Structure and Stereodynamics of Fe(CO)₄L Complexes (L = P(o-tolyl)₃, As(o-tolyl)₃, P(o-tolyl)₂CH₂Ph, (o-tolyl)₂PP(o-tolyl)₂)

The crystal structures and variable-temperature NMR spectra of (CO)₄FeP(o-tolyl)₃, (CO)₄FeAs(o-tolyl)₃, (CO)₄FeP(o-tolyl)₂CH₂Ph, and (CO)₄Fe(o-tolyl)₂PP(o-tolyl)₂ (1a–d) are reported. In the solid state, complexes 1a–c contain the phosphine in an axial position of the trigonal bipyramid; complex 1d is equatorially substituted in the solid state but exists as an axial/equatorial mixture in solution. All complexes exhibit P-C restricted rotation, which in the case of 1a may be linked to axial/equatorial CO exchange. Crystallographic data: 1a, C₂₅H₂₁FeO₄P, monoclinic, P2₁/n, a = 10.188(3) Å, b = 10.429(2) Å, c = 21.755(6) Å, β = 99.79(2)°, Z = 4; 1b, C₂₅H₂₁AsFeO₄, monoclinic, P2₁/n, a = 10.265(2) Å, b = 10.517(1) Å, c = 21.679(3) Å, β = 99.16(2)°, Z = 4; 1c, C₂₅H₂₁FeO₄P, triclinic, P1̄, a = 9.618(3) Å, b = 15.282(3) Å, c = 17.130(5) Å, α = 66.92(2)°, β = 79.51(2)°, γ = 86.42(2)°, Z = 4; 1d, C₃₂H₃₈FeO₄P₂, orthorhombic, Pbca, a = 15.947(6) Å, b = 20.009(3) Å, c = 15.470(4) Å, Z = 8.