Two [1,2,4-(Me3C)3C5H2]2CeH molecules are involved in hydrogenation of pyridine to piperidine as shown by experiments and computations.

Hydrogenation of pyridine to piperidine catalyzed by [1,2,4-(Me3C)3C5H2]2CeH, abbreviated as Cp'2CeH or [Ce]'-H, is reported. The reaction proceeds from Cp'2Ce(2-pyridyl), isolated from the reaction of pyridine with Cp'2CeH, to Cp'2Ce(4,5,6-trihydropyridyl), and then to Cp'2Ce(piperidyl). The cycle is completed by the addition of pyridine, which generates Cp'2Ce(2-pyridyl) and piperidine.

Intermediate-valence tautomerism in decamethylytterbocene complexes of methyl-substituted bipyridines.

Multiconfigurational, intermediate valent ground states are established in several methyl-substituted bipyridine complexes of bis(pentamethylcyclopentadienyl)ytterbium, Cp2*Yb (Me(x)-bipy). In contrast to Cp2*Yb(bipy) and other substituted-bipy complexes, the nature of both the ground state and the first excited state are altered by changing the position of the methyl or dimethyl substitutions on the bipyridine rings. In particular, certain substitutions result in multiconfigurational, intermediate valent open-shell singlet states in both the ground state and the first excited state.

The reaction of bis(1,2,4-tri-t-butylcyclopentadienyl)ceriumbenzyl, Cp'2CeCH2Ph, with methylhalides: a metathesis reaction that does not proceed by a metathesis transition state.

The experimental reaction between [1,2,4-(Me(3)C)(3)C(5)H(2)](2)CeCH(2)Ph and CH(3)X, X = F, Cl, Br, and I, yields the metathetical exchange products, [1,2,4-(Me(3)C)(3)C(5)H(2)](2)CeX and CH(3)CH(2)Ph. The reaction is complicated by the equilibrium between the benzyl derivative and the metallacycle [1,2,4-(Me(3)C)(3)C(5)H(2)][(Me(3)C)(2)C(5)H(2)C(CH(3))(2)CH(2)]Ce, plus toluene since the metallacycle reacts with CH(3)X. Labelling studies show that the methyl group of the methylhalide is transferred intact to the benzyl group.

Fluorine for hydrogen exchange in the hydrofluorobenzene derivatives C6H(x)F(6-x), where x = 2, 3, 4 and 5 by monomeric [1,2,4-(Me3C)3C5H2]2CeH: the solid state isomerization of [1,2,4-(Me3C)3C5H2]2Ce(2,3,4,5-C6HF4) to [1,2,4-(Me3C)3C5H2]2Ce(2,3,4,6-C6HF4).

The reaction between monomeric bis(1,2,4-tri-tert-butylcyclopentadienyl)cerium hydride, Cp'2CeH, and several hydrofluorobenzene derivatives is described. The aryl derivatives that are the primary products, Cp'2Ce(C6H(5-x)F(x)) where x = 1,2,3,4, are thermally stable enough to be isolated in only two cases, since all of them decompose at different rates to Cp'2CeF and a fluorobenzyne; the latter is trapped by either solvent when C6D6 is used or by a Cp'H ring when C6D12 is the solvent. The trapped products are identified by GC/MS analysis after hydrolysis.

Reactions of monomeric [1,2,4-(Me3C)3C5H2]2CeH and CO with or without H2: an experimental and computational study.

Addition of CO to [1,2,4-(Me3C)3C5H2]2CeH,Cp'2 CeH, in toluene yields the cis-(Cp'2Ce)2(mu-OCHCHO), in which the cis-enediolate group bridges the two metallocene fragments. The cis-enediolate quantitatively isomerizes intramolecularly to the trans-enediolate in C6D6 at 100 degrees C over 7 months. When the solvent is pentane, Cp'2Ce(OCH2)CeCp'2 forms, in which the oxomethylene group or the formaldehyde dianion bridges the two metallocene fragments.

Hydrogen for fluorine exchange in CH4-xFx by monomeric [1,2,4-(Me3C)3C5H2]2CeH: experimental and computational studies.

The monomeric metallocenecerium hydride, Cp'(2)CeH (Cp' = 1,2,4-tri-tert-butylcyclopentadienyl), reacts instantaneously with CH(3)F, but slower with CH(2)F(2), to give Cp'(2)CeF and CH(4) in each case, a net H for F exchange reaction. The hydride reacts very slowly with CHF(3), and not at all with CF(4), to give Cp'(2)CeF, H(2), and 1,2,4- and 1,3,5-tri-tert-butylbenzene. The substituted benzenes are postulated to result from trapping of a fluorocarbene fragment derived by alpha-fluoride abstraction from Cp'(2)CeCF(3).

Hydrogen for fluorine exchange in C6F6 and C6F5H by monomeric [1,3,4-(Me3C)3C5H2]2CeH: experimental and computational studies.

The net reaction of monomeric Cp'(2)CeH [Cp' = 1,3,4-(Me(3)C)(3)(C(5)H(2))] in C(6)D(6) with C(6)F(6) is Cp'(2)CeF, H(2), and tetrafluorobenzyne. The pentafluorophenylmetallocene, Cp'(2)Ce(C(6)F(5)), is formed as an intermediate that decomposes slowly to Cp'(2)CeF and C(6)F(4) (tetrafluorobenzyne), and the latter is trapped by the solvent C(6)D(6) as a [2+4] cycloadduct. In C(6)F(5)H, the final products are also Cp'(2)CeF and H(2), which are formed from the intermediates Cp'(2)Ce(C(6)F(5)) and Cp'(2)Ce(2,3,5,6-C(6)F(4)H) and from an unidentified metallocene of cerium and the [2+4] cycloadducts of tetra- and trifluorobenzyne with C(6)D(6).