Gas‐Phase Formation of Grignard‐type Organolanthanide (III) Ions RLnCl3‐: the Influences of Lanthanide Center and Hydrocarbyl Group

Rationale

Compared with organomagnesium compounds (Grignard reagents), the Grignard-type organolanthanides (III) exhibit several utilizable differences in reactivity. However, 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 electrospray ionization (ESI) mass spectrometry in combination with density functional theory (DFT) calculations.

Methods

The (RCO₂)LnCl₃^– (R = CH₃, Ln = La-Lu except Pm; Ln = La, R = CH₃CH₂, CH₂CH, HCC, C₆H₅ and C₆H₁₁) precursor ions were produced in the gas phase via ESI of LnCl₃ and RCO₂H or RCO₂Na mixtures in methanol. Collision-induced dissociation (CID) was employed to examine whether the Grignard-type organolanthanide (III) ions RLnCl₃^– can be obtained via decarboxylation of lanthanide chloride carboxylate ions (RCO₂)LnCl₃^–. With the aid of DFT calculations, the influences of lanthanide center and hydrocarbyl group on the formation of RLnCl₃^– can be uncovered.

Results

When R = CH₃, CID of (CH₃CO₂)LnCl₃^– (Ln = La-Lu except Pm) all gave decarboxylation products (CH₃)LnCl₃^– and reduction products 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 complies with the trend of Ln (III)/Ln (II) reduction potentials in general. When Ln = La and hydrocarbyl groups were varied as CH₃CH₂, CH₂CH, HCC, C₆H₅ and C₆H₁₁, the fragmentation behaviors of these (RCO₂)LaCl₃^– precursor ions are diverse. Except for (C₆H₁₁CO₂)LaCl₃^–, the four remaining (RCO₂)LaCl₃^– (R = CH₃CH₂, CH₂CH, HCC and C₆H₅) ions all underwent decarboxylation to give RLaCl₃^–. (CH₂CH)LaCl₃^– and especially (CH₃CH₂)LaCl₃^– are prone to undergo β-hydride transfer to form LaHCl₃^–, while (HCC)LaCl₃^– and (C₆H₅)LaCl₃^– not. Minor reduction product, LaCl₃·^–, was formed via C₆H₅ radical loss of (C₆H₅)LaCl₃^–. The relative intensities of RLaCl₃^– compared to (RCO₂)LaCl₃^– decrease as follow: HCC > 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, HCC and C₆H₅) were generated from (RCO₂)LnCl₃^– via CO₂ loss while (C₆H₁₁)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 of (RCO₂)LnCl₃^–.