Diverse modes of functionalisation of ruthenium coordinated β-ketoiminate analogues

Abstract

This article compares the reactivity patterns of β-ketoiminate (AcNac) and β-thioacetyliminate (SacNac), with special reference to the unsymmetrical β-diketiminate (NacNac), on the selective {Ru(acac)₂} metal platform that encompasses the electronically rich acac (= acetylacetonate) moiety. In this regard, structural and spectroelectrochemical aspects have been reported for the newly designed complexes [Ru^III(acac)₂(AcNac^R)] (1a–1c), [Ru^III(acac)₂(SacNac^H)] (2) and [Ru^III(acac)₂(NacNac^R)] (3a–3c) [R = para-substituents (H, Cl, OMe) of the N-bearing aryl group]. The subsequent exploration of the impact of metal chelation on the reactivity profile of the β-ketoiminate analogues revealed the following: (a) the facile oxygenation of the methine centre (C_β–H) of the unsymmetrical NacNac in 3 led to ketodiimine (L1) in [Ru^II(acac)₂(L1)] (4), while analogues AcNac and SacNac in 1 and 2, respectively, remained resistant to oxidative functionalisation due to their relatively lower charge densities at the methine (C_β) centres. (b) Hydrolysis of the relatively weak C–S bond of SacNac resulted in a μ₃-S bridged [{Ru(acac)₂}₃(μ₃-S)] complex (2′). (c) Unlike 2 and 3, AcNac in 1 underwent an interesting transformation selectively in a non-polar solvent (toluene) to the 3-acetyl AcNac (L2⁻) moiety in 5 ([Ru^III(acac)₂(L2)]) via the generation of a new C–C bond at its backbone, indicating the ambiphilic feature of AcNac. The paper also addresses the aforesaid transformation processes and fractional redox non-innocence of AcNac, SacNac and NacNac in 1ⁿ, 2ⁿ and 3ⁿ (n = +1, 0, −1), respectively.