34
S. El-Tarhuni et al. / Journal of Organometallic Chemistry 752 (2014) 30e36
reaction filtrate followed by recrystallisation from CH2Cl2/dieth-
halide bond in [MoX(dppe)(
h
7-C7H7)] (X ¼ I, Br) towards halogen
ylether, contains several impurities, not observed in the analogous
exchange with chlorinated solvents has been investigated by 31P
preparation of the Br derivative. Thus analysis of the sample by 31
P
{1H} NMR spectroscopy. The bromide derivative [MoBr(dppe)(h7
C7H7)] has been shown to react with dichloromethane to give
[MoCl(dppe)(
7-C7H7)] both on alumina and on prolonged contact
-
{1H} NMR in CD2Cl2 reveals the presence of [MoCl(dppe)( 7-C7H7)]
h
(ca. 70%), [Mo(CO)4(dppe)] (ca. 3%), dppe (ca. 20%), and further
impurities with 31P resonances at 40.6 ppm and 31.5 ppm (see
Supplementary data). Almost identical results were obtained with a
repeated preparation. However effective separation of [MoCl(dp-
h
with dichloromethane in solution.
The direct thermal substitution reaction of [MoBr(CO)2(h
7-C7H7)]
with dppe provides a convenient and large scale preparation of
pe)(h
7-C7H7)] from all the above reaction by-products was ach-
[MoBr(dppe)(
h
7-C7H7)] provided that contamination of the product
ieved by column chromatography on alumina, Brockmann grade II
with small quantities of the by-product [Mo(CO)4(dppe)] can be
accepted; in practice many of the subsequent reactions of
(see experimental and supplementary 31P{1H} NMR data) leading
to isolation of [MoCl(dppe)(
h
7-C7H7)]$CH2Cl2 as a green, dichloro-
[MoBr(dppe)(h
7-C7H7)] lead to cationic products which are readily
methane solvate [20b]. Overall, the preparation of [MoCl(dppe)(h7
-
separated from [Mo(CO)4(dppe)]. However, in cases where
contamination by [Mo(CO)4(dppe)] is an issue, further purification
by chromatography is required with attendant complications arising
from halide exchange. Under these circumstances, preparation of the
C7H7)] proceeds in much lower yield than for the bromide analogue
but it offers the advantage that halide exchange resulting from the
chromatographic procedure does not affect the identity of the final
isolated product.
chloride derivative [MoCl(dppe)(h
7-C7H7)]$CH2Cl2 is recommended
with the qualification that much lower overall yields are obtained.
2.5. Effect of halide X (I, Br, Cl) on reaction product distribution
4. Experimental
The successful preparation of the chloride derivative
[MoCl(dppe)(
ing from [MoCl(CO)2(
h
7-C7H7)] in a thermally initiated substitution start-
4.1. General procedures
h
7-C7H7)] contrasts with the analogous
cyclopentadienyl iron system for which direct thermal reaction of
[FeCl(CO)2Cp] with dppe affords almost exclusively [Fe(CO)(dppe)
Cp]Cl [16]. This observation prompted a further investigation of the
effect of the identity of the halide X (X ¼ I, Br, Cl) on the reaction
The preparation, purification and reactions of the complexes
described were carried out under dry nitrogen. All solvents were
dried by standard methods, distilled and deoxygenated before use.
The complex [{Fe(CO)2Cp}2] was purchased from Sigma Aldrich and
between [MoX(CO)2(
h
7-C7H7)] and dppe for comparison with the
[MoBr(CO)2(dppe)(h
3-C7H7)] was prepared by a published proce-
analogous substitution chemistry of [FeX(CO)2Cp]. When the iodide
dure [25]. Preparative column chromatography was carried out on
Brockmann Grade II aluminium oxide purchased from Alfa Aesar.
NMR spectra were recorded on a Bruker Avance 400 (400 MHz 1H,
162 MHz 31P{1H}) spectrometer. Infrared spectra were obtained on
a Perkin Elmer FT RX1 spectrometer and MALDI mass spectra were
recorded using a Micromass/Waters TOF Spec 2E instrument. Mi-
croanalyses were conducted by the staff of the Microanalytical
Service of the School of Chemistry, University of Manchester.
derivative [MoI(CO)2(
h
7-C7H7)] was treated dropwise with dppe in
refluxing toluene under identical conditions to those described for
bromide and chloride analogues, the isolated product distribution
between [MoI(dppe)(h -
7-C7H7)] (50%) and [Mo(CO)(dppe)(h7
C7H7)]I (42%) suggests only a limited dependence upon the identity
of the halide, in sharp contrast to the corresponding cyclo-
pentadienyl iron chemistry. In common with the bromide deriva-
tive, the iodide complex [MoI(dppe)(h
7-C7H7)] is labile to halide
exchange in chlorinated solvents and 31P{1H} NMR studies in
CD2Cl2/Cp2Co revealed approximately 50% conversion to
4.1.1. Preparation of [FeI(CO)2Cp], 1
A mixture of [{Fe(CO)2Cp}2] (3.00 g, 8.47 mmol) and I2 (2.36 g,
9.29 mmol) in CHCl3 (40 cm3) was refluxed with stirring for 1 h to
give a deep purple solution. Addition of hexane and reduction of
solvent volume in vacuo resulted in precipitation of the crude
product. Recrystallisation from CH2Cl2/hexane gave the product as
[MoCl(dppe)(h
7-C7H7)] after 12 h.
3. Conclusions
Multi-gram quantities of [FeI(dppe)Cp], 3 can be prepared in a
convenient two step thermal synthesis, starting from commercially
available [{Fe(CO)2Cp}2] and via the intermediate [FeI(CO)2Cp]. The
need for an aqueous work up procedure for [FeI(CO)2Cp] and sub-
sequent photochemical activation to effect CO substitution has
been avoided. The analogous thermal substitution process for the
synthesis of the cycloheptatrienyl molybdenum complexes
a black solid, yield 3.22 g (63%). IR (CH2Cl2) (
n
(CO)/cmꢀ1): 2039,
1995. 1H NMR (CDCl3), (
d, ppm): 4.99, s (Cp). Anal. Calcd. (%) for
C7H5O2FeI: C, 27.6%; H, 1.6%. Found, C, 27.4%; H, 1.9%
4.1.2. Preparation of [FeI(dppe)Cp], 3
In a three necked flask [FeI(CO)2Cp] (2.50 g, 8.23 mmol) was
dissolved in toluene (60 cm3) and the solution brought to gentle
reflux. Then a solution of dppe (3.275 g, 8.23 mmol) dissolved in
toluene (40 cm3), was added dropwise to the stirred reaction
mixture over a period of one hour. After addition was complete,
reflux was continued for a further 18 h then the reaction mixture
was filtered hot to remove the by-product [Fe(CO)(dppe)Cp]I and
the filtrate reduced to dryness in vacuo. The residue was recrys-
tallised from CH2Cl2/diethylether to give the product as a black
[MoX(dppe)(
h
7-C7H7)] (X ¼ halide) is complicated by the operation
of two alternative pathways in the reaction of [MoX(CO)2(h
7-C7H7)]
with dppe. Where X ¼ Br, the associative process, which proceeds
via the intermediacy of ring slipped [MoBr(CO)2(dppe)(
3-C7H7)],
leads to formation of [Mo(CO)(dppe)(
7-C7H7)]Br as the principal
h
h
product. Conditions designed to promote a dissociative process
(dropwise addition of dppe to a refluxing solution of [MoX(-
CO)2(
and assist generation of [MoX(dppe)(
[Mo(CO)(dppe)(
7-C7H7)]X and [Mo(CO)4(dppe)] are still signifi-
cant reaction by-products. The isolated yield of [MoX(dppe)(h7
h
7-C7H7)]) suppress formation of [Mo(CO)(dppe)(
h
7-C7H7)]X
solid, yield 2.53 g (48%). 1H NMR (CD2Cl2/Cp2Co) (
7.05, 20H, m (Ph, dppe); 4.09, 5H, s (Cp); 2.56, 4H, m (CH2, dppe).
31P{1H} NMR (CD2Cl2/Cp2Co), (
, ppm) 97.9. Anal. Calcd. (%) for
31H29P2FeI: C, 57.6%; H, 4.5%. Found, C, 56.8%; H, 4.2%.
d, ppm): 7.94e
h
7-C7H7)] although
h
d
-
C
C7H7)] is not significantly dependent upon the identity of X in
contrast to the analogous chemistry of the cyclopentadienyl iron
system where preferential formation of [FeX(dppe)Cp] over
[Fe(CO)(dppe)Cp]X is promoted by X ¼ I. The lability of the metal-
4.1.3. Thermolysis of [MoBr(CO)2(dppe)(
h
3-C7H7)], 5
red solution of [MoBr(CO)2(dppe)(
3-C7H7)] (1.62 g,
2.25 mmol) in toluene (80 cm3) was refluxed for 18 h to give a
A
h