Unique {H(SiR3)2}, (H2SiR3), H(HSiR3), and (H2)SiR3 Ligand Sets Supported by the {Fe(Cp)(L)} Platform (L=CO, PR3)

AbstractThis work deals with the type and incidence of nonclassical SiH and HH interactions in a family of silylhydride complexes [Fe(Cp)(OC)(SiMenCl3−n)H(X)] (X=SiMenCl3−n, H, Me, n=0–3) and [Fe(Cp)(Me3P)(SiMenCl3−n)2H] (n=0–3). DFT calculations complemented by atom‐in‐molecule analysis and calculations of NMR hydrogen–silicon coupling constants revealed a surprising diversity of nonclassical SiH and HH interligand interactions. The compounds [Fe(Cp)(L)(SiMenCl3−n)2H] (L=CO, PMe3; n=0–3) exhibit an unusual distortion from the ideal piano‐stool geometry in that the silyl ligands are strongly shifted toward the hydride and there is a strong trend towards flattening of the {FeSi2H} fragment. Such a distortion leads to short SiH contacts (range 2.030–2.075 Å) and large Mayer bond orders. A novel feature of these extended SiH interactions is that they are rather insensitive towards the substitution at the silicon atom and the orientation of the silyl ligand relatively the FeH bond. NMR spectroscopy and bonding features of the related complexes [Fe(Cp)(OC)(SiMenCl3−n)H(Me)] (n=0–3) allow for their rationalization as usual η2‐SiH silane σ‐complexes. The series of “dihydride” complexes [Fe(Cp)(OC)(SiMenCl3−n)H2] (n=0–3) is different from the previous two families in that the type of interligand interactions strongly depends on the substitution on silicon. They can be classified either as usual dihydrogen complexes, for example, [Fe(Cp)(OC)(SiMe2Cl)(η2‐H2)], or as compounds with nonclassical HSi interactions, for example, [Fe(Cp)(OC)(H)2(SiMe3)] (16). These nonclassical interligand interactions are characterized by increased negative J(H,Si) (e.g. −27.5 Hz) and increased J(H,H) (e.g. 67.7 Hz).