Allenylidene iron(II) complexes and their deprotonation, nucleophilic addition reactions, and cathodic protonation toward alkynyl derivatives: A chemical and electrochemical study

Article abstract of DOI:10.1021/om050408a

The allenylidene complexes trans-[FeBr(=C=C=CRR′)(depe) ₂][Y] (R = Me, R′ = Ph, 1; R = R′ = Ph, 2; R = R′ = Et, 3; depe = Et₂PCH₂CH₂PEt₂; Y = BF₄, BPh₄) were obtained by reaction of trans-[FeBr ₂(depe)₂] with the appropriate alkynol HC≡CCRR′(OH), in MeOH and in the presence of Na[BF₄] or Na[BPh₄]. Deprotonation of 3 or nucleophilic γ-addition to 2 led to the neutral enynyl and alkynyl complexes trans-[FeBr{-C≡CC(=CHMe) Et}-(depe)₂] (4) and trans-[FeBr(-Ca≡CCPh₂R″) (depe)₂] (R″ = CN (5a), MeO (5b)), respectively. Complex 2 (Y = BPh₄) also leads to the cationic alkynyl compounds trans-[Fe(NCMe){-C≡ CCPh₂(X)}(depe)₂][BPh ₄] (X = NMe₂ (6a), NHMe (6b)) and trans-[Fe(NCMe){- C≡CCPh₂-(PMe₃)}(depe)₂]Y₂ (Y₂ = [BPh₄]₂ (7a), [BPh₄] _2-xBr_x (7b)), in acetonitrile solution, upon reaction with NHMe₂, NH₂Me, and PMe₃, respectively. The complexes have been characterized by multinuclear NMR and IR spectroscopy, FAB-MS, and elemental analysis and, in the cases of 5a and 6a, also by X-ray diffraction analysis. Controlled-potential electrolysis of 2 yields the alkynyl species trans-[FeBr{-C≡CCPh₂(H)}(depe)₂] (8) via a 2e^-/H⁺ process, and the oxidation potential of the complexes, measured by cyclic voltammetry, has allowed us to estimate the electrochemical Pickett (P_L) and Lever (E_L) ligand parameters for the cumulenic ligands. These are then ordered (together with related ligands) according to their net π-electron acceptor minus σ-donor ability as follows: carbynes > aminocarbyne > CO > vinylidenes > aryl allenylidene > alkyl allenylidene > NCR ? phosphonium alkynyl > cyanoalkynyl, Br, NCO → alkynyl, enynyl, aminoalkynyl.

Full text of DOI:10.1021/om050408a

4654
Organometallics 2005, 24, 4654-4665
Allenylidene Iron(II) Complexes and Their
Deprotonation, Nucleophilic Addition Reactions, and
Cathodic Protonation toward Alkynyl Derivatives:
A Chemical and Electrochemical Study
Ana I. F. Venaˆncio,† M. Fa´tima C. Guedes da Silva,†,‡
Lu´ısa M. D. R. S. Martins,†,§ Joa˜o J. R. Frau´sto da Silva,† and
Armando J. L. Pombeiro*,†
Centro de Quı´mica Estrutural, Complexo I, Instituto Superior Te´cnico, Av. Rovisco Pais,
1049-001 Lisboa, Portugal, Universidade Luso´fona de Humanidades e Tecnologias, Campo
Grande, 376, 1749-024 Lisboa, Portugal, and Secc¸a˜o de Qu´ımica Inorgaˆnica, DEQ, ISEL,
R. Conselheiro Emı´dio Navarro, 1950-062 Lisboa, Portugal
Received May 24, 2005
The allenylidene complexes trans-[FeBr(dCdCdCRR′)(depe)2][Y] (R ) Me, R′ ) Ph, 1; R
) R′ ) Ph, 2; R ) R′ ) Et, 3; depe ) Et2PCH2CH2PEt2; Y ) BF4, BPh4) were obtained by
reaction of trans-[FeBr2(depe)2] with the appropriate alkynol HCtCCRR′(OH), in MeOH
and in the presence of Na[BF4] or Na[BPh4]. Deprotonation of 3 or nucleophilic γ-addition
to 2 led to the neutral enynyl and alkynyl complexes trans-[FeBr{-CtCC(dCHMe)Et}-
(depe)2] (4) and trans-[FeBr(-CtCCPh2R′′)(depe)2] (R′′ ) CN (5a), MeO (5b)), respectively.
Complex 2 (Y ) BPh4) also leads to the cationic alkynyl compounds trans-[Fe(NCMe){-Ct
CCPh2(X)}(depe)2][BPh4] (X ) NMe2 (6a), NHMe (6b)) and trans-[Fe(NCMe){-CtCCPh2-
(PMe3)}(depe)2]Y2 (Y2 ) [BPh4]2 (7a), [BPh4]2-xBrx (7b)), in acetonitrile solution, upon reaction
with NHMe2, NH2Me, and PMe3, respectively. The complexes have been characterized by
multinuclear NMR and IR spectroscopy, FAB-MS, and elemental analysis and, in the cases
of 5a and 6a, also by X-ray diffraction analysis. Controlled-potential electrolysis of 2 yields
the alkynyl species trans-[FeBr{-CtCCPh2(H)}(depe)2] (8) via a 2e-/H+ process, and the
oxidation potential of the complexes, measured by cyclic voltammetry, has allowed us to
estimate the electrochemical Pickett (PL) and Lever (EL) ligand parameters for the cumulenic
ligands. These are then ordered (together with related ligands) according to their net
π-electron acceptor minus σ-donor ability as follows: carbynes > aminocarbyne > CO >
vinylidenes > aryl allenylidene > alkyl allenylidene > NCR . phosphonium alkynyl >
cyanoalkynyl, Br-, NCO- > alkynyl, enynyl, aminoalkynyl.
Introduction
significance of complexes with such an unsaturated
carbon chain as potential precursors for molecular wires
or polymers in the field of new materials with optoelec-
tronics properties (namely liquid crystals and species
with nonlinear optical properties),7,10,14,18-27 (ii) their
application in the organic synthesis field8,28-35 and in
The dehydration of propargylic alcohols (alkynols),
HCtCCRR′(OH), by transition metals was discovered
by Selegue1 in 1982, providing a general method for the
synthesis of compounds containing cumulenic chains
such as allenylidene complexes (MdCdCdCRR′), al-
though the first allenylidene complex was synthesized
in a different way by Fischer2 and Berke.3 The chem-
istry of the allenylidene complexes has attracted a great
deal of interest,1-64 various factors, such as (i) the
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* To whom correspondence should be addressed. E-mail: pombeiro@
ist.utl.pt.
† Instituto Superior Te´cnico.
‡ Universidade Luso´fona de Humanidades e Tecnologias.
§ DEQ, ISEL.
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10.1021/om050408a CCC: $30.25 © 2005 American Chemical Society
Publication on Web 08/09/2005

Allenylidene Iron(II) Complexes
Organometallics, Vol. 24, No. 19, 2005 4655
particular as catalysts, especially Ru complexes, in
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{FeBr(depe)2}+ (depe ) Et2PCH2CH2PEt2). To this end,
the cyclic alkynol HCtCC(C5H10)OH leads to a cyclic
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mate of the corresponding PL and EL ligand parameters)
and compare them with those of other unsaturated
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4656 Organometallics, Vol. 24, No. 19, 2005
Venaˆncio et al.
Scheme 1. Syntheses of the Allenylidene Complexes 1-3 and Enynyl Derivative
trans-[FeBr{-CtCC(dCHMe)Et}(depe)2] (4)
(3b)). These complexes were obtained according to a
procedure recently described60 by treatment of a MeOH
solution of trans-[FeBr2(depe)2], in the presence of Na-
[BF4] or Na[BPh4], with the appropriate alkynol HCt
CCRR′(OH) (e.g. reaction 3, Scheme 1, for R ) R′ ) Et).
The reaction proceeds smoothly at 40 °C, leading to dark
blue (1 and 2) or red (3a and 3b) products with isolated
yields of 58-34%. They have been characterized by IR
and multinuclear NMR spectroscopy, FAB+-MS spec-
trometry, and elemental analysis. For 1 and 2, the IR
and NMR data are identical with or very similar to those
of the corresponding compounds with [BPh4]- as the
counterion,60 obviously without the data associated to
this ion. In the IR spectra, the characteristic asymmetric
stretching vibration ν(CdCdC) is observed as a strong-
or medium-intensity band at 1897 (1), 1880 (2), 1908
(3a), or 1907 cm-1 (3b), within the usual range (1988-
1870 cm-1)7 for allenylidene complexes.
reported72-74 for other allenylidene complexes. However,
the other two resonances cannot be unambiguously
assigned, although the order of the corresponding JCP
values (4-5 and 6.5 Hz) for their quintet structures
could suggest their assignment to Cγ and Câ, respec-
tively, as reported earlier73 for some Ru allenylidene
complexes. The resonance structures did not display a
sufficient resolution for the detection of any clear nJCH
,
and thus the confirmation of that Cγ and Câ assignment
was not possible.
It is noteworthy to mention that in our complexes the
change of a group at Cγ results only in a minor effect
on δ(CR) but in substantial ones on δ(Câ) and δ(Cγ),
in contrast to what has been observed73,74 in other
Ru allenylidene complexes, for which the influence of
the group at Cγ on the chemical shift is maximum for
CR.
For 3b the resonances of the CH2 and CH3 groups of
the allenylidene (dCdCdCEt2) are observed as quintets
(JCP ) ca. 2 Hz) at δ 41.2 and 11.2. All the other
resonances of the allenylidene and depe ligands have
also been assigned in 1H, 13C{1H}, and 13C NMR spectra,
including those of the ipso, ortho, meta, and para atoms
of the phenyl rings.
The trans geometry of not only these complexes but
also of all the others of this work has been assigned on
the basis of the singlet observed in the 31P{1H} NMR
spectra (except for complex 7; see below). In the 13C-
{1H} NMR spectra the carbon atoms of the cumulenic
chain are observed at ca. δ 306-307 (CR), 220-245 (Cγ
or Câ), and 149-171 (Câ or Cγ). The assignment to CR
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2
of the lowest field resonance (a quintet, JCP ) ca. 36
Hz, for 1 and 2) is based on the comparable data

Allenylidene Iron(II) Complexes
Organometallics, Vol. 24, No. 19, 2005 4657
Scheme 2. Syntheses of Neutral and Mono- and Dicationic Alkynyl Complexes
Further, the FAB+-MS spectra of the complexes
exhibit the corresponding molecular ion [M]+, whose
fragmentation pattern is initiated by the stepwise
elimination of the bromide, [M - Br]+, allenylidene, [M
- CdCdCRR′]+, or depe, [M - depe]+, ligands.
1.2. Neutral Alkynyl Complexes. The diethylalle-
nylidene complex trans-[FeBr(dCdCdCEt2)(depe)2]-
[BPh4] (3b) undergoes deprotonation in CH2Cl2 by
NaOMe, which acts as a Brønsted base toward an ethyl
group, yielding the neutral enynyl complex trans-[FeBr-
{-CtCC(dCHCH3)Et}(depe)2] (4) (Scheme 1, reaction
4) isolated as a pink solid, in ca. 85% yield. When 4 and
HBF4 are combined in thf, protonation occurs to regen-
erate the parent diethylallenylidene complex 3a (Scheme
1, reaction 5).
and dCdCdC(Me)Ph in 3 and 1, respectively, the
diphenylallenylidene ligand in trans-[FeBr(dCdCd
CPh2)(depe)2]+ (2) undergoes nucleophilic addition to the
Cγ atom upon treatment, in a CH2Cl2 or MeOH solution,
with [NBu4]CN or NaOMe. This leads to the formation
of the neutral alkynyl complexes trans-[FeBr(-Ct
CCPh2R′′)(depe)2] (R′′ ) CN (5a), MeO (5b)), respec-
tively (Scheme 2, reactions 1 and 2), isolated as salmon
(5a) or red (5b) solids, in ca. 80% yields.
They exhibit, in the IR spectra, a strong- (5a) or
medium-intensity (5b) ν(CtC) vibration at 2043 and
2087 cm-1, respectively, and, for 5a, ν(CtN) appears
as a weak band at 2229 cm-1. These features are
comparable with those quoted for other Ru π-ligand
1
complexes.39,75-79 In the H NMR spectrum, the reso-
In the IR spectrum of 4, the ν(CtC) and ν(CdC)
bands appear at 2024 and 1610 cm-1, respectively,
values comparable with those for the related complex
trans-[FeBr{-CtCC(dCH2)Ph}(depe)2] (2020 and 1552
cm-1),60 obtained by deprotonation of the methyl group
of trans-[FeBr{dCdCdC(Me)Ph}(depe)2][BPh4]. The
unsaturated -CtCC(dCHMe)Et ligand has been clearly
nance of the methoxy protons at the acetylenic chain
CtCCPh2(OCH3) in 5b overlaps with those of the
methylenic phosphinic protons at δ 2.2-1.3, in accord
with the chemical shift (δ 2.2) reported78 for trans-
[RuCl{-CtCCPh2(OCH3)}(Ph2PCH2PPh2)2]. In the 13C-
{1H} and 13C NMR spectra of 5a, the CR, Câ, and Cγ
resonances of the alkynyl ligand appear at much higher
1
2
identified by H and 13C{1H} NMR and, for example,
fields, δ 132.0 (qnt, JCP ) 27 Hz), 110.8 (m), and 49.8
the latter spectrum exhibits a quintet (2JCP ) 28 Hz,
CR) at δ 132.5, a quintet (JCP ) 2 Hz, Câ or Cγ) at δ
131.2, a multiplet at δ 122.5 (Cγ or Câ), a multiplet at δ
118.6 (dCHCH3), and a singlet at δ 16.0 (dCHCH3),
whereas, for the ethyl group, the CH2CH3 resonance is
a quintet (5JCP ) 2 Hz) at 33.9 and CH2CH3 gives a
singlet at 15.2 ppm. In the 13C NMR spectrum, those
resonances split into the expected structures.
(m), respectively, compared with those of the alle-
nylidene precursor trans-[FeBr(dCdCdCPh2)(depe)2]+
(CR 305.5, Cγ 244.9, and Câ 149.4 ppm),60 and the CtN
resonance occurs as a quintet (5JCP ) 1 Hz) at 122.2
ppm. All the other resonances of the alkynyl and depe
ligands have also been assigned in the 1H, 13C{1H}, and
13C NMR spectra. Comparable 13C chemical shifts have
In the FAB+-MS spectrum, the molecular ion was
detected, [M]+ (m/z 640), as well as a fragmentation
pattern initiated by the stepwise elimination of the
bromide [M - Br]+ (m/z 561), the alkynyl [M - (-Ct
CC(dCHMe)Et)]+ (m/z 547), and the depe [M - depe]+
(m/z 434) ligands.
(75) Cadierno, V.; Conejero, S.; Gamasa, M. P.; Gimeno, J. Dalton
Trans. 2000, 451.
(76) Bruce, M. I.; Low, P. J.; Tiekink, E. R. T. J. Organomet. Chem.
1999, 572, 3.
(77) Cadierno, V.; Gamasa, M. P.; Gimeno, J.; Lastra, E. J. Orga-
nomet. Chem. 1994, 474, C27.
(78) Pirio, N.; Touchard, D.; Toupet, L.; Dixneuf, P. H. J. Chem. Soc.,
Chem. Commun. 1991, 980.
(79) Crochet, P.; Demerseman, B.; Vallejo, M. I.; Gamasa, M. P.;
Gimeno, J.; Borge, J.; Garc´ıa-Granda, S. Organometallics 1997, 16,
5406.
In contrast with the proton abstraction reactions
exhibited by the ligated alkylallenylidenes dCdCdCEt2

4658 Organometallics, Vol. 24, No. 19, 2005
Venaˆncio et al.
been quoted for the cyanoalkynyl ligand in some Ru
π-ligand complexes.39,76,77
The FAB+-MS spectra of complexes 5a,b show the
corresponding molecular ion, [M]+ (m/z 763 (5a), 767
(5b)), which by loss of Br, R′′, alkynyl, or depe leads to
the derived fragments.
1.3. Cationic Alkynyl Complexes. Treatment of a
NCMe solution of trans-[FeBr(dCdCdCPh2)(depe)2]-
[BPh4] with dimethylamine, methylamine, or trimeth-
ylphosphine leads to the formation of the monocationic
alkynyl complexes trans-[Fe(NCMe){-CtCC(NR1R2)-
Ph2}(depe)2][BPh4] (R1, R2 ) Me (6a); R1 ) H, R2 ) Me
(6b)) (Scheme 2, reactions 3 and 4) or to the dicationic
complexestrans-[Fe(NCMe){-CtCC(PMe3)Ph2}(depe)2]-
Y2 (Y2 ) [BPh4]2 (7a), [BPh4]2-xBrx (7b)), respectively
(Scheme 2, reaction 5), isolated as yellow (6a), yellowish
green (6b), or dark green (7) solids, in ca. 80% (6a,b)
and 60% (7) yields. Thus, the replacement of the
effective electron donor Br- ligand by the much weaker
donor NCMe conceivably favors the nucleophilic attack
at the Cγ atom of the cumulenic chain of the diphenyl-
allenylidene complex. Moreover, the bromide may some-
how assist the N deprotonation.
Figure 1. Molecular structure of trans-[FeBr{-CtCCPh2-
(CN)}(depe)2] (5a).
In the IR spectra, the characteristic ν(NtC) and ν(Ct
C) vibrations are observed as medium- and strong-
intensity bands, respectively, at 2246 and 2048 (6a),
2239 and 2054 (6b), and 2247 and 2012 cm-1 (7a). The
ν(CtC) values are comparable with those quoted for Ru
alkynyl π-ligand complexes.33,80 in the 1H NMR spectra,
the presence of the methyl protons at the alkynyl ligand
is accounted for by the multiplet observed at δ ca. 2 (6
Η, N(CH3)2, 6a; 3 H, NH(CH3), 6b) or the doublet (2JHP
) 12 Hz) at δ 1.0 (P(CH3)3, 7a).
In accord with the trans geometry, in the 31P{1H}
NMR spectrum of complex 7, the four equivalent P
Figure 2. Molecular structure of the cation trans-[Fe-
(NCMe){-CtCCPh2(NMe2)}(depe)2]+ of compound 6a.
5
nuclei of depe are observed as a doublet (4P, JPP′ ) 5
Hz) at δ 70.3 and the PMe3 resonance as a quintet (1P,
5JP′P ) 6 Hz) at 31.9 ppm. The latter δ value shows a
significant shift from the value for free PMe3 (δ -60.8
ppm) and is comparable to those of some Ru π-ligand
complexes.33,80
In the FAB+-MS spectra of the cationic alkynyl
complexes, the molecular ion, [M]+, is not observed, but
their corresponding fragments derived from the step-
wise elimination of the amine (6a,b) or the phosphine
(7b) and the acetonitrile ligand, [M - NMe2 - NCMe]+
(m/z 659), [M - NHMe - NCMe]+ (m/z 659), or [M -
NCMe - PMe3]+ (m/z 658), respectively, are clearly
observed.
2. Crystal Structure Analyses. The molecular
structures of 5a and 6a (Figures 1 and 2 and Tables 1
and 2 for selected bond distances and angles, respec-
tively) were unambiguously established by X-ray dif-
fraction analyses.
For both molecules 5a and 6a, the overall geometry
around iron can be described as an octahedron with the
two diphosphine ligands chelating at the equatorial
positions. The axial positions are occupied by the
alkynyl ligand and a bromide (5a) or an acetonitrile (6a).
In the neutral complex 5a the metal-P distances are
slightly shorter (2.227(4)-2.246(4) Å) than those ob-
served for the cationic 6a (2.2411(14)-2.2919(15) Å), as
is known in other cases.81,82 The Fe-C distances
(1.877(11) Å (5a) and 1.929(5) Å (6a)) are not un-
In the 13C{1H} NMR spectra, the carbon atoms of the
alkynyl chain are also observed at much higher fields,
δ 119.0 (6a), 120.2 (6b), or 116.8 (7b) ppm (m, CR,
respectively), δ 110.7 (6a), 110.0 (6b), or 107.1 (7b) ppm
3
2
(qnt, JCP ) 28 (6a), 30 (6b) Hz; d, JCP′ ) 7 Hz (7b),
Câ), and δ 72.0 (6a), 66.6 (6b), or 65.7 (7b) ppm (qnt,
4JCP ) 1 (6a), 2 (6b) Hz; m (7b), Cγ), than for the alle-
nylidene precursor trans-[FeBr(dCdCdCPh2)(depe)2]+
(CR 305.5 ppm,, Cγ 244.9 ppm, and Câ 149.4 ppm).60 The
methylamine carbons, in the 13C{1H} NMR spectra,
occur as a broad singlet (6a and 6b) at δ ca. 40 ppm
which, in the 13C NMR spectra, splits into the expected
quartet, 1JCH ) ca. 134 Hz (quartet of quartets, 3JCH
)
+
5 Hz, for 6a). The -P(CH3)3 resonance appears as a
doublet (1JCP′ ) 41 Hz) at much higher field, 9.5 ppm,
and splits into the corresponding quartet (1JCH ) 128
Hz) of doublets in the 13C NMR spectrum. All of the
other resonances of the alkynyl and depe ligands have
also been assigned (see Experimental Section) in the 1H,
13C{1H} and 13C NMR spectra, including those of ipso,
ortho, meta, and para atoms of the phenyl rings.
(81) Hirano, M.; Akita, M.; Morikita, T.; Kubo, H.; Fukuoka, A.;
Komiya, S. J. Chem. Soc., Dalton Trans. 1997, 3453.
(82) Morikita, T.; Hirano, M.; Sasaki, A.; Komiya, S. Inorg. Chim.
Acta 1999, 291, 341.
(80) Cadierno, V.; Gamasa, M. P.; Gimeno, J.; Lo´pez-Gonza´lez, M.
C.; Borge, J.; Garc´ıa-Granda, S. Organometallics 1997, 16, 4453.

Allenylidene Iron(II) Complexes
Organometallics, Vol. 24, No. 19, 2005 4659
Table 1. Selected Bond Lengths (Å) and Angles
(deg) for the Complexes
Table 2. First Oxidation Potentiala of the
Complexes trans-[FeBr(L)(depe)2]n (1-3, L )
Allenylidene, n ) +1; 4, 5, 8, 9, L ) Alkynyl, n ) 0),
trans-[Fe(NCMe)(L)(depe)2]+ (6, L ) Alkynyl), and
trans-[Fe(NCMe)(L)(depe)2]2+ (7, L ) Phosphonium
Alkynyl) and Estimated PL and EL Parameters for
the Allenylidene and Alkynyl Ligands
trans-[FeBr{-CtCCPh2(CN)}(depe)2] (5a) and
trans-[Fe(NCMe){-CtCCPh2(NMe2)}(depe)2][BPh4]‚
C6H6 (6a‚C6H6)
5a
6a‚C6H6
C(1)-C(2)
C(1)-Fe(1)
C(2)-C(3)
C(3)-C(4)
C(3)-N(1)
C(4)-N(1)
C(5)-N(1)
C(6)-N(2)
C(6)-C(7)
Fe(1)-N(2)
P(1)-Fe(1)
P(2)-Fe(1)
P(3)-Fe(1)
P(4)-Fe(1)
Fe(1)-Br(1)
1.192(14)
1.877(11)
1.540(16)
1.48(2)
1.206(6)
1.929(5)
1.494(6)
ox a
b
c
complex
ligand
E1/2
PL
EL
1
CdCdC(Me)Ph
CdCdCPh2
0.93
0.97
-0.35
-0.32
-0.38
-1.34
-1.18
-1.35
-1.34
-1.08
-1.32
-1.25
0.42
0.45
2
1.496(6)
3
4
5a
6a
6b
7
CdCdCEt2
0.90
0.40
1.118(17)
1.470(6)
CtCC(dCHMe)Et
CtCCPh2(CtN)
CtCCPh2(NMe2)
CtCCPh2(NHMe)
CtCCPh2(P+Me3)
CtCCPh2(H)
-0.16
0.02
-0.40
-0.27
-0.49
-0.47
-0.28
-0.38
-0.33
1.471(6)
1.136(6)
0.47
1.461(6)
0.48
1.937(4)
0.74
2.246(4)
2.227(4)
2.240(4)
2.242(4)
2.527(3)
2.2411(14)
2.2528(15)
2.2886(14)
2.2919(15)
8
9
-0.13
-0.06
CtCC(dCH2)Ph
a Potential values in V ((0.02) vs SCE; they can be converted
to V vs NHE by adding 0.245 V. The first oxidation is followed, at
higher potential (ca. 0.7-1.3 V more anodic) by a second one,
reversible or irreversible, assigned to the FeIII/IV redox couple; for
ionic compounds with the [BPh4]- counterion, the oxidation waves
of this ion are observed at ca. 1.0 and 2.2 V. b Pickett’s electro-
chemical ligand parameter,94 in V, estimated from eq 1. c Lever’s
electrochemical ligand parameter,96 in V vs NHE, estimated from
C(2)-C(1)-Fe(1)
C(1)-C(2)-C(3)
C(2)-C(3)-N(1)
C(4)-C(3)-C(2)
N(1)-C(4)-C(3)
N(2)-C(6)-C(7)
C(1)-Fe(1)-N(2)
C(1)-Fe(1)-P(1)
C(1)-Fe(1)-P(2)
N(2)-Fe(1)-P(1)
N(2)-Fe(1)-P(2)
C(1)-Fe(1)-P(3)
N(2)-Fe(1)-P(3)
C(1)-Fe(1)-P(4)
N(2)-Fe(1)-P(4)
C(1)-Fe(1)-Br(1)
P(2)-Fe(1)-Br(1)
P(3)-Fe(1)-Br(1)
P(4)-Fe(1)-Br(1)
P(1)-Fe(1)-Br(1)
C(4)-N(1)-C(5)
176.1(11)
170.9(14)
175.2(4)
176.6(5)
109.1(4)
105.8(10)
178.4(16)
I
ox
178.6(6)
eq 2 and using E1/2 values vs NHE.
175.36(17)
89.12(13)
84.27(14)
94.46(11)
93.14(13)
92.59(14)
90.23(12)
86.28(13)
90.34(11)
90.3(4)
87.5(4)
88.4(4)
90.5(4)
179.2(4)
92.00(12)
92.20(12)
90.04(12)
89.16(11)
108.9(4)
113.8(4)
113.6(4)
176.5(4)
C(4)-N(1)-C(3)
C(5)-N(1)-C(3)
C(6)-N(2)-Fe(1)
usual,83,84 and the C(1)-C(2) alkynyl bond distances
(1.192(14) Å (5a) and 1.206(6) Å (6a)) clearly indicate a
triple-bond character and are comparable to those
observed in other alkynyl complexes.83,84
The X-ray analysis of 6a also revealed the expected
presence of a [BPh4]- anion together with a C6H6
molecule of crystallization, whose refinement gave large
anisotropic displacement parameters for all C atoms
which influenced the final R1 parameter. The presence
of the C6H6 molecule probably results from [BPh4]-
decomposition in acidic medium (note the liberation of
HBr in reactions 3 and 4 of Scheme 2), a possible85,86
type of reaction shown to occur in other cases.
3. Electrochemical Behavior. Interestingly, the
alkynyl complex trans-[FeBr{-CtCCPh2(H)}(depe)2]
(8), previously obtained60 by nucleophilic hydride addi-
tion at trans-[FeBr(dCdCdCPh2)(depe)2][BPh4], can
also be formed upon electrochemical reduction of the
Figure 3. Cyclic voltammograms for a solution of trans-
[FeBr(dCdCdCPh2)(depe)2]+ (2; c ) 0.48 × 10-3 M) in 0.2
M [NBu4][BF4]/CH2Cl2, recorded at a scan rate of 0.2 V s-1
,
at a Pt-disk working electrode: (a) before the controlled-
potential electrolysis; (b) after exhaustive controlled-
potential electrolysis at ca. -1.5 V vs SCE.
(83) Field, L. D.; Turnbull, A. J.; Turner, P. J. Am. Chem. Soc. 2002,
124, 3692.
(84) Buys, I. E.; Field, L. D.; George, A. V.; Hambley, T. W. Aust. J.
Chem. 1997, 50, 159.
(85) Almeida, S. S. P. R.; Guedes da Silva, M. F. C.; Frau´sto da Silva,
J. J. R.; Pombeiro, A. J. L. J. Chem. Soc., Dalton Trans. 1999, 467.
(86) Amrhein, P. I.; Lough, A. J.; Morris, R. H. Inorg. Chem. 1996,
35, 4523.
latter compound. This complex exhibits (Figure 3a), by
cyclic voltammetry (CV) in 0.2 M [NBu4][BF4]/CH2Cl2,
a single-electron reversible reduction wave (I) at IE1/2
red
) -0.63 V vs SCE which is followed, at a lower

4660 Organometallics, Vol. 24, No. 19, 2005
Scheme 3. Cathodic Behavior of trans-[FeBr(dCdCdCPh2)(depe)2]+ (2)
Venaˆncio et al.
potential, by a single-electron irreversible reduction
wave (II) (IIEpred ) -1.53 V, measured at a scan rate of
0.2 V s-1). The reduction process at wave II generates
a product (see below) that is oxidized at the anodic wave
III.
the final alkynyl complex, consists of a proton addition,
conceivably from traces of moisture in the electrolytic
medium.
The observed cathodic process is quite distinct from
the electron-transfer-induced C-C coupling reactions
known87-91 to occur in some cases with vinylidene and
other cumulenylidene ligands.
In contrast to the above ligand-based irreversible
reductions, both the allenylidene and the alkynyl com-
plexes undergo metal-centered reversible one-electron
oxidations (FeII/III redox couple), in accord with the
reported studies for related iron(II) nitrile92 and isocya-
nide12 complexes and for ruthenium(II) allenylidene
compounds.27,44 The first reversible oxidation is followed,
at a higher potential (at least 0.7 V more anodic), by a
second one, reversible or irreversible, assigned to the
FeIII f FeIV oxidation, which was not further investi-
gated. The anodic behavior has been preliminarily
reported93 for complexes 1-3 and 8.
Exhaustive controlled-potential electrolysis (CPE) of
a CH2Cl2 solution of trans-[FeBr(dCdCdCPh2)(depe)2]-
[BPh4] at the potential of the reduction wave II con-
sumes 2 F/mol of complex and leads to the formation of
the neutral alkynyl product trans-[FeBr{-CtCCPh2-
(H)}(depe)2] (8). This is indicated by the following
evidence: (i) detection, in the electrolyzed solution, of
ox
a reversible oxidation wave (III, Figure 3b) at an E1/2
value identical with that (-0.13 V) observed for 8, (ii)
detection, by 31P{1H} NMR of the electrolyzed solution,
of a singlet at a chemical shift (70.3 ppm) identical with
that of 8, and (iii) similarity of the colors (both are
orange) of the electrolyzed solution and of a genuine
solution of 8 (along the electrolysis, the electrolytic
solution color gradually changes from dark blue, that
of the starting allenylidene complex, to orange, i.e., that
of the final product 8).
The cathodic conversion of trans-[FeBr(dCdCdCPh2)-
(depe)2][BPh4] into trans-[FeBr{-CtCCPh2(H)}(depe)2]
(8) follows an overall 2e-/H+ process (Scheme 2, reaction
6) which is believed to involve the initial formation of
the neutral radical trans-[FeBr(CCCPh2)(depe)2] (a)
derived from the first electron transfer. The reversibility
of the reduction wave I of trans-[FeBr(dCdCdCPh2)-
(depe)2][BPh4] (Figure 3a and Scheme 3) indicates that
this radical (a) is stable in the cyclic voltammetric time
scale. The unpaired electron in a is expected to be
located on the terminal trisubsituted carbon atom (Cγ)
of the cumulene chain, i.e. trans-[FeBr(-CtCCPh2)-
(depe)2] (a), as proved by others44 by EPR for the related
one-electron reductions of the metallacumulenes trans-
[RuCl(dCdCdCR2)(dppe)2][PF6] (R ) Me, Ph) and
trans-[RuCl(dCdCdCdCdCPh2)(dppe)2][PF6].
The neutral species a undergoes a further one-
electron reduction at a lower potential (wave II, Figure
3a and Scheme 3), leading to the corresponding anionic
species, which is unstable. The latter undergoes a
chemical reaction (irreversible wave II) to give the
alkynyl product trans-[FeBr{-CtCCPh2(H)}(depe)2]
(8), whose formation is detected by cyclic voltammetry
(oxidation wave III) upon scan reversal following a
cathodic scan comprising the reduction wave II. The
chemical reaction at the cathodic process of wave II, i.e.,
the conversion of the anionic species formed therein into
The first oxidation potential values (E1/2ox) are listed
in Table 2 and follow the overall order cationic alle-
nylidene-bromo complexes 1-3 (0.97-0.90 V vs SCE)
> cationic alkynyl-acetonitrile complexes 7 and 6a,b,
(0.74-0.47 V vs SCE) > neutral alkynyl-bromo com-
plexes 4, 5a, and 8 (0.02 to -0.16 V vs SCE). This is in
agreement with the expected stronger electron donor
character of the formally anionic alkynyl and bromide
ligands in comparison with the neutral ligated alle-
nylidenes (see also below).
3.1. Estimate of Electrochemical Ligand Param-
eters. The measured oxidation potentials (E1/2ox) of the
above complexes viewed as closed-shell octahedral-type
complexes [MSL] with the allenylidene or alkynyl ligand
L bound to the 16-electron {MS} ) trans-{FeBr(depe)2}+
site (complexes 1, 2, 3a, 4, 5a, and 8) or {MS} ) trans-
{Fe(NCMe)(depe)2}2+ center (6a,b and 7b) allows us to
(87) Valyaev, D. A.; Semeikin, O. V.; Ustynyuk, N. A. Coord. Chem.
Rev. 2004, 248, 1679.
(88) Rigaut, S.; Touchard, D.; Dixneuf, P. H. Coord. Chem. Rev.
2004, 248, 1585.
(89) Venkatesan, K.; Blacque, O.; Fox, T.; Montserrat, A.; Schmalle,
H. W.; Berke, H. Organometallics 2004, 23, 1183.
(90) Bonomo, L.; Stern, C.; Solari, E.; Scopelliti, R.; Floriani, C.
Angew. Chem., Int. Ed. 2001, 40, 1449.
(91) Connely, N. G. In Molecular Electrochemistry of Inorganic,
Bioinorganic and Organometallic Compounds; NATO ASI Series 385;
Kluwer Academic: Dordrecht, The Netherlands, 1993; p 317.
(92) Guedes da Silva, M. F. C.; Martins, L. M. D. R. S.; Pombeiro,
A. J. L. Collect. Czech. Chem. Commun. 2001, 66, 139.
(93) (a) Venaˆncio, A. I. F.; Martins, L. M. D. R. S.; Pombeiro, A. J.
L. Port. Electrochim. Acta 2001, 19, 361. (b) Venaˆncio, A. I. F.; Martins,
L. M. D. R. S.; Pombeiro, A. J. L. Port. Electrochim. Acta 2003, 21, 85.

Allenylidene Iron(II) Complexes
Organometallics, Vol. 24, No. 19, 2005 4661
estimate, for the allenylidene and alkynyl ligands, the
electrochemical PL ligand parameter. This has been
defined by Pickett et al.94 as the shift of the Cr0
oxidation potential upon replacement of one CO ligand
in [Cr(CO)6] by the ligand L under consideration and
constitutes a measure of the net π-electron acceptor
minus σ-donor character of the ligand. By applying the
-0.38 V, EL ) 0.40 V vs NHE) g alkylphenylalle-
nylidene CdCdC(Me)Ph (PL ) -0.35 V, EL ) 0.42 V vs
NHE) g diphenylallenylidene CdCdCPh2 (PL ) -0.32
V, EL ) 0.45 V vs NHE).
The alkynyls and the enynyl are the strongest net
electron donors, and they can be even more effective
than phenylalkynyl CtCPh (PL ) -1.22 V)98 or bromide
(PL ) -1.17 V).94 However, those complexes with the
electron-acceptor cyano or phosphonium groups are not
strong electron donors, the former behaving similarly
to bromide or NCO- (PL ) -1.17 or -1.16 V, respec-
tively)94 and the latter being a slightly weaker electron
donor.
The allenylidenes are much weaker net electron
donors: i.e., they present a higher net π-electron ac-
ceptor minus σ-donor ability which is even slightly
stronger than that of organonitriles (with PL values in
the range from -0.44 to -0.55 V, at the same metal
center92). However, they behave as significantly less
effective net π-electron acceptors than vinylidenes Cd
CHR (PL ) -0.21 to -0.27 V for R ) H, alkyl, aryl)68
and are much weaker than carbonyl (PL ) 0 V),
aminocarbyne (PL ) +0.09 V),99 or carbyne CCH2R (PL
) +0.21 to +0.23 V for R ) H, alkyl, aryl).68,69,98 Hence,
such ligands can be ordered as follows on account of
their net π-electron acceptance: NtCR < CdCdCRR′
< CdCHR < CO < C+NH2 < CCH2R.
ox
linear relationship (1)94 between E1/2 and PL to our
complexes and considering the known values of the
electron richness (ES) and polarizability (â) for their
iron(II) binding site (ES ) 1.32 V, â ) 1.10 for the former
site92 and ES ) 1.81 V, â ) 0.99 for the latter site95), we
have estimated the PL values for those ligands (Table
2).
E1/2ox[MSL] ) ES + âPL
(1)
Another redox potential parametrization approach for
octahedral complexes was developed by Lever,96 who
proposed the linear relationship (2), in which the redox
potential (in volts vs NHE) of a complex is related to
electrochemical parameters determined by the ligands
and the metal redox center. ∑EL is the sum of the values
E1/2ox ) IM + S ( E ) (V vs NHE)
(2)
∑
M
L
of the EL ligand parameter for all the ligands, SM and
IM are the slope and intercept, respectively (dependent
upon the metal, redox couple, spin state, and stereo-
chemistry). The EL values were normally obtained96
through a statistical analysis of the reported redox
potentials of the large number of known complexes with
the standard RuIII/II redox couple (for which ideally IM
) 0 and SM ) 1) and the possible ligands.
Within the allenylidene ligands, the observed order
of PL or EL values follows the expected net π-electron
acceptance, i.e. CdCdCEt2 < CdCdC(Me)Ph < CdCd
CPh2.
Conclusions
Alkyl, aryl, or mixed alkyl/aryl allenylidene (CdCd
CRR′) complexes of Fe(II) can be readily obtained from
reaction of the dibromo complex trans-[FeBr2(depe)2]
with the appropriate alkynol. They can behave either
as (i) a Brønsted acid when they present an alkyl (R)
group which undergoes deprotonation or as (ii) a Lewis
acid (when R, R′ ) aryl) adding, at Cγ, various nucleo-
philes. The former type of behavior (i) provides an easy
entry to enynyl species
From the application of eq 2 to our complexes (with
oxidation potentials converted to volts vs NHE) and the
knowledge of IM (-0.57 in V vs NHE) and SM (1.32) for
the FeII/FeIII redox center92 and of EL for the various
coligands96 (-0.22, 0.34, 0.28 for Br-, NCMe, and depe,
respectively), we have obtained the EL values for the
various allenylidene and alkynyl ligands indicated in
Table 2.
The PL and EL ligand parameters are normally related
(except for strong π-acceptor ligands, e.g. CO,96 isocya-
nides,96,97 and carbynes68) by the empirical equation (3),
also proposed by Lever,96 which generally also reason-
ably fits our data.
with an extra (ene) functional site available for further
reactivity. The latter behavior (ii) allows the preparation
of a variety of neutral or mono- or dicationic alkynyl
species
PL (V) ) 1.17EL - 0.86
(3)
As indicated by their PL and EL values, the L ligands
can be ordered as follows according to their net electron
donor character: alkynyls and aminoalkynyls CtCCPh2-
(R) (R ) H, NHMe, NMe2), alkylenynyl CtCC(dCHMe)-
Et (PL ) -1.35 to -1.32 V; EL ) -0.49 to -0.38 V vs
NHE) > phenylenynyl CtCC(dCH2)Ph (PL ) -1.25 V,
EL ) -0.33 vs NHE) > cyanoalkynyl CtCCPh2(CtN)
(PL ) -1.18 V, EL ) -0.27 V vs NHE) > phosphonium
alkynyl CtCCPh2(P+Me3) (PL ) -1.08 V, EL ) -0.28
functionalized at the Cγ with a cyano, alkoxy, amino,
or phosphonium group (X).
The labile bromide ligand in a trans position can also
play an active role by assisting the addition of the
nucleophile (amine or phosphine) upon replacement by
acetonitrile, a weaker electron donor. For a sufficiently
strong nucleophile, such as cyanide or methoxide, the
addition occurs without requiring bromide displace-
ment.
V vs NHE) . dialkylallenylidene CdCdCEt2 (PL
)
(94) Chatt, J.; Kan, C. T.; Leigh, G. J.; Pickett, C. J.; Stanley, D. R.
J. Chem. Soc., Dalton Trans. 1980, 2032.
(95) Martins, L. M. D. R. S. Ph.D. Thesis, IST, 1996; Chapter 2.
(96) Lever, A. B. P. Inorg. Chem. 1990, 29, 1271.
(98) Pombeiro, A. J. L. New J. Chem. 1997, 21, 649.
(99) Lemos, M. A. N. D. A.; Pombeiro, A. J. L. J. Organomet. Chem.
1988, 356, C79.
(97) Facchin, G.; Mozzon, M.; Michelin, R. A.; Ribeiro, M. T. A.;
Pombeiro, A. J. L. J. Chem. Soc., Dalton Trans. 1992, 2827.

4662 Organometallics, Vol. 24, No. 19, 2005
Venaˆncio et al.
Data for compound 1 are as follows. Anal. Calcd for C30H56-
BF4BrP4Fe: C, 47.2; H, 7.4. Found: C, 46.8; H, 7.8. IR (KBr,
cm-1): ν(CdCdC) 1897 (m).
Data for compound 2 are as follows. Anal. Calcd for C35H58-
BF4BrP4Fe: C, 50.9; H, 7.1. Found: C, 50.6; H, 7.1. IR (KBr,
cm-1): ν(CdCdC) 1880 (m).
The type of reactivity of the diphenylallenylidene
ligand can be reversed on reduction of the complex: i.e.,
the Cγ character changes from electrophilic to basic,
undergoing protonation via a 2e-/H+ process to yield an
alkynyl
The preparation of 3 is as follows. To a stirred solution of
trans-[FeBr2(depe)2] (0.200 g, 0.318 mmol) in MeOH (50 mL),
under dinitrogen and at room temperature, was added an
excess (molar ratio 2:1) of a methanolic solution of the HCt
CCEt2(OH) alkynol (0.636 mmol in 10 mL). The solution was
stirred at 40 °C for ca. 3-4 h, and during this time its color
changed from pale green to dark red. Addition of a MeOH
solution (10 mL) of Na[BF4] (0.038 g, 0.350 mmol) or Na[BPh4]
(0.120 g, 0.350 mmol) led to the precipitation, as a dark red
solid, of the allenylidene compound 3a or 3b, respectively. It
was separated by filtration, recrystallized from CH2Cl2/Et2O,
and dried in vacuo. Yield: 34% (0.078 g) for 3a and 44% (0.136
g) for 3b.
derivative, thus disclosing the synthetic significance of
electrochemical methods to achieve electron-transfer-
induced reactions. These methods can also be applied
to investigate the electronic properties of the alle-
nylidene, enynyl, and alkynyl ligands by allowing the
estimation of their electrochemical PL and EL ligand
parameters and thus to compare their net π-electron-
acceptor/σ-electron-donor characters (also with those of
related ligands). The following order of such a character
has thus been established alkynyls, aminoalkynyls,
enynyls < cyanoalkynyl, Br-, NCO- < phosphonium
alkynyl , NCR < dialkylallenylidene e alkylphenyl-
allenylidene e diphenylallenylidene < vinylidenes < CO
< amonicarbyne (CNH2) < carbynes (CCH2R).
Data for 3a are as follows. Anal. Calcd for C27H58BF4BrP4-
Fe: C, 44.5; H, 8.0. Found: C, 44.3; H, 8.1. IR (KBr, cm-1):
ν(CdCdC) 1908 (m).
Data for 3b are as follows. Anal. Calcd for C51H78BBrP4Fe:
C, 62.0; H, 8.4. Found: C, 61.9; H, 8.6. IR (KBr, cm-1): ν(Cd
CdC) 1907 (m). 1H NMR (CDCl3): δ 7.29 (m, 8H, Ho from
BPh4-), 6.99 (t, JHH ) 7.1 Hz, 8H, Hm from BPh4-), 6.85 (t,
JHH ) 6.8 Hz, 4H, Hp from BPh4-), 2.43 (dq, JHP ) 13.8, JHH
Experimental Section
1
) 6.9 Hz, 4H,
/ (CH3CH2)2PCH2CH2P(CH2CH3)2), 2.08 (m,
4
4H, 1/2(CH3CH2)2PCH2CH2P(CH2CH3)2), 1.84 (m, 4H, 1/2(CH3-
CH2)2PCH2CH2P(CH2CH3)2), 1.77-1.59 (m, 16H, CdCdC(CH2-
Me)2 and 3/4(CH3CH2)2PCH2CH2P(CH2CH3)2), 1.29-1.07 (m,
30H, CdCdC(CH2CH3)2 and (CH3CH2)2PCH2CH2P(CH2CH3)2).
31P{1H} NMR (CDCl3): δ 56.0 ppm (s). 13C{1H} NMR: δ 307.4
(m, CR), 219.6 (m, Cγ or Câ), 170.7 (m, Câ or Cγ), 164.1 (q, 1JCB
) 49 Hz, Ci from BPh4-), 136.0 (s, Cm from BPh4-), 125.8 (m,
Co from BPh4-), 121.9 (s, Cp from BPh4-), 41.2 (qnt, JCP ) 2
Hz, CdCdC(CH2Me)2), 21.7 (qnt, JCP ) 6 Hz, 1/2(CH3-
CH2)2PCH2CH2P(CH2CH3)2), 20.0 (qnt, JCP ) 11 Hz, (CH3CH2)2-
PCH2CH2P(CH2CH3)2), 19.6 (qnt, JCP ) 6 Hz, 1/2(CH3CH2)2-
PCH2CH2P(CH2CH3)2), 11.2 (qnt, JCP ) 2 Hz, CdCdC(CH2-
CH3)2), 9.7 (s, 1/2(CH3CH2)2PCH2CH2P(CH2CH3)2), 9.3 (s, 1/2(CH3-
CH2)2PCH2CH2P(CH2CH3)2). 13C NMR: δ 307.4 (m), 219.6 (m),
170.7 (m), 164.1 (q), 136.0 (dt, 1JCH ) 153, 2JCH ) 6 Hz), 125.8
(dm, 1JCH ) 153 Hz), 121.9 (dt, 1JCH ) 158, 2JCH ) 7 Hz), 41.2
All the manipulations and reactions were carried out in the
absence of air using standard inert-gas-flow and high-vacuum
techniques. Solvents were purified and dried by standard
methods and freshly distilled under dinitrogen. The complex
trans-[FeBr2(depe)2] was prepared by a published method,100,101
and the alkynols were used as purchased from Aldrich. The
IR spectra (4000-400 cm-1) were recorded on a Bio-Rad FTS
3000MX instrument in KBr pellets and the NMR spectra (run
in CD2Cl2 unless stated otherwise) on a Varian UNITY 300
1
spectrometer at room temperature. H, 13C, and 13C{1H} and
31P{1H} chemical shifts (δ) are reported in ppm relative to TMS
and H3PO4, respectively. In the 13C NMR data, assignments
and coupling constants common to the 13C{1H} NMR spectra
are not repeated. Abbreviations: s ) singlet; d ) doublet; t )
triplet; q ) quartet; qnt ) quintet; dq ) doublet of quartets;
dd ) doublet of doublets; dt ) doublet of triplets; dm ) doublet
of multiplets; tqnt ) triplet of quintets; tm ) triplet of
multiplets; qq ) quartet of quartets; qqnt ) quartet of
quintets; qm ) quartet of multiplets; m ) multiplet; b ) broad.
C, H, and N elemental analyses were carried out by the
Microanalytical Service of the Instituto Superior Te´cnico.
Positive-ion FAB mass spectra were obtained on a Trio 2000
instrument by bombarding 3-nitrobenzyl alcohol matrixes of
the samples with 8 keV (ca. 1.28 × 10-15 J) of Xe atoms.
Nominal molecular masses were calculated using the isotopes
56Fe and 79Br. However, further complexity due to addition
(from matrix) or loss of hydrogen was not taken into account.
Mass calibration for data system acquisition was achieved
using CsI.
Linear Allenylidene Complexes trans-[FeBr(dCdCd
CRR′)(depe)2][Y] (R ) Me, R′ ) Ph, Y ) BF4 (1); R ) R′ )
Ph, Y ) BF4 (2); R ) R′ ) Et, Y ) BF4 (3a), BPh4 (3b)).
Complexes 1 and 2 were obtained according to the procedure
described in a previous work,60 but by using Na[BF4] instead
of Na[BPh4], and these products were recrystallized from CH2-
Cl2/Et2O to give dark blue solids. Yield: 58% (0.070 g) for 1
and 50% (0.065 g) for 2. NMR spectra of the complex cations
are identical with those60 of the corresponding compounds with
[BPh4]- as the counterion.
1
1
1
(tm, JCH ) 128 Hz), 21.7 (tm, JCH ) 130 Hz), 20.0 (tm, JCH
1
) 133 Hz), 19.6 (m), 11.2 (m), 9.7 (q, JCH ) 127 Hz), 9.3 (q,
1JCH ) 130 Hz). FAB+-MS (m/z): 641 [M]+, 562 [M - Br]+,
547 [M - (dCdCdCEt2)]+, 435 [M - depe]+, 341 [M - depe -
(dCdCdCEt2)]+.
Enynyl Complex trans-[FeBr{-CtCC(dCHMe)Et}-
(depe)2] (4). To a solution containing the diethylallenylidene
compound trans-[FeBr(dCdCdCEt2)(depe)2][BPh4] (0.200 g,
0.201 mmol) in CH2Cl2 (40 mL) was added NaOMe in a 2-fold
molar amount (0.021 g, 0.402 mmol). The solution was stirred,
at room temperature and under dinitrogen, for 2 h and its color
changed from dark red to pink. The solvent was removed in
vacuo, yielding an oily residue. Extraction with diethyl ether
followed by filtration, concentration, and cooling at ca. -20
°C resulted in the precipitation of 4 as a crystalline pink solid.
This precipitate was isolated by filtration and dried in vacuo.
Yield: 85% (0.113 g).
Data for 4 are as follows. Anal. Calcd for C27H57BrP4Fe: C,
51.3; H, 9.4. Found: C, 50.9; H, 9.8. IR (KBr, cm-1): ν(C≡C)
2024 (s), ν(CdC) 1610 (m). 1H NMR (C6D6): δ 5.14 (q, J ) 6.5
Hz, 1H, -CtCC(dCHMe)Et), 2.54 (dq, JHP ) 15.2 and J )
1
7.6 Hz, 8H, /2(CH3CH2)2PCH2CH2P(CH2CH3)2), 2.08 (q, J )
7.8 Hz, 2H, -CtCC(dCHMe)(CH2Me)), 1.88 (d, J ) 6.9 Hz,
1
3H, -CtCC(dCHCH3)Et), 1.86-1.71 (m, 12H, /4(CH3CH2)2-
PCH2CH2P(CH2CH3)2 and (CH3CH2)2PCH2CH2P(CH2CH3)2),
(100) Evans, D. J.; Henderson, R. A.; Hills, A.; Hughes, D. L.; Oglive,
K. E. J. Chem. Soc., Dalton Trans. 1992, 1259.
(101) Wold, A.; Ruff, J. K. Inorg. Synth. 1973, 14, 102.
1
1.63 (dq, JHP ) 15.4 and J ) 7.7 Hz, 4H, /4(CH3CH2)2PCH2-
CH2P(CH2CH3)2), 1.11 (m, 27H, (CH3CH2)2PCH2CH2P(CH2CH3)2

Allenylidene Iron(II) Complexes
Organometallics, Vol. 24, No. 19, 2005 4663
and -CtCC(dCHMe)(CH2CH3)). 31P{1H} NMR (C6D6):
δ
alkynyl complex 5b is converted into the respective alle-
nylidene, even in the solid state. For these reasons it was not
possible to obtain an analytically pure sample for elemental
analysis and the reaction yield could not be estimated.
Data for 5b are as follows. IR (KBr, cm-1): ν(CtC) 2087
(m). 1H NMR: δ 7.60-6.85 (m, Ho, Hm, Hp from alkynyl,
partially overlapped with the [BPh4]- impurity resonance),
70.1 ppm (s). 13C{1H} NMR (C6D6): δ 132.5 (qnt, JCP ) 28 Hz,
CR), 131.2 (qnt, JCP ) 2 Hz, Cγ or Câ), 122.5 (m, Câ or Cγ), 118.6
5
(m, -CtCC(dCHMe)Et), 33.9 (qnt, JCP
)
2
Hz,
-CtCC(dCHMe)(CH2Me)), 21.6 (qnt, JCP ) 11 Hz, (CH3-
CH2)2PCH2CH2P(CH2CH3)2), 21.3-21.0 (m, (CH3CH2)2PCH2-
CH2P(CH2CH3)2), 16.0 (s, -CtCC(dCHCH3)Et), 15.2 (s, -Ct
1
1
CC(dCHMe)(CH2CH3)), 11.0 (qnt, JCP ) 2 Hz, /2(CH3CH2)2-
2.24 (dq, JHP ) 16.0 and J ) 8.0 Hz, 4H, /4(CH3CH2)2PCH2-
PCH2CH2P(CH2CH3)2), 10.4 (qnt, JCP ) 2 Hz, 1/2(CH3CH2)2-
PCH2CH2P(CH2CH3)2). 13C NMR (C6D6): δ 132.5 (qnt), 131.2
3
CH2P(CH2CH3)2), 2.20-1.32 (m, 23H,
/ (CH3CH2)2PCH2-
4
CH2P(CH2CH3)2, (CH3CH2)2PCH2CH2P(CH2CH3)2 and OCH3),
1.13 (m, 12H, 1/2(CH3CH2)2PCH2CH2P(CH2CH3)2), 1.11 (m,
12H, 1/2(CH3CH2)2PCH2CH2P(CH2CH3)2. 31P{1H} NMR: δ 66.1
ppm (s). 13C{1H} and 13C NMR spectra could not be obtained,
due to the instability of the compound. FAB+-MS (m/z): 767
[M]+, 737 [M - OMe]+, 688 [M - Br]+, 547 [M - (-CtCCPh2-
(OMe))]+, 341 [M - depe - (-CtCCPh2(OMe))]+.
Cationic Alkynyl Complexes trans-[Fe(NCMe){-Ct
CCPh2(X)}(depe)2][BPh4] (X ) NMe2 (6a), NHMe (6b)). 6a
was prepared as follows. The allenylidene complex trans-
[FeBr(dCdCdCPh2)(depe)2][BPh4] (0.200 g, 0.189 mmol) was
dissolved in a minimum of NCMe (ca. 10 mL), and an excess
of a 40% aquous solution of dimethylamine (6 mL, 0.048 mol)
was added. The color of the solution changed from dark blue
to green, and after 30-60 min we observed the formation of a
green suspension from which complex 6a was separated by
filtration as a crystalline green-yellow solid, which was dried
in vacuo. Yield: 90% (0.180 g).
1
1
(m), 122.5 (m), 118.6 (dm, JCH ) 152 Hz), 33.9 (tm, JCH
)
1
1
126 Hz), 21.6 (tm, JCH ) 124 Hz), 21.3-21.0 (tm, JCH ) 128
Hz), 16.0 (qd, 1JCH ) 125, 2JCH ) 5 Hz), 15.2 (qts, 1JCH ) 124,
2JCH ) 4 Hz), 11.0 (qm, JCH ) 127 Hz), 10.4 (qm, JCH ) 127
Hz). FAB+-MS (m/z): 640 [M]+, 561 [M - Br]+, 547 [M - (-Ct
CC(dCHMe)Et)]+, 434 [M - depe]+, 341 [M - depe - (-Ct
CC(dCHMe)Et)]+.
1
1
NeutralAlkynylComplexestrans-[FeBr(-CtCCPh2R′′)-
(depe)2] (R′′ ) CN (5a), OMe (5b)). 5a was prepared as
follows. To a solution of trans-[FeBr(dCdCdCPh2)(depe)2]-
[BPh4] (0.200 g, 0.189 mmol) in CH2Cl2 (20 mL) was added a
CH2Cl2 solution (2 mL) of [NBu4]CN (0.079 g, 0.284 mmol).
The color of the solution changed immediately from dark blue
to pink, and the mixture was stirred at room temperature for
30 min. It was taken to dryness by evaporation of the solvent
in vacuo, resulting in an oily product. Extraction with diethyl
ether followed by filtration, concentration, and cooling to ca.
-18 °C led to precipitation of a pink solid of 5a ,which was
separated by filtration and dried in vacuo. Yield: 80% (0.116
g).
Data for 6a are as follows. Anal. Calcd for C63H87N2P4Fe:
C, 71.2; H, 8.2; N, 2.6%. Found: C, 71.3; H, 8.5; N, 2.2%. IR
1
(KBr, cm-1): ν(NtC) 2246 (m), ν(CtC) 2048 (s). H NMR: δ
7.35 (m, 12H, Ho from BPh4- and alkynyl), 7.20 (t, J ) 7.4 Hz,
4H, Hm from alkynyl), 7.00 (t, J ) 6.9 Hz, 2H, Hp from alkynyl),
6.99 (t, J ) 7.4 Hz, 8H, Hm from BPh4-), 6.85 (t, J ) 7.2 Hz,
4H, Hp from BPh4-), 2.22 (dq, JHP ) 15.6 and J ) 7.8 Hz, 4H,
1/4(CH3CH2)2PCH2CH2P(CH2CH3)2), 1.96 (m, 6H, N(CH3)2),
1.83 (m, 4H, 1/2(CH3CH2)2PCH2CH2P(CH2CH3)2), 1.64-1.54 (m,
16H, 3/4(CH3CH2)2PCH2CH2P(CH2CH3)2 and 1/2(CH3CH2)2-
PCH2CH2P(CH2CH3)2), 1.13 (m, 27H, (CH3CH2)2PCH2CH2P-
(CH2CH3)2 and NCCH3). 31P{1H} NMR: δ 70.3 ppm (s). 13C{1H}
Data for 5a are as follows. Anal. Calcd for C36H58NBrP4Fe:
C, 54.3; H, 7.4; N, 1.7%. Found: C, 54.0; H, 8.2; N, 1.6. IR
(KBr, cm-1): ν(CtN) 2229 (w), ν(CtC) 2043 (s). 1H NMR
(C6D6): δ 7.53 (d, J ) 7.5 Hz, 4H, Ho from alkynyl), 7.04 (t, J
) 7.4 Hz, 4H, Hm from alkynyl), 6.95 (t, J ) 7.0 Hz, 2H, Hp
from alkynyl), 2.48 (dq, JHP ) 15.4 and J ) 7.7 Hz, 4H,
1/4(CH3CH2)2PCH2CH2P(CH2CH3)2), 2.25 (dq, JHP ) 15.2 and
J ) 7.6 Hz, 4H, 1/4(CH3CH2)2PCH2CH2P(CH2CH3)2), 1.82-1.62
(m, 12H, 1/4(CH3CH2)2PCH2CH2P(CH2CH3)2 and (CH3CH2)2-
PCH2CH2P(CH2CH3)2), 1.52 (dq, JHP ) 15.0 and J ) 7.5 Hz,
4H, 1/4(CH3CH2)2PCH2CH2P(CH2CH3)2), 1.07 (m, 12H, 1/2(CH3-
CH2)2PCH2CH2P(CH2CH3)2, 1.05 (m, 12H, 1/2(CH3CH2)2PCH2-
CH2P(CH2CH3)2. 31P{1H} NMR (C6D6): δ 67.7 ppm (s). 13C{1H}
NMR (C6D6): δ 144.1 (m, Ci), 132.0 (qnt, JCP ) 27 Hz, CR),
129.1 (s, Co), 127.9 (s, Cp), 127.8 (s, Cm), 122.2 (qnt, JCP ) 1
Hz, CN), 110.8 (m, Câ), 49.8 (m, Cγ), 21.6 (qnt, JCP ) 12 Hz,
(CH3CH2)2PCH2CH2P(CH2CH3)2), 21.1 (qnt, JCP ) 4 Hz, (CH3-
CH2)2PCH2CH2P(CH2CH3)2), 11.0 (qnt, JCP ) 2 Hz, 1/2(CH3-
CH2)2PCH2CH2P(CH2CH3)2), 10.4 (qnt, JCP ) 2 Hz, 1/2(CH3-
CH2)2PCH2CH2P(CH2CH3)2). 13C NMR (C6D6): δ 144.1 (m),
132.0 (qnt), 129.1 (dd, JCH ) 168, JCH ) 1 Hz), 127.9 (dm,
partially overlapped with the solvent resonance), 127.8 (dm,
1JCH ) 158 Hz), 122.2 (m), 110.8 (m), 49.8 (m), 21.6 (m), 21.1
(tm, 1JCH ) 128 Hz), 11.0 (qm, 1JCH ) 127 Hz), 10.4 (qm, 1JCH
) 127 Hz). FAB+-MS (m/z): 763 [M]+, 737 [M - CN]+, 684 [M
- Br]+, 557 [M - depe]+, 547 [M - (-CtCCPh2(CN))]+, 341
[M - depe - (-CtCCPh2(CN))]+.
5b was prepared as follows. To a MeOH solution (30 mL) of
the allenylidene complex trans-[FeBr(dCdCdCPh2)(depe)2]-
[BPh4] (0.200 g, 0.189 mmol) was added a MeOH solution (5
mL) of NaOMe (0.122 g, 226.9 mmol), and the system was
stirred at room temperature and kept under dinitrogen for ca.
6 h. The color changed gradually from dark blue to dark violet.
The solution was cooled to ca. -18 °C, leading to the precipita-
tion of a red solid, which was separated by filtration and dried
in vacuo. 1H and 31P{1H} NMR and IR spectroscopic analyses
revealed that this solid is the trans-[FeBr{-CtCCPh2(OMe)}-
(depe)2] alkynyl complex 5b contaminated with Na[BPh4].
Recrystallization from CH2Cl2 leads to decomposition into the
starting material trans-[FeBr(dCdCdCPh2)(depe)2][BPh4]. It
was also proved (by 1H and 31P{1H} NMR and IR) that the
NMR: δ 164.4 (q, JCB ) 49 Hz, Ci from BPh4-), 143.5 (bs, Ci
1
from alkynyl), 136.2 (s, Cm from BPh4-), 128.8 (s, Cm from
alkynyl), 128.0 (bs, NCMe), 127.4 (s, Co from alkynyl), 126.3
2
(s, Cp from alkynyl), 125.9 (q, JCB ) 3 Hz, Co from BPh4-),
122.0 (s, Cp from BPh4-), 119.0 (m, CR or Câ), 110.7 (qnt, JCP
4
) 28 Hz, Câ or CR), 72.0 (qnt, JCP ) 1 Hz, Cγ), 40.4 (bs,
N(CH3)2), 20.8 (qnt, JCP ) 11 Hz, (CH3CH2)2PCH2CH2P(CH2-
CH3)2), 19.7 (qnt, JCP ) 6 Hz, 1/2(CH3CH2)2PCH2CH2P(CH2-
CH3)2), 19.5 (qnt, JCP ) 4 Hz, 1/2(CH3CH2)2PCH2CH2P(CH2-
CH3)2), 9.6 (m, 1/2(CH3CH2)2PCH2CH2P(CH2CH3)2), 9.4 (m,
1/2(CH3CH2)2PCH2CH2P(CH2CH3)2), 4.2 (s, NCCH3). 13C NMR:
1
2
1
2
δ 164.4 (q), 143.5 (m), 136.2 (dt, JCH ) 153, JCH ) 6 Hz),
1
2
2
128.8 (dt, JCH ) 159, JCH ) 6 Hz), 128.0 (q, JCH ) 10 Hz),
1
2
1
127.4 (dd, JCH ) 159, JCH ) 7 Hz), 126.3 (dt, JCH ) 160,
2JCH ) 8 Hz), 125.9 (dm, JCH ) 153 Hz), 122.0 (dt, JCH
)
1
1
2
157, JCH ) 8 Hz), 119.0 (m), 110.7 (qnt), 72.0 (m), 40.4 (qq,
1JCH ) 134, JCH ) 5 Hz), 20.8 (tm, JCH ) 132 Hz), 19.7 (m),
3
1
1
1
19.5 (tm, JCH ) 125 Hz), 9.6 (qm, JCH ) 127 Hz), 9.4 (qm,
1JCH ) 128 Hz), 4.2 (q, JCH ) 138 Hz). FAB+-MS (m/z): 812
1
[M - 3Me - depe + BPh4]+, 685 [M - NMe2 - Me]+, 659 [M
- NMe2 - NCMe]+, 478 [M - NMe2 - Me - depe]+.
6b was prepared as follows. To a solution of trans-[FeBr-
(dCdCdCPh2)(depe)2][BPh4] (0.200 g, 0.189 mmol) in NCMe
(20 mL) was added, drop by drop, an excess of a 35% aquous
solution of NH2Me (12 mL, 0.121 mol), leading to a color
change, after ca. 1 h, from dark blue to yellow. Evaporation of
the solvent in vacuo led to the precipitation of a crystalline
yellow solid of 6b, which was separated by filtration, washed
with Et2O, and dried in vacuo. Yield: 80% (0.160 g).
Data for 6b are as follows. Anal. Calcd for C62H85N2P4Fe:
C, 71.0; H, 8.2; N, 2.7. Found: C, 71.1; H, 8.7; N, 2.4. IR (KBr,
1
cm-1): ν(NtC) 2239 (m), ν(CtC) 2054 (s). H NMR: δ 7.29

4664 Organometallics, Vol. 24, No. 19, 2005
Venaˆncio et al.
Table 3. Crystallographic Data for
(m, 8H, Ho from BPh4-), 7.23-7.11 (m, 10H, C6H5 from
alkynyl), 6.99 (t, J ) 7.5 Hz, 8H, Hm from BPh4- alkynyl), 6.84
(t, J ) 7.2 Hz, 4H, Hp from BPh4-), 2.21 (dq, JHP ) 15.2 and
J ) 7.6 Hz, 4H, 1/4(CH3CH2)2PCH2CH2P(CH2CH3)2), 2.01 (s,
3H, NH(CH3)), 1.88 (bs, 4H, 1/2(CH3CH2)2PCH2CH2P(CH2-
CH3)2), 1.75-1.50 (m), 3/4(CH3CH2)2PCH2CH2P(CH2CH3)2,
1/2(CH3CH2)2PCH2CH2P(CH2CH3)2 and NHMe), 1.11 (m, 27H,
(CH3CH2)2PCH2CH2P(CH2CH3)2 and NCCH3). 31P{1H} NMR:
trans-[FeBr{-CtCCPh2(CN)}(depe)2] (5a) and
trans-[Fe(NCMe){-CtCCPh2(NMe2)}(depe)2][BPh4]
(6a)
5a
6a
empirical formula
C36H58NBrP4Fe C69H93N2P4Fe
fw
temp, K
λ, Å
764.47
1140.99
298
293
1
δ 70.1 ppm (s). 13C{1H} NMR: δ 164.5 (q, JCB ) 49 Hz, Ci
0.710 69
monoclinic
1.541 50
orthorhombic
from BPh4-), 147.7 (bs, Ci from alkynyl), 136.3 (s, Cm from
BPh4-), 128.1 (qnt, JCP ) 2 Hz, NCMe), 127.9 (s, Co from
alkynyl), 127.5 (s, Cm from alkynyl), 126.5 (s, Cp from alkynyl),
125.9 (q, 2JCB ) 3 Hz, Co from BPh4-), 122.0 (s, Cp from BPh4-),
120.2 (m, CR or Câ), 110.0 (qnt, JCP ) 30 Hz, Câ or CR), 66.6
(qnt, 4JCP ) 2 Hz, Cγ), 31.0 (bs, NH(CH3)), 20.7 (qnt, JCP ) 12
Hz, (CH3CH2)2PCH2CH2P(CH2CH3)2), 19.6 (qnt, JCP ) 6 Hz,
1/2(CH3CH2)2PCH2CH2P(CH2CH3)2), 19.4 (qnt, JCP ) 4 Hz,
1/2(CH3CH2)2PCH2CH2P(CH2CH3)2), 9.6 (m, 1/2(CH3CH2)2PCH2-
CH2P(CH2CH3)2), 9.4 (m, 1/2(CH3CH2)2PCH2CH2P(CH2CH3)2),
4.3 (s, NCCH3). 13C NMR: δ 164.5 (q), 147.7 (m), 136.3 (dm,
cryst syst
space group
a, Å
P21/c:b1 (No. 14) Pbca (No. 61)
16.552(2)
13.2079(17)
18.9008(18)
3907.4(8)
4
1.300
1.597
11.311(3)
25.042(4)
45.647(3)
12930(4)
8
1.172
3.104
b, Å
c, Å
V, Å3
Z
F
calcd, g/mL
µ(Mo KR), mm-1
θ range for data collecn (deg) 1.92-25.97
3.53-67.24
0 e h e 13,
0 e k e 29,
-54 e l e 0
0.0801
limiting indices
-18 e h e 18,
-15 e k e 0,
0 e l e 21
0.1159
1
2
1JCH ) 153), 128.1 (m), 127.9 (dd, JCH ) 156, JCH ) 6 Hz),
R1 (I > 2σ(I))a
R1 (all data)
127.5 (dt, 1JCH ) 158, 2JCH ) 6 Hz), 126.5 (dt, 1JCH ) 161, 2JCH
0.3660
0.1214
1
1
) 8 Hz), 125.9 (dm, JCH ) 150 Hz), 122.0 (dt, JCH ) 157,
2JCH ) 7 Hz), 120.2 (m), 110.0 (qnt), 66.6 (m), 31.0 (qm, JCH
1
a R1 ) ∑||Fo| - |Fc||/∑|Fo|.
) 133 Hz), 20.7 (tm, 1JCH ) 120 Hz), 19.6 (tm, 1JCH ) 121 Hz),
1
1
19.4 (m), 9.6 (qm, JCH ) 127 Hz), 9.4 (qm, JCH ) 128 Hz),
(m, (CH3CH2)2PCH2CH2P(CH2CH3)2 and (CH3CH2)2PCH2CH2-
P(CH2CH3)2), 10.0 (m, (CH3CH2)2PCH2CH2P(CH2CH3)2), 9.5 (d,
1JCP ) 41 Hz, P(CH3)3), 2.0 (s, NCCH3). 13C NMR: δ 164.1 (q),
146.1 (m), 136.0 (dt, 1JCH ) 153, 2JCH ) 8 Hz), 130.1 (m), 129.3
4.3 (q, JCH ) 138 Hz). FAB+-MS (m/z): 813 [M - NHMe -
1
depe + BPh4]+ or [M - 2Me - depe + BPh4]+, 812 [M - 2Me
- H - depe + BPh4]+, 685 [M - NHMe - Me]+, 659 [M -
NHMe - NCMe]+.
1
1
(dm, JCH ) 162 Hz), 129.1 (m), 128.7 (dm, JCH ) 158 Hz),
1
1
2
125.7 (dm, JCH ) 155 Hz), 121.8 (dt, JCH ) 157, JCH ) 8
Hz), 116.8 (m), 107.1 (d), 65.7 (m), 22.4 (m), 21.2 (m), 20.0 (m),
10.0 (qm, 1JCH ) 127 Hz), 9.5 (qd, 1JCH ) 128 Hz), 2.0 (q, 1JCH
) 137 Hz). FAB+-MS (m/z): 1053 [M - NCMe + BPh4]+, 768/
770 [M - 3Me - NCMe + Br]+, 699 [M - PMe3]+, 698 [M -
Ph]+, 658 [M - NCMe - PMe3), 528 [M - NCMe - depe]+.
Reaction of trans-[FeBr{-CtCC(dCHMe)Et}(depe)2]
(4) with HBF4. To a solution of the enynyl complex trans-
[FeBr{-CtCC(dCHMe)Et}(depe)2] (4; 0.060 g, 0.094 mmol)
in CH2Cl2 (20 mL) was added a slight excess (1.2:1) of HBF4
(0.112 mmol, ca. 170 µL of a 54% solution in Et2O). The color
of the solution changed immediately from pink to dark red.
Concentration and addition of Et2O (ca. 10 mL) led to the
precipitation of the allenylidene complex 3a as a pink solid,
which was isolated by filtration and dried in vacuo. IR and 1H
and 31P{1H} NMR (spectra identical with those of 3b, except
for the features concerning the different counterions) confirmed
the formulation.
Structural Analyses of Complexes 5a and 6a. Diffrac-
tion analyses were carried out at room temperature on an
Enraf-Nonius CAD4 diffractometer equipped with a graphite
monochromator and Mo KR (5a; λ ) 0.710 69 Å) or Cu KR (6a;
λ ) 1.541 50 Å) radiation. Cell dimensions were obtained from
centered reflections with θ between 1.92 and 25.97° (5a) and
between 3.53 and 67.24° (6a). The intensities of 7676 (5a) and
11 033 (6a) reflections were observed, and a total of 7437 (5a)
and 11 033 (6a) unique reflections were used for structure
determinations. The structures were solved by direct methods
by using the SHELXS-97 package102 and refined with SHELXL-
97103 with the WinGX graphical user interface.104 Molecular
structures with their correspondent numbering schemes are
shown in Figures 1 and 2. Selected bond lengths and angles
are given in Table 1, and crystallographic data are summarized
in Table 3.
Dicationic Alkynyl Complexes trans-[Fe(NCMe){-Ct
CCPh2(PMe3)}(depe)2]Y2 (Y2 ) [BPh4]2 (7a), [BPh4]2-xBrx
(7b)). 7a was prepared as follows. The allenylidene complex
trans-[FeBr(dCdCdCPh2)(depe)2][BPh4] (0.200 g, 0.189 mmol)
was dissolved in 60 mL of NCMe, and an excess of PMe3 (1.89
mL of a 1 M toluene solution) was added. The system was
stirred at room temperature and kept under dinitrogen. After
ca. 24 h the color of the solution had changed from dark blue
to dark green and Na[BPh4] (0.065 g; 0.189 mmol) was added.
The solvent was removed in vacuo, yielding an oily residue,
which was recrystallized from CH2Cl2/Et2O. Yield: 56% (0.150
g).
7b was prepared following the procedure described above.
After the 24 h reaction, Et2O was added but no precipitation
was observed. The solution was then concentrated in vacuo,
yielding a green oily residue, which was separated by decanta-
tion. The oil was dried in vacuo and recrystallized from CH2-
Cl2/Et2O, leading to compound 7b. It was not possible to
determine accurately the relative quantities of Br- and [BPh4]-
for the counterions [BPh4]2-xBrx.
Data for 7a are as follows. Anal. Calcd for C88H110NP5Fe:
C, 73.0; H, 7.8; N, 0.9. Found: C, 73.1; H, 8.2; N, 0.9. IR (KBr,
1
cm-1): ν(CtN) 2247 (m), ν(CtC) 2012 (s). H NMR: δ 7.39-
-
7.23 (m, 20H, Ho from BPh4 and Ho or Hm from alkynyl),
-
7.02-6.92 (m, 18H, Hm from BPh4 and Hp from alkynyl),
6.89-6.83 (m, 12H, Hp from BPh4- and Hm or Ho from alkynyl),
1.80 (m, 8H, (CH3CH2)2PCH2CH2P(CH2CH3)2), 1.60-1.40 (m,
16H, (CH3CH2)2PCH2CH2P(CH2CH3)2), 1.14 (m, 27H, (CH3-
CH2)2PCH2CH2P(CH2CH3)2 and NCCH3), 0.98 (d, 2JHP ) 12.0
Hz, 9H, P(CH3)3). 31P{1H} NMR: δ 70.3 (d, JPP′ ) 5.3 Hz, 4P,
(CH3CH2)2PCH2CH2P(CH2CH3)2), 31,9 (qnt, JP′P ) 5.5 Hz, 1P,
PMe3).
1
Data for 7b are as follows. 13C{1H} NMR: δ 164.1 (q, JCB
) 49 Hz, Ci from BPh4-), 146.1 (m, Ci from alkynyl), 136.0 (s,
Cm from BPh4-), 130.1 (m, NCMe), 129.3 (s, Co or Cm from
alkynyl), 129.1 (s, Cp from alkynyl), 128.7 (s, Cm or Co from
In both structures the hydrogen atoms were inserted in
calculated positions. Least-squares refinements with aniso-
tropic thermal motion parameters for all the non-hydrogen
2
alkynyl), 125.7 (q, JCB ) 3 Hz, Co from BPh4-), 121.8 (s, Cp
from BPh4-), 116.8 (m, CR or Câ), 107.1 (d, JCP ) 7 Hz, Câ or
CR), 65.7 (m, Cγ), 22.4 (m, (CH3CH2)2PCH2CH2P(CH2CH3)2 and
(CH3CH2)2PCH2CH2P(CH2CH3)2), 21.2 (m, (CH3CH2)2PCH2-
CH2P(CH2CH3)2 and (CH3CH2)2PCH2CH2P(CH2CH3)2), 20.0
(102) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46, 467.
(103) Sheldrick, G. M. SHELXL-97; University of Go¨ttingen, Go¨t-
tingen, Germany, 1997.
(104) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837.

Allenylidene Iron(II) Complexes
Organometallics, Vol. 24, No. 19, 2005 4665
atoms and isotropic for the remaining atoms gave R1 ) 0.1159
(5a), 0.0801 (6a) (I > 2σ(I)) and R1 ) 0.3660 (5a), 0.1214 (6a)
(all data).
redox potential values are normally quoted relative to the SCE
by using the [Fe(η5-C6H5)2]0/+ (E1/2 ) 0.525 V vs SCE) redox
ox
couple in 0.2 M [NBu4][BF4] in CH2Cl2. For the application of
the Lever equation (2), they have been converted to volts vs
NHE by adding 0.245 V.96
Electrochemical Studies. The electrochemical experi-
ments were performed on an EG&G PAR 273A potentiostat/
galvanostat connected to a computer through a GPIB interface.
Cyclic voltammograms were obtained in 0.2 M solutions of
[NBu4][BF4] in CH2Cl2, at a platinum-disk working electrode
(0.5 mm diameter) probed by a Luggin capillary connected to
a silver-wire pseudo-reference electrode; a Pt auxiliary elec-
trode was employed. Controlled-potential electrolyses (CPE)
were carried out in electrolyte solutions with the aforemen-
tioned composition, in a two-compartment-three-electrode cell,
separated by a glass frit and equipped with platinum-gauze
working and counter electrodes. A Luggin capillary, probing
the working electrode, was connected to a silver-wire pseudo-
reference electrode. The CPE experiments were monitored
regularly by cyclic voltammetry (CV), thus ensuring that no
significant potential drift occurred along the electrolyses. The
electrochemical experiments were performed under a N2
atmosphere at room temperature.
Acknowledgment. The work has been partially
supported by the Fundac¸a˜o para a Cieˆncia e a Tecno-
logia (FCT) and by the PRAXIS XXI and POCTI
Programs (FEDER funded). We also thank Dr. M.
Caˆndida Vaz (Instituto Superior Te´cnico) for the el-
emental analysis services she coordinates and Mr.
Indale´cio Marques (Centro de Qu´ımica Estrutural) for
running the FAB-MS spectra.
Supporting Information Available: CIF files giving
X-ray crystallographic data for trans-[FeBr{-CtCCPh2(CN)}-
(depe)2] (5a) and trans-[Fe(NCMe){-CtCCPh2(NMe2)}(depe)2]-
[BPh4]‚C6H6 (6a‚C6H6). This material is available free of charge
via the Internet at http://pubs.acs.org.
The potentials of the complexes were measured by CV in
the presence of ferrocene as the internal standard, and the
OM050408A