Study of the effects on coordination of thioether sites. 1. Complexation study of bromopentacarbonylmanganese(I) with tripodal P3-nSn (n = 0-3) ligands

Article abstract of DOI:10.1021/om00030a043

Manganese(I) complexes fac-(η²-P_3-nS_n)Mn(CO)₃Br (n = 0-3) [P₃ W = Z = PPh₂; P₂S W = PPh₂, Z = SPh; PS₂ Z = SPh, W = PPh₂; S₃ W = Z = SPh in CH₃C(CH₂W)₂(CH₂Z)] formed from the corresponding tripodal ligand have been prepared and isolated as pairs of isomers. The reaction of P₂S with BrMn(CO)₅ in chloroform produced a pair of stereoisomers, syn-fac-(P,P′-P₂S)Mn(CO)₃Br (1a) and anti-fac-(P,P′-P₂S)Mn(CO)₃Br (1b), which were separated and fully characterized. Equilibration (K₁ = 2/3) between 1a and 1b was established. For PS₂, the equilibrium constant (K₂) between syn-fac-(P,S-PS₂)Mn(CO)₃Br (2a) and anti-fac-(P,S-PS₂)Mn(CO)₃Br (2b) was unity. Kinetic studies of isomerization of 1a to 1b and 2a to 2b were carried out by using an NMR spectrometer. The activation parameters were obtained: ΔH?_1a = 30.5 ± 0.4 kcal/mol, ΔS?_1a = 11 ± 1 eu for complex 1a; ΔH?_2a = 24.9 ± 0.7 kcal/mol, ΔS?_2a = 7 ± 2 eu for complex 2a. A mechanistic pathway for these isomerizations is proposed. Crystal structures were determined for three complexes: 1a, 1b, and 2a. X-ray data were collected on a CAD-4 diffractometer at room temperature and were refined by a least-squares treatment. For 1a: a = 10.669(2) A?, b = 17.864(3) A?, c = 18.841(12) A?, β = 105.30(2)°, monoclinic, Z = 4, P2_1/c, R(F_o) = 0.051, R_w(F_o) = 0.042 for 3043 reflections with I_o > 2σ(I_o). For 2b: a = 10.855(3) A?, b = 20.322(7) A?, c = 17.887(9) A?, β = 104.73(3)°, monoclinic, Z = 4, P2_1/n, R(F_o) = 0.059, R_w(F_o) = 0.047 for 3316 reflections with I_o > 2σ(I_o). For 2a: a = 8.670(5) A?, b = 9.539(3) A?, c = 18.921(9) A?, a = 93.09(3)°, β = 90.27(5)°, γ = 101.21(4)°, triclinic, Z = 2, P1, R(F_o) = 0.052, R_w(F_o) = 0.054 for 2513 reflections with I_o > 2σ(I_o). The conformations of the chelate rings are discussed.