Chromium-(II) and -(III) complexes containing hydrazines or hydrazinecarboxylates as ligands

Abstract

The complexes [{CrX2(R2R1NNH2)2}n](X = Cl, R1= H, Me or Ph, R2= H; R1= R2= Me; X = Br, R1= H or Ph, R2= H) have been prepared and spectroscopic data acquired which suggest that the monomethylhydrazine complex is analogous to the well known hydrazine complexes with bridging NH2NHR (R = H or Me) ligands and terminal halide ligands, whereas the N,N-dimethyl- and phenylhydrazine complexes involve unidentate hydrazine and bridging halide ligands. The quadruple metal–metal bonded complexes [{Cr2(O2CMe)4(µ-R2R1NNH2)}n](R1= H or Me, R2= H; R1= R2= Me) containing bridging NH2NR1R2 ligands and [Cr2(O2CMe)4(PhNHNH2)2] containing unidentate NH2NHPh ligands have also been prepared and characterised. Chromium(II) hydrazinecarboxylate, [{Cr(O2CNHNH2)2(H2O)}n] has been prepared by either cleavage of the metal–metal bonds of [Cr2(O2CMe)4L2](L = H2O or ½N2H4) or ligand-displacement reactions of mononuclear chromium(II) complexes. Its infrared spectrum and that of the fully deuteriated analogue have been recorded and vibrational assignments proposed. Oxidation of [{Cr(O2CNHNH2)2(H2O)}n] or other chromium(II) species in aqueous [N2H5][O2CNHNH2] leads to the chromium(III) complex [Cr(O2CNHNH2)3]·2H2O. The substituted hydrazinecarboxylates [Cr{O2CN(Me)NH2}3]·H2O and [Cr2(O2CNHNHPh)4(MeOH)2] have also been isolated, the latter probably containing carboxylate-O,O′ groups bridging a metal–metal bonded Cr2 unit in the manner well established for other carboxylate anions.