Synthesis and 1H‐, 13C‐, and 57Fe‐NMR spectra of mono‐ and bis[tricarbonyl(η4‐diene)iron], and (η3‐allyl)tetracarbonyliron trifluoroborate complexes

Abstract

AbstractA variety of mono‐ and bis[Fe(CO)3(η4‐diene)] complex with alky, CH2OH, CHO, COCH3, COOR, and CN substituents on the 1,3‐diene system have been synthesized. Dienes with a (Z)‐configuration terminal Me group show steric inhibition of metal complexation resulting in lower yields and formation of tetracarbonyl(η2‐diene) and tricarbonyl(η4‐heterodiene) complexes as additional products. Regioselective attack by C‐nucleophiles at the carbonyl C‐atoms of the functional group with or without concomitant 1,3 mogration of the Fe(CO)3 group was used to synthesize polyenes and isoprenoid building blocks as mono‐ or dinucliar Fe(CO)3 complexes. Wittig‐Horner‐type reactions of Fe(co)3‐complexed synthons result in sterospecific formation of (E)‐configurated olefins. The 1H‐, 13C‐ and 57Fe‐NMR spectra of olefinic and allylic organoiron complexes are reported, H,H,C,H, and C,C coupling constants have been evaluated and are analyzed in terms of the geometry of the coordinated diene. The results are corroborated by the crystal structure of tricarbonyl[3–6‐η‐((E)‐6‐methyl‐3,5‐heptadiene‐2‐one)]iron(34) which shows an unusual distortion of the (CH3)2C = group, The 57Fe‐NMR chemical shifts extend over the ranges of 0–600 ppm for [Fe(CO)3(η4‐diene)] complexes, 780–1710 ppm for [Fe(CO)4(η3‐allyl)] [BF4] and [FeX(CO)3(η4‐allyl)] complexes, and 1270–1690 ppm for [Fe(CO)3(η4‐enone)] complexes, relative to Fe(CO)5.