Reduktive aktivierung des metallaheterocyclobutadienkomplexes {A figure is presented}

The compound {A figure is presented} (1a) may be described as an Fe(CO)₃ derivative of a 1,2-ferrathiacyclobutadiene ligand. The CO groups of 1a, which are very difficult to substitute by thermal activation, are readily exchanged when compared with P(OMe)₃, by reductive electrocatalysis. Reductive initiation of substitution is also possible by the reduction of 1a with Na/Hg or t-BuLi. The mechanism of the reductively-initiated formation of the products 1b and 1c, in which one or two carbonyl groups, respectively, of 1a are replaced by P(OMe)₃ as well as the formation of a monosubstituted derivative of 1a, in which an axial CO group of the heterometallacyclobutadiene ligand is replaced by ^tBuP(OMe)₂ (1d) is discussed with respect to electrochemical, spectroscopic and structural data. ^tBuLi can activate 1a not only by single electron transfer: the addition of ^tBu^- at the sulfur center of 1a leads to an anionic CO-insertion product, which, by subsequent alkylation, may be trapped as {A figure is presented} (2b). Insertion of CO in 1a is also initiated by Na/Hg reduction; oxidative work up with I₂ gives {A figure is presented} (3). Thermal activation readily decarbonylates 3 to give 1a. The individual results are consistently described in a common reaction scheme. The structures of 1d, 2 and 3 have been determined by X-ray diffraction studies.