102747-18-2Relevant academic research and scientific papers
Pentadienyl-metal-phosphine chemistry. 6. Syntheses, structures, and solution dynamics of (η5-pentadienyl)[tris(phosphine)]manganese complexes
Bleeke, John R.,Stanley, George G.,Kotyk, John J.
, p. 1642 - 1647 (2008/10/08)
Reaction of MnBr2 with potassium pentadienide-tetrahydrofuran and the electron-rich chelating tris(phosphine) ligands (Me2PCH2)3CMe or (Et2PCH2CH2)2PPh produces (η5-pentadienyl)Mn[(Me2PCH2) 3CMe] (1) or (η5-pentadienyl)Mn[(Et2PCH2CH 2)2PPh] (2) in high yield. Substitution of potassium 2,4-dimetnylpentadienide-tetrahydrofuran for potassium pentadienide-tetrahydrofuran in the above reaction system leads to the syntheses of the 2,4-dimethylpentadienyl analogues of 1 and 2, namely, (η5-2,4-dimethylpentadienyl)Mn[(Me2PCH 2)3CMe] (3) and (η5-2,4-dimethylpentadienyl)Mn[(Et2PCH 2CH2)2PPh] (4). Single-crystal X-ray diffraction studies of 2 and 3 have been carried out. 2 crystallizes in the orthorhombic space group P212121 with a = 16.69 (1) A?, b = 17.06 (1) A?, c = 8.513 (3) A?, V = 2423 (4) A?3, and Z = 4. 3 also crystallizes in space group P212121 with a = 14.788 (3) A?, b = 9.709 (3) A?, c = 14.761 (4) A?, V = 2119 (2) A?3, and Z = 4. Both complexes assume approximate octahedral geometries with C1, C3, and C5 of the pentadienyl ligands and the three phosphorus atoms of the tris(phosphine) ligands occupying the six coordination sites. In 2, the chelating tris(phosphine) ligand is oriented unsymmetrically with one of the terminal phosphine groups situated beneath the open mouth of the pentadienyl ligand and the other terminal phosphine group under an edge of the pentadienyl ligand. This unsymmetrical orientation of the tris(phosphine) ligand also manifests itself in the room-temperature NMR spectra of 2. However, as the temperature is raised, the rate of rotation of the pentadienyl group with respect to the MnP3 fragment increases, exchanging the ends of the tris(phosphine) ligand and the ends of the pentadienyl ligand. Line-shape simulations of the variable-temperature 31P NMR spectra have enabled us to calculate rotational barriers (ΔG?'s) of 18.3 ± 0.5 kcal/mol for 2 and 17.3 ± 0.2 kcal/mol for 4. For compounds 1 and 3, rotation is rapid at room temperature but can be slowed by cooling the solutions. Again, line-shape simulations of the variable-temperature 31P NMR spectra have yielded rotational barriers (ΔG?'s) of 11.4 ± 0.6 kcal/mol and 10.9 ± 0.2 kcal/mol for 1 and 3, respectively.
