Regio- and stereoselective hydride addition at μ-vinyliminium ligands in cationic diiron complexes

Article abstract of DOI:10.1021/om049868e

The vinyliminium complexes [Fe₂{μ-η¹: η³-C_γ(R′)=C_βHC _α=NMe₂}(μ-CO)(CO)(Cp)₂] [SO ₃CF₃] (R′ = Tol, 2a; SiMe₃, 2b; Me, 2c; CH₂

Full text of DOI:10.1021/om049868e

3348
Organometallics 2004, 23, 3348-3354
Regio- a n d Ster eoselective Hyd r id e Ad d ition a t
µ-Vin ylim in iu m Liga n d s in Ca tion ic Diir on Com p lexes
Vincenzo G. Albano,‡ Luigi Busetto,† Fabio Marchetti,† Magda Monari,‡
Stefano Zacchini,† and Valerio Zanotti*,†
Dipartimento di Chimica Fisica ed Inorganica, Universita` di Bologna, Viale Risorgimento 4,
I-40136 Bologna, Italy, and Dipartimento di Chimica “G. Ciamician”, Universita` di Bologna,
Via Selmi 2, I-40126 Bologna, Italy
Received February 24, 2004
The vinyliminium complexes [Fe2{µ-η1:η3-Cγ(R′)dCâHCRdNMe2}(µ-CO)(CO)(Cp)2][SO3CF3]
(R′ ) Tol, 2a ; SiMe3, 2b; Me, 2c; CH2OH, 2d ) undergo hydride addition at the iminium
carbon (CR), upon treatment with NaBH4, affording the corresponding µ-vinylalkylidene
complexes [Fe2{µ-η1:η3-C(R′)CHdCHNMe2}(µ-CO)(CO)(Cp)2] (R′ ) Tol, 5a ; SiMe3, 5b; Me,
5c; CH2OH, 5d ). Similarly, the complexes [Fe2{µ-η1:η3-Cγ(R′)dCâHCRdN(Me)(CH2Ph)}(µ-
CO)(CO)(Cp)2][SO3CF3] (R′ ) Tol, 4a ; SiMe3, 4b; COOMe, 4c) react with NaBH4 at the CR,
yielding [Fe2{µ-η1:η3-Cγ(R′)CâHdCR(H)N(Me)(CH2Ph)}(µ-CO)(CO)(Cp)2] (R′ ) Tol, 7a ; SiMe3,
7b; COOMe, 7c). By contrast, the reactions of NaBH4 with [Fe2{µ-η1:η3-Cγ(R′)dCâHCRd
N(Me)(Xyl)}(µ-CO)(CO)(Cp)2] (R′ ) Tol, 3a ; SiMe3, 3b; Me, 3c; CH2OH, 3d ; Ph, 3e; COOMe,
3f; Bun, 3g; H, 3h ), in which the substituent at the iminium nitrogen is the more sterically
hindered Xyl group (Xyl ) 2,6-Me2C6H3), lead to the formation of the bis-alkylidene complexes
[Fe2{µ-η1:η2-C(R′)CH2CN(Me)(Xyl)}(µ-CO)(CO)(Cp)2] (R′ ) Tol, 6a ; SiMe3, 6b; Me, 6c; CH2-
OH, 6d ; Ph, 6e; COOMe, 6f; Bun, 6g; H, 6h ). Compounds 6a -h result from regioselective
hydride addition at the Câ, presumably because of the steric protection exerted by the Xyl
group on the CR carbon. All the new compounds have been investigated by IR and NMR
spectroscopy, and the molecular structures of complexes 5a and 6f have been elucidated by
X-ray diffraction studies. LiHBEt3 selectively attacks the CR carbon, despite the presence of
the Xyl substituent; therefore [Fe2{µ-η1:η3-Cγ(R′)dCâHCRdN(Me)(Xyl)}(µ-CO)(CO)(Cp)2][SO3-
CF3] (R′ ) Me, 3c; COOMe, 3f) are converted into the corresponding µ-vinylalkylidene
complexes [Fe2{µ-η1:η3-C(R′)CHdCHN(Me)(Xyl)}(µ-CO)(CO)(Cp)2] (R′ ) Me, 8a ; COOMe, 8b).
In tr od u ction
The above reactions, which are part of our studies on
the formation of carbon-carbon bonds in dinuclear
µ-carbyne complexes,2 allow the synthesis of vinylimin-
ium ligands in an unusual coordination mode (µ-η1:η3).
In fact bridging coordination is rare,3 and vinyliminium
ligands have been found mostly in mononuclear com-
plexes, adopting different coordination geometries, i.e.,
σ-coordinated through the iminium carbon (CR),4 η2-
coordinated by the vinyl end,5 and coordinated via both
CR and Cγ.6 Information on the reactivity of the ligand
is even more limited and includes the hydride addition
We have recently reported that a variety of alkynes
(R′CtCR′′; R′′ ) H; R′ ) H, Me, Bun, Ph, Tol, SiMe3,
CH2OH, COOMe; R′ ) R′′ ) Me, Et, COOMe) insert into
the metal-carbon bond of diiron µ-aminocarbynes [Fe2-
{µ-CN(Me)(R)}(µ-CO)(CO)(MeCN)(Cp)2][SO3CF3] (R )
Xyl, 1a ; CH2Ph, 1b; Me, 1c; Xyl ) 2,6-Me2C6H3), af-
fording the corresponding µ-vinyliminium complexes
[Fe2{µ-η1:η3-Cγ(R′)dCâ(R′′)CRdN(Me)(R)}(µ-CO)(CO)-
(Cp)2][SO3CF3].1 The reaction requires the presence of
a labile ligand (MeCN) in the parent compound, sug-
gesting that alkyne coordination is a preliminary step.
Analogously, alkyne insertion takes place, even more
efficiently, in the chloride complexes [Fe2{µ-CN(Me)(R)}-
(µ-CO)(CO)(Cl)(Cp)2], upon Cl- removal, by treatment
with Ag+. In particular it has been found that the
insertion of primary alkynes is regiospecific and C-C
bond formation selectively occurs between the µ-carbyne
carbon and the CH moiety of the alkyne.
(2) (a) Bordoni, S.; Busetto, L.; Camiletti, C.; Zanotti, V.; Albano,
V. G.; Monari, M.; Prestopino, F. Organometallics 1997, 16, 1224. (b)
Albano, V. G.; Bordoni, S.; Busetto, L.; Camiletti, C.; Monari, M.;
Palazzi, A.; Prestopino, F.; Zanotti, V. J . Chem. Soc., Dalton Trans.
1997, 4665. (c) Albano, V. G.; Busetto, L.; Camiletti, C.; Castellari, C.;
Monari, M.; Zanotti, V. J . Chem. Soc., Dalton Trans. 1997, 4671. (d)
Albano, V. G.; Busetto, L.; Camiletti, C.; Monari, M.; Zanotti, V. J .
Organomet. Chem. 1998, 563, 153. (c) Albano, V. G.; Bordoni, S.;
Busetto, L.; Marchetti, F.; Monari, M.; Zanotti, V. J . Organomet. Chem.
2003, 37, 684.
(3) (a) Churchill, M. R.; Lake, C. H.; Lashewycz-Rubycz, R. A.; Yao,
H.; McCargar, R. D.; Keister, J . B. J . Organomet. Chem. 1993, 452,
151. (b) Aime, S.; Osella, D.; Deeming, A. J .; Arce, A. J . J . Chem. Soc.,
Dalton Trans. 1986, 1459.
(4) (a) Bernard, D. J .; Esteruelas, M. A.; Lopez, A. M.; Modrego, J .;
Puerta, M. C.; Valerga, P. Organometallics 1999, 18, 4995. Mantovani,
N.; Marvelli, L.; Rossi, R.; Bertolasi, V.; Bianchini, C.; de los Rios, I.;
Peruzzini, M. Organometallics 2002, 21, 2382.
(5) Gamble, A. S.; White, P. S.; Templeton, J . L. Organometallics
1991, 10, 693.
* Correspondingauthor.Tel: +39-0512093700.Fax: +39-0512093690.
E-mail: valerio.zanotti@unibo.it.
† Dipartimento di Chimica Fisica ed Inorganica.
‡ Dipartimento di Chimica “G. Ciamician”.
(1) (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.
10.1021/om049868e CCC: $27.50 © 2004 American Chemical Society
Publication on Web 05/27/2004

Hydride Addition in Cationic Diiron Complexes
Organometallics, Vol. 23, No. 13, 2004 3349
Sch em e 1
at the iminium carbon in [Tp′(CO)2Mo{η2-C(Ph)dC(H)C-
(H)dN(But)(Me)}][BF4] [Tp′ ) hydridotris(pyrazolyl)-
borate]5 and the deprotonation of the vinyl end of the
ligand in [Ru(Cp){C(dNEt2)CHdCPh2}(CO)(PPri3)][BF4]
to form the amino allenyl derivative [Ru(Cp){C(NEt2)d
F igu r e 1. ORTEP drawing of the complex [Fe2{µ-η1:η3-
C(Tol)CHdCHNMe2}(µ-CO)(CO)(Cp)2] (5a ) (thermal ellip-
soids at the 30% probability level).
Ta ble 1. Com p a r ison of Releva n t Bon d
P a r a m eter s in 5a a n d 6f a n d Rela ted
Vin ylim in iu m Com p lexesa
CdCPh2)}(CO)(PPri )].4a
3
This work was aimed at investigating the reactivity
of the vinyliminium ligand in the complexes [Fe2{µ-η1:
η3-Cγ(R′)dCâHCRdN(Me)(R)}(µ-CO)(CO)(Cp)2][SO3-
CF3] toward hydride addition and at determining which
site of the ligand (CR or Câ) was preferentially attacked.
Different substituents at the iminium nitrogen (R ) Me,
2; Xyl, 3; CH2Ph, 4) and at the Cγ position (R′ ) Tol,
SiMe3, Me, CH2OH, Ph, COOMe, H) have been consid-
ered in order to evaluate electronic and steric factors
that influence the regiochemistry of the reaction.
I
II
III
5a
6f
Fe(1)-Fe(2) 2.557(1) 2.549(1)
Fe(1)-C(1) 1.976(7) 1.954(7)
Fe(2)-C(1) 1.878(7) 1.929(7)
C(1)-O(1)
Fe(2)-C(2) 1.736(8) 1.750(9)
C(2)-O(2) 1.155(8) 1.137(9)
2.562(1) 2.555(1) 2.521(1)
1.944(8) 1.849(7) 1.842(3)
1.894(8) 2.012(6) 2.019(3)
1.181(9) 1.183(7) 1.172(3)
1.750(9) 1.729(6) 1.736(3)
1.150(9) 1.157(7) 1.147(3)
1.955(7) 1.977(6) 1.990(2)
2.035(7) 1.979(6) 1.969(2)
2.080(7) 2.070(6)
1.167(7) 1.155(8)
Fe(2)-C(3) 1.970(6) 1.954(6)
Fe(1)-C(3) 2.028(6) 2.017(6)
Fe(1)-C(4) 2.052(7) 2.081(6)
Fe(1)-C(5) 1.844(6) 1.843(6)
C(3)-C(6)
1.839(7) 2.299(6) 1.874(2)
1.492(9)ph 1.54(1)
1.472(3)
1.39(1) 1.441(8) 1.535(3)
1.43(1) 1.408(9) 1.489(3)
1.314(8) 1.375(8) 1.317(3)
Resu lts a n d Discu ssion
C(3)-C(4)
C(4)-C(5)
N-C(5)
1.412(8) 1.396(8)
1.406(8) 1.421(8)
1.320(7) 1.289(7)
The reaction of [Fe2{µ-η1:η3-C(R′)dCHCdNMe2}(µ-
CO)(CO)(Cp)2][SO3CF3] 2a -d (R′ ) Tol, 2a , Tol )
4-MeC6H4; R ) SiMe3, 2b; R ) Me, 2c; R ) CH2OH,
2d ) with NaBH4, in tetrahydrofuran solution, results
in the formation of the corresponding µ-vinylalkylidene
complexes [Fe2{µ-η1:η3-C(R′)CHdCHNMe2}(µ-CO)(CO)-
(Cp)2] (R′ ) Tol, 5a ; R ) SiMe3, 5b; R ) Me, 5c; R )
CH2OH, 5d ) (Scheme 1), in good yields (70-90%).
Complexes 5a -d have been isolated by column chro-
matography on alumina and fully characterized by
spectroscopy and elemental analysis. The structure of
5a , ascertained by an X-ray diffraction experiment, is
shown in Figure 1, and relevant bond lengths and angles
are reported in Table 1.
a
I ) [Fe2{µ-σ:η3-C(SiMe3)dCHCdN(Me)(Xyl)}(µ-CO)(CO)(Cp)2]-
[SO3CF3] (ref 1a); II ) [Fe2{µ-σ:η3-C(CO2Me)dCHCdN(Me)(Xyl)}-
(µ-CO)(CO)(Cp)2][SO3CF3] (ref 1b); III ) cis-[Fe2{µ-σ:η3-C(Me)d
C(Me)CdN(Me)(Xyl)}(µ-CO)(CO)(Cp)2][SO3CF3] (ref 1b).
F igu r e 2. Description as vinylalkylidene (A) and bridging
allylidene (B) of the CCC fragment in type 5 compounds.
bond character as the N atom turns from iminium to
enamine. Some pyramidalization of the geometry around
N is also detectable [distance of N from the plane of the
pertinent carbons, 0.222(7) Å]. The C(5)-Fe(1) interac-
tion [2.299(6) Å] is 0.46 Å longer than in the cationic
precursors, as expected, because of the transformation
from a σ- to a π-interaction. The electronic structure of
the Fe-C-C-C-Fe grouping is not a simple one, and
the C(3)-C(4)-C(5) unit is a mix of vinyl and allyl
contributions (structures A and B, respectively, in
Figure 2); however the distances C(4)-C(5) [1.408(9) Å]
and C(3)-C(4) [1.441(8) Å] clearly identify the structure
A as the more appropriate description. Therefore C(3)
can be described as a bridging alkylidene [C(3)-Fe(1)
1.979(6), C(3)-Fe(2) 1.977(6) Å] and C(4)-C(5) [1.408-
(9) Å] as a coordinated double bond (dotted lines in
Figure 1).
Relevant features of the molecular structure are the
bond effects produced by the H- addition at CR [C(5) in
Figure 1], which has been attacked from the less
hindered side opposite the Cp ligands (see also further
on). They can be appreciated by a comparison with the
corresponding structural parameters in the cationic
precursors [Fe2{µ-η1:η3-C(SiMe3)dCHCdN(Me)(Xyl)}(µ-
CO)(CO)(Cp)2]+,1a [Fe2{µ-η1:η3-C(CO2Me)dCHCdN(Me)-
(Xyl)}(µ-CO)(CO)(Cp)2]+,1b and [Fe2{µ-η1:η3-C(Me)d
C(Me)CdN(Me)(Xyl)}(µ-CO)(CO)(Cp)2]+,1b reported in
Table 1. The C(5)-C(4) interaction [1.408(9) Å] retains
some double-bond character, while some lengthening of
the N-C(5) bond [1.375(8) Å] indicates a loss of multiple-
(6) (a) Adams, C. J .; Anderson, K. M.; Bartlett, I. M.; Connelly, N.
G., Orpen, A. G.; Paget, T. J .; Phetmung, H.; Smith, D. W. J . Chem.
Soc., Dalton Trans. 2001, 1284.

3350 Organometallics, Vol. 23, No. 13, 2004
Albano et al.
Sch em e 2
The bridging carbonyl ligand [C(1)-O(1)] adopts a
markedly asymmetric geometry [C(1)-Fe(1) 1.849(7),
C(1)-Fe(2) 2.012(6) Å], suggesting a semibridging char-
acter. The bond asymmetry is opposite and more
pronounced than that found in the cationic precursor.
The change should be ascribed to the disappearance of
the net charge, formally located at the iminium nitrogen
in the cations, that allows a better donation to Fe(1) and,
as a consequence, more π back-donation from Fe(1) to
the bridging carbonyl ligand.
The infrared spectra of 5a -d in CH2Cl2 show the
usual ν(CO) band pattern consisting of two strong
absorptions (e.g., at 1929 and 1747 cm-1 for 5a ),
attributable to the terminal and bridging CO, respec-
tively. The absorptions are about 60 cm-1 lower with
respect to those of the parent complexes 2a -d .
The NMR spectra of 5a -d , in CDCl3 solution, show
the presence of one single isomer, indicating that the
hydride addition is regio- and stereospecific. The 1H
NMR spectra exhibit an upfield shifted resonance (in
the 1.5-1.9 ppm range) assigned to the CRH, which
appears as a doublet because of the coupling with CâH.
The coupling constant of about 10 Hz indicates that CRH
and CâH are mutually trans, in accord with the X-ray
diffraction structure (Figure 1). The two N-bonded
methyl groups give rise to a single resonance in both
1H and 13C NMR spectra (for 5a at 2.41 and 40.8 ppm)
as a result of fast rotation (on the NMR time scale) at
room temperature, around the CR-N bond. Correspond-
ingly, in the parent cations 2a -d , two resonances are
observed because of the double-bond character of the
CR-N(iminium) interaction.
NR2 groups. These complexes, obtained from coordina-
tion of ynamines, have been described as metalated
µ-aminoallyls.
Treatment of [Fe2{µ-η1:η3-C(R′)dCHCdN(Me)(Xyl)}-
(µ-CO)(CO)(Cp)2][SO3CF3], 3a -h (R′ ) Tol, 3a ; SiMe3,
3b; Me, 3c; CH2OH, 3d ; Ph, 3e; COOMe, 3f; Bun, 3g;
H, 3h ), with NaBH4, in tetrahydrofuran solution, under
conditions similar to those above described for the
synthesis of 5, results in the formation of the corre-
sponding bis-alkylidene complexes [Fe2{µ-η1:η2-C(R′)CH2-
CN(Me)(Xyl)}(µ-CO)(CO)(Cp)2] (R′ ) Tol, 6a ; SiMe3, 6b;
Me, 6c; CH2OH, 6d ; Ph, 6e; COOMe, 6f; Bun, 6g; H,
6h ) (Scheme 2).
Complexes 6a -h have been characterized by spec-
troscopic methods and elemental analyses. A detailed
description of the structure of 6f has been obtained by
X-ray diffraction. The molecular model is illustrated in
Figure 3, and relevant bond parameters are reported
in Table 1. An inspection of the geometry immediately
shows that the steric hindrance of the Xyl group exerts
a protective effect on CR [C(5)], while Câ [C(4)] appears
to be more accessible. The transformation of C(4) in a
saturated tetracoordinate carbon [bond lengths C(4)-
C(3) 1.535(3), C(4)-C(5) 1.489(3) Å] breaks off the
π-bond connection between the bridging alkylidene C(3)
and the terminal alkylidene C(5). The effect on the
iron-carbon interactions in comparison to 5a is negli-
gible for the bridging C(3) [Fe(1)-C(3) 1.969(2), Fe(2)-
C(3) 1.990(2) Å] but substantial for C(5) [Fe(1)-C(5)
1.874(2) Å]. This molecule is therefore a genuine bis-
alkylidene species in which the terminal alkylidene
function is stabilized by significant π-bond delocalization
involving the nitrogen atom [N-C(5) 1.317(3), C(5)-Fe-
(1) 1.874(2) Å ]. The C(1)-O(1) bridging ligand exhibits
bonding asymmetry very similar to that just discussed
for 5a [C(1)-Fe(1) 1.842, C(1)-Fe(2) 2.019(3) Å].
The 13C NMR spectra of 5a -d show resonances
attributable to the CR, Câ, and Cγ carbons in the
expected range (e.g., for 5a at 105.6, 64.8, and 181.5
ppm, respectively). In particular, the Cγ resonance
appears downfield shifted, in accord with its µ-alkyli-
dene character.
Bridging vinylalkylidene ligands in 5a -d are pre-
sumably the result of a simple (direct) hydride addition
at the iminium carbon, rather than the outcome of a
more complex reaction pattern, involving addition at the
Câ followed by intramolecular hydrogen migration.7 This
is clearly evidenced by the reaction of 2a with NaBD4,
which leads to the formation of [Fe2{µ-η1:η3-C(Tol)CHd
C(D)NMe2}(µ-CO)(CO)(Cp)2]. The 13C NMR spectrum
shows a triplet for the CR (1J CD ) 25.8 Hz), at 105.6 ppm.
The 1H NMR shows a broad singlet for the CâH, together
with the disappearance of the CRH resonance, whereas
the other signals remain unchanged with respect to 5a .
Four-electron-donor µ-vinylalkylidene ligands (η1:η3-
coordinated) are common among dinuclear complexes,
including diiron,8 diruthenium,9 and dirhodium10 com-
pounds. In complexes 5a -d , the vinyl end of the
bridging ligand bears the NMe2 substituent; therefore,
it can be described also as an enamine. Compounds
5a -d can be compared to [Mn2(CO)8(µ-η2C3H3NEt2)],11
[Re2(CO)8(µ-η2C3H3NMe2)],12 and [Mn2(CO)7(µ-η4C3H3-
NEt2)],11 where the bridging C3H3 unit is bonded to a
(9) (a) Colborn R. E.; Dyke, A. F.; Knox, S. A. R.; Mcpherson, K. A.;
Orpen, A. G. J . Organomet. Chem. 1982, 239, C15. (b) Eisenstadt, A.;
Efraty, A. Organometallics 1982, 1, 1100. (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) Colborn R. E.; Davies, D. L.; Dyke,
A. F.; Knox, S. A. R.; Mead, K. A.; Orpen, A. G.; Guerchais, J . E.; Roue´
J . J . Chem. Soc., Dalton Trans. 1989, 1799. (e) Akita, M.; Hua, R.;
Nakanishi, S.; Tanaka, M.; Moro-oka, Y. Organometallics 1997, 16,
5572.
(10) Kaneko, J .; Suzuki, T.; Isobe, K.; Maitlis P. M. J . Organomet.
Chem. 1998, 554, 155.
(11) Adams, R. D.; Chen, G.; Chi, Y. Organometallics 1992, 11, 1473.
(12) Adams, R. D.; Chen, G.; Chi, Y.; Wu, W.; Yin, J . Organometallics
1992, 11, 1480.
(7) Albano, V. G.; Bordoni, S.; Busetto, L.; Monari, M.; Zanotti V.
Organometallics 1995, 14, 5455.
(8) (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., J r.; Collier, J . A.;
Pettit, R. Organometallics 1982, 1, 1350. (c) Casey, C. P.; Niccolai, G.
P. Organometallics 1994, 13, 2527.

Hydride Addition in Cationic Diiron Complexes
Organometallics, Vol. 23, No. 13, 2004 3351
Moreover, the reaction of 3c with NaBD4 affords the
expected complex [Fe2{µ-η1:η2-C(Me)C(HD)CN(Me)-
(Xyl)}(µ-CO)(CO)(Cp)2], which is the partially deuter-
ated counterpart of 6c and displays a stereogenic center
1
at Câ. The corresponding H NMR spectrum suggests
that deuteride addition is stereospecific: in fact, both
E and Z isomers exhibit one single CâH resonance (at
3.56 and 4.21 ppm, respectively). A possible explanation
of the stereospecific character of the reaction is that
nucleophilic attack at Câ is hampered by the more
hindered Cp side of the precursor 3c. Support for this
hypothesis comes from a NOE experiment on the more
abundant E isomer of 6c, which has allowed the
assignment of the resonances of the CâH2 protons. The
signal at 3.56 ppm, which is also observed in the
deuterated counterpart of 6c, corresponds to the hydro-
gen pointing toward the Cp ligands. Therefore Câ-D is
on the opposite side, where we believe the approach of
the nucleophile is favored.
Concerning the 13C NMR data of 6a -h , the most
noticeable resonances are those that evidence the
peculiarity of the bridging ligand, consisting of both a
bridging and a terminal alkylidene. Indeed the µ-alkyl-
idene carbon (Cγ) resonance falls in the expected range,
around 130-180 ppm. The Câ resonance occurs at
higher field (e.g., for 6a at 73.1 ppm), while the amino-
alkylidene nature of the CR is evidenced by the corre-
sponding low-field resonance (at about 280 ppm), well
within the typical range of terminally bonded diiron
aminocarbene complexes.13
F igu r e 3. ORTEP drawing of the complex [Fe2{µ-η1:η2-
C(COOMe)CH2CN(Me)(Xyl)}(µ-CO)(CO)(Cp)2] (6f) (thermal
ellipsoids at the 30% probability level).
F igu r e 4. E-Z isomers for 6a -h .
The hydride addition to complexes 3a -h is reversible,
and the parent compounds can be regenerated in good
yields upon treatment of 6a -h with HSO3CF3.
Compounds 6a -h display the usual ν(CO) band
pattern consisting of two absorptions attributable to the
terminal and bridging CO (e.g., for 6a at 1922 and 1738
cm-1).
Comparison of the reactions shown in Schemes 1 and
2 evidences the regioselective character of the hydride
addition, which occurs at CR and Câ, respectively. This
remarkable regioselectivity is originated by structural
differences in the precursors 2a -d and 3a -h , i.e., the
presence in the latter complexes of a Xyl substituent in
place of a methyl at the iminium nitrogen. The sterically
demanding Xyl group protects the adjacent CR from
nucleophilic attack and redirects hydride addition to the
less hindered Câ position. The observed attack at Câ
indicates that electronic effects are not relevant, Xyl
being more electron-withdrawing than Me.
The NMR spectra of 6a -h , in CDCl3 solution, reveal
the presence of two isomers, in about 2-1.5:1 ratio, as
observed for their precursors 3a -h . In particular, the
1H NMR spectra show two signals, for each isomer,
attributable to the nonequivalent geminal CâH2 protons
(e.g., for 6a at 3.74, 3.45 ppm and 4.64, 4.45 ppm,
respectively). The isomers arise from the orientations
of the Me and Xyl group around the CR-N interaction,
whose double-bond character (see Figure 4) has already
been discussed for 6f.
NOE experiments performed on 6f and comparison
of the NMe chemical shifts of the two isomeric forms
for each of the complexes 6a -h indicate that the
preferred orientation is E, corresponding to the geom-
etry observed in the solid (Figure 3); indeed irradiation
of the N-Me resonance (3.57 ppm) of the major isomer
of complex 6f has resulted in significant NOE enhance-
ments of the resonances due to one Cp ligand (4.63 ppm)
and the two methyl groups on the Xyl ring (2.04 and
1.83 ppm), whereas no effect has been detected on the
resonance due to the CâH. On the other hand, by
irradiating the N-Me resonance (2.97 ppm) of the minor
isomer, remarkable enhancements of the resonances due
to CâH (4.59 and 3.86 ppm) and COOMe (3.89 ppm)
have been detected.
To further investigate the steric effects on the imin-
ium reactivity, we have examined the reaction of NaBH4
with [Fe2{µ-η1:η3-C(R′)dCHCdN(Me)(CH2Ph)}(µ-CO)-
(CO)(Cp)2][SO3CF3] (R′ ) Tol, 4a ; SiMe3, 4b; COOMe,
4c), in which the iminium substituents are Me and CH2-
Ph. The benzyl group is less sterically demanding than
Xyl, and complexes 4a -c consist of a mixture of E and
Z isomers, in almost equivalent amount.
The reactions of 4a -c with NaBH4 take place as
described for compounds 2a -d , and hydride addition
occurs exclusively at the iminium carbon (CR), yielding
the vinylalkylidene complexes [Fe2{µ-η1:η3-C(R′)CHd
CHN(Me)(CH2Ph)}(µ-CO)(CO)(Cp)2] (R′ ) Tol, 7a; SiMe3,
7b; COOMe, 7c) (Scheme 3). Complexes 7a ,b display
spectroscopic properties similar to those of the analo-
gous compounds 5a and 5b, respectively. Only one
It is worth noting that the precursors 3a -h also
present E, Z isomers, as a consequence of the different
orientation of the iminium substituents (Me, Xyl), with
predominance of the E isomer, which exhibits the Xyl
group facing the CâH.
(13) Zanotti, V.; Bordoni, S.; Busetto, L.; Carlucci, L.; Palazzi, A.;
Serra, R.; Albano, V. G.; Monari, M.; Prestopino, F.; Laschi, F.; Zanello,
P. Organometallics 1995, 14, 5232.

3352 Organometallics, Vol. 23, No. 13, 2004
Albano et al.
Sch em e 3
convert these species, upon heating in THF solution at
reflux temperature, were unsuccessful.
Finally, reaction of 3c with LiDBEt3 places the
deuterium exclusively on the CR, indicating that no
hydrogen migration occurs between Câ and CR sites.
Con clu sion s
We have described the reactivity of bridging vi-
nyliminium ligands in diiron complexes toward NaBH4
and the factors controlling its regio- and stereoselectiv-
ity. The iminium carbon CR is apparently the preferen-
tial site of attack, and in the absence of encumbering
substituents at the nitrogen, hydride addition yields
stable µ-vinylalkylidene products. However, H- addition
is directed at Câ, with formation of bis-alkylidene
complexes, when a Xyl group replacing a Me group (at
the iminium nitrogen) makes CR less accessible. We
have evidenced that also other factors, including the
strength of the nucleophile, are to be considered. The
regioselectivity is accompanied by the stereoselectivity
generated by the steric hindrance of the Cp ligands that
permit the attack only from the less crowded terminal
CO side (of the molecule), irrespective of the carbon
atom undergoing hydride addition.
Sch em e 4
Exp er im en ta l Section
Gen er a l Da ta . All reactions were routinely carried out
under a nitrogen atmosphere, using standard Schlenk tech-
niques. Unless otherwise stated, solvents were distilled im-
mediately 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 on
a Perkin-Elmer Spectrum 2000 FT-IR spectrophotometer, and
elemental analyses were performed on a ThermoQuest Flash
1112 Series EA Instrument. All NMR measurements were
performed at 298 K on Varian Gemini 300 and Mercury Plus
400 instruments. The chemical shifts for 1H and 13C were
referenced to internal TMS. The spectra were fully assigned
via DEPT experiments. NMR signals due to a second isomeric
form (where it has been possible to detect and/or resolve them)
are italicized. NOE measurements were recorded using the
DPFGSE-NOE sequence.14 All the reagents were commercial
products (Aldrich) of the highest purity available and used as
received. [Fe2(CO)4(Cp)2] was purchased from Strem and used
as received. Compounds 2a -d , 3a -h , and 4a -c were prepared
as described in the literature.1
isomer is observed, and hydride addition is exclusively
trans to Câ-H. Therefore, only the Xyl group, among the
substituents investigated, prevents attack of NaBH4 at
the iminium carbon (CR).
It should be noted that the above considerations
concern the use of NaBH4 and that a different hydride
source could, in principle, lead to a different result. To
investigate this point, we have studied the reactivity of
[Fe2{µ-η1:η3-C(R′)dCHCdN(Me)(Xyl)}(µ-CO)(CO)(Cp)2]-
[SO3CF3] (R′ ) Me, 3c; COOMe, 3f) with LiHBEt3
(superhydride). By contrast with the corresponding
reactions with NaBH4, hydride addition selectively
occurs at the iminium carbon CR, with the formation of
the corresponding vinylalkylidene complexes [Fe2{µ-η1:
η3-C(R′)CHdCHN(Me)(Xyl)}(µ-CO)(CO)(Cp)2] (R′ ) Me,
8a ; COOMe, 8b) (Scheme 4). No traces of compounds
6c and 6f, expected from attack at the Câ, have been
detected.
Syn th eses of [F e2{µ-η1:η3-Cγ(R′)Câ(H)dCr(H)NMe2}(µ-
CO)(CO)(Cp )2] (R′ ) Tol, 5a ; SiMe3, 5b; Me, 5c; CH2OH,
5d ). Complex 2a (60 mg, 0.0969 mmol) was treated with an
excess of NaBH4 (11 mg, 0.289 mmol) in THF solution (10 mL).
The mixture was stirred at room temperature for 15 min, then
the solvent was removed under reduced pressure and the
residue filtered on an alumina pad, using a mixture of CH2-
Cl2 and petroleum ether (1:1) as eluent. Green crystals of 5a ,
suitable for X-ray analysis, were obtained by crystallization
at -20 °C from a CH2Cl2 solution layered with petroleum
ether. Yield: 40 mg, 87%. Anal. Calcd for C24H25Fe2NO2: C,
61.18; H, 5.35; N, 2.97. Found: C, 61.23; H, 5.24; N, 3.01. IR
(CH2Cl2): ν(CO) 1929 (vs), 1747 (s) cm-1. 1H NMR (CDCl3): δ
The spectroscopic properties of 8a ,b resemble those
1
of the complexes of type 5. Their H MMR spectra show
two doublets (e.g., at 1.78 and 3.96 ppm for 8a ), assigned
to CRH and CâH, respectively: the coupling constant
(10.4 Hz) indicates that they are mutually trans, as
observed for the analogous µ-vinylalkylidenes 5a -d and
7a -c. The bridging alkylidene carbon gives rise to the
expected low-field 13C NMR resonance (at 184.6 ppm
for 8a ).
-
-
The different behavior of BH4 and HBEt3 toward
these substrates is interesting in several respects. It
confirms the intuitive feeling that the CR carbons are
more acidic sites than Câ. The reaction with the more
nucleophilic LiHBEt3 appears to be governed by elec-
tronic rather than steric factors. By contrast, steric
control dominates the regiochemistry in the case of the
weaker nucleophile NaBH4.
3
7.75, 7.28 (d, 4 H, J HH ) 7 Hz, C6H4-Me); 4.62, 4.42 (s, 10 H,
3
Cp); 3.93 (d, 1 H, J HH ) 9.5 Hz, CâH); 2.45 (s, 3 H, C6H4Me);
2.41 (s, 6 H, NMe); 1.86 (d, 1 H, 3J HH ) 9.5 Hz, CRH). 13C NMR
(CDCl3) δ 278.1 (µ-CO); 217.4 (CO); 181.5 (Cγ); 157.3 (ipso-
C6H4Me); 134.3, 128.8, 128.3 (C6H4Me); 105.6 (CR); 87.6, 81.1
(Cp); 64.8 (Câ); 40.8 (NMe); 21.1 (C6H4Me).
It should be remarked that 8a ,b and the correspond-
ing complexes 6c,f are isomers, resulting from hydride
additions at CR and Câ, respectively. Attempts to inter-
(14) Stott, K.; Stonehouse, J .; Keeler, J .; Hwang, T. L.; Shaka, A. J .
J . Am. Chem. Soc. 1995, 117, 4199.

Hydride Addition in Cationic Diiron Complexes
Organometallics, Vol. 23, No. 13, 2004 3353
Complexes 5b,c were obtained following the same procedure
described for the synthesis of 5a , by reacting 2b,c with NaBH4,
respectively.
2.07, 1.85 (s, 6 H, Me2C6H3); E/Z ratio 3:2. 13C NMR (CDCl3):
δ 282.2, 281.8 (CR); 273.0, 271.6 (µ-CO); 218.9, 218.4 (CO);
172.6, 172.2 (Cγ); 146.3, 142.2 (ipso-Me2C6H3); 135.2-127.8
(Me2C6H3); 87.0, 86.7, 86.6, 85.3 (Cp); 78.5, 76.1 (Câ); 47.5, 47.3
(CγMe); 45.9, 40.9 (NMe); 18.0, 17.9, 17.6, 17.0 (Me2C6H3).
5b. Yield: 93%. Anal. Calcd for C20H27Fe2NO2Si: C, 53.00;
H, 6.00; N, 3.09. Found: C, 53.12; H, 5.91; N, 3.08. IR (CH2-
Cl2): ν(CO) 1928 (vs), 1751 (s) cm-1. 1H NMR (CDCl3): δ 4.69,
6d . Yield: 77%. Anal. Calcd for C25H27Fe2NO3: C, 59.91;
H, 5.43, N, 2.73. Found: C, 60.06; H, 5.40; N, 2.79. IR (CH2-
Cl2): ν(CO) 1916 (vs), 1733 (s), ν(CN) 1511 (w) cm-1. 1H NMR
(CDCl3): δ 7.04-6.82 (m, 3 H, Me2C6H3); 5.24 (br, 1 H, OH);
4.60, 4.55, 4.48, 4.43 (s, 10 H, Cp); 3.59 (s, 3 H, NMe); 3.64,
3
4.52 (s, 10 H, Cp); 4.15 (d, 1 H, J HH ) 9.5 Hz, CâH); 2.37 (s,
3
6 H, NMe); 1.66 (d, 1 H, J HH ) 9.5 Hz, CRH); 0.62 (s, 9 H,
SiMe3). 13C NMR (CDCl3): δ 277.5 (µ-CO); 217.4 (CO); 173.3
(Cγ); 108.1 (CR); 85.5, 79.3 (Cp); 67.7 (Câ); 40.7 (NMe); 3.4
(SiMe3).
3.52 (d, 2 H, 2J HH ) 12 Hz, CH2OH); 3.53, 3.29 (d, 2 H, 2J HH
)
20 Hz, CâH2); 2.04, 1.82 (s, 6 H; Me2C6H3); E/Z ratio 15:1. 13C
NMR (CDCl3) δ 282.1 (CR); 273.0 (µ-CO); 218.8 (CO); 172.5 (Cγ);
142.2 (ipso-Me2C6H3); 132.7, 131.6, 128.9, 128.2, 128.0 (Me2-
C6H3); 86.6, 85.3 (Cp); 76.1 (Câ); 47.2 (CH2OH); 45.9 (NMe);
17.5, 16.9 (Me2C6H3).
5c. Yield: 84%. Anal. Calcd for C18H21Fe2NO2: C, 54.73; H,
5.36; N, 3.55. Found: C, 54.76; H 5.32; N, 3.52. IR (CH2Cl2):
ν(CO) 1928 (vs), 1754 (s) cm-1
(s, 10 H, Cp); 3.96 (d, 1 H, J HH ) 10 Hz, CâH); 3.85 (s, 3 H,
CγMe); 2.35 (s, 6 H, NMe); 1.49 (d, 1 H, J HH ) 10 Hz, CRH).
.
1H NMR (CDCl3): 4.65, 4.42
3
3
13C NMR (CDCl3): δ 275.9 (µ-CO); 217.6 (CO); 185.2 (Cγ); 102.4
(CR); 86.5, 80.9 (Cp); 68.2 (Câ); 42.0 (NMe); 41.1 (CγMe).
Complex 5d was obtained following the same procedure
described for the synthesis of 5a , by reacting 2d with NaBH4
and using THF as eluent in the column chromatography.
5d . Yield: 68%. Anal. Calcd for C18H21Fe2NO3: C, 52.60;
H, 5.15; N, 3.41. Found: C, 52.49; H 5.16; N, 3.44. IR (CH2-
6e. Yield: 79%. Anal. Calcd for C30H29Fe2NO2: C, 65.84; H,
5.34; N, 2.56. Found: C, 65.91; H, 5.27; N, 2.54. IR (CH2Cl2):
ν(CO) 1922 (vs), 1743 (s), ν(CN) 1513 (w) cm-1 1H NMR
.
(CDCl3): δ 7.74-6.92 (m, 8 H, Me2C6H3 and Ph); 4.71, 4.38,
2
4.35, 4.05 (s, 10 H, Cp); 4.63, 4.47, 3.75, 3.45 (d, 2 H, J HH
)
21 Hz, CâH2); 3.68, 3.03 (s, 3 H, NMe); 2.24, 2.18, 1.98, 1.92
(s, 6 H, Me2C6H3); E/Z ratio 2:1. 13C NMR (CDCl3): δ 282.9,
282.3 (CR); 270.8, 269.9 (µ-CO); 218.9, 218.3 (CO); 165.3, 164.9
(Cγ); 160.9, 160.2 (ipso-Ph); 146.0, 142.4 (ipso-Me2C6H3);
135.3-122.7 (Me2C6H3 and Ph); 88.5, 88.2, 85.3, 85.1 (Cp);
75.3, 72.9 (Câ); 45.3, 40.9 (NMe); 18.3, 17.8, 17.1 (Me2C6H3).
1
Cl2): ν(CO) 1929 (vs), 1755 (s) cm-1. H NMR (CDCl3): δ 6.57
(br, 1 H, OH); 5.99, 5.74 (m, 2 H, CH2OH); 4.69, 4.47 (s, 10 H,
Cp); 4.15 (d, 1 H, 3J HH ) 10 Hz, CâH); 2.34 (s, 6 H, NMe); 1.64
3
(d, 1 H, J HH ) 10 Hz, CRH). 13C NMR (CDCl3): 273.7 (µ-CO);
217.5 (CO); 182.0 (Cγ); 105.6 (CR); 85.7, 80.2 (Cp); 67.9 (CH2-
OH); 66.7 (Câ); 40.9 (NMe).
6f. Yield: 95%. Anal. Calcd for C26H27Fe2NO4: C, 59.01; H,
5.14, N, 2.65. Found: C, 59.03; H, 5.11; N, 2.61. IR (CH2Cl2):
ν(CO) 1930 (vs), 1763 (s), 1664 (w), 1636 (w), ν(CN) 1512 (w)
cm-1. 1H NMR (CDCl3): δ 7.24-6.85 (m, 3 H, Me2C6H3); 4.67,
4.65, 4.63, 4.04 (s, 10 H, Cp); 4.59, 3.86, 3.78, 2.77 (d, 2 H,
2J HH ) 20 Hz, CâH2); 3.97, 3.89 (s, 3 H, CO2Me); 3.57, 2.97 (s,
3 H, NMe); 2.22, 2.14, 2.04, 1.83 (s, 6 H, Me2C6H3); E/Z ratio
3:2. 13C NMR (CDCl3): δ 276.1, 276.0 (CR); 268.8, 267.4 (µ-
CO); 217.7, 217.5 (CO); 186.0, 185.5 (CO2Me); 145.9, 142.0
(ipso-Me2C6H3); 134.9-128.0 (Me2C6H3); 133.0 (Cγ); 87.3, 87.1,
86.1, 85.5 (Cp); 69.6, 67.4 (Câ); 50.9, 50.8 (CO2Me); 45.8, 41.3
(NMe); 18.1, 17.7, 16.9 (Me2C6H3).
Syn th esis of [F e2{µ-η1:η2-C(R′)CH2CN(Me)(Xyl)}(µ-CO)-
(CO)(Cp )2] (R′ ) Tol, 6a ; SiMe3, 6b; Me, 6c; CH2OH, 6d ;
P h , 6e; COOMe, 6f; Bu n , 6g; H, 6h ). Complex [Fe2{µ-η1:η3-
C(Tol)dCHCdN(Me)(Xyl)}(µ-CO)(CO)(Cp)2][SO3CF3], 3a (90
mg, 0.127 mmol), was treated with an excess of NaBH4 (26
mg, 0.684 mmol) in THF solution (10 mL). The mixture was
stirred at room temperature for 15 min, then the solvent was
removed under reduced pressure and the residue filtered on
an alumina pad, using CH2Cl2 as eluent. Crystallization at
-20 °C from a CH2Cl2 solution layered with n-hexane afforded
6a . Yield: 54 mg, 76%. Anal. Calcd for C31H31Fe2NO2: C,
66.34; H, 5.57; N, 2.50. Found: C, 66.38; H, 5.55, N, 2.51. IR
6g. Yield: 92%. Anal. Calcd for C28H33Fe2NO2: C, 63.78;
H, 6.31; N, 2.66. Found: C, 63.80; H, 6.36; N, 2.64. IR (CH2-
Cl2): ν(CO) 1917 (vs), 1735 (s), ν(CN) 1511 (w) cm-1. 1H NMR
(CDCl3): δ 7.24-6.89 (m, 3 H, Me2C6H3); 4.64, 4.60, 4.49, 3.94
(s, 10 H, Cp); 4.30, 4.10, 3.41, 3.23 (d, 2 H, 2J HH ) 20 Hz, CâH2);
1
(CH2Cl2): ν(CO) 1922 (vs), 1738 (s), ν(CN) 1512 (w) cm-1. H
NMR (CDCl3) δ 7.47-6.91 (m, 7 H, Me2C6H3 and C6H4Me);
4.69, 4.38, 4.36, 4.04 (s, 10 H, Cp); 4.64, 4.45, 3.74, 3.45 (d, 2
H, 2J HH ) 19 Hz, CâH2); 3.67, 3.02 (s, 3 H, NMe); 2.39, 2.35 (s,
3 H, C6H4Me); 2.24, 2.17, 1.97, 1.92 (s, 6 H, Me2C6H3); E/Z ratio
3:1. 13C NMR (CDCl3): δ 283.4, 282.8 (CR); 271.0, 270.1 (µ-
CO); 219.0, 218.3 (CO); 162.8, 162.4, 161.5, 160.8 (Cγ and ipso-
C6H4Me); 142.5 (ipso-Me2C6H3); 135.3-124.7 (Me2C6H3 and
C6H4Me); 88.6, 88.3, 85.3, 85.1 (Cp); 75.5, 73.1 (Câ); 45.3, 40.9
(NMe); 21.1 (C6H4Me); 18.3, 18.2, 17.8, 17.1 (Me2C6H3).
Complexes 6b-h were obtained following the same proce-
dure described for the synthesis of 6a , by reacting complexes
3b-h with NaBH4, respectively.
6b. Yield: 76%. Anal. Calcd for C27H33Fe2NO2Si: C, 59.69;
H, 6.12, N, 2.58. Found: C, 59.77; H, 6.04; N, 2.56. IR (CH2-
Cl2): ν(CO) 1921 (vs), 1739 (s), ν(CN) 1511 (w) cm-1. 1H NMR
(CDCl3) δ 7.30-6.90 (m, 3 H, Me2C6H3); 4.77, 4.72, 4.61, 3.99
(s, 10 H, Cp); 4.62, 4.04, 3.90, 2.82 (d, 2 H, 2J HH ) 20 Hz, CâH2);
3.61, 2.94 (s, 3 H, NMe); 2.21, 2.20, 2.03, 1.85 (s, 6 H, Me2C6H3);
0.51, 0.41 (s, 9 H, SiMe3); E/Z ratio 2:1. 13C NMR (CDCl3): δ
281.3, 282.2 (CR); 269.2, 268.0 (µ-CO); 219.0, 218.5 (CO); 160.1,
159.4 (Cγ); 146.1, 142.6 (ipso-Me2C6H3); 135.2-127.9 (Me2C6H3);
85.6, 85.5, 84.1, 83.7 (Cp); 70.6, 67.5 (Câ); 45.1, 40.8 (NMe);
18.1, 18.0, 17.4, 16.9 (Me2C6H3); 2.9, 2.8 (SiMe3).
2
3
4.08, 4.04, 3.80, 3.58 (dt, 2 H, J HH ) 4 Hz, J HH ) 13 Hz,
CγCH2); 3.63, 2.97 (s, 3 H, NMe); 2.21, 2.16, 2.06, 1.84 (s, 6 H,
Me2C6H3); 1.81 (m, 2 H, CγCH2CH2); 1.70, 1.59 (m, 2 H, Cγ-
3
CH2CH2CH2); 1.16, 1.04 (t, 3 H, J HH ) 7 Hz, CγCH2CH2-
CH2CH3); E/Z ratio 3:2. 13C NMR (CDCl3): δ 282.3 (CR); 273.8,
272.2 (µ-CO); 219.2, 218.8 (CO); 177.6 (Cγ); 142.3-127.8
(Me2C6H3); 86.8, 86.4, 85.4, 84.8 (Cp); 75.7, 73.4 (Câ); 60.6
(CγCH2); 45.9, 40.9 (NMe); 33.3, 33.2 (CγCH2CH2); 23.8, 23.6
(CγCH2CH2CH2); 18.1, 17.9, 17.6, 16.9 (Me2C6H3); 14.7, 14.5
(CγCH2CH2CH2CH3).
6h . Yield: 88%. Anal. Calcd for C24H25Fe2NO2: C, 61.18;
H, 5.35, N, 2.97. Found: C, 61.10; H, 5.42; N, 2.89. IR (CH2-
Cl2): ν(CO) 1918 (vs), 1740 (s), ν(CN) 1512 (w) cm-1. 1H NMR
3
3
(CDCl3): δ 11.23, 11.10 (dd, 1 H, J HH ) 7 Hz, J HH ) 2 Hz,
CγH); 7.24-6.88 (m, 3 H, Me2C6H3); 4.64, 4.61, 4.52, 3.98 (s,
2
3
10 H, Cp); 4.82, 4.16 (dd, 1 H, J HH ) 20 Hz, J HH ) 7 Hz,
2
CâH); 3.59, 2.97 (s, 3 H, NMe); 4.19, 3.07 (dd, 1 H, J HH ) 20
Hz, 3J HH ) 2 Hz, CâH); 2.22, 2.09, 2.06, 1.80 (s, 6 H, Me2C6H3);
E/Z ratio 6:5. 13C NMR (CDCl3): δ 281.0, 280.9 (CR); 272.7,
271.4 (µ-CO); 218.1, 218.0 (CO); 149.9, 149.6 (Cγ); 146.1, 142.1
(ipso-Me2C6H3); 135.1-127.8 (Me2C6H3); 85.6, 85.4, 84.0, 83.5
(Cp); 69.0, 66.7 (Câ); 45.8, 41.0 (NMe); 17.9, 17.8, 17.6, 17.0
(Me2C6H3).
6c. Yield: 85%. Anal. Calcd for C25H27Fe2NO2: C, 61.89; H,
5.61, N, 2.89. Found: C, 61.89; H, 5.58, N, 2.90. IR (CH2Cl2):
ν(CO) 1915 (vs), 1736 (s), ν(CN) 1512 (w) cm-1 1H NMR
.
(CDCl3) δ 7.24-6.89 (m, 3 H, Me2C6H3); 4.64, 4.59, 4.46, 3.91
(s, 10 H, Cp); 4.42, 4.21, 3.56, 3.34 (d, 2 H, 2J HH ) 20 Hz, CâH2);
3.65, 3.56 (s, 3 H, CγMe); 3.62, 2.97 (s, 3 H, NMe); 2.22, 2.16,
Syn th esis of [F e2{µ-η1:η3-C(R′)CHdCHN(Me)(CH2P h )}-
(µ-CO)(CO)(Cp )2] (R′ ) Tol, 7a ; SiMe3, 7b; COOMe, 7c).
Complex 7a was obtained following the same procedure

3354 Organometallics, Vol. 23, No. 13, 2004
Albano et al.
Ta ble 2. Cr ysta l Da ta a n d Exp er im en ta l Deta ils
for 5a a n d 6f
described for the synthesis of 5a , by treating 4a (110 mg, 0.158
mmol) with NaBH4.
7a . Yield: 97%. Anal. Calcd for C30H29Fe2NO2: C, 65.84;
H, 5.34; N, 2.56. Found: C, 65.91; H 5.35; N, 2.55. IR (CH2-
Cl2): ν(CO) 1930 (vs), 1747 (s) cm-1. 1H NMR (CDCl3): δ 7.96-
7.27 (m, 9 H, Ph and C6H4Me); 4.52, 4.42 (s, 10 H, Cp); 4.01
5a
6f
formula
fw
T, K
C
24H25Fe2NO2
C
26H27Fe2NO4
471.15
298(2)
529.19
298(2)
3
2
(d, 1 H, J HH ) 9 Hz, CâH); 4.02, 3.87 (d, 2 H, J HH ) 15 Hz,
CH2Ph); 2.46 (s, 3 H, NMe); 2.24 (s, 3 H, C6H4Me); 2.08 (d, 1
H, 3J HH ) 9 Hz, CRH). 13C NMR (CDCl3): δ 278.3 (µ-CO); 217.4
(CO); 181.7 (Cγ); 157.4 (ipso-C6H4Me); 136.9, 134.2, 128.8,
128.5, 128.3, 127.4 (Ph and C6H4Me); 105.6 (CR); 87.6, 81.6
(Cp); 64.0 (Câ); 60.0 (CH2Ph); 35.9 (NMe); 21.1 (C6H4Me).
Complex 7b and 7c were obtained following the same
procedure described for the synthesis of 5a , by reacting 4b
and 4c with NaBH4, respectively.
λ, Å
0.71073
triclinic
P1h
0.71073
monoclinic
P21/c
10.6352(3)
13.2769(3)
16.3383(4)
90
94.627(1)
90
2299.5(1)
4
cryst symmetry
space group
a, Å
8.1439(8)
10.349(1)
12.818(1)
83.718(3)
78.364(3)
79.393(3)
1037.0(2)
2
b, Å
c, Å
R, deg
â, deg
γ, deg
cell volume, Å3
Z
7b. Yield: 80%. Anal. Calcd for C26H31Fe2NO2Si: C, 59.00;
H, 5.90; N, 2.65. Found: C, 58.92; H 5.96; N, 2.62. IR (CH2-
Cl2): ν(CO) 1930 (vs), 1751 (s) cm-1. 1H NMR (CDCl3): δ 7.49-
Dc, Mg m-3
µ(Mo KR), mm-1
F(000)
1.509
1.419
488
1.529
1.295
1096
7.26 (m, 5 H, Ph); 4.69, 4.40 (s, 10 H, Cp); 4.17 (d, 1 H, 3J HH
)
2
cryst size, mm
θ limits, deg
0.10 × 0.15 × 0.25
0.20 × 0.25 × 0.28
9 Hz, CâH); 3.97, 3.81 (d, 2 H, J HH ) 15 Hz, CH2Ph); 2.20 (s,
3 H, NMe); 1.88 (d, 1 H, 3J HH ) 9 Hz, CRH); 0.60 (s, 9 H, SiMe3).
13C NMR (CDCl3): δ 278.4 (µ-CO); 217.6 (CO); 173.8 (Cγ);
136.8, 128.9, 128.5, 128.4, 127.4 (Ph); 108.3 (CR); 85.6, 79.8
(Cp); 66.8 (Câ); 60.1 (CH2Ph); 35.8 (NMe); 3.4 (SiMe3).
Complex 7c was obtained following the same procedure
described for the synthesis of 3a , by reacting 4c (110 mg, 0.166
mmol) with NaBH4.
2.59-25.99
1.92-30.04
no. of reflns collected 10 287 ((h, (k, (l) 29 796 ((h, (k, (l)
no. of unique obsd
4055 [R(int) )
0.0575]
6718 [R(int) )
0.0792]
0.849
0.0406, 0.0901
0.659/-0.508
reflns [Fo > 4σ(Fo)]
goodness-of-fit on F2 1.019
R1(F)a, wR2(F2)b
0.0645, 0.1588
largest diff peak and 1.110/-0.739
hole, e‚Å-3
7c. Yield: 66%. Anal. Calcd for C25H25Fe2NO4: C, 58.29; H,
4.89; N, 2.72. Found: C, 58.30; H, 4.83; N, 2.69. IR (CH2Cl2):
R1 ) ∑||Fo| - |Fc|/∑|Fo|. wR2 ) [∑w(Fo - Fc2)2/∑w(Fo2)2]1/2
a
b
2
where w ) 1/[σ2(Fo2) + (aP)2 + bP] where P ) (Fo + 2Fc2)/3.
2
1
ν(CO) 1936 (vs), 1762 (s), 1689 (w) cm-1. H NMR (CDCl3): δ
7.46-7.28 (m, 5 H, Ph); 4.66, 4.43 (s, 10 H, Cp); 4.39 (d, 1 H,
3J HH ) 9 Hz, CâH); 4.05 (s, 3 H, CO2Me); 3.94, 3.84 (d, 2 H,
2J HH ) 14 Hz, CH2Ph); 2.24 (s, 3 H, NMe); 2.02 (d, 1 H,
3J HH ) 9 Hz, CRH). 13C NMR (CDCl3): δ 271.6 (µ-CO); 217.3
(CO); 172.0 (CO2Me); 157.8 (Cγ); 136.1, 128.6, 128.5, 127.6 (Ph);
107.6 (CR); 86.6, 82.0 (Cp); 62.9 (Câ); 60.5 (CH2Ph); 51.8
(CO2Me); 35.6 (NMe).
Syn th esis of [F e2{µ-η1:η3-C(R′)CHdCHN(Me)(Xyl)}(µ-
CO)(CO)(Cp )2] (R′ ) Me, 8a COOMe, 8b). A THF solution
of 3c (46 mg, 0.0727 mmol), cooled to -30 °C, was treated with
a solution of LiBHEt3 in THF (0.10 mmol); the mixture was
stirred at room temperature for 30 min, then the solvent was
removed. Chromatography of the residue on an alumina
column afforded an orange band, corresponding to 8a , collected
using CH2Cl2 as eluent. Yield: 20 mg, 57%. Anal. Calcd for
data were measured over a full diffraction sphere using 0.3°
wide ω scans, crystal-to-detector distance 5.0 cm. The software
SMART15 was used for collecting frames of data, indexing
reflections, and determination of lattice parameters. The
collected frames were then processed for integration by the
software SAINT,15 and an empirical absorption correction was
applied using SADABS.16 The structures were solved by direct
methods (SIR97)17 and subsequent Fourier syntheses and
refined by full-matrix least-squares calculations on F2 (SHELX-
TL)18 attributing anisotropic thermal parameters to all the
non-hydrogen atoms. The methyl and aromatic hydrogen
atoms, although observed in the electron density maps, were
placed in calculated positions and allowed to ride the carrier
carbons with thermal parameters tied to those of the pertinent
atoms. The other H atoms were located and their parameters
refined individually. Crystallographic data and structure
refinement details for 5a and 6f are given in Table 2.
C
25H27Fe2NO2: C, 61.89; H, 5.61; N, 2.89. Found: C, 61.93; H
1
5.68; N, 2.90. IR (CH2Cl2): ν(CO) 1922 (vs), 1751 (s) cm-1. H
NMR (CDCl3): δ 7.24-6.88 (m, 3 H, Me2C6H3); 4.61, 4.38 (s,
3
Ackn owledgm en t. We thank the Ministero dell’Uni-
versita` e della Ricerca Scientifica e Tecnologica (MIUR)
(project: New strategies for the control of reactions:
interactions of molecular fragments with metallic sites
in unconventional species) and the University of Bolog-
na for financial support.
10 H, Cp); 3.96 (d, 1 H, J HH ) 10.4 Hz, CâH); 3.94 (s, 3 H,
CγMe); 2.58, 2.54 (s, 6 H, Me2C6H3 and NMe); 1.93 (s, 3 H,
3
Me2C6H3); 1.78 (d, 1 H, J HH ) 10.4 Hz, CRH). 13C NMR
(CDCl3): δ 278.0 (µ-CO); 217.6 (CO); 184.6 (Cγ); 145.2-126.7
(Me2C6H3); 104.7 (CR); 86.4, 82.1 (Cp); 64.8 (Câ); 42.5 (NMe);
36.3 (CγMe); 18.9, 17.6 (Me2C6H3).
Complex 8b was obtained following the same procedure
described for the synthesis of 8a , by treating 3f (50 mg, 0.074
mmol) with LiBHEt3.
Su p p or tin g In for m a tion Ava ila ble: Tables giving all
crystal data, atomic coordinates, and bond lengths and angles
for 5a and 6f; these crystallographic data are also available
as CIF files. This material is available free of charge via the
Internet at http://pubs.acs.org.
8b. Yield: 82%. Anal. Calcd for C26H27Fe2NO4: C, 59.01;
H, 5.14; N, 2.65. Found: C, 59.07; H 5.08; N, 2.65. IR (CH2-
Cl2): ν(CO) 1931 (vs), 1769 (s), 1690 (w) cm-1 1H NMR
.
(CDCl3): δ 7.10-6.92 (m, 3 H, Me2C6H3); 4.62, 4.52 (s, 10 H,
OM049868E
3
Cp); 4.41 (d, 1 H, J HH ) 10.4 Hz, CâH); 4.09 (s, 3 H, CO2Me);
2.61, 2.51, 1.93 (s, 9 H, Me2C6H3 and NMe); 2.05 (d, 1 H,
3J HH ) 10.4 Hz, CRH). 13C NMR (CDCl3): δ 260.5 (µ-CO); 217.1
(CO); 171.2 (CO2Me); 156.4 (Cγ); 144.6 (ipso-Me2C6H3); 136.4-
127.2 (Me2C6H3); 111.2 (CR); 86.5, 82.6 (Cp); 61.2 (Câ); 51.9
(CO2Me); 36.6 (NMe); 18.7, 17.6 (Me2C6H3).
X-r a y Cr ysta llogr a p h y. The diffraction experiments for
5a and 6f were carried out at room temperature on a Bruker
AXS SMART 2000 CCD based diffractometer using graphite-
monochromated Mo KR radiation (λ ) 0.71073 Å). Intensity
(15) SMART & SAINT Software Reference Manuals, version 5.051
(Windows NT Version); Bruker Analytical X-ray Instruments Inc.:
Madison, Wi, 1998.
(16) Sheldrick, G. M. SADABS, program for empirical absorption
correction; University of Go¨ttingen: Germany, 1996.
(17) 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, 115-119.
(18) Sheldrick, G. M. SHELXTLplus Version 5.1 (Windows NT
version) Structure Determination Package; Bruker Analytical X-ray
Instruments Inc.: Madison, WI, 1998.