Reactions of the phosphinidene-bridged complexes [Fe2(η 5-C5H5)2(μ-PR)(μ-CO)(CO) 2] (R = Cy, Ph) with electrophiles based on p-block elements

Article abstract of DOI:10.1039/c2dt31506h

The title complexes reacted readily with the methylating agents MeI and CF₃SO₃Me, chalcogens (O₂, S₈) and borane adducts BH₃·L (L = THF, N^tBu₃, PPh₃) to initially give the corresponding neutral or cationic derivatives of the type [Fe₂Cp₂{μ-P(E)R}(μ-CO)(CO) ₂]ⁿ (Cp = η⁵-C₅H₅; n = 0, E = O, S, BH₃; n = +1, E = Me), which could be further functionalized through additional reactions. Thus, the oxophosphinidene complex [Fe₂Cp₂{μ-P(O)Cy}(μ-CO)(CO)₂] could be protonated or alkylated with HBF₄·OEt₂ or CF ₃SO₃Me, to give the complexes [Fe₂Cp ₂{μ-P(OR′)Cy}(μ-CO)(CO)₂]⁺ (R′ = H, Me) respectively, while the photochemical treatment of compounds [Fe₂Cp₂{μ-P(BH₃)R}(μ-CO)(CO) ₂] gave the dicarbonyl derivatives [Fe₂Cp ₂{μ-κ¹:κ¹,η²- P(BH₃)R}(μ-CO)(CO)], with a phosphinidene-borane ligand displaying coordination of a B-H bond to one of the iron atoms in a side-on fashion (Fe-H = 1.78(4) A, Fe-B = 2.351(5) A for the PCy compound). The title complexes also reacted readily with 3,5-di-tert-butyl-o-benzoquinone or benzyl azide. The first reaction gave the phosphonite complex [Fe₂Cp ₂(μ-CO)₂(CO){P(O₂C₆H ₂^tBu₂)R}], while the second reaction yielded initially the corresponding 1:1 adducts [Fe₂Cp₂{μ- P(N₃CH₂Ph)R}(μ-CO)(CO)₂], with a P:P-bound phosphatriazadiene ligand. The PCy compound underwent clean denitrogenation in toluene at 368 K to give the iminophosphinidene complex [Fe₂Cp ₂{μ-P(NCH₂Ph)Cy}(μ-CO)(CO)₂], which in turn could be protonated selectively with [NH₄]PF₆ at the P-bound nitrogen atom, to yield the aminophosphide derivative [Fe ₂Cp₂{μ-P(NHCH₂Ph)Cy}(μ-CO)(CO) ₂]PF₆ (Fe-Fe = 2.6362(8) A). Denitrogenation could be also induced photochemically on the phosphatriazadiene complex, but this also caused fragmentation and recombination of different bonds to give the trinuclear compound [Fe₃Cp₃(μ₃-PCy){μ- κ¹:κ¹-C(O)(NHCH₂Ph)}(μ-CO) ₂], having phosphinidene and C:O-bound aminoacyl ligands bridging the metal atoms.

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PAPER
Reactions of the phosphinidene-bridged complexes [Fe2(η5-C5H5)2(μ-PR)-
(μ-CO)(CO)2] (R = Cy, Ph) with electrophiles based on p-block elements†
M. Angeles Alvarez, M. Esther García, Rocío González and Miguel A. Ruiz*
Received 9th July 2012, Accepted 18th September 2012
DOI: 10.1039/c2dt31506h
The title complexes reacted readily with the methylating agents MeI and CF3SO3Me, chalcogens (O2, S8)
and borane adducts BH3·L (L = THF, NtBu3, PPh3) to initially give the corresponding neutral or cationic
derivatives of the type [Fe2Cp2{μ-P(E)R}(μ-CO)(CO)2]n (Cp = η5-C5H5; n = 0, E = O, S, BH3; n = +1,
E = Me), which could be further functionalized through additional reactions. Thus, the oxophosphinidene
complex [Fe2Cp2{μ-P(O)Cy}(μ-CO)(CO)2] could be protonated or alkylated with HBF4·OEt2 or
CF3SO3Me, to give the complexes [Fe2Cp2{μ-P(OR′)Cy}(μ-CO)(CO)2]+ (R′ = H, Me) respectively, while
the photochemical treatment of compounds [Fe2Cp2{μ-P(BH3)R}(μ-CO)(CO)2] gave the dicarbonyl
derivatives [Fe2Cp2{μ-κ1:κ1,η2-P(BH3)R}(μ-CO)(CO)], with a phosphinidene–borane ligand displaying
coordination of a B–H bond to one of the iron atoms in a side-on fashion (Fe–H = 1.78(4) Å, Fe–B =
2.351(5) Å for the PCy compound). The title complexes also reacted readily with 3,5-di-tert-butyl-o-
benzoquinone or benzyl azide. The first reaction gave the phosphonite complex [Fe2Cp2(μ-CO)2(CO)-
t
{P(O2C6H2 Bu2)R}], while the second reaction yielded initially the corresponding 1 : 1 adducts
[Fe2Cp2{μ-P(N3CH2Ph)R}(μ-CO)(CO)2], with a P:P-bound phosphatriazadiene ligand. The PCy
compound underwent clean denitrogenation in toluene at 368 K to give the iminophosphinidene complex
[Fe2Cp2{μ-P(NCH2Ph)Cy}(μ-CO)(CO)2], which in turn could be protonated selectively with [NH4]PF6 at
the P-bound nitrogen atom, to yield the aminophosphide derivative [Fe2Cp2{μ-P(NHCH2Ph)Cy}(μ-CO)-
(CO)2]PF6 (Fe–Fe = 2.6362(8) Å). Denitrogenation could be also induced photochemically on the
phosphatriazadiene complex, but this also caused fragmentation and recombination of different bonds to
give the trinuclear compound [Fe3Cp3(μ3-PCy){μ-κ1:κ1-C(O)(NHCH2Ph)}(μ-CO)2], having
phosphinidene and C:O-bound aminoacyl ligands bridging the metal atoms.
Introduction
The study of the formation and reactivity of phosphinidene (PR)
complexes has been a very active area of research within the
organometallic chemistry during the last three decades.1 The
phosphinidene group is a very versatile ligand that can act either
as a two-electron (A to C in Chart 1) or as a four-electron donor
(D to H in Chart 1), and it can bind efficiently up to four metal
atoms in many different ways (Chart 1). The phosphorus
environment changes dramatically among these coordination
modes, and this in turn gives rise to quite different chemical
behaviours. Most of the previous research has been devoted to
the terminal complexes (A, B and D). Since the M–P bonds in
these species have a considerable multiplicity, these compounds
are highly reactive, especially in the cases of bent coordination
(A and B), where a lone pair at the phosphorus atom is also
Chart 1
Departamento de Química Orgánica e Inorgánica/IUQOEM,
Universidad de Oviedo, E-33071 Oviedo, Spain.
E-mail: mara@uniovi.es
†CCDC 890680 (9a), 890681 (12) and 890682 (13). For crystallo-
graphic data in CIF or other electronic format see DOI: 10.1039/
c2dt31506h
present. This inherent reactivity, added to the conceptual analogy
established between the chemistry of multiple M–P and M–C
bonds, according to which the bent-phosphinidene complexes
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are usually compared to carbenes and can be analogously
classified as either electrophilic or nucleophilic,1d,g,h,2 have
turned these compounds into very useful intermediates in the
synthesis of new organophosphorus derivatives,1 and their reac-
tivity is still the subject of extensive research.1,3
separately. Moreover, in order to examine the influence of the
substituent at the phosphorus atom, we have also studied some
reactions of the phenylphosphinidene complex [Fe2Cp2(μ-PPh)-
(μ-CO)(CO)2] (1b), a molecule less congested than 1a. As will
be shown below, these reactions not only confirm the high
nucleophilicity of our diiron phosphinidene complexes, but they
also allow the synthesis, either directly or after additional pro-
cesses, of a variety of complexes having phosphine, phosphide
or phosphinidene ligands functionalized in different ways.
In contrast, the chemistry of binuclear complexes having phos-
phinidene bridges has remained comparatively little explored
until recently, even though the presence of multiple M–P bonds
or lone pairs at phosphorus in their different coordination modes
(C, E and F) should render them quite reactive.4,5 Recently, we
developed efficient synthetic procedures to prepare new stable
diiron compounds of the type [Fe2Cp2(μ-PR)(μ-CO)(CO)2] (R =
Results and discussion
t
Cy, Ph, 2,4,6-C6H2Me3 or 2,4,6-C6H2 Bu3), with a pyramidal
Methylation reactions of compounds 1
phosphinidene bridge (type C) having a strongly nucleophilic
character.6 Within the chemistry of binuclear phosphinidene
compounds we noticed that, in particular, the number of iron
derivatives previously described in the literature was very scarce,
and that most of them were either thermally unstable (as the
cyclopentadienyl complex [Fe2Cp2(μ-PPh)(CO)4])7 or transient
species generated in situ from suitable precursors, such as
[Fe2{μ-P(NiPr2)}2(CO)6],8 [Fe2(μ-PtBu)(CO)6],9 [Fe3(μ2-PPh)-
The phosphinidene complexes 1a,b react instantaneously with
methyl iodide at room temperature or below to give, as the
initial product, the corresponding methylphosphide complexes
[Fe2Cp2(μ-PMeR)(μ-CO)(CO)2]I, [R = Cy (2a), Ph (2b)], result-
ing from the nucleophilic attack of the phosphinidene ligand on
the carbon atom of the added electrophile (Scheme 1). However,
the phenyl compound 2b was only stable at temperatures below
273 K, otherwise rearranging rapidly to give the neutral iodo
complex [Fe2Cp2I(μ-PMePh)(CO)3] (3) almost completely. This
new complex exists in solution as a mixture of two diastereo-
isomers (A and B) and results from subsequent nucleophilic
attack of I− on one of the iron atoms of the cation in 2b, this
inducing the cleavage of the intermetallic bond and rearrange-
ment of the bridging carbonyl ligand to a terminal position.
Such a process, surely facilitated by the smaller size and lower
donor properties of the PPh ligand (compared to the PCy one), is
reversible since the removal of the solvent partially regenerates
the cationic form 2b (see Scheme 1 and the Experimental
section). To avoid the interference of the external ion we tested
the reaction of 1b with CF3SO3Me; this led selectively to the
triflate salt [Fe2Cp2(μ-PMePh)(μ-CO)(CO)2]CF3SO3 (2b′), which
expectedly does not undergo any further anion–cation reaction.
(μ3-PPh)(CO)9]n− (n = 1, 2),10 or [Fe2(μ-PR)2(CO)6]2− 11
All
.
these circumstances impose significant restrictions upon the
study of their chemical behaviour, which remains largely unex-
plored. Even if some recent examples of isolable diiron phos-
phinidene complexes can be mentioned, such as [Fe2{μ-P-
(OR)}2(CO)6]12 and [Fe2(μ-PPh)2(L2)2]13 (both of them having
bulky protecting groups: R = 4,2,6-C6H2MetBu2, L2 = HC-
i
(CMeNC6H3 Pr2)2), no reactivity appears to have been developed
around them. In this context, the relative stability of our diiron
complexes provided us with an excellent opportunity to study in
detail the unexplored chemistry of strongly nucleophilic diiron
phosphinidene complexes.14
Our preliminary studies on the chemistry of [Fe2Cp2(μ-PR)-
(μ-CO)(CO)2] complexes revealed that these neutral species react
under mild conditions with different unsaturated organic mole-
cules, such as 1-alkenes, 1-alkynes or diazoalkanes, to give
novel organophosphorus ligands involving transformations that
had not been observed in comparable reactions using complexes
with bent-terminal (A and B in Chart 1) or trigonal-bridging
(E and F in Chart 1) phosphinidene ligands.6c,14d,e Our diiron
complexes also proved to be suitable substrates for the rational
synthesis of heterometallic derivatives and clusters,14c and par-
ticularly intriguing was the remarkable ability of the super-
t
mesitylphosphinidene complex [Fe2Cp2{μ-P(2,4,6-C6H2 Bu3)}-
(μ-CO)(CO)2] to react with dihydrogen at room temperature,14a
a
chemical behaviour previously unreported for organophosphorus
molecules, except under Frustrated Lewis Pairs conditions.15 In
this paper we report a complete study on the reactions of the
cyclohexylphosphinidene complex [Fe2Cp2(μ-PCy)(μ-CO)-
(CO)2] (1a) toward different electrophilic reagents based on
p-block elements, such as the methylating agents MeI and
CF3SO3Me, several elemental chalcogens (O2, S8) and borane
adducts (BH3·L), as well as its reactions with several organic
molecules containing multiple C–N or C–O bonds, such as
azides and quinones. Some of these reactions were included in a
preliminary report on this chemistry.6c Besides this, the reactions
with organic molecules having triple CuC bonds turned out to
be of great complexity, and full details of them will be reported
Scheme 1
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Synthesis and reactivity of chalcogenophosphinidene complexes
The phosphinidene complexes 1a,b react rapidly at room temp-
erature with different sources of oxygen atoms and with elemental
sulphur to give the corresponding derivatives [Fe2Cp2{μ-P(E)R}-
(μ-CO)(CO)2] [E = O; R = Cy (4a), Ph (4b). E = S; R = Cy (5a),
Ph (5b)], containing oxo- or thiophosphinidene ligands bridging
the dimetal centre exclusively through the P atom (Scheme 2).
The synthesis of the P(O)R complexes 4 was not straightforward
since the outcome of the reaction turned out to be strongly
dependent on the phosphinidene substrate (1a or 1b) and the
oxygenating reagent used (air, m-chloroperbenzoic acid –
MCPBA, olefin oxides, etc.). Air gave a clean reaction with the
PCy complex 1a, but led to an intractable mixture of products
with the more reactive PPh complex 1b. For the latter substrate,
the highest yields of the oxophosphinidene product were
obtained when using MCPBA as an oxygen source.
The chemistry of chalcogenophosphinidene species is of inte-
rest to both organic and inorganic chemists. Most of the studies
carried out to date are related to uncoordinated phosphinidene
oxides (R–PvO), unstable molecules which are thought to be
generated in the thermal or photochemical decomposition of
several precursors, such as phospholene, phosphirane or phos-
phanorbornadiene oxides, and others.16 These transient species
undergo processes such as addition to dienes and diones or inser-
tion into O–H and S–S bonds, and are therefore efficient reagents
for the synthesis of new organophosphorus derivatives.16a,17
Although stabilization of R–PvO species can be achieved
through coordination to metal centres, only a few oxophosphini-
dene complexes have been reported so far, and their reactivity
has been little explored.18,19 In fact, only another diiron complex
having a P(O)R ligand seems to have been previously reported
([Fe2Cp2{μ-P(O)OH}(μ-CO)(CO)2]).20 On the other hand, pre-
cedents for diiron complexes having thiophosphinidene ligands
are very scarce too, actually restricted to the phenyl derivatives
[Fe2Cp2{μ-P(S)Ph}(CO)n] (n = 3, 4), both of which have no
metal–metal bonds.21 Actually, the latter tricarbonyl complex is
an isomer of 5b, but with a μ-P:P,S-bound thiophosphinidene
ligand and no bridging carbonyls.
Scheme 2
The presence of uncoordinated PvO and PvS groups in
complexes 4 and 5 should facilitate further functionalization of
these molecules through the reactions with suitable electrophiles.
In particular, we have found that the P(O)R complex 4a reacts
readily with HBF4·OEt2 to give the hydroxyphosphide complex
[Fe2Cp2{μ-P(OH)Cy}(μ-CO)(CO)2]BF4 (6), while the reaction
with CF3SO3Me gives the analogous methoxyphosphide
Scheme 3
analogous to that occurring in the formation of the diplatinum
complex [Pt2(dppe)2{μ-κ1:κ1-P(BH3)Mes}2].18c As expected,
the more labile THF adduct reacted rapidly with both 8a and 8b
at room temperature, but the more robust adducts BH3·NtBu3
and BH3·PPh3 reacted only with the more basic PCy complex
1a, still this needing some thermal activation (343 K).
Surprisingly, complexes 8 exhibited considerable thermal stab-
ility, since they could be heated at 358 K in a toluene solution
for 1 h without noticeable decomposition. Moreover, these com-
plexes could be purified by column chromatography without
hydrolysis of the BH3 group. They underwent clean decarbonyl-
ation under photochemical activation, also without BH3 degra-
dation (Scheme 3), to give the dicarbonyl derivatives
[Fe2Cp2{μ-κ1:κ1,η2-P(BH3)R}(μ-CO)(CO)] (9a,b). In these pro-
ducts the loss of a carbonyl ligand is counterbalanced by the
complex
[Fe2Cp2{μ-P(OMe)Cy}(μ-CO)(CO)2]CF3SO3
(7)
(Scheme 2). The formation of these two compounds involves the
addition of the electrophile to the oxygen atom of the oxopho-
sphinidene ligand and illustrates the residual nucleophilicity of
the new chalcogenophosphinidene complexes that enables them
for further functionalization of the P atom.
Synthesis and reactivity of borane adducts
Compounds 1a,b react readily with several borane adducts
BH3·L (L = THF, NtBu3, PPh3) to give the corresponding acid–
base adducts [Fe2Cp2{μ-P(BH3)R}(μ-CO)(CO)2] (R = Cy (8a),
Ph (8b), Scheme 3). These products follow from a process
14500 | Dalton Trans., 2012, 41, 14498–14513
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coordination of one of the B–H bonds of the RPBH3 ligand, thus
rendering an agostic Fe–H–B interaction. We note that related tri-
centric interactions are well known in the chemistry of iron com-
plexes,22 and that phosphine–borane adducts PR3·BH3 are
known to bind metal centres via their B–H bonds.23 However,
we have found no iron complexes described with a comparable
phosphinidene–borane ligand. In fact, the coordination
mode observed in 9 has a single precedent, the complex
[Mo2Cp2{μ-κ1:κ1,η2-P(BH3)H}(CO)2(η6-HMes*)] recently pre-
pared in our laboratory.5g Unlike their precursors, complexes 9a,
b were easily hydrolyzed upon addition of water or just when
attempting their chromatographic purification on hydrated
alumina, to give the corresponding hydride–phosphide com-
plexes [Fe2Cp2(μ-H)(μ-PRH)(CO)2], a reaction with no synthetic
use, since the same products have been previously synthesized
by us using more direct routes.14b
Reactivity towards organic azides
Free phosphines (PR3) react easily with organic azides to give
initially phosphoranylidenetriazenes R3PN3R′, a type of mole-
cule usually of low thermal stability that lose nitrogen at room
temperature or below to yield the corresponding imino-
phosphines R3PvNR′.24 This process, known as the Staudinger
reaction,25 has different uses in synthetic organic chemistry, for
instance the formation of new CvN bonds via the aza-Wittig
reaction.26 On this basis, it might be anticipated that phosphini-
dene complexes might analogously react with organic azides to
give coordinated phosphatriazadiene ligands (RPN3R′) initially,
and perhaps iminophosphinidene (or phosphaimine) ligands
(RPvNR′), if spontaneous denitrogenation would take place
afterwards. Surprisingly, however, the reactions of PR complexes
towards these molecules have been explored only recently,
on complexes of the types B and F, these leading invariably to
iminophosphinidene derivatives.3c,4j It was thus of interest to
examine the behaviour of the PR-bridged compounds 1 towards
organic azides (Scheme 4).
Compound 1a reacts under mild conditions with benzyl azide
to give [Fe2Cp2{μ-P(N3CH2Ph)Cy}(μ-CO)(CO)2] (10a), which
displays a P:P-bridged phosphatriazadiene ligand resulting from
the biphilic P–N interaction of the phosphinidene ligand with the
terminal nitrogen of the azide, without elimination of dinitrogen.
A similar reaction takes place with the PPh complex 1b to give
the corresponding derivative [Fe2Cp2{μ-P(N3CH2Ph)Ph}(μ-CO)-
(CO)2] (10b). However, the latter compound has a low thermal
stability, and it decomposes above 263 K to give several unstable
species that could be neither isolated nor properly characterized.
We note that compounds 10 appear to be the first phosphatriaz-
adiene complexes to be reported.
Scheme 4
almost quantitatively, it turned out to be very air-sensitive, to
give several species that could be neither isolated nor properly
characterized. Fortunately, the presence of a lone electron pair at
the N atom in 11 allows for further functionalization of the
ligand, yielding more stable derivatives. In particular, we found
that 11 reacts instantaneously with [NH4]PF6 to give the cationic
complex [Fe2Cp2{μ-P(NHCH2Ph)Cy}(μ-CO)(CO)2]PF6 (12) in
quantitative yield, with an aminophosphide ligand resulting from
the attachment of a proton to the nitrogen atom of the imino-
phosphinidene group of the precursor.
Irradiation of toluene solutions of 10a induced a slow but
complex reaction eventually yielding the trinuclear complex
[Fe3Cp3(μ3-PCy){μ-κ1:κ1-C(O)(NHCH2Ph)}(μ-CO)2] (13), as
the only organometallic species present in the reaction mixture.
This product displays a trimetal core bridged by a phosphinidene
and a C,O-bound aminoacyl ligand, and its formation obviously
requires several elemental steps, these including denitrogenation,
P–N and Fe–Fe bond cleavage and H atom abstraction processes
(perhaps from trace amounts of water in the medium), among
others. IR and 31P{1H} NMR monitoring of this reaction
allowed the detection of complex 11 and a second intermediate
species at shorter reaction times. This suggests that denitrogena-
tion (to give 11) most likely is the first event also in the photo-
chemical reaction. As for the second species, it is likely a
trinuclear compound already, since it displays a quite deshielded
Thermal and photochemical activation experiments were per-
formed on 10a to examine potential denitrogenation processes or
rearrangements involving the coordination of the N atoms to the
dimetal centre (see our studies on the related phosphadiazadiene
derivatives of 1a).14d First we found that heating toluene
solutions of 10a at 368 K gave rapidly the complex [Fe2Cp2{μ-P-
(NCH2Ph)Cy}(μ-CO)(CO)2] (11), with a P:P-bound iminophos-
phinidene ligand resulting from denitrogenation in the phospha-
triazadiene precursor (Scheme 4). Although 11 was obtained
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31P NMR resonance at 430 ppm, possibly corresponding to a
μ3-PCy ligand, but we could neither isolate nor properly charac-
terize it.
corresponding cis and trans isomers (Chart 2). Their IR spectra
(Table 1) display two C–O stretches for the bridging CO ligands,
with the pattern expected for a transoid relative positioning of
these ligands,28 and two C–O stretches for the terminal CO
ligand, which agree with the presence in solution of the men-
tioned isomers. By comparing the frequency and relative inten-
sity of the latter bands with analogous diiron complexes
described in the literature, we conclude that the trans isomer is
the major product, as usually observed in this sort of com-
plexes.29 As expected, complex 14a displays two 31P NMR reso-
nances at ca. 280 ppm with different intensities. In contrast, the
phenyl compound 14b displays just one broad resonance at
ca. 240 ppm at this temperature, suggesting that the inter-
conversion process between isomers is fast on the NMR time-
scale. Indeed this resonance eventually splits upon cooling, and
two sharp resonances are observed at 233 K. It should be noted
that the equilibrium process observed for these compounds has
Reactivity towards quinones
Compounds 1a,b react rapidly with 3,5-di-tert-butyl-o-benzoqui-
none to generate the corresponding derivatives [Fe2Cp2-
t
(μ-CO)2(CO){P(O2C6H2 Bu2)R}] [R = Cy (14a), Ph (14b)],
with a phosphonite ligand formally derived from the oxidative
addition of the quinone to the P atom of the PR ligand, a process
analogous to that observed for the reactions of the free phos-
phines with this type of quinones.27 Under similar conditions
(room temperature or below) compounds 1a,b also react with
p-benzoquinone. The IR spectra of the resulting solutions are
analogous to those recorded for complexes 14, this suggesting
that the newly formed species contain a similar local structure.
However, these products had a low solubility in most common
solvents and exhibited very broad resonances in the correspond-
1
ing 31P{1H} and H NMR spectra, so we could neither isolate
nor properly characterize them. This situation could be related to
the fact that, in the case of p-benzoquinone, the binding of both
oxygen atoms of the quinone to the same phosphorus atom is
not possible. As a result, the reaction likely involves the inter-
action of the quinone with two molecules of the complex, thus
triggering an oligomerization process.
Spectroscopic data available in solution for compounds 14
indicate the presence of an equilibrium mixture of the
Chart 2
Table 1 Selected IRa and 31P{1H}NMRb data for new compounds
Compound
ν(CO)
δP (JPB)
[Fe2Cp2(μ-PMeCy)(μ-CO)(CO)2]I (2a)
[Fe2Cp2(μ-PMePh)(μ-CO)(CO)2]I (2b)
[Fe2Cp2(μ-PMePh)(μ-CO)(CO)2]CF3SO3 (2b′)
[Fe2Cp2I(μ-PMePh)(CO)3] (3)
2015 (vs), 1985 (w), 1829 (m)
2024 (vs), 1991 (w), 1831 (m)
2025 (vs), 1992 (w), 1830 (m)
2024 (vs), 1995 (w, sh), 1976 (s), 1923 (m)
271.2
250.6c
248.3
37.5 (A)c
32.5 (B)c
343.8c
[Fe2Cp2{μ-P(O)Cy}(μ-CO)(CO)2] (4a)
[Fe2Cp2{μ-P(O)Ph}(μ-CO)(CO)2] (4b)
[Fe2Cp2{μ-P(S)Cy}(μ-CO)(CO)2] (5a)
[Fe2Cp2{μ-P(S)Ph}(μ-CO)(CO)2] (5b)
[Fe2Cp2{μ-P(OH)Cy}(μ-CO)(CO)2]BF4 (6)
1985 (vs), 1951 (w), 1788 (m)
1997 (vs), 1964 (w), 1795 (m)
1989 (vs), 1957 (w), 1794 (m)
2001 (vs), 1971 (w), 1799 (m)
2015 (vs), 1985 (w), 1826 (m)
319.6c
345.6c
313.4c
370.9 (cis, anti)
352.6 (cis, syn)
385.3 (cis, anti)
387.9 (cis, syn)
392.2 (trans)
367.9 (41)
343.0 (33)
304.7 (62)
250.3 (64)
319.1
[Fe2Cp2{μ-P(OMe)Cy}(μ-CO)(CO)2]CF3SO3 (7)
2016 (vs), 1988 (w), 1831 (m)
[Fe2Cp2{μ-P(BH3)Cy}(μ-CO)(CO)2] (8a)
[Fe2Cp2{μ-P(BH3)Ph}(μ-CO)(CO)2] (8b)
1993 (vs), 1960 (w), 1797 (m)
2004 (vs), 1971 (w), 1802 (m)
1972 (vs), 1801 (m)d
[Fe2Cp2{μ-κ1:κ1,η2-P(BH3)Cy}(μ-CO)(CO)] (9a)
[Fe2Cp2{μ-κ1:κ1,η2-P(BH3)Ph}(μ-CO)(CO)] (9b)
[Fe2Cp2{μ-P(N3CH2Ph)Cy}(μ-CO)(CO)2] (10a)
[Fe2Cp2{μ-P(N3CH2Ph)Ph}(μ-CO)(CO)2] (10b)
[Fe2Cp2{μ-P(NCH2Ph)Cy}(μ-CO)(CO)2] (11)
[Fe2Cp2{μ-P(NHCH2Ph)Cy}(μ-CO)(CO)2]PF6 (12)
[Fe3Cp3(μ3-PCy){μ-κ1:κ1-C(O)(NHCH2Ph)}(μ-CO)2] (13)
1974 (vs), 1813 (m)d
1989 (vs), 1957 (w), 1793 (m)
2000 (vs), 1964 (w), 1798 (m)
1977 (vs), 1943(w), 1773 (m)
2011 (vs), 1984 (w), 1824 (m)
1776 (vs), 1727 (w)
302.8e
274.6
315.1
624.8
277.5 (trans)
280.0 (cis)
237.3 (trans)g
240.8 (cis)g
t
[Fe2Cp2(μ-CO)2(CO){P(O2C6H2 Bu2)Cy}] (14a)
1967 (w, sh), 1951 (m), 1782 (w), 1743 (vs)
[Fe2Cp2(μ-CO)2(CO){P(O2C6H2 Bu2)Ph}] (14b)
1972 (s), 1951 (s), 1794 (w), 1763 (vs)f
t
a Recorded in a dichloromethane solution, with C–O stretching bands (ν(CO)) in cm−1
.
b Recorded in CD2Cl2 solutions at 290 K and 162.00 MHz
unless otherwise stated; δ in ppm relative to external 85% aqueous H3PO4, and JPB in Hz. c In CDCl3 solution. d In toluene solution. e Recorded at
203 K. f In petroleum ether solution. g Recorded in toluene-d8 solution at 233 K.
14502 | Dalton Trans., 2012, 41, 14498–14513
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been studied in detail previously for analogous complexes
[Fe2Cp2(μ-CO)2(CO)L] (L = P(OPh)3,30 CO),31 and therefore
needs not to be discussed in detail.
all of them share the same basic structural features, in turn con-
sistent with the solid-state structure just discussed for 4a. In par-
ticular, their IR spectra exhibit three C–O stretching bands
indicative of the retention in solution of a bridging CO
(ca. 1795 cm−1) and almost parallel terminal CO ligands.28 The
pattern is similar to that displayed by the parent phosphinidene
complexes 1,6 but the bands are generally shifted by some
10–20 cm−1 to higher frequencies, in agreement with the
expected decrease of electron density at the dimetal centre
derived from the coordination of the phosphorus lone pair to the
incoming electrophile. It should be noted, however, that this
effect is not dominated by the electronegativity of the acceptor
atom, since the experimental ordering of the average C–O
stretches is BH3 > S ≥ N3R > O > NR ≥ 1a,b. It seems therefore
that π bonding between P and the electrophile (absent in
the borane adducts and expected to be prevalent for O and NR′
groups) partially cancels the drift of charge away from
the dimetal centre. Incidentally, the above data suggest that the
π(P–N) interaction in the phosphatriazadiene complexes 10 is
not as strong as the one in the iminophosphinidene complex 11,
an effect that could be derived from a significant delocalization
of the π interaction along the P–N–N–N chain in the former
complex (represented by canonical forms of the type Fe2RP+–
NvN–R′N−).
Structural characterization of neutral μ-P(E)R complexes (4, 5,
8, 10 and 11)
The structure of the P(O)R complex 4a was confirmed in a pre-
liminary study (Fig. 1 and Table 2).6c The molecule is built up
from two CpFe(CO) fragments placed in a cisoid relative
arrangement and bridged by a carbonyl and a P:P-bound oxo-
phosphinidene ligand. The intermetallic distance of 2.601(2) Å
is consistent with the single Fe–Fe bond to be proposed accord-
ing to the EAN formalism, and it is very similar to that measured
in [Fe2Cp2{μ-P(O)OH}(μ-CO)(CO)2] (2.615(4) Å),20 while the
bridging carbonyl ligand is slightly off the plane defined by the
iron and phosphorus atoms. The cyclohexyl group in the brid-
ging oxophosphinidene ligand points away from the cyclopenta-
dienyl ligands, a conformation identical to those found in all
phosphinidene precursors of type 1,6 and presumably more
favoured on steric grounds. The Fe–P distances of 2.219 (2) and
2.216 (2) Å are comparable to those observed for the mentioned
diiron complex (ca. 2.19 Å), and are marginally lower (by
ca. 0.04 Å) than those observed for the phenylphosphinidene
complex 1b.6c The P–O bond length of 1.503(3) Å is also very
similar to that measured in the mentioned oxophosphinidene
complex, and it is consistent with the formulation of a double
bond between these atoms. In any case, all the above data indi-
cate that the incorporation of an oxygen atom does not disturb
the geometry of the phosphinidene ligand to a significant extent,
except for a slight shortening of the Fe–P lengths.
Our neutral P(E)R complexes display 31P NMR resonances in
the range 275–370 ppm, some 200 ppm more shielded than
those of the parent phosphinidene complexes 1. The borane
adducts 8a and 8b gave the less shielded resonances, expectedly
broadened due to scalar coupling to the 11B nucleus, with the
corresponding constants (JPB = 41 and 33 Hz, respectively)
being similar to those measured in other species containing
P–BH3 bonds.32 We finally note that the high symmetry of this
group of compounds is clearly reflected in their 1H and 13C
NMR spectra (see the Experimental section), which denote in
each case the presence of an effective symmetry plane relating
both metal fragments of the molecule.
The spectroscopic data available for the neutral μ-P(E)R com-
plexes (R = Cy, Ph; E = O, S, BH3, N3R′, NR′) are similar to
each other (Table 1 and Experimental section) and indicate that
Structural characterization of cationic μ-P(E)R complexes
(2, 6, 7 and 12)
The geometry of the cation in 12 (Fig. 2 and Table 3) can be
related to that of the P(O)R complex 4a, and even more closely
to those of the phosphadiazadiene complex [Fe2Cp2{μ-P-
(N2CH2)Cy}(μ-CO)(CO)2] and its aminophosphide derivative
[Fe2Cp2{μ-P(NHNCH2)Cy}(μ-CO)(CO)2]BF4.14d The cation can
be described as two cisoid FeCp fragments connected by a
single metal–metal bond (2.6362(8) Å) and symmetrically brid-
ging carbonyl and aminophosphide ligands. The coordination
spheres around the metal atoms are completed by two terminal
carbonyls, placed almost parallel to each other. The P–N
distance of 1.657(4) Å is longer than the corresponding length
in the neutral complex [Fe2Cp2{μ-P(N2CH2)Cy}(μ-CO)(CO)2]
(1.612(2) Å), taken here as a reference for a double PvN bond,
and is comparable to that measured in the mentioned aminophos-
phide complex (1.669(2) Å). These distances actually approach
the single-bond lengths of ca. 1.67–1.72 Å measured in different
aminophosphine iron complexes.33 Thus we must conclude that,
upon protonation at the N atom, the π(N–P) bonding interaction
Fig. 1 ORTEP diagram (30% probability) of compound 4a, with H
atoms omitted for clarity.6c
Table 2 Selected bond lengths (Å) and angles (°) for 4a6c
Fe1–Fe2
Fe1–P1
Fe2–P1
Fe1–C1
Fe1–C3
Fe2–C2
Fe2–C3
P1–O4
2.601(2)
2.219(2)
2.216(2)
1.747(5)
1.914(5)
1.748(5)
1.926(4)
1.503(3)
C1–Fe1–Fe2
C2–Fe2–Fe1
C1–Fe1–C3
C2–Fe2–C3
C1–Fe1–P1
C2–Fe2–P1
Fe1–P1–O4
Fe2–P1–O4
99.2(1)
99.4(2)
89.3(2)
90.3(2)
92.0(1)
91.3(1)
121.6(1)
120.7(1)
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Fig. 3 Projections of the possible isomers of compounds 6 and 7,
viewed along the axis joining the bridging PCyOR′ and CO ligands.
alkylphosphide34 and alkoxyphosphide29c,35 ligands bridging
two metal atoms connected by a metal–metal bond. However,
while the methylphosphide complexes 2a,b exhibit a single reso-
nance in the corresponding 31P{1H} NMR spectra, compound 6
displays two resonances and compound 7 three resonances, with
their relative intensities being solvent-dependent in each case
(see the Experimental section). This implies the presence in
solution of interconverting isomers in each case.
Fig. 2 ORTEP diagram (30% probability) of the cation in compound
12, with H atoms (except H1) omitted for clarity.
Table 3 Selected bond lengths (Å) and angles (°) for 12
Fe1–Fe2
Fe1–C1
Fe1–C3
Fe2–C2
Fe2–C3
Fe1–P1
Fe2–P1
P1–N1
2.6362(8)
1.768(4)
1.973(5)
1.776(5)
1.924(5)
2.187(1)
2.193(1)
1.657(4)
0.94(5)
Fe1–Fe2–C2
Fe2–Fe1–C1
P1–Fe1–C1
P1–Fe2–C2
P1–N1–C14
P1–N1–H1
H1–N1–C14
Fe1–P1–N1
Fe2–P1–N1
100.4(1)
96.8(1)
90.5(1)
91.9(1)
129.4(3)
113(3)
116(3)
123.4(1)
122.5(1)
The major isomer (unique in the case of compounds 2) most
likely is the one present for the parent compounds 1a,b and in
their protonated derivatives [Fe2Cp2(μ-PHR)(μ-CO)(CO)2]BF4
(R = Cy, Mes, Mes*),6 that is, the one with the R group pointing
away from the Cp ligands (isomer cis, anti in Fig. 3), expectedly
more favoured on steric grounds. Out of the two other possible
isomers (Fig. 3), we propose the cis, syn structure for the minor
N1–H1
N1–C14
1.470(6)
1
isomer of 6, since it gives rise to single 13C and H NMR Cp
resonances. Finally, the two minor isomers of 7 can be also
identified on the basis of the number of Cp resonances as the
cis, syn and trans isomers respectively, although their relative
amount is always very small under all conditions examined (see
the Experimental section).
in the parent iminophosphinidene ligand is substantially dimin-
ished, and therefore the resulting ligand can be properly
described as an aminophosphide ligand. Yet, the degree of pyr-
amidalization at the N atom is negligible (Σ X–N–Y ca. 358°; X,
Y = C(14), P(1), H(1)), a circumstance still quite common
for aminophosphine complexes, and the benzyl and cyclohexyl
substituents are arranged in an anti conformation, more favoured
on steric grounds.
Compound 12 exhibits a single 31P NMR resonance at
315.1 ppm, a position very similar to that of the aminophos-
phide complex [Fe2Cp2{μ-P(NHNCH2)Cy}(μ-CO)(CO)2]BF4
1
(313.7 ppm).14d In the H NMR spectrum, the Cp (5.20 ppm)
and CH2 (4.50 ppm) groups give rise to single resonances, con-
sistent with the symmetry plane relating both FeCp(CO) frag-
ments in a cis isomer, while the NH resonance is located at
4.40 ppm.
The spectroscopic data available for the cationic μ-P(E)R com-
plexes (R = Cy, Ph; E = Me, OH, OMe, NHR′) are similar to
each other (Table 1 and Experimental section), indicating that all
of them share the same basic structural features, in turn consist-
ent with the structure of 12 in the crystal. Their IR spectra
display three C–O stretching bands indicative of the retention in
solution of a bridging CO and two terminal CO ligands almost
parallel to each other, also denoted by the presence of resonances
Structure of the iodide complex 3
Although compound 3 exists in solution as an equilibrium
mixture of two diastereoisomers giving rise to separated NMR
resonances, its IR spectrum gives no hint of it, since it displays
three C–O stretches that might be assigned to a single complex
having relatively uncoupled M(CO)2 and M(CO) oscillators. In
fact, the observed pattern is comparable to that reported for
[Fe2Cp2{μ-κ1:κ2-P(S)Ph}(CO)3].21 From this we conclude that
the two isomers of 3 must have very similar local environments
at their metal centres, consistent with its identification as the two
possible diastereoisomers in a complex having two stereogenic
metal centres. It is also to be noted that the 31P resonances for
at ca. 255 and 210 ppm (1 : 2 intensity) in the corresponding 13
C
{1H} NMR spectra. The pattern of the C–O stretches is similar
to that of their neutral precursors, but the bands are shifted by
ca. 40 cm−1 to higher frequencies, as expected from the cationic
nature of these complexes. Moreover, the solid-state IR spectrum
of the hydroxyphosphide complex 6 (Nujol mull) displays a
broad band at ca. 3225 cm−1 corresponding to the O–H stretch.
Compounds 2, 6 and 7 display 31P NMR resonances at
chemical shifts (ca. 250 ppm for compounds 2, ca. 380 ppm for
compounds 6 and 7) expected for complexes having respectively
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these isomers are located at ca. 35 ppm, that is, some 200 ppm
more shielded than the resonance of the cationic isomer 2b. This
is consistent with the presence of phosphide ligands bridging
metal atoms not connected by a metal–metal bond,34 a con-
sequence here of the coordination of the iodide ion.
conformational change (from anti to syn) has occurred during
the formation of compounds 9, surely induced photochemically.
The Fe2–B1 bond length of 2.351(5) Å falls in the upper limit
of the range usually found for agostic Fe–H–B interactions
(2.05–2.38 Å),36 it being similar to that measured in the carba-
borane complex [FeCp(CO)2(η2-B9C2H12)] (2.377(1) Å),36a and
exceeds by ca. 0.4 Å the values measured for conventional two-
centre/two-electron Fe–B interactions.37 As expected, the unco-
ordinated B1–H02 and B1–H03 bonds have lengths similar to
those observed in simple phosphine–borane adducts such as
(NH2)3P–BH3 (1.1–1.2 Å),38 while the coordinated B1–H01
bond is enlarged by some 0.1 Å, an effect comparable to that
measured in the only other phosphinidene–borane complex
structurally characterized so far (1.24(5) Å in [Mo2Cp2-
{μ-κ1:κ1,η2-P(BH3)H}(CO)2(η6-HMes*)], which displays an
analogous M–H–B interaction.5g Finally, the B–P length of
1.912(5) Å can be viewed as a conventional figure for a single
bond between these atoms.32a,38
Solid-state and solution structure of agostic phosphinidene–
borane complexes
The molecule of the PCy complex 9a in the crystal (Fig. 4 and
Table 4) is built from two CpFe fragments placed in a cisoid rela-
tive arrangement and connected by a single metal–metal bond
(ca. 2.63 Å) and two bridging ligands: carbonyl and phosphini-
dene–borane (CyPBH3). The latter formally behaves as a four-
electron donor and is symmetrically bound to both metals
through its phosphorus atom (P–Fe = 2.181(1) Å), while one of
its B–H bonds binds the Fe2 atom, thus establishing an agostic
M–H–B interaction that fills the vacancy left by the removal of a
terminal CO ligand in the parent tricarbonyl 8a; besides, the Fe1
completes its coordination sphere with a terminal carbonyl
ligand. To balance the lower donor ability of the B–H bond
(compared to the terminal CO ligand), the bridging carbonyl
expectedly binds the Fe2 atom much more tightly (Fe–C lengths
1.849(4) Å and 2.069(4) Å, respectively) and indeed it might be
considered as semibridging. From a conformational point of
view, we note that the cyclohexyl group in 9a is arranged syn
with respect to the Cp ligands. This is unusual, since all deriva-
tives of the phosphinidene complexes 1 usually retain the anti
conformation present in the starting materials. This implies that a
The spectroscopic data in solution for complexes 9a,b are con-
sistent with the solid-state structure of 9a just discussed. In par-
ticular, the IR spectra display two C–O stretching bands at
ca. 1973 cm−1 and 1807 cm−1, corresponding to the terminal
and bridging carbonyls, respectively, which in turn give rise to
quite differently deshielded 13C resonances (at ca. 214 and
260 ppm, respectively), as expected. Their 31P{1H} and 11B
NMR spectra exhibit resonances at ca. 275 ppm and
ca. −35 ppm, respectively, with chemical shifts somewhat lower
than those of the corresponding precursors. As expected for fully
1
asymmetric molecules, the H NMR spectra of these complexes
display independent resonances for the three protons of the BH3
group, at ca. 0.5, −2 and −23 ppm. The most shielded resonance
is thus unambiguously assigned to the H atom interacting with
the iron atom. Although its very low chemical shift would be
itself consistent with the presence of a hydride ligand bridging
the iron atoms,14b,29a,b the broadness of this resonance (w1/2
ca. 100 Hz for 9a, transformed into a sharp multiplet in the
1H{11B} NMR spectrum) denotes an unresolved coupling to the
11B nucleus of some 30–40 Hz, and hence the presence of direct
H–B binding, if weakened, therefore consistent with an agostic
B–H–Fe interaction. This coupling is to be compared with an
H–B coupling of 149 Hz for the “normal” B–H protons in 9a,
while the B–H couplings in the precursors 8a and 8b have inter-
mediate values of ca. 100 Hz. Thus, as judged from these
figures, we conclude that the agostic coordination of one of the
B–H bonds in 9 causes a considerable weakening in that bond
(in agreement with the increased B–H distance in the crystal),
and a significant strengthening in the other two B–H bonds.
Given the very low B–H coupling estimated for the agostic
H atom, we are tempted to propose that such agostic interaction
for compounds 9 in solution might be actually stronger than in
the crystal. Should this be the case, we would anticipate a
lower asymmetry for the bridging carbonyl in solution. Indeed,
the spectroscopic parameters for this ligand in compounds 9
(ν(C–O) ca. 1807 cm−1 and δC ca. 260 ppm) are indicative of
the presence of a rather normal bridging (instead of semibridg-
ing) carbonyl in solution.
Fig. 4 ORTEP diagram (30% probability) of compound 9a, with H
atoms (except those bound to B1) omitted for clarity.
Table 4 Selected bond lengths (Å) and angles (°) for 9a
Fe1–Fe2
Fe1–P1
Fe2–P1
Fe1–C1
Fe1–C2
Fe2–C2
Fe2–B1
Fe2–H1
B1–P1
2.6300(7)
2.181(1)
2.181(1)
1.765(5)
2.069(4)
1.849(4)
2.351(5)
1.78(4)
P1–Fe1–Fe2
P1–Fe2–Fe1
C1–Fe1–Fe2
B1–Fe2–Fe1
C2–Fe1–Fe2
C2–Fe2–Fe1
O2–C2–Fe1
O2–C2–Fe2
H1–Fe2–P1
Fe2–P1–B1
P1–B1–H1
52.9(1)
52.9(1)
104.2(1)
85.7(1)
44.4(1)
51.5(1)
129.3(3)
146.5(3)
80(1)
1.912(5)
1.27(4)
1.19(4)
1
Compound 9b displayed independent H and 13C NMR reso-
B1–H01
B1–H02
B1–H03
69.8(1)
105(1)
100(2)
nances for all atoms in the phenyl ring, indicating the unexpected
absence of free rotation of this ring around the P–C bond at
1.13(4)
B1–H1–Fe2
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room temperature. A standard NOESY 1H NMR experiment
revealed that there is a positive NOE between one of the hydro-
gen atoms of the BH3 group (δ 0.87 ppm) and one of the ortho
protons of the ring (δ 8.28 ppm). Thus we propose for 9b in
solution the presence of dihydrogen bonding interactions
between a BH3 proton (negatively polarized) and one of
the ortho protons of the phenyl ring (positively polarized).
Dihydrogen bonds are inter- or intramolecular interactions
typically occurring between positively charged hydrogen atoms
of H–A bonds (A = O, N, C in alkenes, aromatic rings, …) and
negatively charged hydrogen atoms of H–X bonds (X = B,
Al, Ga, …).39
Chart 3
short (ca. 2.16–2.18 Å), indicate a strong coordination of the
PCy group. In this ligand, the chemical environment around the
P atom is not of the common tetrahedral type, but rather of a dis-
torted trigonal-pyramidal type, with the P1, C26, Fe1 and Fe2
atoms placed almost in the same plane (Σ X–P–Y ca. 359°; X,
Y = C26, Fe1, Fe2) and the third metal atom (Fe3) occupying
the apical position. This environment, however, seems to be
characteristic of 50-electron Fe3(μ3-PR) and related clusters.1n,41
The aminoacyl ligand in 13 spans a non-bonding Fe1⋯Fe2
distance of ca. 3.50 Å, with the coordinated O and C atoms
defining an almost flat OCFe2 motif (torsion angle Fe1–O3–C3–
Fe2 ca. 2°). In such a geometry, a generic metal–acyl interaction
can be described as a resonance hybrid of acyl and oxycarbene
canonical forms (A and B in Chart 3).42 In the case of an amino-
acyl ligand, a third resonance form C involving the electron
pair of the amino group still might be invoked. Indeed the facts
that the H and C atoms of the amino group in 13 are placed
in the OCFe2 plane, and that the N–C3 length of 1.359(5) Å is
ca. 0.11 Å shorter than the N–C4 one are consistent with such
an interaction. Interestingly, although there are only a few amino-
acyl-bridged diiron complexes previously characterized, all of
them also display a conformation of the amino group coplanar
with the OCFe2 plane.43 Incidentally, all these compounds are
metal–metal bonded complexes of the type [Fe2(μ-κ1:κ1-C(O)-
NR2)(μ-X)(CO)4L2], and display Fe–C, C–O, O–Fe and C–N
distances of ca. 1.98, 1.27, 1.99 and 1.34 Å ( 0.01 Å) respecti-
vely. The corresponding lengths in 13 are similar, except for the
Fe2–C3 length of 1.941(4) Å, which is ca. 0.04 Å shorter, but
still comparable to the single Fe–C lengths usually measured for
bridging carbonyls. This suggests that, rather than due to a larger
contribution of the oxycarbene form B, the stronger Fe–C inter-
action apparent in 13 might be just derived from a more favour-
able geometry: because of the large (nonbonding) intermetallic
separation in 13, the Fe2–C3–O3 angle is 124.4(3)°, optimal for
a strong σ bond involving an sp2-hybridized C atom. In contrast,
the short intermetallic distances in the mentioned aminoacyl
complexes force the corresponding Fe–C–O angles to be more
acute (ca. 113°), this causing a less optimal Fe–C overlap, and
therefore longer interatomic distances.
Structural characterization of the acyl triiron complex 13
The molecule of 13 in the crystal (Fig. 5 and Table 5) is built up
from three CpFe fragments bridged by a μ3-PCy ligand and
defining a V-shaped metal core. The external FeCp groups are
further bridged by an aminoacyl ligand and connected to the
central metal atom by intermetallic bonds and a carbonyl bridge
in each case. These three bridging ligands are placed opposite to
the phosphinidene ligand, relative to the intermetallic plane, a
feature also observed for other μ3-PR trinuclear complexes
recently reported by us.14b,c The Fe–Fe lengths of 2.6188(7) and
2.6000(8) Å in 13 are within the range of values previously
measured for related 48- and 50-electron Fe3(μ3-PR) clus-
ters,40,41 while the Fe–P distances, similar to each other and
Fig. 5 ORTEP diagram (30% probability) of compound 13, with H
atoms (except H1) and the Cy ring (except the C1 atom) omitted for
clarity.
Table 5 Selected bond lengths (Å) and angles (°) for 13
Spectroscopic data in solution for 13 are consistent with the
structure in the crystal. Its IR spectrum exhibits two C–O
stretches in the region of the bridging carbonyls, with relative
intensities indicative of a cisoid arrangement,28 while the band
corresponding to the acyl ligand is located at much lower
frequencies (1404 cm−1), as expected. At the same time, the
13C NMR spectrum displays three quite deshielded resonances at
281.7, 279.2 and 233.4 ppm. The two most deshielded ones fall
within the usual range of bridging CO ligands at diiron com-
plexes (ca. 260–290 ppm), therefore the less deshielded
resonance is assigned to the acyl group. The chemical shift of
233.4 ppm is comparable to those found in related complexes
Fe1–Fe3
Fe2–Fe3
Fe1–C1
Fe2–C2
Fe2–C3
Fe3–C1
Fe3–C2
Fe1–P1
Fe2–P1
Fe3–P1
Fe1–O3
C3–O3
C3–N1
N1–C4
2.6188(7)
2.6000(8)
1.936(4)
1.881(4)
1.941(4)
1.913(4)
1.949(4)
2.163(1)
2.173(1)
2.179(1)
1.982(3)
1.284(5)
1.359(5)
1.470(5)
Fe1–Fe3–Fe2
Fe1–P1–Fe2
Fe1–P1–Fe3
Fe2–P1–Fe3
Fe1–O3–C3
Fe2–C3–O3
Fe1–P1–C26
Fe2–P1–C26
Fe3–P1–C26
C3–N1–H1
C3–N1–C4
C4–N1–H1
83.6(1)
106.7(1)
74.2(1)
73.4(1)
123.6(2)
124.4(3)
130.8(2)
121.1(1)
128.1(1)
116(3)
122.6(3)
120(3)
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having terminal acyl ligands,44 and far from the values expected
for a carbene ligand, thus suggesting little participation of
the oxycarbene form B, in agreement with the crystal data. The
31P{1H} NMR spectra of 13 exhibit a resonance at 624.8 ppm,
a relatively high chemical shift, but not unusual for 48- and
50-electron clusters having iron atoms.14b,c We finally note that
the resonance of the HC1 proton of the Cy group is unusually
deshielded (δ 4.87 ppm). This could be a combined deshielding
effect of the three anisotropic Cp rings of the molecule, relatively
close to that H atom.
obtained from the usual commercial suppliers and used as
received. Photochemical experiments were performed using
jacketed quartz or Pyrex Schlenk tubes, cooled by tap water
(ca. 288 K) unless otherwise stated. A 400 W mercury lamp
placed ca. 1 cm away from the Schlenk tube was used for all the
experiments. Chromatographic separations were carried out
using jacketed columns cooled by tap water (ca. 288 K) or by a
closed 2-propanol circuit, kept at the desired temperature with a
cryostat. Commercial aluminum oxide (activity I, 150 mesh) was
degassed under vacuum prior to use. The latter was mixed under
nitrogen with the appropriate amount of water to reach the
activity desired. Filtrations were performed using diatomaceous
earth unless otherwise stated. IR C–O stretching frequencies
were measured in solution or Nujol mulls, are referred to as νCO
(solvent) or νCO (Nujol), respectively, and are given in wave-
number units (cm−1). Nuclear Magnetic Resonance (NMR)
spectra were routinely recorded at 400.13 (1H), 162.00
(31P{1H}), 128.38 (11B) or 100.62 MHz (13C{1H}) at 290 K in
CD2Cl2 solutions unless otherwise stated. Chemical shifts (δ)
are given in ppm, relative to internal tetramethylsilane (1H, 13C),
external 85% aqueous H3PO4 solution (31P) or external
BF3·OEt2 (11B). Coupling constants (J) are given in hertz (Hz).
Concluding remarks
The phosphinidene complexes [Fe2Cp2(μ-PR)(μ-CO)(CO)2] (R =
Cy, Ph) are strong nucleophiles able to react under mild con-
ditions with different electrophilic reagents based on p-block
elements, to give neutral or cationic derivatives of the type
[Fe2Cp2{μ-P(E)R}(μ-CO)(CO)2]n (n = 0, +1). After additional
protonation, alkylation or photochemical processes, these com-
plexes can lead to novel phosphide or phosphinidene derivatives
otherwise difficult to prepare, such as the hydroxy- and alkoxy-
phosphide cations [Fe2Cp2{μ-P(OR′)Cy}(μ-CO)(CO)2]+ or the
agostic phosphinidene–borane complexes [Fe2Cp2{μ-κ1:κ1,η2-P-
(BH3)R}(μ-CO)(CO)]. Our phosphinidene complexes are also
very reactive toward organic molecules containing multiple C–O
or C–N bonds, such as quinones and azides, to give respectively
Preparation of [Fe2Cp2(μ-PMeCy)(μ-CO)(CO)2]I (2a).
Methyl iodide (28 μL, 0.450 mmol) was added to a freshly pre-
pared solution of complex 1a (ca. 0.025 g, 0.057 mmol) in
dichloromethane (5 mL), and the mixture was stirred at room
temperature for 10 min to give a red solution which was filtered.
The solvent was then removed from the filtrate under vacuum,
and the residue was washed with petroleum ether (2 × 5 mL) and
dried under vacuum to give compound 2a as a red microcrystal-
line solid (0.030 g, 91%). Anal. calcd for C20H24Fe2IO3P: C,
41.28; H, 4.16. Found: C, 41.12; H, 4.05. δH(200.13 MHz)
5.37 (s, 10H, Cp), 2.93 (d, JHP = 12, 3H, Me), 2.06–0.88
(m, 11H, Cy).
t
phosphonite [Fe2Cp2(μ-CO)2(CO){P(O2C6H2 Bu2)R}] and phos-
phatriazadiene [Fe2Cp2{μ-P(N3CH2Ph)R}(μ-CO)(CO)2] deriva-
tives. The latter are the first examples containing a μ-P:P-
coordinated phosphatriazadiene ligand. Dinitrogen elimination
can be forced upon the cyclohexyl product through either
thermal or photochemical activation. In the first case, the corres-
ponding iminophosphinidene complex [Fe2Cp2{μ-P(NCH2Ph)
Cy}(μ-CO)(CO)2] is obtained, an air-sensitive product that could
be transformed through protonation into a more stable amino-
phosphide derivative. In contrast, photochemical activation
triggers additional bond-cleavage and formation processes
(including H atom transfer) to eventually yield the trinuclear
derivative [Fe3Cp3(μ3-PCy){μ-κ1:κ1-C(O)(NHCH2Ph)}(μ-CO)2],
having phosphinidene and C:O-bound aminoacyl bridging
ligands. The smaller size and poorer donor properties of the PPh
ligand, compared to the PCy ligand, make complex 1b less
nucleophilic than 1a (as shown in the reactions with borane
adducts), but more susceptible to further reactions in their
derivatives (as shown in the reactions with MeI or O2), which
seem to be in general less stable than their cyclohexyl
counterparts.
Preparation of [Fe2Cp2I(μ-PMePh)(CO)3] (3). Methyl iodide
(8 μL, 0.129 mmol) was added to a freshly prepared solution of
complex 1b (ca. 0.050 g, 0.115 mmol) in dichloromethane
(5 mL) cooled at 273 K, and the mixture was stirred for 10 min
at this temperature to give a red solution shown (by IR) to
contain essentially pure complex [Fe2Cp2(μ-PMePh)(μ-CO)-
(CO)2]I (2b). The solution was then filtered and the solvent was
removed from the filtrate under vacuum. The residue was then
washed with petroleum ether (3 × 5 mL) and dried under
vacuum to give a brown solid shown (by IR in Nujol mull) to be
a mixture of the isomers 2b and 3 (0.058 g, 88%). When this
solid was dissolved in CH2Cl2 and stirred at room temperature
for ca. 1 h, then a brown solution was obtained, shown by IR
and NMR to be an equilibrium mixture of compounds 2b (very
minor) and 3 (major), with the latter in turn appearing as two
isomers A and B. The equilibrium ratio 2b : A : B was measured
(by 31P{1H} NMR) to be ca. 1 : 55 : 60 in CDCl3 solution at
room temperature. Anal. calcd for C20H18Fe2IO3P: C, 41.71; H,
3.15. Found: C, 41.57; H, 3.10. Spectroscopic data for the
mixture of 2b and 3: νCO (Nujol): 2016 (s), 1966 (vs), 1917 (s),
1817 (w). Spectroscopic data for isomer A: δH(300.13 MHz,
CDCl3) 7.90–7.25 (m, 5H, Ph), 5.09 (d, JHP = 1, 5H, Cp), 4.29
(s, 5H, Cp), 2.10 (d, JHP = 7, 3H, Me). Spectroscopic data for
Experimental section
General procedures and starting materials
All manipulations and reactions were carried out under a nitro-
gen (99.995%) atmosphere using standard Schlenk techniques.
Solvents were purified according to literature procedures and dis-
tilled prior to use.45 Petroleum ether refers to that fraction distil-
ling in the range 338–343 K. Compounds [Fe2Cp2(μ-PR)-
(μ-CO)(CO)2] (Cp = η5-C5H5; R = Cy(1a), Ph(1b)] were pre-
pared as described previously.6a,c All other reagents were
This journal is © The Royal Society of Chemistry 2012
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Preparation of [Fe2Cp2{μ-P(S)Ph}(μ-CO)(CO)2] (5b). The
procedure is completely analogous to that described for 5a, but
using complex 1b instead (ca. 0.025 g, 0.058 mmol). In this way
compound 5b was obtained as a red-brown microcrystalline
solid (0.022 g, 82%). Anal. calcd for C19H15Fe2O3PS: C, 48.97;
H, 3.24. Found: C, 48.73; H, 3.11. δH(200.13 MHz, CDCl3)
7.75 (m, 2H, Ph), 7.35–7.30 (m, 3H, Ph), 4.97 (s, 10H, Cp).
isomer B: δH(300.13 MHz, CDCl3) 7.90–7.25 (m, 5H, Ph), 5.00
(d, JHP = 1, 5H, Cp), 4.27 (s, 5H, Cp), 2.48 (d, JHP = 7, 3H,
Me). The resonances due to isomer 2b could not be identified in
the H NMR spectrum due to its low proportion and/or super-
imposition with the resonances of the major isomers.
1
Preparation of [Fe2Cp2(μ-PMePh)(μ-CO)(CO)2]CF3SO3 (2b′).
Methyl triflate (8 μL, 0.071 mmol) was added to a freshly pre-
pared solution of complex 1b (ca. 0.025 g, 0.058 mmol) in
dichloromethane (5 mL) cooled at 273 K, and the mixture was
stirred for 10 min at this temperature to give a red solution which
was filtered. The solvent was then removed from the filtrate
under vacuum, and the residue was washed with petroleum ether
(2 × 5 mL) to give compound 2b′ as a red microcrystalline solid
(0.030 g, 88%). Anal. calcd for C21H18F3Fe2O6PS: C, 40.99;
H, 3.10. Found: C, 41.10; H, 3.22. δH(300.13 MHz) 7.78–7.50
(m, 5H, Ph), 5.43 (s, 10H, Cp), 2.96 (d, JHP = 12, 3H, Me).
Preparation of [Fe2Cp2{μ-P(OH)Cy}(μ-CO)(CO)2]BF4 (6). A
slight excess of HBF4·OEt2 (18 μL of a 54% solution in Et2O,
0.131 mmol) was added to a dichloromethane solution (5 mL) of
compound 5a (0.050 g, 0.110 mmol), and the mixture was
stirred at room temperature for 5 min to give a red solution. The
solvent was then removed under vacuum, and the residue
was washed with Et2O (3 × 5 mL) and then petroleum ether
(2 × 5 mL) to give compound 6 as a red microcrystalline solid
(0.057 g, 96%). This complex exists in solution as an equili-
brium mixture of the corresponding cis, anti and cis, syn
isomers, with their relative proportions being solvent-dependent
(5/2 in CD2Cl2 and 7/1 in acetone-d6). Anal. calcd for
C19H22BF4Fe2O4P: C, 41.96; H, 4.08. Found: C, 42.10; H, 4.20.
Spectroscopic data for 6: νOH (Nujol): 3224 (w, br); νCO
(Nujol): 2012 (vs), 1978 (s), 1835 (s). Spectroscopic data for
cis, anti-6: δP(acetone-d6) 367.0. δH 8.74 (s, br, 1H, OH), 5.22
(s, 10H, Cp), 2.46–1.20 (m, 11H, Cy). δH(acetone-d6) 10.29
(s, br, 1H, OH), 5.48 (s, 10H, Cp), 2.47 (m, 2H, Cy), 2.30 (m,
2H, Cy), 1.95 (m, 2H, Cy), 1.74 (m, 1H, Cy), 1.57 (m, 1H, Cy),
1.49–1.22 (m, 3H, Cy). δC(acetone-d6) 257.2 (s, μ-CO), 210.6
(d, JCP = 18, FeCO), 90.6 (s, Cp), 58.2 [d, JCP = 33, C1(Cy)],
30.2 [d, JCP = 7, C2(Cy)], 27.4 [d, JCP = 14, C3(Cy)], 26.3 [s,
C4(Cy)]. Spectroscopic data for cis, syn-6: δP(acetone-d6) 348.7.
δH 5.15 (s, 10H, Cp), 2.46–1.20 (m, 11H, Cy). δH(acetone-d6)
8.99 (s, br, 1H, OH), 5.37 (s, 10H, Cp), 2.54–1.22 (m, 11H, Cy).
δC(acetone-d6) 90.3 (s, Cp), 61.6 [d, JCP = 25, C1(Cy)]; other
resonances of this minor isomer could not be identified in the
corresponding spectra due to its low proportion and/or super-
imposition with the resonances of the major isomer.
Preparation of [Fe2Cp2{μ-P(O)Cy}(μ-CO)(CO)2] (4a). Air
was admitted into a Schlenk tube containing a freshly prepared
solution of complex 1a (ca. 0.025 g, 0.057 mmol) in dichloro-
methane (5 mL), and the mixture was stirred at r.t. for 10 min to
give a dark red solution. After removal of the solvent under
vacuum, the residue was dissolved in a minimum amount of
dichloromethane/petroleum ether (1/1) and chromatographed on
alumina (activity IV) at 288 K. Elution with acetone gave a red
fraction yielding, after removal of solvents, compound 4a as a
red microcrystalline solid (0.021 g, 81%). Anal. calcd for
C19H21Fe2O4P: C, 50.04; H, 4.64. Found: C, 49.72; H, 4.30.
νCO (toluene): 1983 (vs), 1949 (w), 1791 (m). δH(200.13 MHz,
CDCl3) 4.87 (s, 10H, Cp), 2.30–1.25 (m, 11H, Cy).
Preparation of [Fe2Cp2{μ-P(O)Ph}(μ-CO)(CO)2] (4b). Solid
m-chloroperbenzoic acid (0.010 g, 0.058 mmol) was added to
a freshly prepared solution of complex 1b (ca. 0.025 g,
0.058 mmol) in dichloromethane (5 mL), and the mixture was
stirred at room temperature for 5 min to give a red solution
which was filtered. The solvent was then removed from the
filtrate under vacuum, and the residue was washed with
petroleum ether (3 × 5 mL) to give compound 4b as a red micro-
crystalline solid (0.020 g, 77%). Anal. calcd for C19H15Fe2O4P:
C, 50.71; H, 3.36. Found: C, 50.59; H, 3.27. δH(300.13 MHz,
CDCl3) 8.11–7.26 (m, 5H, Ph), 5.07 (s, 10H, Cp).
Preparation of [Fe2Cp2{μ-P(OMe)Cy}(μ-CO)(CO)2]CF3SO3
(7). Neat methyl triflate (40 μL, 0.354 mmol) was added to
a dichloromethane solution (5 mL) of compound 5a (0.040 g,
0.088 mmol), and the mixture was stirred at room temperature
for 2 h to give a red solution which was filtered. Solvent was
then removed from the filtrate under vacuum and the residue
was washed with Et2O (3 × 5 mL) and then petroleum ether
(2 × 5 mL) to give compound 7 as a red microcrystalline solid
(0.052 g, 95%). This complex exists in solution as an equili-
brium mixture of the corresponding cis, anti, cis, syn and trans
isomers, with their relative proportions being solvent-dependent
(ca. 20 : 1 : 1 in CD2Cl2 and 40 : 2 : 1 in acetone-d6). Anal. calcd
for C21H24F3Fe2O7PS: C, 40.67; H, 3.90. Found: C, 40.45;
H, 3.75. Spectroscopic data for cis, anti-7: δH 5.34 (s, 10H, Cp),
4.20 (d, JHP = 11, 3H, OMe), 2.38 [m, 2H, HC2(Cy)], 2.17 [m,
2H, HC2(Cy)], 1.98 [m, 2H, HC3(Cy)], 1.76 [m, 1H, HC4(Cy)],
1.53 [m, 1H, HC1(Cy)], 1.38 [m, 1H, HC4(Cy)], 1.27 [m, 2H,
HC3(Cy)]. δH(acetone-d6) 5.64 (s, 10H, Cp), 4.36 (d, JHP = 11,
3H, OMe), 2.49 [m, 2H, HC2(Cy)], 2.25 [m, 2H, HC2(Cy)],
1.94 [m, 2H, HC3(Cy)], 1.74 [m, 1H, HC4(Cy)], 1.57 [m, 1H,
HC1(Cy)], 1.43 [m, 1H, HC4(Cy)], 1.28 [m, 2H, HC3(Cy)].
Preparation of [Fe2Cp2{μ-P(S)Cy}(μ-CO)(CO)2] (5a). Solid
sulphur (0.007 g, 0.218 mmol) was added to a freshly prepared
solution of complex 1a (ca. 0.025 g, 0.057 mmol) in dichloro-
methane (5 mL), and the mixture was stirred at room temperature
for 5 min to give a red-brown solution. After removal of the
solvent, the residue was dissolved in a minimum amount of
dichloromethane/petroleum ether (1/1) and the extract was chro-
matographed on alumina (activity IV) at 288 K. Elution with the
same solvent mixture gave a red fraction yielding, after removal
of solvents, compound 5a as a red-brown microcrystalline solid
(0.025 g, 92%). Anal. calcd for C19H21Fe2O3PS: C, 48.34;
H, 4.48. Found: C, 48.16; H, 4.13. δH(300.13 MHz, CDCl3)
4.81 (s, 10H, Cp), 2.44–1.25 (m, 11H, Cy). δC(75.48 MHz,
CDCl3) 267.5 (s, μ-CO), 210.3 (d, JCP = 14, FeCO), 91.8
(s, Cp), 62.7 [d, JCP = 20, C1(Cy)], 31.3 [d, JCP = 4, C2(Cy)],
26.6 [d, JCP = 13, C3(Cy)], 25.7 [s, C4(Cy)].
14508 | Dalton Trans., 2012, 41, 14498–14513
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δC 254.2 (s, μ-CO), 208.1 (d, JCP = 17, FeCO), 89.2 (s, Cp),
60.9 (d, JCP = 12, OMe), 60.0 [d, JCP = 28, C1(Cy)], 31.5 [d,
JCP = 6, C2(Cy)], 27.3 [d, JCP = 13, C3(Cy)], 25.9 [s, C4(Cy)].
quartz Schlenk tube for 30 min, while keeping a gentle N2
purge, to give a green solution which was filtered using a canula.
The solvent was then removed from the filtrate under vacuum,
and the residue was washed with petroleum ether (2 × 4 mL) to
give compound 9a as a green microcrystalline solid (0.034 g,
90%). The crystals used in the X-ray diffraction study were
grown by the slow diffusion of a layer of petroleum ether into a
dichloromethane solution of the complex at 253 K. Anal. calcd
for C18H24BFe2O2P: C, 50.77; H, 5.68. Found: C, 50.55;
H, 5.49. δB −36.8 (s, br). δH 4.67, 4.59 (2s, 2 × 5H, Cp), 3.65
[m, 1H, HC1(Cy)], 2.70 [m, 1H, HC2(Cy)], 2.33 [m, 1H,
HC2(Cy)], 2.21–1.61 (m, 7H, Cy), 1.56 [m, 1H, C4(Cy)], 0.40,
−2.02 (2m, JHB = 141, 2 × 1H, BH2), −22.69 (s, br, 1H, B–H–
1
The assignment of the H NMR resonances of the Cy ring was
1
made on the basis of a standard J(13C–1H) correlation exper-
iment (HSQC). Spectroscopic data for cis, syn-7: δH 5.30 (s,
10H, Cp), 3.87 (d, JHP = 11, 3H, OMe), 2.42–1.20 (m, 11H, Cy).
δH(acetone-d6) 5.58 (s, 10H, Cp), 4.01 (d, JHP = 11, 3H, OMe),
2.50–1.27 (m, 11H, Cy). δC 89.1 (s, Cp). Spectroscopic data for
trans-7: δH 5.24 (d, JHP = 1, 5H, Cp), 5.13 (s, 5H, Cp), 4.06 (d,
JHP = 12, 3H, OMe), 2.50–1.27 (m, 11H, Cy). δH(acetone-d6)
5.50, 5.40 (2s, 2 × 5H, Cp), 4.13 (d, JHP = 12, 3H, OMe),
2.50–1.27 (m, 11H, Cy). δH 90.8, 89.5 (2s, Cp). Other reson-
ances of the minor isomers could not be identified in the corre-
sponding spectra due to their low proportion and/or
superimposition with the resonances of the major isomer.
1
Fe). H{11B} NMR: δ 0.40 (dd, JHH = 8, JHP = 7, 1H, BH2),
−2.02 (d, JHH = 21, 1H, BH2), −22.69 (ddd, JHH = 21, 8, JHP
=
3, 1H, B–H–Fe). δC 262.2 (s, μ-CO), 214.0 (d, JCP = 30, FeCO),
83.2, 83.0 (2s, Cp), 43.4 [d, JCP = 3, C1(Cy)], 36.0 [s, C2(Cy)],
33.7 [d, JCP = 3, C2(Cy)], 28.3 [d, JCP = 14, C3(Cy)], 27.7
[d, JCP = 10, C3(Cy)], 26.6 [s, C4(Cy)]. The assignment of the
1H NMR resonances of the Cy ring was made on the basis of a
standard 1J(13C–1H) correlation experiment (HSQC).
Preparation of [Fe2Cp2{μ-P(BH3)Cy}(μ-CO)(CO)2] (8a).
Method A: a solution of BH3·THF (102 μL of a 1 M solution in
THF, 0.102 mmol) was added to a freshly prepared solution of
complex 1a (ca. 0.030 g, 0.068 mmol) in dichloromethane
(5 mL), and the mixture was stirred at room temperature for
30 min to give a red solution. The solvent was then removed
under vacuum, and the residue was dissolved in a minimum
amount of dichloromethane/petroleum ether (1/1) and chromato-
graphed on alumina (activity IV) at 288 K. Elution with the
same solvent mixture gave a red fraction yielding, after removal
of solvents, compound 8a as a red microcrystalline solid
(0.028 g, 94%).
Preparation of [Fe2Cp2{μ-κ1:κ1,η2-P(BH3)Ph}(μ-CO)(CO)]
(9b). The procedure is completely analogous to that described
for compound 9a but using compound 8b as starting material
(0.030 g, 0.067 mmol) in a Pyrex Schlenk tube, with an
irradiation time of 25 min. After a similar workup, compound
9b was obtained as a green microcrystalline solid (0.027 g,
93%). Anal. calcd for C18H18BFe2O2P: C, 51.50; H, 4.32.
t
Method B: solid BH3·NH2 Bu (0.012 g, 0.138 mmol) was
Found: C, 51.17; H, 4.21. δB −33.4 (s, br). δH 8.28 (dd, JHH =
added to a freshly prepared solution of complex 1a (ca. 0.030 g,
0.068 mmol) in toluene (5 mL), and the mixture was stirred at
348 K for 1 h to give a red solution. After workup as described
above, compound 8a was obtained as a red microcrystalline solid
(0.027 g, 91%).
12, JHP = 2, 1H, Ph), 8.24 (dd, JHH = 12, JHP = 3, 1H, Ph),
7.62–7.56 (m, 3H, Ph), 4.80, 4.42 (2s, 2 × 5H, Cp), 0.87, −1.61
1
(2m, JHB = 149, 2 × 1H, BH2), −22.48 (s, br, 1H, B–H–Fe). H
{11B} NMR: δ 0.87 (ddd, JHH = 8, 5, JHP = 13, 1H, BH2),
−1.61 (dd, JHH = 21, 5, 1H, BH2), −22.48 (ddd, JHH = 21, 8,
JHP = 2, 1H, B–H–Fe). δC 257.6 (s, μ-CO), 213.6 (d, JCP = 31,
FeCO), 143.1 [d, JCP = 2, C1(Ph)], 133.5 [d, JCP = 10, C2(Ph)],
129.3 [s, C3(Ph)], 129.1 [d, JCP = 10, C2(Ph)], 128.5 [s, C3(Ph)],
127.7 [s, C4(Ph)], 84.5, 83.2 (2s, Cp).
Method C: the procedure is completely analogous to that
described in method B, but using BH3·PPh3 instead (0.038 g,
0138 mmol). In this way compound 8a was obtained as a red
microcrystalline solid (0.027 g, 91%). Anal. calcd for
C19H24BFe2O3P: C, 50.28; H, 5.33. Found: C, 50.05; H, 5.14.
δB −25.7 (qd, JBH = 96, JBP = 41). δH 4.93 (d, JHP = 1, 10H,
Preparation of [Fe2Cp2{μ-P(N3CH2Ph)Cy}(μ-CO)(CO)2] (10a).
Neat benzyl azide (12 μL, 0.096 mmol) was added to a freshly
prepared solution of complex 1a (ca. 0.040 g, 0.091 mmol) in
dichloromethane (5 mL), and the mixture was stirred at room
temperature for 5 min to give a dark green solution. The solvent
was then removed from the mixture under vacuum and the
residue was washed with petroleum ether (2 × 3 mL) to give
compound 10a as a green microcrystalline solid (0.051 g, 98%).
Anal. calcd for C26H28Fe2N3O3P: C, 54.48; H, 4.92; N, 7.33.
Found: C, 54.26; H, 4.77; N, 7.03. δH 7.35–7.25 (m, 4H, Ph),
7.17 (m, 1H, Ph), 4.99 (s, 10H, Cp), 4.82 (s, 2H, CH2), 2.44,
2.28, 1.87 (3m, 3 × 2H, Cy), 1.68 (m, 1H, Cy), 1.50–0.86 (m,
4H, Cy). δC 267.3 (s, μ-CO), 211.2 (d, JCP = 11, FeCO), 139.7
[s, C1(Ph)], 129.2 [s, C3(Ph)], 128.7 [s, C2(Ph)], 127.1
[s, C4(Ph)], 88.1 (s, Cp), 67.0 (s, CH2), 55.7 [d, JCP = 52,
C1(Cy)], 31.9 [d, JCP = 6, C2(Cy)], 27.7 [d, JCP = 12, C3(Cy)],
26.3 [s, C4(Cy)].
Cp), 2.29 (qt, JHH = JHP = 13, JHH = 4, 2H, Cy), 1.79 (m, JHB
=
96, 3H, BH3), 1.91–1.68 (m, 6H, Cy), 1.39 (qt, JHH = JHP = 13,
1
JHH = 4, 1H, Cy), 1.18 (m, 2H, Cy). H{11B} NMR: δ 1.79
(d, JHP = 10, 3H, BH3).
Preparation of [Fe2Cp2{μ-P(BH3)Ph}(μ-CO)(CO)2] (8b). The
procedure is completely analogous to that described for com-
pound 8a (method A) but using compound 1b (0.050 g,
0.115 mmol) and BH3·THF (290 μL of a 1 M solution in THF,
0.290 mmol). A similar workup yielded compound 8b as a red
microcrystalline solid (0.049 g, 95%). Anal. calcd for
C19H18BFe2O3P: C, 50.96; H, 4.05. Found: C, 50.78; H, 4.19.
δB −18.0 (qd, JBH = 97, JBP = 33). δH 7.62 (m, 2H, Ph),
7.33–7.24 (m, 3H, Ph), 5.08 (d, JHP = 1, 10H, Cp), 1.97 (m, JHB
= 97, 3H, BH3). 1H{11B} NMR: δ 1.97 (d, JHP = 9, 3H, BH3).
Preparation of [Fe2Cp2{μ-κ1:κ1,η2-P(BH3)Cy}(μ-CO)(CO)]
(9a). A toluene solution (4 mL) of complex 8a (0.040 g,
0.088 mmol) was irradiated with visible-UV light at 288 K in a
Preparation of [Fe2Cp2{μ-P(N3CH2Ph)Ph}(μ-CO)(CO)2] (10b).
Neat benzyl azide (8 μL, 0.064 mmol) was added to a freshly
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prepared solution of complex 1b (ca. 0.025 g 0.058 mmol) in
dichloromethane (4 mL) at 203 K, and the mixture was stirred at
this temperature for 5 min to give a green solution. The solvent
was then removed from the mixture under vacuum, keeping the
temperature below 253 K, to give compound 10b as a green
microcrystalline solid. This species is thermally unstable and any
manipulation in solution or in the solid state at temperatures
above 263 K caused its progressive decomposition. δH (203 K)
7.92–7.28 (m, 10H, Ph), 5.20 (s, 10H, Cp), 4.90 (s, 2H, CH2).
yielding, after removal of solvents, compound 13 as a garnet-
brown microcrystalline solid (0.047 g, 40%). The crystals used
in the X-ray diffraction study were grown by the slow diffusion
of a layer of petroleum ether into a dichloromethane solution
of the complex at room temperature. Anal. calcd for
C31H34Fe3NO3P: C, 55.81; H, 5.14; N, 2.10. Found: C, 55.68;
H, 3.98; N, 1.99. δH 7.25 (false t, JHH = 7, 2H, m-Ph), 7.18
(t, JHH = 7, 1H, p-Ph), 6.90 (d, JHH = 7, 2H, o-Ph), 5.64 (dd,
ABX, JHH = 6, 5, 1H, NH), 4.87 [qt, JHH = 12, 4, JHP = 12, 1H,
HC1(Cy)], 4.50, 4.31, 4.26 (3s, 3 × 5H, Cp), 3.61 (dd, ABX,
JHH = 15, 6, 1H, CH2), 3.35 (dd, ABX, JHH = 15, 5, 1H, CH2),
3.40–3.31 [m, 2H, HC2(Cy)], 3.01, 2.75 [2 × tq, JHH = 12, 4,
JHP = 4, 2 × 1H, HC2(Cy)], 2.40–2.28 [m, 2H, HC3(Cy)], 2.16
Preparation of [Fe2Cp2{μ-P(NCH2Ph)Cy}(μ-CO)(CO)2] (11).
A
toluene solution (4 mL) of complex 10a (0.030 g,
0.052 mmol) was stirred at 368 K for 10 min to give a dark
green solution. The solvent was then removed under vacuum,
and the residue was washed with petroleum ether (2 × 3 mL) and
dried under vacuum conditions to give compound 11 as a dark
green, very air-sensitive microcrystalline solid (0.026 g, 90%).
Unfortunately, no satisfactory elemental analysis could be
obtained for this product due to its rapid decomposition upon
manipulation in the air. δH 7.73 (m, 2H, Ph), 7.41–7.20 (m, 3H,
Ph), 4.92 (d, JHP = 25, 2H, CH2), 4.42 (s, 10H, Cp), 2.85–1.29
(m, 11H, Cy).
[m, 1H, HC4(Cy)], 2.09–1.96 [m, 2H, HC3(Cy)], 1.85 [qt, JHH
=
13, 4, 1H, HC4(Cy)]. δC 281.7, 279.2 (2s, μ-CO), 233.4 (d, JCP
= 17, NCO), 140.5 [s, C1(Ph)], 128.5 [s, C3(Ph)], 127.6 [s,
C2(Ph)], 126.9 [s, C4(Ph)], 86.4, 84.3, 80.6 (3s, Cp), 56.3 [d, JCP
= 14, C1(Cy)], 44.7 (s, CH2), 36.0, 35.6 [2s, C2(Cy)], 28.7 [d,
JCP = 11, C3(Cy)], 28.6 [d, JCP = 9, C3(Cy)], 27.2 [s, C4(Cy)].
1
The assignment of the H NMR resonances of the Cy ring was
1
made on the basis of a standard J(13C–1H) correlation experi-
ment (HSQC).
Preparation of [Fe2Cp2{μ-P(NHCH2Ph)Cy}(μ-CO)(CO)2]PF6
(12). Solid NH4PF6 (0.010 g, 0.061 mmol) was added to a
freshly prepared solution of complex 11 (ca. 0.026 g,
0.048 mmol) in dichloromethane (5 mL), and the mixture was
stirred at room temperature for 5 min to give a red solution
which was filtered using a canula. After removal of the solvent
from the filtrate under vacuum, the residue was washed with
Et2O (3 × 4 mL) and then with petroleum ether (2 × 4 mL) to
give compound 12 as a red microcrystalline solid (0.031 g,
95%). The crystals used in the X-ray diffraction study were
grown by the slow diffusion of layers of toluene and petroleum
ether into a dichloromethane solution of the complex at room
temperature. Anal. calcd for C26H29F6Fe2NO3P2: C, 45.18; H,
4.23; N, 2.03. Found: C, 45.05; H, 3.98; N, 1.96. δH 7.35–7.25
(m, 4H, Ph), 7.39 (m, 1H, Ph), 5.20 (s, 10H, Cp), 4.50 (m,
A2BX, JHH = JHP = 8, 2H, CH2), 4.40 (m, A2BX, JHH = 8, JHP
= 5, 1H, NH), 2.34, 2.10 [2m, 2 × 2H, HC2(Cy)], 1.95 [m, 2H,
HC3(Cy)], 1.75 [m, 1H, HC4(Cy)], 1.54 [m, 1H, HC1(Cy)],
1.41–1.21 (m, 3H, Cy). δC 256.3 (s, μ-CO), 208.7 (d, JCP = 16,
FeCO), 138.7 [s, C1(Ph)], 129.7 [s, C3(Ph)], 128.6 [s, C4(Ph)],
127.1 [s, C2(Ph)], 89.1 (s, Cp), 56.4 [d, JCP = 34, C1(Cy)], 49.9
(d, JCP = 4, CH2), 32.2 [d, JCP = 6, C2(Cy)], 27.5 [d, JCP = 13,
C3(Cy)], 25.8 [s, C4(Cy)]. The assignment of the 1H NMR
resonances of the Cy ring was made on the basis of a standard
1J(13C–1H) correlation experiment (HSQC).
t
Preparation of [Fe2Cp2(μ-CO)2(CO){P(O2C6H2 Bu2)Cy}]
(14a). Solid
3,5-di-tert-butyl-o-benzoquinone
(0.016
g,
0.072 mmol) was added to a freshly prepared solution of
complex 1a (ca. 0.030 g, 0.068 mmol) in dichloromethane
(5 mL), and the mixture was stirred at room temperature for
5 min to give a green-garnet solution. The solvent was then
removed under vacuum, and the residue was dissolved in a
minimum amount of dichloromethane/petroleum ether (1/6) and
chromatographed on alumina (activity IV) at 288 K. Elution
with dichloromethane/petroleum ether (1/4) gave a green-garnet
fraction yielding, after removal of solvents, compound 14a as a
green-garnet microcrystalline solid (0.042 g, 93%). This
complex exists in solution as an equilibrium mixture of the cor-
responding trans and cis isomers, with the ratio trans/cis being
ca. 14/1 in CD2Cl2 at room temperature (from the 31P{1H}
NMR spectrum). Anal. calcd for C33H41Fe2O5P: C, 60.02; H,
6.26. Found: C, 59.83; H, 5.98. Spectroscopic data for 14a: νCO
(petroleum ether): 1953 (m), 1797 (w), 1761 (vs). Spectroscopic
data for trans-14a: δH 6.85, 6.80 (2d, JHH = 2, 2 × 1H, C6H2),
4.75, 4.66 (2s, 2 × 5H, Cp), 1.97, 1.86 (2m, 2 × 1H, Cy),
1.72–1.68 (m, 3H, Cy), 1.60 (m, 1H, Cy), 1.36, 1.28 (2s,
2 × 9H, tBu), 1.21–1.04 (m, 5H, Cy). δC 278.1, 277.8 (2d, JCP
=
15, μ-CO), 214.1 (s, FeCO), 147.8 [d, JCP = 5, C1,2(C6H2)],
145.5 [s, C5(C6H2)], 143.5 [d, JCP = 5, C2,1(C6H2)], 134.1
[d, JCP = 4, C3(C6H2)], 116.6 [s, C4(C6H2)], 107.4 [d, JCP = 5,
C6(C6H2)], 87.9, 87.0 (2s, Cp), 52.1 [d, JCP = 13, C1(Cy)], 35.1,
34.6 [2s, C1(tBu)], 31.7, 29.5 [2s, C2(tBu)], 26.6 [m, C3(Cy)],
26.3 [s, C2(Cy)], 27.2 [s, C4(Cy)]. The resonances due to the
isomer cis-14a could not be identified in the corresponding
1H and 13C{1H} NMR spectra due to its low proportion and/or
superimposition with the resonances of the major isomer.
Preparation of [Fe3Cp3(μ3-PCy){μ-κ1:κ1-C(O)(NHCH2Ph)}
(μ-CO)2] (13). A toluene solution (6 mL) of complex 10a
(0.100 g, 0.174 mmol) was irradiated for 5 h with visible-UV
light in a quartz Schlenk tube refrigerated with tap water while
gently bubbling N2 through the solution, to give a garnet-brown
mixture. After removal of the solvent under vacuum, the residue
was dissolved in a minimum amount of dichloromethane/
petroleum ether (1/2) and chromatographed on alumina (activity
IV) at 263 K. Elution with the same solvent mixture gave a red
fraction containing [Fe2Cp2(CO)4]. Elution with dichloro-
methane/petroleum ether (2/1) gave a garnet-brown fraction
t
Preparation
of
[Fe2Cp2(μ-CO)2(CO){P(O2C6H2 Bu2)Ph}]
(14b). The procedure is completely analogous to that described
for 14a but using compound 1b (0.035 g, 0.081 mmol) as start-
ing material and 0.018 g (0.082 mmol) of 3,5-di-tert-butyl-o-
14510 | Dalton Trans., 2012, 41, 14498–14513
This journal is © The Royal Society of Chemistry 2012

View Article Online
Table 6 Crystal data for new compounds
Compound
9a
12
13·1.5C7H8
Mol formula
Mol wt
Cryst syst
Space group
Radiation (λ, Å)
a (Å)
b (Å)
c (Å)
α (°)
C18H24BFe2 O2P
425.85
Orthorhombic
Pbca
C26H29Fe2 NO3PF6P
691.14
Monoclinic
P21
C83H92Fe6 N2O6P2
1610.63
Monoclinic
C2/c
0.71073
0.71073
0.71073
15.2331(11)
11.0731(10)
21.585(2)
90
9.8882(2)
11.9548(3)
12.1755(3)
90
25.7535(5)
15.5862(4)
19.4501(3)
90
β (°)
90
90
3640.9(5)
8
1.554
1.688
100(2)
100.9890(10)
90
1412.89(6)
2
1.625
1.209
111.9560(10)
90
7241.0(3)
4
1.477
1.271
γ (°)
V (Å3)
Z
Calcd density (g cm−3
)
)
Absorpt. coeff. (mm−1
Temperature (K)
100(2)
100(2)
θ range (°)
Index ranges (h, k, l)
No. of reflns collected
1.89 to 25.35
0, 18; 0, 13; −25, 0
17 547
1.7 to 25.24
−11, 11; −14, 14; 0, 14
13 282
2.26 to 25.24
−30, 28; 0, 18; 0, 23
27 142
No. of indep reflns (Rint
Reflns with I > 2σ(I)
)
3258 (0.0571)
2497
R1 = 0.0385
wR2 = 0.0967b
R1 = 0.0632
wR2 = 0.1212b
1.176
4857 (0.0297)
4637
R1 = 0.0291
wR2 = 0.0805c
R1 = 0.0369
wR2 = 0.1129c
1.242
6290 (0.0378)
5223
R1 = 0.0447
wR2 = 0.135d
R1 = 0.0569
wR2 = 0.1563d
1.108
R indexes [data with I > 2σ(I)]a
R indexes (all data)a
GOF
No. Of restraints/params
0/226
0.691, −0.583
1/366
0.713, −0.923
0/454
1.996, −0.907
Δρ (max, min) (e Å−3
)
a R = Σ||Fo| − |Fc||/Σ|Fo|. wR = [Σw(|Fo|2 − |Fc|2)2/Σw|Fo|2]1/2. w = 1/[σ2(Fo ) + (aP)2 + bP] where P = (Fo2 + 2Fc )/3. b a = 0.0635, b = 0.4074. c a =
2
2
0.0720, b = 0.0000. d a = 0.0899, b = 28.2765.
benzoquinone. After a similar workup, compound 14b was
obtained as a green-purple microcrystalline solid (0.048 g, 91%).
This complex also exists in solution as an equilibrium mixture of
the corresponding trans and cis isomers, with the ratio trans/cis
performed with the programs HKL Denzo and Scalepack.47
A
semi-empirical absorption correction was applied using the
program SORTAV.48 Using the program suite WinGX,49 the
structures were solved by Patterson interpretation and phase
expansion using SHELXL97, and refined with full-matrix least
squares on F2 using SHELXL97.50 All non-hydrogen atoms
were refined anisotropically and all hydrogen atoms were fixed at
calculated positions except for the BH3 (9a) and NH (12, 13) H
atoms, which were located in the Fourier maps and refined; all of
them were given an overall isotropic thermal parameter. For
compound 13 a molecule of toluene was found to be present in
the asymmetric unit and a second one (half a molecule per mole-
cule of the complex) placed on a −x + 1, y, −z + 1/2 binary
axis. Both of them contained its methyl group disordered, but
the modelling of this disorder leads to an appropriate con-
vergence just for the second of them (symmetry-imposed dis-
order over two positions). Further crystallographic data and
structure refinement details are collected in Table 6. Full crystal-
lographic data have been deposited at the Cambridge Crystallo-
graphic Data Centre [deposition numbers CCDC 890680 (9a),
890681 (12) and 890682 (13)].
1
being ca. 4/1 in toluene-d8 at 233 K (from the H NMR spec-
trum). Anal. calcd for C33H35Fe2O5P: C, 60.58; H, 5.39. Found:
C, 60.27; H, 5.43. Spectroscopic data for 14b: νCO (CH2Cl2):
1958 (m), 1783 (w), 1749 (vs). νCO (toluene): 1963 (m), 1789
(w), 1763 (vs). δP(toluene-d8) 239.4 (s, br). δH(toluene-d8)
7.74–7.66 (m, 2H, C6H2), 7.12–6.78 (m, 5H, Ph), 4.38 (s, br,
t
10H, Cp), 1.50, 1.06 (2s, 2 × 9H, Bu). Spectroscopic data
for trans-14b: δH(toluene-d8, 233 K) 7.72–7.66 (m, 2H,
C6H2), 7.12–6.74 (m, 5H, Ph), 4.26, 4.24 (2s, 2 × 5H, Cp),
t
1.54, 1.01 (2s, 2 × 9H, Bu). Spectroscopic data for cis-14b:
δH(toluene-d8, 233 K) 4.45, 4.39 (2s, 2 × 5H, Cp), 1.46, 1.03
t
(2s, 2 × 9H, Bu); other resonances of this isomer could not be
identified due to its superimposition with those of the major
isomer.
X-ray structure determination for compounds 9a, 12 and
13. The X-ray intensity data were collected at 100 K on a
Nonius KappaCCD single crystal diffractometer, using graphite-
monochromated MoKα radiation. Images were collected at a
fixed crystal-detector distance (40 mm for 9a, 39 mm for 12,
30 mm for 13) using the oscillation method, with 1° (9a) or 2°
oscillations, and 60 s (9a) or 20 s exposure time per image
respectively. Data collection strategies were calculated with the
program Collect.46 Data reduction and cell refinement were
Acknowledgements
We thank the DGI of Spain (Project CTQ2009-09444) and the
COST action CM0802 ‘‘PhoSciNet’’ for supporting this work,
and the MEC of Spain for a grant (to R. G.).
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 14498–14513 | 14511

View Article Online
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