RhICl(cyclopentadienone) Complexes
Organometallics, Vol. 27, No. 22, 2008 5981
1
Figure 7. Aromatic region of the H NMR spectra of complex 4
in CD2Cl2 at 8.7 mM (a), in CD2Cl2 at 51.4 mM (b), and in CD3CN
at 15.9 mM (c).
Figure 5. Molecular structure of complex 7 in the crystal. The
cocrystallized solvent molecules (3 CH3CN) and the hydrogen
atoms, except those involved in secondary interactions, are not
shown for clarity. The thermal ellipsoids are set at 50% probability.
crystallizes as a tetramer is evidence that higher aggregates than
trimers are also possible. We assume that the tetramer is formed
at the very high concentrations that are present during the
crystallization process.
1
The H NMR spectra of complex 1 in CD3CN were very
broad and showed strong concentration dependence (Figure
6c,d). This suggests that dynamic aggregates of different size
are present in solution. These aggregates may consist of chloro-
bridged dimers such as 6 or salts such as 7, but the quality of
the NMR data impeded further conclusions.
For CD2Cl2 solutions of the new complex 4, the situation
was similar to what has been observed for 1. At low concentra-
tions, a single set of signals was observed, but a second complex
was formed at higher concentrations, accompanied by peak
broadening (Figure 7a,b). In CD3CN, however, complex 4 gave
very distinct spectra compared to what had been observed for
1
complex 1. The H NMR spectra showed a single set of sharp
1
signals, and the spectra were not concentration dependent
(Figure 7c). From the NMR spectra, it can be concluded that a
single species is present in acetonitrile. This is likely the dimer
6, which was characterized crystallographically.
The naphthyl-substituted complex 3 and the phencyclone
complex 5 were only sparingly soluble in dichloromethane and
acetonitrile. NMR studies with variable concentrations were
therefore not performed.
Figure 6. Aromatic region of the H NMR spectra of complex 1
in CD2Cl2 at 0.2 mM (a), in CD2Cl2 at 7.1 mM (b), in CD3CN at
0.9 mM (c), and in CD3CN at 8.0 mM (d).
(2.45914 or 2.45815 Å). As for 1, 4, and 5, intramolecular
hydrogen bonds between the ortho-hydrogens of the phenyl rings
and the bridging chloro ligands are observed (Cl1 · · · H54 )
2.75, Cl3 · · · H52 ) 2.69 Å).
To obtain additional information about the structures in
solution, we have recorded NMR spectra at variable concentra-
tions in different solvents. First, we investigated the known
complex 1, for which molecular weight measurements in
chloroform had predicted a dimeric structure. In CD2Cl2 at a
concentration of [RhCl(C4Ph4CO)] ) 0.2 mM, we observed a
single set of signals in the 1H NMR spectrum (Figure 6a). When
the concentration was increased to 7.1 mM, however, peaks of
a new species were clearly visible (Figure 6b). The relative
amount of this new species was determined by integration of
selected signals for a series of 1H NMR spectra at concentrations
between 2.38 and 14.15 mM of Rh. These data could best be
fitted to a dimer-trimer equilibrium. We therefore conclude
that complex 1 exists in dichloromethane at low concentrations
predominantly as a dimer, but at concentrations >1 mM there
are significant amounts of a trimeric species. The latter has likely
a structure that is similar to what has been observed for
complexes 4 and 5 in the solid state. The fact that complex 1
Conclusion
RuII complexes with cyclopentadienone ligands have been
used extensively as catalysts for organic transformations.16 The
chemistry of RhI complexes with cyclopentadienone ligands is
less developed, but recent results demonstrate that interesting
catalytic transformations can be observed as well.5,6 The present
study was performed to obtain more information about the key
starting materials for this type of chemistry. Although RhI
-
Cl(cyclopentadienone) complexes have been known since 1965,
structural data were so far not available. We demonstrate that
from noncoordinating solvents these complexes can crystallize
as trimers or tetramers, in which the RhICl(cyclopentadienone)
fragments aggregate via Rh-(µ-Cl) and Rh-(µ-OC) bonds. In
CD2Cl2 solution, they form dynamic equilibria with dimers. A
driving force for the formation of higher aggregates is the
(16) For selected references see: (a) Haak, E. Eur. J. Org. Chem. 2007,
2815–2824. (b) Hollmann, D.; Ba¨hn, S.; Tillack, A.; Beller, M. Angew.
Chem., Int. Ed. 2007, 46, 8291–8294. (c) Karvembu, R.; Prabhakaran, R.;
Natarajan, K. Coord. Chem. ReV. 2005, 249, 911–918. (d) Pa`mies, O.;
Ba¨ckvall, J.-E. Chem. ReV. 2003, 103, 3247–3262. (e) Menashe, N.; Shvo,
Y. Organometallics 1991, 10, 3885–3891. (f) Shvo, Y.; Czarkie, D. J.
Organomet. Chem. 1989, 368, 357–365.
(13) Ohta, K.; Hashimoto, M.; Takahashi, Y.; Hikichi, S.; Akita, M.;
Moro-oka, Y. Organometallics 1999, 18, 3234–3240.
(14) Han, W. S.; Lee, S. W. J. Organomet. Chem. 2003, 678, 102–107.
(15) Gauthier, S.; Quebatte, L.; Scopelliti, R.; Severin, K. Inorg. Chem.
Commun. 2004, 7, 708–712.
Rechavi, Dalit
