Syntheses of di-hydrocarbyl derivatives of carbonyl phosphine complexes of iron

Article abstract of DOI:10.1016/j.ica.2005.05.036

Complexes cis,trans-Fe(CO)₂(PMe₃) ₂RR′ (R = CH₃, R′ = Ph (2); R = CH ₃, R′ = CHCH₂ (3); R = CHCH₂, R′ = Ph (4); R = R′ = CHCH₂ (5); R = R′ = CH₃ (6)) were prepared by reaction of cis,trans-Fe(CO)₂(PMe₃) ₂RCl (1) with organolithium reagents LiR′. All complexes were characterized in solution by IR and ¹H, ³¹P and, in a few cases, ¹³C NMR mono- and bi-dimensional spectroscopies. Complexes 5 and 6 were structurally characterized by X-ray diffractometric methods. In solution complexes 2, 3 and 4 undergo slowly coupling of the σ-hydrocarbyl substituents leading to Fe(CO)₃(PMe₃)₂ and other decomposition products. Complex 6 was very stable in solution in the absence of nucleophiles and in the solid state. Complex 5 transformed through intramolecular coupling of the vinyl groups into Fe(CO)(PMe₃) ₂(η⁴-butadiene) (7), which was characterized in solution by IR and NMR spectroscopies.

Full text of DOI:10.1016/j.ica.2005.05.036

Inorganica Chimica Acta 358 (2005) 3815–3823
www.elsevier.com/locate/ica
Syntheses of di-hydrocarbyl derivatives of carbonyl
phosphine complexes of iron
*
Chiara Venturi, Gianfranco Bellachioma, Giuseppe Cardaci ,
Alceo Macchioni, Cristiano Zuccaccia
`
Dipartimento di Chimica, Universita di Perugia, via Elce di Sotto, 8, 06123 Perugia, Italy
Received 18 March 2005; received in revised form 26 May 2005; accepted 30 May 2005
Available online 14 July 2005
Abstract
Complexes cis,trans-Fe(CO)2(PMe3)2RR0 (R = CH3, R0 = Ph (2); R = CH3, R0 = CH@CH2 (3); R = CH@CH2, R0 = Ph (4);
R = R0 = CH@CH2 (5); R = R0 = CH3 (6)) were prepared by reaction of cis,trans-Fe(CO)2(PMe3)2RCl (1) with organolithium
reagents LiR0. All complexes were characterized in solution by IR and 1H, 31P and, in a few cases, 13C NMR mono- and bi-dimen-
sional spectroscopies. Complexes 5 and 6 were structurally characterized by X-ray diffractometric methods. In solution complexes 2,
3 and 4 undergo slowly coupling of the r-hydrocarbyl substituents leading to Fe(CO)3(PMe3)2 and other decomposition products.
Complex 6 was very stable in solution in the absence of nucleophiles and in the solid state. Complex 5 transformed through intra-
molecular coupling of the vinyl groups into Fe(CO)(PMe3)2(g4-butadiene) (7), which was characterized in solution by IR and NMR
spectroscopies.
Ó 2005 Elsevier B.V. All rights reserved.
Keywords: Hydrocarbyl complexes; Iron complexes; Elimination reaction; Metallation; C–C coupling
1. Introduction
In general di-hydrocarbyl complexes are prepared
following procedures similar to those employed for the
synthesis of analogous mono-hydrocarbyl complexes.
Di-alkyl ruthenium complexes Ru(CO)2(L)2RR0, for
example, were obtained by Mawby and co-workers by
reaction of the corresponding mono-alkyl derivatives
Ru(CO)2L2RX with lithium alkyl reagents R0Li [9].
Mono-vinyl derivatives were prepared by alkyne inser-
tion into the Ru–H bond of Ru(CO)2L2HCl [10] and
by phenylacetilene insertion into M(CO)(P-iPr3)2(H)Cl
(M = Ru, Os) [11]; the further reaction with suitable
lithium reagents yielded the di-hydrocarbyl derivatives
Ru(CO)2L2(CH@CH2)R and M(CO)(P-iPr3)2(CH@
CHPh)R, respectively.
Metal-hydrocarbyls, such as metal-alkyl, metal-aryl
and metal-vinyl are known to be intermediates in C–C
bond-forming reactions [1]. These complexes can be pre-
pared by a variety of methods [2,3]: nucleophilic attack
on metal halides by organolithium or Grignard reagents
(metallation processes) [4]; electrophilic attack by organ-
ic halides on the metal [5]; oxidative addition on unsat-
urated and saturated complexes [6] and insertion of
olefins in the M–H and M–C bonds [7].
Organometallic compounds with two hydrocarbyl li-
gands undergo C–C bond-forming reactions between
the hydrocarbyl ligands and their reactivity is a key-step
in the C–C bond formation during many important cat-
alytic processes [8].
Recently, we described a general method for prepar-
ing monoalkyl, monoaryl and monovinyl derivatives of
carbonyl phosphine complexes of iron(II), by reaction
of cis,trans,cis-Fe(CO)2L2X2 (L = PMe3, X = Br, I, Cl)
with organolithium and Grignard reagents [12].
*
Corresponding author.
E-mail address: cardchim@unipg.it (G. Cardaci).
0020-1693/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2005.05.036

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C. Venturi et al. / Inorganica Chimica Acta 358 (2005) 3815–3823
In the present paper, we describe the synthesis of di-
our from orange to green was observed. The reaction
was checked by IR and was completed in a few minutes.
The final solution was washed with H2O to decompose
the excess of PhLi. The ether phase was dehydrated by
MgSO4, filtered and dried. Complex 2 was crystallized
in n-hexane at ꢀ20 °C (Yield: 35%). Anal. Calc. for
C15H26FeO2P2: C, 50.58; H, 7.36. Found: C, 50.73; H,
alkyl, alkyl-vinyl, alkyl-aryl, di-vinyl and vinyl-aryl
complexes of iron(II), their characterization in both
solution (IR and NMR) and, in a few cases, solid state
(single crystal X-ray diffraction) and discuss some as-
pects of C–C elimination reaction.
1
7.45%, mCO (cmꢀ1, DE): 1978, 1913. H NMR (C6D6,
2. Experimental
298 K): d 8.04 (br, o-H), 7.76 (br, o-H), 7.24 (m-H, bur-
ied under residual proton resonance of C6D6; in CD2Cl2
this resonance appears at 6.9 ppm), 7.18 (p-H), 0.95
Unless otherwise stated, all operations were carried
under nitrogen using standard Schlenk techniques.
Diethylether (DE) was purified by refluxing with NaOH
pellets, distilled, then refluxed with Na and benzophe-
none and freshly distilled under nitrogen before use; n-
hexane was dehydrated with Na and distilled under
nitrogen.
j2 + 4j
(tHarris
,
J
= 7.7 Hz, PMe3), 0.13 (t, 3JHP = 8.8 Hz,
HP
CH3). 31P{1H} NMR (C6D6, 298 K): d 21.4 (s, PMe3).
13C{1H} NMR (C6D6, 298 K): d 16.5 (PMe3). The data
on the other bands of the 13C NMR spectrum could not
be collected due to the decomposition of complex 2.
cis,trans,cis-Fe(CO)2(PMe3)2Cl2 and cis,trans-Fe-
(CO)2(PMe3)2(CH3)I were prepared as described in
[13,14], respectively. cis,trans-Fe(CO)2(PMe3)2(CH@
CH2)Cl and cis,trans-Fe(CO)2(PMe3)2(C6H5)Br were
prepared as described in [12]. Vinyl lithium was prepared
according to [15]. Phenyl lithium was a commercial
product.
2.3. cis,trans-Fe(CO)2(PMe3)2(CH3)(CH@CH2) (3)
Complex 3 was prepared by reacting complex 1 with
an DE solution of CH2@CHLi (0.22 M) [15] (molar
ratio: 1/1.5) following the procedure described for com-
plex 2. Yield: 30%. Anal. Calc. for C11H24FeO2P2: C,
1H, 31P{1H} and 13C{1H} NMR spectra were re-
corded on a Bruker DRX 400 spectrometer; referencing
was relative to TMS (1H and 13C) and 85% H3PO4 (31P).
NMR samples were prepared by dissolving about 20 mg
of the compounds in 0.5 mL of deuterated solvents.
Infrared spectra were recorded on a Perkin–Elmer
1725X FTIR spectrophotometer. Elemental analyses
were performed on a Carlo Erba 1106 elemental micro-
analyzer. Thermogravimetric analyses were carried out
with a TG-DTA/DSC Netzch STS thermobalance.
43.16; H, 7.90. Found: C, 43.29; H, 7.97%, mCO (cmꢀ1
,
DE): 1980, 1918. 1H NMR (CD2Cl2, 298 K): d 6.72
3
3
3
(ddt, JHH = 18.7 Hz, JHH = 10.1 Hz, JHP = 4.0 Hz,
3
4
CH@CH2), 5.8 (ddt, JHH = 10.1 Hz, JHP = 6.6 Hz,
2JHH = 2.7 Hz, CH@CH2(cis)), 5.4 (m, buried under
j2 + 4j
CD2Cl2, CH@CH2(trans)), 1.28 (tHarris
,
J
=
HP
7.5 Hz, PMe3), ꢀ0.37 (t, JHP = 9.5 Hz, CH3). 31P{1H}
3
NMR (CD2Cl2, 298 K): d 22.0 (s, PMe3).
2.4. cis,trans-Fe(CO)2(PMe3)2Ph(CH@CH2) (4)
2.1. cis,trans-Fe(CO)2(PMe3)2(CH3)Cl (1)
170 mg of cis,trans-Fe(CO)2(PMe3)2(CH@CH2)Cl
were dissolved in 30 mL of DE; 35 mL of 2 M DE solu-
tion of PhLi were added dropwise to the solution
thermostatted at ꢀ15 °C. The reaction was completed
in a few minutes. The solution was washed with H2O,
dehydrated by MgSO4 and dried. Complex 4 was ex-
tracted by n-hexane and crystallized at ꢀ20 °C (Yield:
40%). Anal. Calc. for C16H26FeO2P2: C, 52.22; H,
7.12. Found: C, 52.37; H, 7.18%, mCO (cmꢀ1, DE):
1985, 1923. 1H NMR (CD2Cl2, 298 K): d 7.70 (d,
3JHH = 6.8 Hz, o-H), 7.30 (m, CH@CH2), 7.00 (t,
1 g of cis,trans-Fe(CO)2(PMe3)2(CH3)I was dissolved
in CH3OH. An excess of tetrabutylammoniumchloride
(molar ratio = 1/5) was added under stirring. The halide
exchange was fast and completed in a few minutes. The
solution was dried and complex 1 was extracted with n-
hexane and crystallized at ꢀ20 °C (Yield: 80%). Anal.
Calc. for C10H21ClFeO2P2: C, 36.83; H, 6.49. Found:
C, 36.66; H, 6.52%, mCO (cmꢀ1, n-hexane): 2002, 1939.
3
1H NMR (CD2Cl2,j22+948j K): d 0.37 (t, JHP = 9.3 Hz,
CH3), 1.51 (tHarris
,
J
= 8.3 Hz, PMe3). 31P{1H}
HP
NMR (CD2Cl2, 298 K): d 18.6 (s, PMe3). 13C{1H}
3JHH = 7.5 Hz; m-H), 6.94 (t, JHH = 7.1 Hz; p-H), 6.0
3
2
3
2
4
NMR (CD2Cl2, 298 K): d 4.24 (t, JCP = 20.2 Hz,
(ddt, JHH = 11.0 Hz, JHH = 2.8 Hz, JHP = 5.4 Hz,
1
3
2
CH3), 15.24 (t, JCP = 14.5 Hz, PMe3).
CH@CH2(cis)), 5.58 (ddt, JHH = 18.7 Hz, JHH =
4
2.8 Hz, JHP = 3.6 Hz, CH@CH2(trans)), 1.16 (tHarris
,
j2 + 4j
2.2. cis,trans-Fe(CO)2(PMe3)2(CH3)Ph (2)
J
= 8.1 Hz, PMe3). 31P{1H} NMR (CD2Cl2,
HP
298 K): d 18.6 (s, PMe3). Relatively fast decomposition
of complex 4 at room temperature prevented the record
of the 13C NMR spectrum. The presence of styrene was
not observed in the decomposition products.
0.5 g of complex 1 were dissolved in DE (50 mL) at
ꢀ15 °C; 9 mL of 2 M ether solution of PhLi were added
dropwise (molar ratio: 1/1.5). A sudden change of col-

C. Venturi et al. / Inorganica Chimica Acta 358 (2005) 3815–3823
3817
1
2.5. cis,trans,cis-Fe(CO)2(PMe3)2(CH@CH2)2 (5)
2JCP = 3.3 Hz, CH@CH2), 15.6 (t, JCP = 13.8 Hz,
PMe3).
200 mg of cis,trans,cis-Fe(CO)2(PMe3)2Cl2 were dis-
solved in 20 mL of DE at ꢀ15 °C; CH2@CHLi (0.22 M
solution in DE) was added dropwise. The reaction
occurred in two steps as can be inferred from IR spectros-
copy: in the first step the formation of cis,trans-Fe-
2.8. Reduction of cis,trans-Fe(CO)2(PMe3)2PhBr with
sodium borohydride
A solution of cis,trans-Fe(CO)2(PMe3)2PhBr (0.1 g)
in diethylether (25 mL) was treated with an excess of
NaBH4. The reaction mixture was stirred at room tem-
perature and the reduction was completed in 20 h. The
results of the UV–Vis and GC analyses showed the for-
mation of benzene.
(CO)2(PMe3)2(CH@CH2)Cl (mCO = 2010, 1965 cmꢀ1
)
was observed; CH2@CHLi was added until the disappear-
ance of the mono-vinyl derivative. The final reaction mix-
ture was washed with H2O; the ether phase was
dehydrated with MgSO4 and dried. The solid residue
was extracted with n-hexane and crystallized at ꢀ20 °C.
Yellow crystals (Yield: 50%) were obtained. Anal. Calc.
for C12H24FeO2P2: C, 45.31; H, 7.60. Found: C, 45.53;
H, 7.75%, mCO (cmꢀ1, DE): 1987, 1927. 1H NMR
2.9. X-ray crystal structure determination of 5 and 6
Single crystals of complexes 5 and 6 were obtained by
crystallization in n-hexane at ꢀ20 °C. Crystal data and
details about structure refinement are reported in Table
1. Diffraction intensities were collected at 293 K on a
XCALIBUR (Kuma 4CCD) diffractometer, using
(CD2Cl2, 298 K):
d
6.86 (ddt, 3JHH = 18.7 Hz,
3
3JHH = 10.8 Hz, JHP = 3.9 Hz, CH@CH2), 5.89 (ddt,
3JHH = 10.8 Hz,
3JHH = 2.8 Hz,
4JHP = 6.4 Hz,
3
3
CH@CH2(cis)), 5.45 (ddt, JHH = 18.7 Hz, JHH
=
4
˚
2.8 Hz, JHP = 4.6 Hz, CH@CH2(trans)), 1.26 (tHarris
,
graphite monochromated Mo Ka (k = 0.71069 A). The
j2 + 4j
J
= 8.1 Hz, PMe3). 31P{1H} NMR (CD2Cl2,
scans and the frame data were acquired with CRYSALIS
(CCD169) software. The frames were processed using
CRYSALIS (RED 169) software to give the hkl file cor-
rected for scan speed, background and Lorentz polariza-
tion effects. Standard reflections, measured periodically,
showed no apparent variation in intensity during data
collection, so no correction for crystal decomposition
was necessary. The data were corrected for absorption
by using the SADABS program [17]. The structure was
solved by direct methods using the Sir97 program [18]
HP
298 K): d 18.3 (s, PMe3). 13C{1H} NMR (CD2Cl2,
2
298 K): 214.1 (t, JCP = 15.5 Hz, CO), 176.7 (t,
2JCP = 33.2 Hz, CH@CH2), 124.5 (t, JCP = 5.9 Hz,
3
CH@CH2), 15.6 (t, 1JCP = 15.4 Hz, PMe3).
2.6. cis,trans,cis-Fe(CO)2(PMe3)2(CH3)2 (6)
Method A: Complex 6 was prepared following the
method described for the above complexes, by reacting
complex cis,trans, cis-Fe(CO)2(PMe3)2Cl2 with a solu-
tion of CH3Li (1 M solution in DE) (Yield: 70%).
Method B: A solution of complex cis,trans-Fe(CO)2(P-
Me3)2(CH3)I (0.5 g) in dry DE (50 mL) was treated with
an 1 M solution of CH3Li. The lithium reagent was
added until the CO stretching bands of the starting com-
plex. completely disappeared (Yield: 55%). The charac-
terization of complex 6 was previously published [16].
Table 1
Crystal data and details for complexes 5 and 6
Complex 5
Complex 6
Colour
yellow
318.10
triclinic
orange
294.08
monoclinic
C2/c
Formula weight
Crystal system
Space group
Cell parameters
ꢀ
P1
˚
a (A)
9.013 (2)
13.085 (2)
15.390 (3)
85.42 (2)
88.91 (2)
69.62 (2)
1695.9 (6)
4
24.944 (5)
8.502 (5)
23.064 (5)
90
39.692 (5)
90
3124 (2)
8
1.250
˚
2.7. Fe(CO)(PMe3)2(g4-CH2@CH–CH@CH2) (7)
b (A)
˚
c (A)
a (°)
b (°)
c (°)
0.2 g of complex 5 were dissolved in CH2Cl2 and the
resulting solution was left overnight at room tempera-
ture. The solution was dried and various attempts were
made to crystallize complex 7 from n-hexane and other
solvents in order to obtain crystals suitable for X-ray
investigation. However, a liquid was always obtained.
The IR spectrum shows a single CO stretching at
3
˚
V (A )
Z
D(calc) (g/cm3)
1.246
Absorption coefficient (mmꢀ1
Total data collected
Unique observed data
Criterium for observed
Observed data (I > 2.0r)
)
1.068
11643
7725
Fc > 4r(Fo)
5672
1.154
7353
3865
Fc > 4r(Fo)
2472
1919 cmꢀ1
.
1H NMR (CD2Cl2, 298 K): d 4.2 (t,
3
3JHH(cis) ꢁ JHH(trans) = 9.9 Hz,j2C+H4j = CH2), 1.79 (m,
Number of refined parameters
313
140
CH@CH2(cis)), 1.48 (tHarris
,
J
= 7.85, PMe3),
HP
R
Rw
0.0399
0.0962
1.004
672
5.29, 27.92
0.0424
0.1016
0.974
1248
3.63, 28.52
ꢀ0.07 (dt, 3JHH(trans) = 9.9, 3JHP = 5.12; CH@
CH2(trans)). 31P{1H} NMR (CD2Cl2, 298 K): d 26.3 (s,
PMe3). 13C{1H} NMR (CD2Cl2, 298 K): d 216.7 (t,
2JCP = 28 Hz, CO), 80.4 (m, CH@CH2), 48.2 (t,
Goodness-of-fit
F (0 0 0)
H (°)

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C. Venturi et al. / Inorganica Chimica Acta 358 (2005) 3815–3823
and refined on F2 by the full-matrix least squares meth-
od using SHELXL-97 [19] WinGX [20] version. All non-
hydrogen atoms were refined anisotropically. The
hydrogen atoms were added at the calculated positions
and refined using a riding mode. Refinement converged
at a final R = 0.0399, Rw = 0.0962 and GOF = 1.004 for
The IR spectra of hydrocarbyl complexes 2–6 show
two CO stretching bands of similar intensity in the CO
stretching region, indicating that the carbonyl ligands
are mutually cis. The values of the frequencies are given
in Table 2.
1
In H NMR spectra the PMe3 substituents appear
complex
GOF = 0.974 for complex 6.
5
and R = 0.0424, Rw = 0.1016 and
as an Harris triplet [21], indicating that these ligands
are chemically equivalent as confirmed by 31P{1H}
NMR spectra in which the phosphine ligands show a
singlet resonance. The values of the phosphorus chem-
ical shifts are given in Table 2. For complex 5 the
13C{1H} NMR carbon monoxide resonance appears
as a triplet due to the coupling with two equivalent
phosphorus atoms, indicating that phosphine ligands
are in the trans position. Then both IR and NMR
results confirm that the complexes contain two CO
ligands in the cis position and two PMe3 ligands in
the trans position.
The proton spectra of complexes 3, 4 and 5, contain-
ing the vinyl substituent, show three distinct resonances,
further split by two equivalent phosphorus nuclei. The
coupling constants of ꢁ18 Hz were attributed to the
trans coupling (3JHH); the values of ꢁ10 and ꢁ3 Hz were
attributed to the cis (3JHH) and geminal coupling con-
stants (2JHH) of the vinyl group, respectively.
The proton NMR spectrum of cis,trans-Fe(CO)2(P-
Me3)2(CH3)Ph (2) exhibits two broad signals for both
the inequivalent ortho protons of the phenyl ring. This
indicates the presence of an hindered rotation around
the metal–phenyl bond as observed in the monophenyl
derivatives of iron [12].
The CO stretching frequencies are only slightly
influenced by the R substituents in both the mono-
[12] and di-hydrocarbyl derivatives. Notwithstanding,
significant trends can be observed in the series of
complexes (Table 2).
3. Results
Dihydrocarbyl complexes cis,trans-Fe(CO)2(PMe3)2-
RR0 (R = CH3, R0 = Ph (2); R = CH3, R0 = CH@CH2
(3); R = CH@CH2, R0 = Ph (4); R = R0 = CH@CH2
(5); R = R0 = CH3 (6)) were prepared by metallation
reaction of monosubstituted hydrocarbyl chloride com-
plexes cis,trans-Fe(CO)2(PMe3)2RCl with organolithium
reagents (R0Li) according to Scheme 1.
The reaction yields were low (35–60%) owing to sec-
ondary reactions that formed 17 electron radical prod-
ucts, which, by reaction with oxygen, gave
Fe(CO)3(PMe3)2 as end product. Chloride complexes
Fe(CO)2(PMe3)2RCl showed higher yields than bromide
and iodide derivatives and the lithium reagents were
more efficient than Grignard reagents as observed in
the preparation of monosubstituted hydrocarbyl deriva-
tives cis,trans-Fe(CO)2(PMe3)2RX (X = Cl, Br, I) [12].
Complexes 2–6 were characterized by IR and 1H,
31P{H} and 13C{H} NMR spectroscopies; the proton
1
and carbon resonances were assigned by using both H
COSY and H, 13C HMQC spectra.
1
PMe3
PMe3
OC
OC
R
OC
R
R'Li
Fe
Fe
LiCl
In Table 2, the complexes cis,trans-Fe(CO)2(PMe3)2-
RR0 are shown in three different series in which the li-
gand R is held constant (CH3, CH@CH2, Ph) and the
ligand R0 is varied (R0 = Cl, Br, I, CH3, Ph, CH@CH2).
The substituent effect is similar in the three series
as indicated by the linear variation of the higher CO
Cl
PMe3
OC
R'
PMe3
R=CH3,Ph, CH=CH2
R'=CH3,CH=CH2
Scheme 1.
Table 2
CO stretching frequencies (cmꢀ1) in DE and 31P chemical shifts (ppm) in CD2Cl2
R0
Fe(CO)2(PMe3)2CH3R0
mCO (cmꢀ1
Fe(CO)2(PMe3)2(CH@CH2)R0
Fe(CO)2(PMe3)2PhR0
mCO (cmꢀ1
)
d31P (ppm)
mCO (cmꢀ1
)
d31P (ppm)
)
d31P (ppm)
Cl
2002, 1939
1999, 1938
1998, 1936
1973, 1908b
1978, 1913
1980, 1918
18.6
15.3
11.3
25.8b
18.3
22.0
2010, 1945
2009, 1946
2005, 1946
1980, 1918
1985, 1924
1987, 1927
15.0
12.0
2012, 1942a
2009, 1941
2003, 1939
1978, 1913
15.0a
11.7
8.3
Bra
Ia
CH3
Ph
CH@CH2
21.4
18.6
18.6
22.0
1985, 1924
18.3
a
From Ref. [12].
From Ref. [16].
b

C. Venturi et al. / Inorganica Chimica Acta 358 (2005) 3815–3823
3819
stretching frequencies of cis,trans-Fe(CO)2(PMe3)2-
(CH3)R0 versus those of cis,trans-Fe(CO)2(PMe3)2-
(CH@CH2)R0 for the different R0 substituents (Fig. 1).
The CO stretching frequencies of cis,trans-Fe(CO)2-
(PMe3)2RR0 complexes follow the order:
differences in the phenyl and vinyl substituents. The ef-
fect of the substituents follows the order:
CH3 > CH@CH2 > Ph ꢁ Cl > Br > I
All the organic substituents show a linear trend be-
tween d31P and the Hammett rp [22] (Fig. 3). Halides
show also a linear trend; however, owing to the small
difference in the rp values, this trend is not very signifi-
cant; a better linear trend is observed with the r (Taft)
values; better withdrawing substituents, decreasing the
electron charge on the iron, deshield phosphorus and in-
Cl > Br > I ꢂ CH3 > Ph > CH@CH2
and a good linear trend is observed with the Taft r con-
stants [22] in agreement with the negative inductive ef-
fect of the substituents (Fig. 2); apparently the p effect
is not very important.
While the chemical shift of the PMe3 protons is not
significantly influenced by the nature of the substituents,
the change of chemical shifts of the 31P is notable. The
values are given in Table 2. The substituent effects in
the three series of complexes are similar with only slight
crease d31P.
Recently, d31P was related to the electron charge of
the metal in complexes Cp*Fe(dppe)X (X = F, Cl, Br,
I, H, CH3) [23]. If this relation is valid for complexes
cis,trans-Fe(CO)2(PMe3)2RR0, the electron density on
the iron follows the trend:
I > Br > Cl ꢁ Ph > CH@CH2 > CH3.
2015
This trend is opposite to that observed for Cp*Fe(dp-
pe)X and can be explained on the basis of electronega-
tivity of halides [24] and delocalization of the p
electrons in the organic ligands (Ph > CH@CH2 > CH3).
In this work, we studied the elimination reactions of
the di-hydrocarbyl complexes from the qualitative point
of view. The decomposition of complex cis,trans-Fe-
(CO)2(PMe3)2(CH3)Ph at room temperature yields tolu-
ene, which was revealed by its typical resonances in the
1H NMR spectrum. During the reduction of cis,trans-
Fe(CO)2(PMe3)2PhBr with sodium borohydride, ben-
zene was eliminated, which was recognized by the
UV–Vis spectrum and by the GC analysis of the solu-
tion after the reduction.
2010
2005
2000
1995
1990
1985
1980
1975
Br
Cl
I
CH=CH2
Ph
CH3
1970
1980
1990
νCO(cm-1) (B)
2000
2010
Dimethyl complex cis,trans-Fe(CO)2(PMe3)2(CH3)2
(6) is very stable; no decomposition was observed in
Fig. 1. Higher CO stretching frequencies (mCO, cmꢀ1) of cis,trans-
Fe(CO)2(PMe3)2(CH@CH2)R0 (A) vs. higher CO stretching frequen-
cies of cis,trans-Fe(CO)2(PMe3)2(CH3)R0 (B).
28
26
24
22
20
18
16
14
12
10
CH3
Br
2010
Cl
I
CH=CH2
Ph
Cl
2000
I
Br
Cl
1990
1980
1970
CH=CH2
CH3
Ph
Br
CH=CH2
Ph
I
CH3
0.0
-0.1
0.1
0.2
σ Taft
0.3
0.4
0.5
-0.2
-0.1
0.0
0.1
0.2
0.3
σp Hammett
Fig. 2. Higher CO stretching frequencies of cis,trans-Fe(CO)2(PMe3)2-
(CH@CH2)R0 (m) and of cis,trans-Fe(CO)2(PMe3)2(CH3)R0 (j) vs.
the r Taft constants of R0 substituents.
31
Fig. 3. P chemical shift (ppm) of cis,trans-Fe(CO)2(PMe3)2(CH3)R0
vs. the rp Hammett constants of R0 substituents.

3820
C. Venturi et al. / Inorganica Chimica Acta 358 (2005) 3815–3823
solution up to 50 °C in the absence of nucleophiles. In
the presence of CO, elimination of diacetyl was observed
with the formation of Fe(CO)3(PMe3)2 [16]. Complex 6
remains stable up to 110 °C in the solid state as shown in
the thermogravimetric experiments. At 110 °C the
weight loss of a mass corresponding to acetone was ob-
served; a successive decomposition was also observed at
180 °C.
the presence of the Cs symmetry plane. In structure B
the phosphine ligands become equivalent in the presence
of rapid rearrangement of the butadiene ligand [29].
Pentacoordinated butadiene complexes of iron, de-
scribed in the literature [30], prefer structure A.
The molecular structures of complexes 5 and 6 in the
solid state, obtained by single crystal X-ray investiga-
tions, are given in Figs. 4 and 5, respectively. Tables 3
and 4 report selected bond distances and angles for com-
plexes 5 and 6, respectively. Complex 5 shows a spatial
cis,trans,cis-Fe(CO)2(PMe3)2(CH@CH2)2 (5) rear-
ranges at room temperature to Fe(CO)(PMe3)2(g4-buta-
diene) (7) by C–C coupling. Various attempts were made
to crystallize complex 7 in different solvents but a liquid
was always obtained. The characterization of this com-
plex was therefore based on the spectroscopic informa-
tion in solution. The complex shows a CO stretching
band at 1919 cmꢀ1 in CH2Cl2. This frequency is similar
to that observed in Fe(CO)(PPh2CH2CH2PPh2)(g4-
butadiene) (mCO = 1905 cmꢀ1 in Nujol) [25] and for
analogous complexes of ruthenium and osmium [26].
The proton spectrum shows an Harris triplet, assigned
to two chemically equivalent PMe3 ligands; the butadi-
ene group shows three resonances, assigned to the anti,
syn and inner protons, according to the coupling con-
stants observed in the literature for tetrahapto-butadi-
ene iron complexes [27]. The presence of only three
resonances indicates that the complex has Cs symmetry,
so that the couple of anti, syn and inner hydrogens be-
come chemically equivalent. The 31P{1H} NMR spec-
trum presents a single resonance, confirming the
chemical equivalence of the PMe3 ligands. The
13C{1H} NMR spectrum shows a triplet at 216.7 ppm,
assigned to the CO ligand, which couples with two
equivalent phosphorus atoms; the small value of the
coupling constant (JCP = 28 Hz) supports the cis posi-
tion of the phosphine ligands with respect to CO [28].
Two other carbon resonances at 80.43 ppm (inner car-
bons) and at 48.16 ppm (outer carbons) are observed
for butadiene ligand in agreement with the presence of
a symmetry plane in the complex.
ꢀ
group P1 where there are two molecules for each asym-
metric unit. Between these there appears to be a 2/m
symmetry axis that could bring to a possible monoclinic
cell with a higher symmetry. However, examining more
carefully the experimental data, it is possible to show
that the two planes defined by the atoms Fe1C1C2C3C4
of the first molecule and Fe2C21C22C23C24 of the
second molecule, form an 82.25° angle and not one of
C24
O4
P2
C23
C26
C2
O1
C5
P3
Fe1
C6
C1
Fe2
C25
P4
C3
O2
O3
C21
P1
C4
C22
Fig. 4. ORTEP molecular structure of complex 5.
C6
C5
C7
P1
These spectroscopic properties support both struc-
tures A and B presented in Scheme 2.
O2
Structure A is square pyramidal with the CO ligand
in the apical position; structure B is bipyramidal trigonal
with the CO and butadiene ligands lying in the trigonal
plane. A symmetry plane is present in both A and B. In
structure A the phosphine ligands are equivalent and the
couples of syn, anti and inner hydrogens and the couples
of inner and outer carbons become equivalent owing to
C2
C3
Fe
C1
O1
C8
C4
P2
PMe3
CO
Me3P
OC Fe
Fe
Me3P
C10
PMe3
(B)
(A)
C9
Scheme 2.
Fig. 5. ORTEP molecular structure of complex 6.

C. Venturi et al. / Inorganica Chimica Acta 358 (2005) 3815–3823
3821
Table 3
Table 4
˚
˚
Relevant bond lengths (A) and angles (°) for complex 5
Relevant bond lengths (A) and angles (°) for complex 6
Fe1–P1
Fe1–P2
Fe1–C1
Fe1–C3
Fe1–C5
Fe1–C6
C1–C2
C3–C4
O1–C5
O2–C6
Fe2–P3
Fe2–P4
Fe2–C21
Fe2–C23
Fe2–C25
Fe2–C26
C21–C22
C23–C24
O3–C25
O4–C26
2.2076 (10)
2.2130 (11)
2.012 (3)
2.020 (3)
1.764 (3)
1.764 (3)
1.291 (5)
1.317 (6)
1.144 (4)
1.135 (4)
2.2139 (10)
2.2120 (10)
2.007 (3)
2.021 (3)
1.773 (3)
1.753 (3)
1.304 (4)
1.320 (5)
1.139 (3)
1.141 (3)
Fe–P1
Fe–P2
Fe–C1
Fe–C2
Fe–C3
Fe–C4
O1–C1
O2–C2
2.2204 (16)
2.2174 (16)
1.771 (4)
1.756 (5)
2.137 (3)
2.132 (5)
1.124 (5)
1.152 (7)
P1–Fe–P2
P1–Fe–C1
P1–Fe–C2
P1–Fe–C3
P1–Fe–C4
P2–Fe–C1
P2–Fe–C2
P2–Fe–C3
P2–Fe–C4
C1–Fe–C2
C1–Fe–C3
C1–Fe–C4
C2–Fe–C3
C2–Fe–C4
C3–Fe–C4
Fe–C1–O1
Fe–C2–O2
169.08 (5)
94.41 (11)
92.94 (11)
85.92 (8)
86.74 (10)
94.52 (12)
92.55 (11)
84.92 (9)
87.71 (10)
95.0 (2)
176.8 (2)
85.4 (2)
P1–Fe1–P2
165.81 (4)
84.57 (9)
84.19 (10)
94.84 (10)
95.62 (10)
85.65 (9)
85.49 (10)
95.10 (10)
93.70 (10)
89.57 (12)
88.20 (12)
177.47 (12)
177.64 (13)
87.94 (13)
179.5 (3)
179.7 (3)
132.8 (2)
132.3 (2)
166.30 (4)
84.95 (9)
84.61 (9)
93.96 (10)
95.28 (10)
84.53 (9)
85.49 (9)
94.50 (10)
94.90 (10)
88.53 (11)
89.06 (12)
177.13 (12)
177.58 (12)
88.62 (12)
179.0 (3)
179.5 (3)
131.6 (2)
132.3 (2)
88.18 (18)
179.54 (13)
91.48 (18)
178.2 (5)
179.1 (8)
P1–Fe1–C1
P1–Fe1–C3
P1–Fe1–C5
P1–Fe1–C6
P2–Fe1–C1
P2–Fe1–C3
P2–Fe1–C5
P2–Fe1–C6
C1–Fe1–C3
C1–Fe1–C5
C1–Fe1–C6
C3–Fe1–C5
C3–Fe1–C6
Fe1–C5–O1
Fe1–C6–O2
Fe1–C1–C2
Fe1–C3–C4
P3–Fe2–P4
P3–Fe2–C21
P3–Fe2–C23
P3–Fe2–C25
P3–Fe2–C26
P4–Fe2–C21
P4–Fe2–C23
P4–Fe2–C25
P4–Fe2–C26
C21–Fe2–C23
C21–Fe2–C25
C21–Fe2–C26
C23–Fe2–C25
C23–Fe2–C26
Fe2–C25–O3
Fe2– C26–O4
Fe2–C21–C22
Fe2–C23–C24
The two columns of Table 3 refer to bond distances
and angles of the two nearly perpendicular units of com-
plex 5, present in the elementary cell (Fig. 4). The values
of the bond distances and angles of the two units are
similar. Both complexes 5 and 6 show the same octahe-
dral structure of the hydrocarbyl complexes of iron, de-
scribed previously [12,31], with the trans PMe3 ligands
bent far away from the CO ligands.
In complex 5, the vinyl groups are cis and lie in the
equatorial plane with a butterfly structure. The iron-vi-
nyl bond lengths measured for this complex are the
shortest (Fe–C1 = 2.010 A, Fe–C3 = 2.020 A and Fe2–
C21 = 2.007, Fe2–C23 = 2.021 A) observed in the series
of hydrocarbyl complexes of iron [12,31], in agreement
with a high p electron delocalization. The vinyl double
bond lengths (C1–C2 = 1.291 A, C3–C4 = 1.317 A and
C21–C22 = 1.304 A, C23–C24 = 1.320 A) and the iron
vinyl angles (Fe1–C1–C2 = 122.8°, Fe1–C3–
C4 = 132.3° and Fe2–C21–C22 = 131.6°, Fe2–C23–
C24 = 132.6°) are in the range of other vinyl complexes
described in the literature [32].
Complex 6 has the longest Fe–C (Fe–C3 = 2.137 A,
Fe–C4 = 2.132 A) and the shortest C–O (O1–
˚
˚
˚
˚
˚
˚
˚
˚
˚
˚
˚
C1 = 1.121 A, O2–C2 = 1.152 A) bond lengths observed
in the iron hydrocarbyl complexes [12,31].
90°. Therefore, attempts to transform the triclinic cell
into monoclinic cell, do not give satisfactory results in
the refinement of the structure. Then we can conclude
that complex 5 crystallizes in a pseudo-monoclinic sys-
tem and therefore is treated as a triclinic system.
4. Discussion
In agreement with the previous results obtained dur-
ing the synthesis of mono-hydrocarbyl iron complexes

3822
C. Venturi et al. / Inorganica Chimica Acta 358 (2005) 3815–3823
[12], the yields of the di-hydrocarbyl complexes 2, 3, 4, 5
and 6, obtained according to Scheme 1, are low owing to
a secondary radical reaction. Lithium reagents (MeLi,
PhLi, CH2@CHLi) behave as monoelectronic reducing
reagents, forming 19 electron species, which undergo
chloride loss giving 17 electron species [33], according
to Scheme 3.
ment with a fast elimination reaction at low temperature
as observed in other hydride-hydrocarbyl complexes [36].
Complexes cis,trans-Fe(CO)2(PMe3)2(CH3)Ph (2),
cis,trans-Fe(CO)2(PMe3)2(CH3)(CH@CH2) (3), cis,trans-
Fe(CO)2(PMe3)2Ph(CH@CH2) (4) showed slow decom-
position at room temperature. In the case of complex 2,
the formation of toluene was observed. In vinyl complexes
3 and 4, intramolecular coupling with the formation of
dihapto derivatives having structures of the type Fe-
(CO)2(PMe3)2(g2-CHR@CH2), hypothesized to be inter-
mediates in other similar elimination reactions [37], were
not observed, even though they should be very stable [38].
Complex cis,trans,cis-Fe(CO)2(PMe3)2(CH@CH2)2
(5) reacted slowly in solution at room temperature yield-
ing the tetrahapto Fe(CO)(PMe3)2(g4-butadiene) (7)
complex. Vinyl–vinyl coupling occurs in many catalytic
and stoichiometric coupling reactions such as palla-
dium-catalyzed Stille reactions [39], Suzuki–Miyaura
coupling [40] and other reactions [41] involved in the
syntheses of conjugated 1,3-dienes. The key step of these
reactions is the reductive elimination step. The coupling
of two vinyl ligands is common in the chemistry of
ruthenium and osmium. Pentacoordinated ruthenium
and osmium complexes M(CO)(PiPr3)2(CH@ CHPh)-
(CH@CH2) afford M(CO)(PiPr3)2(g4-C4H5Ph) [19];
octahedral ruthenium complex Ru(PMe3)4(CH@CH2)2
There is no experimental evidence of 19 electron rad-
ical intermediates; the formation of these species in
Scheme 3 is suggested by the strong tendency of iron
halide complexes, well documented in literature
[34,35], to form 19 electron radicals which give 17 elec-
tron radicals and halide anions by reductive elimina-
tion. The 17 electron species [Fe(CO)2(PMe3)2R] are
green or emerald green; they decompose easily in the
presence of oxygen, which favours the radical R
abstraction leading to the formation of the 16 electron
intermediate Fe(CO)2(PMe3)2, that rearranges to Fe-
(CO)3(PMe3)2. Various attempts were made to obtain
higher yields of di-hydrocarbyl complexes; different
experiments indicated that the chloride complexes give
higher yields than the iodide and bromide ones
and the lithium reagents are more efficient than the
Grignard reagents. The chloride substituent, which
decreases the electronic density on iron, probably
increases the reaction rate with Rꢀ more than the
mono-electron reduction, so increasing the yield of
the di-hydrocarbyl derivatives.
The reductive elimination of di-hydrocarbyl com-
plexes 2, 3, 4, 5 and 6, depends strongly on the nature
of the hydrocarbyl. The dimethyl complex 6 is stable
in solution at least up to 50 °C; in the presence of CO,
elimination of diacetyl was also observed at room tem-
perature [16]. In the solid state, during the thermogravi-
metric analysis, a weight lose corresponding to acetone
was observed at 110 °C.
The behaviour of Fe(CO)2(PMe3)2PhH, intermediate
of the reduction of cis,trans-Fe(CO)2(PMe3)2PhBr with
borohydride, is different. The hydride complex was not
observed also when the reduction was carried out at
ꢀ45 °C. The analysis of the decomposition products how-
ever revealed the formation of benzene. This is in agree-
affords Ru(PMe3)3(g4-C4H6) by dissociation of
a
phosphine ligand [42]. In contrast, Ru(CO)(PiPr3)2-
(CH@CHPh)(CH@CH2) does not afford tetrahapto
derivative owing to the difficulty to dissociate a CO or
a phosphine ligand [26]. In addition, Mawby and
co-workers [7,10] showed that during the reaction of Ru-
(CO)2LL0(CH@CHR)(C6H4-p-X) complexes (R = Ph,
CMe3, H; X = H, Cl, OMe; L, L0 = various phosphine li-
gands) with carbon monoxide, Ru(CO)LL0(g4-
CHR@CH–CO–C6H4X) is formed via CO insertion in
the Ru–C6H4X bond, coupling between CH@CHR and
COC6H4X groups and chelation of the heterodiene ligand
by expulsion of a CO ligand. The behaviour of cis,tran-
s,cis-Fe(CO)2(PMe3)2(CH@CH2)2 (5)issimilartothislast
example which indicates that dissociation of CO occurs,
even though the iron–CO bond is very strong.
A quantitative study of the elimination reaction of
the di-hydrocarbyl complexes was not possible, since
in the presence of nucleophiles, which can stabilize the
reaction products, an easy carbon monoxide insertion
is observed with successive elimination of ketones [16];
in the absence of nucleophiles, Fe(CO)3(PMe3)2 and
decomposition products are observed but the reaction
stoichiometry is not clear.
PMe3
R
PMe3
R
OC
OC
OC
OC
R'Li
Fe
Fe
Cl
PMe3
Cl
PMe3
PMe3
OC
OC
LiCl R'
5. Supplementary material
Fe
R
PMe3
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Scheme 3.

C. Venturi et al. / Inorganica Chimica Acta 358 (2005) 3815–3823
3823
[16] G. Bellachioma, G. Cardaci, A. Macchioni, C. Zuccaccia, J.
Organometal. Chem. 628 (2001) 255.
Data Center, CCDC No. 26410 for complex 4a, CCDC
No. 26411 for complex 5. Copies of this information
may be obtained free of charge from The Director,
CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK
(fax: +44 1223 336033; e-mail: deposit@ccdc.cam.ac.uk
or www.ccdc.cam.ac.uk).
[17] G.M. Sheldrick, SADABS: Program for the Empirical Correction of
Area Detector Data, University of Gottingen, Germany, 1996.
[18] A. Altomare, M.C. Burla, M. Camalli, G. Cascarano, G.
Giacovazzo, A. Gagliardi, A.G.G. Moliterni, G. Polidori, R.
Spagna, Sir97: a new tool for crystal structure determination and
refinement, J. Appl. Cryst. 32 (1999) 115.
[19] G.M. Sheldrick, SHELXL-97, University of Gottingen, Germany,
1997.
[20] L.J. Farrugia, J. Appl. Cryst. 32 (1999) 837.
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