Neighbouring metal induced oxidative addition at the iron centre amongst the iron-arylpyridylphosphine complexes

Article abstract of DOI:10.1016/j.ica.2008.04.040

Complexes of the type (η⁴-BuC₅H₅)Fe(CO)₂(P) (P = PPh₂Py 3, PPhPy₂ 4, PPy₃ 5; Py = 2-pyridyl) were satisfactorily prepared. Upon treatment of 3 with M(CO)₃(EtCN)_3<

Full text of DOI:10.1016/j.ica.2008.04.040

Inorganica Chimica Acta 362 (2009) 477–482
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Neighbouring metal induced oxidative addition at the iron centre amongst the
iron–arylpyridylphosphine complexes
a,c
Olalere G. Adeyemi a,b, , Ling-Kang Liu
*
a Department of Chemical Sciences, College of Natural Sciences, Redeemer’s University, KM 46, Lagos-Ibadan Expressway, Redemption City, Nigeria
b Institute of Chemistry, Academia Sinica, Nankang, Taipei 11529, Taiwan, ROC
c Department of Chemistry, National Taiwan University, Taipei 10767, Taiwan, ROC
a r t i c l e i n f o
a b s t r a c t
Complexes of the type (g
4-BuC5H5)Fe(CO)2(P) (P = PPh2Py 3, PPhPy2 4, PPy3 5; Py = 2-pyridyl) were sat-
isfactorily prepared. Upon treatment of 3 with M(CO)3(EtCN)3 (M = Mo, 6a; W, 6b), the pyridyl N-atom
Article history:
Received 28 March 2008
Received in revised form 24 April 2008
Accepted 24 April 2008
could be coordinated to the metal M, which then eliminates a CO ligand from the Fe-centre and induced
an oxidative addition of the endo-C–H of (
g
4-BuC5H5). This results in a bridged hydrido heterodimetallic
Available online 6 May 2008
complex [( -P,N-PPh2Py)(l-H)M(CO)4] (M = Mo, 7a, 81%; W, 7b, 76%). The reaction of
g
5-BuC5H4)Fe(CO)(
l
4 or 5 with 6a,b did not give the induced oxidative addition, although these complexes contain more than
Keywords:
Oxidative addition
Hydrides
Iron complexes
Arylpyridylphosphines
one pyridyl N-atom. The reaction of 4 with M(CO)4(EtCN)2 (M = Mo, 9a; W, 9b) produced heterodimetal-
lic complexes [(g l
4-BuC5H5)Fe(CO)2( -P:N,N0-PPhPy2)M(CO)4] (M = Mo, 10a, 81%; W, 10b, 83%). Treat-
ment of 5 with 6a,b gave [(
g
4-BuC5H5)Fe(CO)2(
l
-P:N,N0,N00-PPy3)M(CO)3] (M = Mo, 12a, 96%; W, 12b,
78%).
Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction
hydrogen of (g
4-BuC5H5)Fe(CO)2(PPh3ꢀnPyn) were smoothly car-
ried out by Lewis acid, HBF4 ꢁ OEt2 to give [(
g
5-BuC5H4)Fe-
The coordination chemistry of arylpyridylphosphines PPh3ꢀnPyn
(n = 1–3; Py = 2-pyridyl) has largely developed. It is of particular
interest because of the use of metal complexes containing such li-
gands in homogeneous catalysis, especially with a potential appli-
cation in aqueous media [1]. The presence of a basic N-atom in
each pendant pyridine in PPh3ꢀnPyn ligands distinguishes it from
PPh3 ligand. Hence, there is enhanced acid–base chemistry
involved by the presence of pyridyl N-atom(s) and more coordina-
tion modes are available for PPh3ꢀnPyn as ligand than only the
P-donor mode in PPh3. For instance, PPh2Py could behave in mono-
nuclear complexes as a P-donor ligand and in dinuclear complexes
as a P,N-bridging ligand with or without metal–metal bonding.
PPhPy2 and PPy3 can bind further with a variety of coordination
modes: through two pyridyl groups (N,N0; PPh2Py and PPy3),
through three pyridyl groups (N,N0,N00 PPy3), and via the phospho-
rus and two pyridyl groups (P,N,N0; PPhPy2 and PPy3) [2].
(CO)2(PPh3ꢀnPyn)]+[BF4]ꢀ (n = 1–2) [3].
In this paper, we incorporated the PPh3ꢀnPyn ligands into com-
plexes of the type (
4-BuC5H5)Fe(CO)2(PPh3ꢀnPyn) and studied the
g
effect of the presence of the dangling pyridyl N-atom(s), known to
be able to coordinate to a second metal centre [2]. In the case of the
PPh2Py complex which contains one pyridyl N-atom, a neighbour-
ing Mo or W metal originally with three labile ligands could induce
an oxidative addition on the Fe-centre. Similar chemistry could not
be observed for the PPhPy2 and PPy3 analogues.
2. Experimental
2.1. General
All manipulations were performed under an atmosphere of pre-
purified nitrogen with standard Schlenk techniques and a double-
fold vacuum line. All solvents were distilled from an appropriate
drying agent [4]. For instance, THF, Et2O and n-hexane were dried
over sodium benzophenone ketal. CH3CN and CH3CH2CN were
dried over P2O5 and CaH2 was used for CH2Cl2. Infrared spectra
were recorded in CH2Cl2 using CaF2 optics on a Perkin–Elmer
(FT-IR) Paragon 1000 spectrophotometer. The 1H NMR and 13C
NMR spectra were obtained on Bruker AC200/AC300 spectrome-
ters, with chemical shifts reported in d values, downfield positive,
relative to the residual solvent resonance of CDCl3 (1H d 7.24, 13C
Few years ago we reported the synthesis of (g
4-BuC5H5)Fe-
(CO)2(PPh3ꢀnPyn) (n = 1–3). A three-component reaction was uti-
lized to produce the complexes. The hydride abstraction of endo-
* Corresponding author. Address: Department of Chemical Sciences, College of
Natural Sciences, Redeemer’s University, KM 46, Lagos-Ibadan Expressway,
Redemption City, Nigeria. Tel.: +234 805 5516450.
E-mail addresses: drlereadeyemi@yahoo.com, adeyemio@run.edu.ng (O.G.
Adeyemi).
0020-1693/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2008.04.040

478
O.G. Adeyemi, L.-K. Liu / Inorganica Chimica Acta 362 (2009) 477–482
NMR d 77.0). The 31P NMR spectra were obtained on Bruker AC200/
AC300 spectrometers using 85% H3PO4 as an external standard (d
0.00). The melting points were determined on a Yanaco MPL melt-
ing-point apparatus and are uncorrected. Mass spectra were re-
corded on a VG 70 – 250S mass Spectrometer, using fast atomic
bombardment technique, independently operated by the Institute
of Chemistry, Academia Sinica. Chemical analysis was performed
on a Perkin–Elmer 2400 CHN elemental analyzer, also indepen-
dently operated by the Institute of Chemistry, Academia Sinica.
Compounds 1, [5], 2, 3, 4, 5 [3], 6a,b, [6] and 9a,b [7] were prepared
according to literature procedure. Ligands PPh2Py [8a], PPhPy2
[8b], PPy3 [8c] were prepared using Li–Br exchange method in
good yield. PC13, PPhC12, PPh2C1, and o-C5H4NBr were obtained
from commercial sources, distilled twice and degassed prior to
use. Other reagents were obtained from commercial sources and
used without further purification.
with ether/n-hexane mixture (1:1) and filtered to give a brick red
solid of 10a. Using (C7H8)Mo(CO)4 (80 mg, 0.27 mmol, C7H8 = bicy-
clo [2,2] hepta-2,5-diene) to replace 9a, the result is the same with
very similar yields.
Compound 10a: yield: 0.114 g, 81%, mp: 138 °C (dec.); IR
(CH2C12) mCO 1977 (s), 1919 (vs) 1816 (s, b) cmꢀ1 31P NMR
;
(CDC13)
d d 9.24 (b, 2H, Py),
95.5 (s); 1H NMR (CDC13)
4JPH = 4.95 Hz, 6.53–8.30 (m, 11H, Ph and Py), 4.95 (b, 2H,
–CH@CHCHBu–), 2.49 (b, 1H, –CH@CHCHBu–), 2.22 (b, 2H,
–CH@CHCHBu–), 0.51–1.08 (m, 9H, Bu), MS (m/z) 497
(M+ꢀMo(CO)4 + 1), 441 (M+ꢀMo(CO)6+1). Anal. Calc. C31H27FeMo-
N2O6P: C, 52.69; H, 3.82; N, 3.97. Found: C, 52.16; H, 4.43; N,
3.65%.
2.5. [(g l
4-BuC5H5)Fe(CO)2( -P:N,N0-PPhPy2)W(CO)4] 10b
The procedure is similar to that of the reaction of the molybde-
num analogue with (0.30 g, 0.60 mmol) and 9b (0.30 g,
2.2. [(
g
5-BuC5H4)Fe(CO)(
l-P:N-PPh2Py)(l-H)Mo(CO)4] 7a
4
0.74 mmol) in dry THF (10 mL). Dark purple solid of 10b was col-
lected after the necessary work-up.
Compound 3 (0.30 g, 0.60 mmol) reacted with 6a (0.30 g,
0.87 mmol) and were dissolved in dry THF (30 mL). The mixture
was warmed up to ensure complete dissolution, to give orange
solution. The mixture was then stirred at room temperature for
2 h to give a deep orange solution which was filtered via a pad
of dry celite under nitrogen and washed with dry ether until col-
ourless to give clear orange solution. The solvent was removed un-
der vacuum. The ensuing orange solid was dissolved in a little
quantity of CH2C12 and mixed well with a little quantity of Al2O3
before being pack on a short Al2O3 column. The orange band was
eluted with 1:8–1:5 EtOAc/n-hexane mixtures. Bright orange
powder of 7a was collected after removing the solvent under
vacuum.
Compound 10b : yield: 0.40 g, 83%; mp: 143 °C (dec.); IR
(CH2C12) mCO 1977 (s), 1912 (vs) 1813 (s, b) cmꢀ1 31P NMR
;
(CDC13) d 97.9 (s); 1H NMR (CDC13) d 9.30 (b, 2H, Py), 6.40–8.28
(m, 11H, Ph and Py), 4.98 (b, 2H, –CH@CHCHBu–), 2.52 (b, 1H, –
CH@CHCHBu–), 2.29 (b, 2H, –CH@CHCHBu–), 0.56–1.06 (m, 9H,
Bu), MS m/z 767 (M+ꢀCO+1) 497, (M+ꢀW(CO)4+1). Anal. Calc. for
C31H27FeN2O6PW: C, 46.85; H, 3.40; N, 3.53. Found: C, 46.32; H,
3.66; N, 3.33%.
2.6. [(g l
4-BuC5H5)Fe(CO)2( -P:N,N0N00-PPy3)Mo(CO)3] 12a
Compound 5 (0.20 g, 0.40 mmol) and 6a (0.20 g, 0.58 mmol)
were completely dissolved in dry THF (20 mL). The mixture turned
purple immediately. The reaction was left for 1 h before being fil-
tered under nitrogen through a pad of dry celite and washed with
dry ether until colourless. The solvent was removed under vacuum,
resulting in a dark purple solid, which was dissolved in a small
quantity of CH2C12 and mixed completely with a small quantity
of alumina. The CH2C12 was removed under vacuum. The residue
was packed on top of an alumina column and then eluted with a
Compound 7a: yield: 0.33 g, 81%; mp: 111 °C (dec.); IR (CH2Cl2)
mCO 2016 (m), 1927 (vs), 1896 (s), 1879 (sh), 1830 (s) cmꢀ1 31P
;
NMR (CDCl3) d 86.12 (s); 1H NMR (CDCl3) d 9.25 (b, 1H, Py),
6.93–7.68 (m, 13H, Ph and Py), 4.75, 4.66, 4.41, 4.30 (4 ꢂ b,
4 ꢂ 1H, Cp), 0.87–2.42 (m, 9H, Bu), ꢀ16.46 (d, 1H,
l-H,
2JPH = 56 Hz); MS m/z 678 (M++1). Anal. Calc. for C31H28FeMoNO5P:
C, 54.95; H, 4.14; N, 2.07. Found: C, 55.24; H, 4.85; N 1.77%.
2.3. [(
g
5-BuC5H4)Fe(CO)(
l-P:N-PPh2Py)(l-H)W(CO)4] 7b
3:1 EtOAc/n-hexane mixture. A deep purple solid 12a was
collected.
Compound 3 (0.30 g, 0.60 mmol) and 6b (0.30 g, 0.69 mmol)
were dissolved in dry THF (30 mL). The procedure is similar to that
of the reaction of the molybdenum analogue except that the puri-
fication was carried out using a silica gel column. The orange solid
was dissolved in a small quantity of CH2C12 and mixed well with a
small quantity of silica gel before being packed on top of a silica gel
column, and then eluted with a EtOAc/n-hexane mixture. The or-
ange powder of 7b was collected after solvent removal under
vacuum.
Compound 12a: yield: 0.26 g, 96%; mp: 158 °C (dec.); IR
(CH2C12) mCO 1981 (m), 1924 (m), 1905 (vs), 1788 (s, b) cmꢀ1
;
31P NMR (CDC13) d 75.4 (s); 1H NMR (CDC13) d 9.47 (b, 3H), 8.48
(b, 3H), 7.85 (b, 3H), 7.20 (b, 3H) for pyridine, 5.35 (b, 2H, –
CH@CHCHBu–), 3.27 (b, 2H, –CH@CHCHBu–), 3.04 (b, 1H, –
CH@CHCHBu–), 0.83–1.15 (m, 9H, Bu), MS m/z 498 (M+ꢀMo(CO)3).
Anal. Calc. C29H25FeMoN3O5P: C, 51.33; H, 3.69; N, 6.19. Found: C,
50.38; H, 3.95; N, 5.73%.
Compound 7b: yield: 0.35 g, 76%, mp: 120 °C (dec.); IR (CH2C12)
2.7. [(g l
4-BuC5H5)Fe(CO)2( -P:N,N0N00-PPy3)W(CO)3] 12b
mCO 2009 (m), 1927 (s) 1886 (vs, b), 1827 (s) cmꢀ1 31P NMR
;
(CDC13) d 88.6 (s); 1H NMR (CDC13) d 9.38 (b, 1H, Py), 6.90–7.48
Compound 5 (0.20 g, 0.40 mmol) and 6b (0.20 g, 0.46 mmol)
were dissolved in dry THF (10 mL). Again the mixture immediately
changed to purple colour. The reaction was then left for 2 h. Other
procedure and work-up were similar to those used in the molybde-
num analogue.
(m, 13H, Ph and Py), 4.77, 4.72, 4.51, 4.31 (4 ꢂ b, 4 ꢂ 1H, Cp),
2
0.87–2.63 (m, 9H, Bu), ꢀ14.21 (d, 1H,
l
-H, JPH = 54 Hz); MS m/z
766 (M++1). Anal. Calc. C31H28FeNO5PW: C, 48.63; H, 3.66; N,
1.83. Found: C, 48.78; H, 3.98; N, 1.75%.
Compound 12b: yield: 0.24 g, 78%; mp: 165 °C (dec.); IR
2.4. [(
g
4-BuC5H5)Fe(CO)2(
l
-P:N,N0-PPhPy2)Mo(CO)4] 10a
(CH2C12) mCO 1982 (m), 1926 (s), 1895 (vs), 1782 (s, b) cmꢀ1 31P
;
NMR (CDC13) d 77.2 (s); 1H NMR (CDC13) d 9.48 (b, 3H) 8.50
(b, 3H), 7.88 (b, 3H), 7.15 (b, 3H) for pyridine, 5.38 (b, 2H,
–CH@CHCHBu–), 3.31 (b, 2H, –CH@CHCHBu–), 3.06 (b, 1H,
–CH@CHCHBu–), 0.82–1.24 (m, 9H, Bu); MS m/z 498 (M+ꢀW(CO)3).
Anal. Calc. for C29H25FeN3O5PW: C, 45.43; H, 3.26; N, 5.43. Found:
C, 44.98; H, 3.63; N, 5.00%.
Compound 4 (0.10 g, 0.20 mmol) and 9a (0.10 g, 0.31 mmol)
were completely dissolved in dry THF (10 mL). The colour changed
to blood red immediately. The mixture was allowed to stir for 1.5 h
before filtration over a bed of dry celite under nitrogen. The solvent
was removed under vacuum and the red solid re-crystallized twice

O.G. Adeyemi, L.-K. Liu / Inorganica Chimica Acta 362 (2009) 477–482
479
complexes (3, n = 1, 68%; 4, n = 2, 72%; 5, n = 3, 74%). The chemistry
followed the same pathway as in the PPh3 case [3].
3. Results and discussion
Scheme 1 shows the two stages in the three-component prepa-
ration of compounds 2–5. The first drop of n-BuLi acted as a reduc-
ing agent [9] to initiate an electron-transfer chain catalysis [10] of
the replacement of iodide on 1 by PPh3ꢀnPyn with the P-donor
3.1. Preparation of arylpyridylphosphine ligands
The preparation of PPh3ꢀnPyn (n = 1–3) followed the literature
procedures but with a slight local modification [8a,8b,8c]. In our
own experience, the preparation of PPhPy2 gave a yield of 19.7%
when the Grignard reagent on the pyridyl side is used for coupling
with PPhCl2. The preparation of PPhPy2 gave a much better yield of
54.5% by using the Li–Br exchange reaction between n-BuLi and o-
C5H4NBr, then the coupling reaction with PPhC12. The preparation
of PPh3ꢀnPyn (n = 1–3) in the present study involved the n-BuLi
route and the yields were satisfactory (PPh2Py, 82%; PPhPy2, 55%;
PPy3, 62%). Pure PPy3 was stored in the dry box in order to avoid
oxidation of the phosphine to Py3P@O.
mode. The cation [(
instantaneously obtained in this reaction [11]. The stoichiometric
n-BuLi then acts as a normal nucleophile to add on to the (g5
C5H5)-ring [12,13]. The electron rich (
5-C5H5)-ring of neutral 1
did not react with the electron rich [Buꢀ] anion in an ordinary
way. In its cationic form, the (
5-C5H5)-ring is more likely acti-
vated as a Lewis-acid. [(
5-C5H5)Fe(CO)2(PPh3ꢀnPyn)+] is much
more electrophilic towards [Buꢀ] and the addition of [Buꢀ] anion
on the (
5-C5H5)-ring is favoured [3].
g
5-C5H5)Fe(CO)2(PPh3ꢀnPyn)+] (n = 0–4) is
-
g
g
g
g
3.2. (g
4-BuC5H5)Fe(CO)2(PPh3ꢀnPyn) complexes
3.3. Heterodimetallic complexes
In the main synthetic routes to organo-transition metal hy-
drides, the intramolecular oxidative addition is a key to the facile
The arylpyridylphosphine ligands were reacted with a stoichi-
ometric amount of (
5-C5H5)Fe(CO)2I (1) and a slight excess
amount of n-BuLi, using the same conditions as those used in the
preparation of (
4-BuC5H5)Fe(CO)2(PPh3) (2) [3]. With one basic
g
loss of hydrogen, for example, in (
with an intermediate formation of (
yield (
5-C5H5)Fe(CO)2]2 [14]. Yet, it is possible to independently
synthesize
5-C5H5)Fe(CO)2H from the acidification of
g
4-C5H6)Fe(CO)3 which proceeds
g
5-C5H5)Fe(CO)2H, to finally
g
g
N-atom in each pendant pyridine, the arylpyridylphosphines re-
(g
( -
g5
acted smoothly in the three-component reaction and gave simi-
larly (g
4-BuC5H5)Fe(CO)2(PPh 3ꢀnPyn) in good yields of relevant
C5H5)Fe(CO)2Na. In the literature, it was not synthesized directly
Bu
H
I-
n-BuLi
cat n-BuLi
+
+
Fe
PR3
Fe
-78 oC
-78 oC to RT
Fe
OC
I
OC
PR3
OC
-LiI
PR3
CO
1
CO
CO
PR3
PPh3
2
3
4
5
(83%)
(68%)
(72%)
(74%)
PPh2Py
PPhPy2
PPy3
Scheme 1.
Bu
H
Bu
-3L
L
CO
CO
N
CO
CO
L
H
Fe
Fe
M
N
M
P
+
OC
Ph2
OC
OC
CO
L
CO
Ph2P
CO
M = Mo 6a
7a, b
W
6b
-3L
L = CH3CH2CN
Bu
Bu
Bu
H
CO
M
CO
CO
H
CO
CO
CO
CO
CO
CO
H
Fe
Ph2P
Fe
Fe
M
N
M
N
CO
OC
OC
OC
OC
OC
Ph2P
Ph2P
N
Scheme 2.

480
O.G. Adeyemi, L.-K. Liu / Inorganica Chimica Acta 362 (2009) 477–482
from (g
4-C5H6)Fe(CO)3 due to competing and/or consecutive reac-
and W) [16] was assigned as intramolecularly converted from the
tions [15].
We discuss below a clean activation of the endo-C–H bond of 3
that was formally a (
4-cyclopentadiene)-Fe complex in PPh2Py
endo-H and the CO on Fe-centre, based on quantitative yield during
synthesis. The hydride remained un-changed with the deuterium
atoms of d-solvent when the reaction was performed in d8-THF.
It is pertinent to state that, crystal suitable for X-ray crystallogra-
phy for these compounds was attempted, but did not succeed.
Apparently in Scheme 2, it shows that, upon pyridyl N-atom
ligation to the second metal (M = Mo, W), this neighbouring metal
M induces an oxidative addition of the endo-C–H of cyclopentadi-
ene on the initial Fe-centre, by taking away a CO ligand from the
Fe-centre. Originally the Fe-centre in 3 is penta-coordinate. The
loss of CO to M-centre results in a tetra-coordinate Fe(0), ready
to activate the nearby endo C–H bond. Along the reaction coordi-
nate, Fe(0) then changes to a hexa-coordinate Fe(II). At a later
stage, the second metal M traps the newly formed Fe–H bond in
the form of ‘‘3c–2e” M–H–Fe structure. The relative conformation
with respect to Fe and M is not yet clear during the stage of the
pyridyl N-atom ligation or during the stage of the CO-migration.
The final conformation with respect to Fe and M is in a syn-form
in 7a,b.
g
derivative. When 3 is reacted with M(CO)3(EtCN)3 (M = Mo, 6a;
W, 6b) with the labile EtCN to be replaced by the pyridyl N-atom
and others, the result is the hydridobridged heterodimetallic com-
plex [(g l-P:N-PPh2Py)(l-H)M(CO)4] (M = Mo, 7a,
5-BuC5H4)Fe(CO)(
81%; W, 7b, 76%) with six-membered heterocyclic ring (Scheme 2).
The environments around Fe and M in 7a,b changed substan-
tially from the starting environments of 3 and 6a,b as shown by
the complete disappearance of all the original IR mCO bands: the
1966 (s) cmꢀ1 bands for the two CO ligands connected to Fe in 3,
the 1921 (s), 1801 (s) cmꢀ1 for the three CO ligands connected to
Mo in 6a, and the 1910 (s), 1793 (s) cmꢀ1 for the three CO ligands
connected to W in 6b. The 1H NMR data also indicated that the
2:1:2 integration ratios for the (
peared. Whereas a 4-peak, equal-intensity pattern characteristic
of a (
5-BuC5H4) connected to a chiral metal centre appeared (cf.
g
4-BuC5H5) fragment of 3 disap-
g
at d 4.75, 4.66, 4.41, 4.30 in 7a and at d 4.77, 4.72, 4.51, 4.31 in
2
7b). The doublet hydrides at d ꢀ16.5 with JPH = 56 Hz in 7a and
2
at d ꢀ14.2 with JPH = 54 Hz in 7b were observed in the 1H NMR
M
P
M
P
M'
N
spectra. The molecular structure of 7a,b was finalized on the basis
of a similar compound [(
-H)M(CO)4] (M = Mo and W) [16] that was prepared from 6a,b
and a [(
4-MeC5H5)Fe(CO)2( 1-PPh2CH2PPh2) with the dangling
g l
4-MeC5H4)Fe(CO)( -P:P0-PPh2CH2PPh2)-
(l
Ar
Ar
g
g
Ar
Ar
PPh2 working the same way as the present pyridyl N-atom. The
dppm analogue revealed very similar spectroscopic data in the IR
and 1H NMR spectra to those of 7a,b, especially those of the hy-
N
M'
syn-form
anti-form
Drawings of syn- and anti- forms
dride and (g
5-MeC5H4) ligands connected to a chiral metal centre.
Earlier, the origin of the hydride and additional CO on M-centre of
[(g
5-MeC5H4)Fe(CO)(
l
-P:P0-PPh2CH2PPh2)(
l-H)M(CO)4] (M = Mo
Bu
Bu
H
L
CO
CO
L
H
CO
CO
Fe
Fe
M
+
M
OC
OC
OC
CO
L
N
P
N
P
CO
OC
6a, b
N
N
4
8a, b
+CO (1 atm)
Bu
Bu
H
H
L
CO
L
CO
M
Fe
Fe
M
+
N
N
CO
CO
OC
OC
CO
OC
N
P
P
CO
OC
OC
M = Mo 9a
CO
W
9b
N
L = CH3CH2CN
4
10a, b
Scheme 3.

O.G. Adeyemi, L.-K. Liu / Inorganica Chimica Acta 362 (2009) 477–482
481
Bu
H
Bu
L
CO
CO
M
L
H
CO
CO
Fe
Fe
M
+
OC
OC
OC
CO
L
N
P
N
P
CO
OC
N
N
M = Mo 6a
W
6b
N
N
L = CH3CH2CN
5
11a, b
Bu
H
Fe
N
N
OC
P
M
OC
N
12a, b
Scheme 4.
With two pyridyl N-atoms, 4 gave no hydride formation when it
was reacted with 6a,b. There was no spectroscopic evidence to
support the structure [(
M(CO)4] (M = Mo, 8a; W, 8b) (Scheme 3).
of cyclopentadiene iron with one pyridyl N-atom and M(CO)3L3
(M = Mo, W; L = labile ligand). Yet, there is no hydride formation
g l-P:N-PPhPy2)(l-H)-
5-BuC5H4)Fe(CO)(
with complexes of more than one pyridyl N-atoms e.g. (g4
-
BuC5H5)Fe(CO)2(PPhPy2) and (g
4-BuC5H5)Fe(CO)2(PPy3). The CO
When 4 was treated with M(CO)4(EtCN)2 (M = Mo, 9a; W, 9b) as
transfer from Fe to M shown in Scheme 2 is more likely to be the
slow step than the pyridyl N-ligation to M, to the state, ready for
oxidative addition of Fe(0) in the reaction coordinate. Apparently,
in 4 and 5, extra pyridyl N-atom(s) are involved to mask the migra-
tion of CO ligand from Fe-centre to M-centre. Accordingly, these
two compounds do not exhibit an induced activation of the endo-
C–H bond of the cyclopentadiene on Fe-centre.
shown in Scheme 3, the N,N0-chelated heterodimetallic complex
was collected in high yield, i.e., [(g l
4-BuC5H5)Fe(CO)2( -P:N,N0-
PPhPy2)M(CO)4] (M = Mo, 10a, 81%; W, 10b, 83%) (C7H8Mo(CO)4
(C7H8 = bicyclo [2,2] hepta-2,5-diene) replacing 9a gave the same
result). Alternative route to the synthesis of 10a, b was achieved
when CO (1 atm) was bubbled into the solution of 4 and 6a,b to
produce variable yields of 10a,b.
The reaction of 5 and6a,b shown in Scheme 4, did not give com-
Acknowledgement
pound [(
11a; W, 11b), but the N,N0N00-coordinated heterodimetallic com-
plex [(
4-BuC5H5)Fe(CO)2( -P:N,N0,N00-PPy3)M(CO)3] (M = Mo,
12a, 96%; W, 12b, 78%).
The IR CO data for the two CO ligands connected to Fe exhibit a
g l-P:N-PPy3)(l-H)M(CO)4] (M = Mo,
5-BuC5H4)Fe(CO)(
Thanks are due to the National Science Council and Academia
Sinica for the kind financial support.
g
l
m
shift to higher wave numbers upon attachment of M(CO)3 to the
three pyridyl N-sites of PPy3, i.e., from 1969, 1909 cmꢀ1 in 5 to
1981, 1924 cmꢀ1 in 12a and 1982, 1926 cmꢀ1 in 12b. Upon attach-
ment of M(CO)4 to the two pyridyl N-sites of PPhPy2, similar shifts
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