Organometallics
COMMUNICATION
bridging hydrogen atoms and a RhÀH hydride ligand, respectively.
This 1H pattern is diagnostic of cationic {RhSB9H10(NC5H5)}+ vs
a neutral {RhSB9H9(NC5H5)} cage. The 19F{1H} spectrum of 6
exhibits a signal at δ(19F) À79.8 ppm typical of a noncoordinated
OTfÀ anion, supporting the existence of the polyhedral triflate salt
in solution. The 31P{1H} spectrum reveals two doublets of doub-
lets, in agreement with the proposed asymmetric structure of
the polyhedral cation in 6. The growth of monocrystals of the salt
6 has been elusive in our hands, prompting us to calculate the
structure and the nuclear magnetic chemical shielding properties.
The 11B chemical shifts calculated for the cation in 6 reproduce
the experimental trend and show a reasonable agreement
(Table S1). Boron nuclear shielding properties calculated via
the GIAO approach are a reasonable measure of the validity
of the calculated structures of polyhedral boron-contain-
ing compounds; therefore, the DFT-calculated structure of
the rhodathiaborane cation in 6 can be regarded as a good
model (Figure 3).
In summary, the 11-vertex rhodathiaboranes 1À3 react
cleanly with Brønsted acids. The reactivity of the clusters varies
with the rhodium-bound exo-polyhedral ligands and the nature
of the acid. With HCl, the 11-vertex closo derivatives 2 and 3
undergo structural transformation to the nido form and con-
comitant heterolytic addition of the acid to the cluster, yielding
the (11 + 1)-SEP unsaturated cluster 4 and the (11 + 2)-SEP
saturated cluster 5, respectively. The reactivity of the nido-
hydridorhodathiaborane 1 depends on the acid, affording the
chloro-ligated cluster 4 with HCl or the salt 6, formed by simple
protonation of 1, with triflic acid. The results delineate further
the bifunctional acid/base nature of these 11-vertex rhodathia-
boranes, which can also promote the heterolytic cleavage of H2.9
Given their distinctive electronic structure and their dramatic
structural and electronic responses to Brønsted acids, these
clusters represent a unique system with nido to closo redox
flexibility that enables the activation of small molecules. Their
easy preparation, stability, and potential facile functionalization
via, for example, chlorine abstraction or ligand substitutional
chemistry make this new series of compounds attractive for
potential catalytic applications. We are presently exploring the
reactions of these complexes with different unsaturated organic
molecules and evaluating their catalytic activity.
Aragꢀon” for a predoctoral scholarship and ESRF BM16 beamline
staff for their support on data acquisition of 5.
’ DEDICATION
Dedicated to the memory of an outstanding and creative scientist,
Prof. F. Gordon A. Stone, Doctor Honoris Causa by the University
of Zaragoza. He has been a superb mentor of a number of Spanish
scientists working on organometallic chemistry.
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’ ASSOCIATED CONTENT
(20) Calvo, B.; Kess, M.; Macias, R.; Cunchillos, C.; Lahoz, F. J.;
Kennedy, J. D.; Oro, L. A. Dalton Trans. 2011, 40, 6555–6564.
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S
Supporting Information. CIF files giving crystallographic
b
data for 4 and 5 and text, tables, and figures giving experimental and
DFT-calculated NMR data for 4À6 and DFT-calculated coordi-
nates for 6. This material is available free of charge via the Internet at
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: rmacias@unizar.es (R.M.); oro@unizar.es (L.A.O.).
’ ACKNOWLEDGMENT
We acknowledge the Spanish Ministry of Science and Innova-
tion (CTQ2009-10132, CONSOLIDER INGENIO, CSD2009-
00050, MULTICAT and CSD2006-0015, Crystallization Factory)
for support of this work. B.C. thanks the “Diputaciꢀon General de
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dx.doi.org/10.1021/om200707m |Organometallics 2012, 31, 2526–2529
Calvo, Beatriz
