Preparation and properties of carbonyliron complexes of 1-aza-4-oxa-1,3-butadiene (alpha-imino ketone) - X-ray crystal structures of Fe(CO)(3)[MeN=C(Ph)C(Ph)=O] and Fe-2(CO)(4)[tBuN=C(H)(Me)C(O)(O)C(Me)C(H)=NtBu]

The reaction of Fe-2(CO)(9) at room temperature in THF or toluene with the alpha-imino ketones (RN)-N-1=C(R-2)-C(R-3)=O (L) (R-1 = alkyl, R-2 = H, Me, Ph, R-3 = Me, Ph) (a-k), initially results in the formation of the mononuc lear chelate Fe(CO)(3)(alpha-imino ketone) complexes 6 which can be isolate d in moderate (6h) to high (6e-g) yield. Under these reaction conditions, c omplexes 6 subsequently react with [Fe(CO)(4)] fragments or dimerise, to fo rm the dinuclear complexes Fe-2(CO)(6)(alpha-imino ketone) (7a-j) or Fe-2(C O)(4)(L-L) (8a,b,k), respectively. The complexes 8 contain two alpha-imino ketone ligands C-C coupled at the ketone carbon atoms. Complexes 8a,b react with CO at elevated temperatures to quantitatively yield Fe(CO)(3)(alpha-i mino ketone) (6a,b). This reaction can be reversed photochemically. Irradia tion of a solution of 6a,b in the low-energy band results in the reformatio n of 8a,b in almost quantitative yield. The extremely air-sensitive complex es 6 and the dinuclear complexes 7 and 8 have been characterised spectrosco pically (IR, UV/Vis, H-1 and C-13 NMR) and by elemental analysis. The solid state structures of complexes 6g and 8a have been determined by single-cry stal X-ray diffraction. The molecular structure of 6g confirms the flat sig ma-O,sigma-N chelate coordination of the alpha-imino ketone. The structure of 8a consists of two metal-metal-bonded Fe(CO)(2) units, bridged by a form ally 10e-donating dianionic C-C coupled (tBu-ADO) ligand. A mechanism for t he formation of complexes 8 is discussed.