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.

1,3-Dipolar cycloaddition to the FeSC fragment 20. Preparation and properties of carbonyliron complexes of di-thiooxamide. Reactivity of the mononuclear (di-thiooxamide)Fe(CO)3 towards dimethyl acetylenedicarboxylate

“…The absorption bands at low energy show hardly any solvatochromic behaviour [7a; 616 nm (hexane), 623 nm (THF): 7b; 637 nm (hexane), 641 nm (THF)]. The pattern of the bands in the UV-Vis spectra of complexes 7 resembles that found for Fe(CO) 3 (R-DAB) [31,78] and Fe(CO) 3 (a-iminoketone) [33], except that the low energy band is further redshifted by 80 to 120 nm. The absence of solvatochromism in Fe(CO) 3 (R-DAB) and Fe(CO) 3 (a-iminoketone) has been attributed, on basis of MO-calculations and resonance Raman spectra, to a strong mixing of the metal d p -(HOMO) orbitals and the low lying a-diimine p*-(LUMO) orbitals [31].…”

“…The h 2 -C S coordinated thiocarbonyl carbon atom resonance, observed at 95.7 ppm, is shifted 91.4 ppm to lower frequency. These shifts are typical for a s-S, m 2 -S, h 2 -C S co-ordination of the DTO ligand and have also been observed for the isostructural complexes M 2 (CO) 6 (L) (Fe, Ru, Os; L = R-DAB, aimino-ketone and ester) [33,52,53,55,85].…”

“…The cyclo-DTO ligand in 8a is s-S, m 2 -S%, h 2 -C S% coordinated, donating six electrons to the metal centres, which is confirmed by a single crystal X-ray structure determination of 8a. This type of co-ordination is well known and observed in many other M 2 (CO) 6 (L) complexes (M=Fe, Ru, FeRu; L= R-DAB [51 -54], a-iminoketone [33] and a-iminoester [55]). When the reaction of a with Fe 2 (CO) 9 is performed in toluene instead of THF, a new dimeric complex (9a) is formed in very low yield besides 8a.…”

“…The central C C bond is accordingly shortened because the p*-orbital is bonding between these two carbons. This shortening of the central C-C bond is also found in the solid state structures of Fe(CO) 3 (R-DAB) [31,32] complexes and Fe(CO) 3 (MeN C(Ph) C(Ph) O) [33].…”

“…As a result of the extensive p-back donation, the thiocarbonyl carbon atom resonances are shifted 22.7 and 19.4 ppm to lower frequency in comparison with those of the free ligands. Comparable shifts to lower frequency have been observed for the ketone carbon atom in Fe(CO) 3 (a-iminoketone) [33], whereas somewhat smaller shifts have been found for the imine carbon atoms in Fe(CO) 3 (R-DAB) [32] and Fe(CO) 3 (a-iminoketone). The three terminal CO ligands in complexes 7a,d give rise to a single resonance at 213.6 and 210.8 ppm indicating that they rapidly interchange on the NMR time scale at 263 K. This interchange has also been observed for the M(CO) 3 (R-DAB) (M = Fe, Ru) [76,82,83] and Fe(CO) 3 (a-iminoketone) and may be explained by Berry pseudo-rotations [84].…”