Diels−Alder Reactions of Benzyne with Indenyl Iron Complexes

The indenyl iron compound (η5-C9H7)Fe(η5-C5H5) (1) was found to react with benzyne,
generated from o-trimethylsilylphenyl triflate by fluoride-induced 1,2-elimination, to afford
the Diels−Alder adduct 1,2-(1,4-dihydro-naphthalen-1,4-diyl) ferrocene (2). When the bis(indenyl) iron complexes (η5-R-C9H6)2Fe [R = H (3); 2-Me (6); 1-SiMe3 (9)] reacted with
benzyne, the bisadducts [R = H (5); 2-Me (8); 1-SiMe3 (11)] were obtained along with the
corresponding monoadducts [R = H (4); 2-Me (7); 1-SiMe3 (10)]. The reaction of tetramethyldisilylene-bridged bis(indenyl) iron (Me2SiSiMe2)(η5-C9H6)2Fe (12) with benzyne gave only
the monoadduct (13). Complex 2 was also tested for ring-opening metathesis polymerization
(ROMP) in the presence of Grubbs' catalyst [(PCy3)2RuCl2CHPh] but was found to be
inactive under normal conditions. The molecular structures of 2, 5, 8, and 13 have been
determined by X-ray diffraction.