Is the R3Si Moiety in Metal‐Silyl Complexes a Z ligand ? An Answer from the Interaction Energy

The computation of metal-silyl interaction energies indicates the existence of situations where the silyl group behaves as a Z-type ligand according to Green's covalent bond classification method. It is shown that a scale of relative intrinsic silylicity Π, defined as the ratio of the intrinsic silyl-to-triflate interaction energy of a silyltriflate taken as reference compound and that of the silyl-to-metal interaction of given complex, can reveal in a straightforward manner the propensity of SiR₃ groups to behave chemically as metal-bound "silyliums" [SiR₃]+. Emblematic cases of the literature, either taken from the Cambridge Structural Database or constructed for the purpose of this study, were also investigated under the lights of ETS-NOCV and QTAIM analyses. It is shown in one case, i.e. POBMUP the iridium-POCOP complex isolated by Brookhart et al., how slight variations of molecular charge and structure can affect drastically the relative intrinsic silylicity of the SiEt₃ group that is weakly bonded to the hydrido-iridium motif.