M4(CH2)4 Cubane-Type Rare-Earth Methylidene Complexes: Unique Reactivity toward Unsaturated C-O, C-N, and C-S Bonds

The reactivity of the cubane-type rare-earth methylidene complex [Cp'Lu(mu(3)-CH2)](4) (1, Cp'=C5Me4-SiMe3) with various unsaturated electrophiles was investigated. The reaction of 1 with CO (1 atm) at room temperature gave the bis(ketene dianion)/dimethylidene complex [Cp'Lu-4(4)(mu(3)-CH2)(2)(mu(3),eta(2)-O-C = CH2)(2)] (2) in 86?% yield through the insertion of two molecules of CO into two of the four lutetiummethylidene units. In the reaction with the sterically demanding N,N-diisopropylcarbodiimide at 60 degrees C, only one of the four methylidene units in 1 reacted with one molecule of the carbodiimide substrate to give the mono(ethylene diamido)/trimethylidene complex [Cp'Lu-4(4)(mu(3)-CH2)(3){iPrNC-(CH2)NiPr}] (3) in 83?% yield. Similarly, the reaction of 1 with phenyl isothiocyanate gave the ethylene amido thiolate/trimethylidene complex [Cp'Lu-4(4)(mu(3)-CH2)(3){PhNC(S)=CH2}] (4). In the case of phenyl isocyanate, two of the four methylidene units in 1 reacted with four molecules of the substrate at ambient temperature to give the malonodiimidate/dimethylidene complex [Cp'Lu-4(4)(mu(3)-CH2)(2)-{PhN=C(O)CH2(O)C?NPh}(2)] (5) in 87?% yield. In this reaction, each of the two lutetiummethylidene bonds per methylidene unit inserted one molecule of phenyl isocyanate. All the products have been fully characterized by NMR spectroscopy, X-ray diffraction, and microelemental analyses.