Gas-phase formation of Grignard-type organolanthanide (III) ions RLnCl : 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 gas-phase investigation using electrospray ionization (ESI) mass spectrometry in combination with density functional theory (DFT) calculations.

METHODS

The (RCO )LnCl (R = CH , Ln = La-Lu except Pm; Ln = La, R = CH CH , CH CH, HCC, C H , and C H ) precursor ions were produced in the gas phase via ESI of LnCl and RCO H or RCO Na mixtures in methanol. Collision-induced dissociation (CID) was employed to examine whether the Grignard-type organolanthanide (III) ions RLnCl can be obtained via decarboxylation of lanthanide chloride carboxylate ions (RCO )LnCl . DFT calculations can be used to determine the influences of lanthanide center and hydrocarbyl group on the formation of RLnCl .

RESULTS

When R = CH , CID of (CH CO )LnCl (Ln = La-Lu except Pm) yielded decarboxylation products (CH )LnCl and reduction products LnCl · with a variation in the relative intensity ratio of (CH )LnCl /LnCl · . The trend is as follows: (CH )EuCl /EuCl ·  < (CH )YbCl /YbCl ·  ≈ (CH )SmCl /SmCl ·  < other (CH )LnCl /LnCl · , which complies with the trend of Ln (III)/Ln (II) reduction potentials in general. When Ln = La and hydrocarbyl groups were varied as CH CH , CH CH, HCC, C H , and C H , the fragmentation behaviors of these (RCO )LaCl precursor ions were diverse. Except for (C H CO )LaCl , the four remaining (RCO )LaCl (R = CH CH , CH CH, HCC, and C H ) ions all underwent decarboxylation to yield RLaCl . (CH CH)LaCl and especially (CH CH )LaCl are prone to undergo β-hydride transfer to form LaHCl , whereas (HCC)LaCl and (C H )LaCl are not. A minor reduction product, LaCl · , was formed via C H radical loss of (C H )LaCl . The relative intensities of RLaCl compared to (RCO )LaCl decrease as follows: HCC > CH CH > C H  > CH  > CH CH  >> C H (not visible).

CONCLUSION

A series of Grignard-type organolanthanide (III) ions RLnCl (R = CH , Ln = La-Lu except Pm; Ln = La, R = CH CH , CH CH, HCC, and C H ) were produced from (RCO )LnCl via CO loss, whereas (C H )LaCl 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 via decarboxylation of (RCO )LnCl .