Photochemistry
FULL PAPER
tion of [Fe(CO) PPh
A
H
R
U
G
copy under 355 nm photolysis of [Fe (CO) ] and [Fe-
3
3
3
5
3
12
suggested that the reaction shown in Equation (5) is prefer-
red over reaction that in Equation (6), and this in turn sug-
gested that the detachment of CO [Eq. (2)] is more likely to
A
T
E
N
ous literature reports have indirectly pointed towards the
existence of this species by examining the nature of the final
products, its direct detection here lends good support to the
p-allyl mechanism operating for the isomerization of allyl al-
cohols as opposed to the metal–hydride addition–elimina-
occur than the detachment of PPh [Eq. (3)]. However, the
3
sensitivity of FTIR monitoring is not high enough to prove
the complete absence of these two reactions [Eqs. (3) and
[8,10]
(
6)].
At first it seems surprising that we observed the same two
vibrational bands attributed to [FeH(CO)3(C H OH)] in this
tion mechanism.
AHCTREUNG
3
4
phosphine-containing catalytic system. It appears that a
common iron allyl hydride species acts as the key intermedi-
ate in these two systems. The simplest explanation to ac-
Acknowledgements
T.S.C. thanks the Institute of Chemical Engineering and Sciences (ICES),
ASTAR Singapore for a research scholarship. This work is supported
under an NUS grant (143-000-210-112).
count for the formation of [FeH(CO) (C H OH)] is due to
A
H
R
U
G
3 3 4
the production of [Fe(CO) ] formed from a direct dissocia-
3
tion of two ligands (CO and PPh ) from [Fe(CO) PPh ],
3
4
3
since the photolysis of [Fe(CO) ] itself is also known to pro-
5
[1] J. C. Mitchener, M. S. Wrighton, J. Am. Chem. Soc. 1983, 105, 1065.
[2] J C. Mitchener, M. S. Wrighton, J. Am. Chem. Soc. 1981, 103, 975.
duce [Fe(CO) ]. If it were the major pathway, it would ex-
3
[
3] A. J. Ouderkirk, P. Wermer, N. L. Schultz, E. Weitz, J. Am. Chem.
Soc. 1983, 105, 3354.
plain the presence of the hydride species in this phosphine-
containing system as well.
However there is an alternate way to consider how the
[
[
4] N. Iranpoor, E. Mottaghinejad, J. Organomet. Chem. 1992, 423, 399.
5] D. B. Chase, F. J. Weigert, J. Am. Chem. Soc. 1981, 103, 977.
hydride species could be formed. Since [Fe(CO)4
was not detected in this system or is present only as a minor
component, the possibility of forming [FeH(CO) (C H OH)]
A
H
R
U
G
[6] V. Branchadell, C. Crevisy, R. Gree, Chem. Eur. J. 2003, 9, 2062.
[7] C. Crevisy, M. Wietrich, V. Le Boulaire, R. Uma, R. Gree, Tetrahe-
dron Lett. 2001, 42, 395.
3
5
AHCTREUNG
3
3
4
[
8] R. C. van der Drift, E. Bouwman, E. Drent, J. Organomet. Chem.
002, 650, 1 .
from [Fe(CO) (C H OH)] would have to be excluded
A
C
H
T
R
E
U
N
G
4 3 5
2
[
Eq. (9)]. The reaction shown in Equation (7), however, re-
mains a possible pathway for generating the hydride species,
since [Fe(CO) PPh (C H OH)] has been spectrally ob-
[
9] R. Uma, N. Gouault, C. Crevisy, R. Gree, Tetrahedron Lett. 2003,
44, 6187.
[
[
[
10] R. Uma, C. Crevisy, R. Gree, Chem. Rev. 2003, 103, 27.
11] H. Cherkaoui, M. Soufiaoui, R. Gree, Tetrahedron 2001, 57, 2379.
12] J. L. Graff, R. D. Sanner, M. S. Wrighton, Organometallics 1982, 1,
AHCTREUNG
3
3
3
5
served. The release of a bulky group like PPh instead of a
3
CO ligand upon photolysis is quite a common occurrence in
metal–phosphine systems as it places less constraint on
steric congestion upon intramolecular hydrogen migration.
We have shown that the p-allyl iron carbonyl hydride spe-
8
37.
[13] T. S Chong, P. Li, W. K. Leong, W. Y. Fan, J. Organomet. Chem.
2005, 690, 4132.
14] P. Portius, J. Yang, X. Sun, D. C. Grills, P. Matousek, A. W. Parker,
[
M. Towrie, M. W. George, J. Am. Chem. Soc. 2004, 126, 10713.
cies [FeH(CO) (C H OH)] is present and most probably
A
C
H
T
R
E
U
N
G
3 3 4
takes part in the catalytic cycle for all the three systems in-
vestigated here. It was detected directly using FTIR spectros-
Received: January 14, 2006
Published online: April 27, 2006
Chem. Eur. J. 2006, 12, 5128 – 5133
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
5133