An Unusual Example of Hypervalent Silicon: A Five-Coordinate Silyl Group Bridging Two Palladium or Nickel Centers through a Nonsymmetrical Four-Center Two-Electron Bond

Pd and Ni dimers supported by PSiP ligands in which two hypervalent five‐coordinate Si atoms bridge the two metal centers are reported. Crystallographic characterization revealed a rare square‐pyramidal geometry at Si and an unusual asymmetric M2Si2 core (M=Pd or Ni). DFT calculations showed that the unusual structure of the core is also found in a model in which the phosphine and Si centers are not part of a pincer group, thus indicating that the observed geometry is not imposed by the PSiP ligand. NBO analysis showed that an asymmetric four‐center two‐electron (4c‐2e) bond stabilizes the hypervalent Si atoms in the M2Si2 core. Strange to the core: In Pd and Ni dimers supported by PSiP ligands in which two hypervalent five‐coordinate Si atoms bridge the two metal centers, a rare square‐pyramidal geometry at Si and an unusual asymmetric M2Si2 core were observed. Natural bond orbital analysis showed that an asymmetric four‐center two‐electron (4c‐2e) bond stabilizes the hypervalent Si atoms in the M2Si2 core (see picture).