P-O and C-O bond cleavages in the thermal or photochemical reactions of [Fe2( η5-C5H5)2(CO)4] with tetraethyl diphosphite

Article abstract of DOI:10.1021/om030201m

The thermal and photochemical reactions of [Fe₂Cp₂(CO)₄] and the bidentate ligand (EtO)₂POP(OEt)₂ (tedip) proceed with different P-O or C-O bond cleavages in the diphosphite ligand. Thus, boiling toluene solutions of the above species yield the known compound [FeCp(CO)₂{P(O)(OEt)₂}] and the new dicarbonyl complexes [Fe₂Cp₂{μ-(EtO)₂POP(O)(OEt)}{μM-P(OEt) ₂}(CO)₂] (three isomers). The latter are slowly decarbonylated at room temperature by atmospheric oxygen to give the metal-metal-bonded complex [Fe₂Cp₂{μ(EtO)₂POP(O)(OEt)}{μ-P(OEt) ₂}(μ-CO)]. In contrast, the photochemical reaction between the iron dimer and the diphosphite ligand gives the phosphido-phosphonate complexes [Fe₂Cp₂{μ-OP(OEt)₂}{μ-P(OEt)₂} (CO)₂], as a mixture of cis and trans isomers. The latter compounds experience a remarkable P-O bond reductive elimination in boiling xylenes under a CO atmosphere, whereby the diphosphite-bridged complex [Fe₂Cp₂(μ-CO)₂(μ-tedip)] is formed in moderate yield. The structure of the latter was analyzed through an X-ray study. The related complexes [Fe₂Cp₂(μ-CO)₂(CO)(κ¹-tedip )] and [{Fe₂Cp₂(μ-CO)₂(CO)}₂(μ-tedip) ] were prepared from [Fe₂Cp₂(μ-CO)₂(CO)(NCMe)] and the diphosphite ligand, and their role as potential precursors of the above dicarbonyl complexes was evaluated. The structures of the new complexes are analyzed on the basis of the corresponding IR and NMR (¹H, ³¹P, ¹³C) data, and the reaction pathways operative in these complex reactions are discussed on the basis of the available data and some cross-experiments.

Full text of DOI:10.1021/om030201m

Organometallics 2003, 22, 3039-3048
3039
P -O a n d C-O Bon d Clea va ges in th e Th er m a l or
P h otoch em ica l Rea ction s of [F e2(η5-C5H5)2(CO)4] w ith
Tetr a eth yl Dip h osp h ite
Celedonio M. Alvarez, Bele´n Gala´n, M. Esther Garc´ıa, V´ıctor Riera, and
Miguel A. Ruiz*
Departamento de Quı´mica Orga´nica e Inorga´nica/ IUQOEM, Universidad de Oviedo,
E-33071 Oviedo, Spain
Claudette Bois
Laboratoire de Chimie Inorganique et Mate´riaux Moleculaires, Universite´ P. et M. Curie,
75252 Paris Cedex 05, France
Received March 17, 2003
The thermal and photochemical reactions of [Fe2Cp2(CO)4] and the bidentate ligand
(EtO)2POP(OEt)2 (tedip) proceed with different P-O or C-O bond cleavages in the
diphosphite ligand. Thus, boiling toluene solutions of the above species yield the known
compound [FeCp(CO)2{P(O)(OEt)2}] and the new dicarbonyl complexes [Fe2Cp2{µ-(EtO)2-
POP(O)(OEt)}{µ-P(OEt)2}(CO)2] (three isomers). The latter are slowly decarbonylated at room
temperature by atmospheric oxygen to give the metal-metal-bonded complex [Fe2Cp2{µ-
(EtO)2POP(O)(OEt)}{µ-P(OEt)2}(µ-CO)]. In contrast, the photochemical reaction between the
iron dimer and the diphosphite ligand gives the phosphido-phosphonate complexes [Fe2-
Cp2{µ-OP(OEt)2}{µ-P(OEt)2}(CO)2], as a mixture of cis and trans isomers. The latter
compounds experience a remarkable P-O bond reductive elimination in boiling xylenes under
a CO atmosphere, whereby the diphosphite-bridged complex [Fe2Cp2(µ-CO)2(µ-tedip)] is
formed in moderate yield. The structure of the latter was analyzed through an X-ray study.
The related complexes [Fe2Cp2(µ-CO)2(CO)(κ1-tedip)] and [{Fe2Cp2(µ-CO)2(CO)}2(µ-tedip)]
were prepared from [Fe2Cp2(µ-CO)2(CO)(NCMe)] and the diphosphite ligand, and their role
as potential precursors of the above dicarbonyl complexes was evaluated. The structures of
the new complexes are analyzed on the basis of the corresponding IR and NMR (1H, 31P,
13C) data, and the reaction pathways operative in these complex reactions are discussed on
the basis of the available data and some cross-experiments.
In tr od u ction
tadienyl ligand, or (c) P-X bond oxidative addition of
the backbone of the diphosphine or diphosphite ligand.
The P-O bond cleavage was found to require lower
thermal activation than the P-CH2 cleavage, and it was
also shown to be reversible. We also noticed a substan-
tial influence of the nature of the metal (Mo or W) on
the relative efficiencies of the above reaction pathways.4
Because of the general interest in the activation of C-H,
P-C, and P-O bonds present in ligands coordinated to
organometallic substrates, we decided to extend our
studies to related substrates having different metal
atoms. In particular, we next considered extending our
studies to A2PXPA2-bridged diiron and diruthenium
cyclopentadienyl complexes. In this paper we present
our results on the Fe2/tedip system, while our studies
on the dppm derivatives will be reported separately.
In our previous studies on the thermal and photo-
chemical decarbonylation reactions of the binuclear
compounds [M2Cp2(CO)4(µ-A2PXPA2)] (Cp ) η5-C5H5; A2-
PXPA2 ) Ph2PCH2PPh2 (dppm), Me2PCH2PMe2 (dmpm),
M2 ) W2,1 Mo2,2 MoW;3 A2PXPA2 ) (EtO)2POP(OEt)2
4
(tedip), M2 ) Mo2, W2 ) we concluded that the unsatur-
ated tricarbonyl intermediates initially formed in those
reactions can experience three major and mutually
competitive subsequent processes (Scheme 1): (a) fur-
ther decarbonylation to generate a stable triple M-M
bond, (b) C-H bond oxidative addition of the cyclopen-
* To whom correspondence should be addressed. E-mail: mara@
sauron.quimica.uniovi.es.
(1) (a) Alvarez, M. A.; Garc´ıa, M. E.; Riera, V.; Ruiz, M. A.; Falvello,
L.; Bois, C. Organometallics 1997, 16, 354. (b) Alvarez, M. A.; Garc´ıa,
M. E.; Riera, V.; Ruiz, M. A.; Falvello, L.; Bois, C.; J eannin, Y. J . Am.
Chem. Soc. 1993, 115, 3786.
(2) (a) Garc´ıa, G.; Garc´ıa, M. E.; Melo´n, S.; Riera, V.; Ruiz, M. A.;
Villafan˜e, F. Organometallics 1997, 16, 626. (b) Riera, V.; Ruiz, M. A.;
Villafan˜e, F.; Bois, C.; J eannin, Y. J . Organomet. Chem. 1989, 375,
C23.
(3) Alvarez, C.; Garc´ıa, M. E.; Riera, V.; Ruiz, M. A. Organometallics
1997, 16, 1378.
In the first place, we noticed the lack of an appropri-
ate starting substrate: that is, a tedip-bridged diiron-
cyclopentadienyl complex. Haines and co-workers re-
ported that the thermal or photochemical reaction
between [Fe2Cp2(CO)4] and tedip gave the phosphonate
complex [FeCp(CO)2{P(O)(OEt)2}] and other nonchar-
acterized species.5 It was thus clear to us that P-O bond
(4) Alvarez, M. A.; Alvarez, C.; Garc´ıa, M. E.; Riera, V.; Ruiz, M.
A.; Bois, C. Organometallics 1997, 16, 2581.
10.1021/om030201m CCC: $25.00 © 2003 American Chemical Society
Publication on Web 06/20/2003

3040 Organometallics, Vol. 22, No. 15, 2003
Alvarez et al.
Sch em e 1. Th e Th r ee Differ en t Rea ction
P a th w a ys Detected d u r in g th e Deca r bon yla tion
Stu d ies of Com p ou n d s [M2Cp 2(CO)4(µ-A2P XP A2)]
(M ) Mo, W; X ) CH2, A ) P h ; X ) O, A ) OEt)1-4
Ch a r t 1
more insight on the factors governing the ill-documented
P-O cleavages of the backbone of the tedip ligand. As
will be shown next, different bond cleavages in the tedip
ligand are almost invariably present in all reactions
studied.
cleavages of the backbone of the tedip ligand were likely
to be operating in the system, as found in our Mo and
W complexes. Therefore, we decided to reinvestigate the
thermal and photochemical reactions of [Fe2Cp2(CO)4]
and tedip. Extensive studies on the thermal or photo-
chemical6,7 reactions of [Fe2L2(CO)4] complexes (L )
cyclopentadienyl or related ligand) have shown that the
primary species formed are the tricarbonyls [Fe2L2(µ-
CO)3] (isolable for L ) C5Me5)8 and [Fe2L2(µ-η1:η2-CO)-
(CO)2] (isolable for L ) C5H5)9 and the 17-electron
radicals [FeL(CO)2], resulting from homolytic cleavage
of the Fe-Fe bond. None of these intermediates appear
to have been recognized as being involved in the
activation of coordinated ligands. We notice, however,
that a C-H (cyclopentadienyl) activation occurs during
the photolysis of chloroform solutions of [Fe2Cp2(µ-CO)2-
(µ-dppm)] to yield [Fe2Cp{η5-C5H4(CHO)}(µ-CO)2(µ-
dppm)],6,10 although the relevant intermediate species
have not been identified in this case.
Resu lts a n d Discu ssion
Th er m a l R ea ct ion of Com p ou n d 1 w it h t ed ip .
Thermal reactions between 1 and tedip were carried out
at different temperatures and solvents. It was found
necessary to use at least conditions of refluxing toluene
in order to initiate any reaction. Best results were
obtained when a 1:2 mixture of 1 and tedip was boiled
in toluene for 30 min. In this way, three isomers of the
formula [Fe2Cp2{µ-(EtO)2POP(O)(OEt)}{µ-P(OEt)2}-
(CO)2] (2a -c; Chart 1) were obtained with an overall
57% yield (23%, 2a ; 22%, 2b; 12%, 2c). A significant
amount of the known phosphonate complex [FeCp{P(O)-
(OEt)2}(CO)2] was also formed.5,11 We noticed that the
relative amount of the latter decreases somewhat under
extreme exclusion of oxygen during the reaction. On the
other hand, we also noticed that the use of a longer
reaction time had no influence on the relative amount
of the isomers, and no further transformations were
observed either. The relative amounts of reagents had
no influence on the isomer ratio, but a general decrease
in all yields was observed when using equimolecular
mixtures of reagents, as expected. The formation of
compounds 2 from 1 requires the elimination of two CO
ligands, the cleavage of the metal-metal bond, and the
coordination of two new three-electron-donor ligands,
they being necessarily formed through important trans-
formations in two tedip molecules which imply respec-
tively P-O and C-O bond cleavages. The similarity in
the spectroscopic data for complexes 2 (Table 1 and
Experimental Section) indicates that they are structural
isomers (Chart 1).
In summary, the present study on the reactions of
[Fe2Cp2(CO)4] (1) and diphosphite (EtO)2POP(OEt)2
(tedip) was initiated (a) to synthesize tedip-bridged
cyclopentadienyl diiron complexes, (b) to establish the
relative efficiencies of C-H (Cp) and P-O (tedip) bond
cleavages at unsaturated diiron centers, and (c) to gain
(5) (a) Du Preez, A. L.; Marais, I. L.; Haines, R. J .; Pidcock, A.;
Safari, M. J . Chem. Soc., Dalton Trans. 1981, 1918. (b) Haines, R. J .;
Du Preez, A. L. J . Organomet. Chem. 1971, 28, 405.
(6) Bitterwolf, T. E. Coord. Chem. Rev. 2000, 206-207, 419.
(7) (a) Wrighton, M. Chem. Rev. 1974, 74, 401. (b) Hooker, R. H.;
Mamound, K. A.; Rest, A. J . J . Chem. Soc., Chem. Commun. 1983,
1022. (c) Zhang, S.; Brown, T. L. J . Am. Chem. Soc. 1992, 114, 2723.
(d) Zhang, S.; Brown, T. L. Organometallics 1992, 11, 4166. (e) Zhang,
S.; Brown, T. L. J . Am. Chem. Soc. 1993, 115, 1779. (f) Vitale, K. K.;
Lee, C. F.; Hille, R.; Gustafson, T. L.; Bursten, B. E. J . Am. Chem.
Soc. 1995, 117, 2286.
The 31P{1H} NMR spectrum for each of the isomers
2a -c exhibits three mutually coupled signals (Table 1).
The resonance at high chemical shift (ca. 350 ppm) is
assigned to the phosphorus atom of a dialkoxyphosphido
(8) Blaha, J . P.; Burten, B. E.; Dewan, J . C.; Frankel, R. B.;
Randolph, C. L.; Wilson, B. A.; Wrighton, M. A. J . Am. Chem. Soc.
1985, 107, 4561.
(9) Alvarez, M. A.; Garc´ıa, M. E.; Riera, V.; Ruiz, M. A. Unpublished
results.
(10) Shade, J . E.; Pearson, W. H.; Brown, J . E.; Bitterwolf, T. E.
Organometallics 1995, 14, 157.
(11) The IR spectrum is in agreement with the literature report for
this product.5 In our hands, this complex is also characterized by a
broad 31P NMR resonance at 104 ppm.

Reactions of [Fe2(η5-C5H5)2(CO)4] with (EtO)2POP(OEt2)
Organometallics, Vol. 22, No. 15, 2003 3041
Ta ble 1. IR a n d NMR Da ta for New Com p ou n d s
δ(P)b
J PP
compd
νst(CO)a
P1
P2
P3
J 12 J 13 J 23
[Fe2Cp2{µ-(EtO)2POP(O)(OEt)}{µ-P(OEt)2}(CO)2] (2a )
[Fe2Cp2{µ-(EtO)2POP(O)(OEt)}{µ-P(OEt)2}(CO)2] (2b)
[Fe2Cp2{µ-(EtO)2POP(O)(OEt)}{µ-P(OEt)2}(CO)2] (2c)
[Fe2Cp2{µ-(EtO)2POP(O)(OEt)}{µ-P(OEt)2}(µ-CO)] (3)
cis-[Fe2Cp2(µ-CO)2(CO)(κ1-tedip)] (cis-4)
1965 (vs), 1943 (s)
1965 (s), 1936 (vs)
1955 (s), 1943 (vs)
1763c
1955 (m), 1743 (vs)
1933 (m), 1743 (vs)
350.9 157.6
339.4 153.0
344.9 155.8
360.4 163.2
165.5d
135.9
128.0
127.7
133.0
126.4d
126.5d
77
83
74
92
77
91
86
92
9
22
9
74
12
trans-[Fe2Cp2(µ-CO)2(CO)(κ1-tedip)] (tr a n s-4)
168.6d
trans,cis-[{Fe2Cp2(µ-CO)2(CO)}2(µ-tedip)] (tr a n s,cis-5) 1955 (m), 1933 (m), 1743 (vs)
163.0, 159.4e
80
cis,cis-[{Fe2Cp2(µ-CO)2(CO)}2(µ-tedip)] (cis,cis-5)
cis-[Fe2Cp2{µ-OP(OEt)2}{µ-P(OEt)2}(CO)2] (cis-6)
1955 (m), 1743 (vs)
159.5e
353.8 190.4
346.1 184.7
179.1
1972 (vs), 1962 (sh)c
81
74
trans-[Fe2Cp2{µ-OP(OEt)2}{µ-P(OEt)2}(CO)2] (tr a n s-6) 1943 (sh), 1937 (vs)c
[Fe2Cp2(µ-CO)2(µ-tedip)] (7)
1744 (w), 1698 (vs)f
a
b
Recorded in toluene solution, unless otherwise stated. ν is given in cm-1
.
Recorded in C6D6 solution at 290 K and 121.50 MHz,
unless otherwise stated. δ is given in ppm relative to external 85% aqueous H3PO4; coupling constants are given in Hertz. phosphorus
atoms are labeled (P1-P3) according to the figure shown. c In petroleum ether. In CD2Cl2; cis:trans ) 9:1. e In toluene-d8 solution.
d
cis,cis:cis,trans ) 6:1, at 253 K. Recorded in CD2Cl2. f In CH2Cl2 solution. When recorded in petroleum ether, ν(CO) bands appear at 1765
(vw), 1754 (vw), 1721 (vs), and 1712 (vs) cm-1
.
ligand, this being a shielding similar to that reported
by Verkade et al. for compounds of the type [Fe2Cp2{µ-
P(OR)2}2(CO)2].12 The second resonance appears at ca.
155 ppm, a value similar to those found for tedip-bridged
dimolybdenum,4 dimanganese,13 or diiron5a complexes,
and is thus assigned to a phosphite-type phosphorus of
a bridged group (P2 in Table 1). The third resonance,
however, exhibits a significantly lower chemical shift
(ca. 130 ppm), indicative of a relevant transformation
in the corresponding phosphorus atom (P3 in Table 1).
In fact, there are different pieces of evidence that
conclusively establish the loss of an ethyl group from
tedip to generate the three-electron-donor bridging
phosphonate (P3) groups of the bidentate ligand are
kept around 80 Hz, in agreement with the PMP angles
expected (ca. 120°) for an almost flat M2P3O ring. In
contrast, the coupling inside the bidentate ligand ex-
hibits a considerably lower value (J 23 ) 9-22 Hz), an
effect which can be attributed to the presence of an
oxygen atom (rather than a metal) connecting the
phosphorus nuclei.15
The main difference among isomers 2a -c stems from
their distinct arrangement of the carbonyl ligands, in
all cases being one terminal CO group bonded to each
iron center, as deduced from the 13C NMR and IR
spectra. The latter are specially informative, as they
show the pattern characteristic of M2(CO)2 oscillators
having a cisoid (2a ) or transoid (2b,c) geometry.16 On
the basis of the higher steric demands of the Cp groups
(relative to the CO ligands) we propose for isomer 2a
to adopt just one out of the two possible cis isomers,
that one having the Cp group close to the PdO moiety
(Chart 1). For the same reason, in the case of the trans
isomers we propose for the more abundant isomer (2b)
the same local environment.
1
ligand (EtO)2POP(O)(OEt). (a) The H NMR spectra of
compounds 2a -c exhibit in each case five inequivalent
resonances for the methyl groups. (b) The solid-state IR
spectrum of 2b exhibits a band at ca. 1155 cm-1, which
can be assigned to the P-O stretch of a PdO bond,
reported to appear in the range 1200-1100 cm-1 5b,14
.
(c) The 13C NMR spectrum of either 2a or 2b, recorded
with selective decoupling of the P3 resonance, revealed
decoupling in just one of the five inequivalent OEt
resonances. In agreement with this formulation, the
mass spectra of 2a ,b displayed in both cases the
corresponding molecular ions at m/z 648. The P-P
couplings for compounds 2 do not change much from
one isomer to other (Table 1), thus suggesting that the
relative arrangement of both phosphorus ligands is the
same in all these isomers. Two-bond coupling between
the phosphido atom (P1) and the phosphite (P2) or
We finally note that the IR spectra of compounds 2,
when recorded in petroleum ether, exhibit an additional
shoulder close to one of the two main bands. This can
be attributed to the presence in solution of rapidly
interconverting isomers differing in the orientation of
the OEt groups, as previously found for the tedip-
bridged complexes [Fe2(µ-CO)(CO)8-2x(µ-tedip)x] (x ) 1,
2).5a
Oxygen -In du ced Decar bon ylation of Com pou n ds
2. When solutions of 2a ,b in petroleum ether or THF
are stirred at room temperature in contact with air,
black-brown suspensions or solutions are slowly formed.
These were shown to contain [Fe2Cp2{µ-(EtO)2POP(O)-
(OEt)}{µ-P(OEt)2}(µ-CO)] (3) as the major species.
(12) Spencer, J . T.; Spencer, J . A.; J acobson, R. A.; Verkade, J . G.
New J . Chem. 1989, 13, 275.
(13) (a) Gimeno, J .; Riera, V.; Ruiz, M. A.; Manotti-Lanfredi, A. M.;
Tiripicchio, A. J . Organomet. Chem. 1984, 268, C13. (b) Riera, V.; Ruiz,
M. A.; Tiripicchio, A.; Tiripicchio-Camellini, M. J . Chem. Soc., Chem.
Commun. 1985, 1505. (c) Riera, V.; Ruiz, M. A.; Tiripicchio, A.;
Tiripicchio-Camellini, M. J . Chem. Soc., Dalton Trans. 1987, 1551. (d)
Carren˜o, R.; Riera, V.; Ruiz, M. A.; Bois, C.; J eannin, Y. Organome-
tallics 1993, 12, 1946.
(14) (a) Bellamy, L. J . The Infrared Spectra of Complex Molecules;
Wiley: New York, 1975; Chapter 18. (b) Wong, E. H.; Ravenelle, R.
M.; Gabe, E. J .; Lee, F. L.; Prasaad, L. J . Organomet. Chem. 1982,
233, 321.
(15) J ameson, C. J . In Phosphorus-31 NMR Spectroscopy in Stere-
ochemical Analysis; Verkade, J . G., Quin, L. D., Eds. VCH: Deerfield
Beach, FL, 1987; Chapter 6.
(16) Braterman, P. S. Metal Carbonyl Spectra; Academic Press:
London, 1975; Chapter 3.

3042 Organometallics, Vol. 22, No. 15, 2003
Alvarez et al.
Ch a r t 2
Compound 3 results from decarbonylation of isomers
2a ,b with a change in the coordination mode of the
remaining CO ligand (from terminal to bridging mode)
and the formation of a new Fe-Fe bond. This reaction
can be then considered as resulting from oxidation of a
CO ligand by atmospheric oxygen to form CO2, much
in the same way as the well-known decarbonylation
reactions induced by Me3NO and related amine oxides.17
Usually, however, CO oxidation by oxygen is accompa-
nied by coordination of oxygen atoms to the metal, as
either terminal or bridging ligands.18,19
The signals observed in the 31P{1H} NMR spectrum
of compound 3 (Table 1) display chemical shifts and P-P
couplings similar to those present in the spectra of 2,
indicating that the phosphorus ligands keep the same
coordination mode and similar spatial arrangement. The
1
same can be deduced from the H NMR spectrum, this
revealing the presence of two inequivalent Cp ligands
and five different ethoxy groups. The most significant
change in the NMR data for 3 is the strong increase of
the coupling between the phosphite- and phosphonate-
type phosphorus nuclei (J 13 ) 74 Hz). This can be
attributed to the presence of the new metal-metal bond,
which allows a new (PMMP) three-bond contribution to
the coupling, now added to the small two-bond contribu-
tion (POP) already present in isomers 2.
The IR spectrum of 3 in the solid state exhibits an
absorption at 1172 cm-1, which can be assigned to the
P-O stretch of a PdO bond, showing that this struc-
tural feature remains intact in the molecule. The IR
spectrum in solution displays just one band in the CO
stretching region. Its low frequency (1763 cm-1) is
clearly indicative of a bridging coordination mode for
this ligand.16
Syn th esis a n d Str u ctu r e of Tr ica r bon yl Der iva -
tives w ith ted ip Liga n d s. As we have just discussed,
the thermal reaction between 1 and tedip does not lead
to the formation of any tedip-bridged diiron derivative.
This is in contrast with the behavior of the dppm ligand
under similar conditions, reported to give the bridged
derivative [Fe2Cp2(µ-CO)2(µ-dppm)] in high yield.20 To
prepare a similar tedip-bridged dicarbonyl compound,
we then considered carrying out substitution reactions
on suitable labile precursors of the type [Fe2Cp2(CO)3-
(L)], such as the acetonitrile adduct [Fe2Cp2(CO)3-
(NCMe)].21 It is well-known that the acetonitrile ligand
is weakly coordinated to the iron atom in this compound
and that it can be substituted very easily by two-
electron-donor ligands. As expected, the tricarbonyl
compound [Fe2Cp2(CO)3(NCMe)] reacts rapidly with
tedip in toluene even at 0 °C to give either the dinuclear
[Fe2Cp2(µ-CO)2(CO)(κ1-tedip)] (4) or the tetranuclear
complex [{Fe2Cp2(µ-CO)2(CO)}2(µ-tedip)] (5) (Chart 2),
depending on the stoichiometry used.
NMR spectrum, which exhibits two weakly coupled
doublets. The signal at 165.5 ppm (Table 1) has the
chemical shift expected for tedip-bridged complexes,4,5a,13
while the signal at 126.4 ppm has a chemical shift very
close to that for the free tedip ligand (128.4 ppm in
C6D6). Therefore, it can be safely assigned to the
uncoordinated phosphorus atom of a κ1-tedip group. In
addition to these signals, the 31P spectra of 4 always
exhibit a weaker pair of doublets, which we assign to a
minor isomer of compound 4. This can be confirmed
through the IR spectrum, where, in addition to the
strong band observed in the bridging C-O frequencies,
there are two bands in the terminal C-O region. This
has been observed in the isostructural complexes [Fe2-
Cp2(µ-CO)2(CO){P(OR)3}],22 where cis and trans isomers
are present and can be distinguished through the
frequency of the terminal C-O stretch, which is higher
for the cis isomer. We then conclude that cis-4 is the
major isomer present in the solutions of this compound.
Compound 4 is air sensitive (as is the free ligand
itself), probably due to the presence of a tedip ligand
coordinated through just one phosphorus atom. When
the compound is heated in toluene at 80 °C for 1 h,
complete decomposition occurs to yield [Fe2Cp2(CO)4]
and [FeCp{P(O)(OEt)2}(CO)2]. No other species could be
detected by IR or 31P NMR monitoring of this reaction.
Complex 5 exhibits stretching C-O bands identical
with those of compound 4. The presence of terminal and
equivalent bridging CO ligands has been also confirmed
through the 13C{1H} NMR spectrum, which also denotes
the presence of double number of bridging than terminal
CO ligands. The 1H NMR spectrum of complex 5
exhibits two signals corresponding to the Cp ligands but
a single triplet for the OEt groups of the ligand (relative
intensities 10:10:12). The implied equivalence of both
phosphorus atoms of the tedip ligand is corroborated
by the 31P{1H} NMR spectrum at room temperature,
which exhibits a singlet resonance at 158.9 ppm, as
expected. All this supports an structure built from two
cis-[Fe2Cp2(µ-CO)2(CO)] moieties bridged by the diphos-
phite ligand (cis,cis-5, Chart 2). A closer inspection of
the 31P spectrum at room temperature reveals the
presence of a weaker, broad resonance at 162.0 ppm.
Compound 4 is a rare example of a metal complex
having a tedip ligand coordinated through a single
phosphorus atom. This is clearly shown in the 31P{1H}
(17) Cotton, F. A.; Wilkinson, G. Advanced Inorganic Chemistry, 5th
ed.; Wiley: New York, 1988; Chapter 22.
(18) Riera, V.; Ruiz, M. A.; Villafan˜e, F.; Bois, C.; J eannin, Y.
Organometallics 1993, 12, 124.
(19) Bottomley, F.; Sutin, L. Adv. Organomet. Chem. 1988, 28, 339.
(20) Haines, R. J .; Du Preez, A. L. J . Organomet. Chem. 1970, 21,
181.
(21) Labinger, J . A.; Madhaven, S. J . Organomet. Chem., 1977, 134,
381.
(22) Haines, R. J .; Du Preez, A. L. Inorg. Chem. 1969, 8, 1459.

Reactions of [Fe2(η5-C5H5)2(CO)4] with (EtO)2POP(OEt2)
Organometallics, Vol. 22, No. 15, 2003 3043
Ch a r t 3
resonances at ca. 350 and 190 ppm. The less shielded
resonances appear in the usual region for the alkoxy-
phosphido bridging ligands (400-250 ppm),4,12 while the
other resonances appear in the expected range for
diethylphosphonates bridging Mo, W, or Mn binuclear
complexes (200-150 ppm).4,24 The 1H and 13C{1H} NMR
spectra for both isomers are consistent with the pro-
posed structure, which implies the presence of two
signals for the Cp ligands and four different sets
assigned to the inequivalent ethoxy groups. The dicar-
bonyl nature of both isomers is confirmed by their 13C-
{1H} NMR and IR spectra. As expected, the 13C carbonyl
resonances exhibit coupling to one or two phosphorus
nuclei, depending on the iron atom to which these CO
ligands are coordinated. The identification of the cis and
trans isomers is derived from the IR spectra recorded
in petroleum ether, which then exhibit two sharp bands
in the region of the terminal C-O stretches. The relative
intensity of these bands, weak and strong for one isomer
and strong and weak (in order of decreasing frequency)
for the other one, allow us to identify them as trans and
cis isomers, respectively.16
When the 31P{1H} NMR spectrum is recorded at 253
K, this broad resonance splits into two doublets at 163.0
and 159.4 ppm with a coupling constant of 80 Hz. By
comparing these values with that of the major isomer
cis,cis-5 and taking into account the relative 31P shifts
in the isomers present in 4 (δtrans - δcis ) 3 ppm), we
propose the minor isomer to be tr a n s,cis-5 (Chart 2).
This is in agreement with the presence of a shoulder at
1933 cm-1 in the IR spectrum of toluene solutions of 5
(Table 1) and with the lack of equivalence of the
corresponding four Cp ligands (only three of the corre-
Syn th esis a n d Str u ctu r e of [F e2Cp 2(µ-CO)2(µ-
ted ip )] (7). When the photochemical reaction of 1 and
tedip is carried out at 15 °C, a mixture of isomers 6 and
ca. 5% of the tedip-bridged [Fe2Cp2(µ-CO)2(µ-tedip)] (7,
Chart 3) is obtained. Unfortunately, we have not been
able to improve the yield of complex 7 by changing the
experimental conditions of the photolysis. We also note
that photolysis of toluene solutions of the tricarbonyl
4, a complex with the right structure to yield 7 after
CO ejection, apparently gives 7 cleanly, as deduced from
the IR and 31P spectra of the reaction mixture, but the
yield after chromatography of the reaction mixture is
very low.
1
sponding resonances located in the H NMR spectrum
at 253 K).
P h otoch em ica l Rea ction s of Com p ou n d 1 w ith
Ted ip . As stated above, the photochemical reaction
between 1 and tedip was studied by Haines in 1981,5a
but only the mononuclear complex [FeCp{P(O)(OEt)2}-
(CO)2] could be isolated and identified from the corre-
sponding reaction mixtures. We have now reinvestigat-
ed this reaction, and we have found results quite
different from either our thermal reaction or the previ-
ous photochemical results.
Photolysis of stoichiometric amounts of 1 and tedip
leads to a mixture of the dicarbonyl compounds cis- and
trans-[Fe2Cp2{µ-OP(OEt)2}{µ-P(OEt)2}(CO)2] (cis-6 and
tr a n s-6, Chart 3) in good yield (ca. 1:1 ratio). Best
results are obtained using low reaction temperatures
(-15 °C) and toluene as a solvent. We have also found
that the reaction time has no significant influence on
the ratio of isomers, although prolonged photolysis leads
to a decrease in the overall yield. The formation of these
two isomers involve the elimination of two molecules of
CO, cleavage of the Fe-Fe bond, and the activation of
one of the P-O bonds of the backbone of the tedip
ligand, to give two new bridging three-electron-donor
ligands (the diethoxyphosphido and diethylphosphonate
bridges).
The best synthetic route we have found for 7 is based
on the high-temperature transformation 6/7 under a CO
atmosphere. This requires the reductive elimination of
a P-O bond between the diethoxyphosphido group and
the diethylphosphonate ligand to regenerate the tedip
molecule, a process previously observed only at Mo2
centers.4 In this way, complex 7 can be isolated in an
overall yield of 15% (based on [Fe2Cp2(CO)4]), which
means that the P-O bond reductive elimination step
has an efficiency of ca. 50%. Once formed, the tedip-
bridged 7 cannot be converted back into the phosphido
precursors 6 either in refluxing xylenes or under vis-
ible-UV irradiation.
The structure of 7 has been solved through an X-ray
study and is depicted in Figure 1, while Table 2 lists
the most relevant bond distances and angles. The
molecule displays two iron cyclopentadienyl fragments
bridged by a tedip and two carbonyl ligands. The Fe2P2O
ring defined by the diphosphite and iron atoms is almost
flat, and the bridging carbonyls lie almost in a plane
perpendicular to it (see projection in Figure 1). The
intermetallic separation (Fe1-Fe2 ) 2.512(2) Å) is very
similar to the values found (ca. 2.52 Å) for the diphos-
phine-bridged [Fe2CpCp′(µ-CO)2(µ-Ph2PCH2CH2PPh2)]
(Cp′ ) C5H5, C5H4CHO)10 and shorter than the tedip-
The structure of isomers 6 has been proposed on the
basis of the corresponding spectroscopic data and com-
parison with data for the related complexes [M2Cp2{µ-
OP(OEt)2}{µ-P(OEt)2}(CO)2] (M ) Mo, W)4 and [Fe2-
Cp2{µ-N(Ph)P(OPh)2}{µ-P(OPh)2}(CO)2].23 The H and
1
31P{1H} NMR spectra of compounds 6 are very similar,
as expected for cis and trans isomers (Table 1 and
Experimental Section). Each of the isomers displays two
(24) (a) Liu, X. Y.; Riera, V.; Ruiz, M. A.; Lanfranchi, M.; Tiripicchio,
A.; Tiripicchio-Camellini, M. Organometallics 1994, 13, 1940. (b) Liu,
X. Y.; Riera, V.; Ruiz, M. A.; Tiripicchio, A.; Tiripicchio-Camellini, M.
Organometallics 1996, 15, 974.
(23) Balakrishna, M. S.; Krishnamurthy, S. S. Indian J . Chem. 1991,
30A, 536.

3044 Organometallics, Vol. 22, No. 15, 2003
Alvarez et al.
F igu r e 1. (a) CAMERON diagram of the molecular structure of compound 7. Ellipsoids represent 30% probability. (b)
View of the molecule along the Fe-Fe direction.
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for Com p ou n d 7
the two first-mentioned bands correspond to the mol-
ecule present in the crystal, while the other two bands
would arise from a slight structural modification of the
former. We note again that complexes [Fe2(µ-CO)-
(CO)8-2x(µ-tedip)x] (x ) 1, 2)25 also exhibit splitting of
the bridging CO bands, which has been explained in
terms of more than one conformer in solution resulting
from different relative orientations of ethoxy groups in
the tedip ligand.
d (Å)
θ (deg)
Fe(1)-Fe(2)
Fe(1)-P(1)
Fe(2)-P(2)
Fe(1)-C(1)
Fe(2)-C(1)
Fe(1)-C(2)
Fe(2)-C(2)
P(1)-O(3)
P(2)-O(3)
P(1)-O(4)
P(1)-O(5)
P(2)-O(6)
P(2)-O(7)
O(1)-C(1)
O(2)-C(2)
2.512(2)
2.111(4)
2.101(4)
1.91(1)
1.90(1)
1.92(1)
1.90(1)
1.659(8)
1.631(9)
1.587(9)
1.605(9)
1.59(1)
1.59(1)
1.18(1)
1.17(1)
Fe(2)-Fe(1)-P(1)
Fe(1)-Fe(2)-P(2)
Fe(1)-C(1)-Fe(2)
Fe(1)-C(2)-Fe(2)
Fe(1)-C(1)-O(1)
Fe(2)-C(1)-O(1)
Fe(1)-C(2)-O(2)
Fe(2)-C(2)-O(2)
P(1)-O(3)-P(2)
Fe(1)-P(1)-O(3)
Fe(2)-P(2)-O(3)
O(4)-P(1)-O(5)
O(6)-P(2)-O(7)
C(1)-Fe(2)-P(2)
C(1)-Fe(1)-P(1)
C(2)-Fe(2)-P(2)
C(2)-Fe(1)-P(1)
94.6(1)
94.7(1)
82.3(5)
82.5(5)
138.7(10)
138.6(10)
136.7(10)
140.1(10)
120.9(5)
114.0(3)
115.1(3)
98.9(4)
98.2(6)
87.9(4)
92.0(4)
91.4(4)
Rea ction P a th w a ys of ted ip a t Diir on Cen ter s.
As we have just discussed, the diphosphite ligand tedip
reacts with [Fe2Cp2(CO)4] to give mainly products
derived of the cleavage of either C-O (compounds 2) or
P-O bonds (compounds 2 and 6) of the ligand. The
simple substitution product 7 is obtained only in low
yields under photochemical conditions and room tem-
perature. All those products require several elementary
steps to be formed; thus, the detailed reaction pathways
in operation must be necessarily complex and cannot
be inferred from a synthetic work. Despite this, by
taking into account all our data and the general
knowledge available on the decarbonylation reactions
of 1, we can draw a rational picture of the main reaction
pathways likely to be operative in the system under
study (Schemes 2 and 3).
87.4(4)
bridged iron(0) complex [Fe2(µ-CO)(CO)4(µ-tedip)2] (2.666-
(2) Å),25 as expected.
Spectroscopic data in solution for 7 are consistent with
the highly symmetric solid-state structure. This is
reflected in the chemical equivalence of both phosphorus
atoms and of cyclopentadienyl and ethoxy H and C
nuclei (Table 1 and Experimental Section). The IR
spectrum of 7 in most solvents exhibits, around 1700
cm-1, a very weak band and a strong band in order of
decreasing frequency, in agreement with the presence
of two bridging carbonyls defining almost a 180° relative
angle.16 When recorded in petroleum ether, however,
both bands appear split. As the NMR spectra of 7 in
toluene-d8 remained unchanged down of -90 °C, we
rather attribute this splitting of the ν(CO) bands to the
presence of two very similar conformers, rapidly inter-
converting on the NMR time scale. In fact, when
recording the IR spectrum of a petroleum ether solution
freshly prepared from crystals of 7, we observe first the
predominance of those bands at 1765 (vw) and 1721 (vs)
cm-1, but then bands at 1754 (vw) and 1712 (vs) cm-1
progressively grow so as to reach an intensity compa-
rable to that of the former bands after 1 h. No further
changes occur in the spectrum. All this suggests that
As stated in the Introduction, substitution reactions
on compound 1 can occur through initial CO dissociation
or homolytic cleavage of the Fe-Fe bond. In the first
case, this would be expectedly followed by addition of
the ligand to give the tricarbonyl complex 4. However,
we have shown through separate experiments that
neither thermal nor photochemical treatment of 4 give
significant amounts of either 2 or 6. From this we
conclude that initial CO dissociation from 1 is not a
significant pathway in the reactions under study. We
rather trust that both the thermal and the photochemi-
cal reactions between 1 and tedip are initiated by the
homolytic cleavage of the Fe-Fe bond to give the [FeCp-
(CO)2] radical A,6,7 which is well-known to experience
easy CO substitution by ligands. In our case, A would
thus easily give the 17-electron tedip derivative [FeCp-
(CO)(κ1-tedip)] (B).7c At this point, three radical recom-
binations can occur: A-A, A-B or B-B (Scheme 2).
The first one affords the starting complex 1, which
(25) Cotton, F. A.; Haines, R. J .; Hanson, B. E.; Sekutowski, J . C.
Inorg. Chem. 1978, 17, 2010.

Reactions of [Fe2(η5-C5H5)2(CO)4] with (EtO)2POP(OEt2)
Organometallics, Vol. 22, No. 15, 2003 3045
Sch em e 2. P r op osed Rea ction P a th w a ys in th e
Th er m a l Rea ction of 1 a n d ted ip
of complexes 2 and 6, as stated above. The dimerization
process B + B could happen as well, but this is expected
to be slow, as shown for other phosphine-substituted
radicals of the type [FeCp(CO)(L)]. As a result, further
evolution of the radicals A and B, different from simple
recombination, should be involved in order to explain
our experimental results.
Under thermal conditions, we propose that elimina-
tion of an ethyl radical occurs from B, as has been
observed before in the reaction of the rhodium dimer
[Rh2L4]2 (L4 ) porphyrin ligand) with trimethyl phos-
phite.26 This would lead to the formation of the 16-
electron intermediate G, which rapidly would react with
any 2-electron ligand available, for instance the unco-
ordinated phosphorus atom of radical B, to give the
dinuclear radical H. This complex could evolve by
extrusion of a P(O)(OEt)2 radical to finally give com-
plexes 2. We note that the phosphonate radical [P(O)-
(OEt)2] has been proposed as a precursor in several
syntheses of phosphonate complexes.27 Reaction of the
latter radical with intermediate A also explains the
appearance of significant amounts of the complex [FeCp-
{P(O)(OEt)2}(CO)2] in our thermal reactions.
Under photochemical conditions, it is proposed that
either of the radicals A and B could experience further
decarbonylation to give 15-electron radicals.7c In our
case, this would lead to radicals C and D, the combina-
tion of which would give the monocarbonyl intermediate
E, isoelectronic with the compound [Fe2Cp2(µ-η1:η2-CO)-
(CO)2]6b,9 and also having probably a µ-η1:η2 bridging
CO ligand. This intermediate could lead to the formation
of complex 7 after carbonylation or to complexes 6 by
intramolecular oxidative addition of a P-O bond of the
tedip ligand, via intermediate F , and further carbon-
ylation. The transformations 7/E/F /6 are similar to
those previously postulated to explain the thermal
isomerization between [Mo2Cp2{µ-(EtO)2POP(OEt)2}-
(CO)4] and [Mo2Cp2{µ-OP(OEt)2}{µ-P(OEt)2}(CO)4].4 Our
experimental observations indicate that the transforma-
tion E/F would be reversible, with a significant influence
of temperature on the equilibrium ratio. At high tem-
peratures the tedip-bridged E would dominate, while
phosphonate F would prevail at low temperature. This
hypothesis explains the photochemical production of just
complex 6 at -30 °C and the appearance of moderate
amounts of 7 in the room-temperature photolytic ex-
periments. On the other hand, this hypothesis gives a
rationale for the high-temperature transformation of 6
into 7 and the observation that the yield increases in
the presence of CO.
Sch em e 3. P r op osed Rea ction P a th w a ys in th e
P h otoch em ica l Rea ction of 1 a n d ted ip
Con clu sion
The reactions between [Fe2Cp2(CO)4] and the diphos-
phite ligand (EtO)2POP(OEt)2 seem to proceed mainly
through the radical intermediates [FeCp(CO)2] and
[FeCp(CO)(κ1-tedip)], which invariably experience ad-
ditional C-O (ethoxy) or P-O (backbone) bond cleav-
ages of the phosphorus ligand, but no activation of the
C-H bonds in the cyclopentadienyl ligand. Under
(26) Wayland, B. B.; Woods, B. A. J . Chem. Soc., Chem. Commun.
1981, 475.
(27) Goh, L. Y.; D’Aniello, M. J ., J r.; Slater, S.; Muetterties, E. L.;
Tavanaiepour, I.; Chang, M. I.; Fredrich, M. F.; Day, V. W. Inorg.
Chem. 1979, 18, 192.
obviously must be in equilibrium with radical A under
photolytic conditions. Reaction A + B would give
compound 4, but this cannot account for the formation

3046 Organometallics, Vol. 22, No. 15, 2003
Alvarez et al.
{1H} NMR (100.63 MHz, C6D6, assignment of PC couplings
from selectively decoupled spectra): δ 218.8 (dd, J CP3 ) 52,
J CP1 ) 23, CO), 217.5 (dd, J CP2 ) 41, J CP1 ) 20, CO), 85.6, 84.1
(2 × s, Cp), 61.6 (d, J CP2 ) 8, CH2), 61.4 (d, J CP1 ) 7, CH2),
thermal activation, both the above cleavages occur, to
generate phosphite-phosphonate (µ-(EtO)2POP(O)-
(OEt)) and phosphonate (µ-OP(OEt)2) bridging groups.
Under photochemical conditions, backbone P-O bond
oxidative addition of the tedip ligand dominates, to give
phosphonate and alkoxyphosphido [µ-P(OEt)2] bridging
groups, even at -25 °C. This last transformation is
reversible, and PO bond reductive elimination to regen-
erate the tedip ligand can be forced in refluxing xylenes.
61.3 (d, J CP2 ) 9, CH2), 61.1 (d, J CP1 ) 9, CH2), 58.2 (d, J CP3
)
9, CH2), 17.4 (d, J CP3 ) 5, Me), 16.3 (d, J CP2 ) 6, Me), 16.05,
16.00 (2 × d, J CP1 ) 7, J CP2 ) 7, 2 × Me), 15.4 (d, J CP1 ) 5,
Me). FAB-MS: m/z (%) 648(15) [M+], 620(85) [M+ - CO], 603-
(100) [M+ - OEt], 528(75) [M+ - CO - P(O)(OEt)]. Data for
2b are as follows. Anal. Calcd for C22H35O9P3Fe2: C, 40.77; H,
1
5.44. Found: C, 40.95; H, 5.51. H NMR (200.13 MHz, C6D6):
δ 4.66, 4.62 (2 × s, 2 × 5H, Cp), 4.50-3.60 (m, 10H, CH2),
1.39, 1.31, 1.28, 1.13, 1.09 (5 × t, J HH ) 7, 5 × 3H, Me). 31P-
{1H} NMR (80.01 MHz, C6D6): δ 339.5 (dd, J PP ) 91, 83, µ-P,
Exp er im en ta l Section
Gen er a l Com m en ts. All manipulations and reactions were
carried out using standard Schlenk techniques under an
atmosphere of dry, oxygen-free nitrogen. Solvents were puri-
fied according to standard literature procedures28 and distilled
under nitrogen prior to use. Petroleum ether refers to the
fraction distilling in the range 60-65 °C. The compound [Fe2-
Cp2(CO)3(NCMe)] was prepared as described previously.21 The
compounds [Fe2Cp2(CO)4] and tedip were obtained from the
usual commercial suppliers and used without further purifica-
tion. Photochemical experiments were preformed using jack-
eted Pyrex or quartz Schlenk tubes, refrigerated by a closed
2-propanol circuit kept at the desired temperature with a
cryostat or by tap water. A 400 W mercury lamp (Applied
Photophysics), placed ca. 1 cm away from the Schlenk tube,
was used for these experiments. Low-temperature chromato-
graphic separations were carried out analogously using jack-
eted columns. Commercial aluminum oxide (Aldrich, activity
I, 150 mesh) was degassed under vacuum prior to use. The
latter was mixed afterward under nitrogen with the appropri-
ate amount of water to reach the activity desired. Filtrations
were carried out using diatomaceous earth. NMR spectra were
recorded at 400.13 (1H), 163.01 (31P{1H}), or 100.62 MHz (13C-
{1H} and 13C{1H, 31P}), at room temperature unless otherwise
stated. Chemical shifts (δ) are given in ppm, relative to
internal TMS (1H, 13C) or external 85% H3PO4 aqueous solution
(31P), with positive values for frequencies higher than that of
the reference. Coupling constants (J ) are given in hertz. 13C-
{1H} NMR spectra were routinely recorded on solutions
containing a small amount of tris(acetylacetonato)chromium-
(III) as a relaxation reagent.
P r epar ation of Isom er s [Fe2Cp2{µ-(EtO)2P OP (O)(OEt)}-
{µ-P (OEt)2}(CO)2] (2). A toluene solution (15 mL) of com-
pound 1 (0.300 g, 0.84 mmol) and tedip (0.26 mL, 1.06 mmol)
was refluxed for 30 min to give a yellow-orange solution. This
solution was concentrated under vacuum and chromato-
graphed at -15 °C on an alumina column (activity 3.5, 30 ×
2.5 cm) prepared in petroleum ether. Elution with THF/
petroleum ether (1:5) gave a yellow fraction containing a
mixture of compounds that were not identified. Elution with
THF/petroleum ether (1:2) gave two yellow fractions containing
isomers 2a ,b, respectively. Elution with THF/petroleum ether
(3:1) gave a third yellow fraction containing isomer 2c. Finally,
elution with pure THF gave a yellow-orange fraction contain-
ing the compound [FeCp{PO(OEt2)}(CO)2]. Removal of solvents
under vacuum from the different fractions gave respectively
compounds 2a (0.100 g, 23%), 2b (0.094 g, 22%), and 2c (0.054
g, 12%) as yellow oily solids. The latter can be converted into
microcrystalline powders after recrystallization from petro-
leum ether solutions at -20 °C. Data for 2a are as follows.
Anal. Calcd for C22H35O9P3Fe2: C, 40.77; H, 5.44. Found: C,
41.02; H, 5.42. 1H NMR (200.13 MHz, C6D6): δ 4.73, 4.72 (2 ×
s, 2 × 5H, Cp), 4.40-3.60 (m, 10H, CH2), 1.38, 1.28, 1.19, 1.12,
1.08 (5 × t, J HH ) 7, 5 × 3H, Me). 31P{1H} NMR (80.01 MHz,
C6D6): δ 350.9 (t, J PP ) 77, µ-P, P1), 157.7 (dd, J PP ) 77, 9,
[P(OEt)2], P2), 135.9 (dd, J PP ) 77, 9, [P(O)(OEt)], P3). 13C-
P1), 153.1 (dd, J PP ) 83, 22, [P(OEt)2], P2), 128.0 (dd, J PP
)
91, 22, [P(O)(OEt)], P3). 13C{1H} NMR (100.63 MHz, C6D6,
assignment of PC couplings from selectively decoupled spec-
tra): δ 219.4 (dd, J CP3 ) 47, J CP1 ) 22, CO), 217.4 (dd, J CP2
)
41, J CP1 ) 22, CO), 84.6, 84. (2 × s, Cp), 62.8 (d, J CP2 ) 9,
CH2), 62.4 (d, J CP1 ) 10, CH2), 61.5 (d, J CP1 ) 10, CH2), 61.4
(d, J CP2 ) 11, CH2), 58.1 (d, J CP3 ) 10, CH2), 17.4 (d, J CP3 ) 6,
Me), 16.5 (d, J CP1 ) 7, Me), 16.4 (d, J CP2 ) 7, Me), 16.2 (d, J CP2
) 7, Me), 16.1 (d, J CP1 ) 8, Me). FAB-MS: m/z (%) 648(15)
[M+], 621(25) [M+ + H - CO], 603(100) [M+ - OEt], 528(75)
1
[M+ - CO - P(O)(OEt)]. Data for 2c are as follows. H NMR
(200.13 MHz, C6D6): δ 4.64, 4.54 (2 × s, 2 × 5H, Cp), 4.70-
3.70 (m, 10H, CH2), 1.30, 1.25, 1.20, 1.19, 1.15 (5 × t, J HH ) 7,
5 × 3H, Me). 31P{1H} NMR (80.01 MHz, C6D6): δ 344.9 (dd,
J PP ) 86, 74, µ-P), 155.8 (dd, J PP ) 74, 9, [P(OEt)2]), 127.7
(dd, J PP ) 86, 9, [P(O)(OEt)]).
P r ep a r a tion of [F e2Cp 2{µ-(EtO)2P OP (O)(OEt)}{µ-P (O-
Et)2}(µ-CO)] (3). A petroleum ether solution (10 mL) of
compound 2a (0.094 g, 0.26 mmol) was stirred at room
temperature in a Schlenk flask without previous exclusion of
air for about 3 weeks, at which point a brown suspension was
formed. The solvent was then removed under vacuum, the
residue was extracted with toluene, and the extract was
filtered. The filtrate was concentrated under vacuum, layered
with 5 mL of petroleum ether, and then allowed to mix by slow
diffusion to yield black-brown crystals of compound 3 (0.028
g, 30%). Anal. Calcd for C21H35O8P3Fe2: C, 40.67; H, 5.69.
Found: C, 40.62; H, 5.67. 1H NMR (C6D6): δ 5.40-5.30 (m,
2H, CH2), 4.65, 4.40 (2 × s, 2 × 5H, Cp), 4.30-4.20 (m, 2H,
CH2), 4.20-4.00 (m, 2H, CH2), 4.00-3.80 (m, 4H, CH2), 1.48,
1.30, 1.20, 1.10, 1.02 (5 × t, J HH ) 7, 5 × 3H, Me). 31P{1H}
NMR (C6D6): δ 360.4 (t, J PP ) 92, µ-P), 163.2 (dd, J PP ) 92,
74, [P(OEt)2]), 133.0 (dd, J PP ) 92, 74, [P(O)(OEt)]).
P r ep a r a tion of [F e2Cp 2(µ-CO)2CO)(K1-ted ip )] (4). A cold
(0 °C) toluene solution (10 mL) of tedip (0.15 mL, 0.545 mmol)
was transferred over 0.100 g of [Fe2Cp2(CO)3(NCMe)] (0.273
mmol) placed in a refrigerated flask at 0 °C, and the mixture
was stirred at this temperature for 15 min to yield a red-violet
solution. Solvent was then removed under vacuum, and the
residue was dissolved in CH2Cl2/petroleum ether (1:2) and
chromatographed at -15 °C on an alumina column (activity
3.5, 12 × 1.5 cm) prepared in petroleum ether. Elution with
the same solvent mixture gave a red fraction, containing [Fe2-
Cp2(CO)4], and two violet fractions. These two fractions
contained compound 4 and small amounts of compound 5,
respectively. Removal of solvents from the major violet fraction
yielded compound 4 (0.092 g, 58%) as a violet air-sensitive
1
powder. H NMR (CD2Cl2): cis-4, δ 4.69, 4.55 (2 × s, 2 × 5H,
Cp), 4.00 (q, J HP ) J HH ) 7, 4H, CH2), 3.94, 3.74 (2 × m, 2 ×
2H, CH2), 1.29 (t, J HH ) 7, 6H, Me), 1.11 (br, 6H, Me). 31P{1H}
NMR (CD2Cl2): cis-4, δ 165.5 (d, J PP ) 12, P-Fe), 126.4 (d,
J PP ) 12, P); tr a n s-4, δ 168.6 (br, P-Fe), 126.5 (br, P); cis:
trans ) 9:1. 13C{1H} NMR (CD2Cl2): cis-4, δ 280.0 (d, J CP
)
24, 2 × µ-CO), 215.8 (s, CO), 87.4, 86.8 (2 × s, Cp), 61.1 (d,
J CP ) 6, CH2), 58.9 (d, J CP ) 10, CH2), 17.0 (d, J CP ) 4, Me),
16.0 (br, Me).
(28) Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory
Chemicals; Pergamon Press: Oxford, U.K., 1988.

Reactions of [Fe2(η5-C5H5)2(CO)4] with (EtO)2POP(OEt2)
Organometallics, Vol. 22, No. 15, 2003 3047
Ta ble 3. Cr ysta l Da ta for Com p ou n d 7
P r ep a r a tion of [{F e2Cp 2(µ-CO)2(CO)}2(µ-ted ip )] (5). The
procedure is identical with that described for 4, except that
35 µL of tedip (0.136 mmol) was used. Two violet fractions were
collected, containing compounds 4 (minor) and 5 (major),
respectively. Workup of the major fraction yielded compound
5 (0.100 g, 75%) as a violet powder. Anal. Calcd for C34H40O11P2-
Fe4: C, 44.88; H, 4.43. Found: C, 44.80; H, 4.49. 1H NMR
(toluene-d8): cis,cis-5, δ 4.49, 4.28 (2 × s, 2 × 5H, Cp), 4.20-
4.00 (m, 8H, CH2), 1.13 (t, J HH ) 7, 12H, Me). 1H NMR
(toluene-d8, 253 K): cis,cis-5, δ 4.45, 4.34 (2 × s, 2 × 10H,
Cp), 4.06-3.90 (m, 8H, CH2), 1.13 (t, J HH ) 7, 12H, Me);
tr a n s,cis-5, δ 4.55, 4.50, 4.45 (3 × s, 3 × 5H, Cp), other
resonances for this isomer obscured by those of the major
isomer. cis,cis:trans,cis ) 6:1. 31P{1H} NMR (toluene-d8): cis,-
cis-5, δ 158.9 (s); tr a n s,cis-5, δ 162.0 (br). 31P{1H} NMR
(toluene-d8, 253 K): cis,cis-5, δ 159.5 (s); tr a n s,cis-5, δ 163.0
(d, J PP ) 80, P), 159.4 (d, J PP ) 80, P). 13C{1H} NMR (50.33
MHz, CD2Cl2): cis,cis-5, δ 280.4 (false t, J CP + J CP′ ) 11,
µ-CO), 215.7 (s, CO), 87.6, 87.0 (2 × s, Cp), 62.1 (s, CH2), 16.0
(s, Me).
mol formula
mol wt
C20H30Fe2O7P2
556.09
cryst syst
orthorhombic
space group
cryst color
cryst shape
radiation (λ, Å)
a, Å
Pbca
black-violet
parallelepiped
Mo KR (λ ) 0.710 69 Å)
18.152(8)
b, Å
16.066(7)
c, Å
16.359(8)
4771(6)
V, Å3
Z
8
1.55
13.8
calcd density, g cm-3
µ(Mo KR), cm-1
diffractometer
temp, K
Philips-PW 1100
293
scan type
ω/2θ
θ limits, deg
scan width
total no. of unique data
no. of unique data used
Ra
1-25
1.2 + 0.345 tan θ
4203
1437 ((Fo)2 > 3σ(Fo)2)
P r ep a r a tion of cis- a n d tr a n s-[F e2Cp 2{µ-OP (OEt)2}{µ-
P (OEt)2}(CO)2] (6). A toluene solution (20 mL) of compound
1 (0.300 g, 0.84 mmol) and tedip (0.26 mL, 1.06 mmol) was
placed in a jacketed Pyrex flask and photolyzed at -25 °C for
1 h with a N2 purge to give a green solution. This solution
was chromatographed at -15 °C on an alumina column
(activity 3, 30 × 2.5 cm) prepared in petroleum ether. Elution
with CH2Cl2/petroleum ether (1:1) gave a yellow fraction
containing a small amount of an uncharacterized compound
(IR: 2013 (w), 1961 (w), and 1923 (vs) cm-1 in toluene),
followed by a small amount of the starting compound 1.
Elution with CH2Cl2/petroleum ether (2:1) gave a green
fraction containing compound tr a n s-6. Finally, elution with
CH2Cl2/petroleum ether (3:1) gave another green fraction
containing compound cis-6. Removal of solvents under vacuum
from the last two fractions gave compounds tr a n s-6 (0.100 g,
23%) and cis-6 (0.094 g, 22%) as green solids, respectively.
Data for tr a n s-6 are as follows. Anal. Calcd for C20H30O7P2-
Fe2: C, 43.20; H, 5.44. Found: C, 43.29; H, 5.45. 1H NMR
(200.13 MHz, C6D6): δ 4.51, 4.50 (2 × s, 2 × 5H, Cp), 4.10-
3.90 (m, 5H, CH2), 3.76-3.62 (m, 3H, CH2), 1.30, 1.29, 1.25,
1.18 (4 × t, J HH ) 7, 4 × 3H, Me). 31P{1H} NMR (80.01 MHz,
C6D6): δ 346.1 (d, J PP ) 74, µ-P(OEt)2), 184.7 (d, J PP ) 74,
µ-OP(OEt)2). 13C{1H} NMR (50.33 MHz, C6D6): δ 222.3 (d, J CP
) 29, CO), 216.6 (dd, J CP ) 42, 24, CO), 83.5, 82.8 (2 × s, Cp),
0.049
0.052
0.88, 1.25
282
-0.37
0.39
b
Rw
abs coeff cor (min, max)
no. of variables
∆Fmin (e Å-3
)
)
∆Fmax (e Å-3
a
b
2 1/2
R ) ∑|Fo - |Fc||/∑Fo. Rw ) [∑w(Fo - |Fc|)2/∑wFo
] .
solution of the complex in petroleum ether. Anal. Calcd for
C20H30O7P2Fe2: C, 43.20; H, 5.44. Found: C, 43.51; H, 5.32.
1H NMR (C6D6): δ 4.54 (s, 10H, Cp), 4.21-4.12 (m, 4H, CH2),
4.12-4.00 (m, 4H, CH2), 1.09 (t, J HH ) 7, 12H, Me). 31P{1H}
NMR (C6D6): δ 179.1 (s).
X-r a y Str u ctu r e Deter m in a tion for Com p ou n d 7. A
selected crystal was set up on an automatic diffractometer.
Unit cell dimensions with estimated standard deviations were
obtained from least-squares refinements of the setting angles
of 25 well-centered reflections. Two standard reflections were
monitored periodically; they showed no change during data
collection. Crystallographic data and other information are
summarized in Table 3. Corrections were made for Lorentz
and polarization effects. Empirical absorption correction (Di-
fabs)29 and extinction correction were applied.
Computations were performed by using the PC version of
CRYSTALS.30 Atomic form factors for neutral Fe, P, O, C, and
H were taken from ref 31. Real and imaginary parts of
anomalous dispersion were taken into account. The structure
was solved by direct methods (SHELXS)32 and successive
Fourier maps. Hydrogen atoms were geometrically located, and
they were given an overall isotropic thermal parameter, while
non-hydrogen atoms were anisotropically refined.
Full-matrix least-squares refinements were carried out in
three blocks by minimizing the function ∑w(Fo - |Fc|)2 where
Fo and Fc are the observed and calculated structure factors,
respectively. Models reached convergence with R and Rw
having values defined and listed in Table 3. The weighting
scheme was unity. Figure 1 represents a CAMERON33 view
of compound 7.
62.9 (d, J CP ) 11, CH2), 62.4 (d, J CP ) 13, CH2), 59.8 (d, J CP
)
5, CH2), 57.9 (d, J CP ) 10, CH2), 16.8 (d, J CP ) 6, Me), 16.6 (d,
J CP ) 7, 2 × Me), 16.5 (d, J CP ) 5, Me). Data for cis-6 are as
follows. 1H NMR (C6D6): δ 4.45, 4.35 (2 × s, 2 × 5H, Cp), 4.10-
3.65 (m, 8H, CH2), 1.41, 1.22, 1.14, 1.13 (4 × t, J HH ) 7, 4 ×
3H, Me). 31P{1H} NMR (C6D6): δ 353.8 (d, J PP ) 81, µ-P(OEt)2),
190.4 (d, J PP ) 81, µ-OP(OEt)2).
P r ep a r a tion of [F e2Cp 2(µ-CO)2(µ-ted ip )] (7). A mixture
of isomers 6 was prepared as described above, but starting
from [Fe2Cp2(CO)4] (0.198 g, 0.56 mmol). The crude reaction
mixture was filtered and the solvent removed under vacuum.
The residue was then dissolved in xylenes (12 mL) and the
solution refluxed for 3 h while gently bubbling CO through it.
Solvent was afterward removed from the resulting brownish
solution, and the residue was dissolved in CH2Cl2/petroleum
ether (1:2) and chromatographed at -15 °C on an alumina
column (activity 3.5, 15 × 2.5 cm) prepared in petroleum ether.
Elution with the same solvent mixture gave a yellow fraction
containing a small amount of an uncharacterized compound
(IR: 1950 cm-1 in CH2Cl2). Elution with CH2Cl2/petroleum
ether (1:1) gave a purple fraction containing compound 7.
Finally, elution with pure THF gave a yellow-orange fraction
containing the compound [FeCp{PO(OEt)2}(CO)2]. Removal of
solvent under vacuum from the purple fraction gave compound
7 as a violet powder (0.035 g, 15%). The crystals used in the
X-ray study were grown at -20 °C from a concentrated
Ack n ow led gm en t. We thank the Ministerio de
Ciencia y Tecnolog´ıa of Spain for financial support
(29) Walker, N.; Stuart, D. Acta Crystallogr., Sect. A 1983, 39, 158.
(30) Watkin, D. J .; Carruthers, J . R.; Betteridge, P. W. CRYSTALS,
An Advanced Crystallographic Computer Program; Chemical Crystal-
lography Laboratory, Oxford, U.K., 1988.
(31) International Tables for X-ray Crystallography; Kynoch Press:
Birmingham, U.K., 1974; Vol. IV.
(32) Sheldrick, G. M. SHELXS 86, Program for Crystal Structure
Solution; University of Go¨ttingen, Go¨ttingen, Germany, 1986.
(33) Pearce, L. J .; Watkin, D. J . CAMERON; Chemical Crystal-
lography Laboratory, Oxford, U.K., 1989.

3048 Organometallics, Vol. 22, No. 15, 2003
Alvarez et al.
anisotropic thermal parameters, and bond lengths and angles
for compound 7. This material is available free of charge via
the Internet at http://pubs.acs.org.
(Projects BQU2000-0220 and BQU2000-0944) and the
Universidad de Oviedo for a grant to C.M.A.
Su p p or tin g In for m a tion Ava ila ble: Tables of atomic
coordinates for non-hydrogen atoms and for hydrogen atoms,
OM030201M