrast, the alternative
isomer (Cγ-H) would resonate in the higher frequency range
of methylidene protons. NOE experiments confirm that the
bridging chain sequence is N-CR-Câ(H)-Cγ(R) and give
further information on the geometry of the complexes in
solution: the Cp ligands are mutually cis and the imine N-Me
group is in the Z configuration, as found in the solid state for
2c.
Major features of the 13C NMR spectra of 2a-h include the
CR carbon resonance at about 195 ppm and the Cγ resonance
in the 180-200 ppm range, which are consistent with their
iminoacyl and alkylidene nature. Conversely, the Câ resonance
is found at ca. δ 50 ppm.
The reaction described in Scheme 2 deserves further com-
ment. Metal-assisted coupling reactions between alkynes and
isocyanides are known for both mononuclear14 and dinuclear
complexes of Mn,15 Os,16 and Rh.17 Among these examples only
the dirhodium complex [Rh2Cp2(CO){µ-C(NR)C(CF3)C(CF3)]
(14) (a) Adams, C. J.; Anderson, K. M.; Bartlett, I. M.; Connelly, N.
G.; Orpen, A. G.; Paget, T. J. Organometallics 2002, 21, 3454. (b) Barnea,
E.; Andrea, T.; Kapon, M.; Berthet, J. C.; Ephritikhine, M.; Eisen, M. S. J.
Am. Chem. Soc. 2004, 126, 10860. (c) Werner, H.; Heinemann, A.;
Windmueller, B.; Steinert, P. Chem. Ber. 1996, 129, 903.
(15) Adams, R. D.; Mingsheng, H.; Organometallics, 1995, 14, 506.

Diiron µ-Vinyliminium Complexes
Organometallics, Vol. 26, No. 14, 2007 3451
Chart 2
Scheme 4
Figure 3. ORTEP drawing of [Fe2{µ-η2:η4-C(OH)C(CO2Me)C-
(H)CN(Me)(CHdCHCO2Me}(CO)(Cp)2] (4). Only the hydrogen
atom bound to O(1) is shown. Thermal ellipsoids are given at the
30% probability level.
Scheme 3
in η4 coordination to one metal atom (Fe(1)). Compound 4 can
be described as being composed of a [Fe2(Cp)2(CO)] moiety
coordinated by a bridging µ-η2:η4-{C(OH)dC(CO2Me)C(H)d
CN(Me)(CHdCHCO2Me)} ligand (Scheme 3). A more appeal-
ing rationalization of the molecular architecture can be inferred
from the following geometrical features: the atoms C(3)-C(4)-
C(5)-C(1)-Fe(2) form a five-membered ring described as
metallacyclopentadienyl (deviations from the average plane in
the range -0.06 to +0.12 Å, C-C distances in the range 1.42-
1.46(1) Å, C(1,3)-Fe(2) distances 1.91 and 1.99(1) Å). The
metalla ring is almost parallel to the Cp ring (C(13)-C(17))
bound to Fe(1) (dihedral angle 10.3(4)°). In conclusion, the
molecule can be viewed as a ferrocene analogue, in which one
ring incorporates one metal atom (Fe(2)) and has different
substituents containing heteroatoms (Chart 2).
has a bridging enimine ligand with a structure and coordination
mode similar to that found in 2a-h.17 Indeed, alkyne-
isocyanide couplings present a variety of outcomes, mostly as
a consequence of multiple insertions, rearrangements, or inclu-
sion of other molecular fragments. Moreover, the µ-η1:η3
coordination described above is not the only way for an enimine
(azabutadienyl) fragment to bridge two metal centers.18 Ac-
cording to the variety of possible combinations between alkynes
and isocyanides, not all the reactions that we have investigated
proceed as described in Scheme 2. This is the case of the
reaction of 1 with methyl propiolate, which under the same
reaction conditions as for 2a-h affords complex 4, with no
trace of the expected analogue of 2a-h (Scheme 3). Even when
the reaction was performed with 1 equiv of HCtCCO2Me,
instead of a large excess, compound 4 was the only identified
product, although formed in lower yield. Complex 4 has been
isolated by chromatography and characterized by spectroscopy
and X-ray diffraction. The ORTEP molecular diagram is shown
in Figure 3, whereas relevant bond lengths and angles are
reported in Table 2.
The reaction sequence leading to the formation of 4 is far
from being understood and involves displacement of one CO
ligand from 1, combination of two HCtCCO2Me molecules
with the isocyanide and the bridging CO ligand, and the addition
of two hydrogen atoms. One propiolate molecule is terminally
added to the nitrogen atom, giving the dangling chain that does
not interact with the metal core. The other propiolate molecule
undergoes further rearrangements which involve addition to the
carbon atoms of the bridging ligands: i.e., the isocyanide (C(3))
and bridging carbonyl (C(1)). The resulting fragment is engaged
The IR spectrum of 4 (in CH2Cl2 solution) shows one terminal
ν(CO) absorption, at 1965 cm-1, together with two absorptions
attributable to the carboxylate groups (at 1686 and 1672 cm-1
)
and a band due to ν(CdC) at 1601 cm-1. The 1H NMR spectrum
exhibits two separate resonances for the inequivalent Cp rings
(at δ 4.94 and 4.31 ppm). Four singlets (at δH 10.00, 5.24, 3.74,
and 3.31 ppm) are attributable to the OH, CâH, carboxylate
methyl, and N-bound methyl, respectively. Moreover, the
protons of the enamine moiety resonate as doublets at 8.35 and
4.90 ppm. Finally, the carbon atoms of the metallacyclopenta-
dienyl ring resonate, in the 13C NMR spectrum, at 179.0 (CR),
79.3 (Câ), 67.2 (Cγ), and 216.6 (COH) ppm, respectively.
Formation of Vinyliminium Complexes. The reactivity of
the bridging enimine (azabutadienyl) ligand in 2a-h was then
investigated. Conversion of 2a-h into the corresponding
vinyliminium species [Fe2{µ-η1:η3-C(R)dC(R′)CdN(Me2)}(µ-
CO)(CO)(Cp)2][CF3SO3] appears to be possible simply via
N-methylation. For instance, 2e reacts with 1 equiv of CF3SO3-
CH3, in dichloromethane solution, to give the known vinyl-
iminium complex [Fe2{µ-η1:η3-C(Tol)dC(H)CdN(Me)2}(µ-
CO)(CO)(Cp)2][CF3SO3]5a in almost quantitative yield. Likewise,
the reactions of 2a and (cis + trans)-2c with HBF4 result in
the formation of the new vinyliminium species [Fe2{µ-η1:η3-
C(R)dC(R)CdN(Me)(H)}(µ-CO)(CO)(Cp)2][BF4] (R ) Ph, 5a;
R ) Et, 5b) (Scheme 4). The reaction is completely reversible,
and the parent complexes are recovered after treatment of 5a,b
with Et3N.
(16) Huang, J.-Y.; Lin, J.-J.; Chi, K.-M.; Lu, K.-L. J. Chem. Soc., Dalton
Trans. 1997, 15.
(17) Dickson, R. S.; Fallon, G. D.; Nesbit, R. J.; Pateras, H. Organo-
metallics 1987, 6, 2517.
(18) Lemke, F. R.; Szalda, D. J.; Bullock, R. M. Organometallics 1992,
11, 876.
It should be noted that vinyliminium complexes of type 5
are not otherwise obtainable, because the usual approach,
consisting of alkyne insertion into the aminocarbyne complex,

3452 Organometallics, Vol. 26, No. 14, 2007
Albano et al.
Chart 3
Figure 4. ORTEP drawing of the cation of [Fe2{µ-η1:η3-C(Ph)d
C(Ph)CdN(Me)(H)}(µ-CO)(CO)(Cp)2][BF4] (5a). Only the hydro-
gen atom bound to N(1) is shown. Thermal ellipsoids are given at
the 30% probability level.
Scheme 5
is unsuccessful in the case of [Fe2{µ-CN(Me)(H)}(µ-CO)(CO)2-
(Cp)2]+.19 Indeed, this latter species, upon treatment with alkynes
in the presence of Me3NO, undergoes deprotonation rather than
alkyne insertion.
Complex 5a has been structurally characterized by X-ray
crystallography (Figure 4, and Table 1). In the crystal two
conformers of the cation of [Fe2{µ-η1:η3-C(Ph)dC(Ph)Cd
N(Me)(H)}(µ-CO)(CO)(Cp)2][BF4] (5a) are present. Since the
difference between the two conformers resides in the mutual
orientation of the phenyl rings, only the stereogeometry of one
is represented in Figure 4, whereas relevant bond lengths and
angles for both are reported in Table 1. The molecular structure
of 5a closely resembles those of the related vinyliminium
complexes [M2{µ-η1:η3-C(R′)dC(R′′)CdN(Me)(R)}(µ-CO)-
(CO)(Cp)2][SO3CF3],5 as can be inferred by a comparison of
the corresponding bond distances and angles. The iminium group
presents a Z conformation, with the N-Me group pointing in
the opposite direction with respect to the Câ-Ph group.
The IR spectrum of 5a (in CH2Cl2 solution) exhibits two
bands due to the terminal and bridging carbonyls, at 2004 and
1804 cm-1, respectively. Moreover, a sharp band, due to ν(NH),
is observed at 3246 cm-1 (in KBr pellets). The 1H NMR
spectrum of 5a reveals the presence of two isomers in solution,
in an 8:5 ratio. These have been identified as (cis,E)-5a and
(cis,Z)-5a (Chart 3), on the basis of NOE investigations. The
NH proton gives rise to a broad resonance at low field (10.37
ppm). Relevant 13C NMR features include the resonances of
CR, Câ, and Cγ (at δ 226.5, 71.8, and 200.8 ppm, respectively,
for (cis,E)-5a), in the range typical for vinyliminium ligands.5
Conversely, the IR spectrum of 5b (in CH2Cl2 solution) suggests
the presence of a mixture of cis and trans isomers: the carbonyl
absorptions related to the cis isomer are found at 2000 and 1807
by the observation that the isomer ratio does not change upon
heating at reflux temperature, in THF, for 120 min. These
findings appear in contrast with the behavior of disubstituted
vinyliminium complexes of the type [Fe2{µ-η1:η3-C(R)dC(R)Cd
N(Me)(Xyl)}(µ-CO)(CO)(Cp)2][CF3SO3] (R ) Me, Et),5b in
which the trans isomer is easily converted into the cis species
by heating at reflux temperature in THF.
The nucleophilic character of the imine nitrogen in 2 can be
further exploited to prepare new N-functionalized vinyliminium
complexes. Thus, 2a reacts with allyl iodide (ICH2CHdCH2)
and methyl chloroformate (ClCOOMe), affording the species
[Fe2{µ-η1:η3-C(Ph)dC(Ph)CdN(Me)(CH2CHdCH2)}(µ-CO)-
(CO)(Cp)2][I] (6) and [Fe2{µ-η1:η3-C(Ph)dC(Ph)CdN(Me)-
(COOMe)}(µ-CO)(CO)(Cp)2][Cl] (7), respectively (Scheme 5).
Compounds 6 and 7 have been fully characterized by IR and
NMR spectroscopy, elemental analysis, and mass spectrometry
(see the Experimental Section). Their properties resemble those
of related vinyliminium complexes.5 Complex 6 exists in
solution as mixture of cis,E and cis,Z isomers, in comparable
amounts, as indicated by NOE investigations. In contrast, the
1H NMR spectrum of complex 7 shows a single set of
resonances, but it has not been possible to establish the
configuration adopted by the nitrogen substituents.
cm-1, and those of the trans isomer are at 1978 and 1789 cm-1
.
The presence of an isomeric mixture is well evidenced in
the 1H NMR spectrum of 5b, which exhibits two sets of
resonances in a 6:1 ratio. NOE studies indicate that the major
isomer is (trans,Z)-5b, whereas the minor species is (cis,Z)-5b
(Chart 3). The presence of cis and trans isomers is consistent
with the fact that the parent compound 2c also contains a mixture
of cis and trans isomers. However, also the reaction of pure
cis-2c with HBF4 affords a mixture of cis-5b and trans-5b,
suggesting that the observed isomeric mixture corresponds to
an equilibrium composition. This hypothesis is also strengthened
Complexes 6 and 7 are of interest because the vinyliminium
complexes so far reported have been limited to species contain-
ing the CRN(Me)(R) fragment, in which R ) Me, CH2Ph, Xyl.
In fact the ligand is generated from the bridging aminocarbyne
CN(Me)R, which, in turn, is conveniently obtained from
available isocyanides (CNR) and strong alkylating agents
(19) Willis, S.; Manning, A. R.; Stephens, F. S. J. Chem. Soc., Dalton
Trans. 1979, 23.

Diiron µ-Vinyliminium Complexes
Scheme 6
Organometallics, Vol. 26, No. 14, 2007 3453
Experimental Section
General Procedures. All reactions were routinely carried out
under a nitrogen atmosphere, using standard Schlenk techniques.
Solvents were distilled immediately before use under nitrogen from
appropriate drying agents. Chromatography separations were carried
out on columns of deactivated alumina (4% w/w water). Glassware
was oven-dried before use. Infrared spectra were recorded at 298
K on a Perkin-Elmer Spectrum 2000 FT-IR spectrophotometer, and
elemental analyses were performed on a ThermoQuest Flash 1112
Series EA instrument. ESI MS spectra were recorded on a Waters
Micromass ZQ 4000 instrument with samples dissolved in CH3-
CN. All NMR measurements were performed on Varian Gemini
300 and Mercury Plus 400 spectrometers. The chemical shifts for
1H and 13C were referenced to internal TMS. The spectra were fully
1
assigned via DEPT experiments and H, 13C correlation through
gs-HSQC and gs-HMBC experiments.20 Unless otherwise stated,
all NMR spectra were recorded at 298 K; NMR signals due to a
second isomeric form (when it was possible to detect and/or resolve
them) are given in italics. NOE measurements were recorded using
the DPFGSE-NOE sequence.21 All of the reagents were commercial
products (Aldrich) of the highest purity available and were used as
received. [Fe2(CO)4(Cp)2] was purchased from Strem and used as
received. The compounds [Fe2(CNMe)(CO)3(Cp)2] (1)12 and (cis,Z)-
[Fe2{µ-C(Et)dC(Et)CdN(Me)(Xyl)}(µ-CO)(CO)(Cp)2][CF3SO3] (3)
were prepared by published methods.5b Crystals of 3 suitable for
X-ray analysis were obtained by a CH2Cl2 solution layered with
diethyl ether, at -20 °C.
(MeSO3CF3). Thus, the synthesis of 6 and 7 demonstrates that
nitrogen functionalization can be extended to a range of different
substituents, overcoming the aforementioned limits.
It has been previously shown that the substituents on the
iminium nitrogen influence the reactivity of the ligand. Indeed,
the Xyl group exerts a “steric protection” on the iminium carbon
(CR), the most reactive site of the ligand, and hinders the addition
of hydride or cyanide at that position.7,8 The syntheses of 6 and
7 provide the opportunity to extend the investigations and
observe possible effects due to the allyl or carboxylate groups.
Therefore, the reactions of 6 and 7 with NaBH4 and [(NBu4)-
(CN)] have been studied. Unexpectedly, the reactions of 7 with
H- or CN- simply reverse the alkylation step and result in the
formation of the parent complex 2a. The reaction of 6 with
NaBH4 affords the enamino-alkylidene compound [Fe2{µ-η1:
η3-C(Ph)C(Ph)dC(H)N(Me)(CH2CHdCH2)}(µ-CO)(CO)-
(Cp)2] (8), while with (NBut4)(CN) the result is the formation
of the cyano-functionalized allylidene species [Fe2{µ-η1:η3-
C(Ph)C(Ph)C(CN)N(Me)(CH2CHdCH2)}(µ-CO)(CO)(Cp)2] (9)
(Scheme 6). Compounds 8 and 9 have been fully characterized
by spectroscopy (see the Experimental Section), and their
properties are consistent with those of strictly related com-
pounds.7,8
Synthesis of (Z)-[Fe2{µ-η1:η3-C(R)C(R′)CdN(Me)}(µ-CO)-
(CO)(Cp)2] (R ) R′) Ph, 2a; R ) R′ ) Me, 2b; R ) R′ ) Et,
2c; R ) Ph, R′ ) H, 2d; R ) C6H4Me (Tol), R′ ) H, 2e; R )
SiMe3, R′ ) H, 2f; R ) Me, R′ ) H, 2g; R ) CH2OH, R′ ) H,
2h). A solution of [Fe2(CNMe)(CO)3(Cp)2] (1; 310 mg, 0.845
mmol), in diethyl ether (25 mL), was treated with PhCtCPh (306
mg, 1.72 mmol) and irradiated by a UV lamp for 6 h. Hence, the
mixture was chromatographed on alumina, and a band correspond-
ing to 2a was collected with THF. The product was obtained as an
emerald green powder upon removal of the solvent under reduced
pressure. Yield: 245 mg, 56%. Anal. Calcd for C28H23Fe2NO2: C,
65.03; H, 4.48; N, 2.71. Found: C, 65.13; H, 4.42; N, 2.70. IR
(CH2Cl2): ν(CO) 1972 (vs), 1778 (s), ν(CdN) 1729 (w) cm-1. 1H
NMR (CDCl3): δ 8.10-7.00 (m, 3 H, Me2C6H3 and Ph); 4.86,
4.56 (s, 10 H, Cp); 3.85 (s, 3 H, NMe). 13C{1H} NMR (CDCl3):
δ 264.8 (µ-CO); 211.9 (CO); 192.5 (CR); 188.5 (Cγ); 155.7, 136.3
(ipso-Ph); 130.6, 128.5, 127.9, 127.8, 127.7, 126.9, 125.9, 124.8
(Ph); 89.5, 85.3 (Cp); 47.6 (Câ); 41.2 (NMe).
Compounds 2b-h were prepared by the same procedure
described for 2a, by reacting 1 with the appropriate alkyne. The
synthesis of 2b was performed in toluene solution. Conversion of
the cis/trans mixtures of 2b,c into the respective neat cis forms
were accomplished by heating in boiling toluene solutions, for 2
h. Crystals suitable for X-ray analysis were obtained by a CH2Cl2
solution of 2c layered with n-pentane, at -20 °C.
2b (yield 60%; reaction time 4 h; green). Anal. Calcd for C18H19-
Fe2NO2: C, 55.01; H, 4.87; N, 3.56. Found: C, 54.09; H, 4.87; N,
3.52. IR (CH2Cl2): ν(CO) 1966 (s), 1954 (vs), 1796 (s), ν(CdN)
1714 (m) cm-1. 1H NMR (CDCl3): δ 4.84, 4.58, 4.54, 4.37 (s, 10
H, Cp); 3.81, 3.77 (s, 3 H, CγMe); 3.75, 3.68 (s, 3 H, NMe); 1.59,
1.46 (s, 3 H, CâMe). Trans/cis ratio 6:5. 13C{1H} NMR (CDCl3):
δ 266.9, 265.2 (µ-CO); 211.9, 211.6 (CO); 197.3, 193.8 (CR); 196.0
(Cγ); 88.5, 88.3, 88.0, 85.0 (Cp); 49.2, 48.9 (Câ); 41.4, 36.2 (NMe);
35.7, 35.1 (CγMe); 16.9, 15.0 (CâMe).
The results shown in Scheme 6 are consistent with the
nucleophilic attack at CR exhibited by the vinyliminium
complexes [Fe2{µ-η1:η3-C(R′)dC(R′′)CdN(Me)(R)}(µ-CO)-
(CO)(Cp)2][SO3CF3] (R ) Me, CH2Ph; R′ ) Me, Tol, SiMe3,
COOMe, R′′ ) H; R′ ) R′′ ) Me, Et, COOMe) in their
7
reactions with NaBH4 and [(NBu4)(CN)].8
Conclusions
Photochemical reactions of the diiron isocyanide complex
[Fe2(CNMe)(CO)3(Cp)2] with alkynes yield novel bridging
enimine complexes by alkyne insertion into the metal-carbon
bond of the bridging isocyanide. The reaction takes place with
a variety of alkynes, except for HCtC(CO2Me), which yields
an unprecedented ferrocene-like complex. The insertion of
monosubstituted alkynes is regiospecific, and the C-C bond
formation exclusively occurs between the less hindered al-
kyne carbon and the isocyanide. The N atom in the bridging
enimine ligand can be easily protonated or alkylated, providing
a route for the synthesis of new functionalized vinyliminium
complexes, whose reactivity parallels that of strictly related
complexes.
2c (yield 64%; reaction time 3 h; emerald green). Anal. Calcd
for C20H23Fe2NO2: C, 57.05; H, 5.51; N, 3.33. Found: C, 57.12;
(20) Wilker, W.; Leibfritz, D.; Kerssebaum, R.; Beimel, W. Magn. Reson.
Chem. 1993, 31, 287.
(21) Stott, K.; Stonehouse, J.; Keeler, J.; Hwang, T. L.; Shaka, A. J. J.
Am. Chem. Soc. 1995, 117, 4199.

3454 Organometallics, Vol. 26, No. 14, 2007
Albano et al.
H, 5.55; N, 3.28. IR (CH2Cl2): ν(CO) 1964 (s), 1940 (vs), 1780
(100 mg, 0.193 mmol) in CH2Cl2 (10 mL) was treated with HBF4
(0.20 mmol). The mixture was stirred for 10 min, and then the
solvent was removed under reduced pressure. The residue was
washed with diethyl ether (2 × 10 mL) and dissolved in CH2Cl2,
and this solution was filtered on a Celite pad. The product was
obtained as dark brown crystals upon removal of the solvent.
Yield: 106 mg (91%). Crystals suitable for X-ray analysis were
obtained by a CH3CN solution of 5a layered with diethyl ether, at
-20 °C. Anal. Calcd for C28H24BF4Fe2NO2: C, 55.59; H, 4.00; N,
2.32. Found: C, 55.56; H, 4.08; N, 2.26. IR (KBr pellets): ν(NH)
3246 (m) cm-1. IR (CH2Cl2): ν(CO) 2004 (vs), 1804 (s), ν(CdN)
1674 (m) cm-1. 1H NMR (CDCl3): δ 10.37 (br, 1 H, NH); 7.82-
6.81 (m, 10 H, Ph); 5.32, 5.24, 4.98, 4.91 (s, 10 H, Cp); 3.77, 2.59
(s), 1773 (m), ν(CdN) 1718 (w), 1715 (w) cm-1 1H NMR
.
(CDCl3): δ 4.82, 4.54, 4.52, 4.38 (s, 10 H, Cp); 4.21, 4.11 (m, 2
H, CγCH2); 3.74, 3.70 (s, 3 H, NMe); 2.45, 1.30 (m, 2 H, CâCH2);
1.71 (dd, 3 H, 3JHH ) 7.32 Hz, 3JHH ) 7.69 Hz, CγCH2CH3); 1.64
3
3
(dd, 3 H, JHH ) 7.32 Hz, JHH ) 7.32 Hz, CγCH2CH3); 1.19 (m,
3 H, CâCH2CH3); 1.10 (dd, 3 H, 3JHH ) 7.32 Hz, 3JHH ) 7.69 Hz,
CâCH2CH3). Cis/trans ratio 5:2. 13C{1H} NMR (CDCl3): δ 265.8,
264.2 (µ-CO); 212.6, 212.1 (CO); 201.6, 198.9 (Cγ); 195.4, 192.3
(CR); 88.2, 87.8, 86.3, 84.4 (Cp); 54.3, 50.8 (Câ); 42.7, 41.7 (NMe);
42.6, 42.2 (CγCH2); 24.4, 23.7 (CâCH2); 18.8, 18.5 (CγCH2CH3);
12.5, 12.1 (CâCH2CH3).
2d (yield 55%; reaction time 3.5 h; green). Anal. Calcd for
C22H19Fe2NO2: C, 59.91; H, 4.34; N, 3.18. Found: C, 59.98; H,
4.26; N, 3.08. IR (CH2Cl2): ν(CO) 1970 (vs), 1778 (s), ν(CdN)
3
(d, JHH ) 4.94 ppm, 3 H, NMe). E/Z ratio 8:5. 13C{1H} NMR
(CDCl3): δ 255.4, 252.6 (µ-CO); 226.5 (CR); 210.2, 208.4 (CO);
200.8, 198.9 (Cγ); 153.5, 153.2 (ipso-Ph); 132.8-123.7 (Ph); 91.9,
91.7, 88.6, 87.5 (Cp); 71.8 (Câ); 39.7, 37.1 (NMe).
1
1732 (w) cm-1. H NMR (CDCl3): δ 8.05-7.31 (m, 5 H, Ph);
4.82, 4.64 (s, 10 H, Cp); 3.82 (s, 3 H, NMe); 2.99 (s, 1 H, CâH).
13C{1H} NMR (CDCl3): δ 264.2 (µ-CO); 211.5 (CO); 196.7 (Cγ);
192.2 (CR); 157.6 (ipso-Ph); 128.0, 127.9, 125.9 (Ph); 88.7, 84.8
(Cp); 41.6 (NMe); 35.0 (Câ).
2e (yield 60%, reaction time 2.5 h; brownish green). Anal. Calcd
for C23H21Fe2NO2: C, 60.70; H, 4.65; N, 3.08. Found: C, 60.66;
H, 4.68; N, 3.12. IR (CH2Cl2): ν(CO) 1969 (vs), 1778 (s), ν(Cd
Compound 5b was prepared by the same procedure described
for 6a, by reacting 2c (88 mg, 0.209 mmol) with HBF4 (0.25 mmol):
yield: 98 mg (92%); green. Anal. Calcd for C20H24BF4Fe2NO2:
C, 47.20; H, 4.75; N, 2.75. Found: C, 47.16; H, 4.79; N, 2.83. IR
(KBr pellets): ν(NH) 3226 (m) cm-1. IR (CH2Cl2): ν(CO) 2000
1
(s), 1978 (vs), 1807 (m), 1789 (s), ν(CdN) 1671 (m) cm-1. H
1
3
N) 1730 (w) cm-1. H NMR (CDCl3): δ 7.64, 7.28 (d, 4 H, JHH
) 8.0 Hz, C6H4Me); 4.80, 4.64 (s, 10 H, Cp); 3.81 (s, 3 H, NMe);
2.96 (s, 1 H, CâH); 2.45 (s, 3 H, C6H4Me). 13C{1H} NMR
(CDCl3): δ 264.5 (µ-CO); 211.6 (CO); 197.0 (Cγ); 192.6 (CR);
154.9 (ipso-C6H4Me); 135.5, 129.2, 128.6, 127.9 (C6H4Me); 88.8,
84.8 (Cp); 41.6 (NMe); 35.0 (Câ); 21.1 (C6H4Me).
NMR (CDCl3): δ 10.09 (s br, 1 H, NH); 5.15, 4.84, 4.75, 4.61 (s,
10 H, Cp); 4.34, 4.06, 4.12, 4.02 (m, 2 H, CγCH2); 3.78, 3.24 (s,
3 H, NMe); 2.72, 2.51, 2.01, 1.88 (m, 2 H, CâCH2); 1.86, 1.68 (m,
3 H, CγCH2CH3); 1.20, 1.18 (m, 3 H, CâCH2CH3). Trans/cis ratio
6:1. 13C{1H} NMR (CDCl3): δ 254.5 (µ-CO); 223.8 (CR); 209.2
(CO); 203.0 (Cγ); 89.4, 88.0 (Cp); 74.3 (Câ); 43.5 (NMe); 37.7
(Cγ-CH2); 23.5 (Câ-CH2); 18.2 (CγCH2CH3); 12.8 (CâCH2CH3).
2f (yield 60%; reaction time 5 h; brownish green). Anal. Calcd
Synthesis of [Fe2{µ-η1:η3-C(Ph)dC(Ph)CdN(Me)(CH2CHd
CH2)}(µ-CO)(CO)(Cp)2][I] (6). CH2CHCH2I (0.70 mmol) was
added to a solution of 2a (90 mg, 0.174 mmol) in CH2Cl2 (10 mL).
The mixture was stirred for 20 min, and then the solvent was
removed. Chromatography of the residue on alumina, with MeOH
as eluent, afforded a red band corresponding to 7. Yield: 99 mg
(83%). Anal. Calcd for C31H28Fe2INO2: C, 54.34; H, 4.12; N, 2.04.
Found: C, 54.32; H, 4.12; N, 2.07. IR (CH2Cl2): ν(CO) 1994 (vs),
for C19H23Fe2NO2Si: C, 52.20; H, 5.30; N, 3.20. Found: C, 52.23;
H, 5.25; N, 3.26. IR (CH2Cl2): ν(CO) 1974 (vs), 1789 (s) cm-1
.
1H NMR (CDCl3): δ 5.02, 4.70 (s, 10 H, Cp); 3.76 (s, 3 H, NMe);
3.19 (s, 1 H, CâH); 0.59 (s, 9 H, SiMe3). 13C{1H} NMR (CDCl3):
δ 261.1 (µ-CO); 210.6 (CO); 191.8 (CR); 179.7 (Cγ); 87.4, 86.1
(Cp); 41.4 (NMe); 38.3 (Câ); 2.9 (SiMe3).
2g (yield 61%; reaction time 9 h; green). Anal. Calcd for C17H17-
Fe2NO2: C, 53.87; H, 4.52; N, 3.70. Found: C, 53.80; H, 4.49; N,
3.74. IR (CH2Cl2): ν(CO) 1972 (vs), 1780 (s), ν(CdN) 1727 (w)
cm-1. 1H NMR (CDCl3): δ 4.88, 4.60 (s, 10 H, Cp); 3.85 (s, 3 H,
NMe); 3.73 (s, 3 H, CγMe); 2.88 (s, 1 H, CâH). 13C{1H} NMR
(CDCl3): δ 263.2 (µ-CO); 211.9 (CO); 195.8 (Cγ); 192.0 (CR);
88.0, 86.6 (Cp); 41.0 (NMe); 37.6 (Câ); 38.9 (CγMe).
1
1813 (s), ν(CdN) 1653 (m), ν(CdC) 1637 (w) cm-1. H NMR
(CDCl3): δ 7.64-7.03 (m, 10 H, Ph); 5.94, 5.27 (m, 1 H,
NCH2CH); 5.51, 5.46, 5.11, 5.10 (s, 10 H, Cp); 5.50, 5.28 (m, 2
H, NCH2CHCH2); 4.97 (m, 1 H, NCH2CH); 4.02, 2.63 (s, 3 H,
NMe); 3.66, 3.63, 3.48, 3.44 (m, 2 H, NCH2). E/Z ratio 6:5. 13C-
{1H} NMR (CDCl3): δ 254.8, 254.1 (µ-CO); 224.7, 223.9 (CR);
210.2, 209.9 (CO); 201.1, 201.0 (Cγ); 152.9 (ipso-Ph); 133.0-122.8
(Ph); 123.0, 122.8 (NCH2CHCH2); 122.9 (NCH2CHCH2); 92.1,
92.0, 88.4, 88.3 (Cp); 72.4, 72.1 (Câ); 64.8, 61.6 (NCH2); 44.6,
42.8 (NMe). ESI-MS (ES+): m/z 558. ESI-MS (ES-): m/z 127.
Synthesis of [Fe2{µ-η1:η3-C(Ph)dC(Ph)CdN(Me)(CO2Me)}-
(µ-CO)(CO)(Cp)2][Cl] (7). ClC(O)OMe (0.90 mmol) was added
to a solution of 2a (95 mg, 0.184 mmol) in CH2Cl2 (15 mL), and
the mixture was stirred for 20 min. Removal of the volatile materials
gave 7 as a red microcrystalline powder. Yield: 90 mg (80%). Anal.
Calcd for C30H26ClFe2NO4: C, 58.91; H, 4.28; N, 2.29. Found:
C, 58.97; H, 4.24; N, 2.25. IR (CH2Cl2): ν(CO) 2007 (vs), 1832
(s), 1774 (s), ν(CdN) 1556 (m) cm-1. 1H NMR (CDCl3): δ 8.10-
6.75 (m, 10 H, Ph); 5.19, 5.10 (s, 10 H, Cp); 4.18 (s, 3 H, CO2-
Me); 3.28 (s, 3 H, NMe). 13C{1H} NMR (CDCl3): δ 249.2 (µ-
CO); 217.0 (CR); 207.9 (CO); 202.5 (Cγ); 161.3 (CO2Me); 152.9
(ipso-Ph); 146.6-124.6 (Ph); 94.2, 91.7 (Cp); 71.9 (Câ); 55.4
(CO2Me); 43.0 (NMe).
2h (yield 59%; reaction time 7 h; green). Anal. Calcd for C17H17-
Fe2NO3: C, 51.69; H, 4.34; N, 3.55. Found: C, 51.62; H, 4.39; N,
3.58. IR (CH2Cl2): ν(CO) 1978 (vs), 1789 (s), ν(CdN) 1740 (w)
1
2
cm-1. H NMR (CD3CN): δ 6.15, 5.88 (d, 2 H, JHH ) 14.6 Hz,
CH2OH); 5.14, 4.75 (s, 10 H, Cp); 5.06 (br, 1 H, OH); 3.48 (s, 3
H, NMe); 2.85 (s, 1 H, CâH). 13C{1H} NMR (CD3CN): δ 264.2
(µ-CO); 212.1 (CO); 196.7 (Cγ); 191.9 (CR); 89.3, 88.5 (Cp); 74.9
(CH2OH); 45.6 (NMe); 35.3 (Câ).
Synthesis of [Fe2{µ-η2:η4-C(OH)C(CO2Me)C(H)CN(Me)-
(CHdCHCO2Me}(CO)(Cp)2] (4). This product was prepared by
the same procedure described for 2a-h, by reacting 1 (185 mg,
0.365 mmol) with HCtCCO2Me (3.6 mmol): reaction time 6 h;
green; yield 104 mg (56%). Anal. Calcd for C22H23Fe2NO6: C,
51.90; H, 4.55; N, 2.75. Found: C, 51.92; H, 4.47; N, 2.60. IR
(CH2Cl2): ν(CO) 1965 (vs), 1686 (m), 1672 (m), ν(CdC) 1601
(vs) cm-1. 1H NMR (CDCl3): δ 10.00 (s, 1 H, OH); 8.35 (d, 2 H,
3
3JHH ) 13.54 Hz, HCdCHCO2Me); 4.90 (d, 2 H, JHH ) 13.54
Hz, HCdCHCO2Me); 5.24 (s, 1 H, CâH); 4.94, 4.31 (s, 10 H, Cp);
3.74 (s, 6 H, COOMe); 3.31 (s, 3 H, NMe). 13C{1H} NMR
(CDCl3): δ 218.8 (CO); 216.6 (COH); 179.0 (CR); 176.2, 169.6
(COOMe); 152.5 (HCdCHCO2Me); 87.9 (HCdCHCO2Me); 84.1,
77.7 (Cp); 79.3 (Câ); 67.2 (Cγ); 51.7, 50.8 (COOMe); 40.0 (NMe).
Synthesis of [Fe2{µ-η1:η3-C(R)dC(R)CdN(Me)(H)}(µ-CO)-
(CO)(Cp)2][BF4] (R ) Ph, 5a; R ) Et, 5b). A solution of 2a
Synthesis of [Fe2{µ-η1:η3-C(Ph)C(Ph)dC(H)N(Me)(CH2CHd
CH2)}(µ-CO)(CO)(Cp)2] (8). Complex 6 (50 mg, 0.0730 mmol)
was dissolved in THF (10 mL) and treated with NaBH4 (14 mg,
0.368 mmol). The mixture was stirred for 15 min, and then it was
filtered on alumina. Solvent removal and chromatography of the
residue on alumina, with CH2Cl2 as eluent, gave a green band

Diiron µ-Vinyliminium Complexes
Organometallics, Vol. 26, No. 14, 2007 3455
Table 3. Crystal Data and Experimental Details for 2c, 3, 4‚CH2Cl2, and 5a
2c
3
4‚CH2Cl2
5a
formula
fw
C20H23Fe2NO2
421.09
C29H32F3Fe2NO5S
675.32
C23H25Cl2Fe2NO6
594.04
C28H24BF4Fe2NO2
604.99
T, K
296(2)
296(2)
296(2)
296(2)
λ, Å
0.71073
monoclinic
P21/c
9.693(2)
12.446(3)
15.295(3)
90
91.781(5)
90
1844.3(7)
4
0.71073
triclinic
P1h
0.71073
monoclinic
P21/c
9.0847(18)
35.133(7)
8.4489(17)
90
115.43(3)
90
2435.4(8)
4
0.71073
monoclinic
P21/n
13.911(3)
22.709(5)
17.018(3)
90
101.16(3)
90
5274.5(18)
8
cryst syst
space group
a, Å
b, Å
8.2804(3)
12.4402(4)
15.0634(5)
107.4700(10)
101.8190(10)
91.7950(10)
1441.55(8)
2
c, Å
R, deg
â, deg
γ, deg
cell vol, Å3
Z
Dc, g cm-3
1.517
1.585
872
1.556
1.138
696
1.620
1.450
1216
1.524
1.155
2464
µ, mm-1
F(000)
cryst size, mm
θ limits, deg
no. of rflns collected
no. of indep rflns
goodness of fit on F2
R1 (I > 2σ(I))a
wR2 (all data)b
largest diff peak and hole, e Å-3
0.25 × 0.23 × 0.21
2.66-28.70
21 343 (Rint ) 0.0610)
4754
1.102
0.0604
0.28 × 0.25 × 0.23
2.53-28.00
16 496 (Rint ) 0.0291)
6926
1.042
0.0660
0.25 × 0.21 × 0.15
2.55-25.00
18 651 (Rint ) 0.1111)
3765
1.131
0.0817
0.23 × 0.19 × 0.14
1.51-25.03
46 377 (Rint ) 0.0740)
9319
1.048
0.0592
0.1625
1.103/-1.800
0.2112
1.264/-0.919
0.1850
0.997/-0.769
0.1787
0.880/-0.700
2
2
2
2
2
2
a R1 ) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) [∑w(Fo - Fc )2/∑w(Fo )2]1/2, where w ) 1/[σ2(Fo ) + (aP)2 + bP], where P ) (Fo + 2Fc )/3.
corresponding to 8. Yield: 35 mg (86%). Anal. Calcd for C31H29-
Fe2NO2: C, 66.58; H, 5.23; N, 2.50. Found: C, 66.52; H, 5.29; N,
2.58. IR (CH2Cl2): ν(CO) 1933 (vs), 1754 (s), ν(CdC) 1591 (w)
SADABS.23 The structures were solved by direct methods (SIR
97)24 and subsequent Fourier syntheses and refined by full-matrix
least squares on F2 (SHELXTL),25 using anisotropic thermal
parameters for all non-hydrogen atoms except the cyclopentadienyl
ligands in 4. In 3, some disorder was detected for both the fluorine
and oxygen atoms of the CF3SO3- group, which were refined over
two sites, yielding occupation factors of 0.55 and 0.57 for the main
images of the F atoms bound to C(39) and O atoms bound to S,
respectively. Crystals of 4 were found to contain one CH2Cl2
molecule in the asymmetric unit. In the solid state 5a is present in
two conformers. In both conformers one cyclopentadienyl ring
(bound to Fe(2)) is disordered over two positions and the site
occupation factors were refined to 0.69 for the main image in both
conformers. All hydrogen atoms, except the hydrogen bound to
O(1) in 4 and to N(1) in 5a, which were found in the Fourier map
and refined isotropically, were added in calculated positions,
included in the final stage of refinement with isotropic thermal
parameters, U(H) ) 1.2 Ueq(C) (U(H) ) 1.5 Ueq(C-Me)), and
allowed to ride on their carrier carbons. Crystal data and details of
the data collection for all structures are reported in Table 3.
1
cm-1. H NMR (CDCl3): δ 8.19-6.65 (m, 10 H, Ph); 5.91 (m, 1
H, NCH2CH); 5.15 (m, 2 H, NCH2CHCH2); 4.85, 4.32 (s, 10 H,
Cp); 3.21 (m, 2 H, NCH2); 1.90 (s, 3 H, NMe); 0.91 (s, 1H, CRH).
13C{1H} NMR (CDCl3): δ 278.7 (µ-CO); 217.8 (CO); 185.8 (Cγ);
156.7 (ipso-C6H4Me); 139.7, 134.5, 131.3, 129.2, 128.8, 127.1,
125.6, 123.2 (Ph); 123.3 (NCH2CH); 117.9 (NCH2CHCH2); 97.3
(CR); 88.6, 81.8 (Cp); 83.7 (Câ); 59.6 (NCH2); 38.6 (NMe).
Synthesis of [Fe2{µ-η1:η3-C(Ph)C(Ph)C(CN)N(Me)(CH2CHd
CH2)}(µ-CO)(CO)(Cp)2] (9). NBut4CN (23 mg, 0.0858 mmol) was
added to a solution of 6 (48 mg, 0.0701 mmol) in CH2Cl2 (15 mL).
The mixture was stirred for 30 min, and then it was filtered on
alumina. The product was obtained as a red powder upon removal
of the solvent under reduced pressure. Yield: 36 mg (88%). Anal.
Calcd for C32H28Fe2N2O2: C, 65.78; H, 4.83; N, 4.79. Found: C,
65.66; H, 4.79; N, 4.88. IR (CH2Cl2): ν(CtN) 2187 (w), ν(CO)
1972 (vs), 1788 (s), ν(CdC) 1591 (w) cm-1. 1H NMR (CDCl3): δ
7.95-7.02 (m, 10 H, Ph); 5.73, 5.72 (m, 1 H, NCH2CH); 5.12,
5.04 (m, 2 H, NCH2CHCH2); 4.82, 4.80, 4.57 (s, 10 H, Cp); 4.13,
3.10, 2.99, 2.80 (dd, 2 H, 2JHH ) 12.8 Hz, 3JHH ) 2.9 Hz, NCH2);
2.48, 2.05 (s, 3H, NMe). Isomer ratio 6:5. 13C{1H} NMR
(CDCl3): δ 264.6, 264.1 (µ-CO); 213.4, 213.0 (CO); 197.6, 197.1
(Cγ); 157.3, 157.2 (ipso-Ph); 139.6, 139.4, 135.6, 134.8, 132.1,
128.2, 128.0, 127.9, 127.8, 127.2, 126.9, 126.6 (Ph); 124.1, 124.0
(NCH2CH); 120.2, 120.0 (CtN); 118.0, 117.2 (NCH2CHCH2);
90.6, 90.4, 87.2, 87.1 (Cp); 96.6, 95.7 (Câ); 65.8, 59.3 (NCH2);
64.2, 63.0 (CR); 45.9, 39.9 (NMe).
Acknowledgment. We thank the Ministero dell’Universita`
e della Ricerca (MUR; project “New strategies for the control
of reactions: interactions of molecular fragments with metallic
sites in unconventional species”) and the University of Bologna
for financial support.
Supporting Information Available: CIF files giving X-ray
crystallographic data for the structure determinations of 2c, 3, 4‚
CH2Cl2, and 5a. This material is available free of charge via the
Internet at http://pubs.acs.org.
X-ray Crystallography. The X-ray intensity data for 2c, 3, 4‚
CH2Cl2, and 5a were measured on a Bruker AXS SMART 2000
diffractometer, equipped with a CCD detector. Cell dimensions and
the orientation matrix were initially determined from a least-squares
refinement on reflections measured in 3 sets of 20 exposures,
collected in 3 different ω regions, and eventually refined against
all data. For all crystals, a full sphere of reciprocal space was
scanned by 0.3° ω steps, with the detector kept at 5.0 cm from the
sample. The software SMART22 was used for collecting frames of
data, indexing reflections, and determining lattice parameters. The
collected frames were then processed for integration by the SAINT
program,22 and an empirical absorption correction was applied using
OM070097Z
(22) SMART & SAINT Software Reference Manuals, Version 5.051
(Windows NT Version); Bruker Analytical X-ray Instruments Inc.: Madison,
WI, 1998.
(23) Sheldrick, G. M. SADABS, Program for Empirical Absorption
Correction; University of Go¨ttingen, Go¨ttingen, Germany, 1996.
(24) Altomare, A.; Burla, M. C.; Cavalli, M.; Cascarano, G. L.;
Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna,
R. J. Appl. Crystallogr. 1999, 32, 115.
(25) Sheldrick, G. M. SHELXTLplus Version 5.1 (Windows NT version)
Structure Determination Package; Bruker Analytical X-ray Instruments Inc.,
Madison, WI, 1998.