Is the R3Si Moiety in Metal-Silyl Complexes a Z ligand? AnAnswer from the Interaction Energy

The computation of metal-silyl interaction energies indicates the existence of situations in which the silyl group behaves as a Z-type ligand according to the Green method of covalent-bond classification. There is a scale of relative intrinsic silylicity , defined as the ratio of the intrinsic silyl-to-triflate interaction energy of a silyltriflate as a reference compound relative to the silyl-to-metal interaction of given complex, that can reveal in a straightforward manner the propensity of SiR3 groups to behave chemically as metal-bound silylium ions, namely, [SiR3](+). Emblematic cases, either taken from the Cambridge Structural Database (CSD) or constructed for the purpose of this study, were also investigated from the viewpoints of extended transition-state natural orbitals for chemical valence (ETS-NOCV) and quantum theory of atoms in molecules (QTAIM) analyses. It is shown in the case of POBMUPwhich is the iridium 1,3-bis[(di-tert-butylphosphino)oxy]benzene (POCOP) complex isolated by Brookhart etal.how slight variations of molecular charge and structure can drastically affect the relative intrinsic silylicity of the SiEt3 group that is weakly bonded to the hydrido-iridium motif.