Bis(silylenyl)-substituted ferrocene-stabilized η6-arene iron(0) complexes: synthesis, structure and catalytic application. Issue 47 (2nd October 2017)

• Record Type: Journal Article
• Authors: Luecke, Marcel-Philip; Porwal, Digvijay; Kostenko, Arseni; Zhou, Yu-Peng; Yao, Shenglai; Keck, Matthias; Limberg, Christian; Oestreich, Martin; Driess, Matthias
• Is Part Of: Dalton transactions. Volume 46:Issue 47(2017)
• Page Start: 16412
• Page End: 16418
• Publication Date: 2017-10-02
• Subjects: Chemistry, Inorganic -- Periodicals; Chemistry, Physical and theoretical -- Periodicals; Chemistry, Inorganic -- Periodicals; 546.05
• DOI: 10.1039/c7dt03301j
• Languages: English
• ISSNs: 1477-9226

Abstract

Abstract : The synthesis of the first ferrocene bis(NHSi)-stabilized iron(arene) complexes and their application in the catalytic hydrogenation of ketones is reported. Abstract : Reaction of FeX2 (thf) n (X = Cl n = 1.5, Br n = 2) with the chelating 1, 1′-bis(silylenyl)-substituted ferrocene ligand Si Fc Si A (Fc = ferrocendiyl, Si = PhC(N t Bu)2 Si:) furnishes the corresponding dihalido Fe(ii ) complexes [( Si Fc Si )FeX2 ] (X = Cl, 1 and X = Br, 2 ) in high yields. Reduction of the latter with an excess of KC8 in the presence of benzene and toluene leads to the unprecedented bis(silylene) stabilized Fe 0 complexes [( Si Fc Si )Fe-η 6 (C6 H6 )]3 and [( Si Fc Si )Fe-η 6 (C7 H8 )]4, respectively. The 57 Fe Mössbauer spectrum of3 at 13 K exhibits parameters ( σ = 0.3676 mm s −1 ; Δ E Q = 1.334 mm s −1 ) which are consistent with the presence of a pentacoordinated Fe 0 atom in a pseudo trigonal–bipyramidal coordination environment, with two dative Si→Fe bonds and three coordination sites occupied by the η 6 -coordinated arene ligand. Results from DFT calculations, 57 Fe Mössbauer parameters and the diamagnetic NMR spectra confirm the redox-innocent nature of these ligands and the zero oxidation state of the iron center. The catalytic ability of3 was investigated with respect to ketone hydrogenation. In all cases, good to excellent yields to the corresponding alcohols were obtained at 50 °C and 50 bar H2 pressure. Electron-donating as well as -withdrawing substituents were tolerated with excellent to good yields. Conversions of bulkier ketones and unactivated aliphatic ketones lead merely to moderate yields. This represents the first example of a silylene-iron metal complex which has been utilized as a highly active precatalyst in the hydrogenation of ketones. The results underline the powerful ability of chelating bis(N-heterocyclic silylene) ligands acting as strong σ-donor ligands in stabilizing a new generation of low-valent, electron-rich transition metal complexes for catalytic transformations.