Preparation and properties of carbonyliron complexes of 1-aza-4-oxa-1,3-butadiene (alpha-imino ester). X-ray crystal structures of Fe(CO)(2)(sigma(N):sigma(C)-i-PrN(H)C(H)C(O)OEt)(2) and Fe(CO)(2)(sigma(N):sigma(C)-i-PrN(H)C(H)C(O)OMe) (i-PrN=C(H)C(O)O)

Reaction of Fe-2(CO)(9) at room temperature in THF or toluene with the alph a-imino esters (L) (RN)-N-1=C(R-2)C(R-3)=O (a-i; R-1 = alkyl, R-2 = H, R-3 = O-alkyl), results in the formation of several mono- and binuclear complex es, depending on the bulkiness of the R1 substituent. With all ligands empl oyed, the known type of complex Fe-2(CO)(6)(L) (6) is formed. Reaction of t he less bulky R-1 substituted Ligands a-e (R-1 = neo-Pe, i-Pr, 1-cyclohexyl ethyl) leads to the formation of Fe(CO)(2)(sigma(N): sigma(C)-i-PrN(H)C(H)C (O)OEt)(2) (10a-d/10'a-d) as a mixture of two noninterconverting isomers to gether with the known type of complexes Fe-2(CO)(6)(L-L) (7). Complexes 7 c ontain two (former) alpha-imino ester Ligands joined at the imine carbon at oms. In the presence of water, the reaction in THF leads to the formation o f Fe(CO)(2)(sigma(N): sigma(C)-i-PrN(H)C(H)C(O)OMe)(i-PrN=C(H)C(O)O) (11/11 '). The unusual sigma(N):sigma(C) coordination of the newly formed ligands in 10 and 11 is confirmed by X-ray structure determinations. Thermal or pho tochemical activation of 7 in toluene leads to the formation of Fe-2(CO)(4) (L-L) (9), and reaction of 7 with HCl leads to displacement of the N-proton ated C-C coupled organic compounds 8. Reaction of 9 with CO (1 atm) at room temperature results in the re-formation of 7. Reaction with the bulky subs tituted R-1 ligands f-i (R-1 = t-BU, 2-methyl-butlyl) results in the format ion of the new binuclear complexes Fe-2(CO)(5)(L-L) (12) in which, like in 7, two alpha alpha-imino ester ligands are C-C coupled on the imine carbon atoms. In contrast to 7, the C=O oxygen atoms in 12 are coordinated, and in stead of a metal-metal bond a bridging CO is present. All complexes and the organic products have been characterized by spectroscopy (IR, H-1 and C-13 NMR, FD/FAB-mass) and by elemental analyses. An explanation for the produc t distribution and the possible mechanisms for the formation of the complex es is discussed.