Comparison of the molecular structures and solution stereodynamics of (diene)Fe(CO)2L complexes (L = CO, PPh3, P(OMe)3, PMe3, NMe3, pyridine, CNMe)

Several (diene)Fe(CO)₂L complexes (1b-g) of methyl 5-formyl-2,4-pentadienoate have been structurally characterized in solution and the solid state. Crystal structures of 1e,f (L = NMe₃, PMe₃) allow a direct stereochemical comparison of NMe₃ and PMe₃ ligands in otherwise isostructural compounds. In solution, complex 1d (L = pyridine) undergoes differential rates of axial/basal and basal/basal exchange which are not observed with the phosphite or isonitrile complexes (1c,g). A theoretical interpretation of this phenomenon is presented. Crystal structure data: 1d, monoclinic, space group P2₁/n, a = 8.417(1) Å, b = 9.147(2) Å, c = 19.235(3) Å, β = 98.84(2)°, Z = 4, R_w = 0.041 for 191 parameters using 2575 observed reflections; 1e, monoclinic, space group P2₁/n, a = 15.167(4) Å, b = 8.048(3) Å, c = 26.334(9) Å, Z = 8, R_w = 0.082 for 344 parameters using 2691 observed reflections; If, triclinic, space group P1̅, a = 7.984(1) Å, b = 12.439(2) Å, c = 16.249(3) Å, α = 110.85(2)°, β = 90.48(2)°, γ = 101.13(2)°, Z = 4, R_w = 0.062 for 341 parameters using 2468 observed reflections.