Mono- and Bis(hydrazine) Complexes of Osmium(II): Synthesis, Reactions, and X-ray Crystal Structure of the [Os(NH₂NH₂)₂{P(OEt)₃}₄](BPh₄)₂ Derivative

Reaction of OsH2P4 [P = P(OEt)3, PPh(OEt)2, PPh2OEt] with methyl triflate followed by the treatment with hydrazines gave the [OsH(RNHNH2)P4]BPh4 (1−3) (R = H, CH3, C6H5, 4-NO2C6H4) derivatives. Instead, the reaction of OsH2P4 first with methyl triflate, then with triflic acid, and finally with an excess of the appropriate hydrazine afforded the bis(hydrazine) [Os(RNHNH2)2P4](BPh4)2 (4, 5) (R = H, CH3, C6H5) complexes. Also the [Os(NH2NH2){P(OEt)3}5](BPh4)2 (7) derivative was prepared. All the hydrazine complexes were fully characterized by IR and 1H and 31P NMR spectra, and a single-crystal X-ray structure determination of the complex [Os(NH2NH2)2{P(OEt)3}4](BPh4)2·C2H5OH (4a) is reported. The compound crystallizes in the space group P21/c with a = 20.550(4) Å, b = 19.663(4) Å, c = 20.843(4) Å, β = 99.84(9)°, and Z = 4. The coordination around the osmium atom is octahedral and the orientation of the ligands in the [Os(NH2NH2)2{P(OEt)3}4]2+ cation is determined by several strong hydrogen bonds involving hydrazine nitrogen and phosphite oxygen atoms. Amidrazone complexes [Os{η2-NHC(R1)N(R)NH2}{P(OEt)3}4](BPh4)2 (8, 9) (R = H, CH3; R1 = CH3, 4-CH3C6H4) were prepared by allowing nitrile complexes [Os(R1CN)2P4](BPh4)2 to react with hydrazine NH2NH2 or methylhydrazine CH3NHNH2. Reaction of complexes containing substituted hydrazine ligands of the type [OsH(RNHNH2)P4]BPh4 and [Os(RNHNH2)2P4](BPh4)2 [P = P(OEt)3; R = CH3, C6H5] with Pb(OAc)4 at −30 °C results in the selective oxidation of the hydrazine affording the corresponding diazene [OsH(RNNH)P4]BPh4 (10) and [Os(RNNH)2P4](BPh4)2 (11) derivatives. The first bis(methyldiazene) complex [Os(CH3NNH)2{P(OEt)3}4](BPh4)2 (11b) was thus prepared.