Molybdenum(V) on an Oxide String. Synthesis and Structure of the Novel Linear Trinuclear Complex {[MoO(TPP)][O−Mo(TPP)−O][MoO(TPP)]}ClO₄

The syntheses and crystallographic characterization of the linear trinuclear complex [Mo3O4(TPP)3]ClO4 and the monomeric precursors [MoO(TPP)(OClO3)] and [MoO(TPP)(OH2)]ClO4 are described. The crystallographic analyses of [MoO(TPP)(OClO3)] and [MoO(TPP)(OH2)]ClO4 show that these similar complexes are typical oxomolybdenum(V)−porphyrin complexes whose only significant structural differences are related to their respective axial ligands. [Mo3O4(TPP)3]ClO4 is obtained by the controlled hydrolysis of [MoO(TPP)(OClO3)] or by the direct reaction of [MoO(TPP)(OClO3)] with {[MoO(TPP)]2O}. This hydrolysis product contains the novel [Mo3O4(TPP)3]+ ion, which has an unprecedented linear [OMo−O−Mo−O−MoO]7+ unit and three nearly parallel 24-atom porphyrin mean planes. The central porphyrin is found to be rotated 29.3° and 29.7° with respect to the two terminal porphyrin ligands, which are nearly eclipsed (twist angle 0.44°). The formation of [Mo3O4(TPP)3]ClO4 instead of the μ-hydroxo-bridged binuclear complexes obtained from the hydrolysis of analogous mononuclear metalloporphyrin complexes is rationalized on the basis of the greater π-acceptor ability of Mo(V). Crystal data for [MoO(TPP)(OClO3)·0.9CH2Cl2: a = 11.437(2) Å, b = 13.567(6) Å, c = 13.764(4) Å, α = 89.15(1)°, β = 108.86(1)°, γ = 103.96(2)°, triclinic, space group P1̄, Z = 2, T = 293(2) K. Crystal data for [MoO(TPP)(OH2)ClO4·1.5C7H8: a = 13.2138(7) Å, b = 13.5959(12) Å, c = 14.6676(11) Å, α = 74.292(8)°, β = 69.114(8)°, γ = 69.030(5)°, triclinic, space group P1̄, Z = 2, T = 127(2) K. Crystal data for [Mo3O4(TPP)3]ClO4·C6H14·3.4CH2Cl2·4H2O: a = 26.428(6) Å, b = 18.683(6) Å, c = 28.692(4) Å, β = 113.98(2)°, monoclinic, space group P21/c, Z = 4, T = 127(2) K.