Dispersion Force Stabilized Two-Coordinate Transition Metal???Amido Complexes of the ???N({SiMe}$_{\textrm{3}}$)Dipp (Dipp = C$_{\textrm{6}}$H$_{\textrm{3}}$-2,6-Pr$^{\textrm{i}}$$_{\textrm{2}}$) Ligand: Structural, Spectroscopic, Magnetic, and Computational Studies

A series of high spin, two-coordinate first row transition metal?amido complexes, M\{N({SiMe}3)Dipp\}2 \{M = Fe (1), Co (2), or Ni (3); Dipp = C6H3-2,6-Pri2\} and a tetranuclear C?H activated chromium amide, [Cr\{N({SiMe}2CH2)Dipp\}2Cr]2({THF}) (4), were synthesized by reaction of their respective metal dihalides with 2 equiv of the lithium amide salt. They were characterized by X-ray crystallography, electronic and infrared spectroscopy, {SQUID} magnetic measurements, and computational methods. Contrary to steric considerations, the structures of 1?3 display planar eclipsed M\{{NSiC}(ipso)\}2 arrays and short M?N distances. {DFT} calculations, corrected for dispersion effects, show that dispersion interactions involving C?H?H?C moieties likely stabilize the structures by 21.1?29.4 kcal mol?1, depending on the level of the calculations employed. {SQUID} measurements confirm high spin electron configurations for all the complexes and substantial orbital contributions for 1 and 2.