Water Activation by Methyllanthanides: Hydrogen Versus Methane Evolution.

RATIONALE: The lanthanide hydrocarbyl complexes often exhibit exceptional performance in organic synthesis, catalytic process, and small molecule activation, and they generally exhibit several valuable differences in reactivity which can be influenced by the metal center and its oxidation state. Decarboxylation of metal carboxylate precursor is a powerful means to obtain multitudinous organometallic complexes which are well suited for gas-phase investigation by employing electrospray ionization mass spectrometry (ESI-MS) experiments in combination with density functional theory (DFT) calculations.

METHODS: The (CH3CO2)LnCl3 - and (CH3CO2)2LnCl2 - (Ln = Sm, Eu, and Yb) precursor anions were produced in the gas phase via ESI of LnCl3 and CH3CO2Na mixtures in methanol. Collision-induced dissociation (CID) technique was employed to obtain (CH3)LnIIICl3 - and (CH3)LnIICl2 - via fragmentation reactions of lanthanide acetate chloride anions. Activation of water molecule by (CH3)LnIIICl3 - or (CH3)LnIICl2 - via CH4 or H2 release was investigated by ion-molecule reaction (IMR) experiments. With the support of DFT calculations, the influences of lanthanide center and its oxidation state were also explored.

RESULTS: (CH3)LnIIICl3 - was generated via decarboxylation of (CH3CO2)LnCl3 - (Ln = Sm, Eu, and Yb) upon CID, while (CH3CO2)2LnCl2 - underwent consecutive two-step CO2/CH3 or one-step CH3CO2·and CO2 losses to give (CH3)LnIICl2 -. All three (CH3)LnIIICl3 - anions spontaneously reacted with H2O to form Ln (OH)Cl3 - accompanied by methane release, and the reaction extent is generally following as (CH3)SmIIICl3 - > (CH3)EuIIICl3 - > (CH3)YbIIICl3 -. For (CH3)EuIIICl3 - with H2O, there was minor (CH3O)EuCl3 - produced through hydrogen loss reaction as well. Three (CH3)LnIICl2 - anions reacted much more quickly than (CH3)LnIIICl3 - with H2O via CH4 loss, and the reactivity enhancement extent is following as Yb > Eu > Sm, which agrees well with Ln-C bond elongation trend from (CH3)LnIIICl3 - to (CH3)LnIICl2 -. Moreover, (CH3)SmIICl2 - and (CH3)YbIICl2 - rather than (CH3)EuIICl2 - underwent H2 loss reaction with H2O, which is on the contrary with the cases of (CH3)LnIIICl3 -.

CONCLUSION: The reactivity of the methyllanthanide chloride complexes towards water is significantly influenced by the lanthanide center and its oxidation state. In general, the methyllanthanide (II) chloride complexes (CH3)LnIICl2 - is much more reactive than the methyllanthanide (III) chloride complexes (CH3)LnIIICl3 -. Besides, the reactivity of (CH3)LnIIICl3 - is following as Sm > Eu > Yb, while that of (CH3)LnIICl2 - is Eu > Sm ≈ Yb.