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 an effective method to obtain organometallic ions that are well suited for gasphase investigation using electrospray ionization (ESI) mass spectrometry in combination with density functional theory (DFT) calculations. Methods: The (RCO2)LnCl(3)(-) (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 LnCl(3) and RCO2H or RCO2Na mixtures in methanol. Collision-induced dissociation (CID) was employed to examine whether the Grignard-type organolanthanide (III) ions RLnCl(3)(-) can be obtained via decarboxylation of lanthanide chloride carboxylate ions (RCO2)LnCl(3)(-). DFT calculations can be used to determine the influences of lanthanide center and hydrocarbyl group on the formation of RLnCl(3)(-). Results: When R = CH3, CID of (CH3CO2)LnCl(3)(-) (Ln = La-Lu except Pm) yielded decarboxylation products (CH3)LnCl(3)(-) and reduction products LnCl(3)(-) with a variation in the relative intensity ratio of (CH3)LnCl(3)(-)/LnCl(3)(-). The trend is as follows: (CH3)EuCl3- /EuCl3- < (CH3)YbCl3- /YbCl3- approximate to (CH3)SmCl3- / SmCl3- < other (CH3)LnCl3-/LnCl(3)(-), 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 were diverse. Except for (C6H11CO2)LaCl3-, the four remaining (RCO2)LaCl3- (R = CH3CH2, CH2CH, HCC, and C6H5) ions all underwent decarboxylation to yield RLaCl3-. (CH2CH)LaCl3- and especially (CH3CH2)LaCl3- are prone to undergo beta-hydride transfer to form LaHCl3-, whereas (HCC)LaCl3- and (C6H5)LaCl3- are not. A minor reduction product, LaCl3-, was formed via C6H5 radical loss of (C6H5)LaCl3-. The relative intensities of RLaCl3- compared to (RCO2)LaCl3- decrease as follows: HCC > CH2CH > C6H5 > CH3 > CH3CH(2) >> C6H11 (not visible). Conclusion: A series of Grignard-type organolanthanide (III) ions RLnCl(3)(-) (R = CH3, Ln = La-Lu except Pm; Ln = La, R = CH3CH2, CH2CH, HCC, and C6H5) were produced from (RCO2)LnCl(3)(-) via CO2 loss, whereas (C6H11)LaCl3- did 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 important roles in promoting or limiting the formation of RLnCl(3)(-) via decarboxylation of (RCO2)LnCl(3)(-).