Reactions of the σ,π-furyl complex [Fe2(CO) 6(μ-Fu)(μ-PFu2)] (Fu = C4H3O) with phosphines: Carbonyl substitution, migratory carbonyl insertion and cyclometallation-induced furan elimination

Article abstract of DOI:10.1016/j.jorganchem.2013.05.026

The reactivity of the σ,π-furyl complex [Fe₂(CO) ₆(m-Fu)(μ-PFu₂)] (1) towards PPh₃ and a range of bidentate phosphines has been studied and a number of different reaction products have been identified. With PPh₃, carbonyl substitution affords [Fe₂(CO)₅(PPh₃)(μ-Fu) (m-PFu₂)] (2) in which the new phosphine is coordinated to the iron center that is σ-coordinated by the bridging furyl moiety. With small bite-angle diphosphines - bis(diphenylphosphino)methane (dppm) and 1,8-bis(diphenylphosphino)naphthalene (dppn) - carbonyl substitution and migratory carbonyl insertion result to give the furyleacyl complexes with bridging, [Fe₂(CO)₄(μ-dppm)(m-O=C-Fu)(μ-PFu ₂)] (3), or chelating, [Fe₂(CO)₄(κ ²-dppn)(μ=OCeFu)(μ-PFu₂)] (4), diphosphines, respectively. With the more flexible diphosphines Ph₂P(CH ₂)_nPPh₂ (n = 2, dppe, n = 3, dppp), the cyclometallated products [Fe₂(CO)₅{μ, κ²-C₆H₄PPh(CH₂) _nPPh₂}(μ-PFu₂)] (n = 2, 5; n = 3, 6) are isolated as a result of carbonyl substitution and furan elimination, and a similar complex [Fe₂(CO)₅{μ,κ²-C ₆H₄PPh(C₆H₄)PPh₂}(μ- PFu₂)] (7) is generated from the more rigid diphosphine bis(diphenylphosphino) benzene (dppb). With bis(diphenylphosphino)-1,1- binaphthalene (1,1-BINAP) the novel tridentate phosphine complex [Fe ₂(CO)₅{μ,κ³-C₆H ₄P(C₂₀H₁₂PPh₂)C₆H ₄PFu}] (8) results from the putative coupling of cyclometallated diphosphine and difurylphosphido ligands, following elimination of two equivalents of furan. The crystal structures of 2, 3, 5 and 8 have been determined and allow a detailed insight into the overall reaction profile.

Full text of DOI:10.1016/j.jorganchem.2013.05.026

Journal of Organometallic Chemistry 751 (2014) 326e335
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Reactions of the s,p-furyl complex [Fe2(CO)6(m-Fu)(m-PFu2)]
(Fu ¼ C4H3O) with phosphines: Carbonyl substitution, migratory
carbonyl insertion and cyclometallation-induced furan elimination
,
,
,
Ahibur Rahaman a b, Fakir Rafiqul Alam b c, Shishir Ghosh a d, Derek A. Tocher d,
Matti Haukka e, Shariff E. Kabir b , Ebbe Nordlander
, Graeme Hogarth
,
a,
d,
*
**
**
a Inorganic Chemistry Research Group, Chemical Physics, Center for Chemistry and Chemical Engineering, Lund University, Box 124, SE-221 00 Lund, Sweden
b Department of Chemistry, Jahangirnagar University, Savar, Dhaka 1342, Bangladesh
c Department of Chemistry, National University, Gazipur 1704, Bangladesh
d Department of Chemistry, University College London, 20 Gordon Street, London WC1H OAJ, UK
e Department of Chemistry, University of Jyveskylä, Box 111, FI-40014 Jyväskylä, Finland
a r t i c l e i n f o
a b s t r a c t
Article history:
The reactivity of the s,p-furyl complex [Fe2(CO)6(m-Fu)(m-PFu2)] (1) towards PPh3 and a range of bidentate
Received 8 April 2013
Received in revised form
20 May 2013
phosphines has been studied and a number of different reaction products have been identified. With
PPh3, carbonyl substitution affords [Fe2(CO)5(PPh3)( -Fu)( -PFu2)] (2) in which the new phosphine is
coordinated to the iron center that is -coordinated by the bridging furyl moiety. With small bite-angle
m
m
s
Accepted 21 May 2013
diphosphines e bis(diphenylphosphino)methane (dppm) and 1,8-bis(diphenylphosphino)naphthalene
(dppn) e carbonyl substitution and migratory carbonyl insertion result to give the furyleacyl complexes
Keywords:
Diiron
Furyl
Migratory insertion
Cyclometallation
with bridging, [Fe2(CO)4(
PFu2)] (4), diphosphines, respectively. With the more flexible diphosphines Ph2P(CH2)nPPh2 (n ¼ 2, dppe,
n ¼ 3, dppp), the cyclometallated products [Fe2(CO)5{ -PFu2)] (n ¼ 2, 5; n ¼ 3, 6)
2-C6H4PPh(CH2)nPPh2}(
are isolated as a result of carbonyl substitution and furan elimination, and a similar complex [Fe2(CO)5{
k2
C6H4PPh(C6H4)PPh2}( -PFu2)] (7) is generated from the more rigid diphosphine bis(diphenylphosphino)
benzene (dppb). With bis(diphenylphosphino)-1,1-binaphthalene (1,1-BINAP) the novel tridentate phos-
phine complex [Fe2(CO)5{
3-C6H4P(C20H12PPh2)C6H4PFu}] (8) results from the putative coupling of
m-dppm)(m-O]CeFu)(m-PFu2)] (3), or chelating, [Fe2(CO)4(k m-O]CeFu)(m-
2-dppn)(
m
,k
m
m
, -
m
Carbonephosphorus bond formation
m,k
cyclometallated diphosphine and difurylphosphido ligands, following elimination of two equivalents of
furan. The crystal structures of 2, 3, 5 and 8 have been determined and allow a detailed insight into the
overall reaction profile.
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
to study the reactivity of the furyl ligand at the diiron center. Herein
we describe our initial studies in this area, which have focused on
The organometallic chemistry of tri(2-furyl)phosphine (PFu3)
has been of interest as it is sterically similar to triphenylphosphine,
but the electron-withdrawing nature of the 2-furyl ring makes it a
poorer s-donor than PPh3 [1]. In a recent contribution we reported
that the reaction of PFu3 with [Fe3(CO)12] leads to both phosphine
the addition of mono- and bidentate phosphines. While these re-
actions may be expected to result in direct carbonyl substitution, it
is found that a range of transformations take place, including
carbonyl substitution, migratory carbonyl insertion into the metal-
bound furyl ligand, reductive elimination of furan and reductive
coupling of phosphorus-containing ligands.
coordination and carbon-phosphorus bond scission to yield the
s,p-furyl complex [Fe2(CO)6(m-Fu)(m-PFu2)] (1) (Scheme 1) [2]. This
behaviour is akin to that found for the corresponding triruthenium
2. Experimental
cluster [3,4] and this convenient route to 1 gave us the opportunity
2.1. General procedures
Unless otherwise stated, purification of solvents, reactions, and
manipulation of compounds were carried out under a nitrogen
atmosphere with the use of standard Schlenk techniques.
* Corresponding author. Tel.: þ44 (0)2076794664.
** Corresponding authors.
E-mail address: g.hogarth@ucl.ac.uk (G. Hogarth).
0022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.05.026

A. Rahaman et al. / Journal of Organometallic Chemistry 751 (2014) 326e335
327
12 h. The solvent was removed under reduced pressure and the
residue was chromatographed by TLC on silica gel. Elution with
cyclohexane/CH2Cl2 (9:1 v/v) developed two bands. The faster band
O
thf, rt
was unreacted 1 (3 mg) while the slower band afforded [Fe2(CO)4(k2
-
Fe(CO)3
(CO)3Fe
[Fe3(CO)12
]
+ PFu3
P
NaPh2CO cat.
dppn)(m-O]CeFu)(m-PFu2)] (4) (12 mg, 34%) as red crystals after
Fu2
recrystallization from hexane/CH2Cl2 at 4 ꢁC. Spectral data for 4:
1
Anal. Calcd for C51H35Fe2O8P3: C, 62.47; H, 3.61. Found: C, 62.70; H,
3.95%. IR (
(CDCl3): 6.49 (m, 3H, Fu), 7.01 (m, 6H, Fu), 7.15e7.41 (m, 20H, Ph),
n .
(CO), CH2Cl2): 2010 vs, 1954 s, 1941 w cmꢀ1 1H NMR
Scheme 1.
d
7.67e7.43 (m, 6H). 31P{1H} NMR (CDCl3):
d
61.5 (t, J ¼ 19 Hz), 59.1 (d,
All solvents were dried by distillation over appropriate drying
agents. All phosphine ligands were purchased from Acros Organics
Chemicals Inc. and used without further purification. Complex 1
was prepared as previously reported [2]. All chromatographic
separations and ensuing work-up were carried out in open air. Thin
layer chromatography was carried out on glass plates pre-coated
with Merck 60 0.5 mm silica gel. Infra-red spectra were recorded
as solutions in 0.5 mm NaCl cells on a Nicolet Avatar 360 FT-IR-
spectrometer with carbon monoxide as calibrant. Fast atom
bombardment (FAB) mass spectra were obtained on a JEOL SX-102
spectrometer using 3-nitrobenzyl alcohol as matrix and CsI as
calibrant. Proton and 31P{1H} NMR spectra were recorded on a
Varian Unity 500 MHz NMR spectrometer.
J ¼ 19 Hz), 58.6 (d, J ¼ 19 Hz). ESI-MS: m/z 980 [M]þ.
2.5. Reaction with bis(diphenylphosphino)ethane (dppe)
A benzene solution (20 mL) of 1 (30 mg, 0.059 mmol) and dppe
(23.5 mg, 0.059 mmol) was refluxed under a nitrogen atmosphere
for 12 h. The solvent was removed under reduced pressure and the
residue was chromatographed by TLC on silica gel. Elution with
cyclohexane/CH2Cl2 (9:1 v/v) developed three bands. The faster
band was unreacted 1 (4 mg) and the slower band afforded
[Fe2(CO)5{m,k m-PFu2)] (5) (15 mg, 41%) as
2-C6H4PPh(CH2)2PPh2}(
red crystals after recrystallization from hexane/CH2Cl2 at 4 ꢁC.
Spectral data for 5: Anal. Calcd for C39H29Fe2O7P3: C, 57.52; H, 3.60.
2.2. Reaction with PPh3
Found: C, 57.62; H, 3.88%. IR (
n(CO), CH2Cl2): 2038 s, 1982vs, 1941
w cmꢀ1. 1H NMR (CDCl3):
d
2.62e2.66 (m, 2H), 2.88e2.94 (m, 2H),
A benzene solution (20 mL) of 1 (25 mg, 0.049 mmol) and PPh3
(13 mg, 0.049 mmol) was heated to reflux under a nitrogen at-
mosphere for 10 h. The solvent was removed under reduced pres-
sure and the resultant residue was separated by TLC on silica gel.
Elution with hexane/CH2Cl2 (v/v 9:1) developed three bands. The
faster moving band gave unreacted 1 (3 mg) and the second band
6.10 (m, 1H, Fu), 6.15 (m, 1H, Fu), 6.19e6.20 (m, 1H, Fu), 6.21 (m, 1H,
Fu), 6.72e6.75 (m, 1H, Fu), 6.79e6.82 (m,1H, Fu), 7.13e7.31 (m,14H,
Ph), 7.45e7.48 (m, 3H, Ph), 7.59e7.63 (m, 1H, Ph), 7.99e8.03 (m, 1H,
Ph). 31P{1H} NMR (CDCl3):
d
101.0 (dd, J ¼ 134, 15, Hz), 83.9 (dd,
J ¼ 134, 19 Hz), 81.0 (t, J ¼ 17 Hz).
gave orange [Fe2(CO)5(PPh3)(
third band gave a small amount (2 mg) of a red solid tentatively
formulated as [Fe2(CO)4(PPh3)2( -Fu)( -PFu2)].
Spectral and analytical data for 2: Anal. Calcd for C35H24Fe2O8P2:
C, 56.32; H, 3.24. Found: C, 57.20; H, 3.52%. IR ( (CO), CH2Cl2): 2042
vs, 1989 vs, 1954 w cmꢀ1. 1H NMR (CDCl3):
7.61 (m, 1H, Fu), 7.30
m-Fu)(m-PFu2)] (2) (14 mg, 44%). A
2.6. Reaction with bis(diphenylphosphino)propane (dppp)
m
m
A benzene solution (20 mL) of 1 (30 mg, 0.059 mmol) and dppp
(24 mg, 0.059 mmol) was refluxed under a nitrogen atmosphere for
11 h. The solvent was removed under reduced pressure and the
residue was chromatographed by TLC on silica gel. Elution with
cyclohexane/CH2Cl2 (9:1 v/v) developed two bands. The faster band
n
d
(m, 3H, Fu), 6.50 (m, 1H, Fu), 6.35 (m, 1H, Fu), 6.10 (m, 1H, Fu), 5.79
(m, 1H, Fu), 4.03 (m, 1H, Fu), 7.26 (m, 6H, Ph) 7.21 (m, 9H, Ph). 31P
was unreacted
1 (3 mg) while the slower band afforded
{1H} NMR (CDCl3):
d
67.7 (brs), 71.7 (brs). ESI-MS: m/z 746 [M]þ.
[Fe2(CO)5{m-k m-PFu2)] (6) (12 mg, 31%) as
2-C6H4PPh(CH2)3PPh2}(
red crystals after recrystallization from hexane/CH2Cl2 at 4 ꢁC.
2.3. Reaction with bis(diphenylphosphino)methane (dppm)
Spectral data for 6: Anal. Calcd for C40H31Fe2O7P3: C, 57.98; H, 3.78.
Found: C, 58.62; H, 3.98%. IR (
n(CO), CH2Cl2): 2043 s,1987 vs,1941 w
cmꢀ1. 1H NMR (CDCl3):
d
1.8e2.00 (m, 2H), 2.22e2.6 (m, 2H), 3.8e
A benzene solution (20 mL) of 1 (30 mg, 0.059 mmol) and dppm
(23 mg, 0.059 mmol) was refluxed under a nitrogen atmosphere for
12 h. The solvent was removed under reduced pressure and the
residue was chromatographed by TLC on silica gel. Elution with
cyclohexane/CH2Cl2 (9:1 v/v) developed two bands. The faster band
4.1 (m, 2H), 6.15 (m, 1H, Fu), 6.32 (m, 2H, Fu), 6.48 (m, 1H, Fu), 6.40
(m, 1H, Fu), 6.5 (m, 1H, Fu), 7.10e7.54 (m, 19H, Ph). 31P{1H} NMR
(CDCl3):
d
73.5 (br), 56.4 (brs), 31.9 (d, J ¼ 116 Hz).
was unreacted 1 (4 mg) while the slower band afforded [Fe2(CO)4(m-
2.7. Reaction with 1,2-bis(diphenylphosphino)benzene (dppb)
dppm)(m-O]CeFu)(m-PFu2)] (3) (15 mg, 34%) as red crystals after
recrystallization from hexane/CH2Cl2 at 4 ꢁC. Spectral data for 3:
Anal. Calcd for C42H31Fe2O8P3: C, 58.09; H, 3.60. Found: C, 58.62; H,
A toluene solution (20 mL) of 1 (22 mg, 0.043 mmol) and dppb
(18 mg, 0.043 mmol) was refluxed under a nitrogen atmosphere for
27 h. The solvent was removed under reduced pressure and the
residue was chromatographed by TLC on silica gel. Elution with
cyclohexane/CH2Cl2 (4:1 v/v) developed two bands. The faster band
was unreacted 1 (2 mg) while the slower moving band afforded
3.86%. IR (
NMR (CDCl3):
n
(CO), CH2Cl2): 1990 s, 1961 vs, 1926 m, 1913 sh cmꢀ1. 1H
d
2.71 (ddd, J ¼ 19.5, 10.5, 9.0 Hz, 1H), 3.51e3.59 (m,
1H), 6.01e6.013 (m,1H, Fu), 6.03 (d, J ¼ 3.5 Hz,1H Fu), 6.20e6.21 (m,
1H, Fu), 6.40 (dd, J ¼ 3.0, 1.5 Hz, 1H, Fu), 6.60 (br, 1H, Fu), 6.75 (d,
J ¼ 3.0 Hz, 1H, Fu), 6.95 (s, 1H, Fu), 7.57 (s, 1H, Fu), 7.61 (s, 1H, Fu),
7.06e7.07 (m, 3H, Ph), 7.11e7.15 (m, 2H, Ph), 7.23e7.29 (m, 6H, Ph),
7.34e7.37 (m, 5H, Ph), 7.42e7.47 (m, 4H, Ph). 31P{1H} NMR (CDCl3):
[Fe2(CO)5{m,k m-PFu2)] (7) (20 mg, 66%) as
2-C6H4PPh(C6H4)PPh2}(
red crystals after recrystallization from hexane/CH2Cl2 at 4 ꢁC.
Spectral data for 7: Anal. Calcd for C39H29Fe2O7P3: C, 57.52; H, 3.60.
d
136.3 (dd, J ¼ 115, 59Hz), 54.4 (t, J ¼ 115 Hz), 43.4(dd, J ¼ 115, 59Hz).
Found: C, 57.62; H, 3.88%. IR (
n(CO), CH2Cl2): 2023 s,1983 vs,1945 w
cmꢀ1 1H NMR (CDCl3):
.
d
5.72e5.63 (m, 1H, Fu), 6.08 (m, 1H, Fu),
2.4. Reaction with 1,8-bis(diphenylphosphino)naphthalene (dppn)
6.20 (m,1H, Fu), 6.29 (m, 2H, Fu), 6.31 (m,1H, Fu), 6.53e6.41 (m, 2H,
Ph), 6.83e6.80 (m, 3H, Ph), 7.18e7.10 (m, 5H, Ph), 7.48e7.30 (m, 9H,
A benzene solution (20 mL) of 1 (25 mg, 0.049 mmol) and dppn
(24.2 mg, 0.049 mmol) was refluxed undera nitrogen atmosphere for
Ph), 7.96e7.62 (m, 4H, Ph). 31P{1H} NMR (CDCl3):
d
138.7 (dd, J ¼ 54,
30 Hz), 90.5 (t, J ¼ 55 Hz), 82.7 (dd, J ¼ 50, 30 Hz).

328
A. Rahaman et al. / Journal of Organometallic Chemistry 751 (2014) 326e335
2.8. Reaction with bis(diphenylphosphino)-1,10-binaphthalene
(BINAP)
crystallises in the orthorhombic space group P212121, the absolute
structure parameter was ꢀ0.008(10). Single crystals of 2 and 8 were
immersed in cryo-oil, mounted in a Nylon loop, and measured at
120 K and 150 K, respectively. The X-ray diffraction data was
A toluene solution (20 mL) of 1 (20 mg, 0.039 mmol) and BINAP
(24 mg, 0.039 mmol) was refluxed under a nitrogen atmosphere for
24 h. The solvent was removed under reduced pressure and the
residue was chromatographed by TLC on silica gel. Elution with
cyclohexane/CH2Cl2 (3:2 v/v) developed two bands. The faster band
collected on a Bruker Kappa Apex II Duo diffractometer using Mo-
ꢀ
Ka
radiation (
l
¼ 0.71073 A). The APEX2 [7] program package was
used for cell refinements and data reductions. The structure was
solved by direct methods using the SHELXS-86 (2) [8] or SHELXS-97
(8) [9] program with the WinGX [10] graphical user interface. A
multi-scan absorption correction based on equivalent reflections
(SADABS) [6] was applied to the data. Structural refinement was
carried out using SHELXL-97. In 8, the electron density due to the
solvent of crystallization could not be unambiguously resolved and
it was equated to one dichloromethane and one n-hexane mole-
cules by using the SQUEEZE routine of PLATON [11]. The missing
solvent was taken into account in the unit cell content. The
hydrogen atoms were positioned geometrically and constrained to
was unreacted
[Fe2(CO)5{
3-C6H4P(C20H12PPh2)C6H4PFu}] (8) (5 mg, 18%) as red
crystals after recrystallization from hexane/CH2Cl2 at 4 ꢁC. Spectral
data for 8: IR (
(CO), CH2Cl2): 2043 s, 2023 m, 1981 vs, 1954 w cmꢀ1
1H NMR (CDCl3):
5.22 (m, 11H), 5.38 (m, 4H), 5.68 (m, 2H), 6.32
(m, 1H), 6.49 (m, 1H), 6.74 (m, 2H), 7.18 (m, 9H), 7.30 (m, 7H), 7.48
(m, 2H), 7.74 (m, 3H). 31P{1H} NMR (CDCl3):
1 (5 mg) while the slower band afforded
m,k
n
.
d
d
154.4 (dd, J ¼ 57,
34 Hz), 90.7 (dd, J ¼ 57, 34 Hz), 64.4 (t, J ¼ 57 Hz).
ꢀ
ꢀ
ride on their parent atoms, with CeH ¼ 0.95e1.00 A, BeH ¼ 1.12 A,
and Uiso ¼ 1.2e1.5 Ueq (parent atom). Details of data collection and
structure refinement are given in Table 1.
2.9. X-ray crystallography
Single crystals of 3 and 5 were mounted on fibres and diffraction
data collected on a Bruker SMART APEX diffractometer at 150 K
ꢀ
using Mo-K
a
radiation (
l
¼ 0.71073 A). Data collection, indexing
3. Results and discussion
and initial cell refinements were all done using SMART software.
Data reduction was accomplished with SAINT software [5] and
SADABS [6] programs were used to apply empirical absorption
corrections. The structures were solved by direct methods and
refined by a full matrix least-squares method. All non-hydrogen
atoms were refined anisotropically and hydrogen atoms were
included using a riding model. Scattering factors were taken from
the International Tables for X-ray Crystallography. For 3, which
3.1. Reaction of 1 with PPh3 e formation of the carbonyl
substitution product [Fe2(CO)5(PPh3)(m-Fu)(m-PFu2)] (2)
Heating a benzene solution of 1 with an equimolar amount of
PPh3 for 10 h resulted in the isolation of the carbonyl substitution
product [Fe2(CO)5(PPh3)(m-Fu)(m-PFu2)] (2) in 44% yield after
chromatography (Scheme 2). Characterization was relatively
Table 1
Crystal data and experimental details for [Fe2(CO)5(PPh3)(
[Fe2(CO)5{
m-Fu)(m-PFu2)] (2), [Fe2(CO)4(
m
-dppm)(
m-O]CeFu)(m-PFu2)] (3), [Fe2(CO)5{
m,
k
2-C6H4PPh(CH2)2PPh2}(
m-PFu2)] (5),
m,k
3-C6H4P(C20H12PPh2)C6H4PFu}] (8).
Compound
2
3
5
8
Empirical formula
Formula weight
Temp (K)
C35H24O8Fe2P2
746.18
120(2)
0.71073
Monoclinic
P21/c
10.0094(4)
30.993(1)
12.5811(4)
90
124.796(2)
90
3205.0(2)
4
1.546
1.058
C42H31O8Fe2P3
868.28
150(2)
0.71073
Orthorhombic
P212121
9.807(2)
18.617(3)
20.920(4)
90
90
90
3819(1)
4
1.510
C39H29O7Fe2P3
814.238
150(2)
0.71073
Triclinic
P 1 bar
9.443(1)
11.135(2)
17.781(2)
105.656(2)
90.651(2)
95.419(2)
1790.9(4)
24
C60H47O6Fe2P3Cl2
1139.49
150(2)
0.71073
Triclinic
ꢀ
Wavelength (A)
Crystal system
Space group
P 1 bar
ꢀ
a (A)
11.3018(6)
13.1349(7)
17.819(1)
106.003(2)
101.143(2)
94.570(2)
2469.8(2)
2
ꢀ
b (A)
ꢀ
c (A)
a
b
g
(ꢁ)
(ꢁ)
(ꢁ)
3
ꢀ
Volume (A )
Z
Dcalc (Mg mꢀ3
)
1.510
0.994
1.532
0.849
m
(Mo K
a
) (mmꢀ1
)
0.940
F(000)
1520
1776
832
1172
Crystal colour
Red
Red
Red
Red
Crystal size (mm)
q
0.27 ꢂ 0.21 ꢂ 0.16
0.46 ꢂ 0.16 ꢂ 0.04
0.46 ꢂ 0.19 ꢂ 0.04
0.28 ꢂ 0.26 ꢂ 0.21
1.86e25.50
ꢀ13 ꢃ h ꢄ 13
ꢀ15 ꢃ k ꢄ 15
0 ꢃ l ꢄ 21
Direct methods
9098
range (ꢁ)
2.08e30.00
2.29e28.24
2.38e28.31
Limiting indices
ꢀ14 ꢃ h ꢄ 13
ꢀ43 ꢃ k ꢄ 40
ꢀ17 ꢃ l ꢄ 17
Direct methods
47,305
ꢀ12 ꢃ h ꢄ 12
ꢀ23 ꢃ k ꢄ 23
ꢀ27 ꢃ l ꢄ 26
Direct methods
31,859
ꢀ12 ꢃ h ꢄ 12
ꢀ14 ꢃ k ꢄ 14
ꢀ22 ꢃ l ꢄ 22
Direct methods
14,903
Structure solution
Reflections collected
Independent reflections (Rint
Max. and min. transmission
Data/restraints/parameters
Goodness of fit on F2
)
9326 (0.0252)
0.8532 and 0.7668
9326/0/424
8908 (0.0497)
0.9634 and 0.6718
8908/0/496
7879 (0.0276)
0.9613 and 0.6577
7879/0/460
9098 (0.0361)
0.8426 and 0.7946
9098/0/577
1.076
1.032
0.996
1.040
Final R indices [I > 2
s
(I)]
R1 ¼ 0.0305
R1 ¼ 0.0354
R1 ¼ 0.0513
R1 ¼ 0.0505
wR2 ¼ 0.1296
R1 ¼ 0.0840
wR2 ¼ 0.1427
0.838 and ꢀ0.497
wR2 ¼ 0.0682
R1 ¼ 0.0423
wR2 ¼ 0.0761
R1 ¼ 0.0430
wR2 ¼ 0.1315
R1 ¼ 0.0670
R indices (all data)
wR2 ¼ 0.0723
0.544 and ꢀ0.470
wR2 ¼ 0.0800
0.602 and ꢀ0.305
wR2 ¼ 0.1451
1.231 and ꢀ0.366
ꢀꢀ3
Largest peak and hole (e A
)

A. Rahaman et al. / Journal of Organometallic Chemistry 751 (2014) 326e335
329
ꢀ
larger than those of around 0.1 A for simple aryl- or alkyl-
O
O
ꢀ
substituted diironealkenyl complexes and the value of 0.193(4) A
in 2 underscores the idea that furyl (and thienyl) are special ex-
amples of
The reaction of 1 with PPh3 is akin to that of the ruthenium
analogue [Ru2(CO)6( -Fu)( -PFu2)] (1-Ru) which also yields the
substitution product [Ru2(CO)5(PPh3)( -Fu)( -PFu2)] (2-Ru)
Ph3P
OC
OC
PPh3
Fe(CO)3
(CO)3Fe
Fe
Fe(CO)3
s,p-alkenyl ligands.
C H ,
Δ
6
6
P
P
Fu2
Fu2
- CO
m
m
1
2
m
m
although the required reaction conditions and yields vary signifi-
cantly [13]. Thus 2-Ru is formed in high yield upon simply stirring
1-Ru and PPh3 in dichloromethane in a reaction that has been
shown to be associative in nature [13]. The more forcing conditions
required for formation of 2 and the low isolated yields suggest that
this transformation is more likely to be of a dissociative nature, but
further studies are needed in order to assess the mechanism of this
substitution reaction.
Scheme 2.
straightforward with IR spectra being particularly informative of
the degree of carbonyl substitution, the highest frequency carbonyl
vibration at 2042 cmꢀ1 being characteristic of a Fe2(CO)5L frame-
work. The 1H NMR displayed a multiplet at
d
4.03 that is assigned to
-carbon of the furyl ligand, the chemical
shift being quite characteristic, while other furyl and phenyl pro-
tons were observed between
7.6e5.8. The 31P{1H} NMR spectrum
the proton attached to the
b
3.2. Reaction of 1 with bis(diphenylphosphino)methane (dppm) and
1,8-bis(diphenylphosphino)naphthalene (dppn) e formation of the
d
consisted of two broad singlets at 71.7 and 67.7 ppm, suggesting
that the complex is fluxional in solution. In order to elucidate the
position of phosphine substitution and also to confirm that the
furyl ligand was still intact (see below), a single crystal X-ray
diffraction study of 2 was carried out, the results of which are
summarized in Fig. 1 and its caption.
migratory carbonyl insertion products [Fe2(CO)4(
m
-dppm)(
m-O]Ce
Fu)( -PFu2)] (3) and [Fe2(CO)4( -O]CeFu)(m
m
k
2-dppn)(
m
-PFu2)] (4)
Heating a benzene solution of 1 and dppm for 12 h led to the
isolation of [Fe2(CO)4( -dppm)( -O]CeFu)( -PFu2)] (3) in 34%
m
m
m
yield as the sole reaction product (Scheme 3). The IR spectrum of 3
is characteristic of a Fe2(CO)4L2 bridge framework in which the
diphosphine spans the metalemetal bond, the highest frequency
carbonyl vibration appearing at 1990 cmꢀ1. In the 31P{1H} NMR
spectrum, three well-resolved signals are observed at 43.4, 54.4 and
136.3 ppm, showing that the diiron center is unsymmetrically
bridged e the low-field signal being assigned to the difur-
ylphosphido bridge. The 1H NMR spectrum showed a pair of high-
The gross structural features of 2 are similar to those in 1 and the
substituted analogue [Fe2(CO)5(PFu3)(m-Fu)(m-PFu2)] (2-PFu3) [2].
ꢀ
The ironeiron vector of 2.5884(3) A is spanned by furyl and difur-
ylphosphido ligands in relative cis disposition. Unlike the above-
mentioned PFu3 derivative, in which the phosphine is coordi-
nated to the p-bound iron atom [2], the triphenylphosphine ligand
in 2 is coordinated to the s-bound iron atom, lying approximately
trans to the ironeiron vector [Fe(2)eFe(1)eP(2) 143.55(1)ꢁ]. In
field multiplets at
d 2.71 and 3.55 characteristic of the methylene
previous work we have considered the nature of the alkenyl
protons on the diphosphine, but all other signals appeared down-
field of 6 ppm, suggesting that the furyl ligand is not bridging the
diiron center. In order to elucidate the nature of the bridging ligand,
the structure of 3 was determined by a single crystal X-ray
diffraction study, the results of which are summarized in Fig. 2 and
its caption.
bonding to the diiron center through the parameters
defined as {(FepeCa) ꢀ (FeseCa)} and {(FepeCa) ꢀ (FepeCb)},
respectively [12], with Ca being a measure of how symmetrically
the -carbon bridges the diiron center and Fep differentiating
between metalla-olefin and metallacyclic binding modes [12]. For 1
DCa and DFep,
D
a
D
ꢀ
and 2-PFu3
DCa values of 0.172(4)e0.223(4) A are significantly
The diphosphine bridges the diiron center, lying approximately
trans to the difurylphosphido moiety [P(1)eFe(1)eP(2) 141.80(3),
P(1)eFe(2)eP(3) 152.05(3)ꢁ] and, at approximately right angles to
both, lies a furyleacyl ligand that most likely is the result of
carbonyl insertion into the metal-bound furyl ligand. The bridging
carbonyl moiety is characterized by ironecarbon and ironeoxygen
ꢀ
ꢀ
distances of 1.935(2) A [Fe(1)eC(6)] and 1.998(2) A [Fe(2)eO(5)],
and the furyl group lies approximately in the Fe2CO plane, sug-
gesting that there is electronic delocalization/conjugation between
ꢀ
the acyl and furyl moieties. The C(6)eO(5) bond length of 1.270(3) A
compares well with related diiron acyl complexes [14e17].
Similarly, reaction of 1 with 1,8-bis(diphenylphosphino)naph-
thalene (dppn) results in the loss of one carbonyl and insertion of a
second into the diiron-furyl subunit to afford [Fe2(CO)4(
O]CeFu)( -PFu2)] (4) in 34% yield (Scheme 3). The key difference
k m-
2-dppn)(
m
between 3 and 4 is that in the latter the diphosphine binds in a
chelating fashion to a single iron atom. This is clearly seen from the
IR spectrum, where the carbonyl region consists of three absorp-
tions at 2010 vs, 1954 s and 1941 m cmꢀ1, the positions and pattern
of which is characteristic of an Fe2(CO)4L2 chelate framework. The
diphosphine can potentially chelate to either the oxygen- or
carbon-bound iron atom but it is known that the former is fav-
oured. For example, in closely related work, we have shown by X-
ray crystallography that in both [Fe2(CO)4(
k
2-dppe)(
-PTh2)] the diphos-
m-O]CeTh)(m-
PTh2)] and [Fe2(CO)4( -O]CeTh)(m
k
2-dppb)(
m
Fig. 1. Molecular structure of [Fe2(CO)5(PPh3)(m-Fu)(m-PFu2)] (2) with selected bond
lengths (A) and angles ( ): Fe(1)eFe(2) 2.5884(3), Fe(1)eP(2) 2.2219(4), Fe(1)eC(6)
1.958(2), Fe(2)eC(7) 2.303(2), Fe(2)eC(6) 2.151(2), Fe(1)eFe(2)eP(2) 143.55(1).
ꢁ
ꢀ
phine is coordinated to the oxygen-bound iron atom [18]. Assuming
that this is the case for 4, three geometric isomers are possible.

330
A. Rahaman et al. / Journal of Organometallic Chemistry 751 (2014) 326e335
O
O
C
O
C
O
CO
Fu2
dppn
dppm
P
Fe
(CO)3Fe
Ph2
P
1
Fe
Fe(CO)2
PPh2
(CO)2
Ph2P
C6H6,
- CO
Δ
Δ
C6H6,
- CO
P
Fu2
P
Ph2
3
4
Scheme 3.
The 31P{1H} NMR spectrum of 4 indicates that only one geometric
isomer is formed. Three sharp signals are seen, an apparent
triplet at 61.5 ppm (J ¼ 19 Hz) and a pair of doublets at 59.1 and
58.6 ppm. We assign the (apparent) triplet resonance to the
difurylphosphido-bridge, the lack of any large couplings suggesting
that the isomer shown in Scheme 3 is selectively adopted, i.e. a
structure with the bulky diphosphine occupying equatorial sites in
a distorted trigonal bipyramidal metal center, with the carbonyl
and phosphido groups occupying the axial positions.
Wong and co-workers have studied the reaction of the
di-ruthenium analogue [Ru2(CO)6( -Fu)( -PFu2)] (1-Ru) with
dppm and related diphosphines that are known to bridge metale
metal bonds [21]. For the diruthenium complex, carbonyl substi-
tution takes place in all cases; for example, with dppm the sole
m
m
product is [Ru2(CO)4(m-dppm)(m-Fu)(m-PFu2)] that has been crys-
tallographically characterized. It is not clear whether addition of
the second phosphorus atom at the diruthenium center is a
straight-forward substitution process or occurs via initial migratory
In light of the isolation of the carbonyl substitution product 2
from the reaction of triphenylphosphine with 1, it is tempting to
speculate that formation of 3 and 4 results via the intermediate
formation of monodentate complexes bearing a dangling phos-
phine moiety. Coordination of this free phosphine moiety would
then lead to migratory carbonyl insertion to give the observed
products based on the known propensity for dppm to bridge metal
atoms [19] and dppn to act as a chelating ligand [20]. This is akin to
insertion to give [Ru2(CO)4(m-dppm)(m-O]CeFu)(m-PFu2)] that
subsequently loses the inserted carbonyl. Carbonyl loss from
binuclear vinyl-acyl complexes has been documented [16] and
is facile for diironethiolate complexes but less so for related
phosphido-bridged complexes.
3.3. Reaction of 1 with 1,2-bis(diphenylphosphino)ethane (dppe),1,3-
bis(diphenylphosphino)propane (dppp) and 1,2ebis(diphenyl-
phosphino)benzene (dppb) e orthometallation and furan loss to give
the behaviour noted previously for [Fe2(CO)6(
PPh2)] in which the intermediate monodentate dppm complex,
[Fe2(CO)5( -HC]CHPh)( -PPh2)], was isolated and
1-dppm)(
shown to transform into the vinyleacyl complex [Fe2(CO)4(
dppm)( -O]CeHC]CHPh)( -PPh2)] upon further heating [17].
m-HC]CHPh)(m-
[Fe2(CO)5{
m
,
k
k
2-C6H4PPh(CH2)nPPh2}(
2-C6H4PPh(C6H4)PPh2}(
m
-PFu2)] (n ¼ 2, 5; n ¼ 3, 6) and
k
m
m
[Fe2(CO)5{
m
,
m-PFu2)] (7)
m-
m
m
Reactions of 1 with 1,2-bis(diphenylphosphino)ethane (dppe) in
refluxing benzene afforded [Fe2(CO)5{
2-C6H4PPh(CH2)2PPh2}(
PFu2)] (5) in 41% yield after workup, while a similar reaction with
1,3-bis(diphenylphosphino)propane (dppp) yielded [Fe2(CO)5{
2-C6H4PPh(CH2)3PPh2}(
-PFu2)] (6) in 31% yield. In a similar
manner, heating 1 and 1,2-bis(diphenylphosphino)benzene (dppb)
in toluene gave [Fe2(CO)5{ -PFu2)] (7) in
2-C6H4PPh(C6H4)PPh2}(
m,
k
m-
m
-
k
m
m,k
m
66% yield (Scheme 4). While it was clear from the IR spectra that 5e
7 contained an Fe2(CO)5L2 core, and from the 31P{1H} NMR spectra
that the three phosphorus atoms were metal-bound, their struc-
tures only became apparent following an X-ray crystallographic
study of 5, the results of which are summarized in Fig. 3 and its
caption.
The diiron unit is still spanned by a difurylphosphido ligand but
the furyl moiety has been lost and one of the iron atoms is instead
bound to an orthometallated phenyl ring from the diphosphine.
The latter chelates to one metal center via both phosphorus atoms
[P(2)eFe(2)eP(3) 85.28(3)ꢁ] and spans the diiron center via the
ꢀ
orthometallated phenyl ligand [C(14)eFe(2) 2.042(3) A]. In ac-
ꢀ
commodating this new ligand, the ironeiron bond of 2.7639(6) A in
5 is significantly elongated with respect to those in 2 and 3. The two
phosphorus-containing ligands lie approximately cis to one another
[P(1)eFe(1)eP(2) 96.25(3), P(1)eFe(1)eP(3) 113.11(3)ꢁ]. Thus the
Fe(1) center can be considered to possess a distorted trigonal
bipyramidal coordination geometry with P(2) and C(2) occupying
axial sites [P(2)eFe(1)eC(2) 174.63(9)ꢁ] and P(1), P(3) and C(1)
lying in the equatorial plane. We call this geometry cis (axeeq)
(Scheme 5) as the cyclometallated phosphorus and phosphido
groups lie cis to one another while the phosphorus atoms of the
diphosphine occupy axial and equatorial sites. An alternative
conformation is trans (eqeeq) and here the cyclometallated
Fig. 2. Molecular structure of [Fe2(CO)4(m-dppm)(m-O]C-Fu)(m-PFu2)] (3) with
ꢁ
ꢀ
selected bond lengths (A) and angles ( ): Fe(1)eFe(2) 2.6598(6), Fe(1)eP(1) 2.1894(8),
Fe(1)eP(2) 2.2197(8), Fe(2)eP(1) 2.2044(8), Fe(2)eP(3) 2.2554(8), Fe(2)eO(5) 1.998(2),
Fe(1)eC(6) 1.935(2), C(6)eO(5) 1.270(3), P(1)eFe(1)eP(2) 141.80(3), P(1)eFe(2)eP(3)
152.05(3).

A. Rahaman et al. / Journal of Organometallic Chemistry 751 (2014) 326e335
331
Ph
Ph
H2C
P
n
P
dppe or dppp
dppb
Ph2P
OC
Ph2P
OC
1
Fe
OC
Fe(CO)3
Fe
OC
Fe(CO)3
C7H8, Δ
C6H6, Δ
- CO, - C4H4O
P
P
Fu2
Fu2
- CO, - C4H4O
7
5 n = 2, 6 n = 3
Scheme 4.
phosphorus and phosphido groups subtend a much larger angle.
While in the solid-state it is clear that the molecule exists in the cis
(axeeq) conformation, this appears not to be the case in solution.
Thus the 31P{1H} NMR spectrum of 5 consists of three sharp mul-
tiplets, a doublet of doublets at 101.0 (J ¼ 134, 15 Hz) ppm assigned
to the phosphido-bridge, a second doublet of doublets at 83.9
(J ¼ 134, 19 Hz) ppm and a triplet at 81.0 (J ¼ 17 Hz) ppm. The large
coupling constant cannot be easily explained on the basis of the
observed solid-state structure and is more consistent with a trans
(eqeeq) conformation. Thus we suggest that the two forms are in
equilibrium in solution with the trans (eqeeq) conformation being
favoured.
Further insight into this dynamic equilibrium comes from close
inspection of the 31P{1H} NMR spectra of the dppe and dppb de-
rivatives 6 and 7, respectively. For 7, this consists of three sharp
signals e a doublet of doublets at 138.7 (J ¼ 55, 30 Hz) ppm
assigned to the phosphido-bridge, a second doublets of doublets at
82.7 (J ¼ 55, 30 Hz) ppm and an apparent triplet at 90.5
(J ¼ 55 Hz) ppm. Thus, it seems that the cis (axeeq) isomer of 7 is
prevalent in solution. For the dppp complex 6 the situation is less
clear as there is significant broadening of two of the three reso-
nances, consistent with interconversion of isomers at room tem-
perature. Thus, the high-field signal at 31.9 ppm appears as a broad
doublet (J ¼ 116 Hz), while the two other signals at 73.5 and
56.4 ppm are broadened significantly and no coupling information
could be extracted.
Interestingly, Wong and co-workers have reported similar
chemistry with [Ru2(CO)6(
and dppp-derived complexes, [Ru2(CO)5{
-PFu2)] (n ¼ 2e3) have been crystallographically characterized
m-Fu)(
m
-PFu2)] (1-Ru), and both dppe-
m,k
2-C6H4PPh(CH2)nPPh2}
(m
[21]. Both adopt the cis (axeeq) conformation found for 5 in the
solid-state, although in solution they show quite different 31P{1H}
NMR spectra. Thus, the dppe-derived complex is characterized by
phosphorusephosphorus coupling constants of 124, 25 and 25 Hz,
while for the dppp-derived complex the three coupling constants
are 38, 31 and 4 Hz. This data supports the postulated equilibrium
between the two isomers (Scheme 5) and also suggests that the cis
(axeeq) isomer is favoured in the solid-state.
The mode of formation of the cyclometallated complexes 5e7
remains unclear but, based on the facile nature of the carbonyl
insertion noted upon reaction of 1 with dppm and dppn, we favour
a process in which species akin to 4 are now intermediates.
Oxidative addition of a carbon-hydrogen bond to the diiron unit
could be facilitated by switching of the furyleacyl ligand from a
bridging to a monodentate coordination mode via cleavage of the
ironeoxygen bond with subsequent elimination of furan, resulting
in formation of the observed products. The high volatility of furan
makes it difficult to show that this is indeed eliminated. The rela-
tively flexible nature of the methylene backbones in dppe and dppp
might be expected to facilitate such a transformation, and the
relatively high yield obtained for the dppb product 7 suggests that
it is predisposed to cyclometallation. The dppn complex 4 does not
appear to undergo cyclometallation and we speculate that this may
be a consequence of the extremely bulky and inflexible nature of
the naphthalene linking unit which does not allow close approach
of a phenyl group to the diiron center.
3.4. Reaction of 1 with bis(diphenylphosphino)-1,10-binaphthalene
(BINAP) e unexpected formation of the triphosphine complex
[Fe2(CO)5{m,k
3-C6H4P(C20H12PPh2)C6H4PFu}] (8)
Over the past two decades, BINAP has found widespread in
transition metal chemistry [22] but it is only relatively recently that
the coordination chemistry of this ligand at polynuclear metal
centers has been reported [23]. Heating 1 and BINAP in toluene for
24 h resulted in the isolation of the new triphosphine complex
Fu2
P
Fu2
P
OC
OC
OC
OC
OC
CO
PPh2
CO
PPh2
Fe
P
Fe
Fe
Fe
OC
P
Ph
X
X
CO
Fig. 3. Molecular structure of [Fe2(CO)5{m,k m-PFu2)] (5) with
2-C6H4PPh(CH2)2PPh2}(
CO
Ph
trans (eq-eq)
ꢁ
ꢀ
selected bond lengths (A) and angles ( ): Fe(1)eFe(2) 2.7639(6), Fe(1)eP(1) 2.2199(9),
Fe(1)eP(2) 2.24369(9), Fe(1)eP(3) 2.2198(81), Fe(2)eP(1) 2.2023(9), Fe(2)eC(14)
2.042(3), P(1)eFe(1)eP(2) 96.25(3), P(1)eFe(1)eP(3) 113.11(3), P(2)eFe(1)eP(3)
85.28(3), P(1)eFe(2)eC(14) 85.60(9).
cis (ax-eq)
Scheme 5.

332
A. Rahaman et al. / Journal of Organometallic Chemistry 751 (2014) 326e335
spectrum consists of three well-resolved signals, the new
phosphido-bridge appearing as a doublet of doublets at 154.4
(J ¼ 57, 34 Hz) ppm and the modified BINAP ligand as a doublet of
doublets at 90.7 (J ¼ 57, 34 Hz) and an apparent triplet a 64.4
(J ¼ 57 Hz) ppm. Given the solid state structure, a large coupling
constant might be expected between the phosphorus atoms P(1)
and P(3) and the lack of such a coupling suggests that this structure
is not maintained in solution. The predominance in solution of an
isomer in which the diphenylphosphine moiety occupies the axial
site (approximately parallel to the ironeiron vector), with all three
phosphorus atoms lying approximately cis to one another, would be
more in accord with the NMR data.
P
PPh2
CO
1,1-BINAP
C7H8, Δ
1
(OC)3Fe
Fe
P
Fu
- CO, - 2 C4H4O
CO
8
Scheme 6.
As far as we are aware, the metallation of BINAP as seen in 8 has
not previously been reported. Although orthometallation of phe-
nylphosphines is well-established, BINAP is a very robust ligand that
retains its integrity under a wide range of conditions. There are a
number of reports of BINAP degradation under catalytic conditions.
In a few instances, especially at ruthenium(II) centers, cleavage of a
diphenylphosphino moiety has been documented [24].
[Fe2(CO)5{m,k
3-C6H4P(C20H12PPh2)C6H4PFu}] (8) in 18% yield after
workup (Scheme 6). Characterization of 8 relied heavily on a single
crystal X-ray diffraction study, the results of which are summarized
in Fig. 4 and its caption.
The structure is somewhat related to that of 5 but in 8 both
phenyl rings on one phosphorus atom have been metallated. The
first phenyl moiety links across to the second iron center as seen in
5 but the other is now linked to a furylphosphido moiety via for-
mation of a new carbonephosphorus bond and (the putative) loss
of a second equivalent of furan. The BINAP-derived part of the
new triphosphine chelates to one iron atom [P(1)eFe(1)eP(2)
89.71(4)ꢁ], while the new phosphido moiety still spans the metale
metal bond [Fe(1)eP(3)eFe(2) 82.26(4)ꢁ], the latter being signifi-
3.5. Overall reaction scheme
From reactions of [Fe2(CO)6(m-Fu)(m-PFu2)] (1) with various
phosphines we have isolated five different product types and in
seeking to understand how they are interrelated we favour a sce-
nario outlined in Scheme 7. In all reactions it seems likely that
initial carbonyl substitution occurs to give the pentacarbonyl
ꢀ
cantly elongated [Fe(1)eFe(2) 2.8668(7) A]. The remaining diphe-
nylphosphino group lies approximately trans to the phosphido-
bridge [P(1)eFe(1)eP(3) 152.08(4)ꢁ], while the central phos-
phorus atom lies approximately cis [P(2)eFe(1)eP(3) 80.37(4)ꢁ].
Overall, the new phosphine donates eight electrons to the diiron
center through the three phosphorus atoms and the orthometal-
complexes [Fe2(CO)5(phosphine)(m-Fu)(m-PFu2)] as characterized
here for PPh3 (complex 2) and previously shown for PFu3 [2]. The
relatively forcing conditions required to bring about this trans-
formation (heating at > 80 ꢁC) are in stark contrast to the behaviour
noted for the analogous diruthenium complex that undergoes
substitution at room temperature [4]. We believe this points to-
wards a dissociative mechanism operating for 1, the associative
mechanism shown to occur for 1-Ru [13] being less favourable
either due to the smaller size of iron vs ruthenium or the tighter
ꢀ
lated ring [Fe(2)eC(53) 2.073(3) A].
The coordination geometry at the Fe(1) is now best described as
a distorted square-based pyramid in which CO(1) occupies the axial
site; thus, C(1) subtends angles at Fe(1) of 109.0(1), 89.2(1), 97.0(1)
and 89.4(2) o with P(1), P(2), P(3) and C(2), respectively, while P(2)
lies trans to C(2) [P(1)eFe(1)eC(2) 176.3(1)ꢁ] and P(1) trans to P(3)
[P(1)eFe(1)eP(3) 150.08(4)ꢁ]. Spectroscopic data again suggest
some degree of flexibility in solution. Thus, the 31P{1H} NMR
binding of the furyl ligand, which precludes formation of the h1
state that is proposed for 1-Ru [13].
-
From this state, a second carbonyl substitution could potentially
occur to yield complexes of the type [Fe2(CO)4(phosphine)2(
m-
ꢀ
Fig. 4. Two views of the molecular structure of [Fe2(CO)5{
2.278(1), Fe(1)eP(2) 2.207(1), Fe(1)eP(3) 2.168(1), Fe(2)eP(3) 2.190(1), Fe(2)eC(53) 2.073(3), P(1)eFe(1)eP(2) 89.71(4), P(1)eFe(1)eP(3) 152.08(4), P(2)eFe(1)eP(3) 80.37(4).
3-C6H4P(C20H12PPh2)C6H4PFu}] (8) with selected bond lengths (A) and angles ( ): Fe(1)eFe(2) 2.8668(7), Fe(1)eP(1)
ꢁ
m,k

A. Rahaman et al. / Journal of Organometallic Chemistry 751 (2014) 326e335
333
O
C
O
Fu2
P
Fe(CO)2
PPh2
(CO)2Fe
Ph2P
X
3 X = CH2
migratory
insertion
O
O
Ph2PXPPh2
- CO
(CO)
(OC)3Fe
Fe
(CO)
(OC)3Fe
Fe
2
3
P
P
PPh2
Fu2
Fu2
carbonyl substitution
Ph2PX
1
2 Ph2PX = Ph
migratory
insertion
carbonyl
extrusion
O
Ph2
P
Ph2
O
C
O
OC
P
X
X
Fe
(CO)
Fe
(CO)3Fe
(CO)3Fe
P
P
(CO)
Ph2
P
P
Ph2
Fu2
Fu2
4 X = C10H6
- C4H4O
cyclometallation
(OC)3Fe
Ph
X
P
P
cyclometallation
X
PPh2
Fe
(CO)2
PPh2
(OC)3Fe
Fe
(CO)2
- C4H4O
P
P
Fu2
Fu
8 X = C20H12
5 X = (CH2)2, 6 X = (CH2)3, 7 X = C6H4
Scheme 7.
Fu)(
m
-PFu2)] or [Fe2(CO)4(diphosphine)(
m
-Fu)(
m
-PFu2)], but no such
chemistry, where [Fe2(CO)5{
formed upon heating [Fe2(CO)4(k m-O]CeTh)(m-PTh2)] in
m
,
k
2-C6H4PPh(C6H4)PPh2}(
m
-PTh2)] is
complexes have been detected in this investigation. This is in
2-dppb)(
contrast to the reported reactivity of 1-Ru with PPh3, which gives
toluene [18]. We favour a process that proceeds via initial carbonyl
extrusion to afford a species (shown in Scheme 7) with a termi-
nally bonded furyl ligand, in keeping with maintaining the 34-
a mixture of [Ru2(CO)5(PPh3)(
m-Fu)(m-PFu2)] and [Ru2(CO)4(PPh3)2
(m
-Fu)( -PFu2)] when carried out in refluxing toluene [25]. Instead,
m
it appears that at the diiron unit, coordination of the second
phosphine moiety (of a diphosphine) promotes migratory carbonyl
insertion to give furyleacyl complexes with the diphosphine either
bridging the metalemetal bond (dppm) or coordinating in a
chelate manner to the oxygen-bound iron atom (dppn). In the
analogous thienyl chemistry, chelating thienyleacyl complexes
electon count, but cannot rule out an intermediate with a
bridging furyl moiety and no metalemetal bond, which also fulfils
the latter criterion. Oxidative addition of a phenyl ring to the
second metal atom and subsequent elimination of furan would
then give the isolated cyclometallated complexes 5e7. As dis-
cussed earlier, isolation of the furyleacyl complex 4 suggests that
such a process is less facile for the dppn ligand and we attribute
this to the larger steric bulk of this ligand that precludes close
approach to the diiron center of the phenyl groups.
[Fe2(CO)4(k m-O]CeTh)(m-PTh2)] are formed with
2-diphosphine)(
a large range of diphosphines, including dppe, dppp and dppb [18].
For 1, reaction with these diphosphines affords only the cyclo-
metallated complexes 5e7 resulting from the putative elimination
of furan. We believe that these complexes are generated via furyle
acyl intermediates, in parallel with the analogous thienyl
In the case of 1,1-BINAP, a second equivalent of furan is puta-
tively eliminated to yield the isolated triphosphine (diphosphinee
phosphide) complex 8. The BINAP ligand is very bulky but, unlike

334
A. Rahaman et al. / Journal of Organometallic Chemistry 751 (2014) 326e335
dppn, the backbone is highly flexible and presumably allows for
close approach of one or more phenyl rings to the binuclear center.
We favour a scenario whereby 8 forms via an intermediate of the
type 5e7. Formation of 8 also requires cleavage of a furyl group
from the difurylphosphido ligand. Although this is unusual, it is not
Appendix A. Supplementary material
CCDC 932550e932553 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via www.
ccdc.cam.ac.uk/data_request/cif.
unprecedented. Thus, in recent work we have shown that [(
Ru3(CO)7( -dppm)(m3-C4H2O)( -PFu2)] transforms into the phos-
phinidine cluster [Ru3(CO)7( -dppm)(m3-C4H2O)(m3-PFu)] in 70%
m-H)
m
m
m
yield in refluxing toluene [26]. It is not appropriate to speculate
how this might happen at the diiron center, and putative elimina-
tion of furan and formation of a new carbon-phosphorus bond are
also required for the formation of 8. Nevertheless the basic
framework is very similar to those found in 5e7, suggesting that
this structural unit is thermodynamically favoured at the diiron
center.
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This research has been part sponsored by the Ministry of Edu-
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thank the European Union (Erasmus Mundus) and the Common-
wealth Scholarship Commission for scholarships to AR and SG
respectively. We also thank Professor Brian K. Nicholson for
recording mass spectra and Dr Abdul Mottalib for recording some
of the NMR spectra.

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