Reactions of (azadiene)tricarbonyliron(0) complexes and bromine induced alkene/epoxide interactions
The bromination of alkene/epoxide mixtures leads to the fonnation of B,B'-dibromoethers (BrCR2CR20CR2CR2Br) [R=H,Me] and dibromoalkanes. The amount of B,B' -dibromoether fonned was optimised relative to the amount of dibromoalkane fonned by carrying jout the reaction in pentane at -78°C. The reaction is believed to proceed via a three step mechanism, two steps of which (the opening of bromonium ion by epoxide, and the opening of oxonium ion by Br) have been shown to occur stereospecifically. (Cinnamaldehydeanil)/tricarbonyliron(O) (4), (PhCHCHCHNPh)Fe(COh, a representative (l-azadiene )tricarbonyliron(O) complex can be prepared in 41 % yield by heating cinnamaldehydeanil (5) (PhCHCHCHNPh) with Fez(CO)9 (17). This yield could be improved to 82% by the use of ultrasound, or to 80% via a transfer reaction from a (l-oxadiene)tricarbonyliron(O) complex. l-Azadiene complexes could themselves be used as a source of -Fe(COh for a transfer reaction to butadiene ligands, the first reported use of (azadiene)tricarbonyliron(O) complexes in this way. (l-Azadiene)tricarbonyliron(O) was found to be unreactive with respect to Diels-Alder reactions. (2-Azadiene)tricarbonyliron(O) complexes (109) have never been reported. A series of 2-azadiene ligands (ArCHNCHCHCH3) [Ar = Ph- (114); Ar = 4-CIC6H4- (116); Ar = 4-MeOC6H4- (115)] were prepared, but complexation with Fe2(CO)9 (17) or Fe(CO)s (26) did not produce a tricarbonyliron(O) complex. Complexation of (115) with Fe2(CO)9 (17), however, produced a Fe2(CO)6 containing compound (118) [(4-MeO-C6H3-CH2NCHCHCH3)-Fe2(CO)6] in 10% yield.