Diels-Alder Reactions of Benzyne with Indenyl Iron Complexes

The indenyl iron compound (η 5 -C 9 H 7 )Fe(η 5 -C 5 H 5 ) (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 (η 5 -R-C 9 H 6 ) 2 Fe [R = H (3); 2-Me (6); 1-SiMe 3 (9)] reacted with benzyne, the bisadducts [R = H (5); 2-Me (8); 1-SiMe 3 (11)] were obtained along with the corresponding monoadducts [R = H (4); 2-Me (7); 1-SiMe 3 (10)]. The reaction of tetramethyl-disilylene-bridged bis(indenyl) iron (Me2SiSiMe2)(η 5 -C 9 H 6 ) 2 Fe (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 [(PCy 3 ) 2 RuCl 2 =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.