Synthesis of dibridged diphosphine metal carbonyl complexes and related phosphine transfer reactions

Article abstract of DOI:10.1016/S0022-328X(98)00592-0

A series of dibridged diphosphine metal complexes of general formula [5,5′-dppx¹-{(η⁴-C₆H₇)Fe(CO)₂}₂-(μ-dppx²)][BF₄]₂ (x¹, x²=p, p (IX); x¹, x²=b, b (X); x¹, x²=n, n (XI); x¹, x²=h, h (XII); x¹=p, x²=b (XIII); x¹=b, x²=n (XIV); x¹=n, x²=h (XV)) containing both metal-metal and ring-ring diphosphine bridges are reported. In the course of the synthetic studies, phosphine transfer reactions (both mono and diphosphine) were observed between a metal bonded phosphine and a sufficiently electrophilic metal carbonyl cation. Phosphine transfer also occurs when normal hydride abstraction reactions are attempted with only stoichiometric amounts of [Ph₃C][BF₄].

Full text of DOI:10.1016/S0022-328X(98)00592-0

Journal of Organometallic Chemistry 574 (1999) 219–227
Synthesis of dibridged diphosphine metal carbonyl complexes and
related phosphine transfer reactions
David A. Brown *, William K. Glass, Tracy A. Kelly
Department of Chemistry, Uni6ersity College Dublin, Belfield, Dublin 4, Ireland
Received 17 February 1998
Abstract
A series of dibridged diphosphine metal complexes of general formula [5,5%-dppx1-{(p4-C6H7)Fe(CO)2}2-(v-dppx2)][BF4]2 (x1,
x2=p, p (IX); x1, x2=b, b (X); x1, x2=n, n (XI); x1, x2=h, h (XII); x1=p, x2=b (XIII); x1=b, x2=n (XIV); x1=n, x2=h
(XV)) containing both metal–metal and ring–ring diphosphine bridges are reported. In the course of the synthetic studies,
phosphine transfer reactions (both mono and diphosphine) were observed between a metal bonded phosphine and a sufficiently
electrophilic metal carbonyl cation. Phosphine transfer also occurs when normal hydride abstraction reactions are attempted with
only stoichiometric amounts of [Ph3C][BF4]. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Carbonyl; Dibridged; Dinuclear; Diphosphine; Iron; Oligomer; Phosphine transfer
the metal atoms, e.g. [{(p7-C7H7)Mo(CO)2}2-(v-diphos-
phine)][PF6]2 [5,6].
1. Introduction
However, in the past few years, we have shown that
diphosphines can form a series of complexes with a
variety of different bridging modes, ring–ring, metal–
ring as well as metal–metal [7–9]. Thus the diphosphine
ring–ring bridged dimers, [5,5%-exo-PPh2(CH2)iPPh2-
{(p4-CxHy)Fe(CO)3}2][BF4]2 (i=2–6; x=6, y=7; x=
7, y=9) have been reported [7], and the presence of the
ring–ring bridge was confirmed in a crystal structure
determination of the analogous [5,5%-exo-PPh2(CH2)3
PPh2-{(p6-C7H7)Cr(CO)3}2][BF4]2 [8]. A series of binu-
clear complexes containing metal–ring diphosphine brid-
ges have also been reported, with [(p5-C5H5)Fe(CO)2-
{PPh2(CH2)3PPh2-(p6-C7H7)Cr(CO)3}][BF4]2 as a typical
example [9]. In view of the above proven ability of
diphosphines to form various types of bridges (metal–
metal, metal–ring, ring–ring), it was of interest to
attempt the synthesis of polynuclear complexes contain-
ing two diphosphine bridges of different types, e.g.
metal–metal and ring–ring and to investigate their
properties.
The coordination of cyclic y-hydrocarbons to transi-
tion metals generally results in activation of the ring to
nucleophilic addition to produce a monofunctionalized
y-hydrocarbon [1–3]. In the case of addition of phosphi-
nes, both mechanistic and synthetic studies have been
reviewed [4]. For example, the tricarbonyl(p-1,5-cyclo-
hexadienylium) iron cation reacts with monophosphines,
PR3 (R=n-Bu, Ph), to form the 5-exo ring adduct
[(p4-C6H7-5-exo-PR3)Fe(CO)3]BF4 via a bimolecular
process [4]. In contrast, diphosphines such as
PPh2(CH2)iPPh2 (dppx; x=p, i=3; x=b, i=4; x=n,
i=5; x=h, i=6) generally bond to the metal atoms of
metal carbonyl complexes forming three main types of
substituted complexes: (a) monosubstituted e.g. [(p7-
C7H7)Mo(CO)2(p1-diphosphine)]+; (b) chelated com-
plexes, e.g. [(p7-C7H7)Mo(CO)(p2-diphosphine)]+and
(c) binuclear complexes in which the diphosphine bridges
* Corresponding author.
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII S0022-328X(98)00592-0

220
D.A. Brown et al. / Journal of Organometallic Chemistry 574 (1999) 219–227
A series of complexes of general formula [5,5%-
PPh2Me][BF4], with IR carbonyl stretching frequencies
at 2042, 2000, 1986 and 1930 cm−1. We suggest that,
although there is no free phosphine present, formation
of the above phosphine ring adduct occurs by initial
formation of the ‘normal’ hydride abstraction product,
[(p5-C6H7)Fe(CO)2PPh2Me][BF4], in which the ring is
sufficiently electrophilic to attack the Fe–P bond of
unreacted substrate (p4-C6H8)Fe(CO)2PPh2Me with
formation of the ring adduct, Scheme 1. This mecha-
nism was confirmed by direct reaction between [(p5-
C6H7)Fe(CO)2PPh2Me][BF4] and (p4-C6H8)Fe(CO)2-
PPh2Me in acetonitrile at room temperature, which
gave the ring adduct [(p4-C6H7-5-exo-PPh2Me)Fe
(CO)2PPh2Me][BF4] (see below and Table 1).
dppx1-{(p4-C6H7)Fe(CO)2}2-(v-dppx2)][BF4]2 (x1, x2=
p, p (IX); x1, x2=b, b (X); x1, x2=n, n (XI); x1,
x2=h, h (XII); x1=p, x2=b (XIII); x1=b, x2=n
(XIV); x1=n, x2=h (XV)), containing both metal–
metal and ring–ring diphosphine bridges, have been
obtained as described below. However, during these
studies it was noted that organometallic cations such
as [(p5-C6H7)Fe(CO)2L]BF4 (L=CO, PPh3, P(OPh)3,
PPh2
Me, PMe3) not only react with free monophosphines,
PR3, to give the well established ring adducts [(p4-
C6H7-5-exo-PR3)Fe(CO)2L]BF4, but are sufficiently
electrophilic to react with metal bonded monophosphi-
nes to give the same products as those formed with
free monophosphines, albeit at a much slower rate. In
other words, a phosphine transfer reaction occurs
from the metal bonded phosphine complex to the elec-
trophilic cation. Similar transfer reactions also occur
with diphosphines as discussed below. Interestingly,
phosphine transfer reaction also occurs with suffi-
ciently electrophilic cations, containing metal–phos-
phine entities, when normal hydride abstraction
reactions are attempted with the customary hydride
abstraction reagent [Ph3C][BF4] present in only stoi-
chiometric amounts.
2.2. Phosphine transfer reactions in the absence of
[Ph3C][BF4]
The above reaction in which monophosphine trans-
fer occurs from a metal bonded monophosphine to a
sufficiently electropositive metal carbonyl cation, is a
general reaction. This was confirmed by reacting a
series of cations [(p5-C6H7)Fe(CO)2L][BF4] (L=CO,
PPh3, PPh2Me, P(OPh3), PMe3) with a series of neu-
tral ring hydride adducts, (p4-C6H8)Fe(CO)2L% (L%=
PPh3, PPh2Me, PMe3) in the absence of [Ph3C][BF4].
In all cases, [(p4-C6H7-5-exo-L)Fe(CO)2L%][BF4] was
obtained and characterised by analytical, infrared and
31P-NMR spectroscopy (see supplementary material).
The rate of the above phosphine transfer reaction was
always much slower than the corresponding direct re-
action between [(p5-C6H7)Fe(CO)2L][BF4] and L% (see
Table 1) although, of course, the final ring adducts are
confirmed as identical by analytical and spectroscopic
data (see supplementary material and experimental
section for a typical pair of reactions). Although ki-
netic studies of the phosphine transfer reactions were
not possible because of accompanying decomposition,
an approximate estimate of comparative rates of reac-
tion was obtained by noting the time at which the
infrared carbonyl stretching frequencies of both
reagents had been replaced by those of the phospho-
nium ring adduct (see Table 1). A number of general
conclusions emerge. As expected, the reactions with
free ligand L% are much faster than with the corre-
sponding Fe–L% complex, so clearly the strength of the
Fe–L% bond is a factor. Also, the ring electrophilicity
of the cation is involved since reactions between
weaker electrophiles e.g. [(p5-C6H7)Fe(CO)2PMe3][BF4]
and the neutral series are measurably slower than
2. Results and discussion
2.1. Phosphine transfer reactions induced by
[Ph3C][BF4]
Hydride abstraction from a diene metal carbonyl
complex by [Ph3C][BF4] is a ubiquitous reaction, dat-
ing from the early observation of the formation of
tropylium metal complexes from the corresponding cy-
cloheptatriene complexes [10]. Similarly, the complexes
(p4-C6H8)Fe(CO)2L (L=CO, PPh3, PPh2Me, PPhMe2,
PMe3) react with excess [Ph3C][BF4] to form [(p5-
C6H7)Fe(CO)2L][BF4] [11]. However, when (p4-
C6H8)Fe(CO)2PPh2Me, for example, was reacted with
only
a stoichiometric amount of [Ph3C][BF4], in
dichloromethane at room temperature, after about 30
min not only were the IR carbonyl stretching frequen-
cies of the above complex observed—at 1964 and
1904 cm−1, together with bands at 2042 and 2000
cm−1 due to the expected hydride abstraction product
[(p5-C6H7)Fe(CO)2PPh2Me][BF4]—but in addition new
bands occurred at 1986 and 1930 cm−1 which were
assigned to the ring adduct [(p-C6H7-5-exo-PPh2Me)Fe
(CO)2PPh2Me][BF4], although the reaction mixture
contained no free PPh2Me. Overnight reaction resulted
in a mixture of the expected hydride abstraction pro-
duct, [(p5-C6H7)Fe(CO)2PPh2Me][BF4] together with
the ring adduct [(p4-C6H7-5-exo-PPh2Me)Fe(CO)2-
those
with
stronger
electrophiles
e.g.
[(p-
C6H7)Fe(CO)2PPh3][BF4] (see Table 1). These qualita-
tive comparisons suggest an associative transition state
for the phosphine transfer reaction involving both C–
P bond formation and Fe–P bond breaking.

D.A. Brown et al. / Journal of Organometallic Chemistry 574 (1999) 219–227
221
Scheme 1. Monophosphine transfer.
2.3. Diphosphine transfer reactions induced by
[Ph3C][BF4]
using infrared spectroscopy in acetonitrile. For exam-
ple, after 5 min of reaction between {(p4-C6H8)Fe
(CO)2}2-(v-dppn) (III) and [{(p5-C6H7)Fe(CO)2}2-(v-
dppn)][BF4]2 (VII), w(CO) bands of the neutral (III)
and cationic (VII) metal–metal dimers, at 1963, 1903,
2044 and 2004 cm−1, respectively, were observed;
however, after 10 min, new bands at 1983 and 1923
cm−1, assigned to [5,5%-dppn-{(p4-C6H8)Fe(CO)2}2-(v-
dppn)][BF4]2 (XI), appeared and after 2 h were the
only bands present.
In a reaction similar to that in Section 2.1 above, it
was found that treatment of the neutral metal–
metal diphosphine mono-bridged complexes {(p4-C6-
H8)Fe(CO)2}2-(v-dppx) (dppx=PPh2(CH2)iPPh2; x=
p, i=3 (I); x=b, i=4 (II); x=n, i=5 (III); x=h,
i=6 (IV)) with stoichiometric amounts of [Ph3C][BF4]
gave a series of dibridged diphosphine complexes
[5,5%-dppx1-{(p4-C6H8)Fe(CO)2}2-(v-dppx2)][BF4]2 (x1,
x2=p, p (IX); x1, x2=b, b (X); x1, x2=n, n (XI); x1,
x2=h, h (XII); x1, x2=p, b (XIII); x1, x2=b, n
(XIV); x1, x2=n, h (XV)), which were identical with
the same series prepared by the synthetic route de-
scribed below (Section 2.4). As in the case of the
analogous monophosphine complexes (Section 2.1),
formation of the dibridged diphosphine series occurs
by initial formation of the normal hydride abstraction
product, [{(p5-C6H7)Fe(CO)2}2-(v-dppx)][BF4]2, which
is sufficiently electrophilic to attack the Fe–P bonds
of unreacted neutral {(p4-C6H8)Fe(CO)2}2-(v-dppx),
with formation of the dibridged complex, [5,5%-dppx1-
{(p4-C6H8)Fe(CO)2}2-(v-dppx2)][BF4]2. This mecha-
nism was confirmed by monitoring these reactions
As in the analogous monophosphine transfer reac-
tion (Section 2.2), this mechanism was confirmed by
direct reaction between the neutral ((I)–(IV)) and
cationic metal–metal dimers ((V)–(VIII)), in the ab-
sence of [Ph3C][BF4] and in
a
1:1 ratio in
dichloromethane, yielding the dibridged series [5,5%-
dppx1-{(p4-C6H7)Fe(CO)2}2-(v-dppx2)][BF4]2 (x1, x2=
p, p (IX); x1, x2=b, b (X); x1, x2=n, n (XI); x1,
x2=h, h (XII); x1, x2=p, b (XIII); x1, x2=b, n
(XIV); x1, x2=n, h (XV)), Scheme 2. The analytical
and spectroscopic properties of the complexes pre-
pared by this method were identical with those pre-
pared by the more efficient route described below (see
Section 2.4 and Table 2).

222
D.A. Brown et al. / Journal of Organometallic Chemistry 574 (1999) 219–227
2.4. Synthesis of the dibridged diphosphine complexes
[5,5%-dppx1-{(p4-C6H7)Fe(CO)2}2-(v-dppx2)][BF4]2 (x1,
x2=p, p (IX); x1, x2=b, b (X); x1, x2=n, n (XI);x1,
x2=h, h (XII); x1, x2=p, b (XIII); x1, x2=b, n
(XIV); x1, x2=n, h (XV))
[{(p5-C6H7)Fe(CO)2}2-(v-dppx)][BF4]2 (x=p1 (V); x=b
(VI); x=n (VII); x=h (VIII)) by normal hydride ab-
straction, in contrast to the diphosphine transfer reaction
which occurs when only 1:1 ratios of {(p4-
C6H8)Fe(CO)2}2-(v-dppx) and [Ph3C][BF4] are used
(Section 2.3). Again, the reaction can be monitored
conveniently by infrared spectroscopy. For example,
when the neutral dimer {(p4-C6H8)Fe(CO)2}2-(v-dppn)
(III) was reacted with a 3 M excess of [Ph3C][BF4] in
dichloromethane, the w(CO) stretching frequencies of
(III) at 1963 and 1903 cm−1 were quickly replaced by
bands at 2044 and 1998 cm−1 assigned to the dicationic
metal–metal dimer [{(p5-C6H7)Fe(CO)2}2-(v-dppn)]
[BF4]2 (VII). The dicationic complexes (V)–(VIII) were
characterised by microanalysis and 1H, 13C and 31P-
NMR spectroscopy (see Table 2).
The synthetic route shown in Scheme 3, involving
Steps (a), (b) and (c), was used to prepare the above series
of dibridged diphosphine complexes.
Firstly in Step (a), the neutral metal–metal diphos-
phine linked dimers, {(p4-C6H8)Fe(CO)2}2-(v-dppx)
(x=p, (I); x=b, (II); x=n, (III); x=h, (IV)), were
prepared by refluxing (p4-C6H8)Fe(CO)3 and the appro-
priate diphosphine in a 2:1 ratio in cyclohexanol for :48
h. The reaction was monitored by infrared spectroscopy
and considered complete when the initial w(CO) carbonyl
frequencies at 2042 and 1969 cm−1 were replaced by
bands at :1963 and 1903 cm−1, due to {(p4-
C6H8)Fe(CO)2}2-(v-dppx) (x=p, (I); x=b, (II); x=n,
(III); x=h, (IV)) which were characterised by microanal-
ysis, 1H-, 13C- and 31P-NMR spectroscopy. The latter was
especially useful with only one region of absorption, at
:l 63.3 ppm, assigned to the metal bonded P atoms,
with no high field resonances characteristic of a pendant
P atom, thereby excluding any mononuclear products
such as (p4-C6H8)Fe(CO)2-(p1-dppx) (Table 2 and sup-
plementary material).
In the final step, Step (c), the synthesis of the dibridged
diphosphine complexes consists of forming the 5-5%
ring–ring diphosphine bridge by reacting [{(p5-C6H7)
Fe(CO)2}2-(v-dppx2)][BF4]2 (V)–(VIII) in a 1:1 ratio
with a free diphosphine ligand, dppx1. For example,
reaction between [{(p5-C6H7)Fe(CO)2}2-(v-dppb)][BF4]2
(VI) and free dppb, in dichloromethane as solvent, was
complete in :10 min, indicated by the rapid replacement
of the w(CO) stretching frequencies of (VI), at 2043 and
1998 cm−1, by two new bands at 1980 and 1922 cm−1
,
due to [5,5%-dppb-{(p4-C6H7)Fe(CO)2}2-(v-dppb)][BF4]2
(X). The rapid formation of the second diphosphine
bridge under such mild conditions supports the forma-
tion of a ring–ring bridge rather than metal–ring bridges
which would involve breaking of the strong metal–metal
diphosphine bridge. A series of new dibridged complexes
[5,5%-dppx1-{(p4-C6H7)Fe(CO)2}2-(v-dppx2)][BF4]2 (IX–
XV) were isolated as yellow solids and characterised by
analysis, 13C and 31P spectroscopy (Table 2). In general,
In step (b), reaction of the above neutral metal–metal
diphosphine dimers (I–IV) with excess [Ph3C][BF4] (ratio
1:3), in dichloromethane as solvent, gave good yields of
the dicationic metal–metal diphosphine linked dimers
Table 1
Comparison of relative rates of phosphine transfer to electrophiles
from metal bonded and free phosphines, reactions A and B, respec-
tively
1
the H-NMR spectra were broad and featureless (see
supplementary material), but there was no evidence for
paramagnetic impurities and variable temperature H-
1
L
L%
Reaction Time
Aa
NMR measurements gave no improvement. The 31P-
NMR spectra (Table 2) showed two groups of
absorptions, one group around l 60 ppm and the second
around l 30 ppm; the former group was assigned to
metal-bonded P atoms and the latter to ring–carbon
bonded P atoms. For example, for [5,5%-dppn-{(p4-
C6H7)Fe(CO)2}2-(v-dppn)][BF4]2 (XI), the 31P-NMR res-
onances occurred at l 61.7, 60.4, 60.3, and at l 30.3, 30.2,
29.6 ppm. The reasons for these multiple peaks are not
clear. Coupling between the phosphorus atoms is ruled
out by the long chain lengths of the diphosphine bridges.
It is possible that the complex spectra may arise from the
presence of isomers with different types of bridging
modes, e.g. an isomer containing two metal–ring bridges
or conformers within the diphosphine ring–ring bridge
may be present. However the presence of oligomers
cannot be excluded.
Bb
5 min
5 min
15 min
30 min
30 min
5 min
CO
CO
CO
P(OPh)3
PPh3
PPh3
72 h
48 h
48 h
48 h
48 h
24 h
72 h
no reaction
48 h
48 h
96 h
96 h
96 h
PPh2Me
PMe3
PPh3
PPh3
PPh3
PPh3
PPh2Me
PMe3
PPh3
PPh2Me
Pme3
PPh3
PPh2Me
Pme3
5 min
90 min
5 min
PPh2Me
PPh2Me
PPh2Me
PMe3
PMe3
PMe3
5 min
c
5 min
15 min
a Reaction A [(p5-C6H7)Fe(CO)2L]BF4+(p4-C6H8)Fe(CO)2L%“[(p4-
C6H7-5-L%)Fe(CO)2L]BFb4 Reaction
B
[(p5-C6H7)Fe(CO)2L]BF4+
L%“[(p4-C6H7-5-L%)Fe(CO)2L]BFc4 Does not go to completion.
In the absence of suitable crystals for X-ray crystal
structure determinations, the Electrospray Mass Spec-
1 This complex has been prepared before [7].

D.A. Brown et al. / Journal of Organometallic Chemistry 574 (1999) 219–227
223
Scheme 2. Diphosphine transfer.
tra of complexes (X), (XII), (XIII) and (XV) were
measured, and confirmed the presence of the dibridged
dimer for [5,5%-dppn-{(p4-C6H7)Fe(CO)2}2-(v-dpph)]-
[BF4]2 (XV), [5,5%-dppb-{(p4-C6H7)Fe(CO)2}2-(v-dppb)]-
[BF4]2 (X) and [5,5%-dppp-{(p4-C6H7)Fe(CO)2}2-(v-
dppb)][BF4]2 (XIII), with major molecular ion peaks at
1363, 1321 and 1307 Da e−1 (m/z), respectively (Table
3). No peaks of mass higher than the molecular ion
were observed, although fragmentation peaks occurred.
For example, loss of BF4 and the ring bonded diphos-
phine ligand from [5,5%-dppp-{(p4-C6H7)Fe(CO)2}2-(v-
dppb)][BF4]2 (X) yielded the fragment [{(p4-C6H7)Fe
(CO)2}2-(v-dppb)]BF4 at 895 Da e−1; loss of (p4-
C6H7)Fe(CO)2 and BF4 yielded [{(p4-C6H7)Fe(CO)2}-
(p1-dppb)] at 617 Da e−1; further loss of CO and the
cyclohexadienyl ring yielded the fragments [{(p4-
C6H7)Fe}-(p1-dppb)] and [Fe–dppb] at 561 and 482
Da e−1, respectively; whilst the dppb ligand was ob-
served at 426 Da e−1. [5,5%-dppn-{(p4-C6H7)Fe(CO)2}2-
(v-dpph)][BF4]2 (XV) yielded the fragment [{(p4-C6H7)-
Fe(CO)2}2-(v-dpph)]BF4 at 923 Da e−1. The formation
of these fragments in which the metal–metal diphos-
phine bridge is retained and the weaker ring–ring
bridge is cleaved provides support for the formulation
of this series as dibridged diphosphine complexes con-
taining metal–metal and ring–ring bridges. As outlined
in Table 3, a similar fragmentation pattern was ob-
served for (XIII).
However,
in
contrast,
for
[5,5%-dpph-{(p4-
C6H7)Fe(CO)2}2-(v-dpph)][BF ] (XII), peaks of mass
4 2
between 1500–3000 Da e−1 were obtained. In addition
to a molecular ion peak at 1377 Da e−1, assigned to
[5,5%-dpph-{(p4-C6H7)Fe(CO)2}2-(v-dpph)]BF4, and a
fragmentation pattern similar to that obtained for the
above complexes (X), (XIII), and (XV) (Table 3). The
high mass peak at 2840 Da e−1 is tentatively assigned
to the molecular ion of the tetramer [5,5%-(dpph)2-{(p4-
C6H7)Fe(CO)2}4-(v-dpph)2][BF4]4 (XIIa). The fragmen-
tation pattern of such a tetrameric structure can be
described in terms of sequential loss of BF4, (p4-
C6H7)Fe(CO)2 or a diphosphine ligand, Table 3. Thus
the peak at 2475 Da e−1 represents [5-dpph-{(p4-
C6H7)Fe(CO)2}4-(v-dpph)2][BF4]4 (loss of dpph); [5-
dpph-{(p4-C6H7)Fe(CO)2}4-(v-dpph)2][BF4]3 (loss of
dpph and BF4) is observed at 2386 Da e−1; a peak at
2108 Da e−1 is assigned to [5-dpph-{(p4-C6H7)Fe-
(CO)2}3-(v-dpph)2][BF4]2 (loss of (p4-C6H7)Fe(CO)2
and BF4); [5-dpph-{(p4-C6H7)Fe(CO)2}4-(v-dpph)]-
[BF4]2 (loss of two BF4 and dpph ligands) is observed at

224
D.A. Brown et al. / Journal of Organometallic Chemistry 574 (1999) 219–227
Table 2
Analytical data, IR carbonyl stretching frequencies and 31P-NMR data for the diphosphine complexes
Complex
Anal. found (Calcd.)%
IR w(CO)
(cm−1
l Pa
l Pb
C
H
P
)
(ppm)
(ppm)
Neutral diphosphine linked metal–metal dimers
{(p4-C6H8)Fe(CO)2}2-v-dppp (I)a
{(p4-C6H8)Fe(CO)2}2-v-dppb (II)
{(p4-C6H8)Fe(CO)2}2-v-dppn (III)
{(p4-C6H8)Fe(CO)2}2-v-dpph (IV)
64.5 (64.8)
65.0 (65.1)
65.4 (65.5)
65.5 (65.8)
5.39 (5.28)
5.51 (5.43)
5.61 (5.58)
5.77 (5.73)
7.37 (7.79)
7.49 (7.65)
7.44 (7.52)
7.37 (7.40)
1963, 1903
1963, 1903
1962, 1903
1962, 1902
—
—
—
—
63.1
63.2
63.3
63.3
Cationic diphosphine linked metal–metal dimers
[(p5-C6H7)Fe(CO)2}2-v-dppp][BF4]2 (V)
[{(p5-C6H7)Fe(CO)2}2-v-dppb][BF4]2 (VI)
[{(p5-C6H7)Fe(CO)2}2-v-dppn][BF4]2 (VII)
[{(p5-C6H7)Fe(CO)2}2-v-dpph][BF4]2(VIII)
52.9 (53.0)
4.27 (4.12)
4.56 (4.26)
4.75 (4.42)
4.67 (4.54)
6.47 (6.38)
6.37 (6.29)
6.97 (6.23)
6.08 (6.11)
2041, 1998
2043, 1998
2044, 1998
2044, 1998
—
—
—
—
58.3
61.5
59.5
59.2
53.5 (53.5)
54.3 (54.2)
54.4 (54.4)
Diphosphine linked dibridged dimers
[5,5%-dppp-{(p4-C6H7)Fe(CO)2}2-v-dppp]
60.5 (60.8)
59.9 (61.3)
61.8 (61.8)
61.2 (62.2)
60.0 (61.1)
59.9 (61.6)
62.2 (62.0)
4.98 (4.78)
5.68 (4.97)
5.36 (5.15)
5.54 (5.32)
4.91 (4.88)
5.25 (5.06)
5.24 (5.24)
8.78 (8.98)
8.45 (8.81)
8.99 (8.64)
8.43 (8.46)
7.90 (8.89)
8.87 (8.72)
7.93 (8.55)
1983, 1929 31.3, 32.1, 33.0 59.8, 61.8, 62.3
1980, 1922 32.0, 32.8, 33.9 59.2, 60.6, 60.3
1983, 1923 29.1, 29.8, 31.0 61.0, 62.4, 63.0
1983, 1923 28.3, 29.9, 30.5 61.3, 61.7, 63.0
1980, 1923 30.0, 30.6, 31.4 61.9, 62.1, 62.8
1981, 1924 29.0, 30.3, 30.9 61.0, 62.6, 63.8
1979, 1922 29.0, 29.8, 31.2 60.9, 62.0, 62.9
[BF4]2 (IX)
[5,5%-dppb-{(p4-C6H7)Fe(CO)2}2-v-dppb]
[BF4]2(X)
[5,5%-dppn-{(p4-C6H7)Fe(CO)2}2-v-dppn]
[BF4]2 (XI)
[5,5%-dpph-{(p4-C6H7)Fe(CO)2}2-v-dpph]
[BF4]2 (XII)
[5,5%-dppp-{(p4-C6H7)Fe(CO)2}2-v-dppb]
[BF4]2(X III)
[5,5%-dppb-{(p4-C6H7)Fe(CO)2}2-v-dppn]
[BF4]2(X IV)
[5,5%-dppn-{(p4-C6H7)Fe(CO)2}2-v-dpph]
[BF4]2 (XV)
Pa=ring bonded phosphorous atom and Pb=metal bonded phosphorus atom, relative to 85% H3PO4.
a Ref. 7.
1933 Da e−1 and a peak at 1655 Da e−1 is assigned to
[5-dpph-{(p4-C6H7)Fe(CO)2}3-(v-dpph)][BF4]2 (loss of
(p4-C6H7)Fe(CO)2).
high purity nitrogen. The tertiary monophosphine and
diphosphine ligands were obtained commercially and
used without further purification. The neutral com-
pounds (p4-C6H8)Fe(CO)2L (L=CO, PPh3, PPh2Me,
P(OPh)3, PMe3) and the corresponding dienyl cations
[(p5-C6H7)Fe(CO)2L]BF4 were prepared following pub-
lished methods [12,13].
3. Conclusions
The 31P-NMR spectra taken in conjunction with the
ESMS studies confirm that complexes (IX–XV) are
dibridged dimers containing metal–metal and ring–
ring bridges with the possible presence of isomers con-
taining metal–ring bridges. In the case of (XII), the
ESMS provides evidence for both the above type of
dibridged dimer (XII) and a tetramer (XIIa), which
may contain ring–ring bridges between the rings of
separate metal–metal bridged moieties.
Infrared spectra were recorded on a Mattson Galaxy
FT3000 Spectrometer, using CaF2 plates with 0.1 mm
1
spacings. H, 13C, and 31P-NMR spectra were recorded
using a JEOL GX270 FT spectrometer. Analyses were
performed by the Microanalytical laboratory of the
Chemical Services Unit of this department.
The electrospray experiments were carried out in the
University of Warwick, using a Fisons’ ‘Quattro II’
triple quadrupole mass spectrometer equipped with an
atmospheric pressure ionisation (API) source operated
in the nebulizer-assisted electrospray mode. The poten-
tial on the electrospray needle was set at 3.6 kV, and
the extraction cone voltage was normally set at 40 V.
Mass spectra were acquired over the range m/z 3500–
500 m/z.
4. Experimental details
Solvents were freshly dried prior to use, according to
standard methods. All reactions were carried out under

D.A. Brown et al. / Journal of Organometallic Chemistry 574 (1999) 219–227
225
Scheme 3. Preparation of the dibridged linked dimers via a three step process.
4.1. Preparation of the monophosphine ring adducts
[(p4-C6H7-5-PR3)Fe(CO)2L]BF4 (PR3=PPh3,
PPh2Me, PMe3; L=CO, P(OPh)3, PPh3, PPh2Me,
PMe3)
and PPh2Me (0.21 g; 1.05 mmol) were mixed in 50 ml
of dry acetonitrile. The reaction was monitored
by infrared spectroscopy and was complete after 5
min.
Removal of solvent under reduced pressure and re-
The preparation of [(p4-C6H7-5-PPh2Me)Fe(CO)2
PPh2Me]BF4 is given as a general example, although
reaction times vary and are summarised in Table 1.
[(p5-C6H7)Fe(CO)2PPh2Me]BF4 (0.5 g; 1.05 mmol)
crystallisation from CH2Cl2/diethyl ether; gave [(p4-
C6H7-5-PPh2Me)Fe(CO)2PPh2Me]BF
as a yellow
4
solid (0.56 g; 79%). Analytical and spectroscopic de-
tails are given in the supplementary material.

226
D.A. Brown et al. / Journal of Organometallic Chemistry 574 (1999) 219–227
Table 3
ES mass spectral data (m/z) for the dibridged complexes (X), (XII), (XIII), (VX)
Fragment (m/z)
Complex
(XIII)
(X)
(XV)
(XII)
(XIIa)
dppx1
dppx2
dppp
dppb
dppb
dppb
dppn
dpph
dpph
dpph
dpph
dpph
[5,5%-dppx1-{(p4-C6H7)Fe(CO)2}2-(v-dppx2)][BF4]2
[5,5%-dppx1-{(p4-C6H7)Fe(CO)2}2-(v-dppx2)]BF+4
[5,5%-dppx1-{(p4-C6H7)Fe(CO)2}2-(v-dppx2)]+
[{(p4-C6H7)Fe(CO)2}-v-dppx2)]BF+4
[5,5%-dppx1-{(p4-C6H7)Fe(CO)2}]BF+4
[(p4-C6H7)Fe(CO)2-(v-dppx2)]+
1394
1307
1029
895
887
617
—
561
481
429
—
—
—
—
—
—
—
—
—
1408
1321
1043
895
—
617
—
561
482
427
—
—
—
—
—
—
—
—
—
1450
1363
—
923
—
645
617
538
510
454
—
—
—
—
—
—
—
—
—
1464
1377
—
923
—
645
617
538
510
454
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
[(p4-C6H7)Fe(CO)-(p-dppx2)]+
[(p4-C6H7)Fe-(p-dppx2)]+
[Fe-(p-dppx2)]+
—
—
[dppx2]+
[5,5%-(dppx1)2{(p4-C6H7)Fe(CO)2}4-(v-dppx2)2][BF4]4
[5,5%-(dppx1)2{(p4-C6H7)Fe(CO)2}4-(v-dppx2)2][BF4]3+
[5,5%-dppx1-{(p4-C6H7)Fe(CO)2}4-(v-dppx2)2][BF4]4+
[5,5%-dppx1-{(p4-C6H7)Fe(CO)2}4-(v-dppx2)2][BF4]3+
[5,5%-dppx1-{(p4-C6H7)Fe(CO)2}4-(v-dppx2)2]+
[5,5%-dppx1-{(p4-C6H7)Fe(CO)2}4-(v-dppx2)2][BF4]2+
[5,5%-dppx1-{(p4-C6H7)Fe(CO)2}4-(v-dppx2)][BF4]2+
[5,5%-dppx1-{(p4-C6H7)Fe(CO)2}4-(v-dppx2)][BF4]2+
[5-dppx1-{(p4-C6H7)Fe(CO)2}2-(v-dppx2)][BF4]2+
[5-dppx1-{(p4-C6H7)Fe(CO)2}2-(v-dppx2)]BF4+
[{(p4-C6H7)Fe(CO)2}2-(v-dppx2)]BF+4
[{(p-C6H7)Fe(CO)2}2-(v-dppx2)]+
2928
2867
2475
2386
2126
2108
1933
1655
1464
1377
923
645
617
538
510
454
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
[{(p4-C6H7)Fe(CO)2}(v-dppx2)]+
[Fe(CO)-(p-dppx2)]+
[Fe-(p-dppx2)]+
[dppx2]+
4.2. Formation of phosphonium ring adducts
4.3. Preparation of the neutral metal–metal
[(p4-C6H7-5-PR3-)Fe(CO)2L]BF4 by electrophilic attack
of [(p5-C6H7)Fe(CO)2L]BF4 on the metal–phosphorus
bond of (p4-C6H8)Fe(CO)2PR3 (PR3=PPh3, PPh2Me,
PMe3; L=CO, P(OPh)3, PPh3, PPh2Me, PMe3)
diphosphine linked dimers
{(p4-C6H8)Fe(CO)2}2-(v-dppx) (x=p (I); x=b (II);
x=n (III); x=h (IV))
(I)–(IV)
were
prepared
by
reacting
(p4-
The reaction between [(p5-C6H7)Fe(CO)3]BF4 and (p4-
C6H8)Fe(CO)3 with dppx (x=p, b, n, h) in a 2:1 ratio.
For example, (2.0 g; 9.0 mmol) of (p4-C6H8)Fe(CO)3
and (2.0 g; 4.5 mmol) of dppn were dissolved in 100 ml
of cyclohexanol and refluxed for 48 h. The reaction
mixture was cooled and 50 ml of petroleum ether
(40/60) added, precipitating black decomposition prod-
ucts. The solution was filtered and cyclohexanol
removed by vacuum distillation. The yellow residue
was purified by chromatography on a short column
of alumina and eluted with 1:3 CH2Cl2/petroleum
ether (40/60). Removal of solvent under reduced
pressure gave the product as a yellow solid (2.6 g;
64%). Analytical and spectroscopic details are given in
Table 2.
C6H8)Fe(CO)2PPh2Me is given as an example, although
all of the reactions were carried out following the same
procedure. The results are summarised in Table 1.
[(p5-C6H7)Fe(CO)3]BF4 (0.5 g; 1.63 mmol) and (p4-
C6H8)Fe(CO)2PPh2Me (0.64 g; 1.63 mmol) were reacted
in 50 ml of dry acetonitrile, at room temperature. The
w(CO) frequencies at 2114 and 2068 cm−1 for the cations
and 1964 and 1904 cm−1 for the neutral complex, were
replaced by those of the product (XVI)–(XXV), at 2056
and 1982 cm−1 after 48 h.
The solution was filtered, solvent removed under
reduced pressure and the product recrystallised form
CH2Cl2/diethyl ether, and characterised by analysis, IR
and 31P-NMR spectroscopy (0.20 g; 30%). (See supple-
mentary material.)

D.A. Brown et al. / Journal of Organometallic Chemistry 574 (1999) 219–227
227
4.7. Reaction of {(p4-C6H8)Fe(CO)2}2-(v-dppx) (x=p,
b, n, h) with a deficiency of [Ph3C][BF4]
4.4. Preparation of the metal–metal diphosphine linked
dimers [{(p5-C6H7)Fe(CO)2}2-(v-dppx)][BF4]2 (x=p,
(V); x=b, (VI); x=n, (VII); x=h, (VIII))
To {(p4-C6H8)Fe(CO)2}2-(v-dppb) (II) (0.5 g; 0.56
mmol) in 50 ml of CH2Cl2, at room temperature,
[Ph3C][BF4] (0.20 g; 0.58 mmol) was added. After 30
min, w(CO) stretching frequencies of the neutral com-
plex {(p4-C6H8)Fe(CO)2}2-(v-dppb) (II) at 1965 and
1903 cm−1, were accompanied by peaks at 2044 and
1998 cm−1 assigned to [{(p5-C6H7)Fe(CO)2}2-(v-
dppb)][BF4]2 (VI) as well as peaks at 1982 and 1928
cm−1 assigned to [5,5%-dppb-{(p5-C6H7)Fe(CO)2}2-(v-
dppb)][BF4]2 (X).
{(p4-C6H8)Fe(CO)2}2-v-dppn (0.5 g; 0.56 mmol) was
dissolved in 50 ml of CH2Cl2. [Ph3C][BF4] (0.63 g; 1.9
mmol) was added to the solution. After 15 min, diethyl
ether was added to the reaction mixture, precipitating
the product [{(p5-C6H7)Fe(CO)2}2-(v-dppp)][BF4]2. Fil-
tration and recrystallisation from CH2Cl2/diethyl ether
gave a yellow solid (0.48 g; 80%). Analytical and spec-
troscopic details are given in Table 2.
Stirring overnight resulted in a mixture of [{(p5-
C6H7)Fe(CO)2}2-(v-dppb)][BF4]2 (VI) and [5,5%-dppp-
{(p5-C6H7)Fe(CO)2}2-(v-dppp)][BF4]2 (X), confirmed
from the w(CO) stretching frequencies at 2044, 1998,
4.5. Preparation of the dibridged series
[5,5%-dppx1-{(p4-C6H7)Fe(CO)2}2-(v-dppx2)][BF4]2 (x1,
x2=p, p (IX); x1, x2=b, b (X); x1, x2=n, n (XI);
x1, x2=h, h (XII); x1, x2=p, b (XIII); x1, x2=b, n
(XIV); x1, x2=n, h (XV))
1982 and 1928 cm−1
.
Two types of these complexes were prepared by
similar procedures: (i) dppx1=dppx2, with the same
type of diphosphine ligand at both linkages; (ii)
dppx1"dppx2, with different diphosphine ligands at
the two linkages.
Acknowledgements
We thank Professor T.J. Kemp, Department of
Chemistry, University of Warwick, (UK), for the mea-
surement of the Electrospray Mass Spectra and
Geraldine Fitzpatrick for her help with the NMR spec-
tra.
[{(p5-C6H7)Fe(CO)2}2-(v-dppn)][BF4]2 (VII) (0.5 g;
0.52 mmol) in 50 ml of CH2Cl2. (0.22 g; 0.54 mmol) of
dppn was added. After 30 min, the solvent was re-
moved under reduced pressure and recrystallisation
from CH2Cl2/diethyl ether gave a dark yellow solid
(0.43 g; 60%). Analytical and spectroscopic details are
given in Tables 2 and 3.
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4.6. Reaction of (p4-C6H8)Fe(CO)2PR3 (PR3=PPh3,
PPh2Me, PMe3) with a deficiency of [Ph3C][BF4]
To (p4-C6H8)Fe(CO)2PPh2Me (0.5 g; 1.28 mmol) in
50 ml of dry CH2Cl2, at room temperature, [Ph3C][BF4]
(0.4 g; 1.20 mmol) was added. After 30 min, w(CO)
stretching frequencies of the neutral complex (p4-
C6H8)Fe(CO)2PPh2Me at 1964 and 1904 cm−1, were
accompanied by bands at 2042 and 2000 cm−1 assigned
to [(p5-C6H7)Fe(CO)2PPh2Me]BF4 as well as bands at
1986 and 1930 cm−1 assigned to the ring adduct [(p4-
C6H7-5-PPh2Me)Fe(CO)2PPh2Me]BF4.
Stirring overnight gave
a
mixture of [(p5-
C6H7)Fe(CO)2PPh2Me]BF4 and the phosphonium ring
adduct [(p4-C6H7-5-PPh2Me)Fe(CO)2PPh2Me]B F4,
confirmed from the w(CO) stretching frequencies at
2042, 2000, 1986 and 1930 cm−1
.
.
.