A Linear Two-Coordinate Cr(II) Complex: Synthesis, Characterization, and Reactivity

The synthesis and characterization of a linear two-coordinate Cr(II) amido complex, Cr{N(tBu)Dipp}2 (Dipp=2,6-diisopropylphenyl), from the reaction of 1 molar equivalent (equiv) of CrCl2 and 2 equiv. of LiN(tBu)Dipp is reported. Single-crystal X-ray diffractometry (SC-XRD) analysis revealed that it has a short Cr-N bond distance of 1.8878(9) angstrom, which could be attributed to the relatively less bulky nature of the amido ligand compared with reported systems. Furthermore, the oxidation reaction of the two-coordinate Cr(II) complex was explored. The oxidation reaction of Cr{N(tBu)Dipp}2 with the one-electron oxidants AgOTf and [FeCp2][BArF4] (BArF4-=[B{C6H3-3,5-(CF3)2}4]-) afforded the trigonal planar three- and bent two-coordinate Cr(III) complexes Cr{N(tBu)Dipp}2(OTf) and [Cr{N(tBu)Dipp}2][BArF4], respectively. The reaction of Cr{N(tBu)Dipp}2 with 1 equiv. of the organic azides AdN3 (Ad=1-adamantyl) and PhN3 afforded the three-coordinate Cr(IV) imido complexes Cr{N(tBu)Dipp}2(NAd) and Cr{N(tBu)Dipp}2(NPh), respectively. The reaction of Cr{N(tBu)Dipp}2 and two equiv. of Me3NO afforded the Cr(VI) dioxo complex Cr{N(tBu)Dipp}2(O)2. The reaction of Cr{N(tBu)Dipp}2 with 1 equiv. of CyN=C=NCy resulted in the insertion of the carbodiimide into the Cr-N bond, with the formation of a three-coordinate Cr(II) complex. Finally, density functional theory (DFT) calculations were used to elucidate the electronic structure of these complexes. A simple linear two-coordinate Cr(II) amido complex is synthesized. Magnetic, spectroscopic, and computational studies indicate that it has a high-spin S=2 ground state. Reactivity studies provide access to a variety of low-coordinate, high oxidation state Cr complexes.+ image