Gas-Phase Formation of Grignard-type Organolanthanide(III) Ions RLnCl3-:
the Influences of Lanthanide Center and Hydrocarbyl Group
Abstract
Rationale: The fundamental understanding of Grignard-type
organolanthanides(III) is still in its infancy. Decarboxylation of metal
carboxylate ions is a powerful method to obtain organometallic ions
which are well suited for gas-phase investigation by using ESI-MS in
combination with DFT calculations. Methods: (RCO2)LnCl3- (R = CH3, Ln =
La-Lu except Pm; Ln = La, R = CH3CH2, CH2CH, CHC, C6H5 and C6H11) ions
were produced via ESI of LnCl3 and RCO2H/RCO2Na in methanol.
Collision-induced dissociation (CID) was employed to examine whether
RLnCl3- can be obtained via decarboxylation of (RCO2)LnCl3-. With the
aid of DFT calculations, the influences of Ln and R on the formation of
RLnCl3- can be uncovered. Results: When R was fixed as methyl, CID of
(CH3CO2)LnCl3- (Ln = La-Lu except Pm) all gave (CH3)LnCl3- and LnCl3·-
with a variation in the relative intensity ratio of (CH3)LnCl3-/LnCl3·-.
The trend is following as (CH3)EuCl3-/EuCl3·- <
(CH3)YbCl3-/YbCl3·- ≈ (CH3)SmCl3-/SmCl3·- < other
(CH3)LnCl3-/LnCl3·-, which generally complies with the trend of
Ln(III)/Ln(II) reduction potentials. When Ln was fixed as La and R
groups were varied as CH3CH2, CH2CH, CHC, C6H5 and C6H11, the
fragmentation behaviors of these (RCO2)LaCl3- are diverse. Except for
(C6H11CO2)LaCl3-, the rest four (RCO2)LaCl3- ions all underwent
decarboxylation to give RLaCl3-. The relative intensities of RLaCl3-
compared to (RCO2)LaCl3- decrease as follow: CHC > CH2CH
> C6H5 > CH3 > CH3CH2
>> C6H11 (not visible). Conclusion: A series
of Grignard-type organolanthanide(III) ions RLnCl3- (R = CH3, Ln = La-Lu
except Pm; Ln = La, R = CH3CH2, CH2CH, CHC and C6H5) were generated from
(RCO2)LnCl3- via CO2 loss while (C6H5)LaCl3- not. The experimental and
theoretical results suggest that the reduction potentials of
Ln(III)/Ln(II) couples as well as the bulkiness and hybridization of
hydrocarbyl groups play crucial roles in promoting or limiting the
formation of RLnCl3- via decarboxylation.