SYNTHESIS AND FLUXIONAL BEHAVIOR OF (BIS(TRIALKYLPHOSPHINE)NICKELIO)ANTHRACENE (ALKYL = ET, BU)

The title compounds were prepared from the respective (R3P)2NiCl2 complexes and magnesium-anthracene-(THF)3 (or anthracene in the presence of Mg or C8K). The assignment of the anthracene proton NMR signals using NOE in conjunction with magnetization-transfer techniques is described. The complexes undergo haptotropic rearrangements in which the (R3P)2Ni moiety migrates between the two terminal rings of the coordinated anthracene. The rates of these processes are concentration independent and unaffected by the presence of free anthracene and tris(trialkylphosphine)nickel. Kinetic studies in the temperature range -60 to +70-degrees-C using line shape analysis and spin saturation transfer techniques were carried out. It was found that DELTA-H double-ended-dagger = 13.6 kcal mol-1 and DELTA-S double-ended-dagger = -4.3 eu for the haptotropic rearrangement in 2, and similar values were found for 1. Possible mechanisms are discussed. According to H-1, C-13, and P-31 NMR data, the coordination number between the anthracene and the (R3P)2Ni moiety is 4. However, an equilibrium between two eta(2) structures with DELTA-G double-ended-dagger less-than-or-equal-to 4 kcal mol-1 cannot be ruled out.