Synthesis of [(HIPTNCH2CH2)3N]Cr compounds (HIPT=3,5-(2,4,6-i-Pr3C6H2)2C6H3) and an evaluation of chromium for the reduction of dinitrogen to ammonia

Red-black [HIPTN3N] Cr (1) ([HIPTN3N](3-) = [(HIPTNCH2CH2)(3)N](3-) where HIPT = 3,5-(2,4,6-i-Pr3C6H2)(2)C6H3) HexaIsoPropylTerphenyl) can be prepared from CrCl3, while green-black [HIPTN3N]Cr(THF) (2) can be prepared from CrCl3(THF)(3). Reduction of {1 vertical bar 2} ( which means either 1 or 2) with potassium graphite in ether at room temperature yields [HIPTN3N]CrK (3) as a yellow-orange powder. There is no evidence that dinitrogen is incorporated into 1, 2, or 3. Compounds that can be prepared readily from {1 vertical bar 2} include red [HIPTN3N] CrCO (4), blood-red [HIPTN3N] CrNO (6), and purple [HIPTN3N] CrCl ( 7, upon oxidation of {1 vertical bar 2} with AgCl). The dichroic (purple/green) Cr(VI) nitride, [HIPTN3N] CrN (8) was prepared from Bu4NN3 and 7. X-ray studies have been carried out on 4, 6, and 7, and on two co-crystallized compounds, 7 and [HIPTN3N] CrN3 ( 65: 35) and [HIPTN3N]CrN3 and 8 (50: 50). Exposure of a degassed solution of {1 vertical bar 2} to an atmosphere of ammonia does not yield Cr(NH3) as a stable and well-behaved species analogous to Mo(NH3). An attempt to reduce dinitrogen under conditions described for the catalytic reduction of dinitrogen by [HIPTN3N] Mo compounds with 8 yielded a substoichiometric amount (0.8 equiv) of ammonia, which suggests that some ammonia is formed from the nitride but none is formed from dinitrogen.