Zerovalent Rh and Ir Silatranes Featuring 2-center, 3-electron Polar Sigma Bonds.

Species with 2-center, 3-electron (2c/3e-) σ-bonds are of interest owing to their fascinating electronic structures and potential for interesting reactivity patterns. Herein we report the synthesis and characterization of a pair of zerovalent (d9) trigonal pyramidal Rh and Ir complexes that feature 2c/3e- σ-bonds to the Si atom of a tripodal tris(phosphine)silatrane ligand. X-ray diffraction, continuous wave and pulse electron paramagnetic resonance, density functional theory calculations, and reactivity studies have been used to characterize these electronically distinctive compounds. The data available highlight a 2c/3e- bonding framework with a σ*-SOMO of metal 4- or 5dz2 parentage that is partially stabilized by significant mixing with Si (3pz) and metal (5- or 6pz) orbitals. Metal-ligand covalency thus buffers the expected destabilization of transition metal (TM)-silyl σ*-orbitals via d-p mixing, affording well-characterized examples of TM-to-main group, and hence polar, 2c/3e- σ "half-bonds".