[96206-23-4] · C19H36FeN2O4 · Tetra-n-butylammonium Tricarbonylnitrosylferrate · (MW 412.42)
Physical Data: mp 56-56.5 °C.
Solubility: sol conventional organic solvents such as benzene and THF.
Preparative Method: prepared in 84% yield by the addition of a benzene solution of Pentacarbonyliron (15 mmol in 5 mL) to a mixture of Sodium Nitrite (15 mmol) and Tetra-n-butylammonium Bromide (15 mmol) in water, stirring for 3 h, and separation and concentration of the benzene layer.1
Handling, Storage, and Precautions: is less susceptible than sodium tricarbonylnitrosylferrate to air or moisture, allowing handling in the open atmosphere. Storage under inert atmosphere in a glove box is recommended.
Tetrabutylammonium tricarbonylnitrosylferrate catalyzes the allylation of malonate anion by allyl carbonates.1 The reagent serves as a more air-stable substitute (albeit less reactive5) for sodium tricarbonylnitrosylferrate. Allylation occurs predominantly without allyl migration, and with a high degree of retention of configuration at a chiral center of the allyl unit (eq 1).4 Typical conditions employ sodium diethyl malonate (2 equiv), Bu4N[Fe(CO)3(NO)] (25 mol %), and the allyl carbonate in THF at reflux under a CO atmosphere. The reaction is thought to proceed by two successive SN2 reactions, and an h1-allyliron intermediate.
Using stoichiometric amounts of Bu4N[Fe(CO)3(NO)], a wider variety of stabilized carbanions (anions of malonates, b-keto esters, dicyanomethane) and enamines have been allylated by allylic halides or mesylates, via an isolated h3-allyliron intermediate.2,6 The reaction has been applied to 2-trimethylsiloxyallyl halides and 3-trimethylsiloxyallyl halides to give 1,4-dicarbonyl compounds and 1,5-dicarbonyl compounds, respectively (eq 2).7 In the stoichiometric reactions, nucleophilic attack is predominantly at the less substituted side of the allyl unit, and anti to the face of the allyl unit bearing the iron residue.
The h3-allyliron complexes formed from Bu4N[Fe(CO)3(NO)] and allyl halides may also function as nucleophiles with allyl or propargyl halides or acid chlorides.2 The 1-silyloxyallyliron complexes (formed from 3-trimethylsilyloxyallyl iodides) also react in this fashion with allyl or propargyl halides to afford b-allyl or propargyl ketones or esters upon workup, thereby serving as nucleophilic homoenolate equivalents.6 In these cases the prior addition of Triphenyl Phosphite gives enhanced yields (eq 3). Regiochemistry of attack is predominantly at the less substituted end of the allyl halide, and attack by the allyl halide is syn to iron.
Alkyl halides are carbonylated by stoichiometric amounts of Bu4N[Fe(CO)3(NO)] in the presence of Carbon Monoxide (eq 4).3 Primary benzyl halides react much more efficiently than secondary benzylic ones. Formation of aldehydes may compete in the case of alkyl halides. Allylic halides may be carbonylated in a two-step process featuring the addition of diphos (1,2-Bis(diphenylphosphino)ethane) with Bu4N[Fe(CO)3(NO)] in the initial step.
James R. Green
University of Windsor, Ontario, Canada