A variety of mono-and bis[Fe(CO),(v4-diene)] complexes with alkyl, CH,OH, CHO, COCH,, COOR, and CN substituents on the 1,3-diene system have been synthesized. Dienes with a (Z)-configurated terminal Me group show steric inhibition of metal complexation resulting in lower yields and formation of tetracarbonyI($-diene) and tricarbonyl(v4-heterodiene) complexes as additional products. Regioselective attack by C-nucleophiles at the carbonyl C-atom of the functional group with or without concomitant 1,3 migration of the Fe(CO), group was used to synthesize polyenes and isoprenoid building blocks as mono-or dinuclear Fe(CO), complexes. Witfig-Homer-type reactions of Fe(CO),-complexed synthons result in stereospecific formation of (E)-configurated olefins. The 'H-, I3C-, and 57Fe-NMR spectra of 73 olefinic and allylic organoiron complexes are reported. H,H, C,H, and C,C coupling constants have been evaluated and are analyzed in tenns of the geometry of the coordinated diene. The results are corroborated by the crystal structure of tricarbonyl[3-6-q-((E)-6-methyl-3,5-heptadiene-2one)]iron (34) which shows an unusual distortion of the (CH,),C= group. The ,'Fe-NMR chemical shifts extend over the ranges of 0-600 ppm for [Fe(C0),(r14-dIene)] complexes, 7 8 N 7 10 ppm for [Fe(CO),(q'-allyl)] [BF4] and [FeX(CO),(q3-allyl)] complexes, and 1270-1690 ppm for [Fe(CO)3(q4-enone)] complexes, relative to Fe(C0)5.
