Chromium chalcogen complexes. Insertion of elemental sulphur into [{Cr(cp)(CO)2}2Se] and [Cr(cp)2(CO)4Se2](cp =η-C5H5)

The facile insertion of elemental sulphur into the cumulated linear triple bond CrSeCr, of [Cr2(cp)2(CO)4Se](cp =η-C5H5) resulted in the isolation of [Cr2(cp)2(CO)4Se2], [Cr2(cp)2(CO)4S2], and [Cr2(cp)2(CO)4S], with relative yields dependent on the reaction conditions, as well as the sulphur selenides S7Se and S6Se2. Detailed n.m.r. and t.l.c. studies indicated that the transformation occurred via dichalcogen species of the type [Cr2(cp)2(CO)4S(Se)] and [Cr2(cp)2(CO)5S(Se)]. It was demonstrated that [Cr2(cp)2(CO)4Se2] also can undergo a rapid reaction with elemental sulphur to give [Cr2(cp)2(CO)4S] as the ultimate product.