Bis(diethylcyanamide) [Fe(NCNEt₂)₂L₄](BPh₄)₂1a and bis(cyanoguanidine) [Fe{NCN(H)C(NH₂)NH}₂L₄](BPh₄)₂1b [L = P(OEt)₃] complexes were prepared by allowing iron(II) chloride to react first with an excess of P(OEt)₃ and then of the appropriate cyanamide, followed by addition of an excess of NaBPh₄. Instead, bis(complexes) of ruthenium and osmium [M(NCNEt₂)₂L₄](BPh₄)₂2a, 3a and [M{NCN(H)C(NH₂)NH}₂L₄](BPh₄)₂2b, 3b (M = Ru 2, Os 3) were prepared by reacting hydrides MH₂L₄ first with either triflic acid HOTf or methyltriflate MeOTf and then with an excess of the appropriate cyanamide. Hydride-diethylcyanamide [MH(NCNEt₂)L₄]BPh₄4a, 5a and hydride-cyanoguanidine complexes [MH{NCN(H)C(NH₂)NH}L₄](BPh₄)₂4b, 5b (M = Ru 4, Os 5) were also obtained by reacting MH₂L₄ first with one equivalent of HOTf or MeOTf and then with the appropriate cyanamide. Treatment of bis(cyanamide) and bis(cyanoguanidine) complexes 1–3 with hydrazines RNHNH₂ afforded hydrazinecarboximidamide derivatives [M{η²-N(H)C(NEt₂)N(R)NH₂}L₄](BPh₄)₂6a–12a and [M{η²-N(H)C[NC(NH₂)₂]N(R)NH₂}L₄](BPh₄)₂6b–12b (M = Fe 6–8, Ru 9, 10, Os 11, 12; R = H 6, 9, 11, Me 7, 10, 12, Ph 8). A reaction path involving nucleophilic attack by hydrazine on the cyanamide carbon atom is proposed. All the complexes were characterised by spectroscopy and X-ray crystal structure determination of [Os{η²-NHC[NC(NH₂)₂]N(CH₃)NH₂}{P(OEt)₃}₄](BPh₄)₂12b.