Protic Ferrocenyl Acyclic Diamino Carbene Gold(I) Complexes

Abstract

Two mononuclear protic ferrocenyl acyclic diamino carbene gold(I) complexes AuCl[C(NHFc)(NR 2 )] were prepared by nucleophilic attack of diethylamine (R = Et) and diisopropylamine (R = i Pr) at the ferrocenyl substituted isocyanide complex chlorido (isocyanoferrocene)gold(I) AuCl(CNÀ Fc). In the solid state, the multifunctional protic carbene gold(I) complexes display intermolecular aurophilic interactions or intermolecular NH•••Cl hydrogen bonding in addition to intramolecular non-classical NH•••Fe hydrogen bonds. Oxidation of the AuCl[C(NHFc)(NR 2 )] complexes initially takes place at the iron centres giving highly coloured ferrocenium ions, which subsequently likely undergo electron transfer from gold(I) to iron(III) yielding putative EPRactive gold(II) species.

Synthesis and Electrochemical Behavior of Metal Carbonyl Isocyanoferrocene Compounds [M(CO)6‐n(C≡NFc)n] (M=Cr, Mo, W; n=1, 2, 3)

“…[32,35] The ferrocenyl groups display for the C 5 H 5 one, and for the C 5 H 4 ligands three carbon signals at 66-81 ppm, as expected (Experimental). [13,14,16,17,23,41] The electronic properties of 2, 3 a-c, 5 and 6 were studied using cyclic (= CV) and square wave voltammetry (= SWV) as well as in situ IR spectroelectrochemistry (3 a-c) (Table 1; Figures 1 and 2; Figures SI1-SI8, see the ESI). The electrochemical measurements were performed under an atmosphere of argon in anhydrous dichloromethane solutions containing [NBu 4 ][B(C 6 F 5 ) 4 ] (0.1 mol L À 1 ) as supporting electrolyte at 25 °C.…”

“…[11,12] Hitherto, organometallic complexes with functionalized isocyanoferrocenes with a wide range of transition metals (Cr, Rh, Pd, Cu, Au, …) are known. [13][14][15][16][17][18][19][20][21][22][23] In this context, homoleptic complexes of type [Cr(C�NFc) 6 ] and [Cr(C�NFc) 6 ] n + (n = 1, 2; Fc=Fe(η 5 À C 5 H 4 )(η 5 À C 5 H 5 )), [19,20I] as well as barely characterized metal carbonyl isocyanoferrocenes [M(CO) 6-n (C�NFc) n ] (M=Cr, n = 1; M=Mo; n = 2), [18,21] [Fe(η 5 À C 5 H 4 N�CÀ Cr(CO) 5 ) 2 ] [22] and [Cr-(CO) 5 (C�NCHRFc)] (R=Me, i Pr, t Bu, c Hex) [18] exist. The electrochemical investigations are limited to a few of these complexes and were performed with [PF 6 ] À or [BF 4 ] À ions as supporting electrolyte.…”

Unlocking the catalytic potential of gold(ii) complexes: a comprehensive reassessment

“…In 2022, Heinze's group introduced a novel ferrocenyl acyclic diamino carbene. 74 This carbene displayed reversible oxidation, evidenced through cyclic and square wave voltammetry. The initial formation of ferrocenium ions was uniquely confirmed using EPR spectroscopy, followed by a slower, potentially intramolecular, electron transfer.…”

Redox Activation of Acyclic (Aryl)(amino)carbene Gold(I) Complexes

“…52 This EPR-active species had been assigned to a persistent gold(II) radical with the unpaired electron occupying an orbital of mainly 5d x 2 −y 2 character. 45,52 These proposed active gold(II) species are hence placed in between gold(I) and gold(III) catalysts.…”

“…Oxidation of ferrocenyl carbene complexes 4a and 4b with the oxidant [N(4-C 6 H 4 Br) 3 ] •+ in THF bleached the sharp EPR resonance of [N(4-C 6 H 4 Br) 3 ] •+ at g = 2.016. 52 45,52 A slow intramolecular electron transfer (valence isomerization) from gold(I) to iron(III) had been suggested resulting in a gold(II)/iron(II) character of the paramagnetic EPR-active species. 45,52 As ferrocene possesses a diamagnetic low-spin iron(II) ion, the unpaired electron is essentially localized at the gold center.…”