Reversible Dinitrogen Binding by an Intermediate Spin Monovalent Chromium Complex

A unique low valent 15 e- Cr(I) species, Cp*Cr(CNArDipp2)2 (2) (Cp* = Me5C5, CNArDipp2 = 2,6-(2,6-(iPr)2C6H3)2C6H3) was isolated under Ar atmosphere. It’s intermediate spin ground state (S = 3/2) was determined via Evans’s method with 1H NMR spectroscopy, and electron paramagnetic resonance (EPR) spectroscopy. N2 reversibly binds 2 to afford a 17 e- low spin (S = 1/2) complex, Cp*CrN2(CNArDipp2)2 (2-N2), This dynamic N2 coordination was characterized based upon their distinct magnetic properties via collaborative analysis of Evans’s method and SQUID magnetometry. One electron reduction of 2 or 2-N2 under N2 atmosphere effectively suppress the N2 elimination to give a saturated monoanionic species, KCp*CrN2(CNArDipp2)2 (4). Compound 2 can also be further reduced with 2 equiv. of KC8 to generate a dianionic unsaturated metalloradical, K2Cp*Cr(CNArDipp2)2 (5), The exceedingly red shifted vCN stretching bands suggest highly activated C-N triple bond of the bulky terphenyl isocyanide ligands.