A Novel Method for the Demetalation of Tricarbonyliron-Diene Complexes by a Photolytically Induced Ligand Exchange Reaction with Acetonitrile

Abstract

The photochemical exchange of all three carbonyl ligands with acetonitrile converts tricarbonyliron-diene complexes into the very labile triacetonitrile-iron-diene complexes. These easily demetalate in high yields to the corresponding free ligands on injection of air at -30°C [Eq. (1)]. The novel demetalation procedure is applied to the tricarbonyliron complexes of cyclopentadienones, cyclohexa-1,3-dienes, and buta-1,3-dienes.

Synthesis of Fe–H/Si–H and Fe–H/Ge–H Bifunctional Complexes and Their Catalytic Hydrogenation Reactions toward Nonpolar Unsaturated Organic Molecules

“…A similar AN/CO exchange reaction has been reported by Knolker and co-workers. 15 The reaction of Et 2 EH 2 (E = Si, Ge) with 3 gave the corresponding iron hydride complexes bearing an Si−H or Ge− H functional group on the ligand, [2,5-bis(triphenylsilyl)-3,4-butylene-(η 5 -C 4 COEEt 2 H)]Fe(CO) 2 H (E = Si (4; 87% yield), Ge (5; 70% yield)) (Scheme 3). Characteristic Fe−H signals of C 6 D 6 solutions of 4 and 5 in the 1 H NMR spectra were recorded at −10.89 and −11.04 ppm, respectively.…”

“…These molecular structures are similar to those of the trimethylsilyl analogues reported by Knolker and co-workers [2,5-bis(trimethylsilyl)-3,4-butylene-(η 4 -C 4 CO)]Fe(CO) 3 16 and [2,5-bis(trimethylsilyl)-3,4-butylene-(η 4 -C 4 CO)]Fe(CO)(NCCH 3 ) 2 . 15 Complexes 4 and 6 have one hydride ligand, one η 5 -2,5-bis(triphenylsilyl)-3,4-butylene-1-diethylsiloxycyclopentadienyl (or η 5 -2,5-bis-(triphenylsilyl)-3,4-butylene-1-tetramethyldisiloxyl) ligand, and two carbonyl ligands.…”

Novel Routes to Pyrroles, Indoles and Carbazoles - Applications in Natural Product Synthesis

“…Demetalation of complex 13 with trimethylamine N-oxide afforded the tetrahydroindole 14 in 77% yield [17]. This result could be improved using the demetalation via a photolytically induced ligand exchange reaction with acetonitrile (85% yield of 14) [13]. A variety of substituted indole derivatives useful for further functionalization can be obtained by this methodology.…”

“…Using trimethylamine N-oxide, the standard reagent for this synthetic transformation [12], the yield of the cyclopentadienone 7 is only 66% [10b, c]. We developed two novel procedures for the demetalation of tricarbonyl(η 4 -cyclopentadienone)iron complexes, which provide much better results [13,14]. Photolysis of complex 6 in acetonitrile solution at -30°C led via a triple ligand exchange reaction to an intermediate triacetonitrile(η 4 -cyclopentadienone)iron complex which was demetalated to compound 7 (89% yield) by bubbling air through the solution at -30°C [13].…”

“…We developed two novel procedures for the demetalation of tricarbonyl(η 4 -cyclopentadienone)iron complexes, which provide much better results [13,14]. Photolysis of complex 6 in acetonitrile solution at -30°C led via a triple ligand exchange reaction to an intermediate triacetonitrile(η 4 -cyclopentadienone)iron complex which was demetalated to compound 7 (89% yield) by bubbling air through the solution at -30°C [13]. Alternatively, Hieber reaction of complex 6 with sodium hydroxide to an intermediate dicarbonyl(η 5 -hydroxycyclopentadienyl)hydridoiron complex followed by treatment with iodopentane gave a dicarbonyl(η 5 -hydroxycyclopentadienyl) iodoiron complex.…”