The chemistry of cyclopentadienyl nitrosyl and related complexes of molybdenum. Part 9. Reactions of bis(cyclopentadienyl) complexes with dienophilic acetylenes and olefins

Metal-Assisted Cycloaddition Reactions in Organotransition Metal Chemistry

“…Stereochemical investigations with fumaro-and maleonitrile have confirmed a concerted [4+2] mechanism. 563 Analogous reactions of various dienophiles with η 1 -Cp in complexes such as (COD)(η 1 -Cp) 2 Pt, (COD)(η 1 -Cp)Pt(CH 3 ), [567][568][569] (η 5 -Cp)(η 1 -Cp)Mo(NO)(η 2 -S 2 CNMe 2 ), 570 or (η 5 -Cp) 2 (η 1 -Cp) 2 Nb, 571 (Cp) 2 MCl 2 (M ) Ti, Zr) 572 have also been described, giving cycloadducts such as 323-326, respectively. Nickelocene, (η 5 -Cp) 2 Ni, has also been shown to give, besides binuclear compounds with bridging acetylene, low to moderate yields of formal Diels-Alder products 327; 573,574 however, the mechanism by which these are formed is not clear.…”