Versatile reactions of a para-bromophenylacetylide iron(II) derivative and X-ray structure of the fluoro analogue.: Synthesis of new redox-active organoiron(II) synthons

The synthesis of the new (η2-dppe)(η5-C5Me5)FeCC1,3-(C6H4X) (m-2a/2b; X=F/Br) and (η2-dppe)(η5-C5Me5)FeCC1,4-(C6H4I) (2c) complexes, as well as the solid-state structure of the known (η2-dppe)(η5-C5Me5)FeCC1,4-(C6H4F) (2a) complex are described. The catalytic coupling reactions of the bromo complexes with various alkynes were next investigated. Starting from the known (η2-dppe)(η5-C5Me5)FeCC1,4-(C6H4Br) complex (2b), the synthesis of the (η2-dppe)(η5-C5Me5)FeCC1,4-(C6H4)CCH complex (6d) and of the corresponding silyl-protected precursors (η2-dppe)(η5-C5Me5)FeCC1,4-(C6H4)CCSiR3 (6b/6c; R=iPr/Me) are reported. By use of lithiumbromine exchange reactions on 2b, the silyl- (7a; E=Si; R=Me) and tin- (7b–7d; E=Sn; R=Me, Bu, Ph) substituted analogues (η2-dppe)(η5-C5Me5)FeCC1,4-(C6H4)ER3 are also isolated. The spectroscopic and electrochemical characterisations of all these new Fe(II)/Fe(III) redox-active building blocks are presented and the electronic substituent parameters for the “(η2-dppe)(η5-C5Me5)FeCC” group are determined by means of 19F-NMR.