The iron phosphine complex cis-[Fe(DMeOPrPE)(2)(eta(2)-N2H4)][BPh4](2) {DMeOPrPE = 1,2-bis[bis(methoxypropyl)phosphino]ethane} was synthesized and structurally characterized. The structure exhibits the first eta(2) coordination of hydrazine to iron, which may be relevant to intermediates trapped during nitrogenase turnover. The reaction of I with acid results in the formation of ammonia via a disproportionation reaction.