Maher Henary

Transmetalation of tetranuclear copper complexes. VIII: Transmetalation of tetranuclear copper(I) complexes with a Co(NS)3 reagent

Transmetallation des complexes (DENC) 4 Cu 4 X 4 (DENC=diethylnicotinamide), par le tris(S-methyl isopropylidenehydrazinocarbodithioate)-Co(III) dans les solvants aprotiques sous N 2

Transmetalation of tetranuclear copper(I) complexes with an Fe(NS)3 reagent

Abstract Stoichiometric transmetalation of tetranuclear copper(I) complexes N4Cu4X4 (I; N = N,N-diethyl- nicotinamide; X  Cl or Br) by 1 mol or excess tris(S- methyl isopropylidenehydrazinecarbodithioato)iron- (III) (Fe(NS)3, IIa) in aprotic solvents under dinitrogen is preceded by electron transfer from copper- (I) to iron(III) and gives tetranuclear iron(II)-containing products: I + IIa → N4Cu2ICuIIFeII(NS)2X4 (III′) + Cu(NS)(s). The rates of reaction of I with M(NS)3 and M(NS)2 reagents (M = Co, Ni, Cu, Zn) decrease in the order Co(NS)3 (II) > IIa > M(NS)2. Products III′ react stoichiometrically with 1 mol of II or M(NS)2 or with 2 mols of II or M(NS)2 to give iron(III)-containing dimers N4MFe(OH)X4 (VIII′) and trimers N3M2Fe(OH)X4O (X′), respectively, after oxidation with dioxygen and isolation. Transmetalation of III′ with equimolar mixed transmetalators M(NS)2 and M′(NS)2 is selective but gives dimers N4MM′X4 instead of VIII′ because Fe(NS)2 is more thermodynamically stable than M′(NS)2. Aprotic oxidation of III′ by dioxygen proceeds in two distinct stages, the first corresponding to four-electron oxidation of the two copper(I) and two coordinated NS ligands of III′ and the second to oxidation of the iron(II) center of III′. The isolated oxidation products are (μ4-O, μ-O)N4- Cu3Fe(OH)X4 (IV′). Products IV′ characteristically lose 1 mol CuO on transmetalation with 2 mol of M(NS)2 or II to give trimers X′. Products IV′ also react with 1 or 2 mol of Fe(NS)3 to give trimers (μ3-O)N3Fe(OH)CuFe(NS)X4 (XI′) and (μ3-O)N3Fe(OH)(Fe(NS))2X4 (XII′), respectively. The major differences between Co(NS)3 and Fe(NS)3 as transmetalators of I, III′ and IV′ are (i) lack of reaction of III and III′ with excess Fe(NS)3; (ii) facile oxidation of iron(II) in transmetalated products by dioxygen; (iii) case of transmetalation of these iron(II) centers with M(NS)2; (iv) stability of Fe(NS) centers in transmetalated products XI′ and XII′.