Preparation and Properties of Carbonyliron Complexes of 1-Aza-4-oxa-1,3-butadiene (α-Imino Ester). X-ray Crystal Structures of Fe(CO)₂(σ(N): σ(C)-i-PrN(H)C(H)C(O)OEt)₂and Fe(CO)₂(σ(N): σ(C)-i-PrN(H)C(H)C(O)OMe)(i-PrNC(H)C(O)O)

Abstract

Reaction of Fe 2 (CO) 9 at room temperature in THF or toluene with the R-imino esters (L) R 1 NdC(R 2 )C(R 3 )dO (a-i; R 1 ) alkyl, R 2 ) H, R 3 ) O-alkyl), results in the formation of several mono-and binuclear complexes, depending on the bulkiness of the R 1 substituent. With all ligands employed, the known type of complex Fe 2 (CO) 6 (L) (6) is formed. Reaction of the less bulky R 1 substituted ligands a-e (R 1 ) neo-Pe, i-Pr, 1-cyclohexylethyl) leads to the formation of Fe(CO) 2 (σ(N):as a mixture of two noninterconverting isomers together with the known type of complexes Fe 2 (CO) 6 (L-L) (7). Complexes 7 contain two (former) R-imino ester ligands joined at the imine carbon atoms. In the presence of water, the reaction in THF leads to the formation of Fe(CO) 2 (σ(N):). The unusual σ(N):σ(C) coordination of the newly formed ligands in 10 and 11 is confirmed by X-ray structure determinations. Thermal or photochemical 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-protonated 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 substituted R 1 ligands f-i (R 1 ) t-Bu, 2-methyl-2-butyl) results in the formation of the new binuclear complexes Fe 2 (CO) 5 (L-L) (12) in which, like in 7, two R-imino ester ligands are C-C coupled on the imine carbon atoms. In contrast to 7, the CdO oxygen atoms in 12 are coordinated, and instead of a metal-metal bond a bridging CO is present. All complexes and the organic products have been characterized by spectroscopy (IR, 1 H and 13 C NMR, FD/FAB-mass) and by elemental analyses. An explanation for the product distribution and the possible mechanisms for the formation of the complexes 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

“…At 263 K, three sharp resonances are observed of equal intensity, while at room temperature a fourth resonance is observed which does not lie at the weighted average ppm value of the three signals at 263 K. This is indicative for local scrambling of the carbonyl groups on one iron centre at 263 K, while the carbonyl groups on the other iron centre are in the limit of slow exchange. The same dynamic behaviour has been found for Fe 2 (CO) 6 (a-iminoester) [55]. Like in the Fe 2 (CO) 6 (a-iminoester) complexes, the three separate CO resonances observed at 263 K correspond to the s-S%, h 2 -S coordinated Fe(CO) 3 centre and the single resonance, observed at room temperature, belongs to the m 2 -S, h 2 -C S coordinated Fe(CO) 3 fragment.…”

“…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 co-ordination geometry around the central Fe (2) . These angles are less distorted from an ideal octahedral geometry than those of the isostructural [2.2.1] iron [11,69] (e.g. 6 in Scheme 1) and ruthenium [7] complexes.…”

“…In order to extend the synthetic potential of this reaction we studied the reaction of the isostructural mononuclear Fe(CO) 3 (NO) (NO = a-iminoketone and a-iminoester) complexes and found that they react via a similar reaction sequence [9,10]. This was proven by the solid state structure of the initial bicyclo[2.2.1]Fe(Ph 2 PCH 2 CH 2 PPh 2 )(CO) adduct 6 [11] and the isolation of the stable adducts 2 (cf. Scheme 1; X= O, L =PR 3 ).…”