Ring Closure of Alkoxycarbonyl(tetracarbonyl)pyruvoyliron Complexes into Metallalactones Induced by Nucleophilic Attack of Carbanions

Abstract

International audienceThe reaction of carbanions with the pyruvoyl-substituted iron complex [(CO)4Fe(CO2CH3){C(O)C(O)CH3}] (1) affords the anionic trifunctionalized metallalactones [(CO)3Fe{C(O)C(CH3)(CRR′R″)OC4(O)(Fe–C4)}(CO2CH3)]– (3), whose formation results from the addition of the nucleophile to the β carbonyl of the pyruvoyl moiety, followed by attack of the oxygen of this β carbonyl on a terminal carbonyl ligand. These anionic lactones react, at low temperature, with HCl to give rise to the neutral lactones [(CO)4Fe{C(O)C(CH3)(CRR′R″)OC4(O)(Fe–C4)}] (2), which were previously obtained by addition of NuH nucleophiles to 1. Complex 3(3), whose lactonic ring formation has been performed using the diethyl malonate anion (R = R′ = CO2C2H5; R″ = H), and the dimethyl-substituted neutral lactone 2(1) (R = R′ = R″ = H) have been characterized by X-ray diffraction studie

Thermal properties and reactions towards nucleophiles of an iron complex displaying an acetyl and a pyruvoyl ligands

“…The angle between the acetyl and the pyruvoyl ligands (C(5)-Fe-C(7) = 85.7 (1)°) has a value intermediate between those generally observed for complexes displaying two organic carbonylated ligands in cis position on the metal (88.93 (8)°for a pyruvoyl-alkoxycarbonyl [7] or 88.5 (2)°for a bis alkoxycarbonyl [12]) and those, smaller, measured for five membered iron metallacycle (from 79.3 to 82.6°) [4,[6][7][8]13]. As usually observed for cis disubstituted iron complexes, the two axial terminal carbonyls are bent towards the plane which contains the two carbonylated organic ligands (C(5)-Fe-C(7) plane).…”

“…The values of these frequencies which fall between those observed for monofunctionalized anionic compounds (1910 cm À1 [24]) and those displayed by neutral difunctionalized iron complexes (from 2115 to 2040 cm À1 for complexes 1(1) or 1 (2)) suggested, as observed for analogous reactions performed with 1(1) [7,8], the possible formation of anionic fac trifunctionalized complexes 3 (Scheme 5).…”

“…The observation of three mC"O bands instead of the two bands formally required by a fac L 3 Fe(CO) 3 geometry could result as previously mentioned [7,8], from the presence of a metallacycle on these complexes. These products are obtained as gray powders which are, for most of them, poorly soluble in organic solvents.…”

“…The crystallized isomer is very probably the same compound than that already observed in solution by NMR spectroscopy. Recall that a close geometry has already been observed by us for the alkoxycarbonyl homologue of 3(5) [8]. The presence on the metal of a five membered ring induces, as generally observed for such metallacycles [4,[6][7][8]13], a value of the bite angle smaller than that required by a regular octahedron: C(7)-Fe-C(5) from 83.1(6) to 84.0(6)°.…”

“…The observed reactions are indicative of regioselective additions of the nucleophile reagents at the b-carbonyl of the pyruvoyl ligand of 1 (1). We recently performed the same reaction with anionic nucleophiles (C 2 H 5 O À , CH 3 S À , (C 6 H 5 ) 2 P À , (C 6 H 11 )P À or carbanions: CH À 3 ½C 2 H 5 OCðOÞ 2 - CH À , [CH 3 C(O)] 2 CH À , (CN) 2 CH À etc) and observed the formation of anionic trifunctionalised metallalactones 3 (Scheme 1c) [7,8]. As shown in Scheme 2, two reaction paths can explain the formation of 3.…”