Communication
Dalton Transactions
Acknowledgements
The Deutsche Forschungsgemeinschaft (DFG) is gratefully
acknowledged for funding part of this research. E. H. thanks
the DFG for a fellowship within the scheme HU 2512/1-1. We
gratefully acknowledge Niels Lefeld for performing the Raman
spectroscopy measurements. We thank Umicore (Hanau,
Germany) for a donation of precious metals.
Notes and references
Fig. 3 Selected compliance constants and coupling constants (in
italics) given in units of Å mdyn−1. Larger compliance constants indicate
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determined, which allows to unravel weak covalent and non-
covalent interactions (Fig. 3).20,21 As larger numerical values
are indicative of weaker bonds, the Si–Si bond in 1 is expect-
edly significantly stronger in 1 (0.679 Å mdyn−1) than in 2
(2.396 Å mdyn−1). However, the CSiSi value of 2 is not negligible
and indeed points to a weak Si⋯Si through space interaction.
The compliance coupling constants reveal substantial coupling
between the Si⋯Si fragment and the two Si–Rh fragments
giving rise to CSiSi/RhSi values of 0.309 Å mdyn−1 and 0.209 Å
mdyn−1, respectively. Inclusion of London dispersion on the
compliance matrix leads to smaller compliance constants and
coupling constants by 6–16% indicating a slightly stronger
Si⋯Si interactions upon inclusion of London dispersion
(Fig. 3). Interestingly, the coupling constants between the two
Si–Rh fragments itself are negligible.
The mild oxidative addition of a strong unpolar Si–Si-bond
at rhodium(I) was studied experimentally using a proximity
enforcing ligand (PEL), namely, (5-Ph2P-Ace-6-SiMe2)2 (1). The
product of the oxidative addition, the spirocyclic rhodium(III)
complex (5-Ph2P-Ace-6-SiMe2)2RhCl (2) contains an acute Si–
Rh–Si angle (85.08(2)°) and a short Si⋯Si bond distance (3.123
(1) Å), which gives rise to a weak non-covalent interaction. Our
experimental results are comparable to those of Bourissou
et al. who studied the reactivity of 1,2-bis(o-diphenylphosphi-
nophenyl)-1,1,2,2-tetramethyldisilane towards coinage metals
salts.22 They observed a similar oxidative addition at gold(I) to
give a spirocyclic gold(III) complex, which also comprises an
acute Si–Au–Si angle (84.95(2)°), but a substantially longer
Si⋯Si distance (3.417(1) Å). While this distance still lies below
the van der Waals limit (approx. 4.40 Å), the question whether
or not this is still an interaction was not addressed in their
study.22
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15 R. W. F. Bader, Atoms in Molecules. A Quantum Theory,
Cambridge University Press, Oxford U.K., 1991.
Conflicts of interest
There are no conflicts to declare.
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