A Heterometallic σ-Silane Adduct from Cooperative Reactivity of an Fe–Al Complex

Protonation of an Fe–Al heterometallic silanide complex with an alcohol led to selective formation of the corresponding σ-silane complex. This reaction does not require the use of a weakly coordinating anion, but rather the synergistic action of both metals of the heterometallic complex, with the electropositive Al site sequestering the alkoxide anion from the protonation, and the resulting silane coordinating directly to Fe. The new heterometallic silanide and σ-silane complexes have been characterised by standard techniques including multinuclear NMR and IR spectroscopy, along with X-ray crystallography. Bonding analysis using calculations (NBO, QTAIM, ETS-NOCV, IBO) suggest that the σ-silane complex possesses a non-classical structure involving not only the expected 3-centre,2-electron interaction with donation of electron density from the Si–H bond to Fe, but also a secondary interaction between a further hydride ligand on iron and the silicon centre. Competition and crossover experiments suggest that the protonation event may be controlled by an initial non-reversible coordination of the alcohol to the Lewis-acidic aluminium site of the heterometallic complex.