Bimetallic Synergy Enables Silole Insertion into THF and the Synthesis of Erbium Single-Molecule Magnets.

The potassium silole K 2 [SiC 4 -2,5-(SiMe 3 ) 2 -3,4-Ph 2 ] reacts with [M(η 8 -COT)(THF) 4 ][BPh 4 ] (M=Er, Y; COT=cyclo-octatetraenyl) in THF to give products that feature unprecedented insertion of the nucleophilic silicon centre into a carbon-oxygen bond of THF. The structure of the major product, [(μ-η 8  : η 8 -COT)M(μ-L 1 )K] ∞ (1 M ), consists of polymeric chains of sandwich complexes, where the spiro-bicyclic silapyran ligand [C 4 H 8 OSiC 4 (SiMe 3 ) 2 Ph 2 ] 2- (L 1 ) coordinates to potassium via the oxygen. The minor product [(μ-η 8  : η 8 -COT)M(μ-L 1 )K(THF)] 2 (2 M ) features coordination of the silapyran to the rare-earth metal. In forming 1 M and 2 M , silole insertion into THF only occurs in the presence of potassium and the rare-earth metal, highlighting the importance of bimetallic synergy. The lower nucleophilicity of germanium(II) leads to contrasting reactivity of the potassium germole K 2 [GeC 4 -2,5-(SiMe 3 ) 2 -3,4-Me 2 ] towards [M(η 8 -COT)(THF) 4 ][BPh 4 ], with intact transfer of the germole occurring to give the coordination polymers [{η 5 -GeC 4 (SiMe 3 ) 2 Me 2 }M(η 8 -COT)K] ∞ (3 M ). Despite the differences in reactivity induced by the group 14 heteroatom, the single-molecule magnet properties of 1 Er , 2 Er and 3 Er are similar, with thermally activated relaxation occurring via the first-excited Kramers doublet, subject to effective energy barriers of 122, 80 and 91 cm -1 , respectively. Compound 1 Er is also analysed by high-frequency dynamic magnetic susceptibility measurements up to 10 6  Hz.