?-Arene Complexes of Nickel(II). Synthesis (from Metal Atoms) of (?-Arene)bis(pentafluorophenyl)nickel(II). Properties, ?-Arene Lability, and Chemistry

Article abstract of DOI:10.1021/ja00535a023

A new series of transition-metal-?-arene complexes has been prepared by a metal atom synthetic method.The deposition of Ni vapor, C6F5Br, and arenes has prodused high yields of (C6F5)2Ni-?-arene complexes.A variety of ?-arene ligands are η⁶ bound by the (C6F5)2Ni moiety, resulting in soluble highly labile materials, where the ?-arene ligand is exchangeble at room temperature.These complexes have not been isolable when ?-bonding ligands other then C6F5 have been employed.The formation of the ?-toluene complex proceeds through a pseudostable C6F5NiBr species that can be trapped at -80 deg C with R3P but decomposes by reductive elimination of CF5-CF5 in the absence of R3P or electron-rich arenes.It is likely that C6F5NiBr-?-arene is formed initially, which then disproportionates to (C6F5)2Ni-?-arene and NiBr2.Due to the high lability of the ?-arene ligand, these complexes possess a rich chemistry.Displacement of the ?-arene ligand can bee carried out cleanly and in high yield by P(Et)3, 1,5-cyclooctadiene, and THF to form (C6F5)2NiL2.Treatment of (?-toluene)bis(pentafluorophenyl)nickel (1) with norbornadiene at 0 deg C causes the formation of a high polymer of norbornadiene as well as (?-norbornadiene)bis(pentafluorophenyl)nickel, which appears to be either the active polymerization catalyst or its precursor.Similarly, treatment of 1 with 1,3-butadiene at 25 deg C and <1 atm causes the formation of new organometallic compound and the production of cyclic tetramers of 1,3-butadiene.When 1 was treated with cyclopentadiene at 0 deg C, a rapid production of C6F5H was observed with the subsequent formation of a dimeric nickel complex (C6F5)2(Cp)2Ni2(C5H6) where the Ni atoms appear to be bound together through a mutually ?-bonded cyclopentadiene (C5H6) ligand.Reductive elimination reactions have also been induced under mild conditions by addition of CO or C2H4.With CO a nearly quantitative production of C6F5C6F5 and Ni(CO)4 took place.Lastly, 1 served as a short-lived arene hydrogenation catalyst at room temperature.