Reactions of Mono(dinitrogen) Complexes of Molybdenum. Isolation and Characterization of Hydrazido(2-) and Mono- and Dihydride Complexes. Crystal Structure of MoBr[PhP(CH ₂CH₂PPh₂)₂](Me₂PCH₂PMe₂)·¹/₂C₅H₁₂

The reactions of a series of mono(dinitrogen) complexes of molybdenum Mo(N₂)(dpepp)(L₂) [where dpepp = PhP(CH₂CH₂PPh₂)₂and L₂= 2 PMe₂Ph (1), Me₂PCH₂PMe₂(dmpm) (2), 1,2-(Me₂As)₂C₆H₄(diars) (3), Ph₂PCH₂PPh₂(dppm) (4), Ph₂PCH₂CH₂PPh₂(dppe) (5)] with acids are reported. Reactions of 1 with excess HX (X = Br, C1) in the solid state or HX (2 mol) in toluene led to the isolation of the hydrazido(2-) complexes [MoX(NNH₂)(η²-dpepp)(PMe₂Ph)₂]X [6 (X = C1) and 7 (X = Br)] in which dpepp is bidentate. Similar results were obtained with CF₃SO₃H. Heating a toluene solution of 7 led to the loss of one PMe₂Ph and reincorporation of the pendant phosphine to form mer-[MoBr(NNH₂)(dpepp)(PMe₂Ph)]Br. Complexes 6 and 7 yielded ammonia and hydrazine when treated with HCl and HBr. The pendant phosphine can be protonated (HBr) and alkylated. Complex 1 reacted with HBr (1 mol) to initially (0.25 h) produce an equimolar mixture of 1 and 7. These two complexes reacted (15 h) to give an almost quantitative yield of Mo(H)Br(dpepp)(PMe₂Ph) (10). With HBr (1 mol), 10 produced Mo(H)₂Br₂(dpepp)(PMe₂Ph). Solid 2 reacted with excess HX (X = Br, Cl, SO₃CF₃) to produce the unstable hydrazido(2-) dication [Mo(NNH₂)(dpepp)(dmpm)]²⁺without loss of a ligand. In solution the stability of the dication increased with decreasing basicity of the anion: Cl < Br < SO₃CF₃. [Mo(NNH₂)(dpepp)(dmpm)] [SO₃CF₃]₂was isolated. Decomposition of the dication in solution led to loss of N₂and formation of a pair of isomeric eight-coordinate dihydrides, [Mo(H)₂Cl(dpepp)(dmpm)][HCl₂] (16). Reaction of 2 with HBr (1 mol) in benzene led to the isolation of [Mo(H)₂Br(dpepp)(dmpm)]Br (13, single isomer), MoBr(dpepp)(dmpm) (14), and Mo(H)Br(dpepp)(dmpm) (15, single isomer). A similar reaction with HCl produced Mo(H)-Cl(dpepp)(dmpm) (17) as a pair of isomers. Complex 14 crystallizes with 0.5 mol of pentane in the monoclinic space group P2₁/c with a = 12.452 (2) Å, b = 15.738 (2) Å, c = 21.677 (3) Å, β = 98.94 (1)°, and Z = 4. Complexes 3–5 gave evidence of hydrazido(2-) formation upon treatment with acid, but in solution N₂was rapidly evolved and hydrides were formed. Structural assignments of new complexes are based upon ³¹P and ¹H NMR spectral data. Dpepp is shown to adopt both fac and mer configurations. The protonation of metal-N₂complexes is discussed.