Catalytic Formation of Asymmetric Carbodiimides at Mononuclear Chromium(II/IV) Bis(alkoxide) Complexes
2015-10-26T00:00:00Z (GMT) by
Herein we report the synthesis of Cr imido complexes in bis(alkoxide) ligand environments and their nitrene transfer reactivity with isocyanides. The reaction of Cr2(OR)4 (OR = OCtBu2Ph) with bulky aryl or alkyl azide results in the formation of the trigonal-planar Cr(IV) mono(imido) complexes Cr(OR)2(NR1), whereas less bulky aryl azides form the Cr(VI) bis(imido) complexes Cr(OR)2(NR1)2. Cr(IV) mono(imido) complexes undergo facile reaction with 1 equiv of 2,6-dimethylphenyl isocyanide (CNR2) to form the corresponding carbodiimides R1NCNR2. In contrast, no reaction of Cr(OR)2(NR1)2 complexes with CNR2 is observed. The reaction of Cr(OR)2(NR1) with excess isocyanide leads to the isolation of the Cr(II) complex Cr(OR)2(CNR2)4, along with the observation of the anticipated carbodimide product. Cr(OR)2(CNR2)4, which can also be obtained by treating Cr2(OR)4 with 4 equiv of isocyanide, reacts with azides N3R1 (R1 = adamantyl, mesityl) to produce the respective carbodiimides. Catalytic formation of carbodiimides R1NCNR2 is observed from the mixtures of azides R1N3 (R1 = mesityl, 2,6-diethylphenyl, 2-isopropylphenyl, adamantyl) and several different aryl isocyanides CNR2 using 2.5 mol % of Cr2(OR)4.