Preparation and Properties of Carbonyliron Complexes of 1-Aza-4-oxa-1,3-butadiene (α-Imino Ketone) – X-ray Crystal Structures of Fe(CO)3[MeNC(Ph)C(Ph)=O] and Fe2(CO)4[tBuNC(H)(Me)C(O)(O)C(Me)C(H)=NtBu

Abstract

The reaction of Fe2(CO)9 at room temperature in THF or toluene with the α-imino ketones R1N=C(R2)–C(R3)=O (L) (R1 = alkyl, R2 = H, Me, Ph, R3 = Me, Ph) (a–k), initially results in the formation of the mononuclear chelate Fe(CO)3(α-imino ketone) complexes 6 which can be isolated in moderate (6h) to high (6e–g) yield. Under these reaction conditions, complexes 6 subsequently react with [Fe(CO)4] fragments or dimerise, to form the dinuclear complexes Fe2(CO)6(α-imino ketone) (7a–j) or Fe2(CO)4(L–L) (8a,b,k), respectively. The complexes 8 contain two α-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(α-imino ketone) (6a,b). This reaction can be reversed photochemically. Irradiation of a solution of 6a,b in the low-energy band results in the reformation of 8a,b in almost quantitative yield. The extremely air-sensitive complexes 6 and the dinuclear complexes 7 and 8 have been characterised spectroscopically (IR, UV/Vis, 1H and 13C NMR) and by elemental analysis. The solid state structures of complexes 6g and 8a have been determined by single-crystal X-ray diffraction. The molecular structure of 6g confirms the flat σ-O,σ-N chelate coordination of the α-imino ketone. The structure of 8a consists of two metal–metal-bonded Fe(CO)2 units, bridged by a formally 10e-donating dianionic C–C coupled (tBu-ADO) ligand. A mechanism for the formation of complexes 8 is discussed.