Synthesis and Properties of Bis(pentamethylcyclopentadienyl) Actinide Hydrocarbyls and Hydrides. A New Class of Highly Reactive f-Element Organometallic Compounds

Article abstract of DOI:10.1021/ja00412a021

This paper reports the synthesis and chemical and physicochemical properties of thorium and uranium bis(pentamethylcyclopentadienyl) chlorides, hydrocarbyls, chlorohydrocarbyls, and hydrides.The reaction of the precursor compounds M<η⁵-(CH3)5C5>2Cl2 with 2 equiv of lithium reagent RLi produces M<η⁵-(CH3)5C5>R2 compounds where R = CH3, CH2Si(CH3)3, CH2C(CH3)3, CH2C6H5 and C6H5 (M = Th) and R = CH3, CH2Si(CH3)3, CH2C6H5, and C6H5 (M = U) in good yield.With 1 equiv of lithium reagent, M<η⁵-(CH3)3C5>2(R)Cl compounds where R = CH2C(CH3)3, CH2Si(CH3)3, CH2C6H5, and C6H5 (M = Th) and R = CH2C(CH3)3, CH2Si(CH3)3, CH2C6H5, and C6H5 (M = U) are formed in high yield.The M<η⁵-(CH3)5C5>2(CH3)Cl compounds can be synthesized by redistribution between the corresponding dimethyl and dichloro complexes.The new organoactinides were thoroughly characterized by elemental analysis, 1H NMR and vibrational spectroscopy, and in many cases cryoscopic molecular weight measurements.The hydrocarbyls and chlorohydrocarbyls generally exhibit high thermal stability.However, the diphenyl compounds react readily with C6D6 to yield, via a benzyne complex, the corresponding M(C6D5)2 compounds.The thorium bis(neopentyl) complex reacts with benzene to produce the corresponding diphenyl complex.In probes of bond polarity, the dimethyl complexes react rapidly with acetone, alcohols, and iodine to produce respectively the corresponding tert-butoxides, alkoxides plus methane, and iodides plus methyl iodide.Competition experiments at -78 deg C indicate that the thorium complexes are more reactive than those of uranium.The M<η⁵-(CH3)5C5>2R2 compounds undergo hydrogenolysis to yield organoactinide hydrides, 5-(CH3)5C5>2(μ-H)H2>2 and RH.While the thorium hydride exhibits high thermal stability, that of uranium readily (and reversibly) eliminates H2 forming a uranium (III) hydride.The new hydrides react vigorously with methyl chloride to produce methane and the corresponding chloro complexes, with acetone to produce isopropoxy complexes, and with alcohols to produce alkoxides and H2.The thorium chlorohydride, 5-(CH3)5C5>2(μ-H)Cl>2, can be prepared by redistribution of the dichloride and dihydride; an alkoxyhydride, Th<η⁵-(CH3)5C5>2H, can be prepared by hydrogenolysis of Th<η⁵-(CH3)5C5>CH3.In solution, the methal-bound hydrides of 5-(CH3)5C5>2(μ-H)H>2 rapidly exchange with dissolved H2; this hydride also reacts with ethylene to yield the corresponding diethyl complex.The olefin addition and hydrogenolysis reactions can be coupled to effect homogeneous, catalytic olefin hydrogenation.The differences between thorium and uranium chemistry appear largely to reflect differences in accessible oxidation states and in metal-ligand bond polarity.