3d/4f Coordination Clusters as Cooperative Catalysts for Highly Diastereoselective Michael Addition Reactions

Abstract

Michael addition (MA) is one of the most well studied chemical transformation in synthetic chemistry. Here, we report the synthesis and crystal structures of a library of 3d/4f coordination clusters (CCs) formulated as [ZnYL(solv)(Z)] and study their catalytic properties toward the MA of nitrostyrenes with barbituric acid derivatives. Each CC presents two borderline hard/soft Lewis acidic Zn centers and two hard Lewis acidic Y centers in a defect dicubane topology that brings the two different metals into a proximity of ∼3.3 Å. Density functional theory computational studies suggest that these tetrametallic CCs dissociate in solution to give two catalytically active dimers, each containing one 3d and one 4f metal that act cooperatively. The mechanism of catalysis has been corroborated via NMR, electron paramagnetic resonance, and UV-vis. The present work demonstrates for the first time the successful use of 3d/4f CCs as efficient and high diastereoselective catalysts in MA reactions.

The modular synthesis of rare earth-transition metal heterobimetallic complexes utilizing a redox-active ligand

“…The inspiration for our approach was the Tb analogue of the [{(SiMe 3 ) 2 N}Ln] 2 N 2 K system. This complex was remarkable both for the (N 2 ) 3•-anion and the SMM behaviour. 4 It generated significant subsequent interest in multimetallic lanthanide radical bridged complexes.…”

“…In particular there is research interest in the design of rare earth-transition metal singlemolecule magnets (SMM) and catalysts. 2,3 The chemistry of multimetallic complexes containing f-elements is significantly less well developed than that of transition metals. This is attributable to the fact that the directed synthesis of f-d complexes is non-trivial.…”

“…16 These groups subsequently published a number of studies demonstrating that pd will selectively bind N,N′ with a coordination chemistry precursor or O,O′ with a reducing organometallic precursor and can form homo-and heterometallic transition metal complexes. [17][18][19] Prior to this work there are just two reports of structurally characterised molecular lanthanide complexes of pd, both by Faulkner and Ward, which describe the sensitised NIR emission of [Ln(tta) 3 (N,N'-O,O'-pd)Pt(PPh 3 ) 2 ] (Ln = La, Nd, Gd, Er, Yb; tta = 1-thenoyl-5,5,5-trifluoroacetylacetonate). 12,20 We note that there are reports of the biological activity of combinations of Ln and pd.…”

“…Here we report a robust and modular synthesis and first structural characterisation of [Ln(hfac) 3 (N,N'-pd)] (Ln = Y, Gd) complexes. We also report the reduction of these coordination chemistry complexes using vanadocenes to form heterobimetallic rare earth-transition metal complexes.…”

“…[Ln(hfac) 3 (N,N'-pd)] (Ln = Y [1], Gd [2]; hfac = hexafluoroacetylacetonate) were synthesised in high yield.…”