Synthesis and Characterization of Six-Coordinate Nitrido Complexes of Vanadium(V), Chromium(V), and Manganese(V). Isolation of a Dinuclear, Mixed-Valent μ-Nitrido Chromium(III)/Chromium(V) Species

Photolysis of a series of octahedral monoazido complexes of the type [LMIII(didentate ligand)(N3)] n +X n of vanadium(III), chromium(III), and manganese(III) in the solid state or in solution yields quantitatively the corresponding six-coordinate nitrido complexes [LMV(didentate ligand)(N)] n +X n and 1 equiv of dinitrogen. L represents the macrocycle 1,4,7-triazacyclononane or its N-methylated derivative (L‘), the didentate ligands are pentane-2,4-dionate (acac), 2,2,6,6-tetramethylheptane-3,5-dionate (tacac), picolinate (pic), phenanthroline (phen), and oxalate (ox), and X- represents perchlorate or hexafluorophosphate. The following nitrido complexes were prepared: [LVV(N)(acac)](ClO4) (6), [LCrV(N)(acac)](ClO4) (13), [LCrV(N)(tacac)](ClO4) (14), [LCrV(N)(pic)](ClO4) (15), [LCrV(N)(phen)](ClO4)2 (16), [LCrV(N)(ox)] (19), [L‘MnV(N)(acac)]PF6 (21). Photolysis of [LCrIII(N3)(ox)] (17) in the solid state produces the μ-nitrido-bridged mixed-valent species [L2Cr2(ox)2(μ-N)](N3) (18). The structures of the precursor complex [L‘Mn(acac)(N3)]BPh4 (20), of 13, and of [L‘MnV(N)(acac)]BPh4 (21) have been determined by X-ray crystallography. Complex 13 crystallizes in the orthorhombic space group Pnma, with cell constants a = 27.187(5) Å, b = 9.228(2) Å, c = 7.070(1) Å, V = 1773.7(6) Å3, and Z = 4; complex 20 crystallizes in the triclinic space group P1̄ with a = 14.769(5) Å, b = 16.83(1) Å, c = 16.96(1) Å, α = 108.19(5)°, β = 105.06(4)°, γ = 99.78(4)°, V = 3719(2) Å3, and Z = 4; and complex 21 crystallizes in the monoclinic space group P21/n with a = 10.443(3) Å, b = 16.035(4) Å, c = 21.463(5) Å, β = 95.76(1)°, V = 3575.9(14) Å3, and Z = 4. The CrV⋮N and MnV⋮N distances are short at 1.575(9) and 1.518(4) Å, respectively, and indicate a metal-to-nitrogen triple bond.