3696 Organometallics, Vol. 19, No. 18, 2000
Hung et al.
metrical coordination of the metal fragment with the
six-membered ring of indene or indenyl ligand have also
been observed in other complexes, but in these com-
plexes, the bond distances between the metal and the
two bridgehead carbon atoms are significantly longer
than those between the former and the other four carbon
atoms of the ring; that is, the metal shows slippage
toward η4-coordination to the six-membered ring.14 The
P(1)-Ru-P(2) angle (89.28(2)°), which is much larger
than that of 1 (71.27(2)°), is in consonance with the well-
known phenomenon that P-M-P angles in three-legged
piano-stool complexes with larger chelating diphos-
phines are much larger than the corresponding angles
in similar complexes containing the dppm ligand.
In the protonation reactions of indenyl complexes 1-4
at -60 °C, the initial products are η2-dihydrogen
complex, dihydride, or mixtures of both. Products of
direct proton attack at the indenyl ligand have never
been observed in our studies, although it is also a
potential site of proton attachment. However, in warm-
ing the solutions to room temperature, the initial
products 5-8 are converted to the η6-indene hydride
complexes 9-12 via η5 f η6 haptotropic rearrangement.
Such rearrangement is a combination of proton transfer
from the metal fragment to an endo position of the
indenyl ligand and migration of the former from the five-
membered ring of indene to the six-membered one.
Migration of the metal fragment from one ring to the
other in indene has been studied by extended Hu¨ckel
methods. It has been shown that the most favored
pathway involves migration via the periphery of the
rings, not the one across the center of the bond shared
by two rings.17
Discu ssion
Protonation of indenyl ruthenium complexes of the
formula [(η5-C9H7)Ru(L2)(H)] can, in principle, occur at
a variety of sites; oxidative addition of a proton to the
metal center generates the dihydride complex, while
proton attack at the hydride ligand leads to the forma-
tion of the nonclassical dihydrogen complex,15 and
finally if the site of proton attack is the indenyl ligand,
the η6-indene complex [(η6-C9H8)Ru(L2)(H)]+ would be
formed after the metal fragment migrates from the five-
membered ring to the six-membered ring of the indene
ligand. This kind of indenyl protonation and subsequent
hapotropic migration has been observed in protonation
of the η5-indenyl manganese complex (η5-C9H7)Mn-
(CO)3.1d
The protonation reactions of related ruthenium cy-
clopentadienyl hydride complexes (η5-C5R5)Ru(L)(L′)H
have been extensively studied, but those of the indenyl
analogues have been rarely reported. Previous studies
have shown that, depending on the nature of the
ligands, the compositions of the final protonation prod-
ucts at ambient temperatures may adopt the dihydrogen
form [(η5-C5R5)Ru(L)(L′)(H2)]+ or the dihydride form
trans-[(η5-C5R5)Ru(L)(L′)(H)2]+, or a mixture of both.2
The initial protonation products may, however, be quite
different from the final thermodynamic ones. Chinn and
Heinekey have studied the protonation of a series of
ruthenium complexes of the types Cp*Ru(L)(L′)H and
CpRu(L)(L′)H at 195 K and have found out in every case
that the kinetic product is the dihydrogen complex, but
an intramolecular isomerization occurs to give variable
amounts of the transoid dihydride form in equilibrium.
For example, protonation of Cp′Ru(PPh3)2H (Cp′ ) Cp,
Cp*) at 195 K led to exclusive formation of the dihy-
drogen complexes [Cp′Ru(PPh3)2(H2)]+, and isomeriza-
tion to the transoid dihydride was observed for [CpRu-
(PPh3)2(H2)]+ and [Cp*Ru(PPh3)2(H2)]+ at 222 and 253
K, respectively, and proceeded to completion upon
warming to ambient temperature.16
The proton transfer from the metal fragment to the
indenyl ligand may go through the dihydrogen inter-
mediate or the dihydride intermediate. In the hapto-
tropic rearrangement of [(η5-C9H7)Ru(dppm)(H2)]CF3-
SO3 (5), the proton is likely transferred to the indenyl
ligand directly from the η2-H2 ligand, although transfer
from transient dihydride intermediate could not be
completely excluded. Proton transfers from the η2-H2
ligand to other intramolecular organic ligands have been
reported. For instance, transfer of a proton from the η2-
H2 ligand to the R-carbon of alkyl or vinyl ligands has
been invoked to explain the catalytic activity of [Fe(PP3)-
19
(H2)H]+ (PP3 ) P(CH2CH2PPh2)318 and RuHCl(PPh3)3
in hydrogenation of olefins and acetylenes. A σ-bond
metathesis reaction between η2-H2 and the metal-alkyl
bond has also been proposed for the reactions of some
d0 alkyl complexes with H2 to give hydride complexes
and alkanes.20 In the course of η5 f η6 haptotropic
rearrangement, no isomerization of the dihydrogen
complex [(η5-C9H7)Ru(dppm)(H2)]CF3SO3 (5) to the di-
hydride tautomer has been observed by NMR spectros-
copy. It is known that the Cp analogue of 5 does not
undergo isomerization at ambient temperature too.21
In the η5 f η6 haptotropic rearrangement of [(η5-
C9H7)Ru(PPh3)2(H)2]CF3SO3 (8), the proton is likely
transferred from one of the hydride ligands, as we have
not detected any intermediate.
The initial products of protonation of both the dppe
complex 2 and dppp complex 3 are mixtures of η2-
dihydrogen complexes and their dihydride tautomers.
In both cases, the former isomerizes to the latter with
increasing temperatures (Figure 1). But it can be seen
from Figure 1a that at 238 K a third hydride signal,
which is assignable to the η6-indene complex [(η6-
C9H8)Ru(dppe)H]CF3SO3 (10), becomes visible, and this
triplet increases in intensity at the expense of the
(14) (a) Stradiotto, M.; Hazendonk, P.; Bain, A. D.; Brook, M. A.;
McGlinchey, M. J . Organometallics 2000, 19, 590. (b) Bonifaci, C.;
Ceccon, A.; Gambaro, A.; Ganis, P.; Santi, S.; Valle, G.; Venzo, A.
Organometallics 1993, 12, 4211. (c) Bonifaci, C.; Ceccon, A.; Gambaro,
A.; Ganis, P.; Santi, S.; Valle, G.; Venzo, A. J . Organomet. Chem. 1995,
492, 35. (d) Kudinov, A. R.; Petrovskii, P. V.; Struchkov, Yu. T.;
Yanovskii, A. I.; Rybinskaya, M. I. J . Organomet. Chem. 1991, 421,
91.
(15) (a) J essop, P. G.; Morris, R. H. Coord. Chem. Rev.1992, 121,
155. (b) Heinekey, D. M.; Oldham, W. J ., J r. Chem. Rev. 1993, 93, 913.
(16) Chinn, M. S.; Heinekey, D. M. J . Am. Chem. Soc. 1990, 112,
5166.
(17) (a) Albright, T. A.; Hofmann, P.; Hoffmann, R.; Lillya, C. P.;
Dobosh, P. A. J . Am. Chem. Soc. 1983, 105, 3396. (b) Silvestre, J .;
Albright, T. A. J . Am. Chem. Soc. 1985, 107, 6829.
(18) Bianchini, C.; Meli, A.; Peruzzini, M.; Frediani, P.; Bohanna,
C.; Esteruelas, M. A.; Oro, L. A. Organometallics 1992, 11, 138.
(19) Crabtree, R. H. The Organometallic Chemistry of The Transition
Metals, 2nd ed.; J ohn Wiley & Sons: New York, 1994; p 221.
(20) Ziegler, T.; Folga, E.; Berces, A. J . Am. Chem. Soc. 1993, 115,
636, and references therein.
(21) Conroy-Lewis, F. J .; Simpson, S. J . J . Chem. Soc., Chem.
Commun. 1987, 1675.
Hung, Mei Yuen
