Mass spectra of organometallic compounds : III. Benzocyclobutadieneiron carbonyl derivatives

Abstract

The mass spectra of the benzocyclobutadieneiron complexes C 8H 6Fe(CO) 3 and C 8H 6Fe(CO) 2E(C 6H 5) 3 [E = P, As and Sb] have been studied at 80 eV. These complexes undergo fragmentations involving unimolecular carbonyl dissociation and (C 6H 5) 3E elimination which are similar to those of the related manganese complexes, (π-L)Mn(CO) 3 and (π-L)Mn(CO) 2E(C 6H 5) 3 [L = cyclopentadienyl, indenyl and fluorenyl; E = P, As and Sb]. Noteworthy are the ions [C 8H 6] +, [C 8H 6Fe] +, [C 6H 4] + and [C 6H 4Fe] +, which have been assigned the structures of the free and coordinated benzocyclobutadiene and benzyne, respectively. In the case of the more volatile derivative, C 8H 6Fe(CO) 3, these ions are formed by processes which are supported by the presence of appropriate metastable ions. The presence of a free benzocyclobutadiene ion, [C 8H 6] +, in the mass spectra of these iron complexes contrasts with the failure to detect related cyclobutadiene (or substituted cyclobutadiene) ions in the mass spectra of the other cyclobutadienemetal complexes. The enhanced stability of [C 8H 6] + compared with that of [R 4C 4] + (R = H, CH 3, C 6H 5 etc.) may be explained from its fused ring structure.