Ruthenium Tris(pyrazolyl)borate Diazo Complexes: Preparation of Aryldiazenido, Aryldiazene, and Hydrazine Derivatives

Tris(pyrazolyl)borate aryldiazenido complexes [RuTpLL‘(ArN2)](BF4)2 (1−3) [Ar = C6H5, 4-CH3C6H4; Tp = hydridotris(pyrazolyl)borate; L = P(OEt)3 or PPh(OEt)2, L‘ = PPh3; L = L‘ = P(OEt)3] were prepared by allowing dihydrogen [RuTp(η2-H2)LL‘]+ derivatives to react with aryldiazonium cations. Spectroscopic characterization (IR, 15N NMR) using the 15N-labeled derivatives strongly supports the presence of a linear [Ru]-N≡N-Ar aryldiazenido group. Hydrazine complexes [RuTp(RNHNH2)LL‘]BPh4 (4−6) [R = H, CH3, C6H5, 4-NO2C6H4; L = P(OEt)3 or PPh(OEt)2, L‘ = PPh3; L = L‘ = P(OEt)3] were also prepared by reacting the [RuTp(η2-H2)LL‘]+ cation with an excess of hydrazine. The complexes were characterized spectroscopically (IR and NMR) and by X-ray crystal structure determination of the [RuTp(CH3NHNH2){P(OEt)3}(PPh3)]BPh4 (4d) derivative. Tris(pyrazolyl)borate aryldiazene complexes [RuTp(ArN=NH)LL‘]BPh4 (7−9) (Ar = C6H5, 4-CH3C6H4) were prepared following three different methods: (i) by allowing hydride species RuHTpLL‘ to react with aryldiazonium cations in CH2Cl2; (ii) by treating aryldiazenido [RuTpLL‘(ArN2)](BF4)2 with LiBHEt3 in CH2Cl2; (iii) by oxidizing arylhydrazine [RuTp(ArNHNH2)LL‘]BPh4 complexes with Pb(OAc)4 in CH2Cl2 at −30 °C. Methyldiazene complexes [RuTp(CH3N=NH)LL‘]BPh4 were also prepared by the oxidation of the corresponding methylhydrazine [RuTp(CH3NHNH2)LL‘]BPh4 with Pb(OAc)4.