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.