Aryldiazene complexes [Mn(CO)(3)(ArN=NH)P-2]BF4 (1, 2) and [{Mn(CO)(3)P-2}(2)(mu-HN=NArArN=NH)](BF4)(2) (3, 4) [P = PPh(OEt)(2), PPh(2)OEt; Ar = C6H5, 2-CH3C6H4, 4-CH3C6H4, 4-CH3OC6H4; ArAr = 4,4’-C6H4C6H4, 4,4’-(2-CH3)C6H3C6H3(2-CH3), 4,4’-C6H6CH2C6H4] were prepared by reacting hydride species MnH(CO)(3)P-2 with the appropriate aryldiazonium cations in CH2Cl2 or acetone solutions at -80 degrees C. The compounds were characterized by IR, H-1 and P-31 NMR spectra (with N-15 isotopic substitution), and a single-crystal X-ray structure determination. The complex [Mn(CO)(3)(4-CH3C6H4N=NH) {PPh(OEt)(2)}(2)]BF4 (1c) crystallizes in the space group C2/c with a 31.857(5) Angstrom, b = 11.119(2) Angstrom, c = 22.414(3) Angstrom, beta = 97.82(1)degrees, and Z = 8. Treatment of aryldiazene compounds 1-4 with NEt(3) gave the pentacoordinate aryldiazenido [Mn(CO)(2)(ArN2)P-2] (5, 6) and [{Mn(CO)(2)P-2}(2)(mu-N-2-ArArN2)] (7, 8) [P = PPh(OEt)(2), PPh(2)OEt; Ar = C6H5, 4-CH3C6H4; ArAr = 4,4’-C6H4C6H4, 4,4’-(2-CH3)C6H3C6H3(2-CH3)] derivatives. Protonation reactions of these aryldiazenido complexes 5-8 with HCl afforded the aryldiazene [MnCl(CO)(2)(ArN=NH)P-2] (9) and [{MnCl(CO)(2)P-2}(2)(mu-HN=NArArN=NH)] (10) derivatives. Hydrazine complexes [Mn(CO)(3)(RNHNH(2))P-2]BPh(4) (11, 12) [P = PPh(OEt)(2), PPh(2)OEt; R = H, CH3, C6H5, 4-NO2C6H4] were prepared by allowing hydride species MnH(CO)(3)P-2 to react first with triflic acid and then with the appropriate hydrazine. Their characterization by IR, H-1 and P-31 NMR spectra, and an X-ray crystal structure determination is reported. The compound [Mn(CO)(3)(NH2NH2){PPh(OEt)(2)}(2)]BPh(4) (11a) crystallizes in the space group P (1) over bar with a = 13.772(3) Angstrom, b = 14.951(4) Angstrom, c = 13.319(3) Angstrom, alpha = 104.47(1)degrees, beta = 100.32(1)degrees, gamma = 111.08(1)degrees, and Z = 2. Oxidation reactions of hydrazine compounds 11 and 12 with Pb(OAc)(4) at -40 degrees C gave stable aryldiazene [Mn(CO)(3)(RN=NH)P-2]BPh(4) and thermally unstable (upon reaching -40 degrees C) diazene [Mn(CO)(3)(HN=NH)P-2]BPh(4) derivatives.