Hydrocarbon Activation by Gas-Phase Lanthanide Cations: Interaction of Pr+, Eu+, and Gd+ with Small Alkanes, Cycloalkanes, and Alkenes

Article abstract of DOI:10.1021/ja00209a002

We describe ion beam studies of the interaction of gas-phase lanthanide ions, praseodymium (Pr⁺), europium (Eu⁺), and gadolinium (Gd⁺), with small alkanes, cycloalkanes, alkenes, and several oxygen-containing compounds.Only Gd⁺ is seen to activate C-H and C-C bonds of alkanes.The ground-state electronic configuration of Gd⁺ (4f⁷5d¹6s¹) is different from those of Pr⁺ (4f³6s¹) and Eu⁺ (4f⁷6s¹), leading to the conclusion that the f electrons play little part in the metal ion reactivity.Gd⁺ can be thought of as having two valence electrons, and indeed it reacts similarly to Sc⁺ and the other group 3 metal ions Y⁺ and La⁺, yielding products corresponding to elimination of hydrogen, alkanes, and alkenes.The elimination of neutral alkenes in the reaction of Gd⁺ with alkanes results in the formation of metal dialkyl or hydrido-alkyl complexes.This finding leads to estimates for the sum of two Gd⁺ ? bond dissociation energies of between 110 and 130 kcal/mol.Gd⁺ and Pr⁺ react readily with alkenes, yielding mostly dehydrogenation products along with smaller amounts of C-C bond cleavage products.Reactions of Gd⁺ and Pr⁺ with oxyen-containing species such as nitric oxide, formaldehyde, acetaldehyde, and acetone yield primarily the metal oxide ions and provide a lower limit for D(M⁺-O) of 179 kcal/mol, in good agreement with literature values of D(Pr⁺-O) = 188.4 +/- 5.2 kcal/mol and D(Gd⁺-O) = 181.0 +/- 4.4 kcal/mol.In keeping with the strong metal ? bonds, Gd⁺ is also seen to readily react with formaldehyde to eliminate CO and form GdH2⁺.