Consecutive fragmentations of the cubane-like zinc cluster [CH3Zn(O-i-C3H7)]4 upon electron ionization

The sequential dissociations of the tetranuclear zinc cluster-ion [(CH3)3Zn4(O-i-C3H7)4]+ obtained by dissociative electron ionization of neutral [(CH3)Zn(O-i-C3H7)]4 are investigated by tandem mass spectrometry. After initial loss of a neutral (CH3)Zn(O-i-C3H7) unit to afford [(CH3)2Zn3(O-i-C3H7)3]+, hydrogen migration leads to the expulsion of neutral acetone concomitant with [(CH3)2Zn3(O-i-C3H7)2(H)]+ as ionic fragment. Unimolecular dissociation of the latter gives rise to [(CH3)2Zn2(O-i-C3H7)]+ and neutral HZn(O-i-C3H7). As demonstrated by collisional ionization of the neutral product, in the fragmentation of the dinuclear cluster [(CH3)2Zn2(O-i-C3H7)]+ neutral CH3ZnH is formed, rather than the more stable fragments Zn + CH4. From the resulting mononuclear species CH3Zn(OC(CH3)2)+ acetone is eliminated to afford CH3Zn+ as a quasi-terminal fragment ion.